MBE growth and electrical behaviour of single and double Si δ-doped InGaAs-layers

The use of δ-doping to form the channel of a field-effect transistor (FET) was proposed earlier to give better pinch-off behaviour, higher transconductance, and high drain-gate breakdown voltages compared to a uniformly doped channel layer. In the present work δ-doping of InGaAs MBE grown layers using Si is investigated. Furthermore, the design of an improved δ-doped JFET is proposed which comprises double δ-doped atomic planes within the channel layer to increase the effective carrier mobility and saturated drift velocity. Consequently higher transconductance and frequency limits are expected. Reduced sheet resistance values have been measured in double δ-doped channels compared to single δ-doped channels comprising the same sheet concentration.     

Fabrication and characterization of zirconia-toughened alumina obtained by inorganic and organic precursors

In zirconia-toughened alumina (ZTA) the martensitic transformation of zirconia (tetragonal→ monoclinic) is at the origin of toughening. If the zirconia particles have a mean grain size less thand’ _c, they remain tetragonal; if their size is betweend’ _c andd _c (d _c>d’ _c), they are stress-induced transformed into the monoclinic form; if their size is larger thand _c, particles are transformed. We prepared ZTA using different precursors and compared their microstructures. The coprecipitation of aluminium and zirconium chlorides gives an hydroxide mixture. Thus the zirconium hydrate is amorphous, and the aluminium hydroxide structure varies with the precipitation temperature and pH values at the end of the neutralization. Alumina is mixed with zirconia obtained by gas-phase reaction. Zirconia is prepared by vaporization of zirconium chloride in an oxygen-hydrogen flame. Alumina powder is impregnated by a zirconium acetate solution. Zirconium acetate is thermally decomposed in a spray-dryer, then by calcination. The cohydrolysis of II Al-butoxide and IV Zr-propoxide was carried out in an alkaline solution. The hydrolysis pH (10 or 12) changes the grain size of the oxide powders. Mechanical property measurements and microstructural analysis allow a comparison of the different composites. The mean grain-size evolution differs according to the preparative route, and may be varied by different elaboration parameters. Fine microstructures were always observed. The mean grain size of dispersed zirconia being very small (neard’ _c), we observed a little influence of transformation toughening. We noticed a large increase in rupture strength, while toughness was not noticeably improved.     

Electron-microscopic examination of silicon-carbide-coated endovascular stents

The problem of restenosis in blood vessels after balloon angioplasty could not be overcome by the use of metallic stents as had been anticipated. With respect to restenosis, clinical and experimental results now focus the attention on the risk that stents could initiate or potentiate vascular lesions, especially by inhomogenous stent expansion. Here the stent design seems to dominante depending on the use of well rounded structural stent-elements with appropriate surfaces and a material deposition which is compatible with a homogeneous stent expansion. With respect to hemocompatibility the surface quality of the stents is of great importance, too. Coating of surfaces of metallic stents for the enhancement of hemocompatibility might create new risks of blood vessel damages and requires a careful consideration of the co-expansional behaviour of the metallic substrate and the coating material. With these problems in mind the surface coated stent Tensum 3 of the Biotronik company was investigated.     

The elastic behaviour of Ce3S4 and La3S4

The hydrostatic pressure and temperature dependences of the elastic stiffnesses of the cubic, Th₃P₄ structure compounds Ce₃S₄ and La₃S₄ have been measured using the ultrasonic pulse echo overlap technique. Although Ce₃S₄, unlike La₃S₄ (T _c = 103 K), does not undergo a phase transition when its temperature is lowered to 16 K, its elastic stiffnesses (C₁₁-C₁₂)/2 and C₁₁ soften with decreasing temperature (in a similar manner but less markedly than those of La₃S₄); this lattice instability indicates an incipient phase transition. In both compounds the elastic constants increase under pressure: the long-wavelength acoustic-mode Grüneisen parameters are all positive, and the application of pressure does not induce acoustic phonon-mode softening.     

Recovery of gene function by gene duplication in Saccharomyces cerevisiae

A prototroph revertant (Rev9) selected from an ATCase^? mutant of the URA2 gene containing three nonsense mutations was shown to contain two ATCase coding sequences. We cloned both ATCase coding areas to show that the duplicated locus (dl9) was the only functional one. Its size corresponded roughly to the second half of the URA2 wild-type gene. Sequence analysis of the 5′ end of dl9 indicated that this duplicated sequence was inserted within the intergenic region close to the MRS3 gene and was transcribed from an unknown promoter divergently from the MRS3 gene. The event leading to the revertant strain Rev9 included a rearrangement that increased the size of chromosome X by about 60 kb. In agreement with such a rearrangement, recombination was undetectable in the vicinity of the locus dl9. Genetic mapping confirms that the MRS3 gene is 2 cM distal to the URA2 gene on the right arm of chromosome X.     

