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Dynamic Stability (dynamic + stability)

Distribution by Scientific Domains

Engineering	35%
Humanities and Social Sciences	14%

Selected Abstracts

The Taylor Rule and Dynamic Stability in a Small Macroeconomic Model

ECONOMIC NOTES, Issue 3 2003
David Chappell
In this paper, we embed the Taylor interest rate rule in a simple macroeconomic model with Calvo contracts. We contrast this with the case in which the interest rate is determined by the conventional LM curve along with a fixed value for the monetary aggregate. We derive conditions under which the adjustment of the economy is characterized by a unique saddle,path and show that the conditions required for this to be the case are more stringent when the authorities adopt the Taylor rule. In both cases, the possible failure of the saddle,path condition arises when there are debt,deflation effects in the IS curve. If interest rates are set according to the Taylor rule, then debt,deflation is always enough to cause the failure of the saddle,path condition. However, when interest rates are determined by the LM curve then it is possible that the real balance effect from the LM curve may offset the debt,deflation effect and produce a saddle,path. (J.E.L. E4, E5). [source]

Fabrication and Characterization of Superhydrophobic Surfaces with Dynamic Stability

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2010
Xi Yao
Abstract Superhydrophobic surfaces of dynamic stability are crucial for applications in water-repellent materials. In this work, a hierarchical structure composed of a dendritic microporous surface with nanostructured porosity is demonstrated that shows robust superhydrophobicity with dynamic stability. The hierarchical structures are obtained on both copper foils and wires by a dynamic gas-bubble template-assisted electrochemical deposition method. The substrates can then be modified with alkyl thiols to obtain the surface superhydrophobicity. A new kind of testing, mechanical monitor-assisted continuous water surface strokes, is developed to reveal the dynamic stability of the as-prepared superhydrophobic copper wires. The as-prepared superhydrophobic copper wires can exert a high propulsive force, and particularly, show little adhesive force in the process of continuous strokes on the water surface, exhibiting robust superhydrophobicity with dynamic stability. The approach allows a strategy for the fabrication of superhydrophobic surfaces with dynamic stability, and suggests a new method to evaluate the dynamic stability of superhydrophobic surfaces. [source]

Dynamic stability of a porous rectangular plate

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006
Daniel Debowski
The study is devoted to a axial compressed porous-cellular rectangular plate. Mechanical properties of the plate vary across is its thickness which is defined by the non-linear function with dimensionless variable and coefficient of porosity. The material model used in the current paper is as described by Magnucki, Stasiewicz papers. The middle plane of the plate is the symmetry plane. First of all, a displacement field of any cross section of the plane was defined. The geometric and physical (according to Hook's law) relationships are linear. Afterwards, the components of strain and stress states in the plate were found. The Hamilton's principle to the problem of dynamic stability is used. This principle was allowed to formulate a system of five differential equations of dynamic stability of the plate satisfying boundary conditions. This basic system of differential equations was approximately solved with the use of Galerkin's method. The forms of unknown functions were assumed and the system of equations was reduced to a single ordinary differential equation of motion. The critical load determined used numerically processed was solved. Results of solution shown in the Figures for a family of isotropic porous-cellular plates. The effect of porosity on the critical loads is presented. In the particular case of a rectangular plate made of an isotropic homogeneous material, the elasticity coefficients do not depend on the coordinate (thickness direction), giving a classical plate. The results obtained for porous plates are compared to a homogeneous isotropic rectangular plate. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Dynamic stability of the three-dimensional axisymmetric Navier-Stokes equations with swirl

COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 5 2008
Thomas Y. Hou
In this paper, we study the dynamic stability of the three-dimensional axisymmetric Navier-Stokes Equations with swirl. To this purpose, we propose a new one-dimensional model that approximates the Navier-Stokes equations along the symmetry axis. An important property of this one-dimensional model is that one can construct from its solutions a family of exact solutions of the three-dimensionaFinal Navier-Stokes equations. The nonlinear structure of the one-dimensional model has some very interesting properties. On one hand, it can lead to tremendous dynamic growth of the solution within a short time. On the other hand, it has a surprising dynamic depletion mechanism that prevents the solution from blowing up in finite time. By exploiting this special nonlinear structure, we prove the global regularity of the three-dimensional Navier-Stokes equations for a family of initial data, whose solutions can lead to large dynamic growth, but yet have global smooth solutions. © 2007 Wiley Periodicals, Inc. [source]

Development of dynamic stability in children's rhythmic movement

DEVELOPMENTAL PSYCHOBIOLOGY, Issue 6 2009
Eric G. James
Abstract This study examined the hypothesis that the stability of rhythmic motor patterns increases with developmental age in children. Children aged 6 and 10 years and adults (18- to 23-year-olds) rocked back and forth at their preferred amplitude and frequency while seated on a wooden box placed atop a force platform. Participants performed the seated rocking task with their feet supported and unsupported. There was an age-related decrease in rocking frequency and variability of the rocking cycle period, while the stability of the rocking dynamics increased, as indexed by the standard deviation of the phase angle of center of pressure motion. The presence of foot support decreased the stability of the rocking dynamics and reduced cycle period variability in the children, but not the adults. The results revealed that increments of age are associated with an increase in the stability of rhythmic motor patterns even when environmental conditions are altered. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 465,473, 2009 [source]

Fabrication and Characterization of Superhydrophobic Surfaces with Dynamic Stability

