1,753 research outputs found
The geometry of spontaneous spiking in neuronal networks
The mathematical theory of pattern formation in electrically coupled networks
of excitable neurons forced by small noise is presented in this work. Using the
Freidlin-Wentzell large deviation theory for randomly perturbed dynamical
systems and the elements of the algebraic graph theory, we identify and analyze
the main regimes in the network dynamics in terms of the key control
parameters: excitability, coupling strength, and network topology. The analysis
reveals the geometry of spontaneous dynamics in electrically coupled network.
Specifically, we show that the location of the minima of a certain continuous
function on the surface of the unit n-cube encodes the most likely activity
patterns generated by the network. By studying how the minima of this function
evolve under the variation of the coupling strength, we describe the principal
transformations in the network dynamics. The minimization problem is also used
for the quantitative description of the main dynamical regimes and transitions
between them. In particular, for the weak and strong coupling regimes, we
present asymptotic formulas for the network activity rate as a function of the
coupling strength and the degree of the network. The variational analysis is
complemented by the stability analysis of the synchronous state in the strong
coupling regime. The stability estimates reveal the contribution of the network
connectivity and the properties of the cycle subspace associated with the graph
of the network to its synchronization properties. This work is motivated by the
experimental and modeling studies of the ensemble of neurons in the Locus
Coeruleus, a nucleus in the brainstem involved in the regulation of cognitive
performance and behavior
Superbroad Component in Emission Lines of SS 433
We have detected new components in stationary emission lines of SS 433; these
are the superbroad components that are low-contrast substrates with a width of
2000--2500 km s-1 in He I and H and 4000--5000 km s-1 in
He II . Based on 44 spectra taken during four years of
observations from 2003 to 2007, we have found that these components in the He
II and He I lines are eclipsed by the donor star; their behavior with
precessional and orbital phases is regular and similar to the behavior of the
optical brightness of SS 433. The same component in H shows neither
eclipses nor precessional variability. We conclude that the superbroad
components in the helium and hydrogen lines are different in origin. Electron
scattering is shown to reproduce well the superbroad component of H at a
gas temperature of 20--35 kK and an optical depth for Thomson scattering 0.25--0.35. The superbroad components of the helium lines are probably
formed in the wind from the supercritical accretion disk. We have computed a
wind model based on the concept of Shakura-Sunyaev supercritical disk
accretion. The main patterns of the He II line profiles are well reproduced in
this model: not only the appearance of the superbroad component but also the
evolution of the central two-component part of the profile of this line during
its eclipse by the donor star can be explained.Comment: 17 pages, 13 figures, 2 tables, published in Astronomy Letters, 2013,
vol. 39, N 12, pp. 826 - 84
Anti-Aggregation Function of Blood Vessels in Piglets of Dairy and Plant Nutrition
Modern pig farming is a significant sector of modern agriculture in many countries. The attractiveness of its products is associated with their excellent taste and economic affordability. The intensive development of pig breeding considers the latest achievements in the field of pig biology during their early ontogenesis. Optimal functioning of hemostasis in growing piglets relies on platelet activity. Its low severity during the phase of milk and vegetable nutrition provides them with the optimal functional state of primary hemostasis, the success of microcirculation in the internal organs, and sufficient activity of all functional and biochemical processes. In the blood of healthy piglets during the phase of dairy and plant nutrition, a decrease in the number of peroxidation products was noted due to an increase in the level of antioxidant protection of their plasma. This minimized their platelet and vascular wall alteration and provided optimal platelet-vascular interactions. This study shows that the gradual increase in the platelet aggregation that develops in piglets at this age is functionally balanced by the increase in the disaggregation properties of blood vessels and creates conditions for optimal blood flow in small-caliber vessels.
