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  • Artikel  (5.373)
  • Springer  (5.373)
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  • 1
    Digitale Medien
    Digitale Medien
    Curves and surfaces for computer aided design usingC 2 rational cubic splines (1995)
    Springer
    Engineering with computers 11 (1995), S. 94-102 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Rational cubic ; Bernstein-Bézier ; Shape control ; Tension
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract This paper is concerned with the problem of fitting curves and surfaces, for computer aided design (CAD), via an ordered set of control points, so that the result is satisfactory for the user's needs. Piecewise rational functions with cubic numerator and quadratic denominator are used in the construction of the scheme, in such a way that the descriptions of the parameters control the shape of the picture in the desired area. A general solution is obtained for points inN-space, although the scheme is only meaningful in the cases whereN=2 andN=3.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01312203
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  • 2
    Digitale Medien
    Digitale Medien
    Data fusion for adaptive control in manufacturing: Impact on engineering information models (1995)
    Springer
    Engineering with computers 11 (1995), S. 145-156 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Database ; Date fusson ; Date model ; Information architecture ; Information model ; Manufacturing ; Sensors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Data fusion is the integration and analysis of data from multiple sensors to develop a more accurate understanding of a situation and determine how to respond to it. Although data fusion can be applied in many situations, this paper focuses on its application to manufacturing and how it changes some of the more traditional, less adaptive information models that support the design and manufacturing functions. The paper consists of four parts. The first section explains what data fusion is and its impact on manufacturing. The second section describes what an information system architecture is and explains the natural language-based information modeling methodology used by this research project. The third section identifies the major design and manufacturing functions, reviews the information models required to support them, and then shows how these models must be extended to support data fusion. The fourth section discusses the future directions of this work.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01271280
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  • 3
    Digitale Medien
    Digitale Medien
    Modeling evolving product data for concurrent engineering (1995)
    Springer
    Engineering with computers 11 (1995), S. 167-172 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Concurrent engineering ; Configuration management ; Data model ; Design Process ; Engineering data management ; Product data management
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract In order to make the traditional product structure tree representation amenable to concurrent engineering relationships likeperspective-of anddependent-on have to be added to the essentialpart-of relationship. Complex data can be held in proprietary formats, while simple data will be in a common representation for direct access by diverse disciplines. Coordination among team members in a project can be carried out using such a model. Besides, a virtually unified view of all the data is possible, though they may lie in distributed and heterogeneous data bases. A very necessary characteristic of such a model is that its time evolution should be easy to represent in order to reflect the dynamic nature of product development, where the model itself, and not merely the data values change. Managing versions is also facilitated by the comprehensive structure of the Unified Product Data Model (UPDM).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01271282
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  • 4
    Digitale Medien
    Digitale Medien
    Information management for integrated design environments (1995)
    Springer
    Engineering with computers 11 (1995), S. 227-245 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Conceptual design ; Design process ; Design studies ; Engineering information systems ; Product data
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract This paper identifies requirements for an engineering design information management system. Future CAD systems must support a wide range of activities — such as definition, manipulation and analyses of complex product information models. These models represent not only conventional data associated with current CAD applications, but also design information characterizing the correlations between the requirements, functions, behaviors and physical form of the product. Such functionality is important for both the individual designer and the design organization, as the need to manage information as a corporate asset is becoming a critical component of business strategy. This paper explores these needs using two design studies. The first study illustrates some major concepts relative to non-routine design activities, while the second study focuses on the routine design activities relative to organization interactions. These studies were used to elicit high level requirements which serve as the basis for the development of prototype software systems. These prototypes are briefly introduced here.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01208816
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  • 5
    Digitale Medien
    Digitale Medien
    An object design framework for structural engineering (1995)
    Springer
    Engineering with computers 11 (1995), S. 213-226 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Communication channel ; Communication path ; Data attribute ; Design object ; Method group ; Object-oriented ; Receiving interface ; Relationship ; Relationship attribute ; Sending method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Object-oriented principles have introduced several useful concepts for developing complex software systems. As a result, several methodologies have been suggested for the overall design of software systems based on these concepts. Methodologies and frameworks for designing objects that are to be part of the software systems are currently lacking. This paper proposes anobject design framework andmethodology, which utilizes the object-oriented concepts, for planning, organizing and designing structural engineering design objects. Design objects in an integrated structural engineering system are complex and often related to each other in various different ways. The paper also identifies several important relationships among structural engineering design objects. These relationships serve as communication channels through wich design objects send messages to and receive responses from each other. Several examples, drawn from reinforced concrete structures, will be presented to demonstrate the object design methodology and to illustrate how the framework is effective in reducing the complexity of design objects in an integrated structural engineering system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01208815
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  • 6
    Digitale Medien
    Digitale Medien
    Verification of an active control system using temporal process algebra (1996)
    Springer
    Engineering with computers 12 (1996), S. 46-61 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Active structural control ; Calculus of communicating systems (CCS) ; Concurrency workbench ; Modechart ; Real-time systems ; Simulation ; Temporal CCS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract In this paper we describe complementary approaches that can be used to ensure the reliability of real-time systems, such as those used in active structural control systems. These approaches include both model-checking and simulation, and are based on a temporal process algebra. We combine these formal methods with a high-level, graphical modeling technique, Modechart, to specify an active structural control system consisting of several processors. Timing requirements on the system are specified and verified with a combination of process algebraic models and modal logic, and various simulation concepts are described for debugging models and for gaining insight into system behavior.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01200261
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  • 7
    Digitale Medien
    Digitale Medien
    Adaptive mesh refinement using piecewise-linear shape functions based on the blending function method (1996)
    Springer
    Engineering with computers 12 (1996), S. 84-93 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Adaptive mesh refinement ; Finite element method ; Mesh generation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Use of quadrilateral elements for finite element mesh refinement can lead either to so-called ‘irregular’ meshes or the necessity of adjustments between finer and coarser parts of the mesh necessary. In the case of ‘irregular’ meshes, constraints have to be introduced in order to maintain continuity of the displacements. Introduction of finite elements based on blending function interpolation shape functions using piecewise boundary interpolation avoids these problems. This paper introduces an adaptive refinement procedure for these types of elements. The refinement is anh-method. Error estimation is performed using the Zienkiewicz-Zhu method. The refinement is controlled by a switching function representation. The method is applied to the plane stress problem. Numerical examples are given to show the efficiency of the methodology.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01299394
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  • 8
    Digitale Medien
    Digitale Medien
    Parallel three-dimensional mesh generation on distributed memory MIMD computers (1996)
    Springer
    Engineering with computers 12 (1996), S. 94-106 
    Details
    ISSN: 1435-5663
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract This paper discusses the development of an automatic mesh generation technique designed to operate effectively on multiple instruction multiple data (MIMD) parallel computers. The meshing approach is hierarchical, that is, model entities are meshed after their boundaries have been meshed. Focus is on the region meshing step. An octree is constructed to serve as a localization tool and for efficiency. The tree is also key to the efficient parallelization of the meshing process since it supports the distribution of load to processors. The parallel mesh generation procedure repartitions the domain to be meshed and applies on processor face removals until all face removals with local data have been performed. The portion of the domain to be meshed remaining is dynamically repartitioned at the octant level using an Inertial Recursive Bisection method and local face removals are reperformed. Migration of a terminal octant involves migration of the octant data and the octant's mesh faces and/or mesh regions. Results show relatively good speed-ups for parallel face removals on small numbers of processors. Once the three-dimensional mesh has been generated, mesh regions may be scattered across processors. Therefore, a final dynamic repartitioning step is applied at the region level to produce a partition ready for finite element analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01299395
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  • 9
    Digitale Medien
    Digitale Medien
    Adaptive finite element procedures in elasticity and plasticity (1996)
    Springer
    Engineering with computers 12 (1996), S. 120-141 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Discontinuous Galerkin ; Error estimation adaptivity ; Postprocessing ; Superconvergence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract The paper discusses error estimation and h-adaptive finite element procedures for elasticity and plasticity problems. For the spatial discretization error, an enhanced Superconvergent Patch Recovery (SPR) technique which improves the error estimation by including fulfillment of equilibrium and boundary conditions in the smoothing procedure is discussed. It is known that an accurate error estimation on an early stage of analysis results in a more rapid and optimal adaptive process. It is shown that node patches and element patches give similar quality of the postprocessed solution. For dynamic problems, a postprocessed type of error estimate and an adaptive procedure for the semidiscrete finite element method are discussed. It is shown that the procedure is able to update the spatial mesh and the time step size so that both spatial and time discretization errors are controlled within specified tolerances. A time-discontinuous Galerkin method for solving the second-order ordinary differential equations in structural dynamics is also presented. Many advantages of the new approach such as high order accuracy, possibility to filter effects of spurious modes and convenience to apply adaptive analysis are observed. For plasticity problems, some recent work that improved plastic strains and plastic localization is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01299397
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  • 10
    Digitale Medien
    Digitale Medien
    Two and three-quarter dimensional meshing facilitators (1996)
    Springer
    Engineering with computers 12 (1996), S. 144-154 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Automatic mesh generation ; Mesh control ; Mapped meshing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract This paper presents generated enhancements for robust ‘two and three-quarter dimensional meshing’, including: (1) automated interval assignment by integer programming for submapped surfaces and volumes, (2) surface submapping, and (3) volume submapping. An introduction to the simplex method, an optimization technique of integer programming, is presented. Simplification of complex geometry is required for the formulation of the integer programming problem. A method of ‘i-j unfolding’ is defined which explains how irregular geometry can be realigned into a simplified form that is suitable for submap interval assignment solutions. Also presented is the processes by which submapping eliminates the decomposition of surface geometry, through a pseudodecomposition process, producing suitable mapped meshes. The process of submapping involves the creation of ‘interpolated virtual edges’, user defined ‘vertex types’ and ‘i-j-k space’ traversals. The creation of ‘interpolated virtual edges’ is the method by which submapping automatically subdivides surface geometry. The ‘interpolated virtual edge’ is formulated according to an interpolation scheme using the node discretization of curves on the surface. User defined ‘vertex types’ allow direct user control of surface decomposition and interval assignment by modifying ‘i-j-k space’ traversals. Volume submapping takes the geometry decomposition to a higher level by using ‘mapped virtual surfaces’ to eliminate decomposition of complex volumes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198730
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  • 11
    Digitale Medien
    Digitale Medien
    Automatic, parallel and fault tolerant mesh generation from CAD (1996)
    Springer
    Engineering with computers 12 (1996), S. 178-185 
    Details
    ISSN: 1435-5663
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract HEXAR, a new software product developed at Cray Research, Inc., automatically generates good quality meshes directly from surface data produced by computeraided design (CAD) packages. The HEXAR automatic mesh generator is based on a proprietary and parallel algorithm that relies on pattern recognition, local mesh refinement and coarsening, and variational mesh smoothing techniques to create all-hexahedral volume meshes. HEXAR generates grids two to three orders of magnitude faster than current manual approaches. Although approximate by design, the resulting meshes have qualities acceptable by many commercial structural and CFD (computational fluid dynamics) software. HEXAR turns mesh generation into an automatic process for most commercial engineering applications.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198733
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  • 12
    Digitale Medien
    Digitale Medien
    Progress in grid generation via the advancing front technique (1996)
    Springer
    Engineering with computers 12 (1996), S. 186-210 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Finite elements ; Grid generation ; Tetrahedra ; Unstructured grids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract We describe recent extensions and improvements to the advancing front grid generation technique. These improvements target a range of applicability, speed and user friendliness. The range of applicability is enlarged by the ability to produce volumetric grids around thin surfaces (such as shells, membranes, fabrics or surfaces with cusps), the generation of high aspect ratio grids for Navier-Stokes applications, the generation of higher order triangular and tetrahedral elements, and the generation of quadrilateral and hexahedral elements. Speed improvements are the result of reduced search overheads, as well as vectorization and parallelization. User friendliness is enhanced by the ability to grid directly discrete data and simpler ways of specifying the desired element size and shape in space. Numerous examples are included that demonstrate the versatility and maturity that advancing front grid generators have achieved.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198734
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  • 13
    Digitale Medien
    Digitale Medien
    Development of an information model for composites design data (1997)
    Springer
