Numerical simulation of stability and stability control of high speed compressible rotating couette flow

NASA Technical Reports Server (NTRS)

Biringen, Sedat; Hatay, Ferhat F.

1993-01-01

The nonlinear temporal evolution of disturbances in compressible flow between infinitely long, concentric cylinders is investigated through direct numerical simulations of the full, three-dimensional Navier-Stokes and energy equations. Counter-rotating cylinders separated by wide gaps are considered with supersonic velocities of the inner cylinder. Initially, the primary disturbance grows exponentially in accordance with linear stability theory. As the disturbances evolve, higher harmonics and subharmonics are generated in a cascading order eventually reaching a saturation state. Subsequent highly nonlinear stages of the evolution are governed by the interaction of the disturbance modes, particularly the axial subharmonics. Nonlinear evolution of the disturbance field is characterized by the formation of high-shear layers extending from the inner cylinder towards the center of the gap in the form of jets similar to the ejection events in transitional and turbulent wall-bounded shear flows.

Stability Analysis of an Encapsulated Microbubble against Gas Diffusion

PubMed Central

Katiyar, Amit; Sarkar, Kausik

2009-01-01

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

Regulating thrombus growth and stability to achieve an optimal response to injury

PubMed Central

Brass, Lawrence F.; Wannemacher, Kenneth M.; Ma, Peisong; Stalker, Timothy J.

2012-01-01

An optimal platelet response to injury can be defined as one in which blood loss is restrained and haemostasis is achieved without the penalty of further tissue damage caused by unwarranted vascular occlusion. This brief review considers some of the ways in which thrombus growth and stability can be regulated so that an optimal platelet response can be achieved in vivo. Three related topics are considered. The first focuses on intracellular mechanisms that regulate the early events of platelet activation downstream of G protein coupled receptors for agonists such as thrombin, thromboxane A2 and ADP. The second considers the ways in which signalling events that are dependent on stable contacts between platelets can influence the state of platelet activation and thus affect thrombus growth and stability. The third focuses on the changes that are experienced by platelets as they move from their normal environment in freely-flowing plasma to a very different environment within the growing haemostatic plug, an environment in which the narrowing gaps and junctions between platelets not only facilitate communication, but also increasingly limit both the penetration of plasma and the exodus of platelet-derived bioactive molecules. PMID:21781243

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

NASA Astrophysics Data System (ADS)

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

2009-04-01

dam's state of safety. This study considered the SSR (Shear Strength Reduction) technique for slope stability numerical modelling. In the SSR finite element technique, elasto-plastic strength is assumed for dam's materials and shear strengths are progressively reduced until collapse occurs. Numerical modelling was performed on the most critical profile choosed through analysis of geophysical and geotechnical informational volume achieved by insitu or in laboratory tests. Finite element analysis were considered in two situations: first, before geophysical investigations and second considering the whole informational of data achieved. Both situations were analysed in static and pseudo-static conditions. The factor of safety before geophysical investigations is high enough to describe a stable state of stability even for the seismic load. The total displacement distributions were modified by the presence of internal erosional element giving a high state of instability, especially for the pseudo-static case. These analysis using the finite element method prove the importance of structural disturbance elements that may occure inside the dam body produced by internal erosional processes.

Dynamic State Estimation for Multi-Machine Power System by Unscented Kalman Filter With Enhanced Numerical Stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qi, Junjian; Sun, Kai; Wang, Jianhui

In this paper, in order to enhance the numerical stability of the unscented Kalman filter (UKF) used for power system dynamic state estimation, a new UKF with guaranteed positive semidifinite estimation error covariance (UKFGPS) is proposed and compared with five existing approaches, including UKFschol, UKF-kappa, UKFmodified, UKF-Delta Q, and the squareroot UKF (SRUKF). These methods and the extended Kalman filter (EKF) are tested by performing dynamic state estimation on WSCC 3-machine 9-bus system and NPCC 48-machine 140-bus system. For WSCC system, all methods obtain good estimates. However, for NPCC system, both EKF and the classic UKF fail. It is foundmore » that UKFschol, UKF-kappa, and UKF-Delta Q do not work well in some estimations while UKFGPS works well in most cases. UKFmodified and SRUKF can always work well, indicating their better scalability mainly due to the enhanced numerical stability.« less

Numerical study on the Welander oscillatory natural circulation problem using high-order numerical methods

DOE PAGES

Zou, Ling; Zhao, Haihua; Kim, Seung Jun

2016-11-16

In this study, the classical Welander’s oscillatory natural circulation problem is investigated using high-order numerical methods. As originally studied by Welander, the fluid motion in a differentially heated fluid loop can exhibit stable, weakly instable, and strongly instable modes. A theoretical stability map has also been originally derived from the stability analysis. Numerical results obtained in this paper show very good agreement with Welander’s theoretical derivations. For stable cases, numerical results from both the high-order and low-order numerical methods agree well with the non-dimensional flow rate analytically derived. The high-order numerical methods give much less numerical errors compared to themore » low-order methods. For stability analysis, the high-order numerical methods could perfectly predict the stability map, while the low-order numerical methods failed to do so. For all theoretically unstable cases, the low-order methods predicted them to be stable. The result obtained in this paper is a strong evidence to show the benefits of using high-order numerical methods over the low-order ones, when they are applied to simulate natural circulation phenomenon that has already gain increasing interests in many future nuclear reactor designs.« less

The role of opacity and transparency in achieving strategic stability in South Asia.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajain, Arpit; Ashraf, Tariq Mahmud

According to international relations theory, deterrence can be used as a tool to achieve stability between potentially hostile nations. India and Pakistan's long history of periodic crises raises the question of how they can achieve deterrence stability. 'Transparency' describes the flow of information between parties and plays a key role in establishing a deterrence relationship. This paper studies the balance needed between opacity and transparency in nuclear topics for the maintenance of deterrence stability between India and Pakistan. States with nuclear weapons are postulated to implement transparency in four categories: potential, capability, intent, and resolve. The study applies these categoriesmore » to the nuclear components of the ongoing India-Pakistan Composite Dialogue Working Group for Peace and Security including CBMs. To focus our efforts, we defined four scenarios to characterize representative strategic/military/political conditions. The scenarios are combinations of these two sets of opposite poles: competition - cooperation; extremism - moderation (to be understood primarily in a religious/nationalistic sense). We describe each scenario in terms of select focal areas (nuclear doctrine, nuclear command and control, nuclear stockpile, nuclear delivery/defensive systems, and conventional force posture). The scenarios help frame the realm of possibilities, and have been described in terms of expected conditions for the focal areas. We then use the conditions in each scenario to prescribe a range of information-sharing actions that the two countries could take to increase stability. We also highlight the information that should not be shared. These actions can be political (e.g., declarations), procedural (e.g., advance notice of certain military activities), or technologically based (e.g., seismic monitoring of the nuclear test moratorium).« less

The Influence of Pre-University Students' Mathematics Test Anxiety and Numerical Anxiety on Mathematics Achievement

ERIC Educational Resources Information Center

Seng, Ernest Lim Kok

2015-01-01

This study examines the relationship between mathematics test anxiety and numerical anxiety on students' mathematics achievement. 140 pre-university students who studied at one of the institutes of higher learning were being investigated. Gender issue pertaining to mathematics anxieties was being addressed besides investigating the magnitude of…

Equilibrium points, stability and numerical solutions of fractional-order predator-prey and rabies models

NASA Astrophysics Data System (ADS)

Ahmed, E.; El-Sayed, A. M. A.; El-Saka, H. A. A.

2007-01-01

In this paper we are concerned with the fractional-order predator-prey model and the fractional-order rabies model. Existence and uniqueness of solutions are proved. The stability of equilibrium points are studied. Numerical solutions of these models are given. An example is given where the equilibrium point is a centre for the integer order system but locally asymptotically stable for its fractional-order counterpart.

Recommendations for Achieving Accurate Numerical Simulation of Tip Clearance Flows in Transonic Compressor Rotors

NASA Technical Reports Server (NTRS)

VanZante, Dale E.; Strazisar, Anthony J.; Wood, Jerry R,; Hathaway, Michael D.; Okiishi, Theodore H.

2000-01-01

The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. While numerical simulations of these flows are quite sophisticated. they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip clearance flow details (e.g. trajectory and radial extent) with corresponding data obtained from a numerical simulation. Recommendations for achieving accurate numerical simulation of tip clearance flows are presented based on this comparison. Laser Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor was simulated using a Navier-Stokes turbomachinery solver that incorporates an advanced k-epsilon turbulence model derived for flows that are not in local equilibrium. Comparison between measured and simulated results indicates that simulation accuracy is primarily dependent upon the ability of the numerical code to resolve important details of a wall-bounded shear layer formed by the relative motion between the over-tip leakage flow and the shroud wall. A simple method is presented for determining the strength of this shear layer.

Combined analytical and numerical approaches in Dynamic Stability analyses of engineering systems

NASA Astrophysics Data System (ADS)

Náprstek, Jiří

2015-03-01

Dynamic Stability is a widely studied area that has attracted many researchers from various disciplines. Although Dynamic Stability is usually associated with mechanics, theoretical physics or other natural and technical disciplines, it is also relevant to social, economic, and philosophical areas of our lives. Therefore, it is useful to occasionally highlight the general aspects of this amazing area, to present some relevant examples and to evaluate its position among the various branches of Rational Mechanics. From this perspective, the aim of this study is to present a brief review concerning the Dynamic Stability problem, its basic definitions and principles, important phenomena, research motivations and applications in engineering. The relationships with relevant systems that are prone to stability loss (encountered in other areas such as physics, other natural sciences and engineering) are also noted. The theoretical background, which is applicable to many disciplines, is presented. In this paper, the most frequently used Dynamic Stability analysis methods are presented in relation to individual dynamic systems that are widely discussed in various engineering branches. In particular, the Lyapunov function and exponent procedures, Routh-Hurwitz, Liénard, and other theorems are outlined together with demonstrations. The possibilities for analytical and numerical procedures are mentioned together with possible feedback from experimental research and testing. The strengths and shortcomings of these approaches are evaluated together with examples of their effective complementing of each other. The systems that are widely encountered in engineering are presented in the form of mathematical models. The analyses of their Dynamic Stability and post-critical behaviour are also presented. The stability limits, bifurcation points, quasi-periodic response processes and chaotic regimes are discussed. The limit cycle existence and stability are examined together with their

Experimental and numerical investigation on the ignition and combustion stability in solid fuel ramjet with swirling flow

NASA Astrophysics Data System (ADS)

Musa, Omer; Xiong, Chen; Changsheng, Zhou

2017-08-01

The present article investigates experimentally and numerically the ignition and flame stability of high-density polyethylene solid fuel with incoming swirling air through a solid fuel ramjet (SFRJ). A new design of swirler is proposed and used in this work. Experiments on connected pipes test facility were performed for SFRJ with and without swirl. An in-house code has been developed to simulate unsteady, turbulent, reacting, swirling flow in the SFRJ. Four different swirl intensities are utilized to study experimentally and numerically the effect of swirl number on the transient regression, ignition of the solid fuel in a hot-oxidizing flow and combustion phenomenon in the SFRJ. The results showed that using swirl flow decreases the ignition time delay, recirculation zone length, and the distance between the flame and the wall, meanwhile, increases the residence time, heat transfer, regression rate and mixing degree, thus, improving the combustion efficiency and stability.

Stability analysis of the Euler discretization for SIR epidemic model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suryanto, Agus

2014-06-19

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

The Measurement Structure, Stability and Mediating Effects of Achievement Goals in Math with Middle-School Student Data

ERIC Educational Resources Information Center

Chiang, Yu-Tzu; Lin, Sunny S. J.

2014-01-01

This study examined the measurement structure, cross-year stability of achievement goals, and mediating effects of achievement goals between self-efficacy and math grades in a national sample of Taiwan middle school students. The measurement model with factorial structure showed good fit to the data. In the panel data (N?=?343), four achievement…

Thermal Noise Limit in Frequency Stabilization of Lasers with Rigid Cavities

NASA Technical Reports Server (NTRS)

Numata, Kenji; Kemery, Amy; Camp, Jordan

2005-01-01

We evaluated thermal noise (Brownian motion) in a rigid reference cavity Used for frequency stabilization of lasers, based on the mechanical loss of cavity materials and the numerical analysis of the mirror-spacer mechanics with the direct application of the fluctuation dissipation theorem. This noise sets a fundamental limit for the frequency stability achieved with a rigid frequency-reference cavity of order 1 Hz/rtHz at 10mHz at room temperature. This level coincides with the world-highest level stabilization results.

Experimental and numerical analysis of the influence of tyres' properties on the straight running stability of a sport-touring motorcycle

NASA Astrophysics Data System (ADS)

Cossalter, Vittore; Doria, Alberto; Formentini, Matteo; Peretto, Martino

2012-03-01

The behaviour of a motorcycle on the road is largely governed by tyre properties. This paper presents experimental and numerical analyses dealing with the influence of tyre properties on the stability of weave and wobble in straight running. The final goal is to find optimal sets of tyre properties that improve the stability of a motorcycle. The investigation is based on road tests carried out on a sport-touring motorcycle equipped with sensors. Three sets of tyres are tested at different speeds in the presence of weave and wobble. The analysis of telemetry data highlights significant differences in the trends of frequency and damping of weave and wobble against speed. The experimental analysis is integrated by a parametric numerical analysis. Tyre properties are varied according to the design of experiments method, in order to highlight the single effects on stability of lateral and cornering coefficient of front and rear tyres.

Density controls the kinetic stability of ultrastable glasses

NASA Astrophysics Data System (ADS)

Fullerton, Christopher J.; Berthier, Ludovic

2017-08-01

We use a swap Monte Carlo algorithm to numerically prepare bulk glasses with kinetic stability comparable to that of glass films produced experimentally by physical vapor deposition. By melting these systems into the liquid state, we show that some of our glasses retain their amorphous structures longer than 105 times the equilibrium structural relaxation time. This “exceptional” kinetic stability cannot be achieved for bulk glasses produced by slow cooling. We perform simulations at both constant volume and constant pressure to demonstrate that the density mismatch between the ultrastable glass and the equilibrium liquid accounts for a major part of the observed kinetic stability.

Thermal Noise Limit in Frequency Stabilization of Lasers with Rigid Cavities

NASA Technical Reports Server (NTRS)

Numata, Kenji; Kemery, Amy; Camp, Jordan

2004-01-01

We evaluated thermal noise (Brownian motion) in a rigid reference cavity used for frequency stabilization of lasers, based on the mechanical loss of cavity materials and the numerical analysis of the mirror-spacer mechanics with t.he direct application of the fluctuation dissipation theorem. This noise sets a fundamental limit for the frequency stability achieved with a rigid frequency- reference cavity of order 1 Hz/square root Hz(0.01 Hz/square root Hz) at 10 mHz (100 Hz) at room temperature. This level coincides with the world-highest level stabilization results.

Simultaneous stability and sensitivity in model cortical networks is achieved through anti-correlations between the in- and out-degree of connectivity

PubMed Central

Vasquez, Juan C.; Houweling, Arthur R.; Tiesinga, Paul

2013-01-01

Neuronal networks in rodent barrel cortex are characterized by stable low baseline firing rates. However, they are sensitive to the action potentials of single neurons as suggested by recent single-cell stimulation experiments that reported quantifiable behavioral responses in response to short spike trains elicited in single neurons. Hence, these networks are stable against internally generated fluctuations in firing rate but at the same time remain sensitive to similarly-sized externally induced perturbations. We investigated stability and sensitivity in a simple recurrent network of stochastic binary neurons and determined numerically the effects of correlation between the number of afferent (“in-degree”) and efferent (“out-degree”) connections in neurons. The key advance reported in this work is that anti-correlation between in-/out-degree distributions increased the stability of the network in comparison to networks with no correlation or positive correlations, while being able to achieve the same level of sensitivity. The experimental characterization of degree distributions is difficult because all pre-synaptic and post-synaptic neurons have to be identified and counted. We explored whether the statistics of network motifs, which requires the characterization of connections between small subsets of neurons, could be used to detect evidence for degree anti-correlations. We find that the sample frequency of the 3-neuron “ring” motif (1→2→3→1), can be used to detect degree anti-correlation for sub-networks of size 30 using about 50 samples, which is of significance because the necessary measurements are achievable experimentally in the near future. Taken together, we hypothesize that barrel cortex networks exhibit degree anti-correlations and specific network motif statistics. PMID:24223550

The numerical simulation on the stability of steep rock slope by DDA

NASA Astrophysics Data System (ADS)

Zhu, Jianye; Xue, Yiguo; Tao, Yufan; Zhang, Kai; Li, Zhiqiang; Zhang, Xuedong; Yang, Ying

2017-05-01

China is a mountainous country, especially in the southwest area. Recently, the variety of geological disasters such as landslides caused by roadway excavation has become a growing concern for our society. Blindly pursuing mining interests without regard for either the environment or residents in the surrounding areas has created a dangerous situation. In recent years, frequent collapses have occurred at Zengzi Rock in Chongqing, especially after torrential rains [1]. This landslide site is a typical example of collapse caused by mine roadway excavations. To study the mechanism of mining slope stability, we conducted a numerical simulation by DDA based on Zengzi Rock in Chongqing, China. The numerical simulation analyzes the slopes under different engineering conditions and rainfall conditions. The results show that the slope has already been changed under the action of its own joints and fissures. After the excavation of the roadway and the rainfall action, this change is drastically increased and the effect is obvious. Through the result graph, we can find that the change of the displacement and stress distribution is obvious, and the simulation results can be great significance to the mining and support of similar mountain conditions.

Is crisis stability still achievable?

NASA Astrophysics Data System (ADS)

Pollack, Joshua

During the Cold War, the idea of crisis stability concerned whether the United States and the Soviet Union would be faced with powerful incentives to strike each other first with their nuclear weapons during periods of tension. This idea influenced the design of nuclear forces and guided aspects of nuclear arms control. The United States and Russia continue to operate large, alert nuclear forces, but at least three new factors have emerged that add significantly greater complexity to this picture. The first new factor consists of the development and deployment of new strategic military technologies that are entangled with nuclear weapons. These include strategic ballistic missile defenses, counter-space weapons, and strategic conventional weapons. The second new factor consists of new dyads of interacting strategic forces beyond US-Russia. These include US-China, US-North Korea, India-Pakistan, and India-China. The third new factor consists of the emergence of three-actor crisis stability dynamics, where the third actor is not necessarily nuclear-armed. This paper illustrates the concept with the US-North Korea-South Korea triangle. It briefly discusses the implications of these developments and reflects on the broad policy options that may be available.

Numerical Boundary Condition Procedures

NASA Technical Reports Server (NTRS)

1981-01-01

Topics include numerical procedures for treating inflow and outflow boundaries, steady and unsteady discontinuous surfaces, far field boundaries, and multiblock grids. In addition, the effects of numerical boundary approximations on stability, accuracy, and convergence rate of the numerical solution are discussed.

Is Cu involved in prion oligopeptide stability? Experiments and numerical simulations

NASA Astrophysics Data System (ADS)

Minicozzi, V.; Morante, S.

The high-sociological impact of neurodegenerative diseases (like Alzheimer disease, Transmissible Spongiform Encephalopathies, Parkinson disease, etc.) has renewed the interest of researchers in the study of misfolding processes and in particular of the rôle played by metals in plaque formation as their unbalanced concentration can be regarded as a possible concurrent cause of protein aggregation. Metals are essential players in many of the fundamental activities of cells. Storing, metabolism, and trafficking of metals through the cellular membrane and within the cytoplasm are mediated by many proteins via well-tuned mechanisms because of the toxicity of free ions. In this review article, we summarize the results of the most recent experimental and numerical investigations aimed at understanding the possible rôle of Cu in stabilizing the Prion protein structure and in the formation of protein polymers.

Hyperbolic heat conduction problems involving non-Fourier effects - Numerical simulations via explicit Lax-Wendroff/Taylor-Galerkin finite element formulations

NASA Technical Reports Server (NTRS)

Tamma, Kumar K.; Namburu, Raju R.

1989-01-01

Numerical simulations are presented for hyperbolic heat-conduction problems that involve non-Fourier effects, using explicit, Lax-Wendroff/Taylor-Galerkin FEM formulations as the principal computational tool. Also employed are smoothing techniques which stabilize the numerical noise and accurately predict the propagating thermal disturbances. The accurate capture of propagating thermal disturbances at characteristic time-step values is achieved; numerical test cases are presented which validate the proposed hyperbolic heat-conduction problem concepts.

Anion control as a strategy to achieve high-mobility and high-stability oxide thin-film transistors.

PubMed

Kim, Hyun-Suk; Jeon, Sang Ho; Park, Joon Seok; Kim, Tae Sang; Son, Kyoung Seok; Seon, Jong-Baek; Seo, Seok-Jun; Kim, Sun-Jae; Lee, Eunha; Chung, Jae Gwan; Lee, Hyungik; Han, Seungwu; Ryu, Myungkwan; Lee, Sang Yoon; Kim, Kinam

2013-01-01

Ultra-definition, large-area displays with three-dimensional visual effects represent megatrend in the current/future display industry. On the hardware level, such a "dream" display requires faster pixel switching and higher driving current, which in turn necessitate thin-film transistors (TFTs) with high mobility. Amorphous oxide semiconductors (AOS) such as In-Ga-Zn-O are poised to enable such TFTs, but the trade-off between device performance and stability under illumination critically limits their usability, which is related to the hampered electron-hole recombination caused by the oxygen vacancies. Here we have improved the illumination stability by substituting oxygen with nitrogen in ZnO, which may deactivate oxygen vacancies by raising valence bands above the defect levels. Indeed, the stability under illumination and electrical bias is superior to that of previous AOS-based TFTs. By achieving both mobility and stability, it is highly expected that the present ZnON TFTs will be extensively deployed in next-generation flat-panel displays.

Anion control as a strategy to achieve high-mobility and high-stability oxide thin-film transistors

PubMed Central

Kim, Hyun-Suk; Jeon, Sang Ho; Park, Joon Seok; Kim, Tae Sang; Son, Kyoung Seok; Seon, Jong-Baek; Seo, Seok-Jun; Kim, Sun-Jae; Lee, Eunha; Chung, Jae Gwan; Lee, Hyungik; Han, Seungwu; Ryu, Myungkwan; Lee, Sang Yoon; Kim, Kinam

2013-01-01

Ultra-definition, large-area displays with three-dimensional visual effects represent megatrend in the current/future display industry. On the hardware level, such a “dream” display requires faster pixel switching and higher driving current, which in turn necessitate thin-film transistors (TFTs) with high mobility. Amorphous oxide semiconductors (AOS) such as In-Ga-Zn-O are poised to enable such TFTs, but the trade-off between device performance and stability under illumination critically limits their usability, which is related to the hampered electron-hole recombination caused by the oxygen vacancies. Here we have improved the illumination stability by substituting oxygen with nitrogen in ZnO, which may deactivate oxygen vacancies by raising valence bands above the defect levels. Indeed, the stability under illumination and electrical bias is superior to that of previous AOS-based TFTs. By achieving both mobility and stability, it is highly expected that the present ZnON TFTs will be extensively deployed in next-generation flat-panel displays. PMID:23492854

Stabilization of computational procedures for constrained dynamical systems

NASA Technical Reports Server (NTRS)

Park, K. C.; Chiou, J. C.

1988-01-01

A new stabilization method of treating constraints in multibody dynamical systems is presented. By tailoring a penalty form of the constraint equations, the method achieves stabilization without artificial damping and yields a companion matrix differential equation for the constraint forces; hence, the constraint forces are obtained by integrating the companion differential equation for the constraint forces in time. A principal feature of the method is that the errors committed in each constraint condition decay with its corresponding characteristic time scale associated with its constraint force. Numerical experiments indicate that the method yields a marked improvement over existing techniques.

Evaluating the Effect of Rainfall Infiltration on the Slope Stability of T16 tower of Taipei Mao-kong Gondola by Numerical Methods

NASA Astrophysics Data System (ADS)

RUNG, J.

2013-12-01

In this study, a series of rainfall-stability analyses were performed to simulate the failure mechanism and the function of remediation works of the down slope of T-16 tower pier, Mao-Kong gondola (or T-16 Slope) at the hillside of Taipei City using two-dimensional finite element method. The failure mechanism of T-16 Slope was simulated using the rainfall hyetograph of Jang-Mi typhoon in 2008 based on the field investigation data, monitoring data, soil/rock mechanical testing data and detail design plots of remediation works. Eventually, the numerical procedures and various input parameters in the analysis were verified by comparing the numerical results with the field observations. In addition, 48 hrs design rainfalls corresponding to 5, 10, 25 and 50 years return periods were prepared using the 20 years rainfall data of Mu-Zha rainfall observation station, Central Weather Bureau for the rainfall-stability analyses of T-16 Slope to inspect the effect of the compound stabilization works on the overall stability of the slope. At T-16 Slope, without considering the longitudinal and transverse drainages on the ground surface, there totally 4 types of stabilization works were installed to stabilize the slope. From the slope top to the slope toe, the stabilization works of T-16 Slope consists of RC-retaining wall with micro-pile foundation at the up-segment, earth anchor at the up-middle-segment, soil nailing at the middle-segment and retaining pile at the down-segment of the slope. The effect of each individual stabilization work on the slope stability under rainfall condition was examined and evaluated by raising field groundwater level.

Stability of nonuniform rotor blades in hover using a mixed formulation

NASA Technical Reports Server (NTRS)

Stephens, W. B.; Hodges, D. H.; Avila, J. H.; Kung, R. M.

1980-01-01

A mixed formulation for calculating static equilibrium and stability eigenvalues of nonuniform rotor blades in hover is presented. The static equilibrium equations are nonlinear and are solved by an accurate and efficient collocation method. The linearized perturbation equations are solved by a one step, second order integration scheme. The numerical results correlate very well with published results from a nearly identical stability analysis based on a displacement formulation. Slight differences in the results are traced to terms in the equations that relate moments to derivatives of rotations. With the present ordering scheme, in which terms of the order of squares of rotations are neglected with respect to unity, it is not possible to achieve completely equivalent models based on mixed and displacement formulations. The one step methods reveal that a second order Taylor expansion is necessary to achieve good convergence for nonuniform rotating blades. Numerical results for a hypothetical nonuniform blade, including the nonlinear static equilibrium solution, were obtained with no more effort or computer time than that required for a uniform blade.

Numerical proof of stability of roll waves in the small-amplitude limit for inclined thin film flow

NASA Astrophysics Data System (ADS)

Barker, Blake

2014-10-01

We present a rigorous numerical proof based on interval arithmetic computations categorizing the linearized and nonlinear stability of periodic viscous roll waves of the KdV-KS equation modeling weakly unstable flow of a thin fluid film on an incline in the small-amplitude KdV limit. The argument proceeds by verification of a stability condition derived by Bar-Nepomnyashchy and Johnson-Noble-Rodrigues-Zumbrun involving inner products of various elliptic functions arising through the KdV equation. One key point in the analysis is a bootstrap argument balancing the extremely poor sup norm bounds for these functions against the extremely good convergence properties for analytic interpolation in order to obtain a feasible computation time. Another is the way of handling analytic interpolation in several variables by a two-step process carving up the parameter space into manageable pieces for rigorous evaluation. These and other general aspects of the analysis should serve as blueprints for more general analyses of spectral stability.

Numerical stability analysis of two-dimensional solute transport along a discrete fracture in a porous rock matrix

NASA Astrophysics Data System (ADS)

Watanabe, Norihiro; Kolditz, Olaf

2015-07-01

This work reports numerical stability conditions in two-dimensional solute transport simulations including discrete fractures surrounded by an impermeable rock matrix. We use an advective-dispersive problem described in Tang et al. (1981) and examine the stability of the Crank-Nicolson Galerkin finite element method (CN-GFEM). The stability conditions are analyzed in terms of the spatial discretization length perpendicular to the fracture, the flow velocity, the diffusion coefficient, the matrix porosity, the fracture aperture, and the fracture longitudinal dispersivity. In addition, we verify applicability of the recently developed finite element method-flux corrected transport (FEM-FCT) method by Kuzmin () to suppress oscillations in the hybrid system, with a comparison to the commonly utilized Streamline Upwinding/Petrov-Galerkin (SUPG) method. Major findings of this study are (1) the mesh von Neumann number (Fo) ≥ 0.373 must be satisfied to avoid undershooting in the matrix, (2) in addition to an upper bound, the Courant number also has a lower bound in the fracture in cases of low dispersivity, and (3) the FEM-FCT method can effectively suppress the oscillations in both the fracture and the matrix. The results imply that, in cases of low dispersivity, prerefinement of a numerical mesh is not sufficient to avoid the instability in the hybrid system if a problem involves evolutionary flow fields and dynamic material parameters. Applying the FEM-FCT method to such problems is recommended if negative concentrations cannot be tolerated and computing time is not a strong issue.

Experimental and numerical studies of a microfluidic device with compliant chambers for flow stabilization

NASA Astrophysics Data System (ADS)

Iyer, V.; Raj, A.; Annabattula, R. K.; Sen, A. K.

2015-07-01

This paper reports experimental and numerical studies of a passive microfluidic device that stabilizes a pulsating incoming flow and delivers a steady flow at the outlet. The device employs a series of chambers along the flow direction with a thin polymeric membrane (of thickness 75-250 µm) serving as the compliant boundary. The deformation of the membrane allows accumulation of fluid during an overflow and discharge of fluid during an underflow for flow stabilization. Coupled fluid-structure simulations are performed using Mooney-Rivlin formulations to account for a thin hyperelastic membrane material undergoing large deformations to accurately predict the device performance. The device was fabricated with PDMS as the substrate material and thin PDMS membrane as the compliant boundary. The performance of the device is defined in terms of a parameter called ‘Attenuation Factor (AF)’. The effect of various design parameters including membrane thickness, elastic modulus, chamber size and number of chambers in series as well as operating conditions including the outlet pressure, mean input flow rate, fluctuation amplitude and frequency on the device performance were studied using experiments and simulations. The simulation results successfully confront the experimental data (within 10%) which validates the numerical simulations. The device was used at the exit of a PZT actuated valveless micropump to take pulsating flow at the upstream and deliver steady flow downstream. The amplitude of the pulsating flow delivered by the micropump was significantly reduced (AF = 0.05 for a device with three 4 mm chambers) but at the expense of a reduction in the pressure capability (<20%). The proposed device could potentially be used for reducing flow pulsations in practical microfluidic circuits.

Children’s Mapping between Non-Symbolic and Symbolic Numerical Magnitudes and Its Association with Timed and Untimed Tests of Mathematics Achievement

PubMed Central

Brankaer, Carmen; Ghesquière, Pol; De Smedt, Bert

2014-01-01

The ability to map between non-symbolic numerical magnitudes and Arabic numerals has been put forward as a key factor in children’s mathematical development. This mapping ability has been mainly examined indirectly by looking at children’s performance on a symbolic magnitude comparison task. The present study investigated mapping in a more direct way by using a task in which children had to choose which of two choice quantities (Arabic digits or dot arrays) matched the target quantity (dot array or Arabic digit), thereby focusing on small quantities ranging from 1 to 9. We aimed to determine the development of mapping over time and its relation to mathematics achievement. Participants were 36 first graders (M = 6 years 8 months) and 46 third graders (M = 8 years 8 months) who all completed mapping tasks, symbolic and non-symbolic magnitude comparison tasks and standardized timed and untimed tests of mathematics achievement. Findings revealed that children are able to map between non-symbolic and symbolic representations and that this mapping ability develops over time. Moreover, we found that children’s mapping ability is related to timed and untimed measures of mathematics achievement, over and above the variance accounted for by their numerical magnitude comparison skills. PMID:24699664

Numerical exploration of Kaldorian interregional macrodynamics: stability and the trade threshold for business cycles under fixed exchange rates.

PubMed

Asada, Toichiro; Douskos, Christos; Markellos, Panagiotis

2011-01-01

The stability of equilibrium and the possibility of generation of business cycles in a discrete interregional Kaldorian macrodynamic model with fixed exchange rates are explored using numerical methods. One of the aims is to illustrate the feasibility and effectiveness of the numerical approach for dynamical systems of moderately high dimensionality and several parameters. The model considered is five-dimensional with four parameters, the speeds of adjustment of the goods markets and the degrees of economic interactions between the regions through trade and capital movement. Using a grid search method for the determination of the region of stability of equilibrium in two-dimensional parameter subspaces, and coefficient criteria for the flip bifurcation - and Hopf bifurcation - curve, we determine the stability region in several parameter ranges and identify Hopf bifurcation curves when they exist. It is found that interregional cycles emerge only for sufficient interregional trade. The relevant threshold is predicted by the model at 14 - 16 % of trade transactions. By contrast, no minimum level of capital mobility exists in a global sense as a requirement for the emergence of interregional cycles; the main conclusion being, therefore, that cycles may occur for very low levels of capital mobility if trade is sufficient. Examples of bifurcation and Lyapunov exponent diagrams illustrating the occurrence of cycles or period doubling, and examples of the development of the occurring cycles, are given. Both supercritical and subcritical bifurcations are found to occur, the latter type indicating coexistence of a point and a cyclical attractor.

Improving the Numerical Stability of Fast Matrix Multiplication

DOE PAGES

Ballard, Grey; Benson, Austin R.; Druinsky, Alex; ...

2016-10-04

Fast algorithms for matrix multiplication, namely those that perform asymptotically fewer scalar operations than the classical algorithm, have been considered primarily of theoretical interest. Apart from Strassen's original algorithm, few fast algorithms have been efficiently implemented or used in practical applications. However, there exist many practical alternatives to Strassen's algorithm with varying performance and numerical properties. Fast algorithms are known to be numerically stable, but because their error bounds are slightly weaker than the classical algorithm, they are not used even in cases where they provide a performance benefit. We argue in this study that the numerical sacrifice of fastmore » algorithms, particularly for the typical use cases of practical algorithms, is not prohibitive, and we explore ways to improve the accuracy both theoretically and empirically. The numerical accuracy of fast matrix multiplication depends on properties of the algorithm and of the input matrices, and we consider both contributions independently. We generalize and tighten previous error analyses of fast algorithms and compare their properties. We discuss algorithmic techniques for improving the error guarantees from two perspectives: manipulating the algorithms, and reducing input anomalies by various forms of diagonal scaling. In conclusion, we benchmark performance and demonstrate our improved numerical accuracy.« less

Polyhedral meshing in numerical analysis of conjugate heat transfer

NASA Astrophysics Data System (ADS)

Sosnowski, Marcin; Krzywanski, Jaroslaw; Grabowska, Karolina; Gnatowska, Renata

2018-06-01

Computational methods have been widely applied in conjugate heat transfer analysis. The very first and crucial step in such research is the meshing process which consists in dividing the analysed geometry into numerous small control volumes (cells). In Computational Fluid Dynamics (CFD) applications it is desirable to use the hexahedral cells as the resulting mesh is characterized by low numerical diffusion. Unfortunately generating such mesh can be a very time-consuming task and in case of complicated geometry - it may not be possible to generate cells of good quality. Therefore tetrahedral cells have been implemented into commercial pre-processors. Their advantage is the ease of its generation even in case of very complex geometry. On the other hand tetrahedrons cannot be stretched excessively without decreasing the mesh quality factor, so significantly larger number of cells has to be used in comparison to hexahedral mesh in order to achieve a reasonable accuracy. Moreover the numerical diffusion of tetrahedral elements is significantly higher. Therefore the polyhedral cells are proposed within the paper in order to combine the advantages of hexahedrons (low numerical diffusion resulting in accurate solution) and tetrahedrons (rapid semi-automatic generation) as well as to overcome the disadvantages of both the above mentioned mesh types. The major benefit of polyhedral mesh is that each individual cell has many neighbours, so gradients can be well approximated. Polyhedrons are also less sensitive to stretching than tetrahedrons which results in better mesh quality leading to improved numerical stability of the model. In addition, numerical diffusion is reduced due to mass exchange over numerous faces. This leads to a more accurate solution achieved with a lower cell count. Therefore detailed comparison of numerical modelling results concerning conjugate heat transfer using tetrahedral and polyhedral meshes is presented in the paper.

Further studies on stability analysis of nonlinear Roesser-type two-dimensional systems

NASA Astrophysics Data System (ADS)

Dai, Xiao-Lin

2014-04-01

This paper is concerned with further relaxations of the stability analysis of nonlinear Roesser-type two-dimensional (2D) systems in the Takagi-Sugeno fuzzy form. To achieve the goal, a novel slack matrix variable technique, which is homogenous polynomially parameter-dependent on the normalized fuzzy weighting functions with arbitrary degree, is developed and the algebraic properties of the normalized fuzzy weighting functions are collected into a set of augmented matrices. Consequently, more information about the normalized fuzzy weighting functions is involved and the relaxation quality of the stability analysis is significantly improved. Moreover, the obtained result is formulated in the form of linear matrix inequalities, which can be easily solved via standard numerical software. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed result.

Numerical Modeling of Sliding Stability of RCC dam

NASA Astrophysics Data System (ADS)

Mughieda, O.; Hazirbaba, K.; Bani-Hani, K.; Daoud, W.

2017-06-01

Stability and stress analyses are the most important elements that require rigorous consideration in design of a dam structure. Stability of dams against sliding is crucial due to the substantial horizontal load that requires sufficient and safe resistance to develop by mobilization of adequate shearing forces along the base of the dam foundation. In the current research, the static sliding stability of a roller-compacted-concrete (RCC) dam was modelled using finite element method to investigate the stability against sliding. A commercially available finite element software (SAP 2000) was used to analyze stresses in the body of the dam and foundation. A linear finite element static analysis was performed in which a linear plane strain isoperimetric four node elements was used for modelling the dam-foundation system. The analysis was carried out assuming that no slip will occur at the interface between the dam and the foundation. Usual static loading condition was applied for the static analysis. The greatest tension was found to develop in the rock adjacent to the toe of the upstream slope. The factor of safety against sliding along the entire base of the dam was found to be greater than 1 (FS>1), for static loading conditions.

An approach toward the numerical evaluation of multi-loop Feynman diagrams

NASA Astrophysics Data System (ADS)

Passarino, Giampiero

2001-12-01

A scheme for systematically achieving accurate numerical evaluation of multi-loop Feynman diagrams is developed. This shows the feasibility of a project aimed to produce a complete calculation for two-loop predictions in the Standard Model. As a first step an algorithm, proposed by F.V. Tkachov and based on the so-called generalized Bernstein functional relation, is applied to one-loop multi-leg diagrams with particular emphasis to the presence of infrared singularities, to the problem of tensorial reduction and to the classification of all singularities of a given diagram. Successively, the extension of the algorithm to two-loop diagrams is examined. The proposed solution consists in applying the functional relation to the one-loop sub-diagram which has the largest number of internal lines. In this way the integrand can be made smooth, a part from a factor which is a polynomial in xS, the vector of Feynman parameters needed for the complementary sub-diagram with the smallest number of internal lines. Since the procedure does not introduce new singularities one can distort the xS-integration hyper-contour into the complex hyper-plane, thus achieving numerical stability. The algorithm is then modified to deal with numerical evaluation around normal thresholds. Concise and practical formulas are assembled and presented, numerical results and comparisons with the available literature are shown and discussed for the so-called sunset topology.

Achieving Vibration Stability of the NSLS-II Hard X-ray Nanoprobe Beamline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simos, N.; Chu, Y. N.; Broadbent, A.

2010-08-30

The Hard X-ray Nanoprobe (HXN) Beamline of National Synchrotron Light Source II (NSLS-lI) requires high levels of stability in order to achieve the desired instrument resolution. To ensure that the design of the endstation helps meet the stringent criteria and that natural and cultural vibration is mitigated both passively and actively, a comprehensive study complimentary to the design process has been undertaken. Vibration sources that have the potential to disrupt sensitive experiments such as wind, traffic and NSLS II operating systems have been studied using state of the art simulations and an array of field data. Further, final stage vibrationmore » isolation principles have been explored in order to be utilized in supporting endstation instruments. This paper presents results of the various study aspects and their influence on the HXN design optimization.« less

Early Dynamics and Stabilization Mechanisms of Oil-in-Water Emulsions Containing Colloidal Particles Modified with Short Amphiphiles: A Numerical Study.

PubMed

Cerbelaud, Manuella; Videcoq, Arnaud; Alison, Lauriane; Tervoort, Elena; Studart, André R

2017-12-19

Emulsions stabilized by mixtures of particles and amphiphilic molecules are relevant for a wide range of applications, but their dynamics and stabilization mechanisms on the colloidal level are poorly understood. Given the challenges to experimentally probe the early dynamics and mechanisms of droplet stabilization, Brownian dynamics simulations are developed here to study the behavior of oil-in-water emulsions stabilized by colloidal particles modified with short amphiphiles. Simulation parameters are based on an experimental system that consists of emulsions obtained with octane as the oil phase and a suspension of alumina colloidal particles modified with short carboxylic acids as the continuous aqueous medium. The numerical results show that attractive forces between the colloidal particles favor the formation of closely packed clusters on the droplet surface or of a percolating network of particles throughout the continuous phase, depending on the amphiphile concentration. Simulations also reveal the importance of a strong adsorption of particles at the liquid interface to prevent their depletion from the droplet surface when another droplet approaches. Strongly adsorbed particles remain immobile on the droplet surface, generating an effective steric barrier against droplet coalescence. These findings provide new insights into the early dynamics and mechanisms of stabilization of emulsions using particles and amphiphilic molecules.

Stability of finite difference numerical simulations of acoustic logging-while-drilling with different perfectly matched layer schemes

NASA Astrophysics Data System (ADS)

Wang, Hua; Tao, Guo; Shang, Xue-Feng; Fang, Xin-Ding; Burns, Daniel R.

2013-12-01

In acoustic logging-while-drilling (ALWD) finite difference in time domain (FDTD) simulations, large drill collar occupies, most of the fluid-filled borehole and divides the borehole fluid into two thin fluid columns (radius ˜27 mm). Fine grids and large computational models are required to model the thin fluid region between the tool and the formation. As a result, small time step and more iterations are needed, which increases the cumulative numerical error. Furthermore, due to high impedance contrast between the drill collar and fluid in the borehole (the difference is >30 times), the stability and efficiency of the perfectly matched layer (PML) scheme is critical to simulate complicated wave modes accurately. In this paper, we compared four different PML implementations in a staggered grid finite difference in time domain (FDTD) in the ALWD simulation, including field-splitting PML (SPML), multiaxial PML(MPML), non-splitting PML (NPML), and complex frequency-shifted PML (CFS-PML). The comparison indicated that NPML and CFS-PML can absorb the guided wave reflection from the computational boundaries more efficiently than SPML and M-PML. For large simulation time, SPML, M-PML, and NPML are numerically unstable. However, the stability of M-PML can be improved further to some extent. Based on the analysis, we proposed that the CFS-PML method is used in FDTD to eliminate the numerical instability and to improve the efficiency of absorption in the PML layers for LWD modeling. The optimal values of CFS-PML parameters in the LWD simulation were investigated based on thousands of 3D simulations. For typical LWD cases, the best maximum value of the quadratic damping profile was obtained using one d 0. The optimal parameter space for the maximum value of the linear frequency-shifted factor ( α 0) and the scaling factor ( β 0) depended on the thickness of the PML layer. For typical formations, if the PML thickness is 10 grid points, the global error can be reduced to <1

A study of numerical methods for hyperbolic conservation laws with stiff source terms

NASA Technical Reports Server (NTRS)

Leveque, R. J.; Yee, H. C.

1988-01-01

The proper modeling of nonequilibrium gas dynamics is required in certain regimes of hypersonic flow. For inviscid flow this gives a system of conservation laws coupled with source terms representing the chemistry. Often a wide range of time scales is present in the problem, leading to numerical difficulties as in stiff systems of ordinary differential equations. Stability can be achieved by using implicit methods, but other numerical difficulties are observed. The behavior of typical numerical methods on a simple advection equation with a parameter-dependent source term was studied. Two approaches to incorporate the source term were utilized: MacCormack type predictor-corrector methods with flux limiters, and splitting methods in which the fluid dynamics and chemistry are handled in separate steps. Various comparisons over a wide range of parameter values were made. In the stiff case where the solution contains discontinuities, incorrect numerical propagation speeds are observed with all of the methods considered. This phenomenon is studied and explained.

Improving stability of regional numerical ocean models

NASA Astrophysics Data System (ADS)

Herzfeld, Mike

2009-02-01

An operational limited-area ocean modelling system was developed to supply forecasts of ocean state out to 3 days. This system is designed to allow non-specialist users to locate the model domain anywhere within the Australasian region with minimum user input. The model is required to produce a stable simulation every time it is invoked. This paper outlines the methodology used to ensure the model remains stable over the wide range of circumstances it might encounter. Central to the model configuration is an alternative approach to implementing open boundary conditions in a one-way nesting environment. Approximately 170 simulations were performed on limited areas in the Australasian region to assess the model stability; of these, 130 ran successfully with a static model parameterisation allowing a statistical estimate of the model’s approach toward instability to be determined. Based on this, when the model was deemed to be approaching instability a strategy of adaptive intervention in the form of constraint on velocity and elevation was invoked to maintain stability.

Stabilization of numerical interchange in spectral-element magnetohydrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sovinec, C. R.

In this study, auxiliary numerical projections of the divergence of flow velocity and vorticity parallel to magnetic field are developed and tested for the purpose of suppressing unphysical interchange instability in magnetohydrodynamic simulations. The numerical instability arises with equal-order C 0 finite- and spectral-element expansions of the flow velocity, magnetic field, and pressure and is sensitive to behavior at the limit of resolution. The auxiliary projections are motivated by physical field-line bending, and coercive responses to the projections are added to the flow-velocity equation. Their incomplete expansions are limited to the highest-order orthogonal polynomial in at least one coordinate ofmore » the spectral elements. Cylindrical eigenmode computations show that the projections induce convergence from the stable side with first-order ideal-MHD equations during h-refinement and p-refinement. Hyperbolic and parabolic projections and responses are compared, together with different methods for avoiding magnetic divergence error. Lastly, the projections are also shown to be effective in linear and nonlinear time-dependent computations with the NIMROD code [C. R. Sovinec, et al., J. Comput. Phys. 195 (2004) 355-386], provided that the projections introduce numerical dissipation.« less

Stabilization of numerical interchange in spectral-element magnetohydrodynamics

DOE PAGES

Sovinec, C. R.

2016-05-10

In this study, auxiliary numerical projections of the divergence of flow velocity and vorticity parallel to magnetic field are developed and tested for the purpose of suppressing unphysical interchange instability in magnetohydrodynamic simulations. The numerical instability arises with equal-order C 0 finite- and spectral-element expansions of the flow velocity, magnetic field, and pressure and is sensitive to behavior at the limit of resolution. The auxiliary projections are motivated by physical field-line bending, and coercive responses to the projections are added to the flow-velocity equation. Their incomplete expansions are limited to the highest-order orthogonal polynomial in at least one coordinate ofmore » the spectral elements. Cylindrical eigenmode computations show that the projections induce convergence from the stable side with first-order ideal-MHD equations during h-refinement and p-refinement. Hyperbolic and parabolic projections and responses are compared, together with different methods for avoiding magnetic divergence error. Lastly, the projections are also shown to be effective in linear and nonlinear time-dependent computations with the NIMROD code [C. R. Sovinec, et al., J. Comput. Phys. 195 (2004) 355-386], provided that the projections introduce numerical dissipation.« less

Numerical Modeling of a Vortex Stabilized Arcjet. Ph.D. Thesis, 1991 Final Report

NASA Technical Reports Server (NTRS)

Pawlas, Gary E.

1992-01-01

Arcjet thrusters are being actively considered for use in Earth orbit maneuvering applications. Experimental studies are currently the chief means of determining an optimal thruster configuration. Earlier numerical studies have failed to include all of the effects found in typical arcjets including complex geometries, viscosity, and swirling flow. Arcjet geometries are large area ratio converging nozzles with centerbodies in the subsonic portion of the nozzle. The nozzle walls serve as the anode while the centerbody functions as the cathode. Viscous effects are important because the Reynolds number, based on the throat radius, is typically less than 1,000. Experimental studies have shown that a swirl or circumferential velocity component stabilizes a constricted arc. This dissertation describes the equations governing flow through a constricted arcjet thruster. An assumption that the flowfield is in local thermodynamic equilibrium leads to a single fluid plasma temperature model. An order of magnitude analysis reveals the governing fluid mechanics equations are uncoupled from the electromagnetic field equations. A numerical method is developed to solve the governing fluid mechanics equations, the Thin Layer Navier-Stokes equations. A coordinate transformation is employed in deriving the governing equations to simplify the application of boundary conditions in complex geometries. An axisymmetric formulation is employed to include the swirl velocity component as well as the axial and radial velocity components. The numerical method is an implicit finite-volume technique and allows for large time steps to reach a converged steady-state solution. The inviscid fluxes are flux-split, and Gauss-Seidel line relaxation is used to accelerate convergence. Converging-diverging nozzles with exit-to-throat area ratios up to 100:1 and annular nozzles were examined. Quantities examined included Mach number and static wall pressure distributions, and oblique shock structures. As

Winning the Peace: How Can the Military More Effectively and Efficiently Integrate Civilians in Post-Conflict Operations to Achieve Stability

DTIC Science & Technology

withdraw a large majority of troops months into the operation, but a stable environment required almost a decade to achieve. Stabilization in such a...scenario requires Political, Social , Justice, Economic and Security needs to be met. The military has not been equipped to meet these needs by themselves

Weight Multispectral Reconstruction Strategy for Enhanced Reconstruction Accuracy and Stability With Cerenkov Luminescence Tomography.

PubMed

Hongbo Guo; Xiaowei He; Muhan Liu; Zeyu Zhang; Zhenhua Hu; Jie Tian

2017-06-01

Cerenkov luminescence tomography (CLT) provides a novel technique for 3-D noninvasive detection of radiopharmaceuticals in living subjects. However, because of the severe scattering of Cerenkov light, the reconstruction accuracy and stability of CLT is still unsatisfied. In this paper, a modified weight multispectral CLT (wmCLT) reconstruction strategy was developed which split the Cerenkov radiation spectrum into several sub-spectral bands and weighted the sub-spectral results to obtain the final result. To better evaluate the property of the wmCLT reconstruction strategy in terms of accuracy, stability and practicability, several numerical simulation experiments and in vivo experiments were conducted and the results obtained were compared with the traditional multispectral CLT (mCLT) and hybrid-spectral CLT (hCLT) reconstruction strategies. The numerical simulation results indicated that wmCLT strategy significantly improved the accuracy of Cerenkov source localization and intensity quantitation and exhibited good stability in suppressing noise in numerical simulation experiments. And the comparison of the results achieved from different in vivo experiments further indicated significant improvement of the wmCLT strategy in terms of the shape recovery of the bladder and the spatial resolution of imaging xenograft tumors. Overall the strategy reported here will facilitate the development of nuclear and optical molecular tomography in theoretical study.

Numerical studies on convective stability and flow pattern in three-dimensional spherical mantle of terrestrial planets

NASA Astrophysics Data System (ADS)

Yanagisawa, Takatoshi; Kameyama, Masanori; Ogawa, Masaki

2016-09-01

We explore thermal convection of a fluid with a temperature-dependent viscosity in a basally heated 3-D spherical shell using linear stability analyses and numerical experiments, while considering the application of our results to terrestrial planets. The inner to outer radius ratio of the shell f assumed in the linear stability analyses is in the range of 0.11-0.88. The critical Rayleigh number Rc for the onset of thermal convection decreases by two orders of magnitude as f increases from 0.11 to 0.88, when the viscosity depends sensitively on the temperature, as is the case for real mantle materials. Numerical simulations carried out in the range of f = 0.11-0.55 show that a thermal boundary layer (TBL) develops both along the surface and bottom boundaries to induce cold and hot plumes, respectively, when f is 0.33 or larger. However, for smaller f values, a TBL develops only on the bottom boundary. Convection occurs in the stagnant-lid regime where the root mean square velocity on the surface boundary is less than 1 per cent of its maximum at depth, when the ratio of the viscosity at the surface boundary to that at the bottom boundary exceeds a threshold that depends on f. The threshold decreases from 106.5 at f = 0.11 to 104 at f = 0.55. If the viscosity at the base of the convecting mantle is 1020-1021 Pa s, the Rayleigh number exceeds Rc for Mars, Venus and the Earth, but does not for the Moon and Mercury; convection is unlikely to occur in the latter planets unless the mantle viscosity is much lower than 1020 Pa s and/or the mantle contains a strong internal heat source.

