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  • stability  (301)
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  • Kiel: Kiel Institute for the World Economy (IfW)
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Computational mechanics 23 (1999), S. 8-19 
    ISSN: 1432-0924
    Schlagwort(e): Keywords: Material characteristic length ; strain-rate gradient ; dominant growth rate ; viscoplastic material ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract We study thermomechanical deformations of a viscoplastic body deformed in simple shear. The strain gradients are taken as independent kinematic variables and the corresponding higher order stresses are included in the balance laws, and the equation for the yield surface. Three different functional relationships, the power law, and those proposed by Wright and Batra, and Johnson and Cook are used to relate the effective strain rate to the effective stress and temperature. Effects of strain hardening of the material and elastic deformations are neglected. The homogeneous solution of the problem is perturbed and the stability of the problem linear in the perturbation variables is studied. Following Wright and Ockendon's postulate that the wavelength whose initial growth rate is maximum determines the minimum spacing between adjacent shear bands, the shear band spacing is computed. It is found that the minimum shear band spacing is very sensitive to the thermal softening coefficient/exponent, the material characteristic length and the nominal strain-rate. Approximate analytical expressions for the critical wave length for heat conducting nonpolar materials and locally adiabatic deformations of gradient dependent materials are also derived.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Optical review 6 (1999), S. 28-36 
    ISSN: 1349-9432
    Schlagwort(e): optical propagation equation ; stability ; picosecond pulse ; 3-dimensional computation ; Fresnel’s distribution ; fast Fourier transform
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present a new simulation code able to simulate the entire propagation of laser pulse, from the amplifiers level up to the focusing stage. This algorithm has some new characteristics that we intend to present. It computes the three-dimensional optical propagation equation using no approximation other than its picosecond expression. The stability has been carefully studied so that it can be applied to any geometry. This is a great improvement since, up to now only cylindrical geometry was accessible for accuracy. In this paper we also present a method using Fast Fourier Transform able to evaluate with a high accuracy, Fresnel’s distribution of a focused laser pulse. The advantages provided by our algorithm are its rapidity and its high physical understanding of the focusing phenomena.
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    The journal of Fourier analysis and applications 5 (1999), S. 105-125 
    ISSN: 1531-5851
    Schlagwort(e): 26B05 ; 42B10 ; 42C99 ; frame ; Gabor system ; Riesz basis ; stability ; wavelet
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract If the sequence of functions ϕj, k is a wavelet frame (Riesz basis) or Gabor frame (Riesz basis), we obtain its perturbation system ψj,k which is still a frame (Riesz basis) under very mild conditions. For example, we do not need to know that the support of ϕ or ψ $$(\hat \phi or\hat \psi )$$ is compact as in [14]. We also discuss the stability of irregular sampling problems. In order to arrive at some of our results, we set up a general multivariate version of Littlewood-Paley type inequality which was originally considered by Lemarié and Meyer [17], then by Chui and Shi [9], and Long [16].
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 1177-1184 
    ISSN: 1572-8943
    Schlagwort(e): differential scanning calorimetry ; DNA triple helix ; oligonucleotides ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract In this work we report a thermodynamic characterization of stability and melting behaviour of two 24-mer DNA triplexes. The third strand, that binds the Watson-Crick double helix with Hoogsteen hydrogen bonds, contains 3′-3′ phosphodiester junction that determines the polarity inversion. The target double helix is composed of adjacent and alternate fragments of oligopurine-oligopyrimidine tracts. The two helices differ from the substitution of the cytosine, involved in the junction, with the thymine. Calorimetric data reported here provide a quantitative measure of the influence of pH and base modification on the stability of a DNA triplex.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of productivity analysis 12 (1999), S. 55-75 
    ISSN: 1573-0441
    Schlagwort(e): Data envelopment analysis (DEA) ; returns to scale (RTS) ; sensitivity ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract Sensitivity of the returns to scale (RTS) classifications in data envelopment analysis is studied by means of linear programming problems. The stability region for an observation preserving its current RTS classification (constant, increasing or decreasing returns to scale) can be easily investigated by the optimal values to a set of particular DEA-type formulations. Necessary and sufficient conditions are determined for preserving the RTS classifications when input or output data perturbations are non-proportional. It is shown that the sensitivity analysis method under proportional data perturbations can also be used to estimate the RTS classifications and discover the identical RTS regions yielded by the input-based and the output-based DEA methods. Thus, our approach provides information on both the RTS classifications and the stability of the classifications. This sensitivity analysis method can easily be applied via existing DEA codes.
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    GeoJournal 49 (1999), S. 279-288 
    ISSN: 1572-9893
    Schlagwort(e): globalisation ; growth ; information technology ; infrastructure ; knowledge ; modernisation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geographie
    Notizen: Abstract This study examines the modernising role played by infrastructure and the transition of emphasis from physical infrastructure to knowledge-based infostructure as a source of economic growth in Singapore, noting the factors behind the change in strategy. Occupying a strategic sea route location and serving a resource-rich hinterland, Singapore inherited from the old British empire a well-established infrastructure when it achieved self-government in 1959. Since 1965, Singapore's development has been led by a pro-business developmentalist government, and strongly linked to technological advances in the West on which it also relies heavily for its exports and multinational corporation investments. From the 1980s, the government has launched a series of pro-IT plans to prepare the city-state's transition to an `intelligent island', and a regional hub for high-technology, and international financial transactions, a full-swing state-initiated strategy to leap from a semi-peripheral economy to be part of the developed core, and enhance its status to that of a world city. Despite barriers, some positive results have been observed. In terms of IT's spatial effect, it is largely overshadowed by the predeterministic long-term plans of the state's powerful planning authority.
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  • 7
    ISSN: 1572-977X
    Schlagwort(e): Avicennia alba ; growth ; internodal sequences ; mangrove age determination ; Rhizophora apiculata ; Sonneratia caseolaris ; Thailand
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The occurrence of periodic changes in the length of the internodes of the seedlings of SE Asian mangrove species (Rhizophora apiculata, Avicennia alba, and Sonneratia caseolaris) growing in the Pak Phanang estuary (Nakhon Si Thammarat, SE Thailand) was confirmed. The annual nature of these periodic changes was verified through comparisons with the observed average number of internodes produced by plants tagged for one year. The cycles in the sequence of internodal length of the seedlings had an average (± SE) period of 16.0 ± 0.78 internodes for Avicennia alba, 25.0 ± 1.2 internodes for Sonneratia caseolaris, and 8.29 ± 0.40 internodes for Rhizophora apiculata. These values are remarkably close to, and not significantly different (t‐test, P 〉 0.05) from the average (± SE) annual number of internodes of 17.6 ± 0.8 for Avicennia alba, 28.8 ± 2.1 for Sonneratia caseolaris, and 8.03 ± 0.36 for Rhizophora apiculata produced in a year by tagged plants. In addition, the average (± SE) growth of the tagged plants was 0.39 ± 0.018 cm day-1 for Avicennia alba, 0.24 ± 0.015 cm day-1 for Sonneratia caseolaris, and 0.091 ± 0.0036 cm day-1 for Rhizophora apiculata. These estimates were very close to those (0.45 ± 0.06 cm day-1 for Avicennia alba, 0.32 ± 0.01 cm day-1 for Sonneratia caseolaris, and 0.13 ± 0.005 cm day-1 for Rhizophora apiculata) derived as the product of the mean number of internodes produced per day, calculated from the inferred number of internodes produced per year, and the mean length of the internodes of the plants. These findings indicate that the use of regular, annual changes in the length of the internodes of mangrove seedlings can be used reliably to determine their age and to estimate their growth rate.
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 95 (1999), S. 835-850 
    ISSN: 1572-9613
    Schlagwort(e): quasicrystals ; nonperiodic tilings ; classical lattice-gas models ; nonperiodic ground states ; nonperiodic Gibbs states ; stability ; frustration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract One of the fundamental problems of quasicrystals is to understand their occurrence in microscopic models of interacting particles. We review here recent attempts to construct stable quasicrystalline phases. In particular, we compare two recently constructed classical lattice-gas models with translation-invariant interactions and without periodic ground-state configurations. The models are based on nonperiodic tilings of the plane by square-like tiles. In the first model, all interactions can be minimized simultaneously. The second model is frustrated; its nonperiodic ground state can arise only by the minimization of the energy of competing interactions. We put forward some hypotheses concerning stabilities of nonperiodic ground states. In particular, we introduce two criteria, the so-called strict boundary conditions, and prove their equivalence to the zero-temperature stability of ground states against small perturbations of potentials of interacting particles. We discuss the relevance of these conditions for the low-temperature stability, i.e., for the existence of thermodynamically stable nonperiodic equilibrium states.
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 95 (1999), S. 867-902 
    ISSN: 1572-9613
    Schlagwort(e): kinetics of phase transitions ; domain coarsening ; asymptotic behavior ; self-similarity ; stability ; chaos
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The classical Lifshitz–Slyozov–Wagner theory of domain coarsening predicts asymptotically self-similar behavior for the size distribution of a dilute system of particles that evolve by diffusional mass transfer with a common mean field. Here we consider the long-time behavior of measure-valued solutions for systems in which particle size is uniformly bounded, i.e., for initial measures of compact support. We prove that the long-time behavior of the size distribution depends sensitively on the initial distribution of the largest particles in the system. Convergence to the classically predicted smooth similarity solution is impossible if the initial distribution function is comparable to any finite power of distance to the end of the support. We give a necessary criterion for convergence to other self-similar solutions, and conditional stability theorems for some such solutions. For a dense set of initial data, convergence to any self-similar solution is impossible.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of intelligent and robotic systems 26 (1999), S. 91-100 
    ISSN: 1573-0409
    Schlagwort(e): robots ; neural networks ; adaptiveness ; stability ; approximation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract An indirect adaptive control approach is developed in this paper for robots with unknown nonlinear dynamics using neural networks (NNs). A key property of the proposed approach is that the actual joint angle values in the control law are replaced by the desired joint angles, angle velocities and accelerators, and the bound on the NN reconstruction errors is assumed to be unknown. Main theoretical results for designing such a neuro-controller are given, and the control performance of the proposed controller is verified with simulation studies.
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Empirical economics 24 (1999), S. 23-44 
    ISSN: 1435-8921
    Schlagwort(e): Key words: Cointegration ; convergence ; growth ; Kalman filter ; JEL classifications: C22 ; O47 ; O57
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract. Augmented Dickey Fuller (ADF) and Kalman filter convergence tests are applied to annual GDPs per head to 16 industrialised countries from 1890 to 1989. Results favour convergence towards the US with a structural break following the Second World War. Estimates suggest that steady-states were higher after the war and that speeds of convergence are different across countries. The Kalman filter method dismissed the no convergence hypothesis more often than its ADF counterpart. This could explain the apparent contradiction in earlier empirical work on similar data sets (cross-section methods tended to favour convergence while time series methods were unable to dismiss the no convergence hypothesis.)
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 32 (1999), S. 99-130 
    ISSN: 1572-9443
    Schlagwort(e): neural network ; inhibition ; stability ; Markov process ; fluid limit ; Harris-recurrence ; transience
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The subject of the paper is the stability analysis of some neural networks consisting of a finite number of interacting neurons. Following the approach of Dai [5] we use the fluid limit model of the network to derive a sufficient condition for positive Harris-recurrence of the associated Markov process. This improves the main result in Karpelevich et al. [11] and, at the same time, sheds some new light on it. We further derive two different conditions that are sufficient for transience of the state process and illustrate our results by classifying some examples according to positive recurrence or transience.
