58,580 research outputs found
Quantum phase transition and engineering in two-component BEC in optical lattices
In this paper we review recent progress in studying quantum phase transitions
in one- and two-component Bose-Einstein condensates (BEC) in optical lattices.
These phase transitions involve the emergence and disappearance of quantum
coherence over whole optical lattice and of linear superposition of macroscopic
quantum states. The latter may provide new means to engineer and to manipulate
novel macroscopic quantum states and novel coherent atomic beams for quantum
information processing, quantum computing etc.Comment: Format: LaTex2e. 7 pages, no figure. Talk at the Yang Symposium (in
honor of C.N. Yang's 80th birthday), Beijing, China, June 2002. To appear in
the Proceeding
Surface-wave solitons on the interface between a linear medium and a nonlocal nonlinear medium
We address the properties of surface-wave solitons on the interface between a
semi-infinite homogeneous linear medium and a semi-infinite homogeneous
nonlinear nonlocal medium. The stability, energy flow and FWHM of the surface
wave solitons can be affected by the degree of nonlocality of the nonlinear
medium. We find that the refractive index difference affects the power
distribution of the surface solitons in two media. We show that the different
boundary values at the interface can lead to the different peak position of the
surface solitons, but it can not influence the solitons stability with a
certain degree of nonlocality.Comment: 8 pages, 14 figures, 15 references, and so o
Properties of Mg-doped Nd-Ba-Cu-O generic seed crystals for the top seeded melt growth of (RE)-Ba-Cu-O bulk superconductors
We have recently developed a new generic seed crystal that has been used successfully to fabricate any oriented, single grain (RE)-Ba-Cu-O bulk superconductor by a cold seeding technique. In this paper we report the chemical, structural and microstructural properties of these seed crystals, including the variation of melting point, crystallographic parameters and volume fraction of Mg-rich inclusions in the Nd1 + xBa 2-x(Cu1-yMgy)3Oz matrix as a function of externally added MgO content. The influence of Mg-doping on the superconducting transition temperatures of YBCO grains fabricated using these seeds is investigated. Finally, an optimum MgO content of the generic seed that effectively controls the orientation of the seeded grain without compromising its superconducting properties is suggested from the many seed crystals fabricated with a wide range of Mg-rich addition
Effect of charged impurities on graphene thermoelectric power near the Dirac point
In graphene devices with a varying degree of disorders as characterized by
their carrier mobility and minimum conductivity, we have studied the
thermoelectric power along with the electrical conductivity over a wide range
of temperatures. We have found that the Mott relation fails in the vicinity of
the Dirac point in high-mobility graphene. By properly taking account of the
high temperature effects, we have obtained good agreement between the Boltzmann
transport theory and our experimental data. In low-mobility graphene where the
charged impurities induce relatively high residual carrier density, the Mott
relation holds at all gate voltages
Extended Schmidt law holds for faint dwarf irregular galaxies
The extended Schmidt law (ESL) is a variant of the Schmidt law which relates
the surface densities of gas and star formation, with the surface density of
stellar mass added as an extra parameter. We empirically investigate for the
first time whether low metallicity faint dwarf irregular galaxies (dIrrs)
follow the ESL. Here we consider the `global' law where surface densities are
averaged over the galactic discs. dIrrs are unique not only because they are at
the lowest end of mass and star formation scales for galaxies, but also because
they are metal-poor compared to the general population of galaxies. Our sample
is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) which is the
largest survey of atomic hydrogen in such galaxies. The gas surface densities
are determined using their atomic hydrogen content. The star formation rates
are calculated using GALEX far ultraviolet fluxes after correcting for dust
extinction, whereas the stellar surface densities are calculated using Spitzer
3.6 m fluxes. All surface densities are calculated over stellar discs
defined by the 3.6 m images. We find dIrrs indeed follow the extended
Schmidt law. The mean deviation of the FIGGS galaxies from the relation is 0.01
dex, with a scatter around the relation of less than half that seen in the
original relation. In comparison, we also show that the FIGGS galaxies are much
more deviant when compared to the `canonical' Kennicutt-Schmidt relation. Our
results help strengthen the universality of the extended Schmidt law,
especially for galaxies with low metallicities. We suggest that models of star
formation in which feedback from previous generations of stars set the pressure
in the ISM, are promising candidates for explaining the ESL. We also confirm
that ESL is an independent relation and not a form of a relation between star
formation efficiency and metallicity.Comment: Accepted for publication in Astronomy & Astrophysics. Figure 2 on
Page 5 shows the main resul
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