136 Matching Results

Search Results

Advanced search parameters have been applied.

Evolutionary conservation of sequence and secondary structures in CRISPR repeats

Description: Clustered Regularly Interspaced Palindromic Repeats (CRISPRs) are a novel class of direct repeats, separated by unique spacer sequences of similar length, that are present in {approx}40% of bacterial and all archaeal genomes analyzed to date. More than 40 gene families, called CRISPR-associated sequences (CAS), appear in conjunction with these repeats and are thought to be involved in the propagation and functioning of CRISPRs. It has been proposed that the CRISPR/CAS system samples, maintains a record of, and inactivates invasive DNA that the cell has encountered, and therefore constitutes a prokaryotic analog of an immune system. Here we analyze CRISPR repeats identified in 195 microbial genomes and show that they can be organized into multiple clusters based on sequence similarity. All individual repeats in any given cluster were inferred to form characteristic RNA secondary structure, ranging from non-existent to pronounced. Stable secondary structures included G:U base pairs and exhibited multiple compensatory base changes in the stem region, indicating evolutionary conservation and functional importance. We also show that the repeat-based classification corresponds to, and expands upon, a previously reported CAS gene-based classification including specific relationships between CRISPR and CAS subtypes.
Date: September 1, 2006
Creator: Kunin, Victor; Sorek, Rotem & Hugenholtz, Philip
Partner: UNT Libraries Government Documents Department

Molecular mechanisms of extensive mitochondrial gene rearrangementin plethodontid salamanders

Description: Extensive gene rearrangement is reported in the mitochondrial genomes of lungless salamanders (Plethodontidae). In each genome with a novel gene order, there is evidence that the rearrangement was mediated by duplication of part of the mitochondrial genome, including the presence of both pseudogenes and additional, presumably functional, copies of duplicated genes. All rearrangement-mediating duplications include either the origin of light strand replication and the nearby tRNA genes or the regions flanking the origin of heavy strand replication. The latter regions comprise nad6, trnE, cob, trnT, an intergenic spacer between trnT and trnP and, in some genomes, trnP, the control region, trnF, rrnS, trnV, rrnL, trnL1, and nad1. In some cases, two copies of duplicated genes, presumptive regulatory regions, and/or sequences with no assignable function have been retained in the genome following the initial duplication; in other genomes, only one of the duplicated copies has been retained. Both tandem and non-tandem duplications are present in these genomes, suggesting different duplication mechanisms. In some of these mtDNAs, up to 25 percent of the total length is composed of tandem duplications of non-coding sequence that includes putative regulatory regions and/or pseudogenes of tRNAs and protein-coding genes along with otherwise unassignable sequences. These data indicate that imprecise initiation and termination of replication, slipped-strand mispairing, and intra-molecular recombination may all have played a role in generating repeats during the evolutionary history of plethodontid mitochondrial genomes.
Date: June 1, 2005
Creator: Mueller, Rachel Lockridge & Boore, Jeffrey L.
Partner: UNT Libraries Government Documents Department

Temperature distributions in a reactor fuel plate

Description: A report about the effects upon the fuel plate temperatures of introducing channel spacers into the proposed curved plate subassembly for the super critical water reactor.
Date: 1954
Creator: Redmond, R. F.; Chastain, Joel W.; Long, J. K.; Jung, R. G. & Fawcett, Sherwood L.
Partner: UNT Libraries Government Documents Department

Switching a magnetic vortex by interlayer coupling in epitaxially grown Co/Cu/Py/Cu(001) trilayer disks

