4,768 research outputs found
Unified theory of bound and scattering molecular Rydberg states as quantum maps
Using a representation of multichannel quantum defect theory in terms of a
quantum Poincar\'e map for bound Rydberg molecules, we apply Jung's scattering
map to derive a generalized quantum map, that includes the continuum. We show,
that this representation not only simplifies the understanding of the method,
but moreover produces considerable numerical advantages. Finally we show under
what circumstances the usual semi-classical approximations yield satisfactory
results. In particular we see that singularities that cause problems in
semi-classics are irrelevant to the quantum map
Microwave fidelity studies by varying antenna coupling
The fidelity decay in a microwave billiard is considered, where the coupling
to an attached antenna is varied. The resulting quantity, coupling fidelity, is
experimentally studied for three different terminators of the varied antenna: a
hard wall reflection, an open wall reflection, and a 50 Ohm load, corresponding
to a totally open channel. The model description in terms of an effective
Hamiltonian with a complex coupling constant is given. Quantitative agreement
is found with the theory obtained from a modified VWZ approach [Verbaarschot et
al, Phys. Rep. 129, 367 (1985)].Comment: 9 pages 5 figur
Decoherence of spin echoes
We define a quantity, the so-called purity fidelity, which measures the rate
of dynamical irreversibility due to decoherence, observed e.g in echo
experiments, in the presence of an arbitrary small perturbation of the total
(system + environment) Hamiltonian. We derive a linear response formula for the
purity fidelity in terms of integrated time correlation functions of the
perturbation. Our relation predicts, similarly to the case of fidelity decay,
faster decay of purity fidelity the slower decay of time correlations is. In
particular, we find exponential decay in quantum mixing regime and faster,
initially quadratic and later typically gaussian decay in the regime of
non-ergodic, e.g. integrable quantum dynamics. We illustrate our approach by an
analytical calculation and numerical experiments in the Ising spin 1/2 chain
kicked with tilted homogeneous magnetic field where part of the chain is
interpreted as a system under observation and part as an environment.Comment: 22 pages, 10 figure
Cognitive Behavioral Therapy for Anxiety Disorders in Youth
Cognitive behavioral therapies (CBTs) have been shown to be efficacious for the treatment of anxiety disorders in children and adolescents. Randomized clinical trials indicate that approximately two-thirds of children treated with CBT will be free of their primary diagnosis at posttreatment. Although several CBT treatment packages have been investigated in youth with diverse anxiety disorders, common core components have been identified. A comprehensive assessment, development of a good therapeutic relationship and working alliance, cognitive restructuring, repeated exposure with reduction of avoidance behavior, and skills training comprise the core procedures for the treatment of anxiety disorders in youth
Learning goal orientation and psychological capital among students: A pathway to academic satisfaction and performance
This study explores the mediating role of psychological capital (PsyCap) in the association between learning goal orientation (LGO), academic satisfaction, and performance among college students. We suggest that PsyCap provides positive psychological resources through which learningâoriented students sustain the effort in academic achievement situations, contributing to academic satisfaction and performance. Seven hundred and sixtyâeight (nâ=â768) college students completed an academic wellâbeing survey, including LGO, PsyCap, and academic satisfaction measures. Academic performance was collected 5âmonths later from the University academic records of students. Path analysis results showed that LGO was directly related to academic satisfaction and performance and indirectly related through PsyCap. Statistically significant indirect effects showed a partial mediation. These results highlight the importance of positive education through investment in psychological resources to increase performance and satisfaction among college students
Avalanches and the Distribution of Reconnection Events in Magnetized Circumstellar Disks
Cosmic rays produced by young stellar objects can potentially alter the
ionization structure, heating budget, chemical composition, and accretion
activity in circumstellar disks. The inner edges of these disks are truncated
by strong magnetic fields, which can reconnect and produce flaring activity
that accelerates cosmic radiation. The resulting cosmic rays can provide a
source of ionization and produce spallation reactions that alter the
composition of planetesimals. This reconnection and particle acceleration are
