Deviations from Matthiessen's Rule for SrRuO3{\rm SrRuO_3} and CaRuO3{\rm CaRuO_3}

We have measured the change in the resistivity of thin films of ${\rm SrRuO_3}$ and ${\rm CaRuO_3}$ upon introducing point defects by electron irradiation at low temperatures, and we find significant deviations from Matthiessen's rule. For a fixed irradiation dose, the induced change in resistivity {\it decreases} with increasing temperature. Moreover, for a fixed temperature, the increase in resistivity with irradiation is found to be {\it sublinear}. We suggest that the observed behavior is due to the marked anisotropic scattering of the electrons together with their relatively short mean free path (both characteristic of many metallic oxides including cuprates) which amplify effects related to the Pippard ineffectiveness condition

Sequential low-temperature depolymerization and liquefaction of US coals

Suitable conditions for high-yield conversion of a Pittsburgh [number sign]8 (Pennsylvania) coal sample, supplied by the Argonne program and designated below as PB(PA) coal, were previously developed (see Progress Report no. 4, pp. 3--15; and Progress Report no. 6, pp- 3--4). In some recent experiments, the yield of low-boiling hydrocarbon fuel fractions (gasoline, kerosene and gas oil; b.p. up to 325[degrees]C) from this coal was further increased to a level of 70--72 wt % (MAF basis). The main emphasis of the research work during the reporting period was on the structural analysis of the depolymerized PB(PA) coal, with the uftimate objective of developing an average molecular structure for the predominant (71.5 -- 76.0 wt %) oil fraction (fr. no. 6, Figure 1) as well as for the small asphattene and asphaftol fractions (fr. no. 7 and 8, Figure 1) of this depolymerized product. The oil and asphaftene fractions of the depolymerized PB(PA) coal (Figure 1, fractions [number sign]6 and 7, respectively) were analyzed by gas chromatography/mass spectrometry (GC/MS). Figure 2 shows the reconstructed ion chromatogram for the oil fraction of the depolymerized PB(PA) coal. As seen, the bulk of the compounds present in this fraction elute in the 125--225[degrees]C range as an incompletely resolved hump. It is indicated that the oil contains a wide range of compound types

Sequential low-temperature depolymerization and liquefaction of US coals

A Beulah-Zap (North Dakota) lignite sample, designated below as BZ(ND) lignite, was obtained from the Argonne National Laboratory premium coal program. This lignite had the following ultimate analysis (MAF basis) in wt.%: C, 71.05; H, 5.58; N, 1.17; S, 1.60; 0 (diff), 20.6. The ash content (dry basis) was 6.0 wt.%. As expected, the BZ(ND) lignite had a considerably higher oxygen content ([approximately]20.6%) in comparison with that of previously studied coals (Progress Reports nos. 1--4). The BZ(ND) lignite was subjected to a previously developed stepwise depolymerization-liquefaction procedure [for details and recent applications see J. Shabtai and T. Skulthai, Proc. 1987 Internat. Confer. Coal Science, Elsevier, Amsterdam (J.A. Moulijn, K.A. Nater, and H.A.G. Chermin, Eds.), 1987, pp. 761764; and J. Shabtai, T. Skulthai, and I. Saito, Am. Chem. Soc. Div. Fuel Chem. Prepr., 31 (4), 15--23 (1986)]. The procedure, as summarized in Figure 1, consists essentially of the following sequential steps: (1) intercalation of the coal sample with catalytic amounts (5--20 %) of FeCl[sub 3] followed by mild hydrotreatment (HT) of the coal-FeCl[sub 3] intercalate; (2) base-catalyzed depolymerization (BCD) of the product from step 1, under super-critical conditions; and (3) hydroprocessing (HPR) of the depolymerized product from the two preceding steps, using a sulfided 6Co8Mo catalyst. The results obtained in processing the BZ(ND) lignite according to the above procedure are described

Sequential low-temperature depolymerization and liquefaction of US coals

Results obtained in the studies with BS(IL) coal as feed can be summarized as follows: (1) The low-temperature depolymerization - liquefaction procedure, summarized in Figure 1, is easily adaptable and applicable to a high-sulfur, Burning Star (Illinois No. 6) coal sample. The final product obtained consists of a fully desulfurized, light hydrocarbon oil. (2)Suitable processing conditions for each step of the stepwise depolymerization - liquefaction of the above coal were determined. (3)Direct hydroprocessing of the Burning Star (Illinois No. 6) coal with sulfided catalysts is ineffective for its conversion into a light hydrocarbon product. In accordance with the research program the depolymerized, THF-soluble coal products will be subjected to detailed analysis for the purpose of deriving average molecular structures for the oil, asphaltene and asphaltol fractions. The data obtained will be used to develop a structural model for the BS(IL) coal

