17,996 research outputs found
Electronic Raman scattering in Magnetite, Spin vs. Charge gap
We report Raman scattering data of single crystals of magnetite (Fe3O4) with
Verwey transition temperatures (Tv) of 123 and 117K, respectively. Both single
crystals reveal broad electronic background extending up to 900 wavenumbers
(~110 meV). Redistribution of this background is observed when samples are
cooled below Tv. In particular, spectra of the low temperature phase show
diminished background below 300 wavenumbers followed by an enhancement of the
electronic background between 300 and 400 wavenumbers. To enhance the effect of
this background redistribution we divide the spectra just below the transition
by the spectra just above the transition. A resultant broad peak-like feature
is observed, centered at 370 wavenumbers (45 meV). The peak position of this
feature does not scale with the transition temperature. We discuss two
alternative assignments of this feature to a spin or charge gap in magnetite.Comment: 4 figures, 1 tabl
Monopole clusters, Z(2) vortices and confinement in SU(2)
We extend our previous study of magnetic monopole currents in the maximally
Abelian gauge [hep-lat/9712003] to larger lattices at small lattice spacings
(20^4 at beta = 2.5 and 32^4 at beta = 2.5115). We confirm that at these weak
couplings there continues to be one monopole cluster that is very much longer
than the rest and that the string tension, K, is entirely due to it. The
remaining clusters are compact objects whose population as a function of radius
follows a power law that deviates from the scale invariant form, but much too
weakly to suggest a link with the analytically calculable size distribution of
small instantons. We also search for traces of Z(2) vortices in the Abelian
projected fields; either as closed loops of `magnetic' flux or through
appropriate correlations amongst the monopoles. We find, by direct calculation,
that there is no confining condensate of such flux loops. We also find, through
the calculation of doubly charged Wilson loops within the monopole fields, that
there is no suppression of the q=2 effective string tension out to at distances
of at least r ~ 1.6/sqrt{K}, suggesting that if there are any vortices they are
not encoded in the monopole fields.Comment: 26 pages of LaTeX and PostScript figure
Three-photon detachment of electrons from the fluorine negative ion
Absolute three-photon detachment cross sections are calculated for the
fluorine negative ion within the lowest-order perturbation theory. The Dyson
equation of the atomic many-body theory is used to obtain the ground-state 2p
wavefunction with correct asymptotic behaviour, corresponding to the true
(experimental) binding energy. We show that in accordance with the adiabatic
theory (Gribakin and Kuchiev 1997 {Phys. Rev. A} {\bf 55} 3760) this is crucial
for obtaining absolute values of the multiphoton cross sections. Comparisons
with other calculations and experimental data are presented.Comment: 10 pages, two figures, Latex, IOP styl
Dynamic multilateral markets
We study dynamic multilateral markets, in which players' payoffs result from intra-coalitional bargaining. The latter is modeled as the ultimatum game with exogenous (time-invariant) recognition probabilities and unanimity acceptance rule. Players in agreeing coalitions leave the market and are replaced by their replicas, which keeps the pool of market participants constant over time. In this infinite game, we establish payoff uniqueness of stationary equilibria and the emergence of endogenous cooperation structures when traders experience some degree of (heterogeneous) bargaining frictions. When we focus on market games with different player types, we derive, under mild conditions, an explicit formula for each type's equilibrium payoff as the market frictions vanish
Threshold detachment of negative ions by electron impact
The description of threshold fragmentation under long range repulsive forces
is presented. The dominant energy dependence near threshold is isolated by
decomposing the cross section into a product of a back ground part and a
barrier penetration probability resulting from the repulsive Coulomb
interaction. This tunneling probability contains the dominant energy variation
and it can be calculated analytically based on the same principles as Wannier's
description for threshold ionization under attractive forces. Good agreement is
found with the available experimental cross sections on detachment by electron
impact from , and .Comment: 4 pages, 4 figures (EPS), to appear in Phys.Rev.Lett, Feb. 22nd, 199
Confining strings in SU(N) gauge theories
We calculate the string tensions of -strings in SU() gauge theories in
both 3 and 4 dimensions. In D=3+1, we find that the ratio of the string
tension to the fundamental string tension is consistent, at the level, with both the M(-theory)QCD-inspired conjecture and with
`Casimir scaling'. In D=2+1 we see a definite deviation from the MQCD formula,
as well as a much smaller but still significant deviation from Casimir scaling.