Description: Epitaxial Py/Cu/Co/Cu(001) trilayers were patterned into micron sized disks and imaged using element-specific photoemission electron microscopy. By varying the Cu spacer layer thickness, we study how the coupling between the two magnetic layers influences the formation of magnetic vortex states. We find that while the Py and Co disks form magnetic vortex domains when the interlayer coupling is ferromagnetic, the magnetic vortex domains of the Py and Co disks break into anti-parallel aligned multidomains when the interlayer coupling is antiferromagnetic. We explain this result in terms of magnetic flux closure between the Py and Co layers for the antiferromagnetic coupling case.
Date: July 16, 2010
Creator: Wu, J.; Carlton, D.; Oelker, E.; Park, J. S.; Jin, E.; Arenholz, E. et al.
Partner: UNT Libraries Government Documents Department

Nonlinear motion of coupled magnetic vortices in ferromagnetic/non-magnetic/ferromagnetic trilayer

Description: We have investigated a coupled motion of two vortex cores in ferromagnetic/nonmagnetic/ferromagnetic trilayer cynliders by means of micromagnetic simulation. Dynamic motion of two vortex with parallel and antiparallel relative chiralities of curling spins around the vortex cores have been examined after excitation by 1-ns pulsed external field. With systematic variation in non-magnetic spacer layer thickness from 0 to 20 nm, the coupling between two cores becomes significant as the spacer becomes thinner. Significant coupling leads to a nonlinear chaotic coupled motion of two vortex cores for the parallel chiralities and a faster coupled gyrotropic oscillation for the antiparallel chiralities.
Date: July 5, 2009
Creator: Jun, Su-Hyeong; Shim, Je-Ho; Oh, Suhk-Kun; Yu, Seong-Cho; Kim, Dong-Hyun; Mesler, Brooke et al.
Partner: UNT Libraries Government Documents Department

Beta-Phosphinoethylboranes as Ambiphilic Ligands in Nickel-Methyl Complexes

Description: The ambiphilic {beta}-phosphinoethylboranes Ph{sub 2}PCH{sub 2}CH{sub 2}BR{sub 2} (BR{sub 2} = BCy{sub 2} (1a), BBN (1b)), which feature a ethano spacer CH{sub 2}CH{sub 2} between the Lewis acidic boryl and Lewis basic phosphino groups, were synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds 1a and 1b were fully characterized by elemental analysis, and by NMR and IR spectroscopy. X-ray crystallographic studies of compound 1b revealed infinite helical chains of the molecules connected through P{hor_ellipsis}B donor-acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors and acceptors was highlighted by their reactions with (dmpe)NiMe{sub 2}. Zwitterionic complexes (dmpe)NiMe(Ph{sub 2}PCH{sub 2}CH{sub 2}BCy{sub 2}Me) (2a) and (dmpe)NiMe(Ph{sub 2}PCH{sub 2}CH{sub 2}[BBN]Me) (2b) were generated via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray crystallography. Furthermore, B(C{sub 6}F{sub 5}){sub 3} abstracts the methyl group of a coordinated borate ligand to generate a free, 3-coordinate borane center in [(dmpe)NiMe(1a)]{sup +}[MeB(C{sub 6}F{sub 5}){sub 3}]{sup -} (3).
Date: October 28, 2007
Creator: Fischbach, Andreas; Bazinet, Patrick R.; Waterman, Rory & Tilley, T. Don
Partner: UNT Libraries Government Documents Department

CRISPR Recognition Tool (CRT): a tool for automatic detection ofclustered regularly interspaced palindromic repeats

