Quantum FFLO state in clean layered superconductors

We investigate the influence of Landau quantization on the superconducting instability for a pure layered superconductor in the magnetic field directed perpendicular to the layers. We demonstrate that the quantization corrections to the Cooper-pairing kernel with finite Zeeman spin splitting promote the formation of the nonuniform state in which the order parameter is periodically modulated along the magnetic field, i.e., between the layers (Fulde-Ferrell-Larkin-Ovchinnikov [FFLO] state). The conventional uniform state experiences such a quantization-induced FFLO instability at low temperatures even in a common case of predominantly orbital suppression of superconductivity when the Zeeman spin splitting is expected to have a relatively weak effect. The maximum relative FFLO temperature is given by the ratio of the superconducting transition temperature and the Fermi energy. This maximum is realized when the ratio of the spin-spitting energy and the Landau-level separation is half-integer. These results imply that the FFLO states may exist not only in the Pauli-limited superconductors but also in very clean materials with small Zeeman spin-splitting energy. We expect that the described quantization-promoted FFLO instability is a general phenomenon, which may be found in materials with different electronic spectra and order-parameter symmetries.Comment: 18 pages, 10 figures, minor correction

Interplay between orbital-quantization effects and the Fulde-Ferrell-Larkin-Ovchinnikov instability in multiple-band layered superconductors

We explore superconducting instability for a clean two-band layered superconductor with deep and shallow bands in the magnetic field applied perpendicular to the layers. In the shallow band, the quasiclassical approximation is not applicable, and Landau quantization has to be accounted for exactly. The electronic spectrum of this band in the magnetic field is composed of the one-dimensional Landau-level minibands. With increasing magnetic field the system experiences series of Lifshitz transitions when the chemical potential enters and exits the minibands. These transitions profoundly influence the shape of the upper critical field at low temperatures. In addition, the Zeeman spin splitting may cause the nonuniform state with interlayer modulation of the superconducting order parameter (Fulde-Ferrell-Larkin-Ovchinnikov state). Typically, the quantization effects in the shallow band strongly promote the formation of this state. The uniform state remains favorable only in the exceptional resonance cases when the spin-splitting energy exactly matches the Landau-level spacing. Furthermore, for specific relations between electronic spectrum parameters, the alternating FFLO state may realize, in which the order parameter changes sign between the neighboring layers. For all above cases, the reentrant high-field superconducting states may emerge at low temperatures if the shallow band has significant contribution to the Cooper pairing.Comment: 25 pages, 14 figures, minor revisions and more references adde

Strong Landau-quantization effects in high-magnetic-field superconductivity of a two-dimensional multiple-band metal near the Lifshitz transition

We investigate the onset of superconductivity in magnetic field for a clean two-dimensional multiple-band superconductor in the vicinity of the Lifshitz transition when one of the bands is very shallow. Due to small number of carriers in this band, the quasiclassical Werthamer-Helfand approximation breaks down and Landau quantization has to be taken into account. We found that the transition temperature TC2(H) has giant oscillations and is resonantly enhanced at the magnetic fields corresponding to full occupancy of the Landau levels in the shallow band. This enhancement is especially pronounced for the lowest Landau level. As a consequence, the reentrant superconducting regions in the temperature-field phase diagram emerge at low temperatures near the magnetic fields at which the chemical potential matches the Landau levels. The specific behavior depends on the relative strength of the intraband and interband pairing interactions and the reentrance is most pronounced in the purely interband coupling scenario. The reentrant behavior is suppressed by the Zeeman spin splitting in the shallow band, the separated regions disappear already for very small spin-splitting factors. On the other hand, the reentrance is restored in the resonance cases when the spin-splitting energy exactly matches the separation between the Landau levels. The predicted behavior may realize in the gate-tuned FeSe monolayer.Comment: 23 pages, 9 figures, more references added and one figure adde

Time domain computational modelling of 1D arterial networks in monochorionic placentas

