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Massive gravity on a brane

Description: At present no theory of a massive graviton is known that is consistent with experiments at both long and short distances. The problem is that consistency with long distance experiments requires the graviton mass to be very small. Such a small graviton mass however implies an ultraviolet cutoff for the theory at length scales far larger than the millimeter scale at which gravity has already been measured. In this paper we attempt to construct a model which avoids this problem. We consider a brane world setup in warped AdS spacetime and we investigate the consequences of writing a mass term for the graviton on a the infrared brane where the local cutoff is of order a large (galactic) distance scale. The advantage of this setup is that the low cutoff for physics on the infrared brane does not significantly affect the predictivity of the theory for observers localized on the ultraviolet brane. For such observers the predictions of this theory agree with general relativity at distances smaller than the infrared scale but go over to those of a theory of massive gravity at longer distances. A careful analysis of the graviton two-point function, however, reveals the presence of a ghost in the low energy spectrum. A mode decomposition of the higher dimensional theory reveals that the ghost corresponds to the radion field. We also investigate the theory with a brane localized mass for the graviton on the ultraviolet brane, and show that the physics of this case is similar to that of a conventional four dimensional theory with a massive graviton, but with one important difference: when the infrared brane decouples and the would-be massive graviton gets heavier than the regular Kaluza-Klein modes, it becomes unstable and it has a finite width to decay off the brane into the continuum ...
Date: December 11, 2003
Creator: Chacko, Z.; Graesser, M.L.; Grojean, C. & Pilo, L.
Partner: UNT Libraries Government Documents Department

Measurement and simulation of the UMERbeam in the sourceregion

Description: As the beam propagates in the University of Maryland Electron Ring (UMER) complex transverse density structure including halos has been observed. A primary objective of the experiment is to understand the evolution of a space-charge-dominated beam as it propagates over a substantial distance. It is therefore important to understand which details of the beam structure result from propagation of the beam in the ring and which characteristics result from the specific details of the initial distribution. Detailed measurements of the initial beam characteristics have therefore been performed. These include direct measurement of the density using a phosphor screen, as well as pepper pot measurements of the initial transverse distribution function. Detailed measurements of the distribution function have also been obtained by scanning a pinhole aperture across a beam diameter, and recording phosphor screen pictures of the beam downstream of the pinhole. Simulations of the beam characteristics in the gun region have also been performed using the WARP P.I.C. code. From these simulations, the observed behavior has been attributed to a combination of perturbations to the transverse distribution by a cathode grid that is used to modulate the beam current, as well as the complex transverse dynamics that results from the combination of the nonlinear external focusing fields of the gun structure and the nonlinear space charge forces.
Date: June 11, 2004
Creator: Haber, I.; Bernal, S.; Kishek, R.A.; O'Shea, P.G.; Quinn, B.; Reiser, M. et al.
Partner: UNT Libraries Government Documents Department

An analytical solution for estimating percolation rate by fitting temperature profiles in the Vadose Zone

Description: We present a simple analytical solution for one dimensional steady heat transfer with convection and conduction through a multi-layer system such as a vadose zone. We assume that each layer is homogeneous and has a constant thermal diffusivity. The mass/heat flow direction is perpendicular to the layers, and the mass flow rate is a constant. The analytical solution presented in this study also assumes constant known temperatures at the two boundaries of the system. Although the analytical solution gives the temperature as a function of a few parameters, we focus on the inverse application to estimate the percolation rate to high degree of accuracy (e.g., to mm/y). In some other cases the solution may also be helpful in characterizing potential lateral flow along layer divides.
Date: March 11, 2003
Creator: Shan, Chao & Bodvarsson, Gudmundur
Partner: UNT Libraries Government Documents Department

Performance characteristics of the Cray X1 and their implicationsfor application performance tuning

