Physical Sciences and Mathematics Commons^™

Metal Modulation Epitaxy Growth For Extremely High Hole Concentrations Above 10(19) Cm(-3) In Gan, Gon Namkoong, Elaissa Trybus, Kyung Keun Lee, Michael Moseley, W. Alan Doolittle, David C. Look

Applied Research Center Publications

The free hole carriers in GaN have been limited to concentrations in the low 10¹⁸ cm⁻³ range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ~10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ~1.5 x 10¹⁹ cm⁻³.

© 2008 American Institute of Physics.

Unit Rectangle Visibility Graphs, Alice M. Dean, Joanna A. Ellis-Monaghan, Sarah J. Hamilton, Greta Pangborn

Mathematics, Statistics and Computer Science Faculty Research and Publications

Over the past twenty years, rectangle visibility graphs have generated consider- able interest, in part due to their applicability to VLSI chip design. Here we study unit rectangle visibility graphs, with fixed dimension restrictions more closely modeling the constrained dimensions of gates and other circuit components in computer chip applications. A graph G is a unit rectangle visibility graph (URVG) if its vertices can be represented by closed unit squares in the plane with sides parallel to the axes and pairwise disjoint interiors, in such a way that two vertices are adjacent if and only if there is a non-degenerate …

Nevada Interagency Volunteer Program: Helping Hands Across Public Lands – Phase Ii: Quarterly Progress Report, Period Covering October 1 – December 31, 2007, Margaret N. Rees

Get Outdoors Nevada

• The number of records in the volunteer database increased 12% over last quarter. The database now contains 4,937 records.
• Website activity decreased, recording an average of 82,859 hits per month, a decrease of 31% from last quarter, with an average of 8,191 pages viewed per month.
• Volunteer fall training has been completed.
• Three National Public Land Day Events have been completed.
• Two hundred and ten people attended the Volunteer Recognition Event.

Lake Mead National Recreation Area Sensitive Wildlife Species Monitoring And Analysis: Quarterly Progress Report, Period Ending December 31, 2007, Margaret N. Rees

Wildlife Monitoring

Project 1. Relict Leopard Frog Monitoring, Management, and Research

• Fall surveys completed at all natural and translocation sites.
• Coordination for a potential translocation site on BLM lands in the Gold Butte area ongoing – the aim is that this site will be ready for translocations in 2008.
• Coordination ongoing for evaluation of a translocation site on BLM lands in the Black Mountains, AZ – the plan is to complete compliance in 2008.
• Coordination and assistance provided to UNLV research efforts on habitat improvements at Blue Point, Rogers, and Pupfish Refuge springs.
• Relict Leopard Frog Conservation Team meeting held in December. …

Lake Mead National Recreation Area Vegetation Monitoring And Analysis: Quarterly Progress Report, October 1, 2007 To December 31, 2007, Margaret N. Rees

Vegetation Monitoring

Executive Summary

• The Weed Sentry program surveyed more than 750 miles of federal lands in Clark County for invasive, exotic plant species.
• Weed Sentry also removed more than 600,000 individual invasive plants from federal
  lands. These removals represent pro-active efforts that may have forestalled large
  infestations difficult and costly to eradicate.
• In response to a request by the manager of the Fish and Wildlife Service Desert National
  Wildlife Refuge, a major effort of surveying springs for plant community composition
  and invasive plants provided unique knowledge services by the Weed Sentry program.
  No such baseline information existed for the Sheep Range. …

Limnological Assistance For The Lake Mead National Recreation Area In Meeting The Challenge Of The Water 2025 Initiative: Quarterly Progress Report, Period Ending: December 31, 2007, Margaret N. Rees

Limnological Studies

• The limnologist position has been announced.
• Project 1: Review of the draft Boulder Basin Adaptive Management Plan is underway.
• Project 2: Development of a white paper expressing the joint needs of the entities involved in Water 2025 projects is being coordinated.
• Project 3: A bibliographic reference spreadsheet organizing literature citations related to quagga and zebra mussel research has been completed.
• Project 4: A comprehensive literature search of Lake Mead limnology is well underway; an Access database has been designed to organize reference citations; and a special collections library at UNLV is being established to house original rare documents and other …

Interagency Science And Research: Quarterly Progress Report, Period Ending December 31, 2007, Margaret N. Rees

