Optical and Structural Phenomena at Multipulse Interference Femtosecond Laser Fabrication of Metasurfaces on a Thin Film of Amorphous Silicon

JETP Letters - The spatial dependence of the differential conductivity of ultrathin Pb films deposited on the Si(111)7 × 7 surface has been studied by low-temperature scanning tunneling...     

Synthesis of carbon planar structures with specified properties

A new method is proposed that allows an integrated technology to be used for the synthesis of carbon planar structures with predetermined properties. The method is based on the avalanche annealing of amorphous short-period superlattices. The synthesized samples are investigated by Raman spectroscopy and photoluminescence. The possibility of synthesizing carbon layers with diamond-like, graphite-like, graphene, or other structures is demonstrated experimentally using the example of a C/SiC superlattice.     

First passage time for multivariate jump‐diffusion processes in finance and other areas of applications

The first passage time (FPT) problem is an important problem with a wide range of applications in science, engineering, economics, and industry. Mathematically, such a problem can be reduced to estimating the probability of a stochastic process first to reach a boundary level. In most important applications in the financial industry, the FPT problem does not have an analytical solution and the development of efficient numerical methods becomes the only practical avenue for its solution. Most of our examples in this contribution are centered around the evaluation of default correlations in credit risk analysis, where we are concerned with the joint defaults of several correlated firms, the task that is reducible to a FPT problem. This task represents a great challenge for jump‐diffusion processes (JDP). In this contribution, we develop further our previous fast Monte Carlo method in the case of multivariate (and correlated) JDP. This generalization allows us, among other things, to evaluate the default events of several correlated assets based on a set of empirical data. The developed technique is an efficient tool for a number of financial, economic, and business applications, such as credit analysis, barrier option pricing, macroeconomic dynamics, and the evaluation of risk, as well as for a number of other areas of applications in science and engineering, where the FPT problem arises. Copyright © 2008 John Wiley & Sons, Ltd.     

Formation of J-Aggregates of 21-thia-5,10,15,20-tetra-(4-sulfonatophenyl)-porphyrin in Acidified Aqueous Solutions

Journal of Applied Spectroscopy - The formation of Jaggregates of 21-thia-5,10,15,20-(tetra-4-sulfonatophenyl)-porphyrin in acidified aqueous solutions is reported for the first time. The...     

Modeling of the dynamics of diffusion crystal growth from a cooling magmatic melt

The process of diffusion growth of a single crystal of plagioclase (consisting of two components: albite and anorthite) from a cooling magma melt is considered. Crystallization starts when the temperature becomes lower than the melting (liquidus) temperature and occurs as a result of the diffusion of melt components to the boundary of the growing crystal. The crystallization process is simulated by solving a system of nonlinear, linked by cross terms, nonstationary diffusion equations for albite, anorthite, and residual melt in the coordinate system moving with the growing crystal boundary. The dependence of the crystal growth rate on undercooling and temperature and of its composition on temperature and pressure is taken into account. Both quantities substantially depend on the component concentration ratio in the melt on the crystal-melt interface. The competition between the diffusion and crystal growth processes and the complex dependence of these processes on the current melt and crystal compositions and the system temperature lead to a strong nonlinearity of the problem. As a result of numerical simulation, it is established that with a linear decrease in temperature the growing crystal composition changes nonmonotonically. This makes it possible to propose a novel interpretation of the crystal zoning typical of natural magmatic systems.     

Hydrogen-bonded coordination network in crystal structures of [Cu(3-PM)4Cl2] and [Cu(4-PM)4Cl]Cl, (PM = pyridylmethanol)