Description: During the last decade the scientific computing community has optimized many applications for execution on superscalar computing platforms. The recent arrival of the Japanese Earth Simulator has revived interest in vector architectures especially in the US. It is important to examine how to port our current scientific applications to the new vector platforms and how to achieve high performance. The success of porting these applications will also influence the acceptance of new vector architectures. In this paper, we first investigate the memory performance characteristics of the Cray X1, a recently released vector platform, and determine the most influential performance factors. Then, we examine how to optimize applications tuned on superscalar platforms for the Cray X1 using its performance characteristics as guidelines. Finally, we evaluate the different types of optimizations used, the effort for their implementations, and whether they provide any performance benefits when ported back to superscalar platforms.
Date: May 11, 2004
Creator: Shan, Hogzhang & Strohmaier, Erich
Partner: UNT Libraries Government Documents Department

A Hybrid Semi-Analytical and Numerical Method for ModelingWellbore Heat Transmission

Description: Fluid flow in geothermal production and injection wells can be strongly affected by heat transfer effects with the formations surrounding the wellbore. Various techniques and approximations to model wellbore heat transmission have been presented in the literature. The objective of the present work is to develop a treatment of conductive heat transfer in the formations surrounding a wellbore that is simple, yet provides good accuracy for transient effects at early time. This is accomplished by adapting the well known semi-analytical heat transfer method of Vinsome and Westerveld (1980) to the problem of heat transfer to and from a flowing well. The Vinsome-Westerveld method treats heat exchange between a reservoir and adjacent cap and base rocks by means of a hybrid numerical-analytical method, in which temperature distributions in the conductive domain are approximated by simple trial functions, whose parameters are obtained concurrently with the numerical solution for the flow domain. This method can give a very accurate representation of conductive heat transfer even for non-monotonic temperature variations over a broad range of time scales. The only enhancement needed for applying the method to wellbore heat transmission is taking account of the cylindrical geometry around a flowing well, as opposed to the linear flow geometry in cap and base rocks. We describe the generalization of trial functions needed for cylindrical geometry, and present our implementation into the TOUGH2 reservoir simulator. The accuracy of the method is evaluated through application to non-isothermal flow through a pipe.
Date: January 11, 2005
Creator: Pruess, Karsten & Zhang, Yingqi
Partner: UNT Libraries Government Documents Department

Lithium Ethylene Dicarbonate Identified as the Primary Product ofChemical and Electrochemical Reduction of EC in EC:EMC/1.2M LiPF6Electrolyte

Description: Lithium ethylene dicarbonate (CH2OCO2Li)2 was chemically synthesized and its Fourier Transform Infrared (FTIR) spectrum was obtained and compared with that of surface films formed on Ni after cyclic voltammetry (CV) in 1.2M lithium hexafluorophosphate(LiPF6)/ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7, w/w) electrolyte and on metallic lithium cleaved in-situ in the same electrolyte. By comparison of IR experimental spectra with that of the synthesized compound, we established that the title compound is the predominant surface species in both instances. Detailed analysis of the IR spectrum utilizing quantum chemical (Hartree-Fock) calculations indicates that intermolecular association through O...Li...O interactions is very important in this compound. It is likely that the title compound in passivation layer has a highly associated structure, but the exact intermolecular conformation could not be established based on analysis of the IR spectrum.
Date: May 11, 2005
Creator: Zhuang, Guorong V.; Xu, Kang; Yang, Hui; Jow, T. Richard & RossJr., Philip N.
Partner: UNT Libraries Government Documents Department

Aerosol organic carbon to black carbon ratios: Analysis ofpublished data and implications for climate forcing

Description: Measurements of organic carbon (OC) and black carbon (BC)concentrations over a variety of locations worldwide, have been analyzed to infer the spatial distributions of the ratios of OC to BC. Since these ratios determine the relative amounts of scattering and absorption, they are often used to estimate the radiative forcing due to aerosols. An artifact in the protocol for filter measurements of OC has led to widespread overestimates of the ratio of OC to BC in atmospheric aerosols. We developed a criterion to correct for this artifact and analyze corrected OC to BC ratios. The OC to BC ratios, ranging from 1.3to 2.4, appear relatively constant and are generally unaffected by seasonality, sources or technology changes, at the locations considered here. The ratios compare well with emission inventories over Europe and China but are a factor of two lower in other regions. The reduced estimate for OC/BC in aerosols strengthens the argument that reduction of soot emissions maybe a useful approach to slow global warming.
Date: July 11, 2005
Creator: Novakov, T.; Menon, S.; Kirchstetter, T.W.; Koch, D. & Hansen, J.E.
Partner: UNT Libraries Government Documents Department

