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Full-Text Articles in Chemistry
A Patching Model For Surface Tension Of Spherical Droplet And Tolman Length. Ii, T.V. Bykov, Xiao Cheng Zeng
A Patching Model For Surface Tension Of Spherical Droplet And Tolman Length. Ii, T.V. Bykov, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
In the framework of density functional theory (DFT), two patching models for the density profile of spherical liquid droplet are developed. The patching is based on analytical expressions of the asymptote of the density profiles. The first model leads to analytic expressions of the Tolman length and the effective rigidity constant, from which the temperature dependence of the Tolman length and effective rigidity constant can be determined. The second model is developed particularly for small spherical droplets, from which the dependence of chemical potential and the surface tension of the droplet on the radius are obtained. The results are compared …
Langmuir Monolayers As Disordered Solids: Disorder And Elastic Fluctuations In Mesophases , Tadeusz Luty, Craig J. Eckhardt, Jacques Lefebvre
Langmuir Monolayers As Disordered Solids: Disorder And Elastic Fluctuations In Mesophases , Tadeusz Luty, Craig J. Eckhardt, Jacques Lefebvre
Craig J. Eckhardt Publications
Ordering in Langmuir monolayer mesophases is examined using an approach based on the elastic theory of crystals. Molecular tails are modeled as ‘‘defects’’ grafted onto a two-dimensional elastic medium and are characterized by elastic dipoles. It is assumed that disorder in the parent, LS, phase is due to competition between local (within a domain) and global (hexagonal arrangement of domains) structure. By treating the LS phase as a mixture of rectangular and/or oblique domains (rectangular and/or oblique defects within the two-dimensional elastic medium), density fluctuations due to elastic interactions between domains are analyzed. The correlation function for the elastic dipoles …
Confined Water In Hydrophobic Nanopores: Dynamics Of Freezing Into Bilayer Ice, Jan Slovak, Kenichiro Koga, Hideki Tanaka, Xiao Cheng Zeng
Confined Water In Hydrophobic Nanopores: Dynamics Of Freezing Into Bilayer Ice, Jan Slovak, Kenichiro Koga, Hideki Tanaka, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Molecular dynamics simulations for a thin film of water confined to a slit nanopore are performed in order to investigate the dynamic process of crystallization of the system. The system upon freezing creates a bilayer ice crystal composed of two layers of hexagonal rings. We perform one simulation at T=257 K during which the system remains a supercooled liquid state, and another one at T=253 K during which the system freezes. Many patterns of molecular arrangement are found upon freezing, and an account is given of the origin of multiple peaks in the distributions of binding energy and …
Imaging Point Defects In A Liquid Environment: A Model Afm Study, Kenichiro Koga, Xiao Cheng Zeng
Imaging Point Defects In A Liquid Environment: A Model Afm Study, Kenichiro Koga, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Effects of the liquid on atomic force microscopy (AFM) imaging are examined for a model system consisting of a hexagonal flake of seven Lennard-Jones (LJ) atoms as a multiatom tip, a monolayer of LJ crystal containing a single point defect as a substrate, and three-site model water as the liquid. A previous simulation [Koutsos et al., Europhys. Lett. 26, 103 (1994)] has shown that the true atomic resolution of a point defect cannot be achieved in vacuum by use of the multiatom tip. Here we examine the feasibility of such atomic resolution when both the tip and substrate are immersed …
Method Of Storing Active Zero Valent Zinc Metal, Reuben D. Rieke
Method Of Storing Active Zero Valent Zinc Metal, Reuben D. Rieke
Chemistry Department: Faculty Publications
A novel Zerovalent Zinc species and an organozinc reagent are disclosed. The Zerovalent Zinc species is directly pro duced by reaction of a reducing agent on a Zinc Salt, preferably Zn(CN). The organozinc regent results from the reaction of the Zerovalent Zinc species and an organic compound having one or more stable anionic leaving groups. These organozinc reagents include a wide spectrum of functional groups in the organic radical, and are useful in a variety of reactions Schemes.
