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  • Artikel  (3.093)
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  • 101
    Digitale Medien
    Digitale Medien
    A method for following the unstable path between two saddle-node bifurcation points in nonlinear dynamic system (1999)
    Springer
    Applied mathematics and mechanics 20 (1999), S. 1384-1388 
    Details
    ISSN: 1573-2754
    Schlagwort(e): nonlinear dynamic system ; bifurcation ; stability ; TB123 ; O322
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract A computation algorithm based on the Poincaré Mapping in combination with Pseudo-Arc Length Continuation Method is presented for calculating the unstable response with saddle-node bifurcation, and the singularity, which occurs using the general continuation method combined with Poincaré Mapping to follow the path, is also proved. A normalization equation can be introduced to avoid the singularity in the process of iteration, and a new iteration algorithm will be presented too. There will be two directions in which the path can be continued at each point, but only one can be used. The method of determining the direction will be presented in the paper. It can be concluded that is method is effective in analysis of nonlinear dynamic system with saddle-node bifurcations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02459172
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  • 102
    Digitale Medien
    Digitale Medien
    Some dynamical properties of a viscoelastic cylindrical shell (1999)
    Springer
    Applied mathematics and mechanics 20 (1999), S. 233-240 
    Details
    ISSN: 1573-2754
    Schlagwort(e): viscoelasticity ; cylindrical shell ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract In this paper, the dynamic stability of a viscoelastic circular cylindrical shell subject to an axial compressive force and a uniformly distributed radial compressive load is discussed. By using the Laplace transformation, stability conditions of viscoelastic shell under constant loads are yielded. By using synthetically the classical dynamic methods, the various dynamical properties for the dynamical system defined by the viscoelastic shell and the effect of parameters on the stability of structure are obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02463847
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  • 103
    Digitale Medien
    Digitale Medien
    Convergence of Delayed Dynamical Systems (1999)
    Springer
    Neural processing letters 10 (1999), S. 267-271 
    Details
    ISSN: 1573-773X
    Schlagwort(e): recurrent neural networks ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper, we point out that the conditions given in [1] are sufficient but unnecessary for the global asymptotically stable equilibrium of a class of delay differential equations. Instead, we prove that under weaker conditions, it is still global asymptotically stable.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018753013035
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  • 104
    Digitale Medien
    Digitale Medien
    Stable and Real-Time Scheduling of a Class of Hybrid Dynamic Systems (1999)
    Springer
    Discrete event dynamic systems 9 (1999), S. 45-64 
    Details
    ISSN: 1573-7594
    Schlagwort(e): hybrid dynamic systems ; event feedback ; real-time scheduling ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Based on some practical engineering problems arising from process control and space-structure control, this paper studies a class of hybrid dynamic systems in which N plants are controlled by a central controller in sharing time manner, where the plants are described by differential equations and the controller works according to the mechanism of discrete events. An event feedback strategy is suggested to be a scheduling policy such that one and only one plant among N plants is chosen to be controlled at any time. Some conditions of asymptotical and exponential stability are then given and an exponential upper bound of states norm is also estimated for the event feedback scheduling strategy. An algorithm based on event feedback strategy is presented to determine the control laws of the plants to meet the given performance. An example follows to illustrate the application and effect of the results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008320614629
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  • 105
    Digitale Medien
    Digitale Medien
    Explicit second-order accurate schemes for the nonlinear Schrödinger equations (1999)
    Springer
    Lithuanian mathematical journal 39 (1999), S. 20-32 
    Details
    ISSN: 1573-8825
    Schlagwort(e): Schrödinger equation ; explicit finite-difference schemes ; stability ; energy conservation ; convergence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We consider three-level explicit schemes for solving the nonlinear variable coefficient Schrödinger-type equation. Using spectral and energy methods we establish the stability and convergence of these schemes. The existence of discrete conservation laws is investigated. General results are applied for the DuFort-Frankel and leap-frog diffenrence schemes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02465532
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  • 106
    Digitale Medien
    Digitale Medien
    Role of the Minimal State Variable Criterion in Rational Expectations Models (1999)
    Springer
    International tax and public finance 6 (1999), S. 621-639 
    Details
    ISSN: 1573-6970
    Schlagwort(e): expectations ; bubbles ; uniqueness ; stability ; state variables ; multiplicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract This paper concerns the minimal-state-variable (MSV) criterion for selection among solutions in rational expectationsmodels that feature a multiplicity of paths that satisfy all of the model's conditions. It compares the MSVcriterion with others, including the widely used saddle-path (dynamic stability) criterion. It is emphasized that theMSV criterion can be viewed as a scientifically useful classification scheme that delineates the unique solutionthat is free of bubble components. In the process of demonstrating uniqueness for a broad class of linear models,the paper exposits a convenient computational procedure. Applications to current issues are outlined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008746610773
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  • 107
    Digitale Medien
    Digitale Medien
    Numerical modeling of nonlinear deformation and buckling of composite plate-shell structures under pulsed loading (1999)
    Springer
    Mechanics of composite materials 35 (1999), S. 495-506 
    Details
    ISSN: 1573-8922
    Schlagwort(e): layered structure ; shells ; frames ; stringers ; nonlinearity ; stability ; pulsed loading ; numerical methods
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Nonlinear three-dimensional problems of dynamic deformation, buckling, and posteritical behavior of composite shell structures under pulsed loads are analyzed. The structure is assumed to be made of rigidly joined plates and shells of revolution along the lines coinciding with the coordinate directions of the joined elements. Individual structural elements can be made of both composite and conventional isotropic materials. The kinematic model of deformation of the structural elements is based on Timoshenko-type hypotheses. This approach is oriented to the calculation of nonstationary deformation processes in composite structures under small deformations but large displacements and rotation angles, and is implemented in the context of a simplified version of the geometrically nonlinear theory of shells. The physical relations in the composite structural elements are based on the theory of effective moduli for individual layers or for the package as a whole, whereas in the metallic elements this is done in the framework of the theory of plastic flow. The equations of motion of a composite shell structure are derived based on the principle of virtual displacements with some additional conditions allowing for the joint operation of structural elements. To solve the initial boundary-value problem formulated, an efficient numerical method is developed based on the finite-difference discretization of variational equations of motion in space variables and an explicit second-order time-integration scheme. The permissible time-integration step is determined using Neumann's spectral criterion. The above method is especially efficient in calculating thin-walled shells, as well as in the case of local loads acting on the structural element, when the discretization grid has to be condensed in the zones of rapidly changing solutions in space variables. The results of analyzing the nonstationary deformation processes and critical loads are presented for composite and isotropic cylindrical shells reinforced with a set of discrete ribs in the case of pulsed axial compression and external pressure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02259471
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  • 108
    Digitale Medien
    Digitale Medien
    On Invariant Manifolds in Singularly Perturbed Systems (1999)
    Springer
    Journal of dynamical and control systems 5 (1999), S. 501-507 
    Details
    ISSN: 1573-8698
    Schlagwort(e): Singular perturbation ; invariant manifold ; overflowing manifold ; stability ; characteristic numbers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract A singularly perturbed system with a small parameter ε at the velocity of the slow variable y and with the fast variable x is considered. The main hypothesis is that for all y from some bounded domain D, the fast subsystem has a stable invariant or overflowing manifold M 0(y) and that the motions in this system going in the directions transversal to M 0(y) are more fast than the mutual approaching of trajectories on M 0(y) (a precise statement is given in terms of appropriate Lyapunov-type characteristic numbers). It is proved that for a sufficiently small ε, the whole system has an invariant manifold close to $$\bigcup\limits_{y \in D} {M_0 (y) \times \{ y\}}$$ the degree of its smoothness is specifed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021739205527
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  • 109
    Digitale Medien
    Digitale Medien
    Preparation and Characterization of Carmustine Loaded Polyanhydride Wafers for Treating Brain Tumors (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 762-765 
    Details
    ISSN: 1573-904X
    Schlagwort(e): polymer implant ; brain cancer ; carmustine ; polyanhydride ; stability ; controlled release
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1011995728760
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  • 110
    Digitale Medien
    Digitale Medien
    Formulation and Lyoprotection of Poly(Lactic Acid-Co-Ethylene Oxide) Nanoparticles: Influence on Physical Stability and In Vitro Cell Uptake (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 859-866 
    Details
    ISSN: 1573-904X
    Schlagwort(e): nanoparticles ; poly(lactic acid) ; poly(lactic acid-co-ethylene oxide) ; freeze-drying ; stability ; flow cytometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. To investigate the feasibility of producing freeze-dried poly-(ethylene oxide) (PEO)-surface modified nanoparticles and to study their ability to avoid the mononuclear phagocytic system (MPS), as a function of the PEO chain length and surface density. Methods. The nanoparticles were produced by the salting-out method using blends of poly(D,L-lactic acid) (PLA) and poly(D,L-lactic acid-co-ethylene oxide) (PLA-PEO) copolymers. The nanoparticles were purified by cross-flow filtration and freeze-dried as such or with variable amounts of trehalose as a lyoprotectant. The redispersibility of the particles was determined immediately after freeze-drying and after 12 months of storage at −25° C. The uptake of the nanoparticles by human monocytes was studied in vitro by flow cytometry. Results. PLA-PEO nanoparticles could be produced from all the polymeric blends used. Particle aggregation after freeze-drying was shown to be directly related to the presence of PEO. Whereas this problem could be circumvented by use of trehalose, subsequent aggregation was shown to occur during storage. These phenomena were possibly related to the specific thermal behaviours of PEO and trehalose. In cell studies, a clear relationship between the PEO content and the decrease of uptake was demonstrated. Conclusions. The rational design of freeze-dried PEO-surface modified nanoparticles with potential MPS avoidance ability is feasible by using the polymer blends approach combined with appropriate lyoprotection and optimal storage conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018826103261
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  • 111
    Digitale Medien
    Digitale Medien
    Isolation, Characterization, and Stability of Positional Isomers of Mono-PEGylated Salmon Calcitonins (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 813-818 
    Details
    ISSN: 1573-904X
    Schlagwort(e): calcitonin ; polyethylene glycol ; PEGylation ; peptide ; tryptic digestion ; stability ; HPLC
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. To separate and characterize the different positional isomers of mono-PEGylated salmon calcitonins (mono-PEG-sCTs) and to evaluate the effects of the PEGylation site on the stability of different mono-PEG-sCTs in rat kidney homogenate. Methods. Mono-PEG-sCTs were prepared using succinimidyl carbonate monomethoxy polyethylene glycol (5,000 Da) and separated by gel-filtration HPLC followed by reversed-phase HPLC. To characterize PEGylated sCTs, matrix-assisted laser desorption ionization time of flight mass spectrometry (M ALDI-TOF MS) and reversed-phase HPLC of the trypsin digested samples were performed. Mono-PEG-sCTs and sCT in rat kidney homogenates were measured by column-switching reversed-phase HPLC with on-line detection of the radioiodinated samples using a flow-through radioisotope detector. Results. Three different mono-PEGylated sCTs were separated by reversed-phase gradient HPLC. From the MALDI-TOF MS analysis, the average molecular weight of mono-PEG-sCTs was confirmed as around 8650 Da. The presence of PEG moiety in the mono-PEG-sCTs was also manifested by the fact that the distance between two adjacent mass spectum lines was 44 Da which corresponds to PEG monomer unit. Tryptic digestion analysis demonstrated that these mono-PEG-sCTs are 3 positional isomers of N-terminus, Lys18- and Lys11-residue modified mono-PEGylated sCTs. The degradation half-life of these 3 positional isomers in rat kidney homogenates significantly increased in order of the N-terminus (125.5 min), Lys11- (157.3 min), and Lysl8-residue modified mono-PEGylated sCT (281.5 min) over the native sCT (4.8 min). Conclusions. Three positional isomers of mono-PEGylated sCTs were purified and characterized. Of these, the resistance to proteolytic degradation was highest for the Lysl8-residue modified mono-PEG-sCT. These studies demonstrate that the in vivo stability of PEGylated sCTs is highly dependent on the site of PEG molecule attachment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018861616465
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  • 112
    Digitale Medien
    Digitale Medien
    Phase and aggregation behaviour of double-chain cationic surfactants from the class of N-alkyl-N-alkyl′-N, N-dimethylammonium bromide surfactants (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 856-867 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Key words Double chain surfactants ; Aggregates ; Phase diagrams ; Lamellar phases ; Electron microscopy ; SANS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C x C y DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies: unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical Lα phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were carried out.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003960050462
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  • 113
    Digitale Medien
    Digitale Medien
    On the Stability of a Laminar Wall Jet with Heat Transfer (1999)
    Springer
    Flow, turbulence and combustion 62 (1999), S. 137-162 
    Details
    ISSN: 1573-1987
