Local stability

We describe a method for the visual interactive simulation of wires contacting with rigid multibodies. The physical model used is a hybrid combining lumped elements and massless quasistatic representations. The latter is based on a kinematic constraint preserving the total length of the wire along a segmented path which can involve multiple bodies simultaneously and dry frictional contact nodes used for roping, lassoing and fastening. These nodes provide stick and slide friction along edges of the contacting geometries. The lumped element resolution is adapted dynamically based on local stability criteria, becoming coarser as the tension increases, and up to the purely kinematic representation. Kinematic segments and contact nodes are added and deleted and propagated based on contact geometries and dry friction configurations. The method gives dramatic increase on both performance and robustness because it quickly decimates superfluous nodes without loosing stability, yet adapts to complex configurations with many contacts and high curvature, keeping a fixed, large integration time step. Numerical results demonstrating the performance and stability of the adaptive multiresolution scheme are presented along with an array of representative simulation examples illustrating the versatility of the frictional contact model.

The objectives of this paper are to (1) provide analytical expressions for the elastic cross-section local buckling stresses, including element interaction, of hot-rolled steel structural shapes, and (2) compare these local buckling results to the assumptions inherent in the local slenderness limits of the US AISC structural steel specification. The cross-section local buckling stress is determined by finite strip analysis (FSA). Local stability of each cross-section in the AISC shapes database (excluding pipes) is considered in axial compression, as well as positive and negative bending about the major and minor geometric axes. Local buckling stresses are converted into plate buckling coefficients (k's) and simplified expressions are provided for all observed k's. The new k's explicitly include elastic web-flange interaction amongst the elements comprising the cross-section. The k values from the FSA are compared to those inherently assumed in the AISC Specification, significant differences are observed.

Epidemiology and ecology are traditionally treated as independent research areas, but there are many commonalities between these two fields. It is frequently observed in nature that the former has an encroachment into the later and changes the system dynamics significantly. In population ecology, in particular, the predator-prey interaction in presence of parasites can produce more complex dynamics including switching of stability, extinction and oscillations. On the other hand, harvesting practices may play a crucial role in a host-parasite system. Reasonable harvesting can remove a parasite, in principle, from their host. In this paper, we study theoretically the role of harvesting in a predator-prey-parasite system. Our study shows that, using impulsive harvesting effort as control parameter, it is not only possible to control the cyclic behavior of the system populations leading to the persistence of all species, but other desired stable equilibrium including disease-free can also be obtained.

The paper aims to express the spontaneous regression and progression of a malignant tumor system as a prey-predator like system. The model is a three dimensional deterministic system, consisting of tumor cells, hunting predator cells and resting predator cells. Local stability analysis is performed along with numerical simulations to support the analytical findings. Moreover, the deterministic model is extended to a stochastic one allowing random fluctuations around the positive interior equilibrium. The stochastic stability properties of the model are investigated both analytically and numerically. The thresholds obtained from our study may be helpful to control the malignant tumor growth.

Exploiting local stability, we show what neuronal characteristics are essential to ensure that coherent oscillations are asymptotically stable in a spatially homogeneous network of spiking neurons. Under standard conditions, a necessary and, in the limit of a large number of interacting neighbors, also sufficient condition is that the postsynaptic potential is increasing in time as the neurons fire. If the postsynaptic potential is decreasing, oscillations are bound to be unstable. This is a kind of locking theorem and boils down to a subtle interplay of axonal delays, postsynaptic potentials, and refractory behavior. The theorem also allows for mixtures of excitatory and inhibitory interactions. On the basis of the locking theorem, we present a simple geometric method to verify the existence and local stability of a coherent oscillation.

The effect of increasing length on the stability of a hanging fluid-conveying pipe is investigated. Experiments show that there exists a critical length above which the flow velocity necessary to cause flutter becomes independent of the pipe length. The fluid-structure interaction is thus modelled by following the work of Bourrières and of Païdoussis. Computations using a standard Galerkin method confirm this evolution. A short pipe model is then considered, where gravity plays a negligible role. Transition between this short length model and the asymptotic situation is found to occur where a local stability criterion is satisfied at the upstream end of the pipe. For longer pipes, a model is proposed where the zone of stable waves is totally disregarded. Comparison of these models with experiments and computations show a good agreement over all ranges of mass ratios between the flowing fluid and the pipe.

