Competition between different order parameters in a quasi-one-dimensional superconductor

We show that, under rather general assumptions, the phase diagram of a quasi-one-dimensional repulsive Fermi system consists of two ordered phases: the density wave, spin or charge, and the superconductivity. It is demonstrated that the symmetry of the superconducting order parameter is a non-universal property sensitive to microscopic details of the model. Three potentially stable superconducting states are identified: they are triplet $f$-wave, singlet $d_{x^2-y^2}$-wave, and $d_{xy}$-wave. Presence of multiple competing superconducting states implies that for a real material this symmetry is difficult to predict theoretically and hard to probe experimentally, since artifacts of theoretical approximations or variations in experimental conditions could tip the balance between the superconducting phases.Comment: 6 pages, 1 eps figur

Superconductivity without attraction in a quasi-one-dimensional metal

An array of one-dimensional conductors coupled by transverse hopping and interaction is studied with the help of a variational wave function. This wave function is devised as to account for one-dimensional correlation effects. We show that under broad conditions our system possesses the superconducting ground state even if no attraction is present. The superconducting mechanism is of many-body nature and deviates substantially from BCS. The phase diagram of the model is mapped. It consists of two ordered phases competing against each other: density wave, spin or charge, and unconventional superconductivity. These phases are separated by the first order transition. The symmetry of the superconducting order parameter is a non-universal property. It depends on particulars of the Hamiltonian. Within the framework of our model possible choices are the triplet $f$-wave and the singlet $d_{xy}$-wave. Organic quasi-one-dimensional superconductors have similar phase diagram.Comment: 12 pages, 2 Encapsulated PostScript figures, revtex4; the model's Hamiltonian is revised as compared to previous version, this revision affects prediction of the order parameter symmetr

ANALYSIS AND VERIFICATION OF THE OPERATION OF THE STABILIZING ROBUST CONTROLLER'S ELECTRICAL CIRCUIT OF THE ROTOR FLUX-LINKAGE CONTROL SYSTEM

On the basis of the classical theory of robust control, the theory of stability and the theory of continued fractions, the linearized mathematical model, the procedure for calculating and designing an analog electrical circuit of the H∞-suboptimal robust controller of the flux-linkage control system of the rotor of an asynchronous electric drive, protected by Ukrainian Patent no.137157, were built. The circuit contains three operational amplifiers, several resistors and capacitors. The proposed mathematical model, the procedure for calculating and choosing the parameters of the resistors and capacitors of the circuit take into account the random variations of the object and the controller within the specified boundaries. An analytical relationship between the transfer function coefficients and the resistances of the resistors and the capacitances of the capacitors of the controller's electrical circuit was established. On a specific example, by calculation according to the developed algorithm, the limiting values of the tolerances of the circuit's resistances of the resistors and capacitances of the capacitors were identified and these values were selected with a margin from the standard series. Analysis of noise filtering by the electrical circuit of the controller in the Multisim package shows its insensitivity to noise spreads within fairly wide boundaries. На базі класичної теорії робастного управління, теорії стійкості і теорії ланцюгових дробів побудовано лінеаризована математична модель, процедура розрахунку і проектування аналогової електричної схеми Н∞-субоптимального робастного регулятора системи управління потокозчепленням ротора асинхронного електроприводу, що захищена патентом України № 137157. Схема містить три операційних підсилювача, кілька резисторів і конденсаторів. Запропонована математична модель, процедура розрахунку і вибору параметрів резисторів і конденсаторів схеми враховують випадкові варіації об’єкта і регулятора в заданих межах. Встановлено аналітичний зв’язок між коефіцієнтами передавальної функції і опорами резисторів і ємностями конденсаторів електричної схеми регулятора. На конкретному прикладі розрахунковим шляхом за розробленим алгоритмом виявлені граничні значення допусків опорів резисторів і ємностей конденсаторів схеми і здійснений їх вибір із запасом зі стандартних рядів. Аналіз фільтрації завад електричною схемою регулятора в пакеті Multisim показує її нечутливість до розмахів завад у досить широких межах

