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Articles 991 - 1020 of 1553

Full-Text Articles in Chemistry

Ultrasonically Initiated Free Radical-Catalyzed Emulsion Polymerization Of Methyl Methacrylate (Ii): Radical Generation Process Studies And Kinetic Data Interpretation, H. C.Joe Chou, James O. Stoffer May 1999

Ultrasonically Initiated Free Radical-Catalyzed Emulsion Polymerization Of Methyl Methacrylate (Ii): Radical Generation Process Studies And Kinetic Data Interpretation, H. C.Joe Chou, James O. Stoffer

Chemistry Faculty Research & Creative Works

In the previous work, we have studied the effects of acoustic intensity, argon gas flow rate, surfactant concentration, and initial monomer concentration on polymerization rate, polymer particle number, and polymer molecular weight in the ultrasonically initiated emulsion polymerization of methyl methacrylate. In this study, radical trapping experiments were used to investigate the effect of acoustic intensity, argon gas flow rate, and sodium lauryl sulfate concentration on the extent of free radical generation in aqueous sodium dodecyl sulfate solutions. In these radical trapping experiments, aqueous solutions of sodium lauryl sulfate were ultrasonically irradiated in the presence of a radical scavenger. The …

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Plant And Soil Enantioselective Biodegradation Of Racemic Phenoxyalkanoic Herbicides, J. M. Schneiderheinze, Daniel W. Armstrong, Alain Berthod May 1999

Plant And Soil Enantioselective Biodegradation Of Racemic Phenoxyalkanoic Herbicides, J. M. Schneiderheinze, Daniel W. Armstrong, Alain Berthod

Chemistry Faculty Research & Creative Works

The biodegradation of the chiral phenoxyalkanoic herbicides 2-(2,4- dichlorophenoxy)propionic aid (2,4-DP) and 2-(4-chloro-2- methylphenoxy)propionic acid (MCPP) was investigated using enantioselective HPLC and chiroptical detection. Racemic mixtures of 2,4-DP and MCPP were applied to three species of turf grass, four species of broadleaf weeds, and soil. Preferential degradation of the S- (-) enantiomer of each herbicide was observed in most species of broadleaf weeds and soil, while the degradation in all species of grass occurred without enantioselectivity. The biodegradation in all systems appeared to follow pseudo first-order kinetics with the fastest degradation occurring in broadleaf weeds, followed by the grasses. The …

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Planarity Of Para Hexaphenyl, Suchismita Guha, Wilhelm Graupner, Roland Resel, Meera Chandrasekhar, H. R. Chandrasekhar, Rainer Glaser, Günther Leising May 1999

Planarity Of Para Hexaphenyl, Suchismita Guha, Wilhelm Graupner, Roland Resel, Meera Chandrasekhar, H. R. Chandrasekhar, Rainer Glaser, Günther Leising

Chemistry Faculty Research & Creative Works

We present experimental and theoretical findings on the geometry of polycrystalline para hexaphenyl via Raman scattering. The planarity of the molecule is affected by hydrostatic pressure and temperature. Our studies indicate that the potential energy curve which governs the torsional motion between neighboring phenyl rings is "W" shaped. We determine the activation energy to promote the molecule from a nonplanar to a planar state to be 0.04 eV, in good agreement with our quantum chemical calculations. From the relative intensities of the 1280cm-1 to the 1220cm-1 Raman modes we show that high pressure planarizes the molecules, modifying the …

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Liquid Reaction Apparatus For Surface Analysis, Charles C. Chusuei, T. S. Murrell, J. S. Corneille, M. G. Nooney, S. M. Vesecky, L. R. Hossner, D. W. Goodman May 1999

Liquid Reaction Apparatus For Surface Analysis, Charles C. Chusuei, T. S. Murrell, J. S. Corneille, M. G. Nooney, S. M. Vesecky, L. R. Hossner, D. W. Goodman

Chemistry Faculty Research & Creative Works

A design for a liquid reaction apparatus is described which allows surfaces prepared in ultrahigh vacuum (UHV) to be reacted with solutions of a wide pH range under dry nitrogen atmosphere and subsequently returned to UHV for surface analysis.

