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1

A reference model approach to stability analysis of neural networks

In this paper, a novel methodology called a refer- ence model approach to stability analysis of neural networks is proposed. The core of the new approach is to study a neural net- work model with reference to other related models, so that dif- ferent modeling approaches can be combinatively used and pow- erfully cross-fertilized. Focused on two representative neural net-

Hong Qiao; Jigen Peng; Zong-ben Xu; Bo Zhang

2003-01-01

2

Drosophila Circadian Rhythms: Stability Robustness Analysis and Model Reduction

Drosophila Circadian Rhythms: Stability Robustness Analysis and Model Reduction Jorge M. Gonc investigates two models of circadian rhythms in Drosophila: one by Gonze et al. and a more generic model by Vilar et al. that describes the biological clock in Drosophila as well as other organisms. For both

Gonçalves, Jorge

3

Stability analysis of within-host parasite models with delays

Stability analysis of within-host parasite models with delays Abderrahman Iggidr a, Joseph Mbang a. Abstract We provide a global analysis of systems of within-host parasitic infections. The sys- tems studied be thought as systems arising from within-host parasitic systems with distributed continuous delays. We

Paris-Sud XI, UniversitÃ© de

4

Nonlinear stability analysis of a disk brake model

It has become commonly accepted by scientists and engineers that brake squeal is generated by friction-induced self-excited\\u000a vibrations of the brake system. The noise-free configuration of the brake system loses stability through a flutter-type instability\\u000a and the system starts oscillating in a limit cycle. Usually, the stability analysis of disk brake models, both analytical\\u000a as well as finite element based,

Daniel Hochlenert

2009-01-01

5

A Coupled Aeroelastic Model for Launch Vehicle Stability Analysis

NASA Technical Reports Server (NTRS)

A technique for incorporating distributed aerodynamic normal forces and aeroelastic coupling effects into a stability analysis model of a launch vehicle is presented. The formulation augments the linear state-space launch vehicle plant dynamics that are compactly derived as a system of coupled linear differential equations representing small angular and translational perturbations of the rigid body, nozzle, and sloshing propellant coupled with normal vibration of a set of orthogonal modes. The interaction of generalized forces due to aeroelastic coupling and thrust can be expressed as a set of augmenting non-diagonal stiffness and damping matrices in modal coordinates with no penalty on system order. While the eigenvalues of the structural response in the presence of thrust and aeroelastic forcing can be predicted at a given flight condition independent of the remaining degrees of freedom, the coupled model provides confidence in closed-loop stability in the presence of rigid-body, slosh, and actuator dynamics. Simulation results are presented that characterize the coupled dynamic response of the Ares I launch vehicle and the impact of aeroelasticity on control system stability margins.

Orr, Jeb S.

2010-01-01

6

Linear Stability Analysis of Thermo-Lattice Boltzmann Models

The numerical stability of thermo-lattice Boltzmann (TLBE) models is presented.The TLBE algorithm is linearized and represented in matrix form. The spectral radius of the resulting matrix is obtained by the method of powers. In particular, the numerical stability of two 2-speed 13-bit TLBE models—one based on the hexagonal lattice, and the other on a square lattice—is examined. For these two

Pavol Pavlo; George Vahala; Linda Vahala; Min Soe

1998-01-01

7

Stability analysis of the Euler discretization for SIR epidemic model

NASA Astrophysics Data System (ADS)

In this paper we consider a discrete SIR epidemic model obtained by the Euler method. For that discrete model, existence of disease free equilibrium and endemic equilibrium is established. Sufficient conditions on the local asymptotical stability of both disease free equilibrium and endemic equilibrium are also derived. It is found that the local asymptotical stability of the existing equilibrium is achieved only for a small time step size h. If h is further increased and passes the critical value, then both equilibriums will lose their stability. Our numerical simulations show that a complex dynamical behavior such as bifurcation or chaos phenomenon will appear for relatively large h. Both analytical and numerical results show that the discrete SIR model has a richer dynamical behavior than its continuous counterpart.

Suryanto, Agus

2014-06-01

8

Stability and bifurcation analysis in a delayed SIR model

In this paper, a time-delayed SIR model with a nonlinear incidence rate is considered. The existence of Hopf bifurcations at the endemic equilibrium is established by analyzing the distribution of the characteristic values. A explicit algorithm for determining the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions are derived by using the normal form and

Zhichao Jiang; Junjie Wei

2008-01-01

9

Modeling uncertainty in stability analysis for design of embankment dams on difficult foundations

A probabilistic 3-D slope stability analysis model (PTDSSAM) is developed to evaluate the stability of embankment dams and their foundations under conditions of staged construction taking into consideration uncertainty, spatial variabilities and correlations of shear strength parameters, as well as the uncertainties in pore water pressure. The model has the following capabilities: (1) conducting undrained shear strength analysis (USA) and

Azm S. Al-Homoud; Najat Tanash

2004-01-01

10

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

To facilitate stability analysis of discrete-time bidirectional associative memory (BAM) neural networks, they were converted\\u000a into novel neural network models, termed standard neural network models (SNNMs), which interconnect linear dynamic systems\\u000a and bounded static nonlinear operators. By combining a number of different Lyapunov functionals with S-procedure, some useful\\u000a criteria of global asymptotic stability and global exponential stability of the equilibrium

Zhang Sen-lin; Liu Mei-qin

2005-01-01

11

Slope Stability Analysis Using Radial Slices: A Mathematical Model

NASA Astrophysics Data System (ADS)

In this paper, a mathematical model has been formulated for calculating the factor of safety of a slope. Corresponding computer code has also been developed. Limit equilibrium method (moment equilibrium) has been adopted for calculating the net resulting driving and resisting forces. The probable slip circle region has been divided into radial slices for the simulation process. In this approach, the inter-slice shear forces are zero. Thus, the calculation process becomes simpler as compared to that with vertical slices. The slope stability analyses were done. Validation of the present program was done with existing limit equilibrium based methods. Various models were prepared and analysed with varying geometry and soil strength parameters. These models were also analysed with other limit equilibrium methods like Bishop, Janbu and Spencer method. The results were found to be in agreement with the results of other limit equilibrium methods for the same dump soil properties and slope parameters.

Kumar, Gyan Prakash; Das, Adarsha; Rai, Rajesh; Jaiswal, Ashok

2015-02-01

12

Algebraic Geometrization of the Kuramoto Model: Equilibria and Stability Analysis

Finding equilibria of the finite size Kuramoto model amounts to solving a nonlinear system of equations, which is an important yet challenging problem. We translate this into an algebraic geometry problem and use numerical methods to find all of the equilibria for various choices of coupling constants K, natural frequencies, and on different graphs. We note that for even modest sizes (N ~ 10-20), the number of equilibria is already more than 100,000. We analyze the stability of each computed equilibrium as well as the configuration of angles. Our exploration of the equilibrium landscape leads to unexpected and possibly surprising results including non-monotonicity in the number of equilibria, a predictable pattern in the indices of equilibria, counter-examples to popular conjectures, multi-stable equilibrium landscapes, scenarios with only unstable equilibria, and multiple distinct extrema in the stable equilibrium distribution as a function of the number of cycles in the graph.

Dhagash Mehta; Noah Daleo; Florian Dörfler; Jonathan D. Hauenstein

2015-01-03

13

This paper presents the theoretical background and analytical methods developed for BC Hydro's on-line transient stability assessment (TSA) module. It concentrates on the preprocessing modeling, stability analysis\\/margin calculation and post processing techniques, the architecture, hardware and implementation are presented in a companion paper. BC Hydro's TSA has been tested with thousands of cases using a large scale detailed basecase derived

Y. Mansour; E. Vaahedi; A. Y. Chang; B. R. Corns; B. W. Garrett; K. Demaree; T. Athay; K. Cheung

1995-01-01

14

Distributed nonlinear modeling and stability analysis of axial compressor stall and surge

This paper presents a nonlinear formulation of the Moore-Greitzer rotating stall model that is suitable for control analysis and design. The model is validated by comparing stall inception experiments to simulated stall inception transients. The shape of the nonlinear compressor characteristic is shown to be a primary determinant of stall inception transient behavior. A Lyapunov stability analysis procedure is then

Catherine A. Mansoux; Daniel L. Gysling; Joga D. Setiawan; James D. Paduano

1994-01-01

15

NASA Astrophysics Data System (ADS)

This paper presents an extended intelligent driver traffic flow model, in which the power of the considered vehicle is strengthened in proportion to that of the immediately preceding vehicle. We analyze the stability against a small perturbation by use of the linear stability method for the proposed traffic flow model on a single lane under open boundary condition, with the finding that the traffic flow stability can be improved by increasing the proportion of the direct power cooperation of the preceding vehicle. The participation of forward power cooperation can help to stabilize the traffic flow and suppress the traffic jams. In addition, the simulations under open boundary single lane are conducted to validate the correctness on theoretical deduction, which shows that numerical results in large-wave and short-wave stability are in good agreement with those of theoretical analysis.

Li, Zhipeng; Li, Wenzhong; Xu, Shangzhi; Qian, Yeqing

2015-02-01

16

Stability Analysis of a Simplified Yet Complete Model for Chronic Myelogenous Leukemia

Stability Analysis of a Simplified Yet Complete Model for Chronic Myelogenous Leukemia Marie Doumic and of chronic myelogenous leukemia, and it presents the advantage of having fewer parameters, which makes, hematopoiesis, chronic myelogenous leukemia, model simplification. 1 INRIA Paris-Rocquencourt, BANG, BP105, F

Perthame, Benoit

17

Stability Analysis of a Simplified Yet Complete Model for Chronic Myelegenous Leukemia

Stability Analysis of a Simplified Yet Complete Model for Chronic Myelegenous Leukemia Marie Doumic is of value in understanding the dynamics of hematopoiesis and of chronic myelogenous leukemia leukemia, model simplification. 1 INRIA Paris-Rocquencourt, BANG, BP105, F78153 LeChesnay Cedex. Email

Jauffret, Marie Doumic

18

Stability analysis of dynamic collaboration model with control signals on two lanes

NASA Astrophysics Data System (ADS)

In this paper, the influence of control signals on the stability of two-lane traffic flow is mainly studied by applying control theory with lane changing behaviors. We present the two-lane dynamic collaboration model with lateral friction and the expressions of feedback control signals. What is more, utilizing the delayed feedback control theory to the two-lane dynamic collaboration model with control signals, we investigate the stability of traffic flow theoretically and the stability conditions for both lanes are derived with finding that the forward and lateral feedback signals can improve the stability of traffic flow while the backward feedback signals cannot achieve it. Besides, direct simulations are conducted to verify the results of theoretical analysis, which shows that the feedback signals have a significant effect on the running state of two vehicle groups, and the results are same with the theoretical analysis.

Li, Zhipeng; Zhang, Run; Xu, Shangzhi; Qian, Yeqing; Xu, Juan

2014-12-01

19

Analytical modeling of the input admittance of an electric drive for stability analysis purposes

NASA Astrophysics Data System (ADS)

Embedded electric HVDC distribution network are facing difficult issues on quality and stability concerns. In order to help to resolve those problems, this paper proposes to develop an analytical model of an electric drive. This self-contained model includes an inverter, its regulation loops and the PMSM. After comparing the model with its equivalent (abc) full model, the study focuses on frequency analysis. The association with an input filter helps in expressing stability of the whole assembly by means of Routh-Hurtwitz criterion.

Girinon, S.; Baumann, C.; Piquet, H.; Roux, N.

2009-07-01

20

Stability analysis and optimal vaccination of an SIR epidemic model

Almost all mathematical models of diseases start from the same basic premise: the population can be subdivided into a set of distinct classes dependent upon experience with respect to the relevant disease. Most of these models classify individuals as either a susceptible individual S, infected individual I or recovered individual R. This is called the susceptible–infected–recovered (SIR) model. In this

Gul Zaman; Yong Han Kang; Il Hyo Jung

2008-01-01

21

Stability of the Human Respiratory Control System. Part I: Analysis of a twodimensional delay models of the human respiratory control system have been developed since 1940 to study a wide range signals to the respiratory control system has been studied since the work of Grodins et al. in the early

22

Stability Analysis of a Model of Atherosclerotic Plaque Growth

Atherosclerosis, the formation of life-threatening plaques in blood vessels, is a form of cardiovascular disease. In this paper, we analyze a simplified model of plaque growth to derive physically meaningful results about the growth of plaques. In particular, the main results of this paper are two conditions, which express that the immune response increases as LDL cholesterol levels increase and that diffusion prevails over inflammation in a healthy artery.

Reddy, Sushruth; Seshaiyer, Padmanabhan

2015-01-01

23

Analysis of stability and density waves of traffic flow model in an ITS environment

NASA Astrophysics Data System (ADS)

By introducing relative velocities of arbitrary number of cars ahead into the full velocity difference models (FVDM), we present a forward looking relative velocity model (FLRVM) of cooperative driving control system. To our knowledge, the model is an improvement over the similar extension in the forward looking optimal velocity models (FLOVM), because it is more reasonable and realistic in implement of incorporating intelligent transportation system in traffic. Then the stability criterion is investigated by the linear stability analysis with finding that new consideration theoretically lead to the improvement of the stability of traffic flow, and the validity of our theoretical analysis is confirmed by direct simulations. In addition, nonlinear analysis of the model shows that the three waves: triangular shock wave, soliton wave and kink-antikink wave appear respectively in stable, metastable and unstable regions. These correspond to the solutions of the Burgers equation, Korteweg-de Vries (KdV) equation and modified Korteweg-de Vries (mKdV) equation.

Li, Z.-P.; Liu, Y.-C.

2006-10-01

24

The stability analysis of the full velocity and acceleration velocity model

NASA Astrophysics Data System (ADS)

The stability analysis is one of the important problems in the traffic flow theory, since the congestion phenomena can be regarded as the instability and the phase transition of a dynamical system. Theoretically, we analyze the stable conditions of the full velocity and acceleration difference model (FVADM), which is proposed by introducing the acceleration difference term based on the previous car-following models (the optimal velocity model and the full velocity difference model, OVM and FVDM). By numerical simulations, it is found that when the traffic flow is unstable, the traffic jam in the FVADM is weaker than that in the FVDM. Also it is observed that the spreading speed of the jam is slower in the FVADM than that in the FVDM and the fluctuations of vehicles in the FVADM are smaller than those in the FVDM. Therefore, the acceleration difference term has strong effects on traffic dynamics and plays an important role in stabilizing the traffic flow.

Xiaomei, Zhao; Ziyou, Gao

2007-03-01

25

Sensitivity analysis and calibration of a coupled hydrological/slope stability model (TRIGRS)

NASA Astrophysics Data System (ADS)

Shallow landslides potentially endanger human living in mountain regions worldwide. In order to prevent impacts of such gravitational mass movements it is necessary to fully understand the processes involved. Shallow landslides are usually understood as gravitational mass movements of the translational, slope-parallel type comprising of a mixture of earth and debris with a maximum depth of 1-2 m. Depending on the degree of saturation the initial sliding can turn into a flow-like movement. Numerous approaches for modelling shallow landslide susceptibility with different degrees of complexity exist. Regardless of the modelling approach it is crucial to provide sufficient field data, mainly on regolith characteristics. As for the TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability) model, numerous hydraulic and geotechnical parameters have to be known area-wide. Hence, as spatial interpolation of these input parameters is generally problematic in terms of accuracy, calibrating the model accordingly is a crucial step before conducting any simulations. This study presents a sensitivity analysis and the calibration of the coupled hydrological/slope stability model TRIGRS for a study area in Vorarlberg (Austria). The results of the sensitivity analysis show that in case of the stability model cohesion is the driving parameter while for the hydrological model it is the initial depth of the water table and the saturated hydraulic conductivity. The calibration of the stability model was carried out using a landslide inventory assuming completely saturated conditions. The use of geotechnical parameters extracted from literature for mapped soil types generally lead to unlikely stable conditions. In order to simulate mapped landslide initial areas correctly values for soil cohesion had to be adapted. However, the calibration of the stability model generally supports the assumption of saturated conditions. In absence of meteorological or hydrological data the hydrological model was calibrated using the landslide inventory aiming at saturated conditions for the respective landslide initial zones. Simulations conducted with the calibrated input parameters generally lead to conservatively unstable conditions. However, it has to be noted that the TRIGRS model does not account for effects of vegetation on slope hydrology and stability (e.g. interception or root cohesion). This work has been conducted within C3S-ISLS, which is funded by the Austrian Climate and Energy Fund, 5th ACRP Program. http://www.uibk.ac.at/geographie/lidar/c3s/c3s.html

Zieher, Thomas; Rutzinger, Martin; Perzl, Frank; Meißl, Gertraud

2014-05-01

26

NASA Technical Reports Server (NTRS)

Results of dynamic response and stability wind tunnel tests of three 62.2 cm (24.5 in) diameter models of the Prop-Fan, advanced turboprop, are presented. Measurements of dynamic response were made with the rotors mounted on an isolated nacelle, with varying tilt for nonuniform inflow. One model was also tested using a semi-span wing and fuselage configuration for response to realistic aircraft inflow. Stability tests were performed using tunnel turbulence or a nitrogen jet for excitation. Measurements are compared with predictions made using beam analysis methods for the model with straight blades, and finite element analysis methods for the models with swept blades. Correlations between measured and predicted rotating blade natural frequencies for all the models are very good. The IP dynamic response of the straight blade model is reasonably well predicted. The IP response of the swept blades is underpredicted and the wing induced response of the straight blade is overpredicted. Two models did not flutter, as predicted. One swept blade model encountered an instability at a higher RPM than predicted, showing predictions to be conservative.

Bansal, P. N.; Arseneaux, P. J.; Smith, A. F.; Turnberg, J. E.; Brooks, B. M.

1985-01-01

27

NASA Astrophysics Data System (ADS)

Most of the slopes of the hilly areas of the Apennines are composed of colluvial soils originating from the weathering of the bedrock and down slope transportation. Shallow slides affect this superficial cover, depend largely on the surface topography and are a recurrent problem. SINMAP and SHALSTAB are terrain stability models that combine steady state hydrology assumptions with the infinite slope stability model to quantify shallow slope stability. They have a similar physical basis but they use different indices to quantify instability. The purposes of this study are to test and compare the approaches of SINMAP and SHALSTAB models for slope stability analysis and to compare the results of these analyses with the locations of the shallow landslides that occurred on November 2002 in an area of the Oltrepo Pavese (Northern Apennines). The territory of S. Giuletta, characterized by clayey-silty colluvial soils, represents the test site. The Digital Elevation Model was constructed from a 1:5000 scale contour map and was used to estimate the slope of the terrain as well as the potential soil moisture conditions. In situ and laboratory tests provided the basis for measuring values for soil hydraulic and geotechnical parameters (moisture content, soil suction, Atterberg limits, methylene blue dye adsorption, hydraulic conductivity). Soil thickness was extracted from a soil database. An inventory of landslide from interpretation of aerial photographs and field surveys was used to document sites of instability (mostly soil slips) and to provide a test of model performance by comparing observed landslide locations with model predictions. The study discusses the practical advantages and limitations of the two models in connection with the geological characteristics of the studied area, which could be representative of similar geological contexts in the Apennines.

Meisina, C.; Scarabelli, S.

2007-06-01

28

NASA Technical Reports Server (NTRS)

Hybrid Heavy Lift Airship (HHLA) is a proposed candidate vehicle aimed at providing heavy lift capability at low cost. This vehicle consists of a buoyant envelope attached to a supporting structure to which four rotor systems, taken from existing helicopters are attached. Nonlinear equations of motion capable of modelling the dynamics of this coupled multi-rotor/support frame/vehicle system have been developed. Using these equations of motion the aeroelastic and aeromechanical stability analysis is performed aimed at identifying potential instabilities which could occur for this type of vehicle. The coupling between various blade, supporting structure and rigid body modes is identified. Furthermore, the effects of changes in buoyancy ratio (Buoyant lift/total weight) on the dynamic characteristics of the vehicle are studied. The dynamic effects found are of considerable importance for the design of such vehicles. The analytical model developed is also useful for studying the aeromechanical stability of single rotor and tandem rotor coupled rotor/fuselage systems.

Venkatesan, C.; Friedmann, P. P.

1984-01-01

29

Stability analysis of an e-SEIAR model with point-to-group worm propagation

NASA Astrophysics Data System (ADS)

Internet worms have drawn significant attention due to their enormous threats to the Internet. The main goal of this paper is to explore the interaction dynamics between a malicious worm and an benign worm, using a mathematical model, namely e-SEIAR. The e-SEIAR model takes two important network environment factors into consideration: point-to-group worm propagation mode and benign worms. Furthermore, some related dynamics properties are studied, along with the analysis of how to combat the worm prevalence based on the stability of equilibria. Simulation results show that the performance of our proposed models is effective in combating such worms, in terms of decreasing the number of hosts infected by the malicious worm and reducing the malicious worm propagation speed. Based on our simulations, we believe there is great potential for an effective method to use benign worms to combat malicious worms in some point-to-group applications.

Wang, Fangwei; Zhang, Yunkai; Wang, Changguang; Ma, Jianfeng

2015-03-01

30

The Stability Analysis for an Extended Car Following Model Based on Control Theory

NASA Astrophysics Data System (ADS)

A new method is proposed to study the stability of the car-following model considering traffic interruption probability. The stability condition for the extended car-following model is obtained by using the Lyapunov function and the condition for no traffic jam is also given based on the control theory. Numerical simulations are conducted to demonstrate and verify the analytical results. Moreover, numerical simulations show that the traffic interruption probability has an influence on driving behavior and confirm the effectiveness of the method on the stability of traffic flow.

Ge, Hong-Xia; Meng, Xiang-Pei; Zhu, Ke-Qiang; Cheng, Rong-Jun

2014-08-01

31

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

32

This paper deals with modeling and stability analysis of a doubly-fed induction generator (DFIG)-based wind-power unit that is interfaced with the grid via a series-compensated transmission line. A detailed mathematical model is developed in this paper that takes into account dynamics of the flux observer, phase-locked loop (PLL), controllers of the power-electronic converter, and wind turbine. Using the model and

Amir Ostadi; Amirnaser Yazdani; Rajiv K. Varma

2009-01-01

33

NASA Astrophysics Data System (ADS)

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 10-5 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.

2009-11-01

34

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

35

Stability of the Human Respiratory Control System. Part I: Analysis of a two-dimensional delay of the human respiratory control system have been developed since 1940 to study a wide range of features. 1 Introduction and Modeling Considerations The human respiratory system acts to exchange carbon

36

Steady-state and stability analysis of a population balance based nonlinear ice cream the key phenomenons of the crystallization process. In ice cream crystallization, it is well known that the quality of the product, that is the hardness and the texture of the ice cream, depends on the ice crystal

Boyer, Edmond

37

Steady-state and stability analysis of a population balance based nonlinear ice cream that adequately describes the key phenomena of the crystallization process. In ice cream crystallization, it is well known that the quality of the product, that is the hardness and the texture of the ice cream

Boyer, Edmond

38

Fluid-to-fluid modeling of natural circulation boiling loops for stability analysis

Gravity driven flows may induce oscillations influencing the stability of natural circulation nuclear boiling water reactors. To experimentally study such phenomenon, a facility based on fluid-to-fluid downscaling modeling is proposed. New design criteria are developed for that purpose. It is found that a unique geometrical scale has to be used for all radial and axial dimensions. Moreover, the geometry and

C. P. Marcel; M. Rohde; T. H. J. J. Van der Hagen

2008-01-01

39

NASA Astrophysics Data System (ADS)

A nonlocal continuum shell model is developed to study the stability of nanocones under combined loading: external pressure and compression force. The nonlinear governing equations of motion of nanocone are obtained using Hamilton's principle and the external loads are considered as prestress. Based on Eringen's nonlocal elasticity theory the small-scale effect is accounted in the governing equations of motion. To obtain the critical loads, the equations are solved using Galerkin technique and the effect of small-scale parameter and geometry on the stability of nanocone is studied.

Firouz-Abadi, R. D.; Fotouhi, M. M.; Haddadpour, H.

2012-06-01

40

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

41

NASA Technical Reports Server (NTRS)

In pursuit of higher performance, the XV-15 Tiltrotor Research Aircraft was modified by the installation of new composite rotor blades. Initial flights with the Advanced Technology Blades (ATB's) revealed excessive rotor control loads that were traced to a dynamic mismatch between the blades and the aircraft control system. The analytical models of both the blades and the mechanical controls were extensively revised for use by the CAMRAD computer program to better predict aeroelastic stability and loads. This report documents the most important revisions and discusses their effects on aeroelastic stability predictions for airplane-mode flight. The ATB's may be flown in several different configurations for research, including changes in blade sweep and tip twist. The effects on stability of 1 deg and 0 deg sweep are illustrated, as are those of twisted and zero-twist tips. This report also discusses the effects of stiffening the rotor control system, which was done by locking out lateral cyclic swashplate motion with shims.

Acree, C. W., Jr.

1993-01-01

42

NASA Astrophysics Data System (ADS)

Real-world traffic flow usually contains a mixture of passenger vehicles (PV) and heavy vehicles (HV). In this paper, the four types of car-truck following combinations are considered: the car-following-car case, car-following-truck case, truck-following-car case and truck-following-truck case. The effect of different combinations on the stability of traffic flow is explored by converting the original Bando’s optimal velocity (OV) model to a heterogeneous form. A new linear stability analysis method that can derive the stability criterion of the heterogeneous traffic flow mixed by cars and trucks is introduced. Moreover, the effect of the proportions of the four car-truck following combinations on traffic flow is examined through the trajectory analysis. It concludes that the linear stability of the car-truck mixed traffic flow is determined more by the proportions of the different car-truck following scenarios, rather than the numbers of the cars and trucks. Moreover, cars and trucks can both stabilize and destabilize traffic flow depending on the density of the traffic flow and the parameters of the heterogeneous OV model.

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

2014-02-01

43

Local and global stability analysis of a two prey one predator model with help

NASA Astrophysics Data System (ADS)

In this paper we propose and study a three dimensional continuous time dynamical system modelling a three team consists of two preys and one predator with the assumption that during predation the members of both teams of preys help each other and the rate of predation of both teams are different. In this work we establish the local asymptotic stability of various equilibrium points to understand the dynamics of the model system. Different conditions for the coexistence of equilibrium solutions are discussed. Persistence, permanence of the system and global stability of the positive interior equilibrium solution are discussed by constructing suitable Lyapunov functional. At the end, numerical simulations are performed to substantiate our analytical findings.

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

2014-09-01

44

Stability Analysis of a Simplified Yet Complete Model for Chronic Myelegenous Leukemia

We analyze the asymptotic behavior of a partial differential equation (PDE) model for hematopoiesis. This PDE model is derived from the original agent-based model formulated by (Roeder et al., Nat. Med., 2006), and it describes the progression of blood cell development from the stem cell to the terminally differentiated state. To conduct our analysis, we start with the PDE model of (Kim et al, JTB, 2007), which coincides very well with the simulation results obtained by Roeder et al. We simplify the PDE model to make it amenable to analysis and justify our approximations using numerical simulations. An analysis of the simplified PDE model proves to exhibit very similar properties to those of the original agent-based model, even if for slightly different parameters. Hence, the simplified model is of value in understanding the dynamics of hematopoiesis and of chronic myelogenous leukemia, and it presents the advantage of having fewer parameters, which makes comparison with both experimental data and alternative...

Jauffret, Marie Doumic; Perthame, Benoît

2009-01-01

45

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

46

Stability analysis and optimal control of an SIR epidemic model with vaccination.

This paper focuses on the study of a nonlinear mathematical SIR epidemic model with a vaccination program. We have discussed the existence and the stability of both the disease free and endemic equilibrium. Vaccine induced reproduction number is determined and the impact of vaccination in reducing the vaccine induced reproduction number is discussed. Then to achieve control of the disease, a control problem is formulated and it is shown that an optimal control exists for our model. The optimality system is derived and solved numerically using the Runge-Kutta fourth order procedure. PMID:21315798

Kar, T K; Batabyal, Ashim

2011-01-01

47

Thermohaline circulation stability : a box model

A thorough analysis of the stability of uncoupled and coupled versions of an inter-hemispheric 3-box model of Thermohaline Circulation (THC) is presented. The model consists of a northern high latitudes box, a tropical ...

Lucarini, Valerio

2003-01-01

48

Stability analysis of an SIS epidemic model with feedback mechanism on networks

NASA Astrophysics Data System (ADS)

In this paper, an epidemic model with feedback mechanism on networks is investigated. We obtain the basic reproductive number R0, and analyze the stability behaviors of disease-free equilibrium E0 and endemic equilibrium E?. When R0<1, the disease-free equilibrium is globally asymptotically stable, and when R0>1, the endemic equilibrium is asymptotically stable. Although the feedback mechanism cannot change the basic reproductive number R0 as we prove, it should be indicated that it can weaken the spreading of diseases and reduce the endemic level. Finally, the results of the stability and the effectiveness of the feedback mechanism are illustrated by some numerical simulations.

Zhang, Jiancheng; Sun, Jitao

2014-01-01

49

Amyloid-? (A?) oligomers appear to play a pivotal role in Alzheimer’s disease. A 42 residue long alloform, A?42, is closely related to etiology of the disease. In vitro results show evidences of hexamers; however structures of these hexamers have not been resolved experimentally. Here, we use Discrete Molecular Dynamics (DMD) to analyze long duration stabilities of A?42 hexamer models developed previously in our lab. The hydrophobic core of these models is a six-stranded ?-barrel with 3-fold radial symmetry formed by residues 30–40. This core is shielded from water by residues 1–28. The nine models we analyzed differ by the relative positions of the core ?-strands, and whether the other segments surrounding the core contain ? helices or ?-strands. A model of an annular protofibril composed of 36 A? peptides was also simulated. Results of these model simulations were compared with results of aggregation simulations that started from six well separated random coils of A?42 and with simulations of two known ?barrel structures. These results can be categorized into three groups: stable models with properties similar or superior to those of experimentally-determined ?-barrel proteins, aggregation-prone models, and an amorphous aggregate from random coils. Conformations at the end of the simulation for aggregation-prone models have exposed hydrophobic core with dangling ?-strands on the surface. Hydrogen bond patterns within the ?-barrel were a critical factor for stability of the ?-barrel models. Aggregation-prone conformations imply that the association of these hexamers may be possible, which could lead to the formation of larger assemblies. PMID:21186130

Yun, Sijung; Yun, Sajung; Guy, H. Robert

2011-01-01

50

A simplified spatial model for BWR stability

A spatial reduced order model for the study of BWR stability, based on the phenomenological model of March-Leuba et al., is presented. As one dimensional spatial dependence of the neutron flux, fuel temperature and void fraction is introduced, it is possible to describe both global and regional oscillations of the reactor power. Both linear stability analysis and numerical analysis were applied in order to describe the parameters which govern the model stability. The results were found qualitatively similar to past results. Doppler reactivity feedback was found essential for the explanation of the different regions of the flow-power stability map. (authors)

Berman, Y. [Dept. of Physics, Ben-Gurion Univ. of the Negev, Nuclear Research Center-Negev, Beer-Sheva (Israel); Lederer, Y. [Dept. of Physics, Nuclear Research Center-Negev, Beer-Sheva (Israel); Meron, E. [Dept. of Solar Energy and Environmental Physics, Dept. of Physics, Ben-Gurion Univ. of the Negev, Beer-Sheva (Israel)

2012-07-01

51

MAP stability, design, and analysis

NASA Technical Reports Server (NTRS)

The Microwave Anisotropy Probe (MAP) is a follow-on to the Differential Microwave Radiometer (DMR) instrument on the Cosmic Background Explorer (COBE) spacecraft. The design and analysis of the MAP attitude control system (ACS) have been refined since work previously reported. The full spacecraft and instrument flexible model was developed in NASTRAN, and the resulting flexible modes were plotted and reduced with the Modal Significance Analysis Package (MSAP). The reduced-order model was used to perform the linear stability analysis for each control mode, the results of which are presented in this paper. Although MAP is going to a relatively disturbance-free Lissajous orbit around the Earth-Sun L(2) Lagrange point, a detailed disturbance-torque analysis is required because there are only a small number of opportunities for momentum unloading each year. Environmental torques, including solar pressure at L(2), aerodynamic and gravity gradient during phasing-loop orbits, were calculated and simulated. Thruster plume impingement torques that could affect the performance of the thruster modes were estimated and simulated, and a simple model of fuel slosh was derived to model its effect on the motion of the spacecraft. In addition, a thruster mode linear impulse controller was developed to meet the accuracy requirements of the phasing loop burns. A dynamic attitude error limiter was added to improve the performance of the ACS during large attitude slews. The result of this analysis is a stable ACS subsystem that meets all of the mission's requirements.

Ericsson-Jackson, A. J.; Andrews, S. F.; O'Donnell, J. R., Jr.; Markley, F. L.

1998-01-01

52

NASA Astrophysics Data System (ADS)

We propose a new procedure to monitor and forecast the onset of transitions in high-dimensional complex systems. We describe our procedure by an application to the tangled nature model of evolutionary ecology. The quasistable configurations of the full stochastic dynamics are taken as input for a stability analysis by means of the deterministic mean-field equations. Numerical analysis of the high-dimensional stability matrix allows us to identify unstable directions associated with eigenvalues with a positive real part. The overlap of the instantaneous configuration vector of the full stochastic system with the eigenvectors of the unstable directions of the deterministic mean-field approximation is found to be a good early warning of the transitions occurring intermittently.

Cairoli, Andrea; Piovani, Duccio; Jensen, Henrik Jeldtoft

2014-12-01

53

PrimeSupplier Cross-Program Impact Analysis and Supplier Stability Indicator Simulation Model

NASA Technical Reports Server (NTRS)

PrimeSupplier, a supplier cross-program and element-impact simulation model, with supplier solvency indicator (SSI), has been developed so that the shuttle program can see early indicators of supplier and product line stability, while identifying the various elements and/or programs that have a particular supplier or product designed into the system. The model calculates two categories of benchmarks to determine the SSI, with one category focusing on agency programmatic data and the other focusing on a supplier's financial liquidity. PrimeSupplier was developed to help NASA smoothly transition design, manufacturing, and repair operations from the Shuttle program to the Constellation program, without disruption in the industrial supply base.

Calluzzi, Michael

2009-01-01

54

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

55

Stability analysis of free piston Stirling engines

NASA Astrophysics Data System (ADS)

This paper presents a stability analysis of a free piston Stirling engine. The model and the detailed calculation of pressures losses are exposed. Stability of the machine is studied by the observation of the eigenvalues of the model matrix. Model validation based on the comparison with NASA experimental results is described. The influence of operational and construction parameters on performance and stability issues is exposed. The results show that most parameters that are beneficial for machine power seem to induce irregular mechanical characteristics with load, suggesting that self-sustained oscillations could be difficult to maintain and control.

Bégot, Sylvie; Layes, Guillaume; Lanzetta, François; Nika, Philippe

2013-03-01

56

NASA Technical Reports Server (NTRS)

Results of static stability wind tunnel tests of three 62.2 cm (24.5 in) diameter models of the Prop-Fan are presented. Measurements of blade stresses were made with the Prop-Fans mounted on an isolated nacelle in an open 5.5 m (18 ft) wind tunnel test section with no tunnel flow. The tests were conducted in the United Technology Research Center Large Subsonic Wind Tunnel. Stall flutter was determined by regions of high stress, which were compared with predictions of boundaries of zero total viscous damping. The structural analysis used beam methods for the model with straight blades and finite element methods for the models with swept blades. Increasing blade sweep tends to suppress stall flutter. Comparisons with similar test data acquired at NASA/Lewis are good. Correlations between measured and predicted critical speeds for all the models are good. The trend of increased stability with increased blade sweep is well predicted. Calculated flutter boundaries generaly coincide with tested boundaries. Stall flutter is predicted to occur in the third (torsion) mode. The straight blade test shows third mode response, while the swept blades respond in other modes.

Smith, Arthur F.

1985-01-01

57

Stability analysis of multi-group deterministic and stochastic epidemic models with vaccination rate

NASA Astrophysics Data System (ADS)

We discuss in this paper a deterministic multi-group MSIR epidemic model with a vaccination rate, the basic reproduction number ?0, a key parameter in epidemiology, is a threshold which determines the persistence or extinction of the disease. By using Lyapunov function techniques, we show if ?0 is greater than 1 and the deterministic model obeys some conditions, then the disease will prevail, the infective persists and the endemic state is asymptotically stable in a feasible region. If ?0 is less than or equal to 1, then the infective disappear so the disease dies out. In addition, stochastic noises around the endemic equilibrium will be added to the deterministic MSIR model in order that the deterministic model is extended to a system of stochastic ordinary differential equations. In the stochastic version, we carry out a detailed analysis on the asymptotic behavior of the stochastic model. In addition, regarding the value of ?0, when the stochastic system obeys some conditions and ?0 is greater than 1, we deduce the stochastic system is stochastically asymptotically stable. Finally, the deterministic and stochastic model dynamics are illustrated through computer simulations.

Wang, Zhi-Gang; Gao, Rui-Mei; Fan, Xiao-Ming; Han, Qi-Xing

2014-09-01

58

Stability analysis of an acoustically levitated disk

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

NASA Astrophysics Data System (ADS)

Reinforcement measures are often used in high-arch dams with complicated geological foundations. The geomechanical model test is an effective method to study the global stability of arch dams and to evaluate the reinforcement effects of foundation treatments. The block masonry technique was developed to simulate the jointed rock mass, tectonic discontinuities, and reinforcement measures. A tailor-made low-strength binder and small blocks were developed to simulate the strength and deformation of the jointed rock mass and discontinuities, respectively. We applied this technique to geomechanical model tests of the Dagangshan arch dam with and without foundation reinforcements. A rupture test was conducted, and the stress and displacement distribution of the dam and abutments were recorded; the failure mechanisms and processes were explored. The reinforcement effects of the foundation treatment were evaluated by comparing the test results of the models with and without foundation reinforcements. Our analysis indicates that foundation reinforcements can improve the stress distribution, decrease deformation, prevent slides, reduce fault movement, and improve the global stability of high-arch dams.

Zhang, L.; Liu, Y. R.; Yang, Q.

2015-03-01

60

Linear stability analysis for an optimum Glauert rotor modelled by an actuator disc

NASA Astrophysics Data System (ADS)

We approximate a wind turbine using the Actuator Disc methodology with loading for an optimum Glauert rotor, and vary blade length and tip speed ratio, to determine base flows for linear stability computations at a Reynolds number of 100. Results from such computations suggest that the least stable mode is axisymmetric and insensitive to changes in tip speed operation, suggesting that the stability properties in the farfield wake for an optimised rotor are independent of the chosen tip speed optimization point. Higher azimuthal modes promote greater variation in velocities and may be relevant to cases at higher Reynolds numbers.

Smith, D. M.; Blackburn, H. M.; Sheridan, J.

