Origin of Low-Frequency Negative Transconductance Dispersion in p-HEMT

Measurements of low-frequency transconductance dispersion at different temperatures and conductance deep level transient spectroscopic(CDLTS) studies of an AlGaAs/InGaAs pseudomorphic HEMT were carried out. The experimental results show the presence of defect states at the AlGaAs/InGaAs hetero-interface. A mobility degradation model was developed to explain the low frequency negative transconductance dispersion as well as the apparent hole-like peaks observed in the CDLTS spectra. This model incorporates a time dependent change in 2DEG mobility due to ionised impurity scattering by the remaining charge states at the adjoining AlGaAs/InGaAs hetero-interface

Quantum Transport in Semiconductor Nanostructures

I. Introduction (Preface, Nanostructures in Si Inversion Layers, Nanostructures in GaAs-AlGaAs Heterostructures, Basic Properties). II. Diffusive and Quasi-Ballistic Transport (Classical Size Effects, Weak Localization, Conductance Fluctuations, Aharonov-Bohm Effect, Electron-Electron Interactions, Quantum Size Effects, Periodic Potential). III. Ballistic Transport (Conduction as a Transmission Problem, Quantum Point Contacts, Coherent Electron Focusing, Collimation, Junction Scattering, Tunneling). IV. Adiabatic Transport (Edge Channels and the Quantum Hall Effect, Selective Population and Detection of Edge Channels, Fractional Quantum Hall Effect, Aharonov-Bohm Effect in Strong Magnetic Fields, Magnetically Induced Band Structure).Comment: 111 pages including 109 figures; this review from 1991 has retained much of its usefulness, but it was not yet available electronicall

Identification of phospholipase B from Dictyostelium discoideum reveals a new lipase family present in mammals, flies and nematodes, but not yeast

The social amoeba Dictyostelium discoideum exhibits high activities of phospholipase and lysophospholipase [Ferber, Munder, Fischer and Gerisch (1970) Eur. J. Biochem. 14, 253–257]. We assayed Dictyostelium lysates to demonstrate the presence of a highly active phospholipase B (PLB) enzyme that removed both fatty-acid chains from phosphatidylcholine and produced the water-soluble glycerophosphorylcholine. We purified the PLB activity from Dictyostelium cytosol using standard agarose media (size exclusion and ion exchange), and combined this with an affinity purification step using myristoylated ARF1 (ADP-ribosylation factor 1), a protein which has a single fatty acid at its N-terminus. Two proteins co-purified (48 kDa and 65 kDa), and the 48 kDa protein was digested with trypsin, peptide fragments were separated by reverse-phase chromatography, and the resultant peptides were sequenced by Edman degradation. From the peptide sequences obtained, database searches revealed a gene which encodes a protein of 65 kDa with unknown function. The 48 kDa protein therefore appears to be a fragment of the full-length 65 kDa product. Expression of the gene in Escherichia coli confirmed that it encodes a PLB. Characterization of its substrate specificity indicated that, in addition to phosphatidylcholine deacylation, the enzyme also hydrolysed phosphatidylinositol and phosphatidylethanolamine. The PLB identified in the present study is not related to existing PLBs found in bacteria, fungi or mammals. There are, however, genes similar to Dictyostelium PLB in mammals, flies, worms and Giardia, but not in yeast. We therefore have identified a novel family of intracellular PLBs

High gain low noise TEGFET devices for 18-40~GHz use

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