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1996

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Articles 541 - 570 of 2437

Full-Text Articles in Physical Sciences and Mathematics

A Stable Β-Silyl Carbocation, Joseph B. Lambert, Yan Zhao Aug 1996

A Stable Β-Silyl Carbocation, Joseph B. Lambert, Yan Zhao

Yan Zhao

The β effect of silicon, whereby a carbon-silicon bond substantially stabilizes an adjacent carbocation (Si-C-C+), has been widely studied mechanistically and exploited synthetically. 1-25 The phenomenon normally is invoked in reactive intermediates. Attempts to prepare stable Me3SiCH2CPh2 + under standard magic acid conditions led to loss of trimethylsilyl and observation only of CH3CPh2 +.11 A 2-(trimethylsilyl)allyl cation stable only at -100 °C did not comprise a β-effect system, as the silyl group destabilized the ion and the C-Si bond was orthogonal to the carbocation ð orbitals.21 Siehl and Kaufmann23 prepared 1-arylvinyl cations stabilized by β-silyl groups in magic acid at …

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49. J. Johan Lindberg, Otto Vogl, Franciska Sundholm Aug 1996

49. J. Johan Lindberg, Otto Vogl, Franciska Sundholm

Otto Vogl

No abstract provided.

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The Probe, Issue 168 – August 1996 Aug 1996

The Probe, Issue 168 – August 1996

The Probe: Newsletter of the National Animal Damage Control Association

Personal Reflections: On Encountering a Lion, by Robert M. Timm, Editor, The PROBE
Pigeons Foil French Efforts
Sea Lions Gorge on Depleted Northwest Salmon
Coyote Attacks, Wounds Young Boy
Book Review: Mole Traps: A Collector's Manual, by Rex E. Marsh, Department of Wildlife, Fish, and Conservation Biology, University of California, Davis. RonMunro, Principal Illustrator. 1995. 169 pp.

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Self-Consistency: A Fundamental Concept In Statistics, Thaddeus Tarpey, Bernard Flury Aug 1996

Self-Consistency: A Fundamental Concept In Statistics, Thaddeus Tarpey, Bernard Flury

Mathematics and Statistics Faculty Publications

The term ''self-consistency'' was introduced in 1989 by Hastie and Stuetzle to describe the property that each point on a smooth curve or surface is the mean of all points that project orthogonally onto it. We generalize this concept to self-consistent random vectors: a random vector Y is self-consistent for X if E[X|Y] = Y almost surely. This allows us to construct a unified theoretical basis for principal components, principal curves and surfaces, principal points, principal variables, principal modes of variation and other statistical methods. We provide some general results on self-consistent random variables, give …

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A Scheduling Expert Advisor For The Bond Environment, Mihai G. Sirbu, Dan C. Marinescu Aug 1996

A Scheduling Expert Advisor For The Bond Environment, Mihai G. Sirbu, Dan C. Marinescu

Department of Computer Science Technical Reports

No abstract provided.

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A Laboratory Environment For Experimenting With Xinu, Douglas E. Comer, John C. Lin Aug 1996

A Laboratory Environment For Experimenting With Xinu, Douglas E. Comer, John C. Lin

Department of Computer Science Technical Reports

No abstract provided.

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Gauss: An Automatic Algorithm Selection System For Quadrature, N. Ramakrishnan, John R. Rice Aug 1996

Gauss: An Automatic Algorithm Selection System For Quadrature, N. Ramakrishnan, John R. Rice

Department of Computer Science Technical Reports

No abstract provided.

