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Behavior of W and WSi(x) Contact Metallization on n- and p- Type GaN
Sputter-deposited W-based contacts on p-GaN (N{sub A} {approximately} 10{sup 18} cm{sup {minus}3}) display non-ohmic behavior independent of annealing temperature when measured at 25 C. The transition to ohmic behavior occurs above {approximately} 250 C as more of the acceptors become ionized. The optimum annealing temperature is {approximately} 700 C under these conditions. These contacts are much more thermally stable than the conventional Ni/Au metallization, which shows a severely degraded morphology even at 700 C. W-based contacts may be ohmic as-deposited on very heavily doped n-GaN, and the specific contact resistance improves with annealing up to {approximately} 900 C.
Date:
January 5, 1999
Creator:
Abernathy, C. R.; Cao, X. A.; Cole, M. W.; Eizenberg, M.; Lothian, J. R.; Pearton, S. J. et al.
Object Type:
Article
System:
The UNT Digital Library
Inductively Coupled Plasma Etching of III-Nitrides in Cl(2)/Xe,Cl(2)/Ar and Cl(2)/He
The role of additive noble gases He, Ar and Xe to C&based Inductively Coupled Plasmas for etching of GaN, AIN and InN were examined. The etch rates were a strong function of chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with C12/Xe, while the highest rates for AIN and GaN were obtained with C12/He. Efficient breaking of the 111-nitrogen bond is crucial for attaining high etch rates. The InN etching was dominated by physical sputtering, in contrast to GaN and AIN. In the latter cases, the etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of -80 for InN to GaN and InN to AIN were obtained.
Date:
January 5, 1999
Creator:
Abernathy, C.R.; Cho, H.; Donovan, S.M.; Hahn, Y.B.; Hays, D.C.; Jung, K.B. et al.
Object Type:
Article
System:
The UNT Digital Library
Biological Conversion of Synthesis Gas
Syngas is known to contain approximately 1 percent H[sub 2]S, along with CO[sub 2], C0[sub 2], H[sub 2] and CH[sub 4]. Similarly, the syngas may become contaminated with oxygen, particularly during reactor start-up and during maintenance. Previous studies with the water-gas shift bacterium Rhodospirillum rubrum have shown that the bacterium is tolerant of small quantities of oxygen, but the effects of oxygen on CO-consumption are unknown. Similarly, R. rubrum is known to be tolerant of H[sub 2]S, with high concentrations of H[sub 2]S negatively affecting CO-uptake. Batch experiments were thus carried out to determine the effects of H[sub 2]S and O[sub 2] on CO-uptake by R. rubrum. The results of these experiments were quantified by using Monod equations modified by adding terms for CO, H[sub 2]S and O[sub 2] inhibition. The techniques used in determining kinetic expressions previously shown for other gas-phase substrate bacterial systems including R. rubrum were utilized.
Date:
January 5, 1993
Creator:
Ackerson, M. D.; Clausen, E. C. & Gaddy, J. L.
Object Type:
Report
System:
The UNT Digital Library
Biological Conversion of Synthesis Gas. Project Status Report, October 1, 1992--December 31, 1992
Syngas is known to contain approximately 1 percent H{sub 2}S, along with CO{sub 2}, C0{sub 2}, H{sub 2} and CH{sub 4}. Similarly, the syngas may become contaminated with oxygen, particularly during reactor start-up and during maintenance. Previous studies with the water-gas shift bacterium Rhodospirillum rubrum have shown that the bacterium is tolerant of small quantities of oxygen, but the effects of oxygen on CO-consumption are unknown. Similarly, R. rubrum is known to be tolerant of H{sub 2}S, with high concentrations of H{sub 2}S negatively affecting CO-uptake. Batch experiments were thus carried out to determine the effects of H{sub 2}S and O{sub 2} on CO-uptake by R. rubrum. The results of these experiments were quantified by using Monod equations modified by adding terms for CO, H{sub 2}S and O{sub 2} inhibition. The techniques used in determining kinetic expressions previously shown for other gas-phase substrate bacterial systems including R. rubrum were utilized.
Date:
January 5, 1993
Creator:
Ackerson, M. D.; Clausen, E. C. & Gaddy, J. L.