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In Situ Measurement Of The Aerosol Size Distribution In Stratospheric Solid Rocket Motor Exhaust Plumes, Martin N. Ross, Philip D. Whitefield, Donald E. Hagen, Alfred R. Hopkins Apr 1999

In Situ Measurement Of The Aerosol Size Distribution In Stratospheric Solid Rocket Motor Exhaust Plumes, Martin N. Ross, Philip D. Whitefield, Donald E. Hagen, Alfred R. Hopkins

Chemistry Faculty Research & Creative Works

The concentration and size distribution of aerosol in the stratospheric exhaust plumes of two Space Shuttle rockets and one Titan IV rocket were measured using a two component aerosol sampling system carried aboard a WB‐57F aircraft. Aerosol size distribution in the 0.01 µm to 4 µm diameter size range was measured using a two component sampling system. The measured distributions display a trimodal form with modes near 0.005 µm, 0.09 µm, and 2.03 µm and are used to infer the relative mass fractionation among the three modes. While the smallest mode has been estimated to contain as much as 10% …

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Magnetic And Mössbauer Spectral Study Of Mixed Valent La₀.₂Sr₀.₈Cu₀.₂Fe₀.₈O2.68 And Related Perovskites, Gary J. Long, Dimitri Hautot, Amitabh Mohan, Ingeborg Kaus, Harlan U. Anderson, Fernande Grandjean Apr 1999

Magnetic And Mössbauer Spectral Study Of Mixed Valent La₀.₂Sr₀.₈Cu₀.₂Fe₀.₈O2.68 And Related Perovskites, Gary J. Long, Dimitri Hautot, Amitabh Mohan, Ingeborg Kaus, Harlan U. Anderson, Fernande Grandjean

Chemistry Faculty Research & Creative Works

The La0.2Sr0.8Cu1-xFexO 3-δ perovskites are important because they are mixed electron and oxygen anion conductors and thus are able to serve as dense oxygen separation membranes. In order to better understand the mechanism for this separation a Mössbauer spectral study has been carried out to determine the ratio of iron(III) to iron(IV) in these mixed valent compounds. The Mössbauer spectra of La0.2Sr0.8Cu0.2Fe0.8O 3-δ obtained between 4.2 and 78 K reveal that its Néel temperature is ~75 K and the two well-resolved magnetic sextets observed …

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Structural, Magnetic, And Mössbauer Spectral Properties Of Pr₂Fe₁₇Hₓ Where X Is 1, 2, And 3, Fernande Grandjean, Dimitri Hautot, Gary J. Long, Olivier Isnard, Salvatore Miraglia, Daniel Fruchart Apr 1999

Structural, Magnetic, And Mössbauer Spectral Properties Of Pr₂Fe₁₇Hₓ Where X Is 1, 2, And 3, Fernande Grandjean, Dimitri Hautot, Gary J. Long, Olivier Isnard, Salvatore Miraglia, Daniel Fruchart

Chemistry Faculty Research & Creative Works

The 295 K unit cell parameters of Pr2Fe17Hx, where x is 0, 1, 2, and 3, have been determined by x-ray diffraction. Upon hydrogenation, the unit cell volume expands anisotropically with a 1.2% expansion of the a axis and no expansion of the c axis for x=3. The Curie temperatures are 286, 374, 440, and 484 K, for x=0, 1, 2, and 3, respectively. The Mössbauer spectra have been measured between 4.2 and 295 K, and the spectra of Pr2Fe17H and Pr2Fe17H2, obtained above …

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Atomic Structure And Magnetism Of Ordered And Disordered Al₀.₅Fe₀.₅₋ₓmnₓ Alloys, V. G. Harris, D. J. Fatemi, K. B. Hathaway, Q. Huang, Amitabh Mohan, Gary J. Long Apr 1999

