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Thermal stability of the martensitic transformation of Cu-Al-Ni-Mn-Ti

Fernandez, J.; Benedetti, A. V.; Guilemany, J. M.; Zhang, X. M.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 723-725
ENG
Relevância na Pesquisa
36.03%
The development of new shape memory alloys with high martensitic transformation temperature increases the potential for applications. The development and use of these new alloys depends on the stability of the structure during cycling at high temperatures. If it is possible to guarantee that on alloys keeps the structure during cycling, then the alloy can be used because of the shape memory properties. The aim of this work is to obtain a kinetic model of the forward and backward martensitic transformation of two Cu-Al-Ni-Mn-Ti alloys. Differential scanning calorimetry has been performed in order to establish the kinetic stability of the martensite and the beta transformation. (c) 2006 Elsevier B.V. All rights reserved.

DETERMINATION OF INSTANTANEOUS STABILITY AGAINST BACKWARD BALANCE LOSS: TWO COMPUTATIONAL APPROACHES

Yang, Feng; Passariello, Fausto; Pai, Yi-Chung
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.25%
The purposes of this study were (1) to develop two computation methods and (2) to compare their performance (i.e. the accuracy and the time demand) in determining instantaneous stability, i.e., the shortest distance from an instantaneous center of mass (COM) state to all interpolated points on the stability boundary in the COM position-velocity state space. The intuitive numerical method interpolated the stability boundary against backward balance loss based on four sets of discrete boundary values with a spline function and a preset step size (Δx). Then a brute-force search approach was used to determine this shortest distance. The analytical method uses quadratic polynomial functions to represent the boundaries. The stability was then determined by using the Lagrange multiplier method to find the optimum for the analytical expression of the distance from this given COM state to the boundary. Because reducing Δx can supposedly improve the accuracy of spline fitting, we used this approach to establish the benchmark employed to determine the accuracy level of all other computations. Based on the results from a database of 67 sit-to-stand-slip trials and 687 gait-slip trials, we would recommend the numerical method with Δx =0.1 to reach an adequate accuracy level of 10−2. By changing one order of Δx from 0.1 to 0.01...

Predicted threshold against backward balance loss in gait

Yang, Feng; Anderson, Frank C.; Pai, Yi-Chung
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.32%
The purpose of this study was to determine the minimum forward center of mass (COM) velocity required to prevent backward loss of balance in gait as function of the initial COM position. We hypothesized that these threshold values would be different from those previously published for standing because of the postural differences between gait and standing. To investigate this issue, we constructed a seven-link, nine-degree-of-freedom biomechanical model and employed dynamic optimization to estimate these threshold values under two initial postural conditions: (1) the posture at the beginning of swing phase (i.e., at toe-off), and (2) symmetric bipedal standing. In particular, for a range of possible COM positions posterior to the base of support (BOS), simulated annealing was used to search for the minimum velocity that could carry the COM into the BOS and avoid backward loss of balance. We found that the stability boundary against backward balance loss in walking had a similar overall trend as that previously published for standing. In general, the minimal COM velocity necessary to prevent a backward loss of balance in walking was greater than that in symmetric bipedal standing, and the difference could approach 30% or more when the COM started 0.5 and 1.0 foot-lengths behind the BOS. These discrepancies suggest that simpler biomechanical models...

Stability of Visual Masking Performance in Recent-Onset Schizophrenia: An 18-Month Longitudinal Study

Lee, Junghee; Nuechterlein, Keith H.; Subotnik, Kenneth L.; Sugar, Catherine A.; Ventura, Joseph; Gretchen-Doorly, Denise; Kelly, Kimberly; Green, Michael F.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.18%
Visual masking deficit in schizophrenia has been suggested to be a potential vulnerability marker for schizophrenia. An important characteristic of a vulnerability marker is stability over time, but relatively little is known about the longitudinal course of masking performance of schizophrenia patients. In this study, we examined the stability of visual masking performance in recent-onset schizophrenia patients over an 18-month period. We administered both forward and backward masking trials with multiple stimulus onset asynchronies for four masking conditions at three time points (baseline, 6-month, and 18-month). Recent-onset schizophrenia patients showed stable masking performance for both forward and backward conditions over a period of 18 months. Furthermore, the stable performance was observed across all four masking conditions. The findings of this study provide further support for the view that visual masking deficits reflect a possible vulnerability marker for schizophrenia.

