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1

Saturation Modeling and Stability Analysis of Synchronous Reluctance Generator  

Microsoft Academic Search

A new method of representing magnetic saturation in synchronous reluctance generator has been proposed in this paper. A linearized model of synchronous reluctance generator has been developed applying the proposed saturation model to perform the steady-state stability analysis. The effect of - and -axis saturation on the steady-state stability of a synchronous reluctance generator has been investigated using the proposed

Souvik Guha; Narayan C. Kar

2008-01-01

2

An advanced reduced order model for BWR stability analysis  

Microsoft Academic Search

An advanced reduced order model was developed and qualified in the framework of a novel approach for nonlinear stability analysis of boiling water nuclear reactors (BWRs). This approach is called the RAM–ROM method where RAM is a synonym for system code and ROM stands for reduced order model. In the framework of the RAM–ROM method, integrated BWR (system) codes and

Carsten Lange; Dieter Hennig; Antonio Hurtado

2011-01-01

3

Stability Analysis of a Reaction-Diffusion System Modeling Atherogenesis  

Microsoft Academic Search

This paper presents a linear, asymptotic stability analysis for a reaction-diffusion- convection system modeling atherogenesis, the initiation of atherosclerosis, as an in- flammatory instability. Motivated by the disease paradigm articulated by Russell Ross, atherogenesis is viewed as an inflammatory spiral with positive feedback loop involving key cellular and chemical species interacting and reacting within the intimal layer of muscular arteries.

Akif Ibragimov; Laura Ritter; Jay R. Walton

2010-01-01

4

TOBI: A nonlinear model for boiling water reactor stability analysis  

SciTech Connect

The magnitude and the divergent nature of the oscillations during the LaSalle unit 2 nuclear power plant even on March 9, 1988, renewed concern about the state of knowledge on boiling water reactor (BWR) instabilities and was followed by many activities, e.g., the Idaho Stability Symposium. For appropriate representation of the physical processes, typical BWR time-domain stability calculations with, e.g., TRAC, RETRAN, or THERMIT require a large number of axial nodes and are very costly with regard to computer time. Linear models are inexpensive, but only valid as long as the parameters have no large deviation from the reference operating conditions. The objective of this work is the development of a physical model that is applicable for stability analysis in the nonlinear regime, but without the disadvantage of numerical problems and excessive computing times. The basic concept of the model TOBI is the integral study of the interaction between the time-dependent single- and two-phase regions. A series of calculations for purely thermal-hydraulic systems and BWRs has shown that TOBI is a convenient tool for stability analysis. Because of the simple but physically realistic modeling, it is very helpful in achieving an improved understanding of the mechanisms that affect BWR stability, and it is inexpensive, with regard to computer time, to perform extensive parameter sensitivity studies, even in the nonlinear regime.

Wehle, F. (Siemens/KWU, Offenbach (West Germany)); Pruitt, D.W.

1990-06-01

5

Stability analysis and modeling of rotating flexible structures  

SciTech Connect

A method is presented for determining the nonlinear stability of undamped flexible structures spinning about a principal axis of inertia. Equations of motion are developed for structures that are free of applied forces and moments. The development makes use of a floating reference frame which follows the overall rigid body motion. Within this frame, elastic deformations are assumed to be given functions of n generalized coordinates. A transformation of variables is devised which shows the equivalence of the equations of motion to a Hamiltonian system with n + 1 degrees of freedom. Using this equivalence, stability criteria are developed based upon the normal form of the Hamiltonian. It is shown that a motion which is spin stable in the linear approximation may be unstable when nonlinear terms are included. A stability analysis of a simple flexible structure is provided to demonstrate the application of the stability criteria. Results from numerical integration of the equations of motion are shown to be consistent with the predictions of the stability analysis. A new method for modeling the dynamics of rotating flexible structures is developed and investigated. The method is similar to conventional assumed displacement (modal) approaches with the addition that quadratic terms are retained in the kinematics of deformation. Retention of these terms is shown to account for the geometric stiffening effects which occur in rotating structures. Computational techniques are developed for the practical implementation of the method. The techniques make use of finite element analysis results, and thus are applicable to a wide variety of structures. Motion studies of specific problems are provided to demonstrate the validity of the method. Excellent agreement is found both with simulations presented in the literature for different approaches and with results from a commercial finite element analysis code. The computational advantages of the method are demonstrated.

Dohrmann, C.R.

1993-01-01

6

Stability analysis and modeling of rotating flexible structures  

NASA Astrophysics Data System (ADS)

A method is presented for determining the nonlinear stability of undamped flexible structures spinning about a principal axis of inertia. Equations of motion are developed for structures that are free of applied forces and moments. The development makes use of a floating reference frame which follows the overall rigid body motion. Within this frame, elastic deformations are assumed to be given functions of n generalized coordinates. A transformation of variables is devised which shows the equivalence of the equations of motion to a Hamiltonian system with n + 1 degrees of freedom. Using this equivalence, stability criteria are developed based upon the normal form of the Hamiltonian. It is shown that a motion which is spin stable in the linear approximation may be unstable when nonlinear terms are included. A stability analysis of a simple flexible structure is provided to demonstrate the application of the stability criteria. Results from numerical integration of the equations of motion are shown to be consistent with the predictions of the stability analysis. A new method for modeling the dynamics of rotating flexible structures is developed and investigated. The method is similar to conventional assumed displacement (modal) approaches with the addition that quadratic terms are retained in the kinematics of deformation. Retention of these terms is shown to account for the geometric stiffening effects which occur in rotating structures. Computational techniques are developed for the practical implementation of the method. The techniques make use of finite element analysis results and thus, are applicable to a wide variety of structures. Motion studies of specific problems are provided to demonstrate the validity of the method. Excellent agreement is found both with simulations presented in the literature for different approaches and with results from a commercial finite element analysis code. The computational advantages of the method are demonstrated.

Dohrmann, C. R.

1993-01-01

7

Lattice Boltzmann equation linear stability analysis: Thermal and athermal models  

NASA Astrophysics Data System (ADS)

Although several thermal lattice Boltzmann models have been proposed, this method has not yet been shown to be able to describe nonisothermal fully compressible flows in a satisfactory manner, mostly due to the presence of important deviations from the advection-diffusion macroscopic equations and also due to numerical instabilities. In this context, this paper presents a linear stability analysis for some lattice Boltzmann models that were recently derived as discrete forms of the continuous Boltzmann equation [P. C. Philippi, L. A. Hegele, Jr., L. O. E. dos Santos, and R. Surmas, Phys. Rev. E 63, 056702 (2006)], in order to investigate the sources of instability and to find, for each model, the upper and lower limits for the macroscopic variables, between which it is possible to ensure a stable behavior. The results for two-dimensional (2D) lattices with 9, 17, 25, and 37 velocities indicate that increasing the order of approximation of the lattice Boltzmann equation enhances stability. Results are also presented for an athermal 2D nine-velocity model, the accuracy of which has been improved with respect to the standard D2Q9 model, by adding third-order terms in the lattice Boltzmann equation.

Siebert, D. N.; Hegele, L. A., Jr.; Philippi, P. C.

2008-02-01

8

Stability analysis and modeling of rotating flexible structures  

NASA Astrophysics Data System (ADS)

Equations of motion are developed for undamped, rotating flexible structures free of applied forces and moments. The development is based upon the use of a floating reference frame which follows the overall rigid body motion of the structure. Within this frame, elastic deformations are expressed as functions of n generalized degrees of freedom. A nonlinear transformation of variables is devised which shows the equivalence of the equations of motion to a Hamiltonian system with n + 1 degrees of freedom. A method is developed for the stability analysis of flexible structures rotating about this axis of minimum moment of inertia. Central to the development is the equivalence established between the governing equations and a Hamiltonian system. It is shown that unstable motion can occur only if a certain characteristic frequency of the system is involved in a lower-order resonance relation. Stability criteria for systems satisfying a single resonance relation are developed in detail. General guidelines are also provided for assessing the stability of systems possessing multiple resonance relations. Examples are provided which demonstrate the application of the stability criteria. Results obtained from numerical integration of the equations of motion are shown to be consistent with the predictions of stability analyses. It also shows that motion which is stable in the linear approximation may be unstable when nonlinear terms are included. A new method for modeling the dynamics of rotating flexible structures is developed and investigated. The method is similar to conventional assumed displacement approaches with the addition that quadratic terms are retained in the kinematics of deformation. Retention of these terms is shown to account for the geometric stiffening effects which occur in rotating structures. Computational techniques are developed for the practical implementation of the new method. The techniques make use of finite element analysis results, and thus are applicable to a wide variety of structures. Motion studies of specific problems are provided to demonstrate the validity of the method. analysis code. &The computational advantages of the method are demonstrated.

Dohrmann, Clark Richard

1992-09-01

9

Global stability analysis in delayed Hopfield neural network models  

Microsoft Academic Search

In this paper, without assuming the boundedness, monotonicity and differentiability of the activation functions, we present new conditions ensuring existence, uniqueness, and global asymptotical stability of the equilibrium point of Hopfield neural network models with fixed time delays or distributed time delays. The results are applicable to both symmetric and nonsymmetric interconnection matrices, and all continuous nonmonotonic neuron activation functions.

Jiye Zhang; Xuesong Jin

2000-01-01

10

Stability analysis of two prey one predator model  

NASA Astrophysics Data System (ADS)

In this paper we study a two prey one predator model with team approach. We analyze local stability behaviour of the system with the help of linearization and persistence behaviour of the system with the help of persistence of all three teams individually.

Tripathi, Jai Prakash; Abbas, Syed; Thakur, Manoj

2012-09-01

11

Neural-network-based load modeling and its use in voltage stability analysis  

Microsoft Academic Search

Voltage stability analysis is very important for predicting potential voltage instability. Load modeling plays a key role in voltage stability assessment. In the literature, most available approaches to the voltage stability problem are either static or quasistatic, which do not take load dynamics into account. First, this paper presents a survey of those approaches, makes a comparison between them, and

Dingguo Chen; Ronald R. Mohler

2003-01-01

12

Stability analysis of a model for foreign body fibrotic reactions.  

PubMed

Implanted medical devices often trigger immunological and inflammatory reactions from surrounding tissues. The foreign body-mediated tissue responses may result in varying degrees of fibrotic tissue formation. There is an intensive research interest in the area of wound healing modeling, and quantitative methods are proposed to systematically study the behavior of this complex system of multiple cells, proteins, and enzymes. This paper introduces a kinetics-based model for analyzing reactions of various cells/proteins and biochemical processes as well as their transient behavior during the implant healing in 2-dimensional space. In particular, we provide a detailed modeling study of different roles of macrophages (M?) and their effects on fibrotic reactions. The main mathematical result indicates that the stability of the inflamed steady state depends primarily on the reaction dynamics of the system. However, if the said equilibrium is unstable by its reaction-only system, the spatial diffusion and chemotactic effects can help to stabilize when the model is dominated by classical and regulatory macrophages over the inflammatory macrophages. The mathematical proof and counter examples are given for these conclusions. PMID:23193430

Ibraguimov, A; Owens, L; Su, J; Tang, L

2012-09-13

13

Stability Analysis of a Model for Foreign Body Fibrotic Reactions  

PubMed Central

Implanted medical devices often trigger immunological and inflammatory reactions from surrounding tissues. The foreign body-mediated tissue responses may result in varying degrees of fibrotic tissue formation. There is an intensive research interest in the area of wound healing modeling, and quantitative methods are proposed to systematically study the behavior of this complex system of multiple cells, proteins, and enzymes. This paper introduces a kinetics-based model for analyzing reactions of various cells/proteins and biochemical processes as well as their transient behavior during the implant healing in 2-dimensional space. In particular, we provide a detailed modeling study of different roles of macrophages (M?) and their effects on fibrotic reactions. The main mathematical result indicates that the stability of the inflamed steady state depends primarily on the reaction dynamics of the system. However, if the said equilibrium is unstable by its reaction-only system, the spatial diffusion and chemotactic effects can help to stabilize when the model is dominated by classical and regulatory macrophages over the inflammatory macrophages. The mathematical proof and counter examples are given for these conclusions.

Ibraguimov, A.; Owens, L.; Su, J.; Tang, L.

2012-01-01

14

Nuclear power plant modeling and steam generator stability analysis. [TRANSG-P Code  

Microsoft Academic Search

This thesis describes the development of a computer model simulating the transient behavior of a pressurized water reactor (PWR) nuclear steam supply system (NSSS) and a stability analysis of steam generators in an overall NSSS structure. In the analysis of stream generator stability characteristics, an emphasis was placed on the physical interpretation of density wave oscillation (DWO) phenomena in boiling

Kornfilt

1981-01-01

15

Accuracy Analysis of Static Voltage Stability Indices Based On Power Flow Model  

Microsoft Academic Search

There are some voltage stability indices for voltage security assessment and calculating stable margin from operating point to voltage instability at each load bus. Most of those indices are based on static analyses using power flow model. This paper aims to verifying the accuracy of representative power flow model based indices by small signal stability analysis and dynamic time domain

Huadong Sun; Xiaoxin Zhou; Ruomei Li

2005-01-01

16

Disturbance Decoupling and Robustness of Stability. Modelling, Analysis and Simulation.  

National Technical Information Service (NTIS)

In this paper we investigate the interaction of disturbance decoupling requirement with the robustness of closed loop stability in the sense of normalized coprime factor perturbations. The disturbance decoupling and the robust stabilization requirements a...

U. Baser M. K. K. Cevik J. M. Schumacher

1998-01-01

17

Stability analysis of a multi-phase car-following model  

NASA Astrophysics Data System (ADS)

This paper presents a numerical stability analysis of a multi-phase car-following model under mild to severe disturbances. The results show that local stability was always conformed. An asymptotically unstable region was found for traffic in congested states. One of the previously calibrated boundary conditions for close-following situations was found to be in conflict with the stable condition required by the car-following model, which had attributed to speed oscillations during transition of the traffic from a non-congested to a congested state. Suggestions were made to the choice of model parameter values to meet the stability conditions and ways to improve the model.

Liu, Ronghui; Li, Xiang

2013-06-01

18

DYNAMIC MODELLING AND STABILITY ANALYSIS OF AXIALLY OSCILLATING CANTILEVER BEAMS  

Microsoft Academic Search

Dynamic stability of an axially oscillating cantilever beam is investigated in this paper. Equations of motion for the axially oscillating beam are derived and transformed into dimensionless forms. The equations include harmonically oscillating parameters which are related to the motion-induced stiffness variation. Stability diagrams of the first and the second order approximate solutions are obtained by using the multiple scale

S. H. HYUN; H. H. Yoo

1999-01-01

19

Stability analysis and modeling of rotating flexible structures.  

National Technical Information Service (NTIS)

A method is presented for determining the nonlinear stability of undamped flexible structures spinning about a principal axis of inertia. Equations of motion are developed for structures that are free of applied forces and moments. The development makes u...

C. R. Dohrmann

1993-01-01

20

Stability analysis of a class of biological network models  

Microsoft Academic Search

In this paper, we establish stability conditions for a special class of interconnected systems arisen in several biochemical applications. It is known that most of the biochemical processes can be represented using quasi-polynomial systems. We show that a special class of quasi-polynomial systems can be cast in the Lotka-Volterra canonical form. We study the asymptotic stability properties of a class

Nader Motee; Bassam Bamieh; Mustafa Khammash

2010-01-01

21

Floquet stability analysis of the longitudinal dynamics of two hovering model insects  

PubMed Central

Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considered—a dronefly and a hawkmoth. The former had relatively high wingbeat frequency and small wing-mass to body-mass ratio, and hence very small amplitude of body oscillation; while the latter had relatively low wingbeat frequency and large wing-mass to body-mass ratio, and hence relatively large amplitude of body oscillation. For comparison, analysis using the averaged-model theory (fixed-point stability analysis) was also made. Results of both the cyclic-motion stability analysis and the fixed-point stability analysis were tested by numerical simulation using complete equations of motion coupled with the Navier–Stokes equations. The Floquet theory (cyclic-motion stability analysis) agreed well with the simulation for both the model dronefly and the model hawkmoth; but the averaged-model theory gave good results only for the dronefly. Thus, for an insect with relatively large body oscillation at wingbeat frequency, cyclic-motion stability analysis is required, and for their control analysis, the existing well-developed control theories for systems of fixed-point equilibrium are no longer applicable and new methods that take the cyclic variation of the flight dynamics into account are needed.

Wu, Jiang Hao; Sun, Mao

2012-01-01

22

Floquet stability analysis of the longitudinal dynamics of two hovering model insects.  

PubMed

Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considered-a dronefly and a hawkmoth. The former had relatively high wingbeat frequency and small wing-mass to body-mass ratio, and hence very small amplitude of body oscillation; while the latter had relatively low wingbeat frequency and large wing-mass to body-mass ratio, and hence relatively large amplitude of body oscillation. For comparison, analysis using the averaged-model theory (fixed-point stability analysis) was also made. Results of both the cyclic-motion stability analysis and the fixed-point stability analysis were tested by numerical simulation using complete equations of motion coupled with the Navier-Stokes equations. The Floquet theory (cyclic-motion stability analysis) agreed well with the simulation for both the model dronefly and the model hawkmoth; but the averaged-model theory gave good results only for the dronefly. Thus, for an insect with relatively large body oscillation at wingbeat frequency, cyclic-motion stability analysis is required, and for their control analysis, the existing well-developed control theories for systems of fixed-point equilibrium are no longer applicable and new methods that take the cyclic variation of the flight dynamics into account are needed. PMID:22491980

Wu, Jiang Hao; Sun, Mao

2012-04-04

23

Stability analysis and modeling of rotating flexible structures  

Microsoft Academic Search

A method is presented for determining the nonlinear stability of undamped flexible structures spinning about a principal axis of inertia. Equations of motion are developed for structures that are free of applied forces and moments. The development makes use of a floating reference frame which follows the overall rigid body motion. Within this frame, elastic deformations are assumed to be

C. R. Dohrmann

1993-01-01

24

Stability analysis of a stochastic logistic model with infinite delay  

NASA Astrophysics Data System (ADS)

This report is concerned with a stochastic logistic equation with infinite delay. We establish the sufficient conditions for global asymptotical stability of the zero solution and the positive equilibrium. Some classical results are improved and extended. Several numerical simulations are introduced to illustrate the main results.

Liu, Meng; Fan, Dejun; Wang, Ke

2013-09-01

25

Stability analysis for the quartic Landau-Ginzburg model  

Microsoft Academic Search

The three-dimensional stability of static one-dimensional solutions of the Landau-Ginzburg equation is investigated. A general formula for the growth or decay rate is obtained for arbitrary local free energies, using a method developed earlier by Rowlands and Infeld (1979) for different equations. The results are then applied to quartic free energies. Among the real finite solutions obtained earlier, conoidal waves

A. M. Grundland; E. Infeld; G. Rowlands; P. Winternitz

1990-01-01

26

Flexible multibody dynamics based fixture-workpiece analysis model for fixturing stability  

Microsoft Academic Search

The machining force and torque exerted on a workpiece vary as the cutter moves along the tool path, therefore a dynamic approach is essential for fixturing stability analysis. This paper presents a technique to dynamically model and analyze the fixture-workpiece system subjected to time-varying machining loads. Combining the advantages of FEA (Finite Element Analysis) and nonlinear rigid body dynamics, a

Y. J. Gene Liao; S. Jack Hu

2000-01-01

27

RAH66 Comanche Linear Aeroservoelastic Stability Analysis: Model Improvements and Flight Test Correlation  

Microsoft Academic Search

The RAH-66 Comanche linear aeroservoelastic (ASE) model provides concurrent handling qualities and closed-loop, high-frequency stability analyses. Using analytical models, flight and ground test data, and numerical model predictions, this paper describes new insights into problems of general relevance to the design and analysis of high-bandwidth rotorcraft which have come about as a result of the ASE model development effort. Empirical

Bruce D. Kothmann; Steven J. Ingle

1998-01-01

28

Stability and Control Analysis Based on Airship Dynamic Modeling  

Microsoft Academic Search

This paper presents a 6DOF (degree of freedom) nonlinear dynamic model for a special kind of airship, which is based on the body axes coordinate system with the origin at the center of the volume. Firstly, the related physical principles of airship are comprehensively reviewed. Then, the nonlinear dynamic model is linearized based on linear perturbation theory, and divided into

Yu Liu; Yueming Hu; Yilin Wu

2007-01-01

29

Delay-dependent stability analysis for Two-Dimensional discrete systems with shift delays by the General Models  

Microsoft Academic Search

This paper is concerned with stability analysis for two-dimensional (2-D) discrete systems with shift delays in the general models (GM). Delay-dependent sufficient conditions for stability are derived and expressed in terms of linear matrix inequalities (LMIs). The stability theorem concludes stability theorems for 2D discrete systems by the general models and the Fornasini-Marchesini local state space models as special cases.

Shuxia Ye; Yun Zou; Weiqun Wang; Juan Yao

2008-01-01

30

The application of cause-and-effect analysis to mathematical models of geophysical phenomena. II - Stability analysis  

NASA Astrophysics Data System (ADS)

The 'cause-and-effect analysis' (CEA) technique is applied to investigate the stability of mathematical models of geophysical phenomena. It is shown that the ith coefficient of p(lambda) is equal to -PL sup (i), the ith order loop effect of the graph analog of matrix B - I, where I is the identity matrix. The classical conditions for stability for both discrete process (DP) and continuous process (CP) systems are then reformulated in terms of the PL sup (i) determined from the graph analog of the system. The use of the result graph analog stability conditions is illustrated by application to two CP systems, the Chapman photochemical cycle and an energy balance climate model, and to a DP system, a finite-differenced differential equation. CEA stability analysis elucidates the interactions among a system's internal variables and thus determines the cause of an instability and facilitates modification of the system to make it stable.

Andronova, Nataliia G.; Schlesinger, Michael E.

1992-04-01

31

Bipedal locomotion stabilized by impact and switching: II. Structural stability analysis of a four-element bipedal locomotion model  

Microsoft Academic Search

A nonlinear model for a four-element bipedal locomotion system, which includes the impact of the swinging limb with the ground and the switching of pivot is developed. The structural stability of the nonlinear, discontinuous model is studied.

Yildirim Hürmüzlü; Gordon D. Moskowitz

1987-01-01

32

Stability Analysis and Performance Design for Fuzzy Model-based Control Systems using a BMI-based Approach  

Microsoft Academic Search

This chapter presents the stability analysis and performance design for nonlinear systems. To facilitate the stability analysis,\\u000a the T-S fuzzy model is employed to represent the nonlinear plant. A fuzzy controller with enhanced stabilization ability is\\u000a proposed to close the feedback loop. Membership functions different from those of the fuzzy model are used by the fuzzy controller\\u000a to simplify its

H. K. Lam; F. H. F. Leung

33

Modeling and Simulation of Voltage Source Converter–Medium-voltage DC System for Stability Analysis  

Microsoft Academic Search

This article presents the modeling and simulation of a simple two-terminal and a multi-terminal voltage source converter based medium-voltage DC system, representing a simplified shipboard distribution network, for angular stability analysis. The control modes considered for the voltage source converter include the voltage control mode and the active and reactive power control schemes. The impact of these control modes on

Seetharama Rudraraju; Suresh C. Srivastava; Anurag K. Srivastava; Noel N. Schulz

2011-01-01

34

Towards comprehensive analysis of protein family quantitative stability-flexibility relationships using homology models.  

PubMed

The Distance Constraint Model (DCM) is a computational modeling scheme that uniquely integrates thermodynamic and mechanical descriptions of protein structure. As such, quantitative stability-flexibility relationships (QSFR) that describe the interrelationships of thermodynamics and mechanics can be quickly computed. Using comparative QSFR analyses, we have previously investigated these relationships across a small number of protein orthologs, ranging from two to a dozen [1, 2]. However, our ultimate goal is provide a comprehensive analysis of whole protein families, which requires consideration of many more structures. To that end, we have developed homology modeling and assessment protocols so that we can robustly calculate QSFR properties for proteins without experimentally derived structures. The approach, which is presented here, starts from a large ensemble of potential homology models and uses a clustering algorithm to identify the best models, thus paving the way for a comprehensive QSFR analysis across hundreds of proteins in a protein family. PMID:24061925

Verma, Deeptak; Guo, Jun-Tao; Jacobs, Donald J; Livesay, Dennis R

2014-01-01

35

Stability analysis of a state dependent delayed, coupled two DOF model of drill-stringvibration  

NASA Astrophysics Data System (ADS)

Stick-slip and bit-bounce are dangerous dynamic phenomena encountered during rotary drilling of oil-wells, but their exact origins and interplay are far from obvious. In this paper, we consider a fully coupled two degrees-of-freedom model, which assumes a state-dependent time delay and a viscous damping for both the axial and torsional motions. Without making any asymptotic assumptions, we have conducted a detailed linear stability analysis of the resultant mathematical model, which is composed of two coupled delay differential equations. The main significance of our work lies in providing practically useful results, which are in the form of stability charts in the plane of drilling rates and rotary speeds.

Nandakumar, K.; Wiercigroch, Marian

2013-05-01

36

Stability analysis of an epidemic model with diffusion and stochastic perturbation  

NASA Astrophysics Data System (ADS)

In this paper, we investigate the stability of an epidemic model with diffusion and stochastic perturbation. We first show both the local and global stability of the endemic equilibrium of the deterministic epidemic model by analyzing corresponding characteristic equation and Lyapunov function. Second, for the corresponding reaction-diffusion epidemic model, we present the conditions of the globally asymptotical stability of the endemic equilibrium. And we carry out the analytical study for the stochastic model in details and find out the conditions for asymptotic stability of the endemic equilibrium in the mean sense. Furthermore, we perform a series of numerical simulations to illustrate our mathematical findings.

Rao, Feng; Wang, Weiming; Li, Zhibin

2012-06-01

37

A model of feedback control system on network and its stability analysis  

NASA Astrophysics Data System (ADS)

A model of feedback control system on network is constructed. Some criterions ensuring the robust stability and global exponential stability for the model are established, by applying Lyapunov method and generalized Kirchhoff's matrix tree theorem. These criterions have a close relation to the topology property of networks. Finally, two examples and simulations are provided to illustrate the theoretical results.

Su, Huan; Qu, Yanbin; Gao, Shang; Song, Huihui; Wang, Ke

2013-07-01

38

Cellular control models with linked positive and negative feedback and delays. II. Linear analysis and local stability.  

PubMed

An analysis of local behavior is made of two nonlinear models which incorporate both an induction or positive feedback control mechanism and a repression or negative feedback control mechanism. The systems of differential equations with delays are linearized about their equilibria. The related characteristic equations which are exponential polynomials are studied to determine the local stability of the models. Computer studies are included to show the range of stability for different parameter values, and the biological significance is discussed briefly. PMID:6369003

Mahaffy, J M

1984-01-21

39

Slope Stability Analysis Program  

NSDL National Science Digital Library

This site provides information as well as a downloadable demo version of a slope stability and reinforced soil analysis and design software. The software includes an analysis option which analyzes strata profile and groundwater conditions, surcharge loads and earthquake forces, slip surfaces, and reinforced soil options. Data input and editing can also be performed as well as output from the program and graphics.

2008-07-17

40

Safe distance car-following model including backward-looking and its stability analysis  

NASA Astrophysics Data System (ADS)

The focus of this paper is the car-following behavior including backward-looking, simply called the bi-directional looking car-following behavior. This study is motivated by the potential changes of the physical properties of traffic flow caused by the fast developing intelligent transportation system (ITS), especially the new connected vehicle technology. Existing studies on this topic focused on general motors (GM) models and optimal velocity (OV) models. The safe distance car-following model, Gipps' model, which is more widely used in practice have not drawn too much attention in the bi-directional looking context. This paper explores the property of the bi-directional looking extension of Gipps' safe distance model. The stability condition of the proposed model is derived using the linear stability theory and is verified using numerical simulations. The impacts of the driver and vehicle characteristics appeared in the proposed model on the traffic flow stability are also investigated. It is found that taking into account the backward-looking effect in car-following has three types of effect on traffic flow: stabilizing, destabilizing and producing non-physical phenomenon. This conclusion is more sophisticated than the study results based on the OV bi-directional looking car-following models. Moreover, the drivers who have the smaller reaction time or the larger additional delay and think the other vehicles have larger maximum decelerations can stabilize traffic flow.

Yang, Da; Jin, Peter Jing; Pu, Yun; Ran, Bin

2013-03-01

41

Analysis of Composite Load Models on Load Margin of Voltage Stability  

Microsoft Academic Search

While it has been widely accepted that the constant P-Q leads to conservative load margin calculation of voltage stability, lately the studies show that induction motor loads can lead to an even more conservative load margin calculation. This paper analyzes the impacts of the composite load model (the composite of ZIP and induction motor load models) on the load margin

Shao-Hua Li; Hsiao-Dong Chiang; Sheng Liu

2006-01-01

42

Approximate linear stability analysis of a model of adiabatic shear-band formation  

SciTech Connect

The formation of adiabatic shear bands in ductile metals under dynamic loading conditions is generally thought to result from a material instability, which is associated with a peak in the curve of engineering plastic flow stress vs engineering shear strain. This instability arises from the effect of thermal softening, caused by irreversible adiabatic heating, which counteracts the tendency of the material to harden with increasing plastic strain. An approximate linear stability analysis of a one-dimensional rigid-thermoviscoplastic model, based on data taken from dynamic torsion experiments on thin-walled tubes of mild steel, shows that shear band formation in this situation can be interpreted as a bifurcation from a homogeneous simple shearing deformation which occurs at the peak in the homogeneous stress vs strain curve. The asymptotic method of multiple scales is used to show that the growth rate of small perturbations on the homogeneous deformation is controlled by the ratio of the slope of the homogeneous stress vs strain curve to the material viscosity, i.e., the rate of change of the plastic flow stress with respect to the strain-rate. In addition, it is shown that this growth rate is essentially independent of wavelength in any small perturbation. Numerical methods are used to show that this growth rate beyond the bifurcation point may not be sufficiently large for the model to account for the experimental data, and some suggestions are made on how to modify the constitutive equation so that it better fits the experimental data.

Burns, T.J.

1983-10-01

43

THE GREAT OXIDATION OF EARTH'S ATMOSPHERE: CONTESTING THE YOYO MODEL VIA TRANSITION STABILITY ANALYSIS  

SciTech Connect

A significant controversy regarding the climate history of the Earth and its relationship to the development of complex life forms concerns the rise of oxygen in the early Earth's atmosphere. Geological records show that this rise occurred about 2.4 Gyr ago, when the atmospheric oxygen increased from less than 10{sup -5} present atmospheric level (PAL) to more than 0.01 PAL and possibly above 0.1 PAL. However, there is a debate whether this rise happened relatively smoothly or with well-pronounced ups and downs (the Yoyo model). In our study, we explore a simplified atmospheric chemical system consisting of oxygen, methane, and carbon that is driven by the sudden decline of the net input of reductants to the surface as previously considered by Goldblatt et al. Based on the transition stability analysis for the system equations, constituting a set of non-autonomous and non-linear differential equations, as well as the inspection of the Lyapunov exponents, it is found that the equations do not exhibit chaotic behavior. In addition, the rise of oxygen occurs relative smoothly, possibly with minor bumps (within a factor of 1.2), but without major jumps. This result clearly argues against the Yoyo model in agreement with recent geological findings.

Cuntz, M.; Roy, D.; Musielak, Z. E., E-mail: cuntz@uta.ed, E-mail: dipanjan.roy@etumel.univmed.f, E-mail: zmusielak@uta.ed [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States)

2009-11-20

44

Modeling a washboard road: From experimental measurements to linear stability analysis  

NASA Astrophysics Data System (ADS)

When submitted to the repeated passages of vehicles unpaved roads made of sand or gravel can develop a ripply pattern known as washboard or corrugated road. We propose a stability analysis based on experimental measurements of the force acting on a blade (or plow) dragged on a circular sand track and show that a linear model is sufficient to describe the instability near onset. The relation between the trajectory of the plow and the profile of the sand bed left after its passage is studied experimentally. The various terms in the expression of the lift force created by the flow of granular material on the plow are determined up to first order by imposing a sinusoidal trajectory to the blade on an initially flat sand bed, as well as by imposing a horizontal trajectory on an initially rippled sand bed. Our model recovers all the previously observed features of washboard road and accurately predicts the most unstable wavelength near onset as well as the critical velocity for the instability.

Percier, Baptiste; Manneville, Sébastien; Taberlet, Nicolas

2013-01-01

45

Modeling a washboard road: from experimental measurements to linear stability analysis.  

PubMed

When submitted to the repeated passages of vehicles unpaved roads made of sand or gravel can develop a ripply pattern known as washboard or corrugated road. We propose a stability analysis based on experimental measurements of the force acting on a blade (or plow) dragged on a circular sand track and show that a linear model is sufficient to describe the instability near onset. The relation between the trajectory of the plow and the profile of the sand bed left after its passage is studied experimentally. The various terms in the expression of the lift force created by the flow of granular material on the plow are determined up to first order by imposing a sinusoidal trajectory to the blade on an initially flat sand bed, as well as by imposing a horizontal trajectory on an initially rippled sand bed. Our model recovers all the previously observed features of washboard road and accurately predicts the most unstable wavelength near onset as well as the critical velocity for the instability. PMID:23410322

Percier, Baptiste; Manneville, Sébastien; Taberlet, Nicolas

2013-01-17

46

Large signal stability analysis based on gyrator model with constant power load  

Microsoft Academic Search

Power electronic converters are widely used in advanced automobiles, especially in electrical vehicles (EVs). However, the stability analysis of the advanced automotive electrical systems which composed by multi-voltage level hybrid ac and dc systems is much complex than a single converter. In the system level, the downstream converter behaves as a constant power load (CPL) which shows negative incremental resistance

Weijing Du; Junming Zhang; Yang Zhang; Zhaoming Qian; Fangzheng Peng

2011-01-01

47

A distributed model for slope stability analysis using radar detected rainfall intensity  

NASA Astrophysics Data System (ADS)

The term shallow landslides is widely used in literature to describe a slope movement of limited size that mainly develops in soils up to a maximum of a few meters. Shallow landslides are usually triggered by heavy rainfall because, as the water starts to infiltrate in the soil, the pore-water pressure increases so that the shear strength of the soil is reduced leading to slope failure. We have developed a distributed hydrological-geotechnical model for the forecasting of the temporal and spatial distribution of shallow landslides to be used as a warning system for civil protection purpose. The model uses radar detected rainfall intensity as the input for the hydrological simulation of the infiltration. Using the rainfall pattern detected by the radar is in fact possible to dynamically control the redistribution of groundwater pressure associated with transient infiltration of rain so as to infer the slope stability of the studied area. The model deals with both saturated and unsaturated conditions taking into account the effect of soil suction when the soil is not completely saturated. Two pilot sites have been chosen to develop and test this model: the Armea basin (Liguria, Italy) and the Ischia Island (Campania, Italy). In recent years several severe rainstorms have occurred in both these areas. In at least two cases these have triggered numerous shallow landslides that have caused victims and damaged roads, buildings and agricultural activities. In its current stage, the basic basin-scale model applied for predicting the probable location of shallow landslides involves several stand-alone components. The solution suggested by Iverson for the Richards equation is used to estimate the transient groundwater pressure head distribution according to radar detected rainfall intensity. A soil depth prediction scheme and a limit-equilibrium infinite slope stability algorithm are used to calculate the distributed factor of safety (FS) at different depths and to record the lowest value in the final output file. The additional ancillary data required have been collected during fieldwork. To test the effectiveness of the model, near-real time simulations have been performed in the two test sites using data measured during the past rainfall events: December 2006 for the Armea basin and April 2006 for the Island of Ischia. The landslides triggered by rainfall during these two events were known thanks to the data collected during the fieldwork and to the photointerpretation performed on satellite images. Through the analysis of the factor of safety maps obtained during these simulations, it has been possible to evaluate the behaviour of the model in response to different and complex rainfall patterns. Moreover, the comparison of the results with the new landslide inventory map, has provided a spatial validation of the model for the Armea basin.

Leoni, L.; Rossi, G.; Catani, F.

2009-04-01

48

The stability of trophic mass-balance models of marine ecosystems: a comparative analysis  

Microsoft Academic Search

Dynamic simulations of 18 ecopath mass-balance marine trophic models are used to explore the stability of systems when briefly impacted by a fishery on the key `wasp–waist' populations occurring at intermediate trophic levels. The results are related to different ecosystem goal functions previously identified as representative of three attributes of ecosystems development: community complexity, homeostasis and energetics. System recovery time,

Marcelo Vasconcellos; Steven Mackinson; Katherine Sloman; Daniel Pauly

1997-01-01

49

Stability analysis of discrete-time recurrent neural networks based on standard neural network models  

Microsoft Academic Search

In order to conveniently analyze the stability of various discrete-time recurrent neural networks (RNNs), including bidirectional\\u000a associative memory, Hopfield, cellular neural network, Cohen-Grossberg neural network, and recurrent multiplayer perceptrons,\\u000a etc., the novel neural network model, named standard neural network model (SNNM) is advanced to describe this class of discrete-time\\u000a RNNs. The SNNM is the interconnection of a linear dynamic system

Meiqin Liu

2009-01-01

50

Global stability analysis - a key enabler in reduced order models and flow control  

NASA Astrophysics Data System (ADS)

In the current study, Reduced Order Models (ROMs) targeting strategies for experimental feedback flow control are discussed. For practical reasons, such models should incorporate a range of flow operating conditions with a small number of degrees of freedom. Standard POD Galerkin models are challenged by overoptimization at one operating condition [1]. The extension of dynamic range with additional global flow stability modes is the first applied technique. Further side constraints for control-oriented ROMs are taken into account by a "least-dimensional" Galerkin approximation based on a novel technique for continuous mode interpolation [2]. This interpolation preserves the model dimension of a single state while covering several states by adjusting (interpolated) modes. The resulting three-dimensional (3D) Galerkin model is presented for the transient flow around NACA-0012 airfoil and shown to be in a good agreement with the corresponding direct numerical simulation (DNS).

Morzy?ski, M.; Stankiewicz, W.; Thiele, F.; Noack, B. R.; Tadmor, G.

2012-01-01

51

A single compartment model of pacemaking in dissasociated Substantia nigra neurons : Stability and energy analysis.  

PubMed

Spontaneous oscillations in the mid-brain dopaminergic neurons are an important feature of motor control. The degeneration of these neurons is involved in movement disorders, particularly Parkinson's Disease. Modelling of this activity is an important part of developing an understanding of the pathogenic process. We develop a mathematical paradigm to describe this activity with a single compartment approach and a CellML version is made publicly available. The model explicitly describes the dynamics of the transmembrane potential with changes in the levels of important cations and is consistent with two major observations in the literature regarding its behaviour in the presence of channel blockers. Stability of the model behaviour is determined from the properties of its Monodromy matrix. We also discuss from the perspective of energy, a pharmacological intervention suggested in the treatment of Parkinson's Disease. PMID:23686304

Francis, Febe; García, Míriam R; Middleton, Richard H

2013-05-19

52

Stability analysis of an HIV/AIDS epidemic model with treatment  

NASA Astrophysics Data System (ADS)

An HIV/AIDS epidemic model with treatment is investigated. The model allows for some infected individuals to move from the symptomatic phase to the asymptomatic phase by all sorts of treatment methods. We first establish the ODE treatment model with two infective stages. Mathematical analyses establish that the global dynamics of the spread of the HIV infectious disease are completely determined by the basic reproduction number [real]0. If [real]0<=1, the disease-free equilibrium is globally stable, whereas the unique infected equilibrium is globally asymptotically stable if [real]0>1. Then, we introduce a discrete time delay to the model to describe the time from the start of treatment in the symptomatic stage until treatment effects become visible. The effect of the time delay on the stability of the endemically infected equilibrium is investigated. Moreover, the delay model exhibits Hopf bifurcations by using the delay as a bifurcation parameter. Finally, numerical simulations are presented to illustrate the results.

Cai, Liming; Li, Xuezhi; Ghosh, Mini; Guo, Baozhu

2009-07-01

53

Bifurcation analysis and dynamic stability  

SciTech Connect

Using tools of bifurcation analysis, we examine the long-term behavior of implicit differential equations which are defined by simultaneous ordinary differential equations and implicit algebraic equations. The analysis shows how certain nonlinearities can make the long term behavior of such dynamic systems sensitive to very small amplitude uncertainties and noise. This sensitivity makes the long term behavior practically unpredictable. At the same time the analysis suggests simple stochastic models in case of such unpredictable behavior. Implicit differential equations are often used in modeling the dynamic behavior of electric power systems. Our analysis indicates essential limitations on the ability of such models to predict long term behavior of the system, and it suggests ways to improve the ability of these models to describe important features of long term behavior. This analysis of implicit differential equations has significant implications for the study of the long term dynamic stability of power systems. The analysis also sheds light on the origin and significance of multiple solutions of the load flow equations.

Washburn, R.B. Jr.; Mehra, R.K.

1980-01-01

54

Stochastic modeling of high-stability ground clocks in GPS analysis  

NASA Astrophysics Data System (ADS)

In current global positioning system (GPS) applications, receiver clocks are typically estimated epoch-wise in the data analyses even for clocks with high performance like Hydrogen-masers (H-maser). Applying an appropriate clock model for high-stability receiver clocks should, in view of the strong correlation between the station height and the clock parameters, significantly improve the positioning results. Recent experiments have shown that modeling the deterministic behavior of high-quality receiver clocks can improve the kinematic precise point positioning considerably. In this paper, well-behaving ground clocks are studied in detail applying constraints between subsequent and near-subsequent clock parameters. The influence of different weights for these relative clock constraints on the positioning quality, especially on the height, is investigated. For excellent clocks, an improvement of up to a factor of 3 can be obtained for the repeatability of the kinematic height estimates. This may be essential to detect small but sudden changes in the vertical component (e.g., caused by earthquakes). Troposphere zenith path delays (ZPD) are also heavily correlated with the receiver clock estimates and station heights. All these parameters are usually estimated simultaneously. We show that the use of relative clock constraints allows for a higher time resolution of the ZPD estimates (smaller than 2 h) without compromising the quality of the kinematic height estimates.

Wang, Kan; Rothacher, Markus

2013-05-01

55

Stability analysis for the flow of granular materials down an inclined plane using kinetic model. Quarterly report, January 1, 1993--March 31, 1993  

SciTech Connect

In the previous report the linearized stability equations for the flow of granular materials down an inclined plane, modeled by the kinetic constitutive theory [cf Richman & Marciniec (1990)] were derived. Here, we use the approximate solution of Richman & Marciniec (1990) as the base solution for the linearized stability analysis. The governing equations obtained are solved numerically to obtain the marginal stability curves which are presented in this report.

Rajagopal, K.R.

1993-07-01

56

Tailings dams stability analysis using numerical modelling of geotechnical and geophysical data  

NASA Astrophysics Data System (ADS)

Methods for monitoring seepage and detecting internal erosion are essential for the safety evaluation of embankment dams. Internal erosion is one of the major reasons for embankment dam failures, and there are thousands of large tailings dams and waste-rock dumps in the world that may pe considered as hotspots for environmental impact. In this research the geophysical survey works were performed on Cetatuia 2 tailings dam. Electrical resistivity imaging (ERI) method was able to detect spatially anomalous zones inside the embankment dam. These anomalies are the results of internal erosion phenomena which may progressing inside the dam and is difficult to detect by conventional methods. Data aquired by geophysical survey together with their interpretations were used in the numerical model for slope stability assessment. The final results show us the structural weakness induced by the presence of internal erosion elements especially for seismic loading case. This research methodology may be also available for tailings dam monitoring purposes. Electrical Rezistivity Imaging (ERI) was performed on Cetatuia 2 dam at the Uranium Milling Plant Feldioara, in order to map areas with lateral and vertical changes in resistivity. The electrodes are connected to an automated computer operated switch box that selects the 4 electrodes to be used. A computer controls the switch box and the measuring device, and runs a program that selects the electrodes, makes the measurement, and stores the measurement. For inversion processing procedures was used Res2Din software. The measured resistivity were plotted by the pseudo section contouring method. There are five resistivity pseudosections obtained from the Cetatuia 2 tailings dam during the october 2007 measurements. Four transversal profiles trans1 to trans4 are perpendicular to the berms and the longitudinal one long1 is placed along dam's crest. The high resistivities near the berms surfaces corresponds to unsaturated fill materials and the low resistivities near the crest correspond to water saturated material. The resistivities values greater then 80 ohm.m may be explained by some error obtained for that inversion model. Profiles trans3 and trans4 were measured on perpendicular directions to berm alignment and show two distinct zones. The upward low resistivities zone correspond to water saturated materials especially from the compacted clay dam's core and the downward high resistivities zone belongs to unsaturated fill materials. The boundary between high and low resistivity at the depth of about 5 to 7 meters shows the groundwater level. The continuation of the high resistivity zones towards the end of the profile trans3, which is different from other profiles is probably due to the presence of dry coarse materials in shallow depth correspondingly to sandy clay. The sand fractions from the clay matrix may be affected by internal erosional phenomena, due to seepage currents that overpassed the material critical gradient. In this case the relative high resistivities values were considered as a presumptive erosional pattern. This profile was considered for the slope stability finite element modelling. The profile long1 which is placed along dam's crest is the longest profiles and extends up to nearly 420 m. The boundary between high and low resistivity at the depth of about 4 to 8 meters shows the groundwater across the dam core. The central part of the profile (about meter 200) shows the same relative high resistivities that occurred on transversal profile trans3. Resistivity data was used for building the 3D electrical resistivity model. The water saturated materials have locations very close to dam's crest (resistivity values usually lower then 10 ohm.m) and on both dam's arms. The groundwater levels were confirmed by the piezometric measurements. Electrical Rezistivity Imaging method had the possibility to show the most important disturbant elements that in certain conditions may weak the dam's state of safety. This study considered the SSR (Shear Strength Reduction) technique for sl

Mihai, S.; Zlagnean, M.; Oancea, I.; Petrescu, A.

