4,313 research outputs found
Convergent expansions for properties of the Heisenberg model for CaVO
We have carried out a wide range of calculations for the Heisenberg
model with nearest- and second-neighbor interactions on a two-dimensional
lattice which describes the geometry of the vanadium ions in the spin-gap
system CaVO. The methods used were convergent high-order perturbation
expansions (``Ising'' and ``Plaquette'' expansions at , as well as
high-temperature expansions) for quantities such as the uniform susceptibility,
sublattice magnetization, and triplet elementary excitation spectrum.
Comparison with the data for CaVO indicates that its magnetic
properties are well described by nearest-neighbor exchange of about 200K in
conjunction with second-neighbor exchange of about 100K.Comment: Uses REVTEX macros. Four pages in two-column format, five postscript
figures. Files packaged using uufile
The twistor geometry of three-qubit entanglement
A geometrical description of three qubit entanglement is given. A part of the
transformations corresponding to stochastic local operations and classical
communication on the qubits is regarded as a gauge degree of freedom. Entangled
states can be represented by the points of the Klein quadric a space
known from twistor theory. It is shown that three-qubit invariants are
vanishing on special subspaces of . An invariant vanishing for the
class is proposed. A geometric interpretation of the canonical
decomposition and the inequality for distributed entanglement is also given.Comment: 4 pages RevTeX
Effective-Medium Theory for the Normal State in Orientationally Disordered Fullerides
An effective-medium theory for studying the electronic structure of the
orientationally disordered A3C60 fullerides is developed and applied to study
various normal-state properties. The theory is based on a cluster-Bethe-lattice
method in which the disordered medium is modelled by a three-band Bethe
lattice, into which we embed a molecular cluster whose scattering properties
are treated exactly. Various single-particle properties and the
frequency-dependent conductivity are calculated in this model, and comparison
is made with numerical calculations for disordered lattices, and with
experiment.Comment: 12 pages + 2 figures, REVTeX 3.
Generic singularities of symplectic and quasi-symplectic immersions
For any k<2n we construct a complete system of invariants in the problem of
classifying singularities of immersed k-dimensional submanifolds of a
symplectic 2n-manifold at a generic double point.Comment: 12 page
Dynamical Structure Factors for Dimerized Spin Systems
We discuss the transition strength between the disordered ground state and
the basic low-lying triplet excitation for interacting dimer materials by
presenting theoretical calculations and series expansions as well as inelastic
neutron scattering results for the material KCuCl_3. We describe in detail the
features resulting from the presence of two differently oriented dimers per
unit cell and show how energies and spectral weights of the resulting two modes
are related to each other. We present results from the perturbation expansion
in the interdimer interaction strength and thus demonstrate that the wave
vector dependence of the simple dimer approximation is modified in higher
orders. Explicit results are given in 10th order for dimers coupled in 1D, and
in 2nd order for dimers coupled in 3D with application to KCuCl_3 and TlCuCl_3.Comment: 17 pages, 6 figures, part 2 is based on cond-mat/021133
Minimal distance transformations between links and polymers: Principles and examples
The calculation of Euclidean distance between points is generalized to
one-dimensional objects such as strings or polymers. Necessary and sufficient
conditions for the minimal transformation between two polymer configurations
are derived. Transformations consist of piecewise rotations and translations
subject to Weierstrass-Erdmann corner conditions. Numerous examples are given
for the special cases of one and two links. The transition to a large number of
links is investigated, where the distance converges to the polymer length times
the mean root square distance (MRSD) between polymer configurations, assuming
curvature and non-crossing constraints can be neglected. Applications of this
metric to protein folding are investigated. Potential applications are also
discussed for structural alignment problems such as pharmacophore
identification, and inverse kinematic problems in motor learning and control.Comment: Submitted to J. Phys.:Condens. Matte
On the relation between p-adic and ordinary strings
The amplitudes for the tree-level scattering of the open string tachyons,
generalised to the field of p-adic numbers, define the p-adic string theory.
There is empirical evidence of its relation to the ordinary string theory in
the p_to_1 limit. We revisit this limit from a worldsheet perspective and argue
that it is naturally thought of as a continuum limit in the sense of the
renormalisation group.Comment: 13 pages harvmac (b), 2 eps figures; v2: revtex, shortened, published
versio
PLAGIARISM IN DISSERTATIONS
Introduction. Originality and independence is the first, absolute and general requirement to the content of dissertations, regardless of an academic degree and research direction. At the same time, recently a considerable fraction of different types of plagiarism have been found out in the Russian dissertation works. The aim is an analysis of the most frequent plagiarism in candidate and doctoral dissertations. Results. We consider the established practices in the evaluation of independence in academic works. Unethical use of someone else’s work and materials by the authors of dissertations include, in particular, copying from official documents and abstracts without acknowledgement the source and with no citation; replication of existing reviews and chapters from already defended dissertations; falsification by refreshing of outdated data with substituted dates, and or wordfor-word copy-pasting with substitution of the research object. The latter type of the plagiarism involving fraud in experimental and statistical data constitutes a special peril for the science and for the society in general. The primary principle for assessment of independence in dissertations has to be proper citing and referencing that should allow a reader to distinguish the author’s contribution from someone else’s text. Undocumented verbatim quotations in dissertations are inadmissible, whether the author claims scientific novelty or not. At that, it does not matter whether well-known or unique data are provided, and whether the source is protected by a copyright. Practical significance. The qualitative analysis of the factual material, based on the author’s observations, can serve as a starting point for the subsequent quantitative analysis of plagiarism in scientific texts. Введение. Оригинальность и самостоятельность – первое, абсолютное и не подлежащее каким-либо исключениям и оговоркам общее требование, предъявляемое к содержанию диссертаций, независимо от ученой степени, на которую претендует соискатель, и от научного направления исследования. Вместе с тем в последние годы различные виды плагиата приобрели в российских диссертационных работах массовый характер. Цель статьи – типологический анализ неправомерных заимствований, наиболее часто встречающихся в текстах кандидатских и докторских диссертаций. Результаты. С критических позиций рассмотрена сложившаяся практика оценки степени самостоятельности научного текста. Показаны и разобраны распространенные варианты недобросовестного использования диссертантами фрагментов чужих работ и материалов: копирование без указания источников частей из официальных документов и авторефератов, тиражирование обзорных глав и шаблонных изложений, фальсификации посредством «осовременивания» устаревших данных или дословного плагиата с подменой объекта исследования. Последняя разновидность заимствований, сопряженных с подлогом экспериментальных и статистических данных, представляет особую опасность для науки и для общества в целом. Подчеркивается, что базовым принципом экспертной оценки самостоятельности диссертационной работы должно быть требование адекватного оформления в ней заимствований, позволяющего отделить собственный текст диссертанта от чужого текста. Независимо от того, претендует автор на научную новизну или нет, недокументированные заимствования в диссертациях недопустимы. При этом не имеет значения, приводятся ли общеизвестные или уникальные сведения и охраняется ли источник заимствования авторским правом. Практическая значимость. Предлагаемый к обсуждению качественный анализ фактического материала, основанный на наблюдениях автора, может служить отправной точкой для последующего количественного анализа плагиата в научных текстах
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