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Chemistry Faculty Research & Creative Works

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Articles 781 - 810 of 939

Full-Text Articles in Chemistry

Resolution Of Enantiomeric Hydrocarbon Biomarkers Of Geochemical Importance, Daniel W. Armstrong, Yubing Tang, Janusz Zukowski Dec 1991

Resolution Of Enantiomeric Hydrocarbon Biomarkers Of Geochemical Importance, Daniel W. Armstrong, Yubing Tang, Janusz Zukowski

Chemistry Faculty Research & Creative Works

Chlral isoprenoid and hydroaromatic compounds occur in all crude oils, coals, shales, and most sediments. Many of these compounds are referred to as biological markers since they are thought to be derived from biological sources and their presence, relative concentrations, or stereochemistry can provide information as to a geological deposit's age, maturity, diagenetic history, and so forth. Because of the previous lack of effective and efficient analytical methodologies for resolving hydrocarbon enantiomers, the stereochemical information encoded in these molecules is largely untouched. A series of derivatized α-, β-, and γ-cyclodextrin chiral stationary phases (CSPs) were used for the gas chromatographic …

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Change Of Magnetic Properties Of Th₂Fe₁₇ Due To Interstitial Solution Of C And N, T. H. Jacobs, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. Buschow Nov 1991

Change Of Magnetic Properties Of Th₂Fe₁₇ Due To Interstitial Solution Of C And N, T. H. Jacobs, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. Buschow

Chemistry Faculty Research & Creative Works

The changes in magnetic and crystallographic properties in the series Th2Fe17Cx and Th2Fe 17Nx have been studied. The changes in the latter series were also studied by 57Fe Mössbauer spectroscopy. The ultimate enhancements of the saturation moments in these series are 13% and 24%, respectively. This is much larger than observed previously in the corresponding rare-earth compounds, although the Curie temperature enhancements are of comparable magnitude. In the Th-Fe-C system a novel compound of the BaCd 11 type was found, having a Curie temperature around 370 K.

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A Mössbauer-Effect Study Of A Series Of R₂Fe₁₄C Hard Magnetic Materials, Gary J. Long, Oran Allan Pringle, Gaya Kanishka Marasinghe, Fernande Grandjean, K. H. Buschow Apr 1991

A Mössbauer-Effect Study Of A Series Of R₂Fe₁₄C Hard Magnetic Materials, Gary J. Long, Oran Allan Pringle, Gaya Kanishka Marasinghe, Fernande Grandjean, K. H. Buschow

Chemistry Faculty Research & Creative Works

The 57Fe Mössbauer-effect spectra of the series of hard magnetic materials, R2Fe14C, where R is Nd, Gd, Tb, Dy, Ho, and Lu, have been measured at 295 K. All of these carbides exhibit uniaxial magnetic anisotropy. The spectra resemble those obtained for the related R 2Fe14B compounds and have been fit with the model used earlier for Nd2Fe14B. The magnitude of the hyperfine field on each site, as a function of rare earth, parallels the Curie temperature; the maximum hyperfine fields and the maximum Curie temperature are observed …

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Evaluation Of D-Amino Acid Levels In Human Urine And In Commercial L-Amino Acid Samples, Daniel W. Armstrong, J. D. Duncan, S. C. Lee Feb 1991

Evaluation Of D-Amino Acid Levels In Human Urine And In Commercial L-Amino Acid Samples, Daniel W. Armstrong, J. D. Duncan, S. C. Lee

Chemistry Faculty Research & Creative Works

Detectable levels of four free D-amino acids (phenylalanine, tyrosine, tryptophan and leucine) were found in human urine. This was accomplished using a liquid chromatographic coupled column (i.e., achiral-chiral) method that was developed for the rapid and sensitive analysis of these compounds. The technique was tested on a series of commercial L-amino acids. Care was taken to minimize racemization. Trace to percent levels of contaminating D-enantiomers were found in all commercial samples. In urine the D-amino acids ranged from several hundredths of a percent up to percent levels of the corresponding excreted natural L-amino acids. There were no apparent correlations between …

