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Articles 361 - 379 of 379

Full-Text Articles in Chemistry

Overview: Nonlinear Dynamics Related To Polymeric Systems, Irving R. Epstein, John A. Pojman Jun 1999

Overview: Nonlinear Dynamics Related To Polymeric Systems, Irving R. Epstein, John A. Pojman

Faculty Publications

No abstract provided.

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Period-Doubling Behavior In Frontal Polymerization Of Multifunctional Acrylates, Jonathan Masere, Felicia Stewart, Timothy Meehan, John A. Pojman Jun 1999

Period-Doubling Behavior In Frontal Polymerization Of Multifunctional Acrylates, Jonathan Masere, Felicia Stewart, Timothy Meehan, John A. Pojman

Faculty Publications

Front dynamics in the frontal polymerization of two multifunctional acrylate monomers, 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane ethoxylate triacrylate (TMPTA), with Lupersol 231 [1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane] as the initiator, are studied. In most frontal polymerization systems, the dynamics are associated with a planar front propagating through the sample. However, in some cases, front behavior can be altered: the front becomes nonplanar characterized by complex patterns like spin modes and pulsations. To determine how these periodic and aperiodic modes arise, reactant solutions consisting of HDDA diluted with diethyl phthalate (DEP) and TMPTA diluted with dimethyl sulfoxide (DMSO) were used in the study. …

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Orientational Susceptibility And Elastic Constants Near The Nematic-Isotropic Phase Transition For Trimers With Terminal-Lateral-Lateral-Terminal Connections, Daeseung Kang, Milind P. Mahajan, Rolfe G. Petschek, Charles Rosenblatt, Chaobin He, Puwei Lu, A.C. Griffin Aug 1998

Orientational Susceptibility And Elastic Constants Near The Nematic-Isotropic Phase Transition For Trimers With Terminal-Lateral-Lateral-Terminal Connections, Daeseung Kang, Milind P. Mahajan, Rolfe G. Petschek, Charles Rosenblatt, Chaobin He, Puwei Lu, A.C. Griffin

Faculty Publications

Magnetically induced Freedericksz measurements were performed in the nematic liquid crystal phase to extract the elastic constants of a terminal-lateral-lateral-terminal trimer, i.e., a trimer in which the connections to the first and third mesogens are at the end of the mesogen and both attachments to the central mesogen are lateral. Polymeric liquid crystals based on this unit have negative Poisson ratios. Additionally, electric field Kerr measurements were performed in the isotropic phase to extract the orientational susceptibility. The elastic constants were found to be similar to values obtained for typical monomers, albeit with a slightly enhanced ratio K-33/K-11 and reduced …

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The Effect Of Convection On A Propagating Front With A Liquid Product: Comparison Of Theory And Experiments, B. Mccaughey, John A. Pojman, C. Simmons, V.A. Volpert Jun 1998

The Effect Of Convection On A Propagating Front With A Liquid Product: Comparison Of Theory And Experiments, B. Mccaughey, John A. Pojman, C. Simmons, V.A. Volpert

Faculty Publications

This work is devoted to the investigation of propagating polymerization fronts converting a liquid monomer into a liquid polymer. We consider a simplified mathematical model which consists of the heat equation and equation for the depth of conversion for one-step chemical reaction and of the Navier-Stokes equations under the Boussinesq approximation. We fulfill the linear stability analysis of the stationary propagating front and find conditions of convective and thermal instabilities. We show that convection can occur not only for ascending fronts but also for descending fronts. Though in the latter case the exothermic chemical reaction heats the cold monomer from …

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Single-Head Spin Modes In Frontal Polymerization, Victor M. Ilyashenko, John A. Pojman Mar 1998

Single-Head Spin Modes In Frontal Polymerization, Victor M. Ilyashenko, John A. Pojman

Faculty Publications

The single-head spin mode is the first two-dimensional pattern of self-propagating thermal reaction fronts observed after the planar front loses stability. A "hot spot" is observed to propagate around the periphery of the front. The dynamics of the single-head frontal polymerization regime were studied experimentally, and two novel results were found. The "hot spot" was measured and found to be superadiabatic. The relationship between the rotational velocity and the propagating velocity was found. Experimental data were also compared with the theoretical results based on the linear stability analysis and found to be in a reasonable agreement. (C) 1998 American institute …

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In Situ Detection Method For Glutaminyl Cyclase Activity In Polyacrylamide Gels, Justin B. Houseknecht, Jeffrey S. Temple, Robert C. Bateman Jr. Mar 1998

In Situ Detection Method For Glutaminyl Cyclase Activity In Polyacrylamide Gels, Justin B. Houseknecht, Jeffrey S. Temple, Robert C. Bateman Jr.

Faculty Publications

No abstract provided.

