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Material and time dependence of the voltage noise generated bycathodic vacuum arcs

Description: The high frequency fluctuations of the burning voltage of cathodic vacuum arcs have been investigated in order to extract information on cathode processes. Eight cathode materials (W, Ta, Hf, Ti, Ni, Au, Sn, Bi) were selected covering a wide range of cohesive energy. The voltage noise was recorded using both a broad-band voltage divider and an attenuator connected to a fast oscilloscope (limits 1 GHz analog and 5 GS/s digital). Fast Fourier transform revealed a power spectrum that is linear in log-log presentation, with a slope of 1/f{sup 2}, where f is the frequency (brown noise). The amplitude of the spectral power of the voltage noise was found to scale with the cohesive energy, in agreement with earlier measurements at lower resolution. These basic results do not depend on the time after arc initiation. However, lower arc current in the beginning of the pulse shows greater voltage noise, suggesting an inverse relation between the noise amplitude and number of emission sites (cathode spot fragments).
Date: July 15, 2005
Creator: Rosen, Johanna & Anders, Andre
Partner: UNT Libraries Government Documents Department

Time-Dependent Interfacial Properties and DNAPL Mobility

Description: Interfacial properties play a major role in governing where and how dense nonaqueous phase liquids (DNAPLs) move in the subsurface. Interfacial tension and contact angle measurements were obtained for a simple, single component DNAPL (tetrachloroethene, PCE), complex laboratory DNAPLs (PCE plus Sudan IV dye), and a field DNAPL from the Savannah River Site (SRS) M-Area DNAPL (PCE, trichloroethene [TCE], and maching oils). Interfacial properties for complex DNAPLs were time-dependent, a phenomenon not observed for PCE alone. Drainage capillary pressure-saturation curves are strongly influenced by interfacial properties. Therefore time-dependence will alter the nature of DNAPL migration and penetration. Results indicate that the time-dependence of PCE with relatively high Sudan IV dye concentrations is comparable to that of the field DNAPL. Previous DNAPL mobility experiments in which the DNAPL was dyed should be reviewed to determine whether time-dependent properties influenced the resutls. Dyes appear to make DNAPL more complex, and therefore a more realistic analog for field DNAPLs than single component DNAPLs.
Date: March 10, 1999
Creator: Tuck, D.M.
Partner: UNT Libraries Government Documents Department

Limits on expanding relativistic shells from Gamma-Ray Burst temporal structure

Description: The author calculates the expected envelope of emission for relativistic shells under the assumption of local spherical symmetry. Gamma-Ray Burst envelopes rarely conform to the expected shape, which has a fast rise and a smooth, slower decay. Furthermore, the duration of the decay phase is related to the time the shell expands before converting its energy to gamma rays. From this, one can estimate the energy required for the shell to sweep up the ISM. The energy greatly exceeds 10{sup 53} erg unless the bulk Lorentz factor is less than 75. This puts extreme limits on the {open_quotes}external{close_quotes} shock models. However, the alternative, {open_quotes}internal{close_quotes} shocks from a central engine, has one extremely large problem: the entire long complex time history lasting hundreds of seconds must be postulated at the central site.
Date: December 31, 1996
Creator: Fenimore, E. E.
Partner: UNT Libraries Government Documents Department

Retention and Switching Kinetics of Protonated Gate Field Effect Transistors

Description: The switching and memory retention time has been measured in 50 {micro}m gatelength pseudo-non-volatile memory MOSFETs containing, protonated 40 nm gate oxides. Times of the order of 3.3 seconds are observed for fields of 3 MV cm{sup {minus}1}. The retention time with protons placed either at the gate oxide/substrate or gate oxide/gate electrode interfaces is found to better than 96% after 5,000 seconds. Measurement of the time dependence of the source-drain current during switching provides clear evidence for the presence of dispersive proton transport through the gate oxide.
Date: June 27, 2000
Creator: Devine, R. A. B. & Herrera, Gilbert V.
Partner: UNT Libraries Government Documents Department

