1,631 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
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
Isotopic Grand Unification with the Inclusion of Gravity (revised version)
We introduce a dual lifting of unified gauge theories, the first
characterized by the isotopies, which are axiom- preserving maps into broader
structures with positive-definite generalized units used for the representation
of matter under the isotopies of the Poincare' symmetry, and the second
characterized by the isodualities, which are anti-isomorphic maps with
negative-definite generalized units used for the representation of antimatter
under the isodualities of the Poincare' symmetry. We then submit, apparently
for the first time, a novel grand unification with the inclusion of gravity for
matter embedded in the generalized positive-definite units of unified gauge
theories while gravity for antimatter is embedded in the isodual isounit. We
then show that the proposed grand unification provides realistic possibilities
for a resolution of the axiomatic incompatibilities between gravitation and
electroweak interactions due to curvature, antimatter and the fundamental
space-time symmetries.Comment: 20 pages, Latex, revised in various details and with added reference
On the Resolution of the Time-Like Singularities in Reissner-Nordstrom and Negative-Mass Schwarzschild
Certain time-like singularities are shown to be resolved already in classical
General Relativity once one passes from particle probes to scalar waves. The
time evolution can be defined uniquely and some general conditions for that are
formulated. The Reissner-Nordstrom singularity allows for communication through
the singularity and can be termed "beam splitter" since the transmission
probability of a suitably prepared high energy wave packet is 25%. The high
frequency dependence of the cross section is w^{-4/3}. However, smooth
geometries arbitrarily close to the singular one require a finite amount of
negative energy matter. The negative-mass Schwarzschild has a qualitatively
different resolution interpreted to be fully reflecting. These 4d results are
similar to the 2d black hole and are generalized to an arbitrary dimension d>4.Comment: 47 pages, 5 figures. v2: See end of introduction for an important
note adde
Premelting of Thin Wires
Recent work has raised considerable interest on the nature of thin metallic
wires. We have investigated the melting behavior of thin cylindrical Pb wires
with the axis along a (110) direction, using molecular dynamics and a
well-tested many-body potential. We find that---in analogy with cluster
melting---the melting temperature of a wire with radius is lower
than that of a bulk solid, , by . Surface melting
effects, with formation of a thin skin of highly diffusive atoms at the wire
surface, is observed. The diffusivity is lower where the wire surface has a
flat, local (111) orientation, and higher at (110) and (100) rounded areas. The
possible relevance to recent results on non-rupturing thin necks between an STM
tip and a warm surface is addressed.Comment: 10 pages, 4 postscript figures are appended, RevTeX, SISSA Ref.
131/94/CM/S
Graviton Resonances in E+ E- -> MU+ MU- at Linear Colliders with Beamstrahlung and ISR Effects
Electromagnetic radiation emitted by the colliding beams is expected to play
an important role at the next generation of high energy e^+ e^- linear
collider(s). Focusing on the simplest process e+e- -> mu+ mu-, we show that
radiative effects like initial state radiation (ISR) and beamstrahlung can lead
to greatly-enhanced signals for resonant graviton modes of the Randall-Sundrum
model.Comment: 20 pages Latex, 7 eps figure
How spiking neurons give rise to a temporal-feature map
A temporal-feature map is a topographic neuronal representation of temporal attributes of phenomena or objects that occur in the outside world. We explain the evolution of such maps by means of a spike-based Hebbian learning rule in conjunction with a presynaptically unspecific contribution in that, if a synapse changes, then all other synapses connected to the same axon change by a small fraction as well. The learning equation is solved for the case of an array of Poisson neurons. We discuss the evolution of a temporal-feature map and the synchronization of the single cellsâ synaptic structures, in dependence upon the strength of presynaptic unspecific learning. We also give an upper bound for the magnitude of the presynaptic interaction by estimating its impact on the noise level of synaptic growth. Finally, we compare the results with those obtained from a learning equation for nonlinear neurons and show that synaptic structure formation may profit
from the nonlinearity
The Approach to Ergodicity in Monte Carlo Simulations
The approach to the ergodic limit in Monte Carlo simulations is studied using
both analytic and numerical methods. With the help of a stochastic model, a
metric is defined that enables the examination of a simulation in both the
ergodic and non-ergodic regimes. In the non-ergodic regime, the model implies
how the simulation is expected to approach ergodic behavior analytically, and
the analytically inferred decay law of the metric allows the monitoring of the
onset of ergodic behavior. The metric is related to previously defined measures
developed for molecular dynamics simulations, and the metric enables the
comparison of the relative efficiencies of different Monte Carlo schemes.
Applications to Lennard-Jones 13-particle clusters are shown to match the model
for Metropolis, J-walking and parallel tempering based approaches. The relative
efficiencies of these three Monte Carlo approaches are compared, and the decay
law is shown to be useful in determining needed high temperature parameters in
parallel tempering and J-walking studies of atomic clusters.Comment: 17 Pages, 7 Figure
Signature of small rings in the Raman spectra of normal and compressed amorphous silica: A combined classical and ab initio study
We calculate the parallel (VV) and perpendicular (VH) polarized Raman spectra
of amorphous silica. Model SiO2 glasses, uncompressed and compressed, were
generated by a combination of classical and ab initio molecular-dynamics
simulations and their dynamical matrices were computed within the framework of
the density functional theory. The Raman scattering intensities were determined
using the bond-polarizability model and a good agreement with experimental
spectra was found. We confirm that the modes associated to the fourfold and
threefold rings produce most of the Raman intensity of the D1 and D2 peaks,
respectively, in the VV Raman spectra. Modifications of the Raman spectra upon
compression are found to be in agreement with experimental data. We show that
the modes associated to the fourfold rings still exist upon compression but do
not produce a strong Raman intensity, whereas the ones associated to the
threefold rings do. This result strongly suggests that the area under the D1
and D2 peaks is not directly proportional to the concentration of small rings
in amorphous SiO2.Comment: 21 pages, 8 figures. Phys. Rev. B, in pres
Cold Plasma Wave Analysis in Magneto-Rotational Fluids
This paper is devoted to investigate the cold plasma wave properties. The
analysis has been restricted to the neighborhood of the pair production region
of the Kerr magnetosphere. The Fourier analyzed general relativistic
magnetohydrodynamical equations are dealt under special circumstances and
dispersion relations are obtained. We find the -component of the complex
wave vector numerically. The corresponding components of the propagation
vector, attenuation vector, phase and group velocities are shown in graphs. The
direction and dispersion of waves are investigated.Comment: 22 pages, 18 figures, accepted for publication in Astrophys. Space
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