521 research outputs found
Viscous Brane Cosmology with a Brane-Bulk Energy Interchange Term
We assume a flat brane located at y=0, surrounded by an AdS space, and
consider the 5D Einstein equations when the energy flux component of the
energy-momentum tensor is related to the Hubble parameter through a constant Q.
We calculate the metric tensor, as well as the Hubble parameter on the brane,
when Q is small. As a special case, if the brane is tensionless, the influence
from Q on the Hubble parameter is absent. We also consider the emission of
gravitons from the brane, by means of the Boltzmann equation. Comparing the
energy conservation equation derived herefrom with the energy conservation
equation for a viscous fluid on the brane, we find that the entropy change for
the fluid in the emission process has to be negative. This peculiar effect is
related to the fluid on the brane being a non-closed thermodynamic system. The
negative entropy property for non-closed systems is encountered in other areas
in physics also, in particular, in connection with the Casimir effect at finite
temperature.Comment: 12 pages, latex, no figure
CFT driven cosmology and the DGP/CFT correspondence
We present a dual 5D braneworld picture of a recently suggested model for a
microcanonical description of a 4D cosmology driven by a conformal field theory
with a large number of quantum fields. The 5D side of the duality relation is
represented by a generalized brane induced gravity model in a Schwarzschild-de
Sitter bulk. The values of the bulk cosmological and the induced 4D
cosmological constants are determined by requiring the absence of conical
singularity at the de Sitter horizon of the Euclidean Schwarzschild-de Sitter
bulk. Those values belong to the vicinity of the upper bound of a range of
admissible values for the cosmological constant. This upper bound is enforced
by the 4D CFT and coincides with the natural gravitational cutoff in a theory
with many quantum species. The resulting DGP/CFT duality suggests the
possibility of a new type of {\em background independent} correspondence. A
mechanism for inverting the sign of the effective cosmological constant is
found, which might reconcile a negative value of the primordial cosmological
constant compatible with supersymmetry with the one required by inflationary
cosmology.Comment: LaTeX, 23 pages, 3 figure
Isotopic Insights into Biological Regulation of Zinc in Contaminated Systems
AbstractAquatic organisms use a variety ofbiogeochemical reactions to regulate essential and non-essential trace metals. Many of these mechanisms can lead to isotopic fractionation, thus measurement of metal isotopes may yield insights into the processes by which organisms respond to metal exposure. We illustrate these concepts with two case studies, one involving an intra- and the other an extra-cellular mechanism of Zn sequestration. In the first study, the mayflyNeocloeontrianguliferwas grown in the laboratory, and fed a diet of Zn-doped diatoms at Zn levels exceeding the requirements for normal mayfly life functions. The N. trianguliferlarvae consumed the diatoms and retained their Zn isotopic signature. Upon metamorphosis, the subimago life stage lost Zn mass either in the exuvia or by excretion, and the Zn retainedwas isotopically enriched. Thus, Zn uptake is non-fractionating, but Zn regulation favors the lighter isotope. Thus the Zn remaining in the subimago was isotopically heavier. In the second study, Zn was adsorbed on the cell walls and exopolysaccharide secretions of cyanobacteria, which favored the heavier Zn isotope.Continued adsorption eventually resulted in nucleation and biomineralization of hydrozincite {Zn5(CO3)2(OH)6}. These case studies demonstrate the utility of Zn isotopes to provide insights into how aquatic insects respond to metal exposure
Fast Non-Adiabatic Two Qubit Gates for the Kane Quantum Computer
In this paper we apply the canonical decomposition of two qubit unitaries to
find pulse schemes to control the proposed Kane quantum computer. We explicitly
find pulse sequences for the CNOT, swap, square root of swap and controlled Z
rotations. We analyze the speed and fidelity of these gates, both of which
compare favorably to existing schemes. The pulse sequences presented in this
paper are theoretically faster, higher fidelity, and simpler than existing
schemes. Any two qubit gate may be easily found and implemented using similar
pulse sequences. Numerical simulation is used to verify the accuracy of each
pulse scheme
A comment on multiple vacua, particle production and the time dependent AdS/CFT correspondence
We give an explicit formulation of the time dependent AdS/CFT correspondence
when there are multiple vacua present in Lorentzian signature. By computing
sample two point functions we show how different amplitudes are related by
cosmological particle production. We illustrate our methods in two example
spacetimes: (a) a ``bubble of nothing'' in AdS space, and (b) an asymptotically
locally AdS spacetime with a bubble of nothing on the boundary. In both cases
the alpha vacua of de Sitter space make an interesting appearance.Comment: 9 page
Modelling the probability of microhabitat formation on trees using cross-sectional data
The rate of TreM formation per unit diameter growth was modelled as a function of tree diameter at breast height (DBH), and the model was calibrated considering cross-sectional observations TreMs on trees of different sizes. The model predicted realistic TreM formation rates at the tree and stand levels in forests dominated by Abies alba and Fagus sylvatica. This approach opens new perspectives to the analysis of forest biodiversity conservation strategies
Trace anomaly driven inflation
This paper investigates Starobinsky's model of inflation driven by the trace
anomaly of conformally coupled matter fields. This model does not suffer from
the problem of contrived initial conditions that occurs in most models of
inflation driven by a scalar field. The universe can be nucleated
semi-classically by a cosmological instanton that is much larger than the
Planck scale provided there are sufficiently many matter fields. There are two
cosmological instantons: the four sphere and a new ``double bubble'' solution.