    Engineering with computers 13 (1997), S. 48-64 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Composite materials ; Conceptual modeling ; Database design ; Fiber-reinforced plastics ; information modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Material properties data, particularly those of advanced composite materials such as fiber-reinforced plastics, provides a very complex domain which is difficult to computerize. As a foundational activity supporting the development of material property databases, we have examined and modeled the data contained within this large, diverse, and intricate domain. Our primary objective was to gain a better understanding of the data involved in this system and their transformation and use. We examined the life cycle of a fiber-reinforced composite material, from a raw material to a manufactured product, focusing on the various applications which require and/or supply materials data and the types of materials data which must be included. A high-level information model was created to illustrate the overall picture of composite materials data which emerged from this analysis. This model provides a global view of the data encompassed in the domain of composite materials, and forms the basis of a formal conceptual model from which databases may be developed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01201860
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  • 14
    Digitale Medien
    Digitale Medien
    A data management model for collaborative design in a CAD environment (1997)
    Springer
    Engineering with computers 13 (1997), S. 65-86 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Collaborative design ; Version control ; Configuration scheme ; Change management
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract This paper presents a data management model to support collaborative design. More specifically, it addresses the storing and managing of changes among designers in a multidisciplinary design project. We propose a three-layered model ofversions, assemblies, andconfigurations. Versions maintain evolving descriptions of primitive entities within a single discipline.Assemblies integrate component instances to describe more complex entities, as well as designs within individual disciplines.Configurations provide a framework to represent an overall project design which is composed of designs from the participating disciplines. We apply a concept ofequivalent operations for developing operators that store, detect and manage changes among versions of a primitive design entity. The close coupling of the version, assembly, and configuration layers enables computed version changes to be recursively combined to characterize changes at the assembly and configuration levels. This applies for both project coordination throughasynchronous communication of changes among designers, and project monitoring through systematic tracking of evolving project descriptions. This paper also presents an implementation of the data management model in a CAD paradigm. We use a simple multidisciplinary facility design example to demonstrate the change management capabilities of the proposed model. This example has been tested on a prototype implementation in an AUTOCAD environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01350751
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  • 15
    Digitale Medien
    Digitale Medien
    Using objects to handle complexity in finite element software (1997)
    Springer
    Engineering with computers 13 (1997), S. 99-111 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Finite elements ; Object oriented methods
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Engineering software is becoming ever more complex. Finite element programs have sophisticated graphical input and output facilities, and are increasingly required to be linked to other software such as CAD or databases. The paper shows how an object oriented approach to finite element programming can be used to handle this complexity. This requires an approach that is very different from that adopted in more traditional programming. A foundation finite element class system is developed. This represents the essential data structure of the main finite element classes. It is then shown how this system can be used in a graphical model of two dimensional structures. The finite element system imposed no constraints on the development of the graphical model, yet could still be used easily. An important feature is that the nodes and elements are distributed around the graphical model, rather than being held centrally. For instance nodes may belong to points or lines of the graphical model. This means that the data structure used in the program more closely matches the way that the user of the program is likely to think.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01350753
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  • 16
    Digitale Medien
    Digitale Medien
    Elimination of the adverse effects of small model features by the local modification of automatically generated meshes (1997)
    Springer
    Engineering with computers 13 (1997), S. 134-152 
    Details
    ISSN: 1435-5663
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Issues related to the automated identification and elimination of the adverse influence of small geometric model features on the quality of automatically generated meshes, using local mesh modification operators, are addressed. The definition of mesh validity with respect to the geometric model is extended to include multiple mesh entity classifications. Checks based on mesh topology are used to ensure no dimensional reductions in the locally modified mesh. Example geometric models of varied complexity containing small geometric features are used to demonstrate the ability of presented procedures to improve mesh quality in terms of aspect ratio and small angle metrics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01221211
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  • 17
    Digitale Medien
    Digitale Medien
    Local refinement of three-dimensional finite element meshes (1997)
    Springer
    Engineering with computers 13 (1997), S. 165-174 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Mesh refinement ; Mixed element meshes ; Unstructured meshes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Mesh refinement is an important tool for editing finite element meshes in order to increase the accuracy of the solution. Refinement is performed in an iterative procedure in which a solution is found, error estimates are calculated, and elements in regions of high error are refined. This process is repeated until the desired accuracy is obtained. Much research has been done on mesh refinement. Research has been focused on two-dimensional meshes and three-dimensional tetrahedral meshes ([1] Ning et al. (1993) Finite Elements in Analysis and Design, 13, 299–318; [2] Rivara, M. (1991) Journal of Computational and Applied Mathematics 36, 79–89; [3] Kallinderis; Vijayar (1993) AIAA Journal,31, 8, 1440–1447; [4] Finite Element Meshes in Analysis and Design,20, 47–70). Some research has been done on three-dimensional hexahedral meshes ([5] Schneiders; Debye (1995) Proceedings IMA Workshop on Modelling, Mesh Generation and Adaptive Numerical Methods for Partial Differential Equations). However, little if any research has been conducted on a refinement algorithm that is general enough to be used with a mesh composed of any three-dimensional element (hexahedra, wedges, pyramids, and/or retrahedra) or any combination of three-dimensional elements (for example, a mesh composed of part hexahedra and part wedges). This paper presents an algorithm for refinement of three-dimensional finite element meshes that is general enough to refine a mesh composed of any combination of the standard three-dimensional element types.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01221213
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  • 18
    Digitale Medien
    Digitale Medien
    A simple genetic algorithm for the design of reinforced concrete beams (1997)
    Springer
    Engineering with computers 13 (1997), S. 185-196 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Artificial intelligence ; Design optimization ; Genetic algorithms ; Structural optimization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract We present an optimization model for the design of rectangular reinforced concrete beams subject to a specified set of constraints. Our model is more realistic than previously published models because it minimizes the cost of the beam on strength design procedures, while also considering the costs of concrete, steel and shuttering. Thus our method leads to very practical designs. As there is an infinite number of possible beam dimensions and reinforcement ratios that yield the same moment of resistance, an efficient search technique is preferred over the more traditional iterative methods. We employ a simple genetic algorithm as the search engine, and we compare our results with those obtained via geometric programming. Since the adjustment of parameters in a genetic algorithm (e.g., population size, crossover and mutation rates, and maximum number of generations) is a significant problem for any application, we present our own methodology to deal with this problem. A prototype of this system is currently being tested in México, in order to evaluate its potential as a reliable design tool for real world applications.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01200046
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  • 19
    Digitale Medien
    Digitale Medien
    Object-oriented analysis of spatial multibody systems based on graph theory (1997)
    Springer
    Engineering with computers 13 (1997), S. 211-221 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Graph theory ; Joint coordinate method ; Linked lists of objects ; Object oriented hierarchy ; System matrices
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract The purpose of this paper is to illustrate the implementation of efficient methods in the analysis of general multibody systems. The main goal is a total general purpose program which is able to handle the analysis of open as well as closed loop systems. The development of a general purpose program necessitates considerations concerning storing of code and data access facilities of the analysis code. Many of the building blocks for the analysis are supposed to solve the same problems although this is obtained in different ways depending on the specific type of block. These considerations lead to the creation of an object oriented structure of the analysis code. The development of the analysis algorithms is based on the kinematics of the system. The implementation of these schemes is based on graph theory and is presented through an example by the end of the paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01200048
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  • 20
    Digitale Medien
    Digitale Medien
    Design of multi-component structural systems for optimal layout topology and joint locations (1997)
    Springer
    Engineering with computers 13 (1997), S. 235-243 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Structural connections ; Structural optimization ; Topology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Present day topology optimization techniques for continuum structures consider the design of single structural components, while most real life engineering design problems involve multiple components or structures. It is therefore necessary to have a methodology that can address the design of multi-component systems and generate designs for the optimal layouts of individual structures and locations for interconnections. The interconnections include supports provided by the ground, joints and rigid connections like rivets, bolts and welds between components. While topology optimization of structures has been extensively researched, relatively little work has been done on optimizing the locations of the interconnections. In this research, a method to model and define domains for the interconnections has been developed. The optimization process redistributes material in the component design domains and locates the connections optimally based on an energy criterion. Some practical design examples are used to illustrate the capability of this method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01200050
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  • 21
    Digitale Medien
    Digitale Medien
    Self-intersections of offsets of quadratic surfaces: Part II, implicit surfaces (1998)
    Springer
    Engineering with computers 14 (1998), S. 14-22 
    Details
    ISSN: 1435-5663
    Schlagwort(e): NC machining ; Offset surfaces ; Self-intersections ; Trimmed offset
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract The paper investigates self-intersections of offsets of implicit quadratic surfaces. The quadratic surfaces are the simplest curved objects, referred to as quadrics, and are widely used in mechanical design. In an earlier paper, we have investigated the self-intersections of offsets of explicit quadratic surfaces, such as elliptic paraboloid, hyperbolic paraboloid and parabolic cylinder, since not only are they used in mechanical design, but also any regular surface can be locally approximated by such explicit quadratic surfaces. In this paper, we investigate the rest of the quadrics whose offsets may degenerate, i.e. the implicit quadratic-surfaces (ellipsoid, hyperboloid, elliptic cone, elliptic cylinder and hyperbolic cylinder). We found that self-intersection curves of offsets of all the implicit quadratic surfaces are planar implicit conics and their corresponding curve on the progenitor surface can be expressed as the intersection curve between an ellipsoid, whose semi-axes are proportional to the offset distance, and the implicit quadratic surfaces themselves.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198971
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  • 22
    Digitale Medien
    Digitale Medien
    Analysis and verification of the boundary surfaces of solid objects (1998)
    Springer
    Engineering with computers 14 (1998), S. 36-47 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Discretised surfaces ; Intersections ; Mesh generation ; Solid objects ; Topology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Triangulation of complex three-dimensional objects is a time-consuming process, and the boundary surfaces of the object have to be checked very carefully to ensure no crror is made. With the increased use of computer graphics in the generation of complicated object shapes, such as aircraft, space vessels, machine parts, physical models, etc., visual inspection alone is not good enough to affirm the validity of the object, and a thorough verification of the output from a CAD system is necessary to ensure that the object is well defined and complies with the input requirements of the mesh generator. This paper describes such a data verification procedure for general curved surfaces and objects defined by the boundary surface modelling technique. The quality of individual elements, the overall topological structures, and geometrical correctness in terms of intersections, close touches and sharp angles will all be studied and verified. Several engineering objects are analysed to illustrate the practical applications of the procedure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198973
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  • 23
    Digitale Medien
    Digitale Medien
    Distributed finite element computations using object-oriented techniques (1998)
    Springer
    Engineering with computers 14 (1998), S. 59-72 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Distributed computing ; Finite element analysis ; Object-oriented analysis/design ; Parallel processing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract An object-oriented parallel finite element framework has been developed to facilitate rapid prototyping of a wide variety of parallel finite element computations. Parallel computing and object-oriented technologies are integrated to achieve efficiency in both computation and software development. The paper presents various reusable and extensible components that constitute the parallel finite element architecture.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198975
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  • 24
    Digitale Medien
    Digitale Medien
    Seed specification for displaying a streamline in an irregular volume (1998)
    Springer
    Engineering with computers 14 (1998), S. 73-80 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Critical point ; Data interpolation ; Finite element method ; Irregular volume ; Scientific visualisation ; Spatial point location ; Volume visualisation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Two techniques are presented for specifying seed points, which are the starting points for streamlines, in an irregular volume. One is an interactive seed specification technique, in which efficient data probing is achieved by traversing the adjacency graph of the volume. The other is an automatic seed specification technique. A seed point is placed near a critical point, where the velocity vector is zero. Efficient algorithms are given for finding and classifying the critical point by using a tetrahedral cell. A successful application of these techniques to a problem in a clean room is also described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198976
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  • 25
    Digitale Medien
    Digitale Medien
    High-level operations dedicated to the integration of mechanical analysis within a design process (1998)
    Springer
    Engineering with computers 14 (1998), S. 81-92 
    Details
    ISSN: 1435-5663
    Schlagwort(e): Mechanical analysis ; Design process ; Geometric modelling ; Multi-representations ; Integration ; Object-oriented approach