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 33 (1999), S. 293-325 
    ISSN: 1572-9443
    Schlagwort(e): stability ; fluid models ; multiclass queueing networks ; piecewise linear Lyapunov functions ; linear Lyapunov functions ; monotone global stability ; static buffer priority disciplines
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper studies the stability of a three‐station fluid network. We show that, unlike the two‐station networks in Dai and Vande Vate [18], the global stability region of our three‐station network is not the intersection of its stability regions under static buffer priority disciplines. Thus, the “worst” or extremal disciplines are not static buffer priority disciplines. We also prove that the global stability region of our three‐station network is not monotone in the service times and so, we may move a service time vector out of the global stability region by reducing the service time for a class. We introduce the monotone global stability region and show that a linear program (LP) related to a piecewise linear Lyapunov function characterizes this largest monotone subset of the global stability region for our three‐station network. We also show that the LP proposed by Bertsimas et al. [1] does not characterize either the global stability region or even the monotone global stability region of our three‐station network. Further, we demonstrate that the LP related to the linear Lyapunov function proposed by Chen and Zhang [11] does not characterize the stability region of our three‐station network under a static buffer priority discipline.
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Celestial mechanics and dynamical astronomy 74 (1999), S. 19-57 
    ISSN: 1572-9478
    Schlagwort(e): stability ; Hamiltonian ; two centers ; oblate planet ; galactic disks ; dipole
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Relative equilibria occur in a wide variety of physical applications, including celestial mechanics, particle accelerators, plasma physics, and atomic physics. We derive sufficient conditions for Lyapunov stability of circular orbits in arbitrary axisymmetric gravitational (electrostatic) and magnetic fields, including the effects of local mass (charge) and current density. Particularly simple stability conditions are derived for source‐free regions, where the gravitational field is harmonic (∇2U = 0) or the magnetic field irrotational (∇ × B = 0). In either case the resulting stability conditions can be expressed geometrically (coordinate‐free) in terms of dimensionless stability indices. Stability bounds are calculated for several examples, including the problem of two fixed centers, the J2 planetary model, galactic disks, and a toroidal quadrupole magnetic field.
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Celestial mechanics and dynamical astronomy 75 (1999), S. 251-285 
    ISSN: 1572-9478
    Schlagwort(e): unrestricted problem ; rotational motion ; rigid body dynamics ; libration points ; stability ; resonances
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present an analysis of the model introduced by Kokoriev and Kirpichnikov (1988) for the study of unrestricted planar motion of a point mass and a symmetric rigid body whose gravity field is approximated by two point masses (a dumb-bell model). To show possible generalization of the model, we give a systematic derivation of equations of motion for a more general unrestricted problem of a point and a rigid body possessing a plane of dynamical symmetry. We give a simple description of bifurcation of triangular libration points, and we perform an analysis of their linear stability. We propose to extend the model of Kokoriev and Kirpichnikov (1988) to a case when the symmetric body is oblate. In the proposed model the gravity field of moving and rotating body is approximated by two complex masses at complex distance (a complex dumb-bell model). An analysis of bifurcation of the triangular libration points in this model is also presented.
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Set-valued analysis 7 (1999), S. 209-238 
    ISSN: 1572-932X
    Schlagwort(e): nonsmooth analysis ; subdifferentials ; coderivatives ; implicit function theorem ; solvability ; stability ; open mapping theorem ; metric regularity ; multidirectional mean value inequality
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We prove a general implicit function theorem for multifunctions with a metric estimate on the implicit multifunction and a characterization of its coderivative. Traditional open covering theorems, stability results, and sufficient conditions for a multifunction to be metrically regular or pseudo-Lipschitzian can be deduced from this implicit function theorem. We prove this implicit multifunction theorem by reducing it to an implicit function/solvability theorem for functions. This approach can also be used to prove the Robinson–Ursescu open mapping theorem. As a tool for this alternative proof of the Robinson–Ursescu theorem, we also establish a refined version of the multidirectional mean value inequality which is of independent interest.
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Computational & mathematical organization theory 5 (1999), S. 5-30 
    ISSN: 1572-9346
    Schlagwort(e): network models ; organization theory ; rule following ; self organized ; stability ; work teams ; work routine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Self-organized rule-following systems are increasingly relevant objects of study in organization theory due to such systems&2018; capacity to maintain control while enabling decentralization of authority. This paper proposes a network model for such systems and examines the stability of the networks&2018; repetitive behavior. The networks examined are Ashby nets, a fundamental class of binary systems: connected aggregates of nodes that individually compute an interaction rule, a binary function of their three inputs. The nodes, which we interpret as workers in a work team, have two network inputs and one self-input. All workers in a given team follow the same interaction rule. We operationalize the notion of stability of the team&2018;s work routine and determine stability under small perturbations for all possible rules these teams can follow. To study the organizational concomitants of stability, we characterize the rules by their memory, fluency, homogeneity, and autonomy. We relate these measures to work routine stability, and find that stability in ten member teams is enhanced by rules that have low memory, high homogeneity, and low autonomy.
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 32 (1999), S. 131-168 
    ISSN: 1572-9443
    Schlagwort(e): stability ; positive recurrence ; fluid limit ; polling system ; exhaustive service policy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We introduce a generalized criterion for the stability of Markovian queueing systems in terms of stochastic fluid limits. We consider an example in which this criterion may be applied: a polling system with two stations and two heterogeneous servers.
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 31 (1999), S. 171-206 
    ISSN: 1572-9443
    Schlagwort(e): scheduling ; open multiclass queueing networks ; discrete-review policies ; fluid models ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper describes a family of discrete-review policies for scheduling open multiclass queueing networks. Each of the policies in the family is derived from what we call a dynamic reward function: such a function associates with each queue length vector q and each job class k a positive value r k (q), which is treated as a reward rate for time devoted to processing class k jobs. Assuming that each station has a traffic intensity parameter less than one, all policies in the family considered are shown to be stable. In such a policy, system status is reviewed at discrete points in time, and at each such point the controller formulates a processing plan for the next review period, based on the queue length vector observed. Stability is proved by combining elementary large deviations theory with an analysis of an associated fluid control problem. These results are extended to systems with class dependent setup times as well as systems with alternate routing and admission control capabilities.
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 32 (1999), S. 195-231 
    ISSN: 1572-9443
    Schlagwort(e): window flow control ; TCP ; stability ; multiclass networks ; stationary ergodic point processes ; (max,+)-linear system
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We focus on window flow control as used in packet-switched communication networks. The approach consists in studying the stability of a system where each node on the path followed by the packets of the controlled connection is modeled by a FIFO (First-In-First-Out) queue of infinite capacity which receives in addition some cross traffic represented by an exogenous flow. Under general stochastic assumptions, namely for stationary and ergodic input processes, we show the existence of a maximum throughput allowed by the flow control. Then we establish bounds on the value of this maximum throughput. These bounds, which do not coincide in general, are reached by time-space scalings of the exogenous flows. Therefore, the performance of the window flow control depends not only on the traffic intensity of the cross flows, but also on fine statistical characteristics such as the burstiness of these flows. These results are illustrated by several examples, including the case of a nonmonotone, nonconvex and fractal stability region.
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    BIT 39 (1999), S. 385-402 
    ISSN: 1572-9125
    Schlagwort(e): Gaussian elimination ; stability ; backward error analysis ; growth factor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A new backward error analysis of LU factorization is presented. It allows to obtain a sharper upper bound for the forward error and a new definition of the growth factor that we compare with the well known Wilkinson growth factor for some classes of matrices. Numerical experiments show that the new growth factor is often of order approximately log2 n whereas Wilkinson's growth factor is of order n or $$\sqrt n$$ .
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  • 22
    ISSN: 1572-9036
    Schlagwort(e): (discrete-time) Markov control processes ; expected total cost ; value iteration ; policy iteration ; stability ; transient control models
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract This paper studies the expected total cost (ETC) criterion for discrete-time Markov control processes on Borel spaces, and possibly unbounded cost-per-stage functions. It presents optimality results which include conditions for a control policy to be ETC-optimal and for the ETC-value function to be a solution of the dynamic programming equation. Conditions are also given for the ETC-value function to be the limit of the α-discounted cost value function as α ↑ 1, and for the Markov control process to be `stable" in the sense of Lagrange and almost surely. In addition, transient control models are fully analized. The paper thus provides a fairly complete, up-dated, survey-like presentation of the ETC criterion for Markov control processes on Borel spaces.
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Advances in computational mathematics 10 (1999), S. 115-133 
    ISSN: 1572-9044
    Schlagwort(e): Runge–Kutta–Nyström methods ; predictor–corrector methods ; stability ; parallelism ; 65M12 ; 65M20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract This paper describes the construction of block predictor–corrector methods based on Runge–Kutta–Nyström correctors. Our approach is to apply the predictor–corrector method not only with stepsize h, but, in addition (and simultaneously) with stepsizes a i h, i = 1 ...,r. In this way, at each step, a whole block of approximations to the exact solution at off‐step points is computed. In the next step, these approximations are used to obtain a high‐order predictor formula using Lagrange or Hermite interpolation. Since the block approximations at the off‐step points can be computed in parallel, the sequential costs of these block predictor–corrector methods are comparable with those of a conventional predictor–corrector method. Furthermore, by using Runge–Kutta–Nyström corrector methods, the computation of the approximation at each off‐step point is also highly parallel. Numerical comparisons on a shared memory computer show the efficiency of the methods for problems with expensive function evaluations.
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    BIT 39 (1999), S. 620-645 
    ISSN: 1572-9125
    Schlagwort(e): Numerical integrator ; oscillatory solutions ; Schrödinger equation ; quantum-classical coupling ; error bounds ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We study time integration methods for equations of mixed quantum-classical molecular dynamics in which Newtonian equations of motion and Schrödinger equations are nonlinearly coupled. Such systems exhibit different time scales in the classical and the quantum evolution, and the solutions are typically highly oscillatory. The numerical methods use the exponential of the quantum Hamiltonian whose product with a state vector is approximated using Lanczos' method. This allows time steps that are much larger than the inverse of the highest frequencies. We describe various integration schemes and analyze their error behaviour, without assuming smoothness of the solution. As preparation and as a problem of independent interest, we study also integration methods for Schrödinger equations with time-dependent Hamiltonian.
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Lithuanian mathematical journal 39 (1999), S. 20-32 
    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.
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Photosynthetica 36 (1999), S. 597-599 
    ISSN: 1573-9058
    Schlagwort(e): biomass ; chlorophyll ; detoxification ; growth ; Hill reaction activity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract In Abelmoschus esculentus L. uniconazole brought about a marked decrease in cadmium-induced loss of chlorophyll and Hill reaction activity, but it did not completely prevent cadmium toxicity.
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of composite materials 35 (1999), S. 495-506 
    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.
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  • 28
    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.
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  • 29
    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.
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  • 30
    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
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  • 31
    ISSN: 1573-8264
    Schlagwort(e): aminopeptidase ; carboxypeptidase ; growth ; ×Haynaldoticum sardoum ; proteinase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effect of 50 to 200 mM NaCl on two lines (CP with solid stem and CV with hollow stem) of ×Haynaldoticum sardoum was studied. NaCl significantly reduced root and shoot fresh and dry masses, root length and less markedly shoot length of CP and CV plants. The sodium accumulated in the leaves in relation to the concentration of NaCl and length of the treatment; CP leaves contained twice as much sodium as CV leaves. The leaf chlorophyll a/b ratio was not affected by NaCl. NaCl decreased the leaf water and osmotic potentials. The pressure potential increased due to the increased concentration of dissolved solutes in the leaf, particularly sodium. The proteinase and exopeptidase activities increased during NaCl treatment.