Object Type:
Report
System:
The UNT Digital Library
Trade Primer: Qs and As on Trade Concepts, Performance, and Policy
The 112th Congress has a full legislative and oversight agenda on international trade. The agenda may include considering legislation to implement pending free trade agreements with Panama, South Korea, and Colombia, enhanced enforcement of U.S. trade agreements, as well as oversight of the World Trade Organization's Doha Round and trade relations with China. This report provides information and context for many of these topics. The report is divided into four sections in a question-and-answer format: trade concepts, U.S. trade performance, formulation of U.S. trade policy, and trade and investment issues.
Date:
January 5, 2011
Creator:
Ahearn, Raymond J.
Object Type:
Report
System:
The UNT Digital Library
Exploring Prompt Measurement Methods for (n,2n) Cross Sections on Radioactive Targets
This report summarizes a study of possible neutron detection technologies for performing prompt (n,2n) measurements on radioactive targets of the type that could be made at the Rare Isotope Accelerator (RIA). The report recommends conducting further research on high-pressure {sup 3}He gas scintillators as it is the best candidate technology. These detectors meet the requirements of a fast response time (fall times around 5-10 ns), gamma ray suppression, (all gamma rays below about 900 keV can be easily discriminated against), and can be easily configured into a 4{pi} array. The one requirement that these detectors fall short is efficiency, but less than a factor of 10 improvement is needed. The possibility of pulse shape discrimination should also be explored for these detectors as this would help to distinguish gamma rays above 900 keV from neutrons. In addition to R&D work on these detectors, Monte Carlo simulations and target development are also recommended areas of further study.
Date:
January 5, 2006
Creator:
Ahle, L.
Object Type:
Report
System:
The UNT Digital Library
The role of parallel heat transport in the relation between upstream scrape-off layer widths and target heat flux width in H-mode plasmas of NSTX.
The physics of parallel heat transport was tested in the Scrape-off Layer (SOL) plasma of the National Spherical Torus Experiment (NSTX) [M. Ono, et al., Nucl. Fusion 40, 557 (2000) and S. M. Kaye, et al., Nucl. Fusion 45, S168 (2005)] tokamak by comparing the upstream electron temperature (T{sub e}) and density (n{sub e}) profiles measured by the mid-plane reciprocating probe to the heat flux (q{sub {perpendicular}}) profile at the divertor plate measured by an infrared (IR) camera. It is found that electron conduction explains the near SOL width data reasonably well while the far SOL, which is in the sheath limited regime, requires an ion heat flux profile broader than the electron one to be consistent with the experimental data. The measured plasma parameters indicate that the SOL energy transport should be in the conduction-limited regime for R-R{sub sep} (radial distance from the separatrix location) < 2-3 cm. The SOL energy transport should transition to the sheath-limited regime for R-R{sub sep} > 2-3cm. The T{sub e}, n{sub e}, and q{sub {perpendicular}} profiles are better described by an offset exponential function instead of a simple exponential. The conventional relation between mid plane electron temperature decay length ({lambda}{sub Te}) and target …
Date:
January 5, 2009
Creator:
Ahn, J W; Boedo, J A; Maingi, R & Soukhanovskii, V A
Object Type:
Article
System:
The UNT Digital Library
Structure of the Lithosphere and Upper Mantle Across the Arabian Peninsula
Analysis of modern broadband (BB) waveform data allows for the inference of seismic velocity structure of the crust and upper mantle using a variety of techniques. This presentation will report inferences of seismic structure of the Arabian Plate using BB data from various networks. Most data were recorded by the Saudi Arabian National Digital Seismic Network (SANDSN) which consists of 38 (26 BB, 11 SP) stations, mostly located on the Arabian Shield. Additional data were taken from the 1995-7 Saudi Arabian IRIS-PASSCAL Deployment (9 BB stations) and other stations across the Peninsula. Crustal structure, inferred from teleseismic P-wave receiver functions, reveals thicker crust in the Arabian Platform (40-45 km) and the interior of the Arabian Shield (35-40 km) and thinner crust along the Red Sea coast. Lithospheric thickness inferred from teleseismic S-wave receiver functions reveals very thin lithosphere (40-80 km) along the Red Sea coast which thickens rapidly toward the interior of the Arabian Shield (100-120 km). We also observe a step of 20-40 km in lithospheric thickness across the Shield-Platform boundary. Seismic velocity structure of the upper mantle inferred from teleseismic P- and S-wave travel time tomography reveals large differences between the Shield and Platform, with the Shield being …
Date:
January 5, 2007
Creator:
Al-Amri, A. & Rodgers, A.