Quantitative comparison of planar coded aperture imaging reconstruction methods

Imaging distributions of radioactive sources plays a substantial role in nuclear medicine as well as in monitoring nuclear waste and its deposit. Coded Aperture Imaging (CAI) has been proposed as an alternative to parallel or pinhole collimators, but requires image reconstruction as an extra step. Multiple reconstruction methods with varying run time and computational complexity have been proposed. Yet, no quantitative comparison between the different reconstruction methods has been carried out so far. This paper focuses on a comparison based on three sets of hot-rod phantom images captured with an experimental γ-camera consisting of a Tungsten-based MURA mask with a 2 mm thick 256 × 256 pixelated CdTe semiconductor detector coupled to a Timepix© readout circuit. Analytical reconstruction methods, MURA Decoding, Wiener Filter and a convolutional Maximum Likelihood Expectation Maximization (MLEM) algorithm were compared to data-driven Convolutional Encoder-Decoder (CED) approaches. The comparison is based on the contrast-to-noise ratio as it has been previously used to assess reconstruction quality. For the given set-up, MURA Decoding, the most commonly used CAI reconstruction method, provides robust reconstructions despite the assumption of a linear model. For single image reconstruction, however, MLEM performed best of all analytical reconstruction methods, but took on average 45 times longer than MURA Decoding. The fastest reconstruction method is the Wiener Filter with a run time 4.3 times faster compared to MURA Decoding and a mediocre quality. The CED with a specifically tailored training set was able to succeed the most commonly used MURA decoding on average by a factor between 1.37 and 2.60 and an equal run time

Синтез нових спіроциклічних N-арилзаміщених 2-тіопіримідин-4,6-діонів

A convenient and efficient method for the synthesis of new unsaturated spiro-annulated N-aryl-4,6-dioxopyrimidine-2-thione derivatives has been developed. The resulting compounds can be potential biological active molecules or precursors for further chemical modification.Aim. To develop the methods for the synthesis of new unsaturated spiro-annulated 2-thiopyrimidine-4,6-dione derivatives, which can be used as potentially biological active molecules or precursors for their formation.Results and discussion. By condensation of N-aryl-substituted thioureas and allylmalonic acid using acetic anhydride or acetyl chloride the series of 5-allyl-substituted 2-thiopyrimidinediones has been synthesized. Their further alkylation with allyl bromide or metallyl chloride led to formation of 5,5-dialkenyl derivatives, which were converted to the corresponding unsaturated spirocyclic dioxopyrimidine-2-thiones by ring-closing metathesis. Experimental part. The synthesis of the starting compounds and title products was performed by preparative chemical methods, TLC and column chromatography, elemental analysis, NMR-spectroscopy.Conclusions. The efficient three-step synthetic route of new unsaturated spiro-annulated N-aryl-4,6-dioxopyrimidine-2-thione derivatives from the starting N-arylsubstituted thioureas and allylmalonic acid has been developed. The spiro-annulated products obtained can find application in biological and pharmaceutical science or as starting substrates for further chemical modification.