Description: Clustered Regularly Interspaced Palindromic Repeats (CRISPRs) are a novel type of direct repeat found in a wide range of bacteria and archaea. CRISPRs are beginning to attract attention because of their proposed mechanism; that is, defending their hosts against invading extrachromosomal elements such as viruses. Existing repeat detection tools do a poor job of identifying CRISPRs due to the presence of unique spacer sequences separating the repeats. In this study, a new tool, CRT, is introduced that rapidly and accurately identifies CRISPRs in large DNA strings, such as genomes and metagenomes. CRT was compared to CRISPR detection tools, Patscan and Pilercr. In terms of correctness, CRT was shown to be very reliable, demonstrating significant improvements over Patscan for measures precision, recall and quality. When compared to Pilercr, CRT showed improved performance for recall and quality. In terms of speed, CRT also demonstrated superior performance, especially for genomes containing large numbers of repeats. In this paper a new tool was introduced for the automatic detection of CRISPR elements. This tool, CRT, was shown to be a significant improvement over the current techniques for CRISPR identification. CRT's approach to detecting repetitive sequences is straightforward. It uses a simple sequential scan of a DNA sequence and detects repeats directly without any major conversion or preprocessing of the input. This leads to a program that is easy to describe and understand; yet it is very accurate, fast and memory efficient, being O(n) in space and O(nm/l) in time.
Date: May 1, 2007
Creator: Bland, Charles; Ramsey, Teresa L.; Sabree, Fareedah; Lowe,Micheal; Brown, Kyndall; Kyrpides, Nikos C. et al.
Partner: UNT Libraries Government Documents Department

Initiation Pressure Thresholds from Three Sources

Description: Pressure thresholds are minimum pressures needed to start explosive initiation that ends in detonation. We obtain pressure thresholds from three sources. Run-to-detonation times are the poorest source but the fitting of a function gives rough results. Flyer-induced initiation gives the best results because the initial conditions are the best known. However, very thick flyers are needed to give the lowest, asymptotic pressure thresholds used in modern models and this kind of data is rarely available. Gap test data is in much larger supply but the various test sizes and materials are confusing. We find that explosive pressures are almost the same if the distance in the gap test spacers are in units of donor explosive radius. Calculated half-width time pulses in the spacers may be used to create a pressure-time curve similar to that of the flyers. The very-large Eglin gap tests give asymptotic thresholds comparable to extrapolated flyer results. The three sources are assembled into a much-expanded set of near-asymptotic pressure thresholds. These thresholds vary greatly with density: for TATB/LX-17/PBX 9502, we find values of 4.9 and 8.7 GPa at 1.80 and 1.90 g/cm{sup 3}, respectively.
Date: February 28, 2007
Creator: Souers, P. C. & Vitello, P.
Partner: UNT Libraries Government Documents Department

Recent Developments in the Site-Specific Immobilization of Proteins onto Solid Supports

Description: Immobilization of proteins onto surfaces is of great importance in numerous applications, including protein analysis, drug screening, and medical diagnostics, among others. The success of all these technologies relies on the immobilization technique employed to attach a protein to the corresponding surface. Non-specific physical adsorption or chemical cross-linking with appropriate surfaces results in the immobilization of the protein in random orientations. Site-specific covalent attachment, on the other hand, leads to molecules being arranged in a definite, orderly fashion and allows the use of spacers and linkers to help minimize steric hindrances between the protein and the surface. The present work reviews the latest chemical and biochemical developments for the site-specific covalent attachment of proteins onto solid supports.
Date: February 21, 2007
Creator: Camarero, J A
Partner: UNT Libraries Government Documents Department

Highly Insulating Glazing Systems using Non-Structural Center Glazing Layers

Description: Three layer insulating glass units with two low-e coatings and an effective gas fill are known to be highly insulating, with center-of-glass U-factors as low as 0.57 W/m{sup 2}-K (0.10 Btu/h-ft{sup 2}- F). Such units have historically been built with center layers of glass or plastic which extend all the way through the spacer system. This paper shows that triple glazing systems with non-structural center layers which do not create a hermetic seal at the edge have the potential to be as thermally efficient as standard designs, while potentially removing some of the production and product integration issues that have discouraged the use of triples.
Date: April 9, 2008
Creator: Kohler, Christian; Arasteh, Dariush; Goudey, Howdy & Kohler, Christian
Partner: UNT Libraries Government Documents Department

Voltage controlled spintronics device for logic applications.