New exponential stability criteria for stochastic BAM neural networks with impulses

NASA Astrophysics Data System (ADS)

Sakthivel, R.; Samidurai, R.; Anthoni, S. M.

2010-10-01

In this paper, we study the global exponential stability of time-delayed stochastic bidirectional associative memory neural networks with impulses and Markovian jumping parameters. A generalized activation function is considered, and traditional assumptions on the boundedness, monotony and differentiability of activation functions are removed. We obtain a new set of sufficient conditions in terms of linear matrix inequalities, which ensures the global exponential stability of the unique equilibrium point for stochastic BAM neural networks with impulses. The Lyapunov function method with the Itô differential rule is employed for achieving the required result. Moreover, a numerical example is provided to show that the proposed result improves the allowable upper bound of delays over some existing results in the literature.

Pitching stability analysis of half-rotating wing air vehicle

NASA Astrophysics Data System (ADS)

Wang, Xiaoyi; Wu, Yang; Li, Qian; Li, Congmin; Qiu, Zhizhen

2017-06-01

Half-Rotating Wing (HRW) is a new power wing which had been developed by our work team using rotating-type flapping instead of oscillating-type flapping. Half-Rotating Wing Air Vehicle (HRWAV) is similar as Bionic Flapping Wing Air Vehicle (BFWAV). It is necessary to guarantee pitching stability of HRWAV to maintain flight stability. The working principle of HRW was firstly introduced in this paper. The rule of motion indicated that the fuselage of HRWAV without empennage would overturn forward as it generated increased pitching movement. Therefore, the empennage was added on the tail of HRWAV to balance the additional moment generated by aerodynamic force during flight. The stability analysis further shows that empennage could weaken rapidly the pitching disturbance on HRWAV and a new balance of fuselage could be achieved in a short time. Case study using numerical analysis verified correctness and validity of research results mentioned above, which could provide theoretical guidance to design and control HRWAV.

Numerical Study of the Plasticity-Induced Stabilization Effect on Martensitic Transformations in Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Junker, Philipp; Hempel, Philipp

2017-12-01

It is well known that plastic deformations in shape memory alloys stabilize the martensitic phase. Furthermore, the knowledge concerning the plastic state is crucial for a reliable sustainability analysis of construction parts. Numerical simulations serve as a tool for the realistic investigation of the complex interactions between phase transformations and plastic deformations. To account also for irreversible deformations, we expand an energy-based material model by including a non-linear isotropic hardening plasticity model. An implementation of this material model into commercial finite element programs, e.g., Abaqus, offers the opportunity to analyze entire structural components at low costs and fast computation times. Along with the theoretical derivation and expansion of the model, several simulation results for various boundary value problems are presented and interpreted for improved construction designing.

Class B Alkaline Stabilization to Achieve Pathogen Inactivation

PubMed Central

Bean, Christine L.; Hansen, Jacqueline J.; Margolin, Aaron B.; Balkin, Helene; Batzer, Glenda; Widmer, Giovanni

2007-01-01

Liming is a cost-effective treatment currently employed in many Class B biosolids production plants in the United States. A bench scale model of lime stabilization was designed to evaluate the persistence of viral, bacterial and parasitic pathogens. The survival of fecal coliforms, Salmonella, adenovirus type 5, rotavirus Wa, bacteriophage MS-2, Cryptosporidium parvum oocysts, Giardia lamblia cysts, and Ascaris lumbricoides ova was evaluated under lime stabilization conditions in a water matrix. Fecal coliforms and Salmonella were undetectable following 2 hours of lime stabilization, demonstrating a 7-log reduction. Adenovirus, MS-2 and rotavirus were below detectable levels following 2 h of liming, demonstrating a 4-log reduction. G. lamblia cysts were also inactivated. A. lumbricoides ova remained viable following 72 hours of liming as did C. parvum oocysts. While this study confirmed that Ascaris ova are resistant to liming, their scarcity in sludge and low recovery efficiencies limit their use as indicator. The persistence of C. parvum oocysts after exposure to lime, suggests that this parasite would be a better choice as indicator for evaluating biosolids intended for land application. The studies done with adenovirus Type 5, rotavirus Wa and male specific bacteriophage provided preliminary data demonstrating similar inactivation rates. Monitoring anthropogenic viruses is a time consuming, labor intensive and expensive process. If further studies could demonstrate that phage could be used as an indicator of other enteric viruses, enhanced monitoring could result in greater acceptance of land application of biosolids while demonstrating no increased public health threat. PMID:17431316

Fault stability under conditions of variable normal stress

USGS Publications Warehouse

Dieterich, J.H.; Linker, M.F.

1992-01-01

The stability of fault slip under conditions of varying normal stress is modelled as a spring and slider system with rate- and state-dependent friction. Coupling of normal stress to shear stress is achieved by inclining the spring at an angle, ??, to the sliding surface. Linear analysis yields two conditions for unstable slip. The first, of a type previously identified for constant normal stress systems, results in instability if stiffness is below a critical value. Critical stiffness depends on normal stress, constitutive parameters, characteristic sliding distance and the spring angle. Instability of the first type is possible only for velocity-weakening friction. The second condition yields instability if spring angle ?? <-cot-1??ss, where ??ss is steady-state sliding friction. The second condition can arise under conditions of velocity strengthening or weakening. Stability fields for finite perturbations are investigated by numerical simulation. -Authors

Extreme trajectory approach to the problem of determining the degree of stability of a laser surface scanning system

NASA Astrophysics Data System (ADS)

Nikitin, V. N.; Chemodanov, V. B.

2018-02-01

The degree of stability of a laser system for surface scanning with nonlinear multiplicative crosstalks is discussed. To determine its stability, the action functional is introduced, which is defined on the set of virtual (achievable) trajectories. The action functional is a measure of external action, which should be applied to a system to move it along a predetermined trial trajectory in the state space.The degree of stability of the system depends on the minimum value of the action functional which is reached on the extreme trajectory transferring the laser scanning system from equilibrium to the limit of the normal operation range. Numerical methods are proposed for calculating the degree of stability.

Trapped particle stability for the kinetic stabilizer

NASA Astrophysics Data System (ADS)

Berk, H. L.; Pratt, J.

2011-08-01

A kinetically stabilized axially symmetric tandem mirror (KSTM) uses the momentum flux of low-energy, unconfined particles that sample only the outer end-regions of the mirror plugs, where large favourable field-line curvature exists. The window of operation is determined for achieving magnetohydrodynamic (MHD) stability with tolerable energy drain from the kinetic stabilizer. Then MHD stable systems are analysed for stability of the trapped particle mode. This mode is characterized by the detachment of the central-cell plasma from the kinetic-stabilizer region without inducing field-line bending. Stability of the trapped particle mode is sensitive to the electron connection between the stabilizer and the end plug. It is found that the stability condition for the trapped particle mode is more constraining than the stability condition for the MHD mode, and it is challenging to satisfy the required power constraint. Furthermore, a severe power drain may arise from the necessary connection of low-energy electrons in the kinetic stabilizer to the central region.

Numerically solving the relativistic Grad-Shafranov equation in Kerr spacetimes: numerical techniques

NASA Astrophysics Data System (ADS)

Mahlmann, J. F.; Cerdá-Durán, P.; Aloy, M. A.

2018-07-01

The study of the electrodynamics of static, axisymmetric, and force-free Kerr magnetospheres relies vastly on solutions of the so-called relativistic Grad-Shafranov equation (GSE). Different numerical approaches to the solution of the GSE have been introduced in the literature, but none of them has been fully assessed from the numerical point of view in terms of efficiency and quality of the solutions found. We present a generalization of these algorithms and give a detailed background on the algorithmic implementation. We assess the numerical stability of the implemented algorithms and quantify the convergence of the presented methodology for the most established set-ups (split-monopole, paraboloidal, BH disc, uniform).

Numerically solving the relativistic Grad-Shafranov equation in Kerr spacetimes: Numerical techniques

NASA Astrophysics Data System (ADS)

Mahlmann, J. F.; Cerdá-Durán, P.; Aloy, M. A.

2018-04-01

The study of the electrodynamics of static, axisymmetric and force-free Kerr magnetospheres relies vastly on solutions of the so called relativistic Grad-Shafranov equation (GSE). Different numerical approaches to the solution of the GSE have been introduced in the literature, but none of them has been fully assessed from the numerical point of view in terms of efficiency and quality of the solutions found. We present a generalization of these algorithms and give detailed background on the algorithmic implementation. We assess the numerical stability of the implemented algorithms and quantify the convergence of the presented methodology for the most established setups (split-monopole, paraboloidal, BH-disk, uniform).

Exact and Approximate Stability of Solutions to Traveling Salesman Problems.

PubMed

Niendorf, Moritz; Girard, Anouck R

2018-02-01

This paper presents the stability analysis of an optimal tour for the symmetric traveling salesman problem (TSP) by obtaining stability regions. The stability region of an optimal tour is the set of all cost changes for which that solution remains optimal and can be understood as the margin of optimality for a solution with respect to perturbations in the problem data. It is known that it is not possible to test in polynomial time whether an optimal tour remains optimal after the cost of an arbitrary set of edges changes. Therefore, this paper develops tractable methods to obtain under and over approximations of stability regions based on neighborhoods and relaxations. The application of the results to the two-neighborhood and the minimum 1 tree (M1T) relaxation are discussed in detail. For Euclidean TSPs, stability regions with respect to vertex location perturbations and the notion of safe radii and location criticalities are introduced. Benefits of this paper include insight into robustness properties of tours, minimum spanning trees, M1Ts, and fast methods to evaluate optimality after perturbations occur. Numerical examples are given to demonstrate the methods and achievable approximation quality.

Numerical investigations of passive scalar transport in Taylor-Couette flows: Counter-rotation effect

NASA Astrophysics Data System (ADS)

Ouazib, Nabila; Salhi, Yacine; Si-Ahmed, El-Khider; Legrand, Jack; Degrez, G.

2017-07-01

Numerical methods for solving convection-diffusion-reaction (CDR) scalar transport equation in three-dimensional flow are used in the present investigation. The flow is confined between two concentric cylinders both the inner cylinder and the outer one are allowed to rotate. Direct numerical simulations (DNS) have been achieved to study the effects of the gravitational and the centrifugal potentials on the stability of incompressible Taylor-Couette flow. The Navier-Stokes equations and the uncoupled convection-diffusion-reaction equation are solved using a spectral development in one direction combined together with a finite element discretization in the two remaining directions. The complexity of the patterns is highlighted. Since, it increases as the rotation rates of the cylinders increase. In addition, the effect of the counter-rotation of the cylinders on the mass transfer is pointed out.

Formation and stability of a double subduction system: a numerical study

NASA Astrophysics Data System (ADS)

Pusok, A. E.; Stegman, D. R.

2017-12-01

Examples of double subduction systems can be found in both modern (Izu-Bonin-Marianas and Ryukyu arcs, e.g. Hall [1997]) and ancient (Kohistan arc in Western Himalayas, e.g. Burg et al. [2006]) tectonic record. A double subduction system has been proposed to explain the high convergence rate observed for the India-Eurasia convergence [Aitchison et al., 2000, Jagoutz et al., 2015; Holt et al., 2017]. Rates of convergence across coupled double subduction systems can be significantly faster than across single subduction systems because of slab pull by two slabs. However, despite significant geological and geophysical observations, questions regarding double subduction remain largely unexplored. For example, it is unclear how a double subduction system forms and remains stable over millions of years. Previous numerical studies of double subduction either introduced weak zones to initiate subduction [Mishin et al., 2008] or both the subduction systems were already initiated [Jagoutz et al., 2015, Holt et al., 2017], thus assuming a priori information regarding the initial position of the two subduction zones. Moreover, the driving forces initiating a stable double subduction system remain unclear. In the context of India-Eurasia, Cande and Stegman [2011] found evidence the Reunion mantle plume head provided an ephemeral driving force on both the Indian and African plates for as long as 25 Million years, and had significant influence on plate boundaries in the region. In this study, we perform 2D and 3D numerical simulations using the code LaMEM [Kaus et al., 2016] to investigate i) subduction initiation of a secondary system in an already initiated single subduction system, and ii) the dynamics and stability of the newly formed double subduction system. We start from a single subduction setup, where subduction is already initiated (mature) and we stress the system by controlling the convergence rate of the system (i.e. imposing influx/outflux boundary conditions). Under

A novel single thruster control strategy for spacecraft attitude stabilization

NASA Astrophysics Data System (ADS)

Godard; Kumar, Krishna Dev; Zou, An-Min

2013-05-01

Feasibility of achieving three axis attitude stabilization using a single thruster is explored in this paper. Torques are generated using a thruster orientation mechanism with which the thrust vector can be tilted on a two axis gimbal. A robust nonlinear control scheme is developed based on the nonlinear kinematic and dynamic equations of motion of a rigid body spacecraft in the presence of gravity gradient torque and external disturbances. The spacecraft, controlled using the proposed concept, constitutes an underactuated system (a system with fewer independent control inputs than degrees of freedom) with nonlinear dynamics. Moreover, using thruster gimbal angles as control inputs make the system non-affine (control terms appear nonlinearly in the state equation). This necessitates the control algorithms to be developed based on nonlinear control theory since linear control methods are not directly applicable. The stability conditions for the spacecraft attitude motion for robustness against uncertainties and disturbances are derived to establish the regions of asymptotic 3-axis attitude stabilization. Several numerical simulations are presented to demonstrate the efficacy of the proposed controller and validate the theoretical results. The control algorithm is shown to compensate for time-varying external disturbances including solar radiation pressure, aerodynamic forces, and magnetic disturbances; and uncertainties in the spacecraft inertia parameters. The numerical results also establish the robustness of the proposed control scheme to negate disturbances caused by orbit eccentricity.

Stability Limits and Dynamics of Nonaxisymmetric Liquid Bridges

NASA Technical Reports Server (NTRS)

Alexander, J. Iwan D.

1996-01-01

Theoretical and experimental investigation of the stability of nonaxisymmetric and axisymmetric bridges contained between equal and unequal radii disks as a function of Bond and Weber number with emphasis on the transition from unstable axisymmetric to stable nonaxisymmetric shapes. Numerical analysis of the stability of nonaxisymmetric bridges between unequal disks for various orientations of the gravity vector Experimental and numerical investigation of bridge stability (nonaxisymmetric and axisymmetric), large amplitude (nonaxisymmetric) oscillations and breaking.

Entropy Splitting and Numerical Dissipation

NASA Technical Reports Server (NTRS)

Yee, H. C.; Vinokur, M.; Djomehri, M. J.

1999-01-01

A rigorous stability estimate for arbitrary order of accuracy of spatial central difference schemes for initial-boundary value problems of nonlinear symmetrizable systems of hyperbolic conservation laws was established recently by Olsson and Oliger (1994) and Olsson (1995) and was applied to the two-dimensional compressible Euler equations for a perfect gas by Gerritsen and Olsson (1996) and Gerritsen (1996). The basic building block in developing the stability estimate is a generalized energy approach based on a special splitting of the flux derivative via a convex entropy function and certain homogeneous properties. Due to some of the unique properties of the compressible Euler equations for a perfect gas, the splitting resulted in the sum of a conservative portion and a non-conservative portion of the flux derivative. hereafter referred to as the "Entropy Splitting." There are several potential desirable attributes and side benefits of the entropy splitting for the compressible Euler equations that were not fully explored in Gerritsen and Olsson. The paper has several objectives. The first is to investigate the choice of the arbitrary parameter that determines the amount of splitting and its dependence on the type of physics of current interest to computational fluid dynamics. The second is to investigate in what manner the splitting affects the nonlinear stability of the central schemes for long time integrations of unsteady flows such as in nonlinear aeroacoustics and turbulence dynamics. If numerical dissipation indeed is needed to stabilize the central scheme, can the splitting help minimize the numerical dissipation compared to its un-split cousin? Extensive numerical study on the vortex preservation capability of the splitting in conjunction with central schemes for long time integrations will be presented. The third is to study the effect of the non-conservative proportion of splitting in obtaining the correct shock location for high speed complex shock

Limits to Stability

ERIC Educational Resources Information Center

Cottey, Alan

2012-01-01

The author reflects briefly on what limited degree of global ecological stability and human cultural stability may be achieved, provided that humanity retains hope and does not give way to despair or hide in denial. These thoughts were triggered by a recent conference on International Stability and Systems Engineering. (Contains 5 notes.)

Discrete-time systems with random switches: From systems stability to networks synchronization.

PubMed

Guo, Yao; Lin, Wei; Ho, Daniel W C

2016-03-01

In this article, we develop some approaches, which enable us to more accurately and analytically identify the essential patterns that guarantee the almost sure stability of discrete-time systems with random switches. We allow for the case that the elements in the switching connection matrix even obey some unbounded and continuous-valued distributions. In addition to the almost sure stability, we further investigate the almost sure synchronization in complex dynamical networks consisting of randomly connected nodes. Numerical examples illustrate that a chaotic dynamics in the synchronization manifold is preserved when statistical parameters enter some almost sure synchronization region established by the developed approach. Moreover, some delicate configurations are considered on probability space for ensuring synchronization in networks whose nodes are described by nonlinear maps. Both theoretical and numerical results on synchronization are presented by setting only a few random connections in each switch duration. More interestingly, we analytically find it possible to achieve almost sure synchronization in the randomly switching complex networks even with very large population sizes, which cannot be easily realized in non-switching but deterministically connected networks.

Comparing Interval Management Control Laws for Steady-State Errors and String Stability

NASA Technical Reports Server (NTRS)

Weitz, Lesley A.; Swieringa, Kurt A.

2018-01-01

Interval Management (IM) is a future airborne spacing concept that leverages avionics to provide speed guidance to an aircraft to achieve and maintain a specified spacing interval from another aircraft. The design of a speed control law to achieve the spacing goal is a key aspect in the research and development of the IM concept. In this paper, two control laws that are used in much of the contemporary IM research are analyzed and compared to characterize steady-state errors and string stability. Numerical results are used to illustrate how the choice of control laws gains impacts the size of steady-state errors and string performance and the potential trade-offs between those performance characteristics.

Scale-Limited Lagrange Stability and Finite-Time Synchronization for Memristive Recurrent Neural Networks on Time Scales.

PubMed

Xiao, Qiang; Zeng, Zhigang

2017-10-01

The existed results of Lagrange stability and finite-time synchronization for memristive recurrent neural networks (MRNNs) are scale-free on time evolvement, and some restrictions appear naturally. In this paper, two novel scale-limited comparison principles are established by means of inequality techniques and induction principle on time scales. Then the results concerning Lagrange stability and global finite-time synchronization of MRNNs on time scales are obtained. Scaled-limited Lagrange stability criteria are derived, in detail, via nonsmooth analysis and theory of time scales. Moreover, novel criteria for achieving the global finite-time synchronization are acquired. In addition, the derived method can also be used to study global finite-time stabilization. The proposed results extend or improve the existed ones in the literatures. Two numerical examples are chosen to show the effectiveness of the obtained results.

Validation of three-dimensional incompressible spatial direct numerical simulation code: A comparison with linear stability and parabolic stability equation theories for boundary-layer transition on a flat plate

NASA Technical Reports Server (NTRS)

Joslin, Ronald D.; Streett, Craig L.; Chang, Chau-Lyan

1992-01-01

Spatially evolving instabilities in a boundary layer on a flat plate are computed by direct numerical simulation (DNS) of the incompressible Navier-Stokes equations. In a truncated physical domain, a nonstaggered mesh is used for the grid. A Chebyshev-collocation method is used normal to the wall; finite difference and compact difference methods are used in the streamwise direction; and a Fourier series is used in the spanwise direction. For time stepping, implicit Crank-Nicolson and explicit Runge-Kutta schemes are used to the time-splitting method. The influence-matrix technique is used to solve the pressure equation. At the outflow boundary, the buffer-domain technique is used to prevent convective wave reflection or upstream propagation of information from the boundary. Results of the DNS are compared with those from both linear stability theory (LST) and parabolized stability equation (PSE) theory. Computed disturbance amplitudes and phases are in very good agreement with those of LST (for small inflow disturbance amplitudes). A measure of the sensitivity of the inflow condition is demonstrated with both LST and PSE theory used to approximate inflows. Although the DNS numerics are very different than those of PSE theory, the results are in good agreement. A small discrepancy in the results that does occur is likely a result of the variation in PSE boundary condition treatment in the far field. Finally, a small-amplitude wave triad is forced at the inflow, and simulation results are compared with those of LST. Again, very good agreement is found between DNS and LST results for the 3-D simulations, the implication being that the disturbance amplitudes are sufficiently small that nonlinear interactions are negligible.

Analysis of stability for stochastic delay integro-differential equations.

PubMed

Zhang, Yu; Li, Longsuo

2018-01-01

In this paper, we concern stability of numerical methods applied to stochastic delay integro-differential equations. For linear stochastic delay integro-differential equations, it is shown that the mean-square stability is derived by the split-step backward Euler method without any restriction on step-size, while the Euler-Maruyama method could reproduce the mean-square stability under a step-size constraint. We also confirm the mean-square stability of the split-step backward Euler method for nonlinear stochastic delay integro-differential equations. The numerical experiments further verify the theoretical results.

Nonlinear dynamics and numerical uncertainties in CFD

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sweby, P. K.

1996-01-01

The application of nonlinear dynamics to improve the understanding of numerical uncertainties in computational fluid dynamics (CFD) is reviewed. Elementary examples in the use of dynamics to explain the nonlinear phenomena and spurious behavior that occur in numerics are given. The role of dynamics in the understanding of long time behavior of numerical integrations and the nonlinear stability, convergence, and reliability of using time-marching, approaches for obtaining steady-state numerical solutions in CFD is explained. The study is complemented with spurious behavior observed in CFD computations.

A numerical comparison of discrete Kalman filtering algorithms: An orbit determination case study

NASA Technical Reports Server (NTRS)

Thornton, C. L.; Bierman, G. J.

1976-01-01

The numerical stability and accuracy of various Kalman filter algorithms are thoroughly studied. Numerical results and conclusions are based on a realistic planetary approach orbit determination study. The case study results of this report highlight the numerical instability of the conventional and stabilized Kalman algorithms. Numerical errors associated with these algorithms can be so large as to obscure important mismodeling effects and thus give misleading estimates of filter accuracy. The positive result of this study is that the Bierman-Thornton U-D covariance factorization algorithm is computationally efficient, with CPU costs that differ negligibly from the conventional Kalman costs. In addition, accuracy of the U-D filter using single-precision arithmetic consistently matches the double-precision reference results. Numerical stability of the U-D filter is further demonstrated by its insensitivity of variations in the a priori statistics.

Stabilizing canonical-ensemble calculations in the auxiliary-field Monte Carlo method

NASA Astrophysics Data System (ADS)

Gilbreth, C. N.; Alhassid, Y.

2015-03-01

Quantum Monte Carlo methods are powerful techniques for studying strongly interacting Fermi systems. However, implementing these methods on computers with finite-precision arithmetic requires careful attention to numerical stability. In the auxiliary-field Monte Carlo (AFMC) method, low-temperature or large-model-space calculations require numerically stabilized matrix multiplication. When adapting methods used in the grand-canonical ensemble to the canonical ensemble of fixed particle number, the numerical stabilization increases the number of required floating-point operations for computing observables by a factor of the size of the single-particle model space, and thus can greatly limit the systems that can be studied. We describe an improved method for stabilizing canonical-ensemble calculations in AFMC that exhibits better scaling, and present numerical tests that demonstrate the accuracy and improved performance of the method.

A Numerical Study of Wind-Turbine Wakes for Three Atmospheric Stability Conditions

NASA Astrophysics Data System (ADS)

Xie, Shengbai; Archer, Cristina L.

2017-10-01

The effects of atmospheric stability on wind-turbine wakes are studied via large-eddy simulations. Three stability conditions are considered: stable, neutral, and unstable, with the same geostrophic wind speed aloft and the same Coriolis frequency. Both a single 5-MW turbine and a wind farm of five turbines are studied. The single-turbine wake is strongly correlated with stability, in terms of velocity deficit, turbulence kinetic energy (TKE) and temperature distribution. Because of the Coriolis effect, the wake shape deviates from a Gaussian distribution. For the wind-farm simulations, the separation of the core region and outer region is clear for the stable and neutral cases, but less distinct for the unstable case. The unstable case exhibits strong horizontal variations in wind speed. Local accelerations such as related to aisle jets are also observed, whose features depend on stability. The added TKE in the wind farm increases with stability. The highest power extraction and lowest power deficit are observed for the unstable case.

Constrained evolution in numerical relativity

NASA Astrophysics Data System (ADS)

Anderson, Matthew William

The strongest potential source of gravitational radiation for current and future detectors is the merger of binary black holes. Full numerical simulation of such mergers can provide realistic signal predictions and enhance the probability of detection. Numerical simulation of the Einstein equations, however, is fraught with difficulty. Stability even in static test cases of single black holes has proven elusive. Common to unstable simulations is the growth of constraint violations. This work examines the effect of controlling the growth of constraint violations by solving the constraints periodically during a simulation, an approach called constrained evolution. The effects of constrained evolution are contrasted with the results of unconstrained evolution, evolution where the constraints are not solved during the course of a simulation. Two different formulations of the Einstein equations are examined: the standard ADM formulation and the generalized Frittelli-Reula formulation. In most cases constrained evolution vastly improves the stability of a simulation at minimal computational cost when compared with unconstrained evolution. However, in the more demanding test cases examined, constrained evolution fails to produce simulations with long-term stability in spite of producing improvements in simulation lifetime when compared with unconstrained evolution. Constrained evolution is also examined in conjunction with a wide variety of promising numerical techniques, including mesh refinement and overlapping Cartesian and spherical computational grids. Constrained evolution in boosted black hole spacetimes is investigated using overlapping grids. Constrained evolution proves to be central to the host of innovations required in carrying out such intensive simulations.

Dispersion stability of a ceramic glaze achieved through ionic surfactant adsorption.

PubMed

Panya, Preecha; Arquero, Orn-anong; Franks, George V; Wanless, Erica J

2004-11-01

The adsorption of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) onto a ceramic glaze mixture composed of limestone, feldspar, quartz, and kaolin has been investigated. Both adsorption isotherms and the average particle zeta potential have been studied in order to understand the suspension stability as a function of pH, ionic strength, and surfactant concentration. The adsorption of small amounts of cationic CPC onto the primarily negatively charged surfaces of the particles at pH 7 and 9 results in strong attraction and flocculation due to hydrophobic interactions. At higher surfactant concentrations a zeta potential of more than +60 mV results from the bilayered adsorbed surfactant, providing stability at salt concentrations < or = 0.01 M. At 0.1 M salt poor stability results despite substantial zeta potential values. Three mechanisms for SDBS adsorption have been identified. When anionic SDBS monomers either adsorb by electrostatic interactions with the few positive surface sites at high pH or adsorb onto like charged negative surface sites due to dispersion or hydrophobic interactions, the magnitude of the negative zeta potential increases slightly. At pH 9 this increase is enough to promote stability with an average zeta potential of more than -55 mV, whereas at pH 7 the zeta potential is lower at about -45 mV. The stability of suspensions at pH 7 is additionally due to steric repulsion caused by the adsorption of thick layers of neutrally charged Ca(DBS)2 complexes created when the surfactant interacts with dissolved calcium ions from the calcium carbonate component.

Hydrodynamic stability

NASA Astrophysics Data System (ADS)

Drazin, P. G.; Reid, W. H.

The book is written from the point of view intrinsic to fluid mechanics and applied mathematics. The analytical aspects of the theory are emphasized. However, it has also been tried, wherever possible, to relate the theory to experimental and numerical results. Mechanisms of instability are considered along with fundamental concepts of hydrodynamic stability, the Kelvin-Helmholtz instability, and the break-up of a liquid jet in air. Aspects of thermal instability are investigated, taking into account the equations of motion, the stability problem, general stability characteristics, particular stability characteristics, the cells, and experimental results. The inviscid theory and the viscous theory are examined in connection with a study of parallel shear flows. Centrifugal instability is discussed along with uniform asymptotic approximations, and problems of nonlinear stability. Attention is also given to baroclinic instability, the instability of the pinch, the development of linear instability in time and space, and the instability of unsteady flows.

Boattail juncture shaping for spin-stabilized rounds in supersonic flight

NASA Astrophysics Data System (ADS)

Jiajan, W.; Chue, R. S. M.; Nguyen, T.; Yu, S. C. M.

2015-03-01

In this paper, the effects of boattail junction shaping on aerodynamic drag and stability of supersonic spin-stabilized rounds are investigated using computational fluid dynamics. For a generic round body comprising of a secant-ogive nose, a cylindrical body and a conical boattail, the shaping technique was achieved by adding a convex surface of varying degrees of radius of curvature to the junction between the cylindrical body and the boattail. It was shown through numerical simulations that this shaping technique can provide a reduction in aerodynamic drag of up to 5.4 % without destabilizing the round bodies when the radius of curvature is less than 8.8 times the diameter of the cylindrical body. The more gradual change of the flow characteristics, e.g., the pressure over the convex surface, was identified as the main reason for the drag reduction. A unique aspect of the current work is that stability is treated as an integral part of the performance assessment. It was also found that the dynamic instability encountered at large radii of curvature is due to the Magnus effects.

Dynamical behavior and Jacobi stability analysis of wound strings

NASA Astrophysics Data System (ADS)

Lake, Matthew J.; Harko, Tiberiu

2016-06-01

We numerically solve the equations of motion (EOM) for two models of circular cosmic string loops with windings in a simply connected internal space. Since the windings cannot be topologically stabilized, stability must be achieved (if at all) dynamically. As toy models for realistic compactifications, we consider windings on a small section of mathbb {R}^2, which is valid as an approximation to any simply connected internal manifold if the winding radius is sufficiently small, and windings on an S^2 of constant radius mathcal {R}. We then use Kosambi-Cartan-Chern (KCC) theory to analyze the Jacobi stability of the string equations and determine bounds on the physical parameters that ensure dynamical stability of the windings. We find that, for the same initial conditions, the curvature and topology of the internal space have nontrivial effects on the microscopic behavior of the string in the higher dimensions, but that the macroscopic behavior is remarkably insensitive to the details of the motion in the compact space. This suggests that higher-dimensional signatures may be extremely difficult to detect in the effective (3+1)-dimensional dynamics of strings compactified on an internal space, even if configurations with nontrivial windings persist over long time periods.

Preliminary numerical simulation for shallow strata stability of coral reef in South China Sea

NASA Astrophysics Data System (ADS)

Tang, Qinqin; Zhan, Wenhuan; Zhang, Jinchang

2017-04-01

Coral reefs are the geologic material and special rock and soil, which live in shallow water of the tropic ocean and are formed through biological and geological action. Since infrastructure construction is being increasingly developed on coral reefs during recent years, it is necessary to evaluate the shallow strata stability of coral reefs in the South China Sea. The paper is to study the borehole profiles for shallow strata of coral reefs in the South China Sea, especially in the hydrodynamic marine environment?, and to establish a geological model for numerical simulation with Geo-Studio software. Five drilling holes show a six-layer shallow structure of South China Sea, including filling layer, mid-coarse sand, coral sand gravel, fine sand, limestone debris and reef limestone. The shallow coral reef profile next to lagoon is similar to "layers cake", in which the right side close to the sea is analogous to "block cake". The simulation results show that coral reef stability depends on wave loads and earthquake strength, as well as the physical properties of coral reefs themselves. The safety factor of the outer reef is greater than 10.0 in the static condition, indicating that outer reefs are less affected by the wave and earthquake. However, the safety factor next to lagoon is ranging from 0.1 to 4.9. The main reason for the variations that the strata of coral reefs close to the sea are thick. For example, the thickness of reef limestone is more than 10 m and equivalent to the block. When the thickness of inside strata is less than 10 m, they show weak engineering geological characteristics. These findings can provide useful information for coral reef constructions in future. This work was funded by National Basic Research Program of China (contract: 2013CB956104) and National Natural Science Foundation of China (contract: 41376063).

Efficient stabilization and acceleration of numerical simulation of fluid flows by residual recombination

NASA Astrophysics Data System (ADS)

Citro, V.; Luchini, P.; Giannetti, F.; Auteri, F.

2017-09-01

The study of the stability of a dynamical system described by a set of partial differential equations (PDEs) requires the computation of unstable states as the control parameter exceeds its critical threshold. Unfortunately, the discretization of the governing equations, especially for fluid dynamic applications, often leads to very large discrete systems. As a consequence, matrix based methods, like for example the Newton-Raphson algorithm coupled with a direct inversion of the Jacobian matrix, lead to computational costs too large in terms of both memory and execution time. We present a novel iterative algorithm, inspired by Krylov-subspace methods, which is able to compute unstable steady states and/or accelerate the convergence to stable configurations. Our new algorithm is based on the minimization of the residual norm at each iteration step with a projection basis updated at each iteration rather than at periodic restarts like in the classical GMRES method. The algorithm is able to stabilize any dynamical system without increasing the computational time of the original numerical procedure used to solve the governing equations. Moreover, it can be easily inserted into a pre-existing relaxation (integration) procedure with a call to a single black-box subroutine. The procedure is discussed for problems of different sizes, ranging from a small two-dimensional system to a large three-dimensional problem involving the Navier-Stokes equations. We show that the proposed algorithm is able to improve the convergence of existing iterative schemes. In particular, the procedure is applied to the subcritical flow inside a lid-driven cavity. We also discuss the application of Boostconv to compute the unstable steady flow past a fixed circular cylinder (2D) and boundary-layer flow over a hemispherical roughness element (3D) for supercritical values of the Reynolds number. We show that Boostconv can be used effectively with any spatial discretization, be it a finite

A Combined Remote Sensing-Numerical Modelling Approach to the Stability Analysis of Delabole Slate Quarry, Cornwall, UK

NASA Astrophysics Data System (ADS)

Havaej, Mohsen; Coggan, John; Stead, Doug; Elmo, Davide

2016-04-01

Rock slope geometry and discontinuity properties are among the most important factors in realistic rock slope analysis yet they are often oversimplified in numerical simulations. This is primarily due to the difficulties in obtaining accurate structural and geometrical data as well as the stochastic representation of discontinuities. Recent improvements in both digital data acquisition and incorporation of discrete fracture network data into numerical modelling software have provided better tools to capture rock mass characteristics, slope geometries and digital terrain models allowing more effective modelling of rock slopes. Advantages of using improved data acquisition technology include safer and faster data collection, greater areal coverage, and accurate data geo-referencing far exceed limitations due to orientation bias and occlusion. A key benefit of a detailed point cloud dataset is the ability to measure and evaluate discontinuity characteristics such as orientation, spacing/intensity and persistence. This data can be used to develop a discrete fracture network which can be imported into the numerical simulations to study the influence of the stochastic nature of the discontinuities on the failure mechanism. We demonstrate the application of digital terrestrial photogrammetry in discontinuity characterization and distinct element simulations within a slate quarry. An accurately geo-referenced photogrammetry model is used to derive the slope geometry and to characterize geological structures. We first show how a discontinuity dataset, obtained from a photogrammetry model can be used to characterize discontinuities and to develop discrete fracture networks. A deterministic three-dimensional distinct element model is then used to investigate the effect of some key input parameters (friction angle, spacing and persistence) on the stability of the quarry slope model. Finally, adopting a stochastic approach, discrete fracture networks are used as input for 3D

Numerical computation of homogeneous slope stability.

PubMed

Xiao, Shuangshuang; Li, Kemin; Ding, Xiaohua; Liu, Tong

2015-01-01

To simplify the computational process of homogeneous slope stability, improve computational accuracy, and find multiple potential slip surfaces of a complex geometric slope, this study utilized the limit equilibrium method to derive expression equations of overall and partial factors of safety. This study transformed the solution of the minimum factor of safety (FOS) to solving of a constrained nonlinear programming problem and applied an exhaustive method (EM) and particle swarm optimization algorithm (PSO) to this problem. In simple slope examples, the computational results using an EM and PSO were close to those obtained using other methods. Compared to the EM, the PSO had a small computation error and a significantly shorter computation time. As a result, the PSO could precisely calculate the slope FOS with high efficiency. The example of the multistage slope analysis indicated that this slope had two potential slip surfaces. The factors of safety were 1.1182 and 1.1560, respectively. The differences between these and the minimum FOS (1.0759) were small, but the positions of the slip surfaces were completely different than the critical slip surface (CSS).

Individual differences in non-symbolic numerical abilities predict mathematical achievements but contradict ATOM.

PubMed

Agrillo, Christian; Piffer, Laura; Adriano, Andrea

2013-07-01

A significant debate surrounds the nature of the cognitive mechanisms involved in non-symbolic number estimation. Several studies have suggested the existence of the same cognitive system for estimation of time, space, and number, called "a theory of magnitude" (ATOM). In addition, researchers have proposed the theory that non-symbolic number abilities might support our mathematical skills. Despite the large number of studies carried out, no firm conclusions can be drawn on either topic. In the present study, we correlated the performance of adults on non-symbolic magnitude estimations and symbolic numerical tasks. Non-symbolic magnitude abilities were assessed by asking participants to estimate which auditory tone lasted longer (time), which line was longer (space), and which group of dots was more numerous (number). To assess symbolic numerical abilities, participants were required to perform mental calculations and mathematical reasoning. We found a positive correlation between non-symbolic and symbolic numerical abilities. On the other hand, no correlation was found among non-symbolic estimations of time, space, and number. Our study supports the idea that mathematical abilities rely on rudimentary numerical skills that predate verbal language. By contrast, the lack of correlation among non-symbolic estimations of time, space, and number is incompatible with the idea that these magnitudes are entirely processed by the same cognitive system.

Lattice Boltzmann model for numerical relativity.

PubMed

Ilseven, E; Mendoza, M

2016-02-01

In the Z4 formulation, Einstein equations are written as a set of flux conservative first-order hyperbolic equations that resemble fluid dynamics equations. Based on this formulation, we construct a lattice Boltzmann model for numerical relativity and validate it with well-established tests, also known as "apples with apples." Furthermore, we find that by increasing the relaxation time, we gain stability at the cost of losing accuracy, and by decreasing the lattice spacings while keeping a constant numerical diffusivity, the accuracy and stability of our simulations improve. Finally, in order to show the potential of our approach, a linear scaling law for parallelization with respect to number of CPU cores is demonstrated. Our model represents the first step in using lattice kinetic theory to solve gravitational problems.

An extended continuum model considering optimal velocity change with memory and numerical tests

NASA Astrophysics Data System (ADS)

Qingtao, Zhai; Hongxia, Ge; Rongjun, Cheng

2018-01-01

In this paper, an extended continuum model of traffic flow is proposed with the consideration of optimal velocity changes with memory. The new model's stability condition and KdV-Burgers equation considering the optimal velocities change with memory are deduced through linear stability theory and nonlinear analysis, respectively. Numerical simulation is carried out to study the extended continuum model, which explores how optimal velocity changes with memory affected velocity, density and energy consumption. Numerical results show that when considering the effects of optimal velocity changes with memory, the traffic jams can be suppressed efficiently. Both the memory step and sensitivity parameters of optimal velocity changes with memory will enhance the stability of traffic flow efficiently. Furthermore, numerical results demonstrates that the effect of optimal velocity changes with memory can avoid the disadvantage of historical information, which increases the stability of traffic flow on road, and so it improve the traffic flow stability and minimize cars' energy consumptions.

Discrete-time systems with random switches: From systems stability to networks synchronization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Yao; Lin, Wei, E-mail: wlin@fudan.edu.cn; Shanghai Key Laboratory of Contemporary Applied Mathematics, LMNS, and Shanghai Center for Mathematical Sciences, Shanghai 200433

2016-03-15

In this article, we develop some approaches, which enable us to more accurately and analytically identify the essential patterns that guarantee the almost sure stability of discrete-time systems with random switches. We allow for the case that the elements in the switching connection matrix even obey some unbounded and continuous-valued distributions. In addition to the almost sure stability, we further investigate the almost sure synchronization in complex dynamical networks consisting of randomly connected nodes. Numerical examples illustrate that a chaotic dynamics in the synchronization manifold is preserved when statistical parameters enter some almost sure synchronization region established by the developedmore » approach. Moreover, some delicate configurations are considered on probability space for ensuring synchronization in networks whose nodes are described by nonlinear maps. Both theoretical and numerical results on synchronization are presented by setting only a few random connections in each switch duration. More interestingly, we analytically find it possible to achieve almost sure synchronization in the randomly switching complex networks even with very large population sizes, which cannot be easily realized in non-switching but deterministically connected networks.« less

Impact of aerobic stabilization on the characteristics of treatment sludge in the leather tanning industry.

PubMed

Cokgor, Emine Ubay; Aydinli, Ebru; Tas, Didem Okutman; Zengin, Gulsum Emel; Orhon, Derin

2014-01-01

The efficiency of aerobic stabilization on the treatment sludge generated from the leather industry was investigated to meet the expected characteristics and conditions of sludge prior to landfill. The sludge types subjected to aerobic stabilization were chemical treatment sludge, biological excess sludge, and the mixture of both chemical and biological sludges. At the end of 23 days of stabilization, suspended solids, volatile suspended solids and total organic carbon removal efficiencies were determined as 17%, 19% and 23% for biological sludge 31%, 35% and 54% for chemical sludge, and 32%, 34% and 63% for the mixture of both chemical and biological sludges, respectively. Model simulations of the respirometric oxygen uptake rate measurements showed that the ratio of active biomass remained the same at the end of the stabilization for all the sludge samples. Although mixing the chemical and biological sludges resulted in a relatively effective organic carbon and solids removal, the level of stabilization achieved remained clearly below the required level of organic carbon content for landfill. These findings indicate the potential risk of setting numerical restrictions without referring to proper scientific support.

Lens-mount stability trade-off: a survey exemplified for DUV wafer inspection objectives

NASA Astrophysics Data System (ADS)

Bouazzam, Achmed; Erbe, Torsten; Fahr, Stephan; Werschnik, Jan

2015-09-01

The position stability of optical elements is an essential part of the tolerance budget of an optical system because its compensation would require an alignment step after the lens has left the factory. In order to achieve a given built performance the stability error contribution needs to be known and accounted for. Given a high-end lens touching the edge of technology not knowing, under- or overestimating this contribution becomes a serious cost and risk factor. If overestimated the remaining parts of the budget need to be tighter. If underestimated the total project might fail. For many mounting principles the stability benchmark is based on previous systems or information gathered by elaborated testing of complete optical systems. This renders the development of a new system into a risky endeavour, because these experiences are not sufficiently precise and tend to be not transferable when scaling of the optical elements is intended. This contribution discusses the influences of different optical mounting concepts on the position stability using the example of high numerical aperture (HNA) inspection lenses working in the deep ultraviolet (DUV) spectrum. A method to investigate the positional stability is presented for selected mounting examples typical for inspection lenses.

Numerical Computation of Homogeneous Slope Stability

PubMed Central

Xiao, Shuangshuang; Li, Kemin; Ding, Xiaohua; Liu, Tong

2015-01-01

To simplify the computational process of homogeneous slope stability, improve computational accuracy, and find multiple potential slip surfaces of a complex geometric slope, this study utilized the limit equilibrium method to derive expression equations of overall and partial factors of safety. This study transformed the solution of the minimum factor of safety (FOS) to solving of a constrained nonlinear programming problem and applied an exhaustive method (EM) and particle swarm optimization algorithm (PSO) to this problem. In simple slope examples, the computational results using an EM and PSO were close to those obtained using other methods. Compared to the EM, the PSO had a small computation error and a significantly shorter computation time. As a result, the PSO could precisely calculate the slope FOS with high efficiency. The example of the multistage slope analysis indicated that this slope had two potential slip surfaces. The factors of safety were 1.1182 and 1.1560, respectively. The differences between these and the minimum FOS (1.0759) were small, but the positions of the slip surfaces were completely different than the critical slip surface (CSS). PMID:25784927

Olive-oil nanocapsules stabilized by HSA: influence of processing variables on particle properties

NASA Astrophysics Data System (ADS)

Molina-Bolívar, J. A.; Galisteo-González, F.

2015-10-01

Liquid lipid nanocapsules (LLN) are considered to be promising drug carriers in the medical field. The size and the surface charge of these nanocarriers are of major importance, affecting their bioavailability and the in vivo behaviour after intravenous injection. This research provides a comprehensive study on the preparation of olive-oil nanocapsules stabilized with a human serum albumin shell (HSA). LLN were prepared by modified solvent-displacement method. Numerous experimental variables were examined in order to characterize their impact on LLN size, distribution, and electrophoretic mobility. Physicochemical parameters of LLN were controlled by adjusting the nanodroplet stabilizing shell of adsorbed protein molecules, which was affected by the oil:HSA ratio, pH, and ionic strength of aqueous medium. The stronger the repulsion between adsorbed HSA molecules, the smaller and more monodisperse the particles proved. Other process parameters, including the ethanol:acetone ratio, organic:aqueous phase ratio, speed of organic-phase injection, and stirring rate were examined to achieve optimum preparation conditions. LLN produced by our standardized formulation were in the range of 170-175 nm with low polydispersity index (<0.1). Long-term colloidal stability of samples was evaluated after 6 months of storage. Efficient incorporation of curcumin, a model for a water-insoluble drug, into olive-oil nanocapsules was achieved (90 %). Encapsulation of curcumin into LLN had a stabilizing effect with respect to drug photodecomposition compared to that of the free molecule in solution.

Numerical slope stability simulations of chasma walls in Valles Marineris/Mars using a distinct element method (dem).

NASA Astrophysics Data System (ADS)

Imre, B.

2003-04-01

NUMERICAL SLOPE STABILITY SIMULATIONS OF CHASMA WALLS IN VALLES MARINERIS/MARS USING A DISTINCT ELEMENT METHOD (DEM). B. Imre (1) (1) German Aerospace Center, Berlin Adlershof, bernd.imre@gmx.net The 8- to 10-km depths of Valles Marineris (VM) offer excellent views into the upper Martian crust. Layering, fracturing, lithology, stratigraphy and the content of volatiles have influenced the evolution of the Valles Marineris wallslopes. But these parameters also reflect the development of VM and its wall slopes. The scope of this work is to gain understanding in these parameters by back-simulating the development of wall slopes. For that purpose, the two dimensional Particle Flow Code PFC2D has been chosen (ITASCA, version 2.00-103). PFC2D is a distinct element code for numerical modelling of movements and interactions of assemblies of arbitrarily sized circular particles. Particles may be bonded together to represent a solid material. Movements of particles are unlimited. That is of importance because results of open systems with numerous unknown variables are non-unique and therefore highly path dependent. This DEM allows the simulation of whole development paths of VM walls what makes confirmation of the model more complete (e.g. Oreskes et al., Science 263, 1994). To reduce the number of unknown variables a proper (that means as simple as possible) field-site had to be selected. The northern wall of eastern Candor Chasma has been chosen. This wall is up to 8-km high and represents a significant outcrop of the upper Martian crust. It is quite uncomplex, well-aligned and of simple morphology. Currently the work on the model is at the stage of performing the parameter study. Results will be presented via poster by the EGS-Meeting.

Stability analysis of multigrid acceleration methods for the solution of partial differential equations

NASA Technical Reports Server (NTRS)

Fay, John F.

1990-01-01

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.

Stabilization of dynamics of oscillatory systems by nonautonomous perturbation.

PubMed

Lucas, Maxime; Newman, Julian; Stefanovska, Aneta

2018-04-01

Synchronization and stability under periodic oscillatory driving are well understood, but little is known about the effects of aperiodic driving, despite its abundance in nature. Here, we consider oscillators subject to driving with slowly varying frequency, and investigate both short-term and long-term stability properties. For a phase oscillator, we find that, counterintuitively, such variation is guaranteed to enlarge the Arnold tongue in parameter space. Using analytical and numerical methods that provide information on time-variable dynamical properties, we find that the growth of the Arnold tongue is specifically due to the growth of a region of intermittent synchronization where trajectories alternate between short-term stability and short-term neutral stability, giving rise to stability on average. We also present examples of higher-dimensional nonlinear oscillators where a similar stabilization phenomenon is numerically observed. Our findings help support the case that in general, deterministic nonautonomous perturbation is a very good candidate for stabilizing complex dynamics.

Stabilization of dynamics of oscillatory systems by nonautonomous perturbation

NASA Astrophysics Data System (ADS)

Lucas, Maxime; Newman, Julian; Stefanovska, Aneta

2018-04-01

Synchronization and stability under periodic oscillatory driving are well understood, but little is known about the effects of aperiodic driving, despite its abundance in nature. Here, we consider oscillators subject to driving with slowly varying frequency, and investigate both short-term and long-term stability properties. For a phase oscillator, we find that, counterintuitively, such variation is guaranteed to enlarge the Arnold tongue in parameter space. Using analytical and numerical methods that provide information on time-variable dynamical properties, we find that the growth of the Arnold tongue is specifically due to the growth of a region of intermittent synchronization where trajectories alternate between short-term stability and short-term neutral stability, giving rise to stability on average. We also present examples of higher-dimensional nonlinear oscillators where a similar stabilization phenomenon is numerically observed. Our findings help support the case that in general, deterministic nonautonomous perturbation is a very good candidate for stabilizing complex dynamics.

Guidelines for LTS magnet design based on transient stability

NASA Astrophysics Data System (ADS)

Seo, Kazutaka; Morita, Masao

2006-05-01

Stabilities of low critical temperature superconducting (LTS) magnets and their designs are studied and discussed. There are two contradictory necessities; those are low cost and high performance, in the other words, high magnetic field and large current density. Especially, the maximum magnetic fields of the latest high performance Nb 3Sn magnets are around 20 T. Mentioned necessities result in the small stability margins. Needless to say, the superconducting magnet must produce its nominal field reliably. Therefore, maintaining adequate stability margin, the magnet design to draw out the high potential of the superconductor is required. The transient stability of the superconducting magnet is determined by the relationship between mechanical disturbance energy and stability margin. The minimum quench energy (MQE) is one of the index of stability margin and it is defined as the minimum energy to trigger quenching of a superconductor. MQE should be beyond any possible disturbance energy during the operation. It is difficult to identify the mechanical disturbance energy quantitatively. On the contrary, MQE had been evaluated precisely by means of our developed resistive carbon paste heater (CPH). At the same time, we can predict MQE by numerical simulations. Because the magnet comes to quench if the mechanical disturbance exceeds the MQE, the disturbance energies are suspected to be equivalent to MQEs during the magnet-training. When we achieved somewhat larger MQE, we may exclude numbers of training quenches. In this paper, we discuss the guidelines of LTS magnet design from the standpoint of MQE. We represent some case studies for various superconducting magnets and/or some different winding methods.

