1,321 research outputs found
Thermal-Mechanical Properties of Polyurethane-Clay Shape Memory Polymer Nanocomposites
Shape memory nanocomposites of polyurethane (PU)-clay were fabricated by melt mixing of PU and nano-clay. Based on nano-indentation and microhardness tests, the strength of the nanocomposites increased dramatically as a function of clay content, which is attributed to the enhanced nanoclayâpolymer interactions. Thermal mechanical experiments demonstrated good mechanical and shape memory effects of the nanocomposites. Full shape memory recovery was displayed by both the pure PU and PU-clay nanocomposites.
A progressive refinement approach for the visualisation of implicit surfaces
Visualising implicit surfaces with the ray casting method is a slow procedure. The design cycle of a new implicit surface is, therefore, fraught with long latency times as a user must wait for the surface to be rendered before being able to decide what changes should be introduced in the next iteration. In this paper, we present an attempt at reducing the design cycle of an implicit surface modeler by introducing a progressive refinement rendering approach to the visualisation of implicit surfaces. This progressive refinement renderer provides a quick previewing facility. It first displays a low quality estimate of what the final rendering is going to be and, as the computation progresses, increases the quality of this estimate at a steady rate. The progressive refinement algorithm is based on the adaptive subdivision of the viewing frustrum into smaller cells. An estimate for the variation of the implicit function inside each cell is obtained with an affine arithmetic range estimation technique. Overall, we show that our progressive refinement approach not only provides the user with visual feedback as the rendering advances but is also capable of completing the image faster than a conventional implicit surface rendering algorithm based on ray casting
Jet broadening in deeply inelastic scattering
In deeply inelastic lepton-nucleus scattering (DIS), the average jet
transverse momentum is broadened because of the multiple scattering in the
nuclear medium. The size of jet broadening is proportional to the multi-parton
correlation functions inside nuclei. We show that at leading order, jet
broadening in DIS and nulcear enhancement in di-jet momentum imbalance and
Drell-Yan share the same four-parton correlation functions. We
argue that jet broadening in DIS provide an indenpendent measurement of the
four-parton correlation functions and a test of QCD treatment of multiple
scattering.Comment: Latex, 18 pages, five figures; a few typos were correcte
Systematic model behavior of adsorption on flat surfaces
A low density film on a flat surface is described by an expansion involving
the first four virial coefficients. The first coefficient (alone) yields the
Henry's law regime, while the next three correct for the effects of
interactions. The results permit exploration of the idea of universal
adsorption behavior, which is compared with experimental data for a number of
systems
Study of the , , and in the radiative decays
In this paper we present an approach to study the radiative decay modes of
the into a photon and one of the tensor mesons ,
, as well as the scalar ones and .
Especially we compare predictions that emerge from a scheme where the states
appear dynamically in the solution of vector meson--vector meson scattering
amplitudes to those from a (admittedly naive) quark model. We provide evidence
that it might be possible to distinguish amongst the two scenarios, once
improved data are available.Comment: The large Nc argument improved; version published in EPJA
Heavy quark distribution functions in heavy baryons
Using the Bethe-Salpeter (BS) equations for heavy baryons ÎQ, ÎŁQ, ÎQ and ΩQ (Q=b or c), which were established in previous work, we calculate the heavy quark distribution functions in these baryons. The numerical results indicate that these distribution functions have an obvious peak at some fraction α0 of the baryonâs light-cone âplusâ momentum component carried by the heavy quark, and that as mQ becomes heavier this peak becomes sharper and closer to 1. The dependence of the distribution functions on various input parameters in the BS model is also discussed. The results are seen to be qualitatively similar to an existing phenomenological model.X.-H. Guo, A. W. Thomas, and A. G. William
Twist Four Longitudinal Structure Function in Light-Front QCD
To resolve various outstanding issues associated with the twist four
longitudinal structure function we perform an analysis
based on the BJL expansion for the forward virtual photon-hadron Compton
scattering amplitude and equal (light-front) time current algebra. Using the
Fock space expansion for states and operators, we evaluate the twist four
longitudinal structure function for dressed quark and gluon targets in
perturbation theory. With the help of a new sum rule which we have derived
recently we show that the quadratic and logarithmic divergences generated in
the bare theory are related to corresponding mass shifts in old-fashioned
light-front perturbation theory. We present numerical results for the and
structure functions for the meson in two-dimensional QCD in the one pair
approximation. We discuss the relevance of our results for the problem of the
partitioning of hadron mass in QCD.Comment: 25 pages, 2 ps figures, accepted for publication in Physical Review
Evolution and Flare Activity of Delta-Sunspots in Cycle 23
The emergence and magnetic evolution of solar active regions (ARs) of
beta-gamma-delta type, which are known to be highly flare-productive, were
studied with the SOHO/MDI data in Cycle 23. We selected 31 ARs that can be
observed from their birth phase, as unbiased samples for our study. From the
analysis of the magnetic topology (twist and writhe), we obtained the following
results. i) Emerging beta-gamma-delta ARs can be classified into three
topological types as "quasi-beta", "writhed" and "top-to-top". ii) Among them,
the "writhed" and "top-to-top" types tend to show high flare activity. iii) As
the signs of twist and writhe agree with each other in most cases of the
"writhed" type (12 cases out of 13), we propose a magnetic model in which the
emerging flux regions in a beta-gamma-delta AR are not separated but united as
a single structure below the solar surface. iv) Almost all the "writhed"-type
ARs have downward knotted structures in the mid portion of the magnetic flux
tube. This, we believe, is the essential property of beta-gamma-delta ARs. v)
The flare activity of beta-gamma-delta ARs is highly correlated not only with
the sunspot area but also with the magnetic complexity. vi) We suggest that
there is a possible scaling-law between the flare index and the maximum umbral
area
Tree method for quantum vortex dynamics
We present a numerical method to compute the evolution of vortex filaments in
superfluid helium. The method is based on a tree algorithm which considerably
speeds up the calculation of Biot-Savart integrals. We show that the
computational cost scales as Nlog{(N) rather than N squared, where is the
number of discretization points. We test the method and its properties for a
variety of vortex configurations, ranging from simple vortex rings to a
counterflow vortex tangle, and compare results against the Local Induction
Approximation and the exact Biot-Savart law.Comment: 12 pages, 10 figure
- âŠ