bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonant laser excitation of molecular wires
Authors: Kohler Sigmund , Lehmann Jörg , Camalet Sébastien , Hänggi Peter
Published: April 2004

We investigate the influence of external laser excitations on the average current through bridged molecules. For the computation of the current, we use a numerically very efficient formalism that is based on the Floquet solutions of the time‐dependent molecule Hamiltonian. It is found that the current as a function of the laser frequency exhibits characteristic peaks originating from resonant excitations of electrons to bridge levels that are unoccupied in the absence of radiation. The electric current through the molecule can exhibit a drastic enhancement by several orders of magnitude.
Diffusion‐Weighted MRI and Response to Anti‐Cancer Therapies
Authors: Galons Jean Philippe , Morse David L. , Jennings Dominique R. , Gillies Robert J.
Published: April 2004

In oncology practice, longitudinal studies are routinely conducted to monitor the size and enhancement of tumors in cancer patients undergoing therapy. Imaging protocols typically use gadolinium‐enhanced T1‐weighted images or T2‐weighted images from which tumor size is inferred and tumor response estimated. The past few years have also seen the emergence of diffusion‐weighted magnetic resonance imaging (DWMRI) as a potential alternative to monitor therapeutic response (Kauppinen, R.A., NMR Biomed. 2002, 15, 6). The attractiveness of DWMRI resides in its ability to detect local microstructural changes associated with treatment long before their effects are translated into effective size changes. Damage to cell membrane integrity, changes in viscosity, and/or relative size of intra‐ vs. extracellular compartments all translate into changes in the apparent diffusion coefficient of tumor water measured by DWMRI. This dependence makes DWMRI a particularly sensitive method to detect response to a wide variety of chemotherapeutic agents. This review will focus on the emerging role of DWMRI to monitor the response of tumors to anti‐cancer chemotherapies.
Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non‐Gaussian Diffusion
Authors: Liu Chunlei , Bammer Roland , Moseley Michael E.
Published: April 2004

For non‐Gaussian distributed random displacement, which is common in restricted diffusion, a second‐order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second‐order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher‐order partial differential equation (PDE). The relationship between the higher‐order tensor coefficients of the PDE and the higher‐order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher‐order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher‐order tensor coefficients can be measured using conventional diffusion‐weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non‐Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q‐space approach. The second‐order approximation of GDTI was shown to be DTI.
A Density Functional Study of Ethylene Insertion into the M‐methyl (M = Ti, Zr) Bond for Different Catalysts, with a QM/MM Model for the Counterion, B(C6F5)3CH3−
Authors: Vanka Kumar , Xu Zhitao , Ziegler Tom
Published: April 2004

Single site homogeneous catalysts have been studied extensively in recent years as alternatives to traditional heterogeneous catalysts. The current theoretical study uses density functional theory to study the insertion process of the ethylene monomer into the titanium‐carbon chain for contact ion‐pair systems of the type [L1L2TiCH3‐μ‐CH3‐B(C6F5)3], where L1, L2, are Cp, NPH3, and other ligands. Different modes of approach cis and trans to the μ‐CH3 bridge were considered. The counterion, B(C6F5)3CH3−, was modeled by QM/MM methods. The value of ΔHtot—the total barrier to insertion—was found to be positive (in the range of 4–15 kcal/mol). The ability of the ancillary ligands, L1 and L2, to stabilize the ion‐pair was found to be an important factor in determining the value of δHtot. On replacing the titanium metal center with zirconium, the ΔHtot values were found to be lowered (in the range of 2–9 kcal/mol), indicating that they would be better catalysts than their titanium analogues. The size of the ligands L1 and L2 was increased by replacing hydrogens in the ligands with tertiary butyl groups. The value of ΔHtot was found to increase (in the range of 10–28 kcal/mol) in contrast to the simple systems, for both the cis and trans cases of approach, with the cis mode of approach giving lower values of ΔHtot. Solvent effects were incorporated with cyclohexane (ε = 2.023) as the solvent, and were found to have a minor influence, ±(0.5–1.5) kcal/mol) on the insertion barrier for all the cases studied.
Binding of cadmium, copper, and zinc to humic substances originating from municipal solid waste compost
Authors: Kaschl Arno , Römheld Volker , Chen Yona
Published: April 2004

The application of municipal solid waste (MSW) compost increases both the trace metal loading and the organic matter in the soil. To characterize the quality and metal‐binding capacity of the compost OM, we extracted humic acid (HA) and fulvic acid (FA) from mature MSW compost and analyzed them for elemental composition, acid‐titratable functional groups, total metal content, and structural components (by 13C NMR). HA constituted 67% of all extracted humic substances and differed significantly from HAs of cultivated lands: The compost HA exhibited smaller molecular size, a higher N content, and lower aromaticity due to large amounts of saturated aliphatic components. Metal complexation studies of the extracted HA and FA were performed by equilibrium dialysis titration. The complexing capacity (CC) was highest for Cu: CCHA = 3357 and CCFA = 5221 μmol Cu g−1 of dissolved organic carbon (DOC) at pH 5. Zn and Cd were bound (at pH 7) in smaller concentrations: CCHA(Zn) = 2167, CCFA(Zn) = 2809, CCHA(Cd) = 2386, and CCFA(Cd) = 2468 μmol metal g−1 of DOC. Stability constants for binding on the strongest sites (pKint) were determined as pKintHA = 6.6 and pKintFA = 7.3 for Cu at pH 5; and pKintHA = 8.0 and pKintFA = 6.4 for Cd at pH 7. Since these measured parameters fall within the ranges of values obtained for soil humic substances, we conclude that in soils with little organic matter, compost addition will significantly increase the amount of highly reactive organic complexing agents for trace metals in the soil.
Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acids
Authors: Meffert Anja , Grotemeyer Jürgen
Published: April 2004

The cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4‐dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization‐time‐of‐flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano‐ or femtosecond laser pulses.

Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well‐known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process.
Thermal effects in the ultrafast photoinduced electron transfer from a molecular donor anchored to a semiconductor acceptor
Authors: Stier William , Prezhdo Oleg V.
Published: April 2004

A nonadiabatic molecular dynamics (MD) simulation of the photoinduced electron transfer (ET) from a molecular electron donor to the TiO2 semiconductor acceptor is carried out in a microcanonical ensemble with an average temperature of 350 K. The electronic structure of the dye–semiconductor system and the adiabatic dynamics are simulated by ab initio MD, while the nonadiabatic (NA) effects are incorporated by a quantum‐classical mean‐field approach. The ET dynamics are driven by thermal fluctuations that dominate ionic motions at the simulated temperature. The ground and excited state ion dynamics are similar; therefore, the change in the quantum force due to the electronic photoexcitation can be neglected, and the analysis is greatly simplified. The simulated ET occurs on a 5‐fs timescale, in agreement with recent ultrafast experimental data. Vibrational motions of the chromophore ring carbons induce an oscillation of the photoexcited state energy, resulting in a bimodal distribution of the initial conditions for ET. At low energies the photoexcited state is localized primarily on the chromophore, while at high energies the photoexcited state is substantially delocalized into the TiO2 surface. Thermally driven adiabatic transfer is the dominant ET mechanism. Compared to the earlier simulation at 50 K, the rate of NA transfer at 350 K remains almost unchanged, whereas the rate of adiabatic ET increases substantially.
Printed organic transistors and molded plastic lasers
Authors: Rogers John A. , Tate Jennifer , Li Wenjie , Bao Zhenan , Dodabalapur Ananth
Published: April 2004

We describe the use of microcontact printing and elastomeric molding for fabricating two types of devices that incorporate thin films of active organic materials: thin film transistors and plastic lasers. The simplicity of these techniques and the good performance of devices formed with them suggest their potential utility for emerging applications of organic materials in electronic and optical systems.
Mass‐independent isotope effects and their use in understanding natural processes
Authors: Thiemens Mark H.
Published: April 2004

In 1983, Thiemens and Heidenreich (Science 219, 1073) reported the discovery of a mass‐independent isotope process in oxygen. Subsequently, mass‐independent isotopic compositions were observed in meteorites, atmospheric O2, CO2, O3, H2O2, CO, N2O, and aerosol sulfate and nitrate. In addition, solid samples from the Namibian Desert, Antarctic dry valleys, Miocene volcanic ash, and Death Valley varnishes all possess mass‐independent isotopic compositions that have permitted new scientific insights to be obtained. Sulfur mass‐independent isotopic anomalies in Precambrian samples have provided a completely new mechanism to track atmospheric O2 levels and the evolution of life from ∼3.9 to 2.2 × 109 years ago. Measurements of mass‐independent isotopic compositions in Martian meteoritic sulfates and carbonates have also provided new information on Martian atmosphere‐regolith interactions and history.

In sum, the use of mass‐independent isotopic compositions has advanced a wide range of geo‐ and cosmo‐chemical frontiers. In addition, these newly discovered effects have provided a new means to probe the chemical physics of molecular transition state theory.
Surface Model for Gas‐Phase Polymerizations of Ethylene and Propylene Using Supported Metallocene/Methylalumoxane Catalysts
Authors: Kaminsky Walter , Lemstra Piet J. , Loos Joachim , Müller Fabian , Niemantsverdriet J.W. (Hans) , Thüne Peter C. , Weingarten Ulrich
Published: April 2004

In order to obtain more detailed information about supported metallocene/methylaluminoxane catalysts, two catalysts are supported onto a flat silicon wafer by spincoating impregnation. These model catalysts are characterized by SEM and EDX showing a film of metallocene catalyst dispersed inside the methylaluminoxane matrix, as well as regions of a localized increased concentration of the catalyst. Applying these model catalysts in a gas‐phase polymerization reactor results in rather homogeneous films of polyethylene and polypropylene, respectively. In addition, crater‐like and spherical polymer structures can be observed, probably formed by inhomogeneous catalyst distribution.
Syndiospecific Living Catalysts for Propylene Polymerization: Effect of Fluorination on Activity, Stereoselectivity, and Termination
Authors: Mason Andrew F. , Tian Jun , Hustad Philip D. , Lobkovsky Emil B. , Coates Geoffrey W.
Published: April 2004