This paper describes the various analysis and design aspects of a fiber reinforced plastic (FRP) bridge. The design methodology is illustrated by describing the steps taken in the design of the first US FRP cable-stayed pedestrian bridge to be constructed in Lincoln, Nebraska. The analysis is made using three dimensional (3-D) macro models of the bridge to describe its overall behavior under static and dynamic loads. Separate analysis is done to study the local stability of the different structural elements. The orthotropy of the material is taken into account during this analysis. The short term and long term stiffnesses and strengths are evaluated and accounted for in the design process.

Functional stability is dependent on integrated local and global muscle function. Mechanical stability dysfunction presents as segmental (articular) and multi-segmental (myofascial) dysfunction. These dysfunctions present as combinations of restriction of normal motion and associated compensations (give) to maintain function. Stability dysfunction is diagnosed by the site and direction of give or compensation that relates to symptomatic pathology. Strategies to manage mechanical stabililty dysfunction require specific mobilization of articular and connective tissue restrictions, regaining myofascial extensibility, retraining global stability muscle control of myofascial compensations and local stability muscle recruitment to control segmental motion. Stability re-training targets both the local and global stability systems. Activation of the local stability system to increase muscle stiffness along with functional low-load integration in the neutral joint position controls segmental or articular give. Global muscle retraining is required to correct multisegmental or myofascial dysfunction in terms of controlling the site and direction of load that relates to provocation. The strategy here is to train low-load recruitment to control and limit motion at the site of pathology and then actively move the adjacent restriction, regain through range control of motion with the global stability muscles and regain sufficient extensibility in the global mobility muscles to allow normal function. Individual strategies for integrating local and global recruitment retraining back into normal function are suggested. #

This paper studies the local exact controllability and the local stabilization of the semilinear Schr\"odinger equation posed on a product of $n$ intervals ($n\ge 1$). Both internal and boundary controls are considered, and the results are given with periodic (resp. Dirichlet or Neumann) boundary conditions. In the case of internal control, we obtain local controllability results which are sharp as

Overcomplete representations are attracting interest in signal processing theory, particularly due to their potential to generate sparse representations of signals. However, in general, the problem of finding sparse representations must be unstable in the presence of noise. We prove the possibility of stable recovery under a combination of sufficient sparsity and favorable structure of the overcomplete system.

The delta plain of the Rhone shows many sandy beach ridges cropping out at the surface. We propose here a radiocarbon chronology for the accumulation of the sedimentary bodies and an interpretation of the morphology of the mouth lobes that they form. Morphologies of the lobes depend on four principal factors: (1) the variation of the relative sea level, which constitutes the morphogenic base level, (2) the fluvial input (volume of water discharge and sedimentary input, number and position of the mouths), (3) marine dynamics (volume and direction of the longshore drift, dominant wave direction) (4) the accommodation space created by the rise of relative sea level, along with the paleobathymetry onto which the lobe will prograde immediately in front of the delta and at sea.Our conclusions are: the main Holocene paleo-delta lobes of Ulmet and Saint Ferréol were contemporaneous, being deposited from 4000 to 2000 yr BP. However, the fluvial style of their downstream channel (meandering for Ulmet channel and linear for Saint-Ferréol) and the lobe morphologies of both channels are contrasted: rounded in the case of Ulmet and elongated for Saint-Ferréol. The role of the accommodation space is confirmed by two recent drillholes traversing the entire Holocene succession, which reveal a prior stage of sedimentary filling in the case of the Saint-Ferréol lobe, thus limiting the accommodation space and favouring a rapid and pointed progradation of this lobe.The decoupling between hydrological activity and progradation of lobe indicates the complexity of mechanisms in the large catchment basin of Rhône. However, the high rate of progradation of Saint-Ferréol lobe after 2900 BP is probably a consequence of the increase of human activity after this date.The variation of relative sea level remains an important factor controlling the evolution of the Rhone delta after 6000 BP. The local (?) stabilization of the relative sea level between 4585 BP and 3520 BP played an important role in the triggering of coastal progradation (Saint-Ferréol lobe, eastern margin Rhône delta).

