bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Nitroxide Quasi‐Equilibrium in the Alkoxyamine‐Mediated Radical Polymerization of Styrene
Authors: Saldívar‐Guerra Enrique , Bonilla José , Becerril Fabiola , Zacahua Gregorio , Albores‐Velasco Martha , Alexander‐Katz Roberto , Flores‐Santos Leticia , Alexandrova Larissa
Published: February 2006

Summary: The range of validity of two popular versions of the nitroxide quasi‐equilibrium (NQE) approximation used in the theory of kinetics of alkoxyamine mediated styrene polymerization, are systematically tested by simulation comparing the approximate and exact solutions of the equations describing the system. The validity of the different versions of the NQE approximation is analyzed in terms of the relative magnitude of (dN/dt)/(dP/dt). The approximation with a rigorous NQE, kc[P][N] = kd[PN], where P, N and PN are living, nitroxide radicals and dormant species respectively, with kinetic constants kc and kd, is found valid only for small values of the equilibrium constant K (10−11–10−12 mol · L−1) and its validity is found to depend strongly of the value of K. On the other hand, the relaxed NQE approximation of Fischer and Fukuda, kc[P][N] = kd[PN]0 was found to be remarkably good up to values of K around 10−8 mol · L−1. This upper bound is numerically found to be 2–3 orders of magnitude smaller than the theoretical one given by Fischer. The relaxed NQE is a better one due to the fact that it never completely neglects dN/dt. It is found that the difference between these approximations lies essentially in the number of significant figures taken for the approximation; still this subtle difference results in dramatic changes in the predicted course of the reaction. Some results confirm previous findings, but a deeper understanding of the physico‐chemical phenomena and their mathematical representation and another viewpoint of the theory is offered. Additionally, experiments and simulations indicate that polymerization rate data alone are not reliable to estimate the value of K, as recently suggested.

Validity of the rigorous nitroxide quasi‐equilibrium assumption as a function of the nitroxide equilibrium constant.

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Validity of the rigorous nitroxide quasi‐equilibrium assumption as a function of the nitroxide equilibrium constant.
Modeling the Effect of Oxygen on Photopolymerization Kinetics
Authors: O'Brien Allison K. , Bowman Christopher N.
Published: February 2006

Summary: A comprehensive one‐dimensional photopolymerization model was utilized to investigate the effect of oxygen on the free‐radical photopolymerization kinetics. The spatial profiling aspect of the model provided insight into the heterogeneity of the cure kinetics due to oxygen inhibition, specifically the variance in the concentration profile of monomer and oxygen. Double bond conversion was negligible for the top ten microns of the film due to continuous oxygen diffusion, and increased with increasing depth. Similarly, the oxygen concentration decreased with increasing depth due to the competition between oxygen diffusion time and the polymerization rate. The effect of initiation rate on the extent of oxygen inhibition was investigated for various oxygen concentrations. As the initiation rate increased, the polymerization rate increased, and eventually approached that of a sample in an inert environment. Similarly, as the oxygen concentration was decreased, the polymerization rate increased. The effect of varying the initiation rate on the cure profile in the oxygen‐exposed film was also studied. It was found that the unpolymerized tacky layer decreased from 50 µm to 5 µm with a 3 order of magnitude increase in initiation rate. Using the pseudo steady state approximation, the relationship between polymerization rate and initiation rate was derived for films in an oxygen environment. A direct relationship between the polymerization and initiation rate was found for films in air. The polymerization model supported this derivation and found that as the oxygen concentration was decreased, the dependence on initiation rate, or alpha, decreased, reaching the accepted value of 0.5 for alpha in inert environments.

Double bond conversion versus film depth and cure time.

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Double bond conversion versus film depth and cure time.
Mesoscopic Morphology of Proton‐Conducting Polyelectrolyte Membranes of Nafion® Type: A Self‐Consistent Mean Field Simulation
Authors: Galperin Dmitry Y. , Khokhlov Alexei R.
Published: February 2006

Summary: A SCMF simulation is presented for a coarse‐grained model of Nafion®. Based on a number of simplifying assumptions, this study predicts distinct morphological changes in the material upon alteration of temperature and water content. We found that the hydration level corresponding to the microphase segregation depends on the temperature of the system. Spherical clusters constituting the hydrophilic microphase of the membrane at relatively low water content (but above the transition point) grow in size, coalesce and form a network of channels responsible for the ionic transport at higher hydration levels. This hydrophilic phase is shielded from the hydrophobic matrix by the sidechains of Nafion®, their end‐groups being turned towards the water clusters. The results obtained are similar to those reported from dissipative particle dynamics studies and support the “cluster‐network” model for the low hydration levels and the “sponge” model at higher hydration levels. The simulation approach chosen proved to be effective for the mesoscopic structure analysis of the heterogeneous polymeric material.

Schematic representation of the structure of Nafion®‐water blends.

