Method for growing low defect, high purity crystalline layers utilizing lateral overgrowth of a patterned mask

A method for growing a high purity, low defect layer of semiconductor is described. This method involves depositing a patterned mask of a material impervious to impurities of the semiconductor on a surface of a blank. When a layer of semiconductor is grown on the mask, the semiconductor will first grow from the surface portions exposed by the openings in the mask and will bridge the connecting portions of the mask to form a continuous layer having improved purity, since only the portions overlying the openings are exposed to defects and impurities. The process can be iterated and the mask translated to further improve the quality of grown layers

ANN Model For SiGe HBTs Constructed From Time-Domain Large-Signal Measurements

We construct a large-signal artificial neural network (ANN) model for SiGe HBTs, directly from time-domain large-signal measurements. It is known that HBTs are very sensitive to self-heating and therefore we explicitly study the effect on the model accuracy of the incorporation of the self-heating effect in the behavioural model description. Finally, we show that this type of models can be accurate at extreme operating conditions, where classical compact models start to fail

Extraction of small-signal model parameters of Si/SiGe heterojunction bipolar transistor using least squares support vector machines

A novel straightforward methodology for extracting bias-dependent small-signal equivalent circuit model parameters (SSECMPs) of silicon/silicon–germanium heterojunction bipolar transistors is presented. The inverse mapping between SSECMPs and scattering (S) parameters is established and fitted using simulated data of the SSECM. Since the problem has large input space, S-parameters at many frequency points, the least squares support vector machines concept is used as regression technique. Physical SSECMPs values are obtained using the proposed methodology. Moreover, an excellent agreement is noted between the S-parameters measurements and their simulated counterpart using the extracted SSECMPs in the frequency range from 40 MHz to 40 GHz at different bias conditions

A stochastic model of irrigation adaptation to climate change in southern Europe

This paper develops a modeling framework that links hydrologic, agronomic, and economic variables within a discrete stochastic programming model. The model is used to analyze climate change adaptation measures in the irrigated agriculture of southern Europe. A wide range of both on-farm and institutional adaptation measures are considered. Results indicate that climate change will have sizable negative impacts on irrigation activities of southern Europe. The severity of these impacts depends on the policy choices and farmers ‟ investment decisions, which are interrelated. Results suggest that adaptation does not necessarily require substantial changes in the current European institutional setting. Rather, the main thrust should be placed on enhancing the adaptive capacity at farm level, and improving farmers ‟ knowledge of climate change impacts for better long-run investment decisions

SIMULTANEOUS SEPARATION AND PRECONCENTRATION OF TRACE AMOUNT OF COPPER, NICKEL, CADMIUM AND ZINC IONS ONTO MODIFIED AMBERLITE XAD-4 LOADED WITH 5-Br-PADAP

In this work, a simple, rapid, selective, sensitive and economical method has been developed for the simultaneous separation and preconcentration of trace amounts of copper, nickel, cadmium, and zinc in aqueous medium using XAD-4 resins that were modified with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as an analytical reagent. The sorption is quantitative in the pH range 7.0-9.5, whereas quantitative desorption occurs instantaneously with 2 M HCl and selected trace elements have been determined using flame atomic absorption spectrometry. The linearity is maintained between 0.04-4.0 mg L-1 for copper, 0.1-4.0 mg L-1 for nickel, 0.02-1.3 mg L-1 for cadmium and 0.01-1.4 mg L-1 for zinc. The detection limits were 12 μg L-1 for Cu(II), 30 μg L-1 for Ni(II), 6 μg L-1 for Cd(II), and 4 μg L-1 for Zn(II) in the final solution. Various parameters such as the effect of pH, flow rate, breakthrough volume and interference of a large number of anions and cations have been studied and the proposed method was used for determination of these metal ions in water and standard samples. In order to compare the proposed method, the actual water samples were analyzed by direct FAAS (using standard addition method). Determination of these metal ions in standard samples confirmed that the proposed method has good accuracy. KEY WORDS: Simultaneous separation and preconcentration, Determination of Cu, Ni, Cd, and Zn, Amberlite XAD-4 resins modified with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), Analytical reagent Bull. Chem. Soc. Ethiop. 2006, 20(1), 1-7

Thalassaemia Intermedia: an Update

Our understanding of the molecular and pathophysiological mechanisms underlying the disease process in patients with thalassaemia intermedia (TI) has substantially increased over the past decade. TI encompasses a wide clinical spectrum of beta-thalassaemia phenotypes. Some TI patients are asymptomatic until adult life, whereas others are symptomatic from as young as 2 years of age. A number of clinical complications commonly associated with TI are rarely seen in thalassaemia major, including extramedullary hematopoiesis, leg ulcers, gallstones, thrombosis and pulmonary hypertension. There are a number of options currently available for managing patients with TI, including transfusion therapy, iron chelation therapy, modulation of foetal haemoglobin production and haematopoietic stem cell transplantation. However, at present, there are no clear guidelines for an orchestrated optimal treatment plan

Electrical and Optical Properties of Flexible Transparent Silver Nanowires electrodes

AgNWs were produced by the one-pot polyol method, and it had been produced by reduction of AgNO3 by ethylene glycol in presence of polyvinylpyrrolidone (PVP) and KCl at high temperature of about 160 oC. AgNWs suspension were purified by centrifuging at 3000 rpm for three times then re-depressed in deionized water with a concentration of 1%. The purified suspension was diluted to different concentrations (2-5) mg. mL-1 using 1% of hydroxy methylcellulose to design different AgNWs transparent conductive films (AgNWs-TCFs). AgNWs suspension inks were coated on the glass and polyethylene terephthalate (PET) substrates. Different AgNWs diameters were obtained by changing the synthesis conditions. It has been observed that the wire diameter will greatly affect both the optical and electrical properties of the obtained AgNWs-TCFs. The best obtained AgNWs-TCFs had high transparency of about 91.5 %, small sheet resistance of about 14 .03 Ω and optical haze less than 2%, which met the requirements for the manufacture of optoelectronic and sensor equipment. Keywords: Silver nanowires, transparent conductive electrode, flexible electrodes, polyol method, AgNWs size control, AgNWs size-dependent and one-pot synthesis

High efficiency supercontinuum generation using ultra-long Raman fiber cavities

Supercontinuum generation in a multi-fiber ultra-long Raman fiber laser cavity is experimentally investigated for the first time. We demonstrate significantly enhanced spectral flatness and supercontinuum generation efficiency using only conventional single mode silica fiber. With a pump power of only 1.63W a ~15dB bandwidth >260 nm wide (from 1440 to >1700nm) supercontinuum source is reported with a flatness of <1dB over 180nm using an optimised hybrid TW/HNLF cavity. We address the dependence of the supercontinuum spectrum on the input pump power and ultra-long Raman cavity