Object Type:
Article
System:
The UNT Digital Library
Biological impacts and context of network theory
Many complex systems can be represented and analyzed as networks, and examples that have benefited from this approach span the natural sciences. For instance, we now know that systems as disparate as the World-Wide Web, the Internet, scientific collaborations, food webs, protein interactions and metabolism all have common features in their organization, the most salient of which are their scale-free connectivity distributions and their small-world behavior. The recent availability of large scale datasets that span the proteome or metabolome of an organism have made it possible to elucidate some of the organizational principles and rules that govern their function, robustness and evolution. We expect that combining the currently separate layers of information from gene regulatory-, signal transduction-, protein interaction- and metabolic networks will dramatically enhance our understanding of cellular function and dynamics.
Date:
January 5, 2007
Creator:
Almaas, E
Object Type:
Article
System:
The UNT Digital Library
A Miniature Mixer Settler
Unit developed at Knolls Atomic Power Laboratory for extraction and overcomes the disadvantages of the batch countercurrent units currently in use.
Date:
January 5, 1956
Creator:
Alter, H. Ward; Coplan, B. V. & Zebroski, E. L.
Object Type:
Report
System:
The UNT Digital Library
Three-dimensional position sensing and field shaping in orthogonal-strip germanium gamma-ray detectors.
None
Date:
January 5, 2000
Creator:
Amman, M. & Luke, P. N.
Object Type:
Article
System:
The UNT Digital Library
Baling-Press.
Patent for a baling-press meant to bale cotton. In this machine, "the power as applied to the plunger is increased in proportion to the resistance offered by the material being baled and whereby the forward movement of the plunger is automatically checked at the limit of its path and is returned to its initial positioin without effort upon the part of the operator" (lines 10-17).
Date:
January 5, 1897
Creator:
Anderson, Alva E.
Object Type:
Patent
System:
The Portal to Texas History
Measurement of CP Content and Time-Dependent CP Violation in B0 --> D*+D*- Decays
This dissertation presents the measurement of the Cp-odd fraction and time-dependent CP violation parameters for the B{sup 0} {yields} D*{sup +} D*{sup -} decay. These results are based on the full BABAR dataset of (467 {+-} 5) x 10{sup 6} B{bar B} pairs collected at the PEP-II B Factory at the Stanford Linear Accelerator Center. An angular analysis finds that the CP-odd fraction of the B{sup 0} {yields} D*{sup +} D*{sup -} decay is R{sub {perpendicular}} = 0.158 {+-} 0.028 {+-} 0.006, where the first uncertainty is statistical, and the second is systematic. A fit to the flavor-tagged, time-dependent, angular decay rate yields C{sub +} = 0.02 {+-} 0.12 {+-} 0.02; C{sub {perpendicular}} = 0.41 {+-} 0.50 {+-} 0.08; S{sub +} = -0.76 {+-} 0.16 {+-} 0.04; S{sub {perpendicular}} = -1.81 {+-} 0.71 {+-} 0.16, for the CP-odd ({perpendicular}) and CP-even (+) contributions. Constraining these two contributions to be the same results in C = 0.047 {+-} 0.091 {+-} 0.019; S = -0.71 {+-} 0.16 {+-} 0.03. These measurements are consistent with the Standard Model and with measurements of sin2{beta} from B{sup 0} {yields} (c{bar c})K{sup 0} decays.
Date:
January 5, 2009
Creator:
Anderson, Jacob M.
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
Low-Water Alarm For Boilers
Patent for "improvements in low water alarms for steam boilers and more particularly to those which are operated by the heat from the steam in the boiler, after the water therein has fallen below a predetermined danger point" (lines 15-20).
Date:
January 5, 1915
Creator:
Anderson, Williamson D. & Shearer, Edward J.
Object Type:
Patent
System:
The Portal to Texas History
Optical Properties in Non-equilibrium Phase Transitions
An open question about the dynamical behavior of materials is how phase transition occurs in highly non-equilibrium systems. One important class of study is the excitation of a solid by an ultrafast, intense laser. The preferential heating of electrons by the laser field gives rise to initial states dominated by hot electrons in a cold lattice. Using a femtosecond laser pump-probe approach, we have followed the temporal evolution of the optical properties of such a system. The results show interesting correlation to non-thermal melting and lattice disordering processes. They also reveal a liquid-plasma transition when the lattice energy density reaches a critical value.
