Resource Type

105 Matching Results

Results open in a new window/tab.

Computation of self-consistent 2-D MHD with neutral-beam and bootstrap currents in elongated plasmas (open access)

Computation of self-consistent 2-D MHD with neutral-beam and bootstrap currents in elongated plasmas

The observation of substantial current drive from neutral beam injection (NBI) in TFTR, JET and DIII-D has led to renewed interest in a steady state, non-inductively driven tokamak. The discovery of apparently considerable neoclassical (bootstrap) current in TFTR, makes a steady state device even more attractive since the bootstrap portion of the current could be obtained without additional power input. Motivated by these results, we have developed a code, ACCOME, which self-consistently computes the 2-D MHD equilibrium with the current driven by neutral beams, bootstrap and the electric field. In this paper we first describe some details of the code in the next section and in the subsequent section show some applications to DIII-D and to a possible ITER design.
Date: April 5, 1983
Creator: Devoto, R. S.; Tani, K. & Azumi, M.
System: The UNT Digital Library
Biosynthesis of a Fully Functional Cyclotide inside Living Bacterial Cells (open access)

Biosynthesis of a Fully Functional Cyclotide inside Living Bacterial Cells

The cyclotide MCoTI-II is a powerful trypsin inhibitor recently isolated from the seeds of Momordica cochinchinensis, a plant member of cucurbitaceae family. We report for the first time the in vivo biosynthesis of natively-folded MCoTI-II inside live E. coli cells. Our biomimetic approach involves the intracellular backbone cyclization of a linear cyclotide-intein fusion precursor mediated by a modified protein splicing domain. The cyclized peptide then spontaneously folds into its native conformation. The use of genetically engineered E. coli cells containing mutations in the glutathione and thioredoxin reductase genes considerably improves the production of folded MCoTI-II in vivo. Biochemical and structural characterization of the recombinant MCoTI-II confirmed its identity. Biosynthetic access to correctly-folded cyclotides allows the possibility of generating cell-based combinatorial libraries that can be screened inside living cells for their ability to modulate or inhibit cellular processes.
Date: April 5, 2007
Creator: Camarero, J A; Kimura, R H; Woo, Y; Cantor, J & Shekhtman, A
System: The UNT Digital Library
Protein Microarrays--Without a Trace (open access)

Protein Microarrays--Without a Trace

Many experimental approaches in biology and biophysics, as well as applications in diagnosis and drug discovery, require proteins to be immobilized on solid supports. Protein microarrays, for example, provide a high-throughput format to study biomolecular interactions. The technique employed for protein immobilization is a key to the success of these applications. Recent biochemical developments are allowing, for the first time, the selective and traceless immobilization of proteins generated by cell-free systems without the need for purification and/or reconcentration prior to the immobilization step.
Date: April 5, 2007
Creator: Camarero, J A
System: The UNT Digital Library
Quadratic function approaching method for magnetotelluric soundingdata inversion (open access)

Quadratic function approaching method for magnetotelluric soundingdata inversion

The quadratic function approaching method (QFAM) is introduced for magnetotelluric sounding (MT) data inversion. The method takes the advantage of that quadratic function has single extreme value, which avoids leading to an inversion solution for local minimum and ensures the solution for global minimization of an objective function. The method does not need calculation of sensitivity matrix and not require a strict initial earth model. Examples for synthetic data and field measurement data indicate that the proposed inversion method is effective.
Date: April 5, 2004
Creator: Liangjun, Yan; Wenbao, Hu & Zhang, Keni
System: The UNT Digital Library
Melting Sequence of Quarkonia (open access)

Melting Sequence of Quarkonia

In this talk I discuss what we can learn about quarkonium dissociation from lattice-potential based models, and summarize the current understanding of lattice data on quarkonium.
Date: April 5, 2008
Creator: Mocsy,A.
System: The UNT Digital Library
Simulations of Fracture and Fragmentation of Geologic Materials using Combined FEM/DEM/SPH Analysis (open access)

Simulations of Fracture and Fragmentation of Geologic Materials using Combined FEM/DEM/SPH Analysis