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Stroke Recurrence Within 2 Years After Ischemic Infarction, D. (Daniel) B. Hier, M. A. Foulkes, M. Swiontoniowski, R. L. Sacco, P. B. Gorelick, J. P. Mohr, T. R. Price, P. A. Wolf Jan 1991

Stroke Recurrence Within 2 Years After Ischemic Infarction, D. (Daniel) B. Hier, M. A. Foulkes, M. Swiontoniowski, R. L. Sacco, P. B. Gorelick, J. P. Mohr, T. R. Price, P. A. Wolf

Chemistry Faculty Research & Creative Works

We Prospectively Studied Stroke Recurrence in 1,273 Patients with Ischemic Stroke Who Were Entered into the Stroke Data Bank. Median Follow-Up Was 13 Months. the 2-Year Cumulative Recurrence Rate among These Patients Was 14.1%. Age, Sex, Race, History of Hypertension, Atrial Fibrillation, or Transient Ischemic Attacks, and Stroke Location Were Not Associated with a Higher Risk of Stroke Recurrence. Patients with an Elevated Blood Pressure, an Abnormal Initial Computed Tomogram, or a History of Diabetes Mellitus Were at a Higher Risk of Stroke Recurrence. in Contrast, Patients with an Infarct of Unknown Cause Were at a Lower Risk of Stroke …

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Clinical-Computed Tomographic Correlations Of Lacunar Infarction In The Stroke Data Bank, A. Chamorro, R. L. Sacco, J. P. Mohr, M. A. Foulkes, C. S. Kase, T. K. Tatemichi, P. A. Wolf, T. R. Price, D. (Daniel) B. Hier Jan 1991

Clinical-Computed Tomographic Correlations Of Lacunar Infarction In The Stroke Data Bank, A. Chamorro, R. L. Sacco, J. P. Mohr, M. A. Foulkes, C. S. Kase, T. K. Tatemichi, P. A. Wolf, T. R. Price, D. (Daniel) B. Hier

Chemistry Faculty Research & Creative Works

Lacunar Stroke Was Diagnosed in 337 (26%) of the 1,273 Patients with Cerebral Infarction among the 1,805 Total in the Stroke Data Bank. We Analyzed the 316 Patients with Classic Lacunar Syndromes. among These, 181 (57%) Had Pure Motor Hemiparesis, 63 (20%) Sensorimotor Syndrome, 33 (10%) Ataxic Hemiparesis, 21 (7%) Pure Sensory Syndrome, and 18 (6%) Dysarthria-Clumsy Hand Syndrome. No Striking Differences Were Found among the Risk Factors for the Lacunar Subtypes, But Differences Were Found between Lacunar Stroke as a Group and Other Types of Infarcts. Compared to 113 Patients with Large-Vessel Atherosclerotic Infarction, Those with Lacunar Stroke Had …

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Deriving Clinical Prediction Rules From Stroke Outcome Research, Daniel B. Hier, Gilda Edelstein Jan 1991

Deriving Clinical Prediction Rules From Stroke Outcome Research, Daniel B. Hier, Gilda Edelstein

Chemistry Faculty Research & Creative Works

Background and Purpose. Our Purpose Was to Determine Whether Clinical Prediction Rules Could Be Derived from Current Stroke Outcome Research. Summary of Report. We Reviewed 92 Articles on Stroke Outcome Research to Determine their Suitability for Implementation as a Clinical Prediction Rule. Methodological Problems in Many of These Studies Made Implementation of their Results as a Clinical Prediction Rule Difficult. Conclusions. Implementation of Stroke Outcome Research as Clinical Prediction Rules Would Be Facilitated by Description of Patient Population Demographics; Precise Definitions of Predictor and Outcome Measures; Stratification of Patients by Stroke Mechanism; Use of Adequate Patient Sample Sizes; and Description …

