Characterizing the nano and micro structure of concrete to improve its durability (open access)

Characterizing the nano and micro structure of concrete to improve its durability

New and advanced methodologies have been developed to characterize the nano and microstructure of cement paste and concrete exposed to aggressive environments. High resolution full-field soft X-ray imaging in the water window is providing new insight on the nano scale of the cement hydration process, which leads to a nano-optimization of cement-based systems. Hard X-ray microtomography images on ice inside cement paste and cracking caused by the alkali-silica reaction (ASR) enables three-dimensional structural identification. The potential of neutron diffraction to determine reactive aggregates by measuring their residual strains and preferred orientation is studied. Results of experiments using these tools will be shown on this paper.
Date: October 22, 2008
Creator: Monteiro, P. J. M.; Kirchheim, A. P.; Chae, S.; Fischer, P.; MacDowell, A. A.; Schaible, E. et al.
System: The UNT Digital Library
Recent Searches for Exotic Physics at the BaBar/PEP-II B-factory (open access)

Recent Searches for Exotic Physics at the BaBar/PEP-II B-factory

I present three recent results from searches for exotic physics at the BABAR/PEP-II B-factory. These results span many of the samples produced at the B-factory, including B mesons, {tau} leptons, and {Upsilon}(3S) mesons. We have searched for CPT-violation in B{sup 0} mixing and find no significant deviation from the no-violation hypothesis. We have also searched for lepton-flavor-violating decays of the {tau} using {tau}{sup -} {yields} {omega}{ell}{sup -} and {tau}{sup -} {yields} {ell}{sup -}{ell}{sup +}{ell}{sup -} and their charge conjugates. We find no evidence for these processes and set upper limits on their branching fractions. Finally, we have searched for a low-mass Higgs boson in the decay {Upsilon}(3S) {yields} {gamma}A{sup 0}, where the Higgs decays invisibly. We find no evidence for such a decay and set upper limits across a range of possible Higgs masses.
Date: October 22, 2008
Creator: Sekula, Stephen Jacob
System: The UNT Digital Library
The National Ignition Facility: The world's largest optical system (open access)

The National Ignition Facility: The world's largest optical system

None
Date: October 22, 2007
Creator: Stolz, C J
System: The UNT Digital Library
Potential of Photovoltaics (open access)

Potential of Photovoltaics

Presented at the Association of Industrial Metallizers, Coaters and Laminators (AIMCAL) Fall Technical Conference 2008 and 22nd International Vacuum Web Coating Conference held October 19-22, 2008 in Myrtle Beach, South Carolina. This presentation discusses PV in the world energy portfolio, PV basics, PV technologies, and vacuum web-coating applications in PV.
Date: October 22, 2008
Creator: Nelson, B. P.
System: The UNT Digital Library
On The Reproducibility of Seasonal Land-surface Climate (open access)

On The Reproducibility of Seasonal Land-surface Climate

The sensitivity of the continental seasonal climate to initial conditions is estimated from an ensemble of decadal simulations of an atmospheric general circulation model with the same specifications of radiative forcings and monthly ocean boundary conditions, but with different initial states of atmosphere and land. As measures of the ''reproducibility'' of continental climate for different initial conditions, spatio-temporal correlations are computed across paired realizations of eleven model land-surface variables in which the seasonal cycle is either included or excluded--the former case being pertinent to climate simulation, and the latter to seasonal anomaly prediction. It is found that the land-surface variables which include the seasonal cycle are impacted only marginally by changes in initial conditions; moreover, their seasonal climatologies exhibit high spatial reproducibility. In contrast, the reproducibility of a seasonal land-surface anomaly is generally low, although it is substantially higher in the Tropics; its spatial reproducibility also markedly fluctuates in tandem with warm and cold phases of the El Nino/Southern Oscillation. However, the overall degree of reproducibility depends strongly on the particular land-surface anomaly considered. It is also shown that the predictability of a land-surface anomaly implied by its reproducibility statistics is consistent with what is inferred from more conventional predictability …
Date: October 22, 2004
Creator: Phillips, T J
System: The UNT Digital Library
U.S. and Russian Collaboration in the Area of Nuclear Forensics (open access)

