420 research outputs found
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LLNL Workshop on TEM of Pu
On Sept. 10, 1996, LLNL hosted a workshop aimed at answering the question: Is it possible to carry out transmission electron microscopy (TEM) on plutonium metal in an electron microscope located outside the LLNL plutonium facility. The workshop focused on evaluation of a proposed plan for Pu microscopy both from a technical and environment, health, and safety point of view. After review and modification of the plan, workshop participants unanimously concluded that: (1) the technical plan is sound, (2) this technical plan, including a proposal for a new TEM, provides significant improvements and unique capabilities compared with the effort at LANL and is therefore complementary, (3) there is no significant environment, health, and safety obstacle to this plan
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Influence of Processing Method on the Grain Boundary Character Distribution and Network Connectivity
There exists a growing body of literature that correlates the fraction of ''special'' boundaries in a microstructure, as described by the Coincident Site Lattice Model, to properties such as corrosion resistance, intergranular stress corrosion cracking, creep, etc. Several studies suggest that the grain boundary character distribution (GBCD), which is defined in terms of the relative fractions of ''special'' and ''random'' grain boundaries, can be manipulated through thermomechanical processing. This investigation evaluates the influence of specific thermomechanical processing methods on the resulting GBCD in FCC materials such as oxygen-free electronic (ofe) copper and Inconel 600. We also demonstrate that the primary effect of thermomechanical processing is to reduce or break the connectivity of the random grain boundary network. Samples of ofe Cu were subjected to a minimum of three different deformation paths to evaluate the influence of deformation path on the resulting GBCD. These include: rolling to 82% reduction in thickness, compression to 82% strain, repeated compression to 20% strain followed by annealing. In addition, the influence of annealing temperature was probed by applying, for each of the processes, three different annealing temperatures of 400, 560, and 800 C. The observations obtained from automated electron backscatter diffraction (EBSD) characterization of the microstructure are discussed in terms of deformation path, annealing temperature, and processing method. Results are compared to previous reports on strain-annealed ofe Cu and sequential processed Inconel 600. These results demonstrate that among the processes considered, sequential processing is the most effective method to disrupt the random grain boundary network and improve the GBCD
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Correlating Observations of Deformation Microstructures by TEM and Automated EBSD Techniques
The evolution of the deformed microstructure as a function of imposed plastic strain is of interest as it provides information on the material hardening characteristics and mechanism(s) by which cold work energy is stored. This has been extensively studied using transmission electron microscopy (TEM), where the high spatial and orientational resolution of the technique is used to advantage to study local phenomenon such as dislocation core structures and interactions of dislocations. With the recent emergence of scanning electron microscope (SEM) based automated electron backscatter diffraction (EBSD) techniques, it has now become possible to make mesoscale observations that are statistical in nature and complement the detailed TEM observations. Correlations of such observations will be demonstrated for the case of Ni-base alloys, which are typically non-cell forming solid solution alloys when deformed at ambient temperatures. For instance, planar slip is dominant at low strain levels but evolves into a microstructure where distinct crystallographic dislocation-rich walls form as a function of strain and grain orientation. Observations recorded using both TEM and EBSD techniques are presented and analyzed for their implication on subsequent annealing characteristics
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Use of strain-annealing to evolve the grain boundary character distribution in polycrystalline copper
We have used a two-step (low and high temperature) strain-annealing process to evolve the grain boundary character distribution (GBCD) in fully recrystallized oxygen-free electronic (OFE) Cu bar that was forged and rolled. Orientation imaging microscopy has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries was {similar_to}70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high-temperature process resulted in a reduction in the fraction of special GBs while both the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of the low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher temperature anneal and commensurate increase in the special fraction
HIGHLY EFFICIENT SINGLE-LONGITUDINAL-MODE BETA-BAB2O4 OPTICAL PARAMETRIC OSCILLATOR WITH A NEW CAVITY DESIGN
A new coupled-cavity design for single-longitudinal-mode operation of an optical parametric oscillator (OPO) is presented. The OPO is based on a beta-BaB2O4 crystal and is pumped by the third harmonic of a Nd:YAG laser. With this design, we achieved single-longitudinal-mode operation of the OPO with a decrease in the threshold and an increase in external efficiency compared with those of a conventional grazing-incidence OPO. A mathematical model that describes the mode spacings for this cavity is given. (C) 1995 Optical Society of Americ
A self-interaction corrected pseudopotential scheme for magnetic and strongly-correlated systems
Local-spin-density functional calculations may be affected by severe errors
when applied to the study of magnetic and strongly-correlated materials. Some
of these faults can be traced back to the presence of the spurious
self-interaction in the density functional. Since the application of a fully
self-consistent self-interaction correction is highly demanding even for
moderately large systems, we pursue a strategy of approximating the
self-interaction corrected potential with a non-local, pseudopotential-like
projector, first generated within the isolated atom and then updated during the
self-consistent cycle in the crystal. This scheme, whose implementation is
totally uncomplicated and particularly suited for the pseudopotental formalism,
dramatically improves the LSDA results for a variety of compounds with a
minimal increase of computing cost.Comment: 18 pages, 14 figure
Erasmus Language students in a British University – a case study
Students’ assessment of their academic experience is actively sought by Higher Education institutions, as evidenced in the National Student Survey introduced in 2005. Erasmus students, despite their growing numbers, tend to be excluded from these satisfaction surveys, even though they, too, are primary customers of a University. This study aims to present results from bespoke questionnaires and semi-structured interviews with a sample of Erasmus students studying languages in a British University. These methods allow us insight into the experience of these students and their assessment as a primary customer, with a focus on language learning and teaching, university facilities and student support. It investigates to what extent these factors influence their levels of satisfaction and what costs of adaptation if any, they encounter. Although excellent levels of satisfaction were found, some costs affect their experience. They relate to difficulties in adapting to a learning methodology based on a low number of hours and independent learning and to a guidance and support system seen as too stifling. The results portray this cohort’s British University as a well-equipped and well-meaning but ultimately overbearing institution, which may indicate that minimising costs can eliminate some sources of dissatisfaction
Aerosolized Amiloride for the Treatment of Lung Disease in Cystic Fibrosis
To the Editor: The April 26 issue of the Journal presented encouraging results by Knowles et al. regarding the beneficial effects of aerosolized amiloride in the treatment of cystic fibrosis.1 The introduction and discussion sections of this article described the function of amiloride as an inhibitor of sodium transport in the airway epithelium, and the authors suggested that the beneficial effects observed were exerted “at least in part by increasing the clearance of secretions.” Although the results of this investigation were promising in terms of the improvement in the decline of forced vital capacity in patients with cystic fibrosis, this
Powder Bed Layer Characteristics: The Overseen First-Order Process Input
A discrete element powder model is used in conjunction with a finite volume melting model on the first layer of a powder bed selective laser melting process
N-body simulations of gravitational dynamics
We describe the astrophysical and numerical basis of N-body simulations, both
of collisional stellar systems (dense star clusters and galactic centres) and
collisionless stellar dynamics (galaxies and large-scale structure). We explain
and discuss the state-of-the-art algorithms used for these quite different
regimes, attempt to give a fair critique, and point out possible directions of
future improvement and development. We briefly touch upon the history of N-body
simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu
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