An overview of the Lawrence Discrete Element Code (LDEC) is presented, and results from a study investigating the effect of explosive and impact loading on geologic materials using the Livermore Distinct Element Code (LDEC) are detailed. LDEC was initially developed to simulate tunnels and other structures in jointed rock masses using large numbers of polyhedral blocks. Many geophysical applications, such as projectile penetration into rock, concrete targets, and boulder fields, require a combination of continuum and discrete methods in order to predict the formation and interaction of the fragments produced. In an effort to model this class of problems, LDEC now includes implementations of Cosserat point theory and cohesive elements. This approach directly simulates the transition from continuum to discontinuum behavior, thereby allowing for dynamic fracture within a combined finite element/discrete element framework. In addition, a Smooth Particle Hydrodynamics (SPH) capability has been incorporated into LDEC, permitting the simulation of fluid-structure interaction. We will present results from a study of detonation-induced fracture and fragmentation of geologic media surrounding a tunnel using LDEC.
Date: April 5, 2007
Creator: Morris, J. P. & Johnson, S. M.
System: The UNT Digital Library
Imaging at high spatial resolution: Soft x-ray microscopy to 15nm (open access)

Imaging at high spatial resolution: Soft x-ray microscopy to 15nm

Soft x-ray microscopy has now achieved 15 nm spatial resolution with new zone plates and bending magnet radiation. Combined with elemental sensitivity and flexible sample environment (applied magnetic or electric fields, wet samples, windows, overcoatings) this emerges as a valuable tool for nanoscience and nanotechnology, complimenting common electron and scanning tip microscopies. In this presentation we describe recent advances in spatial resolution, expectations for the near future, and applications to magnetic materials, bio-tomography, etc.
Date: April 5, 2006
Creator: Attwood, D.; Chao, W.; Anderson, E.; Liddle, J. A.; Harteneck, B.; Fischer, P. et al.
System: The UNT Digital Library
The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites (open access)

The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites

Samarium-neodymium isotopic analyses of unleached and acid-leached mineral fractions from the recently identified olivine-bearing shergottite Northwest Africa 1195 yield a crystallization age of 348 {+-} 19 Ma and an {var_epsilon}{sub Nd}{sup 143} value of +40.1 {+-} 1.3. Maskelynite fractions do not lie on the Sm-Nd isochron and appear to contain a martian surface component with low {sup 147}Sm/{sup 144}Nd and {sup 143}Nd/{sup 144}Nd ratios that was added during shock. The Rb-Sr system is disturbed and does not yield an isochron. Terrestrial Sr appears to have affected all of the mineral fractions, although a maximum initial {sup 87}Sr/{sup 86}Sr ratio of 0.701614 {+-} 16 is estimated by passing a 348 Ma reference isochron through the maskelynite fraction that is least affected by contamination. The high initial {var_epsilon}{sub Nd}{sup 143} value and the low initial {sup 87}Sr/{sup 86}Sr ratio, combined with the geologically young crystallization age, indicate that Northwest Africa 1195 is derived from a source region characterized by a long-term incompatible element depletion. The age and initial Sr and Nd isotopic compositions of Northwest Africa 1195 are very similar to those of Queen Alexandra Range 94201, indicating these samples were derived from source regions with nearly identical Sr-Nd isotopic systematics. These …
Date: April 5, 2007
Creator: Symes, S; Borg, L; Shearer, C & Irving, A
System: The UNT Digital Library
Simulation of Flow and Transport at the Micro (Pore) Scale (open access)

Simulation of Flow and Transport at the Micro (Pore) Scale

An important problem in porous media involves the ability of micron and submicron-sized biological particles such as viruses or bacteria to move in groundwater systems through geologic media characterized by rock or mixed gravel, clay and sand materials. Current simulation capabilities require properly upscaled (continuum) models of colloidal filtration and adsorption to augment existing theories of fluid flow and chemical transport. Practical models typically address flow and transport behavior in aquifers over distances of 1 to 10 km where, for example, fluid momentum balance is governed by the simple Darcy's Law as a function of a pressure gradient, elevation gradient and a medium-dependent permeability parameter. In addition to fluid advection, there are multiple transport processes occurring in these systems including diffusion, dispersion and chemical interactions with solids or other aqueous chemical species. Particle transport is typically modeled in the same way as dissolved species, except that additional loss terms are incorporated to model particle filtration (physical interception), adsorption (chemical interception) and inactivation. Proper resolution of these processes at the porous medium continuum scale constitutes an important closure problem in subsurface science. We present a new simulation capability based on enabling technologies developed for microfluidics applications to model transport of colloidal-sized …
Date: April 5, 2007
Creator: Trebotich, D & Miller, G H
System: The UNT Digital Library
A systematic study of J/psi suppression in cold nuclear matter (open access)

