359 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 LightâMattersimulator 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 KohnâSham 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 Maxwellâs 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 LightâMatter 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 Maxwellâs equations describing the time evolution of the electromagnetic field. Solution method: Electron dynamics is calculated by solving the time-dependent KohnâSham 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 KohnâSham 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 predictorâcorrector step when necessary. For the propagation of the laser pulse in a bulk solid, Maxwellâs 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
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
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
Ambitious subsidy reform by the WTO presents opportunities for ocean health restoration
This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordThe World Trade Organization (WTO) is in a unique position to deliver on Sustainable Development Goal (SDG) 14.6 by reforming global fisheries subsidies in 2020. Yet, a number of unanswered questions threaten to inhibit WTO delegates from crafting a smart agreement that improves global fisheries health. We combine global data on industrial fishing activity, subsidies, and stock assessments to show that: (1) subsidies prop up fishing effort all across the worldâs ocean and (2) larger subsidies tend to occur in fisheries that are poorly managed. When combined, this evidence suggests that subsidy reform could have geographically-extensive consequences for many of the worldâs largest fisheries. While much work remains to establish causality and make quantitative predictions, this evidence informs the rapidly-evolving policy debate and we conclude with actionable policy suggestions.Pew Charitable Trust
The Effective Fragment Molecular Orbital Method for Fragments Connected by Covalent Bonds
We extend the effective fragment molecular orbital method (EFMO) into
treating fragments connected by covalent bonds. The accuracy of EFMO is
compared to FMO and conventional ab initio electronic structure methods for
polypeptides including proteins. Errors in energy for RHF and MP2 are within 2
kcal/mol for neutral polypeptides and 6 kcal/mol for charged polypeptides
similar to FMO but obtained two to five times faster. For proteins, the errors
are also within a few kcal/mol of the FMO results. We developed both the RHF
and MP2 gradient for EFMO. Compared to ab initio, the EFMO optimized structures
had an RMSD of 0.40 and 0.44 {\AA} for RHF and MP2, respectively.Comment: Revised manuscrip
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Multi-lingual and multi-cultural information literacy; perspectives, models and good practice
Purpose
This paper reviews current approaches to, and good practice, in information literacy development in multi-lingual and multi-cultural settings, with particular emphasis on provision for international students.
Design/methodology/approach
A selective and critical review of published literature is extended by evaluation of examples of multi-lingual information literacy tutorials and MOOCs.
Findings
Multi-lingual and multi-cultural information literacy are umbrella terms covering a variety of situations and issues. This provision is of increasing importance in an increasingly mobile and multi-cultural world. This article evaluates current approaches and good practice, focusing on issues of culture vis a vis language, the balance between individual and group needs, specific and generic information literacy instruction, and models for information literacy, pedagogy and culture. Recommendations for good practice and for further research are given,
Originality/value
This is one of very few articles critically reviewing how information literacy development is affected by linguistic and cultural factors
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