Non-hydrostatic semi-elastic hybrid-coordinate SISL extension of HIRLAM. Part II: numerical testing

NASA Astrophysics Data System (ADS)

Rõõm, Rein; Männik, Aarne; Luhamaa, Andres; Zirk, Marko

2007-10-01

The semi-implicit semi-Lagrangian (SISL), two-time-level, non-hydrostatic numerical scheme, based on the non-hydrostatic, semi-elastic pressure-coordinate equations, is tested in model experiments with flow over given orography (elliptical hill, mountain ridge, system of successive ridges) in a rectangular domain with emphasis on the numerical accuracy and non-hydrostatic effect presentation capability. Comparison demonstrates good (in strong primary wave generation) to satisfactory (in weak secondary wave reproduction in some cases) consistency of the numerical modelling results with known stationary linear test solutions. Numerical stability of the developed model is investigated with respect to the reference state choice, modelling dynamics of a stationary front. The horizontally area-mean reference temperature proves to be the optimal stability warrant. The numerical scheme with explicit residual in the vertical forcing term becomes unstable for cross-frontal temperature differences exceeding 30 K. Stability is restored, if the vertical forcing is treated implicitly, which enables to use time steps, comparable with the hydrostatic SISL.

The stability cycle—A universal pathway for the stability of films over topography

NASA Astrophysics Data System (ADS)

Schörner, Mario; Aksel, Nuri

2018-01-01

In the present study on the linear stability of gravity-driven Newtonian films flowing over inclined topographies, we consider a fundamental question: Is there a universal principle, being valid to describe the parametric evolution of the flow's stability chart for variations of different system parameters? For this sake, we first screened all experimental and numerical stability charts available in the literature. In a second step, we performed experiments to fill the gaps which remained. Variations of the fluid's viscosity and the topography's specific shape, amplitude, wavelength, tip width, and inclination were considered. That way, we identified a set of six characteristic patterns of stability charts to be sufficient to describe and unify all results on the linear stability of Newtonian films flowing over undulated inclines. We unveiled a universal pathway—the stability cycle—along which the linear stability charts of all considered Newtonian films flowing down periodically corrugated inclines evolved when the system parameters were changed.

On the stability analysis of a pair of van der Pol oscillators with delayed self-connection, position and velocity couplings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Kun; Department of Mathematics, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon; Chung, Kwok-wai, E-mail: makchung@cityu.edu.hk

2013-11-15

In this paper, we perform a stability analysis of a pair of van der Pol oscillators with delayed self-connection, position and velocity couplings. Bifurcation diagram of the damping, position and velocity coupling strengths is constructed, which gives insight into how stability boundary curves come into existence and how these curves evolve from small closed loops into open-ended curves. The van der Pol oscillator has been considered by many researchers as the nodes for various networks. It is inherently unstable at the zero equilibrium. Stability control of a network is always an important problem. Currently, the stabilization of the zero equilibriummore » of a pair of van der Pol oscillators can be achieved only for small damping strength by using delayed velocity coupling. An interesting question arises naturally: can the zero equilibrium be stabilized for an arbitrarily large value of the damping strength? We prove that it can be. In addition, a simple condition is given on how to choose the feedback parameters to achieve such goal. We further investigate how the in-phase mode or the out-of-phase mode of a periodic solution is related to the stability boundary curve that it emerges from a Hopf bifurcation. Analytical expression of a periodic solution is derived using an integration method. Some illustrative examples show that the theoretical prediction and numerical simulation are in good agreement.« less

Engineering the Pores of Biomass-Derived Carbon: Insights for Achieving Ultrahigh Stability at High Power in High-Energy Supercapacitors.

PubMed

Thangavel, Ranjith; Kaliyappan, Karthikeyan; Ramasamy, Hari Vignesh; Sun, Xueliang; Lee, Yun-Sung

2017-07-10

Electrochemical supercapacitors with high energy density are promising devices due to their simple construction and long-term cycling performance. The development of a supercapacitor based on electrical double-layer charge storage with high energy density that can preserve its cyclability at higher power presents an ongoing challenge. Herein, we provide insights to achieve a high energy density at high power with an ultrahigh stability in an electrical double-layer capacitor (EDLC) system by using carbon from a biomass precursor (cinnamon sticks) in a sodium ion-based organic electrolyte. Herein, we investigated the dependence of EDLC performance on structural, textural, and functional properties of porous carbon engineered by using various activation agents. The results demonstrate that the performance of EDLCs is not only dependent on their textural properties but also on their structural features and surface functionalities, as is evident from the electrochemical studies. The electrochemical results are highly promising and revealed that the porous carbon with poor textural properties has great potential to deliver high capacitance and outstanding stability over 300 000 cycles compared with porous carbon with good textural properties. A very low capacitance degradation of around 0.066 % per 1000 cycles, along with high energy density (≈71 Wh kg -1 ) and high power density, have been achieved. These results offer a new platform for the application of low-surface-area biomass-derived carbons in the design of highly stable high-energy supercapacitors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Existence and Stability of Viscoelastic Shock Profiles

NASA Astrophysics Data System (ADS)

Barker, Blake; Lewicka, Marta; Zumbrun, Kevin

2011-05-01

We investigate existence and stability of viscoelastic shock profiles for a class of planar models including the incompressible shear case studied by Antman and Malek-Madani. We establish that the resulting equations fall into the class of symmetrizable hyperbolic-parabolic systems, hence spectral stability implies linearized and nonlinear stability with sharp rates of decay. The new contributions are treatment of the compressible case, formulation of a rigorous nonlinear stability theory, including verification of stability of small-amplitude Lax shocks, and the systematic incorporation in our investigations of numerical Evans function computations determining stability of large-amplitude and nonclassical type shock profiles.

School Achievement Strongly Predicts Midlife IQ

ERIC Educational Resources Information Center

Spinks, Ruth; Arndt, Stephan; Caspers, Kristin; Yucuis, Rebecca; McKirgan, L. William; Pfalzgraf, Christopher; Waterman, Elijah

2007-01-01

The relationship between measures of IQ and standardized school achievement tests is well established at around r~0.5 when the two are measured in close proximity. The current paper examined the stability of this correlation when comparing elementary school achievement (grades 3-8) and midlife IQ. Iowa Adoption Study participants who had…

Calculation of the lateral-dynamic stability of aircraft

NASA Technical Reports Server (NTRS)

Raikh, A

1952-01-01

Graphs and formulas are given with the aid of which all the aerodynamic coefficients required for computing the lateral dynamic stability can be determined. A number of numerical examples are given for obtaining the stability derivatives and solving the characteristic-stability equation. Approximate formulas are derived with the aid of which rapid preliminary computations may be made and the stability coefficients corrected for certain modifications of the airplane. A derivation of the lateral-dynamic-stability equations is included.

Observer enhanced control for spin-stabilized tethered formation in earth orbit

NASA Astrophysics Data System (ADS)

Guang, Zhai; Yuyang, Li; Liang, Bin

2018-04-01

This paper addresses the issues relevant to control of spin-stabilized tethered formation in circular orbit. Due to the dynamic complexities and nonlinear perturbations, it is challenging to promote the control precision for the formation deployment and maintenance. In this work, the formation dynamics are derived with considering the spinning rate of the central body, then major attention is dedicated to develop the nonlinear disturbance observer. To achieve better control performance, the observer-enhanced controller is designed by incorporating the disturbance observer into the control loop, benefits from the disturbance compensation are demonstrated, and also, the dependences of the disturbance observer performance on some important parameters are theoretically and numerically analyzed.

Vertically stabilized elongated cross-section tokamak

DOEpatents

Sheffield, George V.

1977-01-01

This invention provides a vertically stabilized, non-circular (minor) cross-section, toroidal plasma column characterized by an external separatrix. To this end, a specific poloidal coil means is added outside a toroidal plasma column containing an endless plasma current in a tokamak to produce a rectangular cross-section plasma column along the equilibrium axis of the plasma column. By elongating the spacing between the poloidal coil means the plasma cross-section is vertically elongated, while maintaining vertical stability, efficiently to increase the poloidal flux in linear proportion to the plasma cross-section height to achieve a much greater plasma volume than could be achieved with the heretofore known round cross-section plasma columns. Also, vertical stability is enhanced over an elliptical cross-section plasma column, and poloidal magnetic divertors are achieved.

Spreading of a surfactant-laden droplet down an inclined and pre-wetted plane - Numerics, Asymptotics and Linear Stability Analysis

NASA Astrophysics Data System (ADS)

Goddard, Joseph

2012-11-01

Non-uniformities in surfactant concentration result in a surface shear stress, known as the Marangoni stress. This stress, if sufficiently large, can influence the flow at the interface. Naturally occurring surfactants in the mammalian lung reduce the surface tension within the liquid lining the airways and help to prevent collapse of smaller airways. Premature infants produce insufficient surfactant because the lungs are under developed. Resulting Respiratory Distress Syndrome is treated by Surfactant Replacement Therapy. Motivated by this medical application we theoretically investigate a model problem involving the spreading of a drop laden with an insoluble surfactant down an inclined and pre-wetted plane. Our focus is on understanding the mechanisms behind a ``fingering'' instability observed experimentally by high-resolution numerics revealing a multi-region asymptotic structure of the spreading droplet. Approximate solutions for each region are then derived using asymptotic analysis. In particular, a quasi-steady similarity solution is obtained for the leading edge of the droplet and a linear stability analysis shows that the base state is linearly unstable to long-wavelength perturbations for all inclination angles. The Marangoni effect is shown to be behind this instability at small inclination angles. A stability criterion is derived at small wave number and it's implication in the onset of the instability will be discussed.

Numerical analysis of the Magnus moment on a spin-stabilized projectile

NASA Astrophysics Data System (ADS)

Cremins, Michael; Rodebaugh, Gregory; Verhulst, Claire; Benson, Michael; van Poppel, Bret

2016-11-01

The Magnus moment is a result of an uneven pressure distribution that occurs when an object rotates in a crossflow. Unlike the Magnus force, which is often small for spin-stabilized projectiles, the Magnus moment can have a strong detrimental effect on flight stability. According to one source, most transonic and subsonic flight instabilities are caused by the Magnus moment [Modern Exterior Ballistics, McCoy], and yet simulations often fail to accurately predict the Magnus moment in the subsonic regime. In this study, we present hybrid Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES) predictions of the Magnus moment for a spin-stabilized projectile. Velocity, pressure, and Magnus moment predictions are presented for multiple Reynolds numbers and spin rates. We also consider the effect of a sting mount, which is commonly used when conducting flow measurements in a wind tunnel or water channel. Finally, we present the initial designs for a novel Magnetic Resonance Velocimetry (MRV) experiment to measure three-dimensional flow around a spinning projectile. This work was supported by the Department of Defense High Performance Computing Modernization Program (DoD HPCMP).

Spin Stabilized Impulsively Controlled Missile (SSICM)

NASA Astrophysics Data System (ADS)

Crawford, J. I.; Howell, W. M.

1985-12-01

This patent is for the Spin Stabilized Impulsively Controlled Missile (SSICM). SSICM is a missile configuration which employs spin stabilization, nutational motion, and impulsive thrusting, and a body mounted passive or semiactive sensor to achieve very small miss distances against a high speed moving target. SSICM does not contain an autopilot, control surfaces, a control actuation system, nor sensor stabilization gimbals. SSICM spins at a rate sufficient to provide frequency separation between body motions and inertial target motion. Its impulsive thrusters provide near instantaneous changes in lateral velocity, whereas conventional missiles require a significant time delay to achieve lateral acceleration.

Mechanical stability of propped hydraulic fractures: A numerical study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asgian, M.I.; Cundall, P.A.; Brady, B.H.

1995-03-01

Proppant is sometimes produced along with hydrocarbons in hydraulically fractured petroleum wells. Sometimes 10% to 20% of the proppant is backproduced, which can lead to damaged equipment and downtime. Furthermore, proppant flowback can lead to a substantial loss of fracture conductivity. A numerical study was conducted to help understand what conditions are likely to lead to proppant flowback. In the simulations, the mechanical interaction of a larger number (several thousand) individual proppant grains was modeled with a distinct-element-type code. The numerical simulations show that hydraulic fractures propped with cohesionless, unbonded proppant fail under closure stress at a critical ratio ofmore » mean grain diameter to fracture width. This is consistent with published laboratory studies. The simulations identify the mechanism (arch failure) that triggers the mechanical instability and also show that the primary way that drawdowns (less than {approx} 75 psi/ft) affect proppant flowback is to transport loose proppant grains in front of the stable arch to the wellbore. Drawdowns > 75 psi/ft are sufficient to destabilize the arch and to cause progressive failure of the propped fractures.« less

Stability of mixing layers

NASA Technical Reports Server (NTRS)

Tam, Christopher; Krothapalli, A

1993-01-01

The research program for the first year of this project (see the original research proposal) consists of developing an explicit marching scheme for solving the parabolized stability equations (PSE). Performing mathematical analysis of the computational algorithm including numerical stability analysis and the determination of the proper boundary conditions needed at the boundary of the computation domain are implicit in the task. Before one can solve the parabolized stability equations for high-speed mixing layers, the mean flow must first be found. In the past, instability analysis of high-speed mixing layer has mostly been performed on mean flow profiles calculated by the boundary layer equations. In carrying out this project, it is believed that the boundary layer equations might not give an accurate enough nonparallel, nonlinear mean flow needed for parabolized stability analysis. A more accurate mean flow can, however, be found by solving the parabolized Navier-Stokes equations. The advantage of the parabolized Navier-Stokes equations is that its accuracy is consistent with the PSE method. Furthermore, the method of solution is similar. Hence, the major part of the effort of the work of this year has been devoted to the development of an explicit numerical marching scheme for the solution of the Parabolized Navier-Stokes equation as applied to the high-seed mixing layer problem.

Finite-time fault tolerant attitude stabilization control for rigid spacecraft.

PubMed

Huo, Xing; Hu, Qinglei; Xiao, Bing

2014-03-01

A sliding mode based finite-time control scheme is presented to address the problem of attitude stabilization for rigid spacecraft in the presence of actuator fault and external disturbances. More specifically, a nonlinear observer is first proposed to reconstruct the amplitude of actuator faults and external disturbances. It is proved that precise reconstruction with zero observer error is achieved in finite time. Then, together with the system states, the reconstructed information is used to synthesize a nonsingular terminal sliding mode attitude controller. The attitude and the angular velocity are asymptotically governed to zero with finite-time convergence. A numerical example is presented to demonstrate the effectiveness of the proposed scheme. © 2013 Published by ISA on behalf of ISA.

Recent advances in numerical PDEs

NASA Astrophysics Data System (ADS)

Zuev, Julia Michelle

In this thesis, we investigate four neighboring topics, all in the general area of numerical methods for solving Partial Differential Equations (PDEs). Topic 1. Radial Basis Functions (RBF) are widely used for multi-dimensional interpolation of scattered data. This methodology offers smooth and accurate interpolants, which can be further refined, if necessary, by clustering nodes in select areas. We show, however, that local refinements with RBF (in a constant shape parameter [varepsilon] regime) may lead to the oscillatory errors associated with the Runge phenomenon (RP). RP is best known in the case of high-order polynomial interpolation, where its effects can be accurately predicted via Lebesgue constant L (which is based solely on the node distribution). We study the RP and the applicability of Lebesgue constant (as well as other error measures) in RBF interpolation. Mainly, we allow for a spatially variable shape parameter, and demonstrate how it can be used to suppress RP-like edge effects and to improve the overall stability and accuracy. Topic 2. Although not as versatile as RBFs, cubic splines are useful for interpolating grid-based data. In 2-D, we consider a patch representation via Hermite basis functions s i,j ( u, v ) = [Special characters omitted.] h mn H m ( u ) H n ( v ), as opposed to the standard bicubic representation. Stitching requirements for the rectangular non-equispaced grid yield a 2-D tridiagonal linear system AX = B, where X represents the unknown first derivatives. We discover that the standard methods for solving this NxM system do not take advantage of the spline-specific format of the matrix B. We develop an alternative approach using this specialization of the RHS, which allows us to pre-compute coefficients only once, instead of N times. MATLAB implementation of our fast 2-D cubic spline algorithm is provided. We confirm analytically and numerically that for large N ( N > 200), our method is at least 3 times faster than the

Stability of the discretization of the electron avalanche phenomenon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villa, Andrea, E-mail: andrea.villa@rse-web.it; Barbieri, Luca, E-mail: luca.barbieri@rse-web.it; Gondola, Marco, E-mail: marco.gondola@rse-web.it

2015-09-01

The numerical simulation of the discharge inception is an active field of applied physics with many industrial applications. In this work we focus on the drift-reaction equation that describes the electron avalanche. This phenomenon is one of the basic building blocks of the streamer model. The main difficulty of the electron avalanche equation lies in the fact that the reaction term is positive when a high electric field is applied. It leads to exponentially growing solutions and this has a major impact on the behavior of numerical schemes. We analyze the stability of a reference finite volume scheme applied tomore » this latter problem. The stability of the method may impose a strict mesh spacing, therefore a proper stabilized scheme, which is stable whatever spacing is used, has been developed. The convergence of the scheme is treated as well as some numerical experiments.« less

Radiative Kähler moduli stabilization

NASA Astrophysics Data System (ADS)

Kobayashi, Tatsuo; Omoto, Naoya; Otsuka, Hajime; Tatsuishi, Takuya H.

2018-05-01

We propose a new type of Kähler moduli stabilization mechanisms in type IIB superstring theory on Calabi-Yau manifolds with the positive Euler number. The overall Kähler modulus can be perturbatively stabilized by radiative corrections due to sparticles. Its minimum is the anti-de Sitter vacuum, where supersymmetry is broken. We can uplift it to the de Sitter vacuum by introducing anti-D-branes, keeping the modulus stabilized. Although our numerical results depend on the choice of the cutoff scale and degeneracies of sparticles, at any rate there exist the parameter spaces where the masses of Kaluza-Klein and stringy modes are larger than the cutoff scale. Furthermore, this stabilization scenario predicts an ultralight axion.

Stabilizing photoassociated Cs2 molecules by optimal control

NASA Astrophysics Data System (ADS)

Zhang, Wei; Xie, Ting; Huang, Yin; Wang, Gao-Ren; Cong, Shu-Lin

2013-01-01

We demonstrate theoretically that photoassociated molecules can be stabilized to deeply bound states. This process is achieved by transferring the population from the outer well to the inner well using the optimal control theory, the Cs2 molecule is taken as an example. Numerical calculations show that weakly bound molecules formed in the outer well by a pump pulse can be compressed to the inner well via a vibrational level of the ground electronic state as an intermediary by an additionally optimized laser pulse. The positively chirped pulse can enhance the population of the target state. With a transform-limited dump pulse, nearly all the photoassociated molecules in the inner well of the excited electronic state can be transferred to the deeply vibrational level of the ground electronic state.

Numerical simulation and stability analysis of solutocapillary effect in ultrathin films

NASA Astrophysics Data System (ADS)

Gordeeva, V. Yu.; Lyushnin, A. V.

2017-04-01

Polar fluids, like water or polydimethylsiloxane, are widely used in technical and medical applications. Capillary effects arising from surface tension gradients can be significant in thin liquid films. The present paper is dedicated to investigation of capillary flow due to a surfactant added to a polar liquid under conditions when intermolecular forces and disjoining pressure play an important role. Evolution equations are formulated for a film profile and the surfactant concentration. Stability analysis shows that the Marangoni effect destabilizes the film, and oscillatory modes appear at slow evaporation rates. We find that the film has four stability modes of at slow evaporation: monotonic stable, monotonic unstable, oscillatory stable, and oscillatory unstable, depending on the wave number of disturbances.

A Polynomial Time, Numerically Stable Integer Relation Algorithm

NASA Technical Reports Server (NTRS)

Ferguson, Helaman R. P.; Bailey, Daivd H.; Kutler, Paul (Technical Monitor)

1998-01-01

Let x = (x1, x2...,xn be a vector of real numbers. X is said to possess an integer relation if there exist integers a(sub i) not all zero such that a1x1 + a2x2 + ... a(sub n)Xn = 0. Beginning in 1977 several algorithms (with proofs) have been discovered to recover the a(sub i) given x. The most efficient of these existing integer relation algorithms (in terms of run time and the precision required of the input) has the drawback of being very unstable numerically. It often requires a numeric precision level in the thousands of digits to reliably recover relations in modest-sized test problems. We present here a new algorithm for finding integer relations, which we have named the "PSLQ" algorithm. It is proved in this paper that the PSLQ algorithm terminates with a relation in a number of iterations that is bounded by a polynomial in it. Because this algorithm employs a numerically stable matrix reduction procedure, it is free from the numerical difficulties, that plague other integer relation algorithms. Furthermore, its stability admits an efficient implementation with lower run times oil average than other algorithms currently in Use. Finally, this stability can be used to prove that relation bounds obtained from computer runs using this algorithm are numerically accurate.

An Attributional Theory of Achievement Motivation and Emotion.

ERIC Educational Resources Information Center

Weiner, Bernard

1985-01-01

This article advances an attributional theory of motivation and emotion, with achievement strivings as the theoretical focus. Causes of success and failure share three common properties: locus, stability, and controllability. Stability of causes influences changes in expectancy of success. Expectancy and affect guide motivated behavior.…

Stability of the mode-locking regime in tapered quantum-dot lasers

NASA Astrophysics Data System (ADS)

Bardella, P.; Drzewietzki, L.; Rossetti, M.; Weber, C.; Breuer, S.

2018-02-01

We study numerically and experimentally the role of the injection current and reverse bias voltage on the pulse stability of tapered, passively mode-locked, Quantum Dot (QD) lasers. By using a multi-section delayed differential equation and introducing in the model the QD inhomogenous broadening, we are able to predict the onset of leading and trailing edge instabilities in the emitted pulse trains and to identify specific trends of stability in dependence on the laser biasing conditions. The numerical results are confirmed experimentally trough amplitude and timing stability analysis of the pulses.

A locally conservative stabilized continuous Galerkin finite element method for two-phase flow in poroelastic subsurfaces

NASA Astrophysics Data System (ADS)

Deng, Q.; Ginting, V.; McCaskill, B.; Torsu, P.

2017-10-01

We study the application of a stabilized continuous Galerkin finite element method (CGFEM) in the simulation of multiphase flow in poroelastic subsurfaces. The system involves a nonlinear coupling between the fluid pressure, subsurface's deformation, and the fluid phase saturation, and as such, we represent this coupling through an iterative procedure. Spatial discretization of the poroelastic system employs the standard linear finite element in combination with a numerical diffusion term to maintain stability of the algebraic system. Furthermore, direct calculation of the normal velocities from pressure and deformation does not entail a locally conservative field. To alleviate this drawback, we propose an element based post-processing technique through which local conservation can be established. The performance of the method is validated through several examples illustrating the convergence of the method, the effectivity of the stabilization term, and the ability to achieve locally conservative normal velocities. Finally, the efficacy of the method is demonstrated through simulations of realistic multiphase flow in poroelastic subsurfaces.

Numerical Modelling of Seismic Slope Stability

NASA Astrophysics Data System (ADS)

Bourdeau, Céline; Havenith, Hans-Balder; Fleurisson, Jean-Alain; Grandjean, Gilles

Earthquake ground-motions recorded worldwide have shown that many morphological and geological structures (topography, sedimentary basin) are prone to amplify the seismic shaking (San Fernando, 1971 [Davis and West 1973] Irpinia, 1980 [Del Pezzo et al. 1983]). This phenomenon, called site effects, was again recently observed in El Salvador when, on the 13th of January 2001, the country was struck by a M = 7.6 earthquake. Indeed, while horizontal accelerations on a rock site at Berlin, 80 km from the epicentre, did not exceed 0.23 g, they reached 0.6 g at Armenia, 110 km from the epicentre. Armenia is located on a small hill underlaid by a few meters thick pyroclastic deposits. Both the local topography and the presence of surface layers are likely to have caused the observed amplification effects, which are supposed to have contributed to the triggering of some of the hundreds of landslides related to this seismic event (Murphy et al. 2002). In order to better characterize the way site effects may influence the triggering of landslides along slopes, 2D numerical elastic and elasto-plastic models were developed. Various geometrical, geological and seismic conditions were analysed and the dynamic behaviour of the slope under these con- ditions was studied in terms of creation and location of a sliding surface. Preliminary results suggest that the size of modelled slope failures is dependent on site effects.

Spherical gyroscopic moment stabilizer for attitude control of microsatellites

NASA Astrophysics Data System (ADS)

Keshtkar, Sajjad; Moreno, Jaime A.; Kojima, Hirohisa; Uchiyama, Kenji; Nohmi, Masahiro; Takaya, Keisuke

2018-02-01

This paper presents a new and improved concept of recently proposed two-degrees of freedom spherical stabilizer for triaxial orientation of microsatellites. The analytical analysis of the advantages of the proposed mechanism over the existing inertial attitude control devices are introduced. The extended equations of motion of the stabilizing satellite including the spherical gyroscope, for control law design and numerical simulations, are studied in detail. A new control algorithm based on continuous high-order sliding mode algorithms, for managing the torque produced by the stabilizer and therefore the attitude control of the satellite in the presence of perturbations/uncertainties, is presented. Some numerical simulations are carried out to prove the performance of the proposed mechanism and control laws.

Numerical equilibrium analysis for structured consumer resource models.

PubMed

de Roos, A M; Diekmann, O; Getto, P; Kirkilionis, M A

2010-02-01

In this paper, we present methods for a numerical equilibrium and stability analysis for models of a size structured population competing for an unstructured resource. We concentrate on cases where two model parameters are free, and thus existence boundaries for equilibria and stability boundaries can be defined in the (two-parameter) plane. We numerically trace these implicitly defined curves using alternatingly tangent prediction and Newton correction. Evaluation of the maps defining the curves involves integration over individual size and individual survival probability (and their derivatives) as functions of individual age. Such ingredients are often defined as solutions of ODE, i.e., in general only implicitly. In our case, the right-hand sides of these ODE feature discontinuities that are caused by an abrupt change of behavior at the size where juveniles are assumed to turn adult. So, we combine the numerical solution of these ODE with curve tracing methods. We have implemented the algorithms for "Daphnia consuming algae" models in C-code. The results obtained by way of this implementation are shown in the form of graphs.

Generalized Hill-stability criteria for hierarchical three-body systems at arbitrary inclinations

NASA Astrophysics Data System (ADS)

Grishin, Evgeni; Perets, Hagai B.; Zenati, Yossef; Michaely, Erez

2017-04-01

A fundamental aspect of the three-body problem is its stability. Most stability studies have focused on the co-planar three-body problem, deriving analytic criteria for the dynamical stability of such pro/retrograde systems. Numerical studies of inclined systems phenomenologically mapped their stability regions, but neither complement it by theoretical framework, nor provided satisfactory fit for their dependence on mutual inclinations. Here we present a novel approach to study the stability of hierarchical three-body systems at arbitrary inclinations, which accounts not only for the instantaneous stability of such systems, but also for the secular stability and evolution through Lidov-Kozai cycles and evection. We generalize the Hill-stability criteria to arbitrarily inclined triple systems, explain the existence of quasi-stable regimes and characterize the inclination dependence of their stability. We complement the analytic treatment with an extensive numerical study, to test our analytic results. We find excellent correspondence up to high inclinations (˜120°), beyond which the agreement is marginal. At such high inclinations, the stability radius is larger, the ratio between the outer and inner periods becomes comparable and our secular averaging approach is no longer strictly valid. We therefore combine our analytic results with polynomial fits to the numerical results to obtain a generalized stability formula for triple systems at arbitrary inclinations. Besides providing a generalized secular-based physical explanation for the stability of non-co-planar systems, our results have direct implications for any triple systems and, in particular, binary planets and moon/satellite systems; we briefly discuss the latter as a test case for our models.

Evaluation of stabilization techniques for ion implant processing

NASA Astrophysics Data System (ADS)

Ross, Matthew F.; Wong, Selmer S.; Minter, Jason P.; Marlowe, Trey; Narcy, Mark E.; Livesay, William R.

1999-06-01

With the integration of high current ion implant processing into volume CMOS manufacturing, the need for photoresist stabilization to achieve a stable ion implant process is critical. This study compares electron beam stabilization, a non-thermal process, with more traditional thermal stabilization techniques such as hot plate baking and vacuum oven processing. The electron beam processing is carried out in a flood exposure system with no active heating of the wafer. These stabilization techniques are applied to typical ion implant processes that might be found in a CMOS production process flow. The stabilization processes are applied to a 1.1 micrometers thick PFI-38A i-line photoresist film prior to ion implant processing. Post stabilization CD variation is detailed with respect to wall slope and feature integrity. SEM photographs detail the effects of the stabilization technique on photoresist features. The thermal stability of the photoresist is shown for different levels of stabilization and post stabilization thermal cycling. Thermal flow stability of the photoresist is detailed via SEM photographs. A significant improvement in thermal stability is achieved with the electron beam process, such that photoresist features are stable to temperatures in excess of 200 degrees C. Ion implant processing parameters are evaluated and compared for the different stabilization methods. Ion implant system end-station chamber pressure is detailed as a function of ion implant process and stabilization condition. The ion implant process conditions are detailed for varying factors such as ion current, energy, and total dose. A reduction in the ion implant systems end-station chamber pressure is achieved with the electron beam stabilization process over the other techniques considered. This reduction in end-station chamber pressure is shown to provide a reduction in total process time for a given ion implant dose. Improvements in the ion implant process are detailed across

Stabilization of the Rayleigh-Taylor instability in quantum magnetized plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, L. F.; Ye, W. H.; He, X. T.

2012-07-15

In this research, stabilization of the Rayleigh-Taylor instability (RTI) due to density gradients, magnetic fields, and quantum effects, in an ideal incompressible plasma, is studied analytically and numerically. A second-order ordinary differential equation (ODE) for the RTI including quantum corrections, with a continuous density profile, in a uniform external magnetic field, is obtained. Analytic expressions of the linear growth rate of the RTI, considering modifications of density gradients, magnetic fields, and quantum effects, are presented. Numerical approaches are performed to solve the second-order ODE. The analytical model proposed here agrees with the numerical calculation. It is found that the densitymore » gradients, the magnetic fields, and the quantum effects, respectively, have a stabilizing effect on the RTI (reduce the linear growth of the RTI). The RTI can be completely quenched by the magnetic field stabilization and/or the quantum effect stabilization in proper circumstances leading to a cutoff wavelength. The quantum effect stabilization plays a central role in systems with large Atwood number and small normalized density gradient scale length. The presence of external transverse magnetic fields beside the quantum effects will bring about more stability on the RTI. The stabilization of the linear growth of the RTI, for parameters closely related to inertial confinement fusion and white dwarfs, is discussed. Results could potentially be valuable for the RTI treatment to analyze the mixing in supernovas and other RTI-driven objects.« less

Stability of streamwise vortices

NASA Technical Reports Server (NTRS)

Khorrami, M. K.; Grosch, C. E.; Ash, R. L.

1987-01-01

A brief overview of some theoretical and computational studies of the stability of streamwise vortices is given. The local induction model and classical hydrodynamic vortex stability theories are discussed in some detail. The importance of the three-dimensionality of the mean velocity profile to the results of stability calculations is discussed briefly. The mean velocity profile is provided by employing the similarity solution of Donaldson and Sullivan. The global method of Bridges and Morris was chosen for the spatial stability calculations for the nonlinear eigenvalue problem. In order to test the numerical method, a second order accurate central difference scheme was used to obtain the coefficient matrices. It was shown that a second order finite difference method lacks the required accuracy for global eigenvalue calculations. Finally the problem was formulated using spectral methods and a truncated Chebyshev series.

Stabilizing oscillating universes against quantum decay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mithani, Audrey T.; Vilenkin, Alexander, E-mail: audrey.todhunter@tufts.edu, E-mail: vilenkin@cosmos.phy.tufts.edu

2015-07-01

We investigate the effect of vacuum corrections, due to the trace anomaly and Casimir effect, on the stability of an oscillating universe with respect to decay by tunneling to the singularity. We find that these corrections do not generally stabilize an oscillating universe. However, stability may be achieved for some specially fine-tuned non-vacuum states.

Stabilizing oscillating universes against quantum decay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mithani, Audrey T.; Vilenkin, Alexander

We investigate the effect of vacuum corrections, due to the trace anomaly and Casimir effect, on the stability of an oscillating universe with respect to decay by tunneling to the singularity. We find that these corrections do not generally stabilize an oscillating universe. However, stability may be achieved for some specially fine-tuned non-vacuum states.

Dynamic Stability Experiment of Maglev Systems,

DTIC Science & Technology

1995-04-01

This report summarizes the research performed on maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also... maglev system, it is important to consider this phenomenon in the development of all maglev systems. This report presents dynamic stability experiments...on maglev systems and compares their numerical simulation with predictions calculated by a nonlinear dynamic computer code. Instabilities of an

Interval stability for complex systems

NASA Astrophysics Data System (ADS)

Klinshov, Vladimir V.; Kirillov, Sergey; Kurths, Jürgen; Nekorkin, Vladimir I.

2018-04-01

Stability of dynamical systems against strong perturbations is an important problem of nonlinear dynamics relevant to many applications in various areas. Here, we develop a novel concept of interval stability, referring to the behavior of the perturbed system during a finite time interval. Based on this concept, we suggest new measures of stability, namely interval basin stability (IBS) and interval stability threshold (IST). IBS characterizes the likelihood that the perturbed system returns to the stable regime (attractor) in a given time. IST provides the minimal magnitude of the perturbation capable to disrupt the stable regime for a given interval of time. The suggested measures provide important information about the system susceptibility to external perturbations which may be useful for practical applications. Moreover, from a theoretical viewpoint the interval stability measures are shown to bridge the gap between linear and asymptotic stability. We also suggest numerical algorithms for quantification of the interval stability characteristics and demonstrate their potential for several dynamical systems of various nature, such as power grids and neural networks.

Optimal subinterval selection approach for power system transient stability simulation

DOE PAGES

Kim, Soobae; Overbye, Thomas J.

2015-10-21

Power system transient stability analysis requires an appropriate integration time step to avoid numerical instability as well as to reduce computational demands. For fast system dynamics, which vary more rapidly than what the time step covers, a fraction of the time step, called a subinterval, is used. However, the optimal value of this subinterval is not easily determined because the analysis of the system dynamics might be required. This selection is usually made from engineering experiences, and perhaps trial and error. This paper proposes an optimal subinterval selection approach for power system transient stability analysis, which is based on modalmore » analysis using a single machine infinite bus (SMIB) system. Fast system dynamics are identified with the modal analysis and the SMIB system is used focusing on fast local modes. An appropriate subinterval time step from the proposed approach can reduce computational burden and achieve accurate simulation responses as well. As a result, the performance of the proposed method is demonstrated with the GSO 37-bus system.« less

The stability issues in problems of mathematical modeling

NASA Astrophysics Data System (ADS)

Mokin, A. Yu.; Savenkova, N. P.; Udovichenko, N. S.

2018-03-01

In the paper it is briefly considered various aspects of stability concepts, which are used in physics, mathematics and numerical methods of solution. The interrelation between these concepts is described, the questions of preliminary stability research before the numerical solution of the problem and the correctness of the mathematical statement of the physical problem are discussed. Examples of concrete mathematical statements of individual physical problems are given: a nonlocal problem for the heat equation, the Korteweg-de Fries equation with boundary conditions at infinity, the sine-Gordon equation, the problem of propagation of femtosecond light pulses in an area with a cubic nonlinearity.

Stability of outer planetary orbits around binary stars - A comparison of Hill's and Laplace's stability criteria

NASA Technical Reports Server (NTRS)

Kubala, A.; Black, D.; Szebehely, V.

1993-01-01

A comparison is made between the stability criteria of Hill and that of Laplace to determine the stability of outer planetary orbits encircling binary stars. The restricted, analytically determined results of Hill's method by Szebehely and coworkers and the general, numerically integrated results of Laplace's method by Graziani and Black (1981) are compared for varying values of the mass parameter mu. For mu = 0 to 0.15, the closest orbit (lower limit of radius) an outer planet in a binary system can have and still remain stable is determined by Hill's stability criterion. For mu greater than 0.15, the critical radius is determined by Laplace's stability criterion. It appears that the Graziani-Black stability criterion describes the critical orbit within a few percent for all values of mu.

Robust control design with real parameter uncertainty using absolute stability theory. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

How, Jonathan P.; Hall, Steven R.

1993-01-01

The purpose of this thesis is to investigate an extension of mu theory for robust control design by considering systems with linear and nonlinear real parameter uncertainties. In the process, explicit connections are made between mixed mu and absolute stability theory. In particular, it is shown that the upper bounds for mixed mu are a generalization of results from absolute stability theory. Both state space and frequency domain criteria are developed for several nonlinearities and stability multipliers using the wealth of literature on absolute stability theory and the concepts of supply rates and storage functions. The state space conditions are expressed in terms of Riccati equations and parameter-dependent Lyapunov functions. For controller synthesis, these stability conditions are used to form an overbound of the H2 performance objective. A geometric interpretation of the equivalent frequency domain criteria in terms of off-axis circles clarifies the important role of the multiplier and shows that both the magnitude and phase of the uncertainty are considered. A numerical algorithm is developed to design robust controllers that minimize the bound on an H2 cost functional and satisfy an analysis test based on the Popov stability multiplier. The controller and multiplier coefficients are optimized simultaneously, which avoids the iteration and curve-fitting procedures required by the D-K procedure of mu synthesis. Several benchmark problems and experiments on the Middeck Active Control Experiment at M.I.T. demonstrate that these controllers achieve good robust performance and guaranteed stability bounds.

Craton stability and continental lithosphere dynamics during plume-plate interaction

NASA Astrophysics Data System (ADS)

Wang, H.; Van Hunen, J.; Pearson, D.

2013-12-01

Survival of thick cratonic roots in a vigorously convecting mantle system for billions of years has long been studied by the geodynamical community. A high cratonic root strength is generally considered to be the most important factor. We first perform and discuss new numerical models to investigate craton stability in both Newtonian and non-Newtonian rheology in the stagnant lid regime. The results show that only a modest compositional rheological factor of Δη=10 with non-Newtonian rheology is required for the survival of cratonic roots in a stagnant lid regime. A larger rheological factor (100 or more) is needed to maintain similar craton longevity in a Newtonian rheology environment. Furthermore, chemical buoyancy plays an important role on craton stability and its evolution, but could only work with suitable compositional rheology. During their long lifespan, cratons experienced a suite of dynamic, tectonothermal events, such as nearby subduction and mantle plume activity. Cratonic nuclei are embedded in shorter-lived, more vulnerable continental areas of different thickness, composition and rheology, which would influence the lithosphere dynamic when tectonothermal events happen nearby. South Africa provides a very good example to investigate such dynamic processes as it hosts several cratons and there are many episodic thermal events since the Mesozoic as indicated by a spectrum of magmatic activity. We numerically investigate such an integrated system using the topographic evolution of cratons and surrounding lithosphere as a diagnostic observable. The post-70Ma thinning of pericratonic lithosphere by ~50km around Kaapvaal craton (Mather et al., 2011) is also investigated through our numerical models. The results show that the pericratonic lithosphere cools and grows faster than cratons do, but is also more likely to be effected by episodic thermal events. This leads to surface topography change that is significantly larger around the craton than within

Stability analysis of unsteady ablation fronts

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

1993-08-01

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.

Stability analysis of unsteady ablation fronts

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

1993-11-08

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.

Stabilization of ring dark solitons in Bose-Einstein condensates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wenlong; Kevrekidis, P. G.; Carretero-González, R.

Earlier work has shown that ring dark solitons in two-dimensional Bose-Einstein condensates are generically unstable. In this work, we propose a way of stabilizing the ring dark soliton via a radial Gaussian external potential. We investigate the existence and stability of the ring dark soliton upon variations of the chemical potential and also of the strength of the radial potential. Numerical results show that the ring dark soliton can be stabilized in a suitable interval of external potential strengths and chemical potentials. Furthermore, we also explore different proposed particle pictures considering the ring as a moving particle and find, wheremore » appropriate, results in very good qualitative and also reasonable quantitative agreement with the numerical findings.« less

Stabilization of ring dark solitons in Bose-Einstein condensates

DOE PAGES

Wang, Wenlong; Kevrekidis, P. G.; Carretero-González, R.; ...

2015-09-14

Earlier work has shown that ring dark solitons in two-dimensional Bose-Einstein condensates are generically unstable. In this work, we propose a way of stabilizing the ring dark soliton via a radial Gaussian external potential. We investigate the existence and stability of the ring dark soliton upon variations of the chemical potential and also of the strength of the radial potential. Numerical results show that the ring dark soliton can be stabilized in a suitable interval of external potential strengths and chemical potentials. Furthermore, we also explore different proposed particle pictures considering the ring as a moving particle and find, wheremore » appropriate, results in very good qualitative and also reasonable quantitative agreement with the numerical findings.« less

An extended macro model accounting for acceleration changes with memory and numerical tests

NASA Astrophysics Data System (ADS)

Cheng, Rongjun; Ge, Hongxia; Sun, Fengxin; Wang, Jufeng

2018-09-01

Considering effect of acceleration changes with memory, an improved continuum model of traffic flow is proposed in this paper. By applying the linear stability theory, we derived the new model's linear stability condition. Through nonlinear analysis, the KdV-Burgers equation is derived to describe the propagating behavior of traffic density wave near the neutral stability line. Numerical simulation is carried out to study the extended traffic flow model, which explores how acceleration changes with memory affected each car's velocity, density and fuel consumption and exhaust emissions. Numerical results demonstrate that acceleration changes with memory have significant negative effect on dynamic characteristic of traffic flow. Furthermore, research results verify that the effect of acceleration changes with memory will deteriorate the stability of traffic flow and increase cars' total fuel consumptions and emissions during the whole evolution of small perturbation.

Longitudinal Effects of Perceived Control on Academic Achievement

ERIC Educational Resources Information Center

You, Sukkyung; Hong, Sehee; Ho, Hsiu-Zu

2011-01-01

It is well established that perceived control plays an important role in student academic achievement, but little is known about its longitudinal stability, ethnic variation, and developmental effects on subsequent achievement during adolescence. Findings from this study indicated (a) perceived control remains stable during adolescence for each of…

Numerical computation of linear instability of detonations

NASA Astrophysics Data System (ADS)

Kabanov, Dmitry; Kasimov, Aslan

2017-11-01

We propose a method to study linear stability of detonations by direct numerical computation. The linearized governing equations together with the shock-evolution equation are solved in the shock-attached frame using a high-resolution numerical algorithm. The computed results are processed by the Dynamic Mode Decomposition technique to generate dispersion relations. The method is applied to the reactive Euler equations with simple-depletion chemistry as well as more complex multistep chemistry. The results are compared with those known from normal-mode analysis. We acknowledge financial support from King Abdullah University of Science and Technology.

Physical stability of R-(+)-Limonene emulsions stabilized by Ulva fasciata algae polysaccharide.

PubMed

Shao, Ping; Ma, Huiling; Qiu, Qiang; Jing, Weiping

2016-11-01

The physical stability of R-(+)-Limonene emulsions stabilized by Ulva fasciata polysaccharide (UFP) was investigated in this study. Emulsion physical stability was evaluated under different polysaccharide concentrations (1%-5%, wt/wt) and pH values (3.0-11.0). The stability of R-(+)-Limonene emulsions was demonstrated by droplet size distribution, rheological properties, zeta potential and visual phase separation. R-(+)-Limonene emulsions displayed monomodal droplet size distributions, high absolute values of zeta potential and good storage stability when 3% (wt/wt) UFP was used. The rheological properties and stability of R-(+)-Limonene emulsions appeared to be dependent on polysaccharide concentration. The emulsion stability was impacted by pH. Higher zeta potential (-52.6mV) and smaller mean droplet diameter (2.45μm) were achieved in neutral liquid environment (pH 7.0). Extreme acidity caused the flocculation of emulsions, which was manifested as phase separation, while emulsions were quite stable in an alkaline environment. Through comparing the stabilities of emulsions stabilized by different emulsifiers (i.e. UFP, GA and Gelatin), the result suggested that UFP was the best emulsifying agent among them. Copyright © 2016 Elsevier B.V. All rights reserved.

Numerical and Permeability Constraints on Simulation of Sill-Driven Hydrothermal Convection

NASA Astrophysics Data System (ADS)

Carr, P. M.; Cathles, L. M.; Barrie, C. T.; Manhardt, P.

2004-05-01

Volcanic-associated massive sulfide deposits are formed where seawater, heated to ~350oC by subsurface magma intrusions, is quenched by cold water at or near the seafloor. Many VMS districts, like the one at Matagami, Quebec, contain their zinc, lead, and copper in about a dozen discrete ore bodies, with one or two deposits containing more than half of the district's resources. We construct numerical models to investigate the causes of variations in deposit size. These models show that a process which stabilizes the location of hydrothermal venting plumes is required to numerically generate discrete VMS ore bodies by sill-driven hydrothermal convection. This is achieved in our models by increasing rock permeability in a fashion that makes vent plumes more permeable than their surroundings. Maintaining the Courant number ≤1 (so that a thermal anomaly traverses only one grid cell in one timestep of the simulation) is shown to be crucial to numerical convergence. If this rule is violated, visually compelling but incorrect hydrothermal vents result. Small hydrothermal convection cells over the interior of an areally-extensive sill with a tabular edge are smaller than those formed at the sill edge. However, for a sill with the geometry of that at Matagami, numerical simulations indicate that large ore deposits should form near the thickest part of the sill where metals extracted from the underside of the still-hot portions of the sill can optimally contribute. Thus it is essential to construct a model of the entire domain rather than slicing a portion local to the deposition. The numerical models replicate the ten-fold range in deposit size variation, and predict the largest deposits at Matagami will be discovered at 5 to 8 km depth between currently known deposits in the South Flank and Phelps Dodge areas.

Numerical solution of the general coupled nonlinear Schrödinger equations on unbounded domains.

PubMed

Li, Hongwei; Guo, Yue

2017-12-01

The numerical solution of the general coupled nonlinear Schrödinger equations on unbounded domains is considered by applying the artificial boundary method in this paper. In order to design the local absorbing boundary conditions for the coupled nonlinear Schrödinger equations, we generalize the unified approach previously proposed [J. Zhang et al., Phys. Rev. E 78, 026709 (2008)PLEEE81539-375510.1103/PhysRevE.78.026709]. Based on the methodology underlying the unified approach, the original problem is split into two parts, linear and nonlinear terms, and we then achieve a one-way operator to approximate the linear term to make the wave out-going, and finally we combine the one-way operator with the nonlinear term to derive the local absorbing boundary conditions. Then we reduce the original problem into an initial boundary value problem on the bounded domain, which can be solved by the finite difference method. The stability of the reduced problem is also analyzed by introducing some auxiliary variables. Ample numerical examples are presented to verify the accuracy and effectiveness of our proposed method.

Direct numerical simulation of axisymmetric laminar low-density jets

NASA Astrophysics Data System (ADS)

Gomez Lendinez, Daniel; Coenen, Wilfried; Sevilla, Alejandro

2017-11-01

The stability of submerged laminar axisymmetric low-density jets has been investigated experimentally (Kyle & Sreenivasan 1993, Hallberg & Strykowski 2006) and with linear analysis (Jendoubi & Strykowski 1994, Coenen & Sevilla 2012, Coenen et al. 2017). These jets become globally unstable when the Reynolds number is larger than a certain critical value which depends on the density ratio and on the velocity profile at the injector outlet. In this work, Direct Numerical Simulations using FreeFEM + + (Hecht 2012) with P1 elements for pressure and P2 for velocity and density are performed to complement the above mentioned studies. Density and velocity fields are analyzed at long time showing the unforced space-time evolution of nonlinear disturbances propagating along the jet. Using the Stuart-Landau model to fit the numerical results for the self-excited oscillations we have computed a neutral stability curve that shows good agreement with experiments and stability theory. Thanks to Spanish MINECO under projects DPI2014-59292-C3-1-P and DPI2015-71901-REDT for financial support.

Frequency-tunable Pre-stabilized Lasers for LISA via Sideband-locking

NASA Technical Reports Server (NTRS)

Livas, Jeffrey C.; Thorpe, James I.; Numata, Kenji; Mitryk, Shawn; Mueller, Guido; Wand, Vinzenz

2008-01-01

Laser frequency noise mitigation is one of the most challenging aspects of the LISA interferometric measurement system. The unstabilized frequency fluctuations must be suppressed by roughly twelve orders of magnitude in order to achieve stability sufficient for gravitational wave detection. This enormous suppression will be achieved through a combination of stabilization and common-mode rejection. The stabilization component will itself be achieved in two stages: pre-stabilization to a local optical cavity followed by arm-locking to some combination of the inter-spacecraft distances. In order for these two stabilization stages to work simultaneously, the lock-point of the pre-stabilization loop must be frequency tunable. The current baseline stabilization technique, locking to an optical cavity, does not provide tunability between cavity resonances, which are typically spaced by 100s of MHz. Here we present a modification to the traditional Pound-Drever-Hall cavity locking technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This technique requires no modifications to the optical cavity itself, thus preserving the stability of the frequency reference. We present measurements of the system performance and demonstrate that we can meet implement the first two stages of stabilization.

DYNAMIC STABILITY OF THE SOLAR SYSTEM: STATISTICALLY INCONCLUSIVE RESULTS FROM ENSEMBLE INTEGRATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeebe, Richard E., E-mail: zeebe@soest.hawaii.edu

Due to the chaotic nature of the solar system, the question of its long-term stability can only be answered in a statistical sense, for instance, based on numerical ensemble integrations of nearby orbits. Destabilization of the inner planets, leading to close encounters and/or collisions can be initiated through a large increase in Mercury's eccentricity, with a currently assumed likelihood of ∼1%. However, little is known at present about the robustness of this number. Here I report ensemble integrations of the full equations of motion of the eight planets and Pluto over 5 Gyr, including contributions from general relativity. The resultsmore » show that different numerical algorithms lead to statistically different results for the evolution of Mercury's eccentricity (e{sub M}). For instance, starting at present initial conditions (e{sub M}≃0.21), Mercury's maximum eccentricity achieved over 5 Gyr is, on average, significantly higher in symplectic ensemble integrations using heliocentric rather than Jacobi coordinates and stricter error control. In contrast, starting at a possible future configuration (e{sub M}≃0.53), Mercury's maximum eccentricity achieved over the subsequent 500 Myr is, on average, significantly lower using heliocentric rather than Jacobi coordinates. For example, the probability for e{sub M} to increase beyond 0.53 over 500 Myr is >90% (Jacobi) versus only 40%-55% (heliocentric). This poses a dilemma because the physical evolution of the real system—and its probabilistic behavior—cannot depend on the coordinate system or the numerical algorithm chosen to describe it. Some tests of the numerical algorithms suggest that symplectic integrators using heliocentric coordinates underestimate the odds for destabilization of Mercury's orbit at high initial e{sub M}.« less

Numerical implementation of complex orthogonalization, parallel transport on Stiefel bundles, and analyticity

NASA Astrophysics Data System (ADS)

Avitabile, Daniele; Bridges, Thomas J.

2010-06-01

Numerical integration of complex linear systems of ODEs depending analytically on an eigenvalue parameter are considered. Complex orthogonalization, which is required to stabilize the numerical integration, results in non-analytic systems. It is shown that properties of eigenvalues are still efficiently recoverable by extracting information from a non-analytic characteristic function. The orthonormal systems are constructed using the geometry of Stiefel bundles. Different forms of continuous orthogonalization in the literature are shown to correspond to different choices of connection one-form on the Stiefel bundle. For the numerical integration, Gauss-Legendre Runge-Kutta algorithms are the principal choice for preserving orthogonality, and performance results are shown for a range of GLRK methods. The theory and methods are tested by application to example boundary value problems including the Orr-Sommerfeld equation in hydrodynamic stability.

Investigation of Rock Mass Stability Around the Tunnels in an Underground Mine in USA Using Three-Dimensional Numerical Modeling

NASA Astrophysics Data System (ADS)

Xing, Yan; Kulatilake, P. H. S. W.; Sandbak, L. A.