Atomic Structure And Magnetism Of Ordered And Disordered Al₀.₅Fe₀.₅₋ₓmnₓ Alloys, V. G. Harris, D. J. Fatemi, K. B. Hathaway, Q. Huang, Amitabh Mohan, Gary J. Long

Chemistry Faculty Research & Creative Works

The equiatomic FeAl alloy has been modified by partial substitution of Mn for Fe, and its magnetic and structural properties investigated by neutron diffraction (ND), x-ray absorption fine structure (XAFS) spectroscopy, Mössbauer spectroscopy (MS), and SQUID magnetometry both for the ordered (B2) and disordered states. The unit cell volume is measured to increase linearly with Mn concentration. XAFS measurements indicate local structural displacements occur at the Mn sites in both ordered and disordered states that may act to frustrate long-range magnetic order (LRMO). Although MS and ND show no evidence of LRMO, SQUID magnetometry indicates an induced movement in the …

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Electron Affinities Of The Oxides Of Aluminum, Silicon, Phosphorus, Sulfur, And Chlorine, Nicole R. Brinkmann, Gregory S. Tschumper, Henry F. Schaefer Apr 1999

Electron Affinities Of The Oxides Of Aluminum, Silicon, Phosphorus, Sulfur, And Chlorine, Nicole R. Brinkmann, Gregory S. Tschumper, Henry F. Schaefer

Chemistry Faculty Research & Creative Works

The adiabatic electron affinities of five second row atoms (Al, Si, P, S, Cl) and their monoxides and dioxides were determined using six different densities functional or hybrid Hartree-Fock/density functional methods. The 15 species selected form a convenient closed set for which reliable experimental electron affinities exist for 13 of the species. Zero-point vibrational energy corrected electron affinities are also reported. Equilibrium geometries and vibrational frequencies were determined with each density functional method. The method based on the Becke exchange functional and the Lee-Yang-Parr correlation (BLYP) functional reproduced the experimental electron affinities most accurately, having an average absolute error of …

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Activated Carbon Produced From Agricultural Residues, Daniel W. Armstrong, V. J. Flanigan, William Joseph James, Jui-Lung Li, Kimber L. Rundlett Mar 1999

Activated Carbon Produced From Agricultural Residues, Daniel W. Armstrong, V. J. Flanigan, William Joseph James, Jui-Lung Li, Kimber L. Rundlett

Chemistry Faculty Research & Creative Works

A process for producing activated carbon from agricultural residues by heating the residues to a temperature in the range of about 250° C. to about 550° C. to volatilize organic compounds in the residues and to carbonize the residues and further heating to activate the carbonized residues. Activated carbon produced from agricultural residues.

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Infrared Cavity Ringdown Spectroscopy Of Methanol Clusters: Single Donor Hydrogen Bonding, R. A. Provencal, J. B. Paul, K. Roth, C. Chapo, R. N. Casaes, R. J. Saykally, G. S. Tschumper, H. F. Schaefer Mar 1999

Infrared Cavity Ringdown Spectroscopy Of Methanol Clusters: Single Donor Hydrogen Bonding, R. A. Provencal, J. B. Paul, K. Roth, C. Chapo, R. N. Casaes, R. J. Saykally, G. S. Tschumper, H. F. Schaefer

Chemistry Faculty Research & Creative Works

Infrared cavity ringdown laser absorption spectroscopy has been used to study the O-H stretching vibrations of jet-cooled methanol clusters in direct absorption. Rovibrational bands for (CH3OH)2, (CH3OH)3, and (CH3OH)4 have been measured. Both bonded and free O-H stretches were measured for the dimer, indicating that its structure is linear. Five bands were assigned to the methanol trimer, indicating the presence of a second cyclic isomer in the molecular beam. A detailed study of the free O-H stretching region shows that methanol clusters larger than dimer must exist in cyclic …

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Macrocyclic Antibiotics As Separation Agents, Daniel W. Amstrong Feb 1999

Macrocyclic Antibiotics As Separation Agents, Daniel W. Amstrong

Chemistry Faculty Research & Creative Works

Macrocyclic antibiotics having ring structures with at least 10 members act as separation agents in crystallization, precipitation, filtration, electrophoresis and chromatography. The macrocyclic antibiotics include ansamacrolides, macrolides, marocyclic peptides, polyenes and derivatives thereof. The process has been found to be especially advantageous for separation of optical isomers by electrophoresis and chromatography.