Published versio

Позиціонування вугільної галузі у зовнішньому енергетичному балансі України

Здійснено формування зовнішнього енергетичного балансу з розрахунком показника чистого експорту. Виконано комплексну оцінку співвідношення обсягів виробництва та споживання вугілля в Україні. Виявлено невідповідність обсягів виробленого та спожитого вугілля та його акумуляцію в Україні. Обґрунтовано необхідність зменшення обсягів імпорту вугілля. Ключові слова: виробництво, зовнішній баланс, імпорт, комплексна оцінка, споживання, формування, чистий експорт.Осуществлено формирование внешнего энергетического баланса с расчетом показателя чистого экспорта. Выполнена комплексная оценка соотношения объемов производства и потребления угля в Украине. Выявлены несоответствие объемов произведенного и потребленного угля и его аккумуляция в Украине. Обоснована необходимость уменьшения объемов импорта угля. Ключевые слова: внешний баланс, импорт, комплексная оценка, потребление, производство, формирование, чистый экспорт.Under present-day conditions it is important to maximize the consumption of energy resources produced in Ukraine, in particular coal resources. It will contribute to solving several macroeconomic problems of Ukraine like raising the energy assurance level as a component of national security of Ukraine, improving the competitiveness of domestic enterprises and the trade balance of Ukraine. At the present stage of development the most popular energy resources are oil and natural gas which is conditioned by their high heating and ecological characteristics. At the same time the reduction of these resources, irregularity of their deposits and other objective factors make for consumption of local energy resources, in particular coal resources. It is defined that foreign energy balance is an index system that shows the demand-consumption ratio of an energy resource in a given period of time inside the country. A foreign energy balance model has been designed which includes calculation of the net export and makes it possible to clear up the modern tendencies that established in our country’s external economic relations of energy resources trade. It has been proved that the basic factor reducing the net export of energy resources is a great volume of imported natural gas though the trade balance of coal and peat operations is negative as well. A complex evaluation of production and consumption ratio of coal in Ukraine based on reduction coefficient to oil equivalent has been carried out which makes it possible to reveal the discrepancy between the volume of coal produced and the volume of coal consumed with its latter accumulation in Ukraine. The necessity of reducing the volume of coal import is proved. Keywords: foreign energy balance, import, complex evaluation, consumption, production, formation, net export

Efficacy of Some Combination Regimens of Oral Hypoglycaemic Agents in Type 2 Diabetes Mellitus Patients

Purpose: To examine the efficacy of selected oral hypoglycaemic agent (OHA) regimens in a small group of patients receiving such treatment.Methods: This was a retrospective, observational study that involved patients who had been diagnosed with type 2 diabetes mellitus and undergoing routine follow-up at a teaching hospital. By reviewing patients’ medical records, changes in fasting blood glucose (FPG) and glycated haemoglobin (HbA1c) levels induced by several OHA cobmination regimens were documented. Target FPG and HbA1c were defined as 4.4 - 6.1 mmol/L and 6.5 %, respectively.Results: Based on the medical records of 156 patients reviewed, the combination of metformin and gliclazide was the most commonly prescribed regimen (63.46 %). The use of gliclazide + rosiglitazone + acarbose produced the greatest reduction in FPG and HbA1c (-4.80 mmol/L and -4.20 %, respectively), but the number of patients receiving this combination was too small to allow definitive conclusions to be made. More patients in the triple OHA group were able to achieve the desired glycaemic control than those in the dual OHA group (FPG, 44.44 % versus 41.18 %; HbA1c, 52.94 % versus 47.06 %), highlighting the important benefits conferred by the use of multiple OHAs.Conclusion: The efficacy of various OHA combinations varies, and adding a third drug to a dual-agent regimen further reduces FPG and HbA1c levels. Though gliclazide + rosiglitazone + acarbose produces the greatest reduction in FPG and HbA1c levels, larger studies are required to confirm these findings.Keywords: Type 2 Diabetes Mellitus, Oral Hypoglycaemic Agents, Fasting Plasma Glucose (FPG), Glycated Haemoglobin (HbA1c), Combination Therapy, Gliclazide, Rosiglitazone, Acarbos

Enhanced surface transfer doping of diamond by V2O5 with improved thermal stability

