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2002

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Articles 151 - 180 of 182

Full-Text Articles in Chemistry

Overexpression And Divalent Metal Binding Properties Of The Methionyl Aminopeptidase From Pyrococcus Furiosus, Lu Meng, Shane Ruebush, Ventris M. D'Souza, Alicja J. Copik, Susumu Tsunasawa, Richard C. Holz Jan 2002

Overexpression And Divalent Metal Binding Properties Of The Methionyl Aminopeptidase From Pyrococcus Furiosus, Lu Meng, Shane Ruebush, Ventris M. D'Souza, Alicja J. Copik, Susumu Tsunasawa, Richard C. Holz

Chemistry Faculty Research and Publications

The gene encoding for the methionyl aminopeptidase from the hyperthermophilic archaeon Pyrococcus furiosus (PfMetAP-II; EC 3.4.11.18) has been inserted into a pET 27b(+) vector and overexpressed in Escherichia coli. The new expression system resulted in a 5-fold increase in purified enzyme obtained from a 5 L fermentor growth. The as-purified PfMetAP-II enzyme, to which no exogenous metal ions or EDTA was added, was found to have 1.2 equiv of zinc and 0.1 equiv of iron present by ICP-AES analysis. This enzyme had a specific activity of 5 units/mg, a 60-fold decrease from the fully loaded Fe(II) …

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Steric Hindrance As A Mechanistic Probe For Olefin Reactivity:  Variability Of The Hydrogenic Canopy Over The Isomeric Adamantylideneadamantane/Sesquihomoadamantene Pair (A Combined Experimental And Theoretical Study), Rajendra Rathore, Sergey V. Lindeman, C.-J. Zhu, T. Mori, R. Schleyer, Jay K. Kochi Jan 2002

Steric Hindrance As A Mechanistic Probe For Olefin Reactivity:  Variability Of The Hydrogenic Canopy Over The Isomeric Adamantylideneadamantane/Sesquihomoadamantene Pair (A Combined Experimental And Theoretical Study), Rajendra Rathore, Sergey V. Lindeman, C.-J. Zhu, T. Mori, R. Schleyer, Jay K. Kochi

Chemistry Faculty Research and Publications

Access to each CC face of adamantylideneadamantane (AA) and sesquihomoadamantene (SA) is hindered by the hydrogenic canopy consisting of four β-hydrogens; otherwise, these olefins have quite normal environments. X-ray crystallography and density functional (DFT) calculations show a 0.5 Å larger annular opening in the protective cover of AA than that in SA. This contributes to the remarkable differences in reactivity toward various reagents, not only by limiting access to the olefin site in SA but also by inhibiting reactions which force these hydrogens closer together. Thus, AA is subject to typical olefin-addition reactions with bromine, …

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Novel Bis-Arene (Sandwich) Complexes With No+ Acceptor. Isolation, X-Ray Crystallography And Electronic Structure, Sergiy V. Rosokha, Sergey V. Lindeman, Jay K. Kochi Jan 2002

Novel Bis-Arene (Sandwich) Complexes With No+ Acceptor. Isolation, X-Ray Crystallography And Electronic Structure, Sergiy V. Rosokha, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

The unusual charge-transfer complexes of various arene donors (ArH) with the nitrosonium cation (NO+) resulting from bimolecular [1 ∶ 1] associations can be extended at suitably high ArH concentrations to termolecular processes leading to the analogous [2 ∶ 1] complexes. Spectral analyses of the intense color changes accompanying the arene interaction with NO+ provide optimum conditions for the isolation of pure crystalline ternary complexes. Single crystal X-ray crystallographic determinations establish the unique sandwich structure consisting of the NO moiety interposed (parallel) between a pair of cofacial arene donors—reminiscent of the well-known transition metal sandwich complexes with aromatic …