Structural topology optimization of vibrating structures with specified eigenfrequencies and eigenmode shapes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2006
Y. Maeda
Abstract In vibration optimization problems, eigenfrequencies are usually maximized in the optimization since resonance phenomena in a mechanical structure must be avoided, and maximizing eigenfrequencies can provide a high probability of dynamic stability. However, vibrating mechanical structures can provide additional useful dynamic functions or performance if desired eigenfrequencies and eigenmode shapes in the structures can be implemented. In this research, we propose a new topology optimization method for designing vibrating structures that targets desired eigenfrequencies and eigenmode shapes. Several numerical examples are presented to confirm that the method presented here can provide optimized vibrating structures applicable to the design of mechanical resonators and actuators. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Dynamic Control of a Large Scale of Pneumatic Multichain Systems

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 4 2004
M. Guihard
The aim of this paper is to propose a general principle able to manage the supervision, coordination, and control problems of a large scale of multichain structures in dynamic and interacting tasks. The main originality lays in its modular feature. The number of chains and of joint per chain are indeed not restricted. The only assumption is that all the chains are linked to a principal element from which the dynamic stability will be computed. This is for example the case for multi-finger and multi-legged structures for which respectively the palm and the trunk represent the principal element. The principle consists in controlling the stability of this element and distributing the effort on the other chains to maintain the stability of the whole. To increase the compliant feature, we consider that each joint is pneumatically actuated. Each joint is then dynamically controlled to ensure the asymptotic stability of the local chain it belongs to. A global architecture is presented where each part is detailed. An example is then displayed showing the performances of a two-legged robot in the standing posture under external perturbation effects. © 2004 Wiley Periodicals, Inc. [source]

Dynamic modeling, stability, and energy efficiency of a quadrupedal walking machine

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2001
Ben Sheng Lin
In the past, the dynamics of walking machines was studied based on very simple or simplified leg structures. A more complete dynamic model is essential for the further development of a practical walking machine. In this paper, the dynamic model of a realistic quadrupedal walking machine is derived for simulation and real-time control purposes. The walker has four cylindrical pantograph legs, and the whole system consists of twenty-nine links. The walking gait is wave gait with at least three feet on the ground at any time. Significant efforts have been made to improve the computational efficiency of the inverse dynamics, and the required CPU time is less than 10 ms on an IBM 3090. The derived dynamic model is then applied to study two practical issues of walking: dynamic stability and mechanical efficiency of different legs and gaits. Simulation results show clear advantages of one leg type over another, and of some walking strategies in terms of adjusting velocities, strokes, and duty factors for greater efficiency. © 2001 John Wiley & Sons, Inc. [source]

Wearable Data Collection System for Online Gait Stability Analysis

NEUROMODULATION, Issue 3 2004
Tomaz Karcnik DSc
Abstract We had shown in our previous research that the stability assessment and control are essential for generation of faster and more energy efficient functional electrical stimulation (FES) and/or crutch-assisted gait. The objective of our recent research work has been to design a wearable and portable system for gait stability analysis with online capabilities that is also applicable to crutch-assisted gait modes. The developed wearable stability assessment system for as yet only biped gait consists of foot switches and goniometers attached to the leg joints. The instantaneous static and dynamic stability is, within the wearable system, assessed from the trajectory of the estimated body center of gravity (COGHAT) and the supporting area shape/size as derived from step length and foot-floor contact state. We used motion analysis system data as reference for testing the wearable system accuracy. The wearable system was tested on five healthy subjects and one above-knee amputee. It proved to be reasonably accurate if compared to the classical, motion analysis system based method. However, additional work is required to port the system to the FES assisted and/or crutch assisted gait. [source]

Specification issues in models of population and employment growth*

PAPERS IN REGIONAL SCIENCE, Issue 1 2005
Marlon G. Boarnet
Spatial econometrics; population and employment growth Abstract., This article examines two specification issues common to spatial econometric population-employment growth models: the specification of the weight matrix and the dynamic stability implied by estimated lag parameters. Using data on Orange County census tracts from 1980 to 1990, we estimate a simultaneous system of regressions for tract population and employment growth. Six different weight matrices are tested, ranging from simple contiguity matrices to more complex matrices based on commute flows between census tracts. We also examine whether the inclusion of detailed information on land use improves performance of the lagged adjustment model. The results provide insights for future applications of econometric population-employment growth models. We found that the estimated lag parameters were consistent with dynamic stability for the models that included detailed land use data. Results varied for different weight matrices, but variation was mostly confined to interaction between population and employment growth. [source]

Dynamic stability of a porous rectangular plate

Probing the ,-Helical Structural Stability of Stapled p53 Peptides: Molecular Dynamics Simulations and Analysis

CHEMICAL BIOLOGY & DRUG DESIGN, Issue 4 2010
Zuojun Guo
Reactivation of the p53 cell apoptosis pathway through inhibition of the p53-hDM2 interaction is a viable approach to suppress tumor growth in many human cancers and stabilization of the helical structure of synthetic p53 analogs via a hydrocarbon cross-link (staple) has been found to lead to increased potency and inhibition of protein,protein binding (J. Am. Chem. Soc. 129: 5298). However, details of the structure and dynamic stability of the stapled peptides are not well understood. Here, we use extensive all-atom molecular dynamics simulations to study a series of stapled ,-helical peptides over a range of temperatures in solution. The peptides are found to exhibit substantial variations in predicted ,-helical propensities that are in good agreement with the experimental observations. In addition, we find significant variation in local structural flexibility of the peptides with the position of the linker, which appears to be more closely related to the observed differences in activity than the absolute ,-helical stability. These simulations provide new insights into the design of ,-helical stapled peptides and the development of potent inhibitors of ,-helical protein,protein interfaces. [source]