Interagency Science and Research Strategy

• Meetings were held with the SNAP Recreation Team and the SNAP Cultural Resources Team to request assistance in the development of the science strategy. Draft versions of interagency goals, subgoals, science questions, and associated tasks were given to each team for review and input.
• Plans were prepared for the peer review of science proposals submitted for consideration as Conservations Initiatives in SNPLMA Round 9.
• Proceedings of the natural resources management workshop held on September 13 were completed and sent to the Science & Research Team for review by members.
• An important focus of the Science and Research Team was the …

Muon-Fluorine Entangled States In Molecular Magnets, T Lancaster, S J. Blundell, P J. Baker, M L. Brooks, W Hayes, F L. Pratt, Jamie L. Manson, M M. Conner, J A. Schlueter

Chemistry and Biochemistry Faculty Publications

The information accessible from a muon-spin relaxation experiment can be limited due to a lack of knowledge of the precise muon stopping site. We demonstrate here the possibility of localizing a spin polarized muon in a known stopping state in a molecular material containing fluorine. The muon-spin precession that results from the entangled nature of the muon spin and surrounding nuclear spins is sensitive to the nature of the stopping site. We use this property to identify three classes of sites that occur in molecular magnets and describe the extent to which the muon distorts its surroundings.

Optical Estimation Of Auroral Ion Upflow: Theory, M. Zettergren, J. L. Semeter, P. L. Blelly, M. Diaz

Publications

This work presents a systematic analysis of optical emissions related to auroral ion upflow. Optical intensities and field‐aligned ion transport are computed for a set of monoenergetic incident electron beams using a combined fluid‐kinetic model. The kinetic portion models the energetic particle transport with a multiple stream approach and provides ionization, excitation, and heating rates to an eight‐moment fluid model of the ionosphere, which then calculates the resulting ion upflow. The analysis is used to develop a technique for estimating upward ion flux from photometric measurements at five discrete wavelengths: 427.8 nm, 557.7 nm, 630.0 nm, 732 nm, and 844.6 …

Unresolved Issues With The Assessment Of Multidecadal Global Land Surface Temperature Trends, Roger A. Pielke Sr., Christopher A. Davey, Dev Niyogi, Souleymane Fall, Jesse Steinweg-Woods, Ken Hubbard, Xiaomao Lin, Ming Cai, Young-Kwon Lim, Hong Li, John Nielsen-Gammon, Kevin Gallo, Robert Hale, Rezaul Mahmood, Stuart Foster, Richard T. Mcnider, Peter Blanken

School of Natural Resources: Faculty Publications

This paper documents various unresolved issues in using surface temperature trends as a metric for assessing global and regional climate change. A series of examples ranging from errors caused by temperature measurements at a monitoring station to the undocumented biases in the regionally and globally averaged time series are provided. The issues are poorly understood or documented and relate to micrometeorological impacts due to warm bias in nighttime minimum temperatures, poor siting of the instrumentation, effect of winds as well as surface atmospheric water vapor content on temperature trends, the quantification of uncertainties in the homogenization of surface temperature data, …

Theory And Numerics Of Gravitational Waves From Preheating After Inflation, Jean-François Dufaux, Amanda Bergman, Gary Felder, Lev Kofman, Jean-Philippe Uzan

Physics: Faculty Publications

Preheating after inflation involves large, time-dependent field inhomogeneities, which act as a classical source of gravitational radiation. The resulting spectrum might be probed by direct detection experiments if inflation occurs at a low enough energy scale. In this paper, we develop a theory and algorithm to calculate, analytically and numerically, the spectrum of energy density in gravitational waves produced from an inhomogeneous background of stochastic scalar fields in an expanding universe. We derive some generic analytical results for the emission of gravity waves by stochastic media of random fields, which can test the validity/accuracy of numerical calculations. We contrast our …

Science Plan For Potential 2008 Experimental High Flow At Glen Canyon Dam, Grand Canyon Monitoring And Research Center

All U.S. Government Documents (Utah Regional Depository)

No abstract provided.