2018-02-01

The stability of the rock mass around the tunnels in an underground mine was investigated using the distinct element method. A three-dimensional model was developed based on the available geological, geotechnical, and mine construction information. It incorporates a complex lithological system, persistent and non-persistent faults, and a complex tunnel system including backfilled tunnels. The strain-softening constitutive model was applied for the rock masses. The rock mass properties were estimated using the Hoek-Brown equations based on the intact rock properties and the RMR values. The fault material behavior was modeled using the continuously yielding joint model. Sequential construction and rock supporting procedures were simulated based on the way they progressed in the mine. Stress analyses were performed to study the effect of the horizontal in situ stresses and the variability of rock mass properties on tunnel stability, and to evaluate the effectiveness of rock supports. The rock mass behavior was assessed using the stresses, failure zones, deformations around the tunnels, and the fault shear displacement vectors. The safety of rock supports was quantified using the bond shear and bolt tensile failures. Results show that the major fault and weak interlayer have distinct influences on the displacements and stresses around the tunnels. Comparison between the numerical modeling results and the field measurements indicated the cases with the average rock mass properties, and the K 0 values between 0.5 and 1.25 provide satisfactory agreement with the field measurements.

Phase Stabilization of Zirconia.

DTIC Science & Technology

1997-01-30

preparing stabilized zirconia pursuant to this disclosure, an insoluble alumina powder is mixed with zirconia powder using a liquid dispersant, such...in a drying oven or a furnace. When mixing the alumina and zirconia powders , it is not necessary to have zirconia in any particular phase to achieve...phase stabilization, as disclosed herein. When mixed with alumina powder, zirconia powder can be in cubic, tetragonal or 20 monoclinic phases

Computation of the stability derivatives via CFD and the sensitivity equations

NASA Astrophysics Data System (ADS)

Lei, Guo-Dong; Ren, Yu-Xin

2011-04-01

The method to calculate the aerodynamic stability derivates of aircrafts by using the sensitivity equations is extended to flows with shock waves in this paper. Using the newly developed second-order cell-centered finite volume scheme on the unstructured-grid, the unsteady Euler equations and sensitivity equations are solved simultaneously in a non-inertial frame of reference, so that the aerodynamic stability derivatives can be calculated for aircrafts with complex geometries. Based on the numerical results, behavior of the aerodynamic sensitivity parameters near the shock wave is discussed. Furthermore, the stability derivatives are analyzed for supersonic and hypersonic flows. The numerical results of the stability derivatives are found in good agreement with theoretical results for supersonic flows, and variations of the aerodynamic force and moment predicted by the stability derivatives are very close to those obtained by CFD simulation for both supersonic and hypersonic flows.

Attitude stability of a spinning spacecraft during appendage deployment/retraction

NASA Technical Reports Server (NTRS)

Fitz-Coy, Norman; Fullerton, Wayne

1994-01-01

The work presented is motivated by the need for a national satellite rescue policy, not the ad hoc policy now in place. In studying different approaches for a national policy, the issue of capture and stabilization of a tumbling spacecraft must be addressed. For a rescue mission involving a tumbling spacecraft, it may be advantageous to have a rescue vehicle which is compact and 'rigid' during the rendezvous/capture phase. After capture, passive stabilization techniques could be utilized as an efficient means of detumbling the resulting system (i.e., both the rescue vehicle and captures spacecraft). Since the rescue vehicle is initially compact and 'rigid,' significant passive stabilization through energy dissipation can only be achieved through the deployment of flexible appendages. Once stabilization is accomplished, retraction of the appendages before maneuvering the system to its final destination may also prove advantageous. It is therefore of paramount interest that we study the effect of appendage deployment/retraction on the attitude stability of a spacecraft. Particular interest should be paid to appendage retraction, since if this process is destabilizing, passive stabilization as proposed may not be useful. Over the past three decades, it has been an 'on-again-off-again affair' with the problem of spacecraft appendage deployment. In most instances, these studies have been numerical simulations of specific spacecraft configurations for which there were specific concerns. The primary focus of these studies was the behavior of the appendage during deployment; the effects of appendage retraction was considered only in one of these studies. What is missing in the literature is a thorough study of the effects of appendage deployment/retraction on the attitude stability of a spacecraft. This paper presents a rigorous analysis of the stability of a spinning spacecraft during the deployment or the retraction of an appendage. The analysis is simplified such that

Stability Analysis of Distributed Order Fractional Chen System

PubMed Central

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

2013-01-01

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

Method for Studying Helicopter Longitudinal Maneuver Stability

NASA Technical Reports Server (NTRS)

Amer, Kenneth B

1954-01-01

A theoretical analysis of helicopter maneuver stability is made and the results are compared with experimental results for both a single and a tandem rotor helicopter. Techniques are described for measuring in flight the significant stability derivatives for use with the theory to aid in design studies of means for achieving marginal maneuver stability for a prototype helicopter.

Determination of Global Stability of the Slosh Motion in a Spacecraft via Num Erical Experiment

NASA Astrophysics Data System (ADS)

Kang, Ja-Young

2003-12-01

The global stability of the attitude motion of a spin-stabilized space vehicle is investigated by performing numerical experiment. In the previous study, a stationary solution and a particular resonant condition for a given model were found by using analytical method but failed to represent the system stability over parameter values near and off the stationary points. Accordingly, as an extension of the previous work, this study performs numerical experiment to investigate the stability of the system across the parameter space and determines stable and unstable regions of the design parameters of the system.

Numerical FEM modeling in dental implantology

NASA Astrophysics Data System (ADS)

Roateşi, Iulia; Roateşi, Simona

2016-06-01

This paper is devoted to a numerical approach of the stress and displacement calculation of a system made up of dental implant, ceramic crown and surrounding bone. This is the simulation of a clinical situation involving both biological - the bone tissue, and non-biological - the implant and the crown, materials. On the other hand this problem deals with quite fine technical structure details - the threads, tapers, etc with a great impact in masticatory force transmission. Modeling the contact between the implant and the bone tissue is important to a proper bone-implant interface model and implant design. The authors proposed a three-dimensional numerical model to assess the biomechanical behaviour of this complex structure in order to evaluate its stability by determining the risk zones. A comparison between this numerical analysis and clinical cases is performed and a good agreement is obtained.

Truncation effect on Taylor-Aris dispersion in lattice Boltzmann schemes: Accuracy towards stability

NASA Astrophysics Data System (ADS)

Ginzburg, Irina; Roux, Laetitia

2015-10-01

The Taylor dispersion in parabolic velocity field provides a well-known benchmark for advection-diffusion (ADE) schemes and serves as a first step towards accurate modeling of the high-order non-Gaussian effects in heterogeneous flow. While applying the Lattice Boltzmann ADE two-relaxation-times (TRT) scheme for a transport with given Péclet number (Pe) one should select six free-tunable parameters, namely, (i) molecular-diffusion-scale, equilibrium parameter; (ii) three families of equilibrium weights, assigned to the terms of mass, velocity and numerical-diffusion-correction, and (iii) two relaxation rates. We analytically and numerically investigate the respective roles of all these degrees of freedom in the accuracy and stability in the evolution of a Gaussian plume. For this purpose, the third- and fourth-order transient multi-dimensional analysis of the recurrence equations of the TRT ADE scheme is extended for a spatially-variable velocity field. The key point is in the coupling of the truncation and Taylor dispersion analysis which allows us to identify the second-order numerical correction δkT to Taylor dispersivity coefficient kT. The procedure is exemplified for a straight Poiseuille flow where δkT is given in a closed analytical form in equilibrium and relaxation parameter spaces. The predicted longitudinal dispersivity is in excellent agreement with the numerical experiments over a wide parameter range. In relatively small Pe-range, the relative dispersion error increases with Péclet number. This deficiency reduces in the intermediate and high Pe-range where it becomes Pe-independent and velocity-amplitude independent. Eliminating δkT by a proper parameter choice and employing specular reflection for zero flux condition on solid boundaries, the d2Q9 TRT ADE scheme may reproduce the Taylor-Aris result quasi-exactly, from very coarse to fine grids, and from very small to arbitrarily high Péclet numbers. Since free-tunable product of two

Basic numerical competences in large-scale assessment data: Structure and long-term relevance.

PubMed

Hirsch, Stefa; Lambert, Katharina; Coppens, Karien; Moeller, Korbinian

2018-03-01

Basic numerical competences are seen as building blocks for later numerical and mathematical achievement. The current study aimed at investigating the structure of early numeracy reflected by different basic numerical competences in kindergarten and its predictive value for mathematical achievement 6 years later using data from large-scale assessment. This allowed analyses based on considerably large sample sizes (N > 1700). A confirmatory factor analysis indicated that a model differentiating five basic numerical competences at the end of kindergarten fitted the data better than a one-factor model of early numeracy representing a comprehensive number sense. In addition, these basic numerical competences were observed to reliably predict performance in a curricular mathematics test in Grade 6 even after controlling for influences of general cognitive ability. Thus, our results indicated a differentiated view on early numeracy considering basic numerical competences in kindergarten reflected in large-scale assessment data. Consideration of different basic numerical competences allows for evaluating their specific predictive value for later mathematical achievement but also mathematical learning difficulties. Copyright © 2017 Elsevier Inc. All rights reserved.

School Stability: Improving Academic Achievement for NJ Foster Children. Policy Brief

ERIC Educational Resources Information Center

Bernard-Rance, Kourtney; Parello, Nancy

2014-01-01

Children in New Jersey's foster care system are more likely to remain in their home school when they enter foster care, thanks to a law passed in 2010, giving these fragile children improved educational stability. The law allows children to remain in their "school of origin" when they are placed in foster care, even if the foster home is…

Optimal Recursive Digital Filters for Active Bending Stabilization

NASA Technical Reports Server (NTRS)

Orr, Jeb S.

2013-01-01

In the design of flight control systems for large flexible boosters, it is common practice to utilize active feedback control of the first lateral structural bending mode so as to suppress transients and reduce gust loading. Typically, active stabilization or phase stabilization is achieved by carefully shaping the loop transfer function in the frequency domain via the use of compensating filters combined with the frequency response characteristics of the nozzle/actuator system. In this paper we present a new approach for parameterizing and determining optimal low-order recursive linear digital filters so as to satisfy phase shaping constraints for bending and sloshing dynamics while simultaneously maximizing attenuation in other frequency bands of interest, e.g. near higher frequency parasitic structural modes. By parameterizing the filter directly in the z-plane with certain restrictions, the search space of candidate filter designs that satisfy the constraints is restricted to stable, minimum phase recursive low-pass filters with well-conditioned coefficients. Combined with optimal output feedback blending from multiple rate gyros, the present approach enables rapid and robust parametrization of autopilot bending filters to attain flight control performance objectives. Numerical results are presented that illustrate the application of the present technique to the development of rate gyro filters for an exploration-class multi-engined space launch vehicle.

Stability analysis of neural networks with time-varying delay: Enhanced stability criteria and conservatism comparisons

NASA Astrophysics Data System (ADS)

Lin, Wen-Juan; He, Yong; Zhang, Chuan-Ke; Wu, Min

2018-01-01

This paper is concerned with the stability analysis of neural networks with a time-varying delay. To assess system stability accurately, the conservatism reduction of stability criteria has attracted many efforts, among which estimating integral terms as exact as possible is a key issue. At first, this paper develops a new relaxed integral inequality to reduce the estimation gap of popular Wirtinger-based inequality (WBI). Then, for showing the advantages of the proposed inequality over several existing inequalities that also improve the WBI, four stability criteria are derived through different inequalities and the same Lyapunov-Krasovskii functional (LKF), and the conservatism comparison of them is analyzed theoretically. Moreover, an improved criterion is established by combining the proposed inequality and an augmented LKF with delay-product-type terms. Finally, several numerical examples are used to demonstrate the advantages of the proposed method.

An embedded mesh method using piecewise constant multipliers with stabilization: mathematical and numerical aspects

DOE PAGES

Puso, M. A.; Kokko, E.; Settgast, R.; ...

2014-10-22

An embedded mesh method using piecewise constant multipliers originally proposed by Puso et al. (CMAME, 2012) is analyzed here to determine effects of the pressure stabilization term and small cut cells. The approach is implemented for transient dynamics using the central difference scheme for the time discretization. It is shown that the resulting equations of motion are a stable linear system with a condition number independent of mesh size. Furthermore, we show that the constraints and the stabilization terms can be recast as non-proportional damping such that the time integration of the scheme is provably stable with a critical timemore » step computed from the undamped equations of motion. Effects of small cuts are discussed throughout the presentation. A mesh study is conducted to evaluate the effects of the stabilization on the discretization error and conditioning and is used to recommend an optimal value for stabilization scaling parameter. Several nonlinear problems are also analyzed and compared with comparable conforming mesh results. Finally, we show several demanding problems highlighting the robustness of the proposed approach.« less

Numerical Simulation And Experimental Investigation Of The Lift-Off And Blowout Of Enclosed Laminar Flames

NASA Technical Reports Server (NTRS)

Venuturmilli, Rajasekhar; Zhang, Yong; Chen, Lea-Der

2003-01-01

Enclosed flames are found in many industrial applications such as power plants, gas-turbine combustors and jet engine afterburners. A better understanding of the burner stability limits can lead to development of combustion systems that extend the lean and rich limits of combustor operations. This paper reports a fundamental study of the stability limits of co-flow laminar jet diffusion flames. A numerical study was conducted that used an adaptive mesh refinement scheme in the calculation. Experiments were conducted in two test rigs with two different fuels and diluted with three inert species. The numerical stability limits were compared with microgravity experimental data. Additional normal-gravity experimental results were also presented.

Numerical investigation of the pseudopotential lattice Boltzmann modeling of liquid-vapor for multi-phase flows

NASA Astrophysics Data System (ADS)

Nemati, Maedeh; Shateri Najaf Abady, Ali Reza; Toghraie, Davood; Karimipour, Arash

2018-01-01

The incorporation of different equations of state into single-component multiphase lattice Boltzmann model is considered in this paper. The original pseudopotential model is first detailed, and several cubic equations of state, the Redlich-Kwong, Redlich-Kwong-Soave, and Peng-Robinson are then incorporated into the lattice Boltzmann model. A comparison of the numerical simulation achievements on the basis of density ratios and spurious currents is used for presentation of the details of phase separation in these non-ideal single-component systems. The paper demonstrates that the scheme for the inter-particle interaction force term as well as the force term incorporation method matters to achieve more accurate and stable results. The velocity shifting method is demonstrated as the force term incorporation method, among many, with accuracy and stability results. Kupershtokh scheme also makes it possible to achieve large density ratio (up to 104) and to reproduce the coexistence curve with high accuracy. Significant reduction of the spurious currents at vapor-liquid interface is another observation. High-density ratio and spurious current reduction resulted from the Redlich-Kwong-Soave and Peng-Robinson EOSs, in higher accordance with the Maxwell construction results.

Local bounds preserving stabilization for continuous Galerkin discretization of hyperbolic systems

NASA Astrophysics Data System (ADS)

Mabuza, Sibusiso; Shadid, John N.; Kuzmin, Dmitri

2018-05-01

The objective of this paper is to present a local bounds preserving stabilized finite element scheme for hyperbolic systems on unstructured meshes based on continuous Galerkin (CG) discretization in space. A CG semi-discrete scheme with low order artificial dissipation that satisfies the local extremum diminishing (LED) condition for systems is used to discretize a system of conservation equations in space. The low order artificial diffusion is based on approximate Riemann solvers for hyperbolic conservation laws. In this case we consider both Rusanov and Roe artificial diffusion operators. In the Rusanov case, two designs are considered, a nodal based diffusion operator and a local projection stabilization operator. The result is a discretization that is LED and has first order convergence behavior. To achieve high resolution, limited antidiffusion is added back to the semi-discrete form where the limiter is constructed from a linearity preserving local projection stabilization operator. The procedure follows the algebraic flux correction procedure usually used in flux corrected transport algorithms. To further deal with phase errors (or terracing) common in FCT type methods, high order background dissipation is added to the antidiffusive correction. The resulting stabilized semi-discrete scheme can be discretized in time using a wide variety of time integrators. Numerical examples involving nonlinear scalar Burgers equation, and several shock hydrodynamics simulations for the Euler system are considered to demonstrate the performance of the method. For time discretization, Crank-Nicolson scheme and backward Euler scheme are utilized.

Structural Stability of Mathematical Models of National Economy

NASA Astrophysics Data System (ADS)

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

2011-12-01

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

Assessing the Psychometric Properties of the Achievement Goals Questionnaire across Task Contexts

ERIC Educational Resources Information Center

Muis, Krista R.; Winne, Philip H.

2012-01-01

A program of research is necessary to examine the psychometric properties of instruments designed to measure individuals' achievement goal orientations. Recently, research on achievement goal orientation has examined the stability of achievement goals to assess how context might influence individuals' achievement goals. Accordingly, studies are…

A priori stability results for PFC

NASA Astrophysics Data System (ADS)

Rossiter, J. A.

2017-02-01

Despite its popularity in industry and obvious efficacy, predictive functional control has few rigorous a priori stability results in the literature. In many cases, common sense and intuition with some trial and error are the main design tools. This paper seeks to tackle that gap by providing some analysis of the control law and showing what forms of stability assurances can be given and how these depend on the user choices of coincidence horizon and desired closed-loop pole. The conditions are separated into necessary, but not sufficient conditions for stability and, conversely, sufficient but not necessary conditions. Numerical examples demonstrate the efficacy of these conditions and the ease of use.

The Superconducting Cavity Stabilized Oscillator

NASA Technical Reports Server (NTRS)

Turneaure, J. P.; Buchman, Saps; Lipa, John

1997-01-01

Superconducting Cavity Stabilized Oscillators (SCSOs) have produced the most stable clocks to date for integration times between 10(exp 2) and 10(exp 3) seconds, achieving a fractional frequency stability of 2 x 10(exp -16) for a sampling time of 100 s. The principal contributors to cavity frequency variations are: (1) acceleration effects due to gravity and vibrations; (2) temperature variations; (3) variations in the energy stored in the cavity; and (4) noise introduced by the frequency stabilization circuit. We discuss the prospects for improvements in all these areas for both ground-based and space-based SCSOs, which may lead to SCSOs with fractional frequency stabilities below 10(exp -17). SCSOs of this frequency stability will be useful for testing fundamental physical principles.

Numerical Researches on Dynamical Systems with Relativistic Spin

NASA Astrophysics Data System (ADS)

Han, W. B.

2010-04-01

It is well known that spinning compact binaries are one of the most important research objects in the universe. Especially, EMRIs (extreme mass ratio inspirals) involving stellar compact objects which orbit massive black holes, are considered to be primary sources of gravitational radiation (GW) which could be detected by the space-based interferometer LISA. GW signals from EMRIs can be used to test general relativity, measure the masses and spins of central black holes and study essential physics near horizons. Compared with the situation without spin, the complexity of extreme objects, most of which rotate very fast, is much higher. So the dynamics of EMRI systems are numerically and analytically studied. We focus on how the spin effects on the dynamics of these systems and the produced GW radiations. Firstly, an ideal model of spinning test particles around Kerr black hole is considered. For equatorial orbits, we present the correct expression of effective potential and analyze the stability of circular orbits. Especially, the gravitational binding energy and frame-dragging effect of extreme Kerr black hole are much bigger than those without spin. For general orbits, spin can monotonically enlarge orbital inclination and destroy the symmetry of orbits about equatorial plane. It is the most important that extreme spin can produce orbital chaos. By carefully investigating the relations between chaos and orbital parameters, we point out that chaos usually appears for orbits with small pericenter, big eccentricity and orbital inclination. It is emphasized that Poincaré section method is invalid to detect the chaos of spinning particles, and the way of systems toward chaos is the period-doubling bifurcation. Furthermore, we study how spins effect on GW radiations from spinning test particles orbiting Kerr black holes. It is found that spins can increase orbit eccentricity and then make h+ component be detected more easily. But for h× component, because spins change

Numerical Modeling in Geodynamics: Success, Failure and Perspective

NASA Astrophysics Data System (ADS)

Ismail-Zadeh, A.

2005-12-01

A real success in numerical modeling of dynamics of the Earth can be achieved only by multidisciplinary research teams of experts in geodynamics, applied and pure mathematics, and computer science. The success in numerical modeling is based on the following basic, but simple, rules. (i) People need simplicity most, but they understand intricacies best (B. Pasternak, writer). Start from a simple numerical model, which describes basic physical laws by a set of mathematical equations, and move then to a complex model. Never start from a complex model, because you cannot understand the contribution of each term of the equations to the modeled geophysical phenomenon. (ii) Study the numerical methods behind your computer code. Otherwise it becomes difficult to distinguish true and erroneous solutions to the geodynamic problem, especially when your problem is complex enough. (iii) Test your model versus analytical and asymptotic solutions, simple 2D and 3D model examples. Develop benchmark analysis of different numerical codes and compare numerical results with laboratory experiments. Remember that the numerical tool you employ is not perfect, and there are small bugs in every computer code. Therefore the testing is the most important part of your numerical modeling. (iv) Prove (if possible) or learn relevant statements concerning the existence, uniqueness and stability of the solution to the mathematical and discrete problems. Otherwise you can solve an improperly-posed problem, and the results of the modeling will be far from the true solution of your model problem. (v) Try to analyze numerical models of a geological phenomenon using as less as possible tuning model variables. Already two tuning variables give enough possibilities to constrain your model well enough with respect to observations. The data fitting sometimes is quite attractive and can take you far from a principal aim of your numerical modeling: to understand geophysical phenomena. (vi) If the number of

Stability boundaries for command augmentation systems

NASA Technical Reports Server (NTRS)

Shrivastava, P. C.

1987-01-01

The Stability Augmentation System (SAS) is a special case of the Command Augmentation System (CAS). Control saturation imposes bounds on achievable commands. The state equilibrium depends only on the open loop dynamics and control deflection. The control magnitude to achieve a desired command equilibrium is independent of the feedback gain. A feedback controller provides the desired response, maintains the system equilibrium under disturbances, but it does not affect the equilibrium values of states and control. The saturation boundaries change with commands, but the location of the equilibrium points in the saturated region remains unchanged. Nonzero command vectors yield saturation boundaries that are asymmetric with respect to the state equilibrium. Except for the saddle point case with MCE control law, the stability boundaries change with commands. For the cases of saddle point and unstable nodes, the region of stability decreases with increasing command magnitudes.

Numerical simulation of a two-sex human papillomavirus (HPV) vaccination model

NASA Astrophysics Data System (ADS)

Suryani, I.; Adi-Kusumo, F.

2014-02-01

Human Papillomavirus (HPV) is a major cause of cervical cancer, precancerous lesions, cancer and other disease. HPV is the most common sexually transmitted infection. Although HPV virus primarily affects woman but it can also affects man because it cause of cancer of the anus, vulva, vagina, penis and some other cancers. HPV vaccines now used to prevent cervical cancer and genital warts because the vaccine protect against four types of HPV that most commonly cause disease are types 6, 11, 16, and 18. This paper is sequel work of Elbasha (2008). Difference with Elbasha (2008) are give alternative proof global stability, numerical simulation and interpretation. Global stability of the equilibrium on the model of a two-sex HPV vaccination were explored by using Lyapunov. Although we use the same lyapunov function, we use the largest invariant set to proof the global stability. The result show that the global stability of the equilibrium depends on the effective reproduction number (R). If R < 1 then the infection-free equilibrium is asymptotically stable globally. If R > 1 then endemic equilibrium have globally asymptotically stable properties. Then equilibrium proceed with the interpretation of numerical simulation.

Interpreting Popov criteria in Lure´ systems with complex scaling stability analysis

NASA Astrophysics Data System (ADS)

Zhou, J.

2018-06-01

The paper presents a novel frequency-domain interpretation of Popov criteria for absolute stability in Lure´ systems by means of what we call complex scaling stability analysis. The complex scaling technique is developed for exponential/asymptotic stability in LTI feedback systems, which dispenses open-loop poles distribution, contour/locus orientation and prior frequency sweeping. Exploiting the technique for alternatively revealing positive realness of transfer functions, re-interpreting Popov criteria is explicated. More specifically, the suggested frequency-domain stability conditions are conformable both in scalar and multivariable cases, and can be implemented either graphically with locus plotting or numerically without; in particular, the latter is suitable as a design tool with auxiliary parameter freedom. The interpretation also reveals further frequency-domain facts about Lure´ systems. Numerical examples are included to illustrate the main results.

Numerical analysis of a fluidic oscillator

NASA Astrophysics Data System (ADS)

Hoettges, Stefan; Schenkel, Torsten; Oertel, Herbert

2010-11-01

The technology of fluid logic or fluidic has its origins in 1959 when scientists were looking for alternatives to electronics to realize measuring or automatic control tasks. In recent years interest in fluidic components has been renewed. Possible applications of fluidic oscillators have been tested in flow control, to reduce or eliminate separation regions, to avoid resonance noise in the flow past cavities, to improve combustion processes or for efficient cooling of turbine blades or electronic components. The oscillatory motion of the jet is achieved only by suitable shaping of the nozzle geometry and fluid-dynamic interactions, hence no moving components or external sources of energy are necessary. Therefore fluidic oscillators can be used in extreme environmental conditions, such as high temperatures, aggressive media or within electromagnetic fields. In the present study the working principle of the fluidic oscillator has been identified using three-dimensional unsteady RANS simulations and stability analysis. The numerical models used have been validated successfully against experimental data. Furthermore the effects of changes in inlet velocity, geometry and working fluid on the oscillation frequency have been investigated. Based on the results a new dimensionless number has been derived in order to characterize the unsteady behavior of the fluidic oscillator.

Culturally Responsive Pedagogies in Arizona and Latino Students' Achievement

ERIC Educational Resources Information Center

López, Francesca A.

2016-01-01

Background: Despite numerous educational reform efforts aimed at aggressively addressing achievement disparities, Latinos continue to underperform in school. In sharp contrast to the belief that the inordinate achievement disparities among Latino students stem from deficiencies, some researchers assert that culturally responsive teaching (CRT)…

Relationship between the Wide Range Achievement Test 3 and the Wechsler Individual Achievement Test.

PubMed

Smith, T D; Smith, B L

1998-12-01

The present study examined the relationship between the Wide Range Achievement Test 3 and the Wechsler Individual Achievement Test for a sample of children with learning disabilities in two rural school districts. Data were collected for 87 school children who had been classified as learning disabled and placed in special education resource services. Pearson product-moment correlations between scores on the two measures were significant and moderate to high; however, mean scores were not significantly different on Reading, Spelling, and Arithmetic subtests of the Wide Range Achievement Test 3 compared to those for the basic Reading, Spelling, and Mathematics Reasoning subtests of the Wechsler Individual Achievement Test. Although there were significant mean differences between scores on Reading and Reading Comprehension and on Arithmetic and Numerical Operations, magnitudes were small. It appears that the two tests provide similar results when screening for reading, spelling, and arithmetic.

p21 stability: linking chaperones to a cell cycle checkpoint.

PubMed

Liu, Geng; Lozano, Guillermina

2005-02-01

Progression through the cell cycle is regulated by numerous proteins, one of which is the cyclin-dependent kinase inhibitor, p21. A new study identifies a novel protein complex that stabilizes p21. The stability of this complex is critical in effecting the p53-mediated cell cycle checkpoint.

Towards standard testbeds for numerical relativity

NASA Astrophysics Data System (ADS)

Alcubierre, Miguel; Allen, Gabrielle; Bona, Carles; Fiske, David; Goodale, Tom; Guzmán, F. Siddhartha; Hawke, Ian; Hawley, Scott H.; Husa, Sascha; Koppitz, Michael; Lechner, Christiane; Pollney, Denis; Rideout, David; Salgado, Marcelo; Schnetter, Erik; Seidel, Edward; Shinkai, Hisa-aki; Shoemaker, Deirdre; Szilágyi, Béla; Takahashi, Ryoji; Winicour, Jeff

2004-01-01

In recent years, many different numerical evolution schemes for Einstein's equations have been proposed to address stability and accuracy problems that have plagued the numerical relativity community for decades. Some of these approaches have been tested on different spacetimes, and conclusions have been drawn based on these tests. However, differences in results originate from many sources, including not only formulations of the equations, but also gauges, boundary conditions, numerical methods and so on. We propose to build up a suite of standardized testbeds for comparing approaches to the numerical evolution of Einstein's equations that are designed to both probe their strengths and weaknesses and to separate out different effects, and their causes, seen in the results. We discuss general design principles of suitable testbeds, and we present an initial round of simple tests with periodic boundary conditions. This is a pivotal first step towards building a suite of testbeds to serve the numerical relativists and researchers from related fields who wish to assess the capabilities of numerical relativity codes. We present some examples of how these tests can be quite effective in revealing various limitations of different approaches, and illustrating their differences. The tests are presently limited to vacuum spacetimes, can be run on modest computational resources and can be used with many different approaches used in the relativity community.

DYNAMIC NEUROMUSCULAR STABILIZATION & SPORTS REHABILITATION

PubMed Central

Kobesova, Alena; Kolar, Pavel

2013-01-01

Dynamic neuromuscular (core) stability is necessary for optimal athletic performance and is not achieved purely by adequate strength of abdominals, spinal extensors, gluteals or any other musculature; rather, core stabilization is accomplished through precise coordination of these muscles and intra‐abdominal pressure regulation by the central nervous system. Understanding developmental kinesiology provides a framework to appreciate the regional interdependence and the inter‐linking of the skeleton, joints, musculature during movement and the importance of training both the dynamic and stabilizing function of muscles in the kinetic chain. The Dynamic Neuromuscular Stabilization (DNS) approach provides functional tools to assess and activate the intrinsic spinal stabilizers in order to optimize the movement system for both pre‐habilitation and rehabilitation of athletic injuries and performance. Level of Evidence: 5 PMID:23439921

Development of Online Raw Achievement Battery Test for Primary Level

ERIC Educational Resources Information Center

Hanif, Maria; Khan, Tamim Ahmed; Masroor, Uzma; Amjad, Amira

2017-01-01

Achievement test is a mechanism to measure student's knowledge and abilities. Numerous categories of achievement tests have been developed by different scholars and psychologists. Since they do not directly consider curriculum adopted during the course of study of students, they do not reflect truly upon the achievements of students. We propose an…

Global stability of plane Couette flow beyond the energy stability limit

NASA Astrophysics Data System (ADS)

Fuentes, Federico; Goluskin, David

2017-11-01

This talk will present computations verifying that the laminar state of plane Couette flow is nonlinearly stable to all perturbations. The Reynolds numbers up to which this globally stability is verified are larger than those at which stability can be proven by the energy method, which is the typical method for demonstrating nonlinear stability of a fluid flow. This improvement is achieved by constructing Lyapunov functions that are more general than the energy. These functions are not restricted to being quadratic, and they are allowed to depend explicitly on the spectrum of the velocity field in the eigenbasis of the energy stability operator. The optimal choice of such a Lyapunov function is a convex optimization problem, and it can be constructed with computer assistance by solving a semidefinite program. This general method will be described in a companion talk by David Goluskin; the present talk focuses on its application to plane Couette flow.

Stabilized finite element methods to simulate the conductances of ion channels

NASA Astrophysics Data System (ADS)

Tu, Bin; Xie, Yan; Zhang, Linbo; Lu, Benzhuo

2015-03-01

We have previously developed a finite element simulator, ichannel, to simulate ion transport through three-dimensional ion channel systems via solving the Poisson-Nernst-Planck equations (PNP) and Size-modified Poisson-Nernst-Planck equations (SMPNP), and succeeded in simulating some ion channel systems. However, the iterative solution between the coupled Poisson equation and the Nernst-Planck equations has difficulty converging for some large systems. One reason we found is that the NP equations are advection-dominated diffusion equations, which causes troubles in the usual FE solution. The stabilized schemes have been applied to compute fluids flow in various research fields. However, they have not been studied in the simulation of ion transport through three-dimensional models based on experimentally determined ion channel structures. In this paper, two stabilized techniques, the SUPG and the Pseudo Residual-Free Bubble function (PRFB) are introduced to enhance the numerical robustness and convergence performance of the finite element algorithm in ichannel. The conductances of the voltage dependent anion channel (VDAC) and the anthrax toxin protective antigen pore (PA) are simulated to validate the stabilization techniques. Those two stabilized schemes give reasonable results for the two proteins, with decent agreement with both experimental data and Brownian dynamics (BD) simulations. For a variety of numerical tests, it is found that the simulator effectively avoids previous numerical instability after introducing the stabilization methods. Comparison based on our test data set between the two stabilized schemes indicates both SUPG and PRFB have similar performance (the latter is slightly more accurate and stable), while SUPG is relatively more convenient to implement.

Experimental and Numerical Investigation of Vortical Structures in Lean Premixed Swirl-Stabilized Combustion

NASA Astrophysics Data System (ADS)

Taamallah, Soufien; Chakroun, Nadim; Shanbhogue, Santosh; Kewlani, Gaurav; Ghoniem, Ahmed

2015-11-01

A combined experimental and LES investigation is performed to identify the origin of major flow dynamics and vortical structures in a model gas turbine's swirl-stabilized turbulent combustor. Swirling flows in combustion lead to the formation of complex flow dynamics and vortical structures that can interact with flames and influence its stabilization. Our experimental results for non-reacting flow show the existence of large scale precession motion. The precessing vortex core (PVC) dynamics disappears with combustion but only above a threshold of equivalence ratio. In addition, large scale vortices along the inner shear layer (ISL) are observed. These structures interact with the ISL stabilized flame and contribute to its wrinkling. Next, the LES setup is validated against the flow field's low-order statistics and point temperature measurement in relevant areas of the chamber. Finally, we show that LES is capable of predicting the precession motion as well as the ISL vortices in the reacting case: we find that ISL vortices originate from a vortex core that is formed right downstream of the swirler's centerbody. The vortex core has a conical spiral shape resembling a corkscrew that interacts - as it winds out - with the flame when it reaches the ISL.

Comprehensive numerical methodology for direct numerical simulations of compressible Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reckinger, Scott James; Livescu, Daniel; Vasilyev, Oleg V.

A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.

Closing the Minority Achievement Gap in Math

ERIC Educational Resources Information Center

Holloway, John H.

2004-01-01

Minority students face numerous academic barriers for achievement in the classroom as well as outside the school. The National Council of Teachers of Mathematics (NCTM) suggests six principles for maintaining the standard of school mathematics.

Factors affecting the achievement of Japanese-style deep knee flexion after total knee arthroplasty using posterior-stabilized prosthesis with high-flex knee design.

PubMed

Niki, Yasuo; Takeda, Yuki; Harato, Kengo; Suda, Yasunori

2015-11-01

Achievement of very deep knee flexion after total knee arthroplasty (TKA) can play a critical role in the satisfaction of patients who demand a floor-sitting lifestyle and engage in high-flexion daily activities (e.g., seiza-sitting). Seiza-sitting is characterized by the knees flexed >145º and feet turned sole upwards underneath the buttocks with the tibia internally rotated. The present study investigated factors affecting the achievement of seiza-sitting after TKA using posterior-stabilized total knee prosthesis with high-flex knee design. Subjects comprised 32 patients who underwent TKA with high-flex knee prosthesis and achieved seiza-sitting (knee flexion >145º) postoperatively. Another 32 patients served as controls who were capable of knee flexion >145º preoperatively, but failed to achieve seiza-sitting postoperatively. Accuracy of femoral and tibial component positions was assessed in terms of deviation from the ideal position using a two-dimensional to three-dimensional matching technique. Accuracies of the component position, posterior condylar offset ratio and intraoperative gap length were compared between the two groups. The proportion of patients with >3º internally rotated tibial component was significantly higher in patients who failed at seiza-sitting (41 %) than among patients who achieved it (13 %, p = 0.021). Comparison of intraoperative gap length between patient groups revealed that gap length at 135º flexion was significantly larger in patients who achieved seiza-sitting (4.2 ± 0.4 mm) than in patients who failed at it (2.7 ± 0.4 mm, p = 0.007). Conversely, no significant differences in gap inclination were seen between the groups. From the perspective of surgical factors, accurate implant positioning, particularly rotational alignment of the tibial component, and maintenance of a sufficient joint gap at 135º flexion appear to represent critical factors for achieving >145º of deep knee flexion after TKA.

Cumulative carbon as a policy framework for achieving climate stabilization

PubMed Central

Matthews, H. Damon; Solomon, Susan; Pierrehumbert, Raymond

2012-01-01

The primary objective of the United Nations Framework Convention on Climate Change is to stabilize greenhouse gas concentrations at a level that will avoid dangerous climate impacts. However, greenhouse gas concentration stabilization is an awkward framework within which to assess dangerous climate change on account of the significant lag between a given concentration level and the eventual equilibrium temperature change. By contrast, recent research has shown that global temperature change can be well described by a given cumulative carbon emissions budget. Here, we propose that cumulative carbon emissions represent an alternative framework that is applicable both as a tool for climate mitigation as well as for the assessment of potential climate impacts. We show first that both atmospheric CO2 concentration at a given year and the associated temperature change are generally associated with a unique cumulative carbon emissions budget that is largely independent of the emissions scenario. The rate of global temperature change can therefore be related to first order to the rate of increase of cumulative carbon emissions. However, transient warming over the next century will also be strongly affected by emissions of shorter lived forcing agents such as aerosols and methane. Non-CO2 emissions therefore contribute to uncertainty in the cumulative carbon budget associated with near-term temperature targets, and may suggest the need for a mitigation approach that considers separately short- and long-lived gas emissions. By contrast, long-term temperature change remains primarily associated with total cumulative carbon emissions owing to the much longer atmospheric residence time of CO2 relative to other major climate forcing agents. PMID:22869803

Study report on guidelines and test procedures for investigating stability of nonlinear cardiovascular control system models

NASA Technical Reports Server (NTRS)

Fitzjerrell, D. G.

1974-01-01

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

A numerical study of variable density flow and mixing in porous media

NASA Astrophysics Data System (ADS)

Fan, Yin; Kahawita, René

1994-10-01

A numerical study of a negatively buoyant plume intruding into a neutrally stratified porous medium has been undertaken using finite different methods. Of particular interest has been to ascertain whether the experimentally observed gravitational instabilities that form along the lower edge of the plume are reproduced in the numerical model. The model has been found to faithfully reproduce the mean flow as well as the gravitational instabilities in the intruding plume. A linear stability analysis has confirmed the fact that the negatively buoyant plume is in fact gravitationally unstable and that the stability depends on two parameters: a concentration Rayleigh number and a characteristic length scale which is dependent on the transverse dispersivity.

Stability and stabilization of the lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Brownlee, R. A.; Gorban, A. N.; Levesley, J.

2007-03-01

We revisit the classical stability versus accuracy dilemma for the lattice Boltzmann methods (LBM). Our goal is a stable method of second-order accuracy for fluid dynamics based on the lattice Bhatnager-Gross-Krook method (LBGK). The LBGK scheme can be recognized as a discrete dynamical system generated by free flight and entropic involution. In this framework the stability and accuracy analysis are more natural. We find the necessary and sufficient conditions for second-order accurate fluid dynamics modeling. In particular, it is proven that in order to guarantee second-order accuracy the distribution should belong to a distinguished surface—the invariant film (up to second order in the time step). This surface is the trajectory of the (quasi)equilibrium distribution surface under free flight. The main instability mechanisms are identified. The simplest recipes for stabilization add no artificial dissipation (up to second order) and provide second-order accuracy of the method. Two other prescriptions add some artificial dissipation locally and prevent the system from loss of positivity and local blowup. Demonstration of the proposed stable LBGK schemes are provided by the numerical simulation of a one-dimensional (1D) shock tube and the unsteady 2D flow around a square cylinder up to Reynolds number Rẽ20000 .

Dynamic response and stability of a gas-lubricated Rayleigh-step pad

NASA Technical Reports Server (NTRS)

Cheng, C.; Cheng, H. S.

1973-01-01

The quasi-static, pressure characteristics of a gas-lubricated thrust bearing with shrouded, Rayleigh-step pads are determined for a time-varying film thickness. The axial response of the thrust bearing to an axial forcing function or an axial rotor disturbance is investigated by treating the gas film as a spring having nonlinear restoring and damping forces. These forces are related to the film thickness by a power relation. The nonlinear equation of motion in the axial mode is solved by the Ritz-Galerkin method as well as the direct, numerical integration. Results of the nonlinear response by both methods are compared with the response based on the linearized equation. Further, the gas-film instability of an infinitely wide Rayleigh step thrust pad is determined by solving the transient Reynolds equation coupled with the equation of the motion of the pad. Results show that the Rayleigh-step geometry is very stable for bearing number A up to 50. The stability threshold is shown to exist only for ultrahigh values of Lambda equal to or greater than 100, where the stability can be achieved by making the mass heavier than the critical mass.

Adapting livestock behaviour to achieve management goals

USDA-ARS?s Scientific Manuscript database

Using livestock to efficiently achieve management goals requires melding animal behavior with mechanical and electronic equipment. Practices such as autonomously obtaining individual animal liveweight when combined with individual animal electronic identification can produce numerous cost saving ad...

Geometric stability of topological lattice phases

PubMed Central

Jackson, T. S.; Möller, Gunnar; Roy, Rahul

2015-01-01

The fractional quantum Hall (FQH) effect illustrates the range of novel phenomena which can arise in a topologically ordered state in the presence of strong interactions. The possibility of realizing FQH-like phases in models with strong lattice effects has attracted intense interest as a more experimentally accessible venue for FQH phenomena which calls for more theoretical attention. Here we investigate the physical relevance of previously derived geometric conditions which quantify deviations from the Landau level physics of the FQHE. We conduct extensive numerical many-body simulations on several lattice models, obtaining new theoretical results in the process, and find remarkable correlation between these conditions and the many-body gap. These results indicate which physical factors are most relevant for the stability of FQH-like phases, a paradigm we refer to as the geometric stability hypothesis, and provide easily implementable guidelines for obtaining robust FQH-like phases in numerical or real-world experiments. PMID:26530311

Numerical investigation of CO{sub 2} emission and thermal stability of a convective and radiative stockpile of reactive material in a cylindrical pipe of variable thermal conductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lebelo, Ramoshweu Solomon, E-mail: sollyl@vut.ac.za

In this paper the CO{sub 2} emission and thermal stability in a long cylindrical pipe of combustible reactive material with variable thermal conductivity are investigated. It is assumed that the cylindrical pipe loses heat by both convection and radiation at the surface. The nonlinear differential equations governing the problem are tackled numerically using Runge-Kutta-Fehlberg method coupled with shooting technique method. The effects of various thermophysical parameters on the temperature and carbon dioxide fields, together with critical conditions for thermal ignition are illustrated and discussed quantitatively.

Computing Evans functions numerically via boundary-value problems

NASA Astrophysics Data System (ADS)

Barker, Blake; Nguyen, Rose; Sandstede, Björn; Ventura, Nathaniel; Wahl, Colin

2018-03-01

The Evans function has been used extensively to study spectral stability of travelling-wave solutions in spatially extended partial differential equations. To compute Evans functions numerically, several shooting methods have been developed. In this paper, an alternative scheme for the numerical computation of Evans functions is presented that relies on an appropriate boundary-value problem formulation. Convergence of the algorithm is proved, and several examples, including the computation of eigenvalues for a multi-dimensional problem, are given. The main advantage of the scheme proposed here compared with earlier methods is that the scheme is linear and scalable to large problems.

Do biodegradable magnesium alloy intramedullary interlocking nails prematurely lose fixation stability in the treatment of tibial fracture? A numerical simulation.

PubMed

Wang, Haosen; Hao, Zhixiu; Wen, Shizhu

2017-01-01

Intramedullary interlocking nailing is an effective technique used to treat long bone fractures. Recently, biodegradable metals have drawn increased attention as an intramedullary interlocking nailing material. In this study, numerical simulations were implemented to determine whether the degradation rate of magnesium alloy makes it a suitable material for manufacturing biodegradable intramedullary interlocking nails. Mechano-regulatory and bone-remodeling models were used to simulate the fracture healing process, and a surface corrosion model was used to simulate intramedullary rod degradation. The results showed that magnesium alloy intramedullary rods exhibited a satisfactory degradation rate; the fracture healed and callus enhancement was observed before complete dissolution of the intramedullary rod. Delayed magnesium degradation (using surface coating techniques) did not confer a significant advantage over the non-delayed degradation process; immediate degradation also achieved satisfactory healing outcomes. However, delayed degradation had no negative effect on callus enhancement, as it did not cause signs of stress shielding. To avoid risks of individual differences such as delayed union, delayed degradation is recommended. Although the magnesium intramedullary rod did not demonstrate rapid degradation, its ability to provide high fixation stiffness to achieve earlier load bearing was inferior to that of the conventional titanium alloy and stainless steel rods. Therefore, light physiological loads should be ensured during the early stages of healing to achieve bony healing; otherwise, with increased loading and degraded intramedullary rods, the fracture may ultimately fail to heal. Copyright © 2016 Elsevier Ltd. All rights reserved.

Learned Helplessness, Test Anxiety, and Academic Achievement: A Longitudinal Analysis.

ERIC Educational Resources Information Center

Fincham, Frank D.; And Others

1989-01-01

Examines the stability of individual differences in test anxiety and learned helplessness of 82 children in third grade and later in fifth grade. Results indicate that teacher reports of helplessness had the strongest and most consistent relation to concurrent achievement and to achievement test scores two years later. (RJC)

Residential Stability and Academic Sense of Control

ERIC Educational Resources Information Center

Gigliotti, Richard J.

1976-01-01

Suggests that stability level of an individual and the community in which he operates is directly related to a child's sense of control and consequently his achievement in school. Findings indicate that for whites, community stability is positively and significantly related to sense of control, with the inverse for blacks. (Author/AM)

Formation flying design and applications in weak stability boundary regions.

PubMed

Folta, David

2004-05-01

Weak stability regions serve as superior locations for interferomertric scientific investigations. These regions are often selected to minimize environmental disturbances and maximize observation efficiency. Designs of formations in these regions are becoming ever more challenging as more complex missions are envisioned. The development of algorithms to enable the capability for formation design must be further enabled to incorporate better understanding of weak stability boundary solution space. This development will improve the efficiency and expand the capabilities of current approaches. The Goddard Space Flight Center (GSFC) is currently supporting multiple formation missions in weak stability boundary regions. This end-to-end support consists of mission operations, trajectory design, and control. It also includes both algorithm and software development. The Constellation-X, Maxim, and Stellar Imager missions are examples of the use of improved numeric methods to attain constrained formation geometries and control their dynamical evolution. This paper presents a survey of formation missions in the weak stability boundary regions and a brief description of formation design using numerical and dynamical techniques.

The structure of non-hierarchical triple system stability regions

NASA Astrophysics Data System (ADS)

Martynova, A. I.; Orlov, V. V.; Rubinov, A. V.

2009-08-01

A detailed study of the two-dimensional initial conditions region section in the planar three-body problem is performed. The initial conditions for the three well-known stable periodic orbits (the Schubart’s orbit, the Broucke’s orbit and the eight-like orbit) belong to this section. Continuous stability regions (for the fixed integration interval) generated by these periodic orbits are found. Zones of the quick stability violation are outlined. The analysis of some concrete trajectories coming from various stability regions is performed. In particular, trajectories possessing varying number of “eights” formed by moving triple system components are discovered. Orbits with librations are also found. The new periodic orbit originated from the zone siding with the Schubart’s orbit region is discovered. This orbit has reversibility points (each of the outer bodies possess a reversibility point) and two points of close double approach of the central body to each of the outer bodies. The influence of the numerical integration accuracy on the results is studied. The stability regions structure is preserved during calculations with different values of the precision parameter, numerical integration methods and regularization algorithms of the equations of motion.

Guidelines for Computing Longitudinal Dynamic Stability Characteristics of a Subsonic Transport

NASA Technical Reports Server (NTRS)

Thompson, Joseph R.; Frank, Neal T.; Murphy, Patrick C.

2010-01-01

A systematic study is presented to guide the selection of a numerical solution strategy for URANS computation of a subsonic transport configuration undergoing simulated forced oscillation about its pitch axis. Forced oscillation is central to the prevalent wind tunnel methodology for quantifying aircraft dynamic stability derivatives from force and moment coefficients, which is the ultimate goal for the computational simulations. Extensive computations are performed that lead in key insights of the critical numerical parameters affecting solution convergence. A preliminary linear harmonic analysis is included to demonstrate the potential of extracting dynamic stability derivatives from computational solutions.

Numerical and experimental validation of a particle Galerkin method for metal grinding simulation

NASA Astrophysics Data System (ADS)

Wu, C. T.; Bui, Tinh Quoc; Wu, Youcai; Luo, Tzui-Liang; Wang, Morris; Liao, Chien-Chih; Chen, Pei-Yin; Lai, Yu-Sheng

2018-03-01

In this paper, a numerical approach with an experimental validation is introduced for modelling high-speed metal grinding processes in 6061-T6 aluminum alloys. The derivation of the present numerical method starts with an establishment of a stabilized particle Galerkin approximation. A non-residual penalty term from strain smoothing is introduced as a means of stabilizing the particle Galerkin method. Additionally, second-order strain gradients are introduced to the penalized functional for the regularization of damage-induced strain localization problem. To handle the severe deformation in metal grinding simulation, an adaptive anisotropic Lagrangian kernel is employed. Finally, the formulation incorporates a bond-based failure criterion to bypass the prospective spurious damage growth issues in material failure and cutting debris simulation. A three-dimensional metal grinding problem is analyzed and compared with the experimental results to demonstrate the effectiveness and accuracy of the proposed numerical approach.

On the Stability of Strange Dwarf Hybrid Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alford, Mark G.; Harris, Steven P.; Sachdeva, Pratik S., E-mail: harrissp@wustl.edu

2017-10-01

We investigate the stability of “strange dwarfs”: white-dwarf-sized stars with a density discontinuity between a small dense core of quark matter and a thick low-density mantle of degenerate electrons. Previous work on strange dwarfs suggested that such a discontinuity could stabilize stars that would have been classified as unstable by the conventional criteria based on extrema in the mass–radius relation. We investigate the stability of such stars by numerically solving the Sturm–Liouville equations for the lowest-energy modes of the star. We find that the conventional criteria are correct, and strange dwarfs are not stable.

Numerical and Calculation Abilities in Children with ADHD

ERIC Educational Resources Information Center

Colomer, Carla; Re, Anna M.; Miranda, Ana; Lucangeli, Daniela

2013-01-01

The aim of this study was to investigate the specific numerical and calculation abilities of 28 children with ADHD without comorbid mathematical learning disabilities (LD), ranging from the 1st to the 5th grade of primary school, and to examine the stability or the development of the arithmetic profile. Our results showed that a high percentage of…

Fraction Development in Children: Importance of Building Numerical Magnitude Understanding

ERIC Educational Resources Information Center

Jordan, Nancy C.; Carrique, Jessica; Hansen, Nicole; Resnick, Ilyse

2016-01-01

This chapter situates fraction learning within the integrated theory of numerical development. We argue that the understanding of numerical magnitudes for whole numbers as well as for fractions is critical to fraction learning in particular and mathematics achievement more generally. Results from the Delaware Longitudinal Study, which examined…

Prop-fan with improved stability

NASA Technical Reports Server (NTRS)

Rothman, Edward A. (Inventor); Violette, John A. (Inventor)

1988-01-01

Improved prop-fan stability is achieved by providing each blade of the prop-fan with a leading edge which, outwardly, from a location thereon at the mid-span of the blade, occupy generally a single plane.