The polymerization of propylene using a variety of fluorinated bis(phenoxyimine)titanium complexes is reported. The synthesis of ten complexes containing varying fluorinated N‐aryl substituents is described. X‐ray structural and solution NMR data indicate that these complexes are C2‐symmetric in the solid state, although in some cases C1‐symmetric isomers are observed in solution. When activated with methylalumoxane, all complexes formed syndiotactic polypropylene. Catalysts with ortho‐fluorine substituents formed polymers with very narrow molecular weight distributions, indicative of a living polymerization. Catalysts with fluorine in at least the ortho and para positions exhibited the highest syndio‐specificities. Catalysts with meta‐ or para‐fluorine‐containing substituents were more active for propylene polymerization than the corresponding non‐fluorinated catalyst.
Asymmetric Aldol Reactions Using Boron Enolates
Authors: Cowden Cameron J. , Paterson Ian
Published: April 2004

The directed aldol reaction allows the construction of new carbon–carbon bonds in a regio‐, diastereo‐, and enantioselective manner. The kinetically controlled, boron‐mediated aldol reaction is particularly powerful for the efficient synthesis of β‐hydroxy carbonyl compounds. Compared to other metal enolates, the boron–oxygen bond in boron enolates is relatively short which, on addition to aldehydes, leads to tight cyclic transition states and highly stereoselective carbon–carbon bond formation. Moreover, variation of the steric demands of the ligands on boron allows discrimination between competing transition states. Chiral auxiliaries attached to the boron enolate are frequently employed to control the relative and absolute stereochemistry of the aldol products. Asymmetric reactions using chiral ligands on boron are also possible and these produce useful enantiomerically enriched adducts. The utility of boron‐mediated aldol reactions has been demonstrated in numerous total syntheses of complex polyoxygenated natural products, and several of these are highlighted in the Application to Synthesis section of this chapter.

Several reviews of the directed aldol reaction are available, including the
Organic Reactions
chapter by Mukaiyama in 1981.
9
The material covered in this review concerns only the asymmetric formation of β‐hydroxy carbonyl compounds using boron enolates and surveys the literature from 1981 until the end of 1995.
Epoxide Migration (Payne Rearrangement) and Related Reactions
Authors: Hanson Robert M.
Published: April 2004

Under a variety of basic conditions, 2,3‐epoxy alcohols rearrange with inversion at C‐2. The reaction, originally referred to in the literature as the β‐oxanol rearrangement, is now exclusively referred to as epoxide migration or Payne rearrangement.

Epoxide migration is reversible, often leading to a mixture of epoxy alcohol isomers. Furthermore, in the presence of hydroxide or other nucleophiles,in situopening of the equilibrating species may be observed. When such opening is desired, epoxide migration becomes a powerful method for the introduction of functionality into a substrate containing a 2,3‐epoxy alcohol moiety. However, when opening is not desired, epoxide migration can become a significant problem.

The epoxide migration process lends itself to other synthetically useful manipulations. For example, the anionic equilibrating species may also be trapped with electrophiles such as alkyl and silyl halides, alkyl sulfonates, and epoxides. Electrophilic trapping may be inter‐ or intramolecular, and has been used as a means of delivering functionality to either C‐2 or C‐3 selectively.

The intent of this chapter is to provide a comprehensive review of epoxide migration, including factors influencing the equilibrium position, conditions leading toin situepoxide opening, and examples of electrophilic trapping. The reaction is discussed in relation to its utility as a synthetic method as well as its prevention as an unwanted side reaction.

Related rearrangements in which either the epoxide or hydroxy oxygen has been replaced with nitrogen or sulfur have also been studied. These reactions, referred to in the literature as aza‐Payne and thia‐Payne rearrangements, respectively, are comprehensively included in this chapter as well. For the purposes of this discussion, the term “forward” aza‐Payne rearrangement refers to the direction of reaction leading from oxirane to aziridine. Similarly, “forward” thia‐Payne rearrangement refers to the direction of reaction leading from oxirane to thiirane. In the case of aza‐Payne rearrangements, both forward and reverse reactions have been effected, and in this chapter the term “reverse” aza‐Payne rearrangement refers to reactions leading from aziridine to oxirane.