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An Xps Investigation Of Thermal Degradation And Charring Of Pmma Clay Nanocomposites, Jianxin Du, Jin Zhu, Charles A. Wilkie, Jiangqi Wang Jan 2002

An Xps Investigation Of Thermal Degradation And Charring Of Pmma Clay Nanocomposites, Jianxin Du, Jin Zhu, Charles A. Wilkie, Jiangqi Wang

Chemistry Faculty Research and Publications

Poly(methyl methacrylate)–clay nanocomposites have been studied using X-ray photoelectron spectroscopy. It is clear that as the polymer undergoes thermal degradation, the clay accumulates at the surface and the barrier properties which result from this clay accumulation have been described as the reason for the decreased heat release rate for nanocomposites. The surface composition of the clay changes as the nanocomposite is heated and the changes are affected by the organic-modification that were applied to the clay in order to prepare the nanocomposite.

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A Comparison Of Various Methods For The Preparation Of Polystyrene And Poly(Methyl Methacrylate) Nanocomposites, Dongyan Wang, Jin Zhu, Qiang Yao, Charles A. Wilkie Jan 2002

A Comparison Of Various Methods For The Preparation Of Polystyrene And Poly(Methyl Methacrylate) Nanocomposites, Dongyan Wang, Jin Zhu, Qiang Yao, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polymer−clay nanocomposites of styrene and methyl methacrylate have been prepared by bulk, solution, suspension, and emulsion polymerization as well as by melt blending. Two different organic modifications of montmorillonite have been used:  one contains a styryl monomer on the ammonium ion while the other has no double bond. The organic modification as well as the mode of preparation determines if the material will be exfoliated or intercalated. Exfoliation is more likely to occur if the ammonium ion contains a double bond which can participate in the polymerization reaction, but the mere presence of this double bond is not sufficient to …

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Electronic Structure And Bonding In Unligated And Ligated Feii Porphyrins, M.-S. Liao, Steve Scheiner Jan 2002

Electronic Structure And Bonding In Unligated And Ligated Feii Porphyrins, M.-S. Liao, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The electronic structure and bonding in a series of unligated and ligated FeII porphyrins (FeP) are investigated by density functional theory (DFT). All the unligated four-coordinate iron porphyrins have a 3A2g ground state that arises from the (dxy)2(dz2)2(dπ)2 configuration. The calculations confirm experimental results on Fe tetraphenylporphine but do not support the resonance Raman assignment of Fe octaethylporphine as 3Eg, nor the early assignment of Fe octamethyltetrabenzporphine as 5B2g. For the six-coordinate Fe–P( …

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Parameters Affecting Partitioning Of 6 Pcb Congeners In Natural Sediments, Eid A. Alkhatib, Carl Weigand Jan 2002

Parameters Affecting Partitioning Of 6 Pcb Congeners In Natural Sediments, Eid A. Alkhatib, Carl Weigand

Chemistry & Physics Faculty Publications

Polychlorinated biphenyls (PCBs) released by bottom sediments were determined by experiments in which the sediments were artificially resuspended using sediment contaminated with PCBs in a particle entrainment simulator (PES). Sediment cores, spiked with PCBs, were collected from the Housatonic River in Connecticut and run in the PES at simulated shear stresses from 0 to 0.6 N m(-2). Experimental results from these simulations have shown that mean concentration of PCBs in the solid phase for sites with high volatile organic carbon (VOC) were significantly greater than samples with low VOC; the reverse was true for the water phase. In addition, on …

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Biological Reduction Of Perchlorate In Ion Exchange Regenerant Solutions Containing High Salinity And Ammonium Levels, Tina M. Gingras, Jacimaria R. Batista Jan 2002

Biological Reduction Of Perchlorate In Ion Exchange Regenerant Solutions Containing High Salinity And Ammonium Levels, Tina M. Gingras, Jacimaria R. Batista