2009-04-01

57

Tree Level Vacuum Stability in Multi Higgs Doublet Models: A Cumbersome Analysis?  

Microsoft Academic Search

We introduce a simple approach to obtain the constraint for multi Higgs doublet potentials to be stable, i.e. to have tree-level\\u000a vacuum stability. We use the methodology for some special cases with three doublets.

S. Zarrinkamar; H. Hassanabadi; A. A. Rajabi

2010-01-01

58

Stability analysis of an acoustically levitated disk  

Microsoft Academic Search

In this paper, a model is developed for the stability analysis of an acoustically levitated disk on the basis of analyzing eddy acoustic streaming and acoustic viscous stress. In the model, the effect of the acoustic streaming outside the boundary layer that is on the surface of the levitated disk is properly taken into account. Also, the calculation of sound

Junhui Hu; Kentaro Nakamura; Sadayuki Ueha

2003-01-01

59

Dynamic modeling and stability analysis of a power-generating tumbleweed rover  

Microsoft Academic Search

This paper introduces a novel tumbleweed rover design that employs a pendulum–generator system to harvest electrical power\\u000a from the wind. First, the dynamics of this multibody system are developed, including the internal pendulum dynamics, resistance\\u000a (damping) provided by the electrical generators, external wind force, and rolling constraints between the sphere and the ground.\\u000a Second, the stability of the system (without

James R. Forbes; Timothy D. Barfoot; Christopher J. Damaren

2010-01-01

60

Stability of interfaces in a random environment. A rigorous renormalization group analysis of a hierarchical model  

NASA Astrophysics Data System (ADS)

We study a hierarchical model of domain walls in a D-dimensional bond disordered Ising model at low temperatures. Using a renormalization group method inspired by the work of Bricmont and Kupiainen for the random field Ising model, we prove the existence of rigid interfaces at low enough temperatures in dimensions D>3.

Bovier, Anton; Picco, Pierre

1991-01-01

61

The stabilizing effects of the acquired immunity on the schistosomiasis transmission modeling - the sensitivity Analysis  

Microsoft Academic Search

A mathematical model is proposed to analyze the effects of acquired immunity on the transmission of schistosomiasis in the human host. From this model the prevalence curve dependent on four parameters can be obtained. These parameters were estimated fitting the data by the maximum likelihood method. The model showed a good retrieving capacity of real data from two endemic areas

Mo Yang Hyun; Ariana Campos Yang

1998-01-01

62

Stability analysis of real-time dynamic substructuring using delay differential equation models  

Microsoft Academic Search

Real-time dynamic substructuring is an experimental technique for testing the dynamic behaviour of complex structures. It involves creating a hybrid model of the entire structure by combining an experimental test piece-the substructure-with a numerical model describing the remainder of the system. The technique is useful when it is impractical to experimentally test the entire structure or complete numerical modelling is

M. I. Wallace; J. Sieber; S. A. Neild; D. J. Wagg; B. Krauskopf

2005-01-01

63

LMI-based stability analysis of fuzzy-model-based control systems using approximated polynomial membership functions.  

PubMed

Relaxed linear-matrix-inequality-based stability conditions for fuzzy-model-based control systems with imperfect premise matching are proposed. First, the derivative of the Lyapunov function, containing the product terms of the fuzzy model and fuzzy controller membership functions, is derived. Then, in the partitioned operating domain of the membership functions, the relations between the state variables and the mentioned product terms are represented by approximated polynomials in each subregion. Next, the stability conditions containing the information of all subsystems and the approximated polynomials are derived. In addition, the concept of the S-procedure is utilized to release the conservativeness caused by considering the whole operating region for approximated polynomials. It is shown that the well-known stability conditions can be special cases of the proposed stability conditions. Simulation examples are given to illustrate the validity of the proposed approach. PMID:21095873

Narimani, Mohammand; Lam, H K; Dilmaghani, R; Wolfe, Charles

2010-11-18

64

Centrifugal model analysis of coal waste embankment stability. Open file report (final) Oct 77Mar 79  

Microsoft Academic Search

Centrifugal model embankments with varying geometries and materials were constructed of coal waste material, accelerated from 100 to 120 times earth's gravity, and subjected to various throughflow rates until failure occurred. Complementary laboratory tests were performed on the waste materials to obtain strength and permeability parameters for analytical calculations to predict observed centrifugal model behavior. Failures in the form of

F. C. Townsend; D. J. Goodings; A. N. Schofield; M. M. Al-Hussaini

1979-01-01

65

Nonlinear state-dependent delay modeling and stability analysis of internet congestion control  

Microsoft Academic Search

It is shown that the queuing delay involved in the congestion control algorithm is state-dependent and does not depend on the current time. Then, using an accurate formulation for buffers, networks with arbitrary topologies can be built. At equilibrium, our model reduces to the widely used setup by Paganini et al. Using this model, the delay-derivative is analyzed and it

Corentin Briat; Håkan Hjalmarsson; Karl Henrik Johansson; Ulf T. Jönsson; Gunnar Karlsson; Henrik Sandberg

2010-01-01

66

Stability analysis of sleep apnea time series using identified models: a case study.  

PubMed

This paper investigates the use of identified nonlinear multivariable autonomous models in the classification of breathing patterns of a patient with sleep apnea. Details about the identification procedure are provided and the results reported for the case study at hand suggest that identified models could be useful in computer-based monitoring. PMID:15047435

Aguirre, Luis Antonio; Souza, Alvaro V P

2004-04-01

67

Energy function analysis for power system stability  

Microsoft Academic Search

Energy Function Analysis for Power System Stability presents the concept of energy function, which has found wide-spread applications for power systems in recent years. The most recent advances in five distinct areas are reviewed: Development of energy functions for structure preserving models, which can incorporate non-linear load models; energy functions which include a detailed model of the generating unit (i.e.

M. A. Pai

1989-01-01

68

Wheel-rail dynamics with closely conformal contact Part 1: dynamic modelling and stability analysis  

Microsoft Academic Search

Observations on the Vancouver mass transit system suggest that noise, vibration and corrugation of the rail appear to be associated with close conformity between the transverse profiles of the wheel and rail. To investigate this, a dynamic model of the wheel and rail under conditions of close conformity has been developed. Previous work has suggested that motion of the wheel

A Bhaskar; K L Johnson; G D Wood; J Woodhouse

1997-01-01

69

Unified power flow controller: Modeling, stability analysis, control strategy and control system design  

NASA Astrophysics Data System (ADS)

Unified power flow controller (UPFC) has been the most versatile Flexible AC Transmission System (FACTS) device due to its ability to control real and reactive power flow on transmission lines while controlling the voltage of the bus to which it is connected. UPFC being a multi-variable power system controller it is necessary to analyze its effect on power system operation. To study the performance of the UPFC in damping power oscillations using PSCAD-EMTDC software, a de-coupled control system has been designed for the shunt inverter to control the UPFC bus voltage and the DC link capacitor voltage. The series inverter of a UPFC controls the real power flow in the transmission line. One problem associated with using a high gain PI controller (used to achieve fast control of transmission line real power flow) for the series inverter of a UPFC to control the real power flow in a transmission line is the presence of low damping. This problem is solved in this research by using a fuzzy controller. A method to model a fuzzy controller in PSCAD-EMTDC software has also been described. Further, in order to facilitate proper operation between the series and the shunt inverter control system, a new real power coordination controller has been developed and its performance was evaluated. The other problem concerning the operation of a UPFC is with respect to transmission line reactive power flow control. Step changes to transmission line reactive power references have significant impact on the UPFC bus voltage. To reduce the adverse effect of step changes in transmission line reactive power references on the UPFC bus voltage, a new reactive power coordination controller has been designed. Transient response studies have been conducted using PSCAD-EMTDC software to show the improvement in power oscillation damping with UPFC. These simulations include the real and reactive power coordination controllers. Finally, a new control strategy has been proposed for UPFC. In this proposed control strategy, the shunt inverter controls the DC link capacitor voltage and the transmission line reactive power flow. The series inverter controls the transmission line real power flow and the UPFC bus voltage. PSCAD-EMTDC simulations have been conducted to show the viability of the control strategy in damping power oscillations.

Sreenivasachar, Kannan

2001-07-01

70

Voltage Stability Analysis of Radial Distribution Networks  

Microsoft Academic Search

The paper presents voltage stability analysis of radial distribution networks. A new stability index is proposed to identify the nodes that are on the verge of voltage collapse. The value of the proposed voltage stability index is calculated at each node of the network. A modified load flow method is used for voltage stability analysis. The modified load flow method

R. RANJAN; D. DAS

2003-01-01

71

Voltage stability analysis of multi-infeed HVDC systems using small-signal stability assessment  

Microsoft Academic Search

This paper presents an analysis of multi-infeed HVDC systems voltage stability using small-signal analysis techniques (eigen-structure analysis). A correlation ratio relating to voltage stability is put forward. A small test system with two HVDC infeeds is built to study the voltage stability of the multi-infeed HVDC system. Then the detailed dynamic models of the HVDC system including DC system control

Y. Shao; Y. Tang

2010-01-01

72

Global Stability Analysis for Linear Dynamics  

NASA Astrophysics Data System (ADS)

Global stability analysis of fluid flows is presented as a method of extracting physical eigenmodes with associated linear dynamic models. These reduced-order models (ROM) are optimal for the transients near the onset of instability. We describe the computational aspects of the eigenmode extraction in detail. This outline includes (i) the discretization technique of the eigenproblem in the framework of computational fluid dynamics (CFD) and (ii) the solution algorithms for the discretized eigenproblem. As regards physical aspects, the linear ROM are improved by enriching the basis with POD modes and by incorporating weakly nonlinear base flow variations. Results of stability computations are presented for the circular cylinder wake, the flow around a NACA-0012 airfoil and the optimization of passive control. Preliminary 3D eigensolutions show the potential of the global stability method.

Morzy?ski, Marek; Noack, Bernd R.; Tadmor, Gilead

73

Analysis of the stability and density waves for traffic flow  

Microsoft Academic Search

In this paper, the optimal velocity model of traffic is extended to take into account the relative velocity. The stability and density waves for traffic flow are investigated analytically with the perturbation method. The stability criterion is derived by the linear stability analysis. It is shown that the triangular shock wave, soliton wave and kink wave appear respectively in our

Yu Xue

2002-01-01

74

Kinetic analysis of thermal stability of human low density lipoproteins: a model for LDL fusion in atherogenesis[S  

PubMed Central

Fusion of modified LDL in the arterial wall promotes atherogenesis. Earlier we showed that thermal denaturation mimics LDL remodeling and fusion, and revealed kinetic origin of LDL stability. Here we report the first quantitative analysis of LDL thermal stability. Turbidity data show sigmoidal kinetics of LDL heat denaturation, which is unique among lipoproteins, suggesting that fusion is preceded by other structural changes. High activation energy of denaturation, Ea = 100 ± 8 kcal/mol, indicates disruption of extensive packing interactions in LDL. Size-exclusion chromatography, nondenaturing gel electrophoresis, and negative-stain electron microscopy suggest that LDL dimerization is an early step in thermally induced fusion. Monoclonal antibody binding suggests possible involvement of apoB N-terminal domain in early stages of LDL fusion. LDL fusion accelerates at pH < 7, which may contribute to LDL retention in acidic atherosclerotic lesions. Fusion also accelerates upon increasing LDL concentration in near-physiologic range, which likely contributes to atherogenesis. Thermal stability of LDL decreases with increasing particle size, indicating that the pro-atherogenic properties of small dense LDL do not result from their enhanced fusion. Our work provides the first kinetic approach to measuring LDL stability and suggests that lipid-lowering therapies that reduce LDL concentration but increase the particle size may have opposite effects on LDL fusion.

Lu, Mengxiao; Gantz, Donald L.; Herscovitz, Haya; Gursky, Olga

2012-01-01

75

Simple model for ablative stabilization  

SciTech Connect

We present a simple analytic model for ablative stablization of the Rayleigh-Taylor instability. In this model the effect of ablation is to move the peak of the perturbations to the location of peak pressure. This mechanism enhances the density-gradient stabilization, which is effective at short wavelengths, and it also enhances the stabilization of long-wavelength perturbations due to finite shell thickness. We consider the following density profile: exponential blowoff plasma with a density gradient {beta}, followed by a constant-density shell of thickness {delta}{ital t}. For perturbations of arbitrary wave number {ital k}, we present an explicit expression for the growth rate {gamma} as a function of {ital k}, {beta}, and {delta}{ital t}. We find that thick'' shells defined by {beta} {delta}{ital t}{ge}1 have {gamma}{sup 2}{ge}0 for any {ital k}, while thin'' shells defined by {beta} {delta}{ital t}{lt}1 can have {gamma}{sup 2}{lt}0 for {ital small} {ital k}, reflecting stability by proximity to the back side of the shell. We also present LASNEX simulations that are in good agreement with our analytic formulas.

Mikaelian, K.O. (University of California, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States))

1992-11-15

76

Population Models: Stability in One Dimension1  

Microsoft Academic Search

Some of the simplest models of population growth are one dimensional nonlinear difference equations. While such models can display wild behavior in- cluding chaos, the standard biological models have the interesting property that they display global stability if they display local stability. Various researchers have sought a simple explanation for this agreement of local and global stability. Here, we show

Paul Cull

2006-01-01

77

The stability of colorectal cancer mathematical models  

NASA Astrophysics Data System (ADS)

Colorectal cancer is one of the most common types of cancer. To better understand about the kinetics of cancer growth, mathematical models are used to provide insight into the progression of this natural process which enables physicians and oncologists to determine optimal radiation and chemotherapy schedules and develop a prognosis, both of which are indispensable for treating cancer. This thesis investigates the stability of colorectal cancer mathematical models. We found that continuous saturating feedback is the best available model of colorectal cancer growth. We also performed stability analysis. The result shows that cancer progress in sequence of genetic mutations or epigenetic which lead to a very large number of cells population until become unbounded. The cell population growth initiate and its saturating feedback is overcome when mutation changes causing the net per-capita growth rate of stem or transit cells exceed critical threshold.

Khairudin, Nur Izzati; Abdullah, Farah Aini

2013-04-01

78

Analysis of voltage stability enhancement via unified power flow controller  

Microsoft Academic Search

This paper discusses the control of the unified power flow controller (UPFC) to improve power system voltage stability. A dynamical UPFC model is presented. The impact of the UPC model on voltage stability is clarified through bifurcation analysis. Robust techniques are employed for the series and shunt branches control and the DC capacitor voltage control. Only local measurements are required

H. Chen; Y. Wang; R. Zhou

2000-01-01

79

Massively Parallel Linear Stability Analysis with P_ARPACK for 3D Fluid Flow Modeled with MPSalsa  

SciTech Connect

We are interested in the stability of three-dimensional fluid flows to small dkturbances. One computational approach is to solve a sequence of large sparse generalized eigenvalue problems for the leading modes that arise from discretizating the differential equations modeling the flow. The modes of interest are the eigenvalues of largest real part and their associated eigenvectors. We discuss our work to develop an effi- cient and reliable eigensolver for use by the massively parallel simulation code MPSalsa. MPSalsa allows simulation of complex 3D fluid flow, heat transfer, and mass transfer with detailed bulk fluid and surface chemical reaction kinetics.

Lehoucq, R.B.; Salinger, A.G.

1998-10-13

80

Relocation Analysis of Stabilizing MAC  

NASA Astrophysics Data System (ADS)

The designers of media access control (MAC) protocols often do not consider the relocation of mobile nodes. Alternatively, when they do assume that the nodes are not stationary, designers tend to assume that some nodes temporarily do not change their location and coordinate the communications among mobile nodes. An understanding is needed of the relationship between the performances of MAC algorithms and the different settings by which the location of the mobile nodes is modeled. We study this relationship with an emphasis on stabilization concepts, which are imperative in mobile ad hoc networks (MANETs). We show that efficient MAC algorithms must balance a trade-off between two strategies; one that is oblivious to the history of local broadcasts and one that is not.

Leone, Pierre; Papatriantafilou, Marina; Schiller, Elad M.

81

IMFIT Integrated Modeling Applications Supporting Experimental Analysis: Multiple Time-Slice Kinetic EFIT Reconstructions, MHD Stability Limits, and Energy and Momentum Flux Analyses  

NASA Astrophysics Data System (ADS)

This presentation summarizes several useful applications provided by the IMFIT integrated modeling framework to support DIII-D and EAST research. IMFIT is based on Python and utilizes modular task-flow architecture with a central manager and extensive GUI support to coordinate tasks among component modules. The kinetic-EFIT application allows multiple time-slice reconstructions by fetching pressure profile data directly from MDS+ or from ONETWO or PTRANSP. The stability application analyzes a given reference equilibrium for stability limits by performing parameter perturbation studies with MHD codes such as DCON, GATO, ELITE, or PEST3. The transport task includes construction of experimental energy and momentum fluxes from profile analysis and comparison against theoretical models such as MMM95, GLF23, or TGLF.

Collier, A.; Lao, L. L.; Abla, G.; Chu, M. S.; Prater, R.; Smith, S. P.; St. John, H. E.; Guo, W.; Li, G.; Pan, C.; Ren, Q.; Park, J. M.; Bisai, N.; Srinivasan, R.; Sun, A. P.; Liu, Y.; Worrall, M.

2010-11-01

82

Vacuum stability of Standard Model++  

NASA Astrophysics Data System (ADS)

The latest results of the ATLAS and CMS experiments point to a preferred narrow Higgs mass range (m_h \\simeq 124 - 126 GeV) in which the effective potential of the Standard Model (SM) develops a vacuum instability at a scale 10^{9} -10^{11} GeV, with the precise scale depending on the precise value of the top quark mass and the strong coupling constant. Motivated by this experimental situation, we present here a detailed investigation about the stability of the SM^{++} vacuum, which is characterized by a simple extension of the SM obtained by adding to the scalar sector a complex SU(2) singlet that has the quantum numbers of the right-handed neutrino, H", and to the gauge sector an U(1) that is broken by the vacuum expectation value of H". We derive the complete set of renormalization group equations at one loop. We then pursue a numerical study of the system to determine the triviality and vacuum stability bounds, using a scan of 10^4 random set of points to fix the initial conditions. We show that, if there is no mixing in the scalar sector, the top Yukawa coupling drives the quartic Higgs coupling to negative values in the ultraviolet and, as for the SM, the effective potential develops an instability below the Planck scale. However, for a mixing angle -0.35 \\alt \\alpha \\alt -0.02 or 0.01 \\alt \\alpha \\alt 0.35, with the new scalar mass in the range 500 GeV \\alt m_{h"} \\alt 8 TeV, the SM^{++} ground state can be absolutely stable up to the Planck scale. These results are largely independent of TeV-scale free parameters in the model: the mass of the non-anomalous U(1) gauge boson and its branching fractions.

Anchordoqui, Luis A.; Antoniadis, Ignatios; Goldberg, Haim; Huang, Xing; Lüst, Dieter; Taylor, Tomasz R.; Vlcek, Brian

2013-02-01

83

Expanding Panjabi's stability model to express movement: a theoretical model.  

PubMed

Novel theoretical models of movement have historically inspired the creation of new methods for the application of human movement. The landmark theoretical model of spinal stability by Panjabi in 1992 led to the creation of an exercise approach to spinal stability. This approach however was later challenged, most significantly due to a lack of favourable clinical effect. The concepts explored in this paper address and consider the deficiencies of Panjabi's model then propose an evolution and expansion from a special model of stability to a general one of movement. It is proposed that two body-wide symbiotic elements are present within all movement systems, stability and mobility. The justification for this is derived from the observable clinical environment. It is clinically recognised that these two elements are present and identifiable throughout the body in different joints and muscles, and the neural conduction system. In order to generalise the Panjabi model of stability to include and illustrate movement, a matching parallel mobility system with the same subsystems was conceptually created. In this expanded theoretical model, the new mobility system is placed beside the existing stability system and subsystems. The ability of both stability and mobility systems to work in harmony will subsequently determine the quality of movement. Conversely, malfunction of either system, or their subsystems, will deleteriously affect all other subsystems and consequently overall movement quality. For this reason, in the rehabilitation exercise environment, focus should be placed on the simultaneous involvement of both the stability and mobility systems. It is suggested that the individual's relevant functional harmonious movements should be challenged at the highest possible level without pain or discomfort. It is anticipated that this conceptual expansion of the theoretical model of stability to one with the symbiotic inclusion of mobility, will provide new understandings on human movement. The use of this model may provide a universal system for body movement analysis and understanding musculoskeletal disorders. In turn, this may lead to a simple categorisation system alluding to the functional face-value of a wide range of commonly used passive, active or combined musculoskeletal interventions. Further research is required to investigate the mechanisms that enable or interfere with harmonious body movements. Such work may then potentially lead to new and evolved evidence based interventions. PMID:23561576

Hoffman, J; Gabel, P

2013-04-03

84

Population Models: Stability in One Dimension 1  

Microsoft Academic Search

Some of the simplest models of population growth are one dimensional nonlinear difference equations. While such models can\\u000a display wild behavior including chaos, the standard biological models have the interesting property that they display global\\u000a stability if they display local stability. Various researchers have sought a simple explanation for this agreement of local\\u000a and global stability. Here, we show that

Paul Cull

2007-01-01

85

Slope stability analysis of Valles Marineris, Mars  

NASA Astrophysics Data System (ADS)

Valles Marineris (VM) in the equatorial area of Mars exhibits several gravitational failures which resulted in a series of large landslides up to several hundred cubic kilometers in volume. Questions arise as to forces at play and rock strength in the stability of the walls of VM. In this work we address the stability analysis of the walls of VM by considering the strength of the materials of the chasma walls and the causes of landslides. Using finite element calculations and the limit analysis upper bound method, we explore the range of cohesion and friction angle values associated to realistic failure geometries, and compare predictions with the classical Culmann's wedge model. Our analysis is based both on synthetic, simplified slope profiles and also on the real shape of the walls of VM taken from the MOLA topographic data. Validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre- and post-failure profiles and estimated failure surface geometry. This offers a link between rock mass properties, slope geometry and volume of the observed failure. Pseudo-static seismic analyses generated another set of dimensionless charts. Our pseudo-static analyses show that low seismicity events induced by meteoroids impacts compatible with the size of craters could be a cause for some of the observed landslides if poor rock properties for VM is assumed.

Vittorio De Blasio, Fabio; Battista Crosta, Giovanni; Castellanza, Riccardo; Utili, Stefano

2013-04-01

86

Stability analysis of intershaft squeeze film dampers  

NASA Astrophysics Data System (ADS)

Intershaft squeeze film dampers have been investigated for damping of dual rotor aircraft jet engines. Initial investigations indicated that the intershaft dampers would attenuate the amplitude of the engine vibration and decrease the force transmitted through the intershaft bearing, thereby increasing its life. Also it was thought that the intershaft damper would enhance the stability of the rotor-bearing system. Unfortunately, it was determined both theoretically and experimentally that the intershaft squeeze film damper was unstable above the engine's first critical speed. In this paper, a stability analysis of rotors incorporating intershaft squeeze film dampers is performed. A rotor model consisting of two Jeffcott rotors with two intershaft squeeze film dampers is investigated. Examining the system characteristic equation for the conditions at which the roots indicate an ever growing unstable motion results in the stability conditions. The cause of the instability is identified as the rotation of the oil in the damper clearance. The oil rotation adds energy to the forward whirl of the rotor system above the critical speed and thus causes the instability. Below the critical speed the oil film removes energy from the forward rotor whirl. It is also shown that the backward whirl of the rotor system is always stable. Several proposed configurations of intershaft squeeze film dampers are discussed, and it is shown that the intershaft dampers are stable supercritically only with a configuration in which the oil film does not rotate.

El-Shafei, A.

1991-08-01

87

Stability analysis of dynamic thin shells  

Microsoft Academic Search

We analyse the stability of generic spherically symmetric thin shells to linearized perturbations around static solutions. We include the momentum flux term in the conservation identity, deduced from the 'ADM' constraint and the Lanczos equations. Following the Ishak Lake analysis, we deduce a master equation which dictates the stable equilibrium configurations. Considering the transparency condition, we study the stability of

Francisco S. N. Lobo; Paulo Crawford

2005-01-01

88

On the stick-slip flow from slit and cylindrical dies of a Phan-Thien and Tanner fluid model. II. Linear stability analysis  

NASA Astrophysics Data System (ADS)

During extrusion of viscoelastic fluids various flow instabilities may arise resulting in a distorted free surface. In order to investigate the factors generating these instabilities we performed a linear stability analysis at zero Reynolds number around the steady solution of the cylindrical or planar stick-slip flow for a viscoelastic fluid following the affine exponential Phan-Thien Tanner (PTT) model. Stick-slip flow is an important special case of the extrudate swell problem, since the latter reduces to it in the limit of infinite surface tension but avoids the complications of a free-boundary flow. The linear stability analysis is performed for various values of the rheological parameters of the PTT model in order to determine the effects of all material properties. It is found that the flow becomes unstable as the Weissenberg number increases above a critical value, due to a Hopf bifurcation suggesting that the flow will become periodic in time. Both the critical value of the Weissenberg number and the frequency of the instability depend strongly on the rheological parameters of the viscoelastic model. The corresponding eigenvectors indicate that the perturbed flow field has a spatially periodic structure, initiated at the rim of the die, extending for up to 5-7 die gaps downstream, but confined close to the surface of the extrudate, in qualitative agreement with existing experiments. This suggests that instability is generated by the combination of the singularity in the velocity and stress fields at the die lip and the strong extension that the extruded polymer undergoes near its surface. The elasticity alone can be responsible for the appearance of instabilities in the extrusion process of viscoelastic fluids and the often used assumptions of wall slip or compressibility, although they might be present, are not required. Finally, the mechanisms that produce these instabilities are examined through energy analysis of the disturbance flow.

Karapetsas, George; Tsamopoulos, John

2013-09-01

89

Atomization of Non-Newtonian Liquids by a High Momentum Coaxial Gas Jet. Stability Analysis, Modelling and Experimental Validation  

NASA Astrophysics Data System (ADS)

The atomization of a liquid jet by a co-flowing, high-speed gas has been studied for non-Newtonian polymer solutions. In this study, the R-T model originally developed by Varga et al. (2003) is extended to viscous and non-Newtonian fluids by applying the general dispersion relation developed by Joseph et al. (2002). When viscous effects are negligible the maximum amplification wavenumber is k?=?a ?l/(3?). On the contrary, when viscous effects are dominant, the wavenumber for maximum amplification can be approximated by k?=?[3]a ?l^2/?l^2. If the effects of surface tension and viscosity are assumed to be additive, the resulting R-T instability wavelength can be estimated as ?RT= 2 ?(?3 ?/ (a ?l) + C2?[3]?l^2/(a ?l^2)). The model obtained from the theoretical analysis has been validated from droplet diameter measurements of the atomization of six different liquids under a wide range of experimental conditions. The diameter and axial velocity of the liquid droplets was measured by Phase Doppler Particle Analyzer.

Aliseda, Alberto; Hopfinger, Emil; Kremer, Douglas M.; Berchielli, Alfred; Connolly, Emilia K.; Lasheras, Juan C.

2007-11-01

90

Linear stability analysis of convective chemical fronts  

NASA Astrophysics Data System (ADS)

A chemical front propagating upward in a fluid separates heavy unreacted fluid from light reacted fluid. The density difference caused by the front propagation leads to convection. Convection enhances the front speed and curves the front as it propagates upward in a tube. The convective front propagates with constant speed and is steady in a frame of reference comoving with the front. This paper presents a linear stability analysis of the convective front. The fronts are modeled using a front evolution equation coupled to Darcy's law for flow in porous media and the Navier-Stokes for viscous flow. The solutions can be either axisymmetric or nonaxisymmetric as observed in experiments in tubes. For flow in porous media, there is a region of bistability between both types, whereas in viscous flow the axisymmetric front is always unstable.

Vasquez, Desiderio A.

1997-12-01

91

STABILITY AND ACCURACY OF NUMERICAL BOUNDARY CONDITIONS IN AEROELASTIC ANALYSIS  

Microsoft Academic Search

This paper analyses the accuracy and numerical stability of couplingprocedures in aeroelastic modelling. A two-dimensional modelproblem assuming unsteady inviscid flow past an oscillating wall leadsto an even simpler one-dimensional model problem. Analysis of differentnumerical algorithms shows that in general the coupling proceduresare numerically stable, but care is required to achieve accuracywhen using very few timesteps per period of natural oscillation

M. B. Giles

1997-01-01

92

Geotechnical vs. Geophysical models for slope stability  

NASA Astrophysics Data System (ADS)

Current approaches to landslide forecasting are based either on empirical models, which search for correlations between rainfall data and landslide occurrences, or on physically based models, which combine hydrological models with slope stability analyses for the computation of the Factor of Safety. Traditionally, the calculation of the Factor of Safety is based on accurate geotechnical measurements, which provide information on the internal structure and the mechanical properties of the investigated soils through the analysis of samples of very reduced size. Hence, both empirical and physically based traditional approaches are based on point information, which refer to very small rainwater collecting areas of rain gauges and very small soil volumes around porous probes. To overcome the limit of point-sampled information, we propose a semi-empirical approach based on the use of a geophysical Factor of Safety introduced in terms of local resistivities and slope angles. Starting from two resistivity tomography surveys performed on a test area on Sarno Mountains (Southern Italy) during the autumnal and spring seasons, we present an application of the proposed geophysical approach and compared the results with those coming from the infinite slope analysis. Advantages and disadvantages of geotechnical and geophysical approaches are shown.

Piegari, E.; Di Maio, R.

2012-04-01

93

Moduli stabilization in stringy ISS models  

SciTech Connect

We present a stringy realization of the ISS metastable SUSY breaking model with moduli stabilization. The mass moduli of the ISS model is stabilized by gauging of a U(1) symmetry and its D-term potential. The SUSY is broken both by F-terms and D-terms. It is possible to obtain de Sitter vacua with a vanishingly small cosmological constant by an appropriate fine-tuning of flux parameters.

Nakayama, Yu; Nakayama, Yu; Yamazaki, Masahito; Yanagida, T.T.

2007-09-28

94

Robust stability and performance analysis of sampled-data systems  

Microsoft Academic Search

The authors consider the robust stability and performance analysis of a general linear interconnection of a continuous-time plant and a discrete-time controller via sample and hold devices. They obtain necessary and sufficient conditions for the robust stability of the feedback system consisting of an uncertain plant represented as a known linear time-invariant (nominal) model with time-varying norm bounded uncertainty and

N. Sivashankar; Pramod P. Khargonekar

1993-01-01

95

Stability analysis of unsteady ablation fronts  

SciTech Connect

The linear stability analysis of unsteady ablation fronts, is carried out for a semi-infinite uniform medium. For a laser accelerated target, it is shown that a properly selected modulation of the laser intensity can lead to the dynamic stabilization or growth-rate reduction of a large portion of the unstable spectrum. The theory is in qualitative agreement with the numerical results obtained by using the two-dimensional hydrodynamic code ORCHID.

Betti, R.; McCrory, R.L.; Verdon, C.P.

1993-08-01

96

The role of context on alpha-helix stabilization: host-guest analysis in a mixed background peptide model.  

PubMed Central

The helix content of a series of peptides containing single substitutions of the 20 natural amino acids in a new designed host sequence, succinyl-YSEEEEKAKKAXAEEAEKKKK-NH2, has been determined using CD spectroscopy. This host is related to one previously studied, in which triple amino acid substitutions were introduced into a background of Glu-Lys blocks completely lacking alanine. The resulting free energies show that only Ala and Glu- prove to be helix stabilizing, while all other side chains are neutral or destabilizing. This agrees with results from studies of alanine-rich peptide modela, but not the previous Glu-Lys block oligomers in which Leu and Met also stabilize helix. The helix propensity scale derived from the previous block oligomers correlated well with the frequencies of occurrence of different side chains in helical sequences of proteins, whereas the values from the present series do not. The role of context in determining scales of helix propensity values is discussed, and the ability of algorithms designed to predict helix structure from sequence is compared.

Yang, J.; Spek, E. J.; Gong, Y.; Zhou, H.; Kallenbach, N. R.

1997-01-01

97

Modeling of power system dynamic devices incorporated in Dynamic Computation for Power Systems (DCPS) for transient stability analysis  

Microsoft Academic Search

An electrical power system consists of many individual dynamic devices connected together to form a large and complex dynamic system. To analyze the behavior of such devices, its physical model needs to be transformed into mathematical model before it can be solved on a computer. In electric utility practices, the aspect of modeling and computational methods for power system dynamic

N. Hashim; N. R. Hamzah; P. Mohd Arsad; R. Baharom; N. F. Nik Ismail; N. Aminudin; D. Johari; A. A. Sallehhudin

2011-01-01

98

Stability diagram for the forced Kuramoto model  

NASA Astrophysics Data System (ADS)

We analyze the periodically forced Kuramoto model. This system consists of an infinite population of phase oscillators with random intrinsic frequencies, global sinusoidal coupling, and external sinusoidal forcing. It represents an idealization of many phenomena in physics, chemistry, and biology in which mutual synchronization competes with forced synchronization. In other words, the oscillators in the population try to synchronize with one another while also trying to lock onto an external drive. Previous work on the forced Kuramoto model uncovered two main types of attractors, called forced entrainment and mutual entrainment, but the details of the bifurcations between them were unclear. Here we present a complete bifurcation analysis of the model for a special case in which the infinite-dimensional dynamics collapse to a two-dimensional system. Exact results are obtained for the locations of Hopf, saddle-node, and Takens-Bogdanov bifurcations. The resulting stability diagram bears a striking resemblance to that for the weakly nonlinear forced van der Pol oscillator.

Childs, Lauren M.; Strogatz, Steven H.

2008-12-01

99

Stability analysis of reduced and original pupillary light reflex system by RMS Model Order Reduction MATLAB Tool  

Microsoft Academic Search

New methods for the reduction of high-order, linear time invariant systems is proposed. The methods are based on the different techniques and generates low order stable models retaining both the initial Markov parameters and time-moments, of the original system. Theses models give a better approximation for both the steady-state as well as the transient part of the time response. The

P. Munaswamy; R. V. S. Satyanarayana

2012-01-01

100

Stability analysis for air film drag reduction  

Microsoft Academic Search

A linear stability analysis of an air-water interface is studied for basic understanding of air film physics applied to a ship hull for drag reduction purposes. Three different flows are studied. In the first case, viscosity is considered and is a special case of the problem studied by Yih (1967) when the thickness of two layers is the same and

Chinar Aphale; William Schultz; Steven Ceccio

2006-01-01

101

Stress transducer interpretation analysis and stability data  

Microsoft Academic Search

A semi-conductor strain gage transducer was developed for use in measuring stress in solid propellant grain rocket motors. The requirements for survival and performance are such that the sensor has direct use as a general pressure transducer especially where small size and high reliability are a requirement. The design work, gage interpretation analysis and some long-term stability results are summarized.

E. C. Francis; R. E. Thompson

1984-01-01

102

Stability analysis of a phase-field model of gravity-driven unsaturated flow through porous media  

Microsoft Academic Search

The formation of preferential flow paths during infiltration of water into homogeneous, dry soil is an important phenomenon whose explanation and prediction have remained elusive under the standard theories of multiphase flow in porous media. We have recently proposed a macroscopic phase-field model of unsaturated flow in porous media, which explains why such fingering occurs [L. Cueto-Felgueroso and R. Juanes,

Luis Cueto-Felgueroso; Ruben Juanes

2009-01-01

103

Stability analysis of a simple walking model driven by an oscillator with a phase reset using sensory feedback  

Microsoft Academic Search

This paper deals with the analytical examination of the dynamic properties of the walking motion of a biped robot based on a simple model. The robot is driven by rhythmic signals from an oscillator, which receives feedback signals from touch sensors at the tips of the legs. Instantly, the oscillator resets its phase and modifies the walking motion according to

Shinya Aoi; Kazuo Tsuchiya

2006-01-01

104

Analysis on Stability of Regional Logistics Enterprises Alliance  

Microsoft Academic Search

Facing with fierce market competition, more and more logistics enterprises choose alliance. A Bertrand model is used to compare and analyze the effectiveness of the logistics enterprises before and after the establishment of a regional logistics enterprises alliance. Through introducing the variable of discount factor and making an extended analysis of the stability, we obtain the confidence interval in which

Zhengchi Liu; Mingyong Lai; Liang Li

2009-01-01

105

Stability of the human respiratory control systemII. Analysis of a three-dimensional delay state-space model  

Microsoft Academic Search

.   A number of mathematical models of the human respiratory control system have been developed since 1940 to study a wide range\\u000a of features of this complex system. Among them, periodic breathing (including Cheyne-Stokes respiration and apneustic breathing)\\u000a is a collection of regular but involuntary breathing patterns that have important medical implications. The hypothesis that\\u000a periodic breathing is the result

J. J. Batzel; H. T. Tran

2000-01-01

106

Stability of the human respiratory control systemI. Analysis of a two-dimensional delay state-space model  

Microsoft Academic Search

.   A number of mathematical models of the human respiratory control system have been developed since 1940 to study a wide range\\u000a of features of this complex system. Among them, periodic breathing (including Cheyne-Stokes respiration and apneustic breathing)\\u000a is a collection of regular but involuntary breathing patterns that have important medical implications. The hypothesis that\\u000a periodic breathing is the result

J. J. Batzel; H. T. Tran

2000-01-01

107

Stability Analysis in a Model of 1,2-dichloroethane Biodegradation by Klebsiella Oxytoca va 8391Immobilized on Granulated Activated Carbon  

NASA Astrophysics Data System (ADS)

We consider an ecological model for biodegradation of toxic substances in aquatic and atmospheric biotic systems. The model, which is described by a nonlinear system of four ordinary differential equations, is known to be experimentally validated. We compute the equilibrium points of the model and study their asymptotic stability. The Maple package BifTools is used to calculate one- and two-parameter bifurcations of the equilibrium points.

Borisov, M.; Dimitrova, N.

2011-11-01

108

Periodic points and stability in Clark's delayed recruitment model  

Microsoft Academic Search

We provide further insight on the dynamics of Clark's delayed recruitment equation, depending on the relevant parameters involved in the model. We pay special attention to the stability and bifurcations from the positive equilibrium, and to the existence and attraction properties of nontrivial cycles. A detailed analysis is worked out for a three-dimensional example.

H ELMORSHEDY; Víctor Jiménez López; Eduardo Liz

2008-01-01

109

Periodic points and stability in Clark's delayed recruitment model  

Microsoft Academic Search

We provide further insight on the dynamics of Clark's delayed recruitment equation, depending on the relevant parameters involved in the model. We pay special attention to the stability and bifurcations from the positive equilibrium, and to the existence and attraction properties of nontrivial cycles. A detailed analysis is worked out for a three-dimensional example. 2007 Elsevier Ltd. All rights reserved.

Hassan A. El-Morshedy; Víctor Jiménez López; Eduardo Liz

110

Stability of PEEC models with respect to partial element accuracy  

Microsoft Academic Search

We examine the passivity and stability of quasi-static partial element equivalent circuit (PEEC) models. The impact of inaccuracies in the computed partial element values is considered as a possible source of time domain instabilities. Our analysis shows how existing partial element calculation routines, analytical and numerical, and the use of poor mesh generators can introduce large errors in partial element

Jonas Ekman; G. Antonini; A. Orlandi; A. E. Ruehli

2004-01-01

111

DYNAMIC LANDSCAPES, STABILITY AND ECOLOGICAL MODELING  

EPA Science Inventory

The image of a ball rolling along a series of hills and valleys is an effective heuristic by which to communicate stability concepts in ecology. However, the dynamics of this landscape model have little to do with ecological systems. Other landscape representations, however, are ...

112

Stability Analysis and Numerical Simulation of Differential Frost Heave  

Microsoft Academic Search

Differential frost heave is often implicated in the formation of patterned ground in regions subject to recurrent freezing\\u000a and thawing. A linear stability analysis (LSA) indicates that a continuum model of frost heave is linearly unstable under\\u000a typical natural freezing conditions of silty-clay soils. A two-dimensional non-linear numerical analysis corroborates the\\u000a frozen time LSA results, and also indicates the importance

Rorik A. Peterson

2008-01-01

113

Aeroelastic stability analysis of a Darrieus wind turbine  

SciTech Connect

An aeroelastic stability analysis has been developed for predicting flutter instabilities on vertical axis wind turbines. The analytical model and mathematical formulation of the problem are described as well as the physical mechanism that creates flutter in Darrieus turbines. Theoretical results are compared with measured experimental data from flutter tests of the Sandia 2 Meter turbine. Based on this comparison, the analysis appears to be an adequate design evaluation tool.

Popelka, D.

1982-02-01

114

Analysis of Stabilization Mechanisms in Lifted Flames  

NASA Astrophysics Data System (ADS)

Flame stabilization and the mechanisms that govern the dynamics at the flame base have been subject to numerous studies in recent years. Recent results using a combined Large Eddy Simulation-Conditional Moment Closure (LES-CMC) approach to model the turbulent flow field and the turbulence-chemistry interactions has been successful in predicting flame ignition and stabilization by auto-ignition, but LES-CMCs capability of the accurate modelling of the competition between turbulent quenching and laminar and turbulent flame propagation at the anchor point has not been resolved. This paper will consolidate LES-CMC results by analysing a wide range of lifted flame geometries with different prevailing stabilization mechanisms. The simulations allow a clear distinction of the prevailing stabilization mechanisms for the different flames, LES-CMC accurately predicts the competition between turbulence and chemistry during the auto-ignition process, however, the dynamics of the extinction process and turbulent flame propagation are not well captured. The averaging process inherent in the CMC methods does not allow for an instant response of the transported conditionally averaged reactive species to the changes in the flow conditions and any response of the scalars will therefore be delayed. Stationary or quasi-stationary conditions, however, can be well predicted for all flame configurations.

Navarro-Martinez, S.; Kronenburg, A.

2009-12-01

115

Stability analysis for air film drag reduction  

NASA Astrophysics Data System (ADS)

A linear stability analysis of an air-water interface is studied for basic understanding of air film physics applied to a ship hull for drag reduction purposes. Three different flows are studied. In the first case, viscosity is considered and is a special case of the problem studied by Yih (1967) when the thickness of two layers is the same and a long-wave stability analysis is performed. The second and third case are inviscid basic flows with unequal thicknesses and inviscid and viscous velocity profiles, respectively. Unstable conditions are determined according to Rayleigh theorem. Interesting inferences are drawn if limits are considered on thicknesses and wave numbers that might be considered for plenums on the hull surface.

Aphale, Chinar; Schultz, William; Ceccio, Steven

2006-11-01

116

Stability analysis of White Oak Dam  

SciTech Connect

White Oak Dam is located in the White Oak Creek watershed which provides the primary surface drainage for Oak Ridge National Laboratory. A stability analysis was made on the dam by Syed Ahmed in January 1994 which included an evaluation of the liquefaction potential of the embankment and foundation. This report evaluates the stability of the dam and includes comments on the report prepared by Ahmed. Slope stability analyses were performed on the dam and included cases for sudden drawdown, steady seepage, partial pool and earthquake. Results of the stability analyses indicate that the dam is stable and failure of the structure would not occur for the cases considered. The report prepared by Ahmed leads to the same conclusions as stated above. Review of the report finds that it is complete, well documented and conservative in its selection of soil parameters. The evaluation of the liquefaction potential is also complete and this report is in agreement with the findings that the dam and foundation are not susceptible to liquefaction.

NONE

1995-04-11

117

Stability of the Einstein static universe in open cosmological models  

SciTech Connect

The stability properties of the Einstein static solution of general relativity are altered when corrective terms arising from modification of the underlying gravitational theory appear in the cosmological equations. In this paper the existence and stability of static solutions are considered in the framework of two recently proposed quantum gravity models. The previously known analysis of the Einstein static solutions in the semiclassical regime of loop quantum cosmology with modifications to the gravitational sector is extended to open cosmological models where a static neutrally stable solution is found. A similar analysis is also performed in the framework of Horava-Lifshitz gravity under detailed balance and projectability conditions. In the case of open cosmological models the two solutions found can be either unstable or neutrally stable according to the admitted values of the parameters.