U.S. and Russian Collaboration in the Area of Nuclear Forensics

Nuclear forensics has become increasingly important in the fight against illicit trafficking in nuclear and other radioactive materials. The illicit trafficking of nuclear materials is, of course, an international problem; nuclear materials may be mined and milled in one country, manufactured in a second country, diverted at a third location, and detected at a fourth. There have been a number of articles in public policy journals in the past year that call for greater interaction between the U. S. and the rest of the world on the topic of nuclear forensics. Some believe that such international cooperation would help provide a more certain capability to identify the source of the nuclear material used in a terrorist event. An improved international nuclear forensics capability would also be important as part of the IAEA verification toolkit, particularly linked to increased access provided by the additional protocol. A recent study has found that, although international progress has been made in securing weapons-usable HEU and Pu, the effort is still insufficient. They found that nuclear material, located in 40 countries, could be obtained by terrorists and criminals and used for a crude nuclear weapon. Through 2006, the IAEA Illicit Trafficking Database had recorded a …
Date: October 22, 2007
Creator: Kristo, M J
System: The UNT Digital Library
Diffusion of a Highly-Charged Supramolecular Assembly: Direct Observation of Ion-Association in Water (open access)

Diffusion of a Highly-Charged Supramolecular Assembly: Direct Observation of Ion-Association in Water

Understanding the solution behavior of supramolecular assemblies is essential for a full understanding of the formation and chemistry of synthetic host-guest systems. While the interaction between host and guest molecules is generally the focus of mechanistic studies of host-guest complexes, the interaction of the host-guest complex with other species in solution remains largely unknown, although in principle accessible by diffusion studies. Several NMR techniques are available to monitor diffusion and have recently been reviewed. Pulsed gradient spin-echo (PGSE) NMR methods have attracted increasing interest, since they allow diffusion coefficients to be measured with high accuracy; they have been successfully used with observation of {sup 7}Li and {sup 31}P nuclei as well as with {sup 1}H NMR. We report here the direct measurement of diffusion coefficients to observe ion-association interactions by counter cations with a highly-charged supramolecular assembly. Raymond and coworkers have described the design and chemistry of a class of metal-ligand supramolecular assemblies over the past decade. The [Ga{sub 4}L{sub 6}]{sup 12-} (L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene) (1) (Figure 1) assembly has garnered the most attention, with the exploration of the dynamics and mechanism of guest exchange as well as the ability of 1 to achieve either stoichiometric or catalytic reactions inside …
Date: October 22, 2007
Creator: University of California, Berkeley; Laboratory, Lawrence Berkeley National; Raymond, Kenneth; Pluth, Michael D.; Tiedemann, Bryan E.F.; van Halbeek, Herman et al.
System: The UNT Digital Library
Facilities for Development of Modified Nitride-Based Fuel Pellets (open access)

Facilities for Development of Modified Nitride-Based Fuel Pellets

Facilities to support development of modified nitride-based reactor fuel pellets have been activated and are now in operation at Lawrence Livermore National Laboratory. These facilities provide the controls and monitored laboratory conditions required to produce, evaluate, and verify quality of the nitride-based product required for this fuel application. By preserving the high melting point, high thermal conductivity, and high actinide density properties of nitride fuel while enhancing stoichiometry, density, and grain structure, and by applying inert matrix (ZrN) and neutron absorbing (HfN) additives for improved stability and burn-up characteristics, the requirements for a long-life fuel to support sealed core reactor applications may be met. This paper discusses requirements for producing the modified nitride powders for sintering of fuel pellets, translation of these requirements into facility specifications, and implementation of these specifications as facility capabilities.
Date: October 22, 2003
Creator: Meier, T.; Ebbinghaus, B. & Choi, J.
System: The UNT Digital Library
Evaluation of the Relative Importance of Parameters Influencing Perforation Cleanup (open access)

Evaluation of the Relative Importance of Parameters Influencing Perforation Cleanup

Completion of cased and cemented wells by shaped-charge perforation results in damage to the formation, which can significantly reduce well productivity. Typically, underbalanced conditions are imposed during perforation in an effort to remove damaged rock and shaped-charge debris from the perforation tunnel. Immediately after the shaped-charge jet penetrates the formation, there is a transient surge of fluid from the formation through the perforation and into the well bore. Experimental evidence suggests that it is this transient pressure surge that leads to the removal of damaged rock and charge debris leaving an open perforation tunnel. We have developed a two-stage computational model to simulate the perforation process and subsequent pressure surge and debris removal. The first stage of the model couples a hydrocode with a model of stress-induced permeability evolution to calculate damage to the formation and the resulting permeability field. The second stage simulates the non-Darcy, transient fluid flow from the formation and removes damaged rock and charge debris from the perforation tunnel. We compare the model to a series of API RP43 section 4 flow tests and explore the influence of fluid viscosity and rock strength on the final perforation geometry and permeability.
Date: October 22, 2003
Creator: Detwiler, R L; Morris, J P; Karacan, C O; Halleck, P M & Hardesty, J
System: The UNT Digital Library
Density-functional calculations of a, b, g, d, dp, and e plutonium (open access)

