Resource Type

Material dynamics at extreme pressures and strain rates (open access)

Material dynamics at extreme pressures and strain rates

Solid state experiments at extreme pressures (10-100 GPa) and strain rates ({approx}10{sup 6}-10{sup 8}s{sup -1}) are being developed on high-energy laser facilities, and offer the possibility for exploring new regimes of materials science. [Re 2004] These extreme solid-state conditions can be accessed with either shock loading or with quasi-isentropic ramped pressure pulses being developed on the Omega laser. [Ed 2004] Velocity interferometer measurements establish the high strain rates. Constitutive models for solid-state strength under these conditions are tested by comparing 2D continuum simulations with experiments measuring perturbation growth due to the Rayleigh-Taylor instability in solid-state samples. Lattice compression, phase, and temperature are deduced from extended x-ray absorption fine structure (EXAFS) measurements, from which the shock-induced a-w phase transition in Ti is inferred to occur on sub-nanosecond time scales. [Ya 2004] Time resolved lattice response and phase can be inferred from dynamic x-ray diffraction measurements, where the elastic-plastic (1D-3D) lattice relaxation in shocked Cu is shown to occur promptly (< 1 ns). [Lo 2003] Subsequent large-scale MD simulations have elucidated the microscopic dynamics that underlie the 3D lattice relaxation. Deformation mechanisms are identified by examining the residual microstructure in recovered samples. [Re 2004] For example, the slip-twinning threshold in single-crystal Cu …
Date: August 25, 2004
Creator: Remington, Bruce A.; Cavallo, Rob M.; Edwards, Michael J.; Ho, David D.; Lasinski, Barbara F.; Lorenz, Karl T. et al.
System: The UNT Digital Library
Materials Science at the Extremes of Pressure and Strain Rate (open access)

Materials Science at the Extremes of Pressure and Strain Rate

Solid state experiments at very high pressures and strain rates are possible on high power laser facilities, albeit over brief intervals of time and spatial small scales. A new shockless drive has been developed on the Omega laser. VISAR measurements establish the high strain rates, 10{sup 7}-10{sup 8} s{sup -1}. Solid-state strength is inferred using the Rayleigh-Taylor instability as a ''diagnostic''. Temperature and compression in polycrystalline samples can be deduced from EXAFS measurements. Lattice response can be inferred from time-resolved x-ray diffraction. Deformation mechanisms can be identified by examining recovered samples. We will briefly review this new area of laser-based materials science research, then present a path forward for carrying these solid-state experiments to much higher pressures, P >> 1 Mbar, on the NIF laser facility.
Date: August 20, 2003
Creator: Remington, B. A.; Cavallo, R. M.; Edwards, M. J.; Lasinski, B. F.; Lorenz, K. T.; Lorenzana, H. E. et al.
System: The UNT Digital Library
Multi-fluid code simulations including anomalous non-diffusive transport of plasma and impurities in the tokamak SOL (open access)

Multi-fluid code simulations including anomalous non-diffusive transport of plasma and impurities in the tokamak SOL

Fast intermittent transport has been observed in the scrape-off layer (SOL) of major tokamaks including Alcator C-Mod, DIII-D, and NSTX. This kind of transport is not diffusive but rather convective. It strongly increases plasma flux to the chamber walls and enhances the recycling of neutral particles in the main chamber. We discuss anomalous cross-field convection (ACFC) model for impurity and main plasma ions and its relation to intermittent transport events, i.e. plasma density blobs and holes in the SOL. Along with plasma diffusivity coefficients, our transport model introduces time-independent anomalous cross-field convective velocity. In the discharge modelling, diffusivity coefficients and ACFC velocity profiles are adjusted to match a set of representative experimental data. We use this model in the edge plasma physics code UEDGE to simulate the multi-fluid two-dimensional transport for these three tokamaks. We present simulation results suggesting the dominance of anomalous convection in the far SOL transport. These results are consistent with the hypothesis that the chamber wall is an important source of impurities and that different impurity charge states have different directions of anomalous convective velocity.
Date: November 25, 2003
Creator: Pigarov, A. Yu; West, W. P.; Soukhanovskii, V.; Rognlien, T. D.; Maingi, R.; Lipschultz, B. et al.
System: The UNT Digital Library
Large plasma pressure perturbations and radial convective transport in a tokamak (open access)

