Giant dispersion of critical currents in superconductor with fractal clusters of a normal phase

The influence of fractal clusters of a normal phase on the dynamics of a magnetic flux trapped in a percolative superconductor is considered. The critical current distribution and the current-voltage characteristics of fractal superconducting structures in the resistive state are obtained for an arbitrary fractal dimension of the cluster boundaries. The range of fractal dimensions, where the dispersion of critical currents becomes infinite, is found. It is revealed that the fractality of clusters depresses of the electric field caused by the magnetic flux motion thus increasing the critical current value. It is expected that the maximum current-carrying capability of a superconductor can be achieved in the region of giant dispersion of critical currents.Comment: 7 pages with 3 figure

Информационная поддержка анализа навыков и умений контингента студентов высшего учебного заведения

In the below article, the application of the fuzzy logical conclusion method is considered as decision-maker in the process of analyzing the students skills and abilities based on the requirements of potential employers, in order to reduce the time of the first interview for potential candidates on a vacant position. When analyzing the results of the assessment of the competence of university students, a certain degree of fuzziness arises. In modern practice, fuzzy logic is used in many different assessment methods, including questioning, interviewing, testing, descriptive method, classification method, pairwise comparison, rating method, business games competence models, and the like. Each of the methods has its advantages and disadvantages, but they are effective only as part of a unified personnel management system. As a method for implementing a systematic approach to the assessment of the contingent of students, it is proposed to use fuzzy logic, a mathematical apparatus that allows you to build a model of an object based on fuzzy judgments. The use of fuzzy logic, the mathematical apparatus of which allows you to build a model of the object, based on fuzzy reasoning and rules. The most important condition for creating such a model is to translate the fuzzy, qualitative assessments used by man into the language of mathematics, which will be understood by the computer. The most used are fuzzy inferences using the Mamdani and Sugeno methods. In a fuzzy inference of the Mamdani type, the value of the output variable is given by fuzzy terms, in the conclusion of the Sugeno type, as a linear combination of the input variables. Research in the field of application of fuzzy logic in socio-economic systems suggests that it can be used to assess the competencies of university students.В данной работе рассмотрено использование метода нечеткого логического вывода для поддержки принятия решения в задачах анализа навыков и умений контингента студентов исходя из требований потенциальных работодателей, с целью уменьшения времени на первичную обработку информации касательно потенциальных кандидатов на вакантную должность. При анализе результатов оценки компетентности студентов вузов возникает определенная степень нечеткости. В современной практике нечеткая логика применяется во многих различных методах оценки, в том числе анкетирование, интервью, тестирование, описательный метод, метод классификации, парное сравнение, рейтинговый метод, деловые игры модели компетентности и тому подобное. Каждый из методов имеет свои преимущества и недостатки, но эффективны они только в составе единой системы управления персоналом. Как метод для реализации системного подхода к оценке контингента студентов предложено использовать нечеткую логику, математический аппарат, который позволяет построить модель объекта, основанную на нечетких суждениях. Использование нечеткой логики, математический аппарат которой позволяет построить модель объекта, основываясь на нечетких рассуждениях и правилах. Важнейшее условие создания такой модели заключается в том, чтобы перевести нечеткие, качественные оценки, применяемые человеком, на язык математики, которая будет понятна вычислительной машине. Наиболее используемыми являются нечеткие выводы с помощью способов Мамдани и Сугено. В нечетком выводе типа Мамдани значение выходной переменной задаются нечеткими термами, в заключении типа Сугено – как линейная комбинация входных переменных. Исследования в области применения нечеткой логики в социоэкономических системах позволяют говорить о возможности ее использования для оценки компетенций студентов вузов

Comments on ``A note on first-order formalism and odd-derivative actions'' by S. Deser

We argue that the obstacles to having a first-order formalism for odd-derivative actions presented in a pedagogical note by Deser are based on examples which are not first-order forms of the original actions. The general derivation of an equivalent first-order form of the original second-order action is illustrated using the example of topologically massive electrodynamics (TME). The correct first-order formulations of the TME model keep intact the gauge invariance presented in its second-order form demonstrating that the gauge invariance is not lost in the Ostrogradsky process.Comment: 6 pages, references are adde

