555,349 research outputs found
Rigorous statistical detection and characterization of a deviation from the Gutenberg-Richter distribution above magnitude 8 in subduction zones
We present a quantitative statistical test for the presence of a crossover c0
in the Gutenberg-Richter distribution of earthquake seismic moments, separating
the usual power law regime for seismic moments less than c0 from another faster
decaying regime beyond c0. Our method is based on the transformation of the
ordered sample of seismic moments into a series with uniform distribution under
condition of no crossover. The bootstrap method allows us to estimate the
statistical significance of the null hypothesis H0 of an absence of crossover
(c0=infinity). When H0 is rejected, we estimate the crossover c0 using two
different competing models for the second regime beyond c0 and the bootstrap
method. For the catalog obtained by aggregating 14 subduction zones of the
Circum Pacific Seismic Belt, our estimate of the crossover point is log(c0)
=28.14 +- 0.40 (c0 in dyne-cm), corresponding to a crossover magnitude mW=8.1
+- 0.3. For separate subduction zones, the corresponding estimates are much
more uncertain, so that the null hypothesis of an identical crossover for all
subduction zones cannot be rejected. Such a large value of the crossover
magnitude makes it difficult to associate it directly with a seismogenic
thickness as proposed by many different authors in the past. Our measure of c0
may substantiate the concept that the localization of strong shear deformation
could propagate significantly in the lower crust and upper mantle, thus
increasing the effective size beyond which one should expect a change of
regime.Comment: pdf document of 40 pages including 5 tables and 19 figure
On the Timescale for the Formation of Protostellar Cores in Magnetic Interstellar Clouds
We revisit the problem of the formation of dense protostellar cores due to
ambipolar diffusion within magnetically supported molecular clouds, and derive
an analytical expression for the core formation timescale. The resulting
expression is similar to the canonical expression = t_{ff}^2/t_{ni} ~ 10 t_{ni}
(where t_{ff} is the free-fall time and t_{ni} is the neutral-ion collision
time), except that it is multiplied by a numerical factor C(\mu_{c0}), where
\mu_{c0} is the initial central mass-to-flux ratio normalized to the critical
value for gravitational collapse. C(\mu_{c0}) is typically ~ 1 in highly
subcritical clouds (\mu_{c0} << 1), although certain conditions allow
C(\mu_{c0}) >> 1. For clouds that are not highly subcritical, C(\mu_{c0}) can
be much less than unity, with C(\mu_{c0}) --> 0 for \mu_{c0} --> 1,
significantly reducing the time required to form a supercritical core. This,
along with recent observations of clouds with mass-to-flux ratios close to the
critical value, may reconcile the results of ambipolar diffusion models with
statistical analyses of cores and YSO's which suggest an evolutionary timescale
\~ 1 Myr for objects of mean density ~ 10^4 cm^{-3}. We compare our analytical
relation to the results of numerical simulations, and also discuss the effects
of dust grains on the core formation timescale.Comment: 11 pages, 2 figures, accepted for publication in the Astrophysical
Journa
Gap States in Dilute Magnetic Alloy Superconductors
We study states in the superconducting gap induced by magnetic impurities
using self-consistent quantum Monte Carlo with maximum entropy and formally
exact analytic continuation methods. The magnetic impurity susceptibility has
different characteristics for T_{0} \alt T_{c0} and T_{0} \agt T_{c0}
(: Kondo temperature, : superconducting transition temperature)
due to the crossover between a doublet and a singlet ground state. We
systematically study the location and the weight of the gap states and the gap
parameter as a function of and the concentration of the
impurities.Comment: 4 pages in ReVTeX including 4 encapsulated Postscript figure
Charmed quark component of the photon wave function
We determine the c-anti-c component of the photon wave function on the basis
of (i) the data on the transitions e+ e- -> J/psi(3096), psi(3686), psi(4040),
psi(4415), (ii) partial widths of the two-photon decays eta_{c0}(2979),
chi_{c0}(3415), chi_{c2}(3556) -> gamma-gamma, and (iii) wave functions of the
charmonium states obtained by solving the Bethe-Salpeter equation for the
c-anti-c system. Using the obtained c-anti-c component of the photon wave
function we calculate the gamma-gamma decay partial widths for radial
excitation 2S state, eta_{c0}(3594) -> gamma-gamma, and 2P states
chi_{c0}(3849), chi_{c2}(3950) -> gamma-gamma.Comment: 20 pages, 8 figure
Annihilation Rate of Heavy 0^{++} P-wave Quarkonium in Relativistic Salpeter Method
Two-photon and two-gluon annihilation rates of P-wave scalar charmonium and
bottomonium up to third radial excited states are estimated in the relativistic
Salpeter method. We solved the full Salpeter equation with a well defined
relativistic wave function and calculated the transition amplitude using the
Mandelstam formalism. Our model dependent estimates for the decay widths:
keV,
keV, eV and eV. We also give estimates of total widths by the two-gluon
decay rates: MeV,
MeV, MeV and
MeV.Comment: 8 pages, 1 figure, 4 table
Hall coefficient in heavy fermion metals
Experimental studies of the antiferromagnetic (AF) heavy fermion metal in a magnetic field indicate the presence of a jump in the Hall
coefficient at a magnetic-field tuned quantum state in the zero temperature
limit. This quantum state occurs at and induces the jump even
though the change of the magnetic field at is infinitesimal. We
investigate this by using the model of heavy electron liquid with the fermion
condensate. Within this model the jump takes place when the magnetic field
reaches the critical value at which the ordering temperature
of the AF transition vanishes. We show that at ,
this second order AF phase transition becomes the first order one, making the
corresponding quantum and thermal critical fluctuations vanish at the jump. At
and , the Gr\"uneisen ratio as a function of temperature
diverges. We demonstrate that both the divergence and the jump are determined
by the specific low temperature behavior of the entropy with , and are temperature independent
constants.Comment: 5 pages, 2 figure
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