The crystal and molecular structures of [Cu(3-PM)₄Cl₂] (1) and [Cu(4-PM)₄Cl]Cl (2) have been determinated by X-ray crystallography. Complex 1 crystallizes in the triclinic system, space group P–1, with lattice parameters a = 7.972(2) Å, b = 8.293(2) Å, c = 10.707(2) Å, = 105.73(3)°, = 90.04(3)°, = 110.38(3)°, and Z = 1 at 100 K. The coordination geometry of each Cu atom is approximately octahedral formed by four nitrogen atoms of pyridine rings of 3-pyridylmethanol molecules in the equatorial plane and two chlorine atoms occupying the axial positions. The O—HsO, C—HsCl, and O—HsCl intermolecular hydrogen bonds and s stacking link the molecules in 3-D hydrogen-bonded coordination network. Complex 2 crystallizes in the tetragonal system, space group P4/n, with lattice parameters a = 10.464(1) Å, c = 11.339(2) Å, and Z = 2 at 217 K and a = 10.352(1) Å, c = 11.201(2) Å, and Z = 2 at 293 K. The coordination geometry of Cu atom in the [Cu(4-PM)₄Cl]⁺ ion is approximately square pyramidal formed by four nitrogen atoms of pyridine rings of 4-pyridylmethanol molecules in equatorial plane and one chlorine atom in axial position. The O—HsCl and C—HsCl intermolecular hydrogen bonds link the molecules in 2-D hydrogen-bonded coordination network.     

Lugdunomycin,an Angucycline‐Derived Molecule with Unprecedented Chemical Architecture

The angucyclines form the largest family of polycyclic aromatic polyketides, and have been studied extensively. Herein, we report the discovery of lugdunomycin, an angucycline‐derived polyketide, produced by Streptomyces species QL37. Lugdunomycin has unique structural characteristics, including a heptacyclic ring system, a spiroatom, two all‐carbon stereocenters, and a benzaza‐[4,3,3]propellane motif. Considering the structural novelty, we propose that lugdunomycin represents a novel subclass of aromatic polyketides. Metabolomics, combined with MS‐based molecular networking analysis of Streptomyces sp. QL37, elucidated 24 other rearranged and non‐rearranged angucyclines, 11 of which were previously undescribed. A biosynthetic route for the lugdunomycin and limamycins is also proposed. This work demonstrates that revisiting well‐known compound families and their producer strains still is a promising approach for drug discovery.     

Hydrodynamic stability of evaporation fronts in porous media

The stability of phase transition fronts in water flows through porous media is considered. In the short-wave approximation a linear stability analysis is carried out and a sufficient condition of hydrodynamic instability of the phase discontinuity is proposed. The problem of injection of a water-vapor mixture into a two-dimensional mixture-saturated formation is solved and its numerical solution is compared with an exact solution of the corresponding one-dimensional self-similar problem. It is discovered that, instead of the unstable discontinuities in the one-dimensional formulation, in the two-dimensional case a lengthy mixing zone with a characteristic scale that increases self-similarly with time is formed.     

Isomers in the chemistry of mercury coordination compounds

The coordination chemistry of mercury is an extremelybroad field, as shown by a survey covering the crystallographic and structural data of over 550 examples. About 12% of those complexes exist as isomers and are summarised and classified in this review. Included are distortion (73%), polymerisation (20.6%), coordination number (3.2%) and ligand (3.2%) isomerism. These are discussed in terms of the coordination around the mercury atoms, and correlations are drawn between donor atoms, bond distances and bond angles. Distortion isomers, differing only by the degree of distortion in the Hg — L and L — Hg — L angles, are the most common. These isomers are discussed and compared with those found in the chemistry of zinc and cadmium.      

Isomers in the chemistry of iron coordination compounds

The coordination chemistry of iron covers a wide field, as shown by a survey covering the crystallographic and structural data of almost one thousand and three hundred coordination complexes. About 6.7% of these complexes exist as isomers and are summarized in this review. Included are distortion (96.6%) and cis — trans (3.4%) isomers. These are discussed in terms of the coordination about the iron atom, bond length and interbond angles. Distortion isomers, differing only by degree of distortion in Fe-L, Fe-L-Fe and L-Fe-L parameters, are the most common. Iron is found in the oxidation states zero, +2 and +3 of which +3 is most common. The stereochemistry around iron centers are tetrahedral, five — coordinated (mostly trigonal — bipyramid) and six — coordinated. The most common ligands have O and N donor sites.