Разработан удобный и эффективный метод синтеза новых ненасыщенных спиро-аннелированных N-арилзамещенных 2-тиопиримидин-4,6-дионов. Полученные соединения могут быть потенциальными биоактивными молекулами или исходными веществами для дальнейшей химической модификации.Цель работы – разработка методов получения новых ненасыщенных спиро-аннелированных производных 2-тиопиримидин-4,6-диона как потенциальных биологически активных соединений или полупродуктов для их получения.Результаты и их обсуждение. Конденсацией N-арилзамещенных тиомочевин и аллилмалоновой кислоты с использованием уксусного ангидрида или ацетилхлорида синтезирован ряд 5-аллилзамещенных 2-тиопиримидиндионов. При их последующем алкилировании аллилбромидом или металлилхлоридом получены 5,5-диалкенильные производные, которые реакциями метатезиса с закрытием цикла были конвертированы в соответствующие непредельные спироциклические диоксопиримидин-2-тионы.   Экспериментальная часть. Синтез исходных соединений и целевых продуктов классическими методами препаративной химии; очистка и идентификация полученных соединений проводились методами тонкослойной и колоночной хроматографии, методом элементного анализа, спектроскопией ЯМР.Выводы. Разработан эффективный трехстадийный путь получения из исходных тиомочевин и аллилмалоновой кислоты новых ненасыщенных спиро-аннелированных производных N-арил-4,6-диоксопиримидин-2-тиона. Полученные спироциклические продукты могут найти применение в биологии и фармацевтической науке, а также использоваться как исходные соединения для дальнейшей химической модификации.Розроблено зручний та ефективний метод синтезу нових ненасичених спіро-анельованих N-арилзаміщених 2-тіопіримідин-4,6-діонів. Одержані сполуки можуть бути потенційними біоактивними молекулами або прекурсорами для подальшої хімічної модифікації. Мета роботи – розробка методів одержання нових ненасичених спіро-анельованих похідних 2-тіопіримідин-4,6-діону як потенційних біологічно активних сполук або напівпродуктів для їх отримання. Результати та їх обговорення. КонденсацієюN-арилзаміщених тіосечовин та алілмалонової кислоти із застосуванням оцтового ангідриду або ацетилхлориду синтезовано серію 5-алілзаміщених 2-тіопіримідиндіонів. При подальшому їх алкілуванні алілбромідом або металілхлоридом одержано 5,5-діалкенільні похідні, які реакціями метатезису із закриттям циклу було перетворено на відповідні ненасичені спіроциклічні діоксопіримідин-2-тіони.Експериментальна частина. Синтез вихідних сполук та цільових продуктів класичними методами препаративної хімії; очистку та ідентифікацію отриманих сполук здійснено методами тонкошарової та колонкової хроматографії, елементним аналізом, ЯМР-спектроскопією.Висновки. Розроблено ефективний тристадійний шлях отримання з вихідних тіосечовин та алілмалонової кислоти нових ненасичених спіро-анельованих похідних N-арил-4,6-діоксопіримідин-2-тіону. Одержані спіроциклічні продукти можуть знайти застосування в біології та фармацевтичній науці, або використовуватись як вихідні сполуки для подальшої хімічної модифікації