Creation and destruction of C{sub 60} and other fullerene solids. Final report

Description: The 1990 announcement of the Huffman-Kratschmer fullerene-production technique set off a world-wide explosion of research into the properties and potential applications of C{sub 60} and C{sub 70}. In the last five years, 4,000+ fullerene articles have appeared in the scientific literature dealing with these fascinating molecules and their condensed phases. They possess a complex chemistry reminiscent of the alkenes, and this has led to the syntheses of numerous new compounds and fullerene-based materials, with suggested applications ranging from medicine to photo-conducting polymers to rocket fuel. The work summarized in this report focused on the creation and destruction of fullerene-based materials, for the purpose of producing new materials of interest. This three year project was supported by a grant from the Advanced Energy Projects Division, Office of Basic Energy Sciences, U.S. Department of Energy (DE-FG03-93ER12133). Following are outlines of the work completed in each of the three years, a section devoted to the professional and educational development of those involved, a brief section on the outlook for fullerene-based materials, and an appendix listing the publications resulting from this project.
Date: June 5, 1996
Creator: Huffman, D. R.
Partner: UNT Libraries Government Documents Department

Using Graphs for Fast Error Term Approximation of Time-varying Datasets

Description: We present a method for the efficient computation and storage of approximations of error tables used for error estimation of a region between different time steps in time-varying datasets. The error between two time steps is defined as the distance between the data of these time steps. Error tables are used to look up the error between different time steps of a time-varying dataset, especially when run time error computation is expensive. However, even the generation of error tables itself can be expensive. For n time steps, the exact error look-up table (which stores the error values for all pairs of time steps in a matrix) has a memory complexity and pre-processing time complexity of O(n2), and O(1) for error retrieval. Our approximate error look-up table approach uses trees, where the leaf nodes represent original time steps, and interior nodes contain an average (or best-representative) of the children nodes. The error computed on an edge of a tree describes the distance between the two nodes on that edge. Evaluating the error between two different time steps requires traversing a path between the two leaf nodes, and accumulating the errors on the traversed edges. For n time steps, this scheme has a memory complexity and pre-processing time complexity of O(nlog(n)), a significant improvement over the exact scheme; the error retrieval complexity is O(log(n)). As we do not need to calculate all possible n2 error terms, our approach is a fast way to generate the approximation.
Date: February 27, 2003
Creator: Nuber, C; LaMar, E C; Pascucci, V; Hamann, B & Joy, K I
Partner: UNT Libraries Government Documents Department

Simulating Electron Clouds in High-Current Ion Accelerators withSolenoid Focusing

Description: Contamination from electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high-energy-density physics (HEDP). These electrons are produced directly by beam ions hitting lattice elements and intercepting diagnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the Solenoid Transport Experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to included the physics needed to simulate electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and electrons.
Date: September 20, 2006
Creator: Sharp, W.M.; Grote, D.P.; Cohen, R.H.; Friedman, A.; Vay, J.-L.; Seidl, P.A. et al.
Partner: UNT Libraries Government Documents Department

Luminosity Lifetime

Description: In a symmetric or 'energy transparent' relativistic collider, the luminosity is given by L = N{sup 2}f{sub c}/4{pi}{sigma}*{sub x}{sigma}*{sub y} where N is the number of electrons or positrons per bunch, {sigma}*{sub x} ({sigma}*{sub y}) is the horizontal (vertical) rms beam size at the interaction point (IP), and f{sub c} is the collision frequency. If the beam sizes remain constant as the luminosity decreases, then the time dependence of luminosity is contained entirely in the time dependence of the beam currents, i.e., N O N(t), and we can rewrite the equation as L(t) = N{sup 2}(t)f{sub c}/4{pi}{sigma}*{sub x}{sigma}*{sub y}. There are two distinct categories for luminosity loss. In the first category are loss processes due to collisions between the two beams, that is, processes associated directly with the luminosity. In the second category (see below) are single-beam loss processes. The processes in the first category relevant to a high-energy collider are Bhabha scattering (e{sup +}e{sup -} O e{sup +}e{sup -}) and 'radiative' Bhabha scattering (e{sup +}e{sup -} O e{sup +}e{sup -}{gamma}). In the first process, a beam particle is lost if its angular deflection is beyond the ring's transverse acceptance; in the second process, loss occurs if the beam particle's momentum change is outside the longitudinal acceptance of the ring (typically determined by the RF bucket height).
Date: April 1, 1997
Creator: Zisman, M.S.
Partner: UNT Libraries Government Documents Department

