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1999

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Articles 2341 - 2370 of 2555

Full-Text Articles in Physical Sciences and Mathematics

The Characterization Of Na_2 Co_3 Activated Kütahya Bentonite, Nuray Yildiz, Yüksel Sarikaya, Ayla Çalimli Jan 1999

The Characterization Of Na_2 Co_3 Activated Kütahya Bentonite, Nuray Yildiz, Yüksel Sarikaya, Ayla Çalimli

Turkish Journal of Chemistry

A calcium bentonite from Kütahya region (Turkey) was activated with Na_2CO_3 at various ratios (1, 2, 2.5, 5, 10, 15g / 100 g bentonite). Due to ion exchange, the original Ca-bentonite was converted to Na-bentonite by Na_2CO_3 when the Na_2CO_3/bentonite ratio was 2.5\% (2.5 g Na_2CO_3/100 22g bentonite, A2.5). Na-bentonite (A2.5) obtained by soda activation was treated with 3 g CaCl_2/ 100 g bentonite and converted to Ca-bentonite again. The products were investigated by chemical analysis, X-ray diffraction and micropore analysis. It was observed that the cation exchange capacity (CEC) did not change until the soda ratio was 2.5\%. After …

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Mass Spectral Studies Of Some Triorganotin Derivatives Containing Carboxylates, Moazzam Hussain Bhatti, Sagib Ali, Muhammad Mazhar, Muhammad Danish, Muhammad Azi̇z Chaudhary Jan 1999

Mass Spectral Studies Of Some Triorganotin Derivatives Containing Carboxylates, Moazzam Hussain Bhatti, Sagib Ali, Muhammad Mazhar, Muhammad Danish, Muhammad Azi̇z Chaudhary

Turkish Journal of Chemistry

The mass spectra of 16 triorganotin compounds having the general formula R_3SnL where R= CH_3, C_4H_9, C_6H_5, C_6H_{11} and L=trans-3-(2-furanyl)-2-propenoate, trans-m-methyl cinnamate, 2-(2,3-dimethylphenyl)aminobenzoate and trans-3-(2-thienyl)-2- propenoate, were investigated. The possible fragmentation pattern is discussed in detail.

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Effect Of Temperature On The Electrooxidation Of Some Organic Molecules On Pt Doped Conducting Polymer Coated Electrodes, İpek Beceri̇k, Fehmi̇ Fiçicioğlu, Fi̇gen Kadirgan Jan 1999

Effect Of Temperature On The Electrooxidation Of Some Organic Molecules On Pt Doped Conducting Polymer Coated Electrodes, İpek Beceri̇k, Fehmi̇ Fiçicioğlu, Fi̇gen Kadirgan

Turkish Journal of Chemistry

Polymer modified electrodes are of importance as possible electrocatalysts for various electrode reactions, i.e., platinum incorporated into polypyrrole or polyaniline films are known to be good systems for the electrooxidation of various organic molecules. In this study, the effect of temperature on the electrooxidation of D. glucose and methanol on Pt doped films was investigated, apparent activation energies were calculated and the results were evaluated.

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Electrochemical Reduction Of Methyl Cinnamate In The Presence Of 1,3-Bis(4-Methyl Phenylsulphonyloxy)Propane, Mustafa Güllü Jan 1999

Electrochemical Reduction Of Methyl Cinnamate In The Presence Of 1,3-Bis(4-Methyl Phenylsulphonyloxy)Propane, Mustafa Güllü

Turkish Journal of Chemistry

Electrochemical reduction of methyl cinnamate in the presence of a dielectrophile, such as 1,3-bis(4-methyl phenylsulphonyloxy)propane gives two major products: trans- (\pm) methyl 2-phenylcyclopentanecarboxylate and trans- (\pm) methyl 2,3-diphenyl-5-oxo-cyclopentanecarboxylate. The ratio of products basically depends on the electrolysis conditions.