Einsatz der BiCMOS-Technik bei Operationsverstärkern mit extrem neidriger Versorgungsspannung

Übersicht Der Einsatz der BiCMOS-Technik bei Niederspannungs-Operationsverstärkern wird im Überblick betrachtet, wobei Eingangsstufe, die zweite Verstärkerstufe, Ausgangsstufen sowie ein Spannungsgenerator angesprochen werden. Die Nachteile von Rail-to-rail Eingangsstufen aus komplementären Differenzverstärkern werden diskutiert. Eine mit Hilfe von einer chipintern erzeugten Hilfsspannung aufgebaute Eingangsstufe mit verbesserter Performance wird vorgestellt. Problempunkte von Rail-to-rail Ausgangsstufen in Class-AB Technik sowie der Verfahren zur Regelung des Querstromes werden erläutert. Eine Rail-to-rail Spannungsfolger-Ausgangsstufe mit Hilfsspannungsversorgung des Bias-Zweiges wird vorgestellt. Nachdem der Aufbau des Spannungsvervielfachers betrachtet wurde, wird eine Operationsverstärkerschaltung vorgestellt, in der die diskutierten Teilschaltungen zum Einsatz kommen.

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Use of BiCMOS-techniques in low-voltage operational amplifiers

Contents We will present an overview of the use of BiCMOS-Techniques in low-voltage operational amplifiers. Focus will be on input-, intermediate-and output-stages as well as on a voltage generator circuit. The disadvantages of rail-to-rail input-stages built of complementary differential amplifiers will be discussed. An input-stage with improved performance, that uses an on-chip generated additional voltage, will be shown. The drawbacks of rail-to-rail class-AB output-stages and methods to control the quiescent current will be considered. A rail-to-rail voltage-follower output-stage using the generated additional voltages for biasing will be proposed. The on-chip voltage generator will be presented. Finally, we will direct toward to total circuit of the proposed low-voltage operational amplifier.

     

Nephrotoxicity of cyclosporine in humans: effect of cyclosporine on glomerular filtration and proximal tubular reabsorption

The chronic nephrotoxic effects of cyclosporine (CsA) include proximal tubular atrophy and vacuolization. This study investigated the effect of CsA on renal hemodynamics and segmental electrolyte transport in CsA-treated patients. The clearance of inulin (CIn) and PAH para-amino-hippuric acid (CPAH) was determined; proximal tubular function was studied using a lithium clearance method and calculating tubular phosphate reabsorption per milliliter of glomerular filtrate (TP/CIn). Twenty patients without renal disease were investigated: ten treated with CsA because of nonrenal grafting (group 1) and ten healthy volunteers (group 2). The results obtained were compared with those from 20 renal allograft recipients, of whom ten were treated with CsA and methylprednisolone (group 3) and ten with azathioprine and methylprednisolone (group 4). CIn and CPAH were significantly impaired in patients treated with CsA. No significant impairment of lithium clearance as induced by CsA was observed. The fractional excretion of lithium was slightly increased in patients treated with CsA compared to their respective controls. TP/CIn was lower in graft recipients compared to controls; no impairment of phosphate reabsorption as induced by CsA was found. The fractional tubular excretion of lithium was slightly increased compared to controls, rising evidence that proximal tubular reabsorption of lithium was decreased. Tubular reabsorption of phosphate was not impaired. The decrease in glomerular filtration and renal perfusion during chronic treatment with CsA was accompanied by a reduced proximal reabsorptive capacity, as was shown by lithium clearance. Our data do not support the hypothesis that functional parameters of the proximal tubular system can be used as indicators of CsA-induced nephrotoxicity.     

Identification of mimicry peptides based on sequential motifs of epitopes derived from 65-kDa glutamic acid decarboxylase

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease with a predominantly non-hereditary etiology that results in a destruction of pancreatic beta cells by autoaggressive T lymphocytes. Neither the mechanism of initial stimulation of these T cells nor the nature of the environmental factors implicated in the disease have so far been identified. However, both issues are taken into account by the hypothesis of initial T cell activation by viral or bacterial mimicry peptides with sequence similarities to pancreatic self antigens. We determined sequential epitope motifs to search for mimicry peptides stimulating T cell lines specific for two epitopes derived from the IDDM autoantigen 65-kDa glutamic acid decarboxylase (GAD65). These were GAD65 (88-99), presented by HLA-DRB1*0101, and GAD65 (248-257), presented by HLA-DRB5*0101. T cell stimulation by peptides with substitutions in HLA anchor or T cell contact positions was analyzed to establish degenerate epitope motifs for database searching. Out of 28 tested candidate mimicry peptides derived from bacterial, viral and human proteins, 3 stimulated T cell lines and a T cell clone specific for epitope GAD65 (248-257). Our results demonstrate that mono- and polyclonal GAD65-specific T cells from IDDM patients can be stimulated by viral and bacterial peptides with little apparent sequence homology with autoantigenic epitopes. Moreover, in a synopsis with related published studies, our findings suggest that simple degenerate search motifs comprising principal T cell contacts plus HLA class II binding motifs may suffice to identify most mimicry peptides.