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Enantiomeric Composition Of Nornicotine, Anatabine, And Anabasine In Tobacco, Daniel W. Armstrong, Xiande Wang, Jauh Tzuoh Lee, Yan Song Liu Jan 1999

Enantiomeric Composition Of Nornicotine, Anatabine, And Anabasine In Tobacco, Daniel W. Armstrong, Xiande Wang, Jauh Tzuoh Lee, Yan Song Liu

Chemistry Faculty Research & Creative Works

Literature reports on the optical purity of the minor alkaloids in tobacco leaf and its products often contradict one another. The enantiomeric compositions of nornicotine, anatabine, and anabasine were measured using gas chromatography/mass spectrometry (GC/MS) (with a chiral stationary phase) in three types of tobacco leaf (Burley, Turkish, and Virginia); three types of smokeless tobacco (loose-leaf, dry snuff, and moist snuff); and four types of cigarettes. Regardless of the tobacco type or product, anabasine always had the highest relative percentage of the minor (R)-(+)-enantiomeric component (between 40 and 46% vs. 54-60% of the (S)-(-)-enantiomer). Of the four common tobacco alkaloids, …

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X-Ray Absorption, Neutron Diffraction, And Mössbauer Effect Studies Of Mnzn-Ferrite Processed Through High-Energy Ball Milling, D. J. Fatemi, V. G. Harris, Mingxing Chen, Satish K. Malik, William B. Yelon, Gary J. Long, Amitabh Mohan Jan 1999

X-Ray Absorption, Neutron Diffraction, And Mössbauer Effect Studies Of Mnzn-Ferrite Processed Through High-Energy Ball Milling, D. J. Fatemi, V. G. Harris, Mingxing Chen, Satish K. Malik, William B. Yelon, Gary J. Long, Amitabh Mohan

Physics Faculty Research & Creative Works

MnZn-ferrite has been prepared via high-energy ball milling of elemental oxides MnO, ZnO, and α-Fe2O3. Neutron diffraction measurements suggest a high density of vacancies in a spinel structure. The spinel phase appears to comprise 99.8 wt % of the material in the sample milled for 40 h, with the remainder attributable to unreacted α-Fe2O3. The x-ray absorption near-edge structure was analyzed to provide an understanding of the charge state of the constituent Fe ions. This analysis reveals about 2/3 of Fe cations to be trivalent, increasing to about 3/4 after a 5 …

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1-Hydroxyethyl-2,2′-Biimidazole, Geng Lin, Harvest L. Collier, Russell G. Baughman Jan 1999

1-Hydroxyethyl-2,2′-Biimidazole, Geng Lin, Harvest L. Collier, Russell G. Baughman

Chemistry Faculty Research & Creative Works

The two imidazole rings in the title compound, C8H10N4O, are almost coplanar, having an angle of 2.3 (2)° about the C-C bond connecting the rings. the conformation adopted is such that the nitrogen substituents (-H and -CH2CH2OH) are in a trans orientation. the molecules are connected by intermolecular O-H. . .O and N-H. . .N hydrogen bonds to yield an arrangement of pairs of molecules reminiscent of side-by-side stacks of crinkled ribbon.

