4,736 research outputs found
Elementary Excitations in Quantum Antiferromagnetic Chains: Dyons, Spinons and Breathers
Considering experimental results obtained on three prototype compounds, TMMC,
CsCoCl3 (or CsCoBr3) and Cu Benzoate, we discuss the importance of non-linear
excitations in the physics of quantum (and classical) antiferromagnetic spin
chains.Comment: Invited at the International Symposium on Cooperative Phenomena of
Assembled Metal Complexes, November 15-17, 2001, Osaka, Japa
Thermodynamic Properties of the Spin-1/2 Antiferromagnetic ladder Cu2(C2H12N2)2Cl4 under Magnetic Field
Specific heat () measurements in the spin-1/2
Cu(CHN)Cl system under a magnetic field up to
are reported and compared to the results of numerical calculations
based on the 2-leg antiferromagnetic Heisenberg ladder. While the temperature
dependences of both the susceptibility and the low field specific heat are
accurately reproduced by this model, deviations are observed below the critical
field at which the spin gap closes. In this Quantum High Field phase,
the contribution of the low-energy quantum fluctuations are stronger than in
the Heisenberg ladder model. We argue that this enhancement can be attributed
to dynamical lattice fluctuations. Finally, we show that such a Heisenberg
ladder, for , is unstable, when coupled to the 3D lattice, against a
lattice distortion. These results provide an alternative explanation for the
observed low temperature ( -- ) phase (previously
interpreted as a 3D magnetic ordering) as a new type of incommensurate gapped
state.Comment: Minor changes, list of authors complete
Study on the neuronal circuits implicated in postural tremor and hypokinesia
The effect of various tegmentary lesions at the level of the pontomesenchphalon in monkeys on motor function was observed. The importance of the monoaminergic mechanisms of the brainstem is discussed. The results also show the importance of the descending tegmentary rubral system and the rubroolivocerebellar circuit in controlling peripheral motor activity. The destruction of the sensory motor cortex proves to be a more effective way of eliminating spontaneous or harmaline induced tremor than the complete interruption of the pyramidal system on the level of the cerebral peduncle
Mixed Heisenberg Chains. II. Thermodynamics
We consider thermodynamic properties, e.g. specific heat, magnetic
susceptibility, of alternating Heisenberg spin chains. Due to a hidden Ising
symmetry these chains can be decomposed into a set of finite chain fragments.
The problem of finding the thermodynamic quantities is effectively separated
into two parts. First we deal with finite objects, secondly we can incorporate
the fragments into a statistical ensemble. As functions of the coupling
constants, the models exhibit special features in the thermodynamic quantities,
e.g. the specific heat displays double peaks at low enough temperatures. These
features stem from first order quantum phase transitions at zero temperature,
which have been investigated in the first part of this work.Comment: 12 pages, RevTeX, 12 embedded eps figures, cf. cond-mat/9703206,
minor modification
Charge Ordering and Spin Dynamics in NaV2O5
We report high-resolution neutron inelastic scattering experiments on the
spin excitations of NaV2O5. Below Tc, two branches associated with distinct
energy gaps are identified. From the dispersion and intensity of the spin
excitation modes, we deduce the precise zig-zag charge distribution on the
ladder rungs and the corresponding charge order (about 0.6). We argue that the
spin gaps observed in the low-T phase of this compound are primarily due to the
charge transfer.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
Quantum internal modes of solitons in 1d easy-plane antiferromagnet in strong magnetic field
In presence of a strong external magnetic field the dynamics of solitons in a
one-dimensional easy-plane Heisenberg antiferromagnet exhibits a number of
peculiarities. Dynamics of internal soliton degrees of freedom is essentially
quantum, and they are strongly coupled to the "translational" mode of soliton
movement. These peculiarities lead to considerable changes in the response
functions of the system which can be detected experimentally.Comment: 8 pages, RevTeX, 6 figures, uses psfig.sty, submitted to PR
Amp\`ere-Class Pulsed Field Emission from Carbon-Nanotube Cathodes in a Radiofrequency Resonator
Pulsed field emission from cold carbon-nanotube cathodes placed in a
radiofrequency resonant cavity was observed. The cathodes were located on the
backplate of a conventional -cell resonant cavity operating at
1.3-GHz and resulted in the production of bunch train with maximum average
current close to 0.7 Amp\`ere. The measured Fowler-Nordheim characteristic,
transverse emittance, and pulse duration are presented and, when possible,
compared to numerical simulations. The implications of our results to
high-average-current electron sources are briefly discussed.Comment: 5 pages, 6 figures; submitted to Applied Physics Letter
Introducing the Dark Energy Universe Simulation Series (DEUSS)
In this "Invisible Universe" proceedings, we introduce the Dark Energy
Universe Simulation Series (DEUSS) which aim at investigating the imprints of
realistic dark energy models on cosmic structure formation. It represents the
largest dynamical dark energy simulation suite to date in term of spatial
dynamics. We first present the 3 realistic dark energy models (calibrated on
latest SNIa and CMB data): LambdaCDM, quintessence with Ratra-Peebles
potential, and quintessence with Sugra potential. We then isolate various
contributions for non-linear matter power spectra from a series of pre-DEUSS
high-resolution simulations (130 million particles). Finally, we introduce
DEUSS which consist in 9 Grand Challenge runs with 1 billion particles each
thus probing scales from 4 Gpc down to 3 kpc at z=0. Our goal is to make these
simulations available to the community through the "Dark Energy Universe
Virtual Observatory" (DEUVO), and the "Dark Energy Universe Simulations" (DEUS)
consortium.Comment: 6 pages, 3 figures, to appear in the AIP proceedings of the
'Invisible Universe International Conference', UNESCO-Paris, June 29-July 3,
200
A magnetic model for the incommensurate I phase of spin-Peierls systems
A magnetic model is proposed for describing the incommensurate I phase of
spin-Peierls systems. Based on the harmonicity of the lattice distortion, its
main ingredient is that the distortion of the lattice adjusts to the average
magnetization such that the system is always gapful. The presence of dynamical
incommensurabilities in the fluctuation spectra is also predicted. Recent
experimental results for CuGeO_3 obtained by NMR, ESR and light scattering
absorption are well understood within this model.Comment: 8 pages, 3 figures, Latex with EPL style files all include
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