Canonico, Rosangela; Parisi, Luca [Dipartimento di Fisica 'E. R. Caianiello', Universita di Salerno, Via Ponte Don Melillo, I-84081 Baronissi (Italy); INFN, Sezione di Napoli, GC di Salerno, Via Ponte Don Melillo, I-84081 Baronissi (Italy)

2010-09-15

118

Seismic reliability analysis of earth slopes under short term stability conditions  

Microsoft Academic Search

Different models were developed for evaluating the probabilistic three-dimensional (3-D) stability analysis of earth slopes and embankments under earthquake loading. The 3-D slope stability model assumed is that of a simple cylindrical failure surface. The probabilistic models evaluate the probability of failure under seismic loading considering the randomness of earthquake occurrence, and earthquake induced acceleration and uncertainties stemming from the

Azm S. Al-Homoud; Wisam W. Tahtamoni

2002-01-01

119

Dynamic Landscapes, Stability and Ecological Modeling  

Microsoft Academic Search

The image of a ball rolling along a series of hills and valleys is an effective heuristic by which to communicate stability\\u000a concepts in ecology. However, the dynamics of this landscape model have little to do with ecological systems. Other landscape\\u000a representations, however, are possible. These include the particle on an energy landscape, the potential landscape, and the\\u000a Lyapunov function

Christopher W. Pawlowski

2006-01-01

120

Distribution system modelling for voltage stability studies  

Microsoft Academic Search

This paper presents a method to include a radial distribution system, with cascaded tap-changers, in voltage stability studies. A rural distribution system, including the 50 kV, 20 kV, 10 kV and 0.4 kV levels, has been studied. A detailed model of the network down to the customer level, with all lines and transformers explicitly represented, has been compared with a

Rikard Lind; D. Karlsson

1996-01-01

121

STABILITY ANALYSIS OF THE ITER TF CONDUCTOR  

SciTech Connect

The stability analysis of the reference Nb{sub 3}Sn conductor for the International Thermonuclear Experimental Reactor (ITER) Toroidal Field (TF) coils is performed using the Mithrandir code. From the point of view of the temperature margin, the most critical conductor in the winding pack, as well as the most critical location along it, is identified by a Vincenta code analysis, which also provides the initial and boundary conditions for the stability study. With this approach, the 1D Mithrandir analysis can be restricted to the most critical conductor, using a much finer grid than Vincenta, in order to capture the details of normal zone initiation and possible recovery to SC state. Two different disturbances are considered: one short in space and time (0.01 m, 1 ms), simulating a disturbance of mechanical nature, the other longer (3 m, 100 ms), corresponding to AC losses (plasma disruption). Both disturbances are applied to the superconducting cable at end-of-burn, in the reference ITER inductive operation scenario. The grid-independence of the results was verified first. Since the results are strongly influenced by the choice of the heat transfer coefficient between strands and helium, this effect has been also parametrically investigated. In all cases, the computed minimum quench energies turn out to be above the level of the expected disturbances.

Savoldi Richard, L.; Zanino, R. [Dipartimento di Energetica, Politecnico Torino, I-10129 (Italy)

2008-03-16

122

Aeroelastic analysis of turbomachinery : Part II – stability computations  

Microsoft Academic Search

Part II of the two-part paper describes an aeroelastic analysis program and its application for stability computations of turbomachinery blade rows. Unsteady Euler or Navier-Stokes equations are solved on dynamically deforming, body fitted, and grid to obtain the aeroelastic characteristics. Blade structural response is modeled using a modal representation of the blade and the work-per-cycle method is used to evaluate

R. Srivastava; M. A. Bakhle; T. G. Keith Jr; D. Hoyniak

2004-01-01

123

Mathematical modeling and simulation of seated stability.  

PubMed

Various methods have been used to quantify the kinematic variability or stability of the human spine. However, each of these methods evaluates dynamic behavior within the stable region of state space. In contrast, our goal was to determine the extent of the stable region. A 2D mathematical model was developed for a human sitting on an unstable seat apparatus (i.e., the "wobble chair"). Forward dynamic simulations were used to compute trajectories based on the initial state. From these trajectories, a scalar field of trajectory divergence was calculated, specifically a finite time Lyapunov exponent (FTLE) field. Theoretically, ridges of local maxima within this field are expected to partition the state space into regions of qualitatively different behavior. We found that ridges formed at the boundary between regions of stability and failure (i.e., falling). The location of the basin of stability found using the FTLE field matched well with the basin of stability determined by an alternative method. In addition, an equilibrium manifold was found, which describes a set of equilibrium configurations that act as a low dimensional attractor in the controlled system. These simulations are a first step in developing a method to locate state space boundaries for torso stability. Identifying these boundaries may provide a framework for assessing factors that contribute to health risks associated with spinal injury and poor balance recovery (e.g., age, fatigue, load/weight, and distribution). Furthermore, an approach is presented that can be adapted to find state space boundaries in other biomechanical applications. PMID:20018288

Tanaka, Martin L; Ross, Shane D; Nussbaum, Maury A

2009-12-16

124

Theory and modelling of nanocarbon phase stability.  

SciTech Connect

The transformation of nanodiamonds into carbon-onions (and vice versa) has been observed experimentally and has been modeled computationally at various levels of sophistication. Also, several analytical theories have been derived to describe the size, temperature and pressure dependence of this phase transition. However, in most cases a pure carbon-onion or nanodiamond is not the final product. More often than not an intermediary is formed, known as a bucky-diamond, with a diamond-like core encased in an onion-like shell. This has prompted a number of studies investigating the relative stability of nanodiamonds, bucky-diamonds, carbon-onions and fullerenes, in various size regimes. Presented here is a review outlining results of numerous theoretical studies examining the phase diagrams and phase stability of carbon nanoparticles, to clarify the complicated relationship between fullerenic and diamond structures at the nanoscale.

Barnard, A. S.

2006-01-01

125

Stress transducer interpretation analysis and stability data  

NASA Astrophysics Data System (ADS)

A semi-conductor strain gage transducer was developed for use in measuring stress in solid propellant grain rocket motors. The requirements for survival and performance are such that the sensor has direct use as a general pressure transducer especially where small size and high reliability are a requirement. The design work, gage interpretation analysis and some long-term stability results are summarized. Design of this reliable stress transducer for embedment in a solid propellant rocket motor has utilized finite element structural analysis to minimize the stress disturbance above the transducer body and to reduce diaphragm interaction with the nonlinear viscoelastic solid propellant. Minimizing the interaction between solid propellant and transducer diaphragm required that the transducer body and flexural diaphragm be much stiffer than conventional pressure transducers.

Francis, E. C.; Thompson, R. E.

1984-02-01

126

Thermodynamic performance vs. dynamic stability in an enzymatic reaction model  

NASA Astrophysics Data System (ADS)

Previous studies on thermal engine models and energy-converting biological systems have shown that some of the parameters affecting their thermodynamic performance also affect their dynamic stability. In some cases, such parameters represent a tradeoff between these two generic properties. In the present work we carry out a similar analysis on a simple model for an enzymatic reaction. Despite its simplicity, this model captures the essential characteristics of numerous biochemical reactions where an endothermic reaction is made possible by coupling it (via an enzyme) with an exothermic reaction. Our results indicate that the global reaction chemical potential gap (?) affects both the thermodynamic properties and stability of the steady state. Larger ? values imply a higher power output and a higher efficiency, but also a less strongly stable steady state.

Díaz-Hernández, Orlando; Páez-Hernández, Ricardo; Santillán, Moisés

2010-09-01

127

Stability and Hopf bifurcation analysis on a simplified BAM neural network with delays  

Microsoft Academic Search

A delay-differential equation modelling a bidirectional associative memory (BAM) neural network with three neurons is investigated. Its dynamics are studied in terms of local analysis and Hopf bifurcation analysis. By analyzing the associated characteristic equation, its linear stability is investigated and Hopf bifurcations are demonstrated. The stability and direction of the Hopf bifurcation are determined by applying the normal form

Yongli Song; Maoan Han; Junjie Wei

2005-01-01

128

Kahler stabilized, modular invariant heterotic string models  

SciTech Connect

We review the theory and phenomenology of effective supergravity theories based on orbifold compactifications of the weakly-coupled heterotic string. In particular, we consider theories in which the four-dimensional theory displays target space modular invariance and where the dilatonic mode undergoes Kahler stabilization. A self-contained exposition of effective Lagrangian approaches to gaugino condensation and heterotic string theory is presented, leading to the development of the models of Binétruy, Gaillard and Wu. Various aspects of the phenomenology of this class of models are considered. These include issues of supersymmetry breaking and superpartner spectra, the role of anomalous U(1) factors, issues of flavor and R-parity conservation, collider signatures, axion physics, and early universe cosmology. For the vast majority of phenomenological considerations the theories reviewed here compare quite favorably to other string-derived models in the literature. Theoretical objections to the framework and directions for further research are identified and discussed.

Gaillard, Mary K.; Gaillard, Mary K.; Nelson, Brent D.

2007-03-19

129

BWR stability analysis at Brookhaven National Laboratory  

SciTech Connect

Following the unexpected, but safely terminated, power and flow oscillations in the LaSalle-2 Boiling Water Reactor (BWR) on March 9, 1988, the Nuclear Regulatory Commission (NRC) Offices of Nuclear Reactor Regulation (NRR) and of Analysis and Evaluation of Operational Data (AEOD) requested that the Office of Nuclear Regulatory Research (RES) carry out BWR stability analyses, centered around fourteen specific questions. Ten of the fourteen questions address BWR stability issues in general and are dealt with in this paper. The other four questions address local, out-of-phase oscillations and matters of instrumentation; they fall outside the scope of the work reported here. It was the purpose of the work documented in this report to answer ten of the fourteen NRC-stipulated questions. Nine questions are answered by analyzing the LaSalle-2 instability and related BWR transients with the BNL Engineering Plant Analyzer (EPA) and by performing an uncertainty assessment of the EPA predictions. The tenth question is answered on the basis of first principles. The ten answers are summarized

Wulff, W.; Cheng, H.S.; Mallen, A.N.; Rohatgi, U.S.

1991-01-01

130

BWR stability analysis at Brookhaven National Laboratory  

SciTech Connect

Following the unexpected, but safely terminated, power and flow oscillations in the LaSalle-2 Boiling Water Reactor (BWR) on March 9, 1988, the Nuclear Regulatory Commission (NRC) Offices of Nuclear Reactor Regulation (NRR) and of Analysis and Evaluation of Operational Data (AEOD) requested that the Office of Nuclear Regulatory Research (RES) carry out BWR stability analyses, centered around fourteen specific questions. Ten of the fourteen questions address BWR stability issues in general and are dealt with in this paper. The other four questions address local, out-of-phase oscillations and matters of instrumentation; they fall outside the scope of the work reported here. It was the purpose of the work documented in this report to answer ten of the fourteen NRC-stipulated questions. Nine questions are answered by analyzing the LaSalle-2 instability and related BWR transients with the BNL Engineering Plant Analyzer (EPA) and by performing an uncertainty assessment of the EPA predictions. The tenth question is answered on the basis of first principles. The ten answers are summarized

Wulff, W.; Cheng, H.S.; Mallen, A.N.; Rohatgi, U.S.

1991-12-31

131

Stability Assessment of Surrounding Rock of Underground Cavern Complexes Based on Energy-Dissipation Model  

Microsoft Academic Search

Stability analysis of surrounding rock is a complicated and always experience depended work in underground excavation engineering. In this paper, An Energy-Dissipation Model for stability assessment of surrounding rock of underground cavern complexes in hydropower plant is proposed. Firstly, the general FEM procedure to simulate underground excavation is put forward. Then, the Energy-Dissipation Model is expounded by introducing certain damage

Huibo Liu; Ming Xiao

2010-01-01

132

Analysis of the stability of looped-out and stacked-in conformations of an adenine bulge in DNA using a continuum model for solvent and ions.  

PubMed

A combination of conformational search, energy minimization, and energetic evaluation using a continuum solvent treatment has been employed to study the stability of various conformations of the DNA fragment d(CGCAGAA)/d(TTCGCG) containing a single adenine bulge. The extra-helical (looped-out) bulge conformation derived from a published x-ray structure and intra-helical (stacked bulge base) model structures partially based on nuclear magnetic resonance (NMR) data were used as start structures for the conformational search. Solvent-dependent contributions to the stability of the conformations were calculated from the solvent exposed molecular surface area and by using the finite difference Poisson-Boltzmann approach. Three classes (I-III) of bulge conformations with calculated low energies can be distinguished. The lowest-energy conformations were found in class I, corresponding to structures with the bulge base stacked between flanking helices, and class II, composed of structures forming a triplet of the bulge base and a flanking base pair. All extra-helical bulge structures, forming class III, were found to be less stable compared with the lowest energy structures of class I and II. The results are consistent with NMR data on an adenine bulge in the same sequence context indicating an intra-helical or triplet bulge conformation in solution. Although the total energies and total electrostatic energies of the low-energy conformations show only relatively modest variations, the energetic contributions to the stability were found to vary significantly among the classes of bulge structures. All intra-helical bulge structures are stabilized by a more favorable Coulomb charge-charge interaction but destabilized by a larger electrostatic reaction field contribution compared with all extra-helical and most triplet bulge structures. Van der Waals packing interactions and nonpolar surface-area-dependent contributions appear to favor triplet class II structures and to a lesser degree also the intra-helical stacked bulge conformations. The large conformational variation found for class III conformers might add a favorable entropic contribution to the stability of the extra-helical bulge form. PMID:9414214

Zacharias, M; Sklenar, H

1997-12-01

133

Soliton stability in some knot soliton models  

SciTech Connect

We study the issue of stability of static solitonlike solutions in some nonlinear field theories which allow for knotted field configurations. Concretely, we investigate the Aratyn-Ferreira-Zimerman model [Phys. Lett. B 456, 162 (1999); Phys. Rev. Lett. 83, 1723 (1999)], based on a Lagrangian quartic in first derivatives with infinitely many conserved currents, for which infinitely many soliton solutions are known analytically. For this model we find that sectors with different (integer) topological charges (Hopf index) are not separated by an infinite energy barrier. Further, if variations which change the topological charge are allowed, then the static solutions are not even critical points of the energy functional. We also explain why soliton solutions can exist at all, in spite of these facts. In addition, we briefly discuss the Nicole model [J. Phys. G 4, 1363 (1978)], which is based on a sigma-model-type Lagrangian. For the Nicole model we find that different topological sectors are separated by an infinite energy barrier.

Adam, C.; Sanchez-Guillen, J.; Wereszczynski, A. [Departamento de Fisica de Particulas, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela (Spain) and Instituto Galego de Fisica de Altas Enerxias (IGFAE), Universidad de Santiago de Compostela, E-15782 Santiago de Compostela (Spain); Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Cracow (Poland)

2007-02-15

134

Stability analysis of miscible displacement processes  

SciTech Connect

This paper presents a linear perturbation analysis of viscosity- and gravity-induced instability in miscible displacement processes. The analysis takes into account the time-dependent behavior of the basic flow solution. It also considers the velocity dependence in the hydrodynamic dispersion expressions. By solving analytically the perturbation equations, the necessary and sufficient conditions for instability in miscible displacement processes are derived. These criteria are related to the well-known Dumore's velocity and to a critical wavelength for finger growth. Furthermore, they are calculated at the most unstable location in the solvent-oil mixing zone. The equations derived then relate quantitatively major process variables to the onset of instability in a miscible displacement process. Examples are presented to illustrate the applications of the criteria derived. It is shown that as the displacement process proceeds, the injection rate can be gradually increased. Furthermore, for dipping and stratified reservoirs, and for laboratory core experiments, a threshold time can be reached, after which the process is said to be in a state of unconditional stability.

Lee, S.T.; Culham, W.E.; Gary, K.M.

1984-04-01

135

Small signal stability analysis considering grid-connected wind farms of DFIG type  

Microsoft Academic Search

In this paper, small signal stability analysis considering grid-connected wind farms of doubly-fed induction generator (DFIG) type is conducted. A simplified and practical DFIG model is presented firstly, and the stator flux-oriented vector control based method is employed to implement stator active and reactive powers control in modelling rotor-side converter. The power system small signal stability analysis is then carried

Chen Wang; Libao Shi; Liming Wang; Yixin Ni

2008-01-01

136

Design and analysis of an adaptive fuzzy power system stabilizer  

SciTech Connect

Power system stabilizers (PSS) must be capable of providing appropriate stabilization signals over a broad range of operating conditions and disturbances. Traditional PSS rely on robust linear design methods. In an attempt to cover a wider range of operating conditions, expert or rule-based controllers have also been proposed. Recently, fuzzy logic as a novel robust control design method has shown promising results. The emphasis in fuzzy control design centers around uncertainties in system parameters and operating conditions. Such an emphasis is of particular relevance as the difficulty of accurately modelling the connected generation is expected to increase under power industry deregulation. Fuzzy logic controllers are based on empirical control rules. In this paper, a systematic approach to fuzzy logic control design is proposed. Implementation for a specific machine requires specification of performance criteria. This performance criteria translates into three controller parameters which can be calculated off-line or computed in real-time in response to system changes. The robustness of the controller is emphasized. Small signal and transient analysis methods are discussed. This work is directed at developing robust stabilizer design and analysis methods appropriate when fuzzy logic is applied.

Hoang, P.; Tomsovic, K. [Washington State Univ., Pullman, WA (United States). School of Electrical Engineering and Computer Science

1996-06-01

137

Postburn roof stability analysis for the TONO CRIP UCG burn  

SciTech Connect

During the Ninth Annual Underground Coal Gasification Symposium, Sutherland, Hommert, Taylor, and Benzley presented a preburn prediction for the burn, roof fall and surface subsidence for the TONO CRIP UCG site in Washington state. That burn has now been completed and postburn measurements of cavity sizes have become available. In this manuscript we show that the preburn predictions are, in general, in good agreement with the postburn examination of the burn site. Discrepancies between the predictions and the measurements are shown to arise for two reasons. The first is that the burn sequence analyzed in the prediction was not followed during the course of the experiment due to experimental difficulties. The second reason is that the stratigraphic section analyzed in the preburn predictions is slightly different from that observed above the burn. To clarify the discrepancies, the roof stability of the measured burn cavity is analyzed using the two analysis schemes that were used in the preburn analysis. The first technique is the Rubble model. It uses a continuum description of the rubblization process that occurs as roof material fails and falls into the cavity below it. This technique is based on a standard finite element numerical analysis scheme. The second technique is the BLOCKS model. This technique divides the geologic strata into a collection of discrete, individual blocks and monitors all the collisions which occur between them. Both techniques yield very good descriptions of the roof stability for the measured burn cavity. 10 refs., 7 figs.

Taylor, L.M.; Sutherland, H.J.; Kuszmaul, J.S.

1985-01-01

138

Stability analysis of a nuclear power plant by large-scale system Lyapunov methods  

Microsoft Academic Search

An attempt to apply modern large-scale system stability theory to a complex nuclear power plant is presented. The effectiveness of both the vector and the scalar Lyapunov methods for stability analysis were examined in this application. A dynamic model was derived comprising the components of the nuclear power plant, namely, the reactor, the pressurizer, the steam generator, the turbines, the

Abbaspour Tehrani Fard

1984-01-01

139

STATCOM Modeling for Voltage and Angle Stability Studies  

Microsoft Academic Search

This paper proposes and validates models to accurately represent STATic Syn- chronous Shunt COMpensators (STATCOM) in voltage and angle stability studies of powers systems. The proposed STATCOM stability models are justified based on the basic operational characteristics of this Flexible AC Transmission System (FACTS) controller for both phase and PWM control strategies. These models are first validated by means of

Claudio A. Canizares; Massimo Pozzi; Sandro Corsi; Edvina Uzunovic

2003-01-01

140

Analysis of Power System Stability Enhancement by Static VAR Compensators  

Microsoft Academic Search

The paper presents a fundamental analysis of the application of static VAr compensators (SVC) for stabilizing power systems. Basic SVC control strategies are examined in terms of enhancing the dynamic and transient stabilities, improving tieline transmission capacity and damping power oscillations. Synchronizing and damping torque contributions of the SVC are determined for different controls. The analysis is supplemented by digital

A. E. Hammad

1986-01-01

141

CG-DAMS: Concrete gravity dam stability analysis software  

SciTech Connect

CG-DAMS is a finite element based program written specifically for the stability analysis of concrete gravity dams. The code automates the prediction and evaluation of cracking in the dam, along the dam-rock interface, and in the foundation using incremental nonlinear analysis techniques based on the smeared crack'' approach. Its primary application is in the computation of dam-rock interface sliding stability factors of safety. The automated procedure for crack propagation analysis replaces the trial-and-error cracked-base analysis method commonly used in gravity dam safety analyses. This Application manual of CG-DAMS illustrates, through sample problems, the many features of the software. Example problems illustrate the capabilities of both CG-DAMS-PC and CG-DAMS-ABAQUS. CG-DAMS-PC is a menu driven program that runs on 386/486 PCs under the DOS operating system (4 Megabytes RAM, 25 Megabytes of hard disk space). CG-DAMS-ABAQUS is a pre- and post-processor along with a concrete constitutive model and distributed load module that interfaces with the ABAQUS general purpose finite element program. The PC program contains thermal analysis capabilities, a rough crack constitutive model, and an interface to the CRFLOOD software not available with the ABAQUS version. The CG-DAMS-ABAQUS program contains time marching dynamic analysis capabilities not available with the PC program. Example analyses presented include static, pseudo dynamic, and time marching dynamic analyses. The manual also presents sensitivity evaluations on mesh size and foundation material strength. Comparisons are presented between CG-DAMS and gravity method calculations. Comparisons with other finite element software are included for the dynamic time history analyses.

Not Available

1993-01-01

142

Dynamic Stabilization of Atmospheric Single Column Models.  

NASA Astrophysics Data System (ADS)

Single column models (SCMs) provide an economical framework for assessing the sensitivity of atmospheric temperature and humidity to natural and imposed perturbations, and also for developing improved representations of diabatic processes in weather and climate models. Their economy is achieved at the expense of ignoring interactions with the circulation dynamics; thus, advection by the large-scale flow is either prescribed or neglected. This artificial decoupling of the diabatic and adiabatic tendencies can often cause rapid error growth in SCM integrations, especially in the Tropics where large-scale vertical advection is important. As a result, SCMs can quickly develop highly unrealistic thermodynamic structures, making it pointless to study their subsequent evolution.This paper suggests one way around this fundamental difficulty through a simple coupling of the diabatic and adiabatic tendencies. In essence, the local vertical velocity at any instant is specified by a formula that links the local vertical temperature advection to the evolution of SCM-generated diabatic heating rates up to that instant. This vertical velocity is then used to determine vertical humidity advection, and also horizontal temperature and humidity advection under an additional assumption that the column is embedded in a uniform environment. The parameters in the formula are estimated in a separate set of calculations, from the approach to equilibrium of a linearized global primitive equation model forced by steady heat sources. As a test, the parameterized dynamics are used to predict the linear model's local response to oscillating heat sources, and found to perform remarkably well over a wide range of space and time scales. In a second test, the parameterization is found to capture important aspects of a general circulation model's vertical advection and temperature tendencies and their lead lag relationships with diabatic heating fluctuations at convectively active locations in the Tropics.When implemented in the NCAR SCM, the dynamically coupled SCM shows a clear improvement over its uncoupled counterpart for tropical conditions observed during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). Coupling effectively stabilizes the SCM. As a result, short-term prediction errors are substantially reduced, the ensemble spread is reduced in ensemble runs, and the SCM is able to maintain realistic thermodynamic structures in extended runs. Such a dynamically coupled SCM should therefore be more useful not only for isolating physical parameterization errors in weather and climate models, but also for economical simulations of regional climate variability.

Bergman, John W.; Sardeshmukh, Prashant D.

2004-03-01

143

Nonlinear stability analysis of the attitude motion of spin-stabilized thrusting spacecraft  

Microsoft Academic Search

The attitude dynamics of a class of spin-stabilized, thrusting, upperstage spacecraft is examined. Certain spacecraft in the class has been observed to develop oscillations about their transverse axes which increase exponentially in magnitude by the time the solid propellant motor burns out. After burnout, the oscillations stabilize with approximately constant amplitudes. The basic model for examination consists of a rigid

Ja Young Kang

1992-01-01

144

DETERMINATION OF ELECTROCHEMICAL PERFORMANCE, AND THERMO-MECHANICALCHEMICAL STABILITY OF SOFCS FROM DEFECT MODELING  

SciTech Connect

The objectives of this project were to: provide fundamental relationships between SOFC performance and operating conditions and transient (time dependent) transport properties; extend models to thermo-mechanical stability, thermo-chemical stability, and multilayer structures; incorporate microstructural effects such as grain boundaries and grain-size distribution; experimentally verify models and devise strategies to obtain relevant material constants; and assemble software package for integration into SECA failure analysis models.

Wachsman, E.D.; Duncan, K.L.; Ebrahimi, F.

2005-01-27

145

Laminar Body Analysis Heat Plus Suction Stabilized.  

National Technical Information Service (NTIS)

An analytical investigation of the effectiveness of combined surface heating and suction in stabilizing a laminar boundary layer within a region of adverse pressure gradient was carried out. The study is of an applied nature in that two candidate vehicle ...

R. S. Scotti K. T. Corbett

1976-01-01

146

Analysis of Small Signal Stability of Grid-Connected Doubly Fed Induction Generators  

Microsoft Academic Search

In this paper the analysis of small signal stability of grid-connected doubly fed induction generators (DFIG) is presented. The detailed model of grid-connected DFIG wind turbine is firstly established, and the eigenvalues are classified and characterized based on participation factors. Then the modal analysis including its converter and pitch controllers is studied, and model simplification of the DFIG wind turbine

Shan-Ying Li; Yu Sun; Tao Wu; Qun-Ju Li; Hui Liu

2010-01-01

147

Symbolic Model Checking for Self-Stabilizing Algorithms  

Microsoft Academic Search

A distributed system is said to be self-stabilizing if it converges to safe states regardless of its initial state. In this paper we present our results of using symbolic model checking to verify distributed algorithms against the self-stabilizing property. In general, the most difficult problem with model checking is state explosion; it is especially serious in verifying the self-stabilizing property,

Tatsuhiro Tsuchiya; Shin'ichi Nagano; Rohayu Bt Paidi; Tohru Kikuno

2001-01-01

148

Stability analysis of large electric power systems  

SciTech Connect

Modern electric power systems are large and complicated, and, in many regions of the world, the generation and transmission systems are operating near their limits. Ensuring the reliable operation of the power system requires engineers to study the response of the system to various disturbances. The responses to large disturbances are examined by numerically solving the nonlinear differential-algebraic equations describing the power system. The response to small disturbances is typically studied via eigenanalysis. The Electric Power Research Institute (EPRI) recently developed the Extended Transient/Mid-term Stability Program (ETMSP) to study large disturbance stability and the Small Signal Stability Program Package (SSSP) to study small signal stability. The primary objectives of the work described in this report were to (1) explore ways of speeding up ETMSP, especially on mid-term voltage stability problems, (2) explore ways of speeding up the Multi-Area Small-Signal Stability program (MASS), one of the codes in SSSP, and (3) explore ways of increasing the size of problem that can be solved by the Cray version of MASS.

Elwood, D.M.

1993-01-01

149

Stability analysis of implicit multi-fluid schemes  

SciTech Connect

A new implicit method has been developed for solving the viscous full multi-fluid equations, which incorporate transport and generation of mass and momentum for each component present in a system. This work presents stability analysis and application of the important full multi-fluid system in a fully implicit algorithm. The stability analyses presented demonstrate the performance of several iterative schemes applied to the solution of the linearized systems which arise in the formulation. These include block Jacobi and symmetric block Gauss-Siedel schemes with various preconditioners applied. A hierarchy of increasing physical complexity is pursued, starting with one-dimensional, two-fluid systems with minimum inter-field dynamic coupling and no mass transfer. These analyses are extended to systems employing physically important inter-field forces (drag, turbulence dispersion, virtual mass). The effects of mass transfer, multiple fields (i.e., n{phi} > 2) and multiple dimensions are also considered. A two-fluid Navier-Stokes code has been developed based on this new scheme. Results are presented which verify the validity of the stability analyses presented for the coupled scheme. Multi-phase flows which require full multi-fluid modeling arise in a wide class of engineering problems, where non-equilibrium dynamics and thermodynamics of the interfaces between constituents play important roles in the evolution of the ensemble averaged mean flow. Examples include cyclone separators, two-phase flow in jets and curved ducts and boiling flow in heat exchangers.

Kunz, R.F.; Cope, W.K. [Lockheed Martin, Schenectady, NY (United States); Venkateswaran, S. [Pennsylvania State Univ., University Park, PA (United States)

1997-06-01

150

Convergence and stability of the FSR CNN model  

Microsoft Academic Search

Stability and convergency results are reported for a modified continuous-time CNN model. The signal range of the state variables is equal to the unitary interval, independently of the application, Stability and convergency properties are similar to those of the original model and, for given templates and offset coefficients. The results are generally identical. In addition, robustness and area-efficiency of VLSI

S. Espejo; A. Rodriguez-Vazquez; R. Dominguez-Castro; R. Carmona

1994-01-01

151

Impact of partial element accuracy on PEEC model stability  

Microsoft Academic Search

This paper details the impact of partial element accuracy on quasi-static partial element equivalent circuit (PEEC) model stability in the time domain. The potential sources of inaccurate partial element values are found to be poor geometrical meshing and the use of unsuitable partial element calculation routines. The impact on PEEC model stability of erroneous partial element values, and the coefficients

Jonas Ekman; Giulio Antonini; Antonio Orlandi; Albert E. Ruehli

2006-01-01

152

A sharp global stability result for a discrete population model  

NASA Astrophysics Data System (ADS)

We get a sharp global stability result for a first order difference equation modelling the growth of bobwhite quail populations. The corresponding higher-dimensional model is also discussed, and our stability conditions improve other recent results for the same equation.

Liz, Eduardo

2007-06-01

153

Do cardiac stabilizers really stabilize? Experimental quantitative analysis of mechanical stabilization.  

PubMed

In order to assess the three-dimensional movement of the coronary arteries both during normal cardiac activity and after mechanical stabilization, a polypropylene black marker was placed in 10 pigs on the middle portion of the three main coronary branches. Marker motion was recorded for 10 s using two TV-digital cameras and was estimated with a precision of 50 microm. After stabilization with three different mechanical stabilizers (Medtronic, Genzyme, CTS-Guidant), a remnant coronary artery excursion of about 1.5-2.4 mm was found. There is a significant residual coronary artery motion after mechanical stabilization, which could affect the quality of anastomosis, especially in unfavourable situations. PMID:17670397

Lemma, Massimo; Mangini, Andrea; Redaelli, Alberto; Acocella, Fabio

2005-03-29

154

A critical assessment of the continuous-system approximate methods for the stability analysis of a sampled data system  

Microsoft Academic Search

A critical assessment of the approximate methods for the stability analysis of a pulse-width modulated (PWM) static volt-ampere reactive (VAr) compensator is presented. Different continuous system approximate models for the stability analysis of the system are developed and their validity is investigated. In particular, it is shown that continuous system approximate models, in which only the principal component of the

Hassan Ali Kojori; J. Douglas Lavers; Shashi B. Dewan

1993-01-01

155

Nonlinear stability analysis of pre-stressed elastic bodies  

Microsoft Academic Search

   This article is concerned with the nonlinear analysis of the stability of thick elastic bodies subjected to finite elastic\\u000a deformations. The analysis is based on the theory of small elastic deformations superimposed on a finite elastic deformation.\\u000a Attention is drawn to methods developed in the stability analysis of fluids and of thin shells and plates which are readily\\u000a applicable

Y. B. Fu; R. W. Ogden

1999-01-01

156

Equation-Free Multiscale Computations in Social Networks: from Agent-based Modelling to Coarse-grained Stability and Bifurcation Analysis  

Microsoft Academic Search

We focus at the interface between multiscale computations, bifurcation theory\\u000aand social networks. In particular we address how the Equation-Free approach, a\\u000arecently developed computational framework, can be exploited to systematically\\u000aextract coarse-grained, emergent dynamical information by bridging detailed,\\u000aagent-based models of social interactions on networks, with macroscopic,\\u000asystems-level, continuum numerical analysis tools. For our illustrations we use\\u000aa simple

A. C. Tsoumanis; C. I. Siettos; I. G. Kevrekidis; G. V. Bafas

2009-01-01

157

Systematic Analysis of Stability Patterns in Plant Primary Metabolism  

PubMed Central

Metabolic networks are characterized by complex interactions and regulatory mechanisms between many individual components. These interactions determine whether a steady state is stable to perturbations. Structural kinetic modeling (SKM) is a framework to analyze the stability of metabolic steady states that allows the study of the system Jacobian without requiring detailed knowledge about individual rate equations. Stability criteria can be derived by generating a large number of structural kinetic models (SK-models) with randomly sampled parameter sets and evaluating the resulting Jacobian matrices. Until now, SKM experiments applied univariate tests to detect the network components with the largest influence on stability. In this work, we present an extended SKM approach relying on supervised machine learning to detect patterns of enzyme-metabolite interactions that act together in an orchestrated manner to ensure stability. We demonstrate its application on a detailed SK-model of the Calvin-Benson cycle and connected pathways. The identified stability patterns are highly complex reflecting that changes in dynamic properties depend on concerted interactions between several network components. In total, we find more patterns that reliably ensure stability than patterns ensuring instability. This shows that the design of this system is strongly targeted towards maintaining stability. We also investigate the effect of allosteric regulators revealing that the tendency to stability is significantly increased by including experimentally determined regulatory mechanisms that have not yet been integrated into existing kinetic models.

Girbig, Dorothee; Grimbs, Sergio; Selbig, Joachim

2012-01-01

158

Effect analysis of bearing and interface dynamics on tool point FRF for chatter stability in machine tools by using a new analytical model for spindle–tool assemblies  

Microsoft Academic Search

Self-excited vibration of the tool, regenerative chatter, can be predicted and eliminated if the stability lobe diagram of the spindle–holder–tool assembly is known. Regardless of the approach being used, analytically or numerically, forming the stability lobe diagram of an assembly implies knowing the point frequency response function (FRF) in receptance form at the tool tip. In this paper, it is

A. Ertürk; H. N. Özgüven; E. Budak

2007-01-01

159

Effect analysis of bearing and interface dynamics on tool point FRF for chatter stability in machine tools by using a new analytical model for spindle–tool assemblies  

Microsoft Academic Search

Abstract Self-excited vibration of the tool, regenerative chatter, can be predicted and eliminated if the stability lobe diagram of the spindle–holder–tool assembly is known. Regardless of the approach being used, analytically or numerically, forming the stability lobe diagram of an assembly implies knowing the point frequency response function (FRF) in receptance form at the tool tip. In this paper, it

A. Ertu Rk; H. n. O Zgu Ven; E. Budak

160

pp ii Stability and Hopf bifurcation analysis on a simplified BAM neural network with delays  

NASA Astrophysics Data System (ADS)

A delay-differential equation modelling a bidirectional associative memory (BAM) neural network with three neurons is investigated. Its dynamics are studied in terms of local analysis and Hopf bifurcation analysis. By analyzing the associated characteristic equation, its linear stability is investigated and Hopf bifurcations are demonstrated. The stability and direction of the Hopf bifurcation are determined by applying the normal form theory and the center manifold reduction. Numerical simulation results are given to support the theoretical predictions.

Song, Yongli; Han, Maoan; Wei, Junjie

2005-01-01

161

Compact YORP formulation and stability analysis  

NASA Astrophysics Data System (ADS)

We present a concise analytical formulation of the YORP effect, with exact formulae for torques on convex bodies and motion-averaged components applicable to any shapes. We analyze the main features of the secular torques for zero and nonzero thermal inertia that are function series dependent on only a few coefficients. Using these, we investigate the stability of the YORP effect against shape perturbations with analytical and numerical estimates. We define a quantity describing the YORP capacity of any shape, and estimate YORP stability with it.

Kaasalainen, Mikko; Nortunen, Hari

2013-10-01

162

Performance and Stability Analysis of a Shrouded-Fan UAV  

Microsoft Academic Search

This paper deals with the estimation of the performance and stability for a shrouded-fan unmanned rotorcraft whose mission profile also prescribes the flight in ground effect. The not so simple estimation of the aerodynamic coefficients and of the thrust in the various situations makes the performance calculation and the stability analysis difficult tasks. This is due to the strong interaction

Nicola de Divitiis

2009-01-01

163

A Simplified Framework For String Stability Analysis In Ahs  

Microsoft Academic Search

. One of the most important issues in longitudinal control of vehicles in automatedhighway systems (AHS) is string stability, that is, the attenuation of spacingerrors as they propagate upstream the platoon. In this paper we use a mass-springdampersystem as a simplified framework for string stability analysis and study theproperties of several longitudinal control schemes which have been proposed in theliterature.Keywords.

Diana Yanakiev; Ioannis Kanellakopoulos

1996-01-01

164

Neuromechanical models for insect locomotion: Stability, maneuverability, and proprioceptive feedback  

NASA Astrophysics Data System (ADS)

We describe a hierarchy of models for legged locomotion, emphasizing relationships among feedforward (preflexive) stability, maneuverability, and reflexive feedback. We focus on a hexapedal geometry representative of insect locomotion in the ground plane that includes a neural central pattern generator circuit, nonlinear muscles, and a representative proprioceptive sensory pathway. Although these components of the model are rather complex, neglect of leg mass yields a neuromechanical system with only three degrees of freedom, and numerical simulations coupled with a Poincaré map analysis shows that the feedforward dynamics is strongly stable, apart from one relatively slow mode and a neutral mode in body yaw angle. These modes moderate high frequency perturbations, producing slow heading changes that can be corrected by a stride-to-stride steering strategy. We show that the model's response to a lateral impulsive perturbation closely matches that of a cockroach subject to a similar impulse. We also describe preliminary studies of proprioceptive leg force feedback, showing how a reflexive pathway can reinforce the preflexive stability inherent in the system.

Kukillaya, R.; Proctor, J.; Holmes, P.

2009-06-01

165

Stability analysis of networked control systems  

Microsoft Academic Search

We introduce a control network protocol, try-once-discard (TOD), for networked control systems (NCS), and provide, for the first time, an analytic proof of global exponential stability for both the new protocol and the commonly used statically scheduled access methods. Controllers are designed without regarding the presence of the network in the feedback loop, so consequently many controller design techniques may

Gregory C. Walsh; Hong Ye; Linda Bushnell

1999-01-01

166

Stability analysis of historic underground quarries  

Microsoft Academic Search

This work, carried out at the Department of Civil, Environmental and Territory Engineering and Architecture (DICATeA) of the University of Parma, analyzes the stability conditions of the ancient underground quarries of Viggiù (Varese, Italy). The objective of the study is to verify the actual structural predisposition to instability phenomena of the old Viggiù quarries, within the context of a historical

Anna Maria Ferrero; Andrea Segalini; Gian Paolo Giani

2010-01-01

167

Stability analysis of parked wind turbine blades  

Microsoft Academic Search

Wind turbine blades in parked position can experience extremely high flow angles of attack in the region of ±90 o , depending on the direction of the incoming wind. Under such conditions the flow is massively separated over the entire blade span and therefore stall induced vibrations are likely to occur with obvious implications on loads and stability. The present

E. S. Politis; P. K. Chaviaropoulos; V. A. Riziotis; S. G. Voutsinas

168

White Oak Dam stability analysis. Volume I  

SciTech Connect

A parametric study was conducted to evaluate the stability of the White Oak Dam (WOD) embankment and foundation. Slope stability analyses were performed for the upper and lower bound soil properties at three sections of the dam using the PCSTABL4 computer program. Minimum safety factors were calculated for the applicable seismic and static loading conditions. Liquefaction potential of the dam embankment and foundation solid during the seismic event was assessed by using simplified procedures. The WOD is classified as a low hazard facility and the Evaluation Basis Earthquake (EBE) is defined as an earthquake with a magnitude of m{sub b} = 5.6 and a Peak Ground Accelerator (PGA) of 0.13 g. This event is approximately equivalent to a Modified Mercalli Intensity of VI-VIII. The EBE is used to perform the seismic evaluation for slope stability and liquefaction potential. Results of the stability analyses and the liquefaction assessment lead to the conclusion that the White Oak Dam is safe and stable for the static and the seismic events defined in this study. Ogden Environmental, at the request of MMES, has checked and verified the calculations for the critical loading conditions and performed a peer review of this report. Ogden has determined that the WOD is stable under the defined static and seismic loading conditions and the embankment materials are in general not susceptible to liquefaction.

Ahmed, S.B.

1994-01-01

169

Systematic Analysis of Stability Patterns in Plant Primary Metabolism  

Microsoft Academic Search

Metabolic networks are characterized by complex interactions and regulatory mechanisms between many individual components. These interactions determine whether a steady state is stable to perturbations. Structural kinetic modeling (SKM) is a framework to analyze the stability of metabolic steady states that allows the study of the system Jacobian without requiring detailed knowledge about individual rate equations. Stability criteria can be

Dorothee Girbig; Sergio Grimbs; Joachim Selbig

2012-01-01

170

Confined three-dimensional stability analysis of the cylinder wake  

Microsoft Academic Search

A spatially confined stability analysis is reported for the cylinder wake at Reynolds numbers 190 and 260. The two three-dimensional instabilities at these Reynolds numbers are shown to be driven by the flow just behind the cylinder.

Dwight Barkley

2005-01-01

171

Stabilized Shock Hydrodynamics: V. Von Neumann Stability Analysis of a Predictor\\/Multi-corrector Lagrangian Method  

Microsoft Academic Search

The typical structure of the linearized equations of Lagran gian shock-hydrodynamics is given by the first-order system form of the wave equation with dissipative effects. This article presents the complete von Neumann stability and dispersion analysis for a predictor\\/multi-corrector time integrator applied to a stabilized va riational multiscale finite element formulation of such sys tem of equations. Bounds for stable

G. Scovazzi; W. J. Rider; J. N. Shadidb Love

172

Joint stability after total shoulder arthroplasty in a cadaver model  

Microsoft Academic Search

A cadaver model was used to test the hypothesis that glenohumeral joint stability is independent of articular surface conformity after total shoulder arthroplasty. For the purposes of this study joint stability was defined as the minimum force required for joint dislocation. After arthroplasty components were implanted into fresh-frozen glenohumeral joints, specimens were mounted on a load frame and tested for

Andrew R Karduna; Gerald R Williams; John L Williams; Joseph P Iannotti

1997-01-01

173

DQ-transformation approach for modelling and stability analysis of AC-DC power system with controlled PWM rectifier and constant power loads  

Microsoft Academic Search

In this paper a technique for analysing aircraft frequency wild power systems with constant power loads is developed and demonstrated. Power electronic based loads often behave as constant power loads, especially when feeding machine or actuator drives under current and speed control. The constant power (CP) loads can affect the stability of the power system. The problem is a particular

K.-N. Areerak; S. V. Bozhko; G. M. Asher; D. W. P. Thomas

2008-01-01

174

A synchronous generator stabilizer based on a universal model  

Microsoft Academic Search

A power system stabilizer (PSS) based on a universal model is developed. The universal model is proposed to approximate an arbitrary system using the input-output data only rather than a mathematical model. The conventional LQR (Linear Quadratic Regulator) method is adapted for PSS design based on a universal model. A state observer is not needed in the proposed PSS by

Young-Moon Park; Jin-Ho Lee; Seung-Ho Hyun; Kwang Y. Lee

1998-01-01

175

Linear Stability Analysis of Jets in Cross Flow  

NASA Astrophysics Data System (ADS)

A linear stability analysis of the round jet injected into cross flow is performed. The effect of the presence of a cross flow is accounted for by a perturbation expansion using the free jet as the lowest order solution. The cross flow to jet velocity ratio is the small parameter used in the analysis. The model base flow used is composed of Michalke's hyperbolic tangent free-jet velocity profile(A. Michalke and G. Hermann, JFM), vol. 114, pp. 343--359, 1982. coupled together with Coelho and Hunt's inviscid 3D transverse-jet model(S. L. V. Coelho and J. C. R. Hunt, JFM), vol. 200, pp. 95--120, 1989.. This study allows estimation of the frequencies and growth rates of the instability modes associated with the transverse jet vortex roll-up. The cross flow tends to make the first helical mode more unstable than the axisymmetric mode. The transverse jet natural frequency deviates gradually from the free jet one as the cross flow velocity magnitude is increased from zero. These results are compared to the ones obtained from 3D transient vortex-element simulations (L. Cortelezzi and A. R. Karagozian, JFM), vol. 446, pp. 347--373, 2001. and recent experiments performed at UCLA.

Alves, Leonardo; Kelly, Robert; Karagozian, Ann

2003-11-01

176

Structural Stability of Mathematical Models of National Economy  

NASA Astrophysics Data System (ADS)

In the paper we test robustness of particular dynamic systems in a compact regions of a plane and a weak structural stability of one dynamic system of high order in a compact region of its phase space. The test was carried out based on the fundamental theory of dynamical systems on a plane and based on the conditions for weak structural stability of high order dynamic systems. A numerical algorithm for testing the weak structural stability of high order dynamic systems has been proposed. Based on this algorithm we assess the weak structural stability of one computable general equilibrium model.

