411 research outputs found
Dynamical Structure Factors of the S=1/2 Bond-Alternating Spin Chain with a Next-Nearest-Neighbor Interaction in Magnetic Fields
The dynamical structure factor of the S=1/2 bond-alternating spin chain with
a next-nearest-neighbor interaction in magnetic field is investigated using the
continued fraction method based on the Lanczos algorithm. When the plateau
exists on the magnetization curve, the longitudinal dynamical structure factor
shows a large intensity with a periodic dispersion relation, while the
transverse one shows a large intensity with an almost dispersionless mode. The
periodicity and the amplitude of the dispersion relation in the longitudinal
dynamical structure factor are sensitive to the coupling constants. The
dynamical structure factor of the S=1/2 two-leg ladder in magnetic field is
also calculated in the strong interchain-coupling regime.
The dynamical structure factor shows gapless or gapful behavior depending on
the wave vector along the rung.Comment: 8 pages, 4 figures, to appear in Journal of the Physical Society of
Japan, vol. 69, no. 10, (2000
Guardians Ad Litem as Surrogate Parents: Implication for Role Definition and Confidentiality
SALMON (Scalable Ab-initio LightāMattersimulator for Optics and Nanoscience, http://salmon-tddft.jp) is a software package for the simulation of electron dynamics and optical properties of molecules, nanostructures, and crystalline solids based on first-principles time-dependent density functional theory. The core part of the software is the real-time, real-space calculation of the electron dynamics induced in molecules and solids by an external electric field solving the time-dependent KohnāSham equation. Using a weak instantaneous perturbing field, linear response properties such as polarizabilities and photoabsorptions in isolated systems and dielectric functions in periodic systems are determined. Using an optical laser pulse, the ultrafast electronic response that may be highly nonlinear in the field strength is investigated in time domain. The propagation of the laser pulse in bulk solids and thin films can also be included in the simulation via coupling the electron dynamics in many microscopic unit cells using Maxwellās equations describing the time evolution of the electromagnetic fields. The code is efficiently parallelized so that it may describe the electron dynamics in large systems including up to a few thousand atoms. The present paper provides an overview of the capabilities of the software package showing several sample calculations. Program summary Program Title: SALMON: Scalable Ab-initio LightāMatter simulator for Optics and Nanoscience Program Files doi:http://dx.doi.org/10.17632/8pm5znxtsb.1 Licensing provisions: Apache-2.0 Programming language: Fortran 2003 Nature of problem: Electron dynamics in molecules, nanostructures, and crystalline solids induced by an external electric field is calculated based on first-principles time-dependent density functional theory. Using a weak impulsive field, linear optical properties such as polarizabilities, photoabsorptions, and dielectric functions are extracted. Using an optical laser pulse, the ultrafast electronic response that may be highly nonlinear with respect to the exciting field strength is described as well. The propagation of the laser pulse in bulk solids and thin films is considered by coupling the electron dynamics in many microscopic unit cells using Maxwellās equations describing the time evolution of the electromagnetic field. Solution method: Electron dynamics is calculated by solving the time-dependent KohnāSham equation in real time and real space. For this, the electronic orbitals are discretized on a uniform Cartesian grid in three dimensions. Norm-conserving pseudopotentials are used to account for the interactions between the valence electrons and the ionic cores. Grid spacings in real space and time, typically 0.02 nm and 1 as respectively, determine the spatial and temporal resolutions of the simulation results. In most calculations, the ground state is first calculated by solving the static KohnāSham equation, in order to prepare the initial conditions. The orbitals are evolved in time with an explicit integration algorithm such as a truncated Taylor expansion of the evolution operator, together with a predictorācorrector step when necessary. For the propagation of the laser pulse in a bulk solid, Maxwellās equations are solved using a finite-difference scheme. By this, the electric field of the laser pulse and the electron dynamics in many microscopic unit cells of the crystalline solid are coupled in a multiscale framework
Nonlinear Parabolic Equations arising in Mathematical Finance
This survey paper is focused on qualitative and numerical analyses of fully
nonlinear partial differential equations of parabolic type arising in financial
mathematics. The main purpose is to review various non-linear extensions of the
classical Black-Scholes theory for pricing financial instruments, as well as
models of stochastic dynamic portfolio optimization leading to the
Hamilton-Jacobi-Bellman (HJB) equation. After suitable transformations, both
problems can be represented by solutions to nonlinear parabolic equations.