    Schlagwort(e): laminar wall jet ; heat transfer ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The hydrodynamic stability of a low speed, plane, non-isothermal laminar wall jet at a constant temperature boundary condition was investigated theoretically and experimentally. The mean velocity and temperature profiles used in the stability analysis were obtained by implementing the Illingworth–Stewartson transformation that allows one to extend the classical Glauert solution to a thermally non-uniform flow. The stability calculations showed that the two unstable eigenmodes coexisting at moderate Reynolds numbers are significantly affected by the heat transfer. Heating is destabilizing the flow while cooling is stabilizing it. However, the large-scale instabilities associated with the inflection point of the velocity profile still amplify in spite of the high level of the stabilizing temperature difference. The calculated stability characteristics of the wall jet with heat transfer were compared with experimental data. The comparison showed excellent agreement for small amplitudes of the imposed perturbations. The agreement is less good for the phase velocities of the sub-harmonic wave and this is attributed to experimental difficulties and to nonlinear effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009965531203
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  • 114
    Digitale Medien
    Digitale Medien
    Orbital Migration Of Giant Planets: Using Numerical Integration To Investigate Consequences For Other Bodies (1999)
    Springer
    Earth, moon and planets 87 (1999), S. 103-115 
    Details
    ISSN: 1573-0794
    Schlagwort(e): Accretion ; exoplanetary system ; extrasolar planets ; numerical integration ; orbital migration ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract A number of extrasolar planets have been detected in close orbits around nearby stars. It is probable that these planets did not form in these orbits but migrated from their formation locations beyond the ice line. Orbital migration mechanisms involving angular momentum transfer through tidal interactions between the planets and circumstellar gas-dust disks or by gravitational interaction with a residual planetesimal disk together with several means of halting inward migration have been identified. These offer plausible schemes to explain the orbits of observed extrasolar giant planets and giant planets within the Solar System. Recent advances in numerical integration methods and in the power of computer workstations have allowed these techniques to be applied to modelling directly the mechanisms and consequences of orbital migration in the Solar System. There is now potential for these techniques also to be applied to modelling the consequences of the orbital migration of planets in the observed exoplanetary systems. In particular the detailed investigation of the stability of terrestrial planets in the habitable zone of these systems and the formation of terrestrial planets after the dissipation of the gas disk is now possible. The stability of terrestrial planets in the habitable zone of selected exoplanetary systems has been established and the possibility of the accretion of terrestrial planets in these systems is being investigated by the author in collaboration with Barrie W. Jones (Open University), and with John Chambers (NASA-Ames) and Mark Bailey of Armagh Observatory, using numerical integration. The direct simulation of orbital migration by planetesimal scattering must probably await faster hardware and/or more efficient algorithms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1017996927696
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  • 115
    Digitale Medien
    Digitale Medien
    Robust Stability of Multivariate Polynomials. Part 1: Small Coefficient Perturbations (1999)
    Springer
    Multidimensional systems and signal processing 10 (1999), S. 7-20 
    Details
    ISSN: 1573-0824
    Schlagwort(e): multivariate polynomials ; stability ; robust stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract This paper presents a detailed analysis of some classes of stable multivariate polynomials. The main aim of the analysis is to give conditions under which polynomials preserve stability when they are subjected to small coefficient variations. The maximal class of such polynomials is introduced. Some basic properties of polynomials from this class are obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008456918178
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  • 116
    Digitale Medien
    Digitale Medien
    Synthesis of colloids and films of Pr, Er and Yb with nonaqueous solvents (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 164-173 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Keywords Nanostructures ; Thin films ; Vapor deposition ; Electron microscopy ; Optical properties
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Colloidal dispersions of Yb, Er and Pr have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with 2-methoxyethanol and ethanol to produce solvated metal atoms. The particle size of the dispersions was determined by transmission electron microscopy to range from 52 to 1080 Å; the particles had spherical shapes. After solvent evaporation under vacuum, active solids and amorphous powder were deposited over Cu and Al metal. Dispersion stability, particle size, UV/Vis absorption and zeta potential were studied. The solids prepared by solvent evaporation were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The films prepared on Al were studied by scanning electron microscopy. The most stable colloid was obtained using 2-methoxyethanol: several concentrations were stable for several months and the zeta potential indicated that this colloid stability is mainly due to solvation effects. FTIR spectroscopy of the solids indicated solvent incorporation in the film. This observation was corroborated by thermal analysis. Information on the thermal stability of the films was obtained by TGA. The UV/Vis absorption spectrum was measured at several concentrations under different conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003960050381
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  • 117
    Digitale Medien
    Digitale Medien
    Stability and resilience in benthic macroinvertebrate assemblages (1999)
    Springer
    Hydrobiologia 403 (1999), S. 123-133 
    Details
    ISSN: 1573-5117
    Schlagwort(e): disturbance ; stability ; resilience ; Trichoptera ; Ephemeroptera ; Psychomyia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Benthic macroinvertebrate assemblages of Bushkill Creek, Northampton County, PA were studied at the same site during the 1970s (11 dates) and 1990s (8 dates) to evaluate stability and resilience. In the 1970s, a Surber sampler was used, and in the 1990s, a Hess sampler. Assemblages appeared stable over a wide range of environmental stresses with the exception of 1994–1995 when total numbers and total Trichoptera decreased. Taxa richness and EPT indices varied little in 1994–1995 from other sampled years. By July 1996, all metrics (Trichoptera numbers, total numbers, taxa richness, EPT index, Bray-Curtis Index) resembled the 1970s exception for lower wet weight. Bray-Curtis indices and taxa composition were similar in July 1972 and July 1996, suggesting assemblage stability over 25 years. The Trichoptera, Psychomyia (Psychomiidae) and Leucotrichia (Hydroptilidae), decreased during the 1990s and never rebounded to 1970s numbers. During winter 1994, the coldest temperatures and greatest cumulative snowfall occurred in the region. These conditions probably stressed the assemblage with low temperatures, anchor/frazil ice and ice break-up. The assemblage was then exposed to four bankful floods in winter/spring 1994 and five bankful floods in winter/spring 1996. Recovery time following these multiple disturbances was 27 months. Previous recovery times from winter and flood disturbances were considerably shorter (2–5 months). The 1990s recovery time (5–9 times previusly recorded) for this assemblage was apparently extended by multiple physical disturbances, outside the predicted range. The assemblages had not been previously exposed to such severe conditions and, therefore, recovery time was extended. Despite severe weather conditions, the assemblage recovered and exhibited both stability and resilience in its return to an assemblage similar to the 1970s.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003711928980
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  • 118
    Digitale Medien
    Digitale Medien
    Procedures for the characterisation of bioaerosol particles. Part I: aerosolisation and recovery agent effects (1999)
    Springer
    Aerobiologia 15 (1999), S. 267-280 
    Details
    ISSN: 1573-3025
    Schlagwort(e): aerosolisation effects ; bioaerosol ; bioaerosol sampling ; effects of recovery agents ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The sampling and assay of bioaerosols are important ina number of industrial and health-care applications. Airborne microorganisms are notoriously difficult toenumerate accurately under such conditions and nosingle procedure is suitable for all applications. Problems are compounded by the differences in assaymethod or sampler type selected, making theinterpretation of results difficult.Understanding the airborne behaviour of microorganismsover a range of environmental conditions is vital ifprocedures are to be defined and recommended for theassessment of bioaerosols. Microorganisms that arerobust over a wide range of conditions are ideal astracer particles. Unfortunately, the large majorityof non-fungal bioaerosols are susceptible to damage. A predictable assessment procedure is required whichwill not affect the viability of the collectedsample. This paper examines how aerosolisation may affect the characteristics of two speciesof microorganism (Pseudomonas fluorescens andMS2 coliphage). It forms part of a larger programmeto develop standards for the assessment of biologicalparticles. The aim of the work was to develop procedures toexamine the effects of aerosolisation onmicroorganisms, with particular reference topre-aerosolisation protocol (spray suspension age) andpost-sampling handling protocol (aerosol age incollection solution). These procedures were then usedto examine the effect of recovery agents, addedto the spray suspension prior to aerosolisation, onthe culturability of E.coli. Aerosolisation reduces the culturability of P. fluorescensand the viability of viability of MS2coliphage. Pre-sampling and post-collection handlingand storage of these aerosolised microorganisms werealso found to have an effect. This and earlierstudies have shown that the culturable fraction ofmicroorganisms can be affected by the same factorsdescribed above. Of five microorganisms tested so farin the main programme, only Penicillium expansumspores were shown to be robust and stable with aconstant culturable fraction. Therefore, recommendinga particular microorganism (apart from P. expansum) as an airborne biological standard foraerosol studies is not advised. It is recommendedthat a microorganism, representative of the envisagedapplication, be characterised it in terms of theaerosolisation parameters, storage time and conditionsin the manner reported in this study. This can beachieved using the experimental equipment described.The addition of 0.1 mM concentrations of the sugarsinositol, trehalose and raffinose to spray suspensionsof Escherichia coli, prior to aerosolisation,made no significant difference to the culturablefraction of the aerosol.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007638711384
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  • 119
    Digitale Medien
    Digitale Medien
    Equilibrium stability of generalized Birkhoff's autonomous system (1999)
    Springer
    Applied mathematics and mechanics 20 (1999), S. 564-567 
    Details
    ISSN: 1573-2754
    Schlagwort(e): generalized Birkhoff's system ; equilibrium state ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract In this paper, equilibrium stability of generalized Birkhoff's autonomous system is discussed. First, equilibrium equations of generalized Birkhoff's autonomous system are set up, and then the linear approximate method and direct method of stability in equilibrium state are studied. Some results on equilibrium of generalized Birkhoff's autonomous system are obtained on the basis of Lyapunov's thorem. Last, the application of the results is illustrated with an example.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02463754
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  • 120
    Digitale Medien
    Digitale Medien
    Portfolio optimization via stochastic programming: Methods of output analysis (1999)
    Springer
    Mathematical methods of operations research 50 (1999), S. 245-270 
    Details
    ISSN: 1432-5217
    Schlagwort(e): Key words: Portfolio optimization ; stochastic programming ; stability ; postoptimality ; worst-case analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Wirtschaftswissenschaften
    Notizen: Abstract. Solutions of portfolio optimization problems are often influenced by errors or misspecifications due to approximation, estimation and incomplete information. Selected methods for analysis of results obtained by solving stochastic programs are presented and their scope illustrated on generic examples – the Markowitz model, a multiperiod bond portfolio management problem and a general strategic investment problem. The approaches are based on asymptotic and robust statistics, on the moment problem and on results of parametric optimization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001860050097
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  • 121
    Digitale Medien
    Digitale Medien
    Determination of ochratoxin a in beer by high-performance liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 543-546 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; MS-MS detection ; Electrospray-Ionization (ESI) ; Beer ; Ochratoxin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Ochratoxin A (OTA) is a nephrotoxic and nephrocacinogenic mycotoxin commonly produced by several ubiquitousAspergillus andPenicillium species. OTA is found predominantly in cereals and derived products, and therefore OTA may be transferred into beer from contaminated grain. Thirty-five samples of German beers were analyzed: OTA was extracted with toluene and purified by solid phase extraction using silica cartridges. OTA was determined by high-performance liquid chromatography with fluorescence detection. Since of fluorescence detection is not specific in this instance, the beer samples were also analyzed by high-performance liquid chromatography electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS). OTA levels in the range of 0.1–0.2 μg L−1 were found in 9 beer samples, 21 samples contained trace amounts of OTA (〈0.1 μg L−1) and in 5 samples no OTA was detectable.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467756
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  • 122
    Digitale Medien
    Digitale Medien
    Analysis of doxorubicin in cell culture media and human plasma using solid phase extraction and HPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 557-561 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Solid phase extraction ; Doxorubicin ; Cell culture media ; Human plasma ; Fluorescence detection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Doxorubicin is an antineoplastic antibiotic isolated fromStreptomyces peucetius var.cesius clinically used in the treatment of tumors such as lung or breast, Hodgkin's disease and various types of leukemias. The main goal of this study was to develop a simple and sensitive HPLC method with fluorescence detection for the quantitation of doxorubicin in cell culture media collected during an in vitro studies and in human plasma. Solid phase extraction (C2 silica) was applied. The experiment established five-point standard curve (1 ng mL−1 to 100 ng mL−1). The standard curves prepared in blank cell tissue media were linear over the range of doxorubicin assayed and had a mean correlation coefficient of 0.9973±9.43×10−4 and slope 0.02545±1.85×10−3. The standard curves prepared in human plasma were linear and had mean correlation coefficient of 0.997 and slope 0.01885±5.19×10−4. The limit of quantitation for doxorubicin in both specimens was arbitrarily established to be 1 ng mL−1. Intra-day variabilities were determined using 3–4 replicates of control solutions of doxorubicin (3 ng mL−1 and 30 ng mL−1) in blank plasma and cell culture media. Inter-day variabilities were determined over a four day period analyzing replicates of controls. All precision and accuracy values fell within the acceptable range.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467759
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  • 123
    Digitale Medien
    Digitale Medien
    Separation of human serum albumin components by RP-HPLC and CZE and their characterization by ESI-MS (1999)
    Springer