Civil and Environmental Engineering and Construction Faculty Research

The most promising technologies to remove perchlorate from water are ion exchange and biological reduction. Although successful, ion exchange only separates perchlorate from water; it does not eliminate it from the environment. The waste streams from these systems contain the caustic or saline regenerant solutions used in the process as well as high levels of perchlorate. Biological reduction could be used to treat the regenerant waste solutions from the ion exchange process. A treatment scheme, combining ion exchange and biodegradation, is proposed to completely remove perchlorate from the environment. Perchlorate-laden resins generate brines containing salt concentrations up to 6% or …

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How Does Water Freeze Inside Carbon Nanotubes?, Kenichiro Koga, G.T. Gao, Hideki Tanaka, Xiao Cheng Zeng Jan 2002

How Does Water Freeze Inside Carbon Nanotubes?, Kenichiro Koga, G.T. Gao, Hideki Tanaka, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

Phase behavior of quasi-one-dimensional water confined inside a carbon nanotube is studied in the thermodynamic space of temperature, pressure, and diameter of the cylindrical container. Four kinds of solid-like ordered structures—ice nanotubes—form spontaneously from liquid-like disordered phases at low temperatures. In the model system that comprises of TIP4P water molecules interacting with each other via short-range Lennard–Jones and long-range Coulomb site–site potentials under a periodic boundary condition in the axial direction, the phase change occurs either discontinuously or continuously depending on the path in the thermodynamic space. That the isotherms for a given diameter are found to be similar to …

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Theoretical Investigation Of The Ground And Excited States Of Coumarin 151 And Coumarin 120, Robert J. Cave, Kieron Burke, Edward W. Castner Jr. Jan 2002

Theoretical Investigation Of The Ground And Excited States Of Coumarin 151 And Coumarin 120, Robert J. Cave, Kieron Burke, Edward W. Castner Jr.

All HMC Faculty Publications and Research

We present calculations of various properties of the ground and excited states of Coumarins 151 and 120. These and related coumarins are important in investigating ultrafast solvation processes in liquids and complex solutions as well as being important acceptors in model electron-transfer systems. We calculate the following:  (1) the electronic excitation energies to several low-lying singlet states, (2) ground and excited-state dipole moments, (3) solvation effects on excitation energies, and (4) the properties of single Coumarin 151-water complexes. We test our Time-Dependent Density Functional Theory (TDDFT) calculations against CASSCF, CASPT2 (both single and multistate versions), CIS, and ZINDO. Using TDDFT, …

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Multistate Effects In Calculations Of The Electronic Coupling Element For Electron Transfer Using The Generalized Mulliken−Hush Method, Michael Rust '01, Jason Lappe '00, Robert J. Cave Jan 2002

Multistate Effects In Calculations Of The Electronic Coupling Element For Electron Transfer Using The Generalized Mulliken−Hush Method, Michael Rust '01, Jason Lappe '00, Robert J. Cave

All HMC Faculty Publications and Research

A simple diagnostic is developed for the purpose of determining when a third state must be considered to calculate the electronic coupling element for a given pair of diabatic states within the context of the generalized Mulliken−Hush approach (Chem. Phys. Lett. 1996, 275, 15−19). The diagnostic is formulated on the basis of Löwdin partitioning theory. In addition, an effective 2-state GMH expression is derived for the coupling as it is modified by the presence of the third state. Results are presented for (i) a model system involving charge transfer from ethylene to methaniminium cation, (ii) a …

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Electrical Network-Based Time-Dependent Model Of Electrical Breakdown In Water, R. P. Joshi, J. Qian, K. H. Schoenbach Jan 2002

Electrical Network-Based Time-Dependent Model Of Electrical Breakdown In Water, R. P. Joshi, J. Qian, K. H. Schoenbach

