414 Matching Results

Search Results

Advanced search parameters have been applied.

Methods of Opacity Calculations

Description: "Methods for calculating the opacity of materials at high temperatures are discussed in this report. Minor improvements are outlined for the treatment of continuous absorption processes, and a small error usually made in treating the scattering process is corrected. In contrast to all previous calculations of opacity, the effect of line absorption is carefully examined, for it may well be the dominant process under certain conditions of temperature and density. Detailed methods for calculating the line absorption contribution are, therefore, developed. To illustrate the principles involved, the opacity of pure iron at a temperature of 1000 volts and normal density is worked out in detail" (p. ii).
Date: 1949
Creator: Mayer, Harris
Partner: UNT Libraries Government Documents Department

PG 0946+301: the Rosetta Stone of BALQSOs?

Description: We describe the motivation and features of a multiwavelength spectroscopic campaign on broad absorption line (BAL) QSO PG 0946+301. The main goal of this project is to determine the ionization equilibrium and abundances (IEA) in BAL outflows. Previous studies of IEA in BALQSOs were based on the assumption that the BALs are not saturated so that the column densities inferred from the apparent optical depths are realistic. This critical assumption is at odds with several recent observations and with analysis of existing data which indicate that the absorption troughs are heavily saturated even when they are not black. In addition, X-ray observations, which are important for constraining the ionizing continuum, were not available for those objects that had UV spectral data. Quantifying the level of saturation in the BALs necessitates UV spectroscopy with much higher S/N and broader-spectral coverage than currently exist. After taking into account the capabilities of available observatories, our best hope for a substantial improvement in understanding the IEA in BALQSOs is to concentrate considerable observational resources on the most promising object. Our studies of available HST and ground-based spectra show that PG 0946+301 is by far the best candidate for such a program. This BALQSO is at least five times brighter, shortward of 1000 {Angstrom}, rest frame, than any other object, and due to its low redshift it has an especially sparse Ly{alpha} forest. At the same time PG 0946+301 is a typical BALQSO and therefore its IEA should be representative. To this effect we are developing a multiwavelength spectroscopic campaign (UV, FUV, X-ray and optical) on BALQSO PG 0946+301. We discuss the goals and feasibility of each observational component: HST, FUSE, ASCA and ground-based.
Date: June 1, 1998
Creator: Arav, N., LLNL
Partner: UNT Libraries Government Documents Department

Ultraviolet absorption spectra of aromatic amines in isooctane and in water

Description: Report discusses the results of a study of the ultraviolet absorption spectra in the 3200 A to 2500 A region of 27 aromatic amines in iscoctane and and in water solutions. Factors that affect the absorption spectra of aromatic amines were investigated, and the spectra in the two different solvents were compared. The main variables affecting the absorption are the nature of the solvent, the purity of the aromatic amines, and photochemical decomposition of the aromatic amines.
Date: November 1945
Creator: Tischler, Adelbert O. & Howard, J. Nelson
Partner: UNT Libraries Government Documents Department

Density functional theory study of the structural, electronic, lattice dynamical, and thermodynamic properties of Li4SiO4 and its capability for CO2 capture

Description: The structural, electronic, lattice dynamical, optical, thermodynamic, and CO{sub 2} capture properties of monoclinic and triclinic phases of Li{sub 4}SiO{sub 4} are investigated by combining density functional theory with phonon lattice dynamics calculations. We found that these two phases have some similarities in their bulk and thermodynamic properties. The calculated bulk modulus and the cohesive energies of these two phases are close to each other. Although both of them are insulators, the monoclinic phase of Li{sub 4}SiO{sub 4} has a direct band gap of 5.24 eV while the triclinic Li{sub 4}SiO{sub 4} phase has an indirect band gap of 4.98 eV. In both phases of Li{sub 4}SiO{sub 4}, the s orbital of O mainly contributes to the lower-energy second valence band (VB{sub 2}) and the p orbitals contribute to the fist valence band (VB{sub 1}) and the conduction bands (CBs). The s orbital of Si mainly contributes to the lower portions of the VB1 and VB{sub 2}, and Si p orbitals mainly contribute to the higher portions of the VB{sub 1} and VB{sub 2}. The s and p orbitals of Li contribute to both VBs and to CBs, and Li p orbitals have a higher contribution than the Li s orbital. There is possibly a phonon soft mode existing in triclinic {gamma}-Li{sub 4}SiO{sub 4}; in the monoclinic Li{sub 4}SiO{sub 4}, there are three phonon soft modes, which correspond to the one type of Li disordered over a few sites. Their LO-TO splitting indicates that both phases of Li{sub 4}SiO{sub 4} are polar anisotropic materials. The calculated infrared absorption spectra for LO and TO modes are different for these two phases of Li{sub 4}SiO{sub 4}. The calculated relationships of the chemical potential versus temperature and CO{sub 2} pressure for reaction of Li{sub 4}SiO{sub 4} with CO{sub 2} shows that Li{sub 4}SiO{sub ...
Date: January 1, 2011
Creator: Duan, Yuhua & Parlinski, K.
Partner: UNT Libraries Government Documents Department

