VTechWorks Repository :: Browsing by Author "Virginia Tech"

Browsing by Author "Virginia Tech"

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1/N expansion for the degenerate Anderson model in the mixed-valence regime
Zhang, F. C.; Lee, T. K. (American Physical Society, 1983-07)
The 1N expansion method for the degenerate Anderson model is formulated. N is the degeneracy factor of one of the f-electron configurations. Various ground-state properties are calculated. Excellent agreement with the result of Bethe ansatz for N=6 is shown. The rate of convergence of the series is analyzed. The merit and inadequacy of the method are discussed. At zero temperature the ratio of the magnetic susceptibility and the specific-heat linear coefficient is shown to lie within a range of 1 and 1+(N-1)-1.
10 kpc Scale Seyfert Galaxy Outflow: HST/COS Observations of IRAS F22456-5125
Borguet, Benoit C. J.; Edmonds, Douglas; Arav, Nahum; Dunn, Jay; Kriss, Gerard A. (IOP Publishing Ltd., 2012-06)
We present analysis of the UV spectrum of the low-z AGN IRAS F22456-5125 obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The spectrum reveals six main kinematic components, spanning a range of velocities of up to 800 km s (1), which for the first time are observed in troughs associated with C II, C IV, N V, Si II, Si III, Si IV, and S IV. We also obtain data on the O VI troughs, which we compare to those available from an earlier Far Ultraviolet Spectroscopic Explorer epoch. Column densities measured from these ions allow us to derive a well-constrained photoionization solution for each outflow component. Two of these kinematic components show troughs associated with transitions from excited states of Si II and C II. The number density inferred from these troughs, in combination with the deduced ionization parameter, allows us to determine the distance to these outflow components from the central source. We find these components to be at a distance of similar to 10 kpc. The distances and the number densities derived are consistent with the outflow being part of a galactic wind.
14-year program monitoring the flux densities of 33 radio sources at low frequencies
Salgado, José Francisco; Altschuler, Daniel R.; Ghosh, Tapasi; Dennison, Brian K.; Mitchell, Kenneth J.; Payne, Harry E. (IOP PUBLISHING LTD, 1999-01)
We present the results of a low-frequency flux density monitoring program of 33 extragalactic radio sources. The light curves at 318 and 430 MHz over a 14 yr period are presented. The measurements were made with the NAIC Arecibo 305 m radio telescope at approximately bimonthly intervals between 1980 January and 1989 February and at less regular intervals between 1989 October and 1993 October, for a total of 64 observing sessions. In addition, we provide a first discussion of the results, pointing out several source properties and interesting objects.
1998 General Assembly Legislation Related to Water
Virginia Water Resources Research Center; Manfre, Joseph (Virginia Water Resources Research Center, 1998)
The Virginia General Assembly held its regular session from January 14 to March 17, then reconvened April 22-23 to respond to the governor’s vetoes. A special session on April 23-24 passed the budget along with car-tax and school-construction-grant legislation. During the regular session, 2152 bills were considered (939 passing, 651 failing, and 562 carried over until 1999), along with 730 joint resolutions (580 passing, 115 failing, and 36 carried over). Among all this legislative action were 97 water-related bills and joint resolutions.1 (Hereafter, we will use “bills” to include both bills and joint resolutions.) To identify bills related to water, we used the Legislative Information System’s subject index, looking first under two categories: “Waters of the State, Ports and Harbors” and “Water and Sewer Systems.” Of the 97 bills listed below, 73 were in one of these two categories. We then found 24 other pertinent bills under these categories: Conservation; Fisheries and Habitat of Tidal Waters; and Game, Inland Fisheries and Boating.
$29 for 70 Items or 70 Items for $29? How Presentation Order Affects Package Perceptions
Bagchi, Rajesh; Davis, Derick F. (University of Chicago Press, 2012-06)
When consumers consider a package (multi- item) price, which presentation order is more appealing, price first ($29 for 70 items) or item quantity first (70 items for $29)? Will this depend on package size (larger [70 items] vs. smaller [7 items]) or unit price calculation difficulty (higher [$29 for 70 items] vs. lower [$20 for 50 items])? Why? Three studies demonstrate how presentation order affects package evaluations and choice under different levels of package size and unit price calculation difficulty. The first piece of information becomes salient and affects evaluations when packages are larger and unit price calculations are difficult (i. e., priceitem [item-price] makes price [items] salient, negatively [positively] affecting evaluations). These effects do not persist with smaller packages or easier unit price calculations. Our findings contribute to several literatures (e. g., numerosity, computational difficulty) but primarily to the order effects literature and have implications for measurement and practice (e. g., pricing).
