347,910 research outputs found
The finite-temperature thermodynamics of a trapped unitary Fermi gas within fractional exclusion statistics
We utilize a fractional exclusion statistics of Haldane and Wu hypothesis to
study the thermodynamics of a unitary Fermi gas trapped in a harmonic
oscillator potential at ultra-low finite temperature. The entropy per particle
as a function of the energy per particle and energy per particle versus
rescaled temperature are numerically compared with the experimental data. The
study shows that, except the chemical potential behavior, there exists a
reasonable consistency between the experimental measurement and theoretical
attempt for the entropy and energy per particle. In the fractional exclusion
statistics formalism, the behavior of the isochore heat capacity for a trapped
unitary Fermi gas is also analyzed.Comment: 6 pages, 6 figure
Finite size effects in metallic superlattice systems
Clean metallic superlattice systems composed of alternating layers of
superconducting and normal materials are considered, particularly aspects of
the proximity effect as it affects the critical temperature. A simple model is
used to address the question of when a finite--sized system theoretically
approximates well a true infinite superlattice. The methods used in the
analysis afford some tests of the approximation used that the pair amplitude of
the Cooper pairs is constant over a superconducting region. We also use these
methods to construct a model of a single superconducting layer which intends to
incorporate a more realistic form of the pair amplitude than a simple constant.Comment: 16 ReVTeX pages + 12 PostScript figures encoded with uufile
Ageing and Temperature Influence on Polarization/Depolarization Current Behaviour of Paper Immersed in Natural Ester
Transformers play an important role in providing a reliable and efficient electricity supply and are one of the most critical equipments in electric power transmission and distribution systems. The most commonly used liquid in power transformers is mineral oil due to its low price and good properties. However the performance of mineral oil starts to be limited due to environmental consideration [1]. Natural ester insulating fluid offers fire safety, environment and insulation aging advantages over mineral oil and are found to be suitable for the use in transformer insulation system [1]. However, transformer owners require to assess the status of the cellulose insulation in transformer non-destructively. Polarization/depolarization Current (PDC) measurement [2] is one of the non-destructive techniques which have been used to achieve this aim. At the present, there are few publications about the PDC behaviour of natural ester-paper insulation, though the natural ester becomes more widely used in transformers. In this paper, the influence of ageing and temperature on the PDC behaviour of the paper immersed in natural ester and mineral oil were compared. Results show PDC technique can be used to assess the aging condition of the natural-ester paper insulation. The ageing and temperature have similar influence on the PDC behaviour of the paper immersed in natural ester and in mineral oil. The depolarization current of paper immersed in natural ester is lower than that immersed in mineral oil at the same test temperature. The depolarization current of the paper immersed in natural ester and mineral oil increase with the aging time increased. Therefore, the depolarization current can be used to indicate the aging status of natural ester-paper insulation
Ab Initio Simulation of the Nodal Surfaces of Heisenberg Antiferromagnets
The spin-half Heisenberg antiferromagnet (HAF) on the square and triangular
lattices is studied using the coupled cluster method (CCM) technique of quantum
many-body theory. The phase relations between different expansion coefficients
of the ground-state wave function in an Ising basis for the square lattice HAF
is exactly known via the Marshall-Peierls sign rule, although no equivalent
sign rule has yet been obtained for the triangular lattice HAF. Here the CCM is
used to give accurate estimates for the Ising-expansion coefficients for these
systems, and CCM results are noted to be fully consistent with the
Marshall-Peierls sign rule for the square lattice case. For the triangular
lattice HAF, a heuristic rule is presented which fits our CCM results for the
Ising-expansion coefficients of states which correspond to two-body excitations
with respect to the reference state. It is also seen that Ising-expansion
coefficients which describe localised, -body excitations with respect to the
reference state are found to be highly converged, and from this result we infer
that the nodal surface of the triangular lattice HAF is being accurately
modeled. Using these results, we are able to make suggestions regarding
possible extensions of existing quantum Monte Carlo simulations for the
triangular lattice HAF.Comment: 24 pages, Latex, 3 postscript figure
Waveguide cooling system