Extracting Critical Path Graphs from MPI Applications

Description: The critical path is one of the fundamental runtime characteristics of a parallel program. It identifies the longest execution sequence without wait delays. In other words, the critical path is the global execution path that inflicts wait operations on other nodes without itself being stalled. Hence, it dictates the overall runtime and knowing it is important to understand an application's runtime and message behavior and to target optimizations. We have developed a toolset that identifies the critical path of MPI applications, extracts it, and then produces a graphical representation of the corresponding program execution graph to visualize it. To implement this, we intercept all MPI library calls, use the information to build the relevant subset of the execution graph, and then extract the critical path from there. We have applied our technique to several scientific benchmarks and successfully produced critical path diagrams for applications running on up to 128 processors.
Date: July 27, 2005
Creator: Schulz, M
Partner: UNT Libraries Government Documents Department

Deterministic methods for time-dependent stochastic neutron transport

Description: A numerical method is presented for solving the time-dependent survival probability equation in general (lD/2D/3D) geometries using the multi group SNmethod. Although this equation was first formulated by Bell in the early 1960's, it has only been applied to stationary systems (for other than idealized point models) until recently, and detailed descriptions of numerical solution techniques are lacking in the literature. This paper presents such a description and applies it to a dynamic system representative of a figurative criticality accident scenario.
Date: January 1, 2009
Creator: Baker, Randal S
Partner: UNT Libraries Government Documents Department

Resolution depths for some transmitter receiverconfigurations

Description: Away from a conductive body, secondary magnetic fields due to currents induced in the body by a time varying external magnetic field are approximated by (equivalent) magnetic dipole fields. Approximating the external magnetic field by its value at the location of the equivalent magnetic dipoles, the equivalent magnetic dipoles' strengths are linearly proportional to the external magnetic field, for a given time dependence of external magnetic field, and are given by the equivalent dipole polarizability matrix. The polarizability matrix and its associated equivalent dipole location is estimated from magnetic field measurements made with at least three linearly independent polarizations of external magnetic fields at the body. Uncertainties in the polarizability matrix elements and its equivalent dipole location are obtained from analysis of a linearized inversion for polarizability and dipole location. Polarizability matrix uncertainties are independent of the scale of the polarizability matrix. Dipole location uncertainties scale inversely with the scale of the polarizability matrix. Uncertainties in principal polarizabilities and directions are obtained from the sensitivities of eigenvectors and eigenvalues to perturbations of a symmetric matrix. In application to synthetic data from a magnetic conducting sphere and to synthetic data from an axially symmetric elliptic conducting body, the estimated polarizability matrices, equivalent dipole locations and principal polarizabilities and directions are consistent with their estimated uncertainties.
Date: August 28, 2002
Creator: Smith, J. Torquil; Morrison, H. Frank & Becker, Alex
Partner: UNT Libraries Government Documents Department

Models of glassy behavior that attempt to understand mode coupling theories

Description: Glass transitions are said to be long time scale and short length scale phenomena. This makes the problem extremely difficult to treat theoretically. In this respect the current mode coupling theory (MCT) for glassy behavior, which is the only existing first principle dynamical theory has conceptual problems despite its spectacular successes. Proper understanding for the reasons of success is still lacking. There is an urgent need for deeper understanding and proper extention of the theory below the so-called mode coupling temperature below which the theory generally fails. With this aim in mind we have been developing a mean field type toy model. We are also developing a dynamical generalization of van der Waals model with Kac-type long range interaction. The talk will try to explain these and related developments in a plain language.
Date: January 1, 2002
Creator: Kawasaki, Kyozi,
Partner: UNT Libraries Government Documents Department

Computing Path Tables for Quickest Multipaths In Computer Networks

Description: We consider the transmission of a message from a source node to a terminal node in a network with n nodes and m links where the message is divided into parts and each part is transmitted over a different path in a set of paths from the source node to the terminal node. Here each link is characterized by a bandwidth and delay. The set of paths together with their transmission rates used for the message is referred to as a multipath. We present two algorithms that produce a minimum-end-to-end message delay multipath path table that, for every message length, specifies a multipath that will achieve the minimum end-to-end delay. The algorithms also generate a function that maps the minimum end-to-end message delay to the message length. The time complexities of the algorithms are O(n{sup 2}((n{sup 2}/logn) + m)min(D{sub max}, C{sub max})) and O(nm(C{sub max} + nmin(D{sub max}, C{sub max}))) when the link delays and bandwidths are non-negative integers. Here D{sub max} and C{sub max} are respectively the maximum link delay and maximum link bandwidth and C{sub max} and D{sub max} are greater than zero.
Date: December 21, 2004
Creator: Grimmell, W.C.
Partner: UNT Libraries Government Documents Department

Suppressing nonphysical overheating with a modified implicit Monte Carlo method for time-dependent radiative transfer

