High speed p-type SiGe modulation-doped field-effect transistors

We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (f_T) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (g_m) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K     

Multiplexer model for RTL satisfiability using MILP

New approaches to the satisfiability problem (SAT) for register transfer level (RTL) designs combine arithmetic blocks with Boolean logic to form a mixed integer linear program (MILP). Two-to-one multiplexers with word-level inputs can be decomposed to logic gates, but it is more efficient to describe them in MILP constraints as arithmetic operators. Larger multiplexers are built using a multilevel selection tree. However, such an approach should be improved to optimise the overall efficiency in solving the SAT problem. Proposed is a new MILP model for multiplexers. Experimental results indicate a 50% decrease in the number of constraints and a reduction in MILP complexity from /spl Omega/(N/sup 2.4/) to /spl Omega/(N/sup 1.7/), measured in CPU time.     

Microcrystalline/micromorph silicon thin-film solar cells prepared by VHF-GD technique

Hydrogenated microcrystalline silicon prepared at low temperatures by the glow discharge technique is examined here with respect to its role as a new thin-film photovoltaic absorber material. XRD and TEM characterisations reveal that microcrystalline silicon is a semiconductor with a very complex morphology. Microcrystalline p–i–n cells with open-circuit voltages of up to 560–580 mV could be prepared. “Micromorph” tandem solar cells show under outdoor conditions higher short-circuit currents due to the enhanced blue spectra of real sun light and therefore higher efficiencies than under AM1.5 solar simulator conditions. Furthermore, a weak air mass dependence of the short-circuit current density could be observed for such micromorph tandem solar cells. By applying the monolithic series connection based on laser patterning a first micromorph mini-module (total area of 23.6 cm²) with 9% cell conversion efficiency could be fabricated.     

How many mountains can we mine? Assessing the regional degradation of central appalachian rivers by surface coal mining

Surface coal mining is the dominant form of land cover change in Central Appalachia, yet the extent to which surface coal mine runoff is polluting regional rivers is currently unknown. We mapped surface mining from 1976 to 2005 for a 19,581 km(2) area of southern West Virginia and linked these maps with water quality and biological data for 223 streams. The extent of surface mining within catchments is highly correlated with the ionic strength and sulfate concentrations of receiving streams. Generalized additive models were used to estimate the amount of watershed mining, stream ionic strength, or sulfate concentrations beyond which biological impairment (based on state biocriteria) is likely. We find this threshold is reached once surface coal mines occupy >5.4% of their contributing watershed area, ionic strength exceeds 308 μS cm(-1), or sulfate concentrations exceed 50 mg L(-1). Significant losses of many intolerant macroinvertebrate taxa occur when as little as 2.2% of contributing catchments are mined. As of 2005, 5% of the land area of southern WV was converted to surface mines, 6% of regional streams were buried in valley fills, and 22% of the regional stream network length drained watersheds with >5.4% of their surface area converted to mines.     

The Joint Evaluation Procedure for Active Substances contained in Plant Protection Products within the European Community – 10?Years of the ECCO-Project

Pflanzenschutzmittel müssen seit 1993 in den Mitgliedstaaten der Europ?ischen Gemeinschaft nach der Richtlinie 91/414/EWG des Rates bewertet und zugelassen werden. Das Programm zur Bewertung von alten Wirkstoffen (welche vor Juli 1993 auf dem Markt waren) beinhaltet mehrere Schritte und Stufen, die früher über einen Zeitraum von bis zu 10 Jahren zu bew?ltigen waren; heute sind dafür jedoch 15 Jahre vorgesehen. Das Programm wurde seit 1996 von der Europ?ischen Kommission mit Unterstützung des ECCO-Teams(European Community Co-Ordination) koordiniert. Das ECCO-Team bestand aus zwei Gruppen: eine im Pesticides Safety Directorate – PSD in York (Gro?britannien) und eine im Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL) bzw. vor November 2002 in der Biologischen Bundesanstalt für Land- und Forstwirtschaft in Braunschweig. Sie unterstüzten das Programm zur Bewertung von Wirkstoffen im Namen der Kommission in technischer und administrativer Hinsicht und zeichneten sich insbesondere für das ECCO Peer Review Programm (Expertenprüfungen) verantwortlich. Im November 2003 übernahm die Europ?ische Beh?rde für Lebensmittelsicherheit (EFSA) die Verantwortung für die wissenschaftliche überprüfung der von den Mitgliedstaaten erstellten Bewertungen durch Experten. Das ECCO-Team leistete jedoch weiterhin der Europ?ischen Kommission Unterstützung bei der Durchführung anderer Verfahrensaspekte, vor allem im Bereich der Managementaufgaben der Europ?ischen Kommission. Insgesamt war das Programm au?erordentlich erfolgreich. Es wurden für 162 Wirkstoffen zwischen 1996 und 2003 der Inhalt der von den Mitgliedstaaten erstellten Bewertungsberichte durch eine Expertengruppe diskutiert und füberprüft, was ma?geblich eine Entscheidungsfindung zur Akzeptabilitf?t dieser Wirkstoffe auf Gemeinschaftsebene erm?glicht hat.     

