Theory of workhardening 1934-1984

The evolution of the theory of workhardening through the past fifty years has laid a secure basis, but much research still lies ahead. A guiding principle in the prevailing, so-called meshlength theory is that glide dislocations arrange into stress-screened, low-energy structures, the most common being the cell structure, and that the flow stress is the stress needed to generate new glide dislocations. Further, it makes extensive use of the “principle of similitude”. Remnant stresses due to dislocations with just one Burgers vector orientation are very often relieved by additional dislocations with other Burgers vectors which form not in response to the applied stress but to those remnant stresses. Such dislocations are commonly misnamed “forest” dislocations. The theory closely reproduces stages II and III of the typical workhardening curve. Stage I results in single glide from sources which initially are isolated from each other so that pile-ups form, which then may interact among neighboring pile-ups of opposite sign, so as to generate mats of dipoles parallel to the active glide plane. Stage II behavior is expected as long as similitude is obeyed so that the average free dislocation path shrinks inversely proportional with the root of the dislocation density. Stage III, finally, results when the free dislocation path is constant. At low temperatures, thermal activation can make the critical difference for the release of hair-trigger poised loops. This is the cause of creep effects whose magnitude is limited to less than the elastic strain. Computer calculations indicate the presence of longer-range (i.e., cell diameter scale) stresses whose sign changes with the cell’s sense of rotation. This suggests that rectangled dislocation cells with a common rotation axis, arranged into a three-dimensional checkerboard pattern in which the sense of rotation alternates from cell to cell, should minimize stored energy. Such cell patterns are increasingly reported in the literature. The fact that the average cell diameter tends to be inversely proportional to the applied stress is also readily explained through those stresses. In retrospect, Taylor’s theory of workhardening may be recognized as a variant of the meshlength theory of stage III, in that it is based on a stress-screened network obeying the principle of similitude while the free dislocation path, given by the spacing between the mosaic block walls, remains constant. This paper is based on a presentation made at the symposium “50th Anniversary of the Introduction of Dislocations” held at the fall meeting of the TMS-AIME in Detroit, Michigan in October 1984 under the TMS-AIME Mechanical Metallurgy and Physical Metallurgy Committees.     

Dimensions of affective experience in three age groups.

The dimensions by which adults of differing ages experience emotion were studied by self-administering questionnaires administered to older adults (n?=?828) recruited from Elderhostel programs, middle-aged (aged 30–59 yrs) children of Elderhostel attenders (n?=?231), and young adult (aged 18–29 yrs) Ss recruited from college classes or through Elderhostel participants (n?=?207). Elders were higher in emotional control, mood stability, and emotional maturity through moderation and leveling of positive affect and lower in surgency, psychophysiological responsiveness, and sensation seeking. These findings are consistent with the hypothesized increase in self-regulatory capacity with age. These cross-sectional differences cannot, however, be distinguished from cohort-related explanations; they require considerable replication across different types of Ss and further characterization of the dimensions in terms of their functions for self-regulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoinitiated Electron Transfer in Carotenoporphyrin-Quinone Triads: Enhanced Quantum Yields via Control of Reaction Exergonicity

Carotenoporphyrin-quinone triad molecules have previously been found to successfully mimic many aspects of photosynthetic electron and energy transfer. These molecules generate long-lived, energetic charge-separated states via a biomimetic multistep electron transfer scheme. In many of these molecules, the overall quantum yield for charge separation has been limited by an unfavorable partitioning of an intermediate charge-separated state between charge recombination and further reaction to yield the desired species. One strategy for overcoming this limitation is based on the fact that, in general, electron transfer rate constants do not depend linearly on reaction free energy change. In the triads, raising the energy of the intermediate charge-separated state would be expected to speed up the desired electron transfer (“normal” Marcus behavior), but slow down charge recombination (which formally lies in the “inverted” region). Laser flash photolysis and transient fluorescence measurements on two new triad molecules reveal enhanced quantum yields of long-lived charge-separated states which are consistent with this expectation.     

Software verification effort at the MIMICAD center for microstrip passive components

A software verification effort to verify the accuracy of the simulation program developed by the Center for Microwave/Millimeter-Wave Computer-Aided Design (MIMICAD) is described. A set of single-layer microstrip structures selected by the MIMICAD sponsors were fabricated on GaAs substrates for testing purposes. Ranging from an interdigitated capacitor to radial stubs to a section of meander line, these test structures are components commonly used in MMIC designs. Round-robin measurements of the test structures were carried out among the MIMICAD sponsors to assess measurement consistency. Comparisons between the measured and simulated results as well as the effect of discretization in the simulation process are discussed.     

Graphene Actively Mode‐Locked Lasers

Actively mode‐locked lasers offer varying degrees of flexibility for a wider range of applications than their passively modulated counterparts, due to their capability for electrically controlled ultrahigh repetition rate operation. Graphene based electrooptic modulators with unique advantages of broad operation bandwidth and ultrafast speed are suitable for light modulation in various optoelectronic applications. Here, an actively mode‐locked laser with a graphene based electrooptic modulator is reported for the first time. The active mode‐locking technique combined together with the intracavity nonlinear pulse shortening effect allows the generation of transform‐limited 1.44 ps pulses with pulse energy of 844 pJ. The electrically controlled repetition rate of generated pulses, a key performance advantage of active mode‐locking, is also demonstrated. These results provide a practical and effective approach for actively mode‐locked lasers with broad operation bandwidth and compact footprint, which contributes a new way for applications of two‐dimensional (2D) layered materials in ultrafast lasers.     

Separation von Starterkulturen nach Hochdruck‐Homogenisierung

The present work demonstrates how shearing through a high‐pressure homogenizer affects the separation properties of exopolysaccaride producing bacterial starter cultures. In addition to changes in medium viscosity and sedimentation velocity significant differences in the compactness of the cell sediment were observed. The scalability of the laboratory results obtained through analytical centrifugation in larger scale using a stack disc separator is also demonstrated.     

A multi-level approach to ubiquitous modeling and solving constraints in combinatorial optimization problems in production and distribution

Constraints, although ubiquitous in production and distribution planning, scheduling and control, often lead to inconsistencies in the decision-making process. The constraint-based modeling helps circumvent many organization-impacting issues. To address this, we developed a multi-level approach to the modeling and solving of combinatorial optimization problems. It is versatile and effective owing to the use of multi-level presolving and multiple paradigms, such as constraint programming, logic programming, mathematical programming and fuzzy logic, for their complementary strengths. The capability of this framework and its advantage over mathematical programming alone or over hybrid frameworks is shown in the illustrative example, in which combinatorial optimization is used as a benchmark to prove the effectiveness of the proposed approach. Knowledge of the problem is stored in the form of facts.