The signature of a double quantum-dot structure in the I-V characteristics of a complex system

We demonstrate that by carefully analyzing the temperature dependent characteristics of the I-V measurements for a given complex system it is possible to determine whether it is composed of a single, double or multiple quantum-dot structure. Our approach is based on the orthodox theory for a double-dot case and is capable of simulating I-V characteristics of systems with any resistance and capacitance values and for temperatures corresponding to thermal energies larger than the dot level spacing. We compare I-V characteristics of single-dot and double-dot systems and show that for a given measured I-V curve considering the possibility of a second dot is equivalent to decreasing the fit temperature. Thus, our method allows one to gain information about the structure of an experimental system based on an I-V measurement.Comment: 12 pages 7 figure

Universal transport in 2D granular superconductors

The transport properties of quench condensed granular superconductors are presented and analyzed. These systems exhibit transitions from insulating to superconducting behavior as a function of inter-grain spacing. Superconductivity is characterized by broad transitions in which the resistance drops exponentially with reducing temperature. The slope of the log R versus T curves turns out to be universaly dependent on the normal state film resistance for all measured granular systems. It does not depend on the material, critical temperature, geometry, or experimental set-up. We discuss possible physical scenarios to explain these findings.Comment: 4 pages, 3 figure

Curamycin. II. Structure of the hydrolysis products 'curacin' and 'd-curamicose'

Fil:Gros, E.G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Deulofeu, V. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Galmarini, O.L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Frydman, B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Zero bias anomaly in a two dimensional granular insulator

We compare tunneling density of states (TDOS) into two ultrathin Ag films, one uniform and one granular, for different degrees of disorder. The uniform film shows a crossover from Altshuler-Aronov (AA) zero bias anomaly to Efros Shklovskii (ES) like Coulomb gap as the disorder is increased. The granular film, on the other hand, exhibits AA behavior even deeply in the insulating regime. We analyze the data and find that granularity introduces a new regime for the TDOS. While the conductivity is dominated by hopping between clusters of grains and is thus insulating, the TDOS probes the properties of an individual cluster which is "metallic".Comment: 4 pages, 4 figure

Two-dimensional array of diffusive SNS junctions with high-transparent interfaces

We report the first comparative study of the properties of two-dimensional arrays and single superconducting film - normal wire - superconducting film (SNS) junctions. The NS interfaces of our SNS junctions are really high transparent, for superconducting and normal metal parts are made from the same material (superconducting polycrystalline PtSi film). We have found that the two-dimensional arrays reveal some novel features: (i) the significant narrowing of the zero bias anomaly (ZBA) in comparison with single SNS junctions, (ii) the appearance of subharmonic energy gap structure (SGS), with up to n=16 (eV=\pm 2\Delta/n), with some numbers being lost, (iii) the transition from 2D logarithmic weak localization behavior to metallic one. Our experiments show that coherent phenomena governed by the Andreev reflection are not only maintained over the macroscopic scale but manifest novel pronounced effects as well. The behavior of the ZBA and SGS in 2D array of SNS junctions strongly suggests that the development of a novel theoretical approach is needed which would self-consistently take into account the distribution of the currents, the potentials, and the superconducting order parameter.Comment: RevTex, 5 pages, 5 figure

Theory of AC Josepson Effect in Superconducting Constrictions

We have developed a microscopic theory of ac Josephson effect in short ballistic superconducting constrictions with arbitrary electron transparency and in constrictions with diffusive electron transport. The theory is valid for arbitrary miscroscopic structure of the superconducting electrodes of the constriction. As applications of the theory we study smearing of the subgap current singularities by pair-breaking effects and also the structure of these singularities in the constrictions between the composite S/N electrodes with the proximity-induced gap in the normal layer.Comment: 11 pages, RevTex, 3 figures available on reques

Інформаційна технологія організації моніторингу впливу мотивованого вибору спеціальності студентом на успішність навчання в ЗВО