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Biologia plantarum 42 (1999), S. 631-636 
    ISSN: 1573-8264
    Schlagwort(e): allocation pattern ; 14C-sucrose ; Cecropia pachystachya ; growth ; Hymenaea courbaril ; Myroxylon peruiferum ; Schizolobium parahyba ; tropical tree species
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Carbon translocation was affected by shade in different tropical tree species differing in successional status and degree of shade tolerance. Plants of the early-successional shade-intolerant species Cecropia pachystachya and Schizolobium parahyba and of the late-successional shade-tolerant species Myroxylon peruiferum and Hymenaea courbaril were grown under full sun (FS) and natural shade treatments (NS) and assessed for [14C]-sucrose translocation. Most of the 14C was retained in the fed leaf after a 24 h translocation period. Under FS, the growing apical part of the plant was the most intense sink for most species. Shade affected growth and sink intensity differently in early and late successional species. Growth was more markedly affected in the early species. Whereas these continued to invest carbon into the growing apical part of the plant under shade conditions, the late successional species invested relatively more into other sinks.
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  • 33
    ISSN: 1573-5168
    Schlagwort(e): growth ; mass spectrometry ; 15N-phenylalanine ; protein synthesis ; stable isotope technology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract In vivo rates of protein synthesis in fish have predominantly been measured using a single flooding dose injection of a solution containing 3H-Phenylalanine as a tracer. However, use of a radiolabelled tracer restricts the application of this technique to controlled laboratory conditions. In this study, the flooding dose technique was used to successfully measure in vivo rates of protein synthesis in Atlantic salmon (Salmo salar L.) smolts utilising a stable isotope labelled amino acid, L-[15N]-Phenylalanine, as an alternative tracer. Methodologies are presented allowing the 15N enrichment in the free amino acid pool and in body protein to be measured using mass spectrometry. In this study, the fractional rates of protein consumption (kr), synthesis (ks) and growth (kg) of Atlantic salmon smolts (37 ± 1.4 g) were measured as 4.7, 3.3 and 1.6% day−1 respectively. Protein synthesis retention efficiency (kgks) and protein growth efficiency (kgkr)were calculated as 48.5 and 34.0% respectively. The ks, kgks and kgkr values obtained in this study were found to be within the range of values available in the literature for juvenile salmonid fish of a comparable size. The use of L-[15N]-Phenylalanine provides an alternative tracer to radiolabelled amino acids for measuring in vivo rates of protein synthesis in fish using the flooding dose' technique and also allows studies of fish protein metabolism to be carried out in environmentally sensitive (field and laboratory) conditions where the use of radiolabels is prohibited.
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  • 34
    ISSN: 1573-5168
    Schlagwort(e): Atlantic salmon ; growth ; individual feed consumption rate ; plasma insulin ; protein synthesis capacity ; trypsin isozymes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Growth was found to be associated with the changes of trypsin activity in the pyloric caecal tissues and the level of plasma insulin in Atlantic salmon (Salmo salar L.). A decrease in trypsin activity accompanied by an increase in plasma insulin was detected one month before an enhanced growth was observed. There were significant relationships between weight specific consumption rate, plasma insulin levels and fish growth. The correlation of weight specific consumption rate was higher with growth rate (R2=0.7, p〈0.0001) than with plasma insulin concentration (R2=0.4, p〈0.0001). When the comparison was made between Atlantic salmon carrying and lacking the trypsin variant TRP-2*92, the fish with the variant had lower maintenance ration (p〈0.05), higher capacity for protein synthesis in the white muscle (p〈0.02), and a greater ability to utilize the feed at a restricted ration than the fish without the variant. In Atlantic salmon lacking the variant, both plasma insulin concentrations and growth rates were significantly lower (p〈0.05) in the fish fed 0.5% bw day−1 than those fed 1% bw day−1. Whilst the growth rates of TRP-2*92 salmon fed the different rations became similar one month after similar levels of plasma insulin were observed between them. The TRP-2*92 salmon may be defined as a high protein growth efficiency fish with low protein turnover rate. Genetic variation in trypsin isozyme pattern affects feed utilization, plasma insulin levels and growth in Atlantic salmon.
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Archive of applied mechanics 69 (1999), S. 47-54 
    ISSN: 1432-0681
    Schlagwort(e): Key words Bifurcation ; stability ; multibody system dynamics ; singularity theory ; Liapunov's direct method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Summary In this paper, the global behavior of relative equilibrium states of a three-body satellite with flexible connection under the action of the gravitational torque is studied. With geometric method, the conditions of existence of nontrivial solutions to the relative equilibrium equations are determined. By using reduction method and singularity theory, the conditions of occurrence of bifurcation from trivial solutions are derived, which agree with the existence conditions of nontrivial solutions, and the bifurcation is proved to be pitchfork-bifurcation. The Liapunov stability of each equilibrium state is considered, and a stability diagram in terms of system parameters is presented.
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Biological cybernetics 81 (1999), S. 211-225 
    ISSN: 1432-0770
    Schlagwort(e): Key words: Hebbian learning rule ; attractor dynamics ; symmetric connections ; multiplicative normalization ; self-organization ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract. While learning and development are well characterized in feedforward networks, these features are more difficult to analyze in recurrent networks due to the increased complexity of dual dynamics – the rapid dynamics arising from activation states and the slow dynamics arising from learning or developmental plasticity. We present analytical and numerical results that consider dual dynamics in a recurrent network undergoing Hebbian learning with either constant weight decay or weight normalization. Starting from initially random connections, the recurrent network develops symmetric or near-symmetric connections through Hebbian learning. Reciprocity and modularity arise naturally through correlations in the activation states. Additionally, weight normalization may be better than constant weight decay for the development of multiple attractor states that allow a diverse representation of the inputs. These results suggest a natural mechanism by which synaptic plasticity in recurrent networks such as cortical and brainstem premotor circuits could enhance neural computation and the generation of motor programs.
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Aquaculture international 7 (1999), S. 179-187 
    ISSN: 1573-143X
    Schlagwort(e): feeding ; growth ; larvae ; micro-algae ; pearl oyster (Pinctada margaritifera L.) ; survival
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract This paper reports on an experiment to determine growth and survival of blacklip pearl oyster, Pinctada margaritifera (L.), larvae fed a 1:1 mixture of Isochrysis aff. galbana clone T-ISO and Pavlova salina at six different densities (1, 2, 5, 10, 20 and 30 × 103 cells ml-1. Larval growth and survival were assessed every four days over a 20–day period. Exponential and logistic regression models were fitted to the growth and survival responses, respectively. Overall growth of larvae fed ≥5 × 103 cells ml-1 was significantly greater (p 〉 0.01) than growth of larvae reared at other algal densities. The optimal food ration for maximum larval growth was 20 × 103 cells ml-1, which resulted in larvae with antero-posterior shell length of 230 μm after 20 days. These larvae were significantly larger (p 〉 0.05) than those in all other treatments at the end of the experiment. Survival of larvae fed 0, 1 and 2 × 103 cells ml-1 was significantly lower than that of larvae in all other treatments at the end of 15 days (p 〉 0.01). Maximal survival (8%) over the 20 day period was shown by larvae fed 10 × 103 cells ml-1, while lower survival was shown by larvae fed 2 × 103 cells ml-1 (2%) and 1 × 103 cells ml-1 (0%).
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Aquaculture international 7 (1999), S. 1-12 
    ISSN: 1573-143X
    Schlagwort(e): Convict cichlid (Cichlasoma nigrofasciatum ; environmental UV effects ; growth ; ultraviolet radiation ; UVA
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The long term (two generations) effect an enhanced (5%) sub-lethal ultraviolet-A (320–400 nm) irradiation on growth and survival rate of a convict cichlid (Cichlasoma nigrofasciatum is presented. Two UVA irradiated populations (G1-UVA and G2-UVA) and two control populations (G1-control and G2-control) were observed from age 60 to 403 days. The UVA populations were exposed to enhanced UVA irradiation from 4 months of age (G1-UVA and from egg's state (G2-UVA). The specific growth rates (daily weight and length increase) and the condition factors of the populations were not affected by the enhanced UVA, it depended more on the population size. At the adapted temperature range (27–29 °C) the survival rate of those populations was not affected by enhanced UVA. A combined effect of enhanced UVA and increased temperature (31–32 °C) was responsible for a high mortality rate in the GI-UVA. A total of 67% of the G1-UVA population died just within a week of exposure to high temperature.
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Aquaculture international 7 (1999), S. 251-260 
    ISSN: 1573-143X
    Schlagwort(e): bacterial biofilm ; common carp (Cyprinus carpio) ; growth ; rohu (Labeo rohita) ; Tilapia (Oreochromis mossambicus)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Experiments were conducted to enhance the growth of common carp (Cyprinus carpio), rohu (Labeo rohita) and Mozambique tilapia (Oreochromis mossambicus) through use of sugarcane bagasse as substrate. Bagasse was suspended in water with or without supplementation with fertilizers. Bagasse supplemented with cattle dung and urea favoured higher zooplankton production and significantly (p 〈 0.05) increased fish growth by over 50% compared to bagasse or fertilizers on their own. This higher production of fish is attributed to bacterial biofilm promoted on the substrate which, apart from forming food for zooplankton and fish, contributed to improved water quality by lowering ammonia.
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  • 40
    ISSN: 1573-143X
    Schlagwort(e): bighead carp (Aristichthys nobilis) ; growth ; Laguna Lake ; salinity tolerance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Bighead carp (Aristichthys nobilis Oshima) fry of various ages (11, 18, and 35 days post-hatch) were exposed to the low salinities encountered during the annual intrusion of seawater in Laguna Lake, Philippines. Practical indices of salinity tolerance assessed the effect of a 96 h direct exposure to low salinities (0–16‰). Mean (MST) and median survival times (MST50) of fry decreased as salinity of rearing medium increased. Younger fry were less able to tolerate exposure to these salinities than their older cohorts. Median lethal salinity after 96 h (MLS) revealed higher tolerance among 35–day old fry (7.6‰) than 11 (2.3‰) and 18–day old fry (6.0‰), demonstrating that survival in saline water depends on their age at initial exposure to low salinities. Mean body weight of 18–day old fry reared in 0 and 2‰ for 3 and 4 weeks was higher than for those reared in 4 and 6‰ for the same period. Growth over these periods was inversely related with the range of salinities tested. These results demonstrate that, despite their known stenohalinity, bighead carp fry possess some degree of osmoregulatory capability, allowing them to survive and grow in lakes subjected periodically to saltwater inflow.
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    International tax and public finance 6 (1999), S. 621-639 
    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.
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Journal of economic growth 4 (1999), S. 55-80 
    ISSN: 1573-7020
    Schlagwort(e): mercantilism ; growth ; taxation ; openness ; familiarity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract Nations close themselves voluntarily to varying degrees. Restrictions on the flow of ideas are difficult to understand, since open countries have higher relative incomes. This article provides an explanation based on the existence of two channels of public finance—traditional and mercantilistic. The latter refers to monopoly creation to provide a stream of government revenue. Strong, profitable monopolies require that the nation be closed to new ideas about technology and organization. The government sets the degree of restriction to balance current mercantilistic revenue with future revenue from traditional sources. The model is supported with numerical simulations and historical illustrations.
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Journal of economic growth 4 (1999), S. 81-111 
    ISSN: 1573-7020
    Schlagwort(e): growth ; investment ; regimes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract The absence of continuous regime type measures that focus on institutions rather than outcomes besets studies on whether democratic or authoritarian regimes grow faster. Additional shortcomings include the failure to consider development stages and the erroneous endogenous specification of regimes. Given panel data on 105 countries from 1960 to 1989, the effective party/constitutional framework measure does not correlate with growth or investment in the total sample. But considering development levels, some evidence indicates that discretion decreases growth in advanced areas, and, contrary to theory, inhibits investment in poorer countries. Also, single-party dictatorships have higher investment ratios but do not grow faster than party-less regimes.