Starspots And Relativity: Applied Doppler Imaging For The Gravity Probe B Mission, Stephen C. Marsden, Svetlana V. Berdyugina, Jean-Francois Donati, Joel A. Eaton, Michael H. Williamson

Information Systems and Engineering Management Research Publications

We present Doppler images and surface differential rotation measurements for the primary of the RS CVn binary IM Pegasi, the guide star for the Gravity Probe B experiment. The data used is a subset of that taken during optical support of the mission and was obtained almost nightly over a near three year period from the Automatic Spectroscopic Telescope operated by Tennessee State University. Using the technique of least-squares deconvolution to increase the signal-to-noise ratio of the data, we have reconstructed 31 maximum entropy Doppler images of the star. The images show that the spot features are relatively stable for …

Validation Of The Aura Microwave Limb Sounder Hnomeasurements, M L. Santee, A Lambert, W G. Read, N J. Livesey, R E. Cofield, D T. Cuddy, W H. Daffer, B J. Drouin, L Froidevaux, R A. Fuller, R F. Jarnot, B W. Knosp, G L. Manney, V S. Perun, W V. Snyder, P C. Stek, R P. Thurstans, P A. Wagner, J W. Waters, G Muscari, R L. De Zafra, Jack E. Dibb, D W. Fahey, P J. Popp, T P. Marcy, K W. Jucks, G C. Toon, R A. Stachnik, P F. Bernath, C D. Boone, K A. Walker, J Urban, D Murtagh

Earth Sciences

We assess the quality of the version 2.2 (v2.2) HNO₃ measurements from the Microwave Limb Sounder (MLS) on the Earth Observing System Aura satellite. The MLS HNO₃ product has been greatly improved over that in the previous version (v1.5), with smoother profiles, much more realistic behavior at the lowest retrieval levels, and correction of a high bias caused by an error in one of the spectroscopy files used in v1.5 processing. The v2.2 HNO₃ data are scientifically useful over the range 215 to 3.2 hPa, with single-profile precision of ∼0.7 ppbv throughout. Vertical resolution is 3–4 km …

Exploiting Self-Assembly For Ligand-Scaffold Optimization: Substrate-Tailored Ligands For Efficient Catalytic Asymmetric Hydroboration, Shin A. Moteki, James M. Takacs

James Takacs Publications

A self-assembled ligand library (SAL XY) affords a wide range of R/S ratios in Rh-catalyzed asymmetric hydroboration (nbd = 2,5norbornadiene, R* is a chiral substituent). Ligand-scaffold optimization reveals “substrate-tailored” ligands that afford high regio- and enantioselectivity for a variety of ortho-substituted styrene derivatives.

Includes article (4 pp.) and supporting information (106 pp.).

Phase Dynamics Of Inas/Gaas Quantum Dot Semiconductor Optical Amplifiers, T. Piwonski, Guillaume Huyet, Et. Al.

Physical Sciences Publications

The gain and phase dynamics of InAs∕GaAs quantum dot amplifiers are studied using single and two-color heterodyne pump probe spectroscopy. The relaxation of the wetting layer carrier density is shown to have a strong effect on the phase dynamics of both ground and excited state transients, while having a much weaker effect on the gain dynamics. In addition, the dynamical alpha factor may also display a constant value after an initial transient. Such behavior is strongly encouraging for reduced pattern effect operation in high speed optical networks.

Model-Robust Bayesian Regression And The Sandwich Estimator, Adam A. Szpiro, Kenneth M. Rice, Thomas Lumley

UW Biostatistics Working Paper Series

PLEASE NOTE THAT AN UPDATED VERSION OF THIS RESEARCH IS AVAILABLE AS WORKING PAPER 338 IN THE UNIVERSITY OF WASHINGTON BIOSTATISTICS WORKING PAPER SERIES (http://www.bepress.com/uwbiostat/paper338).

In applied regression problems there is often sufficient data for accurate estimation, but standard parametric models do not accurately describe the source of the data, so associated uncertainty estimates are not reliable. We describe a simple Bayesian approach to inference in linear regression that recovers least-squares point estimates while providing correct uncertainty bounds by explicitly recognizing that standard modeling assumptions need not be valid. Our model-robust development parallels frequentist estimating equations and leads to intervals …

Imaging Thermal Stratigraphy In Freshwater Lakes Using Georadar, John H. Bradford, Cody R. Johnson, Troy Brosten, James P. Mcnamara, Michael N. Gooseff

CGISS Publications and Presentations

Thermal stratification exerts significant control over biogeochemical processing in freshwater lakes. Thus, the temporal and spatial distribution of the thermal structure is an important component in understanding lake ecosystems. We present the first reported observations of lake thermal stratification from surface based georadar measurements acquired over two small freshwater lakes. This method is very useful because it can provide rapid acquisition of 2D or 3D lotic stratification.

