197 research outputs found
Eden growth model for aggregation of charged particles
The stochastic Eden model of charged particles aggregation in two-dimensional
systems is presented. This model is governed by two parameters: screening
length of electrostatic interaction, , and short range attraction
energy, . Different patterns of finite and infinite aggregates are observed.
They are of following types of morphologies: linear or linear with bending,
warm-like, DBM (dense-branching morphology), DBM with nucleus, and compact
Eden-like. The transition between the different modes of growth is studied and
phase diagram of the growth structures is obtained in
co-ordinates. The detailed aggregate structure analysis, including analysis of
their fractal properties, is presented. The scheme of the internal
inhomogeneous structure of aggregates is proposed.Comment: Revtex, 9 pages with 12 postscript figure
Deterministic growth model of Laplacian charged particle aggregates
The results of the computer simulation of the aggregates growth of the
similarly charged particles in the framework of deterministic Laplacian growth
model on a square lattice are presented. Cluster growth is controlled by three
parameters , where - Laplacian growth parameter, -
energy of a particle sticking to a cluster, - the screening length of
electrostatic interactions. The phase diagram of cluster growth is built in the
co-ordinates . The zones of different cluster morphology are
selected: I-the zone of finite X-like structures,II-the zone of infinite
ramified structures, controlled by electrostatic interactions, III-the zone of
infinite structures with electrostatic interactions effectively switched off.
Simple electrostatic estimations of the locations of the zone boundaries are
presented. It is shown that in general case within the zone II the continuous
change of , controlled by parameters , takes place. In the
degeneration limit when the given model transforms into deterministic version
of the Eden model (at ), the crossover from linear to compact
structures is observed when passing through the boundary between the
zones I and II.Comment: REVTEX, 3 pages with 4 postscript figure
Tapping into rhythm generation circuitry in humans during simulated weightlessness conditions
An ability to produce rhythmic activity is ubiquitous for locomotor pattern generation and modulation. The role that the rhythmogenesis capacity of the spinal cord plays in injured populations has become an area of interest and systematic investigation among researchers in recent years, despite its importance being long recognized by neurophysiologists and clinicians. Given that each individual interneuron, as a rule, receives a broad convergence of various supraspinal and sensory inputs and may contribute to a vast repertoire of motor actions, the importance of assessing the functional state of the spinal locomotor circuits becomes increasingly evident. Air-stepping can be used as a unique and important model for investigating human rhythmogenesis since its manifestation is largely facilitated by a reduction of external resistance. This article aims to provide a review on current issues related to the "locomotor" state and interactions between spinal and supraspinal influences on the central pattern generator (CPG) circuitry in humans, which may be important for developing gait rehabilitation strategies in individuals with spinal cord and brain injuries
Coupling of upper and lower limb pattern generators during human crawling at different arm/leg speed combinations
A crawling paradigm was performed by healthy adults to examine inter-limb coupling patterns and to understand how central pattern generators (CPGs) for the upper and lower limbs are coordinated. Ten participants performed hands-and-feet crawling on two separate treadmills, one for the upper limbs and another one for the lower limbs, the speed of each of them being changed independently. A 1:1 frequency relationship was often maintained even when the treadmill speed was not matched between the upper and lower limbs. However, relative stance durations in the upper limbs were only affected by changes of the upper limb treadmill speed, suggesting that although absolute times are adjusted, the relative proportions of stances and swing do not adapt to changes in lower limb treadmill speeds. With large differences between treadmill speeds, changes in upper and lower limb coupling ratio tended to occur when the upper limbs stepped at slower speeds than the lower limbs, but more rarely the other way around. These findings are in sharp contrast with those in the cat, where forelimbs always follow the rhythm of the faster moving hindlimbs. However, the fact that an integer frequency ratio is often maintained between the upper and lower limbs supports evidence of coupled CPG control. We speculate that the preference for the upper limb to decrease step frequency at lower speeds in humans may be due to weaker ascending propriospinal connections and/or a larger influence of cortical control on the upper limbs which allows for an overriding of spinal CPG control
Shape of primary proton spectrum in multi-TeV region from data on vertical muon flux
It is shown, that primary proton spectrum, reconstructed from sea-level and
underground data on muon spectrum with the use of QGSJET 01, QGSJET II, NEXUS
3.97 and SIBYLL 2.1 interaction models, demonstrates not only model-dependent
intensity, but also model-dependent form. For correct reproduction of muon
spectrum shape primary proton flux should have non-constant power index for all
considered models, except SIBYLL 2.1, with break at energies around 10-15 TeV
and value of exponent before break close to that obtained in ATIC-2 experiment.