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  • 44
    Digitale Medien
    Digitale Medien
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    Journal of economic growth 4 (1999), S. 213-232 
    ISSN: 1573-7020
    Schlagwort(e): education ; work experience ; self-employment ; growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract We examine the implications for growth and development of the existence of two types of human capital: entrepreneurial and professional. Entrepreneurs accumulate human capital through a work-experience intensive process, whereas professionals’ human capital accumulation is education-intensive. Moreover, the return to entrepreneurship is uncertain. We show how skill-biased technological progress leads to changes in the composition of aggregate human capital; as technology improves, individuals devote less time to the accumulation of human capital through work experience and more to the accumulation of human capital through professional training. Thus, our model explains why entrepreneurs play a relatively more important role in intermediate-income countries and professionals are relatively more abundant in richer economies. It also shows that those countries that initially have too little of either entrepreneurial or professional human capital may end up in a development trap.
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  • 45
    Digitale Medien
    Digitale Medien
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    Journal of economic growth 4 (1999), S. 331-349 
    ISSN: 1573-7020
    Schlagwort(e): growth ; fertility ; income distribution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract This article analyzes the interaction between growth and fertility via income distribution in a model in which fertility decisions are motivated by old-age support. It provides an explanation of the demographic transition of an economy from a stage of increasing fertility and low growth to a stage of low fertility, high human capital investments, and high growth.
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Journal of economic growth 4 (1999), S. 429-445 
    ISSN: 1573-7020
    Schlagwort(e): growth ; R&D ; education ; regime shift
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract The role of learning and R&D in economic development is addressed in an endogenous growth model. When human capital is below a threshold level, the model predicts that skills are accumulated as the only growth-generating activity, whereas both innovation activities and learning drive growth above this level. Hence, an endogenous regime shift is triggered when the level of human capital reaches the threshold level because it becomes profitable to innovate.
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  • 47
    Digitale Medien
    Digitale Medien
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    Journal of economic growth 4 (1999), S. 119-137 
    ISSN: 1573-7020
    Schlagwort(e): growth ; technology ; Solow
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract Growth accounting breaks down economic growth into components associated with changes in factor inputs and the Solow residual, which reflects technological progress and other elements. After a presentation of the standard model, the analysis considers dual approaches to growth accounting (which considers changes in factor prices rather than quantities), spillover effects and increasing returns, taxes, and multiple types of factor inputs. Later sections place the growth-accounting exercise within the context of two recent strands of endogenous growth theory—varieties-of-products models and quality-ladders models. Within these settings, the Solow residual can be interpreted in terms of measures of the endogenously changing level of technology.
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  • 48
    Digitale Medien
    Digitale Medien
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    Journal of economic growth 4 (1999), S. 305-330 
    ISSN: 1573-7020
    Schlagwort(e): growth ; convergence clubs ; poverty trap ; cultural factors ; location
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract This study investigates the sources of heterogeneity across a worldwide set of countries. Unspecified ex ante and unanticipated cultural (Protestant versus Catholic), geographical (continents), and institutional (OECD versus non-OECD) clubs emerge endogenously and naturally as homogeneous classes on the basis of their economic structure. The dynamics both within and across the identified groups of countries are consistent with multiple equilibrium-growth models proposed by, for instance, Azariadis and Drazen (1990), therefore strengthening the viability of the convergence club hypothesis. In particular, higher stages of development are, on average, non linearly associated with higher stages of growth.
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  • 49
    Digitale Medien
    Digitale Medien
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    Review of industrial organization 14 (1999), S. 391-396 
    ISSN: 1573-7160
    Schlagwort(e): Fate ; growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract Fate bringeth economic growth and malfeasance giveth its gains
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  • 50
    Digitale Medien
    Digitale Medien
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    Photosynthetica 36 (1999), S. 259-266 
    ISSN: 1573-9058
    Schlagwort(e): chlorophyll fluorescence ; fern ; fertilization ; growth ; photosynthesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Plants grown at low irradiance were fertilized with 0, 60, and 600 g m-3 NH4NO3 once every fortnight. Plants treated with high N concentrations showed an increased growth, producing longer and broader fronds with larger areas, and were darker green in colour. Nitrogen also increased the content of chlorophyll (Chl) and carotenoids per leaf area unit. Different N treatments did not affect the photosynthetic efficiency of photosystem 2, as reflected by the high values of Chl fluorescence kinetics Fv/Fm, ranging between 0.81 to 0.84, and Fv/F0 of 4.30 to 5.10. An increase in photochemical quenching (qP), accompanied by a decrease in non-photochemical quenching (qN), was observed in sporophytes fertilized with increased concentrations of NH4NO3. Nitrogen availability allowed sporophytes of Acrostichum aureum to become more established under natural condi tions.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    Evolutionary ecology 13 (1999), S. 395-409 
    ISSN: 1573-8477
    Schlagwort(e): body size ; development ; Drosophila melanogaster ; dung flies ; growth ; life history ; resource limitation ; Scathophaga stercoraria ; seasonality ; Sepsis cynipsea ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Growth responses to temperature and resource limitation in three dipteran species with similar life histories were compared. With respect to current life history theory, two points are raised. First, growth rate in real time increased steeply with temperature in all species, following the standard pattern. However, when expressed in physiological time growth rate increased as temperature decreased in the yellow dung fly Scathophaga stercoraria, remained approximately constant in Sepsis cynipsea, and increased in Drosophila melanogaster. These responses can be understood as adaptations to climate and seasonality. It is concluded that some patterns of adaptation may be more easily interpreted if, and some may even go undetected unless, they are analysed in physiological time. Second, a decrease in body size, development rate and growth rate when resources are limited is believed to be nearly universal and generally predicted by life history models. Despite their similar life histories, the three species investigated showed qualitatively different growth responses to larval food shortage. At unlimited resources, yellow dung flies showed the fastest initial larval body mass gain per unit time, while those of S. cynipsea and D. melanogaster were lower and about equal. The period of no body mass gain at the end of larval development was longest in S. stercoraria and shortest in S. cynipsea. When facing resource limitation, S. stercoraria emerged smaller but earlier (thus nearly maintaining their growth rate), S. cynipsea smaller after the same development period, and D. melanogaster smaller and later (showing reduced and much reduced growth, respectively). It is concluded that whether growth really slows when resources are limited depends on the precise ecological circumstances of the species in question. More refined models, particularly those where mortality costs are independent of time, and more experiments are necessary to account for the variation in growth and size and age at maturity present in nature.
    Materialart: Digitale Medien
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  • 52
    Digitale Medien
    Digitale Medien
    Springer
    Reaction kinetics and catalysis letters 68 (1999), S. 243-247 
    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.
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  • 53
    Digitale Medien
    Digitale Medien
    Springer
    Advances in computational mathematics 10 (1999), S. 271-289 
    ISSN: 1572-9044
    Schlagwort(e): delay differential equations ; steady state solutions ; stability ; 34K20 ; 65J10
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract The characteristic equation of a system of delay differential equations (DDEs) is a nonlinear equation with infinitely many zeros. The stability of a steady state solution of such a DDE system is determined by the number of zeros of this equation with positive real part. We present a numerical algorithm to compute the rightmost, i.e., stability determining, zeros of the characteristic equation. The algorithm is based on the application of subspace iteration on the time integration operator of the system or its variational equations. The computed zeros provide insight into the system’s behaviour, can be used for robust bifurcation detection and for efficient indirect calculation of bifurcation points.
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  • 54
    Digitale Medien
    Digitale Medien
    Springer
    Biodegradation 10 (1999), S. 177-191 
    ISSN: 1572-9729
    Schlagwort(e): AQUASIM ; biodegradation ; biofilm ; growth ; kinetics ; methane ; modelling ; nitrification
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Energietechnik , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract This article discusses the growth of methanotrophic biofilms. Several independent biofilm growths scenarios involving different inocula were examined. Biofilm growth, substrate removal and product formation were monitored throughout the experiments. Based on the oxygen consumption it was concluded that heterotrophs and nitrifiers co-existed with methanotrophs in the biofilm. Heterotrophic biomass grew on soluble polymers formed by the hydrolysis of dead biomass entrapped in the biofilm. Nitrifier populations developed because of the presence of ammonia in the mineral medium. Based on these experimental results, the computer program AQUASIM was used to develop a biological model involving methanotrophs, heterotrophs and nitrifiers. The modelling of six independent growth experiments showed that stoichiometric and kinetic parameters were within the same order of magnitude. Parameter estimation yielded an average maximum growth rate for methanotrophs, μm, of 1.5 ± 0.5 d−1, at 20 °C, a decay rate, bm, of 0.24 ± 0.1 d−1, a half saturation constant, $${\text{K}}_{{\text{S(CH}}_{\text{4}} {\text{)}}} $$ , of 0.06 ± 0.05 mg CH4/L, and a yield coefficient, $$Y_{CH_4 } $$ , of 0.57 ±: 0.04 g X/g CH4. In addition, a sensitivity analysis was performed on this model. It indicated that the most influential parameters were those related to the biofilm (i.e. density; solid-volume fraction; thickness). This suggests that in order to improve the model, further research regarding the biofilm structure and composition is needed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 55
    Digitale Medien
    Digitale Medien
    Springer
    Agroforestry systems 45 (1999), S. 131-158 
    ISSN: 1572-9680
    Schlagwort(e): competition ; fertility ; microclimate ; risk ; stability ; water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The first ecosystem mimic hypothesis suggests clear advantages if man-made land use systems do not deviate greatly in their resource use patterns from natural ecosystems typical of a given climatic zone. The second hypothesis claims that additional advantages will accrue if agroecosystems also maintain a substantial part of the diversity of natural systems. We test these hypotheses for the savannah zone of sub-Saharan Africa, with its low soil fertility and variable rainfall. Where annual food crops replace the natural grass understorey of savannah systems, water use will decrease and stream and groundwater flow change, unless tree density increases relative to the natural situation. Increasing tree density, however, will decrease crop yields, unless the trees meet specific criteria. Food crop production in the parkland systems may benefit from lower temperatures under tree canopies, but water use by trees providing this shade will prevent crops from benefiting. In old parkland trees that farmers have traditionally retained when opening fields for crops, water use per unit shade is less than in most fast growing trees introduced for agroforestry trials. Strong competition between plants adapted to years with different rainfall patterns may stabilise total system productivity -- but this will be appreciated by a farmer only if the components are of comparable value. The best precondition for farmers to maintain diversity in their agroecosystem hinges on the availability of a broad basket of choices, without clear winners or 'best bets'.
