Decay of metastable current states in one-dimensional resonant tunneling devices

Current switching in a double-barrier resonant tunneling structure is studied in the regime where the current-voltage characteristic exhibits intrinsic bistability, so that in a certain range of bias two different steady states of current are possible. Near the upper boundary V_{th} of the bistable region the upper current state is metastable, and because of the shot noise it eventually decays to the stable lower current state. We find the time of this switching process in strip-shaped devices, with the width small compared to the length. As the bias V is tuned away from the boundary value V_{th} of the bistable region, the mean switching time \tau increases exponentially. We show that in long strips \ln\tau \propto (V_{th} -V)^{5/4}, whereas in short strips \ln\tau \propto (V_{th} -V)^{3/2}. The one-dimensional geometry of the problem enables us to obtain analytically exact expressions for both the exponential and the prefactor of \tau. Furthermore, we show that, depending on the parameters of the system, the switching can be initiated either inside the strip, or at its ends.Comment: 12 pages, 5 figures, update to published versio

Stochastic current switching in bistable resonant tunneling systems

Current-voltage characteristics of resonant-tunneling structures often exhibit intrinsic bistabilities. In the bistable region of the I-V curve one of the two current states is metastable. The system switches from the metastable state to the stable one at a random moment in time. The mean switching time \tau depends exponentially on the bias measured from the boundary of the bistable region V_{th}. We find full expressions for \tau (including prefactors) as functions of bias, sample geometry, and in-plane conductivity. Our results take universal form upon appropriate renormalization of the threshold voltage V_{th}. We also show that in large samples the switching initiates inside, at the edge, or at a corner of the sample depending on the parameters of the system.Comment: 21 pages, 5 figure

Magnetic system for cleaning the gamma beam at the LUE-40 electron linac output

The bremsstrahlung of accelerated electrons passing through a converter is used to study multiparticle photo-nuclear reactions. The results of calculations, numerical modeling, design, and testing of a special magnetic cleaning system to obtain a "pure" beam of bremsstrahlung quanta when studying the cross-sections of such reactions at the LUE-40 linac are presented. The system is based on commercially available permanent magnets of rectangular cross-sections. The maximum on-axis field is 0.9 T, which provides sufficient separation of the electron beam and gamma rays at a distance of more than 90 mm from the magnet.Comment: 9 pages, 8 figure

Influence of boric anhydride upon the physical and chemical properties of ferrosilicon slag

The authors study the influence of boric anhydride upon the physical and chemical properties of slag in the manufacture of ferrosilicon. It is established that adding boric anhydride to the slag changes its refractory quality and its viscosity and eases pouring slag and metal. Slags with optimal composition and properties are described

Structural data of phenanthrene-9,10-dicarbonitriles

In this data article, we present the single-crystal XRD data of phenanthrene-9,10-dicarbonitriles. Detailed structure analysis and photophysical properties were discussed in our previous study, "Intermolecular interactions-photophysical properties relationships in phenanthrene-9,10-dicarbonitrile assemblies" (Afanasenko et al., 2020). The data include the intra- and intermolecular bond lengths and angles. (c) 2019 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Immune mechanisms of the regulation of fetoplacental complex development

The aim of the research: the evaluation of the prognostic significance of the estimation of cytokines, growth factors and vasoactive regulators in the development of fetoplacental hemodynamic damage and fetoplacental insufficiency. 57 women in progress of physiological and pathological pregnancy were examined. The main group consisted of 45 women with evident FPI in the second half of pregnancy: 17 women with compensated FPI, 15 women with subcompensated FPI accompanied by IUGR without hemodynamic problems and 13 women with subcompensated FPI accompanied by IUGR with compromised utero-placental blood flow. It has been found that the first trimester of pregnancy complicated by FPI, is characterized by the decreased production of angiogenic factors and increased levels of proinflammatory, including angiogenesis inhibitors, and markers of vasoconstriction and endothelium dysfunction. Change-over to Th1 type of immune reaction and disturbance of trophoblast invasion and placentation due to interferons hyrerproduction and deficiency of hemopoetic growth factors and receptors for them may lead to FPI development. The degree of the depression of the growth factors production directly depends on the activity if compensation processes in FPI. The damage of vascular endothelium may leads to the decrease of angiogenesis because of the decreased production of growth factors and restricted endotheliocytes sensitivity towards proangiogenic stimuli.Целью работы явилась оценка прогностической значимости определения цитокинов, факторов роста и вазоактивных регуляторов в развитии нарушений гемодинамики фетоплацентарного комплекса и формировании ФПН. Обследовано 57 женщин в динамике физиологически и патологически протекающей беременности. Основную группу составили 45 женщин с манифестацией ФПН во второй половине беременности: 17 женщин с компенсированной формой ФПН, 15 женщин с субкомпенсированной формой ФПН, сопровождавшейся развитием СЗРП без гемодинамических нарушений и 13 женщин с субкомпенсированной формой ФПН, сопровождавшейся развитием СЗРП с нарушением маточно-плацентарного кровотока. Установлено, что первый триместр беременности, осложнившейся впоследствии ФПН, характеризуется снижением продукции ангиогенных факторов, увеличением уровня провоспалительных цитокинов, в том числе ингибиторов ангиогенеза, а также маркеров вазоконстрикции и дисфункции эндотелия. Развитию ФПН может способствовать не только переключение на иммунный ответ Th 1 —типа, но и нарушение процессов инвазии трофобласта и плацентации, связанное с гиперпродукцией интерферонов и недостаточной выработкой гемопоэтических факторов роста и рецепторов к ним. Степень подавления продукции факторов роста находится в прямой зависимости от выраженности процессов компенсации при ФПН. Повреждение эндотелия сосудов может приводить к подавлению процессов ангиогенеза в результате снижения продукции факторов роста и уменьшения чувствительности эндотелиоцитов к проангиогенным стимулам

Fluctuation corrections to bubble nucleation

The fluctuation determinant which determines the preexponential factor of the transition rate for minimal bubbles is computed for the electroweak theory with $\sin \Theta_W = 0$. As the basic action we use the three-dimensional high-temperature action including, besides temperature dependent masses, the $T \Phi^3$ one-loop contribution which makes the phase transition first order. The results show that this contribution (which has then to be subtracted from the exact result) gives the dominant contribution to the one-loop effective action. The remaining correction is of the order of, but in general larger than the critical bubble action and suppresses the transition rate. The results for the Higgs field fluctuations are compared with those of an approximate heat kernel computation of Kripfganz et al., good agreement is found for small bubbles, strong deviations for large thin-wall bubbles.Comment: 19 pages, LaTeX, no macros, no figure

A search for two body muon decay signals

Lepton family number violation is tested by searching for $\mu^+\to e^+X^0$ decays among the 5.8$\times 10^8$ positive muon decay events analyzed by the TWIST collaboration. Limits are set on the production of both massless and massive $X^0$ bosons. The large angular acceptance of this experiment allows limits to be placed on anisotropic $\mu^+\to e^+X^0$ decays, which can arise from interactions violating both lepton flavor and parity conservation. Branching ratio limits of order $10^{-5}$ are obtained for bosons with masses of 13 - 80 MeV/c$^2$ and with different decay asymmetries. For bosons with masses less than 13 MeV/c$^{2}$ the asymmetry dependence is much stronger and the 90% limit on the branching ratio varies up to $5.8 \times 10^{-5}$. This is the first study that explicitly evaluates the limits for anisotropic two body muon decays.Comment: 7 pages, 5 figures, 2 tables, accepted by PR