Asymptotic Analysis of the Current-Voltage Curve of a pnpn Semiconductor Device

We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure.     

Stage effects of negative emotion on spatial and verbal working memory

Background  

The effects of negative emotion on different processing periods in spatial and verbal working memory (WM) and the possible brain mechanism of the interaction between negative emotion and WM were explored using a high-time resolution event-related potential (ERP) technique and time-locked delayed matching-to-sample task (DMST).     

Plasmapolymerisierte Organosilane – Photolumineszenz,Infrarotabsorption und Struktur

Plasma Polymerized Organosilanes – Photoluminescence, Infrared Absorption and Structure The structure of amorphous hydrogen‐containing silicon‐carbon thin films (a‐Si_1–xC_x : H) is difficult to access as known for disordered materials. In this paper we attempt to develop structure models for a‐Si_1–xC_x : H from photoluminescence and infrared transmission, and to support these models through molecular dynamic and LCAO calculations. The modelling is further based on the knowledge of the starting materials in the plasma.     

Rare earth element (REE) in surface mangrove sediment by instrumental neutron activation analysis

A study is carried out on the concentrations of rare earth element (REE) elements present in surface mangrove sediments from 10 locations throughout west coast Malaysia. In carrying out the analysis, the best and most convenient method being the instrumental neutron activation analysis (INAA). Samples were obtained, dried, crushed to powdery form and samples prepared for INAA. All the samples for analysis were weighted approximately 150 mg for short irradiation and 200 mg for long irradiation time. As calibration and quality control procedures, blank samples, standard reference material SL-1 were then irradiated with thermal neutron flux of 4 × 10¹² cm^?2 s^?1 at the MINT TRIGA Mark II research reactor which operated at 750 kW by using a pneumatic transport facility. The REE elements of surface sediment samples in this study are Dy, Sm, Eu,Yb, Lu, Tb, La and Ce. It was found that the level of concentrations of all the REE elements varies in the range (0.35–117.4 mg/kg). The geochemical behavior of REEs in surface sediments and normalized pattern (chondrite and shale) has been studied. The degree of sediments contaminations were computed using an enrichment factor. The results showed that the enrichment factor varied in the range (0.75–6.75).     

Are nuclei withN∼43 deformed?

The level schemes of⁷⁵Se and⁷⁹Kr have been established through gamma ray and conversion electron spectroscopy following⁷⁵As (p, nγ ^?e) and⁷⁹Br (p, nγe^?) reactions. The data on these nuclei and the nuclei in the neighbourhood of this mass region are discussed and evidence is presented to show that the nuclei withN～43 are deformed.     

New HPLC methods for analysing α-and β-emitters as part of destructive testing of low- and intermediate-level waste

Low- and intermediate-level waste is frequently supercompacted or solidified in cement for final disposal. In waste characterisation matrix problems arise in analysing the drum content by chromatographic methods. The cations from the cement occupy the capacity of the column and no separation of the analytes takes place. By a selective complexation the analytes get separated from the matrix. The analytes Pb, Ni, Co and Se are bound by sodiumdiethyldithiocarbamate (NaDDTC) as complexes on a precolumn and subsequently separated on a reversed-phase column. Detection is performed by a UV/VIS spectral range detector and a liquid scintillation detector (Pb-210, Ni-63, Co-60) in series. Received: 15 July 1997 / Revised: 19 December 1997 / Accepted: 23 December 1997     

Conformational restriction of nucleosides by spirocyclic annulation at C4' including synthesis of the complementary dideoxy and didehydrodideoxy analogues

The concept of spirocyclic restriction, when generically applied to nucleoside mimics, allows for the preparation of diastereomeric pairs carrying either a syn- or anti-oriented hydroxyl at C-5'. Reported herein are convenient synthetic routes to enantiomerically pure 1-oxaspiro[4.4]nonanes featuring fully dihydroxylated end products as well as congeners having dideoxy and didehydrodideoxy substitution patterns. Notable use is made of the capacity for introducing unsaturation in the furanose sector via phenylsulfenylation and the incorporation of uracil and thymine by way of their silylated derivatives under catalysis with stannic chloride.     

An efficient preparation of beta-aryl-beta-ketophosphonates by the TFAA/H3PO4-mediated acylation of arenes with phosphonoacetic acids

Beta-aryl-beta-ketophosphonates can be efficiently prepared in good yield by using a TFAA/85% H 3PO 4-mediated acylation of electron-rich arenes with phosphonoacetic acids. The conditions offer advantages over existing methods of preparing these useful compounds by not requiring the use of strong base, cryogenics, or an anhydrous and inert atmosphere. Furthermore, some functional groups not tolerated with the reaction conditions used in existing methods are compatible with the herein described conditions.     

Fabrication of semiconductor-and polymer-based photonic crystals using nanoimprint lithography

The technology of fabricating photonic crystals with the use of nanoimprint lithography is described. One-and two-dimensional photonic crystals are produced by direct extrusion of polymethyl methacrylate by Si moulds obtained via interference lithography and reactive ion etching. The period of 2D photonic crystals, which present a square array of holes, ranges from 270 to 700 nm; the aperture diameter amounts to the half-period of the structure. The holes are round-shaped with even edges. One-dimensional GaAs-based photonic crystals are fabricated by reactive ion etching of GaAs to a depth of 1 μm through a mask formed using nanoimprint lithography. The resulting crystals have a period of 800 nm, a ridge width of 200 nm, and smooth nearly vertical side walls.     

1-Oxaspiro[4.4]nonan-6-ones. Synthetic access via oxonium ion technology, optical resolution, and conversion into enantiopure spirocyclic alpha,beta-butenolides

A general approach to the synthesis of enantiomerically pure spirocyclic alpha,beta-butenolides is presented where the fundamental framework is rapidly elaborated by acid- or bromonium ion-induced rearrangement of the carbinol derived by addition of 2-lithio-4,5-dihydrofuran to cyclobutanone. Subsequent resolution of the resulting ketones by either sulfoximine or mandelate acetal technology has been applied effectively. The availability of these building blocks makes possible in turn the acquisition of the enantiomers of dihydrofurans typified by 17, 35, and 38 and lactones such as 25 and 31, as well as the targeted title compounds. Complementary reductions of the early intermediates provide the added advantage that the alpha- and beta-stereoisomeric carbinol series can be obtained on demand. These capabilities have been coordinated to allow the crafting of any member of the series in relatively few steps.