To validate presence of this break understanding of inclusive spectra behavior
in fragmentation region in p-air collisions should be improved, but we show,
that it is impossible to do on the basis of the existing experimental data on
primary nuclei, atmospheric muon and hadron fluxes.Comment: Submitted to Phys. Rev.
Spinal motoneurons of the human newborn are highly synchronized during leg movements
Motoneurons of neonatal rodents show synchronous activity that modulates the development of the neuromuscular system. However, the characteristics of the activity of human neonatal motoneurons are largely unknown. Using a noninvasive neural interface, we identified the discharge timings of individual spinal motoneurons in human newborns. We found highly synchronized activities of motoneurons of the tibialis anterior muscle, which were associated with fast leg movements. Although neonates' motor units exhibited discharge rates similar to those of adults, their synchronization was significantly greater than in adults. Moreover, neonatal motor units showed coherent oscillations in the delta band, which is directly translated into force generation. These results suggest that motoneuron synchronization in human neonates might be an important mechanism for controlling fast limb movements, such as those of primitive reflexes. In addition to help revealing mechanisms of development, the proposed neural interface might monitor children at risk of developing motor disorders
Is PSR B0943+10 a low-mass quark star?
A recent X-ray observation has shown that the radio pulsar PSR B0943+10, with
clear drifting subpulses, has a much smaller polar cap area than that of
conventional pulsars with mass of \sim\msun and radius of km. Zhang
et al. (2005) addressed then that this new result conflicts with the standard
vacuum gap model. Nonetheless, the discrepancy could be explained if PSR
B0943+10 is actually a low-mass quark star. It is found that the potential drop
in the open-field-line region of oblique pulsars (i.e., inclination angle
) might be times that of aligned pulsars, and that
PSR B0943+10 with could be well above the deathline. We
thus conclude that the Ruderman-Sutherland-type vacuum gap model still works
well for this pulsar if it is a bare quark star with a mass of and a radius of km.Comment: 10 pages, 2 figures, accepted for publication in ApJ Letter
International standards of penitentiary activity: impact on the development of the penitentiary activity of the CIS countries
Overcrowding in prisons is a common problem that affects many countries. It is difficult to define this term because there is no single internationally accepted standard. This article presents a comparative study of international standards for the activities of doctors in penitentiary institutions as an integral part of international standards of penitentiary activity. The authors investigated the methods and the degree of their impact on the penitentiary legislation of the Russian Federation and other CIS countries. The conclusion is drawn about the positive role of such standards in improving the national penitentiary legislation in order to increase the level of medical care for prisoner
Blocking from continuum and monopoles in gluodynamics
We review the method of blocking of topological defects from continuum used
as a non--perturbative tool to construct effective actions for these defects.
The actions are formulated in the continuum limit while the couplings of these
actions can be derived from simple observables calculated numerically on
lattices with a finite lattice spacing. We demonstrate the success of the
method in deriving the effective actions for Abelian monopoles in the pure
SU(2) gauge models in an Abelian gauge. In particular, we discuss the
gluodynamics in three and four space--time dimensions at zero and non--zero
temperatures. Besides the action the quantities of our interest are the
monopole density, the magnetic Debye mass and the monopole condensate.Comment: 24 pages, 16 figures, RevTeX 4; To be published in Phys. Atom. Nucl.
dedicated to the 70th Birthday of Professor Yu. A. Simono
Rotating Black Hole, Twistor-String and Spinning Particle
We discuss basic features of the model of spinning particle based on the Kerr
solution. It contains a very nontrivial {\it real} stringy structure consisting
of the Kerr circular string and an axial stringy system.
We consider also the complex and twistorial structures of the Kerr geometry
and show that there is a {\it complex} twistor-string built of the complex N=2
chiral string with a twistorial structure. By imbedding into the
real Minkowski , the N=2 supersymmetry is partially broken and string
acquires the open ends. Orientifolding this string, we identify the chiral and
antichiral structures. Target space of this string is equivalent to the
Witten's `diagonal' of the Comment: 19 p. 4 figures, extended version of hep-th/0412065, based on the
talk given at the Conference `Symmetries and Spin'(SPIN-Praha-2004) July 200
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