Ashimov, Abdykappar A.; Sultanov, Bahyt T.; Borovskiy, Yuriy V.; Adilov, Zheksenbek M.; Ashimov, Askar A.

2011-12-01

177

Stability of an SEIR epidemic model with independent stochastic perturbations  

NASA Astrophysics Data System (ADS)

For an epidemic model of the type mentioned, we prove a theorem on almost sure exponential stability of the disease-free equilibrium. For small values of the diffusion parameter, ?, we describe the stability of the disease free equilibrium point in terms of an appropriate analogue, R?, of the basic reproduction number R0 of the deterministic special case. Whenever ?>0 then R?stability theorem guarantees almost sure exponential stability whenever R?<1. We also discuss the effect of increasing ?.

Witbooi, Peter J.

2013-10-01

178

Shear-ballooning stability analysis of low-. beta. plasmas  

SciTech Connect

A model of magnetic configurations that has both shear and variation of the field curvature along the magnetic field is constructed. The stability analysis of this system is performed by expanding the perturbation functions to phi/sub 0/ which is constant along the field and phi/sub 1/ which is sinusoidally varied along the field line. The shear term is retained in the form of differntial operations in zeta, the coordinate parallel to the pressure gradient. After several simplifications, the equation reduces itself to the fourth order differential equation. The eigenvalue of this equation is numerically obtained. The calculated critical ..beta.. plotted versus the well depth parameter, h, makes a smooth transition between h < 0 (maximum average B) and h > 0 (minimum average B). Using the same technique, the nondivergent solution to the localized shear mode (Suydam mode) is also obtained by retaining the inertia term.

Yoshikawa, S.

1981-11-01

179

Single-shell tank interim stabilization risk analysis  

SciTech Connect

The purpose of the Single-Shell Tank (SST) Interim Stabilization Risk Analysis is to provide a cost and schedule risk analysis of HNF-2358, Rev. 1, Single-Shell Tank Interim Stabilization Project Plan (Project Plan) (Ross et al. 1998). The analysis compares the required cost profile by fiscal year (Section 4.2) and revised schedule completion date (Section 4.5) to the Project Plan. The analysis also evaluates the executability of the Project Plan and recommends a path forward for risk mitigation.

Basche, A.D.

1998-07-31

180

Small signal stability analysis and control of the wind turbine with the direct-drive permanent magnet generator integrated to the grid  

Microsoft Academic Search

In this paper, a model of the wind turbine (WT) with direct-drive permanent magnet generator (DDPMG) and its associated controllers is presented, based on which a small signal stability analysis model is derived. The small signal stability analysis shows that the WT with DDPMG without the controllers is stable, and the controller can improve the small signal stability of the

F. Wu; Xiao-Ping Zhang; P. Ju

2009-01-01

181

Gravothermal catastrophe: The dynamical stability of a fluid model  

NASA Astrophysics Data System (ADS)

A re-investigation of the gravothermal catastrophe is presented. By means of a linear perturbation analysis, we study the dynamical stability of a spherical self-gravitating isothermal fluid of finite volume and find that the conditions for the onset of the gravothermal catastrophe, under different external conditions, coincide with those obtained from thermodynamical arguments. This suggests that the gravothermal catastrophe may reduce to Jeans instability, rediscovered in an inhomogeneous framework. We find normal modes and frequencies for the fluid system and show that instability develops on the dynamical time scale. We then discuss several related issues. In particular, (1) for perturbations at constant total energy and constant volume, we introduce a simple heuristic term in the energy budget to mimic the role of binaries. (2) We outline the analysis of the two-component case and show how linear perturbation analysis can also be carried out in this more complex context in a relatively straightforward way. (3) We compare the behavior of the fluid model with that of the collisionless sphere. In the collisionless case the instability seems to disappear, which is at variance with the linear Jeans stability analysis in the homogeneous case. We argue that a key ingredient for understanding the difference lies in the role of the detailed angular momentum in a collisionless system. A spherical stellar system is expected to undergo the gravothermal catastrophe only in the presence of some collisionality, which suggests that the instability is dissipative and not dynamical. Finally, we briefly comment on the meaning of the Boltzmann entropy and its applicability to the study of the dynamics of self-gravitating inhomogeneous gaseous systems. Appendices are available in electronic form at http://www.aanda.org

Sormani, M. C.; Bertin, G.

2013-04-01

182

Fourier stability analysis of two-dimensional finite element schemes for shallow water equations  

Microsoft Academic Search

This article presents a stability-based analysis of amplification factors obtained using Fourier or von Neumann method for the finite element formulation of shallow water equations. A Galerkin finite element model is developed for two-dimensional shallow water equations to obtain a linearised form of the error equations. Fourier analysis is performed at the element as well as nodal levels to propose

Jagadeesh Anmala; Rabi H. Mohtar

2011-01-01

183

Bounce-Averaged Stability Analysis of High Beta Flux Tubes  

NASA Astrophysics Data System (ADS)

A novel numerical procedure has been developed for analyzing the stability of a particular flux tube to ballooning-interchange modes in plasmas for which the beta value ? is very high O(1 ~ 10). The stability of a stressed dipole configuration in response to arbitrary fully electromagnetic perturbations is studied, including the effects of finite larmor radius, parallel electric fields, arbitrary complex frequency, and trapped/untrapped particle populations. This procedure has been applied to the problem of determining the trigger mechanism for magnetospheric substorms in the stressed geomagnetic tail where realistic equilibrium fields are used to compute the bounce averaged curvature and grad-B drifts. Previously, MHD-like modes were found to be unstable between two critical ? 's, (? 1, ?2). Local analysis concluded that instabilities due to kinetic resonances might persist above ? 2. In this work the local approximation is dropped yielding a large matrix eigenvalue problem for which a parallel machine is well suited. Results are compared to different fluid models that include Hall and finite larmor radius effects. The energy released by such unstable modes is calculated and compared with measurements of auroral brightening. This work was supported by the National Science Foundation Grant ATM-9907637 and the U.S. Dept. of Energy Contract No. DE-FG03-96ER-54346.

Crabtree, C.; Horton, W.; Wong, H.; Van Dam, J.

2001-12-01

184

Self-similar Solutions in the Nonsteady Propellant Burning Rate Theory and their Stability Analysis  

Microsoft Academic Search

The problem of the non-steady burning of the propellant for the decreasing pressure is considered. Self-similar solutions are obtained for two models of the burning: with constant surface temperature and with variable surface temperature. As is shown for the constant surface temperature model there are two solutions of the problem corresponding to the high and low nonsteadinesses. The stability analysis

V. B. LIBROVICH; B. V. NOVOZHILOV

1971-01-01

185

A stability model for the advanced series compensator (ASC)  

SciTech Connect

This paper develops an accurate and general stability model for the ASC. The model is valid for both the capacitive and inductive regions of the ASC operation. It is accurate in that the instantaneous voltage and current waveforms and also the fundamental component of the capacitor voltage (needed for stability) are determined every half-cycle by solving the differential equations of the ASC circuit. The model is capable of incorporating any control algorithms. The validity of the model is demonstrated by comparing the model with the Electro-magnetic Transient Program (EMTP) digital simulations using step time of 10 {micro}s.

Jalali, S.G.; Hedin, R.A. [Siemens Energy and Automation, Atlanta, GA (United States); Pereira, M.; Sadek, K. [Siemens AG, Erlangen (Germany)

1996-04-01

186

Stochastic stability for model-based networked control systems  

Microsoft Academic Search

In this paper we study the stochastic stability properties of certain networked control system. Specifically we study the stability of the model-based network control system introduced in [L.A. Montestruque et. al., 41st IEEE Conference on Decision and Control, December 2002.] under time-varying communication. The model-based network control system uses knowledge of the plant to reduce the number of packet exchanges

Luis A. Montestruque; Panos J. Antsaklis

2003-01-01

187

Moduli stabilization in a de Sitter compactification model  

NASA Astrophysics Data System (ADS)

We discuss the moduli stabilization in a de Sitter compactification model obtained coupling D-dimensional gravity to scalar and gauge fields. This class of models is characterized by two moduli: one related to the volume of the internal space, the other to the warp factor. While the volume modulus can be fixed by appropriately tuning the gauge field strength, curvature of the internal space, and cosmological constant, the same mechanism does not work for the warp modulus. In this paper we discuss a stabilization mechanism based on quantum effects and show that both moduli can be efficiently stabilized.

Flachi, Antonino; Minamitsuji, Masato; Uzawa, Kunihito

2013-08-01

188

Electromagnetic Modeling of the Passive Stabilization Loop at EAST  

NASA Astrophysics Data System (ADS)

A passive stabilization loop (PSL) has been designed and manufactured in order to enhance the control of vertical instability and accommodate the new stage for high-performance plasma at EAST. Eddy currents are induced by vertical displacement events (VDEs) and disruption, which can produce a magnetic field to control the vertical instability of the plasma in a short timescale. A finite element model is created and meshed using ANSYS software. Based on the simulation of plasma VDEs and disruption, the distribution and decay curve of the eddy currents on the PSL are obtained. The largest eddy current is 200 kA and the stress is 68 MPa at the outer current bridge, which is the weakest point of the PSL because of the eddy currents and the magnetic fields. The analysis results provide the supporting data for the structural design.

Ji, Xiang; Song, Yuntao; Wu, Songtao; Wang, Zhibin; Shen, Guang; Liu, Xufeng; Cao, Lei; Zhou, Zibo; Peng, Xuebing; Wang, Chenghao

2012-09-01

189

DYNAMIC STABILITY DERIVATIVES OF A MANUEVERING COMBAT AIRCRAFT MODEL  

Microsoft Academic Search

The purpose of this experimental study presented in this paper is to measure the dynamic stability derivatives of a generic combat aircraft model in the Ankara Wind Tunnel by using the direct forced oscillation technique. The model, which is used for the oscillatory tests is known as the AGARD, Standard Dynamic Model (SDM) and is manufactured as a generic combat

Mehmet ALTUN; Hava Harp; Okulu Yesilyurt-ISTANBUL

190

Self-optimization, community stability, and fluctuations in two individual-based models of biological coevolution  

Microsoft Academic Search

We compare and contrast the long-time dynamical properties of two individual-based models of biological coevolution. Selection occurs via multispecies, stochastic population dynamics with reproduction probabilities that depend nonlinearly on the population densities of all species resident in the community. New species are introduced through mutation. Both models are amenable to exact linear stability analysis, and we compare the analytic results

Per Arne Rikvold

2005-01-01

191

Stability Analysis of Recurrent Fuzzy Systems: A Hybrid System and SOS Approach  

Microsoft Academic Search

This paper presents a new approach to the stability analysis of recurrent fuzzy systems (RFSs). RFSs are rule-based dynamic fuzzy systems that are usually obtained from heuristic or data-driven modeling. In the presented approach, the stability of both continuous-time and discrete-time RFS can be analyzed in a common framework. It is based on the representation of an RFS as a

Andreas Schwung; Thomas Gusner; Jürgen Adamy

2011-01-01

192

Instantaneous postural stability characterization using time-frequency analysis  

Microsoft Academic Search

Postural stability assessment is critical to a more accurate understanding of sway and balance control. The center of pressure (COP) metric has been shown to be a suitable output measure for time and frequency analysis. However, the center of pressure is a non-stationary signal. Standard time and frequency analysis methods may not be adequate for monitoring the dynamic changes in

Mohammed Ferdjallah; Gerald F. Harris; Jacqueline J. Wertsch

1999-01-01

193

Application of Three Aeroservoelastic Stability Analysis Techniques.  

National Technical Information Service (NTIS)

This report describes two types of instabilities encountered by the YF-16 airplane that were caused by a coupling between the active control system and structural dynamics. Three mathematical models of the airplane were evaluated to determine the degree o...

R. P. Peloubet R. L. Haller A. M. Cunningham E. E. Cwach D. Watts

1976-01-01

194

Stability Analysis of Absorption Chiller-Heaters by Applying Transfer Function  

NASA Astrophysics Data System (ADS)

A transfer function approach is found to be a practical method for ensuring stable operation of absorption chiller-heaters. The transfer function model is based on a solution-circuit of the machine, which dominates the stability of the operation. This model includes a solution pump, a generator with an overflow weir, and a float valve. We found that the solution-circuit system is designed with the cascade control, which makes the system stable. In this construction, the float valve actuates a primary control loop, and the overflow weir actuates a secondary loop. The effects of the characteristic of the solution pump and the overflow weir are estimated by the degree of the stabilities, which are the gain margin and the phase margin. We found that the characteristic of the solution pump strongly effects the stability by enhancing the effect of the cascade control and improving the stability. So it is essential for a better stability analysis model. According to these results, the established model is useful for quantitatively predicting the stabilities of a chiller-heater in operation, and simultaneously reducing its size and improving the stability of operation. We conclude that the methodology based on transfer function can provide compact and reliable absorption chiller-heaters.

Fujii, Tatsuo; Miyake, Satoshi; Oka, Masahiro; Mori, Kiyoyuki

195

Stabilization Method of Calculating Resonance Energies: Model Problem  

NASA Astrophysics Data System (ADS)

We have applied the stabilization method of calculating resonance energies to the elastic scattering from a one-dimensional model potential containing a barrier. For sufficiently large basis sets, the stabilization method yields good approximations to the inner part of the exact scattering wave functions at energies equal to the eigenvalues of the truncated matrix of the Hamiltonian in both the resonant and nonresonant energy regions. We have calculated good approximations to the exact phase shifts from the square-integrable wave functions produced by the stabilization method. We have derived a simple model to explain the behavior of the eigenvalues as a function of the size of the basis. The degree of stability of the eigenvalues approximating the resonance energy is proportional to the width of the resonance. Both the energy and the width of the resonance can be calculated from the change in the stable eigenvalue as the size of the basis increases.

Hazi, Andrew U.; Taylor, Howard S.

1970-04-01

196

RELATION OF URBAN MODEL PERFORMANCE TO STABILITY  

EPA Science Inventory

The RAM model performance in estimating SO2 concentrations in St. Louis, MO for 1976 has been discussed in several previous papers by the authors. In these studies the model estimates were compared to the observed concentrations of SO2 at 13 sites in the St. Louis metropolitan ar...

197

The Absolute Stability Analysis in Fuzzy Control Systems with Parametric Uncertainties and Reference Inputs  

NASA Astrophysics Data System (ADS)

This study analyzes the absolute stability in P and PD type fuzzy logic control systems with both certain and uncertain linear plants. Stability analysis includes the reference input, actuator gain and interval plant parameters. For certain linear plants, the stability (i.e. the stable equilibriums of error) in P and PD types is analyzed with the Popov or linearization methods under various reference inputs and actuator gains. The steady state errors of fuzzy control systems are also addressed in the parameter plane. The parametric robust Popov criterion for parametric absolute stability based on Lur'e systems is also applied to the stability analysis of P type fuzzy control systems with uncertain plants. The PD type fuzzy logic controller in our approach is a single-input fuzzy logic controller and is transformed into the P type for analysis. In our work, the absolute stability analysis of fuzzy control systems is given with respect to a non-zero reference input and an uncertain linear plant with the parametric robust Popov criterion unlike previous works. Moreover, a fuzzy current controlled RC circuit is designed with PSPICE models. Both numerical and PSPICE simulations are provided to verify the analytical results. Furthermore, the oscillation mechanism in fuzzy control systems is specified with various equilibrium points of view in the simulation example. Finally, the comparisons are also given to show the effectiveness of the analysis method.

Wu, Bing-Fei; Ma, Li-Shan; Perng, Jau-Woei

198

Stability Analysis for HIFiRE Experiments.  

National Technical Information Service (NTIS)

The HIFiRE-1 flight experiment provided a valuable database pertaining to boundary layer transition over a 7-degree half-angle, circular cone model from supersonic to hypersonic Mach numbers, and a range of Reynolds numbers and angles of attack. This pape...

C. L. Chang D. Adamczak F. Li J. A. White M. Borg M. M. Choudhari M. S. Smith R. Kimmel S. Stanfield

2012-01-01

199

Stability Modeling and Comparative Study of Series Vectorial Compensators  

Microsoft Academic Search

Complete stability analyses, including voltage, small perturbation and transient stability studies, and the associated models and controls of a series vectorial compensator (SVeC) are presented in this paper. It is also shown through detailed simulations that the SVeC is a competitive device against series power-flow controllers and it might be a better option for similar purposes where space and costs

Juan Miguel Gonzalez; Claudio A. Canizares; Juan M. Ramirez

2010-01-01

200

Analysis of Human Body Bipedal Stability for Neuromotor Disabilities  

NASA Astrophysics Data System (ADS)

The analysis of different biomechanical aspects of balance and equilibrium is presented in the first part of the paper. We analyzed the posture, balance and stability of human body for a normal person and for a person with loco-motor or neuro-motor disabilities (in the second part). In the third part of the paper we presented the methodology and the experimental setup used to record the human body behavior in postural stability for persons with neuro-motors disabilities. The results and the conclusions are presented in the final part of the paper and also in the future work meant to establish the computer analysis for rehabilitation neuromotor disabilities.

Baritz, Mihaela; Cristea, Luciana; Rogozea, Liliana; Cotoros, Diana; Repanovici, Angela

2009-04-01

201

Advances in Computational Stability Analysis of Composite Aerospace Structures  

SciTech Connect

European aircraft industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real structures under realistic loading conditions. This paper presents different advances from the area of computational stability analysis of composite aerospace structures which contribute to that field. For stringer stiffened panels main results of the finished EU project COCOMAT are given. It investigated the exploitation of reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse. For unstiffened cylindrical composite shells a proposal for a new design method is presented.

Degenhardt, R. [DLR, Inst. Composite Structures and Adaptive Systems, Lilienthalplatz 7, 38108 Braunschweig (Germany); PFH, Private University of Applied Sciences Goettingen, Composite Engineering Campus Stade (Germany); Araujo, F. C. de [Dept Civil Eng, UFOP, 35400-000 Ouro Preto, MG (Brazil)

2010-09-30

202

Advances in Computational Stability Analysis of Composite Aerospace Structures  

NASA Astrophysics Data System (ADS)

European aircraft industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real structures under realistic loading conditions. This paper presents different advances from the area of computational stability analysis of composite aerospace structures which contribute to that field. For stringer stiffened panels main results of the finished EU project COCOMAT are given. It investigated the exploitation of reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse. For unstiffened cylindrical composite shells a proposal for a new design method is presented.

Degenhardt, R.; de Araújo, F. C.

2010-09-01

203

Edge stability analysis of ITER baseline plasma simulations  

NASA Astrophysics Data System (ADS)

A stability analysis using equilibria from CORSICA transport simulations finds that the maximum stable pedestal pressure in ITER 15 MA baseline plasma is 110 kPa corresponding to a pedestal temperature of 5.9 keV. The height of the stable pedestal is robust for the assumption of the pedestal height varying only by about 10% if the width of the pedestal is varied by 30%. A conducting first wall has a stabilizing effect on the peeling-ballooning modes that limit the edge pressure. However, the stabilization is unlikely to significantly change the stability limits, but could affect the ELM dynamics by lowering the growth rate of the ELM triggering peeling-ballooning modes. The entire pedestal region is stable against n = ? ballooning modes for all studied pedestal temperatures. This is due to the high bootstrap current keeping the magnetic shear in the region of large pressure gradient.

Saarelma, S.; Casper, T.; Chapman, I. T.; Huijsmans, G. T. A.; Kwon, O.; Lee, J.; Loarte, A.

2012-10-01

204

Stability of differential susceptibility and infectivity epidemic models  

PubMed Central

We introduce classes of differential susceptibility and infectivity epidemic models. These models address the problem of flows between the different susceptible, infectious and infected compartments and differential death rates as well. We prove the global stability of the disease free equilibrium when the basic reproduction ratio ? 1 and the existence and uniqueness of an endemic equilibrium when > 1. We also prove the global asymptotic stability of the endemic equilibrium for a differential susceptibility and staged progression infectivity model, when > 1. Our results encompass and generalize those of [18, 22]. AMS Subject Classification : 34A34,34D23,34D40,92D30

Bonzi, B.; Fall, A. A.; Iggidr, Abderrahman; Sallet, Gauthier

2011-01-01

205

Climate stability and sensitivity in some simple conceptual models  

Microsoft Academic Search

A theoretical investigation of climate stability and sensitivity is carried out using three simple linearized models based on the top-of-the-atmosphere energy budget. The simplest is the zero-dimensional model (ZDM) commonly used as a conceptual basis for climate sensitivity and feedback studies. The others are two-zone models with tropics and extratropics of equal area; in the first of these (Model A),

J. Ray Bates

2010-01-01

206

Climate stability and sensitivity in some simple conceptual models  

Microsoft Academic Search

A theoretical investigation of climate stability and sensitivity is carried out using three simple linearized models based\\u000a on the top-of-the-atmosphere energy budget. The simplest is the zero-dimensional model (ZDM) commonly used as a conceptual\\u000a basis for climate sensitivity and feedback studies. The others are two-zone models with tropics and extratropics of equal\\u000a area; in the first of these (Model A),

J. Ray Bates

207

Bidirectional ring laser: Stability analysis and time-dependent solutions  

SciTech Connect

We provide a comprehensive analysis of the standard model of the bidirectional ring laser in which only one mode can be supported in each direction and in the limit that the polarization can be eliminated adiabatically. The interaction between the two counterpropagating modes can be derived and it is most naturally viewed as a coupling between them via scattering from a spatial grating formed in the population inversion. If the grating is a sufficiently small modulation of the spatial average of the population inversion, it can be approximated by a sinusoidal function. A systematic derivation of the model with only a sinusoidal grating for the homogeneously broadened case is presented that reveals and corrects errors in several previously published analyses. The stability of the steady-state solution is analyzed. The bidirectional steady-state solution is unstable and the unidirectional steady-state solutions may be stable or unstable depending on the parameters. The well-established result of bistability between the two modes when the cavity is tuned to resonance is recovered, a result that persists, in part, even when the losses between the two modes are different.

Zeghlache, H.; Mandel, P.; Abraham, N.B.; Hoffer, L.M.; Lippi, G.L.; Mello, T.

1988-01-15

208

Induction motor modeling in stability simulation: Final report  

SciTech Connect

The objective of this project is to help utilities choose models of large motor loads when simulating electric system transient stability behavior during severe contingencies. Various motor models were evaluated through comparisons between simulations and field recordings obtained in this project. Guidelines are developed to assist engineers in applying typically available data describing large motors. 10 refs., 35 figs.

Carlson, D.L.; Fedora, C.M.

1988-12-01

209

Constraint handling and stability properties of model-predictive control  

Microsoft Academic Search

Effects of hard constraints in the stability of model-predictive control (MPC) are reviewed. Assuming a fixed active set, the optimal solution can be expressed in a general state-feedback closed form, which corresponds to a piecewise linear controller for the linear model case. Changes in the original unconstrained solution by the active constraints and other effects related to the loss of

Nuno M. C. de Oliveira; Lorenz T. Biegler

1994-01-01

210

Exposure Analysis Modeling System  

EPA Science Inventory

The Exposure Analysis Modeling System (EXAMS) is an interactive software application for formulating aquatic ecosystem models and evaluating the fate, transport, and exposure concentrations of synthetic organic chemicals including pesticides, industrial materials, and leachates f...

211

Application of three-dimensional discrete element face-to-face contact model with fissure water pressure to stability analysis of landslide in Panluo iron mine  

Microsoft Academic Search

Three-dimensional discrete element face-to-face contact model with fissure water pressure is established in this paper and\\u000a the model is used to simulate three-stage process of landslide under fissure water pressure in the opencast mine, according\\u000a to the actual state of lands lide in Panluo iron mine where landslide happened in 1990 and was fathered in 1999. The calculation\\u000a results show

Lei Zhang; Zuoan Wei; Xiaoyu Liu; Shihai Li

2005-01-01

212

Effect of model selection on combustor performance and stability using ROCCID  

NASA Astrophysics Data System (ADS)

The ROCket Combustor Interactive Design (ROCCID) methodology is an interactive computer program that combines previously developed combustion analysis models to calculate the combustion performance and stability of liquid rocket engines. Test data from a 213 kN (48,000 lbf) Liquid Oxygen (LOX)/RP-1 combustor with a O-F-O (oxidizer-fuel-oxidizer) triplet injector were used to characterize the predictive capabilities of the ROCCID analysis models for this injector/propellant configuration. Thirteen combustion performance and stability models have been incorporated into ROCCID, and ten of them, which have options for triplet injectors, were examined in this study. Calculations using different combinations of analysis models, with little or no anchoring, were carried out on a test matrix of operating conditions matching those of the test program. Results of the computer analyses were compared to test data, and the ability of the model combinations to correctly predict combustion stability or instability was determined. For the best model combination(s), sensitivity of the calculations to fuel drop size and mixing efficiency was examined. Error in the stability calculations due to uncertainty in the pressure interaction index (N) was examined. The recommended model combinations for this O-F-O triplet LOX/RP-1 configuration are proposed.

Giuliani, James E.; Klem, Mark D.

1992-07-01

213

Effect of model selection on combustor performance and stability predictions using ROCCID  

NASA Astrophysics Data System (ADS)

The ROCket Combustor Interactive Design (ROCCID) methodology is an interactive computer program that combines previously developed combustion analysis models to calculate the combustion performance and stability of liquid rocket engines. Test data from 213 kN (48,000 lbf) Liquid Oxygen (LOX)/RP-1 combustor with an O-F-O (oxidizer-fuel-oxidizer) triplet injector were used to characterize the predictive capabilities of the ROCCID analysis models for this injector/propellant configuration. Thirteen combustion performance and stability models were incorporated into ROCCID, and ten of them, which have options for triplet injectors, were examined. Calculations using different combinations of analysis models, with little or no anchoring, were carried out on a test matrix of operating combinations matching those of the test program. Results of the computer analyses were compared to test data, and the ability of the model combinations to correctly predict combustion stability or instability was determined. For the best model combination(s), sensitivity of the calculations to fuel drop size and mixing efficiency was examined. Error in the stability calculations due to uncertainty in the pressure interaction index (N) was examined. The recommended model combinations for this O-F-O triplet LOX/RP-1 configuration are proposed.

Giuliani, James E.; Klem, Mark D.

1992-07-01

214

Infiltration analysis to evaluate the surficial stability of two-layered slopes considering rainfall characteristics  

Microsoft Academic Search

Shallow slope failures in residual soil during periods of prolonged infiltration are common throughout the world. Using a one-dimensional infiltration model and an infinite slope analysis, this study examines an approximate method of determining how infiltration influences the surficial stability of two-layered slopes. The method extends Moore's infiltration model, which is based on the Green–Ampt model, to cover more general

Sung Eun Cho

2009-01-01

215

Analysis of atmospheric stability using AIRS data  

NASA Astrophysics Data System (ADS)

An optimal cloud-clearing method using collocated MODIS clear pixels is applied to AIRS partly cloudy radiance. Temperature and humidity profiles with 100 layers are retrieved from cloud-free and cloud-cleared AIRS radiance. Using these retrieved profiles, atmospheric environment parameters (include Convective Available Potential Energy, CAPE; Convective Inhibition, CIN) and instability indices (include K index, Lifted Index, Showalter Index) are calculated and compared with that calculated from AIRS and ATOVS operational products and ECMWF analysis fields. These different datasets have different spatial resolution (both in vertical and in horizontal) and spectral resolution. Results show that spatial resolution have obviously influence to the calculations, the lower spatial resolution is likely to have some small energy region lost or reduce the calculation precision. And the profiles derived from partly cloudy area are more meaningful to weather events. The CAPE values of typhoon rain region show differences to that of trough region.

Cai, RongHui; Jiang, DeMing; Qu, YouMing; Wu, Xiaojing

2008-11-01

216

Hydra - an Implicit Partial Differential Equation Relaxation Stability Analysis Package  

NASA Astrophysics Data System (ADS)

A brief description is given of HYDRA, a numerical analysis code designed to provide a rather complete analysis of many difficult problems often encountered in astrophysical contexts. The primary use for this system is the solution of implicit partial differential equations. Given the difference equations and a trial solution, options include (1) forward time integration, (2) relaxation to steady state, (3) stability of steady state and time evolution, (4) numerical stability check, and (5) driven oscillations. Extensive input/output and debug facilities are provided, including dump/restart, variable plots, and initialization from a given state with an eigenvector perturbation. Generalization to solve global problems such as computations of periodic solutions and their stability is straightforward.

Stellingwerf, R. F.

1983-08-01

217

Nonisothermal model of glass fiber drawing stability  

Microsoft Academic Search

Draw resonance is caused by a constant speed winder that leads to non-constant axial forces (Schultz, 1984). The well studied isothermal Newtonian fiber drawing predicts very modest critical draw ratios (around 20, much less than the typical production draw ratios for glass fibers of 103 – 105). The nonisothermal fiber drawing model presented here shows that cooling along the spin

Gyanesh K. Gupta; William W. Schultz; Ellen M. Arruda; Xiaoyong Lu

1996-01-01

218

Constrained model predictive control: Stability and optimality  

Microsoft Academic Search

Model predictive control is a form of control in which the current control action is obtained by solving, at each sampling instant, a finite horizon open-loop optimal control problem, using the current state of the plant as the initial state; the optimization yields an optimal control sequence and the first control in this sequence is applied to the plant. An

David Q. Mayne; James B. Rawlings; Christopher V. Rao; P. O. M. Scokaert

2000-01-01

219

Stabilizing a Bicycle: A Modeling Project  

ERIC Educational Resources Information Center

|This article is a project that takes students through the process of forming a mathematical model of bicycle dynamics. Beginning with basic ideas from Newtonian mechanics (forces and torques), students use techniques from calculus and differential equations to develop the equations of rotational motion for a bicycle-rider system as it tips from…

Pennings, Timothy J.; Williams, Blair R.

2010-01-01

220

Dimensional Stability Analysis of Seventeen Stepped Specimens of 18NI 200 Grade, PH13-8MO and a-286.  

National Technical Information Service (NTIS)

This report documents the results of a dimensional stability analysis of seventeen stepped specimens that were used in the evaluation of factors influencing warpage in metallic alloys being used for cryogenic wind tunnel models. Specimens used in the anal...

D. A. Wigley

1983-01-01

221

A Distributed Slope Stability Model for Steep Forested Basins  

NASA Astrophysics Data System (ADS)

A distributed, physically based slope stability model (dSLAM), based on an infinite slope model, a kinematic wave groundwater model, and a continuous change vegetation root strength model, is presented. It is integrated with a contour line-based topographic analysis and a geographic information system (GIS) for spatial data extraction and display. The model can be run with either individual rainfall events or long-term sequences of storms. These inputs can be either actual storm records or synthesized random events based on Monte Carlo simulation. The model is designed to analyze rapid, shallow landslides and the spatial distribution of safety factor (FS) in steep, forested areas. It can investigate the slope stability problem in both temporal and spatial dimensions, for example, the impact of timber harvesting on slope stability either at a given time or through an extended management period, the probability of landslide occurrence for a given year, and the delivery of landslide sediments to headwater streams. The dSLAM model was applied in a steep, forested drainage of Cedar Creek in the Oregon Coast Ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975. Simulated volume and number of failures were 733 m3 and 4, respectively. These values agreed closely with field measurements following the 1975 storm. However, the effect of parameter uncertainty may complicate this comparison. For example, when soil cohesion values of 2.0 and 3.0 kPa were used, the failure volume changed by factors of 2.04 and 0.41, respectively, compared with the average condition of 2.5 kPa used in the simulation. For soil depths 30% higher and lower than the standard condition, the failure volume changed by factors of 2.0 and 0.27, respectively. When maximum root cohesion changed from 12.5 kPa (average condition) to 10 kPa, the failure volume increased 1.73-fold; for the case of 15 kPa, the failure volume changed by a factor of 0.55. The simulated failures caused by the storm were mostly in hollows. The simulations show that the spatial distribution of FS is controlled mainly by topography and timber-harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms. Most areas with FS < 3.0 corresponded with the distribution of blocks clear-cut in 1968, and all elements with FS < 2.0 were in areas clear-cut in 1968. Areas with low FS (1.0-1.6) expanded dramatically during the rainstorm and decreased at a slow rate after the storm. Factors of safety in hollows declined sharply during the storm.

Wu, Weimin; Sidle, Roy C.

1995-08-01

222

ABDOMINAL MUSCLE ACTIVATION INCREASES LUMBAR SPINAL STABILITY: ANALYSIS OF CONTRIBUTIONS OF DIFFERENT MUSCLE GROUPS  

PubMed Central

Background Antagonistic activation of abdominal muscles and raised intra-abdominal pressure are associated with both spinal unloading and spinal stabilization. Rehabilitation regimens have been proposed to improve spinal stability via selective recruitment of certain trunk muscle groups. This biomechanical study used an analytical model to address whether lumbar spinal stability is increased by selective activation of abdominal muscles. Methods The biomechanical model included anatomically realistic three-layers of curved abdominal musculature connected by fascia, rectus abdominis and 77 symmetrical pairs of dorsal muscles. The muscle activations were calculated with the model loaded with either flexion, extension, lateral bending or axial rotation moments up to 60 Nm, along with intra-abdominal pressure up to 5 or 10 kPa (37.5 or 75 mm Hg) and partial bodyweight. After solving for muscle forces, a buckling analysis quantified spinal stability. Subsequently, different patterns of muscle activation were studied by forcing activation of selected abdominal muscles to at least 10% or 20% of maximum. Findings The spinal stability increased by an average factor of 1.8 with doubling of intra-abdominal pressure. Forced activation of obliques or transversus abdominis muscles to at least 10% of maximum increased stability slightly for efforts other than flexion, but forcing at least 20% activation generally did not produce further increase in stability. Forced activation of rectus abdominis did not increase stability. Interpretation Based on predictions from an analytical spinal buckling model, the degree of stability was not substantially influenced by selective forcing of muscle activation. This casts doubt on the supposed mechanism of action of specific abdominal muscle exercise regimens that have been proposed for low back pain rehabilitation.

Stokes, Ian A.F.; Gardner-Morse, Mack G.; Henry, Sharon M.

2011-01-01

223

Analysis of the stability of hemoglobin S double strands.  

PubMed Central

The deoxyhemoglobin S (deoxy-HbS) double strand is the fundamental building block of both the crystals of deoxy-HbS and the physiologically relevant fibers present within sickle cells. To use the atomic-resolution detail of the hemoglobin-hemoglobin interaction known from the crystallography of HbS as a basis for understanding the interactions in the fibers, it is necessary to define precisely the relationship between the straight double strands in the crystal and the twisted, helical double strands in the fibers. The intermolecular contact conferring the stability of the double strand in both crystal and fiber is between the beta6 valine on one HbS molecule and residues near the EF corner of an adjacent molecule. Models for the helical double strands were constructed by a geometric transformation from crystal to fiber that preserves this critical interaction, minimizes distortion, and makes the transformation as smooth as possible. From these models, the energy of association was calculated over the range of all possible helical twists of the double strands and all possible distances of the double strands from the fiber axis. The calculated association energies reflect the fact that the axial interactions decrease as the distance between the double strand and the fiber axis increases, because of the increased length of the helical path taken by the double strand. The lateral interactions between HbS molecules in a double strand change relatively little between the crystal and possible helical double strands. If the twist of the fiber or the distance between the double strand and the fiber axis is too great, the lateral interaction is broken by intermolecular contacts in the region around the beta6 valine. Consequently, the geometry of the beta6 valine interaction and the residues surrounding it severely restricts the possible helical twist, radius, and handedness of helical aggregates constructed from the double strands. The limitations defined by this analysis establish the structural basis for the right-handed twist observed in HbS fibers and demonstrates that for a subunit twist of 8 degrees, the fiber diameter cannot be more than approximately 300 A, consistent with electron microscope observations. The energy of interaction among HbS molecules in a double strand is very slowly varying with helical pitch, explaining the variable pitch observed in HbS fibers. The analysis results in a model for the HbS double strand, for use in the analysis of interactions between double strands and for refinement of models of the HbS fibers against x-ray diffraction data.

Mu, X Q; Makowski, L; Magdoff-Fairchild, B

1998-01-01

224

Stability analysis of the pulmonary liquid bilayer.  

NASA Astrophysics Data System (ADS)

The lung consists of liquid-lined compliant airways that convey air to and from the alveoli where gas exchange takes place. Because the airways are coated with a bilayer consisting of a mucus layer on top of a periciliary fluid layer, a surface tension instability can generate flows within the bilayer and induce the formation of liquid plugs that block the passage of air. This is a problem for example with premature neonates whose lungs do not produce sufficient quantities of surfactant and suffer from respiratory distress syndrome. To study this instability a system of coupled nonlinear evolution equations are derived using lubrication theory for the thicknesses of the two liquid layers which are assumed to be Newtonian. A normal mode analysis is used to investigate the initial growth of the disturbances, and reveals how the grow rate is affected by the ratio of viscosities ?, film thicknesses ? and surface tensions ? of the two layers which can change by disease. Numerical solutions of the evolution equations show that there is a critical bilayer thickness ?c above which closure occurs, and that a more viscous and thicker layer compared to the periciliary layer closes more slowly. However, ?cis weakly dependent on ?, ? and ?. We also examine the potential impact of wall shear stress and normal stress on cell damage. This work is funded by NIH HL85156.

Halpern, David; Grotberg, James

2010-11-01

225

Mechanical models for insect locomotion: stability and parameter studies  

NASA Astrophysics Data System (ADS)

We extend the analysis of simple models for the dynamics of insect locomotion in the horizontal plane, developed in [Biol. Cybern. 83 (6) (2000) 501] and applied to cockroach running in [Biol. Cybern. 83 (6) (2000) 517]. The models consist of a rigid body with a pair of effective legs (each representing the insect's support tripod) placed intermittently in ground contact. The forces generated may be prescribed as functions of time, or developed by compression of a passive leg spring. We find periodic gaits in both cases, and show that prescribed (sinusoidal) forces always produce unstable gaits, unless they are allowed to rotate with the body during stride, in which case a (small) range of physically unrealistic stable gaits does exist. Stability is much more robust in the passive spring case, in which angular momentum transfer at touchdown/liftoff can result in convergence to asymptotically straight motions with bounded yaw, fore-aft and lateral velocity oscillations. Using a non-dimensional formulation of the equations of motion, we also develop exact and approximate scaling relations that permit derivation of gait characteristics for a range of leg stiffnesses, lengths, touchdown angles, body masses and inertias, from a single gait family computed at `standard' parameter values.

Schmitt, J.; Holmes, P.

2001-08-01

226

Stability analysis of air-core superconducting power transformer  

Microsoft Academic Search

The air-core superconducting power transformer is being investigated as a transformer having the function of a shunt reactor. From the results of the authors' previous analysis, the magnetic field acting on the superconducting wires of an air-core transformer under load includes the rotating component besides the alternating component. Since this rotating component has a possibility of affecting the wire stability,

Hiroshi Yamaguchi; Teruo Kataoka

1997-01-01

227

A New Approach for Aeroelastic Robust Stability Analysis  

Microsoft Academic Search

Air vehicles undergo variations in structural mass and stiffness because of fuel consumption and the failure of structural components, which might lead to serious influences on the aeroelastic characteristics. An approach for aeroelastic robust stability analysis taking into account the perturbations of structural mass and stiffness is developed. Applying the perturbation method and harmonic unsteady aerodynamic forces, the frequency-domain linear

Wu Zhigang; Yang Chao

2008-01-01

228

Probabilistic Slope Stability Analysis Based on the Upper Bound Theorem  

Microsoft Academic Search

This paper presents a probabilistic numerical approach for stability analysis of soil and rock slopes. The slope is divided into a family of inclined slices, and according to the upper bound theorem in plasticity theory, a work-energy balance equation is constructed for each soil\\/rock slice. Geotechnical parameters such as the cohesion, the friction angle and the pore pressure ratio etc.

Hongtao Zhang; Yufei Zhao; Chenfeng Li

2010-01-01

229

Confined three-dimensional stability analysis of the cylinder wake.  

PubMed

A spatially confined stability analysis is reported for the cylinder wake at Reynolds numbers 190 and 260. The two three-dimensional instabilities at these Reynolds numbers are shown to be driven by the flow just behind the cylinder. PMID:15697775

Barkley, Dwight

2005-01-03

230

Stability of Model Membranes in Extreme Environments  

Microsoft Academic Search

The first forms of cellular life required a source of amphiphilic compounds capable of assembling into stable boundary structures.\\u000a Membranes composed of fatty acids have been proposed as model systems of primitive membranes, but their bilayer structure\\u000a is stable only within a narrow pH range and low ionic strength. They are particularly sensitive to aggregating effects of\\u000a divalent cations (Mg+2,

Trishool Namani; David W. Deamer

2008-01-01

231

Flow stability analysis of a particle bed reactor fuel element  

SciTech Connect

This paper describes an investigation of thermal hydraulic flow stability in a particle bed reactor fuel element. The work starts from an adaptation of the stability criterion used by Bussard and DeLauer (1958 and 1965). A one-dimensional evaluation was then performed, using the Ergun relation (1952) to evaluate numerically the pressure drop. If one considers the entire element from cold frit to hot frit, the analysis would indicate flow stability for all conditions. When one uses the pressure drop in the bed for the criterion, the resultant criterion curve has the same shape as the curve obtained by using the Bussard-DeLauer methodology, but predicts higher flow rates are required for stability. A two-dimensional thermal hydraulic study used to verify the one-dimensional analysis yields consistent results. Finally, results from an evaluation to determine if the heat deposition shape within the bed could impact the stability show that, for a chosen average element operating condition, a flat deposition shape was stable, while an axial cosine shape was unstable.

Witter, J.K. (Massachusetts Institute of Technology, 138 Albany Street, Building NW12, Room 307, Cambridge, Massachusetts 02139 (United States)); Lanning, D.D. (Massachusetts Institute of Technology, Nuclear Engineering Department, Building 24, Room 210, Cambridge, Massachusetts 02139 (United States)); Meyer, J.E. (Massachusetts Institute of Technology, Nuclear Engineering Department, Building 24, Room 202, Cambridge, Massachusetts 02139 (United States))

1993-01-20

232

Analysis of energy stabilization inside the hydrophobic core of rubredoxin.  

PubMed

The hydrophobic core of globular proteins is responsible for major stabilization of the protein tertiary structure. The prevailing amino-acid residues in the core are of aliphatic or aromatic character, and therefore, the core in a folded protein structure is mostly stabilized by noncovalent interactions of van der Waals origin between the amino-acid side chains. Herein, we present a theoretical analysis of the interaction energy between the amino acids of the hydrophobic core of the small globular protein rubredoxin (Rd) based on the symmetry-adapted perturbation theory (SAPT) method. The results show uniform proportions between the second-order dispersion and first-order electrostatic energy terms in favor of dispersion interaction, which plays a major role in the stabilization of this important structural element. To demonstrate the contrast between systems stabilized by different mechanisms, we perform a SAPT analysis of the typical hydrogen bonds involved in the formation of protein secondary structure elements in Rd, where dispersion still plays a non-negligible role but electrostatic energy is the major stabilizing factor. PMID:19170065

Berka, Karel; Hobza, Pavel; Vondrásek, Jirí

2009-02-23

233

Stability analysis of axisymmetric supersonic wakes using various basic states  

NASA Astrophysics Data System (ADS)

Two-dimensional stability analyses are conducted of turbulent axisymmetric supersonic wakes at M = 2.46. The aim is to investigate which azimuthal modes are dominant and how the stability behaviour is influenced by the choice of basic state. To that end, axisymmetric (two dimensional) and three dimensional direct numerical simulations (DNS) with either laminar or turbulent inflow conditions were conducted of supersonic wakes to provide the respective basic states for the stability analysis. The global stability analyses were then performed by computing the temporal pulse response using forced Navier-Stokes simulations for each basic state. Using the time- and azimuthally-averaged data from the 3D DNS with turbulent inflow as basic state, an absolute instability of the axisymmetric mode at a Reynolds number, based on wake-generating body diameter and freestream velocity, ReD = 100,000 was found. This is in contrast to results obtained earlier using an axisymmetric flow solution as the basic state. The linear stability analysis for all basic states is presented showing the temporal growth of various azimuthal modes and the respective radial mode shapes. The results are also contrasted to those obtained from nonlinear DNS.

Sandberg, Richard D.

2011-12-01

234

Wave front interaction model of stabilized propagating wave segments.  