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Research Needs For The Risk Assessment Of Health And Environmental Effects Of Endocrine Disruptors: A Report Of The Us Epa-Sponsored Workshop, Rj Kavlock, Gp Daston, C Derosa, P Fennercrisp, Le Gray, S Kaattari, Et Al Aug 1996

Research Needs For The Risk Assessment Of Health And Environmental Effects Of Endocrine Disruptors: A Report Of The Us Epa-Sponsored Workshop, Rj Kavlock, Gp Daston, C Derosa, P Fennercrisp, Le Gray, S Kaattari, Et Al

VIMS Articles

The hypothesis has been put forward that humans and wildlife species have suffered adverse health effects after exposure to endocrine-disrupting chemicals. Reported adverse effects include declines in populations, increases in cancers, and reduced reproductive function. The U.S. Environmental Protection Agency sponsored a workshop in April 1995 to bring together interested parties in an effort to identify research gaps related to this hypothesis and to establish priorities for future research activities. Approximately 90 invited participants were organized into work groups developed around the principal reported health effects-carcinogenesis, reproductive toxicity, neurotoxicity, and immunotoxicity--as well as along the risk assessment paradigm--hazard identification, dose-response …

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Experimental Evidence For The Dynamic Jahn-Teller Effect In La0.65Ca0.35Mno3, P. Dai, Jiandi Zhang, H.A. Mook, Sy_Hwang Liou, Peter A. Dowben, E. Ward Plummer Aug 1996

Experimental Evidence For The Dynamic Jahn-Teller Effect In La0.65Ca0.35Mno3, P. Dai, Jiandi Zhang, H.A. Mook, Sy_Hwang Liou, Peter A. Dowben, E. Ward Plummer

Peter Dowben Publications

Recently, it has been argued that a strong electron-phonon interaction arising from the Jahn-Teller splitting of the outer Mn d level plays a crucial role in understanding the nonmetal-to-metal transition observed in the La1-xAxMnO3 (A=Ca, Sr, Ba) system. We show, by neutron powder diffraction, that La0.65Ca0.35MnO3 exhibits an anomalous volume and oxygen/manganese displacement change around Tc, in qualitative agreement with the theoretical prediction.

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Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris Aug 1996

Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris

Physics Faculty Research & Creative Works

Time-of-flight measurements on a wide variety of molecularly-doped polymers reveal carrier mobilities that exhibit an exponential dependence on the square root of the applied electric field. Recent attempts to explain the observed field dependence have focused on the role played by spatial and energetic disorder. It as also been conjectured that the charge-dipole interactions often identified as the source of energetic disorder could be of sufficient range to lead to correlations in the energies of neighboring hopping sites. We have analytically explored the effect of such correlations on high field carrier transport in random potentials, and discuss how particular features …

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Positive Solutions For A Semilinear Elliptic Problem With Critical Exponent, Ismail Ali, Alfonso Castro Aug 1996

Positive Solutions For A Semilinear Elliptic Problem With Critical Exponent, Ismail Ali, Alfonso Castro

All HMC Faculty Publications and Research

No abstract provided in article.

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Comparison And Modeling Study Of Vancomycin, Ristocetin A, And Teicoplanin For Ce Enantioseparations, Mary P. Gasper, Alain Berthod, Usha B. Nair, Daniel W. Armstrong Aug 1996

Comparison And Modeling Study Of Vancomycin, Ristocetin A, And Teicoplanin For Ce Enantioseparations, Mary P. Gasper, Alain Berthod, Usha B. Nair, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

The structurally related glycopeptide antibiotics vancomycin, ristocetin A, and teicoplanin can all be used as chiral selectors in capillary electrophoresis (CE). Both experimental and modeling studies were done to elucidate their similarities and differences. There are identifiable morphological differences in the aglycon macrocyclic portions of these three compounds. In addition, there are other structural distinctions that can affect their CE enantioselectivity, migration times, and efficiency. Teicoplanin is the most distinct of the three and is the only one that is surface active. Its aggregational properties appear to affect its enantioselectivity among other things. The similar but not identical structures of …

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On Hall Scattering Factors For Holes In Gaas, David C. Look, C. E. Stutz, J. R. Sizelove, K. R. Evans Aug 1996

On Hall Scattering Factors For Holes In Gaas, David C. Look, C. E. Stutz, J. R. Sizelove, K. R. Evans

Physics Faculty Publications

Hall scattering factors for electrons and holes in molecular beam epitaxial GaAs layers have been determined by comparing carrier concentrations measured by the Hall effect with those measured by the electrochemical capacitance–voltage technique. The conclusion is that both the electron and hole scattering factors are near unity for n ranging from 2×1016 to 7×1017 cm−3, and p ranging from 5×1016 to 4×1019 cm−3. This conclusion is consistent with the present theory for electrons, but not with that for holes.

