7,165 research outputs found
Generalized parton distributions in the deuteron
We introduce generalized quark and gluon distributions in the deuteron, which
can be measured in exclusive processes like deeply virtual Compton scattering
and meson electroproduction. We discuss the basic properties of these
distributions, and point out how they probe the interplay of nucleon and parton
degrees of freedom in the deuteron wave function
Critical adsorption near edges
Symmetry breaking surface fields give rise to nontrivial and long-ranged
order parameter profiles for critical systems such as fluids, alloys or magnets
confined to wedges. We discuss the properties of the corresponding universal
scaling functions of the order parameter profile and the two-point correlation
function and determine the critical exponents eta_parallel and
eta_perpendicular for the so-called normal transition.Comment: 22 pages, 5 figures, accepted for publication in PR
Critical adsorption on curved objects
A systematic fieldtheoretic description of critical adsorption on curved
objects such as spherical or rodlike colloidal particles immersed in a fluid
near criticality is presented. The temperature dependence of the corresponding
order parameter profiles and of the excess adsorption are calculated
explicitly. Critical adsorption on elongated rods is substantially more
pronounced than on spherical particles. It turns out that, within the context
of critical phenomena in confined geometries, critical adsorption on a
microscopically thin `needle' represents a distinct universality class of its
own. Under favorable conditions the results are relevant for the flocculation
of colloidal particles.Comment: 52 pages, 10 figure
Large-n expansion for m-axial Lifshitz points
The large-n expansion is developed for the study of critical behaviour of
d-dimensional systems at m-axial Lifshitz points with an arbitrary number m of
modulation axes. The leading non-trivial contributions of O(1/n) are derived
for the two independent correlation exponents \eta_{L2} and \eta_{L4}, and the
related anisotropy index \theta. The series coefficients of these 1/n
corrections are given for general values of m and d with 0<m<d and
2+m/2<d<4+m/2 in the form of integrals. For special values of m and d such as
(m,d)=(1,4), they can be computed analytically, but in general their evaluation
requires numerical means. The 1/n corrections are shown to reduce in the
appropriate limits to those of known large-n expansions for the case of
d-dimensional isotropic Lifshitz points and critical points, respectively, and
to be in conformity with available dimensionality expansions about the upper
and lower critical dimensions. Numerical results for the 1/n coefficients of
\eta_{L2}, \eta_{L4} and \theta are presented for the physically interesting
case of a uniaxial Lifshitz point in three dimensions, as well as for some
other choices of m and d. A universal coefficient associated with the
energy-density pair correlation function is calculated to leading order in 1/n
for general values of m and d.Comment: 28 pages, 3 figures. Submitted to: J. Phys. C: Solid State Phys.,
special issue dedicated to Lothar Schaefer on the occasion of his 60th
birthday. V2: References added along with corresponding modifications in the
text, corrected figure 3, corrected typo
Surface critical behavior of random systems at the ordinary transition
We calculate the surface critical exponents of the ordinary transition
occuring in semi-infinite, quenched dilute Ising-like systems. This is done by
applying the field theoretic approach directly in d=3 dimensions up to the
two-loop approximation, as well as in dimensions. At
we extend, up to the next-to-leading order, the previous
first-order results of the expansion by Ohno and Okabe
[Phys.Rev.B 46, 5917 (1992)]. In both cases the numerical estimates for surface
exponents are computed using Pade approximants extrapolating the perturbation
theory expansions. The obtained results indicate that the critical behavior of
semi-infinite systems with quenched bulk disorder is characterized by the new
set of surface critical exponents.Comment: 11 pages, 11 figure
Surface critical behavior of driven diffusive systems with open boundaries
Using field theoretic renormalization group methods we study the critical
behavior of a driven diffusive system near a boundary perpendicular to the
driving force. The boundary acts as a particle reservoir which is necessary to
maintain the critical particle density in the bulk. The scaling behavior of
correlation and response functions is governed by a new exponent eta_1 which is
related to the anomalous scaling dimension of the chemical potential of the
boundary. The new exponent and a universal amplitude ratio for the density
profile are calculated at first order in epsilon = 5-d. Some of our results are
checked by computer simulations.Comment: 10 pages ReVTeX, 6 figures include
The effect of harmonized emissions on aerosol properties in global models – an AeroCom experiment
The effects of unified aerosol sources on global aerosol fields simulated by different models are examined in this paper. We compare results from two AeroCom experiments, one with different (ExpA) and one with unified emissions, injection heights, and particle sizes at the source (ExpB). Surprisingly, harmonization of aerosol sources has only a small impact on the simulated diversity for aerosol burden, and consequently optical properties, as the results are largely controlled by model-specific transport, removal, chemistry (leading to the formation of secondary aerosols) and parameterizations of aerosol microphysics (e.g. the split between deposition pathways) and to a lesser extent on the spatial and temporal distributions of the (precursor) emissions.
The burdens of black carbon and especially sea salt become more coherent in ExpB only, because the large ExpA diversity for these two species was caused by few outliers. The experiment also indicated that despite prescribing emission fluxes and size distributions, ambiguities in the implementation in individual models can lead to substantial differences.
These results indicate the need for a better understanding of aerosol life cycles at process level (including spatial dispersal and interaction with meteorological parameters) in order to obtain more reliable results from global aerosol simulations. This is particularly important as such model results are used to assess the consequences of specific air pollution abatement strategies
Kinetics of Phase Separation in Thin Films: Simulations for the Diffusive Case
We study the diffusion-driven kinetics of phase separation of a symmetric
binary mixture (AB), confined in a thin-film geometry between two parallel
walls. We consider cases where (a) both walls preferentially attract the same
component (A), and (b) one wall attracts A and the other wall attracts B (with
the same strength). We focus on the interplay of phase separation and wetting
at the walls, which is referred to as {\it surface-directed spinodal
decomposition} (SDSD). The formation of SDSD waves at the two surfaces, with
wave-vectors oriented perpendicular to them, often results in a metastable
layered state (also referred to as ``stratified morphology''). This state is
reminiscent of the situation where the thin film is still in the one-phase
region but the surfaces are completely wet, and hence coated with thick wetting
layers. This metastable state decays by spinodal fluctuations and crosses over
to an asymptotic growth regime characterized by the lateral coarsening of
pancake-like domains. These pancakes may or may not be coated by precursors of
wetting layers. We use Langevin simulations to study this crossover and the
growth kinetics in the asymptotic coarsening regime.Comment: 39 pages, 19 figures, submitted to Phys.Rev.
Angle-resolved photoelectron spectrometry studies of the autoionization of the 2s22p 2P triply excited state of atomic lithium: experimental results and R-matrix calculations
We have measured the angle-resolved energy dependence of the electrons emitted over the energy range of the triply excited 2s22p2P lithium resonance using synchrotron radiation. We have also calculated the behavior of the angular distribution parameter β using the R-matrix approximation. Experimental and theoretical results are in good agreement and show deep minima in the 1s2p1,3P ionic channels. The energy at which the minima occur does not coincide with the resonance energy, but is shifted towards higher energy
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