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Schematic representation of the structure of Nafion®‐water blends.
Botulinum toxin changes intrafusal feedback in dystonia: A study with the tonic vibration reflex
Authors: Trompetto Carlo , Currà Antonio , Buccolieri Alessandro , Suppa Antonello , Abbruzzese Giovanni , Berardelli Alfredo
Published: February 2006

To investigate the possible role of botulinum toxin (BT‐A) injection in reducing muscle afferent feedback, we evaluated electrophysiologically 10 right‐handed patients with writer's cramp before and 3 weeks after treatment. The ratio between pre‐ and postinjection values of maximal M‐wave (M‐max), maximal voluntary contraction (MVC), and tonic vibration reflex (TVR) were measured in the injected muscles (wrist flexors or extensors). In all the subjects, BT‐A injection reduced the TVR more than the M‐max and MVC (mean ratio ± SD: TVR, 0.24 ± 0.22; MVC, 0.59 ± 0.32; M‐max, 0.68 ± 0.24; P = 0.003). Long‐term evaluation of 2 patients disclosed that, after 7 months, when some clinical benefits persisted, M‐max and MVC had fully recovered, whereas the TVR was still depressed. This special sensitivity of the TVR to suppression by BT‐A injection could be mediated by the chemodenervation of intrafusal muscle fibers, leading to a reduction in spindle inflow to the central nervous system during vibration. The action on intrafusal fibers could alter sensorimotor integration, thus contributing to the clinical benefits of BT‐A injection. © 2006 Movement Disorder Society
Revision of annulated orthoceridan cephalopods of the Baltoscandic Ordovician
Authors: Kröger B. , Isakar M.
Published: February 2006

Abstract. The annulated orthoceridans of the Middle and Late Ordovician of Baltoscandia are described and their systematic frame is revised. The revision of these nautiloids, which are part of the Orthocerida and Pseudorthocerida, is based on the investigation of characters of the septal neck, the siphuncular tube, and the apex. An unequivocal terminology of these characters is suggested and applied. The shape of the septal neck and the siphuncular tube are described for the first time in Palaeodawsonoceras n. gen., Striatocycloceras n. gen., Dawsonoceras fenestratum Eichwald, 1860, and Gorbyoceras textumaraneum (Roemer, 1861). Ctenoceras sweeti n. sp. is erected. The apex of Dawsonoceras barrandei Horný, 1956 is figured and described for the first time. The distribution of the character states of the apex and the septal neck support the emendation of the families Orthoceratidae, Dawsonoceratidae, and Proteoceratidae. The analysis shows also that the families Kionoceratidae, and Leuroceratidae must be refused because they represent not natural groups. However, it is also shown that the present knowledge is not sufficient to establish an unequivocal classification of the Middle, and Late Ordovician annulate cephalopods. Die orthoceriden Cephalopoden des Mittleren bis Späten Ordoviziums im Baltoskandium werden beschrieben und revidiert. Die Revision dieser Cephalopoden, welche zu den Orthocerida und Pseudorthocerida gehören, stützt sich auf die Untersuchung der Apikalenden, der Septalduten und der Form der Siphonalröhre. Eine eindeutige Terminologie für diese Merkmale wird vorgeschlagen und angewandt. Die Form der Septalduten und der Siphonalröhre von Palaeodawsonoceras n. gen., Striatocycloceras n. gen., Dawsonoceras fenestratum, Eichwald, 1860 und Gorbyoceras textumaraneum (Roemer, 1861) wird erstmals beschrieben. Die Art Ctenoceras sweeti n. sp. wird aufgestellt. Der Apex von Dawsonoceras barrandei Horný, 1956 wird erstmals beschrieben und dargestellt. Die neu gefundenen Merkmale stützen eine Emendation der Familien Orthoceratidae, Dawsonoceratidae und Proteoceratidae. Es wird daher dafür plädiert, die Familien Kionoceratidae (Hyatt, 1900) und Leuroceratidae (Sweet, 1964) nicht mehr zu verwenden, da diese keine natürlichen Gruppen repräsentieren. Die Untersuchung zeigt aber auch, dass es derzeit noch nicht möglich ist die annulaten Cephalopoden des Mittleren und Oberen Ordoviziums zweifelsfrei zu klassifizieren. doi:10.1002/mmng.200600005
Feasibility of simultaneous temperature and tissue stiffness detection by MRE
Authors: Le Yuan , Glaser Kevin , Rouviere Olivier , Ehman Richard , Felmlee Joel P.
Published: February 2006

Temperature and tissue stiffness are two indices that can be used to monitor MRI‐guided focused ultrasound thermal therapy. It would be beneficial to have both measures available to monitor treatment progression during thermal therapy. MR Elastography (MRE) has already been shown to provide tissue stiffness information; the purpose of this work is to demonstrate how temperature can be derived from the same MRE data acquisition. MRE data were acquired from 1.5% agarose phantoms and ex vivo porcine muscle tissue (from a grocery store) while they were heated slowly. The temperatures were measured using a fluorescent thermometer. The phase average from the MRE acquisition was used to calculate the phase shift induced by the proton resonance frequency shift associated with the temperature change. The results show that the phase shift due to temperature extracted from MRE data correlate well with the temperature change recorded by thermometer, yielding a temperature coefficient of −0.0096 ppm/°C for the agarose phantom, and −0.0103 ppm/°C for the ex vivo porcine tissue. These results indicate that it is possible to simultaneously measure both temperature and tissue shear stiffness using a new method of MRE data reconstruction. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Measurement of arterial input functions for dynamic susceptibility contrast magnetic resonance imaging using echoplanar images: Comparison of physical simulations with in vivo results
Authors: Duhamel Guillaume , Schlaug Gottfried , Alsop David C.
Published: February 2006

