2,040 research outputs found
Strong damping of phononic heat current by magnetic excitations in SrCu_2(BO_3)_2
Measurements of the thermal conductivity as a function of temperature and
magnetic field in the 2D dimer spin system SrCu(BO) are presented.
In zero magnetic field the thermal conductivity along and perpendicular to the
magnetic planes shows a pronounced double-peak structure as a function of
temperature. The low-temperature maximum is drastically suppressed with
increasing magnetic field. Our quantitative analysis reveals that the heat
current is due to phonons and that the double-peak structure arises from
pronounced resonant scattering of phonons by magnetic excitations.Comment: a bit more than 4 pages, 2 figures included; minor changes to improve
the clarity of the presentatio
Collective Singlet Excitations and Evolution of Raman Spectral Weights in the 2D Spin Dimer Compound SrCu2(BO3)2
We present a Raman light scattering study of the two-dimensional quantum spin
system SrCu2(BO3)2 and show that the magnetic excitation spectrum has a rich
structure, including several well-defined bound state modes at low temperature,
and a scattering continuum and quasielastic light scattering contributions at
high temperature. The key to the understanding of the unique features of
SrCu2(BO3)2 is the presence of strong interactions between well-localized
triplet excitations in the network of orthogonal spin dimers realized in this
compound. Based on our analysis of the Heisenberg model relevant for this
material, we argue that the collective excitations involving two and
three-particle singlet bound states have large binding energies and are
observed as well-defined peaks in the Raman spectrum.Comment: 5 pages, 2 figures. Revised version, to appear in Phys. Rev. Lett.
(2000
Magnetization Plateaus in the Shastry-Sutherland Model for SrCu_2(BO_3)_2: Results of Fourth-Order Perturbation Expansion with a Low-Density Approximation
Magnetization plateaus in the Shastry-Sutherland model for are studied by the perturbation expansion method. The
fourth-order effective Hamiltonian which describes the dynamics of triplet
dimers (TD's) with in the singlet sea is derived and then
partially diagonalized for the space that consists of the TD configurations
with the lowest second-order energy. The fourth-order terms are treated within
a low-density approximation. Our procedure makes clear how TD interactions are
responsible for the formation of magnetization plateaus. Particularly, the
1/4-plateau is obtained by the fourth-neighbor TD repulsion in the fourth-order
perturbation, and a diagonal stripe arrangement of TD's appears at this
plateau.Comment: 8 pages, 12 figure
Geodynamo and mantle convection simulations on the Earth Simulator using the Yin-Yang grid
We have developed finite difference codes based on the Yin-Yang grid for the
geodynamo simulation and the mantle convection simulation. The Yin-Yang grid is
a kind of spherical overset grid that is composed of two identical component
grids. The intrinsic simplicity of the mesh configuration of the Yin-Yang grid
enables us to develop highly optimized simulation codes on massively parallel
supercomputers. The Yin-Yang geodynamo code has achieved 15.2 Tflops with 4096
processors on the Earth Simulator. This represents 46% of the theoretical peak
performance. The Yin-Yang mantle code has enabled us to carry out mantle
convection simulations in realistic regimes with a Rayleigh number of
including strongly temperature-dependent viscosity with spatial contrast up to
.Comment: Plenary talk at SciDAC 200
Dzyaloshinski-Moriya Interaction in the 2D Spin Gap System SrCu2(BO3)2
The Dzyaloshinski-Moriya interaction partially lifts the magnetic frustration
of the spin-1/2 oxide SrCu2(BO3)2. It explains the fine structure of the
excited triplet state and its unusual magnetic field dependence, as observed in
previous ESR and new neutron inelastic scattering experiments. We claim that it
is mainly responsible for the dispersion. We propose also a new mechanism for
the observed ESR transitions forbidden by standard selection rules, that relies
on an instantaneous Dzyaloshinski-Moriya interaction induced by spin-phonon
couplings.Comment: 5 pages, 4 figures, symmetries clarified, added references, (v3)
correct addres
Estrutura genética e sistema de acasalamento de Piper hispidinervum.