Epoxides have long been considered important in the chemistry of carbohydrates, and epoxide migration in the context of carbohydrate chemistry has been discussed in several reviews. In addition, particularly since discovery of the catalytic asymmetric epoxidation of allylic alcohols and the rise in importance of enantiomerically enriched acyclic epoxy alcohols, epoxide migration within situopening in acyclic systems has been much studied. The tabular survey summarizes the literature of epoxide migration and related reactions, including equilibration, in situ opening and trapping, aza‐Payne rearrangements, and thia‐Payne rearrangements, from 1931 to 1999. Reports referring to reactions involving addition at C‐1 or C‐3 without inversion of stereochemistry at C‐2 as “Payne rearrangements” are not covered in this review.
Dioxirane Epoxidation of Alkenes
Authors: Adam Waldemar , Saha‐Möller Chantu R. , Zhao Cong‐Gui
Published: April 2004

An ideal oxidant should be highly reactive, selective, and environmentally benign. It should transform a broad range of substrates with diverse functional groups, preferably under catalytic conditions, and be readily generated from commercially available and economical starting materials. Of course, such an ideal oxidant has not yet been invented; however, the dioxiranes, which have risen to prominence during the past few decades, appear to fulfill these requirements in many respects. These three membered ring cyclic peroxides are very efficient in oxygen transfer, yet very mild toward the substrate and product. They exhibit chemo‐, regio‐, diastereo‐, and enantioselectivities, act catalytically, and can be readily prepared from a suitable ketone (for example, acetone) and potassium monoperoxysulfate (2KHSO
5
· K
2
SO
4
· Caroate
®
, Oxone
®
, or Curox
®
), which are low‐cost commercial bulk chemicals. Throughout the text KHSO
5
is used to specify this oxygen source, rather than refer to one of the commercial trade names.

Isolated dioxiranes (as solutions in the parent ketones) perform oxidation under strictly neutral conditions so that many elusive oxyfunctionalized products have been successfully prepared in this way for the first time. Epoxidations, heteroatom oxidations, and X‐H insertions constitute the most investigated oxidations by dioxiranes. An overview of these transformations is displayed in a rosette scheme. These preparatively useful oxidations have been extensively reviewed during the last decade in view of their importance in synthetic chemistry.

This chapter deals mainly with the epoxidation of carbon‐carbon double bonds [π bonds in simple alkenes and with these electron donors (ED), electron acceptors (EA), and with both ED and EA] with either isolated or
in situ
generated dioxiranes. In view of the vast amount of material on alkene oxidation, the epoxidation of the double bonds in cumulenes (allenes, acetylenes) and arenes is covered in a separate chapter, together with the oxidation of heteroatom functionalities (nonbonding electron pairs), X‐H insertions (σ bonds) and transition‐metal complexes.
Self‐tuning control for polynomial systems using a receding horizon observer and control strategy
Authors: Mareels Iven
Published: April 2004

A receding horizon observer and control scheme is introduced for non‐linear systems described by polynomial maps. This control scheme has a natural interpretation as a two‐stage adaptive or self‐tuning control algorithm. The non‐linear feedback that results is defined only on the basis of past input and output measurements. The computational complexity aspects of this approach to adaptive or self‐tuning control are briefly discussed. A linear system and a Hénon map example are used to illustrate the ideas. Copyright © 2004 John Wiley & Sons, Ltd.
Thermal and morphological studies on γ‐Fe2O3 polystyrene composites and the affect of additives
Authors: Govindaraj B. , Sastry N. V. , Venkataraman A.
Published: April 2004

γ‐Fe2O3polystyrene (PS) composite films were prepared by a gel‐casting technique to obtain monodisperse composite films. To understand the effect of additives on the prepared composite films, additives such as rice husk ash and thiourea were made to disperse into the PS matrix. The as‐prepared γ‐Fe2O3 PS composite films, along with their additives, were subjected to characterization and study by X‐ray diffraction, scanning electron microscopy, thermal, IR, and dielectric measurement techniques. These studies showed monodisperse and chemically homogenous composite films with an increase in thermal behavior. An interesting self‐assembly of rod‐like nanoparticles of γ‐Fe2O3 particles into the polymer matrix, which formed spherical packets, was observed for the γ‐Fe2O3PS composite film. The electrical behavior of these films was interesting, as some showed conduction whereas others showed an increase in dielectric behavior. This nature was explained by the dielectric measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 778–788, 2004
Wear properties and mechanisms of nylon and carbon‐fiber‐reinforced nylon in dry and wet conditions
Authors: Wang Junxiang , Gu Mingyuan
Published: April 2004

A microinjection machine was used to prepare specimens of nylon 1010 and carbon fiber (CF)‐reinforced nylon 1010 composites. The friction and wear properties were investigated with a ring–block wear tester in wet and dry conditions. The wear rate of nylon 1010 increased, but the friction coefficient decreased in water in comparison to that in dry sliding. The wear resistance of CF–nylon increased remarkably by two orders of magnitude due to the reinforcement of the CF. The minimum wear rate was obtained with a 20 vol % content of CF filled in nylon in wet lubrication. The wear rate of CF–nylon in dry sliding friction was as much as approximately eight times, and the friction coefficient decreased to approximately half its value compared with that in water under a load of 200 N. The morphologies and the wear mechanisms of worn surfaces were also examined with Fourier transform infrared spectroscopy and scanning electron microscopy. The results show that the hydrolization of amide groups and the resulting decrease in hydrogen bonds between the molecules of nylon 1010 were important factors that led to a high wear rate of nylon in water. We concluded that the fiber, protruding out of the rubbing surface and carrying the main load between the contacting surfaces, held up the swelling properties and improved the mechanical strength of nylon, which would account for the evident reduction of wear in the nylon composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 789–795, 2004
Cibacron Blue F3GA incorporated magnetic poly(2‐hydroxyethyl methacrylate) beads for lysozyme adsorption
Authors: Odabaşı Mehmet , Denizli Adil
Published: April 2004

