17,861 research outputs found
Generalized Parton Distributions, Deeply Virtual Compton Scattering and TMDs
Parton distributions in impact parameter space, which are obtained by Fourier
transforming GPDs, exhibit a significant deviation from axial symmetry when
target and/or quark are transversely polarized. In combination with the final
state interactions, this transverse deformation provides a natural mechanism
for naive-T odd transverse single-spin asymmetries in semi-inclusive DIS. The
deformation of PDFs in impact parameter space can also be related to the
transverse force acting on the active quark in polarized DIS at higher twist.Comment: 4 pages, invited talk at CIPANP0
Influence of friction on granular segregation
Vertical shaking of a mixture of small and large beads can lead to
segregation where the large beads either accumulate at the top of the sample,
the so called Brazil Nut effect (BNE), or at the bottom, the Reverse Brazil Nut
effect (RBNE). Here we demonstrate experimentally a sharp transition from the
RBNE to the BNE when the particle coefficient of friction increases due to
aging of the particles. This result can be explained by the two competing
mechanisms of buoyancy and sidewall-driven convection, where the latter is
assumed to grow in strength with increasing friction.Comment: 3 pages, 2 figure
Non-equilibrium cluster-perturbation theory
The cluster perturbation theory (CPT) is one of the simplest but systematic
quantum cluster approaches to lattice models of strongly correlated electrons
with local interactions. By treating the inter-cluster potential, in addition
to the interactions, as a perturbation, it is shown that the CPT can be
reformulated as an all-order re-summation of diagrams within standard
weak-coupling perturbation theory where vertex corrections are neglected. This
reformulation is shown to allow for a straightforward generalization of the CPT
to the general non-equilibrium case using contour-ordered Green's functions.
Solving the resulting generalized CPT equation on the discretized
Keldysh-Matsubara time contour, the transient dynamics of an essentially
arbitrary initial pure or mixed state can be traced. In this way, the
time-dependent expectation values of one-particle observables can be obtained
within an approximation that neglects spatial correlations beyond the extension
of the reference cluster. The necessary computational effort is very moderate.
A detailed discussion and simple test calculations are presented to demonstrate
the strengths and the shortcomings of the proposed approach. The
non-equilibrium CPT is systematic and is controlled in principle by the inverse
cluster size. It interpolates between the non-interacting and the atomic or
decoupled-cluster limit which are recovered exactly and is found to predict the
correct dynamics at very short times in a general non-trivial case. The effects
of initial-state correlations on the subsequent dynamics and the necessity to
extend the Keldysh contour by the imaginary Matsubara branch are analyzed
carefully and demonstrated numerically. It is furthermore shown that the
approach can describe the dissipation of spin and charge to an uncorrelated
bath with an essentially arbitrary number of degrees of freedom.Comment: 14 pages, 9 figure
Transport of toroidal magnetic field by the meridional flow at the base of the solar convection zone
In this paper we discuss the transport of toroidal magnetic field by a weak
meridional flow at the base of the convection zone. We utilize the differential
rotation and meridional flow model developed by Rempel and incorporate feedback
of a purely toroidal magnetic field in two ways: directly through the Lorentz
force (magnetic tension) and indirectly through quenching of the turbulent
viscosity, which affects the parametrized turbulent angular momentum transport
in the model. In the case of direct Lorentz force feedback we find that a
meridional flow with an amplitude of around 2 m/s can transport a magnetic
field with a strength of 20 to 30 kG. Quenching of turbulent viscosity leads to
deflection of the meridional flow from the magnetized region and a significant
reduction of the transport velocity if the magnetic field is above
equipartition strength.Comment: 8 pages, 6 figure
Reply to [arXiv:1201.5347] "Comment on 'Vortex-assisted photon counts and their magnetic field dependence in single-photon superconducting detectors'"
We argue that cutoff in the London model cannot be settled without use of the
microscopic theory
Adsorption of Xe atoms on metal surfaces: New insights from first-principles calculations
The adsorption of rare gases on metal surfaces serve as the paradigm of weak
adsorption where it is typically assumed that the adsorbate occupies maximally
coordinated hollow sites. Density-functional theory calculations using the
full-potential linearized augmented plane wave method for Xe adatoms on
Mg(0001), Al(111), Ti(0001), Cu(111), Pd(111), and Pt(111), show, however, that
Xe prefers low-coordination on-top sites in all cases. We identify the
importance of polarization and a site-dependent Pauli repulsion in actuating
the site preference and the principle nature of the rare-gas atom--metal
surface interaction.Comment: 5 pages including 4 figure files. Related publications can be found
at http://www.fhi-berlin.mpg.de/th/paper.htm
A NONLINEAR MODEL OF INFORMATION AND COORDINATION IN HOG PRODUCTION: TESTING THE COASIAN-FOWLERIAN DYNAMIC HYPOTHESES
The pig-cycle 'explanation' expunded by Coase and Fowler followed a well-integrated economic logic and provides tremendous insight into our understanding of commodity cycles. The paper presents a simulation model that replicates all of Coase and Fowler's results and tests its robustness with an application to U.S. hog production.Livestock Production/Industries, Research Methods/ Statistical Methods,
Leaf beetles are ant-nest beetles: the curious life of the juvenile stages of case-bearers (Coleoptera, Chrysomelidae, Cryptocephalinae)
Although some species of Cryptocephalinae (Coleoptera: Chrysomelidae) have been documented with ants (Hymenoptera: Formicidae) for almost 200 years, information on this association is fragmentary. This contribution synthesizes extant literature and analysizes the data for biological patterns. Myrmecophily is more common in the tribe Clytrini than in Cryptocephalini, but not documented for Fulcidacini or the closely-related Lamprosomatinae. Myrmecophilous cryptocephalines (34 species in 14 genera) primarily live among formicine and myrmecines ants as hosts. These two ant lineages are putative sister-groups, with their root-node dated to between 77–90 mya. In the New World tropics, the relatively recent radiation of ants from moist forests to more xeric ecosystems might have propelled the association of cryptocephalines and ant nests. Literature records suggest that the defensive behavioral profile or chemical profile (or both) of these ants has been exploited by cryptocephalines. Another pattern appears to be that specialized natural enemies, especially parasitoid Hymenoptera, exploit cryptocephaline beetles inside the ant nests. With the extant data at hand, based on the minimum age of a fossil larva dated to 45 mya, we can infer that the origin of cryptocephaline myrmecophily could have arisen within the Upper Cretaceous or later. It remains unknown how many times myrmecophily has appeared, or how old is the behavior. This uncertainty is compounded by incongruent hypotheses about the origins of Chrysomelidae and angiosperm-associated lineages of cryptocephalines. Living with ants offers multiple advantages that might have aided the colonization of xeric environments by some cryptocephaline species.Fil: Agrain, Federico Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Buffington, Matthew L.. National Museum of Natural History; Estados UnidosFil: Chaboo, Caroline S.. University of Kansas; Estados UnidosFil: Chamorro, Maria L.. National Museum of Natural History; Estados UnidosFil: Schöller, Matthias. Humboldt-Universität zu Berlin; Alemani
- …