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract Here we present the high-level operators of the Mechanical Analysis Module, which is a software architecture dedicated to a better integration of the structural analysis phase within an integrated Computer-Aided Design environment. This generic module is independent of the mechanical analysis method used, and takes place in a distributed software architecture of an integrated design environment. The paper shows that the mechanical operators defined are split among geometric and mechanical treatments in order to enforce this distributed architecture. Thus, the interface between the geometric treatments and the mechanical analysis environment shows the adequacy of the boolean operators when used with mechanical analysis treatments. However, this is demonstrated for a restricted domain of the mechanical analysis, and open ended questions still exist as to when the geometry of the models is diversified. Also, requirements for new geometric treatments and extensions of the current geometric representation are listed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01198977
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  • 26
    Digitale Medien
    Digitale Medien
    A comparative study of etching enamel by acid and laser (1995)
    Springer
    Lasers in medical science 10 (1995), S. 37-42 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Enamel ; Etch ; Laser ; Acid ; Nd-YAG
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Acid etching is regarded as one of the main means of providing additional retention in aesthetic dentistry. Alternative methods of achieving bonding to tooth tissue which have been proposed include laser etching. Conflicting results on bond strength to enamel have been reported for laser etching. Here the tensile bond strength of composite resin to acid- and laser-etched enamel was measured and the topographical differences between the surfaces were evaluated using the scanning electron microscope. The laser used was a pulsed Nd-YAG laser at 10 pulses per second with a pulse length of 150μs, 80mJ pulse−1, 1.064μm wavelength. The results obtained indicate that the bond strength of laser-etched enamel was significantly lower than that of acid-etched enamel. In this study the difference may be attributable to the chromophore used. Variations in the rate of traverse of the laser tip across the surface did not appear to produce significant alterations in the bond strength.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02133162
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  • 27
    Digitale Medien
    Digitale Medien
    Laserthermia kills acidotic cancer cells more effectively than conventional hyperthermia (1995)
    Springer
    Lasers in medical science 10 (1995), S. 31-36 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Embryonal carcinoma ; F9 cells ; Laser ; Hyperthermia ; Nigericin ; Acidosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract The aim of this study was to investigate how acidosis affects the sensitivity of F9 embryonal carcinoma cells to conventionally induced hyperthermia and Nd-YAG laser-induced laserthermia. Nigericin, a polyether ionophore, was used to reduce the intracellular pH to 6.8, while the control cells were maintained at a physiological pH of 7.4. Acidosis increased the heat sensitivity significantly. After the water bath only 75% of the acidotic F9S1 cells were viable, whereas all of the control cells at pH 7.4 survived. When the laser was used, the difference was even more pronounced. Only 9% of the acidotic cells were viable after a 2-min treatment and 0.2% after a 4-min treatment. At physiological pH a 2-min treatment left 41% of the cells viable and a 4-min treatment 2%. This study showed that laserthermia is significantly more effective in killing cells with low intracellular pH than it is in killing cells with normal intracellular pH. The core of a tumour is often acidotic and thus radioresistant. It is suggested that laserthermia could be a good choice when treating acidotic radioresistant cancer cells, and its effect as an adjuvant to radiation therapy should be investigated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02133161
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  • 28
    Digitale Medien
    Digitale Medien
    Diode lasers: Experimental and clinical review (1995)
    Springer
    Lasers in medical science 10 (1995), S. 157-163 
    Details
    ISSN: 1435-604X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Diode lasers are now capable of delivering up to 60 W of power down thin optical fibres, and their medical applications have increased considerably over the past 5 years. Most of the recent experimental and clinical work has been performed using the 805 nm diode laser wavelength, which is more heavily absorbed and is less penetrating than the 1064 nm Nd-YAG wavelength in most tissues. In contact and non-contact mode, the overall tissue effects from the diode laser are similar to the Nd-YAG laser, but with interstitial therapy the 805 nm wavelength produces significantly greater necrosis than the 1064 nm wavelength. Experimental work has established the effectiveness of the diode laser and clinical work has confirmed its suitability for a wide variety of procedures. Diode lasers have the major advantages of being small, compact, portable, efficient, easy to use and virtually maintenance free; they are likely to replace more cumbersome lasers for many medical applications.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02133326
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  • 29
    Digitale Medien
    Digitale Medien
    Transmyocardial revascularization (1995)
    Springer
    Lasers in medical science 10 (1995), S. 83-91 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Transmyocardial revascularization ; Lasers ; Coronary artery disease ; Ischaemia ; Tissue hibernation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Transmyocardial revascularization (TMR) is a puncture technique proposed as a solution for patients with coronary artery disease who cannot be efficiently treated with the standard revascularization procedures such as bypass surgery or percutaneous transluminal coronary angioplasty (PTCA). The studies presented in this review have investigated the use of lasers to revascularize ischaemic myocardium. Needle puncture methods are also briefly described. The results from experimental studies are not conclusive but the encouraging clinical reports raise further questions about the mechanism of angina relief.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02150845
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  • 30
    Digitale Medien
    Digitale Medien
    The effect of the illumination time when treating port-wine stains (1995)
    Springer
    Lasers in medical science 10 (1995), S. 93-104 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Copper vapour laser ; Electron microscopy ; Illumination time ; Numerical modelling ; Optimal treatment ; Port-wine stain
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract This paper reports the electron microscopy results obtained from two patients who were treated with 5 W of yellow (578 nm) light from a copper vapour laser with an illumination time of 3.6 ms and a 0.3 mm spot diameter. The endpoint of treatment was transient blanching. Following treatment, erythema was observed. There was minimal damage to the epidermis and non-vascular tissue such as the nerve fibres. There was severe damage to the endothelial cells of the ectatic vessels. Twenty-four hours after treatment, platelet activation and collagen were present, indicating that these vessels were no longer viable. Theoretical calculations are used to determine the flow of heat within and away from a 50μm diameter vessel. From this, heating of the entire vessel is shown to occur with illumination times of 4 ms, with minimal heating of the non-vascular tissue. Shorter illuminations do not heat the entire vessel, while the use of longer illumination times will cause excessive damage to the surrounding non-vascular tissue. Illumination times close to 4 ms must be regarded as optimal.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02150846
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  • 31
    Digitale Medien
    Digitale Medien
    Photodynamic therapy to the oral cavity, tongue and larynx: a canine normal tissue tolerance study (1995)
    Springer
    Lasers in medical science 10 (1995), S. 13-18 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Photodynamic therapy ; Larynx ; Oval cavity ; Light dose rates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Photodynamic therapy (PDT) has the potential to treat early carcinomas of the oral cavity and larynx while preserving normal tissue. However, normal tissues retain the photosensitizing agents and may be activated by high light fluence and dose rates resulting in normal tissue necrosis. The effects of varying dose rates of light delivery on various tissues in the upper aerodigestive tract have not been evaluated to date and are necessary to determine a ‘therapeutic light dose range’ that will result in selective tumour necrosis. Thirty adult mongrel dogs received intravenous Photofrin, 2 mg kg−1, 48 h prior to PDT treatment. Photodynamic therapy was administered to the tongue, buccal mucosa and larynx with a microlens fibre and implantable cylindrical diffuser at various dose rates from 20 to 125 J cm−2 at 150 mW cm−2. At the same dose rate of light delivery, the tongue was the most sensitive organ, followed by the buccal mucosa, and last by the larynx. The differential tissue effect of identical dose rates of therapy must be taken into account when administering PDT so that selective tumour necrosis with normal tissue preservation may be achieved. This study indicates the need to perform evaluations of the effect of PDT on other tissue types in an animal model with each new photosensitizer prior to administering PDT to those areas in humans.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02133158
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  • 32
    Digitale Medien
    Digitale Medien
    The relevance of pulse repetition rate and radiant exposure to the neurophysiological effects of low-intensity laser (820 nm/pulsed wave) irradiation upon skin temperature and antidromic conduction latencies in the human median nerve (1995)
    Springer
    Lasers in medical science 10 (1995), S. 253-259 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Nerve conduction ; Laser therapy ; Skin temperature ; Biostimulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract The effects of low-intensity near-infra-red laser irradiation (820 nm; 1.5 and 9.0 J cm−2; pulsed at 12 Hz, 73 Hz and 5 kHz) upon peripheral neurophysiology and skin temperature were investigated using antidromic conduction studies in the human median nerve in vivo. Healthy human volunteers (n = 90) were recruited and allocated randomly to either a control group (n=10) or one of eight experimental groups (two radiant exposures, 1.5 J cm−2 and 9.0 J cm−2 at one of three pulse repetition rates, 12 Hz, 73 Hz or 5 kHz, in addition to a placebo group for each radiant exposure;n = 10 all groups). Analysis of variance (ANOVA) demonstrated a significant (p≤0.05) decrease in skin temperature following irradiation at the lowest radiant exposure (1.5 J cm−2) combined with pulse repetition rates of 73 Hz and 5 kHz, with the greatest effect at 73 Hz. These changes in skin temperature were coupled with increases in negative peak latency (NPL); ie changes in NPL were inversely related to changes in skin temperature. However, in contrast to the authors' previous findings using continuous wave (CW) laser irradiation, differences in NPL were not found to be significant. These findings, therefore, provide little evidence of the neuro-physiological effects of low-intensity infra-red irradiation at the dosage levels and pulse repetition rates used here.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02133617
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  • 33
    Digitale Medien
    Digitale Medien
    Vascular and other non-tumour applications of photodynamic therapy (1996)
    Springer
    Lasers in medical science 11 (1996), S. 3-10 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Photodynamic therapy ; Non-tumour ; Arteries ; Fibrocellular intimal hyperplasia ; Aminolaevulinic acid ; Phthalocyanine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Photodynamic therapy is being investigated as a cancer therapy. As a cytotoxic treatment, it may also have therapeutic benefits in certain non-tumour conditions. The mechanism of photodynamic therapy is discussed in relation to its cancer therapy. The literature on non-tumour applications of photodynamic therapy is subsequently reviewed, highlighting its vascular applications in particular. Arterial angioplasty restenosis has proved resistant to all treatments tried thus far. Because fibrocellular intimal hyperplasia arising from the proliferation of vascular medial smooth muscle cells forms the pathological basis of restenosis, photodynamic therapy has been considered in its prevention. The literature on two second-generation photosensitizers (5-aminolaevulinic acid and phthalocyanine) which are likely to achieve clinical application are reviewed with regard to their photodynamic effects on fibrocellular intimal hyperplasia. This review concludes that photodynamic therapy shows enough promise for the inhibition of fibrocellular intimal hyperplasia for large animal studies to be pursued.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02161287
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  • 34
    Digitale Medien
    Digitale Medien
    Meeting reports (1996)
    Springer
    Lasers in medical science 11 (1996), S. 59-60 
    Details
    ISSN: 1435-604X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02161294
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  • 35
    Digitale Medien
    Digitale Medien
    Uvulopalatopharyngoplasty with CO2, contact ND-YAG or combined CO2 and ND-YAG laser beams (1996)
    Springer
    Lasers in medical science 11 (1996), S. 53-58 
    Details
    ISSN: 1435-604X
    Schlagwort(e): CO2 laser ; Contact Nd-YAG laser ; Combined CO2 and Nd-YAG laser ; Uvulopalatopharyngoplasty ; Sleep apnoea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Three different surgical lasers, ie CO2, contact Nd-YAG and Combolaser (combined simultaneous and co-axial CO2+Nd-YAG laser beam), were used for 76 uvulopalatopharyngoplasty (UPPP) operations. The effects of different lasers on intra-operative bleeding, operation time and post-operative pain were compared. Sixty patients with obstructive sleep apnoea syndrome (OSAS) and 16 patients with socially disturbing snoring were operated on. The CO2 laser was used in 24 patients, contact Nd-YAG was used in 27 patients and Combolaser was used in 25 patients. The Combolaser was associated with significantly less intra-operative bleeding and a shorter operation time. During the immediate recovery period, post-operative pain was most mild after operations with the CO2 laser when graded according to need for analgesics, or by the patients' subjective evaluation. Concerning possible post-operative complaints or overall outcome of the UPPP operation, no differences were found between the lasers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02161293
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  • 36
    Digitale Medien
    Digitale Medien
    A study of the radiological use of laser angioplasty in Britain (1996)
    Springer
    Lasers in medical science 11 (1996), S. 79-95 
    Details
    ISSN: 1435-604X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Laser recanalization was introduced and developed in Britain in the 1980s in an attempt to deal with the limitations associated with the conventional technique of percutaneous transluminal angioplasty (PTA). Since then, the use of this technique has decreased. This paper reports the findings of a comprehensive literature survey and interviews with a representative sample of British interventional radiologists on the reasons for this decline, and suggests the likely future direction for this technology. It has been determined that the main reasons for the decline are improvements in conventional guidewire and catheter technology, the high cost of the laser system, and the lack of evidence of any improvement in results compared with conventional PTA. However, despite current disenchantment, the majority of radiologists questioned felt that lasers could have a future role to play and that development of these systems should continue.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02133205
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  • 37
    Digitale Medien
    Digitale Medien
    Laser Doppler velocimetry in retinal arteries of infants (1995)
    Springer
    Lasers in medical science 10 (1995), S. 267-272 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Blood flow pulsatility ; Human infants ; Laser Doppler velocimetry ; Retinal blood flow
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract The present study was conducted to assess the feasibility of laser Doppler velocimetry in young infants, as a prelude to ultimately undertaking such measurements in premature infants. A portable, unidirectional laser Doppler velocimeter was developed based on a Kowa RC-2 hand-held fundus camera. Six infants between 1 and 21 weeks of age were studied. Relative red blood cell velocity (δfmax) at the centre of retinal arteries was measured over approximately 10 heart cycles. A pulsatility parameter (P=1−δfmax.dia/δfmax.sys), a summary index of vascular status, was determined from the average diastolic and systolic values of δfmax. Velocity waveforms were obtained in four of the six infants. Arterial pulsatility for the group was 0.63±0.13. Precise non-invasive measurement of arterial red blood cell velocity waveforms in young infants was achieved. The high signal-to-noise ratio and temporal resolution of this data suggest that relative measurements of retinal blood flow may permit assessment of haemodynamic changes in premature infants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02133619
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  • 38
    Digitale Medien
    Digitale Medien
    Sensitization and photodynamic therapy of normal pancreas, duodenum and bile ducts in the hamster using 5-aminolaevulinic acid (1996)
    Springer
