102 research outputs found
Form factors in RQM approaches: constraints from space-time translations
Different relativistic quantum mechanics approaches have recently been used
to calculate properties of various systems, form factors in particular. It is
known that predictions, which most often rely on a single-particle current
approximation, can lead to predictions with a very large range. It was shown
that accounting for constraints related to space-time translations could
considerably reduce this range. It is shown here that predictions can be made
identical for a large range of cases. These ones include the following
approaches: instant form, front form, and "point-form" in arbitrary momentum
configurations and a dispersion-relation approach which can be considered as
the approach which the other ones should converge to. This important result
supposes both an implementation of the above constraints and an appropriate
single-particle-like current. The change of variables that allows one to
establish the equivalence of the approaches is given. Some points are
illustrated with numerical results for the ground state of a system consisting
of scalar particles.Comment: 37 pages, 7 figures; further comments in ps 16 and 19; further
references; modified presentation of some formulas; corrected misprint
Evolving networks with disadvantaged long-range connections
We consider a growing network, whose growth algorithm is based on the
preferential attachment typical for scale-free constructions, but where the
long-range bonds are disadvantaged. Thus, the probability to get connected to a
site at distance is proportional to , where is a
tunable parameter of the model. We show that the properties of the networks
grown with are close to those of the genuine scale-free
construction, while for the structure of the network is vastly
different. Thus, in this regime, the node degree distribution is no more a
power law, and it is well-represented by a stretched exponential. On the other
hand, the small-world property of the growing networks is preserved at all
values of .Comment: REVTeX, 6 pages, 5 figure
К вопросу о биотерроризме и биобезопасности
The article offers a brief discussion of biosecurity and bioterrorism policy issues that are directly connected with genetics value determinants, responsibility and outlook of scientist engaged in biotechnology and nanotechnology and also with the problems of nanostructures used when creating genetically modified organisms and products.В статье предлагается рассмотреть вопросы биобезопасности и биотерроризма, что непосредственно связано с ценностными детерминантами генетики, мировоззрением и ответственностью ученого, занимающегося биотехнологиями, нанотехнологиями, а также вопросами применения наноструктур при создании генетически модифицированных организмов и продуктов
Безопасная экзистенция современного человека и функции государственного регулирования
В статье раскрываются функции государственного регулирования сферы безопасности, а также кратко представлены цели и типы регулирующих отношений, которые выступают интегрирующим фактором многообразных социальных интересов как государственного аппарата, так и других субъектов регулирования. Ключевые слова: безопасность, регулирование, субъекты государственного регулирования, типы, функции регулирующих отношений в сфере безопасности. The article describes the state security sector regulatory functions, as well as summarizes the objectives and types of regulating relationships that are the integrating factor of the diverse social interests as the state apparatus, and other regulatory entities. Keywords: safety, regulation, state regulation of subjects, types, functions, regulating relations in the sphere of security
Relativistic Quantum Mechanics - Particle Production and Cluster Properties
This paper constructs relativistic quantum mechanical models of particles
satisfying cluster properties and the spectral condition which do not conserve
particle number. The treatment of particle production is limited to systems
with a bounded number of bare-particle degrees of freedom. The focus of this
paper is about the realization of cluster properties in these theories.Comment: 36 pages, Late
Correlations in Scale-Free Networks: Tomography and Percolation
We discuss three related models of scale-free networks with the same degree
distribution but different correlation properties. Starting from the
Barabasi-Albert construction based on growth and preferential attachment we
discuss two other networks emerging when randomizing it with respect to links
or nodes. We point out that the Barabasi-Albert model displays dissortative
behavior with respect to the nodes' degrees, while the node-randomized network
shows assortative mixing. These kinds of correlations are visualized by
discussig the shell structure of the networks around their arbitrary node. In
spite of different correlation behavior, all three constructions exhibit
similar percolation properties.Comment: 6 pages, 2 figures; added reference
Constraints of cluster separability and covariance on current operators
Realistic models of hadronic systems should be defined by a dynamical unitary
representation of the Poincare group that is also consistent with cluster
properties and a spectral condition. All three of these requirements constrain
the structure of the interactions. These conditions can be satisfied in
light-front quantum mechanics, maintaining the advantage of having a kinematic
subgroup of boosts and translations tangent to a light front. The most
straightforward construction of dynamical unitary representations of the
Poincare group due to Bakamjian and Thomas fails to satisfy the cluster
condition for more than two particles. Cluster properties can be restored, at
significant computational expense, using a recursive method due to Sokolov. In
this work we report on an investigation of the size of the corrections needed
to restore cluster properties in Bakamjian-Thomas models with a light-front
kinematic symmetry. Our results suggest that for models based on nucleon and
meson degrees of freedom these corrections are too small to be experimentally
observed.Comment: Contribution to Light Cone 2011, Dallas TX, 4 pages, 2 figure
Voronoi-Delaunay analysis of normal modes in a simple model glass
We combine a conventional harmonic analysis of vibrations in a one-atomic
model glass of soft spheres with a Voronoi-Delaunay geometrical analysis of the
structure. ``Structure potentials'' (tetragonality, sphericity or perfectness)
are introduced to describe the shape of the local atomic configurations
(Delaunay simplices) as function of the atomic coordinates. Apart from the
highest and lowest frequencies the amplitude weighted ``structure potential''
varies only little with frequency. The movement of atoms in soft modes causes
transitions between different ``perfect'' realizations of local structure. As
for the potential energy a dynamic matrix can be defined for the ``structure
potential''. Its expectation value with respect to the vibrational modes
increases nearly linearly with frequency and shows a clear indication of the
boson peak. The structure eigenvectors of this dynamical matrix are strongly
correlated to the vibrational ones. Four subgroups of modes can be
distinguished
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