Ferrofluids: Modeling, numerical analysis, and scientific computation

NASA Astrophysics Data System (ADS)

Tomas, Ignacio

This dissertation presents some developments in the Numerical Analysis of Partial Differential Equations (PDEs) describing the behavior of ferrofluids. The most widely accepted PDE model for ferrofluids is the Micropolar model proposed by R.E. Rosensweig. The Micropolar Navier-Stokes Equations (MNSE) is a subsystem of PDEs within the Rosensweig model. Being a simplified version of the much bigger system of PDEs proposed by Rosensweig, the MNSE are a natural starting point of this thesis. The MNSE couple linear velocity u, angular velocity w, and pressure p. We propose and analyze a first-order semi-implicit fully-discrete scheme for the MNSE, which decouples the computation of the linear and angular velocities, is unconditionally stable and delivers optimal convergence rates under assumptions analogous to those used for the Navier-Stokes equations. Moving onto the much more complex Rosensweig's model, we provide a definition (approximation) for the effective magnetizing field h, and explain the assumptions behind this definition. Unlike previous definitions available in the literature, this new definition is able to accommodate the effect of external magnetic fields. Using this definition we setup the system of PDEs coupling linear velocity u, pressure p, angular velocity w, magnetization m, and magnetic potential ϕ We show that this system is energy-stable and devise a numerical scheme that mimics the same stability property. We prove that solutions of the numerical scheme always exist and, under certain simplifying assumptions, that the discrete solutions converge. A notable outcome of the analysis of the numerical scheme for the Rosensweig's model is the choice of finite element spaces that allow the construction of an energy-stable scheme. Finally, with the lessons learned from Rosensweig's model, we develop a diffuse-interface model describing the behavior of two-phase ferrofluid flows and present an energy-stable numerical scheme for this model. For a

Special Year on Numerical Linear Algebra

DTIC Science & Technology

1988-09-01

ORNL) Worley, Pat (ORNL) A special acknowledgement should go to Mary Drake (UT) and Mitzy Denson (ORNL) who carried the burden of making the innumerable...a time step appropriate for the regular cells with no stability restriction. Entrance to Y-12 requires a pass. Contact Mitzy Denson (615) 574-3125 to...requires a pass. Contact Mitzy Denson (615) 574-3125 to obtain one. ’This seminar is part of the Special Year on Numerical Linear Algebra sponsored by the

Vibration-enhanced posture stabilization achieved by tactile supplementation: may blind individuals get extra benefits?

PubMed

Magalhães, Fernando Henrique; Kohn, André Fabio

2011-08-01

Diminished balance ability poses a serious health risk due to the increased likelihood of falling, and impaired postural stability is significantly associated with blindness and poor vision. Noise stimulation (by improving the detection of sub-threshold somatosensory information) and tactile supplementation (i.e., additional haptic information provided by an external contact surface) have been shown to improve the performance of the postural control system. Moreover, vibratory noise added to the source of tactile supplementation (e.g., applied to a surface that the fingertip touches) has been shown to enhance balance stability more effectively than tactile supplementation alone. In view of the above findings, in addition to the well established consensus that blind subjects show superior abilities in the use of tactile information, we hypothesized that blind subjects may take extra benefits from the vibratory noise added to the tactile supplementation and hence show greater improvements in postural stability than those observed for sighted subjects. If confirmed, this hypothesis may lay the foundation for the development of noise-based assistive devices (e.g., canes, walking sticks) for improving somatosensation and hence prevent falls in blind individuals. Copyright © 2011 Elsevier Ltd. All rights reserved.

Stability analysis of magnetized neutron stars - a semi-analytic approach

NASA Astrophysics Data System (ADS)

Herbrik, Marlene; Kokkotas, Kostas D.

2017-04-01

We implement a semi-analytic approach for stability analysis, addressing the ongoing uncertainty about stability and structure of neutron star magnetic fields. Applying the energy variational principle, a model system is displaced from its equilibrium state. The related energy density variation is set up analytically, whereas its volume integration is carried out numerically. This facilitates the consideration of more realistic neutron star characteristics within the model compared to analytical treatments. At the same time, our method retains the possibility to yield general information about neutron star magnetic field and composition structures that are likely to be stable. In contrast to numerical studies, classes of parametrized systems can be studied at once, finally constraining realistic configurations for interior neutron star magnetic fields. We apply the stability analysis scheme on polytropic and non-barotropic neutron stars with toroidal, poloidal and mixed fields testing their stability in a Newtonian framework. Furthermore, we provide the analytical scheme for dropping the Cowling approximation in an axisymmetric system and investigate its impact. Our results confirm the instability of simple magnetized neutron star models as well as a stabilization tendency in the case of mixed fields and stratification. These findings agree with analytical studies whose spectrum of model systems we extend by lifting former simplifications.

Numerical methods for multi-scale modeling of non-Newtonian flows

NASA Astrophysics Data System (ADS)

Symeonidis, Vasileios

This work presents numerical methods for the simulation of Non-Newtonian fluids in the continuum as well as the mesoscopic level. The former is achieved with Direct Numerical Simulation (DNS) spectral h/p methods, while the latter employs the Dissipative Particle Dynamics (DPD) technique. Physical results are also presented as a motivation for a clear understanding of the underlying numerical approaches. The macroscopic simulations employ two non-Newtonian models, namely the Reiner-Ravlin (RR) and the viscoelastic FENE-P model. (1) A spectral viscosity method defined by two parameters ε, M is used to stabilize the FENE-P conformation tensor c. Convergence studies are presented for different combinations of these parameters. Two boundary conditions for the tensor c are also investigated. (2) Agreement is achieved with other works for Stokes flow of a two-dimensional cylinder in a channel. Comparison of the axial normal stress and drag coefficient on the cylinder is presented. Further, similar results from unsteady two- and three-dimensional turbulent flows past a flat plate in a channel are shown. (3) The RR problem is formulated for nearly incompressible flows, with the introduction of a mathematically equivalent tensor formulation. A spectral viscosity method and polynomial over-integration are studied. Convergence studies, including a three-dimensional channel flow with a parallel slot, investigate numerical problems arising from elemental boundaries and sharp corners. (4) The round hole pressure problem is presented for Newtonian and RR fluids in geometries with different hole sizes. Comparison with experimental data is made for the Newtonian case. The flaw in the experimental assumptions of undisturbed pressure opposite the hole is revealed, while good agreement with the data is shown. The Higashitani-Pritchard kinematical theory for RR, fluids is recovered for round holes and an approximate formula for the RR Stokes hole pressure is presented. The mesoscopic

Super-sensitive time-resolved fluoroimmunoassay for thyroid-stimulating hormone utilizing europium(III) nanoparticle labels achieved by protein corona stabilization, short binding time, and serum preprocessing.

PubMed

Näreoja, Tuomas; Rosenholm, Jessica M; Lamminmäki, Urpo; Hänninen, Pekka E

2017-05-01

Thyrotropin or thyroid-stimulating hormone (TSH) is used as a marker for thyroid function. More precise and more sensitive immunoassays are needed to facilitate continuous monitoring of thyroid dysfunctions and to assess the efficacy of the selected therapy and dosage of medication. Moreover, most thyroid diseases are autoimmune diseases making TSH assays very prone to immunoassay interferences due to autoantibodies in the sample matrix. We have developed a super-sensitive TSH immunoassay utilizing nanoparticle labels with a detection limit of 60 nU L -1 in preprocessed serum samples by reducing nonspecific binding. The developed preprocessing step by affinity purification removed interfering compounds and improved the recovery of spiked TSH from serum. The sensitivity enhancement was achieved by stabilization of the protein corona of the nanoparticle bioconjugates and a spot-coated configuration of the active solid-phase that reduced sedimentation of the nanoparticle bioconjugates and their contact time with antibody-coated solid phase, thus making use of the higher association rate of specific binding due to high avidity nanoparticle bioconjugates. Graphical Abstract We were able to decrease the lowest limit of detection and increase sensitivity of TSH immunoassay using Eu(III)-nanoparticles. The improvement was achieved by decreasing binding time of nanoparticle bioconjugates by small capture area and fast circular rotation. Also, we applied a step to stabilize protein corona of the nanoparticles and a serum-preprocessing step with a structurally related antibody.

Stability Test for Transient-Temperature Calculations

NASA Technical Reports Server (NTRS)

Campbell, W.

1984-01-01

Graphical test helps assure numerical stability of calculations of transient temperature or diffusion in composite medium. Rectangular grid forms basis of two-dimensional finite-difference model for heat conduction or other diffusion like phenomena. Model enables calculation of transient heat transfer among up to four different materials that meet at grid point.

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

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan

2004-01-01

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.

El Salvador: Aid Compensates for Economic Losses but Achieves Little Growth

DTIC Science & Technology

1991-02-15

earthquake. Aid Helped Achieve Almost half of U.S. economic assistance to El Salvador has supported its Economic Stability but economy by providing cash to the...Economic Growth 15 Economic Stability but Conclusions 21 Little Growth Chapter 3 22 Maintaining Social Funds for Health and Education Are Limited 22...comments as appropriate. Page I I GAO/NSIAD-91-97 El Salvador Chapter 2 U.S. and Salvadoran Efforts Bring Economic Stability but Little Growth AID’S

Nonparallel stability of three-dimensional compressible boundary layers. Part 1: Stability analysis

NASA Technical Reports Server (NTRS)

El-Hady, N. M.

1980-01-01

A compressible linear stability theory is presented for nonparallel three-dimensional boundary-layer flows, taking into account the normal velocity component as well as the streamwise and spanwise variations of the basic flow. The method of multiple scales is used to account for the nonparallelism of the basic flow, and equations are derived for the spatial evolution of the disturbance amplitude and wavenumber. The numerical procedure for obtaining the solution of the nonparallel problem is outlined.

Admission Requirements for Teacher Education as a Factor of Achievement

ERIC Educational Resources Information Center

Lukaš, Mirko; Samardžic, Darko

2015-01-01

Numerous researches have demonstrated the enormous role of teachers in achievements of students. Educated and motivated teacher that cares about the success of students devotes more effort to preparing the lesson and thus provides the students better conditions for achieving results. The problem occurs when teachers are not equally qualified,…

Computerized Numerical Control Test Item Bank.

ERIC Educational Resources Information Center

Reneau, Fred; And Others

This guide contains 285 test items for use in teaching a course in computerized numerical control. All test items were reviewed, revised, and validated by incumbent workers and subject matter instructors. Items are provided for assessing student achievement in such aspects of programming and planning, setting up, and operating machines with…

Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers.

PubMed

Rosén, T; Einarsson, J; Nordmark, A; Aidun, C K; Lundell, F; Mehlig, B

2015-12-01

We numerically analyze the rotation of a neutrally buoyant spheroid in a shear flow at small shear Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small shear Reynolds number Re(a). As Re(a)→0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical predictions valid to linear order in Re(a) for the case of an unbounded shear. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at shear Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal shear Reynolds number predicts a bifurcation of the tumbling orbit at aspect ratio λ(c)≈0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the λ-Re(a) plane that reaches λ≈0.1275 at the smallest shear Reynolds number (Re(a)=1) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results.

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

NASA Astrophysics Data System (ADS)

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

2012-12-01

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

A Physics-Based Temperature Stabilization Criterion for Thermal Testing

NASA Technical Reports Server (NTRS)

Rickman, Steven L.; Ungar, Eugene K.

2009-01-01

Spacecraft testing specifications differ greatly in the criteria they specify for stability in thermal balance tests. Some specify a required temperature stabilization rate (the change in temperature per unit time, dT/dt), some specify that the final steady-state temperature be approached to within a specified difference, delta T , and some specify a combination of the two. The particular values for temperature stabilization rate and final temperature difference also vary greatly between specification documents. A one-size-fits-all temperature stabilization rate requirement does not yield consistent results for all test configurations because of differences in thermal mass and heat transfer to the environment. Applying a steady-state temperature difference requirement is problematic because the final test temperature is not accurately known a priori, especially for powered configurations. In the present work, a simplified, lumped-mass analysis has been used to explore the applicability of these criteria. A new, user-friendly, physics-based approach is developed that allows the thermal engineer to determine when an acceptable level of temperature stabilization has been achieved. The stabilization criterion can be predicted pre-test but must be refined during test to allow verification that the defined level of temperature stabilization has been achieved.

Non-Linear Spring Equations and Stability

ERIC Educational Resources Information Center

Fay, Temple H.; Joubert, Stephan V.

2009-01-01

We discuss the boundary in the Poincare phase plane for boundedness of solutions to spring model equations of the form [second derivative of]x + x + epsilonx[superscript 2] = Fcoswt and the [second derivative of]x + x + epsilonx[superscript 3] = Fcoswt and report the results of a systematic numerical investigation on the global stability of…

Developing Talents: A Longitudinal Examination of Intellectual Ability and Academic Achievement

ERIC Educational Resources Information Center

McCoach, D. Betsy; Yu, Huihui; Gottfried, Allen W.; Gottfried, Adele Eskeles

2017-01-01

The Fullerton Longitudinal Study offers a unique opportunity to model the stability of intelligence and achievement and their relations from elementary through secondary school. Using latent variable modeling, we fit a cross-lagged panel model to examine the relations between intelligence and achievement in two academic domains: mathematics and…

Stability of Detached Solidification

NASA Technical Reports Server (NTRS)

Mazuruk, K.; Volz, M. P.; Croell, A.

2009-01-01

Bridgman crystal growth can be conducted in the so-called "detached" solidification regime, where the growing crystal is detached from the crucible wall. A small gap between the growing crystal and the crucible wall, of the order of 100 micrometers or less, can be maintained during the process. A meniscus is formed at the bottom of the melt between the crystal and crucible wall. Under proper conditions, growth can proceed without collapsing the meniscus. The meniscus shape plays a key role in stabilizing the process. Thermal and other process parameters can also affect the geometrical steady-state stability conditions of solidification. The dynamic stability theory of the shaped crystal growth process has been developed by Tatarchenko. It consists of finding a simplified autonomous set of differential equations for the radius, height, and possibly other process parameters. The problem then reduces to analyzing a system of first order linear differential equations for stability. Here we apply a modified version of this theory for a particular case of detached solidification. Approximate analytical formulas as well as accurate numerical values for the capillary stability coefficients are presented. They display an unexpected singularity as a function of pressure differential. A novel approach to study the thermal field effects on the crystal shape stability has been proposed. In essence, it rectifies the unphysical assumption of the model that utilizes a perturbation of the crystal radius along the axis as being instantaneous. It consists of introducing time delay effects into the mathematical description and leads, in general, to stability over a broader parameter range. We believe that this novel treatment can be advantageously implemented in stability analyses of other crystal growth techniques such as Czochralski and float zone methods.

Theoretical prediction of the energy stability of graphene nanoblisters

NASA Astrophysics Data System (ADS)

Glukhova, O. E.; Slepchenkov, M. M.; Barkov, P. V.

2018-04-01

The paper presents the results of a theoretical prediction of the energy stability of graphene nanoblisters with various geometrical parameters. As a criterion for the evaluation of the stability of investigated carbon objects we propose to consider the value of local stress of the nanoblister atomic grid. Numerical evaluation of stresses experienced by atoms of the graphene blister framework was carried out by means of an original method for calculation of local stresses that is based on energy approach. Atomistic models of graphene nanoblisters corresponding to the natural experiment data were built for the first time in this work. New physical regularities of the influence of topology on the thermodynamic stability of nanoblisters were established as a result of the analysis of the numerical experiment data. We built the distribution of local stresses for graphene blister structures, whose atomic grid contains a variety of structural defects. We have shown how the concentration and location of defects affect the picture of the distribution of the maximum stresses experienced by the atoms of the nanoblisters.

Stabilization Approaches for Linear and Nonlinear Reduced Order Models

NASA Astrophysics Data System (ADS)

Rezaian, Elnaz; Wei, Mingjun

2017-11-01

It has been a major concern to establish reduced order models (ROMs) as reliable representatives of the dynamics inherent in high fidelity simulations, while fast computation is achieved. In practice it comes to stability and accuracy of ROMs. Given the inviscid nature of Euler equations it becomes more challenging to achieve stability, especially where moving discontinuities exist. Originally unstable linear and nonlinear ROMs are stabilized here by two approaches. First, a hybrid method is developed by integrating two different stabilization algorithms. At the same time, symmetry inner product is introduced in the generation of ROMs for its known robust behavior for compressible flows. Results have shown a notable improvement in computational efficiency and robustness compared to similar approaches. Second, a new stabilization algorithm is developed specifically for nonlinear ROMs. This method adopts Particle Swarm Optimization to enforce a bounded ROM response for minimum discrepancy between the high fidelity simulation and the ROM outputs. Promising results are obtained in its application on the nonlinear ROM of an inviscid fluid flow with discontinuities. Supported by ARL.

Exponential stability of stochastic complex networks with multi-weights based on graph theory

NASA Astrophysics Data System (ADS)

Zhang, Chunmei; Chen, Tianrui

2018-04-01

In this paper, a novel approach to exponential stability of stochastic complex networks with multi-weights is investigated by means of the graph-theoretical method. New sufficient conditions are provided to ascertain the moment exponential stability and almost surely exponential stability of stochastic complex networks with multiple weights. It is noted that our stability results are closely related with multi-weights and the intensity of stochastic disturbance. Numerical simulations are also presented to substantiate the theoretical results.

Thermo-Mechanical Methodology for Stabilizing Shape Memory Alloy Response

NASA Technical Reports Server (NTRS)

Padula, Santo

2013-01-01

This innovation is capable of significantly reducing the amount of time required to stabilize the strain-temperature response of a shape memory alloy (SMA). Unlike traditional stabilization processes that take days to weeks to achieve stabilized response, this innovation accomplishes stabilization in a matter of minutes, thus making it highly useful for the successful and practical implementation of SMA-based technologies in real-world applications. The innovation can also be applied to complex geometry components, not just simple geometries like wires or rods.

Magnitude knowledge: the common core of numerical development.

PubMed

Siegler, Robert S

2016-05-01

The integrated theory of numerical development posits that a central theme of numerical development from infancy to adulthood is progressive broadening of the types and ranges of numbers whose magnitudes are accurately represented. The process includes four overlapping trends: (1) representing increasingly precisely the magnitudes of non-symbolic numbers, (2) connecting small symbolic numbers to their non-symbolic referents, (3) extending understanding from smaller to larger whole numbers, and (4) accurately representing the magnitudes of rational numbers. The present review identifies substantial commonalities, as well as differences, in these four aspects of numerical development. With both whole and rational numbers, numerical magnitude knowledge is concurrently correlated with, longitudinally predictive of, and causally related to multiple aspects of mathematical understanding, including arithmetic and overall math achievement. Moreover, interventions focused on increasing numerical magnitude knowledge often generalize to other aspects of mathematics. The cognitive processes of association and analogy seem to play especially large roles in this development. Thus, acquisition of numerical magnitude knowledge can be seen as the common core of numerical development. © 2016 John Wiley & Sons Ltd.

For numerical differentiation, dimensionality can be a blessing!

NASA Astrophysics Data System (ADS)

Anderssen, Robert S.; Hegland, Markus

Finite difference methods, such as the mid-point rule, have been applied successfully to the numerical solution of ordinary and partial differential equations. If such formulas are applied to observational data, in order to determine derivatives, the results can be disastrous. The reason for this is that measurement errors, and even rounding errors in computer approximations, are strongly amplified in the differentiation process, especially if small step-sizes are chosen and higher derivatives are required. A number of authors have examined the use of various forms of averaging which allows the stable computation of low order derivatives from observational data. The size of the averaging set acts like a regularization parameter and has to be chosen as a function of the grid size h. In this paper, it is initially shown how first (and higher) order single-variate numerical differentiation of higher dimensional observational data can be stabilized with a reduced loss of accuracy than occurs for the corresponding differentiation of one-dimensional data. The result is then extended to the multivariate differentiation of higher dimensional data. The nature of the trade-off between convergence and stability is explicitly characterized, and the complexity of various implementations is examined.

Numerical Analysis of Ginzburg-Landau Models for Superconductivity.

NASA Astrophysics Data System (ADS)

Coskun, Erhan

Thin film conventional, as well as High T _{c} superconductors of various geometric shapes placed under both uniform and variable strength magnetic field are studied using the universially accepted macroscopic Ginzburg-Landau model. A series of new theoretical results concerning the properties of solution is presented using the semi -discrete time-dependent Ginzburg-Landau equations, staggered grid setup and natural boundary conditions. Efficient serial algorithms including a novel adaptive algorithm is developed and successfully implemented for solving the governing highly nonlinear parabolic system of equations. Refinement technique used in the adaptive algorithm is based on modified forward Euler method which was also developed by us to ease the restriction on time step size for stability considerations. Stability and convergence properties of forward and modified forward Euler schemes are studied. Numerical simulations of various recent physical experiments of technological importance such as vortes motion and pinning are performed. The numerical code for solving time-dependent Ginzburg-Landau equations is parallelized using BlockComm -Chameleon and PCN. The parallel code was run on the distributed memory multiprocessors intel iPSC/860, IBM-SP1 and cluster of Sun Sparc workstations, all located at Mathematics and Computer Science Division, Argonne National Laboratory.

Linear feedback stabilization of a dispersively monitored qubit

NASA Astrophysics Data System (ADS)

Patti, Taylor Lee; Chantasri, Areeya; García-Pintos, Luis Pedro; Jordan, Andrew N.; Dressel, Justin

2017-08-01

The state of a continuously monitored qubit evolves stochastically, exhibiting competition between coherent Hamiltonian dynamics and diffusive partial collapse dynamics that follow the measurement record. We couple these distinct types of dynamics together by linearly feeding the collected record for dispersive energy measurements directly back into a coherent Rabi drive amplitude. Such feedback turns the competition cooperative and effectively stabilizes the qubit state near a target state. We derive the conditions for obtaining such dispersive state stabilization and verify the stabilization conditions numerically. We include common experimental nonidealities, such as energy decay, environmental dephasing, detector efficiency, and feedback delay, and show that the feedback delay has the most significant negative effect on the feedback protocol. Setting the measurement collapse time scale to be long compared to the feedback delay yields the best stabilization.

Developments in Cylindrical Shell Stability Analysis

NASA Technical Reports Server (NTRS)

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

1998-01-01

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.

Pharmacovigilance in Space: Stability Payload Compliance Procedures

NASA Technical Reports Server (NTRS)

Daniels, Vernie R.; Putcha, Lakshmi

2007-01-01

Pharmacovigilance is the science of, and activities relating to the detection, assessment, understanding, and prevention of drug-related problems. Over the lase decade, pharmacovigilance activities have contributed to the development of numerous technological and conventional advances focused on medication safety and regulatory intervention. The topics discussed include: 1) Proactive Pharmacovigilance; 2) A New Frontier; 3) Research Activities; 4) Project Purpose; 5) Methods; 6) Flight Stability Kit Components; 7) Experimental Conditions; 8) Research Project Logistics; 9) Research Plan; 10) Pharmaceutical Stability Research Project Pharmacovigilance Aspects; 11) Security / Control; 12) Packaging/Containment Actions; 13) Shelf-Life Assessments; 14) Stability Assessment Parameters; 15) Chemical Content Analysis; 16) Preliminary Results; 17) Temperature/Humidity; 18) Changes in PHysical and Chemical Assessment Parameters; 19) Observations; and 20) Conclusions.

The stability of freak waves with regard to external impact and perturbation of initial data

NASA Astrophysics Data System (ADS)

Smirnova, Anna; Shamin, Roman

2014-05-01

We investigate solutions of the equations, describing freak waves, in perspective of stability with regard to external impact and perturbation of initial data. The modeling of freak waves is based on numerical solution of equations describing a non-stationary potential flow of the ideal fluid with a free surface. We consider the two-dimensional infinitely deep flow. For waves modeling we use the equations in conformal variables. The variant of these equations is offered in [1]. Mathematical correctness of these equations was discussed in [2]. These works establish the uniqueness of solutions, offer the effective numerical solution calculation methods, prove the numerical convergence of these methods. The important aspect of numerical modeling of freak waves is the stability of solutions, describing these waves. In this work we study the questions of stability with regards to external impact and perturbation of initial data. We showed the stability of freak waves numerical model, corresponding to the external impact. We performed series of computational experiments with various freak wave initial data and random external impact. This impact means the power density on free surface. In each experiment examine two waves: the wave that was formed by external impact and without one. In all the experiments we see the stability of equation`s solutions. The random external impact practically does not change the time of freak wave formation and its form. Later our work progresses to the investigation of solution's stability under perturbations of initial data. We take the initial data that provide a freak wave and get the numerical solution. In common we take the numerical solution of equation with perturbation of initial data. The computing experiments showed that the freak waves equations solutions are stable under perturbations of initial data.So we can make a conclusion that freak waves are stable relatively external perturbation and perturbation of initial data both. 1

Numerical difficulties associated with using equality constraints to achieve multi-level decomposition in structural optimization

NASA Technical Reports Server (NTRS)

Thareja, R.; Haftka, R. T.

1986-01-01

There has been recent interest in multidisciplinary multilevel optimization applied to large engineering systems. The usual approach is to divide the system into a hierarchy of subsystems with ever increasing detail in the analysis focus. Equality constraints are usually placed on various design quantities at every successive level to ensure consistency between levels. In many previous applications these equality constraints were eliminated by reducing the number of design variables. In complex systems this may not be possible and these equality constraints may have to be retained in the optimization process. In this paper the impact of such a retention is examined for a simple portal frame problem. It is shown that the equality constraints introduce numerical difficulties, and that the numerical solution becomes very sensitive to optimization parameters for a wide range of optimization algorithms.

Feasibility of potable water generators to meet vessel numeric ballast water discharge limits.

PubMed

Albert, Ryan J; Viveiros, Edward; Falatko, Debra S; Tamburri, Mario N

2017-07-15

Ballast water is taken on-board vessels into ballast water tanks to maintain vessel draft, buoyancy, and stability. Unmanaged ballast water contains aquatic organisms that, when transported and discharged to non-native waters, may establish as invasive species. Technologies capable of achieving regulatory limits designed to decrease the likelihood of invasion include onboard ballast water management systems. However, to date, the treatment development and manufacturing marketplace is limited to large vessels with substantial ballast requirements. For smaller vessels or vessels with reduced ballast requirements, we evaluated the feasibility of meeting the discharge limits by generating ballast water using onboard potable water generators. Case studies and parametric analyses demonstrated the architectural feasibility of installing potable water generators onboard actual vessels with minimal impacts for most vessel types evaluated. Furthermore, land-based testing of a potable water generator demonstrated capability to meet current numeric discharge limits for living organisms in all size classes. Published by Elsevier Ltd.

Numerical simulations of recent proton acceleration experiments with sub-100 TW laser systems

NASA Astrophysics Data System (ADS)

Sinigardi, Stefano

2016-09-01

Recent experiments carried out at the Italian National Research Center, National Optics Institute Department in Pisa, are showing interesting results regarding maximum proton energies achievable with sub-100 TW laser systems. While laser systems are being continuously upgraded in laboratories around the world, at the same time a new trend on stabilizing and making ion acceleration results reproducible is growing in importance. Almost all applications require a beam with fixed performance, so that the energy spectrum and the total charge exhibit moderate shot to shot variations. This result is surely far from being achieved, but many paths are being explored in order to reach it. Some of the reasons for this variability come from fluctuations in laser intensity and focusing, due to optics instability. Other variation sources come from small differences in the target structure. The target structure can vary substantially, when it is impacted by the main pulse, due to the prepulse duration and intensity, the shape of the main pulse and the total energy deposited. In order to qualitatively describe the prepulse effect, we will present a two dimensional parametric scan of its relevant parameters. A single case is also analyzed with a full three dimensional simulation, obtaining reasonable agreement between the numerical and the experimental energy spectrum.

Numerical capacities as domain-specific predictors beyond early mathematics learning: a longitudinal study.

PubMed

Reigosa-Crespo, Vivian; González-Alemañy, Eduardo; León, Teresa; Torres, Rosario; Mosquera, Raysil; Valdés-Sosa, Mitchell

2013-01-01

The first aim of the present study was to investigate whether numerical effects (Numerical Distance Effect, Counting Effect and Subitizing Effect) are domain-specific predictors of mathematics development at the end of elementary school by exploring whether they explain additional variance of later mathematics fluency after controlling for the effects of general cognitive skills, focused on nonnumerical aspects. The second aim was to address the same issues but applied to achievement in mathematics curriculum that requires solutions to fluency in calculation. These analyses assess whether the relationship found for fluency are generalized to mathematics content beyond fluency in calculation. As a third aim, the domain specificity of the numerical effects was examined by analyzing whether they contribute to the development of reading skills, such as decoding fluency and reading comprehension, after controlling for general cognitive skills and phonological processing. Basic numerical capacities were evaluated in children of 3(rd) and 4(th) grades (n=49). Mathematics and reading achievements were assessed in these children one year later. Results showed that the size of the Subitizing Effect was a significant domain-specific predictor of fluency in calculation and also in curricular mathematics achievement, but not in reading skills, assessed at the end of elementary school. Furthermore, the size of the Counting Effect also predicted fluency in calculation, although this association only approached significance. These findings contrast with proposals that the core numerical competencies measured by enumeration will bear little relationship to mathematics achievement. We conclude that basic numerical capacities constitute domain-specific predictors and that they are not exclusively "start-up" tools for the acquisition of Mathematics; but they continue modulating this learning at the end of elementary school.

Discontinuous Galerkin Method with Numerical Roe Flux for Spherical Shallow Water Equations

NASA Astrophysics Data System (ADS)

Yi, T.; Choi, S.; Kang, S.

2013-12-01

In developing the dynamic core of a numerical weather prediction model with discontinuous Galerkin method, a numerical flux at the boundaries of grid elements plays a vital role since it preserves the local conservation properties and has a significant impact on the accuracy and stability of numerical solutions. Due to these reasons, we developed the numerical Roe flux based on an approximate Riemann problem for spherical shallow water equations in Cartesian coordinates [1] to find out its stability and accuracy. In order to compare the performance with its counterpart flux, we used the Lax-Friedrichs flux, which has been used in many dynamic cores such as NUMA [1], CAM-DG [2] and MCore [3] because of its simplicity. The Lax-Friedrichs flux is implemented by a flux difference between left and right states plus the maximum characteristic wave speed across the boundaries of elements. It has been shown that the Lax-Friedrichs flux with the finite volume method is more dissipative and unstable than other numerical fluxes such as HLLC, AUSM+ and Roe. The Roe flux implemented in this study is based on the decomposition of flux difference over the element boundaries where the nonlinear equations are linearized. It is rarely used in dynamic cores due to its complexity and thus computational expensiveness. To compare the stability and accuracy of the Roe flux with the Lax-Friedrichs, two- and three-dimensional test cases are performed on a plane and cubed-sphere, respectively, with various numbers of element and polynomial order. For the two-dimensional case, the Gaussian bell is simulated on the plane with two different numbers of elements at the fixed polynomial orders. In three-dimensional cases on the cubed-sphere, we performed the test cases of a zonal flow over an isolated mountain and a Rossby-Haurwitz wave, of which initial conditions are the same as those of Williamson [4]. This study presented that the Roe flux with the discontinuous Galerkin method is less

Race, School Achievement, and Educational Inequality: Toward a Student-Based Inquiry Perspective

ERIC Educational Resources Information Center

Wiggan, Greg

2007-01-01

Over the past four decades, there have been numerous discussions on student achievement and school failure. Within this time, the debate over the causes and consequences of racial differences in achievement has been at the heart of the nation's social and political life. The author discusses the major developments in achievement research over the…

Teachers' Judgements of Students' Foreign-Language Achievement

ERIC Educational Resources Information Center

Zhu, Mingjing; Urhahne, Detlef

2015-01-01

Numerous studies have been conducted on the accuracy of teacher judgement in different educational areas such as mathematics, language arts and reading. Teacher judgement of students' foreign-language achievement, however, has been rarely investigated. The study aimed to examine the accuracy of teacher judgement of students' foreign-language…

Stability of hypersonic compression cones

NASA Astrophysics Data System (ADS)

Reed, Helen; Kuehl, Joseph; Perez, Eduardo; Kocian, Travis; Oliviero, Nicholas

2012-11-01

Our activities focus on the identification and understanding of the second-mode instability for representative configurations in hypersonic flight. These include the Langley 93-10 flared cone and the Purdue compression cone, both at 0 degrees angle of attack at Mach 6. Through application of nonlinear parabolized stability equations (NPSE) and linear parabolized stability equations (PSE) to both geometries, it is concluded that mean-flow distortion tends to amplify frequencies less than the peak frequency and stabilize those greater by modifying the boundary-layer thickness. As initial disturbance amplitude is increased and/or a broad spectrum disturbance is introduced, direct numerical simulations (DNS) or NPSE appear to be the proper choices to model the evolution, and relative evolution, because these computational tools include these nonlinear effects (mean-flow distortion). Support from AFOSR/NASA National Center for Hypersonic Research in Laminar-Turbulent Transition through Grant FA9550-09-1-0341 is gratefully acknowledged. The authors also thank Pointwise, AeroSoft, and Texas Advanced Computing Center (TACC).

Numerical simulation of conservation laws

NASA Technical Reports Server (NTRS)

Chang, Sin-Chung; To, Wai-Ming

1992-01-01

A new numerical framework for solving conservation laws is being developed. This new approach differs substantially from the well established methods, i.e., finite difference, finite volume, finite element and spectral methods, in both concept and methodology. The key features of the current scheme include: (1) direct discretization of the integral forms of conservation laws, (2) treating space and time on the same footing, (3) flux conservation in space and time, and (4) unified treatment of the convection and diffusion fluxes. The model equation considered in the initial study is the standard one dimensional unsteady constant-coefficient convection-diffusion equation. In a stability study, it is shown that the principal and spurious amplification factors of the current scheme, respectively, are structurally similar to those of the leapfrog/DuFort-Frankel scheme. As a result, the current scheme has no numerical diffusion in the special case of pure convection and is unconditionally stable in the special case of pure diffusion. Assuming smooth initial data, it will be shown theoretically and numerically that, by using an easily determined optimal time step, the accuracy of the current scheme may reach a level which is several orders of magnitude higher than that of the MacCormack scheme, with virtually identical operation count.

High- β equilibrium and ballooning stability of the low aspect ratio CNT stellarator

DOE PAGES

Hammond, K. C.; Lazerson, S. A.; Volpe, F. A.

2017-04-07

In the paper, the existence and ballooning-stability of low aspect ratio stellarator equilibria is predicted for the Columbia Neutral Torus (CNT) with the aid of 3D numerical tools. In addition to having a low aspect ratio, CNT is characterized by a low magnetic field and small plasma volume. Also, highly overdense plasmas were recently heated in CNT by means of microwaves. These characteristics suggest that CNT might attain relatively high values of plasma beta and thus be of use in the experimental study of stellarator stability to high-beta instabilities such as ballooning modes. As a first step in that direction,more » here the ballooning stability limit is found numerically. Depending on the particular magnetic configuration we expect volume-averaged β limits in the range 0.9%–3.0%, and possibly higher, and observe indications of a second region of ballooning stability. As the aspect ratio is reduced, stability is found to increase in some configurations and decrease in others. Energy-balance estimates using stellarator scaling laws indicate that the lower β limit may be attainable with overdense heating at powers of 40 to 100 kW. The present study serves the additional purpose of testing VMEC and other stellarator codes at high values of β and at low aspect ratios. For this reason, the study was carried out both for free boundary, for maximum fidelity to experiment, as well as with a fixed boundary, as a numerical test.« less

Cognitive Predictors of Achievement Growth in Mathematics: A Five Year Longitudinal Study

PubMed Central

Geary, David C.

2011-01-01

The study's goal was to identify the beginning of first grade quantitative competencies that predict mathematics achievement start point and growth through fifth grade. Measures of number, counting, and arithmetic competencies were administered in early first grade and used to predict mathematics achievement through fifth (n = 177), while controlling for intelligence, working memory, and processing speed. Multilevel models revealed intelligence, processing speed, and the central executive component of working memory predicted achievement or achievement growth in mathematics and, as a contrast domain, word reading. The phonological loop was uniquely predictive of word reading and the visuospatial sketch pad of mathematics. Early fluency in processing and manipulating numerical set size and Arabic numerals, accurate use of sophisticated counting procedures for solving addition problems, and accuracy in making placements on a mathematical number line were uniquely predictive of mathematics achievement. Use of memory-based processes to solve addition problems predicted mathematics and reading achievement but in different ways. The results identify the early quantitative competencies that uniquely contribute to mathematics learning. PMID:21942667

Stability limits of unsteady open capillary channel flow

NASA Astrophysics Data System (ADS)

Grah, Aleksander; Haake, Dennis; Rosendahl, Uwe; Klatte, J.?Rg; Dreyer, Michael E.

This paper is concerned with steady and unsteady flow rate limitations in open capillary channels under low-gravity conditions. Capillary channels are widely used in Space technology for liquid transportation and positioning, e.g. in fuel tanks and life support systems. The channel observed in this work consists of two parallel plates bounded by free liquid surfaces along the open sides. The capillary forces of the free surfaces prevent leaking of the liquid and gas ingestion into the flow.In the case of steady stable flow the capillary pressure balances the differential pressure between the liquid and the surrounding constant-pressure gas phase. Increasing the flow rate in small steps causes a decrease of the liquid pressure. A maximum steady flow rate is achieved when the flow rate exceeds a certain limit leading to a collapse of the free surfaces due to the choking effect. In the case of unsteady flow additional dynamic effects take place due to flow rate transition and liquid acceleration. The maximum flow rate is smaller than in the case of steady flow. On the other hand, the choking effect does not necessarily cause surface collapse and stable temporarily choked flow is possible under certain circumstances.To determine the limiting volumetric flow rate and stable flow dynamic properties, a new stability theory for both steady and unsteady flow is introduced. Subcritical and supercritical (choked) flow regimes are defined. Stability criteria are formulated for each flow type. The steady (subcritical) criterion corresponds to the speed index defined by the limiting longitudinal small-amplitude wave speed, similar to the Mach number. The unsteady (supercritical) criterion for choked flow is defined by a new characteristic number, the dynamic index. It is based on pressure balances and reaches unity at the stability limit.The unsteady model based on the Bernoulli equation and the mass balance equation is solved numerically for perfectly wetting incompressible

Stabilization of axisymmetric liquid bridges through vibration-induced pressure fields.

PubMed

Haynes, M; Vega, E J; Herrada, M A; Benilov, E S; Montanero, J M

2018-03-01

Previous theoretical studies have indicated that liquid bridges close to the Plateau-Rayleigh instability limit can be stabilized when the upper supporting disk vibrates at a very high frequency and with a very small amplitude. The major effect of the vibration-induced pressure field is to straighten the liquid bridge free surface to compensate for the deformation caused by gravity. As a consequence, the apparent Bond number decreases and the maximum liquid bridge length increases. In this paper, we show experimentally that this procedure can be used to stabilize millimeter liquid bridges in air under normal gravity conditions. The breakup of vibrated liquid bridges is examined experimentally and compared with that produced in absence of vibration. In addition, we analyze numerically the dynamics of axisymmetric liquid bridges far from the Plateau-Rayleigh instability limit by solving the Navier-Stokes equations. We calculate the eigenfrequencies characterizing the linear oscillation modes of vibrated liquid bridges, and determine their stability limits. The breakup process of a vibrated liquid bridge at that stability limit is simulated too. We find qualitative agreement between the numerical predictions for both the stability limits and the breakup process and their experimental counterparts. Finally, we show the applicability of our technique to control the amount of liquid transferred between two solid surfaces. Copyright © 2017 Elsevier Inc. All rights reserved.

High-power hybrid plasma spraying of large yttria-stabilized zirconia powder

NASA Astrophysics Data System (ADS)

Huang, Heji; Eguchi, Keisuke; Yoshida, Toyonobu

2006-03-01

To testify to the advantage of large ceramic powder spraying, numerical simulations and experimental studies on the behavior of large yttria-stabilized zirconia (YSZ) powder in a high-power hybrid plasma spraying process have been carried out. Numeric predictions and experimental results showed that, with the high radio frequency (RF) input power of 100 kW, the most refractory YSZ powder with particle sizes as large as 88 μm could be fully melted and well-flattened splats could be formed. A large degree of flattening (ξ) of 4.7 has been achieved. The improved adhesive strength between the large splat and the substrate was confirmed based on the measurement of the crack density inside of the splats. A thick YSZ coating >300 μm was successfully deposited on a large CoNiCrAlY-coated Inconel substrate (50×50×4 mm in size). The ultradense microstructure without clear boundaries between the splats and the clean and crack-free interface between the top-coat and the bond-coat also indicate the good adhesion. These results showed that highpower hybrid plasma spraying of large ceramic powder is a very promising process for deposition of highquality coatings, especially in the application of thermal barrier coatings (TBCs).

Numerical prediction of turbulent flame stability in premixed/prevaporized (HSCT) combustors

NASA Technical Reports Server (NTRS)

Winowich, Nicholas S.

1990-01-01

A numerical analysis of combustion instabilities that induce flashback in a lean, premixed, prevaporized dump combustor is performed. KIVA-II, a finite volume CFD code for the modeling of transient, multidimensional, chemically reactive flows, serves as the principal analytical tool. The experiment of Proctor and T'ien is used as a reference for developing the computational model. An experimentally derived combustion instability mechanism is presented on the basis of the observations of Proctor and T'ien and other investigators of instabilities in low speed (M less than 0.1) dump combustors. The analysis comprises two independent procedures that begin from a calculated stable flame: The first is a linear increase of the equivalence ratio and the second is the linear decrease of the inflow velocity. The objective is to observe changes in the aerothermochemical features of the flow field prior to flashback. It was found that only the linear increase of the equivalence ratio elicits a calculated flashback result. Though this result did not exhibit large scale coherent vortices in the turbulent shear layer coincident with a flame flickering mode as was observed experimentally, there were interesting acoustic effects which were resolved quite well in the calculation. A discussion of the k-e turbulence model used by KIVA-II is prompted by the absence of combustion instabilities in the model as the inflow velocity is linearly decreased. Finally, recommendations are made for further numerical analysis that may improve correlation with experimentally observed combustion instabilities.

Theoretical and Numerical Investigations on Shallow Tunnelling in Unsaturated Soils

NASA Astrophysics Data System (ADS)

Soranzo, Enrico; Wu, Wei

2013-04-01

Excavation of shallow tunnels with the New Austrian Tunnelling Method (NATM) requires proper assessing of the tunnel face stability, to enable an open-face excavation, and the estimation of the correspondent surface settlements. Soils in a partially saturated condition exhibit a higher cohesion than in a fully saturated state, which can be taken into account when assessing the stability of the tunnel face. For the assessment of the face support pressure, different methods are used in engineering practice, varying from simple empirical and analytical formulations to advanced finite element analysis. Such procedures can be modified to account for the unsaturated state of soils. In this study a method is presented to incorporate the effect of partial saturation in the numerical analysis. The results are then compared with a simple analytical formulation derived from parametric studies. As to the numerical analysis, the variation of cohesion and of Young's modulus with saturation can be considered when the water table lies below the tunnel in a soil exhibiting a certain capillary rise, so that the tunnel is driven in a partially saturated layer. The linear elastic model with Mohr-Coulomb failure criterion can be extended to partially saturated states and calibrated with triaxial tests on unsaturated. In order to model both positive and negative pore water pressure (suction), Bishop's effective stress is incorporated into Mohr-Coulomb's failure criterion. The effective stress parameter in Bishop's formulation is related to the degree of saturation as suggested by Fredlund. If a linear suction distribution is assumed, the degree of saturation can be calculated from the Soil Water Characteristic Curve (SWCC). Expressions exist that relate the Young's modulus of unsaturated soils to the net mean stress and the matric suction. The results of the numerical computation can be compared to Vermeer & Ruse's closed-form formula that expresses the limit support pressure of the

Applications of Laplace transform methods to airfoil motion and stability calculations

NASA Technical Reports Server (NTRS)

Edwards, J. W.

1979-01-01

This paper reviews the development of generalized unsteady aerodynamic theory and presents a derivation of the generalized Possio integral equation. Numerical calculations resolve questions concerning subsonic indicial lift functions and demonstrate the generation of Kutta waves at high values of reduced frequency, subsonic Mach number, or both. The use of rational function approximations of unsteady aerodynamic loads in aeroelastic stability calculations is reviewed, and a reformulation of the matrix Pade approximation technique is given. Numerical examples of flutter boundary calculations for a wing which is to be flight tested are given. Finally, a simplified aerodynamic model of transonic flow is used to study the stability of an airfoil exposed to supersonic and subsonic flow regions.

Process for stabilization of coal liquid fractions

DOEpatents

Davies, Geoffrey; El-Toukhy, Ahmed

1987-01-01

Coal liquid fractions to be used as fuels are stabilized against gum formation and viscosity increases during storage, permitting the fuel to be burned as is, without further expensive treatments to remove gums or gum-forming materials. Stabilization is accomplished by addition of cyclohexanol or other simple inexpensive secondary and tertiary alcohols, secondary and tertiary amines, and ketones to such coal liquids at levels of 5-25% by weight with respect to the coal liquid being treated. Cyclohexanol is a particularly effective and cost-efficient stabilizer. Other stabilizers are isopropanol, diphenylmethanol, tertiary butanol, dipropylamine, triethylamine, diphenylamine, ethylmethylketone, cyclohexanone, methylphenylketone, and benzophenone. Experimental data indicate that stabilization is achieved by breaking hydrogen bonds between phenols in the coal liquid, thereby preventing or retarding oxidative coupling. In addition, it has been found that coal liquid fractions stabilized according to the invention can be mixed with petroleum-derived liquid fuels to produce mixtures in which gum deposition is prevented or reduced relative to similar mixtures not containing stabilizer.

Phases and stability of non-uniform black strings

NASA Astrophysics Data System (ADS)

Emparan, Roberto; Luna, Raimon; Martínez, Marina; Suzuki, Ryotaku; Tanabe, Kentaro

2018-05-01

We construct solutions of non-uniform black strings in dimensions from D ≈ 9 all the way up to D = ∞, and investigate their thermodynamics and dynamical stability. Our approach employs the large- D perturbative expansion beyond the leading order, including corrections up to 1 /D 4. Combining both analytical techniques and relatively simple numerical solution of ODEs, we map out the ranges of parameters in which non-uniform black strings exist in each dimension and compute their thermodynamics and quasinormal modes with accuracy. We establish with very good precision the existence of Sorkin's critical dimension and we prove that not only the thermodynamic stability, but also the dynamic stability of the solutions changes at it.

Relationship between rotor-bearing system stability and supporting bearings

NASA Astrophysics Data System (ADS)

Xu, Longxiang; Zhu, Jun

1993-04-01

Results of an investigation of the relationship between the rotor-bearing system stability of a large rotating machinery and the supporting bearings are presented. The contribution factor of the bearings to the system stability is established. The bearing with the largest contribution factor yields the greatest contribution to the system stability. Rotor-bearing system stability depends mainly on the dynamic characteristic performance of the sensitive bearings. Appropriate readjustment in the type or design parameters of these bearings will result in a significant improvement in the stability margin. Numerical examples are carried out for a model rotor-bearing system with five bearings in a domestic 200-MW turbine generator set; they show that the calculated results are in good agreement with those measured for some actual rotating machinery. A scheme to reconstruct the domestic 200-MW turbine generator set is discussed.

Analytic theory for the determination of velocity and stability of bubbles in a Hele-Shaw cell. Part 2: Stability

NASA Technical Reports Server (NTRS)

Tanveer, Saleh

1989-01-01

The analysis is extended to determine the linear stability of a bubble in a Hele-Shaw cell analytically. Only the solution branch corresponding to largest possible bubble velocity U for given surface tension is found to be stable, while all the others are unstable, in accordance with earlier numerical results.

Stability of Ensemble Models Predicts Productivity of Enzymatic Systems

DOE PAGES

Theisen, Matthew K.; Lafontaine Rivera, Jimmy G.; Liao, James C.

2016-03-10

Stability in a metabolic system may not be obtained if incorrect amounts of enzymes are used. Without stability, some metabolites may accumulate or deplete leading to the irreversible loss of the desired operating point. Even if initial enzyme amounts achieve a stable steady state, changes in enzyme amount due to stochastic variations or environmental changes may move the system to the unstable region and lose the steady-state or quasi-steady-state flux. This situation is distinct from the phenomenon characterized by typical sensitivity analysis, which focuses on the smooth change before loss of stability. Here we show that metabolic networks differ significantlymore » in their intrinsic ability to attain stability due to the network structure and kinetic forms, and that after achieving stability, some enzymes are prone to cause instability upon changes in enzyme amounts. We use Ensemble Modelling for Robustness Analysis (EMRA) to analyze stability in four cell-free enzymatic systems when enzyme amounts are changed. Loss of stability in continuous systems can lead to lower production even when the system is tested experimentally in batch experiments. The predictions of instability by EMRA are supported by the lower productivity in batch experimental tests. Finally, the EMRA method incorporates properties of network structure, including stoichiometry and kinetic form, but does not require specific parameter values of the enzymes.« less

Straightening: existence, uniqueness and stability

PubMed Central

Destrade, M.; Ogden, R. W.; Sgura, I.; Vergori, L.

2014-01-01

One of the least studied universal deformations of incompressible nonlinear elasticity, namely the straightening of a sector of a circular cylinder into a rectangular block, is revisited here and, in particular, issues of existence and stability are addressed. Particular attention is paid to the system of forces required to sustain the large static deformation, including by the application of end couples. The influence of geometric parameters and constitutive models on the appearance of wrinkles on the compressed face of the block is also studied. Different numerical methods for solving the incremental stability problem are compared and it is found that the impedance matrix method, based on the resolution of a matrix Riccati differential equation, is the more precise. PMID:24711723

Improved result on stability analysis of discrete stochastic neural networks with time delay

NASA Astrophysics Data System (ADS)

Wu, Zhengguang; Su, Hongye; Chu, Jian; Zhou, Wuneng

2009-04-01

This Letter investigates the problem of exponential stability for discrete stochastic time-delay neural networks. By defining a novel Lyapunov functional, an improved delay-dependent exponential stability criterion is established in terms of linear matrix inequality (LMI) approach. Meanwhile, the computational complexity of the newly established stability condition is reduced because less variables are involved. Numerical example is given to illustrate the effectiveness and the benefits of the proposed method.

The Analysis, Numerical Simulation, and Diagnosis of Extratropical Weather Systems

DTIC Science & Technology

2003-09-30

The Analysis, Numerical Simulation, and Diagnosis of Extratropical Weather Systems Dr. Melvyn A. Shapiro NOAA/Office of Weather and Air Quality...predictability of extratropical cyclones. APPROACH My approach toward achieving the above objectives has been to foster national and...TITLE AND SUBTITLE The Analysis, Numerical Simulation, and Diagnosis of Extratropical Weather Systems 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM

Numerical study of fractional nonlinear Schrödinger equations.

PubMed

Klein, Christian; Sparber, Christof; Markowich, Peter

2014-12-08

Using a Fourier spectral method, we provide a detailed numerical investigation of dispersive Schrödinger-type equations involving a fractional Laplacian in an one-dimensional case. By an appropriate choice of the dispersive exponent, both mass and energy sub- and supercritical regimes can be identified. This allows us to study the possibility of finite time blow-up versus global existence, the nature of the blow-up, the stability and instability of nonlinear ground states and the long-time dynamics of solutions. The latter is also studied in a semiclassical setting. Moreover, we numerically construct ground state solutions of the fractional nonlinear Schrödinger equation.

Numerical study of fractional nonlinear Schrödinger equations

PubMed Central

Klein, Christian; Sparber, Christof; Markowich, Peter

2014-01-01

Using a Fourier spectral method, we provide a detailed numerical investigation of dispersive Schrödinger-type equations involving a fractional Laplacian in an one-dimensional case. By an appropriate choice of the dispersive exponent, both mass and energy sub- and supercritical regimes can be identified. This allows us to study the possibility of finite time blow-up versus global existence, the nature of the blow-up, the stability and instability of nonlinear ground states and the long-time dynamics of solutions. The latter is also studied in a semiclassical setting. Moreover, we numerically construct ground state solutions of the fractional nonlinear Schrödinger equation. PMID:25484604

Stability of Nonlinear Principal Components Analysis: An Empirical Study Using the Balanced Bootstrap

ERIC Educational Resources Information Center

Linting, Marielle; Meulman, Jacqueline J.; Groenen, Patrick J. F.; van der Kooij, Anita J.