    Lasers in medical science 11 (1996), S. 11-21 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Photodynamic therapy ; 5-Aminolaevulinic acid ; Pancreas ; Bile duct ; Duodenum ; Fluorescence microscopy ; Light dosimetry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Photodynamic therapy (PDT) using 5-aminolaevulinic-acid-(ALA)-induced protoporphyrin IX (PPIX) increases survival in hamsters with pancreatic cancer. However, experiments with other photosensitizers on this model show a high risk of duodenal perforation. In this paper, the pharmacokinetics and PDT effects of ALA on normal tissues in the pancreatobiliary region are presented. Using quantitative fluorescence microscopy, maximum PPIX fluorescence was seen in the bile ducts, less in the duodenal mucosa and least in the muscularis propria and pancreas. For PDT, light was delivered either using a bare fibre touching the tissue (single-point illumination), or irradiating a 1.5 cm diameter circular area. Single-point PDT (50 J) produced only localized reversible damage without perforation. Surface irradiation of the whole periampullary region (50 J cm−2) caused extensive damage, sometimes with perforation. Before PDT can be used safely to treat tumours of the pancreas and bile duct, further studies are necessary to understand its effect on larger areas of normal tissue.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02161288
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  • 39
    Digitale Medien
    Digitale Medien
    Editorial (1996)
    Springer
    Lasers in medical science 11 (1996), S. 217-217 
    Details
    ISSN: 1435-604X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02134910
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  • 40
    Digitale Medien
    Digitale Medien
    Tetra(m-hydroxyphenyl)chlorin clinical photodynamic therapy of early bronchial and oesophageal cancers (1996)
    Springer
    Lasers in medical science 11 (1996), S. 227-235 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Photodynamic therapy ; PDT ; mTHPC ; Early cancer ; Squamous cell carcinoma ; Oesophagus ; Bronchi ; Photosensitizer ; Light dosimetry ; Clinical
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract There have been few studies to date of clinical photodynamic therapy (PDT) with tetra(m-hydroxyphenyl)chlorin (mTHPC). This paper describes the results of the authors' experience with this second-generation photosensitizer, used in the treatment of 40 early cancers of the oesophagus and the bronchi. Surface illumination of the tumour was performed, in most cases, 4 days after intravenous injection of 0.15 mg kg−1 of mTHPC, using 652 nm or 514 nm continuous wave laser light. Endoscopic follow-up with biopsies and brushings was possible for 35 tumours: 27 (77%) showed no recurrence after disease-free follow-ups that ranged from 3 to 38 months. Major complications, all of which were after red light illumination, included one bronchial stenosis, one oesophagotracheal fistula and two probable occult perforations of the oesophagus. Photodynamic therapy with green light renders such perforations of the oesophageal wall essentially impossible at the applied conditions, and appears not to reduce the efficacy of the treatment. Skin photosensitization, which was never observed later than the first week after injection, occurred in 12 patients. Hence, PDT with mTHPC is a safe and effective treatment for early carcinomas of the oesophagus and the tracheobronchial tree.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02134913
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  • 41
    Digitale Medien
    Digitale Medien
    Photodynamic therapy of 168 early stage cancers of the lung and oesophagus: a japanese multi-centre study (1996)
    Springer
    Lasers in medical science 11 (1996), S. 255-259 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Photodynamic therapy ; Early stage lung cancer ; Superficial oesophageal cancer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract In 1994, the Ministry of Health and Welfare of Japan approved photodynamic therapy (PDT) for the treatment of early stage lung cancer (T0 and T1), superficial oesophageal cancer, superficial early stage gastric cancer and carcinoma in situ and/or dysplasia of the cervix. The decision to do so was based on studies carried out by the PDT Research Group of the Ministry, including PDT treatment of 168 early stage central lung cancers (123 superficial lesions and 45 nodular lesions) and 32 superficial oesophageal cancers. The results presented in this article were analysed according to the extent of the lesion. Of the 123 superficial lung cancers, complete remission (CR) was obtained in 93% of 89 lesions less than 1.0 cm in diameter. Larger lesions responded less well. Complete remission was obtained in 97% of the 33 superficial oesophageal cancers, although three of six patients with lesions over 3.0 cm in diameter later died of metastatic disease. The authors believe PDT to be a suitable and effective treatment for early stage lung and oesophageal cancers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02134916
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  • 42
    Digitale Medien
    Digitale Medien
    Human tissue levels and plasma pharmacokinetics of temoporfin (Foscan®, mTHPC) (1996)
    Springer
    Lasers in medical science 11 (1996), S. 267-272 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Photosensitizer ; Photodynamic therapy ; mTHPC ; Temoporfin ; Pharmacokinetics ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract A Phase I photodynamic therapy (PDT) clinical trial was carried out with Temoporfin (Foscan®, mTHPC) at the Departments of Otolaryngology at Orebro Medical Center (OMC) and Long Island Jewish Medical Center (LIJMC). A range of drug doses, consisting of 0.3, 0.15, 0.075 and 0.0375 mg kg−1, were utilized. Light treatment was performed on the sixth day after injection of the photosensitizer mTHPC. Photodynamic therapy was done on prostate cancer (six cases), bronchial cancer (one case), nasopharyngeal cancer (three cases), laryngeal cancer (eight cases), mesothelioma (one case), laryngeal papilloma (five cases) and basal cell nevus syndrome (one case). A number of patients were treated more than once. Plasma was collected and analysed at 1, 24, 48, 72, 96, 120 and 144 h and at 2 weeks post-injection, to follow the loading and clearance rate of the photosensitizer. Normal and malignant tissues were collected immediately prior to PDT, chemically extracted, and analysed for drug content spectrofluorometrically. Plasma drug levels were proportional to the dose. The half-life of the drug was 45.4 h across the entire dose range. The ratio of the drug in the tumour compared to normal adjacent mucosa was in the range of 2–3. There were no significant adverse effects. These data establish the basis for full clinical trials.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02134918
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  • 43
    Digitale Medien
    Digitale Medien
    Quantification of polydimethylsiloxane concentration in turbid samples using raman spectroscopy and the method of partial least squares (1998)
    Springer
    Lasers in medical science 13 (1998), S. 32-41 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Biomedical diagnostics ; Breast implant leakage ; Optical spectroscopy ; Partial least squares ; Polydimethylsiloxane (PDMS) ; Raman spectroscopy ; Silicone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract This paper presents a preliminary application of Raman spectroscopy in conjunction with the chemometric method of partial least squares to predict silicone concentrations in homogenous turbid samples. The chemometric technique is applied to Raman spectra to develop an empirical, linear model relating sample spectra to polydimethylsiloxane (silicone) concentration. This is done using a training set of samples having optical properties and known concentrations representative of those unknown samples to be predicted. Partial least squares, performed via cross-validation, was able to predict silicone concentrations in good agreement with true values. The detection limit obtained for this preliminary investigation is similar to that reported in the magnetic resonance spectroscopy literature. The data acquisition time for this Raman-based method is 200 s which compares favourably with the 17 h acquisition required for magnetic resonance spectroscopy to obtain a similar sensitivity. The combination of Raman spectroscopy and chemometrics shows promise as a tool for quantification of silicone concentrations from turbid samples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00592958
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  • 44
    Digitale Medien
    Digitale Medien
    Measurement of radiometric surface temperature and integrated backscattered light intensity during feedback-controlled laser-assisted cartilage reshaping (1998)
    Springer
    Lasers in medical science 13 (1998), S. 66-72 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Cartilage ; Laser-induced reshaping ; Nd:YAG laser ; Plastic surgery ; Reconstructive surgery ; Stress relaxation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Cartilage undergoes characteristic mechanical stress relaxation following laser irradiation below the ablation threshold. Porcine auricular cartilage (1–2 mm thickness) was irradiated with a Nd:YAG laser (λ=1.32 μm) at two power levels (W/cm2). Surface temperature (S c (t) (°C)) (monitored using a single element HgCdTe infrared detector, 10-14 μm spectral range), and integrated back scattered light intensityI(t) were measured during laser irradiation. A HeNe laser beam (λ=632.8 nm) was incident on the back surface of the cartilage specimen and fractional integrated backscattered light intensity was measured using an integrating sphere anda silicon photodiode. Laser irradiation (5.83 W/cm2, 50 Hz pulse repetition rate (PRR)) continued until surface temperature reached approximately 70°C, during which cartilage mechanical stress relaxation was observed. Integrated back scattered light intensity reached a plateau at about 70°C). At higher laser power (39.45 W/cm2, 50 Hz PRR), a feedback-controlled cryogen spray was used to maintain surface temperature below 50°C. A similar plateau response was noted in integrated backscattered light intensity. This signal may be used to optimise the process of stress relaxation in laser cartilage reshaping. Several clinical applications involving reconstructive surgery are proposed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00592961
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  • 45
    Digitale Medien
    Digitale Medien
    Laser therapy of varicosities with the flashlamp-pumped pulsed dye laser (1996)
    Springer
    Lasers in medical science 11 (1996), S. 193-197 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Varicosities ; Pulsed dye laser
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract The flashlamp-pumped pulsed dye laser with an output wavelength of 585 nm and a pulse duration of 450μm was used to treat 102 areas of blue and red varicosities in the lower limbs of female patients. Varicosities could be divided into two groups, early red varicosities and more developed blue varicosities. Forty-two areas of blue varicosities were treated with a single pulse, and only 20% of these were eliminated. Blue varicosities were then treated in three treatment sessions, 3 weeks apart, and none of them could be occluded. Red varicosities responded better; all of the varicosities treated were occluded in three treatment sessions separated by 3 weeks. The use of two consecutive pulses with only 6.5 Jcm−2 in a single treatment session resulted in only 54% of the varicosities being eliminated. Finally, seven areas of red varicosities were treated in a single treatment with an argon laser at 2 W; only 10–20% of these lesions responded. The pulsed dye laser is therefore of most use in treating red varicosities.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02156764
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  • 46
    Digitale Medien
    Digitale Medien
    Guest editorial (1996)
    Springer
    Lasers in medical science 11 (1996), S. 219-219 
    Details
    ISSN: 1435-604X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02134911
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  • 47
    Digitale Medien
    Digitale Medien
    Time-resolved confocal fluorescence microscopy of porphyrins for phototherapy (1996)
    Springer
    Lasers in medical science 11 (1996), S. 237-246 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Fluorescence ; Time-resolved confocal microscopy ; Porphyrins ; Fluorescence polarization ; Photodynamic therapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract The application of a novel time-resolved confocal fluorescence microspectrometer to studies of the distribution and speciation of porphyrin photosensitizers in rat C6 cerebral glioma cells is described. The instrument combines a mode-locked argon ion laser excitation source with time-correlated single photon counting fluorescence detection and has sub-micron spatial and sub-nanosecond temporal resolution. The porphyrins studied were haematoporphyrin derivative (HpD), haematoporphyrin IX (HP), porphyrinc (Pc) and the tetrakiscarborane carboxylate ester of 2,4-(α,β-dihydroxyethyl) deuteroporphyrin IX (BOPP). From the heterogeneous emission observed in vitro, assignments and spatial location of various porphyrin species are proposed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02134914
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  • 48
    Digitale Medien
    Digitale Medien
    New laser literature (1996)
    Springer
    Lasers in medical science 11 (1996), S. 273-275 
    Details
    ISSN: 1435-604X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02134919
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  • 49
    Digitale Medien
    Digitale Medien
    Optical spectroscopy for the early diagnosis of gastrointestinal malignancy (1998)
    Springer
    Lasers in medical science 13 (1998), S. 3-13 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Biopsy ; Fluorescence ; Optical ; Raman ; Spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract The early diagnosis of gastrointestinal malignancy will allow eradication of the disease prior to invasive cancer. At present, fluorescence spectroscopy offers the most realistic prospect of an early clinical system and is currently under evaluation. Optical coherence tomography can differentiate the layers of the oesophageal wall and has greater reolution than ultrasound. Although complicated, Raman spectroscopy offers the greatest information with possible development of a molecular endoscope.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00592955
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  • 50
    Digitale Medien
    Digitale Medien
    Design and Characterisation of a Tissue Phantom System for Optical Diagnostics (1998)
    Springer
    Lasers in medical science 13 (1998), S. 160-171 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Absorption; Fluorescence; Integrating sphere; Optical tissue phantom; Scattering
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: We present an optical phantom system especially suited to investigating the generation and transport of laser-induced fluorescence in biological tissues. The phantom system consists of micrometre-sized particles of aluminium oxide, iron and coloured resin dispersed in a solid, transparent host (polyorganosiloxane), from which mechanically stable samples can be made. Mie theory is applied to predict the radiation transport parameters from the optical properties of the isolated components. The predictions are in good agreement with the results of integrating sphere measurements. The radiation transport parameters of the samples are reproducible and temporally stable.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050070
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  • 51
    Digitale Medien
    Digitale Medien
    Photosensitisation of red blood cell haemolysis by photodynamic agents (1998)
    Springer
    Lasers in medical science 13 (1998), S. 42-54 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Erythrocyte membranes ; Hemolysis ; Photosensitising agent
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Photosensitised haemolysis of red blood cells (RBC) by sodium hypericin, haematoporphyrin, protoporphyrin, Photofrin® and benzoporphyrin derivative monoacid ring A were investigated for broad spectrum near-ultraviolet (UVA)-visible light and monochromatic 630 nm irradiations. The delayed photohaemolysis rate (1/t 50) increased with the approximate square of the incident light dose, wheret 50 is the dark incubation time required for 50% haemolysis. The power dependence of 1/t 50 on the sensitiser concentration varied with the specific sensitiser and the irradiation conditions. Energy calculations for protoporphyrin show that the quantum efficiency of delayed photohaemolysis at 630 run is independent of the sensitiser concentration at constantt 50 and increases witht 50 The protective effects of water-soluble singlet oxygen quenchers are indicative of a Type II photosensitisation pathway for these agents. Pretreatment of RBC with hydrogen peroxide suppressed photosensitisation by protoporphyrin accompanied by lipid peroxidation and oxidation of haemoglobin. The photohaemolysis curves are analysed with a target theory model which postulates that haemolysis requires thermal activation of photochemical damage. The model calculations indicate that photosensitised haemolysis requires two photochemical hits and a highly cooperative thermal process.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00592959
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  • 52
    Digitale Medien
    Digitale Medien
    132-hydroxy-bacteriopheophorbidea-methylester pharmacokinetics in mice bearing Lewis lung carcinoma (1998)
    Springer
