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1

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

GonĂ§alves, Jorge

2

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

3

Stability analysis for a peri-implant osseointegration model.

We investigate stability of the solution of a set of partial differential equations, which is used to model a peri-implant osseointegration process. For certain parameter values, the solution has a 'wave-like' profile, which appears in the distribution of osteogenic cells, osteoblasts, growth factor and bone matrix. This 'wave-like' profile contradicts experimental observations. In our study we investigate the conditions, under which such profile appears in the solution. Those conditions are determined in terms of model parameters, by means of linear stability analysis, carried out at one of the constant solutions of the simplified system. The stability analysis was carried out for the reduced system of PDE's, of which we prove, that it is equivalent to the original system of equations, with respect to the stability properties of constant solutions. The conclusions, derived from the linear stability analysis, are extended for the case of large perturbations. If the constant solution is unstable, then the solution of the system never converges to this constant solution. The analytical results are validated with finite element simulations. The simulations show, that stability of the constant solution could determine the behavior of the solution of the whole system, if certain initial conditions are considered. PMID:22327881

Prokharau, Pavel; Vermolen, Fred

2013-01-01

4

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

5

Models and Stability Analysis of Boiling Water Reactors

We have studied the nuclear-coupled thermal-hydraulic stability of boiling water reactors (BWRs) using a model that includes: space-time modal neutron kinetics based on spatial w-modes; single- and two-phase flow in parallel boiling channels; fuel rod heat conduction dynamics; and a simple model of the recirculation loop. The BR model is represented by a set of time-dependent nonlinear ordinary differential equations, and is studied as a dynamical system using the modern bifurcation theory and nonlinear dynamical systems analysis. We first determine the stability boundary (SB) - or Hopf bifurcation set- in the most relevant parameter plane, the inlet-subcooling-number/external-pressure-drop plane, for a fixed control rod induced external reactivity equal to the 100% rod line value; then we transform the SB to the practical power-flow map used by BWR operating engineers and regulatory agencies. Using this SB, we show that the normal operating point at 100% power is very stable, that stability of points on the 100% rod line decreases as the flow rate is reduced, and that operating points in the low-flow/high-power region are least stable. We also determine the SB that results when the modal kinetics is replaced by simple point reactor kinetics, and we thereby show that the first harmonic mode does not have a significant effect on the SB. However, we later show that it nevertheless has a significant effect on stability because it affects the basin of attraction of stable operating points. Using numerical simulations we show that, in the important low-flow/high-power region, the Hopf bifurcation that occurs as the SB is crossed is subcritical; hence, growing oscillations can result following small finite perturbations of stable steady-states on the 100% rod line at points in the low-flow/high-power region. Numerical simulations are also performed to calculate the decay ratios (DRs) and frequencies of oscillations for various points on the 100% rod line. It is determined that the U.S. NRC requirement of DR is not rigorously satisfied in the low-flow/high-power region; hence, this region should be avoided during normal startup and shutdown operations. The frequency of oscillation is shown to decrease as the flow rate is reduced. Moreover, the simulation frequency of 0.5Hz determined in the low-flow/high-power region is consistent with those observed during actual instability incidents. Additional numerical simulations show that in the low-flow/high-power region, for the same initial conditions, the use of point kinetics leads to damped oscillations, whereas the model that includes the modal neutron kinetics equations results in growing nonlinear oscillations.

John Dorning

2002-04-15

6

Stability Analysis of a Model for Foreign Body Fibrotic Reactions

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

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

2012-01-01

7

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

8

An approach for stability analysis of polynomial fuzzy model-based control systems

Stability analysis of polynomial fuzzy model-based (PFMB) control systems under the parallel distributed compen- sation (PDC) design technique is investigated. A new polynomial fuzzy controller (PFC) is introduced to release conservativeness in the existing approaches. Compared to the conventional (PFC), the controller under consideration in this paper has a favorable property which introduces some more variables in the stability conditions

Mohammand Narimani; H. K. Lam; K. Althoefer; R. Dilmaghani; Charles Wolfe; C. Deters

2011-01-01

9

Stability analysis of two-dimensional models of three-dimensional convection

Analytical and numerical methods are used to study the linear stability of spatially periodic solutions for various two-dimensional equations which model thermal convection in fluids. This analysis suggests new model equations that will be useful for investigating questions such as wave number selection, pattern formation, and the onset of turbulence in large aspect ratio Rayleigh-Benard systems. In particular, we construct a nonrelaxational model that has stability boundaries similar to those calculated for intermediate Prandtl number fluids.

Greenside, H.S.; Cross, M.C.

1984-12-01

10

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

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

Wu, Jiang Hao; Sun, Mao

2012-01-01

11

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

12

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

13

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

14

Stability of the Human Respiratory Control System. Part I: Analysis of a twoÂdimensional 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

15

A synergetic model describing the state of an ultrathin lubricant layer squeezed between two atomically smooth solid surfaces operating in the boundary friction mode has been developed further. To explain the presence of different operation modes of the system for various sets of its main parameters, the mathematical analysis of the synergetic model is carried out. The type of functioning a tribological system is described in accordance with the stability character of singular points, and the diagrams distinguishing various operation modes are obtained. Phase portraits corresponding to different stability types are plotted for all diagram areas. A stick-slip mode of motion that is often observed experimentally is described.

Iakov A. Lyashenko; Nataliia N. Manko

2014-01-17

16

Stability analysis of sampled-data output-feedback polynomial fuzzy-model-based control systems

This paper presents the stability analysis of sampled-data output-feedback polynomial fuzzy-model-based control systems. A sampled-data output-feedback polynomial fuzzy controller is proposed to control the nonlinear plant represented by the polynomial fuzzy model. The proposed sampled-data output-feedback polynomial fuzzy controller makes use of the system output for control. Furthermore, due to the sampling activity, the control signal will be kept constant

H. K. Lam; Mohammad Narimani

2010-01-01

17

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

18

The paper describes concept and implementation details of integrating a finite element module for dike stability analysis Virtual Dike into an early warning system for flood protection. The module operates in real-time mode and includes fluid and structural sub-models for simulation of porous flow through the dike and for dike stability analysis. Real-time measurements obtained from pore pressure sensors are fed into the simulation module, to be compared with simulated pore pressure dynamics. Implementation of the module has been performed for a real-world test case - an earthen levee protecting a sea-port in Groningen, the Netherlands. Sensitivity analysis and calibration of diffusivities have been performed for tidal fluctuations. An algorithm for automatic diffusivities calibration for a heterogeneous dike is proposed and studied. Analytical solutions describing tidal propagation in one-dimensional saturated aquifer are employed in the algorithm to generate initial estimates of diffusivities.

Melnikova, N B; Sloot, P M A

2012-01-01

19

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

20

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

NASA Astrophysics Data System (ADS)

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

Nandakumar, K.; Wiercigroch, Marian

2013-05-01

21

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

22

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

23

NASA Astrophysics Data System (ADS)

For a number of years, the United States Federal Government has been formulating the Next Generation Air Transportation System plans for National Airspace System improvement. These improvements attempt to address air transportation holistically, but often address individual improvements in one arena such as ground or in-flight equipment. In fact, air transportation system designers have had only limited success using traditional Operations Research and parametric modeling approaches in their analyses of innovative operations. They need a systemic methodology for modeling of safety-critical infrastructure that is comprehensive, objective, and sufficiently concrete, yet simple enough to be deployed with reasonable investment. The methodology must also be amenable to quantitative analysis so issues of system safety and stability can be rigorously addressed. The literature suggests that both agent-based models and network analysis techniques may be useful for complex system development and analysis. The purpose of this research is to evaluate these two techniques as applied to analysis of commercial air carrier schedule (route) stability in daily operations, an important component of air transportation. Airline-like routing strategies are used to educe essential elements of applying the method. Two main models are developed, one investigating the network properties of the route structure, the other an Agent-based approach. The two methods are used to predict system properties at a macro-level. These findings are compared to observed route network performance measured by adherence to a schedule to provide validation of the results. Those interested in complex system modeling are provided some indication as to when either or both of the techniques would be applicable. For aviation policy makers, the results point to a toolset capable of providing insight into the system behavior during the formative phases of development and transformation with relatively low investment. Both Agent-Based Modeling and Network Analysis were found to be useful in this context, particularly when applied with an eye towards the system context, and concentrated effort on capturing the salient features of the system of interest.

Conway, Sheila Ruth

24

Slope Stability Analysis Program

NSDL National Science Digital Library

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

2008-07-17

25

NASA Astrophysics Data System (ADS)

Magnetic shape memory alloys (MSMAs) are a class of active materials that deform under magnetic and mechanical loading conditions. This work is concerned with the modeling of MSMAs constitutive responses. The hysteretic magneto-mechanical responses of such materials are governed by two major mechanisms which are variant reorientation and field induced phase transformation (FIPT). The most widely used material for variant reorientation is Ni2MnGa which can produce up to 6% magnetic field induced strain (MFIS) under 5 MPa actuation stress. The major drawback of this material is a low blocking stress, which is overcome in the NiMnCoIn material system through FIPT. This magnetic alloy can exhibit 5% MFIS under 125 MPa actuation stress. The focus of this work is to capture the key magneto-thermo-mechanical responses of such mechanisms through phenomenological modeling. In this work a detailed thermodynamic framework for the electromagnetic interaction within a continuum solid is presented. A Gibbs free energy function is postulated after identifying the external and internal state variables. Material symmetry restrictions are imposed on the Gibbs free energy and on the evolution equations of the internal state variables. Discrete symmetry is considered for single crystals whereas continuous symmetry is considered for polycrystalline materials. The constitutive equations are derived in a thermodynamically consistent way. A specific form of Gibbs free energy for FIPT is proposed and the explicit form of the constitutive equations is derived from the generalized formulation. The model is calibrated from experimental data and different predictions of magneto-thermo-mechanical loading conditions are presented. The generalized constitutive equations are then reduced to capture variant reorientation. A coupled magneto-mechanical boundary value problem (BVP) is solved that accounts for variant reorientation to investigate the influence of the demagnetization effect on the magnetic field and the effect of Maxwell stress on the Cauchy stress. The BVP, which mimics a real experiment, provides a methodology to correlate the difference between the externally measured magnetic data and internal magnetic field of the specimen due to the demagnetization effect. The numerical results show that localization zones appear inside the material between a certain ranges of applied magnetic field. Stability analysis is performed for variant reorientation to analyze these numerical observations. Detailed numerical and analytical analysis is presented to investigate these localization zones. Magnetostatic stability analysis reveals that the MSMA material system becomes unstable when localizations appear due to non-linear magnetization response. Coupled magneto-mechanical stability analysis shows that magnetically induced localization creates stress-localizations in the unstable zones. A parametric study is performed to show the constraints on material parameters for stable and unstable material responses.

Haldar, Krishnendu

26

Stability analysis of a viscoelastic model for ion-irradiated silicon

To study the effect of stress within the thin amorphous film generated atop Si irradiated by Ar+, we model the film as a viscoelastic medium into which the ion beam continually injects biaxial compressive stress. We find that at normal incidence, the model predicts a steady compressive stress of a magnitude comparable to experiment. However, linear stability analysis at normal incidence reveals that this mechanism of stress generation is unconditionally stabilizing due to a purely kinematic material flow, depending on none of the material parameters. Thus, despite plausible conjectures in the literature as to its potential role in pattern formation, we conclude that beam stress at normal incidence is unlikely to be a source of instability at any energy, supporting recent theories attributing hexagonal ordered dots to the effects of composition. In addition, we find that the elastic moduli appear in neither the steady film stress nor the leading order smoothening, suggesting that the primary effects of stress can be captured even if elasticity is neglected. This should greatly simplify future analytical studies of highly nonplanar surface evolution, in which the beam-injected stress is considered to be an important effect.

Scott A. Norris

2012-01-12

27

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

28

NASA Technical Reports Server (NTRS)

NASA developed stability and frequency response analysis techniques were applied to a dynamic blade row compression component stability model to provide a more economic approach to surge line and frequency response determination than that provided by time-dependent methods. This blade row model was linearized and the Jacobian matrix was formed. The clean-inlet-flow stability characteristics of the compressors of two J85-13 engines were predicted by applying the alternate Routh-Hurwitz stability criterion to the Jacobian matrix. The predicted surge line agreed with the clean-inlet-flow surge line predicted by the time-dependent method to a high degree except for one engine at 94% corrected speed. No satisfactory explanation of this discrepancy was found. The frequency response of the linearized system was determined by evaluating its Laplace transfer function. The results of the linearized-frequency-response analysis agree with the time-dependent results when the time-dependent inlet total-pressure and exit-flow function amplitude boundary conditions are less than 1 percent and 3 percent, respectively. The stability analysis technique was extended to a two-sector parallel compressor model with and without interstage crossflow and predictions were carried out for total-pressure distortion extents of 180 deg, 90 deg, 60 deg, and 30 deg.

Tesch, W. A.; Moszee, R. H.; Steenken, W. G.

1976-01-01

29

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

30

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

31

NASA Astrophysics Data System (ADS)

Miyashita found that the long-term memory of visual stimuli is stored in the monkey’s inferior temporal cortex and that the temporal correlation in terms of the learning order of visual stimuli is converted into spatial correlation in terms of the firing rate patterns of the neuron group. To explain Miyashita’s findings, Griniasty et al. [Neural Comput. 5 (1993) 1] and Amit et al. [J. Neurosci. 14 (1994) 6435] proposed the attractor neural network model, and the Amit model has been examined only for the stable state acquired by storing memory patterns in a fixed sequence. In the real world, however, the learning order has statistical continuity but it also has randomness, and the stability of the state changes depending on the statistical properties of learning order when memory patterns are stored randomly. In addition, it is preferable for the stable state to become an appropriate attractor that reflects the relationship between memory patterns by the statistical properties of the learning order. In this study, we examined the dependence of the stable state on the statistical properties of the learning order without modifying the Amit model. The stable state was found to change from the correlated attractor to the Hopfield or Mp attractor, which is the mixed state with all memory patterns when the rate of random learning increases. Furthermore, we found that if the statistical properties of the learning order change, the stable state can change to an appropriate attractor reflecting the relationship between memory patterns.

Tomoyuki Kimoto,; Tatsuya Uezu,; Masato Okada,

2010-06-01

32

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

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

Marcelo Vasconcellos; Steven Mackinson; Katherine Sloman; Daniel Pauly

1997-01-01

33

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

34

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

35

Modelling of rotary converter in electrical railway traction power-systems for stability analysis

The central European 16.7-Hz railway grid is fed-beside by own power sources- by rotary and static converters. In context of recent low-frequency stability problems in the Scandinavia region, primary the interaction of four-quadrant line-side traction-converter control and surrounding rotary converters is a major concern. Therefore, adequate models for time-domain simulation are necessary. In this paper, a set of differential equations-representing

Carsten Heising; Jie Fang; Roman Bartelt; Volker Staudt; Andreas Steimel

2010-01-01

36

We examine the global, hydrodynamic stability of solar latitudinal differential rotation in a ``shallow-water'' model of the tachocline. Charbonneau, Dikpati, & Gilman have recently shown that two-dimensional disturbances are stable in the tachocline (which contains a pole-to-equator differential rotation s=18%), driven primarily by the kinetic energy of differential rotation extracted through the work of the Reynolds stress. For low effective

Mausumi Dikpati; Peter A. Gilman

2001-01-01

37

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

38

Gamete and early embryo development are important stages when genome-scale epigenetic transitions are orchestrated. The apparent lack of remodeling of differential imprinted DNA methylation during preimplantation development has lead to the argument that epigenetic disruption by assisted reproductive technologies (ARTs) is restricted to imprinted genes. We contend that aberrant imprinted methylation arising from assisted reproduction or infertility may be an indicator of more global epigenetic instability. Here, we review the current literature on the effects of ARTs, including ovarian stimulation, in vitro oocyte maturation, oocyte cryopreservation, IVF, ICSI, embryo culture, and infertility on genomic imprinting as a model for evaluating epigenetic stability. Undoubtedly, the relationship between impaired fertility, ARTs, and epigenetic stability is unquestionably complex. What is clear is that future studies need to be directed at determining the molecular and cellular mechanisms giving rise to epigenetic errors. PMID:22956517

Denomme, Michelle M; Mann, Mellissa R W

2012-10-01

39

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

40

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

41

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

42

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 L2 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 L2, and aerodynamic and gravity gradient during phasing-loop orbits, were calculated and simulated. 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.; ODonnell, J. R., Jr.; Markley, F. L.

1998-01-01

43

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. PMID:25615342

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

2014-12-31

44

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

45

Stability Analysis and Stabilization of Randomly Switched Systems

Stability Analysis and Stabilization of Randomly Switched Systems Debasish Chatterjee, and Daniel Liberzon, Abstract-- This article is concerned with stability analysis and stabilization of randomly for stochastic stability of the switched system when the subsystems do not possess control inputs; not every

Sontag, Eduardo

46

Implementation of a Single-Stage-To-Orbit (SSTO) model for stability and control analysis

NASA Technical Reports Server (NTRS)

Three NASA centers: Marshall Space Flight Center (MSFC), Langley Research Center (LaRC), and Johnson Space Center (JSC) are currently involved in studying a family of single-stage- and two-stage-to-orbit (SSTO/TSTO) vehicles to serve as the next generation space transportation system (STS). A rocketed winged-body is the current focus. The configuration (WB001) is a vertically-launched, horizontally-landing system with circular cross-section. Preliminary aerodynamic data was generated by LaRC and is a combination of wind-tunnel data, empirical methods, and Aerodynamic Preliminary Analysis System-(APAS) generated values. JSC's efforts involve descent trajectory design, stability analysis, and flight control system synthesis. Analysis of WB001's static stability indicates instability in 'tuck' (C(sub mu) less than 0: Mach = 0.30, alpha greater than 3.25 deg; Mach = 0.60, alpha greater than 8.04), an unstable dihedral effects (C(sub l(beta)) greater than 0: Mach = 30,alpha less than 12 deg.; Mach = 0.60, alpha less than 10.00 deg.), and, most significantly, an unstable weathercock stability derivative, C(sub n(beta)), at all angles of attack and subsonic Mach numbers. Longitudinal trim solutions for Mach = 0.30 and 0.60 indicate flight path angle possibilities ranging from around 12 (M = 0.30) to slightly over 20 degrees at Mach = 0.60. Trim angles of attack increase from 6.24 at Mach 0.60 and 10,000 feet to 17.7 deg. at Mach 0.30, sea-level. Lateral trim was attempted for a design cross-wind of 25.0 knots. The current vehicle aerodynamic and geometric characteristics will only yield a lateral trim solution at impractical tip-fin deflections (approximately equal to 43 deg.) and bank angles (21 deg.). A study of the lateral control surfaces, tip-fin controllers for WB001, indicate increased surface area would help address these instabilities, particularly the deficiency in C(sub n(beta)), but obviously at the expense of increased vehicle weight. Growth factors of approximately 7 were determined using a design C(sub n(beta)) of 0.100/radian (approximate subsonic values for the orbiter).

Ingalls, Stephen A.

1995-01-01

47

Implementation of a Single-Stage-To-Orbit (SSTO) model for stability and control analysis

NASA Astrophysics Data System (ADS)

Three NASA centers: Marshall Space Flight Center (MSFC), Langley Research Center (LaRC), and Johnson Space Center (JSC) are currently involved in studying a family of single-stage- and two-stage-to-orbit (SSTO/TSTO) vehicles to serve as the next generation space transportation system (STS). A rocketed winged-body is the current focus. The configuration (WB001) is a vertically-launched, horizontally-landing system with circular cross-section. Preliminary aerodynamic data was generated by LaRC and is a combination of wind-tunnel data, empirical methods, and Aerodynamic Preliminary Analysis System-(APAS) generated values. JSC's efforts involve descent trajectory design, stability analysis, and flight control system synthesis. Analysis of WB001's static stability indicates instability in 'tuck' (C(sub mu) less than 0: Mach = 0.30, alpha greater than 3.25 deg; Mach = 0.60, alpha greater than 8.04), an unstable dihedral effects (C(sub l(beta)) greater than 0: Mach = 30,alpha less than 12 deg.; Mach = 0.60, alpha less than 10.00 deg.), and, most significantly, an unstable weathercock stability derivative, C(sub n(beta)), at all angles of attack and subsonic Mach numbers. Longitudinal trim solutions for Mach = 0.30 and 0.60 indicate flight path angle possibilities ranging from around 12 (M = 0.30) to slightly over 20 degrees at Mach = 0.60. Trim angles of attack increase from 6.24 at Mach 0.60 and 10,000 feet to 17.7 deg. at Mach 0.30, sea-level. Lateral trim was attempted for a design cross-wind of 25.0 knots. The current vehicle aerodynamic and geometric characteristics will only yield a lateral trim solution at impractical tip-fin deflections (approximately equal to 43 deg.) and bank angles (21 deg.). A study of the lateral control surfaces, tip-fin controllers for WB001, indicate increased surface area would help address these instabilities, particularly the deficiency in C(sub n(beta)), but obviously at the expense of increased vehicle weight. Growth factors of approximately 7 were determined using a design C(sub n(beta)) of 0.100/radian (approximate subsonic values for the orbiter).

Ingalls, Stephen A.

1995-07-01

48

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

49

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

50

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

Rajagopal, K.R.

1993-07-01

51

Stability analysis of Newtonian polytropes

We analyze the stability of Newtonian polytropic static fluid spheres, described by the Lane-Emden equation. In the general case of arbitrary polytropic indices the Lane-Emden equation is a non-linear second order ordinary differential equation. By introducing a set of new variables, the Lane-Emden equation can be reduced to an autonomous system of two ordinary differential equations, which in turn may be transformed to another regular second order differential equation. We perform the study of stability by using linear stability analysis, the Jacobi stability analysis (Kosambi-Cartan-Chern theory) and the Lyapunov function method. Depending on the values of the polytropic index characterizing the fluid, these different methods yield different qualitative results on the stability of the solutions. On the other hand, these techniques offer a powerful method for constraining the physical properties of the Newtonian stars.

Boehmer, Christian G

2009-01-01

52

We consider a simplified characterization of the postural control system that embraces two broad components: one representing the musculoskeletal dynamics in the sagittal plane and the other representing proprioceptive feedback and the central nervous system (CNS). Specifically, a planar four-segment neuromusculoskeletal model consisting of the ankle, knee, and hip degrees-of-freedom (DOFs) is described in this paper. The model includes important physiological constructs such as Hill-type muscle model, active and passive muscle stiffnesses, force feedback from the Golgi tendon organ, muscle length and rate feedback from the muscle spindle, and transmission latencies in the neural pathways. A proportional-integral-derivative (PID) controller for each individual DOF is assumed to represent the CNS analog in the modeling paradigm. Our main hypothesis states that all stabilizing PID controllers for such multisegment biomechanical models can be parametrized and analytically synthesized. Our analytical and simulation results show that the proposed representation adequately shapes a postural control that (a) possesses good disturbance rejection and trajectory tracking, (b) is robust against feedback latencies and torque perturbations, and (c) is flexible to embrace changes in the musculoskeletal parameters. We additionally present detailed sensitivity analysis to show that control under conditions of limited or no proprioceptive feedback results in (a) significant reduction in the stability margins, (b) substantial decrease in the available stabilizing parameter set, and (c) oscillatory movement trajectories. Overall, these results suggest that anatomical arrangement, active muscle stiffness, force feedback, and physiological latencies play a major role in shaping motor control processes in humans. PMID:19045918

Iqbal, Kamran; Roy, Anindo

2009-01-01

53

Relaxed LMI-based stability conditions for fuzzy model-based (FMB) control systems are proposed. Considering LMI-based shape-dependent stability conditions, containing relations between state variables and membership functions, some more relaxed stability conditions for FMB control systems with `Parallel Distributed Compensation'(PDC) design technique are derived. In the aforementioned approach, product terms of fuzzy model and fuzzy controller membership functions are approximated by polynomials

Mohammand Narimani; Hak-Keung Lam; R. Dilmaghani; Charles Wolfe

2010-01-01

54

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

55

Voltage stability evaluation using modal analysis

The authors discuss the voltage stability analysis of large power systems by using a modal analysis technique. The method computes, using a steady-state system model, a specified number of the smallest eigenvalues and the associated eigenvectors of a reduced Jacobian matrix. The eigenvalues, each of which is associated with a mode of voltage\\/reactive power variation, provide a relative measure of

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

1992-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

57

Stability of accretion models.

NASA Astrophysics Data System (ADS)

Critical analyses of the standard accretion models is presented. The authors consider the model stability of the theory of disc accretion on to black holes and of the theories of spherical/disc accretion on to a magnetosphere. They take into account the real physical processes and geometry (inner magnetic field in an accreted plasma, finite conductivity, finite length of the field lines, finite rotation of the accreted object and magnetic shear on the boundary between the magnetosphere and the accreted plasma). The authors show that the influence of these factors leads to radical change in both the pattern of accretion as a whole and the character of the energy release in the accreted system. A strong current sheet and Z-pinch-like structure have to arise over the polar region of the accreted object. Particle acceleration in the electric fields of current discharges in these regions may be a source of effective energy conversion into non-thermal particles and emission observed from many accreted objects.