PubMed

A wave front interaction model is developed to describe the relationship between excitability and the size and shape of stabilized wave segments in a broad class of weakly excitable media. These wave segments of finite size are unstable but can be stabilized by feedback to the medium excitability; they define a separatrix between spiral wave behavior and contracting wave segments. Unbounded wave segments (critical fingers) lie on the asymptote of this separatrix, defining the boundary between excitable and subexcitable media. The model predictions are compared with results from numerical simulations. PMID:15783780

Zykov, Vladimir S; Showalter, Kenneth

2005-02-14

235

LISA Pathfinder E2E performance simulation: optical and self-gravity stability analysis  

NASA Astrophysics Data System (ADS)

End-to-end (E2E) modelling and simulation, i.e. verifying the science performance of LISA Pathfinder (spacecraft and payload), is mandatory in order to minimize mission risks. In this paper, focus is on two particular applications of the E2E performance simulator currently being developed at EADS Astrium GmbH: the opto-dynamical stability and the self-gravity disturbance stability analysis. The E2E models applied here comprise the opto-dynamical modelling of the optical metrology systems (OMS) laser interferometry, the thermo-elastic distortion modelling of the OMS optical elements and the self-gravity disturbance model accounting for structural distortions. Preliminary analysis results are presented in detail, identifying shortcomings of the current LISA technology package (LTP) mounting baseline. As a consequence, the design is now being revised.

Brandt, N.; Fichter, W.; Kersten, M.; Lucarelli, S.; Montemurro, F.

2005-05-01

236

Analysis and stability of aldehydes and terpenes in electropolished canisters  

Microsoft Academic Search

Aldehydes and terpenes are important classes of polar VOC contaminants for which few sampling and analysis methods have been validated. This study reports on the analysis, stability and recovery of seven aldehydes (butanal, pentanal, hexanal, heptanal, octanal, nonanal and benzaldehyde) and four terpenes (?-pinene, ?-pinene, limonene and 3-carene) prepared at trace levels (3–5ppb) and stored in electropolished stainless-steel canisters. Humidified

Stuart A. Batterman; Guo-Zheng Zhang; Melissa Baumann

1998-01-01

237

Modeling of craton stability using a viscoelastic rheology  

NASA Astrophysics Data System (ADS)

Archean cratons belong to the most remarkable features of our planet, since they represent continental crust that has avoided reworking for several billions of years. Even more, it has become evident from both geophysical and petrological studies that cratons exhibit deep lithospheric keels which equally remained stable ever since the formation of the cratons in the Archean. Dating of inclusions in diamonds from kimberlite pipes give Archean ages, showing that the Archean lithosphere must have been cold soon after its formation in the Archean, in order to allow for the existence of diamonds, and must have stayed in that state ever since. Yet, whereas the stability of Archean cratonic lithosphere for billions of years is a fact, some numerical models failed to reproduce this observed long-term stability (see review by King, 2005). We devised a viscoelastic mantle convection model for exploring cratonic stability. Our modeling results indicate that the application of sufficiently high temperature-dependent viscosity ratio can provide for the observed cratonic stability for billions of years. From our numerical simulations, we derived a relation between Rayleigh number, viscosity ratio, size of the model craton and time to instability of the cratonic root. The comparison between simulations with viscous and viscoelastic rheology indicates no significant influence of elasticity on craton stability. Yet, stress distributions within the model craton differ significantly between viscous and viscoelastic rheologies. This has important implications for future models that include stress-dependent processes like plasticity, power law creep and shear heating. If those processes are to be modeled accurately in mantle convection models that include the lithosphere, a viscoelastic rheology would have to be applied.

Beuchert, Marcus; Podladchikov, Yuri; Simon, Nina; Rüpke, Lars

2010-05-01

238

Scale and stability analysis of selected atmospheric blocking events  

NASA Astrophysics Data System (ADS)

Global six year climatology of mid latitude atmospheric blocking events, during the period 1999--2004, is presented based on the scale and stability analysis, using the NCEP/NCAR re-analysis data. A total of 278 blocking events over the Northern as well as the Southern Hemispheres are analyzed. The 500 mb geopotential height is decomposed into the planetary- and the synoptic-scale geopotential heights. The heights are then averaged over a 40° x 60° latitude longitude box D, harboring the blocking event. The averaged heights are compared with their corresponding monthly mean values during the month in which the blocking event has occurred. A positive planetary-scale geopotential height dominance behavior for a given blocking event is defined as a positive planetary-scale height anomaly above its monthly mean value. Similar procedure is adopted to define synoptic-scale dominance behavior. It is pointed out that globally, over the six year period, 83% of the blocking events have single-scale dominance, whereas remaining 17% of the blocking events have an alternating-scale dominance behavior. In the Northern Hemisphere, during the later half of the six year period, a 28% rise in the planetary-scale dominance behavior blocking events is noticed over the synoptic-scale dominance behavior blocking events. Stability analysis of the blocking events over the six year period is performed, under the assumption of barotropic flow, using the following three stability indicators: i) max |?psi|, ii) max|?Oa |, and iii) D |O|²(y)dxdy. Here, psi is geosptrophic stream function, Oa is the absolute vorticity and O = - ?u/ ?y, in usual meteorological notation. A comparison of the time variability of the three stability indicators over the entire life cycle of the selected blocking events with earlier works performing the synoptic and dynamics studies shows that the three stability indicators can be used as climatologically reliable stability indicators giving useful insight into the stability of the flow attending the blocking event. It is noticed that in the scale dependent flow, the scale that dominates during the mature stage of the blocking event determines the stability of the flow during the blocking, and that the blocking is relatively more stable state than the more frequent zonal flow, irrespective of which scale dominates the flow during blocking. For the selected blocking events, the calculations for both the scale height dominance as well as for the stability of the flow attending the blocking are extended to include the stratospheric signals as well, for operational relevance.

Hussain, Athar

239

Game Analysis of Stability of the Fourth Party Logistics Implementation  

Microsoft Academic Search

As information technology advances, the emerging fourth party logistics (4PL) has become a new kind of logistics operation model to help companies reduce operating costs in recent years. Based on evolutionary game theory, this paper analyzed the stability of fourth party logistics of small and medium enterprises in China, aiming at promoting small and medium enterprises to achieve a smooth

Tian-kun Fang; Song-wen Tang; Li Cheng

2010-01-01

240

Stability analysis of bidirectional associative memory networks with time delays.  

PubMed

By using the method of Liapunov functional, a model for bidirectional associative memory networks with time delays is studied. The asymptotic stability is global in the state space of the neuronal activations and is also independent of the delays. Our results can be applied to a variety of situations that arise both in the field of biological and artificial neural networks. PMID:18244600

Feng, Chunhua; Plamondon, R

2003-01-01

241

Simulation analysis of influence factors on bus maneuverability and stability  

Microsoft Academic Search

Bus dynamics is analyzed and 4 degrees of freedom dynamics model is established according to basic dynamic characteristics of bus. The corresponding computer simulation program is developed by using Matlab software. From practical view, structural parameters which are impacted by bus maneuverability and stability such as tire cornering stiffness, steering wheel rotational inertia, steering transmission ratio, aligning torque, around the

Hao Zhang; Xiansheng Li; Xuelian Zheng; Hongfei Liu

2010-01-01

242

Stability analysis of bidirectional associative memory networks with time delays  

Microsoft Academic Search

By using the method of Liapunov functional, a model for bidirectional associative memory networks with time delays is studied. The asymptotic stability is global in the state space of the neuronal activations and is also independent of the delays. Our results can be applied to a variety of situations that arise both in the field of biological and artificial neural

Chunhua Feng; Réjean Plamondon

2003-01-01

243

Nonlinear aeroelastic stability analysis of wind turbine blade with bending–bending–twist coupling  

NASA Astrophysics Data System (ADS)

In this study, the nonlinear aeroelastic stability of wind turbine blade with bending–bending–twist coupling has been investigated for composite thin-walled structure with pretwist angle. The aerodynamic model used here is the differential dynamic stall nonlinear ONERA model. The nonlinear aeroelastic equations are reduced to ordinary equations by Galerkin method, with the aerodynamic force decomposition by strip theory. The nonlinear resulting equations are solved by a time-marching approach, and are linearized by small perturbation about the equilibrium point. The nonlinear aeroelastic stability characteristics are investigated through eigenvalue analysis, nonlinear time domain response, and linearized time domain response.

Liu, Tingrui; Ren, Yongsheng; Yang, Xinghua

2013-10-01

244

Analysis of the soil organic matter stability in spruce forests of Krkonose in Czechia on the basis of the ROMUL mathematical model  

NASA Astrophysics Data System (ADS)

Computational experiments with the ROMUL mathematical model were performed for studying the dynamics of soil organic matter (SOM) in spruce forests of northeastern Czechia that were disturbed because of the atmospheric sulfur deposition in the second half of the 20th century. The effect of the soil acidification on the decomposition dynamics of the forest die-back in the model is of importance. Conditions of the forest productivity were found under which the SOM pool could be preserved. It was shown that, later on, the content of the litter will decrease because of the forest degradation, and the succession changes due to the effect of the contamination will affect the type of vegetation, as well as the type of soil organic matter. The total SOM content will decrease in this case. However, the maintenance of the grass productivity can slow down this process. It was noted that the quantitative prediction of the SOM dynamics requires measurements of the productivity parameters of the forest as a whole and the living ground cover, including the content of root litter, and the hydrothermal regime of the soil determining the transformation of the litter and humus.

Nadporozhskaya, M. A.; ?udlin, P.; Novak, F.; Bykhovets, S. S.; Chertov, O. G.; Komarov, A. S.; Mikhailov, A. V.

2009-06-01

245

Nonlinear stability analysis of the attitude motion of spin-stabilized thrusting spacecraft  

NASA Astrophysics Data System (ADS)

The attitude dynamics of a class of spin-stabilized, thrusting, upperstage spacecraft is examined. Certain spacecraft in the class has been observed to develop oscillations about their transverse axes which increase exponentially in magnitude by the time the solid propellant motor burns out. After burnout, the oscillations stabilize with approximately constant amplitudes. The basic model for examination consists of a rigid body, representing the spacecraft main body; and a point-mass spherical pendulum, representing a deposit of 'slag' formed as a by-product of the combustion of the solid propellant. Exact nonlinear equations of motion for the model are derived. Approximate nonlinear equations are obtained from these, by assuming that the mass of the slag deposit is much less than the total mass of the system. By applying certain additional restrictions, the coupled, approximate nonlinear equations are further simplified, and approximate near-resonant solutions are obtained by using the method of multiple scales. The results show that the slosh resonances caused by parametric and external type excitations due to the main body may occur. However, since the present system is a time-varying, nonstationary, nonlinear system, this study emphasizes the use of numerical methods based on using the exact nonlinear equations and real flight parameters of the WESTAR 4 spacecraft. Various slag disturbance models are used in the basic model. These include models of the effects of slag mass discharge, solidification, and viscosity. Attitude motions that result from numerical experiments performed using these slag models are very similar to observed motions of typical spin-stabilized upper stages. The best results are obtained by using the model in which a part of the slag mass is discharged through the nozzle near burnout time.

Kang, Ja Young

1992-02-01

246

Stability analysis for stochastic BAM nonlinear neural network with delays  

NASA Astrophysics Data System (ADS)

In this paper, stochastic bidirectional associative memory neural networks with constant or time-varying delays is considered. Based on a Lyapunov-Krasovskii functional and the stochastic stability analysis theory, we derive several sufficient conditions in order to guarantee the global asymptotically stable in the mean square. Our investigation shows that the stochastic bidirectional associative memory neural networks are globally asymptotically stable in the mean square if there are solutions to some linear matrix inequalities(LMIs). Hence, the global asymptotic stability of the stochastic bidirectional associative memory neural networks can be easily checked by the Matlab LMI toolbox. A numerical example is given to demonstrate the usefulness of the proposed global asymptotic stability criteria.

Lv, Z. W.; Shu, H. S.; Wei, G. L.

2008-02-01

247

Stability analysis of nonlinear Roesser-type two-dimensional systems via a homogenous polynomial technique  

NASA Astrophysics Data System (ADS)

This paper is concerned with the problem of stability analysis of nonlinear Roesser-type two-dimensional (2D) systems. Firstly, the fuzzy modeling method for the usual one-dimensional (1D) systems is extended to the 2D case so that the underlying nonlinear 2D system can be represented by the 2D Takagi—Sugeno (TS) fuzzy model, which is convenient for implementing the stability analysis. Secondly, a new kind of fuzzy Lyapunov function, which is a homogeneous polynomially parameter dependent on fuzzy membership functions, is developed to conceive less conservative stability conditions for the TS Roesser-type 2D system. In the process of stability analysis, the obtained stability conditions approach exactness in the sense of convergence by applying some novel relaxed techniques. Moreover, the obtained result is formulated in the form of linear matrix inequalities, which can be easily solved via standard numerical software. Finally, a numerical example is also given to demonstrate the effectiveness of the proposed approach.

Zhang, Tie-Yan; Zhao, Yan; Xie, Xiang-Peng

2012-12-01

248

Theoretical modelling of the feedback stabilization of external MHD modes in toroidal geometry  

NASA Astrophysics Data System (ADS)

A theoretical framework for understanding the feedback mechanism for stabilization of external MHD modes has been formulated. Efficient computational tools - the GATO stability code coupled with a substantially modified VACUUM code - have been developed to effectively design viable feedback systems against these modes. The analysis assumed a thin resistive shell and a feedback coil structure accurately modelled in ? and phi, albeit with only a single harmonic variation in phi. Time constants and induced currents in the enclosing resistive shell are calculated. An optimized configuration based on an idealized model has been computed for the DIII-D device. Up to 90% of the effectiveness of an ideal wall can be achieved.

Chance, M. S.; Chu, M. S.; Okabayashi, M.; Turnbull, A. D.

2002-03-01

249

Stability of a general SEIV epidemic model with time delay  

NASA Astrophysics Data System (ADS)

An SEIV epidemic model with a general nonlinear incidence rate, vaccination and time delay in treatment is considered. Sufficient conditions for the time delay to keep the stability of the endemic equilibria are given. A numerical simulations is given to illustrate our results.

Hikal, M. M.; El-Sheikh, M. M. A.

2013-10-01

250

A Stabilization Method for the Hydrogen Diffusion Model in Materials  

Microsoft Academic Search

In this paper, we highlight the existence of some instability in finite element method appearing for high values of the Peclet number in the model of hydrogen diffusion in materials. A stabilization technique is used to overcome the instability problem and therefore improve this scheme. We manage to improve the scheme and decrease the instability, and we highlight the strong

Stephane Ndong-Mefane; Hiroshi Kanayama; Masao Ogino; M. F. El-Amin

2008-01-01

251

Stability Modeling of DIII-D Discharges with Transport Barriers  

NASA Astrophysics Data System (ADS)

The stability of DIII--D discharges with transport barriers is systematically studied by modeling the pressure profiles using a hyperbolic tangent representation with various radii, widths, and amplitudes. The q profiles are modeled using a spline representation with varying q(0), q_min, and ?_q_min. The equilibria are computed using the EFIT and the TOQ codes based on the parameters from a strongly shaped high triangurality DIII--D long pulse high performance discharge. Stability against the ideal low n=1 and 2 modes is evaluated using the GATO code with a conducting wall at 1.5 a. The results show that the stability improves with increasing transport barrier width and radius but varies weakly with q(0). When the transport barriers are L--mode like and have narrow widths in the plasma core, the stability is limited by the n=1 mode. When they are H--mode like and have large widths extending toward the edge, the stability is limited by the n=2 mode.

Lao, L. L.; Ferron, J. R.; Lin-Liu, Y. R.; Strait, E. J.; Turnbull, A. D.; Taylor, T. S.; Murakami, M.

1999-11-01

252

Conjugation of ?-amylase with dextran for enhanced stability: process details, kinetics and structural analysis.  

PubMed

The influence of enzyme polysaccharide interaction on enzyme stability and activity was elucidated by covalently binding dextran to a model enzyme, ?-amylase. The conjugation process was optimized with respect to concentration of oxidizing agent, pH of enzyme solution, ratio of dextran to enzyme concentration, temperature and time of conjugate formation, and was found to affect the stability of ?-amylase. ?-Amylase conjugated under optimized conditions showed 5% loss of activity but with enhanced thermal and pH stability. Lower inactivation rate constant of conjugated ?-amylase within the temperature range of 60-80 °C implied its better stability. Activation energy for denaturation of ?-amylase increased by 8.81 kJ/mol on conjugation with dextran. Analysis of secondary structure of ?-amylase after covalent binding with dextran showed helix to turn conversion without loss of functional properties of ?-amylase. Covalent bonding was found to be mandatory for the formation of conjugate. PMID:22944451

Jadhav, Swati B; Singhal, Rekha S

2012-08-04

253

Gravitational stability of spherical self-gravitating relaxation models  

Microsoft Academic Search

The gravitational stability of spherical, self-gravitating, hydrostatically pre-stressed planetary models remains a subject of active interest. Love (1907, 1911) was the first to show that purely elastic models can become unstable when values of rigidity and bulk modulus are insufficient to counteract self-gravitational collapse. We revisit his calculations and extend his work to show that so-called dilatational (or `D') modes

L. L. A. Vermeersen; J. X. Mitrovica

2000-01-01

254

Modeling Food-Web Dynamics: Complexity-Stability Implications  

Microsoft Academic Search

We discuss theoretical aspects of the broader food-web research agenda, particularly the background and various approaches used for modeling food-web dynamics in abstract systems with more than two taxa. Much of this type of modeling has oriented itself around the classic and enduring complexity-stability debate in ecology, especially those aspects which relate to the theoretical and associated empirical food-web research

Jennifer A. Dunne; Ulrich Brose; Richard J. Williams; Neo D. Martinez

255

Multistate Structural Modeling and Voltage-Clamp Analysis of Epilepsy/Autism Mutation Kv10.2-R327H Demonstrate the Role of This Residue in Stabilizing the Channel Closed State.  

PubMed

Voltage-gated potassium channel Kv10.2 (KCNH5) is expressed in the nervous system, but its functions and involvement in human disease are poorly understood. We studied a human Kv10.2 channel mutation (R327H) recently identified in a child with epileptic encephalopathy and autistic features. Using multistate structural modeling, we demonstrate that the Arg327 residue in the S4 helix of voltage-sensing domain has strong ionic interactions with negatively charged residues within the S1-S3 helices in the resting (closed) and early-activation state but not in the late-activation and fully-activated (open) state. The R327H mutation weakens ionic interactions between residue 327 and these negatively charged residues, thus favoring channel opening. Voltage-clamp analysis showed a strong hyperpolarizing (?70 mV) shift of voltage dependence of activation and an acceleration of activation. Our results demonstrate the critical role of the Arg327 residue in stabilizing the channel closed state and explicate for the first time the structural and functional change of a Kv10.2 channel mutation associated with neurological disease. PMID:24133262

Yang, Yang; Vasylyev, Dmytro V; Dib-Hajj, Fadia; Veeramah, Krishna R; Hammer, Michael F; Dib-Hajj, Sulayman D; Waxman, Stephen G

2013-10-16

256

Stability of building gene regulatory networks with sparse autoregressive models  

PubMed Central

Background Biological networks are constantly subjected to random perturbations, and efficient feedback and compensatory mechanisms exist to maintain their stability. There is an increased interest in building gene regulatory networks (GRNs) from temporal gene expression data because of their numerous applications in life sciences. However, because of the limited number of time points at which gene expressions can be gathered in practice, computational techniques of building GRN often lead to inaccuracies and instabilities. This paper investigates the stability of sparse auto-regressive models of building GRN from gene expression data. Results Criteria for evaluating the stability of estimating GRN structure are proposed. Thereby, stability of multivariate vector autoregressive (MVAR) methods - ridge, lasso, and elastic-net - of building GRN were studied by simulating temporal gene expression datasets on scale-free topologies as well as on real data gathered over Hela cell-cycle. Effects of the number of time points on the stability of constructing GRN are investigated. When the number of time points are relatively low compared to the size of network, both accuracy and stability are adversely affected. At least, the number of time points equal to the number of genes in the network are needed to achieve decent accuracy and stability of the networks. Our results on synthetic data indicate that the stability of lasso and elastic-net MVAR methods are comparable, and their accuracies are much higher than the ridge MVAR. As the size of the network grows, the number of time points required to achieve acceptable accuracy and stability are much less relative to the number of genes in the network. The effects of false negatives are easier to improve by increasing the number time points than those due to false positives. Application to HeLa cell-cycle gene expression dataset shows that biologically stable GRN can be obtained by introducing perturbations to the data. Conclusions Accuracy and stability of building GRN are crucial for investigation of gene regulations. Sparse MVAR techniques such as lasso and elastic-net provide accurate and stable methods for building even GRN of small size. The effect of false negatives is corrected much easier with the increased number of time points than those due to false positives. With real data, we demonstrate how stable networks can be derived by introducing random perturbation to data.

2011-01-01

257

Stability of nonradial g\\/sup +\\/-mode pulsations in 1 M\\/sub sun\\/ models  

Microsoft Academic Search

The stability of nonradial g\\/sup +\\/ modes with low l in evolutionary solar models is examined by employing a linear nonadiabatic analysis. In order to include the effect of the interaction between pulsation and convection, we use a time-dependent convection theory which suppresses rapid spatial oscillations of thermal eigenfunctions. The analysis confirms previous results based on quasi-adiabatic analyses. That is,

Saio

1980-01-01

258

Computational analysis of noise reduction devices in axial fans with stabilized finite element formulations  

NASA Astrophysics Data System (ADS)

The paper illustrates how a computational fluid mechanic technique, based on stabilized finite element formulations, can be used in analysis of noise reduction devices in axial fans. Among the noise control alternatives, the study focuses on the use of end-plates fitted at the blade tips to control the leakage flow and the related aeroacoustic sources. The end-plate shape is configured to govern the momentum transfer to the swirling flow at the blade tip. This flow control mechanism has been found to have a positive link to the fan aeroacoustics. The complex physics of the swirling flow at the tip, developing under the influence of the end-plate, is governed by the rolling up of the jet-like leakage flow. The RANS modelling used in the computations is based on the streamline-upwind/Petrov-Galerkin and pressure-stabilizing/Petrov-Galerkin methods, supplemented with the DRDJ stabilization. Judicious determination of the stabilization parameters involved is also a part of our computational technique and is described for each component of the stabilized formulation. We describe the flow physics underlying the design of the noise control device and illustrate the aerodynamic performance. Then we investigate the numerical performance of the formulation by analysing the inner workings of the stabilization operators and of their interaction with the turbulence model.

Corsini, A.; Rispoli, F.; Sheard, A. G.; Tezduyar, T. E.

2012-12-01

259

Coupled three-dimensional aeroelastic stability analysis of bladed disks  

Microsoft Academic Search

In the present work an algorithm for the coupled aeromechanical computation of three-dimensional compressor cascades vibrating in a traveling-wave mode is presented and applied to the determination of aeroelastic stability of a transonic fan rotor. The initial vibratory modes are computed using a finite-element structural analysis code. The unsteady flow field response to blade vibration is estimated by numerical integration

G. A. Gerolymos

1993-01-01

260

Stability Analysis of Functionally Graded Plates Subject to Thermal Loads  

Microsoft Academic Search

\\u000a Stability analysis of functionally graded ceramic–metal plates under thermal loads is presented using the first order shear\\u000a deformation theory. The effective material properties of the functionally graded plates are assumed to vary through their\\u000a thickness direction according to the power-law distribution of the volume fractions of the constituents. The thermal loads\\u000a are assumed to be uniform, linear and non-linear distribution

Mokhtar Bouazza; A. Tounsi; E. A. Adda-Bedia; A. Megueni

261

M-theory model-building and proton stability  

SciTech Connect

The authors study the problem of baryon stability in M theory, starting from realistic four-dimensional string models constructed using the free-fermion formulation of the weakly-coupled heterotic string. Suitable variants of these models manifest an enhanced custodial gauge symmetry that forbids to all orders the appearance of dangerous dimension-five baryon-decay operators. The authors exhibit the underlying geometric (bosonic) interpretation of these models, which have a Z{sub 2} x Z{sub 2} orbifold structure similar, but not identical, to the class of Calabi-Yau threefold compactifications of M and F theory investigated by Voisin and Borcea. A related generalization of their work may provide a solution to the problem of proton stability in M theory.

Ellis, J. [CERN, Geneva (Switzerland). Theory Div.; Faraggi, A.E. [Florida Univ., Gainesville, FL (United States). Inst. for Fundamental Theory; Nanopoulos, D.V. [Texas A and M Univ., College Station, TX (United States)]|[Houston Advanced Research Center, The Woodlands, TX (United States). Astroparticle Physics Group]|[Academy of Athens (Greece). Div. of Natural Sciences

1997-09-01

262

Self-optimization, community stability, and fluctuations in two individual-based models of biological coevolution  

Microsoft Academic Search

We compare and contrast the long-time dynamical properties of two individual-based models of biological coevolution. Selection\\u000a occurs via multispecies, stochastic population dynamics with reproduction probabilities that depend nonlinearly on the population\\u000a densities of all species resident in the community. New species are introduced through mutation. Both models are amenable\\u000a to exact linear stability analysis, and we compare the analytic results

Per Arne Rikvold

2007-01-01

263

MODELLING UNCERTAINTIES IN PILLAR STABILITY ANALYSIS  

Microsoft Academic Search

Many countries are now facing problems related to their past mining activities. One of the greatest problems they have to deal with concerns the potential surface instability. In areas where a bord-and-pillar extraction method was used, deterministic methodologies are generally used to assess the risk of surface collapses. However those methodologies suffer from not being able to take into account

CAUVIN Maxime; VERDEL Thierry; SALMON Romuald

264

Time-dependent analysis of stability of surface coal mine spoil slope under groundwater pressure  

SciTech Connect

The procedure involves two distinct research areas. First is the analysis of groundwater conditions in the pile. The second is the stability of the pile under the groundwater conditions. The procedure utilizes fixed and variable input parameters. Fixed parameters include spoil pile material content, mode of pile formation, pile geometry and orientation. The variable parameters are spoil permeability, different sources of water inflow and time. In this procedure, the transient groundwater conditions are determined by a finite element modeling technique. After establishing the development of phreatic surface with time, and knowing the strength parameters, a zonalized cross-section and failure mode, the stability analysis is done by an appropriate limit equilibrium method. The procedure was extensively validated using hypothetical and real world data. The research shows that the spoils with saturated hydraulic conductivity and effective average rainfall in a ratio of 1.0 or less are more sensitive for build-up of groundwater pressure with time. The model predicts better results for spoil in areas where average rainfall is well distributed over a year. The simulation technique developed in this thesis can be used to bind an optimum spoil configuration and to analyze stabilization aspects of unstable abandoned mine slopes. The technique, along with measurement of water levels, can be used for monitoring spoil pile stability and for providing warning of impending stability problems.

Surana, D.M.

1989-01-01

265

Strength and stability analysis of deep sea drilling risers  

Microsoft Academic Search

In order to analyze the influence of vortex-induced vibration on the strength and stability of marine drilling risers, a simplified\\u000a analytical model was established and a method for calculating vortex-induced dynamic response was developed. A case study\\u000a indicated that at primary resonance, first-order dynamic displacement response is greater than higher-order mode responses,\\u000a but the influence of dynamic moment and shearing

Yang Jin; Liu Caihong; Liu Hanbin; Xie Renjun; Cao Shijing

2007-01-01

266

Improved helicopter aeromechanical stability analysis using segmented constrained layer damping and hybrid optimization  

NASA Astrophysics Data System (ADS)

Aeromechanical stability plays a critical role in helicopter design and lead-lag damping is crucial to this design. In this paper, the use of segmented constrained damping layer (SCL) treatment and composite tailoring is investigated for improved rotor aeromechanical stability using formal optimization technique. The principal load-carrying member in the rotor blade is represented by a composite box beam, of arbitrary thickness, with surface bonded SCLs. A comprehensive theory is used to model the smart box beam. A ground resonance analysis model and an air resonance analysis model are implemented in the rotor blade built around the composite box beam with SCLs. The Pitt-Peters dynamic inflow model is used in air resonance analysis under hover condition. A hybrid optimization technique is used to investigate the optimum design of the composite box beam with surface bonded SCLs for improved damping characteristics. Parameters such as stacking sequence of the composite laminates and placement of SCLs are used as design variables. Detailed numerical studies are presented for aeromechanical stability analysis. It is shown that optimum blade design yields significant increase in rotor lead-lag regressive modal damping compared to the initial system.

Liu, Qiang; Chattopadhyay, Aditi

2000-06-01

267

Anisotropic stress and stability in modified gravity models  

SciTech Connect

The existence of anisotropic stress of a purely geometrical origin seems to be a characteristic of higher order gravity models, and has been suggested as a probe to test these models observationally, for example, in weak lensing experiments. In this paper, we seek to find a class of higher order gravity models of f(R,G) type that would give us a zero anisotropic stress and study the consequences for the viability of the actual model. For the special case of a de Sitter background, we identify a subclass of models with the desired property. We also find a direct link between anisotropic stress and the stability of the model as well as the presence of extra degrees of freedom, which seems to be a general feature of higher order gravity models. Particularly, setting the anisotropic stress equal to zero for a de Sitter background leads to a singularity that makes it impossible to reach the de Sitter evolution.

Saltas, Ippocratis D. [Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom); Kunz, Martin [Departement de Physique Theorique, Universite de Geneve, 1211 Geneva 4 (Switzerland)

2011-03-15

268

Fuzzy cluster stability analysis with missing values using resampling.  

PubMed

Exploratory data analysis is often necessary to evaluate potential hypotheses for subsequent studies such as grouping the data in clusters. In real data sets the occurrence of incompleteness is very common. We propose a method that tolerates missing values for fuzzy clustering using resampling (bootstrapping) and cluster stability analysis. The quality of classification is based on the measures like F1 and Hubert. The central idea is to compare a reference cluster with many clusters from sub-samples of the original data set. The results demonstrate that our method is capable of identifying relevant partitions even with high presence of missing values. PMID:19324606

Milagre, Selma T; Maciel, Carlos Dias; Pereira, José Carlos; Pereira, Adriano A

2009-01-01

269

Theoretical study of vapor-liquid homogeneous nucleation using stability analysis of a macroscopic phase.  

PubMed

Stability analysis is generally used to verify that the solution to phase equilibrium calculations corresponds to a stable state (minimum of the free energy). In this work, tangent plane distance analysis for stability of macroscopic mixtures is also used for analyzing the nucleation process, reconciling thus this analysis with classical nucleation theories. In the context of the revised nucleation theory, the driving force and the nucleation work are expressed as a function of the Lagrange multiplier corresponding to the mole fraction constraint from the minimization problem of stability analysis. Using a van der Waals fluid applied to a ternary mixture, Lagrange multiplier properties are illustrated. In particular, it is shown how the Lagrange multiplier value is equal to one on the binodal and spinodal curves at the same time as the driving force of nucleation vanishes on these curves. Finally, it is shown that, on the spinodal curve, the nucleation work from the revised and generalized nucleation theories are characterized by two different local minima from stability analysis, irrespective of any interfacial tension models. PMID:23061836

Carreón-Calderón, Bernardo

2012-10-14

270

Stability Analysis and Control of Orbits around a Small Body  

NASA Astrophysics Data System (ADS)

An important component of future space missions is to explore small solar system bodies such as asteroids and/or comets with inexpensive spacecraft. In deep space missions, human assistance would hardly be available due to the long round-trip delay of communication with earth. Furthermore, especially in case of small bodies, the shape, mass, density, gravity field and span of such bodies cannot be observed from the earth. Therefore, autonomy and environment adaptation are strongly required, the orbit determination and control technology around small bodies is getting more difficult than ever. This paper discusses the problem of stability and autonomous control of orbit around a small body. Given a model gravitational field and rotational state of small body, equations of orbit dynamic for micro-explorer around small body is given in the body-fixed frame of the small body. Orbit stabilization of flying-around the small body is analyzed and the stable condition is given. Mainly, to maintain micro-explorer stable flying-around a small body for long time, the stable condition that is transformed into sliding mode and a variable structure controller is presented. It is shown that stabilization of flying orbit under bound perturbation and injecting error is assured if variable structure controller is used. Simulation result also shows that stabilization of orbit of flying-around small body is maintained with given control scheme. Keywords: Small Bodies; Variable Structure Control; Orbit Control

Cui, Hutao; Cui, Pingyuan; Shi, Xueyan

2002-01-01

271

Standard model stability bounds for new physics within LHC reach  

Microsoft Academic Search

We analyse the stability lower bounds on the Standard Model Higgs mass by carefully controlling the scale independence of the effective potential. We include resummed leading and next-to-leading-log corrections, and physical pole masses for the Higgs boson, MH, and the top-quark, Mt. Particular attention is devoted to the cases where the scale of new physics ? is within LHC reach,

J. A. Casas; J. R. Espinosa; M. Quirós

1996-01-01

272

Standard model stability bounds for new physics within LHC reach  

Microsoft Academic Search

We analyse the stability lower bounds on the Standard Model Higgs mass by carefully controlling the scale independence of the effective potential. We include resummed leading and next-to-leading-log corrections, and physical pole masses for the Higgs boson, MH, and the top-quark, Mt. Particular attention is devoted to the cases where the scale of new physics Lambda is within LHC reach,

J. A. Casas; J. R. Espinosa; M. Quirós

1996-01-01

273

Numerical modelling of turbulent catalytically stabilized channel flow combustion  

Microsoft Academic Search

The turbulent catalytically stabilized combustion of lean hydrogen–air premixtures is investigated numerically in plane channels with platinum-coated isothermal walls. The catalytic wall temperature is 1220K and the incoming mixture has a mean velocity of 15m\\/s and a turbulent kinetic energy of 1.5m2\\/s2. A two-dimensional elliptic model is developed with elementary heterogeneous and homogeneous chemical reactions. The approach is based on

John Mantzaras; Christoph Appel; Peter Benz; Urs Dogwiler

2000-01-01

274

Gravitational stability of spherical self-gravitating relaxation models  

NASA Astrophysics Data System (ADS)

The gravitational stability of spherical, self-gravitating, hydrostatically pre-stressed planetary models remains a subject of active interest. Love (1907, 1911) was the first to show that purely elastic models can become unstable when values of rigidity and bulk modulus are insufficient to counteract self-gravitational collapse. We revisit his calculations and extend his work to show that so-called dilatational (or `D') modes of a viscoelastic sphere can also become unstable to self-gravitation in a specific region of Lamé parameter space. As an example, we derive a marginal stability curve for the dilatational modes of a homogeneous planetary model at spherical harmonic degree two. We demonstrate that the stability conditions are independent of viscosity and that the instability will occur only when the homogeneous earth model is already unstable to the elastic instability described by Love (1907, 1911). Finally, we also consider a class of Rayleigh-Taylor (or `RT') instabilities related to unstable density stratification in planetary models. This convective instability is explored using both a homogeneous Maxwell viscoelastic sphere (which has an unstable layering at all depths) and a suite of Maxwell earth models that adopt the elastic and density structure of the seismic model PREM (which has regions of unstable density stratification within the upper mantle). We argue that previous studies have significantly overestimated the potential importance of these modes to Earth evolution. For example, suggestions that the timescale of the RT modes is short relative to the age of the Earth face the fundamental problem that the ensuing convective instability would have long ago destroyed the unstable layering and produced an adiabatic profile. We predict that at low degrees the RT instabilities for a PREM density profile and realistic viscosity stratification have timescales comparable to the age of the Earth. It is unclear, in any event, whether the unstable density layering in the PREM upper mantle is robust.

Vermeersen, L. L. A.; Mitrovica, J. X.

2000-08-01

275

JT-60 Upgrade vertical stability experiments and analysis  

NASA Astrophysics Data System (ADS)

The JT-60 Upgrade tokamak (JT-60U), can produce plasmas with vertical elongation (kappa approximately = 1.6), and thus allows investigation of vertical instability phenomena. The present work describes investigation of the vertical stability characteristics of JT-60U plasmas through experimental results and simulation. Experiments described include feedback turnoff cases and high beta(sub p) unstable plasma cases. For purposes of simulation, the plasma is modeled as a rigid assembly of current-carrying axisymmetric loops. A nominal conductor model based on design geometry was modified to reproduce the results of a series of coil excitation experiments using a reduced order system identification approach. A two-coil model was used to fit the experimental coil excitation behavior, and the full order conductor model was modified to allow the dominant modes to reflect the low order dynamic response. The resulting plasma-conductor model is shown to reproduce the vertical stability behavior of JT-60U fairly well. Theoretical predictions of limits on the value of Shafranov (Lambda) achievable in JT-60U are made.

Humphreys, D. A.; Yoshino, Ryuji

1992-05-01

276

A Six Degree of Freedom Trajectory Analysis of Spin-Stabilized Projectiles  

NASA Astrophysics Data System (ADS)

A full six degrees of freedom (6-DOF) flight dynamics model is proposed for the accurate prediction of short and long-range trajectories of high and low spin-stabilized projectiles via atmospheric flight to final impact point. The projectile is assumed to be both rigid (non-flexible), and rotationally symmetric about its spin axis launched at low and high pitch angles. The projectile maneuvering motion depends on the most significant force and moment variations in addition to gravity and Magnus Effect. The computational flight analysis takes into consideration the Mach number and total angle of attack effects by means of the variable aerodynamic coefficients. For the purposes of the present work, linear interpolation has been applied from the tabulated database of McCoy's book. The aforementioned variable flight model is compared with a trajectory atmospheric motion based on appropriate constant mean values of the aerodynamic projectile coefficients. Static stability, also called gyroscopic stability, is examined as a necessary condition for stable flight motion in order to locate the initial spinning projectile rotation. Static stability examination takes into account the overturning moment variations with Mach number flight motion. The developed method gives satisfactory results compared with published data of verified experiments and computational codes on atmospheric dynamics model analysis.

Gkritzapis, Dimitrios N.; Panagiotopoulos, Elias E.; Margaris, Dionissios P.; Papanikas, Dimitrios G.

2007-12-01

277

Climate stability and sensitivity in some simple conceptual models  

NASA Astrophysics Data System (ADS)

A theoretical investigation of climate stability and sensitivity is carried out using three simple linearized models based on the top-of-the-atmosphere energy budget. The simplest is the zero-dimensional model (ZDM) commonly used as a conceptual basis for climate sensitivity and feedback studies. The others are two-zone models with tropics and extratropics of equal area; in the first of these (Model A), the dynamical heat transport (DHT) between the zones is implicit, in the second (Model B) it is explicitly parameterized. It is found that the stability and sensitivity properties of the ZDM and Model A are very similar, both depending only on the global-mean radiative response coefficient and the global-mean forcing. The corresponding properties of Model B are more complex, depending asymmetrically on the separate tropical and extratropical values of these quantities, as well as on the DHT coefficient. Adopting Model B as a benchmark, conditions are found under which the validity of the ZDM and Model A as climate sensitivity models holds. It is shown that parameter ranges of physical interest exist for which such validity may not hold. The 2 × CO2 sensitivities of the simple models are studied and compared. Possible implications of the results for sensitivities derived from GCMs and palaeoclimate data are suggested. Sensitivities for more general scenarios that include negative forcing in the tropics (due to aerosols, inadvertent or geoengineered) are also studied. Some unexpected outcomes are found in this case. These include the possibility of a negative global-mean temperature response to a positive global-mean forcing, and vice versa.

Bates, J. Ray

2012-02-01

278

The CMS Analysis Model  

NASA Astrophysics Data System (ADS)

We review the options for performing user analyses at CMS. In this text we put the CMS physics analysis software framework and other tools in the context of a bigger picture of performing data analysis. The flow of physics data through layers of skimming is briefly described, and the user options for analyzing objects on local computing resources or laptop discussed in turn. We present the first experiences with this model obtained after the recent start of the LHC physics programme.

Hegner, Benedikt

2011-12-01

279

ATLAS analysis model  

NASA Astrophysics Data System (ADS)

As we near the collection of the first data from the Large Hadron Collider, the ATLAS collaboration is preparing the software and computing infrastructure to allow quick analysis of the first data and support of the long-term steady-state ATLAS physics program. As part of this effort considerable attention has been paid to the 'Analysis Model', a vision of the interplay of the software design, computing constraints, and various physics requirements. An important input to this activity has been the experience of Tevatron and B-Factory experiments, one topic which was explored and discussed in the ATLAS October 2006 Analysis Model workshop. Recently, much of the Analysis Model has focused on ensuring the ATLAS software framework supports the required manipulations of event data; the event data design and content is consistent with foreseen calibration and physics analysis tasks; the event data is optimized in size, access speed, and is accessible both inside and outside the software framework; and that the analysis software may be developed collaboratively.

Farbin, A.

2008-07-01

280

Power system transient stability indexes for on-line analysis of ''worst-case'' dynamic contingencies  

SciTech Connect

The need for on-line analysis of power systems stability vis-a-vis postulated disturbances is felt more than ever before in modern energy control centers. The lack of a general practically implementable analytical method, makes it necessary to consider special classes of contingencies each with its own particular a prior characterization amenable to on-line analysis. In this paper a particular class of disturbances, namely faults near generator terminals, are considered; these are regarded to be ''worst-case'' conditions. The effects of breaker operation and the load model are taken into account. Two stability indexes are defined depending on the load model. Their computation for individual faults involves evaluation of straightforward algebraic expressions and is thus extremely fast. Simulation results are presented which demonstrate the discrimination capability of the indexes and the validity of the overall approach.

Rahimi, A.; Schaffer, G.

1986-01-01

281

Stability and stabilization for models of chemostats with multiple limiting substrates.  

PubMed

We study chemostat models in which multiple species compete for two or more limiting nutrients. First, we consider the case where the nutrient flow and species removal rates and input nutrient concentrations are all given as positive constants. In that case, we use Brouwer degree theory to give conditions guaranteeing that the models admit globally asymptotically stable componentwise positive equilibrium points, from all componentwise positive initial states. Then we use the results to develop stabilization theory for a class of controlled chemostats with two or more limiting nutrients. For cases where the dilution rate and input nutrient concentrations can be selected as controls, we prove that many different componentwise positive equilibria can be made globally asymptotically stable. This extends the existing control results for chemostats with one limiting nutrient. We demonstrate our methods in simulations. PMID:22873608

Mazenc, Frédéric; Malisoff, Michael

2012-01-01

282

Stability Analysis of Rock Slopes Against Block-Flexure Toppling Failure  

NASA Astrophysics Data System (ADS)

Block-flexure is the most common type of toppling failure in rock slopes. In this case, some rock blocks fail due to tensile bending stresses and some overturn under their own weights. In this paper, first, a literature review of toppling failures is summarized. Then, a theoretical model is proposed for rock slopes with a potential for block-flexure toppling instability. Next, a new analytical approach is presented for the stability analysis of such slopes. Finally, a special computer code is developed for a quick stability assessment of the failures based on the proposed method. This code receives the rock slope parameters from the user as the input data and predicts its stability, along with the corresponding factor of safety against the failure, as the output. In addition, two case studies are used for practical verification of the proposed approach and the corresponding computer code as well.

Amini, Mehdi; Majdi, Abbas; Veshadi, Mohammad Amin

2012-07-01

283

Stability analysis and controller design in microbial continuous culture with discrete time delay.  

PubMed

In this paper, stability analysis and controller design in microbial continuous culture with discrete time delay are studied. The dissimilation process of glycerol to 1,3-propanediol cannot avoid the disturbances caused by time delay. Time delay can limit and degrade the achievable performance of controlled systems, and even induce instability. Based on the biodynamic model, some properties of its solutions are discussed. In addition, we investigate how the time-delay affects the stability of the system. A linear matrix inequalities method is applied to find a feedback controller to ensure the stability of the closed-loop system. The simulation results indicate that this controller might be feasible for continuous bioprocess control. PMID:23586672

Zhu, Xi; Gao, Jinggui; Feng, Enmin; Xiu, Zhilong; Jin, Sheng

2013-07-01

284

Stability analysis of a delayed Hopfield neural network  

NASA Astrophysics Data System (ADS)

In this paper, we study a class of neural networks, which includes bidirectional associative memory networks and cellular neural networks as its special cases. By Brouwer’s fixed point theorem, a continuation theorem based on Gains and Mawhin’s coincidence degree, matrix theory, and inequality analysis, we not only obtain some different sufficient conditions ensuring the existence, uniqueness, and global exponential stability of the equilibrium but also estimate the exponentially convergent rate. Our results are less restrictive than previously known criteria and can be applied to neural networks with a broad range of activation functions assuming neither differentiability nor strict monotonicity.

Guo, Shangjiang; Huang, Lihong

2003-06-01

285

Stability analysis of a delayed Hopfield neural network.  