2007-01-01

Principal components analysis (PCA) is used to explore the structure of data sets containing linearly related numeric variables. Alternatively, nonlinear PCA can handle possibly nonlinearly related numeric as well as nonnumeric variables. For linear PCA, the stability of its solution can be established under the assumption of multivariate…

Time domain numerical calculations of unsteady vortical flows about a flat plate airfoil

NASA Technical Reports Server (NTRS)

Hariharan, S. I.; Yu, Ping; Scott, J. R.

1989-01-01

A time domain numerical scheme is developed to solve for the unsteady flow about a flat plate airfoil due to imposed upstream, small amplitude, transverse velocity perturbations. The governing equation for the resulting unsteady potential is a homogeneous, constant coefficient, convective wave equation. Accurate solution of the problem requires the development of approximate boundary conditions which correctly model the physics of the unsteady flow in the far field. A uniformly valid far field boundary condition is developed, and numerical results are presented using this condition. The stability of the scheme is discussed, and the stability restriction for the scheme is established as a function of the Mach number. Finally, comparisons are made with the frequency domain calculation by Scott and Atassi, and the relative strengths and weaknesses of each approach are assessed.

Numerical Modeling of Gas Turbine Combustor Utilizing One-Dimensional Acoustics

NASA Astrophysics Data System (ADS)

Caley, Thomas M.

This study focuses on the numerical modeling of a gas turbine combustor set-up with known regions of thermoacoustic instability. The proposed model takes the form of a hybrid thermoacoustic network, with lumped elements representing boundary conditions and the flame, and 3-dimensional geometry volumes representing the geometry. The model is analyzed using a commercial 3-D finite element method (FEM) software, COMSOL Multiphysics. A great deal of literature is available covering thermoacoustic modeling, but much of it utilizes more computationally expensive techniques such as Large-Eddy Simulations, or relies on analytical modeling that is limited to specific test cases or proprietary software. The present study models the 3-D geometry of a high-pressure combustion chamber accurately, and uses the lumped elements of a thermoacoustic network to represent parts of the combustor system that can be experimentally tested under stable conditions, ensuring that the recorded acoustic responses can be attributed to that element alone. The numerical model has been tested against the experimental model with and without an experimentally-determined impedance boundary condition. Eigenfrequency studies are used to compare the frequency and growth rates (and from that, the thermoacoustic stability) of resonant modes in the combustor. The flame in the combustor is modeled with a flame transfer function that was determined from experimental testing using frequency forcing. The effect of flow rate on the impedance boundary condition is also examined experimentally and numerically to qualify the practice of modeling an orifice plate as an acoustically-closed boundary. Using the experimental flame transfer function and boundary conditions in the numerical model produced results that closely matched previous experimental tests in frequency, but not in stability characteristics. The lightweight nature of the numerical model means additional lumped elements can be easily added when

Numerical Capacities as Domain-Specific Predictors beyond Early Mathematics Learning: A Longitudinal Study

PubMed Central

Reigosa-Crespo, Vivian; González-Alemañy, Eduardo; León, Teresa; Torres, Rosario; Mosquera, Raysil; Valdés-Sosa, Mitchell

2013-01-01

The first aim of the present study was to investigate whether numerical effects (Numerical Distance Effect, Counting Effect and Subitizing Effect) are domain-specific predictors of mathematics development at the end of elementary school by exploring whether they explain additional variance of later mathematics fluency after controlling for the effects of general cognitive skills, focused on nonnumerical aspects. The second aim was to address the same issues but applied to achievement in mathematics curriculum that requires solutions to fluency in calculation. These analyses assess whether the relationship found for fluency are generalized to mathematics content beyond fluency in calculation. As a third aim, the domain specificity of the numerical effects was examined by analyzing whether they contribute to the development of reading skills, such as decoding fluency and reading comprehension, after controlling for general cognitive skills and phonological processing. Basic numerical capacities were evaluated in children of 3rd and 4th grades (n=49). Mathematics and reading achievements were assessed in these children one year later. Results showed that the size of the Subitizing Effect was a significant domain-specific predictor of fluency in calculation and also in curricular mathematics achievement, but not in reading skills, assessed at the end of elementary school. Furthermore, the size of the Counting Effect also predicted fluency in calculation, although this association only approached significance. These findings contrast with proposals that the core numerical competencies measured by enumeration will bear little relationship to mathematics achievement. We conclude that basic numerical capacities constitute domain-specific predictors and that they are not exclusively “start-up” tools for the acquisition of Mathematics; but they continue modulating this learning at the end of elementary school. PMID:24255710

Razumikhin-Type Stability Criteria for Differential Equations with Delayed Impulses.

PubMed

Wang, Qing; Zhu, Quanxin

2013-01-01

This paper studies stability problems of general impulsive differential equations where time delays occur in both differential and difference equations. Based on the method of Lyapunov functions, Razumikhin technique and mathematical induction, several stability criteria are obtained for differential equations with delayed impulses. Our results show that some systems with delayed impulses may be exponentially stabilized by impulses even if the system matrices are unstable. Some less restrictive sufficient conditions are also given to keep the good stability property of systems subject to certain type of impulsive perturbations. Examples with numerical simulations are discussed to illustrate the theorems. Our results may be applied to complex problems where impulses depend on both current and past states.

Does the market maker stabilize the market?

NASA Astrophysics Data System (ADS)

Zhu, Mei; Chiarella, Carl; He, Xue-Zhong; Wang, Duo

2009-08-01

The market maker plays an important role in price formation, but his/her behavior and stabilizing impact on the market are relatively unclear, in particular in speculative markets. This paper develops a financial market model that examines the impact on market stability of the market maker, who acts as both a liquidity provider and an active investor in a market consisting of two types of boundedly rational speculative investors-the fundamentalists and trend followers. We show that the market maker does not necessarily stabilize the market when he/she actively manages the inventory to maximize profits, and that rather the market maker’s impact depends on the behavior of the speculators. Numerical simulations show that the model is able to generate outcomes for asset returns and market inventories that are consistent with empirical findings.

Stabilization of a spatially uniform steady state in two systems exhibiting Turing patterns

NASA Astrophysics Data System (ADS)

Konishi, Keiji; Hara, Naoyuki

2018-05-01

This paper deals with the stabilization of a spatially uniform steady state in two coupled one-dimensional reaction-diffusion systems with Turing instability. This stabilization corresponds to amplitude death that occurs in a coupled system with Turing instability. Stability analysis of the steady state shows that stabilization does not occur if the two reaction-diffusion systems are identical. We derive a sufficient condition for the steady state to be stable for any length of system and any boundary conditions. Our analytical results are supported with numerical examples.

Numerical implementation of multiple peeling theory and its application to spider web anchorages.

PubMed

Brely, Lucas; Bosia, Federico; Pugno, Nicola M

2015-02-06

Adhesion of spider web anchorages has been studied in recent years, including the specific functionalities achieved through different architectures. To better understand the delamination mechanisms of these and other biological or artificial fibrillar adhesives, and how their adhesion can be optimized, we develop a novel numerical model to simulate the multiple peeling of structures with arbitrary branching and adhesion angles, including complex architectures. The numerical model is based on a recently developed multiple peeling theory, which extends the energy-based single peeling theory of Kendall, and can be applied to arbitrarily complex structures. In particular, we numerically show that a multiple peeling problem can be treated as the superposition of single peeling configurations even for complex structures. Finally, we apply the developed numerical approach to study spider web anchorages, showing how their function is achieved through optimal geometrical configurations.

Numerical implementation of multiple peeling theory and its application to spider web anchorages

PubMed Central

Brely, Lucas; Bosia, Federico; Pugno, Nicola M.

2015-01-01

Adhesion of spider web anchorages has been studied in recent years, including the specific functionalities achieved through different architectures. To better understand the delamination mechanisms of these and other biological or artificial fibrillar adhesives, and how their adhesion can be optimized, we develop a novel numerical model to simulate the multiple peeling of structures with arbitrary branching and adhesion angles, including complex architectures. The numerical model is based on a recently developed multiple peeling theory, which extends the energy-based single peeling theory of Kendall, and can be applied to arbitrarily complex structures. In particular, we numerically show that a multiple peeling problem can be treated as the superposition of single peeling configurations even for complex structures. Finally, we apply the developed numerical approach to study spider web anchorages, showing how their function is achieved through optimal geometrical configurations. PMID:25657835

Models for small-scale structure on cosmic strings. II. Scaling and its stability

NASA Astrophysics Data System (ADS)

Vieira, J. P. P.; Martins, C. J. A. P.; Shellard, E. P. S.

2016-11-01

We make use of the formalism described in a previous paper [Martins et al., Phys. Rev. D 90, 043518 (2014)] to address general features of wiggly cosmic string evolution. In particular, we highlight the important role played by poorly understood energy loss mechanisms and propose a simple Ansatz which tackles this problem in the context of an extended velocity-dependent one-scale model. We find a general procedure to determine all the scaling solutions admitted by a specific string model and study their stability, enabling a detailed comparison with future numerical simulations. A simpler comparison with previous Goto-Nambu simulations supports earlier evidence that scaling is easier to achieve in the matter era than in the radiation era. In addition, we also find that the requirement that a scaling regime be stable seems to notably constrain the allowed range of energy loss parameters.

Stability of sequences generated by nonlinear differential systems. [for analysis of glider jet aircraft motion

NASA Technical Reports Server (NTRS)

Brown, R. L.

1979-01-01

A local stability analysis is presented for both the analytic and numerical solutions of the initial value problem for a system of ordinary differential equations. It is shown that, using a proper choice of Liapunov function, a connected region of stable initial values of both the analytic solution and the one-leg k-step numerical solution can be approximated. Attention is given to the example of the two-dimensional problem involving the stability of the longitudinal equations of motion of a gliding jet aircraft.

Approaches to Numerical Relativity

NASA Astrophysics Data System (ADS)

d'Inverno, Ray

2005-07-01

Introduction Ray d'Inverno; Preface C. J. S. Clarke; Part I. Theoretical Approaches: 1. Numerical relativity on a transputer array Ray d'Inverno; 2. Some aspects of the characteristic initial value problem in numerical relativity Nigel Bishop; 3. The characteristic initial value problem in general relativity J. M. Stewart; 4. Algebraic approachs to the characteristic initial value problem in general relativity Jõrg Frauendiener; 5. On hyperboidal hypersurfaces Helmut Friedrich; 6. The initial value problem on null cones J. A. Vickers; 7. Introduction to dual-null dynamics S. A. Hayward; 8. On colliding plane wave space-times J. B. Griffiths; 9. Boundary conditions for the momentum constraint Niall O Murchadha; 10. On the choice of matter model in general relativity A. D. Rendall; 11. A mathematical approach to numerical relativity J. W. Barrett; 12. Making sense of the effects of rotation in general relativity J. C. Miller; 13. Stability of charged boson stars and catastrophe theory Franz E. Schunck, Fjodor V. Kusmartsev and Eckehard W. Mielke; Part II. Practical Approaches: 14. Numerical asymptotics R. Gómez and J. Winicour; 15. Instabilities in rapidly rotating polytropes Scott C. Smith and Joan M. Centrella; 16. Gravitational radiation from coalescing binary neutron stars Ken-Ichi Oohara and Takashi Nakamura; 17. 'Critical' behaviour in massless scalar field collapse M. W. Choptuik; 18. Goudunov-type methods applied to general relativistic gravitational collapse José Ma. Ibánez, José Ma. Martí, Juan A. Miralles and J. V. Romero; 19. Astrophysical sources of gravitational waves and neutrinos Silvano Bonazzola, Eric Gourgoulhon, Pawel Haensel and Jean-Alain Marck; 20. Gravitational radiation from triaxial core collapse Jean-Alain Marck and Silvano Bonazzola; 21. A vacuum fully relativistic 3D numerical code C. Bona and J. Massó; 22. Solution of elliptic equations in numerical relativity using multiquadrics M. R. Dubal, S. R. Oliveira and R. A. Matzner; 23

On the numerical treatment of nonlinear source terms in reaction-convection equations

NASA Technical Reports Server (NTRS)

Lafon, A.; Yee, H. C.

1992-01-01

The objectives of this paper are to investigate how various numerical treatments of the nonlinear source term in a model reaction-convection equation can affect the stability of steady-state numerical solutions and to show under what conditions the conventional linearized analysis breaks down. The underlying goal is to provide part of the basic building blocks toward the ultimate goal of constructing suitable numerical schemes for hypersonic reacting flows, combustions and certain turbulence models in compressible Navier-Stokes computations. It can be shown that nonlinear analysis uncovers much of the nonlinear phenomena which linearized analysis is not capable of predicting in a model reaction-convection equation.

Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas

NASA Astrophysics Data System (ADS)

Aiba, N.; Pamela, S.; Honda, M.; Urano, H.; Giroud, C.; Delabie, E.; Frassinetti, L.; Lupelli, I.; Hayashi, N.; Huijsmans, G.; JET Contributors, the; Research Unit, JT-60SA

2018-01-01

The stability with respect to a peeling-ballooning mode (PBM) was investigated numerically with extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift ({ω }* {{i}}), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into account both the rotation and {ω }* {{i}} effects in the numerical analysis. When deuterium poloidal rotation is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes the PBM because of an acceleration of rotation and a decrease in {ω }* {{i}}. The difference in the amount of ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the difference in the linear stability property, due not to the rotation direction but to the plasma density profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and {ω }* {{i}} effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.

Impact of implant design on primary stability of orthodontic mini-implants.

PubMed

Wilmes, Benedict; Ottenstreuer, Stephanie; Su, Yu-Yu; Drescher, Dieter

2008-01-01

Skeletal anchorage with mini-implants has greatly broadened the treatment possibilities in orthodontics over the last few years. To reduce implant failure rates, it is advisable to obtain adequate primary stability. The aim of this study was to quantitatively analyze the impact of implant design and dimension on primary stability. Forty-two porcine iliac bone segments were prepared and embedded in resin. To evaluate the primary stability, we documented insertion torques of the following mini-implants: Aarhus Screw, AbsoAnchor, LOMAS, Micro-Anchorage-System, ORLUS and Spider Screw. In each bone, five Dual Top Screws were inserted for reference purposes to achieve comparability among the specimens. We observed wide variation in insertion torques and hence primary stability, depending on mini-implant design and dimension; the great impact that mini-implant diameter has on insertion torques was particularly conspicuous. Conical mini-implants achieved higher primary stabilities than cylindrical designs. The diameter and design of the mini-implant thread have a distinctive impact on primary stability. Depending on the region of insertion and local bone quality, the choice of the mini-implant design and size is crucial to establish sufficient primary stability.

Dynamics of Numerics & Spurious Behaviors in CFD Computations. Revised

NASA Technical Reports Server (NTRS)

Yee, Helen C.; Sweby, Peter K.

1997-01-01

The global nonlinear behavior of finite discretizations for constant time steps and fixed or adaptive grid spacings is studied using tools from dynamical systems theory. Detailed analysis of commonly used temporal and spatial discretizations for simple model problems is presented. The role of dynamics in the understanding of long time behavior of numerical integration and the nonlinear stability, convergence, and reliability of using time-marching approaches for obtaining steady-state numerical solutions in computational fluid dynamics (CFD) is explored. The study is complemented with examples of spurious behavior observed in steady and unsteady CFD computations. The CFD examples were chosen to illustrate non-apparent spurious behavior that was difficult to detect without extensive grid and temporal refinement studies and some knowledge from dynamical systems theory. Studies revealed the various possible dangers of misinterpreting numerical simulation of realistic complex flows that are constrained by available computing power. In large scale computations where the physics of the problem under study is not well understood and numerical simulations are the only viable means of solution, extreme care must be taken in both computation and interpretation of the numerical data. The goal of this paper is to explore the important role that dynamical systems theory can play in the understanding of the global nonlinear behavior of numerical algorithms and to aid the identification of the sources of numerical uncertainties in CFD.

Dynamic stability experiment of Maglev systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Y.; Mulcahy, T.M.; Chen, S.S.

1995-04-01

This report summarizes the research performed on Maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also documents magnetic-force data obtained from both measurements and calculations. Because dynamic instability is not acceptable for any commercial Maglev system, it is important to consider this phenomenon in the development of all Maglev systems. This report presents dynamic stability experiments on Maglev systems and compares their numerical simulation with predictions calculated by a nonlinear dynamic computer code. Instabilities of an electrodynamic system (EDS)-type vehicle model were obtained from both experimental observations and computer simulations for a five-degree-of-freedom Maglevmore » vehicle moving on a guideway consisting of double L-shaped aluminum segments attached to a rotating wheel. The experimental and theoretical analyses developed in this study identify basic stability characteristics and future research needs of Maglev systems.« less

The Numerical Studies Program for the Atmospheric General Circulation Experiment (AGCE) for Spacelab Flights

NASA Technical Reports Server (NTRS)

Fowlis, W. W. (Editor); Davis, M. H. (Editor)

1981-01-01

The atmospheric general circulation experiment (AGCE) numerical design for Spacelab flights was studied. A spherical baroclinic flow experiment which models the large scale circulations of the Earth's atmosphere was proposed. Gravity is simulated by a radial dielectric body force. The major objective of the AGCE is to study nonlinear baroclinic wave flows in spherical geometry. Numerical models must be developed which accurately predict the basic axisymmetric states and the stability of nonlinear baroclinic wave flows. A three dimensional, fully nonlinear, numerical model and the AGCE based on the complete set of equations is required. Progress in the AGCE numerical design studies program is reported.

Stability analysis of fractional-order Hopfield neural networks with time delays.

PubMed

Wang, Hu; Yu, Yongguang; Wen, Guoguang

2014-07-01

This paper investigates the stability for fractional-order Hopfield neural networks with time delays. Firstly, the fractional-order Hopfield neural networks with hub structure and time delays are studied. Some sufficient conditions for stability of the systems are obtained. Next, two fractional-order Hopfield neural networks with different ring structures and time delays are developed. By studying the developed neural networks, the corresponding sufficient conditions for stability of the systems are also derived. It is shown that the stability conditions are independent of time delays. Finally, numerical simulations are given to illustrate the effectiveness of the theoretical results obtained in this paper. Copyright © 2014 Elsevier Ltd. All rights reserved.

Stability analysis of cylinders with circular cutouts

NASA Technical Reports Server (NTRS)

Almroth, B. O.; Brogan, F. A.; Marlowe, M. B.

1973-01-01

The stability of axially compressed cylinders with circular cutouts is analyzed numerically. An extension of the finite-difference method is used which removes the requirement that displacement components be defined in the directions of the grid lines. The results of this nonlinear analysis are found to be in good agreement with earlier experimental results.

Effect of Rotational Speed on the Stability of Two Rotating Side-by-side Circular Cylinders at Low Reynolds Number

NASA Astrophysics Data System (ADS)

Dou, Huashu; Zhang, Shuo; Yang, Hui; Setoguchi, Toshiaki; Kinoue, Yoichi

2018-04-01

Flow around two rotating side-by-side circular cylinders of equal diameter D is numerically studied at the Reynolds number 40≤ Re ≤200 and various rotation rate θ i . The incoming flow is assumed to be two-dimensional laminar flow. The governing equations are the incompressible Navier-Stokes equations and solved by the finite volume method (FVM). The ratio of the center-to-center spacing to the cylinder diameter is T/D=2. The objective of the present work is to investigate the effect of rotational speed and Reynolds number on the stability of the flow. The simulation results are compared with the experimental data and a good agreement is achieved. The stability of the flow is analyzed by using the energy gradient theory, which produces the energy gradient function K to identify the region where the flow is the most prone to be destabilized and the degree of the destabilization. Numerical results reveal that K is the most significant at the separated shear layers of the cylinder pair. With Re increases, the length of the wake is shorter and the vortex shedding generally exhibits a symmetrical distribution for θ i < θ crit . It is also shown that the unsteady vortex shedding can be suppressed by rotating the cylinders in the counter-rotating mode.

Stability of suxamethonium in pharmaceutical solution for injection by validated stability-indicating chromatographic method.

PubMed

Beck, William; Kabiche, Sofiane; Balde, Issa-Bella; Carret, Sandra; Fontan, Jean-Eudes; Cisternino, Salvatore; Schlatter, Joël

2016-12-01

To assess the stability of pharmaceutical suxamethonium (succinylcholine) solution for injection by validated stability-indicating chromatographic method in vials stored at room temperature. The chromatographic assay was achieved by using a detector wavelength set at 218 nm, a C18 column, and an isocratic mobile phase (100% of water) at a flow rate of 0.6 mL/min for 5 minutes. The method was validated according to the International Conference on Harmonization guidelines with respect to the stability-indicating capacity of the method including linearity, limits of detection and quantitation, precision, accuracy, system suitability, robustness, and forced degradations. Linearity was achieved in the concentration range of 5 to 40 mg/mL with a correlation coefficient higher than 0.999. The limits of detection and quantification were 0.8 and 0.9 mg/mL, respectively. The percentage relative standard deviation for intraday (1.3-1.7) and interday (0.1-2.0) precision was found to be less than 2.1%. Accuracy was assessed by the recovery test of suxamethonium from solution for injection (99.5%-101.2%). Storage of suxamethonium solution for injection vials at ambient temperature (22°C-26°C) for 17 days demonstrated that at least 95% of original suxamethonium concentration remained stable. Copyright © 2016 Elsevier Inc. All rights reserved.

On the impact of atmospheric thermal stability on the characteristics of nocturnal downslope flows

NASA Astrophysics Data System (ADS)

Ye, Z. J.; Garratt, J. R.; Segal, M.; Pielke, R. A.

1990-04-01

The impacts of background (or ambient) and local atmospheric thermal stabilities, and slope steepness, on nighttime thermally induced downslope flow in meso-β domains (i.e., 20 200 km horizontal extent) have been investigated using analytical and numerical model approaches. Good agreement between the analytical and numerical evaluations was found. It was concluded that: (i) as anticipated, the intensity of the downslope flow increases with increased slope steepness, although the depth of the downslope flow was found to be insensitive to slope steepness in the studied situations; (ii) the intensity of the downslope flow is generally independent of background atmospheric thermal stability; (iii) for given integrated nighttime cooling across the nocturnal boundary layer (NBL), Q s the local atmospheric thermal stability exerts a strong influence on downslope flow behavior: the downslope flow intensity increases when local atmospheric thermal stability increases; and (iv) the downslope flow intensity is proportional to Q s 1/2.

Stability and Bifurcation Analysis in a Maglev System with Multiple Delays

NASA Astrophysics Data System (ADS)

Zhang, Lingling; Huang, Jianhua; Huang, Lihong; Zhang, Zhizhou

This paper considers the time-delayed feedback control for Maglev system with two discrete time delays. We determine constraints on the feedback time delays which ensure the stability of the Maglev system. An algorithm is developed for drawing a two-parametric bifurcation diagram with respect to two delays τ1 and τ2. Direction and stability of periodic solutions are also determined using the normal form method and center manifold theory by Hassard. The complex dynamical behavior of the Maglev system near the domain of stability is confirmed by exhaustive numerical simulation.

Dynamic stability of unidirectional fiber-reinforced viscoelastic composite plates

NASA Technical Reports Server (NTRS)

Chandiramani, N. K.; Librescu, L.

1989-01-01

This paper deals with a dynamic stability analysis of unidirectional fiber-reinforced composite viscoelastic plates subjected to compressive edge loads. The integrodifferential equations governing the stability problem are obtained by using, in conjunction with a Boltzmann hereditary constitutive law for a three-dimensional viscoelastic medium, a higher-order shear deformation theory of orthotropic plates. Such a theory incorporates transverse shear deformation, transverse normal stress, and rotatory inertia effects. The solution of the stability problem as considered within this paper concerns the determination of the critical in-plane edge loads yielding the asymptotic instability. Numerical applications, based on material properties derived within the framework of Aboudi's micromechanical model, are presented and pertinent conclusions concerning the nature of the loss of stability and the influence of various parameters are outlined.

Stable Numerical Approach for Fractional Delay Differential Equations

NASA Astrophysics Data System (ADS)

Singh, Harendra; Pandey, Rajesh K.; Baleanu, D.

2017-12-01

In this paper, we present a new stable numerical approach based on the operational matrix of integration of Jacobi polynomials for solving fractional delay differential equations (FDDEs). The operational matrix approach converts the FDDE into a system of linear equations, and hence the numerical solution is obtained by solving the linear system. The error analysis of the proposed method is also established. Further, a comparative study of the approximate solutions is provided for the test examples of the FDDE by varying the values of the parameters in the Jacobi polynomials. As in special case, the Jacobi polynomials reduce to the well-known polynomials such as (1) Legendre polynomial, (2) Chebyshev polynomial of second kind, (3) Chebyshev polynomial of third and (4) Chebyshev polynomial of fourth kind respectively. Maximum absolute error and root mean square error are calculated for the illustrated examples and presented in form of tables for the comparison purpose. Numerical stability of the presented method with respect to all four kind of polynomials are discussed. Further, the obtained numerical results are compared with some known methods from the literature and it is observed that obtained results from the proposed method is better than these methods.

A new numerical approximation of the fractal ordinary differential equation

NASA Astrophysics Data System (ADS)

Atangana, Abdon; Jain, Sonal

2018-02-01

The concept of fractal medium is present in several real-world problems, for instance, in the geological formation that constitutes the well-known subsurface water called aquifers. However, attention has not been quite devoted to modeling for instance, the flow of a fluid within these media. We deem it important to remind the reader that the concept of fractal derivative is not to represent the fractal sharps but to describe the movement of the fluid within these media. Since this class of ordinary differential equations is highly complex to solve analytically, we present a novel numerical scheme that allows to solve fractal ordinary differential equations. Error analysis of the method is also presented. Application of the method and numerical approximation are presented for fractal order differential equation. The stability and the convergence of the numerical schemes are investigated in detail. Also some exact solutions of fractal order differential equations are presented and finally some numerical simulations are presented.

Impaired math achievement in patients with acute vestibular neuritis.

PubMed

Moser, Ivan; Vibert, Dominique; Caversaccio, Marco D; Mast, Fred W

2017-12-01

Broad cognitive difficulties have been reported in patients with peripheral vestibular deficit, especially in the domain of spatial cognition. Processing and manipulating numbers relies on the ability to use the inherent spatial features of numbers. It is thus conceivable that patients with acute peripheral vestibular deficit show impaired numerical cognition. Using the number Stroop task and a short math achievement test, we tested 20 patients with acute vestibular neuritis and 20 healthy, age-matched controls. On the one hand, patients showed normal congruency and distance effects in the number Stroop task, which is indicative of normal number magnitude processing. On the other hand, patients scored lower than healthy controls in the math achievement test. We provide evidence that the lower performance cannot be explained by either differences in prior math knowledge (i.e., education) or slower processing speed. Our results suggest that peripheral vestibular deficit negatively affects numerical cognition in terms of the efficient manipulation of numbers. We discuss the role of executive functions in math performance and argue that previously reported executive deficits in patients with peripheral vestibular deficit provide a plausible explanation for the lower math achievement scores. In light of the handicapping effects of impaired numerical cognition in daily living, it is crucial to further investigate the mechanisms that cause mathematical deficits in acute PVD and eventually develop adequate means for cognitive interventions. Copyright © 2017 Elsevier Ltd. All rights reserved.

A note on a corrector formula for the numerical solution of ordinary differential equations

NASA Technical Reports Server (NTRS)

Chien, Y.-C.; Agrawal, K. M.

1979-01-01

A new corrector formula for predictor-corrector methods for numerical solutions of ordinary differential equations is presented. Two considerations for choosing corrector formulas are given: (1) the coefficient in the error term and (2) its stability properties. The graph of the roots of an equation plotted against its stability region, of different values, is presented along with the tables that correspond to various corrector equations, including Hamming's and Milne and Reynolds'.

The use of vitamin K supplementation to achieve INR stability: a systematic review and meta-analysis.

PubMed

Kramps, Melissa; Flanagan, Abigail; Smaldone, Arlene

2013-10-01

Systematically review and quantitatively synthesize evidence on use of oral vitamin K supplementation in reducing international normalized ratio (INR) variability. PubMed, The Cochrane Library, PsycINFO, Cumulative Index of Nursing and Allied Health Literature (CINAHL), Turning Research Into Practice (TRIP), Web of Science were searched for studies meeting predetermined inclusion/exclusion criteria. Five studies meeting criteria (three randomized trials, one quasi-experimental pre-post study, one retrospective case series) were appraised for quality and data synthesized by two reviewers. Pooled effect size of time in INR therapeutic range (TTR) was estimated using random effects meta-analysis. Pooled effect size representing data from four studies (678 subjects) was 0.31, 95% confidence interval 0.03-0.59 (Cochran Q = 7.1; p = .07; I(2) = 57.8) and favored vitamin K supplementation. Given wide variability among individual studies, there is not enough evidence to advise for or against the routine use of vitamin K supplementation to achieve INR stability. However, evidence does suggest that it may be of some benefit for some patients with INR instability. There is insufficient evidence to support routine supplementation with vitamin K in patients on chronic anticoagulation therapy but select patients, particularly those with persistent INR instability despite known adherence to regimen and no dietary or drug-drug interactions, may benefit from the intervention. Future research is warranted. ©2013 The Author(s) ©2013 American Association of Nurse Practitioners.

Numerical time-domain electromagnetics based on finite-difference and convolution

NASA Astrophysics Data System (ADS)

Lin, Yuanqu

Time-domain methods posses a number of advantages over their frequency-domain counterparts for the solution of wideband, nonlinear, and time varying electromagnetic scattering and radiation phenomenon. Time domain integral equation (TDIE)-based methods, which incorporate the beneficial properties of integral equation method, are thus well suited for solving broadband scattering problems for homogeneous scatterers. Widespread adoption of TDIE solvers has been retarded relative to other techniques by their inefficiency, inaccuracy and instability. Moreover, two-dimensional (2D) problems are especially problematic, because 2D Green's functions have infinite temporal support, exacerbating these difficulties. This thesis proposes a finite difference delay modeling (FDDM) scheme for the solution of the integral equations of 2D transient electromagnetic scattering problems. The method discretizes the integral equations temporally using first- and second-order finite differences to map Laplace-domain equations into the Z domain before transforming to the discrete time domain. The resulting procedure is unconditionally stable because of the nature of the Laplace- to Z-domain mapping. The first FDDM method developed in this thesis uses second-order Lagrange basis functions with Galerkin's method for spatial discretization. The second application of the FDDM method discretizes the space using a locally-corrected Nystrom method, which accelerates the precomputation phase and achieves high order accuracy. The Fast Fourier Transform (FFT) is applied to accelerate the marching-on-time process in both methods. While FDDM methods demonstrate impressive accuracy and stability in solving wideband scattering problems for homogeneous scatterers, they still have limitations in analyzing interactions between several inhomogenous scatterers. Therefore, this thesis devises a multi-region finite-difference time-domain (MR-FDTD) scheme based on domain-optimal Green's functions for solving

Force-controlled absorption in a fully-nonlinear numerical wave tank

NASA Astrophysics Data System (ADS)

Spinneken, Johannes; Christou, Marios; Swan, Chris

2014-09-01

An active control methodology for the absorption of water waves in a numerical wave tank is introduced. This methodology is based upon a force-feedback technique which has previously been shown to be very effective in physical wave tanks. Unlike other methods, an a-priori knowledge of the wave conditions in the tank is not required; the absorption controller being designed to automatically respond to a wide range of wave conditions. In comparison to numerical sponge layers, effective wave absorption is achieved on the boundary, thereby minimising the spatial extent of the numerical wave tank. In contrast to the imposition of radiation conditions, the scheme is inherently capable of absorbing irregular waves. Most importantly, simultaneous generation and absorption can be achieved. This is an important advance when considering inclusion of reflective bodies within the numerical wave tank. In designing the absorption controller, an infinite impulse response filter is adopted, thereby eliminating the problem of non-causality in the controller optimisation. Two alternative controllers are considered, both implemented in a fully-nonlinear wave tank based on a multiple-flux boundary element scheme. To simplify the problem under consideration, the present analysis is limited to water waves propagating in a two-dimensional domain. The paper presents an extensive numerical validation which demonstrates the success of the method for a wide range of wave conditions including regular, focused and random waves. The numerical investigation also highlights some of the limitations of the method, particularly in simultaneously generating and absorbing large amplitude or highly-nonlinear waves. The findings of the present numerical study are directly applicable to related fields where optimum absorption is sought; these include physical wavemaking, wave power absorption and a wide range of numerical wave tank schemes.

Lean Stability augmentation study

NASA Technical Reports Server (NTRS)

Mcvey, J. B.; Kennedy, J. B.

1979-01-01

An analytical and experimental program was conducted to investigate techniques and develop technology for improving the lean combustion limits of premixing, prevaporizing combustors applicable to gas turbine engine main burners. Three concepts for improving lean stability limits were selected for experimental evaluation among twelve approaches considered. Concepts were selected on the basis of the potential for improving stability limits and achieving emission goals, the technological risks associated with development of practical burners employing the concepts, and the penalties to airline direct operating costs resulting from decreased combustor performance, increased engine cost, increased maintenance cost and increased engine weight associated with implementation of the concepts. Tests of flameholders embodying the selected concepts were conducted.

Full-frame video stabilization with motion inpainting.

PubMed

Matsushita, Yasuyuki; Ofek, Eyal; Ge, Weina; Tang, Xiaoou; Shum, Heung-Yeung

2006-07-01

Video stabilization is an important video enhancement technology which aims at removing annoying shaky motion from videos. We propose a practical and robust approach of video stabilization that produces full-frame stabilized videos with good visual quality. While most previous methods end up with producing smaller size stabilized videos, our completion method can produce full-frame videos by naturally filling in missing image parts by locally aligning image data of neighboring frames. To achieve this, motion inpainting is proposed to enforce spatial and temporal consistency of the completion in both static and dynamic image areas. In addition, image quality in the stabilized video is enhanced with a new practical deblurring algorithm. Instead of estimating point spread functions, our method transfers and interpolates sharper image pixels of neighboring frames to increase the sharpness of the frame. The proposed video completion and deblurring methods enabled us to develop a complete video stabilizer which can naturally keep the original image quality in the stabilized videos. The effectiveness of our method is confirmed by extensive experiments over a wide variety of videos.

Varus-valgus stability at 90° flexion correlates with the stability at midflexion range more widely than that at 0° extension in posterior-stabilized total knee arthroplasty.

PubMed

Hino, Kazunori; Kutsuna, Tatsuhiko; Watamori, Kunihiko; Kiyomatsu, Hiroshi; Ishimaru, Yasumitsu; Takeba, Jun; Watanabe, Seiji; Shiraishi, Yoshitaka; Miura, Hiromasa

2017-10-01

Midflexion stability can potentially improve the outcome of total knee arthroplasty (TKA). The purpose of this study was to evaluate the correlation between varus-valgus stability at 0° of extension and 90° of flexion and that at the midflexion range in posterior-stabilized (PS)-TKA. Forty-three knees that underwent PS-TKA were evaluated. Manual mild passive varus-valgus stress was applied to the knees, and the postoperative maximum varus-valgus stability was measured every 10° throughout range of motion, using a navigation system. Correlations between the stability at 0°, 90° of flexion, and that at each midflexion angle were evaluated using Spearman's correlation coefficients. The stability of 0° modestly correlated with that of 10°-20°, but it did not significantly correlate with that of 30°-80°. However, the stability of 90° strongly correlated with that of 60°-80°, modestly correlated with that of 40°-50°, weakly correlated with that of 20°-30°, and did not correlate with that of 10°. The present study confirmed the importance of acquiring stability at 90° flexion to achieve midflexion stability in PS-TKA. However, initial flexion stability did not strongly correlate with the stability at either 0° or 90°. Our findings can provide useful information for understanding varus-valgus stability throughout the range of motion in PS-TKA. Attention to soft tissue balancing is necessary to stabilize a knee at the initial flexion range in PS-TKA.

A Riccati solution for the ideal MHD plasma response with applications to real-time stability control

NASA Astrophysics Data System (ADS)

Glasser, Alexander; Kolemen, Egemen; Glasser, A. H.

2018-03-01

Active feedback control of ideal MHD stability in a tokamak requires rapid plasma stability analysis. Toward this end, we reformulate the δW stability method with a Hamilton-Jacobi theory, elucidating analytical and numerical features of the generic tokamak ideal MHD stability problem. The plasma response matrix is demonstrated to be the solution of an ideal MHD matrix Riccati differential equation. Since Riccati equations are prevalent in the control theory literature, such a shift in perspective brings to bear a range of numerical methods that are well-suited to the robust, fast solution of control problems. We discuss the usefulness of Riccati techniques in solving the stiff ordinary differential equations often encountered in ideal MHD stability analyses—for example, in tokamak edge and stellarator physics. We demonstrate the applicability of such methods to an existing 2D ideal MHD stability code—DCON [A. H. Glasser, Phys. Plasmas 23, 072505 (2016)]—enabling its parallel operation in near real-time, with wall-clock time ≪1 s . Such speed may help enable active feedback ideal MHD stability control, especially in tokamak plasmas whose ideal MHD equilibria evolve with inductive timescale τ≳ 1s—as in ITER.

Novel numerical techniques for magma dynamics

NASA Astrophysics Data System (ADS)

Rhebergen, S.; Katz, R. F.; Wathen, A.; Alisic, L.; Rudge, J. F.; Wells, G.

2013-12-01

We discuss the development of finite element techniques and solvers for magma dynamics computations. These are implemented within the FEniCS framework. This approach allows for user-friendly, expressive, high-level code development, but also provides access to powerful, scalable numerical solvers and a large family of finite element discretisations. With the recent addition of dolfin-adjoint, FeniCS supports automated adjoint and tangent-linear models, enabling the rapid development of Generalised Stability Analysis. The ability to easily scale codes to three dimensions with large meshes, and/or to apply intricate adjoint calculations means that efficiency of the numerical algorithms is vital. We therefore describe our development and analysis of preconditioners designed specifically for finite element discretizations of equations governing magma dynamics. The preconditioners are based on Elman-Silvester-Wathen methods for the Stokes equation, and we extend these to flows with compaction. Our simulations are validated by comparison of results with laboratory experiments on partially molten aggregates.

Racial and Social Class Differences in How Parents Respond to Inadequate Achievement: Consequences for Children’s Future Achievement

PubMed Central

Robinson, Keith; Harris, Angel L.

2013-01-01

Objective Despite numerous studies on parental involvement in children’s academic schooling, there is a dearth of knowledge on how parents respond specifically to inadequate academic performance. This study examines whether 1) racial differences exist in parenting philosophy for addressing inadequate achievement, 2) social class has implications for parenting philosophy, and 3) parents’ philosophies are consequential for children’s academic achievement. Methods Using data from the Child Development Supplement (N=1041) to the Panel Study of Income Dynamics, we sort parents into two categories—those whose parenting repertoires for addressing poor achievement include punitive responses and those whose repertoires do not. We then determine whether racial differences exist between these categories and how various responses within the aforementioned categories are related to students’ academic achievement. Results The findings show that white and black parents have markedly different philosophies on how to respond to inadequate performance, and these differences appear to impact children’s achievement in dramatically different ways. Conclusion Educators and policy makers should pay particular attention to how parents respond to inadequate achievement as imploring parents of inadequately performing students to be more involved without providing them with some guidance might exacerbate the problem. PMID:24563554

Comparison of Numerical Modeling Methods for Soil Vibration Cutting

NASA Astrophysics Data System (ADS)

Jiang, Jiandong; Zhang, Enguang

2018-01-01

In this paper, we studied the appropriate numerical simulation method for vibration soil cutting. Three numerical simulation methods, commonly used for uniform speed soil cutting, Lagrange, ALE and DEM, are analyzed. Three models of vibration soil cutting simulation model are established by using ls-dyna.The applicability of the three methods to this problem is analyzed in combination with the model mechanism and simulation results. Both the Lagrange method and the DEM method can show the force oscillation of the tool and the large deformation of the soil in the vibration cutting. Lagrange method shows better effect of soil debris breaking. Because of the poor stability of ALE method, it is not suitable to use soil vibration cutting problem.

Carrier-envelope phase stabilization with sub-10 as residual timing jitter.

PubMed

Borchers, B; Koke, S; Husakou, A; Herrmann, J; Steinmeyer, G

2011-11-01

We demonstrate carrier-envelope phase (CEP) stabilization of a mode-locked Ti:sapphire oscillator with unprecedented timing jitter of eight attoseconds. The stabilization performance is obtained by a combination of two different stabilization approaches. In a first step the drift of the CEP is stabilized with a conventional feedback loop by means of controlling the oscillator pump power with an acousto-optic modulator (AOM). In a second step we utilize a recently developed feed-forward type stabilization scheme which has a much higher control bandwith. Here an acousto-optic frequency shifter (AOFS) produces the stabilized output in the first diffraction order. Moreover, we present numerical results on the optimization of the length of the photonic crystal fiber, which is used to generate an octave-spanning spectrum, in order to optimize the sensitivity in the f-to-2f interferometers.

Background feature descriptor for offline handwritten numeral recognition

NASA Astrophysics Data System (ADS)

Ming, Delie; Wang, Hao; Tian, Tian; Jie, Feiran; Lei, Bo

2011-11-01

This paper puts forward an offline handwritten numeral recognition method based on background structural descriptor (sixteen-value numerical background expression). Through encoding the background pixels in the image according to a certain rule, 16 different eigenvalues were generated, which reflected the background condition of every digit, then reflected the structural features of the digits. Through pattern language description of images by these features, automatic segmentation of overlapping digits and numeral recognition can be realized. This method is characterized by great deformation resistant ability, high recognition speed and easy realization. Finally, the experimental results and conclusions are presented. The experimental results of recognizing datasets from various practical application fields reflect that with this method, a good recognition effect can be achieved.

Dynamical stability of plutonium alloys

NASA Astrophysics Data System (ADS)

Torrent, Marc; Dorado, Boris; Bieder, Jordan

Plutonium sits at the center of the actinide series and marks the transition between localization and delocalization of the 5 f electrons. From a metallurgical standpoint, the monoclinic α phase (stable at low T) is brittle, not suitable for engineering applications, as opposed to the ductile fcc δ phase (stable at 580K). The δ - α transition can be avoided by alloying δ-Pu with ''deltagen'' elements. There is a wide unexplored area for Pu when it comes to lattice dynamics. Due to the changes in the composition, the dynamical stability of is constantly challenged. Displ. cascades are created in the material, which in turn produce numerous of point defects. Therefore, the accumulation of defects preclude a thermodynamic equilibrium. Given the importance for engineering applications, it is crucial that we understand the mechanisms that lead to stabilization with respect to the alloy composition. We use first-principles calculations to provide evidence of the effect of defects/impurities (C, O, Al, Fe, Ni, Ga, Ce, U, Am) on the dynamical stability of δ-Pu. We show that this phase is dynamically unstable at low T and that it depends on the 5 f orbital occupancies. We investigate how defects affect the stability by comparing the phonon DoS.

Continuous control of chaos based on the stability criterion.

PubMed

Yu, Hong Jie; Liu, Yan Zhu; Peng, Jian Hua

2004-06-01

A method of chaos control based on stability criterion is proposed in the present paper. This method can stabilize chaotic systems onto a desired periodic orbit by a small time-continuous perturbation nonlinear feedback. This method does not require linearization of the system around the stabilized orbit and only an approximate location of the desired periodic orbit is required which can be automatically detected in the control process. The control can be started at any moment by choosing appropriate perturbation restriction condition. It seems that more flexibility and convenience are the main advantages of this method. The discussions on control of attitude motion of a spacecraft, Rössler system, and two coupled Duffing oscillators are given as numerical examples.

The analysis of EEG coherence reflects middle childhood differences in mathematical achievement.

PubMed

González-Garrido, Andrés A; Gómez-Velázquez, Fabiola R; Salido-Ruiz, Ricardo A; Espinoza-Valdez, Aurora; Vélez-Pérez, Hugo; Romo-Vazquez, Rebeca; Gallardo-Moreno, Geisa B; Ruiz-Stovel, Vanessa D; Martínez-Ramos, Alicia; Berumen, Gustavo

2018-07-01

Symbolic numerical magnitude processing is crucial to arithmetic development, and it is thought to be supported by the functional activation of several brain-interconnected structures. In this context, EEG beta oscillations have been recently associated with attention and working memory processing that underlie math achievement. Due to that EEG coherence represents a useful measure of brain functional connectivity, we aimed to contrast the EEG coherence in forty 8-to-9-year-old children with different math skill levels (High: HA, and Low achievement: LA) according to their arithmetic scores in the Fourth Edition of the Wide Range Achievement Test (WRAT-4) while performing a symbolic magnitude comparison task (i.e. determining which of two numbers is numerically larger). The analysis showed significantly greater coherence over the right hemisphere in the two groups, but with a distinctive connectivity pattern. Whereas functional connectivity in the HA group was predominant in parietal areas, especially involving beta frequencies, the LA group showed more extensive frontoparietal relationships, with higher participation of delta, theta and alpha band frequencies, along with a distinct time-frequency domain expression. The results seem to reflect that lower math achievements in children mainly associate with cognitive processing steps beyond stimulus encoding, along with the need of further attentional resources and cognitive control than their peers, suggesting a lower degree of numerical processing automation. Copyright © 2018 Elsevier Inc. All rights reserved.

Comparison of Implant Stability Using Resonance Frequency Analysis: Osteotome Versus Conventional Drilling

PubMed Central

Sadeghi, Rokhsareh; Miremadi, Asghar

2015-01-01

Objectives: Implant primary stability is one of the important factors in achieving implant success. The osteotome technique may improve primary stability in patients with poor bone quality. The aim of this study was to compare implant stability using two different techniques namely osteotome versus conventional drilling in the posterior maxilla. Materials and Methods: In this controlled randomized clinical trial, 54 dental implants were placed in 32 patients; 29 implants were placed in the osteotome group and 25 in the conventional drilling group. Implant stability was assessed at four time intervals namely at baseline, one, two and three months after implant placement using resonance frequency analysis (RFA). Results: Primary stability based on implant stability quotient (ISQ) units was 71.4±7 for the osteotome group and 67.4±10 for the control group. There was no statistically significant difference between the two groups in implant stability at any of the measurement times. In each group, changes in implant stability from baseline to one month and also from two months to three months post-operatively were not significant but from one month to two months after implant placement, implant stability showed a significant increase in both groups. Conclusion: The results of this study revealed that in both techniques, good implant stability was achieved and osteotome technique did not have any advantage compared to conventional drilling in this regard. PMID:27148375

Stabilized high-order Galerkin methods based on a parameter-free dynamic SGS model for LES

NASA Astrophysics Data System (ADS)

Marras, Simone; Nazarov, Murtazo; Giraldo, Francis X.

2015-11-01

The high order spectral element approximation of the Euler equations is stabilized via a dynamic sub-grid scale model (Dyn-SGS). This model was originally designed for linear finite elements to solve compressible flows at large Mach numbers. We extend its application to high-order spectral elements to solve the Euler equations of low Mach number stratified flows. The major justification of this work is twofold: stabilization and large eddy simulation are achieved via one scheme only. Because the diffusion coefficients of the regularization stresses obtained via Dyn-SGS are residual-based, the effect of the artificial diffusion is minimal in the regions where the solution is smooth. The direct consequence is that the nominal convergence rate of the high-order solution of smooth problems is not degraded. To our knowledge, this is the first application in atmospheric modeling of a spectral element model stabilized by an eddy viscosity scheme that, by construction, may fulfill stabilization requirements, can model turbulence via LES, and is completely free of a user-tunable parameter. From its derivation, it will be immediately clear that Dyn-SGS is independent of the numerical method; it could be implemented in a discontinuous Galerkin, finite volume, or other environments alike. Preliminary discontinuous Galerkin results are reported as well. The straightforward extension to non-linear scalar problems is also described. A suite of 1D, 2D, and 3D test cases is used to assess the method, with some comparison against the results obtained with the most known Lilly-Smagorinsky SGS model.

Stability of numerous novel potassium chlorides at high pressure

NASA Astrophysics Data System (ADS)

Zhang, Weiwei; Oganov, Artem R.; Zhu, Qiang; Lobanov, Sergey S.; Stavrou, Elissaios; Goncharov, Alexander F.

2016-05-01

K-Cl is a simple system displaying all four main types of bonding, as it contains (i) metallic potassium, (ii) elemental chlorine made of covalently bonded Cl2 molecules held together by van der Waals forces, and (iii) an archetypal ionic compound KCl. The charge balance rule, assigning classical charges of “+1” to K and “-1” to Cl, predicts that no compounds other than KCl are possible. However, our quantum-mechanical variable-composition evolutionary simulations predict an extremely complex phase diagram, with new thermodynamically stable compounds K3Cl, K2Cl, K3Cl2, K4Cl3, K5Cl4, K3Cl5, KCl3 and KCl7. Of particular interest are 2D-metallic homologs Kn+1Cln, the presence of positively charged Cl atoms in KCl7, and the predicted stability of KCl3 already at nearly ambient pressures at zero Kelvin. We have synthesized cubic -KCl3 at 40-70 GPa and trigonal -KCl3 at 20-40 GPa in a laser-heated diamond anvil cell (DAC) at temperature exceeding 2000 K from KCl and Cl2. These phases were identified using in situ synchrotron X-ray diffraction and Raman spectroscopy. Upon unloading to 10 GPa, -KCl3 transforms to a yet unknown structure before final decomposition to KCl and Cl2 at near-ambient conditions.

Methods and apparatus for broadband frequency comb stabilization

DOEpatents

Cox, Jonathan A; Kaertner, Franz X

2015-03-17

Feedback loops can be used to shift and stabilize the carrier-envelope phase of a frequency comb from a mode-locked fibers laser or other optical source. Compared to other frequency shifting and stabilization techniques, feedback-based techniques provide a wideband closed-loop servo bandwidth without optical filtering, beam pointing errors, or group velocity dispersion. It also enables phase locking to a stable reference, such as a Ti:Sapphire laser, continuous-wave microwave or optical source, or self-referencing interferometer, e.g., to within 200 mrad rms from DC to 5 MHz. In addition, stabilized frequency combs can be coherently combined with other stable signals, including other stabilized frequency combs, to synthesize optical pulse trains with pulse durations of as little as a single optical cycle. Such a coherent combination can be achieved via orthogonal control, using balanced optical cross-correlation for timing stabilization and balanced homodyne detection for phase stabilization.

Stability Limits and Dynamics of Nonaxisymmetric Liquid Bridges

NASA Technical Reports Server (NTRS)

Alexander, J. Iwan D.

1998-01-01

Theoretical and experimental investigation of the stability of nonaxisymmetric and nonaxisymmetric bridges contained between equal and unequal radii disks as a function of Bond and Weber number with emphasis on the transition from unstable axisymmetric to stable nonaxisymmetric shapes. Numerical analysis of the stability of nonaxisymmetric bridges for various orientations of the gravity vector for equal and unequal disks. Experimental and theoretical investigation of large (nonaxisymmetric) oscillations and breaking of liquid bridges. This project involves both experimental and theoretical work. Static and dynamic experiments are conducted in a Plateau tank which makes a range of static Bond numbers accessible.

Note on the stability of viscous roll waves

NASA Astrophysics Data System (ADS)

Barker, Blake; Johnson, Mathew A.; Noble, Pascal; Rodrigues, Luis Miguel; Zumbrun, Kevin

2017-02-01

In this note, we announce a complete classification of the stability of periodic roll-wave solutions of the viscous shallow water equations, from their onset at Froude number F ≈ 2 up to the infinite Froude limit. For intermediate Froude numbers, we obtain numerically a particularly simple power-law relation between F and the boundaries of the region of stable periods, which appears potentially useful in hydraulic engineering applications. In the asymptotic regime F → 2 (onset), we provide an analytic expression of the stability boundaries, whereas in the limit F → ∞, we show that roll waves are always unstable.