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Status Of Aluminum As A Risk Factor For Dialysis Encephalopathy And Alzheimer's Disease, P. B. Gorelick, D. (Daniel) B. Hier, C. Mangone, S. Robbins, A. Plioplys, S. Kathpalia Jan 1991

Status Of Aluminum As A Risk Factor For Dialysis Encephalopathy And Alzheimer's Disease, P. B. Gorelick, D. (Daniel) B. Hier, C. Mangone, S. Robbins, A. Plioplys, S. Kathpalia

Chemistry Faculty Research & Creative Works

No abstract provided.

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Mössbauer-Effect, Magnetic, And Neutron-Diffraction Study Of Nafep₂O₇, R. C. Mercader, L. Terminiello, Gary J. Long, D. G. Reichel, K. Dickhaus, R. Zysler, R. Sanchez, M. Tovar Jul 1990

Mössbauer-Effect, Magnetic, And Neutron-Diffraction Study Of Nafep₂O₇, R. C. Mercader, L. Terminiello, Gary J. Long, D. G. Reichel, K. Dickhaus, R. Zysler, R. Sanchez, M. Tovar

Chemistry Faculty Research & Creative Works

Neutron-diffraction, magnetic-susceptibility, specific-heat, and Mössbauer-effect studies of NaFeP2O7 reveal that it is a normal Heisenberg isotropic three-dimensional antiferromagnetic material with a Néel temperature of 29.0 K. NaFeP2O7 has the monoclinic P21/c magnetic space group, which is the same as the nuclear crystallographic space group. The easy axis of magnetization lies in the monoclinic ac plane at an angle of 21.0° from the c axis. The specific-heat measurements reveal a λ-type anomaly at 28.7(2) K. A molecular-field model analysis indicates that the intrasublattice magnetic exchange coupling Jaa=Jbb=-0.37 cm-1, whereas …

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Polar-Liquid, Derivatized Cyclodextrin Stationary Phases For The Capillary Gas Chromatography Separation Of Enantiomers, Daniel W. Armstrong, Weiyong Li, Chau Dung Chang, Josef Pitha Apr 1990

Polar-Liquid, Derivatized Cyclodextrin Stationary Phases For The Capillary Gas Chromatography Separation Of Enantiomers, Daniel W. Armstrong, Weiyong Li, Chau Dung Chang, Josef Pitha

Chemistry Faculty Research & Creative Works

A new class of hydrophilic, relatively polar liquid, cyclodextrin (CD) derivatives have been used as highly selective chiral stationary phases (CSPs) for capillary gas chromatography (GC). Several possible requirements for liquidity In CD derivatives are discussed. O-(S)-2-Hydroxypropyl derivatives of α-, β-, and γ-cyclodextrlns were synthesized, exclusively characterized, permethylated, and evaluated for enantloselectlvity. Seventy pairs of enantiomers were resolved. They represent a wide variety of structural types and classes of compounds including chlral alkyl amines, amino alcohols, epoxides, pyrans, furans, sugars, dlols, esters, ketones, bicyclic compounds, alcohols, and so on. Many of these compounds were not aromatic and cannot be resolved …

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Reversing Enantioselectivity In Capillary Gas Chromatography With Polar And Nonpolar Cyclodextrin Derivative Phases, Daniel W. Armstrong, Weiyong Li, Josef Pitha Jan 1990

Reversing Enantioselectivity In Capillary Gas Chromatography With Polar And Nonpolar Cyclodextrin Derivative Phases, Daniel W. Armstrong, Weiyong Li, Josef Pitha

Chemistry Faculty Research & Creative Works

No abstract provided.