A Patching Model For Surface Tension And The Tolman Length, T.V. Bykov, Xiao Cheng Zeng
A Patching Model For Surface Tension And The Tolman Length, T.V. Bykov, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
In the framework of density functional theory (DFT), a patching model for the density profile of the liquid–vapor interface is developed. The patching is based on analytical expressions of the asymptote of the density profiles. Derived from the model the surface tension of planar liquid–vapor interface as well as the Tolman length can be computed from analytic expressions. Two prototype systems are considered; the Yukawa and the Lennard-Jones. As a result, the temperature dependence of the surface tension as well as the Tolman length are obtained. The results are compared with numerical DFT calculations.
Two-Dimensional Nuclear Magnetic Resonance Correlation Spectroscopy At Zero Field, Ming-Yuan Liao, Gerard S. Harbison
Two-Dimensional Nuclear Magnetic Resonance Correlation Spectroscopy At Zero Field, Ming-Yuan Liao, Gerard S. Harbison
Gerard Harbison Publications
Three methods for two-dimensional correlation nuclear magnetic resonance spectroscopy at zero field are discussed. All three involve coherence transfer via longitudinal polarization, double quantum coherence, or both in parallel. The double quantum pulse sequences exploit the spinor property of spin states. These sequences have been applied to connected Δm=1 transitions, as well as for the indirect detection of forbidden or nearly forbidden Δm.1 transitions.
Nickelocene Adsorption On Single-Crystal Surfaces, D. L. Pugmire, C. M. Woodbridge, S. Root, Marjorie Langell
Nickelocene Adsorption On Single-Crystal Surfaces, D. L. Pugmire, C. M. Woodbridge, S. Root, Marjorie Langell
Marjorie A. Langell Publications
Nickelocene adsorption onto Ag(100), Ni(100), and NiO(100)/Ni(100) surfaces was studied with x-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy at 135 K for monolayer and multilayer coverages of NiCp2. On the relatively inert Ag(100) surface, nickelocene physisorbs molecularly, with its molecular axis perpendicular to the surface plane. Exposure to the reactive Ni(100) surface results in the decomposition of nickelocene into acetylene and acetylene-like fragments and, when this surface is warmed to 273 K, carbide contamination is observed. There is evidence for double-bond carbon on nickelocene-exposed NiO(100), and vinyl and propenyl fragments are the most likely decomposition products …
Intermediate Species Possessing Bent Dna Are Present Along The Pathway To Formation Of A Final Tbp-Tata Complex, Kay M. Parkhurst, Robyn M. Richards, Michael Brenowitz, Lawrence J. Parkhurst
Intermediate Species Possessing Bent Dna Are Present Along The Pathway To Formation Of A Final Tbp-Tata Complex, Kay M. Parkhurst, Robyn M. Richards, Michael Brenowitz, Lawrence J. Parkhurst
Lawrence Parkhurst Publications
Binding of the TATA-binding protein (TBP) to the “TATA” sequences present in the promoters of eukaryotic class II genes is the first step in the sequential assembly of transcription pre-initiation complexes. Myriad structural changes, including severe bending of the DNA, accompany TBP-TATA complex formation. A detailed kinetic study has been conducted to elucidate the mechanistic details of TBP binding and DNA bending. The binding of Saccharomyces cerevisiae TBP to the adenovirus major late promoter (AdMLP) was followed in real-time through a range of temperatures and TBP concentrations using fluorescence resonance energy transfer (FRET) and stopped-flow mixing. The results of association …
Methylene-Only Subspectra In 13C Cpmas Using A New Double Quantum Filtering Sequence, Paola Rossi, Raju Subramanian, Gerard S. Harbison
Methylene-Only Subspectra In 13C Cpmas Using A New Double Quantum Filtering Sequence, Paola Rossi, Raju Subramanian, Gerard S. Harbison
Gerard Harbison Publications