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Autocatalytic Reduction Of Dichloro 5, 10, 15, 20 Tetraphenylporphinatoplatinum(Iv) By 1-Methylimidazole, F. Ece Bulak Jan 1999

Autocatalytic Reduction Of Dichloro 5, 10, 15, 20 Tetraphenylporphinatoplatinum(Iv) By 1-Methylimidazole, F. Ece Bulak

Turkish Journal of Chemistry

It was observed that in toluene solution, excess 1-methyl-imidazole (Melm) reduces dichloro 5, 10, 15, 20 tetraphenyl-porphinatoplatinum(IV) (PtTPPCl_2) to tetraphenylporphinato-platinum(II) (PtTPP) autocatalytically (Fig. 1). There was no Pt(III) intermediate or 1-methylimidazole radical detected by Electron Resonance Spectroscopy (ESR) at 25°C. The reaction was found to be autocatalyzed by the PtTPP product when the 1-methylimidazole to PtTPPCl_2 concentration ratio is about 10^4 or more. From the data obtained it is reasonable to suppose that aggregation of the PtTPP product with PtTPPCl_2 plays an important role in this reduction process.

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Thermal Plasmaspheric Morphology: Effect Of Geomagnetic And Solar Activity, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, J. Lemaire, R.R. Meier, D.J. Melendez-Alvira Jan 1999

Thermal Plasmaspheric Morphology: Effect Of Geomagnetic And Solar Activity, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, J. Lemaire, R.R. Meier, D.J. Melendez-Alvira

Publications

A multispecies kinetic model of the thermal plasma in the plasmasphere is used to predict the spatial dependence of the hydrogen ion and helium ion density and temperature for different levels of geomagnetic and solar activity. The particular convection electric field model chosen is intended for the time intervals between substorms. The plasma density and temperature in the equatorial plane are found to exhibit a local-time variation that is sensitive to the details of the convection electric field. In particular, the parallel temperature increases with altitude and the perpendicular temperature decreases with altitude, except in the postmidnight sector, features that …

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Environmental Vulnerability And Agriculture In The Karstic Domain: Landscape Indicators And Cases In The Atlas Highlands, Morocco, Brahim Akdim, Mohammed Amyay Jan 1999

Environmental Vulnerability And Agriculture In The Karstic Domain: Landscape Indicators And Cases In The Atlas Highlands, Morocco, Brahim Akdim, Mohammed Amyay

International Journal of Speleology

After the brief presentation of the major karstic areas in Morocco, the article focused essentially on the Atlas mountains to investigate the impact of the agriculture on the natural systems equilibrium. Socio-economic changes (demographic pressure, escalation of the landscape use, utilisation of new techniques in water harvesting, etc...) have sometimes fathered mechanisms of degradation. Many indicators seem to reflect these mechanisms. The pedologic indicators, soil erosion, the hydrologic and geomorphic indicators, are apprehended to demonstrate existent correlation between different variables and the often negative impacts of land over-use in the karstic domain of the Middle Atlas.

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On 2-Reptiles In The Plane, Sze-Man Ngai, Víctor F. Sirvent, J. J. P. Veerman, Yang Wang Jan 1999

On 2-Reptiles In The Plane, Sze-Man Ngai, Víctor F. Sirvent, J. J. P. Veerman, Yang Wang

Mathematics and Statistics Faculty Publications and Presentations

We classify all rational 2-reptiles in the plane. We also establish properties concerning rational reptiles in the plane in general.

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Nonextensivity And Quantum Groups, Metin Arik Jan 1999

Nonextensivity And Quantum Groups, Metin Arik

Turkish Journal of Physics

Classical set theory is nonextensive since the mathematical definition of a set excludes the possibility that more than one copy of the same element can be in a set. We show that the description of random sets in terms of an algebra of creation operators and their hermitean conjugates yields an interpretation of the unitary quantum group SU_q(d) as the symmetry associated with the construction of d random sets from a given source set of M=(1-q)^{-1} elements.

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Statistical Physics, Neural Networks, Brain Studies, Gerard Toulouse Jan 1999

Statistical Physics, Neural Networks, Brain Studies, Gerard Toulouse

Turkish Journal of Physics

An overview of some aspects of a vast domain, located at the crossroads of physics, biology and computer science is presented: 1) During the last fifteen years, physicists advancing along various pathways have come into contact with biology (computational neurosciences) and engineering (formal neural nets). 2) This move may actually be viewed as one component in a larger picture. A prominent trend of recent years, observable over many countries, has been the establishment of interdisciplinary centers devoted to the study of: cognitive sciences; natural and artificial intelligence; brain, mind and behaviour; perception and action; learning and memory; robotics; man-machine communication, …

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Weak Localization In Disordered Two-Dimensional Crystals With Half-Filled Band, E.P. Nakhmedov, T. Kaya Jan 1999

