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We studied the c-axis transport of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) cross-whisker junctions formed by annealing ``naturally'' formed whisker junctions. These frequently appear during growth when the $ab$-faces of neighboring whiskers come in contact. We obtained Fraunhofer patterns of the cross-junction critical currents in a parallel magnetic field, and found a sharp increase in the quasiparticle tunneling conductance at $eV=50-60$ mV, indicating high junction quality. For our weak junctions, the interface critical current density is about 0.03 of the critical current density across the stack of bulk intrinsic junctions, as is the room temperature conductivity, and is independent of the twist angle, in contrast to most of the data reported on ``artificial'' cross-whisker junctions [Y. Takano {\it et al.}, Phys. Rev. B {\bf 65}, 140513(R) (2002)]. Our results provide strong evidence of incoherent interface tunneling and for at least a small s-wave order parameter component in the bulk of Bi2212 for $T\le T_c$. They are also consistent with the bicrystal twist experiments of Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)]., Comment: 6 pages, five figures, submitted to Phys. Rev. B

This comment points out that the recent paper by Maki and Haas [Phys. Rev. B {\bf 67}, 020510 (2003)] is completely wrong., Comment: 1 page, submittted to Phys. Rev. B

We calculate the critical current density $J^J_c$ for c-axis Josephson tunneling between identical high temperature superconductors twisted an angle $\phi_0$ about the c-axis. We model the tunneling matrix element squared as a Gaussian in the change of wavevector q parallel to the junction, $<|t({\bf q})|^2>\propto\exp(-{\bf q}^2a^2/2\pi^2\sigma^2)$. The $J^J_c(\phi_0)/J^J_c(0)$ obtained for the s- and extended-s-wave order parameters (OP's) are consistent with the Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ data of Li {\it et al.}, but only for strongly incoherent tunneling, $\sigma^2\ge0.25$. A $d_{x^2-y^2}$-wave OP is always inconsistent with the data. In addition, we show that the apparent conventional sum rule violation observed by Basov et al. might be understandable in terms of incoherent c-axis tunneling, provided that the OP is not $d_{x^2-y^2}$-wave., Comment: 6 pages, 6 figures

We calculate exactly the Josephson current for $c$-axis coherent tunneling between two layered superconductors, each with internal coherent tight-binding intra- and interlayer quasiparticle dispersions. Our results also apply when one or both of the superconductors is a bulk material, and include the usually neglected effects of surface states. For weak tunneling, our results reduce to our previous results derived using the tunneling Hamiltonian. Our results are also correct for strong tunneling. However, the $c$-axis tunneling results of Tanaka and Kashiwaya are shown to be incorrect in any limit. In addition, we consider the $c$-axis coherent critical current between two identical layered superconductors twisted an angle $\phi_0$ about the $c$-axis with respect to each other. Regardless of the order parameter symmetry, our coherent tunneling results using a tight-binding intralayer quasiparticle dispersion are inconsistent with the recent $c$-axis twist bicrystal Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ twist junction experiments of Li {\it et al.}, Comment: 11 pages, 13 figures, submitted to Physical Review B

Li et al. found that the critical current density JcJ across atomically clean c-axis twist junctions of Bi2Sr2CaCu2O(8+x) is the same as that of the constituent single crystal, JcS, independent of the twist angle phi0, even at Tc. We investigated theoretically if a dx2-y2-wave order parameter might twist by mixing in dxy components, but find that such twisting cannot possibly explain the data near to Tc. Hence, the order parameter contains an s-wave component, but not any dx2-y2-wave component. In addition, the c-axis Josephson tunneling is completely incoherent. We also propose a c-axis junction tricrystal experiment which does not rely upon expensive substrates., Comment: 3 pages, 4 figures, Invited talk to be published in AIP Proceedings of the University of Miami Conference on High Temperature Superconductivity (HTS99), Jan. 7-13, 1999, edited by S. E. Barnes

The symmetry operations of the crystal groups relevant for the high temperature superconductors HgBa2CuO4+x (Hg1201), YBa2Cu3O7-x (YBCO), and Bi2Sr2CaCu2O8+x (BSCCO) are elucidated. The allowable combinations of the superconducting order parameter (OP) components are presented for both the angular momentum and lattice representations. For tetragonal Hg1201, the spin singlet OP components are composed from four sets of compatible basis functions, which combine to give the generalized s-, dx2-y2-, dxy-, and gxy(x2-y2)- wave OPs. In YBCO, elements of s- and dx2-y2- wave sets are compatible, but in BSCCO, elements of s- and dxy- wave sets are compatible. The Josephson critical current density JcJ across c-axis twist junctions in the vicinity of Tc is then evaluated as a function of the twist angle phi0, for each allowable OP combination, for both coherent and incoherent tunneling. Recent experiments of Li et al. demonstrated the independence of JcJ(phi0)/JcS upon phi0 at and below Tc, where JcS is the critical current density of a constituent single crystal. These experiments are shown to be consistent with an OP containing an s-wave component, but inconsistent with an OP containing the purported dx2-y2-wave component. In addition, they demonstrate that the interlayer tunneling across untwisted layers in single crystal BSCCO is entirely incoherent. We propose a new type of tricrystal experiment using single crystal c-axis twist junctions, that does not employ substrate grain boundaries., Comment: 16 pages, 11 figures, 7 tables; text shortened, references added; submitted to Phys. Rev. B1