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Soft X-Ray Photochemistry At The L₂,₃-Edges In K₃[Fe(Cn)₆], [Co(Acac)₃] And [Cp₂Fe][Bf₄], David Collison, Catherine David Garner, Catherine M. Mcgrath, J. Fred Willem Mosselmans, Mark D. Roper, Jon M. W Seddon, Ekkehard Sinn, Nigel A. Young Jan 1999

Soft X-Ray Photochemistry At The L₂,₃-Edges In K₃[Fe(Cn)₆], [Co(Acac)₃] And [Cp₂Fe][Bf₄], David Collison, Catherine David Garner, Catherine M. Mcgrath, J. Fred Willem Mosselmans, Mark D. Roper, Jon M. W Seddon, Ekkehard Sinn, Nigel A. Young

Chemistry Faculty Research & Creative Works

Soft X-ray photoreduction has been observed in K3[Fe(CN)6], [Co(acac)3] and [Cp2Fe][BF4].

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Thermal Characterization Of Pmma Thin Films On Silica Using Modulated Differential Scanning Calorimetry, Crystal E. Porter, Frank D. Blum Jan 1999

Thermal Characterization Of Pmma Thin Films On Silica Using Modulated Differential Scanning Calorimetry, Crystal E. Porter, Frank D. Blum

Chemistry Faculty Research & Creative Works

The number of studies of thin polymer films has increased over recent years as technological processes incorporate the use of nanomaterials. An enhanced understanding of these films would enable us to predict bound-polymer behavior and thus improve the efficiency of processes and the quality of products. This is especially true as the thickness of the films approach molecular dimensions. The glass transition temperature of a polymer is one of the most important properties for characterization because it indicates how the polymer might perform macroscopically. when a polymer is confined, such as one the surface of a substrate, its behavior is …

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Preparation Of Phase Homogeneous Mn-Zn Ferrite Powder By Spray Pyrolysis, Xinyu Zhao, Baicun Zheng, Hongchen Gu, Chunzhong Li, Shi C. Zhang, P. D. Ownby Jan 1999

Preparation Of Phase Homogeneous Mn-Zn Ferrite Powder By Spray Pyrolysis, Xinyu Zhao, Baicun Zheng, Hongchen Gu, Chunzhong Li, Shi C. Zhang, P. D. Ownby

Materials Science and Engineering Faculty Research & Creative Works

Two kinds of aqueous precursor solutions are used to synthesize Mn-Zn ferrite powders: (i) nitrate (NO) precursor-derived from solutions of Mn(NO3)2, Zn(NO3)2, and Fe(NO3)3; and (ii) acetate (AC) precursor-derived from solutions of Mn(CH3COOO)2, Zn(CHCH3COOO)2, and Fe(NO3)3. The composition of the powders synthesized from the precursor AC is very uniform, whereas powders derived from the precursor NO have Mn and Zn segregated on the particle surfaces. In addition, the powders synthesized from precursor AC are solid spherical …

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Avoparcin, A New Macrocyclic Antibiotic Chiral Run Buffer Additive For Capillary Electrophoresis, K. Helen Ekborg-Ott, Gina A. Zientara, Jeffrey M. Schneiderheinze, Kyung Gahm, Daniel W. Armstrong Jan 1999

Avoparcin, A New Macrocyclic Antibiotic Chiral Run Buffer Additive For Capillary Electrophoresis, K. Helen Ekborg-Ott, Gina A. Zientara, Jeffrey M. Schneiderheinze, Kyung Gahm, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Avoparcin, like vancomycin, teicoplanin, and ristocetin A, belongs to the family of macrocyclic glycopeptide antibiotics. These antibiotics have all been used as effective chiral selectors for capillary electrophoresis (CE), thin-layer chromatography (TLC), and high-performance liquid chromatography (HPLC). The present work focuses on avoparcin, which has been shown to be an excellent chiral selector for the CE enantioseparation of many N-blocked amino acids, as well as several anti-inflammatory drugs of pharmaceutical importance. The use of avoparcin as a chiral run buffer additive in CE is discussed, as well as the effects of changing experimental parameters, like avoparcin concentration, pH, organic modifiers, …

