2,056 research outputs found
Perturbative spectrum of Trapped Weakly Interacting Bosons in Two Dimensions
We study a trapped Bose-Einstein condensate under rotation in the limit of
weak, translational and rotational invariant two-particle interactions. We use
the perturbation-theory approach (the large-N expansion) to calculate the
ground-state energy and the excitation spectrum in the asymptotic limit where
the total number of particles N goes to infinity while keeping the total
angular momentum L finite. Calculating the probabilities of different
configurations of angular momentum in the exact eigenstates gives us a clear
view of the physical content of excitations. We briefly discuss the case of
repulsive contact interaction.Comment: Revtex, 10 pages, 1 table, to appear in Phys. Rev.
Large oxygen-isotope effect in Sr_{0.4}K_{0.6}BiO_{3}: Evidence for phonon-mediated superconductivity
Oxygen-isotope effect has been investigated in a recently discovered
superconductor Sr_{0.4}K_{0.6}BiO_{3}. This compound has a distorted perovskite
structure and becomes superconducting at about 12 K. Upon replacing ^{16}O with
^{18}O by 60-80%, the T_c of the sample is shifted down by 0.32-0.50 K,
corresponding to an isotope exponent of alpha_{O} = 0.40(5). This isotope
exponent is very close to that for a similar bismuthate superconductor
Ba_{1-x}K_{x}BiO_{3} with T_c = 30 K. The very distinctive doping and T_c
dependencies of alpha_{O} observed in bismuthates and cuprates suggest that
bismuthates should belong to conventional phonon-mediated superconductors while
cuprates might be unconventional supercondutors.Comment: 9 pages, 5 figure
Landau-Khalatnikov two-fluid hydrodynamics of a trapped Bose gas
Starting from the quantum kinetic equation for the non-condensate atoms and
the generalized Gross-Pitaevskii equation for the condensate, we derive the
two-fluid hydrodynamic equations of a trapped Bose gas at finite temperatures.
We follow the standard Chapman-Enskog procedure, starting from a solution of
the kinetic equation corresponding to the complete local equilibrium between
the condensate and the non-condensate components. Our hydrodynamic equations
are shown to reduce to a form identical to the well-known Landau-Khalatnikov
two-fluid equations, with hydrodynamic damping due to the deviation from local
equilibrium. The deviation from local equilibrium within the thermal cloud
gives rise to dissipation associated with shear viscosity and thermal
conduction. In addition, we show that effects due to the deviation from the
diffusive local equilibrium between the condensate and the non-condensate
(recently considered by Zaremba, Nikuni and Griffin) can be described by four
frequency-dependent second viscosity transport coefficients. We also derive
explicit formulas for all the transport coefficients. These results are used to
introduce two new characteristic relaxation times associated with hydrodynamic
damping. These relaxation times give the rate at which local equilibrium is
reached and hence determine whether one is in the two-fluid hydrodynamic
region.Comment: 26 pages, 3 postscript figures, submitted to PR
Model of a fluid at small and large length scales and the hydrophobic effect
We present a statistical field theory to describe large length scale effects
induced by solutes in a cold and otherwise placid liquid. The theory divides
space into a cubic grid of cells. The side length of each cell is of the order
of the bulk correlation length of the bulk liquid. Large length scale states of
the cells are specified with an Ising variable. Finer length scale effects are
described with a Gaussian field, with mean and variance affected by both the
large length scale field and by the constraints imposed by solutes. In the
absence of solutes and corresponding constraints, integration over the Gaussian
field yields an effective lattice gas Hamiltonian for the large length scale
field. In the presence of solutes, the integration adds additional terms to
this Hamiltonian. We identify these terms analytically. They can provoke large
length scale effects, such as the formation of interfaces and depletion layers.
We apply our theory to compute the reversible work to form a bubble in liquid
water, as a function of the bubble radius. Comparison with molecular simulation
results for the same function indicates that the theory is reasonably accurate.