Weak Localization In Disordered Two-Dimensional Crystals With Half-Filled Band, E.P. Nakhmedov, T. Kaya

Turkish Journal of Physics

Effect of subtitutional impurities on electron localization in two dimensional (2D) lattice near the middle of the band is studied. Calculation of density of the electronic states, \rho (\varepsilon ), increases logaritmically in the middle of the band. This singularity in the density of states of noninteracting electron gas on lattice gives rise to anomalous dependencies of thermodynamic quantities on the temperature. The quantum correction to the conductivity of a nonintreracting electron gas due to Umklapp electron--impurity scattering is calculated. This correction to the conductivity is shown to compete with that from the localization corrrection for a Normal scattering process. …

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Angular Momentum Evolution In Close Late-Type Binaries, Carla Maceroni Jan 1999

Angular Momentum Evolution In Close Late-Type Binaries, Carla Maceroni

Turkish Journal of Physics

Accurate monitoring of the orbital period of late-type close binaries can provide important information on their secular evolution and on the structural changes of their components on very short timescales (i.e. decades). The orbital period turns out to be a powerful tool of investigation: it can be measured to great accuracy even with simple equipments and its change produces an easily detectable cumulative effect over time. This paper focuses on two physical mechanisms that cause orbital periods changes in late type binaries with negligible mass loss from the system: the dynamical evolution due to magnetic braking in tidally locked systems, …

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The Experimental Studies On Zr Photoelectron Spectra, I. Buribayev, N. A. Nurmatov, N. Talipov Jan 1999

The Experimental Studies On Zr Photoelectron Spectra, I. Buribayev, N. A. Nurmatov, N. Talipov

Turkish Journal of Physics

Photoelectron spectra (PES) taken from crystalline Zr at 8.4 eV and 10 eV have been studied by a high resolution photoelectron analyzer, with \Delta E = 0.1 eV, and the results were compared to the results calculated for electron density of states in the valence band. Photoelectron work function (WF) measured from the atomically clean Zr surface by Fowler isothermal curves was found to be 3.95 eV \pm 0.02 eV. It was shown that a small dose of residual gas, namely CO, absorbed on the Zr surface, resulted in a decrease of the WF by 0.15-0.25 eV as well as …

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Electrons And Phonons In Gan Semiconductor Quantum Well Devices, M. Babiker, N. A. Zakhleniuk, C. R. Bennett, V. N. Stavrou, B. K. Ridley Jan 1999

Electrons And Phonons In Gan Semiconductor Quantum Well Devices, M. Babiker, N. A. Zakhleniuk, C. R. Bennett, V. N. Stavrou, B. K. Ridley

Turkish Journal of Physics

Electrons and polar optical phonons and their interactions are considered in the context of semiconductor quantum well devices, with particular reference to real quantum well laser structures. Distinction is made between wide-barrier and narrow-barrier structures and we explore the implications of these regimes for the description of the electron capture process. Special emphasis is made on the significant effects arising from the large effective mass ratio in AlN/GaN structures.

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Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves Jan 1999

Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves

Turkish Journal of Physics

No abstract provided.

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Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen Jan 1999

Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen

Turkish Journal of Physics

The numerical results of the study of a novel wavelength converter which can be tuned with the application of an external field are presented. For this device, exciton binding energies, radiuses and the absorption coefficient are numerically analysed as a function of electric field. We showed that the interband transition energy and the overlap function between electron and hole changes abruptly when an electric field is applied. This phenomenon can be used the increase the change in the absorption coefficient and reduce the on-state transmission loss in electroabsorption modulators.

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Electromagnetic Waves In Disordered Dielectric Media: Coupled-Dipole Model, Arkadiusz Orlowski, Marian Rusek Jan 1999

Electromagnetic Waves In Disordered Dielectric Media: Coupled-Dipole Model, Arkadiusz Orlowski, Marian Rusek

Turkish Journal of Physics

An effective approach to multiple scattering of electromagnetic waves by disordered dielectric media is developed. A self-consistent energy-conserving coupled-dipole model is used. Applications to the Anderson localization of electromagnetic waves are presented. A complete set of Maxwell's equations is used to describe the propagation of waves and the vector character of the electromagnetic field is fully taken into account.