Large plasma pressure perturbations and radial convective transport in a tokamak

Strongly localized plasma structures with large pressure inhomogeneities (such as plasma blobs in the scrape-off-layer (SOL)/shadow regions, pellet clouds, ELMs) observed in the tokamaks, stellarators and linear plasma devices. Experimental studies of these phenomena reveal striking similarities including more convective rather than diffusive radial plasma transport. We suggest that rather simple models can describe many essentials of blobs, ELMs, and pellet clouds dynamics. The main ingredient of these models is the effective plasma gravity caused by magnetic curvature, centrifugal or friction forces effects. As a result, the equations governing plasma transport in such localized structures appear to be rather similar to that used to describe nonlinear evolution of thermal convection in the Boussinesq approximation (directly related to the Rayleigh-Taylor instability).
Date: February 4, 2004
Creator: Krasheninnikov, S.; Ryutov, D. & Yu, G.
System: The UNT Digital Library
From Crisis to Transition: The State of Russian Science Based on Focus Groups with Nuclear Physicists (open access)

From Crisis to Transition: The State of Russian Science Based on Focus Groups with Nuclear Physicists

The collapse of the Soviet system led to a sharp contraction of state funding for science. Formerly privileged scientists suddenly confronted miserly salaries (often paid late), plummeting social prestige, deteriorating research facilities and equipment, and few prospects for improvement. Many departed the field of science for more lucrative opportunities, both within Russia and abroad. The number of inventions, patent applications, and publications by Russian scientists declined. Reports of desperate nuclear physicists seeking work as tram operators and conducting hunger strikes dramatized the rapid collapse of one of the contemporary world's most successful scientific establishments. Even more alarming was the 1996 suicide of Vladimir Nechai, director of the second largest nuclear research center in Russia (Chelyabinsk-70, now known as Snezhinsk). Nechai, a respected theoretical physicist who spent almost 40 years working on Soviet and Russian nuclear programs, killed himself because he could no longer endure his inability to rectify a situation in which his employees had not been paid for more than 5 months and were ''close to starvation.'' The travails of Russia's scientists sparked interest in the West primarily because of the security threat posed by their situation. The seemingly relentless crisis in science raised fears that disgruntled scientists might …
Date: December 9, 2001
Creator: Gerber, T P & Ball, D Y
System: The UNT Digital Library
In-situ Diffraction Studies of Shock Compressed Single-Crystal Iron (open access)

In-situ Diffraction Studies of Shock Compressed Single-Crystal Iron

The technique of in-situ wide angle diffraction has been used to study materials such as Si and Cu. We have extended our studies of shocked single crystal materials to include Fe (001) that is shock compressed by direct laser irradiation using the OMEGA and Janus lasers. A series of experiments was conducted in Fe at pressures above the Hugoniot Elastic Limit. Transient x-ray was used to record the response of multiple lattice planes simultaneously. This technique of wide-angle diffraction provides information on the lattice response both parallel and oblique to the shock propagation direction. In these experiments, compressions of up to 14% in the (002) planes were observed. Details on the experiments and analysis of the dynamic lattice compression will be presented.
Date: July 16, 2004
Creator: Kalantar, D H; Colvin, J D; Eggert, J; Lorenzana, H; Stolken, J; Hawreliak, J et al.
System: The UNT Digital Library
Monolithic Nickel (II) Oxide Aerogels Using an Organic Epoxide: The Importance of the Counter Ion (open access)

Monolithic Nickel (II) Oxide Aerogels Using an Organic Epoxide: The Importance of the Counter Ion