Pustil'Nik, L. A.; Ikhsanov, N. R.

58

Lateral stability analysis for X-29A drop model using system identification methodology

NASA Technical Reports Server (NTRS)

A 22-percent dynamically scaled replica of the X-29A forward-swept-wing airplane has been flown in radio-controlled drop tests at the NASA Langley Research Center. A system identification study of the recorded data was undertaken to examine the stability and control derivatives that influence the lateral behavior of this vehicle with particular emphasis on an observed wing rock phenomenon. All major lateral stability derivatives and the damping-in-roll derivative were identified for angles of attack from 5 to 80 degrees by using a data-partitioning methodology and a modified stepwise regression algorithm.

Raney, David L.; Batterson, James G.

1989-01-01

59

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

60

NASA Astrophysics Data System (ADS)

Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as "permafrost", can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features.

Curtaz, M.; Ferrero, A. M.; Roncella, R.; Segalini, A.; Umili, G.

2014-03-01

61

Stability Analysis of Bow Shocks

We present a linear stability analysis of bow shocks created by the interaction of a spherical wind moving with respect to its surrounding medium. The bounding shocks are assumed isothermal and with Mach number M = ?. Following Soker, we study the evolution of short-wavelength perturbations. We find that the motion is unstable in this limit. Moreover, the ratio of

Ruth Dgani; Dave van Buren; Alberto Noriega-Crespo

1996-01-01

62

Cage stability analysis for SSME HPOTP bearings

NASA Technical Reports Server (NTRS)

A numerical model of cage motion (CAGEDYN) was used to analyze the stability of bearing cages in the Space Shuttle main engine (SSME) high pressure oxygen turbopump (HPOTP). The stability of existing bearing geometries, as well as perturbations of these geometries, was analyzed for various operating conditions. Results of the analyses show that some combinations of operating parameters, exacerbated by the sparse lubrication that exist in the HPOTP bearings, can cause unstable cage oscillations. Frequencies of cage oscillations were predicted by the CAGEDYN numerical model by Fourier analysis of predicted cage motions. Under conditions that cause unstable cage motion, high frequency oscillations were predicted that could cause premature cage failures.

Merriman, T. L.; Kannel, J. W.

1988-01-01

63

NASA Astrophysics Data System (ADS)

Stability of parametrically excited torsional vibrations of a shaft system composed of two torsionally elastic shafts interconnected through a Hooke's joint is studied. The shafts are considered to be continuous (distributed-parameter) systems and an approximate discrete model for the torsional vibrations of the shaft system is derived via a finite element scheme. The stability of the solutions of the linearized equations of motion, consisting of a set of Mathieu-Hill type equations, is examined by means of a monodromy matrix method and the results are presented in the form of a Strutt-Ince diagram visualizing the effects of the system parameters on the stability of the shaft system.

Bulut, Gökhan

2014-08-01

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

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

66

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

a stem cell (or a bone-marrow) transplant [14]. The main result of that work was that a slightly elevated development from the stem cell to the terminally differentiated state. To conduct our analysis, we start emerged from the idea of cancer stem cells [5]. This hypothesis states that a variety of cancers originate

67

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

between the immune system and cancer cells after a stem cell (or a bone-marrow) transplant [14]. The main development from the stem cell to the terminally differentiated state. To conduct our analysis, we start favors remission. A new paradigm of cancer development emerged from the idea of cancer stem cells [5

Jauffret, Marie Doumic

68

Global Stability Analysis of SEIR Model with Holling Type II Incidence Function

A deterministic model for the transmission dynamics of a communicable disease is developed and rigorously analysed. The model, consisting of five mutually exclusive compartments representing the human dynamics, has a globally asymptotically stable disease-free equilibrium (DFE) whenever a certain epidemiological threshold, known as the basic reproduction number (?0), is less than unity; in such a case the endemic equilibrium does not exist. On the other hand, when the reproduction number is greater than unity, it is shown, using nonlinear Lyapunov function of Goh-Volterra type, in conjunction with the LaSalle's invariance principle, that the unique endemic equilibrium of the model is globally asymptotically stable under certain conditions. Furthermore, the disease is shown to be uniformly persistent whenever ?0 > 1. PMID:23091562

Safi, Mohammad A.; Garba, Salisu M.

2012-01-01

69

Global stability analysis of SEIR model with holling type II incidence function.

A deterministic model for the transmission dynamics of a communicable disease is developed and rigorously analysed. The model, consisting of five mutually exclusive compartments representing the human dynamics, has a globally asymptotically stable disease-free equilibrium (DFE) whenever a certain epidemiological threshold, known as the basic reproduction number (??), is less than unity; in such a case the endemic equilibrium does not exist. On the other hand, when the reproduction number is greater than unity, it is shown, using nonlinear Lyapunov function of Goh-Volterra type, in conjunction with the LaSalle's invariance principle, that the unique endemic equilibrium of the model is globally asymptotically stable under certain conditions. Furthermore, the disease is shown to be uniformly persistent whenever ?? > 1. PMID:23091562

Safi, Mohammad A; Garba, Salisu M

2012-01-01

70

Modified Freeman Model: A Stability Analysis and Application to Pattern Recognition

, principe}@cnel.ufl.edu Abstract-- The biologically realistic Freeman model of the olfactory cortex has been that the modified system can be used as an auto-associative memory. I. INTRODUCTION Understanding the information behavior not necessarily trying to mimic the exact olfactory system. With the analyzable nature

Slatton, Clint

71

CDC01-REG1559 Stability and reachability analysis of a hybrid model

is able to sense when a quorum of bacteria, a minimum population unit is achieved. Under these conditions sensing system found in unicellular bacteria that exhibit bioluminescence. The luminescence is governed systems to the quorum sensing system, and demonstrates that bioluminescence can be modeled and understood

Belta, Calin A.

72

CDC01REG1559 Stability and reachability analysis of a hybrid model

is able to sense when a quorum of bacteria, a minimum population unit is achieved. Under these conditions sensing system found in uniÂ cellular bacteria that exhibit bioluminescence. The luminescence is governed systems to the quorum sensing system, and demonstrates that bioluminescence can be modeled and understood

Dang, Thao

73

Overview and Comparative Analysis of Gas Turbine Models for System Stability Studies

Gas turbines have become increasingly popular in the different power systems, due to their lower greenhouse emission as well as the higher efficiency, especially when connected in a combined cycle setup. With increasing installations of gas turbines scheduled in different countries, the dynamics of the gas turbines become increasingly more important. In order to study such dynamics, accurate models of

Soon Kiat Yee; Jovica V. Milanovic ´; F. Michael Hughes

2008-01-01

74

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. The hypothesis that periodic breathing is the result of delay in the feedback signals to the respiratory control

75

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

76

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

77

NASA Technical Reports Server (NTRS)

This report documents results from the NASA-Langley sponsored Euler Technology Assessment Study conducted by Lockheed-Martin Tactical Aircraft Systems (LMTAS). The purpose of the study was to evaluate the ability of the SPLITFLOW code using viscous and inviscid flow models to predict aerodynamic stability and control of an advanced fighter model. The inviscid flow model was found to perform well at incidence angles below approximately 15 deg, but not as well at higher angles of attack. The results using a turbulent, viscous flow model matched the trends of the wind tunnel data, but did not show significant improvement over the Euler solutions. Overall, the predictions were found to be useful for stability and control design purposes.

Jordan, Keith J.

1998-01-01

78

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

79

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

80

Stability in generic mitochondrial models

In this paper, we use a variety of mathematical techniques to explore existence, local stability, and global stability of equilibria in abstract models of mitochondrial metabolism. The class of models constructed is defined by the biological description of the system, with minimal mathematical assumptions. The key features are an electron transport chain coupled to a process of charge translocation across a membrane. In the absence of charge translocation these models have previously been shown to behave in a very simple manner with a single, globally stable equilibrium. We show that with charge translocation the conclusion about a unique equilibrium remains true, but local and global stability do not necessarily follow. In sufficiently low dimensions - i.e. for short electron transport chains - it is possible to make claims about local and global stability of the equilibrium. On the other hand, for longer chains, these general claims are no longer valid. Some particular conditions which ensure stability of the equilibrium for chains of arbitrary length are presented.

Pete Donnell; Murad Banaji; Stephen Baigent

2007-06-25

81

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

82

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

83

This paper investigates the system stability of a sampled-data fuzzy-model-based control system, formed by a nonlinear plant and a sampled-data fuzzy controller connected in a closed loop. The sampled-data fuzzy controller has an advantage that it can be implemented using a microcontroller or a digital computer to lower the implementation cost and time. However, discontinuity introduced by the sampling activity

H. K. Lam

2009-01-01

84

Vacuum Stability Bound on Extended GMSB Models

Extensions of GMSB models were explored to explain the recent reports of the Higgs boson mass around 124-126 GeV. Some models predict a large mu term, which can spoil the vacuum stability of the universe. We study two GMSB extensions: i) the model with a large trilinear coupling of the top squark, and ii) that with extra vector-like matters. In both models, the vacuum stability condition provides upper bounds on the gluino mass if combined with the muon g-2. The whole parameter region is expected to be covered by LHC at sqrt{s} = 14 TeV. The analysis is also applied to the mSUGRA models with the vector-like matters.

Motoi Endo; Koichi Hamaguchi; Sho Iwamoto; Norimi Yokozaki

2012-02-13

85

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

86

Stability Analysis of Explicit Congestion Control Protocols

1 Stability Analysis of Explicit Congestion Control Protocols Hamsa Balakrishnan, Nandita Dukkipati, nickm, tomlin}@stanford.edu Abstract Much recent attention has been devoted to analyzing the stability by linearization, and the linearization is then used to derive conditions for stability using techniques based

Gummadi, Ramakrishna

87

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

88

NASA Astrophysics Data System (ADS)

The relaxation property of both Eigen model and Crow-Kimura model with a single peak fitness landscape is studied from phase transition point of view. We first analyze the eigenvalue spectra of the replication mutation matrices. For sufficiently long sequences, the almost crossing point between the largest and second-largest eigenvalues locates the error threshold at which critical slowing down behavior appears. We calculate the critical exponent in the limit of infinite sequence lengths and compare it with the result from numerical curve fittings at sufficiently long sequences. We find that for both models the relaxation time diverges with exponent 1 at the error (mutation) threshold point. Results obtained from both methods agree quite well. From the unlimited correlation length feature, the first order phase transition is further confirmed. Finally with linear stability theory, we show that the two model systems are stable for all ranges of mutation rate. The Eigen model is asymptotically stable in terms of mutant classes, and the Crow-Kimura model is completely stable.

Feng, Xiao-Li; Li, Yu-Xiao; Gu, Jian-Zhong; Zhuo, Yi-Zhong

2009-10-01

89

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

90

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

91

Power System Transient Stability Analysis through a Homotopy Analysis Method

As an important function of energy management systems (EMSs), online contingency analysis plays an important role in providing power system security warnings of instability. At present, N-1 contingency analysis still relies on time-consuming numerical integration. To save computational cost, the paper proposes a quasi-analytical method to evaluate transient stability through time domain periodic solutions’ frequency sensitivities against initial values. First, dynamic systems described in classical models are modified into damping free systems whose solutions are either periodic or expanded (non-convergent). Second, because the sensitivities experience sharp changes when periodic solutions vanish and turn into expanded solutions, transient stability is assessed using the sensitivity. Third, homotopy analysis is introduced to extract frequency information and evaluate the sensitivities only from initial values so that time consuming numerical integration is avoided. Finally, a simple case is presented to demonstrate application of the proposed method, and simulation results show that the proposed method is promising.

Wang, Shaobu; Du, Pengwei; Zhou, Ning

2014-04-01

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

The stability of the finite-difference approximation of elastic wave propagation in orthotropic homogeneous media in the three-dimensional case is discussed. The model applies second- and fourth-order finite-difference approaches with staggered grid and stress-free boundary conditions in the space domain and second-order finite-difference approach in the time domain. The numerical integration of the wave equation by central differences is conditionally stable and the corresponding stability criterion for the time domain discretisation has been deduced as a function of the material properties and the geometrical discretization. The problem is discussed by applying the method of VonNeumann. Solutions and the calculation of the critical time steps is presented for orthotropic material in both the second- and fourth-order case. The criterion is verified for the special case of isotropy and results in the well-known formula from the literature. In the case of orthotropy the method was verified by long time simulations and by calculating the total energy of the system. PMID:19913266

Veres, István A

2010-03-01

94

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

95

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

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

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

98

Stability analysis of cylindrical Vlasov equilibria

A method is presented for the fully kinetic, nonlocal stability analysis of cylindrically symmetric equilibria. Applications to the lower hybrid drift instability and the modes associated with a finite-width relativistic E-layer are discussed.

Short, R W

1980-02-01

99

Recently global, quasi-two-dimensional instabilities of tachocline latitudinal differential rotation have been studied using a so-called shallow-water model. While purely hydrodynamic shallow-water type disturbances were found to destabilize only the overshoot tachocline, the MHD analysis showed that in the presence of a broad toroidal field, both the radiative and overshoot parts of the tachocline can be unstable. We explore here instability

Mausumi Dikpati; Peter A. Gilman; Matthias Rempel

2003-01-01

100

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

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

Stability analysis of steady states for surface diffusion equation in a bounded domain

. . Stability analysis of steady states for surface diffusion equation in a bounded domain Aspects of Crystal Growth 30 July, 2010 Y. Kohsaka (Muroran Inst. of Tech.) Stability analysis for surface. of Tech.) Stability analysis for surface diffusion 30 July, 2010 2 / 19 #12;Model The surface diffusion

Ishii, Hitoshi

103

Performance of partial least squares regression (PLSR) is enhanced in the presented work by three multivariate models, including weighted regression PLSR (Weighted-PLSR), genetic algorithm PLSR (GA-PLSR), and wavelet transform PLSR (WT-PLSR). The proposed models were applied for the stability-indicating analysis of mixtures of mebeverine hydrochloride (meb) and sulpiride (sul) in the presence of their reported impurities and degradation products. The work introduced in this paper aims to compare these different chemometric methods, showing the underlying algorithm for each and making a comparison of analysis results. For proper analysis, a 6-factor, 5-level experimental design was established resulting in a training set of 25 mixtures containing different ratios of the interfering species. A test set consisting of 5 mixtures was used to validate the prediction ability of the suggested models. Leave one out (LOO) and bootstrap were applied to predict number of PLS components. The GA-PLSR proposed method was successfully applied for the analysis of raw material (test set 101.03% ± 1.068, 101.47% ± 2.721 for meb and sul, respectively) and pharmaceutical tablets containing meb and sul mixtures (10.10% ± 0.566, 98.16% ± 1.081 for meb and sul). PMID:21898859

Darwish, Hany W; Naguib, Ibrahim A

2013-05-01

104

Controllability and Stability Analysis of Planar Snake Robot Locomotion

This paper contributes to the understanding of snake robot locomotion by employing nonlinear system analysis tools for investigating fundamental properties of snake robot dynamics. The paper has five contributions: 1) a partially feedback linearized model of a planar snake robot influenced by viscous ground fric- tion is developed. 2) A stabilizability analysis is presented proving that any asymptotically stabilizing control

Pĺl Liljeback; Kristin Y. Pettersen; Řyvind Stavdahl; Jan Tommy Gravdahl

2011-01-01

105

Voltage stability analysis in the new deregulated environment

NASA Astrophysics Data System (ADS)

Nowadays, a significant portion of the power industry is under deregulation. Under this new circumstance, network security analysis is more critical and more difficult. One of the most important issues in network security analysis is voltage stability analysis. Due to the expected higher utilization of equipment induced by competition in a power market that covers bigger power systems, this issue is increasingly acute after deregulation. In this dissertation, some selected topics of voltage stability analysis are covered. In the first part, after a brief review of general concepts of continuation power flow (CPF), investigations on various matrix analysis techniques to improve the speed of CPF calculation for large systems are reported. Based on these improvements, a new CPF algorithm is proposed. This new method is then tested by an inter-area transaction in a large inter-connected power system. In the second part, the Arnoldi algorithm, the best method to find a few minimum singular values for a large sparse matrix, is introduced into the modal analysis for the first time. This new modal analysis is applied to the estimation of the point of voltage collapse and contingency evaluation in voltage security assessment. Simulations show that the new method is very efficient. In the third part, after transient voltage stability component models are investigated systematically, a novel system model for transient voltage stability analysis, which is a logical-algebraic-differential-difference equation (LADDE), is offered. As an example, TCSC (Thyristor controlled series capacitors) is addressed as a transient voltage stabilizing controller. After a TCSC transient voltage stability model is outlined, a new TCSC controller is proposed to enhance both fault related and load increasing related transient voltage stability. Its ability is proven by the simulation.

Zhu, Tong

106

Stability Analysis and Stabilization of Randomly Switched Systems Debasish Chatterjee and Daniel Liberzon Abstract. This article is concerned with stability analysis and stabilization of randomly switched conditions for stochastic stability of the switched system, when the subsystems do not possess control inputs

Liberzon, Daniel

107

Stability analysis of graphite crystal lattice with moment interactions

Stability analysis of graphite crystal lattice with moment interactions Igor E. Berinskiy A. M a math- ematical model for interaction between carbon atoms in hexagonal graphite lattice. The 2D layer of graphite lattice is considered. The model is based on usage of moment interactions. Carbon atom

Krivtsov, Anton M.

108

NASA Astrophysics Data System (ADS)

A comparison between support vector regression (SVR) and Artificial Neural Networks (ANNs) multivariate regression methods is established showing the underlying algorithm for each and making a comparison between them to indicate the inherent advantages and limitations. In this paper we compare SVR to ANN with and without variable selection procedure (genetic algorithm (GA)). To project the comparison in a sensible way, the methods are used for the stability indicating quantitative analysis of mixtures of mebeverine hydrochloride and sulpiride in binary mixtures as a case study in presence of their reported impurities and degradation products (summing up to 6 components) in raw materials and pharmaceutical dosage form via handling the UV spectral data. For proper analysis, a 6 factor 5 level experimental design was established resulting in a training set of 25 mixtures containing different ratios of the interfering species. An independent test set consisting of 5 mixtures was used to validate the prediction ability of the suggested models. The proposed methods (linear SVR (without GA) and linear GA-ANN) were successfully applied to the analysis of pharmaceutical tablets containing mebeverine hydrochloride and sulpiride mixtures. The results manifest the problem of nonlinearity and how models like the SVR and ANN can handle it. The methods indicate the ability of the mentioned multivariate calibration models to deconvolute the highly overlapped UV spectra of the 6 components' mixtures, yet using cheap and easy to handle instruments like the UV spectrophotometer.

Naguib, Ibrahim A.; Darwish, Hany W.

2012-02-01

109

A comparison between support vector regression (SVR) and Artificial Neural Networks (ANNs) multivariate regression methods is established showing the underlying algorithm for each and making a comparison between them to indicate the inherent advantages and limitations. In this paper we compare SVR to ANN with and without variable selection procedure (genetic algorithm (GA)). To project the comparison in a sensible way, the methods are used for the stability indicating quantitative analysis of mixtures of mebeverine hydrochloride and sulpiride in binary mixtures as a case study in presence of their reported impurities and degradation products (summing up to 6 components) in raw materials and pharmaceutical dosage form via handling the UV spectral data. For proper analysis, a 6 factor 5 level experimental design was established resulting in a training set of 25 mixtures containing different ratios of the interfering species. An independent test set consisting of 5 mixtures was used to validate the prediction ability of the suggested models. The proposed methods (linear SVR (without GA) and linear GA-ANN) were successfully applied to the analysis of pharmaceutical tablets containing mebeverine hydrochloride and sulpiride mixtures. The results manifest the problem of nonlinearity and how models like the SVR and ANN can handle it. The methods indicate the ability of the mentioned multivariate calibration models to deconvolute the highly overlapped UV spectra of the 6 components' mixtures, yet using cheap and easy to handle instruments like the UV spectrophotometer. PMID:22137012

Naguib, Ibrahim A; Darwish, Hany W

2012-02-01

110

Developments in Cylindrical Shell Stability Analysis

NASA Technical Reports Server (NTRS)

Today high-performance computing systems and new analytical and numerical techniques enable engineers to explore the use of advanced materials for shell design. This paper reviews some of the historical developments of shell buckling analysis and design. The paper concludes by identifying key research directions for reliable and robust methods development in shell stability analysis and design.

Knight, Norman F., Jr.; Starnes, James H., Jr.

1998-01-01

111

Fuzzy model based control: stability, robustness, and performance issues

A nonlinear controller based on a fuzzy model of MIMO dynamical systems is described and analyzed. The fuzzy model is based on a set of ARX models that are combined using a fuzzy inference mechanism. The controller is a discrete-time nonlinear decoupler, which is analyzed both for the adaptive and the fixed parameter cases. A detailed stability analysis is carried

Tor A. Johansen

1994-01-01

112

Stability analysis of unsteady ablation fronts

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

Betti, R.; McCrory, R.L.; Verdon, C.P. (Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States))

1993-11-08

113

Stability analysis of unsteady ablation fronts

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

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

1993-08-01

114

Stability analysis of unsteady ablation fronts

NASA Astrophysics Data System (ADS)

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

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

1993-08-01

115

Stability analysis of unsteady ablation fronts

NASA Astrophysics Data System (ADS)

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

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

1993-11-01

116

Stability analysis of near-limit stretched premixed flames

NASA Astrophysics Data System (ADS)

The dynamics of radiative, near-limit, stretched premixed flames was investigated analytically and numerically, with emphasis on pulsating stability for sub-unity Lewis numbers. The analysis includes both flame stretch and order-unity heat loss, and yields a dispersion equation for the stability of radiative stretched flames subjected to symmetrical and asymmetrical perturbations. The dispersion equation reduces to that of the classical thermo-diffusional stability analysis of Sivashinsky in the limit of small heat loss, small stretch rate, and infinite flame separation distance. Results show that sub-limit flames are stable near both radiation and stretch extinction limits, and that oscillation occurs only at moderate flame stretch rates. The unstable regime and the stability diagram were obtained. Numerical simulation with detailed chemical kinetics and transport models yielded results that are in good agreement with theory. The present work also provides a satisfactory explanation of the experimental results obtained in microgravity.

Minaev, S.; Fursenko, R.; Ju, Y.; Law, C. K.

2003-08-01

117

The Dark Energy Star and Stability analysis

We have proposed a new model of dark energy star consisting of three zones namely, an inhomogeneous interior region with anisotropic pressures, thin shell and the exterior vacuum region of Schwarzschild spacetime. 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

2014-09-12

118

ASTROP2 users manual: A program for aeroelastic stability analysis of propfans

NASA Technical Reports Server (NTRS)

A user's manual is presented for the aeroelastic stability and response of propulsion systems computer program called ASTROP2. The ASTROP2 code preforms aeroelastic stability analysis of rotating propfan blades. This analysis uses a two-dimensional, unsteady cascade aerodynamics model and a three-dimensional, normal-mode structural model. Analytical stability results from this code are compared with published experimental results of a rotating composite advanced turboprop model and of nonrotating metallic wing model.

Narayanan, G. V.; Kaza, K. R. V.

1991-01-01

119

Generalized modified gravity models: the stability issue

A brief introduction on the issue of stability in generalized modified gravity is presented and the dynamical system methods are used in the investigation of the stability of spatially flat homogeneous cosmologies within a large class of generalized modified gravity models in the presence of a relativistic matter-radiation fluid.

Guido Cognola; Sergio Zerbini

2008-11-17

120

Performance and Stability Analysis of a Shrouded-Fan UAV

This paper deals with the estimation of the performance and stability for a shrouded-fan unmanned rotorcraft whose mission profile also prescribes the flight in ground effect. The not so simple estimation of the aerodynamic coefficients and of the thrust in the various situations makes the performance calculation and the stability analysis difficult tasks. This is due to the strong interaction between the fan flow and shroud that causes quite different flow structures about the airframe depending on flight conditions. A further difficulty is related to the ground effect which produces substantial modifications in the rotor thrust and aerodynamic coefficients. To evaluate performance and stability, two models have been developed. One determines the aerodynamic coefficients of the shroud, whereas the other one calculates thrust and moment of the rotors system. Both models take into account the mutual interference between fan flow and fuselage and ground effect. Performance and stability are then discussed with ...

de Divitiis, Nicola

2009-01-01

121

Wind-hydro hybrid power system stability analysis

The method of wind power modeling, stability analysis and calculation in wind-hydro hybrid power systems is described by the authors in this paper. A case study of wind-hydro hybrid power system in China's Aletai region, Buerjin County, Xinjiang Province is also presented

Fan Yanfang; Wang Yibo; Chao Qin

2001-01-01

122

Short Communication Microscopic analysis of structure stabilities

. This new combination of two classical methods allows a progressive discovery of the microscopic relevant2005 Short Communication Microscopic analysis of structure stabilities in the ionic compounds B primary order distortion, and thus find the microscopic interactions responsible for the symmetry breaking

Boyer, Edmond

123

The helix content of a series of peptides containing single substitutions of the 20 natural amino acids in a new designed host sequence, succinyl-YSEEEEKAKKAXAEEAEKKKK-NH2, has been determined using CD spectroscopy. This host is related to one previously studied, in which triple amino acid substitutions were introduced into a background of Glu-Lys blocks completely lacking alanine. The resulting free energies show that only Ala and Glu- prove to be helix stabilizing, while all other side chains are neutral or destabilizing. This agrees with results from studies of alanine-rich peptide modela, but not the previous Glu-Lys block oligomers in which Leu and Met also stabilize helix. The helix propensity scale derived from the previous block oligomers correlated well with the frequencies of occurrence of different side chains in helical sequences of proteins, whereas the values from the present series do not. The role of context in determining scales of helix propensity values is discussed, and the ability of algorithms designed to predict helix structure from sequence is compared. PMID:9194186

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

1997-01-01

124

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

125

The stationary-state solutions of magnetization dynamics under a spin-polarized current that was polarized in an arbitrary direction were investigated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation for a single-domain magnet. Taking into consideration the uniaxial magnetic anisotropy, the equilibrium directions of the magnetization vectors were analytically obtained by solving an algebraic cubic equation. It was found that one to three pairs of magnetization equilibrium states existed, depending on the current intensity and the direction of the spin polarization. By numerically analyzing the stabilities of these equilibrium states, the threshold switching current for the reversing the magnetic vector was obtained under different current polarization configurations, which may be useful for use in future spintronics devices.