A comparison of physical and chemical properties of milk fat fractions obtained by two processing technologies

Milk fat fractions from supercritical carbon dioxide (SC-CO₂) extraction were compared with commercial melt crystallization (MC) fractions for their physical and chemical properties. The fractions were analyzed for fatty acids, triacylglycerols, cholesterol, total carotenoid content, and volatile compounds. The fractions were also evaluated for solid fat content (SFC) by pulsed nuclear magnetic resonance and thermal profiles by differential scanning calorimeter (DSC). The distribution of fatty acids and triacylglycerols in the fractions depended on the fractionation technique used. SC-CO₂ separated fractions based on molecular weight rather than on melting point, which is the driving force for the MC process. The differences among the fractions were quantified from their SFC and DSC curves. Triacylglycerol profiles by high-performance liquid chromatography showed that the SC-CO₂ fractions were distinctly different from each other and from MC fractions. The SC-CO₂ solid fraction (super stearin) was the most unique. It had a high concentration of long-chain, unsaturated fatty acid-containing triacylglycerols in a narrow range of high molecular weight, indicating a homogeneity of this fraction that has not been attainable by other techniques. It was also enriched in β-carotene and was devoid of volatile compounds. As compared to liquid MC fractions, the liquid SC-CO₂ fraction had a high concentration of low-melting triacylglycerols and was enriched in volatile compounds. With SC-CO₂, it is thus possible to simultaneously fractionate and produce a flavor-rich concentrate at no extra processing cost.     

Micro/nanometric investigations of the effects of laser ablation in the generation of micro-tools from solid CVD diamond structures

Using pulsed laser ablation, a novel method has been successfully developed for the generation of micro-features in diamond thus enabling the production of precision abrasive like micro-cutting elements into solid diamond micro-grinding tools. This paper examines the effects of the laser ablation on the generation of abrasive micro-features in diamond by using electron energy loss spectroscopy (EELS) and transmission electron microscopy (TEM). Site specific specimen preparation by a focus ion beam (FIB) material removal process has been made possible by the application of platinum and tungsten protective layers, providing the necessary specimen surface stability during the ion beam milling and lift-out operations. The prepared thin section orientated orthogonally to the cutting edge of a laser generated abrasive feature, has allowed the identification of the graphite and diamond allotropes across the ablated interface using EELS. A sequence of TEM images has revealed the extent of surface graphitisation and the high integrity of the diamond substructure. TEM examinations at nanometric resolutions have allowed the visualisation of the diamond and graphite allotropes at molecular level while depicting the abrupt graphite to diamond transition resulting in a highly defined boundary, thereby endorsing the capabilities of the laser ablation process to generate cutting edges with minimal structural damage.     

Specular reflection in radiant heat transport across a spherical void

The emissivity factor for radiant heat transport across a spherical void with specular surfaces in a conducting solid is derived. To calculate the emissivity factor, the probability of all possible paths for radiation are formulated and summed. Emissivity factors for the diffuse and specular limits are compared. The resulting temperature dependence of void space radiation for several typical oxide materials is discussed.     

Zero base budgeting for human service agencies

This paper describes the development of a zero base budgeting process as part of an integral planning-budgeting-control system relating client needs with service programs. Particular attention is focused on designing, gaining acceptance for and implementing a new budgeting system for the human services agencies of a rural county government. The relationship of the zero base budgeting process to the client case management and evaluation system are explored. Problems encountered in implementing the system and an evaluation of the results are discussed.