385 research outputs found
Study of the heating effect contribution to the nonlinear dielectric response of a supercooled liquid
We present a detailed study of the heating effects in dielectric measurements
carried out on a liquid. Such effects come from the dissipation of the electric
power in the liquid and give a contribution to the nonlinear third harmonics
susceptibility chi_3 which depends on the frequency and temperature. This study
is used to evaluate a possible `spurious' contribution to the recently measured
nonlinear susceptibility of an archetypical glassforming liquid (Glycerol).
Those measurements have been shown to give a direct evaluation of the number of
dynamically correlated molecules temperature dependence close to the glass
transition temperature T_g~190K (Crauste-Thibierge et al., Phys. Rev. Lett
104,165703(2010)). We show that the heating contribution is totally negligible
(i) below 204K at any frequency; (ii) for any temperature at the frequency
where the third harmonics response chi_3 is maximum. Besides, this heating
contribution does not scale as a function of f/f_{\alpha}, with f_{\alpha}(T)
the relaxation frequency of the liquid. In the high frequency range, when
f/f_{\alpha} >= 1, we find that the heating contribution is damped because the
dipoles cannot follow instantaneously the temperature modulation due to the
heating phenomenon. An estimate of the magnitude of this damping is given.Comment: 25 pages, 10 figures, Accepted for publication in Journal of Chemical
Physic
A non-trivial spectrum for the trivial \phi^4 theory
It is pointed out that one-component \phi^4 lattice theory in four dimensions
has a non-perturbative sector which can be studied by means of an exact duality
transformation of its Ising limit. This duality maps it to a membrane model. As
a consequence, the \phi^4-theory turns out to have, in the broken symmetry
phase, a remarkably rich spectrum of physical states corresponding to membrane
excitations. A numerical study of the correlators between dual variables allows
to evaluate the masses of the first few states.Comment: 3 pages, talk given at LATTICE'97, Edinburg
Effects of Intravenous Aspirin on Prostaglandin Synthesis and Kidney Function in Intensive Care Patients
The effects of intravenous acetylsalicylic acid (1.0 g bolus) on renal function and prostaglandin synthesis were evaluated in a prospective, controlled study in eight patients in an intensive care unit. Four of these patients had congestive heart failure. Administration of acetylsalicylic acid caused significant antidiuresis (−56%), antinatriuresis (−82%), renin suppression (−26%) and decreased GFR (−41%). All of these changes were completely reversible within 1-2 hours and tended to be more pronounced in the patients with congestive heart failure. Urinary excretion of prostaglandin E was depressed profoundly (−93%) and did not return to more than 45% of control 6 h after the administration of acetylsalicylic acid. We conclude that intravenous acetylsalicylic acid affects kidney function in a manner similar to other prostaglandin synthesis inhibitors. Its effects are, however, short-lived. The inhibition of urinary PGE2 excretion outlasts GFR depression, antidiuresis, antinatriuresis and renin suppression by several hour
Many-body effects in nuclear structure
We calculate, for the first time, the state-dependent pairing gap of a finite
nucleus (120Sn) diagonalizing the bare nucleon-nucleon potential (Argonne v14)
in a Hartree-Fock basis (with effective k-mass m_k eqult to 0.7 m), within the
framework of the BCS approximation including scattering states up to 800 MeV
above the Fermi energy to achieve convergence. The resulting gap accounts for
about half of the experimental gap. We find that a consistent description of
the low-energy nuclear spectrum requires, aside from the bare nucleon-nucleon
interaction, not only the dressing of single-particle motion through the
coupling to the nuclear surface, to give the right density of levels close to
the Fermi energy (and thus an effective mass m* approximately equal to m), but
also the renormalization of collective vibrational modes through vertex and
self-energy processes, processes which are also found to play an essential role
in the pairing channel, leading to a long range, state dependent component of
the pairing interaction. The combined effect of the bare nucleon-nucleon
potential and of the induced pairing interaction arising from the exchange of
low-lying surface vibrations between nucleons moving in time reversal states
close to the Fermi energy accounts for the experimental gap.Comment: 5 pages, 4 figures; author list correcte
La sédimentation lacustre indicateur de changements des paléoenvironnements au cours des 30 000 dernières années (Carajas, Amazonie, Brésil)
Les résultats de l'analyse par spectrométrie infrarouge des échantillons de deux carottes prélevées dans deux dépressions marécageuses de la Serra Sul dos Carajas (Amazonie Orientale), mettent en évidence cinq grandes étapes paléohydrologiques au cours des 30 000 dernières années. La comparaison avec les résultats de la palynologie permet de mieux comprendre l'impact de changements climatiques brefs sur les paléoenvironnements. (Résumé d'auteur
Flow equations for QED in the light front dynamics
The method of flow equations is applied to QED on the light front. Requiring
that the partical number conserving terms in the Hamiltonian are considered to
be diagonal and the other terms off-diagonal an effective Hamiltonian is
obtained which reduces the positronium problem to a two-particle problem, since
the particle number violating contributions are eliminated. No infrared
divergencies appear. The ultraviolet renormalization can be performed
simultaneously.Comment: 15 pages, Latex, 3 pictures, Submitted to Phys.Rev.
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