Parity-Affected Persistent Currents in Superconducting Nanorings

We argue that at sufficiently low temperatures T superconducting parity effect may strongly influence equilibrium persistent currents (PC) in isolated superconducting nanorings containing a weak link with few conducting modes. For a single channel quantum point contact at T=0 we predict a novel effect of parity-induced blocking of PC. In nanorings with SNS junctions a $\pi$-state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux.Comment: Published versio

Testing the equation of state for viscous dark energy

Some cosmological scenarios with bulk viscosity for the dark energy fluid are considered. Based on some considerations related to hydrodynamics, two different equations of state for dark energy are assumed, leading to power-law and logarithmic effective corrections to the pressure. The models are tested with the latest astronomical data from type Ia supernovae (Pantheon sample), measurements of the Hubble parameter HðzÞ, baryon acoustic oscillations and cosmic microwave background radiation. In comparison with the ΛCDM model, some different results are obtained and their viability is discussed. The power-law model shows some modest results, achieved under negative values of bulk viscosity, while the logarithmic scenario provide good fits in comparison to the ΛCDM model.Ministerio de Economía, Industria y Competitividad (project FIS2016-76363-P)Agencia de Gestión de Ayudas Universitarias y de Investigación (project 2017 SGR 247)CANTATA COST action (grant CA15117

Parity effect and spontaneous currents in superconducting nanorings

New physical effects emerge from an interplay between the electron parity number and persistent currents in superconducting nanorings. An odd electron, being added to the ring, produces a countercurrent which may substantially modify the ground state properties of the system. In superconducting nanorings with an embedded normal metal layer a novel ``$\pi /N$-junction'' state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux. Further peculiar features of the parity effect are expected in structures with resonant electron transport across the weak link.Comment: 9 pages, 5 figures. Invited talk at the International Conference "Frontiers of Quantum and Mesoscopic Thermodynamics", Prague, July 200

Early Dark Energy with Power-law F(R) Gravity

We study a power-law $F(R)$ gravity with an early dark energy term, that can describe both the early-time and the late-time acceleration of the Universe. We confront this scenario with recent observational data including the Pantheon Type Ia supernovae, measurements of the Hubble parameter $H(z)$ (Cosmic Chronometers), data from Baryon Acoustic Oscillations and standard rulers data from the Cosmic Microwave Background (CMB) radiation. The model demonstrates some achievements in confronting with these observations and can be compared with the $\Lambda$-Cold-Dark-Matter model. In particular, in both models we obtain very close estimates for the Hubble constant $H_0$, but it is not true for $\Omega_m^0$. The early dark energy term supports viability of the considered $F(R)$ gravity model.Comment: PLB Accepte

Exponential F(R) gravity with axion dark matter

The cosmological evolution within the framework of exponential $F(R)$ gravity is analysed by assuming two forms for dark matter: (a) a standard dust-like fluid and (b) an axion scalar field. As shown in previous literature, an axion-like field oscillates during the cosmological evolution but can play the role of dark matter when approaching the minimum of its potential. Both scenarios are confronted with recent observational data including the Pantheon Type Ia supernovae, Hubble parameter estimations (Cosmic Chronometers), Baryon Acoustic Oscillations and Cosmic Microwave Background distances. The models show great possibilities in describing these observations when compared with the $\Lambda$CDM model, supporting the viability of exponential $F(R)$ gravity. The differences between both descriptions of dark matter is analysed.Comment: 13 pages, 3 figures. To be published in Phys. Dark Univers

Hadronic Regge Trajectories: Problems and Approaches

We scrutinized hadronic Regge trajectories in a framework of two different models --- string and potential. Our results are compared with broad spectrum of existing theoretical quark models and all experimental data from PDG98. It was recognized that Regge trajectories for mesons and baryons are not straight and parallel lines in general in the current resonance region both experimentally and theoretically, but very often have appreciable curvature, which is flavor-dependent. For a set of baryon Regge trajectories this fact is well described in the considered potential model. The standard string models predict linear trajectories at high angular momenta J with some form of nonlinearity at low J.Comment: 15 pages, 9 figures, LaTe

О применении нечетких нейронных сетей в рамках рискориентированного подхода к контрольно-надзорной деятельности в гражданской авиации

