84,530 research outputs found
Comment on ``Stripes and the t-J Model''
This is a comment being submitted to Physical Review Letters on a recent
letter by Hellberg and Manousakis on stripes in the t-J model.Comment: One reference correcte
ROSAT PSPC observations of the outer regions of the Perseus cluster of galaxies
We present an analysis of four off-axis ROSAT PSPC observations of the
Perseus cluster of galaxies (Abell~426). We detect the surface brightness
profile to a radius of 80 arcmin ( Mpc) from the X-ray
peak. The profile is measured in various sectors and in three different energy
bands. Firstly, a colour analysis highlights a slight variation of over
the region, and cool components in the core and in the eastern sector. We apply
the -model to the profiles from different sectors and present a solution
to the, so-called, -problem. The residuals from an azimuthally-averaged
profile highlight extended emission both in the East and in the West, with
estimated luminosities of about 8 and 1 , respectively.
We fit several models to the surface brightness profile, including the one
obtained from the Navarro, Frenk and White (1995) potential. We obtain the best
fit with the gas distribution described by a power law in the inner, cooling
region and a -model for the extended emission. Through the best-fit
results and the constraints from the deprojection of the surface brightness
profiles, we define the radius where the overdensity inside the cluster is 200
times the critical value, , at Mpc. Within Mpc (), the total mass in the Perseus cluster is
and its gas fraction is about 30 per cent.Comment: 21 pages, 23 figures; accepted for publication in MNRAS; also
available at http://www-xray.ast.cam.ac.uk/~settori/paper.htm
A systematic study of Rayleigh-Brillouin scattering in air, N2 and O2 gases
Spontaneous Rayleigh-Brillouin scattering experiments in air, N2 and O2 have
been performed for a wide range of temperatures and pressures at a wavelength
of 403 nm and at a 90 degrees scattering angle. Measurements of the
Rayleigh-Brillouin spectral scattering profile were conducted at high
signal-to-noise ratio for all three species, yielding high-quality spectra
unambiguously showing the small differences between scattering in air, and its
constituents N2 and O2. Comparison of the experimental spectra with
calculations using the Tenti S6 model, developed in 1970s based on linearized
kinetic equations for molecular gases, demonstrates that this model is valid to
high accuracy. After previous measurements performed at 366 nm, the Tenti S6
model is here verified for a second wavelength of 403 nm. Values for the bulk
viscosity for the gases are derived by optimizing the model to the
measurements. It is verified that the bulk viscosity parameters obtained from
previous experiments at 366 nm, are valid for wavelengths of 403 nm. Also for
air, which is treated as a single-component gas with effective gas transport
coefficients, the Tenti S6 treatment is validated for 403 nm as for the
previously used wavelength of 366 nm, yielding an accurate model description of
the scattering profiles for a range of temperatures and pressures, including
those of relevance for atmospheric studies. It is concluded that the Tenti S6
model, further verified in the present study, is applicable to LIDAR
applications for exploring the wind velocity and the temperature profile
distributions of the Earth's atmosphere. Based on the present findings,
predictions can be made on the spectral profiles for a typical LIDAR
backscatter geometry, which deviate by some 7 percent from purely Gaussian
profiles at realistic sub-atmospheric pressures occurring at 3-5 km altitude in
the Earth's atmosphere
Hole-pair hopping in arrangements of hole-rich/hole-poor domains in a quantum antiferromagnet
We study the motion of holes in a doped quantum antiferromagnet in the
presence of arrangements of hole-rich and hole-poor domains such as the
stripe-phase in high- cuprates. When these structures form, it becomes
energetically favorable for single holes, pairs of holes or small bound-hole
clusters to hop from one hole-rich domain to another due to quantum
fluctuations. However, we find that at temperature of approximately 100 K, the
probability for bound hole-pair exchange between neighboring hole-rich regions
in the stripe phase, is one or two orders of magnitude larger than single-hole
or multi-hole droplet exchange. As a result holes in a given hole-rich domain
penetrate further into the antiferromagnetically aligned domains when they do
it in pairs. At temperature of about 100 K and below bound pairs of holes hop
from one hole-rich domain to another with high probability. Therefore our main
finding is that the presence of the antiferromagnetic hole-poor domains act as
a filter which selects, from the hole-rich domains (where holes form a
self-bound liquid), hole pairs which can be exchanged throughout the system.
This fluid of bound hole pairs can undergo a superfluid phase ordering at the
above mentioned temperature scale.Comment: Revtex, 6 two-column pages, 4 figure
High frequency, high power capacitor development
A program to develop a special high energy density, high power transfer capacitor to operate at frequency of 40 kHz, 600 V rms at 125 A rms plus 600 V dc bias for space operation. The program included material evaluation and selection, a capacitor design was prepared, a thermal analysis performed on the design. Fifty capacitors were manufactured for testing at 10 kHz and 40 kHz for 50 hours at Industrial Electric Heating Co. of Columbus, Ohio. The vacuum endurance test used on environmental chamber and temperature plate furnished by Maxwell. The capacitors were energized with a special power conditioning apparatus developed by Industrial Electric Heating Co. Temperature conditions of the capacitors were monitored by IEHCo test equipment. Successful completion of the vacuum endurance test series confirmed achievement of the main goal of producing a capacitor or reliable operation at high frequency in an environment normally not hospitable to electrical and electronic components. The capacitor developed compared to a typical commercial capacitor at the 40 kHz level represents a decrease in size and weight by a factor of seven
A Renormalization Group Method for Quasi One-dimensional Quantum Hamiltonians
A density-matrix renormalization group (DMRG) method for highly anisotropic
two-dimensional systems is presented. The method consists in applying the usual
DMRG in two steps. In the first step, a pure one dimensional calculation along
the longitudinal direction is made in order to generate a low energy
Hamiltonian. In the second step, the anisotropic 2D lattice is obtained by
coupling in the transverse direction the 1D Hamiltonians. The method is applied
to the anisotropic quantum spin half Heisenberg model on a square lattice.Comment: 4 pages, 4 figure
Wilson line approach to gravity in the high energy limit
We examine the high energy (Regge) limit of gravitational scattering using a
Wilson line approach previously used in the context of non-Abelian gauge
theories. Our aim is to clarify the nature of the Reggeization of the graviton
and the interplay between this Reggeization and the so-called eikonal phase
which determines the spectrum of gravitational bound states. Furthermore, we
discuss finite corrections to this picture. Our results are of relevance to
various supergravity theories, and also help to clarify the relationship
between gauge and gravity theories.Comment: 33 pages, 5 figure
Vortices and turbulence in trapped atomic condensates
After over a decade of experiments generating and studying the physics of
quantized vortices in atomic gas Bose-Einstein condensates, research is
beginning to focus on the roles of vortices in quantum turbulence, as well as
other measures of quantum turbulence in atomic condensates. Such research
directions have the potential to uncover new insights into quantum turbulence,
vortices and superfluidity, and also explore the similarities and differences
between quantum and classical turbulence in entirely new settings. Here we
present a critical assessment of theoretical and experimental studies in this
emerging field of quantum turbulence in atomic condensates
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