27,532 research outputs found
X(1835): A Natural Candidate of 's Second Radial Excitation
Recently BES collaboration observed one interesting resonance X(1835). We
point out that its mass, total width, production rate and decay pattern favor
its assignment as the second radial excitation of meson very
naturally
Field-induced structure transformation in electrorheological solids
We have computed the local electric field in a body-centered tetragonal (BCT)
lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to
examine the effects of a structure transformation on the local field strength.
For the ground state of an electrorheological solid of hard spheres, we
identified a novel structure transformation from the BCT to the face-centered
cubic (FCC) lattices by changing the uniaxial lattice constant c under the hard
sphere constraint. In contrast to the previous results, the local field
exhibits a non-monotonic transition from BCT to FCC. As c increases from the
BCT ground state, the local field initially decreases rapidly towards the
isotropic value at the body-centered cubic lattice, decreases further, reaching
a minimum value and increases, passing through the isotropic value again at an
intermediate lattice, reaches a maximum value and finally decreases to the FCC
value. An experimental realization of the structure transformation is
suggested. Moreover, the change in the local field can lead to a generalized
Clausius-Mossotti equation for the BCT lattices.Comment: Submitted to Phys. Rev.
Effects Of A Borehole Environment And Residual Hydrocarbon On Stoneley Wave Amplitude And Reflectivity
In recent years, borehole Stoneley wave amplitude and reflectivity have been used for
estimating formation permeability based on the strong correlation between Stoneley
wave attenuation, reflectivity and formation fluid conductivity. There are other factors,
however, that may cause substantial Stoneley attenuation and reflection in a borehole
environment. To make better use of Stoneley measurements for formation permeability
estimation, it is desirable to identify and quantify those causes of Stoneley attenuation
and reflection that do not directly result from formation permeability. In this study,
a simplified Biot-Rosenbaum model developed by Tang et at. (1991) is adopted to systematically model Stoneley attenuation and reflection in various borehole environments
and formation configurations. By changing pore fluid, formation porosity, lithology,
bed boundaries and thickness in the modeling, the sensitivity of Stoneley wave propagation to these conditions are quantitatively assessed. It is found that the presence of a light hydrocarbon in the formation, especially a natural gas residual in the immediate vicinity of the borehole wall, even with only 5% contained in pore fluid, may also cause substantial Stoneley attenuation and reflection. This phenomenon, on the other hand, can be used to evaluate a nonfractured, low permeability gas reservoir when combined with shear wave velocity data. For the full gas-saturated zone, Stoneley wave reflection may be observed even when the permeability is as low as a few milliDarcies. Compared to the effects of pore fluid, the effects due to lithology contrasts at the boundaries and the changes of nonfracture porosity are insignificant in the cases studied here. For a residual gas-bearing zone of moderate permeability, Stoneley wave attenuation and reflection may be observed if the zone is thicker than 0.5 meter.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumERL/nCUBE Geophysical Center for Parallel ProcessingUnited States. Dept. of Energy (Contract DE-FG02-86ER13636
Probing the electron-phonon coupling in ozone-doped graphene by Raman spectroscopy
We have investigated the effects of ozone treatment on graphene by Raman
scattering. Sequential ozone short-exposure cycles resulted in increasing the
doping levels as inferred from the blue shift of the 2 and peak
frequencies, without introducing significant disorder. The two-phonon 2 and
2 Raman peak intensities show a significant decrease, while, on the
contrary, the one-phonon G Raman peak intensity remains constant for the whole
exposure process. The former reflects the dynamics of the photoexcited
electrons (holes) and, specifically, the increase of the electron-electron
scattering rate with doping. From the ratio of 2 to 2 intensities, which
remains constant with doping, we could extract the ratio of electron-phonon
coupling parameters. This ratio is found independent on the number of layers up
to ten layers. Moreover, the rate of decrease of 2 and 2 intensities
with doping was found to slowdown inversely proportional to the number of
graphene layers, revealing the increase of the electron-electron collision
probability
Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear
We study the impact of catastrophic errors occurring in the photometric
redshifts of galaxies on cosmological parameter estimates with cosmic shear
tomography. We consider a fiducial survey with 9-filter set and perform photo-z
measurement simulations. It is found that a fraction of 1% galaxies at
z_{spec}~0.4 is misidentified to be at z_{phot}~3.5. We then employ both chi^2
fitting method and the extension of Fisher matrix formalism to evaluate the
bias on the equation of state parameters of dark energy, w_0 and w_a, induced
by those catastrophic outliers. By comparing the results from both methods, we
verify that the estimation of w_0 and w_a from the fiducial 5-bin tomographic
analyses can be significantly biased. To minimize the impact of this bias, two
strategies can be followed: (A) the cosmic shear analysis is restricted to
0.5<z<2.5 where catastrophic redshift errors are expected to be insignificant;
(B) a spectroscopic survey is conducted for galaxies with 3<z_{phot}<4. We find
that the number of spectroscopic redshifts needed scales as N_{spec} \propto
f_{cata}\times A where f_{cata}=1% is the fraction of catastrophic redshift
errors (assuming a 9-filter photometric survey) and A is the survey area. For
A=1000 {deg}^2, we find that N_{spec}>320 and 860 respectively in order to
reduce the joint bias in (w_0,w_a) to be smaller than 2\sigma and 1\sigma. This
spectroscopic survey (option B) will improve the Figure of Merit of option A by
a factor \times 1.5 thus making such a survey strongly desirable.Comment: 25 pages, 9 figures. Revised version, as accepted for publication in
Ap
Doubly heavy baryon production at polarized photon collider
We study the inclusive production of doubly heavy baryon at
polarized photon collider. Our results show that proper choice of the initial
beam polarizations may increase the production rate of approximately
10%.Comment: 9 pages, 5 figure
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