Wang, Zhiyuan; Sun, Z. Z., E-mail: phzzsun@suda.edu.cn [School of Physical Science and Technology, Soochow University, Suzhou, Jiangsu 215006 (China)

2014-02-14

126

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

127

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

128

Elementary Applications of a Rotorcraft Dynamic Stability Analysis

NASA Technical Reports Server (NTRS)

A number of applications of a rotorcraft aeroelastic analysis are presented to verify that the analysis encompasses the classical solutions of rotor dynamics, and to examine the influence of certain features of the model. Results are given for the following topics: flapping frequency response to pitch control; forward flight flapping stability; pitch/flap flutter and divergence; ground resonance instability; and the flight dynamics of several representative helicopters.

Johnson, W.

1976-01-01

129

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

130

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

131

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

132

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

133

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

134

Stability analysis of free piston Stirling engine power generation system

NASA Astrophysics Data System (ADS)

This paper presents a stability analysis of the free-piston Stirling engine and linear alternator power generation system. Such a system operates under sustained mechanical oscillators, stability of the system is important for proper operation, and as a criterion in selecting the tuning capacitor. The stability criterion of the system is that the rate of change in power dissipation and electric power output is always faster than the rate of the power generated by the engine. The dynamic equations and model of the system are developed in this paper. Frequency domain analysis and Bode plot techniques are utilized in the study. The stable operating frequency region corresponding to different levels of power output are then determined.

Fu, Z. X.; Nasar, S. A.; Rosswurm, Mark

135

Stability analysis and \\mu-synthesis control of brake systems

The concept of friction-induced brake vibrations, commonly known as judder, is investigated. Judder vibration is based on the class of geometrically induced or kinematic constraint instability. After presenting the modal coupling mechanism and the associated dynamic model, a stability analysis as well as a sensitivity analysis have been conducted in order to identify physical parameters for a brake design avoiding friction-induced judder instability. Next, in order to reduce the size of the instability regions in relation to possible system parameter combinations, robust stability via \\mu-synthesis is applied. By comparing the unstable regions between the initial and controlled brake system, some general indications emerge and it appears that robust stability via \\mu-synthesis has some effect on the instability of the brake system.

Lignon, Sylvain; Jezequel, Louis

2008-01-01

136

ADVANCED NUMERICAL TECHNIQUES IN ROCK SLOPE STABILITY ANALYSIS APPLICATIONS AND LIMITATIONS

ADVANCED NUMERICAL TECHNIQUES IN ROCK SLOPE STABILITY ANALYSIS Â APPLICATIONS AND LIMITATIONS Doug slope stability analysis emphasising recent developments in numerical modelling, including advances/or the equilibrium conditions of a natural slope. The analysis technique chosen depends on both site conditions

137

Delay-dependent stability analysis of linear systems with time-varying delay

Stability analysis of linear systems with time- varying delay is investigated. In order to highlight the relations between the variation of the delay and the states, redundant equations are introduced to construct a new modeling of the delay system. New types of Lyapunov Krasovskii functionals are then proposed allowing to reduce the conservatism of the stability criterion. Delay dependent stability

Yassine Ariba; F. Gouaisbaut

2007-01-01

138

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

139

Linear stability analysis of dynamical quadratic gravity

NASA Astrophysics Data System (ADS)

We study the linear stability of dynamical, quadratic gravity, focusing on two particular subclasses (the even-parity sector, exemplified by Einstein-Dilaton-Gauss-Bonnet gravity, and the odd-parity sector, exemplified by dynamical Chern-Simons modified gravity) in the high-frequency, geometric optics approximation. This analysis is carried out by studying gravitational and scalar modes propagating on spherically symmetric and axially symmetric, vacuum solutions of the theory and finding the associated dispersion relations. These relations are solved in two separate cases (the scalar regime and the gravitational wave regime, defined by requiring the ratio of the amplitude of the perturbations to be much greater or smaller than unity) and found in both cases to not lead to exponential growth of the propagating modes, suggesting linearly stability. The modes are found to propagate at subluminal and superluminal speeds, depending on the propagating modes' direction relative to the background geometry, just as in dynamical Chern-Simons gravity.

Ayzenberg, Dimitry; Yagi, Kent; Yunes, Nicolás

2014-02-01

140

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

141

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

142

Stability of an elastic cytoskeletal tensegrity model

An elastic cytoskeletal tensegrity structure composed by six inextensible elastic struts and 24 elastic cables is considered. The model is studied, adopting delay convention for stability. Critical conditions for simple and compound instabilities are defined. Post-critical behavior is also described. Equilibrium states with buckling of the struts are also considered. It is revealed that critical Euler buckling load of the

K. A. Lazopoulos

2005-01-01

143

STABILITY ANALYSIS OF LINEAR CONTROL SYSTEMS WITH UNCERTAIN PARAMETERS

STABILITY ANALYSIS OF LINEAR CONTROL SYSTEMS WITH UNCERTAIN PARAMETERS by YUGUANG FANG Submitted January, 1994 i #12;STABILITY ANALYSIS OF LINEAR CONTROL SYSTEMS WITH UNCERTAIN PARAMETERS ABSTRACT by YUGUANG FANG In this dissertation, we study stochastic stability of linear systems whose parameters

Latchman, Haniph A.

144

Stability analysis for class of switched nonlinear systems

Stability analysis for a class of switched nonlinear systems is addressed in this paper. Two linear matrix inequality (LMI) based sufficient conditions for asymptotic stability are proposed for switched nonlinear systems. ...

Shaker, Hamid Reza

145

Stability of the Einstein static universe in open cosmological models

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

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

2010-09-15

146

This paper presents the stability analysis of parameter identification. The Takagi Sugeno fuzzy model is employed to represent the discrete time nonlinear dynamical systems. Once the structure of the fuzzy model is fixed, the parameters can be optimized. The parameter identification is accomplished by applying the gradient method where the iteration rates are specific to each parameter. The stability of

Sonia ALIMI; Mohamed CHTOUROU

2009-01-01

147

Stability of a model food web.

We investigate numerically the stability of a model food web, introduced by Nunes Amaral and Meyer [Phys. Rev. Lett. 82, 652 (1999)]. The model describes a system of species located in niches at several levels. Upper level species are predating on those from a lower level. We show that the model web is more stable when it is larger, although the number of niches is more important than the number of levels. The food web is self-organizing itself, trying to reach a certain degree of complexity, i.e., number of species and links among them. If the system cannot achieve this state, it will go extinct. We demonstrate that the average number of links per species and the reduced number of species depend in the same way on the number of niches. We also determine how the stability of the food web depends on another parameter of the model, the killing probability. Despite keeping the ratio of the creation and killing probabilities constant, increasing the latter reduces significantly the stability of the model food web. We show that connectance dependence on the number of niches has a power-type character, which agrees with the field data, and that it decreases with the number of species also as a power-type function. PMID:19391786

Szwabi?ski, Janusz; Pekalski, Andrzej

2009-02-01

148

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. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:416-423, 2015. PMID:25212829

Mills, Brittney J; Laurence, Jennifer S

2015-02-01

149

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

150

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

2012-02-13

151

Stability analysis of free piston Stirling engine power generation system

This paper presents a stability analysis of the free-piston Stirling engine and linear alternator power generation system. Such a system operates under sustained mechanical oscillators, stability of the system is important for proper operation, and as a criterion in selecting the tuning capacitor. The stability criterion of the system is that the rate of change in power dissipation and electric

Z. X. Fu; S. A. Nasar; Mark Rosswurm

1992-01-01

152

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

153

An Analysis of the 'Stability Pact'

We analyse the proposed ‘stability pact’ for countries joining a European Monetary Union (EMU). Within EMU shortsighted governments fail to fully internalize the inflationary consequences of their debt policies, which results in excessive debt accumulation. Hence, although in the absence of EMU governments have no incentive to sign a stability pact, within EMU they prefer a stability pact which punishes

H. F. H. V. S. Uhlig; R. M. W. J. Beetsma

1997-01-01

154

Thermodynamic performance vs. dynamic stability in an enzymatic reaction model

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

155

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

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

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

Zacharias, M; Sklenar, H

1997-12-01

158

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

159

Fully Parallel MHD Stability Analysis Tool

NASA Astrophysics Data System (ADS)

Feasibility study of fully parallelizing plasma stability code MARS is made. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHD-kinetic plasma models. It is a powerful tool for studying MHD and MHD-kinetic instabilities and it is widely used by fusion community. Parallel version of MARS is intended for simulations on local parallel clusters. It will be an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, already implemented in MARS. Parallelization of the code includes parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Two approaches of parallelization of the solution of the eigenvalue problem are evaluated: 1) repeat steps of the present MARS algorithm using parallel libraries and procedures; 2) solve linear block-diagonal sets of equations, formulated in the inverse iteration algorithm in MARS, by parallel libraries and procedures. The results of these studies will be reported.

Svidzinski, Vladimir; Galkin, Sergei; Kim, Jin-Soo; Liu, Yueqiang

2012-10-01

160

Operator Training Simulator with real-time transient stability analysis

The Operator Training Simulator (OTS) system, which is integrated with a real-time transient stability analysis program, has been in operation at the training center of Hokuriku Electric Power Co., since July, 1990. The developed OTS system achieves real-time transient stability analysis with approximately 100 generator and 400 node power systems by parallel processing performed on a computer system with multiprocessor

S. Kyuwa; T. Yoshida; S. Yuasa; K. Omata; K. Mitamura

1994-01-01

161

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

162

Evaluating alternative models for power system dynamic stability studies

A dynamic stability model for detailed stability studies on synchronous power systems is presented in such a form that it can be systematically reduced to models of reduced complexity. The complete model includes representation of stator and network transient effects as well as shaft torsional oscillation effects. The family of models of reduced cemplexity span the range of models found

R. T. H. Alden; P. J. Nolan

1976-01-01

163

L2-stability of hinging hyperplane models via integral quadratic constraints

This paper is concerned with L2-stability analysis of hinging hyperplane autoregressive models with exogenous inputs (HHARX). The proposed approach relies on analysis results for systems with repeated nonlinearities based on the use of integral quadratic constraints. An equivalent linear fractional representation of HHARX models is firstly derived. In this representation, an HHARX model is seen as the feedback interconnection of

Gianni Bianchini; Simone Paoletti; Antonio Vicino

2008-01-01

164

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

165

Bond Graph Based Stability Analysis of a Railway Traction System

; Several analysis methods are directly applicable on BGs, such as structural or modal analysis [3- 51 Bond Graph Based Stability Analysis of a Railway Traction System G. Gandanegara1 , X. Roboam1 , B This paper emphasises the interest of the Bond Graph approach for analysis and system design of heterogeneous

Boyer, Edmond

166

Stability Analysis of Periodic Solutions via Integral Quadratic Constraints

The paper considers stability of periodic solutions in a class of periodically forced nonlinear systems depending on a scalar\\u000a parameter and subject to disturbances. A result concerning local existence of a family of periodic solutions for such systems\\u000a is also given. The stability analysis — based on a combined use of linearization techniques and frequency-domain stability\\u000a criteria expressed via Integral

Michele Basso; Lorenzo Giovanardi; Roberto Genesio

167

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

168

Asymptotic analysis of stability for prismatic solids under axial loads

This work addresses the stability of axially loaded prismatic beams with any simply connected crosssection. The solids obey a general class of rate-independent constitutive laws, and can sustain finite strains in either compression or tension. The proposed method is based on multiple scale asymptotic analysis, and starts with the full Lagrangian formulation for the three-dimensional stability problem, where the boundary

W. Scherzinger; N. Triantafyllidis

1998-01-01

169

Operator training simulator with real-time transient stability analysis

The operator training simulator (OTS) system, which is integrated with a real-time transient stability analysts program, has been in operation at the training center of Hokuriku Electric Power Company since July, 1990. The developed OTS system achieves real-time transient stability analysis with approximately 100 generator and 400 node power systems by parallel processing performed on a computer system with multiprocessor

S. Kyuwa; T. Yoshida; S. Yuasa; K. Omata; K. Mitamura

1993-01-01

170

Space Shuttle Main Engine real time stability analysis

NASA Technical Reports Server (NTRS)

The Space Shuttle Main Engine (SSME) is a reusable, high performance, liquid rocket engine with variable thrust. The engine control system continuously monitors the engine parameters and issues propellant valve control signals in accordance with the thrust and mixture ratio commands. A real time engine simulation lab was installed at MSFC to verify flight software and to perform engine dynamic analysis. A real time engine model was developed on the AD100 computer system. This model provides sufficient fidelity on the dynamics of major engine components and yet simplified enough to be executed in real time. The hardware-in-the-loop type simulation and analysis becomes necessary as NASA is continuously improving the SSME technology, some with significant changes in the dynamics of the engine. The many issues of interfaces between new components and the engine can be better understood and be resolved prior to the firing of the engine. In this paper, the SSME real time simulation Lab at the MSFC, the SSME real time model, SSME engine and control system stability analysis, both in real time and non-real time is presented.

Kuo, F. Y.

1993-01-01

171

Systematic Analysis of Stability Patterns in Plant Primary Metabolism

Metabolic networks are characterized by complex interactions and regulatory mechanisms between many individual components. These interactions determine whether a steady state is stable to perturbations. Structural kinetic modeling (SKM) is a framework to analyze the stability of metabolic steady states that allows the study of the system Jacobian without requiring detailed knowledge about individual rate equations. Stability criteria can be derived by generating a large number of structural kinetic models (SK-models) with randomly sampled parameter sets and evaluating the resulting Jacobian matrices. Until now, SKM experiments applied univariate tests to detect the network components with the largest influence on stability. In this work, we present an extended SKM approach relying on supervised machine learning to detect patterns of enzyme-metabolite interactions that act together in an orchestrated manner to ensure stability. We demonstrate its application on a detailed SK-model of the Calvin-Benson cycle and connected pathways. The identified stability patterns are highly complex reflecting that changes in dynamic properties depend on concerted interactions between several network components. In total, we find more patterns that reliably ensure stability than patterns ensuring instability. This shows that the design of this system is strongly targeted towards maintaining stability. We also investigate the effect of allosteric regulators revealing that the tendency to stability is significantly increased by including experimentally determined regulatory mechanisms that have not yet been integrated into existing kinetic models. PMID:22514655

Girbig, Dorothee; Grimbs, Sergio; Selbig, Joachim

2012-01-01

172

We consider the stability and convergence analysis of pressure stabilized finite element approximations of the transient Stokes' equation. The analysis is valid for a class of symmetric pres- sure stabilization operators, but also for standard, inf-sup stable, velocity\\/pressure spaces without stabilization. Provided the initial data is chosen as a specific (method dependent) Ritz-projection, we get unconditional stability and optimal convergence

Erik Burman; Miguel A. Fernández

2008-01-01

173

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

174

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

175

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

176

Stability and Dissipativity Analysis of Distributed Delay Cellular Neural Networks

In this brief, the problems of delay-dependent stability analysis and strict (Q,S,R)-?-dissipativity analysis are investigated for cellular neural networks (CNNs) with distributed delay. First, by introducing an integral partitioning technique, two new forms of Lyapunov-Krasovskii functionals are con- structed, and improved distributed delay-dependent stability conditions are established in terms of linear matrix inequalities. Based on this criterion, a new sufficient

Zhiguang Feng; James Lam

2011-01-01

177

Methods of stability analysis in nonlinear mechanics

We review our recent work on methods to study stability in nonlinear mechanics, especially for the problems of particle accelerators, and compare our ideals to those of other authors. We emphasize methods that (1) show promise as practical design tools, (2) are effective when the nonlinearity is large, and (3) have a strong theoretical basis. 24 refs., 2 figs., 2 tabs.

Warnock, R.L.; Ruth, R.D.; Gabella, W.; Ecklund, K.

1989-01-01

178

Ageostrophic linear stability analysis of the Labrador Current

NASA Astrophysics Data System (ADS)

The water mass transformation process in the Labrador Sea during winter plays an important role for the Atlantic meridional overturning circulation and the global climate system. The Labrador Sea Water (LSW) is exported within the deep Labrador Current (LC) after the convection process. LSW takes up large amounts of atmospheric tracer gases as CO2 and oxygen, and is thus one of the major agent for ventilation of the abyssal ocean. It is shown that enhanced eddy kinetic energy (EKE) along the LC shows up in a 1/12° ocean model simulation during the transformation process. Moored in-situ measurements within the LC also show enhanced EKE levels during winter. This instability processes within the LC is important as it might alter the water mass properties of the (LSW) by frontal mixing processes during the water mass transformation and export within the LC. The frontal instability process, which lead to enhanced EKE along the LC during winter is investigated using ageostrophic linear stability analysis. Dense and weakly stratified water masses produced during the wintertime transformation process lead to weaker stratification and a strengthening of the lateral density gradients within the LC. Weak stratification and enhanced vertical shear result in low Richardson numbers and the growth rate of baroclinic waves increases significantly within the shelf break LC during winter. Rapid frontogenesis along the whole LC sets in resulting in enhance EKE. During the rest of the year strong stratification and weak vertical shear leads to larger Richardson numbers and smaller growth rates. Ageostrophic linear stability analysis shows that a geostrophic interior mode has similar wavelengths as the first wavelike disturbances in the model simulations. A shallow mode with lateral scales O (1 km) is also predicted, which can be associated with mixed layer instabilities and submesoscale variability but remains unresolved by the model simulation.

Thomsen, S.; Eden, C.

2012-12-01

179

Stability Analysis of ITER Side Correction Coils

NASA Astrophysics Data System (ADS)

The stability of the Side Correction Coils (SCC) cable-in-conduit conductors (CICC) for the International Thermonuclear Experimental Reactor (ITER) has been analyzed by the formulas and the code Gandalf. This paper describes the 1-dimensional mathematical code Gandalf, uses the code to simulate the quench and the recovery status of ITER SCC CICC, discusses the dependence of the stability margin on various operating parameters including operating current, operating temperature and mass flow rate, and analyzes the differences between the simulated values and the calculated values. The ITER SCC's quenching is also simulated to investigate its temperature distribution and temperature margin. Dependence of temperature margin on magnetic fields and operating temperature has been researched. The studies of ITER SCC provide a basis for the stable operation and optimization design of SCC CICC.

Jin, Fang; Xiaoyu, Chen; Wei, Zhou; Liangfeng, Liu; Yuntao, Song; Weiyue, Wu

180

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. Membranes composed of fatty acids have been proposed as model systems of primitive membranes, but their bilayer structure is stable only within a narrow pH range and low ionic strength. They are particularly sensitive to aggregating effects of divalent cations (Mg+2, Ca+2, Fe+2) that would be present in Archaean sea water. Here we report that mixtures of alkyl amines and fatty acids form vesicles at strongly basic and acidic pH ranges which are resistant to the effects of divalent cations up to 0.1 M. Vesicles formed by mixtures of decylamine and decanoic acid (1:1 mole ratio) are relatively permeable to pyranine, a fluorescent anionic dye, but permeability could be reduced by adding 2 mol% of a polycyclic aromatic hydrocarbon such as pyrene. Permeability to the dye was also reduced by increasing the chain length of the amphiphiles. For instance, 1:1 mole ratio mixtures of dodecylamine and dodecanoic acid were able to retain pyranine dye during and following gel filtration. We conclude that primitive cell membranes were likely to be composed of mixtures of amphiphilic and hydrophobic molecules that manifested increased stability over pure fatty acid membranes. PMID:18560991

Namani, Trishool; Deamer, David W

2008-08-01

181

System model of an image stabilization system

NASA Astrophysics Data System (ADS)

The Polarimetric and Helioseismic Imager (PHI) instrument is part of the remote instruments for the ESA Solar Orbiter (SO), which is scheduled to launch in 2017. PHI captures polarimetric images from the Sun to better understand our nearest star, the Sun. A set of images is acquired with different polarizations, and afterwards is processed to extract the Stokes parameters. As Stokes parameters require the subtraction of the image values, in order to get the desired quality it is necessary to have good contrast in the image and very small displacements between them. As a result an Image Stabilization System (ISS) is required. This paper is focused in the behavior and the main characteristics of this system. This ISS is composed of a camera, a tip-tilt mirror and a control system. The camera is based on a STAR1000 sensor that includes a 10 bits resolution high-speed Analog-to-Digital Converter (ADC). The control system includes a Correlation Tracking (CT) algorithm that determines the necessary corrections. The tip-tilt mirror is moved based on this corrections to minimize the effects of the spacecraft (S/C) drift and jitter with respect to the Sun. Due to its stringent requirements, a system model has been developed in order to verify that the required parameters can be satisfied. The results show that the ISS is feasible, although the margins are very small.

Carmona, Manuel; Gómez, José María.; Roma, David; Casas, Albert; López, Manel; Bosch, José; Herms, Atilŕ; Sabater, Josep; Volkmer, Reiner; Heidecke, Frank; Maue, Thorsten; Nakai, Eiji; Schmidt, Wolfgang

2014-08-01

182

Input-to-State Stability: A Unifying Framework for Robust Model Predictive Control

This paper deals with the robustness of Model Predictive Controllers for constrained uncertain nonlinear systems. The uncertainty\\u000a is assumed to be modeled by a state and input dependent signal and a disturbance signal. The framework used for the analysis\\u000a of the robust stability of the systems controlled by MPC is the wellknown Input-to-State Stability. It is shown how this notion

D. Limon; T. Alamo; D. M. Raimondo; D. de la Peńa; J. Bravo; A. Ferramosca; E. Camacho

183

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

184

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

185

Stability analysis and synthesis of multivariable fuzzy systems using interval arithmetic

This paper deals with the design of stable rule-based fuzzy control systems. Interval analysis is applied to design a stable fuzzy Takagi–Sugeno–Kang controller using a robust condition to ensure the stability. The presented methodology starts with a state model of the plant, finds a candidate fuzzy controller and uses an interval arithmetic algorithm to verify the stability of closed-loop fuzzy

José M. Andújar; José Manuel Bravo; Antonio Peregrín

2004-01-01

186

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

187

Dynamic stability margin analysis on SRAM

MODELING ON SRAM..................................................... 7 2.1 How Does the SRAM Work........................................................... 7 2.2 Level-1 Spice Model... ...................................................................... 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...

Ho, Yenpo

2009-05-15

188

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

189

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

190

Dynamic flight stability of a hovering model insect: lateral motion

NASA Astrophysics Data System (ADS)

The lateral dynamic flight stability of a hovering model insect (dronefly) was 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. The main results are as following. (i) Three natural modes of motion were identified: one unstable slow divergence mode (mode 1), one stable slow oscillatory mode (mode 2), and one stable fast subsidence mode (mode 3). Modes 1 and 2 mainly consist of a rotation about the horizontal longitudinal axis ( x-axis) and a side translation; mode 3 mainly consists of a rotation about the x-axis and a rotation about the vertical axis. (ii) Approximate analytical expressions of the eigenvalues are derived, which give physical insight into the genesis of the natural modes of motion. (iii) For the unstable divergence mode, t d, the time for initial disturbances to double, is about 9 times the wingbeat period (the longitudinal motion of the model insect was shown to be also unstable and t d of the longitudinal unstable mode is about 14 times the wingbeat period). Thus, although the flight is not dynamically stable, the instability does not grow very fast and the insect has enough time to control its wing motion to suppress the disturbances.

Zhang, Yanlai; Sun, Mao

2010-05-01

191

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

2014-07-26

192

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

193

Analysis of Human Body Bipedal Stability for Neuromotor Disabilities

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

194

Borehole stability analysis at the Coporo-1 well, Colombia

BOREHOLE STABILITY ANALYSIS AT THE COPORO-I WELL, COLOMBIA A Thesis by HENRY ARIAS Submitted to the Ofttce of Graduate Studies of Texas A&M University in partial fulfillme u of:he requirements for thc degree of lvlASTER OF SCIENCE August... 2000 Major Subject: Petroleum Engineering BOREHOLE STABILITY ANALYSIS AT THE COPORO-I WELL, COLOMBIA A Thesis bv HENRY ARIAS Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIFNCE...

