bluuebunny/crossref_metadata_2025 huggingface dataset:
Accuracy and uniqueness of three in vivo measurements of atherosclerotic carotid plaque morphology with black blood MRI
Authors: Luo Ying , Polissar Nayak , Han Chao , Yarnykh Vasily , Kerwin William S. , Hatsukami Thomas S. , Yuan Chun
Published: June 2003

High‐resolution MRI provides unique information about morphology of atherosclerotic carotid plaque. In this study, the accuracy and precision of measurements of carotid plaque burden and lumen narrowing were determined for in vivo black blood MRI assessment with respect to ex vivo MRI in a group of 37 atherosclerosis patients who underwent carotid endarterectomy (CEA). Three different plaque measures were compared between paired in vivo and ex vivo MR images: maximum wall area (MWA), minimum lumen area (mLA), and wall volume (WV). MWA and WV are measures of plaque burden, while mLA is a measure of lumen narrowing. The matched in vivo and ex vivo measurements showed good agreement (the correlation coefficients for in/ex vivo WV, MWA, and mLA were 0.92, 0.91, 0.90, respectively) with predictable bias. This study indicates that in vivo black blood MRI can be used to directly estimate the morphology of the plaque. Comparison of the three plaque measures showed that mLA and MWA or WV provide different information regarding the atherosclerotic lesions (the correlation coefficients between mLA and MWA or WV were less than 0.3). Black blood MRI technique is a potentially powerful clinical tool to characterize the severity of atherosclerotic plaque. It can provide accurate measurements on different aspects of the plaque, from plaque burden to lumen narrowing. Magn Reson Med 50:75–82, 2003. © 2003 Wiley‐Liss, Inc.
Peripheral nerve stimulation properties of head and body gradient coils of various sizes
Authors: Zhang Beibei , Yen Yi‐Fen , Chronik Blaine A. , McKinnon Graeme C. , Schaefer Daniel J. , Rutt Brian K.
Published: June 2003

Peripheral nerve stimulation (PNS) caused by time‐varying magnetic fields has been studied both theoretically and experimentally. A human volunteer study performed on three different body‐size gradient coils and one head‐size gradient coil is presented in this work. The experimental results were used to generate average PNS threshold parameters for the tested gradient systems. It was found that the average stimulation threshold increases while gradient‐region‐of‐uniformity size decreases. In addition, linear relationships between PNS parameters and diameter of homogeneous gradient spherical volume (DSV) were discovered: SRmin and ΔGmin both vary inverse linearly with DSV. More importantly, the chronaxie value was found to vary inversely linearly with the DSV. This finding indicates that, contrary to the general understanding, the parameter “chronaxie” in the commonly accepted simple stimulation models cannot be considered to be a single‐value, nerve‐specific constant. A modified linear model for gradient‐induced PNS based on these results was developed, which may permit, for the first time, the general prediction of nerve stimulation properties for gradient coils of arbitrary linear region dimension. Magn Reson Med 50:50–58, 2003. © 2003 Wiley‐Liss, Inc.
Real‐time imaging of two‐dimensional cardiac strain using a harmonic phase magnetic resonance imaging (HARP‐MRI) pulse sequence
Authors: Sampath Smita , Derbyshire J. Andrew , Atalar Ergin , Osman Nael F. , Prince Jerry L.
Published: June 2003

The harmonic phase (HARP) method provides automatic and rapid analysis of tagged magnetic resonance (MR) images for quantification and visualization of myocardial strain. In this article, the development and implementation of a pulse sequence that acquires HARP images in real time are described. In this pulse sequence, a CINE sequence of images with 1‐1 spatial modulation of magnetization (SPAMM) tags are acquired during each cardiac cycle, alternating between vertical and horizontal tags in successive heartbeats. An incrementing train of imaging RF flip angles is used to compensate for the decay of the harmonic peaks due to both T1 relaxation and the applied imaging pulses. The magnitude images displaying coarse anatomy are automatically reconstructed and displayed in real time after each heartbeat. HARP strain images are generated offline at a rate of four images per second; real‐time processing should be possible with faster algorithms or computers. A comparison of myocardial contractility in non‐breath‐hold and breath‐hold experiments in normal humans is presented. Magn Reson Med 50:154–163, 2003. © 2003 Wiley‐Liss, Inc.
Evaluation of systematic quantification errors in velocity‐selective arterial spin labeling of the brain
Authors: Duhamel Guillaume , de Bazelaire Cédric , Alsop David C.
Published: June 2003

