6,681 research outputs found
Confirmation of Lagrange Hypothesis for Twisted Elastic Rod
The history of structural optimization as an exact science begins possibly
with the celebrated Lagrange problem: to find a curve which by its revolution
about an axis in its plane determines the rod of greatest efficiency. The
Lagrange hypothesis, that the optimal rod possesses the constant cross-section
was abandoned for Euler buckling problem. In this Article the Lagrange
hypothesis is proved to be valid for Greenhill's problem of torque buckling.
The corresponding isoperimetric inequality is affirmed.Comment: 4 page
Stressors, social support and psychological responses to sport injury in high and low-performance standard participants
publication-status: Publishedtypes: ArticleCopyright © 2010 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Psychology of Sport and Exercise. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Psychology of Sport and Exercise , 2010, Vol. 11, Issue 6, pp. 505 – 51 http://dx.doi.org/10.1016/j.psychsport.2010.07.002Objective The purpose of the present study was to examine the main and buffering effect relationships between social support and psychological responses to sport injury with samples of high- and low-performance standard injured participants. Method High- (N = 147) and low-performance (N = 114) standard injured participants completed measures of perceived social support, injury-related stressors and psychological responses during physiotherapy clinic visits. Results Moderated hierarchical regression analyses revealed the following key findings: a) in the high-performance sample, there were significant (p < 0.05) main effects for social support in relation to psychological responses; b) in the low-performance sample, there were significant buffering effects for social support in relation to psychological responses. That is, in the low-performance sample, the detrimental relationships between stressors and psychological responses were reduced for those with high social support compared to those with low social support, but level of social support was relatively unimportant at low levels of stressors. Conclusion These results highlight that the relationships between social support, stressors, and psychological responses to sport injury may differ, depending upon the performance standard of the athlete. The impact of social support in the injury process may therefore be more complicated than first thought, and this has implications for interventions aimed at increasing social support for injured athletes
The Effect of Antigen Stimulation on the Migration of Mature T Cells from the Peripheral Lymphoid Tissues to the Thymus
Although the maturation and export of T cells from the thymus has been extensively studied,
the movement of cells in the opposite direction has been less well documented. In particular,
the question of whether T cells which have been activated by antigen in the periphery are
more likely to return to the thymus had been raised but not clearly answered. We examined
this issue by activating T cells present in the periphery with their cognate antigen, and assessing migration to the thymus. TCR-transgenic cells from OT-I mice (Thy1.2+), which recognise the ovalbumin peptide OVA257–264 in the context of H-2Kb, were transferred into otherwise unmanipulated Thy1.1+ C57BL/6 mice. Recipient mice were injected i.v. with
5 μg peptide (SIINFEKL) approximately 24 hours later. The numbers of donor-derived (Thy1.2+)
cells in the thymus and peripheral lymphoid tissue were determined. The results clearly show
increased numbers of transgenic cells in the thymus 3 days after antigenic stimulation. However,
since numbers of transgenic cells increased in the spleen and LN in about the same proportion,
the data do not support the notion that there is highly increased selective migration of
activated T cells to the thymus. Rather, they suggest that a sample of peripheral cells enters
the thymus each day, and that the mature immigrants detected in the thymus merely reflect the
contents of the peripheral T cell pool
Grover's Quantum Search Algorithm and Diophantine Approximation
In a fundamental paper [Phys. Rev. Lett. 78, 325 (1997)] Grover showed how a
quantum computer can find a single marked object in a database of size N by
using only O(N^{1/2}) queries of the oracle that identifies the object. His
result was generalized to the case of finding one object in a subset of marked
elements. We consider the following computational problem: A subset of marked
elements is given whose number of elements is either M or K, M<K, our task is
to determine which is the case. We show how to solve this problem with a high
probability of success using only iterations of Grover's basic step (and no
other algorithm). Let m be the required number of iterations; we prove that
under certain restrictions on the sizes of M and K the estimation m <
(2N^{1/2})/(K^{1/2}-M^{1/2}) obtains. This bound sharpens previous results and
is known to be optimal up to a constant factor. Our method involves
simultaneous Diophantine approximations, so that Grover's algorithm is
conceptualized as an orbit of an ergodic automorphism of the torus. We comment
on situations where the algorithm may be slow, and note the similarity between
these cases and the problem of small divisors in classical mechanics.Comment: 8 pages, revtex, Title change
Chiral density waves in quark matter within the Nambu--Jona-Lasinio model in an external magnetic field
A possibility of formation of static dual scalar and pseudoscalar density
wave condensates in dense quark matter is considered for the
Nambu--Jona-Lasinio model in an external magnetic field. Within a mean-field
approximation, the effective potential of the theory is obtained and its minima
are numerically studied; a phase diagram of the system is constructed. It is
shown that the presence of a magnetic field favors the formation of spatially
inhomogeneous condensate configurations at low temperatures and arbitrary
non-zero values of the chemical potential.Comment: 13 pages, 4 figure
Lorentz-Invariant "Elements of Reality" and the Question of Joint Measurability of Commuting Observables
It is shown that the joint measurements of some physical variables
corresponding to commuting operators performed on pre- and post-selected
quantum systems invariably disturb each other. The significance of this result
for recent proofs of the impossibility of realistic Lorentz invariant
interpretation of quantum theory (without assumption of locality) is discussed.Comment: 15 page
Branching ratios for the beta decay of 21Na
We have measured the beta-decay branching ratio for the transition from 21Na
to the first excited state of 21Ne. A recently published test of the standard
model, which was based on a measurement of the beta-nu correlation in the decay
of 21Na, depended on this branching ratio. However, until now only relatively
imprecise (and, in some cases, contradictory) values existed for it. Our new
result, 4.74(4)%, reduces but does not remove the reported discrepancy with the
standard model.Comment: Revtex4, 2 fig
The Casimir Effect for Parallel Plates Revisited
The Casimir effect for a massless scalar field with Dirichlet and periodic
boundary conditions (b.c.) on infinite parallel plates is revisited in the
local quantum field theory (lqft) framework introduced by B.Kay. The model
displays a number of more realistic features than the ones he treated. In
addition to local observables, as the energy density, we propose to consider
intensive variables, such as the energy per unit area , as
fundamental observables. Adopting this view, lqft rejects Dirichlet (the same
result may be proved for Neumann or mixed) b.c., and accepts periodic b.c.: in
the former case diverges, in the latter it is finite, as is shown by
an expression for the local energy density obtained from lqft through the use
of the Poisson summation formula. Another way to see this uses methods from the
Euler summation formula: in the proof of regularization independence of the
energy per unit area, a regularization-dependent surface term arises upon use
of Dirichlet b.c. but not periodic b.c.. For the conformally invariant scalar
quantum field, this surface term is absent, due to the condition of zero trace
of the energy momentum tensor, as remarked by B.De Witt. The latter property
does not hold in tha application to the dark energy problem in Cosmology, in
which we argue that periodic b.c. might play a distinguished role.Comment: 25 pages, no figures, late
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