Local structure of 5- and 6-connected graphs

We prove that if graph on n vertices is minimally and contraction critically 5-connected, then it has 4n/7 vertices of degree 5. We also prove that if graph on n vertices is minimally and contraction critically 6-connected, then it has n/2 vertices of degree 6. Bibliography: 7 titles.     

Low-voltage nonstationary electron emission from single-walled carbon nanotubes as exoelectron emission

Low-voltage nonstationary electron emission from single-walled carbon nanotubes after the passage of high autoemission current has been observed. This emission is assumed to be exoelectron emission associated with mechanical stresses and defects appearing in nanotubes due to electrostatic forces acting on nanotubes in a strong electric field.     

Dynamics and spectra of excited states of water-micellar suspensions of single-walled carbon nanotubes

The dynamics of the photoinduced differential absorption and excited-state bleaching spectra of single-walled carbon nanotubes suspended in a micellar solution were studied in the spectral range from 40 to 1000 nm within a time interval from 70 fs to 150 ps under excitation by 50-fs pulses with photon energies 2 and 4 eV. The bleaching and absorption bands were observed in the spectra; the positions of the bleaching peaks were independent of the photon energy of the exciting femtosecond pulse in the range 2–4 eV. It was established that, for delay times shorter than 1 ps, the shape of the differential spectrum of excited nanotubes coincided with the shape of the second derivative of the absorption spectrum of unexcited nanotubes in the frequency range of exciting pulse above 18000 cm^?1 (the range of absorption bands of metallic nanotubes). In the frequency range below 16000 cm^?1 (the range of absorption peaks of semiconducting nanotubes), the bleaching peaks in the differential spectrum of excited nanotubes undergo a high-frequency shift of 200–300 cm^?1 with respect to the second-derivative spectrum of unexcited nanotubes. The excited-state relaxation rate constants were measured. They are well approximated by the exponential dependences and depend on the probe-pulse wavelength. An assumption was made about the nature of the observed spectra of excited nanotubes and about the excitation relaxation.     

Formation of new hybrid structures: Fullerene C<Subscript>60</Subscript>–amphiphilic copolymer of <Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone with (di)methacrylates in isopropyl alcohol

New hybrid structures of fullerene C₆₀ and an amphiphilic copolymer of N-vinylpyrrolidone with lauryl methacrylate and triethylene glycol dimethacrylate have been obtained via solubilization of fullerene by individual macromolecules and their micelle-like aggregates that form in isopropyl alcohol. The volume ratios of copolymer and C₆₀ solutions in toluene at which there is suppression of aggregation of fullerene and fullerene–polymer particles and the existence of stable hybrid structures in solution have been found. With the use of absorption electron spectroscopy, it has been shown that, with time, fullerene undergoes binding to donor groups of the copolymer and forms a donor–acceptor complex. According to the data of optical microscopy, fullerene is homogeneously distributed as spherical aggregates in the solid polymer matrix.     

Investigation of mechanical strains in porous silicon by difference Raman spectroscopy

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 49, No. 4, pp. 612–615, October, 1988.     

Carbon-nanotube-based saturable absorbers for near infrared solid state lasers

We demonstrate the passive mode-locking of a diode-pumped Nd⁺³:YAG (central wavelength: 1.32 μm; pulse duration: 50 ps; output energy: up to 70 μJ) laser using a polymer film containing single-wall carbon nanotubes. The mode-locking regime is stable at a pump repetition rate of up to 1 kHz. We also investigate the temporal evolution of the light-induced absorption change of the polymer film containing carbon nanotubes in the spectral range of 1.3–1.5 μm by femtosecond time-resolved pump-probe measurements. The measurements reveal that light-induced transmission exhibits fast and slow components that last 280 fs and more than 10 ps, respectively. The third-order susceptibility of the polymer film containing single wall carbon nanotubes is as high as 10⁻¹¹ esu.     

Self-oscillations in an electromechanical system with a field emitter

Electromechanical oscillations have been detected in a system consisting of a vacuum diode with a field cathode made of single-walled carbon nanotubes. As a dc voltage between such a cathode and an anode is applied, stable mechanical oscillations are observed along with oscillations of the self-sustained emission current. An empirical model of this phenomenon is proposed. It is described with a system of one-dimensional equations of mechanical motion and electrical processes in the system. An analysis of these equations is performed and a qualitative consistency of theoretical and experimental results is demonstrated. It is proved that the observed phenomenon is common for all systems with field nanoemitters. The suggested mechanism of the excitation of the self-sustained oscillations can be used to explain the experimentally observed features of such nanoemitters.     

Photoelectric properties of In/p-(Cu, Ag)Ga(Se, Te)2 surface-barrier structures

Based on single crystals of AgGaSe₂, AgGaTe₂, CuGaTe₂ of the p-type, surface-barrier structures were manufactured by vacuum thermal deposition on illumination of which the photovoltaic effect was observed. It is established that the longwave edge of the photosensitivity of such structures possesses several inflections attributable to photoactive absorption involving paracipation of levels of lattice defects. It is shown that In/p-(Cu, Ag)Ga(Se, Te)₂ surface-barrier structures can be used as wide-band transducers and photoanalyzers of linearily polarized radiation. Translated from Zhurrnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 141–144, January–February, 1999.     

Nanodiamonds thermoluminescence

Nanodiamonds thermoluminescence was studied. It was compared with thermoluminescence of synthetic diamonds of relative purity, weakly and strongly boron-doped. A dependence of the nanodiamond thermoluminescence on an irradiation dose was examined.     

Preparation of the amphiphilic copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate nanoparticles and the study of their properties in vitro

Russian Chemical Bulletin - According to DLS the amphiphilic copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate of branched topology forms micelle-like particles in isopropyl...