2014-06-01

61

Energy function analysis for power system stability

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

62

Objective. This study was designed to explore relationships of resonance frequency analysis (RFA)—assessed implant stability (ISQ values) with bone morphometric parameters and bone quality in an ex vivo model of dental implants placed in human femoral heads and to evaluate the usefulness of this model for dental implant studies. Material and Methods. This ex vivo study included femoral heads from 17 patients undergoing surgery for femoral neck fracture due to osteoporosis (OP) (n = 7) or for total prosthesis joint replacement due to severe hip osteoarthrosis (OA) (n = 10). Sixty 4.5 × 13?mm Dentsply Astra implants were placed, followed by RFA. CD44 immunohistochemical analysis for osteocytes was also carried out. Results. As expected, the analysis yielded significant effects of femoral head type (OA versus OA) (P < 0.001), but not of the implants (P = 0.455) or of the interaction of the two factors (P = 0.848). Bonferroni post hoc comparisons showed a lower mean ISQ for implants in decalcified (50.33 ± 2.92) heads than in fresh (66.93 ± 1.10) or fixated (70.77 ± 1.32) heads (both P < 0.001). The ISQ score (fresh) was significantly higher for those in OA (73.52 ± 1.92) versus OP (67.13 ± 1.09) heads. However, mixed linear analysis showed no significant association between ISQ scores and morphologic or histomorphometric results (P > 0.5 in all cases), and no significant differences in ISQ values were found as a function of the length or area of the cortical layer (both P > 0.08). Conclusion. Although RFA-determined ISQ values are not correlated with morphometric parameters, they can discriminate bone quality (OP versus OA). This ex vivo model is useful for dental implant studies. PMID:24995307

Hernández-Cortés, Pedro; Galindo-Moreno, Pablo; Catena, Andrés; Ortega-Oller, Inmaculada; Salas-Pérez, José; Gómez-Sánchez, Rafael; Aguilar, Mariano; Aguilar, David

2014-01-01

63

Curcumin (diferuloyl methane) is the physiologically and pharmacologically active component of turmeric (Curcuma longa L.). Solubility and stability of curcumin are the limiting factors for realizing its therapeutic potential. ?-Lactoglobulin (?LG), the major whey protein, can solubilize and bind many small hydrophobic molecules. The stability of curcumin bound to ?LG in solution is enhanced 6.7 times, in comparison to curcumin alone (in aqueous solution). The complex formation of curcumin with ?LG has been investigated employing spectroscopic techniques. ?LG interacts with curcumin at pH 7.0 with an association constant of 1.04 ± 0.1 × 10(5) M(-1) to form a 1:1 complex at 25 °C. Entropy and free energy changes for the interaction derived from the van't Hoff plot are 18.7 cal mol(-1) K(-1) and -6.8 kcal mol(-1) at 25 °C, respectively; the interaction is hydrophobic in nature. The interaction of ?LG with curcumin does not affect either the conformation or the state of association of ?LG. Competitive ligand binding measurements, binding studies with denatured ?LG, effect of pH on the curcumin-?LG interaction, Förster energy transfer measurements, and molecular docking studies suggest that curcumin binds to the central calyx of ?LG. These binding studies have prompted the preparation and encapsulation of curcumin in ?LG nanoparticles. Nanoparticles of ?LG prepared by desolvation are found to encapsulate curcumin with >96% efficiency. The solubility of curcumin in ?LG nanoparticle is significantly enhanced to ?625 ?M in comparison with its aqueous solubility (30 nM). Nanoparticles of ?LG, by virtue of their ability to enhance solubility and stability of curcumin, may fit the choice as a carrier molecule. PMID:20925386

Sneharani, Athahalli H; Karakkat, Jimsheena V; Singh, Sridevi Annapurna; Rao, A G Appu

2010-10-27

64

DYNAMIC CHARACTERIZATION AND STABILITY OF A LARGE SIZE MULTIBODY TILTROTOR MODEL BY POD ANALYSIS

A great level of flexibility and accuracy can be gained by em- ploying a multibody approach as the modeling strategy for servo- aeroelastic analyses of rotating wing aircraft. However, the re- sulting models are often large, in terms of degrees of freedom, and fully nonlinear, making the dynamic characterization phase cumbersome and computationally demanding. Moreover, non- minimal set formulations such

Pierangelo Masarati; Giuseppe Quaranta; Massimiliano Lanz; Paolo Mantegazza

65

In this paper, a modified Jeffcott model is proposed and studied in order to shed light into the dynamics of a complex system, the Short Electrodynamic Tether (SET), which is similar to an unbalanced rotor. Due to the internal damping, a geometrically linear SET model appears to be unstable as predicted by the linear rotordynamics theory. Some studies in the

J. Valverde; J. L. Escalona; E. Freire; J. Domínguez

2005-01-01

66

This paper investigates a RVF epidemic model by qualitative analysis and numerical simulations. Qualitative analysis have been used to explore the stability dynamics of the equilibrium points while visualization techniques such as bifurcation diagrams, Poincaré maps, maxima return maps and largest Lyapunov exponents are numerically computed to confirm further complexity of these dynamics induced by the seasonal forcing on the mosquitoes oviposition rates. The obtained results show that ordinary differential equation models with external forcing can have rich dynamic behaviour, ranging from bifurcation to strange attractors which may explain the observed fluctuations found in RVF empiric outbreak data, as well as the non deterministic nature of RVF inter-epidemic activities. Furthermore, the coexistence of the endemic equilibrium is subjected to existence of certain number of infected Aedes mosquitoes, suggesting that Aedes have potential to initiate RVF epidemics through transovarial transmission and to sustain low levels of the disease during post epidemic periods. Therefore we argue that locations that may serve as RVF virus reservoirs should be eliminated or kept under control to prevent multi-periodic outbreaks and consequent chains of infections. The epidemiological significance of this study is: (1) low levels of birth rate (in both Aedes and Culex) can trigger unpredictable outbreaks; (2) Aedes mosquitoes are more likely capable of inducing unpredictable behaviour compared to the Culex; (3) higher oviposition rates on mosquitoes do not in general imply manifestation of irregular behaviour on the dynamics of the disease. Finally, our model with external seasonal forcing on vector oviposition rates is able to mimic the linear increase in livestock seroprevalence during inter-epidemic period showing a constant exposure and presence of active transmission foci. This suggests that RVF outbreaks partly build upon RVF inter-epidemic activities. Therefore, active RVF surveillance in livestock is recommended. PMID:25271641

Pedro, Sansao A.; Abelman, Shirley; Ndjomatchoua, Frank T.; Sang, Rosemary; Tonnang, Henri E. Z.

2014-01-01

67

Magnetic shape memory alloys (MSMAs) are a class of active materials that de- form under magnetic and mechanical loading conditions. This work is concerned with the modeling of MSMAs constitutive responses. The hysteretic magneto...

Haldar, Krishnendu 1978-

2012-12-06

68

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

69

Variance components in errors-in-variables models: estimability, stability and bias analysis

NASA Astrophysics Data System (ADS)

Although total least squares has been substantially investigated theoretically and widely applied in practical applications, almost nothing has been done to simultaneously address the estimation of parameters and the errors-in-variables (EIV) stochastic model. We prove that the variance components of the EIV stochastic model are not estimable, if the elements of the random coefficient matrix can be classified into two or more groups of data of the same accuracy. This result of inestimability is surprising as it indicates that we have no way of gaining any knowledge on such an EIV stochastic model. We demonstrate that the linear equations for the estimation of variance components could be ill-conditioned, if the variance components are theoretically estimable. Finally, if the variance components are estimable, we derive the biases of their estimates, which could be significantly amplified due to a large condition number.

Xu, Peiliang; Liu, Jingnan

2014-08-01

70

Stability analysis of a new model for floating caliper disk brake

The customers' demand for ride comfort has led the automotive industries to look for the various ways to reduce and control the brake noise. Intensive research on brake squeal (high frequency noise between 1-12 kHz) has been carried out. A large variety of mathematical-mechanical models has been developed, studying various instability phenomena. The squeal is ascribed mainly to three reasons:

T. Jearsiripongkul; G. Chakraborty; P. Hagedorn

2002-01-01

71

Enhanced rotor modeling tailored for rub dynamic stability analysis and simulation

NASA Technical Reports Server (NTRS)

New methods are presented that allow straightforward application of complex nonlinearities to finite element based rotor dynamic analyses. The key features are: (1) the methods can be implemented with existing finite element or dynamic simulation programs, (2) formulation is general for simple application to a wide range of problems, and (3) implementation is simplified because nonlinear aspects are separated from the linear part of the model. The new techniques are illustrated with examples of inertial nonlinearity and torquewhirl which can be important in rubbing turbomachinery. The sample analyses provide new understanding of these nonlinearities which are discussed.

Davis, R. R.

1989-01-01

72

NASA Astrophysics Data System (ADS)

Many plants could not escape from diseases caused by fungi. The use of fungicide can help to reduce the spread of the fungi but if it used continuously with the same dosage, the fungi would be invulnerable to fungicide eventually. Hence, it is critical to know the appropriate level of fungicide application and its impact on the dynamics of the plants. In this paper we use an explicit model of fungal outbreaks of plant by taking into account a curative factor including the dynamic of fungicides itself. Granting of fungicide on crops is useful to control the infected plants as well as protecting the vulnerable plants. Optimal control is used to find out how many doses of the appropriate fungicide should be used to cure infected plants. Optimal control is obtained by applying Pontryagin's Minimum Principle. We found that the presence of appropriate level of fungicide speeds up the reduction of infected plants as well as accelerates the growth of healthy plants.

Anggriani, N.; Putri, L. Nurul; Supriatna, A. K.

2015-03-01

73

An SIR epidemic model of a general age-dependent vaccination of a vertically as well as horizontally transmitted disease is investigated when the total population is in steady state. We assume proportionate mixing and age-dependent fertility, mortality and removal rates. We determine the steady states and examine their stabilities. PMID:10994509

el-Doma, M

2000-06-01

74

Cosmological Models and Stability

NASA Astrophysics Data System (ADS)

Principles in the form of heuristic guidelines or generally accepted dogma play an important role in the development of physical theories. In particular, philosophical considerations and principles figure prominently in the work of Albert Einstein. As mentioned in the talk by Ji?í Bi?ák at this conference, Einstein formulated the equivalence principle, an essential step on the road to general relativity, during his time in Prague 1911-1912. In this talk, I would like to discuss some aspects of cosmological models. As cosmology is an area of physics where "principles" such as the "cosmological principle" or the "Copernican principle" play a prominent role in motivating the class of models which form part of the current standard model, I will start by comparing the role of the equivalence principle to that of the principles used in cosmology. I will then briefly describe the standard model of cosmology to give a perspective on some mathematical problems and conjectures on cosmological models, which are discussed in the later part of this paper.

Andersson, Lars

75

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

76

NASA Technical Reports Server (NTRS)

Aerodynamic analysis are performed using the Lockheed-Martin Tactical Aircraft Systems (LMTAS) Splitflow computational fluid dynamics code to investigate the computational prediction capabilities for vortex-dominated flow fields of two different tailless aircraft models at large angles of attack and sideslip. These computations are performed with the goal of providing useful stability and control data to designers of high performance aircraft. Appropriate metrics for accuracy, time, and ease of use are determined in consultations with both the LMTAS Advanced Design and Stability and Control groups. Results are obtained and compared to wind-tunnel data for all six components of forces and moments. Moment data is combined to form a "falling leaf" stability analysis. Finally, a handful of viscous simulations were also performed to further investigate nonlinearities and possible viscous effects in the differences between the accumulated inviscid computational and experimental data.

Charlton, Eric F.

1998-01-01

77

NASA Astrophysics Data System (ADS)

Since soil moisture is an important influencing factor of the hydrological cycle, knowledge of its spatio-temporal dynamics is crucial for climate and hydrological modeling. In recent years several soil moisture data products from satellite information have become available with global coverage and sub-monthly resolution. Since the remote sensing of soil moisture is an indirect measurement method and influenced by a large number of factors (e.g. atmospheric correction, vegetation, soil roughness, etc.), a comprehensive validation of the resulting soil moisture products is required. However, the coarse spatial resolution of these products hampers the comparison with point-scale in situ measurements. Therefore, upscaling of in situ to the scale of the satellite data is needed. We present the validation results of the soil moisture products of the years 2010-2012 retrieved from the Soil Moisture and Ocean Salinity (SMOS) and the Advanced Scatterometer (ASCAT) for the Rur and Erft catchments in western Germany. For the upscaling of in situ data obtained from three test sites of the Terrestrial Environmental Observatories (TERENO) initiative we used the hydrological model WaSiM ETH. Correlation of the SMOS product to modeled and upscaled soil moisture resulted in a mean correlation coefficient of 0.28 whereas for ASCAT a correlation coefficient of 0.50 was obtained. However, for specific regions the SMOS product showed similar correlation coefficients as the ASCAT product. While for ASCAT correlation was mainly dependent on topography and vegetation, SMOS was also influenced by radiofrequency interferences in our study area. Both products show dry biases as compared to the soil moisture reference. However, while SMOS showed relatively constant bias values, ASCAT bias is variable throughout the year. As an additional validation method we performed a temporal stability analysis of the retrieved spatio-temporal soil moisture data. Through investigation of mean relative differences of soil moisture for every pixel, their standard deviations and their rankings, we analyzed the temporal persistence of spatial patterns. Our results show high standard deviations for both SMOS and ASCAT soil moisture products as compared to modeled soil moisture, indicating a lower temporal persistence. The consistence of ranks of mean relative differences was low for SMOS and relative ASCAT soil moisture compared to modeled soil moisture, while ASCAT soil moisture, converted to absolute values, showed higher rank consistence.

Rötzer, K.; Montzka, C.; Bogena, H.; Wagner, W.; Kerr, Y. H.; Kidd, R.; Vereecken, H.

2014-11-01

78

BACKGROUND: Understanding and predicting protein stability upon point mutations has wide-spread importance in molecular biology. Several prediction models have been developed in the past with various algorithms. Statistical potentials are one of the widely used algorithms for the prediction of changes in stability upon point mutations. Although the methods provide flexibility and the capability to develop an accurate and reliable

Vijaya Parthiban; M Michael Gromiha; Madenhalli Abhinandan; Dietmar Schomburg

2007-01-01

79

Stability analysis and future singularity of the $m^2 R \\Box^{-2} R$ model of non-local gravity

We analyse the classical stability of the model proposed by Maggiore and Mancarella, where gravity is modified by a term $\\sim m^2 R \\Box^{-2} R$ to produce the late-time acceleration of the expansion of the universe. Our study takes into account all excitations of the metric that can potentially drive an instability. There are some subtleties in identifying these modes, as a non-local field theory contains dynamical fields which yet do not correspond to degrees of freedom. Since some of them are ghost-like, we clarify the impact of such modes on the stability of the solutions of interest that are the flat space-time and cosmological solutions. We then find that flat space-time is unstable under scalar perturbations, but the instability manifests itself only at cosmological scales, i.e. out of the region of validity of this solution. It is therefore the stability of the FLRW solution which is relevant there, in which case the scalar perturbations are known to be well-behaved by numerical studies. By finding the analytic solution for the late-time behaviour of the scale factor, which leads to a big rip singularity, we argue that the linear perturbations are bounded in the future because of the domination of Hubble friction. In particular, this effect damps the scalar ghost perturbations which were responsible for destabilizing Minkowski space-time. Thus, the model remains phenomenologically viable.

Yves Dirian; Ermis Mitsou

2014-12-02

80

NASA Astrophysics Data System (ADS)

Polytype stability is very important for high quality SiC single crystal growth. However, the growth conditions for the 4H, 6H and 15R polytypes are similar, and the mechanism of polytype stability is not clear. The kinetics aspects, such as surface-step nucleation, are important. The kinetic Monte Carlo method is a common tool to study surface kinetics in crystal growth. However, the present lattice models for kinetic Monte Carlo simulations cannot solve the problem of the competitive growth of two or more lattice structures. In this study, a competitive lattice model was developed for kinetic Monte Carlo simulation of the competition growth of the 4H and 6H polytypes of SiC. The site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. Surface steps on seeds and large ratios of diffusion/deposition have positive effects on the 4H polytype stability. The 3D polytype distribution in a physical vapor transport method grown SiC ingot showed that the facet preserved the 4H polytype even if the 6H polytype dominated the growth surface. The theoretical and experimental results of polytype growth in SiC suggest that retaining the step growth mode is an important factor to maintain a stable single 4H polytype during SiC growth.

Guo, Hui-Jun; Huang, Wei; Liu, Xi; Gao, Pan; Zhuo, Shi-Yi; Xin, Jun; Yan, Cheng-Feng; Zheng, Yan-Qing; Yang, Jian-Hua; Shi, Er-Wei

2014-09-01

81

Stability analysis and future singularity of the m2 R square-2 R model of non-local gravity

NASA Astrophysics Data System (ADS)

We analyse the classical stability of the model proposed by Maggiore and Mancarella, where gravity is modified by a term ~ m2 R square-2 R to produce the late-time acceleration of the expansion of the universe. Our study takes into account all excitations of the metric that can potentially drive an instability. There are some subtleties in identifying these modes, as a non-local field theory contains dynamical fields which yet do not correspond to degrees of freedom. Since some of them are ghost-like, we clarify the impact of such modes on the stability of the solutions of interest that are the flat space-time and cosmological solutions. We then find that flat space-time is unstable under scalar perturbations, but the instability manifests itself only at cosmological scales, i.e. out of the region of validity of this solution. It is therefore the stability of the FLRW solution which is relevant there, in which case the scalar perturbations are known to be well-behaved by numerical studies. By finding the analytic solution for the late-time behaviour of the scale factor, which leads to a big rip singularity, we argue that the linear perturbations are bounded in the future because of the domination of Hubble friction. In particular, this effect damps the scalar ghost perturbations which were responsible for destabilizing Minkowski space-time. Thus, the model remains phenomenologically viable.

Dirian, Yves; Mitsou, Ermis

2014-10-01

82

Aeroelastic stability analysis and passive instability suppression

using parameter variations to support the design of turbines with good passive stability propertiesAeroelastic stability analysis and passive instability suppression Thomas Buhl, Helen Markou author: thomas.buhl@risoe.dk Abstract: Aeroelastic stability issues become more important in the design

83

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

84

Stability analysis of cooperation system of two robot arms

In this paper we study the stability problem of a hybrid system composed of two robots, where the appropriate cooperation of robots are expected to work efficiently. The performance of system depends directly upon one main factor: the coordination movement of the robots. The stability analysis of the system results in a model of uniform Euler-Bernoulli beams with linear and

Chen Yunlan; Xu Genqi

2010-01-01

85

Performance and stability analysis of a photovoltaic power system

NASA Technical Reports Server (NTRS)

The performance and stability characteristics of a 10 kVA photovoltaic power system are studied using linear Bode analysis and a nonlinear analog simulation. Power conversion efficiencies, system stability, and system transient performance results are given for system operation at various levels of solar insolation. Additionally, system operation and the modeling of system components for the purpose of computer simulation are described.

Merrill, W. C.; Blaha, R. J.; Pickrell, R. L.

1978-01-01

86

Boiling water reactor stability analysis with RETRAN-03

An MOC option has been developed to eliminate the numerical diffusion associated with the time domain analysis of small perturbations. This model has been implemented as an option in RETRAN-03 and evaluated for BWR stability applications by comparing RETRAN analyses results with data from a series of stability tests from the Vermont Yankee reactor. The results indicate that the MOC

P. A. Bergeron; N. Fujita; M. P. Paulsen; J. H. McFadden; L. J. Agee

1994-01-01

87

Short Communication Microscopic analysis of structure stabilities

2005 Short Communication Microscopic analysis of structure stabilities in the ionic compounds B an analysis of the relative stability of two structural phases in an ionic compound at zero temperature a given ionic compound cristallizes in one structure rather than in another one [1] . But only recently

Boyer, Edmond

88

Stability Analysis of ISS Medications

NASA Technical Reports Server (NTRS)

It is known that medications degrade over time, and that extreme storage conditions will hasten their degradation. The temperature and humidity conditions of the ISS have been shown to be within the ideal ranges for medication storage, but the effects of other environmental factors, like elevated exposure to radiation, have not yet been evaluated. Current operational procedures ensure that ISS medications are re-stocked before expiration, but this may not be possible on long duration exploration missions. For this reason, medications that have experienced long duration storage on the ISS were returned to JSC for analysis to determine any unusual effects of aging in the low- Earth orbit environment. METHODS Medications were obtained by the JSC Pharmacy from commercial distributors and were re-packaged by JSC pharmacists to conserve up mass and volume. All medication doses were part of the ISS crew medical kit and were transported to the International Space Station (ISS) via NASA's Shuttle Transportation System (Space Shuttle). After 568 days of storage, the medications were removed from the supply chain and returned to Earth on a Dragon (SpaceX) capsule. Upon return to Earth, medications were transferred to temperature and humidity controlled environmental chambers until analysis. Nine medications were chosen on the basis of their availability for study. The medications included several of the most heavily used by US crewmembers: 2 sleep aids, 2 antihistamines/decongestants, 3 pain relievers, an antidiarrheal and an alertness medication. Each medication was available at a single time point; analysis of the same medication at multiple time points was not possible. Because the samples examined in this study were obtained opportunistically from medical supplies, there were no control samples available (i.e. samples aged for a similar period of time on the ground); a significant limitation of this study. Medications were analyzed using the HPLC/MS methods described in the United States Pharmacopeia (USP) to measure the amount of intact active ingredient, identify degradation products and measure their amounts. Some analyses were conducted by an independent analytical laboratory, but certain (Schedule) medications could not be shipped to their facility and were analyzed at JSC. RESULTS Nine medications were analyzed with respect to active pharmaceutical ingredient (API) and degradant amounts. Results were compared to the USP requirements for API and degradants/impurities content for every FDA-approved medication. One medication met USP requirements at 5 months after its expiration date. Four of the nine (44% of those tested) medications tested met USP requirements up to 8 months post-expiration. Another 3 medications (33% of those tested) met USP guidelines 2-3 months before expiration. One medication, a compound classed by the FDA as a dietary supplement and sometimes used as a sleep aid, failed to meet USP requirements at 11 months post-expiration. CONCLUSION Analysis of each medication at a single time point provides limited information on the stability of a medication stored in particular conditions; it is not possible to predict how long a medication may be safe and effective from these data. Notwithstanding, five of the nine medications tested (56%) met USP requirements for API and degradants/impurities at least 5 months past expiration dates. The single compound that failed to meet USP requirements is not regulated as strictly as prescription medications are during manufacture; it is unknown if this medication would have met the requirements prior to flight. Notably, it was the furthest beyond its expiration date. Only more comprehensive analysis of flight-aged samples compared to appropriate ground controls will permit determination of spaceflight effects on medication stability.

Wotring, V. E.

2014-01-01

89

The flow of granular materials down an inclined plane is modeled by the Richman & Marciniec (1990) in which, they consider a kinetic constitutive theory that includes the effects of particle transport and collisions. Richman & Marciniec (1990) obtained closed form solution for the granular temperature profile, by replacing the volume fraction by its depth-averaged value in the balance equation`s, and thereby from constitutive relations for the normal and shear stresses they obtained the volume fraction and velocity profiles. Here, we use the model proposed by Richman & marciniec (1990) to study the linearized stability for the flow of granular materials down an inclined plane. The governing equations are obtained from the conservation of mass, balance of linear momentum and balance of energy. The basic flow equations and the order of {epsilon} equations are derived, but we intend to use the approximate solution of Richman & Marciniec (1990) as the base solution for the linearized stability analysis.

Rajagopal, K.R.

1992-12-31

90

In this paper, the authors study a laser using a nonlinear Fabry-Perot etalon as a cavity mirror. First, using the semiclassical laser theory and the differential equation for the lossy nonlinear Fabry-Perot etalon, they develop dynamic equations describing this system for single-mode operation. In this model, the frequency-pulling effect, a finite response time of the nonlinear medium, and a finite-cavity round-trip time of the Fabry-Perot etalon are included. Second, based on this model, they analyze the stability of this laser and give some numerical results. The results show that (1) this system can exist in the stable state and in the unstable state; (2) there are not only saddle-node bifurcations but also Hopf bifurcations; (3) the detuning parameter will effect the characteristics of the bistability and the number and distribution of Hopf bifurcation points.

Li, S.; Pons, R. (Autonoma de Barcelona (Spain). Dept. of Fisica); Zhang, Y. (Chongqing Inst. of Posts and Telecommunications, Sichuan (China). Telecommunications Engineering Dept.)

1994-08-01

91

NASA Astrophysics Data System (ADS)

We investigate an in-host model with general incidence and removal rate, as well as distributed delays in virus infections and in productions. By employing Lyapunov functionals and LaSalle's invariance principle, we define and prove the basic reproductive number R0 as a threshold quantity for stability of equilibria. It is shown that if R0>1, then the infected equilibrium is globally asymptotically stable, while if R0?1, then the infection free equilibrium is globally asymptotically stable under some reasonable assumptions. Moreover, n+1 distributed delays describe (i) the time between viral entry and the transcription of viral RNA, (ii) the n-1-stage time needed for activated infected cells between viral RNA transcription and viral release, and (iii) the time necessary for the newly produced viruses to be infectious (maturation), respectively. The model can describe the viral infection dynamics of many viruses such as HIV-1, HCV and HBV.

Wang, Jinliang; Liu, Shengqiang

2015-01-01

92

Aeromechanical stability analysis of COPTER

NASA Technical Reports Server (NTRS)

A plan was formed for developing a comprehensive, second-generation system with analytical capabilities for predicting performance, loads and vibration, handling qualities, aeromechanical stability, and acoustics. This second-generation system named COPTER (COmprehensive Program for Theoretical Evaluation of Rotorcraft) is designed for operational efficiency, user friendliness, coding readability, maintainability, transportability, modularity, and expandability for future growth. The system is divided into an executive, a data deck validator, and a technology complex. At present a simple executive, the data deck validator, and the aeromechanical stability module of the technology complex were implemented. The system is described briefly, the implementation of the technology module is discussed, and correlation data presented. The correlation includes hingeless-rotor isolated stability, hingeless-rotor ground-resonance stability, and air-resonance stability of an advanced bearingless-rotor in forward flight.

Yin, Sheng K.; Yen, Jing G.

1988-01-01

93

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

94

NASA Technical Reports Server (NTRS)

Results of wind tunnel tests at low forward speed for blade dynamic response and stability of three 62.2 cm (24.5 in) diameter models of the Prop-Fan, advanced turboprop, are presented. Measurements of dynamic response were made with the rotors mounted on an isolated nacelle, with varying tilt for nonuniform inflow. Low speed stall flutter tests were conducted at Mach numbers from 0.0 to 0.35. Measurements are compared to Eigen-solution flutter boundaries. Calculated 1P stress response agrees favorably with experiment. Predicted stall flutter boundaries correlate well with measured high stress regions. Stall flutter is significantly reduced by increased blade sweep. Susceptibility to stall flutter decreases rapidly with forward speed.

Smith, Arthur F.

1985-01-01

95

A distributed slope stability model for steep forested basins

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

Weimin Wu; Roy C. Sidle

1995-01-01

96

On the predictive capability and stability of rubber material models

Due to the high non-linearity and incompressibility constraint of rubber materials, the predictive capability and stability of rubber material models require specific attention for practical engineering analysis. In this ...

Zheng, Haining

2008-01-01

97

It is known that the human spine exhibits non-linear behavior, and its intervertebral discs play a role in the mechanism of internal load transfer. It is important to simulate its nonlinear behavior in computational models for better delineation of intrinsic responses, especially during cyclic loading activities, a mode pertinent to civilian and military populations. For developing a robust ?material model? of the disc, this study used experimental tensile-compressive cyclic loading responses from four human cadaver cervical functional spinal units. Disc deformations were measured using an ultrasound system at 42 samples per second. Using experimental data, a three-network non-linear ?material model? was developed using an optimization procedure and finite-element analysis. The model used 12 parameters to capture loading and unloading in tension and compression, including hysteresis. A sensitivity analysis performed to test the robustness of the ?material model? indicated that seven of the 12 parameters were sensitive to tension, compressive, or both loading modes. Stability analysis was also performed under nine different loading conditions. The developed ?material model? is robust and stable to capture intervertebral disc responses in tensile-compressive cyclic loading and can be used in future finite-element models. PMID:25405399

Arun, Mike W J; Yoganandan, Narayan; Stemper, Brian D; Zheng, Mingxin; Masoudi, Aidin; Snyder, Brian

2014-01-01

98

High beta and second stability region transport and stability analysis

This report describes ideal and resistive studies of high-beta plasmas and of the second stability region. Emphasis is focused on supershot'' plasmas in TFIR where MHD instabilities are frequently observed and which spoil their confinement properties. Substantial results are described from the analysis of these high beta poloidal plasmas. During these studies, initial pressure and safety factor profiles were obtained from the TRANSP code, which is used extensively to analyze experimental data. Resistive MBD stability studies of supershot equilibria show that finite pressure stabilization of tearing modes is very strong in these high {beta}p plasmas. This has prompted a detailed re-examination of linear tearing mode theory in which we participated in collaboration with Columbia University and General Atomics. This finite pressure effect is shown to be highly sensitive to small scale details of the pressure profile. Even when an ad hoc method of removing this stabilizing mechanism is implemented, however, it is shown that there is only superficial agreement between resistive MBD stability computation and the experimental data. While the mode structures observed experimentally can be found computationally, there is no convincing correlation with the experimental observations when the computed results are compared with a large set of supershot data. We also describe both the ideal and resistive stability properties of TFIR equilibria near the transition to the second region. It is shown that the highest {beta} plasmas, although stable to infinite-n ideal ballooning modes, can be unstable to the so called infernal'' modes associated with small shear. The sensitivity of these results to the assumed pressure and current density profiles is discussed. Finally, we describe results from two collaborative studies with PPPL. The first involves exploratory studies of the role of the 1/1 mode in tokamaks and, secondly, a study of sawtooth stabilization using ICRF.

Hughes, M.H.; Phillps, M.W.; Todd, A.M.M.; Krishnaswami, J.; Hartley, R.

1992-09-01

99

Stability analysis of shallow wake flows

NASA Astrophysics Data System (ADS)

Experimentally observed periodic structures in shallow (i.e. bounded) wake flows are believed to appear as a result of hydrodynamic instability. Previously published studies used linear stability analysis under the rigid-lid assumption to investigate the onset of instability of wakes in shallow water flows. The objectives of this paper are: (i) to provide a preliminary assessment of the accuracy of the rigid-lid assumption; (ii) to investigate the influence of the shape of the base flow profile on the stability characteristics; (iii) to formulate the weakly nonlinear stability problem for shallow wake flows and show that the evolution of the instability is governed by the Ginzburg Landau equation; and (iv) to establish the connection between weakly nonlinear analysis and the observed flow patterns in shallow wake flows which are reported in the literature. It is found that the relative error in determining the critical value of the shallow wake stability parameter induced by the rigid-lid assumption is below 10% for the practical range of Froude number. In addition, it is shown that the shape of the velocity profile has a large influence on the stability characteristics of shallow wakes. Starting from the rigid-lid shallow-water equations and using the method of multiple scales, an amplitude evolution equation for the most unstable mode is derived. The resulting equation has complex coefficients and is of Ginzburg Landau type. An example calculation of the complex coefficients of the Ginzburg Landau equation confirms the existence of a finite equilibrium amplitude, where the unstable mode evolves with time into a limit-cycle oscillation. This is consistent with flow patterns observed by Ingram & Chu (1987), Chen & Jirka (1995), Balachandar et al. (1999), and Balachandar & Tachie (2001). Reasonable agreement is found between the saturation amplitude obtained from the Ginzburg Landau equation under some simplifying assumptions and the numerical data of Grubi[sbreve]ic et al. (1995). Such consistency provides further evidence that experimentally observed structures in shallow wake flows may be described by the nonlinear Ginzburg Landau equation. Previous works have found similar consistency between the Ginzburg Landau model and experimental data for the case of deep (i.e. unbounded) wake flows. However, it must be emphasized that much more information is required to confirm the appropriateness of the Ginzburg Landau equation in describing shallow wake flows.

Kolyshkin, A. A.; Ghidaoui, M. S.

2003-11-01

100

Aerobic digestion batch tests were run on a sludge model that contained only two fractions, the heterotrophic biomass (XH) and its endogenous residue (XP). The objective was to describe the stabilization of the sludge and estimate the endogenous decay parameters. Modeling was performed with Aquasim, based on long-term data of volatile suspended solids and chemical oxygen demand (VSS, COD). Sensitivity analyses were carried out to determine the conditions for unique identifiability of the parameters. Importantly, it was found that the COD/VSS ratio of the endogenous residues (1.06) was significantly lower than for the active biomass fraction (1.48). The decay rate constant of the studied sludge (low bH, 0.025 d(-1)) was one-tenth that usually observed (0.2d(-1)), which has two main practical significances. Digestion time required is much more long; also the oxygen uptake rate might be <1.5 mg O?/gTSSh (biosolids standards), without there being significant decline in the biomass. PMID:24907570

Martínez-García, C G; Olguín, M T; Fall, C

2014-08-01

101

Solar Dynamic Power System Stability Analysis and Control

NASA Technical Reports Server (NTRS)

The objective of this research is to conduct dynamic analysis, control design, and control performance test of solar power system. Solar power system consists of generation system and distribution network system. A bench mark system is used in this research, which includes a generator with excitation system and governor, an ac/dc converter, six DDCU's and forty-eight loads. A detailed model is used for modeling generator. Excitation system is represented by a third order model. DDCU is represented by a seventh order system. The load is modeled by the combination of constant power and constant impedance. Eigen-analysis and eigen-sensitivity analysis are used for system dynamic analysis. The effects of excitation system, governor, ac/dc converter control, and the type of load on system stability are discussed. In order to improve system transient stability, nonlinear ac/dc converter control is introduced. The direct linearization method is used for control design. The dynamic analysis results show that these controls affect system stability in different ways. The parameter coordination of controllers are recommended based on the dynamic analysis. It is concluded from the present studies that system stability is improved by the coordination of control parameters and the nonlinear ac/dc converter control stabilize system oscillation caused by the load change and system fault efficiently.

Momoh, James A.; Wang, Yanchun

1996-01-01

102

NASA Technical Reports Server (NTRS)

Small-signal modeling techniques are used in a system stability analysis of a breadboard version of a complete functional electrical power system. The system consists of a regulated switching dc-to-dc converter, a solar-cell-array simulator, a solar-array EMI filter, battery chargers and linear shunt regulators. Loss mechanisms in the converter power stage, including switching-time effects in the semiconductor elements, are incorporated into the modeling procedure to provide an accurate representation of the system without requiring frequency-domain measurements to determine the damping factor. The small-signal system model is validated by the use of special measurement techniques which are adapted to the poor signal-to-noise ratio encountered in switching-mode systems. The complete electrical power system with the solar-array EMI filter is shown to be stable over the intended range of operation.

Wong, R. C.; Owen, H. A., Jr.; Wilson, T. G.; Rodriguez, G. E.

1980-01-01

103

Voltage stability analysis using static and dynamic approaches

The authors discuss voltage stability analysis of power systems using static and dynamic techniques. Using a small test system, results of time domain simulations are presented to clarify the phenomenon of voltage instability and to better understand modeling requirements. The same system is then analyzed using a static approach in which modal analysis is performed using system conditions, or snapshots,

G. K. Morison; B. Gao; P. Kundur

1993-01-01

104

The stability of input structures in a supply-driven input-output model: A regional analysis

Disruptions in the supply of strategic resources or other crucial factor inputs often present significant problems for planners and policymakers. The problem may be particularly significant at the regional level where higher levels of product specialization mean supply restrictions are more likely to affect leading regional industries. To maintain economic stability in the event of a supply restriction, regional planners may therefore need to evaluate the importance of market versus non-market systems for allocating the remaining supply of the disrupted resource to the region`s leading consuming industries. This paper reports on research that has attempted to show that large short term changes on the supply side do not lead to substantial changes in input coefficients and do not therefore mean the abandonment of the concept of the production function as has been suggested (Oosterhaven, 1988). The supply-driven model was tested for six sectors of the economy of Washington State and found to yield new input coefficients whose values were in most cases close approximations of their original values, even with substantial changes in supply. Average coefficient changes from a 50% output reduction in these six sectors were in the vast majority of cases (297 from a total of 315) less than +2.0% of their original values, excluding coefficient changes for the restricted input. Given these small changes, the most important issue for the validity of the supply-driven input-output model may therefore be the empirical question of the extent to which these coefficient changes are acceptable as being within the limits of approximation.

Allison, T.

1994-06-01

105

3D Global Flow Stability Analysis on Unstructured Grids

Three-dimensional global flow stability analysis generates very large complex generalized eigenvalue problem. Solution of\\u000a the global flow stability problem delivers not only information about the growth rate of disturbances and respective frequencies.\\u000a Eigenvectors of this system constitute physical modes space necessary in Low Dimensional Modeling of the flow and flow control\\u000a design. Difficulties in solution of the eigenvalue problem limited

Marek Morzynski; Frank Thiele

2007-01-01

106

Stability/Instability Analysis of Rotating Machinery

NASA Technical Reports Server (NTRS)

Numerical index of stability calculated for nonlinear system. Technique for determining rotor stability or instability from analysis of measurements adapted for use with computer simulations of rotor motion. Involves calculation of log decrement or increment of vibration amplitude. Applicable to rotors mounted in loose bearings and to similar problems in which load-versus-deflection characteristics nonlinear. Developed for assessments of vibrational characteristics of turbopump rotors, technique also usable with such mechanisms as high-speed ball bearings.

Powers, Richard W.

1987-01-01

107

Background Understanding and predicting protein stability upon point mutations has wide-spread importance in molecular biology. Several prediction models have been developed in the past with various algorithms. Statistical potentials are one of the widely used algorithms for the prediction of changes in stability upon point mutations. Although the methods provide flexibility and the capability to develop an accurate and reliable prediction model, it can be achieved only by the right selection of the structural factors and optimization of their parameters for the statistical potentials. In this work, we have selected five atom classification systems and compared their efficiency for the development of amino acid atom potentials. Additionally, torsion angle potentials have been optimized to include the orientation of amino acids in such a way that altered backbone conformation in different secondary structural regions can be included for the prediction model. This study also elaborates the importance of classifying the mutations according to their solvent accessibility and secondary structure specificity. The prediction efficiency has been calculated individually for the mutations in different secondary structural regions and compared. Results Results show that, in addition to using an advanced atom description, stepwise regression and selection of atoms are necessary to avoid the redundancy in atom distribution and improve the reliability of the prediction model validation. Comparing to other atom classification models, Melo-Feytmans model shows better prediction efficiency by giving a high correlation of 0.85 between experimental and theoretical ??G with 84.06% of the mutations correctly predicted out of 1538 mutations. The theoretical ??G values for the mutations in partially buried ?-strands generated by the structural training dataset from PISCES gave a correlation of 0.84 without performing the Gaussian apodization of the torsion angle distribution. After the Gaussian apodization, the correlation increased to 0.92 and prediction accuracy increased from 80% to 88.89% respectively. Conclusion These findings were useful for the optimization of the Melo-Feytmans atom classification system and implementing them to develop the statistical potentials. It was also significant that the prediction efficiency of mutations in the partially buried ?-strands improves with the help of Gaussian apodization of the torsion angle distribution. All these comparisons and optimization techniques demonstrate their advantages as well as the restrictions for the development of the prediction model. These findings will be quite helpful not only for the protein stability prediction, but also for various structure solutions in future. PMID:17705837

Parthiban, Vijaya; Gromiha, M Michael; Abhinandan, Madenhalli; Schomburg, Dietmar

2007-01-01

108

Advanced stability analysis for laminar flow control

NASA Technical Reports Server (NTRS)

Five classes of problems are addressed: (1) the extension of the SALLY stability analysis code to the full eighth order compressible stability equations for three dimensional boundary layer; (2) a comparison of methods for prediction of transition using SALLY for incompressible flows; (3) a study of instability and transition in rotating disk flows in which the effects of Coriolis forces and streamline curvature are included; (4) a new linear three dimensional instability mechanism that predicts Reynolds numbers for transition to turbulence in planar shear flows in good agreement with experiment; and (5) a study of the stability of finite amplitude disturbances in axisymmetric pipe flow showing the stability of this flow to all nonlinear axisymmetric disturbances.