Steps to Take to Enhance Gait Stability: The Effect of Stride Frequency, Stride Length, and Walking Speed on Local Dynamic Stability and Margins of Stability

Hak, Laura; Houdijk, Han; Beek, Peter J.; van Dieën, Jaap H.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 13/12/2013 EN
Relevância na Pesquisa
26.42%
The purpose of the current study was to investigate whether adaptations of stride length, stride frequency, and walking speed, independently influence local dynamic stability and the size of the medio-lateral and backward margins of stability during walking. Nine healthy subjects walked 25 trials on a treadmill at different combinations of stride frequency, stride length, and consequently at different walking speeds. Visual feedback about the required and the actual combination of stride frequency and stride length was given during the trials. Generalized Estimating Equations were used to investigate the independent contribution of stride length, stride frequency, and walking speed on the measures of gait stability. Increasing stride frequency was found to enhance medio-lateral margins of stability. Backward margins of stability became larger as stride length decreased or walking speed increased. For local dynamic stability no significant effects of stride frequency, stride length or walking speed were found. We conclude that adaptations in stride frequency, stride length and/or walking speed can result in an increase of the medio-lateral and backward margins of stability, while these adaptations do not seem to affect local dynamic stability. Gait training focusing on the observed stepping strategies to enhance margins of stability might be a useful contribution to programs aimed at fall prevention.

Differences in long-term memory stability and AmCREB level between forward and backward conditioned honeybees (Apis mellifera)

Felsenberg, Johannes; Dyck, Yan; Feige, Janina; Ludwig, Jenny; Plath, Jenny Aino; Froese, Anja; Karrenbrock, Melanie; Nölle, Anna; Heufelder, Karin; Eisenhardt, Dorothea
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 27/04/2015 EN
Relevância na Pesquisa
26.41%
In classical conditioning a predictive relationship between a neutral stimulus (conditioned stimulus; CS) and a meaningful stimulus (unconditioned stimulus; US) is learned when the CS precedes the US. In backward conditioning the sequence of the stimuli is reversed. In this situation animals might learn that the CS signals the end or the absence of the US. In honeybees 30 min and 24 h following backward conditioning a memory for the excitatory and inhibitory properties of the CS could be retrieved, but it remains unclear whether a late long-term memory is formed that can be retrieved 72 h following backward conditioning. Here we examine this question by studying late long-term memory formation in forward and backward conditioning of the proboscis extension response (PER). We report a difference in the stability of memory formed upon forward and backward conditioning with the same number of conditioning trials. We demonstrate a transcription-dependent memory 72 h after forward conditioning but do not observe a 72 h memory after backward conditioning. Moreover we find that protein degradation is differentially involved in memory formation following these two conditioning protocols. We report differences in the level of a transcription factor...

Measuring the Determinants of Backward Linkages from FDI in Developing Economies : Is it a Matter of Size?

Sanchez-Martin, Miguel Eduardo; De Pinies, Jaime; Antoine, Kassia
Fonte: World Bank Group, Washington, DC Publicador: World Bank Group, Washington, DC
EN_US
Relevância na Pesquisa
36.16%
The main focus of the paper is the measurement of the potential for externalities related to foreign direct investment. A series of novel proxies are drawn from the Enterprise Survey database of the World Bank-IFC and tested against hypotheses considered in the foreign direct investment literature. Using these proxies, an econometric assessment of the determinants of backward linkages in developing economies is presented. The results show that export-oriented foreign direct investment, wholly owned subsidiaries (as opposed to joint ventures), and foreign owned firms relying on foreign technologies are less likely to develop links with domestic companies. In addition, the analysis finds that some sectors (food, wood, auto, and auto-parts) are more prone than others (textiles and electronics) in developing backward linkages. Apart from the type of foreign direct investment and sector-specific characteristics, the size of the host economy matters. Foreign owned subsidiaries in most service oriented Caribbean islands buy a low percentage of inputs from domestic firms. This may be because in small islands there are not enough local suppliers with sufficient quality and capacity to meet the demands of multinationals. However...