Importantly, simulating the large length scale field involves binary arithmetic
only. It thus provides a computationally convenient scheme to incorporate
explicit solvent dynamics and structure in simulation studies of large
molecular assemblies
Synthesis and crystal structure of N-6-[(4-pyridylamino) carbonyl]-pyridine-2-carboxylic acid methyl ester zinc complex
A reaction between monoamide ligand namely N-6-[(4-pyridylamino)carbonyl]-pyridine-2-carboxylic acid methyl ester (L4) and zinc chloride has been attempted in order to generate a carboxylate complex suitable for anion inclusion. This reaction gives rise to a formation of discrete complex with general formula [ZnCl2(L4)2]. Complex [ZnCl2(L4)2] crystallizes in the monoclinic space group, P21/c, with one zinc(II) center, one molecule of ligand L4, one coordinated chloride and one methanol molecule in the asymmetric unit. The extended structure of this molecule shows that the zinc atom is coordinated by four donors: two L4 and two chloride anions. The zinc atom adopts distorted tetrahedral geometry with the angles between the donors in the range 103.62(11)-122.74(8)°. In this study, the amide cavity is bound with methanol through hydrogen-bonding interactions. The methanol molecules is hydrogen bonded to the amide moiety with bond lengths O30-H8···O12 and N17-H17···O30 of 1.988 and 2.078 Å, respectively
Persistent currents in a Bose-Einstein condensate in the presence of disorder
We examine bosonic atoms that are confined in a toroidal,
quasi-one-dimensional trap, subjected to a random potential. The resulting
inhomogeneous atomic density is smoothened for sufficiently strong, repulsive
interatomic interactions. Statistical analysis of our simulations show that the
gas supports persistent currents, which become more fragile due to the
disorder.Comment: 5 pages, RevTex, 3 figures, revised version, to appear in JLT
Studies on the Binding Interactions of Grass Carp (Ctenopharyngodon idella) Myosin with Chlorogenic Acid and Rosmarinic Acid
There are many polyphenols used for the preservation of fish, but the interaction mechanism between polyphenols and fish protein is rarely reported. In the present study, the interactions between two kinds of polyphenols (chlorogenic acid (CGA) and rosmarinic acid (RA)) and the myosin of grass carp (Ctenopharyngodon idella) were explored using multi-spectroscopic techniques. Both CGA and RA were found to be involved in reducing the intrinsic fluorescence and surface hydrophobicity of myosin and increasing the UV absorption intensity. This indicates that interactions between CGA, RA, and myosin ultimately result in the formation of polyphenol-myosin complexes. The binding process of CGA and RA for the formation of the complex was spontaneous. The main binding forces between RA and myosin are hydrogen bonding and van der Waals forces, whereas hydrophobic interactions were observed between CGA and myosin. The results of circular dichroism (CD) showed that the presence of CGA and RA increased the content of myosin alpha-helix. CGA and RA caused myosin aggregation which reduced the corresponding solution dispersibility. CGA and RA protected the myosin sulfhydryl groups and reduced the degree of their oxidation. Furthermore, the complexes formed by the combination of myosin, CGA, and RA exhibited the strongest synergistic antioxidant properties than any one of them. The findings of the present study provide insights into our understanding of the mechanism of interactions between myosin and polyphenols which could provide information on the application of polyphenols in preserving aquatic products
Quantum control and the Strocchi map
Identifying the real and imaginary parts of wave functions with coordinates
and momenta, quantum evolution may be mapped onto a classical Hamiltonian
system. In addition to the symplectic form, quantum mechanics also has a
positive-definite real inner product which provides a geometrical
interpretation of the measurement process. Together they endow the quantum
Hilbert space with the structure of a K\"{a}ller manifold. Quantum control is
discussed in this setting. Quantum time-evolution corresponds to smooth
Hamiltonian dynamics and measurements to jumps in the phase space. This adds
additional power to quantum control, non unitarily controllable systems
becoming controllable by ``measurement plus evolution''. A picture of quantum
evolution as Hamiltonian dynamics in a classical-like phase-space is the
appropriate setting to carry over techniques from classical to quantum control.
This is illustrated by a discussion of optimal control and sliding mode
techniques.Comment: 16 pages Late
Trispectrum from Ghost Inflation
Ghost inflation predicts almost scale-invariant primordial cosmological
perturbations with relatively large non-Gaussianity. The bispectrum is known to
have a large contribution at the wavenumbers forming an equilateral triangle
and the corresponding nonlinear parameter is typically of
order . In this paper we calculate trispectrum from ghost inflation
and show that the corresponding nonlinear parameter is typically of
order . We investigate the shape dependence of the trispectrum and see
that it has some features different from DBI inflation. Therefore, our result
may be useful as a template to distinguish ghost inflation from other models of
inflation by future experiments.Comment: 25 pages, 10 figure
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