Orszag, S. A.

1981-01-01

109

Understanding & Modeling State Stability: Exploiting System Dynamics

The potential loss of state stability in various parts of the world is a source of threat to U.S. national security. Every case is unique, but there are common processes. Accordingly, we develop a system dynamics model of state stability by representing the nature and dynamics of `loads' generated by insurgency activities, on the one hand, and by articulating the

Nazli Choucri; Christi Electris; Daniel Goldsmith; Dinsha Mistree; Stuart E. Madnick; J. B. Morrison; Michael D. Siegel; Margaret Sweitzer-Hamilton

2006-01-01

110

Stability Analysis of an Encapsulated Microbubble against Gas Diffusion

Linear stability analysis is performed for a mathematical model of diffusion of gases from an encapsulated microbubble. It is an Epstein-Plesset model modified to account for encapsulation elasticity and finite gas permeability. Although, bubbles, containing gases other than air is considered, the final stable bubble, if any, contains only air, and stability is achieved only when the surrounding medium is saturated or oversaturated with air. In absence of encapsulation elasticity, only a neutral stability is achieved for zero surface tension, the other solution being unstable. For an elastic encapsulation, different equilibrium solutions are obtained depending on the saturation level and whether the surface tension is smaller or higher than the elasticity. For an elastic encapsulation, elasticity can stabilize the bubble. However, imposing a non-negativity condition on the effective surface tension (consisting of reference surface tension and the elastic stress) leads to an equilibrium radius which is only neutrally stable. If the encapsulation can support net compressive stress, it achieves actual stability. The linear stability results are consistent with our recent numerical findings. Physical mechanisms for the stability or instability of various equilibriums are provided. PMID:20005522

Katiyar, Amit; Sarkar, Kausik

2009-01-01

111

Moduli stabilization in stringy ISS models

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

112

Stability monitoring of fuzzy systems using trend analysis

Research in stability analysis of fuzzy logic controlled systems have intensified in the last decade without producing an adequate stability theory for the design of such systems. The paper presents an on-line stability indicator that identifies the stability state of the control system by monitoring system response. Unlike most stability analyses, the indicator does not depend on the development of

Natalie R. Spooner; Patrick P. K. Lim

1996-01-01

113

Stability Analysis of the Slowed-Rotor Compound Helicopter Configuration

NASA Technical Reports Server (NTRS)

The stability and control of rotors at high advance ratio are considered. Teetering, articulated, gimbaled, and rigid hub types are considered for a compound helicopter (rotor and fixed wing). Stability predictions obtained using an analytical rigid flapping blade analysis, a rigid blade CAMRAD II model, and an elastic blade CAMRAD II model are compared. For the flapping blade analysis, the teetering rotor is the most stable, showing no instabilities up to an advance ratio of 3 and a Lock number of 18. A notional elastic blade model of a teetering rotor is unstable at an advance ratio of 1.5, independent of pitch frequency. Analysis of the trim controls and blade flapping shows that for small positive collective pitch, trim can be maintained without excessive control input or flapping angles.

Floros, Matthew W.; Johnson, Wayne

2007-01-01

114

Stability Analysis of the Slowed-Rotor Compound Helicopter Configuration

NASA Technical Reports Server (NTRS)

The stability and control of rotors at high advance ratio are considered. Teetering, articulated, gimbaled, and rigid hub types are considered for a compound helicopter (rotor and fixed wing). Stability predictions obtained using an analytical rigid flapping blade analysis, a rigid blade CAMRAD II model, and an elastic blade CAMRAD II model are compared. For the flapping blade analysis, the teetering rotor is the most stable, 5howing no instabilities up to an advance ratio of 3 and a Lock number of 18. With an elastic blade model, the teetering rotor is unstable at an advance ratio of 1.5. Analysis of the trim controls and blade flapping shows that for small positive collective pitch, trim can be maintained without excessive control input or flapping angles.

Johnson, Wayne; Floros, Matthew W.

2004-01-01

115

Dynamic stability margin analysis on SRAM

...................................................................... 10 2.3 Definition of S(x) and Modified Set of Current Equation ............. 12 2.4 SRAM Cell Modeling Equations .................................................. 14 III NONLINEAR SYSTEM THEORIES AND CELL DYNAMICS OF SRAM..................................... 21 3.4 System Stability Theories and Concepts........................................ 26 3.5 Nullclines on Phase Portrait ........................................................... 32 3.6 Noise Induced Bifurcation...

Ho, Yenpo

2009-05-15

116

Aeroelastic stability analysis of a Darrieus wind turbine

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

117

Aeroelastic stability analysis of a Darrieus wind turbine

NASA Astrophysics Data System (ADS)

An aeroelastic stability analysis was 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

118

Stability Analysis for a Multi-Camera Photogrammetric System

Consumer-grade digital cameras suffer from geometrical instability that may cause problems when used in photogrammetric applications. This paper provides a comprehensive review of this issue of interior orientation parameter variation over time, it explains the common ways used for coping with the issue, and describes the existing methods for performing stability analysis for a single camera. The paper then points out the lack of coverage of stability analysis for multi-camera systems, suggests a modification of the collinearity model to be used for the calibration of an entire photogrammetric system, and proposes three methods for system stability analysis. The proposed methods explore the impact of the changes in interior orientation and relative orientation/mounting parameters on the reconstruction process. Rather than relying on ground truth in real datasets to check the system calibration stability, the proposed methods are simulation-based. Experiment results are shown, where a multi-camera photogrammetric system was calibrated three times, and stability analysis was performed on the system calibration parameters from the three sessions. The proposed simulation-based methods provided results that were compatible with a real-data based approach for evaluating the impact of changes in the system calibration parameters on the three-dimensional reconstruction. PMID:25196012

Habib, Ayman; Detchev, Ivan; Kwak, Eunju

2014-01-01

119

Stability analysis for a multi-camera photogrammetric system.

Consumer-grade digital cameras suffer from geometrical instability that may cause problems when used in photogrammetric applications. This paper provides a comprehensive review of this issue of interior orientation parameter variation over time, it explains the common ways used for coping with the issue, and describes the existing methods for performing stability analysis for a single camera. The paper then points out the lack of coverage of stability analysis for multi-camera systems, suggests a modification of the collinearity model to be used for the calibration of an entire photogrammetric system, and proposes three methods for system stability analysis. The proposed methods explore the impact of the changes in interior orientation and relative orientation/mounting parameters on the reconstruction process. Rather than relying on ground truth in real datasets to check the system calibration stability, the proposed methods are simulation-based. Experiment results are shown, where a multi-camera photogrammetric system was calibrated three times, and stability analysis was performed on the system calibration parameters from the three sessions. The proposed simulation-based methods provided results that were compatible with a real-data based approach for evaluating the impact of changes in the system calibration parameters on the three-dimensional reconstruction. PMID:25196012

Habib, Ayman; Detchev, Ivan; Kwak, Eunju

2014-01-01

120

The Dark Energy Star and Stability analysis

We have proposed a new model of dark energy star consisting of five zones namely, solid core of constant energy density, the thin shell between core and interior, an inhomogeneous interior region with anisotropic pressures, thin shell and the exterior vacuum region. We have discussed various physical properties. The model satisfies all the physical requirements. The stability condition under small linear perturbation has also been discussed.

Piyali Bhar; Farook Rahaman

2015-01-12

121

The dark energy star and stability analysis

NASA Astrophysics Data System (ADS)

We propose a new model of dark energy star consisting of five zones, namely, the solid core of constant energy density, the thin shell between core and interior, an inhomogeneous interior region with anisotropic pressures, a thin shell, and the exterior vacuum region. We discuss various physical properties. The model satisfies all the physical requirements. The stability condition under a small linear perturbation is also discussed.

Bhar, Piyali; Rahaman, Farook

2015-02-01

122

The Role Fore Air Flow in Soil Slope Stability Analysis

In order to investigate the effect of the pore air flow in the soil slope stability analysis, a water-air two-phase flow model, based on the multi-phase flow theory, is proposed and with the model, the water-phase and air-phase seepages of the soil slope in the stable seepage and rainfall situations are simulated. The soil slope safety coefficients are obtained according

Xiao-yue ZHANG; Yue-ming ZHU; Chun-hui FANG

2009-01-01

123

Stability analysis of automobile driver steering control

NASA Technical Reports Server (NTRS)

In steering an automobile, the driver must basically control the direction of the car's trajectory (heading angle) and the lateral deviation of the car relative to a delineated pathway. A previously published linear control model of driver steering behavior which is analyzed from a stability point of view is considered. A simple approximate expression for a stability parameter, phase margin, is derived in terms of various driver and vehicle control parameters, and boundaries for stability are discussed. A field test study is reviewed that includes the measurement of driver steering control parameters. Phase margins derived for a range of vehicle characteristics are found to be generally consistent with known adaptive properties of the human operator. The implications of these results are discussed in terms of driver adaptive behavior.

Allen, R. W.

1981-01-01

124

Sensitivity of system stability to model structure

A community is stable, and resilient, if the levels of all community variables can return to the original steady state following a perturbation. The stability properties of a community depend on its structure, which is the network of direct effects (interactions) among the variables within the community. These direct effects form feedback cycles (loops) that determine community stability. Although feedback cycles have an intuitive interpretation, identifying how they form the feedback properties of a particular community can be intractable. Furthermore, determining the role that any specific direct effect plays in the stability of a system is even more daunting. Such information, however, would identify important direct effects for targeted experimental and management manipulation even in complex communities for which quantitative information is lacking. We therefore provide a method that determines the sensitivity of community stability to model structure, and identifies the relative role of particular direct effects, indirect effects, and feedback cycles in determining stability. Structural sensitivities summarize the degree to which each direct effect contributes to stabilizing feedback or destabilizing feedback or both. Structural sensitivities prove useful in identifying ecologically important feedback cycles within the community structure and for detecting direct effects that have strong, or weak, influences on community stability. The approach may guide the development of management intervention and research design. We demonstrate its value with two theoretical models and two empirical examples of different levels of complexity. ?? 2009 Elsevier B.V. All rights reserved.

Hosack, G.R.; Li, H.W.; Rossignol, P.A.

2009-01-01

125

Modeling historical climate variability and slope stability

NASA Astrophysics Data System (ADS)

This study presents scenario models for historical variations of climate and slope stability. A model for historical annual patterns of temperature and rainfall was established on the basis of seasonal proxies. A process-based, spatio-temporal model for groundwater variations and slope stability was developed using the GIS environment of the software PCRaster. We applied the slope stability model to study the effects of the different climate scenarios on slope stability for three different hillslopes in the area around Bonn (Germany). The findings indicate three climatic phases with different annual temperature and precipitation patterns over the historic period. The modeling results show that a climatic scenario representing unstable conditions of a transition from the more humid Little Ice Age to dryer recent climate produces the highest slope instabilities. The intensity of this impact, however, varies with the sensitivity of the geomorphic system, i.e. local landforms and lithology, and cannot be generally related to the stability of a specific hillslope. More unstable areas are not necessarily more sensitive to climatic changes: the location of permeable layers (prone to groundwater rise) in relation to sensitive layers (lower strength) and higher gradients (higher stress) influences the sensitivity of a site with respect to climate changes. The presented method is capable of modeling landscape sensitivity to climate change with respect to groundwater-controlled landslides.

Schmidt, Jochen; Dikau, Richard

2004-06-01

126

In this paper, an Susceptible-Vaccines-Exposed-Infectious-Recovered model with continuous age-structure in the exposed and infectious classes is investigated. These two ages are assumed to have arbitrary distributions that are represented by age-specific rates leaving the exposed and the infectious classes. We investigate the global dynamics of this model in the sense of basic reproduction number via constructing Lyapunov functions. The asymptotic smoothness of solutions and uniform persistence of the system is shown from reformulating the system as a system of Volterra integral equations. PMID:25689314

Wang, Jinliang; Zhang, Ran; Kuniya, Toshikazu

2015-12-01

127

The ankyrin transient receptor potential channel TRPA1 is a polymodal sensor for noxious stimuli, and hence a promising target for treating chronic pain. This tetrameric six-transmembrane segment (S1-S6) channel can be activated by various pungent chemicals, such as allyl isothiocyanate or cinnamaldehyde, but also by intracellular Ca(2+) or depolarizing voltages. Within the S4-S5 linker of human TRPA1, a gain-of-function mutation, N855S, was recently found to underlie familial episodic pain syndrome, manifested by bouts of severe upper body pain, triggered by physical stress, fasting, or cold. To clarify the structural basis for this channelopathy, we derive a structural model of TRPA1 by combining homology modeling, molecular dynamics simulations, point mutagenesis and electrophysiology. In the vicinity of N855, the model reveals inter-subunit salt bridges between E854 and K868. Using the heterologous expression of recombinant wild-type and mutant TRPA1 channels in HEK293T cells, we indeed found that the charge-reversal mutants E854R and K868E exhibited dramatically reduced responses to chemical and voltage stimuli, whereas the charge-swapping mutation E854R/K868E substantially rescued their functionalities. Moreover, mutation analysis of highly conserved charged residues within the S4-S5 region revealed a gain-of-function phenotype for R852E with an increased basal channel activity, a loss of Ca(2+)-induced potentiation and an accelerated Ca(2+)-dependent inactivation. Based on the model and on a comparison with the recently revealed atomic-level structure of the related channel TRPV1, we propose that inter-subunit salt bridges between adjacent S4-S5 regions are crucial for stabilizing the conformations associated with chemically and voltage-induced gating of the TRPA1 ion channel. PMID:25724085

Zíma, Vlastimil; Witschas, Katja; Hynkova, Anna; Zímová, Lucie; Barvík, Ivan; Vlachova, Viktorie

2015-06-01

128

NASA Astrophysics Data System (ADS)

We propose a detailed stability analysis of the Lugiato-Lefever model for Kerr optical frequency combs in whispering-gallery-mode resonators when they are pumped in either the anomalous- or normal-dispersion regime. We analyze the spatial bifurcation structure of the stationary states depending on two parameters that are experimentally tunable; namely, the pump power and the cavity detuning. Our study demonstrates that, in both the anomalous- and normal-dispersion cases, nontrivial equilibria play an important role in this bifurcation map because their associated eigenvalues undergo critical bifurcations that are actually foreshadowing the existence of localized and extended spatial dissipative structures. The corresponding bifurcation maps are evidence of a considerable richness from a dynamical standpoint. The case of anomalous dispersion is indeed the most interesting from the theoretical point of view because of the considerable variety of dynamical behavior that can be observed. For this case we study the emergence of super- and subcritical Turing patterns (or primary combs) in the system via modulational instability. We determine the areas where bright isolated cavity solitons emerge, and we show that soliton molecules can emerge as well. Very complex temporal patterns can actually be observed in the system, where solitons (or soliton complexes) coexist with or without mutual interactions. Our investigations also unveil the mechanism leading to the phenomenon of breathing solitons. Two routes to chaos in the system are identified; namely, a route via the destabilization of a primary comb, and another via the destabilization of solitons. For the case of normal dispersion, we unveil the mechanism leading to the emergence of weakly stable Turing patterns. We demonstrate that this weak stability is justified by the distribution of stable and unstable fixed points in the parameter space (flat states). We show that dark cavity solitons can emerge in the system, and also show how these solitons can coexist in the resonator as long as they do not interact with each other. We find evidence of breather solitons in this normal dispersion regime as well. The Kerr frequency combs corresponding to all these spatial dissipative structures are analyzed in detail, along with their stability properties. A discussion is led about the possibility to gain unifying comprehension of the observed spectra from the dynamical complexity of the system.

Godey, Cyril; Balakireva, Irina V.; Coillet, Aurélien; Chembo, Yanne K.

2014-06-01

129

Stability Analysis for HIFiRE Experiments

NASA Technical Reports Server (NTRS)

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 paper reports selected findings from the ongoing computational analysis of the measured in-flight transition behavior. Transition during the ascent phase at nearly zero degree angle of attack is dominated by second mode instabilities except in the vicinity of the cone meridian where a roughness element was placed midway along the length of the cone. The growth of first mode instabilities is found to be weak at all trajectory points analyzed from the ascent phase. For times less than approximately 18.5 seconds into the flight, the peak amplification ratio for second mode disturbances is sufficiently small because of the lower Mach numbers at earlier times, so that the transition behavior inferred from the measurements is attributed to an unknown physical mechanism, potentially related to step discontinuities in surface height near the locations of a change in the surface material. Based on the time histories of temperature and/or heat flux at transducer locations within the aft portion of the cone, the onset of transition correlated with a linear N-factor, based on parabolized stability equations, of approximately 13.5. Due to the large angles of attack during the re-entry phase, crossflow instability may play a significant role in transition. Computations also indicate the presence of pronounced crossflow separation over a significant portion of the trajectory segment that is relevant to transition analysis. The transition behavior during this re-entry segment of HIFiRE-1 flight shares some common features with the predicted transition front along the elliptic cone shaped HIFiRE-5 flight article, which was designed to provide hypersonic transition data for a fully 3D geometric configuration. To compare and contrast the crossflow dominated transition over the HIFiRE-1 and HIFiRE-5 configurations, this paper also analyzes boundary layer instabilities over a subscale model of the HIFiRE-5 flight configuration that was tested in the Mach 6 quiet tunnel facility at Purdue University.

Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan; White, Jeffery A.; Kimmel, Roger; Adamczak, David; Borg, Matthew; Stanfield, Scott; Smith, Mark S.

2012-01-01

130

Stability analysis of White Oak Dam

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

131

ON THE STABILITY OF HOMOGENEOUS SOLUTIONS TO SOME AGGREGATION MODELS

Vasculogenesis, i.e. self-assembly of endothelial cells leading to capillary network formation, has been the object of many experimental in- vestigations in recent years, due to its relevance both in physiological and in pathological conditions. We performed a detailed linear stability analysis of two models of in vitro vasculogenesis, with the aim of checking their potential for structure formation starting from

R. Kowalczyk; A. Gamba; L. Preziosi

2004-01-01

132

Stability Analysis for Impedance Control of Robot in Human-Robot Cooperative Task System

NASA Astrophysics Data System (ADS)

In this paper, we consider a stability analysis for the impedance control of the robot in the human-robot cooperative task system. In the stability analysis, the effect of modeling conditions is investigated, such as the impedance characteristic of the robot, the time delay of a human operator and control of the robot, the compliance of the structure of the robot and environmental stiffness in interactive system. The proposed simulation of the stability analysis reveals that these conditions have significant effects on the stability of the system. To confirm the usefulness of stability analysis simulation, a verification experiment using a Mitsubishi PA-10 robot arm was performed. Experimental results show that the proposed stability analysis is effective in simulating the stability of the human-robot cooperative task system.

Tsumugiwa, Toru; Fuchikami, Yasunori; Kamiyoshi, Atsushi; Yokogawa, Ryuichi; Yoshida, Kazunobu

133

Analysis of the stabilized supralinear network‡

We study a rate-model neural network composed of excitatory and inhibitory neurons in which neuronal input-output functions are power laws with a power greater than 1, as observed in primary visual cortex. This supralinear input-output function leads to supralinear summation of network responses to multiple inputs for weak inputs. We show that for stronger inputs, which would drive the excitatory subnetwork to instability, the network will dynamically stabilize provided feedback inhibition is sufficiently strong. For a wide range of network and stimulus parameters, this dynamic stabilization yields a transition from supralinear to sublinear summation of network responses to multiple inputs. We compare this to the dynamic stabilization in the “balanced network”, which yields only linear behavior. We more exhaustively analyze the 2-dimensional case of 1 excitatory and 1 inhibitory population. We show that in this case dynamic stabilization will occur whenever the determinant of the weight matrix is positive and the inhibitory time constant is sufficiently small, and analyze the conditions for “supersaturation”, or decrease of firing rates with increasing stimulus contrast (which represents increasing input firing rates). In work to be presented elsewhere, we have found that this transition from supralinear to sublinear summation can explain a wide variety of nonlinearities in cerebral cortical processing. PMID:23663149

Ahmadian, Yashar; Rubin, Daniel B.; Miller, Kenneth D.

2014-01-01

134

Linear stability analysis of the whole spectrum of static hedgehog solutions of the Skyrme model on the three-sphere of radius L is carried out. It turns out that only solutions that in the limit of infinite L tend to skyrmions (localized at the poles) are linearly stable. The other solutions are unstable and, for a given solution, the number of instabilities, for L sufficiently large, is equal to the index of a harmonic map to which this solution tends pointwise in the limit of infinite L. Solutions which tends pointwise to harmonic maps and which in addition have a definite parity, undergo a transition by +1 in the number of instabilities as L grows. Due to the instability, new solutions, with spontaneously broken reflection symmetry, appeare by bifurcations. In the case of the 1-skyrmion this critical phenomenon can be fully described analytically. As a result, in some neighbourhood of critical radius at which 1-skyrmion bifurcates from the identity solution, one gets unique series expansions for the profile of the 1-skyrmion and for its energy, though the series coefficients, due to nonlinearity, are not known in general form. To the author's best knowledge the series were not given in literature so far. A similar mechanism of spontaneous breaking of parity is also observed when other solutions appear by bifurcations from symmetric solutions.

Lukasz Bratek

2004-09-03

135

Advanced Pogo stability analysis for liquid rockets

NASA Astrophysics Data System (ADS)

In the present model for determination of liquid rocket engine-coupled Pogo oscillation modes due to the interaction of structural vibrations with pressure and flow oscillations in the propulsion system, a time-invariant linearized mathematical model of the system views propulsion system perturbations via finite-element representations for its various physical elements. Each element's structural motion is described in terms of the overall vehicle's structural modes. This treatment of arbitrary motions of the vessels through which fluids flow is rigorous; a powerful numerical eigensolver yields eigenvalues and eigenvectors directly. The eigensolutions can be used to evaluate Pogo stability derivatives and margins.

Oppenheim, Bohdan W.; Rubin, Sheldon

136

This paper presents the application of adaptive rational spectral methods to the linear stability analysis of nonlinear fourth-order problems. Our model equation is a phase-field model of infiltration, but the proposed ...

Juanes, Ruben

137

Thermodynamic modeling of natural zeolite stability

Zeolites occur in a variety of geologic environments and are used in numerous agricultural, commercial, and environmental applications. It is desirable to understand their stability both to predict future stability and to evaluate the geochemical conditions resulting in their formation. The use of estimated thermodynamic data for measured zeolite compositions allows thermodynamic modeling of stability relationships among zeolites in different geologic environments (diagenetic, saline and alkaline lakes, acid rock hydrothermal, basic rock, deep sea sediments). This modeling shows that the relative cation abundances in both the aqueous and solid phases, the aqueous silica activity, and temperature are important factors in determining the stable zeolite species. Siliceous zeolites (e.g., clinoptilolite, mordenite, erionite) present in saline and alkaline lakes or diagenetic deposits formed at elevated silica activities. Aluminous zeolites (e.g., natrolite, mesolite/scolecite, thomsonite) formed in basic rocks in association with reduced silica activities. Likewise, phillipsite formation is favored by reduced aqueous silica activities. The presence of erionite, chabazite, and phillipsite are indicative of environments with elevated potassium concentrations. Elevated temperature, calcic water conditions, and reduced silica activity help to enhance the laumontite and wairakite stability fields. Analcime stability increases with increased temperature and aqueous Na concentration, and/or with decreased silica activity.

Chipera, S.J.; Bish, D.L.

1997-06-01

138

Linearised Stability Analysis of Generic Thin Shells

NASA Astrophysics Data System (ADS)

We construct generic spherically symmetric thin shells by using the cut-and-paste procedure. We take considerable effort to make the analysis as general and unified as practicable; investigating both the internal physics of the transition layer and its interaction with "external forces" arising due to interactions between the transition layer and the bulk spacetime. We demonstrate in full generality that stability of the thin shell is equivalent to choosing suitable properties for the material residing on the junction interface. Applications to gravastars and wormhole geometries are also explored.

Lobo, Francisco S. N.; Martin-Moruno, Prado; Garcia, Nadiezhda Montelongo; Visser, Matt

2015-01-01

139

DYNAMIC LANDSCAPES, STABILITY AND ECOLOGICAL MODELING

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 ...

140

Stabilization control of a hovering model insect: lateral motion

NASA Astrophysics Data System (ADS)

Our previous study shows that the lateral disturbance motion of a model drone fly does not have inherent stability (passive stability), because of the existence of an unstable divergence mode. But drone flies are observed to fly stably. Constantly active control must be applied to stabilize the flight. In this study, we investigate the lateral stabilization control of the model drone fly. The method of computational fluid dynamics is used to compute the lateral control derivatives and the techniques of eigenvalue and eigenvector analysis and modal decomposition are used for solving the equations of motion. Controllability analysis shows that although inherently unstable, the lateral disturbance motion is controllable. By feeding back the state variables (i.e. lateral translation velocity, yaw rate, roll rate and roll angle, which can be measured by the sensory system of the insect) to produce anti-symmetrical changes in stroke amplitude and/or in angle of attack between the left and right wings, the motion can be stabilized, explaining why the drone flies can fly stably even if the flight is passively unstable.

Zhang, Yan-Lai; Sun, Mao

2011-10-01

141

Bounded Linear Stability Margin Analysis of Nonlinear Hybrid Adaptive Control

NASA Technical Reports Server (NTRS)

This paper presents a bounded linear stability analysis for a hybrid adaptive control that blends both direct and indirect adaptive control. Stability and convergence of nonlinear adaptive control are analyzed using an approximate linear equivalent system. A stability margin analysis shows that a large adaptive gain can lead to a reduced phase margin. This method can enable metrics-driven adaptive control whereby the adaptive gain is adjusted to meet stability margin requirements.

Nguyen, Nhan T.; Boskovic, Jovan D.

2008-01-01

142

Voltage Stability Analysis of a Multiple-Infeed Load Center Using Phasor Measurement Data

Voltage stability is a security concern for modern power systems. It can be analyzed using detailed or equivalent models. In this paper a new approach is presented for voltage stability analysis using synchronized phasor measurement data. Simple equivalent models of the interconnected system and load side at a measurement point are estimated from the data, and then used for calculating

Mostafa Parniani; Joe H. Chow; Luigi Vanfretti; Bharat Bhargava; Armando Salazar

2006-01-01

143

Vector fields during cosmic inflation: Stability analysis and phenomenological signatures

NASA Astrophysics Data System (ADS)

This thesis is based on the study of vector fields during cosmic inflation. Cosmic inflation has proven to be an accurate description of the very early universe, not only because of its success in resolving the classical problems of big bang cosmology, but also for introducing a natural mechanism for the generation of primordial fluctuations which give rise to the structure (galaxies and cluster of galaxies) in the universe. For simplicity, most inflationary scenarios assume that the expansion is driven by a scalar field. However, due to the fact that the underlying particle physics model of inflation is unknown, and due to some features emerged in some studies of the cosmic microwave background data, there have recently been considerable interest in vector field driven models of inflation. In this thesis, I present a complete stability analysis of some of the compelling models where vector fields are assumed to play an important role during inflation. The stability analysis is performed by studying all possible fluctuations around the background solution of these models. It is explicitly proven that for models where the gauge invariance of the vector field is broken, the background solution is unstable. The proof is performed both (1) by studying the quadratic action for the fluctuations, and showing that ghost instabilities are present in the model; and (2) by studying the linearized Einstein equations and showing that the solutions diverge close to horizon crossing. For models that are free of instabilities, relevant power spectra are computed and the resulting phenomenology is discussed.

Himmetoglu, Burak

144

Metals are a key component of many diagnostic imaging and biotechnology applications, and the majority of cancer patients receive a platinum-based drug as part of their treatment. Significant effort has been devoted to developing tight binding synthetic chelators to enable effective targeted delivery of metal-based conjugates, with most successes involving lanthanides rather than transition metals for diagnostic imaging. Chemical conjugation modifies the protein's properties and generates a heterogeneous mixture of products. Chelator attachment is typically carried out by converting the amino group on lysines to an amide, which can impact the stability and solubility of the targeting protein and these properties vary among the set of individual conjugate species. Site-specific attachment is sought to reduce complexity and control stability. Here, the metal abstraction peptide technology was applied to create the claMP Tag, an inline platform for generating site-specific conjugates involving transition metals. The claMP Tag was genetically encoded into epidermal growth factor (EGF) and loaded with nickel(II) as a model system to demonstrate that the tag within the homogeneous inline conjugate presents sufficient solution stability to enable biotechnology applications. The structure and disulfide network of the protein and chemical stability of the claMP Tag and EGF components were characterized. PMID:25212829

Mills, Brittney J; Laurence, Jennifer S

2015-02-01

145

Truck Roll Stability Data Collection and Analysis

The principal objective of this project was to collect and analyze vehicle and highway data that are relevant to the problem of truck rollover crashes, and in particular to the subset of rollover crashes that are caused by the driver error of entering a curve at a speed too great to allow safe completion of the turn. The data are of two sorts--vehicle dynamic performance data, and highway geometry data as revealed by vehicle behavior in normal driving. Vehicle dynamic performance data are relevant because the roll stability of a tractor trailer depends both on inherent physical characteristics of the vehicle and on the weight and distribution of the particular cargo that is being carried. Highway geometric data are relevant because the set of crashes of primary interest to this study are caused by lateral acceleration demand in a curve that exceeds the instantaneous roll stability of the vehicle. An analysis of data quality requires an evaluation of the equipment used to collect the data because the reliability and accuracy of both the equipment and the data could profoundly affect the safety of the driver and other highway users. Therefore, a concomitant objective was an evaluation of the performance of the set of data-collection equipment on the truck and trailer. The objective concerning evaluation of the equipment was accomplished, but the results were not entirely positive. Significant engineering apparently remains to be done before a reliable system can be fielded. Problems were identified with the trailer to tractor fiber optic connector used for this test. In an over-the-road environment, the communication between the trailer instrumentation and the tractor must be dependable. In addition, the computer in the truck must be able to withstand the rigors of the road. The major objective--data collection and analysis--was also accomplished. Using data collected by instruments on the truck, a ''bad-curve'' database can be generated. Using this database, instrumented vehicles would not need roadside beacons. The speed, acceleration, and roll stability of the vehicle could be determined prior to entering a curve, and a warning issued, if appropriate, for curves that have been characterized in the database. Thus, the analysis indicates that the data can be effectively used to provide a timely warning of rollover risk.

Stevens, SS

2001-07-02

146

Linear stability analysis of transverse dunes

Sand-moving winds blowing from a constant direction in an area of high sand availability form transverse dunes, which have a fixed profile in the direction orthogonal to the wind. Here we show, by means of a linear stability analysis, that transverse dunes are intrinsically unstable. Any along-axis perturbation on a transverse dune amplify in the course of dune migration due to the combined effect of two main factors, namely: the lateral transport through avalanches along the dune's slip-face, and the scaling of dune migration velocity with the inverse of the dune height. Our calculations provide a quantitative explanation for recent observations from experiments and numerical simulations, which showed that transverse dunes moving on the bedrock cannot exist in a stable form and decay into a chain of crescent-shaped barchans.

Hygor P. M. Melo; Eric J. R. Parteli; José S. Andrade Jr; Hans J. Herrmann

2012-02-16

147

Linear stability analysis of transverse dunes

Sand-moving winds blowing from a constant direction in an area of high sand availability form transverse dunes, which have a fixed profile in the direction orthogonal to the wind. Here we show, by means of a linear stability analysis, that transverse dunes are intrinsically unstable. Any along-axis perturbation on a transverse dune amplify in the course of dune migration due to the combined effect of two main factors, namely: the lateral transport through avalanches along the dune's slip-face, and the scaling of dune migration velocity with the inverse of the dune height. Our calculations provide a quantitative explanation for recent observations from experiments and numerical simulations, which showed that transverse dunes moving on the bedrock cannot exist in a stable form and decay into a chain of crescent-shaped barchans.

Melo, Hygor P M; Andrade, José S; Herrmann, Hans J

2012-01-01

148

Control design and stability analysis of a surgical teleoperator

This paper presents stability and performance analysis of a surgical force reflecting master slave system, which currently is under development. Telemanipulation with a stiff slave manipulator against a stiff environment like human bone material causes stability problems. The influence on stability depending on the hand grip of the master stick is examined. The result of the simulations with the identified

H. Flemmer; B. Eriksson; J. Wikander

1999-01-01

149

Bifurcation Analysis of Endogenous Growth Models

parameter space, the dynamics of the Uzawa-Lucas endogenous growth model. We examine the stability properties of both centralized and decentralized versions of the model and locate Hopf and transcritical bifurcation boundaries. In an extended analysis, we...

Ghosh, Taniya

2013-05-31

150

Shapes and stability of algebraic nuclear models

NASA Technical Reports Server (NTRS)

A generalization of the procedure to study shapes and stability of algebraic nuclear models introduced by Gilmore is presented. One calculates the expectation value of the Hamiltonian with respect to the coherent states of the algebraic structure of the system. Then equilibrium configurations of the resulting energy surface, which depends in general on state variables and a set of parameters, are classified through the Catastrophe theory. For one- and two-body interactions in the Hamiltonian of the interacting Boson model-1, the critical points are organized through the Cusp catastrophe. As an example, we apply this Separatrix to describe the energy surfaces associated to the Rutenium and Samarium isotopes.

Lopez-Moreno, Enrique; Castanos, Octavio

1995-01-01

151

Global stability analysis of a metapopulation SIS epidemic Abderrahman Iggidr1

Global stability analysis of a metapopulation SIS epidemic model Abderrahman Iggidr1 , Gauthier The conjecture of Arino and van den Driessche (2003) that a SIS type model in a mover- stayer epidemic model manifold of the disease free equilibrium. Keywords: Metapopulation models; SIS models; nonlinear dynamical

Paris-Sud XI, UniversitÃ© de

152

Global stability analysis of a Curzon-Ahlborn heat engine using the Lyapunov method

NASA Astrophysics Data System (ADS)

In the present work, we analyze the global stability of a heat engine working at maximum power regime. We use the Lyapunov stability theory to construct the Lyapunov function to prove the asymptotic stability behavior about the steady-state of intermediate temperatures in the engine model. Our analysis is focused on the characterization of the global stability by considering internal irreversibilities and a linear heat transfer law in the thermal couplings. Besides, numerical integrations were performed to corroborate the findings of the global asymptotic stability of the system.

Reyes-Ramírez, Israel; Barranco-Jiménez, Marco A.; Rojas-Pacheco, A.; Guzmán-Vargas, Lev

2014-04-01

153

Mathematical Modeling and Simulation of Seated Stability

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.

2009-01-01

154

Theory and modelling of nanocarbon phase stability.

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

155

Global stability for an SIR epidemic model with delay and nonlinear incidence

A recent paper [R. Xu, Z. Ma, Global stability of a SIR epidemic model with nonlinear incidence rate and time delay, Nonlinear Anal. RWA 10 (2009) 3175–3189] presented an SIR model of disease transmission with delay and nonlinear incidence. The analysis there only partially resolves the global stability of the endemic equilibrium for the case where the reproduction number R0

C. Connell McCluskey

2010-01-01

156

Stability of earthquake clustering models: Criticality and branching ratios

NASA Astrophysics Data System (ADS)

We study the stability conditions of a class of branching processes prominent in the analysis and modeling of seismicity. This class includes the epidemic-type aftershock sequence (ETAS) model as a special case, but more generally comprises models in which the magnitude distribution of direct offspring depends on the magnitude of the progenitor, such as the branching aftershock sequence (BASS) model and another recently proposed branching model based on a dynamic scaling hypothesis. These stability conditions are closely related to the concepts of the criticality parameter and the branching ratio. The criticality parameter summarizes the asymptotic behavior of the population after sufficiently many generations, determined by the maximum eigenvalue of the transition equations. The branching ratio is defined by the proportion of triggered events in all the events. Based on the results for the generalized case, we show that the branching ratio of the ETAS model is identical to its criticality parameter because its magnitude density is separable from the full intensity. More generally, however, these two values differ and thus place separate conditions on model stability. As an illustration of the difference and of the importance of the stability conditions, we employ a version of the BASS model, reformulated to ensure the possibility of stationarity. In addition, we analyze the magnitude distributions of successive generations of the BASS model via analytical and numerical methods, and find that the compound density differs substantially from a Gutenberg-Richter distribution, unless the process is essentially subcritical (branching ratio less than 1) or the magnitude dependence between the parent event and the direct offspring is weak.

Zhuang, Jiancang; Werner, Maximilian J.; Harte, David S.

2013-12-01

157

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

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

158

SLOPE STABILITY ANALYSIS OF THE ILIAMNA VOLCANO, ALASKA, USING ASTER TIR, SRTM DEM and digital elevation models to create a hazard index that characterizes slope stability on active volcanoes. Introduction Volcano monitoring in the Aleutians is of great importance due to the heavy amount of airplane

159

Stability Analysis for a Landfill Experiencing Elevated Temperatures Timothy D. Stark1

Stability Analysis for a Landfill Experiencing Elevated Temperatures Timothy D. Stark1 , F. ASCE, P and stability analyses for a municipal solid waste (MSW) landfill experiencing elevated temperatures due, and possible leachate levels. The MSW that was thermally degraded at this site was modeled using an effective

160

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

1997-01-01

161

Analysis of Power System Stability Enhancement by Static VAR Compensators

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

162

Dynamic flight stability of a hovering model dragonfly.

