Physical Sciences and Mathematics Commons^™

Production Of O(1d) Following Electron Impact On Co2, Wladyslaw Kedzierski, J. D. Hein, C. J. Tiessen, D. Lukic, J. A. Trocchi, T. Z. Mlinaric, J. W. Mcconkey

Physics Publications

We have studied the excitation of metastable O(¹D) following dissociative excitation of CO₂ in the electron impact energy range from threshold to 400 eV. A solid Ne matrix at ∼20 K forms the heart of the detector. This is sensitive to the metastable species through the formation of excited excimers (NeO*), The resultant excimer radiation is readily detected, providing a means of measuring the production of the metastables. Using a pulsed electron beam and time-of-flight techniques, we have measured the O(¹D) kinetic energy spectrum and its relative production cross sections as a function of electron …

Vector Acoustic Intensity Around A Tuning Fork, Daniel A. Russell, Justin Junell, Daniel O. Ludwigsen

Physics Publications

The acoustic intensity vector field around a tuning fork is investigated. Theory for a longitudinal quadrupole source predicts a well-defined transition between near-field and far-field, with significant circulation of sound energy in the near-field. Vector components of the time-averaged intensity were measured using a two-microphone intensity probe and found to agree well with predictions from theory. The vector intensity map is interpreted, and shown to provide useful information about the near-field of an acoustic source.

Sensitive And Specific Discrimination Of Pathogenic And Nonpathogenic Escherichia Coli Using Raman Spectroscopy - A Comparison Of Two Multivariate Analysis Techniques, Steven Rehse, Khozima Hamasha, Qassem I. Mohaidat, Russell A. Putnam, Ryan C. Woodman, Sunil Palchaudhuri

Physics Publications

The determination of bacterial identity at the strain level is still a complex and time-consuming endeavor. In this study, visible wavelength spontaneous Raman spectroscopy has been used for the discrimination of four closely related Escherichia coli strains: pathogenic enterohemorrhagic E. coli O157:H7 and non-pathogenic E. coli C, E. coli Hfr K-12, and E. coli HF4714. Raman spectra from 600 to 2000 cm-1 were analyzed with two multivariate chemometric techniques, principal component-discriminant function analysis and partial least squares-discriminant analysis, to determine optimal parameters for the discrimination of pathogenic E. coli from the non-pathogenic strains. Spectral preprocessing techniques such as smoothing with …

A Comparison Of Multivariate Analysis Techniques And Variable Selection Strategies In A Laser-Induced Breakdown Spectroscopy Bacterial Classification, Russell Putnam, Q.I. Mohaidat, Andrew Daabous, Steven Rehse

Physics Publications

Laser-induced breakdown spectroscopy has been used to obtain spectral fingerprints from live bacterial specimens from thirteen distinct taxonomic bacterial classes representative of five bacterial genera. By taking sums, ratios, and complex ratios of measured atomic emission line intensities three unique sets of independent variables (models) were constructed to determine which choice of independent variables provided optimal genuslevel classification of unknown specimens utilizing a discriminant function analysis. A model composed of 80 independent variables constructed from simple and complex ratios of the measured emission line intensities was found to provide the greatest sensitivity and specificity. This model was then used in …

Hydroxyl-Decorated Graphene Systems As Candidates For Organic Metal-Free Ferroelectrics, Multiferroics, And High-Performance Proton Battery Cathode Materials, Menghao Wu, J. D. Burton, Evgeny Y. Tsymbal, Xiao Cheng Zeng, Puru Jena

Physics Publications

Using a first-principles method we show that graphene based materials, functionalized with hydroxyl groups, constitute a class of multifunctional, lightweight, and nontoxic organic materials with functional properties such as ferroelectricity, multiferroicity, and can be used as proton battery cathode materials. For example, the polarizations of semihydroxylized graphane and graphone, as well as fully hydroxylized graphane, are much higher than any organic ferroelectric materials known to date. Further, hydroxylized graphene nanoribbons with proton vacancies at the end can have much larger dipole moments. They may also be applied as high-capacity cathode materials with a specific capacity that is six times larger …

The Effect Of Sulfur Covalent Bonding On The Electronic Shells Of Silver Clusters, Anthony F. Pedicini, Arthur C. Reber, Shiv N. Khanna

Physics Publications

The nature of the bonding in Ag n S m ^0/− clusters, n = 1–7; m = 1–4, has been analyzed to understand its effect on the electronic shell structure of silver clusters. First-principle investigations reveal that the sulfur atoms prefer 2 or 3-coordinate sites around a silver core, and that the addition of sulfur makes the planar structures compact. Molecular orbital analysisfinds that the 3p orbitals of sulfur form a bonding orbital and two weakly bonding lone pairs withsilver. We examine the electronic shell structures of Ag 6Sm, which are two electrons deficient of a spherical closed electronic shell …

Communication: In Search Of Four-Atom Chiral Metal Clusters, Xinxing Zhang, Bradley Visser, Martin Tschurl, Evan Collins, Yi Wang, Qian Wang, Yawei Li, Qiang Sun, Puru Jena, Gerd Gantefoer, Ulrich Boesl, Ulrich Heiz, Kit H. Bowen Jr.

