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Articles 1 - 11 of 11

Full-Text Articles in Physical Sciences and Mathematics

Nitrogenase Substrates As Intercluster Bridging Units Between The Molybdenum Atoms In Doubly Bridged, Double Cubanes. The Synthesis And Characterization Of The [Mofe3s4cl2(Cl4cat)]2(.Mu.2-S)(.Mu.2-L)]N- Anions (L = N2h4, N = 4; L = Cn-, N = 5), Paul Challen, Sang Koo, C. Kim, W. Dunham, D. Coucouvanis Oct 1990

Nitrogenase Substrates As Intercluster Bridging Units Between The Molybdenum Atoms In Doubly Bridged, Double Cubanes. The Synthesis And Characterization Of The [Mofe3s4cl2(Cl4cat)]2(.Mu.2-S)(.Mu.2-L)]N- Anions (L = N2h4, N = 4; L = Cn-, N = 5), Paul Challen, Sang Koo, C. Kim, W. Dunham, D. Coucouvanis

Paul R. Challen

No abstract provided.


Structural And Energetic Evidence For Oxygen-Lithium-Nitrogen Chelation In A Model For Asymmetric Induction., Edward Arnett, Michael Nichols, Andrew Mcphail Sep 1990

Structural And Energetic Evidence For Oxygen-Lithium-Nitrogen Chelation In A Model For Asymmetric Induction., Edward Arnett, Michael Nichols, Andrew Mcphail

Michael A Nichols

No abstract provided.


On The Electrochemical Etching Of Tips For Scanning Tunneling Microscopy, Nancy Burnham, J. Ibe, P. Bey Jr., S. Brandow, R. Brizzolara, D. Dilella, K. Lee, C. K. Marrian, R. Colton Jun 1990

On The Electrochemical Etching Of Tips For Scanning Tunneling Microscopy, Nancy Burnham, J. Ibe, P. Bey Jr., S. Brandow, R. Brizzolara, D. Dilella, K. Lee, C. K. Marrian, R. Colton

Nancy A. Burnham

The sharpness of tips used in scanning tunneling microscopy(STM) is one factor which affects the resolution of the STM image. In this paper, we report on a direct‐current (dc) drop‐off electrochemicaletching procedure used to sharpen tips for STM. The shape of the tip is dependent on the meniscus which surrounds the wire at the air–electrolyte interface. The sharpness of the tip is related to the tensile strength of the wire and how quickly the electrochemical reaction can be stopped once the wire breaks. We have found that the cutoff time of the etch circuit has a significant effect on the …


Atomistic Mechanisms And Dynamics Of Adhesion, Nanoindentation, And Fracture, Nancy Burnham, Uzi Landman, Wd Luedtke, Richard Colton Apr 1990

Atomistic Mechanisms And Dynamics Of Adhesion, Nanoindentation, And Fracture, Nancy Burnham, Uzi Landman, Wd Luedtke, Richard Colton

Nancy A. Burnham

Molecular dynamics simulations and atomic force microscopy are used to investigate the atomistic mechanisms of adhesion, contact formation, nanoindentation, separation, and fracture that occur when a nickel tip interacts with a gold surface. The theoretically predicted and experimentally measured hysteresis in the force versus tip-to-sample distance relationship, found upon approach and subsequent separation of the tip from the sample, is related to inelastic deformation of the sample surface characterized by adhesion of gold atoms to the nickel tip and formation of a connective neck of atoms. At small tipsample distances, mechanical instability causes the tip and surface to jump-to-contact, which …


Probing The Surface Forces Of Monolayer Films With An Atomic-Force Microscope, Nancy Burnham, Dawn Dominguez, Robert Mowery, Richard Colton Apr 1990

Probing The Surface Forces Of Monolayer Films With An Atomic-Force Microscope, Nancy Burnham, Dawn Dominguez, Robert Mowery, Richard Colton

Nancy A. Burnham

Using an atomic force microscope (AFM), we have studied the attractive and adhesive forces between a cantilever tip and sample surfaces as a function of sample surface energy. The measured forces systematically increased with surface energy. The AFM is very sensitive; changes in the surface forces (i.e., attraction and adhesion) of monolayer covered samples could be clearly discerned when only the surface group of the monolayer film was changed from -CH3 to -CF3.