Density-functional calculations of a, b, g, d, dp, and e plutonium

Total energies for the six known polymorphs of plutonium metal have been calculated within spin and orbital polarized density-functional theory as a function of lattice constant. Theoretical equilibrium volumes and bulk moduli correspond well with experimental data and the calculated total energies are consistent with the known phase diagram of Pu. It is shown that a preference for formation of magnetic moments, increasing through the {alpha} {yields} {beta} {yields} {gamma} phases, explain their position in the ambient pressure phase diagram and their anomalous variation of atomic density. A simple model is presented that establishes a relationship between atomic density, crystal symmetry, and magnetic moments which is universally valid for all Pu phases.
Date: October 22, 2003
Creator: Soderlind, P & Sadigh, B
System: The UNT Digital Library
Integrated process modeling for the laser inertial fusion Energy (LIFE) generation system (open access)

Integrated process modeling for the laser inertial fusion Energy (LIFE) generation system

A concept for a new fusion-fission hybrid technology is being developed at Lawrence Livermore National Laboratory. The primary application of this technology is base-load electrical power generation. However, variants of the baseline technology can be used to 'burn' spent nuclear fuel from light water reactors or to perform selective transmutation of problematic fission products. The use of a fusion driver allows very high burn-up of the fission fuel, limited only by the radiation resistance of the fuel form and system structures. As a part of this process, integrated process models have been developed to aid in concept definition. Several models have been developed. A cost scaling model allows quick assessment of design changes or technology improvements on cost of electricity. System design models are being used to better understand system interactions and to do design trade-off and optimization studies. Here we describe the different systems models and present systems analysis results. Different market entry strategies are discussed along with potential benefits to US energy security and nuclear waste disposal. Advanced technology options are evaluated and potential benefits from additional R&D targeted at the different options is quantified.
Date: October 22, 2009
Creator: Meier, W. R.; Anklam, T. M.; Erlandson, A. C.; Miles, R. R.; Simon, A. J.; Sawicki, R. et al.
System: The UNT Digital Library
Conference on Nuclear Energy and Science for the 21st Century: Atoms for Peace Plus Fifty - Washington, D.C., October 2003 (open access)

Conference on Nuclear Energy and Science for the 21st Century: Atoms for Peace Plus Fifty - Washington, D.C., October 2003

This conference's focus was the peaceful uses of the atom and their implications for nuclear science, energy security, nuclear medicine and national security. The conference also provided the setting for the presentation of the prestigious Enrico Fermi Prize, a Presidential Award which recognizes the contributions of distinguished members of the scientific community for a lifetime of exceptional achievement in the science and technology of nuclear, atomic, molecular, and particle interactions and effects. An impressive group of distinguished speakers addressed various issues that included: the impact and legacy of the Eisenhower Administration’s “Atoms for Peace” concept, the current and future role of nuclear power as an energy source, the challenges of controlling and accounting for existing fissile material, and the horizons of discovery for particle or high-energy physics. The basic goal of the conference was to examine what has been accomplished over the past fifty years as well as to peer into the future to gain insights into what may occur in the fields of nuclear energy, nuclear science, nuclear medicine, and the control of nuclear materials.
Date: October 22, 2006
Creator: Pfaltzgraff, Robert L
System: The UNT Digital Library
EVALUATION OF FLOWSHEET CHANGES FOR THE HIGHLY ENRICHED URANIUM BLENDDOWN PROGRAM (open access)

EVALUATION OF FLOWSHEET CHANGES FOR THE HIGHLY ENRICHED URANIUM BLENDDOWN PROGRAM

H Canyon is considering a flowsheet change for Plutonium (Pu) Contaminated Scrap (PuCS) material. The proposed change is to route dissolved PuCS material directly to a uranium (U) storage tank. As a result, the PuCS solution will bypass Head End and First U Cycle, and will be purified by solvent extraction in Second U Cycle. The PuCS solution contains appreciable amounts of boron (B) and fluoride (F{sup -}), which are currently at trace levels in the U storage tank. Though unlikely, if the B concentration in the U storage tank were to reach 1.8 g B/g U, the entire contents of the U storage tank would likely require a second pass through Second U Cycle to provide sufficient decontamination to meet the Tennessee Valley Authority (TVA) Blend Grade Highly Enriched Uranium (HEU) specification for B, which is 30 {micro}g/g U. In addition, Second U Cycle is expected to provide sufficient decontamination of F{sup -} and Pu regardless of the amount of PuCS solution sent to the storage tank. Though aluminum (Al) is not present in the PuCS solution, B can be credited as a complexant of F{sup -}. Both stability constants from the literature and Savannah River National Laboratory (SRNL) …
Date: October 22, 2007
Creator: Crowder, M.; Rudisill, T.; Laurinat, J. & Mickalonis, J.
System: The UNT Digital Library
RE-EVALUATION OF THE PERMEABLE MATERIAL AT THE BASE OF THE UNCONFINED AQUIFER NEAR LERF HANFORD SITE WASHINGTON (open access)

