Ion beam induced charge characterisation of a silicon microdosimeter using a heavy ion microprobe

An ion beam induced charge (IBIC) facility has been added to the existing capabilities of the ANSTO heavy ion microprobe and the results of the first measurements are presented. Silicon on insulator (SOI) diode arrays with microscopic junction sizes have recently been proposed as microdosimeters for hadron therapy. A 20 MeV carbon beam was used to perform IBIC imaging of a 10 μm thick SOI device.     

Optically stimulated intersubband absorption in undoped amorphous Si/SiO2 qiantum well

Intersubband absorption has been observed in undoped amorphous multiple-quantum-well (MQW) strucctures under interband excitation. The transitions take place between the first and second subbands of the conduction band and involve non-equilibrium electrons excited into the first subband by optical pumping. The absorption band FWHM of 0.1 eV is much larger than for crystalline MQWs, a fact which reflects the relaxation of the electron momentum conservation in the QW plane. The high joint density of states and oscillator strength for the intersubband transitions in amorphous QWs allow one to observe the absorption at low electron concentrations (N_e ≈ 10¹³ cm^?3) in the ground conduction subband.     

AVHRR-based mapping of fires in Russia: New products for fire management and carbon cycle studies

A new database of fire activity in Russia derived from 1-km resolution remote sensing imagery is presented and discussed. The procedure used to generate this burned-area product is described, including active-fire detection and burn-scar mapping approaches. Fire detection makes use of a probabilistic procedure using image data from the United States National Oceanic and Atmospheric Administration's (NOAA) advanced very high resolution radiometer (AVHRR) system. Using the combination of AVHRR data collected at the Krasnoyarsk, Russia, high-resolution picture transmission (HRPT) receiving station, and data from the NOAA Satellite Active Archive (SAA), fire maps are being created for all of Russia for 1995 to 1997 and all of Eastern Russia (east of the Ural Mountains) for 1995 to 2002. This mapping effort has resulted in the most complete set of historic fire maps available for Russia. An initial validation indicates that the burned-area estimates are conservative because the approaches do not detect smaller fires, and, in many cases, fire areas are slightly underestimated. Analyses using the fire database showed that an average of 7.7×10⁶ ha yr⁻¹ of fire occurred in Eastern Russia between 1996 and 2002 and that fire was widely dispersed in different regions. The satellite-based burned-area estimates area were two to five times greater than those contained in official government burned-area statistics. The data show that there is significant interannual variability in area burned, ranging between a low of 1.5×10⁶ ha in 1997 to a high of 12.1×10⁶ ha in 2002. Seasonal patterns of fire are similar to patterns seen in the North American boreal region, with large-fire seasons experiencing more late-season burning (in August and September) than during low-fire years. There was a distinct zonal distribution of fires in Russia; 65% of the area burned occurred in the taiga zone, which includes southern, middle, and northern taiga subzones, 20% in the steppe and forest steppe zones, 12% in the mixed forest zone, and 3% in the tundra and forest-tundra zones. Lands classified as forest experienced 55% of all burned area, while crops and pastures, swamps and bogs, and grass and shrubs land cover categories experienced 13% to 15% each. Finally, the utility of the products is discussed in the context of fire management and carbon cycling.     

Comparison of U.S.S.R. Codes and U.S. Army Manual for design of foundations on permafrost

A comparative study was made of design criteria and analytical methods for footings and pile foundations on permafrost employed in U.S.S.R. Design Code SNiP II-18-76 (1977) and U.S. Army Cold Regions Research and Engineering Laboratory Special Report 80-34 developed in the early 1970s by the U.S. Army Corps of Engineers and published in 1980. The absence of adequate constitutive equations for frozen soils and of rigorous solutions of the boundary problems has made it necessary to incorporate (explicitly or implicitly) various safety factors in the foundation analyses. From the review it is concluded that the principal difference between these practices is in the assessment and application of appropriate values of safety factors, which leads to a substantial discrepancy in the dimensions and costs of footings and pile foundations in permafrost.     

Magnetohydrodynamic instability in annular linear induction pump: Part I. Experiment and numerical analysis

The present paper describes an experimental and analytical study of the magnetohydrodynamic instability arising in an annular linear induction pump. In the experiment, the instability was investigated in detail using an electromagnetic pump of flow rate 7 m³/min. The experimental results show that the instability occurs when the magnetic Reynolds number is larger than unity and the instability becomes more intensive as the slip increases. The instability is characterized by low frequency pressure pulsation, non-uniform magnetic field along the azimuth, wide-frequency vibration of the pump and pipe, fluctuation of winding voltage and current. The numerical analysis reveals that when the magnetic Reynolds number is larger than unity, an azimuthal non-uniformity of the applied magnetic field or of the sodium inlet velocity brings about sodium vortices and hence a low frequency pressure pulsation occurs. In addition, the non-uniformity causes a decrease of the developed pressure and sometimes a dip on the P–Q curve.     

Thin fullerene-containing films synthesized by ion beam sputtering of fullerene mixtures with doping additives in vacuum

A new approach to the synthesis of films containing fullerenes and doping elements is described. It is suggested that a cluster mechanism of the target sputtering by accelerated ions makes possible the deposition of fullerenes on a substrate with a certain probability for dopant atoms being introduced into the cavities of fullerene molecules and a higher probability of their occurrence between fullerene molecules. The proposed method has been experimentally implemented by using an Ar⁺ ion beam to sputter C₆₀/C₇₀ fullerene mixtures (synthesized in a plasmachemical reactor at a pressure of 10⁵ Pa) pressed into disk targets with a doping element (Fe, Na, B, Gd, or Se). The ion beam sputtering of dopant-containing fullerene mixtures in a vacuum of ～10^?2 Pa allowed micron-thick films containing C₆₀ and C₇₀ fullerenes and the corresponding dopant element (Fe, Na, B, Gd, or Se) to be grown on quartz substrates.     

Vibration influence on morphological instability of a solidification front

The paper deals with the vibration influence on the stability of a planar solidification front moving with constant average velocity. The case of high frequency vibrations with small amplitude is studied. The density dependence on the solute concentration is accounted for in the framework of the Boussinesq approach. The equations for average velocity and concentration fields are obtained by multiple scale and averaging methods. A number of limit cases are studied analytically, by perturbation methods. For finite values of governing parameters the threshold of morphological instability is determined numerically. It is found that the vibrations normal to the solidification front exert destabilizing effect whereas tangential vibrations suppress the development of morphological instability.