A risk-oriented approach implemented in conducting control and supervisory activities in Civil Aviation organizations makes it possible to increase the effectiveness of such activities, the objectivity of assessments, to reduce costs and the additionalburden on business. The main provisions, regulating the activities of control and supervision bodies, including the issues of risk assessment, are generally specified in regulatory documents. However, uncertainty remains regarding the use of so-called risk indicators, which are designed to forecast risks for flight safety. Currently, there are no guidelines on the number and composition of such indicators, there are no methods to use them for the intended purpose. The article proposes a solution to this problem using elements of artificial intelligence. Based on the example of risk indicators distinctive for air traffic service organizations, the feasibility of forecasting the level of risk through a fuzzy (hybrid) neural network is shown. As is well known, such hybrid structures, combining neural networks and fuzzy logic, collect the best properties of both methods. The formation of a set of risk ndicators and initial data for network training is carried out with the involvement of qualified experts with extensive experience in flight safety management and control and supervisory activities. The trained network allows us to quantify a forecasted level of risk in an airline based on the identified risk indicators considering the degree of their manifestation. All the stages of building and using the network in the ANFIS editor of the MATLAB software package are shown. The proposed method can also be used in the flight safety management systems for various providers of aviation services.Рискориентированный подход, реализуемый при проведении контрольно-надзорных мероприятий в организациях гражданской авиации, позволяет повысить эффективность таких мероприятий, объективность оценок, снизить расходы и дополнительную нагрузку на бизнес. Основные положения, регулирующие деятельность органов контроля и надзора, в том числе и в вопросах оценки рисков, в целом указаны в нормативных документах. Однако остается неопределенность в части использования так называемых индикаторов риска, которые предназначены для прогнозирования рисков для безопасности полетов. В настоящее время нет каких-либо указаний по количеству и составу таких индикаторов, отсутствуют методики их использования по назначению. В статье предлагается решение этого вопроса с использованием элементов искусственного интеллекта. На примере индикаторов риска, характерных для организаций обслуживания воздушного движения, показана возможность прогнозировать уровень риска посредством нечеткой (гибридной) нейронной сети. Как известно, такие гибридные структуры, объединяющие в себе нейронные сети и нечеткую логику, собирают наилучшие свойства обоих методов. Формирование набора индикаторов риска и исходных данных для обучения сети проводится с привлечением квалифицированных экспертов с большим опытом управления безопасностью полетов и контрольно-надзорной работы. Обученная сеть позволяет количественно оценить прогнозируемый уровень риска на авиапредприятии на основании выявленных индикаторов риска с учетом степени их проявления. Показаны все этапы построения и использования сети в редакторе ANFIS программного пакета Matlab. Предлагаемый метод может использоваться также и в системах управления безопасностью полетов различных поставщиков авиационных услуг

Minigap, Parity Effect and Persistent Currents in SNS Nanorings

We have evaluated a proximity-induced minigap in the density of states (DOS) of SNS junctions and SNS nanorings at an arbitrary concentration of non-magnetic impurities. We have demonstrated that an isotropic energy minigap in the electron spectrum opens up already at arbitrarily weak disorder, while angle resolved DOS at higher energies can remain strongly anisotropic. The minigap value $\epsilon_g$ can be tuned by passing a supercurrent through an SNS junction or by applying a magnetic flux $\Phi$ to an SNS ring. A non-monotonous dependence of $\epsilon_g$ on $\Phi$ has been found at weak disorder. We have also studied persistent currents in isolated SNS nanorings. For odd number of electrons in the ring we have found a non-trivial current-phase (current-flux) relation which -- at relatively high disorder -- may lead to a $\pi$-junction state and spontaneous currents in the ground state of the system.Comment: 7 pages, 8 figure

Variable Star Candidates in an ACS Field of M31

A search for variable stars is performed using two epochs of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging data for a 9.28 square arcminute portion of M31. This data set reveals 254 sources that vary by at least 4-sigma between epochs. The positions and 2-epoch B-band (equivalent) photometry of these sources are presented. The photometry suggests that this catalog includes most of the RR Lyrae population of this portion of M31.Comment: 22 pages, 3 tables, 5 figures, accepted for publication in A