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Numerical Modeling Of Self-Propagating Polymerization Fronts: The Role Of Kinetics On Front Stability, Stanislav E. Solovyov, Victor M. Ilyashenko, John A. Pojman Jun 1997

Numerical Modeling Of Self-Propagating Polymerization Fronts: The Role Of Kinetics On Front Stability, Stanislav E. Solovyov, Victor M. Ilyashenko, John A. Pojman

Faculty Publications

Frontal propagation of a highly exothermic polymerization reaction in a liquid is studied with the goal of developing a mathematical model of the process. As a model case we consider monomers such as methacrylic acid and n-butyl acrylate with peroxide initiators, although the model is not limited to these reactants and can be applied to any system with the similar basic polymerization mechanism. A three-step reaction mechanism, including initiation, propagation and termination steps, as well as a more simple one-step mechanism, were considered. For the one-step mechanism the loss of stability of propagating front was observed as a sequence …

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Inhomogeneity In Gelation And Nonuniversality Of Sol-To-Gel Transitions Studied By A Computer Simulation Model, Yi-Min Liu, R.B. Pandey Dec 1996

Inhomogeneity In Gelation And Nonuniversality Of Sol-To-Gel Transitions Studied By A Computer Simulation Model, Yi-Min Liu, R.B. Pandey

Faculty Publications

No abstract provided.

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Kinetics And Jamming Coverage In A Random Sequential Adsorption Of Polymer Chains, Jian-Sheng Wang, Ras B. Pandey Aug 1996

Kinetics And Jamming Coverage In A Random Sequential Adsorption Of Polymer Chains, Jian-Sheng Wang, Ras B. Pandey

Faculty Publications

No abstract provided.

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Dynamics And Conformation Of Polymer Chains In A Porous Medium, Grace M. Foo, R.B. Pandey, D. Stauffer Apr 1996

Dynamics And Conformation Of Polymer Chains In A Porous Medium, Grace M. Foo, R.B. Pandey, D. Stauffer

Faculty Publications

No abstract provided.

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Structure Factors Of Binary Fluids In A Dilute Gel, J.C. Lee Oct 1995

Structure Factors Of Binary Fluids In A Dilute Gel, J.C. Lee

Faculty Publications

The statio and dynamic structure factors of binary fluids in a dilute gel are computed using a two-dimensional kinetic Ising model. The wetting effect of the gel strands is modeled with ''gel atoms'' which are distributed randomly among the spins and impose a field on their neighboring spins, all in the same direction. The result for the static structure factor shows the presence of adsorption clusters which mask the gel atoms. The result for the dynamic Structure factor shows an extremely slow relaxation-at late times which cannot be fitted in the form of the activated dynamic scaling known for random-field …

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Accuracy Of Deoxynucleotide Incorporation By Soybean Chloroplast Dna-Polymerases Is Independent Of The Presence Of A 3' To 5' Exonuclease, J. Clinton Bailey Ii, Sabine Heinhorst, Gordon C. Cannon Apr 1995

Accuracy Of Deoxynucleotide Incorporation By Soybean Chloroplast Dna-Polymerases Is Independent Of The Presence Of A 3' To 5' Exonuclease, J. Clinton Bailey Ii, Sabine Heinhorst, Gordon C. Cannon

Faculty Publications

DNA polymerase was purified from soybean (Glycine max) chloroplasts that were actively replicating DNA. The main form (form I) of the enzyme was associated with a low level of 3' to 5' exonuclease activity throughout purification, although the ratio of exonuclease to polymerase activity decreased with each successive purification step. A second form (form II) of DNA polymerase, which elutes from DEAE-cellulose at a higher salt concentration than form I, was devoid of any exonuclease activity. To assess the potential function of the 3' to 5' exonuclease in proofreading, the fidelity of deoxynucleotide incorporation was measured for form I DNA …

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Purification And Characterization Of A Gamma-Like Dna-Polymerase From Chenopodium Album L., K. Meißner, Sabine Heinhorst, Gordon C. Cannon, T. Börner Oct 1993

Purification And Characterization Of A Gamma-Like Dna-Polymerase From Chenopodium Album L., K. Meißner, Sabine Heinhorst, Gordon C. Cannon, T. Börner

Faculty Publications

A DNA polymerase activity from mitochondria of the dicotyledonous angiosperm Chenopodium album L. was purified almost 9000 fold by successive column chromatography steps on DEAE cellulose, heparin agarose and ssDNA cellulose. The enzyme was characterized as a gamma-class polymerase, based on its resistance to inhibitors of the nuclear DNA polymerase alpha and its preference for poly(rA).(dT)12-18 over activated DNA in vitro. The molecular weight was estimated to be 80,000 - 90,000. A 3' to 5' exonuclease activity was found to be tightly associated with the DNA polymerase activity through all purification steps. This is the first report of an association …

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Radially Symmetrical Flow Of Reacting Liquid With Changing Viscosity, S.E. Solovyov, V.A. Volpert, S.P. Davytan Aug 1993

Radially Symmetrical Flow Of Reacting Liquid With Changing Viscosity, S.E. Solovyov, V.A. Volpert, S.P. Davytan

Faculty Publications

Frontal regimens for one-dimensional flow of reacting liquid with changing viscosity are studied. Stationary solutions are investigated for the case of narrow reaction zones that shrink to a front. The results of numerical solution of the nonstationary problem are presented. Complex oscillations resulting from period-doubling bifurcations are found.

