3,397 research outputs found
E. P. Hoffmann et Robbin F. Laird, The Soviet Polity in the Modern Era
No full textFerro Marc. E. P. Hoffmann et Robbin F. Laird, The Soviet Polity in the Modern Era. In: Annales. Économies, Sociétés, Civilisations. 40ᵉ année, N. 4, 1985. pp. 873-874
Kontrolle der Polarität und Dotierung in Aluminium Gallium Nitrid
No full textAlGaN basierte Laterale Polare Strukturen (LPS) können mit Hilfe der metallorganischen Gasphasenepitaxie gewachsen werden, indem man die c-Achse periodisch invertiert. Derartige Strukturen haben das Potential, um für Frequenzverdopplung von kohärentem Licht in das ultraviolette (UV) Spektralgebiet verwendet zu werden. Weitere Anwendungen liegen im Bereich lateraler p/n-Übergänge. Bezüglich ihrer Herstellung gibt es derzeit noch zwei wesentliche Herausforderungen, die gelöst werden müssen, um das volle Potential des Materialsystems für optoelektronische Bauelemente im UV ausnutzen zu können: (1) In AlGaN kann eine hohe Konzentration von intrinsischen und extrinsischen Störstellen zu einer reduzierten Quanteneffizienz von optischen Bauelementen führen. Dies ist besonders bei höheren Dotierungen der Fall, da es dort zur Selbstko mpensation des Dotanden kommen kann. (2) Werden III- und N-polare Domänen nebeneinanderliegend in einer LPS gewachsen, so wird in der Regel ein Schichtdickenunterschied zwischen den Domänen beobachtet. In der vorliegenden Arbeit wurden beide genannten Herausforderungen detailliert bearbeitet und gelöst. Im Fall von mit Si oder Mg dotiertem AlGaN führen hohe Störstellen-konzentrationen wie Stickstoffvakanzen, H oder O zu hohen Widerständen und einer niedrigen Beweglichkeit der freien Ladungsträger. Diese hohen Konzentrationen werden dadurch erklärt, dass im Bereich hoher Dotierungen die Formierungsenergien dieser S törstellen verringert werden, was zu einem erhöhten Einbau von Kompensatoren führt. Bestrahlt man AlGaN Filme während des Wachstums mit UV-Licht (entsprechend einer Anregungsenergie größer als die Bandlücke), führt dies zu einem verringertem Einbau von Störstellen. So kann z.B. in GaN:Mg eine stark reduzierte blaue Lumineszenz (2.8 eV) gemessen werden, was auf einen verringerten Einbau von Stickstoffvakanzen schließen lässt und zu einem geringerem elektrischen Widerstand führt. Des Weiteren wird im Rahmen dieser Arbeit gezeigt, dass das hier vorgestellte Modell zur Kontrolle des Einbaus von Defekten sowohl für n- als auch p-leitende Halbleiter verwendet werden kann. Die zweite Herausforderung des Schichtdickenunterschiedes der N- und III-polaren Domänen in LPS (2) wird in dieser Arbeit durch einen Oberflächenmassentransport zwischen den polaren GaN Domänen erklärt. Abhängig von der Wachstumsbedingung führt dieser Massentransport zu einem bevorzugten Wachstum jeweils einer polaren Domäne. Folglich konnten aber auch Bedingungen gefunden werden, in denen die Wachstumsrate der Domänen identisch ist und hoch qualitative AlGaN LPS mit Mikrometer großen Domäne n gewachsen werden. Abschließend wurden die Erkenntnisse aus (1) und (2) kombiniert und verbesserte elektrische und optische Eigenschaften lateraler p/n Übergänge nachgewiesen, wenn diese mit UV-Licht während des Wachstums bestrahlt wurden. Beides, sowohl die Störstellenkontrolle mittels UV-Bestrahlung als auch die Kontrolle der N- und III-polaren Domänen in LPS, wurde nie zuvor demonstriert und eröffnen einzigartige neue Möglichkeiten.AlGaN can be used for the fabrication of lateral polar structures (LPS) by a periodic inversion of the c-axis as achieved by a polarity control scheme during its growth by metal organic chemical vapor deposition (MOCVD). These structures can be used for second harmonic generation in the ultraviolet spectral region, as well as for lateral p/n-junctions. The two major challenges addressed in this work exist in the general implementation of the AlGaN technology and in the fabrication of AlGaN LPS, and both prevent the realization of AlGaN UV-emitters. These challenges are: (1) the presence of a high concentrations of native defects and extrinsic impurities in AlGaN that can reduce the efficiency of optoelectronic devices, especially in the case of high doping with Mg or Si, and (2) as typically observed, a growth rate difference that exists during the simultaneous growth of III- and N-polar domains adjacent to each other in a LPS.