50-kHz-rate 2D imaging of temperature and H2O concentration at the exhaust plane of a J85 engine using hyperspectral tomography
Ma, Lin; Li, Xuesong; Sanders, Scott T.; Caswell, Andrew W.; Roy, Sukesh; Plemmons, David H.; Gord, James R. (Optical Society of America, 2013-01-01)
This paper describes a novel laser diagnostic and its demonstration in a practical aero-propulsion engine (General Electric J85). The diagnostic technique, named hyperspectral tomography (HT), enables simultaneous 2-dimensional (2D) imaging of temperature and water-vapor concentration at 225 spatial grid points with a temporal response up to 50 kHz. To our knowledge, this is the first time that such sensing capabilities have been reported. This paper introduces the principles of the HT techniques, reports its operation and application in a J85 engine, and discusses its perspective for the study of high-speed reactive flows. (C) 2013 Optical Society of America
A-site doping-induced renormalization of structural transformations in the PbSc0.5Nb0.5O3 relaxor ferroelectric under high pressure
Maier, B. J.; Welsch, A. M.; Angel, R. J.; Mihailova, B.; Zhao, J.; Engel, J. M.; Schmitt, L. A.; Paulmann, C.; Gospodinov, M.; Friedrich, A.; Bismayer, U. (American Physical Society, 2010-05-01)
The effect of A-site incorporated Ba2+ and Bi3+ on the pressure-driven structural transformations in Pb-based perovskite-type relaxor ferroelectrics has been studied with in situ x-ray diffraction and Raman scattering of PbSc0.5Nb0.5O3, Pb0.93Ba0.07Sc0.5Nb0.5O3, and Pb0.98Bi0.02Sc0.51Nb0.49O3 in the range from ambient pressure to 9.8 GPa. The substitution of Ba2+ for Pb2+ represents the case in which A-site divalent cations with stereochemically active lone-pair electrons are replaced by isovalent cations with a larger ionic radius and no active lone pairs, leading to formation of strong local elastic fields. In contrast, substitution of Bi3+ for Pb2+ involves the replacement of divalent A-site cations with active lone-pair electrons by aliovalent cations with nearly the same ionic radius and active lone pairs so it induces local electric fields but not strong elastic fields. The two types of dopants have rather distinct effects on the changes in the atomic structure under pressure. The embedding of Ba2+ and associated elastic fields hinders the development of pressure-induced ferroic ordering and thus smears out the phase transition. The addition of Bi3+ enlarges the fraction of spatial regions with a pressure-induced ferroic distortion, resulting in a more pronounced phase transition of the average structure, i.e., the preserved lone-pair order and the absence of strong local elastic fields enhances the development of the ferroic phase at high pressure. For all compounds studied, the high-pressure structure exhibits glide-plane pseudosymmetry associated with a specific octahedral tilt configuration.
Abacus proofs of Schur function identities
Loehr, N. A. (Siam Publications, 2010)
This article uses combinatorial objects called labeled abaci to give direct combinatorial proofs of many familiar facts about Schur polynomials. We use abaci to prove the Pieri rules, the Littlewood-Richardson rule, the equivalence of the tableau definition and the determinant definition of Schur polynomials, and the combinatorial interpretation of the inverse Kostka matrix (first given by Egecioglu and Remmel). The basic idea is to regard formulas involving Schur polynomials as encoding bead motions on abaci. The proofs of the results just mentioned all turn out to be manifestations of a single underlying theme: when beads bump, objects cancel.
