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One of the interesting features of the photoemission spectra of the high temperature cuprate superconductors is the presence of a large signal (referred to as the 'background') in the unoccupied region of the Brillouin zone. Here we present data indicating that the background signal is a component of the photocurrent that is separate from the spectral function and is most likely due to strong scattering of the photoelectrons. We also present an analytical method that can be used to subtract the background signal.

Linear-response theory provides an efficient approach for calculating the vibrational properties of solids. Moreover, because the use of supercells is eliminated, points with little or no symmetry in the Brillouin zone can be handled. This allows accurate determinations of quantities such as real-space force constants and electron-phonon coupling parameters. The authors present highly converged calculations of the spectral function {alpha}{sup 2}F({omega}) and the average electron-phonon coupling for Al, Pb, and Li. They also present results for the free energy of vacancy formation in Al calculated within the harmonic approximation.

The consequences of disordered charge stripes and antiphase spin domains for the properties of the high-temperature superconductors are studied. We give a semiphenomenological description of angle-resolved photoemission experiments and optical conductivity, and show that the many unusual features of the experimentally observed spectra can be understood naturally in this way. This interpretation of the data, when combined with evidence from neutron scattering, suggests that disordered and fluctuating stripe phases are a common feature of high-temperature superconductors. {copyright} {ital 1996 The American Physical Society.}

After a general introduction, this thesis is divided into 3 parts: indirect fluorescence detection of sugars separated by capillary zone electrophoresis with visible laser excitation, absorption detection in capillary electrophoresis by fluorescence energy transfer, and increased selectivity for electrochromatography by dynamic ion exchange.

The present invention is directed to a method of eliminating the cold spot zones presently used on Hg.sup.196 isotope separation lamps and filters by the use of a mercury amalgams, preferably mercury - indium amalgams. The use of an amalgam affords optimization of the mercury density in the lamp and filter of a mercury enrichment reactor, particularly multilamp enrichment reactors. Moreover, the use of an amalgam in such lamps and/or filters affords the ability to control the spectral line width of radiation emitted from lamps, a requirement for mercury enrichment.

The optical and electrical properties were measured for single crystals of NbC/sub x/ for x = 0.98, 0.87, and 0.76, and for one hot-isostatically-pressed sample of NbC/sub 0.88/. Specular reflectance was measured between 0.025 and 11 eV, and ellipsometry measurements were made at 1.96 eV. By using the phase obtained from ellipsometry data to correct the Kramers-Kronig analyses of the reflectances, we were able to improve the accuracy of the resulting optical functions. For energies below 6.5 eV, there are differences in the reflectance and optical functions of the samples which are due to differences in x. We interpret the low-energy optical data in terms of intraband transitions, which allows us to calculate the dc conductivity as well as other electronic transport parameters. These parameters agree well with the electrical conductivities and the Hall coefficients obtained by the van der Pauw technique. The higher-energy optical data are interpreted in light of recent electronic-structure calculations, which suggest that most interband transitions occur near the square face of the Brillouin zone.

Lasar-induced fluorescence is used to determine the distribution of relative concentration to neutral and singly ionized manganese in the interfacial zone of a gas tungsten arc over a molten pool of type 304 stainless steel. (AIP)

Thermotransmission and thermoreflectance spectra were obtained for Cu, Pd, Ag, Pt, and Au in the 10 --30 eV spectral region. Structures due to transitions from the Fermi level to high-density bands 15 eV above the Fermi level were identified in Pt. All metals showed structures arising from interband transitions between the d bands and the same flat bands, 15--20 eV above the Fermi energy. Attempts to fit to interband critical points in Au revealed over 40 possible critical points in the region of these structures, most of them near the Brillouin-zone centers. Systematic trends in the series of metals make the qualitative identification of the structures more secure, and no energy shifts of calculated energy bands are required. The observed widths of structures are sometimes much narrower than the widths of free-electron-like bands at comparable energies.

One method of demonstrating the stability of a power reactor is to impress the critical reactor with a sinusoidal oscillating reactivity and measure its power response as a function of frequency. The computer code FLUZ synthesizes such a test for oscillations of small amplitudes. The same technique may be used to experimentally measure different coefficients of reactivity of a given reactor. By varying the period of the impressed reactivity it is possible to change, due to finite heat transfer times, the relative importance of various reactivity feedback mechanisms, such as the fuel Doppler effect or coolant density.

An expression is derived for the total change in neutron resonance absorption when only one region of the reactor is heated. The departure from the normal Doppler effect for U²³⁸ is calculated for a fast oxide-fueled reactor.