A scheme of a modular plasma-opening-switch-based generator of megaampere currents for experiments with Z-pinches

A modular scheme of a megaampere current pulse generator on the plasma opening switch (POS) basis with insulation of the POS interelectrode gap by a magnetic field created by an external source is proposed for experiments with wire liners and other applications. The POS is fed from independent modules that are switched on in parallel. On the basis of an НК-50-3 (50 kV, 3 μF) capacitor, a supply module with a current through the equivalent part of the POS of up to 200 kA is designed and tested. The limiting POS parameters and the maximum permissible number of modules are determined, and circuit designs of the basic units of the generator are presented.     

Radioecological state of the territory and water area in Guba Andreev

The radioecological conditions which developed on the territory over the long operating time of the object of the naval fleet in Guba Andreev are described. The results of an analysis of the sources of the real and potential danger and measures to prevent dangerous effects for the environment and the workers at the time remediation work is performed are discussed. __________ Translated from Atomnaya énergiya, Vol. 101, No. 1, pp. 49–55, July, 2006.     

Isolation and certain properties of mutant alkaline phosphatase of Escherichia coli

Natural and mutant alkaline phosphatases with amino acid substitutions in the processing site and N-terminal domain of the mature polypeptide chain Val for Ala(-1), Gln for Glu (+4) and simultaneously Gln for Glu (+4) and Ala for Arg (+1) have been isolated from the periplasm and cultural fluid of E. coli. It has been found that these substitutions have little effect on the dependence of the enzyme activity on pH, ionic strength and temperature but influence its isoenzymic spectrum and decrease (almost twofold) the maximal rate of the enzyme-catalyzed reaction. Extracellular enzymes display, in contrast with periplasmic ones, other catalytic properties (Vmax) and binding activity (Km). After translocation through the outer membrane all the enzymes display decreased Vmax and increased Km. These changes are especially well-pronounced in case of the mutant protein PhoA46 which contains an uncleaved signal peptide due to the impossibility of processing resulting from the substitution of Val for Ala(-1). The Vmax for this protein is decreased 20 times, while the Km is increased 4-fold. The protein also shows a higher (in comparison with other proteins) sensitivity towards proteolytic enzymes and is less resistant upon storage. The experimental data suggest that the changes in the N-end of alkaline phosphatase located at a long distance from its active center influence the enzyme function.     

Application of spectromicroscopy tools to explore local origins of sensor activity in quasi-1D oxide nanostructures

We have tested a range of imaging and spectroscopic techniques to address their ability to locally explore the interplay between surface reactivity and transport properties of the metal oxide nanostructure wired as a chemiresistor and chemi-FET. In particular, we used scanning surface potential microscopy (SSPM) to monitor the spatial and temporal particularities of the dc potential distributions in an operating device. We also successfully implemented synchrotron radiation-based photoelectron emission microscopy (PEEM) to explore submicron lateral compositional and electronic (work function) inhomogeneity on the surface of an individual nanowire sensor. These results open new avenues to visualize and spectroscopically address the chemical phenomena on an individual quasi-1D nanostructure both in real time and at nano-?and mesoscopic level.     

Voltage-gated ion transport through semiconducting conical nanopores formed by metal nanoparticle-assisted plasma etching

Nanopores with conical geometries have been found to rectify ionic current in electrolytes. While nanopores in semiconducting membranes are known to modulate ionic transport through gated modification of pore surface charge, the fabrication of conical nanopores in silicon (Si) has proven challenging. Here, we report the discovery that gold (Au) nanoparticle (NP)-assisted plasma etching results in the formation of conical etch profiles in Si. These conical profiles result due to enhanced Si etch rates in the vicinity of the Au NPs. We show that this process provides a convenient and versatile means to fabricate conical nanopores in Si membranes and crystals with variable pore-diameters and cone-angles. We investigated ionic transport through these pores and observed that rectification ratios could be enhanced by a factor of over 100 by voltage gating alone, and that these pores could function as ionic switches with high on-off ratios of approximately 260. Further, we demonstrate voltage gated control over protein transport, which is of importance in lab-on-a-chip devices and biomolecular separations.     

