29,857 research outputs found
Statistical evidence links exceptional 1995 Atlantic hurricane season to record sea warming
Tropical cyclones rank above earthquakes as the major geophysical cause of loss of life and property (Bryant, 1991; Houghton, 1994). In the United States alone, the damage bill from mainland landfalling hurricanes over the last 50 years averages $2.0 billion per year (Hebert et al., 1996). Years with high numbers of hurricanes provide new insight on the environmental factors influencing interannual variability; hence the interest in the exceptional 1995 Atlantic season which saw 11 hurricanes and a total of 19 tropical storms, double the 50-year average. While most environmental factors in 1995 were favourable for tropical cyclone development, we show that a factor not fully explored before, the sea surface temperature (SST) was the most significant. For the 10 degrees-20 degrees N, 20 degrees-60 degrees W region where 93% of the anomalous 1995 hurricanes developed, similar to 45 year statistical regressions show that SST is the dominating influence, independent of all known other factors, behind the interannual variance in Atlantic hurricance numbers. With this SST experiencing record warm levels in 1995, 0.66 degrees C above the 1946-1995 mean, these regressions indicate that sea warming explains 61+/-34% of the anomalous hurricane activity in 1995 to 95% confidence
Renormalization group for the probability distribution of magnetic impurities in a random-field model
Extending the usual Ginzburg-Landau theory for the random-field Ising model,
the possibility of dimensional reduction is reconsidered. A renormalization
group for the probability distribution of magnetic impurities is applied. New
parameters corresponding to the extra coupling constants in the
replica Hamiltonian are introduced. Although they do not affect the critical
phenomena near the upper critical dimension, they can when dimensions are
lowered.Comment: 16 pages, 11 figures, revte
Detailed study of B037 based on {\sl HST} images
B037 is of interest because it is both the most luminous and the most highly
reddened cluster known in M31. Images of deep observations and of highly
spatial resolutions with the Advanced Camera for Surveys on the {\sl HST}
firstly show that this cluster is crossed by a dust lane. Photometric data in
the F606W and F814W filters obtained in this paper provide that, colors of
() in the dust lane are redder mags than ones in
the other regions of B037. The {\sl HST} images show that, this dust lane seems
to be contained in B037, not from the M31 disk or the Milky Way. As we know,
the formation of dust requires gas with a rather high metallicity. However,
B037 has a low metallicity to be . So, it seems
improbable that the observed dust lane is physically associated with B037. It
is clear that the origin of this dust lane is worthy of future study. In
addition, based on these images, we present the precise variation of
ellipticity and position angle, and of surface brightness profile, and
determine the structural parameters of B037 by fitting a single-mass isotropic
King model. In the F606W filter, we derive the best-fitting scale radius,
r_0=0.56\pm0.02\arcsec~(=2.16\pm0.08~\rm{pc}), a tidal radius,
r_t=8.6\pm0.4\arcsec~(=33.1\pm1.5~\rm{pc}), and a concentration index . In the F814W filter, we derive
r_0=0.56\pm0.01\arcsec~(=2.16\pm0.04~\rm{pc}),
r_t=8.9\pm0.3\arcsec~(=34.3\pm1.2~\rm{pc}), and . The extinction-corrected central surface brightness is
in the F606W filter, and in the F814W filter, respectively.Comment: Accepted for Publication in RAA, 13 pages, 5 figures and 7 table
Y.E.S. 4 Health: A Peer Education Approach to Prevention of Diabetes in African American Adolescents
From random walk to single-file diffusion
We report an experimental study of diffusion in a quasi-one-dimensional (q1D)
colloid suspension which behaves like a Tonks gas. The mean squared
displacement as a function of time is described well with an ansatz
encompassing a time regime that is both shorter and longer than the mean time
between collisions. This ansatz asserts that the inverse mean squared
displacement is the sum of the inverse mean squared displacement for short time
normal diffusion (random walk) and the inverse mean squared displacement for
asymptotic single-file diffusion (SFD). The dependence of the single-file 1D
mobility on the concentration of the colloids agrees quantitatively with that
derived for a hard rod model, which confirms for the first time the validity of
the hard rod SFD theory. We also show that a recent SFD theory by Kollmann
leads to the hard rod SFD theory for a Tonks gas.Comment: 4 pages, 4 figure
Five-loop \sqrt\epsilon-expansions for random Ising model and marginal spin dimensionality for cubic systems
The \sqrt\epsilon-expansions for critical exponents of the weakly-disordered
Ising model are calculated up to the five-loop order and found to possess
coefficients with irregular signs and values. The estimate n_c = 2.855 for the
marginal spin dimensionality of the cubic model is obtained by the Pade-Borel
resummation of corresponding five-loop \epsilon-expansion.Comment: 9 pages, TeX, no figure
Making Neutrinos Massive with an Axion in Supersymmetry