Methodology for the assignment of 13C CPMAS spectra is still in its infancy. Previous methods of CPMAS spectral editing have utilized differences in the strength of the 13C–1H dipolar interaction or the rate and spin thermodynamics of crosspolarization from protons to carbon, to differentiate between quaternary, tertiary, and methylene carbons. We introduce a different approach, which is based on the fact that double-quantum coherence develops between the protons of a methylene group considerably faster than between most other proton spin pairs in an organic solid. We generate this coherence, filter it, convert it back to single …
Surface Composition Of CoXNi1-XO Solid Solutions By X-Ray Photoelectron And Auger Spectroscopies, M. W. Nydegger, G. Couderc, Marjorie Langell
Surface Composition Of CoXNi1-XO Solid Solutions By X-Ray Photoelectron And Auger Spectroscopies, M. W. Nydegger, G. Couderc, Marjorie Langell
Marjorie A. Langell Publications
The surface and bulk compositions of the mixed metal oxide CoxNi1-xO have been compared over the entire range of stoichiometry 0 ≤ x ≤ 1. The materials, which were formed as polycrystalline solid solutions, were shown to be well-ordered and homogeneous in the bulk, but tend to deviate in their surface composition for x > 0.6. Auger and X-ray photoelectron spectroscopy gave comparable results and indicated that the surface composition for samples showing deviation from bulk stoichiometry was compatible with the formation of a spinel-like NiCo2O4 surface phase. XPS binding energies and spectral …
Growth Of Nanotubes For Probe Microscopy Tips, Jason H. Hafner, Chin Li Cheung, Charles M. Lieber
Growth Of Nanotubes For Probe Microscopy Tips, Jason H. Hafner, Chin Li Cheung, Charles M. Lieber
Barry Chin Li Cheung Publications
Carbon nanotubes, which have intrinsically small diameters and high aspect ratios and which buckle reversibly, make potentially ideal structures for use as tips in scanning probe microscopies, such as atomic force microscopy (AFM)1, 2, 3, 4. However, the present method of mechanically attaching nanotube bundles for tip fabrication is time consuming and selects against the smallest nanotubes, limiting the quality of tips. We have developed a technique for growing individual carbon nanotube probe tips directly, with control over the orientation, by chemical vapor deposition (CVD) from the ends of silicon tips. Tips grown in this way may become …
Hydrogen Bonding And Cooperative Effects In Mixed Dimers And Trimers Of Methanol And Trifluoromethanol: An Ab Initio Study, Ruben D. Parra, Xiao Cheng Zeng
Hydrogen Bonding And Cooperative Effects In Mixed Dimers And Trimers Of Methanol And Trifluoromethanol: An Ab Initio Study, Ruben D. Parra, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Ab initio calculations are used to provide information on the mixed dimers and cyclic trimers of the methanol-trifluoromethanol system. In order to better understand the systems, the monomers and their corresponding dimers and trimers are also investigated. Molecular structures and harmonic frequencies are obtained at the B3LYP/6-311++G(d,p) level. Interaction energies are calculated with the MP2 and B3LYP methods using the 6-311++G(d,p), 6-311++G(2d,2p), and 6-311++G(3d,2p) basis sets for the dimers and heterodimers. The 6-311++G(d,p) basis set was used to calculate the …
Molecular Dynamics Study Of A Phase-Separating Fluid Mixture Under Shear Flow, Ryoichi Yamamoto, Xiao Cheng Zeng
Molecular Dynamics Study Of A Phase-Separating Fluid Mixture Under Shear Flow, Ryoichi Yamamoto, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Molecular dynamics simulation is carried out to study domain structures and rheological properties of a two-dimensional phase-separating binary fluid mixture under shear flow. In the early stage of the phase separation, anisotropic composition fluctuations appear immediately after the quench. As the domain grows, the anisotropy in the composition fluctuations increases. The quenched system eventually reaches a dynamical steady state, in which anisotropic domain structures are preserved. In the steady state, the shortest characteristic length scale R⊥ of domains decreases with increasing shear rate γ̇ as R⊥∼γ̇-1/3. Stringlike domain structures are observed in the strong shear regime, …
