1,355 research outputs found
Modelling spatial and inter-annual variations of nitrous oxide emissions from UK cropland and grasslands using DailyDayCent
This work contributes to the Defra funded projects AC0116: âImproving the nitrous oxide inventoryâ, and AC0114: âData Synthesis, Management and Modellingâ. Funding for this work was provided by the UK Department for Environment, Food and Rural Affairs (Defra) AC0116 and AC0114, the Department of Agriculture, Environment and Rural Affairs for Northern Ireland, the Scottish Government and the Welsh Government. Rothamsted Research receives strategic funding from the Biotechnology and Biological Sciences Research Council. This study also contributes to the projects: N-Circle (BB/N013484/1), U-GRASS (NE/M016900/1) and GREENHOUSE (NE/K002589/1).Peer reviewedPublisher PD
Local Hidden Variables Underpinning of Entanglement and Teleportation
Entangled states whose Wigner functions are non-negative may be viewed as
being accounted for by local hidden variables (LHV). Recently, there were
studies of Bell's inequality violation (BIQV) for such states in conjunction
with the well known theorem of Bell that precludes BIQV for theories that have
LHV underpinning. We extend these studies to teleportation which is also based
on entanglement. We investigate if, to what extent, and under what conditions
may teleportation be accounted for via LHV theory. Our study allows us to
expose the role of various quantum requirements. These are, e.g., the
uncertainty relation among non-commuting operators, and the no-cloning theorem
which forces the complete elimination of the teleported state at its initial
port.Comment: 24 pages, 1 figure, accepted Found. Phy
The Impact of Stellar Migration on Disk Outskirts
Stellar migration, whether due to trapping by transient spirals (churning),
or to scattering by non-axisymmetric perturbations, has been proposed to
explain the presence of stars in outer disks. After a review of the basic
theory, we present compelling, but not yet conclusive, evidence that churning
has been important in the outer disks of galaxies with type II (down-bending)
profiles, while scattering has produced the outer disks of type III
(up-bending) galaxies. In contrast, field galaxies with type I (pure
exponential) profiles appear to not have experienced substantial migration. We
conclude by suggesting work that would improve our understanding of the origin
of outer disks.Comment: Invited review, Book chapter in "Outskirts of Galaxies", Eds. J. H.
Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library,
Springer, in press 39 pages, 15 figure
Creating Bell states and decoherence effects in quantum dots system
We show how to improve the efficiency for preparing Bell states in coupled
two quantum dots system. A measurement to the state of driven quantum laser
field leads to wave function collapse. This results in highly efficiency
preparation of Bell states. The effect of decoherence on the efficiency of
generating Bell states is also discussed in this paper. The results show that
the decoherence does not affect the relative weight of and in the
output state, but the efficiency of finding Bell states.Comment: 4 pages, 2figures, corrected some typo
Multipartite entangled states in coupled quantum dots and cavity-QED
We investigate the generation of multipartite entangled state in a system of
N quantum dots embedded in a microcavity and examine the emergence of genuine
multipartite entanglement by three different characterizations of entanglement.
At certain times of dynamical evolution one can generate multipartite entangled
coherent exciton states or multiqubit states by initially preparing the
cavity field in a superposition of coherent states or the Fock state with one
photon, respectively. Finally we study environmental effects on multipartite
entanglement generation and find that the decay rate for the entanglement is
proportional to the number of excitons.Comment: 9 pages, 4 figures, to appear in Phys. Rev.
Reaction and Axial Vector Coupling
The reaction is studied in the region of low
to investigate the effect of deuteron structure and width of the
resonance on the differential cross section. The results are used to extract
the axial vector coupling from the experimental data on
this reaction. The possibility to determine this coupling from electroweak
interaction experiments with high intensity electron accelerators is discussed.Comment: 14 pages, REVTEX, 5 figure
A novel determination of the local dark matter density
We present a novel study on the problem of constructing mass models for the
Milky Way, concentrating on features regarding the dark matter halo component.
We have considered a variegated sample of dynamical observables for the Galaxy,
including several results which have appeared recently, and studied a 7- or
8-dimensional parameter space - defining the Galaxy model - by implementing a
Bayesian approach to the parameter estimation based on a Markov Chain Monte
Carlo method. The main result of this analysis is a novel determination of the
local dark matter halo density which, assuming spherical symmetry and either an
Einasto or an NFW density profile is found to be around 0.39 GeV cm with
a 1- error bar of about 7%; more precisely we find a for the Einasto profile and for the NFW. This is in contrast to the
standard assumption that is about 0.3 GeV cm with an
uncertainty of a factor of 2 to 3. A very precise determination of the local
halo density is very important for interpreting direct dark matter detection
experiments. Indeed the results we produced, together with the recent accurate
determination of the local circular velocity, should be very useful to
considerably narrow astrophysical uncertainties on direct dark matter
detection.Comment: 31 pages,11 figures; minor changes in the text; two figures adde
Type IIB Colliding Plane Waves
Four-dimensional colliding plane wave (CPW) solutions have played an
important role in understanding the classical non-linearities of Einstein's
equations. In this note, we investigate CPW solutions in --dimensional
Einstein gravity with a -form flux. By using an isomorphism with the
four-dimensional problem, we construct exact solutions analogous to the
Szekeres vacuum solution in four dimensions. The higher-dimensional versions of
the Khan-Penrose and Bell-Szekeres CPW solutions are studied perturbatively in
the vicinity of the light-cone. We find that under small perturbations, a
curvature singularity is generically produced, leading to both space-like and
time-like singularities. For , our results pertain to the collision of two
ten-dimensional type IIB Blau - Figueroa o'Farrill - Hull - Papadopoulos plane
waves.Comment: 20+10 pages, 2 figures, uses JHEP3.cls; v2: refs [3,10,22] corrected,
remark added below (3.9) on inexistence of conformally flat CPW in our
ansatz, final version to appear in JHE
Solar Wakes of Dark Matter Flows
We analyze the effect of the Sun's gravitational field on a flow of cold dark
matter (CDM) through the solar system in the limit where the velocity
dispersion of the flow vanishes. The exact density and velocity distributions
are derived in the case where the Sun is a point mass. The results are extended
to the more realistic case where the Sun has a finite size spherically
symmetric mass distribution. We find that regions of infinite density, called
caustics, appear. One such region is a line caustic on the axis of symmetry,
downstream from the Sun, where the flow trajectories cross. Another is a
cone-shaped caustic surface near the trajectories of maximum scattering angle.
The trajectories forming the conical caustic pass through the Sun's interior
and probe the solar mass distribution, raising the possibility that the solar
mass distribution may some day be measured by a dark matter detector on Earth.
We generalize our results to the case of flows with continuous velocity
distributions, such as that predicted by the isothermal model of the Milky Way
halo.Comment: 30 pages, 8 figure
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