3,664 research outputs found
Modification of the anisotropy and strength differential effect of extruded AZ31 by extrusion-shear
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1960, 030008 (2018) and may be found at https://doi.org/10.1063/1.5034851.The extrusion of magnesium alloys results in a pronounced fiber texture in which the basal planes are mostly oriented parallel and the c-axes are oriented perpendicular to the extrusion direction. Due to this texture the Strength Differential Effect (SDE), which describes the strength difference between tensile and compression yield strength, and the elastic anisotropy in the sheet plane are obtained during extrusion. The objective of the investigation was to decrease the SDE and anisotropy through specifically influencing the microstructure and texture. To accomplish this objective, the forming processes extrusion (EX) and equal channel angular pressing (ECAP) were combined and integrated into one extrusion die. This combination is called extrusion-shear (ES). With an ES-die, billets of the magnesium alloy AZ31B were formed into a sheet with the thickness of 4â
mm and the width of 70â
mm. The angles of the used ECAP-applications in the ES-dies were set to 90° and 135°. The results show that the extrusion-shear process is able to decrease the anisotropy and SDE through transformation of the texture compared to conventional extrusion process. Also grain refinement could be observed. However, the outcomes seem to be very sensitive to the process parameters. Only by using the ES-die with an angle of 135° the desired effect could be accomplished
Brou\'e's abelian defect group conjecture holds for the double cover of the Higman-Sims sporadic simple group
In the representation theory of finite groups, there is a well-known and
important conjecture, due to Brou\'e saying that for any prime p, if a p-block
A of a finite group G has an abelian defect group P, then A and its Brauer
corresponding block B of the normaliser N_G(P) of P in G are derived
equivalent. We prove in this paper, that Brou\'e's abelian defect group
conjecture, and even Rickard's splendid equivalence conjecture are true for the
faithful 3-block A with an elementary abelian defect group P of order 9 of the
double cover 2.HS of the Higman-Sims sporadic simple group. It then turns out
that both conjectures hold for all primes p and for all p-blocks of 2.HS.Comment: 20 pages. arXiv admin note: substantial text overlap with
arXiv:1011.442
Application of Friction Shear Test for Constitutive Modeling Evaluation of Magnesium Alloy AZ31B at high Temperature
The experimental determination of the flow stress and its mathematical formulation are essential for the numerical simulation of metal forming processes. The hot compression test is widely used to analyze the flow stress evolution as function of temperature, strain and strain rate. The compression test is limited to a relative low strain (Δâ€1) which is acceptable when the stress is minor influenced at higher strains. In the case of magnesium alloys the flow stress is strongly influenced by the strain even at high strain (Δ>1). In this work the thermo-mechanical behavior of the magnesium alloy AZ31B was investigated to improve the constitutive modeling up to high strains. Experimental stress-strain curves obtained from hot compression tests at different temperatures (450 °C-550 °C) and strain rates (0.01 1/s â 10 1/s) were applied to construct conventional material models such as those proposed by Garofalo (Zener-Hollomon) and Hensel-Spittel. In addition, shear tests under sticking friction conditions were carried out at high temperature (400 °C-500 °C) and different shear speeds (0.1 mm/s - 10 mm/s). During this test, the thin contact subsurface of cylindrical specimens experiences a high plastic shear deformation, while the axial force and stroke are simultaneously measured. Furthermore, a new constitutive modeling approach was proposed, which combine the Zener-Hollomon model and the experimental result of the friction shear test to estimate the flow stress at low and high strain respectively. Numerical simulations of the friction shear test applying the conventional models as well as the new constitutive formulation are presented in this study
Financing a portfolio of projects