Formation Free Energy Of Clusters In Vapor-Liquid Nucleation: A Monte Carlo Simulation Study, K.J. Oh, Xiao Cheng Zeng
Formation Free Energy Of Clusters In Vapor-Liquid Nucleation: A Monte Carlo Simulation Study, K.J. Oh, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
The formation free energy of clusters in a supersaturated vapor is obtained by a constrained Monte Carlo technique. A key feature of this approach is to set an upper limit to the size of cluster. This maximum cluster size serves essentially as an extra thermodynamic variable that constrains the system. As a result, clusters larger than the critical cluster of nucleation in the supersaturated vapor can no longer grow beyond the limiting size. Like changing the overall density of the system, changing the maximum cluster size also results in a different supersaturation and thereby a different formation free energy. However, …
Valence-Band Electronic Structure Of Co3O4 Epitaxy On Coo(100), Marjorie Langell, M.D. Anderson, G.A. Carson, L. Peng, S. Smith
Valence-Band Electronic Structure Of Co3O4 Epitaxy On Coo(100), Marjorie Langell, M.D. Anderson, G.A. Carson, L. Peng, S. Smith
Marjorie A. Langell Publications
Valence-band photoemission studies have been performed on a CoO(100) single crystal as it is slowly oxidized under 1×10-4 Torr O2 at 623 K, eventually forming a Co3O4 epitaxial film. The most significant changes occur in 3d-related features, with the peak located at the top of the valence band sharpening and shifting to lower binding energies as the spinel oxide forms. Constant initial-state measurements indicate that Co3O4 contains admixture from neighboring O 2p in its 3d band, as observed for CoO and other monoxide charge-transfer insulators. Unlike the rocksalt …
Thermodynamic Expansion Of Nucleation Free-Energy Barrier And Size Of Critical Nucleus Near The Vapor-Liquid Coexistence, Kenichiro Koga, Xiao Cheng Zeng
Thermodynamic Expansion Of Nucleation Free-Energy Barrier And Size Of Critical Nucleus Near The Vapor-Liquid Coexistence, Kenichiro Koga, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Nucleation free-energy barrier height and size of the critical nucleus are expanded in powers of the chemical potential difference between the supersaturated vapor (or expanded liquid) in the metastable state and the saturated vapor-liquid system in the stable equilibrium state at the same temperature. The coefficients in the expansions are expressed in terms of the thermodynamic properties at the stable equilibrium state. Comparisons with the results obtained from the density-functional calculation for nucleation of the Lennard–Jones fluid show that systematic improvement in predicting properties of the critical nucleus, either liquid droplet or vapor cavity, is achieved by adding the higher …
Langmuir Monolayers As Disordered Solids: Strain-Tilt-Backbone Coupling And Natural Order Parameters For The Swiveling Transitions, Tadeusz Luty, David R. Swanson, Craig J. Eckhardt
Langmuir Monolayers As Disordered Solids: Strain-Tilt-Backbone Coupling And Natural Order Parameters For The Swiveling Transitions, Tadeusz Luty, David R. Swanson, Craig J. Eckhardt
Craig J. Eckhardt Publications
Multistability of Langmuir monolayers, in particular those composed of fatty acids, is reflected by a very rich and complicated phase diagram. We argue that strain-tilt-backbone coupling determines the behavior described by that diagram. Following the solid state approach, we show that a natural order parameter set is defined by thermal averages of spherical harmonics and strain tensor components. In addition, we show that the backbone order parameter can be conveniently represented by an elastic dipole tensor. Treating Langmuir monolayers as disordered solids, we have derived an orientational entropy contribution to the free energy. The swiveling transition between L2 ( …