In this dissertation, solutions to these two challenges are based on two novel and original approaches involving (1) Fermi-level point defect control schemes, and (2) mass transport control between polar domains. In approach (1), the control of point defects and reduction of compensations, VN, H or O are identified as the cause of high resistivity and low mobility in AlGaN due to their low formation energies at high Mg or Si doping concentrations. To confirm and quantify the Fermi-level point defect control scheme, above bandgap illumination during the growth of GaN was demonstrated to control the incorporation of these defects. Significant reductions in the point defect were achieved as evidenced by changes in their corresponding luminescence, for example, the blue luminescence at 2.8 eV (VN-related). Additionally, reduced resistivity and atomic concentrations, such as an order of magnitude lower H concentration, were observed. These studies confirm that the point defect management scheme developed in this work can control compensation in n-type as well as in p-type semiconductors.
In approach (2), mass transport control between polar domains, the surface mass transport between differently oriented domains was determined to be a function of the Ga supersaturation. Using Ga supersaturation as a control, a condition where identical growth rates for both polarities was obtained and high quality AlGaN LPS with domains in the micrometer scale could be fabricated. Furthermore, the first AlN LPS was grown and studied. Finally, the utility of these two new approaches was demonstrated by fabricating an AlGaN lateral p/n-junction that exhibited a marked decrease in compensation effects within each particular domain.
Both point defect control via above bandgap illumination, as well as the control of the growth rate difference of LPS, will have considerable impact on the field of III-V-nitrides as these novel approaches will potentially facilitate a new class of devices in the future
Correlations between phylogenomics and secondary metabolite production in the Hypoxylaceae and other families of the Xylariales
No full text<p>Plenary lecture by Marc Stadler, AMC 2023, Busan, Korea</p>
DS_10.1177_0363546518788355 – Supplemental material for Stabilization of Acute High-Grade Acromioclavicular Joint Separation: A Prospective Assessment of the Clavicular Hook Plate Versus the Double Double-Button Suture Procedure
No full textSupplemental material, DS_10.1177_0363546518788355 for Stabilization of Acute High-Grade Acromioclavicular Joint Separation: A Prospective Assessment of the Clavicular Hook Plate Versus the Double Double-Button Suture Procedure by Thomas Stein, Daniel Müller, Marc Blank, Yana Reinig, Tim Saier, Reinhard Hoffmann, Frederic Welsch and Uwe Schweigkofler in The American Journal of Sports Medicine</p
sj-docx-1-tan-10.1177_17562864231213240 – Supplemental material for Guideline for the management of myasthenic syndromes
No full textSupplemental material, sj-docx-1-tan-10.1177_17562864231213240 for Guideline for the management of myasthenic syndromes by Heinz Wiendl, Angela Abicht, Andrew Chan, Adela Della Marina, Tim Hagenacker, Khosro Hekmat, Sarah Hoffmann, Hans-Stefan Hoffmann, Sebastian Jander, Christian Keller, Alexander Marx, Arthur Melms, Nico Melzer, Wolfgang Müller-Felber, Marc Pawlitzki, Jens-Carsten Rückert, Christiane Schneider-Gold, Benedikt Schoser, Bettina Schreiner, Michael Schroeter, Bettina Schubert, Jörn-Peter Sieb, Fritz Zimprich and Andreas Meisel in Therapeutic Advances in Neurological Disorders</p
AJR912362 Supplemental Material - Supplemental material for Symptom Control of Patients With Chronic Rhinosinusitis With Nasal Polyps Under Maintenance Therapy With Daily Acetylsalicylic Acid
No full textSupplemental material, AJR912362 Supplemental Material for Symptom Control of Patients With Chronic Rhinosinusitis With Nasal Polyps Under Maintenance Therapy With Daily Acetylsalicylic Acid by Janina Hahn, Heike Appel, Marc O. Scheithauer, Florian Petereit, Jens Greve, Jörg Lindemann, Thomas K. Hoffmann, Johannes A. Veit and Fabian Sommer in American Journal of Rhinology & Allergy</p
Pulse length and amplitude dependent resistive switching mechanisms in Pt-Pr0.67Ca0.33MnO3-Pt sandwich structures