Middle-Income Countries : Development Challenges and Growing Global Role

Fallon, Peter; Hon, Vivian; Qureshi, Zia; Ratha, Dilip
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: Policy Research Working Paper; Publications & Research
ENGLISH; EN_US
Relevância na Pesquisa
26.22%
There has been much debate recently about the role of international development institutions, such as the World Bank in middle-income countries. Some observers have suggested that middle-income countries have reached a stage in their economic development that calls into question the rationale for development institutions' continued engagement in these countries. But the authors find that middle-income countries continue to face significant development challenges. The nature of these challenges varies substantially, but all of these countries face an agenda calling for continued partnership with the international development community. Middle-income countries still have high levels of poverty. They are home to more than three-quarters of the world's poor (those living on less than U$S 2 a day). Poverty is pervasive in some middle-income countries, while in others the problem is one of major concentrations of poverty in backward areas. And recent crises have revealed the fragility of some of the gains against poverty in these countries. On the policy front...

Selective bilateral activation of leg muscles after cutaneous nerve stimulation during backward walking

Hoogkamer, Wouter; Massaad, Firas; Jansen, Karen; Bruijn, Sjoerd M.; Duysens, Jacques
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.18%
During human locomotion, cutaneous reflexes have been suggested to function to preserve balance. Specifically, cutaneous reflexes in the contralateral leg's muscles (with respect to the stimulus) were suggested to play an important role in maintaining stability during locomotor tasks where stability is threatened. We used backward walking (BW) as a paradigm to induce unstable gait and analyzed the cutaneous reflex activity in both ipsilateral and contralateral lower limb muscles after stimulation of the sural nerve at different phases of the gait cycle. In BW, the tibialis anterior (TA) reflex activity in the contralateral leg was markedly higher than TA background EMG activity during its stance phase. In addition, in BW a substantial reflex suppression was observed in the ipsilateral biceps femoris during the stance-swing transition in some participants, while for medial gastrocnemius the reflex activity was equal to background activity in both legs. To test whether the pronounced crossed responses in TA could be related to instability, the responses were correlated with measures of stability (short-term maximum Lyapunov exponents and step width). These measures were higher for BW compared with forward walking, indicating that BW is less stable. However...

Can Observational Training Substitute Motor Training in Preventing Backward Balance Loss After an Unexpected Slip During Walking?

Bhatt, T.; Pai, Y.-C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.18%
A person's awareness of potential slippery walking conditions induces a cautious gait pattern. The purposes of this study were to determine whether neuromechanical changes associated with such cognitive conditioning are sufficient to alter the outcome of a slip and whether the effects of such conditioning are comparable to those of motor training. Prior to their own first slip exposure, 18 young subjects watched videos and slides demonstrating where and how the slip would occur and how people adapted to repeated-slip exposure (observe). The outcomes of the first slip exposure experienced by another 16 subjects who did not receive any such information were used as controls (naïve). The latter subjects subsequently experienced an additional 23 slips and thus served in a dual-role as the motor training group (motor). Gait stability as measured against backward loss of balance (BLOB) was obtained for pre- and postslip instances. A protective step landing posterior to the slipping-limb identified each BLOB outcome. The observe group had a greater postslip stability and lower slip displacement and velocity than the naïve group. However, such effects were insufficient to prevent balance loss (100% BLOB). The motor group showed significantly better performance on the last training slip (0% BLOB) than did the observe group. The results indicated that updating the cognitive centers of the CNS with awareness and perceptual knowledge through observational training can yield tangible benefits. Nonetheless observation could not replace the task-specific motor training that adaptively updated the internal representations of stability limits for prevention of BLOB.

Backward stability of polynomial root-finding using Fiedler companion matrices

Terán Vergara, Fernando de; Martínez Dopico, Froilan C.; Pérez, J.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article; info:eu-repo/semantics/conferenceObject
Publicado em 08/09/2014 ENG
Relevância na Pesquisa
66.45%
Computing roots of scalar polynomials as the eigenvalues of Frobenius companion matrices using backward stable eigenvalue algorithms is a classical approach. The introduction of new families of companion matrices allows for the use of other matrices in the root-finding problem. In this paper, we analyze the backward stability of polynomial root-finding algorithms via Fiedler companion matrices. In other words, given a polynomial p(z), the question is to determine whether the whole set of computed eigenvalues of the companion matrix, obtained with a backward stable algorithm for the standard eigenvalue problem, are the set of roots of a nearby polynomial or not. We show that, if the coefficients of p(z) are bounded in absolute value by a moderate number, then algorithms for polynomial root-finding using Fiedler matrices are backward stable, and Fiedler matrices are as good as the Frobenius companion matrices. This allows us to use Fiedler companion matrices with favorable structures in the polynomial root-finding problem. However, when some of the coefficients of the polynomial are large, Fiedler companion matrices may produce larger backward errors than Frobenius companion matrices, although in this case neither Frobenius nor Fiedler matrices lead to backward stable computations. To prove this we obtain explicit expressions for the change...