Prediction of slope stability based on numerical modeling of stress–strain state of rocks

NASA Astrophysics Data System (ADS)

Kozhogulov Nifadyev, KCh, VI; Usmanov, SF

2018-03-01

The paper presents the developed technique for the estimation of rock mass stability based on the finite element modeling of stress–strain state of rocks. The modeling results on the pit wall landslide as a flow of particles along a sloped surface are described.

Social Capital and Educational Achievements: Coleman vs. Bourdieu

ERIC Educational Resources Information Center

Rogošic, Silvia; Baranovic, Branislava

2016-01-01

The influence of social capital on an individual's educational achievements is the subject of numerous scientific papers. Research on social capital is most frequently based on Coleman's (1988) or Bourdieu's (1986) theories of capital, which are related to different paradigms of social theory: whereas Coleman's approach has its roots in structural…

Marital Values and Factors Associated With Marriage Stability.

ERIC Educational Resources Information Center

Rambo, Brenda Clanton; And Others

The breakdown of marriage within American society is a serious problem as evidenced by high divorce rates and numerous separations and family problems. A Marriage Values Questionnaire, developed to determine reasons for marrying and staying married and the impact of religion on marital stability, was completed by 305 subjects, ranging in age from…

An input-to-state stability approach to verify almost global stability of a synchronous-machine-infinite-bus system.

PubMed

Schiffer, Johannes; Efimov, Denis; Ortega, Romeo; Barabanov, Nikita

2017-08-13

Conditions for almost global stability of an operating point of a realistic model of a synchronous generator with constant field current connected to an infinite bus are derived. The analysis is conducted by employing the recently proposed concept of input-to-state stability (ISS)-Leonov functions, which is an extension of the powerful cell structure principle developed by Leonov and Noldus to the ISS framework. Compared with the original ideas of Leonov and Noldus, the ISS-Leonov approach has the advantage of providing additional robustness guarantees. The efficiency of the derived sufficient conditions is illustrated via numerical experiments.This article is part of the themed issue 'Energy management: flexibility, risk and optimization'. © 2017 The Author(s).

Onto the stability analysis of hyperbolic secant-shaped Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Sabari, S.; Murali, R.

2018-05-01

We analyze the stability of the hyperbolic secant-shaped attractive Bose-Einstein condensate in the absence of external trapping potential. The appropriate theoretical model for the system is described by the nonlinear mean-field Gross-Pitaevskii equation with time varying two-body interaction effects. Using the variational method, the stability of the system is analyzed under the influence of time varying two-body interactions. Further we confirm that the stability of the attractive condensate increases by considering the hyperbolic secant-shape profile instead of Gaussian shape. The analytical results are compared with the numerical simulation by employing the split-step Crank-Nicholson method.

The stability of portfolio investment in stock crashes

NASA Astrophysics Data System (ADS)

Li, Yun-Xian; Qian, Zhen-Wei; Li, Jiang-Cheng; Tang, Nian-Sheng; Mei, Dong-Cheng

2016-08-01

The stability of portfolio investment in stock market crashes with Markowitz portfolio is investigated by the method of theoretical and empirical simulation. From numerical simulation of the mean escape time (MET), we conclude that: (i) The increasing number (Np) of stocks in Markowitz portfolio induces a maximum in the curve of MET versus the initial position; (ii) A critical value of Np in the behavior of MET versus the long-run variance or amplitude of volatility fluctuations maximumlly enhances the stability of portfolio investment. When Np takes value below the critical value, the increasing Np enhances the stability of portfolio investment, but restrains it when Np takes value above the critical value. In addition, a good agreement of both the MET and probability density functions of returns is found between real data and theoretical results.

Influence of the Roof Movement Control Method on the Stability of Remnant

NASA Astrophysics Data System (ADS)

Adach-Pawelus, Karolina

2017-12-01

In the underground mines, there are geological and mining situations that necessitate leaving behind remnants in the mining field. Remnants, in the form of small, irregular parcels, are usually separated in the case of: significant problems with maintaining roof stability, high rockburst hazard, the occurrence of complex geological conditions and for random reasons (ore remnants), as well as for economic reasons (undisturbed rock remnants). Remnants left in the mining field become sites of high stress values concentration and may affect the rock in their vicinity. The values of stress inside the remnant and its vicinity, as well as the stability of the remnant, largely depend on the roof movement control method used in the mining field. The article presents the results of the numerical analysis of the influence of roof movement control method on remnant stability and the geomechanical situation in the mining field. The numerical analysis was conducted for the geological and mining conditions characteristic of Polish underground copper mines owned by KGHM Polska Miedz S.A. Numerical simulations were performed in a plane strain state by means of Phase 2 v. 8.0 software, based on the finite element method. The behaviour of remnant and rock mass in its vicinity was simulated in the subsequent steps of the room and pillar mining system for three types of roof movement control method: roof deflection, dry backfill and hydraulic backfill. The parameters of the rock mass accepted for numerical modelling were calculated by means of RocLab software on the basis of the Hoek-Brown classification. The Mohr-Coulomb strength criterion was applied.

Delay-slope-dependent stability results of recurrent neural networks.

PubMed

Li, Tao; Zheng, Wei Xing; Lin, Chong

2011-12-01

By using the fact that the neuron activation functions are sector bounded and nondecreasing, this brief presents a new method, named the delay-slope-dependent method, for stability analysis of a class of recurrent neural networks with time-varying delays. This method includes more information on the slope of neuron activation functions and fewer matrix variables in the constructed Lyapunov-Krasovskii functional. Then some improved delay-dependent stability criteria with less computational burden and conservatism are obtained. Numerical examples are given to illustrate the effectiveness and the benefits of the proposed method.

Stability and Evolution of Multiple Planet and Satellite Systems

NASA Astrophysics Data System (ADS)

Quillen, Alice

Numerous multiple planet systems have recently been discovered with the Kepler Mission, suggesting that multiple planet systems are common. Multiple- body nearly coplanar satellite systems are also found in the Solar system. Multiple planet and satellite systems exhibit rich dynamics as they are affected by three-body and secular resonances affecting short timescale behavior and long timescale stability. Interactions with debris disks and planetesimal belts and tidal interactions can both reduce and induce instability. Using both numerical and analytical studies, we propose to develop a broadly applicable framework to estimate diffusion rates and stability regimes both in resonant and non- resonant configurations. Understanding of resonant dynamics is needed to understand each of these systems and a broader general theory would cover scenarios and mechanisms that are relevant for all of them. Architectures and dynamical mechanisms will be used to test scenarios for formation and evolution of multiple body systems and constrain poorly known quantities such as masses, eccentricities, inclinations, radii, and the existence of undetected bodies.

An apparent contradiction: increasing variability to achieve greater precision?

PubMed

Rosenblatt, Noah J; Hurt, Christopher P; Latash, Mark L; Grabiner, Mark D

2014-02-01

To understand the relationship between variability of foot placement in the frontal plane and stability of gait patterns, we explored how constraining mediolateral foot placement during walking affects the structure of kinematic variance in the lower-limb configuration space during the swing phase of gait. Ten young subjects walked under three conditions: (1) unconstrained (normal walking), (2) constrained (walking overground with visual guides for foot placement to achieve the measured unconstrained step width) and, (3) beam (walking on elevated beams spaced to achieve the measured unconstrained step width). The uncontrolled manifold analysis of the joint configuration variance was used to quantify two variance components, one that did not affect the mediolateral trajectory of the foot in the frontal plane ("good variance") and one that affected this trajectory ("bad variance"). Based on recent studies, we hypothesized that across conditions (1) the index of the synergy stabilizing the mediolateral trajectory of the foot (the normalized difference between the "good variance" and "bad variance") would systematically increase and (2) the changes in the synergy index would be associated with a disproportionate increase in the "good variance." Both hypotheses were confirmed. We conclude that an increase in the "good variance" component of the joint configuration variance may be an effective method of ensuring high stability of gait patterns during conditions requiring increased control of foot placement, particularly if a postural threat is present. Ultimately, designing interventions that encourage a larger amount of "good variance" may be a promising method of improving stability of gait patterns in populations such as older adults and neurological patients.

BiPOD Arthroscopic Acromioclavicular Repair Restores Bidirectional Stability.

PubMed

De Beer, Joe; Schaer, Michael; Latendresse, Kim; Raniga, Sumit; Moor, Beat K; Zumstein, Matthias A

2017-01-01

Stabilizing the acromioclavicular joint in the vertical and horizontal planes is challenging, and most current techniques do not reliably achieve this goal. The BiPOD repair is an arthroscopically assisted procedure performed with image intensifier guidance that reconstructs the coracoclavicular ligaments as well as the acromioclavicular ligaments to achieve bidirectional stability. Repair is achieved with a combination of 2-mm FiberTape (Arthrex, Naples, Florida) and 20-mm Poly-Tape (Neoligaments, Leeds, England) to achieve rigid repair, prevent bone abrasion, and promote tissue ingrowth. This study is a prospective review of the first 6 patients treated for high-grade acute acromioclavicular injury with the BiPOD technique. The study included 6 men who were 21 to 36 years old (mean, 27 years). At 6-month follow-up, complications were recorded and radiographic analysis was used to determine the coracoclavicular distance for vertical reduction and the amount of acromioclavicular translation on the Alexander axillary view was used to determine horizontal reduction. One patient had a superficial infection over the tape knot. The difference in coracoclavicular distance between the operated side and the uninvolved side was 9±2 mm preoperatively and 0.3±2 mm at 6-month follow-up. On Alexander axillary view, all 6 patients showed stable reduction, which is defined as a clavicle that is in line with the acromion. The findings show that BiPOD acromioclavicular reconstruction restores bidirectional stability of the acromioclavicular joint at 6 months. [Orthopedics. 2017; 40(1):e35-e43.]. Copyright 2016, SLACK Incorporated.

Exploratory Research on Bearing Characteristics of Confined Stabilized Soil

NASA Astrophysics Data System (ADS)

Wu, Shuai Shuai; Gao, Zheng Guo; Li, Shi Yang; Cui, Wen Bo; Huang, Xin

2018-06-01

The performance of a new kind of confined stabilized soil (CSS) was investigated which was constructed by filling the stabilized soil, which was made by mixing soil with a binder containing a high content of expansive component, into an engineering plastic pipe. Cube compressive strength of the stabilized soil formed with constraint and axial compression performance of stabilized soil cylinders confined with the constraint pipe were measured. The results indicated that combining the constraint pipe and the binder containing expansion component could achieve such effects: higher production of expansive hydrates could be adopted so as to fill more voids in the stabilized soil and improve its strength; at the same time compressive prestress built on the core stabilized soil, combined of which hoop constraint provided effective radial compressive force on the core stabilized soil. These effects made the CSS acquire plastic failure mode and more than twice bearing capacity of ordinary stabilized soil with the same binder content.

The numerical dynamic for highly nonlinear partial differential equations

NASA Technical Reports Server (NTRS)

Lafon, A.; Yee, H. C.

1992-01-01

Problems associated with the numerical computation of highly nonlinear equations in computational fluid dynamics are set forth and analyzed in terms of the potential ranges of spurious behaviors. A reaction-convection equation with a nonlinear source term is employed to evaluate the effects related to spatial and temporal discretizations. The discretization of the source term is described according to several methods, and the various techniques are shown to have a significant effect on the stability of the spurious solutions. Traditional linearized stability analyses cannot provide the level of confidence required for accurate fluid dynamics computations, and the incorporation of nonlinear analysis is proposed. Nonlinear analysis based on nonlinear dynamical systems complements the conventional linear approach and is valuable in the analysis of hypersonic aerodynamics and combustion phenomena.

Numerical and experimental study of the dynamics of a superheated jet

NASA Astrophysics Data System (ADS)

Sinha, Avick; Gopalakrishnan, Shivasubramanian; Balasubramanian, Sridhar

2015-11-01

Flash-boiling is a phenomenon where a liquid experiences low pressures in a system resulting in it getting superheated. The sudden drop in pressures results in accelerated expansion and violent vapour formation. Understanding the physics behind the jet disintegration and flash-boiling phenomenon is still an open problem, with applications in automotive and aerospace combustors. The behaviour of a flash-boiling jet is highly dependent on the input parameters, inlet temperature and pressure. In the present study, the external (outside nozzle) and the internal (inside nozzle) flow characteristics of the two-phase flow has been studied numerically and experimentally. The phase change from liquid to vapour takes place over a finite period of time, modeled sing Homogeneous Relaxation Model (HRM). In order to validate the numerical results, controlled experiments were performed. Optical diagnostic techniques such as Particle Image Velocimetry (PIV) and Shadowgraphy were used to study the flow characteristics. Spray angle, penetration depth, droplet spectra were obtained which provides a better understanding of the break-up mechanism. Linear stability analysis is performed to study the stability characteristics of the jet.

Approximate message passing for nonconvex sparse regularization with stability and asymptotic analysis

NASA Astrophysics Data System (ADS)

Sakata, Ayaka; Xu, Yingying

2018-03-01

We analyse a linear regression problem with nonconvex regularization called smoothly clipped absolute deviation (SCAD) under an overcomplete Gaussian basis for Gaussian random data. We propose an approximate message passing (AMP) algorithm considering nonconvex regularization, namely SCAD-AMP, and analytically show that the stability condition corresponds to the de Almeida-Thouless condition in spin glass literature. Through asymptotic analysis, we show the correspondence between the density evolution of SCAD-AMP and the replica symmetric (RS) solution. Numerical experiments confirm that for a sufficiently large system size, SCAD-AMP achieves the optimal performance predicted by the replica method. Through replica analysis, a phase transition between replica symmetric and replica symmetry breaking (RSB) region is found in the parameter space of SCAD. The appearance of the RS region for a nonconvex penalty is a significant advantage that indicates the region of smooth landscape of the optimization problem. Furthermore, we analytically show that the statistical representation performance of the SCAD penalty is better than that of \

A nonlinear SIR with stability

NASA Astrophysics Data System (ADS)

Trisilowati, Darti, I.; Fitri, S.

2014-02-01

The aim of this work is to develop a mathematical model of a nonlinear susceptible-infectious-removed (SIR) epidemic model with vaccination. We analyze the stability of the model by linearizing the model around the equilibrium point. Then, diphtheria data from East Java province is fitted to the model. From these estimated parameters, we investigate which parameters that play important role in the epidemic model. Some numerical simulations are given to illustrate the analytical results and the behavior of the model.

Physiology driven adaptivity for the numerical solution of the bidomain equations.

PubMed

Whiteley, Jonathan P

2007-09-01

Previous work [Whiteley, J. P. IEEE Trans. Biomed. Eng. 53:2139-2147, 2006] derived a stable, semi-implicit numerical scheme for solving the bidomain equations. This scheme allows the timestep used when solving the bidomain equations numerically to be chosen by accuracy considerations rather than stability considerations. In this study we modify this scheme to allow an adaptive numerical solution in both time and space. The spatial mesh size is determined by the gradient of the transmembrane and extracellular potentials while the timestep is determined by the values of: (i) the fast sodium current; and (ii) the calcium release from junctional sarcoplasmic reticulum to myoplasm current. For two-dimensional simulations presented here, combining the numerical algorithm in the paper cited above with the adaptive algorithm presented here leads to an increase in computational efficiency by a factor of around 250 over previous work, together with significantly less computational memory being required. The speedup for three-dimensional simulations is likely to be more impressive.

An efficient technique for the numerical solution of the bidomain equations.

PubMed

Whiteley, Jonathan P

2008-08-01

Computing the numerical solution of the bidomain equations is widely accepted to be a significant computational challenge. In this study we extend a previously published semi-implicit numerical scheme with good stability properties that has been used to solve the bidomain equations (Whiteley, J.P. IEEE Trans. Biomed. Eng. 53:2139-2147, 2006). A new, efficient numerical scheme is developed which utilizes the observation that the only component of the ionic current that must be calculated on a fine spatial mesh and updated frequently is the fast sodium current. Other components of the ionic current may be calculated on a coarser mesh and updated less frequently, and then interpolated onto the finer mesh. Use of this technique to calculate the transmembrane potential and extracellular potential induces very little error in the solution. For the simulations presented in this study an increase in computational efficiency of over two orders of magnitude over standard numerical techniques is obtained.

Asymptotic theory of neutral stability of the Couette flow of a vibrationally excited gas

NASA Astrophysics Data System (ADS)

Grigor'ev, Yu. N.; Ershov, I. V.

2017-01-01

An asymptotic theory of the neutral stability curve for a supersonic plane Couette flow of a vibrationally excited gas is developed. The initial mathematical model consists of equations of two-temperature viscous gas dynamics, which are used to derive a spectral problem for a linear system of eighth-order ordinary differential equations within the framework of the classical linear stability theory. Unified transformations of the system for all shear flows are performed in accordance with the classical Lin scheme. The problem is reduced to an algebraic secular equation with separation into the "inviscid" and "viscous" parts, which is solved numerically. It is shown that the thus-calculated neutral stability curves agree well with the previously obtained results of the direct numerical solution of the original spectral problem. In particular, the critical Reynolds number increases with excitation enhancement, and the neutral stability curve is shifted toward the domain of higher wave numbers. This is also confirmed by means of solving an asymptotic equation for the critical Reynolds number at the Mach number M ≤ 4.

Stability of organic solar cells: challenges and strategies.

PubMed

Cheng, Pei; Zhan, Xiaowei

2016-05-03

Organic solar cells (OSCs) present some advantages, such as simple preparation, light weight, low cost and large-area flexible fabrication, and have attracted much attention in recent years. Although the power conversion efficiencies have exceeded 10%, the inferior device stability still remains a great challenge. In this review, we summarize the factors limiting the stability of OSCs, such as metastable morphology, diffusion of electrodes and buffer layers, oxygen and water, irradiation, heating and mechanical stress, and survey recent progress in strategies to increase the stability of OSCs, such as material design, device engineering of active layers, employing inverted geometry, optimizing buffer layers, using stable electrodes and encapsulation. Some research areas of device stability that may deserve further attention are also discussed to help readers understand the challenges and opportunities in achieving high efficiency and high stability of OSCs towards future industrial manufacture.

Numerical simulation of unsteady viscous flows

NASA Technical Reports Server (NTRS)

Hankey, Wilbur L.

1987-01-01

Most unsteady viscous flows may be grouped into two categories, i.e., forced and self-sustained oscillations. Examples of forced oscillations occur in turbomachinery and in internal combustion engines while self-sustained oscillations prevail in vortex shedding, inlet buzz, and wing flutter. Numerical simulation of these phenomena was achieved due to the advancement of vector processor computers. Recent progress in the simulation of unsteady viscous flows is addressed.

Fundamental Aerodynamic Investigations for Development of Arrow-Stabilized Projectiles

NASA Technical Reports Server (NTRS)

Kurzweg, Hermann

1947-01-01

The numerous patent applications on arrow-stabilized projectiles indicate that the idea of projectiles without spin is not new, but has appeared in various proposals throughout the last decades. As far as projectiles for subsonic speeds are concerned, suitable shapes have been developed for sometime, for example, numerous grenades. Most of the patent applications, though, are not practicable particularly for projectiles with supersonic speed. This is because the inventor usually does not have any knowledge of aerodynamic flow around the projectile nor any particular understanding of the practical solution. The lack of wind tunnels for the development of projectiles made it necessary to use firing tests for development. These are obviously extremely tedious or expensive and lead almost always to failures. The often expressed opinion that arrow-stabilized projectiles cannot fly supersonically can be traced to this condition. That this is not the case has been shown for the first time by Roechling on long projectiles with foldable fins. Since no aerodynamic investigations were made for the development of these projectiles, only tedious series of firing tests with systematic variation of the fins could lead to satisfactory results. These particular projectiles though have a disadvantage which lies in the nature cf foldable fins. They occasionally do not open uniformly in flight, thus causing unsymmetry in flow and greater scatter. The junctions of fins and body are very bad aerodynamically and increase the drag. It must be possible to develop high-performance arrow-stabilized projectiles based on the aerodynamic research conducted during the last few years at Peenemuende and new construction ideas. Thus the final shape, ready for operational use, could be developed in the wind tunnel without loss of expensive time in firing tests. The principle of arrow-stabilized performance has been applied to a large number of caliburs which were stabilized by various means Most

The Stability of Chandra Telescope Pointing and Spacial Resolution

NASA Astrophysics Data System (ADS)

Zhao, Ping

2018-01-01

Chandra X-ray Observatory revolutionized the X-ray astronomy as being the first, and so far the only, X-ray telescope achieving sub-arcsecond spacial resolution. Chandra is comprised of three principal elements: the High Resolution Mirror Assembly (HRMA), Pointing Control and Aspect Determination (PCAD) system, and the Science Instrument Module (SIM), which is where the X-ray detectors mounted and is connected to the HRMA by a 10-meter long Optical Bench Assembly. To achieve and retain the unprecedented imaging quality, it is critical that these three principal elements to stay rigid and stable for the entire life time of the Chandra operation. I will review the issues of telescope pointing stability, optical Axis, aimpoint and their impacts to the Chandra operation, and evaluate the integrity and stability of the telescope. I will show images taken from all four detectors since launch to demonstrate the quality and stability of the Chandra spacial resolution.

The Quality and Stability of Chandra Telescope Spacial Resolution

NASA Astrophysics Data System (ADS)

Zhao, Ping

2017-08-01

Chandra X-ray Observatory revolutionized the X-ray astronomy as being the first, and so far the only, X-ray telescope achieving sub-arcsecond spacial resolution. Chandra is comprised of three principal elements: the High Resolution Mirror Assembly (HRMA), Pointing Control and Aspect Determination (PCAD) system, and the Science Instrument Module (SIM), which is where the X-ray detectors mounted and is connected to the HRMA by a 10-meter long Optical Bench Assembly. To achieve and retain the unprecedented imaging quality, it is critical that these three principal elements to stay rigid and stable for the entire life time of the Chandra operation. I will review the issues of telescope pointing stability, optical Axis, aimpoint and their impacts to the Chandra operation, and evaluate the integrity and stability of the telescope. I will show images taken from all four detectors since launch to demonstrate the quality and stability of the Chandra spacial resolution.

Control-based continuation: Bifurcation and stability analysis for physical experiments

NASA Astrophysics Data System (ADS)

Barton, David A. W.

2017-02-01

Control-based continuation is technique for tracking the solutions and bifurcations of nonlinear experiments. The idea is to apply the method of numerical continuation to a feedback-controlled physical experiment such that the control becomes non-invasive. Since in an experiment it is not (generally) possible to set the state of the system directly, the control target becomes a proxy for the state. Control-based continuation enables the systematic investigation of the bifurcation structure of a physical system, much like if it was numerical model. However, stability information (and hence bifurcation detection and classification) is not readily available due to the presence of stabilising feedback control. This paper uses a periodic auto-regressive model with exogenous inputs (ARX) to approximate the time-varying linearisation of the experiment around a particular periodic orbit, thus providing the missing stability information. This method is demonstrated using a physical nonlinear tuned mass damper.

The stability of a trailing-line vortex in compressible flow

NASA Technical Reports Server (NTRS)

Stott, Jillian A. K.; Duck, Peter W.

1992-01-01

We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (aximuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, while new 'center mode' forms, whose stability characteristics, are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex. Throughout the paper, comparison is made between our numerical results and results obtained from the various asymptotic theories.

The Academic Achievement of Immigrant Children in Japan: An Empirical Analysis of the Assimilation Hypothesis

ERIC Educational Resources Information Center

Ishida, Kenji; Nakamuro, Makiko; Takenaka, Ayumi

2016-01-01

In this study, we test the assimilation thesis by comparing the academic achievement between native students and first and second generation immigrant pupils. It is the first empirical study that systematically analyzes the native-immigrant achievement gap in Japan. Although numerous studies have examined the achievement gap, most of them are…

Hydrostatic calculations of axisymmetric flow and its stability for the AGCE model

NASA Technical Reports Server (NTRS)

Miller, T. L.; Gall, R. L.

1981-01-01

Baroclinic waves in the atmospherics general circulation experiment (AGCE) apparatus by the use of numerical hydrostatic primitive equation models were determined. The calculation is accomplished by using an axisymmetric primitive equation model to compute, for a given set of experimental parameters, a steady state axisymmetric flow and then testing this axisymmetric flow for stability using a linear primitive equation model. Some axisymmetric flows are presented together with preliminary stability calculations.

Spontaneous nucleation and topological stabilization of skyrmions in magnetic nanodisks with the interfacial Dzyaloshinskii-Moriya interaction

NASA Astrophysics Data System (ADS)

Kolesnikov, A. G.; Samardak, A. S.; Stebliy, M. E.; Ognev, A. V.; Chebotkevich, L. A.; Sadovnikov, A. V.; Nikitov, S. A.; Kim, Yong Jin; Cha, In Ho; Kim, Young Keun

2017-05-01

One of the major societal challenges is reducing the power consumption of information technology (IT) devices and numerous data centers. Distinct from the current approaches based on switching of magnetic single-domain nanostructures or on movement of domain walls under high currents, an original magnetic skyrmion technology offers ultra-low power, fast, high-density, and scalable spintronic devices, including non-volatile random access memory. Using data-driven micromagnetic simulations, we demonstrate the possibility of spontaneous nucleation and stabilization of different skyrmionic states, such as skyrmions, merons, and meron-like configurations, in heavy metal/ferromagnetic nanodisks with the interfacial Dzyaloshinskii-Moriya interaction (iDMI) as a result of quasi-static magnetization reversal only. Since iDMI is not easily modulated in real systems, we show that skyrmion stabilization is easily achievable by manipulating magnetic anisotropy, saturation magnetization, and the diameters of nanodisks. The state diagrams, presented in terms of the topological charge, allow to explicitly distinguish the intermediate states between skyrmions and merons and can be used for developing a skyrmionic medium, which has been recently proposed to be a building block for future spin-orbitronic devices.

A heterogenous Cournot duopoly with delay dynamics: Hopf bifurcations and stability switching curves

NASA Astrophysics Data System (ADS)

Pecora, Nicolò; Sodini, Mauro

2018-05-01

This article considers a Cournot duopoly model in a continuous-time framework and analyze its dynamic behavior when the competitors are heterogeneous in determining their output decision. Specifically the model is expressed in the form of differential equations with discrete delays. The stability conditions of the unique Nash equilibrium of the system are determined and the emergence of Hopf bifurcations is shown. Applying some recent mathematical techniques (stability switching curves) and performing numerical simulations, the paper confirms how different time delays affect the stability of the economy.

Numerical simulation of disperse particle flows on a graphics processing unit

NASA Astrophysics Data System (ADS)

Sierakowski, Adam J.

In both nature and technology, we commonly encounter solid particles being carried within fluid flows, from dust storms to sediment erosion and from food processing to energy generation. The motion of uncountably many particles in highly dynamic flow environments characterizes the tremendous complexity of such phenomena. While methods exist for the full-scale numerical simulation of such systems, current computational capabilities require the simplification of the numerical task with significant approximation using closure models widely recognized as insufficient. There is therefore a fundamental need for the investigation of the underlying physical processes governing these disperse particle flows. In the present work, we develop a new tool based on the Physalis method for the first-principles numerical simulation of thousands of particles (a small fraction of an entire disperse particle flow system) in order to assist in the search for new reduced-order closure models. We discuss numerous enhancements to the efficiency and stability of the Physalis method, which introduces the influence of spherical particles to a fixed-grid incompressible Navier-Stokes flow solver using a local analytic solution to the flow equations. Our first-principles investigation demands the modeling of unresolved length and time scales associated with particle collisions. We introduce a collision model alongside Physalis, incorporating lubrication effects and proposing a new nonlinearly damped Hertzian contact model. By reproducing experimental studies from the literature, we document extensive validation of the methods. We discuss the implementation of our methods for massively parallel computation using a graphics processing unit (GPU). We combine Eulerian grid-based algorithms with Lagrangian particle-based algorithms to achieve computational throughput up to 90 times faster than the legacy implementation of Physalis for a single central processing unit. By avoiding all data

Endocavitary thermal therapy by MRI-guided phased-array contact ultrasound: experimental and numerical studies on the multi-input single-output PID temperature controller's convergence and stability.

PubMed

Salomir, Rares; Rata, Mihaela; Cadis, Daniela; Petrusca, Lorena; Auboiroux, Vincent; Cotton, François

2009-10-01

Endocavitary high intensity contact ultrasound (HICU) may offer interesting therapeutic potential for fighting localized cancer in esophageal or rectal wall. On-line MR guidance of the thermotherapy permits both excellent targeting of the pathological volume and accurate preoperatory monitoring of the temperature elevation. In this article, the authors address the issue of the automatic temperature control for endocavitary phased-array HICU and propose a tailor-made thermal model for this specific application. The convergence and stability of the feedback loop were investigated against tuning errors in the controller's parameters and against input noise, through ex vivo experimental studies and through numerical simulations in which nonlinear response of tissue was considered as expected in vivo. An MR-compatible, 64-element, cooled-tip, endorectal cylindrical phased-array applicator of contact ultrasound was integrated with fast MR thermometry to provide automatic feedback control of the temperature evolution. An appropriate phase law was applied per set of eight adjacent transducers to generate a quasiplanar wave, or a slightly convergent one (over the circular dimension). A 2D physical model, compatible with on-line numerical implementation, took into account (1) the ultrasound-mediated energy deposition, (2) the heat diffusion in tissue, and (3) the heat sink effect in the tissue adjacent to the tip-cooling balloon. This linear model was coupled to a PID compensation algorithm to obtain a multi-input single-output static-tuning temperature controller. Either the temperature at one static point in space (situated on the symmetry axis of the beam) or the maximum temperature in a user-defined ROI was tracked according to a predefined target curve. The convergence domain in the space of controller's parameters was experimentally explored ex vivo. The behavior of the static-tuning PID controller was numerically simulated based on a discrete-time iterative solution

Time stability of spring and superconducting gravimeters through the analysis of very long gravity records

NASA Astrophysics Data System (ADS)

Calvo, Marta; Hinderer, Jacques; Rosat, Severine; Legros, Hilaire; Boy, Jean-Paul; Ducarme, Bernard; Zürn, Walter

2014-10-01

Long gravity records are of great interest when performing tidal analyses. Indeed, long series enable to separate contributions of near-frequency waves and also to detect low frequency signals (e.g. long period tides and polar motion). In addition to the length of the series, the quality of the data and the temporal stability of the noise are also very important. We study in detail some of the longest gravity records available in Europe: 3 data sets recorded with spring gravimeters in Black Forest Observatory (Germany, 1980-2012), Walferdange (Luxemburg, 1980-1995) and Potsdam (Germany, 1974-1998) and several superconducting gravimeters (SGs) data sets, with at least 9 years of continuous records, at different European GGP (Global Geodynamics Project) sites (Bad Homburg, Brussels, Medicina, Membach, Moxa, Vienna, Wettzell and Strasbourg). The stability of each instrument is investigated using the temporal variations of tidal parameters (amplitude factor and phase difference) for the main tidal waves (O1, K1, M2 and S2) as well as the M2/O1 factor ratio, the later being insensitive to the instrumental calibration. The long term stability of the tidal observations is also dependent on the stability of the scale factor of the relative gravimeters. Therefore we also check the time stability of the scale factor for the superconducting gravimeter C026 installed at the J9 Gravimetric Observatory of Strasbourg (France), using numerous calibration experiments carried out by co-located absolute gravimeter (AG) measurements during the last 15 years. The reproducibility of the scale factor and the achievable precision are investigated by comparing the results of different calibration campaigns. Finally we present a spectrum of the 25 years of SG records at J9 Observatory, with special attention to small amplitude tides in the semi-diurnal and diurnal bands, as well as to the low frequency part.

Dynamic stability of spinning pretwisted beams subjected to axial random forces

NASA Astrophysics Data System (ADS)

Young, T. H.; Gau, C. Y.

2003-11-01

This paper studies the dynamic stability of a pretwisted cantilever beam spinning along its longitudinal axis and subjected to an axial random force at the free end. The axial force is assumed as the sum of a constant force and a random process with a zero mean. Due to this axial force, the beam may experience parametric random instability. In this work, the finite element method is first applied to yield discretized system equations. The stochastic averaging method is then adopted to obtain Ito's equations for the response amplitudes of the system. Finally the mean-square stability criterion is utilized to determine the stability condition of the system. Numerical results show that the stability boundary of the system converges as the first three modes are taken into calculation. Before the convergence is reached, the stability condition predicted is not conservative enough.

Basic and Advanced Numerical Performances Relate to Mathematical Expertise but Are Fully Mediated by Visuospatial Skills

PubMed Central

2016-01-01

Recent studies have highlighted the potential role of basic numerical processing in the acquisition of numerical and mathematical competences. However, it is debated whether high-level numerical skills and mathematics depends specifically on basic numerical representations. In this study mathematicians and nonmathematicians performed a basic number line task, which required mapping positive and negative numbers on a physical horizontal line, and has been shown to correlate with more advanced numerical abilities and mathematical achievement. We found that mathematicians were more accurate compared with nonmathematicians when mapping positive, but not negative numbers, which are considered numerical primitives and cultural artifacts, respectively. Moreover, performance on positive number mapping could predict whether one is a mathematician or not, and was mediated by more advanced mathematical skills. This finding might suggest a link between basic and advanced mathematical skills. However, when we included visuospatial skills, as measured by block design subtest, the mediation analysis revealed that the relation between the performance in the number line task and the group membership was explained by non-numerical visuospatial skills. These results demonstrate that relation between basic, even specific, numerical skills and advanced mathematical achievement can be artifactual and explained by visuospatial processing. PMID:26913930

Effect of current vehicle’s interruption on traffic stability in cooperative car-following theory

NASA Astrophysics Data System (ADS)

Zhang, Geng; Liu, Hui

2017-12-01

To reveal the impact of the current vehicle’s interruption information on traffic flow, a new car-following model with consideration of the current vehicle’s interruption is proposed and the influence of the current vehicle’s interruption on traffic stability is investigated through theoretical analysis and numerical simulation. By linear analysis, the linear stability condition of the new model is obtained and the negative influence of the current vehicle’s interruption on traffic stability is shown in the headway-sensitivity space. Through nonlinear analysis, the modified Korteweg-de Vries (mKdV) equation of the new model near the critical point is derived and it can be used to describe the propagating behavior of the traffic density wave. Finally, numerical simulation confirms the analytical results, which shows that the current vehicle’s interruption information can destabilize traffic flow and should be considered in real traffic.

Prediction of soil stability and erosion in semiarid regions using numerical hydrological model (MCAT) and airborne hyperspectral imagery

NASA Astrophysics Data System (ADS)

Brook, Anna; Wittenberg, Lea

2015-04-01

promising models is the MCAT, which is a MATLAB library of visual and numerical analysis tools for the evaluation of hydrological and environmental models. The model applied in this paper presents an innovative infrastructural system for predicting soil stability and erosion impacts. This integrated model is applicable to mixed areas with spatially varying soil properties, landscape, and land-cover characteristics. Data from a semiarid site in southern Israel was used to evaluate the model and analyze fundamental erosion mechanisms. The findings estimate the sensitivity of the suggested model to the physical parameters and encourage the use of hyperspectral remote sensing imagery (HSI). The proposed model is integrated according to the following stages: 1. The soil texture, aggregation, soil moisture estimated via airborne HSI data, including soil surface clay and calcium carbonate erosions; 2. The mechanical stability of soil assessed via pedo-transfer function corresponding to load dependent changes in soil physical properties due to pre-compression stress (set of equations study shear strength parameters take into account soil texture, aggregation, soil moisture and ecological soil variables); 3. The precipitation-related runoff model program (RMP) satisfactorily reproduces the observed seasonal mean and variation of surface runoff for the current climate simulation; 4. The Monte Carlo Analysis Toolbox (MCAT), a library of visual and numerical analysis tools for the evaluation of hydrological and environmental models, is proposed as a tool for integrate all the approaches to an applicable model. The presented model overcomes the limitations of existing modeling methods by integrating physical data produced via HSI and yet stays generic in terms of space and time independency.

Optical stabilization for time transfer infrastructure

NASA Astrophysics Data System (ADS)

Vojtech, Josef; Altmann, Michal; Skoda, Pavel; Horvath, Tomas; Slapak, Martin; Smotlacha, Vladimir; Havlis, Ondrej; Munster, Petr; Radil, Jan; Kundrat, Jan; Altmannova, Lada; Velc, Radek; Hula, Miloslav; Vohnout, Rudolf

2017-08-01

In this paper, we propose and present verification of all-optical methods for stabilization of the end-to-end delay of an optical fiber link. These methods are verified for deployment within infrastructure for accurate time and stable frequency distribution, based on sharing of fibers with research and educational network carrying live data traffic. Methods range from path length control, through temperature conditioning method to transmit wavelength control. Attention is given to achieve continuous control for relatively broad range of delays. We summarize design rules for delay stabilization based on the character and the total delay jitter.

Stability analysis for stochastic BAM nonlinear neural network with delays

NASA Astrophysics Data System (ADS)

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

2008-02-01

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

Stability of a laminar premixed supersonic free shear layer with chemical reactions

NASA Technical Reports Server (NTRS)

Menon, S.; Anderson, J. D., Jr.; Pai, S. I.

1984-01-01

The stability of a two-dimensional compressible supersonic flow in the wake of a flat plate is discussed. The fluid is a multi-species mixture which is undergoing finite rate chemical reactions. The spatial stability of an infinitesimal disturbance in the fluid is considered. Numerical solutions of the eigenvalue stability equations for both reactive and nonreactive supersonic flows are presented and discussed. The chemical reactions have significant influence on the stability behavior. For instance, a neutral eigenvalue is observed near the freestream Mach number of 2.375 for the nonreactive case, but disappears when the reaction is turned on. For reactive flows, the eigenvalues are not very dependent on the free stream Mach number.

On the Achievable Throughput Over TVWS Sensor Networks

PubMed Central

Caleffi, Marcello; Cacciapuoti, Angela Sara

2016-01-01

In this letter, we study the throughput achievable by an unlicensed sensor network operating over TV white space spectrum in presence of coexistence interference. Through the letter, we first analytically derive the achievable throughput as a function of the channel ordering. Then, we show that the problem of deriving the maximum expected throughput through exhaustive search is computationally unfeasible. Finally, we derive a computational-efficient algorithm characterized by polynomial-time complexity to compute the channel set maximizing the expected throughput and, stemming from this, we derive a closed-form expression of the maximum expected throughput. Numerical simulations validate the theoretical analysis. PMID:27043565

Viscous, resistive MHD stability computed by spectral techniques

NASA Technical Reports Server (NTRS)

Dahlburg, R. B.; Zang, T. A.; Montgomery, D.; Hussaini, M. Y.

1983-01-01

Expansions in Chebyshev polynomials are used to study the linear stability of one dimensional magnetohydrodynamic (MHD) quasi-equilibria, in the presence of finite resistivity and viscosity. The method is modeled on the one used by Orszag in accurate computation of solutions of the Orr-Sommerfeld equation. Two Reynolds like numbers involving Alfven speeds, length scales, kinematic viscosity, and magnetic diffusivity govern the stability boundaries, which are determined by the geometric mean of the two Reynolds like numbers. Marginal stability curves, growth rates versus Reynolds like numbers, and growth rates versus parallel wave numbers are exhibited. A numerical result which appears general is that instability was found to be associated with inflection points in the current profile, though no general analytical proof has emerged. It is possible that nonlinear subcritical three dimensional instabilities may exist, similar to those in Poiseuille and Couette flow.

Influence of foam on the stability characteristics of immiscible flow in porous media

NASA Astrophysics Data System (ADS)

van der Meer, J. M.; Farajzadeh, R.; Rossen, W. R.; Jansen, J. D.

2018-01-01

Accurate field-scale simulations of foam enhanced oil recovery are challenging, due to the sharp transition between gas and foam. Hence, unpredictable numerical and physical behavior is often observed, casting doubt on the validity of the simulation results. In this paper, a thorough stability analysis of the foam model is presented to validate the simulation results. We study the effect of a strongly non-monotonous total mobility function arising from foam models on the stability characteristics of the flow. To this end, we apply the linear stability analysis to nearly discontinuous relative permeability functions and compare the results with those of highly accurate numerical simulations. In addition, we present a qualitative analysis of the effect of different reservoir and fluid properties on the foam fingering behavior. In particular, we consider the effect of heterogeneity of the reservoir, injection rates, and foam quality. Relative permeability functions play an important role in the onset of fingering behavior of the injected fluid. Hence, we can deduce that stability properties are highly dependent on the non-linearity of the foam transition. The foam-water interface is governed by a very small total mobility ratio, implying a stable front. The transition between gas and foam, however, exhibits a huge total mobility ratio, leading to instabilities in the form of viscous fingering. This implies that there is an unstable pattern behind the front. We deduce that instabilities are able to grow behind the front but are later absorbed by the expanding wave. Moreover, the stability analysis, validated by numerical simulations, provides valuable insights about the important scales and wavelengths of the foam model. In this way, we remove the ambiguity regarding the effect of grid resolution on the convergence of the solutions. This insight forms an essential step toward the design of a suitable computational solver that captures all the appropriate scales, while

Modeling stability of growth between mathematics and science achievement during middle and high school.

PubMed

Ma, Xin; Ma, Lingling

2004-04-01

In this study, the authors introduced a multivariate multilevel model to estimate the consistency among students and schools in the rates of growth between mathematics and science achievement during the entire middle and high school years with data from the Longitudinal Study of American Youth (LSAY). There was no evident consistency in the rates of growth between mathematics and science achievement among students, and this inconsistency was not much influenced by student characteristics and school characteristics. However, there was evident consistency in the average rates of growth between mathematics and science achievement among schools, and this consistency was influenced by student characteristics and school characteristics. Major school-level variables associated with parental involvement did not show any significant impacts on consistency among either students or schools. Results call for educational policies that promote collaboration between mathematics and science departments or teachers.

Continuous uniformly finite time exact disturbance observer based control for fixed-time stabilization of nonlinear systems with mismatched disturbances

PubMed Central

Liu, Chongxin; Liu, Hang

2017-01-01

This paper presents a continuous composite control scheme to achieve fixed-time stabilization for nonlinear systems with mismatched disturbances. The composite controller is constructed in two steps: First, uniformly finite time exact disturbance observers are proposed to estimate and compensate the disturbances. Then, based on adding a power integrator technique and fixed-time stability theory, continuous fixed-time stable state feedback controller and Lyapunov functions are constructed to achieve global fixed-time system stabilization. The proposed control method extends the existing fixed-time stable control results to high order nonlinear systems with mismatched disturbances and achieves global fixed-time system stabilization. Besides, the proposed control scheme improves the disturbance rejection performance and achieves performance recovery of nominal system. Simulation results are provided to show the effectiveness, the superiority and the applicability of the proposed control scheme. PMID:28406966

Boundary control of anti-symmetric vibration of satellite with flexible appendages in planar motion with exponential stability

NASA Astrophysics Data System (ADS)

Rad, Hossein Kaviani; Salarieh, Hassan; Alasty, Aria; Vatankhah, Ramin

2018-06-01

In this research, we have investigated the planar maneuver of a flexible satellite with appendages anti-symmetric vibration. The hybrid governing equations are comprised of coupled partial and ordinary differential equations which are derived by employing Hamilton's principle. In this paper, control goals are the tracking desired pitch angle along with the flexible appendages vibration suppression simultaneously by using only one control torque which is applied to the central hub. The boundary control is proposed to fulfill these control aims; furthermore, this boundary control ensures that spillover instability phenomenon is eliminated, and in-domain sensors and actuators implement are excluded. Indeed, the proposed boundary control is able to stabilize an infinite number of vibration modes, which is one of the important benefits of the proposed control when it is considered that different factors including external disturbances and even the satellite maneuver can excite the various vibration modes of the flexible appendages and consequently the excitement of the high order vibration modes will be possible. Lyapunov's direct method is used to prove the exponential stability; moreover, this Proof is achieved in absence of any damping effect in modeling the vibrations of flexible appendages. In addition, the procedure for finding the boundary control coefficients which ensures the exponential stability is provided. Eventually, numerical simulations are presented to illustrate the effectiveness of the proposed boundary control.

Development and flight test evaluation of a pitch stability augmentation system for a relaxed stability L-1011

NASA Technical Reports Server (NTRS)

Rising, J. J.

1982-01-01

The L-1011 has been flight tested to demonstrate the relaxed static stability concept as a means of obtaining significant drag benefits to achieve a more energy efficient transport. Satisfactory handling qualities were maintained with the design of an active control horizontal tail for stability and control augmentation to allow operation of the L-1011 at centers of gravity close to the neutral point. Prior to flight test, a motion base visual flight simulator program was performed to optimize the augmentation system. The system was successfully demonstrated in a test program totaling forty-eight actual flight hours.

Fast Numerical Solution of the Plasma Response Matrix for Real-time Ideal MHD Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glasser, Alexander; Kolemen, Egemen; Glasser, Alan H.

To help effectuate near real-time feedback control of ideal MHD instabilities in tokamak geometries, a parallelized version of A.H. Glasser’s DCON (Direct Criterion of Newcomb) code is developed. To motivate the numerical implementation, we first solve DCON’s δW formulation with a Hamilton-Jacobi theory, elucidating analytical and numerical features of the ideal MHD stability problem. The plasma response matrix is demonstrated to be the solution of an ideal MHD Riccati equation. We then describe our adaptation of DCON with numerical methods natural to solutions of the Riccati equation, parallelizing it to enable its operation in near real-time. We replace DCON’s serial integration of perturbed modes—which satisfy a singular Euler- Lagrange equation—with a domain-decomposed integration of state transition matrices. Output is shown to match results from DCON with high accuracy, and with computation time < 1s. Such computational speed may enable active feedback ideal MHD stability control, especially in plasmas whose ideal MHD equilibria evolve with inductive timescalemore » $$\\tau$$ ≳ 1s—as in ITER. Further potential applications of this theory are discussed.« less

Fast Numerical Solution of the Plasma Response Matrix for Real-time Ideal MHD Control

DOE PAGES

Glasser, Alexander; Kolemen, Egemen; Glasser, Alan H.

2018-03-26

To help effectuate near real-time feedback control of ideal MHD instabilities in tokamak geometries, a parallelized version of A.H. Glasser’s DCON (Direct Criterion of Newcomb) code is developed. To motivate the numerical implementation, we first solve DCON’s δW formulation with a Hamilton-Jacobi theory, elucidating analytical and numerical features of the ideal MHD stability problem. The plasma response matrix is demonstrated to be the solution of an ideal MHD Riccati equation. We then describe our adaptation of DCON with numerical methods natural to solutions of the Riccati equation, parallelizing it to enable its operation in near real-time. We replace DCON’s serial integration of perturbed modes—which satisfy a singular Euler- Lagrange equation—with a domain-decomposed integration of state transition matrices. Output is shown to match results from DCON with high accuracy, and with computation time < 1s. Such computational speed may enable active feedback ideal MHD stability control, especially in plasmas whose ideal MHD equilibria evolve with inductive timescalemore » $$\\tau$$ ≳ 1s—as in ITER. Further potential applications of this theory are discussed.« less

Stability of numerous novel potassium chlorides at high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Weiwei; Oganov, Artem R.; Lobanov, Sergey S.

K-Cl is a simple system displaying all four main types of bonding, as it contains (i) metallic potassium, (ii) elemental chlorine made of covalently bonded Cl 2 molecules held together by van der Waals forces, and (iii) an archetypal ionic compound KCl. The charge balance rule, assigning classical charges of “+1” to K and “–1” to Cl, predicts that no compounds other than KCl are possible. However, our quantum-mechanical variable-composition evolutionary simulations predict an extremely complex phase diagram, with new thermodynamically stable compounds K 3Cl, K 2Cl, K 3Cl 2, K 4Cl 3, K 5Cl 4, K 3Cl 5, KClmore » 3 and KCl 7. Of particular interest are 2D-metallic homologs K n+1Cl n, the presence of positively charged Cl atoms in KCl 7, and the predicted stability of KCl 3 already at nearly ambient pressures at zero Kelvin. We have synthesized cubic Pm3¯n -KCl 3 at 40–70 GPa and trigonal P3¯cl -KCl 3 at 20–40 GPa in a laser-heated diamond anvil cell (DAC) at temperature exceeding 2000 K from KCl and Cl 2. These phases were identified using in situ synchrotron X-ray diffraction and Raman spectroscopy. Lastly, upon unloading to 10 GPa, P3¯cl -KCl 3 transforms to a yet unknown structure before final decomposition to KCl and Cl 2 at near-ambient conditions.« less

Stability of numerous novel potassium chlorides at high pressure

DOE PAGES

Zhang, Weiwei; Oganov, Artem R.; Lobanov, Sergey S.; ...

2016-05-23

K-Cl is a simple system displaying all four main types of bonding, as it contains (i) metallic potassium, (ii) elemental chlorine made of covalently bonded Cl 2 molecules held together by van der Waals forces, and (iii) an archetypal ionic compound KCl. The charge balance rule, assigning classical charges of “+1” to K and “–1” to Cl, predicts that no compounds other than KCl are possible. However, our quantum-mechanical variable-composition evolutionary simulations predict an extremely complex phase diagram, with new thermodynamically stable compounds K 3Cl, K 2Cl, K 3Cl 2, K 4Cl 3, K 5Cl 4, K 3Cl 5, KClmore » 3 and KCl 7. Of particular interest are 2D-metallic homologs K n+1Cl n, the presence of positively charged Cl atoms in KCl 7, and the predicted stability of KCl 3 already at nearly ambient pressures at zero Kelvin. We have synthesized cubic Pm3¯n -KCl 3 at 40–70 GPa and trigonal P3¯cl -KCl 3 at 20–40 GPa in a laser-heated diamond anvil cell (DAC) at temperature exceeding 2000 K from KCl and Cl 2. These phases were identified using in situ synchrotron X-ray diffraction and Raman spectroscopy. Lastly, upon unloading to 10 GPa, P3¯cl -KCl 3 transforms to a yet unknown structure before final decomposition to KCl and Cl 2 at near-ambient conditions.« less

Stabilizing Selection, Purifying Selection, and Mutational Bias in Finite Populations

PubMed Central

Charlesworth, Brian

2013-01-01

Genomic traits such as codon usage and the lengths of noncoding sequences may be subject to stabilizing selection rather than purifying selection. Mutations affecting these traits are often biased in one direction. To investigate the potential role of stabilizing selection on genomic traits, the effects of mutational bias on the equilibrium value of a trait under stabilizing selection in a finite population were investigated, using two different mutational models. Numerical results were generated using a matrix method for calculating the probability distribution of variant frequencies at sites affecting the trait, as well as by Monte Carlo simulations. Analytical approximations were also derived, which provided useful insights into the numerical results. A novel conclusion is that the scaled intensity of selection acting on individual variants is nearly independent of the effective population size over a wide range of parameter space and is strongly determined by the logarithm of the mutational bias parameter. This is true even when there is a very small departure of the mean from the optimum, as is usually the case. This implies that studies of the frequency spectra of DNA sequence variants may be unable to distinguish between stabilizing and purifying selection. A similar investigation of purifying selection against deleterious mutations was also carried out. Contrary to previous suggestions, the scaled intensity of purifying selection with synergistic fitness effects is sensitive to population size, which is inconsistent with the general lack of sensitivity of codon usage to effective population size. PMID:23709636

Active vibration suppression of helicopter horizontal stabilizers

NASA Astrophysics Data System (ADS)

Cinquemani, Simone; Cazzulani, Gabriele; Resta, Ferruccio

2017-04-01

Helicopters are among the most complex machines ever made. While ensuring high performance from the aeronautical point of view, they are not very comfortable due to vibration mainly created by the main rotor and by the interaction with the surrounding air. One of the most solicited structural elements of the vehicle are the horizontal stabilizers. These elements are particularly stressed because of their composite structure which, while guaranteeing lightness and strength, is characterized by a low damping. This work makes a preliminary analysis on the dynamics of the structure and proposes different solutions to actively suppress vibrations. Among them, the best in terms of the relationship between performance and weight / complexity of the system is that based on inertial actuators mounted on the inside of the horizontal stabilizers. The work addresses the issue of the design of the device and its use in the stabilizer from both the numerical and the experimental points of view.