Bioelectrics Publications

A time-dependent, two-dimensional, percolative approach to model dielectric breakdown based on a network of parallel resistor–capacitor elements having random values, has been developed. The breakdown criteria rely on a threshold electric field and on energy dissipation exceeding the heat of vaporization. By carrying out this time-dependent analysis, the development and propagation of streamers and prebreakdown dynamical evolution have been obtained directly. These model simulations also provide the streamer shape, characteristics such as streamer velocity, the prebreakdown delay time, time-dependent current, and relationship between breakdown times, and applied electric fields for a given geometry. The results agree well with experimental data …

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On-Road Remote Sensing Of Automobile Emissions In The Denver Area: Year 3, Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman Jan 2002

On-Road Remote Sensing Of Automobile Emissions In The Denver Area: Year 3, Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman

Fuel Efficiency Automobile Test Publications

No abstract provided.

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On-Road Remote Sensing Of Automobile Emissions In The Los Angeles Area: Year 3 (Riverside), Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman Jan 2002

On-Road Remote Sensing Of Automobile Emissions In The Los Angeles Area: Year 3 (Riverside), Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman

Fuel Efficiency Automobile Test Publications

No abstract provided.

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On-Road Remote Sensing Of Automobile Emissions In The Phoenix Area: Year 3, Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman Jan 2002

On-Road Remote Sensing Of Automobile Emissions In The Phoenix Area: Year 3, Sajal S. Pokharel, Gary A. Bishop, Donald H. Stedman

Fuel Efficiency Automobile Test Publications

No abstract provided.

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Opacity Enhancement Of The On-Road Remote Sensor For Hc, Co And No, Donald H. Stedman, Gary A. Bishop Jan 2002

Opacity Enhancement Of The On-Road Remote Sensor For Hc, Co And No, Donald H. Stedman, Gary A. Bishop

Fuel Efficiency Automobile Test Publications

No abstract provided.

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Article Are Hydrogen Bonds Unique Among Weak Interactions In Their Ability To Mediate Electronic Coupling?, Emily Cukier '03, Sarah Daniels '02, Eric Vinson '01, Robert J. Cave Jan 2002

Article Are Hydrogen Bonds Unique Among Weak Interactions In Their Ability To Mediate Electronic Coupling?, Emily Cukier '03, Sarah Daniels '02, Eric Vinson '01, Robert J. Cave

All HMC Faculty Publications and Research

Superexchange effects on the electronic coupling element for electron transfer are investigated using water dimers and atomic donors and acceptors. We compare the electronic coupling elements obtained with H-bonded dimers to those obtained for other water dimer geometries at given donor−acceptor and oxygen−oxygen distances. The H-bonded orientation does not yield significantly different coupling elements from non-H-bonded orientations at a given oxygen−oxygen distance. In addition, the distance dependence of the coupling mediated by H-bonds is not significantly different from that for other dimer geometries. It is found that protonation of the intervening waters has a significant effect on coupling elements for …

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Time-Dependent Density Functional Theory Investigation Of The Ground And Excited States Of Coumarins 102, 152, 153, And 343, Robert J. Cave, Edward W. Castner Jr. Jan 2002

Time-Dependent Density Functional Theory Investigation Of The Ground And Excited States Of Coumarins 102, 152, 153, And 343, Robert J. Cave, Edward W. Castner Jr.

All HMC Faculty Publications and Research

We present calculations of various properties of the ground and excited electronic states of coumarins 102, 152, 153, and 343. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT), we examine the excitation energies to the S1 and S2 states, the ground and excited-state dipole moments, and the lowest ionization potentials of these coumarins. In the case of C153, we locate two distinct S0 minima due to differing conformations of the julolidyl ring structure and compare properties for the syn and anti conformers. For C343, we examine the possibility of proton transfers in the ground …

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Effect Of Polymer-Surface Mobility On Adhesion In Poly(Methyl Methacrylate)-Tape System, Bhavesh C. Gandhi, Frank D. Blum, Lokeswarappa R. Dharani Jan 2002

Effect Of Polymer-Surface Mobility On Adhesion In Poly(Methyl Methacrylate)-Tape System, Bhavesh C. Gandhi, Frank D. Blum, Lokeswarappa R. Dharani