A comparative analysis of business structures suitable forfarmer-owned wind power projects in the United States

Description: For years, farmers in the United States have looked with envy on their European counterparts' ability to profitably farm the wind through ownership of distributed, utility-scale wind projects. Only within the past few years, however, has farmer- or community-owned wind power development become a reality in the United States. The primary hurdle to this type of development in the United States has been devising and implementing suitable business and legal structures that enable such projects to take advantage of tax-based federal incentives for wind power. This article discusses the limitations of such incentives in supporting farmer- or community-owned wind projects, describes four ownership structures that potentially overcome such limitations, and finally conducts comparative financial analysis on those four structures, using as an example a hypothetical 1.5 MW farmer-owned project located in the state of Oregon. We find that material differences in the competitiveness of each structure do exist, but that choosing the best structure for a given project will largely depend on the conditions at hand; e.g., the ability of the farmer(s) to utilize tax credits, preference for individual versus ''cooperative'' ownership, and the state and utility service territory in which the project will be located.
Date: November 11, 2004
Creator: Bolinger, Mark & Wiser, Ryan
Partner: UNT Libraries Government Documents Department

The Lawrence Berkeley National Laboratory ES&H self-assessmentprogram

Description: Lawrence Berkeley National Laboratory (Berkeley Lab) is a multiprogram national research facility operated by the University of California for the U.S. Department of Energy (DOE). DOE environment, safety, and health (ES&H) policy requires that all Berkeley Lab work be performed safely, with minimal adverse impact on the public and the environment. To facilitate safe and responsible work, Berkeley Lab divisions, directorates, and select departments must develop and implement Integrated Safety Management (ISM) plans. Berkeley Lab operates a formal internal ES&H self-assessment process to evaluate ES&H programs and policies and assure that ISM is implemented at all levels of activities and operations. ISM requires that: (1) work is defined, (2) hazards are identified, (3) controls are developed and implemented, (4) work is performed as authorized, and (5) feedback and improvement are continuous. These five ISM core functions are sustained by applying the seven guiding principles of ISM. These are: (1) line management responsibility and accountability for ES&H, (2) clear ES&H roles and responsibilities, (3) competency commensurate with responsibilities, (4) an ongoing balance between safety on the one hand and research and operational priorities on the other, (5) identification of standards and requirements, (6) hazard controls tailored to the work, and (7) operations authorization. Self-assessment at Berkeley Lab is a continuous process of information gathering and evaluation. The goals of the self-assessment program are: (a) Ensure that work activities and operations are done safely and in a manner that maximizes public and environmental protection. (b) Ensure that the five core functions and seven guiding principles of integrated safety management are employed effectively in work planning and performance. (c) Meet regulatory requirements for DOE oversight, self-assessment, and an integrated safety management system. (d) Meet contractual requirements for ES&H performance and self-assessment. (Berkeley Lab operates under DOE/University of California Contract DE-AC03-7600098, Appendix F.)
Date: February 11, 2003
Creator: Chernowski, John G.
Partner: UNT Libraries Government Documents Department

Perturbing the superconducting planes in CeCoIn5 by Snsubstitution

Description: In contrast to substitution on the Co or Ce site, Sn substitution has a remarkably strong effect on superconductivity in CeCoIn{sub 5-x}Sn{sub x}, with T{sub c} {yields} 0 beyond only {approx}3.6% Sn. Instead of being randomly distributed on in-plane and out-of-plane In sites, extended x-ray absorption fine structure measurements show the Sn atoms preferentially substitute within the Ce-In plane. This result highlights the importance of the In(1) site to impurity scattering and clearly demonstrates the two-dimensional nature of superconductivity in CeCoIn{sub 5}.
Date: January 11, 2005
Creator: Daniel, M.; Bauer, E.D.; Han, S.-W.; Booth, C.H.; Cornelius,A.L.; Pagliuso, P.G. et al.
Partner: UNT Libraries Government Documents Department