The synthesis and characterization of nickel (II) oxide aerogel materials prepared using the epoxide addition method is described. The addition of the organic epoxide propylene oxide to an ethanolic solution of NiCl{sub 2} 6H{sub 2}O resulted in the formation of an opaque light green monolithic gel and subsequent drying with supercritical CO{sub 2} gave a monolithic aerogel material of the same color. This material has been characterized using powder X-ray diffraction, electron microscopy, elemental analysis, and nitrogen adsorption/desorption analysis. The results indicate that the nickel (II) oxide aerogel has very low bulk density (98 kg/m{sup 3} ({approx}98 %porous)), high surface area (413 m{sup 2}/g), and has a particulate-type aerogel microstructure made up of very fine spherical particles with an open porous network. By comparison, a precipitate of Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} is obtained when the same preparation is attempted with the common Ni(NO{sub 3}){sub 2} 6H{sub 2}O salt as the precursor. The implications of the difference of reactivity of the two different precursors are discussed in the context of the mechanism of gel formation via the epoxide addition method. The synthesis of nickel (II) oxide aerogel, using the epoxide addition method, is especially unique in our experience. It is …
Date: January 13, 2004
Creator: Gash, A. E.; Satcher, J. H. & Simpson, R. L.
System: The UNT Digital Library
Mass by Energy Loss Quantitation as a Practical Sub-Microgram Balance (open access)

Mass by Energy Loss Quantitation as a Practical Sub-Microgram Balance

A simple device integrating a thin film support and a standard microcentrifuge tube can be used for making solutions of accurately known concentration of any organic compound in a single step, avoiding serial dilution and the use of microgram balances. Nanogram to microgram quantities of organic material deposited on the thin film are quantified by ion energy loss and transferred to the microcentrifuge tube with high recovery.
Date: September 28, 2004
Creator: Palmblad, M; Bench, G & Vogel, J S
System: The UNT Digital Library
Insights into the Dynamic Response of Tunnels in Jointed Rocks (open access)

Insights into the Dynamic Response of Tunnels in Jointed Rocks

Tunnels in jointed rocks can be subjected to severe dynamic loads because of rock bursts, coal bumps, and large earthquakes. A series of 3-dimensional simulations was performed, based on discrete element analysis to gain insights into the parameters that influence the response of such tunnels. The simulations looked at the effect of joint set orientation, the effect of joint spacing, the effect of pulse shape for a given displacement, and the influence of using rigid versus deformable blocks in the analyses. The results of this modeling were also compared to field evidence of dynamic tunnel failures. This comparison reinforced the notion that 3-dimensional discrete element analysis can capture very well the kinematics of structures in jointed rock under dynamic loading.
Date: November 1, 2004
Creator: Heuze, F E
System: The UNT Digital Library
The 1997/98 El Nino: A Test for Climate Models (open access)

The 1997/98 El Nino: A Test for Climate Models

Version 3 of the Hadley Centre Atmospheric Model (HadAM3) has been used to demonstrate one means of comparing a general circulation model with observations for a specific climate perturbation, namely the strong 1997/98 El Nino. This event was characterized by the collapse of the tropical Pacific's Walker circulation, caused by the lack of a zonal sea surface temperature gradient during the El Nino. Relative to normal years, cloud altitudes were lower in the western portion of the Pacific and higher in the eastern portion. HadAM3 likewise produced the observed collapse of the Walker circulation, and it did a reasonable job of reproducing the west/east cloud structure changes. This illustrates that the 1997/98 El Nino serves as a useful means of testing cloud-climate interactions in climate models.
Date: March 5, 2004
Creator: Lu, R; Dong, B; Cess, R D & Potter, G L
System: The UNT Digital Library
Quantifying the Contribution of Lubrication Oil to Particulate Emissions from a Diesel Engine (open access)

Quantifying the Contribution of Lubrication Oil to Particulate Emissions from a Diesel Engine