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Hormone Anchored Metal Complexes 1: Synthesis, Structure, Spectroscopy And In Vitro Antitumor Activity Of Testosterone Acetate: Thiosemicarbazone And Its Metal Complexes, Anupa Murugkar, Bindu Unnikrishnan, Subhash B. Padhye, Ramesh Ramchandra Bhonde, Simon J. Teat, Evangelia Triantafillou, Ekkehard Sinn Jan 1999

Hormone Anchored Metal Complexes 1: Synthesis, Structure, Spectroscopy And In Vitro Antitumor Activity Of Testosterone Acetate: Thiosemicarbazone And Its Metal Complexes, Anupa Murugkar, Bindu Unnikrishnan, Subhash B. Padhye, Ramesh Ramchandra Bhonde, Simon J. Teat, Evangelia Triantafillou, Ekkehard Sinn

Chemistry Faculty Research & Creative Works

Testosterone acetate thiosemicarbazone (TATSC, 17-β-hydroxyandrost-4-one acetate thiosemicarbazone) was synthesized and characterized by single crystal X-ray structure determination. The copper and platinum complexes of this steroid derivative were synthesized and characterized by spectroscopy and electrochemiatry. The in vitro activity of these compounds against human breast cancer cell line MCF-7 was tested. The highest activity was found for the [Pt(TATSC)Cl 2] followed by [Cu(TATSC)Cl 2] and the ligand in compariosn with cisplatin.

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Dynamics Of Acrylic Coupling Agents At Interfaces Of Composites, Hyoryoon Jo, Frank D. Blum Jan 1999

Dynamics Of Acrylic Coupling Agents At Interfaces Of Composites, Hyoryoon Jo, Frank D. Blum

Chemistry Faculty Research & Creative Works

Most applications of polymers involve composites, wherein a polymer is used in conjunction with another material, typically a solid fiber or filler. A coupling agent can enhance the adhesion between a polymer matrix and an inorganic filler. Organofunctional silanes, RSiX are often used as coupling agents. The methoxy or ethoxy group, X, can typically be hydrolyzed with water and an acid or a base catalyst in a protic solvent. The silanol groups of a hydrolyzed coupling agent can condense with other silanol groups from a glass surface, while the alkyl group, R, blends physically or bonds chemically to the polymer …

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Separation Of Enantiomers By Capillary Electrophoresis Using Pentosan Polysulfate, Xiande Wang, Jauh Tzuoh Lee, Daniel W. Armstrong Jan 1999

Separation Of Enantiomers By Capillary Electrophoresis Using Pentosan Polysulfate, Xiande Wang, Jauh Tzuoh Lee, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Pentosan polysulfate, a semisynthetic polysaccharide, was employed as a chiral un buffer additive in capillary electrophoresis. Twenty-eight racemic analytes were resolved. The separations were successful only at low pH when the analytes were significantly protonated. This suggests that ionic interactions were the dominant associative interactions between the anionic pentosan polysulfate and the positively charged analytes. Compared to other linear, carbohydrate-based chiral selectors (i.e., chondroitin sulfates, heparin and dextran sulfate) pentosan polysulfate has some characteristics common of anionic polysaccharides; yet it has several differences in its structure and properties which account for its unusual enantioselectivity. The effects of pH, concentration of …

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Magnetic And Crystallographic Properties Of Lani₅₋ₓfex, C. Tan, Oran Allan Pringle, Mingxing Chen, William B. Yelon, J. Gebhardt, Naushad Ali, C. Y. Tai, G. K. Marasinghe, George Daniel Waddill, William Joseph James Jan 1999

Magnetic And Crystallographic Properties Of Lani₅₋ₓfex, C. Tan, Oran Allan Pringle, Mingxing Chen, William B. Yelon, J. Gebhardt, Naushad Ali, C. Y. Tai, G. K. Marasinghe, George Daniel Waddill, William Joseph James

Physics Faculty Research & Creative Works

No abstract provided.

