55,831 research outputs found
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
Symmetric Diblock Copolymers in Thin Films (I): Phase stability in Self-Consistent Field Calculations and Monte Carlo Simulations
We investigate the phase behavior of symmetric AB diblock copolymers confined
into a thin film. The film boundaries are parallel, impenetrable and attract
the A component of the diblock copolymer. Using a self-consistent field
technique [M.W. Matsen, J.Chem.Phys. {\bf 106}, 7781 (1997)], we study the
ordered phases as a function of incompatibility and film thickness in
the framework of the Gaussian chain model. For large film thickness and small
incompatibility, we find first order transitions between phases with different
number of lamellae which are parallel oriented to the film boundaries. At high
incompatibility or small film thickness, transitions between parallel oriented
and perpendicular oriented lamellae occur. We compare the self-consistent field
calculations to Monte Carlo simulations of the bond fluctuation model for chain
length N=32. In the simulations we quench several systems from to
and monitor the morphology into which the diblock copolymers
assemble. Three film thicknesses are investigated, corresponding to parallel
oriented lamellae with 2 and 4 interfaces and a perpendicular oriented
morphology. Good agreement between self-consistent field calculations and Monte
Carlo simulations is found.Comment: to appear in J.Chem.Phy
Equation of state and critical behavior of polymer models: A quantitative comparison between Wertheim's thermodynamic perturbation theory and computer simulations
We present an application of Wertheim's Thermodynamic Perturbation Theory
(TPT1) to a simple coarse grained model made of flexibly bonded Lennard-Jones
monomers. We use both the Reference Hyper-Netted-Chain (RHNC) and Mean
Spherical approximation (MSA) integral equation theories to describe the
properties of the reference fluid. The equation of state, the density
dependence of the excess chemical potential, and the critical points of the
liquid--vapor transition are compared with simulation results and good
agreement is found. The RHNC version is somewhat more accurate, while the MSA
version has the advantage of being almost analytic. We analyze the scaling
behavior of the critical point of chain fluids according to TPT1 and find it to
reproduce the mean field exponents: The critical monomer density is predicted
to vanish as upon increasing the chain length while the critical
temperature is predicted to reach an asymptotic finite temperature that is
attained as . The predicted asymptotic finite critical temperature
obtained from the RHNC and MSA versions of TPT1 is found to be in good
agreement with the point of our polymer model as obtained from the
temperature dependence of the single chain conformations.Comment: to appear in J.Chem.Phy
Entropic competition in polymeric systems under geometrical confinement
Using molecular dynamics simulation, we investigate the effect of confinement
on a system that comprises several stiff segmented polymer chains where each
chain has similar segments, but length and stiffness of the segments vary among
the chains which makes the system inhomogeneous. The translational and
orientational entropy loss due to the confinement plays a crucial role in
organizing the chains which can be considered as an entropy-driven segregation
mechanism to differentiate the components of the system. Due to the
inhomogeneity, both weak and strong confinement regimes show the competition in
the system and we see segregation of chains as the confining volume is
decreased. In the case of strong spherical confinement, a chain at the
periphery shows higher angular mobility than other chains, despite being more
radially constrained.Comment: 16 pages, 11 figure
Density fields for branching, stiff networks in rigid confining regions
We develop a formalism to describe the equilibrium distributions for segments
of confined branched networks consisting of stiff filaments. This is applicable
to certain situations of cytoskeleton in cells, such as for example actin
filaments with branching due to the Arp2/3 complex. We develop a grand ensemble
formalism that enables the computation of segment density and polarisation
profiles within the confines of the cell. This is expressed in terms of the
solution to nonlinear integral equations for auxiliary functions. We find three
specific classes of behaviour depending on filament length, degree of branching
and the ratio of persistence length to the dimensions of the geometry. Our
method allows a numerical approach for semi-flexible filaments that are
networked.Comment: 15 pages, revise
Driving steady-state visual evoked potentials at arbitrary frequencies using temporal interpolation of stimulus presentation
Date of Acceptance: 29/10/2015 We thank Renate Zahn for help with data collection. This work was supported by Deutsche Forschungsgemeinschaft (AN 841/1-1, MU 972/20-1). We would like to thank A. Trujillo-Ortiz, R. Hernandez-Walls, A. Castro-Perez and K. BarbaRojo (Universidad Autonoma de Baja California) for making Matlab code for non-sphericity corrections freely available.Peer reviewedPublisher PD
Fuzzy audio similarity measures based on spectrum histograms and fluctuation patterns
Spectrum histograms and fluctuation patterns are representations of audio fragments. By comparing these representations, we can determine the similarity between the corresponding fragments. Traditionally, this is done using the Euclidian distance. We propose fuzzy similarity measures as an alternative. First we introduce some well-known fuzzy similarity measures, together with certain properties that can be desirable or useful in practice. In particular we present several forms of restrictability, which allow to reduce the computation time in practical applications. Next, we show that fuzzy similarity measures can be used to compare spectrum histograms and fluctuation patterns. Finally, we describe some experimental observations for this fuzzy approach of constructing audio similarity measures
A model for the phase separation controlled by doping and the internal chemical pressure in different cuprate superconductors
In the framework of a two-band model, we study the phase separation regime of
different kinds of strongly correlated charge carriers as a function of the
energy splitting between the two sets of bands. The narrow (wide) band
simulates the more localized (more delocalized) type of charge carriers. By
assuming that the internal chemical pressure on the CuO layer due to
interlayer mismatch controls the energy splitting between the two sets of
states, the theoretical predictions are able to reproduce the regime of phase
separation at doping higher than 1/8 in the experimental pressure-doping-
phase diagram of cuprates at large microstrain as it appears in overoxygenated
LaCuO.Comment: 8 pages, 5 figures, submitted to Phys. Rev.
An event-based architecture for solving constraint satisfaction problems
Constraint satisfaction problems (CSPs) are typically solved using
conventional von Neumann computing architectures. However, these architectures
do not reflect the distributed nature of many of these problems and are thus
ill-suited to solving them. In this paper we present a hybrid analog/digital
hardware architecture specifically designed to solve such problems. We cast
CSPs as networks of stereotyped multi-stable oscillatory elements that
communicate using digital pulses, or events. The oscillatory elements are
implemented using analog non-stochastic circuits. The non-repeating phase
relations among the oscillatory elements drive the exploration of the solution
space. We show that this hardware architecture can yield state-of-the-art
performance on a number of CSPs under reasonable assumptions on the
implementation. We present measurements from a prototype electronic chip to
demonstrate that a physical implementation of the proposed architecture is
robust to practical non-idealities and to validate the theory proposed.Comment: First two authors contributed equally to this wor
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