The contribution of lubrication oil to particulate matter (PM) emissions from a Cummins B5.9 Diesel engine was measured using accelerator mass spectrometry to trace carbon isotope concentrations. The engine operated at fixed medium load (285 N-m (210 ft.lbs.) 1600 m) used 100% biodiesel fuel (B100) with a contemporary carbon-14 ({sup 14}C) concentration of 103 amol {sup 14}C/ mg C. The C concentration of the exhaust C02 and PM were 102 and 99 amol {sup 14}C/mg C, respectively. The decrease in I4C content in the PM is due to the consumption of lubrication oil which is {sup 14}C-free. Approximately 4% of the carbon in PM came from lubrication oil under these operating conditions. The slight depression in CO{sub 2} isotope content could be attributed to ambient CO{sub 2} levels and measurement uncertainty.
Date: December 6, 2002
Creator: Cheng, A. S.; Rich, D.; Dibble, R. W. & Buchholz, B. A.
System: The UNT Digital Library
Toward understanding environmental effects in SDSS clusters (open access)

Toward understanding environmental effects in SDSS clusters

We find clusters and superclusters of galaxies using the Data Release 1 of the Sloan Digital Sky Survey. We determine the luminosity function of clusters and find that clusters in a high-density environment have a luminosity a factor of {approx}5 higher than in a low-density environment. We also study clusters and superclusters in numerical simulations. Simulated clusters in a high-density environment are also more massive than those in a low-density environment. Comparison of the density distribution at various epochs in simulations shows that in large low-density regions (voids) dynamical evolution is very slow and stops at an early epoch. In contrast, in large regions of higher density (superclusters) dynamical evolution starts early and continues until the present; here particles cluster early, and by merging of smaller groups very rich systems of galaxies form.
Date: November 1, 2004
Creator: Einasto, Jaan; Tago, E.; Einasto, M.; Saar, E.; Suhhonenko, I.; Heinamaki, P. et al.
System: The UNT Digital Library
NLC photon collider option progress and plans (open access)

NLC photon collider option progress and plans

The idea of producing beams of high energy photons by Compton backscattering of laser photons was proposed over 20 years ago. At the time, producing the required laser pulses was not feasible. However, recent advances in high average power, diode pumped lasers appear to have solved this problem. The US Collaboration is now turning its attention to the engineering requirement of mating the laser and optics components with the accelerator structures in the confined space of the a colliding beam interaction region. The demonstration of a technically feasible interaction region design is planned for the Snowmass conference in 2001.
Date: August 31, 2000
Creator: Gronberg, J.
System: The UNT Digital Library
Manifestation of the Color Glass Condensate in Particle Production at RHIC. (open access)

Manifestation of the Color Glass Condensate in Particle Production at RHIC.

In this paper we discuss the experimental signatures of the new form of nuclear matter--the Color Glass Condensate (CGC) in particle production at RHIC. We show that predictions for particle production in p(d)A and AA collisions derived from these properties are in agreement with data collected at RHIC.
Date: July 26, 2004
Creator: Tuchin, K.
System: The UNT Digital Library
The Weak lensing bispectrum (open access)

The Weak lensing bispectrum

Weak gravitational lensing of background galaxies offers an excellent opportunity to study the intervening distribution of matter. While much attention to date has focused on the two-point function of the cosmic shear, the three-point function, the bispectrum, also contains very useful cosmological information. Here, we compute three corrections to the bispectrum which are nominally of the same order as the leading term. We show that the corrections are small, so they can be ignored when analyzing present surveys. However, they will eventually have to be included for accurate parameter estimates from future surveys.
Date: January 1, 2005
Creator: Dodelson, Scott & Zhang, Pengjie
System: The UNT Digital Library
Seismic Response Prediction of Nupec's Field Model Tests of Npp Structures With Adjacent Building Effect. (open access)

Seismic Response Prediction of Nupec's Field Model Tests of Npp Structures With Adjacent Building Effect.