    Chromatographia 49 (1999), S. S21 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Capillary zone electrophoresis ; Electrospray ionization-mass spectrometry ; Human serum albumin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Human serum albumin (HSA) is one of the most abundant human proteins and has been shown to be heterogeneous. A RP-HPLC method has been developed to separate HSA components in commercially available preparations. Separations were carried out on Aquapore RP-300, C8 columns using gradient elution with a combination of acetonitrile/water mobile phases containing 0.05% trifluoroacetic acid as ion-pairing agent. Optimum resolution was attained on narrow-bore columns using a stepwise, linear gradient that incorporated a shallow intermediate step of 0.20%/min in Mobile Phase B. Under similar elution conditions, separations carried out on standard-size columns showed the expected decrease in resolution due to increased peak widths. A comparative analysis of three commercial products highlighted qualitative and quantitative differences. Capillary zone electrophoresis was used for the analysis of collected RP-HPLC fractions. Results indicated that while the HPLC separation was incomplete, one of the major HPLC peaks was primarily composed of one of the three main components typically separated by CZE. ESI-MS was used to characterize the two major RP-HPLC fractions and also showed that the HPLC separation was incomplete. The MaxEnt transform of the HPLC peaks was consistent with components all being HSA and closely related derivatives.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02468972
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  • 124
    Digitale Medien
    Digitale Medien
    FMOC-Cl as derivatizing agent for the analysis of amino acids and dipeptides by the absolute analysis method (1999)
    Springer
    Chromatographia 49 (1999), S. 317-320 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Amino acids ; FMOC derivatives ; Oligopeptides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary One classical method for quantitation of amino acids in proteins is hydrolysis of the proteins and determination of the free amino acids. Although the drastic experimental conditions necessary for complete hydrolysis always cause degradation of some of the amino acids, if mild hydrolysis conditions are used, a mixture of amino acids and oligopeptides is obtained. If these conditions are adequately tuned, the oligopeptides are almost exclusively dipeptides. For this reason we have initiated a study to find a derivatizing agent suitable for the analysis of amino acids and dipeptides by an absolute method of quantitation already tested for amino acids. FMOC-Cl was found to be a suitable derivatizing agent for this purpose.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467563
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  • 125
    Digitale Medien
    Digitale Medien
    High-performance liquid chromatographic determination/identification of oxytetracycline and sulphadimidine in meat and eggs (1999)
    Springer
    Chromatographia 49 (1999), S. 369-373 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Sep-Pak CN cartridge ; Oxytetracycline ; Sulphadimidine ; Meat and eggs
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A rapid method for the simultaneous determination/identification of residual oxytetracycline (OTC) and sulphadimidine (SDD) in meats (beef, pork, chicken) and eggs by high-performance liquid chromatography (HPLC) was developed. The extraction of OTC and SDD was performed using a Sep-Pak® CN cartridge. The extracts contained OTC/SDD analytes when examined by HPLC using a LiChrospher® 100 RP-8 end-capped column and a mobile phase of acetonitrile-acetic acid-water (28:4:68, v/v/v) with a photodiode array detector. The average recoveries from spiked samples (0.1 μg g−1 and 1.0 μg g−1) were in excess of 80.2% with coefficients of variation between 1.5 and 5.0%. The limits of detection for OTC and SDD were 0.05 and 0.02 μg g−1, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467608
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  • 126
    Digitale Medien
    Digitale Medien
    Improved separation of polyethylene glycols widely differing in molecular weight range by reversed-phase high performance liquid chromatography and evaporative light scattering detection (1999)
    Springer
    Chromatographia 49 (1999), S. 615-620 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Evaporative light-scattering detection ; MALDI-TOF ; Polyethylene glycols
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Polyethylene glycols (PEGs) of nominal molecular weight (M) 200, 400, 600, 1000, 1500, 3000, 4000 and 6000 were chosen as model compounds and subjected to reversed-phase high performance liquid chromatography (RP-HPLC) on an octadecasilyl silica gel (C18) stationary phase using a binary gradient composed of acetonitrile and water and evaporative light scattering detection (ELSD). Satisfactory resolution of oligomers up to M of 3000 was accomplished; the higher M samples PEG-4000 and PEG-6000 could not be further resolved into the constituent oligomers and therefore, M=4000 marks the upper limit of oligomer resolution. Despite some peak overlapping as a consequence of the more or less broad oligomer distribution, individual types of PEG samples can be distinguished from each other by their characteristic chromatographic fingerprint patterns, as shown with a mixture consisting of PEG-400, PEG-1000, PEG-3000, PEG-4000 and PEG-6000. For this reason, the method is well-suited for characterization of samples containing PEGs widely differing in M. In addition, matrix assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF/MS) performed with PEG-600, PEG-1000 and PEG-3000 revealed that the optimum degree of oligomer resolution has been achieved by use of the present method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466902
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  • 127
    Digitale Medien
    Digitale Medien
    Separation of the enantiomers of amino and amide compounds on novel chiral stationary phases derived from a crown ether (1999)
    Springer
    Chromatographia 49 (1999), S. 621-627 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chiral stationary phases ; Crown ether derivatives ; Amino compounds
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The enantiomers of primary amino compounds have previously been resolved on a chiral stationary phase (CSP) CSP-18C6I, prepared by immobilizing (+)-18-crown-6 tetracarboxylic acid. In this study related chiral stationary phases were prepared in an effort to broaden the scope of CSP18C6I. CSP-18C6II, synthesized to investigate the effect of spacer length, resolved the enantiomers of 2-amino-1,2-diphenylethanol and 1-(1-naphthyl)ethylamine (1-NEA) (hydrophobic amino compounds) with the largerk values and smaller α values than on CSP-18C6I, probably because of the greater hydrophobicity of CSP-18C6II. Use of CSP-18C6III, synthesized by modification of carboxylic acid functionality of CSP-18C6II by introduction of another chiral moiety,S-1-NEA, resulted in larger α values for 2-amino-1-phenylethanol and 2-amino-1-phenylpropanol than on CSP-18C6II, but the enantiomers of 1-NEA were not resolved, because of steric hindrance between 1-NEA and the chiral moiety. The amide derivativeN-3,5-dinitrobenzoyl-1-(α-naphthyl)ethylamine (DNN) as π-acceptor (3,5-dinitrobenzoyl function) or π-donor (naphthylethylamide function), and no primary amino functionality, was resolved on CSP-18C6III. The mechanism of separation of the enantiomers of DNN was assumed to be the π−π interaction between the 3,5-dinitrobenzoyl function (π-acceptor) of DNN and theS-1-NEA moiety (π-donor) of CSP-18C6III.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466903
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  • 128
    Digitale Medien
    Digitale Medien
    Determination of alcohols using condensation agent carbazole-9-acetyl-benzene-disulfonate by high performance liquid chromatography with pre-column fluorescence derivatization (1999)
    Springer
    Chromatographia 49 (1999), S. 657-665 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Alcohols ; Pre-column fluorescence derivatization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A sensitive LC method for the determination of alcohols, using fluorescent condensation agent carbazole-9-N-acetylbenzne-disulfonate(CABS), has been developed. A mixture of alcohols and triethylamine catalyst in dichloromethane or chloroform is treated with CABS to give quantitative yields of esters. Emission maximum for the derivatized alcohols is 365 nm (λex 335 nm). The labeled derivatives are very stable, no significant decomposition is observed after heating in 40% at 40°C for 24 h. The method, in conjunction with a multigradient program, offers baseline resolution of common alcohol derivatives on a reversed-phase C18 column. Studies on derivatization conditions indicate that primary and secondary alcohols react very fast with CABS in the presence of triethylamine in dichloromethane or chloroform to give the corresponding fluorescent derivatives. This method is more convenient and more efficient than previous methods which require prior conversion of carboxylic acids to acyl chlorides. The separation of alcohol derivatives has good reproducibility and the rsd's (n=5) for 50 pmol of each alcohol are 4%. Detection limits are at the fmol level.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466908
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  • 129
    Digitale Medien
    Digitale Medien
    Liquid chromatography of jasmonic acid amine conjugates (1999)
    Springer
    Chromatographia 49 (1999), S. 42-46 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chiral resolution ; Jasmonic acid ; Plant growth regulators ; Amine conjugates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Racemic jasmonic acid (3R,7R/3S,7S)-(±)-JA) was chemically conjugated with different biogenic amines originating from aliphatic and aromatic α-amino acids by decarboxylation. The resulting isomeric compounds were subjected to reversed-phase high-performance liquid chromatography (HPLC) and to HPLC on the chiral stationary phases Chiralpak AS and Nucleodex β-PM. Under reversed-phase conditions, all the homologous amine derivatives tested could be separated from each other except the JA-conjugates containing 2-phenyl-ethylamine and 3-methylbutylamine. On both chiral supports the (3R,7R)-(−)-JA conjugates eluted earlier than those of the enantiomeric counterpart (3S,7S)-(+)-JA. On Chiralpak AS all the isomers studied could be separated to baseline with a mobile phase containingn-hexane and 2-propanol. The calculated resolution factors were between 1.80 and 4.17. The pairs of isomers were also chromatographed on the cyclodextrin stationary phase Nucleodex β-PM with methanol-triethylammonium acetate buffer as mobile phase. Under these conditions resolution factors were between 0.74 and 1.29. The individual isomers were chiroptically characterized by measurement of their circular dichroism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467185
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  • 130
    Digitale Medien
    Digitale Medien
    Determination of ethinylestradiol and gestodene in oral contraceptives by micellar electrokinetic chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 65-70 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Micellar electrokinetic chromatography (MEKC) ; Oral contraceptives ; Ethinylestradiol ; Gestodene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A micellar electrokinetic chromatographic method is presented which permits quantification of ethinylestradiol and gestodene in pharmaceutical products. Separation was carried out at 25°C and 25 KV, using a 20 mM borate buffer (pH 9.2), 15 mM sodium dodecylsulfate in 30% acetonitrile-water (v/v). Under these conditions analyses were carried out in 7 min. Four different oral contraceptives were analysed and the results compared favourably with those of a reference liquid chromatographic method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467189
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  • 131
    Digitale Medien
    Digitale Medien
    Determination of yttrium and lanthanum in zirconium dioxide by HPLC, X-ray fluorescence and neutron activation analyses (1999)
    Springer
    Chromatographia 49 (1999), S. 91-94 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Zirconium oxide ceramics ; X-ray fluorescence ; Neutron activation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Lanthania-and yttria-stabilized zirconium oxide ceramics have been examined using High Performance Liquid Chromatography (HPLC), thermal neutron activation (NA) and X-ray Fluorescence (XRF) analyses and thus determine the stabilizer content. Ceramic powders with the composition ZrO2:x mol % La2O3 (x=5, 10, 15, 20 and 33) and ZrO2:x mol % Y2O3 (x=10, 15, 20 and 25) were prepared by the citrate and the co-precipitation techniques, respectively. The lanthanum content was determined by HPLC (x=5.09, 9.78, 14.98, 19.81 and 25.94) and NA (x=5.15, 10.32, 17.25, 21.08 and 27.97) analyses, the yttrium content by HPLC (x=8.5, 13.5, 17.9 and 22.1) and XRF (x=9.9, 15.8, 20.1 and 24.9) analyses. An experimental sequence, based on continuous dilution of ceramic powder solutions, is proposed for preparing samples for HPLC measurements. A swimming pool nuclear reactor is used for NA analysis. The quantitative determinations of yttrium and lanthanum doping levels obtained using those techniques are described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467194
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  • 132
    Digitale Medien
    Digitale Medien
    Stereochemical resolution of racemates, in HPLC, using a chiral stationary phase based upon immobilized α-chymotrypsin. I. Structural chiral separations (1999)
    Springer
    Chromatographia 49 (1999), S. 595-605 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; α-Chymotrypsin immobilized on silica ; In situ immobilization process ; Structural chiral separations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary α-Chymotrypsin was immobilized on an epoxide derivatized silica gel by anin situ immobilization process. Several racemates were resolved by a structural recognition mechanism. The immobilization process and the stability of this α-chymotrypsin stationary phase have been studied. The mobile phase parameters including the ionic strength, pH and the effects of organic modifiers have been also investigated. The retention, efficiency and stereoselectivity of the solutes appear to be related to their molecular structure, hydrophobicity and electrostatic interactions. These relationships determine the recognition mechanism and the position of each enantiomer in the active site.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466900
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  • 133
    Digitale Medien
    Digitale Medien
    Stereoselective analysis of idrapril and its stereoisomers by reversed-phase high-performance liquid chromatography on a chiral-AGP column (1999)
    Springer
    Chromatographia 49 (1999), S. 628-634 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Enantiomer separation ; Chiral-AGP column ; Idrapril ; Temperature effect
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A direct liquid-chromatographic method has been developed for the stereoselective analysis of idrapril and its stereoisomers on a chiral α1 glycoprotein (AGP) column. The influence of flow-rate, temperature, and mobile phase composition on retention and selectivity was evaluated to find the optimum conditions for chiral separation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466904
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  • 134
    Digitale Medien
    Digitale Medien
    Preparation of branched-polyfluoroalkylsilane-coated silica gel columns and their HPLC separation characteristics (1999)
    Springer
    Chromatographia 49 (1999), S. 649-656 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Polyfluoroalkyl-coated silica ; 29Si CP/MAS NMR ; Polyaromatic compounds ; Fluorinated compounds
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The conditions for reaction of the branched polyfluoroalkylsilane D3CL with silica gel have been examined. From elemental analyses and29Si NMR spectra it was found that the surface coverage and endcapping of D3CL-coated silica gel (Fluofix®) were the same as for ODS packings. The separation behavior of these phases was compared that of a variety of other packings. For polyaromatic compounds and benzene derivatives Fluofix worked in the reversed-phase mode and its retention characteristics were similar to those of C1 or CN packings. For fluorinated compound the retention characteristics of the phases is similar to those of ODS although with MeOH-water and MeCN-water mobile phases the pressure loss was lower for the fluorinated phases than for ODS.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466907
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  • 135
    Digitale Medien
    Digitale Medien
    The effect of pH on the high pH anion-exchange chromatography elution of monosaccharides (1999)
    Springer
    Chromatographia 49 (1999), S. 699-702 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Anion-exchange chromatography ; High ph elvents ; Monosaccharides ; Carbopac PA-100