Arias, Henry

2012-06-07

195

Finite Element Stability Analysis for Coupled Rotor and Support Systems

NASA Technical Reports Server (NTRS)

The effects of fuselage motions on stability and random response were analytically assessed. The feasibility of adequate perturbation models from non-linear trim conditions was studied by computer and hardware experiments. Rotor wake-blade interactions were assessed by using a 4-bladed rotor model with the capability of progressing and regressing blade pitch excitation (cyclic pitch stirring), by using a 4-bladed rotor model with hub tilt stirring, and by testing rotor models in sinusoidal up or side flow.

Hohenemser, K. H.; Yin, S. K.

1977-01-01

196

Decentralized, Cooperative Control of Multivehicle Systems: Design and Stability Analysis

characterize the nonlinear vehicle model for the control inputs designed using the decoupled, double-integrator representation. Whereas the kinematics vehicle model presented here is for planar vehicle mo- tion, a guidance model for vehicle motion in three... of Maximum Delay for Stability (No Delays in Kinematics) 141 xiii LIST OF FIGURES FIGURE Page 1 Nonholonomically-constrained vehicle model. ............. 13 2 Leader-follower communication structure for a multivehicle formation. 19 3 Simulation results...

Weitz, Lesley A.

2010-01-16

197

STABILITY OF CLUSTER SOLUTIONS IN A TRITROPHIC FOOD CHAIN MODEL

STABILITY OF CLUSTER SOLUTIONS IN A TRITROPHIC FOOD CHAIN MODEL JUNCHENG WEI AND MATTHIAS WINTER Abstract. We study a tritrophic food chain model which is based on Schnakenberg type kinetics. This model] for which there is only one prey and one predator. In this food chain model there is one predator feeding

Wei, Jun-cheng

198

Mathematical analysis of crossflow magnetically stabilized fluidized bed chromatography

A mathematical model was developed for a crossflow magnetically stabilized fluidized bed (MSB) chromatograph with the pertinent continuity equations derived in partial differential equation form. In the case of linear adsorption isotherms, Fourier transform analysis yielded an expression for the resolution of the elution curves in terms of system parameters and operating conditions. Calculated predictions of the first moment and the variance of the elution curves were in good agreement with experimental results. A systematic parametric study conducted using the model showed that two factors, resistance to mass transfer and the width of the feed zone, have dominant effects on the size of the chomatographic bed. If smaller particles are utilized, which can be accomplished without excessive pressure drop by using an MSB, the mass-transfer resistance is reduced significantly. This allows an increase in the fraction of the bed width devoted to the feed zone and, thus, results in a lower solvent (carrier fluid) to feed ratio and more concentrated product solutions.

Pirkle, J.C. Jr.; Siegell, J.H. (Corporate Research Labs., Exxon Research and Engineering Co., Annandale, NJ (US))

1988-05-01

199

MAGNETOHYDRODYNAMICS Vol. 48 (2012), No. 1, pp. 147155 LINEAR STABILITY ANALYSIS FOR

. Using the modal stability analysis, it has been demonstrated that the magnetic field stabilizes the flow = 0.161531 Ha. Linear stability analysis (modal) and energy methods are two standard toolsMAGNETOHYDRODYNAMICS Vol. 48 (2012), No. 1, pp. 147Â155 LINEAR STABILITY ANALYSIS FOR THE HARTMANN

Abdou, Mohamed

200

. A structure that consists of cables and struts is called a tensegrity structure. Since the cable member has no flexural stiffness, tensegrity structures are usually stabilized by introducing prestresses to maintainStability analysis of cableÂbar structures by inverse-power method for eigenvalue analysis

Kanno, Yoshihiro

201

Energy-Casimir stability of hybrid Vlasov-MHD models

Different variants of hybrid kinetic-fluid models are considered for describing the interaction of a bulk fluid plasma obeying MHD and an energetic component obeying a kinetic theory. Upon using the Vlasov kinetic theory for energetic particles, two planar Vlasov-MHD models are compared in terms of their stability properties. This is made possible by the Hamiltonian structures underlying the considered hybrid systems, whose infinite number of invariants makes the energy-Casimir method effective for determining stability. Equilibrium equations for the models are obtained from a variational principle and in particular a generalized hybrid Grad-Shafranov equation follows for one of the considered models. The stability conditions are then derived and discussed with particular emphasis on kinetic particle effects on classical MHD stability.

Cesare Tronci; Emanuele Tassi; Philip J. Morrison

2014-10-07

202

Stability analysis of shear flows in a Hele-Shaw cell

A mathematical model describing motion of an inhomogeneous incompressible fluid in a Hele-Shaw cell is considered. Linear stability analysis of shear flow class is provided. The role of inertia, linear friction and impermeable boundaries in Kelvin--Helmholtz instability development is studied. Hierarchy of simplified one-dimensional models of viscosity- and density-stratified flows is obtained in long-wave approximation. Interpretation of Saffman--Taylor instability development is given in the framework of these models.

Chesnokov, Alexander

2015-01-01

203

Model reference adaptive control system hyperstability analysis

The stability of the model reference adaptive control system with external disturbance and unmodeling is discussed. Instead of Lyapunov's method, more general results have been acquired for the analysis of hyperstability. It is shown that if only the linear forward block can be made strictly positive real, then the globally asymptotical hyperstability of the error model structure will be guaranteed

ZHAO CHUAN; J. E. Fagan

1993-01-01

204

Stability of Ghost Dark Energy in CBD Model of Gravity

We study the stability of the ghost dark energy model versus perturbation. Since this kind of dark energy is instable in Einsteinian general relativity theory, then we study a new type of Brans-Dicke theory which has non-minimal coupling with matter which is called chameleon Brans-Dicke (CBD) model of gravity. Due to this coupling the equation of conservation energy is modified. For considering the stability of the model we use the adiabatic squared sound speed, $c_s^2$, whose sign of it determines the stability of the model in which for $c_s^2 >0 $ the model is stable and for $c_s^2 <0 $ the model is instable. However, we study the interacting and non-interacting version of chameleon Brans-Dicke ghost dark energy (CBDGDE) with cold dark matter in non flat FLRW metric. We show that in all cases of investigation the model is stable with a suitable choice of parameters.

Khaled Saaidi

2012-02-18

205

Bifurcation analysis of axial flow compressor stability

NASA Technical Reports Server (NTRS)

With a one-mode truncation it is possible to reduce the Moore-Greitzer model for compressor instability to a set of three ordinary differential equations. These are approached from the point of view of bifurcation theory. Most of the bifurcations emerge from a degenerate Takens-Bogdanov bifurcation point. The bifurcation sets are completed using the numerical branch tracking scheme AUTO. Despite the severity of the truncation, the agreement with experimental results is excellent.

Mccaughan, F. E.

1990-01-01

206

Background Antagonistic activation of abdominal muscles and raised intra-abdominal pressure are associated with both spinal unloading and spinal stabilization. Rehabilitation regimens have been proposed to improve spinal stability via selective recruitment of certain trunk muscle groups. This biomechanical study used an analytical model to address whether lumbar spinal stability is increased by selective activation of abdominal muscles. Methods The biomechanical model included anatomically realistic three-layers of curved abdominal musculature connected by fascia, rectus abdominis and 77 symmetrical pairs of dorsal muscles. The muscle activations were calculated with the model loaded with either flexion, extension, lateral bending or axial rotation moments up to 60 Nm, along with intra-abdominal pressure up to 5 or 10 kPa (37.5 or 75 mm Hg) and partial bodyweight. After solving for muscle forces, a buckling analysis quantified spinal stability. Subsequently, different patterns of muscle activation were studied by forcing activation of selected abdominal muscles to at least 10% or 20% of maximum. Findings The spinal stability increased by an average factor of 1.8 with doubling of intra-abdominal pressure. Forced activation of obliques or transversus abdominis muscles to at least 10% of maximum increased stability slightly for efforts other than flexion, but forcing at least 20% activation generally did not produce further increase in stability. Forced activation of rectus abdominis did not increase stability. Interpretation Based on predictions from an analytical spinal buckling model, the degree of stability was not substantially influenced by selective forcing of muscle activation. This casts doubt on the supposed mechanism of action of specific abdominal muscle exercise regimens that have been proposed for low back pain rehabilitation. PMID:21571410

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

2011-01-01

207

Stability analysis of a dynamic inversion based pitch rate controller for an unmanned aircraft

Nonlinear dynamic inversion (NDI) is a very popular method employed in aircraft automatic flight control systems. However, it is known that this technique may have stability and robustness issues as soon as the model parameters used in the inversion process are uncertain or when the measurement data are noisy and biased. Many advanced analysis techniques have been presented to quantify

Guillaume Ducard; Hans Peter Geering

2008-01-01

208

Stability of the Human Respiratory Control System. Part II: Analysis of a threeÂdimensional 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

209

GEOTECHNICAL ANALYSIS FOR REVIEW OF DIKE STABILITY (GARDS). TECHNICAL MANUAL

The structure and capabilities of a user-friendly, interactive computer program developed for the stability analysis of dikes (GARDS) are described. The program was developed under the sponsorship of the U.S. Environmental Protection Agency and therefore emphasizes Hazardous Wast...

210

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

211

STABILITY ANALYSIS OF INTERCONNECTED POWER SYSTEMS COUPLED WITH MARKET DYNAMICS

STABILITY ANALYSIS OF INTERCONNECTED POWER SYSTEMS COUPLED WITH MARKET DYNAMICS F.L. Alvarado1 J-based dispatch. Keywords: market dynamics, power system dynamics, dy- namic coupling, eigenvalues 1 Introduction power system dynamics simultaneously is necessary. There has been relatively little prior work

212

Stability analysis with Popov multipliers and integral quadratic constraints

It is shown that a general form of Popov multipliers can be used in stability analysis based on integral quadratic constraints (IQC). The Popov multiplier is nonproper and a condition that the nominal plant is strictly proper will be imposed in order to ensure boundedness of the IQC corresponding to the Popov multiplier. A consequence of our main result is

Ulf Jönsson

1997-01-01

213

Stability analysis and control of multiple converter based autonomous microgrid

In this paper, the stability of an autonomous microgrid with multiple distributed generators (DG) is studied through eigenvalue analysis. It is assumed that all the DGs are connected through Voltage Source Converter (VSC) and all connected loads are passive. The VSCs are controlled by state feedback controller to achieve desired voltage and current outputs that are decided by a droop

Ritwik Majumder; Arindam Ghosh; Gerard Ledwich; Firuz Zare

2009-01-01

214

Stability Analysis of Networked Control Systems with Unknown Inputs

# , Jitesh H. Panchal and Dengfeng Sun Abstract-- Unknown Input Observers (UIO) use the known plant's inputs robust observers for linear and nonlinear systems, for systems with known and unknown inputsStability Analysis of Networked Control Systems with Unknown Inputs Ahmad F Taha, Ahmed Elmahdi

Sun, Dengfeng

215

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

216

Modeling sawtooth stabilization by energetic ions from neutral beam injection

NASA Astrophysics Data System (ADS)

Recent advances in modeling the effects of anisotropic energetic ion distributions have enabled the development of a complete coherent physics explanation of sawtooth stabilization in both conventional and spherical tokamaks. As an example, a complete model has been developed to explain the asymmetric stabilization of sawteeth with respect to neutral beam injection direction in the Joint European Torus. This asymmetric sawtooth stabilization [M. Nave et al., Phys. Plasmas 13, 014503 (2006)] arises because of both the destabilizing contribution from the counterpassing ions and the strong modification of the stabilizing contribution of the nonadiabatic trapped ions due to flow shear. The fast particle effects including pressure anisotropy, sheared flows, and the adiabatic response to the internal kink mode have been modeled in general toroidal geometry for the first time.

Chapman, I. T.; Pinches, S. D.; Appel, L. C.; Hastie, R. J.; Hender, T. C.; Saarelma, S.; Sharapov, S. E.; Voitsekhovitch, I.; Graves, J. P.

2007-07-01

217

Stability of Differential Susceptibility and Infectivity Epidemic Models

Stability of Differential Susceptibility and Infectivity Epidemic Models B. Bonzi3 , A. A. Fall1-010-0327-y #12;Abstract We introduce classes of differential susceptibility and infectivity epidemic models. These models address the problem of flows between the different susceptible, infectious and infected

218

Aeroelastic stability analyses of two counter rotating propfan designs for a cruise missile model

NASA Technical Reports Server (NTRS)

A modal aeroelastic analysis combining structural and aerodynamic models is applied to counterrotating propfans to evaluate their structural integrity for wind-tunnel testing. The aeroelastic analysis code is an extension of the 2D analysis code called the Aeroelastic Stability and Response of Propulsion Systems. Rotational speed and freestream Mach number are the parameters for calculating the stability of the two blade designs with a modal method combining a finite-element structural model with 2D steady and unsteady cascade aerodynamic models. The model demonstrates convergence to the least stable aeroelastic mode, describes the effects of a nonuniform inflow, and permits the modification of geometry and rotation. The analysis shows that the propfan designs are suitable for the wind-tunnel test and confirms that the propfans should be flutter-free under the range of conditions of the testing.

Mahajan, Aparajit J.; Lucero, John M.; Mehmed, Oral; Stefko, George L.

1992-01-01

219

Fluid Dynamic and Stability Analysis of a Thin Liquid Sheet

NASA Technical Reports Server (NTRS)

Interest in thin sheet flows has recently been renewed due to their potential application in space radiators. Theoretical and experimental studies of the fluid dynamics and stability of thin liquid sheet flows have been carried out in this thesis. A computer program was developed to determine the cross-sectional shape of the edge cylinder given the cross-sectional area of the edge cylinder. A stability analysis was performed on a non-planer liquid sheet. A study was conducted to determine the effects of air resistance on the sheet.

McMaster, Matthew S.

1992-01-01

220

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...

221

Stability Analysis of Gravity-Driven Viscosity - Coating Flows.

NASA Astrophysics Data System (ADS)

This theoretical investigation presents the linear stability analysis of a gravity-driven and viscosity-stratified coating flow useful in covering a planar surface with one or more liquid layers. The challenging stability analysis of a coating flow on a curved substrate surface is discussed. The mathematical foundation on which to analyse the stability of this inherently spatial coating flow problem is provided by a Green's impulse function approach which serves as the appropriate mathematical tool to describe (arbitrary) disturbances imposed on the liquid surface. The temporal analysis showed that a two-layered Newtonian coating flow is susceptible to an instability due to viscosity stratification even without the effects of surface tension, density stratification or, surprisingly, inertia. In addition, waves with the largest growth typically occur at finite wavelengths; the properties of these waves are often of greatest practical interest. However, the temporal growth rate, for the maximally unstable mode, of order 0.0015 was small. The mathematically proper ray-speed approach, originating from a steepest descent method to determine the perturbed film thickness, removed the interpretational quandary present in the classical spatial approach and corroborated the temporal linear stability results.

Figa, Jan

1995-01-01

222

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

223

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

224

Experimental bifurcation analysis of an impact oscillator-Determining stability

NASA Astrophysics Data System (ADS)

We propose and investigate three different methods for assessing stability of dynamical equilibrium states during experimental bifurcation analysis, using a control-based continuation method. The idea is to modify or turn off the control at an equilibrium state and study the resulting behavior. As a proof of concept the three methods are successfully implemented and tested for a harmonically forced impact oscillator with a hardening spring nonlinearity, and controlled by electromagnetic actuators. We show that under certain conditions it is possible to quantify the instability in terms of finite-time Lyapunov exponents. As a special case we study an isolated branch in the bifurcation diagram brought into existence by a 1:3 subharmonic resonance. On this isola it is only possible to determine stability using one of the three methods, which is due to the fact that only this method guarantees that the equilibrium state can be restored after measuring stability.

Bureau, Emil; Schilder, Frank; Elmegĺrd, Michael; Santos, Ilmar F.; Thomsen, Jon J.; Starke, Jens

2014-10-01

225

Stability analysis of mixed retarded-neutral type systems in Hilbert space

Stability analysis of mixed retarded-neutral type systems in Hilbert space R. Rabah G.M. Sklyar P;Stability analysis of mixed retarded-neutral type systems in Hilbert space Rabah Rabah1 , Grigory Sklyar2 stability, strong stability, infinite dimensional systems. 2 hal-00580053,version1-25Mar2011 #12;Abstract We

Boyer, Edmond

226

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 O.

227

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

228

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

229

Analysis: Modelling Problem Understanding

Chapter 2 Analysis: Modelling Problem Understanding The work in this chapter is structured as follows: Section 2.1: Introducing Formal Object Oriented Analysis (FOOA) This section provides a brief review of object orientation and formalisation with respect to the limitations of current analysis

Gibson, J. Paul

230

Preliminary hazards analysis of thermal scrap stabilization system. Revision 1

This preliminary analysis examined the HA-21I glovebox and its supporting systems for potential process hazards. Upon further analysis, the thermal stabilization system has been installed in gloveboxes HC-21A and HC-21C. The use of HC-21C and HC-21A simplified the initial safety analysis. In addition, these gloveboxes were cleaner and required less modification for operation than glovebox HA-21I. While this document refers to glovebox HA-21I for the hazards analysis performed, glovebox HC-21C is sufficiently similar that the following analysis is also valid for HC-21C. This hazards analysis document is being re-released as revision 1 to include the updated flowsheet document (Appendix C) and the updated design basis (Appendix D). The revised Process Flow Schematic has also been included (Appendix E). This Current revision incorporates the recommendations provided from the original hazards analysis as well. The System Design Description (SDD) has also been appended (Appendix H) to document the bases for Safety Classification of thermal stabilization equipment.

Lewis, W.S.

1994-08-23

231

On Stability of Sampling-Reconstruction Models

A useful sampling-reconstruction model should be stable with respect to different kind of small perturbations, regardless whether they result from jitter, measurement errors, or simply from a small change in the model assumptions. In this paper we prove this result for a large class of sampling models. We define different classes of perturbations and quantify the robustness of a model with respect to them. We also use the theory of localized frames to study the frame algorithm for recovering the original signal from its samples.

E. costa-Reyes; A. Aldroubi; I. Krishtal

2007-05-29

232

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...

233

Limitations of Deterministic Modelling of Slope Stability on Volcanic Edifices

NASA Astrophysics Data System (ADS)

The conditions leading to the 18 May 1980 sector collapse of Mount St Helens have been the subject of a number of detailed investigations. Preservation of the initial failure plane(s) allowed Voight et al. (1983) and Donnadieu et al. (2001) to undertake back analyses and determine a range of possible failure conditions. While the models proposed offer major insights into potential failure mechanisms, we will demonstrate that deterministic analyses are of limited usefulness because many of the model parameters, such as cohesion, internal friction and pore pressure, are very poorly constrained. This creates problems of non-uniqueness in the solution. An alternative approach involves a series of Monte Carlo simulations to identify potential combinations of parameters that will produce the observed failure plane. Initial input ranges are specified for each parameter and the predetermined model is run repeatedly, with the parameter values for each model selected at random from within the input ranges. The interaction between parameters can be examined in detail, providing a better understanding of the potential failure conditions. This approach, which has been tested initially on a theoretical slope with predetermined failure conditions, highlights the fact that it is impossible to generate a unique model that fits the data when the slope has poorly defined strength parameters. This has clear implications for the validity of commonly used deterministic approaches. This probabilistic back analysis approach has been used to reanalyse the conditions that led to the May 18 collapse on Mount St Helens. Donnadieu, F., Merle, O., and Besson, J.C., 2001, Volcanic edifice stability during cryptodome intrusion, Bulletin of Volcanology, vol 63, p61-72. Voight, B., Janda, R.J., Glicken, H., and Douglass, P.M., 1983, Nature and Mechanics of the Mount St-Helens Rockslide-Avalanche of 18 May 1980, Geotechnique, vol 33, p243-273.

Burrell, R. V.; Pinkerton, H.; Binley, A.

2004-12-01

234

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

235

Comprehensive gait analysis in posterior-stabilized knee arthroplasty

Sixteen patients implanted with a posterior-stabilized prosthesis (Insall-Burstein PS II, Zimmer, Warsaw, IN) and 32 age-matched control subjects were evaluated by isokinetic muscle testing and comprehensive gait analysis at a mean 46 months following the index arthroplasty. The contralateral knee was normal in 13 patients and an asymptomatic total knee arthroplasty in 3 patients. No significant differences (P > .05)

Stephen A. Wilson; Peter D. McCann; Robert S. Gotlin; H. K. Ramakrishnan; Mary E. Wootten; John N. Insall

1996-01-01

236

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

237

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

238

Dynamic Response and Stability Analysis of AN Automatic Ball Balancer for a Flexible Rotor

NASA Astrophysics Data System (ADS)

Dynamic stability and time responses are studied for an automatic ball balancer of a rotor with a flexible shaft. The Stodola-Green rotor model, of which the shaft is flexible, is selected for analysis. This rotor model is able to include the influence of rigid-body rotations due to the shaft flexibility on dynamic responses. Applying Lagrange's equation to the rotor with the ball balancer, the non-linear equations of motion are derived. Based on the linearized equations, the stability of the ball balancer around the balanced equilibrium position is analyzed. On the other hand, the time responses computed from the non-linear equations are investigated. This study shows that the automatic ball balancer can achieve the balancing of a rotor with a flexible shaft if the system parameters of the balancer satisfy the stability conditions for the balanced equilibrium position.

Chung, J.; Jang, I.

2003-01-01

239

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

Carreón-Calderón, Bernardo

2012-10-14

240

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

241

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

242

On the Stability of a class of Modified Gravitational Models

Motivated by the dark energy issue, a minisuperspace approach to the stability for modified gravitational models in a four dimensional cosmological setting are investigated. Specifically, after revisiting the $f(R)$ case, $R$ being the Ricci curvature, we present a stability condition around a de Sitter solution valid for modified gravitational models of generalized Gauss-Bonnet type $F(R,G,Q)$, $G$ and $Q$ being the Gauss-Bonnet and quadratic Riemann invariants respectively. A generalization to higher order invariants is mentioned.

Guido Cognola; Monica Gastaldi; Sergio Zerbini

2007-01-25

243

NUMERICAL STABILITY ANALYSIS OF THE EULER SCHEME FOR JEAN-FRANOIS CHASSAGNEUX AND ADRIEN RICHOU

NUMERICAL STABILITY ANALYSIS OF THE EULER SCHEME FOR BSDES JEAN-FRANĂ?OIS CHASSAGNEUX AND ADRIEN the numerical stability. We then perform a classical Von Neumann stability analysis in the case of a linear analysis of the pseudo explicit Euler scheme 14 4. Numerical illustration 16 4.1. Linear specifications

Paris-Sud XI, UniversitĂ© de

244

Stability analysis of periodic orbits in the framework of Galerkin approximations

Stability analysis of periodic orbits in the framework of Galerkin approximations Denis Laxalde specifically Galerkin weighted residuals, their stability analysis usually requires a subsequent and sometimes. This paper suggests a general framework for stability analysis of periodic solutions derived using Galerkin

Paris-Sud XI, UniversitĂ© de

245

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

246

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

247

[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

248

Exploring EnKF stability under different type reservoir model

NASA Astrophysics Data System (ADS)

Reservoir properties estimation aims to maximize the recovery, and least squares history matching is one of strategies to achieve this target. A model is matched on historical data until it reproduced the production history. The model can be used to simulate future reservoir production. The Ensemble Kalman Filter (EnKF) is a method designed for non linear history matching. The success of EnKF affected by non linearity of reservoir model. If the reservoir model is highly non linear the EnKF might be unstable. This paper aims to explore the stability of EnKF under different type reservoir models. Three type reservoir models are considered: (1) line source (2) bounded constant rate no flow (3) three grid reservoir. The permeability is estimated based on the matching of observed pressure with predicted pressure (obtained from reservoir model). A simulation experiment is set up to show how EnKF iteration may be used to estimate the permeability. The simulation is set up for an experiment time T, time step ?t, and number of observations m. The prior for permeability is drawn from normal distribution. The stability of the results is presented as plots of pressure history match and permeability updating. The three grid reservoir model shows instability of EnKF method, and an iterative EnKF was proposed to improve the stability of EnKF. The proposed method is able to history match the reservoir models, and exploring the stability of a more general reservoir model is needed for the success of the method.

