Self-consistent simulation of pulsed and continuous microwave discharges in hydrogen

Results are presented from numerical simulations of pulse-periodic and continuous microwave discharges in hydrogen that are used in CVD reactors for chemical vapor deposition of diamond films. Attention is focused on the processes that should be taken into account in order to construct the simplest possible adequate numerical model. It is shown that the processes of vibrational excitation of hydrogen molecules, as well as chemical reactions, play an important role in the establishment of energy balance within the discharges. The results of numerical simulations are compared to the experimental data.     

EDC-mediated DNA attachment to nanocrystalline CVD diamond films

Chemical vapour deposited (CVD) diamond is a very promising material for biosensor fabrication owing both to its chemical inertness and the ability to make it electrical semiconducting that allows for connection with integrated circuits. For biosensor construction, a biochemical method to immobilize nucleic acids to a diamond surface has been developed. Nanocrystalline diamond is grown using microwave plasma-enhanced chemical vapour deposition (MPECVD). After hydrogenation of the surface, 10-undecenoic acid, an omega-unsaturated fatty acid, is tethered by 254 nm photochemical attachment. This is followed by 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide (EDC)-mediated attachment of amino (NH(2))-modified dsDNA. The functionality of the covalently bound dsDNA molecules is confirmed by fluorescence measurements, PCR and gel electrophoresis during 35 denaturation and rehybridisation steps. The linking method after the fatty acid attachment can easily be applied to other biomolecules like antibodies and enzymes.     

Intracavity absorption and emission spectroscopy of atoms in pulsed gas discharges

Absorption and emission spectra of U and Na atoms in the 590-nm spectral range were studied experimentally using pulsed hollow-cathode gas discharges. The spectra were recorded with a high-sensitivity intracavity laser spectrometer. The possibility of generating coherent emission on atomic emission lines in gas-discharge plasmas was demonstrated experimentally.     

Stability of the low-temperature states of high-pressure microwave discharges

Symmetric (planar, cylindrical, and spherical) models of microwave discharges in air are considered assuming that the deposited energy is removed via heat conduction. The characteristic features of spherical discharges are analyzed in detail, and the conditions for discharge stability are examined. It is shown that discharges in the low-temperature (unstable) state can be stabilized by varying the power of a feedback-controlled microwave source.     

Circulating antibody response of mice exposed to 9-GHz pulsed microwave radiation

Female CD-1 mice immunized against the bacterium Streptococcus pneumoniae type III were exposed to 9-GHz pulsed microwaves (pulse repetition rate 970-1,000, pulse width 1.0 microseconds, peak power 1 W/cm2) at an average incident power density of 1 mW/cm2 (calculated SAR congruent to 0.47 W/kg) for 2 h per day for 5 days. Circulating antibody titers for the microwave-exposed animals were not significantly different from those of the sham-irradiated animals, and there were no differences in any of the hematological parameters analyzed, indicating that 9-GHz pulsed microwaves at 1 mW/cm2 do not alter the immune response of mice immunized against S pneumoniae.     

Studies of exposure of rabbits to electromagnetic pulsed fields

Dutch rabbits were acutely exposed to electromagnetic pulsed (EMP) fields (pulse duration 0.4μs, field strengths of 1–2 kV/cm and pulse repetition rates in the range of 10 to 38 Hz) for periods of up to two hours. The dependent variables investigated were pentobarbital-induced sleeping time and serum chemistry (including serum triglycerides, creatine phosphokinase (CPK) isoenzymes, and sodium and potassium). Core temperature measured immediately pre-exposure and postexposure revealed no exposure-related alterations. Over the range of field strengths and pulse durations investigated no consistent, statistically significant alterations were found in the end-points investigated.     

Epitaxial synthesis of diamond layers on a monocrystalline diamond substrate in a torch microwave plasmatron

The epitaxial growth of a diamond single-crystal film in a torch microwave discharge excited by a magnetron of a domestic microwave oven with the power of ≤1 kW in an argon-hydrogen-methane mixture with a high concentration of methane (up to 25% with respect to hydrogen) at atmospheric pressure on a sub-strate of a synthetic diamond single crystal (HPHP) with the orientation (100) and 4 × 4 mm in size is obtained. A discharge with the torch diameter of ∼2 mm and the concentration of the microwave power absorbed in the torch volume of >10³ W/cm³ is shown to be effective for epitaxial enlargement of a single crystal of synthetic diamond. The structure of the deposited film with the thickness up to 10 μm with high-quality morphology is investigated with an optical microscope as well as using the methods of the Raman scattering and scanning electron microscopy.     

Initiation of solid-phase chemical reactions in powder mixtures by microwave discharges

The initiation of exothermic chemical reactions in powder (metal-dielectric) mixtures by irradiating them with a high-power microwave beam is investigated. The initial stage of microwave breakdown is accompanied by the emission in the atomic lines of the metal component of the mixture (Ti, Mo, Sn, Al, etc.). The subsequent microwave discharge generates a continuous optical spectrum, the temperature of the effective Planckian radiator being 2000–3000 K. A prolonged radiation of the mixture after the end of the microwave pulse is caused by the energy release in chemical reactions.     

Design and oxygen-transfer potential of a pulsed continuous tubular fermentor

A new type of continuous fermentor has been developed which features an agitation-aeration system based on pulsed flow across perforated plates the use of plug flow to achieve a concentration gradient. The influence of the agitation-aeration parameters (in this case the pulsed speed) has been measured, and mathematical models have been produced for the gas hold-up, the power dissipated in agitation and aeration, the oxygen-transfer rate, and efficiency. The oxygen transfer is high, up to 600 mmol/liter hr with a transfer efficiency much higher than that published for any other technique.