1,230 Matching Results

Search Results

''6-Degrees of Freedom'' Single Crystal Plasticity Experiments

Description: A deformation experiment has been developed specifically for the purpose of validation of dislocation dynamics simulations of plastic flow up to strains on the order of 1% [1]. The experiment has been designed so that a compressive uniaxial stress field is essentially super imposed on the test sample, and the crystal is free to deform with 3 orthogonal translation directions, and 3 rotation/tilt axes of freedom and has been given the name ''6-degrees of freedom'' (6DOF) experiment. The rotation, tilt and translation of the crystal are monitored by 5 laser displacement gages and 3 extensometers. Experiments are being performed on high purity Mo single crystals orientated for ''single slip''. All of the experiments are performed in pairs, with one test sample having highly polished surfaces for optical light and AFM slip-trace analyses, and the other having 4 strain gage rosettes mounted on the sides for measurement of the bi-axial surface strains during testing. All of the experimental data is used together to determine the slip activity of the orientated single crystal during deformation. Experimental results on high-purity Mo single crystals are presented. The results of these experiments show that slip behavior is in substantial deviation from the expected ''Schmid'' behavior. These experimental results bring into question some of the fundamental assumptions used in both the construction of crystal plasticity constitutive relationships and rules for dislocation mobility use in 3-D dislocation dynamics simulations.
Date: May 21, 2003
Creator: Lassila, D H; Florando, J N; LeBlanc, M M; Arsenlis, T & Rhee, M
Partner: UNT Libraries Government Documents Department

205 kA pulse power supply for neutrino focusing horns

Description: A new underground beamline is being constructed at Fermilab to generate and focus a beam of neutrinos on a detector 450 miles away in Soudan, Minnesota. A compact modulator utilizing capacitive energy storage and SCRs as the switching element has been built and tested at Fermilab. The 0.9 F capacitor bank operates at less than 1 kV. It delivers its output of up to 240 kA directly to the two series connected focusing horns via a multi-layer radiation hard stripline [1]. Dual pulse width capability allows for ready selection of 5.2 ms, for slow beam spills, or 2.6 ms operation for reduced thermal stresses on the focusing horns during fast spill. Intended for installation in an underground equipment room, the design incorporates several novel features to facilitate transport, installation, and maintenance. Various designs were examined to arrive at the most economical approach for providing the high pulse currents to the horns located in the very high radiation field, up to 3 x 10{sup 7} kRads/yr absorbed dose of the beamline. These included charge recovery and electronic polarity reversal systems. The direct coupling approach was selected for its overall economy and compactness. The system has been operational for several months and results of those tests will be discussed. Controls and safety issues will also be discussed.
Date: June 21, 2002
Creator: Kenneth R. Bourkland, Kevin Roon and David Tinsley
Partner: UNT Libraries Government Documents Department

13th annual meeting of the ALS Users' Association

Description: A complement of 266 users, staff, and vendors descended upon the Ernest Orlando Lawrence Berkeley National Laboratory (Berkeley Lab) from Monday through Wednesday, October 16-18, 2000 for the thirteenth edition of the annual Advanced Light Source (ALS) users meeting. In a departure from previous practice, the meeting featured an increased emphasis on workshops with the result that the proceedings were equally divided between oral and poster presentations and the workshops. After the traditional welcomes and facility updates on the first morning, science dominated the first day and a half comprising the formal meeting with a session of highlights from young researchers, three sessions of scientific highlights from the ALS and elsewhere, and a poster session that included a student poster competition. A set of seven workshops covering research areas of current or growing interest at the ALS rounded out the final day and a half of the meeting.
Date: November 21, 2000
Creator: Robinson, Art
Partner: UNT Libraries Government Documents Department

2003 Archaea: Ecology, Metabolism and Molecular Biology

Description: The Gordon Research Conference (GRC) on 2003 Archaea: Ecology, Metabolism and Molecular Biology was held at Proctor Academy, Andover, NH from August 3-8, 2003. The Conference was well-attended with 150 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, ''free time'' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field. I want to personally thank you for your support of this Conference. As you know, in the interest of promoting the presentation of unpublished and frontier-breaking research, Gordon Research Conferences does not permit publication of meeting proceedings. If you wish any further details, please feel free to contact me. Thank you, Dr. Richard F. Shand, 2003 Conference Chair.
Date: September 21, 2004
Creator: Shand, Richard F.
Partner: UNT Libraries Government Documents Department

