1,101 research outputs found
The Application of Domain Decomposition to Time-Domain Computations of Nonlinear Water Waves with a Panel Method
In this paper an iterative domain decomposition method for the solution of Laplace's equation is described and its effectiveness in time-domain computations of nonlinear water waves with a panel method is investigated. An important aspect of these computations is the varying shape of the free surface. The convergence of the iterative method is fast and leads to a speedup of the computations in the aforementioned application. The domain decomposition method gives a considerable reduction of memory requirements. Furthermore, it lends itself naturally for parallel computing
Studies of a weak polyampholyte at the air-buffer interface: The effect of varying pH and ionic strength
We have carried out experiments to probe the static and dynamic interfacial
properties of --casein monolayers spread at the air-buffer interface,
and analysed these results in the context of models of weak polyampholytes.
Measurements have been made systematically over a wide range of ionic strength
and pH. In the semi-dilute regime of surface concentration a scaling exponent,
which can be linked to the degree of chain swelling, is found. This shows that
at pH close to the isoelectric point, the protein is compact. At pH away from
the isoelectric pH the protein is extended. The transition between compact and
extended states is continuous. As a function of increasing ionic strength, we
observe swelling of the protein at the isoelectric pH but contraction of the
protein at pH values away from it. These behaviours are typical of a those
predicted theoretically for a weak polyampholyte. Dilational moduli
measurements, made as a function of surface concentration exhibit maxima that
are linked to the collapse of hydrophilic regions of the protein into the
subphase. Based on this data we present a configuration map of the protein
configuration in the monolayer. These findings are supported by strain (surface
pressure) relaxation measurements and surface quasi-elastic light scattering
(SQELS) measurements which suggest the existence of loops and tails in the
subphase at higher surface concentrations.Comment: Submitted to J. Chem. Phy
Collective CO2 laser scattering on moving discharge structures in the submillimeter range in a magnetohydrodynamic generator
Collective scattering of CO/sub 2/ laser light on electrons is used to determine the radial scale length of the discharge structures occurring in a closed cycle magnetohydrodynamic generator. Heterodyne detection of scattered radiation is used to obtain a spatial resolution in the submillimeter range and to increase the signal to noise ratio. A discharge model is formulated to interpret the measured signals. The scale length of the electron density fluctuations is found to be (2.5+or-0.5)*10/sup -4/
Genome-wide association study of peripheral neuropathy with D-drug-containing regimens in AIDS Clinical Trials Group protocol 384.
Stavudine (d4T) was, until recently, one of the most widely prescribed antiretroviral drugs worldwide. While there has been a major shift away from d4T use in resource-limited countries, a large number of patients have previously received (or continue to receive) d4T, and many have developed peripheral neuropathy. The identification of genetic predictors of increased risk might suggest novel therapeutic targets for such patients. In AIDS Clinical Trials Group protocol 384, antiretroviral-naïve patients were randomized to d4T/didanosine (ddI)- or zidovudine/lamivudine-containing regimens. Data from d4T/ddI recipients were analyzed for genome-wide associations (approximately 1 million genetic loci) with new onset distal sensory peripheral neuropathy. Analyses involved 254 patients (49 % White, 34 % Black, 17 % Hispanic), comprising 90 peripheral neuropathy cases (32 grade 1, 35 grade 2, 23 grade 3) and 164 controls. After correcting for multiple comparisons, no polymorphism was consistently associated with neuropathy among all patients, among White, Black, and Hispanic patients analyzed separately, both in genome-wide analyses (threshold, P < 5.0 × 10(-8)) and focused on 46 neuropathy-associated genes (threshold, P < 3.5 × 10(-5)). In the latter analyses, the lowest P values were in KIF1A among Whites (rs10199388, P = 8.4 × 10(-4)), in LITAF among Blacks (rs13333308, P = 6.0 × 10(-6)), and in NEFL among Hispanics (rs17763685, P = 5.6 × 10(-6)). Susceptibility to d4T/ddI-associated neuropathy is not explained by a single genetic variant with a marked effect
Two-Loop Effects and Current Status of the 4He+ Lamb Shift
We report on recent progress in the treatment of two-loop binding corrections
to the Lamb shift, with a special emphasis on S and P states. We use these and
other results in order to infer an updated theoretical value of the Lamb shift
in 4He+.Comment: 11 pages, nrc1 style; paper presented at PSAS (2006), Venic
Electron transport and energy relaxation in dilute magnetic alloys
We consider the effect of the RKKY interaction between magnetic impurities on
the electron relaxation rates in a normal metal. The interplay between the RKKY
interaction and the Kondo effect may result in a non-monotonic temperature
dependence of the electron momentum relaxation rate, which determines the Drude
conductivity. The electron phase relaxation rate, which determines the
magnitude of the weak localization correction to the resistivity, is also a
non-monotonic function of temperature. For this function, we find the
dependence of the position of its maximum on the concentration of magnetic
impurities. We also relate the electron energy relaxation rate to the
excitation spectrum of the system of magnetic impurities. The energy relaxation
determines the distribution function for the out-of-equilibrium electrons.
Measurement of the electron distribution function thus may provide information
about the excitations in the spin glass phase.Comment: 15 pages, 5 figure
Universality classes in nonequilibrium lattice systems
This work is designed to overview our present knowledge about universality
classes occurring in nonequilibrium systems defined on regular lattices. In the
first section I summarize the most important critical exponents, relations and
the field theoretical formalism used in the text. In the second section I
briefly address the question of scaling behavior at first order phase
transitions. In section three I review dynamical extensions of basic static
classes, show the effect of mixing dynamics and the percolation behavior. The
main body of this work is given in section four where genuine, dynamical
universality classes specific to nonequilibrium systems are introduced. In
section five I continue overviewing such nonequilibrium classes but in coupled,
multi-component systems. Most of the known nonequilibrium transition classes
are explored in low dimensions between active and absorbing states of
reaction-diffusion type of systems. However by mapping they can be related to
universal behavior of interface growth models, which I overview in section six.
Finally in section seven I summarize families of absorbing state system
classes, mean-field classes and give an outlook for further directions of
research.Comment: Updated comprehensive review, 62 pages (two column), 29 figs
included. Scheduled for publication in Reviews of Modern Physics in April
200
Theory of c-axis Josephson tunneling in d-wave superconductors
The temperature and angular dependence of the c-axis Josephson current and
the superfluid density in layered d-wave superconductors are studied within the
framework of an extended Ambegaokar-Baratoff formalism. In particular, the
effects of angle-dependent tunneling matrix elements and Andreev scattering at
grain boundaries are taken into account. These lead to strong corrections of
the low-temperature behavior of the plasma frequency and the Josephson current.
Recent c-axis measurements on the cuprate high-temperature superconductors
HgBa_2CaCu_{1+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} can therefore be
interpreted to be consistent with a d-wave order parameter.Comment: Revtex, 4 pages with 4 eps figures, to appear in PRB R
Pressure and linear heat capacity in the superconducting state of thoriated UBe13
Even well below Tc, the heavy-fermion superconductor (U,Th)Be13 has a large
linear term in its specific heat. We show that under uniaxial pressure, the
linear heat capacity increases in magnitude by more than a factor of two. The
change is reversible and suggests that the linear term is an intrinsic property
of the material. In addition, we find no evidence of hysteresis or of latent
heat in the low-temperature and low-pressure portion of the phase diagram,
showing that all transitions in this region are second order.Comment: 5 pages, 4 figure
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