Qualitative analysis will be focused on issues concerning the existence and
uniqueness of solutions. In the numerical part we discuss a stable
finite-volume and finite difference schemes for solving fully nonlinear
parabolic equations.Comment: arXiv admin note: substantial text overlap with arXiv:1603.0387
Direct Observation of Field-Induced Incommensurate Fluctuations in a One-Dimensional S=1/2 Antiferromagnet
Neutron scattering from copper benzoate, Cu(C6D5COO)2 3D2O, provides the
first direct experimental evidence for field-dependent incommensurate low
energy modes in a one-dimensional spin S = 1/2 antiferromagnet. Soft modes
occur for wavevectors q=\pi +- dq(H) where dq(H) ~ 2 \pi M(H)/g\mu_B as
predicted by Bethe ansatz and spinon descriptions of the S = 1/2 chain.
Unexpected was a field-induced energy gap , where
as determined from specific heat measurements. At H = 7 T
(g\mu_B H/J = 0.52), the magnitude of the gap varies from 0.06 - 0.3 J
depending on the orientation of the applied field.Comment: 11 pages, 5 postscript figures, LaTeX, Submitted to PRL 3/31/97,
e-mail comments to [email protected]
A neutron scattering study of two-magnon states in the quantum magnet copper nitrate
We report measurements of the two-magnon states in a dimerized
antiferromagnetic chain material, copper nitrate (Cu(NO3)2*2.5D2O). Using
inelastic neutron scattering we have measured the one and two magnon excitation
spectra in a large single crystal. The data are in excellent agreement with a
perturbative expansion of the alternating Heisenberg Hamiltonian from the
strongly dimerized limit. The expansion predicts a two-magnon bound state for q
~ (2n+1)pi*d which is consistent with the neutron scattering data.Comment: 11 pages of revtex style with 6 figures include
Dynamical Structure Factors of the Spin-1/2 XXZ Chain with Inverse-Square Exchange and Ising Anisotropy
The dynamical properties of the S=1/2 antiferromagnetic XXZ chain are studied
by the exact diagonalization and the recursion method of finite systems up to
24 sites. Two types of the exchange interaction are considered: one is the
nearest-neighbor type, and the other is the inverse-square one. As the Ising
anisotropy becomes larger, there appears a noticeable difference in the
transverse component S^{xx}(q,\omega) between the two types of the exchange.
For the nearest-neighbor type, the peak frequency of S^{xx}(q,\omega) for each
q approaches the center of the continuum spectrum. On the contrary, the peak
frequency for the inverse-square type moves to the upper edge of the continuum,
and separates from the continuum for the anisotropy larger than the threshold
value. Whether the interaction between domain walls (solitons) is absent or
repulsive in the Ising limit leads to this difference in the behavior of
S^{xx}(q,\omega). In the longitudinal component S^{zz}(q,\omega), on the other
hand, the feature of the dynamics is scarcely different between the two types.
The energy gap and the static properties are also discussed.Comment: 10 pages. A hard copy of 16 figures is available on request.