Synthesis of hcp-Co nanodisks

Description: hcp Co disk-shaped nanocrystals were obtained by rapid decomposition of cobalt carbonyl in presence of linear amines. Other surfactants, in addition to the amines, like phosphine oxides and oleic acid were used to improve size dispersion, shape control and nanocrystal stability. Co disks are ferromagnetic in character and they spontaneously self-assemble into long ribbons. X-ray and electron diffraction, electron microscopy and SQUID magnetometry have been employed to characterize this material.
Date: June 11, 2002
Creator: Puntes, Victor F.; Zanchet, Daniela; Erdonmez, Can K. & Alivisatos, A.P.
Partner: UNT Libraries Government Documents Department

TOUGHREACT: a new code of the TOUGH Family for Non-Isothermal multiphase reactive geochemical transport in variably saturated geologic media

Description: Coupled modeling of subsurface multiphase fluid and heat flow, solute transport and chemical reactions can be used for the assessment of acid mine drainage remediation, waste disposal sites, hydrothermal convection, contaminant transport, and groundwater quality. We have developed a comprehensive numerical simulator, TOUGHREACT, which considers non-isothermal multi-component chemical transport in both liquid and gas phases. A wide range of subsurface thermo-physical-chemical processes is considered under various thermohydrological and geochemical conditions of pressure, temperature, water saturation, and ionic strength. The code can be applied to one-, two- or three-dimensional porous and fractured media with physical and chemical heterogeneity.
Date: March 11, 2003
Creator: Xu, Tianfu; Sonnenthal, Eric; Spycher, Nicolas & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Diagnostics for intense heavy ion beams in the HIF-VNL

Description: Modern diagnostic techniques provide detailed information on beam conditions in injector, transport, and final focus experiments in the HIF-VNL. Parameters of interest include beam current, beam energy, transverse and longitudinal distributions, emittance, and space charge neutralization. Imaging techniques, based on kapton films and optical scintillators, complement and in some cases, may replace conventional techniques based on slit scans. Time-resolved optical diagnostics that provide 4-D transverse information on the experimental beams are in operation on the existing experiments. Current work includes a compact optical diagnostic suitable for insertion in transport lines, improved algorithms for optical data analysis and interpretation, a high-resolution electrostatic energy analyzer, and an electron beam probe. A longitudinal diagnostic kicker generates longitudinal space-charge waves that travel on the beam. Time of flight of the space charge waves and an electrostatic energy analyzer provide an absolute measure of the beam energy. Special diagnostics to detect secondary electrons and gases desorbed from the wall have been developed.
Date: June 11, 2004
Creator: Bieniosek, F.M.; Eylon, S.; Faltens, A.; Friedman, A.; Kwan, J.W.; Leitner, M.A. et al.
Partner: UNT Libraries Government Documents Department

Using Energy Information Systems (EIS): A Guidebook for the U.S. Postal Service

Description: The U.S. Postal Service (Postal Service) recently installed Energy Information Systems (EIS) at 30 facilities in California. These systems integrate electric utility meter data acquisition hardware, software, and communication systems to collect, archive, analyze, and display whole-facility energy consumption data. At some point in the future, these systems could also be integrated with sub-meters that measure the electricity consumption of key end-use equipment. The purpose of this guidebook is to help Postal Service facility managers interpret and act upon energy data available from their EIS, translating the abundance of information these systems provide into knowledge that can be used to reduce energy use and costs. The guidebook first describes basic EIS capabilities and explains the data and reports that Postal Service EIS provide. It outlines a set of strategies for utilizing this information to improve operations and maintenance of building energy use equipment and for facilitating demand response. Finally, the guidebook offers suggestions on creating a routine for tracking and analyzing energy data and integrating this information into regular energy management activities.
Date: October 11, 2004
Creator: Foster, Dale; Hough, Ben; Barbose, Galen; Golove, William & Goldman, Charles
Partner: UNT Libraries Government Documents Department