PubMed

In this paper, we study a class of neural networks, which includes bidirectional associative memory networks and cellular neural networks as its special cases. By Brouwer's fixed point theorem, a continuation theorem based on Gains and Mawhin's coincidence degree, matrix theory, and inequality analysis, we not only obtain some different sufficient conditions ensuring the existence, uniqueness, and global exponential stability of the equilibrium but also estimate the exponentially convergent rate. Our results are less restrictive than previously known criteria and can be applied to neural networks with a broad range of activation functions assuming neither differentiability nor strict monotonicity. PMID:16241256

Guo, Shangjiang; Huang, Lihong

2003-06-12

286

Averaging analysis approach for stability analysis of speed-sensorless induction motor drives with stator resistance estimation  

Microsoft Academic Search

In this paper, the stability property of speed-sensorless induction motor drives with stator resistance estimation is analyzed using the averaging analysis technique. Explicit stability conditions are then derived to clarify analytically when the instability may occur and how the regressor vectors used in the estimation and the integral adaptation gains should be designed to assure stability. The derived stability conditions

Mongkol Saejia; Somboon Sangwongwanich

2006-01-01

287

Quantum Magnetism Analysis Model  

NSDL National Science Digital Library

The Quantum Magnetism Analysis Model was created to help students as well as researchers who are studying magnetism. It provides a very simple interface for defining (theoretical) quantum spin models; sliders are automatically created to vary the parameters in the models; and several plots are automatically created to visualize the results. Within the program, several measured (experimental) data sets are included for a variety of real molecules. These provide the opportunity to experience the modeling process by varying the parameters in the model and exploring how the simulated results compare to the measured data. The interactions between neighboring quantum magnetic moments ("spins") are modeled using the Heisenberg model; calculations are carried out by numerically diagonalizing the matrix representation of the Heisenberg Hamiltonian; and plots display the energy spectrum, magnetization, and magnetic susceptibility as a function of temperature and magnetic field. This simulation is a "Fully Integrated Tool for Magnetic Analysis in Research & Teaching," so we also refer to it with the acronym "FIT-MART". FIT-MART was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking ejs_fitmart.jar file will run the package if Java is installed. In future versions of this simulation, curricular materials will be included to help students to learn about magnetism, and automated fitting routines will be included to help researchers quickly and easily model experimental data. FIT-MART was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking ejs_fitmart.jar file will run the package if Java is installed.

Engelhardt, Larry; Garland, Chad; Rainey, Cameron; Freeman, Austin

2012-07-27

288

Qualitative analysis of the stability of a continuous vermicomposting system.  

PubMed

A mathematical model was established to describe ecological relationships in a continuous vermicomposting system. The distributions of organic matter, microbes and earthworms on non-dimensional specific growth rates were simulated. The range of specific growth rates were visualized utilizing three-dimensional reconstruction technology. The stability of a vermicomposting system was not influenced by the initial concentrations of microbes and earthworms, only their species. The coordinates of the stable point depended on the dilution rate and initial amount of organic matter. The method described could be help for establishing a stable continuous vermicomposting system. PMID:23127841

Hu, Enzhu; Liu, Hong

2012-10-10

289

Validation of IVA Computer Code for Flow Boiling Stability Analysis  

SciTech Connect

IVA is a computer code for modeling of transient multiphase, multi-component, non-equilibrium flows in arbitrary geometry including flow boiling in 3D nuclear reactors. This work presents part of the verification procedure of the code. We analyze the stability of flow boiling in natural circulation loop. Experimental results collected on the AREVA/FANP KATHY loop regarding frequencies, mass flows and decay ratio of the oscillations are used for comparison. The comparison demonstrates the capability of the code to successfully simulate such class of processes. (author)

Ivanov Kolev, Nikolay [Framatome-ANP, PO Box 3220, D-91058, Erlangen (Germany)

2006-07-01

290

Analytical modelling of resistive wall mode stabilization by rotation in toroidal tokamak plasmas  

NASA Astrophysics Data System (ADS)

Stabilization of the resitive wall mode (RWM) may allow fusion power to be doubled for a given magnetic field in advanced tokamak operation. Experimental evidence from DIII-D and other machines suggests that plasma rotation can stabilize the RWM. Several authors (Finn 1995 Phys. Plasmas 2 3782, Bondeson and Xie 1997 Phys. Plasmas 4 2081) have constructed analytical cylindrical models for the RWM, but these do not deal with toroidal effects. The framework of Connor et al (1988 Phys. Fluids 31 577) is used to develop ideal plasma analytic models with toroidicity included. Stepped pressure profiles and careful ordering of terms are used to simplify the analysis. First, a current driven kink mode model is developed and a dispersion relation for arbitrary current profile is calculated. Second, the external pressure driven kink mode is similarly investigated as the most important RWM arises from this mode. Using this latter model it is found that the RWM is stabilized by Alfvén continuum damping with rotation levels similar to those seen in experiments. An expression for the stability of the external kink mode for more general current profiles and a resistive wall is derived in the appendix.

Ham, C. J.; Gimblett, C. G.; Hastie, R. J.

2011-02-01

291

Local stability analysis of spatially homogeneous solutions of multi-patch systems.  

PubMed

Multi-patch systems, in which several species interact in patches connected by dispersal, offer a general framework for the description and analysis of spatial ecological systems. This paper describes how to analyse the local stability of spatially homogeneous solutions in such systems. The spatial arrangement of the patches and their coupling is described by a matrix. For a local stability analysis of spatially homogeneous solutions it turns out to be sufficient to know the eigenvalues of this matrix. This is shown for both continuous and discrete time systems. A bookkeeping scheme is presented that facilitates stability analyses by reducing the analysis of a k-species, n-patch system to that of n uncoupled k-dimensional single-patch systems. This is demonstrated in a worked example for a chain of patches. In two applications the method is then used to analyse the stability of the equilibrium of a predator-prey system with a pool of dispersers and of the periodic solutions of the spatial Lotka-Volterra model. PMID:11072757

Jansen, V A; Lloyd, A L

2000-09-01

292

Analysis and assessment of STATCOM-based damping stabilizers for power system stability enhancement  

Microsoft Academic Search

Power system stability enhancement via STATCOM-based stabilizers is thoroughly investigated in this paper. This study presents a singular value decomposition (SVD)-based approach to assess and measure the controllability of the poorly damped electromechanical modes by STATCOM different control channels. The coordination among the proposed damping stabilizers and the STATCOM internal ac and dc voltage controllers has been taken into consideration.

M. A. Abido

2005-01-01

293

Models of cuspy triaxial stellar systems - I. Stability and chaoticity  

NASA Astrophysics Data System (ADS)

We used the N-body code of Hernquist & Ostriker to build a dozen cuspy (?? 1) triaxial models of stellar systems through dissipationless collapses of initially spherical distributions of 106 particles. We chose four sets of initial conditions that resulted in models morphologically resembling E2, E3, E4 and E5 galaxies, respectively. Within each set, three different seed numbers were selected for the random number generator used to create the initial conditions, so that the three models of each set are statistically equivalent. We checked the stability of our models using the values of their central densities and of their moments of inertia, which turned out to be very constant indeed. The changes of those values were all less than 3 per cent over one Hubble time and, moreover, we show that the most likely cause of those changes are relaxation effects in the numerical code. We computed the six Lyapunov exponents of nearly 5000 orbits in each model in order to recognize regular, partially and fully chaotic orbits. All the models turned out to be highly chaotic, with less than 25 per cent of their orbits being regular. We conclude that it is quite possible to obtain cuspy triaxial stellar models that contain large fractions of chaotic orbits and are highly stable. The difficulty in building such models with the method of Schwarzschild should be attributed to the method itself and not to physical causes.

Zorzi, A. F.; Muzzio, J. C.

2012-06-01

294

Stability of model flocks in turbulent-like flow  

NASA Astrophysics Data System (ADS)

We report numerical simulations of a simple model of flocking particles in the presence of an uncertain background environment. We consider two types of environmental perturbations: random noise applied separately to each particle, and spatiotemporally correlated ‘noise’ provided by a turbulent-like flow field. The effects of these two types of noise are very different; surprisingly, the applied flow field tends to destroy the global order of the flocking model even for vanishingly small flow amplitudes. Local order, however, is preserved in smaller sub-flocks, although their composition changes dynamically. Our results suggest that realistic perturbations must be considered in assessing the stability of models of collective animal behavior, and that random noise is not a sufficient proxy.

Khurana, Nidhi; Ouellette, Nicholas T.

2013-09-01

295

Stability analysis and thermal motion of optically trapped nanowires.  

PubMed

We investigate the stability and thermal motion of optically trapped nanowires, with aspect ratios in the range 10-100. A simple analytical model is used to determine qualitative features of the system, assuming that the nanowire is weakly scattering and the incident beam is paraxial. As expected, the model predicts that the nanowire will align with the beam axis. In this configuration the translational stiffness coefficients of the trap approach their limiting values for long nanowires like O(L(-3)), where L is the nanowire length, the limit for the stiffness parallel to the beam axis being zero. The rotational stiffness coefficients vary more slowly, according to O(L(-1)). Also, it is predicted that defocusing decreases the translational stiffness perpendicular to the beam, while increasing rotational stiffness. These findings are reinforced by comparison with rigorous electromagnetic calculations which additionally reveal the effects of radiation pressure and finite scattering. A strong polarization effect is observed in the numerical simulations and coupled translational and rotational motions arise which influence the trap stability. The use of nanowire traps for force sensing is discusse. PMID:22543265

Simpson, S H; Hanna, S

2012-04-30

296

Structure and stability of quasicrystals: Modulated tiling models  

NASA Astrophysics Data System (ADS)

A modulated tiling model for the structure of an icosahedral quasicrystal of the Al-Zn-Mg class is proposed. Idealized structure models for quasicrystals are constructed on the basis of three-dimensional Penrose tilings with a Henley-Elser decoration of the basic structural units. The stability of these structures is investigated by an isothermal molecular-dynamics annealing of a hierarchy of crystalline approximants to the quasiperiodic structure, based on realistic pair forces derived from pseudopotential theory. We find that quasicrystals are stable only at compositions leading to an electron-per-atom ratio of e/A~=2.1-2.2, thus confirming the existence of a Hume-Rothery or Peierls mechanism for the stability of quasicrystals. Because of the large number of different atomic environments in quasicrystals, any set of interatomic forces leads to a displacive modulation of the idealized quasiperiodic structure. For a stable quasicrystal, the displacement field has the symmetry of the quasilattice. The structural characteristics of the displacively modulated Penrose tilings are investigated in detail. We show that the modulation of the structure substantially improves the agreement of the models with experimental observation.

Kraj?í, M.; Hafner, J.

1992-11-01

297

A minimal model for stabilization of biomolecules by hydrocarbon cross-linking  

NASA Astrophysics Data System (ADS)

Programmed cell death regulating protein motifs play an essential role in the development of an organism, its immune response, and disease-related cellular mechanisms. Among those motifs the BH3 domain of the BCL-2 family is found to be of crucial importance. Recent experiments showed how the isolated, otherwise unstructured BH3 peptide can be modified by a hydrocarbon linkage to regain function. We parametrized a reduced, dynamic model for the stability effects of such covalent cross-linking and confirmed that the model reproduces the reinforcement of the structural stability of the BH3 motif by cross-linking. We show that an analytically solvable model for thermostability around the native state is not capable of reproducing the stabilization effect. This points to the crucial importance of the peptide dynamics and the fluctuations neglected in the analytic model for the cross-linking system to function properly. This conclusion is supported by a thorough analysis of a simulated Go model. The resulting model is suitable for rational design of generic cross-linking systems in silicio.

Hamacher, K.; Hübsch, A.; McCammon, J. A.

2006-04-01

298

A minimal model for stabilization of biomolecules by hydrocarbon cross-linking.  

PubMed

Programmed cell death regulating protein motifs play an essential role in the development of an organism, its immune response, and disease-related cellular mechanisms. Among those motifs the BH3 domain of the BCL-2 family is found to be of crucial importance. Recent experiments showed how the isolated, otherwise unstructured BH3 peptide can be modified by a hydrocarbon linkage to regain function. We parametrized a reduced, dynamic model for the stability effects of such covalent cross-linking and confirmed that the model reproduces the reinforcement of the structural stability of the BH3 motif by cross-linking. We show that an analytically solvable model for thermostability around the native state is not capable of reproducing the stabilization effect. This points to the crucial importance of the peptide dynamics and the fluctuations neglected in the analytic model for the cross-linking system to function properly. This conclusion is supported by a thorough analysis of a simulated Go model. The resulting model is suitable for rational design of generic cross-linking systems in silicio. PMID:16674170

Hamacher, K; Hübsch, A; McCammon, J A

2006-04-28

299

Structural analysis of conditional models  

Microsoft Academic Search

Structural analysis is applied to exploit sparsity in the solving of a system of equations [Direct Methods for Sparse Matrices. Monographs on Numerical Analysis (1989)]. Zaher [Conditional modeling (1995)] studied the issues involved in the structural analysis of conditional models and presented a methodology to ensure consistency in a conditional model, the complexity of such an analysis being combinatorial. In

V Rico-Ramirez; A. W Westerberg

2002-01-01

300

Extensions to the time lag models for practical application to rocket engine stability design  

NASA Astrophysics Data System (ADS)

The combustion instability problem in liquid-propellant rocket engines (LREs) has remained a tremendous challenge since their discovery in the 1930s. Improvements are usually made in solving the combustion instability problem primarily using computational fluid dynamics (CFD) and also by testing demonstrator engines. Another approach is to use analytical models. Analytical models can be used such that design, redesign, or improvement of an engine system is feasible in a relatively short period of time. Improvements to the analytical models can greatly aid in design efforts. A thorough literature review is first conducted on liquid-propellant rocket engine (LRE) throttling. Throttling is usually studied in terms of vehicle descent or ballistic missile control however there are many other cases where throttling is important. It was found that combustion instabilities are one of a few major issues that occur during deep throttling (other major issues are heat transfer concerns, performance loss, and pump dynamics). In the past and again recently, gas injected into liquid propellants has shown to be a viable solution to throttle engines and to eliminate some forms of combustion instability. This review uncovered a clever solution that was used to eliminate a chug instability in the Common Extensible Cryogenic Engine (CECE), a modified RL10 engine. A separate review was also conducted on classic time lag combustion instability models. Several new stability models are developed by incorporating important features to the classic and contemporary models, which are commonly used in the aerospace rocket industry. The first two models are extensions of the original Crocco and Cheng concentrated combustion model with feed system contributions. A third new model is an extension to the Wenzel and Szuch double-time lag model also with feed system contributions. The first new model incorporates the appropriate injector acoustic boundary condition which is neglected in contemporary models. This new feature shows that the injector boundary can play a significant role for combustion stability, especially for gaseous injection systems or a system with an injector orifice on the order of the size of the chamber. The second new model additionally accounts for resistive effects. Advanced signal analysis techniques are used to extract frequency-dependent damping from a gas generator component data set. The damping values are then used in the new stability model to more accurately represent the chamber response of the component. The results show a more realistic representation of stability margin by incorporating the appropriate damping effects into the chamber response from data. The original Crocco model, a contemporary model, and the two new models are all compared and contrasted to a marginally stable test case showing their applicability. The model that incorporates resistive aspects shows the best comparison to the test data. Parametrics are also examined to show the influence of the new features and their applicability. The new features allow a more accurate representation of stability margin to be obtained. The third new model is an extension to the Wenzel and Szuch double-time lag chug model. The feed system chug model is extended to account for generic propellant flow rates. This model is also extended to incorporate aspects due to oxygen boiling and helium injection in the feed system. The solutions to the classic models, for the single-time lag and the double-time lag models, are often plotted on a practical engine operating map, however the models have presented some difficulties for numerical algorithms for several reasons. Closed-form solutions for use on these practical operating maps are formulated and developed. These models are incorporated in a graphical user interface tool and the new model is compared to an extensive data set. It correctly predicts the stability behavior at various operating conditions incorporating the influence of injected helium and boiling oxygen in the feed system.

Casiano, Matthew J.

301

Nonlinear Speed Control Scheme and Its Stability Analysis for SI Engines  

NASA Astrophysics Data System (ADS)

For international combustion engines, due to the combustion cyclic nature, the intake-to-power stroke delay is inherent that causes additional difficulties in control design and validation phases. In this paper, a nonlinear speed control scheme is proposed based on the proportional feedback control method. From the consideration of improving the transient performance, a reference model is introduced to design the feedback controller. Then, the speed controller is formulated as a designed feedback control law connecting with a model-based feedforward compensation. The asymptotic convergence to the desired speed is guaranteed under the presented conditions of the feedback gains, which include the cases of using a speed-depended gain function and a constant gain, respectively. For the stability analysis of the proposed delayed control system, an initial method is presented via Lyapunov-Krasovskii functional stability theorem. Experimental results on the transition speed control are shown to demonstrate the control scheme.

Zhang, Jiangyan; Shen, Tielong; Marino, Riccardo

302

Linear stability analysis for travelling waves of second order in time PDE's  

NASA Astrophysics Data System (ADS)

We study travelling waves ?c of second order in time PDE's u_{tt}+{ L} u+N(u)=0 . The linear stability analysis for these models is reduced to the question of the stability of quadratic pencils in the form \\lambda^2Id+2c\\lambda \\partial_x+{ H}_c , where { H}_c=c^2 \\partial_{xx}+{ L}+N'(\\varphi_c) . If { H}_c is a self-adjoint operator, with a simple negative eigenvalue and a simple eigenvalue at zero, then we completely characterize the linear stability of ?c. More precisely, we introduce an explicitly computable index \\omega^*({ H}_c)\\in (0, \\infty] , so that the wave ?c is stable if and only if |c|\\geq \\omega^*({ H}_c) . The results are applicable both in the periodic case and in the whole line case. The method of proof involves a delicate analysis of a function { G} , associated with { H} , whose positive zeros are exactly the positive (unstable) eigenvalues of the pencil \\lambda^2Id+2c\\lambda \\partial_x+{ H} . We would like to emphasize that the function { G} is not the Evans function for the problem, but rather a new object that we define herein, which fits the situation rather well. As an application, we consider three classical models—the ‘good’ Boussinesq equation, the Klein-Gordon-Zakharov (KGZ) system and the fourth order beam equation. In the whole line case, for the Boussinesq case and the KGZ system (and as a direct application of the main results), we compute explicitly the set of speeds which give rise to linearly stable travelling waves (and for all powers of p in the case of Boussinesq). This result is new for the KGZ system, while it generalizes the results of Alexander et al (2012, personal communication) and Alexander and Sachs (1995 Nonlinear World 2 471-507), which apply to the case p = 2. For the beam equation, we provide an implicit formula (depending only on the function \\|\\varphi_c'\\|_{L^2}) , which works for all p and for both the periodic and the whole line cases. Our results complement (and exactly match, whenever they exist) the results of a long line of investigation regarding the related notion of orbital stability of the same waves. Informally, we have found that in all the examples that we have looked at, our theory applies, whenever the Grillakis-Shatah-Strauss (GSS) theory applies. We believe that the results in this paper (or a variation thereof) will enable the linear stability analysis as well as asymptotic stability analysis for most models in the form u_{tt}+{ L} u+N(u)=0 .

Stanislavova, Milena; Stefanov, Atanas

2012-09-01

303

Tool for bonded optical element thermal stability analysis  

NASA Astrophysics Data System (ADS)

An analytical tool is presented which supports the opto-mechanical design of bonded optical elements. Given the mounting requirements from the optical engineer, the alignment stability and optical stresses in bonded optics can be optimized for the adhesive and housing material properties. While a perfectly athermalized mount is desirable, it is not realistic. The tool permits evaluation of element stability and stress over the expected thermal range at nominal, or worst case, achievable assembly and manufacturing tolerances. Selection of the most appropriate mount configuration and materials, which maintain the optical engineer's design, is then possible. The tool is based on a stress-strain analysis using Hooke's Law in the worst case plane through the optic centerline. The optimal bond line is determined for the selected adhesive, housing and given optic materials using the basic athermalization equation. Since a mounting solution is expected to be driven close to an athermalized design, the stress variations are considered linearly related to strain. A review of the equation set, the tool input and output capabilities and formats and an example will be discussed.

Klotz, Gregory L.

2011-09-01

304

Stability analysis of implicit time discretizations for the Compton-scattering Fokker-Planck equation  

SciTech Connect

The Fokker-Planck equation is a widely used approximation for modeling the Compton scattering of photons in high energy density applications. In this paper, we perform a stability analysis of three implicit time discretizations for the Compton-Scattering Fokker-Planck equation. Specifically, we examine (i) a Semi-Implicit (SI) scheme that employs backward-Euler differencing but evaluates temperature-dependent coefficients at their beginning-of-time-step values, (ii) a Fully Implicit (FI) discretization that instead evaluates temperature-dependent coefficients at their end-of-time-step values, and (iii) a Linearized Implicit (LI) scheme, which is developed by linearizing the temperature dependence of the FI discretization within each time step. Our stability analysis shows that the FI and LI schemes are unconditionally stable and cannot generate oscillatory solutions regardless of time-step size, whereas the SI discretization can suffer from instabilities and nonphysical oscillations for sufficiently large time steps. With the results of this analysis, we present time-step limits for the SI scheme that prevent undesirable behavior. We test the validity of our stability analysis and time-step limits with a set of numerical examples.

Densmore, Jeffery D [Los Alamos National Laboratory; Warsa, James S [Los Alamos National Laboratory; Lowrie, Robert B [Los Alamos National Laboratory; Morel, Jim E [TEXAS A& M UNIV

2008-01-01

305

Stability of Pile Groups.  

National Technical Information Service (NTIS)

Current research focuses on advancing the existing capabilities for stability analysis of pile foundations. To this end, researchers developed a continuum model and a structural model. In the continuum model, three-dimensional solid finite elements and ma...

Z. Zhao H. K. Stolarski

1999-01-01

306

On Fixed-Speed WT Generator Modeling for Rotor Speed Stability Studies  

Microsoft Academic Search

This paper analyzes fixed-speed induction generator modeling oriented to rotor speed stability studies. The single- and double-cage models are compared. The effects of symmetrical voltage sags on generator behavior are studied in detail. The rotor speed stability of the turbine is also examined and rotor speed recovery time is proposed as an indicator of system stability. Significant differences in the

J. Pedra; F. Corcoles; Ll. Monjo; S. Bogarra; A. Rolan

2012-01-01

307

On the stability of a soft-wall model  

SciTech Connect

We investigate the stability and fluctuations of a soft-wall model that has an asymptotically anti-de Sitter metric and a scalar field that has an asymptotically power-law dependence in the conformal coordinate. By imposing UV boundary conditions, the soft-wall mass scale can be fixed to be near the TeV scale and causes the radion to no longer be massless. A hierarchy between the weak scale and the Planck scale can be generated for various particle spectrum behavior, although natural values only occur for a gravitational sector containing scalar fields that act like unparticles. In addition, if bulk standard model fields have nonstandard couplings to the gravitational sector, then a discrete particle spectrum can be realized in the nongravitational sector. This allows for the possibility of an unparticle solution to the hierarchy problem.

Gherghetta, T.; Setzer, N. [School of Physics, University of Melbourne, Victoria, 3010 (Australia)

2010-10-01

308

A coupled distributed hydrological-stability analysis on a terraced slope of Valtellina (northern Italy)  

NASA Astrophysics Data System (ADS)

The aim of this work was to understand and reproduce the hydrological dynamics of a slope, which was terraced using dry-stone retaining walls and its response to these processes in terms of stability at the slope scale. The slope studied is located in Valtellina (northern Italy), near the village of Tresenda, and in the last 30 yr has experienced several soil slip/debris flow events. In 1983 alone, such events caused the death of 18 people. Direct observation of the events of 1983 enabled the principal triggering cause of these events to be recognized in the formation of an overpressure at the base of a dry-stone wall, which caused its failure. To perform the analyses it is necessary to include the presence of dry-stone walls, considering the importance they have in influencing hydrological and geotechnical processes at the slope scale. This requires a very high resolution DEM (1 m × 1 m because the walls are from 0.60 m to 1.0 m wide) that has been appositely derived. A hydrogeological raster-based model, which takes into account both the unsaturated and saturated flux components, was applied. This was able to identify preferential infiltration zones and was rather precise in the prediction of maximum groundwater levels, providing valid input for the distributed stability analysis. Results of the hydrogeological model were used for the successive stability analysis. Sections of terrace were identified from the downslope base of a retaining wall to the top of the next downslope retaining wall. Within each section a global method of equilibrium was applied to determine its safety factor. The stability model showed a general tendency to overestimate the amount of unstable areas. An investigation of the causes of this unexpected behavior was, therefore, also performed in order to progressively improve the reliability of the model.

Camera, C.; Apuani, T.; Masetti, M.

2013-02-01

309

Thermodynamic analysis of alcohol effect on thermal stability of proteins.  

PubMed

Thermal unfolding of ribonuclease A and ?-chymotrypsinogen A was analyzed in various alcohol solutions of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, trifluoroethanol, and glycerol. The change in thermal unfolding ratio with temperature was described well by the van't Hoff equation and the melting temperature and the enthalpy of protein unfolding were obtained. The reciprocal form of the Wyman-Tanford equation, which describes the unfolded-to-folded protein ratio as a function of water activity, was applied to obtain a linear plot. From the slope of this plot and water activity, the stabilization free energy (??G) in a solution was calculated. This shows an important role of water activity in protein stability. ??G was linearly dependent on alcohol concentration and m-values of alcohols for protein unfolding were obtained. This provides a theoretical basis for the linear extrapolation model (LEM). The m-values for alcohols were negative except for glycerol. The negative higher m-value for longer and linear chain alcohols suggested the important role of the disturbance of hydrophobic interactions as well as the hydrogen-bonding in the mechanism of protein destabilization by alcohols. The number of change in bound-alcohol molecules upon protein unfolding was also obtained. PMID:20947421

Miyawaki, Osato; Tatsuno, Michiko

2010-10-13

310

Magnetic Reconstruction and Stability Analysis of PEGASUS Plasmas  

NASA Astrophysics Data System (ADS)

Reconstruction of the magnetic equilibrium for recent discharges in Pegasus are obtained with a locally developed code. This code employs a nonlinear least-squares fitting routine combined with a Grad-Shafranov solver, and has been compared to TokaMak and EFIT analyses. A newly installed, comprehensive set of equilibrium magnetics diagnostics, including a poloidal array of 20 magnetic pick-up coils, 20 poloidal flux loops on the outboard, 6 center stack flux loops, a Rogowski coil for the toroidal plasma current, and a diamagnetic loop are used as constraints. Typical plasmas exhibit broad/flat central q(R) profiles with q(0)< = 2 corresponding to the onset of a large 2/1 mode. The ideal stability limits in q(a) and beta to be expected for Pegasus are under study using the DCON code applied to model equilibria. Plasmas with high edge current gradients are unstable to edge kink modes as expected; a constraint on the edge current gradients was implemented to access more realistic plasmas. A systematic mapping of stability space (e.g. li vs q(0), li vs q(98), etc.) is in progress.

Diem, S. J.; Fonck, R. J.; Garstka, G. D.; Sontag, A. C.; Tritz, K. L.

2001-10-01

311

Effect of detailed power system models in traditional and voltage-stability-constrained optimal power-flow problems  

Microsoft Academic Search

In this paper, detailed generator, exponential load, and static volt-ampere-reactive (VAr) compensator models are incorporated into traditional and voltage-stability-constrained optimal power-flow problems to study the effect that the different models have on costs and system-loadability. The proposed models are compared to typical models by means of a detailed analysis of the results obtained for two IEEE test systems; interior point

William D. Rosehart; Claudio A. Cañizares; Victor H. Quintana

2003-01-01

312

Quantitative analysis of the ion-dependent folding stability of DNA triplexes  

NASA Astrophysics Data System (ADS)

A DNA triplex is formed through binding of a third strand to the major groove of a duplex. Due to the high charge density of a DNA triplex, metal ions are critical for its stability. We recently developed the tightly bound ion (TBI) model for ion-nucleic acids interactions. The model accounts for the potential correlation and fluctuations of the ion distribution. We now apply the TBI model to analyze the ion dependence of the thermodynamic stability for DNA triplexes. We focus on two experimentally studied systems: a 24-base DNA triplex and a pair of interacting 14-base triplexes. Our theoretical calculations for the number of bound ions indicate that the TBI model provides improved predictions for the number of bound ions than the classical Poisson-Boltzmann (PB) equation. The improvement is more significant for a triplex, which has a higher charge density than a duplex. This is possibly due to the higher ion concentration around the triplex and hence a stronger ion correlation effect for a triplex. In addition, our analysis for the free energy landscape for a pair of 14-mer triplexes immersed in an ionic solution shows that divalent ions could induce an attractive force between the triplexes. Furthermore, we investigate how the protonated cytosines in the triplexes affect the stability of the triplex helices.

Chen, Gengsheng; Chen, Shi-Jie

2011-12-01

313

Hydraulic modeling support for conflict analysis: The Manayunk canal revisited  

Microsoft Academic Search

This paper presents a study which used a standard, hydraulic computer model to generate detailed design information to support conflict analysis of a water resource use issue. As an extension of previous studies, the conflict analysis in this case included several scenarios for stability analysis - all of which reached the conclusion that compromising, shared access to the water resources

R. A. Chadderton; R. G. Traver; J. N. Rao

2009-01-01

314

Stability of the thermohaline circulation in a coupled ocean-atmosphere general circulation model.  

National Technical Information Service (NTIS)

The stability of the Atlantic thermohaline circulation against meltwater input is investigated in a coupled ocean-atmosphere general circulation model. We identify four main feedbacks affecting the stability of the thermohaline circulation: the change in ...

A. Schiller U. Mikolajewicz R. Voss

1996-01-01

315

Proton stability and light Z' inspired by string derived models  

SciTech Connect

Proton stability is one of the most perplexing puzzles in particle physics. While the renormalizable standard model forbids proton decay mediating operators due to accidental global symmetries, many of its extensions introduce such dimension four, five and six operators. Furthermore, it is, in general, expected that quantum gravity only respects local gauge, or discreet, symmetries. String theory provides the arena to study particle physics in a consistent framework of perturbative quantum gravity. An appealing proposition, in this context, is that the dangerous operators are suppressed by an Abelian gauge symmetry, which is broken near the TeV scale. A viable U(1) symmetry should also be anomaly free, be family universal, and allow the generation of fermion masses via the Higgs mechanism. We discuss such U(1) symmetries that arise in quasirealistic free fermionic heterotic-string derived models. Ensuring that the U(1) symmetry is anomaly free at the low scale requires that the standard model spectrum is augmented by additional states that are compatible with the charge assignments in the string models. We construct such string-inspired models and discuss some of their phenomenological implications.

Faraggi, Alon E.; Mehta, Viraf M. [Department of Mathematical Sciences, University of Liverpool, Liverpool, L69 7ZL (United Kingdom)

2011-10-15

316

Stability Switches in a Host-Pathogen Model as the Length of a Time Delay Increases  

NASA Astrophysics Data System (ADS)

The destabilising effects of a time delay in mathematical models are well known. However, delays are not necessarily destabilising. In this paper, we explore an example of a biological system where a time delay can be both stabilising and destabilising. This example is a host-pathogen model, incorporating density-dependent prophylaxis (DDP). DDP describes when individual hosts invest more in immunity when population densities are high, due to the increased risk of infection in crowded conditions. In this system, as the delay length increases, there are a finite number of switches between stable and unstable behaviour. These stability switches are demonstrated and characterised using a combination of numerical methods and analysis.

Reynolds, Jennifer J. H.; Sherratt, Jonathan A.; White, Andrew

2013-08-01

317

Stability of haematological parameters and its relevance on the athlete's biological passport model.  

PubMed

The stability of haematological parameters is crucial to guarantee accurate and reliable data for implementing and interpreting the athlete's biological passport (ABP). In this model, the values of haemoglobin, reticulocytes and out-of-doping period (OFF)-score (Hb-60?Ret) are used to monitor the possible variations of those parameters, and also to compare the thresholds developed by the statistical model for the single athlete on the basis of its personal values and the variance of parameters in the modal group. Nevertheless, a critical review of the current scientific literature dealing with the stability of the haematological parameters included in the ABP programme, and which are used for evaluating the probability of anomalies in the athlete's profile, is currently lacking. In addition, we collected information from published studies, in order to supply a useful, practical and updated review to sports physicians and haematologists. There are some parameters that are highly stable, such as haemoglobin and erythrocytes (red blood cells [RBCs]), whereas others, (e.g. reticulocytes, mean RBC volume and haematocrit) appear less stable. Regardless of the methodology, the stability of haematological parameters is improved by sample refrigeration. The stability of all parameters is highly affected from high storage temperatures, whereas the stability of RBCs and haematocrit is affected by initial freezing followed by refrigeration. Transport and rotation of tubes do not substantially influence any haematological parameter except for reticulocytes. In all the studies we reviewed that used Sysmex instrumentation, which is recommended for ABP measurements, stability was shown for 72 hours at 4 ° C for haemoglobin, RBCs and mean curpuscular haemoglobin concentration (MCHC); up to 48 hours for reticulocytes; and up to 24 hours for haematocrit. In one study, Sysmex instrumentation shows stability extended up to 72 hours at 4 ° C for all the parameters. There are significant differences among methods and instruments: Siemens Advia shows lower stability than Sysmex as regards to reticulocytes. However, the limit of 36 hours from blood collection to analysis as recommended by ABP scientists is reasonable to guarantee analytical quality, when samples are transported at 4 ° C and are accompanied by a certified steadiness of this temperature. There are some parameters that are highly stable, such as haemoglobin and RBCs; whereas others, such as reticulocytes, mean cell volume and haematocrit are more unstable. The stability of haematological parameters might be improved independently from the analytical methodology, by refrigeration of the specimens. PMID:22060177

Lombardi, Giovanni; Lanteri, Patrizia; Colombini, Alessandra; Lippi, Giuseppe; Banfi, Giuseppe

2011-12-01

318

Laboratory and modelling studies on the atmospheric stability of levoglucosan  

NASA Astrophysics Data System (ADS)

Aerosol particles are known to influence important atmospheric processes such as cloud formation and the solar radiation budget. Therefore, much effort is spend to characterise and locate the sources of atmospheric particles. Source apportionment studies using molecular tracer compounds are a common approach to distinguish between different sources. The anhydromonosaccharide levoglucosan (1,6-anhydro-?-D-glucopyranose) is an widely used and very specific tracer compound for particle emissions from natural and anthropogenic biomass combustion processes. Levoglucosan is formed in large quantities during the pyrolysis of cellulose at temperatures above 300° C. Even if levoglucosan is widely used in source apportionment studies only few studies investigated the atmospheric stability of this tracer compound so far. Furthermore, oxidation processes by free radicals in aqueous particles are not yet considered as a potential sink reaction for this highly water soluble compound. Therefore, detailed kinetic studies on the reactivity of levoglucosan towards three important atmospheric free radicals (OH, NO3 and SO4-) in aqueous solutions were performed for the first time using the laser flash photolysis technique. Laboratory studies on the stability of levoglucosan were done both in the presence and absence of other water soluble reaction partners. The results obtained in the different experiments will be presented, compared and discussed. Furthermore, the experimental data were implemented into the parcel model SPACCIM (Spectral Aerosol Cloud Chemistry Interaction Model; Wolke et al., 2005) in order to study the degradation fluxes of levoglucosan in cloud droplets and aqueous particles considering a detailed microphysics and multiphase chemistry. The model calculations, performed under different conditions (summer, winter, with cloud passages, without cloud passages, different relative humidity and iron contents), show that levoglucosan can be oxidised readily by OH radicals in the tropospheric aqueous phase. Mean degradation fluxes of about 7.2 ng m-3 h-1 in summer and 4.7 ng m-3 h-1 in winter were calculated. The detailed results of the model calculations will be presented and the influence of the different model scenarios on the calculated degradation fluxes discussed. Model calculations demonstrate that under certain atmospheric conditions the oxidation of levoglucosan can be as fast as that of other atmospherically relevant organic compounds and it may not be as stable as previously thought in the atmosphere particularly under high relative humidity conditions. References: Wolke, R.; Sehili, A. M.; Simmel, M.; Knoth, O.; Tilgner, A.; Herrmann, H. SPACCIM: A parcel model with detailed microphysics and complex multiphase chemistry. Atmos. Environ. 2005, 39, 4375-4388.

Tilgner, Andreas; Hoffmann, Dirk; Iinuma, Yoshiteru; Herrmann, Hartmut

2010-05-01

319

Stability Analysis for Variable Frequency Operation of Synchronous Machines  

Microsoft Academic Search

A stability study of a synchronous machine is performed by applying the Nyquist stability-criterion to the equations which describe the behavior of the machine during small displacements about a steady-state operating point. This investigation reveals that, in some cases, machine instability can occur at low operating speeds. Regions of machine stability are established from the results of a digital computer

THOMAS A. LIPO; PAUL C. KRAUSE

1968-01-01

320

Dynamical voltage stability analysis using Lyapunov function method  

Microsoft Academic Search

This paper presents a method to analyze small perturbation voltage stability for power systems with varying load by mean of a quadratic Lyapunov function. By using the quadratic Lyapunov function, the voltage stability is analyzed algebraically. In this paper, voltage stability proximity indices are also proposed. Numerical tests are carried out on a three-bus power system and a single machine

Abdul Halim; Kazuhiro Takahashi; Bahman Kermanshahi

1998-01-01

321

Stability analysis and synthesis algorithm of bidirectional associative memory  

Microsoft Academic Search

Investigates the qualitative properties of a class of bidirectional associative memories. Networks are described by a system of first order ordinary difference equations which are defined on a closed hypercube of the state space with solutions extended to the boundary of the hypercube. For the present model, a systematic analysis method is developed to completely characterize a given network, i.e.,

Gary G. Yen

1994-01-01

322

Blood coagulation dynamics: mathematical modeling and stability results.  

PubMed

The hemostatic system is a highly complex multicomponent biosystem that under normal physiologic conditions maintains the fluidity of blood. Coagulation is initiated in response to endothelial surface vascular injury or certain biochemical stimuli, by the exposure of plasma to Tissue Factor (TF), that activates platelets and the coagulation cascade, inducing clot formation, growth and lysis. In recent years considerable advances have contributed to understand this highly complex process and some mathematical and numerical models have been developed. However, mathematical models that are both rigorous and comprehensive in terms of meaningful experimental data, are not available yet. In this paper a mathematical model of coagulation and fibrinolysis in flowing blood that integrates biochemical, physiologic and rheological factors, is revisited. Three-dimensional numerical simulations are performed in an idealized stenosed blood vessel where clot formation and growth are initialized through appropriate boundary conditions on a prescribed region of the vessel wall. Stability results are obtained for a simplified version of the clot model in quiescent plasma, involving some of the most relevant enzymatic reactions that follow Michaelis-Menten kinetics, and having a continuum of equilibria. PMID:21631138

Sequeira, Adélia; Santos, Rafael F; Bodnár, Tomás

2011-04-01

323

Power Transmission Path Analysis of Voltage Stability in Shandong Power System  

Microsoft Academic Search

Voltage stability of Shandong power system is analyzed by power transmission path analysis. Weak buses are decided by local voltage stability index. Voltage stability indices of both active power transmission paths from the west to the east and local reactive power transmission paths are computed with load increasing. The reactive power reserve indicator is also calculated and key factors that

Liang Wang; Yutian Liu

2006-01-01

324

Deterministic and probabilistic analysis of static voltage stability in power systems  

Microsoft Academic Search

The mechanism of static voltage stability was examined by a visual explanation, in that way, the static voltage stability criterion was obtained. It was indicated that the static voltage stability is determined by both characteristics in generation side and characteristics in load side. Then each kind of two-dimensional plane analysis can be unified in three-dimensional space. It is pointed that

X. Hou; P. Ju

2009-01-01

325

Stability Analysis and Control of Repetitive Trajectory Systems in the State-Domain: Roller Coaster Application  

Microsoft Academic Search

This paper discusses the concepts of stability and asymptotic stability for state-dependent repetitive trajectory systems. An adaptive compensation method is proposed to compensate for disturbances that are a function of the system state. It will be shown that Lyapunov stability analysis can be performed in the state-domain if certain conditions are satisfied. The main theoretical contribution of the paper is

Hyo-Sung Ahn; Yang Quan Chen; Kevin L. Moore; Wonpil Yu

2007-01-01

326

Bifurcation analysis of parametrically excited bipolar disorder model  

NASA Astrophysics Data System (ADS)

Bipolar II disorder is characterized by alternating hypomanic and major depressive episode. We model the periodic mood variations of a bipolar II patient with a negatively damped harmonic oscillator. The medications administrated to the patient are modeled via a forcing function that is capable of stabilizing the mood variations and of varying their amplitude. We analyze analytically, using perturbation method, the amplitude and stability of limit cycles and check this analysis with numerical simulations.

Nana, Laurent

2009-02-01

327

Linear stability analysis and direct numerical simulation of a miscible two-fluid channel flow  

NASA Astrophysics Data System (ADS)

The temporal evolution of an initially laminar two-fluid channel flow is investigated using linear stability analysis and direct numerical simulation. The stability of a two-fluid shear flow is encountered in numerous situations, including water wave generation by wind, atomization of fuels, aircraft deicing and nuclear reactor cooling. The application of particular interest in this study is liquefying hybrid combustion, for which the two-fluid channel flow is used as a model problem to characterize the relevant mixing and entrainment mechanisms. The two fluids are miscible with dissimilar densities and viscosities. The thickness of one of the fluid layers is much smaller than that of the other, with the denser and more viscous fluid comprising the thin layer. Linear stability analysis is used to identify possibly unstable modes in the two-fluid configuration. The analysis is considered for two different situations. In one case, the fluid density and viscosity change discontinuously across a sharp interface, while in the other, the fluids are separated by a finite thickness transition layer, over which the fluid properties vary continuously. In the sharp interface limit, the linear stability is governed by an Orr-Sommerfeld equation in each fluid layer, coupled by boundary conditions at the interface. A numerical solution of the system of equations is performed using a Chebyshev spectral collocation method. In the case where the fluids are separated by a finite thickness transition zone, an Orr-Sommerfeld-type equation is solved with the compound matrix method. The non-linear stages of the flow evolution are investigated by direct numerical simulation. In a temporal simulation, two of the three spatial dimensions are periodic. Fourier spectral discretization is used in these dimensions, while a compact finite difference scheme is utilized in the non-periodic direction. The time advancement is performed by a projection method with a third order Adams-Bashforth-Moulton predictor-corrector scheme. Initial conditions for the DNS are supplied by the linear stability analysis. Linear stability analysis indicates that the thickness of the transition zone between the fluids has a significant impact on the amplification of the two least stable modes present in the two-fluid channel flow. Compared to the sharp interface limit, one of the modes is damped and the other one is either amplified or damped depending on the Reynolds number. Two dissimilar entrainment mechanisms are observed in the DNS calculations, corresponding to these two modes. One results in significantly more entrainment and mixing between the two fluids. This mechanism exhibits a greater degree of vorticity generation, particularly due to the baroclinic effect.

Haapanen, Siina Ilona

328

Mode switching and linear stability analysis of resonant acoustic flows  

NASA Astrophysics Data System (ADS)

Resonant acoustic flows occur in a wide variety of practical, aerospace-related applications and are a rich source of complex flow-physics. The primary concern associated with these types of flows is the high-amplitude fluctuating pressures associated with the resonant tones that could lead to sonic fatigue failure of sensitive components in the vicinity of such flows. However, before attempting to devise methods to suppress the resonant tones, it is imperative to understand the physics governing these flows in the hope that such an understanding will lead to more robust and effective suppression techniques. To this end, an in-depth study of various resonant acoustic flows was undertaken in this thesis, the main aim being to bring about a better understanding of such flows by revealing physically relevant information. Starting with the resonant acoustic mechanism in underexpanded jets from two-dimensional nozzles, it was shown that, for a variety of flow situations (geometries, shock-cell structures and orientations) in such jets, the nonlinear interaction density acted as a faithful precursor to a, hitherto unpredictable, spanwise instability mode switch. Following this, a study of the occurrence of, previously undocumented and theoretically unexpected, helical instabilities in subsonic impinging jets was undertaken. Using metrics from linear stability analysis, it was shown that the presence of the helical modes was justified. The results from this study on impinging jets are directly applicable to modern Stationary Take-Off and Vertical Landing (STOVL) aircraft that have twin, closely spaced exhausts. Finally, a novel technique that yielded dramatic suppression of resonant acoustic tones using high frequency excitation, in subsonic flows over open cavities, was investigated. Linear stability calculations of the experimentally measured baseline and excited velocity profiles showed that the instability of the high frequency excitation corresponded to a spatially decaying mode, which in turn lead to the resonance suppression associated with this mechanism. The experimental results showed good agreement with linear stability calculations for the measured mean velocity profiles. It is hoped that the work presented in this thesis will further the understanding of resonant acoustic flows and provide insights that can lead to better control techniques in the future.

Panickar, Praveen

329

Joseph Urban Stage Design Models & Documents Stabilization & Access Project  

NSDL National Science Digital Library

Born in Vienna in 1872, Joseph Urban came to the United States in 1912 with thousands of other immigrants. One of the distinguishing elements of Urban's life was that he would go on to design over 500 stage sets for more than 168 productions. By the time of his death in 1933, he had served as the art director of the Boston Opera, stage designer for the Metropolitan Opera, and had been in the employ of Florenz Ziegfeld, working on his famed Follies. This lovely online collection created by the Columbia University Libraries' Preservation Division brings together many items that document his work for a number of these organizations. Within the collection, visitors will find images of 61 three-dimensional stage models, watercolor renderings, libretti, and other such materials. The site also contains a very lengthy and erudite series of essays on Urban's works, along with detailed information about how the collection was preserved and stabilized.

