Structure of connections of single-walled carbon nanotubes with the use of the combined 5–7 and 4–8 topological defects

The structures of zigzag-zigzag, armchair-zigzag, zigzag-chiral, armchair-armchair, armchair-chiral, and chiral-chiral pair connections produced by single-walled carbon nanotubes 1.5–5.0 diameter with the use of the combined 5–7 and 4–8 topological defects have been calculated by molecular mechanics methods. It has been established that the use of the combined 5–7 topological defect makes it possible to produce connections between pairs of single-walled carbon nanotubes with any conductivities, chiralities, and diameters, whereas the use of the combined 4–8 topological defect provides a means for forming connections between nanotubes only with the same type of conductivity. The angles between the axes of nanotubes connected by the combined 5–7 and 4–8 topological defects lie in the ranges 145°–180° and 112°–178°, respectively. It has been revealed that there are correlations between structural parameters of the connections and the relative arrangement of the simple topological defects in the combined topological defects.     

Optical properties of silver selenium indate films obtained by the method of pulse laser vaporization

The spectra of transmission and reflection are measured in the region of 0.4–2.5 μm on thin silver selenium indate films obtained by means of pulse laser vaporization. The magnitudes of the refractive index and absorption coefficient are calculated. The energies of interband transitions and the values of crystalline and spin-orbit splitting are determined. The experimental results for the AgInSe₂ films agree with the data for bulk crystals. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 512–514, July–August, 2000.     

Synthesis and properties of β-modifiedmesotetra(aryl, heteryl)porphyrins

A series of chemical conversions of formyl derivatives of tetraphenylporphyrin is implemented, including the dimerization under the action of low-valence titanium, formation of a vinyl derivative by Wittig's reaction, and also the intramolecular cyclization with formation of isomeric verdins. By means of radical nitration, nitro derivatives of heterylporphyrins are obtained, which are exposed to a reaction of vicarious nucleophilic substitution of hydrogen with formation of 2,3-disubstituted derivatives. The previously unknown derivatives of the above-named porphyrins are obtained, and means for synthesis of well-known compounds are considerably improved. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. I. I. Mechnikov Odessa State University, 2, Dvoryanskaya Str., Odessa, 270026, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 512–515, July–August, 1999.     

Sounding of an artificially perturbed ionosphere by means of an ionosonde/position finder with chirp modulation of the signal

We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz) with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦, 18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don), aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory. At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path), the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 267–278, April 2009.     

Functional neural network analysis in frontotemporal dementia and Alzheimer's disease using EEG and graph theory

Background  

Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks.     

Ab initio,Xα and IEHT Mo calculations of Mössbauer spectroscopy parameters for iron carbonyls

Calculations of charge density and the electric field gradient tensor at the iron nucleus by means of ab initio LCAO SCF, MS-X_α, SCC-X_α and IEHT methods for iron carbonyls Fe(CO)n, n=1–5, are presented. The calculated EFG values for the closed-shell molecule Fe(CO)5 show reasonable agreement with experiment while the values obtained for the open-shell molecules Fe(CO)n, n=1–4, significantly depend on the calculational method. Ab initio results, though using a minimal basis set, are closer to experimental data than X_α and IEHT results.     

Numerical simulation of the response function in measurements by the frequency-domain method in optic-fiber sensors

We consider a method for measuring the temperature and deformation from a distributed source by means of optic-fiber sensors with the use of Brillouin scattering in combination with analysis of the frequency domain. The method is investigated theoretically. It is based on measurements of the complex transfer function. We carry out a numerical simulation of the response function for a single-mode optic fiber with elevated-temperature regions and deformed regions. To whom correspondence should be addressed. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 718–721, September–October, 1999.     

Spectroscopic manifestations of isotope substitution in ultrasound jet-cooled complex molecules and their van der waals complexes

It is shown that, upon formation of ultrasound jet-cooled var der Waals complexes of polar molecules of 9-cyanoanthracene, 3-aminophthalimide, and 3-amino-N-methylphthalimide with water molecules, pronounced manifestations of isotope substitution in the ligand molecules take place, which manifest themselves in shifting 0–0-transitions by 5–7 cm⁻¹ and changes in frequencies of intramolecular vibrations. Spectroscopic effects of isotope substitution of atoms of the amino group are established for substituted phthalimides. We propose a new mechanism of the effect of isotope substitution on frequencies of electronic transitions which cannot be reduced to the known one (realized by means of changes in values of the zero vibrational energy) and is based instead on the change in the charge density distribution in the molecule. Belarusian State University, 4, F. Skorina Ave., Minsk 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 148–154, March–April, 1997.     