The longitudinal dynamic flight stability of a model dragonfly at hovering flight is studied, using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. Three natural modes of motion are identified for the hovering flight: one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. The flight is dynamically unstable owing to the unstable oscillatory mode. The instability is caused by a pitch-moment derivative with respect to horizontal velocity. The damping force and moment derivatives (with respect to horizontal and vertical velocities and pitch-rotational velocity, respectively) weaken the instability considerably. The aerodynamic interaction between the forewing and the hindwing does not have significant effect on the stability properties. The dragonfly has similar stability derivatives, hence stability properties, to that of a one-wing-pair insect at normal hovering, but there are differences in how the derivatives are produced because of the highly inclined stroke plane of the dragonfly. PMID:24486234

Liang, Bin; Sun, Mao

2014-05-01

163

Postburn roof stability analysis for the TONO CRIP UCG burn

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

164

Kahler stabilized, modular invariant heterotic string models

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

165

Kahler Stabilized, Modular Invariant Heterotic String Models

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 Binetruy, 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.

Mary K. Gaillard; Brent D. Nelson

2007-03-26

166

Stability of chameleon scalar field models

The present work is an extensive study of the viable stable solutions of chameleon scalar field models leading to possibilities of an accelerated expansion of the universe. It is found that for various combinations of the chameleon field potential $V(\\phi)$ and the coupling $f(\\phi)$ of the chameleon field with matter, a stable solution for an accelerated expansion is quite possible. The investigation provides a diagnostics for the stability criteria for all sorts of combinations of $V(\\phi)$ and $f(\\phi)$.

Nandan Roy; Narayan Banerjee

2014-11-05

167

Linear stability analysis on supersonic streamwise vortices

NASA Astrophysics Data System (ADS)

In this study, the spatial growth rates of supersonic streamwise vortices were investigated by inviscid linear stability analysis. The freestream Mach numbers were 2.5, 5.0, and 7.5. In previous measurements taken to define the streamwise vortices, the stagnation temperature profile of supersonic flows is approximately uniform. This study found that the growth rate of vortices at the uniform stagnation temperature is smaller than that of isentropic vortices. The instability properties of the streamwise vortices can be explained by the ratio of the circulation to the axial velocity deficit, and also by the Mach number. Moreover, it is found that the compressibility effect, by which the instability reduces as the Mach number increases, is caused by the negative energy arising from the entropy gradient of supersonic vortices that accompanies the axial velocity deficit-like wake. From an energy perspective, the effect may reasonably be correlated with the large density perturbations in supersonic flows. This study also proposes a general convective Mach number for supersonic streamwise vortices. The normalized growth rates are shown to be a function of convective Mach number within the investigated range of ratio parameters.

Hiejima, Toshihiko

2013-11-01

168

Global Stability for a Heroin Model with Two Distributed Delays

Global Stability for a Heroin Model with Two Distributed Delays Bin Fang1,2 , Xue-Zhi Li1 , Maia, we consider global stability for a heroin model with two distributed de- lays. The basic reproduction number of the heroin spread is obtained, which completely determine the stability of equilibria. Using

Martcheva, Maia

169

Landslide stability analysis on basis of LIDAR data extraction

NASA Astrophysics Data System (ADS)

Currently, existing contradictory between remediation and acquisition from natural resource induces a series of divergences. With regard to open pit mining, legal regulation requires human to fill back the open pit area with water or recreate new landscape by other materials; on the other hand, human can not help excavating the mining area due to the shortage of power resource. However, to engineering geologists, one coincident problem which takes place not only in filling but also in mining operation should be paid more attention to, i.e. the slope stability analysis within these areas. There are a number of construction activities during remediation or mining process which can directly or indirectly cause slope failure. Lives can be endangered since local failure either while or after remediation; for mining process, slope failure in a bench, which carries a main haul road or is adjacent to human activity area, would be significant catastrophe to the whole mining program. The stability of an individual bench or slope is controlled by several factors, which are geological condition, morphology, climate, excavation techniques and transportation approach. The task which takes the longest time is to collect the morphological data. Consequently, it is one of the most dangerous tasks due to the time consuming in mining field. LIDAR scanning for morphological data collecting can help to skip this obstacle since advantages of LIDAR techniques as follows: • Dynamic range available on the market: from 3 m to beyond 1 km, • Ruggedly designed for demanding field applications, • Compact, easily hand-carried and deployed by a single operator. In 2009, scanning campaigns for 2 open pit quarry have been carried out. The aim for these LIDAR detections is to construct a detailed 3D quarry model and analyze the bench stability to support the filling planning. The 3D quarry surface was built up by using PolyWorks 10.1 on basis of LIDAR data. LIDAR data refining takes an important role during surface construction for further more precise analysis purpose. 3D geological model can be built based on the connection between surface model and geological data like borehole data in GOCAD. Regarding the bench stability analysis, LEM (Limit Equilibrium Method) analysis using Janbu and FEM (Finite Element Method) have been adopted during this analyzing task. A program was developed to convert GOCAD 2D section data directly into the FEM software. The meshed model is then used for stability analysis. In one quarry, 3 cross sections have been extracted on basis of LIDAR original data (original 3 cross sections). To evaluate the advantages of LIDAR data for slope analysis, the results of safety factor (SF) were compared to simplified slope models as they are used normally. The comparison showed that variations of the SF reach up to 9%. Additionally, conservative evaluation demonstrated by SF results based on simplified model is not adaptive for decision making of filling.

Hu, Hui; Fernandez-Steeger, Tomas M.; Dong, Mei; Azzam, Rafig

2010-05-01

170

Online stability validation using sector analysis

Our previous work has explored the use of compositional stabilization techniques for embedded flight control software[9] based on passivity properties of controller components and systems. Zames[21] presented a compositional behavior-bounding technique for evaluating stability of nonlinear systems based on real intervals representing cones (sectors) that bound possible component behaviors. Many innovations in control theory have developed from his insights. We

Joseph Porter; Graham Hemingway; Nicholas Kottenstette; Gabor Karsai; Janos Sztipanovits

2010-01-01

171

Analysis of slope stabilization by soil bioengineering method

NASA Astrophysics Data System (ADS)

The aim of the project is to create a numerical model which will include the impact of vegetation on the slope stability analysis, considering both mechanical and hydrological factors. This will enrich the current knowledge about how roots reinforce the soil layers on the slope and how it influences the increase of shear strength of the soil. This has to be combined together with hydrological effects caused by evapotranspiration: modified soil moisture regime, dissipation of excess pore pressure and established matric suction. Coupled analyses (mechanical and hydrological) are rarely conducted, or only outdated models are used, which leads to overestimation of the additional shear strength of soil. That is why there is a need to support this branch of landslide hazard assessment and develop a new model. This research will help to raise awareness, that soil bioengineering methods of slope stabilization can in some cases be more appropriate and less expensive than traditional methods. As an input to the model, the appropriate slope geometry and soil properties have to be chosen. It is also important to consider different plant types and root properties, as well as different levels of groundwater table. To assess the effect of evapotranspiration it is necessary to know the geographical location of the slope and the weather conditions in the chosen region. The final output of the model, which will help to quantitatively assess the impact of vegetation on the slope stability, is the factor of safety (FOS) for vegetated slope for different types of soil and degrees of saturation. Results may then be compared with different conditions and factors of safety, calculated for the corresponding non-vegetated slope. It will be possible to specify the most favorable and unfavorable conditions. Moreover, the calculations provide also information on changes of cohesion, caused by mechanical and hydrological effects, as well as the change in the friction angle of soil.

Switala, Barbara Maria; Wu, Wei

2013-04-01

172

Visual optimality and stability analysis of 3DCT scan positions.

Industrial cone-beam X-Ray computed tomography (CT) systems often face problems due to artifacts caused by a bad placement of the specimen on the rotary plate. This paper presents a visual-analysis tool for CT systems, which provides a simulation-based preview and estimates artifacts and deviations of a specimen's placement using the corresponding 3D geometrical surface model as input. The presented tool identifies potentially good or bad placements of a specimen and regions of a specimen, which cause the major portion of artefacts. The tool can be used for a preliminary analysis of the specimen before CT scanning, in order to determine the optimal way of placing the object. The analysis includes: penetration lengths, placement stability and an investigation in Radon space. Novel visualization techniques are applied to the simulation data. A stability widget is presented for determining the placement parameters' robustness. The performance and the comparison of results provided by the tool compared with real world data is demonstrated using two specimens. PMID:20975189

Amirkhanov, Artem; Heinzl, Christoph; Reiter, Michael; Gröller, Eduard

2010-01-01

173

Soliton stability in some knot soliton models

NASA Astrophysics Data System (ADS)

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.; Sánchez-Guillén, J.; Wereszczy?ski, A.

2007-02-01

174

Stability Estimation of ABWR on the Basis of Noise Analysis

NASA Astrophysics Data System (ADS)

In order to investigate the stability of a nuclear reactor core with an oxide mixture of uranium and plutonium (MOX) fuel installed, channel stability and regional stability tests were conducted with the SIRIUS-F facility. The SIRIUS-F facility was designed and constructed to provide a highly accurate simulation of thermal-hydraulic (channel) instabilities and coupled thermalhydraulics-neutronics instabilities of the Advanced Boiling Water Reactors (ABWRs). A real-time simulation was performed by modal point kinetics of reactor neutronics and fuel-rod thermal conduction on the basis of a measured void fraction in a reactor core section of the facility. A time series analysis was performed to calculate decay ratio and resonance frequency from a dominant pole of a transfer function by applying auto regressive (AR) methods to the time-series of the core inlet flow rate. Experiments were conducted with the SIRIUS-F facility, which simulates ABWR with MOX fuel installed. The variations in the decay ratio and resonance frequency among the five common AR methods are within 0.03 and 0.01 Hz, respectively. In this system, the appropriate decay ratio and resonance frequency can be estimated on the basis of the Yule-Walker method with the model order of 30.

Furuya, Masahiro; Fukahori, Takanori; Mizokami, Shinya; Yokoya, Jun

175

Singular Isothermal Disks. I. Linear Stability Analysis

NASA Astrophysics Data System (ADS)

As part of a larger effort to understand how binary and single stars form from the collapse of magnetized molecular cloud cores, we perform a global stability analysis of isopedically magnetized, singular isothermal disks (SIDs). The work described here has precedents in earlier studies of disturbances in power-law disks by Zang in 1976, Toomre in 1977, Lynden-Bell & Lemos in 1993, Syer & Tremaine in 1996, and Goodman & Evans in 1999. We find the analytic criteria for the bifurcation of axisymmetric disks into nonaxisymmetric forms with azimuthal periodicities m=1 (eccentric displacements), 2 (oval distortions), 3 (triangular distortions), etc. These bifurcations, which occur at zero frequency, are the compressible and differentially rotating analogs of how the classical sequence of incompressible and uniformly rotating Maclaurin spheroids bifurcate (secularly, under dissipative forces) to become Dedekind ellipsoids with figure axes that remain fixed in space. Like Syer & Tremaine and Lynden-Bell & Lemos, we also find that zero-frequency logarithmic spirals are possible scale-free disturbances, but our interpretation of the existence of such steadily propagating wavetrains is different. We give a dynamical instability interpretation based on the onset of swing amplification by overreflection at the corotation circle of prograde spiral density waves the pattern speeds of which have nonzero and positive values. Our analysis yields identical instability criteria as the global normal-modes treatment of Goodman & Evans, and we tentatively also identify dynamical barred-spiral instabilities as the ``breathing mode'' limit of two-armed ordinary-spiral instabilities. We prove a general ``reciprocity theorem,'' which states that the overreflection factors are identical for spiral density waves launched from cavities interior or exterior to Q-barriers that straddle the corotation circle. This globally valid result supports a unifying interpretation, advocated for many years by C. C. Lin and his colleagues (see, e.g., work by Bertin & Lin): the coexistence of spiral structure in galaxies arising from the instability of internal normal modes in the combined star/gas disk or from driving by external tidal influences associated with the chance passages of companion bodies.

Shu, Frank H.; Laughlin, Gregory; Lizano, Susana; Galli, Daniele

2000-05-01

176

Stability analysis of large electric power systems

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

177

Static and dynamic stability analysis of the space shuttle vehicle-orbiter

NASA Technical Reports Server (NTRS)

The longitudinal static and dynamic stability of a Space Shuttle Vehicle-Orbiter (SSV Orbiter) model is analyzed using the FLEXSTAB computer program. Nonlinear effects are accounted for by application of a correction technique in the FLEXSTAB system; the technique incorporates experimental force and pressure data into the linear aerodynamic theory. A flexible Orbiter model is treated in the static stability analysis for the flight conditions of Mach number 0.9 for rectilinear flight (1 g) and for a pull-up maneuver (2.5 g) at an altitude of 15.24 km. Static stability parameters and structural deformations of the Orbiter are calculated at trim conditions for the dynamic stability analysis, and the characteristics of damping in pitch are investigated for a Mach number range of 0.3 to 1.2. The calculated results for both the static and dynamic stabilities are compared with the available experimental data.

Chyu, W. J.; Cavin, R. K.; Erickson, L. L.

1978-01-01

178

Stability and Sensitivity Analysis of Non-Newtonian Flow through an Axisymmetric Expansion

NASA Astrophysics Data System (ADS)

This paper deals with a linear stability analysis of the flow in a circular pipe with a sudden expansion. We consider both Newtonian and non-Newtonian fluid models and a thorough comparison is presented. The stability analysis is completed by an adjoint-based investigation on the sensitivity characteristics of perturbations. The results are discussed and compared, when it is possible, to those already published in the pertinent literature.

Giannetti, Flavio; Luchini, Paolo; Marino, Luca

2011-12-01

179

Linear stability analysis of planar reacting shear layers

NASA Astrophysics Data System (ADS)

Non-premixed flames are controlled by the mixing of fuel and oxidizer. These flames are susceptible to instabilities, which arise from hydrodynamic and heat-release instability mechanisms. To characterize these instability modes and their effects on the flame evolution and mixing, a spatial linear instability analysis is performed. In this formulation, a flamelet-formulation is utilized, in order to account for effects of detailed reaction chemistry and variations in thermo-viscous properties. The resulting set of governing equations is solved by employing a matrix method with spectral discretization. By applying this analysis to a methane/air flame in a planar shear layer, effects of molecular transport and reaction chemistry on the flame stability are investigated, and model results are compared detailed computational simulations.

Chee See, Yee; Ihme, Matthias

2010-11-01

180

Stability analysis of Riccati covariance equations of Kalman filter.

NASA Technical Reports Server (NTRS)

The present paper takes the basic mathematical approach to analyze the stability of Riccati equations. First, a simple stability criterion like that of the linear constant coefficient system is sought for the nonlinear constant Riccati Equation. Then, a complete analysis on the limiting covariance P follows. The analysis is focussed on the main theorem. Finally, the computational aspects of the Riccati equations are analyzed with examples. The application of this analysis is to provide a simple stability criterion for the Kalman filter computation to test and predict filter convergence and thus modify filter parameters accordingly.

Teng, L.; Schmidt, D.

1972-01-01

181

NASA Technical Reports Server (NTRS)

A general study of the stability of nonlinear as compared to linear control systems is presented. The analysis is general and, therefore, applies to other types of nonlinear biological control systems as well as the cardiovascular control system models. Both inherent and numerical stability are discussed for corresponding analytical and graphic methods and numerical methods.

Fitzjerrell, D. G.

1974-01-01

182

Stability analysis of two-dimensional pool-boiling systems M. Speetjens

Stability analysis of two-dimensional pool-boiling systems M. Speetjens , A. Reusken , S. Maier In this paper we consider a model for pool-boiling systems known from the liter- ature. This model involves only the temperature distribution within the heater and models the heat exchange with the boiling medium via

183

Stability analysis of geocell-confined soil on rocky slope

The geocell was used for erosion control of a cutting rocky slope by vegetation, and the stability analysis method of soil-geocell was proposed based on the theory of limit equilibrium and field experience. The factors effecting on the stability of geocell were analyzed. The results show that the failure modes of geocell are determined by the shear strength of geocell

Yi Xianren

2010-01-01

184

A unified stability analysis of meshless particle methods

SUMMARY A unied stability analysis of meshless methods with Eulerian and Lagrangian kernels is presented. Three types of instabilities were identied in one dimension: an instability due to rank deciency, a tensile instability and a material instability which is also found in continua. The stability of particle methods with Eulerian and Lagrangian kernels is markedly dierent: Lagrangian kernels do not

Ted Belytschko; Yong Guo; Shao Ping Xiao

2000-01-01

185

Rotor Speed Stability Analysis of Constant Speed Wind Turbine Generators

This paper presents an analysis of rotor speed stability of a constant speed wind turbine generator with active stall control. To analyze the rotor speed stability, a 3-phase short circuit fault on a sample system with a constant speed WTG has been simulated using DIgSILENT software package. From the simulation results, it has been shown that the operating point of

M. G. Kanabar; C. V. Dobariya; S. A. Khaparde

2006-01-01

186

CFD Based Computations of Flexible Helicopter Blades for Stability Analysis

NASA Technical Reports Server (NTRS)

As a collaborative effort among government aerospace research laboratories an advanced version of a widely used computational fluid dynamics code, OVERFLOW, was recently released. This latest version includes additions to model flexible rotating multiple blades. In this paper, the OVERFLOW code is applied to improve the accuracy of airload computations from the linear lifting line theory that uses displacements from beam model. Data transfers required at every revolution are managed through a Unix based script that runs jobs on large super-cluster computers. Results are demonstrated for the 4-bladed UH-60A helicopter. Deviations of computed data from flight data are evaluated. Fourier analysis post-processing that is suitable for aeroelastic stability computations are performed.

Guruswamy, Guru P.

2011-01-01

187

Stability analysis of quasi-brittle materials – creep under multiaxial loading

The aim of this paper is to develop a simple time-dependent Continuum Damage Mechanics model applied to quasi-brittle materials such as rock or concrete. The three-dimensional constitutive visco-damage model describes phenomena like relaxation, creep and rate-dependent loading using a unified framework. A material stability analysis devoted to creep tests highlights a general creep stress stability domain. This convex domain is

Noël Challamel; Christophe Lanos; Charles Casandjian

2006-01-01

188

Wellbore stability analysis in carbonate reservoir considering anisotropic behaviour

NASA Astrophysics Data System (ADS)

Carbonate reservoirs represent a major part of the world oil and gas reserves. In particular, recent discoveries in the pre-salt offshore Brazil place big challenges to exploration and production under high temperatures and pressures (HTHP). During production, the extraction of hydrocarbons reduces pore pressure and thus causes an increase in the effective stress and mechanical compaction in the reservoir. The compactive deformation and failure may be spatially extensive or localized to the vicinity of the wellbore, but in either case the consequences can be economically severe involving surface subsidence, well failure and various production problems. The analysis of wellbore stability and more generally of deformation and failure in carbonate environments hinges upon a relevant constitutive modeling of carbonate rocks over a wide range of porosities, in particular, observed microstructure of samples suggests anisotropic behaviour. In this study, we performed a wellbore stability analysis for a lateral wellbore junction in three dimensions. The complex geometry for the wellbore junction was modeled with tetrahedral finite elements considering a rate independent elastic-plastic isotropic material that presented linear behavior during elastic strain and associated flow rule. A finite element model simulating drilling and production phases were done for field conditions from a deep water reservoir in Campos basin, offshore Brazil. In this context, several scenarios were studied considering true 3D orientation for both in situ stresses and geometry of the wellbore junction itself. We discussed the impact of constitutive modeling, considering anisotropic ductile damage and pressure sensitiveness on the wellbore stability. Parameter values for the analysis were based based on experimental data on two micritic porous carbonates. Series of conventional triaxial experiments were performed at room temperature in dry and wet conditions on samples of Comiso and Tavel limestones of respective porosity 17 and 16%. The wet samples were deformed in drained conditions with 10 MPa pore pressure. The initial yield stresses were identified as the critical stresses at the onset of shear-enhanced compaction, subsequent yield stresses were considered to depend on hardening given by the plastic volumetric strain. For both limestones, we found that water had a moderate effect on the yield stresses but influenced significantly the hardening behavior of the rocks.

Alves, José; Guevara, Nestor; Coelho, Lucia; Baud, Patrick

2010-05-01

189

A linear thermal stability analysis of discretized fluid equations

NASA Astrophysics Data System (ADS)

The effects of discretization on the equations, and their solutions, describing Rayleigh-Bénard convection are studied through linear stability analysis and numerical integration of the discretized equations. Linear stability analyses of the discretized equations were conducted in the usual manner except that the assumed solution contained discretized components (e.g., spatial grid interval in the x direction, {? x} ). As the resolution became infinitely high ({? x ? 0} ), the solutions approached those obtained from the continuous equations. The wavenumber of the maximum growth rate increased with increasing {? x} until the wavenumber reached a minimum resolvable resolution, {? ? x^{-1}} . Therefore, the discretization of equations tends to reproduce higher-wavenumber structures than those predicted by the continuous equations. This behavior is counter intuitive and opposed to the expectation of {? x} leading to blurred simulated convection structures. However, when the analysis is conducted for discretized equations that are not combined into a single equation, as is the case for practically solved numerical models, the maximum growing wavenumber rather tends to decrease with increasing {? x} as intuitively expected. The degree of the decrease depends on the discretization accuracy of the first-order differentials. When the accuracy of the discretization scheme is of low order, the wavenumber monotonically decreases with increasing {? x} . On the other hand, when higher-order schemes are used for the discretization, the wavenumber does increase with increasing {? x} , a similar trend to that in the case of the single-discretized equation for smaller {? x}.

Miyamoto, Yoshiaki; Ito, Junshi; Nishizawa, Seiya; Tomita, Hirofumi

2015-03-01

190

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

191

Long term voltage stability analysis for small disturbances

This dissertation attempts to establish an analytical and comprehensive framework to deal with two critical challenges associated with voltage stability analysis: 1. To study the new competitive environment appropriately and give more incentive...

Men, Kun

2009-05-15

192

Perturbative stability of SFT-based cosmological models

We review the appearance of multiple scalar fields in linearized SFT based cosmological models with a single non-local scalar field. Some of these local fields are canonical real scalar fields and some are complex fields with unusual coupling. These systems only admit numerical or approximate analysis. We introduce a modified potential for multiple scalar fields that makes the system exactly solvable in the cosmological context of Friedmann equations and at the same time preserves the asymptotic behavior expected from SFT. The main part of the paper consists of the analysis of inhomogeneous cosmological perturbations in this system. We show numerically that perturbations corresponding to the new type of complex fields always vanish. As an example of application of this model we consider an explicit construction of the phantom divide crossing and prove the perturbative stability of this process at the linear order. The issue of ghosts and ways to resolve it are briefly discussed.

Galli, Federico; Koshelev, Alexey S., E-mail: fgalli@tena4.vub.ac.be, E-mail: alexey.koshelev@vub.ac.be [Theoretische Natuurkunde, Vrije Universiteit Brussel and The International Solvay Institutes, Pleinlaan 2, B-1050 Brussels (Belgium)

2011-05-01

193

Perturbative stability of SFT-based cosmological models

We review the appearance of multiple scalar fields in linearized SFT based cosmological models with a single non-local scalar field. Some of these local fields are canonical real scalar fields and some are complex fields with unusual coupling. These systems only admit numerical or approximate analysis. We introduce a modified potential for multiple scalar fields that makes the system exactly solvable in the cosmological context of Friedmann equations and at the same time preserves the asymptotic behavior expected from SFT. The main part of the paper consists of the analysis of inhomogeneous cosmological perturbations in this system. We demonstrate numerically that perturbations corresponding to the new type of complex fields always vanish. As an example of application of this model we consider an explicit construction of the phantom divide crossing and prove the perturbative stability of this process.

Galli, Federico

2010-01-01

194

Perturbative stability of SFT-based cosmological models

We review the appearance of multiple scalar fields in linearized SFT based cosmological models with a single non-local scalar field. Some of these local fields are canonical real scalar fields and some are complex fields with unusual coupling. These systems only admit numerical or approximate analysis. We introduce a modified potential for multiple scalar fields that makes the system exactly solvable in the cosmological context of Friedmann equations and at the same time preserves the asymptotic behavior expected from SFT. The main part of the paper consists of the analysis of inhomogeneous cosmological perturbations in this system. We show numerically that perturbations corresponding to the new type of complex fields always vanish. As an example of application of this model we consider an explicit construction of the phantom divide crossing and prove the perturbative stability of this process at the linear order. The issue of ghosts and ways to resolve it are briefly discussed.

Federico Galli; Alexey S. Koshelev

2011-06-14

195

Heavy lift crane/derrick barge stability analysis

HEAVY LIFT CRANE/DERRICK BARGE STABILITY ANALYSIS A Thesis by ROBERT MORRISON LOESCH Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 1988 Major... Subject; Ocean Engineering HEAVY LIFT CRANE/DERRICK BARGE STABILITY ANALYSIS A Thesis by ROBERT MORRISON LOESCH Approved as to style and content by: C eung . Kim (Chai an of Committee) Jack Y. Lou (Member) John B. Herbich (Member) Jam . Nelson...

Loesch, Robert Morrison

1988-01-01

196

White Oak Dam stability analysis. Volume I

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

197

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

198

Oxidative Stability of a Cod-Canola Oil Model System

The oxidative stability of a cod muscle-canola oil model system as affected by the order of tocopherol and canola oil addition to the cod muscle was studied. Oxidation was monitored by the measurement of TBARS and sensory score. The addition oftocopherol to the cod muscle before oil addition significantly (p < 0.01) increased the oxidative stability of the model system

Sivakumar Raghavan; Herbert O. Hultin

2006-01-01

199

GLOBAL STABILITY IN CHEMOSTAT-TYPE COMPETITION MODELS WITH NUTRIENT RECYCLING

GLOBAL STABILITY IN CHEMOSTAT-TYPE COMPETITION MODELS WITH NUTRIENT RECYCLING SHIGUI RUAN AND XUE- type competition models with nutrient recycling. In the first model the recycling is instantaneous, whereas in the second, the recycling is delayed. They carried out the equilibrium analysis and obtained

Ruan, Shigui

200

Sensitivity analysis of hydrodynamic stability operators

NASA Technical Reports Server (NTRS)

The eigenvalue sensitivity for hydrodynamic stability operators is investigated. Classical matrix perturbation techniques as well as the concept of epsilon-pseudoeigenvalues are applied to show that parts of the spectrum are highly sensitive to small perturbations. Applications are drawn from incompressible plane Couette, trailing line vortex flow and compressible Blasius boundary layer flow. Parametric studies indicate a monotonically increasing effect of the Reynolds number on the sensitivity. The phenomenon of eigenvalue sensitivity is due to the non-normality of the operators and their discrete matrix analogs and may be associated with large transient growth of the corresponding initial value problem.

Schmid, Peter J.; Henningson, Dan S.; Khorrami, Mehdi R.; Malik, Mujeeb R.

1992-01-01

201

Stability over time: Is behavior analysis a trait psychology?

Historically, behavior analysis and trait psychology have had little in common; however, recent developments in behavior analysis bring it closer to one of the core assumptions of the trait approach: the stability of behavior over time and, to a lesser extent, environments. The introduction of the concept of behavioral momentum and, in particular, the development of molar theories have produced some common features and concerns. Behavior-analytic theories of stability provide improved explanations of many everyday phenomena and make possible the expansion of behavior analysis into areas that have been inadequately addressed. ImagesFigure 1 PMID:22478416

Vyse, Stuart

2004-01-01

202

Stability over time: is behavior analysis a trait psychology?

Historically, behavior analysis and trait psychology have had little in common; however, recent developments in behavior analysis bring it closer to one of the core assumptions of the trait approach: the stability of behavior over time and, to a lesser extent, environments. The introduction of the concept of behavioral momentum and, in particular, the development of molar theories have produced some common features and concerns. Behavior-analytic theories of stability provide improved explanations of many everyday phenomena and make possible the expansion of behavior analysis into areas that have been inadequately addressed. PMID:22478416

Vyse, Stuart

2004-01-01

203

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

204

This paper mainly studies stability and optimal control for networked control systems with the real-time setup of time-driven sensor, event-driven controller and actuator, and with the assumption that network-induced delay is no longer than certain known times of sampling period. The modeling of this class of networked control systems is given. Then, preliminary stochastic stability analysis of it is presented.

Yuequan Yang; De Xu; Min Tan; Xianzhong Dai

2004-01-01

205

Numerical limit analysis for slope stability and bearing capacity calculations

Limit analysis uses the lower and upper bound theorems of plasticity theory to find the rigorous lower and upper bound solutions of stability problems. The limit analysis theorems are formulated as linear problems to be solved using linear programming techniques. Based on finite element discretization of the soil mass, the stress field is optimized to determine the highest lower bound

Paola Bandini

2003-01-01

206

Evaluation of oxidative stability of canola oils by headspace analysis

Lipid oxidation is a major factor affecting flavor quality and shelf life of vegetable oils. Oxidative stability is therefore\\u000a an important criterion by which oils are judged for usefulness in various food applications. In this study a method based\\u000a on headspace analysis was developed to evaluate relative oxidative stability of canola oils. The method does not require the\\u000a use of

Amy Richards; Chakra Wijesundera; Phil Salisbury

2005-01-01

207

A NUMERICAL METHOD FOR STABILITY ANALYSIS OF PINNED FLEXIBLE MECHANISMS

A technique is presented to investigate the stability of mechanisms with pin-jointed flexible members. The method relies on a special floating frame from which elastic link co-ordinates are defined. Energies are easily developed for use in a Lagrange equation formulation, leading to a set of non-linear and mixed ordinary differential-algebraic equations of motion with constraints. Stability and bifurcation analysis is

D. G. Beale; S. W. Lee

1996-01-01

208

Stability analysis of offshore wind farm and marine current farm

NASA Astrophysics Data System (ADS)

Renewable energy has been playing an important role to meet power demand and 'Green Energy' market is getting bigger platform all over the world in the last few years. Due to massive increase in the prices of fossil fuels along with global warming issues, energy harvesting from renewable energy sources has received considerable interest, nowadays, where extensive researches are going on to ensure optimum use of renewable sources. In order to meet the increasing demand of electricity and power, integration of renewable energy is getting highest priorities around the world. Wind is one of the most top growing renewable energy resources and wind power market penetration is expected to reach 3.35 percent by 2013 from its present market of about 240 GW. A wind energy system is the most environmental friendly, cost effective and safe among all renewable energy resources available. Another promising form of renewable energy is ocean energy which covers 70 % of the earth. Ocean energy can be tapped from waves, tides and thermal elements. Offshore Wind farm (OWF) has already become very popular for large scale wind power integration with the onshore grid. Recently, marine current farm (MCF) is also showing good potential to become mainstream energy sources and already successfully commissioned in United Kingdom. However, squirrel cage induction generator (SCIG) has the stability problem similar to synchronous generator especially during fault location to restore the electromagnetic torque. Series dynamic braking resistor (SDBR) has been known as a useful mean to stabilize fixed speed wind generator system. On the other hand, doubly fed induction generator (DFIG) has the capability of coupling the control of active and reactive power and to provide necessary reactive power demand during grid fault conditions. Series dynamic braking resistor (SDBR) can also be employed with DFIG to limit the rotor over current. An integration of wind and tidal energy represents a new-trend for large electric energy production using offshore wind generators and marine current generators, respectively. Thus DFIG based offshore wind farm can be an economic solution to stabilize squirrel cage induction generator based marine current farm without installing any addition FACTS devices. This thesis first focuses on the stabilization of fixed speed IG based marine current farm using SDBR. Also stabilization of DFIG based variable speed wind farm utilizing SDBR is studied in this work. Finally a co-operative control strategy is proposed where DFIG is controlled in such a way that it can even provide necessary reactive power demand of induction generator, so that additional cost of FACTS devices can be avoided. In that way, the DFIGs of the offshore wind farm (OWF) will actively compensate the reactive power demand of adjacent IGs of the marine current farm (MCF) during grid fault. Detailed modeling and control scheme for the proposed system are demonstrated considering some realistic scenarios. The power system small signal stability analysis is also carried out by eigenvalue analysis for marine current generator topology, wind turbine generator topology and integrated topology. The relation between the modes and state variables are discussed in light of modal and sensitivity analyses. The results of theoretical analyses are verified by MATLAB/SIMULINK and laboratory standard power system simulator PSCAD/EMTDC.

Shawon, Mohammad Hasanuzzaman

209

NASA Astrophysics Data System (ADS)

Recent research results indicate that individual awareness can play an important influence on epidemic spreading in networks. By local stability analysis, a significant conclusion is that the embedded awareness in an epidemic network can increase its epidemic threshold. In this paper, by using limit theory and dynamical system theory, we further give global stability analysis of a susceptible-infected-susceptible (SIS) epidemic model on networks with awareness. Results show that the obtained epidemic threshold is also a global stability condition for its endemic equilibrium, which implies the embedded awareness can enhance the epidemic threshold globally. Some numerical examples are presented to verify the theoretical results.

Li, Ke-Zan; Xu, Zhong-Pu; Zhu, Guang-Hu; Ding, Yong

2014-11-01

210

of the parallel flow in the presence of ion temperature and a negative upper bound on the current gradient, as well as on the ion temperature. In particular, the stability condition requires a gradient, in the presence of pressure gradients and/or parallel velocity gradients. Examples of stable configurations

Boyer, Edmond

211

Aeroelastic Stability of Rotor Blades Using Finite Element Analysis

NASA Technical Reports Server (NTRS)

The flutter stability of flap bending, lead-lag bending, and torsion of helicopter rotor blades in hover is investigated using a finite element formulation based on Hamilton's principle. The blade is divided into a number of finite elements. Quasi-steady strip theory is used to evaluate the aerodynamic loads. The nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The equations of motion are linearized assuming blade motion to be a small perturbation about the steady deflected shape. The normal mode method based on the coupled rotating natural modes is used to reduce the number of equations in the flutter analysis. First the formulation is applied to single-load-path blades (articulated and hingeless blades). Numerical results show very good agreement with existing results obtained using the modal approach. The second part of the application concerns multiple-load-path blades, i.e. bearingless blades. Numerical results are presented for several analytical models of the bearingless blade. Results are also obtained using an equivalent beam approach wherein a bearingless blade is modelled as a single beam with equivalent properties. Results show the equivalent beam model.

Chopra, I.; Sivaneri, N.

1982-01-01

212

Parallel processing techniques applied to transient stability analysis of power systems

processing techniques to the analysis of transient stability in electric power systems. Zn this context bus tearing techniques and the cluster algorithm were specifically utilized to implement the analysis. Simulations on a digital computer are conducted... for the classical and the one-axis machine models, when a fault is introduced in the power system and the dynamic characteristics observed. The various network models are analysed by the bus tearing technique and the cluster algorithm. The results indicat...

Balachandra, Chandrakumar John

1982-01-01

213

Technological Forecasting---Model Selection, Model Stability, and Combining Models

The paper identifies 29 models that the literature suggests are appropriate for technological forecasting. These models are divided into three classes according to the timing of the point of inflexion in the innovation or substitution process. Faced with a given data set and such a choice, the issue of model selection needs to be addressed. Evidence used to aid model

Nigel Meade; Towhidul Islam

1998-01-01

214

Modelling of thermal oxidation of phosphite stabilized polyethylene

The thermal oxidation behaviour of polyethylene films stabilized by various weight ratios of organophosphites (Irgafos 168) has been studied at selected temperatures. The duration of the induction period was found to increase proportionally with the stabilizer concentration, even at temperatures as low as 80 °C. Particular attention was paid to the phosphite–phosphate conversion during the induction period. A kinetic model, involving

Fatma Djouani; Emmanuel Richaud; Bruno Fayolle; Jacques Verdu

2011-01-01

215

Kinematic analysis of rope skipper's stability

NASA Astrophysics Data System (ADS)

There are various kinds of jumping that can be done while performing rope skipping activity. This activity was always associated with injury. But, if the rope skipper can perform the activity in a right way, it is believed that the injury might be reduced. The main purpose of this paper is to observe the stability of rope skipper from a biomechanics perspective, which are the centre of mass, angle at the ankle, knee and hip joints and also the trajectory for the ipsilateral leg between the two types of skip which is one leg and two legs. Six healthy, physically active subject, two males and four females (age: 8.00±1.25 years, weight: 17.90±6.85 kg and height: 1.22±0.08 m) participated in this study. Kinematic data of repeated five cycles of rope skipping activity was captured by using Vicon Nexus system. Based on the data collected, skipping with two legs shows more stable behavior during preparation, flight and landing phases. It is concluded that landing on the balls of the feet, lowering the trajectory positions of the feet from the ground as well as flexion of each joint which would reduce the injury while landing.

Ab Ghani, Nor Atikah; Rambely, Azmin Sham

2014-06-01

216

Analysis and stability of Hyperici oleum.

Hyperici Oleum (St. John's wort oil) used in wound healing contains no hypericin. By using the sunlight maceration method described in the supplement to DAB 6 (EB 6), lipophilic breakdown products of this compound are obtained which lend the oil its red colour. Hyperforin, which is responsible for the oil's therapeutic activity could, for the first time, be identified and quantitatively determined by TLC and HPLC after solid-phase extraction. The stability of hyperforin is limited; sufficient shelf-life could only be achieved by hot maceration of dried flowers with eutanol G and storage in the absence of air. By gradient HPLC further polar hyperforin analogues were detected in those St. John's wort oils in which hyperforin had decomposed. At the same time flavonoids and xanthones could be identified. A procedure for the quantitative determination of flavonoids in St. John's wort was validated. The action of light during preparation of the oil led to a rise in the content of flavonoids. PMID:1438595

Maisenbacher, P; Kovar, K A

1992-08-01

217

Models and Feedback Stabilization of Open Quantum Systems

At the quantum level, feedback-loops have to take into account measurement back-action. We present here the structure of the Markovian models including such back-action and sketch two stabilization methods: measurement-based feedback where an open quantum system is stabilized by a classical controller; coherent or autonomous feedback where a quantum system is stabilized by a quantum controller with decoherence (reservoir engineering). We begin to explain these models and methods for the photon box experiments realized in the group of Serge Haroche (Nobel Prize 2012). We present then these models and methods for general open quantum systems.

Pierre Rouchon

2015-01-08

218

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

219

Analysis of a Belgian Chocolate Stabilization Problem

Feb 20, 2005 ... power of nonsmooth analysis for understanding variational ... A.S. Lewis, School of Operations Research and Industrial Engineering, Cornell University, Ithaca, NY .... number of randomly generated sample points to 2N (twice the number of design variables) ... For our numerical experiments, simply for.

2005-02-20

220

Stability Analysis of the Iter CS Coil Conductors

NASA Astrophysics Data System (ADS)

The stability analysis of the International Thermonuclear Experimental Reactor (ITER) Central Solenoid (CS) coil Nb3Sn conductor is performed following a similar approach to that recently used for the ITER Toroidal Field and Poloidal Field conductors. The most critical conductors in the winding pack, as well as the most critical (minimum temperature margin) location along them, are identified by the application of the Vincenta code, which also provides the initial and boundary conditions in the reference case. The Mithrandir code is then applied to these conductors, using a much finer grid than affordable in the Vincenta analysis, in order to capture the details of normal zone initiation and possible recovery to SC state when different square wave disturbances of length L in the range [0.01 m, 7 m] and duration ? the range [1 ms, 100 ms] are applied to the cable. The computed minimum quench energy is shown to be typically above (in one case borderline to) the expected disturbance. The sensitivity to parametric of the heat transfer coefficient between strands and helium is significant for some disturbances. The inclusion of an external circuit in the model, providing self-consistent boundary conditions, does not influence the results.