We calculate Ic(T) and Rn for both coherent and incoherent electron tunneling across a c-axis break junction between nu=s,d_x^2-y^2-wave superconducting half spaces, each with c-axis bandwidth 2J. Coherent quasiparticle tunneling only occurs for voltages V<2J/e, leading to difficulties in measuring Rn for underdoped samples. The coherent part of Ic(0) is independent of Delta_nu(0) for J/Delta_nu(0)<<1, and can be large. Our results are discussed with regard to recent experiments., Comment: 4 pages, 3 figures

The potential importance of OBrO in atmospheric chemistry has been suggested recently. Although there appear to be no experimental measurements of deltaH(OBrO), estimated values range from 70 to 152 kJ/mol. In the present investigation, the appearance energy (AE) of BrO+ from OBrO was measured by employing a discharge flow-photoionization mass spectrometer that is operated at beamline U-11. The heat of formation was derived from the AE result and the ionization energy of OBrO [IE = 10.29 eV]. The AE experiments yield a threshold at about 98.7 nm that gives, in turn, a value for AH(OBrO) of 180 +/- 10 kJ/mol. The difference with the estimated values mentioned above and the concomitant implications for the atmospheric reactions of OBrO will be discussed.

Photoionization efficiency spectra of FO were measured over the wavelength range 80.0-100.0 nm and in the ionization threshold region, 94.0-100.0 nm, using a discharge flow-photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. FO was generated by the reaction of F2P atoms with NO3 and via a F2O2 discharge. A value of 12.78 +/- 0.03 eV was obtained for the adiabatic ionization energy of FO from photoion thresholds which corresponds to FO(+)(X 3 Sigma -) from FO(X 2 Pi i). These results, which are the first to be obtained by direct Photo-ionization mass spectrometry (PIMS) measurements, corroborate those of a photoelectron spectroscopy (PES) study; however, the ionization energy determined here is free from interferences due to other species which complicated the PES measurement. A value of 109.5 +/- 8.0 kJ/mol for Delta f H 0 298(FO) is computed from the present value of IE(FO) and a previous appearance energy measurement, and a value for the proton affinity of FO is calculated to be 511.5 +/- 10.0 kJ/mol.

The relative efficiencies for two dissociative channels in the vacuum UV photolysis of carbonyl sulphide have been determined using the flash photolysis-resonance fluorescence technique to measure initial yields of atomic oxygen and atomic sulphur. At wavelengths above 105 nm, the dissociation of OCS to form atomic sulphur exceeded that for the formation of atomic oxygen to such an extent that only an upper limit could be placed on the minor process. In addition, the flash photo-excitation of carbonyl sulphide produced a long-lived spontaneous emission in the UV and vacuum UV that might be due to molecular fluorescence from OCS.

The technique employed in the study utilizes the vacuum ultraviolet flash photolysis of H2O combined with time resolved, simultaneous detection of H and O via resonance fluorescence at 121.6 and 130.2 nm respectively. The measurements were made by means of photon counting and multichannel scaling. The sensitivity of the system for H and O is discussed. Experiments are reported in which signals due to H and O were accumulated from the flash photolysis of a mixture of 0.1 torr H2O and 100 torr Ar. Attention is given to the relative importance of two primary processes in the photolysis of water.

The rate parameters for the reaction of O(3P) with carbonyl sulfide, O(3P) + OCS yields CO + SO, have been determined directly by monitoring O(3P) using the flash photolysis-resonance fluorescence technique. The value for reaction rate was measured over a temperature range of 263-502 K and the data were fitted to an Arrhenius expression with good linearity. A comparison of the present results with those from previous studies of this reaction is also presented.

The relative importance of two primary processes in the photolyis of water: (1) H2O + h (nu) yields H + OH, and (2) H2O + h (nu) yields H2 + OD-1 were determined in a direct manner by time resolved detection (via resonance fluorescence) of H and O formed in processes 1 and 2 respectively. The initially formed OD-1 was deactivated to ground state OP-3 prior to detection via resonance fluorescence. The relative quantum yields for processes 1 and 2 are 0.89 and 0.11 for the wavelength interval 105 to 145nm and = to or greater than 0.99, and = to or less than 0.01 for the wavelength interval 145 to 185nm. Rate constants at 300 K for the reactions OD-1 + H2, + Ar, and + He are presented.

Using the technique of flash photolysis-resonance fluorescence, the reaction of ground-state atomic sulfur with carbonyl sulfide has been investigated over the temperature range from 233 to 445 K. Over this temperature range, the experimental data were fitted to an Arrhenius equation of the form k sub 1 = (1.52 plus or minus 0.20) x 10 to the minus 12th power exp(-3.63 plus or minus 0.12 kcal/mol/RT) cu cm/molecule/sec. A comparison of these results with previous investigations on this reaction system is presented.

Spectral output of fluorescent lamps can be precisely adjusted by using computer-assisted analysis for custom blending lamp phosphors. With technique, spectrum of main bank of lamps is measured and stored in computer memory along with emission characteristics of commonly available phosphors. Computer then calculates ratio of green and blue intensities for each phosphor according to manufacturer's specifications and plots them as coordinates on graph. Same ratios are calculated for measured spectrum. Once proper mix is determined, it is applied as coating to fluorescent tubing.

Relatively-inexpensive mirror system splits output scene of single optical probe into three separate parts. System entirely eliminates point-by-point replication, alinement, and registration of multiple-model board assemblies.

First order wave functions orbital correlation energies and electron affinities of first row atoms for low lying electronic states of B, C, N, O, F and Ne

Emittance measuring apparatus for temperatures up to 4000-deg f