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Dna Replication In Chloroplasts, Sabine Heinhorst, Gordon C. Cannon Jan 1993

Dna Replication In Chloroplasts, Sabine Heinhorst, Gordon C. Cannon

Faculty Publications

Chloroplasts contain multiple copies of a DNA molecule (the plastome) that encodes many of the gene products required to perform photosynthesis. The plastome is replicated by nuclear-encoded proteins and its copy number seems to be highly regulated by the cell in a tissue-specific and developmental manner. Our understanding of the biochemical mechanism by which the plastome is replicated and the molecular basis for its regulation is limited. In this commentary we review our present understanding of chloroplast DNA replication and examine current efforts to elucidate its mechanism at a molecular level.

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Drying Of Beulah-Zap Lignite, Karl S. Vorres, David L. Wertz, Vivak Malhotra, Yuhong Dang, J.T. Joseph, Ronald Fisher Sep 1992

Drying Of Beulah-Zap Lignite, Karl S. Vorres, David L. Wertz, Vivak Malhotra, Yuhong Dang, J.T. Joseph, Ronald Fisher

Faculty Publications

Lignite dried in a stream of dry nitrogen at moderate temperatures (20-80-degrees-C) loses water in two distinguishable modes. The first mode represents about 80-85% of the loss of moisture. The second represents the other 15-20% lost under these conditions. The rate follows a unimolecular mechanism (like radioactive decay) for each mode. The activation energy for the first mode is close to the heat of vaporization of water. The rate is dependent upon the gas flow around the sample and the weight (or thickness) of the sample. Work at Amoco Oil Company indicated that the oil yield was higher for the …

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Viscoelastic Properties Of A Liquid-Crystalline Monomer And Its Dimer, Gregory A. Dilisi, Charles Rosenblatt, Anselm C. Griffin, Uma Hari Apr 1992

Viscoelastic Properties Of A Liquid-Crystalline Monomer And Its Dimer, Gregory A. Dilisi, Charles Rosenblatt, Anselm C. Griffin, Uma Hari

Faculty Publications

Quasielastic-light-scattering measurements are reported for a dialkoxyphenylbenzoate monomer and its dimer in their respective nematic phases. The splay and twist elastic moduli of the dimer are found to be nearly independent of molecular length. The dimer's bend modulus, however, shows an anomalous increase with decreasing temperature well below the nematic-isotropic phase transition. Monomer viscosities are consistent with typical literature values, although γ1/ηsplay and ηbend seem to be larger than expected for the dimer, where γ1 is the twist viscosity. The results are discussed in terms of viscoelastic properties of semiflexible rods. The elastic properties in …

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Purification And Characterization Of A Dna Polymerase From The Cyanobacterium Anacystis Nidulans R2, Hsiu-Jin Lin, Gordon C. Cannon, Sabine Heinhorst Nov 1990

Purification And Characterization Of A Dna Polymerase From The Cyanobacterium Anacystis Nidulans R2, Hsiu-Jin Lin, Gordon C. Cannon, Sabine Heinhorst

Faculty Publications

A DNA polymerase has been highly purified from Anacystis nidulans R2. Electrophoretic analysis in sodium dodecyl sulfate-polyacrylamide gels revealed that the final fraction contains three bands of Mr 107,000, 93,000, and 51,000, respectively. Analysis of purified DNA polymerase activity in situ indicates that of the three polypeptides the Mr 107,000 species has the catalytic activities. The native molecular weight of the enzyme was estimated by glycerol gradient sedimentation to be 100,000. The enzyme has an absolute requirement for a divalent cation. Mg2+ can be replaced with Mn2+, but the DNA polymerase is less active. Potassium …

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Chloroplast And Mitochondrial: Dna Polymerases From Cultured Soybean Cells, Sabine Heinhorst, Gordon C. Cannon, Arthur Weissbach Apr 1990

Chloroplast And Mitochondrial: Dna Polymerases From Cultured Soybean Cells, Sabine Heinhorst, Gordon C. Cannon, Arthur Weissbach

Faculty Publications

DNA polymerases were purified from chloroplasts and mitochondria of cultured Glycine max cells. The chloroplast enzyme exists in two forms which are indistinguishable from each other biochemically. All three organellar enzymes have an estimated molecular weight of 85,000 to 90,000 and prefer poly(rA)dT12-18 over activated DNA as a template in vitro. Maximum activity of the chloroplast and mitochondrial DNA polymerases requires KCI and a reducing agent, and the enzymes are completely resistant to inhibitors of DNA polymerase a. Taken together, these properties classify the soybean organellar enzymes as DNA polymerases y. A unique feature that distinguishes the plant enzymes from …

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