Date:
January 5, 2006
Creator:
Ao, T; Ping, Y; Widmann, K; Price, D F; Lee, E; Tam, H et al.
Object Type:
Article
System:
The UNT Digital Library
Individuals with Disabilities Education Act (IDEA): Analysis of Changes Made by P.L. 108-446
This report discusses the Individuals with Disabilities Education Act (IDEA — 20 U.S.C. §1400 et seq.), which is both a grants statute and a civil rights statute. It provides federal funding for the education of children with disabilities and requires, as a condition for the receipt of such funds, the provision of a free appropriate public education (FAPE). The statute also contains detailed due process provisions to ensure the provision of FAPE. Originally enacted in 1975, the act responded to increased awareness of the need to educate children with disabilities, and to judicial decisions requiring that states provide an education for children with disabilities if they provided an education for children without disabilities.
Date:
January 5, 2005
Creator:
Apling, Richard N. & Jones, Nancy Lee
Object Type:
Report
System:
The UNT Digital Library
Logs of exploratory holes 2 and 7, Tatum dome, Lamar County, Mississippi. Technical letter: Dribble-16
None
Date:
January 5, 1961
Creator:
Armstrong, C. A.; Chafin, R. V.; Taylor, R. E. & Harris, H. B.
Object Type:
Report
System:
The UNT Digital Library
Logs of exploratory holes 3 and 9 Tatum dome, Lamar County, Mississippi. Technical letter: Dribble-17
None
Date:
January 5, 1962
Creator:
Armstrong, C. A.; Taylor, R. E.; Chafin, R. V. & Harris, H. B.
Object Type:
Report
System:
The UNT Digital Library
Terrestrial biogeochemical feedbacks in the climate system: from past to future
The terrestrial biosphere plays a major role in the regulation of atmospheric composition, and hence climate, through multiple interlinked biogeochemical cycles (BGC). Ice-core and other palaeoenvironmental records show a fast response of vegetation cover and exchanges with the atmosphere to past climate change, although the phasing of these responses reflects spatial patterning and complex interactions between individual biospheric feedbacks. Modern observations show a similar responsiveness of terrestrial biogeochemical cycles to anthropogenically-forced climate changes and air pollution, with equally complex feedbacks. For future conditions, although carbon cycle-climate interactions have been a major focus, other BGC feedbacks could be as important in modulating climate changes. The additional radiative forcing from terrestrial BGC feedbacks other than those conventionally attributed to the carbon cycle is in the range of 0.6 to 1.6 Wm{sup -2}; all taken together we estimate a possible maximum of around 3 Wm{sup -2} towards the end of the 21st century. There are large uncertainties associated with these estimates but, given that the majority of BGC feedbacks result in a positive forcing because of the fundamental link between metabolic stimulation and increasing temperature, improved quantification of these feedbacks and their incorporation in earth system models is necessary in order to develop …
Date:
January 5, 2010
Creator:
Arneth, A.; Harrison, S. P.; Zaehle, S.; Tsigaridis, K.; Menon, S.; Bartlein, P. J. et al.
Object Type:
Article
System:
The UNT Digital Library
Towards the NNLL Precision in the Decay $\bar B \rightarrow X_s \gamma$
The present NLL prediction for the decay rate of the rare inclusive process {bar B} {yields} X{sub s}{gamma} has a large uncertainty due to the charm mass renormalization scheme ambiguity. We estimate that this uncertainty will be reduced by a factor of 2 at the NNLL level. This is a strong motivation for the on-going NNLL calculation, which will thus significantly increase the sensitivity of the observable {bar B} {yields} X{sub s}{gamma} to possible new degrees of freedom beyond the SM. We also give a brief status report of the NNLL calculation.
Date:
January 5, 2006
Creator:
Asatrian, Hrachia M.; Hovhannisyan, Artyom; Poghosyan, Vahagn; Inst., /Yerevan Phys.; Greub, Christoph; U., /Bern et al.