Best practices guide for residential HVAC Retrofits

Description: This best practices guide for residential HVAC system retrofits is aimed at contractors who want guidance on delivering energy efficient, cost effective and innovative products. It has been developed around the idea of having packages of changes to the building HVAC system and building envelope that are climate and house construction dependent. These packages include materials, procedures and equipment and are designed to remove some of the guesswork from a builder, contractor, installer or homeowner decisions about how best to carry out HVAC changes. The packages are not meant to be taken as rigid requirements--instead they are systems engineered guidelines that form the basis for energy efficient retrofits. Similar approaches have been taken previously for new construction to develop extremely energy efficient homes that are comfortable safe and durable, and often cost less than standard construction. This is best epitomized by the Building America program whose partners have built thousands of residences throughout the U.S. using these principles. The differences between retrofitting and new construction tend to limit the changes one can make to a building, so these packages rely on relatively simple and non-intrusive technologies and techniques. The retrofits also focus on changes to a building that will give many years of service to the occupants. Another key aspect of these best practices is that we need to know how a house is working so that we know what parts have the potential for improvement. To do this we have put together a set of diagnostic tools that combine physical measurements and checklists/questionnaires. The measured test results, observations and homeowner answers to questions are used to direct us towards the best retrofits applicable to each individual house. The retrofits will depend on the current condition of the building envelope and HVAC system, the local climate, the construction methods used ...
Date: August 11, 2003
Creator: Walker, Iain S.
Partner: UNT Libraries Government Documents Department

Barriers in developing and using simulation-based decision-support software

Description: The need for proper consideration of energy-related performance aspects during building design has been identified since the energy crises of the 1970s. However, energy performance is still considered in a very small fraction of building projects, mainly because proper consideration is very expensive. It requires the use of computational software tools, which are not easy to learn and are time-consuming to use. Several attempts have been made to facilitate the use of energy simulation tools, but none has brought a significant increase in the consideration of energy performance. Energy related performance criteria are still considered only in a small fraction of buildings and, in most cases, after most of the building design is complete. This paper is focused on the main barriers in properly considering energy-related performance aspects in building decisions, which range from sociopolitical, to technical. The paper includes consideration of issues related to the general interest of the building industry in energy performance and environmental impact, current practice trends, modeling capabilities and performance of tools, compatibility of computational models and availability of data. Finally, a strategy for government-industry collaboration towards removing the barriers is presented, along with the main issues that need to be resolved towards potential implementation.
Date: March 11, 2002
Creator: Papamichael, Konstantinos & Pal, Vineeta
Partner: UNT Libraries Government Documents Department

Comparative Dosimetric Estimates of a 25 keV Electron Micro-beam with three Monte Carlo Codes

Description: The calculations presented compare the different performances of the three Monte Carlo codes PENELOPE-1999, MCNP-4C and PITS, for the evaluation of Dose profiles from a 25 keV electron micro-beam traversing individual cells. The overall model of a cell is a water cylinder equivalent for the three codes but with a different internal scoring geometry: hollow cylinders for PENELOPE and MCNP, whereas spheres are used for the PITS code. A cylindrical cell geometry with scoring volumes with the shape of hollow cylinders was initially selected for PENELOPE and MCNP because of its superior simulation of the actual shape and dimensions of a cell and for its improved computer-time efficiency if compared to spherical internal volumes. Some of the transfer points and energy transfer that constitute a radiation track may actually fall in the space between spheres, that would be outside the spherical scoring volume. This internal geometry, along with the PENELOPE algorithm, drastically reduced the computer time when using this code if comparing with event-by-event Monte Carlo codes like PITS. This preliminary work has been important to address dosimetric estimates at low electron energies. It demonstrates that codes like PENELOPE can be used for Dose evaluation, even with such small geometries and energies involved, which are far below the normal use for which the code was created. Further work (initiated in Summer 2002) is still needed however, to create a user-code for PENELOPE that allows uniform comparison of exact cell geometries, integral volumes and also microdosimetric scoring quantities, a field where track-structure codes like PITS, written for this purpose, are believed to be superior.
Date: September 11, 2002
Creator: Mainardi, Enrico; Donahue, Richard J. & Blakely, Eleanor A.
Partner: UNT Libraries Government Documents Department