Рассмотрена актуальная проблема организации информационной технологии для проведения исследования для влияния мотивированного выбора специальности студентом на успеваемость при обучении в УВО. Для проведения анкетирования разработано мобильное приложение, созданное на языке программирования Java в интегрированной среде разработки Android Studio. Полученные результаты анализировались с помощью SPSS – программы для статистической обработки данных. По результатам исследования сделаны перспективные выводы.The article explores the actual problem of organization of the information technology for conducting research of the social and psychological climate in the groups of students. Two questionnaires were created for students' questionnaires. The first survey was conducted according to the classical Hans Eysenck methodology for the determination of the temperament (this technique is one of the most popular in modern psychology). The goal was to study the personality of each of the students from several components: extraversion and psychotype, emotional-volitional stability and the classification of the temperament in correspondence with the classical types. The second questionnaire was sociological and was created with the goal to clarify the degree of the motivation level in terms of the choice of the study program, the level of satisfaction with the educational process, substantiation of personal opinion about methods of teaching at the university, and a need of potential changes of the teaching strategies. The survey was conducted among the students of the ten study programs at the Oles Honchar Dnipro National University: "Political Science", "Sociology", "Informatics", "Applied Mathematics", "Software Engineering"; "System analysis"; "Special Education", "Psychology"; "Chemistry", "Social Work". The total number of survey participants included 205 students. In order to optimize the process of collection of the information a mobile questionnaires application was created. This application was created using the Java programming language in the integrated Android Studio mobile application environment. When creating the application, a convenient user interface of the application was developed with an adaptive design, convenient menu, good running functionality, and the ability to select a passing text. View hierarchies and their subclasses were also used. View objects are the widgets of users interface, such as buttons or text fields. The collected information was analized with the help of SPSS and the results were  used  to provide objective summaries. In the future it is planned to add such functions as the option to search for a survey by the survey title; sending the result via email, SMS or via social networks; to view statistics on various surveys at the same time; to increase the number of surveys as well as to optimize the application design.Розглянуто актуальну проблему організації інформаційної технології для проведення дослідження впливу мотивованого вибору спеціальності студентом на успішність навчання в ЗВО. Для проведення анкетувань розроблено мобільний застосунок, який було створено за допомогою мови програмування Java в інтегрованому середовищі розробки Android Studio. Отримані відповіді аналізувалися за допомогою SPSS – програми для статистичної обробки даних. За результатами дослідження зроблено перспективні висновки

RIDME distance measurements using Gd(iii) tags with a narrow central transition

Methods based on pulse electron paramagnetic resonance allow measurement of the electron-electron dipolar coupling between two spin labels. Here we compare the most popular technique, Double Electron-Electron Resonance (DEER or PELDOR), with the dead-time free 5-pulse Relaxation-Induced Dipolar Modulation Enhancement (RIDME) method for Gd(iii)-Gd(iii) distance measurements at W-band (94.9 GHz, ≈3.5 T) using Gd(iii) tags with a small zero field splitting (ZFS). Such tags are important because of their high EPR sensitivity arising from their narrow central transition. Two systems were investigated: (i) a rigid model compound with an inter-spin distance of 2.35 nm, and (ii) two mutants of a homodimeric protein, both labeled with a DOTA-based Gd(iii) chelate and characterized by an inter-spin distance of around 6 nm, one having a narrow distance distribution and the other a broad distribution. Measurements on the model compound show that RIDME is less sensitive to the complications arising from the failure of the weak coupling approximation which affect DEER measurements on systems characterized by short inter-spin distances between Gd(iii) tags having a narrow central transition. Measurements on the protein samples, which are characterized by a long inter-spin distance, emphasize the complications due to the appearance of harmonics of the dipolar interaction frequency in the RIDME traces for S > 1/2 spin systems, as well as enhanced uncertainties in the background subtraction. In both cases the sensitivity of RIDME was found to be significantly better than DEER. The effects of the experimental parameters on the RIDME trace are discussed.This research was supported by the Israeli Science Foundation (grant 334/14) and was made possible in part by the historic generosity of the Harold Perlman Family (D. G.). We also acknowledge the Australian Research Council for a Discovery grant to G. O. and B. G. (DP150100383) and a Future Fellowship to B. G. (FT130100838). D. G. holds the Erich Klieger professorial chair in Chemical Physics

Circuit theory of multiple Andreev reflections in diffusive SNS junctions: the incoherent case

The incoherent regime of Multiple Andreev Reflections (MAR) is studied in long diffusive SNS junctions at applied voltages larger than the Thouless energy. Incoherent MAR is treated as a transport problem in energy space by means of a circuit theory for an equivalent electrical network. The current through NS interfaces is explained in terms of diffusion flows of electrons and holes through tunnel and Andreev resistors. These resistors in diffusive junctions play roles analogous to the normal and Andreev reflection coefficients in OTBK theory for ballistic junctions. The theory is applied to the subharmonic gap structure (SGS); simple analytical results are obtained for the distribution function and current spectral density for the limiting cases of resistive and transparent NS interfaces. In the general case, the exact solution is found in terms of chain-fractions, and the current is calculated numerically. SGS shows qualitatively different behavior for even and odd subharmonic numbers, and the maximum slopes of the differential resistance correspond to the gap subharmonics. The influence of inelastic scattering on the subgap anomalies of the differential resistance is analyzed.Comment: 14 pages, 9 figures, title and text revised, to appear in PR