4,229 research outputs found
Intrinsic time gravity and the Lichnerowicz-York equation
We investigate the effect on the Hamiltonian structure of general relativity
of choosing an intrinsic time to fix the time slicing. 3-covariance with
momentum constraint is maintained, but the Hamiltonian constraint is replaced
by a dynamical equation for the trace of the momentum. This reveals a very
simple structure with a local reduced Hamiltonian. The theory is easily
generalised; in particular, the square of the Cotton-York tensor density can be
added as an extra part of the potential while at the same time maintaining the
classic 2 + 2 degrees of freedom. Initial data construction is simple in the
extended theory; we get a generalised Lichnerowicz-York equation with nice
existence and uniqueness properties. Adding standard matter fields is quite
straightforward.Comment: 4 page
Andreev Bound States in the Kondo Quantum Dots Coupled to Superconducting Leads
We have studied the Kondo quantum dot coupled to two superconducting leads
and investigated the subgap Andreev states using the NRG method. Contrary to
the recent NCA results [Clerk and Ambegaokar, Phys. Rev. B 61, 9109 (2000);
Sellier et al., Phys. Rev. B 72, 174502 (2005)], we observe Andreev states both
below and above the Fermi level.Comment: 5 pages, 5 figure
Anomalous Transmission Phase of a Kondo-Correlated Quantum Dot
We study phase evolution of transmission through a quantum dot with Kondo
correlations. By considering a model that includes nonresonant transmission as
well as the Anderson impurity, we explain unusually large phase evolution of
about in the Kondo valley observed in recent experiments. We argue that
this anomalous phase evolution is a universal property that can be found in the
high-temperature Kondo phase in the presence of the time-reversal symmetry.Comment: 5 pages, 3 figure
Affine group representation formalism for four dimensional, Lorentzian, quantum gravity
Within the context of the Ashtekar variables, the Hamiltonian constraint of
four-dimensional pure General Relativity with cosmological constant, ,
is reexpressed as an affine algebra with the commutator of the imaginary part
of the Chern-Simons functional, , and the positive-definite volume element.
This demonstrates that the affine algebra quantization program of Klauder can
indeed be applicable to the full Lorentzian signature theory of quantum gravity
with non-vanishing cosmological constant; and it facilitates the construction
of solutions to all of the constraints. Unitary, irreducible representations of
the affine group exhibit a natural Hilbert space structure, and coherent states
and other physical states can be generated from a fiducial state. It is also
intriguing that formulation of the Hamiltonian constraint or Wheeler-DeWitt
equation as an affine algebra requires a non-vanishing cosmological constant;
and a fundamental uncertainty relation of the form
(wherein
is the total volume) may apply to all physical states of quantum gravity.Comment: 13 pages. Revised versio
The linearization of the Kodama state
We study the question of whether the linearization of the Kodama state around
classical deSitter spacetime is normalizable in the inner product of the theory
of linearized gravitons on deSitter spacetime. We find the answer is no in the
Lorentzian theory. However, in the Euclidean theory the corresponding
linearized Kodama state is delta-functional normalizable. We discuss whether
this result invalidates the conjecture that the full Kodama state is a good
physical state for quantum gravity with positive cosmological constant.Comment: 14 pages, statement on the corresponding Yang-Mills case correcte
Josephson current in strongly correlated double quantum dots
We study the transport properties of a serial double quantum dot (DQD)
coupled to two superconducting leads, focusing on the Josephson current through
the DQD and the associated 0- transitions which result from the subtle
interplay between the superconductivity, the Kondo physics, and the inter-dot
superexchange interaction. We examine the competition between the
superconductivity and the Kondo physics by tuning the relative strength
of the superconducting gap and the Kondo temperature
, for different strengths of the superexchange coupling determined by the
interdot tunneling relative to the dot level broadening . We find
strong renormalization of , a significant role of the superexchange coupling
, and a rich phase diagram of the 0 and -junction regimes. In
particular, when both the superconductivity and the exchange interaction are in
close competion with the Kondo physics (), there appears
an island of -phase at large values of the superconducting phase
difference.Comment: 4 pages, 4 figure
Three-geometry and reformulation of the Wheeler-DeWitt equation
A reformulation of the Wheeler-DeWitt equation which highlights the role of
gauge-invariant three-geometry elements is presented. It is noted that the
classical super-Hamiltonian of four-dimensional gravity as simplified by
Ashtekar through the use of gauge potential and densitized triad variables can
furthermore be succinctly expressed as a vanishing Poisson bracket involving
three-geometry elements. This is discussed in the general setting of the
Barbero extension of the theory with arbitrary non-vanishing value of the
Immirzi parameter, and when a cosmological constant is also present. A proposed
quantum constraint of density weight two which is polynomial in the basic
conjugate variables is also demonstrated to correspond to a precise simple
ordering of the operators, and may thus help to resolve the factor ordering
ambiguity in the extrapolation from classical to quantum gravity. Alternative
expression of a density weight one quantum constraint which may be more useful
in the spin network context is also discussed, but this constraint is
non-polynomial and is not motivated by factor ordering. The article also
highlights the fact that while the volume operator has become a preeminient
object in the current manifestation of loop quantum gravity, the volume element
and the Chern-Simons functional can be of equal significance, and need not be
mutually exclusive. Both these fundamental objects appear explicitly in the
reformulation of the Wheeler-DeWitt constraint.Comment: 10 pages, LaTeX fil
Selenium Biotransformations in an Engineered Aquatic Ecosystem for Bioremediation of Agricultural Wastewater via Brine Shrimp Production
An engineered aquatic ecosystem was specifically designed to bioremediate selenium (Se), occurring as oxidized inorganic selenate from hypersalinized agricultural drainage water while producing brine shrimp enriched in organic Se and omega-3 and omega-6 fatty acids for use in value added nutraceutical food supplements. Selenate was successfully bioremediated by microalgal metabolism into organic Se (seleno-amino acids) and partially removed via gaseous volatile Se formation. Furthermore, filterfeeding brine shrimp that accumulated this organic Se were removed by net harvest. Thriving in this engineered pond system, brine shrimp (Artemia franciscana Kellogg) and brine fly (Ephydridae sp.) have major ecological relevance as important food sources for large populations of waterfowl, breeding, and migratory shore birds. This aquatic ecosystem was an ideal model for study because it mimics trophic interactions in a Se polluted wetland. Inorganic selenate in drainage water was metabolized differently in microalgae, bacteria, and diatoms where it was accumulated and reduced into various inorganic forms (selenite, selenide, or elemental Se) or partially incorporated into organic Se mainly as selenomethionine. Brine shrimp and brine fly larva then bioaccumulated Se from ingesting aquatic microorganisms and further metabolized Se predominately into organic Se forms. Importantly, adult brine flies, which hatched from aquatic larva, bioaccumulated the highest Se concentrations of all organisms tested
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