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary We have studied the elution behaviour of six common monosaccharides, fucose, galactosamine, glucosamine, galactose, glucose and mannose, on the CarboPac PA-100 column. The relative elution positions of galactose, glucose and mannose were dependent on the sodium hydroxide concentrations, a phenomenon which was likely to be the result of differential ionisation of the hydroxyl groups at ring positions two and four. The optimal resolution of the monosaccharides studied was achieved by elution with 30 mM sodium hydroxide with no appreciable loss in sensitivity at this low concentration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466915
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  • 136
    Digitale Medien
    Digitale Medien
    High performance liquid chromatography method for the determination of meropenem in human plasma (1999)
    Springer
    Chromatographia 49 (1999), S. 253-255 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Meropenem in human plasma ; Solid phase extraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary This paper describes an HPLC method for the determination of meropenem in human plasma. The method uses solid phase extraction (SPE) of the samples and has good sensitivity, precision and accuracy. The limit of quantification in plasma samples is 0.02 μg mL−1. Calibration curves were linear over a large dynamic range, namely within 0.02–50 μg mL−1. The method was applied to the determination of meropenem levels in patients receiving meropenem, as a single dose or at steady state.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467552
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  • 137
    Digitale Medien
    Digitale Medien
    Trace analysis of surfactants derived from fatty alcohols II. Hydrolysis and enrichment techniques (1999)
    Springer
    Chromatographia 49 (1999), S. 12-16 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Fatty alcohol sulfates ; Alkyl polyglycosides ; Trace analysis ; Steam distillation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Acid catalyzed hydrolysis of fatty alcohol sulfates under reflux condition or by microwave heating is compared. Microwave hydrolysis turned out to be faster and more convenient to use. The combination of reflux hydrolysis of fatty alcohol sulfates or alkyl polyglycosides and the simultaneous steam distillation of the generated fatty alcohols gives a very powerful sample preparation and enrichment method for fatty alcohol sulfates and alkyl polyglycosides. The preconcentrated fatty alcohols are derivatized and detected via fluorescence detection. The applicability of the method is demonstrated by the analysis of fatty alcohol sulfates in cosmetics and in river water as matrices spiked with approximately 4 ppb fatty alcohol sulfates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467180
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  • 138
    Digitale Medien
    Digitale Medien
    Identification and quantitation of polyphenols in leaves ofMyrtus communis L. (1999)
    Springer
    Chromatographia 49 (1999), S. 17-20 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; DAD and MS detection ; Liquid-solid extraction ; Catechin derivatives ; Myricetin derivatives
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A liquid-solid extraction and purification procedure (LSE) was developed to identify and quantify polyphenols in the leaf tissue ofMyrtus communis L. Identification and quantitation of individual compounds was performed using HPTLC, HPLC-DAD and HPLC-MS analysis. Leaves ofMyrtus communis L. contain small amounts of phenolic acids (caffeic, ellagic and gallic acids) and quercetin derivatives (quercetin 3-O-galactoside and quercetin 3-O-rhamnoside), whereas catechin derivatives (epigallocatechin, epigallocatechin 3-O-gallate, epicatechin 3-O-gallate) and myricetin derivatives (myricetin 3-O-galactoside, myricetin 3-O-rhamnoside) are present in large amounts. This is the first report on the occurrence of galloyl-derivatives of catechin and gallo-catechin inMyrtus communis L. leaves.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467181
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  • 139
    Digitale Medien
    Digitale Medien
    p-Hydroxymercuribenzoate as thiol-protein modifier for simultaneous determination of glycolytic enzymes by hydrophobic-interaction chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 47-53 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Glycolytic enzymes ; p-Hydroxymercuribenzoate ; 203Hg-labelledp-hydroxymercuribenzoate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The use of hydrophobic-interaction chromatography (HIC) is proposed for the simultaneous determination of more than one thiol-protein after formation of the corresponding mercury mercaptides withp-hydroxymercuribenzoate (PHMB). The new chromatographic procedure, based on the HIC separation of the modified proteins from each other and from excess organomercury reagent has been successfully applied to the quantitative determination of phosphoglucose isomerase (PGI) and phosphoglucose mutase (PGM) in crude PGI powder, and of L-lactate dehydrogenase, PGM and aldolase in crude pyruvate kinase from rabbit muscle. The suitability of203Hg-labelled PHMB has been tested in the analysis of mixtures, which give barely distinguishable UV-peaks owing to the presence of other non-thiol components in the sample. For this purpose glyceraldehyde 3-phosphate dehydrogenase (GAPDHy) and PGIy from bakers yeast have been considered. Results obtained in experiments performed by both procedures are reported.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467186
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  • 140
    Digitale Medien
    Digitale Medien
    Separation of the enantiomers of amino acid esters as benzophenone imine derivatives on polysaccharide-derived chiral stationary phases (1999)
    Springer
    Chromatographia 49 (1999), S. 61-64 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Chiral stationary phases ; Benzophenone imine derivatives ; Amino acid esters ; Enantiomer separation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The liquid-chromatographic separation of the enantiomers of amino acid esters as benzophenone Schiff-base derivatives on polysaccharide-derived chiral stationary phases (CSPs) is described. The performance of Chiralcel OF was superior to that of the other CSPs for resolution of benzophenone imine derivatives of amino acid ethyl and methyl esters. The enantiomers of most of the amino acid esters examined as their benzophenone imine derivatives were resolved to baseline on Chiralcel OF. The L-(−) enantiomers of all the analytes were preferentially retained on Chiralcel OF. The resolution of several imine derivatives of amino acid esters was investigated, as was the effect of eluent composition on the resolution of amino acid ethyl esters as their benzophenone imine derivatives.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467188
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  • 141
    Digitale Medien
    Digitale Medien
    Development and validation of an HPLC method for the simultaneous determination of clozapine and desmethylclozapine in plasma of schizophrenic patients (1999)
    Springer
    Chromatographia 49 (1999), S. 75-80 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Amperometric detection ; Clozapine ; Desmethylclozapine ; Drug monitoring
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A high-performance liquid chromatographic method with amperometric detection has been developed for the determination of levels of clozapine (CLZ) and its active metabolite N-desmethylclozapine (DMC) in human plasma. The analysis was performed on a 5 μm C8 reversed phase column (150×4.6 mm i.d.), with acetonitrile-phosphate buffer (pH 3.5), as the mobile phase. The detection voltage was +800 mV and the cell and column temperature were 50°C. Linear responses were obtained between 2 ng mL−1 and 100 ng mL−1. Absolute recovery for both clozapine and desmethylclozapine exceeded 88% and the detection limit was 1 ng mL−1. Repeatability, intermediate precision and accuracy were satisfactory. The method, which is rapid, sensitive and selective, has been applied to therapeutic drug monitoring in schizophrenic patients following administration of Leponex® tablets. In 21 patients in steady state at a mean daily clozapine dosage of 358 mg (ranging from 150 to 500 mg day−1), clozapine levels averaged 379 ng mL−1 (ranging from 102 to 818 ng mL−1) and DMC levels averaged 233 ng mL−1 (ranging from 70 to 540 ng mL−1). The method requires only a very small amount of plasma (100 μL), and thus it is suitable for pharmacokinetic studies, as well as for therapeutic drug monitoring.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467191
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  • 142
    Digitale Medien
    Digitale Medien
    Study of the chromatographic behavior and inclusion constants of new fluorescence agents by use of cyclodextrin additives under conditions of steady- and dynamic-state equilibrium and with fluorescence detection (1999)
    Springer
    Chromatographia 49 (1999), S. 95-104 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Cyclodextrin additives ; Fluorescence agents
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary We report four new derivatization agents, acridone-N-acetic acid (ARC), carbazole-9-ylacetic acid (CRA), carbazole-9-ylpropionic acid (CRP), and 2-methyl-2-carbazole-9-ylacetic acid (MCRA), with strong fluorescence emission which has low dependence on solvent polarity. The emission maxima for ARC, CRA, CRP, and MCRA were 430 nm (λex 404 nm), 368 nm (λex 335 nm), 356 nm (λex 340 nm) and 360 nm (λex 330 nm), respectively. The effects of mobile-phase composition, pH, and temperature on the liquid chromatographic retention behavior of the four fluorescence agents were investigated. An experimental model was established for calculating the inclusion constants of cyclodextrin (CD) complexes in the dynamic state, using β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) as examples, and different mobilephase compositions. On the basis of the model, the inclusion constants of the solutes in pure water (K fw) were determined by extrapolation. The thermodynamic parameters (ΔH o and ΔS o) and dissociation constantsK am for the solutes in this chromatographic system were obtained by means of capacity factor (k) values using a corresponding model formulation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467195
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  • 143
    Digitale Medien
    Digitale Medien
    Effect of triethylamine in the mobile phase on the retention properties of conventional polymeric and horizontally polymerized octadecylsilica in RPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 635-642 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Interaction of mobile and stationary phases ; Linear solvation energy relationships ; Triethylamine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The effect of triethylamine (TEA) in the mobile phase on the RPLC retention behavior of small organic solutes has been studied on a conventional polymeric octadecylsilica (ODS) and on a horizontally polymerized ODS. Retention factors for a set of solutes were measured on the two phases with methanol-water mobile phases containing triethylamine at different concentrations and analyzed by use of linear solvation energy relationships (LSER). Variation of the resulting LSER coefficients—v (hydrophobicity),r (polarizability),s (dipolarity),b (hydrogen-bond (HB) donating acidity), anda (HB accepting strength)—were examined to see how TEA affects the intermolecular interaction properties of the mobile and stationary phases and hence the retention of the solutes. Addition of TEA to the mobile phase changes the interaction properties of both conventionally polymerized and horizontally polymerized ODS; the effect is greater for the conventional phase. The HB donating acidity (b) of conventional polymeric ODS is significantly reduced by addition of TEA. For the mobile phases studied the magnitudes of theb andv coefficients for the horizontally polymerized ODS phase are greater than for the conventional phase. The different interaction properties of the two polymeric phases arise mainly as a result of differential adsorption of TEA, because of the very different amounts of surface silanol groups present on the two phases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466905
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  • 144
    Digitale Medien
    Digitale Medien
    Preparation and evaluation ofp-tert-butyl-calix[4]arene-bonded silica stationary phases for high performance liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 643-648 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; p-tert-Butyl-calix[4]arene-bonded silica ; Nuclear magnetic resonance spectrometry ; PAHs ; Nucleosides bases
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A new method is proposed for preparation of ap-tert-butyl-calix[4]arene-bonded silica stationary phase. The chemically modifiedp-tert-butyl-calix[4]arene is attached to silica gel via the silane coupling reagent γ-(ethylenediamino)-propyl-triethoxyl-silane. The bonded phase has been characterized by29Si and13C cross polarization/magic angle spinning solid-state nuclear magnetic spectrometry. The retention behavior of polycyclic aromatic hydrocarbons (PAHs), nucleosides and bases has been investigated on the bonded phase in the reversed-phase mode.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466906
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  • 145
    Digitale Medien
    Digitale Medien
    Hydrolysis of microcystins and nodularin by microwave radiation (1999)
    Springer
    Chromatographia 49 (1999), S. 671-677 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Microwave hydrolysis ; Microcystin ; Nodularin ; D- and L-selective amino acid determination
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Microwave radiation has been successfully used for hydrolysis of the hepatotoxic cyclic peptides microcystins and nodularin. Set-up of the microwave device and the operating conditions for microwave hydrolysis were optimized. Results of the microwave hydrolysis were compared with results from conventional hydrolysis for 24 h at 110°C. Microwave hydrolysis of microcystins and nodularin for as little as 10 min at 160°C results in complete cleavage of peptide bonds and high recoveries of amino acids. Enantioselective determination of amino acids was achieved by use of a previously described HPLC method after pre-column derivatization withortho-phthaldialdehyde and the chiral thiolN-iso-butyryl-cysteine.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466910
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  • 146
    Digitale Medien
    Digitale Medien
    Peculiarities of the mechanism of retention of imidazole derivatives when using hydroxypropyl-β-cyclodextrin as mobile phase additive (1999)
    Springer
    Chromatographia 49 (1999), S. 691-698 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Hydroxypropyl-β-cyclodextrin ; Imidazole derivatives ; Retention mechanisms ; Enthalpy-entropy compensation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Two different methods have been used to investigate the retention mechanism of a series of imidazole derivatives in reversed-phase liquid chromatography (RPLC) over a range of column temperatures and with different concentrations of hydroxypropyl-β-cyclodextrin (HP-β-CD) in the mobile phase. The first approach was the separate study of each factor affecting the retention mechanism; the second method was the simultaneous variation of all these factors. Changes in Van't Hoff plots as a function of HP-β-CD concentration were examined. Enthalpy and entropy were determined for two physicochemical processes: (i) solute transfer from the mobile phase to the stationary phase, and (ii) solute complexation by HP-β-CD. These thermodynamic data showed that the mechanism of retention of the solute was dependent on the concentration of HP-β-CD in the mobile phase. For a HP-β-CD concentration,C, greater than to 4 mM, from 28°C to a critical temperature,T *, solute retention was entropy-dominated because of inclusion of the solute in the HP-β-CD cavity. AboveT * retention was enthalpy-dominated, because of interaction of the solute with the RP18 stationary phase. At firstT * increased asC was increased up to a critical value,C **; it the remained relatively constant because of auto-association of the HP-β-CD molecules in the mobile phase. Enthalpy-entropy compensation revealed that HP-β-CD-solute complexation had a greater effect on retention than RP18 stationary phase-solute interaction. This confirms that the main parameter determining retention in RPLC is the distribution of the solute in the mobile phase, and that interactions with the stationary phase play a minor role.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466914