Collaborative editing within the pervasive collaborative computing environment

Description: Scientific collaborations are established for a wide variety of tasks for which several communication modes are necessary, including messaging, file-sharing, and collaborative editing. In this position paper, we describe our work on the Pervasive Collaborative Computing Environment (PCCE) which aims to facilitate scientific collaboration within widely distributed environments. The PCCE provides a persistent space in which collaborators can locate each other, exchange messages synchronously and asynchronously and archive conversations. Our current interest is in exploring research and development of shared editing systems with the goal of integrating this technology into the PCCE. We hope to inspire discussion of technology solutions for an integrated approach to synchronous and asynchronous communication and collaborative editing.
Date: September 11, 2003
Creator: Perry, Marcia & Agarwal, Deb
Partner: UNT Libraries Government Documents Department

Frequency map analysis of nonlinear dynamics in the NLC main damping rings

Description: To avoid radiation damage, the acceptance of linear collider damping rings must be large enough that injection efficiency close to 100 percent can be achieved. Survival plots based on tracking particles in the NLC Main Damping Ring lattice suggest a dynamic aperture with some margin over the specified injected beam size and energy spread. Here, we apply Frequency Map Analysis to give a more detailed picture of the dynamical stability of particle trajectories in the presence of lattice nonlinearities arising from the sextupoles and the damping wiggler. The techniques that we use are of general applicability to nonlinear elements in beamlines, and in particular will be used for analysis of wiggler effects in future damping ring designs.
Date: October 11, 2004
Creator: Wolski, Andrzej; Venturini, Marco; Wan, Weishi & Marks, Steve
Partner: UNT Libraries Government Documents Department

Effect of catalyst structure on oxidative dehydrogenation of ethane and propane on alumina-supported vanadia

Description: The catalytic properties of Al2O3-supported vanadia with a wide range of VOx surface density (1.4-34.2 V/nm2) and structure were examined for the oxidative dehydrogenation of ethane and propane. UV-visible and Raman spectra showed that vanadia is dispersed predominantly as isolated monovanadate species below {approx}2.3 V/nm2. As surface densities increase, two-dimensional polyvanadates appear (2.3-7.0 V/nm2) along with increasing amounts of V2O5 crystallites at surface densities above 7.0 V/nm2. The rate constant for oxidative dehydrogenation (k1) and its ratio with alkane and alkene combustion (k2/k1 and k3/k1, respectively) were compared for both alkane reactants as a function of vanadia surface density. Propene formation rates (per V-atom) are {approx}8 times higher than ethene formation rates at a given reaction temperature, but the apparent ODH activation energies (E1) are similar for the two reactants and relatively insensitive to vanadia surface density. Ethene and propene formation rates (per V-atom) are strongly influenced by vanadia surface density and reach a maximum value at intermediate surface densities ({approx}8 V/nm2). The ratio of k2/k1 depends weakly on reaction temperature, indicating that activation energies for alkane combustion and ODH reactions are similar. The ratio of k2/k1 is independent of surface density for ethane, but increase slightly with vanadia surface density for propane, suggesting that isolated structures prevalent at low surface densities are slightly more selective for alkane dehydrogenation reactions. The ratio of k3/k1 decreases markedly with increasing reaction temperature for both ethane and propane ODH. Thus, the apparent activation energy for alkene combustion (E3) is much lower than that for alkane dehydrogenation (E1) and the difference between these two activation energies decreases with increasing surface density. The lower alkene selectivities observed at high vanadia surface densities are attributed to an increase in alkene adsorption enthalpies with increasing vanadia surface density. The highest yield of alkene is obtained for catalysts ...
Date: September 11, 2001
Creator: Argyle, Morris D.; Chen, Kaidong; Bell, Alexis T. & Iglesia, Enrique
Partner: UNT Libraries Government Documents Department