Velocity‐selective (VS) sequences potentially permit arterial spin labeling (ASL) perfusion imaging with labeling applied very close to the tissue. In this study the effects of cerebrospinal fluid (CSF) motion, radiofrequency (RF) field imperfections, and sequence timing parameters on the appearance and quantitative perfusion values obtained with VS‐ASL were evaluated. Large artifacts related to CSF motion were observed with moderate velocity weighting, which were removed by inversion recovery preparation at the cost of increased imaging time. Imperfect refocusing and excitation pulses resulting from nonuniform RF fields produced systematic errors in the ASL subtraction images. A phase cycling scheme was introduced to eliminate these errors. Quantitative perfusion images were obtained with CSF suppression and phase cycling. Gray matter blood flow of 27.7 ml 100 g–1 min–1, approximately half the value reported in studies using spatially‐selective ASL, was measured. Potential sources for this underestimation are discussed. Magn Reson Med 50:145–153, 2003. © 2003 Wiley‐Liss, Inc.
MR microscopy of magnetically labeled neurospheres transplanted into the Lewis EAE rat brain
Authors: Bulte Jeff W.M. , Ben‐Hur Tamir , Miller Bradley R. , Mizrachi‐Kol Rachel , Einstein Ophira , Reinhartz Etti , Zywicke Holly A. , Douglas Trevor , Frank Joseph A.
Published: June 2003

Stem cell transplantation is being explored as a new paradigm for the treatment of demyelinating diseases. Magnetically labeled multipotential neural precursor cells were transplanted into the ventricles of rats with acute experimental allergic encephalomyelitis (EAE) and high‐resolution (microscopic) MR images were obtained ex vivo. Migration patterns of live cells into periventricular white matter structures could be easily visualized, with a good correlation of the corresponding histopathology. The present results confirm that MR cell tracking can be used to guide the development of successful transplantation protocols. Magn Reson Med 50:201–205, 2003. © 2003 Wiley‐Liss, Inc.
Density of organic matrix of native mineralized bone measured by water‐ and fat‐suppressed proton projection MRI
Authors: Wu Yaotang , Ackerman Jerome L. , Chesler David A. , Graham Lila , Wang Yan , Glimcher Melvin J.
Published: June 2003

Water‐ and fat‐suppressed projection MR imaging (WASPI) utilizes the large difference between the proton Ts of the solid organic matrix and the fluid constituents of bone to suppress the fluid signals while preserving solid matrix signals. The solid constituents include collagen and some molecularly immobile water and exhibit very short T. The fluid constituents include mobile water and fat, with long T. In WASPI, chemical shift selective low‐power π/2 pulses excite mobile water and fat magnetization which is subsequently dephased by gradient pulses, while the magnetization of collagen and immobile water remains mostly in the z‐direction. Additional selective π pulses in alternate scans further cancel the residual water and fat magnetization. Following water and fat suppression, the matrix signal is excited by a short hard pulse and the free induction decay acquired in the presence of a gradient in a 3D projection method. WASPI was implemented on a 4.7 T MR imaging system and tested on phantoms and bone specimens, enabling excellent visualization of bone matrix. The bone matrix signal per unit volume of bovine trabecular specimens was measured by this MR technique and compared with that determined by chemical analysis. This method could be used in combination with bone mineral density measurement by solid state 31P projection MRI to determine the degree of bone mineralization. Magn Reson Med 50:59–68, 2003. © 2003 Wiley‐Liss, Inc.
Reduction of RF power for magnetization transfer with optimized application of RF pulses in k‐space
Authors: Lin Chen , Bernstein Matt A. , Gibbs Gordon F. , Huston John
Published: June 2003

More efficient use of RF power for RF‐intensive applications such as magnetization transfer (MT) is necessary at high field strength (3.0 T or greater) to keep the specific absorption rate (SAR) within regulatory limits. It has been demonstrated that RF power deposition can be reduced with minimal impact on image quality by preferential application of MT pulses to the central phase‐encoding views. This work extends that approach to both phase‐encoding directions in a 3D acquisition (i.e., phase and slice) and further improves it by modulating the flip angle of the MT pulse according to the phase‐encoded view's distance to the center of k‐space. This technique is implemented for 3D time‐of‐flight (TOF) MR angiography (MRA) and the parameters for MT pulse are optimized based on phantom studies at 3.0 T. MT applied with this method at 3.0 T is shown to improve the blood vessel detectability in high‐resolution intracranial 3D TOF MRA exams of 11 patients. Magn Reson Med 50:114–121, 2003. © 2003 Wiley‐Liss, Inc.
Quantitative magnetization transfer mapping of bound protons in multiple sclerosis
Authors: Tozer D. , Ramani A. , Barker G.J. , Davies G.R. , Miller D.H. , Tofts P.S.
Published: June 2003