Darwis, Sutawanir; Gunawan, Agus Yodi; Mutaqin, Aceng Komarudin; Fitriyati, Nina

2012-05-01

249

Stability Analysis for a Saline Boundary Layer Formed by Uniform Up ow Using Finite Elements

Stability Analysis for a Saline Boundary Layer Formed by Uniform Up ow Using Finite Elements G the stability of the boundary layer. Subsequently we focus on Finite Element (FEM) solutions of the governing equations to validate numerically the semi-analytical stability bounds. Furthermore, we analyse stability

Eindhoven, Technische Universiteit

250

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

251

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

252

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

253

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

254

Orbiter Boundary Layer Transition Stability Modeling at Flight Entry Conditions

NASA Technical Reports Server (NTRS)

State of the art boundary layer stability modeling capabilities are increasingly seeing application to entry flight vehicles. With the advent of user friendly and robust implementations of two-dimensional chemical nonequilibrium stability modeling with the STABL/PSE-CHEM software, the need for flight data to calibrate such analyses capabilities becomes more critical. Recent efforts to perform entry flight testing with the Orbiter geometry related to entry aerothermodynamics and boundary layer transition is allowing for a heightened focus on the Orbiter configuration. A significant advancement in the state of the art can likely be achieved by establishing a basis of understanding for the occurrence of boundary layer transition on the Orbiter due to discrete protruding gap fillers and the nominal distributed roughness of the actual thermal protection system. Recent success in demonstrating centerline two-dimensional stability modeling on the centerline of the Orbiter at flight entry conditions provides a starting point for additional investigations. The more detailed paper will include smooth Orbiter configuration boundary layer stability results for several typical orbiter entry conditions. In addition, the numerical modeling approach for establishing the mean laminar flow will be reviewed and the method for determining boundary layer disturbance growth will be overviewed. In addition, if actual Orbiter TPS surface data obtained via digital surface scans become available, it may be possible to investigate the effects of an as-flown flight configuration on boundary layer transition compared to a smooth CAD reference.

Bartkowicz, Matt; Johnson, Heath; Candler, Graham; Campbell, Charles H.

2009-01-01

255

Doubly-fed induction machine models for stability assessment of wind farms

The increasing size of wind farms requires power system stability analysis including dynamic models of the wind power generation. Nowadays, the most widely used generator type for units above 1 MW is the doubly-fed induction machine. Doubly-fed induction machines allow active and reactive power control through a rotor-side converter, while the stator is directly connected to the grid. Detailed models

Markus A. Poller

2003-01-01

256

Ionic liquid thermal stabilities: decomposition mechanisms and analysis tools.

The increasing amount of papers published on ionic liquids generates an extensive quantity of data. The thermal stability data of divergent ionic liquids are collected in this paper with attention to the experimental set-up. The influence and importance of the latter parameters are broadly addressed. Both ramped temperature and isothermal thermogravimetric analysis are discussed, along with state-of-the-art methods, such as TGA-MS and pyrolysis-GC. The strengths and weaknesses of the different methodologies known to date demonstrate that analysis methods should be in line with the application. The combination of data from advanced analysis methods allows us to obtain in-depth information on the degradation processes. Aided with computational methods, the kinetics and thermodynamics of thermal degradation are revealed piece by piece. The better understanding of the behaviour of ionic liquids at high temperature allows selective and application driven design, as well as mathematical prediction for engineering purposes. PMID:23598738

Maton, Cedric; De Vos, Nils; Stevens, Christian V

2013-07-01

257

An input-output stability analysis of a fuzzy controller for a missile autopilot's yaw axis

This paper develops an input-output stability analysis on the basis of the rules, and the control input values generated by the fuzzy controller for each “cell partition” of the phase plane. It is assumed that the rule-base has been designed for a linear plant whose approximate model is available. Furthermore, the rules may have been derived using the operator manual-type

S. S. Farinwata; D. Pirovolou; G. J. Vachtsevanos

1994-01-01

258

Estimation of dynamic stability parameters from drop model flight tests

NASA Technical Reports Server (NTRS)

The overall remotely piloted drop model operation, descriptions, instrumentation, launch and recovery operations, piloting concept, and parameter identification methods are discussed. Static and dynamic stability derivatives were obtained for an angle attack range from -20 deg to 53 deg. It is indicated that the variations of the estimates with angle of attack are consistent for most of the static derivatives, and the effects of configuration modifications to the model were apparent in the static derivative estimates.

Chambers, J. R.; Iliff, K. W.

1981-01-01

259

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

260

Preliminary Slope-Stability Analysis of Augustine Volcano

Augustine Volcano has been a prolific producer of large debris avalanches during the Holocene. Originating as landslides from the steep upper edifice, these avalanches typically slide into the surrounding ocean. At least one debris avalanche that occurred in 1883 during an eruption initiated a far-traveled tsunami. The possible occurrence of another edifice collapse and ensuing tsunami was a concern during the 2006 eruption of Augustine. To aid in hazard assessments, we have evaluated the slope stability of Augustine's edifice, using a quasi-three-dimensional, geotechnically based slope-stability model implemented in the computer program SCOOPS. We analyzed the effects of topography, variations in rock strength, and earthquake-induced strong ground motion on the relative stability of millions of potential large (>0.1 km3 volume) slope failures throughout the edifice. Preliminary results from pre-2006 topography provide three insights. First, the predicted stability of all parts of the upper edifice is approximately the same, suggesting an equal likelihood of slope failure, in agreement with geologic observations that debris avalanches have swept all sectors of the volcano. Second, the least stable (by a small amount) sector is on the east flank where a debris avalanche would flow into deeper ocean water and a resulting tsunami would be directed toward the southwestern part of the Kenai Peninsula. Third, most model scenarios predict stable edifice slopes, and only scenarios assuming extensive weak rocks and moderate to strong ground shaking predict potential large collapses. Because other transient triggering mechanisms, such as shallow magma intrusion, may be needed to instigate slope instability, monitoring ground deformation and seismicity could

Reid, Mark E.; Brien, Dianne L.; Waythomas, Christopher F.

2010-01-01

261

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

262

On the stability and bifurcation analysis of dual-spin spacecraft

NASA Astrophysics Data System (ADS)

The dynamics of dual-spin spacecraft under effects of energy dissipation are considered in this paper, where the damper masses in the platform (P) and the rotor (R) cause energy loss in the system. The Floquet theory is employed to obtain stability charts for different relative spin rates of the subsystem R with respect to the subsystem P. Based on the general model for the system with nutation dampers on both P and R, models are presented for a system whose nutation damper exists only in P as well as a system without nutation damper. The results obtained from the Floquet theory agree with the energy sink analysis in the literature. The bifurcation analysis based on the movement of loci of the Floquet multipliers as the system passes through the flutter stability boundary indicates that the system experiences the secondary Hopf (Neimark-Sacker) bifurcation. The investigations show that for spacecraft whose nutation damper exists only in one of the subsystems, there is no need to apply Floquet theory, and the Routh-Hurwitz criteria provides necessary and sufficient conditions for stability. Furthermore, for the case that only P has damping, the Lyapunov stability criteria agree with Routh-Hurwitz criteria.

Nazari, Morad; Butcher, Eric A.

2014-01-01

263

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

264

Stability analysis for sampled-data systems with a time-varying period Alexandre Seuret

Stability analysis for sampled-data systems with a time-varying period Alexandre Seuret alexandre-- This paper proposes a novel stability analysis of linear systems with sampled-data inputs. Inspired by the input- delay approach and the stability of impulsive systems, this method provides novel sufficient

Paris-Sud XI, UniversitĂ© de

265

Finite-Time Stability of Discrete-Time Nonlinear Systems: Analysis and Design

Finite-Time Stability of Discrete-Time Nonlinear Systems: Analysis and Design S. Mastellone, P. Dorato, C. T. Abdallah Abstract-- Finite-time stability of nonlinear discrete-time systems is studied we propose a new analysis result for fi- nite time stability of deterministic and stochastic discrete

266

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

267

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

268

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

269

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

270

Stability in Model Populations m onographs in p opulation b iology 3 1

Stability in Model Populations m onographs in p opulation b iology Â· 3 1 laurence d. mueller amitabh joshi #12;Stability in Model Populations LAURENCE D. MUELLER AND AMITABH JOSHI PRINCETON--Introduction 000 Historical Development of the Concept of Population Stability 000 What Is Stability? 000

Rose, Michael R.

271

RESOLUTION AND STABILITY ANALYSIS OF AN INVERSE PROBLEM IN ELECTRICAL IMPEDANCE TOMOGRAPHY

RESOLUTION AND STABILITY ANALYSIS OF AN INVERSE PROBLEM IN ELECTRICAL IMPEDANCE TOMOGRAPHY words. elliptic inverse problem, electrical impedance tomography, conductivity imaging, stability, 15A09, 65N99 1. Introduction. In electrical impedance tomography, the problem is to #12;nd

272

Vehicle Dynamics and Stability Analysis with Matlab and Adams Car

The automotive active dynamics and stability control is nowadays available from many manufacturers which offer different hardware and software solutions. To compare the performance obtainable considering different active systems, a mathematical model of a new car was implemented through Adams Car. The model was completed with a powertrain specifically conceived in Matlab environment to overcome problems due to an Adams Car modelling not suitable to describe every operating condition (e.g. standing start, gearshift). A strategy to overcome the problems introduced by the dependence of nominal yaw rate value on the instantaneously available tire-terrain adhesion coefficient was considered. The most important results obtained adopting the described strategy are presented through animations.

N. Arborio; P. Munaretto; M. Velardocchia; N. Riva; E. Suraci

2000-01-01

273

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

274

Fuzzy Current-Mode Control and Stability Analysis

NASA Technical Reports Server (NTRS)

In this paper a current-mode control (CMC) methodology is developed for a buck converter by using a fuzzy logic controller. Conventional CMC methodologies are based on lead-lag compensation with voltage and inductor current feedback. In this paper the converter lead-lag compensation will be substituted with a fuzzy controller. A small-signal model of the fuzzy controller will also be developed in order to examine the stability properties of this buck converter control system. The paper develops an analytical approach, introducing fuzzy control into the area of CMC.

Kopasakis, George

2000-01-01

275

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 the authors 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 allowed 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 form 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.

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

1986-01-01

276

In situ vitrification: Application analysis for stabilization transuranic waste

NASA Astrophysics Data System (ADS)

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 was 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.

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

1982-09-01

277

Aeroelastic stability analyses of two counter rotating propfan designs for a cruise missile model

NASA Technical Reports Server (NTRS)

Aeroelastic stability analyses were performed to insure structural integrity of two counterrotating propfan blade designs for a NAVY/Air Force/NASA cruise missile model wind tunnel test. This analysis predicted if the propfan designs would be flutter free at the operating conditions of the wind tunnel test. Calculated stability results are presented for the two blade designs with rotational speed and Mach number as the parameters. A aeroelastic analysis code ASTROP2 (Aeroelastic Stability and Response of Propulsion Systems - 2 Dimensional Analysis), developed at LeRC, was used in this project. The aeroelastic analysis is a modal method and uses the combination of a finite element structural model and two dimensional steady and unsteady cascade aerodynamic models. This code was developed to analyze single rotation propfans but was modified and applied to counterrotating propfans for the present work. Modifications were made to transform the geometry and rotation of the aft rotor to the same reference frame as the forward rotor, to input a non-uniform inflow into the rotor being analyzed, and to automatically converge to the least stable aeroelastic mode.

Mahajan, Aparajit J.; Lucero, John M.; Mehmed, Oral; Stefko, George L.

1992-01-01

278

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

279

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

Densmore, Jeffery D. [Computational Physics and Methods Group, Los Alamos National Laboratory, P.O. Box 1663, MS D409, Los Alamos, NM 87545 (United States)], E-mail: jdd@lanl.gov; Warsa, James S. [Computational Physics and Methods Group, Los Alamos National Laboratory, P.O. Box 1663, MS D409, Los Alamos, NM 87545 (United States)], E-mail: warsa@lanl.gov; Lowrie, Robert B. [Computational Physics and Methods Group, Los Alamos National Laboratory, P.O. Box 1663, MS D409, Los Alamos, NM 87545 (United States)], E-mail: lowrie@lanl.gov; Morel, Jim E. [Department of Nuclear Engineering, Texas A and M University, 3133 TAMU, College Station, TX 77843 (United States)], E-mail: morel@tamu.edu

2009-09-01

280

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

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

2008-01-01

281

Thermal stability during rotation in space - A scaling and numerical analysis

NASA Technical Reports Server (NTRS)

An analysis of thermal stability in a fluid during rotation is presented. The conditions resulting in thermal stability are examined and numerically verified. It is shown that at least one thermal field exists for any rotating fluid, with or without a gravitational background field, where convection does not occur. The numerical model used is fully nonlinear and 3D. Results are presented on the basis of both steady-state and fully transient models. The thermally stable condition is further investigated in the context of the average net acceleration and the inhomogeneous part of the acceleration field (gradient of acceleration). It is shown that in the thermally stable condition the flow that would result from the average net acceleration is equal and opposite to the flow that would result from the inhomogeneous part of the acceleration field. It is concluded that the thermally stable condition is actually a flow mode transition at Ad = 1.

Arnold, William A.; Regel, Liya L.; Wilcox, William R.

1992-01-01

282

Quantum Magnetism Analysis Model

NSDL National Science Digital Library

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

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

2012-07-27

283

Stability Analysis of Resistive Wall Mode in Rotating High-beta Plasmas in DIII-D

NASA Astrophysics Data System (ADS)

Stability of resistive wall modes (RWM) in rotating high beta DIII-D discharges is analyzed using the MARS-F code. The modes are calculated in axisymmetric toroidal equilibrium using the MHD plasma model with kinetic damping effects. RWM are analyzed for different spacing between the resistive wall and the plasma boundary and for different toroidal rotation profiles. Sensitivity study of the mode's stability on the plasma edge q-profile is made by varying both the edge current profile and the proximity of the plasma boundary to the real X-point geometry. The importance of the edge modeling on accurate RWM stability analysis is revisited. Scans of the mode's growth rate and frequency are made in these settings, and the mode's structure is explored. Quasilinear toroidal torque driven by jxB force due to current and magnetic field perturbations in the RWM is estimated and compared with the experimental estimate of the total toroidal torque on plasma. The dependencies of the RWM growth rate and frequency on the stability and torque parameters are presented.

Svidzinski, V. A.; in, Y.; Kim, J. S.; Chu, M. S.; Liu, Y. Q.

2011-11-01

284

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

285

Modeling and Control of Combustion Dynamics in Lean-Premixed Swirl-Stabilized Combustors

A unified investigation, comprising both numerical simulation and analytical modeling, has been conducted to study the combustion dynamics in lean-premixed (LPM) swirl-stabilized combustors. The numerical analysis treats the conservation equations in three dimensions and takes into account finite-rate chemical reactions and variable thermophysical properties. Turbulence closure is achieved by means of a large-eddy simulation technique. Premixed turbulent combustion is treated

Ying Huang; Vigor Yang

2005-01-01

286

Another Proof of Stability for Global Weak Solutions of 2D Degenerated Shallow Water Models

. We consider non-linear viscous shallow water models with varying topography, extra friction terms and capillary effects, in\\u000a a two-dimensional framework. Water-depth dependent laminar and turbulent friction coefficients issued from an asymptotic analysis\\u000a of the three-dimensional free-surface Navier–Stokes equations are considered here. A new proof of stability for global weak\\u000a solutions is given in periodic domain ? = T2, adapting the

P. Fabrie; F. Marche

2009-01-01

287

Estimation of dynamic stability parameters from drop model flight tests

NASA Technical Reports Server (NTRS)

A recent NASA application of a remotely-piloted drop model to studies of the high angle-of-attack and spinning characteristics of a fighter configuration has provided an opportunity to evaluate and develop parameter estimation methods for the complex aerodynamic environment associated with high angles of attack. The paper discusses the overall drop model operation including descriptions of the model, instrumentation, launch and recovery operations, piloting concept, and parameter identification methods used. Static and dynamic stability derivatives were obtained for an angle-of-attack range from -20 deg to 53 deg. The results of the study indicated that the variations of the estimates with angle of attack were consistent for most of the static derivatives, and the effects of configuration modifications to the model (such as nose strakes) were apparent in the static derivative estimates. The dynamic derivatives exhibited greater uncertainty levels than the static derivatives, possibly due to nonlinear aerodynamics, model response characteristics, or additional derivatives.

Chambers, J. R.; Iliff, K. W.

1981-01-01

288

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

289

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

290

Absolute Stability Analysis of a Phase Plane Controlled Spacecraft

NASA Technical Reports Server (NTRS)

Many aerospace attitude control systems utilize phase plane control schemes that include nonlinear elements such as dead zone and ideal relay. To evaluate phase plane control robustness, stability margin prediction methods must be developed. Absolute stability is extended to predict stability margins and to define an abort condition. A constrained optimization approach is also used to design flex filters for roll control. The design goal is to optimize vehicle tracking performance while maintaining adequate stability margins. Absolute stability is shown to provide satisfactory stability constraints for the optimization.

Jang, Jiann-Woei; Plummer, Michael; Bedrossian, Nazareth; Hall, Charles; Jackson, Mark; Spanos, Pol

2010-01-01

291

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

A DNA triplex is formed through binding of a third strand to the major groove of a duplex. Due to the high charge density of a DNA triplex, metal ions are critical for its stability. We recently developed the tightly bound ion (TBI) model for ion-nucleic acids interactions. The model accounts for the potential correlation and fluctuations of the ion distribution. We now apply the TBI model to analyze the ion dependence of the thermodynamic stability for DNA triplexes. We focus on two experimentally studied systems: a 24-base DNA triplex and a pair of interacting 14-base triplexes. Our theoretical calculations for the number of bound ions indicate that the TBI model provides improved predictions for the number of bound ions than the classical Poisson-Boltzmann (PB) equation. The improvement is more significant for a triplex, which has a higher charge density than a duplex. This is possibly due to the higher ion concentration around the triplex and hence a stronger ion correlation effect for a triplex. In addition, our analysis for the free energy landscape for a pair of 14-mer triplexes immersed in an ionic solution shows that divalent ions could induce an attractive force between the triplexes. Furthermore, we investigate how the protonated cytosines in the triplexes affect the stability of the triplex helices. PMID:22067830

Chen, Gengsheng; Chen, Shi-Jie

2011-12-01

292

Assessment of sampling stability in ecological applications of discriminant analysis

A simulation study was undertaken to assess the sampling stability of the variable loadings in linear discriminant function analysis. A factorial design was used for the factors of multivariate dimensionality, dispersion structure, configuration of group means, and sample size. A total of 32,400 discriminant analyses were conducted, based on data from simulated populations with appropriate underlying statistical distributions. A review of 60 published studies and 142 individual analyses indicated that sample sizes in ecological studies often have met that requirement. However, individual group sample sizes frequently were very unequal, and checks of assumptions usually were not reported. The authors recommend that ecologists obtain group sample sizes that are at least three times as large as the number of variables measured.

Williams, B.K.; Titus, K.

1988-01-01

293

Stability and bifurcations in an epidemic model with varying immunity period

An epidemic model with distributed time delay is derived to describe the dynamics of infectious diseases with varying immunity. It is shown that solutions are always positive, and the model has at most two steady states: disease-free and endemic. It is proved that the disease-free equilibrium is locally and globally asymptotically stable. When an endemic equilibrium exists, it is possible to analytically prove its local and global stability using Lyapunov functionals. Bifurcation analysis is performed using DDE-BIFTOOL and traceDDE to investigate different dynamical regimes in the model using numerical continuation for different values of system parameters and different integral kernels.

K. B. Blyuss; Y. N. Kyrychko

2012-01-22

294

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

295

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

296

A Global Stability Analysis of Clusters of Galaxies with Conduction and AGN Feedback Heating

We investigate a series of steady-state models of galaxy clusters, in which the hot intracluster gas is efficiently heated by active galactic nucleus (AGN) feedback and thermal conduction, and in which the mass accretion rates are highly reduced compared to those predicted by the standard cooling flow models. We perform a global Lagrangian stability analysis. We show for the first time that the global radial instability in cool core clusters can be suppressed by the AGN feedback mechanism, provided that the feedback efficiency exceeds a critical lower limit. Furthermore, our analysis naturally shows that the clusters can exist in two distinct forms. Globally stable clusters are expected to have either: 1) cool cores stabilized by both AGN feedback and conduction, or 2) non-cool cores stabilized primarily by conduction. Intermediate central temperatures typically lead to globally unstable solutions. This bimodality is consistent with the recently observed anticorrelation between the flatness of the temperature profiles and the AGN activity (Dunn & Fabian 2008) and the observation by Rafferty et al. (2008) that the shorter central cooling times tend to correspond to significantly younger AGN X-ray cavities.

Fulai Guo; S. Peng Oh; M. Ruszkowski

2008-08-07

297

Adaptability and stability analysis of the juice yield of yellow passion fruit varieties.

This study analyzed the genotype x environment interaction (GE) for the juice productivity (JuProd) of 12 yellow passion fruit varieties (Passiflora edulis Sims. f. flavicarpa Deg.) using additive main effects and multiplicative interaction (AMMI) model and auxiliary parameters. The experiments were conducted in eight environments of Bahia State, Brazil, using a randomized block design with three replications. Analysis of variance showed significant effects (P ? 0.01) for environments, genotypes, and GE interaction. The first two interaction principal component axes (IPCAs) explained 81.00% of the sum of squares of the GE interaction. The AMMI1 and AMMI2 models showed that varieties 09 and 11 were the most stable. Other parameters, namely, the AMMI stability value (ASV), yield stability (YSI), sustainability, and stability index (StI), indicated that other varieties were more stable. These varying results were certainly a consequence of methodological differences. In contrast, the ranking of varieties for each of the stability parameters showed significant positive correlations (P ? 0.05) between IPCA1 x (ASV, YSI), JuProd x (StI, YSI), YSI x ASV, and StI x YSI. Cluster analysis based on the genotypic profile of the effects of the GE interaction identified three groups that correlated with the distribution of varieties in the AMMI1 biplot. However, the classification of stable genotypes was limited because the association with the productivity was not included in the analysis. Variety 08 showed the most stable and productive behavior, ranking above average in half of the environments, and it should be recommended for use. PMID:25177932

Oliveira, E J; Freitas, J P X; Jesus, O N

2014-01-01

298

Stability analysis of oscillatory systems subject to large delays: a synchronization point of view

Stability analysis of oscillatory systems subject to large delays: a synchronization point of view the qualitative behavior of the stability regions in the delay parameter space of oscillatory systems subjected to large delays, and shed a new light on the corresponding stabilization problem. In particular

299

Stability analysis of networked control systems with asynchronous sampling and input delay

Stability analysis of networked control systems with asynchronous sampling and input delay-Lab-CNRS UMR 5216, Grenoble, France Abstract-- This article proposes a novel approach to assess the stability and input delay based on an extension of existing results on the stability of sampled-data systems

Paris-Sud XI, UniversitĂ© de

300

This paper considers the robust stability analysis of cellular neural networks with discrete and distributed delays. Based on the Lyapunov stability theory and linear matrix inequality (LMI) technique, a novel stability criterion guaranteeing the global robust convergence of the equilibrium point is derived. The criterion can be solved easily by various convex optimization algorithms. An example is given to illustrate

Ju H. Park

2007-01-01

301

Dynamic stability of off-road vehicles: Quasi3D analysis

This paper presents a method to determine the stability of off-road vehicles moving on rough terrain. The measures of stability are defined as the maximum speed and acceleration under which the vehicle does not slide or tip over. To compute these stability measures, we propose a quasi 3D analysis by decomposing the vehicle dynamics into three separate planes: the yaw,

Moshe Mann; Zvi Shiller

2008-01-01

302

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

303

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

304

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

305

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

306

Numerical stability of a family of Osipkov-Merrit models

We have investigated the stability of a set of non-rotating anisotropic spherical models with a phase-space distribution function of the Osipkov-Merritt type. The velocity distribution in these models is isotropic near the center and becomes radially anisotropic at large radii. They are special members of the family studied by Dehnen and Tremaine et al. where the mass density has a power-law cusp $\\rho\\propto r^{-\\gamma}$ at small radii and decays as $\\rho\\propto r^{-4}$ at large radii. The radial-orbit instability of models with $\\gamma$ = 0, 1/2, 1, 3/2, and 2, was studied using an N-body code written by one of us and based on the `self-consistent field' method developed by Hernquist and Ostriker. These simulations have allowed us to delineate a boundary in the $(\\gamma,r_{a})$-plane that separates the stable from the unstable models. This boundary is given by $2T_{r}/T_{t} = 2.31 \\pm 0.27$, for the ratio of the total radial to tangential kinetic energy. We also found that the stability criterion $df/dQ\\le 0$, recently raised by Hjorth, gives lower values compared with our numerical results.

Andres Meza; Nelson Zamorano

1997-07-01

307

NASA Technical Reports Server (NTRS)

A calculation is made of the stability of various relaxation schemes for the numerical solution of partial differential equations. A multigrid acceleration method is introduced, and its effects on stability are explored. A detailed stability analysis of a simple case is carried out and verified by numerical experiment. It is shown that the use of multigrids can speed convergence by several orders of magnitude without adversely affecting stability.

Fay, John F.