New .Mu.2-S2--Coupled, Singly Bridged Double Cubane With The [(Fe4s4cl3)2s]4- Core. The Stepwise Synthesis And Structural Characterization Of (N-Bu4n)2(Ph4p)2[(Fe4s4cl3)2s], Paul Challen, Sang Koo, W. Dunham, D. Coucouvanis Mar 1990

New .Mu.2-S2--Coupled, Singly Bridged Double Cubane With The [(Fe4s4cl3)2s]4- Core. The Stepwise Synthesis And Structural Characterization Of (N-Bu4n)2(Ph4p)2[(Fe4s4cl3)2s], Paul Challen, Sang Koo, W. Dunham, D. Coucouvanis

Paul R. Challen

No abstract provided.


Infrared Spectroelectrochemical Measurements Of The Electrochemical Double Layer: Using Carbon Monoxide As A Double Layer Probe Molecule, Andrea Russell, Stanley Pons, Mark Anderson Feb 1990

Infrared Spectroelectrochemical Measurements Of The Electrochemical Double Layer: Using Carbon Monoxide As A Double Layer Probe Molecule, Andrea Russell, Stanley Pons, Mark Anderson

Mark R. Anderson

The utility of infrared spectroelectrochemical measurements to provide information about the electrochemical interface has been previously demonstrated. The use of small adsorbate molecules as probes of the interface has only recently been investigated. The infrared spectroscopic behavior of adsorbed carbon monoxide in the presence of methanol, ethanol, n-propanol, isopropanol, and ethylene glycol as well as in alcohol/water binary solvent mixtures is presented. Changes in the Stark tuning rate for the adsorbed CO are correlated with solvent dipole reorganization in methanol, ethanol, and n-propanol. No change was observed for ethylene glycol or isopropanol. For the binary mixtures, a dramatic change in …


Structure-Energy Relations For The Aldol Reaction In Nonpolar Media., Edward Arnett, Franklin Fisher, Michael Nichols, Anthony Ribeiro Jan 1990

Structure-Energy Relations For The Aldol Reaction In Nonpolar Media., Edward Arnett, Franklin Fisher, Michael Nichols, Anthony Ribeiro

Michael A Nichols

No abstract provided.


The Vcl Hypothesis Revisited: Patterns Of Femoral Morphology Among Quadrupedal And Saltatorial Prosimian Primates, Robert Anemone Dec 1989

The Vcl Hypothesis Revisited: Patterns Of Femoral Morphology Among Quadrupedal And Saltatorial Prosimian Primates, Robert Anemone

Robert L. Anemone

The descriptive and functional morphology of the postcranium of the vertical clinging and leaping prosimians is of great interest in both adaptational and phylogenetic studies of extant and extinct primates. An analysis of patterns of femoral morphology among quadrupedal and saltatory living prosimians indicates the presence of at least two, and possibly three, distinct femoral adaptations to the demands of an arboreal, saltatory existence. Osteological measurements were taken on 277 postcranial skeletons representing eight prosimian families, with skeletal trunk length (Biegert and Maurer, Folia Primatol. 17:142–156, 1972) used as an estimator of body size in both bivariate and multivariate (discriminant …


Efficient Application Of The Schauder-Tychonoff Theorem To Systems Of Functional Differential Equations, William F. Trench Dec 1989

Efficient Application Of The Schauder-Tychonoff Theorem To Systems Of Functional Differential Equations, William F. Trench

William F. Trench

No abstract provided.


A Note On A Toeplitz Inversion Formula, William F. Trench Dec 1989

A Note On A Toeplitz Inversion Formula, William F. Trench

William F. Trench

No abstract provided.