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The Display Of Photographic-Quality Images On The Web: A Comparison Of Two Technologies, Chiang S. Jao, Daniel B. Hier, Steven U. Brint Jan 1999

The Display Of Photographic-Quality Images On The Web: A Comparison Of Two Technologies, Chiang S. Jao, Daniel B. Hier, Steven U. Brint

Chemistry Faculty Research & Creative Works

Downloading Medical Images on the Web Creates Certain Compromises. the Tradeoff is between Higher Resolution and Faster Download Times. as Resolution Increases, Download Times Increase. High-resolution (Photographic Quality) Electronic Images Can Potentially Play a Key Role in Medical Education and Patient Care. on the Internet, Images Are Typically Formatted as Graphics Interchange Format (GIF) or the Joint Photographic Experts Group (JPEG) Flies. However, These Formats Are Associated with Considerable Data Loss in Both Color Depth and Image Resolution. Furthermore, These Images Are Available in a Single Resolution and Have No Capability of Allowing the User to Adjust Resolution as Needed. …

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Effect Of Temperature On Retention Of Enantiomers Of Β-Methyl Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong, Géza Tóth, Dirk Tourwé Dec 1998

Effect Of Temperature On Retention Of Enantiomers Of Β-Methyl Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong, Géza Tóth, Dirk Tourwé

Chemistry Faculty Research & Creative Works

The isocratic retention of enantiomers of β-methyl amino acids (β-methyltyrosine, β-methylphenylalanine, β-methyltryptophan and β-methyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) was studied on a teicoplanin-containing chiral stationary phase at different temperatures and at different mobile phase compositions, using the reversed-phase mode. With variation of both mobile phase composition and temperature, almost baseline separations could be achieved for all four enantiomers of sterically hindered amino acids. The retention factors and selectivity factors for the enantiomers of all investigated compounds decreased with increasing temperature. The natural logarithms of the retention factors (ln k) of the investigated compounds depended linearly on the inverse of temperature (1/T). van 't …

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Evaluation Of The Macrocyclic Antibiotic Avoparcin As A New Chiral Selector For Hplc, K. Helen Ekborg-Ott, John P. Kullman, Xiande Wang, Kyung Gahm, Lingfeng He, Daniel W. Armstrong Oct 1998

Evaluation Of The Macrocyclic Antibiotic Avoparcin As A New Chiral Selector For Hplc, K. Helen Ekborg-Ott, John P. Kullman, Xiande Wang, Kyung Gahm, Lingfeng He, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Avoparcin is a macrocyclic glycopeptide antibiotic structurally related to vancomycin, teicoplanin, and ristocetin A. When attached to 5-μm spherical silica gel, the avoparcin proved to be an effective chiral stationary phase (CSP) that could be used in the reversed-phase, normal- phase, and polar-organic modes. The avoparcin CSP was complimentary to the other macrocyclic glycopeptide CSPs in that it could resolve some racemates that the others could not, and vice versa. Some important compounds resolved on the avoparcin CSP include verapamil, thyroxine, mephenytoin, and 2- imidazolidone-4-carboxylic acid. The use of this CSP and the optimization of separations on it are discussed. …

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Bubble Fractionation Of Enantiomers From Solution Using Molecularly Imprinted Polymers As Collectors, Daniel W. Armstrong, J. M. Schneiderheinze, Y. S. Hwang, B. Sellergren Sep 1998

Bubble Fractionation Of Enantiomers From Solution Using Molecularly Imprinted Polymers As Collectors, Daniel W. Armstrong, J. M. Schneiderheinze, Y. S. Hwang, B. Sellergren

