Determination of spatial characteristics of the chain reaction wave in silver azide

The paper presents the methodology and results of determination of the spatiotemporal characteristics of the solid-state chain reaction wave in silver azide, initiated by a neodymium laser pulsed. The wave’s leading front width at half maximum is l ₁ = (110 ± 10) μm, the wave’s rear front width at half maximum is l ₂ = (120 ± 20) μm. The spatiotemporal parameters of the reaction wave in silver azide whiskers are calculated using a phenomenological model of the process previously proposed by the authors. It is shown that the calculated values of the velocity and the wave front width are consistent with the available experimental data.     

Synthesis and nitration of <Emphasis Type="Italic">N,N</Emphasis>´-bis(3-R-furoxan-4-yl)methylenediamines

A Mannich reaction of 4-amino-3-R-furoxans with paraformaldehyde in 10% aqueous H₂SO₄ led to the high yields of N,N′-bis(3-R-furoxan-4-yl)methylenediamines, whose structure (using R = Me as an example) was confirmed by X-ray diffraction study. The N,N′-bis-(3-R-furoxan-4-yl)methylenediamines obtained were nitrated to N,N′-dinitro-N,N′-bis-(3-R-furoxan-4-yl)methylenediamines upon the action of 100% HNO₃ in acetic or trifluoroacetic anhydride.     

Wear resistance of the ion-modified surface of zirconium-alloy tubes irradiated by He+ and Ar+ ion beams with wide energy spectra

The results of investigating the wear resistance of E110 alloy samples irradiated by a He⁺ + Ar⁺ beam with a wide energy spectrum are presented. Surface modification under irradiation by an Ar⁺ beam at doses higher than 2 × 10¹⁸ ion/cm² is shown to cause substantial enhancement of the wear resistance of samples because the structural homogeneity of near surface layers increases, the surface roughness decreases, and its microhardness increases. The application of a mechanical-geometrical wear model based on the experimental wear characteristics determined during accelerated tests indicates that the thinning of an alloy cladding can reach rates of 10⁻⁶–10⁻³ mm/s, which agree satisfactorily with data obtained in other simulation experiments. The presence of an oxide film changes a wear process characterized by an abrasive component.     

Mechanism of chemical deposition of nickel-boron coatings in tartrate-glycine solutions

The effect of glycine additive on the deposition of nickel-boron coatings from tartrate-glycine solutions was studied.     

Characterization of polymer materials exposed at the Mir orbital space station

The results of studies of polyimide and fluoropolymer films after a prolonged exposure at the Mir orbital space station are reported. The weight loss of external polyimide films was ～40–60%; the weight of FEP-100A fluoropolymer films remained unchanged, and the weight of F-4MB films increased by ～50%. The external and internal surfaces of polyimide films were hydrophilized. The external surface of a polyimide film acquired anisotropic properties, which manifested themselves as the shape anisotropy of liquid drops, the surface tension and the work of adhesion, the light scattering circular diagrams, and in the formation of spatially oriented fractal structures. The appearance of anisotropic properties is a consequence of the arrangement of a film on the station surface at an angle to the flow of atomic oxygen. The possible reactions of fast and scattered oxygen atoms, which are responsible for the chemical and structural transformations of polyimide, are discussed.     

IR spectroscopic study of filled polymeric films

Distribution of scattering centers (filler particles and pores) in films of an ultra-high-molecular-weight polyethylene xerogel was studied by IR spectroscopy and optical microscopy.     

Specifics of structural organization and properties of lysine dendrimers of different generations and related supramolecular structures

Lysine dendrimers of different generations containing covalently attached anthracene-based luminescent labels (one label per six dendrimer molecules) and fifth-generation heterodendrimers containing various amino acid units located between lysine fragments were synthesized. Homodendrimers were studied by means of the polarized luminescence technique. It was found that the packing density of lysine fragments in macromolecules increases with an increase in the generation number. Their capability of forming supramolecular structures changes in this case; the number of polymacromolecular associates produced in the solution and on the polymer matrix in interpolymer complexes decreases and their complexing power in the reaction with low-molecular-mass compounds increases. It was found that dendrite molecules acquire a looser structure on passing to heterodendrimers and their complexing ability varies in the corresponding manner; the number of polymacromolecular associates in the solution and on the polymer matrix in the interpolymer complexes increases and binding of low-molecular-mass compounds is reduced.     

Controlling spontaneous emission and threshold-less laser oscillation with optical microcavities

We describe the alteration of spontaneous emission of materials in optical microcavities having dimensions on the order of the emitted wavelength. Particular attention is paid to one-dimensional optical confinement structures with pairs of planar reflectors (planar microcavities). The presence of the cavity causes great modifications in the emission spectrum and spatial emission intensity distribution accompanied by changes in the spontaneous emission lifetime. Experimental results are shown for planar microcavities containing GaAs quantum wells or organic dye-embedded Langmuir-Brodgett films as light emitting layers. Also discussed are the laser oscillation properties of microcavities. A remarkable increase in the spontaneous emission coupling into the laser oscillation mode is expected in microcavity lasers. A rate equation analysis shows that increasing the coupling of spontaneous emission into the cavity mode causes the disappearance of the lasing threshold in the input-output curve. Experimentally verification is presented using planar optical microcavities confining an organic dye solution. The coupling ratio of spontaneous emission into a laser mode increases to be as large as 0.2 for a cavity having a half wavelength distance between a pair of mirrors. At this point, the threshold becomes quite fuzzy. Differences between the spontaneous emission dominant regime and the stimulated emission dominant regime are examined with emission spectra and emission lifetime analyses.     

A Simple Analytical Model for Expected Frame Waiting Time Evaluation in IEEE 802.11e HCCA Mode

IEEE 802.11e standard defines two access modes to provide Quality of Service support for 802.11-based Wireless LANs: Enhanced Distributed Channel Access and HCF Controlled Channel Access (HCCA). Only HCCA can guarantee bandwidth per flow which is suitable for various multimedia application requirements. However, the reference scheme HCCA is designed without awareness of variable bit rate (VBR) transmission. Several enhancement techniques have been proposed to address the VBR problem, but there are few research results for a model to capture the characteristics of HCCA. In this paper, an analytical model for the expected packet waiting time is proposed. The model can capture the system behavior per session leading to suitable admission control process for VBR support. The proposed model has been validated using the Network Simulator. The results confirm that the reference admission control scheme with mean data rate acceptance cannot guarantee the required bound on waiting time. Using the model, suitable parameters can be investigated for admission control with VBR support. The model can also be applied with polling based technologies, such as WiMAX.