Absence of Mycobacterium intracellulare and Presence of Mycobacterium chimaera in Household Water and Biofilm Samples of Patients in the United States with Mycobacterium avium Complex Respiratory Disease
Wallace, Richard J. Jr.; Iakhiaeva, Elena; Williams, Myra D.; Brown-Elliott, Barbara A.; Vasireddy, Sruthi; Vasireddy, Ravikiran; Lande, Leah; Peterson, Donald D.; Sawicki, Janet; Kwait, Rebecca; Tichenor, Wellington S.; Turenne, Christine; Falkinham, Joseph O. III (American Society for Microbiology, 2013-03-27)
Recent studies have shown that respiratory isolates from pulmonary disease patients and household water/biofilm isolates of Mycobacterium avium could be matched by DNA fingerprinting. To determine if this is true for Mycobacterium intracellulare, household water sources for 36 patients with Mycobacterium avium complex (MAC) lung disease were evaluated. MAC household water isolates from three published studies that included 37 additional MAC respiratory disease patients were also evaluated. Species identification was done initially using nonsequencing methods with confirmation by internal transcribed spacer (ITS) and/or partial 16S rRNA gene sequencing. M. intracellulare was identified by nonsequencing methods in 54 respiratory cultures and 41 household water/biofilm samples. By ITS sequencing, 49 (90.7%) respiratory isolates were M. intracellulare and 4 (7.4%) were Mycobacterium chimaera. In contrast, 30 (73%) household water samples were M. chimaera, 8 (20%) were other MAC X species (i.e., isolates positive with a MAC probe but negative with species-specific M. avium and M. intracellulare probes), and 3 (7%) were M. avium; none were M. intracellulare. In comparison, M. avium was recovered from 141 water/biofilm samples. These results indicate that M. intracellulare lung disease in the United States is acquired from environmental sources other than household water. Nonsequencing methods for identification of nontuberculous mycobacteria (including those of the MAC) might fail to distinguish closely related species (such as M. intracellulare and M. chimaera). This is the first report of M. chimaera recovery from household water. The study underscores the importance of taxonomy and distinguishing the many species and subspecies of the MAC.
Abundance of horseshoe crabs (Limulus polyphemus) in the Delaware Bay area
Hata, David; Berkson, James M. (National Marine Fisheries Service Scientific Publication Office, 2003-10)
Discusses a study on horseshoe crabs in the vicinity of Delaware Bay. Abundance of horseshoe crabs in the area; Factor that influenced horseshoe crab catchability; Mean abundance estimate for all crabs.
Academic and social integration in cyberspace: Students and e-mail
Gatz, L. B.; Hirt, Joan B. (Johns Hopkins University Press, 2000)
Academic and social integration have traditionally been measured through interactions between students and the college environment (e.g., contact with faculty and other students outside of class). The proliferation of technology in the academy has influenced such interactions. This study examined how traditional-age, residential, first-year students use e-mail and Found that, although students use e-mail extensively, only a limited amount of that correspondence enhances their academic or social integration.
Acceptance Procedures for New and Quality Control Procedures for Existing Types of Corrosion-Resistant Reinforcing Steel
Stephen R. Sharp; Larry J. Lundy; Harikrishnan Nair; Moen, Cristopher D.; Josiah B. Johnson; Sarver, Brian E. (Virginia Center for Transportation Innovation and Research, 2011-06-01)
As the Virginia Department of Transportation (VDOT) continues to move forward with implementing the use of corrosion-resistant reinforcing (CRR) bars, it is important for VDOT to have a means of characterizing the candidate bars as well as ensuring that the quality of approved CRR bars is preserved. This is vital to ensure the bars respond physically in a manner that is consistent with VDOT's expectations. The purpose of this study was to provide VDOT's Materials Division with a method/specification for evaluating CRR bars. The study determined that visual assessment cannot be relied on to determine bar type. Further, steel fabricator markings cannot be relied on to identify the type of steel. However, when questions arise regarding the identification of bars, magnetic sorting provides a quick and easy method for differentiating between magnetic and nonmagnetic alloys. If more quantitative results are required, X-ray fluorescence provides a practical and much-needed method for positively identifying bars. Physically, the bars differ among producers. Relative rib area should be monitored as it also varies among producers. Further, alloying changes not only the corrosion resistance but also other important properties. The results of uniaxial tensile tests showed that the stress-strain behavior, elongation, and reduction in cross-section upon fracture could vary significantly for different CRR