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  • 147
    Digitale Medien
    Digitale Medien
    Analysis of commercial ceramides by non-aqueous reversed-phase liquid chromatography with evaporative light-scattering detection (1999)
    Springer
    Chromatographia 49 (1999), S. 241-248 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Non-aqueous reversed-phase liquid chromatography ; Evaporative light-scattering detection ; Octadecyl grafted silica ; Ceramides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary This paper describes the development of a chromatographic system for analysis of commercial ceramides structurally similar to those found in the stratum corneum. The ceramides used in this study contain different amine based (phytosphingosine, sphingosine and dihydrosphingosine) and fatty acids of different chain lengths and with different functional groups (hydroxylated and unsaturated). Non-aqueous reversed-phase (NARP) liquid chromatography with evaporative light-scattering detection (ELSD) were the techniques chosen in accordance with the nature of the ceramides. The eluent strength and the potential selectivity of different organic solvents were investigated. On a C18-bonded silica, the most promising chromatographic conditions employed a gradient from ACN-THF, 95∶5, to ACN-THF-PrOH, 35∶5∶60, in 15 min with a constant concentration of TEA (10 mM) and a stoichiometric amount of formic acid.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467550
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  • 148
    Digitale Medien
    Digitale Medien
    High-performance liquid chromatographic method for separation and quantification of intact glucosinolates (1999)
    Springer
    Chromatographia 49 (1999), S. 281-284 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Glucosinolates ; Rapseed-mustard ; Brassica
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A simple, economical and efficient HPLC method has been developed for the separation and determination of the individual glucosinolates in rapessed and mustard. The method involves single-step extraction of glucosinolates with boiling water and separation of the individual glucosinolates on a Novapack RP-18 column (3.9 mm ×150mm) with 0.2 M ammonium sulphate as mobile phase. Peaks were monitored at 229 nm. All major glucosinolates could be eluted within 10 min. The method proved effective for routine analysis of glucosinolates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467557
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  • 149
    Digitale Medien
    Digitale Medien
    Determination of flupoxam residues in soil by high performance liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 535-538 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Solid phase extraction ; Herbicides in soil ; Flupoxam
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary High-performance liquid chromatography with UV detection was used to determine the residues of flupoxam (a new herbicide) in soils. Soil samples were extracted with aqueous methanol. The soil extracts were cleaned up and concentrated using two solid phase extraction columns: a polymeric stationary phase based on a polystyrene-divinylbenzene resin (Lichrolut EN) and alumina. Recovery experiments were performed at ppb levels in spiked soil samples. The recovery was 76±1.7% for flupoxam in the range 5–100 μg kg−1 of soil. Limit of determination was 3 μg kg−1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467754
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  • 150
    Digitale Medien
    Digitale Medien
    Stereochemical resolution of racemates, in HPLC, using a chiral stationary phase based upon immobilized α-chymotrypsin. II. Enzyme chiral separations (1999)
    Springer
    Chromatographia 49 (1999), S. 606-614 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; α-Chymotrypsin-CSP ; Enzymatic chiral separations ; Loadability evaluation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Several racemates has been resolved according to an enzymatic recognition mechanism on an α-chymotrypsin chiral stationary phase. The loadability of the ACHT-CSP has been evaluated both in buffered and non-buffered mobile phases under the enzymatic process and compared with the loading capacity obtained by the structural recognition process.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466901
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  • 151
    Digitale Medien
    Digitale Medien
    HPLC resolution of the enantiomers of glycidyl sulfides and glycidyl selenides on amylose tris-(phenylcarbamate) stationary phase (1999)
    Springer
    Chromatographia 49 (1999), S. 572-574 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Enantioseparations ; Amylose phenylcarbamate phase ; Glycidyl sulfides ; Glycidyl selenides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The resolution of the enantiomers of a series of glycidyl sulfides and glycidyl selenides has been examined on a chiral stationary phase prepared by coating aminopropylated silica gel with amylose tris-(phenylcarbamate). Most of the enantiomers of glycidyl monosulfides and monoselenides could be resolved satisfactorily but those of the disulfides could not. The effects of solute structure and of the concentration of 2-propanol in the mobile phase on retention and resolution were investigated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467762
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  • 152
    Digitale Medien
    Digitale Medien
    Determination of cisplatin, transplatin and amminetri-chloroplatinate by high performance liquid chromatography in one run using 4-methyl-2-thiouracil as derivatizing agent (1999)
    Springer
    Chromatographia 49 (1999), S. 562-566 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Cis-diamminedichloroplatinum (II) ; Transdiamminedichloroplatinum (II) ; Amminetri-chloroplatinate ; 4-Methyl-2-thiouracil
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary We have developed a simple, rapid, selective and sensitive method for detecting the antitumour agent cis-diamminedichloroplatinum (II) (cisplatin) (CDDP) and its toxic impurities trans-diamminedichloroplatinum (II) (transplatin) (TDDP) amminetri-chloroplatinat (ATCP) anion using HPLC in one run. By using 4-methyl-2-thiouracil (MTU) as a derivatizing agent, new compounds have been formed from the Pt compounds and separated on a μ-Bondapak C18 column with isocratic elution and detection at 315 nm. Reactant concentration, methanol content, pH and the reaction time on yield of derivatives were investigated and the optimum conditions for the detection response were defined. The derivatives of each of the three platinum compounds formed in an acetate buffer solution containing 40% (v/v) methanol and 0.9% KCl solution at pH 3.7 and ambient temperature were only stable for one hour.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467760
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  • 153
    Digitale Medien
    Digitale Medien
    Unexpected behavior of digoxin at elevated temperatures in reversed-phase liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 306-308 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Digoxin and digoxigenin ; Temperature effects ; Pore size effects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Increased retention of digoxin has been observed at elevated temperatures on both 10 nm and 30 nm porediamter, RP-18 packing. This result is the opposite effect compared with the decreased retention under the same conditions with digoxin aglycon-digoxigenin. Rotation around the C−C σ-bonds in the digoxin molecule is presumed; the rod-like molecules of the newlyobtained digoxin penetrate stationary phase pores more easily thus increasing retention.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467561
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  • 154
    Digitale Medien
    Digitale Medien
    Potentiometric detection of monovalent anions separated by ion chromatography using all solid-state contact PVC matrix membrane electrode (1999)
    Springer
    Chromatographia 49 (1999), S. 338-342 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Ion chromatography ; Monovalent anions determination ; Potentiometric detection ; Ion selective PVC-matrix electrode
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An all solid-state contact tubular PVC-matrix membrane electrode has been applied for potentiometric detection of inorganic and organic monovalent anions using phosphate and hydrogen phosphate eluents at low concentrations. This is a “monovalent detection method” as the selectivity of the electrode towards monovalent anions results in some other anions being undetected unless the concentration of those other anions is higher than 10−3 mol dm−3 in the sample solution injected. It takes only eight minutes to complete the separation with a good resolution. Theoretical and practical considerations are discussed, and in particular, sensitivity, linearity, detection limit and dynamic behaviour are presented. The use of an all solid-state contact bromide-selective electrode as a detector offers so far the best simultaneous sensitivity toward all anions when compared with other detection methods. Determination of Cl− and NO3 − ions in river, rain and drinking water samples without any further sample preconcentration has been successfully achieved. The detection limit is sub-ppb for most of anions in a 20 μL injection volume.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467567
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  • 155
    Digitale Medien
    Digitale Medien
    Normal-phase high performance liquid chromatographic separation and characterization of short- and long-chain triacylglycerols (1999)
    Springer
    Chromatographia 49 (1999), S. 363-368 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Evaporative light scatering detection ; APCI mass spectrometry ; Triacylglycerols
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Short- and long-chain triacylglycerols (SLCT) are a family of lipids prepared by chemical or enzymatic interesterification of triacetin, tripropionin and/or tributyrin, and long-chain (C16!18) hydrogenated vegetable oils. In this study, a normal-phase cyanopropyl high-performance liquid chromatographic (HPLC) method was developed for the separation and quantification of SLCT. The method is capable of separating SLCT mixtures, free fatty acids and the neutral lipid classes of saturated long-chain triacylglycerols, diacylglycerols and monoacylglycerols. To characterize the specific SLCT classes, a normal-phase HPLC procedure using a non-modified silica column was developed to separate the SLCT into individual isomers based on total carbon number and position of fatty acids on the glycerol backbone. Online coupling with a mass detector (LC/MS) allowed the identification of the individual triacylglycerol structures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467607
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  • 156
    Digitale Medien
    Digitale Medien
    Comparison of octadecyl bonded titania phases (1999)
    Springer
    Chromatographia 49 (1999), S. 424-430 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Octadecyl titania ; Surface hydrosilation ; Solid-state NMR C7
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The structure of a C18 phase based on titania (C18-A), synthesized by the method of solution polymerization, is investigated by diffuse reflectance infrared Fourier transform (DRIFT) and solid-state nuclear magnetic resonance (NMR) spectroscopy. The findings are compared with the results of a second C18 phase based on titania (C18-B) which was synthesized by the method of surface hydrosilation. The dynamic behavior of both phases is examined by1H MAS NMR detection of spinlattice relaxation times in the rotating frame (T1pH) and conventional spin-lattice relaxation times (T1). Due to a smaller ligand density, phase C18-A appears to be a somewhat more mobile than phase C18-B. The chromatographic capability of the phase C18-A is demonstrated by the separation of samples containing benzene derivates or anilines. The elution order is analogous to the phase C18-B, but for both test mixtures the polarity of the mobile phase has to be increased. Phase C18-A is classified as being polymeric by the Sander and Wise test, whereas phase C18-B shows intermediate retention behavior.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467618
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  • 157
    Digitale Medien
    Digitale Medien
    High performance liquid chromatography coupled to nuclear magnetic resonance spectroscopy and mass spectrometry applied to plant products: Identification of ecdysteroids fromSilene otites (1999)
    Springer
    Chromatographia 49 (1999), S. 374-378 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; NMR spectroscopy and mass spectrometry ; Plant products ; Silene otites
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary HPLC coupled in parallel to nuclear magnetic resonance (NMR) and mass spectrometry (MS) has been used to obtain1H NMR and mass spectra of a number of ecdysteroids present in an extract of the plantSilene otites. Reversed phase gradient chromatography was performed using a D20-acetonitrile-based solvent system. NMR and mass spectra were obtained for integristerone A, 20-hydroxyecdysone, 2-deoxy-20-hydroxyecdysone and 2-deoxyecdysone to provide structural confirmation using continuous and stopped flow HPLC-NMR. The combined HPLC-NMR-MS system described here provided a more comprehensive analysis of the ecdysteroids present in the extract than HPLC-NMR alone.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467609
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  • 158
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    Digitale Medien
    A system for predicting the retentions of O-alkyl, n-(1-methylthioethylideneamino) phosphoramidates on RP-HPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 444-448 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; O-alkyl, O-(1-methylthioethylideneamino) phosphoramidates ; Quantitative structure-retention relationship (QSRR) ; Reversed-phase LC
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary By using factor analysis, cluster analysis and multiple linear regression methods, two parameters, FHF and ECCR, were selected from eight solute-related structure parameters as showing the best correlation with retention data. The relationship between the retention data (k) and these two structure parameters were established for ten O-alkyl, O-(1-methylthioethylideneamino) phosphoramidate compounds under the experimental conditions studied. Retention data (k) for six other compounds that have a high correlation with structure parameters were predicted using these QSRR equations. The system was evaluated by comparing the experimentalk values with the predicted ones. Good agreement was obtained between the experimental and predictedk values.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02467621
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  • 159
    Digitale Medien
    Digitale Medien
    The effect of Li and La on NiO/Al2O3 catalyst for CH4/O2 to syngas reaction (1999)
    Springer
    Reaction kinetics and catalysis letters 68 (1999), S. 243-247 
    Details
    ISSN: 1588-2837
    Schlagwort(e): Methane partial oxidation ; nickel-based catalysts ; stability ; sintering and loss of nickel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The thermal stability and an 80 h life test over nickel-based catalysts for CH4/O2 to syngas reaction were investigated by flow-reactor, XPS, XRD and AAS analysis. The results indicate that the introduction of Li and La not only stabilized the support γ-Al2O3 phase, but also suppressed the sintering and loss of nickel, and in addition, enhanced the ability to suppress the carbon-deposition over NiO/Al2O3 during the high-temperature reaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02475508
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  • 160
    Digitale Medien
    Digitale Medien
    A Multiple-Shooting Technique for Optimal Control (1999)
    Springer
    Journal of optimization theory and applications 102 (1999), S. 299-313 
    Details
    ISSN: 1573-2878
    Schlagwort(e): Comparison of methods ; optimal control ; sensitivity ; shooting methods ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A new method for solving optimal control problems, here called multiple NOC shooting, is presented. It is developed from NOC shooting. It has some advantages over its parent and over multiple shooting, which are both successful, high-accuracy methods for optimal control. A comparison of the three methods is given, incorporating two examples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021728407151
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  • 161
    Digitale Medien
    Digitale Medien