RE-EVALUATION OF THE PERMEABLE MATERIAL AT THE BASE OF THE UNCONFINED AQUIFER NEAR LERF HANFORD SITE WASHINGTON

None
Date: October 22, 2009
Creator: Smoot, J. L.
System: The UNT Digital Library
Next Generation Safeguards Initiative Workshop on Enhanced Recruiting for International Safeguards (open access)

Next Generation Safeguards Initiative Workshop on Enhanced Recruiting for International Safeguards

In 2007, the National Nuclear Security Administration's Office of Nonproliferation and International Security (NA-24) completed a yearlong review of the challenges facing the international safeguards system today and over the next 25 years. The study found that without new investment in international safeguards, the U.S. safeguards technology base, and our ability to support International Atomic Energy Agency (IAEA) safeguards, will continue to erode and soon may be at risk. To reverse this trend, the then U.S. Secretary of Energy, Samuel Bodman, announced at the 2007 IAEA General Conference that the Department of Energy (DOE) would launch the Next Generation Safeguards Initiative (NGSI). He stated 'IAEA safeguards must be robust and capable of addressing proliferation threats. Full confidence in IAEA safeguards is essential for nuclear power to grow safely and securely. To this end, the U.S. Department of Energy will seek to ensure that modern technology, the best scientific expertise, and adequate resources are available to keep pace with expanding IAEA responsibilities.' To meet this goal, the NGSI objectives include the recruitment of international safeguards experts to work at the U.S. national laboratories and to serve at the IAEA's headquarters. Part of the latter effort will involve enhancing our existing efforts …
Date: October 22, 2008
Creator: Pepper, S.; Rosenthal, M.; Fishbone, L.; Occhiogrosso, D.; Carroll, C.; Dreicer, M. et al.
System: The UNT Digital Library
Performance of the Anti-Coincidence Detector on the GLAST Large Area Telescope (open access)

Performance of the Anti-Coincidence Detector on the GLAST Large Area Telescope

The Anti-Coincidence Detector (ACD), the outermost detector layer in the Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT), is designed to detect and veto incident cosmic ray charged particles, which outnumber cosmic gamma rays by 3-4 orders of magnitude. The challenge in ACD design is that it must have high (0.9997) detection efficiency for singly-charged relativistic particles, but must also have a low probability for self-veto of high-energy gammas by backsplash radiation from interactions in the LAT calorimeter. Simulations and tests demonstrate that the ACD meets its design requirements. The performance of the ACD has remained stable through stand-alone environmental testing, shipment across the U.S., installation onto the LAT, shipment back across the U.S., LAT environmental testing, and shipment to Arizona. As part of the fully-assembled GLAST observatory, the ACD is being readied for final testing before launch.
Date: October 22, 2007
Creator: Thompson, D. J.; Charles, E.; Hartman, R. C.; Moiseev, A. A. & Ormes, J. F.
System: The UNT Digital Library
GRB Simulations in GLAST (open access)

GRB Simulations in GLAST

The Gamma-ray Large Area Space Telescope (GLAST), scheduled to be launched in fall of 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT) is a pair conversion telescope built with a high precision silicon tracker, a segmented CsI electromagnetic calorimeter and a plastic anticoincidence shield. The LAT will survey the sky in the energy range between 20 MeV to more than 300 GeV, shedding light on many issues left open by its highly successful predecessor EGRET. LAT will observe Gamma-Ray Bursts (GRB) in an energy range never explored before; to tie these frontier observations to the better-known properties at lower energies, a second instrument, the GLAST Burst Monitor (GBM) will provide important spectra and timing in the 10 keV to 30 MeV range. We briefly present the instruments onboard the GLAST satellite, their synergy in the GRB observations and the work done so far by the collaboration in simulation, analysis, and GRB sensitivity estimation.
Date: October 22, 2007
Creator: Omodei, Nicola; /INFN, Pisa; Battelino, Milan; Observ., /Stockholm; Komin, Nukri; U., /Montpellier et al.
System: The UNT Digital Library
Exploring the Polarization of Gluons in the Nucleon. (open access)

Exploring the Polarization of Gluons in the Nucleon.

