Fitting DVCS at NLO and beyond

We outline the twist-two analysis of deeply virtual Compton scattering (DVCS)within the conformal partial wave expansion of the amplitude, represented as a Mellin--Barnes integral. The complete next-to-leading order results, including evolution, are obtained in the MS and a conformal factorization scheme. Within the latter, exploiting conformal symmetry, the radiative corrections are evaluated up to next-to-next-to-leading order. Using a new proposed parameterization for GPDs, we study the convergence of perturbation theory and demonstrate for H1 and ZEUS measurements that our formalism is suitable for a fitting procedure of DVCS observables. We comment on a recent claim of a breakdown of collinear factorization and show that a Regge-inspired Q^2 scaling law is ruled out by small x_Bj DVCS data.Comment: 15 pages, 4 figure

Exclusive electroproduction revisited: treating kinematical effects

Generalized parton distributions of the nucleon are accessed via exclusive leptoproduction of the real photon. While earlier analytical considerations of phenomenological observables were restricted to twist-three accuracy, i.e., taking into account only terms suppressed by a single power of the hard scale, in the present study we revisit this differential cross section within the helicity formalism and restore power-suppressed effects stemming from the process kinematics exactly. We restrict ourselves to the phenomenologically important case of lepton scattering off a longitudinally polarized nucleon, where the photon flips its helicity at most by one unit.Comment: 22 pages, 1 figur

Visual adaptation to convexity in macaque area V4

Aftereffects are perceptual illusions caused by visual adaptation to one or more stimulus attribute, such as orientation, motion, or shape. Neurophysiological studies seeking to understand the basis of visual adaptation have observed firing rate reduction and changes in tuning of stimulus-selective neurons following periods of prolonged visual stimulation. In the domain of shape, recent psychophysical work has shown that adaptation to a convex pattern induces a subsequently seen rectangle to appear slightly concave. In the present study, we investigate the possible contribution of V4 neurons of rhesus monkeys, which are thought to be involved in the coding of convexity, to shape-specific adaptation. Visually responsive neurons were monitored during the brief presentation of simple shapes varying in their convexity level. Each test presentation was preceded by either a blank period or several seconds of adaptation to a convex or concave stimulus, presented in two different sizes. Adaptation consistently shifted the tuning of neurons away from the convex or concave adapter, including shifting response to the neutral rectangle in the direction of the opposite convexity. This repulsive shift resembled the known perceptual distortion associated with adaptation to such stimuli. In addition, adaptation caused a nonspecific response decrease, as well as a specific decrease for repeated stimuli. The latter effects were observed whether or not the adapting and test stimuli matched closely in their size. Taken together, these results provide evidence for shape-specific adaptation of neurons in area V4, which may contribute to the perception of the convexity aftereffect

h/2eh/2e--Oscillations for Correlated Electron Pairs in Disordered Mesoscopic Rings

The full spectrum of two interacting electrons in a disordered mesoscopic one--dimensional ring threaded by a magnetic flux is calculated numerically. For ring sizes far exceeding the one--particle localization length $L_1$ we find several $h/2e$--periodic states whose eigenfunctions exhibit a pairing effect. This represents the first direct observation of interaction--assisted coherent pair propagation, the pair being delocalized on the scale of the whole ring.Comment: 4 pages, uuencoded PostScript, containing 5 figures

Technical note: Absorption aerosol optical depth components from AERONET observations of mixed dust plumes

© Author(s) 2019.Absorption aerosol optical depth (AAOD) as obtained from sun–sky photometer measurements provides a measure of the light-absorbing properties of the columnar aerosol loading. However, it is not an unambiguous aerosol-type-specific parameter, particularly if several types of absorbing aerosols, for instance black carbon (BC) and mineral dust, are present in a mixed aerosol plume. The contribution of mineral dust to total aerosol light absorption is particularly important at UV wavelengths. In this study we refine a lidar-based technique applied to the separation of dust and non-dust aerosol types for the use with Aerosol Robotic Network (AERONET) direct sun and inversion products. We extend the methodology to retrieve AAOD related to non-dust aerosol (AAODnd) and BC (AAODBC). We test the method at selected AERONET sites that are frequently affected by aerosol plumes that contain a mixture of Saharan or Asian mineral dust and biomass-burning smoke or anthropogenic pollution, respectively. We find that aerosol optical depth (AOD) related to mineral dust as obtained with our methodology is frequently smaller than coarse-mode AOD. This suggests that the latter is not an ideal proxy for estimating the contribution of mineral dust to mixed dust plumes. We present the results of the AAODBC retrieval for the selected AERONET sites and compare them to coincident values provided in the Copernicus Atmosphere Monitoring System aerosol reanalysis.We find that modelled and AERONET AAODBC are most consistent for Asian sites or at Saharan sites with strong local anthropogenic sources.Peer reviewe

Chain length dependence of the polymer-solvent critical point parameters

We report grand canonical Monte Carlo simulations of the critical point properties of homopolymers within the Bond Fluctuation model. By employing Configurational Bias Monte Carlo methods, chain lengths of up to N=60 monomers could be studied. For each chain length investigated, the critical point parameters were determined by matching the ordering operator distribution function to its universal fixed-point Ising form. Histogram reweighting methods were employed to increase the efficiency of this procedure. The results indicate that the scaling of the critical temperature with chain length is relatively well described by Flory theory, i.e. \Theta-T_c\sim N^{-0.5}. The critical volume fraction, on the other hand, was found to scale like \phi_c\sim N^{-0.37}, in clear disagreement with the Flory theory prediction \phi_c\sim N^{-0.5}, but in good agreement with experiment. Measurements of the chain length dependence of the end-to-end distance indicate that the chains are not collapsed at the critical point.Comment: 13 Pages Revtex, 9 epsf embedded figs. gzipped tar file. To appear in J. Chem. Phy

Magnetic properties of Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals

Magnetic properties were studied for the high quality Al-free orthorhombic Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals (0<=x<=1.0) grown by the flux method. An indication on the interaction between the Pr and Cu(2) magnetic sublattices was found for Pr123. Different signs of magnetic anisotropy were established for the Pr and Gd ions at low temperatures. It was also shown that superconductivity reported by Zou et al. [Phys. Rev. Lett. 80 (1998) 1074] for Pr123 single crystals grown by TSZF method seems to be connected with partial substitution of Ba for the Pr-sites.Comment: 2 pages (LaTeX2e), 4 EPS figures, phbauth style file included. LT22 conference paper accepted to Physica

Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals

Magnetic properties of high-quality Al-free nonsuperconducting GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N clear indications of spin-flop transitions for H||c have been observed on magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic susceptibility (unexpected for Gd-based compounds) has been found above T_N.Comment: 2 pages, 3 figures; LT23 (Aug. 2002; Hiroshima), accepted to Physica