2003 Plant Cell Walls Gordon Conference

Description: This conference will address recent progress in many aspects of cell wall biology. Molecular, genetic, and genomic approaches are yielding major advances in our understanding of the composition, synthesis, and architecture of plant cell walls and their dynamics during growth, and are identifying the genes that encode the machinery needed to make their biogenesis possible. This meeting will bring together international scientists from academia, industry and government labs to share the latest breakthroughs and perspectives on polysaccharide biosynthesis, wood formation, wall modification, expansion and interaction with other organisms, and genomic & evolutionary analyses of wall-related genes, as well as to discuss recent ''nanotechnological'' advances that take wall analysis to the level of a single cell.
Date: September 21, 2004
Creator: Cosgrove, Daniel J.
Partner: UNT Libraries Government Documents Department


Description: The conference will present and discuss current science that underlies solar fuels production, and will focus on direct production pathways for production. Thus, recent advances in design and understanding of molecular systems and materials for light capture and conversion of relevance for solar fuels will be discussed. An important set of topics will be homogeneous, heterogeneous and biological catalysts for the multi-electron processes of water oxidation, hydrogen production and carbon dioxide reduction to useful fuels. Also, progress towards integrated and scalable systems will be presented. Attached is a copy of the formal schedule and speaker program and the poster program.
Date: January 21, 2011
Creator: Hupp, Joseph
Partner: UNT Libraries Government Documents Department

2660 A holographic interferometry of laser produced plasmas from tilted disk targets

Description: Using double exposure holographic interferometry, an investigation has been made of the Nd laser produced plasmas surrounding disk targets irradiated at different angles of incidence. Measurements have produced a detailed description of the plasma profile necessary for realistic simulations of resonance absorption. A 2660A 15 psec probe pulse is produced by frequency quadrupling a fraction of the main Nd laser pulse from the Janus laser. F/1 and f/10 lenses were utilized to irradiate the targets with intensities ranging from 10/sup 13/ w/cm/sup 2/ to 10/sup 16/ w/cm/sup 2/. Measurements have produced the shape of the electron density profile near critical, the direction of the plasma blowoff, and revealed transverse rippling of the isodensity surfaces.
Date: October 21, 1977
Creator: Auerbach, J.M.; Attwood, D.T.; Lee, P.H.Y. & Sweeney, D.W.
Partner: UNT Libraries Government Documents Department

2D spatial gain profiles in multiple-pulse driven Ne-like Ge lasers

Description: In this paper, we present the direct spatial measurement of the two-dimensional gain profiles for the Ne-like Ge 196 Å laser line using a slab target illuminated by the multiple pulse technique. To understand the spatial dependence for Ge plasmas driven by a series of 100 ps pulses 400 ps apart we did a series of Nova experiments backlighting short Ge amplifiers. Two-dimensional, high-resolution, spatial images of the 196 Å laser emission from the output aperture of the amplifiers were measured to determine the spatial position of the gain. The amplifier lengths were chosen to be short enough to avoid the significant refraction effects which have dominated the analysis of previous near field imaging experiments. To assure good temporal overlap, the traveling wave geometry was used to illuminate both the amplifier and backlighter. The amplifier design included a wire fiducial that provided an absolute spatial reference and avoided the usual difficulty of determining the location of the target surface. We compare the measured spatial gain profiles with simulations done using LASNEX, which calculates the hydrodynamic evolution of the plasma, and XRASER, which uses the temperatures and densities from LASNEX to do the gain and kinetics calculations.
Date: September 21, 1998
Creator: Dunn, J; Li, Y; Nilsen, J & Osterheld, A L
Partner: UNT Libraries Government Documents Department