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  • 56
    ISSN: 1573-143X
    Schlagwort(e): apparent digestibility coefficient ; fish meal ; growth ; Nile tilapa (Oreochromis niloticus) ; plant proteins
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Apparent digestibility coefficient (ADC) values for a number of ingredients of plant or animal origin were obtained in order to formulate diets based on such values and to evaluate growth performance of Nile tilapia Oreochromis niloticus fed four experimental diets in which fish meal was gradually replaced by a mixture of other ingredients. The digestibility of various diet components was measured by using an inert marker in the feed and by using the Guelph faeces collecting system. ADC values of the ingredients tested were generally high, especially for fish meal. It was found that extruded pea seed meal (92.6%), defatted soybean meal (94.4%), full-fat toasted soybean (90.0%) and micronized wheat (88.6%) were the best vegetable proteins tested. Lupin seed meal and faba bean meal had similar ADC values for protein and energy. Groups of tilapia, initial mean body weight (SD) 6.7 (0.1) g, were fed experimental diets with the same digestible protein (DP) and digestible energy (DE) containing graded levels of a mixture of vegetable ingredients as partial or total replacement of fish meal protein. A growth trial was conducted over 12 weeks as partial or total replacement of fish meal protein. A growth trial was conducted over 12 weeks at a water temperature of 25 °C. Significant differences were observed for weight gain among tilapia fed diets D0, D33, D66 and D100 (containing only animal protein, 33, 66, and 100% of plant protein, respectively). No significant differences were observed for voluntary intake among tilapia fed diets D0, D33 and D66. These values were significantly lower than those observed for tilapia fed plant protein based diet (D100) and suggest the possibility of partial replacement of fish meal by vegetable proteins without negative effects.
    Materialart: Digitale Medien
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  • 57
    ISSN: 1573-1561
    Schlagwort(e): European corn borer ; Ostrinia nubilalis (Hübner) ; growth ; development ; fecundity ; oviposition ; behavior ; eggs ; DIMBOA ; water extract ; plant extract ; maize ; Peruvian maize ; maize accessions ; host plant resistance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Twelve Peruvian maize, Zea mays, accessions were selected because of their relatively high level of field resistance to first-generation European corn borer (ECB), Ostrinia nubilalis, larval leaf-feeding. Water extracts of freeze-dried, powdered, leaf tissue were incorporated into a standard ECB diet, fed to larvae, and the effects on larval growth, development, and fecundity were measured. Larval and pupal weights were monitored as were the time elapsed in the larval, pupal, and adult stages. Adult fecundity and egg fertility were recorded. The experiment was a randomized block design (larvae and pupae) or a completely randomized design (adults) and analyzed with ANOVA (α = 0.05). Pairwise comparisons were made between groups of insects grown on diets containing extracts from the Peruvian lines, a standard diet, or diets containing extracts of a known susceptible inbred, and a known resistant inbred line. Survival was analyzed with a chi-squared test (α = 0.05). Two Peruvian accessions significantly reduced female larval and pupal weights, extended pupal and adult development time, and decreased survival of pupae and adults. Water extracts also had a pronounced impact on males; two accessions significantly reduced pupal weight and extended the time required to pupate, and one reduced male survival to adults. The results indicate that water-soluble factors from resistant Peruvian accessions inhibit the growth, developmental time, and survival of ECB. These resistance factors could be useful in the development of maize germplasm with insect-resistant traits.
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  • 58
    Digitale Medien
    Digitale Medien
    Springer
    Journal of chemical ecology 25 (1999), S. 1455-1479 
    ISSN: 1573-1561
    Schlagwort(e): Turnera ulmifolia ; Euptoieta hegesia ; cyanogenesis ; Anolis sagrei ; tritrophic interactions ; host range ; sequestration ; growth ; development ; oviposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract We examine the effects of the cyanogenesis polymorphism in Turnera ulmifolia on larvae, pupae, and adults of Euptoieta hegesia, the most damaging herbivore of T. ulmifolia in terms of tissue loss per unit time. We provide evidence that female E. hegesia do not show preference for host plants on the basis of their cyanogenesis level but do prefer T. ulmifolia over equally cyanogenic, closely related secondary host-plant species (Passiflora sp.). Similarly, cyanogenesis in T. ulmifolia has little effect on the food preference, growth, or development of the larvae. The potential host range of E. hegesia is limited, even within the genus Turnera, but this does not appear to be due to host-plant cyanogenesis. Pupae suffer very high mortality levels in the wild that are not associated with host-plant cyanogenesis, although our studies indicate that larvae are capable of sequestering cyanogenic glycosides from their host plants and possibly of synthesizing these or similar compounds. We provide evidence that the presence of sequestered cyanogenic compounds in the larvae protects them from terrestrial-based predators such as Anolis lizards
    Materialart: Digitale Medien
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  • 59
    Digitale Medien
    Digitale Medien
    Springer
    Aquaculture international 7 (1999), S. 357-360 
    ISSN: 1573-143X
    Schlagwort(e): feed intake ; growth ; silver trevally (Pseudocaranx dentex) ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 60
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 55 (1999), S. 727-739 
    ISSN: 1572-8943
    Schlagwort(e): ignition ; polymer combustion modelling ; stability ; steady state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A mathematical model of ignition and burning of organic polymers was used for evaluation and quantification of the tendency of polymers to ignition. The model permits investigation of the influence of one parameter of the polymer on the others. It was found that the model could be used for the verification of the ignitability method developed by Miller et al. [1]. Different steady states of combustion were found when using the model proposed. There is a characteristic steady state for normal flaming combustion, another for non-flaming combustion, and there are also unstable steady states that have no real physical meaning.
    Materialart: Digitale Medien
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  • 61
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 1285-1304 
    ISSN: 1572-8943
    Schlagwort(e): amorphous state ; combined techniques ; drug design ; drug product development ; drug substance ; drug technology ; DSC ; excipients ; failure investigations ; hydrates ; MDSC ; microcalorimetry ; pharmaceuticals ; polymorphism ; polymers ; preformulation ; process optimization ; purity ; quality control ; solvates ; stability ; sub-ambient DSC ; TG ; temperature resolved X-ray diffraction ; water interactions ; thermal microscopy ; water sorption-desorption
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Modern thermal analysis, microcalorimetry and new emerging combined techniques which deliver calorimetric, microscopic and spectroscopic data offer a powerful analytical battery for the study of pharmaceuticals. These techniques are very useful in all steps of development of new drug products as well as methods for quality control in production. The characterization of raw materials enables to understand the relationships between polymorphs, solvates and hydrates and to choose the proper development of new drug products with very small amount of material in a very short time. Information on stability, purity is valuable for new entities as well as for marketed drug substances from different suppliers. Excipients which vary from single organic or inorganic entity to complexes matrixes or polymers need to be characterized and properly controlled. The thermodynamic phase-diagrams are the basis of the studies of drug-excipients interactions. They are very useful for the development of new delivery systems. A great number of new formulations need proper knowledge of the behaviour of the glass transition temperature of the components. Semi-liquid systems, interactions in aqueous media are also successfully studied by these techniques.
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  • 62
    Digitale Medien
    Digitale Medien
    Springer
    Earth, moon and planets 87 (1999), S. 103-115 
    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.
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  • 63
    Digitale Medien
    Digitale Medien
    Springer
    Multidimensional systems and signal processing 10 (1999), S. 7-20 
    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
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  • 64
    Digitale Medien
    Digitale Medien
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 277-289 
    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
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  • 65
    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.
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  • 66
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 392 (1999), S. 205-215 
    ISSN: 1573-5117
    Schlagwort(e): Dreissena ; hypoxia ; thermal stratification ; survival ; growth ; distribution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Experiments and field surveys were conducted in Hargus Lake (Ohio, U.S.) to investigate the effect of lake stratification on the survival, growth and distribution of zebra mussels. During the lake stratification period, relatively stable temperature and dissolved oxygen (DO) gradients persisted across the water column, allowing us to examine the chronic effect of hypoxia on zebra mussels. Zebra mussels were incubated in cages and suspended at different depths in the water column at both pelagic (max. depth = 12 m) and littoral (max. depth = 3.5 m) sites from April 18 to September 28, 1994. No mussel survived to the end of the experiment in cages ≥ 5.5 m, whereas the highest survival rate (76%) occurred at 5 m depth where temperature and DO remained fairly stable for at least 3 months. The threshold oxygen level for survival was between 1.0–1.7 mg l-1 when water temperature was at about 17–18 °C. While zebra mussels′ survival rate was not affected under the sublethal hypoxic conditions, their growth was greatly retarded by poor water quality. The field survey showed that the zebra mussels and macrophytes had about the same distribution and their biomasses were positively related. The percentage of mussels in aggregates increased towards their maximum distribution depth. The maximum distribution depth of the naturally occurring zebra mussels was only 2.8 m, whereas the adult mussels could survive the entire stratification period when being artificially placed on the 3.5 m bottom, and young mussels could colonize the 3.5 m bottom if solid substrates were provided. We conclude that lack of substrate, rather than hypoxia, was the limiting factor of zebra mussel distribution above 5 m depth in Hargus Lake.
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  • 67
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 398-399 (1999), S. 291-297 
    ISSN: 1573-5117
    Schlagwort(e): Porphyra ; conchocelis ; aquaculture ; growth ; Alaska ; nori
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Experiments were performed to determine the range and optima of environmental conditions under which indigenous species of Alaskan Porphyra can grow. Growth of the conchocelis phase of Porphyra abbottae, P. torta and P. pseudolinearis was measured, when cultured in enriched media, under long days (16 h light) and varying conditions of irradiance (20, 40, 80 and 160 μmol photons m−2 s−1), temperature (7, 11, 15 and 19 °C) and salinity (5, 10, 20, 30 and 40‰). Optimal growth (7.6% increase in volume day−1) of P. abbottae occurred at 11 °C, 80 μmol photons m−2 s−1 and 30‰. Porphyra torta grew best (6.5% day−1) at 15 °C, 80 μmol photons m−2 s−1 and 30‰. Porphyra pseudolinearis generally had higher growth rates than the other two species with optimal growth (8.8% day−1) occurring at 7 °C, 160 μmol photons m−2 s−1 and 30‰. For all three species salinity between 20 and 40‰ had little effect on growth, but there was virtually no growth at salinity of 10‰ and below. Irradiances between 20 and 160 μmol photons m−2 s−1 generally had little effect on growth rates. However, growth of P. abbottae increased with irradiance at 7 °C but was inhibited at irradiances over 40 μmol photons m−2 s−1 at 15 °C and higher. Porphyra torta also showed growth inhibition at 15 °C and higher irradiances. Porphyra pseudolinearis appeared to be the most robust species with respect to tolerance to extremes of salinity and irradiance.
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  • 68
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 398-399 (1999), S. 191-199 
    ISSN: 1573-5117
    Schlagwort(e): seaweed ; morphology ; seasonal variation ; growth ; phenotypic modulation ; kelp ; Undaria pinnatifida
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Undaria pinnatifida (Harvey) Suringar is currently divided into two morphological forms, f. typica Yendo. and f. distans Miyabe & Okamura. The objective of this study was to determine the effects of seasonal variation in growth rate on the morphology of U. pinnatifida, and to define the form of U. pinnatifida growing in Otago Harbour, New Zealand. Morphological variables (stipe length, blade length, blade width, sporophyll length and degree of blade incision), growth rates (frond, blade and stipe) and blade erosion were measured each month from August 1993 to February 1995, and compared using correspondence analysis. Variation in the morphology of U. pinnatifida was largely accounted for by varying growth rates. Definition of the form of U. pinnatifida growing in Otago Harbour is equivocal because morphological characteristics of both f. typica and f. distans were exhibited at different times of the year.
