648 research outputs found
Direct observation of the phonon energy in a Bose-Einstein condensate by tomographic imaging
The momentum and energy of phonons in a Bose-Einstein condensate are measured
directly from a time-of-flight image by computerized tomography. We find that
the same atoms that carry the momentum of the excitation also carry the
excitation energy. The measured energy is in agreement with the Bogoliubov
spectrum. Hydrodynamic simulations are performed which confirm our observation.Comment: Letter, 5 figure
Observations on the distribution of chlorinated hydrocarbons in Atlantic Ocean organisms
Industrial polychlorobiphenyls (PCBs) and the DDT family (t-DDT) were measured in several species of organisms collected from the open Atlantic Ocean between 66°N and 35°S latitude. All the organisms had higher concentrations of PCBs than t-DDT. Many trophic levels were represented in the collections, but the analytical data offer no support for food chain magnification among gilled organisms...
Inhibition of Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa biofilm formation with a class of TAGE-triazole conjugates
This is the published version. Copyright Royal Society of ChemistryA chemically diverse library of TAGE-triazole conjugates was synthesized utilizing click chemistry on the TAGE scaffold. This library of small molecules was screened for anti-biofilm activity and found to possess the ability of inhibiting biofilm formation against Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa. One such compound in this library demonstrated the most potent inhibitory effect against Staphylococcus aureus biofilm formation that has been displayed by any 2-aminoimidazole derivative
Synthesis, Crystallographic Characterization and Reactivity of a Phosphinine-B(C6F5)3 Lewis Pair
A phosphinine-borane adduct of a Me3Si-functionalized phosphinine and the Lewis acid B(C6F5)3 has been synthesized and characterized crystallographically for the first time. The reaction strongly depends on the nature of the substituents in the α-position of the phosphorus heterocycle. In contrast, the reaction of B2H6 with various substituted phosphinines leads to an equilibrium between the starting materials and the phosphinine–borane adducts that is determined by the Lewis basicity of the phosphinine. The novel phosphinine borane adduct (6-B(C6F5)3) shows rapid and facile insertion and [4+2] cycloaddition reactivity towards phenylacetylene. A hitherto unknown dihydro-1-phosphabarrelene is formed with styrene. The reaction with an ester provides a new, facile and selective route to 1-R-phosphininium salts. These salts then undergo a [4+2] cycloaddition in the presence of Me3Si−C≡CH and styrene to cleanly form unprecedented derivatives of 1-R-phosphabarrelenium salts
Black hole lasers in Bose-Einstein condensates
We consider elongated condensates that cross twice the speed of sound. In the
absence of periodic boundary conditions, the phonon spectrum possesses a
discrete and finite set of complex frequency modes that induce a laser effect.
This effect constitutes a dynamical instability and is due to the fact that the
supersonic region acts as a resonant cavity. We numerically compute the complex
frequencies and density-density correlation function. We obtain patterns with
very specific signatures. In terms of the gravitational analogy, the flows we
consider correspond to a pair of black hole and white hole horizons, and the
laser effect can be conceived as a self-amplified Hawking radiation. This is
verified by comparing the outgoing flux at early time with the standard black
hole radiation.Comment: iopams, 37 pages, 14 figures, 1 table; for associated gif animations,
see http://people.sissa.it/~finazzi/bec_bhlasers/movies/ or
http://iopscience.iop.org/1367-2630/12/9/095015/media. Published on New. J.
Phys. (http://iopscience.iop.org/1367-2630/12/9/095015/). V2: few new
comments, modified figure
Dynamics of fluctuations in an optical analog of the Laval nozzle
Using the analogy between the description of coherent light propagation in a
medium with Kerr nonlinearity by means of nonlinear Schr\"odinger equation and
that of a dissipationless liquid we propose an optical analogue of the Laval
nozzle. The optical Laval nozzle will allow one to form a transonic flow in
which one can observe and study a very unusual dynamics of classical and
quantum fluctuations including analogue of the Hawking radiation of real black
holes. Theoretical analysis of this dynamics is supported by numerical
calculations and estimates for a possible experimental setup are presented.Comment: 7 pages, 4 figure
Outbursts on normal stars. FH Leo misclassified as a novalike variable
We present high resolution spectroscopy of the common proper motion system FH
Leo (components HD 96273 and BD+07 2411B), which has been classified as a
novalike variable due to an outburst observed by Hipparcos, and we present and
review the available photometry. We show from our spectra that neither star can
possibly be a cataclysmic variable, instead they are perfectly normal late-F
and early-G stars. We measured their radial velocities and derived the
atmospheric fundamental parameters, abundances of several elements including
Fe, Ni, Cr, Co, V, Sc, Ti, Ca and Mg, and we derive the age of the system. From
our analysis we conclude that the stars do indeed constitute a physical binary.
However, the observed outburst cannot be readily explained. We examine several
explanations, including pollution with scattered light from Jupiter, binarity,
microlensing, background supernovae, interaction with unseen companions and
planetary engulfment. While no explanation is fully satisfactory, the scattered
light and star-planet interaction scenarios emerge as the least unlikely ones,
and we give suggestions for further study.Comment: 8 pages, 7 figures. Accepted for publication in A&
The excitation spectrum for weakly interacting bosons in a trap
We investigate the low-energy excitation spectrum of a Bose gas confined in a
trap, with weak long-range repulsive interactions. In particular, we prove that
the spectrum can be described in terms of the eigenvalues of an effective
one-particle operator, as predicted by the Bogoliubov approximation.Comment: LaTeX, 32 page
Quantum critical states and phase transitions in the presence of non equilibrium noise
Quantum critical points are characterized by scale invariant correlations and
correspondingly long ranged entanglement. As such, they present fascinating
examples of quantum states of matter, the study of which has been an important
theme in modern physics. Nevertheless very little is known about the fate of
quantum criticality under non equilibrium conditions. In this paper we
investigate the effect of external noise sources on quantum critical points. It
is natural to expect that noise will have a similar effect to finite
temperature, destroying the subtle correlations underlying the quantum critical
behavior. Surprisingly we find that in many interesting situations the
ubiquitous 1/f noise preserves the critical correlations. The emergent states
show intriguing interplay of intrinsic quantum critical and external noise
driven fluctuations. We demonstrate this general phenomenon with specific
examples in solid state and ultracold atomic systems. Moreover our approach
shows that genuine quantum phase transitions can exist even under non
equilibrium conditions.Comment: 9 pages, 2 figure
Reconstruction of a function from its spherical (circular) means with the centers lying on the surface of certain polygons and polyhedra
We present explicit filtration/backprojection-type formulae for the inversion
of the spherical (circular) mean transform with the centers lying on the
boundary of some polyhedra (or polygons, in 2D). The formulae are derived using
the double layer potentials for the wave equation, for the domains with certain
symmetries. The formulae are valid for a rectangle and certain triangles in 2D,
and for a cuboid, certain right prisms and a certain pyramid in 3D. All the
present inversion formulae yield exact reconstruction within the domain
surrounded by the acquisition surface even in the presence of exterior sources.Comment: 9 figure
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