Chemistry Faculty Research & Creative Works

Adsorptive bubble separation methods have been used to enrich components from both heterogeneous and homogeneous solutions. These methods are particularly effective for processing large solution volumes at low cost Previous work demonstrated that chiral, surface-active collectors could be used to enrich enantiomers from homogeneous solution in a foam fractionation process. In a significant extension of this work, the use of highly selective molecularly imprinted polymers (MIPs) and heterogeneous solutions for the bubble flotation of enantiomers was evaluated. The high selectivity and ease of recycling of the MIP make this a potentially powerful approach for process-scale separations from large-volume bulk solutions. …

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Effects Of N-Acetylcysteine And 2,3-Dimercaptosuccinic Acid On Lead Induced Oxidative Stress In Rat Lenses, Rachel Neal, Katherine Cooper, Nuran Ercal, Hande Gürer-Orhan Sep 1998

Effects Of N-Acetylcysteine And 2,3-Dimercaptosuccinic Acid On Lead Induced Oxidative Stress In Rat Lenses, Rachel Neal, Katherine Cooper, Nuran Ercal, Hande Gürer-Orhan

Chemistry Faculty Research & Creative Works

Lead (Pb) is known to disrupt the pro-oxidant/anti-oxidant balance of tissues which leads to biochemical and physiological dysfunction. The present study investigated the previous termeffectsnext term of exposure on the redox status of the lenses of Fisher 344 rats and examined whether antioxidant or chelator administration reversed these changes. Animals were given 5 weeks of 2000 ppm Pb exposure followed by 1 week of either antioxidant, chelator or distilled water administration. Glutathione (GSH) and cysteine (CYS) levels decreased in the Pb-exposed group. N-previous termacetylcysteinenext term or 2,3-dimercaptopsuccinic previous termacidnext term (Succimer) supplementation following Pb intoxication resulted in increases in the …

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Highly Enantioselective Hplc Separations Using The Covalently Bonded Macrocyclic Antibiotic, Ristocetin A, Chiral Stationary Phase, K. Helen Ekborg-Ott, Youbang Liu, Daniel W. Armstrong Aug 1998

Highly Enantioselective Hplc Separations Using The Covalently Bonded Macrocyclic Antibiotic, Ristocetin A, Chiral Stationary Phase, K. Helen Ekborg-Ott, Youbang Liu, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

The macrocyclic glycopeptide, ristocetin A, was covalently bonded to a silica gel support and evaluated as a liquid chromatographic (LC) chiral stationary phase (CSP). Over 230 racemates were resolved in either the reversed-phase mode, the normal-phase mode, or the polar-organic mode. The retention behavior and selectivity of this CSP were examined in each mode. Optimization of separations on this column is discussed. The ristocetin A CSP appeared to be complimentary to other glycopeptide CSPs (i.e., vancomycin and teicoplanin). Column stability was excellent. The CSP was not irreversibly altered when going from one mobile phase mode to another.

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Neutron Diffraction And Mössbauer Spectral Study Of Nd₂Fe₁₆Ti And Its Nitride, Fernande Grandjean, Peter C. Ezekwenna, Gary J. Long, Oran Allan Pringle, P. H. L'Héritier, Mohamed Ellouze, H. P. Luo, William B. Yelon Aug 1998

Neutron Diffraction And Mössbauer Spectral Study Of Nd₂Fe₁₆Ti And Its Nitride, Fernande Grandjean, Peter C. Ezekwenna, Gary J. Long, Oran Allan Pringle, P. H. L'Héritier, Mohamed Ellouze, H. P. Luo, William B. Yelon

Chemistry Faculty Research & Creative Works

The 295 K powder neutron diffraction patterns and the temperature dependence of the Mössbauer spectra of Nd2Fe17-xTix and Nd2Fe17-xTixNx have been measured. A Rietveld refinement of the neutron diffraction patterns yields the Nd2Fe16.32Ti0.68 and Nd2Fe16.32Ti0.68N2.7 stoichiometries for the two compounds and indicates that titanium occupies only the 6c crystallographic site and nitrogen only the 9e site in the rhombohedral Th2Zn17 structure. The insertion of interstitial nitrogen into Nd2Fe16.32Ti0.68 …

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