    Lasers in medical science 13 (1998), S. 78-81 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Lewis lung carcinoma ; Pharmacokinetics ; Spectroscopy ; 132-hydroxy bacteriopheophorbidea-methylester (132-OH-BPME)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract The photosensitiser 132-hydroxy bacteriopheophorbide a-methylester (132-OH-BPME) is characterised by a high absorption coefficient at the far red wavelength 750 nm and a good singlet oxygen quantum yield. The pharmacokinetics of 132-OH-BPME was studied on the Lewis lung carcinoma in mice after i.v. administration of 5 mg/kg body weight at different incubation intervals. The accumulation dye was chemically extracted from selected tissues and the concentrations were measured by absorption spectroscopy. The parenchymatous organs, liver, spleen and kidney, showed maximum 132-OH-BPME concentrations after 2 h incubation (liver, spleen) and 4 h postinjection (kidney). A high uptake was detected in the lung with the maximum concentration at 2 h. The malignant tissue accumulated high 132-OH-BPME concentrations at 2–12 h postinjection with peaking at 8 h. The 132-OH-BPME concentrations in muscle tissue, representing the normal tumour surroundings, and in the skin were very low. The results of our study suggest that photodynamic therapy (PDT) using 132-OH-BPME could be effective at an incubation time of about 8 h postsensitiser injection, when the tumour 132-OH-BPME concentration has reached its maximum and the muscle and skin concentrations are at a minimum.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00592963
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  • 53
    Digitale Medien
    Digitale Medien
    Temperature Feedback and Collagen Cross-Linking in Argon Laser Vascular Welding (1998)
    Springer
    Lasers in medical science 13 (1998), S. 98-105 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Collagen; Infrared thermometry; Radiometry; Temperature; Tissue fusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. A preliminary single-animal study of in vivo argon laser vascular welding was conducted using a canine model. The effects of temperature feedback control and saline drip cooling on patency and collagen cross-linking were investigated. The surface temperature at the centre of the laser spot was monitored using a two-colour infrared thermometer. The surface temperature was limited by either a saline drip or feedback control of the laser. Acute patency was evaluated and collagen cross-link assays were performed. Though both protocols yielded successful tissue fusion, welds maintained at a surface temperature of 50°C using feedback control had an elevated cross-link count compared to controls, whereas tissues irradiated without feedback control experienced a cross-link decrease. Simulations using the LATIS (LAser-TISsue) computer code suggest that drip-cooled procedures achieve significantly higher temperatures beneath the tissue surface than temperature feedback-controlled procedures. Differences between the volumetric heating associated with drip-cooled and feedback-controlled protocols may account for the different effects on collagen cross-links. Covalent mechanisms may play a role in argon laser vascular fusion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050061
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  • 54
    Digitale Medien
    Digitale Medien
    Photodynamic Therapy (PDT) of Gastrointestinal Tumours: A New Light Delivery System (1998)
    Springer
    Lasers in medical science 13 (1998), S. 137-142 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Colorectum; Intraluminal probe; Non-laser light source; Oesophagus; Paterson lamp; Photodynamic therapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. The Paterson lamp is a convenient, low cost, portable, alternative light source to lasers for photodynamic therapy (PDT). A multiwavelength capability enables the clinician to vary the photosensitiser used. The Paterson lamp has been applied in the field of dermatology using a liquid light guide with distal optics for surface application. We now describe distal optics suitable for use with this light guide for intraluminal applications in the oesophagus and colorectum. The geometry of the site (oesophagus and colorectum) requires distal optics such as a cylindrical diffuser or a side-fire diffuser. We have designed new probes that diffuse light radially from the guide axis (cylindrical diffusion). The tips have a frosted glass surface that scatters and effectively couples light radially into the tissue. An acrylic spacer is placed over the diffuser to position the tissue at a constant diameter from the probe. This is held in position by a silicone sheath placed over the distal one metre. For use in the oesophagus, a channel, to facilitate intubation over a guide wire, is included. The diameter of the entire probe is 8.4 mm and the power output can be adjusted from 0–500 mW. Pilot PDT of tubulovillous adenomas of the rectum and Barrett's oesophagus using this light delivery system is currently underway and has shown good early response in the treated area.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050067
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  • 55
    Digitale Medien
    Digitale Medien
    Real-Time Monitoring of Blood–Brain Barrier Disruption Induced by Ultraviolet Laser Irradiation (1998)
    Springer
    Lasers in medical science 13 (1998), S. 172-180 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Argon laser; Blood–brain barrier; Brain; Evans blue; Guinea-pig; Vasodilation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Ultraviolet laser light of sufficient power can induce focal œdema in the brain. The formation of ultraviolet-induced vasogenic \kdema was monitored by observing real-time changes in the integrity of the blood–brain barrier. The brain surface of guinea-pigs injected with Evans blue was exposed to light from a continuous wave argon laser at 351 nm, delivered via an optical fibre. The integrity of the blood–brain barrier was evaluated by measuring surface reflectance using a separate probing light. The brain was then sectioned and examined using light and electron microscopy. Extravasation of Evans blue following vasodilatation was observed when the irradiation intensity was greater than 0.64 W/cm2. The extent of glial and vascular damage could be correlated with the laser power. Irradiated vascular endothelium exhibited lipping at the tight junction, vacuolation and mitichondrial swelling. These results suggest that disruption of the blood–brain barrier induced by ultraviolet light is preceded by vasodilatation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050071
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  • 56
    Digitale Medien
    Digitale Medien
    Carbon Dioxide Laser Resurfacing of Rhytides and Photodamaged Skin (1998)
    Springer
    Lasers in medical science 13 (1998), S. 232-241 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: CO2 laser, Laser treatment; Rhytides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. Carbon dioxide (CO2) laser resurfacing has been used as a method to treat rhytides and photodamaged skin. This laser offers several advantages over previously utilised modalities but its use has several inherent risks. This article will review important aspects of CO2 laser resurfacing including laser-skin interactions, patient selection, effective pre- and post-operative regimens and potential complications.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050002
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  • 57
    Digitale Medien
    Digitale Medien
    Helium-Neon (He-Ne) Laser Irradiation Increases the Incidence of Unreduced Bovine Oocytes During the First Meiotic Division In Vitro (1998)
    Springer
    Lasers in medical science 13 (1998), S. 260-264 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Bovine; Cell proliferation; He-Ne laser; Oocyte; Photobiology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. Low power He-Ne laser irradiation was applied to immature bovine oocytes to investigate the incidence of unreduced oocytes (diploid oocytes) during the first meiotic division in vitro. Immature bovine oocytes from cows killed at a slaughterhouse were irradiated with He-Ne laser irradiation at 0.05 and 0.25 J/cm2 exposures. An oocyte group was left untreated serving as the control group. All oocytes were matured in TCM-199 medium supplemented with 10% fetal calf serum (FCS). Unreduced oocyte percentages obtained in the irradiated oocytes group were significantly higher (p〈0.01 and p〈0.001, respectively) than those of the control group. Furthermore, the laser-treated oocytes showed a degeneration rate significantly higher (p〈0.01 and p〈0.001, respectively) than those observed in the control group. It is concluded that the application of He-Ne laser irradiation at 0.05 and 0.25 J/cm2 exposures increased the incidence of unreduced oocytes and the percentage of degenerated oocytes during the in vitro meiosis process of immature bovine oocytes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050005
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  • 58
    Digitale Medien
    Digitale Medien
    Review and Classification of Corneal Topographers (1999)
    Springer
    Lasers in medical science 14 (1999), S. 2-19 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Corneal topography; Fluorescence; Holography; Interferometry; Moiré; Partial coherence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. Corneal topography has, due to developments in refractive surgery and contact lens fitting, become a widely used diagnostic tool. Many types of topographers have been introduced, but there is some confusion on classification and subsequent principal possibilities of the various devices offered to the practitioner. The purpose of the study reported here was to make an inventory of developed devices, analyse the basic principles and create a classification based on optical principles. A literature search was done using Medline, the IBM Patent Server, and references found in articles and patents. This search resulted in a variety of descriptions that could be classified into 12 groups according to their use of light source and light-matter interaction of which four groups have representatives on the commercial market. This classification can be used by researchers and practitioners to gain insight into the possibilities of a given device in relation to the desired application.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050015
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  • 59
    Digitale Medien
    Digitale Medien
    Diffusing Fibre Tip for the Minimally Invasive Treatment of Liver Tumours by Interstitial Laser Coagulation (ILC): An Experimental Ex Vivo Study (1999)
    Springer
    Lasers in medical science 14 (1999), S. 32-39 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Interstitial laser coagulation; Laser applicator; Laser induced thermotherapy; Liver tumours; Nd-YAG laser
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. A newly developed diffusing laser applicator was examined for interstitial laser coagulation (ILC) of liver tumours. The applicator consisted of a matted quartz core and a quartz glass dome, also matted on its inner surface and sealed to the fibre. The applicator provided a homogeneous light intensity distribution over an active length of about 20 mm. Lesions were created in an ex-vivo porcine liver model using a Nd-YAG laser comparing the new diffusing tip with a Ringmode®-ITT applicator in order to find optimal laser parameters and damage thresholds. The lesions were investigated using macroscopic size measurement, volume calculation and histological examination (H&E, NADPH-dehydrogenase). The damage threshold of the diffusing tip was 6 W at 14 min exposure time whereas the Ringmode®-ITT applicator had its limit at 5 W and 12 min exposure. Comparing various exposure times showed that treatment over a time of more than 840 s did not significantly increase the lesion volume. At 5 W and 720 s the mean lesion volume was 6.9±1.1 cm3 with the diffusing tip and 6.3±0.6 cm3 with the Ringmode®-ITT applicator, both having a slight ellipsoidal shape. Hence, the created lesions were not significantly different for both applicators when the same laser parameters were applied. On the other hand, the new diffusing tip had a higher damage threshold and was therefore capable of producing maximal coagulation volumes of up to 7.9±0.5 cm3 at 5 W and 20 min. The experiments showed that lesions with a dimension of 31×22 mm can be achieved with the diffusing applicator which seem suitably sized for treating small human liver metastases in a single laser session.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050018
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  • 60
    Digitale Medien
    Digitale Medien
    Laser Myringotomy (L-Myringotomy) and Ventilating Tubes: A Preliminary Comparative Study (1999)
    Springer
    Lasers in medical science 14 (1999), S. 62-66 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Laser myringotomy; Otitis media with effusion; Tympanic membrane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. A prospective comparative study was done to assess the validity of laser myringotomy (L-myringotomy) when compared to the insertion of ventilating tubes (VT). In 23 children with chronic otitis media with effusion, a VT was inserted in the left ear while a laser myringotomy was performed in the right ear by using the CO2 Sharplan 1030 laser. After a six month follow-up conducted during the winter months, the results with the laser myringotomy were equal to those in the left ear with the VT. During the follow-up period, three ears required additional laser myringotomy either for early closure or because of otitis media and the accumulation of effusion in the middle ear cavity. Nevertheless, the use of laser has the advantage that there is no foreign body in the ear, the tympanic membrane is closed after four to seven weeks, and since the procedure is very short, the time for anaesthesia is minimal.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050022
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  • 61
    Digitale Medien
    Digitale Medien
    Photodynamic Therapy of Malignant Ovarian Tumours Cultivated on CAM (1999)
    Springer
    Lasers in medical science 14 (1999), S. 91-96 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Chorioallantoic membrane (CAM); Liposomes; Methylene blue; Ovarian cancer; Photodynamic therapy; Photosensitiser
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. The disappointing results with either surgery alone and/or chemotherapy in the treatment of malignant ovarian tumours have led to an increased interest in additional treatment schedules. Photodynamic therapy (PDT), a modality involving the use of a photosensitising drug and activating light, is being used increasingly as a local treatment for neoplastic lesions. The synthesis and evaluation of new photosensitisers for the treatment of gynaecological lesions and malignancies continues to be an active area of investigation for proper application of the photodynamic process in the gynaecological field. The effect of PDT using methylene blue (free and combined with liposomes) as a photosensitiser for treating human ovarian malignant tumours cultivated on the chorioallantoic membrane was evaluated. Two days after PDT, the treated implanted tumours were markedly decreased in size. Areas of necrosis with black coloration, dryness and eschar formation were observed. Five days after PDT, tumour remission was clearly observed in all the treated tumours. Photodynamic therapy using methylene blue (aqueous and coupled with liposomes) is effective for treating the ovarian malignancies and it will be capable of achieving complete eradication of visible tumours in patients with superficial lesions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050028
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  • 62
    Digitale Medien
    Digitale Medien
    The Monitoring of ALA-Induced Protoporphyrin IX Accumulation and Clearance in Patients with Skin Lesions by In Vivo Surface-Detected Fluorescence Spectroscopy (1999)
    Springer
    Lasers in medical science 14 (1999), S. 112-122 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Aminolaevulinic acid; Dermatology; Photodynamic therapy; Photosensitisation; Protoporphyrin IX; Skin lesions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. The method of surface-detected fluorescence has been used to monitor the emission intensity from 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) in lesions and corresponding adjacent normal skin. Three types of lesions were examined: psoriatic plaques, actinic keratosis and basal cell carcinoma. This study included a total of 14 human volunteers on whom ALA-induced PpIX formation and clearance was monitored for a total of 48 h post-ALA application. Both an ALA dose-ranging study, as well as a comparison of results between normal and lesional tissue at a fixed ALA dose, were carried out. For the dose range examined (10–30%), there was no ALA dose dependency of the PpIX fluorescence for any of the lesions tested. Although all three lesions tested did show enhanced PpIX fluorescence as compared with normal skin, there was considerable lesion-to-lesion variability. Thick psoriatic plaques seem to give longer PpIX retention times than those of thin lesions. Limitations of the surface-detected fluorescence methodology are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050032
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  • 63
    Digitale Medien
    Digitale Medien
    Changes in Local Hepatic Blood Perfusion During Interstitial Laser-Induced Thermotherapy of Normal Rat Liver Measured by Interstitial Laser Doppler Flowmetry (1999)
    Springer