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  • 69
    ISSN: 1573-5117
    Schlagwort(e): Gracilaria ; growth ; irradiance ; plant growth regulators ; salinity ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Growth and tolerance of Gracilaria vermiculophylla (Ohmi) Papenfuss from Shikoku Island were investigated under a variation of temperature (5–30 °C), salinity (5–60‰), and photon irradiance (20–100 μmol photons m−2 s−1) in unialgal culture. G. vermiculophylla showed wide tolerances for all factors tested, characterizing a euryhaline and eurythermal species. Two clones, one of a tetrasporophyte and the other of a female gametophyte, showed different growth rates, attributable to the difference either in phase or in genotype. The optimum temperature for the growth of the tetrasporophyte clone was 15–25 °C while that of the gametophyte clone was 20–30 °C. Maximum growth of both phases was observed at 80–100 μmol m−2 s−1. G. vermiculophylla presented higher growth rates in low salinities (15–30‰). Tissue cultures were established in solid ASP 12-NTA medi um supplemented with plant growth regulators (PGR), 0.5% agar, 1.0% sucrose and 0.5% inositol. Effects of two auxins (indole-3-acetic acid (IAA), and 2,4-dichlorophenoxyacetic acid (2,4-D)), and one cytokinin (6-benzylaminopurine (BA)) were tested in concentrations ranging from 0.1 to 10.0 mg l−1. Growth of apical segments was significantly stimulated by the majority of treatments supplemented with PGR, while maximum growth of calluses was observed in treatments with low concentration of auxins or BA (1.0 mg l−1). All treatments supplemented with PGR significantly promoted the growth of intercalary segments, except for IAA (1.0 mg l−1) in combination with BA (1.0 mg l−1). Growth of calluses originating from intercalary segments was observed in treatments with IAA (0.1 mg l−1), 2,4-D (10.0 mg l−1) or IAA (1.0 mg l−1) in combination with BA (0.1 mg l−1). Tr eatments with high concentration of IAA and BA (10.0 mg l−1) were lethal for apical and intercalary segments. These results show that auxin and cytokinin play a regulatory role on the growth of G. vermiculophylla in tissue culture. Furthermore, results on the effects of temperature, salinity and irradiance indicate that G. vermiculophylla could be cultivated in brackish temperate environments with potential for economic purposes and for pollution management.
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  • 70
    ISSN: 1573-5117
    Schlagwort(e): Gracilaria multipartita ; seasonal variation ; growth ; chemical composition ; agar
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The biology and agar composition and properties of Gracilaria multipartita, a common species along the coasts of Morocco, have been studied on samples collected monthly for one year. Growth of the alga was maximum in spring and autumn, and the seaweed partially decayed after its maximum fertility was reached in June and October. The agar content and composition showed seasonal variations. The agar content was maximal in winter (30% dw), and decreased during the growth periods to minima in June and October (25% dw) which also corresponded to the maxima of fertility. The agar composition was characterized by high 6-O-methyl galactose (38–59 mol%) and 3,6 anhydrogalactose (24–39%) contents together with galactose (12.6–25.7 mol%) and sulphate (24–5.0% dw). The gel strength varied between 246 and 511 g cm−2 and increased after alkali treatment to reach a maximum of 880 g cm−2. The gel stre ngth decreased after the alga reached its maxima of fertility, indicating a possible relationship between growth, fertility and agar metabolism. The content and quality of agar from G. multipartita growing in Morocco are suitable for an industrial use of the seaweed for the production of food-grade agar.
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  • 71
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 403 (1999), S. 123-133 
    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.
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  • 72
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 401 (1999), S. 265-277 
    ISSN: 1573-5117
    Schlagwort(e): nucleic acids ; fish larvae ; RNA/DNA ; condition ; growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nucleic acid analysis has provided useful tools to study recent growth and mortality of young fishes and their responses to environmental variability. The ratio of RNA–DNA (R/D) has been shown to respond to changes in feeding conditions and growth after periods as short as 1–3 days in a variety of fish species. The earliest studies used primarily UV-based methods, but most investigators now use more sensitive, fluorometric dye-binding assays to estimate RNA and DNA in individual larvae. These newer methods are very sensitive to procedural details and choice of standards. Analytical methods, normalization and calibration procedures to optimize information obtained from nucleic acid analysis are discussed. We present examples illustrating the technique's utility, and problems encountered when applying nucleic acid-based indices to fish larvae and early juveniles. The wide use of R/D analysis in studies of fish early life stages, together with a proliferation of analytical methods, demands a major intercalibration exercise.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 40 (1999), S. 985-995 
    ISSN: 1573-5028
    Schlagwort(e): aquaporin ; gene expression ; growth ; Oryza sativa ; plasma membrane intrinsic protein (PIP) ; rice
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Membrane intrinsic proteins facilitate movement of small molecules often times functioning as water channels. We have identified two genes from rice which encode proteins with characteristic features of plasma membrane intrinsic proteins (PIP). They possess six membrane-spanning domains, an NPA repeat, overall high sequence homologies and characteristic C- and N-terminal hallmark motifs which allowed assignment of OsPIP1a to the PIP1 subfamily and of OsPIP2a to the PIP2 subfamily. OsPIP1a and OsPIP2a showed similar but not identical expression patterns. The two genes were expressed at higher levels in seedlings than in adult plants and expression in the primary root was regulated by light. In internodes of deepwater rice plants which were induced to grow rapidly by submergence, transcript levels were slightly induced in the intercalary meristem (IM) and slightly reduced in the elongation zone (EZ) after 18 h. In internodes of GA-induced excised stem sections transcript levels transiently declined in the IM and EZ after 1 h and subsequently recovered to elevated levels after 18 h. GA also induced OsPIP expression in non-growing tissue after 18 h. In the IM of submergence-induced stem sections transcript levels remained constitutive. The different growth-promoting treatments showed no direct correlation between growth rate and OsPIP gene expression in dividing or expanding cells. In fact, treatment of excised stem sections with ABA or drought stress induced similar changes in OsPIP expression in the growing zone during the first 6 h as GA did. We conclude that regulation of OsPIP1a and OsPIP2a expression is not primarily controlled by growth. GA-induced growth may however change the water status of cells which in turn results in altered PIP abundance.
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  • 74
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 216 (1999), S. 93-101 
    ISSN: 1573-5036
    Schlagwort(e): Acacia cyanophylla ; endomycorrhizae ; growth ; nutrition ; Rhizobia ; salinity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The behaviour of Acacia cyanophylla Lind. plants submitted to salinity stress was followed in the greenhouse. The plants were associated with indigenous symbiotic microorganisms isolated from the coastal dunes of the Souss-Massa region. A two months period of salinity had a large negative impact on plant growth and acquisition of macro nutrients. However, the study underlined the role of the microbial inoculum for the plant in the achievement of salt tolerance. An isolate of Bradyrhizobium sp., RCM6 (R1), originating from the Massa dunes, was highly efficient in improving growth and nutrition of the A. cyanophylla. Double inoculation with the rhizobia and an endomycorrhizal complex, isolated from the Lamzar dunes had a clear additional positive effect, i.e. the fungi further increased the tolerance of the A. cyanophylla plants to salinity.
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 217 (1999), S. 1-15 
    ISSN: 1573-5036
    Schlagwort(e): anchorage ; development ; growth ; root systems ; symmetry ; tree stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The stability of shallowly rooted trees can be strongly influenced by the symmetry of the ‘structural’ system of woody roots. Root systems of forest trees are often markedly asymmetric, and many of the factors affecting symmetry, including root initiation and the growth of primary and woody roots, are poorly understood. The internal and environmental factors that control the development, with respect to symmetry and rigidity, of shallow structural root systems are reviewed and discussed with particular reference to Sitka spruce (Picea sitchensis Bong. Carr.). Areas where there is insufficient knowledge are highlighted. A scheme is proposed that represents the root system as a set of spokes that are variable in number, size and radial distribution. Rigidity can vary between and along each of the spokes. The root system is presented as a zone of competition for assimilates, where allocation to individual roots depends upon their position and local variations in conditions. Factors considered include the production of root primordia of different sizes, effects of soil conditions such as the supply of mineral nutrients and water on growth of primary and woody roots, and the effect of forces caused by wind action on growth of the cambium, giving rise to roots which, in cross section, resemble I- or T-beams, and efficiently resist bending.
    Materialart: Digitale Medien
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  • 76
    ISSN: 1573-5117
    Schlagwort(e): zebra mussel ; intermittent halogenation ; Dreissena polymorpha ; growth ; settlement ; survival
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effect of intermittent (2–4 h/day) treatments with chlorine or bromine at levels of 0.5 and 1.0 mg/L (total residual oxidant) upon settling and growth of veliger larvae of the zebra mussel, Dreissena polymorpha, was examined in two successive flow-through studies. The work was conducted in a field laboratory which received a constant supply of water from western Lake Erie. Veliger densities in the water at the field site peaked at 530/L, while mussel densities on settling monitors reached 147,100/m2 over the course of the two studies (early July to late September 1991). In Study 1, a 2-h daily treatment with 1.0 mg/L chlorine reduced mussel settling by 91% as compared with controls, although mussel densities of up to 6,000/m2 still occurred. Treatment with 0.5 mg/L chlorine for 4 h/day produced a similar reduction in mussel settling during the second study. Bromine was less effective than chlorine at reducing settling of veligers. Mussels which remained settled in the treatment tanks had growth rates similar to controls, reaching 2–4 mm in length over a 30-day period. The intermittent halogen treatments similarly had no effect on whole body glycogen levels or growth of adult D. polymorpha. The intermittent chlorination regime used may therefore delay, but would not prevent a mussel fouling problem.
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  • 77
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 398-399 (1999), S. 91-100 
    ISSN: 1573-5117
    Schlagwort(e): Polysiphonia setacea ; Rhodophyta ; culture ; growth ; biogeography ; Mediterranean Sea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The red alga Polysiphonia setacea Hollenberg (=Womersleyella setacea (Hollenberg) R. Norris), described originally from the Hawaiian Islands and later reported for other tropical localities, has recently become widespread in the Mediterranean. In several localities it forms a dense, almost monospecific turf but, despite its abundance, it appears to reproduce only vegetatively; neither sporangia nor sexual reproductive structures have thus far been found. In order to elucidate its life history, plants were cultured in a variety of conditions of temperature, daylength and photon irradiance, and the upper thermal limit was also determined. Isolates of P. setacea grew well in culture, but were more tufted and branched than wild plants. No reproduction by spores or gametes was observed and only an unusual form of vegetative regeneration was found. Some pericentral cells became darker and larger than the others and produced proliferations from which new plants arose. Plants grew best at 15 and 20 °C, and relatively poor growth was observed at 10 and 25 °C. At 20 °C growth was better in long days than in short days. The upper thermal limit was 28 °C, and plants were able to tolerate a temperature as low as 5 °C for 4 weeks without any damage. These observations show that P. setacea is well adapted to the environmental conditions of the western Mediterranean, and there is good agreement with the phenology of the species in the wild. Although this entity has been treated as an introduction from a tropical area, our results suggest that the Mediterranean entity would not be able to survive or grow in surface waters of tropical areas whence this species has been reported. However, the occurrence of thermal ecotypes in P. setacea is a possibility and further studies, based perhaps on molecular data, are necessary to assess the origin of the Mediterranean populations.
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  • 78
    Digitale Medien
    Digitale Medien
    Springer
    Environmental biology of fishes 54 (1999), S. 325-336 
    ISSN: 1573-5133
    Schlagwort(e): population structure ; reproduction ; growth ; mortality ; fish
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Black seabream, Spondyliosoma cantharus, caught off the Canary Islands is characterized by a protogynous hermaphroditism. The size range of the catches is between 8 and 40 cm, with a main distribution between 16 and 24 cm. The mean length of the individuals shows an increase with increasing depth. Males:females ratio is unbalanced in favour of females (1:2.18). The reproductive season extends from late autumn to mid spring, with a peak in spawning activity in January–February. A dichromatism is found between males and females during the spawning season. Males reach maturity at a larger total length, 22.7 cm (3 years old), than females, 17.3 cm (2 years old). Morphometric relationship between length and mass for the whole population is described by the parameters: a=0.00732, and b=3.24747. Otoliths age readings indicate that the exploited population consists of eleven age groups (0–X years), including a very high proportion of individuals between 2 and 3 years old. The von Bertalanffy growth parameters for the whole population are: L∞=43.35 cm, k=0.24 year−1, and t0=−0.11 year. The rates of total, natural and fishing mortality are 1.36, 0.52 and 0.84 year−1, respectively. The length at first capture is 16.8 cm. The exploitation rate indicates that the stock is overfished.
