9,165 research outputs found
The pion form factor: Sudakov suppressions and intrinsic transverse momentum
It is demonstrated that any attempt to calculate the perturbative QCD
contribution to the pion form factor requires the inclusion of intrinsic
transverse momentum besides Sudakov form factors. For momentum transfers of the
order of a few GeV the intrinsic transverse momentum leads to a substantial
suppression of the perturbative QCD contribution.Comment: LaTeX, 12 pages, 3 figures included with epsf-style option
(postscript files added as uuencoded tar-compressed file), CERN-TH.6900, WU-B
93-1
Quantum Horn's lemma, finite heat baths, and the third law of thermodynamics
Interactions of quantum systems with their environment play a crucial role in
resource-theoretic approaches to thermodynamics in the microscopic regime.
Here, we analyze the possible state transitions in the presence of "small" heat
baths of bounded dimension and energy. We show that for operations on quantum
systems with fully degenerate Hamiltonian (noisy operations), all possible
state transitions can be realized exactly with a bath that is of the same size
as the system or smaller, which proves a quantum version of Horn's lemma as
conjectured by Bengtsson and Zyczkowski. On the other hand, if the system's
Hamiltonian is not fully degenerate (thermal operations), we show that some
possible transitions can only be performed with a heat bath that is unbounded
in size and energy, which is an instance of the third law of thermodynamics. In
both cases, we prove that quantum operations yield an advantage over classical
ones for any given finite heat bath, by allowing a larger and more physically
realistic set of state transitions.Comment: 15+4 pages, 6 figures. Version accepted for publication in Quantu
Global detection and analysis of coastline associated rainfall using an objective pattern recognition technique
Coastally associated rainfall is a common feature especially in tropical and
subtropical regions. However, it has been difficult to quantify the
contribution of coastal rainfall features to the overall local rainfall. We
develop a novel technique to objectively identify precipitation associated with
land-sea interaction and apply it to satellite based rainfall estimates. The
Maritime Continent, the Bight of Panama, Madagascar and the Mediterranean are
found to be regions where land-sea interactions plays a crucial role in the
formation of precipitation. In these regions 40% to 60% of the total
rainfall can be related to coastline effects. Due to its importance for the
climate system, the Maritime Continent is a particular region of interest with
high overall amounts of rainfall and large fractions resulting from land-sea
interactions throughout the year. To demonstrate the utility of our
identification method we investigate the influence of several modes of
variability, such as the Madden-Julian-Oscillation and the El Ni\~no Southern
Oscillation, on coastal rainfall behavior. The results suggest that during
large scale suppressed convective conditions coastal effects tend modulate the
rainfall over the Maritime Continent leading to enhanced rainfall over land
regions compared to the surrounding oceans. We propose that the novel objective
dataset of coastally influenced precipitation can be used in a variety of ways,
such as to inform cumulus parametrization or as an additional tool for
evaluating the simulation of coastal precipitation within weather and climate
models
Simulation of Cu-Mg metallic glass: Thermodynamics and Structure
We have obtained effective medium theory (EMT) interatomic potential
parameters suitable for studying Cu-Mg metallic glasses. We present
thermodynamic and structural results from simulations of such glasses over a
range of compositions. We have produced low-temperature configurations by
cooling from the melt at as slow a rate as practical, using constant
temperature and pressure molecular dynamics. During the cooling process we have
carried out thermodynamic analyses based on the temperature dependence of the
enthalpy and its derivative, the specific heat, from which the glass transition
temperature may be determined. We have also carried out structural analyses
using the radial distribution function (RDF) and common neighbor analysis
(CNA). Our analysis suggests that the splitting of the second peak, commonly
associated with metallic glasses, in fact has little to do with the glass
transition itself, but is simply a consequence of the narrowing of peaks
associated with structural features present in the liquid state. In fact the
splitting temperature for the Cu-Cu RDF is well above . The CNA also
highlights a strong similarity between the structure of the intermetallic
alloys and the amorphous alloys of similar composition. We have also
investigated the diffusivity in the supercooled regime. Its temperature
dependence indicates fragile-liquid behavior, typical of binary metallic
glasses. On the other hand, the relatively low specific heat jump of around
indicates apparent strong-liquid behavior, but this can
be explained by the width of the transition due to the high cooling rates.Comment: 12 pages (revtex, two-column), 12 figures, submitted to Phys. Rev.
Thermodynamics of explosions
We present our first attempts to formulate a thermodynamics-like description
of explosions. The motivation is partly a fundamental interest in
non-equilibrium statistical physics, partly the resemblance of an explosion to
the late stages of a heavy-ion collision. We perform numerical simulations on a
microscopic model of interacting billiard-ball like particles, and we analyse
the results of such simulations trying to identify collective variables
describing the degree of equilibrium during the explosion.Comment: 6 pages. Talk presented at "Bologna 2000 - Structure of the nucleus"
international conference, May 29 - June 3, Bologna, Italy. Shortened version,
to appear in the Proceeding
The Overlap Representation of Skewed Quark and Gluon Distributions
Within the framework of light-cone quantisation we derive the complete and
exact overlap representation of skewed parton distributions for unpolarised and
polarised quarks and gluons. Symmetry properties and phenomenological
applications are discussed.Comment: LaTex, 36 pages. v2: incorrect paper attached originally. v3: erratum
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