4,316 research outputs found
Double Phase Transitions in Magnetized Spinor Bose-Einstein Condensation
It is investigated theoretically that magnetized Bose-Einstein condensation
(BEC) with the internal (spin) degrees of freedom exhibits a rich variety of
phase transitions, depending on the sign of the interaction in the spin
channel. In the antiferromagnetic interaction case there exist always double
BEC transitions from single component BEC to multiple component BEC. In the
ferromagnetic case BEC becomes always unstable at a lower temperature, leading
to a phase separation. The detailed phase diagram for the temperature vs the
polarization, the spatial spin structure, the distribution of non-condensates
and the excitation spectrum are examined for the harmonically trapped systems.Comment: 6 pages, 7 figures. Submitted to J. Phys. Soc. Jp
Mean field ground state of a spin-1 condensate in a magnetic field
We revisit the topic of the mean field ground state of a spin-1 atomic
condensate inside a uniform magnetic field () under the constraints that
both the total number of atoms () and the magnetization () are
conserved. In the presence of an internal state (spin component) independent
trap, we also investigate the dependence of the so-called single spatial mode
approximation (SMA) on the magnitude of the magnetic field and . Our
result indicate that the quadratic Zeeman effect is an important factor in
balancing the mean field energy from elastic atom-atom collisions that are
known to conserve both and .Comment: 13 pages, 9 figures, to be published in New J. Phys.
(http://www.njp.org/
Local Spin-Gauge Symmetry of the Bose-Einstein Condensates in Atomic Gases
The Bose-Einstein condensates of alkali atomic gases are spinor fields with
local ``spin-gauge" symmetry. This symmetry is manifested by a superfluid
velocity (or gauge field) generated by the Berry phase of the
spin field. In ``static" traps, splits the degeneracy of the
harmonic energy levels, breaks the inversion symmetry of the vortex nucleation
frequency , and can lead to {\em vortex ground states}. The
inversion symmetry of , however, is not broken in ``dynamic"
traps. Rotations of the atom cloud can be generated by adiabatic effects
without physically rotating the entire trap.Comment: Typos in the previous version corrected, thanks to the careful
reading of Daniel L. Cox. 13 pages + 2 Figures in uuencode + gzip for
First and Second Sound Modes of a Bose-Einstein Condensate in a Harmonic Trap
We have calculated the first and second sound modes of a dilute interacting
Bose gas in a spherical trap for temperatures () and for
systems with to particles. The second sound modes (which exist
only below ) generally have a stronger temperature dependence than the
first sound modes. The puzzling temperature variations of the sound modes near
recently observed at JILA in systems with particles match
surprisingly well with those of the first and second sound modes of much larger
systems.Comment: a shorten version, more discussions are given on the nature of the
second sound. A long footnote on the recent work of Zaremba, Griffin, and
Nikuni (cond-mat/9705134) is added, the spectrum of the (\ell=1, n_2=0) mode
is included in fig.
An intelligent assistant for exploratory data analysis
In this paper we present an account of the main features of SNOUT, an intelligent assistant for exploratory data analysis (EDA) of social science survey data that incorporates a range of data mining techniques. EDA has much in common with existing data mining techniques: its main objective is to help an investigator reach an understanding of the important relationships ina data set rather than simply develop predictive models for selectd variables. Brief descriptions of a number of novel techniques developed for use in SNOUT are presented. These include heuristic variable level inference and classification, automatic category formation, the use of similarity trees to identify groups of related variables, interactive decision tree construction and model selection using a genetic algorithm
Instabilities in a Two-Component, Species Conserving Condensate
We consider a system of two species of bosons of equal mass, with
interactions and for bosons of the same and different
species respectively. We present a rigorous proof -- valid when the Hamiltonian
does not include a species switching term -- showing that, when
, the ground state is fully "polarized" (consists of
atoms of one kind only). In the unpolarized phase the low energy excitation
spectrum corresponds to two linearly dispersing modes that are even a nd odd
under species exchange. The polarization instability is signaled by the vani
shing of the velocity of the odd modes.Comment: To appear in Phys. Rev.
Zero-temperature phase diagram of binary boson-fermion mixtures
We calculate the phase diagram for dilute mixtures of bosons and fermions at
zero temperature. The linear stability conditions are derived and related to
the effective boson-induced interaction between the fermions. We show that in
equilibrium there are three possibilities: a) a single uniform phase, b) a
purely fermionic phase coexisting with a purely bosonic one and c) a purely
fermionic phase coexisting with a mixed phase.Comment: 8 pages, revtex, 3 postscript figures; NORDITA-1999/71 C
Spin domain formation in spinor Bose-Einstein condensation
The spatial structure of the spinor Bose-Einstein condensates with the spin
degrees of freedom is analyzed based on the generalized Gross-Pitaevskii
equation (GP) in the light of the present spin domain experiment on m_F=\pm 1,
and 0 of the hyperfine state F=1 of ^{23}Na atom gases. The GP solutions in
three- and one-spatial dimensional cases reproduce the observed spin domain
structures, revealing the length scale associated with the existence of the
weak interaction of the spin-spin channel, other than the ordinary coherence
length related to the density-density channel. The obtained domain structure in
GP is compared with the result in Thomas-Fermi approximation. The former
solution is found to better describe the observed features than the latter.Comment: 9 pages, 14 figure
Functional impairment of human resident cardiac stem cells by the cardiotoxic antineoplastic agent trastuzumab
Trastuzumab (TZM), a monoclonal antibody against the ERBB2 protein, increases survival in ERBB2-positive breast cancer patients. Its clinical use, however, is limited by cardiotoxicity. We sought to evaluate whether TZM cardiotoxicity involves inhibition of human adult cardiac-derived stem cells, in addition to previously reported direct adverse effects on cardiomyocytes. To test this idea, we exposed human cardiosphere-derived cells (hCDCs), a natural mixture of cardiac stem cells and supporting cells that has been shown to exert potent regenerative effects, to TZM and tested the effects in vitro and in vivo. We found that ERBB2 mRNA and protein are expressed in hCDCs at levels comparable to those in human myocardium. Although clinically relevant concentrations of TZM had no effect on proliferation, apoptosis, or size of the c-kit-positive hCDC subpopulation, in vitro assays demonstrated diminished potential for cardiogenic differentiation and impaired ability to form microvascular networks in TZM-treated cells. The functional benefit of hCDCs injected into the border zone of acutely infarcted mouse hearts was abrogated by TZM: infarcted animals treated with TZM + hCDCs had a lower ejection fraction, thinner infarct scar, and reduced capillary density in the infarct border zone compared with animals that received hCDCs alone (n = 12 per group). Collectively, these results indicate that TZM inhibits the cardiomyogenic and angiogenic capacities of hCDCs in vitro and abrogates the morphological and functional benefits of hCDC transplantation in vivo. Thus, TZM impairs the function of human resident cardiac stem cells, potentially contributing to TZM cardiotoxicity
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