High-pressure/high-temperature synthesis of transition metal oxide perovskites

Perovskite and related Ruddlesden-Popper type transition metal oxides synthesised at high pressures and temperatures during the last decade are reviewed. More than 60 such new materials have been reported since 1995. Important developments have included perovskites with complex cation orderings on A and B sites, multiferroic bismuth-based perovskites, and new manganites showing colossal magnetoresistance (CMR) and charge ordering properties

Plasma contactor research, 1990

Emissive and Langmuir probes were used to measure plasma potential profiles, plasma densities, electron energy distributions, and plasma noise levels near a hollow cathode-based plasma contactor emitting electrons. The effects of electron emission current (100 to 1500 mA) and contactor flowrate (2 to 10 sccm (Xenon)) on these data are examined. Retarding potential analyzer (RPA) measurements showing that high energy ions generally stream from a contactor along with the electrons being emitted are also presented, and a mechanism by which this occurs is postulated. This mechanism, which involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice, results in a region of high positive space charge and high positive potential. Langmuir and RPA probe data suggests that both electrons and ions expand spherically from this potential hill region. In addition to experimental observations, a simple one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and is shown to agree qualitatively with these observations. Experimental results of the first stage of bilateral cooperation with the Italian Institute of Interplanetary Space Physics (IFSI CNR) are presented. Sharp, well-defined double layers were observed downstream of a contactor collecting electrons from an ambient plasma created in the IFSI Facility. The voltage drop across these double layers was observed to increase with the current drawn from the ambient plasma. This observation, which was not as clear in previous IFSI tests conducted at higher neutral pressures, is in agreement with previous experimental observations made at both Colorado State University and NASA Lewis Research Center. Greater double layer voltage drops, multiple double layers, and higher noise levels in the region near the double layers were also observed when a magnetic field was imposed and oriented perpendicular to the line joining the contactor and simulator

Space plasma contractor research, 1988

Results of experiments conducted on hollow cathode-based plasma contractors are reported. Specific tests in which attempts were made to vary plasma conditions in the simulated ionospheric plasma are described. Experimental results showing the effects of contractor flowrate and ion collecting surface size on contactor performance and contactor plasma plume geometry are presented. In addition to this work, one-dimensional solutions to spherical and cylindircal space-charge limited double-sheath problems are developed. A technique is proposed that can be used to apply these solutions to the problem of current flow through elongated double-sheaths that separate two cold plasmas. Two conference papers which describe the essential features of the plasma contacting process and present data that should facilitate calibration of comprehensive numerical models of the plasma contacting process are also included

Pyrolysis of brominated feedstock plastic in a fluidised bed reactor

Fire retarded high impact polystyrene has been pyrolysed using a fluidised bed reactor with a sand bed. The yield and composition of the products have been investigated in relation to fluidised bed temperature. The bromine distribution between the products and a detailed analysis of the oils using GC-FID/ECD, GC-MS, FT-ir, and size exclusion chromatography has been carried out. It was found that the majority of the bromine transfers to the pyrolysis oil and the antimony was detected in both the oil and the char. Oil made up over 89.9% of the pyrolysis products. Over 30% of the oil consisted of benzene, toluene, ethylbenzene, styrene and cumene. The pyrolysis gases were mainly hydrocarbons in the C1-C4 range but some HBr and Br2 was detected

Information flow through a model of the C. elegans klinotaxis circuit

Understanding how information about external stimuli is transformed into behavior is one of the central goals of neuroscience. Here we characterize the information flow through a complete sensorimotor circuit: from stimulus, to sensory neurons, to interneurons, to motor neurons, to muscles, to motion. Specifically, we apply a recently developed framework for quantifying information flow to a previously published ensemble of models of salt klinotaxis in the nematode worm C. elegans. The models are grounded in the neuroanatomy and currently known neurophysiology of the worm. The unknown model parameters were optimized to reproduce the worm's behavior. Information flow analysis reveals several key principles underlying how the models operate: (1) Interneuron class AIY is responsible for integrating information about positive and negative changes in concentration, and exhibits a strong left/right information asymmetry. (2) Gap junctions play a crucial role in the transfer of information responsible for the information symmetry observed in interneuron class AIZ. (3) Neck motor neuron class SMB implements an information gating mechanism that underlies the circuit's state-dependent response. (4) The neck carries non-uniform distribution about changes in concentration. Thus, not all directions of movement are equally informative. Each of these findings corresponds to an experimental prediction that could be tested in the worm to greatly refine our understanding of the neural circuit underlying klinotaxis. Information flow analysis also allows us to explore how information flow relates to underlying electrophysiology. Despite large variations in the neural parameters of individual circuits, the overall information flow architecture circuit is remarkably consistent across the ensemble, suggesting that information flow analysis captures general principles of operation for the klinotaxis circuit

Mapping biodiversity value worldwide: combining higher-taxon richness from different groups

