4,830 research outputs found
Chiral symmetry, Confinement and Nuclear Matter properties
We discuss the possible influence of fundamental QCD properties such as
spontaneous chiral symmetry breaking and nucleon substructure on nuclear matter
properties. We propose a chiral version of the relativistic
model in which the attractive background scalar field is associated with the
chiral invariant field governing the radial fluctuations of the quark
condensate. Nuclear matter stability is ensured once the scalar response of the
nucleon depending on the quark confinement mechanism is properly incorporated.
The needed parameters are estimated from lattice results and a satisfactory
description of bulk properties follows, the only really free parameter being
the coupling constant. Pion loops can be also incorporated to
obtain in a consistent way the finite density chiral susceptibilities. A good
description of the asymmetry energy is obtained once the full rho meson
exchange and Fock terms are included.Comment: Lecture given by G. Chanfray at the Theoretical Nuclear Physics
School, 8-17 may 2007, Les Houches, Franc
Measurement of geometric phase for mixed states using single photon interferometry
Geometric phase may enable inherently fault-tolerant quantum computation.
However, due to potential decoherence effects, it is important to understand
how such phases arise for {\it mixed} input states. We report the first
experiment to measure mixed-state geometric phases in optics, using a
Mach-Zehnder interferometer, and polarization mixed states that are produced in
two different ways: decohering pure states with birefringent elements; and
producing a nonmaximally entangled state of two photons and tracing over one of
them, a form of remote state preparation.Comment: To appear in Phys. Rev. Lett. 4 pages, 3 figure
Injury Risk Estimation Expertise Assessing the ACL Injury Risk Estimation Quiz
Background: Available methods for screening anterior cruciate ligament (ACL) injury risk are effective but limited in application as
they generally rely on expensive and time-consuming biomechanical movement analysis. A potential efficient alternative to biomechanical
screening is skilled movement analysis via visual inspection (ie, having experts estimate injury risk factors based on
observations of athletes’ movements).
Purpose: To develop a brief, valid psychometric assessment of ACL injury risk factor estimation skill: the ACL Injury Risk Estimation
Quiz (ACL-IQ).
Study Design: Cohort study (diagnosis); Level of evidence, 3.
Methods: A total of 660 individuals participated in various stages of the study, including athletes, physicians, physical therapists,
athletic trainers, exercise science researchers/students, and members of the general public in the United States. The ACL-IQ was
fully computerized and made available online (www.ACL-IQ.org). Item sampling/reduction, reliability analysis, cross-validation,
and convergent/discriminant validity analysis were conducted to optimize the efficiency and validity of the assessment.
Results: Psychometric optimization techniques identified a short (mean time, 2 min 24 s), robust, 5-item assessment with high
reliability (test-retest: r = 0.90) and consistent discriminability (average difference of exercise science professionals vs general
population: Cohen d = 1.98). Exercise science professionals and general population individuals scored 74% and 53% correct,
respectively. Convergent and discriminant validity was demonstrated. Scores on the ACL-IQ were most associated with ACL
knowledge and various cue utilities and were least associated with domain-general spatial/decision-making ability, personality,
or other demographic variables. Overall, 23% of the total sample (40% exercise science professionals; 6% general population)
performed better than or equal to the ACL nomogram.
Conclusion: This study presents the results of a systematic approach to assess individual differences in ACL injury risk factor
estimation skill; the assessment approach is efficient (ie, it can be completed in\3 min) and psychometrically robust. The results
provide evidence that some individuals have the ability to visually estimate ACL injury risk factors more accurately than other
instrument-based ACL risk estimation methods (ie, ACL nomogram). The ACL-IQ provides the foundation for assessing the efficacy
of observational ACL injury risk factor assessment (ie, does simple skilled visual inspection reduce ACL injuries?). It also
provides a representative task environment that can be used to increase our understanding of the perceptual-cognitive mechanisms
underlying observational movement analysis and to improve injury risk assessment performance
Distributions of Error Correction Tests for Cointegration
This paper provides cumulative distribution functions, densities, and finite sample critical values for the single-equation error correction statistic for testing cointegration. Graphs and response surfaces summarize extensive Monte Carlo simulations and highlight simple dependencies of the statistic's quantiles on the number of variables in the error correction model, the choice of deterministic components, and the estimation sample size. The response surfaces provide a convenient way for calculating finite sample critical values at standard levels; and a computer program, freely available over the Internet, can be used to calculate both critical values and p-values. Three empirical examples illustrate these tools.
Effects of the -factor in semi-classical kinetic plasma theory
A kinetic theory for spin plasmas is put forward, generalizing those of
previous authors. In the model, the ordinary phase space is extended to include
the spin degrees of freedom. Together with Maxwell's equations, the system is
shown to be energy conserving. Analysing the linear properties, it is found
that new types of wave-particle resonances are possible, that depend directly
on the anomalous magnetic moment of the electron. As a result new wave modes,
not present in the absence of spin, appear. The implications of our results are
discussed.Comment: 4 pages, two figures, version to appear in Physical Review Letter
Fundamental bounds on transmission through periodically perforated metal screens with experimental validation
This paper presents a study of transmission through arrays of periodic
sub-wavelength apertures. Fundamental limitations for this phenomenon are
formulated as a sum rule, relating the transmission coefficient over a
bandwidth to the static polarizability. The sum rule is rigorously derived for
arbitrary periodic apertures in thin screens. By this sum rule we establish a
physical bound on the transmission bandwidth which is verified numerically for
a number of aperture array designs. We utilize the sum rule to design and
optimize sub-wavelength frequency selective surfaces with a bandwidth close to
the physically attainable. Finally, we verify the sum rule and simulations by
measurements of an array of horseshoe-shaped slots milled in aluminum foil.Comment: 10 pages, 11 figures. Updated Introduction and Conclusion
Nuclear halo and the coherent nuclear interaction
The unusual structure of Li11, the first halo nucleus found, is analyzed by
the Preparata model of nuclear structure. By applying Coherent Nucleus Theory,
we obtain an interaction potential for the halo-neutrons that rightly
reproduces the fundamental state of the system.Comment: 9 pages Submitted to International Journal of Modern Physics E
(IJMPE
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