Peierls-Nabarro hardening in the presence of point obstacles

In light of the controversy that has existed between proponents of Peierls-Nabarro hardening and dispersed barrier hardening with regard to possible low temperature deformation mechanisms in bee and hep metals, this paper examines the effect of point obstacles on Peierls-Nabarro hardening. The statics of double kink nucleation over Peierls barrier on finite dislocation segments are studied in detail. Point obstacles such as interstitial impurity atoms are considered to limit the length of the dislocation segments. Adopting the rate theory approach, temperature dependence of the yield stress is then investigated as a function of the concentration of point obstacles. It is found that point obstacles have little or no effect on double kink nucleation processes, when the applied stress is near the Peierls stress or at low test temperatures. At lower applied stresses or at higher test temperatures, the present results are significantly different from predictions of the Dorn-Rajnak calculation. In the present theory, the applied stress on the dislocation, τ, is found to be finite and independent of test temperature in dilute solid solutions at elevated temperatures where the Dorn-Rajnak theory predicts vanishing τ. This apparent “athermal” component of τ increases linearly with the concentration of point obstacles, whereas temperature dependent part of τ decreases. These predictions are consistent with experimental observations on iron-base alloys.     

Mechanism of Work-hardening for Austenitic Manganese Steel under Non-severe Impact Loading Conditions

The effect of C,Mn and heat-treatment onwork-hardening of austenitic Mn steel and thework-hardening mechanism have been investigatedunder non-severe impact loading condition.Theresults show that the ability of work-hardening in-creases with the increase of C and aging tempera-ture but decreases with Mn.The work-hardeningwith high austenitic stability results mainly fromdislocations,and that with low austenitic stabilityresults mainly from combined effects of strain-in-duced martensite and high density of dislocationsunder non-severe impact loading conditions.Thewear resistance of medium manganese steel (Mn7)is 1.64-2.46 times that of Hadfield steel (Mnl3).     

Synthesis of bulk and reinforced

Preforms of nickel powder or nickel/alumina powder blends were infiltrated with molten aluminum to produce nickel aluminides. Application of a pressure of 3.6 and 6.9 MPa on the melt allowed infiltration of preforms with nickel powder particles between 5 and 15 μm in diameter, which could not be infiltrated under the sole action of capillary forces. By varying the initial preform temperature from 705 °C to 280 °C, the diameter of nickel powder particles from 15 to 150 μm, and the volume fraction of alumina from 0 to 34 vol pct, pressure-infiltrated samples with large variations in the extent of reaction between nickel and aluminum were pro- duced. The range of microstructure extended from fully reacted nickel aluminide to essentially unreacted nickel/aluminum samples containing low levels of final porosity. In particular, it was found that reducing the initial preform temperature below the melting point of aluminum results in a reduction of the rate and extent of aluminide formation, allowing, in turn, reduction of macrosegregation within the resulting infiltrated material. Formerly Research Assistant, Department of Materials Science and Formerly Research Assistant, Department of Materials Science and     

Topographic-anatomic study of tissue transplants of the inguinal region

We performed 25 fresh cadaver dissections to describe the anatomy of the superficial and deep circumflex iliac artery and the superficial inferior epigastric artery to determine how they could least to used as donor vessels for the free transfer of groin flaps and living iliac bone. With injection of ink the capillary region of these vessels was stained in (iliac crest) bone, the internal oblique muscle and skin of the groin and thigh. The superficial and deep circumflex iliac artery were shown to be the main supply vessels of the groin and thigh and could be found in 96%-100% of cases. The venous drainage of this region followed from a superficial system (superficial circumflex iliac veins) and a deep venous system (Vv. comitantes accompanying arterial branches). Both venous systems could always be found. The superficial circumflex iliac artery was shown to only supply the skin and was the main donor vessel to the skin and soft tissue transplants. The deep circumflex iliac artery supplied the pelvic bone, the internal oblique muscle and a small constant area of skin above the iliac crest. Bone, muscle and bone, muscle and skin transplants could be obtained with this donor vessel, with enlargement of the skin area possible by combining two arterial branches combined in one transplant. With an average vessel diameter of 1.5 mm (superficial circumflex iliac artery) and 3 mm (deep circumflex iliac artery) both vessels could be used satisfactorily for microvascular transplantation. Different tissues including muscle, bone and skin could be obtained in adequate amounts to replace composite defects in the upper aerodigestive tract.     

The burnt-out chairman.

Discusses what it means to be a department chairperson, based on the author's 6.5 yrs of experience in this position. The frustrations and compensations of the job are considered. It is noted that administrative concerns come to replace concerns about the direction of the department. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A progress report: Basic construction in the open-hearth

A pioneer of basic construction in the open-hearth furnace sketches its history from wartime Germany to the present, with emphasis on US developments. The reasons why the future of basic construction has not been completely established are outlined.     

Pose Estimation in Conformal Geometric Algebra Part I: The Stratification of Mathematical Spaces

2D-3D pose estimation means to estimate the relative position and orientation of a 3D object with respect to a reference camera system. This work has its main focus on the theoretical foundations of the 2D-3D pose estimation problem: We discuss the involved mathematical spaces and their interaction within higher order entities. To cope with the pose problem (how to compare 2D projective image features with 3D Euclidean object features), the principle we propose is to reconstruct image features (e.g. points or lines) to one dimensional higher entities (e.g. 3D projection rays or 3D reconstructed planes) and express constraints in the 3D space. It turns out that the stratification hierarchy [11] introduced by Faugeras is involved in the scenario. But since the stratification hierarchy is based on pure point concepts a new algebraic embedding is required when dealing with higher order entities. The conformal geometric algebra (CGA) [24] is well suited to solve this problem, since it subsumes the involved mathematical spaces. Operators are defined to switch entities between the algebras of the conformal space and its Euclidean and projective subspaces. This leads to another interpretation of the stratification hierarchy, which is not restricted to be based solely on point concepts. This work summarizes the theoretical foundations needed to deal with the pose problem. Therefore it contains mainly basics of Euclidean, projective and conformal geometry. Since especially conformal geometry is not well known in computer science, we recapitulate the mathematical concepts in some detail. We believe that this geometric model is useful also for many other computer vision tasks and has been ignored so far. Applications of these foundations are presented in Part II [36].Bodo Rosenhahn gained his diploma degree in Computer Science in 1999. Since then he has been pursuing his Ph.D. at the Cognitive Systems Group, Institute of Computer Science, Christian-Albrechts University Kiel, Germany. He is working on geometric applications of Clifford algebras in computer vision.Prof. Dr. Gerald Sommer received a diploma degree in physics from the Friedrich-Schiller-Universität Jena, Germany, in 1969, a Ph.D. degree in physics from the same university in 1975, and a habilitation degree in engineering from the Technical University Ilmenau, Germany, in 1988. Since 1993 he is leading the research group Cognitive Systems at the Christian-Albrechts-Universität Kiel, Germany. Currently he is also the scientific coordinator of the VISATEC project.