Lysozyme adsorption onto Cibacron Blue F3GA incorporated magnetic poly(2‐hydroxyethyl methacrylate) (mag‐PHEMA) beads was investigated. Mag‐PHEMA beads (80–120 μm) were produced by dispersion polymerization. The triazine dye Cibacron Blue F3GA was incorporated covalently as a dye ligand. These dye‐incorporated beads, having a swelling ratio of 34% (w/w) and carrying different amounts of Cibacron Blue F3GA (12.2–42.8 μmol/g) were used in lysozyme adsorption studies. The effects of the initial concentration, pH, ionic strength, and temperature on the adsorption efficiency of dye‐incorporated beads were studied in a batch reactor. The effects of the Cibacron Blue F3GA loading on the lysozyme adsorption were also studied. The nonspecific adsorption of lysozyme on the mag‐PHEMA beads was 0.8 mg/g. Cibacron Blue F3GA attachment significantly increased the lysozyme adsorption up to 295 mg/g. More than 90% of the adsorbed lysozyme was desorbed in 1 h in a desorption medium containing 1.0M KSCN at pH 8.0. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 719–725, 2004
Effect of the amorphous segment on the nonisothermal crystallization and morphology of oxyethylene–oxybutylene block copolymers
Authors: Xu Jun‐Ting , Xue Liang , Mai Shao‐Min , Ryan A. J.
Published: April 2004

The nonisothermal crystallization and morphology of three oxyethylene–oxybutylene block copolymers with different architectures (E50B70, B65E75B65, and E35B114E35) were compared with those of three blends (E56B27/B14, B37E77B37/B14, and E38B38E38/B14) with the same composition and morphology (E and B represent oxyethylene and oxybutylene units, respectively, and the subscripts denote the degree of polymerization), and the effect of the amorphous block was examined. The neat block copolymers had larger d‐spacings and higher melting temperatures than the corresponding blends. In nonisothermal crystallization, the neat block copolymers had lower crystallization temperatures at high cooling rates. The difference in the crystallization temperatures became smaller at low cooling rates, and some of the neat block copolymers could have higher crystallization temperatures. Polarized optical microscopy showed that the neat block copolymers had smaller dimensions of crystal growth and smaller size of spherulites than the blends. The lower crystallization temperatures and less perfect morphology were attributed to the slower rate of conformational rearrangement of the amorphous block, which was required by the chain folding of the crystallizable block. This effect was more evident in the E35B114E35 triblock copolymer, in which both ends of the amorphous B block were immobilized at the interface. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 870–876, 2004
Isothermal crystallization behavior of polypropylene catalloys
Authors: Lin Zhonghua , Peng Mao , Zheng Qiang
Published: April 2004

The isothermal crystallization behavior of polypropylene (PP) catalloys and neat PP were studied with differential scanning calorimetry and polarized optical microscopy (POM). The crystallization kinetics of the samples were described with the well‐known Avrami equation. The crystallization rate depended remarkably on the content of the ethylene component in the PP catalloys. The crystallization half‐time increased obviously with the increase of the ethylene component in the PP catalloys. We also observed by POM that in isothermal crystallization, there were many more nuclei in the PP catalloys than that in neat PP and with an increase of the ethylene component, the average size of the spherulites decreased obviously. Even when ethylene content was as high as 27%, the crystallization rate still increased apparently, and this was quite different from common PP melting blends, in which the crystallization rate decreased when the ethylene content was relatively high because of the obstruction effect of dispersed droplets to the spherulite growth of the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 877–882, 2004
Hot compaction of polyethylene naphthalate
Authors: Hine P. J. , Astruc A. , Ward I. M.
Published: April 2004

In this article, we describe the production of single polymer composites from polyethylene naphthalate (PEN) multifilaments by using the hot compaction process. In this process, developed at Leeds University, highly oriented tapes or fibers are processed at a critical temperature such that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the composite. This process is, therefore, a way to produce novel high‐volume fraction polymer/polymer composites where the two phases are chemically the same material. A variety of experimental techniques, including mechanical tests and differential scanning calorimetry, were used to examine the mechanical properties and morphology of the compacted PEN sheets. Bidirectional (0/90) samples were made at a range of compaction temperatures chosen to span the melting range of the PEN multifilaments (268–276°C). Measurement of the mechanical properties of these samples, specifically the in‐plane modulus and strength, allowed the optimum compaction temperature to be ascertained (∼ 271°C), and hence, the optimum mechanical properties. The optimum compacted PEN sheets were found to have an initial modulus close to 10 GPa and a strength of just over 200 MPa. The glass transition temperature of the optimum compacted sheets was measured to be 150°C, nearly 40°C higher than compacted poly(ethylene terephthalate) (PET) sheets. In previous work on polypropylene and PET hot compacted materials, it proved instructive to envisage these materials as a composite where the original oriented multifilaments are regarded as the reinforcing phase, and the melted and recrystallized material are regarded as the matrix phase. Dynamic mechanical bending tests (DMTA) were used here to confirm this for PEN. DMTA tests were carried out on the original fibers and on a sample of completely melted material to determine the fiber and matrix properties, respectively. The composite properties were then predicted by using a simple rule of mixtures and this was found to be in excellent agreement with the magnitude and measured temperature dependence of the hot compacted PEN material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 796–802, 2004
Synthesis and dynamic mechanical behavior of glucose‐mediated poly(ethylene glycol/chitosan) membrane
Authors: Wang Jian‐Wen , Hon Min‐Hsiung
Published: April 2004