330

Sensitivity Analysis for Biomedical Models  

Microsoft Academic Search

This article discusses the application of sensitivity analysis (SA) in biomedical models. Sensitivity analysis is widely applied in physics, chemistry, economics, social sciences and other areas where models are developed. By assigning a prior probability distribution to each model variable, the SA framework appeals to the posterior probabilities of the model to evaluate the relative importance of these variables on

Zhenghui Hu; Pengcheng Shi

2010-01-01

331

Non-Cooperative Stability Definitions for Strategic Analysis of Generic Water Resources Conflicts  

Microsoft Academic Search

In game theory, potential resolutions to a conflict are found through stability analysis, based on stability definitions having\\u000a precise mathematical structures. A stability definition reflects a decision maker’s behavior in a conflict or game, predicts\\u000a how the game is played, and suggests the resolutions or equilibria of the dispute. Various stability definitions, reflecting\\u000a different types of people with different levels

Kaveh Madani; Keith W. Hipel

2011-01-01

332

TRACE/PARCS analysis of the OECD/NEA Oskarshamn-2 BWR stability benchmark  

SciTech Connect

On February 25, 1999, the Oskarshamn-2 NPP experienced a stability event which culminated in diverging power oscillations with a decay ratio of about 1.4. The event was successfully modeled by the TRACE/PARCS coupled code system, and further analysis of the event is described in this paper. The results show very good agreement with the plant data, capturing the entire behavior of the transient including the onset of instability, growth of the oscillations (decay ratio) and oscillation frequency. This provides confidence in the prediction of other parameters which are not available from the plant records. The event provides coupled code validation for a challenging BWR stability event, which involves the accurate simulation of neutron kinetics (NK), thermal-hydraulics (TH), and TH/NK. coupling. The success of this work has demonstrated the ability of the 3-D coupled systems code TRACE/PARCS to capture the complex behavior of BWR stability events. The problem was released as an international OECD/NEA benchmark, and it is the first benchmark based on measured plant data for a stability event with a DR greater than one. Interested participants are invited to contact authors for more information. (authors)

Kozlowski, T. [Univ. of Illinois, Urbana-Champaign, IL (United States); Downar, T.; Xu, Y.; Wysocki, A. [Univ. of Michigan, Ann Arbor, MI (United States); Ivanov, K.; Magedanz, J.; Hardgrove, M. [Pennsylvania State Univ., Univ. Park, PA (United States); March-Leuba, J. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Hudson, N.; Woodyatt, D. [Nuclear Regulatory Commission, Rockville, MD (United States)

2012-07-01

333

Linear stability analysis of parallel shear flows for an inviscid generalized two-dimensional fluid system  

NASA Astrophysics Data System (ADS)

The linear stability of parallel shear flows for an inviscid generalized two-dimensional (2D) fluid system, the so-called ? turbulence system, is studied. This system is characterized by the relation q = -( - ?)?/2? between the advected scalar q and the stream function ?. Here, ? is a real number not exceeding 3 and q is referred to as the generalized vorticity. In this study, a sufficient condition for linear stability of parallel shear flows is derived using the conservation of wave activity. A stability analysis is then performed for a sheet vortex that violates the stability condition. The instability of a sheet vortex in the 2D Euler system (? = 2) is referred to as a Kelvin-Helmholtz (KH) instability; such an instability for the generalized 2D fluid system is investigated for 0 < ? < 3. The sheet vortex is unstable in the sense that a sinusoidal perturbation applied to it grows exponentially with time. The growth rate is finite and depends on the wavenumber of the perturbation as k3 - ? for 1 < ? < 3, where k is the wavenumber of the perturbation. In contrast, for 0 < ? ? 1, the growth rate is infinite. In other words, a transition of the growth rate of the perturbation occurs at ? = 1. A physical model for KH instability in the generalized 2D fluid system, which can explain the transition of the growth rate of the perturbation at ? = 1, is proposed.

Iwayama, T.; Sueyoshi, M.; Watanabe, T.

2013-02-01

334

Dynamical investigation and parameter stability region analysis of a flywheel energy storage system in charging mode  

NASA Astrophysics Data System (ADS)

In this paper, the dynamic behavior analysis of the electromechanical coupling characteristics of a flywheel energy storage system (FESS) with a permanent magnet (PM) brushless direct-current (DC) motor (BLDCM) is studied. The Hopf bifurcation theory and nonlinear methods are used to investigate the generation process and mechanism of the coupled dynamic behavior for the average current controlled FESS in the charging mode. First, the universal nonlinear dynamic model of the FESS based on the BLDCM is derived. Then, for a 0.01 kWh/1.6 kW FESS platform in the Key Laboratory of the Smart Grid at Tianjin University, the phase trajectory of the FESS from a stable state towards chaos is presented using numerical and stroboscopic methods, and all dynamic behaviors of the system in this process are captured. The characteristics of the low-frequency oscillation and the mechanism of the Hopf bifurcation are investigated based on the Routh stability criterion and nonlinear dynamic theory. It is shown that the Hopf bifurcation is directly due to the loss of control over the inductor current, which is caused by the system control parameters exceeding certain ranges. This coupling nonlinear process of the FESS affects the stability of the motor running and the efficiency of energy transfer. In this paper, we investigate into the effects of control parameter change on the stability and the stability regions of these parameters based on the averaged-model approach. Furthermore, the effect of the quantization error in the digital control system is considered to modify the stability regions of the control parameters. Finally, these theoretical results are verified through platform experiments.

Zhang, Wei-Ya; Li, Yong-Li; Chang, Xiao-Yong; Wang, Nan

2013-09-01

335

Analysis of cavern stability at the West Hackberry SPR site.  

SciTech Connect

This report presents computational analyses that simulate the structural response of caverns at the Strategic Petroleum Reserve (SPR) West Hackberry site. The cavern field comprises 22 caverns. Five caverns (6, 7, 8, 9, 11) were acquired from industry and have unusual shapes and a history dating back to 1946. The other 17 caverns (101-117) were leached according to SPR standards in the mid-1980s and have tall cylindrical shapes. The history of the caverns and their shapes are simulated in a three-dimensional geomechanics model of the site that predicts deformations, strains, and stresses. Future leaching scenarios corresponding to oil drawdowns using fresh water are also simulated by increasing the volume of the caverns. Cavern pressures are varied in the model to capture operational practices in the field. The results of the finite element model are interpreted to provide information on the current and future status of subsidence, well integrity, and cavern stability. The most significant results in this report are relevant to Cavern 6. The cavern is shaped like a bowl with a large ceiling span and is in close proximity to Cavern 9. The analyses predict tensile stresses at the edge of the ceiling during repressuization of Cavern 6 following workover conditions. During a workover the cavern is at low pressure to service a well. The wellhead pressures are atmospheric. When the workover is complete, the cavern is repressurized. The resulting elastic stresses are sufficient to cause tension around the edge of the large ceiling span. With time, these stresses relax to a compressive state because of salt creep. However, the potential for salt fracture and propagation exists, particularly towards Cavern 9. With only 200 ft of salt between the caverns, the operational consequences must be examined if the two caverns become connected. A critical time may be during a workover of Cavern 9 in part because of the operational vulnerabilities, but also because dilatant damage is predicted under the ledge that forms the lower lobe in the cavern. The remaining caverns have no significant issues regarding cavern stability and may be safely enlarged during subsequent oil drawdowns. Predicted well strains and subsidence are significant and consequently future remedial actions may be necessary. These predicted well strains certainly suggest appropriate monitoring through a well-logging program. Subsidence is currently being monitored.

Ehgartner, Brian L.; Sobolik, Steven Ronald

2009-05-01

336

Stability of the Atlantic meridional overturning circulation: A model intercomparison  

NASA Astrophysics Data System (ADS)

The evolution of the Atlantic Meridional Overturning Circulation (MOC) in 30 models of varying complexity is examined under four distinct Representative Concentration Pathways. The models include 25 Atmosphere-Ocean General Circulation Models (AOGCMs) or Earth System Models (ESMs) that submitted simulations in support of the 5th phase of the Coupled Model Intercomparison Project (CMIP5) and 5 Earth System Models of Intermediate Complexity (EMICs). While none of the models incorporated the additional effects of ice sheet melting, they all projected very similar behaviour during the 21st century. Over this period the strength of MOC reduced by a best estimate of 22% (18%-25% 5%-95% confidence limits) for RCP2.6, 26% (23%-30%) for RCP4.5, 29% (23%-35%) for RCP6.0 and 40% (36%-44%) for RCP8.5. Two of the models eventually realized a slow shutdown of the MOC under RCP8.5, although no model exhibited an abrupt change of the MOC. Through analysis of the freshwater flux across 30°-32°S into the Atlantic, it was found that 40% of the CMIP5 models were in a bistable regime of the MOC for the duration of their RCP integrations. The results support previous assessments that it is very unlikely that the MOC will undergo an abrupt change to an off state as a consequence of global warming.

Weaver, Andrew J.; Sedlá?ek, Jan; Eby, Michael; Alexander, Kaitlin; Crespin, Elisabeth; Fichefet, Thierry; Philippon-Berthier, Gwenaëlle; Joos, Fortunat; Kawamiya, Michio; Matsumoto, Katsumi; Steinacher, Marco; Tachiiri, Kaoru; Tokos, Kathy; Yoshimori, Masakazu; Zickfeld, Kirsten

2012-10-01

337

Voltage Stability Probabilistic Assessment in Composite Systems: Modeling Unsolvability and Controllability Loss  

Microsoft Academic Search

Several papers have recognized the effect of uncertainties in voltage stability analysis through probabilistic methods. In these papers, the unstable states are generally identified by the unsolvability of the power flow equations or by violations in the voltage stability margin limit. However, voltage stability problems may also be associated with a loss in voltage controllability, when a voltage control action

Anselmo Barbosa Rodrigues; Ricardo B. Prada; Maria Da Guia da Silva

2010-01-01

338

Second order nonlinear spatial stability analysis of compressible mixing layers  

NASA Astrophysics Data System (ADS)

Second order nonlinear spatial stability to three-dimensional perturbation waves is analyzed for compressible mixing layers by expanding the perturbations into amplitude-dependent harmonic waves and truncating the Landau equation to the second term. This leads to a system of nonlinear ordinary differential equations for the harmonics. The two constants in Landau equation are calculated, wherein the independent variable, time t, is replaced by the streamwise coordinate direction x. The basic procedure in this paper is similar to that by Liu for compressible laminar wakes [Phys. Fluids 12, 1763 (1969)]. However, unlike this reference, which does not provide any results for their analysis, the present paper obtained many interesting results. The linear results from the present work compare very favorably with those reported by Day, Reynolds, and Mansour [Phys. Fluids 10, 993 (1998)], who employed a different procedure and limited their analysis to the linear regime. In the present studies, both the linear and nonlinear problems were analyzed in exactly the same manner, with the implication that the nonlinear results are probably accurate. These results include the convergence of the amplitude to an equilibrium value that depends on the two constants in the amplitude equation from Landau's procedure. The present analysis is restricted to exponentially decaying linear solutions at the boundaries and hence to region one in the phase speed-Mach number diagram. However, we have observed that nonlinear effects could introduce constant, decaying, or outgoing wave solutions at the boundaries, depending on the velocity and density ratios and the Mach number of the fast stream. Other effects of these parameters are reported.

Ladeinde, F.; Wu, J.

2002-09-01

339

In situ vitrification: application analysis for stabilization of transuranic waste  

SciTech Connect

The in situ vitrification process builds upon the electric melter technology previously developed for high-level waste immobilization. In situ vitrification converts buried wastes and contaminated soil to an extremely durable glass and crystalline waste form by melting the materials, in place, using joule heating. Once the waste materials have been solidified, the high integrity waste form should not cause future ground subsidence. Environmental transport of the waste due to water or wind erosion, and plant or animal intrusion, is minimized. Environmental studies are currently being conducted to determine whether additional stabilization is required for certain in-ground transuranic waste sites. An applications analysis has been performed to identify several in situ vitrification process limitations which may exist at transuranic waste sites. Based on the process limit analysis, in situ vitrification is well suited for solidification of most in-ground transuranic wastes. The process is best suited for liquid disposal sites. A site-specific performance analysis, based on safety, health, environmental, and economic assessments, will be required to determine for which sites in situ vitrification is an acceptable disposal technique. Process economics of in situ vitrification compare favorably with other in-situ solidification processes and are an order of magnitude less than the costs for exhumation and disposal in a repository. Leachability of the vitrified product compares closely with that of Pyrex glass and is significantly better than granite, marble, or bottle glass. Total release to the environment from a vitrified waste site is estimated to be less than 10/sup -5/ parts per year. 32 figures, 30 tables.

Oma, K.H.; Farnsworth, R.K.; Rusin, J.M.

1982-09-01

340

Physical and numerical model of colloidal silica injection for passive site stabilization  

SciTech Connect

Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. This technology is based on the concept of slow injection of stabilizing materials at the edge of a site and delivery of the stabilizer to the target location, using the natural or augmented groundwater flow. In this research, a box model was used to investigate the ability to uniformly deliver colloidal silica stabilizer to loose sands using low-head injection and extraction wells. Five injection wells and two extraction wells were used to deliver stabilizer in a generally uniform pattern to the loose sand formation. Numerical modeling was used to identify the key parameters affecting stabilizer migration and to determine their effective values for the box experiment. In our modeling approach, the stabilizer is treated as a miscible fluid, the viscosity of which is a function of time and concentration of the stabilizer in the pore water. Inverse modeling techniques are employed to reproduce data from the laboratory experiment for the determination of soil and stabilizer properties. While the details of the stabilizer distribution were difficult to reproduce with the simplified conceptual model employed in this study, the overall system behavior was well captured, providing confidence that numerical simulation is a useful tool for designing centrifuge model tests, pilot tests, and eventually field stabilizer-injection projects.

Gallagher, Patricia M.; Finsterle, Stefan

2004-08-01

341

Breathers in a discrete nonlinear Schrödinger-type model: Exact stability results.  

PubMed

Following our earlier work [Phys. Rev. Lett. 84, 3570 (2000)] we present an exact linear stability analysis of one-site monochromatic breathers in a piecewise smooth discrete nonlinear Schrödinger-type model. Destabilization of the breather occurs by virtue of a growth rate becoming positive as a stability border is crossed, while above a critical spatial decay rate (lambda(c)) the breather is found to be intrinsically unstable. The model admits of other exact breather solutions, including multisite monochromatic breathers for which the profile variable (phi(n)) crosses a relevant threshold at more than one site. In particular, we consider exact two-site breather solutions with phase difference delta between the two sites above threshold, and present stability results for delta=pi (antiphase breather; the in-phase breather with delta=0 happens to be intrinsically unstable). We obtain a band of extended eigenmodes, together with a pair of localized symmetric modes and another pair of localized antisymmetric ones. The frequencies of the localized modes vary as the parameters characterizing the breather are made to vary, and destabilization occurs through the Krein collision of a quartet of growth rates, leading to temporal growth of a pair of symmetric eigenmodes of nonzero frequency. We clarify the limit N--> infinity (N is the gap length between the sites above threshold) when the two-site breather reduces to a pair of decoupled one-site breathers. The model offers the possibility of obtaining spatially random vortex-type breathers. PMID:12513619

Lahiri, Avijit; Panda, Subhendu; Roy, Tarun K

2002-11-18

342

Precessing rotating flows with additional shear: stability analysis.  

PubMed

We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity Omega(0)) and the additional "precessing" Coriolis force (with angular velocity -epsilonOmega(0)), normal to it. A "weak" shear flow, with rate 2epsilon of the same order of the Poincaré "small" ratio epsilon , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler's equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov's [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré's [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small epsilon . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet's theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small epsilon , but significant differences are obtained regarding growth rates and widths of instability bands, if larger epsilon values, up to 0.2, are considered. Finally, both flow cases are briefly discussed in view of a subsequent nonlinear study using pseudospectral direct numerical simulations, which is a natural continuation of RDT. PMID:19392045

Salhi, A; Cambon, C

2009-03-12

343

Long-term stability of Class II, Division 1, nonextraction cervical face-bow therapy: II. Cephalometric analysis  

Microsoft Academic Search

The long-term stability of Class II, Division 1 nonextraction therapy, using cervical face-bows with full fixed orthodontic appliances was evaluated for 42 randomly selected patients. Part 1, a study model analysis, was published in the March 1996 issue of the JOURNAL. Each patient was treated by the same practitioner, with the same techniques, and the treatment goals had been attained

T. N. Elms; P. H. Buschang; R. G. Alexander

1996-01-01

344

On monolithic stability and reinforcement analysis of high arch dams  

Microsoft Academic Search

Monolithic stability safety and reinforcement based on monolithic stability are very important for arch dam design. In this\\u000a paper, the issue is addressed based on deformation reinforcement theory. In this approach, plastic complementary energy norm\\u000a can be taken as safety index for monolithic stability. According to deformation reinforcement theory, the areas where unbalanced\\u000a force exists require reinforcement, and the required

Qiang Yang; YingRu Chen; YaoRu Liu

2007-01-01

345

Impulsive exponential stabilization of discrete population growth models with time delays  

Microsoft Academic Search

The purpose of this paper is to investigate the impulsive exponential stabilization for the positive equilibrium points of a class of discrete population growth models with time delays. By using Lyapunov functionals, some new exponential stability criteria are given. It is shown that impulses can indeed make unstable equilibrium points exponentially stable, and when the impulses are employed to stabilize

Yu Zhang; Jitao Sun

2010-01-01

346

A new approach to the stability analysis of continuous-time distributed consensus algorithms.  

PubMed

In this letter, we propose a new approach for the stability analysis of distributed continuous-time consensus algorithms in directed networks with time-dependent communication patterns. Instead of using a continuous-time Lyapunov function, we show how to analyze such a continuous-time algorithm by converting it to a discrete-time model. By using this method, we obtain a more general convergence result than existing ones. An example with numerical simulation is also provided to illustrate the theoretical results. PMID:23831802

Liu, Bo; Lu, Wenlian; Chen, Tianping

2013-06-20

347

Improvement of stability conditions, accuracy and uniqueness of penalty approach in contact modeling  

NASA Astrophysics Data System (ADS)

The main objective of this paper is to improve stability conditions, uniqueness and convergence of numerical analysis of metal forming processes with contact constraints enforced by the penalty method. A commonly known drawback of this approach is the choice of penalty factor values. When assumed too low, they result in inaccurate fulfillment of the constraints while when assumed too high, they lead to ill-conditioning of the equations system which affects stability and uniqueness of the solution. The proposed modification of the penalty algorithm consists in adaptive estimation of the penalty factor values for the particular system of finite element equations and for the assumed allowed inaccuracy in fulfillment of the contact constraints. The algorithm is tested on realistic examples of sheet metal forming. The finite element code based on flow approach formulation (for rigid-plastic and rigid-viscoplastic material model) has been used.

Bednarek, Tomasz; Kowalczyk, Piotr

2013-06-01

348

Artificial Neural Network Modeling Technique for Voltage Stability Assessment of Radial Distribution Systems  

Microsoft Academic Search

This paper presents an artificial neural network (ANN) based modeling technique for predicting the voltage stability of radial distribution systems. The modeling technique is based on a new voltage stability index for assessment of radial distribution systems Lv . The index is implemented to investigate a 33-bus distribution system. An ANN model which has an input layer with two input

M. M. Hamada; M. A. A. Wahab; N. G. A. Hemdan

2006-01-01

349

Stability Analysis of Large-Scale Incompressible Flow Calculations on Massively Parallel Computers  

SciTech Connect

A set of linear and nonlinear stability analysis tools have been developed to analyze steady state incompressible flows in 3D geometries. The algorithms have been implemented to be scalable to hundreds of parallel processors. The linear stability of steady state flows are determined by calculating the rightmost eigenvalues of the associated generalize eigenvalue problem. Nonlinear stability is studied by bifurcation analysis techniques. The boundaries between desirable and undesirable operating conditions are determined for buoyant flow in the rotating disk CVD reactor.

LEHOUCQ,RICHARD B.; ROMERO,LOUIS; SALINGER,ANDREW G.

1999-10-25

350

On-line robust aeroservoelastic stability margin analysis from wavelet-processed flight testing data  

Microsoft Academic Search

An on-line method based on robust mu analysis is presented to evaluate the stability margin of multi-loop aeroservoelastic system from flight testing data. The flight data is preprocessed to remove noise by wavelet filter in time-frequency domain. The method for stability analysis is described and the classical stability margin used for single-input-single-output (SISO) system has been extended to multi-loop system.

Hongchao Li; Zhongke Shi; Wei Tang

2006-01-01

351

Lyapunov Analysis of Neural Network Stability in an Adaptive Flight Control System  

Microsoft Academic Search

The paper presents the role of self-stabilization analysis in the design, verification and validation of the dynamics of an Adaptive Flight Control System (AFCS). Since the traditional self-stabilization approaches lack the flexibility to deal with the continuous adaptation of the neural network within the AFCS, the paper emphasizes an alternate self-stability analysis approach, namely Lyapunov's Second Method. A Lyapunov function

Sampath Yerramalla; Edgar Fuller; Martin Mladenovski; Bojan Cukic

2003-01-01

352

Dynamics of the Heisenberg model and a theorem on stability  

NASA Astrophysics Data System (ADS)

We consider the general discrete classical Heisenberg model (HM) with z axis anisotropy and external magnetic field and show that its phase space is foliated into a family of invariant manifolds (the leaves) diffeomorphic to (S2)?, where ? is the number of spins. We also show that the flow on each leaf is Hamiltonian. Subsequently, we focus on the isotropic HM in the absence of external field. We discuss the rotational symmetry of the model and further analyze its phase space structure. We prove that the manifold of longitudinal fixed points intersects each leaf orthogonally. For a real local flow with a continuous symmetry, we show that the Lyapunov stability of invariant sets on an invariant subspace can be extended to the whole phase space. This general theorem is the main result of the article. We use it to show that, in the case of the isotropic HM, the ferromagnetic state and the antiferromagnetic state with non-zero total spin are both stable fixed points. The theorem does not apply at total spin zero, and indeed the AF state on an equal-spins leaf is found to be unstable.

Pantelidis, Leonidas

2013-02-01

353

Modelling flank instabilities on stratovolcanoes: Parameter sensitivity and stability analyses of Teide, Tenerife  

NASA Astrophysics Data System (ADS)

Numerous mechanisms have been proposed to explain how the flanks of stratovolcanoes collapse. However, the usefulness of different models has been difficult to quantify, partly because of large uncertainties in rock strength. Recent comprehensive measurements of the geotechnical properties of fresh and hydrothermally altered volcanic materials from Teide, Tenerife are used to improve our understanding of the destabilising potential of different volcanic and non-volcanic processes. A parameter sensitivity analysis has been undertaken, and this allows the first order effects of pore-fluid pressures, magmatic intrusions and transient stresses to be assessed, both individually and in conjunction with other processes. We have assessed the stability of the flanks of Teide through a combined 2D approach of finite element, and limit equilibrium methods. The analysis shows that a circular magmatic intrusion through a central conduit beneath the summit has no effect on the stability of the edifice, whereas a dyke can change the stress regime, increasing the potential for yielding at the break in slope at the base of the edifice. We also show how the depth of potential failure planes is related to cohesion. The effects of peak ground accelerations and pore pressures on stability are presented in ways that show their importance, both individually and when combined in failure planes at different depths. Our analysis of Teide, which takes into account our recent analysis of structural features and hydrothermal alteration on the volcano, suggests that Teide is currently stable (factor of safety 1.3-1.8), and will continue to be so in the event of magmatic intrusions and seismic shocks of magnitudes within the expected range. While the analysis is based on Teide, the analysis and results have potential application to many other stratovolcanoes.

del Potro, Rodrigo; Hürlimann, Marcel; Pinkerton, Harry

2013-04-01

354

Implications of stability analysis for heat transfer at Yucca Mountain  

SciTech Connect

An analytical solution has been obtained to the stability problem for an infinite horizontal layer of gas with Its humidity constrained to 100%. Latent heat transfer makes convective heat transfer much more Important for this moist gas than for a dry gas. The critical Rayleigh number for the onset of convective flow in the moist gas, with a lower no-flow boundary at 97{degrees}C and an upper no-flow boundary at 27{degrees}C, is 0.18, much less than the value of 4m{sup 2} for a dry gas. Although the heat source at Yucca Mountain will be finite in extent, the solution for an infinite horizontal layer still gives a useful criterion for the qualitative importance of convective heat transfer. The critical Rayleigh number of 0.18 corresponds to a permeability of 4 {times} 10{sup {minus}12} m{sup 2} if other parameters ate given values measured at Yucca Mountain. This value falls roughly in the middle of the range of measured permeabilities. The analysis also gives a time constant for the onset of convection, which at twice the critical Rayleigh number is 1000 yr. Thus convection will probably make an important contribution, to host transfer at Yucca Mountain if the rock permeability falls in the upper portion of the range of measurements to date, but only at times after a few hundred or thousand years.

Ross, B.; Yiqiang Zhang; Ning Lu [Disposal Safety, Inc., Washington, DC (United States)

1993-03-01

355

GE simplified boiling water reactor stability analysis in time domain  

Microsoft Academic Search

General Electric Simplified Boiling Water Reactor (SBWR) was designed as a next generation light water reactor. It uses natural circulation to remove the heat from the reactor core. Because of this unique in-vessel circulation feature, SBWR is expected to exhibit different stability behaviors. The main emphasis of this thesis is to study the SBWR stability behavior in the time domain.

Shanlai Lu

1997-01-01

356

NUMERICAL ANALYSIS OF FILTER BASED STABILIZATION FOR EVOLUTION EQUATIONS  

Microsoft Academic Search

We consider filter based stabilization for evolution equations (in general) and for the Navier-Stokes equations (in particular). The first method we consider is to advance in time one time step by a given method and then to apply an (uncoupled and modular) filter to get the approximation at the new time level. This filter based stabilization, although algorithmically appealing, is

VINCENT J. ERVIN; WILLIAM J. LAYTONy; MONIKA NEDAz

357

Stability Analysis of a Reluctance-Synchronous Machine  

Microsoft Academic Search

A stability study of a reluctance-synchronous machine (synchronous-induction machine) is performed by applying the Nyquist stability criterion to the equations which describe the behavior of the machine during small displacements about a steady- state operating point. This investigation reveals that machine instability can occur at low speeds (low frequencies) even though balanced, constant amplitude, sinusoidal voltages are applied to the

THOMAS A. LIPO; PAUL C. KRAUSE

1967-01-01

358

Stability Analysis of a Rectifier-Inverter Induction Motor Drive  

Microsoft Academic Search

A stability study of a rectifier-inverter induction motor drive system is performed by neglecting the harmonic content of the stator voltages and applying Nyquist stability criterion to the small- displacement equations obtained by linearization about an operating point. This investigation reveals that system instability can occur over a wide speed range if the system parameters are improperly selected. It appears

Thomas Lipo; Paul Krause

1969-01-01

359

Power system voltage stability analysis using Modified Differential Evolution  

Microsoft Academic Search

The problem of voltage stability is one of the main concerns in the operation of power systems. Many approaches have been used to estimate the voltage stability limit. One of the approaches is determining the maximum loading point of the system. In this approach, the margin from the current operating point to the maximum loading point of the system is

C. Muthamil Selvi; K. Gnanambal

2011-01-01

360

Rank Stability Analysis of Surface and Profile Soil Moisture  

Technology Transfer Automated Retrieval System (TEKTRAN)

Although several studies have examined the spatial and rank stability of soil moisture at the surface layer (0-5cm) with the purpose of estimating large scale mean soil moisture, the integration of the rank stability of profile (0-60cm) soil moisture has not been fully considered. This research comb...

361

Stability Analysis for Digital PD Control of Flexible Systems  

NASA Astrophysics Data System (ADS)

In this work we extent our recent results on the stability of rigid systems to cases involving flexible ones. We present closed form analytical expressions that describe the boundaries of the stability regions for digital PD control systems. This is obtained using a newly adopted approach based on the critical stability constraints of Jury test. The considered system consists of a single rigid and a single flexible mode. This simulates many practical systems such as antenna, space shuttle, and robot arm. The obtained closed-form stability criterion shows that the stability region is almost a right triangle in the gain space. The right-angle sides of the proposed triangle coincide exactly with two boundaries of the stability region. The hypotenuse of the triangle is found to well approximate the third boundary. An analytical expression is derived for the slope of the hypotenuse. This approximation results in defining the stability region using only two parameters which is convenient for practical applications. Case study is presented to show the practical usefulness of the proposed close-form stability criteria through investigating the control design of high speed flexible robot arm.

Al-Salem, Nabeel

362

Stability analysis of a borehole wall during horizontal directional drilling  

Microsoft Academic Search

In this paper, numerical simulation strategies are proposed and numerical analyses are performed to investigate the stability of a borehole wall during horizontal directional drilling in loose sand with an emphasis on the role of the filter cake in borehole stability. Two computational scenarios, one in the absence of a filter cake and one with the presence of a filter

X. Wang; R. L. Sterling

2007-01-01

363

BiGlobal stability analysis in curvilinear coordinates of massively separated lifting bodies  

Microsoft Academic Search

A methodology based on spectral collocation numerical methods for global flow stability analysis of incompressible external flows is presented. A potential shortcoming of spectral methods, namely the handling of the complex geometries encountered in global stability analysis, has been dealt with successfully in past works by the development of spectral-element methods on unstructured meshes. The present contribution shows that a

Vassili Kitsios; Daniel Rodríguez; Vassilis Theofilis; Andrew Ooi; Julio Soria

2009-01-01

364

Stability control of quad-rotor based on explicit model following with inverse model feedforward method  

Microsoft Academic Search

{as1123 & houzhicheng123}@163.com Abstract -The quad-rotor is expected to carry out many different tasks. It is hoped that the quad-rotor can have different characteristics according to the different mission requirements. For this reason, a flight stability augmentation control system based on explicit model following with inverse model feedforward control method is proposed in this paper. This control system is composed

Yue Bai; Xun Gong; ZhiCheng Hou; YanTao Tian

2011-01-01

365

Spatiotemporal patterns in a dc semiconductor-gas-discharge system: Stability analysis and full numerical solutions  

NASA Astrophysics Data System (ADS)

A system very similar to a dielectric barrier discharge, but with a simple stationary dc voltage, can be realized by sandwiching a gas discharge and a high-ohmic semiconductor layer between two planar electrodes. In experiments this system forms spatiotemporal and temporal patterns spontaneously, quite similarly to, e.g., Rayleigh-Bénard convection. Here it is modeled with a simple discharge model with space charge effects, and the semiconductor is approximated as a linear conductor. In previous work, this model has reproduced the phase transition from homogeneous stationary to homogeneous oscillating states semiquantitatively. In the present work, the formation of spatial patterns is investigated through linear stability analysis and through numerical simulations of the initial value problem; the methods agree well. They show the onset of spatiotemporal patterns for high semiconductor resistance. The parameter dependence of temporal or spatiotemporal pattern formation is discussed in detail.

Rafatov, Ismail R.; Šija?i?, Danijela D.; Ebert, Ute

2007-09-01

366

Modeling of Neoclassical Tearing Mode Stability for NSTX  

NASA Astrophysics Data System (ADS)

Neoclassical tearing modes (NTMs) can lead to disruption and loss of confinement. Previous analysis of these modes used large aspect ratio, low ? approximations to determine the effect of NTMs on tokamak plasmas. A more accurate tool is needed to predict the onset of these instabilities. As a follow-up to recent theoretical work, a code has been written which computes the tearing mode island growth rate for arbitrary tokamak geometry. It calls PEST-3 to compute ?^', the resistive MHD matching parameter. The code also calls routines in NIMROD for D_nc, DI and D_R, which are the bootstrap current driven term and the ideal and resistive interchange mode criterion, respectively. In addition to these components, the NIMROD routines calculate ?_s-H, a new correction to the Pfirsch-Schlüter term. Finite parallel transport effects were added and threshold island widths for several NSTX equilibria were determined. Another program takes the output of PEST-3 and allows the user to specify the rational surface, island width, and amount of detail near the perturbed surface to visualize the total helical flux. The results of this work will determine the stability of NTMs in an ST plasma with greater accuracy than previously achieved.

Rosenberg, A.; Gates, D.; Pletzer, A.; Hegna, C.; Kruger, S.

2000-10-01

367

LMI-based approach for global asymptotic stability analysis of continuous BAM neural networks  

Microsoft Academic Search

Studies on the stability of the equilibrium points of continuous bidirectional associative memory (BAM) neural network have yielded many useful results. A novel neural network model called standard neural network model (SNNM) is ad- vanced. By using state affine transformation, the BAM neural networks were converted to SNNMs. Some sufficient conditions for the global asymptotic stability of continuous BAM neural

ZHANG Sen-lin; LIU Mei-qin

2005-01-01

368

Novel fast voltage stability index (FVSI) for voltage stability analysis in power transmission system  

Microsoft Academic Search

Since a couple of decades ago, voltage stability assessment has received increasing attention due to the complexity of power systems. With the increase in power demand and limited power sources has caused the system to operate at its maximum capacity. Therefore, a study that is able to determine the maximum capacity limit before voltage collapse must be carried out so

Ismail Musirin; Titik Khawa Abdul Rahman

2002-01-01

369

EXPOSURE ANALYSIS MODELING SYSTEM (EXAMS)  

EPA Science Inventory

The Exposure Analysis Modeling System (EXAMS), first published in 1982 (EPA-600/3-82-023), provides interactive computer software for formulating aquatic ecosystem models and rapidly evaluating the fate, transport, and exposure concentrations of synthetic organic chemicals--pesti...

370

Model Cost - Benefit Analysis Scheme.  

National Technical Information Service (NTIS)

A model is proposed to improve resource allocation decisions by CHPs by providing an understanding of the costs and effects of various courses of planning action. This cost - benefit analysis model provides a frame of reference for considering the merits ...

R. L. Paretta D. J. Puglisi L. W. Chadwick

1974-01-01

371

Higgs vacuum stability in the B-L extended standard model  

NASA Astrophysics Data System (ADS)

We study vacuum stability of B-L extension of the Standard Model (SM) and its supersymmetric version. We show that the generation of nonvanishing neutrino masses through TeV inverse seesaw mechanism leads to a cutoff scale of SM Higgs potential stability of order 105GeV. However, in the nonsupersymmetric B-L model, we find that the mixing between the SM-like Higgs boson and the B-L Higgs boson plays a crucial role in alleviating the vacuum stability problem. We also provide the constraints of stabilizing the Higgs potential in the supersymmetric B-L model.

Datta, Alakabha; Elsayed, A.; Khalil, S.; Moursy, A.

2013-09-01

372

Standard model stability bounds for new physics within LHC reach  

NASA Astrophysics Data System (ADS)

We analyse the stability lower bounds on the Standard Model Higgs mass by carefully controlling the scale independence of the effective potential. We include resummed leading and next-to-leading-log corrections, and physical pole masses for the Higgs boson, MH, and the top-quark, Mt. Particular attention is devoted to the cases where the scale of new physics ? is within LHC reach, i.e. ? <= 10 TeV, which have been the object of recent controversial results. We clarify the origin of discrepancies and confirm our earlier results within the error of our previous estimate. In particular for ? = 1 TeV we find thatMH [GeV] > 52 + 0.64 (Mt[GeV] - 175) - 0.50?s(MZ) - 0.118/(0.006) . For fixed values of Mt and ?s(Mz), the error from higher effects, as the lack of exact scale invariance of the effective potential and higher-order radiative corrections, is conservatively estimated to be < 5 GeV.

Casas, J. A.; Espinosa, J. R.; Quirós, M.

1996-02-01

373

An imaging-driven model for liposomal stability and circulation  

PubMed Central

Simultaneous labeling of the drug compartment and shell of delivery vehicles with optical and positron emission tomography (PET) probes is developed and employed to inform a physiologically-based pharmacokinetic model. Based on time-dependent estimates of the concentration of these tracers within the blood pool, reticulo-endothelial system (RES) and tumor interstitium, we compare the stability and circulation of long-circulating and temperature-sensitive liposomes. We find that rates of transport to the RES for long-circulating and temperature-sensitive particles are 0.046 and 0.19 hr?1, respectively. Without the application of exogenous heat, the rates of release from the long-circulating and temperature-sensitive particles circulating within the blood pool are 0.003 and 0.2 hr?1, respectively. Prolonged life-time in circulation and slow drug release from liposomes result in a significantly greater drug area under the curve for the long-circulating particles. Future studies will couple these intrinsic parameters with exogenous heat-based release. Finally, we develop a transport constant for the transport of liposomes from the blood pool to the tumor interstitium, which is on the order of 0.01 hr?1 for the Met-1 tumor system.

Qin, Shengping; Seo, Jai Woong; Zhang, Hua; Qi, Jinyi; Curry, Fitz-Roy E.; Ferrara, Katherine W.

2009-01-01

374

The validity of stability measures: a modelling approach.  

PubMed

Measures calculated from unperturbed walking patterns, such as variability measures and maximum Floquet multipliers, are often used to study the stability of walking. However, it is unknown if, and to what extent, these measures correlate to the probability of falling. We studied whether in a simple model of human walking, i.e., a passive dynamic walker, the probability of falling could be predicted from maximum Floquet multipliers, kinematic state variability, and step time variability. We used an extended version of the basic passive dynamic walker with arced feet and a hip spring. The probability of falling was manipulated by varying the foot radius and hip spring stiffness, or varying these factors while co-varying the slope to keep step length constant. The simulation data indicated that Floquet multipliers and kinematic state variability correlated inconsistently with probability of falling. Step time variability correlated well with probability of falling, but a more consistent correlation with the probability of falling was found by calculating the variability of the log transform of the step time. Our findings speak against the use of maximum Floquet multipliers and suggest instead that variability of critical variables may be a good predictor of the probability to fall. PMID:21762919

Bruijn, Sjoerd M; Bregman, Daan J J; Meijer, Onno G; Beek, Peter J; van Dieën, Jaap H

2011-07-16

375

Vaccine stability study design and analysis to support product licensure.  

PubMed

Stability evaluation supporting vaccine licensure includes studies of bulk intermediates as well as final container product. Long-term and accelerated studies are performed to support shelf life and to determine release limits for the vaccine. Vaccine shelf life is best determined utilizing a formal statistical evaluation outlined in the ICH guidelines, while minimum release is calculated to help assure adequate potency through handling and storage of the vaccine. In addition to supporting release potency determination, accelerated stability studies may be used to support a strategy to recalculate product expiry after an unintended temperature excursion such as a cold storage unit failure or mishandling during transport. Appropriate statistical evaluation of vaccine stability data promotes strategic stability study design, in order to reduce the uncertainty associated with the determination of the degradation rate, and the associated risk to the customer. PMID:19717312

Schofield, Timothy L

2009-08-29

376

Spectral Analysis of Gas Bearing Systems for Stability Studies.  

National Technical Information Service (NTIS)

Stability map for a gas-bearing supported rotor can be constructed from the periodic dynamic perturbation solution of the gas bearing equation about the equilibrium condition. A complete frequency range of the perturbation solution is required. Effective ...

C. H. T. Pan

1964-01-01

377

APPLICATIONS ANALYSIS REPORT: CHEMFIX TECHNOLOGIES, INC., SOLIDIFICATION/STABILIZATION PROCESS  

EPA Science Inventory

The Chemfix Solidification/Stabilization treatment process was evaluated under EPA's SITE program. he process reduced leaching levels of lead and copper. hysical testing results were acceptable. ppropriate applications and process limitations are discussed in this report....

378

Stability analysis of a variable-speed wind turbine  

SciTech Connect

This paper examines the elastomechanical stability of a four-bladed wind turbine over a specific rotor speed range. Stability modes, frequencies, and dampings are extracted using a specialized modal processor developed at NREL that post-processes the response data generated by the ADAMS simulation code. The processor can analyze a turbine with an arbitrary number of rotor blades and offers a novel capability of isolating stability modes that become locked at a single frequency. Results indicate that over a certain rotor speed range, the tower lateral mode and the rotor regressive in-plane mode coalesce, resulting in a self-excited instability. Additional results show the effect of tower and nacelle parameters on the stability boundaries.

Bir, G.S.; Wright, A.D.; Butterfield, C.P.

1996-10-01

379

Stability Analysis of a Finite Difference Scheme Using Symbolic Computation.  

National Technical Information Service (NTIS)

Computer aided symbolic manipulation has previously been used in studies of weakly nonlinear behavior in plasmas. The application of such symbolic manipulation techniques to the study of the stability of a specific finite difference scheme is investigated...

A. Reiman A. Bers

1975-01-01

380

Robust Stability Analysis for Delayed BAM Neural Networks  

Microsoft Academic Search

The problem of robust stability for a class of uncertain bidirectional associative memory neural networks with time delays\\u000a is investigated in this paper. A more general Lyapunov-Krasovskii functional is proposed to derive a less conservative robust\\u000a stability condition within the framework of linear matrix inequalities. A numerical example is given to illustrate the effectiveness\\u000a of the proposed method.

Yijing Wang; Zhiqiang Zuo

2007-01-01

381

A piecewise linear mean flow model for studying stability in a lined channel  

NASA Astrophysics Data System (ADS)

Acoustic liners are used to reduce sound emission by turbofan engines. Under grazing flow they may sustain hydrodynamic instabilities and these are studied using a stability analysis, based on a simplified model: the liner is a mass-spring-damper system, the base channel flow is piecewise linear, and the inviscid, incompressible Rayleigh equation is used. The model is an extension to the channel case of a boundary layer model by Rienstra and Darau. The piecewise linear profile introduces a finite boundary layer thickness which ensures well-posedness, allowing an initial value problem to be conducted to investigate absolute stability. For typical values in aeronautics the flow above the liner is unstable. Absolute instability is obtained for somewhat extreme values of the mean flow (tiny boundary layer thickness), and under realistic conditions the flow is convectively unstable. The effect of finite channel height is investigated in both cases. In particular, for large boundary layer thicknesses associated with convective instability the channel height has little effect on the unstable mode. Favorable outcomes and failures of the model are shown by comparison to a published experimental work.

Marx, David

2012-07-01

382

Food web complexity enhances community stability and climate regulation in a geophysiological model  

Microsoft Academic Search

A central debate in community ecology concerns the relationship between the complexity of communities and their stability. How does the richness of food web structures affect their resistance and resilience to perturbation? Most mathematical models of communities have shown that stability declines as complexity increases but so far, modellers have not included the material environment in their calculations. Here an

Stephan P. Harding

1999-01-01

383

A stabilized discrete empirical interpolation method for model reduction of electrical, thermal, and microelectromechanical systems  

Microsoft Academic Search

We present a few modifications that stabilize nonlinear reduced order models generated by discrete empirical interpolation methods. We combine a different approach to linearization with a multipoint stabilization technique. The examples used to demonstrate our method’s effectiveness are a nonlinear transmission line, a micromachined switch, and a nonlinear thermal model for an RF amplifier.

Amit Hochman; Bradley N. Bond; Jacob K. White

2011-01-01

384

Stability and bifurcation in a neural network model with two delays  

Microsoft Academic Search

A simple neural network model with two delays is considered. Linear stability of the model is investigated by analyzing the associated characteristic transcendental equation. For the case without self-connection, it is found that the Hopf bifurcation occurs when the sum of the two delays varies and passes a sequence of critical values. The stability and direction of the Hopf bifurcation

Junjie Wei; Shigui Ruan

1999-01-01

385

Globally stabilizing switching controllers for a centrifugal compressor model with spool dynamics  

Microsoft Academic Search

In this paper we develop a globally stabilizing stability-based switching controller for a three-state lumped parameter centrifugal compressor surge model. The proposed model involves pressure and mass flow compression system dynamics as well as spool dynamics to account for the influence of speed transients on the compression surge dynamics. The proposed nonlinear switching controller architecture involves throttle and compressor torque

Alexander Leonessa; Wassim M. Haddad; Hua Li

2000-01-01

386

A Mechanical Model of Borehole Stability for Weak Plane Formation Under Porous Flow  

Microsoft Academic Search

Based on influence of porous flow on weak plane model, the authors established a mechanical model of borehole stability for weak plane formation under porous flow and analyzed effect of weak plane on borehole stability under porous flow. The results indicated that porous flow decreased strength of weak plane, enlarged the affecting domains of weak plane for rock mass strength,

Y. H. Lu; M. Chen; Y. Jin; G. Q. Zhang

2012-01-01

387

Modelling of dual stability in a cable-in-conduit conductor.  

National Technical Information Service (NTIS)

A zero dimensional stability model has been developed for cable-in-conduit superconductors. The model is effective in simulating the multi-valued stability behaviour in the vicinity of the limiting current. This has been by modifying the helium heat trans...

L. Bottura J. V. Minervini

1990-01-01

388

Stability criterion for nonlinear systems  

NASA Astrophysics Data System (ADS)

In the example of the Rössler model problem, a method for the practical analysis of the stability of nonlinear systems is considered. It is shown that besides the stability-instability conditions, the proposed criterion makes it possible in the analysis of the eigenvalue spectrum of the evolution matrix to determine the possibility of chaotic behavior of systems upon loss of stability.