3D simulations of axially confined heavy ion beams in round and square pipes

Description: We have been using the 3d PIC code WARP6 to model the behavior of beams in a heavy ion induction accelerator; such linacs are candidates for an ICF driver. Improvements have been added to the code to model an axially confined beam using comoving axial electric fields to simulate the confining ears'' applied to the accelerating pulses in a real system. We have also added a facility for modeling a beam in a round pipe, applying a capacity matrix to each axial Fourier mode in turn. These additions are described along with results, such as the effect of pipe shape on the beam quality degradation from quadrupole misalignments. 5 refs., 6 figs., 1 tab.
Date: March 21, 1991
Creator: Grote, D.P.; Friedman, A. (Lawrence Livermore National Lab., CA (USA)) & Haber, I. (Naval Research Lab., Washington, DC (USA))
Partner: UNT Libraries Government Documents Department

Ab initio and density functional studies of hydrocarbon adsorption in zeolites.

Description: The adsorption energies of methane and ethane in zeolites are investigated with ab initio molecular orbital theory and density functional theory. In this work we have used zeolite cluster models containing two, three, and five tetrahedral (Si, Al) atoms and have found equilibrium structures for complexes of methane, ethane, and propane with an acid site. If a large enough cluster is used and correlation effects are included via perturbation theory, the calculated adsorption energy for ethane is about 5 kcal/mol compared with the experimental value of 7.5 kcal/mol. The B3LYP density functional method gives a much smaller binding of {approximately}1 kcal/mol for ethane. The reason for the failure of density fictional theory is unclear.
Date: August 21, 1998
Creator: Curtiss, L. A.
Partner: UNT Libraries Government Documents Department

Ab initio calculations in a uniform magnetic field using periodic supercells

Description: We present a formulation of ab initio electronic structure calculations in a finite magnetic field, which retains the simplicity and efficiency of techniques widely used in first principles molecular dynamics simulations, based on plane-wave basis sets and Fourier transforms. In addition we discuss results obtained with this method for the energy spectrum of interacting electrons in quantum wells, and for the electronic properties of dense fluid deuterium in a uniform magnetic field.
Date: October 21, 2003
Creator: Cai, W & Galli, G
Partner: UNT Libraries Government Documents Department

Abraham Model Linear Free Energy Relationships as a Means of Extending Solubility Studies to Include the Estimation of Solute Solubilities in Additional Organic Solvents

Description: This article calculates Abraham model solute descriptors for 5-nitro-8-hydroxyquinoline, 2-methyl-6-nitroaniline, and terephthaldialdehyde using experimental solubility data taken from papers published in The Journal of Chemical Thermodynamics in 2016.
Date: July 21, 2016
Creator: Acree, William E. (William Eugene); Horton, Melissa Y.; Higgins, Elizabeth & Abraham, M. H. (Michael H.)
Partner: UNT College of Arts and Sciences

Absolute instrumental neutron activation analysis at Lawrence Livermore Laboratory

Description: The Environmental Science Division at Lawrence Livermore Laboratory has in use a system of absolute Instrumental Neutron Activation Analysis (INAA). Basically, absolute INAA is dependent upon the absolute measurement of the disintegration rates of the nuclides produced by neutron capture. From such disintegration rate data, the amount of the target element present in the irradiated sample is calculated by dividing the observed disintegration rate for each nuclide by the expected value for the disintegration rate per microgram of the target element that produced the nuclide. In absolute INAA, the expected value for disintegration rate per microgram is calculated from nuclear parameters and from measured values of both thermal and epithermal neutron fluxes which were present during irradiation. Absolute INAA does not depend on the concurrent irradiation of elemental standards but does depend on the values for thermal and epithermal neutron capture cross-sections for the target nuclides. A description of the analytical method is presented.
Date: December 21, 1977
Creator: Heft, R.E.
Partner: UNT Libraries Government Documents Department

