Shape resonances in the superconducting order parameter of ultrathin nanowires

We study the shape resonance effect associated with the confined transverse superconducting modes of a cylindrical nanowire in the clean limit. Results of numerical investigations of the Bogoliubov-de Gennes equations show significant deviations of the energy gap parameter from its bulk value with a profound effect on the transition temperature. The most striking is that the size of the resonances is found to be by about order of magnitude larger than in ultrathin metallic films with the same width.Comment: 4 pages, 2 figure

DRAWING OF THE TECHNICAL DOCUMENTATION FOR THE COMMUNAL ROAD 151-DN 6- SECTIONN 1, DRĂGHICENI COMMUNE, OLT COUNTY, BY COMBINED GPS USE – TOTAL STATION

For drawing up the technical documentation of the Communal Road 151 – DN 6 –Section 1, located in the Drăghiceni commune area, Olt County, it was necessary the combined use of the modern GPS topography equipment – total station. The GPS technology was used to determine the points of the support network, and the total station to thicken it and raise the points on the ground.The computational operations were performed based on the field data, thus obtaining the absolute coordinates of the points that delineate the studied land in the Stereographic Projection System 1970.The drawing up of operations of the placement and delineation plan of the property body consist of representing the points that delineate the surface on a sheet of A3 format at a scale of 1:5000

Investigation of irradiated monolithic transistors for space applications

In this paper experimental results on radiation effects on a BICMOS high speed commercial technology, manufactured by STMicroelectronics, are reported. Bipolar transistors were irradiated by neutrons, ions, or by both of them. Fast neutrons, as well as other types of particles, produce defects, mainly by displacing silicon atoms from their lattice positions to interstitial locations, i.e. generating vacancy-interstitial pairs, the so-called Frenkel pairs (FP). Defects introduce trapping energy states which degrade the common emitter current gain β. The gain degradation has been investigated for collector current Ic between 1 μA and 1 mA. It was found a linear dependence of Δ(1/β)=1/βi−1/β (where βi and β are the gain after and before the irradiation) as a function of the concentration of FP. The bipolar transistors made on this technology have shown to be particularly radiation resistant. Both base and collector currents have been also systematically investigated

Study of radiation effects on bipolar transistors

Abstract In this paper it was shown that the irradiation with neutrons and carbon ions leads to gain degradation in bipolar transistors due to generation of defects. The density of these generated defects is independent of the type of irradiation (neutrons or carbon ions). Thus, it is possible to evaluate Δ(1/β), once the expected Frenkel pair density is known. The dependence of the damage constant on collector current is a power law function, with the exception of the lateral pnp transistors, that shows a higher sensitivity to radiation and a different behaviour. Neutrons give a smaller density of Frenkel pairs (CF) than the two sorts of carbon ions of high energy (CHE) and medium energy (CME). It was found that CME causes a higher concentration of CF. The calculated ratio R=CF/Φ, where CF is the Frenkel pair density and Φ fluence does not depend on Φ, for a given type of radiation. However, it depends on the incoming particle type. Its smallest calculated value was obtained for neutrons (R=6.1×10), which increases to 1.25×103 for CHE and to 1.1×104 for CME

Metallic nanograins: spatially nonuniform pairing induced by quantum confinement

It is well-known that the formation of discrete electron levels strongly influences the pairing in metallic nanograins. Here we focus on another effect of quantum confinement in superconducting grains that was not studied previously, i.e., spatially nonuniform pairing. This effect is very significant when single-electron levels form bunches and/or a kind of shell structure: in highly symmetric grains the order parameter can exhibit variations with position by an order of magnitude. Nonuniform pairing is closely related to a quantum-confinement induced modification of the pairing-interaction matrix elements and size-dependent pinning of the chemical potential to groups of degenerate or nearly degenerate levels. For illustration we consider spherical metallic nanograins. We show that the relevant matrix elements are as a rule enhanced in the presence of quantum confinement, which favors spatial variations of the order parameter, compensating the corresponding energy cost. The size-dependent pinning of the chemical potential further increases the spatial variation of the pair condensate. The role of nonuniform pairing is smaller in less symmetric confining geometries and/or in the presence of disorder. However, it always remains of importance when the energy spacing between discrete electron levels $\delta$ is approaching the scale of the bulk gap $\Delta_B$, i.e., $\delta > 0.1$-$0.2\,\Delta_B$

The Modern State of Works in Field of Electron-Beam Technology of Melting and Evaporation of Metals and Non-Metals in a Vacuum

In developing of new processes for growing metal (composite) films, the main attention is given to controlling the metal vapour flows: through energy state of the condensing particles, their molecular composition, intensity, spatial distribution of the flow, etc. It is known that the widely accepted open-type evaporators, including quasi-closed ones, are characterized by instability of the directivity diagram of the vapour flow in time, even at constant temperature. Radiation load on the film growth surface from these sources is sometimes comparable to the energy of vapour flow condensation. Therefore, when they are used, it is quite difficult to produce reproducible film structures with controllable parameters. Particular difficulties arise at high evaporation rates, when micro-drops are usually present in the vapour flow

