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101.
K. Brueckner F. Niebelschuetz K. Tonisch Ch. Foerster V. Cimalla R. Stephan J. Pezoldt T. Stauden O. Ambacher M. A. Hein 《physica status solidi (a)》2011,208(2):357-376
Wide‐bandgap semiconductors represent an attractive option to meet the increasing demands of micro‐ and nano‐electromechanical systems (MEMS/NEMS) by offering new functionalities, high stability, biocompatibility and the potential for miniaturization and integration. Here, we report on resonant MEMS and NEMS devices with functional layers of SiC, AlN and AlGaN/GaN heterostructures on different substrates, which have been investigated and analysed in the course of an interdisciplinary research focus programme of the German Research Foundation (DFG). The specific deposition and etching technologies necessary for the three‐dimensional micro‐structuring are explained. Further, the implementation of appropriate electromechanical transduction schemes is discussed. In case of SiC and AlN resonators, actuation and sensing was achieved by a magnetomotive scheme. A piezoelectric coupling scheme where the counter electrode is formed by the two‐dimensional electron gas at the interface of the III/V heterostructure was realized for the AlGaN/GaN resonators. Thus, flexural and longitudinal vibration modes were excited and characterized using electrical and optical techniques. The measured key parameters of resonant frequency and quality factor are related to geometry, material and environmental parameters using analytical and finite element (FE) models. Finally, potential sensor applications are experimentally investigated. 相似文献
102.
Ch. Foerster V. Cimalla K. Brueckner V. Lebedev R. Stephan M. Hein O. Ambacher 《physica status solidi (a)》2005,202(4):671-676
Micromechanical 3C‐SiC‐ and AlN‐resonator beams with resonant frequencies between 20 kHz and 5 MHz have been realized. The 200 nm thin epitaxial SiC and group III‐nitrides layers were grown on silicon (100) and (111) oriented substrates, respectively. Subsequent the beams were dry‐etched by an electron cyclotron resonance (ECR) plasma technique. This new developed plasma based process allows anisotropic as well as isotropic etching for all materials involved. The created freestanding resonator bars have dimensions in the µm to sub‐µm range. The operation principle based on a magneto motive actuation and a thin conductive metal layer on top of the resonator realizes the detection. We present a measurement setup for the electrical characterization of the bars and show coupled beams, to isolate the sensor signal from the excitation signal. Furthermore, we realized beams with a separate read‐out unit (capacitive) as well as resonator structures with separate actuation (piezoelectric) to solve the problems of the superimposition of actuation and detection. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
103.
Ch. Frster V. Cimalla V. Lebedev J. Pezoldt K. Brueckner R. Stephan M. Hein E. Aperathitis O. Ambacher 《physica status solidi (a)》2006,203(7):1829-1833
Micro‐ and nanomechanical AlN and 3C‐SiC resonator beams with resonant frequencies between 20 kHz and 2 MHz, depending on the resonator geometry, have been realized and characterized at ambient conditions. Up to 200 nm thin epitaxial group III‐nitrides and SiC layers were grown on silicon (111) and (100) oriented substrates, respectively. The beams were dry‐etched by an electron cyclotron resonance (ECR) plasma and an inductive coupled plasma (ICP) technique. The freestanding resonator bars have dimensions in the sub‐µm to nm‐range. The operation principle based on the known magneto motive actuation and a thin conductive metal layer on top of the resonator realizes the detection. The main fabrication steps of the resonator beams are presented. The resonant frequencies, the quality factors of the MEMS and NEMS are investigated in dependence on the geometry and the residual strain in the epitaxial layers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
104.
W. Muchlinsky E. Rother G. Jander O. Pfundt E. Göte W. Schramek L. W. Janssen J. A. C. Teegan A. Schleicher W. Lüdicke E. Denina J. M. Preston N. Rae J. K. Rummel K. Schierjott J. M. Kolthoff T. Kameda L. Blumen J. Pucherna Fr. Hein und H. Pauling 《Fresenius' Journal of Analytical Chemistry》1932,89(3-4):128-135
Ohne Zusammenfassung 相似文献
105.
G. Kuhn W. Schreiber J. Plank D. Mc Intosh T. G. Pearson Fr. Hein W. Daniel B. Rassow L. Wolf K. Sarlo H. A. Krebs O. Warburg F. Kubowitz A. Thiel L. Stoll E. M. Emmert D. F. Novotný F. Toul E. W. Alexejewski H. Leroux K. R. Dietrich H. Löffler 《Analytical and bioanalytical chemistry》1932,90(3-4):122-127
106.
Ohne Zusammenfassung 相似文献
107.
The kinetics of chlorine-isotopic exchange between lithium chloride-36 and cyano- and nitro- substituted 2-chloropyridines were measured in sulpholane, acetone or methanol solution. Activating effects of ortho-nitro and ortho-azu substitution are compared: a nitro-group is 50 × as activating as the aza-group in the p-nitrochlorobenzene system, where as it is the aza-function which is 3 times as activating as the nitro group in the o-nitrochlorobenzene system. The effect of Me substituents placed ortho to an activating nitro-group was studied by comparing 2-chloro-3-cyano-5-nitropyridine and its 6-methyl- and 4,6-dimethyl-derivatives. 相似文献
108.