Richard, L. Savoldi; Bessette, D.; Zanino, R.

2010-04-01

221

Stability of Hopf bifurcation of a delayed SIRS epidemic model with stage structure

In this paper, we deal with an SIRS epidemic model with stage structure and time delays. We perform some bifurcation analysis to the model. The delay ? is used as the bifurcation parameter. We show that the positive equilibrium is locally asymptotically stable when the time delay is suitable small, while change of stability of positive equilibrium will cause a

Tailei Zhang; Junli Liu; Zhidong Teng

2010-01-01

222

High beta and second stability region transport and stability analysis. Final report

This report describes ideal and resistive studies of high-beta plasmas and of the second stability region. Emphasis is focused on ``supershot`` plasmas in TFIR where MHD instabilities are frequently observed and which spoil their confinement properties. Substantial results are described from the analysis of these high beta poloidal plasmas. During these studies, initial pressure and safety factor profiles were obtained from the TRANSP code, which is used extensively to analyze experimental data. Resistive MBD stability studies of supershot equilibria show that finite pressure stabilization of tearing modes is very strong in these high {beta}p plasmas. This has prompted a detailed re-examination of linear tearing mode theory in which we participated in collaboration with Columbia University and General Atomics. This finite pressure effect is shown to be highly sensitive to small scale details of the pressure profile. Even when an ad hoc method of removing this stabilizing mechanism is implemented, however, it is shown that there is only superficial agreement between resistive MBD stability computation and the experimental data. While the mode structures observed experimentally can be found computationally, there is no convincing correlation with the experimental observations when the computed results are compared with a large set of supershot data. We also describe both the ideal and resistive stability properties of TFIR equilibria near the transition to the second region. It is shown that the highest {beta} plasmas, although stable to infinite-n ideal ballooning modes, can be unstable to the so called ``infernal`` modes associated with small shear. The sensitivity of these results to the assumed pressure and current density profiles is discussed. Finally, we describe results from two collaborative studies with PPPL. The first involves exploratory studies of the role of the 1/1 mode in tokamaks and, secondly, a study of sawtooth stabilization using ICRF.

Hughes, M.H.; Phillps, M.W.; Todd, A.M.M.; Krishnaswami, J.; Hartley, R.

1992-09-01

223

Stability investigations of airfoil flow by global analysis

NASA Technical Reports Server (NTRS)

As the result of global, non-parallel flow stability analysis the single value of the disturbance growth-rate and respective frequency is obtained. This complex value characterizes the stability of the whole flow configuration and is not referred to any particular flow pattern. The global analysis assures that all the flow elements (wake, boundary and shear layer) are taken into account. The physical phenomena connected with the wake instability are properly reproduced by the global analysis. This enhances the investigations of instability of any 2-D flows, including ones in which the boundary layer instability effects are known to be of dominating importance. Assuming fully 2-D disturbance form, the global linear stability problem is formulated. The system of partial differential equations is solved for the eigenvalues and eigenvectors. The equations, written in the pure stream function formulation, are discretized via FDM using a curvilinear coordinate system. The complex eigenvalues and corresponding eigenvectors are evaluated by an iterative method. The investigations performed for various Reynolds numbers emphasize that the wake instability develops into the Karman vortex street. This phenomenon is shown to be connected with the first mode obtained from the non-parallel flow stability analysis. The higher modes are reflecting different physical phenomena as for example Tollmien-Schlichting waves, originating in the boundary layer and having the tendency to emerge as instabilities for the growing Reynolds number. The investigations are carried out for a circular cylinder, oblong ellipsis and airfoil. It is shown that the onset of the wake instability, the waves in the boundary layer, the shear layer instability are different solutions of the same eigenvalue problem, formulated using the non-parallel theory. The analysis offers large potential possibilities as the generalization of methods used till now for the stability analysis.

Morzynski, Marek; Thiele, Frank

1992-01-01

224

Stability Analysis of Passive Dynamic Walking of Quadrupeds

We introduce a detailed numerical simulation and analysis framework to extend the principles of passive dynamic walking to quadrupedal locomotion. Non-linear limit cycle methods are used to identify possible gaits and to analyze the stability and efficiency of quadrupedal passive dynamic walking. In doing so, special attention is paid to issues that are inherent to quadrupedal locomotion, such as the

C. David Remy; Keith W. Buffinton; Roland Siegwart

2010-01-01

225

Weakly dispersive hydraulic flows in a contraction --Nonlinear stability analysis

Weakly dispersive hydraulic flows in a contraction -- Nonlinear stability analysis Bernard K. Ee hydraulic solutions of the forced Korteweg de-Vries equation is investigated here. For numerical convenience is destabilized by a hydraulic instability in which superexponential growth occurs prior to satura- tion

Ee, Bernard Kuowei

226

Dynamic stability analysis of a textile rotor nonlinear coupling system

The partial differential equation, describing the lateral deflection of textile, nonlinearly coupled with one ordinary differential equation, describing the whirling vibration of rotor with constant angular velocity, are investigated in the dynamic stability analysis. When the textile is wound on or off by the rotor, the mass, inertia and unbalance magnitude of rotor are time?varying, and the length of textile

1996-01-01

227

Stability analysis of flows of liquid crystal polymers exhibiting a banding structure

A prototype model to describe flows of liquid crystal polymers is analyzed. Under appropriate hypotheses on the constitutive functions, we show existence of steady-state solutions presenting a banding structure parallel to the shear direction, in shear flow geometry. A stability analysis of such solutions is carried out.

Maria-Carme Calderer

1989-01-01

228

Stability of the Human Respiratory Control System. Part II: Analysis of a threedimensional delay models of the human respiratory control system have been developed since 1940 to study a wide range signals to the respiratory control system has been studied since the work of Grodins et al. in the early

229

Stability study of the TCP-RED system using detrended fluctuation analysis

It has been observed that the TCP-RED system may exhibit instability and oscillatory behavior. Control methods proposed in the past have been based on the analytical models that rely on statistical measurements of network parameters. In this paper, we apply the detrended fluctuation analysis (DFA) method to analyze stability of the TCP-RED system. The DFA has been used for detecting

Xi Chen; Siu-Chung Wong; Chi Kong Tse; Ljiljana Trajkovic

2008-01-01

230

Analysis of Stability, Response and LQR Controller Design of a Small Scale Helicopter Dynamics

This paper presents how to use feedback controller with helicopter dynamics state space model. A simplified analysis is presented for controller design using LQR of small scale helicopters for axial and forward flights. Our approach is simple and gives the basic understanding about how to develop controller for solving the stability of linear helicopter flight dynamics.

Dharmayanda, Hardian Reza; Lee, Young Jae; Sung, Sangkyung

2008-01-01

231

Dynamic equivalence to induction generators and wind turbines for power system stability analysis

With increasing installation capacity and energy production, wind power plays more important role in power systems. In transient stability analysis, detailed modeling to each induction generator and wind turbine will introduce lots of calculation effort, which necessitates dynamic equivalence to induction generators and wind turbines in the same wind farm, or wind farms closely located. In this paper, weighted equivalence

Shenghu Li; Zhengkai Liu; Xinjie Hao; Shusen Jia

2010-01-01

232

Stability Analysis and the Stabilisation of Flexural Toppling Failure

NASA Astrophysics Data System (ADS)

Flexural toppling is a mode of failure that may occur in a wide range of layered rock strata in both rock slopes and large underground excavations. Whenever rock mass is composed of a set of parallel discontinuities dipping steeply against the excavated face plane, the rock mass will have the potential of flexural toppling failure as well. In such cases, the rock mass behaves like inclined superimposed cantilever beams that bend under their own weight while transferring the load to the underlying strata. If the bending stress exceeds the rock column’s tensile strength, flexural toppling failure will be initiated. Since the rock columns are “statically indeterminate,” thus, their factors of safety may not be determined solely by equations of equilibrium. The paper describes an analytical model with a sequence of inclined superimposed cantilever rock columns with a potential of flexural topping failure. The model is based on the principle of compatibility equations and leads to a new method by which the magnitudes and points of application of intercolumn forces are determined. On the basis of the proposed model, a safety factor for each rock column can be computed independently. Hence, every rock column will have a unique factor of safety. The least factor of safety that exists in any rock column is selected as the rock mass representative safety factor based on which simple equations are proposed for a conservative rock mass stability analysis and design. As a result, some new relations are established in order to design the length, cross-sectional area and pattern of fully grouted rock bolts for the stabilisation of such rock mass. Finally, the newly proposed equations are compared with the results of existing experimental flexural toppling failure models (base friction and centrifuge tests) for further verification.

Amini, Mehdi; Majdi, Abbas; Aydan, Ömer

2009-10-01

233

The beauty of simple adaptive control and new developments in nonlinear systems stability analysis

NASA Astrophysics Data System (ADS)

Although various adaptive control techniques have been around for a long time and in spite of successful proofs of stability and even successful demonstrations of performance, the eventual use of adaptive control methodologies in practical real world systems has met a rather strong resistance from practitioners and has remained limited. Apparently, it is difficult to guarantee or even understand the conditions that can guarantee stable operations of adaptive control systems under realistic operational environments. Besides, it is difficult to measure the robustness of adaptive control system stability and allow it to be compared with the common and widely used measure of phase margin and gain margin that is utilized by present, mainly LTI, controllers. Furthermore, customary stability analysis methods seem to imply that the mere stability of adaptive systems may be adversely affected by any tiny deviation from the pretty idealistic and assumably required stability conditions. This paper first revisits the fundamental qualities of customary direct adaptive control methodologies, in particular the classical Model Reference Adaptive Control, and shows that some of their basic drawbacks have been addressed and eliminated within the so-called Simple Adaptive Control methodology. Moreover, recent developments in the stability analysis methods of nonlinear systems show that prior conditions that were customarily assumed to be needed for stability are only apparent and can be eliminated. As a result, sufficient conditions that guarantee stability are clearly stated and lead to similarly clear proofs of stability. As many real-world applications show, once robust stability of the adaptive systems can be guaranteed, the added value of using Add-On Adaptive Control along with classical Control design techniques is pushing the desired performance beyond any previous limits.

Barkana, Itzhak

2014-12-01

234

Intrinsic Geometric Analysis of the Network Reliability and Voltage Stability

This paper presents the intrinsic geometric model for the solution of power system planning and its operation. This problem is large-scale and nonlinear, in general. Thus, we have developed the intrinsic geometric model for the network reliability and voltage stability, and examined it for the IEEE 5 bus system. The robustness of the proposed model is illustrated by introducing variations of the network parameters. Exact analytical results show the accuracy as well as the efficiency of the proposed solution technique.

N. Gupta; B. N. Tiwari; S. Bellucci

2010-11-12

235

Stability analysis of buried flexible pipes: a biaxial buckling equation

STABILITY ANALYSIS OF BURIED FLEXIBLE PIPES: A BIAXIAL BUCKLING EQUATION A Thesis by MELISSA TUYET-MAI CHAU Submitted to the Office of Graduate Studies of Texas AkM University in partial fulfillment of the requirements for the degree... of MASTER OF SCIENCE May 1990 Major Subject: Civil Engineering STABLILITY ANALYSIS OF BURIED FLEXIBLE PIPES: A BIAXIAL BUCKLING EQUATION A Thesis by MELISSA TUYET-MAI CHAU Approved as to style and content by: r. obert L. Lytt n (Chair of Committee...

Chau, Melissa Tuyet-Mai

1990-01-01

236

Climate stability for a Sellers-type model. [atmospheric diffusive energy balance model

NASA Technical Reports Server (NTRS)

We study a diffusive energy-balance climate model governed by a nonlinear parabolic partial differential equation. Three positive steady-state solutions of this equation are found; they correspond to three possible climates of our planet: an interglacial (nearly identical to the present climate), a glacial, and a completely ice-covered earth. We consider also models similar to the main one studied, and determine the number of their steady states. All the models have albedo continuously varying with latitude and temperature, and entirely diffusive horizontal heat transfer. The diffusion is taken to be nonlinear as well as linear. We investigate the stability under small perturbations of the main model's climates. A stability criterion is derived, and its application shows that the 'present climate' and the 'deep freeze' are stable, whereas the model's glacial is unstable. A variational principle is introduced to confirm the results of this stability analysis. For a sufficient decrease in solar radiation (about 2%) the glacial and interglacial solutions disappear, leaving the ice-covered earth as the only possible climate.

Ghil, M.

1976-01-01

237

Black tea: chemical analysis and stability.

Tea is the most popular flavored and functional drink worldwide. The nutritional value of tea is mostly from the tea polyphenols that are reported to possess a broad spectrum of biological activities, including anti-oxidant properties, reduction of various cancers, inhibition of inflammation, and protective effects against diabetes, hyperlipidemia and obesity. Tea polyphenols include catechins and gallic acid in green and white teas, and theaflavins and thearubigins as well as other catechin polymers in black and oolong teas. Accurate analysis of black tea polyphenols plays a significant role in the identification of black tea contents, quality control of commercial tea beverages and extracts, differentiation of various contents of theaflavins and catechins and correlations of black tea identity and quality with biological activity, and most importantly, the establishment of the relationship between quantitative tea polyphenol content and its efficacy in animal or human studies. Global research in tea polyphenols has generated much in vitro and in vivo data rationally correlating tea polyphenols with their preventive and therapeutic properties in human diseases such as cancer, and metabolic and cardiovascular diseases etc. Based on these scientific findings, numerous tea products have been developed including flavored tea drinks, tea-based functional drinks, tea extracts and concentrates, and dietary supplements and food ingredients, demonstrating the broad applications of tea and its extracts, particularly in the field of functional food. PMID:23037977

Li, Shiming; Lo, Chih-Yu; Pan, Min-Hsiung; Lai, Ching-Shu; Ho, Chi-Tang

2013-01-01

238

Analysis of a stability valve system for extending the dynamic range of a supersonic inlet

NASA Technical Reports Server (NTRS)

A stability valve system designed for a full-scale, flight, supersonic, mixed-compression inlet was modeled dynamically by using analog computer techniques. The system uses poppet valves mounted in the inlet cowl to bypass airflow and augments the inlet shock position control system by preventing unstarts caused by high-frequency perturbations. The model was used as a design aid to investigate the effects of varying both the physical configurations of the valve and the flight and wind tunnel conditions. Results of the analysis indicate that the stability valve will provide a bandpass operation of 1 hertz to 17 hertz.

Webb, J. A., Jr.; Dustin, M. O.

1975-01-01

239

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

240

CENTRIFUGAL MODEL TESTS FOR THE LINING STABILITY OF A TUNNEL WITH OR WITHOUT AN INVERT

NASA Astrophysics Data System (ADS)

Centrifugal model tests are conducted to clarify the effects of an invert on the lining stability of a tunnel. The pressure which is provided by compressed air within a rubber bag is given in the ground surface under the centrifugal acceleration state. Displacements of the lining and the ground are recorded on digital video tape, and the displacements and shear strains are analyzed by a picture analysis system. The stability of the lining and the development of shear strain of the ground are compared between the cases with and without the invert. Quantitative effects of the invert on the lining stability is made clear.

Hisatake, Masayasu; Ohno, Shiro; Ohmae, Yukihiro; Katayama, Tatsuaki; Suzuki, Keisuke

241

AC system stability analysis and assessment for Shipboard Power Systems

frames of SPS dynamics are presented. Stability problems during SPS reconfiguration are classified as long-term stability problems. Since angle stability is strongly maintained in SPS, voltage stability is studied in this dissertation for SPS stability...

Qi, Li

2006-04-12

242

Analysis of Dynamic Stability Constraints for a Mobile Humanoid Robot

. The work [8] developed a typical model of tip- over dynamics of heavy-duty hydraulic mobile manipulators planning strategy to allow mobile manipulators to perform tasks quickly without generating dynamic forces a quantita- tive criterion for stability measures of manipulators mounted on vehicles, but the mass moments

Li, Yangmin

243

Bounded Linear Stability Analysis - A Time Delay Margin Estimation Approach for Adaptive Control

NASA Technical Reports Server (NTRS)

This paper presents a method for estimating time delay margin for model-reference adaptive control of systems with almost linear structured uncertainty. The bounded linear stability analysis method seeks to represent the conventional model-reference adaptive law by a locally bounded linear approximation within a small time window using the comparison lemma. The locally bounded linear approximation of the combined adaptive system is cast in a form of an input-time-delay differential equation over a small time window. The time delay margin of this system represents a local stability measure and is computed analytically by a matrix measure method, which provides a simple analytical technique for estimating an upper bound of time delay margin. Based on simulation results for a scalar model-reference adaptive control system, both the bounded linear stability method and the matrix measure method are seen to provide a reasonably accurate and yet not too conservative time delay margin estimation.

Nguyen, Nhan T.; Ishihara, Abraham K.; Krishnakumar, Kalmanje Srinlvas; Bakhtiari-Nejad, Maryam

2009-01-01

244

Stability of the car-following model on two lanes

NASA Astrophysics Data System (ADS)

In the case of two-lane traffic, vehicle drivers always worry about the lane changing actions from neighbor lane. This paper studies the stability of a car-following model on two lanes which incorporates the lateral effects in traffic. The stability condition of the model is obtained by using the linear stability theory. The modified Korteweg-de Vries equation is constructed and solved, and three types of traffic flows in the headway-sensitivity space—stable, metastable, and unstable—are classified. Both analytical and simulation results show that the anxiousness about lane changing from neighbor lane indeed has influence upon people’s driving behavior and the consideration of lateral effects could stabilize the traffic flows on both lanes.

Tang, Tie-Qiao; Huang, Hai-Jun; Gao, Zi-You

2005-12-01

245

Exposure Analysis Modeling System

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...

246

The Stability of Radiatively Cooling Jets I. Linear Analysis

NASA Technical Reports Server (NTRS)

The results of a spatial stability analysis of a two-dimensional slab jet, in which optically thin radiative cooling is dynamically important, are presented. We study both magnetized and unmagnetized jets at external Mach numbers of 5 and 20. We model the cooling rate by using two different cooling curves: one appropriate to interstellar gas, and the other to photoionized gas of reduced metallicity. Thus, our results will be applicable to both protostellar (Herbig-Haro) jets and optical jets from active galactic nuclei. We present analytical solutions to the dispersion relations in useful limits and solve the dispersion relations numerically over a broad range of perturbation frequencies. We find that the growth rates and wavelengths of the unstable Kelvin-Helmholtz (K-H) modes are significantly different from the adiabatic limit, and that the form of the cooling function strongly affects the results. In particular, if the cooling curve is a steep function of temperature in the neighborhood of the equilibrium state, then the growth of K-H modes is reduced relative to the adiabatic jet. On the other hand, if the cooling curve is a shallow function of temperature, then the growth of K-H modes can be enhanced relative to the adiabatic jet by the increase in cooling relative to heating in overdense regions. Inclusion of a dynamically important magnetic field does not strongly modify the important differences between an adiabatic jet and a cooling jet, provided the jet is highly supermagnetosonic and not magnetic pressure-dominated. In the latter case, the unstable modes behave more like the transmagnetosonic magnetic pressure-dominated adiabatic limit. We also plot fluid displacement surfaces associated with the various waves in a cooling jet in order to predict the structures that might arise in the nonlinear regime. This analysis predicts that low-frequency surface waves and the lowest order body modes will be the most effective at producing observable features in the jet.

Hardee, Philip E.; Stone, James M.

1997-01-01

247

MODEL DEVELOPMENT FOR INTEGRATED HYBRID ELECTRIC VEHICLE DYNAMIC STABILITY SYSTEMS

This study expanded an existing full car dynamic model (HVOSM.VD2) to enable simulation of electric, hybrid electric, and fuel cell vehicles with integrated vehicle stability systems. A prototype range extending series hybrid vehicle was constructed with independent front wheel drives. A hybrid vehicle stability assist (VSA) algorithm was developed to perform proportional control of yaw rate through left\\/right distribution of

Joel R. Anstrom

2003-01-01

248

The electrically induced coalescence of water-in-oil emulsions stabilized by interfacially active fractions from crude oils has been studied by means of time domain dielectric spectroscopy at high electric fields. The experiments were designed with a 2{sup 7-3} reduced factorial design. Regression analysis clearly shows that the choice of organic solvent and the amount of asphaltenes, as well as the interplay between these variables, are the most significant parameters for determining the stability of these emulsions. It should be pointed out that the asphaltenes were the only surface active fraction tested. No interplay between, for instance, asphaltenes and resins was investigated. The nonlinearity found in the regression analysis is explained by different aggregation states of asphaltenes in aliphatic and aromatic solvents. The influence of the variables upon the emulsion stability is discussed.

Foerdedal, H.; Midttun, O.; Sjoeblom, J.; Kvalheim, O.M. [Univ. of Bergen (Norway). Dept. of Chemistry] [Univ. of Bergen (Norway). Dept. of Chemistry; Schildberg, Y.; Volle, J.L. [Elf Aquitaine Production, Pau (France)] [Elf Aquitaine Production, Pau (France)

1996-09-01

249

Analysis of Force Interactions Between Comb Stabilized Colloidal Particles

NASA Astrophysics Data System (ADS)

Polymer chains that are chemically attached to solid surfaces have important uses in colloidal stabilization. In this investigation, atomic force colloid probe microscopy and Langmuir trough compression have been employed to observe the interactions between colloidal particles stabilized by tethered polymer chains. Monodisperse latexes stabilized by hydrophilic side chains of surface- attached comb polymers are analyzed by the above methods in a water environment. Through the modification of the comb arcitecture to incorporate both hydrophilic and hydrophobic side chains, attractive wells are introduced into the force-distance profiles, in agreement with recent self-consistent mean field predictions. A theoretical model has been developed to explain the differing behaviors of the colloids when analyzed by the above methods.

Olugebefola, Solar; Banerjee, Pallab; Park, Stella; Mayes, Anne; Iyer, J.; Bembenek, Catherine; Hammond, Paula

2001-03-01

250

Stability and optimization in structured population models on graphs.

We prove existence and uniqueness of solutions, continuous dependence from the initial datum and stability with respect to the boundary condition in a class of initial--boundary value problems for systems of balance laws. The particular choice of the boundary condition allows to comprehend models with very different structures. In particular, we consider a juvenile-adult model, the problem of the optimal mating ratio and a model for the optimal management of biological resources. The stability result obtained allows to tackle various optimal management/control problems, providing sufficient conditions for the existence of optimal choices/controls. PMID:25811440

Colombo, Rinaldo M; Garavello, Mauro

2015-04-01

251

Global stability for a class of discrete SIR epidemic models.

In this paper, we propose a class of discrete SIR epidemic models which are derived from SIR epidemic models with distributed delays by using a variation of the backward Euler method. Applying a Lyapunov functional technique, it is shown that the global dynamics of each discrete SIR epidemic model are fully determined by a single threshold parameter and the effect of discrete time delays are harmless for the global stability of the endemic equilibrium of the model. PMID:20462293

Enatsu, Yoichi; Nakata, Yukihiko; Muroya, Yoshiaki

2010-04-01

252

Global Stability of Equilibria for a Metapopulation SIS Model

Global Stability of Equilibria for a Metapopulation SÂIÂS Model Francesca Arrigoni and Andrea of SIS type spreading in a population distributed in an infinite number of households, each one of size N is not unex- pected, because SÂIÂS models have been proved to be stable in populations with spatial structure

Pugliese, Andrea

253

On the Stability of a Model of Testosterone German Enciso

On the Stability of a Model of Testosterone Dynamics German Enciso Eduardo D. Sontag Department of a well-known delayed negative- feedback model of testosterone dynamics, which has been proposed in the presence of delays of arbitrary length. Keywords: testosterone dynamics, monotone systems, negative

Enciso, GermÃ¡n

254

NASA Astrophysics Data System (ADS)

Numerical simulations and linear stability analysis are invaluable tools in complementing experiments to obtain improved understanding about instability mechanisms in non-premixed and premixed flames. By utilizing the experiments of F"uri et al., the objective of this study is to characterize hydrodynamic instability mechanisms in methane/air diffusion flames. To this end, detailed simulations are performed to obtain the reactive mean flow, which is used as input to the linear stability analysis. In order to account for the detailed reaction chemistry and variations in thermo-viscous properties, a flamelet-representation is introduced in the linear stability method. Model predictions for growth rate and phase velocity are compared with experimental data, and parametric studies are performed to quantify effects of heat-release and detailed chemistry in controlling hydrodynamic instabilities.

Chee See, Yee; Ihme, Matthias

2011-11-01

255

RELATION OF URBAN MODEL PERFORMANCE TO STABILITY

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...

256

Shared compliant control: a stability analysis and experiments

Active compliance providing a damped spring for each Cartesian axis of a robot hand is implemented by low-pass-filtering the outputs of the force\\/torque sensors mounted on the robot hand and using these signals to alter the position commands. In this implementation, larger compliance needs higher feedback gain, which tends to destabilize the system. A graphical stability analysis based on Bode

Won S. Kim

1990-01-01

257

A Matrix Stability Analysis of the Carbuncle Phenomenon

The carbuncle phenomenon is a shock instability mechanism which ruins all ef- forts to compute grid-aligned shock waves using low-dissipative upwind schemes. The present study develops a stability analysis for two-dimensional steady shocks on structured meshes based on the matrix method. The numerical resolution of the corresponding eigenvalue problem confirms the typical odd-even form of the unstable mode and displays

Michael Dumbser; Jean-Marc Moschetta; Jeremie Gressier

2003-01-01

258

NSDL National Science Digital Library

The Marine Modeling and Analysis Branch (MMAB) of the Environmental Modeling Center is responsible for the development of improved numerical weather and marine prediction modeling systems. These models provide analysis and real-time forecast guidance on marine meteorological, oceanographic, and cryospheric parameters over the global oceans and coastal areas of the US. This site provides access to MMAB modeling tools for ocean waves (including an interactive presentation,) sea ice, marine meteorology, sea surface temperature and more. The site also features a mailing list, bibliography of publications, and information about modeling products still in the experimental and development phases.

National Centers for Environmental Prediction, National Oceanic and Atmospheric Administration

259

Laboratory and numerical discontinuum modeling of wellbore stability

Wellbore-stability analyses based on intact wellbore walls can be too conservative because failed/fractured zones around wellbores relieve stress and give support. Wellbore-breakout analyses indicate that most drilled wells experience deformation beyond the rupture stage and that this deformation is acceptable for the drilling process. Validation of the methods available to predict wellbore stability requires a comparison of theoretical models with experimental simulations of wellbore behavior. This paper describes a series of scaled laboratory wellbore-stability experiments carried out under various borehole inclinations and stress conditions. The goal was to investigate the influence of the fractured zone, stress anisotropy, well deviation, and well orientation on wellbore stability. Classic log spiral fracture geometries were obtained around the wellbore, and the effect of the fractured zone on wellbore stability was studied with a distinct-element program called the universal distinct-element code (UDEC). Results show the importance of taking into account the stability of the fractured zone and subsequent wellbore breakout when wellbore stability is considered.

Rawlings, C.G.; Barton, N.R. (Norwegian Geotechnical Inst., Oslo (Norway)); Bandis, S.C. (Aristotle Univ. of Thessaloniki (Greece)); Addis, M.A. (BP Exploration Co. Ltd., Sunburry-on-Thames, London (United Kingdom)); Gutierrez, M.S. (Norwegian Geotechnical Inst., Oslo (Norway). Rock Engineering and Reservoir Mechanics Division)

1993-11-01

260

NASA Astrophysics Data System (ADS)

If soil organic matter is predominantly microbial biomass, plant inputs that build biomass should also increase SOM. This seems obvious, but the implications fundamentally change how we think about the relationships between plants, microbes and SOM. Plant residues that build microbial biomass are typically characterized by low C/N ratios and high lignin contents. However, plants with high lignin contents and high C/N ratios are believed to increase SOM, an entrenched idea that still strongly motivates agricultural soil management practices. Here we use a combination of meta-analysis with a new microbial-explicit soil biogeochemistry model to explore the relationships between plant litter chemistry, microbial communities, and SOM stabilization in different soil types. We use the MIcrobial-MIneral Carbon Stabilization (MIMICS) model, newly built upon the Community Land Model (CLM) platform, to enhance our understanding of biology in earth system processes. The turnover of litter and SOM in MIMICS are governed by the activity of r- and k-selected microbial groups and temperature sensitive Michaelis-Menten kinetics. Plant and microbial residues are stabilized short-term by chemical recalcitrance or long-term by physical protection. Fast-turnover litter inputs increase SOM by >10% depending on temperature in clay soils, and it's only in sandy soils devoid of physical protection mechanisms that recalcitrant inputs build SOM. These results challenge centuries of lay knowledge as well as conventional ideas of SOM formation, but are they realistic? To test this, we conducted a meta-analysis of the relationships between the chemistry of plant liter inputs and SOM concentrations. We find globally that the highest SOM concentrations are associated with plant inputs containing low C/N ratios. These results are confirmed by individual tracer studies pointing to greater stabilization of low C/N ratio inputs, particularly in clay soils. Our model and meta-analysis results suggest that current ideas about plant-microbe-SOM relationships are unraveling. If so, our reconsideration of the mechanisms stabilizing SOM will also challenge long-held views about how to optimize plant community management to increase SOM.

Grandy, Stuart; Wieder, Will; Kallenbach, Cynthia; Tiemann, Lisa

2014-05-01

261

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

262

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, John; Holmes, Philip

2001-08-01

263

., Hydrodynamic and Hydromagnetic Stability. 1961, New York: Dover Publications, Inc. 1-654. 3. Criminale, WBibliography of Recommended Books on Hydrodynamic Stability 1. Mathematical Modeling and Simulation in Hydrodynamic Stability, ed. D.N. Riahi. 1996, Singapore: World Scientific. 1-190. 2. Chandrasekhar, S

Slinn, Donald

264

Stability Analysis of The Twisted Superconducting Semilocal Strings

We study the stability properties of the twisted vortex solutions in the semilocal Abelian Higgs model with a global $\\mathbf{SU}(2)$ invariance. This model can be viewed as the Weinberg-Salam theory in the limit where the non-Abelian gauge field decouples, or as a two component Ginzburg-Landau theory. The twisted vortices are characterized by a constant global current ${\\cal I}$, and for ${\\cal I}\\to 0$ they reduce to the semilocal strings, that is to the Abrikosov-Nielsen-Olesen vortices embedded into the semilocal model. Solutions with ${\\cal I}\

Julien Garaud; Mikhail S. Volkov

2008-01-24

265

Enumeration and stability analysis of simple periodic orbits in ?-Fermi Pasta Ulam lattice

We study the well-known one-dimensional problem of N particles with a nonlinear interaction. The special case of quadratic and quartic interaction potential among nearest neighbours is the ?-Fermi-Pasta-Ulam model. We enumerate and classify the simple periodic orbits for this system and find the stability zones, employing Floquet theory. Such stability analysis is crucial to understand the transition of FPU lattice from recurrences to globally chaotic behavior, energy transport in lower dimensional system, dynamics of optical lattices and also its impact on shape parameter of bio-polymers such as DNA and RNA.

Sonone, Rupali L., E-mail: vaidehisonone@gmail.com; Jain, Sudhir R., E-mail: vaidehisonone@gmail.com [Department of Physics, University of Pune, Pune-411007, India and Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai - 400085 (India)

2014-04-24

266

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

267

NASA Technical Reports Server (NTRS)

Testing and evaluation of stability augmentation systems for aircraft flight control were conducted. The flutter suppression system analysis of a scale supersonic transport wing model is described. Mechanization of the flutter suppression system is reported. The ride control synthesis for the B-52 aeroelastic model is discussed. Model analyses were conducted using equations of motion generated from generalized mass and stiffness data.

Sevart, F. D.; Patel, S. M.; Wattman, W. J.

1972-01-01

268

Using tightly-coupled CFD/CSD simulation for rotorcraft stability analysis

NASA Astrophysics Data System (ADS)

Dynamic stall deeply affects the response of helicopter rotor blades, making its modeling accuracy very important. Two commonly used dynamic stall models were implemented in a comprehensive code, validated, and contrasted to provide improved analysis accuracy and versatility. Next, computational fluid dynamics and computational structural dynamics loose coupling methodologies are reviewed, and a general tight coupling approach was implemented and tested. The tightly coupled computational fluid dynamics and computational structural dynamics methodology is then used to assess the stability characteristics of complex rotorcraft problems. An aeroelastic analysis of rotors must include an assessment of potential instabilities and the determination of damping ratios for all modes of interest. If the governing equations of motion of a system can be formulated as linear, ordinary differential equations with constant coefficients, classical stability evaluation methodologies based on the characteristic exponents of the system can rapidly and accurately provide the system's stability characteristics. For systems described by linear, ordinary differential equations with periodic coefficients, Floquet's theory is the preferred approach. While these methods provide excellent results for simplified linear models with a moderate number of degrees of freedom, they become quickly unwieldy as the number of degrees of freedom increases. Therefore, to accurately analyze rotorcraft aeroelastic periodic systems, a fully nonlinear, coupled simulation tool is used to determine the response of the system to perturbations about an equilibrium configuration and determine the presence of instabilities and damping ratios. The stability analysis is undertaken using an algorithm based on a Partial Floquet approach that has been successfully applied with computational structural dynamics tools on rotors and wind turbines. The stability analysis approach is computationally inexpensive and consists of post processing aeroelastic data, which can be used with any aeroelastic rotorcraft code or with experimental data.

Zaki, Afifa Adel

269

A Robustly Stabilizing Model Predictive Control Algorithm

NASA Technical Reports Server (NTRS)

A model predictive control (MPC) algorithm that differs from prior MPC algorithms has been developed for controlling an uncertain nonlinear system. This algorithm guarantees the resolvability of an associated finite-horizon optimal-control problem in a receding-horizon implementation.

Ackmece, A. Behcet; Carson, John M., III

2007-01-01

270

Constrained model predictive control: Stability and optimality

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

271

Floquet stability analysis of Ott Grebogi Yorke and difference control

NASA Astrophysics Data System (ADS)

Stabilization of instable periodic orbits of nonlinear dynamical systems has been a widely explored field theoretically and in applications. The techniques can be grouped into time-continuous control schemes based on Pyragas, and the two Poincaré-based chaos control schemes, Ott Gebogi Yorke (OGY) and difference control. Here, a new stability analysis of these two Poincaré-based chaos control schemes is given by means of the Floquet theory. This approach allows to calculate exactly the stability restrictions occurring for small measurement delays and for an impulse length shorter than the length of the orbit. This is of practical experimental relevance; to avoid a selection of the relative impulse length by trial and error, it is advised to investigate whether the used control scheme itself shows systematic limitations on the choice of the impulse length. To investigate this point, a Floquet analysis is performed. For OGY control the influence of the impulse length is marginal. As an unexpected result, difference control fails when the impulse length is taken longer than a maximal value that is approximately one half of the orbit length for small Ljapunov numbers and decreases with the Ljapunov number.

Claussen, Jens Christian

2008-06-01

272

Stability of Model Membranes in Extreme Environments

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

273

Stability of Turing patterns in the Brusselator model

NASA Astrophysics Data System (ADS)

The selection and competition of Turing patterns in the Brusselator model are reviewed. The stability of stripes and hexagons towards spatial perturbations is studied using the amplitude equation formalism. For hexagonal patterns these equations include both linear and nonpotential spatial terms enabling distorted solutions. The latter modify substantially the stability diagrams and select patterns with wave numbers quite different from the critical value. The analytical results from the amplitude formalism agree with direct simulations of the model. Moreover, we show that slightly squeezed hexagons are locally stable in a full range of distortion angles. The stability regions resulting from the phase equation are similar to those obtained numerically by other authors and to those observed in experiments.

Peña, B.; Pérez-García, C.

2001-11-01

274

[Research on the spectral analysis and stability of copper green].

In the history of Chinese pigment, copper green, a pigment, was used in vast territory and for a long time. In the present paper, the nature, spectral characteristics, thermodynamic stability of the four isomers of the basic copper chlorides and also their application in the polychrome relics were discussed. The four isomers can be identified quickly by Raman spectral analysis which is a micro-damage or even a nondestructive technique. The order of their thermodynamic stability is as follows: clinoatacamite>paratacamite>atacamite>botallackite. It was showed that in the relics samples copper green was mostly botallackite and atacamite which were less stable isomers. According to the Ostwald step rule, the environmental monitoring should be strengthened to prevent the change in their physical and chemical structures. PMID:24611389

Li, Man; Wang, Li-Qin; Xia, Yin; Yang, Qiu-Ying

2013-12-01

275

Robust Stability Analysis of the Space Launch System Control Design: A Singular Value Approach

NASA Technical Reports Server (NTRS)

Classical stability analysis consists of breaking the feedback loops one at a time and determining separately how much gain or phase variations would destabilize the stable nominal feedback system. For typical launch vehicle control design, classical control techniques are generally employed. In addition to stability margins, frequency domain Monte Carlo methods are used to evaluate the robustness of the design. However, such techniques were developed for Single-Input-Single-Output (SISO) systems and do not take into consideration the off-diagonal terms in the transfer function matrix of Multi-Input-Multi-Output (MIMO) systems. Robust stability analysis techniques such as H(sub infinity) and mu are applicable to MIMO systems but have not been adopted as standard practices within the launch vehicle controls community. This paper took advantage of a simple singular-value-based MIMO stability margin evaluation method based on work done by Mukhopadhyay and Newsom and applied it to the SLS high-fidelity dynamics model. The method computes a simultaneous multi-loop gain and phase margin that could be related back to classical margins. The results presented in this paper suggest that for the SLS system, traditional SISO stability margins are similar to the MIMO margins. This additional level of verification provides confidence in the robustness of the control design.

Pei, Jing; Newsome, Jerry R.

2015-01-01

276

A Three-Dimensional Unsteady CFD Model of Compressor Stability

NASA Technical Reports Server (NTRS)

A three-dimensional unsteady CFD code called CSTALL has been developed and used to investigate compressor stability. The code solved the Euler equations through the entire annulus and all blade rows. Blade row turning, losses, and deviation were modeled using body force terms which required input data at stations between blade rows. The input data was calculated using a separate Navier-Stokes turbomachinery analysis code run at one operating point near stall, and was scaled to other operating points using overall characteristic maps. No information about the stalled characteristic was used. CSTALL was run in a 2-D throughflow mode for very fast calculations of operating maps and estimation of stall points. Calculated pressure ratio characteristics for NASA stage 35 agreed well with experimental data, and results with inlet radial distortion showed the expected loss of range. CSTALL was also run in a 3-D mode to investigate inlet circumferential distortion. Calculated operating maps for stage 35 with 120 degree distortion screens showed a loss in range and pressure rise. Unsteady calculations showed rotating stall with two part-span stall cells. The paper describes the body force formulation in detail, examines the computed results, and concludes with observations about the code.

Chima, Rodrick V.