Maps of large-scale biodiversity are urgently needed to guide conservation, and yet complete enumeration of organisms is impractical at present. One indirect approach is to measure richness at higher taxonomic ranks, such as families. The difficulty is how to combine information from different groups on numbers of higher taxa, when these taxa may in effect have been defined in different ways, particularly for more distantly related major groups. In this paper, the regional family richness of terrestrial and freshwater seed plants, amphibians, reptiles and mammals is mapped worldwide by combining: (i) absolute family richness; (ii) proportional family richness; and (iii) proportional family richness weighted for the total species richness in each major group. The assumptions of the three methods and their effects on the results are discussed, although for these data the broad pattern is surprisingly robust with respect to the method of combination. Scores from each of the methods of combining families are used to rank the top five richness hotspots and complementary areas, and hotspots of endemism are mapped by unweighted combination of range-size rarity scores

Giant pop-ins and amorphization in germanium during indentation

Sudden excursions of unusually large magnitude (>1 μm), “giant pop-ins,” have been observed in the force-displacement curve for high load indentation of crystalline germanium(Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or “elbowing,” observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered

Cultural Resources Survey of the Leander Rehabilitation Center, Williamson County, Texas

In August-September 1996, personnel from Prewitt and Associates, Inc., conducted a cultural resources survey of ca. 725 acres of the former Leander Rehabilitation Center. The project area lies adjacent to U.S. Highway 183 and FM 620 in southern Williamson County, Texas. The survey resulted in additional documentation of one previously recorded prehistoric archeological site (41 WM452), the identification and recording of four historic archeological sites (41WM892, 41WM893, 41WM896, and 41WM897), and reconnaissance-level documentation of 45 historic buildings and structures. Site 41WM452 is an extensive upland lithic scatter and lithic procurement site which lacks subsurface deposits, features, and datable materials. Site 41WM892 is a wood-chopper camp that contains a number of rock alignments and limited artifact deposits dating to the first decade of the twentieth century. Site 41WM893 is a remnant of a railroad spur used during the 1937-1941 construction of Marshall Ford Dam (now Mansfield Dam). Site 41WM896 contains a small number of features and sparse artifact deposits associated with the 1937-1945 Rhodes farmstead. Site 41WM897 is an isolated historic well with unknown associations. None of these archeological sites contains important information, and it is recommended that they be considered not eligible for listing in the National Register of Historic Places or for designation as State Archeological Landmarks. The 45 buildings and structures, at 36 locations, are associated with the former State Dairy and Hog Farm. This farm was established in 1942, expanded after 1945, and reached its peak years of production as a hog farm between 1950 and the late 1960s, Created to serve the needs of the State Board of Control and the State Hospital, the facility is significant for its success in food production for eleemosynary institutions in Austin and throughout Texas, as well as for its role in the application of modern psychiatric treatment based on the therapeutic value of manual labor. Among the surveyed resources are dwellings, an office and warehouse building, a dormitory, a variety of agricultural buildings and structures, and infrastructural elements, all built between 1943 and 1955. Twenty-one of the 45 surveyed resources are recommended as being eligible for listing in the National Register of Historic Places under Criteria A and C as Contributing resources in a historic district and for designation as State Archeological Landmarks

Integer programming as projection

We generalise polyhedral projection (Fourier–Motzkin elimination) to integer programming (IP) and derive from this an alternative perspective on IP that parallels the classical theory. We first observe that projection of an IP yields an IP augmented with linear congruence relations and finite-domain variables, which we term a generalised IP. The projection algorithm can be converted to a branch-and-bound algorithm for generalised IP in which the search tree has bounded depth (as opposed to conventional branching, in which there is no bound). It also leads to valid inequalities that are analogous to Chvátal–Gomory cuts but are derived from congruences rather than rounding, and whose rank is bounded by the number of variables. Finally, projection provides an alternative approach to IP duality. It yields a value function that consists of nested roundings as in the classical case, but in which ordinary rounding is replaced by rounding to the nearest multiple of an appropriate modulus, and the depth of nesting is again bounded by the number of variables. For large perturbations of the right-hand sides, the value function is shift periodic and can be interpreted economically as yielding “average” shadow prices

Very weak electron-phonon coupling and strong strain coupling in manganites

The coupling of the manganite stripe phase to the lattice and to strain has been investigated via transmission electron microscopy studies of polycrystalline and thin film manganites. In polycrystalline \PCMOfiftwo a lockin to $q/a^*=0.5$ in a sample with $x>0.5$ has been observed for the first time. Such a lockin has been predicted as a key part of the Landau CDW theory of the stripe phase. Thus it is possible to constrain the size of the electron-phonon coupling in the CDW Landau theory to between 0.04% and 0.05% of the electron-electron coupling term. In the thin film samples, films of the same thickness grown on two different substrates exhibited different wavevectors. The different strains present in the films on the two substrates can be related to the wavevector observed via Landau theory. It is demonstrated that the the elastic term which favours an incommensurate modulation has a similar size to the coupling between the strain and the wavevector, meaning that the coupling of strain to the superlattice is unexpectedly strong.Comment: 6 pages, 7 figure