This paper considers a universe nucleated by the four sphere. The AdS/CFT
correspondence is used to calculate the correlation function for scalar and
tensor metric perturbations during the ensuing de Sitter phase. The analytic
structure of the scalar and tensor propagators is discussed in detail.
Observational constraints on the model are discussed. Quantum loops of matter
fields are shown to strongly suppress short scale metric perturbations, which
implies that short distance modifications of gravity would probably not be
observable in the cosmic microwave background. This is probably true for any
model of inflation provided there are sufficiently many matter fields. This
point is illustrated by a comparison of anomaly driven inflation in four
dimensions and in a Randall-Sundrum brane-world model.Comment: LaTeX, 42 pages, 5 .eps figures. v2: typos corrected, references
added and 2 new paragraphs in conclusions section. v3: comments about strong
coupling and unboundedness of action changed, other minor changes. v4:
Comments about strong coupling changed again (2-point functions of metric
perturbations do not depend on Yang-Mills coupling
A Framework for Organizational Compliance Management Tactics
Abstract. Organizational compliance with laws, industrial standards, procedures and enterprise architectures has become a highly relevant topic for both practitio-ners and academics. However, both the fundamental insights into compliance as a concept and the tactics for bringing an organization into a compliant state have been described in a fragmented manner. Using literature from various disciplines, this paper presents two contributions. First, it describes the fundamental concepts regarding compliance. Second, it presents a framework in which the various tactics for achieving organizational compliance can be positioned
Intrinsic and extrinsic properties of quantum systems
The paper attempts to convince that the orthodox interpretation of quantum
mechanics does not contradict philosophical realism by throwing light onto
certain properties of quantum systems that seem to have escaped attention as
yet. The exposition starts with the philosophical notions of realism. Then, the
quantum mechanics as it is usually taught is demoted to a mere part of the
theory called phenomenology of observations, and the common impression about
its contradiction to realism is explained. The main idea of the paper, the
physical notion of intrinsic properties, is introduced and many examples
thereof are given. It replaces the irritating dichotomy of quantum and
classical worlds by a much softer difference between intrinsic and extrinsic
properties, which concern equally microscopic and macroscopic systems. Finally,
the classicality and the quantum measurement are analyzed and found to present
some still unsolved problems. A possible way of dealing with the
Schr\"{o}dinger cat is suggested that is based on the intrinsic properties. A
simple quantum model of one classical property illustrates how our philosophy
may work.Comment: 20 pages, no figure. Comments are wellcom
Entanglement of positive definite functions on compact groups
We define and study entanglement of continuous positive definite functions on
products of compact groups. We formulate and prove an infinite-dimensional
analog of Horodecki Theorem, giving a necessary and sufficient criterion for
separability of such functions. The resulting characterisation is given in
terms of mappings of the space of continuous functions, preserving positive
definiteness. The relation between the developed group-theoretical formalism
and the conventional one, given in terms of density matrices, is established
through the non-commutative Fourier analysis.Comment: published versio
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