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Caudate Infarcts, Louis R. Caplan, Edward Feldmann, Jeremy D. Schmahmann, Carlos S. Kase, Phillip B. Gorelick, Daniel B. Hier, Cathy Helgason, George Baquis, John P. Greenberg Jan 1990

Caudate Infarcts, Louis R. Caplan, Edward Feldmann, Jeremy D. Schmahmann, Carlos S. Kase, Phillip B. Gorelick, Daniel B. Hier, Cathy Helgason, George Baquis, John P. Greenberg

Chemistry Faculty Research & Creative Works

Eighteen Patients Had Caudate Nucleus Infarcts (10 Left-Sided; 8 Right-Sided). Infarcts Extended into the Anterior Limb of the Internal Capsule in 9 Patients, and Also the Anterior Putamen in 5 Patients. Thirteen Patients Had Motor Signs, Most Often a Slight Transient Hemiparesis. Dysarthria Was Common (11 Patients). Cognitive and Behavioral Abnormalities Were Frequent, and Included Abulia (10 Patients), Agitation and Hyperactivity (7 Patients), Contralateral Neglect (3 Patients, All Right Caudate), and Language Abnormalities (2 Patients, Both Left Caudate). the Majority of Patients Had Risk Factors for Penetrating Artery Disease. Branch Occlusion of Heubner's Artery, or Perforators from the Proximal Anterior …

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Coatings And Surface Modification By Methane Plasma Polymerization, Chung‐Peng ‐P Ho, H. Yasuda Jan 1990

Coatings And Surface Modification By Methane Plasma Polymerization, Chung‐Peng ‐P Ho, H. Yasuda

Chemistry Faculty Research & Creative Works

Polymers formed from plasma‐polymerized methane were employed to modify the surface properties of silicone rubber membrane. Polymers were evaluated based on the energy input parameter W/FM, where W is the discharge power, F is the monomer flow rate, and M is the molecular weight of the monomer. Dealing with the characteristics of plasma polymerization and the deposited polymer film, the effect of pumping rate on deposition rate and the coating thickness, surface energy, and gas permeabilities of methane‐plasma‐polymer‐coated silicone rubber membrane were investigated in three plasma regions. Because more reactive species are expelled at high pumping rates, the monomer‐deficient region …

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Self‐Diffusion Coefficients Of Boc‐Amino Acid Anhydrides Under Conditions Of Solid Phase Peptide Synthesis, Stephen Pickup, Frank D. Blum, Warren T. Ford Jan 1990

Self‐Diffusion Coefficients Of Boc‐Amino Acid Anhydrides Under Conditions Of Solid Phase Peptide Synthesis, Stephen Pickup, Frank D. Blum, Warren T. Ford

Chemistry Faculty Research & Creative Works

No abstract provided.

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Plasma Surface Treatment On Nylon Fabrics By Fluorocarbon Compounds, Yu Iriyama, Takeshi Yasuda, D. L. Cho, H. Yasuda Jan 1990

Plasma Surface Treatment On Nylon Fabrics By Fluorocarbon Compounds, Yu Iriyama, Takeshi Yasuda, D. L. Cho, H. Yasuda

Chemistry Faculty Research & Creative Works

Nylon fabrics were treated by low temperature fluorocarbon plasmas. All of the fluorocarbon plasmas applied altered the surface of nylon fabrics to be hydrophobic and water‐repellent. The durability of hydrophobicity and water repellency was examined by measurements of the water contact angle, the water droplet rolling‐off angle, and the breakthrough water pressure after plasma‐treated fabrics were washed. It was found that the structure of starting fluorocarbon and the plasma energy input were important factors in the durability. After washing, surface dynamics were investigated on different drying conditions. It was found that chemical composition and water repellency were dependent on drying …

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Derivatized Cyclodextrins For Normal-Phase Liquid Chromatographic Separation Of Enantiorners, Daniel W. Armstrong, San Chun Chang, Apryll M. Stalcup, Martha L. Hilton, Jo Dee Duncan, James R. Faulkner Jan 1990