1990-01-01

308

Stability Analysis and the Stabilization of a Class of Discrete-Time Dynamic Neural Networks

This paper deals with problems of stability and the stabilization of discrete-time neural networks. Neural structures under consideration belong to the class of the so-called locally recurrent globally feedforward networks. The single processing unit possesses dynamic behavior. It is realized by introducing into the neuron structure a linear dynamic system in the form of an infinite impulse response filter. In

Krzysztof Patan

2007-01-01

309

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

310

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

311

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

312

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

313

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

314

Thermohaline Circulation Stability: A Box Model Study. Part II: Coupled AtmosphereOcean Model

Thermohaline Circulation Stability: A Box Model Study. Part II: Coupled AtmosphereÂOcean Model of an interhemispheric three-box model of thermohaline circulation (THC) is presented. This study follows a similarly for a brief presentation of the concept of thermohaline circulation (THC) and for a discussion of the relevant

Lucarini, Valerio

315

Foamability and foam stability of molecular reconstituted model sparkling wines.

The present work aims at identifying the contribution of the different wine components to the foaming properties of wines. Twelve fractions were isolated from wine, and foam aptitude of each fraction was measured individually at the concentration at which it was recovered, using wine model solutions. For these concentrations, the maximum foam height (HM) was 8.4-11.7 cm, foam height on stability was 6.9-7.5 cm, and foam stability (TS) was 3.0-6.5 s. Moreover, foam measurements were also performed using 2-, 5-, and 10-fold concentrations of these compounds in wine. The HM increased linearly with the concentration of mannoproteins having low content of protein (MP1), and TS increased exponentially. The fractions that individually showed higher foaming properties were mixed in binary and ternary combinations, demonstrating that MP1 when mixed with low molecular weight hydrophobic compounds strengthens the air/water interface of these solutions, a characteristic that is on the basis of sparkling wines' foamability and foam stability. PMID:21736312

Coelho, Elisabete; Rocha, Sílvia M; Coimbra, Manuel A

2011-08-24

316

Bifurcation analysis of parametrically excited bipolar disorder model

NASA Astrophysics Data System (ADS)

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

Nana, Laurent

2009-02-01

317

Stability analysis of solid-state lasers regarding thermal lensing effect

NASA Astrophysics Data System (ADS)

The stability of solid-state lasers is influenced by the thermal lensing effect in the crystal. This effect is based on the deformation of the end faces of the crystal and the temperature dependence of the refraction index. It also depends on the photoelastic effect produced by thermal induced stress in the crystal. The analysis of the photoelastic effect is important for high power lasers and for lasers with a radially polarized laser beam. In this work, we use FE model to calculate the deformation, heat and stress distribution in the laser crystal with high accuracy. We also simulated the refraction index anisotropy with respect to the crystal orientation using the calculated stress distribution. As a result of our simulation, we can study stability of laser resonators for both radially and azimuthally polarized laser beam.

Graupeter, Thomas; Pflaum, Christoph

2012-06-01

318

NASA Technical Reports Server (NTRS)

New stability theorems are developed for the convergence analysis of a class of one and two-time scale time-varying nonlinear systems using averaging theory. These theorems are applied to a class of continuous time adaptive identifiers and model reference adaptive controllers to obtain estimates of the parameter rate of exponential convergence.

Fu, L.-C.; Bodson, M.; Sastry, S.

1985-01-01

319

for the analysis of various microwave geometries and for the modeling of electromagnetic (EM) wave propagation1004 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 47, NO. 7, JULY 1999 Stability with remarkable accuracy, they cause a numerical phase error during the propagation along the discretized grid

Tentzeris, Manos

320

Cardiovascular & Respiratory Modeling, Analysis & Control

Cardiovascular & Respiratory Systems: Modeling, Analysis & Control J. J. Batzel, F. Kappel, D . . . . . . . . . . . . . . . . 36 1.7.3 Sensitivity analysis . . . . . . . . . . . . . . . . . . . 38 2 Respiratory Modeling 45 2.1 Respiratory Control Physiology . . . . . . . . . . . . . . . . . . 46 2.1.1 General features of respiration

Batzel, Jerry

321

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

322

Modeling genomic data with type attributes, balancing stability and maintainability

Background Molecular biology (MB) is a dynamic research domain that benefits greatly from the use of modern software technology in preparing experiments, analyzing acquired data, and even performing "in-silico" analyses. As ever new findings change the face of this domain, software for MB has to be sufficiently flexible to accommodate these changes. At the same time, however, the efficient development of high-quality and interoperable software requires a stable model of concepts for the subject domain and their relations. The result of these two contradictory requirements is increased complexity in the development of MB software. A common means to reduce complexity is to consider only a small part of the domain, instead of the domain as a whole. As a result, small, specialized programs develop their own domain understanding. They often use one of the numerous data formats or implement proprietary data models. This makes it difficult to incorporate the results of different programs, which is needed by many users in order to work with the software efficiently. The data conversions required to achieve interoperability involve more than just type conversion. Usually they also require complex data mappings and lead to a loss of information. Results To address these problems, we have developed a flexible computer model for the MB domain that supports both changeability and interoperability. This model describes concepts of MB in a formal manner and provides a comprehensive view on it. In this model, we adapted the design pattern "Dynamic Object Model" by using meta data and association classes. A small, highly abstract class model, named "operational model," defines the scope of the software system. An object model, named "knowledge model," describes concrete concepts of the MB domain. The structure of the knowledge model is described by a meta model. We proved our model to be stable, flexible, and useful by implementing a prototype of an MB software framework based on the proposed model. Conclusion Stability and flexibility of the domain model is achieved by its separation into two model parts, the operational model and the knowledge model. These parts are connected by the meta model of the knowledge model to the whole domain model. This approach makes it possible to comply with the requirements of interoperability and flexibility in MB. PMID:19327130

Busch, Norbert; Wedemann, Gero

2009-01-01

323

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

324

Second order nonlinear spatial stability analysis of compressible mixing layers

NASA Astrophysics Data System (ADS)

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

Ladeinde, F.; Wu, J.

2002-09-01

325

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

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

Sampath Yerramalla; Edgar Fuller; Martin Mladenovski; Bojan Cukic

2003-01-01

326

Global mode analysis of axisymmetric bluff-body wakes: Stabilization by base bleed E. Sanmiguel.1063/1.2909609 A note on the stabilization of bluff-body wakes by low density base bleed Phys. Fluids 18, 098102 (2006 instability and global bleed control Phys. Fluids 16, 3460 (2004); 10.1063/1.1773071 A coupled Landau model

Paris-Sud XI, UniversitĂ© de

327

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

328

NASA Astrophysics Data System (ADS)

A numerical stability analysis is presented for the discrete coupled system of seven governing equations for a 3D Navier-Stokes procedure applicable to compressible turbulent flows. The relative importance of grid stretching, rotation, and turbulence source terms, as well as of effective diffusivity, on the stability of the scheme is addressed in light of order-of-magnitude arguments for such internal flows as those of turbomachine applications. The feasibility of incorporating a two-equation k-epsilon turbulence model in an explicit time-marching scheme is noted, where certain numerical-stability constraints are enforced.

Kunz, Robert F.; Lakshminarayana, Budugur

1992-11-01

329

A Note on Local Stability Conditions for Two Types of Monetary Models with Recursive Utility

NASA Astrophysics Data System (ADS)

This note explores local stability conditions for money-in-utility-function (MIUF) and transaction-costs (TC) models with recursive utility. Although Chen et al. [Chen, B.-L., M. Hsu, and C.-H. Lin, 2008, Inflation and growth: impatience and a qualitative equivalent, Journal of Money, Credit, and Banking, Vol. 40, No. 6, 1310-1323] investigated the relationship between inflation and growth in MIUF and TC models with recursive utility, they conducted only a comparative static analysis in a steady state. By establishing sufficient conditions for local stability, this note proves that impatience should be increasing in consumption and real balances. Increasing impatience, although less plausible from an empirical point of view, receives more support from a theoretical viewpoint.

Miyazaki, Kenji; Utsunomiya, Hitoshi

2009-09-01

330

A computational model for the dynamic stabilization of Rayleigh-Bénard convection in a cubic cavity.

The dynamic stability of Rayleigh-Bénard convection with vertical vibration in a cubic container is computationally modeled. Two parametric drives are considered (sinusoidal and rectangular), as well as two thermal boundary conditions on the sidewalls (insulating and conducting). The linearized equations are solved using a spectral Galerkin method and Floquet analysis. Both the synchronous and the subharmonic regions of instability are recovered. The conditions necessary for dynamic stability are reported for a range of Rayleigh numbers from critical to 10(7) and for Prandtl numbers in the range of 0.1-7. The linear model is compared to the data set available in the literature where the performance of an inverted pulse tube cryocooler is measured. PMID:25234875

Carbo, Randy M; Smith, Robert W M; Poese, Matthew E

2014-02-01

331

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

332

Stability analysis of plane wave solutions of the discrete ginzburg-landau equation

The discrete Ginzburg-Landau model for a family of oscillators linearly coupled with their first neighbors is studied. The full linear stability analysis of the nonlinear plane wave solutions is performed by considering both the wave number (k) of the basic states and the wave number (q) of the perturbations as free parameters. In particular, it is shown that nonlinear plane waves can be destabilized not only by long (q-->0) or short (q=pi) wave perturbations, but also by intermediate wave numbers (0

Ravoux; Le Dizes S; Le Gal P

2000-01-01

333

Stability analysis on a set of calcium-regulated viscoelastic equations

NASA Astrophysics Data System (ADS)

In recent years some progress has been made in modelling pattern formation and morphogenesis in biological systems in terms of calcium ion regulation of the viscoelastic properties of the cellular cortex. In this paper, linear stability analysis is used on a set of calcium-regulated viscoelastic equations derived by Goodwin and Trainor [5] for the 3-dimensional medium appropriate to regeneration phenomena in the single celled alga Acetabularia mediterranea. The nature of the instabilities is discussed and it is shown how complex patterns arise naturally from the cross-terms linking viscoelastic strain to calcium concentration and concentration gradients.

Trainor, L. E. H.; Goodwin, B. C.

1986-05-01

334

Stability analysis on a set of calcium-regulated viscoelastic equations

NASA Astrophysics Data System (ADS)

In recent years some progress has been made in modelling pattern formation and morphogenesis in biological systems in terms of calcium ion regulation of the viscoelastic properties of the cellular cortex. In this paper, linear stability analysis is used on a set of calcium-regulated viscoelastic equations derived by Goodwin and Trainor [5] for the 3-dimensional medium appropriate to regeneration phenomena in the single celled alga Acetabularia mediterranea. The nature of the instabilities is discussed and it is shown how complex patterns arise naturally from the cross-terms linking viscoelastic strain to calcium concentration and concentration gradients.

Trainor, L. E. H.; Goodwin, B. C.

1986-08-01

335

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

336

Slope stability analysis by nite elements D. V. GRIFFITHS and P. A. LANE{

Slope stability analysis by Â®nite elements D. V. GRIFFITHSĂ? and P. A. LANE{ The majority of slope stability analysis which is accu- rate, versatile and requires fewer a priori assumptions, especially the zones in which the shear strength of the soil is insufÂ®- cient to resist the shear stresses. The paper

337

Stability analysis of two-layer immiscible viscous fluids in an inclined closed tube

Stability analysis of two-layer immiscible viscous fluids in an inclined closed tube Zhan Wang densities. A linear analysis of normal mode instability of the interface in an inclined closed tube discussed the linear stability of two-layer Couette and plane Poiseuille flows using a long-wave approach

Lebovitz, Norman

338

Thermohaline Circulation Stability: A Box Model Study. Part I: Uncoupled Model VALERIO LUCARINI and essentially affects the surface waters, and the thermohaline circulation (THC), which is characterized

339

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

340

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

341

Unstalled flutter stability predictions and comparisons to test data for a composite prop-fan model

NASA Technical Reports Server (NTRS)

The aeroelastic stability analyses for three graphite/epoxy composite Prop-Fan designs and post-test stability analysis for one of the designs, the SR-3C-X2 are presented. It was shown that Prop-Fan stability can be effectively analyzed using the F203 modal aeroelastic stability analysis developed at Hamilton Standard and that first mode torsion-bending coupling has a direct effect on blade stability. Positive first mode torsion-bending coupling is a destabilizing factor and the minimization of this parameter will increase Prop-Fan stability. It was also shown that Prop-Fan stability analysis using F203 is sensitive to the blade modal data used as input. Calculated blade modal properties varied significantly with the structural analysis used, and these variations are reflected in the F203 calculations.

Turnberg, J. E.

1986-01-01

342

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

343

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

344

Design of Multiple Axis Robotic Platform for Postural Stability Analysis.

This paper presents the design and implementation of IsiMove, a new dynamic posturography platform. It allows the evaluation of the static and dynamic balance of a human placed on a force plate. IsiMove is a robotic platform open kinematic with four degrees of freedom: anteroposterior tilt, mediolateral tilt, vertical rotation and horizontal translation. It is capable of measuring the displacement of the center of pressure over time, with a resolution of 0.1 mm for each foot and support a human of about 120 kg. IsiMove can generate various types of balance perturbations based on parameters such as direction, amplitude, frequency and shape. In this paper, we will give a description of the mechanisms that constitute our platform. First, the technical specifications of the hardware and software architecture will be presented. Then, we will provide details related to extensive experimental evaluations of the platform in both static and dynamic condition as well as result of postural stability analysis with healthy subjects and stroke patients. PMID:24951702

Kharboutly, Haissam; Ma, Jianting; Benali, Abderraouf; Thoumie, Philippe; Pasqui, Viviane; Bouzit, Mourad

2014-06-12

345

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

346

Although polymers and surfactants are commonly used as stabilizers to impart physical stability to the suspensions produced by wet stirred media milling of poorly water-soluble drugs, scant information is available in pharmaceutical literature regarding their impact on the breakage kinetics. We present a combined microhydrodynamics-polymer adsorption analysis to elucidate the roles of stabilizers with a focus on the kinetics. Griseofulvin (GF), a model poorly water-soluble drug, was milled at various concentrations of hydroxypropyl cellulose (HPC) in the presence-absence of sodium dodecyl sulfate (SDS). Particle sizing, scanning electron microscopy, thermal analysis, and rheometry were used to determine the breakage kinetics, adsorption isotherm, and apparent viscosity, which were then used to analyze the aggregation state of the milled suspensions and the microhydrodynamics. In the absence of SDS, an increase in HPC concentration slowed the particle aggregation leading to faster apparent breakage. On the other hand, due to a synergistic stabilizing action of HPC with SDS, lower HPC concentration was needed to stabilize the suspensions, and an optimum HPC concentration for the fastest apparent breakage was identified. The microhydrodynamic analysis quantified, for the first time, the viscous dampening effect of polymers, while only the combined analysis could explain the observed optimum. PMID:23018114

Bilgili, Ecevit; Afolabi, Afolawemi

2012-12-15

347

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

348

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

349

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

350

Stability analysis of a boundary layer over a hump using parabolized stability equations

NASA Astrophysics Data System (ADS)

Parabolized stability equations (PSEs) were used to investigate the stability of boundary layer flows over a small hump. The applicability of PSEs to flows with a small separation bubble was examined by comparing the result with DNS data. It was found that PSEs can efficiently track the disturbance waves with an acceptable accuracy in spite of a small separation bubble. A typical evolution scenario of Tollmien-Schlichting (TS) wave is presented. The adverse pressure gradient and the flow separation due to the hump have a strong effect on the amplification of the disturbances. The effect of hump width and height is also examined. When the width of the hump is reduced, the amplification factor is increased. The height of the hump is found to obviously influence the stability only when it is greater than the critical layer thickness.

Gao, B.; Park, D. H.; Park, S. O.

2011-10-01

351

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

352

On the linear stability of blood flow through model capillary networks.

Under the approximation that blood behaves as a continuum, a numerical implementation is presented to analyze the linear stability of capillary blood flow through model tree and honeycomb networks that are based on the microvascular structures of biological tissues. The tree network is comprised of a cascade of diverging bifurcations, in which a parent vessel bifurcates into two descendent vessels, while the honeycomb network also contains converging bifurcations, in which two parent vessels merge into one descendent vessel. At diverging bifurcations, a cell partitioning law is required to account for the nonuniform distribution of red blood cells as a function of the flow rate of blood into each descendent vessel. A linearization of the governing equations produces a system of delay differential equations involving the discharge hematocrit entering each network vessel and leads to a nonlinear eigenvalue problem. All eigenvalues in a specified region of the complex plane are captured using a transformation based on contour integrals to construct a linear eigenvalue problem with identical eigenvalues, which are then determined using a standard QR algorithm. The predicted value of the dimensionless exponent in the cell partitioning law at the instability threshold corresponds to a supercritical Hopf bifurcation in numerical simulations of the equations governing unsteady blood flow. Excellent agreement is found between the predictions of the linear stability analysis and nonlinear simulations. The relaxation of the assumption of plug flow made in previous stability analyses typically has a small, quantitative effect on the stability results that depends on the specific network structure. This implementation of the stability analysis can be applied to large networks with arbitrary structure provided only that the connectivity among the network segments is known. PMID:25410686

Davis, Jeffrey M

2014-12-01

353

Viscous linear stability analysis of rectangular duct and cavity flows

NASA Astrophysics Data System (ADS)

The viscous linear stability of four classes of incompressible flows inside rectangular containers is studied numerically. In the first class the instability of flow through a rectangular duct, driven by a constant pressure gradient along the axis of the duct (essentially a two-dimensional counterpart to plane Poiseuille flow PPF), is addressed. The other classes of flow examined are generated by tangential motion of one wall, in one case in the axial direction of the duct, in another perpendicular to this direction, corresponding respectively to the two-dimensional counterpart to plane Couette flow (PCF) and the classic lid-driven cavity (LDC) flow, and in the fourth case a combination of both the previous tangential wall motions. The partial-derivative eigenvalue problem which in each case governs the temporal development of global three-dimensional small-amplitude disturbances is solved numerically. The results of Tatsumi & Yoshimura (1990) for pressure-gradient-driven flow in a rectangular duct have been confirmed; the relationship between the eigenvalue spectrum of PPF and that of the rectangular duct has been investigated. Despite extensive numerical experimentation no unstable modes have been found in the wall-bounded Couette flow, this configuration found here to be more stable than its one-dimensional limit. In the square LDC flow results obtained are in line with the predictions of Ding & Kawahara (1998b), Theofilis (2000) and Albensoeder et al. (2001b) as far as one travelling unstable mode is concerned. However, in line with the predictions of the latter two works and contrary to all previously published results it is found that this mode is the third in significance from an instability analysis point of view. In a parameter range unexplored by Ding & Kawahara (1998b) and all prior investigations two additional eigenmodes exist, which are both more unstable than the mode that these authors discovered. The first of the new modes is stationary (and would consequently be impossible to detect using power-series analysis of experimental data), whilst the second is travelling, and has a critical Reynolds number and frequency well inside the experimentally observed bracket. The effect of variable aspect ratio Ain[0.5,4] of the cavity on the most unstable eigenmodes is also considered, and it is found that an increase in aspect ratio results in general destabilization of the flow. Finally, a combination of wall-bounded Couette and LDC flow, generated in a square duct by lid motion at an angle phiin(0,{pi}/{2}) with the homogeneous duct direction, is shown to be linearly unstable above a Reynolds number Rey {=} 800 (based on the lid velocity and the duct length/height) at all phi parameter values examined. The excellent agreement with experiment in LDC flow and the alleviation of the erroneous prediction of stability of wall-bounded Couette flow is thus attributed to the presence of in-plane basic flow velocity components.

Theofilis, V.; Duck, P. W.; Owen, J.

2004-04-01

354

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

355

The stability analysis of rolling motion of hypersonic vehicles and its validations

NASA Astrophysics Data System (ADS)

The stability of the rolling motion of near space hypersonic vehicles with rudder control is studied using method of qualitative analysis of nonlinear differential equations, and the stability criteria of the deflected rolling motions are improved. The outcomes can serve as the basis for further study regarding the influence of pitching and lateral motion on the stability of rolling motion. To validate the theoretical results, numerical simulations were done for the rolling motion of two hypersonic vehicles with typical configurations. Also, wind tunnel experiments for four aircraft models with typical configurations have been done. The results show that: 1) there exist two dynamic patterns of the rolling motion under statically stable condition. The first one is point attractor, for which the motion of aircraft returns to the original state. The second is periodic attractor, for which the aircraft rolls periodically. 2) Under statically unstable condition, there exist three dynamic patterns of rolling motion, namely, the point attractor, periodic attractor around deflected state of rolling motion, and double periodic attractors or chaotic attractors.

Ye, YouDa; Zhao, ZhongLiang; Tian, Hao; Zhang, XianFeng

2014-12-01

356

Instability of elliptic liquid jets: Temporal linear stability theory and experimental analysis

NASA Astrophysics Data System (ADS)

The instability dynamics of inviscid liquid jets issuing from elliptical orifices is studied, and effects of the surrounding gas and the liquid surface tension on the stability behavior are investigated. A dispersion relation for the zeroth azimuthal (axisymmetric) instability mode is derived. Consistency of the analysis is confirmed by demonstrating that these equations reduce to the well-known dispersion equations for the limiting cases of round and planar jets. It is shown that the effect of the ellipticity is to increase the growth rate over a large range of wavenumbers in comparison to those of a circular jet. For higher Weber numbers, at which capillary forces have a stabilizing effect, the growth rate decreases with increasing ellipticity. Similar to circular and planar jets, increasing the density ratio between gas and liquid increases the growth of disturbances significantly. These theoretical investigations are complemented by experiments to validate the local linear stability results. Comparisons of predicted growth rates with measurements over a range of jet ellipticities confirm that the theoretical model provides a quantitatively accurate description of the instability dynamics in the Rayleigh and first wind-induced regimes.

Amini, Ghobad; Lv, Yu; Dolatabadi, Ali; Ihme, Matthias

2014-11-01

357

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.

358

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

NASA Astrophysics Data System (ADS)

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

Bakker, Peter M.; Duveneck, Eric

2011-05-01

359

NASA Technical Reports Server (NTRS)

Schlieren methods of flow visualization and hot-wire anemometry for velocity measurements were used to investigate the wakes generated by hovering model propellers and rotors. The research program was directed toward investigating (1) the stability of the tip vortex, (2) the effects produced by various tip shapes on performance and tip vortex characteristics, and (3) the shock formation and noise characteristics associated with various tip shapes. A free-wake analysis was also conducted for comparison with the vortex stability experimental results. Schlieren photographs showing wake asymmetry, interaction, and instability are presented along with a discussion of the effects produced by the number of blades, collective pitch, and tip speed. Two hot-wire anemometer techniques, used to measure the maximum circumferential velocity in the tip vortex, are discussed.

Tangler, J. L.; Wohlfeld, R. M.; Miley, S. J.

1973-01-01

360

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 ...

361

Stability analysis of a variable-speed wind turbine

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

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

1996-10-01

362

Long term voltage stability analysis for small disturbances

. This dissertation extends our new numerical scheme to stiff systems. When a system is ill-conditioned, the implicit method would be applied to achieve numerical stability. We further demonstrate the validity to combine the intelligent load adjustment technique...

Men, Kun

2009-05-15

363

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

364

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

365

Slope stability analysis: a support vector machine approach

Artificial Neural Network (ANN) such as backpropagation learning algorithm has been successfully used in slope stability problem.\\u000a However, generalization ability of conventional ANN has some limitations. For this reason, Support Vector Machine (SVM) which\\u000a is firmly based on the theory of statistical learning has been used in slope stability problem. An interesting property of\\u000a this approach is that it is

Pijush Samui

2008-01-01

366

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

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

Canavan, G.H.

1997-12-01

367

Improved stability analysis and gain-scheduled controller synthesis for parameter-dependent systems

We present new algorithms for robust stability analysis and gain-scheduled controller synthesis for linear systems affected by time-varying parametric uncertainties. These new techniques can also be applied to parameter-dependent nonlinear systems with real-rational nonlinearities. Sufficient conditions for robust stability, as well as conditions for the existence of a robustly stabilizing gain-scheduled controller, are given in terms of a finite number

Fan Wang; Venkataramanan Balakrishnan

2002-01-01

368

ESF SOUTH PORTAL BOX-CUT/HIGHWALL STABILITY ANALYSIS (SCPB:N/A)

The main purpose and objective of this analysis is to design a Box-Cut at the ESF South Portal to accommodate the Tunnel Boring Machine's (TBM) exit at the conclusion of the ESF Main Loop construction. The stability of the Highwall and the sidewalls at the Box-Cut are assessed using analytical methods by numerical modeling techniques. A ground reinforcement system for the South Ramp Box-Cut slopes will be recommended. This report summarizes the results of the analyses and provides the details of the recommended ground reinforcement system for the Box-Cut slopes at the South Portal. The reinforcement design details are then incorporated into design output documents for implementation in the field. Method of excavation for the Box-Cut is also discussed and a recommendation is provided in this analysis.

