752 research outputs found
Prospects for near-infrared characterisation of hot Jupiters with VSI
In this paper, we study the feasibility of obtaining near-infrared spectra of
bright extrasolar planets with the 2nd generation VLTI Spectro-Imager
instrument (VSI), which has the required angular resolution to resolve nearby
hot Extrasolar Giant Planets (EGPs) from their host stars. Taking into account
fundamental noises, we simulate closure phase measurements of several
extrasolar systems using four 8-m telescopes at the VLT and a low spectral
resolution (R = 100). Synthetic planetary spectra from T. Barman are used as an
input. Standard chi2-fitting methods are then used to reconstruct planetary
spectra from the simulated data. These simulations show that low-resolution
spectra in the H and K bands can be retrieved with a good fidelity for half a
dozen targets in a reasonable observing time (about 10 hours, spread over a few
nights). Such observations would strongly constrain the planetary temperature
and albedo, the energy redistribution mechanisms, as well as the chemical
composition of their atmospheres. Systematic errors, not included in our
simulations, could be a serious limitation to these performance estimations.
The use of integrated optics is however expected to provide the required
instrumental stability (around 10^-4 on the closure phase) to enable the first
thorough characterisation of extrasolar planetary emission spectra in the
near-infrared.Comment: 10 pages, 8 figures, Proc. SPIE conference 7013 "Optical and Infrared
Interferometry" (Marseille 2008
Multiscale non-adiabatic dynamics with radiative decay, case study on the post-ionization fragmentation of rare-gas tetramers
In this supplementary material, we recollect, for reader's convenience, the
general scheme of suggested multiscale model (Sec. 1), and basic informations
about approaches used for pilot study: a detailed description of the
interaction model (Sec. 2) and dynamical methods used for the dark dynamics
step (Sec. 3) reported previously in two preceding studies [1, 2]. In addition,
a detailed description of the treatment of radiative processes is also given
(Sec. 4).Comment: supplementary material for parent paper; 9 pages, 1 figure; corrected
formulae and misleading notation in Sec.4 (pages 7 and 8
Hyperon-Nucleon Final State Interaction in Kaon Photoproduction of the Deuteron
Final state hyperon-nucleon interaction in strangeness photoproduction of the
deuteron is investigated making use of the covariant reaction formalism and the
P-matrix approach to the YN system. Remarkably simple analytical expression for
the amplitude is obtained. Pronounced effects due to final state interaction
are predicted including the manifestation of the 2.13 GeV resonance.Comment: LaTeX, 13 page
Finite Size Scaling for Low Energy Excitations in Integer Heisenberg Spin Chains
In this paper we study the finite size scaling for low energy excitations of
and Heisenberg chains, using the density matrix renormalization
group technique. A crossover from behavior (with as the chain length)
for medium chain length to scaling for long chain length is found for
excitations in the continuum band as the length of the open chain increases.
Topological spin excitations are shown to give rise to the two lowest
energy states for both open and periodic chains. In periodic chains these
two excitations are ``confined'' next to each other, while for open chains they
are two free edge 1/2 spins. The finite size scaling of the two lowest energy
excitations of open chains is determined by coupling the two free edge
spins. The gap and correlation length for open Heisenberg chains
are shown to be 0.082 (in units of the exchange ) and 47, respectively.Comment: 4 pages (two column), PS file, to be appear as a PRB Brief Repor
CuSiO_3 : a quasi - one - dimensional S=1/2 antiferromagnetic chain system
CuSiO_3, isotypic to the spin - Peierls compound CuGeO_3, was discovered
recently as a metastable decomposition product of the silicate mineral
dioptase, Cu_6Si_6O_{18}\cdot6H_2O. We investigated the physical properties of
CuSiO_3 using susceptibility, magnetization and specific heat measurements on
powder samples. The magnetic susceptibility \chi(T) is reproduced very well
above T = 8 K by theoretical calculations for an S=1/2 antiferromagnetic
Heisenberg linear chain without frustration (\alpha = 0) and a nearest -
neighbor exchange coupling constant of J/k_{B} = 21 K, much weaker than in
CuGeO_3. Below 8 K the susceptibility exhibits a substantial drop. This feature
is identified as a second - order phase transition at T_{0} = 7.9 K by specific
heat measurements. The influence of magnetic fields on T_{0} is weak, and ac -
magnetization measurements give strong evidence for a spin - flop - phase at
\mu_0H_{SF} ~ 3 T. The origin of the magnetic phase transition at T_{0} = 7.9 K
is discussed in the context of long - range antiferromagnetic order (AF) versus
spin - Peierls(SP)order. Susceptibility and specific heat results support the
AF ordered ground state. Additional temperature dependent ^{63,65}Cu nuclear
quadrupole resonance experiments have been carried out to probe the Cu^{2+}
electronic state and the spin dynamics in CuSiO_3
Nuclear Magnetic Relaxation in the Haldane-Gap Antiferromagnet Ni(C_2_H_8_N_2_)_2_NO_2_(ClO_4_)
A new theory is proposed to interpret nuclear spin-lattice relaxation-time
(T_1_) measurements on the spin-1 quasi-one-dimensional Heisenberg
antiferromagnet Ni(C_2_H_8_N_2_)_2_NO_2_(ClO_4_) (NENP). While Sagi and Affleck
pioneeringly discussed this subject in terms of field-theoretical languages,
there is no theoretical attempt yet to explicitly simulate the novel
observations of 1/T_1_ reported by Fujiwara et al.. By means of modified spin
waves, we solve the minimum of 1/T_1_ as a function of an applied field,
pending for the past decade.Comment: to be published in J. Phys. Soc. Jpn. 73, No. 4 (2004
Design and synthesis of imidazoline derivatives active on glucose homeostasis in a rat model of type II diabetes.2. Syntheses and biological activities of 1,4-dialkyl-,1,4-dibenzyl and 1-benzyl-4-alkyl-2-(4',5'-dihydro-1' H-imidazol-2'yl)piperazines and isosteric analogues of imidazoline
International audienc
Thermal and magnetic properties of integrable spin-1 and spin-3/2 chains with applications to real compounds
The ground state and thermodynamic properties of spin-1 and spin-3/2 chains
are investigated via exactly solved su(3) and su(4) models with physically
motivated chemical potential terms. The analysis involves the Thermodynamic
Bethe Ansatz and the High Temperature Expansion (HTE) methods. For the spin-1
chain with large single-ion anisotropy, a gapped phase occurs which is
significantly different from the valence-bond-solid Haldane phase. The
theoretical curves for the magnetization, susceptibility and specific heat are
favourably compared with experimental data for a number of spin-1 chain
compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at
zero external magnetic field. A middle magnetization plateau can be triggered
by the single-ion anisotropy term. Overall, our results lend further weight to
the applicability of integrable models to the physics of low-dimensional
quantum spin systems. They also highlight the utility of the exact HTE method.Comment: 38 pages, 15 figure
- …