    Lasers in medical science 14 (1999), S. 143-149 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Interstitial laser therapy; Liver; Perfusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. Interstitial laser Doppler flowmetry was used to measure the effect of interstitial laser-induced thermotherapy on local blood perfusion in normal rat liver in the peripheral treatment region elevated to hyperthermic temperatures. The Nd:YAG laser emitting at 1064 nm was utilised as heat generation source. The plane-cut tip of an optical fibre was placed in the middle of the exteriorised left liver lobe. Blood perfusion and temperature were measured in the liver parenchyma 4 mm from the laser fibre. The temperature at the location of the liver temperature sensor was maintained at 41 or 44°C during 30 min by regulating the power of the heating laser. The laser Doppler signal was recorded during and after heat treatment, for a total time of 60 min. At 41°C, a significant increase in perfusion up to 1.3 times the initial value was observed 2–16 min after start of treatment. At 44°C, perfusion decreased continuously during and after treatment, and was significantly different from control 40 min after start of treatment. The results may be valuable in assessing the thermal response of tissues surrounding the target in interstitial laser-induced thermotherapy of liver tumours during conditions of normal blood flow.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050036
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  • 64
    Digitale Medien
    Digitale Medien
    Picosecond Laser Ablation of Dentine in Endodontics (1999)
    Springer
    Lasers in medical science 14 (1999), S. 168-174 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Endodontics; Laser ablation; Nd:YAG laser; Picosecond laser; Root canal therapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract . The interaction of picosecond laser radiation with human dental tissue was investigated in this study, in order to determine the ablation rates and the surface characteristics of the dentine by using scanning electron microscopy (SEM). Dentine ablation was performed by using tooth sections of different thicknesses (0.5–2.0 mm). Dental tissue samples were irradiated in air with the fundamental wavelength and first harmonic of a regenerative amplifier Nd:YAG laser system, at 1064 nm and 532 nm, respectively, with a pulse duration of 100 ps and a pulse repetition rate of 10 Hz. The results showed very clean craters surrounded by minimum melting of the surface of dentine when the 1064 nm pulses were used. In contrast, when the first harmonic 532 nm pulses were used, the SEM examinations revealed cracks and melting of dentine with irregular surface modification. Consequently, it seems that cleaning and shaping of the root canal walls during endodontic therapy with the picosecond Nd:YAG laser application may be possible in the future. The, as yet unexplored, field of the picosecond laser interaction with hard dental tissue is expected to be a potential alternative for powerful laser processing of biomedical structures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050080
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  • 65
    Digitale Medien
    Digitale Medien
    Photodynamic Inactivation of the Single Crayfish Nerve Cell: Dynamics of Electrophysiological Responses and Comparison of Photosensitisers (1999)
    Springer
    Lasers in medical science 14 (1999), S. 185-195 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Chlorins; Firing; Janus green B; Methylene blue; Neuron; Photodynamic effect; Photoheme; Photoporphyrin IX; Photosens; Photosensitisers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract . The study of single neuron response to photodynamic effect provides a means for the study of the dynamics of cytotoxic events leading to cell death and allows comparison of the phototoxicity of different photosensitisers. Isolated crayfish stretch receptor neurons were photosensitised for 30 min, then irradiated with a He-Ne laser (632.8 nm; 0.3 W/cm2) until irreversible firing cessation. The dynamics of neuron firing frequency were continuously recorded throughout. The following photosensitisers were studied: methylene blue, janus green B, protoporphyrin IX, chlorins e 6 and p 6, haematoporphyrin derivative (Photoheme) and sulphonated aluminium phthalocyanine (Photosens). Nerve cells were found to be insensitive to either He-Ne laser irradiation or photosensitisation alone, but very vulnerable to the photodynamic effect: neurons changed firing rate and died at nanomolar concentrations of photosensitisers. The dynamics of neuron responses was found to depend on photosensitiser type and concentration. The current approach provides a means of evaluation of initial threshold cell membrane alteration and cytotoxic events leading to cell death. The dependence of firing acceleration rate and neuron lifetime on photosensitiser concentration additionally allowed comparison of efficiencies of different photosensitisers. Photosens, Photoheme and chlorin p 6 were found to be the most potent photosensitisers: neurons responded to their photodynamic effects at concentrations as low as 1–5 nM.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050083
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  • 66
    Digitale Medien
    Digitale Medien
    Disinfection of the Optical Fibre of a Nd-YAP Laser Used in Dental Care (1999)
    Springer
    Lasers in medical science 14 (1999), S. 73-80 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Biocides; Disinfection; Laser; Optical fibre
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. In order to set up a disinfection protocol, the tip of the optical fibre of an Nd-YAP laser, λ=1.34 μm, was contaminated in vitro with: Mycobacterium smegmatis (CIP 7326), Candida albicans (ATCC 2091), Bacillus stearothermophilus (ATCC 7953) or Streptococcus sanguis (ATCC 10556). It was then treated with various biocidal solutions, Septinol® V, glutaraldehyde 2%, ethanol 95° and NaOCl 6%, using one of two protocols: 10 s of contact, or 5 s of contact followed by 5 s of wiping. The latter technique proved to be the most effective. Whatever the biocidal solution used, all the bacteria adhering to the fibre were eliminated. The protocol was checked in vivo in the canals of 10 teeth presenting root canal infections. No bacteria withstood the treatment with Septinol® V. This treatment does not alter the qualities and performance of the fibre as far as light transmission is concerned.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050024
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  • 67
    Digitale Medien
    Digitale Medien
    Diode Laser Trabeculoplasty Versus Argon Laser Trabeculoplasty in the Control of Primary Open Angle Glaucoma (1999)
    Springer
    Lasers in medical science 14 (1999), S. 105-108 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Glaucoma, open angle; Intraocular pressure; Laser surgery; Trabecular meshwork; Trabeculoplasty
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. A randomised prospective study was carried out to determine whether diode laser trabeculoplasty (DLT) is as effective as argon laser trabeculoplasty (ALT) in the control of primary open angle glaucoma (POAG). Forty eyes of 40 patients with uncontrolled intraocular pressure (IOP) despite maximum topical medication were entered into the study. Twenty eyes received DLT, spot size 100 μm, exposure time 0.2 s, mean power 1034 (±56.4) mW. Twenty eyes received ALT, spot size 50 μm, exposure time 0.2 s, mean power 528 (±44.7) mW. They were reviewed at 2 h, 2 and 8 weeks, and 3, 6, 12, 18 and 24 months after laser treatment. Two eyes were withdrawn from the DLT group and four from the ALT group because of uncontrolled IOP during follow-up. Of the remaining eyes in the trial, mean IOP reductions for DLT and ALT, respectively, were: 6 months 7.42 (±2.36) mmHg and 6.36 (±2.3) mmHg; 12 months 7.02 (±2.6) mmHg and 6.28 (±2.2) mmHg; 18 months 6.86 (±2.8) mmHg, 5.98 (±2.02) mmHg; 24 months 6.50 (±2.72) mmHg, 5.92 (±2.02) mmHg. There was a significant reduction in each laser group when IOP at each stage was compared with baseline (p〈0.001) (paired Student's t-test), but no significant difference between the two groups. In the ALT group peripheral anterior synechiae developed in four eyes and post laser pain in seven eyes. These complications were not noted following DLT. We conclude that DLT and ALT are equally effective in IOP control, but DLT is associated with less anterior segment inflammation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050030
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  • 68
    Digitale Medien
    Digitale Medien
    Laser-Induced Thermotherapy (LITT) for Retreatment of Locally Advanced Recurrences of Breast Cancer (1999)
    Springer
    Lasers in medical science 14 (1999), S. 136-142 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Colour-coded duplex sonography; Laser induced thermotherapy; Minimal invasive therapy; Recurrent breast cancer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. The effect of laser-induced thermotherapy (LITT) as a palliative method for treatment of patients with local recurrence of breast cancer is investigated. This report describes the use of interstitial laser photocoagulation to manage such lesions. The interstitial laser applications were performed in seven women with locally recurrent breast carcinoma on the chest wall after mastectomy. All patients had been heavily pretreated with conventional modes of therapy (radiotherapy, chemotherapy, hormonal therapy, surgical resection). A Nd:YAG laser with a wavelength of 1064 nm was used to heat the lesions. Heat expansion was controlled digitally and monitored by ultrasonography and colour-coded duplex sonography (CCDS). In five women this minimally invasive method enabled the precise coagulation of the subcutaneous tumour without destruction of the skin or ulceration, although these areas had been pretreated by irradiation up to 60 Gy. In two patients with extensive multiple metastases and with skin infiltration, secondary skin ulceration and delayed healing was observed. For palliative reasons, LITT under CCDS guide can aid in local control of chest wall recurrence following mastectomy in selected patients.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050035
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  • 69
    Digitale Medien
    Digitale Medien
    Killing of the Yeast and Hyphal Forms of Candida albicans Using a Light-Activated Antimicrobial Agent (1999)
    Springer
    Lasers in medical science 14 (1999), S. 150-157 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords:Candida albicansCandidosis; Hyphae; Lethal photosensitisation; Toluidine blue O; Yeast
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract. Oral infections due to Candida albicans are a common occurrence in patients with acquired immunodeficiency syndrome (AIDS). The purpose of this investigation was to determine whether the yeast and hyphal forms of the organism could be killed using the light-activated antimicrobial agent toluidine blue O (TBO). Three variables were investigated: TBO concentration, laser light dose and pre-irradiation time (PIT). Irradiation with light from a helium neon (HeNe) gas laser used in conjunction with the photosensitiser TBO resulted in substantial kills of both the yeast and hyphal forms. Killing was light dose-dependent with 42 J being the most effective dose. The optimum PIT for the yeast form was 5 min, whereas killing of the hyphal form was not affected by PIT. The results of this study have shown that both forms of C. albicans are susceptible to lethal photosensitisation using TBO in conjunction with HeNe laser light, suggesting the possibility that this approach could be useful for eliminating the organism from diseased lesions in vivo.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050037
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  • 70
    Digitale Medien
    Digitale Medien
    Interstitial Laser Photocoagulation with Four Cylindrical Diffusing Fibre Tips: Importance of Mutual Fibre Distance (1999)
    Springer
    Lasers in medical science 14 (1999), S. 216-220 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Beamsplitter; Liver; Metastases; Nd:YAG; Tumour
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract . Simultaneous application of multiple fibres could increase the volume of coagulation produced with interstitial laser photocoagulation (ILP) for solid tumours. To take full advantage of the presumed synergistic thermal effect between the fibres, the optimal combination of laser power and distance between the fibres was investigated. Four fibres with a cylindrical diffusing tip of 2 cm length were used, coupled to an optical beamsplitter for Nd:YAG light (four channels, maximal variation 9.5%, transmission 〉85%). The distance between the fibres was 1, 1.5, 2, 2.5 , 3 or 4 cm with a power output of either 4, 5, 6 or 7 W/fibre; energy per fibre was constant at 1800 J by adjusting exposure time. After laser application, dimensions of the coagulated lesions were measured. The optimal mutual fibre distance was 2 cm ( p〈0.01) at all power levels. This resulted in lesions with a mean (SD) volume of 44.5 (2.1) cm3 and a largest diameter of 5.1 (0.4) cm at 7 W/fibre. Smaller distances between the fibres resulted in smaller lesions with central carbonisation, whereas larger distances resulted in four separate zones of coagulation. It was concluded that simultaneous application of four interstitial fibres may result in a considerable increase of volume of coagulation. Fibre position and mutual fibre distance determines whether synergism of the coagulative effect occurs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050087
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  • 71
    Digitale Medien
    Digitale Medien
    New Laser Literature (1999)
    Springer
    Lasers in medical science 14 (1999), S. 244-246 
    Details
    ISSN: 1435-604X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050091
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  • 72
    Digitale Medien
    Digitale Medien
    A Comparative Optical Analysis of Cylindrical Diffuser Fibres for Laser Therapy Using Fluorescence Imaging (1999)
    Springer
    Lasers in medical science 14 (1999), S. 257-268 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Diffuser; Emission profile; Fluorescence imaging; Interstitial laser photocoagulation; Photodynamic therapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract . Cylindrical light diffusers are commercially available for clinical applications such as photodynamic therapy (PDT) and interstitial laser photocoagulation (ILP). A fluorescence imaging technique has been used to quantify the light distribution produced by each of six different diffuser fibres. The light distribution produced by each device was found to depend on the distance the light propagated in the fluorescent dye solution. At a distance of 1 mm from the diffuser midline, the measured profiles were found to be consistent with published results obtained in air at a similar distance. The three devices intended for PDT utilised scattering particles and reflectors in their construction. The profiles produced by these applicators revealed peaks that were attributed to the reflectors located at their distal tips. By comparison, the two etched ILP fibres displayed either a strong modulation in the profile due to non-uniform etching or a predominant forward peak associated with the conical shape of the tip. We conclude that it is important to take into account the forward-directed light emitted by the diffusers when considering clinical applications using these devices.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050093
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  • 73
    Digitale Medien
    Digitale Medien
    Long Exposure Growth of In-Vivo Interstitial Laser Photocoagulation Lesions (1999)
    Springer
    Lasers in medical science 14 (1999), S. 297-306 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Bioheat transfer equation; ILP; In vivo; LITT; Photocoagulation; Rate kinetics; Temperature distribution; Thermal lesion size; Thermotherapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract . An investigation of the temperature response and growth of thermal lesions resulting from in vivo, interstitial laser photocoagulation at long exposures was conducted to assess extended lesion growth characteristics and test the applicability of first order unimolecular rate kinetics (Arrhenius theory) to thermal lesion growth. Irradiations were performed in vivo in rabbit muscle using a continuous 805 nm diode laser source operating at 1.0 W coupled to an optical fibre with a precharred tip (i.e. point heat source). Temperature responses were measured using a linear array of five microthermocouples. Each temperature–time profile was fitted to a solution of the Weinbaum–Jiji bioheat transfer equation (W–J BHTE). Lesions were resected 48 h post-irradiation and the necrosis boundaries were determined histologically. Numerical integration of the Arrhenius damage integral using temperature–time data at the lesion boundary produced corresponding pairs of activation energy and pre-exponential factor (E a, α) consistent with reported values for various other end-points and tissue types. Lesion radii were 6.0±0.6, 8.7±0.4 and 9.7±0.5 mm for 10, 20 and 30 min irradiations respectively. Thermal lesion growth predicted from Arrhenius theory was consistent with experimental results and is non-asymptotic by 30 min. Thermal parameters generally assumed to be constant when solving the W–J BHTE were found to vary with radial distance from the source, presumably due to a temperature dependence.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050097
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  • 74
    Digitale Medien
    Digitale Medien
    Automated generation and analysis of dynamic system designs (1998)
    Springer
