2,999 research outputs found
ANALYSIS OF VARIATIONS IN FARM REAL ESTATE PRICES OVER HOMOGENEOUS MARKET AREAS IN THE SOUTHEAST
Land Economics/Use,
EFFICIENCY AND EQUITY ASPECTS OF NONPOINT SOURCE POLLUTION CONTROLS
Environmental Economics and Policy,
Lorentz-Invariant "Elements of Reality" and the Question of Joint Measurability of Commuting Observables
It is shown that the joint measurements of some physical variables
corresponding to commuting operators performed on pre- and post-selected
quantum systems invariably disturb each other. The significance of this result
for recent proofs of the impossibility of realistic Lorentz invariant
interpretation of quantum theory (without assumption of locality) is discussed.Comment: 15 page
Volume Weighted Measures of Eternal Inflation in the Bousso-Polchinski Landscape
We consider the cosmological dynamics associated with volume weighted
measures of eternal inflation, in the Bousso-Polchinski model of the string
theory landscape. We find that this measure predicts that observers are most
likely to find themselves in low energy vacua with one flux considerably larger
than the rest. Furthermore, it allows for a satisfactory anthropic explanation
of the cosmological constant problem by producing a smooth, and approximately
constant, distribution of potentially observable values of Lambda. The low
energy vacua selected by this measure are often short lived. If we require
anthropically acceptable vacua to have a minimum life-time of 10 billion years,
then for reasonable parameters a typical observer should expect their vacuum to
have a life-time of approximately 12 billion years. This prediction is model
dependent, but may point toward a solution to the coincidence problem of
cosmology.Comment: 35 pages, 8 figure
Dynamics of a lattice Universe
We find a solution to Einstein field equations for a regular toroidal lattice
of size L with equal masses M at the centre of each cell; this solution is
exact at order M/L. Such a solution is convenient to study the dynamics of an
assembly of galaxy-like objects. We find that the solution is expanding (or
contracting) in exactly the same way as the solution of a
Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average
density as our model. This points towards the absence of backreaction in a
Universe filled with an infinite number of objects, and this validates the
fluid approximation, as far as dynamics is concerned, and at the level of
approximation considered in this work.Comment: 14 pages. No figure. Accepted version for Classical and Quantum
Gravit
Cosmologies with Energy Exchange
We provide a simple mathematical description of the exchange of energy
between two fluids in an expanding Friedmann universe with zero spatial
curvature. The evolution can be reduced to a single non-linear differential
equation which we solve in physically relevant cases and provide an analysis of
all the possible evolutions. Particular power-law solutions exist for the
expansion scale factor and are attractors at late times under particular
conditions. We show how a number of problems studied in the literature, such as
cosmological vacuum energy decay, particle annihilation, and the evolution of a
population of evaporating black holes, correspond to simple particular cases of
our model. In all cases we can determine the effects of the energy transfer on
the expansion scale factor. We also consider the situation in the presence of
anti-decaying fluids and so called phantom fluids which violate the dominant
energy conditions.Comment: 12 pages, 1 figur
Exact Evolution of Discrete Relativistic Cosmological Models
22 pages, 16 figures22 pages, 16 figuresWe study the effects of inhomogeneities on the evolution of the Universe, by considering a range of cosmological models with discretized matter content. This is done using exact and fully relativistic methods that exploit the symmetries in and about submanifolds of spacetimes that themselves possess no continuous global symmetries. These methods allow us to follow the evolution of our models throughout their entire history, far beyond what has previously been possible. We find that while some space-like curves collapse to anisotropic singularities in finite time, others remain non-singular forever. The resulting picture is of a cosmological spacetime in which some behaviour remains close to Friedmann-like, while other behaviours deviate radically. In particular, we find that large-scale acceleration is possible without any violation of the energy conditions
Constraints on the Variation of G from Primordial Nucleosynthesis
We study here the effect of a varying G on the evolution of the early
Universe and, in particular, on primordial nucleosynthesis. This variation of G
is modelled using the Brans-Dicke theory as well as a more general class of
scalar-tensor theories. Modified nucleosynthesis codes are used to investigate
this effect and the results obtained are used to constrain the parameters of
the theories. We extend previous studies of primordial nucleosynthesis in
scalar-tensor theories by including effects which can cause a slow variation of
G during radiation domination and by including a late-time accelerating phase
to the Universe's history. We include a brief discussion on the epoch of
matter-radiation equality in Brans-Dicke theory, which is also of interest for
determining the positions of the cosmic microwave background power-spectrum
peaks.Comment: 10 pages, 7 figures. Published versio
Semicausal operations are semilocalizable
We prove a conjecture by DiVincenzo, which in the terminology of Preskill et
al. [quant-ph/0102043] states that ``semicausal operations are
semilocalizable''. That is, we show that any operation on the combined system
of Alice and Bob, which does not allow Bob to send messages to Alice, can be
represented as an operation by Alice, transmitting a quantum particle to Bob,
and a local operation by Bob. The proof is based on the uniqueness of the
Stinespring representation for a completely positive map. We sketch some of the
problems in transferring these concepts to the context of relativistic quantum
field theory.Comment: 4 pages, 1 figure, revte
Performance of the starâshaped flyer in the study of brittle materials: Three dimensional computer simulations and experimental observations
A three dimensional finite element computer simulation has been performed to assess the effects of release waves in normal impact softârecovery experiments when a starâshaped flyer plate is used. Their effects on the monitored velocityâtime profiles have been identified and their implications in the interpretation of wave spreading and spall signal events highlighted. The calculation shows that the starâshaped flyer plate indeed minimizes the magnitude of edge effects. The major perturbation to the oneâdimensional response within the central region of the target plate results from spherical waves emanating from the corners of the starâshaped plate. Experimental evidence of the development of a damage ring located in coincidence with the eight entrant corners of the flyer plate is reported. Microscopy studies performed in the intact recovered samples revealed that this damage ring eliminates undesired boundary release waves within the central region of the specimen. Consequently, the observed damage in compression and tension within this region can be attributed primarily to the conditions arising from a state of uniaxial strain.
- âŠ