The minimal supersymmetric standard model (MSSM) of particle interactions is
extended to include three singlet (right-handed) neutrino superfields together
with three other singlet superfields. The resulting theory is assumed to be
invariant under an anomalous global U(1) (Peccei-Quinn) symmetry with one
fundamental mass . The soft breaking of supersymmetry at the TeV scale is
shown to generate an axion scale of order . Neutrino masses are
generated by according to the usual seesaw mechanism.Comment: 11 pages, substantially revised with important change
Electromagnetically-Induced-Transparency-Like Effect in the Degenerate Triple-Resonant Optical Parametric Amplifier
We investigate experimentally the absorptive and dispersive properties of
triple-resonant optical parametric amplifier OPA for the degenerate subharmonic
field. In the experiment, the subharmonic field is utilized as the probe field
and the harmonic wave as the pump field. We demonstrate that EIT-like effect
can be simulated in the triple-resonant OPA when the cavity line-width for the
harmonic wave is narrower than that for the subharmonic field. However, this
phenomenon can not be observed in a double-resonant OPA. The narrow
transparency window appears in the reflected field. Especially, in the measured
dispersive spectra of triple-resonant OPA, a very steep variation of the
dispersive profile of the subharmonic field is observed, which can result in a
slow light as that observed in atomic EIT medium.Comment: 10 pages, 4 figures, appear in Opt. Let
Age and structure parameters of a remote M31 globular cluster B514 based on HST, 2MASS, GALEX and BATC observations
B514 is a remote M31 globular cluster which locating at a projected distance
of R_p~55 kpc. Deep observations with the Advanced Camera for Surveys (ACS) on
the Hubble Space Telescope (HST) are used to provide the accurate integrated
light and star counts of B514. By coupling analysis of the distribution of the
integrated light with star counts, we are able to reliably follow the profile
of the cluster out to ~40". Based on the combined profile, we study in detail
its surface brightness distribution in F606W and F814W filters, and determine
its structural parameters by fitting a single-mass isotropic King model. The
results showed that, the surface brightness distribution departs from the
best-fit King model for r>10". B514 is quite flatted in the inner region, and
has a larger half-light radius than majority of normal globular clusters of the
same luminosity. It is interesting that, in the M_V versus log R_h plane, B514
lies nearly on the threshold for ordinary globular clusters as defined by
Mackey & van den Bergh. In addition, B514 was observed as part of the
Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey, using 13
intermediate-band filters covering a wavelength range of 3000--8500 \AA. Based
on aperture photometry, we obtain its SEDs as defined by the 13 BATC filters.
We determine the cluster's age and mass by comparing its SEDs (from 2267 to
20000{\AA}, comprising photometric data in the near-ultraviolet of GALEX, 5
SDSS bands, 13 BATC intermediate-band, and 2MASS near-infrared JHKs} filters)
with theoretical stellar population synthesis models, resulting in age of
Gyr. This age confirms the previous suggestion that B514 is an old
GC in M31. B514 has a mass of , and is a
medium-mass globular cluster in M31.Comment: Accepted for Publication in AJ, 18 pages, 6 figures and 9 table
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Coupling between gamma-band power and cerebral blood volume during recurrent acute neocortical seizures
Characterization of neural and hemodynamic biomarkers of epileptic activity that can be measured using non-invasive techniques is fundamental to the accurate identification of the epileptogenic zone (EZ) in the clinical setting. Recently, oscillations at gamma-band frequencies and above (>30 Hz) have been suggested to provide valuable localizing information of the EZ and track cortical activation associated with epileptogenic processes. Although a tight coupling between gamma-band activity and hemodynamic-based signals has been consistently demonstrated in non-pathological conditions, very little is known about whether such a relationship is maintained in epilepsy and the laminar etiology of these signals. Confirmation of this relationship may elucidate the underpinnings of perfusion-based signals in epilepsy and the potential value of localizing the EZ using hemodynamic correlates of pathological rhythms. Here, we use concurrent multi-depth electrophysiology and 2-dimensional optical imaging spectroscopy to examine the coupling between multi-band neural activity and cerebral blood volume (CBV) during recurrent acute focal neocortical seizures in the urethane-anesthetized rat. We show a powerful correlation between gamma-band power (25-90 Hz) and CBV across cortical laminae, in particular layer 5, and a close association between gamma measures and multi-unit activity (MUA). Our findings provide insights into the laminar electrophysiological basis of perfusion-based imaging signals in the epileptic state and may have implications for further research using non-invasive multi-modal techniques to localize epileptogenic tissue
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