15,168 research outputs found
Evaluation of specific heat for superfluid helium between 0 - 2.1 K based on nonlinear theory
The specific heat of liquid helium was calculated theoretically in the Landau
theory. The results deviate from experimental data in the temperature region of
1.3 - 2.1 K. Many theorists subsequently improved the results of the Landau
theory by applying temperature dependence of the elementary excitation energy.
As well known, many-body system has a total energy of Galilean covariant form.
Therefore, the total energy of liquid helium has a nonlinear form for the
number distribution function. The function form can be determined using the
excitation energy at zero temperature and the latent heat per helium atom at
zero temperature. The nonlinear form produces new temperature dependence for
the excitation energy from Bose condensate. We evaluate the specific heat using
iteration method. The calculation results of the second iteration show good
agreement with the experimental data in the temperature region of 0 - 2.1 K,
where we have only used the elementary excitation energy at 1.1 K.Comment: 6 pages, 3 figures, submitted to Journal of Physics: Conference
Serie
XMM-Newton observation of the interacting galaxies NGC1512 and NGC1510
The galaxy NGC1512 is interacting with the smaller galaxy NGC1510 and shows a
peculiar morphology, characterised by two extended arms immersed in an HI disc
whose size is about four times larger than the optical diameter of NGC1512. For
the first time we performed a deep X-ray observation of the galaxies NGC1512
and NGC1510 with XMM-Newton to gain information on the population of X-ray
sources and diffuse emission in a system of interacting galaxies. We identified
and classified the sources detected in the XMM-Newton field of view by means of
spectral analysis, hardness-ratios calculated with a Bayesian method, X-ray
variability, and cross-correlations with catalogues in optical, infrared, and
radio wavelengths. We also made use of archival Swift (X-ray) and Australia
Telescope Compact Array (radio) data to better constrain the nature of the
sources detected with XMM-Newton. We detected 106 sources in the energy range
of 0.2-12 keV, out of which 15 are located within the D_25 regions of NGC1512
and NGC1510 and at least six sources coincide with the extended arms. We
identified and classified six background objects and six foreground stars. We
discussed the nature of a source within the D_25 ellipse of NGC1512, whose
properties indicate a quasi-stellar object or an intermediate ultra-luminous
X-ray source. Taking into account the contribution of low-mass X-ray binaries
and active galactic nuclei, the number of high-mass X-ray binaries detected
within the D_25 region of NGC1512 is consistent with the star formation rate
obtained in previous works based on radio, infrared optical, and UV
wavelengths. We detected diffuse X-ray emission from the interior region of
NGC1512 with a plasma temperature of kT=0.68(0.31-0.87) keV and a 0.3-10 keV
X-ray luminosity of 1.3E38 erg/s, after correcting for unresolved discrete
sources.Comment: Accepted for publication in Astronomy and Astrophysics. 20 pages.
Appendix B will be published electronically onl
Development of a variational SEASAT data analysis technique
Oceans are data-sparse areas in terms of conventional weather observations. The surface pressure field obtained solely by analyzing the conventional weather data is not expected to possess high accuracy. On the other hand, in entering asynoptic data such as satellite-derived temperature soundings into an atmospheric prediction system, an improved surface analysis is crucial for obtaining more accurate weather predictions because the mass distribution of the entire atmosphere will be better represented in the system as a result of the more accurate surface pressure field. In order to obtain improved surface pressure analyses over the oceans, a variational adjustment technique was developed to help blend the densely distributed surface wind data derived from the SEASAT-A radar observations into the sparsely distributed conventional pressure data. A simple marine boundary layer scheme employed in the adjustment technique was discussed. In addition, a few aspects of the current technique were determined by numerical experiments
New Constraints on the Variable Equation of State Parameter from X-Ray Gas Mass Fractions and SNe Ia
Recent measurements are suggesting that we live in a flat Universe and that
its present accelerating stage is driven by a dark energy component whose
equation of state may evolve in time. Assuming two different parameterizations
for the function , we constrain their free parameters from a joint
analysis involving measurements from X-Ray luminosity of galaxy clusters and
SNe type Ia data.Comment: paper, 6 pages, 1 figure Accepted by Int. Journal of Modern Physics D
(IJPMD
Capillary instability in a two-component Bose-Einstein condensate
Capillary instability and the resulting dynamics in an immiscible
two-component Bose-Einstein condensate are investigated using the mean-field
and Bogoliubov analyses. A long, cylindrical condensate surrounded by the other
component is dynamically unstable against breakup into droplets due to the
interfacial tension arising from the quantum pressure and interactions. A
heteronuclear system confined in a cigar-shaped trap is proposed for realizing
this phenomenon experimentally.Comment: 7 pages, 6 figure
No supercritical supercurvature mode conjecture in one-bubble open inflation
In the path integral approach to false vacuum decay with the effect of
gravity, there is an unsolved problem, called the negative mode problem. We
show that the appearance of a supercritical supercurvature mode in the
one-bubble open inflation scenario is equivalent to the existence of a negative
mode around the Euclidean bounce solution. Supercritical supercurvature modes
are those whose mode functions diverge exponentially for large spatial radius
on the time constant hypersurface of the open universe. Then we propose a
conjecture that there should be ``no supercritical supercurvature mode''. For a
class of models that contains a wide variety of tunneling potentials, this
conjecture is shown to be correct.Comment: 11 pages, 3 postscript figures, tarred, gzipped. submitted to Phys.