Description: We consider logic device concepts based on our previously proposed spintronics device element whose magnetization orientation is controlled by application of a bias voltage instead of a magnetic field. The basic building block is the voltage-controlled rotation (VCR) element that consists of a four-layer structure--two ferromagnetic layers separated by both nanometer-thick insulator and metallic spacer layers. The interlayer exchange coupling between the two ferromagnetic layers oscillates as a function of applied voltage. We illustrate transistor-like concepts and re-programmable logic gates based on VCR elements.
Date: September 3, 1999
Creator: Bader, S. D. & You, C.-Y.
Partner: UNT Libraries Government Documents Department


Description: ABS>Experimental heat transfer data and analysis are reported for the Title II fuel assembly design modifications and refinements. Three distinct mid- length spacer designs are described. All tests are conducted with a 3,000-in. M fuel assembly sleeve and with the six outer tubes (of the seven tube cluster) located on a 2.000-in. BC. The dath are presented as heat transfer correlations and as comparisons of the heat transfer test results of one design with the results obtained from the other two and also the test results of the Title I fuel assembly design spacers. (auth)
Date: October 3, 1960
Creator: McDonald, T.J. & Higgins, R.M.
Partner: UNT Libraries Government Documents Department


Description: The feasibility of utilizing a jet pump and a shroud as a recirculation device within the blanket of the proposed reactcr pressure vessel for the HHE-3 was examined A Schute-Koerting designed jet pump was tested in conjunction with a 1/3 scale plastic model consisting of a core vessel, two constant area shrouds, and a blanket vessel. It was concluded that a jet pump with a ;multinozzle in conjunction with a shroud designed with a sizeable annular flow area provides a very satisfactory recirculation device within the blanket of a two-region reactor pressure vessel. A larger circulating pump head is required, but the fluid flow in the external circuit may be reduced consideraly depending on thee shroud used. (W.D.M.)
Date: August 12, 1958
Creator: Hayes, J.K.
Partner: UNT Libraries Government Documents Department

Debuncher Microwave Absorber Tests of January 1992

Description: This paper describes the tests performed on the microwave absorbers placed in the Debuncher to replace the existing microwave cutoffs. The purpose of the microwave cutoffs is to reduce the transmission of microwave energy through the beam pipe. The old microwave cutoffs consisted of a stainless steel beam pipe of approximately 2.8 inches inside diameter into which a glass tube with an inside diameter of 1.835 inches was placed. The glass tube was coated with a thin coat of microwave absorbing material on its outside. Three of these cutoffs were installed in the Debuncher at locations D6Q5, D1Q7, and D4Q10 (see Figure 1). However, the glass tube was removed from the cutoff at D4Q10 leaving only the metal beam pipe. Please note that there was not an old style microwave cutoff installed at location D2Q09. It was felt that the glass tube cutoff was an aperture restriction in the Debuncher with its small (1.8 inch) inside diameter. It was decided that new cutoffs would be needed that would increase the aperture. The new microwave absorbers consist of a four inch stainless steel beam pipe into which eleven dielectric cores are inserted separated by aluminum spacers. The spacing allows adjustment of the frequency response of the absorber assembly. The inside diameter is 3 inches thus providing an increase of 1.2 inches over the old cutoffs. The new absorbers will be installed at four locations as shown in Figure 1.
Date: January 1, 1992
Creator: Fullett, Ken
Partner: UNT Libraries Government Documents Department