Saeed Bonabian

1996-03-28

369

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

370

High-throughput Analysis of in vivo Protein Stability Technological Innovation and Resources

The regulation of protein stability is critical for cells to maintain the proper functioning of almost every the components in proteolytic pathways that affect protein turnover and to understand the consequencesHigh-throughput Analysis of in vivo Protein Stability 1 Technological Innovation

Dunham, Maitreya

371

A New Bifurcation Analysis for Power System Dynamic Voltage Stability Studies

A New Bifurcation Analysis for Power System Dynamic Voltage Stability Studies Garng M. Huang, Senior Member, IEEE, Liang Zhao, Xuefeng Song Abstract: The dynamic of a large class of power systems can bifurcation, saddle-node and Hopf bifurcation. In this paper the dynamic voltage stability of power system

372

ERIC Educational Resources Information Center

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

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

2010-01-01

373

A dissipation inequality formulation for stability analysis with integral quadratic constraints

Integral quadratic constraints (IQCs) provide a general framework for robustness analysis of feedback inter-connections. The main IQC stability theorem by Megretski and Rantzer was formulated with frequency domain conditions that depend on the IQC multiplier. Their proof of this theorem uses a homotopy method and operator theory. An interesting aspect of this theory is that input\\/output stability (defined as uniformly

Peter Seiler; Andrew K. Packard; Gary J. Balas

2010-01-01

374

In the present review article, we discuss recent progress in stability analysis of the convection of binary solutions which are solidified uni-directionally. Several double-diffusive convective flows with various stability characteristics occur either in sequence or simultaneously in a system, thus affecting seriously the crystalline of the resultant casting. Similar convective flows are also found in, for example, the Earth is

FALIN CHEN

375

Nonlinear stability-analysis of shell and contact-problems including branch-switching

In the analysis of nonlinear elastic shells often the stability and postbuckling behaviour governs the response. Here we discuss problems which also include contact constraints. A nonlinear cylindrical shell element is derived directly from the associated shell theory using one point integration and a stabilization technique. Within a general solution algorithm a simple but effective branch-switching procedure is presented. Additional

E. Stein; W. Wagner; P. Wriggers

1990-01-01

376

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

377

Local and Bi-Global Stability Analysis of a Plasma Actuated Boundary Layer

Local and Bi-Global Stability Analysis of a Plasma Actuated Boundary Layer Mark Riherd and Subrata discharge actuators on a laminar, zero pressure gradi- ent boundary layer. Both methods indicate layer. The general behavior of boundary layer stabilization is consistent with experimental results

Roy, Subrata

378

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...

379

Model reduction for parametric instability analysis in shells conveying fluid

NASA Astrophysics Data System (ADS)

Flexible pipes conveying fluid are often subjected to parametric excitation due to time-periodic flow fluctuations. Such systems are known to exhibit complex instability phenomena such as divergence and coupled-mode flutter. Investigators have typically used weighted residual techniques, to reduce the continuous system model into a discrete model, based on approximation functions with global support, for carrying out stability analysis. While this approach is useful for straight pipes, modelling based on FEM is needed for the study of complicated piping systems, where the approximation functions used are local in support. However, the size of the problem is now significantly larger and for computationally efficient stability analysis, model reduction is necessary. In this paper, model reduction techniques are developed for the analysis of parametric instability in flexible pipes conveying fluids under a mean pressure. It is shown that only those linear transformations which leave the original eigenvalues of the linear time invariant system unchanged are admissible. The numerical technique developed by Friedmann and Hammond (Int. J. Numer. Methods Eng. Efficient 11 (1997) 1117) is used for the stability analysis. One of the key research issues is to establish criteria for deciding the basis vectors essential for an accurate stability analysis. This paper examines this issue in detail and proposes new guidelines for their selection.

Kochupillai, Jayaraj; Ganesan, N.; Padmanabhan, Chandramouli

2003-05-01

380

Mechanical Analysis of the Effects of Cephalic Trim on Lower Lateral Cartilage Stability

Objective To determine how mechanical stability changes in the lower lateral cartilage (LLC) after varying degrees of cephalic resection in a porcine cartilage nasal tip model. Methods Alar cartilage was harvested from fresh porcine crania (n=14) and sectioned to precisely emulate a human LLC in size and dimension. Flexural mechanical analysis was performed both before and after cephalic trims of 0 (control), 4, and 6 mm. Cantilever deformation tests were performed on the LLC models at 3 locations (4, 6, and 8 mm from the midline), and the integrated reaction force was measured. An equivalent elastic modulus of the crura was calculated assuming that the geometry of the LLC model approximated a modified single cantilever beam. A 3-dimensional finite element model was used to model the stress distribution of the prescribed loading conditions for each of the 3 types of LLC widths. Results A statistically significant decrease (P=.02) in the equivalent elastic modulus of the LLC model was noted at the most lateral point at 8 mm and only when 4 mm of the strut remained (P=05). The finite element model revealed that the greatest internal stresses was at the tip of the nose when tissue was flexed 8 mm from the midline. Conclusion Our results provide the mechanical basis for suggested clinical guidelines stating that a residual strut of less than 6 mm can lead to suboptimal cosmetic results owing to poor structural support of the overlying skin soft-tissue envelope by an overly resected LLC. PMID:22250265

Oliaei, Sepehr; Manuel, Cyrus; Protsenko, Dmitriy; Hamamoto, Ashley; Chark, Davin; Wong, Brian

2014-01-01

381

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

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

Canavan, G.H.

1998-12-31

382

Electromechanical coupling properties and stability analysis of ferroelectrets

NASA Astrophysics Data System (ADS)

A constitutive theory of ferroelectrets is developed to analyze the electromechanical coupling properties and stability with large deformations. The equations of equilibrium and the condition of stability are hereby derived from the nonlinear theory. Piezoelectricity with static mechanical and electric loads and stability are investigated. The results show that the pressure and the dc voltage can both improve the piezoelectricity, i.e., increase the piezoelectric coefficient, d33. The value of d33 increases almost linearly with the dc voltage at small deformations, but possesses a nonlinear response at large deformations. To ensure that the ferroelectret is in a stable equilibrium, the corresponding Hessian should be positive definite. Two critical voltages exist and they decrease with the pre-applied pressure. This study is helpful for designing and optimizing applications of ferroelectrets.

Qu, Shaoxing; Yu, Yalin

2011-08-01

383

Linear Stability Regime Analysis of the Compressible Reacting Mixing Layer

NASA Technical Reports Server (NTRS)

Previous investigations have shown that a compressible reacting mixing layer can develop two peaks in the mean density weighted vorticity profile. Linear stability analyses show that at these peaks two distinct 'outer' instability modes appear in addition to the more common central mode, which exists unaccompanied in incompressible nonreacting flows. The present study parametrically analyzes the effects of compressibility, heat release, stoichiometry, and density ratio on the amplification rate and obliquity of each stability mode. The mean profiles used in the spatial stability calculation are generated by self-similar solutions of the compressible boundary layer equations combined with the assumption of infinitely fast chemistry. It is shown that the influence of stoichiometry and density ratio on the peaks of the density weighted vorticity profile determines which modes will dominate. Of particular interest are the conditions where two modes are equally amplified, causing the mixing layer to develop into a 'colayer' structure.

Day, M. J.; Reynolds, William C.; Mansour, N. N.; Rai, Man Mohan (Technical Monitor)

1995-01-01

384

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

385

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...

386

Stability analysis of polarized domains Jos'e A. Miranda and Michael Widom

Stability analysis of polarized domains Jos'e A. Miranda and Michael Widom Department of Physics is the magnetization and fl the line tension (essentially h times the surface tension). Jackson, Goldstein and Cebers

Widom, Michael

387

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...

388

Stability of building gene regulatory networks with sparse autoregressive models

Background: Biological networks are constantly subjected to random perturbations, and efficient feedback and compensatory mechanisms exist to maintain their stability. There is an increased interest in building gene ...

Rajapakse, Jagath

389

It is shown that, in contrast to the MHD model, a perturbation at the boundary of convective stability of a finite-pressure plasma in confinement systems without an averaged minB in the Kruskal-Oberman model is not generally a purely flute one. The reasons for this discrepancy are clarified. The analysis is carried out for axisymmetric configurations formed by a poloidal magnetic field.

Arsenin, V. V. [Russian Research Centre Kurchatov Institute (Russian Federation)

2010-10-15

390

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

391

Analysis of the production stability of mixed grasslands

The increased use of white clover in grasslands has led to new management challenges, as mixed pastures have been associated with unstable herbage production. The stability of mixed pastures depends on a complex of intrinsic ecosystem properties, on the variability of the environment, and on the spatial and temporal scale at which it is studied. In this paper, intrinsic ecosystem

R. P. O Schulte; E. A Lantinga; P. C Struik

2003-01-01

392

STABILITY ANALYSIS OF THE BUTTAHATCHEE RIVER BASIN, MISSISSIPPI AND ALABAMA

Technology Transfer Automated Retrieval System (TEKTRAN)

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

393

Stability analysis of Hopfield-type neural networks

The paper applies several concepts in robust control research such as linear matrix inequalities, edge theorem, parameter-dependent Lyapunov function, and Popov criteria to investigate the stability property of Hopfield-type neural networks. The existence and uniqueness of an equilibrium is formulated as a matrix determinant problem. An induction scheme is used to find the equilibrium. To verify whether the determinant is

Jyh-ching Juang

1999-01-01

394

Stability Analysis of Nonlinear Systems with Slope Restricted Nonlinearities

The problem of absolute stability of Lur'e systems with sector and slope restricted nonlinearities is revisited. Novel time-domain and frequency-domain criteria are established by using the Lyapunov method and the well-known Kalman-Yakubovich-Popov (KYP) lemma. The criteria strengthen some existing results. Simulations are given to illustrate the efficiency of the results. PMID:24592160

Du, Jiajia

2014-01-01

395

Perturbing Numerical Calculations for Statistical Analysis of Floating-Point Program (In)Stability

Perturbing Numerical Calculations for Statistical Analysis of Floating-Point Program (In mathematical techniques for performing error and stability analysis of numerical algorithms. However in numerical analysis and who thus need more automated techniques to analyze their code. In this paper, we

Su, Zhendong

396

] as a new method to bridge the gap between the geometry description and numerical analysis. Similar of a given domain parameterization. Keywords: numerical stability, Isogeometric Analysis, domain for the geometry description and for the numerical analysis. One major advantage of IGA over the classical finite

JĂĽttler, Bert

397

Stability analysis of the TPX toroidal field coil

NASA Astrophysics Data System (ADS)

The energy stability margin of the TPX/TF conductor has been calculated as a response to heat pulses with short initial quench zones and with long initial quench zones. The short IQZ's approximate ramp-rate induced heating, and the long IQZ's approximate heating from a plasma disruption. These IQZ's are centered in the bore inner leg of the double pancake, where the operating field and temperature are maximum. Energy margin stability curves are plotted as a function of current. At the 33.5 kA design current, the minimum calculated stability margin with short IQZ's is 390 mJ/cc. The minimum calculated stability margin with long IQZ's is 205 mJ/cc. A comparison the stability margin with the available enthalpy (short IQZ's) and with the available internal energy (long IQZ's) shows that the conductor utilizes the available helium energy well. The energy margin stability curve is generally divided into two regions. The regions can be characterized on the basis of a decrease or an increase in heating after the initiating heat pulse during a marginal quench. The low current well-cooled region exists when the heating rate during the pulse is greater than the Joule heating after the pulse. Since the heating rate decreases, the energy margin is high. The high current ill-cooled region exists when the heating rate during the pulse is less than the Joule heating after the pulse. Since the heating rate increases, the energy margin is low. In the evaluation of a well-cooled or an ill-cooled condition, this Joule heating should be included in the strength of the initiating pulse. When this is done for the TPX/TF conductor, the limiting current approaches the critical current, explaining why the stability curves are entirely in the well-cooled region. The important result is that the conductor does not exhibit a large decrease in energy margin to an ill-cooled region until the current approaches the critical current.

Wong, R. L.

1994-10-01

398

Passivity approach for controller design and stability analysis of radial power systems

A passivity approach as a framework to analyse stability of power systems and to derive controllers is presented. A radial power system is decomposed according to the component oriented modelling technique which allows to view the whole system as a feedback decomposition suitable to apply the passivity approach. Under assumptions of passive or passified loads, L2-stability properties are proved along

N. Lechevin; P. Sicard; Z. Yao

1999-01-01

399

Incorporating seepage processes into a streambank stability model

Technology Transfer Automated Retrieval System (TEKTRAN)

Seepage processes are usually neglected in bank stability analyses although they can become a prominent failure mechanism under certain field conditions. This study incorporated the effects of seepage (i.e., seepage gradient forces and seepage erosion undercutting) into the Bank Stability and Toe Er...

400

Constraint Analysis of Bumblebee Models

NASA Astrophysics Data System (ADS)

Dirac's Harailtonian constraint analysis is used to study vector theories with spontaneous Lorentz violation known as bumblebee models. In certain of these models, the Nambu-Goldstone sector has properties similar to those of photons in classical electromagnetism. An analysis of the different types of constraints and resulting number of degrees of freedom is presented here for models with different kinetic and potential terms, and the results are compared with electromagnetism.

Gagne, N.; Vrublevskis, A.

2008-03-01

401

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

402

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

403

NASA Technical Reports Server (NTRS)

System safety analysis techniques are well established and are used extensively during the design of safety-critical systems. Despite this, most of the techniques are highly subjective and dependent on the skill of the practitioner. Since these analyses are usually based on an informal system model, it is unlikely that they will be complete, consistent, and error free. In fact, the lack of precise models of the system architecture and its failure modes often forces the safety analysts to devote much of their effort to gathering architectural details about the system behavior from several sources and embedding this information in the safety artifacts such as the fault trees. This report describes Model-Based Safety Analysis, an approach in which the system and safety engineers share a common system model created using a model-based development process. By extending the system model with a fault model as well as relevant portions of the physical system to be controlled, automated support can be provided for much of the safety analysis. We believe that by using a common model for both system and safety engineering and automating parts of the safety analysis, we can both reduce the cost and improve the quality of the safety analysis. Here we present our vision of model-based safety analysis and discuss the advantages and challenges in making this approach practical.

Joshi, Anjali; Heimdahl, Mats P. E.; Miller, Steven P.; Whalen, Mike W.

2006-01-01

404

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

405

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

406

Thermal stability analysis of the fine structure of solar prominences

NASA Technical Reports Server (NTRS)

The linear thermal stability of a 2D periodic structure (alternatively hot and cold) in a uniform magnetic field is analyzed. The energy equation includes wave heating (assumed proportional to density), radiative cooling and both conduction parallel and orthogonal to magnetic lines. The equilibrium is perturbed at constant gas pressure. With parallel conduction only, it is found to be unstable when the length scale 1// is greater than 45 Mn. In that case, orthogonal conduction becomes important and stabilizes the structure when the length scale is smaller than 5 km. On the other hand, when the length scale is greater than 5 km, the thermal equilibrium is unstable, and the corresponding time scale is about 10,000 s: this result may be compared to observations showing that the lifetime of the fine structure of solar prominences is about one hour; consequently, our computations suggest that the size of the unresolved threads could be of the order of 10 km only.

Demoulin, Pascal; Malherbe, Jean-Marie; Schmieder, Brigitte; Raadu, Mickael A.

1986-01-01

407

Oleic acid vesicles have been used as model systems to study the properties of membranes that could be the evolutionary precursors of more complex, stable, and impermeable phospholipid biomembranes. Pure fatty acid vesicles in general show high sensitivity to ionic strength and pH variation, but there is growing evidence that this lack of stability can be counterbalanced through mixtures with other amphiphilic or surfactant compounds. Here, we present a systematic experimental analysis of the oleic acid system and explore the spontaneous formation of vesicles under different conditions, as well as the effects that alcohols and alkanes may have in the process. Our results support the hypothesis that alcohols (in particular 10- to 14-C-atom alcohols) contribute to the stability of oleic acid vesicles under a wider range of experimental conditions. Moreover, studies of mixed oleic-acid-alkane and oleic-acid-alcohol systems using infrared spectroscopy and Langmuir trough measurements indicate that precisely those alcohols that increased vesicle stability also decreased the mobility of oleic acid polar headgroups, as well as the area/molecule of lipid. PMID:22339864

Rendón, Adela; Carton, David Gil; Sot, Jesús; García-Pacios, Marcos; Montes, Ruth; Valle, Mikel; Arrondo, José-Luis R.; Gońi, Felix M.; Ruiz-Mirazo, Kepa

2012-01-01

408

Stability analysis of an approximate scheme for moving horizon estimation.

We analyze the stability properties of an approximate algorithm for moving horizon estimation (MHE). The strategy provides instantaneous state estimates and is thus suitable for large-scale feedback control. In particular, we study the interplay between numerical approximation errors and the convergence of the estimator error. In addition, we establish connections between the numerical properties of the Hessian of the MHE problem and traditional observability definitions. We demonstrate the developments through a simulation case study.

Zavala, V. M. (Mathematics and Computer Science)

2010-01-01

409

Local stability analysis for a planar shock wave

NASA Technical Reports Server (NTRS)

A procedure to study the local stability of planar shock waves is presented. The procedure is applied to a Rankine-Hugoniot shock in a divergent/convergent nozzle, to an isentropic shock in a divergent/convergent nozzle, and to Rankine-Hugoniot shocks attached to wedges and cones. It is shown that for each case, the equation governing the shock motion is equivalent to the damped harmonic oscillator equation.

Salas, M. D.

1984-01-01

410

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 configurations of the F/A-18 E/F were examined. The parameters examined were pulley-cable friction, mach number, dynamic pressure, cable geometry, center of gravity location, cable tension, snubbing the model, drag, and test medium. For the nominal cable geometry (Cable Geometry 1), Configuration One was unstable for cases with higher pulley-cable friction coefficients. A new cable geometry (Cable Geometry 3) was determined in which Configuration One was stable for all cases evaluated. Configuration Two with the nominal center of gravity position was found to be unstable for cases with higher pulley-cable friction coefficients; however, the model was stable when the center of gravity moved forward 1/2. The model was tested using the cable mount system during the initial wind tunnel entry and was stable as predicted.

Thompson, Nancy; Farmer, Moses

1994-01-01

411

Stability of some turbulent vertical models for the ocean mixing boundary layer

We consider four turbulent models to simulate the boundary mixing layer of the ocean. We show the existence of solutions to these models in the steady-state case then we study the mathematical stability of these solutions.

Anne-Claire Bennis; Tomás Chacón Rebollo; Macarena Gomez Marmol; Roger Lewandowski

2006-12-19

412

Assessing stability of gene selection in microarray data analysis

Background The number of genes declared differentially 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 resampling techniques we have found that some genes are selected much less frequently (across sub-samples) than other genes with the same adjusted p-values. The extent to which this type of instability manifests itself can be assessed by a method introduced in this paper. The effect of correlation between gene expression levels on the performance of multiple testing procedures is studied by computer simulations. Conclusion Resampling represents a tool for reducing the set of initially selected genes to those with a sufficiently high selection frequency. Using resampling techniques it is also possible to assess variability of different performance indicators. Stability properties of several multiple testing procedures are described at length in the present paper. PMID:16451725

Qiu, Xing; Xiao, Yuanhui; Gordon, Alexander; Yakovlev, Andrei

2006-01-01

413

Stability and vibration analysis of a complex flexible rotor bearing system

NASA Astrophysics Data System (ADS)

This paper presents the non-linear dynamic analysis of a flexible rotor having unbalanced and supported by ball bearings. The rolling element bearings are modeled as two degree of freedom elements where the kinematics of the rolling elements are taken into account, as well as the internal clearance and the Hertz contact non-linearity. In order to calculate the periodic response of this non-linear system, the harmonic balance method is used. This method is implemented with an exact condensation strategy to reduce the computational time. Moreover, the stability of the non-linear system is analyzed in the frequency-domain by a method based on a perturbation applied to the known harmonic solution in the time domain.

Villa, C.; Sinou, J.-J.; Thouverez, F.

2008-07-01

414

Department of Numerical Analysis Modeling the Austenite Ferrite

Department of Numerical Analysis Modeling the Austenite Ferrite Transformation by Cellular Ferrite Transformation by Cellular Automaton Improving Interface Stability Master of Science Thesis. Computational Materials Science 48.3 (2010): 692-699] for the austenite to ferrite transformation in low

Vuik, Kees

415

Global stability of a multiple infected compartments model for waterborne diseases

NASA Astrophysics Data System (ADS)

In this paper, mathematical analysis is carried out for a multiple infected compartments model for waterborne diseases, such as cholera, giardia, and rotavirus. The model accounts for both person-to-person and water-to-person transmission routes. Global stability of the equilibria is studied. In terms of the basic reproduction number R0, we prove that, if R0?1, then the disease-free equilibrium is globally asymptotically stable and the infection always disappears; whereas if R0>1, there exists a unique endemic equilibrium which is globally asymptotically stable for the corresponding fast-slow system. Numerical simulations verify our theoretical results and present that the decay rate of waterborne pathogens has a significant impact on the epidemic growth rate. Also, we observe numerically that the unique endemic equilibrium is globally asymptotically stable for the whole system. This statement indicates that the present method need to be improved by other techniques.

Wang, Yi; Cao, Jinde

2014-10-01

416

The stability of low-speed spinning process exhibiting spinline flow-induced crystallization (FIC) with no neck-like spinline deformation has been investigated using the method of linear stability analysis. Effects of various process conditions such as fluid viscoelasticity and the spinline cooling on the spinning stability have been found closely related to the development of the spinline crystallinity. It also has been found

Dong Myeong Shin; Joo Sung Lee; Hyun Wook Jung; Jae Chun Hyun

2005-01-01

417

Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics

NASA Technical Reports Server (NTRS)

Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping 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 line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load 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 are compared with the damping and frequency computed from unsteady computational aeroelasticity 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 computational aeroelastic results.

Bartels, Robert E.

2012-01-01

418

Do salt bridges stabilize proteins? A continuum electrostatic analysis.

The electrostatic contribution to the free energy of folding was calculated for 21 salt bridges in 9 protein X-ray crystal structures using a continuum electrostatic approach with the DELPHI computer-program package. The majority (17) were found to be electrostatically destabilizing; the average free energy change, which is analogous to mutation of salt bridging side chains to hydrophobic isosteres, was calculated to be 3.5 kcal/mol. This is fundamentally different from stability measurements using pKa shifts, which effectively measure the strength of a salt bridge relative to 1 or more charged hydrogen bonds. The calculated effect was due to a large, unfavorable desolvation contribution that was not fully compensated by favorable interactions within the salt bridge and between salt-bridge partners and other polar and charged groups in the folded protein. Some of the salt bridges were studied in further detail to determine the effect of the choice of values for atomic radii, internal protein dielectric constant, and ionic strength used in the calculations. Increased ionic strength resulted in little or no change in calculated stability for 3 of 4 salt bridges over a range of 0.1-0.9 M. The results suggest that mutation of salt bridges, particularly those that are buried, to "hydrophobic bridges" (that pack at least as well as wild type) can result in proteins with increased stability. Due to the large penalty for burying uncompensated ionizable groups, salt bridges could help to limit the number of low free energy conformations of a molecule or complex and thus play a role in determining specificity (i.e., the uniqueness of a protein fold or protein-ligand binding geometry). PMID:8003958

Hendsch, Z. S.; Tidor, B.

1994-01-01

419

NASA Astrophysics Data System (ADS)

To impart hands-on training in physics analysis, CMS experiment initiated the concept of CMS Data Analysis School (CMSDAS). It was born over three years ago at the LPC (LHC Physics Centre), Fermilab and is based on earlier workshops held at the LPC and CLEO Experiment. As CMS transitioned from construction to the data taking mode, the nature of earlier training also evolved to include more of analysis tools, software tutorials and physics analysis. This effort epitomized as CMSDAS has proven to be a key for the new and young physicists to jump start and contribute to the physics goals of CMS by looking for new physics with the collision data. With over 400 physicists trained in six CMSDAS around the globe, CMS is trying to engage the collaboration in its discovery potential and maximize physics output. As a bigger goal, CMS is striving to nurture and increase engagement of the myriad talents, in the development of physics, service, upgrade, education of those new to CMS and the career development of younger members. An extension of the concept to the dedicated software and hardware schools is also planned, keeping in mind the ensuing upgrade phase.

Malik, S.; Shipsey, I.; Cavanaugh, R.; Bloom, K.; Chan, Kai-Feng; D'Hondt, J.; Klima, B.; Narain, M.; Palla, F.; Rolandi, G.; Schörner-Sadenius, T.

2014-06-01

420

A stability analysis for the Korteweg-de Vries equation

In this paper the stability of the Korteweg-de Vries (KdV) equation is\\u000ainvestigated. It is shown analytically and numerically that small perturbations\\u000aof solutions of the KdV-equation introduce effects of dispersion, hence the\\u000aperturbation propagates with a different velocity then the unperturbed\\u000asolution. This effect is investigated analytically by formulating a\\u000adifferential equation for perturbations of solutions of the KdV-equation.

H. J. S. Dorren; R. K. Snieder

1996-01-01

421

Stability of landsat-4 thematic mapper outgassing models

Oscillations in radiometric gains of the short wave infrared (SWIR) bands in Landsat-4 (L4) and Landsat-5 (L5) Thematic Mappers (TMs) are observed through an analysis of detector responses to the Internal Calibrator (IC) pulses. The oscillations are believed to be caused by an interference effect due to a contaminant film buildup on the window of the cryogenically cooled dewar that houses these detectors. This process of contamination, referred to as outgassing effects, has been well characterized using an optical thin-film model that relates detector responses to the accumulated film thickness and its growth rate. The current models for L4 TM are based on average detector responses to the second brightest IC lamp and have been derived from three data sets acquired during different times throughout the instrument's lifetime. Unlike in L5 TM outgassing characterization, it was found that the L4 TM responses to all three IC lamps can be used to provide accurate characterization and correction for outgassing effects. The analysis of single detector responses revealed an up to five percent difference in the estimated oscillating periods and also indicated a gradual variation of contaminant growth rate over the focal plane.

