1,425 research outputs found
Aspect ratio analysis for ground states of bosons in anisotropic traps
Characteristics of the initial condensate in the recent experiment on
Bose-Einstein condensation (BEC) of Rb atoms in an anisotropic
magnetic trap is discussed. Given the aspect ratio , the quality of BEC is
estimated. A simple analytical Ansatz for the initial condensate wave function
is proposed as a function of the aspect ratio which, in contrast to the
Baym-Pethick trial wave function, reproduces both the weak and the strong
intaraction limits and which is in better agreement with numerical results than
the latter.Comment: 12 pages, latex, 3 figures added, minor corrections; to appear in J.
Res. Nat. Inst. of Standards and Technolog
Viscosity in the excluded volume hadron gas model
The shear viscosity in the van der Waals excluded volume
hadron-resonance gas model is considered. For the shear viscosity the result of
the non-relativistic gas of hard-core particles is extended to the mixture of
particles with different masses, but equal values of hard-core radius r. The
relativistic corrections to hadron average momenta in thermal equilibrium are
also taken into account. The ratio of the viscosity to the entropy
density s is studied. It monotonously decreases along the chemical freeze-out
line in nucleus-nucleus collisions with increasing collision energy. As a
function of hard-core radius r, a broad minimum of the ratio near fm is found at high collision energies. For the
charge-neutral system at MeV, a minimum of the ratio is reached for fm. To justify a hydrodynamic approach to
nucleus-nucleus collisions within the hadron phase the restriction from below,
fm, on the hard-core hadron radius should be fulfilled in the
excluded volume hadron-resonance gas.Comment: 12 pages, 3 figure
Non-perturbative results for the spectrum of surface-disordered waveguides
We calculated the spectrum of normal scalar waves in a planar waveguide with
absolutely soft randomly rough boundaries beyond the perturbation theories in
the roughness heights and slopes, basing on the exact boundary scattering
potential. The spectrum is proved to be a nearly real non-analytic function of
the dispersion of the roughness heights (with square-root
singularity) as . The opposite case of large boundary defects is
summarized.Comment: REVTEX 3, OSA style, 9 pages, no figures. Submitted to Optics Letter
A simple formula for the L-gap width of a face-centered-cubic photonic crystal
The width of the first Bragg's scattering peak in the (111)
direction of a face-centered-cubic lattice of air spheres can be well
approximated by a simple formula which only involves the volume averaged
and over the lattice unit cell, being the
(position dependent) dielectric constant of the medium, and the effective
dielectric constant in the long-wavelength limit approximated
by Maxwell-Garnett's formula. Apparently, our formula describes the asymptotic
behaviour of the absolute gap width for high dielectric contrast
exactly. The standard deviation steadily decreases well below
1% as increases. For example for the sphere filling
fraction and . On the interval , our
formula still approximates the absolute gap width (the relative
gap width ) with a reasonable precision, namely with a standard
deviation 3% (4.2%) for low filling fractions up to 6.5% (8%) for the
close-packed case. Differences between the case of air spheres in a dielectric
and dielectric spheres in air are briefly discussed.Comment: 13 pages, 4 figs., RevTex, two references added. For more info see
http://www.amolf.nl/external/wwwlab/atoms/theory/index.htm
Photonic crystals of coated metallic spheres
It is shown that simple face-centered-cubic (fcc) structures of both metallic
and coated metallic spheres are ideal candidates to achieve a tunable complete
photonic bandgap (CPBG) for optical wavelengths using currently available
experimental techniques. For coated microspheres with the coating width to
plasma wavelength ratio and the coating and host
refractive indices and , respectively, between 1 and 1.47, one can
always find a sphere radius such that the relative gap width (gap
width to the midgap frequency ratio) is larger than 5% and, in some cases,
can exceed 9%. Using different coatings and supporting liquids, the width
and midgap frequency of a CPBG can be tuned considerably.Comment: 14 pages, plain latex, 3 ps figures, to appear in Europhys. Lett. For
more info on this subject see
http://www.amolf.nl/research/photonic_materials_theory/moroz/moroz.htm
Photonic Band Gaps of Three-Dimensional Face-Centered Cubic Lattices
We show that the photonic analogue of the Korringa-Kohn-Rostocker method is a
viable alternative to the plane-wave method to analyze the spectrum of
electromagnetic waves in a three-dimensional periodic dielectric lattice.
Firstly, in the case of an fcc lattice of homogeneous dielectric spheres, we
reproduce the main features of the spectrum obtained by the plane wave method,
namely that for a sufficiently high dielectric contrast a full gap opens in the
spectrum between the eights and ninth bands if the dielectric constant
of spheres is lower than the dielectric constant of
the background medium. If , no gap is found in the
spectrum. The maximal value of the relative band-gap width approaches 14% in
the close-packed case and decreases monotonically as the filling fraction
decreases. The lowest dielectric contrast for which a
full gap opens in the spectrum is determined to be 8.13. Eventually, in the
case of an fcc lattice of coated spheres, we demonstrate that a suitable
coating can enhance gap widths by as much as 50%.Comment: 19 pages, 6 figs., plain latex - a section on coated spheres, two
figures, and a few references adde
Spectrophotometric experiment on the Verera-11 and Venera-12 descent vehicles: Some results of the analysis of the spectrum of the daytime sky of Venus
The spectra of the daytime sky of Venus were recorded on the Venera-11 and Venera-12 descent vehicles at various altitudes above the planet's surface, within the interval of 4500 to 12,000 Angstroms. The angular distribution of the brightness of the scattered radiation was recorded and the ratio of water and carbon dioxide were studied, with respect to the cloud cover boundaries
SOCIO-ECONOMIC PRECONDITIONS FOR THE DEVELOPMENT OF CIVIL SOCIETY OF UKRAINE
The article analyzes the socio-economic preconditions for the formation of civil society in Ukraine. The events of the history of independent Ukraine are highlighted, which greatly influenced the formation of its institutes of the period of independence. It is substantiated, how exactly legal support has affected the process of institutionalization of civil society. Determined how the state through privatization and privatization, as well as the creation of conditions for a socially oriented market economy, contributed to the formation of a private property institution. The significance of the "Orange Revolution" for the socio-economic development of Ukraine is determined.Key words: civil society, state, democracy, private property, market economy, law, reforms.Мороз Н. О. Соціально-економічні передумови становлення громадянського суспільства України/ Національний технічний університет «Дніпровська політехніка», Україна, м. ДніпроВ статті проаналізовані соціально-економічні передумови становлення громадянського суспільства в Україні. Висвітлюються події історії незалежної України, які значною мірою вплинули на формування його інститутів періоду незалежності. Обґрунтовано, як саме правове забезпечення позначилось на процесі інституалізації громадянського суспільства. Визначено, як держава шляхом роздержавлення та приватизації, а також створенням умов для соціально орієнтованої ринкової економіки сприяли формуванню інституту приватної власності. З’ясовано значення «Помаранчевої революції» для соціально-економічного розвитку України. Ключові слова: громадянське суспільство, держава, демократія, приватна власність, ринкова економіка, закон, реформи
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