Measurement of the arterial input bolus shape is essential to the quantification of mean transit time and blood flow with dynamic susceptibility contrast (DSC) MRI. Input functions derived from the echoplanar signal intensity within or near arteries are highly nonlinear, yet such input functions are widely used. We employed a physical model for the echoplanar signal intensity from an artery as a function of contrast agent concentration, artery size, and angle to the magnetic field to test approaches for the measurement of the arterial input function. The simulated results confirmed the strong nonlinearity of signal in the neighborhood of vessels. Of the input function measurement methods considered, the simulations suggested that measurement of signal near but not within a large vessel is most accurate, but mean transit times (MTT) calculated with these input functions are highly sensitive to peak bolus concentration. Input functions determined from voxels demonstrating the shortest first moment overestimated the MTT but the measured MTTs were more robust to changes in peak concentration. Characteristics of the measured in vivo input functions were consistent with the simulations. Our results emphasize the important contribution of input function errors to the uncertainty in MTT and blood flow imaging with DSC MRI. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
In vivo proton electron double resonance imaging of the distribution and clearance of nitroxide radicals in mice
Authors: Li Haihong , He Guanglong , Deng Yuanmu , Kuppusamy Periannan , Zweier Jay L.
Published: February 2006

Proton electron double resonance imaging (PEDRI) is an emerging technique that utilizes the Overhauser effect to enable in vivo and in vitro imaging of free radicals in biological systems. Nitroxide spin probes enable measurement of tissue redox state based on their reduction to diamagnetic hydroxylamines. PEDRI instrumentation at 0.02 T was applied to assess the ability to image the in vivo distribution, clearance, and metabolism of nitroxide radicals in living mice. Using phantoms of 2,2,5,5‐tetramethyl‐3‐carboxylpyrrolidine‐N‐oxyl (PCA) in normal saline the dependence of the enhancement on RF power and spin probe concentration was determined. Enhancements of up to −23 were obtained in phantoms with 2 mM levels. Maximum enhancement of −7 was observed in vivo. Coronal images of nitroxide‐infused mice enabled visualization of the kinetics of spin probe uptake and clearance in different organs including the great vessels, heart, lungs, kidneys, and bladder with an in‐plane spatial resolution of 0.6 mm. PEDRI of living mice was also performed using 3‐carbamoyl‐proxyl and 2,2,6,6‐tetramethyl‐4‐oxopiperidine‐N‐oxyl to compare the different rate of clearance and metabolism among different nitroxide probes. PCA, due to its intravascular compartmentalization, provided the sharpest contrast for the vascular system and highest enhancement values in the PEDRI images among the three nitroxides. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Robust analysis of short echo time 1H MRSI of human brain
Authors: Zhu X. P. , Young K. , Ebel A. , Soher B. J. , Kaiser L. , Matson G. , Weiner W. M. , Schuff N.
Published: February 2006

Short echo time proton MR Spectroscopic Imaging (MRSI) suffers from low signal‐to‐noise ratio (SNR), limiting accuracy to estimate metabolite intensities. A method to coherently sum spectra in a region of interest of the human brain by appropriate peak alignment was developed to yield a mean spectrum with increased SNR. Furthermore, principal component (PC) spectra were calculated to estimate the variance of the mean spectrum. The mean or alternatively the first PC (PC1) spectrum from the same region can be used for quantitation of peak areas of metabolites in the human brain at increased SNR. Monte Carlo simulations showed that both mean and PC1 spectra were more accurate in estimating regional metabolite concentrations than solutions that regress individual spectra against the tissue compositions of MRSI voxels. Back‐to‐back MRSI studies on 10 healthy volunteers showed that mean spectra markedly improved reliability of brain metabolite measurements, most notably for myo‐inositol, as compared to regression methods. Magn Reson Med, 2006. Published 2006 Wiley‐Liss, Inc.
Cardiac and respiratory double self‐gated cine MRI in the mouse at 7 T
Authors: Hiba Bassem , Richard Nathalie , Janier Marc , Croisille Pierre
Published: February 2006

ECG‐gated cardiac MRI in the mouse is hindered by many technical difficulties in ECG signal recording inside static and variable high magnetic scanner fields. The present study proposes an alternative robust method of acquiring auto‐gated cardiac and respiratory cine images in mouse heart. In our approach, a motion synchronization signal is extracted from the echo peak MR signal of a non‐triggered radial acquisition. This signal is then used for both cardiac and respiratory retrospective gating before cine image reconstruction. Highly asymmetric echoes were acquired to achieve the radial k‐space sampling in order to avoid radial acquisition related artifacts and to increase auto‐gating robustness. In vivo experiments demonstrated the feasibility and robustness of self‐gated cine‐MRI in the mouse heart at 7T. The signal‐to‐noise and contrast‐to‐noise ratios of the self‐gated and ECG‐gated images were comparable, all parameters being equal. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Contrast behavior and relaxation effects of conventional and hyperecho‐turbo spin echo sequences at 1.5 and 3 T
Authors: Weigel Matthias , Hennig Juergen
Published: February 2006