    New Linear Program Performance Bounds for Queueing Networks (1999)
    Springer
    Journal of optimization theory and applications 100 (1999), S. 575-597 
    Details
    ISSN: 1573-2878
    Schlagwort(e): Queueing networks ; scheduling ; stability ; performance evaluation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We obtain new linear programs for bounding the performance and proving the stability of queueing networks. They exploit the key facts that the transition probabilities of queueing networks are shift invariant on the relative interiors of faces and the cost functions of interest are linear in the state. A systematic procedure for choosing different quadratic functions on the relative interiors of faces to serve as surrogates of the differential costs in an inequality relaxation of the average cost function leads to linear program bounds. These bounds are probably better than earlier known bounds. It is also shown how to incorporate additional features, such as the presence of virtual multi-server stations to further improve the bounds. The approach also extends to provide functional bounds valid for all arrival rates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022638523391
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  • 162
    Digitale Medien
    Digitale Medien
    Binding and Ionophoric Properties of Polythioamide Compounds. Ag(I) and Hg(II) Selectivities (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 277-289 
    Details
    ISSN: 1573-1111
    Schlagwort(e): complexes ; stability ; extraction ; transport ; tetrathiolactams
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The synthesis of tetrathiolactams and related di- and tetrathioamide compounds is described. The formation constants of their heavy-metal complexes are determined by using the strong UV absorption of the thioamide chromophore. Extraction and transport abilities of tetrathioamide ionophores show selectivities for Ag(I) and Hg(II) cations over alkali, alkaline-earth or other heavy metal cations including transition metals such as Co(II).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008093510236
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  • 163
    Digitale Medien
    Digitale Medien
    Polarographic Studies on Anion Coordination Chemistry. Host–Guest Interactions of Hexacyclen and Pentacyclen with Pyrophosphate, Selenite, Selenate, Molybdate and Tungstate Anions (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 455-464 
    Details
    ISSN: 1573-1111
    Schlagwort(e): hexacyclen ; pentacyclen ; anion complexes ; stoichiometry ; stability ; polarography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The complexation of protonated hexacyclen and pentacyclen with pyrophosphate, selenite, selenate, molybdate and tungstate anions was studied by differential pulse polarography at 25 °C. The stoichiometry and stability of the resulting anion complexes were evaluated from the pH and concentration-dependence of the peak potentials, respectively. The results established 1 : 1 anion receptor complexation in all cases. In the case of all anions studied, hexacyclen was found to form more stable anion complexes than pentacyclen. The fact that the anion-receptor complexation depends on the structural features of both the anions and the macrocycles used is indicative of a steric controlled interaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008050909119
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  • 164
    Digitale Medien
    Digitale Medien
    Closed-Loop Stability Monitoring of Axial Flow Compression Systems (1999)
    Springer
    Nonlinear dynamics 20 (1999), S. 181-196 
    Details
    ISSN: 1573-269X
    Schlagwort(e): monitoring ; stability ; compressors ; axial flow compressors ; stall ; surge ; bifurcation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Monitoring systems are proposed for the detection of incipient instability in axial flow compression systems. The work employs generic features associated with the response to noise inputs of systems bordering on instability. Based on these generic features, a closed-loop monitoring system is proposed. Numerical simulation is used to illustrate the operation of the proposed closed-loop monitoring system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004596213600
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  • 165
    Digitale Medien
    Digitale Medien
    On the Reconstitution Problem in the Multiple Time-Scale Method (1999)
    Springer
    Nonlinear dynamics 19 (1999), S. 135-158 
    Details
    ISSN: 1573-269X
    Schlagwort(e): perturbation methods ; higher-order approximations ; dynamical systems ; codimension ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Higher-order multiple-scale methods for general multiparameter mechanical systems are studied. The role played by the control and imperfection parameters in deriving the perturbative equations is highlighted. The definition of the codimension of the problem, borrowed from the bifurcation theory, is extended to general systems, excited either externally or parametrically. The concept of a reduced dynamical system is then invoked. Different approaches followed in the literature to deal with reconstituted amplitude equations are discussed, both in the search for steady-state solutions and in the analysis of stability. Four classes of methods are considered, based on the consistency or inconsistency of the approach, and on the completeness or incompleteness of the terms retained in the analysis. The four methods are critically compared and general conclusions drawn. Finally, three examples are illustrated to corroborate the findings and to show the quantitative differences between the various approaches.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008330423238
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  • 166
    Digitale Medien
    Digitale Medien
    Articulated Pipes Conveying Fluid Pulsating with High Frequency (1999)
    Springer
    Nonlinear dynamics 19 (1999), S. 173-193 
    Details
    ISSN: 1573-269X
    Schlagwort(e): fluid conveying pipes ; high-frequency pulsating fluid ; separation of slow and fast motion ; stability ; nonlinear dynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Stability and nonlinear dynamics of two articulated pipes conveying fluid with a high-frequency pulsating component is investigated. The non-autonomous model equations are converted into autonomous equations by approximating the fast excitation terms with slowly varying terms. The downward hanging pipe position will lose stability if the mean flow speed exceeds a certain critical value. Adding a pulsating component to the fluid flow is shown to stabilize the hanging position for high values of the ratio between fluid and pipe-mass, and to marginally destabilize this position for low ratios. An approximate nonlinear solution for small-amplitude flutter oscillations is obtained using a fifth-order multiple scales perturbation method, and large-amplitude oscillations are examined by numerical integration of the autonomous model equations, using a path-following algorithm. The pulsating fluid component is shown to affect the nonlinear behavior of the system, e.g. bifurcation types can change from supercritical to subcritical, creating several coexisting stable solutions and also anti-symmetrical flutter may appear.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008326812760
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  • 167
    Digitale Medien
    Digitale Medien
    Double Hopf Bifurcations and Chaos of a Nonlinear Vibration System (1999)
    Springer
    Nonlinear dynamics 19 (1999), S. 313-332 
    Details
    ISSN: 1573-269X
    Schlagwort(e): double pendulum system ; double Hopf bifurcation ; stability ; chaos
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A double pendulum system is studied for analyzing the dynamic behaviour near a critical point characterized by nonsemisimple 1:1 resonance. Based on normal form theory, it is shown that two phase-locked periodic solutions may bifurcate from an initial equilibrium, one of them is unstable and the other may be stable for certain values of parameters. A secondary bifurcation from the stable periodic solution yields a family of quasi-periodic solutions lying on a two-dimensional torus. Further cascading bifurcations from the quasi-periodic motions lead to two chaoses via a period-doubling route. It is shown that all the solutions and chaotic motions are obtained under positive damping.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008347523779
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  • 168
    Digitale Medien
    Digitale Medien
    Preventing buoyancy-driven flows of two Bingham fluids in a closed pipe – Fluid rheology design for oilfield plug cementing (1999)
    Springer
    Journal of engineering mathematics 36 (1999), S. 327-348 
    Details
    ISSN: 1573-2703
    Schlagwort(e): Bingham fluids ; multi-layer flow ; no-flow/yield criteria ; stability ; variational methods.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Abstract The mechanically unstable situation of a heavy Bingham fluid resting on top of a light Bingham fluid in an inclined closed-ended pipe can be stabilised if the fluids have sufficiently large yield stresses. This paper focuses on determining the yield stresses that are sufficient to keep the fluids statically stable for a given fluid density difference, pipe diameter and pipe inclination. The results are applicable to a broad class of practically observable flows. This situation provides an idealised model for the oilfield process of plug cementing.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004511113745
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  • 169
    Digitale Medien
    Digitale Medien
    A Multibody Motion Stability Analysis (1999)
    Springer
    Multibody system dynamics 3 (1999), S. 287-299 
    Details
    ISSN: 1573-272X
    Schlagwort(e): multibody dynamics ; symbol manipulation ; linearization ; stability ; Floquet theory
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract It is shown that use of AUTOLEV, a symbol manipulation computer program for mechanics analyses, can greatly facilitate the stability analysis of motions of multibody systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009882505218
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  • 170
    Digitale Medien
    Digitale Medien
    The onset of steady Bénard-Marangoni convection in a two-layer system of conducting fluid in the presence of a uniform magnetic field (1999)
    Springer
    Journal of engineering mathematics 35 (1999), S. 385-404 
    Details
    ISSN: 1573-2703
    Schlagwort(e): Bénard-Marangini convection ; conducting fluids ; stability ; two-layer system.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Abstract The onset of steady Bénard-Marangoni convection in two horizontal liquid layers of electrically conducting immiscible fluids subjected to a uniform vertical magnetic field and temperature gradient is analysed by means of a combination of analytical and numerical techniques. The free surface can be either deformable or nondeformable and the interface between the fluids is always assumed to be flat. The effect of the lower layer on the critical values of Rayleigh, Marangoni and wave numbers for the onset of steady convection is investigated. When the free surface is nondeformable, the critical parameters for the onset of pure Marangoni convection are increased, whereas for the onset of pure Bénard convection they are decreased compared to the single-layer model. The results for a single-layer and for two-layers are qualitatively similar for Bénard-Marangoni convection when the free surface is deformable. All disturbances can be stabilized with sufficiently strong magnetic field when the free surface is nondeformable. If the free surface is allowed to deform and gravity waves are excluded, then the layers are always unstable to disturbances with sufficiently small wave number with magnetic field. Inclusion of gravity waves has a stabilizing effect on certain disturbances of small wave number in the presence of weak or moderate magnetic field.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004439231890
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  • 171
    Digitale Medien
    Digitale Medien
    Dynamics of Oscillators with Strongly Nonlinear Asymmetric Damping (1999)
    Springer
    Nonlinear dynamics 20 (1999), S. 221-246 
    Details
    ISSN: 1573-269X
    Schlagwort(e): Coulomb friction ; asymmetric damping ; exact periodic motions ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Dynamics of a class of strongly nonlinear single degree of freedom oscillators is investigated. Their common characteristic is that they possess piecewise linear damping properties, which can be expressed in a general asymmetric form. More specifically, the damping coefficient and a constant parameter appearing in the equation of motion are functions of the velocity direction. This class of oscillators is quite general and includes other important categories of mechanical systems as special cases, like systems with Coulomb friction. First, an analysis is presented for locating directly exact periodic responses of these oscillators to harmonic excitation. Due to the presence of dry friction, these responses may involve intervals where the oscillator is stuck temporarily. Then, an appropriate stability analysis is also presented together with some quite general bifurcation results. In the second part of the work, this analysis is applied to several example systems with piecewise linear damping, in order to reveal the most important aspects of their dynamics. Initially, systems with symmetric characteristics are examined, for which the periodic response is found to be symmetric or asymmetric. Then, dynamical systems with asymmetric damping characteristics are also examined. In all cases, emphasis is placed on investigating the low forcing frequency ranges, where interesting dynamics is noticed. The analytical predictions are complemented with results obtained by proper integration of the equation of motion, which among other responses reveal the existence of quasiperiodic, chaotic and unbounded motions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008398813070
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  • 172
    Digitale Medien
    Digitale Medien
    Reachability of locational Nash equilibria (1998)
    Springer
    OR spectrum 20 (1998), S. 101-107 
    Details
    ISSN: 1436-6304
    Schlagwort(e): Competitive location model ; Nash equilibria ; stability ; reachability ; Wettbewerbsmodelle in der Standorttheorie ; Nash Gleichgewicht ; Stabilität ; Erreichbarkeit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Wirtschaftswissenschaften
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In der Arbeit werden die Standorte von Duopolisten in einem Baum untersucht. Unter der Annahme festgesetzter Preise werden notwendige und hinreichende Bedingungen für Nash Gleichgewichte für Standorte auf Bäumen hergeleitet. Unter Verwendung dieser Bedingungen wird dann gezeigt, daß — angenommen Nash Gleichgewichte existieren — diese in einem wiederholt angewandten sequentiellen Standortfindungsprozeß, in dem beide Duopolisten als Zielfunktion kurzfristige Gewinnmaximierung haben, auch erreicht werden.
    Notizen: Abstract This paper examines the location of duopolists on a tree. Given parametric prices, we first delineate necessary and sufficient conditions for locational Nash equilibria on trees. Given these conditions, we then show that Nash equilibria, provided they exist, can be reached in a repeated sequential relocation process in which both facilities follow short-term profit maximization objectives.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01539861
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  • 173
    Digitale Medien
    Digitale Medien
    Reachability of locational Nash equilibria (1998)
    Springer
    OR spectrum 20 (1998), S. 101-107 
    Details
    ISSN: 1436-6304
    Schlagwort(e): Key words: Competitive location model ; Nash equilibria ; stability ; reachability ; Schlüsselwörter: Wettbewerbsmodelle in der Standorttheorie ; Nash Gleichgewicht ; Stabilität ; Erreichbarkeit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Wirtschaftswissenschaften
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung. In der Arbeit werden die Standorte von Duopolisten in einem Baum untersucht. Unter der Annahme festgesetzter Preise werden notwendige und hinreichende Bedingungen für Nash Gleichgewichte für Standorte auf Bäumen hergeleitet. Unter Verwendung dieser Bedingungen wird dann gezeigt, daß– angenommen Nash Gleichgewichte existieren – diese in einem wiederholt angewandten sequentiellen Standortfindungsprozeß, in dem beide Duopolisten als Zielfunktion kurzfristige Gewinnmaximierung haben, auch erreicht werden. “Equilibrium is a place in heaven, but how do we get there from here?”