Keywords: piglets, phase of dairy and plant nutrition, platelets, aggregation, disaggregation, early ontogenesi
Comparative analysis of order allocation methods and intelligent systems for effective download of production capacities of manufacturing enterprise
The article compares the planning systems of the enterprise, determines their opportunities to use simulation for the process of distribution of production orders. A comparative review of the methods used in production planning systems and the multi-agent approach in solving the problem of the allocation of production orders is carried out. The possibility of approaches in cases when it is impossible to perform production tasks within the established time frame is considered, as well as to effectively load the available capacities of the units. In case it is not possible to produce the necessary quantity to distribute the part to another, similar to the type of equipment used, but different from it by the quantity and production capacity of the unit. Transmission must be carried out under the condition of sufficient capacity in the subdivision. The results of theoretical and experimental studies are presented. In the process of work, we used the BPsim. MAS dynamic modeling system. An automated system with the possibility of using simulation for the allocation of production orders is considered. © 2019 IOP Publishing Ltd. All rights reserved.The work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0006
Fermi-liquid and Fermi surface geometry effects in propagation of low frequency electromagnetic waves through thin metal films
In the present work we theoretically analyze the contribution from a
transverse Fermi-liquid collective mode to the transmission of electromagnetic
waves through a thin film of a clean metal in the presence of a strong external
magnetic field. We show that at the appropriate Fermi surface geometry the
transverse Fermi-liquid wave may appear in conduction electrons liquid at
frequencies significantly smaller than the cyclotron frequency of
charge carriers provided that the mean collision frequency
is smaller than Also, we show that in realistic metals size
oscillations in the transmission coefficient associated with the Firmi-liquid
mode may be observable in experiments. Under certain conditions these
oscillations may predominate over the remaining size effects in the
transmission coefficient.Comment: 9 pages, 5 figures, text adde
Shaping bursting by electrical coupling and noise
Gap-junctional coupling is an important way of communication between neurons
and other excitable cells. Strong electrical coupling synchronizes activity
across cell ensembles. Surprisingly, in the presence of noise synchronous
oscillations generated by an electrically coupled network may differ
qualitatively from the oscillations produced by uncoupled individual cells
forming the network. A prominent example of such behavior is the synchronized
bursting in islets of Langerhans formed by pancreatic \beta-cells, which in
isolation are known to exhibit irregular spiking. At the heart of this
intriguing phenomenon lies denoising, a remarkable ability of electrical
coupling to diminish the effects of noise acting on individual cells.
In this paper, we derive quantitative estimates characterizing denoising in
electrically coupled networks of conductance-based models of square wave
bursting cells. Our analysis reveals the interplay of the intrinsic properties
of the individual cells and network topology and their respective contributions
to this important effect. In particular, we show that networks on graphs with
large algebraic connectivity or small total effective resistance are better
equipped for implementing denoising. As a by-product of the analysis of
denoising, we analytically estimate the rate with which trajectories converge
to the synchronization subspace and the stability of the latter to random
perturbations. These estimates reveal the role of the network topology in
synchronization. The analysis is complemented by numerical simulations of
electrically coupled conductance-based networks. Taken together, these results
explain the mechanisms underlying synchronization and denoising in an important
class of biological models
Steady states in Leith's model of turbulence
We present a comprehensive study and full classification of the stationary solutions in Leith's model of turbulence with a generalised viscosity. Three typical types of boundary value problems are considered: Problems 1 and 2 with a finite positive value of the spectrum at the left (right) and zero at the right (left) boundaries of a wave number range, and Problem 3 with finite positive values of the spectrum at both boundaries. Settings of these problems and analysis of existence of their solutions are based on a phase–space analysis of orbits of the underlying dynamical system. One of the two fixed points of the underlying dynamical system is found to correspond to a 'sharp front' where the energy flux and the spectrum vanish at the same wave number. The other fixed point corresponds to the only exact power-law solution—the so-called dissipative scaling solution. The roles of the Kolmogorov, dissipative and thermodynamic scaling, as well as of sharp front solutions, are discussed
Enrichment of the hot intracluster medium: observations
Four decades ago, the firm detection of an Fe-K emission feature in the X-ray
spectrum of the Perseus cluster revealed the presence of iron in its hot
intracluster medium (ICM). With more advanced missions successfully launched
over the last 20 years, this discovery has been extended to many other metals
and to the hot atmospheres of many other galaxy clusters, groups, and giant
elliptical galaxies, as evidence that the elemental bricks of life -
synthesized by stars and supernovae - are also found at the largest scales of
the Universe. Because the ICM, emitting in X-rays, is in collisional ionisation
equilibrium, its elemental abundances can in principle be accurately measured.
These abundance measurements, in turn, are valuable to constrain the physics
and environmental conditions of the Type Ia and core-collapse supernovae that
exploded and enriched the ICM over the entire cluster volume. On the other
hand, the spatial distribution of metals across the ICM constitutes a
remarkable signature of the chemical history and evolution of clusters, groups,
and ellipticals. Here, we summarise the most significant achievements in
measuring elemental abundances in the ICM, from the very first attempts up to
the era of XMM-Newton, Chandra, and Suzaku and the unprecedented results
obtained by Hitomi. We also discuss the current systematic limitations of these
measurements and how the future missions XRISM and Athena will further improve
our current knowledge of the ICM enrichment.Comment: 49 pages. Review paper. Accepted for publication on Space Science
Reviews. This is the companion review of "Enrichment of the hot intracluster
medium: numerical simulations
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