Perevoznikov, E. N.

2013-07-01

389

Erosion Dynamics and Stability Analysis in a small Alpine Watershed: The Case of the Courset River  

NASA Astrophysics Data System (ADS)

A superficial landslide of around 20'000 m3 occurred on the 26 August 2005 on the Courset watershed. This watershed is located in the Rhone Valley, at the front of the Alpine Helvetic nappes, in the canton of Vaud (West Switzerland). Field observations shows evidence of old movements and erosion processes and help to understand the landslide failure mechanism: water provided by precipitation infiltrates but is confined by flysch layers located one to two meters deep. Water creates a layer between the soil and the rock that permits soil sliding on the surface of the bedrock. This particular event raised questions on the general stability of the zone. The aim of this study is to find out if the watershed will become a zone of intense erosion. To answer this question, various factors and tools are studied in particular erosion processes and slope stability. At first, the equilibrium profile of the Courset is determined to locate the most susceptible zones to erosion and the SLBL (sloping local base level) is used to determine the potential erosion volumes. Then, a classical slope stability analysis is performed, including laboratory tests to constraint geotechnical and hydrological parameters. The Sinmap method is used and compared with a new model developed to better characterize the hydrology. Precipitation data are also analyzed to better understand the trigger of landslide by rain, with a focus on the August 2005 precipitations.

Gavillet, Lauren; Nicolet, Pierrick; Rudaz, Benjamin; Jaboyedoff, Michel

2013-04-01

390

Stability analysis for acoustic wave propagation in tilted TI media by finite differences  

NASA Astrophysics Data System (ADS)

Several papers in recent years have reported instabilities in P-wave modelling, based on an acoustic approximation, for inhomogeneous transversely isotropic media with tilted symmetry axis (TTI media). In particular, instabilities tend to occur if the axis of symmetry varies rapidly in combination with strong contrasts of medium parameters, which is typically the case at the foot of a steeply dipping salt flank. In a recent paper, we have proposed and demonstrated a P-wave modelling approach for TTI media, based on rotated stress and strain tensors, in which the wave equations reduce to a coupled set of two second-order partial differential equations for two scalar stress components: a normal component along the variable axis of symmetry and a lateral component of stress in the plane perpendicular to that axis. Spatially constant density is assumed in this approach. A numerical discretization scheme was proposed which uses discrete second-derivative operators for the non-mixed second-order derivatives in the wave equations, and combined first-derivative operators for the mixed second-order derivatives. This paper provides a complete and rigorous stability analysis, assuming a uniformly sampled grid. Although the spatial discretization operator for the TTI acoustic wave equation is not self-adjoint, this operator still defines a complete basis of eigenfunctions of the solution space, provided that the solution space is somewhat restricted at locations where the medium is elliptically anisotropic. First, a stability analysis is given for a discretization scheme, which is purely based on first-derivative operators. It is shown that the coefficients of the central difference operators should satisfy certain conditions. In view of numerical artefacts, such a discretization scheme is not attractive, and the non-mixed second-order derivatives of the wave equation are discretized directly by second-derivative operators. It is shown that this modification preserves stability, provided that the central difference operators of the second-order derivatives dominate over the twice applied operators of the first-order derivatives. In practice, it turns out that this is almost the case. Stability of the desired discretization scheme is enforced by slightly weighting down the mixed second-order derivatives in the wave equation. This has a minor, practically negligible, effect on the kinematics of wave propagation. Finally, it is shown that non-reflecting boundary conditions, enforced by applying a taper at the boundaries of the grid, do not harm the stability of the discretization scheme.

Bakker, Peter M.; Duveneck, Eric

2011-05-01

391

Method of Performing Captive-Model Experiments to predict the Stability and Control Characteristics of Submarines.  

National Technical Information Service (NTIS)

The methods of performing captive model experiments and using analytical techniques for predicting the stability and control characteristics of submarines at the David Taylor Model Basin are discussed. An outline of Reynolds number scaling issues is provi...

J. P. Feldman

1995-01-01

392

Enterprise Systems Analysis and Modelling  

Microsoft Academic Search

In ES implementations, process modelling is a critical and often overlooked activity. This paper proposes a framework for process modelling of ES. The four steps method involves: Current Situation Analysis, Business Process Improvements and Requirements, Gap Analysis, and To-be process to develop. Outputs of the methodology are an interdependent set of organizational and system proposed changes, and feedback loops to

ANGEL ANTONIO DIAZ; OSWALDO LORENZO

2004-01-01

393

The effects of HNE on ovine oxymyoglobin redox stability in a microsome model.  

PubMed

The effect of 4-hydroxy-2-nonenal (HNE), a secondary lipid oxidation product, on ovine myoglobin (Mb) redox stability was investigated. HNE increased oxymyoglobin (OxyMb) oxidation under all pH/temperature conditions studied. Mono-, di- and tri-HNE adducts were detected by ESI-Q-TOF MS analysis. Sites of adduction, His 120, His 25 and His 65, were determined by ESI-CID-MS/MS analysis. The relationship between ovine Mb (with/without HNE) and lipid oxidation was also studied in a microsome model in the presence of ?-tocopherol. Surprisingly, preincubation of Mb with HNE did not affect subsequent Mb redox stability in the microsome model (P<0.05). Microsomes with elevated concentrations of ?-tocopherol delayed lipid and Mb oxidations relative to controls. HNE-treated ovine Mb caused greater lipid oxidation compared to control ovine Mb in control microsomes (P<0.05). This study demonstrated an interaction between ovine Mb oxidation and lipid oxidation. PMID:23747615

Yin, Shuang; Faustman, Cameron; Tatiyaborworntham, Nantawat; Ramanathan, Ranjith; Sun, Qun

2013-05-07

394

Stability analysis of numerical methods for systems of neutral delay-differential equations  

Microsoft Academic Search

Stability analysis of some representative numerical methods for systems of neutral delay-differential equations (NDDEs) is considered. After the establishment of a sufficient condition of asymptotic stability for linear NDDEs, the stability regions of linear multistep, explicit Runge-Kutta and implicitA-stable Runge-Kutta methods are discussed when they are applied to asymptotically stable linear NDDEs. Some mentioning about the extension of the results

Guang-Da Hu; Taketomo Mitsui

1995-01-01

395

Advanced techniques for the analysis of crisis stability, deterrence, and latency  

SciTech Connect

Studies on crisis stability, deterrence, and latency are presented in chronological order, which also reflects their logical order of development, captures the main features of stability analysis; relates first strike, crisis, and arms control stability as seen from US and Russian perspective; and addresses questions such as whether uncertainty in damage preference or defense deployment can be destabilizing. It illustrates the problems with alternative metrics, latency and reconstitution, and deep unilateral and proportional force reductions.

Canavan, G.H.

1997-12-01

396

Modeling of Neoclassical Tearing Mode Stability for Generalized Toroidal Geometry  

SciTech Connect

Neoclassical tearing modes (NTMs) can lead to disruption and loss of confinement. Previous analysis of these modes used large aspect ratio, low beta (plasma pressure/magnetic pressure) approximations to determine the effect of NTMs on tokamak plasmas. A more accurate tool is needed to predict the onset of these instabilities. As a follow-up to recent theoretical work, a code has been written which computes the tearing mode island growth rate for arbitrary tokamak geometry. It calls PEST-3 [A. Pletzer et al., J. Comput. Phys. 115, 530 (1994)] to compute delta prime, the resistive magnetohydrodynamic (MHD) matching parameter. The code also calls the FLUXGRID routines in NIMROD [A.H. Glasser et al., Plasma Phys. Controlled Fusion 41, A747 (1999)] for Dnc, DI and DR [C.C. Hegna, Phys. Plasmas 6, 3980 (1999); A.H. Glasser et al., Phys. Fluids 18, 875 (1975)], which are the bootstrap current driven term and the ideal and resistive interchange mode criterion, respectively. In addition to these components, the NIMROD routines calculate alphas-H, a new correction to the Pfirsch-Schlter term. Finite parallel transport effects were added and a National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] equilibrium was analyzed. Another program takes the output of PEST-3 and allows the user to specify the rational surface, island width, and amount of detail near the perturbed surface to visualize the total helical flux. The results of this work will determine the stability of NTMs in an spherical torus (ST) [Y.-K.M. Peng et al., Nucl. Fusion 26, 769 (1986)] plasma with greater accuracy than previously achieved.

A.L. Rosenberg; D.A. Gates; A. Pletzer; J.E. Menard; S.E. Kruger; C.C. Hegna; F. Paoletti; S. Sabbagh

2002-08-21

397

Modeling of neoclassical tearing mode stability for generalized toroidal geometry  

NASA Astrophysics Data System (ADS)

Neoclassical tearing modes (NTMs) can lead to disruption and loss of confinement. Previous analysis of these modes used large aspect ratio, low ? (plasma pressure/magnetic pressure) approximations to determine the effect of NTMs on tokamak plasmas. A more accurate tool is needed to predict the onset of these instabilities. As a follow-up to recent theoretical work, a code has been written which computes the tearing mode island growth rate for arbitrary tokamak geometry. It calls PEST-3 [A. Pletzer et al., J. Comput. Phys. 115, 530 (1994)] to compute ?', the resistive magnetohydrodynamic (MHD) matching parameter. The code also calls the FLUXGRID routines in NIMROD [A. H. Glasser et al., Plasma Phys. Controlled Fusion 41, A747 (1999)] for Dnc, DI, and DR [C. C. Hegna, Phys. Plasmas 6, 3980 (1999); A. H. Glasser et al., Phys. Fluids 18, 875 (1975)], which are the bootstrap current driven term and the ideal and resistive interchange mode criterion, respectively. In addition to these components, the NIMROD routines calculate ?s-H, a new correction to the Pfirsch-Schlüter term. Finite parallel transport effects were added and a National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] equilibrium was analyzed. Another program takes the output of PEST-3 and allows the user to specify the rational surface, island width, and amount of detail near the perturbed surface to visualize the total helical flux. The results of this work will determine the stability of NTMs in a spherical torus (ST) [Y.-K. M. Peng et al., Nucl. Fusion 26, 769 (1986)] plasma with greater accuracy than previously achieved.

Rosenberg, A. L.; Gates, D. A.; Pletzer, A.; Menard, J. E.; Kruger, S. E.; Hegna, C. C.; Paoletti, F.; Sabbagh, S.

2002-11-01

398

DIAGNOSIS, ANALYSIS, AND RESOLUTION OF THERMAL STABILITY ISSUES WITH HOM COUPLERS ON PROTOTYPE CEBAF SRF CAVITIES  

SciTech Connect

During initial testing of the prototype cavities incorporated into the developmental cryomodule Renascence severe thermal stability issues were encountered during CW operation. Additional diagnostic instrumentation was added. This enabled identification of an unanticipated thermal impedance between the HOM coupler probe feedthrough assembly and the cavity beamtube. Subsequent detailed FE analysis successfully modeled the situation and indicated the need for alternate cooling path for the couplers on those cavities. HOM damping was measured to be adequate employing only two of the four HOM couplers. The two pickup probes on the couplers at the input power coupler side of each cavity were removed, the remaining HOM probe feedthroughs were heat stationed to two-phase helium supply piping, and a novel heat sink was added to station both the inner and outer conductors of the remaining HOM rf cables. The characterization measurements, analysis, modifications, and resulting performance are presented.

Charles Reece; Edward Daly; G. Davis; William Hicks; Timothy Rothgeb; H. Phillips; Joseph Preble; Haipeng Wang; Genfa Wu

2008-02-12

399

Fixed-speed wind-generator and wind-park modeling for transient stability studies  

Microsoft Academic Search

Increasing levels of wind-turbine generation in modern power systems is initiating a need for accurate wind-generation transient stability models. Because many wind generators are often grouped together in wind parks, equivalence modeling of several wind generators is especially critical. In this paper, a reduced-order dynamic fixed-speed wind-generator model appropriate for transient stability simulation is presented. The model is derived using

Daniel J. Trudnowski; Andrew Gentile; Jawad M. Khan; Eric M. Petritz

2004-01-01

400

Self-optimization, community stability, and fluctuations in two individual-based models of biological coevolution.  

PubMed

We compare and contrast the long-time dynamical properties of two individual-based models of biological coevolution. Selection occurs via multispecies, stochastic population dynamics with reproduction probabilities that depend nonlinearly on the population densities of all species resident in the community. New species are introduced through mutation. Both models are amenable to exact linear stability analysis, and we compare the analytic results with large-scale kinetic Monte Carlo simulations, obtaining the population size as a function of an average interspecies interaction strength. Over time, the models self-optimize through mutation and selection to approximately maximize a community potential function, subject only to constraints internal to the particular model. If the interspecies interactions are randomly distributed on an interval including positive values, the system evolves toward self-sustaining, mutualistic communities. In contrast, for the predator-prey case the matrix of interactions is antisymmetric, and a nonzero population size must be sustained by an external resource. Time series of the diversity and population size for both models show approximate 1/f noise and power-law distributions for the lifetimes of communities and species. For the mutualistic model, these two lifetime distributions have the same exponent, while their exponents are different for the predator-prey model. The difference is probably due to greater resilience toward mass extinctions in the food-web like communities produced by the predator-prey model. PMID:17534620

Rikvold, Per Arne

2007-05-30

401

Model Systems of Precursor Cellular Membranes: Long-Chain Alcohols Stabilize Spontaneously Formed Oleic Acid Vesicles  

PubMed Central

Oleic acid vesicles have been used as model systems to study the properties of membranes that could be the evolutionary precursors of more complex, stable, and impermeable phospholipid biomembranes. Pure fatty acid vesicles in general show high sensitivity to ionic strength and pH variation, but there is growing evidence that this lack of stability can be counterbalanced through mixtures with other amphiphilic or surfactant compounds. Here, we present a systematic experimental analysis of the oleic acid system and explore the spontaneous formation of vesicles under different conditions, as well as the effects that alcohols and alkanes may have in the process. Our results support the hypothesis that alcohols (in particular 10- to 14-C-atom alcohols) contribute to the stability of oleic acid vesicles under a wider range of experimental conditions. Moreover, studies of mixed oleic-acid-alkane and oleic-acid-alcohol systems using infrared spectroscopy and Langmuir trough measurements indicate that precisely those alcohols that increased vesicle stability also decreased the mobility of oleic acid polar headgroups, as well as the area/molecule of lipid.

Rendon, Adela; Carton, David Gil; Sot, Jesus; Garcia-Pacios, Marcos; Montes, Ruth; Valle, Mikel; Arrondo, Jose-Luis R.; Goni, Felix M.; Ruiz-Mirazo, Kepa

2012-01-01

402

Stability of self-consistent solutions for the Hubbard model at intermediate and strong coupling  

NASA Astrophysics Data System (ADS)

We present a general framework for investigating the stability of solutions being a parquet-type extension of the Baym-Kadanoff construction of conserving approximations. To obtain a consistent description of one- and two-particle quantities, needed for the stability analysis, we use explicit equations for one- and two-particle Green functions simultaneously. We formulate a complete set of stability criteria and show that each instability, singularity in a two-particle function, is connected with a symmetry-breaking order parameter, either of density or anomalous type. We explicitly study the Hubbard model at intermediate coupling and demonstrate that approximations with static vertices become unstable with respect to spin flips, before the Mott-Hubbard metal-insulator transition in the paramagnetic phase or the Kondo strong-coupling regime can be reached. Further on, we use the parquet approximation and turn it into a workable scheme with dynamical vertex corrections. We obtain a theory with two-particle self-consistence, the complexity of which is comparable with fluctuation-exchange-type approximations. We show that it is the simplest consistent theory free of spurious phases being able to correctly describe qualitatively, quantum critical points and the transition from weak to strong coupling in correlated electron systems.

Janiš , V.

1999-10-01

403

Perturbed Stability Analysis of External Ideal MHD Modes  

NASA Astrophysics Data System (ADS)

Traditionally, numerical parameter scans are performed to study the effects of equilibrium shaping and profiles on long wavelength ideal MHD instabilities. Previously, we introduced a new perturbative technique to more efficiently explore these dependencies: changes in delta-W due to small equilibrium variations are found using a perturbation of the energy principle rather than with an eigenvalue-solver instability code. With this approach, the stability properties of similar equilibria can be efficiently explored without generating complete numerical results for every set of parameters (which is time-intensive for accurate representations of several configurations). Here, we apply this approach to toroidal geometry using GATO (an ideal MHD stability code) and experimental equilibria. In particular, we explore ideal MHD stability of external kink modes in the spherical tokamak Pegasus and resistive wall modes in DIII-D.

Comer, K. J.; Callen, J. D.; Hegna, C. C.; Garstka, G. D.; Turnbull, A. D.; Garofalo, A. M.; Cowley, S. C.

2002-11-01

404

Analysis of a combined influence of substrate wetting and surface electromigration on a thin film stability and dynamical morphologies  

NASA Astrophysics Data System (ADS)

A PDE-based model combining surface electromigration and wetting is developed for the analysis of morphological stability of ultrathin solid films. Adatom mobility is assumed anisotropic, and two directions of the electric field (parallel and perpendicular to the surface) are discussed and contrasted. Linear stability analyses of small-slope evolution equations are performed, followed by computations of fully nonlinear parametric evolution equations that permit surface overhangs. The results reveal parameter domains of instability for wetting and non-wetting films and variable electric field strength, nonlinear steady-state solutions in certain cases, and interesting coarsening behavior for strongly wetting films.

Khenner, Mikhail

2013-08-01

405

Novel delay-dependent stability analysis of Takagi—Sugeno fuzzy uncertain neural networks with time varying delays  

NASA Astrophysics Data System (ADS)

This paper presents the stability analysis for a class of neural networks with time varying delays that are represented by the Takagi—Sugeno (T—S) model. The main results given here focus on the stability criteria using a new Lyapunov functional. New relaxed conditions and new linear matrix inequality-based designs are proposed that outperform the previous results found in the literature. Numerical examples are provided to show that the achieved conditions are less conservative than the existing ones in the literature.

M. Syed, Ali

2012-07-01

406

Effect of calcification on the mechanical stability of plaque based on a three-dimensional carotid bifurcation model  

PubMed Central

Background This study characterizes the distribution and components of plaque structure by presenting a three-dimensional blood-vessel modelling with the aim of determining mechanical properties due to the effect of lipid core and calcification within a plaque. Numerical simulation has been used to answer how cap thickness and calcium distribution in lipids influence the biomechanical stress on the plaque. Method Modelling atherosclerotic plaque based on structural analysis confirms the rationale for plaque mechanical examination and the feasibility of our simulation model. Meaningful validation of predictions from modelled atherosclerotic plaque model typically requires examination of bona fide atherosclerotic lesions. To analyze a more accurate plaque rupture, fluid-structure interaction is applied to three-dimensional blood-vessel carotid bifurcation modelling. A patient-specific pressure variation is applied onto the plaque to influence its vulnerability. Results Modelling of the human atherosclerotic artery with varying degrees of lipid core elasticity, fibrous cap thickness and calcification gap, which is defined as the distance between the fibrous cap and calcification agglomerate, form the basis of our rupture analysis. Finite element analysis shows that the calcification gap should be conservatively smaller than its threshold to maintain plaque stability. The results add new mechanistic insights and methodologically sound data to investigate plaque rupture mechanics. Conclusion Structural analysis using a three-dimensional calcified model represents a more realistic simulation of late-stage atherosclerotic plaque. We also demonstrate that increases of calcium content that is coupled with a decrease in lipid core volume can stabilize plaque structurally.

2012-01-01

407

Deciphering large landslides: linking hydrological, groundwater and slope stability models through GIS  

NASA Astrophysics Data System (ADS)

Large landslides can deliver substantial volumes of sediment to river channels, with potentially adverse consequences for water quality and fish habitat. When planning land use activities, it is important both to consider the risks posed by landslides and to account for the effects of land use on rates of landslide movement. Of particular interest in the Pacific Northwest are the effects of timber harvest in groundwater recharge areas of landslides. Because of variability between sites, and variability over time in precipitation and other natural environmental factors affecting landslide behaviour, empirical data are usually insufficient for making such determinations. We describe here the use of simple numerical models of site hydrology, groundwater flow and slope stability for estimating the effects of timber harvest on the stability of the Hazel Landslide in northwestern Washington State. These effects are examined relative to those of river bank erosion at the landslide toe. The data used are distributed in time and space, as are the model results. A geographical information system (GIS) provides an efficient framework for data storage, transfer and display. Coupled with process-based numerical models, a GIS provides an effective tool for site-specific analysis of landslide behaviour.

Miller, Daniel J.; Sias, Joan

1998-05-01

408

Coalbed methane modeling analysis  

Microsoft Academic Search

Systems analyses or the Department of Energy's (DOE) Coalbed Methane Project (CMP) were performed at the Morgantown Energy Technology Center (METC). In the analyses, both reservoir and stimulation models were evaluated using data from US Steel's Oak Grove Coal Degasification Field. In the first part of the study two reservoir models designed for predicting methane and water production from coalbeds,

G. L. Covatch; A. W. Layne; S. P. Salamy

1985-01-01

409

Interface stability under biaxial loading of bilayered sheets between rigid surfaces—I. Bifurcation analysis  

Microsoft Academic Search

A bifurcation method has been applied to the plastic stability analysis of a bimetallic sheet between rigid surfaces subjected to biaxial loading. An orthotropic, incrementally-linear solid and plane strain conditions are assumed. In order to predict the stability behaviour near the bimaterial interface, three possible regimes (elliptic, hyperbolic and parabolic) are considered and two modes of instability are mentioned, namely,

J. M. Martínez-Esnaola; J. Gil-Sevillano

1997-01-01

410

Contingency Ranking for Voltage Stability Analysis of Large-Scale Power Systems  

Microsoft Academic Search

In this paper we propose a screening method and suitable software program to analyze contingencies and their impact on static voltage stability in large power systems. The program substantially reduces the number of load flow simulation for contingency analysis and voltage stability studies and is based on the impact of the contingency on the load, and the available Mega Watt

Majid Poshtan; Parviz Rastgoufard; Brij Singh

2004-01-01

411

SPECTROCHEMICAL ANALYSIS OF RADIOACTIVE MATERIALS. II. WALL-STABILIZED ARC DISCHARGE  

Microsoft Academic Search

Attempts were made to improve the reproducibility of the arc discharge ; method for the analysis of radioactive materials and to evaluate the advantages ; or disadvantages so achieved. Construction of the discharge chamber is described ; and illustrated. Discharge space stability was tollowed with a continuously ; recording camera. The discharge space stabilization improved the discharge ; duration reproducibility

Svoboda

1962-01-01

412

Stability analysis of paralleled DC\\/DC converters with active current sharing  

Microsoft Academic Search

A method for assessing the small-signal stability of paralleled converters with active current sharing is derived. The method is general and can be applied to systems with any number of converters. For identical converters, the method results in a particularly simple stability criterion. Illustrative examples show application of the analysis method. Design considerations for using the method are also provided

V. Joseph Thottuvelil; George C. Verghese

1996-01-01

413

An improved harmony search minimization algorithm using different slip surface generation methods for slope stability analysis  

Microsoft Academic Search

An improved harmony search algorithm is proposed which is found to be more efficient than the original harmony search algorithm for slope stability analysis. The effectiveness of the proposed algorithm is examined by considering several published cases. The improved harmony search method is applied to slope stability problems with five types of procedure for generating trial slip surfaces. It is

Y. M. Cheng; L. Li; T. Lansivaara; S. C. Chi; Y. J. Sun

2008-01-01

414

Does Premarital Cohabitation Predict Subsequent Marital Stability and Marital Quality? A Meta-Analysis  

ERIC Educational Resources Information Center

|Cohabitation with a romantic partner has become common in recent decades. This meta-analysis examined the link between premarital cohabitation and marital stability (k = 16) and marital quality (k = 12). Cohabitation had a significant negative association with both marital stability and marital quality. The negative predictive effect on marital…

Jose, Anita; O'Leary, K. Daniel; Moyer, Anne

2010-01-01

415

Linear stability analysis and direct numerical simulation of a miscible two-fluid channel flow  

Microsoft Academic Search

The temporal evolution of an initially laminar two-fluid channel flow is investigated using linear stability analysis and direct numerical simulation. The stability of a two-fluid shear flow is encountered in numerous situations, including water wave generation by wind, atomization of fuels, aircraft deicing and nuclear reactor cooling. The application of particular interest in this study is liquefying hybrid combustion, for

Siina Ilona Haapanen

2008-01-01

416

Stability analysis of resistive wall mode including effects of plasma rotation and error field  

Microsoft Academic Search

We have formulated the resistive wall mode stability analysis via an initial-value approach instead of the conventional normal- mode approach in order to resolve the critical rotation for stability and the braking problems. Plasma inertia and rotation are taken into account at a narrow layer around a rational surface. In the plasma region except for the layer, the Newcomb equation

Masaru Furukawa; Linjin Zheng

2007-01-01

417

Stability Analysis of Speed and Stator Resistance Estimators for Sensorless Induction Motor Drives  

Microsoft Academic Search

This paper presents an analysis by which the stability of a multiple-input-multiple-output system of simultaneous speed and stator resistance estimators for sensorless induction motor drives can be successfully predicted. The instability problem of an adaptive flux observer (AFO) is deeply investigated. In order to achieve stability over a wide range of operation, a design of the observer feedback gain is

Mohamed S. Zaky

2012-01-01

418

Computerized slope-stability analysis of refuse piles and impoundments by the simplified Bishop method  

Microsoft Academic Search

Title 30 Code of Federal Regulations, Part 77.214-216 concerning coal refuse piles and impoundments call for the engineered design and construction of these structures. An integral part of most of these designs is a slope stability analysis that often involves long, tedious and complicated calculations. With the use of a computer, these slope stability analyses can be performed relatively easily

S. G. Sawyer; D. S. Mazzei; K. K. Wu

1978-01-01

419

Analysis and estimation of transient stability for a grid-connected wind turbine with induction generator  

Microsoft Academic Search

Increasing levels of wind energy in modern electrical power system is initiating a need for accurate analysis and estimation of transient stability of wind turbine generation systems. This paper investigates the transient behaviors and possible direct methods for transient stability evaluation of a grid-connected wind turbine with squirrel cage induction generator (SCIG). Firstly, by using an equivalent lump mass method,

H. Li; B. Zhao; C. Yang; H. W. Chen; Z. Chen

2011-01-01

420

Numerical analysis of effective soil porosity and soil thickness effects on slope stability at a hillslope of weathered granitic soil formation  

Microsoft Academic Search

Modeling rainwater infiltration in slopes is vital to the analysis of slope failure induced by heavy rainfall. Amongst the\\u000a soil hydraulic properties, the hydraulic conductivity K has been frequently analyzed for its effects on slope stability. In\\u000a contrast, few studies have been published on the effects of water retention characteristics on slope stability. In this study,\\u000a a numerical model was

Muhammad Mukhlisin; Mohd Raihan Taha; Ken’ichirou Kosugi

2008-01-01

421

Comparison of load margin analysis for steady state voltage stability  

Microsoft Academic Search

Voltage stability becomes an increasing severe problem as the power systems become more complex and heavily loaded. Voltage problems have been a subject of great concern during planning and operation of power systems due to the significant number of serious failures believed to have been caused by this phenomenon. Therefore, how to develop an efficient research technique is one of

Yue Yuan; Xuehong Wen; Chengke Zhou

2007-01-01

422

Accuracy analysis of fixed voltage setpoint indices for voltage stability  

Microsoft Academic Search

There are many voltage stability indices for voltage security assessment and calculating stable margins from operating points to voltage instability at each load bus. Among them, one type of indices based on fixed voltage setpoint is applied in practice. Previous research has proved inaccuracy of these indices with the P-V curve method. This paper aims to verify the accuracy of

Sun Huadong; Tang Yong; Bu Guangquan

2010-01-01

423

Stability analysis of polynomials with coefficients in disks  

Microsoft Academic Search

The aim of this note is to report results on the stability of a class of polynomials from the small gain theorem point of view. The authors consider families of polynomials whose coefficients lie in closed circular disks around their nominal values. Various measures of variation of polynomial coefficients around their nominal value are considered and in each case necessary

Y. Li; K. M. Nagpal; E. B. Lee

1992-01-01

424

Stability of networked control systems: explicit analysis of delay  

Microsoft Academic Search

Recent technological advances have enabled distributed control systems to be implemented via networks. This allows feedback control loops to be closed over a shared communication channel. Network-induced delays are inevitable, however, when transmitting digital data between control devices. This paper analyzes the stability of such networked control systems (NCS). We first review some previous work on this topic, offering some

Michael S. Branicky; Stephen M. Phillips; Wei Zhang

2000-01-01

425

RELIABILITY ANALYSIS OF ON-BOTTOM PIPELINE STABILITY  

Microsoft Academic Search

Submarine pipeline on-bottom stability has been the subject of research in recent years. Some of the pipeline breakouts during severe hurricanes were attributed to excessive movements due to on-bottom instability phenomena. The instability is defined as a condition where the water will push the pipeline but the movement will not necessarily cause a failure. Nevertheless, during a severe hurricane, the

D. S. Riha

2000-01-01

426

STABILITY ANALYSIS OF THE BUTTAHATCHEE RIVER BASIN, MISSISSIPPI AND ALABAMA  

Technology Transfer Automated Retrieval System (TEKTRAN)

The overall purpose of this study was to evaluate the stability of the Buttahatchee River and major tributaries, and to determine if observed instabilities were the result of localized or system-wide disturbances. Instabilities in the channel may lead to excessive sediment erosion and deposition, b...

427

White Oak Dam stability analysis. Appendix. Volume II  

SciTech Connect

A parametric study was conducted to evaluate the stability of the White Oak Dam (WOD) embankment and foundation. Slope stability analyses were performed for the upper and lower bound soil properties at three sections of the dam using the PCSTABL4 computer program. Minimum safety factors were calculated for the applicable seismic and static loading conditions. Liquefaction potential of the dam embankment and foundation solid during the seismic event was assessed by using simplified procedures. The WOD is classified as a low hazard facility and the Evaluation Basis Earthquake (EBE) is defined as an earthquake with a magnitude of m{sub b} = 5.6 and a Peak Ground Accelerator (PGA) of 0.13 g. This event is approximately equivalent to a Modified Mercalli Intensity of VI-VIII. The EBE is used to perform the seismic evaluation for slope stability and liquefaction potential. Results of the stability analyses and the liquefaction assessment lead to the conclusion that the White Oak Dam is safe and stable for the static and the seismic events defined in this study. Ogden Environmental, at the request of MMES, has checked and verified the calculations for the critical loading conditions and performed a peer review of this report. Ogden has determined that the WOD is stable under the defined static and seismic loading conditions and the embankment materials are in general not susceptible to liquefaction.

Ahmed, S.B.

1994-01-01

428

Stability analysis of position and force control for robot arms  

Microsoft Academic Search

Stability issues involving the control of a robot arm under the influence of external forces are discussed. Several different scenarios are considered: position control with the external force as an unmodeled disturbance, compliant control for a bounded external force in some subspace, and compliant control for a force due to the interaction with an environment whose dynamical behavior can be

John T. Wen; Steve Murphy

1991-01-01

429

Analysis grasp stability for multi-fingered robot hand  

Microsoft Academic Search

This paper describes grasp stability for a multi-fingered robot hand, called the KIST hand. The robot hand has controlled by four under-actuated fingers with totally nine DOFs, which are controlled by two linear actuators and linkage knuckles. This mechanism is able to generate high power compare to common robot hands that use rotary actuators. The robot hand has four tactile

Eun-Hye Kim; Myo-Taeg Lim; Yong-Kwun Lee

2010-01-01

430

Stability Analysis of a Field of Nonprecipitating Trade Cumuli  

Microsoft Academic Search

The stability of a field of nonprecipitating Trade cumuli against a small perturbation in the mean flow is investigated. The situation is found to be highly unstable, with an e-folding time for growth typically 10 min for a wavelength of 20 km. The velocity of propagation of the resulting disturbance depends on the wind shear in both the cloud and

Dvm J. RYON

1973-01-01

431

Stability analysis of the TPX toroidal field coil.  

National Technical Information Service (NTIS)

The energy stability margin of the TPX/TF conductor has been calculated as a response to heat pulses with short initial quench zones and with long initial quench zones. The short IQZs approximate ramp-rate induced heating, and the long IQZs approximate he...

R. L. Wong

1994-01-01

432

Fuzzy stability analysis of regenerative chatter in milling  

NASA Astrophysics Data System (ADS)

During machining, unstable self-excited vibrations known as regenerative chatter can occur, causing excessive tool wear or failure, and a poor surface finish on the machined workpiece. Consequently it is desirable to predict, and hence avoid the onset of this instability. Regenerative chatter is a function of empirical cutting coefficients, and the structural dynamics of the machine-tool system. There can be significant uncertainties in the underlying parameters, so the predicted stability limits do not necessarily agree with those found in practice. In the present study, fuzzy arithmetic techniques are applied to the chatter stability problem. It is first shown that techniques based upon interval arithmetic are not suitable for this problem due to the issue of recursiveness. An implementation of fuzzy arithmetic is then developed based upon the work of Hanss and Klimke. The arithmetic is then applied to two techniques for predicting milling chatter stability: the classical approach of Altintas, and the time-finite element method of Mann. It is shown that for some cases careful programming can reduce the computational effort to acceptable levels. The problem of milling chatter uncertainty is then considered within the framework of Ben-Haim's information-gap theory. It is shown that the presented approach can be used to solve process design problems with robustness to the uncertain parameters. The fuzzy stability bounds are then compared to previously published data, to investigate how uncertainty propagation techniques can offer more insight into the accuracy of chatter predictions.

Sims, Neil D.; Manson, Graeme; Mann, Brian

2010-04-01

433

Army Science and Technology Analysis for Stabilization and Reconstruction Operations.  

National Technical Information Service (NTIS)

In the area of stabilization and reconstruction (S&R) operations, this study examines capability gaps and science and technology (S&T) needs and concludes that some areas require renewed emphasis. The Deputy Assistant Secretary of the Army for Research an...

A. Sciarretta D. Shorts R. Chait

2006-01-01

434

Auger analysis of a calcium partially stabilized zirconia  

Microsoft Academic Search

Partially stabilized zirconia (PSZ) offers unique properties compared to other strong ceramics, especially in terms of fracture toughness. This increased toughness is due to the crack tip stressassisted martensitic transformation of tetragonal phase precipitates to the monoclinic phase [1]. The large volume expansion and resulting compressive stresses are believed to retard growing cracks in PSZ. A limitation in applying ceramics

Robert Sherman

1984-01-01

435

Regional Analysis Of Slope Stability For Deepwater Engineering  

Microsoft Academic Search

Prediction of slope stability is necessary for hydrocarbon exploration and production in the deepwafer areas of the Gulf of Mexico. Shallow translational landslides have been found on the flanks of diapirs, on fault-tilted blocks, and locally where there are steep seafloor gradients. One landslide type involves downslope sediment motion over a basal shear surlace coinciding with a discrete bedding plane

James R. Hooper; David B. Prior

1989-01-01

436

A comprehensive analysis of mid-term voltage stability  

Microsoft Academic Search

This paper proposes a comprehensive approach to mid-term voltage stability, combining fast simulation, instability diagnosis and corrective control determination. The fast simulation approximates the mid-term evolution by a succession of equilibrium points, thereby offering a good compromise between efficiency and accuracy. The instability diagnosis and corrective control determination consist of fast sensitivity analyses at some points of the simulated system

T. Van Cutsem; Y. Jacquemart; J.-N. Marquet; P. Pruvot

1995-01-01

437

Stability analysis of networked control systems with Markov delay  

Microsoft Academic Search

The second buffer method is put forward to deal with the wrong order of data packets. The Markov characteristic of delay in networked control systems is analyzed. The evaluation method of element in state transition matrix is given when the wrong order of data packet is considered. Jump linear systems methods arc used to analyze the stability of networked control

Qixin Zhu; Guoping Lu; Jianyun Cao; Shousong Hu

2005-01-01

438

Advanced techniques for the analysis of crisis stability, deterrence, and latency  

SciTech Connect

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The principal results of studies on crisis stability, deterrence, and latency are presented in their order of development. They capture the main features of stability analysis; relate first strike, crisis, and arms control stability as seen from US and Russian perspective; and address whether different metrics, uncertain damage preferences, or the deployment of defenses can be destabilizing. The report explores differences between unilateral and proportional force reductions in the region of deep reductions where concern shifts from stability to latency.

Canavan, G.H.

1998-12-31

439

Short and long-term genome stability analysis of prokaryotic genomes  

PubMed Central

Background Gene organization dynamics is actively studied because it provides useful evolutionary information, makes functional annotation easier and often enables to characterize pathogens. There is therefore a strong interest in understanding the variability of this trait and the possible correlations with life-style. Two kinds of events affect genome organization: on one hand translocations and recombinations change the relative position of genes shared by two genomes (i.e. the backbone gene order); on the other, insertions and deletions leave the backbone gene order unchanged but they alter the gene neighborhoods by breaking the syntenic regions. A complete picture about genome organization evolution therefore requires to account for both kinds of events. Results We developed an approach where we model chromosomes as graphs on which we compute different stability estimators; we consider genome rearrangements as well as the effect of gene insertions and deletions. In a first part of the paper, we fit a measure of backbone gene order conservation (hereinafter called backbone stability) against phylogenetic distance for over 3000 genome comparisons, improving existing models for the divergence in time of backbone stability. Intra- and inter-specific comparisons were treated separately to focus on different time-scales. The use of multiple genomes of a same species allowed to identify genomes with diverging gene order with respect to their conspecific. The inter-species analysis indicates that pathogens are more often unstable with respect to non-pathogens. In a second part of the text, we show that in pathogens, gene content dynamics (insertions and deletions) have a much more dramatic effect on genome organization stability than backbone rearrangements. Conclusion In this work, we studied genome organization divergence taking into account the contribution of both genome order rearrangements and genome content dynamics. By studying species with multiple sequenced genomes available, we were able to explore genome organization stability at different time-scales and to find significant differences for pathogen and non-pathogen species. The output of our framework also allows to identify the conserved gene clusters and/or partial occurrences thereof, making possible to explore how gene clusters assembled during evolution.

2013-01-01

440

Transient Stability Analysis of Wind Turbines with Induction Generators Considering Blades and Shaft Flexibility  

Microsoft Academic Search

Increasing levels of wind turbine generation in modern power system is initiating a need for accurate wind generation transient stability models. Long flexible blades maybe have influence on the transient responses of wind generator systems with the increase in size of wind turbines during an electrical fault. In order to exactly analyze the transient stability of wind generator systems, by

H. Li; Z. Chen

2007-01-01

441

Trajectory Stability Modeling And Tolerances in the LCLS  

SciTech Connect

To maintain stable performance of the Linac Coherent Light Source (LCLS) x-ray free-electron laser, one must control the electron trajectory stability through the undulator to a small fraction of the beam size. BPM-based feedback loops running at 120 Hz will be effective in controlling jitter at low frequencies less than a few Hz. On the other hand, linac and injector stability tolerances must be chosen to limit jitter at higher frequencies. In this paper we study possible sources of high frequency jitter, including: (1) steering coil current regulation; (2) quadrupole magnet transverse vibrations; (3) quadrupole current regulation with transverse misalignments; (4) charge variations coupled to jitter through transverse wakefields of misaligned RF structures; and (5) bunch length variations coupled through coherent synchrotron radiation in the bunch compressor chicanes. Based on this study, we set component tolerances and estimate expected trajectory stability in the LCLS.

Wu, J.; Emma, P.; /SLAC

2007-04-27

442

40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.  

Code of Federal Regulations, 2010 CFR

40 Protection of Environment 33 2011-07-01 2011-07-01... PM-stabilization and weighing environments for gravimetric analysis. 1065...Section 1065.190 Protection of Environment ENVIRONMENTAL PROTECTION...

2011-07-01

443

40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.  

Code of Federal Regulations, 2010 CFR

40 Protection of Environment 32 2009-07-01 2009-07-01... PM-stabilization and weighing environments for gravimetric analysis. 1065...Section 1065.190 Protection of Environment ENVIRONMENTAL PROTECTION...

2009-07-01

444

40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.  

Code of Federal Regulations, 2010 CFR

40 Protection of Environment 32 2010-07-01 2010-07-01... PM-stabilization and weighing environments for gravimetric analysis. 1065...Section 1065.190 Protection of Environment ENVIRONMENTAL PROTECTION...

2010-07-01

445

40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.  

Code of Federal Regulations, 2013 CFR

40 Protection of Environment 34 2013-07-01 2013-07-01... PM-stabilization and weighing environments for gravimetric analysis. 1065...Section 1065.190 Protection of Environment ENVIRONMENTAL PROTECTION...

2013-07-01

446

APPLICATIONS ANALYSIS REPORT: SITE PROGRAM DEMONSTRATION TEST SOLIDITECH, INC. SOLIDIFICATION/ STABILIZATION PROCESS  

EPA Science Inventory

This Applications Analysis Report evaluates the Soliditech, Inc., solidification/ stabilization process for the on-site treatment of waste materials. The Soliditech process mixes and chemically treats waste material with Urrichem (a proprietary reagent), additives, pozzolanic mat...

447

Linear and Nonlinear Stability Analysis, Associated to Experimental Fast Reactors. Part 2.  

National Technical Information Service (NTIS)

The nonlinear effects in fast reactors kinetics and their stability are studied. The Lyapunov criteria and the Lurie-Letov functions for nonlinear systems were established and simulated. Small oscillations were studied by a Fourier analysis to clarify par...

E. S. do Amorim C. de Moura Neto M. A. P. Rosa

1980-01-01

448

SILICATE TECHNOLOGY CORPORATION'S SOLIDIFICATION/ STABILIZATION TECHNOLOGY FOR ORGANIC AND INORGANIC CONTAMINANTS IN SOILS - APPLICATIONS ANALYSIS REPORT  

EPA Science Inventory

This Applications Analysis Report evaluates the solidification/stabilization treatment process of Silicate Technology Corporation (STC) for the on-site treatment of hazardous waste. The STC immobilization technology utilizes a proprietary product (FMS Silicate) to chemically stab...

449

Stability of mixed micellar bile models supersaturated with cholesterol.  

PubMed Central

The maximal equilibrium solubility of cholesterol in mixtures of phosphatidylcholine (PC)1 and bile salts depends on the cholesterol/PC ratio (Rc) and on the effective ratio (Re) between nonmonomeric bile salts and the sum (CT) of PC and cholesterol concentrations (Carey and Small, 1978; Lichtenberg et al., 1984). By contrast, the concentration of bile salts required for solubilization of liposomes made of PC and cholesterol does not depend on Rc (Lichtenberg et al., 1984 and 1988). Thus, for Rc greater than 0.4, solubilization of the PC-cholesterol liposomes yields PC-cholesterol-bile salts mixed micellar systems which are supersaturated with cholesterol. In these metastable systems, the mixed micelles spontaneously undergo partial revesiculation followed by crystallization of cholesterol. The rate of the latter processes depends upon Rc, Re, and CT. For any given Rc and Re, the rate of revesiculation increases dramatically with increasing the lipid concentration CT, reflecting the involvement of many mixed micelles in the formation of each vesicle. The rate also increases, for any given CT and Re, upon increasing the cholesterol to PC ratio, Rc, probably due to the increasing degree of supersaturation. Increasing the cholate to lipid effective ratio, Re, by elevation of cholate concentration at constant Rc and CT has a complex effect on the rate of the revesiculation process. As expected, cholate concentration higher than that required for complete solubilization at equilibrium yields stable mixed micellar systems which do not undergo revesiculation, but for lower cholate concentrations decreasing the degree of supersaturation (by increasing [cholate]) results in faster revesiculation. We interpret these results in terms of the structure of the mixed micelles; micelles with two or more PC molecules per one molecule of cholesterol are relatively stable but increasing the bile salt concentration may cause dissociation of such 1:2 cholesterol:PC complexes, hence reducing the stability of the mixed micellar dispersions. The instability of PC-cholesterol-cholate mixed systems with intermediary range of cholate to lipids ratio may be significant to gallbladder stone formation as: (a) biliary bile contains PC-cholesterol vesicles which may be, at least partially, solubilized by bile salts during the process of bile concentration in the gallbladder, resulting in mixtures similar to our model systems; and (b) the bile composition of cholesterol gallstone patients is within an intermediary range of bile salts to lipids ratio. Images FIGURE 2 FIGURE 2 FIGURE 2 FIGURE 2

Lichtenberg, D; Ragimova, S; Bor, A; Almog, S; Vinkler, C; Kalina, M; Peled, Y; Halpern, Z

1988-01-01

450

Intelligence Analysis Modeling  

Microsoft Academic Search

Intelligence is the process of supporting the policymakers in making their decisions by providing them with the specific information they need. Intelligence analysis is the effort of extracting the nature of intelligence issue with the policy goal in mind. It is performed by intelligence analysts who form judgments that add value to the collected material. With the increased open source

Ahmet Koltuksuz; Selma Tekir

2006-01-01