Derivatized Cyclodextrins For Normal-Phase Liquid Chromatographic Separation Of Enantiorners, Daniel W. Armstrong, San Chun Chang, Apryll M. Stalcup, Martha L. Hilton, Jo Dee Duncan, James R. Faulkner

Chemistry Faculty Research & Creative Works

Several different derivatized β-cyclodextrins were synthesized and used as chiral stationary phases in normal-phase liquid chromatography. The multiply substituted derivatives were made with acetic anhydride, (R)-and (S)-1-(1-naphthyl) ethyl isocyanate, 2, 6-dimethylphenyl isocyanate, and p-toluoyl chloride. The first successful cyclodextrln-based, normal-phase separation of enantiomers was accomplished on these derivative phases. In contrast to chiral separations on the native β-cyclodextrin stationary phase, the enantiomeric separation mechanism on these new phases is not thought to be dependent on inclusion complexation. The similarities and differences between the derivatized cyclodextrin stationary phases and the cellulosic stationary phases are discussed. © 1990, American Chemical Society. All …

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Dementia In Stroke Survivors In The Stroke Data Bank Cohort: Prevalence, Incidence, Risk Factors, And Computed Tomographic Findings, Thomas K. Tatemichi, Mary A. Foulkes, J. P. Mohr, Jeffrey R. Hewitt, Daniel B. Hier, Thomas R. Price, Philip A. Wolf Jan 1990

Dementia In Stroke Survivors In The Stroke Data Bank Cohort: Prevalence, Incidence, Risk Factors, And Computed Tomographic Findings, Thomas K. Tatemichi, Mary A. Foulkes, J. P. Mohr, Jeffrey R. Hewitt, Daniel B. Hier, Thomas R. Price, Philip A. Wolf

Chemistry Faculty Research & Creative Works

We Determined the Prevalence of Dementia in 927 Patients with Acute Ischemic Stroke Aged ≥60 Years in the Stroke Data Bank Cohort based on the Examining Neurologist's Best Judgment Diagnostic Agreement among Examiners Was 68% (K=0.34). of 726 Testable Patients, 116 (16%) Were Demented. Prevalence of Dementia Was Related to Age But Not to Sex, Race, Handedness, Educational Level, or Employment Status Before the Stroke. Previous Stroke and Previous Myocardial Infarction Were Related to Prevalence of Dementia Although Hypertension, Diabetes Mellitus, Atrial Fibrillation, and Previous Use of Antithrombotic Drugs Were Not Prevalence of Dementia Was Most Frequent in Patients with …

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Sans From Tetradecylpyridinium Bromide Based Microemulsions, Paul M. Lindemuth, Boualem Hammouda, Raymond L. Venable Jan 1990

Sans From Tetradecylpyridinium Bromide Based Microemulsions, Paul M. Lindemuth, Boualem Hammouda, Raymond L. Venable

Chemistry Faculty Research & Creative Works

Small-angle neutron scattering is used to investigate tetradecyl pyridinium bromide/pentanol/heptane/heavy water microemulsions in the water-in-oil (W/O) microemulsion phase diagram region. The heavy water content is increased while the other components (surfactant, cosurfactant, hydrocarbon) are kept constant. With use of a simple model assuming spherical micelles interacting with a hard-sphere potential (Percus-Yevick model), aggregate sizes and packing fractions have been extracted and found to agree with values determined from the mixing conditions. These experiments clearly show the transition from the single-particle (heavy water + Stern layer droplet) scattering regime at low water concentration to the mixed single/interdroplet scattering regime when the …

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Relevance Of Enantiomeric Separations In Food And Beverage Analyses, Daniel W. Armstrong, Chau Dung Chang, Wei Yong Li Jan 1990

Relevance Of Enantiomeric Separations In Food And Beverage Analyses, Daniel W. Armstrong, Chau Dung Chang, Wei Yong Li