Symmetry, Optical Properties and Thermodynamics of Neptunium(V) Complexes

Description: Recent results on the optical absorption and symmetry of the Np(V) complexes with dicarboxylate and diamide ligands are reviewed. The importance of recognizing the 'silent' feature of centrosymmetric Np(V) species in analyzing the absorption spectra and calculating the thermodynamic constants of Np(V) complexes is emphasized.
Date: December 21, 2009
Creator: Rao, Linfeng & Tian, Guoxin
Partner: UNT Libraries Government Documents Department

Revisiting the total ion yield x-ray absorption spectra of liquid water microjets

Description: Measurements of the total ion yield (TIY) x-ray absorption spectrum (XAS) of liquid water by Wilson et al. (2002 J. Phys.: Condens. Matter 14 L221 and 2001 J. Phys. Chem. B 105 3346) have been revisited in light of new experimental and theoretical efforts by our group. Previously, the TIY spectrum was interpreted as a distinct measure of the electronic structure of the liquid water surface. However, our new results indicate that the previously obtained spectrum may have suffered from as yet unidentified experimental artifacts. Although computational results indicate that the liquid water surface should exhibit a TIY-XAS that is fundamentally distinguishable from the bulk liquid XAS, the new experimental results suggest that the observable TIY-XAS is actually nearly identical in appearance to the total electron yield (TEY-)XAS, which is a bulk probe. This surprising similarity between the observed TIY-XAS and TEY-XAS likely results from large contributions from x-ray induced electron stimulated desorption of ions, and does not necessarily indicate that the electronic structure of the bulk liquid and liquid surface are identical.
Date: February 16, 2008
Creator: Saykally, Richard J; Cappa, Chris D.; Smith, Jared D.; Wilson, Kevin R. & Saykally, Richard J.
Partner: UNT Libraries Government Documents Department


Description: The interactions of 4-nitroquinoline-1-oxide (NQO) with the four 5{prime}-deoxyribonucleotides were probed using absorption spectra of the charge transfer bands and {sup 1}H and {sup 13}C NMR spectra of nucleotide-NQO mixtures. Applying a Benesi-Hildebrand type equation to the spectral data yielded equilibrium constants (K(dpG:NQO) = 16 M{sup -1} K(dpA:NQO) = 12 M{sup -1}, K(dpT:NQO) = K(dpC:NQO) = 4 M{sup -1}) which suggest the preference of NQO for the guanine residue in a DNA. From {sup 13}C and {sup 1}H NMR data, a structure for the dpG:NQO complex is proposed.
Date: September 1, 1977
Creator: Winkle, S.A. & Tinoco Jr, I.
Partner: UNT Libraries Government Documents Department

Photocarrier relaxation in the quantum kinetics regime

Description: We present a study of carrier relaxation in GaAs in the quantum- kinetics regime. The results cannot be explained by Bolzmann kinetics. They are in satisfactory agreement with quantum-kinetic theory calculation of the occupation number in k-space.
Date: November 1, 1995
Creator: Bar-Ad, S.; Kner, P.; Chemla, D.S. & El Sayed, K.
Partner: UNT Libraries Government Documents Department

Spectral unfolds of PITHON Flash X-ray source.

Description: Using a differential absorption spectrometer we obtained experimental spectral information for the PITHON Flash X-ray Machine located in San Leandro, California at L-3 Communications. Spectral information we obtained pertained to the 200 keV to 800 keV endpoint operation of PITHON. We also obtained data on the temporal behavior of high energy and low energy spectral content.
Date: November 1, 2007
Creator: Zarick, Thomas Andrew; Sheridan, Timothy J.; Hartman, E. Frederick & Riordan, John C. (L-3 Pulse Sciences)
Partner: UNT Libraries Government Documents Department