A systematic study of J/psi suppression in cold nuclear matter

Understanding the effects of cold nuclear matter on J/psi production is a key requirement in order to interpret the J/psi suppression reported in heavy-ion collisions. Based on a Glauber model, the J/psi-nucleon inelastic cross section is determined from a statistical analysis of J/psi world data on nuclear targets. The global fit of all data gives sigmaJ/psiN = 3.4 +/- 0.2 mb, significantly smaller than previous estimates, yet the chi2 of the fit is pretty large, chi2/ndf = 1.5. A similar value, sigmaJ/psiN = 3.5 +/- 0.2 +/- 1.7 mb, is obtained when the De Florian-Sassot modifications of the nuclear parton densities are included in the analysis, although we emphasize that the present uncertainties on gluon (anti)shadowing do not allow for a precise determination of sigmaJ/psiN. Finally, the possible energy dependence of the J/psi-nucleon inelastic cross section is investigated within this framework. No significant energy dependence of the J/psi-N interaction is observed.
Date: April 5, 2008
Creator: Arleo, Francois & Tram, Vi-Nham
System: The UNT Digital Library
Prototype Performance of Novel Muon Telescope Detector at STAR. (open access)

Prototype Performance of Novel Muon Telescope Detector at STAR.

Research on a large-area, cost-effective Muon Telescope Detector (MTD) has been carried out for RHIC and for next generation detectors at future QCD Lab. We utilize state-of-the-art multi-gap resistive plate chambers with large modules and long readout strips in detector design. The results from cosmic ray and beam test will be presented to address intrinsic timing and spatial resolution for a Long-MRPC. The prototype performance of a novel muon telescope detector at STAR will be reported, including muon identification capability, timing and spatial resolution.
Date: April 5, 2008
Creator: Ruan,L.
System: The UNT Digital Library
Electron electric dipole moment experiment using electric-fieldquantized slow cesium atoms (open access)

Electron electric dipole moment experiment using electric-fieldquantized slow cesium atoms

A proof-of-principle electron electric dipole moment (e-EDM)experiment using slow cesium atoms, nulled magnetic fields, and electricfield quantization has been performed. With the ambient magnetic fieldsseen by the atoms reduced to less than 200 pT, an electric field of 6MV/m lifts the degeneracy between states of unequal lbar mF rbar and,along with the low (approximately 3 m/s) velocity, suppresses thesystematic effect from the motional magnetic field. The low velocity andsmall residual magnetic field have made it possible to induce transitionsbetween states and to perform state preparation, analysis, and detectionin regions free of applied static magnetic and electric fields. Thisexperiment demonstrates techniques that may be used to improve the e-EDMlimit by two orders of magnitude, but it is not in itself a sensitivee-EDM search, mostly due to limitations of the laser system.
Date: April 5, 2007
Creator: Amini, Jason M.; Munger Jr., Charles T. & Gould, Harvey.
System: The UNT Digital Library
Motif based Hessian matrixfor ab initio geometry optimization ofnanostructures (open access)

Motif based Hessian matrixfor ab initio geometry optimization ofnanostructures

A simple method to estimate the atomic degree Hessian matrixof a nanosystem is presented. The estimated Hessian matrix, based on themotif decomposition of the nanosystem, can be used to accelerate abinitio atomic relaxations with speedups of 2 to 4 depending on the sizeof the system. In addition, the programing implementation for using thismethod in a standard ab initio package is trivial.
Date: April 5, 2006
Creator: Zhao, Zhengji; Wang, Lin-Wang & Meza, Juan
System: The UNT Digital Library
Fusion-breeder-reactor design studies (open access)

Fusion-breeder-reactor design studies

Studies of the technical and economic feasibility of producing fissile fuel in tandem mirrors and in tokamaks for use in fission reactors are presented. Fission-suppressed fusion breeders promise unusually good safety features and can provide make-up fuel for 11 to 18 LWRs of equal nuclear power depending on the fuel cycle. The increased revenues from sales of both electricity and fissile material might allow the commercial application of fusion technology significantly earlier than would be possible with electricity production from fusion alone. Fast-fission designs might allow a fusion reactor with a smaller fusion power and lower Q value to be economical and thus make this application of fusion even earlier. A demonstration reactor with a fusion power of 400 MW could produce 600 kg of fissile material per year at a capacity factor of 50%. The critical issues, for which small scale experiments are either being carried out or planned, are: (1) material compatibility, (2) beryllium feasibility, (3) MHD effects, and (4) pyrochemical reprocessing.
Date: April 5, 1983
Creator: Moir, R. W.; Lee, J. D. & Coops, M. S.
System: The UNT Digital Library
Evaluation of current regulations and real accident conditions (open access)