Metastable Voltage States of Coupled Josephson Junctions

We investigate a chain of capacitively coupled Josephson junctions in the regime where the charging energy dominates over the Josephson coupling, exploiting the analogy between this system and a multi-dimensional crystal. We find that the current-voltage characteristic of the current-driven chain has a staircase shape, beginning with an (insulating) non-zero voltage plateau at small currents. This behavior differs qualitatively from that of a single junction, which should show Bloch oscillations with vanishing dc voltage. The simplest system where this effect can be observed consists of three grains connected by two junctions. The theory explains the results of recent experiments on Josephson junction arrays.Comment: 5 pages, 4 figures include

Andreev interferometer with three superconducting electrodes

We develop a quasiclassical theory of Andreev interferometers with three superconducting electrodes. Provided tunneling interface resistance between one superconducting electrode and the normal metal strongly exceeds two others, significant current sensitivity to the external magnetic flux is observed only at subgap voltages. If all barrier conductances are comparable, multiple Andreev reflection comes into play and substantial current modulation can be achieved in both subgap and overgap voltage regimes. Our analysis reveals a large variety of interesting features which can be used for performance optimization of Andreev interferometers.Comment: 9 pages, 13 figure

Unstable superheavy relic particles as a source of neutrinos responsible for the ultrahigh-energy cosmic rays

Decays of superheavy relic particles may produce extremely energetic neutrinos. Their annihilations on the relic neutrinos can be the origin of the cosmic rays with energies beyond the Greisen-Zatsepin-Kuzmin cutoff. The red shift acts as a cosmological filter selecting the sources at some particular value z_e, for which the present neutrino energy is close to the Z pole of the annihilation cross section. We predict no directional correlation of the ultrahigh-energy cosmic rays with the galactic halo. At the same time, there can be some directional correlations in the data, reflecting the distribution of matter at red shift z=z_e. Both of these features are manifest in the existing data. Our scenario is consistent with the neutrino mass reported by Super-Kamiokande and requires no lepton asymmetry or clustering of the background neutrinos.Comment: 3 pages, revtex; references adde

OPTIMIZATION OF THE HOT-ELECTRON BOLOMETER AND A CASCADE QUASIPARTICLE AMPLIFIER FOR SPACE ASTRONOMY

Ultra low noise bolometers are required for space - based astronomical observations. Extremely sensitive detectors are necessary for a deep full-sky survey of distant extragalactic sources in the submillimeter-wave region corresponding to the extraterrestrial background spectrum minimum. A deep full-sky survey is the main goal of the Submillimetron project of the cryogenically cooled telescope on the International Space Station [1,2], project CIRCE (NASA) and other projects. Detection of faint sources involvves wide-band continuum observation using direct detectors (bolometers) that are not restricted by the quantum noise of indirect heterodyne receivers. Theoretical estimations and preliminary experiments show that it is possible to realize the necessary sensitivity of 10-18 - 10-19 W/Hz1/2 with a novel concept of the antenna-coupled microbolometers at temperatures 0.1 K. Additional advantages of such detectors are the possibility to operate with a wide range of background load, easy integration in arrays, and direct possibility of polarization measurements

Two-dimensional metric and tetrad gravities as constrained second order systems

Using the Gitman-Lyakhovich-Tyutin generalization of the Ostrogradsky method for analyzing singular systems, we consider the Hamiltonian formulation of metric and tetrad gravities in two-dimensional Riemannian spacetime treating them as constrained higher-derivative theories. The algebraic structure of the Poisson brackets of the constraints and the corresponding gauge transformations are investigated in both cases.Comment: replaced with revised version published in Mod.Phys.Lett.A22:17-28,200

A remark on sphaleron erasure of baryon asymmetry

We complete an existing result for how the baryon asymmetry left over after a period of full thermal equilibrium depends on different lepton asymmetries.Comment: 5 pages; small clarifications and a reference added; to appear in PR