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Free fluorescence spectra in solution and surface-enhanced Raman scattering (SERS) and surface enhanced fluorescence (SEF) spectra of chlorin e6 and water-soluble covalent fullerene-chlorin dyads have been studied. It has been demonstrated that chlorin e6 and covalent fullerene-chlorin dyads have similar characteristic SERS spectra. The fullerene-chlorin dyads show a pronounced SEF signal, while native chlorin e6 has no fluorescence on surface, which is consistent with the theory predicting an inverse dependence of the SEF intensity on the free fluorescence quantum yield. The concentration dependence of the SEF intensity is linear for the dyads in the range 0.1-2.0 μmol/L. These effects allow one to determine, with high sensitivity, the content of fullerene-chlorin dyads with a low quantum yield of free fluorescence in solutions, which opens wide opportunities for study of biological properties of fullerene-chlorin dyads and their applications in medicine. [ABSTRACT FROM AUTHOR]

Surface roughening in uniaxially tensile specimens of commercially pure titanium VT1-0 has been investigated using electron backscatter diffraction, optical and atomic force microscopy, and numerical simulation. It is shown that intragranular slip leads to the rotation of surface grains, due to which the grain surface is inclined and a terrace is formed at the interface with neighboring grains. The effect of the crystallographic grain orientation on the grain shape change and the degree of grain rotation occurring under constrained plastic deformation is demonstrated. [ABSTRACT FROM AUTHOR]

The effect of fullerene-containing amphiphilic (co)polymers of N-vinylpyrrolidone (C60/PVP) differed in composition and topology of the polymer chains on the membrane structure of phosphatidylcholine liposomes was studied. Using the method of fluorescent probes it was found that the C60/PVP structures under study are localized in the phosphatidylcholine membrane in the region of glycerol fragments and fatty acid chains of phospholipids. The C60/PVP copolymers form complexes with 2,7-dibromoproflavin and pyrene probes. The effective equilibrium constants of the probe-C60/PVP complexes in aqueous solutions and in the liposome membrane were determined. It is most likely that the fullerene-containing (co)polymers of N-vinylpyrrolidone form complexes not only with fluorescent probes but also with phospholipids of the liposome membrane, which reduces the stability of the probe-C60/PVP complex. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental studies of the operation of hybrid X-pinches on a modified high-current KING generator. The KING generator is a portable pulse current generator based on four low-inductive pulse capacitors. The output assembly of the generator was modified for greater diagnostic access to the load, which led to an increase in the inductance of the entire circuit and an increase in the duration of the current rise. A series of experiments with hybrid X-pinches with Al, Cu, and Mo wires with a diameter of 25 μm was carried out on the modified KING generator (200–260 kA, 220–280 ns, 45 kV). In experiments, it was shown that such a modification of the generator led to the stable formation of bright soft x-ray sources in X-pinches, suitable for use in point-projection radiography with a spatial resolution of about 10–15 μm. [ABSTRACT FROM AUTHOR]

The approach to synthesize one-dimensional photonic SiO2-TiO2 crystals by sol-gel methods is developed. Using the method of transfer matrices, structures consisting of 13 layers of alternating materials having the properties of one-dimensional photonic crystals with the minimal transmission coefficient of 7% in the photonic band gap range and that of 97.5% in the remaining spectrum parts are calculated and experimentally created. The positions of the photonic band gaps change along with the thicknesses of the layers of the materials composing the photonic crystal. The possibility of creating an optical filter as a result of introducing a structural defect in the form of a layer of doubled thickness is demonstrated. [ABSTRACT FROM AUTHOR]

Plastic flow localization in commercially pure titanium (VT1-0 according to the Russian classification) with the surface modified by low-energy high current electron beams has been numerically studied. The structure and mechanical properties of the modified surface layer and titanium substrate correspond to the experimentally observed ones and are taken into account explicitly as initial data of a dynamic boundary value problem. The tension of titanium structures with a modified surface layer is simulated by the finite difference method in a plane strain formulation. The dependence of the plastic strain localization parameters on the mechanical properties of structural elements in the titanium substrate has been determined. [ABSTRACT FROM AUTHOR]

