Mechanisms and behavioral regularities of the vacuum-arc microparticles near and on a potential electrode immersed in plasma

It is experimentally revealed that the pulse-periodic bias potential provides a multifold decrease in the surface content of microparticles (MPs). It is ascertained that a decrease in the MP concentration at the target can be explained by several physical mechanisms. From experiments with a fine-structure grid, it is found that less than 10% of MPs negatively charged in the plasma can be reflected in the electric field of the charge-separation layer near the sample. A substantial decrease in the MP density occurs after direct interaction between a MP and the sample under the action of a negative HF short-pulse bias potential. Almost half the MP surface density is caused by ion sputtering. A twelvefold reduction in the MP surface density is attained when the target is irradiated for 2 min.     

Retinal Conformation and Dynamics in Activation of Rhodopsin Illuminated by Solid‐state 2H NMR Spectroscopy†

Solid‐state NMR spectroscopy gives a powerful avenue for investigating G protein‐coupled receptors and other integral membrane proteins in a native‐like environment. This article reviews the use of solid‐state ²H NMR to study the retinal cofactor of rhodopsin in the dark state as well as the meta I and meta II photointermediates. Site‐specific ²H NMR labels have been introduced into three regions (methyl groups) of retinal that are crucially important for the photochemical function of rhodopsin. Despite its phenomenal stability ²H NMR spectroscopy indicates retinal undergoes rapid fluctuations within the protein binding cavity. The spectral lineshapes reveal the methyl groups spin rapidly about their three‐fold (C₃) axes with an order parameter for the off‐axial motion of For the dark state, the ²H NMR structure of 11‐cis‐retinal manifests torsional twisting of both the polyene chain and the β‐ionone ring due to steric interactions of the ligand and the protein. Retinal is accommodated within the rhodopsin binding pocket with a negative pretwist about the C11=C12 double bond. Conformational distortion explains its rapid photochemistry and reveals the trajectory of the 11‐cis to trans isomerization. In addition, ²H NMR has been applied to study the retinylidene dynamics in the dark and light‐activated states. Upon isomerization there are drastic changes in the mobility of all three methyl groups. The relaxation data support an activation mechanism whereby the β‐ionone ring of retinal stays in nearly the same environment, without a large displacement of the ligand. Interactions of the β‐ionone ring and the retinylidene Schiff base with the protein transmit the force of the retinal isomerization. Solid‐state ²H NMR thus provides information about the flow of energy that triggers changes in hydrogen‐bonding networks and helix movements in the activation mechanism of the photoreceptor.     

Solid-state 2H NMR structure of retinal in metarhodopsin I

The structural and photochemical changes in rhodopsin due to absorption of light are crucial for understanding the process of visual signaling. We investigated the structure of trans-retinal in the metarhodopsin I photointermediate (MI), where the retinylidene cofactor functions as an antagonist. Rhodopsin was regenerated using retinal that was (2)H-labeled at the C5, C9, or C13 methyl groups and was reconstituted with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. Membranes were aligned by isopotential centrifugation, and rhodopsin in the supported bilayers was then bleached and cryotrapped in the MI state. Solid-state (2)H NMR spectra of oriented rhodopsin in the low-temperature lipid gel state were analyzed in terms of a static uniaxial distribution (Nevzorov, A. A.; Moltke, S.; Heyn, M. P.; Brown, M. F. J. Am. Chem. Soc. 1999, 121, 7636-7643). The line shape analysis allowed us to obtain the methyl bond orientations relative to the membrane normal in the presence of substantial alignment disorder (mosaic spread). Relative orientations of the methyl groups were used to calculate effective torsional angles between the three different planes that represent the polyene chain and the beta-ionone ring of retinal. Assuming a three-plane model, a less distorted structure was found for retinal in MI compared to the dark state. Our results are pertinent to how photonic energy is channeled within the protein to allow the strained retinal conformation to relax, thereby forming the activated state of the receptor.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Properties of calcium phosphate coatings deposited by high-power ion beam ablation plasma

Biocompatible hydroxyapatite coatings (Ca₁₀(PO₄)₆(OH)₂) are used in stomatology and orthopedic surgery as an original structure for production of medical materials. These coatings have been deposited on Si, Ti and VT15-alloy substrates from ablation plasma formed under the impact of pulsed high-power ion beams on a calcium phosphate ceramic target. The nanohardness, Young’s modulus, elastic recovery, adhesion of coatings to substrates, friction constant, and surface roughness were measured.     

Optical properties of cadmium sulfide nanocrystals obtained by the sol-gel method in gelatin

Based on analysis of optical absorption data for CdS nanocrystals obtained by sol-gel technology in gelatin, we have studied the effect of technological factors (reagent concentrations, gelatin concentration) on the growth process and size distribution of the synthesized nanocrystals. Depending on the reagent concentration, we synthesized CdS nanocrystals with mean radii in the range . We have shown that for a low gelatin content (1%), nanocrystals of different sizes are formed (1.7 nm and 2.6 nm). With an increase in the gelatin concentration, the size dispersion decreases and nanocrystals of a single mean radius (2.3 nm) are formed. We have established a correlation between the size dispersion and the shape of the photoluminescence spectrum of the CdS nanocrystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 556–562, July–August, 2008.     

Proton channeling in silicon at various temperatures

A study was made of the channeling of 6. 72 MeV protons in a silicon crystal at 100–800 °K. The experimental dependence of the limiting channeling angle agrees with the theoretical prediction. A relation is found between the relative number of channeled protons and the temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 60–63, June, 1970.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Deposition of fullerene films from the ablation plasma generated by high-power ion beams on graphite targets

A possibility of deposing carbon films with a high content of C₆₀ and C₇₀ fullerenes from an ablation plasma generated as a result of irradiation of graphite targets by pulsed high-power ion beams is shown. The relative contents of the crystalline diamond-like carbon phase, crystalline fullerene phase, and amorphous carbon phase have been determined by X-ray diffraction analysis for different deposition conditions. The nanohardness and Young’s modulus of the deposited films and their adhesion to the single-crystal silicon substrate have been measured.