Enhanced longitudinal mode spacing in blue-violet InGaN semiconductor laser

A novel explanation of observed enhanced longitudinal mode spacing in InGaN semiconductor lasers has been proposed. It has been demonstrated that e-h plasma oscillations, which can exist in the laser active layer at certain driving conditions, are responsible for mode clustering effect. The resonant excitation of the plasma oscillations occurs due to longitudinal mode beating. The separation of mode clusters is typically by an order of magnitude larger that the individual mode spacing.Comment: 3 pages, 2 figure

Computational study of boron nitride nanotube synthesis: how catalyst morphology stabilizes the boron nitride bond

In an attempt to understand why catalytic methods for the growth of boron nitride nanotubes work much worse than for their carbon counterparts, we use first-principles calculations to study the energetics of elemental reactions forming N2, B2 and BN molecules on an iron catalyst. We observe that in the case of these small molecules, the catalytic activity is hindered by the formation of B2 on the iron surface. We also observe that the local morphology of a step edge present in our nanoparticle model stabilizes the boron nitride molecule with respect to B2 due to the ability of the step edge to offer sites with different coordination simultaneously for nitrogen and boron. Our results emphasize the importance of atomic steps for a high yield chemical vapor deposition growth of BN nanotubes and may outline new directions for improving the efficiency of the method.Comment: submitted to physical review

Theory of Thermal Motion in Electromagnetically Induced Transparency: Diffusion, Doppler, Dicke and Ramsey

We present a theoretical model for electromagnetically induced transparency (EIT) in vapor, that incorporates atomic motion and velocity-changing collisions into the dynamics of the density-matrix distribution. Within a unified formalism we demonstrate various motional effects, known for EIT in vapor: Doppler-broadening of the absorption spectrum; Dicke-narrowing and time-of-flight broadening of the transmission window for a finite-sized probe; Diffusion of atomic coherence during storage of light and diffusion of the light-matter excitation during slow-light propagation; and Ramsey-narrowing of the spectrum for a probe and pump beams of finite-size.Comment: Reference added, typos correcte

Bundling up carbon nanotubes through Wigner defects

We show, using ab initio total energy density functional theory, that the so-called Wigner defects, an interstitial carbon atom right besides a vacancy, which are present in irradiated graphite can also exist in bundles of carbon nanotubes. Due to the geometrical structure of a nanotube, however, this defect has a rather low formation energy, lower than the vacancy itself, suggesting that it may be one of the most important defects that are created after electron or ion irradiation. Moreover, they form a strong link between the nanotubes in bundles, increasing their shear modulus by a sizeable amount, clearly indicating its importance for the mechanical properties of nanotube bundles.Comment: 5 pages and 4 figure

Sub-monolayers of carbon on alpha-iron facets: an ab-initio study

Motivated by recent in situ studies of carbon nanotube growth from large transition-metal nanoparticles, we study various alpha-iron (ferrite) facets at different carbon concentrations using ab initio methods. The studied (110), (100) and (111) facets show qualitatively different behaviour when carbon concentration changes. In particular, adsorbed carbon atoms repel each other on the (110) facet, resulting in carbon dimer and graphitic material formation. Carbon on the (100) facet forms stable structures at concentrations of about 0.5 monolayer and at 1.0 monolayer this facet becomes unstable due to a frustration of the top layer iron atoms. The stability of the (111) facet is weakly affected by the amount of adsorbed carbon and its stability increases further with respect to the (100) facet with increasing carbon concentration. The exchange of carbon atoms between the surface and sub-surface regions on the (111) facet is easier than on the other facets and the formation of carbon dimers is exothermic. These findings are in accordance with a recent in situ experimental study where the existence of graphene decorated (111) facets is related to increased carbon concentration

MODELS OF IMAGES WITH RADIAL-CIRCULAR STRUCTURE

The overwhelming majority of known image models are varieties of random fields defined on rectangular two-dimensional grids or grids of higher dimension, for example. In some practical situations, the images have an annular, radial or radial-circular structure. For example, images of the facies (thin film) of dried biological fluid, eyes, cut of a tree trunk or a fruit, blood vessel, erythrocyte, blast pattern, end face detail, etc. In addition, radar and other images are physically obtained in polar or spherical coordinates. These features of images require their consideration in their mathematical models. In this paper, an autoregressive models of homogeneous and inhomogeneous random fields defined on a circle or oval are considered as representations of images with radial or radial-circular structure

Need for the Development of Dialectical Thinking in Pharmaceutical Personnel to Improve Their Performance in the Pharmacovigilance System