analogous to the physical processes that produce flaring in and heating of
stellar coronae. Flaring events on the surface of the Sun exhibit a power-law
distribution of energy, reminiscent of those measured for Earthquakes and
avalanches. Numerical lattice-reconnection models are capable of reproducing
the observed power-law behavior of solar flares under the paradigm of
self-organized criticality. One interpretation of these experiments is that the
solar corona maintains a nonlinear attractor -- or ``critical'' -- state by
balancing energy input via braided magnetic fields and output via reconnection
events. Motivated by these results, we generalize the lattice-reconnection
formalism for applications in the truncation region of magnetized disks. Our
numerical experiments demonstrate that these nonlinear dynamical systems are
capable of both attaining and maintaining criticality in the presence of
Keplerian shear and other complications. The resulting power-law spectrum of
flare energies in the equilibrium attractor state is found to be nearly
universal in magnetized disks. This finding indicates that magnetic
reconnection and flaring in the inner regions of circumstellar disks occur in a
manner similar to activity on stellar surfaces
An analogue study examining Attitude Change Theory and its implications for dissemination and implementation of empirically supported treatments
Despite the promise of research-based treatments, dissemination into community settings has been problematic. Attitudes toward these treatments may be partially responsible for the slow uptake. Building on the functional theory of attitudes, it was hypothesized that presenting emotion-focused rather than cognitively-focused information about a treatment would produce more positive attitudes toward the treatment in individuals interested in clinical practice. To test this hypothesis, 144 students (116 women; Mage = 22.46 years) completed a measure of vocational interest and evaluated a treatment after reading either an emotional or cognitive passage about the treatment. Consistent with the hypothesis, participantsâ interests in clinical activities were related to more favorable reactions to the emotional passage but not the cognitive passage. This effect was partially mediated by message elaboration. Findings suggest that presenting clinicians with emotionally rich information on treatment options may help bridge the gap between research and practice
Multi-Country analysis of palm oil consumption and cardiovascular disease mortality for countries at different stages of economic development: 1980-1997
<p>Abstract</p> <p>Background</p> <p>Cardiovascular diseases represent an increasing share of the global disease burden. There is concern that increased consumption of palm oil could exacerbate mortality from ischemic heart disease (IHD) and stroke, particularly in developing countries where it represents a major nutritional source of saturated fat.</p> <p>Methods</p> <p>The study analyzed country-level data from 1980-1997 derived from the World Health Organization's Mortality Database, U.S. Department of Agriculture international estimates, and the World Bank (234 annual observations; 23 countries). Outcomes included mortality from IHD and stroke for adults aged 50 and older. Predictors included per-capita consumption of palm oil and cigarettes and per-capita Gross Domestic Product as well as time trends and an interaction between palm oil consumption and country economic development level. Analyses examined changes in country-level outcomes over time employing linear panel regressions with country-level fixed effects, population weighting, and robust standard errors clustered by country. Sensitivity analyses included further adjustment for other major dietary sources of saturated fat.</p> <p>Results</p> <p>In developing countries, for every additional kilogram of palm oil consumed per-capita annually, IHD mortality rates increased by 68 deaths per 100,000 (95% CI [21-115]), whereas, in similar settings, stroke mortality rates increased by 19 deaths per 100,000 (95% CI [-12-49]) but were not significant. For historically high-income countries, changes in IHD and stroke mortality rates from palm oil consumption were smaller (IHD: 17 deaths per 100,000 (95% CI [5.3-29]); stroke: 5.1 deaths per 100,000 (95% CI [-1.2-11.0])). Inclusion of other major saturated fat sources including beef, pork, chicken, coconut oil, milk cheese, and butter did not substantially change the differentially higher relationship between palm oil and IHD mortality in developing countries.</p> <p>Conclusions</p> <p>Increased palm oil consumption is related to higher IHD mortality rates in developing countries. Palm oil consumption represents a saturated fat source relevant for policies aimed at reducing cardiovascular disease burdens.</p
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