Effect Of Uniform Electric Field On Homogeneous Vapor–Liquid Nucleation And Phase Equilibria. Ii. Extended Simple Point Charge Model Water, G.T. Gao, K.J. Oh, Xiao Cheng Zeng
Effect Of Uniform Electric Field On Homogeneous Vapor–Liquid Nucleation And Phase Equilibria. Ii. Extended Simple Point Charge Model Water, G.T. Gao, K.J. Oh, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
The effects of a uniform electric field on homogeneous vapor–liquid nucleation of the extended simple point charge (SPC/E) model water have been simulated. A grand canonical Monte Carlo simulation approach [I. Kusaka et al., J. Chem. Phys. 108, 3416 (1998)], which directly gives the equilibrium distribution of physical clusters, is employed to calculate the formation free energy of the SPC/E water cluster. The results show that the formation free energy is lowered in a uniform field if the chemical potential of the supersaturated vapor is fixed; in this case, the field enhances the rate of nucleation. However, if the vapor …
Capillary Electrophoresis/Tandem Mass Spectrometry With Array Detection, L.J. Deterding, K.B. Tomer, J.M.Y. Wellemans, Ronald Cerny, M.L. Gross
Capillary Electrophoresis/Tandem Mass Spectrometry With Array Detection, L.J. Deterding, K.B. Tomer, J.M.Y. Wellemans, Ronald Cerny, M.L. Gross
Ronald Cerny Publications
Mixtures of standard compounds of biological interest were analyzed by capillary electrophoresis in conjunction with tandem four sector mass spectrometry (MS/MS) using an array detector. Capillary electrophoresis offers extremely high separation efficiencies while array detection allows for the simultaneous acquisition of a large fraction of a tandem mass spectrum and high utilization of the sample ions produced. Consequently, improvements in sensitivity and structural information were observed for the combined techniques in comparison to similar measurements with a four-sector and a single-point detector. Coaxial continuous-flow fast atom bombardment was used to create (M + H) precursor ions of the separated analyses …
Affinity Chromatography: A Review Of Clinical Applications, David S. Hage
Affinity Chromatography: A Review Of Clinical Applications, David S. Hage
David Hage Publications
Affinity chromatography is a type of liquid chromatography that makes use of biological-like interactions for the separation and specific analysis of sample components. This review describes the basic principles of affinity chromatography and examines its use in the testing of clinical samples, with an emphasis on HPLCbased methods. Some traditional applications of this approach include the use of boronate, lectin, protein A or protein G, and immunoaffinity supports for the direct quantification of solutes. Newer techniques that use antibody-based columns for on- or off-line sample extraction are examined in detail, as are methods that use affinity chromatography in combination with …
Classification Of Explosives Transformation Products In Plant Tissue, Steven L. Larson, Robert P. Jones, Lynn Escalon, Don Parker
Classification Of Explosives Transformation Products In Plant Tissue, Steven L. Larson, Robert P. Jones, Lynn Escalon, Don Parker
US Army Corps of Engineers
Explosives contamination in surface or groundwater used for the irrigation of food crops and phytoremediation of explosives-contaminated soil or water using plant-assisted biodegradation have brought about concerns as to the fate of explosives in plants. Liquid scintillation counting, high-performance liquid chromatography, and gel permeation chromatography were utilized to characterize explosives (hexahydro-1,3,5-trinitro-1,3,5-triazine and trinitrotoluene) and their metabolites in plant tissues obtained from three separate studies. Analyzing tissues of yellow nutsedge (Cyperus esculentus), corn (Zea mays), lettuce (Lacuta sativa), tomato (Lyopersicum esculentum), radish (Raphanus sativus), and parrot feather (Myriophyllum aquaticum) …