252 research outputs found
Averaged Energy Inequalities for the Non-Minimally Coupled Classical Scalar Field
The stress energy tensor for the classical non-minimally coupled scalar field
is known not to satisfy the point-wise energy conditions of general relativity.
In this paper we show, however, that local averages of the classical stress
energy tensor satisfy certain inequalities. We give bounds for averages along
causal geodesics and show, e.g., that in Ricci-flat background spacetimes, ANEC
and AWEC are satisfied. Furthermore we use our result to show that in the
classical situation we have an analogue to the phenomenon of quantum interest.
These results lay the foundations for analogous energy inequalities for the
quantised non-minimally coupled fields, which will be discussed elsewhere.Comment: 8 pages, RevTeX4. Minor typos corrected; version to appear in Phys
Rev
A review of the decoherent histories approach to the arrival time problem in quantum theory
We review recent progress in understanding the arrival time problem in
quantum mechanics, from the point of view of the decoherent histories approach
to quantum theory. We begin by discussing the arrival time problem, focussing
in particular on the role of the probability current in the expected classical
solution. After a brief introduction to decoherent histories we review the use
of complex potentials in the construction of appropriate class operators. We
then discuss the arrival time problem for a particle coupled to an environment,
and review how the arrival time probability can be expressed in terms of a POVM
in this case. We turn finally to the question of decoherence of the
corresponding histories, and we show that this can be achieved for simple
states in the case of a free particle, and for general states for a particle
coupled to an environment.Comment: 10 pages. To appear in DICE 2010 conference proceeding
Bounds on negative energy densities in flat spacetime
We generalise results of Ford and Roman which place lower bounds -- known as
quantum inequalities -- on the renormalised energy density of a quantum field
averaged against a choice of sampling function. Ford and Roman derived their
results for a specific non-compactly supported sampling function; here we use a
different argument to obtain quantum inequalities for a class of smooth, even
and non-negative sampling functions which are either compactly supported or
decay rapidly at infinity. Our results hold in -dimensional Minkowski space
() for the free real scalar field of mass . We discuss various
features of our bounds in 2 and 4 dimensions. In particular, for massless field
theory in 2-dimensional Minkowski space, we show that our quantum inequality is
weaker than Flanagan's optimal bound by a factor of 3/2.Comment: REVTeX, 13 pages and 2 figures. Minor typos corrected, one reference
adde
Incorporating fishery observer data into an integrated catch-at-age and multiyear tagging model for estimating mortality rates and abundance
Tagging experiments are a useful tool in fisheries for estimating mortality rates and abundance of fish. Unfortunately, nonreporting of recovered tags is a common problem in commercial fisheries which, if unaccounted for, can render these estimates meaningless. Observers are
often employed to monitor a portion of the catches as a means of estimating reporting rates. In our study, observer data were incorporated into an integrated model for multiyear tagging and catch data to provide joint estimates of mortality rates (natural and f ishing), abundance, and reporting rates. Simulations were used to explore model performance under a range of scenarios (e.g., different
parameter values, parameter constraints, and numbers of release and recapture years). Overall, results indicated that all parameters can be estimated with reasonable accuracy, but that fishing mortality, reporting rates, and abundance can be estimated with much higher precision
than natural mortality. An example of how the model can be applied to provide guidance on experimental design for a large-scale tagging study is presented. Such guidance can contribute to the successful and cost-effective management of tagging programs for commercial fisheries
Optical switching of radical pair conformation enhances magnetic sensitivity
The yield of chemical reactions involving intermediate radical pairs is
influenced by magnetic fields well beyond the levels expected from energy
considerations. This dependence can be traced back to the microscopic dynamics
of electron spins and constitutes the basis of the chemical compass. Here we
propose a new experimental approach based on molecular photoswitches to achieve
additional control on the chemical reaction and to allow short-time resolution
of the spin dynamics. Our proposal enables experiments to test some of the
standard assumptions of the radical pair model and improves the sensitivity of
chemical magnetometers by two orders of magnitude
Quantum energy inequalities and local covariance II: Categorical formulation
We formulate Quantum Energy Inequalities (QEIs) in the framework of locally
covariant quantum field theory developed by Brunetti, Fredenhagen and Verch,
which is based on notions taken from category theory. This leads to a new
viewpoint on the QEIs, and also to the identification of a new structural
property of locally covariant quantum field theory, which we call Local
Physical Equivalence. Covariant formulations of the numerical range and
spectrum of locally covariant fields are given and investigated, and a new
algebra of fields is identified, in which fields are treated independently of
their realisation on particular spacetimes and manifestly covariant versions of
the functional calculus may be formulated.Comment: 27 pages, LaTeX. Further discussion added. Version to appear in
General Relativity and Gravitatio
Generalised growth models for aquatic species with an application to blacklip abalone (Haliotis rubra)
This paper presents a maximum likelihood method for estimating growth parameters for an aquatic species that incorporates growth covariates, and takes into consideration multiple tag-recapture data. Individual variability in asymptotic length, age-at-tagging, and measurement error are also considered in the model structure. Using distribution theory, the log-likelihood function is derived under a generalised framework for the von Bertalanffy and Gompertz growth models. Due to the generality of the derivation, covariate effects can be included for both models with seasonality and tagging effects investigated. Method robustness is established via comparison with the Fabens, improved Fabens, James and a non-linear mixed-effects growth models, with the maximum likelihood method performing the best. The method is illustrated further with an application to blacklip abalone ( Haliotis rubra) for which a strong growth-retarding tagging effect that persisted for several months was detected
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