We give an overview of the current status of investigations of the polarization of gluons in the nucleon. We describe some of the physics of the spin-dependent gluon parton distribution and its phenomenology in high-energy polarized hadronic scattering. We also review the recent experimental results.
Date: October 22, 2007
Creator: Stratmann, M. & Vogelsang, W.
System: The UNT Digital Library
LAT Observation of GRBs: Simulations and Sensitivity Studies (open access)

LAT Observation of GRBs: Simulations and Sensitivity Studies

The GLAST Large Area Telescope (LAT) is the next generation satellite experiment for high-energy gamma-ray astronomy. It employs a pair conversion technique to record photons in the energy range from 20 MeV to more than 300 GeV. The LAT will follow the steps from its predecessor EGRET (1991-2000), and will explore the high-energy gamma-ray sky with unprecedented capabilities. The observation of Gamma-Ray Bursts is one of the main science goal of the LAT: in this contribution we compute an estimation of the LAT sensitivity to GRB, adopting a phenomenological description of GRBs, where the high-energy emission in GRB is obtained extrapolating the observed BATSE spectrum up to LAT energies. The effect of the cosmological attenuation is included. We use the BATSE current catalog to build up our statistics.
Date: October 22, 2007
Creator: Omodei, Nicola; /INFN, Pisa; Norris, Jay & U., /Denver
System: The UNT Digital Library
Production of Ultrashort FEL XUV Pulses via a Reverse Undulator Taper (open access)

Production of Ultrashort FEL XUV Pulses via a Reverse Undulator Taper

We adapt the "reverse taper" scheme presented by Saldin etal. (Phys. Rev. ST Accel. Beams, 9, 050702 [2006]) for attosecond pulseproduction to the XUV/soft-xray regime. We find that that GW-level pulsesof a few femtosecond duration or shorter can be produced using electronbeams of quite moderate parameters and undulators of 20-m length orshorter. The output pulse is significantly shifted in wavelength relativeto the main background which permits a further increase in contrast ratiovia simple monochromatization. Moreover, the output pulse has a naturalwavelength chirp that allows further temporal compression, if wanted.Both positive and negative chirps can be produced depending uponthe signof the undulator taper.
Date: October 22, 2007
Creator: Fawley, William M.
System: The UNT Digital Library
Summary (open access)

Summary

The first International GLAST Symposium was held at Stanford, with less than a year to launch. Recent advances in the TeV and MeV ranges augur well for GLAST making major discoveries in GeV astronomy. Expectations for observations of several source types and backgrounds are summarized, along with some remaining organizational challenges.
Date: October 22, 2007
Creator: Blandford, Roger
System: The UNT Digital Library
String Cosmology: A Review (open access)

String Cosmology: A Review

We give an overview of the status of string cosmology. We explain the motivation for the subject, outline the main problems, and assess some of the proposed solutions. Our focus is on those aspects of cosmology that benefit from the structure of an ultraviolet-complete theory.
Date: October 22, 2007
Creator: McAllister, Liam P. & Silverstein, Eva
System: The UNT Digital Library
Proton Form Factors Measurements in the Time-Like Region (open access)

Proton Form Factors Measurements in the Time-Like Region

I present an overview of the measurement of the proton form factors in the time-like region. BABAR has recently measured with great accuracy the e{sup +}e{sup -} {yields} p{bar p} reaction from production threshold up to an energy of {approx} 4.5 GeV, finding evidence for a ratio of the electric to magnetic form factor greater than unity, contrary to expectation. In agreement with previous measurements, BABAR confirmed the steep rise of the magnetic form factor close to the p{bar p} mass threshold, suggesting the possible presence of an under-threshold N{bar N} vector state. These and other open questions related to the nucleon form factors both in the time-like and space-like region, wait for more data with different experimental techniques to be possibly solved.
Date: October 22, 2007
Creator: Anulli, F.
System: The UNT Digital Library
Electromagnetic Models of Extragalactic Jets (open access)

Electromagnetic Models of Extragalactic Jets

Relativistic jets may be confined by large-scale, anisotropic electromagnetic stresses that balance isotropic particle pressure and disordered magnetic field. A class of axisymmetric equilibrium jet models will be described and their radiative properties outlined under simple assumptions. The partition of the jet power between electromagnetic and mechanical forms and the comoving energy density between particles and magnetic field will be discussed. Current carrying jets may be recognized by their polarization patterns. Progress and prospects for measuring this using VLBI and GLAST observations will be summarized.
Date: October 22, 2007
Creator: Lisanti, M.; Blandford, R. & /KIPAC, Menlo Park
System: The UNT Digital Library