A Model for Understanding Numerical Stability

Bornemann, Folkmar
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/03/2005
Relevância na Pesquisa
36.22%
We present a model of roundoff error analysis that combines simplicity with predictive power. Though not considering all sources of roundoff within an algorithm, the model is related to a recursive roundoff error analysis and therefore capable of correctly predicting stability or instability of an algorithm. By means of nontrivial examples, such as the componentwise backward stability analysis of Gaussian elimination with a single iterative refinement step, we demonstrate that the model even yields quantitative backward error bounds that show all the known problem-dependent terms (with the exception of dimension-dependent constants, which are the weak spot of any a priori analysis). The model can serve as a convenient tool for teaching or as a heuristic device to discover stability results before entering a further, detailed analysis.

On the backward stability of the Schwarzschild black hole singularity

Fournodavlos, Grigorios
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/04/2015
Relevância na Pesquisa
36.12%
We study the backwards-in-time stability of the Schwarzschild singularity from a dynamical PDE point of view. More precisely, considering a spacelike hypersurface $\Sigma_0$ in the interior of the black hole region, tangent to the singular hypersurface $\{r=0\}$ at a single sphere, we study the problem of perturbing the Schwarzschild data on $\Sigma_0$ and solving the Einstein vacuum equations backwards in time. We obtain a local well-posedness result for small perturbations lying in certain weighted Sobolev spaces. No symmetry assumptions are imposed. The perturbed spacetimes all have a singularity at a "collapsed" sphere on $\Sigma_0$, where the leading asymptotics of the curvature and the metric match those of their Schwarzschild counterparts to a suitably high order. As in the Schwarzschild backward evolution, the pinched initial hypersurface $\Sigma_0$ `opens up' instantly, becoming a smooth spacelike (cylindrical) hypersurface. This result thus yields classes of examples of non-symmetric vacuum spacetimes, evolving forward-in-time from smooth initial data, which form a Schwarzschild type singularity at a collapsed sphere. We rely on a precise asymptotic analysis of the Schwarzschild geometry near the singularity which turns out to be at the threshold that our energy methods can handle.; Comment: 6 Figures

On the backward stability of the second barycentric formula for interpolation

Mascarenhas, Walter F.; de Camargo, Andre Pierro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.12%
We present a new stability analysis for the second barycentric formula for interpolation, showing that this formula is backward stable when the relevant Lebesgue constant is small.

Detecting Potential Instabilities of Numerical Algorithms

Yang, Yao
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/09/2015
Relevância na Pesquisa
26.46%
It has been the standard teaching of today that backward stability analysis is taught as absolute, just as in Newtonian physics time is taught absolute time. We will prove it is not true in general. It depends on algorithms. We will prove that forward and mixed stability anlaysis are absolutely invalid stability analysis in the sense that they have absolutely wrong reference points for detecting huge element growth of any algoritms(if any), even an "ideal" or "desirable" backward stability analysis is not so "ideal" or "desirable" in general. Any of forward stable, backward stable and mixed stable algorihms as in Demmel, Kahan , Parlett and other's papers and text books, see Demmel(6) and Higham(8)may not be really stable at all because they may fail to detect and expose any potential instabilities of the algorithm in corresponding stability analysis. Therefore, it is impossible to prove an algorithm is stable according to the standard teachin of today, just as it is impossible to prove a mathematical equuation(Maxwell's) is a law of physics according to the standard teaching in Newtonian physics.; Comment: This paper has a different perspectives about stability analysis axioms (forward stability, backward stability and mixed stability axioms as in Demmel...