2006-01-01

277

Stability of Sigma-Model Strings and Textures

In flat space-time, sigma-model strings and textures are both unstable to collapse and subsequent decay. With sufficient cosmological expansion, however, they are stable in a generalized sense: a small perturbation will cause them to change their shape, but they do not decay. The current rate of expansion is sufficient to stabilize strings, but not textures.

R. S. Ward

2002-01-14

278

Stability of travelling waves in models of superconductivity

Stability of travelling waves in models of superconductivity S.J. Chapman Mathematical Institute 24 of phase between nor- mally conducting and superconducting states in a type I superconductor, while the second describes the transition from the superconducting state to the mixed state in a type II

Chapman, Jon

279

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

280

Global stability of a delayed SIRS model with temporary immunity

This paper addresses a time-delayed SIRS model with a linear incidence rate. Immunity gained by experiencing the disease is temporary; whenever infected, the disease individuals will return to the susceptible class after a fixed period of time. First, the local and global stabilities of the infection-free equilibrium are analyzed, respectively. Second, the endemic equilibrium is formulated in terms of the

Luosheng Wen; Xiaofan Yang

2008-01-01

281

Stability of a Ricker-type competition model and the competitive exclusion principle

Our main objective is to study a Ricker-type competition model of two species. We give a complete analysis of stability and bifurcation and determine the centre manifolds, as well as stable and unstable manifolds. It is shown that the autonomous Ricker competition model exhibits subcritical bifurcation, bubbles, period-doubling bifurcation, but no Neimark–Sacker bifurcations. We exhibit the region in the parameter

Rafael Luís; Saber Elaydi; Henrique Oliveira

2011-01-01

282

Stability analysis of position and force control problems for robot arms

NASA Technical Reports Server (NTRS)

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 modeled. In each of these cases, a stability analysis using the Lyapunov method is presented. An explanation of instability is put forth for the case in which the environment has flexibility and the gains are inappropriately chosen. When the environment is stiff in the force control subspace, robust stability can be achieved with the integral force feedback.

Wen, John T.; Murphy, Steve

1990-01-01

283

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

284

A qualitative approach to the transient stability analysis

With the growing stress on today`s power systems, there is a urgent need for implementing on-line Dynamic Security Assessment (DSA). Among the functions of DSA, the most time-consuming function is the dynamic contingency analysis. In this paper, it has been assumed that during this analysis, one is not interested in obtaining trajectories with a very high accuracy but is primarily interested in a qualitative answer to the question: Is the system stable or not? Subsequently, only unstable or marginally stable cases have to be considered for more detailed analyses and preventive control. This idea is applied to parallel-in-time algorithms for transient stability analysis in order to stop the simulation as soon as the stability is detected by the condition of Potential Energy Boundary Surface (PEBS) crossing. The effectiveness of the approach has been validated on the New England test system and a realistic-sized network with 662 buses. An implementation on the nCUBE multiprocessor of a particular parallel-in-time algorithm allows the speed up derived from the proposed approach to be assessed.

La Scala, M. [Univ. degli Studi di Napoli (Italy). Dipt. di Ingegneria Elettrica] [Univ. degli Studi di Napoli (Italy). Dipt. di Ingegneria Elettrica; Lorusso, G.; Sbrizzai, R.; Trovato, M. [Politecnico di Bari (Italy). Dipt. di Elettrotecnica ed Elettronica] [Politecnico di Bari (Italy). Dipt. di Elettrotecnica ed Elettronica

1996-11-01

285

Ant colony optimization analysis on overall stability of high arch dam basis of field monitoring.

A dam ant colony optimization (D-ACO) analysis of the overall stability of high arch dams on complicated foundations is presented in this paper. A modified ant colony optimization (ACO) model is proposed for obtaining dam concrete and rock mechanical parameters. A typical dam parameter feedback problem is proposed for nonlinear back-analysis numerical model based on field monitoring deformation and ACO. The basic principle of the proposed model is the establishment of the objective function of optimizing real concrete and rock mechanical parameter. The feedback analysis is then implemented with a modified ant colony algorithm. The algorithm performance is satisfactory, and the accuracy is verified. The m groups of feedback parameters, used to run a nonlinear FEM code, and the displacement and stress distribution are discussed. A feedback analysis of the deformation of the Lijiaxia arch dam and based on the modified ant colony optimization method is also conducted. By considering various material parameters obtained using different analysis methods, comparative analyses were conducted on dam displacements, stress distribution characteristics, and overall dam stability. The comparison results show that the proposal model can effectively solve for feedback multiple parameters of dam concrete and rock material and basically satisfy assessment requirements for geotechnical structural engineering discipline. PMID:25025089

Lin, Peng; Liu, Xiaoli; Chen, Hong-Xin; Kim, Jinxie

2014-01-01

286

Ant Colony Optimization Analysis on Overall Stability of High Arch Dam Basis of Field Monitoring

A dam ant colony optimization (D-ACO) analysis of the overall stability of high arch dams on complicated foundations is presented in this paper. A modified ant colony optimization (ACO) model is proposed for obtaining dam concrete and rock mechanical parameters. A typical dam parameter feedback problem is proposed for nonlinear back-analysis numerical model based on field monitoring deformation and ACO. The basic principle of the proposed model is the establishment of the objective function of optimizing real concrete and rock mechanical parameter. The feedback analysis is then implemented with a modified ant colony algorithm. The algorithm performance is satisfactory, and the accuracy is verified. The m groups of feedback parameters, used to run a nonlinear FEM code, and the displacement and stress distribution are discussed. A feedback analysis of the deformation of the Lijiaxia arch dam and based on the modified ant colony optimization method is also conducted. By considering various material parameters obtained using different analysis methods, comparative analyses were conducted on dam displacements, stress distribution characteristics, and overall dam stability. The comparison results show that the proposal model can effectively solve for feedback multiple parameters of dam concrete and rock material and basically satisfy assessment requirements for geotechnical structural engineering discipline. PMID:25025089

Liu, Xiaoli; Chen, Hong-Xin; Kim, Jinxie

2014-01-01

287

Stability and Robustness Analysis of the AURORA Airship Control System using Dynamic Inversion

This paper presents a stability and robustness analysis of a nonlinear control system for the autonomous airship of the AURORA project. A Dynamic Inversion controller is implemented with desired dynamics given by a linear optimal compensator. The stability analysis of the nonlinear system is done applying Lyapunov’s stability theory. Robustness tests are performed in order to verify the nonlinear controller

Alexandra Moutinho; José R. Azinheira

2005-01-01

288

Stability and Control Analysis of the F-15B Quiet SpikeTM Aircraft

NASA Technical Reports Server (NTRS)

The primary purpose of the Quiet Spike(TradeMark) flight research program was to analyze the aerodynamic, structural, and mechanical proof-of-concept of a large multi-stage telescoping nose spike installed on the National Aeronautics and Space Administration Dryden Flight Research Center (Edwards, California) F-15B airplane. This report describes the preflight stability and control analysis performed to assess the effect of the spike on the stability, controllability, and handling qualities of the airplane; and to develop an envelope expansion approach to maintain safety of flight. The overall flight test objective was to collect flight data to validate the spike structural dynamics and loads model up to Mach 1.8. Other objectives included validating the mechanical feasibility of a morphing fuselage at operational conditions and determining the near-field shock wave characterization. The two main issues relevant to the stability and control objectives were the effects of the spike-influenced aerodynamics on the F-15B airplane flight dynamics, and the air data and angle-of-attack sensors. The analysis covered the sensitivity of the stability margins, and the handling qualities due to aerodynamic variation and the maneuvering limitations of the F-15B Quiet Spike configuration. The results of the analysis and the implications for the flight test program are also presented.

McWherter, Shaun C.; Moua, Cheng M.; Gera, Joseph; Cox, Timothy H.

2009-01-01

289

NASA Astrophysics Data System (ADS)

We present a linear analytical model coupled with experimental analysis to discuss stability of a levitated proof mass (PM) in a micromachined inductive suspension (MIS), which has been previously introduced and characterized. The model is a function of the MIS geometry, describes the dynamics of a levitated disk-shaped PM near the equilibrium point, and predicts conditions for stable levitation. The experimental setup directly measures the lateral component of the Lorentz force, which has a stabilization role in the MIS structure, as well as the vertical levitation force. The experimental setup is further used to derive mechanical parameters such as stiffness values relative to lateral, vertical and angular displacements, proven to be in excellent agreement with the values predicted by the analytical model.

Poletkin, K.; Lu, Z.; den Hartogh, B.; Wallrabe, U.; Badilita, V.

2014-11-01

290

The Predictive Performance and Stability of Six Species Distribution Models

Background Predicting species’ potential geographical range by species distribution models (SDMs) is central to understand their ecological requirements. However, the effects of using different modeling techniques need further investigation. In order to improve the prediction effect, we need to assess the predictive performance and stability of different SDMs. Methodology We collected the distribution data of five common tree species (Pinus massoniana, Betula platyphylla, Quercus wutaishanica, Quercus mongolica and Quercus variabilis) and simulated their potential distribution area using 13 environmental variables and six widely used SDMs: BIOCLIM, DOMAIN, MAHAL, RF, MAXENT, and SVM. Each model run was repeated 100 times (trials). We compared the predictive performance by testing the consistency between observations and simulated distributions and assessed the stability by the standard deviation, coefficient of variation, and the 99% confidence interval of Kappa and AUC values. Results The mean values of AUC and Kappa from MAHAL, RF, MAXENT, and SVM trials were similar and significantly higher than those from BIOCLIM and DOMAIN trials (p<0.05), while the associated standard deviations and coefficients of variation were larger for BIOCLIM and DOMAIN trials (p<0.05), and the 99% confidence intervals for AUC and Kappa values were narrower for MAHAL, RF, MAXENT, and SVM. Compared to BIOCLIM and DOMAIN, other SDMs (MAHAL, RF, MAXENT, and SVM) had higher prediction accuracy, smaller confidence intervals, and were more stable and less affected by the random variable (randomly selected pseudo-absence points). Conclusions According to the prediction performance and stability of SDMs, we can divide these six SDMs into two categories: a high performance and stability group including MAHAL, RF, MAXENT, and SVM, and a low performance and stability group consisting of BIOCLIM, and DOMAIN. We highlight that choosing appropriate SDMs to address a specific problem is an important part of the modeling process. PMID:25383906

Huang, Min-Yi; Fan, Wei-Yi; Wang, Zhi-Gao

2014-01-01

291

Slope Stability Analysis of Waste Dump in Sandstone Open Pit Osielec

NASA Astrophysics Data System (ADS)

This paper presents the slope stability analysis for the current as well as projected (final) geometry of waste dump Sandstone Open Pit "Osielec". For the stability analysis six sections were selected. Then, the final geometry of the waste dump was designed and the stability analysis was conducted. On the basis of the analysis results the opportunities to improve the stability of the object were identified. The next issue addressed in the paper was to determine the proportion of the mixture containing mining and processing wastes, for which the waste dump remains stable. Stability calculations were carried out using Janbu method, which belongs to the limit equilibrium methods.

Adamczyk, Justyna; Ca?a, Marek; Flisiak, Jerzy; Kolano, Malwina; Kowalski, Micha?

2013-03-01

292

Vacuum Stability and Triviality Analyses of the Renormalizable Coloron Model

The renormalizable coloron model is built around a minimally extended color gauge group, which is spontaneously broken to QCD. The formalism introduces massive color-octet vector bosons (colorons), as well as several new scalars and fermions associated with the symmetry breaking sector. In this paper, we examine vacuum stability and triviality conditions within the context of the renormalizable coloron model up to a cutoff energy scale of 100~TeV, by computing the beta-functions of all relevant couplings and determining their running behavior as a function of the renormalization scale. We constrain the parameter space of the theory for four separate scenarios based on differing fermionic content, and demonstrate that the vectorial scenarios are less constrained by vacuum stability and triviality bounds than the chiral scenarios. Our results are summarized in exclusion plots for the separate scenarios, with previous bounds on the model overlaid for comparison. We find that a 100 TeV hadron collider could explo...

Chivukula, R Sekhar; Simmons, Elizabeth H

2015-01-01

293

Stabilization of a thermoelastic Mindlin-Timoshenko plate model revisited

NASA Astrophysics Data System (ADS)

This paper is a continuation of our work in Grobbelaar-Van Dalsen (Appl Anal 90:1419-1449, 2011) where we showed the strong stability of models involving the thermoelastic Mindlin-Timoshenko plate equations with second sound. For the case of a plate configuration consisting of a single plate, this was accomplished in radially symmetric domains without applying any mechanical damping mechanism. Further to this result, we establish in this paper the non-exponential stability of the model for a particular configuration under mixed boundary conditions on the shear angle variables and Dirichlet boundary conditions on the displacement and thermal variables when the heat flux is described by Fourier's law of heat conduction. We also determine the rate of polynomial decay of weak solutions of the model in a radially symmetric region under Dirichlet boundary conditions on the displacement and thermal variables and free boundary conditions on the shear angle variables.

Grobbelaar-Van Dalsen, Marié

2013-08-01

294

Parallel processing for efficient 3D slope stability modelling

NASA Astrophysics Data System (ADS)

We test the performance of the GIS-based, three-dimensional slope stability model r.slope.stability. The model was developed as a C- and python-based raster module of the GRASS GIS software. It considers the three-dimensional geometry of the sliding surface, adopting a modification of the model proposed by Hovland (1977), and revised and extended by Xie and co-workers (2006). Given a terrain elevation map and a set of relevant thematic layers, the model evaluates the stability of slopes for a large number of randomly selected potential slip surfaces, ellipsoidal or truncated in shape. Any single raster cell may be intersected by multiple sliding surfaces, each associated with a value of the factor of safety, FS. For each pixel, the minimum value of FS and the depth of the associated slip surface are stored. This information is used to obtain a spatial overview of the potentially unstable slopes in the study area. We test the model in the Collazzone area, Umbria, central Italy, an area known to be susceptible to landslides of different type and size. Availability of a comprehensive and detailed landslide inventory map allowed for a critical evaluation of the model results. The r.slope.stability code automatically splits the study area into a defined number of tiles, with proper overlap in order to provide the same statistical significance for the entire study area. The tiles are then processed in parallel by a given number of processors, exploiting a multi-purpose computing environment at CNR IRPI, Perugia. The map of the FS is obtained collecting the individual results, taking the minimum values on the overlapping cells. This procedure significantly reduces the processing time. We show how the gain in terms of processing time depends on the tile dimensions and on the number of cores.

Marchesini, Ivan; Mergili, Martin; Alvioli, Massimiliano; Metz, Markus; Schneider-Muntau, Barbara; Rossi, Mauro; Guzzetti, Fausto

2014-05-01

295

Dynamic stability analysis for a self-mixing interferometry system.

A self-mixing interferometry (SMI) system is a laser diode (LD) with an external cavity formed by a moving external target. The behavior of an SMI system is governed by the injection current J to the LD and the parameters associated with the external cavity mainly including optical feedback factor C, the initial external cavity length (L?) and the light phase (??) which is mapped to the movement of the target. In this paper, we investigate the dynamic behavior of an SMI system by using the Lang-Kobayashi model. The stability boundary of such system is presented in the plane of (C, ??), from which a critical C (denoted as C(critical)) is derived. Both simulations and experiments show that the stability can be enhanced by increasing either L? or J. Furthermore, three regions on the plane of (C, ??) are proposed to characterize the behavior of an SMI system, including stable, semi-stable and unstable regions. We found that the existing SMI model is only valid for the stable region, and the semi-stable region has potential applications on sensing and measurement but needs re-modeling the system by considering the bandwidth of the detection components. PMID:25402164

Fan, Yuanlong; Yu, Yanguang; Xi, Jiangtao; Guo, Qinghua

2014-11-17

296

Synchronized clusters in coupled map networks: Stability analysis

We study self-organized (s-) and driven (d-) synchronization in coupled map networks for some simple networks, namely two and three node networks and their natural generalization to globally coupled and complete bipartite networks. We use both linear stability analysis and Lyapunov function approach for this study and determine stability conditions for synchronization. We see that most of the features of coupled dynamics of small networks with two or three nodes, are carried over to the larger networks of the same type. The phase diagrams for the networks studied here have features very similar to the different kinds of networks studied in Ref. \\cite{sarika-REA2}. The analysis of the dynamics of the difference variable corresponding to any two nodes shows that when the two nodes are in driven synchronization, all the coupling terms cancel out whereas when they are in self-organized synchronization, the direct coupling term between the two nodes adds an extra decay term while the other couplings cancel out.

Sarika Jalan; R. E. Amritkar; Chin-Kun Hu

2003-07-22

297

Reaction diffusion systems are often used to study pattern formation in biological systems. However, most methods for understanding their behavior are challenging and can rarely be applied to complex systems common in biological applications. I present a relatively simple and efficient, nonlinear stability technique that greatly aids such analysis when rates of diffusion are substantially different. This technique reduces a system of reaction diffusion equations to a system of ordinary differential equations tracking the evolution of a large amplitude, spatially localized perturbation of a homogeneous steady state. Stability properties of this system, determined using standard bifurcation techniques and software, describe both linear and nonlinear patterning regimes of the reaction diffusion system. I describe the class of systems this method can be applied to and demonstrate its application. Analysis of Schnakenberg and substrate inhibition models is performed to demonstrate the methods capabilities in simplified settings and show that even these simple models have nonlinear patterning regimes not previously detected. The real power of this technique, however, is its simplicity and applicability to larger complex systems where other nonlinear methods become intractable. This is demonstrated through analysis of a chemotaxis regulatory network comprised of interacting proteins and phospholipids. In each case, predictions of this method are verified against results of numerical simulation, linear stability, asymptotic, and/or full PDE bifurcation analyses. PMID:24158538

Holmes, William R

2014-01-01

298

Stability and bifurcation analysis in hematopoietic stem cell dynamics with multiple delays

NASA Astrophysics Data System (ADS)

This paper is devoted to the analysis of a maturity structured system of hematopoietic stem cell (HSC) populations in the bone marrow. The model is a system of differential equations with several time delays. We discuss the stability of equilibria and perform the analysis of Hopf bifurcation. More precisely, we first obtain a set of improved sufficient conditions ensuring the global asymptotical stability of the zero solution using the Lyapunov method and the embedding technique of asymptotically autonomous semiflows. Then we prove that there exists at least one positive periodic solution for the n-dimensional system as a time delay varies in some region. This result is established by combining Hopf bifurcation theory, the global Hopf bifurcation theorem due to Wu [J. Wu, Symmetric functional differential equations and neural networks with memory, Trans. Amer. Math. Soc. 350 (1998) 4799-4838], and a continuation theorem of coincidence degree theory. Some numerical simulations are also presented to illustrate the analytic results.

Qu, Ying; Wei, Junjie; Ruan, Shigui

2010-10-01

299

Stability analysis of the Witten black hole (cigar soliton) under world-sheet RG flow

We analyze the stability of the Euclidean Witten black hole (the cigar soliton in mathematics literature) under first-order RG (Ricci) flow of the world-sheet sigma model. This analysis is from the target space point of view. We find that the Witten black hole has no unstable normalizable perturbative modes in a linearized mode analysis in which we consider circularly symmetric perturbations. Finally, we discuss a result from mathematics that implies the existence of a non-normalizable mode of the Witten black hole under which the geometry flows to the sausage solution studied by Fateev, Onofri and Zamolodchikov.

Carolyn Lambert; Vardarajan Suneeta

2012-09-01

300

Modeling and Simulation of a Helicopter Slung Load Stabilization Device

NASA Technical Reports Server (NTRS)

This paper addresses the problem of simulation and stabilization of the yaw motions of a cargo container slung load. The study configuration is a UH-60 helicopter carrying a 6ft x 6 ft x 8 ft CONEX container. This load is limited to 60 KIAS in operations and flight testing indicates that it starts spinning in hover and that spin rate increases with airspeed. The simulation reproduced the load yaw motions seen in the flight data after augmenting the load model with terms representing unsteady load yaw moment effects acting to reinforce load oscillations, and augmenting the hook model to include yaw resistance at the hook. The use of a vertical fin to stabilize the load is considered. Results indicate that the CONEX airspeed can be extended to 110 kts using a 3x5 ft fin.

Cicolani, Luigi S.; Ehlers, George E.

2002-01-01

301

A stability theorem for energy-balance climate models

NASA Technical Reports Server (NTRS)

The paper treats the stability of steady-state solutions of some simple, latitude-dependent, energy-balance climate models. For north-south symmetric solutions of models with an ice-cap-type albedo feedback, and for the sum of horizontal transport and infrared radiation given by a linear operator, it is possible to prove a 'slope stability' theorem, i.e., if the local slope of the steady-state iceline latitude versus solar constant curve is positive (negative) the steady-state solution is stable (unstable). Certain rather weak restrictions on the albedo function and on the heat transport are required for the proof, and their physical basis is discussed.

Cahalan, R. F.; North, G. R.

1979-01-01

302

Dynamic flight stability of a model dronefly in vertical flight

NASA Astrophysics Data System (ADS)

The dynamic flight stability of a model dronefly in hovering and upward flight is studied. The method of computational fluid dynamics is used to compute the stability derivatives and the techniques of eigenvalue and eigenvector used to solve the equations of motion. The major finding is as following. Hovering flight of the model dronefly is unstable because of the existence of an unstable longitudinal and an unstable lateral natural mode of motion. Upward flight of the insect is also unstable, and the instability increases as the upward flight speed increases. Inertial force generated by the upward flight velocity coupled with the disturbance in pitching angular velocity is responsible for the enhancement of the instability.

Shen, Chong; Sun, Mao

2014-12-01

303

Numerical modelling of turbulent catalytically stabilized channel flow combustion

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

304

Stability of localized plasma model in two and three dimensions

NASA Technical Reports Server (NTRS)

Stability against catastrophic radial collapse is demonstrated for initially well-behaved, localized solutions in a class of two- and three-dimensional wave equations characterized by saturating nonlinearities, which model various electrostatic and electromagnetic 'caviton' structures in an asymptotically uniform plasma. This result contrasts sharply with mathematical predictions of equations with low-order nonlinearities. Discrete classes of possible quasistationary modes exhibit features comparable to atomic wave functions and differ qualitatively from one-dimensional structures.

Wilcox, J. Z.; Wilcox, T. J.

1975-01-01

305

Dynamic pressure approach to analysis of reactor fuel plate stability

The dynamic pressure model can conveniently be used to evaluate the critical stress regions as a function of flow velocity. For some of the preliminary advanced neutron source reactor plate designs this could be very significant since the flow velocity could be limited by peak stresses in the plates more than by deflection or stability. The dynamic pressure results predicts the differential pressure across a plate as a function of flow velocity. The pressure differential can then be used to find the deflection and/or stress of the plate using traditional plate analyses. Instability would occur when plates are touching at mid-channel such that rapid oscillations of pressure can occur. The technique is conservative and gives a design limit for the plate. This model is one of several methods being used in the design of the ANS fuel elements. 10 refs., 4 figs.

Swinson, W.F.; Yahr, G.T.

1990-01-01

306

Stability analysis of the commensurate monolayer solid of xenon/graphite

NASA Astrophysics Data System (ADS)

A stability analysis based on model calculations of the grand potential finds that the transition from hexagonal incommensurate to commensurate monolayer solid of xenon/graphite is continuous with increasing pressure, in agreement with experimental observations. An atomic-scale interaction model gives an internally consistent account of the thermal expansion of the solid at the two-dimensional sublimation curve and of the chemical potential increase for isothermal compression from monolayer condensation to the commensurate solid. An estimate is given for the corrugation energy of xenon/graphite.

Bruch, L. W.; Novaco, A. D.

2008-03-01

307

Bifurcation analysis of aircraft pitching motions near the stability boundary

NASA Technical Reports Server (NTRS)

Bifuraction theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft subject to single degree of freedom pitching-motion perturbations about a large mean angle of attack. The requisite aerodynamic information in the equations of motion is represented in a form equivalent to the response to finite-amplitude pitching oscillations about the mean angle of attack. This information is deduced from the case of infinitesimal-amplitude oscillations. The bifurcation theory analysis reveals that when the mean angle of attack is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite-amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable (supercritical) or unstable (subcritical). For flat-plate airfoils flying at supersonic/hypersonic speed, the bifurcation is subcritical, implying either that exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.

Hui, W. H.; Tobak, M.

1984-01-01

308

Dynamic blade row compression component model for stability studies

NASA Technical Reports Server (NTRS)

This paper describes a generalized dynamic model which has been developed for use in compression component aerodynamic stability studies. The model is a one-dimensional, pitch-line, blade row, lumped volume system. Arbitrary placement of blade free volumes upstream, within, and downstream of the compression component as well as the removal of bleed flow from the exit of any rotor or stator are model options. The model has been applied to a two-stage fan and an eight-stage compressor. The clean inlet pressure ratio/flow maps and the surge line have been reproduced, thereby validating the capability of the dynamic model to reproduce the steady-flow characteristics of the compression component. A method for determining the onset of an aerodynamic instability which is associated with surge is described. Sinusoidally time-varying inlet and exit boundary conditions have been applied to the eight stage compressor as examples of the manner in which this model may be used for stability studies.

Tesch, W. A.; Steenken, W. G.

1976-01-01

309

Global stability of an SIR epidemic model with information dependent vaccination

We study the global behavior of a non-linear susceptible-infectious-removed (SIR)-like epidemic model with a non-bilinear feedback mechanism, which describes the influence of information, and of information-related delays, on a vaccination campaign. We upgrade the stability analysis performed in d’Onofrio et al. [A. d’Onofrio, P. Manfredi, E. Salinelli, Vaccinating behavior, information, and the dynamics of SIR vaccine preventable diseases, Theor. Popul.

Bruno Buonomo; Alberto d’Onofrio; Deborah Lacitignola

2008-01-01

310

Rotation and plasma stability in the Fitzpatrick-Aydemir model

NASA Astrophysics Data System (ADS)

The rotational stabilization of the resistive wall modes (RWMs) is analyzed within the single-mode cylindrical Fitzpatrick-Aydemir model [R. Fitzpatrick, Phys. Plasmas 9, 3459 (2002)]. Here, the consequences of the Fitzpatrick-Aydemir dispersion relation are derived in terms of the observable growth rate and toroidal rotation frequency of the mode, which allows easy interpretation of the results and comparison with experimental observations. It is shown that this model, developed for the plasma with weak dissipation, predicts the rotational destabilization of RWM in the typical range of the RWM rotation. The model predictions are compared with those obtained in a similar model, but with the Boozer boundary conditions at the plasma surface [A. H. Boozer, Phys. Plasmas 11, 110 (2004)]. Simple experimental tests of the model are proposed.

Pustovitov, V. D.

2007-08-01

311

Stability analysis of three species food chain with competition

NASA Astrophysics Data System (ADS)

We study a food chain system that consists of 1 prey and 2 predators populations. The prey population grows logistically while the predators apply different Holling functional responses. The first predator preys on the prey following Holling type II functional response and the second predator preys on both the prey and the first predator following Holling type II and III functional responses, respectively. The study starts with the stability analysis of critical points of the systems. Then, by using normal form and centre manifold method the information about other nontrivial solutions due to bifurcation including possible limit cycles appearance is obtained. The results are confirmed by numerical simulation using MatCont and biological interpretation of the results are also presented.

Abadi, Savitri, D.

2015-03-01

312

Stability analysis and numerical simulation of simplified solid rocket motors

NASA Astrophysics Data System (ADS)

This paper investigates the Parietal Vortex Shedding (PVS) instability that significantly influences the Pressure Oscillations of the long and segmented solid rocket motors. The eigenmodes resulting from the stability analysis of a simplified configuration, namely, a cylindrical duct with sidewall injection, are presented. They are computed taking into account the presence of a wall injection defect, which is shown to induce hydrodynamic instabilities at discrete frequencies. These instabilities exhibit eigenfunctions in good agreement with the measured PVS vortical structures. They are successfully compared in terms of temporal evolution and frequencies to the unsteady hydrodynamic fluctuations computed by numerical simulations. In addition, this study has shown that the hydrodynamic instabilities associated with the PVS are the driving force of the flow dynamics, since they are responsible for the emergence of pressure waves propagating at the same frequency.

Boyer, G.; Casalis, G.; Estivalèzes, J.-L.

2013-08-01

313

Stability analysis of a natural circulation lead-cooled fast reactor

NASA Astrophysics Data System (ADS)

This dissertation is aimed at nuclear-coupled thermal hydraulics stability analysis of a natural circulation lead cooled fast reactor design. The stability concerns arise from the fact that natural circulation operation makes the system susceptible to flow instabilities similar to those observed in boiling water reactors. In order to capture the regional effects, modal expansion method which incorporates higher azimuthal modes is used to model the neutronics part of the system. A reduced order model is used in this work for the thermal-hydraulics. Consistent with the number of heat exchangers (HXs), the reactor core is divided into four equal quadrants. Each quadrant has its corresponding external segments such as riser, plenum, pipes and HX forming an equivalent 1-D closed loop. The local pressure loss along the loop is represented by a lumped friction factor. The heat transfer process in the HX is represented by a model for the coolant temperature at the core inlet that depends on the coolant temperature at the core outlet and the coolant velocity. Additionally, time lag effects are incorporated into this HX model due to the finite coolant speed. A conventional model is used for the fuel pin heat conduction to couple the neutronics and thermal-hydraulics. The feedback mechanisms include Doppler, axial/radial thermal expansion and coolant density effects. These effects are represented by a linear variation of the macroscopic cross sections with the fuel temperature. The weighted residual method is used to convert the governing PDEs to ODEs. Retaining the first and second modes, leads to six ODEs for neutronics, and five ODEs for the thermal-hydraulics in each quadrant. Three models are developed. These are: 1) natural circulation model with a closed coolant flow path but without coupled neutronics, 2) forced circulation model with constant external pressure drop across the heated channels but without coupled neutronics, 3) coupled system including neutronics with higher modes and thermal-hydraulics. In the second model, the HX and the external flow path are not incorporated and therefore no time delays are considered, and a constant heat source term is assumed. There is no difference among four equivalent loops, and the system is finally described by a set of ODEs. The thermal hydraulics in the first and third models is represented by sets of ODEs with time lags, namely, DDEs, due to external pipes and the HX model. Models 1 and 2 use a constant heat source term rather than coupled neutronics as is the case in model 3. In model 3, the four equivalent loops are linked via modal neutronics. They are represented by twenty-six (six for neutronics; twenty for thermal-hydraulics / five for each loop) equations. Two approaches, one in time domain and the other in frequency domain, are used for stability analyses. For model number 1, based on the characteristic of DDEs, a MATLAB package is used to carry out the stability analysis. Results of the frequency domain analysis are presented in core-height---friction-factor space, dividing the space into stable and unstable regions. Results are also verified in time-domain. For model number 2, eigenvalues of the Jacobian matrix are evaluated for the frequency domain stability analysis. Scenarios including pulse stimulation on coolant velocity, and different friction factors are simulated in the time domain. The third model is studied only in the time domain. Eight different scenarios are simulated. These include system response after different perturbations such as positive or negative reactivity insertion in one or more quadrants. Results show that SUPERSTAR design is very robust, and that the nominal operation points have considerable safety margins. Results also identify regions in design and operation parameter spaces where the reactor becomes less stable or even unstable.

Lu, Qiyue

314

A tracking time domain simulator for real-time transient stability analysis

Real-time transient stability analysis requires analysis of hundreds of contingencies in tens of minutes using on-line data from the state estimation. The final objective is to present timely information about transfer limits and stability margins and eventually implement corrective actions. In this paper, we assume that the dynamic contingency analysis (DCA) has to be repeated every 15 minutes. During this

M. La Scala; R. Sbrizzai; F. Torelli; P. Scarpellini

1998-01-01

315

A general stability analysis of FIT\\/FDTD applied to lossy dielectrics and lumped elements

Stability analysis of the finite-di erence time-domain (FDTD) method is usually performed using von Neumann analysis, where a necessary condition for stability is obtained by requiring the amplitude of discrete Fourier modes defined on the grid to remain bounded. However, this limits the analysis to homogeneous materials, equidistant grids and unbounded domains. A rare situation in practical computations. In this

Fredrik Edelvik; Rolf Schuhmann; Thomas Weiland

2004-01-01

316

Optimal stabilization policy in a model of elasticity dynamics

This paper considers the role of optimal fiscal policy in the context of a macrodynamic model of the open economy. The dynamics of the model are governed by the transition of aggregate demand elasticities from their short-run values to long-run values. If there are no instrument costs attributed to government expenditure, then optimal fiscal policy can achieve perfect stabilization of price and exchange-rate levels. With instrument costs however, this is no longer possible and the optimal fiscal rule is of the linear feedback variety. The paper investigates the properties of this rule.

Bhandari, J.S.; Hanson, D.A.

1983-01-01

317

Advanced kinetic analysis as a tool for formulation development and prediction of vaccine stability.

We have used a protein-based vaccine, a live virus vaccine, and an experimental adjuvant to evaluate the utility of an advanced kinetic modeling approach for stability prediction. The modeling approach uses a systematic and simple procedure for the selection of the most appropriate kinetic equation to describe the degradation rate of compounds subjected to accelerated conditions. One-step and two-step reactions with unlimited combinations of kinetic models were screened for the three products under evaluation. The most appropriate mathematical model for a given product was chosen based on the values of residual sum of squares and the weight parameter w. A relatively simple n-th order kinetic model best fitted the degradation of an adjuvanted protein vaccine with a prediction error lower than 10%. A more complex two-step model was required to describe inactivation of a live virus vaccine under normal and elevated storage temperatures. Finally, an autocatalytic-type kinetic model best fitted the degradation of an oil-in-water adjuvant formulation. The modeling approach described here could be used for vaccine stability prediction, expiry date estimation, and formulation selection. To the best of our knowledge, this is the first report describing a global kinetic analysis of degradation of vaccine components with high prediction accuracy. PMID:25139388

Clénet, Didier; Imbert, Frédéric; Probeck, Patricia; Rahman, Nausheen; Ausar, Salvador F

2014-10-01

318

Supersonic mixing layers: Stability of magnetospheric flanks models

NASA Astrophysics Data System (ADS)

Compressibility has a strong influence on the stability of velocity shear layers when the difference of velocity ?V across the flow becomes supersonic. The flanks of the Earth's magnetopause are normally supersonic Ms > 1, and super-Alfvénic MA > 1, depending on the distance from the dayside terminator (Ms and MA are the sonic and Alfvén Mach numbers of the magnetosheath plasma, respectively). The stability of MHD supersonic flows depends, also on several other features, such as the finite thickness ? of the boundary layer, the relative orientation of velocity and magnetic fields, the density jump across the boundary and the magnetic shear angle. We analyze the MHD stability of some representative flank sites modeled after data from spacecraft crossings of the magnetopause under different interplanetary conditions, complementing these cases with extrapolations of likely conditions upstream, and downstream of the crossing site. Under northward interplanetary magnetic field conditions, there are solar wind regimes such that the near, but already supersonic, flank of the magnetopause may be locally stable. Stability is possible, e.g., when Ms becomes larger than ~1.2-1.4 while MA remains smaller than 1.2, and there is magnetic shear between the geomagnetic and the interplanetary magnetic field. Solar winds favouring local stability of the boundary layer are cold, not-too-dense plasmas, with strong magnetic fields, so that MA is smaller, while Ms is larger, than normal values of the magnetosheath flow. A gap between dayside and tail amplifying regions of Kelvin-Helmholtz disturbances over the magnetopause may exist when the above conditions are realized.

Gnavi, G.; Gratton, F. T.; Farrugia, C. J.; Bilbao, L. E.

2009-05-01

319

A new approach on the stability analysis in ELKO cosmology

In this work it has been developed a new approach to study the stability of a system composed by an ELKO field interacting with dark matter, which could give some contribution in order to alleviate the cosmic coincidence problem. It is assumed that the potential which characterizes the ELKO field is not specified, but it is related to a constant parameter $\\delta$. The strength of the interaction between matter and ELKO field is characterized by a constant parameter $\\beta$ and it is also assumed that both ELKO field as matter energy density are related to their pressures by equations of state parameters $\\omega_\\phi$ and $\\omega_m$, respectively. The system of equations is analysed by a dynamical system approach. It has been found the conditions of stability between the parameters $\\delta$ and $\\beta$ in order to have stable fixed points for the system for different values of the equation of state parameters $\\omega_\\phi$ and $\\omega_m$, and the results are presented in form of tables. The possibility of decay of ELKO field into dark matter or vice versa can be read directly from the tables, since the parameters $\\delta$ and $\\beta$ satisfy some inequalities. It allows us to constrain the potential assuming that we have a stable system for different interactions terms between the ELKO field and dark matter. The cosmic coincidence problem can be alleviated for some specific relations between the parameters of the model.

A. Pinho S. S.; S. H. Pereira; J. F. Jesus

2015-01-05

320

Analysis of cavern stability at the Bryan Mound SPR site.

This report presents computational analyses that simulate the structural response of caverns at the Strategic Petroleum Reserve Bryan Mound site. The cavern field comprises 20 caverns. Five caverns (1, 2, 4, and 5; 3 was later plugged and abandoned) were acquired from industry and have unusual shapes and a history dating back to 1946. The other 16 caverns (101-116) 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 3-D geomechanics model of the site that predicts deformations, strains, and stresses. Future leaching scenarios due 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 result in this report is relevant to caverns 1, 2, and 5. The caverns have non-cylindrical shapes and have potential regions where the surrounding salt may be damaged during workover procedures. During a workover the normal cavern operating pressure is lowered to service a well. At this point the wellhead pressures are atmospheric. When the workover is complete, the cavern is repressurized. The resulting elastic stresses are sufficient to cause tension and large deviatoric stresses at several locations. With time, these stresses relax to a compressive state due to salt creep. However, the potential for salt damage and fracturing exists. The analyses predict tensile stresses at locations with sharp-edges in the wall geometry, or in the case of cavern 5, in the neck region between the upper and lower lobes of the cavern. The effects do not appear to be large-scale, however, so the only major impact is the potential for stress-induced salt falls in cavern 5, potentially leading to hanging string damage. Caverns 1 and 2 have no significant issues regarding leachings due to drawdowns; cavern 5 may require a targeted leaching of the neck region to improve cavern stability and lessen hanging string failure potential. The remaining caverns have no significant issues regarding cavern stability and may be safely enlarged during subsequent oil drawdowns. Well strains are significant and consequently future remedial actions may be necessary. Well strains certainly suggest the need for appropriate monitoring through a well-logging program. Subsidence is currently being monitored; there are no issues identified regarding damage from surface subsidence or horizontal strain to surface facilities.