Evaluation of current regulations and real accident conditions

In order to improve estimates of the effectiveness of current regulatory standards, a program was initiated by the US Nuclear Regulatory Commission (NRC) to have the Lawrence Livermore Laboratory (LLNL) evaluate regulatory standards against real world accident conditions. This paper presents the results of the evaluation performed for the hypothetical 30-foot drop onto an unyielding surface and real world impact conditions which might be experienced by a spent fuel cask being transported by a truck. The results of the evaluations performed for other pertinent accident conditions for truck and train transport will be documented at the conclusion of the program. 10 refs., 8 figs., 3 tabs.
Date: April 5, 1985
Creator: Fischer, L.E.; Kimura, C.Y. & Witte, M.C.
System: The UNT Digital Library
Modal study of refractive effects on x-ray laser coherence (open access)

Modal study of refractive effects on x-ray laser coherence

The role of smoothly varying transverse gain and refraction profiles on x-ray laser intensity and coherence is analyzed by modally expanding the electric field within the paraxial approximation. Comparison with a square transverse profile reveals that smooth-edged profiles lead to: (1) a greatly reduced number of guided modes, (2) the continued cancellation of local intensity from a loosely guided mode by resonant free modes, (3) and the absence of extraneous (or anomalous) free mode resonances. These generic spectral properties should enable a considerable simplification in analyzing and optimizing the coherence properties of laboratory soft x-ray lasers. 6 refs., 3 figs.
Date: April 5, 1991
Creator: Amendt, P.; London, R.A. (Lawrence Livermore National Lab., CA (USA)) & Strauss, M. (Israel Atomic Energy Commission, Beersheba (Israel). Nuclear Research Center-Negev)
System: The UNT Digital Library
From bit-strings (part way) to quaternions (open access)

From bit-strings (part way) to quaternions

We present work in progress on constructing rotations and boosts from bit strings, and a mapping of bit-strings onto integer quaternion coordinates.
Date: April 5, 1991
Creator: Noyes, H. Pierre
System: The UNT Digital Library
Emittance measurements on field emitter diodes (open access)

Emittance measurements on field emitter diodes

On the basis of time-integrated emittance measurements, several different types of field emitter diodes were characterized at 1 to 3 kA, 1 MeV. These measurements were part of the design effort for the injector system of a linear induction accelerator, to be used as a flash x-ray source at Lawrence Livermore Laboratory. The experimental parameters were the cathode type, the anode mesh texture, the diode spacing and voltage, and the level of collimation of the emerging beam. Experimental results are presented that show that over a wide range, the emittance was proportional to the level of collimation. For any one diode, with the spacing left fixed, the emittance was found to be essentially independent of the diode voltage and current. Differential focusing of different energy beam components affects most strongly the peripheral components of the beam, and strong collimation was found to minimize the effects of momentum spread on the emittance. The lowest emittances (30 to 40 mr-cm at 400 A) were obtained with a foil-type cathode in a ball-over-plane configuration, using an etched tungsten mesh anode, and collimating the beam to one quarter of the total current.
Date: April 5, 1979
Creator: Kulke, B. & Kihara, R.
System: The UNT Digital Library
Agriculture, greenhouse, wetland and other beneficial uses of geothermal fluids and heat (open access)

Agriculture, greenhouse, wetland and other beneficial uses of geothermal fluids and heat

The status for related beneficial uses including agriculture, greenhousing, and geothermal wetlands is presented. Data published for the geothermal fluids found in areas of China have been examined and compared with the geothermal fluids used in the agriculture evaluations in the United States. This comparison indicates that the geothermal fluids found in parts of China are similar to those used in the US agriculture experiments. Greenhousing is addressed largely from the standpoint of hardware systems and technology being employed or being proposed in the United States.
Date: April 5, 1981
Creator: Schmitt, R. C.
System: The UNT Digital Library
Symposium: New Trends in Unconventional Approaches to Magnetic Fusion (open access)