To overcome specific absorption rate (SAR) limitations of spin‐echo‐based MR imaging techniques, especially at (ultra) high fields, rapid acquisition relaxation enhancement/TSE (turbo spin echo)/fast spin echo sequences in combination with constant or variable low flip angles such as hyperechoes and TRAPS (hyperTSE) have been introduced. Due to the multiple spin echo and stimulated echo pathways involved in the signal formation, the contrast behavior of such sequences depends on both T2 and T1 relaxation times. In this work, constant and various variable flip angle sequences were analyzed in a volunteer study. It is demonstrated that a single effective echo time parameter TEeff can be calculated that accurately describes the overall T2 weighted image contrast. TEeff can be determined by means of the extended phase graph concept and is practically independent of field strength. Using the described formalism, the contrast of any TSE sequence can be predicted. HyperTSE sequences are demonstrated to show a robust and well‐defined T2 contrast allowing clinical routine MRI to be performed with SAR reductions of typically at least 70%. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
A multilevel passenger screening problem for aviation security
Authors: McLay Laura A. , Jacobson Sheldon H. , Kobza John E.
Published: February 2006

Passenger prescreening is a critical component of aviation security systems. This paper introduces the Multilevel Allocation Problem (MAP), which models the screening of passengers and baggage in a multilevel aviation security system. A passenger is screened by one of several classes, each of which corresponds to a set of procedures using security screening devices, where passengers are differentiated by their perceived risk levels. Each class is defined in terms of its fixed cost (the overhead costs), its marginal cost (the additional cost to screen a passenger), and its security level. The objective of MAP is to assign each passenger to a class such that the total security is maximized subject to passenger assignments and budget constraints. This paper shows that MAP is NP‐hard and introduces a Greedy heuristic that obtains approximate solutions to MAP that use no more than two classes. Examples are constructed using data extracted from the Official Airline Guide. Analysis of the examples suggests that fewer security classes for passenger screening may be more effective and that using passenger risk information can lead to more effective security screening strategies. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006
The Banzhaf value and communication situations
Authors: Alonso‐Meijide J.M. , Fiestras‐Janeiro M.G.
Published: February 2006

Myerson 3 and 4 proposed and characterized a modification of the Shapley value in the context of communication situations. In this paper we propose several characterizations of the extension of the Banzhaf value proposed by Owen 7 to communication situations. In particular we characterize this value with the properties of fairness, isolation, and pairwise merging. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006
Modeling the operation of multireservoir systems using decomposition and stochastic dynamic programming
Authors: Archibald T.W. , McKinnon K.I.M. , Thomas L.C.
Published: February 2006

Stochastic dynamic programming models are attractive for multireservoir control problems because they allow non‐linear features to be incorporated and changes in hydrological conditions to be modeled as Markov processes. However, with the exception of the simplest cases, these models are computationally intractable because of the high dimension of the state and action spaces involved. This paper proposes a new method of determining an operating policy for a multireservoir control problem that uses stochastic dynamic programming, but is practical for systems with many reservoirs. Decomposition is first used to reduce the problem to a number of independent subproblems. Each subproblem is formulated as a low‐dimensional stochastic dynamic program and solved to determine the operating policy for one of the reservoirs in the system. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006
A stochastic model for burn‐in procedures in accelerated environment
Authors: Cha Ji Hwan
Published: February 2006

Burn‐in procedure is a manufacturing technique that is intended to eliminate early failures of system or product. Burning‐in a component or system means to subject it to a period of use prior to being used in field. Generally, burn‐in is considered expensive and so the length of burn‐in is typically limited. Thus, burn‐in is most often accomplished in an accelerated environment in order to shorten the burn‐in process. A new failure rate model for an accelerated burn‐in procedure, which incorporates the accelerated ageing process induced by the accelerated environmental stress, is proposed. Under a more general assumption on the shape of failure rate function of products, which includes the traditional bathtub‐shaped failure rate function as a special case, upper bounds for optimal burn‐in time will be derived. A numerical example will also be given for illustration. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006
A precise numerical method for Rayleigh waves in a stratified half space
Authors: Gao Q. , Lin J. H. , Zhong W. X. , Howson W. P. , Williams F. W.
Published: February 2006

This paper presents theory and results for Rayleigh waves propagating in a transversely isotropic stratified solid resting on an elastic semi‐infinite space. It uses the precise integration method (PIM) and the extended Wittrick–Williams (W–W) algorithm. This problem can be reduced into the eigenvalue problem of ordinary differential equations (ODEs) in the frequency–wavenumber domain. The PIM used here is a precise method for solving the ODEs with two‐point boundary conditions, and the eigenvalue counting method of the extended W–W algorithm is used to ensure that all eigenvalues are found without the possibility of any being missed. Hence the theory presented in this paper is exact, in the sense that its precision is limited only by the precision of the computer used. Copyright © 2006 John Wiley & Sons, Ltd.
Convergence of a spectral projection of the Camassa‐Holm equation
Authors: Kalisch Henrik , Raynaud Xavier
Published: February 2006

A spectral semi‐discretization of the Camassa‐Holm equation is defined. The Fourier‐Galerkin and a de‐aliased Fourier‐collocation method are proved to be spectrally convergent. The proof is supplemented with numerical explorations that illustrate the convergence rates and the use of the dealiasing method. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006
High‐order approximation of 2D convection‐diffusion equation on hexagonal grids
Authors: Karaa Samir
Published: February 2006