Chemistry Faculty Research & Creative Works

A series of new derivatized cyclodextrins have been developed for use as chiral stationary phases in capillary gas chromatography. As a result, a large number of the enantiomeric components in food and beverage products can be resolved relatively quickly and easily. The study focuses on compounds other than amino acids (e.g., malic acid, lactic acid, tartaric acid, esters, alcohols, lactone flavors or fragrances, and so on). The ability to separate and quantitate enantiomers at low levels should be useful for detecting adulterated products, for evaluating fermentation processes, and for the accurate characterization of enantiomeric flavor components, growth regulators, pesticides, and …

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On The Kelvin Electrostatic Generator, S. Desmet, F. Orban, Fernande Grandjean Apr 1989

On The Kelvin Electrostatic Generator, S. Desmet, F. Orban, Fernande Grandjean

Chemistry Faculty Research & Creative Works

The Kelvin generator is an amazing electrostatic device which poses many questions. The authors report the results of their investigations of this device under various controlled conditions with both nonpolar and polar liquids and a sodium chloride aqueous solution. They have found that the generator works well even if the two liquid streams originate from different electrically insulated reservoirs. In addition they propose a model in which the electric charge results from the separation of the hydrogen and hydroxyl ions as the water droplets form.

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Morning Increase In Onset Of Ischemic Stroke, John R. Marler, Thomas R. Price, Gregory L. Clark, James E. Muller, Thomas Robertson, Jay P. Mohr, Daniel B. Hìer, Philip A. Wolf, Louis R. Caplan, Mary A. Foulkes Jan 1989

Morning Increase In Onset Of Ischemic Stroke, John R. Marler, Thomas R. Price, Gregory L. Clark, James E. Muller, Thomas Robertson, Jay P. Mohr, Daniel B. Hìer, Philip A. Wolf, Louis R. Caplan, Mary A. Foulkes

Chemistry Faculty Research & Creative Works

The Time of Onset of Ischemic Stroke Was Determined for 1,167 of 1,273 Patients during the Collection of Data by Four Academic Hospital Centers between June 30, 1983, and June 30, 1986. More Strokes Occurred in Awake Patients from 10:00 Am to Noon Than during Any Other 2-Hour Interval. the Incidence of Stroke Onset Declined Steadily during the Remainder of the Day and Early Evening. the Onset of Stroke is Least Likely to Occur in the Late Evening, Before Midnight. © 1989 American Heart Association, Inc.

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Determinants Of Early Recurrence Of Cerebral Infarction: The Stroke Data Bank, R. L. Sacco, M. A. Foulkes, J. P. Mohr, P. A. Wolf, D. (Daniel) B. Hier, T. R. Price Jan 1989

Determinants Of Early Recurrence Of Cerebral Infarction: The Stroke Data Bank, R. L. Sacco, M. A. Foulkes, J. P. Mohr, P. A. Wolf, D. (Daniel) B. Hier, T. R. Price

Chemistry Faculty Research & Creative Works

We Studied 1,273 Patients with Ischemic Cerebral Infarction Who Were Entered into the Stroke Data Bank, a Prospective, Observational Study Involving Four University Hospitals and the Biometry and Field Studies Branch of the National Institute of Neurological Disorders and Stroke. Forty Patients Had Non-Iatrogenic Recurrent Stroke within 30 Days after the Index Cerebral Infarction. using Life Tables, the 30-Day Cumulative± SE Risk of Early Recurrence for All Infarctions Was 3.3±0.4%. the Risk of Early Recurrence Was Greatest for Atherothrombotic Infarction (7.9±2.2%, Eight of 113 Patients) and Least for Lacunar Infarction (2.2±1.2%, Eight of 337 Patients). Both Cardioembolic Infarction (4.3±0.9%, 10 …

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Predictors Of Survival In Clinically Diagnosed Alzheimer's Disease And Multi-Infarct Dementia, Daniel B. Hier, Joshua D. Warach, Philip B. Gorelick, Joseph Thomas Jan 1989

Predictors Of Survival In Clinically Diagnosed Alzheimer's Disease And Multi-Infarct Dementia, Daniel B. Hier, Joshua D. Warach, Philip B. Gorelick, Joseph Thomas

Chemistry Faculty Research & Creative Works

No abstract provided.