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  • 79
    Digitale Medien
    Digitale Medien
    Springer
    Environmental biology of fishes 55 (1999), S. 215-225 
    ISSN: 1573-5133
    Schlagwort(e): gonadosomatic index ; growth ; maturity ; migration ; mortality ; sex ratio ; spawning ; von Bertalanffy growth model
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Aspects of the life history of Labeo cylindricus in Lake Chicamba, a man made hydroelectric dam in central Mozambique were investigated. L. cylindricus was found to be a potadrometic, synchronous spawner concentrating in river mouths prior to migrating up flowing rivers in January to spawn. Length-at-(50%)-maturity was attained at a fork length (FL) of 96 mm for males and 98 mm for females, both within their first year of life. The adult sex ratio was found to be female dominated at 1 male:1.63 females. Scales were used to age the species, with two growth checks deposited annually. Growth was rapid and was best described by the von Bertalanffy growth model as L t =224.2(1−e-0.66(r+0.03)) mm FL. A maximum age of 4 years was observed for L. cylindricus with the largest male and female measuring 210 mm FL and 235 mm FL, respectively. The rate of natural mortality was estimated to be extremely high at 1.93 year-1 using length-converted catch curve analysis and is possibly a response to heavy predation by the introduced piscivore Micropterus salmoides.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    Springer
    Environmental biology of fishes 55 (1999), S. 413-421 
    ISSN: 1573-5133
    Schlagwort(e): reproduction ; spawning ; age ; growth ; vermilion snapper ; Trinidad ; Tobago
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Reproduction and growth of the vermilion snapper, Rhomboplites aurorubens, were studied in Trinidad and Tobago. The smallest individual caught measured 145 mm total length (TL) and all fish appeared to be mature. It was not possible to precisely determine size at first maturity due to the use of macroscopic techniques. The smallest spent male and female measured 181 and 211 mm TL respectively, suggesting a size at first maturity below these sizes. Spawning occurred throughout the year, with a period of peak spawning from about June to November in the rainy season when river runoff increased. Sagittal otolith sections were used for age determination and the opaque ring, which was counted as the annulus, was deposited from January to May in the dry season. A total of 11 age groups between the ages of 2–12 years (155–505 mm total length) were found. The von Bertalanffy growth parameters were: L∞=532 mm, K=0.13 y−1, and t0=−0.17, where L∞ is the asymptotic length, K is the growth coefficient and t0 is the theoretical age at zero length. The relationship between weight (WT) and length (TL) was WT=3.43×10−5 TL2.82. Vermilion snapper in this study area appears to grow slower and attain a smaller asymptotic length, but has a longer lifespan than found in populations in higher latitudes. This may be attributed to different levels of exploitation, which may be higher in the latter areas.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Springer
    New forests 18 (1999), S. 301-314 
    ISSN: 1573-5095
    Schlagwort(e): chilling stress ; drought stress recovery ; field performance ; growth ; morphology ; nursery culture ; tree nursery
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Five week old white spruce [Picea glauca (Moench) Voss] seedlings were placed within controlled-temperature growth chambers, and subjected to one of four periodic, chilling treatments for approximately 16 weeks. The treatments differed in the frequency of 24 hour exposure to 5 °C the seedlings received, and ranged from no chilling (control), to once every two, three or four days. After 25 weeks of growth, the control seedlings were significantly taller than all chilling-exposed seedlings, but stem diameters were similar. Chilling did not affect either needle length or needle density compared to control seedlings. During a water deficit test, frequently chilling-exposed seedlings maintained significantly higher mid-day shoot water potentials under extreme water stress. Re-watering after the drought resulted in all chilling-treated seedlings recovering faster to pre-stress shoot water potential levels than the control seedlings. Measurements of new root growth after 21 days at 10 °C indicated that previous chilling exposure delayed or inhibited new root production.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 82
    Digitale Medien
    Digitale Medien
    Springer
    Plant growth regulation 29 (1999), S. 101-112 
    ISSN: 1573-5087
    Schlagwort(e): ABA ; cell wall-associated peroxidase ; expansins ; growth ; pH ; XET
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Over the past decade it has become clear that we cannot always explain the observed reduction in leaf expansion rates during drought by measuring the plant's water relations. This has led us to question the possibility of a role for the cell wall and its biochemical machinery in controlling the rate of leaf expansion during drought. However, if we are to reject or modify previous assumptions regarding the control of leaf expansion during drought, then we must offer alternative explanations. This article addresses recent work from this laboratory and in the literature, concerning the involvement of cell wall-enzymes, pH and abscisic acid (ABA) in regulating leaf expansion during water deficit.
    Materialart: Digitale Medien
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  • 83
    ISSN: 1573-4919
    Schlagwort(e): NADH oxidase ; protein disulfide-thiol interchange ; dipyridyl-dithio substrates ; plasma membrane ; auxin ; 2,4-dichlorophenoxyacetic acid ; growth ; plant (Glycine max)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Dipyridyl-dithio substrates were cleaved by isolated vesicles of plasma membranes prepared from etiolated hypocotyls of soybean. The cleavage was stimulated by auxins at physiological concentrations. The substrates utilized were principally 2,2′-dithiodippyrine (DTP) and 6,6′-dithiodinicotinic acid (DTNA). The DTP generated 2 moles of 2-pyridinethione whereas the 6,6′-dithiodinicotinic acid generated 2 moles of 6-nicotinylthionine. Both products absorbed at 340 nm. The auxin herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) stimulated the activity approximately 2-fold to a maximum at about 10 μM. Concentrations of 2,4-D greater than 100 μM inhibited the activity. Indole-3-acetic acid stimulated the activity as well. The growth-inactive auxin, 2,3-dichlorophenoxyacetic acid (2,3-D), was without effect. DTNA cleavage correlated with oxidation of NADH and reduction of protein disulfide bonds reported earlier in terms of location at the external plasma membrane surface, absolute specific activity, pH dependence and auxin specificity. The dipyridyl-dithio substrates provide, for the first time, a direct measure of the disulfide-thiol interchange activity of the protein previously measured only indirectly as an auxin-dependent ability of isolated plasma membrane vesicles to restore activity to scrambled and inactive RNase.
    Materialart: Digitale Medien
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  • 84
    Digitale Medien
    Digitale Medien
    Springer
    Journal of biomolecular NMR 13 (1999), S. 187-191 
    ISSN: 1573-5001
    Schlagwort(e): alignment ; bicelle ; dipolar coupling ; liquid crystal ; pH ; stability ; ubiquitin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract It is demonstrated that mixtures of ditetradecyl- phosphatidylcholine or didodecyl-phoshatidylcholine and dihexyl- phosphatidylcholine in water form lyotropic liquid crystalline phases under similar conditions as previously reported for bicelles consisting of dimyristoyl-phosphatidylcholine (DMPC) and dihexanoyl- phosphatidylcholine (DHPC). The carboxy-ester bonds present in DMPC and DHPC are replaced by ether linkages in their alkyl analogs, which prevents acid- or base-catalyzed hydrolysis of these compounds. 15N-1H dipolar couplings measured for ubiquitin over the 2.3–10.4pH range indicate that this protein retains a backbone conformation which is very similar to its structure at pH 6.5 over this entire range.
    Materialart: Digitale Medien
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  • 85
    ISSN: 1573-5036
    Schlagwort(e): growth ; porewater ; salt marshes ; silicon ; Spartina ; tissue concentrations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Analysis of silicon concentrations of various halophytes from salt marshes in the S.W. Netherlands shows that the silicon concentration of Spartina anglica (Gramineae) is relatively high. To study the influence of dissolved Si concentrations on growth and plant tissue concentrations of S. anglica, silicic acid was introduced into the sediment of natural patches of this halophyte occurring on a tidal flat. This resulted in a strong increase in dissolved silicon levels in the sediment porewater. In addition, S. anglica was cultured in the laboratory on nutrient solution enriched with dissolved silicon. Neither in the field nor in the laboratory experiment did the increased silicon levels have effects on shoot growth or led to consistent increases in the silicon concentration of plant tissues. Finally, different S. anglica stands in a number of salt marshes around the Oosterschelde basin were examined on sediment porewater silicon concentrations and silicon plant tissue concentrations. Sediment porewater silicon levels ranged between 36 and 554 μM. The average silicon concentration of the shoots from the various populations ranged between 3.52 and 11.73 mg/g DW. Consistent with the results of the field and laboratory experiments, there was no correlation between porewater silicon concentrations and average shoot length at the different sites, nor between porewater silicon concentrations and shoot silicon levels. Apparently, vegetative growth and tissue silicon concentrations of S. anglica do not respond to concentrations of dissolved Si in the range to which the plants were exposed naturally or experimentally in the field and in the laboratory (ca. 15–550 μM). In the data set pertaining to the different S. anglica field populations, however, negative correlations were observed between the average number of leaves per shoot at the different locations and the total silicon content of the 4th and 2nd leaves and of the entire shoots. The possible mechanisms explaining differences in tissue Si concentrations are discussed.
    Materialart: Digitale Medien
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  • 86
    ISSN: 1573-5036
    Schlagwort(e): 2 ; 4-D ; germination ; growth ; salinity-tolerance ; seed treatment ; wheat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Experiments were conducted under laboratory and greenhouse conditions to study the effect of 2,4-D on rooting and salinity tolerance of wheat. Seeds of one commercial wheat (Inqalab-91) and three salt-tolerant wheat lines (WL-41, WL-359, and WL-1073 developed through wide hybridization) were included in the study. Preliminary and short-term experiments were conducted to determine the level of 2,4-D (administered through seed soaking for 24.5 h. at 25 °C in the dark) at which the maximum number of roots emerged. Under hydroponic conditions, 2,4-D treatment of seeds caused an increase of 60 to 100% in the number of primary roots. The maximum increase in the number of roots was observed in one of the salt tolerant wheat lines (WL-41). The roots appeared in bunches but showed stunted growth at higher levels of 2,4-D. Dry matter accumulation decreased markedly; the effect was more pronounced in Inqalab-91 which is less tolerant to stress than other wheat lines. In all wheat types, allocation of dry matter to roots relative to shoot increased due to 2,4-D treatment. In soil, seeds treated with different levels of 2,4-D showed a germination delay of 1–3 days. Although the number of primary roots increased, 2,4-D treatment caused a decrease in total dry matter accumulation by plants grown for 40 days. In another experiment, conducted under greenhouse conditions, seed germination and growth of seedlings was significantly retarded in saline compared to that in non-saline (normal) soil. Initially, the pace of germination of treated seeds as well as seedling growth was slower in both soils, but after six weeks, the leaf area of seedlings raised from treated seeds was greater than those raised from untreated seeds. Towards maturity, plants arising from treated seeds developed wider and longer flag leaves leading to enhanced yield. Root biomass decreased in saline soil as compared to normal soil. However, 2,4-D treatment caused a substantial increase in root biomass in saline soil and the roots were harder in texture in wheats other than Inqalab-91. Seed treatment with 2,4-D led to a significant improvement in the number of productive tillers, yield of straw and grain, and grain protein content of all wheats grown in saline soil. Plants grown in normal soil did not show any marked effect of seed treatment on grain yield and other agronomic parameters. The four wheats showed substantial differences for different parameters but the salt tolerant wheat lines performed better compared to the commercial variety Inqalab-91.