Absolute Measurement of Electron Cloud Density

Description: Beam interaction with background gas and walls produces ubiquitous clouds of stray electrons that frequently limit the performance of particle accelerator and storage rings. Counterintuitively we obtained the electron cloud accumulation by measuring the expelled ions that are originated from the beam-background gas interaction, rather than by measuring electrons that reach the walls. The kinetic ion energy measured with a retarding field analyzer (RFA) maps the depressed beam space-charge potential and provides the dynamic electron cloud density. Clearing electrode current measurements give the static electron cloud background that complements and corroborates with the RFA measurements, providing an absolute measurement of electron cloud density during a 5 {micro}s duration beam pulse in a drift region of the magnetic transport section of the High-Current Experiment (HCX) at LBNL.
Date: June 21, 2007
Creator: Covo, M K; Molvik, A W; Cohen, R H; Friedman, A; Seidl, P A; Logan, G et al.
Partner: UNT Libraries Government Documents Department

Absorber height effects on SWA restrictions and 'Shadow' LER

Description: As extreme-ultraviolet lithography (EUVL) approaches introduction at the 22-nm half-pitch node, several key aspects of absorber height effects remain unexplored. In particular, sidewall angle (SWA) restrictions based on the height of the mask absorber has not yet been clearly defined. In addition, the effects of absorber height on line-edge roughness (LER) from shadowing has not been examined. We make an initial investigation into how tight SWA constraints are and the extent to which shadow LER alters basic LER. Our approach to SWA aims to find SWA restrictions based on 10% of the total CD error budget (10% of CD). Thus, we allot the SWA budget a {+-}0.2nm tolerance for 22nm half-pitch. New with EUVL is the off-axis illumination system. One potential pitfall that must be carefully monitored is the effect of mask absorber height blocking light from reaching, and therefore, correctly detecting, the base edge position of a feature. While mask features can correctly compensate sizing to target at the wafer, the effects of this shadowing on LER have not yet been investigated. Specifically, shadow LER may exacerbate or mitigate the inherent LER on the mask. Shadowing may also cause a difference in the observed LER on the right and left side of the features. We carefully probe this issue for a range of spatial frequencies. We do rigorous aerial image modeling of mask features with a nominal SWA of 80 degrees and correctly sized to target 22nm features measured at the top, 70nm TaN absorber on a 40 bilayer ML mirror with a 2.5nm Ru cap. Simulations were on a 4X system with an ideal pupil of NA = 0.32, illumination wavelength 13.4nm at 6{sup o} off-axis, and disk source shape with partial coherence factor of {sigma} = 0.50. We first implement a defocus offset to the aerial image ...
Date: February 21, 2011
Creator: McClinton, Brittany & Naulleau, Patrick
Partner: UNT Libraries Government Documents Department

Accelerator system for neutron radiography

Description: The field of x-ray radiography is well established for doing non-destructive evaluation of a vast array of components, assemblies, and objects. While x-rays excel in many radiography applications, their effectiveness diminishes rapidly if the objects of interest are surrounded by thick, high-density materials that strongly attenuate photons. Due to the differences in interaction mechanisms, neutron radiography is highly effective in imaging details inside such objects. To obtain a high intensity neutron source suitable for neutron imaging a 9-MeV linear accelerator is being evaluated for putting a deuteron beam into a high-pressure deuterium gas cell. As a windowless aperture is needed to transport the beam into the gas cell, a low-emittance is needed to minimize losses along the high-energy beam transport (HEBT) and the end station. A description of the HEBT, the transport optics into the gas cell, and the requirements for the linac will be presented.
Date: September 21, 2000
Creator: Rusnak, B & Hall, J
Partner: UNT Libraries Government Documents Department

Accessing the Inaccessible: The Case for Opening up Russia's Closed Cities

Description: The selling of weapons-related nuclear knowledge by Russian scientists for economic gain constitutes a threat to US national security. Some estimate that the number of Russian scientists seeking permanent employment abroad constitute five to ten percent of all researchers who have left the field of science. And, there is concern that those who have left are ''the better minds.'' Moreover, the issue of brain drain concerns not only those who move abroad permanently, but those who still reside in Russia and travel abroad to sell their knowledge. Of particular concern to the US is the potential sale of WMD knowledge by some. To ''mitigate the risk that economic difficulties...might create the temptation for individuals or institutes to sell expertise to countries of proliferation concern and terrorist organizations,'' the Department of Energy launched a Nuclear Cities Initiative (NCI) in 1998 with the goal of creating commercial jobs and economic diversification in the ten closed cities that form the core of Russia's nuclear weapons complex to accommodate the loss of employment in the nuclear weapons industry. However, unless Russia opens access to the areas of its closed cities that are, or could become, involved in commercial activities-while of course carefully controlling access to the sensitive areas of the institutes and laboratories-economic development will be stymied.
Date: March 21, 2001
Creator: Ball, D Y
Partner: UNT Libraries Government Documents Department

