Critical States in a Dissipative Sandpile Model

A directed dissipative sandpile model is studied in the two-dimension. Numerical results indicate that the long time steady states of this model are critical when grains are dropped only at the top or, everywhere. The critical behaviour is mean-field like. We discuss the role of infinite avalanches of dissipative models in periodic systems in determining the critical behaviour of same models in open systems.Comment: 4 pages (Revtex), 5 ps figures (included

High voltage decoupled high-current power supply

A 10 kW power supply (PS) with smooth adjustment of the load current from zero up to 2 kA is described. The operating mode with a load current stability up to 0.1% and long-term instability of 0.01% is possible. The PS includes the controlled rectifier with the power factor correction, the high-frequency invertor, 35 kV decoupled transformer-rectifier module and the control block.Описан источник питания (ИП) мощностью 10 кВт с плавной регулировкой тока нагрузки от нуля до 2 кА. Возможен режим работы со стабильностью выходного тока до 0.1% и долговременной нестабильностью 0.01%. ИП включает в себя управляемый выпрямитель с корректором коэффициента мощности, высокочастотный инвертор, трансформаторно-выпрямительный модуль с высоковольтной развязкой до 35 кВ и блок управления.Описано джерело живлення (ДЖ) потужністю 10 кВт з плавним регулюванням струму навантаження від нуля до 2 кА. Можливий режим роботи з стабільністю вихідного струму до 0.1% і довгостроковою нестабільністю 0.01%. ДЖ містить у собі керований випрямляч з коректором коефіцієнта потужності, високочастотний інвертор, трансформаторно-випрямляючий модуль з високовольтною розв'язкою до 35 кВ і блок керування

Probing partially localized supergravity background of fundamental string ending on Dp-brane

We study the dynamics of the probe fundamental string in the field background of the partially localized supergravity solution for the fundamental string ending on Dp-brane. We separately analyze the probe dynamics for its motion along the worldvolume direction and the transverse direction of the source Dp-brane. We compare the dynamics of the probe along the Dp-brane worldvolume direction to the BIon dynamics.Comment: 20 pages, LaTeX, revised version to appear in Phys. Rev.

Fuzzy BIon

We construct a solution of the BFSS matrix theory, which is a counterpart of the BIon solution representing a fundamental string ending on a bound state of a D2-brane and D0-branes. We call this solution the `fuzzy BIon' and show that this configuration preserves 1/4 supersymmetry of type IIA superstring theory. We also construct an effective action for the fuzzy BIon by analyzing the nonabelian Born-Infeld action for D0-branes. When we take the continuous limit, with some conditions, this action coincides with the effective action for the BIon configuration.Comment: 11 pages, 1 figure, reference and note adde

Investigations of cold cathode TPI1-10k/50 thyratron parameters at voltage up to 50 kV, current up to 10 kA, pulse duration of hundred nanoseconds

The results of cold cathode TPI1-10k/50 thyratron parameters at voltage up to 50 kV, current up to 10 kA and pulse duration of hundred ns are described. The optimal parameters of thyratron power supply and pulse driver had been found. The jitter and thyratron own rise time as a function of load resistance has been find. The thyratron life time test data are cited.Описаны результаты исследований параметров тиратронов с холодным катодом ТПИ1-10k/50 при напряжениях до 50 кВ, токах до 10 кА и длительности импульсов сотни нс. Выявлены оптимальные параметры импульса запуска и питания тиратронов, измерена длительность фронта импульса, обусловленная тиратроном, в зависимости от сопротивления нагрузки, временной разброс импульса тока относительно импульса запуска. Проведены ресурсные испытания.Описано результати досліджень параметрів тиратронів з холодним катодом ТПІ1-10k/50 при напрузі до 50 кВ, струмах до 10 кА і тривалості імпульсів сотні нс. Виявлено оптимальні параметри імпульсу запуску і живлення тиратронів, обміряна тривалість фронту імпульсу, обумовлена тиратроном, у залежності від опору навантаження, часовий розкид імпульсу струму щодо імпульсу запуску. Проведено ресурсні випробування