Object Type:
Article
System:
The UNT Digital Library
Predicting tropospheric ozone and hydroxyl radical in a global, three-dimensional, chemistry, transport, and deposition model
Two of the most important chemically reactive tropospheric gases are ozone (O{sub 3}) and the hydroxyl radical (OH). Although ozone in the stratosphere is a necessary protector against the sun`s radiation, tropospheric ozone is actually a pollutant which damages materials and vegetation, acts as a respiratory irritant, and is a greenhouse gas. One of the two main sources of ozone in the troposphere is photochemical production. The photochemistry is initiated when hydrocarbons and carbon monoxide (CO) react with nitrogen oxides (NO{sub x} = NO + NO{sub 2}) in the presence of sunlight. Reaction with the hydroxyl radical, OH, is the main sink for many tropospheric gases. The hydroxyl radical is highly reactive and has a lifetime on the order of seconds. Its formation is initiated by the photolysis of tropospheric ozone. Tropospheric chemistry involves a complex, non-linear set of chemical reactions between atmospheric species that vary substantially in time and space. To model these and other species on a global scale requires the use of a global, three-dimensional chemistry, transport, and deposition (CTD) model. In this work, I developed two such three dimensional CTD models. The first model incorporated the chemistry necessary to model tropospheric ozone production from the reactions …
Date:
January 5, 1995
Creator:
Atherton, C.S.
Object Type:
Report
System:
The UNT Digital Library
Three-dimensional Global Model Approaches to Understanding Stratospheric Impacts on Tropospheric Ozone
None
Date:
January 5, 2004
Creator:
Atherton, C; Bergmann, D; Cameron-Smith, P; Connell, P; Dignon, J; Rotman, D et al.
Object Type:
Article
System:
The UNT Digital Library
Measurements of CP-Violating Asymmetries in B^0 toa_1^+(1260) \pi^- Decays
The authors present measurements of CP-violating asymmetries in the decay B{sup 0} {yields} a{sub 1}{sup {+-}}(1260){pi}{sup {-+}} with a{sub 1}{sup {+-}}(1260) {yields} {pi}{sup {-+}}{pi}{sup {+-}}{pi}{sup {+-}}. The data sample corresponds to 384 x 10{sup 6} B{bar B} pairs collected with the BABAR detector at the PEP-II asymmetric B-factory at SLAC. They measure the CP-violating asymmetry {Alpha}{sub CP}{sup a{sub 1}{pi}} = -0.07 {+-} 0.07 {+-} 0.02, the mixing-induced CP violation parameter S{sub a{sub 1}{pi}} = 0.37 {+-} 0.21 {+-} 0.07, the direct Cp violation parameter C{sub a{sub 1}{pi}} = -0.10 {+-} 0.15 {+-} 0.09, and the parameters {Delta}C{sub a{sub 1}{pi}} = 0.26 {+-} 0.15 {+-} 0.07 and {Delta}S{sub a{sub 1}{pi}} = -0.14 {+-} 0.21 {+-} 0.06. From these measured quantities they determine the angle {alpha}{sub eff} = 78.6{sup o} {+-} 7.3{sup o}.
Date:
January 5, 2007
Creator:
Aubert, B.
Object Type:
Article
System:
The UNT Digital Library
Measurements of the Branching Fractions and CP Asymmetries of B -> D0_CP K Decays
We present a study of the decay B{sup -} {yields} D{sub (CP)}{sup 0} K{sup -} and its charge conjugate, where D{sub (CP)}{sup 0} is reconstructed in CP-even, CP-odd, and non-CP flavor eigenstates, based on a sample of 232 million {Upsilon}(4S) {yields} B{bar B} decays collected with the BABAR detector at the PEP-II e{sup +}e{sup -} storage ring. We measure the partial-rate charge asymmetries AC{sub CP{+-}} and the ratios R{sub CP{+-}} of the B {yields} D{sup 0} K decay branching fractions as measured in CP{+-} and non-CP D{sup 0} decays: A{sub CP+} = 0.35 {+-} 0.13(stat) {+-} 0.04(syst), A{sub CP-} = -0.06 {+-} 0.13(stat) {+-} 0.04(syst), R{sub CP+} = 0.90 {+-} 0.12(stat) {+-} 0.04(syst), R{sub CP-} = 0.86 {+-} 0.10(stat) {+-} 0.05(syst).
Date:
January 5, 2006
Creator:
Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
Object Type:
Article
System:
The UNT Digital Library