An improved system is described for cooling high power waveguides by the use of cooling ducts extending along the waveguide, which minimizes hot spots at the flanges where waveguide sections are connected together. The cooling duct extends along substantially the full length of the waveguide section, and each flange at the end of the section has a through hole with an inner end connected to the duct and an opposite end that can be aligned with a flange hole in another waveguide section. Earth flange is formed with a drainage groove in its face, between the through hole and the waveguide conduit to prevent leakage of cooling fluid into the waveguide. The ducts have narrowed sections immediately adjacent to the flanges to provide room for the installation of fasteners closely around the waveguide channel
Frontiers of parasitology research in the People's Republic of China : infection, diagnosis, protection and surveillance
ABSTRACT: Control and eventual elimination of human parasitic diseases in the People's Republic of China (P.R. China) requires novel approaches, particularly in the areas of diagnostics, mathematical modelling, monitoring, evaluation, surveillance and public health response. A comprehensive effort, involving the collaboration of 188 scientists (<85% from P.R. China) from 48 different institutions and universities (80% from P.R. China), covers this collection of 29 articles published in Parasites & Vectors. The research mainly stems from a research project entitled 'Surveillance and diagnostic tools for major parasitic diseases in P.R. China' (grant no. 2008ZX10004-011) and highlights the frontiers of research in parasitology. The majority of articles in this thematic series deals with the most important parasitic diseases in P.R. China, emphasizing Schistosoma japonicum, Plasmodium vivax and Clonorchis sinensis plus some parasites of emerging importance such as Angiostrongylus cantonensis. Significant achievements have been made through the collaborative research programme in the following three fields: (i) development of control strategies for the national control programme; (ii) updating the surveillance data of parasitic infections both in human and animals; and (iii) improvement of existing, and development of novel, diagnostic tools to detect parasitic infections. The progress is considerable and warrants broad validation efforts. Combined with the development of improved tools for diagnosis and surveillance, integrated and multi-pronged control strategies now pave the way for elimination of parasitic diseases in P.R. China. Experiences and lessons learned can stimulate control and elimination efforts of parasitic diseases in other parts of the world
Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions
Nuclei colliding at very high energy create a strong, quasi-classical gluon
field during the initial phase of their interaction. We present an analytic
calculation of the initial space-time evolution of this field in the limit of
very high energies using a formal recursive solution of the Yang-Mills
equations. We provide analytic expressions for the initial chromo-electric and
chromo-magnetic fields and for their energy-momentum tensor. In particular, we
discuss event-averaged results for energy density and energy flow as well as
for longitudinal and transverse pressure of this system. For example, we find
that the ratio of longitudinal to transverse pressure very early in the system
behaves as where
is the longitudinal proper time, is related to the saturation scales
of the two nuclei, and with a scale to
be defined later. Our results are generally applicable if .
As already discussed in a previous paper, the transverse energy flow of
the gluon field exhibits hydrodynamic-like contributions that follow transverse
gradients of the energy density . In addition, a
rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law
and generates non-vanishing angular momentum of the field. We will discuss the
space-time picture that emerges from our analysis and its implications for
observables in heavy ion collisions.Comment: 26 pages, 9 figure
Mass segregation in very young open clusters -- A case study of NGC 2244 and NGC 6530
We derive the proper motions, membership probabilities, and velocity
dispersions of stars in the regions of the young (about 2-4 Myr-old) open
clusters NGC 2244 (the central cluster in the Monoceros R2 association) and NGC
6530 (the dominant cluster in the Sgr OB1 association) from photographic plate
material obtained at Shanghai Astronomical Observatory, with time baselines of
34 and 87 years, respectively. Both clusters show clear evidence of mass
segregation, but they do not exhibit any significant velocity-mass (or,
equivalently, a velocity-luminosity) dependence. This provides strong support
for the suggestion that the observed mass segregation is -- at least partially
-- due to the way in which star formation has proceeded in these complex
star-forming regions (``primordial'' mass segregation). Based on arguments
related to the clusters' published initial mass functions, in conjunction with
our new measurements of their internal velocity dispersions (35 and 8 km/s for
NGC 2244 and NGC 6530, respectively), we provide strong arguments in favor of
the dissolution of NGC 2244 on very short time-scales, while we speculate that
NGC 6530 may be more stable against the effects of internal two-body
relaxation. However, this latter object may well be destroyed by the strong
tidal field prevalent at its location in the Galactic plane in the direction of
the Galactic Center.Comment: 36 pages, 10 figures, accepted to A
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