Active RF Pulse Compression Using Electrically Controlled Semiconductor Switches

Description: In this paper, we present the recent results of our research on the ultra-high power fast silicon RF switch and its application on active X-Band RF pulse compression systems. This switch is composed of a group of PIN diodes on a high purity silicon wafer and has achieved a switching time of 300ns. The wafer is inserted into a cylindrical waveguide operating in the TE01 mode. Switching is performed by injecting carriers into the bulk silicon through a high current pulse. The RF energy is stored in a room-temperature, high-Q 375 ns delay line; it is then extracted out of the line in a short time using the switch. The pulse compression system has achieved a gain of 8, which is the ratio between output and input power.
Date: March 21, 2007
Creator: Guo, J. & Tantawi, S.
Partner: UNT Libraries Government Documents Department

Adapting MARSSIM for FUSRAP site closure.

Description: The Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) provides a coherent, technically defensible process for establishing that exposed surfaces satisfy site cleanup requirements. Unfortunately, many sites have complications that challenge a direct application of MARSSIM. Example complications include Record of Decision (ROD) requirements that are not MARSSIM-friendly, the potential for subsurface contamination, and incomplete characterization information. These types of complications are typically the rule, rather than the exception, for sites undergoing radiologically-driven remediation and closure. One such site is the Formerly Utilized Sites Remedial Action Program (FUSRAP) Linde site in Tonawanda, New York. Cleanup of the site is currently underway. The Linde site presented a number of challenges to designing and implementing a closure strategy consistent with MARSSIM. This paper discusses some of the closure issues confronted by the U.S. Army Corps of Engineers Buffalo District at the Linde site, and describes how MARSSIM protocols were adapted to address these issues.
Date: December 21, 2001
Creator: Johnson, R.; Durham, L.; Rieman, C. & Hoover, R.
Partner: UNT Libraries Government Documents Department

Adaptive mesh refinement in titanium

Description: In this paper, we evaluate Titanium's usability as a high-level parallel programming language through a case study, where we implement a subset of Chombo's functionality in Titanium. Chombo is a software package applying the Adaptive Mesh Refinement methodology to numerical Partial Differential Equations at the production level. In Chombo, the library approach is used to parallel programming (C++ and Fortran, with MPI), whereas Titanium is a Java dialect designed for high-performance scientific computing. The performance of our implementation is studied and compared with that of Chombo in solving Poisson's equation based on two grid configurations from a real application. Also provided are the counts of lines of code from both sides.
Date: January 21, 2005
Creator: Colella, Phillip & Wen, Tong
Partner: UNT Libraries Government Documents Department

AdS/CFT and Exclusive Processes in QCD

Description: The AdS/CFT correspondence between string theory in AdS space and conformal field theories in physical space-time leads to an analytic, semi-classical model for strongly-coupled QCD which has scale invariance and dimensional counting at short distances and color confinement at large distances. One can use holography to map the amplitude describing the hadronic state in the fifth dimension of Anti-de Sitter space AdS5 to the light-front wavefunctions of hadrons in physical space-time, thus providing a relativistic description of hadrons in QCD at the amplitude level. In particular, we show that there is an exact correspondence between the fifth-dimensional coordinate of AdS space z and a specific impact variable {var_sigma} which measures the separation of the quark and gluonic constituents within the hadron in ordinary space-time. New relativistic light-front equations in ordinary space-time can then be derived which reproduce the results obtained using the 5-dimensional theory. The effective light-front equations possess elegant algebraic structures and integrability properties. This connection between the AdS and the light-front representations allows one to compute the analytic form of the frame-independent light-front wavefunctions, the fundamental entities which encode hadron properties and allow the computation of decay constants, form factors, deeply virtual Compton scattering, exclusive heavy hadron decays and other exclusive scattering amplitudes. As specific examples we compute the pion coupling constant f{sub {pi}} and study the behavior of the pion form factor F{sub {pi}}(q{sup 2}) in the space and time-like regions. We also determine the Dirac nucleon form factors F{sup p}{sub 1}(q{sup 2}) and F{sup n}{sub 1} (q{sup 2}) in the space-like region.
Date: September 21, 2007
Creator: Brodsky, Stanley J. & de Teramond, Guy F.
Partner: UNT Libraries Government Documents Department