Description: The 3d4f levels in the spectrum of triply ionized vanadium, V IV, were located by L. Iglesias. She located these levels by identifying transitions from the 3d{sup 2} ground configuration to the 3d4p levels, then to the 3d4d levels and finally to the 3d4f levels. She also identified the transitions from the 3d4d levels to the 3d5p levels, continued up to the 3d5d levels, then back down to the 3d4f levels. Though the 3d4f levels were well established by two routes, the direct transitions from the ground state were not observed, being beyond her experimental range which stopped at 675 {angstrom}. We have photographed the spectrum of vanadium in the region of 190-650 {angstrom} and the direct transitions from 3d{sup 2} to 3d4f have been observed. The spectrum was excited with a vacuum sliding-spark discharge between vanadium metal electrodes separated by a quartz spacer as described previously. Peak discharge current was 1000 {angstrom}. The spectrum was photographed on Kodak SWR plates using the 10 {center_dot} 7 m grazing incidence spectrograph at the National Bureau of Standards in Washington, D.C. The plate factor in the region of interest is about 0.27 {angstrom}/mm. The plates were measured on a Grant comparator. Lines of yttrium IV and V, oxygen III and carbon IV were used for reference standards. The same plates were used to obtain the spectrum of vanadium V as reported previously by van Deurzen. Table I contains 19 transitions from the ground configuration, 3d{sup 2}, to the 3d4f configuration and 3 transitions from the ground configuration to the 3dSp configuration. Column 1 in the table is our measured vacuum wavelengths. The intensities in column 2 are visual estimates on a scale of 0 to 9. Column 3 lists the wavenumber of the measured lines. The classifications of the transitions and the ...
Date: September 1, 1977
Creator: Shalimoff, G. V. & Conway, J.G.
Partner: UNT Libraries Government Documents Department

OCH Button Test

Description: A test was conducted to make a check on the yield stress of the copper spacer buttons to be used in OCH. The tested button was made from Copper no. 110, cold drawn rod, which has a documented yield stress value of 48,000 psi. The button was put into compression with the load applied to the face of the button. The resulting deflection vs. the applied cross load was then charted with the width of the chart having a 10,000 kg scale. While the chart speed was set at 1 cm/min, the cross head speed was set at .05 cm/min. To find a value of Young's Modulus for the OCH button, the compression test was run again with a chart width scale of 5,000 kg. The chart speed was set at 10 cm/min and the cross head speed at .05 cm/min. The curve generated on the chart was linear in nature until the button reached its yield point. Here, the slope of the curve began to change, increasing over a small area until a new linear curve was established. The point at which the slope changed would be considered the yielding point of the material, but here, there was no single distinct point. Instead there was a smooth transition between the two linear portions of the curve. In order to find where the yield point would occur, two lines were drawn, representing the best fit of each of the two slopes of the curve (before and after the yield point). The intersection of these lines was taken to be the point from which the yield stress could be calculated.
Date: May 1, 1987
Creator: Kurita, C.H.
Partner: UNT Libraries Government Documents Department

Test Results for RD3c, A Nb3Sn Common-Coil Racetrack Dipole Magnet

Description: The Superconducting Magnet Group at Lawrence Berkeley Laboratory has been developing racetrack technology for economical, high-field accelerator magnets from brittle superconductor. Recent tests have demonstrated (1) robust, reusable, double-layer, flat racetrack, wind and react Nb{sub 3}Sn coils, (2) a reusable, easily assembled, coil-support structure that can minimize conductor movement, and (3) 15T dipole fields, with no degradation. RD3c is our first attempt to compare measured and calculated field harmonics. A single-layer, Nb{sub 3}Sn, flat racetrack inner-coil was wound on both sides of a bore-plate, and then reacted and potted (as previously). Hard spacers were wound into the inner coils, to adjust the geometric field harmonics, and identify any problems from hard-spacers. Harmonic measurements with a warm rotating coil also required a considerably thicker bore-plate (for the 35mm OD anti-cryostat). The inner coil-module was sandwiched between two existing outer-coil modules, and pre-stressed within the reusable yoke and shell loading structure. The magnet's performance is discussed, and compared with calculations.
Date: August 1, 2002
Creator: Lietzke, A.F.; Caspi, S.; Coccoli, M.; Dietderich, D.R.; Ferracin, P.; Gourlay, S.A. et al.
Partner: UNT Libraries Government Documents Department