    Notizen: Abstract. This paper examines the location of duopolists on a tree. Given parametric prices, we first delineate necessary and sufficient conditions for locational Nash equilibria on trees. Given these conditions, we then show that Nash equilibria, provided they exist, can be reached in a repeated sequential relocation process in which both facilities follow short-term profit maximization objectives.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002910050058
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  • 174
    Digitale Medien
    Digitale Medien
    Money demand stability: Evidence from Spain (1998)
    Springer
    Empirical economics 23 (1998), S. 387-400 
    Details
    ISSN: 1435-8921
    Schlagwort(e): Key words: Money demand ; cointegration ; stability ; regime shift ; JEL classification: E41 ; C22
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract. Using several tests for structural stability in regressions with I(1) variables and for the existence of cointegration in models with regime shifts, the empirical evidence on the existence of a structural break in the Spanish long-run demand for broad money (ALP2) is analysed.  The results indicate that shifts affecting the demand for ALP2 in recent years have substantially altered its long-run properties. As to the cause of this structural break, emphasis is placed on the role played by the increasing openness of the Spanish financial system to international markets as obstacles to free capital movements have progressively disappeared.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001810050027
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  • 175
    Digitale Medien
    Digitale Medien
    Discrete stability of the Differential System Method evaluated with geostatistical techniques (1998)
    Springer
    Stochastic environmental research and risk assessment 12 (1998), S. 191-204 
    Details
    ISSN: 1436-3259
    Schlagwort(e): Keywords: groundwater flow ; inverse problems ; stability ; geostatistical interpolation ; kriging.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract The Differential System Method (DSM) permits identification of the physical parameters of finite-difference groundwater flow models in a confined aquifer when piezometric head and source terms are known at each point of the finite-difference lattice for at least two independent flow situations for which the hydraulic gradients are not parallel. Since piezometric head data are usually few and sparse, interpolation of the measured data onto a regular grid can be performed with geostatistical techniques. We apply kriging to the sparse data of a synthetic aquifer to evaluate the stability of the DSM with respect to uncorrelated measurement errors and interpolation errors. The numerical results show that the DSM is stable.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004770050017
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  • 176
    Digitale Medien
    Digitale Medien
    A Two-Patch Model of Gambian Sleeping Sickness: Application to Vector Control Strategies in a Village and Plantations (1998)
    Springer
    Acta biotheoretica 46 (1998), S. 207-222 
    Details
    ISSN: 1572-8358
    Schlagwort(e): Epidemiology ; sleeping sickness ; vector controls ; differential equations ; spacialization ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A compartmental model is described for the spread of Gambian sleeping sickness in a spatially heterogeneous environment in which vector and human populations migrate between two "patches": the village and the plantations. The number of equilibrium points depends on two "summary parameters": gr the proportion removed among human infectives, and R0, the basic reproduction number. The origin is stable for R0 〈1 and unstable for R0 〉1. Control strategies are assessed by studying the mix of vector control between the two patches that bring R0 below 1. The results demonstrate the importance of vector control in the plantations. For example if 20 percent of flies are in the village and the blood meal rate in the village is 10 percent, then a 20 percent added vector mortality in the village must be combined with a 9 percent added mortality in the plantations in order to bring R0 below 1. The results are quite insentive to the blood meal rate in the village. Optimal strategies (that minimize the total number of flies trapped in both patches) are briefly discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1001776926167
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  • 177
    Digitale Medien
    Digitale Medien
    Stability and Instability of Fourth-Order Solitary Waves (1998)
    Springer
    Journal of dynamics and differential equations 10 (1998), S. 151-188 
    Details
    ISSN: 1572-9222
    Schlagwort(e): Fourth-order solitary waves ; stability ; instability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We study ground-state traveling wave solutions of a fourth-order wave equation. We find conditions on the speed of the waves which imply stability and instability of the solitary waves. The analysis depends on the variational characterization of the ground states rather than information about the linearized operator.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022644629950
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  • 178
    Digitale Medien
    Digitale Medien
    Some Results on Stability of Retarded Functional Differential Equations Using Dichotomic Map Techniques (1998)
    Springer
    Positivity 2 (1998), S. 229-238 
    Details
    ISSN: 1572-9281
    Schlagwort(e): asymptotic stability ; dichotomic maps ; retarded functional differential equation ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract This paper deals with the study of the stability of nonautonomous retarded functional differential equations using the theory of dichotomic maps. After some preliminaries, we prove the theorems on simple and asymptotic stability. Some examples are given to illustrate the application of the method. Main results about asymptotic stability of the equation $$x'(t) = - b(t)x(t - r)$$ and of itsnonlinear generalization $$x'(t) = b(t)f(x(t - r))$$ are established.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009742807025
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  • 179
    Digitale Medien
    Digitale Medien
    On the stability of a partially accessible multi‐station queue with state‐dependent routing (1998)
    Springer
    Queueing systems 29 (1998), S. 55-73 
    Details
    ISSN: 1572-9443
    Schlagwort(e): multi‐server queue ; customer class ; state‐dependent routing ; stability ; Markov chain ; fluid limit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We consider a multi‐station queue with a multi‐class input process when any station is available for the service of only some (not all) customer classes. Upon arrival, any customer may choose one of its accessible stations according to some state‐dependent policy. We obtain simple stability criteria for this model in two particular cases when service rates are either station‐ or class‐independent. Then, we study a two‐station queue under general assumptions on service rates. Our proofs are based on the fluid approximation approach.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019175812444
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  • 180
    Digitale Medien
    Digitale Medien
    On the guaranteed throughput and efficiency of closed re-entrant lines (1998)
    Springer
    Queueing systems 28 (1998), S. 33-54 
    Details
    ISSN: 1572-9443
    Schlagwort(e): queueing networks ; throughput ; closed networks ; efficiency ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A closed network is said to be “guaranteed efficient” if the throughput converges under all non-idling policies to the capacity of the bottlenecks in the network, as the number of trapped customers increases to infinity. We obtain a necessary condition for guaranteed efficiency of closed re-entrant lines. For balanced two-station systems, this necessary condition is almost sufficient, differing from it only by the strictness of an inequality. This near characterization is obtained by studying a special type of virtual station called “alternating visit virtual station”. These special virtual stations allow us to relate the necessary condition to certain indices arising in heavy traffic studies using a Brownian network approximation, as well as to certain policies proposed as being extremal with respect to the asymptotic loss in the throughput. Using the near characterization of guaranteed efficiency we also answer the often pondered question of whether an open network or its closed counterpart has greater throughput - the answer is that neither can assure a greater guaranteed throughput.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019199022922
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  • 181
    Digitale Medien
    Digitale Medien
    Stability and performance analysis of rate-based feedback flow controlled ATM networks (1998)
    Springer
    Queueing systems 29 (1998), S. 129-159 
    Details
    ISSN: 1572-9443
    Schlagwort(e): rate-based feedback control ; ATM networks ; stability ; optimal algorithms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Motivated by ABR class of service in ATM networks, we study a continuous time queueing system with a feedback control of the arrival rate of some of the sources. The feedback about the queue length or the total workload is provided at regular intervals (variations on it, especially the traffic management specification TM 4.0, are also considered). The propagation delays can be nonnegligible. For a general class of feedback algorithms, we obtain the stability of the system in the presence of one or more bottleneck nodes in the virtual circuit. Our system is general enough that it can be useful to study feedback control in other network protocols. We also obtain rates of convergence to the stationary distributions and finiteness of moments. For the single botterneck case, we provide algorithms to compute the stationary distributions and the moments of the sojourn times in different sets of states. We also show analytically (by showing continuity of stationary distributions and moments) that for small propagation delays, we can provide feedback algorithms which have higher mean throughput, lower probability of overflow and lower delay jitter than any open loop policy. Finally these results are supplemented by some computational results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019127929282
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  • 182
    Digitale Medien
    Digitale Medien
    Multiwavelet approximation methods for pseudodifferential equations on curves. Stability and convergence analysis (1998)
    Springer
    Advances in computational mathematics 9 (1998), S. 145-171 
    Details
    ISSN: 1572-9044
    Schlagwort(e): periodic pseudodifferential equations ; multiwavelets ; splines with multiple knots ; generalized Galerkin–Petrov schemes ; boundary element methods ; error analysis ; stability ; Strang–Fix condition ; 65J10 ; 65N30 ; 65N35 ; 65R20 ; 47G30 ; 45P05 ; 41A25 ; 41A30 ; 41A15
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We develop a stability and convergence analysis of Galerkin–Petrov schemes based on a general setting of multiresolution generated by several refinable functions for the numerical solution of pseudodifferential equations on smooth closed curves. Particular realizations of such a multiresolution analysis are trial spaces generated by biorthogonal wavelets or by splines with multiple knots. The main result presents necessary and sufficient conditions for the stability of the numerical method in terms of the principal symbol of the pseudodifferential operator and the Fourier transforms of the generating multiscaling functions as well as of the test functionals. Moreover, optimal convergence rates for the approximate solutions in a range of Sobolev spaces are established.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018977120831
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  • 183
    Digitale Medien
    Digitale Medien
    Nonlinear Stability of the Lagrangian Libration Points in the Chermnykh Problem (1998)
    Springer
    Celestial mechanics and dynamical astronomy 70 (1998), S. 41-58 
    Details
    ISSN: 1572-9478
    Schlagwort(e): three-body problem ; libration points ; stability ; normal forms.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In this paper we consider the problem of motion of an infinitesimal point mass in the gravity field of an uniformly rotating dumb-bell. The aim of our study is to investigate Liapunov stability of Lagrangian libration points of this problem. We analyze the stability of libration points in the whole range of parameters ω, μ of the problem. In particular, we consider all resonance cases when the order of resonance is not greater than five.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008250207046
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  • 184
    Digitale Medien
    Digitale Medien
    On a spherical integral transformation and sections of star bodies (1998)
    Springer
    Monatshefte für Mathematik 126 (1998), S. 117-124 
    Details
    ISSN: 1436-5081
    Schlagwort(e): 52A20 ; 52A22 ; star bodies ; spherical integral transformations ; convex bodies ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract LetK be ad-dimensional star body (with respect to the origino). It is known that the (d−1)-dimensional volume of the intersections ofK with the hyperplanes througho does not uniquely determineK. Uniqueness can only be achieved under additional assumptions, such as central symmetry. Here it is pointed out that if one uses, instead of intersections by hyperplanes, intersections by half-planes that containo on the boundary, then, without any additional assumptions, the volume of these intersections determinesK uniquely. This assertion, and more general results of this kind, together with stability estimates, are obtained from uniqueness results and estimates concerning a particular spherical integral transformation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01473582
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  • 185
    Digitale Medien
    Digitale Medien
    Ethene hydroformylation on Co/SiO2 catalysts (1998)
    Springer
    Catalysis letters 53 (1998), S. 97-101 
    Details
    ISSN: 1572-879X
    Schlagwort(e): ethene hydroformylation ; heterogeneous catalysts ; cobalt catalysts ; gas‐phase deposition ; dispersion ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The results from ethene hydroformylation at 173°C showed that a Co(acac)3/SiO2 catalyst prepared from Co(acac)3 precursor by gas‐phase deposition was three times as active as a catalyst prepared by impregnation from cobalt nitrate, but oxo‐selectivities were similar. The high propanal selectivities on the Co(acac)3/SiO2 seem to be related to the presence of highly dispersed active sites favouring CO insertion. As dispersion is decreased from 23 to 8% due to increasing metal content (from 5 to 16 wt%), oxo‐selectivity decreased from 39 to 25%. The activity of Co(acac)3/SiO2 remained unchanged during 68 h on stream. The gas‐phase deposition technique described here is a promising method for the preparation of active, selective and stable heterogeneous hydroformylation catalysts.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019053805618
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  • 186
    Digitale Medien
    Digitale Medien
    Preparation of model catalysts by laser interference nanolithography followed by metal cluster deposition (1998)
    Springer
    Catalysis letters 56 (1998), S. 1-6 
    Details
    ISSN: 1572-879X
    Schlagwort(e): nanolithography ; model catalyst ; palladium ; copper ; stability ; spin-coating ; SEM ; AFM ; XPS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Metal clusters arranged on nanostructured oxidized silicon wafers are presented as new model catalyst systems. A photoresist layer spun on top of a wafer was patterned by laser interference exposure. The grid obtained after removing the exposed parts of the resist is used as an etching mask. Hollows with diameters of 300 nm and depths between 50 and 60 nm were etched into the oxide layer using wet chemical methods. Two methods were applied to deposit metal clusters (Pd or Cu) in a defined way within the hollows. The particles ranged from 10 to 50 nm in height and from 80 to 200 nm in diameter. The model catalyst systems were characterized by atomic force microscopy and X-ray photoelectron spectroscopy. The method presented here allows us to produce 4 inch wafers that are covered completely by nanometer-sized structures in a reasonable period of time.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019080222823
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  • 187
    Digitale Medien
    Digitale Medien
    Autonomous Intelligent Cruise Control with Actuator Delays (1998)
    Springer
    Journal of intelligent and robotic systems 23 (1998), S. 27-43 
    Details
    ISSN: 1573-0409
    Schlagwort(e): autonomous control ; actuator delays ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract In this paper, we consider the control design problem of vehicle following systems with actuator delays. An upper bound for the time delays is first constructed to guarantee the vehicle stability. Second, sufficient conditions are presented to avoid slinky-effects in the vehicle following. Next, zero steady state achieved by the proposed controller is proven. Finally, simulations are given to examine our claims.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007946007601
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  • 188
    Digitale Medien
    Digitale Medien
    Renormalization of the Chapman–Enskog Expansion: Isothermal Fluid Flow and Rosenau Saturation (1998)
    Springer
    Journal of statistical physics 91 (1998), S. 285-305 
    Details
    ISSN: 1572-9613
    Schlagwort(e): Chapman–Enskog expansion ; Burnett equation ; Boltzmann equation ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract This paper continues the author's study of procedures for rewriting the well-known Chapman–Enskog expansion used in the kinetic theory of gases. The usual Chapman–Enskog expansion, when used in isothermal fluid motion, will introduce nonlinear instability at super-Burnett order O(ε3) truncation. The procedure given here eliminates the truncation instability and produces the desired dissipation inequality.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1023048322851
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  • 189
    Digitale Medien
    Digitale Medien
    Robust Regulator for Flexible-Joint Robots Using Integrator Backstepping (1998)
    Springer
    Journal of intelligent and robotic systems 22 (1998), S. 23-38 
    Details
    ISSN: 1573-0409
    Schlagwort(e): robot dynamic model ; stiffness matrix ; constant disturbance ; integrator backstepping ; Liapunov functions ; Barbalat lemma ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract A robust regulator for flexible-joint robots is proposed, which yields constant torque disturbance rejection acting on the links. The design uses the integrator backstepping technique [4,5] to cancel nonlinearities and disturbance not in the range space of the control. Stability of the closed loop system is shown using iterative Liapunov functions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007947416837
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  • 190
    Digitale Medien
    Digitale Medien
    Morphological and physical characterization of the capsular layer of Vibrio cholerae O139 (1998)
    Springer
