40 research outputs found
Self focusing mechanisms of an electron beam formed in a high voltage nanosecond low pressure discharge
Surface acoustic waves in finite slabs of three-dimensional phononic crystals
We study theoretically, by means of layer-multiple-scattering techniques, the propagation of elastic waves through finite slabs of phononic crystals consisting of metallic spheres in a polyester matrix, embedded in air. In particular, we focus on the study of modes localized on the surfaces of the structure. Their origin and behavior, as well as the physical parameters that influence and determine their appearance, are investigated in detail. Our results reveal the existence of absolute phononic frequency gaps in these finite structures, and point out the possibility, under an appropriate choice of the parameters, of tunable regions of frequency free of propagating and/or surface-localized modes. © 2008 The American Physical Society.Peer Reviewe
Crossover from Luttinger- to Fermi-liquid behavior in strongly anisotropic systems in large dimensions
We consider the low-energy region of an array of Luttinger liquids coupled by
a weak interchain hopping. The leading logarithmic divergences can be re-summed
to all orders within a self-consistent perturbative expansion in the hopping,
in the large-dimension limit. The anomalous exponent scales to zero below the
one-particle crossover temperature. As a consequence, coherent quasiparticles
with finite weight appear along the whole Fermi surface. Extending the
expansion self-consistently to all orders turns out to be crucial in order to
restore the correct Fermi-liquid behavior.Comment: Shortened version to appear in Physical Review Letter
Parquet Graph Resummation Method for Vortex Liquids
We present in detail a nonperturbative method for vortex liquid systems. This
method is based on the resummation of an infinite subset of Feynman diagrams,
the so-called parquet graphs, contributing to the four-point vertex function of
the Ginzburg-Landau model for a superconductor in a magnetic field. We derive a
set of coupled integral equations, the parquet equations, governing the
structure factor of the two-dimensional vortex liquid system with and without
random impurities and the three-dimensional system in the absence of disorder.
For the pure two-dimensional system, we simplify the parquet equations
considerably and obtain one simple equation for the structure factor. In two
dimensions, we solve the parquet equations numerically and find growing
translational order characterized by a length scale as the temperature is
lowered. The temperature dependence of is obtained in both pure and
weakly disordered cases. The effect of disorder appears as a smooth decrease of
as the strength of disorder increases.Comment: 15 pages, 12 PostScript figures, uses multicols.sty and epsf.st
Renormalization group analysis of the 2D Hubbard model
Salmhofer [Commun. Math. Phys. 194, 249 (1998)] has recently developed a new
renormalization group method for interacting Fermi systems, where the complete
flow from the bare action of a microscopic model to the effective low-energy
action, as a function of a continuously decreasing infrared cutoff, is given by
a differential flow equation which is local in the flow parameter. We apply
this approach to the repulsive two-dimensional Hubbard model with nearest and
next-nearest neighbor hopping amplitudes. The flow equation for the effective
interaction is evaluated numerically on 1-loop level. The effective
interactions diverge at a finite energy scale which is exponentially small for
small bare interactions. To analyze the nature of the instabilities signalled
by the diverging interactions we extend Salmhofers renormalization group for
the calculation of susceptibilities. We compute the singlet superconducting
susceptibilities for various pairing symmetries and also charge and spin
density susceptibilities. Depending on the choice of the model parameters
(hopping amplitudes, interaction strength and band-filling) we find
commensurate and incommensurate antiferromagnetic instabilities or d-wave
superconductivity as leading instability. We present the resulting phase
diagram in the vicinity of half-filling and also results for the density