alloys. Therefore, mechanical testing, in addition to corrosion testing, of CRR is necessary to identify the most cost-effective bars with acceptable properties. Finally, the study determined that quality control measures need to be established to ensure VDOT receives the corrosion protection it needs. Further, care should be taken when relying upon international standards for acceptance criteria. The report recommends that VDOT's Materials Division implement the set of test methods provided in the appendices of this report as Virginia Test Methods for CRR acceptance criteria. To simplify the implementation of CRR in Virginia and elsewhere, VDOT's Materials Division should work with the American Association of State Highway and Transportation Officials to develop a single specification for the testing and acceptance of CRR. VDOT's Materials Division should also investigate retrofitting the uniaxial tensile test equipment with a non-contact extensometer to guarantee that stress vs. strain measurements of CRR can be made and ensure the yield strength is determined
Access Control Design on Highway Interchanges
Rakha, Hesham A.; Flintsch, Alejandra Medina; Arafeh, Mazen; Abdel-Salam, Abdel-Salam Gomaa; Dua, Dhruv; Abbas, Montasir M. (Virginia Center for Transportation Innovation and Research, 2008-01-01)
The adequate spacing and design of access to crossroads in the vicinity of freeway ramps are critical to the safety and traffic operations of both the freeway and the crossroad. The research presented in this report develops a methodology to evaluate the safety impact of different access road spacing standards. The results clearly demonstrate the shortcomings of the AASHTO standards and the benefits of enhancing them. The models developed as part of this research were used to compute the crash rate associated with alternative section spacing. The study demonstrates that the models satisfied the statistical requirements and provide reasonable crash estimates. The results demonstrate an eight-fold decrease in the crash rate when the access road spacing increases from 0 to 300 m. An increase in the minimum spacing from 90 m (300 ft) to 180 m (600 ft) results in a 50 percent reduction in the crash rate. The models were used to develop lookup tables that quantify the impact of access road spacing on the expected number of crashes per unit distance. The tables demonstrate a decrease in the crash rate as the access road spacing increases. An attempt was made to quantify the safety cost of alternative access road spacing using a weighted average crash cost. The weighted average crash cost was computed considering that 0.6, 34.8, and 64.6 percent of the crashes were fatal, injury, and property damage crashes, respectively. These proportions were generated from the field observed data. The cost of each of these crashes was provided by VDOT as $3,760,000, $48,200, and $6,500 for fatal, injury, and property damage crashes, respectively. This provided an average weighted crash cost of $43,533. This average cost was multiplied by the number of crashes per mile to compute the cost associated with different access spacing scenarios. These costs can assist policy makers in quantifying the trade-offs of different access management regulations.
Accuracy of Visible and Ultraviolet Light for Estimating Live Root Proportions with Minirhizotrons
Wang, Z. Q.; Burch, W. H.; Mou, P.; Jones, R. H.; Mitchell, R. J. (Ecological Society of America, 1995-10)
Acoustic Effects Accurately Predict an Extreme Case of Biological Morphology
Zhang, Z. W.; Truong, S. N.; Müller, Rolf (American Physical Society, 2009-07-17)
The biosonar system of bats utilizes physical baffle shapes around the sites of ultrasound emission for diffraction-based beam forming. Among these shapes, some extreme cases have evolved that include a long noseleaf protrusion (sella) in a species of horseshoe bat. We have evaluated the acoustic cost function associated with sella length with a computational physics approach and found that the extreme length can be predicted accurately from a fiducial point on this function. This suggests that some extreme cases of biological morphology can be explained from their physical function alone.
An acoustic position sensor
Dong, Shuxiang; Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2003-11-01)
This article presents an acoustic method-the resonance acoustic field sensor or piezoelectric-sound-resonance cavity (PSRC)-for object position detection. This method utilizes the change of acoustic radiation impedance as a sensing mechanism. The PSRC both generates and detects a resonance acoustic field, along both the axial and transverse directions. We have discovered that an inserted object or an object motion in the sound radiation field results in changes in both the voltage and phase of the PSRC. Results have shown that a minimum object displacement of <10 mum can be detected in the axial direction (and <100 mum in the transverse) by this method. (C) 2003 American Institute of Physics.