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New Promise For Electron Bulk Energization In Solar Flares: Preferential Fermi Acceleration Of Electrons Over Protons In Reconnection-Driven Magnetohydrodynamic Turbulence, Ted La Rosa, Ronald L. Moore, James A. Miller, Steven N. Shore Aug 1996

New Promise For Electron Bulk Energization In Solar Flares: Preferential Fermi Acceleration Of Electrons Over Protons In Reconnection-Driven Magnetohydrodynamic Turbulence, Ted La Rosa, Ronald L. Moore, James A. Miller, Steven N. Shore

Faculty Articles

The hard X-ray luminosity of impulsive solar flares indicates that electrons in the low corona are bulk energized to energies of order 25 keV. LaRosa & Moore pointed out that the required bulk energization could be produced by cascading MHD turbulence generated by Alfvénic outflows from sites of strongly driven reconnection. LaRosa, Moore, & Shore proposed that the compressive component of the cascading turbulence dissipates into the electrons via Fermi acceleration. However, for this to be a viable electron bulk energization mechanism, the rate of proton energization by the same turbulence cannot exceed the electron energization rate. In this paper …

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Separate Computation Of Alias Information Fior Reuse, Mary Jean Harrold, Gregg Rothermel Aug 1996

Separate Computation Of Alias Information Fior Reuse, Mary Jean Harrold, Gregg Rothermel

School of Computing: Faculty Publications

Interprocedural data flow information IS useful for many software testing and analysis techniques, including data flow testing, regression testing, program slicing, and impact analysis. For programs with aliases, these testing and analysis techniques can yield invalid results, unless the data flow information accounts for aliasing effects. Recent research provides algorithms for performing interprocedural data flow analysis in the presence of aliases; however, these algorithms are expensive, and achieve precise results only on complete programs. This paper presents an algorithm for performing alias analysis on incomplete programs that lets individual software components such as library routines, subroutines, or subsystems be independently …

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Analyzing Regression Test Selection Techniques, Gregg Rothermel, Mary Jean Harrold Aug 1996

Analyzing Regression Test Selection Techniques, Gregg Rothermel, Mary Jean Harrold

School of Computing: Faculty Publications

Regression testing is a necessary but expensive maintenance activity aimed at showing that code has not been adversely affected by changes. Regression test selection techniques reuse tests from an existing test suite to test a modified program. Many regression test selection techniques have been proposed; however, it is difficult to compare and evaluate these techniques because they have different goals. This paper outlines the issues relevant to regression test selection techniques, and uses these issues as the basis for a framework within which to evaluate the techniques. We illustrate the application of our framework by using it to evaluate existing …

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Bifurcation Of The Periodic Orbits Of Hamiltonian Systems: An Analysis Using Normal Form Theory, D. A. Sadovskii, John B. Delos Aug 1996

Bifurcation Of The Periodic Orbits Of Hamiltonian Systems: An Analysis Using Normal Form Theory, D. A. Sadovskii, John B. Delos

Arts & Sciences Articles

We develop an analytic technique to study the dynamics in the neighborhood of a periodic trajectory of a Hamiltonian system. The theory begins with Poincaré and Birkhoff; major modern contributions are due to Meyer, Arnol'd, and Deprit. The realization of the method relies on local Fourier-Taylor series expansions with numerically obtained coefficients. The procedure and machinery are presented in detail on the example of the ‘‘perpendicular’’ (z=0) periodic trajectory of the diamagnetic Kepler problem. This simple one-parameter problem well exhibits the power of our technique. Thus, we obtain a precise analytic description of bifurcations observed by J.-M. Mao …