Chemistry Faculty Research & Creative Works

The interaction between two polymer layers, especially adhesion between them, plays an important role in polymer processing and other applications. Detailed knowledge of the molecular structure and dynamics of polymer interfaces, and how they relate to macroscopic mechanical properties, should help designers construct more functional systems. Unfortunately, there have been few studies where both molecular and macroscopic studies have been performed on similar systems. In previous studies from our group, we have probed the dynamics of poly(methyl acrylate) (PMA) and thermal behavior of poly(methyl methacrylate) (PMMA) on silica. These studies helped us paint a picture for strongly bound molecules on …

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Fire Retardant Halogen-Antimony-Clay Synergism In Polypropylene Layered Silicate Nanocomposites, Marco Zanetti, Giovanni Camino, Domenico Canavese, Alexander B. Morgan, Frank K. Lamelas, Charles A. Wilkie Jan 2002

Fire Retardant Halogen-Antimony-Clay Synergism In Polypropylene Layered Silicate Nanocomposites, Marco Zanetti, Giovanni Camino, Domenico Canavese, Alexander B. Morgan, Frank K. Lamelas, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites of polypropylene-graft-maleic anhydride with organically modified clays have been prepared and characterized by X-ray diffraction and transmission electron microscopy. Their combustion behavior has been evaluated using oxygen consumption cone calorimetry. Synergy is observed between the nanocomposite formed and conventional vapor phase fire retardants, such as the combination of decabromodiphenyloxide and antimony oxide. The presence of bromine and antimony does not affect the heat release rate curves of the virgin polymer.

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Three-Dimensional Structure Of The Complexin/Snare Complex, Xiaocheng Chen, Diana R. Tomchick, Evgueni Kovriguine, Demet Araç, Mischa Machius, Thomas C. Südhof, Josep Rizo Jan 2002

Three-Dimensional Structure Of The Complexin/Snare Complex, Xiaocheng Chen, Diana R. Tomchick, Evgueni Kovriguine, Demet Araç, Mischa Machius, Thomas C. Südhof, Josep Rizo

Chemistry Faculty Research and Publications

During neurotransmitter release, the neuronal SNARE proteins synaptobrevin/VAMP, syntaxin, and SNAP-25 form a four-helix bundle, the SNARE complex, that pulls the synaptic vesicle and plasma membranes together possibly causing membrane fusion. Complexin binds tightly to the SNARE complex and is essential for efficient Ca2+-evoked neurotransmitter release. A combined X-ray and TROSY-based NMR study now reveals the atomic structure of the complexin/SNARE complex. Complexin binds in an antiparallel α-helical conformation to the groove between the synaptobrevin and syntaxin helices. This interaction stabilizes the interface between these two helices, which bears the repulsive forces between the apposed membranes. These results …

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Molecular Structures Of The Metastable Charge-Transfer Complexes Of Benzene (And Toluene) With Bromine As The Pre-Reactive Intermediates In Electrophilic Aromatic Bromination, Alexandr V. Vasilyev, Sergey V. Lindeman, Jay K. Kochi Jan 2002

Molecular Structures Of The Metastable Charge-Transfer Complexes Of Benzene (And Toluene) With Bromine As The Pre-Reactive Intermediates In Electrophilic Aromatic Bromination, Alexandr V. Vasilyev, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Successful crystallization and X-ray crystallographic analyses of the highly metastable (1∶1) complexes of bromine with benzene and toluene establish the unique (localized) structure B that differs in notable ways from the long-accepted (delocalized) structure A. Furthermore, we demonstrate the (highly structured) charge-transfer complexes [C6H6,Br2] and [CH3C6H5,Br2] to be the pre-reactive intermediates that are converted (via an overall Br+ transfer) to the Wheland intermediates in electrophilic aromatic bromination. The role of the dative ion pairs [C6H6˙+ Br2˙ …