Ehgartner, Brian L.; Sobolik, Steven Ronald

2009-04-01

321

Stability analysis of switching hyperbolic systems: the example of SMB chromatography

Stability analysis of switching hyperbolic systems: the example of SMB chromatography Georges Abstract-- This paper addresses the issue of the exponential stability of hybrid hyperbolic systems chromatography, how exponential stability (in L2-norm) can be established when the switching mechanism

Bastin, Georges

322

In this study, fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC) was employed to trace the behavior of water extractable organic matter and assess the stabilization process during vermicomposting of sewage sludge and cattle dung. Experiments using different mixing ratios of sewage sludge and cattle dung were conducted using Eisenia fetida. The results showed that vermicomposting reduced the DOC, DOC/DON ratio and ammonia, while increased the nitrate content. A three-component model containing two humic-like materials (components 1 and 2) and a protein-like material (component 3) was successfully developed using PARAFAC analysis. Moreover, the initial waste composition had a significant effect on the distribution of each component and the addition of cattle dung improved the stability of sewage sludge in vermicomposting. The PARAFAC results also indicated that protein-like materials were degraded and humic acid-like compounds were evolved during vermicomposting. Pearson correlation analysis showed that components 2 and 3 are more suitable to assess vermicompost maturity than component 1. In all, EEM-PARAFAC can be used to track organic transformation and assess biological stability during the vermicomposting process. PMID:25068534

Lv, Baoyi; Xing, Meiyan; Zhao, Chunhui; Yang, Jian; Xiang, Liang

2014-12-01

323

Modal Voltage Stability Analysis of Multi-infeed HVDC System Considering its Control Systems

NASA Astrophysics Data System (ADS)

This work presents a method for investigating the voltage stability of multi-infeed HVDC systems, which is based on the eigenvalue decomposition technique known as modal analysis. In this method, the eigenvalue of linearized steady-state system power-voltage equations are computed to evaluate the long-term voltage stability. The contributions of this work to modal analysis method are control systems of HVDC system, such as an Automatic Power Regulator (APR) and an Automatic (DC) Current Regulator (ACR) on its rectifier side and a changeover between an Automatic (DC) Voltage Regulator (AVR) and an Automatic extinction advance angle Regulator (A?R) modes on its inverter side, were taken into account, and the formularization for modal analysis considering not only these control systems of HVDC system but also generator and load characteristics was fulfilled and presented in this paper. The application results from an AC/DC model power system with dual HVDC systems verified the efficiency of the proposed method and quantitatively illustrated the influence of control systems of HVDC system on AC/DC system long-term voltage stability.

Wu, Guohong; Minakawa, Tamotsu; Hayashi, Toshiyuki

324

On the stability of equilibrium for a reformulated foreign trade model of three countries

NASA Astrophysics Data System (ADS)

In this paper, we study the stability of equilibrium for a foreign trade model consisting of three countries. As the gravity equation has been proven an excellent tool of analysis and adequately stable over time and space all over the world, we further enhance the problem to three masses. We use the basic Structure of Heckscher-Ohlin-Samuelson model. The national income equals consumption outlays plus investment plus exports minus imports. The proposed reformulation of the problem focus on two basic concepts: (1) the delay inherited in our economic variables and (2) the interaction effect along the three economies involved. Stability and stabilizability conditions are investigated while numerical examples provide further insight and better understanding. Finally, a generalization of the gravity equation is somehow obtained for the model.

Dassios, Ioannis K.; Kalogeropoulos, Grigoris

2014-06-01

325

A multiloop generalization of the circle criterion for stability margin analysis

NASA Technical Reports Server (NTRS)

In order to provide a theoretical tool suited for characterizing the stability margins of multiloop feedback systems, multiloop input-output stability results generalizing the circle stability criterion are considered. Generalized conic sectors with 'centers' and 'radii' determined by linear dynamical operators are employed to specify the stability margins as a frequency dependent convex set of modeling errors (including nonlinearities, gain variations and phase variations) which the system must be able to tolerate in each feedback loop without instability. The resulting stability criterion gives sufficient conditions for closed loop stability in the presence of frequency dependent modeling errors, even when the modeling errors occur simultaneously in all loops. The stability conditions yield an easily interpreted scalar measure of the amount by which a multiloop system exceeds, or falls short of, its stability margin specifications.

Safonov, M. G.; Athans, M.

1979-01-01

326

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

327

Nonlinear flight dynamics and stability of hovering model insects.

Current analyses on insect dynamic flight stability are based on linear theory and limited to small disturbance motions. However, insects' aerial environment is filled with swirling eddies and wind gusts, and large disturbances are common. Here, we numerically solve the equations of motion coupled with the Navier-Stokes equations to simulate the large disturbance motions and analyse the nonlinear flight dynamics of hovering model insects. We consider two representative model insects, a model hawkmoth (large size, low wingbeat frequency) and a model dronefly (small size, high wingbeat frequency). For small and large initial disturbances, the disturbance motion grows with time, and the insects tumble and never return to the equilibrium state; the hovering flight is inherently (passively) unstable. The instability is caused by a pitch moment produced by forward/backward motion and/or a roll moment produced by side motion of the insect. PMID:23697714

Liang, Bin; Sun, Mao

2013-08-01

328

Nonlinear flight dynamics and stability of hovering model insects

Current analyses on insect dynamic flight stability are based on linear theory and limited to small disturbance motions. However, insects' aerial environment is filled with swirling eddies and wind gusts, and large disturbances are common. Here, we numerically solve the equations of motion coupled with the Navier–Stokes equations to simulate the large disturbance motions and analyse the nonlinear flight dynamics of hovering model insects. We consider two representative model insects, a model hawkmoth (large size, low wingbeat frequency) and a model dronefly (small size, high wingbeat frequency). For small and large initial disturbances, the disturbance motion grows with time, and the insects tumble and never return to the equilibrium state; the hovering flight is inherently (passively) unstable. The instability is caused by a pitch moment produced by forward/backward motion and/or a roll moment produced by side motion of the insect. PMID:23697714

Liang, Bin; Sun, Mao

2013-01-01

329

ASTROP2 Users Manual: A Program for Aeroelastic Stability Analysis of Propfans

NASA Technical Reports Server (NTRS)

This manual describes the input data required for using the second version of the ASTROP2 (Aeroelastic STability and Response Of Propulsion systems - 2 dimensional analysis) computer code. In ASTROP2, version 2.0, the program is divided into two modules: 2DSTRIP, which calculates the structural dynamic information; and 2DASTROP, which calculates the unsteady aerodynamic force coefficients from which the aeroelastic stability can be determined. In the original version of ASTROP2, these two aspects were performed in a single program. The improvements to version 2.0 include an option to account for counter rotation, improved numerical integration, accommodation for non-uniform inflow distribution, and an iterative scheme to flutter frequency convergence. ASTROP2 can be used for flutter analysis of multi-bladed structures such as those found in compressors, turbines, counter rotating propellers or propfans. The analysis combines a two-dimensional, unsteady cascade aerodynamics model and a three dimensional, normal mode structural model using strip theory. The flutter analysis is formulated in the frequency domain resulting in an eigenvalue determinant. The flutter frequency and damping can be inferred from the eigenvalues.

Reddy, T. S. R.; Lucero, John M.

1996-01-01

330

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

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

331

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 G? 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

332

Vacuum Stability and Triviality Analyses of the Renormalizable Coloron Model

The renormalizable coloron model is built around a minimally extended color gauge group, which is spontaneously broken to QCD. The formalism introduces massive color-octet vector bosons (colorons), as well as several new scalars and fermions associated with the symmetry breaking sector. In this paper, we examine vacuum stability and triviality conditions within the context of the renormalizable coloron model up to a cutoff energy scale of 100~TeV, by computing the beta-functions of all relevant couplings and determining their running behavior as a function of the renormalization scale. We constrain the parameter space of the theory for four separate scenarios based on differing fermionic content, and demonstrate that the vectorial scenarios are less constrained by vacuum stability and triviality bounds than the chiral scenarios. Our results are summarized in exclusion plots for the separate scenarios, with previous bounds on the model overlaid for comparison. We find that a 100 TeV hadron collider could explore the entire allowed parameter space of the chiral models very effectively.

R. Sekhar Chivukula; Arsham Farzinnia; Elizabeth H. Simmons

2015-04-12

333

Progress in the Integration of Physics-Based MHD Stability Models into the ONETWO Transport Code

NASA Astrophysics Data System (ADS)

Self-consistent integration of MHD stability models in transport analysis is essential for simulation and development of AT scenarios for DIII-D and ITER. High accuracy equilibrium calculations are required for stability studies. To facilitate the coupling of the stability results with transport calculations, the TOQ inverse Grad-Shafranov equilibrium solver has been integrated into ONETWO. The running results of a sample simulation using TOQ and other equilibrium solvers inside ONETWO are generally in agreement. To model the effects of resonant magnetic drag due to error magnetic field on the plasma rotation, a simple inductive motor model has been implemented into ONETWO. Simulation of a DIII-D RWM discharge indicates that the observed plasma slowing down cannot be fully explained by the resonant magnetic damping due to the error magnetic field alone. Non-resonant magnetic damping likely plays a role. Other planned developments include integration of ONETWO with the ELITE edge peeling- ballooning stability code to study ELM dynamics. Details of the development and recent results will be presented.

Zhou, D.; St John, H. E.; Lao, L. L.; Chu, M. S.; Snyder, P. B.; Brennan, D. P.

2004-11-01

334

NASA Technical Reports Server (NTRS)

The atmospheric ionizing radiation (AIR) ER-2 preflight analysis, one of the first attempts to obtain a relatively complete measurement set of the high-altitude radiation level environment, is described in this paper. The primary thrust is to characterize the atmospheric radiation and to define dose levels at high-altitude flight. A secondary thrust is to develop and validate dosimetric techniques and monitoring devices for protecting aircrews. With a few chosen routes, we can measure the experimental results and validate the AIR model predictions. Eventually, as more measurements are made, we gain more understanding about the hazardous radiation environment and acquire more confidence in the prediction models.

Tai, H.; Wilson, J. W.; Maiden, D. L.

2003-01-01

335

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

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

336

Stability analysis of multiple-robot control systems

NASA Technical Reports Server (NTRS)

In a space telerobotic service scenario, cooperative motion and force control of multiple robot arms are of fundamental importance. Three paradigms to study this problem are proposed. They are distinguished by the set of variables used for control design. They are joint torques, arm tip force vectors, and an accelerated generalized coordinate set. Control issues related to each case are discussed. The latter two choices require complete model information, which presents practical modeling, computational, and robustness problems. Therefore, focus is on the joint torque control case to develop relatively model independent motion and internal force control laws. The rigid body assumption allows the motion and force control problems to be independently addressed. By using an energy motivated Lyapunov function, a simple proportional derivative plus gravity compensation type of motion control law is always shown to be stabilizing. The asymptotic convergence of the tracing error to zero requires the use of a generalized coordinate with the contact constraints taken into account. If a non-generalized coordinate is used, only convergence to a steady state manifold can be concluded. For the force control, both feedforward and feedback schemes are analyzed. The feedback control, if proper care has been taken, exhibits better robustness and transient performance.

Wen, John T.; Kreutz, Kenneth

1989-01-01

337

Analysis and stability of aldehydes and terpenes in electropolished canisters

NASA Astrophysics Data System (ADS)

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 (3-5 ppb) and stored in electropolished stainless-steel canisters. Humidified air, humidified N 2, and dry air were used to dilute three sets of canisters. A series of samples was withdrawn from each canister over a period of 16 days, and concentrations were determined by cryogenic preconcentration, gas chromatography and mass spectrometry. The VOCs were easily separated, but butanal and pentanal had high detection limits relative to the other compounds. While measurements were reproducible, concentrations decreased considerably in the first hour (19% in the humidified air-filled canister set), and losses continued over the measurement period, although at a slower rate. The estimated half-lives of aldehydes and terpenes were 18 d in humidified air-filled canisters, 24 d in humidified N 2, and 6 d in dry air. Loss mechanisms and analytical considerations for the target compounds are discussed. Like other VOCs, the collection and storage of aldehydes and terpenes in canisters require humidification; however; the absolute accuracy of samples and standards of mixtures of aldehydes and terpenes stored in canisters may be limited.

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

338

Analysis of a Major Electric Grid -- Stability and Adaptive Protection

NASA Astrophysics Data System (ADS)

Protective systems of the electric grid are designed to detect and mitigate the effects of faults and other disturbances that may occur. Distance relays are used extensively for the detection of faults on transmission lines. Out-of-step relays are used for generator protection to detect loss of synchronism conditions that result from disturbances on the electric grid. Also, when a disturbance occurs and generators may tend to lose synchronism with each other, it is beneficial to separate the overall system into several independent systems that can remain stable. Unfortunately there have been cases, such as the 2003 Northeast blackout where the operation of protective relays, namely the zone 3 distance relay used for transmission line protection, contributed to the cascading effect of the blackout. It is the objective of this dissertation to propose adaptive relays for both distance protection of transmission lines and out-of-step protection of generators. By being adaptive, the relays are made aware of the system operating conditions and can adjust its settings accordingly. Inputs to the adaptive logic can come from system or environmental conditions. As a result of this effort, a new distance relay operating characteristic is proposed, referred to as a mushroom relay, which is a combination of a quadrilateral relay and a Mho relay. Also, a new criterion for determining if a power swing following a disturbance is stable or unstable is proposed. Distance protection of transmission lines is very important when discussing system responses to faults and disturbances. Distance relays are very common worldwide and although they offer great protection, there are limitations that need to be addressed. Parallel line operations (infeed effect) and the loadability limits are among the limitations that lead to improper response of relays. An Adaptive Distance Relays (ADR) offer great benefits to the protection scheme as their settings can be changed in accordance with prefault system conditions. This dissertation introduces a combination of quadrilateral and mho characteristics to create a distance relay with a mushroom shape in R-X diagrams. This new relay offers larger protective reach with a lower limitation on loadability. When major disturbances occur, the power balance between load and generation might be disturbed causing the generators to lose synchronism (to be out-of-step) with each other. Out-of-step protection against power swings is essential to provide supervising signals for distance relays to mitigate the effects of the disturbance. A new R-X criterion is proposed to identify out-of-step conditions for large and complex power systems, such as KEG. A proposed Adaptive Out-of-Step Relay (AOSR) will monitor power system conditions and adjust the relay reach accordingly for better power swing classification. When unstable swings are detected, controllable tripping signals are initiated and system separation will create small subsystems or islands of the power system. These smaller systems will be created to achieve a balance of load and available generation. The electric power system chosen to study and to illustrate the criteria for the proposed adaptive relays was that of the country of Kuwait. The small oil-rich country of Kuwait has been dealing with an electric energy crisis that started summer 2006. With a dry dessert climate and intensely hot summers, the 3.6 million residents of Kuwait depend on continuously operated A/C units for living. This is the major reason why the peak load in a summer month reaches almost 11,000 MW while the peak load in a winter month does not exceed 5,000 MW. The Kuwait Electric Grid (KEG) is modelled and analyzed using Power Analytics' software known as PaladinRTM DesignBase(TM). Performance studies produce data to examine distance and out-of-step protection. Power Flow (PF), Short Circuit Analysis (SCA), and Transient Stability Analysis (TSA) are used to verify the model of KEG. These studies are the starting point when studying any large power system in order to investigate how the s

Alanzi, Sultan

339

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

340

NASA Astrophysics Data System (ADS)

Results based on a local linear stability analysis of the Hall thruster discharge are presented. A one-dimensional azimuthal framework is used including three species: neutrals, singly charged ions, and electrons. A simplified linear model is developed with the aim of deriving analytical expressions to characterize the stability of the ionization region. The results from the local analysis presented here indicate the existence of an instability that gives rise to an azimuthal oscillation in the +E × B direction with a long wavelength. According to the model, the instability seems to appear only in regions where the ionization and the electric field make it possible to have positive gradients of plasma density and ion velocity at the same time. A more complex model is also solved numerically to validate the analytical results. Additionally, parametric variations are carried out with respect to the main parameters of the model to identify the trends of the instability. As the temperature increases and the neutral-to-plasma density ratio decreases, the growth rate of the instability decreases down to a limit where azimuthal perturbations are no longer unstable.

Escobar, D.; Ahedo, E.

2014-04-01

341

Results based on a local linear stability analysis of the Hall thruster discharge are presented. A one-dimensional azimuthal framework is used including three species: neutrals, singly charged ions, and electrons. A simplified linear model is developed with the aim of deriving analytical expressions to characterize the stability of the ionization region. The results from the local analysis presented here indicate the existence of an instability that gives rise to an azimuthal oscillation in the +E?×?B direction with a long wavelength. According to the model, the instability seems to appear only in regions where the ionization and the electric field make it possible to have positive gradients of plasma density and ion velocity at the same time. A more complex model is also solved numerically to validate the analytical results. Additionally, parametric variations are carried out with respect to the main parameters of the model to identify the trends of the instability. As the temperature increases and the neutral-to-plasma density ratio decreases, the growth rate of the instability decreases down to a limit where azimuthal perturbations are no longer unstable.

Escobar, D. [Universidad Politécnica de Madrid, 28040 Madrid (Spain)] [Universidad Politécnica de Madrid, 28040 Madrid (Spain); Ahedo, E., E-mail: eduardo.ahedo@uc3m.es [Universidad Carlos III de Madrid, 28911 Leganés (Spain)

2014-04-15

342

NASA Technical Reports Server (NTRS)

The analysis of results of wind-tunnel stability and control tests of powered airplane models in terms of the flying qualities of full-scale airplanes is advocated. In order to indicated the topics upon which comments are considered desirable in the report of a wind-tunnel stability and control investigation and to demonstrate the nature of the suggested analysis, the present NACA flying-qualities requirements are discussed in relation to wind-tunnel tests. General procedures for the estimation of flying qualities from wind-tunnel tests are outlined.

Kayten, Gerald G

1945-01-01

343

The simplest walking model: stability, complexity, and scaling.

We demonstrate that an irreducibly simple, uncontrolled, two-dimensional, two-link model, vaguely resembling human legs, can walk down a shallow slope, powered only by gravity. This model is the simplest special case of the passive-dynamic models pioneered by McGeer (1990a). It has two rigid massless legs hinged at the hip, a point-mass at the hip, and infinitesimal point-masses at the feet. The feet have plastic (no-slip, no-bounce) collisions with the slope surface, except during forward swinging, when geometric interference (foot scuffing) is ignored. After nondimensionalizing the governing equations, the model has only one free parameter, the ramp slope gamma. This model shows stable walking modes similar to more elaborate models, but allows some use of analytic methods to study its dynamics. The analytic calculations find initial conditions and stability estimates for period-one gait limit cycles. The model exhibits two period-one gait cycles, one of which is stable when 0 < gamma < 0.015 rad. With increasing gamma, stable cycles of higher periods appear, and the walking-like motions apparently become chaotic through a sequence of period doublings. Scaling laws for the model predict that walking speed is proportional to stance angle, stance angle is proportional to gamma 1/3, and that the gravitational power used is proportional to v4 where v is the velocity along the slope. PMID:10412391

Garcia, M; Chatterjee, A; Ruina, A; Coleman, M

1998-04-01

344

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.

345

Randomized algorithms for stability and robustness analysis of high-speed communication networks.

This paper initiates a study toward developing and applying randomized algorithms for stability of high-speed communication networks. The focus is on congestion and delay-based flow controllers for sources, which are "utility maximizers" for individual users. First, we introduce a nonlinear algorithm for such source flow controllers, which uses as feedback aggregate congestion and delay information from bottleneck nodes of the network, and depends on a number of parameters, among which are link capacities, user preference for utility, and pricing. We then linearize this nonlinear model around its unique equilibrium point and perform a robustness analysis for a special symmetric case with a single bottleneck node. The "symmetry" here captures the scenario when certain utility and pricing parameters are the same across all active users, for which we derive closed-form necessary and sufficient conditions for stability and robustness under parameter variations. In addition, the ranges of values for the utility and pricing parameters for which stability is guaranteed are computed exactly. These results also admit counterparts for the case when the pricing parameters vary across users, but the utility parameter values are still the same. In the general nonsymmetric case, when closed-form derivation is not possible, we construct specific randomized algorithms which provide a probabilistic estimate of the local stability of the network. In particular, we use Monte Carlo as well as quasi-Monte Carlo techniques for the linearized model. The results obtained provide a complete analysis of congestion control algorithms for internet style networks with a single bottleneck node as well as for networks with general random topologies. PMID:16252829

Alpcan, Tansu; Ba?ar, Tamer; Tempo, Roberto

2005-09-01

346

In situ vitrification: application analysis for stabilization of transuranic waste

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

347

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

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

348

Analysis of cavern stability at the West Hackberry SPR site.

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

349

Precessing rotating flows with additional shear: Stability analysis

NASA Astrophysics Data System (ADS)

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 ?0 ) and the additional “precessing” Coriolis force (with angular velocity -??0 ), normal to it. A “weak” shear flow, with rate 2? of the same order of the Poincaré “small” ratio ? , 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 ? . 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 ? , but significant differences are obtained regarding growth rates and widths of instability bands, if larger ? 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.

Salhi, A.; Cambon, C.

2009-03-01

350

System reliability analysis of the external stability of reinforced soil structures

A probabilistic model is formulated in order to assess the reliability of the external stability of reinforced soil structures, in the presence of geotechnical and material uncertainty. Three modes of failure are taken into account (bearing capacity, sliding and excessive eccentricity) and overall stability is modelled as an in-series system. Geomaterial shear strength properties are modelled as beta-distributed random variables

Ioannis E. Zevgolis; Philippe L. Bourdeau

2010-01-01

351

Local and global stability analysis of an unsupervised competitive neural network.

Unsupervised competitive neural networks (UCNN) are an established technique in pattern recognition for feature extraction and cluster analysis. A novel model of an unsupervised competitive neural network implementing a multitime scale dynamics is proposed in this letter. The local and global asymptotic stability of the equilibrium points of this continuous-time recurrent system whose weights are adapted based on a competitive learning law is mathematically analyzed. The proposed neural network and the derived results are compared with those obtained from other multitime scale architectures. PMID:18269964

Meyer-Base, A; Thummler, V

2008-02-01

352

NASA Astrophysics Data System (ADS)

In this dissertation, we present algorithmic procedures for sum-of-squares based stability analysis and control design for uncertain nonlinear systems. In particular, we consider the case of robust aircraft control design for a hypersonic aircraft model subject to parametric uncertainties in its aerodynamic coefficients. In recent years, Sum-of-Squares (SOS) method has attracted increasing interest as a new approach for stability analysis and controller design of nonlinear dynamic systems. Through the application of SOS method, one can describe a stability analysis or control design problem as a convex optimization problem, which can efficiently be solved using Semidefinite Programming (SDP) solvers. For nominal systems, the SOS method can provide a reliable and fast approach for stability analysis and control design for low-order systems defined over the space of relatively low-degree polynomials. However, The SOS method is not well-suited for control problems relating to uncertain systems, specially those with relatively high number of uncertainties or those with non-affine uncertainty structure. In order to avoid issues relating to the increased complexity of the SOS problems for uncertain system, we present an algorithm that can be used to transform an SOS problem with uncertainties into a LMI problem with uncertainties. A new Probabilistic Ellipsoid Algorithm (PEA) is given to solve the robust LMI problem, which can guarantee the feasibility of a given solution candidate with an a-priori fixed probability of violation and with a fixed confidence level. We also introduce two approaches to approximate the robust region of attraction (RROA) for uncertain nonlinear systems with non-affine dependence on uncertainties. The first approach is based on a combination of PEA and SOS method and searches for a common Lyapunov function, while the second approach is based on the generalized Polynomial Chaos (gPC) expansion theorem combined with the SOS method and searches for parameter-dependent Lyapunov functions. The control design problem is investigated through a case study of a hypersonic aircraft model with parametric uncertainties. Through time-scale decomposition and a series of function approximations, the complexity of the aircraft model is reduced to fall within the capability of SDP solvers. The control design problem is then formulated as a convex problem using the dual of the Lyapunov theorem. A nonlinear robust controller is searched using the combined PEA/SOS method. The response of the uncertain aircraft model is evaluated for two sets of pilot commands. As the simulation results show, the aircraft remains stable under up to 50% uncertainty in aerodynamic coefficients and can follow the pilot commands.

Ataei-Esfahani, Armin

353

Order-2 Stability Analysis of Particle Swarm Optimization.

Several stability analyses and stable regions of particle swarm optimization (PSO) have been proposed before. The assumption of stagnation and different definitions of stability are adopted in these analyses. In this paper, the order-2 stability of PSO is analyzed based on a weak stagnation assumption. A new definition of stability is proposed and an order-2 stable region is obtained. Several existing stable analyses for canonical PSO are compared, especially their definitions of stability and the corresponding stable regions. It is shown that the classical stagnation assumption is too strict and not necessary. Moreover, among all these definitions of stability, it is shown that our definition requires the weakest conditions, and additional conditions bring no benefit. Finally, numerical experiments are reported to show that the obtained stable region is meaningful. A new parameter combination of PSO is also shown to be good, even better than some known best parameter combinations. PMID:24738856

Liu, Qunfeng

2014-04-16

354

Model based control schemes such as model predictive control are highly related to the accuracy of the proces model. A regional-knowledge index is proposed in this study and applied in the analysis of dynamic artificial neural network models in process control. To tackle the extrapolation problem and assure stability of the control system, we propose to run a neural adaptive

Chia Huang Yen; Po-Feng Tsai; Shi-Shang Jang

2003-01-01

355

A distributed computing approach for real-time transient stability analysis

Power system online dynamic security assessment (DSA) is a challenging computing problem. A key problem in DSA is the analysis of a large number of dynamic stability contingencies every 10-20 minutes using online data. In order to speed up the transient stability analysis, parallel processing has been applied and several results can be found in the literature. In this paper,

G. Aloisio; M. A. Bochicchio; M. La Scala; R. Sbrizzai

1997-01-01

356

Stability Analysis of Distributed Order Fractional Chen System

We first investigate sufficient and necessary conditions of stability of nonlinear distributed order fractional system and then we generalize the integer-order Chen system into the distributed order fractional domain. Based on the asymptotic stability theory of nonlinear distributed order fractional systems, the stability of distributed order fractional Chen system is discussed. In addition, we have found that chaos exists in the double fractional order Chen system. Numerical solutions are used to verify the analytical results. PMID:24489508

Aminikhah, H.; Refahi Sheikhani, A.; Rezazadeh, H.

2013-01-01

357

Development of Harmonic Excitation technique for Machine Tool stability analysis

The project described in this thesis was to establish the instrumentation and technique for analysing stability of machine-tools against chatter by harmonic excitation. To test out the technique, two sets of experiments were performed on centre lathes:\\u000a1) comparison of cutting stability with tour different types of boring bars, and\\u000a2) comparison of cutting stability of a tool oriented in

Michael King-Chun Lau

1973-01-01

358

Stability and Bifurcation Analysis of a Spinning Space Tether

A detailed, geometrically exact bifurcation analysis is performed for a model of a power-generating tethered device of interest\\u000a to the space industries. The structure, a short electrodynamic tether, comprises a thin, long rod that is spun in a horizontal\\u000a configuration from a satellite in low Earth orbit, with a massive electrically conducting disk at its free end. The system\\u000a is

J. Valverde; J. L. Escalona; J. Dominguez; A. R. Champneys

2006-01-01

359

Slope Stability Analysis Using Limit Equilibrium Method in Nonlinear Criterion

In slope stability analysis, the limit equilibrium method is usually used to calculate the safety factor of slope based on Mohr-Coulomb criterion. However, Mohr-Coulomb criterion is restricted to the description of rock mass. To overcome its shortcomings, this paper combined Hoek-Brown criterion and limit equilibrium method and proposed an equation for calculating the safety factor of slope with limit equilibrium method in Hoek-Brown criterion through equivalent cohesive strength and the friction angle. Moreover, this paper investigates the impact of Hoek-Brown parameters on the safety factor of slope, which reveals that there is linear relation between equivalent cohesive strength and weakening factor D. However, there are nonlinear relations between equivalent cohesive strength and Geological Strength Index (GSI), the uniaxial compressive strength of intact rock ?ci, and the parameter of intact rock mi. There is nonlinear relation between the friction angle and all Hoek-Brown parameters. With the increase of D, the safety factor of slope F decreases linearly; with the increase of GSI, F increases nonlinearly; when ?ci is relatively small, the relation between F and ?ci is nonlinear, but when ?ci is relatively large, the relation is linear; with the increase of mi, F decreases first and then increases. PMID:25147838

Lin, Hang; Zhong, Wenwen; Xiong, Wei; Tang, Wenyu

2014-01-01

360

BLSTA: A boundary layer code for stability analysis

NASA Technical Reports Server (NTRS)

A computer program is developed to solve the compressible, laminar boundary-layer equations for two-dimensional flow, axisymmetric flow, and quasi-three-dimensional flows including the flow along the plane of symmetry, flow along the leading-edge attachment line, and swept-wing flows with a conical flow approximation. The finite-difference numerical procedure used to solve the governing equations is second-order accurate. The flow over a wide range of speed, from subsonic to hypersonic speed with perfect gas assumption, can be calculated. Various wall boundary conditions, such as wall suction or blowing and hot or cold walls, can be applied. The results indicate that this boundary-layer code gives velocity and temperature profiles which are accurate, smooth, and continuous through the first and second normal derivatives. The code presented herein can be coupled with a stability analysis code and used to predict the onset of the boundary-layer transition which enables the assessment of the laminar flow control techniques. A user's manual is also included.

Wie, Yong-Sun

1992-01-01

361

Crack stability analysis of low alloy steel primary coolant pipe

At present, cast duplex stainless steel has been used for the primary coolant piping of PWRs in Japan and joints of dissimilar material have been applied for welding to reactor vessels and steam generators. For the primary coolant piping of the next APWR plants, application of low alloy steel that results in designing main loops with the same material is being studied. It means that there is no need to weld low alloy steel with stainless steel and that makes it possible to reduce the welding length. Attenuation of Ultra Sonic Wave Intensity is lower for low alloy steel than for stainless steel and they have advantageous inspection characteristics. In addition to that, the thermal expansion rate is smaller for low alloy steel than for stainless steel. In consideration of the above features of low alloy steel, the overall reliability of primary coolant piping is expected to be improved. Therefore, for the evaluation of crack stability of low alloy steel piping to be applied for primary loops, elastic-plastic future mechanics analysis was performed by means of a three-dimensioned FEM. The evaluation results for the low alloy steel pipings show that cracks will not grow into unstable fractures under maximum design load conditions, even when such a circumferential crack is assumed to be 6 times the size of the wall thickness.

Tanaka, T.; Kameyama, M. [Kansai Electric Power Company, Osaka (Japan); Urabe, Y. [Mitsubishi Heavy Industries, Ltd., Takasago (Japan)] [and others

1997-04-01

362

GIS-based modelling of deep-seated slope stability in complex geology

NASA Astrophysics Data System (ADS)

We use the model r.slope.stability to explore the chances and challenges of physically-based modelling of deep-seated slope stability in complex geology over broad areas and not on individual slopes. The model is developed as a C and python-based raster module within the GRASS GIS software. It makes use of a modification of the three-dimensional sliding surface model proposed by Hovland (1977) and revised and extended by Xie and co-workers (2006). Given a digital elevation model and a set of thematic layers (lithological classes and related geotechnical parameters), the model evaluates the slope stability for a large number of randomly selected potential slip surfaces, ellipsoidal in shape. The bottoms of soil or bedrock layers can also be considered as potential slip surfaces by truncating the ellipsoids. Any single raster cell may be intersected by multiple sliding surfaces, each associated with a computed safety factor. For each pixel, the lowest value of the safety factor and the depth of the associated slip surface are stored. This information can be used to obtain a spatial overview of the potentially unstable regions in the study area. The r.slope.stability model can be executed both in a soil class-based mode, where the input data are mainly structured according to horizontally defined soil classes, and in a layer-based mode, where the data are structured according to a potentially large number of layers. Here, we test the model for the layer-based mode, allowing for the analysis of relatively complex geologic structures. We test the model in the Collazzone area, Umbria, central Italy, which is susceptible to landslides of different types. According to field observations in this area, morpho-structural settings (i.e., the orientation and dip of the geological layers) play a crucial role for the distribution of the deep-seated landslides. We have prepared a lithological model based on aerial photointerpretation, field survey and surface information on the strike and dip directions of each layer. We have further investigated the geotechnical parameters (cohesion and internal friction angle) associated to the layers using direct shear tests. We execute r.slope.stability for various assumptions of the geotechnical parameters, ellipsoid geometry and seepage direction. In this way, we obtain the spatial probability of slope failures which is validated using a pre-existing landslide inventory map, using an ROC plot. Acknowledging the challenges related to the high natural variability of geotechnical parameters in space, the results satisfactorily reproduce the observed distribution of deep-seated landslides in the study area. The assumed direction of seepage (slope-parallel vs. layer-parallel) strongly influences the model results.

Mergili, Martin; Marchesini, Ivan; Schneider-Muntau, Barbara; Cardinali, Mauro; Fiorucci, Federica; Valigi, Daniela; Santangelo, Michele; Bucci, Francesco; Guzzetti, Fausto

2014-05-01

363

Hydrodynamic Stability Analysis of Particle-Laden Solid Rocket Motors

NASA Astrophysics Data System (ADS)

Fluid-wall interactions within solid rocket motors can result in parietal vortex shedding giving rise to hydrodynamic instabilities, or unsteady waves, that translate into pressure oscillations. The oscillations can result in vibrations observed by the rocket, rocket subsystems, or payload, which can lead to changes in flight characteristics, design failure, or other undesirable effects. For many years particles have been embedded in solid rocket propellants with the understanding that their presence increases specific impulse and suppresses fluctuations in the flowfield. This study utilizes a two dimensional framework to understand and quantify the aforementioned two-phase flowfield inside a motor case with a cylindrical grain perforation. This is accomplished through the use of linearized Navier-Stokes equations with the Stokes drag equation and application of the biglobal ansatz. Obtaining the biglobal equations for analysis requires quantification of the mean flowfield within the solid rocket motor. To that end, the extended Taylor-Culick form will be utilized to represent the gaseous phase of the mean flowfield while the self-similar form will be employed for the particle phase. Advancing the mean flowfield by quantifying the particle mass concentration with a semi-analytical solution the finalized mean flowfield is combined with the biglobal equations resulting in a system of eight partial differential equations. This system is solved using an eigensolver within the framework yielding the entire spectrum of eigenvalues, frequency and growth rate components, at once. This work will detail the parametric analysis performed to demonstrate the stabilizing and destabilizing effects of particles within solid rocket combustion.

Elliott, T. S.; Majdalani, J.

2014-11-01

364

The Savannah River Remediation (SRR) Organization requested that Savannah River National Laboratory (SRNL) develop a Computational Fluid Dynamics (CFD) method to mix and blend the miscible contents of the blend tanks to ensure the contents are properly blended before they are transferred from the blend tank; such as, Tank 50H, to the Salt Waste Processing Facility (SWPF) feed tank. The work described here consists of two modeling areas. They are the mixing modeling analysis during miscible liquid blending operation, and the flow pattern analysis during transfer operation of the blended liquid. The transient CFD governing equations consisting of three momentum equations, one mass balance, two turbulence transport equations for kinetic energy and dissipation rate, and one species transport were solved by an iterative technique until the species concentrations of tank fluid were in equilibrium. The steady-state flow solutions for the entire tank fluid were used for flow pattern analysis, for velocity scaling analysis, and the initial conditions for transient blending calculations. A series of the modeling calculations were performed to estimate the blending times for various jet flow conditions, and to investigate the impact of the cooling coils on the blending time of the tank contents. The modeling results were benchmarked against the pilot scale test results. All of the flow and mixing models were performed with the nozzles installed at the mid-elevation, and parallel to the tank wall. From the CFD modeling calculations, the main results are summarized as follows: (1) The benchmark analyses for the CFD flow velocity and blending models demonstrate their consistency with Engineering Development Laboratory (EDL) and literature test results in terms of local velocity measurements and experimental observations. Thus, an application of the established criterion to SRS full scale tank will provide a better, physically-based estimate of the required mixing time, and elevation of transfer pump for minimum sludge disturbance. (2) An empirical equation for a tank with no cooling coils agrees reasonably with the current modeling results for the dual jet. (3) From the sensitivity study of the cooling coils, it was found that the tank mixing time for the coiled tank was about two times longer than that of the tank fluid with no coils under the 1/10th scale, while the coiled tank required only 50% longer than the one without coils under the full scale Tank 50H. In addition, the time difference is reduced when the pumping U{sub o}d{sub o} value is increased for a given tank. (4) The blending time for T-shape dual jet pump is about 20% longer than that of 15{sup o} upward V-shape pump under the 1/10th pilot-scale tank, while the time difference between the two pumps is about 12% for the full-scale Tank 50H. These results are consistent with the literature information. (5) A transfer pump with a solid-plate suction screen operating at 130 gpm can be located 9.5 inches above settled sludge for 2 in screen height in a 85 ft waste tank without disturbing any sludge. Detailed results are summarized in Table 13. Final pump performance calculations were made by using the established CW pump design, and operating conditions to satisfy the two requirements of minimum sludge disturbance, and adequate blending of tank contents. The final calculation results show that the blending times for the coiled and uncoiled tanks coupled with the CW pump design are 159 and 83 minutes, respectively. All the results are provided in Table 16.

Lee, S.

2011-05-05

365

GE simplified boiling water reactor stability analysis in time domain

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

366

Genome-Wide Analysis of Human MicroRNA Stability

Increasing studies have shown that microRNA (miRNA) stability plays important roles in physiology. However, the global picture of miRNA stability remains largely unknown. Here, we had analyzed genome-wide miRNA stability across 10 diverse cell types using miRNA arrays. We found that miRNA stability shows high dynamics and diversity both within individual cells and across cell types. Strikingly, we observed a negative correlation between miRNA stability and miRNA expression level, which is different from current findings on other biological molecules such as proteins and mRNAs that show positive and not negative correlations between stability and expression level. This finding indicates that miRNA has a distinct action mode, which we called “rapid production, rapid turnover; slow production, slow turnover.” This mode further suggests that high expression miRNAs normally degrade fast and may endow the cell with special properties that facilitate cellular status-transition. Moreover, we revealed that the stability of miRNAs is affected by cohorts of factors that include miRNA targets, transcription factors, nucleotide content, evolution, associated disease, and environmental factors. Together, our results provided an extensive description of the global landscape, dynamics, and distinct mode of human miRNA stability, which provide help in investigating their functions in physiology and pathophysiology. PMID:24187663

Li, Yang; Li, Zhixin; Zhou, Shixin; Wen, Jinhua; Geng, Bin; Yang, Jichun; Cui, Qinghua

2013-01-01

367

An analysis of the errors of a gyropendulum gravimeter stabilizer

NASA Astrophysics Data System (ADS)

The errors of a gravimeter mounted on a gyropendulum stabilizer are analyzed for various stabilizer characteristics and perturbations. In particular, attention is given to the case where the perturbation involves random horizontal acceleration of the gravimeter mounting spot due to the orbital motion and rolling of the system. The conditions resulting in a minimum total systematic error of the second order are determined.

Bocharov, A. F.; Kostrov, A. V.; Rivkin, S. S.