dependence of the critical energy scale.Comment: 16 pages, RevTeX, 16 eps figure
СРЕДСТВА РЕГИСТРАЦИИ ИМПУЛЬСНОГО ВИДИМОГО ИЗЛУЧЕНИЯ МАЛОЙ ИНТЕНСИВНОСТИ. ЧАСТЬ 1. ОСОБЕННОСТИ И ВОЗМОЖНОСТИ МНОГОКАНАЛЬНЫХ ФОТОПРИЕМНИКОВ С ВНУТРЕННИМ УСИЛЕНИЕМ. ОБЗОР
The main types of the modern photo detectors applied to single photon registration are analyzed. It is offered to use silicon photomultipliers for production of multi-channel optoelectronic systems with the single photon resolution.Проанализированы основные типы современных фотоприемников, применяемых для регистрации импульсного оптического излучения видимой области спектра. Сделан вывод о том, что для создания многоканальных оптико-электронных систем с однофотонным разрешением целесообразно использовать кремниевые фотоэлектронные умножители
СРЕДСТВА РЕГИСТРАЦИИ ИМПУЛЬСНОГО ВИДИМОГО ИЗЛУЧЕНИЯ МАЛОЙ ИНТЕНСИВНОСТИ. Часть 2. ПРЕДВАРИТЕЛЬНАЯ ОБРАБОТКА СИГНАЛОВ КРЕМНИЕВЫХ ФОТОЭЛЕКТРОННЫХ УМНОЖИТЕЛЕЙ. ОБЗОР
Bias circuits, output signals and readout electronics of silicon photomultipliers are considered. Requirements to analog IC for SiPM signal preliminary processing are formulated. According to requirements the set of radiation hardened analog ICs including the comparator and transresistance amplifiers with different gain and speed is produced.Рассмотрены схемы включения, выходные сигналы и считывающая электроника кремниевых фотоэлектронных умножителей. Сформулированы требования к аналоговым устройствам для предварительной обработки их сигналов, в соответствии с которыми создана серия радиационно-стойких аналоговых микросхем, включающая компаратор напряжения и трансрезистивные усилители с разным коэффициентом преобразования и быстродействием
Parquet solution for a flat Fermi surface
We study instabilities occurring in the electron system whose Fermi surface
has flat regions on its opposite sides. Such a Fermi surface resembles Fermi
surfaces of some high- superconductors. In the framework of the parquet
approximation, we classify possible instabilities and derive
renormalization-group equations that determine the evolution of corresponding
susceptibilities with decreasing temperature. Numerical solutions of the
parquet equations are found to be in qualitative agreement with a ladder
approximation. For the repulsive Hubbard interaction, the antiferromagnetic
(spin-density-wave) instability dominates, but when the Fermi surface is not
perfectly flat, the -wave superconducting instability takes over.Comment: REVTeX, 36 pages, 20 ps figures inserted via psfig. Submitted to
Phys. Rev.
МАЛОШУМЯЩИЙ ЭЛЕКТРОННЫЙ МОДУЛЬ ОБРАБОТКИ СИГНАЛОВ ЛАВИННЫХ ФОТОДИОДОВ
Schematic and design of electronics module for avalanche photodiode signal′s readout based on the pair of specialized analog ICs, are considered. Main specifications including input noise charge vs signal source capacity are presented.Рассмотрен электронный модуль обработки сигналов лавинных фотодиодов, созданный на базе двух специализированных аналоговых микросхем. Приведены результаты измерений основных характеристик и уровня шумов электронного модуля в зависимости от емкости источника сигнала (фотодиода)
ОБЕСПЕЧЕНИЕ РАДИАЦИОННОЙ СТОЙКОСТИ АНАЛОГОВЫХ ИНТЕГРАЛЬНЫХ СХЕМ
Influence of gamma radiation Co60 on static and dynamic characteristics of the transresistance amplifier and the comparator realized on the master slice array «ABMK 1-3» is considered taking into account formulated design rule. At absorbed dose D = 5 Mrad the comparator input current has increased on 25 %, other IC parameters (gain, impulse response of the transresistance amplifier, propagation delay, transition time, output current of the comparator) have changed slightly.Рассмотрено влияние гамма-излучения Co60 на статические и динамические характеристики трансрезистивного усилителя и компаратора напряжения, реализованных на базовом матричном кристалле типа «АБМК 1-3» с учетом сформулированных правил проектирования радиационно-стойких аналоговых интегральных схем (ИС). При поглощенной дозе D = 5 Мрад входной ток компаратора возрос на 25%, остальные параметры ИС (коэффициент преобразования, длительность фронта нарастания и спада трансрезистивного усилителя, задержка переключения, длительность фронта нарастания и спада, выходной ток компаратора) изменились незначительно