The pH‐dependent chitosan/PEG membrane was prepared by a surface‐mediated process with glucose as a source. Swelling study shows that the glucose‐mediated membrane is more stable in a neutral environment than an acidic one and the stability in all soaking environments generally increases with increasing glucose concentration because of an increase in Schiff's reaction product as demonstrated by a mediated degree analysis. DMA analysis shows that as the glucose concentration increases, the rubber plateau of the glucose‐mediated membrane is prolonged and keeps a higher storage modulus, and the tangent δ peak shifts to a high temperature as the temperature increases. In an isothermal mode, as the glucose concentration increases to 10 wt %, the storage modulus shows a small change in frequency dependence, indicating that the mediating effect is obviously affected by glucose addition. It can also be found that surface‐mediated membrane has a higher complex viscosity than chitosan/PEG membrane at high frequencies. Thus, a new way was found to use glucose to produce stable biomaterial. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 809–820, 2004
Blends of polymers with similar glass transition temperatures: A DMTA and DSC study
Authors: Bikiaris D. , Prinos J. , Botev M. , Betchev C. , Panayiotou C.
Published: April 2004

The miscibility of different polymer blends was studied with dynamic mechanical thermal analysis (DMTA) in conjunction with differential scanning calorimetry (DSC). The blends were prepared by melt mixing polymers having similar glass transitions such as polyglutarimide (PGI), styrene‐co‐maleic anhydride random copolymers (SMA), and polystyrene (PS). In PGI/SMA blends, there is only one glass transition detected with DMTA. In the case of PGI/SMA14 blends, the single glass transition temperature is due to their full miscibility. However, PGI/SMA8 blends are immiscible throughout the whole composition range as was verified by optical observation (opaque appearance), DSC, and scanning electron microscopy. The observation of only one glass transition by DMTA was attributed to weak interactions that take place between the two polymers, leading to partial mutual solubility and bringing the slightly different Tg temperatures of the pure polymers even closer. In SMA8/SMA14 blends, there are two glass transitions detected with DSC as well as with DMTA, indicating that the two copolymers are immiscible. However, in all compositions, shifts of the glass transitions were observed with DMTA, which is evidence of partial miscibility. The observation of immiscibility was easiest in PS/SMA blends by both techniques, because of the bigger difference in glass transition temperatures of the initial polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 726–735, 2004
Flexible and conducting composites of polypyrrole and polydimethylsiloxane
Authors: Çakmak Güliz , Küçükyavuz Zuhal , Küçükyavuz Savaş
Published: April 2004

Conductive and flexible polydimethylsiloxane (PDMS)/polypyrrole (PPy) composites were synthesized electrochemically. Electrochemical syntheses were performed at +1.10 V by using p‐toluene sulfonic acid (PTSA) as supporting electrolyte and water as solvent. Composites were characterized by cyclic voltammetry, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared spectroscopy. Conductivity measurements and mechanical tests were also performed. The observed conductivities were in the range of 3.5–7.6 S/cm, indicating that the conductivities of PDMS/PPy composites and that of pure PPy were in the same order of magnitude. Tensile tests revealed that higher percent elongation was obtained by the addition of PDMS. Highly flexible and foldable PDMS/PPy composites were successfully synthesized, which have high conductivities and improved mechanical properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 736–741, 2004
Preparation and properties of ethylene propylene rubber (EPR)–clay nanocomposites based on maleic anhydride‐modified EPR and organophilic clay
Authors: Hasegawa Naoki , Okamoto Hirotaka , Usuki Arimitsu
Published: April 2004

Ethylene propylene rubber–clay nanocomposites (EPR–CNs) were prepared by melt‐compounding maleic anhydride modified EPR (EPR‐MA) with organophilic clay, and their properties were examined. Silicate layers of organophilic clay were found to exfoliate and homogeneously disperse into the nanometer level in the nanocomposites by transmission electron microscopy observation. EPR–CNs exhibited higher tensile moduli compared to EPR‐MA and composites containing conventional fillers such as carbon black, talc. The storage moduli of EPR–CNs were also higher than those of EPR‐MA and the conventional composites. Creep resistances of EPR–CNs were much improved compared for EPR‐MA. Degree of swelling in hexadecane was remarkably restricted. Improvement of these properties is caused because dispersed silicate layers have much large interface with the EPR matrix and are thought to strongly restrain the EPR polymer chains. Nanocomposite technology using small amount of silicate layers is useful to improve properties of thermoplastic elastomer. Various kinds of thermoplastic elastomers are expected to be produced by loading of silicate layers with or without conventional fillers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 758–764, 2004
Gel permeation chromatography calibration based on fractal geometry
Authors: Boborodea A. G. , Clemens M. , Daoust D. , Bailly C.
Published: April 2004