Symposium: New Trends in Unconventional Approaches to Magnetic Fusion

An extensive review of the meeting is given. The concepts discussed included reverse-field pinches, compact tori, advanced stellarators, multipoles, surface magnetic confinement systems, the bumpy torus, and a collection of mirror-based approaches. (MOW)
Date: April 5, 1983
Creator: Post, R. F.
System: The UNT Digital Library
Fluorescence diagnostics in two-step laser excitation of high J atoms (open access)

Fluorescence diagnostics in two-step laser excitation of high J atoms

Using a pair of lasers near 6000 A, the J = 6 ground state is excited to a J = 6 intermediate level and then to a J = 5 upper state. Non-resonant fluorescences from both excited states are separately detected. Results of a set of model calculations are tabulated. Level 3 average populations are always very small, since the system decays rapidly into inaccessible metastable states. This means that chemistry experiments are difficult. The differences between parallel and perpendicular polarization are modest. The fluorescence dips converge to a value near 50%. The level 3 populations do not approach a common value. This means that the most reliable experimental measurement does not determine the level populations. The most striking changes appear in the last two, most exact, models. The difference between the models is that one includes, for the first time, the linear frequency chirp produced by the fanlike spread of the focussed laser beams. This seemingly innocuous change halves the population left in the ground state. It appears that analogues of adiabatic passage and adiabatic rapid passage respectively are being observed.
Date: April 5, 1979
Creator: Stern, Richard C.; Shore, Bruce W. & Lang, Neil C.
System: The UNT Digital Library
Monte Carlo simulation of the microcanonical ensemble (open access)

Monte Carlo simulation of the microcanonical ensemble

We consider simulating statistical systems with a random walk on a constant energy surface. This combines features of deterministic molecular dynamics techniques and conventional Monte Carlo simulations. For discrete systems the method can be programmed to run an order of magnitude faster than other approaches. It does not require high quality random numbers and may also be useful for nonequilibrium studies. 10 references.
Date: April 5, 1984
Creator: Creutz, M.
System: The UNT Digital Library
Transformation as a Design Process and Runtime Architecture for High Integrity Software (open access)

Transformation as a Design Process and Runtime Architecture for High Integrity Software

We have discussed two aspects of creating high integrity software that greatly benefit from the availability of transformation technology, which in this case is manifest by the requirement for a sophisticated backtracking parser. First, because of the potential for correctly manipulating programs via small changes, an automated non-procedural transformation system can be a valuable tool for constructing high assurance software. Second, modeling the processing of translating data into information as a, perhaps, context-dependent grammar leads to an efficient, compact implementation. From a practical perspective, the transformation process should begin in the domain language in which a problem is initially expressed. Thus in order for a transformation system to be practical it must be flexible with respect to domain-specific languages. We have argued that transformation applied to specification results in a highly reliable system. We also attempted to briefly demonstrate that transformation technology applied to the runtime environment will result in a safe and secure system. We thus believe that the sophisticated multi-lookahead backtracking parsing technology is central to the task of being in a position to demonstrate the existence of HIS.
Date: April 5, 1999
Creator: Bespalko, Stephen J. & Winter, Victor L.
System: The UNT Digital Library
DENSITY-FUNCTIONAL CALCULATIONS FOR Ce, Th, AND Pu METALS AND ALLOYS (open access)

DENSITY-FUNCTIONAL CALCULATIONS FOR Ce, Th, AND Pu METALS AND ALLOYS

The phase diagrams of Ce, Th, and Pu metals have been studied by means of density-functional theory (DFT). In addition to these metals, the phase stability of Ce-Th and Pu-Am alloys has been also investigated from first-principles calculations. Equation-of-state (EOS) for Ce, Th, and the Ce-Th alloys has been calculated up to 1 Mbar pressure in good comparison to experimental data. Present calculations shows that the Ce-Th alloys adopt a body-centeredtetragonal (bct) structure upon hydrostatic compression that is in excellent agreement with measurements. The ambient pressure phase diagram of Pu is shown to be very poorly described by traditional DFT but rather well modeled when including magnetic interactions. In particular, the anomalous {var_sigma} phase of Pu is shown to be stabilized by magnetic disorder at elevated temperatures. The Pu-Am system has also been studied in a similar fashion and it is shown that this system, for about 25% Am content, becomes antiferromagnetic below about 400 K that corroborate the recent discovery of a Curie-Weiss behavior in this system.
Date: April 5, 2004
Creator: Landa, A & Soderlind, P
System: The UNT Digital Library