Analysis Procedures for Double-Shell Target Concentricity and Wall Thickness

Description: The LLNL Target Fabrication Team (TFT) asked the Center for Non-Destructive Characterization (CNDC) to use CNDC's KCAT or Xradia's Micro computed tomography (CT) system to collect three-dimensional (3D) tomographic data of a set of double-shell targets and determine, among other items, the following: (1) the concentricity of the outer surface of the inner shell with respect to the inner surface of the outer shell with an accuracy of 1-2 micrometers, and (2) the wall thickness uniformity of the outer shell with an accuracy of 1-2 micrometers. The CNDC used Xradia's Micro CT system to collect the data. Bill Brown performed the concentricity analysis, and John Sain performed the wall thickness uniformity analysis. Harry Martz provided theoretical guidance, and Dan Schneberk contributed technical (software) support. This document outlines the analysis procedures used in each case. The double-shell targets, as shown in Figures 1 and 2, consist of an inner shell (or capsule), a two-piece spherical aerogel intermediary shell, and a two-piece spherical outer shell. The three elements are designed and fabricated to be concentric--with the aerogel shell acting as a spacer between the inner shell and outer shell--with no to minimum air gaps in the final assembly. The outer diameters of the aerogel and outer shells are 444 and 550 micrometers, respectively, so the wall thickness of the outer shell is 53 micrometers.
Date: March 2, 2006
Creator: Sain, J D; Brown, W D; Martz, H E & Schneberk, D J
Partner: UNT Libraries Government Documents Department

New developments for the site-specific attachment of protein to surfaces

Description: Protein immobilization on surfaces is of great importance in numerous applications in biology and biophysics. The key for the success of all these applications relies on the immobilization technique employed to attach the protein to the corresponding surface. Protein immobilization can be based on covalent or noncovalent interaction of the molecule with the surface. Noncovalent interactions include hydrophobic interactions, hydrogen bonding, van der Waals forces, electrostatic forces, or physical adsorption. However, since these interactions are weak, the molecules can get denatured or dislodged, thus causing loss of signal. They also result in random attachment of the protein to the surface. Site-specific covalent attachment of proteins onto surfaces, on the other hand, leads to molecules being arranged in a definite, orderly fashion and uses spacers and linkers to help minimize steric hindrances between the protein surface. This work reviews in detail some of the methods most commonly used as well as the latest developments for the site-specific covalent attachment of protein to solid surfaces.
Date: May 12, 2005
Creator: Camarero, J A
Partner: UNT Libraries Government Documents Department

Micron-gap ThermoPhotoVoltaics (MTPV)

Description: This paper discusses advances made in the field of Micron-gap ThermoPhotoVoltaics (MTPV). Initial modeling has shown that MTPV may enable significant performance improvements relative to conventional far field TPV. These performance improvements include up to a 10x increase in power density, 30% to 35% fractional increase in conversion efficiency, or alternatively, reduced radiator temperature requirements to as low as 550 C. Recent experimental efforts aimed at supporting these predictions have successfully demonstrated that early current and voltage enhancements could be done repeatedly and at higher temperatures. More importantly, these efforts indicated that no unknown energy transfer process occurs reducing the potential utility of MTPV. Progress has been made by running tests with at least one of the following characteristics relative to the MTPV results reported in 2001: Tests at over twice the temperature (900 C); Tests at 50% smaller gaps (0.12 {micro}m); Tests with emitter areas from 4 to 100 times larger (16 mm{sup 2} to 4 cm{sup 2}); and Tests with over 20x reduction in parasitic spacer heat flow. Remaining fundamental challenges to realizing these improvements relative to the recent breakthroughs in conventional far field TPV include reengineering the photovoltaic (PV) diode, filter, and emitter system for MTPV and engineering devices and systems that can achieve submicron vacuum gaps between surfaces with large temperature differences.
Date: August 24, 2004
Creator: DiMatteo, R.; Greiff, P.; Seltzer, D.; Meaulenberg, D.; Brown, E.; Carlen, E. et al.
Partner: UNT Libraries Government Documents Department