The pharmacovigilance system aimed at ensuring the safety of medicines has been functioning in Russia since 1997. However, at the moment, an important part of this system, pharmacy organisations, is not sufficiently involved in pharmacovigilance activities. Pharmacy personnel may be not prepared to collect information on adverse reactions associated with the use of medicinal products and submit it to regulatory authorities. The reason is not only that their knowledge of pharmacovigilance is insufficient, but also that little attention is paid in the educational process to the development of dialectical thinking, which is necessary for successful problem-solving. The available literature does not cover the importance of dialectical thinking as a professional competency of a pharmacy employee sufficiently well.The aim of the study was to substantiate the need in the development of dialectical thinking in employees of pharmacy organisations in order to increase their participation in the pharmacovigilance system.Materials and methods: 166 employees of pharmacies in Kazan were surveyed on the implementation of pharmacovigilance in pharmacy organisations. The authors used Spearman’s rank correlation coefficient to assess the extent of association between the variables identified in the survey (pharmacy’s standing in the pharmacovigilance system, respondents’ competence in pharmacovigilance, their familiarity with pharmacovigilance documentation, adverse reaction reporting, and so forth).Results: the majority of respondents perceive the importance of pharmacies for the pharmacovigilance system as medium (46.99%) and low (17.47%); the same is true for the level of pharmacovigilance development in pharmacies (45.63 and 27.5% of the respondents respectively). According to the correlation analysis, pharmacy employees do not associate the level of pharmacovigilance development in their pharmacy with their competence, which is characteristic of a dialectical failure. Most respondents tend to exaggerate the role of executive authorities, medical organisations, and pharmaceutical companies in the pharmacovigilance system and underestimate the role of pharmacies and pharmacy staff (only 17.62% of the respondents assign this role to pharmacies), which may be the reason for failing to fulfil pharmacovigilance duties and passing the responsibility to other parties to the circulation of medicinal products.Conclusions: according to the consolidated results, pharmacy employees may not consider themselves to be leading implementers of legislative initiatives, causally related to the effectiveness of pharmacovigilance system as a whole. Consequently, there is a need to form dialectical thinking in pharmacy employees within the framework of educational programmes. It will contribute to the development of reflection on their efforts in ensuring the safety of medicines and increase the effectiveness of their participation in pharmacovigilance activities

Plasma instability and amplification of electromagnetic waves in low-dimensional electron systems

A general electrodynamic theory of a grating coupled two dimensional electron system (2DES) is developed. The 2DES is treated quantum mechanically, the grating is considered as a periodic system of thin metal strips or as an array of quantum wires, and the interaction of collective (plasma) excitations in the system with electromagnetic field is treated within the classical electrodynamics. It is assumed that a dc current flows in the 2DES. We consider a propagation of an electromagnetic wave through the structure, and obtain analytic dependencies of the transmission, reflection, absorption and emission coefficients on the frequency of light, drift velocity of 2D electrons, and other physical and geometrical parameters of the system. If the drift velocity of 2D electrons exceeds a threshold value, a current-driven plasma instability is developed in the system, and an incident far infrared radiation is amplified. We show that in the structure with a quantum wire grating the threshold velocity of the amplification can be essentially reduced, as compared to the commonly employed metal grating, down to experimentally achievable values. Physically this is due to a considerable enhancement of the grating coupler efficiency because of the resonant interaction of plasma modes in the 2DES and in the grating. We show that tunable far infrared emitters, amplifiers and generators can thus be created at realistic parameters of modern semiconductor heterostructures.Comment: 28 pages, 15 figures, submitted to Phys. Rev.

Creating nanoporous graphene with swift heavy ions

This article has an erratum: DOI 10.1016/j.carbon.2017.03.065We examine swift heavy ion-induced defect production in suspended single layer graphene using Raman spectroscopy and a two temperature molecular dynamics model that couples the ionic and electronic subsystems. We show that an increase in the electronic stopping power of the ion results in an increase in the size of the pore-type defects, with a defect formation threshold at 1.22–1.48 keV/layer. We also report calculations of the specific electronic heat capacity of graphene with different chemical potentials and discuss the electronic thermal conductivity of graphene at high electronic temperatures, suggesting a value in the range of 1 Wm−1 K−1. These results indicate that swift heavy ions can create nanopores in graphene, and that their size can be tuned between 1 and 4 nm diameter by choosing a suitable stopping power.Peer reviewe

TWO-PHASE DYNAMICS OF BONE MARROW MULTIPOTENT MESENCHYMAL STROMAL CELLS (MMSC) ACTION ON LIVER AT MODELING OF FIBROTIC HEPATITIS

Under the modeling of chronic fibrousing hepatitis in rats (n = 75) the dynamics of fibrolytic effect of bone mar- row MMSC was examined after one or two-time infusion of these cells at the early stage of liver fibrosis. By dynamic measuring of liver fibrotic area and the expression of activated stellate cell markers (desmin, α-SMA) and markers of cell apoptosis (caspase-3 and caspase-9) within 90 days two phases of the development of bone marrow MMSC fibrolytic effect were found. It is shown that the development of fibrolytic effect includes the primary phase of intensification of fibrosis, which is followed by the phase of enhanced fibrolytic process in the liver. It was determined that the two-phase dynamics of liver regeneration was more intensive after two-time infusion of bone marrow MMSC