    Archives of microbiology 170 (1998), S. 339-344 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Key wordsV. cholerae O139 ; Lipopolysaccharide ; Electron microscopy ; Freeze-substitution technique ; Capsule
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The morphological and physical characteristics of the capsule of Vibrio cholerae O139 were examined. An electron microscopic study using the freeze-substitution technique showed that all of the V. cholerae strains of the O139 serogroup examined have a very thin fibrous layer on the outside of the outer membrane. In contrast, the mutants of strain O139, strain MO10T4 (which lacks capsule synthesis), and strain Bengal-2R1 (which fails to synthesize both the capsule and the O-antigen of lipopolysaccharide) were all found to have lost the surface layer. In addition, the capsule layer could also not be observed on the surface of V. cholerae strain O1. To determine the biological characteristics of the capsule of strains of the O139 serogroup, we investigated the serum killing activity and bacterial phagocytosis by polymorphonuclear leukocytes. The O139 strains were more resistant to the serum killing activity than were the V. cholerae O1 strain and the O139 mutant strains, thus suggesting that the existence of the capsule gave a serum-resistant character to the O139 strains. The surface character of the O139 strains had the same hydrophobic character as did that of the O139 mutant strains and the O1 strain. In addition, all the V. cholerae O1 and O139 strains examined, including the mutant strains, were effectively ingested by the human polymorphonuclear leukocytes. The number of ingested bacteria was not significantly different among the strains, and the ingestion of the acapsular O139 mutants thus showed that the capsule does not play an antiphagocytic role. These data suggest that the capsule of V. cholerae O139 has a physiological function different from that of the ordinal hydrophilic capsule that is found in invasive bacteria such as Klebsiella pneumoniae.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002030050651
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  • 191
    Digitale Medien
    Digitale Medien
    Phylogenetic affiliation and ultrastructure of uncultured magnetic bacteria with unusually large magnetosomes (1998)
    Springer
    Archives of microbiology 169 (1998), S. 136-147 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Key words Magnetic bacteria ; Biomineralization ; Magnetite ; 16S rRNA ; In situ hybridization ; Ultrastructure ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Natural enrichments of magnetic bacteria from the Itaipu lagoon near Rio de Janeiro were dominated by coccoid-to-ovoid morphotypes that produced unusually large magnetosomes. To determine the phylogenetic position of these unusual microorganisms, 16S rRNA genes were retrieved from bacteria magnetically separated from sediment of the Itaipu lagoon by in vitro amplification and cloning of PCR products into a plasmid vector. Partial sequencing of the obtained clones revealed two clusters of closely related sequences affiliated to a distinct lineage consisting exclusively of magnetic bacteria within the α-subclass of Proteobacteria. For a detailed phylogenetic analysis, several almost complete sequences of the 16S rRNA genes were determined. One representative clone of each cluster provided a PCR template for the in vitro transcription of group-specific polynucleotide probes complementary to a variable region of the 16S rRNA molecule. At least three different morphotypes of magnetic bacteria were reliably identified by post-embedding hybridization of ultra-thin sections. Electron microscopic analyses of hybridized cells enabled for the first time a detailed description of the morphological variety and ultrastructure of phylogenetically identified, uncultured magnetic bacteria. Two distinct coccoid bacteria were identified by the transcript probe complementary to the 16S rRNA sequence mabrj12, whereas the probe complementary to the sequence mabrj58 allowed the identification of an ovoid morphotype that displayed magnetosomes with the largest volumes observed to date.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002030050553
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  • 192
    Digitale Medien
    Digitale Medien
    X-ray diffractometry and electron microscopy of DNA from Bacillus subtilis bound on clay minerals (1998)
    Springer
    Sciences of soils 3 (1998), S. 1-10 
    Details
    ISSN: 1432-9492
    Schlagwort(e): Transformation ; Clay-DNA complexes ; Nucleases ; X-ray diffraction ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract DNA bound on clay minerals, sand, and humic acids has been shown, both in vitro and in situ, to be capable of transforming bacteria and to resist degradation by nucleases, which could result in the crypticity of genes in soil and other natural habitats. To determine where DNA is bound on clay minerals, which may help to explain how bound DNA becomes resistant to degradation by nucleases but retains the ability to transform competent cells, chromosomal DNA from Bacillus subtilis bound on montmorillonite (M) and kaolinite (K) was examined by X-ray diffractometry and transmission and scanning electron microscopy. X-ray diffraction analysis showed that the basal spacings of M and K were not altered, indicating that this DNA did not significantly intercalate the clays. Scanning and transmission electron microscopy showed that the binding of this DNA was primarily on the edges of M and K, although some binding was also apparent on the planar surfaces. Based on the results of these studies, it is postulated that: 1.extension from the edges of the clays enables the unbound end of DNA to interact with receptor sites on competent cells and result in their transformation; and 2.binding on clays alters the electron distribution and/or conformation of DNA, which reduces its hydrolysis by nucleases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s10112-998-0001-3
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  • 193
    Digitale Medien
    Digitale Medien
    Resilience in the Dynamics of Economy-Environment Systems (1998)
    Springer
    Environmental and resource economics 11 (1998), S. 503-520 
    Details
    ISSN: 1573-1502
    Schlagwort(e): biodiversity ; dynamics ; resilience ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Wirtschaftswissenschaften
    Notizen: Abstract The ecological concept of resilience has begun to inform analysis of change in economy-environment systems. The linkages between resilience and the stability of dynamical systems are discussed, along with its role in understanding of the evolution of such systems. Particular linkages discussed include those between resilience, biodiversity and the sustainability of alternative states. Recent developments in modelling the resilience of joint economy-environment systems suggest the advantages of analysing change in the system as a Markov process, the transition probabilities between states offering a natural measure of the resilience of the system in such states. It is argued that this ‘emergent property’ of the collaboration between ecology and economics has far-reaching implications for the way we think about, model and manage the environmental sustainability of economic development.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008255614276
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  • 194
    Digitale Medien
    Digitale Medien
    Distribution and submicroscopic immunogold localization of cellular prion protein (PrPc) in extracerebral tissues (1998)
    Springer
    Cell & tissue research 292 (1998), S. 77-84 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Prion protein (PrPc) ; Electron microscopy ; Secretory granules ; Membrane ; Extracerebral tissues ; Hamster ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  In transmissible spongiform encephalopathies (TSE), such as scrapie in animals and Creutzfeldt-Jakob disease in humans, the central event is the conversion of a host-encoded amyloidogenic protein (PrPc) into an abnormal isoform (PrPsc) that accumulates as amyloid in TSE brain. PrPc is a membrane sialoglycoprotein synthesized in the central nervous system and elsewhere. We have examined the ultrastructural localization of PrPc in numerous hamster and some human extracerebral tissues, by means of a post-embedding electron-microscopic method combined with immunogold labeling. In stomach, intestine, lung, and kidney from hamsters, and in stomach, kidney, and spleen from humans, immunogold labeling specific for PrPc is observed on various cellular substructures related to secretory pathways: Golgi apparatus, secretory globules, and plasma membrane. In mucous epithelial cells of stomach and intestine, PrPc appears to be concentrated in secretory globules, suggesting a role for PrPc in the secretory function of the digestive tract. The secretory aspect of PrPc may be a key to understanding the physiopathological mechanisms underlying TSE.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051036
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  • 195
    Digitale Medien
    Digitale Medien
    A role for vesicles in human basophil secretion (1998)
    Springer
    Cell & tissue research 293 (1998), S. 1-22 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Piecemeal degranulation ; Histamine ; Charcot-Leyden crystal protein ; Anaphylactic degranulation ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The evidence for vesicular transport as a mechanism for secretion by human basophils is reviewed. Initially, direct electron-microscopic inspection of experimentally produced and sequentially biopsied contact allergy skin lesions revealed a unique form of secretion termed piecemeal degranulation, characterized by the slow emptying of secretory granule contents (with retention of empty containers) in the absence of extrusion of entire granules. Budding of small vesicles to/from secretory granules was observed, and cytoplasmic vesicles were abundant. A generalized degranulation model was proposed to unify classical regulated secretion and this new form of secretion. Investigation of the mechanism(s) of secretion from human basophils required the development of numerous tools and resources. Chief among these were: (a) isolation and purification of circulating basophils; (b) identification of specific growth factors to increase the supply of this rare granulocyte; (c) understanding of secretogogue mechanisms and reliable analyses of secreted basophil products; and (d) development of ultrastructural preparations allowing imaging of small vesicles and quantifiable small electron-dense tags for granule materials in small vesicles. Applications of these tools to well-defined models of basophil secretion have established a role for vesicles as a mechanism for effecting secretion of histamine and the Charcot-Leyden crystal protein from activated human basophils.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051093
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  • 196
    Digitale Medien
    Digitale Medien
    Maturation of rat dendritic cells during intrahepatic translocation evaluated using monoclonal antibodies and electron microscopy (1998)
    Springer
    Cell & tissue research 294 (1998), S. 503-514 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Dendritic cells ; Maturation ; Intrahepatic translocation ; Immunohistochemistry ; Electron microscopy ; Rat (Wistar)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Specific populations of hepatic sinusoidal cells were stained with monoclonal antibodies that recognize monocytes/macrophages (ED1), tissue macrophages (Kupffer cells) (ED2), MHC class II (Ia) antigen (MRC OX6), and dendritic cells/γ,δ T-cells (MRC OX62) and analyzed by light and electron microscopy. The majority of ED1+ and/or ED2+ cells were localized to the hepatic parenchyma, whereas OX6+ and/or OX62+ cells were more densely distributed within Glisson’s sheath than in the hepatic parenchyma. Double-immunoperoxidase staining of normal liver for ED1, ED2, and OX6 identified dendritic cells (DC) of two different phenotypes, ED1+ED2–OX6+ and ED1–ED2–OX6+. DC can be classified into three different types based on ultrastructural characteristics. The first type (type I) is characterized by one or more long cytoplasmic processes and a well-developed lysosomal system. The second type (type II) has an inconspicuous lysosomal system, abundant hyaloplasm, and characteristic short cytoplasmic processes. The third type (type I–II) has cytologic features intermediate between those of type I and type II DC. At the electron-microscopic level, these three cell types are found in the sinusoidal lumen, whereas the majority of type II DC are located in the space of Disse and Glisson’s sheath. Furthermore, some OX6-labeled elongated DC appeared to traverse the lumen of sinusoids through endothelial pores to enter the space of Disse. One hour after intravenous injection of latex particles (0.81 μm in diameter), numerous latex-laden dendritic cells (ED1+OX6+, type I and type I–II) were detected in the lumen of hepatic sinusoids, but not in the space of Disse or Glisson’s sheath. These findings suggest that normal rat liver contains resident dendritic cells which downregulate phagocytic activity and mature into potent accessory cells during migration from the portal vein toward the central vein. These DC then traverse the sinusoidal lumen to the hepatic lymph system via the space of Disse.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051201
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  • 197
    Digitale Medien
    Digitale Medien
    Interaction of the Escherichia coli DnaA protein with bacteriophage k DNA (1998)
    Springer
    Molecular genetics and genomics 259 (1998), S. 679-688 
    Details
    ISSN: 1617-4623
    Schlagwort(e): Key words Bacteriophage λ ; DnaA-DNA interactions ; Electron microscopy ; DNA-protein complexes ; Escherichia coli
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Interaction of the Escherichia coli DnaA (replication initiator) protein with restriction fragments of phage λ DNA demonstrated differential binding of DnaA along the whole λ DNA. Interaction of DnaA with the λ replication region (from the promoter p R to the origin of replication, oriλ) demonstrated a strong binding of DnaA to the region around the p o promoter where synthesis of a short antisense oop RNA is initiated. The four sequences protected by DnaA (two 9mers and two 5mers) are not related even to a relaxed DnaA box. The pattern of protection of these four sequences and the location of three DNase I hypersensitive sites in the λ DNA r strand, together with results of mobility shift assays and electron microscopy studies, may indicate an interaction involving DnaA monomers bound to different DNA positions on one side of the helix and the formation of higher-order nucleoprotein structures. Therefore, it is tempting to suggest that DnaA, in addition to its activity in regulation of replication and transcription, could be considered as a factor which structures certain chromosomal regions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004380050863
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  • 198
    Digitale Medien
    Digitale Medien
    Electron and X-ray microscopic analyses of reaggregated materials obtained after fractionation of dissolved sporopollenin (1998)
    Springer
    Protoplasma 204 (1998), S. 13-21 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Sporopollenin ; Solubilisation ; 2-Aminoethanol ; Reaggregation ; Electron microscopy ; X-ray microscopy ; Thypha angustifolia L
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Exines fromTypha angustifolia L. pollen were dissolved in hot 2-aminoethanol. The solubilisate was successively fractionated and reaggregated via a dialysis cascade with dialysis tubings of different exclusion volumina. Four fractions of reaggregated material with different molecular mass were obtained. Fraction 1 with a molecular mass above 25,000 Da, fraction 2 with a molecular mass between 10,000–25,000 Da, fraction 3 with a molecular mass between 5,000–10,000 Da, and fraction 4 of a molecular mass lower than 5,000 Da. The fractions were comparatively analysed by scanning and transmission electron microscopy and X-ray microscopy. The material of the fractions with a molecular mass above 10,000 Da exhibit high congruence to the initial material. Analysis of the reaggregated material with the lowest molecular mass revealed special distinct substructures which in form and size showed high similarities to substructures of exines described in literature. In detail, spherical substructures consisting of an electron-dense core surrounded by an electron-transparent corona and in addition elongated substructures with a distinctive surface sculpture were detected.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01282289
    Standort Signatur Erwartet Verfügbarkeit
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  • 199
    Digitale Medien
    Digitale Medien
    Stability of linear time variant dynamic systems with multiple time delays (1998)
    Springer
    Acta mechanica Sinica 14 (1998), S. 274-282 
    Details
    ISSN: 1614-3116
    Schlagwort(e): time delay ; stability ; frozen time approach ; retarded dynamic systems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract By means of the frozen time approach and the Kronecker product, two criteria of asymptotic stability are derived for the linear, time variant dynamic systems with either short time delays or with weak feedback involving arbitrary time delays, respectively. It is found that the asymptotic stability of these retarded dynamic systems is governed by the maximal and minimal singular values of the coefficient matrices and their time derivatives.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02487763
    Standort Signatur Erwartet Verfügbarkeit
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  • 200
    Digitale Medien
    Digitale Medien
    Callose deposition and breakdown, followed by phytomelan synthesis in the seed coat ofGasteria verrucosa (Mill.) H. Duval (1998)
    Springer
    Protoplasma 201 (1998), S. 221-230 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Callose ; Electron microscopy ; Gasteria verrucosa ; Phenolics ; Phytomelan ; Seed coat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary In the seed coat ofGasteria verrucosa the deposition of phytomelan takes place during seed development in three stages. Phytomelan is a black cell wall material which is chemically very inert. First the radial walls and part of the transverse cell wall of the outer epidermis of the outer integument become thickened by exocytosis of dictyosome vesicles. Callose is deposited at the tangential plasma membrane against those walls. After the callose deposition about two thirds of the original cell volume is filled with callose. During the second stage the callose is broken down, probably into glucose monomers or small polymers. At the same time cellulose is deposited at the outer tangential plasma membrane, forming a wall between the dissolving callose and the plasma membrane. In the third phase small granules appear in the solution of dissolved callose. which grow out and finally fuse to form a block of phytomelan, consisting of spherical 15-nm units. Remarkable is the function of the callose: it determines the size of the phytomelan block, and it probably functions as carbohydrate source for the phytomelan synthesis and/or for the cellulose inner layer. In this study transmission electron microscopy and cryo scanning electron microscopy are used to study the three developmental stages of the formation of the phytomelan layer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01287418
    Standort Signatur Erwartet Verfügbarkeit
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