7,823 research outputs found
Relaxation of isolated quantum systems beyond chaos
In classical statistical mechanics there is a clear correlation between
relaxation to equilibrium and chaos. In contrast, for isolated quantum systems
this relation is -- to say the least -- fuzzy. In this work we try to unveil
the intricate relation between the relaxation process and the transition from
integrability to chaos. We study the approach to equilibrium in two different
many body quantum systems that can be parametrically tuned from regular to
chaotic. We show that a universal relation between relaxation and
delocalization of the initial state in the perturbed basis can be established
regardless of the chaotic nature of system.Comment: 4+ pages, 4 figs. Closest to published versio
Multifractality of quantum wave packets
We study a version of the mathematical Ruijsenaars-Schneider model, and
reinterpret it physically in order to describe the spreading with time of
quantum wave packets in a system where multifractality can be tuned by varying
a parameter. We compare different methods to measure the multifractality of
wave packets, and identify the best one. We find the multifractality to
decrease with time until it reaches an asymptotic limit, different from the
mulifractality of eigenvectors, but related to it, as is the rate of the
decrease. Our results could guide the study of experimental situations where
multifractality is present in quantum systems.Comment: 6 pages, 4 figures, final version including a new figure (figure 1
Lyapunov decay in quantum irreversibility
The Loschmidt echo -- also known as fidelity -- is a very useful tool to
study irreversibility in quantum mechanics due to perturbations or
imperfections. Many different regimes, as a function of time and strength of
the perturbation, have been identified. For chaotic systems, there is a range
of perturbation strengths where the decay of the Loschmidt echo is perturbation
independent, and given by the classical Lyapunov exponent. But observation of
the Lyapunov decay depends strongly on the type of initial state upon which an
average is done. This dependence can be removed by averaging the fidelity over
the Haar measure, and the Lyapunov regime is recovered, as it was shown for
quantum maps. In this work we introduce an analogous quantity for systems with
infinite dimensional Hilbert space, in particular the quantum stadium billiard,
and we show clearly the universality of the Lyapunov regime.Comment: 8 pages, 6 figures. Accepted in Phil. Trans. R. Soc.
Translation Factors Specify Cellular Metabolic State
In this issue of , Shah et al. present evidence that a subcomplex of the eIF3 translation initiation factor regulates translation of mRNAs encoding components of the mitochondrial electron transport chain and glycolytic enzymes, thus linking translational control with energy metabolism
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Mobile Paving System (MPS): A New Large Scale Freeform Fabrication Method
In the last decade, significant opportunities for automation have been identified in the area of
construction. Soaring labor and material costs have driven multiple research efforts in
construction automation. In this paper, we present a novel means for construction automation
that involves the fusion of the rapid prototyping, controls and mechatronics technologies. The
resultant autonomous construction mechanism has been designed for commercial applications.
Mobile Paving System (MPS) is a new freeform fabrication process which is capable of rapidly
producing variable profiles such as curbs and sidewalks out of materials like cement and asphalt.
Path generation and guidance of the construction operation is controlled by a mobile robot. This
article presents an overview of research and development efforts that are aimed at establishing
the feasibility and the potential of the process.Mechanical Engineerin
In Pursuit of the Ed.D.: A Study of East Tennessee State University\u27s Doctors of Education: Who They are and Why They Persisted.
According to Kerlin (1995a), first-generation students are not expected to survive to doctorate degree attainment because of vulnerability to negative affects associated with their status; yet persist they do at East Tennessee State University. The desire to study the first-generation East Tennessee State University\u27s Doctors of Education and the limited number of first-generation graduate studies available, especially in the academic field of education, promoted developing this study. It was the intent of this study to offer additional empirical research toward understanding variables associated with first-generation persistence as encountered by East Tennessee State University\u27s Doctors of education.
Quantitative analysis derived through survey research served as an explanatory framework to investigate major variables of first-generation persistence. The survey targeted East Tennessee State University\u27s Doctors of Education who received degrees prior to June 2004.
Investigation of empirical evidence revealed that unlike previous first-generation studies (Hayes, 1997; Hurley, 2002; Inman and Mayes, 1999; Khanh, 2002; NCES, 1998; Terenzini, Springer, Yaeger, Pascarella, and Nora, 1996) the bulk (73.7%) of East Tennessee State University Doctors of Education were first-generation. Moreover, although previous studies suggested the presence of unique barriers attributed to first-generation status, no significant differences resulted in either identification or ranking of barriers or facilitators to degree attainment between first-generation East Tennessee State University\u27s Doctors of Education and their non-first-generation counterparts.
The Survey of ETSU Doctors of Education requested respondents prioritize identified barriers and facilitators. After plotting significant bivariate coordinate pairs among ranked barriers and facilitators, flat line (zero sloped) clusters depicted the presence of six weak monotone associations among variables. Facilitator rankings were associated with a respondent\u27s age, parental college attendance, and education specialist degree, while barrier rankings were associated with a respondent\u27s marital status at the time of degree attainment, secondary support source, and post doctorate employment
Weyl law for fat fractals
It has been conjectured that for a class of piecewise linear maps the closure
of the set of images of the discontinuity has the structure of a fat fractal,
that is, a fractal with positive measure. An example of such maps is the
sawtooth map in the elliptic regime. In this work we analyze this problem
quantum mechanically in the semiclassical regime. We find that the fraction of
states localized on the unstable set satisfies a modified fractal Weyl law,
where the exponent is given by the exterior dimension of the fat fractal.Comment: 8 pages, 4 figures, IOP forma
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