    Research in engineering design 10 (1998), S. 15-29 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Automated generation ; Conceptual design ; Genetic algorithms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract This research uses Genetic Algorithms (GA) to suggest new dynamic systems based on topological remapping of system constituents. The bondgraph representation of the dynamic system behavior is evolved by the operators encapsulated in the genetic algorithms to meet the specified design criteria. The resultant evolved graph is assembled by designers with schemes to produce design variants. Behavioral transformation and structural transformation are adopted as strategies to generate design variants that extend beyond the scope of parametric design into innovative design. Behavioral transformation involves changes in the structure of the representation graphs, while maintaining the functions. Structural transformation involves changes in the components and the subsystems represented by the graph fragments. GAs are used to implement the operators of the transformation to search the problem-solution space because GAs are very robust search routines. Further, since the goal is to generate many solutions, genetic speciation is used to diverge the search so as to uncover other desirable solutions. The dynamic systems are modeled using bond graphs. Bond graphs provide a unified approach to the analysis, synthesis and evaluation of dynamic engineering systems. Though the scope of this investigation is limited to systems represented by bond graphs, the domain is wide enough to include many interesting applications like pump systems and vibration isolation systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01580267
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  • 75
    Digitale Medien
    Digitale Medien
    The Datum Flow Chain: A systematic approach to assembly design and modeling (1998)
    Springer
    Research in engineering design 10 (1998), S. 150-165 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Assembly ; Datum flow chain ; Fixtureless assembly ; Kinematic constraint ; Tolerances
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract Current CAD systems are ‘part-centric’ and do not capture the underlying logic of an assembly at an abstract level. We need to make CAD systems ‘assembly-centric’. To be able to lay out, analyze, outsource, assemble and debug complex assemblies, we need ways to capture their fundamental structure in a top-down design process, including the designer's strategy for constraining the parts kinematically and locating them accurately with respect to each other. We describe a concept called the ‘Datum Flow Chain’ to capture this logic. Most assembly problems occur due to ineffective datum logic or the choice of assembly procedures that are not consistent with the datum logic, if any, that was used to design the parts. The DFC relates the datum logic explicitly to the product's key characteristics, assembly sequences, and choice of mating features, and provides the information needed for tolerance analyses. Two types of assemblies are addressed: Type-1, where the assembly process puts parts together at their pre-fabricated mating features, and Type-2, where the assembly process can incorporate in-process adjustments to redistribute variation. Two types of assembly joints are defined: mates that pass dimensional constraint from part to part, and contacts that merely provide support. The scope of DFC in assembly planning is presented using several examples. Analysis tools to evaluate different DFCs and select the ones of interest are also presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01607157
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  • 76
    Digitale Medien
    Digitale Medien
    Product Evolution: A Reverse Engineering and Redesign Methodology (1998)
    Springer
    Research in engineering design 10 (1998), S. 226-243 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Key words: Redesign; Design methods; Reverse engineering
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract: New products drive business. To remain competitive, industry is continually searching for new methods to evolve their products. To address this need, we introduce a new reverse engineering and redesign methodology. We start by formulating the customer needs, followed by reverse engineering, creating a functional model through teardowns. The functional model leads to specifications that match the customer needs. Depending upon required redesign scope, new features are possibly conceived, or not. Next, models of the specifications are developed and optimized. The new product form is then built and further optimized using designed experiments. An electric wok redesign provides an illustration. The methodology has had a positive impact on results by using a systematic approach, both within design education and industrial applications.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001639870003
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  • 77
    Digitale Medien
    Digitale Medien
    Evaluation of Product and Process Design Robustness (1999)
    Springer
    Research in engineering design 11 (1999), S. 20-30 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Key words:Convex robustness – Monte Carlo simulation – Probabilistic design – Robust design methodology – Robust process optimization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract: Critical design decisions are commonly made throughout the product development process assuming known material and process behavior. However, stochastic variation during manufacture can inadvertently result in inferior or unacceptable product performance and reduced production yields. Stochastic simulations have been developed to estimate the end-use performance distribution prior to the commitment of hard tooling. This article proposes a definition for integrated product and process robustness, and extends existing stochastic methods to model the important role of the manufacturing flexibility in elimination of defects and product optimization. The goal is to enable the designer to understand and account for not only the negative effects of manufacturing variation, but also the positive impact of manufacturing flexibility wherein instantaneous corrections in the manufacturing process can frequently improve the product quality and eliminate flaws in the product design. Then, a methodology is introduced and contrasted with conventional development methods in the evaluation of best practices for development of a molded plastic component.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001630050002
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  • 78
    Digitale Medien
    Digitale Medien
    Design Support Using Distributed Web-Based AI Tools (1999)
    Springer
    Research in engineering design 11 (1999), S. 31-44 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Key words:AI as text – Design knowledge – Design support – Distributed design
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract: Currently, designers are faced with searching through a ‘sea’ of on-line knowledge to support their decision making activities. This paper describes WebCADET, which is a reimplementation of the stand-alone CADET – a Knowledge-Based System (KBS) for product design evaluation. WebCADET aims to provide effective and efficient support for designers during their searches for design knowledge. WebCADET uses the ‘AI as text’ approach, where KBSs can be seen as a medium to facilitate the communication of design knowledge between designers. The development of WebCADET to include practical support via World Wide Web-based functionality, which illustrates the potential of the ‘AI as text’ approach, is described in the paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001630050003
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  • 79
    Digitale Medien
    Digitale Medien
    A Theory of Complexity, Periodicity and the Design Axioms (1999)
    Springer
    Research in engineering design 11 (1999), S. 116-132 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Key words:Axiomatic design – Complexity – Design axioms – Periodicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract: One of the topics that has received the attention of mathematicians, scientists and engineers is the notion of complexity. The subject is still being debated, as it lacks a common definition of complexity, concrete theories that can predict complex phenomena, and the mathematical tools that can deal with problems involving complexity. In axiomatic design, complexity is defined only when specific functional requirements or the exact nature of the query are defined. Complexity is defined as a measure of uncertainty in achieving a set of specific functions or functional requirements. Complexity is related to information, which is defined in terms of the probability of success of achieving the Functional Requirements (FRs). There are two classes of complexity: time-dependent complexity and time-independent complexity. There are two orthogonal components of time-independent complexity, i.e., real complexity and imaginary complexity. The vector sum is called absolute complexity. Real complexity of coupled design is larger than that of uncoupled or decoupled designs. Imaginary complexity can be reduced when the design matrix is known. As an example of time-independent imaginary complexity, the design of a printing machine based on xerography is discussed. There are two kinds of time-dependent real complexity: time-dependent combinatorial complexity and time-dependent periodic complexity. Using a robot-scheduling problem as an example, it is shown that a coupled design with a combinatorial complexity can be reduced to a decoupled design with periodic complexity. The introduction of periodicity simplifies the design by making it deterministic, which requires much less information. Whenever a combinatorial complexity is converted to a periodic complexity, complexity and uncertainty is reduced and design simplified.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00003883
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  • 80
    Digitale Medien
    Digitale Medien
    Influences on Solution Search Processes in Design Organisations (1999)
    Springer
    Research in engineering design 11 (1999), S. 158-171 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Key words:Closure – Fixation – Organisation – Search
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract: A study was conducted of what influenced solution search activity in three design organisations. The influences were analysed in terms of how they affected search, whether their effect tended to be conservative or innovative, and the directness of the evidence they provided. Overall, the environment was found to provide more innovative influences than conservative ones. Innovative influences were mostly connected with the triggering of search activity, while conservative influences were mostly linked with restricting the search space of potential solutions. Also, search candidates were often evaluated in terms of their associations rather than their intrinsic merits, and ultimately this makes human judgment an essential component of search and evaluation activity. Finally, the environment provides many ‘seeds’ for effects like design fixation and functional fixedness but also provides strong incentives to positively avoid these effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001630050012
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  • 81
    Digitale Medien
    Digitale Medien
    A Mathematical Framework for the Key Characteristic Process (1999)
    Springer
    Research in engineering design 11 (1999), S. 145-157 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Key words:Key characteristics, Process verification, Quality monitoring – Variation modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract: To maximize product quality, a product design team selects concepts and dimensions to minimize a product’s sensitivity to variation. However, even for the most robust products, it is rarely possible to transition a product into production without encountering any variation-related problems. In a complex product, it is not economically or logistically feasible to control and/or monitor the thousands of tolerances specified in a product’s drawing set. To address this problem, many organizations are using Key Characteristic (KCs) methods to identify where excess variation will most significantly affect product quality, and what product features and tolerances require special attention from manufacturing. As simple as this principle seems, most companies struggle to effectively implement KC methods because no quantitative methods to prioritize KCs exist. This paper develops a mathematical definition of a KC based on a variation propagation model. In addition, it develops a quantitative effectiveness measure used to prioritize where verification, variation reduction, and on-going monitoring should be applied. The effectiveness measure incorporates the cost of control, the benefit of control, and the expected change in process capability. The methods are illustrated using an automotive door assembly.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001630050011
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  • 82
    Digitale Medien
    Digitale Medien
    Kinematic synthesis with configuration spaces (1995)
    Springer
    Research in engineering design 7 (1995), S. 193-213 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Conceptual design ; Configuration ; Constraint programming ; Spaces & Qualitative physics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract This paper introduces a new approach to the conceptual design of mechanical systems from qualitative specifications of behavior. The power of the approach stems from the integration of techniques in qualitative physics and constraint programming. We illustrate the approach with an effective kinematic synthesis method that reasons with qualitative representations of configuration spaces using constraint programming.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01638099
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  • 83
    Digitale Medien
    Digitale Medien
    A study of mechanical configuration optimisation in micro-systems (1997)
    Springer
    Research in engineering design 9 (1997), S. 46-60 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Configuration ; Macro ; Micro ; Scale
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract This paper shows that there are three main categories of factors that make the optimum mechanical design of micro-systems different from macro-systems: scale effects, a limited range of materials, and a limited range of production processes. The combined effect of these factors can make the optimum configuration of a micro-system potentially very different from that of the same system on a macro-scale. In particular, the use of flexible elements for hinges is much more feasible and desirable on a micro-scale.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01607057
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  • 84
    Digitale Medien
    Digitale Medien
    Reliability centered prediction technique for diagnostic modeling and improvement (1997)
    Springer
    Research in engineering design 9 (1997), S. 35-45 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Dependability ; Diagnosability ; Maintainability ; Reliability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract A diagnosability prediction metric is developed for system modeling of component failure rates and unjustified removals. The metric emphasizes ambiguity of system component indications as well as system structure. The metric is evaluated using historical data from the bleed air control system (BACS) on the Boeing737-300. Four design changes are suggested based on improving system diagnosability by changing component functions, modifying indications, and adding or changing sensors. The resulting designs are compared via Boeing's life cycle cost mechanism, DEPCOST model, based on cost improvements. It is shown that system improvements based on this prediction technique will increase the quality of a product since increased diagnosability decreases life cycle costs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01607056
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  • 85
    Digitale Medien
    Digitale Medien
    A conceptual framework for combining artificial intelligence and optimization in engineering design (1997)
    Springer
    Research in engineering design 9 (1997), S. 20-34 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Artificial intelligence ; Design ; Operations Research ; Optimization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract Research in artificial intelligence and optimization (OR) has had significant impact on the formulation and solution of computational methods in engineering design. This paper presents a conceptual framework for understanding a more powerful technology that is evolving from a combination of these approaches. The paper first proposes generalized representations of engineering design models that involve quantitative and qualitative aspects. Second, it presents a general classification of AI and OR models in terms of model attributes, in order to establish mappings with generic solution techniques. Third, the requirements of solution methods are discussed, as well as several schemes for the integration of AI and optimization to identify future research directions. Several specific approaches are included to illustrate various ways in which AI and optimization can be combined for tackling computational design models.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01607055
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  • 86
    Digitale Medien
    Digitale Medien
    Teamwork and design methodology—Observations about teamwork in design education (1997)
    Springer
    Research in engineering design 9 (1997), S. 61-69 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Design education ; Mechanical engineering ; Methodical design ; Teamwork
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Der vorliegende Beitrag beschäftigt sich mit der Frage, wie man Studenten schon in der Ausbildung die Fähigkeiten zur Zusammenarbeit in Konstruktions-Teams beibringen kann, um sie auf die Praxis vorzubereiten. Anhand eines Projekts, in dem Studenten im Team ein Gerät konstruierten und herstellten, werden Vor- und Nachteile der Teamarbeit beim Konstruieren beobachtet. Die Nachteile, die diskutiert werden, enstehen vor allem durch Probleme der Kommunikation zwischen den Teammitgliedern. Ein Vorschlag für die Ausbildung von Studenten beim methodischen Konstruieren im Team wird vorgestellt und die Erfahrungen bei der Umsetzung werden dargestellt. Anregungen für die Konstruktionsausbildung, die aus dem dargestellten Projekt enstanden, sowie Ansätze für die Forschung schließen den Beitrag ab.
