2,932 research outputs found
REDUCING TRANSPORTATION DAMAGE TO GRAPES AND STRAWBERRIES
In-transit vibration damage to grapes and strawberries results in reduced quality for the consumer and reduced profits for the produce industry. To solve this problem, the first step is to determine which vibrational frequencies are causing the damage. In various tests, grapes and strawberries were subjected to different frequencies at constant force levels. The effects of the vibration treatments were evaluated on the basis of grading, color analysis, firmness, respiration rate and ethylene production rate. The critical frequency was found to lie between 7.5 and 10 Hertz for both commodities. Color change and respiration rate were shown to be good indicators of damage in grapes. Strawberries did not show a significant effect due to color. Firmness was not affected by vibration in either commodity.Agribusiness,
Magnetic properties of interacting, disordered electron systems in d=2 dimensions
We compute the magnetic susceptibilities of interacting electrons in the
presence of disorder on a two-dimensional square lattice by means of quantum
Monte Carlo simulations. Clear evidence is found that at sufficiently low
temperatures disorder can lead to an enhancement of the ferromagnetic
susceptibility. We show that it is not related to the transition from a metal
to an Anderson insulator in two dimensions, but is a rather general low
temperature property of interacting, disordered electronic systems.Comment: 5 pages, 6 figure
NLO QCD corrections to processes with multiple electroweak bosons
The VBFNLO program package is a collection of Monte Carlo programs for the
calculation of NLO QCD corrections to vector boson fusion cross sections,
double and triple vector boson production, or the production of two electroweak
bosons in association with an additional jet. An overview is given of the
processes and features implemented in VBFNLO. WWgamma and Wgamma jet production
are discussed as examples.Comment: 6 pages, 3 figures; talk given at RADCOR 2009 - 9th International
Symposium on Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), October 25 - 30 2009, Ascona, Switzerlan
Failure time and microcrack nucleation
The failure time of samples of heterogeneous materials (wood, fiberglass) is
studied as a function of the applied stress. It is shown that in these
materials the failure time is predicted with a good accuracy by a model of
microcrack nucleation proposed by Pomeau. It is also shown that the crack
growth process presents critical features when the failure time is approached.Comment: 13 pages, 4 figures, submitted to Europhysics Letter
Entropy Maximization in the Presence of Higher-Curvature Interactions
Within the context of the entropic principle, we consider the entropy of
supersymmetric black holes in N=2 supergravity theories in four dimensions with
higher-curvature interactions, and we discuss its maximization at points in
moduli space at which an excess of hypermultiplets becomes massless. We find
that the gravitational coupling function F^(1) enhances the maximization at
these points in moduli space. In principle, this enhancement may be modified by
the contribution from higher F^(g)-couplings. We show that this is indeed the
case for the resolved conifold by resorting to the non-perturbative expression
for the topological free energy.Comment: 22 pages, 8 figures, AMS-LaTe
The Discovery of an Embedded Cluster of High-Mass Stars Near SGR 1900+14
Deep I-band imaging to approximately I = 26.5 of the soft gamma-ray repeater
SGR 1900+14 region has revealed a compact cluster of massive stars located only
a few arcseconds from the fading radio source thought to be the location of the
SGR (Frail, Kulkarni, & Bloom 1999). This cluster was previously hidden in the
glare of the pair of M5 supergiant stars (whose light was removed by PSF
subtraction) proposed by Vrba et al. (1996) as likely associated with the SGR
1900+14. The cluster has at least 13 members within a cluster radius of
approximately 0.6 pc, based on an estimated distance of 12-15 kpc. It is
remarkably similar to a cluster found associated with SGR 1806-20 (Fuchs et al.
1999). That similar clusters have now been found at or near the positions of
the two best-studied SGRs suggests that young neutron stars, thought to be
responsible for the SGR phenomenon, have their origins in proximate compact
clusters of massive stars.Comment: 5 pages, 3 figures, accepted Astrophysical Journal Letter
The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Nucleon
The Gerasimov-Drell-Hearn sum rule is one of several dispersive sum rules
that connect the Compton scattering amplitudes to the inclusive photoproduction
cross sections of the target under investigation. Being based on such universal
principles as causality, unitarity, and gauge invariance, these sum rules
provide a unique testing ground to study the internal degrees of freedom that
hold the system together. The present article reviews these sum rules for the
spin-dependent cross sections of the nucleon by presenting an overview of
recent experiments and theoretical approaches. The generalization from real to
virtual photons provides a microscope of variable resolution: At small
virtuality of the photon, the data sample information about the long range
phenomena, which are described by effective degrees of freedom (Goldstone
bosons and collective resonances), whereas the primary degrees of freedom
(quarks and gluons) become visible at the larger virtualities. Through a rich
body of new data and several theoretical developments, a unified picture of
virtual Compton scattering emerges, which ranges from coherent to incoherent
processes, and from the generalized spin polarizabilities on the low-energy
side to higher twist effects in deep inelastic lepton scattering.Comment: 32 pages, 19 figures, review articl
Why do ultrasoft repulsive particles cluster and crystallize? Analytical results from density functional theory
We demonstrate the accuracy of the hypernetted chain closure and of the
mean-field approximation for the calculation of the fluid-state properties of
systems interacting by means of bounded and positive-definite pair potentials
with oscillating Fourier transforms. Subsequently, we prove the validity of a
bilinear, random-phase density functional for arbitrary inhomogeneous phases of
the same systems. On the basis of this functional, we calculate analytically
the freezing parameters of the latter. We demonstrate explicitly that the
stable crystals feature a lattice constant that is independent of density and
whose value is dictated by the position of the negative minimum of the Fourier
transform of the pair potential. This property is equivalent with the existence
of clusters, whose population scales proportionally to the density. We
establish that regardless of the form of the interaction potential and of the
location on the freezing line, all cluster crystals have a universal Lindemann
ratio L = 0.189 at freezing. We further make an explicit link between the
aforementioned density functional and the harmonic theory of crystals. This
allows us to establish an equivalence between the emergence of clusters and the
existence of negative Fourier components of the interaction potential. Finally,
we make a connection between the class of models at hand and the system of
infinite-dimensional hard spheres, when the limits of interaction steepness and
space dimension are both taken to infinity in a particularly described fashion.Comment: 19 pages, 5 figures, submitted to J. Chem. Phys; new version: minor
changes in structure of pape
Molecular binding in interacting quantum walks
We show that the presence of an interaction in the quantum walk of two atoms leads to the formation of a stable compound, a molecular state. The wave function of the molecule decays exponentially in the relative position of the two atoms; hence it constitutes a true bound state. Furthermore, for a certain class of interactions, we develop an effective theory and find that the dynamics of the molecule is described by a quantum walk in its own right. We propose a setup for the experimental realization as well as sketch the possibility to observe quasi-particle effects in quantum many-body systems.DFG/FOR/635European Commission/CORNEREuropean Commission/COQUITEuropean Commission/AQUTENRW Nachwuchsgruppe âQuantenkontrolle auf der NanoskalaâAlexander von Humboldt Foundatio
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