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Reversibility Of Ct And Mr Findings In Neuro-Behçet Disease, Dushyant V. Patel, Michael J. Neuman, Daniel B. Hier Jan 1989

Reversibility Of Ct And Mr Findings In Neuro-Behçet Disease, Dushyant V. Patel, Michael J. Neuman, Daniel B. Hier

Chemistry Faculty Research & Creative Works

A Woman with Neuro-Behçet Disease Characterized by Recurrent Attacks of Meningoencephalitis is Reported. during an Attack of Brain Stem Dysfunction Characterized by Dysarthria, Diplopia, and Ataxia, the Postcontrast CT Showed an Enhancing Lesion of the Upper Brain Stem. during a Subsequent Attack Characterized by Subcortical Dementia and Amnesia, Magnetic Resonance (MR) Showed Abnormal Signal Intensity in the Hypothalamus and Upper Brain Stem. Upon Remission of Her Symptoms, Follow-Up Contrast Enhanced CT and MR Were Entirely Normal. Magnetic Resonance is Especially Useful in Localizing Acute Inflammatory Lesions in Behçet Disease. This Case Suggests that Abnormal MR and CT Findings in Neuro-Behçet …

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Plasma Polymerization By Magnetron Glow Discharge. I. Effect Of Magnetic Field On Breakdown Of Monomers In Low Pressure, K. Sato, Y. Iriyama, D. L. Cho, H. Yasuda Jan 1989

Plasma Polymerization By Magnetron Glow Discharge. I. Effect Of Magnetic Field On Breakdown Of Monomers In Low Pressure, K. Sato, Y. Iriyama, D. L. Cho, H. Yasuda

Chemistry Faculty Research & Creative Works

The breakdown voltage Vb of glow discharge of an organic monomer generally decreases as the system pressure decreases; however, below a certain threshold pressure, the breakdown voltage increases with decreasing system pressure. In the pressure range below 100 mTorr, the breakdown voltage generally increases as a linear function of 1 /p, where p is the system pressure of the reactor. In this region, glow discharge without magnetic enhancement often yields unstable discharge, which is associated with a very steep slope of a line in the Vh vs /p plot. The similar plots for glow discharges of non-polymer-forming gases, such as …

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Polymerization Of Methane, Ashok K. Sharma, H. Yasuda Jan 1989

Polymerization Of Methane, Ashok K. Sharma, H. Yasuda

Chemistry Faculty Research & Creative Works

Plasma polymerization of methane in a magnetically enhanced capacitively coupled bell jar reactor operating at a frequency of 10 kHz is reported. Dependence of polymer deposition rate on monomer feed rate (F), composite power parameter (W/FM), electrode temperature, and electrode cleanliness have been examined. Such functional properties as wettability, adhesion, and thermal stability of the polymer are found to depend on the composite power parameter (W/FM) of the plasma. The permeability studies indicate highly crosslinked nature of the polymer. ESCA studies reveal code position of electrode material with the polymer under high W/FM conditions, potential applications of plasma polymer of …

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A Mössbauer Effect Study Of Y₂Fe₁₄B And Its Aluminum Solid Solutions, Dwayne E. Tharp, Gary J. Long, Oran Allan Pringle, Gaya Kanishka Marasinghe, William Joseph James, Fernande Grandjean Nov 1988

A Mössbauer Effect Study Of Y₂Fe₁₄B And Its Aluminum Solid Solutions, Dwayne E. Tharp, Gary J. Long, Oran Allan Pringle, Gaya Kanishka Marasinghe, William Joseph James, Fernande Grandjean

