36 research outputs found
Nonlinear spinor field in Bianchi type-I Universe filled with viscous fluid: numerical solutions
We consider a system of nonlinear spinor and a Bianchi type I gravitational
fields in presence of viscous fluid. The nonlinear term in the spinor field
Lagrangian is chosen to be , with being a self-coupling
constant and being a function of the invariants an constructed from
bilinear spinor forms and . Self-consistent solutions to the spinor and
BI gravitational field equations are obtained in terms of , where
is the volume scale of BI universe. System of equations for and \ve,
where \ve is the energy of the viscous fluid, is deduced. This system is
solved numerically for some special cases.Comment: 15 pages, 4 figure
Nonlinear model for disordered superconductors
We suggest a novel nonlinear -model for the description of disordered
superconductors. The main distinction from existing models lies in the fact
that the saddle point equation is solved non-perturbatively in the
superconducting pairing field. It allows one to use the model both in the
vicinity of the metal-superconductor transition and well below its critical
temperature with full account for the self-consistency conditions. We show that
the model reproduces a set of known results in different limiting cases, and
apply it for a self-consistent description of the proximity effect at the
superconductor-metal interface.Comment: Revised version, 8 pages, 1 fig., revtex; final version, as
published, contains a few corrections in the summar
Thermostatistics of deformed bosons and fermions
Based on the q-deformed oscillator algebra, we study the behavior of the mean
occupation number and its analogies with intermediate statistics and we obtain
an expression in terms of an infinite continued fraction, thus clarifying
successive approximations. In this framework, we study the thermostatistics of
q-deformed bosons and fermions and show that thermodynamics can be built on the
formalism of q-calculus. The entire structure of thermodynamics is preserved if
ordinary derivatives are replaced by the use of an appropriate Jackson
derivative and q-integral. Moreover, we derive the most important thermodynamic
functions and we study the q-boson and q-fermion ideal gas in the thermodynamic
limit.Comment: 14 pages, 2 figure
Quantum computing implementations with neutral particles
We review quantum information processing with cold neutral particles, that
is, atoms or polar molecules. First, we analyze the best suited degrees of
freedom of these particles for storing quantum information, and then we discuss
both single- and two-qubit gate implementations. We focus our discussion mainly
on collisional quantum gates, which are best suited for atom-chip-like devices,
as well as on gate proposals conceived for optical lattices. Additionally, we
analyze schemes both for cold atoms confined in optical cavities and hybrid
approaches to entanglement generation, and we show how optimal control theory
might be a powerful tool to enhance the speed up of the gate operations as well
as to achieve high fidelities required for fault tolerant quantum computation.Comment: 19 pages, 12 figures; From the issue entitled "Special Issue on
Neutral Particles
Coherent X-ray imaging and microscopy opportunities with a diffraction-limited Energy Recovery Linac (ERL) synchrotron source
A proposed Energy Recovery Linac (ERL) x-ray source at Cornell would be a 5-7 GeV synchrotron
facility based on the energy-recovery principle with a superconducting linac. Because of its ultra-small round
electron source and ultra-short but flexible bunch structure, the ERL has the potential to produce subpicosecond
ultra-bright diffraction-limited hard x-ray beams that are superior to those from existing storage
rings, and would enable new scientific experiments that are difficult or impossible to perform today. In this paper,
we discuss the transverse coherence properties of the ERL source and show how these properties could
benefit various x-ray microscopy applications that require a highly coherent and intense x-ray beam. These applications
include full coherent illumination of wide-aperture zone-plate optics for scanning x-ray microscopy,
diffraction-limited coherent phase-contrast microscopy and tomography, fully coherent hard x-ray diffraction
microscopy, and large-coherence-area x-ray holography techniques
Imaging field-dependent structure in charge-density waves by X-ray diffraction topography
We have imaged field-dependent CDW structure in NbSe3 single crystals by X-ray diffraction topography. Just above ET, the CDW shears along longitudinal steps in crystal thickness associated with small-angle grain boundaries, and at high fields transverse correlations recover. These results demonstrate X-ray topography as an effective probe of CDW structure, and together with earlier transport measurements establish that extrinsic sources dominate the most obvious manifestations of plasticity in this CDW conductor