118 research outputs found
Variety of idempotents in nonassociative algebras
In this paper, we study the variety of all nonassociative (NA) algebras from
the idempotent point of view. We are interested, in particular, in the spectral
properties of idempotents when algebra is generic, i.e. idempotents are in
general position. Our main result states that in this case, there exist at
least nontrivial obstructions (syzygies) on the Peirce spectrum of a
generic NA algebra of dimension . We also discuss the exceptionality of the
eigenvalue which appears in the spectrum of idempotents in
many classical examples of NA algebras and characterize its extremal properties
in metrised algebras.Comment: 27 pages, 1 figure, submitte
Output of a pulsed atom laser
We study the output properties of a pulsed atom laser consisting of an
interacting Bose-Einstein condensate (BEC) in a magnetic trap and an additional
rf field transferring atoms to an untrapped Zeeman sublevel. For weak output
coupling we calculate the dynamics of the decaying condensate population, of
its chemical potential and the velocity of the output atoms analytically.Comment: 4 pages, RevTeX. Full ps file available on
http://mpqibmr1.mpq.mpg.de:5000/~man
Disease-associated missense mutations in bestrophin-1 affect cellular trafficking and anion conductance
Bestrophin-1, an integral membrane protein encoded by the BEST1 gene, is localized predominantly to the basolateral membrane of the retinal pigment epithelium. Mutations in the BEST1 gene have been associated with Best vitelliforme macular dystrophy (BMD), a central retinopathy with autosomal dominant inheritance and variable penetrance. Over 120 disease-causing mutations are known, the majority of which result in amino acid substitutions within four mutational hot-spot regions in the highly conserved N-terminal half of the protein. Although initially thought to impair Clâ» channel function, the molecular pathology of BEST1 mutations is still controversial. We have analyzed the subcellular localization of 13 disease-associated BEST1 mutant proteins in polarized MDCK II cells, an established model of apical to basolateral protein sorting. Immunostaining demonstrated that nine of the 13 mutant proteins failed to integrate into the cell membrane. The defective proteins were predominantly retained in the cytoplasm, whereas wild-type bestrophin-1 revealed cell membrane localization. Functional analysis of Iâ» fluxes in HEK-293 cells showed that all mutants exhibited a significant reduction in anion conductance. Our data indicate that defective intracellular trafficking could be a common cause of BMD accompanied by impaired anion conductance, representing a loss of anion channel function that is probably due to mistargeting of mutant protein
Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene
We report results from two-dimensional Raman spectroscopy studies of
large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large
variation in Raman peak position across the sample resulting from inhomogeneity
in the strain of the graphene film, which we show to be correlated with
physical topography by coupling Raman spectroscopy with atomic force
microscopy. We report that essentially strain free graphene is possible even
for epitaxial graphene.Comment: 10 pages, 3 figure
Spatial coherence and density correlations of trapped Bose gases
We study first and second order coherence of trapped dilute Bose gases using
appropriate correlation functions. Special attention is given to the discussion
of second order or density correlations. Except for a small region around the
surface of a Bose-Einstein condensate the correlations can be accurately
described as those of a locally homogeneous gas with a spatially varying
chemical potential. The degrees of first and second order coherence are
therefore functions of temperature, chemical potential, and position. The
second order correlation function is governed both by the tendency of bosonic
atoms to cluster and by a strong repulsion at small distances due to atomic
interactions. In present experiments both effects are of comparable magnitude.
Below the critical temperature the range of the bosonic correlation is affected
by the presence of collective quasi-particle excitations. The results of some
recent experiments on second and third order coherence are discussed. It is
shown that the relation between the measured quantities and the correlation
functions is much weaker than previously assumed.Comment: RevTeX, 25 pages with 7 Postscript figure
Interference of Bose-Einstein condensates in momentum space
We suggest an experiment to investigate the linear superposition of two
spatially separated Bose-Einstein condensates. Due to the coherent combination
of the two wave functions, the dynamic structure factor, measurable through
inelastic photon scattering at high momentum transfer , is predicted to
exhibit interference fringes with frequency period where
is the distance between the condensates. We show that the coherent
configuration corresponds to an eigenstate of the physical observable measured
in the experiment and that the relative phase of the condensates is hence
created through the measurement process.Comment: 4 pages and 2 eps figure
Raman spectra of epitaxial graphene on SiC and of epitaxial graphene transferred to SiO2
Raman spectra were measured for mono-, bi- and trilayer graphene grown on SiC
by solid state graphitization, whereby the number of layers was pre-assigned by
angle-resolved ultraviolet photoemission spectroscopy. It was found that the
only unambiguous fingerprint in Raman spectroscopy to identify the number of
layers for graphene on SiC(0001) is the linewidth of the 2D (or D*) peak. The
Raman spectra of epitaxial graphene show significant differences as compared to
micromechanically cleaved graphene obtained from highly oriented pyrolytic
graphite crystals. The G peak is found to be blue-shifted. The 2D peak does not
exhibit any obvious shoulder structures but it is much broader and almost
resembles a single-peak even for multilayers. Flakes of epitaxial graphene were
transferred from SiC onto SiO2 for further Raman studies. A comparison of the
Raman data obtained for graphene on SiC with data for epitaxial graphene
transferred to SiO2 reveals that the G peak blue-shift is clearly due to the
SiC substrate. The broadened 2D peak however stems from the graphene structure
itself and not from the substrate.Comment: 27 pages, 8 figure
A method for collective excitation of Bose-Einstein condensate
It is shown that by an appropriate modification of the trapping potential one
may create collective excitation in cold atom Bose-Einstein condensate. The
proposed method is complementary to earlier suggestions. It seems to be
feasible experimentally --- it requires only a proper change in time of the
potential in atomic traps, as realized in laboratories already.Comment: 4 pages, 4 figures; major revision, several references added,
interacting particles case adde
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