Spectroscopic investigation of thermooxidative destruction of ethers on the surface of modified silica

Thermooxidative processes are investigated by the method of temperature-programmed decomposition with the use of a prism infrared spectrometer. Thermal degradation of —OC₄H₉, —OP(H)(O)OC₄H₉ and —OP(H)(O)OC₂H₅ groups on the surface of modified pyrogenic silicas in air is considered. The resemblance between processes of oxidation of surface PH-groups irrespective of the means of silica modification is shown. Institute of Surface Chemistry, National Academy of Sciences of Ukraine, 31, Nauka Ave., Kiev, 252022, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 326–332, May–June, 1998.     

Quantum transport through STM-lifted single PTCDA molecules

Using a scanning tunneling microscope we have measured the quantum conductance through a PTCDA molecule for different configurations of the tip–molecule–surface junction. A peculiar conductance resonance arises at the Fermi level for certain tip to surface distances. We have relaxed the molecular junction coordinates and calculated transport by means of the Landauer/Keldysh approach. The zero bias transmission calculated for fixed tip positions in lateral dimensions but different tip–substrate distances show a clear shift and sharpening of the molecular chemisorption level on increasing the STM–surface distance, in agreement with experiment.     

GEANT4 Simulation of the High-Energy Neutron Beam of the TOF Spectrometer GNEIS

Using the Geant4 software package, a numerical simulation of a neutron source of the time-offlight spectrometer GNEIS created on the basis of the SC-1000 synchrocyclotron with 1 GeV proton energy at the NRC Kurchatov Institute—PNPI (Gatchina) has been carried out. The influence of the structural features of the neutron source of the spectrometer on the spatial and energy distributions of neutrons has been studied. The intensity and spectral characteristics of the neutron flux in the range of 1–1000 MeV have been determined on the basis of the obtained information and detailed allowance for all elements of the neutron beam guide system. It is found that the best agreement between the experiment and calculation performed by means of Geant4 is observed when using the QGSP_INCLXX_HP model. In the neutron energy range of 1–200 MeV, the difference between the experimental and calculated shapes of the spectra is less than 25%.     

Laser optogalvanic spectroscopy of an indium atom

The specific features of the optogalvanic effect in a hollow-cathode discharge on single- and two-stage excitation of indium atoms are studied. The autoionized states of an indium atom in the region 52,651–52,500 cm⁻¹ have been revealed and investigated by means of the method of optogalvanic spectroscopy. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 396–398, May–June, 2000.     

Passive Q-switching of erbium glass laser by magnesium aluminosilicate sitall with cobalt ions

We have studied the radiation output parameters for an erbium glass laser, lasing at a wavelength of 1.54 μm, with passive Q-switching by means of a cobalt-containing magnesium aluminosilicate sitall compared with a saturable absorber based on a magnesium aluminum spinel crystal with cobalt ions. We have shown that the output characteristics of the laser emission when using sitall are not inferior to the analogous characteristics of a laser based on a spinel crystal, and are practically independent of the temperature of the saturable absorber in the range 0°C–80°C. The duration (energy) of the output pulses was 70 nsec (∼4 mJ), the energy dispersion of the radiation pulse relative to the average value was no greater than 3%, the beam divergence was 2.8 mrad, the laser beam quality factor was M² = 1.2. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 126–131, January–February, 2007.     

New sign of vacuum ultraviolet driven crystal growth in ternary oxide Zn 3 V 2 O 8 films

Ternary oxide Zn₃V₂O₈ films was successfully formed on glass substrates only by means of vacuum ultraviolet irradiation to the spin-coated metal–organic solutions. From Fourier transform infrared spectroscopy measurements, we confirmed that the crystal growth proceeded at metal–organic bond cleavage under VUV irradiation. The crystalline size of the obtained materials was estimated to be 1.5–2.5 nm. The prepared Zn₃V₂O₈ films clearly showed yellow luminescence, corresponding to a charge transfer transition in the VO₄ tetrahedra.     