A micromechanical model has been developed to describe deformation-induced surface roughening in polycrystalline materials. The three-dimensional polycrystalline structure is taken into account in an explicit form with regard to the crystallographic orientation of grains to simulate the micro- and mesoscale deformation processes. Constitutive relations for describing the grain response are derived on the basis of crystal plasticity theory that accounts for the anisotropy of elastic-plastic properties governed by the crystal lattice structure. The micromechanical model is used to numerically study surface roughening in microvolumes of polycrystalline aluminum and titanium under uniaxial tensile deformation. Two characteristic roughness scales are distinguished in the both cases. At the microscale, normal displacements relative to the free surface are caused by the formation of dislocation steps in grains emerging on the surface and by the displacement of neighboring grains relative to each other. Microscale roughness is more pronounced in titanium, which is due to the high level of elastic-plastic anisotropy typical of hcp crystals. The mesoscale roughness includes undulations and cluster structures formed with the involvement of groups of grains. The roughness is quantitatively evaluated using a dimensionless parameter, called the degree of roughness, which reflects the degree of surface shape deviation from a plane. An exponential dependence of the roughness degree on the strain degree is obtained. [ABSTRACT FROM AUTHOR]

This paper studies plastic strain localization and stress-strain evolution in commercial titanium specimens with an ultrasonically treated surface. A dynamic plane strain boundary-value problem is numerically solved by the finite difference method. The microstructure and mechanical properties of the composition are specified in the calculations based on microhardness measurements, mechanical tensile tests, and metallographic studies. The dependences of the plastic flow localization characteristics on the geometry and mechanical properties of ultrasonically treated surface layers have been established. Plastic strain localization is found to depend on the geometry and mechanical properties of ultrasonically treated surface layers. [ABSTRACT FROM AUTHOR]

This article addresses the problem of multiscale surface roughening in commercial purity titanium subjected to uniaxial tension. In situ investigations of the evolution of grain- and mesoscale roughness in selected regions of titanium specimens were performed. Based on the experimental data obtained, 3D polycrystalline models with explicit consideration of grain structure were generated and implemented in finite-element calculations. Constitutive models of grains were constructed, using crystal plasticity theory to take into account the elastic-plastic anisotropy on the grain scale. The experimental and numerical results obtained have shown that a series of multiscale surface undulations are formed on the free surface of the specimen subjected to tension. The smallest out-of-plane surface displacements are attributed to intragrain dislocation glide. Larger displacements are associated with relative grain motion. The latter give rise to the formation of an orange peel pattern. The displacements of the two types are a microscale phenomenon. The largest surface displacements formed by the grain groups involved in out-of-plane and in-plane cooperative motion are referred to as the mesoscale roughness. The latter is found to correlate well with local strains of the specimen regions under examination. The main conclusion drawn from the experimental and numerical results is that it is the mesoscale that will furnish a clue to prediction of plastic strain localization and fracture of materials far in advance of the macroscale manifestation of these processes. [ABSTRACT FROM AUTHOR]

The prebreakdown stage of a gas discharge in a diode with strongly overloaded cathode is studied by laser methods (by simultaneous use of multiframe interferometry and shadow and schlieren photographing) at atmospheric pressure. The spatial resolution of the methods is about 20 μm. A probing pulse of a laser (LS-2151 Nd: YAG laser with a half amplitude duration of 70 ps and a pulse energy of up to 40 mJ) is synchronized with a voltage pulse with accuracy of about 1 ns. High field strength at the cathode is achieved due to the use of thin individual metal tips on the electrodes. It is shown that the initial stage of breakdown of a discharge gap is accompanied by the emergence of a dense plasma cloud at the end of a tip with electron density of about 5 × 10 cm with a size of tens of microns, as well as by a sharp increase in the total current through the diode. After the emergence of a dense plasma cloud at the end of a cathode tip, a similar cloud is formed on the surface of the anode; sometime later, these clouds join together and form a tubular current channel. The dynamics of the breakdown, as well as the parameters of the plasma are studied by the abovementioned techniques in three independent optical channels. [ABSTRACT FROM AUTHOR]