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The Role Of Size Exclusion Chromatography-Flame Atomic Absorption Spectrometry In The Treatment Chemistry Of Potable Water, Marina C. Koether Jan 2002

The Role Of Size Exclusion Chromatography-Flame Atomic Absorption Spectrometry In The Treatment Chemistry Of Potable Water, Marina C. Koether

Faculty and Research Publications

The percentage composition of Al13, [AlO4Al12(OH)24(H2O)12]7+, in water treatment coagulants is an important criterion in the development and use of polymeric coagulants. Polymeric coagulants are generally used in cold climates or with highly turbid waters. Size exclusion chromatography–flame atomic absorption spectrometry (SEC-FAAS) can separate Al13 and monomeric Al within 6 min. The percentage composition of Al13 and monomeric Al is determined by solving two simultaneous equations. Due to overlapping peaks, a 10% error is associated with this method of quantification. This method can be …

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Induction Of Myocarditis And Valvuluitis In Lewis Rats By Different Epitopes Of Cardiac Myosin And Its Implications In Rheumatic Carditis, Jeffrey E. Galvin, Mark E. Hemric, Stanley D. Konsanke, Stephen M. Factor, Anthony Quinn, Madeleine W. Cunningham Jan 2002

Induction Of Myocarditis And Valvuluitis In Lewis Rats By Different Epitopes Of Cardiac Myosin And Its Implications In Rheumatic Carditis, Jeffrey E. Galvin, Mark E. Hemric, Stanley D. Konsanke, Stephen M. Factor, Anthony Quinn, Madeleine W. Cunningham

Faculty Publications and Presentations

Immune responses against cardiac myosin and group A streptococcal M protein have been implicated in the pathogenesis of rheumatic heart disease. Although cardiac myosin is known to produce myocarditis in susceptible animals, it has never been investigated for its role in production of valvular heart disease, the most serious sequelae of group A streptococcal infection in acute rheumatic fever. In our study, cardiac myosin induced valvulitis in the Lewis rat, and epitopes responsible for production of valvulitis were located in the rod region. Human and rat cardiac myosins induced severe myocarditis in the Lewis rats as expected. A purified S2 …

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Thermogravimetric Studies Of Pmma On Silica, Bing Zhang, Frank D. Blum Jan 2002

Thermogravimetric Studies Of Pmma On Silica, Bing Zhang, Frank D. Blum

Chemistry Faculty Research & Creative Works

The thermal degradation of poly(methyl methacrylate) (PMMA) has been studied extensively. It is well accepted that the degradation process is a radical chain reaction involving initiation, depropagation, transfer, and termination reactions. In the degradation process, the factors having observable effects on the decomposition behavior include molecular mass, polydispersity, tacticity, and sample dimensions. The effects of tacticity on the degradation behavior of PMMA were investigated by Kashiwagi et al., Jellinek et al. And Chiamtore et al. The results indicated that both isotactic and syndiotactic PMMA have similar decomposition pathways and activation energies. Isotactic PMMA will decompose at a slightly lower temperature …

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Motion Based Event Recognition Using Hmm, Gu Xu, Yu-Fei Ma, Hong-Jiang Zhang, Shiqiang Yang Jan 2002

Motion Based Event Recognition Using Hmm, Gu Xu, Yu-Fei Ma, Hong-Jiang Zhang, Shiqiang Yang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Motion is an important cue for video understanding and is widely used in many semantic video analyses. We present a new motion representation scheme in which motion in a video is represented by the responses of frames to a set of motion filters. Each of these filters is designed to be most responsive to a type of dominant motion. Then we employ hidden Markov models (HMMs) to characterize the motion patterns based on these features and thus classify basketball video into 16 events. The evaluation by human satisfaction rate to classification result is 75%, demonstrating effectiveness of the proposed approach …

