2,527 research outputs found
A Report of the Investigation on Steel Bridge Design Criteria to Help Minimize the Probability of Fracture; Project IHR-304, Illinois Cooperative Highway Transportation Research Program
In this study the nature of actual random traffic stress histories in
steel beam or girder highway bridges has been investigated. Quantitative
field test results have been used to develop mathematical models that can
be used to represent the stress histories for such bridges.
The beta distribution function has been found to be an effective
mathematical model for the actual stress-range histograms and has been
used to establish random stress factors and can be used in fatigue design
to account for the random nature of loadings in highway bridges.State of Illinois. Department of TransportationU.S. Department of Transportation. Federal Highway Administratio
Decoherence from a Chaotic Environment: An Upside Down "Oscillator" as a Model
Chaotic evolutions exhibit exponential sensitivity to initial conditions.
This suggests that even very small perturbations resulting from weak coupling
of a quantum chaotic environment to the position of a system whose state is a
non-local superposition will lead to rapid decoherence. However, it is also
known that quantum counterparts of classically chaotic systems lose exponential
sensitivity to initial conditions, so this expectation of enhanced decoherence
is by no means obvious. We analyze decoherence due to a "toy" quantum
environment that is analytically solvable, yet displays the crucial phenomenon
of exponential sensitivity to perturbations. We show that such an environment,
with a single degree of freedom, can be far more effective at destroying
quantum coherence than a heat bath with infinitely many degrees of freedom.
This also means that the standard "quantum Brownian motion" model for a
decohering environment may not be as universally applicable as it once was
conjectured to be.Comment: RevTeX, 29 pages, 5 EPS figures. Substantially rewritten analysis,
improved figures, additional references, and errors fixed. Final version (to
appear in PRA
Intrinsic decoherence and classical-quantum correspondence in two coupled delta-kicked rotors
We show that classical-quantum correspondence of center of mass motion in two
coupled delta-kicked rotors can be obtained from intrinsic decoherence of the
system itself which occurs due to the entanglement of the center of mass motion
to the internal degree of freedom without coupling to external environment
LOMA: A fast method to generate efficient tagged-random primers despite amplification bias of random PCR on pathogens
10.1186/1471-2105-9-368BMC Bioinformatics9BBMI
Environment-Induced Decoherence and the Transition From Quantum to Classical
We study dynamics of quantum open systems, paying special attention to those
aspects of their evolution which are relevant to the transition from quantum to
classical. We begin with a discussion of the conditional dynamics of simple
systems. The resulting models are straightforward but suffice to illustrate
basic physical ideas behind quantum measurements and decoherence. To discuss
decoherence and environment-induced superselection einselection in a more
general setting, we sketch perturbative as well as exact derivations of several
master equations valid for various systems. Using these equations we study
einselection employing the general strategy of the predictability sieve.
Assumptions that are usually made in the discussion of decoherence are
critically reexamined along with the ``standard lore'' to which they lead.
Restoration of quantum-classical correspondence in systems that are classically
chaotic is discussed. The dynamical second law -it is shown- can be traced to
the same phenomena that allow for the restoration of the correspondence
principle in decohering chaotic systems (where it is otherwise lost on a very
short time-scale). Quantum error correction is discussed as an example of an
anti-decoherence strategy. Implications of decoherence and einselection for the
interpretation of quantum theory are briefly pointed out.Comment: 80 pages, 7 figures included, Lectures given by both authors at the
72nd Les Houches Summer School on "Coherent Matter Waves", July-August 199
Breakdown of correspondence in chaotic systems: Ehrenfest versus localization times
Breakdown of quantum-classical correspondence is studied on an experimentally
realizable example of one-dimensional periodically driven system. Two relevant
time scales are identified in this system: the short Ehrenfest time t_h and the
typically much longer localization time scale T_L. It is shown that
surprisingly weak modification of the Hamiltonian may eliminate the more
dramatic symptoms of localization without effecting the more subtle but
ubiquitous and rapid loss of correspondence at t_h.Comment: 4 pages, 5 figures, replaced with a version submitted to PR
Theories of intramolecular vibrational energy transfer
Intramolecular vibrational energy transfer is a process central to many physical and chemical phenomena in molecules. Here, various theories describing the process are summarized with a special emphasis on nonlinear resonances. A large bibliography supplements the text. © 1991
Fast phonetic similarity search over large repositories
Analysis of unstructured data may be inefficient in the presence of spelling errors. Existing approaches use string similarity methods to search for valid words within a text, with a supporting dictionary. However, they are not rich enough to encode phonetic information to assist the search. In this paper, we present a novel approach for efficiently perform phonetic similarity search over large data sources, that uses a data structure called PhoneticMap to encode language-specific phonetic information. We validate our approach through an experiment over a data set using a Portuguese variant of a well-known repository, to automatically correct words with spelling errors
Intrinsic Decoherence Dynamics in Smooth Hamiltonian Systems: Quantum-classical Correspondence
A direct classical analog of the quantum dynamics of intrinsic decoherence in
Hamiltonian systems, characterized by the time dependence of the linear entropy
of the reduced density operator, is introduced. The similarities and
differences between the classical and quantum decoherence dynamics of an
initial quantum state are exposed using both analytical and computational
results. In particular, the classicality of early-time intrinsic decoherence
dynamics is explored analytically using a second-order perturbative treatment,
and an interesting connection between decoherence rates and the stability
nature of classical trajectories is revealed in a simple approximate classical
theory of intrinsic decoherence dynamics. The results offer new insights into
decoherence, dynamics of quantum entanglement, and quantum chaos.Comment: 12 pages, 7 figures, to appear in Physical Review
Dynamical aspects of quantum entanglement for weakly coupled kicked tops
We investigate how the dynamical production of quantum entanglement for
weakly coupled, composite quantum systems is influenced by the chaotic dynamics
of the corresponding classical system, using coupled kicked tops. The linear
entropy for the subsystem (a kicked top) is employed as a measure of
entanglement. A perturbative formula for the entanglement production rate is
derived. The formula contains a correlation function that can be evaluated only
from the information of uncoupled tops. Using this expression and the
assumption that the correlation function decays exponentially which is
plausible for chaotic tops, it is shown that {\it the increment of the strength
of chaos does not enhance the production rate of entanglement} when the
coupling is weak enough and the subsystems (kicked tops) are strongly chaotic.
The result is confirmed by numerical experiments. The perturbative approach is
also applied to a weakly chaotic region, where tori and chaotic sea coexist in
the corresponding classical phase space, to reexamine a recent numerical study
that suggests an intimate relationship between the linear stability of the
corresponding classical trajectory and the entanglement production rate.Comment: 16 pages, 11 figures, submitted to Phys. Rev.
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