.Prof. Dr. Ing. D. Hein .Dipl.-Ing. W. Kastner .Dipl.-Ing. W. Köhler .Dipl.-Ing. W. Krätzer 《Heat and Mass Transfer》1982,16(4):251-257
Zusammenfassung Werden in einem beheizten Verdampferrohr die Randbedingungen so geändert, daß sich der Ort der Siedekrise in Strömungsrichtung verschiebt, so kann dies vorübergehend zu einer starken Reduktion des Wärmeübergangskoeffizienten im Post-Dryout-Gebiet führen. Es werden die an einem Hochdruckkreislauf gewonnenen zeitlichen Verläufe der Wandtemperaturen analysiert, wie sie bei Absenkung des System-druckes bzw. der Enthalpie der Strömung am Eintritt in das Versuchsrohr auftreten. Anhand der Siedekurve werden die beobachteten Wandtemperaturverläufe interpretiert. Durch Nachrechnung der Experimente mit einem dynamischen Rechen-programm lassen sich die unterschiedlichen Effekte, die während der Transiente auftreten, separieren.
Formelzeichen h Sättigungsenthalpie des Wassers - p Druck - p c kritischer Druck - Q Wärmestrom - q Wärmestromdichte - q1, q2 Wärmestromdichte für Rohrabschnitt l bzw. 2 - t Zeit - x wirklicher Dampfmassenanteil - ¯x bilanzmäßiger Dampfmassenanteil Herrn Prof. Dr.-Ing. U. Grigull zum 70. Geburtstag gewidmet 相似文献
Heat transfer in post-dryout region during transients
A change in the boundary conditions in a heated evaporator tube (moving the location of the boiling crisis downstream) could lead to a strong reduction in the heat transfer coefficient in the Post-Dryout region. The analyzed wall temperature data were obtained in a high pressure test loop by reducing the system pressure, or the enthalpy at the test section inlet. The wall temperature time histories were interpreted using the boiling curve. The various effects occurring during the transient could be separated by recalculating the tests with a dynamic simulation computer program.
Formelzeichen h Sättigungsenthalpie des Wassers - p Druck - p c kritischer Druck - Q Wärmestrom - q Wärmestromdichte - q1, q2 Wärmestromdichte für Rohrabschnitt l bzw. 2 - t Zeit - x wirklicher Dampfmassenanteil - ¯x bilanzmäßiger Dampfmassenanteil Herrn Prof. Dr.-Ing. U. Grigull zum 70. Geburtstag gewidmet 相似文献
109.
Alica Fischle Rico Schwarz Franziska Wendt Marcel Kordt Robert Ramer Lars Boeckmann Martin Hein Peter Langer Steffen Emmert Brigitte Vollmar Burkhard Hinz 《Molecules (Basel, Switzerland)》2022,27(9)
Indirubin was identified as an active component of Danggui Longhui Wan, an herbal mixture used in traditional Chinese medicine, and showed anticancer activity in clinical trials in patients with chronic leukemia. Investigations on the mechanisms of antitumor action of indirubins have mainly focused on the indirubin derivative indirubin-3′-monoxime (I3M). Meanwhile, antiproliferative and cytotoxic properties on cancer cells have also been demonstrated for several synthetic indirubin N-glycosides. In the present study, we demonstrate cytotoxic activity of the thia-analogous indirubin N-glycosides KD87 (3-[3′-oxo-benzo[b]thiophen-2′-(Z)-ylidene]-1-(β-d-glucopyranosyl)-oxindole) and KD85 (3-[3′-oxo-benzo[b]thiophen-2′-(Z)-ylidene]-1-(β-d-mannopyranosyl)-oxindole) against melanoma and squamous cell carcinoma cells as well as lung cancer and glioblastoma cells. The advanced state of preclinical studies on the effects of indirubins conducted to date underscores the need for pharmacokinetic data from cellular, animal, and human studies for which reliable quantification is required. Therefore, a sensitive liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated for the simultaneous measurement of KD87, KD85, and I3M in plasma and cell culture medium. Experimental conditions for sample preparation were optimized for human plasma protein precipitation and liquid-liquid extraction from plasma and cell culture medium. The methods were successfully validated in accordance with the U.S. Food and Drug Administration Bioanalytical Method Validation and evaluated for selectivity, sensitivity, matrix effect, recovery, carryover, calibration curve linearity, accuracy, precision, and stability. The applicability of the methods was demonstrated by the determination of KD87 in mouse plasma after prior intraperitoneal administration to mice. 相似文献
110.
Stefan R. Marsden Dr. Luuk Mestrom Dr. Hein J. Wijma Sander J. Noordam Dr. Duncan G. G. McMillan Prof. Ulf Hanefeld 《ChemCatChem》2021,13(10):2530-2536
Diastereomers are characterised by an intrinsic energy difference, and thermodynamics dictate their distribution within a dynamic equilibrium. The characteristic mechanistic reversibility and non-ideal stereoselectivity of catalysts therefore simultaneously promote both synthesis and epimerization of products during the formation of diastereomers. This feature can even result in the thermodynamic inversion of a chiral centre against the catalyst's stereoselectivity. Here, we provide a comprehensive experimental and theoretical study of factors that govern thermodynamic epimerization in catalysis, using enzymes as example. Our analysis highlights, that the deduction of a catalyst's stereoselectivity based on the absolute configuration of the isolated product constitutes a potential pitfall. The selective formation of either the thermodynamic-, or the kinetic product is less determined by the catalyst, but rather by the reaction conditions. Next to low temperatures, a high maximal extent of conversion was identified to promote kinetically controlled conditions. For bimolecular reactions, conversions can be conveniently modulated via the use of one substrate in excess. Quantum mechanical calculations accurately predicted the diastereomeric excess under equilibrium conditions, which opens the prospect of a rational choice between thermodynamic and kinetic reaction control at an early stage of process design. Our findings are of critical importance for multi-step syntheses of stereocomplex molecules via catalytic cascade reactions or artificial metabolic pathways, as the final stereochemistry may be determined by the absolute configuration of the product that is overall lowest in energy. 相似文献