    Materialart: Digitale Medien
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  • 87
    ISSN: 1573-3017
    Schlagwort(e): Tubifex tubifex ; sediment bioassay ; hormesis ; growth ; reproduction ; egestion rates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Toxicity assessment based on sediment chronic bioassays with the aquatic worm Tubifex tubifex was performed at ten contaminated sites in the industrial area of Bilbao (Northern Spain). One control and three reference sites were also included. Tubifex bioassay measures both survival and reproduction impairment. These endpoints have been contrasted and discussed in relation to somatic growth and both individual and total biomass of cocoons. Survival was only affected at one site which was heavily contaminated by organic compounds, mainly PAHs. A group of four severely ecotoxic sediments was characterised by a drastic reduction in number and size of cocoons, and adult somatic growth. In other group of sediments, some significant increases were found for these variables. It is suggested that these increases represent an effect of hormesis. An index of reproductive effort was used to integrate the relationship between somatic growth and reproduction. Values of reproductive effort at the test sediments were lower than those at the control sediment, suggesting a conservative strategy of oligochaete worms which consisted in an investment into somatic line (growth) at the expenses of offspring. Rates of food consumption which were estimated from egestion rates, were low at the contaminated sites. This fact could be related to the low production levels found at these sites and may reflect avoidance feeding behaviour of the oligochaete worms within the sediments. At some reference sites, high production could have resulted from high nutritional quality of sediments, or to an hormetic effect due to low concentration of some chemicals. Results are discussed in relation to toxicity data from sediment three-brood bioassay with Daphnia magna Straus performed separately on the same sediments.
    Materialart: Digitale Medien
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  • 88
    Digitale Medien
    Digitale Medien
    Springer
    Aquaculture international 7 (1999), S. 201-205 
    ISSN: 1573-143X
    Schlagwort(e): fingerlings ; growth ; light regimes ; photoperiod ; silver catfish (Rhamdia quelen) ; survival
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 89
    ISSN: 1573-143X
    Schlagwort(e): gilthead sea bream (Sparus aurata) ; growth ; hybridization ; red porgy (Pagrus pagrus) ; survival
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Hybridization between gilthead sea bream, Sparus aurata, and red porgy, Pagrus pagrus, was undertaken and viable hybrids were produced by an artificial hormonal-induced cross. The hybrids, from the cross of female red porgy and male gilthead sea bream (Pp × Sa), survived through the yolk-sac larval stage. The hybrids produced from the cross of female gilthead sea bream and male red porgy (Sa × Pp) presented higher mortality in the larval stage (98.4%) compared to gilthead sea bream (80.0%) and red porgy (92.5%). Afterwards, the Sa × Pp hybrid was compared to the offspring of its parental species under the same rearing conditions (tanks of 500 l capacity, natural light, ambient temperature, self-feeding with commercial feed) in a 40–week experiment. In this comparative study, the Sa × Pp hybrid had intermediate mortality rate (6%), compared to gilthead sea bream (0%) and red porgy (21%). The growth profile of this hybrid resembled the slow growing phases of its parents (red porgy in warm period and gilthead sea bream in cold period). The feed conversion ratio between fish forms was not significantly different (1.54–1.84 in the Sa × Pp hybrid, 1.53–1.56 in the maternal species and 1.33–1.40 in the paternal one). The body weight variation in the Sa × Pp hybrid was quite high (31.7–37.9%), compared to that in gilthead sea bream (19.7–24.7%) and red porgy (18.0–31.3%). With respect to body coloration, the Sa × Pp hybrid was distinguishable and classified into groups of red porgy-like (55.1%), gilthead sea bream-like (40.6%), and intermediate forms (4.3%). The preliminary results of this study proved that the produced Sa × Pp hybrid had too low a performance for aquaculture use, but the interesting consequent hereditary potential could be a useful tool in fish hybridization practice.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 90
    Digitale Medien
    Digitale Medien
    Springer
    Aquaculture international 7 (1999), S. 287-293 
    ISSN: 1573-143X
    Schlagwort(e): bone mineralization ; calcium requirement ; feed efficiency ; growth ; semi-purified diet ; tiger puffer (Takifugu rubripes)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Juvenile tiger puffer (Takifugu rubripes) were fed semi-purified diets with graded levels (0–0.40%) of calcium (Ca) supplements for 8 weeks at a temperature of 23.0–25.5 °C. At the end of the feeding experiment, average final body weight increased with increasing dietary Ca levels. A diet without Ca supplement resulted in poor average final body weight and 0.05% dietary Ca supplement could not significantly improve the growth. However, supplemental Ca levels of 0.10–0.40% significantly increased growth. Dietary Ca supplements of 0.10% or more also improved the feed efficiency in tiger puffer. Ca and phosphorus contents of the bone were independent of dietary Ca supplements. However, 0.40% Ca in the diet decreased the zinc and manganese contents of bone. Results indicated that supplemental Ca levels of 0.10–0.20% in a semi-purified diet were required to maintain normal growth, feed utilization and bone mineralization of tiger puffer.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 91
    ISSN: 1573-143X
    Schlagwort(e): body composition ; dietary protein ; fecundity ; gonad maturation ; growth ; Nile tilapia (Oreochromis niloticus)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Six-week-old Nile tilapia (Oreochromis niloticus) fry with an average weight (SD) of 0.51(0.2) g were reared for 140 days on five formulated, isocaloric diets of different protein levels (25, 30, 40 and 45% by dry weight). Fish fed diets of higher protein levels (40 and 45%) showed better growth and feed conversion ratio than those on lower protein levels. Fast-growing fish matured earlier. Maturation rate was affected by the dietary protein levels. Males matured earlier than females: the first mature males were recorded when they were 14 weeks old, whereas the females matured after 18 weeks. In both sexes, mean percentage of mature fish rose with increasing dietary protein level, the percentage of mature males being higher than that of the females. Similarly, the percentage of mature fish rose with the increasing age of fish, with more than 50% males and females mature at the age of 22 and 24 weeks, respectively, the exception being the 25% protein diet fed fish, where the percentage of mature fish was below 50%. In all treatments, spawning was initiated when the fish were 22 weeks old. Smallest size at spawning of males and females was 9.2 cm (13.1 g) and 8.1 cm (8.9 g), respectively, and dietary protein levels influenced the size of fish at first maturity. For both sexes, no difference was found in the gonado-somatic index (GSI) among different treatments. Fecundity increased with increasing dietary protein levels, but significant differences were found only between 40–45% and 25–35% dietary protein levels. The relative fecundity (eggs g−1 female) was higher at the lower dietary protein levels (25–35%) than at the higher dietary protein levels (40–45%). The dietary protein levels did not have any significant influence on the size and weight of mature eggs. The chemical composition of fish and mature ovaries was significantly influenced by the dietary protein level.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 92
    ISSN: 1573-2932
    Schlagwort(e): Genetic variability ; elevated CO2 ; climate change ; pine ; conifer ; photosynthesis ; growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Genetic variability can have profound effects on the interpretation of results from elevated CO2 studies, and future forest management decisions. Information on which varieties are best suited to future atmospheric conditions is needed to develop future forest management practices. A large-scale screening study of the effects of elevated CO2 on 15 half-sibling sources of genetically superior ponderosa pine (Pinus ponderosa Dougl ex P. Laws.) is presented. These sources represent multiple elevations and latitudes throughout California. Among-provenance variability in the effects of elevated CO2 on gas exchange and growth, and their correlation with geographic origin were investigated in ponderosa pine seedlings subjected to ambient or elevated CO2 concentrations (525 μmol mol-1 CO2, and 700 μmol mol-1 CO2) for more than two years in open-top chambers. Substantial among-provenance variability in growth response to elevated CO2 was evident, with 8 sources demonstrating no significant growth response to elevated CO2 while 7 sources responded positively. For all sources, elevated CO2 increased photosynthesis (ranging from 19% increase at 525 μmol mol-1 CO2 to 49% increase at 700 μmol mol-1 CO2). A modest correlation existed between geographic origin and above ground growth response to elevated CO2.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Journal of optimization theory and applications 100 (1999), S. 575-597 
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Journal of optimization theory and applications 102 (1999), S. 299-313 
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Springer
    Water, air & soil pollution 114 (1999), S. 13-25 
    ISSN: 1573-2932
    Schlagwort(e): biomass ; cement dust ; growth ; partitioning ; spruces
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Two-year-old seedlings of Picea abies L., P. glauca L. and P. mariana L. were planted in a sample plot subjected to high concentrations of cement dust and in an unpolluted (control) area in 1990. In 1994, the six-year-old trees were dug up in the pre-bud-break period for morphological assessment. Comparison of biomass formation and the lengths of different organs of the trees showed that alkalization of the growth substrate (pH 8.1) and the high level of dust pollution load (600–2400 g m-2yr-1) are serious factors inhibiting height growth by 61%, the length of shoots and needles by 75 and 28%, respectively, and the dry weights of roots by 88%, stems by 90%, shoots by 91% and needles by 55%. The ratio of roots to shoots dry weights increased in all species of spruces under stress. P. mariana was the most sensitive to dust pollution impact and alkalization of the environment.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Water, air & soil pollution 116 (1999), S. 151-197 
    ISSN: 1573-2932
    Schlagwort(e): air quality ; Physiology ; growth ; biotic and abiotic interactions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract The perceived health of forest ecosystems over large temporal and spatial scales can be strongly influenced by the frames of reference chosen to evaluate both forest condition and the functional integrity of sustaining forest processes. North American forests are diverse in range, species composition, past disturbance history, and current management practices. Therefore the implications of changes in environmental stress from atmospheric pollution and/or global climate change on health of these forests will vary widely across the landscape. Forest health surveys that focus on the average forest condition may do a credible job of representing the near-term trends in economic value while failing to detect fundamental changes in the processes by which these values are sustained over the longer term. Indications of increased levels of environmental stress on forest growth and nutrient cycles are currently apparent in several forest types in North America. Measurements of forest ecophysiological responses to air pollutants in integrated case studies with four forest types (southern pine, western pine, high elevation red spruce, and northeastern hardwoods) indicate that ambient levels of ozone and/or acidic deposition can alter basic processes of water, carbon, and nutrient allocation by forest trees. These changes then provide a mechanistic basis for pollutant stress to enhance a wider range of natural stresses that also affect and are affected by these resources. Future climatic changes may ameliorate (+ CO2) or axacerbate (+ temperature, + UV-B) these effects. Current projections of forest responses to global climate change do not consider important physiological changes induced by air pollutants that may amplify climatic stresses. These include reduced rooting mass, depth, and function, increased respiration, and reduced water use efficiency. Monitoring and understanding the relative roles of natural and anthropogenic stress in influencing future forest health will require programs that are structured to evaluate responses at appropriate frequencies across gradients in both forest resources and the stresses that influence them. Such programs must also be accompanied by supplemental process -oriented and pattern -oriented investigations that more thoroughly test cause and effect relationships among stresses and responses of both forests and the biogeochemical cycles that sustain them.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Nonlinear dynamics 19 (1999), S. 173-193 
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Nonlinear dynamics 20 (1999), S. 221-246 
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Interface science 7 (1999), S. 285-295 
    ISSN: 1573-2746
    Schlagwort(e): computer simulation ; growth ; energy dissipation ; grain boundaries ; triple nodes (Interfaces) ; triple line (Interfaces)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Abstract Vertex dynamics models in two and three dimensions are applied to study grain growth including a limited mobility of triple points (two dimensions) and triple lines (three dimensions). A recent experiment on a triple node is used to validate the proposed model. The reduced triple node/line mobility in the case of a polycrystalline sample is shown to influence both, the grain growth kinetics and the grain size distribution function.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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