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The Role Of Written And Verbal Expression In Improving Communication Skills For Students In An Undergraduate Chemistry Program, Brian P. Coppola, Douglas S. Daniels Aug 1996

The Role Of Written And Verbal Expression In Improving Communication Skills For Students In An Undergraduate Chemistry Program, Brian P. Coppola, Douglas S. Daniels

Chemistry Faculty Publications

Proofreading, editing, and critique, the customary assessment tools scientists use to evaluate professional journal articles, grant applications, and any other writing, can be applied equally well in introductory science instruction. Such feedback is, in fact, crucial to growth and development. When learning anything new, students and faculty alike rely heavily on sources other than themselves (‘external editors’) to assess their understanding as they develop self-assessment skills (or ‘internal editors’). Although they rarely describe it in these terms, faculty nonetheless assume that students have developed and refined their internal skills by the time they take examinations and write term papers. Unfortunately, …

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Synthesis And Characterisation Of New Dimolybdenum (Ii,Ii) Dicarboxylates And Their Use As Polymerization Catalysts, Elizabeth Whelan Aug 1996

Synthesis And Characterisation Of New Dimolybdenum (Ii,Ii) Dicarboxylates And Their Use As Polymerization Catalysts, Elizabeth Whelan

Masters

The purpose of this work was to prepare a series of new dimolybdenum(II,II) dicarboxylate complexes, to characterize the complexes and to investigate their use as potential catalysts for the ring-opening metathesis polymerization (ROMP) of the bicyclic monomer norbornene.

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The Influence Of {Sup 18} F Induced Reactions In The Hot Cno Cycle, K. E. Rehm, M. Paul, Andrew D. Roberts, C. L. Jiang, D. Blumenthal, C. N. Davids, P. Decrock, S. M. Fischer, J. Gehring, D. Henderson, C. J. Lister, Robert J. Nickles, J. Nolen, R. C. Pardo, J. P. Schiffer, R. E. Segel, D. Seweryniak Aug 1996

The Influence Of {Sup 18} F Induced Reactions In The Hot Cno Cycle, K. E. Rehm, M. Paul, Andrew D. Roberts, C. L. Jiang, D. Blumenthal, C. N. Davids, P. Decrock, S. M. Fischer, J. Gehring, D. Henderson, C. J. Lister, Robert J. Nickles, J. Nolen, R. C. Pardo, J. P. Schiffer, R. E. Segel, D. Seweryniak

Physics and Astronomy Department Publications

The contribution of the {sup 18}F(p,{gamma}) reaction to the production of {sup 19}Ne, which is an important isotope in connection with the breakout from the hot CNO cycle, has been investigated in experiments with {sup 18}F beams. Measurements of the cross sections for the {sup 18}F(p,{alpha}){sup 15}O and {sup 18}F(p,{gamma}){sup 19 }Ne reactions indicate that the contribution of the {sup 18}F(p, {gamma}) route to the formation or {sup 19}Ne is small.

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Application Of (E,2e) Spectroscopy To The Electronic Structure Of Valence Electrons In Crystalline And Amorphous Solids, John R. Dennison, A. L. Ritter Aug 1996

Application Of (E,2e) Spectroscopy To The Electronic Structure Of Valence Electrons In Crystalline And Amorphous Solids, John R. Dennison, A. L. Ritter

All Physics Faculty Publications

This review presents theoretical and experimental aspects of (e,2e) spectroscopy specific to the study of crystalline and amorphous solids. The cross section for (e,2e) scattering is proportional to the spectral momentum density of the ejected electron under certain approximations. The theoretical framework for interpreting (e,2e) measurements is summarized here and general properties of the spectral momentum density of solids are discussed. Different designs of the (e,2e) spectrometer are described and sample preparation techniques are briefly reviewed. A summary of (e,2e) experiments on the electronic structure of valence electrons in graphite, ion sputtered and evaporated amorphous carbon, aluminum/aluminum oxide composites, amorphous …

