61,924 research outputs found
Defect energy of infinite-component vector spin glasses
We compute numerically the zero temperature defect energy, Delta E, of the
vector spin glass in the limit of an infinite number of spin components m, for
a range of dimensions 2 <= d <= 5. Fitting to Delta E ~ L^theta, where L is the
system size, we obtain: theta = -1.54 (d=2), theta = -1.04 (d=3), theta = -0.67
(d=4) and theta = -0.37 (d=5). These results show that the lower critical
dimension, d_l (the dimension where theta changes sign), is significantly
higher for m=infinity than for finite m (where 2 < d_l < 3).Comment: 4 pages, 5 figure
Selected aspects of lunar mare geology from Apollo orbital photography
Crater size-frequency distributions were studied (100-500 m) and are shown to provide significant integrated information concerning mare surface ages, subsurface stratigraphy, and surficial geology. Equilibrium cratering is discussed gradually reducing the relative numbers of craters smaller than 300-400 m in diameter as surfaces age and regolith thickens. Results for surface ages are in good agreement with other published crater ages. The existing correlations of large ring structures among various circular mare basins are shown to be based on criteria that are inconsistent and nonstandardized. A means of comparing equivalent ring structures in the different maria is proposed which takes into account the important characteristics of young unflooded basins (Orientale) as well as the progressive development of tectonic and volcanic features within the older flooded maria. Specific geologic aspects of several of the lunar maria are discussed and especially Mare Smythii, because of its great age and significantly different surface morphology. Lunar photographs and maps are shown
Planetary isophotes as a clue to aerosol characteristics
A study was conducted to see how much information could be extracted from the Mariner 9 Mars isophotes taken at a phase angle of approximately 60 deg. It was found that the Minnaert functions and both isotropic and Rayleigh scattering could easily be ruled out, and that it was essential to use forward-peaked phase functions, which were computed from Mie theory. Isophotes similar to those observed assuming a semi-infinite dust cloud with a considerable variation in particle properties and size distribution could be obtained, so long as the ratio of the multiply- to singly-scattered light was held within certain limits. These conditions are met by micron-sized, moderatly absorbing mineral grains whose mean size should not be much larger than a micron. It was also found that a dust cloud of finite optical thickness bounded from below by a Lambert ground would fit the isophote data
Spin glasses in the limit of an infinite number of spin components
We consider the spin glass model in which the number of spin components, m,
is infinite. In the formulation of the problem appropriate for numerical
calculations proposed by several authors, we show that the order parameter
defined by the long-distance limit of the correlation functions is actually
zero and there is only "quasi long range order" below the transition
temperature. We also show that the spin glass transition temperature is zero in
three dimensions.Comment: 9 pages, 13 figure
Progress in resolving charge symmetry violation in nucleon structure
Recent work unambiguously resolves the level of charge symmetry violation in
moments of parton distributions using 2+1-flavor lattice QCD. We introduce the
methods used for that analysis by applying them to determine the strong
contribution to the proton-neutron mass difference. We also summarize related
work which reveals that the fraction of baryon spin which is carried by the
quarks is in fact structure-dependent rather than universal across the baryon
octet.Comment: 8 pages, 4 figures; presented at "The Seventh International Symposium
on Chiral Symmetry in Hadrons and Nuclei", BeiHang Univ. Beijing, Chin
Chiral extrapolation and physical insights
It has recently been established that finite-range regularisation in chiral
effective field theory enables the accurate extrapolation of modern lattice QCD
results to the chiral regime. We review some of the highlights of
extrapolations of quenched lattice QCD results, including spectroscopy and
magnetic moments. The resonance displays peculiar chiral features in
the quenched theory which can be exploited to demonstrate the presence of
significant chiral corrections.Comment: 6 pages, 5 figures, presented at LHP2003, Cairns, Australi
Hadron structure on the back of an envelope
In order to remove a little of the mysticism surrounding the issue of
strangeness in the nucleon, we present simple, physically transparent estimates
of both the strange magnetic moment and charge radius of the proton. Although
simple, the estimates are in quite good agreement with sophisticated
calculations using the latest input from lattice QCD. We further explore the
possible size of systematic uncertainties associated with charge symmetry
violation (CSV) in the recent precise determination of the strange magnetic
moment of the proton. We find that CSV acts to increase the error estimate by
0.003 \mu_N such that G_M^s = -0.046 +/- 0.022 \mu_N.Comment: 9 pages, 1 figure, Invited talk at First Workshop on Quark-Hadron
Duality and the Transition to pQCD, Frascati, June 6-8 200
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