Description: The AdS/CFT correspondence between string theory in AdS space and conformal .eld theories in physical spacetime leads to an analytic, semi-classical model for strongly-coupled QCD which has scale invariance and dimensional counting at short distances and color confinement at large distances. Although QCD is not conformally invariant, one can nevertheless use the mathematical representation of the conformal group in five-dimensional anti-de Sitter space to construct a first approximation to the theory. The AdS/CFT correspondence also provides insights into the inherently non-perturbative aspects of QCD, such as the orbital and radial spectra of hadrons and the form of hadronic wavefunctions. In particular, we show that there is an exact correspondence between the fifth-dimensional coordinate of AdS space z and a specific impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron in ordinary space-time. This connection allows one to compute the analytic form of the frame-independent light-front wavefunctions, the fundamental entities which encode hadron properties and allow the computation of decay constants, form factors, and other exclusive scattering amplitudes. New relativistic lightfront equations in ordinary space-time are found which reproduce the results obtained using the 5-dimensional theory. The effective light-front equations possess remarkable algebraic structures and integrability properties. Since they are complete and orthonormal, the AdS/CFT model wavefunctions can also be used as a basis for the diagonalization of the full light-front QCD Hamiltonian, thus systematically improving the AdS/CFT approximation.
Date: February 21, 2007
Creator: Brodsky, Stanley J.; /SLAC; de Teramond, Guy F. & /SLAC, /Costa Rica U.
Partner: UNT Libraries Government Documents Department

Advanced Binary Geothermal Power Plancts Working Fluid Property Determination and Heat Exchanger Design

Description: The performance of binary geothermal power plants can be improved through the proper choice of a working fluid, and optimization of component designs and operating conditions. This paper reviews the investigations at the Idaho National Engineering Laboratory (INEL) which are examining binary cycle performance improvements: for moderate temperature (350 to 400 F) resources with emphasis on how the improvements may be integrated into design of binary cycles. These investigations are examining performance improvements resulting from the supercritical vaporization of mixed hydrocarbon working fluids and achieving countercurrent integral condensation with these fluids, as well as the modification of the turbine inlet state points to achieve supersaturated turbine vapor expansions. For resources where the brine outlet temperature is restricted, the use of turbine exhaust recuperators is examined. The baseline plant used to determine improvements in plant performance (characterized by the increase in the net brine effectiveness, watt-hours per pound of brine) in these studies operates at conditions similar to the 45 MW Heber binary plant. Through the selection of the optimum working fluids and operating conditions, achieving countercurrent integral condensation, and allowing supersaturated vapor expansions in the turbine, the performance of the binary cycle (the net brine effectiveness) can be improved by 25 to 30% relative to the baseline plant. The design of these supercritical Rankine-cycle (Binary) power plants for geothermal resources requires information about the potential working fluids used in the cycle. In addition, methods to design the various components, (e.g., heat exchangers, pumps, turbines) are needed. This paper limits its view of component design methods to the heat exchangers in binary power plants. The design of pumps and, turbines for these working fluids presents no new problems to the turbine manufacturer. However, additional work is proceeding at the Heat Cycle Research Facility to explore metastable expansions within turbines. This work, ...
Date: March 21, 1989
Creator: Bliem, C.J. & Mines, G.L.
Partner: UNT Libraries Government Documents Department