9,791 research outputs found

    A first-principles study of oxygen vacancy pinning of domain walls in PbTiO3

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    We have investigated the interaction of oxygen vacancies and 180-degree domain walls in tetragonal PbTiO3 using density-functional theory. Our calculations indicate that the vacancies do have a lower formation energy in the domain wall than in the bulk, thereby confirming the tendency of these defects to migrate to, and pin, the domain walls. The pinning energies are reported for each of the three possible orientations of the original Ti-O-Ti bonds, and attempts to model the results with simple continuum models are discussed.Comment: 8 pages, with 3 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/lh_dw/index.htm

    Mash Test No. 3-10 of a Non-Proprietary, High-Tension Cable Median Barrier for Use in 6H:1V V-Ditch (Test No. MWP-8)

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    The Midwest States Pooled Fund Program has been developing a prototype design for a non-proprietary, high-tension cable median barrier for use in a 6H:1V V-ditch. This system incorporates four evenly spaced cables, Midwest Weak Posts (MWP) spaced at 8 to 16 ft (2.4-4.9 m) intervals, and a bolted, tabbed bracket to attach three or four cables to the sides of each post. According to the Manual for Assessing Safety Hardware (MASH) testing matrix for cable barriers installed within a 6H:1V median V-ditch, a series of eight full-scale tests are required to evaluate the safety performance of a system. A ninth test is required to establish the working width for the systems with variable post spacing. Several previous tests have failed due to posts penetrating the occupant compartment. In order to mitigate this behavior, a modified MWP was designed. Test no. MWP-8 was conducted on the modified barrier system, consisting of MWPs with rounded top edges and a Ÿ-in. (19-mm) diameter weakening hole at the groundline. This test was conducted according to MASH test designation no. 3-10 and utilized an 1100C passenger car impacting the barrier on a level terrain. The vehicle was contained by the system. Through the initial two vehicle crossover events across the barrier and posts, no floorpan tearing was observed. During the third impact series with the posts, post penetration into the occupant compartment and floorpan tearing was observed. Therefore, test no. MWP-8 was deemed unacceptable

    A Large, Uniform Sample of X-ray Emitting AGN from the ROSAT All-Sky and Sloan Digital Sky Surveys: the Data Release 5 Sample

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    We describe further results of a program aimed to yield ~10^4 fully characterized optical identifications of ROSAT X-ray sources. Our program employs X-ray data from the ROSAT All-Sky Survey (RASS), and both optical imaging and spectroscopic data from the Sloan Digital Sky Survey (SDSS). RASS/SDSS data from 5740 deg^2 of sky spectroscopically covered in SDSS Data Release 5 (DR5) provide an expanded catalog of 7000 confirmed quasars and other AGN that are probable RASS identifications. Again in our expanded catalog, the identifications as X-ray sources are statistically secure, with only a few percent of the SDSS AGN likely to be randomly superposed on unrelated RASS X-ray sources. Most identifications continue to be quasars and Seyfert 1s with 15<m<21 and 0.01<z<4; but the total sample size has grown to include very substantial numbers of even quite rare AGN, e.g., now including several hundreds of candidate X-ray emitting BL Lacs and narrow-line Seyfert 1 galaxies. In addition to exploring rare subpopulations, such a large total sample may be useful when considering correlations between the X-ray and the optical, and may also serve as a resource list from which to select the "best" object (e.g., X-ray brightest AGN of a certain subclass, at a preferred redshift or luminosity) for follow-on X-ray spectral or alternate detailed studies.Comment: Accepted for publication in AJ; 32 pages, including 11 figures, and 6 example table

    Governmental Context Determines Institutional Value: Independently Certified Performance and Failure in the Spanish Newspaper Industry

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    Many societies demand that independent professionals (e.g. auditors) certify the performance of firms. The value placed on such certification (i.e. the public perception of reliability/unreliability that may impact on an organization's success/failure) is not uniform, however, but contingent upon changing political contexts. This study presents and analyses data on the entire population of newspapers in Spain from 1966 to 1993, a time of peaceful transition from military dictatorship to capitalist democracy. Our results highlight the contingent nature of institutional life, demonstrating how changes in political contexts are associated with varying understandings of institutions. In particular, our findings support the prediction that, under a dictatorship, independently certified performance is not instrumental in organizational success or failure whereas, in a modern democracy, the certification process has a positive effect on the survival chances of firms.Publicad

    Zone-plate focusing of Bose-Einstein condensates for atom optics and erasable high-speed lithography of quantum electronic components

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    We show that Fresnel zone plates, fabricated in a solid surface, can sharply focus atomic Bose-Einstein condensates that quantum reflect from the surface or pass through the etched holes. The focusing process compresses the condensate by orders of magnitude despite inter-atomic repulsion. Crucially, the focusing dynamics are insensitive to quantum fluctuations of the atom cloud and largely preserve the condensates' coherence, suggesting applications in passive atom-optical elements, for example zone plate lenses that focus atomic matter waves and light at the same point to strengthen their interaction. We explore transmission zone-plate focusing of alkali atoms as a route to erasable and scalable lithography of quantum electronic components in two-dimensional electron gases embedded in semiconductor nanostructures. To do this, we calculate the density profile of a two-dimensional electron gas immediately below a patch of alkali atoms deposited on the surface of the nanostructure by zone-plate focusing. Our results reveal that surface-induced polarization of only a few thousand adsorbed atoms can locally deplete the electron gas. We show that, as a result, the focused deposition of alkali atoms by existing zone plates can create quantum electronic components on the 50 nm scale, comparable to that attainable by ion beam implantation but with minimal damage to either the nanostructure or electron gas.Comment: 13 pages, 7 figure
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