The previously developed model [Polym Bull 2000, 44, 525] used to characterize the porous gel inside a gel permeation chromatography (GPC) column, has been extended to also include the interstitial space between the macroscopic gel particles. The hydrodynamic dimensions for 12 polystyrene (PS) standards, measured by GPC with differential refractive index (DRI), differential viscometry (VISCO), and multiangle laser light scattering (MALLS) detectors, have been used to determine the fractal parameters of the polystyrene–divinylbenzene gel corresponding to four commercial columns. The new developed model enables to predict the calibration curve for the sets of coupled columns based on the parameters of each column. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 771–777, 2004
Information grounds and the use of need‐based services by immigrants in Queens, New York: A context‐based, outcome evaluation approach
Authors: Fisher Karen E. , Durrance Joan C. , Hinton Marian Bouch
Published: April 2004

We elaborate on Pettigrew's (1998,1999) theory of information grounds while using an outcome evaluation approach enriched by its focus on context to explore the use of need‐based services by immigrants in New York City. Immigrants have substantial information and practical needs for help with adjusting to life in a new country. Because of differences in language, culture, and other factors such as access, new immigrants are a difficult population to study. As a result, little research has examined their predilections from an information behavior perspective. We report findings from a qualitative study of how literacy and coping skills programs are used by and benefit the immigrant customers of the Queens Borough Public Library (QBPL). From our interviews and observation of 45 program users, staff, and other stakeholders, we derived a grand context (in Pettigrew's terms) woven from three subcontexts: the immigrants of Queens, New York; the QBPL, its service model, and activities for immigrants; and professional contributions of QBPL staff. Our findings are discussed along two dimensions: (a) building blocks toward information literacy, and (b) personal gains achieved by immigrants for themselves and their families. We conclude that successful introduction to the QBPL—as per its mission, programming, and staff—can lead immigrants to a synergistic information ground that can help in meeting broad psychological, social, and practical needs.
A new approach to random mutagenesis in vitro
Authors: Lai Yu‐Ping , Huang Jing , Wang Lin‐Fa , Li Jun , Wu Zi‐Rong
Published: April 2004

Random mutagenesis is a powerful tool for studying the effects of a large number of permutations of a particular DNA sequence and its encoded products. Here we describe a new strategy of conducting in vitro random mutagenesis using ethyl methane sulfonate (EMS). The Bacillus aprN18 gene, coding for a serine protease with fibrinolytic activity, was used as a target gene. To study the mutations of the coding region, rather than the whole plasmid, the 1.4 kb gene fragment was cut out from an expression plasmid and treated with 10 mM EMS at 37°C for 1 h. The treated fragment was then ligated back into the original expression vector and a library of random mutants was constructed in a protease‐deficient Bacillus subtilis strain. A plate assay‐based screening method was used to select for mutant clones with altered enzyme activity, and the change of activity was then confirmed by a semi‐quantitative enzyme assay using liquid culture supernatant. The inserts of five clones with altered enzyme activity were randomly chosen for sequencing analysis. Among the point mutations detected, GC → AT transition accounts for 42.1%, AT → GC transition 34.2% and GC/CG transversion 23.7%, respectively. To our knowledge this is the first application of EMS for in vitro mutagenesis of a defined DNA sequence. © 2004 Wiley Periodicals, Inc.
Fed‐batch optimization of α‐amylase and protease‐producing Bacillus subtilis using Markov chain methods
Authors: Skolpap Wanwisa , Scharer J.M. , Douglas P.L. , Moo‐Young M.
Published: April 2004

A stoichiometry‐based model for the fed‐batch culture of the recombinant bacterium Bacillus subtilis ATCC 6051a, producing extracellular α‐amylase as a desirable product and proteases as undesirable products, was developed and verified. The model was then used for optimizing the feeding schedule in fed‐batch culture. To handle higher‐order model equations (14 state variables), an optimization methodology for the dual‐enzyme system is proposed by integrating Pontryagin's optimum principle with fermentation measurements. Markov chain Monte Carlo (MCMC) procedures were appropriate for model parameter and decision variable estimation by using a priori parameter distributions reflecting the experimental results. Using a simplified Metropolis‐Hastings algorithm, the specific productivity of α‐amylase was maximized and the optimum path was confirmed by experimentation. The optimization process predicted a further 14% improvement of α‐amylase productivity that could not be realized because of the onset of sporulation. Among the decision variables, the switching time from batch to fed‐batch operation (ts) was the most sensitive decision variable. © 2004 Wiley Periodicals, Inc.
Modeling mass transfer in hepatocyte spheroids via cell viability, spheroid size, and hepatocellular functions
Authors: Glicklis Rachel , Merchuk Jose C. , Cohen Smadar
Published: April 2004