Toward A New Generation Of Ice Sheet Models, Christopher M. Little, Michael Oppenheimer, Richard B. Alley, Venkatramani Balaji, Garry K. C. Clarke, Thomas L. Delworth, Robert Hallberg, David Holland, Christina L. Hulbe, Stan Jacobs, Jesse V. Johnson, Hiram Levy, William Lipscomb, Shawn J. Marshall, Byron R. Parizek, Antony J. Payne, Gavin A. Schmidt, Ronald J. Stouffer, David G. Vaughan, Michael Winton

Computer Science Faculty Publications

This report summarizes the conclusions and recommendations of a 1-day workshop on ice sheet modeling held at the NOAA Geophysical Fluid Dynamics Laboratory on 8 January 2007, sponsored by NOAA and by the Program in Science, Technology, and Environmental Policy of the Woodrow Wilson School of Public and International Affairs at Princeton University, N. J.

Tidal Asymmetry And Residual Circulation Over Linear Sandbanks And Their Implication On Sediment Transport: A Process-Oriented Numerical Study, Rosario Sanay, George Voulgaris, John C. Warner

Faculty Publications

A series of process-oriented numerical simulations is carried out in order to evaluate the relative role of locally generated residual flow and overtides on net sediment transport over linear sandbanks. The idealized bathymetry and forcing are similar to those present in the Norfolk Sandbanks, North Sea. The importance of bottom drag parameterization and bank orientation with respect to the ambient flow is examined in terms of residual flow and overtide generation, and subsequent sediment transport implications are discussed. The results show that although the magnitudes of residual flow and overtides are sensitive to bottom roughness parameterization and bank orientation, the …

Tomography Of The Darcy Velocity From Self-Potential Measurements, A. Jardani, A. Revil, A. Bolève, A. Crespy, J.-P. Dupont, W. Barrash, Bwalya Malama

Natural Resources Management and Environmental Sciences

An algorithm is developed to interpret self-potential (SP) data in terms of distribution of Darcy velocity of the ground water. The model is based on the proportionality existing between the streaming current density and the Darcy velocity. Because the inverse problem of current density determination from SP data is underdetermined, we use Tikhonov regularization with a smoothness constraint based on the differential Laplacian operator and a prior model. The regularization parameter is determined by the L-shape method. The distribution of the Darcy velocity depends on the localization and number of non-polarizing electrodes and information relative to the distribution of the …

Measurement Of The Pp̅ → Wz + X Cross Section At √S =1.96 Tev And Limits On Wwz Trilinear Gauge Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

We present measurements of the process pp̅ → WZ + X → ℓ′νℓℓ&#; at √s = 1.96 TeV, where ℓ and ℓ′ are electrons or muons. Using 1 fb^-1 of data from the D0 experiment, we observe 13 candidates with an expected background of 4.5 ± 0.6 events and measure a cross section σ(WZ) = 2.7_-1.3^+1.7 pb. From the number of observed events and the Z boson transverse momentum distribution, we limit the trilinear WWZ gauge couplings to -0.17 ≤ λ_Z ≤ 0.21(Δκ_Z= 0) at the 95% C.L. for a form …

Observation Of P-Wave Threshold Behavior In Electron Attachment To F2 Molecules, M. Braun, M.-W. Ruf, Ilya I. Fabrikant, H. Hotop

Ilya Fabrikant Publications

Using the high resolution laser photoelectron attachment method, we demonstrate that the cross section for F^- formation due to electron capture by F² (X¹Σ_g⁺) molecules at very low energies exhibits p-wave threshold behavior. This finding confirms the theoretical expectation that low-energy attachment to F₂ proceeds through the F₂^-(² Σ_u⁺) p-wave shape resonance in contrast with previous experimental claims for s-wave threshold behavior.

Tomography Of The Darcy Velocity From Self-Potential Measurements, A. Jardani, A. Revil, A. Bolève, A. Crespy, J.-P. Dupont, Warren Barrash, Bwalya Malama

CGISS Publications and Presentations

An algorithm is developed to interpret self-potential (SP) data in terms of distribution of Darcy velocity of the ground water. The model is based on the proportionality existing between the streaming current density and the Darcy velocity. Because the inverse problem of current density determination from SP data is underdetermined, we use Tikhonov regularization with a smoothness constraint based on the differential Laplacian operator and a prior model. The regularization parameter is determined by the L-shape method. The distribution of the Darcy velocity depends on the localization and number of non-polarizing electrodes and information relative to the distribution of the …

Biogeochemical Evolution Of Cryoconite Holes On Canada Glacier, Taylor Valley, Antarctica, Elizabeth A. Bagshaw, Martyn Tranter, Andrew G. Fountain, Kathleen A. Welch, Hassan J. Basagic, W. Berry Lyons

