4,708 research outputs found
On Pair-Particle Distribution in Imperfect Bose Gas
A simple model of estimating the radial distribution function of an imperfect
Bose gas in the ground state is presented. The model is based on
integro-differential equations derived by considering the space boson
distribution in an external field. With the approach proposed, the particular
case of dilute Bose gas is investigated within the hard sphere approximation
and beyond.Comment: 8 pages, LaTEX, no Figures. Submitted to Phys. Lett.
Stretched chemical bonds in Si6H6: A transition from ring currents to localized pi-electrons?
Motivated by solid-state studies on the cleavage force in Si, and the
consequent stretching of chemical bonds, we here study bond stretching in the,
as yet unsynthesized, free space molecule Si6H6. We address the question as to
whether substantial bond stretching (but constrained to uniform scaling on all
bonds) can result in a transition from ring current behaviour, characteristic
say of benzene at its equilibrium geometry, to localized pi-electrons on Si
atoms. Some calculations are also recorded on dissociation into 6 SiH radicals.
While the main studies have been carried out by unrestricted Hartree-Fock (HF)
theory, the influence of electron correlation has been examined using two forms
of density functional theory. Planar Si6H6 treated by HF is bound to be
unstable, not all vibrational frequencies being real. Some buckling is then
allowed, which results in real frequencies and stability. Evidence is then
provided that the non-planar structure, as the Si-Si distance is increased,
exhibits pi-electron localization in the range 1.2-1.5 times the equilibrium
distance
Magnetic screening properties of an incompressible chiral fluid
We study the possible penetration of a static magnetic field in an idealized
sample of many layers supporting a two dimensional charged chiral quantum
fluid, to see whether there is a kind of Meissner effect. This is a non
standard problem since the quantum fluid is incompressible having a gap in its
spectrum. We find that the system shows an intermediate behaviour between
superconducting and non-superconducting fluids, the magnetic field being
screened or not depending on its orientation relative to the layers.Comment: 20 pages, plain tex, SISSA 50/94/E
A Three Dimensional Lattice of Ion Traps
We propose an ion trap configuration such that individual traps can be
stacked together in a three dimensional simple cubic arrangement. The isolated
trap as well as the extended array of ion traps are characterized for different
locations in the lattice, illustrating the robustness of the lattice of traps
concept. Ease in the addressing of ions at each lattice site, individually or
simultaneously, makes this system naturally suitable for a number of
experiments. Application of this trap to precision spectroscopy, quantum
information processing and the study of few particle interacting system are
discussed.Comment: 4 pages, 4 Figures. Fig 1 appears as a composite of 1a, 1b, 1c and
1d. Fig 2 appears as a composite of 2a, 2b and 2
Mean-Field vs Monte-Carlo equation of state for the expansion of a Fermi superfluid in the BCS-BEC crossover
The equation of state (EOS) of a Fermi superfluid is investigated in the
BCS-BEC crossover at zero temperature. We discuss the EOS based on Monte-Carlo
(MC) data and asymptotic expansions and the EOS derived from the extended BCS
(EBCS) mean-field theory. Then we introduce a time-dependent density
functional, based on the bulk EOS and Landau's superfluid hydrodynamics with a
von Weizs\"acker-type correction, to study the free expansion of the Fermi
superfluid. We calculate the aspect ratio and the released energy of the
expanding Fermi cloud showing that MC EOS and EBCS EOS are both compatible with
the available experimental data of Li atoms. We find that the released
energy satisfies an approximate analytical formula that is quite accurate in
the BEC regime. For an anisotropic droplet, our numerical simulations show an
initially faster reversal of anisotropy in the BCS regime, later suppressed by
the BEC fluid.Comment: 13 pages, 3 figures, presented to the 15th International Laser
Physics Workshop (Lausanne, July 24-28, 2006); to be published in Laser
Physic
Effective Theory of a Chiral Superfluid
We consider an effective Lagrangian describing a fluid living on
two-di\-men\-sio\-nal planes. The fluid self-interacts through a Chern-Simons
vector potential, whose field strength is proportional to the density
fluctuation. This effective Lagrangian can be related to the Anyon mean field,
but can also be considered more generally to describe a universality class of
superfluids and, when charged, of superconductors. We study the relevant
physical properties, including the spectrum, the chirality features appearing
in the polarization of scattered EM waves, and the peculiar response under a
magnetic field, i.e. a peculiar kind of anisotropic Meissner effect.Comment: 36 pages, plain Tex. (minor changes for clarifying definitions on
pages 4,5,6
On the Proof by Reductio ad Absurdum of the Hohenberg-Kohn Theorem for Ensembles of Fractionally Occupied States of Coulomb Systems
It is demonstrated that the original reductio ad absurdum proof of the
generalization of the Hohenberg-Kohn theorem for ensembles of fractionally
occupied states for isolated many-electron Coulomb systems with Coulomb-type
external potentials by Gross et al. [Phys. Rev. A 37, 2809 (1988)] is
self-contradictory since the to-be-refuted assumption (negation) regarding the
ensemble one-electron densities and the assumption about the external
potentials are logically incompatible to each other due to the Kato
electron-nuclear cusp theorem. It is however proved that the Kato theorem
itself provides a satisfactory proof of this theorem.Comment: 9 pages. Int. J. Quantum Chem., to appea
Singlet fermionic dark matter
We propose a renormalizable model of a fermionic dark matter by introducing a
gauge singlet Dirac fermion and a real singlet scalar. The bridges between the
singlet sector and the standard model sector are only the singlet scalar
interaction terms with the standard model Higgs field. The singlet fermion
couples to the standard model particles through the mixing between the standard
model Higgs and singlet scalar and is naturally a weakly interacting massive
particle (WIMP). The measured relic abundance can be explained by the singlet
fermionic dark matter as the WIMP within this model. Collider implication of
the singlet fermionic dark matter is also discussed. Predicted is the elastic
scattering cross section of the singlet fermion into target nuclei for a direct
detection of the dark matter. Search of the direct detection of the dark matter
provides severe constraints on the parameters of our model.Comment: 12 pages, 7 figure
Gene editing and gene regulation with CRISPR
Genome editing enables precise changes to be made in the genome of living cells. The technique was
originally developed in the 1980’s but largely limited to use in mice. The discovery that a targeted double
stranded break (DSB) at a unique site in the genome, close to the site to be changed, could substantially
increase the efficiency of editing raised the possibility of using the technique in a broader range of animal
models and potentially human cells. But the challenge was to identify reagents that could create targeted
breaks at a unique genomic location with minimal off-target effects. In 2005, the demonstration that
programmable zinc finger nucleases (ZFNs) could perform this task, led to a number of proof-of-concept
studies, but a limitation was the ease with which effective ZFNs could be produced. In 2009, the
development of TAL-effector nucleases (TALENs) increased the specificity of gene editing and the ease of
design and production. However, it wasn’t until 2013 and the development of the CRISPR Cas9/guideRNA
that gene editing became a research tool that any lab could use
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