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Structural Phase Transition And Tc Distribution In Hf-Doped Lamno3 Investigated Using Perturbed-Angular-Correlation Spectroscopy, William E. Evenson, David D. Allred, Gary L. Catchen Aug 1996

Structural Phase Transition And Tc Distribution In Hf-Doped Lamno3 Investigated Using Perturbed-Angular-Correlation Spectroscopy, William E. Evenson, David D. Allred, Gary L. Catchen

Faculty Publications

Using perturbed-angular-correlation (PAC) spectroscopy, via the Hf-->Ta probe, we have measured Mn-site electric-field gradients (EFG's) at Ta nuclei in ceramic samples of LaMnO3. Two crystallographic phases coexist over a temperature interval of ≈16 K near the orthorhombic-to-rhombohedral transition at ≈724 K, which shows a thermal hysteresis of ≈1.7±0.2 K. Concurrently, in the two phases, we determined the temperature dependence of the EFG parameters, Vzz, ƞ, and δ, and the ratio of the probe concentrations A1/A2. To explain the apparent coexistence of two phases in this weakly first-order transition, we present a model that assumes a spatial distribution of Tc …

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The John Muir Newsletter, Fall 1996, The John Muir Center For Regional Studies Aug 1996

The John Muir Newsletter, Fall 1996, The John Muir Center For Regional Studies

Muir Center Newsletters (1981-2015)

Volume 6, Number 4 NEW DNSERVATIONIST: Agriculture in California's Central Valley by Kevin S. Frazier ;:';:::::;:.'ij ; (Editor's note: our feature article this month was written by a senior at the University of the Pacific, the first recipient of the Rockwell Hunt Summer Research Scholarship for UOP undergraduates.) s I frequently drive through the California Central Valley from my home in Sonora to school in Stockton, my constant companions are expansive agricultural fields. Corn gives way to tomatoes which give way to sugar beets; orchards of walnuts turn to orchards of peaches or apricots; herds of cattle graze by the …

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Single-Layer Channel Routing And Placement With Single-Sided Nets, Ronald I. Greenberg, Jau-Der Shih Aug 1996

Single-Layer Channel Routing And Placement With Single-Sided Nets, Ronald I. Greenberg, Jau-Der Shih

Computer Science: Faculty Publications and Other Works

This paper considers the optimal offset, feasible offset, and optimal placement problems for a more general form of single-layer VLSI channel routing than has usually been considered in the past. Most prior works require that every net has exactly one terminal on each side of the channel. As long as only one side of the channel contains multiple terminals of the same net, we provide linear-time solutions to all three problems. Such results are implausible if the placement of terminals is entirely unrestricted; in fact, the size of the output for the feasible offset problem may be Ω(n^2). The linear-time …

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Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow Aug 1996

Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow

Physics Faculty Research & Creative Works

Six samples of Ce2Fe17-xGax with nominal Ga content x equal to 0, 0.3, 0.5, 0.7, 1.0, 2.0 have been studied by powder neutron diffraction at room temperature. Both crystalline and magnetic refinements have been carried out. All six samples adopt the Th2Zn17-type rhombohedral structure. The only additional phase found is α-iron. Gallium atoms are found to have high affinity for the iron 18h site, and are absent from the 9d and 18f sites. The Ga substitution for Fe leads to an expansion of both the a and c axes. The Curie …

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Independent Center, Independent Electron Approximation For Dynamics Of Molecules And Clusters, James H. Mcguire, Jack C. Straton, J. Wang, Y. D. Wang, O. L. Weaver, S. E. Corchs, R. D. Rivarola Aug 1996

Independent Center, Independent Electron Approximation For Dynamics Of Molecules And Clusters, James H. Mcguire, Jack C. Straton, J. Wang, Y. D. Wang, O. L. Weaver, S. E. Corchs, R. D. Rivarola