Analytical study of magnetohydrodynamic propulsion stability

NASA Astrophysics Data System (ADS)

Abdollahzadeh Jamalabadi, M. Y.

2014-09-01

In this paper an analytical solution for the stability of the fully developed flow drive in a magneto-hydro-dynamic pump with pulsating transverse Eletro-magnetic fields is presented. To do this, a theoretical model of the flow is developed and the analytical results are obtained for both the cylindrical and Cartesian configurations that are proper to use in the propulsion of marine vessels. The governing parabolic momentum PDEs are transformed into an ordinary differential equation using approximate velocity distribution. The numerical results are obtained and asymptotic analyses are built to discover the mathematical behavior of the solutions. The maximum velocity in a magneto-hydro-dynamic pump versus time for various values of the Stuart number, electro-magnetic interaction number, Reynolds number, aspect ratio, as well as the magnetic and electrical angular frequency and the shift of the phase angle is presented. Results show that for a high Stuart number there is a frequency limit for stability of the fluid flow in a certain direction of the flow. This stability frequency is dependent on the geometric parameters of a channel.

Numerical simulation of swept-wing flows

NASA Technical Reports Server (NTRS)

Reed, Helen L.

1991-01-01

Efforts of the last six months to computationally model the transition process characteristics of flow over swept wings are described. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full 3D Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiment. The leading edge region of a swept wing is considered in a 3D spatial simulation with random disturbances as the initial conditions.

Numerical modeling of carrier gas flow in atomic layer deposition vacuum reactor: A comparative study of lattice Boltzmann models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Dongqing; Chien Jen, Tien; Li, Tao

2014-01-15

This paper characterizes the carrier gas flow in the atomic layer deposition (ALD) vacuum reactor by introducing Lattice Boltzmann Method (LBM) to the ALD simulation through a comparative study of two LBM models. Numerical models of gas flow are constructed and implemented in two-dimensional geometry based on lattice Bhatnagar–Gross–Krook (LBGK)-D2Q9 model and two-relaxation-time (TRT) model. Both incompressible and compressible scenarios are simulated and the two models are compared in the aspects of flow features, stability, and efficiency. Our simulation outcome reveals that, for our specific ALD vacuum reactor, TRT model generates better steady laminar flow features all over the domainmore » with better stability and reliability than LBGK-D2Q9 model especially when considering the compressible effects of the gas flow. The LBM-TRT is verified indirectly by comparing the numerical result with conventional continuum-based computational fluid dynamics solvers, and it shows very good agreement with these conventional methods. The velocity field of carrier gas flow through ALD vacuum reactor was characterized by LBM-TRT model finally. The flow in ALD is in a laminar steady state with velocity concentrated at the corners and around the wafer. The effects of flow fields on precursor distributions, surface absorptions, and surface reactions are discussed in detail. Steady and evenly distributed velocity field contribute to higher precursor concentration near the wafer and relatively lower particle velocities help to achieve better surface adsorption and deposition. The ALD reactor geometry needs to be considered carefully if a steady and laminar flow field around the wafer and better surface deposition are desired.« less

Stability of large DC power systems using switching converters, with application to the international space station

NASA Technical Reports Server (NTRS)

Manners, B.; Gholdston, E. W.; Karimi, K.; Lee, F. C.; Rajagopalan, J.; Panov, Y.

1996-01-01

As space direct current (dc) power systems continue to grow in size, switching power converters are playing an ever larger role in power conditioning and control. When designing a large dc system using power converters of this type, special attention must be placed on the electrical stability of the system and of the individual loads on the system. In the design of the electric power system (EPS) of the International Space Station (ISS), the National Aeronautics and Space Administration (NASA) and its contractor team led by Boeing Defense & Space Group has placed a great deal of emphasis on designing for system and load stability. To achieve this goal, the team has expended considerable effort deriving a dear concept on defining system stability in both a general sense and specifically with respect to the space station. The ISS power system presents numerous challenges with respect to system stability, such as high power, complex sources and undefined loads. To complicate these issues, source and load components have been designed in parallel by three major subcontractors (Boeing, Rocketdyne, and McDonnell Douglas) with interfaces to both sources and loads being designed in different countries (Russia, Japan, Canada, Europe, etc.). These issues, coupled with the program goal of limiting costs, have proven a significant challenge to the program. As a result, the program has derived an impedance specification approach for system stability. This approach is based on the significant relationship between source and load impedances and the effect of this relationship on system stability. This approach is limited in its applicability by the theoretical and practical limits on component designs as presented by each system segment. As a result, the overall approach to system stability implemented by the ISS program consists of specific hardware requirements coupled with extensive system analysis and hardware testing. Following this approach, the ISS program plans to begin

Bi-material crystalline whispering gallery mode microcavity structure for thermo-opto-mechanical stabilization

NASA Astrophysics Data System (ADS)

Itobe, Hiroki; Nakagawa, Yosuke; Mizumoto, Yuta; Kangawa, Hiroi; Kakinuma, Yasuhiro; Tanabe, Takasumi

2016-05-01

We fabricated a calcium fluoride (CaF2) whispering gallery mode (WGM) microcavity with a computer controlled ultra-precision cutting process. We observed a thermo-opto-mechanical (TOM) oscillation in the CaF2 WGM microcavity, which may influence the stability of the optical output when the cavity is employed for Kerr comb generation. We studied experimentally and numerically the mechanism of the TOM oscillation and showed that it is strongly dependent on cavity diameter. In addition, our numerical study suggests that a microcavity structure fabricated with a hybrid material (i.e. CaF2 and silicon), which is compatible with an ultra-high Q and high thermal conductivity, will allow us to reduce the TOM oscillation and stabilize the optical output.

Stability and error estimation for Component Adaptive Grid methods

NASA Technical Reports Server (NTRS)

Oliger, Joseph; Zhu, Xiaolei

1994-01-01

Component adaptive grid (CAG) methods for solving hyperbolic partial differential equations (PDE's) are discussed in this paper. Applying recent stability results for a class of numerical methods on uniform grids. The convergence of these methods for linear problems on component adaptive grids is established here. Furthermore, the computational error can be estimated on CAG's using the stability results. Using these estimates, the error can be controlled on CAG's. Thus, the solution can be computed efficiently on CAG's within a given error tolerance. Computational results for time dependent linear problems in one and two space dimensions are presented.

Thermal Stability of Nanocrystalline Alloys by Solute Additions and A Thermodynamic Modeling

NASA Astrophysics Data System (ADS)

Saber, Mostafa

Nanocrystalline alloys show superior properties due to their exceptional microstructure. Thermal stability of these materials is a critical aspect. It is well known that grain boundaries in nanocrystalline microstructures cause a significant increase in the total free energy of the system. A driving force provided to reduce this excess free energy can cause grain growth. The presence of a solute addition within a nanocrystalline alloy can lead to the thermal stability. Kinetic and thermodynamic stabilization are the two basic mechanisms with which stability of a nanoscale grain size can be achieved at high temperatures. The basis of this thesis is to study the effect of solute addition on thermal stability of nanocrystalline alloys. The objective is to determine the effect of Zr addition on the thermal stability of mechanically alloyed nanocrysatillne Fe-Cr and Fe-Ni alloys. In Fe-Cr-Zr alloy system, nanoscale grain size stabilization was maintained up to 900 °C by adding 2 at% Zr. Kinetic pinning by intermetallic particles in the nanoscale range was identified as a primary mechanism of thermal stabilization. In addition to the grain size strengthening, intermetallic particles also contribute to strengthening mechanisms. The analysis of microhardness, XRD data, and measured grain sizes from TEM micrographs suggested that both thermodynamic and kinetic mechanisms are possible mechanisms. It was found that alpha → gamma phase transformation in Fe-Cr-Zr system does not influence the grain size stabilization. In the Fe-Ni-Zr alloy system, it was shown that the grain growth in Fe-8Ni-1Zr alloy is much less than that of pure Fe and Fe-8Ni alloy at elevated temperatures. The microstructure of the ternary Fe-8Ni-1Zr alloy remains in the nanoscale range up to 700 °C. Using an in-situ TEM study, it was determined that drastic grain growth occurs when the alpha → gamma phase transformation occurs. Accordingly, there can be a synergistic relationship between grain growth

Convenient stability criteria for difference approximations of hyperbolic initial-boundary value problems

NASA Technical Reports Server (NTRS)

Goldberg, M.; Tadmor, E.

1985-01-01

New convenient stability criteria are provided in this paper for a large class of finite difference approximations to initial-boundary value problems associated with the hyperbolic system u sub t = au sub x + Bu + f in the quarter plane x or = 0, t or = 0. Using the new criteria, stability is easily established for numerous combinations of well known basic schemes and boundary conditins, thus generalizing many special cases studied in recent literature.

Convenient stability criteria for difference approximations of hyperbolic initial-boundary value problems

NASA Technical Reports Server (NTRS)

Goldberg, M.; Tadmor, E.

1983-01-01

New convenient stability criteria are provided in this paper for a large class of finite difference approximations to initial-boundary value problems associated with the hyperbolic system u sub t = au sub x + Bu + f in the quarter plane x or = 0, t or = 0. Using the new criteria, stability is easily established for numerous combinations of well known basic schemes and boundary conditions, thus generalizing many special cases studied in recent literature.

Numerical solution of the time fractional reaction-diffusion equation with a moving boundary

NASA Astrophysics Data System (ADS)

Zheng, Minling; Liu, Fawang; Liu, Qingxia; Burrage, Kevin; Simpson, Matthew J.

2017-06-01

A fractional reaction-diffusion model with a moving boundary is presented in this paper. An efficient numerical method is constructed to solve this moving boundary problem. Our method makes use of a finite difference approximation for the temporal discretization, and spectral approximation for the spatial discretization. The stability and convergence of the method is studied, and the errors of both the semi-discrete and fully-discrete schemes are derived. Numerical examples, motivated by problems from developmental biology, show a good agreement with the theoretical analysis and illustrate the efficiency of our method.

A case study of multi-seam coal mine entry stability analysis with strength reduction method

PubMed Central

Tulu, Ihsan Berk; Esterhuizen, Gabriel S; Klemetti, Ted; Murphy, Michael M.; Sumner, James; Sloan, Michael

2017-01-01

In this paper, the advantage of using numerical models with the strength reduction method (SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated. A coal mine under variable topography from the Central Appalachian region is used as a case study. At this mine, unexpected roof conditions were encountered during development below previously mined panels. Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-and-pillar panels. Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries. The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations. The SRM-calculated stability factors were compared with observations made during the site visits, and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case. It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines. PMID:28239503

A case study of multi-seam coal mine entry stability analysis with strength reduction method.

PubMed

Tulu, Ihsan Berk; Esterhuizen, Gabriel S; Klemetti, Ted; Murphy, Michael M; Sumner, James; Sloan, Michael

2016-03-01

In this paper, the advantage of using numerical models with the strength reduction method (SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated. A coal mine under variable topography from the Central Appalachian region is used as a case study. At this mine, unexpected roof conditions were encountered during development below previously mined panels. Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-and-pillar panels. Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries. The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations. The SRM-calculated stability factors were compared with observations made during the site visits, and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case. It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines.

Closing Achievement Gaps: Roles and Tasks of Elementary School Counselors

ERIC Educational Resources Information Center

Trusty, Jerry; Mellin, Elizabeth A.; Herbert, James T.

2008-01-01

Achievement gaps among racial-ethnic and socioeconomic status groups are an enduring, pervasive, and multifaceted phenomenon. Therefore, efforts aimed at understanding and addressing these gaps must be developmentally and environmentally broad, involving numerous school counselor roles and tasks, including leadership, advocacy, collaboration, and…

Robust stability of fractional order polynomials with complicated uncertainty structure

PubMed Central

Şenol, Bilal; Pekař, Libor

2017-01-01

The main aim of this article is to present a graphical approach to robust stability analysis for families of fractional order (quasi-)polynomials with complicated uncertainty structure. More specifically, the work emphasizes the multilinear, polynomial and general structures of uncertainty and, moreover, the retarded quasi-polynomials with parametric uncertainty are studied. Since the families with these complex uncertainty structures suffer from the lack of analytical tools, their robust stability is investigated by numerical calculation and depiction of the value sets and subsequent application of the zero exclusion condition. PMID:28662173

Helix formation and stability in membranes.

PubMed

McKay, Matthew J; Afrose, Fahmida; Koeppe, Roger E; Greathouse, Denise V

2018-02-13

In this article we review current understanding of basic principles for the folding of membrane proteins, focusing on the more abundant alpha-helical class. Membrane proteins, vital to many biological functions and implicated in numerous diseases, fold into their active conformations in the complex environment of the cell bilayer membrane. While many membrane proteins rely on the translocon and chaperone proteins to fold correctly, others can achieve their functional form in the absence of any translation apparatus or other aides. Nevertheless, the spontaneous folding process is not well understood at the molecular level. Recent findings suggest that helix fraying and loop formation may be important for overall structure, dynamics and regulation of function. Several types of membrane helices with ionizable amino acids change their topology with pH. Additionally we note that some peptides, including many that are rich in arginine, and a particular analogue of gramicidin, are able passively to translocate across cell membranes. The findings indicate that a final protein structure in a lipid-bilayer membrane is sequence-based, with lipids contributing to stability and regulation. While much progress has been made toward understanding the folding process for alpha-helical membrane proteins, it remains a work in progress. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo. Copyright © 2018 Elsevier B.V. All rights reserved.

A stabilized element-based finite volume method for poroelastic problems

NASA Astrophysics Data System (ADS)

Honório, Hermínio T.; Maliska, Clovis R.; Ferronato, Massimiliano; Janna, Carlo

2018-07-01

The coupled equations of Biot's poroelasticity, consisting of stress equilibrium and fluid mass balance in deforming porous media, are numerically solved. The governing partial differential equations are discretized by an Element-based Finite Volume Method (EbFVM), which can be used in three dimensional unstructured grids composed of elements of different types. One of the difficulties for solving these equations is the numerical pressure instability that can arise when undrained conditions take place. In this paper, a stabilization technique is developed to overcome this problem by employing an interpolation function for displacements that considers also the pressure gradient effect. The interpolation function is obtained by the so-called Physical Influence Scheme (PIS), typically employed for solving incompressible fluid flows governed by the Navier-Stokes equations. Classical problems with analytical solutions, as well as three-dimensional realistic cases are addressed. The results reveal that the proposed stabilization technique is able to eliminate the spurious pressure instabilities arising under undrained conditions at a low computational cost.

An approach to achieve progress in spacecraft shielding

NASA Astrophysics Data System (ADS)

Thoma, K.; Schäfer, F.; Hiermaier, S.; Schneider, E.

2004-01-01

Progress in shield design against space debris can be achieved only when a combined approach based on several tools is used. This approach depends on the combined application of advanced numerical methods, specific material models and experimental determination of input parameters for these models. Examples of experimental methods for material characterization are given, covering the range from quasi static to very high strain rates for materials like Nextel and carbon fiber-reinforced materials. Mesh free numerical methods have extraordinary capabilities in the simulation of extreme material behaviour including complete failure with phase changes, combined with shock wave phenomena and the interaction with structural components. In this paper the benefits from combining numerical methods, material modelling and detailed experimental studies for shield design are demonstrated. The following examples are given: (1) Development of a material model for Nextel and Kevlar-Epoxy to enable numerical simulation of hypervelocity impacts on complex heavy protection shields for the International Space Station. (2) The influence of projectile shape on protection performance of Whipple Shields and how experimental problems in accelerating such shapes can be overcome by systematic numerical simulation. (3) The benefits of using metallic foams in "sandwich bumper shields" for spacecraft and how to approach systematic characterization of such materials.

Delay-Dependent Stability Criterion for Bidirectional Associative Memory Neural Networks with Interval Time-Varying Delays

NASA Astrophysics Data System (ADS)

Park, Ju H.; Kwon, O. M.

In the letter, the global asymptotic stability of bidirectional associative memory (BAM) neural networks with delays is investigated. The delay is assumed to be time-varying and belongs to a given interval. A novel stability criterion for the stability is presented based on the Lyapunov method. The criterion is represented in terms of linear matrix inequality (LMI), which can be solved easily by various optimization algorithms. Two numerical examples are illustrated to show the effectiveness of our new result.

International normalized ratio stabilization in newly initiated warfarin patients with nonvalvular atrial fibrillation.

PubMed

Nelson, Winnie W; Desai, Sunita; Damaraju, C V; Lu, Lang; Fields, Larry E; Wildgoose, Peter; Schein, Jeff R

2014-12-01

Warfarin is effective for stroke prevention in patients with atrial fibrillation (AF), but international normalized ratio (INR) levels fluctuate and frequent monitoring is necessary. This study used data from a large anticoagulation management service database to analyze the relationship between INR stabilization and warfarin utilization for >1 year in patients with nonvalvular AF (NVAF). Anticoagulation records from a large US electronic database collected from 2006 to 2010 were analyzed. Patients with NVAF and ≥ 3 INR values in the dataset were identified (n = 15,276). INR stabilization was defined as the first three consecutive INR values between 2.0 and 3.0 after warfarin initiation. One quarter of patients (n = 3809) failed to reach INR stabilization. After initial stabilization, 30% of subsequent INR values were out of range. The mean (± standard deviation [SD]) follow-up time from stabilization to the end of study for these patients was 494.2 ± 418.1 days. Age ≥ 75 years (odds ratio [OR] = 1.17, 95% confidence interval [CI] = 1.08-1.27), hypertension (OR = 1.19, 95% CI = 1.10-1.29), or prior stroke (OR = 1.29, 95% CI = 1.04-1.61) were positively associated with achieving stabilization; heart failure was negatively associated with stabilization (OR = 0.78, 95% CI = 0.70-0.87). Male gender (p < 0.0001) and hypertension were associated with earlier stabilization (p = 0.0013); heart failure was associated with later stabilization (p = 0.0098). Patients who achieved INR stabilization within 1 year were 10 times more likely to remain on warfarin than patients who did not achieve it. Observational data may contain incomplete records. Data on adherence, concurrent medications, vitamin K intake, genotype, reasons for discontinuation of monitoring, and patient outcomes were not available in the dataset. The study findings were generalizable only to patients with AF who were managed by anticoagulation clinics. Given the importance of stroke prevention among

Avoiding numerical pitfalls in social force models

NASA Astrophysics Data System (ADS)

Köster, Gerta; Treml, Franz; Gödel, Marion

2013-06-01

The social force model of Helbing and Molnár is one of the best known approaches to simulate pedestrian motion, a collective phenomenon with nonlinear dynamics. It is based on the idea that the Newtonian laws of motion mostly carry over to pedestrian motion so that human trajectories can be computed by solving a set of ordinary differential equations for velocity and acceleration. The beauty and simplicity of this ansatz are strong reasons for its wide spread. However, the numerical implementation is not without pitfalls. Oscillations, collisions, and instabilities occur even for very small step sizes. Classic solution ideas from molecular dynamics do not apply to the problem because the system is not Hamiltonian despite its source of inspiration. Looking at the model through the eyes of a mathematician, however, we realize that the right hand side of the differential equation is nondifferentiable and even discontinuous at critical locations. This produces undesirable behavior in the exact solution and, at best, severe loss of accuracy in efficient numerical schemes even in short range simulations. We suggest a very simple mollified version of the social force model that conserves the desired dynamic properties of the original many-body system but elegantly and cost efficiently resolves several of the issues concerning stability and numerical resolution.

Optimal damping profile ratios for stabilization of perfectly matched layers in general anisotropic media

DOE PAGES

Gao, Kai; Huang, Lianjie

2017-11-13

Conventional perfectly matched layers (PML) can be unstable for certain kinds of anisotropic media. Multi-axial PML removes such instability using nonzero damping coe cients in the directions tangential with the PML interface. While using non-zero damping pro le ratios can stabilize PML, it is important to obtain the smallest possible damping pro le ratios to minimize arti cial re ections caused by these non-zero ratios, particularly for 3D general anisotropic media. Using the eigenvectors of the PML system matrix, we develop a straightforward and e cient numerical algorithm to determine the optimal damping pro le ratios to stabilize PML inmore » 2D and 3D general anisotropic media. Numerical examples show that our algorithm provides optimal damping pro le ratios to ensure the stability of PML and complex-frequency-shifted PML for elastic-wave modeling in 2D and 3D general anisotropic media.« less

Optimal damping profile ratios for stabilization of perfectly matched layers in general anisotropic media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Kai; Huang, Lianjie

Conventional perfectly matched layers (PML) can be unstable for certain kinds of anisotropic media. Multi-axial PML removes such instability using nonzero damping coe cients in the directions tangential with the PML interface. While using non-zero damping pro le ratios can stabilize PML, it is important to obtain the smallest possible damping pro le ratios to minimize arti cial re ections caused by these non-zero ratios, particularly for 3D general anisotropic media. Using the eigenvectors of the PML system matrix, we develop a straightforward and e cient numerical algorithm to determine the optimal damping pro le ratios to stabilize PML inmore » 2D and 3D general anisotropic media. Numerical examples show that our algorithm provides optimal damping pro le ratios to ensure the stability of PML and complex-frequency-shifted PML for elastic-wave modeling in 2D and 3D general anisotropic media.« less

Stabilization of magnetic skyrmions by RKKY interactions

NASA Astrophysics Data System (ADS)

Bezvershenko, Alla V.; Kolezhuk, Alexei K.; Ivanov, Boris A.

2018-02-01

We study the stabilization of an isolated magnetic skyrmion in a magnetic monolayer on a nonmagnetic conducting substrate via the Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction. Two different types of the substrate are considered, usual normal metal and single-layer graphene. While the full stability analysis for skyrmions in the presence of the RKKY coupling requires a separate effort that is outside the scope of this work, we are able to study the radial stability (stability of a skyrmion against collapse) using variational energy estimates obtained within first-order perturbation theory, with the unperturbed Hamiltonian describing the isotropic Heisenberg magnet, and the two perturbations being the RKKY exchange and the easy-axis anisotropy. We show that a proper treatment of the long-range nature of the RKKY interaction leads to a qualitatively different stabilization scenario compared to previous studies, where solitons were stabilized by the frustrated exchange coupling (leading to terms with the fourth power of the magnetization gradients) or by the Dzyaloshinskii-Moriya interaction (described by terms linear in the magnetization gradients). In the case of a metallic substrate, the skyrmion stabilization is possible under restrictive conditions on the Fermi surface parameters, while in the case of a graphene substrate the stabilization is naturally achieved in several geometries with a lattice-matching of graphene and magnetic layer.

Linear stability and nonlinear analyses of traffic waves for the general nonlinear car-following model with multi-time delays

NASA Astrophysics Data System (ADS)

Sun, Dihua; Chen, Dong; Zhao, Min; Liu, Weining; Zheng, Linjiang

2018-07-01

In this paper, the general nonlinear car-following model with multi-time delays is investigated in order to describe the reactions of vehicle to driving behavior. Platoon stability and string stability criteria are obtained for the general nonlinear car-following model. Burgers equation and Korteweg de Vries (KdV) equation and their solitary wave solutions are derived adopting the reductive perturbation method. We investigate the properties of typical optimal velocity model using both analytic and numerical methods, which estimates the impact of delays about the evolution of traffic congestion. The numerical results show that time delays in sensing relative movement is more sensitive to the stability of traffic flow than time delays in sensing host motion.

Long-time stability effects of quadrature and artificial viscosity on nodal discontinuous Galerkin methods for gas dynamics

NASA Astrophysics Data System (ADS)

Durant, Bradford; Hackl, Jason; Balachandar, Sivaramakrishnan

2017-11-01

Nodal discontinuous Galerkin schemes present an attractive approach to robust high-order solution of the equations of fluid mechanics, but remain accompanied by subtle challenges in their consistent stabilization. The effect of quadrature choices (full mass matrix vs spectral elements), over-integration to manage aliasing errors, and explicit artificial viscosity on the numerical solution of a steady homentropic vortex are assessed over a wide range of resolutions and polynomial orders using quadrilateral elements. In both stagnant and advected vortices in periodic and non-periodic domains the need arises for explicit stabilization beyond the numerical surface fluxes of discontinuous Galerkin spectral elements. Artificial viscosity via the entropy viscosity method is assessed as a stabilizing mechanism. It is shown that the regularity of the artificial viscosity field is essential to its use for long-time stabilization of small-scale features in nodal discontinuous Galerkin solutions of the Euler equations of gas dynamics. Supported by the Department of Energy Predictive Science Academic Alliance Program Contract DE-NA0002378.

Stability of soliton families in nonlinear Schrödinger equations with non-parity-time-symmetric complex potentials

NASA Astrophysics Data System (ADS)

Yang, Jianke; Nixon, Sean

2016-11-01

Stability of soliton families in one-dimensional nonlinear Schrödinger equations with non-parity-time (PT)-symmetric complex potentials is investigated numerically. It is shown that these solitons can be linearly stable in a wide range of parameter values both below and above phase transition. In addition, a pseudo-Hamiltonian-Hopf bifurcation is revealed, where pairs of purely-imaginary eigenvalues in the linear-stability spectra of solitons collide and bifurcate off the imaginary axis, creating oscillatory instability, which resembles Hamiltonian-Hopf bifurcations of solitons in Hamiltonian systems even though the present system is dissipative and non-Hamiltonian. The most important numerical finding is that, eigenvalues of linear-stability operators of these solitons appear in quartets (λ , - λ ,λ* , -λ*), similar to conservative systems and PT-symmetric systems. This quartet eigenvalue symmetry is very surprising for non- PT-symmetric systems, and it has far-reaching consequences on the stability behaviors of solitons.

Gyro-effect stabilizes unstable permanent maglev centrifugal pump.

PubMed

Qian, Kun-Xi

2007-03-01

According to Earnshaw's Theorem (1839), the passive maglev cannot achieve stable equilibrium and thus an extra coil is needed to make the rotor electrically levitated in a heart pump. The author had developed a permanent maglev centrifugal pump utilizing only passive magnetic bearings, to keep the advantages but to avoid the disadvantages of the electric maglev pumps. The equilibrium stability was achieved by use of so-called "gyro-effect": a rotating body with certain high speed can maintain its rotation stably. This pump consisted of a rotor (driven magnets and an impeller), and a stator with motor coil and pump housing. Two passive magnetic bearings between rotor and stator were devised to counteract the attractive force between the motor coil iron core and the rotor driven magnets. Bench testing with saline demonstrated a levitated rotor under preconditions of higher than 3,250 rpm rotation and more than 1 l/min pumping flow. Rotor levitation was demonstrated by 4 Hall sensors on the stator, with evidence of reduced maximal eccentric distance from 0.15 mm to 0.07 mm. The maximal rotor vibration amplitude was 0.06 mm in a gap of 0.15 mm between rotor and stator. It concluded that Gyro-effect can help passive maglev bearings to achieve stabilization of permanent maglev pump; and that high flow rate indicates good hydraulic property of the pump, which helps also the stability of passive maglev pump.

Basic and advanced numerical performances relate to mathematical expertise but are fully mediated by visuospatial skills.

PubMed

Sella, Francesco; Sader, Elie; Lolliot, Simon; Cohen Kadosh, Roi

2016-09-01

Recent studies have highlighted the potential role of basic numerical processing in the acquisition of numerical and mathematical competences. However, it is debated whether high-level numerical skills and mathematics depends specifically on basic numerical representations. In this study mathematicians and nonmathematicians performed a basic number line task, which required mapping positive and negative numbers on a physical horizontal line, and has been shown to correlate with more advanced numerical abilities and mathematical achievement. We found that mathematicians were more accurate compared with nonmathematicians when mapping positive, but not negative numbers, which are considered numerical primitives and cultural artifacts, respectively. Moreover, performance on positive number mapping could predict whether one is a mathematician or not, and was mediated by more advanced mathematical skills. This finding might suggest a link between basic and advanced mathematical skills. However, when we included visuospatial skills, as measured by block design subtest, the mediation analysis revealed that the relation between the performance in the number line task and the group membership was explained by non-numerical visuospatial skills. These results demonstrate that relation between basic, even specific, numerical skills and advanced mathematical achievement can be artifactual and explained by visuospatial processing. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

Stability with large step sizes for multistep discretizations of stiff ordinary differential equations

NASA Technical Reports Server (NTRS)

Majda, George

1986-01-01

One-leg and multistep discretizations of variable-coefficient linear systems of ODEs having both slow and fast time scales are investigated analytically. The stability properties of these discretizations are obtained independent of ODE stiffness and compared. The results of numerical computations are presented in tables, and it is shown that for large step sizes the stability of one-leg methods is better than that of the corresponding linear multistep methods.

Stabilization of Landslides for the Improvement of Aquatic Habitat

Treesearch

Michael J. Furniss

1989-01-01

Chronic surface and mass erosion from recent landslides often prevents the recovery of productive stream habitats following initial mass failure events. Low-cost methods that can accelerate recovery and stabilization processes have been employed on numerous failed slopes in the Six Rivers National Forest in the northwest corner of California, with notable success. Two...

Numerical analysis for the fractional diffusion and fractional Buckmaster equation by the two-step Laplace Adam-Bashforth method

NASA Astrophysics Data System (ADS)

Jain, Sonal

2018-01-01

In this paper, we aim to use the alternative numerical scheme given by Gnitchogna and Atangana for solving partial differential equations with integer and non-integer differential operators. We applied this method to fractional diffusion model and fractional Buckmaster models with non-local fading memory. The method yields a powerful numerical algorithm for fractional order derivative to implement. Also we present in detail the stability analysis of the numerical method for solving the diffusion equation. This proof shows that this method is very stable and also converges very quickly to exact solution and finally some numerical simulation is presented.

Numerical model for healthy and injured ankle ligaments.

PubMed

Forestiero, Antonella; Carniel, Emanuele Luigi; Fontanella, Chiara Giulia; Natali, Arturo Nicola

2017-06-01

The aim of this work is to provide a computational tool for the investigation of ankle mechanics under different loading conditions. The attention is focused on the biomechanical role of ankle ligaments that are fundamental for joints stability. A finite element model of the human foot is developed starting from Computed Tomography and Magnetic Resonance Imaging, using particular attention to the definition of ankle ligaments. A refined fiber-reinforced visco-hyperelastic constitutive model is assumed to characterize the mechanical response of ligaments. Numerical analyses that interpret anterior drawer and the talar tilt tests reported in literature are performed. The numerical results are in agreement with the range of values obtained by experimental tests confirming the accuracy of the procedure adopted. The increase of the ankle range of motion after some ligaments rupture is also evaluated, leading to the capability of the numerical models to interpret the damage conditions. The developed computational model provides a tool for the investigation of foot and ankle functionality in terms of stress-strain of the tissues and in terms of ankle motion, considering different types of damage to ankle ligaments.

A numerical study of the thermal stability of low-lying coronal loops

NASA Technical Reports Server (NTRS)

Klimchuk, J. A.; Antiochos, S. K.; Mariska, J. T.

1986-01-01

The nonlinear evolution of loops that are subjected to a variety of small but finite perturbations was studied. Only the low-lying loops are considered. The analysis was performed numerically using a one-dimensional hydrodynamical model developed at the Naval Research Laboratory. The computer codes solve the time-dependent equations for mass, momentum, and energy transport. The primary interest is the active region filaments, hence a geometry appropriate to those structures was considered. The static solutions were subjected to a moderate sized perturbation and allowed to evolve. The results suggest that both hot and cool loops of the geometry considered are thermally stable against amplitude perturbations of all kinds.

Modeling of Feedback Stabilization of External MHD Modes in Toroidal Geometry

NASA Astrophysics Data System (ADS)

Chu, M. S.; Chance, M. S.; Okabayashi, M.

2000-10-01

The intelligent shell feedback scheme(C.M. Bishop, Plasma Phys. Contr. Nucl. Fusion 31), 1179 (1989). seeks to utilize external coils to suppress the unstable MHD modes slowed down by the resistive shell. We present a new formulation and numerical results of the interaction between the plasma and its outside vacuum region, with complete plasma response and the inclusion of a resistive vessel in general toroidal geometry. This is achieved by using the Green's function technique, which is a generalization of that previously used for the VACUUM(M.S. Chance, Phys. Plasmas 4), 2161 (1997). code and coupled with the ideal MHD code GATO. The effectiveness of different realizations of the intelligent shell concept is gauged by their ability to minimize the available free energy to drive the MHD mode. Computations indicate poloidal coverage of 30% of the total resistive wall surface area and 6 or 7 segments of ``intelligent coil'' arrays superimposed on the resistive wall will allow recovery of up to 90% the effectiveness of the ideal shell in stabilizing the ideal external kink.

Modeling Nitrogen Decrease in Water Lettuce Ponds from Waste Stabilization Ponds

NASA Astrophysics Data System (ADS)

Putri, Gitta Agnes; Sunarsih

2018-02-01

This paper presents about the dynamic modeling of the Water Lettuce ponds as a form of improvement from the Water Hyacinth ponds. The purpose of this paper is to predict nitrogen decrease and nitrogen transformation in Water Lettuce ponds integrated with Waste Stabilization Ponds. The model consists of 4 mass balances, namely Dissolved Organic Nitrogen (DON), Particulate Organic Nitrogen (PON), ammonium (NH4+), Nitrate and Nitrite (NOx). The process of nitrogen transformation which considered in a Water Lettuce ponds, namely hydrolysis, mineralization, nitrification, denitrification, plant and bacterial uptake processes. Numerical simulations are performed by giving the values of parameters and the initial values of nitrogen compounds based on a review of previous studies. Numerical results show that the rate of change in the concentration of nitrogen compounds in the integration ponds of waste stabilization and water lettuce decreases and reaches stable at different times.

Dynamic Stability Analysis of Linear Time-varying Systems via an Extended Modal Identification Approach

NASA Astrophysics Data System (ADS)

Ma, Zhisai; Liu, Li; Zhou, Sida; Naets, Frank; Heylen, Ward; Desmet, Wim

2017-03-01

The problem of linear time-varying(LTV) system modal analysis is considered based on time-dependent state space representations, as classical modal analysis of linear time-invariant systems and current LTV system modal analysis under the "frozen-time" assumption are not able to determine the dynamic stability of LTV systems. Time-dependent state space representations of LTV systems are first introduced, and the corresponding modal analysis theories are subsequently presented via a stability-preserving state transformation. The time-varying modes of LTV systems are extended in terms of uniqueness, and are further interpreted to determine the system's stability. An extended modal identification is proposed to estimate the time-varying modes, consisting of the estimation of the state transition matrix via a subspace-based method and the extraction of the time-varying modes by the QR decomposition. The proposed approach is numerically validated by three numerical cases, and is experimentally validated by a coupled moving-mass simply supported beam experimental case. The proposed approach is capable of accurately estimating the time-varying modes, and provides a new way to determine the dynamic stability of LTV systems by using the estimated time-varying modes.

Frequency stability of maser oscillators operated with cavity Q. [hydrogen and rubidium masers

NASA Technical Reports Server (NTRS)

Tetu, M.; Tremblay, P.; Lesage, P.; Petit, P.; Audoin, C.

1982-01-01

The short term frequency stability of masers equipped with an external feedback loop to increase the cavity quality factor was studied. The frequency stability of a hydrogen and a rubidium maser were measured and compared with theoretical evaluation. It is shown that the frequency stability passes through an optimum when the cavity Q is varied. Long term fluctuations are discussed and the optimum mid term frequency stability achievably by small size active and passive H-masers is considered.

The role of perceived classroom goal structures, self-efficacy, and engagement in student science achievement

NASA Astrophysics Data System (ADS)

Uçar, F. Melike; Sungur, Semra

2017-04-01

Background: Numerous studies have been conducted to investigate the factors related to science achievement. In these studies, the classroom goal structure perceptions, engagement, and self-efficacy of the students have emerged as important factors to be examined in relation to students' science achievement.

Active and passive stabilization of body pitch in insect flight

PubMed Central

Ristroph, Leif; Ristroph, Gunnar; Morozova, Svetlana; Bergou, Attila J.; Chang, Song; Guckenheimer, John; Wang, Z. Jane; Cohen, Itai

2013-01-01

Flying insects have evolved sophisticated sensory–motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities. We describe a theory that predicts the instability growth rate in body pitch from flapping-wing aerodynamics and reveals two ways of achieving balanced flight: active control with sufficiently rapid reactions and passive stabilization with high body drag. By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability. Moreover, we find that fruit flies with their control sensors disabled can keep upright if high-drag fibres are also attached to their bodies, an observation consistent with our prediction for the passive stability condition. Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots. PMID:23697713

2013 Early Career Achievement Award--Proteomics of muscle- and species-specificity in meat color stability.

PubMed

Suman, S P; Rentfrow, G; Nair, M N; Joseph, P

2014-03-01

Meat color is the most important quality trait influencing consumer purchase decisions. The interinfluential interactions between myoglobin and biomolecules govern color stability in meat. The advances in proteomics, such as high throughput analytical tools in mass spectrometry, 2-dimensional electrophoresis, and bioinformatics, offer themselves as robust techniques to characterize the proteome basis of muscle- and species-specific meat color phenomena. Differential abundance of chaperones and antioxidant proteins contributes to muscle-specific color stability in beef; the greater abundance of chaperones and antioxidant proteins in color-stable Longissimus lumborum than in color-labile Psoas major protects myoglobin and contributes to superior color stability of beef Longissimus steaks. Lipid oxidation-induced myoglobin oxidation is more critical to beef color than pork color due to the inherent differences in myoglobin chemistry; the number of nucleophilic histidine residues adducted by reactive aldehydes is greater in beef myoglobin than in pork myoglobin. Preferential adduction of secondary products of lipid oxidation to beef myoglobin accelerates metmyoglobin formation at a greater degree than in its pork counterpart. Mass spectrometric investigations revealed that although cherry-red carboxymyoglobin is more stable than oxymyoglobin, both redox forms undergo lipid oxidation-induced oxidation in model systems. The accuracy of mass spectrometry to detect the molecular mass of proteins has been applied to differentiate myoglobins from closely related meat animals, such as goats and sheep or emu and ostrich. In addition, this approach indicated that turkey myoglobin is 350 Da greater in molecular mass than beef myoglobin, and the unique biochemistry of turkey myoglobin could be responsible for its greater thermostability in model systems as well as the pink color defect observed in fully cooked uncured turkey products.

Numerical investigation of galloping instabilities in Z-shaped profiles.

PubMed

Gomez, Ignacio; Chavez, Miguel; Alonso, Gustavo; Valero, Eusebio

2014-01-01

Aeroelastic effects are relatively common in the design of modern civil constructions such as office blocks, airport terminal buildings, and factories. Typical flexible structures exposed to the action of wind are shading devices, normally slats or louvers. A typical cross-section for such elements is a Z-shaped profile, made out of a central web and two-side wings. Galloping instabilities are often determined in practice using the Glauert-Den Hartog criterion. This criterion relies on accurate predictions of the dependence of the aerodynamic force coefficients with the angle of attack. The results of a parametric analysis based on a numerical analysis and performed on different Z-shaped louvers to determine translational galloping instability regions are presented in this paper. These numerical analysis results have been validated with a parametric analysis of Z-shaped profiles based on static wind tunnel tests. In order to perform this validation, the DLR TAU Code, which is a standard code within the European aeronautical industry, has been used. This study highlights the focus on the numerical prediction of the effect of galloping, which is shown in a visible way, through stability maps. Comparisons between numerical and experimental data are presented with respect to various meshes and turbulence models.

Finite-Time Stabilization and Adaptive Control of Memristor-Based Delayed Neural Networks.

PubMed

Wang, Leimin; Shen, Yi; Zhang, Guodong

Finite-time stability problem has been a hot topic in control and system engineering. This paper deals with the finite-time stabilization issue of memristor-based delayed neural networks (MDNNs) via two control approaches. First, in order to realize the stabilization of MDNNs in finite time, a delayed state feedback controller is proposed. Then, a novel adaptive strategy is applied to the delayed controller, and finite-time stabilization of MDNNs can also be achieved by using the adaptive control law. Some easily verified algebraic criteria are derived to ensure the stabilization of MDNNs in finite time, and the estimation of the settling time functional is given. Moreover, several finite-time stability results as our special cases for both memristor-based neural networks (MNNs) without delays and neural networks are given. Finally, three examples are provided for the illustration of the theoretical results.Finite-time stability problem has been a hot topic in control and system engineering. This paper deals with the finite-time stabilization issue of memristor-based delayed neural networks (MDNNs) via two control approaches. First, in order to realize the stabilization of MDNNs in finite time, a delayed state feedback controller is proposed. Then, a novel adaptive strategy is applied to the delayed controller, and finite-time stabilization of MDNNs can also be achieved by using the adaptive control law. Some easily verified algebraic criteria are derived to ensure the stabilization of MDNNs in finite time, and the estimation of the settling time functional is given. Moreover, several finite-time stability results as our special cases for both memristor-based neural networks (MNNs) without delays and neural networks are given. Finally, three examples are provided for the illustration of the theoretical results.

Clinical Outcomes and Return to Sport After Arthroscopic Anterior, Posterior, and Combined Shoulder Stabilization

PubMed Central

Kraeutler, Matthew J.; Aberle, Nicholas S.; Brown, Colin C.; Ptasinski, Joseph J.; McCarty, Eric C.

2018-01-01

Background: Glenohumeral instability is a common abnormality, especially among athletes. Previous studies have evaluated outcomes after arthroscopic stabilization in patients with anterior or posterior shoulder instability but have not compared outcomes between groups. Purpose: To compare return-to-sport and other patient-reported outcomes in patients after primary arthroscopic anterior, posterior, and combined anterior and posterior shoulder stabilization. Study Design: Cohort study; Level of evidence, 3. Methods: Patients who underwent primary arthroscopic anterior, posterior, or combined anterior and posterior shoulder stabilization were contacted at a minimum 2-year follow-up. Patients completed a survey that consisted of return-to-sport outcomes as well as the Western Ontario Shoulder Instability Index (WOSI), Single Assessment Numeric Evaluation (SANE), American Shoulder and Elbow Sur’geons (ASES) score, and Shoulder Activity Scale. Results: A total of 151 patients were successfully contacted (anterior: n = 81; posterior: n = 22; combined: n = 48) at a mean follow-up of 3.6 years. No significant differences were found between the groups with regard to age at the time of surgery or time to follow-up. No significant differences were found between the groups in terms of WOSI (anterior: 76; posterior: 70; combined: 78; P = .28), SANE (anterior: 87; posterior: 85; combined: 87; P = .79), ASES (anterior: 88; posterior: 83; combined: 91; P = .083), or Shoulder Activity Scale (anterior: 12.0; posterior: 12.5; combined: 12.5; P = .74) scores. No significant difference was found between the groups in terms of the rate of return to sport (anterior: 73%; posterior: 68%; combined: 75%; P = .84). Conclusion: Athletes undergoing arthroscopic stabilization of anterior, posterior, or combined shoulder instability can be expected to share a similar prognosis. High patient-reported outcome scores and moderate to high rates of return to sport were achieved by all groups. PMID

Direct numerical simulations of mack-mode damping on porous coated cones

NASA Astrophysics Data System (ADS)

Lüdeke, H.; Wartemann, V.

2013-06-01

The flow field over a 3 degree blunt cone is investigated with respect to a hypersonic stability analysis of the boundary-layer flow at Mach 6 with porous as well as smooth walls by comparing local direct numerical simulations (DNS) and linear stability theory (LST) data. The original boundary-layer profile is generated by a finite volume solver, using shock capturing techniques to generate an axisymmetric flow field. Local boundary-layer profiles are extracted from this flow field and hypersonic Mack-modes are superimposed for cone-walls with and without a porous surface used as a passive transition-reduction device. Special care is taken of curvature effects of the wall on the mode development over smooth and porous walls.

Laser frequency stabilization using a commercial wavelength meter

NASA Astrophysics Data System (ADS)

Couturier, Luc; Nosske, Ingo; Hu, Fachao; Tan, Canzhu; Qiao, Chang; Jiang, Y. H.; Chen, Peng; Weidemüller, Matthias

2018-04-01

We present the characterization of a laser frequency stabilization scheme using a state-of-the-art wavelength meter based on solid Fizeau interferometers. For a frequency-doubled Ti-sapphire laser operated at 461 nm, an absolute Allan deviation below 10-9 with a standard deviation of 1 MHz over 10 h is achieved. Using this laser for cooling and trapping of strontium atoms, the wavemeter scheme provides excellent stability in single-channel operation. Multi-channel operation with a multimode fiber switch results in fluctuations of the atomic fluorescence correlated to residual frequency excursions of the laser. The wavemeter-based frequency stabilization scheme can be applied to a wide range of atoms and molecules for laser spectroscopy, cooling, and trapping.

Analysis of a Stabilized CNLF Method with Fast Slow Wave Splittings for Flow Problems

DOE PAGES

Jiang, Nan; Tran, Hoang A.

2015-04-01

In this work, we study Crank-Nicolson leap-frog (CNLF) methods with fast-slow wave splittings for Navier-Stokes equations (NSE) with a rotation/Coriolis force term, which is a simplification of geophysical flows. We propose a new stabilized CNLF method where the added stabilization completely removes the method's CFL time step condition. A comprehensive stability and error analysis is given. We also prove that for Oseen equations with the rotation term, the unstable mode (for which u(n+1) + u(n-1) equivalent to 0) of CNLF is asymptotically stable. Numerical results are provided to verify the stability and the convergence of the methods.

Numerical Schemes for the Hamilton-Jacobi and Level Set Equations on Triangulated Domains

NASA Technical Reports Server (NTRS)

Barth, Timothy J.; Sethian, James A.

1997-01-01

Borrowing from techniques developed for conservation law equations, numerical schemes which discretize the Hamilton-Jacobi (H-J), level set, and Eikonal equations on triangulated domains are presented. The first scheme is a provably monotone discretization for certain forms of the H-J equations. Unfortunately, the basic scheme lacks proper Lipschitz continuity of the numerical Hamiltonian. By employing a virtual edge flipping technique, Lipschitz continuity of the numerical flux is restored on acute triangulations. Next, schemes are introduced and developed based on the weaker concept of positive coefficient approximations for homogeneous Hamiltonians. These schemes possess a discrete maximum principle on arbitrary triangulations and naturally exhibit proper Lipschitz continuity of the numerical Hamiltonian. Finally, a class of Petrov-Galerkin approximations are considered. These schemes are stabilized via a least-squares bilinear form. The Petrov-Galerkin schemes do not possess a discrete maximum principle but generalize to high order accuracy.

Moment stability for a predator-prey model with parametric dichotomous noises

NASA Astrophysics Data System (ADS)

Jin, Yan-Fei

2015-06-01

In this paper, we investigate the solution moment stability for a Harrison-type predator-prey model with parametric dichotomous noises. Using the Shapiro-Loginov formula, the equations for the first-order and second-order moments are obtained and the corresponding stable conditions are given. It is found that the solution moment stability depends on the noise intensity and correlation time of noise. The first-order and second-order moments become unstable with the decrease of correlation time. That is, the dichotomous noise can improve the solution moment stability with respect to Gaussian white noise. Finally, some numerical results are presented to verify the theoretical analyses. Project supported by the National Natural Science Foundation of China (Grant No. 11272051).

Nuclear-coupled thermal-hydraulic stability analysis of boiling water reactors

NASA Astrophysics Data System (ADS)

Karve, Atul A.

We have studied the nuclear-coupled thermal-hydraulic stability of boiling water reactors (BWRs) using a model we developed from: the space-time modal neutron kinetics equations based on spatial omega-modes, the equations for two-phase flow in parallel boiling channels, the fuel rod heat conduction equations, and a simple model for the recirculation loop. The model is represented as a dynamical system comprised of time-dependent nonlinear ordinary differential equations, and it is studied using stability analysis, modern bifurcation theory, and numerical simulations. We first determine the stability boundary (SB) 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 and then transform the SB to the practical power-flow map. Using this SB, we show that the normal operating point at 100% power is very stable, stability of points on the 100% rod line decreases as the flow rate is reduced, and that points are least stable in the low-flow/high-power region. We also determine the SB when the modal kinetics is replaced by simple point reactor kinetics and show that the first harmonic mode has no significant effect on the SB. Later we carry out the relevant numerical simulations where we first show that the Hopf bifurcation, that occurs as a parameter is varied across the SB is subcritical, and that, in the important low-flow/high-power region, growing oscillations can result following small finite perturbations of stable steady-states on the 100% rod line. Hence, a point on the 100% rod line in the low-flow/high-power region, although stable, may nevertheless be a point at which a BWR should not be operated. Numerical simulations are then done to calculate the decay ratios (DRs) and frequencies of oscillations for various points on the 100% rod line. It is determined that the NRC requirement of DR < 0.75-0.8 is not rigorously satisfied in the low

Molecular laser stabilization for LISA

NASA Astrophysics Data System (ADS)

Halloin, Hubert; Acef, Ouali; Argence, Berengere; Jeannin, Olivier; Prat, Pierre; de Vismes, Eden; Plagnol, Eric; Brillet, Alain; Mondin, Linda; Berthon, Jacques; Turazza, Oscar

2017-11-01

The expected performance of LISA relies on two main technical challenges: the ability for the spacecrafts to precisely follow the free-flying masses and the outstanding precision of the phase shift measurement. This latter constraint requires frequency stabilized lasers and efficient numerical algorithms to account for the redundant, delayed noise propagation, thus cancelling laser phase noise by many orders of magnitude (TDI methods). Recently involved in the technical developments for LISA, the goal of our team at APC (France) is to contribute on these two subjects: frequency reference for laser stabilization and benchtop simulation of the interferometer. In the present design of LISA, two stages of laser stabilization are used (not accounting for the "post-processed" TDI algorithm): laser pre-stabilization on a frequency reference and lock on the ultra stable distance between spacecrafts (arm-locking). While the foreseen (and deeply studied) laser reference consists of a Fabry-Perot cavity, other techniques may be suitable for LISA or future metrology missions. In particular, locking to a molecular reference (namely iodine in the case of the LISA Nd:YAG laser) is an interesting alternative. It offers the required performance with very good long-term stability (absolute frequency reference) though the reference can be slightly tuned to account for arm-locking. This technique is currently being investigated by our team and optimized for LISA (compactness, vacuum compatibility, ease of use and initialization, etc.). A collaboration with a French laboratory (the SYRTE) had been started aiming to study a second improved technique consisting in inserting the iodine cell in a Fabry-Perot cavity. Ongoing results and prospects to increase the performance of the system are presented in the present article.

Math at home adds up to achievement in school.

PubMed

Berkowitz, Talia; Schaeffer, Marjorie W; Maloney, Erin A; Peterson, Lori; Gregor, Courtney; Levine, Susan C; Beilock, Sian L

2015-10-09

With a randomized field experiment of 587 first-graders, we tested an educational intervention designed to promote interactions between children and parents relating to math. We predicted that increasing math activities at home would increase children's math achievement at school. We tested this prediction by having children engage in math story time with their parents. The intervention, short numerical story problems delivered through an iPad app, significantly increased children's math achievement across the school year compared to a reading (control) group, especially for children whose parents are habitually anxious about math. Brief, high-quality parent-child interactions about math at home help break the intergenerational cycle of low math achievement. Copyright © 2015, American Association for the Advancement of Science.

Stability numerical analysis of soil cave in karst area to drawdown of underground water level

NASA Astrophysics Data System (ADS)

Mo, Yizheng; Xiao, Rencheng; Deng, Zongwei