The modified Leslie-Gower and Holling-type II predator-prey model is generalized in the context of ecoepidemiology, with disease spreading only among the prey species. A new feature is introduced, the intraspecific competition of infected prey. All the equilibria are characterized and the existence of a Hopf bifurcation at the coexistence equilibrium is shown.

This thesis deals with the problem of adaptively controlling a linear time-invariant plant in the presence of constraints on the input amplitude. A new algorithm is introduced for continuous-time plants and it is shown that it leads to bounded solutions when the initial conditions of the adaptive system lie within a compact set. A similar condition is also put forward for discrete-time plants which ensures bounded trajectories. In both cases the results are valid for open-loop stable as well as unstable plants but are restricted to minimum phase plants. The results are applied to the problem of grasping and manipulating a compliant object using compliant fingerpads.

The paper mathematically frames the relation between window-based and rate-based congestion control algorithms, when the assumption of variable round-trip time conditions is introduced. Under this hypothesis, the local stability analysis of a specific class of source, window-based controls is first developed; then a new, rate-based control suitable for use by multimedia streams is proposed. The novel strategy is demonstrated to guarantee consistent and intra-fair throughput allocation, good responsiveness and satisfying smoothness, even in a first, easy-to-implement version.

Support vector machines have been very successful in pattern recognition and function estimation problems. In this paper we introduce the use of least squares support vector machines (LS-SVM's) for the optimal control of nonlinear systems. Linear and neural full static state feedback controllers are considered. The problem is formulated in such a way that it incorporates the N-stage optimal control problem as well as a least squares support vector machine approach for mapping the state space into the action space. The solution is characterized by a set of nonlinear equations. An alternative formulation as a constrained nonlinear optimization problem in less unknowns is given, together with a method for imposing local stability in the LS-SVM control scheme. The results are discussed for support vector machines with radial basis function kernel. Advantages of LS-SVM control are that no number of hidden units has to be determined for the controller and that no centers have to be speci®ed for the Gaussian kernels when applying Mercer's condition. The curse of dimensionality is avoided in comparison with de®ning a regular grid for the centers in classical radial basis function networks. This is at the expense of taking the trajectory of state variables as additional unknowns in the optimization problem, while classical neural network approaches typically lead to parametric optimization problems. In the SVM methodology the number of unknowns equals the number of training data, while in the primal space the number of unknowns can be in®nite dimensional. The method is illustrated both on stabilization and tracking problems including examples on swinging up an inverted pendulum with local stabilization at the endpoint and a tracking problem for a ball and beam system. q

In this paper, a mathematical model is proposed and analysed to study the dynamics of one-prey two-predators system with ratio-dependent pre- dators growth rate. Criteria for local stability, instabil ity and global stability of the nonnegative equilibria are obtained. The permanent co-existence of the three species is also discussed. Finally, computer simulat ions are performed to investigate the dynamics of the system.

In this paper, a locally stabilized finite element formulation of the Stokes problem is analyzed. A macroelement condition which is sufficient for the stability of (locally stabilized) mixed methods based on a piecewise constant pressure approximation is introduced. By satisfying this condition, the stability of the Q\-Pq, quadrilateral, and the P\-Pq triangular element, can be established.

In this paper, we consider a delayed reaction-diffusion equations which describes a two-species predator-prey system with diffusion terms and stage structure. By using the linearization method and the method of upper and lower solutions, we study the local and global stability of the constant equilibria, respectively. The results show that the free diffusion of the delayed reactiondiffusion equations has no effect on the populations when the diffusion is too slow; otherwise, the free diffusion has a certain influence on the populations, however, the influence can be eliminated by improving the parameters to satisfy some suitable conditions.