We derive a fourth‐order finite difference scheme for the two‐dimensional convection‐diffusion equation on an hexagonal grid. The difference scheme is defined on a single regular hexagon of size h over a seven‐point stencil. Numerical experiments are conducted to verify the high accuracy of the derived scheme, and to compare it with the standard second‐order central difference scheme. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006
An error analysis and the mesh independence principle for a nonlinear collocation problem
Authors: Aitbayev Rakhim
Published: February 2006

A nonlinear Dirichlet boundary value problem is approximated by an orthogonal spline collocation scheme using piecewise Hermite bicubic functions. Existence, local uniqueness, and error analysis of the collocation solution and convergence of Newton's method are studied. The mesh independence principle for the collocation problem is proved and used to develop an efficient multilevel solution method. Simple techniques are applied for estimating certain discretization and iteration constants that are used in the formulation of a mesh refinement strategy and an efficient multilevel method. Several mesh refinement strategies for solving a test problem are compared numerically. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006
Use of G‐CSF in Matched Sibling Donor Pediatric Allogeneic Transplantation: A Consensus Statement from the Children's Oncology Group (COG) Transplant Discipline Committee and Pediatric Blood and Marrow Transplant Consortium (PBMTC) Executive Committee
Authors: Grupp Stephan A. , Frangoul Haydar , Wall Donna , Pulsipher Michael A. , Levine John E. , Schultz Kirk R.
Published: February 2006

Preliminary studies indicate that G‐CSF‐primed marrow harvesting may result in a graft with increased mononuclear cells collected, increased CD34+ stem and progenitor cell dose and a potential for more rapid engraftment. Increased cell dose plus other potential positive effects of G‐CSF priming have resulted in improved survival in non‐randomized preliminary studies. These benefits may be available without the increased risk of chronic graft versus host disease (GVHD) that is experienced with allogeneic peripheral blood stem cell (PBSC) transplant. A phase III Children's Oncology Group (COG)/Pediatric Blood and Marrow Transplant Consortium (PBMTC) trial comparing G‐CSF‐primed marrow to standard marrow has been proposed. This document reviews background studies of G‐CSF‐primed marrow and addresses benefits and risks of G‐CSF administration to normal pediatric donors. We conclude that the approach is promising and warrants further study. Risks of G‐CSF to the donor are minimal and benefits to both donor and recipient may occur. Pediatr Blood Cancer 2006,46:414–421. © 2006 Wiley‐Liss, Inc.
Metal ion permeation properties of silk fibroin/chitosan blend membranes
Authors: Du Chun‐Hui , Zhu Bao‐Ku , Chen Jian‐Yong , Xu You‐Yi
Published: February 2006

Silk fibroin/chitosan (SF/CS) blend membranes were prepared and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy. It was found that SF and CS were compatible in the blend membranes and that the membranes were dense without microscopic phase separation. Swelling experiments showed that the swelling ratio of the blend membranes increased with CS content and reached the highest value when CS content was 70 wt%. Experiments indicated that the permeability coefficient of K+ through the blend membrane was 2–4 times higher than that of pure CS membrane, and 10 times higher than that of pure SF membrane. The permeation rate of K+ increased linearly with CS content in the blend membrane for the lower concentration feeding solution. For different metal ions, the permeability through SF/CS blend membranes was in the sequence K+ > Ca2+ > Cd2+ > Pb2+ > Cu2+ > Ni2+. Copyright © 2006 Society of Chemical Industry
Influence of viscosity ratio on processing and morphology of thermotropic liquid crystal polymer‐reinforced poly(ethylene 2,6‐naphthalate) blends
Authors: Kim Jun Young , Kim Seong Hun
Published: February 2006

Thermotropic liquid crystal polymer (TLCP) microfibril‐reinforced poly(ethylene 2,6‐naphthalate) (PEN) composites with various intrinsic viscosities were prepared by a melt compounding method. Polymer composites consisting of bulk cheap polyester with a small amount of expensive TLCP are of interest from a commercial perspective. The TLCP acts as a nucleating agent in the TLCP/PEN composites, enhancing the crystallization of the PEN matrix through heterogeneous nucleation. The structural viscosity index of the TLCP/PEN composites was lower than that of PEN and TLCP, which was attributed to the formation of TLCP fibrillar structures with elongated fibrils in the PEN matrix. The TLCP/PEN composites with higher intrinsic viscosity than the polymer matrix contained these elongated fibrils, and had a TLCP component with a smaller average diameter, and a narrower diameter distribution than TLCP/PEN composites with lower intrinsic viscosity. The higher intrinsic viscosity of the polymer matrix, the higher shear rate and the lower viscosity ratio of TLCP to PEN can all favour TLCP fibrillation in the polymer composites. Copyright © 2006 Society of Chemical Industry
Titanium‐mediated living radical styrene polymerizations. V. Cp2TiCl‐catalyzed initiation by epoxide radical ring opening: Effect of solvents and additives
Authors: Asandei Alexandru D. , Moran Isaac W. , Saha Gobinda , Chen Yanhui
Published: February 2006

