Visible light emission from silicon: a quantum effect in highlyporous materials

The authors discuss progress in the control of the luminescent properties of porous silicon and in the understanding of the basic mechanisms which govern the light emission. The main features of porous silicon formation and properties are briefly recalled. The photoluminescence characteristics are reported. It is shown that anodic oxidation of porous silicon is a technique which provides photoluminescent layers with good mechanical properties and enhanced emission efficiency. A model accounting for the quite long measured carrier lifetimes is outlined. The electroluminescence which appears during the anodic oxidation of porous silicon in pure water was studied     

秦山三期CANDU核电厂的控制系统

秦山三期ＣＡＤＮＵ核电厂全厂控制系统使用双重冗余数字计算机,自动完成监测,控制、运行信息管理和诊断等功能。采用变量数字控制算法实现对反应堆功率,蒸汽发生器液位和压力。热传输系统压力和装置。慢化剂温度、汽轮机负荷和转速、发电机功率输出以及不停堆换料的控制,保证电厂安全,经济地运行。     

Characterization of individual aerosol particles from the eruption of Lonquimay volcano in Chile

A set of aerosol samples collected during major volcanic activities around the Chilean site Lonquimay in the years 1988–1990 has been subjected to measurements in conventional and microPIXE modes in the Debrecen institute. The aim of the study was the completion of the earlier results with comparative PIXE data and microPIXE measurements for the characterization of individual particles. Results have been obtained on separate particles in terms of their elemental composition, on separate particle groups of different composition by statistical dissimilarity analysis. Si/Al and K/Si elemental ratios have been used for a comparison with published data from other volcanic locations.     

CAFNA(R), coded aperture fast neutron analysis forcontraband detection: preliminary results

We have developed a near field coded aperture imaging system for use with fast neutron techniques as a tool for the detection of contraband and hidden explosives through nuclear elemental analysis. The technique relies on the prompt gamma rays produced by fast neutron interactions with the object being examined. The position of the nuclear elements is determined by the location of the gamma emitters. For existing fast neutron techniques, in pulsed fast neutron analysis (PFNA), neutrons are used with very low efficiency; in fast neutron analysis (FNA), the sensitivity for detection of the signature gamma rays is very low. For the coded aperture fast neutron analysis (CAFNA ^(R)) we have developed, the efficiency for both using the probing fast neutrons and detecting the prompt gamma rays is high     

Quantification in positron emission mammography (PEM) with planardetectors: contrast resolution measurements using a custom breastphantom and novel spherical hot-spots

The authors have previously demonstrated that their Positron Emission Mammography-1 (PEM-1) system can successfully detect small (<2 cm diameter) tumors. Images in the current system are judged qualitatively for the presence of focal uptake of ¹⁸F-FDG. The authors are presently taking steps toward quantifying the emission images. To this end they have constructed a breast phantom and developed a novel technique for fabricating very small wall-less radioactive hot-spots. The hot-spots are made by adding ¹⁸F-FDG to a 25 mg/cc solution of Agarose in water. The heated solution is poured into spherical molds which are separated upon congealing to yield robust wall-less radioactive hot-spots. The hot-spots were uniform to within 1-5 parts in 100. Less than 0.1% of the total hot-spot activity leaked into the background in 30 minutes. Contrast resolution experiments have been performed with 12 mm and 16 mm diameter hot-spots in the breast phantom containing water with various amounts of background activity. In both cases, the observed contrast values agree well with the ideal values. In the case of the 12 mm hot-spot with a 350-650 keV energy window, image contrast differed from the ideal by an average of 11%. The image contrast for 12 mm hot-spot improved by 40% and the number of detected events decreased by 35% when the low energy threshold was increased from 300 keV to 450 keV     

Development of thermal fatigue damage in 1CrMoV rotor steel

Crack initiation endurances have been determined for a 1CrMoV rotor steel in uniaxial service cycle thermo-mechanical fatigue (TMF) tests formulated to simulate a range of steam turbine start cycles with a maximum temperature of 565 °C. The experimental details for these TMF tests are described.Post test inspection has been employed to characterise the associated thermal fatigue damage mechanisms for the steel which are observed to be dependent on the magnitude of the thermal transient in the TMF cycle.The lowest resistance to thermal fatigue damage development occurs in these tests when the conditions determine that the rate of creep damage accumulation below the surface exceeds the rate of fatigue crack development at the surface.