In general, the shear localization process involves initiation and growth. Initiation is expected to be a stochastic process in material space where anisotropy in the elastic-plastic behavior of single crystals and inter-crystalline interactions serve to form natural perturbations to the materialÕs local stability. A hat-shaped sample geometry was used to study shear localization growth. It is an axisymmetric sample with an upper ''hat'' portion and a lower ''brim'' portion with the shear zone located between the hat and brim. The shear zone length is 870-890 lm with deformation imposed through a split-Hopkinson pressure bar system at maximum top-to-bottom velocity in the range of 8-25 m/s. We present experimental results of the deformation response of tantalum and 316L stainless steel samples. The tantalum samples did not form shear bands but the stainless steel sample formed a late stage shear band. We have also modeled these experiments using both conductive and adiabatic continuum models. An anisotropic elasto-viscoplastic constitutive model with damage evolution was used within the finite element code EPIC. A Mie-Gruneisen equation of state and the rate and temperature sensitive MTS flow stress model together with a Gurson flow surface were employed. The models performed well in predicting the experimental data. The numerical results for tantalum suggested a maximum equivalent strain rate on the order of 7 · 10 4 s À1 in the gage section for an imposed top surface displacement rate of 17.5 m/s. The models also suggested that for an initial temperature of 298 K a temperature in the neighborhood of 900 K was reached within the 0749-6419/$ -see front matter Ó (C.A. Bronkhorst).

We formulate epidemiological models for the transmission of a pathogen that can mutate in the host to create a second infectious mutant strain. The models account for mutation rates that depend on how long the host has been infected. We derive explicit formulas for the reproductive number of the epidemic based on the local stability of the infection-free equilibrium. We analyze the existence and stability of the boundary equilibrium, whose infection components are zero and positive, respectively, and the endemic equilibrium, whose components are all positive. We establish the conditions for global stability of the infection-free and boundary equilibria and local stability of the endemic equilibrium for the case where there is no age structure for the pathogen in the infected population. We show that under certain circumstances, there is a Hopf bifurcation where the endemic equilibrium loses its stability, and periodic solutions appear. We provide examples and numerical simulations to illustrate the Hopf bifurcation.

We study time step restrictions due to linear stability constraints of Runge-Kutta Discontinuous Galerkin methods on triangular grids. The scalar advection equation is discretized in space by the Discontinuous Galerkin method with either the Lax-Friedrichs flux or the upwind flux, and integrated in time with various Runge-Kutta schemes designed for linear wave propagation problems or non-linear applications. Von-Neumann-like analyses are performed on structured periodic grids made up of congruent elements, to investigate the influence of element shape on the stability restrictions. We assess CFL conditions based on different element size measures, among which only the radius of the inscribed circle and the shortest height prove appropriate, although they are not totally independent of the triangle shape. We explain their general behaviour with respect to element quality, and report the corresponding Courant numbers with both types of flux and polynomial order p ranging from 1 to 10, for use as guidelines in practical simulations. We also compare the performance of the Lax-Friedrichs flux and the upwind flux, and we draw general conclusions about the relative computational efficiency of RK schemes. The application of CFL conditions to two examples involving respectively an unstructured and a hybrid grid confirms our results, although it shows that local stability criteria tend to yield too restrictive conditions.

The paper presents an open-economy macrodynamical growth model with the aim of giving an endogenous characterisation to the process that leads a small country with a currency-board arrangement to accumulate dangerously high levels of external debt and become vulnerable to macroeconomic instability. The macrodynamics of the model results from the combination of the commitment to maintain the peg - that makes liquidity closely dependent on the dynamics of foreign reserves – and the non-linear real and financial interactions that drives the pro-cyclical behaviour of the economy. Within this context, the external finance ease during an economic upswing leads to debt-supported growth and financial fragility; the consequent deterioration of profitability expectations brings about a capital reversal that, in the absence of monetary stabilization tools, makes the currency arrangement unsustainable. A financial crisis may thus turn into a currency crisis. We run a continuous-time estimation ...

A convex approach to robust regional stability analysis of a class of nonlinear state-delayed systems subject to convex-bounded parameter uncertainty is proposed. Delay-dependent conditions are developed to ensure system robust local stability and obtain an estimate of a domain of attraction of the origin inside a given polytopic region of the state-space. This approach is then extended to provide a delay-dependent solution to the problem of L 2 -gain analysis. The proposed approach is based on a Lyapunov-Krasovskii functional with polynomial dependence on the system state and uncertain parameters and is formulated in terms of linear matrix inequalities. Numerical examples illustrate the potentials of the derived results.