Avalanches in the Weakly Driven Frenkel-Kontorova Model

A damped chain of particles with harmonic nearest-neighbor interactions in a spatially periodic, piecewise harmonic potential (Frenkel-Kontorova model) is studied numerically. One end of the chain is pulled slowly which acts as a weak driving mechanism. The numerical study was performed in the limit of infinitely weak driving. The model exhibits avalanches starting at the pulled end of the chain. The dynamics of the avalanches and their size and strength distributions are studied in detail. The behavior depends on the value of the damping constant. For moderate values a erratic sequence of avalanches of all sizes occurs. The avalanche distributions are power-laws which is a key feature of self-organized criticality (SOC). It will be shown that the system selects a state where perturbations are just able to propagate through the whole system. For strong damping a regular behavior occurs where a sequence of states reappears periodically but shifted by an integer multiple of the period of the external potential. There is a broad transition regime between regular and irregular behavior, which is characterized by multistability between regular and irregular behavior. The avalanches are build up by sound waves and shock waves. Shock waves can turn their direction of propagation, or they can split into two pulses propagating in opposite directions leading to transient spatio-temporal chaos. PACS numbers: 05.70.Ln,05.50.+q,46.10.+zComment: 33 pages (RevTex), 15 Figures (available on request), appears in Phys. Rev.

Modulator power supply for 200 kV electron gun of the VEPP-5 injection complex

The 200 kV electron gun modulator power supply based on the half-bridge converter providing the high frequency partial charge of the capacitive energy storage element is described. The algorithm developed for the power supply driving allows one to provide the soft switching of charging circuits and to achieve a high efficiency of the power supply. The data obtained at operation of the capacitive loaded 300 W power supply are presented. The prospects of developing such type tens-kilowatts power supply are discussed.Описано пристрій високочастотного порціонного заряду ємнісного накопичувача енергії для живлення 200 кВ електронної гармати. Спеціально розроблений алгоритм керування дозволяє забезпечити м'яку комутацію ключів зарядних контурів, домогтися високого ККД зарядного пристрою. Приведено експериментальні дані, зняті при роботі зарядного пристрою на ємнісне навантаження потужністю 300 Вт. Обговорюються перспективи створення зарядних пристроїв такого типу потужністю десятки кіловат.Описано устройство высокочастотного порционного заряда емкостного накопителя энергии для питания 200 кВ электронной пушки. Специально разработанный алгоритм управления позволяет обеспечить мягкую коммутацию ключей зарядных контуров, добиться высокого КПД зарядного устройства. Приведены экспериментальные данные, снятые при работе зарядного устройства на емкостную нагрузку мощностью 300 Вт. Обсуждаются перспективы создания зарядных устройств такого типа мощностью десятки киловатт

Scaling in a Nonconservative Earthquake Model of Self-Organised Criticality

We numerically investigate the Olami-Feder-Christensen model for earthquakes in order to characterise its scaling behaviour. We show that ordinary finite size scaling in the model is violated due to global, system wide events. Nevertheless we find that subsystems of linear dimension small compared to the overall system size obey finite (subsystem) size scaling, with universal critical coefficients, for the earthquake events localised within the subsystem. We provide evidence, moreover, that large earthquakes responsible for breaking finite size scaling are initiated predominantly near the boundary.Comment: 6 pages, 6 figures, to be published in Phys. Rev. E; references sorted correctl

Counting Supertubes

The quantum states of the supertube are counted by directly quantizing the linearized Born-Infeld action near the round tube. The result is an entropy $S = 2\pi \sqrt{2 (Q_{D0}Q_{F1}-J)}$, in accord with conjectures in the literature. As a result, supertubes may be the generic D0-F1 bound state. Our approach also shows directly that supertubes are marginal bound states with a discrete spectrum. We also discuss the relation to recent suggestions of Mathur et al involving three-charge black holes.Comment: 15 pages, v2: reference corrected; v3: few corrections and explicit derivation of a relation are added to appendix

Infinite volume limit of the Abelian sandpile model in dimensions d >= 3

We study the Abelian sandpile model on Z^d. In dimensions at least 3 we prove existence of the infinite volume addition operator, almost surely with respect to the infinite volume limit mu of the uniform measures on recurrent configurations. We prove the existence of a Markov process with stationary measure mu, and study ergodic properties of this process. The main techniques we use are a connection between the statistics of waves and uniform two-component spanning trees and results on the uniform spanning tree measure on Z^d.Comment: First version: LaTeX; 29 pages. Revised version: LaTeX; 29 pages. The main result of the paper has been extended to all dimensions at least 3, with a new and simplyfied proof of finiteness of the two-component spanning tree. Second revision: LaTeX; 32 page