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Electrodynamics With Toroid Polarization, V. M. Dubovik, B. H. Saha Jan 1999

Electrodynamics With Toroid Polarization, V. M. Dubovik, B. H. Saha

Turkish Journal of Physics

A modified system of equations of electrodynamics of continuous media has been obtained. Beside the Lagrangian system an alternative gauge-like formalism has been developed to introduce the toroid moment contributions in the obtained equations. The two potential formalism that was worked out by us earlier has been developed further where along with the two vector potentials we introduce two scalar potentials thus taking into account all four basic equations of electromagnetism.

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Low-Magnetic Field Microwave Absorption In Superconductors And Conducting Polymers, I. L. Khairullin, P. K. Khabibullaev, V. Yu. Sokolov, A. A. Zakhidov Jan 1999

Low-Magnetic Field Microwave Absorption In Superconductors And Conducting Polymers, I. L. Khairullin, P. K. Khabibullaev, V. Yu. Sokolov, A. A. Zakhidov

Turkish Journal of Physics

Low-magnetic field microwave absorption (MA) in superconductors and conducting polymers is analysed in a low-field signal (LFS) version of the MA detecting method. The temperature dependences, hysteretic benavior and other properties of a LFS are compared in superconducting versus non-superonducting systems. Spin selective hopping processes between polarons and bipolarons is proposed to be one of the possible mechanisms of a LFS in non-degenarate conducting polymers.

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Resource Law Notes Newsletter, No. 45, Winter Issue, 1999, University Of Colorado Boulder. Natural Resources Law Center Jan 1999

Resource Law Notes Newsletter, No. 45, Winter Issue, 1999, University Of Colorado Boulder. Natural Resources Law Center

Resource Law Notes: The Newsletter of the Natural Resources Law Center (1984-2002)

No abstract provided.

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Finite Type Link Homotopy Invariants, Blake Mellor Jan 1999

Finite Type Link Homotopy Invariants, Blake Mellor

Mathematics, Statistics and Data Science Faculty Works

Bar-Natan used Chinese characters to show that finite type invariants classify string links up to homotopy. In this paper, I construct the correct spaces of chord diagrams and Chinese characters for links up to homotopy. I use these spaces to show that the only rational finite type invariants of link homotopy are the pairwise linking numbers of the components.

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Measuring The Diameter Of Your Blind Spot, Jeff Sanny Jan 1999

Measuring The Diameter Of Your Blind Spot, Jeff Sanny

Physics Faculty Works

A simple experiment to determine the diameter of the blind spot is described. Students are divided into groups of three and work together to perform the experiment. The procedure takes about 15 minutes and seems to be quite enjoyable to the class.

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Mach’S Principle In A Mixed Newton-Einstein Context, Evert Jan Post, Michael Berg Jan 1999

Mach’S Principle In A Mixed Newton-Einstein Context, Evert Jan Post, Michael Berg

Mathematics, Statistics and Data Science Faculty Works

A closed physical space, in conjunction with scalar versus pseudo scalar distinctions, and an accordingly adapted Gauss theorem, reveal unexpected perspectives on Mach's principle, the mass-energy theorem, and a bonus insight into the nature of the solutions of the Einstein field equations of gravity.

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Resource Allocation And Sucrose Mobilization In Light Limited Eelgrass Zostera Marina, Teresa Alcoverro, Richard C. Zimmerman, Donald G. Kohrs, Randall S. Alberte Jan 1999

Resource Allocation And Sucrose Mobilization In Light Limited Eelgrass Zostera Marina, Teresa Alcoverro, Richard C. Zimmerman, Donald G. Kohrs, Randall S. Alberte

OES Faculty Publications

This study evaluated the ability of Zostera marina L. (eelgrass) to balance the daily photosynthetic deficit by mobilization of carbon reserves stored in below-ground tissues during a period of extreme winter light limitation. A quantitative understanding of the mobilization process and its limitations is essential to the development of robust models predicting minimum light levels required to maintain healthy seagrass populations. Plants were grown in running seawater tanks under 2 light regimes. One treatment was provided with 2 h irradiance-saturated photosynthesis (Hsat) to produce severe Light Limitation, while control plants were grown under 7 h Hsat, …

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Stability Of Paleosinks And Karstic Carbonates In The Southern Fire Clay Mining District Of Missouri, Robert Weiser Dillon Jan 1999

Stability Of Paleosinks And Karstic Carbonates In The Southern Fire Clay Mining District Of Missouri, Robert Weiser Dillon

