We present a new approach of back gate patterning that is compatible with the requirements of highest mobility molecular beam epitaxy. Contrary to common back gating techniques, our method is simple, ...reliable and can be scaled up for entire wafers. The back gate structures are defined by local oxygen implantation into a silicon doped GaAs epilayer, which suppresses the conductance without affecting the surface quality.
We describe the operation of a semiconductor-superlattice parametric oscillator (SPO) at a subterahertz frequency (near 300 GHz). The oscillator is driven by a microwave source (frequency near 100 ...GHz). We also present an analysis indicating that operation at frequencies above 1 THz should be possible. The SPO is based on the ability of conduction electrons in a superlattice to perform Bloch oscillations. Broadband tunability as well as the monochromacy of a driving microwave field are transferred to the SPO.
Structural changes in resistance vessels have been considered an important factor in triggering and maintaining chronic hypertension in humans and in experimental animals. To determine whether the ...increased forearm vascular resistance observed following vasodilator maneuvers in hypertensive patients is predominantly due to structural or to functional changes, we examined the influence of different vasodilator stimuli on forearm blood flow and blood pressure in 22 male patients with established essential hypertension and in 22 age-matched normotensive men (age range, 28–52 years). Blood pressure was measured directly, and blood flow was measured by venous occlusion plethysmography. The maneuvers applied were 1) arterial occlusion combined with handgrip exercise and local heating, 2) intra-arterial infusion of the calcium entry blocker nifedipine, 3) intra-arterial infusion of the nonspecific vasodilator sodium nitroprusside, 4) arterial occlusion initiated after intraarterial infusion of nifedipine. Vascular resistance during vasodilation induced by arterial occlusion or infusion of nifedipine or sodium nitroprusside remained significantly higher in the hypertensive than in the normotensive subjects. However, the maximal vasodilation achieved by the combination of arterial occlusion and nifedipine resulted in a similar resistance in both groups (1.6 ± 0.2 in the hypertensive vs 1.4 ± 0.2 nun Hg/ml/min/100 ml tissue in the normotensive subjects). These data suggest that there is an important functional component of the elevated resistance in patients with essential hypertension.
Global Optimization of HPLC Separations Lankmayr, Ernst P.; Wegscheider, Wolfhard; Budna, Karl W.
Journal of liquid chromatography,
19/1/1/, Letnik:
12, Številka:
1-2
Journal Article
A method suitable for automated optimization of HPLC separations is developed. A sequential strategy based on a non-linear interpolation between measured retention data permits a stepwise ...approximation to a global optimum. This scheme provides a smooth representation of the elution behaviour from an unspecified number of regularly or irregularly spaced data points. The accuracy of the so defined curves can be gradually improved by successive addition of new experimental data as they become available. It is possible, therefore, to employ variables yielding multimodal response hypersurfaces in the optimization work. Further emphasis is given to an individual weighting of all detectable compounds with respect to their analhtical relevance. Examples including an isocratic separation of fat soluble vitamins as well as gradient separations of dansylated amino acids and steroid hormones demonstrate some applications of the proposed procedure.
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