1,654 research outputs found
Gas Transport in Porous Media: Simulations and Experiments on Partially Densified Aerogels
The experimental density dependence of gas (argon and nitrogen) permeability
of partially densified silica aerogels in the Knudsen regime is quantitatively
accounted for by a computer model. The model simulates both the structure of
the sintered material and the random ballistic motion of a point particle
inside its voids. The same model is also able to account for the densit y
dependence of the specific pore surface as measured from nitrogen adsorption
experiments.Comment: RevTex, 11 pages + 5 postscript figures appended using "uufiles".
Published in Europhys. Lett. 29, p. 567 (1995
Phase diagram of the frustrated spin ladder
We re-visit the phase diagram of the frustrated spin-1/2 ladder with two
competing inter-chain antiferromagnetic exchanges, rung coupling J_\perp and
diagonal coupling J_\times. We suggest, based on the accurate renormalization
group analysis of the low-energy Hamiltonian of the ladder, that marginal
inter-chain current-current interaction plays central role in destabilizing
previously predicted intermediate columnar dimer phase in the vicinity of
classical degeneracy line J_\perp = 2J_\times. Following this insight we then
suggest that changing these competing inter-chain exchanges from the previously
considered antiferromagnetic to the ferromagnetic ones eliminates the issue of
the marginal interactions altogether and dramatically expands the region of
stability of the columnar dimer phase. This analytical prediction is
convincingly confirmed by the numerical density matrix renormalization group
and exact diagonalization calculations as well as by the perturbative
calculation in the strong rung-coupling limit. The phase diagram for
ferromagnetic J_\perp and J_\times is determined.Comment: 12 pages, 12 figures, 1 Table. v2: version to appear in Phys. Rev.
Constraining short-range spin-dependent forces with polarized helium 3 at the Laue-Langevin Institute
We have searched for a short-range spin-dependent interaction mediated by a
hypothetical light scalar boson with CP-violating couplings to the neutron
using the spin relaxation of hyperpolarized He. The walls of the He
cell would generate a depolarizing pseudomagnetic field.Comment: Twelfth Conference on the Intersections of Particle and Nuclear
Physics (CIPANP2015), Vail Marriott Mountain Resort, Vail, Colorado, US
Small Angle Scattering by Fractal Aggregates: A Numerical Investigation of the Crossover Between the Fractal Regime and the Porod Regime
Fractal aggregates are built on a computer using off-lattice cluster-cluster
aggregation models. The aggregates are made of spherical particles of different
sizes distributed according to a Gaussian-like distribution characterised by a
mean and a standard deviation . The wave vector dependent
scattered intensity is computed in order to study the influence of the
particle polydispersity on the crossover between the fractal regime and the
Porod regime. It is shown that, given , the location of the
crossover decreases as increases. The dependence of on
can be understood from the evolution of the shape of the center-to-center
interparticle-distance distribution function.Comment: RevTex, 4 pages + 6 postscript figures, compressed using "uufiles",
published in Phys. Rev. B 50, 1305 (1994
Influence of surfactants on the structure of titanium oxide gels : experiments and simulations
We report here on experimental and numerical studies of the influence of
surfactants on mineral gel synthesis. The modification of the gel structure
when the ratios water-precursor and water-surfactant vary is brought to the
fore by fractal dimension measures. A property of {\em polydispersity of the
initial hydrolysis} is proposed to explain these results, and is successfuly
tested through numerical experiments of three dimensional chemically limited
aggregation.Comment: 12 pages, 4 Postscript figures, uses RevTe
Pharmaceutical innovation, reference pricing and therapeutic classes
This paper is a first attempt to model the effects of reference pricing on the
innovation effort of pharmaceutical firms. The model is based on a dynamic
game involving three types of agents: pharmaceutical firms, consumers and
a regulatory entity. The games includes research stages where the innovation
efforts by the firms are determined and introductory stages where a price
for a new medicament is fixed. We model the negotiation between the drug
owner and the regulator to fix the price, first without legal constraint, second
under the regime of reference pricing in therapeutic classes. We then solve
the innovation game where the firms anticipate the results of the negotiation
round on prices. We thus consider the effect of the therapeutic class regulation on both prices and the innovation pace. The final stage consists in calibrating the model with a small data on anti-statine in France and
simulates the effect of the change in regulatory regime
T-cell modulation for the treatment of chronic plaque psoriasis with efalizumab (Raptiva (TM)): Mechanisms of action
Psoriasis is a chronic, incurable, auto-immune disorder with cutaneous manifestations. New evidence on the central role of the immune system in the pathogenesis of psoriasis increasingly provides insight into pathogenic steps that can be modulated to provide disease control. Numerous biological therapies are in various stages of clinical development, with expectation of providing enhanced safety and efficacy over currently available psoriasis therapies. Efalizumab, a recombinant humanized monoclonal IgG1 antibody, is a novel targeted T-cell modulator that inhibits multiple steps in the immune cascade that result in the production and maintenance of psoriatic plaques, including initial T-cell activation and T-cell trafficking into sites of inflammation, including psoriatic skin, with subsequent reactivation in these sites. This article reviews the pharmacodynamic, pharmacokinetic and clinical effects observed during phase I, II and III efalizumab trials in patients with moderate to severe chronic plaque psoriasis. Copyright (C) 2004 S. Karger AG, Basel
Fluctuating Bond Aggregation: a Model for Chemical Gel Formation
The Diffusion-Limited Cluster-Cluster Aggregation (DLCA) model is modified by
including cluster deformations using the {\it bond fluctuation} algorithm. From
3 computer simulations, it is shown that, below a given threshold value
of the volumic fraction , the realization of all intra-aggregate
bonding possibilities prevents the formation of a gelling network. For ,
the sol-gel transition occurs at a time which, in contrast to DLCA,
doesnot diverge with the box size. Several results are reported including small
angle scattering curves and possible applications are discussed.Comment: RevTex, 9 pages + 3 postscript figures appended using "uufiles". To
appear in Phys. Rev. Let
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