This study presents an assessment of walking stability in elderly people, focusing on local dynamic stability of walking. Its main objectives were to propose a technique to quantify local dynamic stability using nonlinear time-series analyses and a portable instrument, and to investigate their reliability in revealing the efficacy of an exercise training intervention for elderly people for improvement of walking stability. The method measured three-dimensional acceleration of the upper body, and computation of Lyapunov exponents, thereby directly quantifying the local stability of the dynamic system. Straight level walking of young and elderly subjects was investigated in the experimental study. We compared Lyapunov exponents of young and the elderly subjects, and of groups before and after the exercise intervention. Experimental results demonstrated that the exercise intervention improved local dynamic stability of walking. The proposed method was useful in revealing effects and efficacies of the exercise intervention for elderly people.

In this paper, a mathematical model consisting of two preys one predator with Beddington–DeAngelis functional response is proposed and analyzed. The local stability analysis of the system is carried out. The necessary and sufficient conditions for the persistence of three species food web model are obtained. For the biologically reasonable range of parameter values, the global dynamics of the system has been investigated numerically. Number of bifurcation diagrams has been obtained; Lyapunov exponents have been computed for different attractor sets. It is observed that the model has different types of attractors including chaos.

If (E, M) is a factorization system on a category C, we define new classes of maps as follows: a map f : A → B is in E if each of its pullbacks lies in E (that is, if it is stably in E), and is in M * if some pullback of it along an effective descent map lies in M (that is, if it is locally in M). We find necessary and sufficient conditions for (E , M * ) to be another factorization system, and show that a number of interesting factorization systems arise in this way. We further make the connexion with Galois theory, where M * is the class of coverings; and include self-contained modern accounts of factorization systems, descent theory, and Galois theory.

The modified Leslie-Gower and Holling-type II predator-prey model is generalized in the context of ecoepidemiology, with disease spreading only among the prey species. A new feature is introduced, the intraspecific competition of infected prey. All the equilibria are characterized and the existence of a Hopf bifurcation at the coexistence equilibrium is shown.

This paper describes the various analysis and design aspects of a fiber reinforced plastic (FRP) bridge. The design methodology is illustrated by describing the steps taken in the design of the first US FRP cable-stayed pedestrian bridge to be constructed in Lincoln, Nebraska. The analysis is made using three dimensional (3-D) macro models of the bridge to describe its overall behavior under static and dynamic loads. Separate analysis is done to study the local stability of the different structural elements. The orthotropy of the material is taken into account during this analysis. The short term and long term stiffnesses and strengths are evaluated and accounted for in the design process.

Large, complex networks of ecological interactions with random structure tend invariably to instability. This mathematical relationship between complexity and local stability ignited a debate that has populated ecological literature for more than three decades. Here we show that, when species interact as predators and prey, systems as complex as the ones observed in nature can still be stable. Moreover, stability is highly robust to perturbations of interaction strength, and is largely a property of structure driven by predator-prey loops with the stability of these small modules cascading into that of the whole network. These results apply to empirical food webs and models that mimic the structure of natural systems as well. These findings are also robust to the inclusion of other types of ecological links, such as mutualism and interference competition, as long as consumer-resource interactions predominate. These considerations underscore the influence of food web structure on ecological dynamics and challenge the current view of interaction strength and long cycles as main drivers of stability in natural communities.

The HIV/AIDS epidemic is a serious public health challenge in South Africa. In this paper, a simple deterministic HIV/AIDS model incorporating condom use, sexual partner acquisition, behavior change and treatment as HIV/AIDS control strategies is formulated using a system of ordinary differential equations with the object of applying it to the current South African situation. Firstly, a theoretical analysis of the model is presented. The analysis of the model shows that the disease free equilibrium point is globally asymptotically stable for the epidemic threshold R (the model reproduction number) less than unit and unstable when this threshold is greater than unit. A unique endemic equilibrium, whose local stability near the threshold R, is determined using the center manifold theory, is shown to be locally asymptotically stable for R > 1. Global stability of the endemic equilibrium is shown for a special case whenever R > 1. Secondly, the model is fitted to data from UN-AIDS/WHO on HIV/AIDS in South Africa. Based on the fit to the prevalence data, projections are made beyond 2007 on the course of the epidemic for various levels of interventions. The results compare very well with other research outcomes on the HIV/AIDS epidemic in South Africa. Projections are made to track the changes in the number of individuals who will be under treatment, an important group as far as public health planning is concerned. The epidemiological implications of such projections on public health planning and management are discussed.