1985-08-01

368

Bifurcation and Stability Analysis of Aircraft Turning Manoeuvres

During ground manoeuvres a loss of lateral stability due to the saturation of the main landing gear tyres can cause the aircraft to enter a skid or a spin. The lateral stability is governed not only by aspects of the gear design, such as its geometry and tyre characteris- tics, but also by operational parameters, for example, the weather and

James Rankin; Mark Lowenberg

369

Assessing stability of gene selection in microarray data analysis

Abstract Background. The number of genes declared dierentially,expressed is a random variable and its variability can be assessed by resampling techniques. Another important stability indicator is the frequency with which a given gene is selected across subsamples. We have conducted studies to assess stability and some other properties of several gene selection procedures with biological and simulated data. Results. Using

Xing Qiu; Yuanhui Xiao; Alexander Gordon; Andrei Yakovlev

2006-01-01

370

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...

371

A highly parallel method for transient stability analysis

A simple but powerful method for solving the transient stability problem with a high degree of parallelism is implemented. The transient stability is seen as a coupled set of nonlinear algebraic and differential equations. By applying a discretization method such as the trapezoidal rule, the overall algebraic-differential set of equations is transformed into a unique algebraic problem at each time

Massimo La Scala; Anjan Bose; Daniel J. Tylavsky; Jian S. Chai

1989-01-01

372

A highly parallel method for transient stability analysis

A method for transient stability simulation is presented that aims to exploit the maximum degree of parallelism that the problem presents. The transient stability problem is viewed as a coupled set of nonlinear algebraic and differential equations; by applying a discretization method such as the trapezoidal rule, the overall algebraic-differential set of equations is thus transformed into an unique algebraic

M. La Scala; A. Bose; D. J. Tylavsky; J. S. Chai

1990-01-01

373

Foam lamellae are the smallest structural elements in foam. Such lamellae can experimentally be studied by analysis of thin liquid films in glass cells. These thin liquid films usually have to be stabilized against rupture by surface active substances, such as proteins or low molecular weight surfactants. However, horizontal thin liquid films of pure water with a radius of 100 ?m also show remarkable stability when created in closed Sheludko cells. To understand thin film stability of surfactant-free films, the drainage behavior and rupture times of films of water and NaCl solutions were determined. The drainage was modeled with an extended Derjaguin-Landau-Verwey-Overbeek (DLVO) model, which combines DLVO and hydrophobic contributions. Good correspondence between experiment and theory is observed, when hydrophobic interactions are included, with fitted values for surface potential (?0,water) of -60 ± 5 mV, hydrophobic strength (Bhb,water) of 0.22 ± 0.02 mJ/m(2), and a range of the hydrophobic interaction (?hb, water) of 15 ± 1 nm in thin liquid films. In addition, Vrij's rupture criterion was successfully applied to model the stability regions and rupture times of the films. The films of pure water are stable over long time scales (hours) and drain to a final thickness >40 nm if the concentration of electrolytes is low (resistivity 18.2 MQ). With increasing amounts of ions (NaCl) the thin films drain to <40 nm thickness and the rupture stability of the films is reduced from hours to seconds. PMID:25689104

Lech, Frederik J; Wierenga, Peter A; Gruppen, Harry; Meinders, Marcel B J

2015-03-10

374

Joint regression analysis and AMMI model applied to oat improvement

NASA Astrophysics Data System (ADS)

In our work we present an application of some biometrical methods useful in genotype stability evaluation, namely AMMI model, Joint Regression Analysis (JRA) and multiple comparison tests. A genotype stability analysis of oat (Avena Sativa L.) grain yield was carried out using data of the Portuguese Plant Breeding Board, sample of the 22 different genotypes during the years 2002, 2003 and 2004 in six locations. In Ferreira et al. (2006) the authors state the relevance of the regression models and of the Additive Main Effects and Multiplicative Interactions (AMMI) model, to study and to estimate phenotypic stability effects. As computational techniques we use the Zigzag algorithm to estimate the regression coefficients and the agricolae-package available in R software for AMMI model analysis.

Oliveira, A.; Oliveira, T. A.; Mejza, S.

2012-09-01

375

Primary posterior stabilized total knee arthroplasty: analysis of different instrumentation

Background Intercondylar femoral bone removal during posterior stabilized (PS) total knee arthroplasty (TKA) makes many cruciate substituting implant designs less appealing than cruciate retaining implants. Bone stock conservation is considered fundamental in the prevision of future revision surgeries. The purpose of this study was to compare the quantity of intercondylar bone removable during PS housing preparation using three contemporary PS TKA instrumentations. Method We compared different box cutting jigs which were utilized for the PS housing of three popular PS knee prostheses. The bone removal area from every PS box cutting jig was three-dimensionally measured. Results Independently from the implant size, the cutting jig for a specific PS TKA always resected significantly less bone than the others: this difference was statistically significant, especially for small- to medium-sized total knee femoral components. Conclusion This study does not establish a clinical relevance of removing more or less bone at primary TKA, but suggests that if a PS design is indicated, it is preferable to select a model which possibly resects less distal femoral bone. PMID:25037275

2014-01-01

376

Proton stability and light Z' inspired by string derived models

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

377

Stability analysis and trend study of a balloon tethered in a wind, with experimental comparisons

NASA Technical Reports Server (NTRS)

A stability analysis and trend study for a balloon tethered in a steady wind are presented. The linearized, stability-derivative type analysis includes balloon aerodynamics, buoyancy, mass (including apparent mass), and static forces resulting from the tether cable. The analysis has been applied to a balloon 7.64 m in length, and the results are compared with those from tow tests of this balloon. This comparison shows that the analysis gives reasonable predictions for the damping, frequencies, modes of motion, and stability boundaries exhibited by the balloon. A trend study for the 7.64-m balloon was made to illustrate how the stability boundaries are affected by changes in individual stability parameters. The trends indicated in this study may also be applicable to many other tethered-balloon systems.

Redd, L. T.; Bland, S. R.; Bennett, R. M.

1973-01-01

378

NASA Astrophysics Data System (ADS)

The effects of blade and root-flexure elasticity and dynamic stall on the stability of hingeless rotor blades are investigated. The dynamic stall description is based on the ONERA models of lift, drag, and pitching moment. The structural analysis is based on three blade models that range from a rigid flap-lag model to two elastic flap-lag-torsion models, which differ in representing root-flexure elasticity. The predictions are correlated with the measured lag damping of an experimental isolated three-blade rotor; the correlation covers rotor operations from near-zero-thrust conditions in hover to highly stalled, high-thrust conditions in foward flight. That correlation shows sensitivity of lag-damping predictions to structural refinements in blade and root-flexure modeling. Moreover, this sensitivity increases with increasing control pitch angle and advance ratio. For high-advance-ratio and high-thrust conditions, inclusion of dynamic stall generally improves the correlation.

Barwey, D.; Gaonkar, Gopal H.

1994-04-01

379

Best-estimate plus uncertainty thermal-hydraulic stability analysis of BWRs using TRACG code

Over the last decade, Boiling Water Reactor (BWR) power up-rates have increased plant rated power output significantly. Subsequent projects have expanded flow domains (e.g. MELLLA+) for operation at these higher power levels. This has resulted in an increase in the power to flow ratio in regions susceptible to reactor thermal-hydraulic instabilities. Since BWRs are susceptible to coupled thermal-hydraulic/nuclear oscillations when operating at these conditions, such oscillations must be prevented or reliably detected and suppressed. The Detect and Suppress Solution - Confirmation Density (DSS-CD) is the most sophisticated GEH BWR instability protection system ever employed. DSS-CD implements algorithms that monitor closely-spaced groups of Local Power Range Monitor (LPRM) detectors to detect periodic behavior typical of reactor instability events. This system is able to detect small, localized power variations in the core, distinguish between true instabilities and plant noise, and trip/scram the reactor while maintaining adequate safety margins. The combination of hardware, software, and system setpoints provides protection against violation of the Safety Limit Minimum Critical Power Ratio (SLMCPR) for anticipated oscillations. To support DSS-CD implementation, the TRACG system code is used to simulate events to confirm the capability of the DSS-CD solution for early oscillation detection and suppression. TRACG is a GEH proprietary version of the Transient Reactor Analysis Code (TRAC). TRACG includes a multi-dimensional, two-fluid model for the reactor thermal-hydraulics and a three-dimensional reactor kinetics model. The models are qualified to simulate a large variety of tests and reactor configurations, including thermal-hydraulic stability events. These features allow for detailed, best-estimate simulation of a wide range of BWR phenomena. A set of integrated TRACG event simulations for reasonably limiting anticipated events can be used to calculate the effect on the Minimum Critical Power Ratio (MCPR) performance. The purpose of the DSS-CD TRACG analysis is to confirm the inherent MCPR margin afforded by the solution design. This paper presents the Best Estimate Plus Uncertainty (BEPU) DSS-CD TRACG methodology and its application to BWR Thermal-Hydraulic (T-H) stability analyses. The statistical Code Scaling, Applicability and Uncertainty (CSAU) methodology (defined in NUREG/CR-5249) is used to calculate the MCPR uncertainty. The TRACG simulation includes a full core individual bundle model in which each fuel bundle is modeled as an individual T-H channel. The complete CSAU analysis of full core individual bundle model is an innovative solution represents the state-of-the-art stability analysis of BWRs and is the first ever full statistical analysis for stability safety analyses. The adoption of BEPU methodologies for stability analyses advances the understanding of the associated physical phenomena and maintains the safety of reactor plant operation in expanded operation domain with up-rated power. (authors)

Vedovi, J.; Yang, J.; Klebanov, L.; Vreeland, D. G.; Zino, J. F. [GE Hitachi Nuclear Energy Americas, 3901 Castle Hayne, Wilmington, NC 28401 (United States)

2012-07-01

380

Modelling and control of a balloon-borne stabilized platform

This dissertation is concerned with the development of a balloon borne stabilized platform for the detection of anisotropy in the Cosmic Background Radiation (CBR). The control and design objective is to develop an accurate altitude-azimuth pointing and stabilizing system to keep the targeted celestial source within the beam size of the antenna and detector system. Since the beam has an angular size of 0.33 to 0.75 degree, the pointing error rms should be better than 0.10 degree both in azimuth and elevation. The experimental setup is described and descriptions of the major hardware used in the experiment are given. A mathematical model of the azimuth pointing system is derived. Using pole placement technique, the model is used as a basis to structure and to design a proportional-integral-derivative (PID) control with constant desaturation of flywheel angular velocity. Model reference adaptive control (MRAC) with constant desaturation of flywheel angular velocity is also developed. Simulation results indicate that both controllers are capable of continuous azimuth pointing with error rms better than 0.01 degree. The development of software programs to coordinate the experiment is discussed. Software development includes the implementation of computer based PID control and MRAC both with constant desaturation of flywheel velocity, stiction and calibration compensations for the elevation pointing system, strategies for trajectory generations, gyro recovery during flight, data scheduling and other flight operations. Extensive ground test results verified that the software programs are adequate and functional. Results also indicate that the system is capable of azimuth and elevation pointing with error rms better than 0.02 degree and 0.04 degree, respectively.

Chingcuanco, A.O.

1989-01-01

381

Stability Analysis of Two-dimension Burnett Equations

NASA Astrophysics Data System (ADS)

Stability analyses of two-dimension conventional Burnett and Woods equations were carried out. The characteristic stability equations of these two equations were first derived and the characteristic curves were achieved. The linearized stability analyses show that the two-dimension conventional Burnett and Woods equations are not stable. The critical Knudsen numbers for these two extended hydrodynamic equations are 0.353 and 0.130, respectively. The critical Knudsen numbers are smaller than those of one-dimension equations. The two-dimension extended hydrodynamic equations are more unstable than one-dimension equations.

Zhu, Z. H.; Bao, F. B.; Lin, J. Z.; Wang, J. X.

2011-09-01

382

NASA Astrophysics Data System (ADS)

Suppression of magnetic islands driven by the neoclassical tearing mode (NTM) is necessary for efficient and sustained operation of tokamak fusion reactors. Compensating for the lack of bootstrap current, due to the pressure profile flattening in the magnetic island, by a localized electron cyclotron current drive (ECCD) has been proved experimentally as an effective method to stabilize NTMs. The effectiveness of this method is limited in practice by the uncertainties in the width of the island, the relative position between the island and the beam, and the ECCD power threshold for NTM stabilization. Heuristic search and suppress algorithms have been proposed and shown effective in improving the alignment of the ECCD beam with the island, using only an estimate of the island width. Making use of this estimate, real-time, non-model-based, extremum-seeking optimization algorithms have also been proposed not only for beam steering but also for power modulation in order to minimize the island-beam misalignment and the time required for NTM stabilization. A control-oriented dynamic model for the effect of ECCD on the magnetic island is proposed in this work to enable both control design and performance analysis of these minimum-seeking type of controllers. The model expands previous work by including the impact of beam modulation parameters such as the island-beam phase mismatch and the beam duty-cycle on the island width dynamics.

Wehner, W.; Schuster, E.

2012-07-01

383

A multiloop generalization of the circle criterion for stability margin analysis

NASA Technical Reports Server (NTRS)

In order to provide a theoretical tool well suited for use in characterizing the stability margins (e.g., gain and phase margins) of multiloop feedback systems, multiloop input-output stability results generalizing the circle stability criterion are considered. Generalized conic sectors with 'centers' and 'radii' determined by linear dynamical operators are employed to enable an engineer to specify the stability margins which he desires as a frequency-dependent convex set of modeling errors (including nonlinearities, gain variations, and phase variations) which the system must be able to tolerate in each feedback loop without instability. The resulting stability criterion gives sufficient conditions for closed-loop stability in the presence of such frequency-dependent modeling errors, even when the modeling errors occur simultaneously in all loops.

Safonov, M. G.; Athans, M.

1981-01-01

384

Lattice refining loop quantum cosmology, anisotropic models, and stability

A general class of loop quantizations for anisotropic models is introduced and discussed, which enhances loop quantum cosmology by relevant features seen in inhomogeneous situations. The main new effect is an underlying lattice which is being refined during dynamical changes of the volume. In general, this leads to a new feature of dynamical difference equations which may not have constant step-size, posing new mathematical problems. It is discussed how such models can be evaluated and what lattice refinements imply for semiclassical behavior. Two detailed examples illustrate that stability conditions can put strong constraints on suitable refinement models, even in the absence of a fundamental Hamiltonian which defines changes of the underlying lattice. Thus, a large class of consistency tests of loop quantum gravity becomes available. In this context, it will also be seen that quantum corrections due to inverse powers of metric components in a constraint are much larger than they appeared recently in more special treatments of isotropic, free scalar models where they were artificially suppressed.

Bojowald, Martin; Cartin, Daniel; Khanna, Gaurav [Institute for Gravitation and the Cosmos, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States); Naval Academy Preparatory School, 197 Elliot Street, Newport, Rhode Island 02841 (United States); Physics Department, University of Massachusetts at Dartmouth, North Dartmouth, Massachusetts 02747 (United States)

2007-09-15

385

Background Cellular differentiation and reprogramming are processes that are carefully orchestrated by the activation and repression of specific sets of genes. An increasing amount of experimental results show that despite the large number of genes participating in transcriptional programs of cellular phenotypes, only few key genes, which are coined here as reprogramming determinants, are required to be directly perturbed in order to induce cellular reprogramming. However, identification of reprogramming determinants still remains a combinatorial problem, and the state-of-art methods addressing this issue rests on exhaustive experimentation or prior knowledge to narrow down the list of candidates. Results Here we present a computational method, without any preliminary selection of candidate genes, to identify reduced subsets of genes, which when perturbed can induce transitions between cellular phenotypes. The method relies on the expression profiles of two stable cellular phenotypes along with a topological analysis stability elements in the gene regulatory network that are necessary to cause this multi-stability. Since stable cellular phenotypes can be considered as attractors of gene regulatory networks, cell fate and cellular reprogramming involves transition between these attractors, and therefore current method searches for combinations of genes that are able to destabilize a specific initial attractor and stabilize the final one in response to the appropriate perturbations. Conclusions The method presented here represents a useful framework to assist researchers in the field of cellular reprogramming to design experimental strategies with potential applications in the regenerative medicine and disease modelling. PMID:24350678

2013-01-01

386

Vortex stability in a multi-layer quasi-geostrophic model: application to Mediterranean Water eddies

NASA Astrophysics Data System (ADS)

The stability of circular vortices to normal mode perturbations is studied in a multi-layer quasi-geostrophic model. The stratification is fitted on the Gulf of Cadiz where many Mediterranean Water (MW) eddies are generated. Observations of MW eddies are used to determine the parameters of the reference experiment; sensitivity tests are conducted around this basic case. The objective of the study is two-fold: (a) determine the growth rates and nonlinear evolutions of unstable perturbations for different three-dimensional (3D) velocity structures of the vortices, (b) check if the different structure of our idealized vortices, mimicking MW cyclones and anticyclones, can induce different stability properties in a model that conserves parity symmetry, and apply these results to observed MW eddies. The linear stability analysis reveals that, among many 3D distributions of velocity, the observed eddies are close to maximal stability, with instability time scales longer than 100 days (these time scales would be less than 10 days for vertically more sheared eddies). The elliptical deformation is most unstable for realistic eddies (the antisymmetric one dominates for small eddies and the triangular one for large eddies); the antisymmetric mode is stronger for cyclones than for anticyclones. Nonlinear evolutions of eddies with radii of about 30 km, and elliptically perturbed, lead to their re-organization into 3D tripoles; smaller eddies are stable and larger eddies break into 3D dipoles. Horizontally more sheared eddies are more unstable and sustain more asymmetric instabilities. In summary, few differences were found between cyclone and anticyclone stability, except for strong horizontal velocity shears.

Carton, Xavier; Sokolovskiy, Mikhail; Ménesguen, Claire; Aguiar, Ana; Meunier, Thomas

2014-12-01

387

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

In support of the U.S. Environmental Protection Agency's (EPA) Superfund Innovative Technology Evaluation (SITE) Program, this report evaluates the Chemfix Technologies, Inc. (Chemfix), solidification/stabilization technology for on-site treatment of hazardous waste. The Chemfix ...

388

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

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....

389

Author's personal copy Mathematical modeling and simulation of seated stability

apparatus isolate motion of the lumbar spine and are used to quantify torso stability (Cholewicki et al to quantify the kinematic variability or stability of the human spine. However, each of these methods understanding of the basin of stability for the human spine and the neuromuscular control parameters

Ross, Shane

390

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.

391

Stability of Li-carbon materials: a molecular modeling study

NASA Astrophysics Data System (ADS)

Materials with exceptionally high content of carbon are used in technologies with various degrees of added value, from quasi-amorphous materials for carbon electrodes used in e.g. lithium batteries to highly-organized materials comprising e.g. nanotubes and fullerenes. The present study aims to test the feasibility of predicting the properties of carbon based materials using (i) molecular modeling and simulation techniques for prediction of compositional stability; and (ii) experimental data regarding materials used for lithium batteries as validation data. It has been found that a higher H/C atomic ratio has a complex influence on lithium uptake. The decrease of the number of the aromatic rings will limit the number of lithium ions allowed in the pore and the increase in pore flexibility will induce a more energetically favorable mechanism for lithium ions uptake (folding/house-of-cards formation against pore expansion).

Nicolau, Dan V.

2004-03-01

392

Linear-Stability Analysis of Immiscible Displacement: Part 1Simple Basic Flow Profiles

The linear stability of immiscible, two-phase-flow displacement processes in porous media is examined. Multiphase-flow characteristics are included in the stability description through relative-permeability and capillary-pressure functions. A linear-stability analysis of the steady-state saturation and pressure distributions is carried out in terms of normal modes. The resulting linearized eigenvalue problems describing the early evolution of unstable modes show a certain similarity

Y. C. Yortsos; A. B. Huang

1986-01-01

393

Stabilizing effects in spatial parasitoid–host and predator–prey models: a review

We review the literature on spatial host–parasitoid and predator–prey models. Dispersal on its own is not stabilizing and can destabilize a stable local equilibrium. We identify three mechanisms whereby limited dispersal of hosts and parasitoids combined with other features, such as spatial and temporal heterogeneity, can promote increased persistence and stability. The first mechanism, “statistical stabilization”, is simply the statistical

Cheryl J. Briggs; Martha F. Hoopes

2004-01-01

394

TASK-LEVEL MODELS FOR IMAGE-STABILIZATION BEHAVIORS IN ANIMALS

TASK-LEVEL MODELS FOR IMAGE-STABILIZATION BEHAVIORS IN ANIMALS by Eatai Roth A dissertation. Animal behavior arises from a concert of sensory, computational, and mechanical systems. Often-stabilization behaviors. Image- stabilization describes a broad class of behaviors in which animals modulate movement

395

NASA Technical Reports Server (NTRS)

Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin is caused by an undamping of the aerodynamics in one of the lower frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic lineloads derived from steady rigid computational fluid dynamics (CFD). However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers where experiment or unsteady computational aeroelastic (CAE) analysis show a reduced or even negative aerodynamic damping. This paper will present a method of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics. The enhanced formulation uses unsteady CFD to compute the response of selected lower frequency modes. The response is contained in a time history of the vehicle lineloads. A proper orthogonal decomposition of the unsteady aerodynamic lineload response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping and mass matrices. The results of the enhanced quasi-static aeroelastic stability analysis are compared with the damping and frequency computed from unsteady CAE analysis and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady CAE analysis.

Bartels, Robert E.

2011-01-01

396

Operations and Modeling Analysis

NASA Technical Reports Server (NTRS)

The Reliability and Maintainability Analysis Tool (RMAT) provides NASA the capability to estimate reliability and maintainability (R&M) parameters and operational support requirements for proposed space vehicles based upon relationships established from both aircraft and Shuttle R&M data. RMAT has matured both in its underlying database and in its level of sophistication in extrapolating this historical data to satisfy proposed mission requirements, maintenance concepts and policies, and type of vehicle (i.e. ranging from aircraft like to shuttle like). However, a companion analyses tool, the Logistics Cost Model (LCM) has not reached the same level of maturity as RMAT due, in large part, to nonexistent or outdated cost estimating relationships and underlying cost databases, and it's almost exclusive dependence on Shuttle operations and logistics cost input parameters. As a result, the full capability of the RMAT/LCM suite of analysis tools to take a conceptual vehicle and derive its operations and support requirements along with the resulting operating and support costs has not been realized.

Ebeling, Charles

2005-01-01

397

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

398

Stability analysis of a noise control system in a duct by using delay differential equation

NASA Astrophysics Data System (ADS)

The paper deals with the criteria for the closed-loop stability of a noise control system in a duct. To study the stability of the system, the model of delay differential equation is derived from the propagation of acoustic wave governed by a partial differential equation of hyperbolic type. Then, a simple feedback controller is designed, and its closed-loop stability is analyzed on the basis of the derived model of delay differential equation. The obtained criteria reveal the influence of the controller gain and the positions of a sensor and an actuator on the closed-loop stability. Finally, numerical simulations are presented to support the theoretical results.

Haraguchi, Masakazu; Hu, Hai Yan

2009-02-01

399

F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis

NASA Technical Reports Server (NTRS)

An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.

Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.

1984-01-01

400

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

401

Global Stability Analysis of an End-to-End Congestion Control Scheme

or variations in round trip time (RTT) the packets experience. Several congestion control and pricing algorithmsGlobal Stability Analysis of an End-to-End Congestion Control Scheme for General Topology Networks the stability properties of an end-to-end congestion control scheme under fixed heterogeneous delays

Alpcan, Tansu

402

Stability of Vortex Pairs over Slender Conical Bodies: Analysis and Numerical Computation

Stability of Vortex Pairs over Slender Conical Bodies: Analysis and Numerical Computation Jinsheng to study the formation and stability of stationary symmetric and asymmetric vortex pairs over slender responsible for the asymmetry of separation vortices over slender conical bodies. I. Introduction AN INITIALLY

Liu, Feng

403

Stability and Change in Work Values: A Meta-Analysis of Longitudinal Studies

ERIC Educational Resources Information Center

A meta-analysis of longitudinal studies was conducted to investigate stability and change in work values across the life span. Both rank-order stability and mean-level change were investigated using an integrative classification for intrinsic, extrinsic, social and status work values (Ross, Schwartz, & Surkis, 1999). Results of rank-order…

Jin, Jing; Rounds, James

2012-01-01

404

Analysis of the stability margins of the Space Station Freedom Electrical Power System

There is a need to define verifiable and testable stability margins for the Space Station Freedom Electric Power System Primary. Source\\/load impedance ratio margins are analyzed as candidates for assessing the power system stability. Limitations, as well as the advantages of the impedance ratio method, are discussed. A correlation is established between using this method and eigenvalue analysis as well

Igor Lazbin; Bruce R. Needham

1993-01-01

405

Pattern memory analysis based on stability theory of cellular neural networks

Pattern memory analysis based on stability theory of cellular neural networks Zhigang Zeng a,*, De-dimensional cellular neural network can have even (62n ) memory patterns. In addition, the estimations of attractive rights reserved. Keywords: Stability; Pattern memory; Cellular neural networks; Isolated equilibrium

Hefei Institute of Intelligent Machines

406

Metacomputing for On-Line Stability Analysis in Power Systems: A Proposal

The on-line Transient Stability Analysis (TSA) is a challenge problem in power systems, concerning the detection of fault conditions (contingencies) which can produce instability in the power networks. In the paper the issues related to the use of metacomputing for on-line TSA have been analyzed and a solution is proposed allowing the simulation of hundreds of dynamic stability contingencies as

Giovanni Aloisio; M. A. Bochicchio; M. La Scala

1996-01-01

407

STABILITY ANALYSIS FOR BUOYANCY-OPPOSED FLOWS IN POLOIDAL DUCTS OF THE DCLL BLANKET

STABILITY ANALYSIS FOR BUOYANCY-OPPOSED FLOWS IN POLOIDAL DUCTS OF THE DCLL BLANKET N. Vetcha, S of the buoyancy assisted flow in DCLL blanket based on the solution of the Orr- Sommefeld equation for MHD flows is used here to address the stability of the buoyancy-opposed (downward) flows in the DCLL blanket

Abdou, Mohamed

408

LINEAR STABILITY ANALYSIS FOR STANDING WAVES OF SECOND ORDER IN TIME PDE'S

LINEAR STABILITY ANALYSIS FOR STANDING WAVES OF SECOND ORDER IN TIME PDE'S MILENA STANISLAVOVA AND ATANAS STEFANOV Abstract. We develop a general theory to treat the linear stability of standing waves - the standing wave solutions of (1). These are solutions in the form u(t, x) = eit(x), where R1 and is real

Stefanov, Atanas G.

409

Frequency analysis of the stability of asteroids in the framework of the restricted, three Cedex 4 (France) (elena@obs-nice.fr) October 16, 2003 Abstract The stability of some asteroids an isoenergetic KAM theorem. More precisely, having fixed a level of energy related to the motion of the asteroid

410

Toward Models for Forensic Analysis

Toward Models for Forensic Analysis Sean Peisert (UC San Diego) Matt Bishop (UC Davis) Sid Karin is Forensic Analysis? Forensic analysis is the process of answering the questions: How did an event take place? What was the nature of the event? What were the effects of the event? Forensic analysis applies

Peisert, Sean

411

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

412

A combined conceptual model for the effects of fissure-induced infiltration on slope stability

NASA Astrophysics Data System (ADS)

In humid and subhumid Mediterranean environments the disruption of the vegetation cover by in particular shallow landslides limits the area in which erodible material is exposed to overland flow. On short temporal scales the hydrological system that allows for the generation of critical pore pressures or soil moisture conditions on the potential shear surface determines the occurrence of these landslides. Hence the relative contribution of landsliding to land degradation processes can be quantified in terms of its magnitude and frequency through a semiphysical hillslope model that links the relevant hydrological processes to a stability analysis. For the development of such a combined model for hydrology and slope stability a conceptualization of the process system is needed. Through the implementation of the resulting model in a GIS environment the effect of topography, to which the occurrence of landslides is intrinsically linked, can be incorporated. In addition, the spatial variation of hydrological and geomechanical parameters can be incorporated in the model. This is important since the occurrence and extent of shallow landslides is directly dependent on the net rainfall input in the hydrological system, as defined by the land cover of the area. In this paper a conceptual model is presented that combines a description of the hydrology with an assessment of the slope stability. The conceptual framework of this model is based on field observations in the Alcoy area (SE Spain). In this area shallow landslides occur on steep, unsaturated slopes in marly deposits of Miocene age, at the boundary between regolith and bedrock (1-2 m depth). Given the low matric permeability of the marl it has been assumed that preferential flow along distinct sets of fissures by-passing slower matric percolation might account for the observed response time of landslides to rainfall events. The fissures in the regolith are either relict primary bedrock structures (discontinuities) or are formed by weathering, creep and shear; they are supplied with water by subsurface flow through the more permeable rootzone. With the combined slope stability model, which is programmed in the meta-language embedded in the PCRaster GIS package, a sensitivity analysis has been performed to assess the impact of fissure flow on the occurrence of landslides in a small catchment of 1.2 km2 near Alcoy.

van Beek, L. P. H.; van Asch, Th. W. J.

413

1 123 Model-Driven Risk Analysis The CORAS Approach | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | >springer.com ISBN 978-3-642-12322-1 Model-DrivenRiskAnalysis Mass Soldal Lund BjÃ¸rnar Solhaug Ketil StÃ¸len LundÂ·Solhaug StÃ¸len Lund Â· Solhaug Â· StÃ¸len Model-Driven Risk Analysis The term"risk"is known from many

StÃ¸len, Ketil

414

Strength Analysis of Coconut Fiber Stabilized Earth for Farm Structures

NASA Astrophysics Data System (ADS)

Investigation of the strength characteristic of soil from alluvial deposit of River Benue in makurdi stabilized with coconut fiber as a stabilizer was carried as local building material for farm structure. Processed coconut fibers were mixed with the soil at four different mix ratios of 1% fiber, 2% fiber, 3% fiber and 4% fiber by percentage weight with 0% fiber as control. Compaction test and compressive strength were carried out on the various stabilizing ratio. From the compaction test, the correlation between the maximum dry density and optimum moisture content is a second order polynomial with a coefficient of 63% obtained at1.91kg/m3and 20.0% respectively while the compressive strength test shows an optimum failure load of 8.62N/mm2 at 2%fibre:100% soil mix ratio at 2.16 maximum dry density.

Enokela, O. S.; P. O, Alada

2012-07-01

415

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

416

40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.

Code of Federal Regulations, 2011 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

417

40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.

Code of Federal Regulations, 2014 CFR

40 Protection of Environment 33 2014-07-01 2014-07-01... PM-stabilization and weighing environments for gravimetric analysis. 1065...Section 1065.190 Protection of Environment ENVIRONMENTAL PROTECTION...

2014-07-01

418

40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.

Code of Federal Regulations, 2012 CFR

40 Protection of Environment 34 2012-07-01 2012-07-01... PM-stabilization and weighing environments for gravimetric analysis. 1065...Section 1065.190 Protection of Environment ENVIRONMENTAL PROTECTION...

2012-07-01

419

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

420

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...

421

Stability and robustness analysis tools for marine robot localization and mapping applications

The aim of this analysis is to explore the fundamental stability issues of a robotic vehicle carrying out localization, mapping, and feedback control in a perturbation-filled environment. Motivated by the application of ...

Englot, Brendan J

2009-01-01

422

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...

423

Short and long-term genome stability analysis of prokaryotic genomes

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. PMID:23651581

2013-01-01

424

EXPOSURE ANALYSIS MODELING SYSTEM (EXAMS)

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...

425

In this work, differential acid neutralization analysis, chemical analysis of selected leachates and mineralogical study (XRD and SEM-EDS) are combined to investigate the relationship between mineralogy and leaching behavior of hydroxide sludge doped in Zn and Cr stabilized\\/solidified by hydraulic binders. The leaching behavior of stabilized hydroxide sludge is controlled by the dissolution of portlandite (pH ~12) followed by the

O. Peyronnard; M. Benzaazoua; D. Blanc; P. Moszkowicz

2009-01-01

426

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

427

Stability analysis of position and force control for robot arms

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

428

Nonlinear global stability analysis of compressor stall phenomena

NASA Technical Reports Server (NTRS)

Compressor stall phenomena are analyzed from the point of view of nonlinear control theory, based on bifurcation-catastrophe techniques. This new approach appears promising and offers insight into such well-known compressor instability problems as surge and rotating stall and suggests strategies for recovery. Three interlocking dynamic nonlinear state space models are developed. It is shown that the problem of rotating stall can be viewed as an induced bifurcation of solution of the unstalled model. Hysteresis effects are shown to exist in the stall/recovery process. Surge cycles are observed for some critical parameter values. The oscillatory behavior is seen to be due to development of limit cycles, generated by Hopf bifurcation of solutions. More specifically, it is observed that at certain critical values of parameters, a family of stable limit cycles with growning and then diminishing amplitudes is generated, then giving rise to an unstable family of limit cycles. This unstable family in turn bifurcates into other unstable families. To further illustrate the utility of the methodology, some partial computation of domains is carried out, and parameter sensitivity analysis is performed.

Razavi, H.

1985-01-01

429

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

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

2013-10-01

430

Stability of the melting hedgehog in a Landau-de Gennes model

Stability of the melting hedgehog in a Landau-de Gennes model Radu IGNAT UniversitÂ´e Paul of the melting hedgehog March 2014, Pavia #12;Landau-de Gennes Model We consider the following (non constants and |Q|2 := tr(Q2 ). Radu Ignat Stability of the melting hedgehog March 2014, Pavia 1 #12;Melting

Segatti, Antonio

431

Atomistic Modeling of Macromolecular Crowding Predicts Modest Increases in Protein Folding that macromolecular crowding can increase protein folding stability, but depending on details of the models (e.g., how on the effects of macro- molecular crowding on protein folding and binding stability has been reached. Crowders

Weston, Ken

432

Generalized modeling of drilling vibrations. Part II: Chatter stability in frequency domain

A time domain model of the drilling process and hole formation mechanism is presented in Part I, and the general solution of drilling chatter stability in frequency domain is presented in this paper. The drill's flexibility in torsional, axial and lateral directions are considered in determining the regenerative chip thickness. Stability is modelled as a fourth order eigenvalue problem with

Jochem C. Roukema; Yusuf Altintas

2007-01-01

433

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

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

434

Modeling and dynamic stabilization for suspension system using tuned LC circuit

The authors develop a transfer function model of magnetic suspension systems using a tuned LC circuit by linearizing system equations near the equilibrium state. This model not only explains nicely the inherent dynamic instability but also gives the necessary condition of stability. The authors also present a novel dynamic stabilization method for magnetic suspension systems using a tuned LC circuit.

Ju Jin; Toshiro Higuchi

1992-01-01

435

The validity of stability measures: a modelling approach.

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

2011-09-01

436

Polynomial elimination theory and non-linear stability analysis for the Euler equations

NASA Technical Reports Server (NTRS)

Numerical methods are presented that exploit the polynomial properties of discretizations of the Euler equations. It is noted that most finite difference or finite volume discretizations of the steady-state Euler equations produce a polynomial system of equations to be solved. These equations are solved using classical polynomial elimination theory, with some innovative modifications. This paper also presents some preliminary results of a new non-linear stability analysis technique. This technique is applicable to determining the stability of polynomial iterative schemes. Results are presented for applying the elimination technique to a one-dimensional test case. For this test case, the exact solution is computed in three iterations. The non-linear stability analysis is applied to determine the optimal time step for solving Burgers' equation using the MacCormack scheme. The estimated optimal time step is very close to the time step that arises from a linear stability analysis.

Kennon, S. R.; Dulikravich, G. S.; Jespersen, D. C.

1986-01-01

437

Transient Stability Simulation of Wind Generator Expressed by Two-Mass Model

NASA Astrophysics Data System (ADS)

Recently, wind power generation is increasing in the world. In the wind power stations, induction machines are mostly used as generators. Since induction generators have a stability problem similar to the transient stability of synchronous machines, it is important to analyze the transient stability of power systems including wind generators. Although there have been some reports analyzing the transient stability problem, wind turbine and wind generator are, in most cases, modeled as one mass shaft system having total inertia constant. This paper presents simulation analyses of transient stability of power system including induction generator which is expressed by a two-mass shaft model and analyzes an effect of shaft system modeling on the transient stability characteristics. Simulations are performed by PSCAD/EMTDC in this study.

Shima, Yoshikazu; Takahashi, Rion; Murata, Toshiaki; Tamura, Junji; Tomaki, Yuichi; Tominaga, Shinobu; Sakahara, Atsushi

438

Linearized stability analysis of gravastars in noncommutative geometry

NASA Astrophysics Data System (ADS)

In this work, we find exact gravastar solutions in the context of noncommutative geometry, and explore their physical properties and characteristics. The energy density of these geometries is a smeared and particle-like gravitational source, where the mass is diffused throughout a region of linear dimension due to the intrinsic uncertainty encoded in the coordinate commutator. These solutions are then matched to an exterior Schwarzschild spacetime. We further explore the dynamical stability of the transition layer of these gravastars, for the specific case of ? = M 2/ ? < 1.9, where M is the black hole mass, to linearized spherically symmetric radial perturbations about static equilibrium solutions. It is found that large stability regions exist and, in particular, located sufficiently close to where the event horizon is expected to form.

Lobo, Francisco S. N.; Garattini, Remo

2013-12-01

439

Time Series Analysis and Stability of ICRF2 sources

NASA Astrophysics Data System (ADS)

We have studied the precision and stability of the positions of the radio sources observed in 3450 VLBI sessions from 1984 to 2011 using VieVS (Vienna VLBI Software). We first estimated time-series of the radio source coordinates. Each time series was then analyzed according to stability and apparent proper motion of the source. The results were compared with the requirements for defining sources as specified by the IERS (Fey et al. 2009). Thus, with this study we aim to produce an updated list of radio sources useful for geodetic and astrometric VLBI as well as to assess the precision of them. Furthermore, we intend to provide an input to the realization of the next ICRF3.

Raposo-Pulido, V.; Krásná, H.; Nilsson, T.; Heinkelmann, R.; Schuh, H.

2013-08-01

440

The planar X-junction flow: stability analysis and control

and ?ij is the Kronecker delta. SEM combines the geometrical flexibility of finite elements with the high accuracy of spectral methods. It results in exponential convergence of the solution when the polynomial order is increased, called p-refinement (see... % of the inflow velocity can stabilize the flow until Re = 150, which is almost double the critical Reynolds number of the uncontrolled case. Higher suction amplitudes were also tested but did not result in any further increase of the critical Reynolds number...

Lashgari, Iman; Tammisola, Outi; Citro, Vincenzo; Juniper, Matthew P.; Brandt, Luca

2014-07-29

441

Stability analysis of an F/A-18 E/F cable mount m odel

NASA Technical Reports Server (NTRS)

A full-span F/A-18 E/F cable mounted wind tunnel model is part of a flutter clearance program at the NASA Langley Transonic Dynamics Tunnel. Parametric analysis of this model using GRUMCBL software was conducted to assess stability for wind tunnel tests. Two configuratio