A Comparison of the First Two Sequenced Chloroplast Genomes in Asteraceae: Lettuce and Sunflower

Description: Asteraceae is the second largest family of plants, with over 20,000 species. For the past few decades, numerous phylogenetic studies have contributed to our understanding of the evolutionary relationships within this family, including comparisons of the fast evolving chloroplast gene, ndhF, rbcL, as well as non-coding DNA from the trnL intron plus the trnLtrnF intergenic spacer, matK, and, with lesser resolution, psbA-trnH. This culminated in a study by Panero and Funk in 2002 that used over 13,000 bp per taxon for the largest taxonomic revision of Asteraceae in over a hundred years. Still, some uncertainties remain, and it would be very useful to have more information on the relative rates of sequence evolution among various genes and on genome structure as a potential set of phylogenetic characters to help guide future phylogenetic structures. By way of contributing to this, we report the first two complete chloroplast genome sequences from members of the Asteraceae, those of Helianthus annuus and Lactuca sativa. These plants belong to two distantly related subfamilies, Asteroideae and Cichorioideae, respectively. In addition to these, there is only one other published chloroplast genome sequence for any plant within the larger group called Eusterids II, that of Panax ginseng (Araliaceae, 156,318 bps, AY582139). Early chloroplast genome mapping studies demonstrated that H. annuus and L. sativa share a 22 kb inversion relative to members of the subfamily Barnadesioideae. By comparison to outgroups, this inversion was shown to be derived, indicating that the Asteroideae and Cichorioideae are more closely related than either is to the Barnadesioideae. Later sequencing study found that taxa that share this 22 kb inversion also contain within this region a second, smaller, 3.3 kb inversion. These sequences also enable an analysis of patterns of shared repeats in the genomes at fine level and of RNA editing by comparison ...
Date: January 20, 2006
Creator: Timme, Ruth E.; Kuehl, Jennifer V.; Boore, Jeffrey L. & Jansen, Robert K.
Partner: UNT Libraries Government Documents Department

Neutron reflectometry as a tool to study magnetism.

Description: Polarized-neutron specular reflectometry (PNR) was developed in the 1980's as a means of measuring magnetic depth profiles in flat films. Starting from simple profiles, and gradually solving structures of greater complexity, PNR has been used to observe or clarify a variety of magnetic phenomena. It has been used to measure the absolute magnetization of films of thickness not exceeding a few atomic planes, the penetration of magnetic fields in micron-thick superconductors, and the detailed magnetic coupling across non-magnetic spacers in multilayers and superlattices. Although PNR is considered a probe of depth dependent magnetic structure, laterally averaged in the plane of the film, the development of new scattering techniques promises to enable the characterization of lateral magnetic structures. Retaining the depth-sensitivity of specular reflectivity, off-specular reflectivity may be brought to resolve in-plane structures over nanometer to micron length scales.
Date: September 21, 1999
Creator: Felcher, G. P.
Partner: UNT Libraries Government Documents Department

Overview of Engine Combustion Research at Sandia National Laboratories

Description: The objectives of this paper are to describe the ongoing projects in diesel engine combustion research at Sandia National Laboratories' Combustion Research Facility and to detail recent experimental results. The approach we are employing is to assemble experimental hardware that mimic realistic engine geometries while enabling optical access. For example, we are using multi-cylinder engine heads or one-cylinder versions of production heads mated to one-cylinder engine blocks. Optical access is then obtained through a periscope in an exhaust valve, quartz windows in the piston crown, windows in spacer plates just below the head, or quartz cylinder liners. We have three diesel engine experiments supported by the Department of Energy, Office of Heavy Vehicle Technologies: a one-cylinder version of a Cummins heavy-duty engine, a diesel simulation facility, and a one-cylinder Caterpillar engine to evaluate combustion of alternative diesel fuels.
Date: April 26, 1999
Creator: Carling, Robert W. & Singh, Gurpreet
Partner: UNT Libraries Government Documents Department