In Xenopus, the activation of the myogenic determination factors MyoD and Myf-5 in the muscle-forming region of the embryo occurs in response to mesoderm-inducing factors (MIFs). Different members of the FGF, TGF-beta, and Wnt protein families have been implicated in this process, but how MIFs induce the myogenic regulators is not known. For MyoD, the induction process may serve to locally stabilize a transient burst of ubiquitous transcription at the midblastula transition, possibly by triggering MyoD's autocatalytic loop. Here we have sought to distinguish separate activating functions during MyoD induction by analyzing when MyoD responds to different MIF signaling or to MyoD autoactivation. We show that MyoD induction depends on the developmental age of the induced cells, rather than on the type or time point of inducer application. At the permissive time, de novo MyoD induction by Activin requires less than 90 min, arguing for an immediate response, rather than a series of inductive events. MyoD autoactivation is direct, but subject to the same temporal restriction as MyoD induction by MIF signaling. Further evidence implicating MyoD autocatalysis as an essential component of the induction process comes from the observation that both autocatalysis and induction of MyoD are selectively repressed by a dominant-negative MyoD mutant. In summary, our observations let us conclude that MyoD's expression domain in the embryo results from an interplay of timed changes in cellular competence, pleiotropic signaling pathways, and autocatalysis.

In general, the shear localization process involves initiation and growth. Initiation is expected to be a stochastic process in material space where anisotropy in the elastic-plastic behavior of single crystals and inter-crystalline interactions serve to form natural perturbations to the materialÕs local stability. A hat-shaped sample geometry was used to study shear localization growth. It is an axisymmetric sample with an upper ''hat'' portion and a lower ''brim'' portion with the shear zone located between the hat and brim. The shear zone length is 870-890 lm with deformation imposed through a split-Hopkinson pressure bar system at maximum top-to-bottom velocity in the range of 8-25 m/s. We present experimental results of the deformation response of tantalum and 316L stainless steel samples. The tantalum samples did not form shear bands but the stainless steel sample formed a late stage shear band. We have also modeled these experiments using both conductive and adiabatic continuum models. An anisotropic elasto-viscoplastic constitutive model with damage evolution was used within the finite element code EPIC. A Mie-Gruneisen equation of state and the rate and temperature sensitive MTS flow stress model together with a Gurson flow surface were employed. The models performed well in predicting the experimental data. The numerical results for tantalum suggested a maximum equivalent strain rate on the order of 7 • 10 4 s À1 in the gage section for an imposed top surface displacement rate of 17.5 m/s. The models also suggested that for an initial temperature of 298 K a temperature in the neighborhood of 900 K was reached within the

We consider the dynamics of a general stage-structured predator-prey model which generalizes several known predator-prey, SEIR, and virus dynamics models, assuming that the intrinsic growth rate of the prey, the predation rate, and the removal functions are given in an unspecified form. Using the Lyapunov method, we derive sufficient conditions for the local stability of the equilibria together with estimations of their respective domains of attraction, while observing that in several particular but important situations these conditions yield global stability results. The biological significance of these conditions is discussed and the existence of the positive steady state is also investigated.

The HIV/AIDS epidemic is a serious public health challenge in South Africa. In this paper, a simple deterministic HIV/AIDS model incorporating condom use, sexual partner acquisition, behavior change and treatment as HIV/AIDS control strategies is formulated using a system of ordinary differential equations with the object of applying it to the current South African situation. Firstly, a theoretical analysis of the model is presented. The analysis of the model shows that the disease free equilibrium point is globally asymptotically stable for the epidemic threshold R (the model reproduction number) less than unit and unstable when this threshold is greater than unit. A unique endemic equilibrium, whose local stability near the threshold R, is determined using the center manifold theory, is shown to be locally asymptotically stable for R>1. Global stability of the endemic equilibrium is shown for a special case whenever R>1. Secondly, the model is fitted to data from UNAIDS/WHO on HIV/AIDS in South Africa. Based on the fit to the prevalence data, projections are made beyond 2007 on the course of the epidemic for various levels of interventions. The results compare very well with other research outcomes on the HIV/AIDS epidemic in South Africa. Projections are made to track the changes in the number of individuals who will be under treatment, an important group as far as public health planning is concerned. The epidemiological implications of such projections on public health planning and management are discussed.