EPR Equilibration Measurement of the C–H Bond Enthalpy in the Methylene Groups of 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (Irganox)

On the basis of previous and current studies, it has been possible to evaluate and compare the bond dissociation energies of the phenol (O–H) bond and of the methylene and methyl (C–H) bonds in Irganox (trade name) by means of electron paramagnetic resonance records of galvinoxyl–irganoxyl hydrogen transfer reaction equilibria. The bond dissociation enthalpy of the C–H methylene and methyl bonds in Irganox was found to be 339.0 ± 3.0 kJ/mol, very close to the previously found value of 340.7 ± 3.0 kJ/mol for the O–H bond of some benzyl–phenolic antioxidant.     

Quantum control of two-qubit entanglement dissipation

We investigate quantum control of the dissipation of entanglement under environmental decoherence. We show by means of a simple two-qubit model that standard control methods – coherent or openloop control – will not in general prevent entanglement loss induced by a Markovian environment. However, we propose a control method utilizing a Wiseman–Milburn feedback/measurement control scheme which will effectively negate environmental entanglement dissipation.     

Effects of nonlinear amplification in quantum-dimensional lasers based on asymmetric heterostructures

We investigated the possibility of describing the processes of radiation generation at two spectrally spaced wavelengths in quantum-dimensional lasers based on asymmetric heterostructures by means of rate equations that take account of the effects of nonlinear amplification. We show that agreement between experimental and theoretical results is achieved in the case where it is assumed that the processes of interaction between spectrally spaced modes prevail over the processes of self-stress of the modes. An analysis of various mechanisms of nonlinear amplification is carried out, and it is found that dynamic heating of charge carriers by radiation is a reason for nonlinear phenomena with the features indicated. To whom correspondence should be addressed. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 697–702, September–October, 1999.     

The ratio of viscosity to entropy density in a pion gas satisfies the KSS holographic bound

We evaluate the ratio of shear viscosity to entropy density in a pion gas employing the Uehling–Uehlenbeck equation and experimental phase-shifts parameterized by means of the SU(2) inverse amplitude method. We find that the ratio for this monocomponent gas stays well above the KSS 1/(4π) bound. We find similar results with other sets of phase-shifts and conclude that the bound is nowhere violated. PACS 05.20.Dd; 51.20.+d     

Polarization of Luminescence in the Nanostructure Si/CaF<Subscript>2</Subscript> Upon Polarization of the Nuclear Spins of Fluorine

The laws governing polarization of luminescence in the nanostructure Si/CaF₂ upon polarization of the spins of the fluorine nuclei by means of optical excitation of charge carriers are considered theoretically. The possibility of studying experimentally the properties of nuclear spins in analyzing luminescence is shown. The polarization of luminescence is most informative in the range of excitation rates of charge carriers from 3⋅10⁷ to 3⋅ 10⁸ sec⁻¹ with the CaF₂ layer of thickness from 0.6 to 0.8 nm and optical excitation polarization degree of 0.1. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 524–529, July–August, 2005.     

Picosecond laser micromachining of nitinol and platinum–iridium alloy for coronary stent applications

The demand for micromachining of coronary stents by means of industrial lasers rises quickly for treating coronary artery diseases, which cause more than one million deaths each year. The most widely used types of laser for stent manufacturing are Nd:YAG laser systems with a wavelength of 1064 nm with pulse lengths of 10⁻³–10⁻² seconds. Considerable post-processing is required to remove heat-affected zones (HAZ), and to improve surface finishes and geometry. Using a third harmonic laser radiation of picosecond laser (6×10⁻¹² s pulse duration) in UV range, the capability of the picosecond laser micromachining of nitinol and platinum–iridium alloy for coronary stent applications are presented. In this study dross-free cut of nitinol and platinum–iridium alloy tubes are demonstrated and topography analysis of the cut surface is carried out. The HAZ characteristics have been investigated by means of microscopic examinations and measurement of micro-hardness distribution near the cut zones.