Features of the Time Shape of the Pressure Pulses of Optical Air Breakdown

The time shape and amplitude of pressure pulses initiated by surface laser air breakdown for different energies of laser pulses (1–180 mJ) has been compared to the results of numerical gasdynamic calculations of unsteady explosive motions with allowance for counterpressure at distances of 0.2 to 30 cm from the breakdown region. It has been established that the experimental pressure pulse has the character of slowly damped quasiperiodic vibrations, whereas the calculated pulse is a bipolar single pulse of a much shorter duration. Good agreement between the experimental and calculated amplitudes of a positive pressure phase has been found throughout the investigated range, whereas the agreement between the corresponding amplitudes and durations of a negative pressure phase is limited in character. The differences observed in the experimental and calculated data have been attributed to the transformation of the shockwave motion to acoustic radiation.     

Wettability of Halides with Molten Metals. Physico-Chemical and Practical Aspects

A study is made on the wettability of sodium chloride and oxygen-free ionic compounds fluorides of alkaline-earth elements (CaF, MgF, BaF) by molten metals. The metals Cu, Sn, Ag, Au, In, and Ga do not wet these materials ( 120-140 deg). The wettability of fluorides by aluminum is somewhat greater ( 90-100 deg), in accordance with the greater chemical affinity of aluminum for fluorine. Chemically highly active and aggressive alloys of Ti, Zr, Hf, and V (with concentrations up to 70-80%) which completely wet and destroy known refractory materials (oxide, nitride, carbide, and carbon refractories, etc.) behave anomalously in regard to fluorides they do not wet their surface and are inert when in contact with them. This is attributable to the formation of an intermediate gaseous phase (a volatile fluoride) which separates the liquid metal from the solid surface. Effective use can be made of this phenomenon to develop refractories (crucibles, containers, jackets, etc.) for use in the isothermal melting, homogenization, and casting of alloys that contain Ti, Zr, Hf, and V.     

Acceleration of He3 up to 35 Mev in the one and one-half meter cyclotron

A method is described for accelerating He ₃ ²⁺ to 35 Mev in a cyclotron. A beam of 30 a with an energy spread of ± 0.3% was obtained on a target 12 m from the cyclotron. Due to the use of a gas recycling system, the loss of He₃ was decreased by two orders and was approximately 5 cm³/hr.The authors wish to express their deep appreciation to N. A. Vlasov and S. P. Kalinin for the continuing interest in the project; to V. I. Lamunin and N. N. Khaldin for constructing the gas recycling system; to N. V. Kartashov for tuning the pulsed ion source; to the staffs of the operating group and machine shop who assisted in the preparation of the apparatus and cyclotron inlet system.     

Structuring of Multiphase Compacts in the SiC′ ― Carbon System. Part 2. Structuring during Sintering

We have studied the effect of particle sizes in the starting powders in the silicon carbide carbon system, and also effects on the structure and phase composition of self-bonded silicon carbide (SBSC) that are associated with structural interactions between the starting components.     

Composite inorganic membranes containing nanoparticles of hydrated zirconium dioxide for electrodialytic separation

The aim of the work was to elucidate the nature of charge-selective properties of macroporous composite inorganic membranes modified with nanoparticles of hydrated zirconium dioxide. The membranes have been investigated using methods of standard contact porosimetry, potentiometry, electron microscopy and small-angle X-ray scattering. The ion exchanger has been found to deposit inside pores of ceramics. Differential curves of pore volume distribution have been resolved using Lorentz functions; each maximum has been related to structure elements of the matrix and ion exchanger by means of calculations according to homogeneous and heterogeneous geometrical models. It was found that the voids, the radius of which is 4 to 8 nm, are responsible for charge selectivity of the composite membranes. These pores are formed due to blocking of macropores of ceramics with aggregates of nanoparticles of the ion exchanger; the radius of these aggregates is 20 to 24 nm. The membranes were applied to desalination of the solution containing NaCl. The removal degree of the salt from the solution reached 95% and 9% for the composite and unmodified membranes, respectively.     

Effect of Mode Transformation in THz Clinotron

Extension of the theory of a clinotron is developed by use of the scattering matrix of an oversized T-junction on the ends of a slow wave system. The matrix contains elements corresponding to the transformation of slow grating modes into fast ones and vice versa. Those fast waves with low ohmic losses provide strong resonant properties of a clinotron even in the case of strong attenuation of the surface mode. Results of the theoretical simulation are compared with experimental ones and obtained dependencies explain strong resonances in sub-THz clinotrons.