Physics Publications

A combined study utilizing anion photoelectron spectroscopy and density functional theory was conducted to search for four-atom, chiral, metal, and mostly metal clusters. The clusters considered were AuCoMnBi−/0, AlAuMnO−/0, AgMnOAl−/0, and AuAlPtAg−/0, where the superscripts, −/0, refer to anionic and neutral cluster species, respectively. Based on the agreement of experimentally and theoretically determined values of both electron affinities and vertical detachment energies, the calculated cluster geometries were validated and examined for chirality. Among both anionic and neutral clusters, five structures were identified as beingchiral.

Unusually Large Spin Polarization And Magnetoresistance In A Femg8-Femg8 Superatomic Dimer, Lin Zhu, Meichun Qian, Shiv N. Khanna

Physics Publications

Electronic transport across a FeMg8 magnetic superatom and its dimer has been investigated using a density functional theory combined with Keldysh nonequilibrium Green's-function formalism. For a single cluster, our studies for the cluster supported in various orientations on a Au(100) surface show that the transport is sensitive to the contact geometry. Investigations covering the cases where the axes of Mg square antiprism are 45°, perpendicular, and parallel to the transport direction, show that the equilibrium conductance, transferred charge, and currentpolarizations can all change significantly with orientation. Our studies on the transport across a magnetic superatom dimer FeMg8–FeMg8 focus on the …

Magnetic Properties Of Co2-Xtmxc And Co3-Xtmxc Nanoparticles, Meichun Qian, Shiv N. Khanna

Physics Publications

Using synthetic chemical approaches, it is now possible to synthesize transition metal carbides nanoparticles with morphology, where the transition metal layers are embedded with intervening layers of carbon atoms. A composite material consisting of Co2C and Co3C nanoparticles has been found to exhibit unusually large coercivity and energy product. Here, we demonstrate that the magnetic moments and the anisotropy can be further enhanced by using a combination of Co and other transition metals (TM). Our studies are based on mixednanoparticles Co2−x TM xC and Co3−x TM xC, in which selected Co sites are replaced with 3d transition elements Cr, Mn, …

Structure And Properties Of Mn4cl9: An Antiferromagnetic Binary Hyperhalogen, Yawei Li, Shunhong Zhang, Qian Wang, Puru Jena

Physics Publications

Calculations based on density functional theory show that the structure of Mn₄Cl₉ anion is that of a Mn atom at the core surrounded by three MnCl₃ moieties. Since Mn is predominantly divalent and MnCl₃ is known to be a superhalogen with a vertical detachment energy (VDE) of 5.27 eV, Mn₄Cl₉ can be viewed as a hyperhalogen with the formula unit Mn(MnCl₃)₃. Indeed, the calculated VDE of Mn₄Cl₉ anion, namely 6.76 eV, is larger than that of MnCl₃ anion. More importantly, unlike previously discovered hyperhalogens, …

An All-Electron Density Functional Theory Study Of The Structure And Properties Of The Neutral And Singly Charged M-12 And M-13 Clusters: M = Sc-Zn, G. L. Gutsev, C. W. Weatherford, K. G. Belay, B. R. Ramachandran, P. Jena

Physics Publications

The electronic and geometrical structures of the M ₁₂ and M ₁₃ clusters where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn along with their singly negatively and positively charged ions are studied using all-electron density functional theory within the generalized gradient approximation. The geometries corresponding to the lowest total energy states of singly and negatively charged ions of V₁₃, Mn₁₂, Co₁₂, Ni ₁₃, Cu ₁₃, Zn ₁₂, and Zn ₁₃ are found to be different from the geometries of the corresponding neutral parents. The computed …

Tunable Thermal Quenching Of Photoluminescence In Mg-Doped P-Type Gan, Michael A. Reshchikov, J. D. Mcnamara, S. Fernández-Garrido, R. Calarco