Calculated optical properties of Si, Ge, and GaAs under hydrostatic pressure

The macroscopic dielectric function in the random-phase-approximation without local field effect has been implemented using the local density approximation with an all electron, full-potential linear muffin-tin orbital basis-set. This method is used to investigate the optical properties of the semiconductors Si, Ge, and GaAs under hydrostatic pressure. The pressure dependence of the effective dielectric function is compared to the experimental data of Go\~ni and coworkers, and an excellent agreement is found when the so called ``scissors-operator'' shift (SOS) is used to account for the correct band gap at $\Gamma$. The effect of the $3d$ semi-core states in the interband transitions hardly changes the static dielectric function, $\epsilon_\infty$; however, their contribution to the intensity of absorption for higher photon energies is substantial. The spin-orbit coupling has a significant effect on $\epsilon_\infty$ of Ge and GaAs, but not of Si. The $E_1$ peak in the dynamical dielectric function is strongly underestimated for Si, but only slightly for Ge and GaAs, suggesting that excitonic effects might be important only for Si.Comment: 29 RevTex pages and 12 figs; in press in Physical Review

The role of the alloy structure in the magnetic behavior of granular systems

The effect of grain size, easy magnetization axis and anisotropy constant distributions in the irreversible magnetic behavior of granular alloys is considered. A simulated granular alloy is used to provide a realistic grain structure for the Monte Carlo simulation of the ZFC-FC curves. The effect of annealing and external field is also studied. The simulation curves are in good agreement with the FC and ZFC magnetization curves measured on melt spun Cu-Co ribbons.Comment: 13 pages, 10 figures, submitted to PR

Exact Kohn-Sham exchange kernel for insulators and its long-wavelength behavior

We present an exact expression for the frequency-dependent Kohn-Sham exact-exchange (EXX) kernel for periodic insulators, which can be employed for the calculation of electronic response properties within time-dependent (TD) density-functional theory. It is shown that the EXX kernel has a long-wavelength divergence behavior of the exact full exchange-correlation kernel and thus rectifies one serious shortcoming of the adiabatic local-density approximation and generalized-gradient approximations kernels. A comparison between the TDEXX and the GW-approximation-Bethe-Salpeter-equation approach is also made.Comment: two column format 6 pages + 1 figure, to be publisehd in Physical Review

Shale Oil Value Enhancement Research. Quarterly Report, September 1 - November 30, 1995

Activities during this quarter focused on compound type analysis of shale oil extraction products and improvement of the continuous extraction process. We have installed a walk-in fume hood to improve the ventilation of our working environment while handling of larger amounts of shale oil and volatile solvents in our Phase-II(a) work. The fume hood accommodates the distillation column, rotary evaporator, and the CLLX column. During the construction period, experimental work was carried on at a smaller scale. Modifications to the thermal hydrodealkylation process unit at the University of Utah have been completed. The higher boiling polar fraction of shale oil was fed and the preliminary ran showed promising results. The search for potential industrial partners is continuing. During this period, the prijcipal investigator has visited six industrial companies that are candidates for partner/buyer relationship. Currently, we are pursuing confidentiality agreements with four of them. It is the intent to focus our research toward addressing the objectives of those companies who show sufficient interest in the shale oil value enhancement project to enter the next level of discussions

Implementation of an all-electron GW approximation based on the PAW method without plasmon pole approximation: application to Si, SiC, AlAs, InAs, NaH and KH

A new implementation of the GW approximation (GWA) based on the all-electron Projector-Augmented-Wave method (PAW) is presented, where the screened Coulomb interaction is computed within the Random Phase Approximation (RPA) instead of the plasmon-pole model. Two different ways of computing the self-energy are reported. The method is used successfully to determine the quasiparticle energies of six semiconducting or insulating materials: Si, SiC, AlAs, InAs, NaH and KH. To illustrate the novelty of the method the real and imaginary part of the frequency-dependent self-energy together with the spectral function of silicon are computed. Finally, the GWA results are compared with other calculations, highlighting that all-electron GWA results can differ markedly from those based on pseudopotential approaches.Comment: 11pages,3figures, submitted to PR