Chemistry Faculty Research & Creative Works

The Mössbauer spectra of Y2Fe14B have been measured from 85 to 296 K. Analysis of the spectra indicates that the near-neighbor rare-earth atoms directly influence the orientation of the principal axis of the electric field gradient. The hyperfine parameters are very similar to those of Nd2Fe14B, but the internal fields are somewhat smaller at room temperature in the yttrium compound. The Mösssbauer spectra of Y2(Fe1-xAlx) 14B, where x equals 0.00, 0.02, 0.04, 0.06, and 0.08, have been measured at 85 K. The average internal hyperfine …

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Kinetics And Mechanisms Of The Aminolysis Of N-Hydroxysuccinimide Esters In Aqueous Buffers, Gary W. Cline, Samir B. Hanna Oct 1988

Kinetics And Mechanisms Of The Aminolysis Of N-Hydroxysuccinimide Esters In Aqueous Buffers, Gary W. Cline, Samir B. Hanna

Chemistry Faculty Research & Creative Works

Rate constants for the aminolysis of the N-hydroxysuccinimide (NHS) ester of ρ-methoxybenzoic acid, in aqueous buffer systems (20% dioxane), have been determined under pseudo-first-order conditions. For the amines studied (pKa = 7.60-11.1), the data fit the rate expression kobsd - KOH-⨯ [OH-] = k1[amine]free. This rate equation is in contrast to the two-term rate equation (kobsd = k1[amine] + k2[amine]2) obtained for this reaction in anhydrous dioxane (Cline, G. W.; Hanna, S. B. J. Am. Chem. Soc. 1987,109, 3087) and is suggestive of a disproportionate …

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Enantiomeric Resolution And Chiral Recognition Of Racemic Nicotine And Nicotine Analogues By Β-Cyclodextrin Complexation: Structure-Enantiomeric Resolution Relationships In Host-Guest Interactions, Jeffrey I. Seeman, Henry V. Secor, Daniel W. Armstrong, Karen D. Timmons, Timothy J. Ward Oct 1988

Enantiomeric Resolution And Chiral Recognition Of Racemic Nicotine And Nicotine Analogues By Β-Cyclodextrin Complexation: Structure-Enantiomeric Resolution Relationships In Host-Guest Interactions, Jeffrey I. Seeman, Henry V. Secor, Daniel W. Armstrong, Karen D. Timmons, Timothy J. Ward

Chemistry Faculty Research & Creative Works

High-performance liquid chromatography using β-cyclodextrin bonded phases was examined for the enantiomeric separation of racemic nicotine and 19 racemic nicotine analogues. Ten pairs of enantiomers were separated by this technique. This represents the first reported facile and direct separation of these racemates. Effects of pH, mobile phase composition, and structural features of the substrates (i.e., position and size of substituents, presence of pyrrolidine ring or hydrogen bonding functionalities, basicity) on the enantioselectivity are examined. Various structural aspects of the compounds were related to retention to the cyclodextrln-modlfied support and to the enantiomeric separations observed. Implications of this work to host-guest …

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Use Of Secondary Equilibria For The Separation Of Small Solutes By Field-Flow Fractionation, Alain Berthod, Daniel W. Armstrong, J. Calvin Giddings, Marcus N. Myers Oct 1988

Use Of Secondary Equilibria For The Separation Of Small Solutes By Field-Flow Fractionation, Alain Berthod, Daniel W. Armstrong, J. Calvin Giddings, Marcus N. Myers

Chemistry Faculty Research & Creative Works

The dynamic range and selectivity of field-flow fractionation (FFF) can be Increased by using secondary chemical equilibria (SCE). SCE are established by adding a macromolecular additive or aggregate, which strongly Interacts with the field, to the carrier solution. In this study an oil-ln-water (O/W) microemulsion was used as the carrier solution in a sedimentation FFF apparatus. The microemulsion droplets (referred to as the "support") interact with the field and are retained relative to the bulk water. Small solutes that partition or bind to the microemulsion droplets are also retained relative to solutes that do not Interact with the support. In …

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