Rev. D1
Electron Cotunneling in a Semiconductor Quantum Dot
We report transport measurements on a semiconductor quantum dot with a small
number of confined electrons. In the Coulomb blockade regime, conduction is
dominated by cotunneling processes. These can be either elastic or inelastic,
depending on whether they leave the dot in its ground state or drive it into an
excited state, respectively. We are able to discriminate between these two
contributions and show that inelastic events can occur only if the applied bias
exceeds the lowest excitation energy. Implications to energy-level spectroscopy
are discussed.Comment: To be published in Phys. Rev. Let
Magnetic Properties of 2-Dimensional Dipolar Squares: Boundary Geometry Dependence
By means of the molecular dynamics simulation on gradual cooling processes,
we investigate magnetic properties of classical spin systems only with the
magnetic dipole-dipole interaction, which we call dipolar systems. Focusing on
their finite-size effect, particularly their boundary geometry dependence, we
study two finite dipolar squares cut out from a square lattice with
and , where is an angle between the direction of the lattice axis
and that of the square boundary. Distinctly different results are obtained in
the two dipolar squares. In the square, the ``from-edge-to-interior
freezing'' of spins is observed. Its ground state has a multi-domain structure
whose domains consist of the two among infinitely (continuously) degenerated
Luttinger-Tisza (LT) ground-state orders on a bulk square lattice, i.e., the
two antiferromagnetically aligned ferromagnetic chains (af-FMC) orders directed
in parallel to the two lattice axes. In the square, on the other
hand, the freezing starts from the interior of the square, and its ground state
is nearly in a single domain with one of the two af-FMC orders. These geometry
effects are argued to originate from the anisotropic nature of the
dipole-dipole interaction which depends on the relative direction of sites in a
real space of the interacting spins.Comment: 21 pages, 13 figures, submitted to Journal of Physical Society Japa
Competition between Pauli and orbital effects in a charge-density wave system
We present angular dependent magneto-transport and magnetization measurements
on alpha-(ET)2MHg(SCN)4 compounds at high magnetic fields and low temperatures.
We find that the low temperature ground state undergoes two subsequent
field-induced density-wave type phase transitions above a critical angle of the
magnetic field with respect to the crystallographic axes. This new phase
diagram may be qualitatively described assuming a charge density wave ground
state which undergoes field-induced transitions due to the interplay of Pauli
and orbital effects.Comment: 11 pages, 4 figures, shown at the APS march meeting 2000, appears in
the Ph.D. thesis of J. S. Qualls (Florida State University, 1999), and
submitted to PR
Quark Number Fluctuations in a Chiral Model at Finite Baryon Chemical Potential
We discuss the net quark and isovector fluctuations as well as off-diagonal
quark flavor susceptibilities along the chiral phase transition line in the
Nambu--Jona-Lasinio (NJL) model. The model is formulated at non-zero quark and
isospin chemical potentials with non-vanishing vector couplings in the
iso-scalar and iso-vector channels. We study the influence of the quark
chemical potential on the quark flavour susceptibilities in detail and the
dependence of the results on model parameters as well as on the quark mass. The
NJL model findings are compared with recent lattice results obtained in
two--flavor QCD at finite chemical potential. On a qualitative level, the NJL
model provides a consistent description of the dependence of quark number
fluctuations on temperature and baryon chemical potential. The phase diagram
and the position of the tricritical point in the NJL model are also discussed
for different parameter sets.Comment: 33 pages, 11 figures; final version accepted for publication in Phys.
Rev.
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