2,448 research outputs found
Formation of forearc basins by collision between seamounts and accretionary wedges : an example from the New Hebrides subduction zone
L'interprétation des données bathymétriques Seabeam obtenues le long de la fosse des Nouvelles-Hébrides permet de proposer un modèle en deux stades pour la formation de bassins avant-arc sub-insulaires. Ces bassins résultent de l'indentation du bas de la marge lors de la collision entre un mont sous-marin et l'arc ainsi que de la reconstruction du bas de la pente par accrétion de sédiments de la plaque plongeante et piégeage de sédiments provenant de l'arc. (Résumé d'auteur
Shape of crossover between mean-field and asymptotic critical behavior in a three-dimensional Ising lattice
Recent numerical studies of the susceptibility of the three-dimensional Ising
model with various interaction ranges have been analyzed with a crossover model
based on renormalization-group matching theory. It is shown that the model
yields an accurate description of the crossover function for the
susceptibility.Comment: 4 pages RevTeX + 3 PostScript figures. Uses epsf.sty and rotate.sty.
Final version; accepted for publication in Physics Letters
Metabolic profiling predicts response to anti-tumor necrosis factor α therapy in patients with rheumatoid arthritis
<p>Objective: Anti–tumor necrosis factor (anti-TNF) therapies are highly effective in rheumatoid arthritis (RA) and psoriatic arthritis (PsA), but a significant number of patients exhibit only a partial or no therapeutic response. Inflammation alters local and systemic metabolism, and TNF plays a role in this. We undertook this study to determine if the patient's metabolic fingerprint prior to therapy could predict responses to anti-TNF agents.</p>
<p>Methods: Urine was collected from 16 RA patients and 20 PsA patients before and during therapy with infliximab or etanercept. Urine metabolic profiles were assessed using nuclear magnetic resonance spectroscopy. Discriminating metabolites were identified, and the relationship between metabolic profiles and clinical outcomes was assessed.</p>
<p>Results: Baseline urine metabolic profiles discriminated between RA patients who did or did not have a good response to anti-TNF therapy according to European League Against Rheumatism criteria, with a sensitivity of 88.9% and a specificity of 85.7%, with several metabolites contributing (in particular histamine, glutamine, xanthurenic acid, and ethanolamine). There was a correlation between baseline metabolic profiles and the magnitude of change in the Disease Activity Score in 28 joints from baseline to 12 months in RA patients (P = 0.04). In both RA and PsA, urinary metabolic profiles changed between baseline and 12 weeks of anti-TNF therapy. Within the responders, urinary metabolite changes distinguished between etanercept and infliximab treatment.</p>
<p>Conclusion: The clear relationship between urine metabolic profiles of RA patients at baseline and their response to anti-TNF therapy may allow development of novel approaches to the optimization of therapy. Differences in metabolic profiles during treatment with infliximab and etanercept in RA and PsA may reflect distinct mechanisms of action.</p>
Asymptotics of the Farey Fraction Spin Chain Free Energy at the Critical Point
We consider the Farey fraction spin chain in an external field . Using
ideas from dynamical systems and functional analysis, we show that the free
energy in the vicinity of the second-order phase transition is given,
exactly, by
Here is a reduced
temperature, so that the deviation from the critical point is scaled by the
Lyapunov exponent of the Gauss map, . It follows that
determines the amplitude of both the specific heat and susceptibility
singularities. To our knowledge, there is only one other microscopically
defined interacting model for which the free energy near a phase transition is
known as a function of two variables.
Our results confirm what was found previously with a cluster approximation,
and show that a clustering mechanism is in fact responsible for the transition.
However, the results disagree in part with a renormalisation group treatment
Numerical studies of the two- and three-dimensional gauge glass at low temperature
We present results from Monte Carlo simulations of the two- and
three-dimensional gauge glass at low temperature using the parallel tempering
Monte Carlo method. Our results in two dimensions strongly support the
transition being at T_c=0. A finite-size scaling analysis, which works well
only for the larger sizes and lower temperatures, gives the stiffness exponent
theta = -0.39 +/- 0.03. In three dimensions we find theta = 0.27 +/- 0.01,
compatible with recent results from domain wall renormalization group studies.Comment: 7 pages, 10 figures, submitted to PR
First order quantum phase transitions
Quantum phase transitions have been the subject of intense investigations in
the last two decades [1]. Among other problems, these phase transitions are
relevant in the study of heavy fermion systems, high temperature
superconductors and Bose-Einstein condensates. More recently there is
increasing evidence that in many systems which are close to a quantum critical
point (QCP) different phases are in competition. In this paper we show that the
main effect of this competition is to give rise to inhomogeneous behavior
associated with quantum first order transitions. These effects are described
theoretically using an action that takes into account the competition between
different order parameters. The method of the effective potential is used to
calculate the quantum corrections to the classical functional. These
corrections generally change the nature of the QCP and give rise to interesting
effects even in the presence of non-critical fluctuations. An unexpected result
is the appearance of an inhomogeneous phase with two values of the order
parameter separated by a first order transition. Finally, we discuss the
universal behavior of systems with a weak first order zero temperature
transition in particular as the transition point is approached from finite
temperatures. The thermodynamic behavior along this line is obtained and shown
to present universal features.Comment: 7 pages, 5 figures. Invited talk at ICM2006, Kyoto. To appear in JMM
Anisotropic magnetization, specific heat and resistivity of RFe2Ge2 single crystals
We have grown RFe2Ge2 single crystals for R = Y and ten members of the
lanthanide series (Pr, Nd, Sm, Gd-Tm, Lu) using Sn flux as the solvent. The
method yields clean, high quality crystal plates as evidenced by residual
resistivities and RRR values in the range of 3-12 uOhm cm and 20-90
respectively. The crystals are also virtually free of magnetic impurities or
secondary phases, allowing the study of the intrinsic anisotropic magnetic
behavior of each compound. Characterization was made with X-Ray diffraction,
and temperature and field dependent magnetization, specific heat and
resistivity. Very strong anisotropies arising mostly from CEF effects were
observed for all magnetic rare earths except Gd. Antiferromagnetic ordering
occurred at temperatures between 16.5 K (Nd) and 1.1 K (Ho) that roughly scale
with the de Gennes factor for the heavy rare earths. For some members there is
also a lower temperature transition associated with changes in the magnetic
structure. Tm did not order down to 0.4 K, and appears to be a van Vleck
paramagnet. All members which ordered above 2 K showed a metamagnetic
transition at 2 K for fields below 70 kOe. The calculated effective moments per
rare earth atom are close to the expected free ion values of R^3+ except for Sm
which displays anomalous behavior in the paramagnetic state. The non-magnetic
members of this series (Y, Lu) are characterized by an unusually large
electronic specific heat coefficient (gamma ~ 60 mJ/mol K^2) and
temperature-independent susceptibility term (chi_0 ~ 0.003 emu/mol), indicative
of a relatively large density of states at the Fermi surface.Comment: 34 pages, 13 figures, 1 table, submitted to J. Magn. Magn. Mate
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