Geography Faculty Publications and Presentations

The cryoconite holes of the McMurdo Dry Valleys are simple, closed biogeochemical systems involving water, ice, mineral and organic debris, which serve as ecosystems for consortia of microorganisms. This study is the first to document the seasonal and annual chemical evolution of solutes in cryoconite holes. Samples of glacier ice, frozen cryoconite holes and those containing water were collected during the austral summer of 2005–2006. The isolation age was calculated from the excess Cl‾ in the holes, and varied from 0 to 5 years (a), consistent with the last hot summer when the cryoconite holes were open to the atmosphere. …

Evidence For A Population Of High-Redshift Submillimeter Galaxies From Interferometric Imaging, Joshua D. Younger, Giovanni G. Fazio, Jia Sheng Huang, Min S. Yun, Grant W. Wilson, Matthew L.N. Ashby, Mark A. Gurwell, Kamson Lai, Alison B. Peck, Glen R. Petitpas, David J. Wilner, Daisuke Iono, Kotaro Kohno, Ryohei Kawabe, David H. Hughes, Itziar Aretxaga, Tracy Webb, Alejo Martínez-Sansigre, Sungeun Kim, Kimberly S. Scott, Jason Austermann, Thushara Perera, James Lowenthal, Eva Schinnerer, Vernesa Smolčić

Astronomy: Faculty Publications

We have used the Submillimeter Array to image a flux-limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 μm with ∼2″ resolution. All of the sources - two radio-bright and five radio-dim - are detected as single point sources at high significance (>6 σ), with positions accurate to ∼0.2″ that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST ACS imaging. As compared to the two radio-bright sources …

An Ab Initio Study Of The Structures, Vibrational Spectra, And Energetics Of Alshx (X = –1, 0, +1), Sujata Guha, Joseph S. Francisco

Chemistry Faculty Research

The ground state of aluminum hydrosulfide, AlSHX (where X = − 1,0, + 1), has been examined using high-level ab initio electronic structure calculations at the CCSD(T) level with an augmented correlation-consistent basis set. The geometries have been optimized up through the aug-cc-pV5Z level and vibrational frequencies calculated using the aug-cc-pV5Z basis set. The energetic properties of AlSH are also examined. The adiabatic ionization potential and electron affinity of AlSH are calculated to be 198.5 and 7.7 kcal mol−1, respectively. Dissociation of AlSH into AlS + H will require 78.2 kcal mol−1 of energy, and the Al-S bond energy is …

Automated Refinement And Augmentation Of Web Service Description Files, Marc Fisher Ii, Sebastian Elbaum, Gregg Rothermel

CSE Technical Reports

Web Service Description Language (WSDL) is being increasingly used to specify web service interfaces. Specifications of this type, however, are often incomplete or imprecise. For example, cursory examination of the WSDL file for Amazon’s E-Commerce Web Service reveals that it often uses a less specific type where a more specific type is applicable, or declares that elements could be missing where other documentation indicates that they are required. Further, specifications reflecting the temporal relationships between operations are completely missing, which is not surprising since they are not supported by the current WSDL standard. These problems in WSDL specifications can cause …

Ultrashort Intense-Field Optical Vortices Produced With Laser-Etched Mirrors, James Strohaber, Timothy D. Scarborough, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We introduce a simple and practical method to create ultrashort intense optical vortices for applications involving high-intensity lasers. Our method utilizes femtosecond laser pulses to laser etch grating lines into laser-quality gold mirrors. These grating lines holographically encode an optical vortex. We derive mathematical equations for each individual grating line to be etched, for any desired (integer) topological charge. We investigate the smoothness of the etched grooves. We show that they are smooth enough to produce optical vortices with an intensity that is only a few percent lower than in the ideal case. We demonstrate that the etched gratings can …

Merged Ionization/Dissociation Fronts In Planetary Nebulae, William J. Henney, R. J. R. Williams, Gary J. Ferland, Gargi Shaw, C. R. O'Dell

Physics and Astronomy Faculty Publications

The hydrogen ionization and dissociation front around an ultraviolet radiation source should merge when the ratio of ionizing photon flux to gas density is sufficiently low and the spectrum is sufficiently hard. This regime is particularly relevant to the molecular knots that are commonly found in evolved planetary nebulae, such as the Helix Nebula, where traditional models of photodissociation regions have proved unable to explain the high observed luminosity in H₂ lines. In this paper we present results for the structure and steady state dynamics of such advection-dominated merged fronts, calculated using the Cloudy plasma/molecular physics code. We find …