Submitted to J. Phys. Soc. Jp
Magnesium reduces calcification in bovine vascular smooth muscle cells in a dose-dependent manner
WOS: 000300421300010PubMed ID: 21750166Vascular calcification (VC), mainly due to elevated phosphate levels, is one major problem in patients suffering from chronic kidney disease. In clinical studies, an inverse relationship between serum magnesium and VC has been reported. However, there is only few information about the influence of magnesium on calcification on a cellular level available. Therefore, we investigated the effect of magnesium on calcification induced by beta-glycerophosphate (BGP) in bovine vascular smooth muscle cells (BVSMCs). BVSMCs were incubated with calcification media for 14 days while simultaneously increasing the magnesium concentration. Calcium deposition, transdifferentiation of cells and apoptosis were measured applying quantification of calcium, von Kossa and Alizarin red staining, real-time reverse transcription-polymerase chain reaction and annexin V staining, respectively. Calcium deposition in the cells dramatically increased with addition of BGP and could be mostly prevented by co-incubation with magnesium. Higher magnesium levels led to inhibition of BGP-induced alkaline phosphatase activity as well as to a decreased expression of genes associated with the process of transdifferentiation of BVSMCs into osteoblast-like cells. Furthermore, estimated calcium entry into the cells decreased with increasing magnesium concentrations in the media. In addition, higher magnesium concentrations prevented cell damage (apoptosis) induced by BGP as well as progression of already established calcification. Higher magnesium levels prevented BVSMC calcification, inhibited expression of osteogenic proteins, apoptosis and further progression of already established calcification. Thus, magnesium is influencing molecular processes associated with VC and may have the potential to play a role for VC also in clinical situations.Fresenius Medical Care Deutschland GmbH, GermanyThis study was supported by Fresenius Medical Care Deutschland GmbH, Germany
Bloch oscillations of magnetic solitons in anisotropic spin-1/2 chains
We study the quantum dynamics of soliton-like domain walls in anisotropic
spin-1/2 chains in the presence of magnetic fields. In the absence of fields,
domain walls form a Bloch band of delocalized quantum states while a static
field applied along the easy axis localizes them into Wannier wave packets and
causes them to execute Bloch oscillations, i.e. the domain walls oscillate
along the chain with a finite Bloch frequency and amplitude. In the presence of
the field, the Bloch band, with a continuum of extended states, breaks up into
the Wannier-Zeeman ladder -- a discrete set of equally spaced energy levels. We
calculate the dynamical structure factor in the one-soliton sector at finite
frequency, wave vector, and temperature, and find sharp peaks at frequencies
which are integer multiples of the Bloch frequency. We further calculate the
uniform magnetic susceptibility and find that it too exhibits peaks at the
Bloch frequency. We identify several candidate materials where these Bloch
oscillations should be observable, for example, via neutron scattering
measurements. For the particular compound CoCl_2.2H_2O we estimate the Bloch
amplitude to be on the order of a few lattice constants, and the Bloch
frequency on the order of 100 GHz for magnetic fields in the Tesla range and at
temperatures of about 18 Kelvin.Comment: 31 single-spaced REVTeX pages, including 7 figures embedded with eps
Electron Spin Resonance in S=1/2 antiferromagnetic chains
A systematic field-theory approach to Electron Spin Resonance (ESR) in the
quantum antiferromagnetic chain at low temperature (compared to the
exchange coupling ) is developed. In particular, effects of a transverse
staggered field and an exchange anisotropy (including a dipolar
interaction) on the ESR lineshape are discussed. In the lowest order
of perturbation theory, the linewidth is given as and
, respectively. In the case of a transverse staggered
field, the perturbative expansion diverges at lower temperature;
non-perturbative effects at very low temperature are discussed using exact
results on the sine-Gordon field theory. We also compare our field-theory
results with the predictions of Kubo-Tomita theory for the high-temperature
regime, and discuss the crossover between the two regimes. It is argued that a
naive application of the standard Kubo-Tomita theory to the
Dzyaloshinskii-Moriya interaction gives an incorrect result. A rigorous and
exact identity on the polarization dependence is derived for certain class of
anisotropy, and compared with the field-theory results.Comment: 53 pages in REVTEX, 7 figures in EPS included; revised version with
missing references and correction
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