Self-Diffusion in Random-Tiling Quasicrystals

The first explicit realization of the conjecture that phason dynamics leads to self-diffusion in quasicrystals is presented for the icosahedral Ammann tilings. On short time scales, the transport is found to be subdiffusive with the exponent $\beta\approx0.57(1)$, while on long time scales it is consistent with normal diffusion that is up to an order of magnitude larger than in the typical room temperature vacancy-assisted self-diffusion. No simple finite-size scaling is found, suggesting anomalous corrections to normal diffusion, or existence of at least two independent length scales.Comment: 11 pages + 2 figures, COMPRESSED postscript figures available by anonymous ftp to black_hole.physics.ubc.ca directory outgoing/diffuse (use bi for binary mode to transfer), REVTeX 3.0, CTP-TAMU 21/9

Galilean noncommutative gauge theory: symmetries & vortices

Noncommutative Chern-Simons gauge theory coupled to nonrelativistic scalars or spinors is shown to admit the ``exotic'' two-parameter-centrally extended Galilean symmetry, realized in a unique way consistent with the Seiberg-Witten map. Nontopological spinor vortices and topological external-field vortices are constructed by reducing the problem to previously solved self-dual equations.Comment: Updated version: some statements rephrased and further references added. LaTex, 17 pages, no figure

Moving vortices in noncommutative gauge theory

Exact time-dependent solutions of nonrelativistic noncommutative Chern - Simons gauge theory are presented in closed analytic form. They are different from (indeed orthogonal to) those discussed recently by Hadasz, Lindstrom, Rocek and von Unge. Unlike theirs, our solutions can move with an arbitrary constant velocity, and can be obtained from the previously known static solutions by the recently found ``exotic'' boost symmetry.Comment: Latex, 6 pages, no figures. A result similar to ours was obtained, independently, by Hadasz et al. in the revised version of their pape

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

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

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

Random walk through fractal environments

We analyze random walk through fractal environments, embedded in 3-dimensional, permeable space. Particles travel freely and are scattered off into random directions when they hit the fractal. The statistical distribution of the flight increments (i.e. of the displacements between two consecutive hittings) is analytically derived from a common, practical definition of fractal dimension, and it turns out to approximate quite well a power-law in the case where the dimension D of the fractal is less than 2, there is though always a finite rate of unaffected escape. Random walks through fractal sets with D less or equal 2 can thus be considered as defective Levy walks. The distribution of jump increments for D > 2 is decaying exponentially. The diffusive behavior of the random walk is analyzed in the frame of continuous time random walk, which we generalize to include the case of defective distributions of walk-increments. It is shown that the particles undergo anomalous, enhanced diffusion for D_F < 2, the diffusion is dominated by the finite escape rate. Diffusion for D_F > 2 is normal for large times, enhanced though for small and intermediate times. In particular, it follows that fractals generated by a particular class of self-organized criticality (SOC) models give rise to enhanced diffusion. The analytical results are illustrated by Monte-Carlo simulations.Comment: 22 pages, 16 figures; in press at Phys. Rev. E, 200

Investigation of quasi-periodic variations in hard X-rays of solar flares. II. Further investigation of oscillating magnetic traps

In our recent paper (Solar Physics 261, 233) we investigated quasi-periodic oscillations of hard X-rays during impulsive phase of solar flares. We have come to conclusion that they are caused by magnetosonic oscillations of magnetic traps within the volume of hard-X-ray (HXR) loop-top sources. In the present paper we investigate four flares which show clear quasi-periodic sequences of HXR pulses. We also describe our phenomenological model of oscillating magnetic traps to show that it can explain observed properties of HXR oscillations. Main results are the following: 1. We have found that low-amplitude quasi-periodic oscillations occur before impulsive phase of some flares. 2. We have found that quasi-period of the oscillations can change in some flares. We interpret this as being due to changes of the length of oscillating magnetic traps. 3. During impulsive phase a significant part of the energy of accelerated (non-thermal) electrons is deposited within the HXR loop-top source. 4. Our analysis suggests that quick development of impulsive phase is due to feedback between pulses of the pressure of accelerated electrons and the amplitude of magnetic-trap oscillation. 5. We have also determined electron number density and magnetic filed strength for HXR loop-top sources of several flares. The values fall within the limits of $N \approx (2 -15) \times 10^{10}$ cm$^{-3}$, $B \approx (45 - 130)$ gauss.Comment: 18 pages, 14 figures, submitted to Solar Physic

Punctuated equilibria and 1/f noise in a biological coevolution model with individual-based dynamics

We present a study by linear stability analysis and large-scale Monte Carlo simulations of a simple model of biological coevolution. Selection is provided through a reproduction probability that contains quenched, random interspecies interactions, while genetic variation is provided through a low mutation rate. Both selection and mutation act on individual organisms. Consistent with some current theories of macroevolutionary dynamics, the model displays intermittent, statistically self-similar behavior with punctuated equilibria. The probability density for the lifetimes of ecological communities is well approximated by a power law with exponent near -2, and the corresponding power spectral densities show 1/f noise (flicker noise) over several decades. The long-lived communities (quasi-steady states) consist of a relatively small number of mutualistically interacting species, and they are surrounded by a ``protection zone'' of closely related genotypes that have a very low probability of invading the resident community. The extent of the protection zone affects the stability of the community in a way analogous to the height of the free-energy barrier surrounding a metastable state in a physical system. Measures of biological diversity are on average stationary with no discernible trends, even over our very long simulation runs of approximately 3.4x10^7 generations.Comment: 20 pages RevTex. Minor revisions consistent with published versio

Prediction of extreme events in the OFC model on a small world network

We investigate the predictability of extreme events in a dissipative Olami-Feder-Christensen model on a small world topology. Due to the mechanism of self-organized criticality, it is impossible to predict the magnitude of the next event knowing previous ones, if the system has an infinite size. However, by exploiting the finite size effects, we show that probabilistic predictions of the occurrence of extreme events in the next time step are possible in a finite system. In particular, the finiteness of the system unavoidably leads to repulsive temporal correlations of extreme events. The predictability of those is higher for larger magnitudes and for larger complex network sizes. Finally, we show that our prediction analysis is also robust by remarkably reducing the accessible number of events used to construct the optimal predictor.Comment: 5 pages, 4 figure