ROMANIAN COUNTRYSIDE - SUPPORT FOR THE DEVELOPMENT OF SUSTAINABLE TOURISM

This paper is focused on presenting the particularities of the Romanian rural space from a touristic point of view with its advantages for the tourists and as reason for supporting the development of sustainable tourism. The specificity of natural capital is amplified by spectacular landscapes, varied configuration of land relief, favourable climatic conditions (reduced frequency of negative phenomena, absence of excessive temperatures), therapeutic value and abundance of natural factors (mineral waters and thermal-mineral waters, curative mud, topoclimate and microclimate, etc.), flora and fauna, etc.The natural capital, for which the Romanian rural area represents a „geographic personality”, must be doubled in time by the tourist vocation.Romania holds an immense treasure of archaeological remains, historical, architectural and art monuments, as well as a priceless patrimony which attests the evolution and continuity of work and life on these lands, the development of the culture and arts of the Romanian people. This entire cultural-historical fund represents a significant part of the potential tourist offer (the so-called potential secondary offer) and a component of the tourist image of Romanian on the international market

Magnetic-field induced quantum-size cascades in superconducting nanowires

In high-quality nanowires, quantum confinement of the transverse electron motion splits the band of single-electron states in a series of subbands. This changes in a qualitative way the scenario of the magnetic-field induced superconductor-to-normal transition. We numerically solve the Bogoliubov-de Gennes equations for a clean metallic cylindrical nanowire at zero temperature in a parallel magnetic field and find that for diameters D < 10-15 nm, this transition occurs as a cascade of subsequent jumps in the order parameter (this is opposed to the smooth second-order phase transition in the mesoscopic regime). Each jump is associated with the depairing of electrons in one of the single-electron subbands. As a set of subbands contribute to the order parameter, the depairing process occurs as a cascade of jumps. We find pronounced quantum-size oscillations of the critical magnetic field with giant resonant enhancements. In addition to these orbital effects, the paramagnetic breakdown of Cooper pairing also contributes but only for smaller diameters, i. e., D < 5 nm

Laser ignition - Spark plug development and application in reciprocating engines

© 2018 The Author(s) Combustion is one of the most dominant energy conversion processes used in all areas of human life, but global concerns over exhaust gas pollution and greenhouse gas emission have stimulated further development of the process. Lean combustion and exhaust gas recirculation are approaches to improve the efficiency and to reduce pollutant emissions; however, such measures impede reliable ignition when applied to conventional ignition systems. Therefore, alternative ignition systems are a focus of scientific research. Amongst others, laser induced ignition seems an attractive method to improve the combustion process. In comparison with conventional ignition by electric spark plugs, laser ignition offers a number of potential benefits. Those most often discussed are: no quenching of the combustion flame kernel; the ability to deliver (laser) energy to any location of interest in the combustion chamber; the possibility of delivering the beam simultaneously to different positions, and the temporal control of ignition. If these advantages can be exploited in practice, the engine efficiency may be improved and reliable operation at lean air-fuel mixtures can be achieved, making feasible savings in fuel consumption and reduction in emission of exhaust gasses. Therefore, laser ignition can enable important new approaches to address global concerns about the environmental impact of continued use of reciprocating engines in vehicles and power plants, with the aim of diminishing pollutant levels in the atmosphere. The technology can also support increased use of electrification in powered transport, through its application to ignition of hybrid (electric-gas) engines, and the efficient combustion of advanced fuels. In this work, we review the progress made over the last years in laser ignition research, in particular that aimed towards realizing laser sources (or laser spark plugs) with dimensions and properties suitable for operating directly on an engine. The main envisaged solutions for positioning of the laser spark plug, i.e. placing it apart from or directly on the engine, are introduced. The path taken from the first solution proposed, to build a compact laser suitable for ignition, to the practical realization of a laser spark plug is described. Results obtained by ignition of automobile test engines, with laser devices that resemble classical spark plugs, are specifically discussed. It is emphasized that technological advances have brought this method of laser ignition close to the application and installation in automobiles powered by gasoline engines. Achievements made in the laser ignition of natural gas engines are outlined, as well as the utilization of laser ignition in other applications. Scientific and technical advances have allowed realization of laser devices with multiple (up to four) beam outputs, but many other important aspects (such as integration, thermal endurance or vibration strength) are still to be solved. Recent results of multi-beam ignition of a single-cylinder engine in a test bench set-up are encouraging and have led to increased research interest in this direction. A fundamental understanding of the processes involved in laser ignition is crucial in order to exploit the technology's full potential. Therefore, several measurement techniques, primarily optical types, used to characterize the laser ignition process are reviewed in this work