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Hydrolysis Of Thionopeptides By The Aminopeptidase From Aeromonas Proteolytica:  Insight Into Substrate Binding, David L. Bienvenue, Danuta M. Gilner, Richard C. Holz Jan 2002

Hydrolysis Of Thionopeptides By The Aminopeptidase From Aeromonas Proteolytica:  Insight Into Substrate Binding, David L. Bienvenue, Danuta M. Gilner, Richard C. Holz

Chemistry Faculty Research and Publications

A series of l-leucine aniline analogues were synthesized that contained either a carbonyl or thiocarbonyl as a part of the amide bond. Additionally, the para-position on the phenyl ring of several substrates was altered with various electron-withdrawing or donating groups. The kinetic constants Km and kcat were determined for the hydrolysis of each of these compounds in the presence of the aminopeptidase from Aeromonas proteolytica (AAP) containing either Zn(II) or Cd(II). The dizinc(II) form of AAP ([ZnZn(AAP)]) was able to cleave both carbonyl and thiocarbonyl containing peptide substrates with similar efficiency. However, the dicadmium(II) form of AAP …

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Polystyrene/Graphite Nanocomposites: Effect On Thermal Stability, Fawn Marie Uhl, Charles A. Wilkie Jan 2002

Polystyrene/Graphite Nanocomposites: Effect On Thermal Stability, Fawn Marie Uhl, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites consisting of polymer and clay have been shown to exhibit a significant reduction in flammability and an increase in mechanical properties. This work examines the effect of thermal stability and mechanical properties of nanocomposites prepared from potassium graphite and styrene. Synthesis of nanocomposites was accomplished by using potassium graphite (KC8) as the initiator in the polymerization of styrene. A slight increase in thermal stability is observed but mechanical properties are decreased.

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Silicon-Methoxide-Modified Clays And Their Polystyrene Nanocomposites, Jin Zhu, Paul Start, Kenneth A. Mauritz, Charles A. Wilkie Jan 2002

Silicon-Methoxide-Modified Clays And Their Polystyrene Nanocomposites, Jin Zhu, Paul Start, Kenneth A. Mauritz, Charles A. Wilkie

Chemistry Faculty Research and Publications

Silicon-methoxide-containing modified clays were obtained through cationic exchange between the sodium clay and the ammoniumcation of [3-(trimethoxysilyl) propyl]octadecyldimethylammoniumchloride (Si18). The nanocomposites were prepared through bulk polymerization of styrene in which the Si18 clay was dispersed. The silicon-methoxide offers the possibility of reaction between the methoxide and a clay hydroxyl group to link together the cation and the clay. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. Their thermal stability and flame retardancy were measured by thermogravimetric analysis (TGA) and cone calorimetry. Linkage between the silicon and the clay apparently occurs in the clay but …

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Electrical And Magnetotransport Properties Of Canted Antiferromagnet Dy₅Si₂Ge₂, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, Zili Chu, William B. Yelon, V. Prasad, A. V. Morozkin, Satish K. Malik, S. V. Subramanyam Jan 2002

Electrical And Magnetotransport Properties Of Canted Antiferromagnet Dy₅Si₂Ge₂, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, Zili Chu, William B. Yelon, V. Prasad, A. V. Morozkin, Satish K. Malik, S. V. Subramanyam

Physics Faculty Research & Creative Works

Summary form only given. Since the giant magnetocaloric effect is encountered in a ferromagnetic Gd5Si2Ge2 alloy near room temperature it is considered as a suitable material for magnetic refrigerator applications. Also a commensurate structural transition occurs at the magnetic transition temperature and there is a good correlation between the crystal structure and magnetic properties. Such observations have triggered numerous experimental studies on similar rare earth alloys and compounds. We have synthesized its Dy- analogue, namely, Dy5Si2Ge2 and have characterized it by means of room temperature X-ray diffraction, ac magnetic susceptibility (15 K - 300 K), electrical resistivity (at zero field …

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