No full textWe report here on the presence of two different nonvolatile resistive switching mechanisms in Pt-Pr0.67Ca0.33MnO3-Pt sandwich structures based on pulsed electrical transport measurements. As a function of pulse length, amplitude and temperature, the devices show two different switching regimes. The first is positive switching (PS) where a high resistance state (HRS) evolves at positive bias at the top electrode in the voltage range of U approximate to 0.5-1.2 V and pulse lengths t(p) approximate to 10(-7) s. In addition, we observe a cross over to negative switching (NS) for U > 1 V and t(p) approximate to 10(-3) s. Here, the HRS evolves at negative bias applied at the top electrode. We present strong evidence that both switching mechanisms take place at the interface between Pr0.67Ca0.33MnO3 and the top electrode. Based on finite element simulations of the temperature evolution during the electrical pulses, we show that the onset of Joule heating is characteristic of the PS regime, whereas drastic temperature increases of several hundred Kelvin evolve during NS. Based on the observed different timescales, pulse amplitudes and temperature dependences of PS and NS, respectively, we suggest that two different switching mechanisms are involved: a fast, short range exchange of oxygen at the interface with the metallic electrode for PS and a slower, long range redistribution of oxygen in the entire PCMO film for the NS.Open Access Publikationsfonds 201
Molecular mechanism of inhibiting the SARS-CoV-2 cell entry facilitator TMPRSS2 with camostat and nafamostat
No full textThe entry of the coronavirus SARS-CoV-2 into human lung cells can be inhibited by the approved drugs camostat and nafamostat. Here we elucidate the molecular mechanism of these drugs by combining experiments and simulations. In vitro assays confirm that both drugs inhibit the human protein TMPRSS2, a SARS-Cov-2 spike protein activator. As no experimental structure is available, we provide a model of the TMPRSS2 equilibrium structure and its fluctuations by relaxing an initial homology structure with extensive 330 microseconds of all-atom molecular dynamics (MD) and Markov modeling. Through Markov modeling, we describe the binding process of both drugs and a metabolic product of camostat (GBPA) to TMPRSS2, reaching a Michaelis complex (MC) state, which precedes the formation of a long-lived covalent inhibitory state. We find that nafamostat has a higher MC population than camostat and GBPA, suggesting that nafamostat is more readily available to form the stable covalent enzyme-substrate intermediate, effectively explaining its high potency. This model is backed by our in vitro experiments and consistent with previous virus cell entry assays. Our TMPRSS2-drug structures are made public to guide the design of more potent and specific inhibitors
Metadata initiatives and emerging technologies to improve resource discovery
No full textThis paper discusses some emerging issues on metadata as a mechanism of resource discovery and its impact on precision of search results in a distributed network environment. It presents a brief account of the recent major developments related to metadata across the globe. Highlights a consistent growth of multiple metadata standards to meet the variety of needs in a hierarchy of complexity. Examines various metadata-harvesting tools and related technologies that fulfill the task implicit in a user’s search. Brings out popular standards, useful protocols, and open-source harvesters along with their intrinsic capabilities for harvesting and presenting metadata and introduces a variety of metadata services viz., OCLC’s catalogue service, UKOLN metadata editor service, OAIster harvester service, DP9 gateway service, etc. explores the underlying principles of metadata-harvesting in DSpace and web search engines. Discusses use of multiple metadata formats in DSpace archives for exposing domain-specific metadata; and the inherent mechanism for extensibility and interoperability functions. Proposes methods for creating metadata that can pursue high-precision document retrieval in dynamic collections. Also discuses semantic web technologies and use of specialized metadata for long-term management and preservation of digital objects
Equilibrium transition study for a hybrid MAV
No full textWind tunnel testing was performed on a VTOL aircraft in order to characterize longitudinal flight behavior during an equilibrium transition between vertical and horizontal flight modes. Trim values for airspeed, pitch, motor speed and elevator position were determined. Data was collected by independently varying the trim parameters, and stability and control derivatives were identified as functions of the trim pitch angle. A linear fractional representation model was then proposed, along with several methods to improve longitudinal control of the aircraft
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