Physics Publications

We have studied the thermal quenching of the ultraviolet luminescence band with a maximum at about 3.25 eV in p-type Mg-doped GaN. The characteristic temperature of the thermal quenching of photoluminescence (PL) gradually shifted to higher temperatures with increasing excitation intensity. This effect is explained by a population inversion of charge carriers at low temperatures, which suddenly converts into a quasiequilibrium population as the temperature increases above the characteristic value. Tunable quenching of PL has been observed only in some of the GaN:Mg samples. The absence of the tunable quenching of PL in another group of GaN:Mg samples is preliminarily …

Enhanced Biocidal Activity Of Au Nanoparticles Synthesized In One Pot Using 2, 4-Dihydroxybenzene Carbodithioic Acid As A Reducing And Stabilizing Agent, Syeda Sohaila Naz, Nazar Ul Islam, Muhammad Raza Shah, Syed Sartaj Alam, Zafar Iqbal, Massimo Bertino, Louis Franzel, Afifa Ahmed

Physics Publications

Background

The conjugation of gold nanoparticles with biocides such as natural products, oligosaccharides, DNA, proteins has attracted great attention of scientists recently. Gold NPs covered with biologically important molecules showed significant enhancement in biological activity in comparison with the activity of the free biocides. However, these reports are not very systematic and do not allow to draw definitive conclusions. We therefore embarked in a systematic study related to the synthesis and characterization of biocidal activities of Au nanoparticles conjugated to a wide variety of synthetic and natural biomolecules. In this specific report, we investigated the activity of a synthetic biocide, …

Quantification Of Biomass And Cell Motion In Human Pluripotent Stem Cell Colonies, Thomas A. Zangle, Jennifer Chun, Jin Zhang, Jason C. Reed, Michael A. Teitell

Physics Publications

Abstract

Somatic cell reprogramming to pluripotency requires an immediate increase in cell proliferation and reduction in cell size. It is unknown whether proliferation and biomass controls are similarly coordinated with early events during the differentiation of pluripotent stem cells (PSCs). This impasse exists because PSCs grow in tight clusters or colonies, precluding most quantifying approaches. Here, we investigate live cell interferometry as an approach to quantify the biomass and growth of HSF1 human PSC colonies before and during retinoic acid-induced differentiation. We also provide an approach for measuring the rate and coordination of intracolony mass redistribution in HSF1 clusters using …

Blue Luminescence And Zn Acceptor In Gan, Denis Demchenko, Michael A. Reshchikov

Physics Publications

In this paper, we present a comparison of exchange-tuned hybrid density functional calculations with experimental data obtained for the Zn acceptor in GaN. Since this acceptor is one of the few reliably identified defects in GaN, we use Zn-doped GaN as a test case for the widely used HSE06 hybrid functional method of calculations of defect properties in semiconductors. Here, we present the experimental results of luminescence measurements in Zn-doped GaN from which we obtain Zn acceptor defect levels. They are compared with theoretically calculated defect thermodynamic and optical transition levels as well as the zero-phonon line associated with this …

Superlinear Increase Of Photoluminescence With Excitation Intensity In Zn-Doped Gan, Michael A. Reshchikov, Anita J. Olsen, Marilyn F. Bishop, Tom Mcmullen

Physics Publications

We have observed a superlinear increase of photoluminescence (PL) intensity in a narrow range of excitation intensities for Zn-doped GaN. The characteristic intensity at which the abrupt increase occurs increases with increasing temperature. This is unlike the usual observations for defects in semiconductors in which the PL intensity increases linearly with excitation intensity, saturating at high intensity because defects become saturated with photogenerated charge carriers. The observed phenomenon is attributed to a redirection of electron and hole flow from nonradiative centers at low excitation intensity to a recombination path via the Zn-Ga acceptor at high excitation intensity. This is the …

Magnetic Hollow Cages With Colossal Moments, Menghao Wu, Puru Jena

Physics Publications

A comprehensive study of the interaction of transition metal clusters with B, C, N, O, and Si reveal novel structure and properties: Co12C6, Mn12C6, and Mn24C18 clusters form stable ferromagnetic hollow cages with total magnetic moments of 14 μB, 38 μB, and 70 μB, respectively. Replacement of C with B, N, O, or Si has significant impact on their structure and magnetic properties. For example, Mn20Si12 cluster forms a ferrimagnetic dodecahedral hollow cage with a total magnetic moment of 36 μB while Mn12N6, X12C6 (X = Ni, Cu, Pd, Pt), and Cu12O6 possess no magnetic moment, although they retain hollow …