The effects of solvents, additives, ligands, and solvent in situ drying agents as well as catalyst and initiator concentrations have been investigated in the Cp2TiCl‐catalyzed radical polymerization of styrene initiated by epoxide radical ring opening. On the basis of the solubilization of Cp2Ti(III)Cl and the polydispersity of the resulting polymer, the solvents rank as follows: dioxane ≥ tetrahydrofuran > diethylene glycol dimethyl ether > methoxybenzene > diphenyl ether ≥ bulk > toluene ≫ pyridine > dimethylformamide > 1‐methyl‐2‐pyrrolidinone > dimethylacetamide > ethylene carbonate, acetonitrile, and trioxane. Alkoxide additives such as aluminum triisopropoxide and titanium(IV) isopropoxide are involved in alkoxide ligand exchange with the epoxide‐derived titanium alkoxide and lead to broad molecular weight distributions, whereas similarly to strongly coordinating solvents, ligands such as bipyridyl block the titanium active site and prevent the polymerization. By contrast, softer ligands such as triphenylphosphine improve the polymerization in less polar solvents such as toluene. Although mixed hydrides such as lithium tri‐tert‐butoxyaluminum hydride, sodium borohydride, and lithium aluminum hydride react with bis(cyclopentadienyl)titanium dichloride to form mixed titanium hydride species ineffective in polymerization control, simple hydrides such as lithium hydride, sodium hydride, and especially calcium hydride are particularly effective as in situ trace water scavengers in this polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2015–2026, 2006
Iron‐catalyzed radical polymerization of acrylamides in the presence of Lewis acid for simultaneous control of molecular weight and tacticity
Authors: Sugiyama Yuya , Satoh Kotaro , Kamigaito Masami , Okamoto Yoshio
Published: February 2006

This work is directed to the stereospecific living radical polymerization of acrylamides such as N,N‐dimethylacrylamide and N‐isopropylacrylamide with an iron complex and a Lewis acid. DMAM was polymerized with [FeCp(CO)2]2 in conjunction with an alkyl iodide [(CH3)2C(CO2Et)I] as an initiator in the presence of Y(OTf)3 in toluene/methanol (1/1) at 60 °C to be converted almost quantitatively to the polymers with controlled molecular weights and high isotacticity (m > 80%), wherein the Fe‐complex generates radical species from a covalent CI bond of the dormant species and the Lewis acid controls the stereochemistry of the polymerization via coordination with the amide groups of the polymer terminal and the monomer. A series of Lewis acids were also used for the iron(I)‐catalyzed DMAM polymerization, and Yb(OTf)3 and Yb(NTf2)3 proved effective in giving isotactic polymers without deteriorating the molecular weight control similar to Y(OTf)3. Furthermore, a slight enhancement of isospecificity was observed for the iron‐catalyzed system in comparison with the α,α‐Azobisisobutyronitrile‐initiated, when coupled with Y(OTf)3. Stereoblock polymerization of DMAM via a one‐pot reaction was also achieved by just adding the Y(OTf)3 methanol solution in the course of the polymerization to give atactic‐b‐isotactic poly(DMAM). A similar but slightly lower control in the molecular weight and tacticity was achieved in the polymerization of NIPAM with [FeCp(CO)2]2/Y(OTf)3. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2086–2098, 2006
Synthesis of comb‐like polystyrene with poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as macroinitiator
Authors: Shi Yan , Fu Zhifeng , Yang Wantai
Published: February 2006

The copolymerization of N‐phenyl maleimide and p‐chloromethyl styrene via reversible addition–fragmentation chain transfer (RAFT) process with AIBN as initiator and 2‐(ethoxycarbonyl)prop‐2‐yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2′‐bipyridine, well‐defined comb‐like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069–2075, 2006
Effect of reaction conditions on the molecular weight and polydispersity of linear poly(arylene ether phosphine oxide)s prepared from an AB monomer
Authors: Kaiti Sridevi , Fossum Eric
Published: February 2006

A thorough study of the polymerization behavior of 4‐fluoro‐4′‐hydroxytriphenyl‐phosphine oxide, 2, under nucleophilic aromatic substitution reactions has been carried out. The synthesis of 2 was achieved in excellent yields by the reaction of bis(4‐fluorophenyl)phenylphosphine oxide, 1, with one equivalent of potassium hydroxide in DMSO/water. The structure and purity of 2 were confirmed via 1H, 13C, and 31P NMR spectroscopy along with elemental analysis. Polymerization reactions of 2 in NMP or DMSO at 180 °C provided the corresponding linear poly(arylene ether phosphine oxide)s, PAEPOs, with number average molecular weights, Mn, ranging from 11,700 to 36,500 Da. All of the polymer samples were completely soluble in chloroform, tetrahydrofuran, DMSO, NMP, and DMAc. The polymerization reactions were accompanied by a competing intramolecular process that resulted in the formation of cyclic oligomeric species that were removed via a final precipitation from methanol. Analysis using 31P NMR spectroscopy and size exclusion chromatography (SEC) confirmed that the majority of the lower molecular weight cyclic species were removed via this process. The polymer samples formed tough films when chloroform solutions were slowly evaporated on a glass slide. The PAEPO samples prepared in this study exhibited excellent thermal stability with Td (5%) values between 503 and 542 in air while the glass transition temperatures ranged from 223 to 237 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2099–2106, 2006
Chromatic Monitoring of DC Plasma Torches: The Latest Developments
Authors: Djakov Boyan E. , Enikov Radomir , Oliver Dick H. , Hrabovsky Milan , Kopecky Vladimir
Published: February 2006