Micijevic, E.; Chander, G.

2006-01-01

422

Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet

The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system.

Frisch, Josef; Chang, Allison; Decker, Valentin; Doyle, Eric; Eriksson, Leif; Hendrickson, Linda; Himel, Thomas; Markiewicz, Thomas; Partridge, Richard; Seryi, Andrei; /SLAC

2006-09-28

423

Hierarchical modeling of population stability and species group attributes from survey data

Many ecological studies require analysis of collections of estimates. For example, population change is routinely estimated for many species from surveys such as the North American Breeding Bird Survey (BBS), and the species are grouped and used in comparative analyses. We developed a hierarchical model for estimation of group attributes from a collection of estimates of population trend. The model uses information from predefined groups of species to provide a context and to supplement data for individual species; summaries of group attributes are improved by statistical methods that simultaneously analyze collections of trend estimates. The model is Bayesian; trends are treated as random variables rather than fixed parameters. We use Markov Chain Monte Carlo (MCMC) methods to fit the model. Standard assessments of population stability cannot distinguish magnitude of trend and statistical significance of trend estimates, but the hierarchical model allows us to legitimately describe the probability that a trend is within given bounds. Thus we define population stability in terms of the probability that the magnitude of population change for a species is less than or equal to a predefined threshold. We applied the model to estimates of trend for 399 species from the BBS to estimate the proportion of species with increasing populations and to identify species with unstable populations. Analyses are presented for the collection of all species and for 12 species groups commonly used in BBS summaries. Overall, we estimated that 49% of species in the BBS have positive trends and 33 species have unstable populations. However, the proportion of species with increasing trends differs among habitat groups, with grassland birds having only 19% of species with positive trend estimates and wetland birds having 68% of species with positive trend estimates.

Sauer, J.R.; Link, W.A.

2002-01-01

424

NASA Astrophysics Data System (ADS)

We present a method to perform stability analysis of nonequilibrium fixed points appearing in self-consistent electron transport calculations. The nonequilibrium fixed points are given by the self-consistent solution of stationary, nonlinear kinetic equation for single-particle density matrix. We obtain the stability matrix by linearizing the kinetic equation around the fixed points and analyze the real part of its spectrum to assess the asymptotic time behavior of the fixed points. We derive expressions for the stability matrices within Hartree-Fock and linear response adiabatic time-dependent density functional theory. The stability analysis of multiple fixed points is performed within the nonequilibrium Hartree-Fock approximation for the electron transport through a molecule with a spin-degenerate single level with local Coulomb interaction.

Dzhioev, Alan A.; Kosov, D. S.

2011-11-01

425

Langley Stability and Transition Analysis Code (LASTRAC) Version 1.2 User Manual

NASA Technical Reports Server (NTRS)

LASTRAC is a general-purposed, physics-based transition prediction code released by NASA for Laminar Flow Control studies and transition research. The design and development of the LASTRAC code is aimed at providing an engineering tool that is easy to use and yet capable of dealing with a broad range of transition related issues. It was written from scratch based on the state-of-the-art numerical methods for stability analysis and modern software technologies. At low fidelity, it allows users to perform linear stability analysis and N-factor transition correlation for a broad range of flow regimes and configurations by using either the linear stability theory or linear parabolized stability equations method. At high fidelity, users may use nonlinear PSE to track finite-amplitude disturbances until the skin friction rise. This document describes the governing equations, numerical methods, code development, detailed description of input/output parameters, and case studies for the current release of LASTRAC.

Chang, Chau-Lyan

2004-01-01

426

Reflectance stability analysis of Spectralon diffuse calibration panels

NASA Technical Reports Server (NTRS)

The Multi-angle Imaging SpectroRadiometer (MISR) plans to use deployable diffuse reflectance panels to provide periodic radiometric calibrations of its nine cameras while in-flight. Near-Lambertian reflectance characteristics are desirable to facilitate flat-field camera intercomparisons. Also required is panel spatial and spectral uniformity, and stability with time. Spectralon, a commercially available polytetrafluoroethylene (PTFE) compound, has been baselined in the MISR design. To assess the suitability of this material, a series of degradation tests were planned and implemented. These included UV vacuum exposure and proton bombardment tests which simulated the exposure levels to be encountered during the mission life. Proton levels are now considered too low to be of concern, but UV vacuum tests demonstrate sensitivity to material contamination. Material investigations have concluded that hydrocarbons are present in the bulk of the material, and that plastic packaging materials can introduce additional surface-layer contamination. It is found however, that these unwanted elements can be eliminated through vacuum pumping at elevated temperatures. Exposure to a UV source, while in vacuum, is again planned for a set of targets which have been vacuum baked. This will assess the stability of the pure PTFE form.

Bruegge, Carol J.; Stiegman, Albert E.; Coulter, Daniel R.; Hale, Robert R.; Diner, David J.; Springsteen, Arthur W.

1991-01-01

427

Sensitivity of resonance frequency analysis method to assess implant stability.

The aim of this human cadaver study was to determine the correlation between bone quality and implant stability parameters, and the relationship between resonance frequency value and peri-implant bone loss. Thirty-two implants were placed into four human cadaver mandibles. The bone density of the implant recipient site was determined using computerized tomography (CT) in Hounsfield units (HU). The peak insertion torque values were recorded. The resonance frequency (RF) measurements were performed immediately following implant insertion and also after one, two and three turns of the implant in a counterclockwise direction, representing peri-implant bone loss. The mean bone density, insertion torque and RFA values of all implants were 152 +/- 264 HU, 41.7 +/- 6 Ncm and 69.7 +/- 9 ISQ. Statistically significant correlations were found between bone density and insertion torque values, bone density and ISQ values, and insertion torque and ISQ values. A significant influence of the peri-implant bone loss on ISQ value was also observed. The findings from this study illustrate significant correlation between bone density and implant stability parameters, and a linear relationship between peri-implant bone levels and resonance frequency value. PMID:22029115

Turkyilmaz, Ilser; Company, Andrea M

2011-01-01

428

A stability analysis of AVE-4 severe weather soundings

NASA Technical Reports Server (NTRS)

The stability and vertical structure of an average severe storm sounding, consisting of both thermodynamic and wind vertical profiles, were investigated to determine if they could be distinguished from an average lag sounding taken 3 to 6 hours prior to severe weather occurrence. The term average is defined here to indicate the arithmetic mean of a parameter, as a function of altitude, determined from a large number of available observations taken either close to severe weather occurrence, or else more than 3 hours before it occurs. The investigative computations were also done to help determine if a severe storm forecast or index could possibly be used or developed. These mean vertical profiles of thermodynamic and wind parameters as a function of severity of the weather, determined from manually digitized radar (MDR) categories are presented. Profile differences and stability index differences are presented along with the development of the Johnson Lag Index (JLI) which is determined entirely upon environmental vertical parameter differences between conditions 3 hours prior to severe weather, and severe weather itself.

Johnson, D. L.

1982-01-01

429

The SNA analysis of a minimal model for bistability in the MAPK signaling cascade model

NASA Astrophysics Data System (ADS)

Successive phosphorylation cascades mediated by mitogen-activated protein kinases (MAPKs) are known to act as switches initiating various cellular processes. In addition, models of the MAPK reaction network are displaying other nonlinear phenomena including bistability and periodic oscillations. Recently bistability has been explained as a consequence of interaction between single and double phosphorylation/dephosphorylation pathways in the Stage 2 subsystem of the Huang-Ferrell model of the MAPK and a core bistable model has been proposed. Here we focus on a detailed stability analysis of the steady states of this minimal model. The analysis uses methods of convex analysis and stoichiometric network theory.

Hada?, O.; Schreiber, I.

2013-12-01

430

Nonlocal stability analysis of the MHD Kelvin-Helmholtz instability in a compressible plasma

A general stability analysis is performed for the Kelvin-Helmholtz instability in sheared magnetohydrodynamic flow of finite thickness in a compressible plasma. The analysis allows for arbitrary orientation of the magnetic field Bâ, velocity flow vâ, and wave vector k in the plane perpendicular to the velocity gradient, and no restrictions are imposed on the sound or Alfven Mach numbers. The

A. Miura; P. L. Pritchett

1982-01-01

431

Systematic reliability analysis of high rock-fill dam slope stability

The reliability of high rock-fill dam slope is a complex systematic reliability analysis, which is one of the core and difficult technological problems in dam design. Based on the deterministic finite element method, the system reliability analysis method of high rock-fill dam slope stability using nonlinear indexes is proposed here by integrating strength reduction method, response surface method, stepping equivalent

Pei Liang; Wu Zhen-yu; Chen Jian-kang

2011-01-01

432

Convective stability analysis of the long-term storage of carbon dioxide in deep saline aquifers

Convective stability analysis of the long-term storage of carbon dioxide in deep saline aquifers Received 5 December 2004; accepted 16 May 2005 Available online 19 July 2005 Abstract Deep saline aquifers analysis of the time-dependent density-driven convection in deep saline aquifers is presented for long

Zhang, Dongxiao

433

Design Analysis Report for 244-AR Interim Stabilization Exhaust Ventilation Ducting

This report documents the design analysis performed for the exhaust ducting associated with the 244-AR Interim Stabilization Project. The exhaust ducting connects portable exhausters PORO5 and PORO6 to the existing east dog house of the 291-AR filter vault and the vessel ventilation system. This analysis examines loads on the ductwork and ductwork supports.

RUTHERFORD, J.

2002-11-21

434

Stability analysis of an interactive system of wave equation and heat equation with memory

NASA Astrophysics Data System (ADS)

This paper is devoted to the stability analysis of an interaction system comprised of a wave equation and a heat equation with memory, where the hereditary heat conduction is due to Gurtin-Pipkin law or Coleman-Gurtin law. First, we show the strong asymptotic stability of solutions to this system. Then, the exponential stability of the interaction system is obtained when the hereditary heat conduction is of Gurtin-Pipkin type. Further, we show the lack of uniform decay of the interaction system when the heat conduction law is of Coleman-Gurtin type.

Zhang, Qiong

2014-10-01

435

The Stability of IQ in People with Low Intellectual Ability: An Analysis of the Literature

ERIC Educational Resources Information Center

A meta-analysis of the stability of low IQ (IQ less than 80) was performed on IQ tests that have been commonly used--tests that were derived by D. Wechsler (1949, 1955, 1974, 1981, 1991, 1997) and those based on the Binet scales (L. M. Terman, 1960; L. M. Terman & Merrill, 1972). Weighted-mean stability coefficients of 0.77 and 0.78 were found for…

Whitaker, Simon

2008-01-01

436

NASA Astrophysics Data System (ADS)

Complex eigenvalue analysis is widely used to investigate the stability of a dynamical system with frictional contact. For finite element models, iterative solvers are needed to precisely calculate complex modes and eigenvalues. However, in cases such as reanalysis studies, optimization or uncertainty propagation processes, computational cost can quickly become too time consuming. For multiple samplings, two methods combining homotopy perturbation and projection techniques are proposed for the reanalysis of quadratic eigenvalue problems. To highlight the efficiency of the proposed methods, a complete numerical application including nominal and perturbed solution calculations, coalescence graph and parametric analysis, is performed. The precision of results and computational time are compared with those obtained using commercial software.

Massa, F.; Lallemand, B.; Tison, T.

2015-02-01

437

Stability of GNSS Monumentation: Analysis of Co-Located Monuments in the Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Geodetic-quality permanent GNSS stations have used a number of different monumentation styles for the purpose of ensuring that the motions of the GNSS antenna reflect those of the Earth's crust while minimizing non-tectonic motions near the surface. Monuments range from simple masts drilled into building roofs or bedrock that cost a few hundred dollars to machine-drilled-braced monuments in soil that cost tens of thousands. Monument stability can depend on their design, the construction techniques used to install them, and the local surface geology where they are installed. Previous studies have separately investigated pairs of identical monuments at a single site, monument type variations using global statistical analysis, and multiple monument styles at a single site. Despite these efforts, the stability of different styles of monumentation in similarly varying geologic conditions has not been adequately determined. Errors in GPS measurements can be dominated by error sources unrelated to the movement of the monument with respect to the Earth's crust, thus making it difficult to isolate monument instability. Contributions from GPS measurement error unrelated to monument stability include, but are not limited to: satellite orbits, satellite clocks, tropospheric delay, and ionospheric delay, antenna phase center variations, near-field multipath, far-field multipath. Installing multiple monuments with small antenna separations at a given test location can help to reduce GPS measurement errors. To increase the understanding of monument stability of various monument styles in diverse geologic conditions UNAVCO has constructed two additional monuments at five existing Plate Boundary Observatory stations during the past year. Deep drilled-braced, short drilled-braced, and single mast type monuments were installed at sites with bedrock at the surface; deep drilled-braced, short driven-braced and pillar type monuments were installed at sites with alluvium or soil at the surface. Sites were selected that comprised a variety of geographic, hydrologic, and geologic conditions. The resulting set of 10-meter spaced monument triangles will yield valuable information regarding the stability of their types in different settings. Data collected from PBO Multi-Monument Experiment are being analyzed using a variety of methods. Each site is characterized using quality-control parameters such as multipath, signal-to-noise and previously determined seasonal variations. High-precision processing by the PBO Analysis Centers with GAMIT and GIPSY software packages using regional and global schemes yield time-series with millimeter-level that determine noise content, overall site stability relative to other PBO sites and differential motions between the individual monuments. Sub-millimeter results from UNAVCO's short-baseline processing efforts will be presented showing further details of monument performance site characterization including the effects of varying elevation cutoff angle and modeling of monument-dependent noise.

Blume, F.; Berglund, H. T.; Feaux, K.; Dittmann, S. T.; Walls, C. P.; Austin, K. E.; Mattioli, G. S.

2013-12-01

438

NASA Astrophysics Data System (ADS)

If an acoustic field is imposed on a fluid within a container, the critical Rayleigh number is a strong function of the frequency and amplitude of that acoustic field as noted by G. Swift. and S. Backhaus, [J. Acoust. Soc. Am. 126(5), 2009]. Results will be reported for nonlinear and linear models constructed to predict the modified critical Rayleigh number, based on a full field solution of the hydrodynamic equations using the approach of A. Yu. Gelfgat, [J. Comp. Phys. 156, 1999]. The spatial portion of the differential equations were solved using the Galerkin method and the dynamic stability for the linear model was determined using Floquet analysis. One of the benefits of the approach compared to the averaging methods used by G. Gershuni and D. Lyubimov, Thermal Vibration Convection, (Wiley, New York, 1998) is that the parametric stability boundary can be recovered. This study includes a variety of container aspect ratios, boundary conditions, and Rayleigh numbers ranging from 10^3 to 10^8.

Carbo, Randy; Smith, Robert; Poese, Matt

2011-11-01

439

Lateral dynamic flight stability of a model bumblebee in hovering and forward flight.

The lateral dynamic flight stability of a model bumblebee in hovering and forward 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. The lateral motion of the model bumblebee is unstable at hovering and low flight speed (advance ratio J=0, 0.13), and becomes neutral or weakly stable at medium and high flight speeds (J=0.31-0.57). The instability at hovering and low speed is mainly caused by a positive roll-moment derivative with respect to the side-slip velocity, which is due to the effect of changing the axial velocity of the leading-edge-vortex (LEV) (i.e. the 'lateral wind' due to the side motion of the insect increases the axial velocity of the LEV on one wing and decreases that on the other wing). As flight speed increases, because the mean position of the wings moves more and more backward, the effect of 'changing-LEV-axial-velocity' becomes weaker and weaker and the roll-moment derivative decreases first and then changes its sign to become negative, resulting in the neutrally or weakly stable motion at medium and high flight speeds. PMID:23220347

Xu, Na; Sun, Mao

2013-02-21

440

Dynamic stability of a rotor blade using finite element analysis

NASA Technical Reports Server (NTRS)

The aeroelastic stability of flap bending, lead-lag bending, and torsion of a helicopter rotor blade in hover is examined using a finite element formulation based on the principle of virtual work. Quasi-steady two-dimensional airfoil theory is used to obtain the aerodynamic loads. The rotor blade is discretized into beam elements, each with ten modal degrees of freedom. The resulting nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The flutter solution is calculated assuming blade motion to be a small perturbation about the steady solution. The normal mode method based on the coupled rotating natural modes about the steady deflections is used to reduce the number of equations in the flutter eigenanalysis. Results are presented for hingeless and articulated rotor blade configurations.

Sivaneri, N. T.; Chopra, I.

1981-01-01

441

In a number of cases, composite structures may be subjected to impulsive and shock loads that result their significant deformation or loss of stability. Modeling of the accompanying unsteady wave processes requires not only the construction of adequate mathematical models of the deformation of the material and structure, but also the development of effective numerical methods and programs to analyze the nonlinear dynamic deformation of composite shells. Most of the studies in this area have been devoted to analysis of the natural frequencies of simple structural elements and linear problems concerning their dynamic behavior. At the same time, not enough attention has been given to nonlinear three-dimensional problems relating to the dynamic deformation of composite shells. In this investigation, we examine the formulation and a numerical method of solving the problem of the nonsteady deformation and loss of stability of multilayered composite shells of revolution subjected to asymmetric impulsive and shock loads.

Abrosimov, N.A.; Bazhenov, V.G.; Elesin, A.V. [Nizhnegorod State Univ., Novgorod (Russian Federation)

1995-07-01

442

ERIC Educational Resources Information Center

To fully understand the roles proteins play in cellular processes, students need to grasp complex ideas about protein structure, folding, and stability. Our current understanding of these topics is based on mathematical models and experimental data. However, protein structure, folding, and stability are often introduced as descriptive, qualitative…

Robic, Srebrenka

2010-01-01

443

Modelling Hydrogen Bond Stability by Regression Trees Igor Chikalov, Mikhail Moshkov

Modelling Hydrogen Bond Stability by Regression Trees Igor Chikalov, Mikhail Moshkov Mathematical-mail: peggyyao@stanford.edu Hydrogen bonds (H-bonds) play a key role in both the formation and stabilization A hydrogen bond (H-bond) corresponds to the attractive electrostatic interaction between a covalent pair D

Pratt, Vaughan

444

Learning Probabilistic Models of Hydrogen Bond Stability from Molecular Dynamics Simulation

Learning Probabilistic Models of Hydrogen Bond Stability from Molecular Dynamics Simulation Background Hydrogen bonds (H-bonds) play a key role in both the formation and stabilization of protein the hydrogen atom H is bonded to a more electronegative donor atom D, and an electronegative acceptor atom A

Pratt, Vaughan

445

Oscillator Models and Collective Motion: Splay State Stabilization of Self-Propelled Particles

This paper presents a Lyapunov design for the stabilization of collective motion in a planar kinematic model of N particles moving at constant speed. We derive a control law that achieves asymptotic stability of the splay state formation, characterized by uniform rotation of N evenly spaced particles on a circle. In designing the control law, the particle headings are treated

Derek A. Paley; Naomi Ehrich Leonard; Rodolphe Sepulchre

2005-01-01

446

Linear stability analysis of Korteweg stresses effect on miscible viscous fingering in porous media

NASA Astrophysics Data System (ADS)

Viscous fingering (VF) is an interfacial hydrodynamic instability phenomenon observed when a fluid of lower viscosity displaces a higher viscous one in a porous media. In miscible viscous fingering, the concentration gradient of the undergoing fluids is an important factor, as the viscosity of the fluids are driven by concentration. Diffusion takes place when two miscible fluids are brought in contact with each other. However, if the diffusion rate is slow enough, the concentration gradient of the two fluids remains very large during some time. Such steep concentration gradient, which mimics a surface tension type force, called the effective interfacial tension, appears in various cases such as aqua-organic, polymer-monomer miscible systems, etc. Such interfacial tension effects on miscible VF is modeled using a stress term called Korteweg stress in the Darcy's equation by coupling with the convection-diffusion equation of the concentration. The effect of the Korteweg stresses at the onset of the instability has been analyzed through a linear stability analysis using a self-similar Quasi-steady-state-approximation (SS-QSSA) in which a self-similar diffusive base state profile is considered. The quasi-steady-state analyses available in literature are compared with the present SS-QSSA method and found that the latter captures appropriately the unconditional stability criterion at an earlier diffusive time as well as in long wave approximation. The effects of various governing parameters such as log-mobility ratio, Korteweg parameters, disturbances' wave number, etc., on the onset of the instability are discussed for, (i) the two semi-infinite miscible fluid zones and (ii) VF of the miscible slice cases. The stabilizing property of the Korteweg stresses effect is observed for both of the above mentioned cases. Critical miscible slice lengths are computed to have the onset of the instability for different governing parameters with or without Korteweg stresses. These stabilizing properties of the Korteweg stresses captured in this present study are in agreement with the numerical simulations of fully nonlinear problem and the experimental observations reported in the literature.

Pramanik, Satyajit; Mishra, Manoranjan

2013-07-01

447

Allografts have recently become increasingly popular for anterior cruciate ligament reconstruction (ACLR) in the United States even though many studies have shown high allograft failure rates (Gorschewsky et al. in Am J Sports Med 33:1202, 2005; Pritchard et al. in Am J Sports Med 23:593, 2005; Roberts et al. in Am J Sports Med 19:35, 2006) and no meta-analysis or systematic review of allograft clinical stability rates in comparison to autog rafts has previously been performed. We hypothesized that allografts would demonstrate overall lower objective stability rates compared to autografts. To test this hypothesis we performed a meta-analysis of autograft and allograft stability data. A pubmed literature search of all allograft series in humans published in English was performed. Articles were then bibliographically cross-referenced to identify additional studies. Series inclusion criteria were arthrometric follow-up data using at least 30 lb or maximum manual force, stratified presentation of stability data and minimum two-year follow-up. Twenty allograft series were thus selected and compared to a previously published data set of all BPTB and Hamstring (HS) autograft ACLR series using the same study inclusion criteria and analytic and statistical methodology. IKDC standards of 0-2 mm (normal) and >5 mm (abnormal) side-to-side differences were adopted to compare studies. Normal stability for all autografts was 72 versus 59% for all allografts (P < 0.01). Abnormal stability was 5% for all autografts versus 14% for all allografts (P < 0.01). Bone-patellar-tendon-bone (BPTB) autograft normal stability was 66% versus 57% for BPTB allografts (P < 0.01). Abnormal BPTB autograft stability was 6 versus 16% for BPTB allograft. Hamstring autograft normal or abnormal stability rates were 77% and 4% and were compared to soft tissue allografts as a group which were 64% and 12% (P < 0.01). This is the first meta-analysis comparing autograft to allograft stability in ACLR. Allografts had significantly lower normal stability rates than autografts. The allograft abnormal stability rate, which usually represents graft failure, was significantly higher than that of autografts: nearly three times greater. It would therefore appear that autografts are the graft of choice for routine ACLR with allografts better reserved for multiple ligament-injured knees where extra tissue may be required. PMID:17437083

Prodromos, Chadwick; Joyce, Brian; Shi, Kelvin

2007-07-01

448

Dynamic Stability Analysis of Blunt Body Entry Vehicles Using Time-Lagged Aftbody Pitching Moments

NASA Technical Reports Server (NTRS)

This analysis defines an analytic model for the pitching motion of blunt bodies during atmospheric entry. The proposed model is independent of the pitch damping sum coefficient present in the standard formulation of the equations of motion describing pitch oscillations of a decelerating blunt body, instead using the principle of a time-lagged aftbody moment as the forcing function for oscillation divergence. Four parameters, all with intuitive physical relevance, are introduced to fully define the aftbody moment and the associated time delay. It is shown that the dynamic oscillation responses typical to blunt bodies can be produced using hysteresis of the aftbody moment in place of the pitch damping coefficient. The approach used in this investigation is shown to be useful in understanding the governing physical mechanisms for blunt body dynamic stability and in guiding vehicle and mission design requirements. A validation case study using simulated ballistic range test data is conducted. From this, parameter identification is carried out through the use of a least squares optimizing routine. Results show good agreement with the limited existing literature for the parameters identified, suggesting that the model proposed could be validated by an experimental ballistic range test series. The trajectories produced by the identified parameters were found to match closely those from the MER ballistic range tests for a wide array of initial conditions and can be identified with a reasonable number of ballistic range shots and computational effort.

Kazemba, Cole D.; Braun, Robert D.; Schoenenberger, Mark; Clark, Ian G.

2013-01-01

449

Stability Analysis of Two Stage Stochastic Mathematical Programs ...

Mar 21, 2010 ... For example, one can use NCP functions such as min-function or Fischer-. Burmeister ... In this section, we present some preliminary results in deterministic MPECs, set-valued analysis and random ...... 12 (1965), 1-12.

2010-03-21

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