F. John's stability conditions vs. A. Carasso's SECB constraint for backward parabolic problems

Lee, Jinwoo; Sheen, Dongwoo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.42%
In order to solve backward parabolic problems F. John [{\it Comm. Pure. Appl. Math.} (1960)] introduced the two constraints "$\|u(T)\|\le M$" and $\|u(0) - g \| \le \delta$ where $u(t)$ satisfies the backward heat equation for $t\in(0,T)$ with the initial data $u(0).$ The {\it slow-evolution-from-the-continuation-boundary} (SECB) constraint has been introduced by A. Carasso in [{\it SIAM J. Numer. Anal.} (1994)] to attain continuous dependence on data for backward parabolic problems even at the continuation boundary $t=T$. The additional "SECB constraint" guarantees a significant improvement in stability up to $t=T.$ In this paper we prove that the same type of stability can be obtained by using only two constraints among the three. More precisely, we show that the a priori boundedness condition $\|u(T)\|\le M$ is redundant. This implies that the Carasso's SECB condition can be used to replace the a priori boundedness condition of F. John with an improved stability estimate. Also a new class of regularized solutions is introduced for backward parabolic problems with an SECB constraint. The new regularized solutions are optimally stable and we also provide a constructive scheme to compute. Finally numerical examples are provided.; Comment: 15 pages. To appear in Inverse Problems

Stability theorems for stochastic differential equations driven by G-Brownian motion

Zhang, Defei
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/05/2011
Relevância na Pesquisa
26.28%
In this paper, stability theorems for stochastic differential equations and backward stochastic differential equations driven by G-Brownian motion are obtained. We show the existence and uniqueness of solutions to forward-backward stochastic differential equations driven by G-Brownian motion. Stability theorem for forward-backward stochastic differential equations driven by G-Brownian motion is also presented.; Comment: 14

Stability of analytical and numerical solutions of nonlinear stochastic delay differential equations

Gan, Siqing; Xiao, Aiguo; Wang, Desheng
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.22%
This paper concerns the stability of analytical and numerical solutions of nonlinear stochastic delay differential equations (SDDEs). We derive sufficient conditions for the stability, contractivity and asymptotic contractivity in mean square of the solutions for nonlinear SDDEs. The results provide a unified theoretical treatment for SDDEs with constant delay and variable delay (including bounded and unbounded variable delays). Then the stability, contractivity and asymptotic contractivity in mean square are investigated for the backward Euler method. It is shown that the backward Euler method preserves the properties of the underlying SDDEs. The main results obtained in this work are different from those of Razumikhin-type theorems. Indeed, our results hold without the necessity of constructing of finding an appropriate Lyapunov functional.; Comment: 23 pages

Backward Bifurcation and Control in Transmission Dynamics of Arboviral Diseases

Abboubakar, Hamadjam; Kamgang, Jean Claude; Tieudjo, Daniel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/09/2015
Relevância na Pesquisa
26.22%
In this paper, we derive and analyze a compartmental model for the control of arboviral diseases which takes into account an imperfect vaccine combined with individual protection and some vector control strategies already studied in the literature. After the formulation of the model, a qualitative study based on stability analysis and bifurcation theory reveals that the phenomenon of backward bifurcation may occur. The stable disease-free equilibrium of the model coexists with a stable endemic equilibrium when the reproduction number, R 0 , is less than unity. Using Lyapunov function theory, we prove that the trivial equilibrium is globally asymptotically stable; When the disease-- induced death is not considered, or/and, when the standard incidence is replaced by the mass action incidence, the backward bifurcation does not occur. Under a certain condition , we establish the global asymptotic stability of the disease--free equilibrium of the full model. Through sensitivity analysis, we determine the relative importance of model parameters for disease transmission. Numerical simulations show that the combination of several control mechanisms would significantly reduce the spread of the disease, if we maintain the level of each control high...

Revisiting the stability of computing the roots of a quadratic polynomial

Nicola, Mastronardi; Paul, Van Dooren
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/09/2014
Relevância na Pesquisa
36.28%
We show in this paper that the roots $x_1$ and $x_2$ of a scalar quadratic polynomial $ax^2+bx+c=0$ with real or complex coefficients $a$, $b$ $c$ can be computed in a element-wise mixed stable manner, measured in a relative sense. We also show that this is a stronger property than norm-wise backward stability, but weaker than element-wise backward stability. We finally show that there does not exist any method that can compute the roots in an element-wise backward stable sense, which is also illustrated by some numerical experiments.; Comment: 13 pages