Method of Personalization of Photopolymer Security Holograms Based on Recording Hidden Encoded Digital Images

Optics and Spectroscopy - The scope of problems of embedding personal data when copying holograms on a photopolymer substrate with the maximum preservation of the region of a hologram during its...     

Near-IR photoluminescence from Si/Ge nanowire-grown silicon wafers: effect of HF treatment

We present the room-temperature near-infrared (NIR) photoluminescence (PL) properties of Si/Ge nanowire (NW)-grown silicon wafers which were treated by vapor of HF:HNO₃ chemical mixture. This treatment activates or enhances the PL intensity in the NIR region ranging from 1000 nm to 1800 nm. The PL consists of a silicon band-edge emission and a broad composite band which is centered at around 1400–1600 nm. The treatment modifies the wafer surface particularly at defect sites especially pits around NWs and NW surfaces by etching and oxidation of Si and Ge. This process can induce spatial confinement of carriers where band-to-band (BB) emission is the dominant property in Si-capped strained Si/Ge NW-grown wafers. Strong signals were observed at sub-band-gap energies in Ge-capped Si/Ge NW-grown wafers. It was found that NIR PL is a competitive property between the Si BB transition and deep-level emission, which is mainly attributable to Si-related defects, Ge dots and strained Ge layers. The enhancement in BB and deep-level PL is discussed in terms of strain, oxygen-related defects, dot formation and carrier-confinement effects. The results demonstrate the effectiveness of this method in enhancing and tuning NIR PL properties for possible applications.     

Group extensions,fiber bundles,and a parametric Yang–Baxter equation

Theoretical and Mathematical Physics - We show that any extension of an Abelian group corresponds to a solution of the parametric Yang–Baxter equation. This statement is a generalization of...     

Drinfeld–Sokolov reduction in quantum algebras: canonical form of generating matrices

We define the second canonical forms for the generating matrices of the Reflection Equation algebras and the braided Yangians, associated with all even skew-invertible involutive and Hecke symmetries. By using the Cayley–Hamilton identities for these matrices, we show that they are similar to their canonical forms in the sense of Chervov and Talalaev (J Math Sci (NY) 158:904–911, 2008).     

Vertex electrical model: Lagrangian and nonnegativity properties

Theoretical and Mathematical Physics - We construct an embedding of the space of electrical networks to the totally nonnegative Lagrangian Grassmannian in a generic situation with the help of the...     

AlInN MOVPE: growth chemistry and analysis of trends

Comprehensive model of AlInN Metal-Organic Vapor Phase Epitaxy (MOVPE) accounting for the gas-phase and surface chemistry including parasitic reactions/particle formation is developed. Experimental data and modeling results suggest that as V/III ratio increases from several tens (growth of pure AlN) to several thousands (growth of AlInN), the partial AlN growth rate decreases even in the absence of strong particle formation. This effect is associated with the formation of heavy molecular weight/low diffusivity gas-phase dimer species at high ammonia concentration. At elevated pressures growth rate decreases with pressure at a weakly changing composition, which is related to the gas-phase losses of In- and Al-containing species due to reaction with AlN particles. Model allows the prediction of both the AlInN growth rate and composition versus group-III flow rates, temperature, and pressure.     

Surface kinetics of GaN evaporation and growth by molecular-beam epitaxy

The kinetics of surface processes during the growth of GaN by molecular-beam epitaxy (MBE) with ammonia as the source of reactive nitrogen is studied theoretically and experimentally. A model of surface processes is developed taking into account specific effects of the blocking of NH₃ adsorption sites by Group III and Group V surface species. Parameters of the model (respective kinetic rate constants) are determined from comparison with experimental data. It is shown that the evaporation rate of GaN in ammonia atmosphere is much lower than that in vacuum. Kinetics of GaN growth under gallium-rich and nitrogen-rich conditions are compared. Under nitrogen-rich conditions the GaN surface is predicted to be enriched by NH_x surface radicals, in contrast to the case of growth under gallium-rich conditions or of free evaporation in vacuum. It is shown that use of the nitrogen-rich conditions allows one to increase the growth temperature by 80–90°C compared with the case of gallium-rich conditions or plasma-activated MBE. The increased growth temperature is favorable in improving the optical and electrical properties of the material grown.     

Hitchin System on Singular Curves

We study the Hitchin system on singular curves. We consider curves obtainable from the projective line by matching at several points or by inserting cusp singularities. It appears that on such singular curves, all basic ingredients of Hitchin integrable systems (moduli space of vector bundles, dualizing sheaf, Higgs field, etc.) can be explicitly described, which can be interesting in itself. Our main result is explicit formulas for the Hitchin Hamiltonians. We also show how to obtain the Hitchin integrable system on such curves by Hamiltonian reduction from a much simpler system on a finite-dimensional space. We pay special attention to a degenerate curve of genus two for which we find an analogue of the Narasimhan–Ramanan parameterization of the moduli space of SL(2) bundles as well as the explicit expressions for the symplectic structure and Hitchin-system Hamiltonians in these coordinates. We demonstrate the efficiency of our approach by rederiving the rational and trigonometric Calogero–Moser systems, which are obtained from Hitchin systems on curves with a marked point and with the respective cusp and node.     

KZ equation,G-opers,quantum Drinfeld–Sokolov reduction,and quantum Cayley–Hamilton identity

The Lax operator of Gaudin-type models is a 1-form at the classical level. In virtue of the quantization scheme proposed by D. Talalaev, it is natural to treat the quantum Lax operator as a connection; this connection is a partcular case of the Knizhnik–Zamolodchikov connection. In this paper, we find a gauge trasformation that produces the “second normal form,” or the “Drinfeld–Sokolov” form. Moreover, the differential operator nurally corresponding to this form is given precisely by the quantum characteristic polynomial of the Lax operator (this operator is called the G-oper or Baxter operator). This observation allows us to relate solutions of the KZ and Baxter equations in an obvious way, and to prove that the immanent KZ equation has only meromorphic solutions. As a corollary, we obtain the quantum Cayley–Hamilton identity for Gaudin-type Lax operators (including the general case). The presented construction sheds a new light on the geometric Langlands correspondence. We also discuss the relation with the Harish-Chandra homomorphism. Bibliography: 19 titles. Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 360, 2008, pp. 246–259.