Surface transfer doping of hydrogen-terminated diamond has been achieved utilising V2O5 as a surface electron accepting material. Contact between the oxide and diamondsurface promotes the transfer of electrons from the diamond into the V2O5 as revealed by the synchrotron-based high resolution photoemission spectroscopy. Electrical characterization by Hall measurement performed before and after V2O5 deposition shows an increase in hole carrier concentration in the diamond from 3.0 × 1012 to 1.8 × 1013 cm−2 at room temperature. High temperature Hall measurements performed up to 300 °C in atmosphere reveal greatly enhanced thermal stability of the hole channel produced using V2O5 in comparison with an air-induced surface conduction channel. Transfer doping of hydrogen-terminated diamond using high electron affinity oxides such as V2O5 is a promising approach for achieving thermally stable, high performance diamond based devices in comparison with air-induced surface transfer dopin

Foreign exchange exposure: Evidence from the U.S. insurance industry

We study the foreign exchange exposure of U.S. insurers. The evidence shows that no systematic difference exists in the currency risk profiles of life and non-life segments within the insurance industry. This suggests that life and non-life insurers have similar risk exposure management strategies arising from similar risk pooling and financial intermediary functions. The empirical results reveal that a sizable proportion of U.S. insurers are exposed to foreign exchange movements against the seven largest U.S. trade partners in insurance services (U.K., Japan, Switzerland, Netherlands, France, Germany and Canada). Significant operational and size effects are also documented and we find that the frequency of foreign exchange exposure increases with time horizon

Transport Modelling During Preparation of General Plans in Big Cities: Reasons and Challenges

Rapidly growing mobility of people in European cities attaches greater importance to the sustainable developmentconcept. The dynamics of European cities are however different. Cites such as Lithuanian, Slovakian and Polishones will rapidly increase traffic flows and car ownership at fast pace. Also in most of Western Europe, even if at lowerrates, private mobility is increasing. In some cities, however, car use and car ownership are finally decreasing, alsothanks to policies implemented. Of course, an increase of traffic flows poses problems in terms of street space, pollutionand liveability of cities. Sustainable integration of all kinds of transport into the urban development process is one ofthe most effective actions in the hands of city planners. The coordination between the planning of residential and businessdevelopment areas and the expansion of public transport and its hierarchical integration is however a difficult butnecessary exercise. Transport modelling tools, in particular, need important advancements to integrate transport andland use in simulations. This article analyses the main challenges in the use of transport models to support the constructionof city plans by means of two case studies of Milan and Vilnius. The analysis deals both with traditional aspects,such as the proper simulation of multimodal choices, the level of detail of zoning, the issues associated to the simulationof traffic management policies. Then, we will focus on two aspects still open: the integration of transport modelling andeconomic assessment or ranking of actions, and the inclusion of land use changes in the modelling

Nanocalorimetric Evidence for Nematic Superconductivity in the Doped Topological Insulator Sr0.1_{0.1}Bi2_{2}Se3_{3}

Spontaneous rotational-symmetry breaking in the superconducting state of doped $\mathrm{Bi}_2\mathrm{Se}_3$ has attracted significant attention as an indicator for topological superconductivity. In this paper, high-resolution calorimetry of the single-crystal $\mathrm{Sr}_{0.1}\mathrm{Bi}_2\mathrm{Se}_3$ provides unequivocal evidence of a two-fold rotational symmetry in the superconducting gap by a \emph{bulk thermodynamic} probe, a fingerprint of nematic superconductivity. The extremely small specific heat anomaly resolved with our high-sensitivity technique is consistent with the material's low carrier concentration proving bulk superconductivity. The large basal-plane anisotropy of $H_{c2}$ is attributed to a nematic phase of a two-component topological gap structure $\vec{\eta} = (\eta_{1}, \eta_{2})$ and caused by a symmetry-breaking energy term $\delta (|\eta_{1}|^{2} - |\eta_{2}|^{2}) T_{c}$. A quantitative analysis of our data excludes more conventional sources of this two-fold anisotropy and provides the first estimate for the symmetry-breaking strength $\delta \approx 0.1$, a value that points to an onset transition of the second order parameter component below 2K