    Notizen: Abstract This paper focuses on the topic how students can learn to cooperate in design teams, to be prepared for industrial practice. Advantages and disadvantages of teamwork in design are observed in a project. In this project students designed and manufactured a device in teams. Most of the disadvantages which are discussed, occur because of problems of communication between the team members. An approach for the education in systematic design and the experiences in using this approach are presented. The paper concludes with suggestions for design education and for research.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01596482
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  • 87
    Digitale Medien
    Digitale Medien
    Managing the integrity of design data generated by multiple applications: The principle of patching (1997)
    Springer
    Research in engineering design 9 (1997), S. 125-145 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Change management ; Concurrent engineering ; Design ; Engineering databases ; Integrity management
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract The purpose of this work is to develop automatic methods of semantic integrity maintenance, in support of concurrent engineering. Semantic integrity relations in any final engineering design are built up incrementally, through the use of different computer applications. Here, the structure of these integrity relations are formalised for representation within a database. When changes to a design have to be made, they can invalidate integrity relations in other parts of the design. Formal methods are defined for identifying what data and integrity relations are invalidated by any change. Methods for making changes that minimise re-design are described and formalised. Opportunities for using semantic integrity to assess progress on a design are reviewed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01596599
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  • 88
    Digitale Medien
    Digitale Medien
    GGREADA: A graph grammar-based machine design algorithm (1997)
    Springer
    Research in engineering design 9 (1997), S. 195-213 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Configuration design ; Generative design ; Grammar-based design ; Machine design
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract A class of graph grammar-based design algorithms for the generation of near-optimal machine designs is proposed. The GGREADA algorithm is implemented to design scale model carts from Meccano® Set components. A graph grammar for the carts is defined. GGREADA successfully designs minimum-weight carts that provide specified load-bed areas. GGREADA's exploration capability is also demonstrated by creating probability frequency plots of likely cart surface areas and weights from random samples taken from the space of all possible cart designs. The advantages that a designer may gain from grammar-based design tools are discussed along with the representational challenges that remain in exploiting grammars for this purpose.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01589682
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  • 89
    Digitale Medien
    Digitale Medien
    What to do next: Using problem status to determine the course of action (1997)
    Springer
    Research in engineering design 9 (1997), S. 214-227 
    Details
    ISSN: 1435-6066
    Schlagwort(e): Bayesian decision model ; Decision sensitivity analysis ; Team decision making
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Technik allgemein
    Notizen: Abstract Formal decision support tools are little used in engineering design. This paper explores the reasons for this and presents a method which is tailored to problems characterized by teams of stakeholders with inconsistent views who generate multiple alternatives and criteria, and who work to reach consensus. This method is especially designed to support activity when much of the information is qualitative, immature, and there is a diversity of views. The methodology assists the team in determining which alternative attributes to invest time in refining in their effort to reach consensus. The underlying mathematical structure (a Bayesian model of multi-attribute team decision making) is presented. This model supports team member belief about an alternative's ability to meet a criteria on two dimensions, knowledge and confidence. The methodology forces recording the rationale used to reach the final decision. A running example is used to explain the details.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01589683
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  • 90
    Digitale Medien
    Digitale Medien
    Linear-quadratic tracking of coupled slow and fast targets (1997)
    Springer
    Mathematics of control, signals, and systems 10 (1997), S. 1-30 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Linear-quadratic tracking ; Singular perturbations ; Limit design ; Near-optimal control ; Averaging ; Infinite horizon
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract The paper examines a singular perturbation model of tracking two targets, one slow and a fast one which is assumed periodic. The plant is linear and the cost is quadratic. A limit problem is displayed. It corresponds to the limit behavior of the perturbed system when the small parameter tends to zero. This limit is not of reduced order, as the fast target is periodic. Rather, an infinite-horizon optimal averaging is performed on the fast scale, and serves as an input to slow-scale optimization. This limit design is used to approximate the optimal solution of the singularly perturbed system. Bounds for the rates of the approximation are given. The optimal limit design is computed in a feedback form in the general case, and for illustrative concrete examples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01219773
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  • 91
    Digitale Medien
    Digitale Medien
    Homogeneous behaviors (1997)
    Springer
    Mathematics of control, signals, and systems 10 (1997), S. 61-75 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Linear behavior ; Compactification of systems ; Shift spaces ; Grothendieck quotient scheme
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract Recently a smooth compactification of the space of linear systems withn states,m inputs, andp outputs has been discovered. In this paper we obtain a concrete interpretation of this compactification as a space of discrete-time behaviors. We use both homogeneous polynomial representations and generalized firstorder representations, and provide a realization theory to link these to each other.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01219776
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  • 92
    Digitale Medien
    Digitale Medien
    Limits of generalized state space systems under proportional and derivative feedback (1997)
    Springer
    Mathematics of control, signals, and systems 10 (1997), S. 97-124 
    Details
    ISSN: 1435-568X
    Schlagwort(e): High-gain feedback ; Singular systems ; Proportional and derivative feedback ; Feedback invariants ; Orbit closures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract In this paper we study the high-gain feedback classification problem for generalized state space systems. We solve this problem for proportional and derivative feedback transformations of regularizable systems, i.e., we give necessary and sufficient conditions for a regularizable system to be a limit of a given system under high-gain proportional and derivative feedback. We also derive a new complete set of invariants for proportional feedback equivalence and specify a set of necessary conditions for a system to be the limit of another system under these feedback transformations. The necessary conditions are sufficient for arbitrary state space systems and for controllable singular systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01213382
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  • 93
    Digitale Medien
    Digitale Medien
    Interpolation with multiple norm constraints (1997)
    Springer
    Mathematics of control, signals, and systems 10 (1997), S. 165-187 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Interpolation theory ; ℋ2/ℋ∞ control ; Multiobjective optimization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract This paper considers the problem of finding matrix-valued rational functions that satisfy two-sided residue interpolation conditions subject to norm constraints on their components. It is shown that this problem can be reduced to a finite-dimensional convex optimization problem. As an application, we show that under suitable assumptions on the plant, multiple objective ℋ2 and ℋ∞ control problems admit finite-dimensional optimal solutions and that such solutions can be computed using finite-dimensional convex programs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01213384
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  • 94
    Digitale Medien
    Digitale Medien
    Stability radii of infinite-dimensional positive systems (1997)
    Springer
    Mathematics of control, signals, and systems 10 (1997), S. 223-236 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Infinite-dimensional systems ; Discrete-time systems ; Robust stability ; Stability radii ; Banach lattices ; Positive systems ; Positive operators
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract We show that for infinite-dimensional discrete-time positive systems the complex and real stability radii coincide. Furthermore, we provide a simple formula for the complex stability radius of positive systems by the associated transfer function. We illustrate our results with an example dealing with a simple type of differential-difference equations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01211504
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  • 95
    Digitale Medien
    Digitale Medien
    New Algorithms for Polynomial J-Spectral Factorization (1999)
    Springer
    Mathematics of control, signals, and systems 12 (1999), S. 24-61 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Key words. Polynomial J-spectral factorization, Two-variable polynomial matrix, Quadratic differential form, Dissipativity, Pick matrix.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract. In this paper new algorithms are developed for J-spectral factorization of polynomial matrices. These algorithms are based on the calculus of two-variable polynomial matrices and associated quadratic differential forms, and share the common feature that the problem is lifted from the original one-variable polynomial context to a two-variable polynomial context. The problem of polynomial J-spectral factorization is thus reduced to a problem of factoring a constant matrix obtained from the coefficient matrices of the polynomial matrix to be factored. In the second part of the paper, we specifically address the problem of computing polynomial J-spectral factors in the context of H ∞ control. For this, we propose an algorithm that uses the notion of a Pick matrix associated with a given two-variable polynomial matrix.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009844
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  • 96
    Digitale Medien
    Digitale Medien
    The Realization Problem for Hidden Markov Models (1999)
    Springer
    Mathematics of control, signals, and systems 12 (1999), S. 80-120 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Key words. Hidden Markov models, Realization, Finite-state Markov process.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract. If {X t} is a finite-state Markov process, and {Y t} is a finite-valued output process with Y t+1 depending (possibly probabilistically) on X t, then the process pair is said to constitute a hidden Markov model. This paper considers the realization question: given the probabilities of all finite-length output strings, under what circumstances and how can one construct a finite-state Markov process and a state-to-output mapping which generates an output process whose finite-length strings have the given probabilities? After reviewing known results dealing with this problem involving Hankel matrices and polyhedral cones, we develop new theory on the existence and construction of the cones in question, which effectively provides a solution to the realization problem. This theory is an extension of recent theoretical developments on the positive realization problem of linear system theory.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009846
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  • 97
    Digitale Medien
    Digitale Medien
    A Global Asymptotic Stability Result for a Class of Totally Asynchronous Discrete Nonlinear Systems (1999)
    Springer
    Mathematics of control, signals, and systems 12 (1999), S. 143-166 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Key words. Asynchronous systems, Total asynchronism, Regular desynchronization, Global stability, Nonlinear discrete-time systems, Hopfield neural nets.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract. This paper proves a global stability result for a class of nonlinear discrete-time systems that are subject to regular desynchronization, also known as total asynchronism. The class of systems studied has its origins in a discrete-time neural net model. The techniques used are of interest in terms of the use of a Lyapunov function for the study of convergence of asynchronous nonlinear dynamical systems and also in terms of applications to neural networks. In the latter context, the main result of this paper strengthens a result of an earlier paper on neural networks, and shows that a class of discrete-time continuous-valued neural nets of the Hopfield type displays global convergence properties even when there exists total asynchronism in the updating of neuron states.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009848
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Linear Quadratic Optimal Control of Time-Varying Systems with Indefinite Costs on Hilbert Spaces (1999)
    Springer
    Mathematics of control, signals, and systems 12 (1999), S. 196-218 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Key words. Infinite-dimensional system, Time-varying system, Mild evolution operator, Riccati equation, Optimal control problem.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract. In this paper we consider time-varying linear systems on Hilbert spaces and study the linear quadratic optimal control problem with an indefinite performance criterion over an infinite time interval. An example shows that in contrast to the finite-dimensional situation, in general, the solvability of the optimal control problem does not imply the solvability of the associated integral Riccati equation. Using an operator theoretic approach towards the time-varying integral Riccati equation, we derive equivalent conditions for the solvability of both problems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009850
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Nonsmooth Robust Stabilization of a Class of Two-Dimensional Nonlinear Systems (1999)
    Springer
    Mathematics of control, signals, and systems 12 (1999), S. 245-269 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Key words. Families of nonlinear systems, Robust stabilization, Nonsmooth state feedback.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract. In this paper we consider a class of parameterized families of nonlinear systems which cannot be robustly asymptotically stabilized by means of C 1 feedback. We construct C 0 state feedback laws which are smooth away from the origin and which robustly asymptotically stabilize these families of systems. We then show that, in some cases, the regularity of the obtained robust asymptotic stabilizers is “maximum” in the sense that the considered families of systems do not admit any Lipschitz continuous robust asymptotic stabilizer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009852
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Orthonormal Basis Functions for Continuous-Time Systems and Lp Convergence (1999)
    Springer
    Mathematics of control, signals, and systems 12 (1999), S. 295-305 
    Details
    ISSN: 1435-568X
    Schlagwort(e): Key words. Orthonormal basis functions, Continuous-time, Fourier series, Lp convergence.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik , Technik allgemein
    Notizen: Abstract. In this paper, model sets for linear-time-invariant continuous-time systems that are spanned by fixed pole orthonormal bases are investigated. These bases generalize the well-known Laguerre and two-parameter Kautz cases. It is shown that the obtained model sets are everywhere dense in the Hardy space H 1(Π) under the same condition as previously derived by the authors for the denseness in the (Π is the open right half plane) Hardy spaces H p(Π), 1〈p〈∞. As a further extension, the paper shows how orthonormal model sets, that are everywhere dense in H p(Π), 1≤p〈∞, and which have a prescribed asymptotic order, may be constructed. Finally, it is established that the Fourier series formed by orthonormal basis functions converge in all spaces H p(Π) and (D is the open unit disk) H p(D), 1〈p〈∞. The results in this paper have application in system identification, model reduction, and control system synthesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009854
    Standort Signatur Erwartet Verfügbarkeit
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