A pimenta-longa (Piper hispidinervum C. DC.) arbusto encontrado em áreas antropizadas no Estado do Acre, possui expressiva importância econĂ´mica decorrente da presença de safrol em seu Ăłleo essencial. O objetivo deste trabalho foi avaliar a estrutura genĂ©tica e o sistema de acasalamento dessa espĂ©cie, utilizando marcadores RAPD (polimorfismo de DNA amplificado ao acaso). A diversidade genĂ©tica entre e dentro de populações naturais foi avaliada em 13 populações do Vale do Rio Acre, distribuĂdas nas Regiões do Baixo e Alto Acre. A taxa preferencial de cruzamento foi estimada em 25 famĂlias de polinização livre de uma população do MunicĂpio de Assis Brasil, Acre. A espĂ©cie apresentou diversidade genĂ©tica estruturada no espaço segundo um padrĂŁo de isolamento por distância. A maior parte da variabilidade genĂ©tica foi encontrada dentro das populações, porĂ©m a diferenciação entre populações, como um todo, foi alta (θP = 0,28). O agrupamento das populações, pela distância genĂ©tica (φST) entre elas, mostrou dois grupos distintos, os quais representam as regiões do Alto Acre e Baixo Acre. A AMOVA mostrou que 20,61% da variabilidade total está entre essas duas regiões. A taxa de cruzamento multilocos foi estimada em 1,033, evidenciando que a espĂ©cie Ă© alĂłgama. A estimativa do coeficiente de endogamia F nĂŁo diferiu de zero e os cruzamentos ocorreram preferencialmente entre indivĂduos nĂŁo-aparentados
MOLECULAR EPIDEMIOLOGY DATABASE OF HIV, HBV, HCV, HDV, HTLV-1/2, AND TTV IN CENTRAL OF JAVA, INDONESIA
Since 2009 an active surveillance has been performed by collecting
epidemiological and clinical data and blood specimens from the high risk
communities for human blood borne viruses infections (correctional facilities,
injecting drug users, men who have sex with men, etc) to build a molecular
epidemiology database of human blood borne viruses in Indonesia focusing on
HIV, HBV, HCV, HDV, HTLV-1/2 and TTV. The 2009’s samples (518 blood
specimens) were screened by serological assays for anti-HIV, HBsAg, anti-HCV,
anti-HDV, anti-HTLV-1/2. In total, 4.8 % (25/518), 3.3 % (17/518), 26.3 %
(136/518), 0.2 % (1/518), 2.9 % (15/518) were positive for anti-HIV, HBsAg,
anti-HCV, anti-HDV, and anti-HTLV-1/2, respectively. Nucleic acid were
extracted from all samples, followed with nested RT-PCR for HIV, HDV, and
HTLV-1/2 and nested PCR for TTV and HBV detection, respectively. The PCR
product for HIV and HCV already sequenced and have been analyzed. Briefly, 13
HIV RNA were succesfully amplified with nested RT PCR for part of HIV pol
region. For HCV, 31 HCV RNA were succesfully amplified with nested RT PCR
for part of HCV E1-E2 and NS5B region. All HBsAg positive samples were
succesfully detected using nested PCR for part of HBV HBsAg gene and HBV
promoter region and precore gene. The isolat was failed detected by molecular
assay. In point of HTLV-1/2, 8 HTLV-1/2 RNA were succesfully amplified by
nested RT PCR for part of HTLV-1/2 LTR and VS region. Also, 104 TTV isolates
were detected using nested PCR addressing the part of TTV N22 region. The
phylogenetic analysis of HIV and HCV isolates revealed that all of our isolates
were different with all HIV and or HCV previous isolated in Indonesia. In 2010
we also collected 400 more samples, and already detected by serological assay for
HIV and HCV. We are going to continue analyse the 2010’s samples in 2011 as
previously described as previously scheduled
Low-Lying Magnetic Excitation of the Shastry-Sutherland Model
By using perturbation calculation and numerical diagonalization, low-energy
spin dynamics of the Shastry-Sutherland model is investigated paying particular
attention to the two-particle coherent motion. In addition to spin-singlet- and
triplet bound states, we find novel branches of coherent motion of a bound
quintet pair, which are usually unstable because of repulsion. Unusual
dispersion observed in neutron-scattering measurements are explained by the
present theory. The importance of the effects of phonon is also pointed out.Comment: 4 pages, 6 figures combined into 1 PSfile. Final version to appear in
Phys.Rev.Lett. (Jan. 2000
X-Band ESR Determination of Dzyaloshinsky-Moriya Interaction in 2D SrCu(BO) System
X-band ESR measurements on a single crystal of SrCu(BO) system in
a temperature range between 10 K and 580 K are presented. The temperature and
angular dependence of unusually broad ESR spectra can be explained by the
inclusion of antisymmetric Dzyaloshinsky-Moriya (DM) interaction, which yields
by far the largest contribution to the linewidth. However, the well-accepted
picture of only out-of-plane interdimer DM vectors is not sufficient for
explanation of the observed angular dependence. In order to account for the
experimental linewidth anisotropy we had to include sizable in-plane components
of interdimer as well as intradimer DM interaction in addition to the
out-of-plane interdimer one. The nearest-neighbor DM vectors lie perpendicular
to crystal anisotropy c-axis due to crystal symmetry. We also emphasize that
above the structural phase transition occurring at 395 K dynamical mechanism
should be present allowing for instantaneous DM interactions. Moreover, the
linewidth at an arbitrary temperature can be divided into two contributions;
namely, the first part arising from spin dynamics governed by the spin
Hamiltonian of the system and the second part due to significant spin-phonon
coupling. The nature of the latter mechanism is attributed to phonon-modulation
of the antisymmetric interaction, which is responsible for the observed linear
increase of the linewidth at high temperatures.Comment: 17 pages, 4 figures, submitted to PR
Magnetization of SrCu2(BO3)2 in ultrahigh magnetic fields up to 118 T
The magnetization process of the orthogonal-dimer antiferromagnet SrCu2(BO3)2
is investigated in high magnetic fields of up to 118 T. A 1/2 plateau is
clearly observed in the field range 84 to 108 T in addition to 1/8, 1/4 and 1/3
plateaux at lower fields. Using a combination of state-of-the-art numerical
simulations, the main features of the high-field magnetization, a 1/2 plateau
of width 24 T, a 1/3 plateau of width 34 T, and no 2/5 plateau, are shown to
agree quantitatively with the Shastry-Sutherland model if the ratio of inter-
to intra-dimer exchange interactions J'/J=0.63. It is further predicted that
the intermediate phase between the 1/3 and 1/2 plateau is not uniform but
consists of a 1/3 supersolid followed by a 2/5 supersolid and possibly a
domain-wall phase, with a reentrance into the 1/3 supersolid above the 1/2
plateau.Comment: 5 pages + 10 pages supplemental materia
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