As part of a verification test program for seismic analysis computer codes for Nuclear Power Plant (NPP) structures, the Nuclear Power Engineering Corporation (NUPEC) of Japan has conducted a series of field model tests to address the dynamic cross interaction (DCI) effect on the seismic response of NPP structures built in close proximity to each other. The program provided field data to study the methodologies commonly associated with seismic analyses considering the DCI effect. As part of a collaborative program between the United States and Japan on seismic issues related to NPP applications, the U.S. Nuclear Regulatory Commission sponsored a program at Brookhaven National Laboratory (BNL) to perform independent seismic analyses which applied common analysis procedures to predict the building response to recorded earthquake events for the test models with DCI effect. In this study, two large-scale DCI test model configurations were analyzed: (1) twin reactor buildings in close proximity and (2) adjacent reactor and turbine buildings. This paper describes the NUPEC DCI test models, the BNL analysis using the SASSI 2000 program, and comparisons between the BNL analysis results and recorded field responses. To account for large variability in the soil properties, the conventional approach of computing seismic responses …
Date: March 4, 2004
Creator: Xu, J.; Hofmayer, C. & Ali, S.
System: The UNT Digital Library
Metallization of Hydrogen and Other Small Molecules at 100 GPa Pressures (open access)

Metallization of Hydrogen and Other Small Molecules at 100 GPa Pressures

Fluid hydrogen, oxygen, and nitrogen become metallic at 100 GPa (1 Mbar) pressures. Disorder is the primary reason for observing a metal at lower pressures in the fluid than expected for the ordered solid. This metallic transition is similar to those observed in fluid Cs and Rb by Hensel et al. All five undergo a Mott transition from a semiconducting to metallic fluid with the same electrical conductivities. In contrast, water is a proton conductor at pressures up to 200 GPa. Extreme conditions were achieved for {approx}100 ns with a reverberating shock wave generated with a two-stage light-gas gun.
Date: August 17, 2001
Creator: Nellis, W J
System: The UNT Digital Library
First Field Trial of Optical Label-Based Switching and Packet Drop on a 477km NTON/Sprint Link (open access)

First Field Trial of Optical Label-Based Switching and Packet Drop on a 477km NTON/Sprint Link

We demonstrate the first field trial of optical label-based wavelength switching and packet drop on 476.8km of the National Transparent Optical Network. Subcarrier multiplexed labels control a switch fabric that includes a tunable wavelength converter and arrayed waveguide grating router.
Date: December 10, 2001
Creator: Hernandez, V. J.; Pan, Z.; Cao, J.; Tsui, V. K.; Bansal, Y.; Fong, S. K. H. et al.
System: The UNT Digital Library
Analysis and Comparison of Test Results from the Small Wind Research Turbine Test Project: Preprint (open access)

Analysis and Comparison of Test Results from the Small Wind Research Turbine Test Project: Preprint

Most small wind turbines furl (yaw or tilt out of the wind) as a means of limiting power and rotor speeds in high winds. The Small Wind Research Turbine (SWRT) testing project was initiated in 2003 with the goal of better characterizing both small wind turbine loads (including thrust) and dynamic behavior, specifically as they relate to furling. The main purpose of the testing was to produce high-quality data sets for model development and validation and to help the wind industry further their understanding of small wind turbine behavior. Testing was conducted on a modified Bergey Excel 10-kW wind turbine. A special shaft sensor was designed to measure shaft loads including thrust, torque, and shaft bending. Analysis of 10-minute mean data showed a strong correlation between furling and center of thrust location, as calculated from the shaft-bending and thrust measurements. Data were collected for three different turbine configurations that included a change in the lateral furling offset and the blades. An analysis of inflow conditions indicated that organized atmospheric turbulence had some impact on furling.
Date: November 1, 2004
Creator: Corbus, D. & Prascher, D.
System: The UNT Digital Library
A Tightly Coupled Particle-Fluid Model for DNA-Laden Flows in Complex Microscale Geometries (open access)

A Tightly Coupled Particle-Fluid Model for DNA-Laden Flows in Complex Microscale Geometries