This article shows that investors financing a portfolio of projects may use the depth of their financial pockets to overcome entrepreneurial incentive problems. Competition for scarce informed capital at the refinancing stage strengthens investorsâ bargaining positions. And yet, entrepreneursâ incentives may be improved, because projects funded by investors with ââshallow pocketsââ must have not only a positive net present value at the refinancing stage, but one that is higher than that of competing portfolio projects. Our article may help understand provisions used in venture capital finance that limit a fundâs initial capital and make it difficult to add more capital once the initial venture capital fund is raised. (JEL G24, G31
Book Review: Chorologische Untersuchungen in dem spĂ€tkeltischen Oppidum bei Manching am Beispiel der GrabungsflĂ€chen der Jahre 1965-1967 und 1971: Lorenz Herbert (â ). Chorologische Untersuchungen in dem spĂ€tkeltischen Oppidum bei Manching am Beispiel der GrabungsflĂ€chen der Jahre 1965-1967 und 1971 and Gersden Hermann . FundstellenĂŒbersicht der Grabungsjahre 1961-1974 (Die Ausgrabungen in Manching 16, Römisch-Germanische Kommission des Deutschen ArchĂ€ologischen Instituts zu Frankfurt am Main). 2 volumes: Vol. I, Text- und Tafelband, x+184 pages, 199 figures, 10 tables; Vol. II, 12 folded plans, CD-ROM with 329 pages, 258 tables. 2004. Stuttgart: Franz Steiner; 3-315-08329-4 hardback âŹ96 both volumes
Context modeling and context retrieval in mobile usage scenarios â a framework for context-aware mobile applications
Die fortschreitende Verbreitung drahtloser Kommunikationsnetze sowie immer leistungsfĂ€higerer mobiler Computer schafft ein groĂes Potenzial fĂŒr ein breites Spektrum innovativer Anwendungen. Kontextsensitive Applikationen adaptieren die Gegebenheiten der jeweiligen Situation des Nutzers, wodurch neuartige, intelligente Anwendungen und Benutzungsschnittstellen möglich werden. Die zunehmende Menge verfĂŒgbarer Sensortechniken und die daraus resultierende Vielfalt erfassbarer Kontextinformationen erschweren jedoch vermehrt die Verbreitung dieser Applikationen. Ein Rahmenwerk zur KontextreprĂ€sentation soll die Entwicklung kontextsensitiver Applikationen ohne BerĂŒcksichtigung von Details der Kontexterfassung und -verwaltung ermöglichen. AuĂerdem sollen Austausch und Wiederverwendbarkeit von Kontextinformationen zwischen Applikationen und Nutzern gestattet werden. In dieser Arbeit wird ein solches Rahmenwerk entwickelt. Zu Beginn steht die Untersuchung von Fragen der Kontextmodellierung, auf deren Grundlage anschlieĂend eine Konzeption erarbeitet wird. Der praktische Teil der Arbeit fĂŒhrt eine Referenzimplementation des Systems durch um zu evaluieren, ob die Konzeption auf Basis aktueller Technologien in die RealitĂ€t umgesetzt, und als Grundlage fĂŒr weitere Untersuchungen herangezogen werden kann.The progressive spreading of wireless networks and increasingly powerful mobile computers creates a big potential for a wide spectrum of innovative applications. Context-aware applications adapt the circumstances of the user s current situation which enables new and intelligent user interfaces. Nevertheless, the sheer diversity of exploitable contexts and the plethora of sensing technologies are actually working against the deployment of context-aware systems. A framework for context retrieval should enable the development of context-aware applications without considering details of context acquisition and context management. Moreover, exchange and reusability of context information should be allowed between applications and users. In this work such a framework is developed. At the beginning, an investigation of questions of context modeling is accomplished. After that, a concept is compiled on that foundation. In the practial part of this thesis a reference implementation of the system is conducted to evaluate whether the concept can be put into practice, and be pulled up as a basis for other investigations
Das Jahrbuch ĂŒber die Fortschritte der Mathematik 1869-1904 / Felix MĂŒller. Kurzbiographien der Mitarbeiter und Referenten des Jahrbuchs / Gabriele Dörflinger. Nachruf Max Henoch / Emil Lampe
Felix MĂŒller (1843-1928), der MitgrĂŒnder des Jahrbuchs ĂŒber die Fortschritte der Mathematik referiert ĂŒber die Entstehung und die ersten Jahrzehnte der Referatezeitschrift. Er benennt - meist nur mit Ortsangabe - zahlreiche Referenten und Mitarbeiter des Jahrbuchs.
Die Kurzbiographien von Gabriele Dörflinger skizzieren den beruflichen Werdegang dieser Personen.
Zum Jahrbuch-Herausgeber Max Henoch (1885-1890) existiert nur EINE biographische Quelle, nÀmlich der Nachruf von Emil Lampe. Dieser Nachruf ist als Faksimile beigegeben
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