Acoustic Receptivity of a Boundary-Layer to Tollmien-Schlichting Waves Resulting From a Finite-Height Hump At Finite Reynolds-Numbers
Nayfeh, Ali H.; Ashour, O. N. (AIP Publishing, 1994-11-01)
The acoustic receptivity of a boundary layer to Tollmien-Schlichting (T-S) waves resulting from a finite-height hump at finite Reynolds numbers is investigated. The steady flow is calculated using an interacting boundary-layer (IBL) scheme that accounts for viscous/inviscid interactions. The unsteady flow is written as the sum of a Stokes wave and a traveling wave generated due to the interaction of the Stokes flow with the steady disturbance resulting from the hump. The traveling wave is governed by a set of nonhomogeneous equations, which is a generalization of the Orr-Sommerfeld equation. The solution of these nonhomogeneous equations is projected onto the quasiparallel eigenmode using the quasiparallel adjoint. This leads to a nonhomogeneous equation with variable coefficients governing the amplitude and phase of the T-S wave. Results are presented for the amplitude variation and the receptivity at finite Reynolds numbers. The results are in good agreement with the experimental results of Saric, Hoos, and Radeztsky [Boundary Layer Stability and Transition to Turbulence (ASME, New York, 1991), FED No. 114, pp. 17-22] for all tested hump heights at the two-tested sound pressure levels. Application of this paper's theory to small humps yields results that agree with those of Choudhari and Streett [Phys. Fluids A 4, 2495 (1992)]; and Crouch [Phys. Fluids A 4, 1408 (1992)]. Application of suction is shown to reduce the receptivity resulting from the hump.
Acousto-Optics: introduction to the feature issue
Poon, Ting-Chung; Tsai, C. S.; Voloshinov, V. B.; Chatterjee, M. R. (Optical Society of America, 2009-03-01)
This Acousto-Optics feature celebrates the scientific careers of two remarkable scientists, Antoni Sliwinski and Adrian Korpel. The feature includes original papers based on a representative selection of topics that were presented at the Tenth Spring School on Acousto-Optics held in Poland in May 2008. (C) 2009 Optical Society of America
Adapting Human Well-being Frameworks for Ecosystem Service Assessments across Diverse Landscapes
Villamagna, Amy M.; Giesecke, C. (Resilience Alliance, 2014)
There is broad support for the notion that ecosystem services influence human well-being (HWB), however, the means to measure such an effect are elusive. Measures of HWB are commonly used within the fields of psychology, economics, and international development, but thus far have not been integrated fully into ecosystem service assessments. We examine the multidimensional nature of HWB and discuss the need for a robust framework that captures its complex relationship with ecosystem services. We review several well-known HWB indices and describe the adaptation of two frameworks-the Economist Intelligence Unit's Quality of Life Index and the Sustainable Livelihoods Framework-to evaluate county-level HWB within the Albemarle-Pamlico Basin (Virginia and North Carolina, USA) using a stakeholder-engaged approach. We present maps of HWB that illustrate the results of both frameworks, discuss the feedback from stakeholders that guided indicator and data selection, and examine the observed differences in HWB throughout the basin. We conclude with suggestions for enhancing the role of ecosystem services in HWB indices.
Adiabatic Following in Two-Photon Transition
Nayfeh, Munir H.; Nayfeh, Ali H. (American Physical Society, 1977-03-01)
The coherent interaction of two smoothly varying, near-resonant, two-photon pulses with a three-level system can be described by "two-photon damped Bloch equations" which are analogous to those for a one-photon transition in a two-level system except for the presence of a two-photon coupling and a frequency shift. These equations are solved for the cases γ1, γ2≪Ω, γ1=γ2, and γ2k2ε4Ω2, γ1≪Ω, where γ1 and γ2 are the atomic energy and phase relaxation widths, respectively, and Ω is the Rabi frequency. The leading contribution to the refractive index is intensity dependent, caused by the level shifts inherent in multiphoton processes; it includes a relaxation dependent part which is important at times shorter than γ−11. The second-order contributions depend on the square of the intensity and the time-integrated square of the intensity. The latter contribution, which is relaxation dependent, causes line asymmetry at the long-wavelength wing; it consists of a term proportional to γ2−γ1 and only important at early times and a term proportional to 2γ2−γ1.

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