Summary: The chromatic‐sensing technique is based on reduction of the optical spectroscopic information about an object to three signals obtained by photodetectors with different spectroscopic responsivities. Each plasma state is represented by a point of the hue, luminance, and saturation (HLS) or C1C2C3 chromaticity space. For specific operating conditions, the plasma fluctuations cause the formation of a ring around the point of S = 0, which makes the measurement of H impossible. Such a situation can be avoided by alternative tuning of the chromatic system. Systematic studies of the output/input correlation for air and water vapour/argon mixture plasmas are made. The results are presented in the form of ‘response surfaces’, which are of interest for an eventual on‐line control. This is illustrated by a ‘C2 vs. argon flow rate and jet axial co‐ordinate’ surface, which can be used to locate the correct powder injection point in a plasma spray process.

Schematic diagram of the chromatic monitoring system.

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Schematic diagram of the chromatic monitoring system.
A Simple Optical Monitoring Technique for Determining the Geometrical Characteristics of a Plasma Jet
Authors: Djakov Boyan E. , Oliver Dick H. , Enikov Radomir , Vasileva Elmira
Published: February 2006

Summary: A sensor device is proposed to evaluate the location, size, and shape of a plasma jet. It consists of a small number (e.g., six) of photodetectors arranged in a cross‐sectional plane of the jet. Tests of the technique are made by simulations based on CCD images of a plasma jet taken simultaneously from three different angles of view.

Photodiode configuration

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Photodiode configuration
Formation of Surfaces Organized on both a Micro‐ and Nanometer Scale by a Laser‐Liquid‐Solid‐Interaction Process
Authors: Pramatarova Lilyana , Pecheva Emilia , Presker Radina
Published: February 2006

Summary: A time‐sparing method for the fabrication of structures organized on both the micro‐ and nanometer‐scale typical of nature is demonstrated by using a laser. In the applied laser‐liquid‐solid‐interaction method, a micrometer scale architecture with precisely controlled size and shape is created by laser irradiation of various surfaces, and nanostructured hydroxyapatite is subsequently grown. Since the latter is known as the major inorganic constituent of bones and teeth, the formation of such a material may have direct application in medicine, dentistry, and tissue engineering, particularly as the population ages.

A schematic drawing of the laser‐liquid‐solid‐interaction method.

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A schematic drawing of the laser‐liquid‐solid‐interaction method.
1,7‐Cyclization of 1‐diazo‐2,4‐pentadiene and its heteroanalogues: DFT study
Authors: Subbotina Julia O. , Bakulev V. A. , Herges R. , Fabian W. M. F.
Published: February 2006

1,7‐Dipolar cyclizations of 1‐diazo‐2,4‐pentadiene1aand its heteroanalogues1b,cand4cwere studied using density functional theory (DFT). Although the heteroanalogue1chas an appropriate electronic structure to allow for pseudopericyclic cyclization, natural bond order (NBO) analysis has provided evidence for the electrocyclic ring closure. Magnetic criteria (anisotropy of the induced current density [ACID], nucleus‐independent chemical shifts [NICS]) confirmed the pericyclic character of the located transition states2a,cand5c. The activation barriers for the cyclization of 1‐diazo‐2,4‐pentadiene1aand its aza analogues1c,4care 3.3, 8.2, and 12.3 kcal/mol at the B3LYP/6‐31G(d) level, respectively. The higher barrier of the1c→3cand4c→3creactions compared with1a→3ais in line with the Hammond postulate. The out‐of‐plane distorted geometry of the cyclic product is an additional factor arguing against a pseudopericyclic mechanism. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Acidity predictions in an electron propagator approach
Authors: Agacino Esther , Gaitán Ricardo , Menconi Italo
Published: February 2006

An alternative way to calculate vertical ionization potentials (VIP) and vertical electron affinity (VEA) is the application of Koopman's theorem, using the electron propagator theory. In the present work, the results of the application of this theorem using the electron propagator formalism have been compared with the experiment in order to validate different basis set. Using the basis set with the best performance, the acidity tendencies in some substituted acetic acid molecules have been analyzed by correlating the proton affinity (PA) with molecular electronegativity (χ) and hardness (η); these last indexes were obtained from the calculated VIP and VEA considering the finite difference approximation. The above correlations were compared with equivalent correlations using the energy of the frontier Hartree–Fock orbitals and the corresponding Kohn–Sham orbitals, which were calculated with the B3LYP‐DFT procedure. The results indicate that the electron propagator theory could be an interesting alternative to evaluate reactivity indexes, since this theory gives reliable values of VIP and VEA. It was also found that (i) the VIP values are very close to experiment, with only a 0.38% of error; (ii) acceptable results are inferred for VEA; (iii) a triple zeta quality function works quite well in these calculations, and particularly the 6‐311G(d,p) basis set is the best, as it had been reported; and (iv) using the depronation energy (DPE), good results were obtained in the correlations δDPE‐VEA and δDPE‐χ. The results tested that P3 approximation in the electron propagator approach can be a new and interesting alternative in predicting VIP, VEA, and some reactivity indexes, such as χ and η, at least for the compounds studied. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Molecular design of a π‐conjugated single‐chain electronically conductive polymer
Authors: Imamura Akira , Aoki Yuriko
Published: February 2006