Kinky Behavior in Josephson Junctions

We analyze nonperturbatively the behavior of a Josephson junction in which two BCS superconductors are coupled through an Anderson impurity. We recover earlier perturbative results which found that a $\delta=\pi$ phase difference is preferred when the impurity is singly occupied and the on-site Coulomb interaction is large. We find a novel intermediate phase in which one of $\delta=0$ and $\delta=\pi$ is stable while the other is metastable, with the energy $E(\delta)$ having a kink somewhere in between. As a consequence of the kink, the $I-V$ characteristics of the junction are modified at low voltages.Comment: 7 pages, 7 encapsulated PostScript figures; figure 3 correcte

STABILITY AND ACCURACY OF THE ROBUST SYSTEM FOR STABILIZING THE ROTOR FLUX-LINKAGE OF AN ASYNCHRONOUS ELECTRIC DRIVE AT RANDOM VARIATIONS OF THE UNCERTAIN PARAMETERS WITHIN THE SPECIFIED BOUNDARIES

Purpose. The aim is to investigate the stability and the accuracy of a robust system for stabilizing the rotor flux-linkage of an asynchronous electric drive at random variations of the uncertain parameters of the object and the regulator within the specified boundaries. Methodology. To make the research, the mathematical model of the rotor flux-linkage channel of the vector control system of an asynchronous electric drive with parametric uncertainty was applied. The transfer function of the Н∞-suboptimal regulator was calculated using the mixed sensitivity method. This transfer function was used to construct the regulator structural scheme in the form of a connection of proportional and integrating links and several adders. Analytical dependences of the coefficients of the regulator's transfer function on the parameters of links of such a connection are determined. These dependences served to researching the influence of uncertain parameters of the regulator links and the object on the stability of the robust system and the accuracy of flux-linkage stabilization. Results. Investigations of the robust system stability and the accuracy of flux-linkage stabilization in the Robust Control Toolbox are done. The curves of the flux-linkage transient processes and the Bode diagram for the open system at random variations of the indeterminate parameters of the object and the regulator links within the specified boundaries are constructed. A choice of variable parameters was carried out by the Monte Carlo method. By the scatter of the obtained curves of the transient processes, the accuracy of flux-linkage stabilization was determined, and according to the Bode diagram, stability reserves in the amplitude and the phase of the robust system were determined. A high accuracy of flux-linkage stabilization (deviation less than 1 %) in fairly wide ranges of changing the uncertain parameters of the object and the regulator, while maintaining the stability of the system with permissible reserves in amplitude and phase, is established. Originality. For the first time, analytical dependences of the coefficients of the transfer function of the Н∞-suboptimal regulator on the parameters of its structural scheme, which represented in the form of a connection of proportional and integrating links, are obtained. The method for calculating the stability of a robust flux-linkage control system and the accuracy of its stabilization at random variations of the uncertain parameters of the object and the regulator links within the specified boundaries is developed. Practical value. The use of the proposed method allows, during the design of the regulator, to ensure the selection of its elements from standard series

Study Of Mass Losses Of Cauliflower At Storage Depending On A Packing Way

Tissues of fresh vegetables are characterized by the high quantity of moisture (80…96 %), active metabolism, low resistance to mechanical lesions, are spoiled fast. Metabolism in cells of tissues, so mass losses, depends on the content of water and dry substances.It is impossible to manage abiotic factors under conditions of open soil. So, there appears a necessity to study the influence of abiotic factors on the process of mass decrease at cauliflower storage that gives a possibility to prognosticate its mass losses and aptitude to storage.The aim of the study was to analyze the influence of weather conditions of the vegetation period of cauliflower, volume, specific mass and porosity of heads and packing methods on the intensity of natural mass losses of cauliflower at storage. The research gives a possibility to decrease natural losses of cauliflower heads and to prolong the storage duration of it. Cauliflower mass losses at the expanse of water evaporation depend on weather conditions of the vegetation period of the plant. It has been established, that there is a middle force reverse connection with the coefficient correlation r=–0,465 between the intensity of water evaporation at cauliflower heads storage and GTC, middle force connection with the coefficient correlation r=0,437 – with the average day temperature, and strong reverse connection r=–0,776 with the relative air humidity. There was elaborated the regression equation that gives an understanding about mass losses of cauliflower heads, packed in PF, at the expanse of water evaporation.The intensity of water evaporation of cauliflower at storage depends on package method. At packing in a stretch-film (SF), the intensity of moisture decrease, % a day, was the least, equal to 0,30–0,31. The ratio between moisture losses to ones of dry substances was 0,45–0,68. At packing in a performed stretch-film (PSF), the intensity of moisture decrease, % a day, was higher a little – 0,37–0,43.The more storage duration of cauliflower of late ripeness was provided by individual packing of heads in a polyethylene stretch-film. This packing type provided less total natural losses of products: in Skywoker F1– 6,0 %, in Kasper F1 and Santamaria F1 – 6,3 %. Natural losses for a day in variants with using a stretch-film were within 0,05–0,06 % depending on hybrid

Feasibility of a Small, Rapid Optical-to-IR Response, Next Generation Gamma Ray Burst Mission

We present motivations for and study feasibility of a small, rapid optical to IR response gamma ray burst (GRB) space observatory. By analyzing existing GRB data, we give realistic detection rates for X-ray and optical/IR instruments of modest size under actual flight conditions. Given new capabilities of fast optical/IR response (about 1 s to target) and simultaneous multi-band imaging, such an observatory can have a reasonable event rate, likely leading to new science. Requiring a Swift-like orbit, duty cycle, and observing constraints, a Swift-BAT scaled down to 190 square cm of detector area would still detect and locate about 27 GRB per yr. for a trigger threshold of 6.5 sigma. About 23 percent of X-ray located GRB would be detected optically for a 10 cm diameter instrument (about 6 per yr. for the 6.5 sigma X-ray trigger).Comment: Elaborated text version of a poster presented at 2012 Malaga/Marbella symposiu