Hepatocyte aggregation into spheroids attributes to their increased activity, but in the absence of a vascular network the cells in large spheroids experience mass transfer limitations. Thus, there is a need to define the spheroid size which enables maximal cell viability and productivity. We developed a combined theoretical and experimental approach to define this optimal spheroid size. Hepatocyte spheroids were formed in alginate scaffolds having a pore diameter of 100 μm, in rotating T‐flasks or spinners, to yield a maximal size of 100, 200, and 600 μm, respectively. Cell viability was found to decrease with increasing spheroid size. A mathematical model was constructed to describe the relationship between spheroid size and cell viability via the oxygen mass balance equation. This enabled the prediction of oxygen distribution profiles and distribution of viable cells in spheroids with varying size. The model describes that no oxygen limitation will take place in spheroids up to 100 μm in diameter. Spheroid size affected the specific rate of albumin secretion as well; it reached a maximal level, i.e., 60 μg/million cells/day in 100‐μm diameter spheroids. This behavior was depicted in an equation relating the specific albumin secretion rate to spheroid size. The calculated results fitted with the experimental data, predicting the need for a critical number of viable hepatocytes to gain a maximal albumin secretion. Taken together, the results on mass transport in spheroids and its effects on cell viability and productivity provide a useful tool for the design of 3D scaffolds with pore diameters of 100 μm. © 2004 Wiley Periodicals, Inc.
Enhancing bioplastic–substrate interaction via pore induction and directed migration of enzyme location
Authors: Lele Bhalchandra S. , Papworth Glenn , Katsemi Vicky , Rüterjans Heinz , Martyano Igor , Klabunde Kenneth J. , Russell Alan J.
Published: April 2004

We demonstrate two novel approaches to enhance interactions of polymer‐immobilized biomolecules with their substrates. In the first approach, diisopropylfluorophosphatase (DFPase) containing poly(urethane) (PU) coatings were made microporous by incorporating, then extracting, poly(ethylene glycol)‐based diesters as porogens. Incorporation of 2% w/w porogen increased the effective diffusion coefficient of diisopropylfluorophosphate (DFP) through the coatings by 30% and increased the apparent turnover number of immobilized DFPase 3‐fold. In the second approach, prior to immobilization, hydrophobic modification of DFPase was achieved through its conjugation with a dimer/trimer mixture of a uretdione based on 1,6‐diisocyanatohexane. When the hydrophobically modified DFPase was immobilized in coatings, catalytic activity was 4‐fold higher than that of the equivalent, immobilized, native DFPase. This activity enhancement was independent of the presence or absence of pores. Confocal microscopy images of coatings containing fluorescently labeled lysozyme show that the native enzyme is distributed uniformly over the entire thickness of the coatings. Hydrophobically modified and fluorescently labeled lysozyme is accumulated only in the upper 10 μm cross‐sectional layer of a 100 μm‐thick coating. Interactions of bioplastics with their substrates are tunable either by pore induction in a polymer or by directed migration of the hydrophobically modified biomolecule to the desired location. The latter approach has broad implications, including overcoming mass transfer limitations experienced by immobilized biocatalysts. © 2004 Wiley Periodicals, Inc.
CFD Sinflow Library: A framework to develop engineering educational codes in CFD and thermal sciences
Authors: Pieritz Romeu André , Mendes Rafael , da Silva Rodrigo F. A. F. , Maliska Clovis R.
Published: April 2004

This work introduces the educational code development library “CFD Sinflow Library” specialized in 2D numerical methods in computational fluid dynamics (CFD) and termal science. This library is for research, educational, and engineering purposes like an open and platform independent architecture. The library was developed with C++ standard programming language using an object‐oriented approach allowing educators and graduation/undergraduation students to access the numerical methods in a simplified way. The numerical capabilities and results quality are evaluated, where comparisons are made with benchmark and analytical solutions. © 2004 Wiley Periodicals, Inc. Comput Appl Eng Educ 12: 31–43, 2004; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.10056
Development and implementation of a MATLAB simulation project for a multidisciplinary graduate course in autonomous robotics
Authors: Joshi Sanjay S.
Published: April 2004

In this paper, we describe a MATLAB computer simulation course project implemented as part of an introductory graduate course in autonomous robotics at the University of California, Davis. The course consisted of students from Mechanical and Aeronautical Engineering, Psychology and Neuroscience, Electrical Engineering, and Computer Science. Creating a valuable class computer project experience for graduate students with greatly varying backgrounds is a challenging undertaking. Graduate students in different majors may have widely different educational backgrounds, field‐specific language and culture, and computer background. It is a main result of this paper that a meaningful autonomous robotics computer project can be developed that allows students to be individually unique and creative, but at the same time allows each student to understand and share ideas, tools, and methods from all the other students. Simulation project conception, teamwork, implementation, results, and lessons learned are described. © 2004 Wiley Periodicals, Inc. Comput Appl Eng Educ 12: 54–64, 2004; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20001