Holling-Tanner model is revised with ratio-dependent functional response since ratio-dependent functional response is more appropriate when predator involves serious searching process. The essential mathematical features of the modified model have been analyzed with the help of local stability, global stability, bifurcation theory. Finally, analytical results have been interpreted in terms of ecology.

This paper introduces and analyzes a decentralized network congestion control algorithm which has dynamic adaptations at both user ends and link ends, a so-called general primal-dual algorithm. We obtain sufficient conditions for local stability of this algorithm in a general topology network with heterogeneous round-trip delays. Then, as an implementation of this algorithm in the Internet, we introduce an AQM (Active Queue Management) scheme called Exponential-RED (E-RED), which outperforms RED and is inherently stable when combined with TCP-Reno or its variants for high-speed networks.

In this paper the analysis of gray level corner detection has been carried out. Performances of various cornerness measures are discussed with respect to four performances of robustness: detection, localization, stability and complexity. We have analyzed the interior dierential features of the image surface of these cornerness measures. This paper presents a new approach called gradient-direction corner detector for the corner detection which is developed from the popular Plessey corner detection. The gradient-direction corner detector is based on the measure of the gradient module of the image gradient direction and the constraints of the false corner response suppression. Ó 1 Electronic Annexes available. See http://www.locate.patrec. 0167-8655/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 -8 6 5 5 ( 9 8 ) 0 0 1 3 4 -2

We show how linear matrix inequalities (LMI) can be used to perform local stability and performance analysis of linear systems with saturating elements. This leads to less conservative information on stability regions, disturbance rejection, and L2-gain than standard global stability and performance analysis. The circle and Popov criteria are used to obtain Lyapunov functions whose sublevel sets provide regions of guaranteed stability and performance within a restricted state space region. Our LMI formulation leads directly to simple convex optimization problems that can be solved efficiently as semidefinite programs. The results cover both single and multiple saturation elements and can be immediately extended to discrete time systems. An obvious application of these techniques is in the analysis of control systems with saturating control inputs

After deriving a model describing the law of evolution of innovators and imitators the article focuses on their relationships under two di¤erent scenarios: prey-predator, in which innovators are regarded as preys, and competing species. Analytic results show that among the feasible equilibria the coexistence equilibrium is the only stable equilibrium under the …rst scenario. We also …nd conditions on the parameters allowing local stability of the coexistence equilibrium in the second scenario. Such conditions imply the existence of an inverse-U shaped relationship between innovation and imitation.

In this paper, we consider the macroeconomic models with policy lag, and study how lags in policy response affect the macroeconomic stability. The local stability of the nonzero equilibrium of this equation is investigated by analyzing the corresponding transcendental characteristic equation of its linearized equation. Some general stability criteria involving the policy lag and the system parameter are derived. By choosing the policy lag as a bifurcation parameter, the model is found to undergo a sequence of Hopf bifurcation. The direction and stability of the bifurcating periodic solutions are determined by using the normal form theory and the center manifold theorem. Moreover, we show that the government can stabilize the intrinsically unstable economy if the policy lag is sufficiently short, but the system become locally unstable when the policy lag is too long. We also find the chaotic behavior in some range of the policy lag.

Background. Cardiopulmonary bypass and cardioplegic arrest result in known physiologic inflammatory, coagulopathic, and embolic states that may result in end-organ damage. Interest in off-pump complete coronary revascularization using sternotomy exposure is therefore increasing.

This paper provides a comparative sensitivity analysis of one-step Newton-Raphson estimators for linear regression. Such estimators have been proposed as a way to combine the global stability of high breakdown estimators with the local stability of generalized maximum likelihood estimators. We analyze this strategy, obtaining upper bounds for the maximum bias induced by ε-contamination of the model. These bounds yield breakdown points and local rates of convergence of the bias as ε decreases to zero. We treat a unified class of Newton-Raphson estimators, including one-step versions of the well-known Schweppe, Mallows and Hill-Ryan GM estimators. Of the three well-known types, the Hill-Ryan form emerges as the most stable in terms of one-step estimation. The Schweppe form is susceptible to a breakdown of the Hessian matrix. For this reason it fails to improve on the local stability of the initial estimator, and it may lead to falsely optimistic estimates of precision.