Effect of Layer Thickness on Structural, Morphological and Superconducting Properties of Nb\u3csub\u3e3\u3c/sub\u3eSn Films Fabricated by Multilayer Sequential Sputtering

Superconducting Nb3Sn films can be synthesized by controlling the atomic concentration of Sn. Multilayer sequential sputtering of Nb and Sn thin films followed by high temperature annealing is considered as a method to fabricate Nb3Sn films, where the Sn composition of the deposited films can be controlled by the thickness of alternating Nb and Sn layers. We report on the structural, morphological and superconducting properties of Nb3Sn films fabricated by multilayer sequential sputtering of Nb and Sn films on sapphire substrates followed by annealing at 950 °C for 3 h. We have investigated the effect of Nb and Sn layer thickness and Nb:Sn ratio on the properties of the Nb3Sn films. The crystal structure, surface morphology, surface topography, and film composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDS). The results showed Sn loss from the surface due to evaporation during annealing. Superconducting Nb3Sn films of critical temperature up to 17.93 K were fabricated

Band bending driven evolution of the bound electron states at the interface between a three-dimensional topological insulator and a three-dimensional normal insulator

In the frame of k⋅p method and variational approach for the effective energy functional of a contact between a three-dimensional topological insulator (TI) and normal insulator (NI), we analytically describe the formation of interfacial bound electron states of two types (ordinary and topological) having different spatial distributions and energy spectra. We show that these states appear as a result of the interplay of two factors: hybridization and band bending of the TI and NI electron states near the TI/NI boundary. These results are corroborated by the density functional theory calculations for the exemplar Bi2Se3/ZnSe system

Magnetic proximity effect at the 3D topological insulator/magnetic insulator interface

The magnetic proximity effect is a fundamental feature of heterostructures composed of layers of topological insulators and magnetic materials since it underlies many potential applications in devices with novel quantum functionality. Within density functional theory we study magnetic proximity effect at the 3D topological insulator/magnetic insulator (TI/MI) interface in Bi$_2$Se$_3$/MnSe(111) system as an example. We demonstrate that a gapped ordinary bound state which spectrum depends on the interface potential arises in the immediate region of the interface. The gapped topological Dirac state also arises in the system owing to relocation to deeper atomic layers of topological insulator. The gap in the Dirac cone is originated from an overlapping of the topological and ordinary interfacial states. This result being also corroborated by the analytic model, is a key aspect of the magnetic proximity effect mechanism in the TI/MI structures.Comment: 10 pages, 3 figure

Effect of tobacco smoke and nicotine on immune response in tuberculosis infection and other lung diseases

The problem of smoking, as well as incidence of tuberculosis, has existed for a long time. The latest WHO data indicate that 1.3 million people die from tuberculosis, and another 7 millions die from smoking every year. Tobacco smoke contains many harmful chemicals, including carbon monoxide, nicotine, nitrogen oxides, and cadmium. A number of studies indicate a high prevalence of smoking among patients with tuberculosis. In most cases, infection with Mycobacterium tuberculosis does not lead to active disease, due to the development of a balanced, homeostatic immune response. The key protective components are inflammatory responses aimed at inhibition of the pathogen growth, its sequestration and final elimination. At the same time, excessive or inadequate immune response may lead to granuloma destruction, tissue damage and, as a result, prolonged duration of treatment due to decreased respiratory function of the lungs. Along with pro-inflammatory mediators, anti-inflammatory mediators are synthesized in the host organism, which can positively or negatively affect the course of disease, depending on the place and time of their production. The balance between pro-and anti-inflammatory mediators in terms of time and expression level plays a crucial role in determining the outcome of infection. In our review, we consider the impact of tobacco smoke on various components of the human immune system, as well as upon the course and outcome of tuberculosis and other lung diseases. In addition, we would like to draw the reader’s attention to the need of adjusting pathogenetic therapy of bronchopulmonary diseases, taking into account the patient’s smoking habits. Tobacco smoking is one of the main causes of the severe course of many infectious and non-infectious diseases of the bronchopulmonary system. The decay products of cigarette smoke disrupt the functioning of the ciliated epithelium of respiratory tract, the production of the mucous component in the bronchi, and reduce the effectiveness of the surfactant system. These negative events interfere with protective mechanisms of the human respiratory system. It is worth of note that tobacco smoke also exerts a systemic effect on the immune system. Data are accumulating on the association between the terms of exposure to tobacco smoke, and a range of adverse tunerculosis manifestations, such as extent of infection, severity of course, reactivation, treatment outcome, and mortality. At the same time, epidemiological studies are able to reveal the associations, but they do not allow us to determine exact causal relationships

Deposition of Nb₃Sn Films by Multilayer Sequential Sputtering for SRF Cavity Application

Nb3Sn is considered as an alternative of Nb for SRF accelerator cavity application due to its potential to obtain higher quality factors and higher accelerating gradients at a higher operating temperature. Magnetron sputtering is one of the effective techniques that can be used to fabricate Nb3Sn on SRF cavity surface. We report on the surface properties of Nb3Sn films fabricated by sputtering multiple layers of Nb and Sn on sapphire and niobium substrates followed by annealing at 950°C for 3 h. The crystal structure, film microstructure, composition and surface roughness were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The RF performance of the Nb3Sn coated Nb substrates were measured by a surface impedance characterization system. We also report on the design of a multilayer sputter deposition system to coat a single-cell SRF cavity

Subsurface radiolocation tomography of cables under dual-polarization probing

It is proposed to use the tomographic approach to the problem of detecting and imaging concealed utility networks. This approach is based on generating the three-dimensional radio images of the space being explored from the results of measuring its location wave projections in a dual-polarization measurement mode. The problem is solved by focusing radiation first on the “air–dielectric” interface and then inside the dielectric. Experimental data processing results and reconstructed threedimensional radio tomograms are provided for a “twisted pair” cable and a fiber-optic cable with no metallic inclusions. The results confirm the operability of the approach

Biological diversity of the coastal zone of the Crimean peninsula: problems, preservation and restoration pathways

The results of complex hydrochemical, hydrobiological and ichthyological investigations by IBSS, NAS of Ukraine, realized in 6 regions of the coastal zone of the Crimean peninsula in the Black Sea and the Sea of Azov are given. The main negative factors causing changes in structural and functional characteristics of hydrobiocenoses in the regions studied are analyzed and “hot ecological spots” are isolated. Variants of different methods of management of the coastal ecosystems, including construction of artificial reefs and usage of biological filters for water cleaning, protection and recreation of biological diversity are taken into consideration