Remote sensing technique for near-surface wind by optical images of rough water surface

The study of a new remote-sensing technique for the investigation of near-surface wind fields is an important oceanographic problem. This article is focused on a new method of recording wind fields by the analysis of optical images of sea surface and range–time–intensity images (RTI images) of the sea surface. An RTI image constructed from optical profiles of the sea surface is an optical analogue of a side-looking radar image of the sea surface but has a higher spatial resolution and some possibility for remote sensing of sea roughness. It is possible to form RTI images with a range from some tens of metres to tens of kilometres, depending on the spatial resolution needed. A set of original optical devices for recoding RTI images using linear arrays of CCD-photodiodes was created. An analytical model of sea surface radiance for visible light was developed taking into account the polarization of light and shadowing of surface waves for grazing view geometry. The principle of remote sensing of near-surface winds by its manifestations on a waved surface under grazing angles based on a comparison of measured and modelled surface radiance is discussed. Investigations of near-surface wind field features in internal reservoirs and various regions of the seas during the last few years have been conducted by optical systems. The structure of near-surface wind fields, eddies, wind fronts, and katabatic wind flows for ranges from hundreds of metres to some tens of kilometres was recorded and analysed. Derived data of optical monitoring of water surfaces may serve for future investigations of near-surface wind features.     

Scale effect in high-rate (spall) failure

Experimental results on the spall strength of copper in which the scale of the system was changed by a factor of ten show that the scale effect for high-rate one-dimensional strain depends on energy. The spall energy per unit surface area for failure increases with time. Arzamas-16. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 6, pp. 88–93, November–December, 1993.     

Plasma density in discharge sustained in inhomogeneous gas flow by high-power radiation in the terahertz frequency range

We have measured the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20–30 μs) in a range of background gas pressures in the discharge chamber from 10^–3 to 300 Torr. The electron concentration at low pressures (10^–3 to 7 Torr) was determined using Starkeffect induced broadening of the H_α atomic emission line (656.3 nm) of hydrogen present in discharge as a small impurity in residual gases. The maximum observed Stark broadening of the H_α line corresponded to a plasma density on the order of 2 × 1016 cm^–3, which exceeded the critical value for the given frequency of radiation sustaining the discharge. At background pressures above 7 Torr, the plasma density was estimated from analysis of the spatiotemporal patterns and waveforms of discharge glow in the visible spectral range. These estimations gave electron concentrations on the level of (1–2) × 10¹⁵ cm^–3.     

Multiparametric gyrotron power control during microwave processing of materials

Optimization of the control of gyrotron generation regime through consistent variation of the cathode voltage and solenoid magnetic field makes possible a significant (up to threefold) decrease in power consumption during microwave processing of materials. It is experimentally established that, for this purpose, it is possible to use fast (with a characteristic time on the order of a fraction of millisecond) modulation of microwave power through variation of the working magnetic field by the current of an auxiliary coil arranged near the cavity.     

Testing metal-dielectric-semiconductor tunnel structures on p-silicon as nuclear particle detectors

Metal-dielectric-semiconductor (MDS) structures with aluminum nitride (AlN) as a tunnel dielectric based on high-ohmic p-type silicon substrates have been studied. The samples were characterized with respect to the charge collection efficiency and energy resolution on probing with 5.4-MeV α particles. In addition, the nature of noises and the state of the AlN-p-Si interface were investigated. It is established that the parameters of these MDS structures as radiation detectors are close to those of widely used Schottky-barrier detectors based on n-Si (Au-n-Si). A decrease in the concentration of deep centers at the AlN-p-Si interface allows the proposed MDS structures to compete successfully with n-Si based detectors, which is due to a higher purity of the initial material.     

Gyrotron frequency control by a phase lock system

The idea of controlling gyrotron frequency by means of voltage variation on an insulated “current-free” anode [1] has been implemented. A gyrotron phase-locked to an external stabilized low-power oscillator exhibits a more than tenfold narrowing of the output spectrum width as compared to that in the free running regime.     

Nucleation of normal phase in the dynamic resistive state in submicron Bi2212 bridges

The resistive state above the Larkin-Ovchinnikov (LO) instability current has been experimentally studied. Analysis of the stepwise I–V curves of thin superconducting bridges ≤1 μm wide, etched from the Bi₂Sr₂Ca₁Cu₂O_y (Bi2212) whiskers, reveals the following scenario of vortex dynamics: first, a pair of current-induced Abrikosov vortices enter the bridge, then they are accelerated by the current above the critical velocity of the LO instability and approach the limiting velocity of the normal phase propagation, of the order of 10⁷ cm/s. Each vortex leaves a tail of normal phase behind itself, which is equivalent to a phase slip line. At low temperatures the tails cover the whole width of the bridge—the I–V curves between the steps become Ohmic.     

Effect of size, manufacturing and prestrain on high-rate failure (spall) of PT-3V titanium alloy and 12Kh18N10T steel

Experimental results are presented on the spall strength of PT-3V titanium alloy and 12Kh18N10T steel as the system size is changed by a factor of five. The effects of a 0.5–5% dynamic prestrain and of the direction of the load relative to the manufacturing rolling direction on spall failure were also studied for the titanium alloy. It was established that failure of these metals under high-rate one-dimensional strain shows significant energy-related size effects. Effects of the rolling direction and prestrain were less pronounced for the titanium alloy than for steel. All-Union Research Institute of Experimental Physics, 607200 Sarov. Translated from Fizika Goreniya i Bzryva, Vol. 31, No. 6, pp. 130–139. November–December, 1995.