This study demonstrates that single‐chain π‐conjugated systems can be made electrically conductive by modifying the molecular structures of both ends of the oligomers making up a polymer. That is, the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps of a fairly long polyyne‐type oligomer with appropriately modified molecular structures at both ends are found to be on the order of thermal energy by calculations using density functional theory (DFT) with B3LYP functionals. This result applies to molecular structures with characteristic bond alternations. The peculiar bond alternations are caused by competition between two effects of the bond alternations of the two mutually perpendicular π‐conjugated systems, which partially cancel each other out. It is probable that we can design one‐dimensional polymers with HOMO–LUMO gaps small enough to be conductive by combining the above‐mentioned oligomers with each other as monomer units in the polymer. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Comment on “Relative Energies, Stereoelectronic Interactions, and Conformational Interconversion in Silacycloalkanes”
Authors: Arnason Ingvar , Kvaran Ágúst , Bodi Andras
Published: February 2006

Relative energies for local minima and transition states on the potential energy surface (PES) of silacylohexane have been calculated at the B3LYP/6‐311+G(d,p) level of theory. STQN(path), and intrinsic reaction path (IRC) calculations were used to calculate the lowest‐energy pathway for the chair‐to‐chair interconversion. Both methods gave identical results. An earlier description of the PES of silacyclohexane, derived with the MM3 force field, was confirmed. A different path for the ring inversion of silacyclohexane, proposed in a recent work, is shown to be incorrect. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Theoretical studies of the geometries of H2GeNaF and its insertion reaction with RH (RF, OH, NH2, CH3)
Authors: Tan Xiaojun , Li Ping , Yang Xiuli , Wang Dangsheng
Published: February 2006

The geometries and insertion reactions of germylene H2GeNaF with RH (RF, OH, NH2, CH3) have been investigated at the B3LYP/6‐311+G level of theory. The potential barriers of the four reactions are ∼52, 120, 184, and 257 kJ/mol, including the ZPVE corrections, respectively. Here, all the mechanisms of the four reactions are identical to each other; i.e., an intermediate has been located during the insertion reaction. The intermediate could dissociate into substituted germylane and NaF with the barrier corresponding to the dissociation energy. Correspondingly, the reaction energies for the four reactions are −43, −4, 21, and 51 kJ/mol, respectively. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
A framework to monitor environment‐induced major genes for developmental trajectories: implication for a prenatal cocaine exposure study
Authors: Hou Wei , Garvan Cynthia W. , Littell Ramon C. , Behnke Marylou , Eyler Fonda Davis , Wu Rongling
Published: February 2006

Whether there are specific genes involved in response to different environmental agents and how such genes regulate developmental trajectories during lifetime are of fundamental importance in health, clinical and pharmaceutical research. In this article, we present a novel statistical model for monitoring environment‐induced genes of major effects on longitudinal outcomes of a trait. This model is derived within the maximum likelihood framework, incorporated by mathematical aspects of growth and developmental processes. A typical structural model is implemented to approximate time‐dependent covariance matrices for the longitudinal trait. This model allows for a number of biologically meaningful hypothesis tests regarding the effects of major genes on overall growth trajectories or particular stages of development. It can be used to test whether and how major genetic effects are expressed differently under altered environmental agents. In a well‐designed case–control study, our model has been employed to detect cocaine‐dependent genes that affect growth trajectories for head circumference during childhood. The detected gene triggers significant effects on growth curves in both cocaine‐exposed (case) and unexposed groups (control), but with different extents. Significant genotype–environment interactions due to this so‐called environment‐sensitive gene are promising for further studies toward its genomic mapping using polymorphic molecular markers. Copyright © 2006 John Wiley & Sons, Ltd.
Social forces in Southern Africa: transformation from below?
Authors: Leysens Anthony J.
Published: February 2006

The majority of southern Africa's inhabitants are economically marginalised. Robert W. Cox's macro-theory of change suggests that the marginalised are a social force that could bring about political economic transformation from below. Other contemporary analysts also stress the importance of focusing on the marginalised as a source of social instability. The paper uses empirical data from the Afrobarometer (Round 1, 1999–2000) to investigate whether this expectation for the marginalised to act as a catalyst for change in seven southern African states is substantiated. The analysis shows that the political protest potential of the marginalised is lower than that of the economically integrated, that they are more tolerant of authoritarian political alternatives, and that they are not significantly more economically dissatisfied than other groups. They are also inclined to accord somewhat more legitimacy to the state than are the integrated. Societies where large parts of the population are poor and marginalised are thus not necessarily more prone to political instability in the form of protest actions (violent or non-violent). Those who are justly concerned about equity and greater inclusiveness must take cognisance of the need to access the profile of the marginalised.
Death of a king, death of a kingdom? Social pluralism and succession to high office in Dagbon, northern Ghana
Authors: MacGaffey Wyatt
Published: February 2006

The ongoing dynastic dispute in the kingdom of Dagbon in northern Ghana, which led to the killing of the king in 2002, remains unresolved and perhaps unresolvable. This paper updates Staniland's account of Dagomba politics from 1880 to 1974, and elaborates on the contradictions inherent in the social pluralism of a post-colonial state.