Doctoral Dissertations

"The Southern Fire Clay District of Missouri was intensely mined during the late-1800’s to mid-1900’s for its valuable resource of high refractory clays deposited within Pennsylvanian sinkholes “paleosinks”. Mining operations have produced modifications in the Ozark aquifer, which in effect has possibly increased the instability of this paleokarst terrain and the potential of further environmental impacts to the land. Evidence supporting this hypothesis are: (1) A southerly shift in the regional groundwater divide relative to the topographic divide. This possibly is caused by the distribution of leaking clay pits, which suggests that the bedrock permeability or hydraulic conductivity has been …

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Reconfigurable Shift Switching Parallel Comparators, R. Lin, S. Olariu Jan 1999

Reconfigurable Shift Switching Parallel Comparators, R. Lin, S. Olariu

Computer Science Faculty Publications

We present novel asynchronous VLSI comparator schemes which are based on recently proposed reconfigurable shift switch logic and the traditional (precharged) CMOS domino logic. The schemes always produce a semaphore as a by-product of the process to indicate the end of domino process, which requires no additional delay and a minimal number of additional devices. For a large percentage of inputs the computations are much faster than traditional synchronous comparators due to the full utilization of the inherent speed of the circuits. Also the schemes are simple, area compact and stable.

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Salinity And Hydrology Of The Fence Road Catchment : A Focus Catchment Of The Blackwood Basin, Ben Whitfield Jan 1999

Salinity And Hydrology Of The Fence Road Catchment : A Focus Catchment Of The Blackwood Basin, Ben Whitfield

Resource management technical reports

It is the clearing of native vegetation and replacement with lower water-use annual crops and pastures that is responsible for the developing salinity problem. Traditional farming practices have led to increased recharge to the groundwater systems resulting in increased storage and/or greater areas or rates of discharge. Groundwater monitoring has revealed variable rates of rise throughout the Fence Road catchment, from static to 0.6 metres per year, in a period of average to below average rainfall.

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Native Vegetation Handbook For The Shire Of Northam, Sarah J. Weaving Jan 1999

Native Vegetation Handbook For The Shire Of Northam, Sarah J. Weaving

Native vegetation handbook series

This booklet provides land managers with information relating to the natural resources of the Shire of Northam, including the existing and original vegetation, fauna and flora, drainage systems, topography and soils. Some of the problems relating to the management of these resources within the Shire and community initiatives to deal with these problems are also discussed. It is hoped that this information will contribute to the long term viability of the agricultural landscape and the conservation of native vegetation within the Shire.

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Coastal Land And Groundwater For Horticulture From Gingin To Augusta, Dennis Van Gool, Werner Runge Jan 1999

Coastal Land And Groundwater For Horticulture From Gingin To Augusta, Dennis Van Gool, Werner Runge

Resource management technical reports

Due to a variety of factors, including infrastructure needs, labour requirements and transport costs, horticulture is normally located near major urban centres. This study focuses on the coastal plain region from Gingin to Augusta. This region accomodates over 80% of Western Australia's population and includes the States major urban centres. This region also accounts for over half the State's horticultural production with a gross value of production of $244 million.

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X-Ray Crystal Structures And The Facile Oxidative (Au−C) Cleavage Of The Dimethylaurate(I) And Tetramethylaurate(Iii) Homologues, Dunming Zhu, Sergey V. Lindeman, Jay K. Kochi Jan 1999

X-Ray Crystal Structures And The Facile Oxidative (Au−C) Cleavage Of The Dimethylaurate(I) And Tetramethylaurate(Iii) Homologues, Dunming Zhu, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Dimethylaurate(I) has been prepared as the crystalline tetrabutylammonium salt for comparison with the known tetramethylaurate(III) analogue. The linear structure of dimethylaurate(I) and the square-planar structure of tetramethylaurate(III) have both been confirmed by X-ray crystallography. One-electron oxidation of dimethylaurate(I) by either ferrocenium or arenediazonium cations produces the metastable dimethylgold(II) intermediate, which can be trapped as the paramagnetic 9,10-phenanthrenequinone (PQ) adduct. Otherwise, dimethylgold(II) is subject to rapid reductive elimination of ethane and affords metallic gold (mirror). The analogous oxidation of tetramethylaurate(III) by ferrocenium, arenediazonium, or nitrosonium cations also proceeds via electron transfer to generate the putative tetramethylgold(IV) intermediate. The highly unstable (CH …

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