Absorption Spectra of Aromatic Disulfides

Description: The effect of solvents and temperature on the optical absorption spectrum of a number of substituted aromatic disulfides is reported. The problems offered by the disulfide link and the exchange reactions between disulfides, and between disulfides and thiols, are receiving increasing attention. Recently the base-catalyzed exchange between various alkyl disulfides and the corresponding thiols was studied by means of a radioactive-tracer technique. Our initial purpose was to extend these investigations to a large number of compounds in a variety of experimental conditions using a spectrophotometric technique that, if applicable, would have been incomparably faster.
Date: October 31, 1956
Creator: Fava, Antonio & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Spectroscopic properties of colloidal indium phosphide quantum wires

Description: Colloidal InP quantum wires are grown by the solution-liquid-solid (SLS) method, and passivated with the traditional quantum dots surfactants 1-hexadecylamine and tri-n-octylphosphine oxide. The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to other experimental results for InP quantum dots and wires, and to the predictions of theory. The photoluminescence behavior of the wires is also investigated. Efforts to enhance photoluminescence efficiencies through photochemical etching in the presence of HF result only in photochemical thinning or photo-oxidation, without a significant influence on quantum-wire photoluminescence. However, photo-oxidation produces residual dot and rod domains within the wires, which are luminescent. The results establish that the quantum-wire band gaps are weakly influenced by the nature of the surface passivation, and that colloidal quantum wires have intrinsically low photoluminescence efficiencies.
Date: July 11, 2008
Creator: Wang, Lin-Wang; Wang, Fudong; Yu, Heng; Li, Jingbo; Hang, Qingling; Zemlyanov, Dmitry et al.
Partner: UNT Libraries Government Documents Department


Description: The iodine species formed either by adding hypochlorite to a basic iodide solution or by adding triiodide to sodium hydroxide, was identified as hypoiodite ion. The absorption spectrum of IO{sup -} was investigated in the wavelength range from 450 m{micro} to 280 m{micro}. The kinetics of the reaction I{sup -} + ClO{sup -} = IO{sup -} + Cl{sup -} was studied spectrophotometrically in alkaline solution. The forward rate law was found to be d(IO{sup -})/dt = k(I{sup -})(ClO{sup -})/OH{sup -}. At 25 C and an ionic strength of 1.00 M, k is 61 {+-} 3 sec{sup -1}. It was found spectrophotometrically that for certain ratios of the initial iodide to hydroxide concentrations, there was evidence of the presence of I{sub 3}{sup -}, I{sub 2}OH{sup -}, and I{sub 2}O{sup 2-} along with IO{sup -}. The equilibrium constants between IO{sup -} and these three species were evaluated by a graphical method. The formal potential of the cell: Pt:H{sub 2}:1 M NaOH : 1M NaOH, KI, NaIO : Au was found to be 1.297 v at 25 C. The equilibrium constant, K{sub 2} = (I{sub 3}{sup -})(OH{sup -}){sup 2}/(IO{sup -})(I{sup -}){sup 2}, of the reaction IO{sup -} + 2I{sup -} + H{sub 2}O {l_reversible} I{sub 3}{sup -} + 2OH{sup -} calculated from emf measurements agreed well with that from spectrophotometric measurements. The ionization constant of HOI was calculated to be 2.3 x 10{sup -11} at 25 C.
Date: June 2, 1958
Creator: Chia, Yuan-tsan.
Partner: UNT Libraries Government Documents Department

Ytterbium divalency and lattice disorder in near-zero thermalexpansion YbGaGe

Description: While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.
Date: May 8, 2006
Creator: Booth, C.H.; Christianson, A.D.; Lawrence, J.M.; Pham, L.; Lashley, J. & Drymiotis, F.R.
Partner: UNT Libraries Government Documents Department

Zn-Site Determination in Protein Encapsulated ZnxFe3-xO4 Nanoparticles

Description: The X-ray absorption spectra of the Fe and Zn L-edges for 6.7 nm Fe{sub 3}O{sub 4} nanoparticles grown inside 12 nm ferritin protein cages with 10%, 15%, 20% and 33% zinc doping, shows that the Zn is substitutional as Zn{sup 2+} within the iron oxide host structure. A Neel-Arrhenius plot of the blocking temperature in the frequency dependent ac-susceptibility measurements show that the particles are non-interacting and that the anisotropy energy barrier is reduced with Zn loading. X-ray magnetic circular dichroism (XMCD) of the Fe displays a linear decrease with Zn-doping in sharp contrast to the initial increase present in the bulk system. The most plausible explanation for the moment decrease is that Zn substitutes preferentially into the tetrahedral A-site as a Zn{sup 2+} cation, generating a mixed spinel.
Date: October 1, 2008
Creator: Pool, V. L.; Klem, M. T.; Holroyd, J.; Harris, T.; Arenholz, E.; Young, M. et al.
Partner: UNT Libraries Government Documents Department