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The generation of a microwave pulse by the plasma created by a stratospheric source of ionizing radiation is examined. The structure, the mechanisms for generating the signal, and the information contained in the signal observed at a satellite positioned directly above the explosion are discussed. It is shown that the microwave pulse is generated by two mechanisms: radiation from the shock front lasting up to one second and radiation from a partially ionized plasma lasting tens of microseconds. A package of programs developed by the authors is used for model calculations of microwave pulses. The parameters of the signal are such that they can be picked up by modern pulse radiometers.Microwave monitoring of the atmosphere is extensively used nowadays for detecting explosions and the consequences of engineering accidents. This type of monitoring is convenient because the microwave technique works in all weather conditions and is accurate, while the air is transparent to microwave radiation. In addition, compact pulsed radiometers are now available, with integration times of 0.1-1 µsec and a sensitivity of hundreds of degrees Kelvin, that can be mounted on the earth's surface or aboard any airborne platform [1].We examine the influence of the mechanisms for generation of incoherent microwave radiation on the structure of the radio-frequency pulse, as well as possible information in the signal which may make it possible to determine the properties of the microwave source. Let us assume that the explosion is accompanied by the release of radiation with a long mean free path, e.g., in the form of neutrons or x-rays and γ rays. The positions O of the point source (explosion) and the radiometer Ra are illustrated in Fig. 1. An explosion takes place at an altitude ranging from H = 10 km to H = 40 km above the earth's surface. The signal is picked up by a radiometer located on a satellite immediately above the explosion at an altitude h = 200 km.Two different mechanisms participate in the formation of a microwave pulse. One is associated with the development of gas dynamic processes in the immediate environment of the explosion and the thermal radio frequency emission from the front of the shock wave. A thermal wave, behind whose front a shock wave develops, initially propagates from the source at the time of the explosion. The shock front moves through the heated medium and, in time, catches up with the front of the thermal wave. The heated layer between the fronts emits radiation. The radio-frequency brightness temperature increases at first, and then falls off sharply as the shock front emerges into the thermal wave front. After a sharp drop, the temperature passes through a minimum; it then rises again owing to radiation from the front of the shock wave and reaches a maximum. At the time when the second maximum is passing, the heated region radiates as an absolute black body. The mechanism for the visible radiation from the shock front was first examined by Zel'dovich and Raizer [2]. Calculations of the microwave

The temperature-dependent electrical resistance behaviour of PrNiO 3 , NdNiO 3 , Nd 0.99 Sr 0.01 NiO 3 and Sm 0.55 Nd 0.45 NiO 3 in zero field as well as in the presence of a magnetic field (H) is reported. The application of H up to 70 kOe does not influence the so-called metalinsulator transition in any of these compounds significantly. Interestingly, the magnitude of the magnetoresistance, ρ/ρ = {ρ(H ) − ρ(0)}/ρ(0), in the vicinity of 35 K is significantly larger than that noted below 10 K. It appears that there are sign crossovers in the magnetoresistance as the temperature is varied below the transition temperature in most of these compounds. The present results suggest that the physics below the transition temperature is quite complex.

In the paper, we show the present state of the art of high pulse repetition frequency (PRF) metal vapor lasers (MVL's) and metal halide vapor lasers (MHVL's) development. We also analyze underlying physical features, which limit optimum and maximum PRF of the above lasers and mention the results of the experimental study of high PRF CuBr and PbBr2 vapor lasers. By use of a powerful tasitron as a switch and a small hydrogen additive to the buffer gas Ne we obtained the output power of a practical use with PRY more than 200 kHz. Given PRF 250 kHz and a laser tube of diameter 2.5 cm and length 76 cm, we have got the output power 1.5 W. For PRF 200 kHz and 100 kHz, the output power 3 W and 10.5 W has been got respectively without gas flow across the discharge tube. Experimental and numerical modelling data evidence that the small H2 (or Cs) additives improve the frequency and output features ofMVL's and MHVL's.