Description: In this note we develop a robust implicit Monte Carlo (IMC) algorithm based on more accurately updating the linearized equilibrium radiation energy density. The method does not introduce oscillations in the solution and has the same limit as {Delta}t{yields}{infinity} as the standard Fleck and Cummings IMC method. Moreover, the approach we introduce can be trivially added to current implementations of IMC by changing the definition of the Fleck factor. Using this new method we develop an adaptive scheme that uses either standard IMC or the modified method basing the adaptation on a zero-dimensional problem solved in each cell. Numerical results demonstrate that the new method alleviates both the nonphysical overheating that occurs in standard IMC when the time step is large and significantly diminishes the statistical noise in the solution.
Date: January 1, 2008
Creator: Mcclarren, Ryan G. & Urbatsch, Todd J.
Partner: UNT Libraries Government Documents Department

Influence of time-dependent factors in the evaluation of critical infrastructure protection measures.

Description: The examination of which protective measures are the most appropriate to be implemented in order to prevent, protect against, respond to, and recover from attacks on critical infrastructures and key resources typically involves a comparison of the consequences that could occur when the protective measure is implemented to those that could occur when it is not. This report describes a framework for evaluation that provides some additional capabilities for comparing optional protective measures. It illustrates some potentially important time-dependent factors, such as the implementation rate, that affect the relative pros and cons associated with widespread implementation of protective measures. It presents example results from the use of protective measures, such as detectors and pretrained responders, for an illustrative biological incident. Results show that the choice of an alternative measure can depend on whether or not policy and financial support can be maintained for extended periods of time. Choice of a time horizon greatly influences the comparison of alternatives.
Date: March 28, 2008
Creator: Buehring, W. A.; Samsa, M. E. & Sciences, Decision and Information
Partner: UNT Libraries Government Documents Department

Time-step limits for a Monte Carlo Compton-scattering method

Description: We perform a stability analysis of a Monte Carlo method for simulating the Compton scattering of photons by free electron in high energy density applications and develop time-step limits that avoid unstable and oscillatory solutions. Implementing this Monte Carlo technique in multi physics problems typically requires evaluating the material temperature at its beginning-of-time-step value, which can lead to this undesirable behavior. With a set of numerical examples, we demonstrate the efficacy of our time-step limits.
Date: January 1, 2009
Creator: Densmore, Jeffery D; Warsa, James S & Lowrie, Robert B
Partner: UNT Libraries Government Documents Department


Description: We report variations in the currents of CdZnTe semiconductor crystals during exposure to a series of light emitting diodes of various wavelengths ranging from 470 to 950 nm. The changes in the steady-state current of one CdZnTe crystal with and without illumination along with the time dependence of the illumination effects are discussed. Analysis of the de-trapping and transient bulk currents during and after optical excitation yield insight into the behaviour of charge traps within the crystal. Similar behaviour is observed for illumination of a second CdZnTe crystal suggesting that the overall illumination effects are not crystal dependent.
Date: April 23, 2012
Creator: Teague, L.; Washington, A. & Duff, M.
Partner: UNT Libraries Government Documents Department

Fast Gradient Elution Reversed-Phase HPLC with Diode-Array Detection as a High Throughput Screening Method for Drugs of Abuse

Description: A new approach has been developed by modifying a conventional gradient elution liquid chromatograph for the high throughput screening of biological samples to detect the presence of regulated intoxicants. The goal of this work was to improve the speed of a gradient elution screening method over current approaches by optimizing the operational parameters of both the column and the instrument without compromising the reproducibility of the retention times, which are the basis for the identification. Most importantly, the novel instrument configuration substantially reduces the time needed to re-equilibrate the column between gradient runs, thereby reducing the total time for each analysis. The total analysis time for each gradient elution run is only 2.8 minutes, including 0.3 minutes for column reequilibration between analyses. Retention times standard calibration solutes are reproducible to better than 0.002 minutes in consecutive runs. A corrected retention index was adopted to account for day-to-day and column-to-column variations in retention time. The discriminating power and mean list length were calculated for a library of 47 intoxicants and compared with previous work from other laboratories to evaluate fast gradient elution HPLC as a screening tool.
Date: December 30, 2005
Creator: Carr, Peter W.; Fuller, K.M.; Stoll, D.R.; Steinkraus, L.D.; Pasha, M.S. & Hardin, Glenn G.
Partner: UNT Libraries Government Documents Department