1,174,377 research outputs found
Optical conductivity of unconventional charge density wave systems: Role of vertex corrections
The optical conductivity of a d-CDW conductor is calculated for electrons on
a square lattice and a nearest-neighbor charge-charge interaction using the
lowest-order conserving approximation. The spectral properties of the
Drude-like peak at low frequencies and the broad hump due to transitions across
the gap at large frequencies are discussed, also as a function of temperature
and of the second-nearest neighbor hopping term t'. We find that vertex
corrections enhance the d.c. conductivity, make the Drude peak narrower and
provide a smooth transition from a renormalized regime at low to the bare
theory at high frequencies. It is also shown that vertex corrections enhance
the temperature dependence of the restricted optical sum leading to a
non-negligible violation of the sum rule in the d-CDW state.Comment: 10 pages, 6 figure
Very high voltage latching relay
Relay consists of high voltage reed switch actuated by rotating permanent magnet mounted on stepper motor shaft, with actuation assembly isolated from high voltage circuit. Unit can be modified for use as double pole or double pole double throw latching relay and can be used in either air or vacuum
Covariance, correlation and entanglement
Some new identities for quantum variance and covariance involving commutators
are presented, in which the density matrix and the operators are treated
symmetrically. A measure of entanglement is proposed for bipartite systems,
based on covariance. This works for two- and three-component systems but
produces ambiguities for multicomponent systems of composite dimension. Its
relationship to angular momentum dispersion for symmetric symmetric spin states
is described.Comment: 30 pages, Latex, to appear in J Phys
Alpha-decay lifetimes semiempirical relationship including shell effects
A new version of the semiempirical formula based on fission approach of alpha
decay is derived, by using the optimum values of the fitting parameters
determined for even-even nuclei, combined with hindrance factors for even-odd,
odd-even, and odd-odd nuclides. The deviations from experimental data for two
regions of nuclear chart (493 alpha emitters with Z=52-118 and 142 transuranium
nuclei including superheavies (Z=92-118), respectively) are compared with those
obtained by using the universal curve and the Viola-Seaborg semiempirical
relationship.Comment: 11 pages, 3 figures, revtex
Searches for radio transients
Exploration of the transient Universe is an exciting and fast-emerging area
within radio astronomy. Known transient phenomena range in time scales from
sub-nanoseconds to years or longer, thus spanning a huge range in time domain
and hinting a rich diversity in their underlying physical processes. Transient
phenomena are likely locations of explosive or dynamic events and they offer
tremendous potential to uncover new physics and astrophysics. A number of
upcoming next-generation radio facilities and recent advances in computing and
instrumentation have provided a much needed impetus for this field which has
remained a relatively uncharted territory for the past several decades. In this
paper we focus mainly on the class of phenomena that occur on very short time
scales (i.e. from milliseconds to nanoseconds), known as {\it
fast transients}, the detections of which involve considerable signal
processing and data management challenges, given the high time and frequency
resolutions required in their explorations, the role of propagation effects to
be considered and a multitude of deleterious effects due to radio frequency
interference. We will describe the techniques, strategies and challenges
involved in their detections and review the world-wide efforts currently under
way, both through scientific discoveries enabled by the ongoing large-scale
surveys at Parkes and Arecibo, as well as technical developments involving the
exploratory use of multi-element array instruments such as VLBA and GMRT. Such
developments will undoubtedly provide valuable inputs as next-generation arrays
such as LOFAR and ASKAP are designed and commissioned. With their wider fields
of view and higher sensitivities, these instruments, and eventually the SKA,
hold great potential to revolutionise this relatively nascent field, thereby
opening up exciting new science avenues in astrophysics.Comment: To appear in the special issue of the Bulletin of the Astronomical
Society of India on Transients at different wavelengths, eds D.J. Saikia and
D.A. Green. 21 pages, 5 figures. http://www.ncra.tifr.res.in/~bas
The Hall conductivity in unconventional charge density wave systems
Charge density waves with unconventional order parameters, for instance, with
d-wave symmetry (DDW), may be relevant in the underdoped regime of high-T_c
cuprates or other quasi-one or two dimensional metals. A DDW state is
characterized by two branches of low-lying electronic excitations. The
resulting quantum mechanical current has an inter-branch component which leads
to an additional mass term in the expression for the Hall conductivity. This
extra mass term is parametrically enhanced near the ``hot spots'' of fermionic
dispersion and is non-neglegible as is shown by numerical calculations of the
Hall number in the DDW state.Comment: 4 pages, 4 figure
High field fractional quantum Hall effect in optical lattices
We consider interacting bosonic atoms in an optical lattice subject to a
large simulated magnetic field. We develop a model similar to a bilayer
fractional quantum Hall system valid near simple rational numbers of magnetic
flux quanta per lattice cell. Then we calculate its ground state, magnetic
lengths, fractional fillings, and find unexpected sign changes in the Hall
current. Finally we study methods for detecting these novel features via shot
noise and Hall current measurements.Comment: 4 pages, 4 figures, accepted by PR
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