We present a stable and convergent method for the computation of flows of DNA-laden fluids in microchannels with complex geometry. The numerical strategy combines a ball-rod model representation for polymers tightly coupled with a projection method for incompressible viscous flow. We use Cartesian grid embedded boundary methods to discretize the fluid equations in the presence of complex domain boundaries. A sample calculation is presented showing flow through a packed array microchannel in 2D.
Date: November 18, 2004
Creator: Trebotich, D; Miller, G H; Colella, P; Graves, D T; Martin, D F & Schwartz, P O
System: The UNT Digital Library
Gas Pressure Forming of Titanium Alloys and Composites by Transformation Superplasticity (open access)

Gas Pressure Forming of Titanium Alloys and Composites by Transformation Superplasticity

By thermally cycling through their transformation temperature range, coarse-grained, polymorphic materials can be deformed superplastically, owing to the emergence of transformation mismatch plasticity (or transformation superplasticity) as a deformation mechanism. This mechanism is investigated under biaxial stress conditions during thermal cycling of unalloyed titanium, Ti-6Al-4V, and their composites (Ti/10 vol.% TiC{sub p}, Ti-6Al-4V/10 vol% TiC{sub p} and Ti-6Al-4V/5 vol.% TiB{sub w}). During gas-pressure dome bulging experiments, the dome height was measured as a function of forming time. Adapting existing models of biaxial doming to the case of transformation superplasticity where the strain-rate sensitivity is unity, we verify the operation of this deformation mechanism in all experimental materials, and compare the biaxial results to uniaxial thermal cycling results on the same materials. Finally, existing thickness distribution models are compared with experimentally measured profiles.
Date: October 23, 2001
Creator: Frary, M; Schuh, C & Dunand, D C
System: The UNT Digital Library
The BOUT Project: Validation and Benchmark of BOUT Code and Experimental Diagnostic Tools for Fusion Boundary Turbulence (open access)

The BOUT Project: Validation and Benchmark of BOUT Code and Experimental Diagnostic Tools for Fusion Boundary Turbulence

A boundary plasma turbulence code BOUT is presented. The preliminary encouraging results have been obtained when comparing with probe measurements for a typical Ohmic discharge in CT-7 tokamak. The validation and benchmark of BOUT code and experimental diagnostic tools for fusion boundary plasma turbulence is proposed.
Date: August 9, 2001
Creator: Xu, X Q
System: The UNT Digital Library
Measurement of the azimuthal angle distribution of leptons from W boson decays as a function of the W transverse momentum in p anti-p collisions at s**(1/2) = 1.8-TeV (open access)

Measurement of the azimuthal angle distribution of leptons from W boson decays as a function of the W transverse momentum in p anti-p collisions at s**(1/2) = 1.8-TeV

We present the first measurement of the A{sub 2} and A{sub 3} angular coefficients of the W boson produced in proton-antiproton collisions. We study W {yields} ev{sub e} and W {yields} {mu}{nu}{sub {mu}} candidate events produced in association with at least one jet at CDF, during Run Ia and Run Ib of the Tevatron at {radical}s = 1.8 TeV. The corresponding integrated luminosity was 110 pb{sup -1}. The jet balances the transverse momentum of the W and introduces QCD effects in W boson production. The extraction of the angular coefficients is achieved through the direct measurement of the azimuthal angle of the charged lepton in the Collins-Soper rest-frame of the W boson. The angular coefficients are measured as a function of the transverse momentum of the W boson. The electron, muon, and combined results are in good agreement with the Standard Model prediction, up to order {alpha}{sub s}{sup 2} in QCD.
Date: April 1, 2005
Creator: Acosta, D.; Affolder, Anthony A.; Albrow, M. G.; Ambrose, D.; Amidei, D.; Anikeev, K. et al.
System: The UNT Digital Library
Measurement of Electron Impact Collisional Excitation Cross Sections of Ni to Ga-Like Gold (open access)

Measurement of Electron Impact Collisional Excitation Cross Sections of Ni to Ga-Like Gold

None
Date: August 24, 2004
Creator: May, M.; Beiersdorfer, P.; Jordan, N.; Scofield, J.; Reed, K.; Hansen, S. et al.
System: The UNT Digital Library