Multifrequency imaging in the intermittent contact mode of atomic force microscopy: beyond phase imaging

The cantilever dynamics in single-frequency scanning probe microscopy (SPM) are undefined due to having only two output variables, which leads to poorly understood image contrast. To address this shortcoming, generalized phase imaging scanning probe microscopy (GP-SPM), based on broad band detection and multi-eigenmode operation, is developed and demonstrated on diamond nanoparticles with different functionalization layers. It is shown that rich information on tip-surface interactions can be acquired by separating the response amplitude, instant resonance frequency, and quality factor. The obtained data allow high-resolution imaging even in the ambient environment. By tuning the strength of tip-surface interaction, different surface functionalizations can be discerned.     

Open-loop band excitation Kelvin probe force microscopy

A multidimensional scanning probe microscopy approach for quantitative, cross-talk free mapping of surface electrostatic properties is demonstrated. Open-loop band excitation Kelvin probe force microscopy (OL BE KPFM) probes the full response-frequency-potential surface at each pixel at standard imaging rates. The subsequent analysis reconstructs work function, tip-surface capacitance gradient and resonant frequency maps, obviating feedback-related artifacts. OL BE KPFM imaging is demonstrated for several materials systems with topographic, potential and combined contrast. This approach combines the features of both frequency and amplitude KPFM and allows complete decoupling of topographic and voltage contributions to the KPFM signal.     

Symmetry relationship and strain-induced transitions between insulating M1 and M2 and metallic R phases of vanadium dioxide

The ability to synthesize VO2 in the form of single-crystalline nanobeams and nano- and microcrystals uncovered a number of previously unknown aspects of the metal-insulator transition (MIT) in this oxide. In particular, several reports demonstrated that the MIT can proceed through competition between two monoclinic (insulating) phases M1 and M2 and the tetragonal (metallic) R phase under influence of strain. The nature of such phase behavior has been not identified. Here we show that the competition between M1 and M2 phases is purely lattice-symmetry-driven. Within the framework of the Ginzburg-Landau formalism, both M phases correspond to different directions of the same four-component structural order parameter, and as a consequence, the M2 phase can appear under a small perturbation of the M1 structure such as doping or stress. We analyze the strain-controlled phase diagram of VO2 in the vicinity of the R-M2-M1 triple point using the Ginzburg-Landau formalism and identify and experimentally verify the pathways for strain-control of the transition. These insights open the door toward more systematic approaches to synthesis of VO2 nanostructures in desired phase states and to use of external fields in the control of the VO2 phase states. Additionally, we report observation of the triclinic T phase at the heterophase domain boundaries in strained quasi-two-dimensional VO2 nanoplatelets, and theoretically predict phases that have not been previously observed.     

Kinematic characteristics of pulsed speed regulators

Experimental kinematic characteristics are presented for pulsed speed regulators with eccentric free-wheel clutch mechanisms of different designs. Formulas have been obtained for the change in transmission ratios of pulsed speed regulators under load.     

Piezoelectric indentation of a flat circular punch accompanied by frictional sliding and applications to scanning probe microscopy

Indentation of a piezoelectric half-space by a flat circular indenter accompanied by frictional sliding is considered. Full-field electroelastic solutions in elementary functions are obtained. The solution is based on the correspondence principle between elastic and piezoelectric problems. Stiffness relations between applied load and resulting displacement are given in elementary functions. In conjunction with the conical and spherical solutions, given previously by Makagon et al. [A. Makagon, M. Kachanov, S.V. Kalinin, E. Karapetian, Indentation and frictional sliding of spherical and conical punches into piezoelectric half-space, Physical Review B 76 (2007) 064115 (14)], this work completes the set of limiting cases of tip geometries utilized in lateral force microscopy (LFM) technology. Implications for quantitative interpretation of scanning probe microscopy (SPM) data and tribological data are analyzed.