Proton acceleration in analytic reconnecting current sheets

Particle acceleration provides an important signature for the magnetic collapse that accompanies a solar flare. Most particle acceleration studies, however, invoke magnetic and electric field models that are analytically convenient rather than solutions of the governing magnetohydrodynamic equations. In this paper a self-consistent magnetic reconnection solution is employed to investigate proton orbits, energy gains, and acceleration timescales for proton acceleration in solar flares. The magnetic field configuration is derived from the analytic reconnection solution of Craig and Henton. For the physically realistic case in which magnetic pressure of the current sheet is limited at small resistivities, the model contains a single free parameter that specifies the shear of the velocity field. It is shown that in the absence of losses, the field produces particle acceleration spectra characteristic of magnetic X-points. Specifically, the energy distribution approximates a power law ~ξ-3/2 nonrelativistically, but steepens slightly at the higher energies. Using realistic values of the “effective” resistivity, we obtain energies and acceleration times that fall within the range of observational data for proton acceleration in the solar corona

Indeterminacy and instability in Petschek reconnection

We explain two puzzling aspects of Petschek's model for fast reconnection. One is its failure to occur in plasma simulations with uniform resistivity. The other is its inability to provide anything more than an upper limit for the reconnection rate. We have found that previously published analytical solutions based on Petschek's model are structurally unstable if the electrical resistivity is uniform. The structural instability is associated with the presence of an essential singularity at the X-line that is unphysical. By requiring that such a singularity does not exist, we obtain a formula that predicts a specific rate of reconnection. For uniform resistivity, reconnection can only occur at the slow, Sweet-Parker rate. For nonuniform resistivity, reconnection can occur at a much faster rate provided that the resistivity profile is not too flat near the X-line. If this condition is satisfied, then the scale length of the nonuniformity determines the reconnection rate

Photon assisted tunneling in pairs of silicon donors

Shallow donors in silicon are favorable candidates for the implementation of solid-state quantum computer architectures because of the promising combination of atomiclike coherence properties and scalability from the semiconductor manufacturing industry. Quantum processing schemes require (among other things) controlled information transfer for readout. Here we demonstrate controlled electron tunneling at 10 K from P to Sb impurities and vice versa with the assistance of resonant terahertz photons

Charge and matter distributions and form factors of light, medium and heavy neutron-rich nuclei

Results of charge form factors calculations for several unstable neutron-rich isotopes of light, medium and heavy nuclei (He, Li, Ni, Kr, Sn) are presented and compared to those of stable isotopes in the same isotopic chain. For the lighter isotopes (He and Li) the proton and neutron densities are obtained within a microscopic large-scale shell-model, while for heavier ones Ni, Kr and Sn the densities are calculated in deformed self-consistent mean-field Skyrme HF+BCS method. We also compare proton densities to matter densities together with their rms radii and diffuseness parameter values. Whenever possible comparison of form factors, densities and rms radii with available experimental data is also performed. Calculations of form factors are carried out both in plane wave Born approximation (PWBA) and in distorted wave Born approximation (DWBA). These form factors are suggested as predictions for the future experiments on the electron-radioactive beam colliders where the effect of the neutron halo or skin on the proton distributions in exotic nuclei is planned to be studied and thereby the various theoretical models of exotic nuclei will be tested.Comment: 26 pages, 11 figures, 3 tables, accepted for publication in Phys. Rev.

Methodology for determining the parameters of drilling mode for directional straight sections of well using screw downhole motors

Article presents results of study on possibility of increasing the efficiency of drilling directional straight sections of wells using screw downhole motors (SDM) with a combined method of drilling with rotation of drilling string (DS). Goal is to ensure steady-state operation of SDM with simultaneous rotation of DS by reducing the amplitude of oscillations with adjusting the parameters of drilling mode on the basis of mathematical modeling for SDM – DS system. Results of experimental study on determination of extrema distribution of lateral and axial oscillations of SDM frame depending on geometrical parameters of gerotor mechanism and modes ensuring stable operation are presented. Approaches to development of a mathematical model and methodology are conceptually outlined that allow determining the range of self-oscillations for SDM – DS system and boundaries of rotational and translational wave perturbations for a heterogeneous rod with an installed SDM at drilling directional straight sections of well. This mathematical model of SDM – DS system's dynamics makes it possible to predict optimal parameters of directional drilling mode that ensure stable operation of borehole assembly

JUSTIFICATION OF THE TECHNOLOGICAL PARAMETERS CHOICE FOR WELL DRILLING BY ROTARY STEERABLE SYSTEMS

Paper presents the analysis of the investigation results of vibrational accelerations and beating amplitudes of the downhole drilling motor, which help to define the ranges of optimum energy characteristics of the gerotor mechanism, ensuring its stable operation. Dependencies describing the operation of the «drilling bit – rotary steerable system with power screw section – drilling string» system and the values of the self-oscillation boundaries and the onset of system resonance when it is used jointly, were defined as a result of computational and full-scale experimental research. A mathematical model is proposed, which allows determining the optimal range of technological parameters for well drilling, reducing the extreme vibration accelerations of the bottomhole assembly by controlling the torque-power and frequency characteristics of the drilling string, taking into account the energy characteristics of the power screw section of the rotary steerable system. Recommendations on the choice of drilling mode parameters were given

The first application of sensory structures based on photoelectric transducer for the study of enzymatic reactions

Background. The development of highly sensitive sensor equipment with the possibility of registering analytes in real time is a fast growing research area and a promising diagnostic biomedical technology. Currently, the standard laboratory method for determining the activities of ATPses is an indirect spectroscopic study of the concentration of inorganic phosphate formed as a result of ATP hydrolysis by these enzymes. However, there is no commercially available phosphate sensor with satisfactory parameters of sensitivity, selectivity and stability over time. The purpose of our research was the deve­lopment of a photoelectric recombination sensor system for the real-time detection of biochemical markers and its testing on the example of screening ATPase activity of rat erythrocyte plasma membrane suspension preparations. Materials and Methods. Experiments were performed on suspension preparations of plasma membranes of erythrocytes of Wistar rats. Preparations of plasma membrane suspensions obtained by Dodge method from each animal were divided into aliquots and used for the simultaneous study of ATPase activity by the reference method of Rathbun & Betlach, as well as the registration of photocurrents induced during the passage of the ATPase reaction using the photoelectric recombination multisensor system of our own design. Results. The application of silicon sensory structures based on photoelectrical transducer principle for detecting the activity of adenosine triphosphate hydrolases on the example of total Mg2+,Na+,K+-ATPases preparations of plasma membranes of rat erythro­cytes has been experimentally tested. The directly measured analytic parameter is the photocurrent of the deep silicon barrier structure under illumination with high absorption coefficient. The physical features of the device operation have been examined. Detection of such metabolites becomes possible due to reactions intermediates with their own dipole moment (inorganic phosphate, which is one of the products of ATP hydrolysis). The drastic change of photocurrent that characterizes the course of biochemical reaction was observed in real time. The effect is explained by local electrostatic influence on the parameters of recombination centers at the silicon surface that results in surface recombination velocity change. The sensor operation is qualitatively explained in the frame of Stevenson-Keyes’s theory. Conclusions. Our approach can be regarded as a promising way to elaborate technically simple and highly sensitive method for detection of quantitative behavior of enzymatic reactions. Moreover, the local modification of silicon surface allows obtaining time depending scenarios of the adsorption and thus improving the sensitivity of the sensor. These circumstances open up the possibility of elaborating the complex sensory structures with optimized parameters for certain enzymatic reactions