We find that in both D=2+1 and D=3+1 the high temperature spatial -string
tensions also satisfy approximate Casimir scaling. We point out that
approximate Casimir scaling arises naturally if the cross-section of the flux
tube is nearly independent of the flux carried, and that this will occur in an
effective dual superconducting description, if we are in the deep-London limit.
We estimate, numerically, the intrinsic width of -strings in D=2+1 and
indeed find little variation with . In addition to the stable -strings we
investigate some ofthe unstable strings, finding in D=2+1 that they satisfy
(approximate) Casimir scaling. We also investigate the basic assumption that
confining flux tubes are described by an effective string theory at large
distances. We estimate the coefficient of the universal L\"uscher correction
from periodic strings that are longer than 1 fermi, and find in
D=3+1 and in D=2+1. These values are within of the
simple bosonic string values and are inconsistent with other simple effective
string theories.Comment: 57 pages, 11 figures. Errors on fits reduced by altering the analysis
to a standard one. Conclusions unchanged; note addedchanged. Some typos
correcte
Interactive 4-D Visualization of Stereographic Images From the Double Orthogonal Projection
The double orthogonal projection of the 4-space onto two mutually
perpendicular 3-spaces is a method of visualization of four-dimensional objects
in a three-dimensional space. We present an interactive animation of the
stereographic projection of a hyperspherical hexahedron on a 3-sphere embedded
in the 4-space. Described are synthetic constructions of stereographic images
of a point, hyperspherical tetrahedron, and 2-sphere on a 3-sphere from their
double orthogonal projections. Consequently, the double-orthogonal projection
of a freehand curve on a 3-sphere is created inversely from its stereographic
image. Furthermore, we show an application to a synthetic construction of a
spherical inversion and visualizations of double orthogonal projections and
stereographic images of Hopf tori on a 3-sphere generated from Clelia curves on
a 2-sphere.Comment: ICGG 2020 submissio
Running marathons in high school: A 5-year review of injury in a structured training program
Objective: The aim in this study was to quantify the number, nature, and severity of injuries sustained by male and female high school students who took part in a running training program that culminated in the completion of a half or full marathon. Design: This study is a retrospective clinical audit. Methods: Injury reports from high school students (grades 9 – 12) who participated in a half or full marathon 30-week progressive training program comprising four training days per week (three running days and one cross-training day) were reviewed. The number of runners completing a marathon, together with the number, nature, severity of injuries, and treatment types, as reported to the program physiotherapist, were the main outcome measures. Results: Program completion was 96% (n = 448/469). Of all participants, 186 (39.6 %) were injured, with 14 withdrawing from the program due to injury. For those who completed a marathon, 172 (38 %) reported 205 musculoskeletal injuries (age of injured runners: 16.3 ± 1.1 years; 88 girls (51.2 %) and 84 boys (48.8 %)). More than half (n = 113, 55.1 %) of the reported injuries were soft tissue injuries. Most injuries were localized to the lower leg (n = 88, 42.9 %) and were of a minor nature (n = 181, 90 %), requiring only 1–2 treatments. Conclusions: There was a low number of relatively minor injuries for high school participants taking part in a graduated and supervised marathon training program. The injury definition was conservative (i.e., any attendance to physiotherapist) and the relative severity of injuries was minor (i.e., requiring 1 – 2 treatment sessions). Overall, these results do not support a need to restrict high school students from taking part in marathon running, though continued emphasis on graduated program development and close supervision of young participants is recommended
Abelian Monopoles in SU(2) Lattice Gauge Theory as Physical Objects
By numerical calculations we show that the abelian monopole currents are
locally correlated with the density of SU(2) lattice action. The correlations
are larger by the order of magnitude in the maximal abelian projection than in
the projections which correspond to the diagonalization of Polyakov line and to
the diagonalization of the plaquette. These facts show that (at least) in the
maximal abelian projection the monopoles are the physical objects, they carry
the SU(2) action. The larger value of \beta, the larger the relative action
carried by monopole. Calculations on the asymmetric lattice show that this
correlation exists also in the deconfinement phase of gluodynamics.Comment: 6 pages, RevTeX, 3 figures, uses epsf.sty; to be published in
Phys.Rev.Lett., replaced to match version accepted for publicatio
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