Physics Faculty Publications and Presentations

A formalism is developed for evaluating probabilities and cross sections for multiple-electron transitions in scattering of molecules and clusters by charged collision partners. First, the molecule is divided into subclusters each made up of identical centers (atoms). Within each subcluster coherent scattering from identical centers may lead to observable phase terms and a geometrical structure factor. Then, using a mean field approximation to describe the interactions between centers we obtain {ital A}{sub {ital I}}{approximately}{summation}{sub {ital k}}{product}{sub {ital ke}}{sup {ital i}{delta}{sup {ital k}}{sub {ital I}}}{ital A}{sub {ital Ik}}. Second, the independent electron approximation for each center may be obtained by neglecting …

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Quantum Deformation Of Quantum Gravity, Seth Major, L. Smolin Aug 1996

Quantum Deformation Of Quantum Gravity, Seth Major, L. Smolin

Articles

We describe a deformation of the observable algebra of quantum gravity in which the loop algebra is extended to framed loops. This allows an alternative nonperturbative quantization which is suitable for describing a phase of quantum gravity characterized by states which are normalizable in the measure of Chern-Simons theory. The spinor identities are extended to a set of relations which are governed by the Kauffman bracket so that the spin network basis is deformed to a basis of SU(2)q spin networks. This deformation parameter, q, is eih̵2G2Λ6" role="presentation" style="box-sizing: border-box; display: inline-block; line-height: normal; font-size: 14.4px; word-wrap: …

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Resource Letter Belfef-1: Biological Effects Of Low-Frequency Electromagnetic Fields, David W. Hafemeister Aug 1996

Resource Letter Belfef-1: Biological Effects Of Low-Frequency Electromagnetic Fields, David W. Hafemeister

Physics

This Resource Letter provides a guide to the literature on the interaction of extremely low-frequency electromagnetic field (ELF/EMF) interactions with biological matter, and on the possibility that such interactions could have a harmful effect on human health. Journal articles and books are cited for the following topics: ELF/EMF theoretical interactions with biological cells, organs and organisms, magnetic dipole interactions, sensing by animals, biomedical–biophysical experiments, epidemiology, and litigation–mitigation risk issues.

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Hydrostratigraphy And Allostratigraphy Of The Cenozoic Alluvium In The Northwestern Part Of Las Vegas Valley, Clark County, Nevada, David J. Donovan Aug 1996

Hydrostratigraphy And Allostratigraphy Of The Cenozoic Alluvium In The Northwestern Part Of Las Vegas Valley, Clark County, Nevada, David J. Donovan

UNLV Theses, Dissertations, Professional Papers, and Capstones

This investigation was conducted to determine the location, nature, and boundaries of the most permeable unit within the alluvial aquifer material in Las Vegas Valley. It was prompted by declines in specific capacity of about 90% at the Las Vegas Valley Water District's West Central Well Field. It was hypothesized that the decline in specific capacity resulted from dewatering of the most permeable interval of the alluvium. Lithologic descriptions from wells and aquifer test information were analyzed for geologic and hydrogeologic variability. New information, in the form of detailed unpublished lithologic and hydrologic information, was available from twenty water wells …

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On Integrating Existing Bibliographic Databases And Structured Databases, Ying Lu, Ee Peng Lim Aug 1996

On Integrating Existing Bibliographic Databases And Structured Databases, Ying Lu, Ee Peng Lim

Research Collection School Of Computing and Information Systems

It is widely accepted that future digital library applications have to be built upon different kinds of database servers to draw different forms of data from them. These data include bibliographic data, text data, multimedia data, and structured data. We address the problem of integrating existing bibliographic and structured databases which reside at different locations in the network. To integrate bibliographic data and structured data, we extended the well-known SQL model to represent bibliographic related attributes and queries. In particular, we have added a new data type to model attributes in the bibliographic database. We have also designed specialized predicates …

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