Quantitative analysis of magnetization transfer images has the potential to allow a more thorough characterization of the protons, both bound and free, in a tissue by extracting a number of parameters relating to the NMR properties of the protons and their local environment. This work develops previously presented techniques to produce estimates of parameters such as the bound proton fraction, f, and the transverse relaxation time of the bound pool, T2B, for the whole brain in a clinically acceptable imaging time. This is achieved by limiting the number of data collected (typically to 10); to collect 28 5‐mm slices with a reconstructed resolution of 0.94 × 0.94 mm. The protocol takes 82 sec per data point. The fitting technique is assessed against previous work and for fitting failures. Maps and analysis are presented from a group of seven controls and 20 multiple sclerosis patients. The maps show that the parameters are sensitive to tissue‐specific differences and can detect pathological change within lesions. Statistically significant differences in parameters such as T2B and f are seen between normal‐appearing white matter, multiple sclerosis lesions, and control white matter. Whole‐brain histograms of these parameters are also presented, showing differences between patients and controls. Magn Reson Med 50:83–91, 2003. © 2003 Wiley‐Liss, Inc.
Super‐parallel MR microscope
Authors: Matsuda Yoshimasa , Utsuzawa Shin , Kurimoto Takeaki , Haishi Tomoyuki , Yamazaki Yukako , Kose Katsumi , Anno Izumi , Marutani Mitsuhiro
Published: June 2003

A super‐parallel MR microscope in which multiple (up to 100) samples can be imaged simultaneously at high spatial resolution is described. The system consists of a multichannel transmitter–receiver system and a gradient probe array housed in a large‐bore magnet. An eight‐channel MR microscope was constructed for verification of the system concept, and a four‐channel MR microscope was constructed for a practical application. Eight chemically fixed mouse fetuses were simultaneously imaged at the 200 μm3 voxel resolution in a 1.5 T superconducting magnet of a whole‐body MRI, and four chemically fixed human embryos were simultaneously imaged at 120 μm3 voxel resolution in a 2.35 T superconducting magnet. Although the spatial resolutions achieved were not strictly those of MR microscopy, the system design proposed here can be used to attain a much higher spatial resolution imaging of multiple samples, because higher magnetic field gradients can be generated at multiple positions in a homogeneous magnetic field. Magn Reson Med 50:183–189, 2003. © 2003 Wiley‐Liss, Inc.
Three‐dimensional BOLD fMRI with spin‐echo characteristics using T2 magnetization preparation and echo‐planar readouts
Authors: Denolin Vincent , Metens Thierry
Published: June 2003

A new approach to mixed T2‐ and T‐weighted BOLD fMRI is presented, which combines T2 magnetization preparation (T2prep) with a series of EPI readouts. This technique allows full 3D, time‐efficient imaging to be performed with low RF power deposition. Steady‐state calculations are performed in order to study signal formation in 3D T2prep‐EPI sequences. Results obtained under the hypothesis of ideal spoiling are compared to full Bloch equation solutions. The theoretical findings are validated by means of in vitro and in vivo signal measurements. Several variants of the 3D T2prep‐EPI approach are shown to be usable for visual cortex fMRI and compared to conventional 3D coherent gradient‐echo EPI. The relative sensitivity of these sequences is shown to be predictable by means of a simple ΔT2/ΔT model. Magn Reson Med 50:132–144, 2003. © 2003 Wiley‐Liss, Inc.
Tracer arrival timing‐insensitive technique for estimating flow in MR perfusion‐weighted imaging using singular value decomposition with a block‐circulant deconvolution matrix
Authors: Wu Ona , Østergaard Leif , Weisskoff Robert M. , Benner Thomas , Rosen Bruce R. , Sorensen A. Gregory
Published: June 2003

Relative cerebral blood flow (CBF) and tissue mean transit time (MTT) estimates from bolus‐tracking MR perfusion‐weighted imaging (PWI) have been shown to be sensitive to delay and dispersion when using singular value decomposition (SVD) with a single measured arterial input function. This study proposes a technique that is made time‐shift insensitive by the use of a block‐circulant matrix for deconvolution with (oSVD) and without (cSVD) minimization of oscillation of the derived residue function. The performances of these methods are compared with standard SVD (sSVD) in both numerical simulations and in clinically acquired data. An additional index of disturbed hemodynamics (oDelay) is proposed that represents the tracer arrival time difference between the AIF and tissue signal. Results show that PWI estimates from sSVD are weighted by tracer arrival time differences, while those from oSVD and cSVD are not. oSVD also provides estimates that are less sensitive to blood volume compared to cSVD. Using PWI data that can be routinely collected clinically, oSVD shows promise in providing tracer arrival timing‐insensitive flow estimates and hence a more specific indicator of ischemic injury. Shift maps can continue to provide a sensitive reflection of disturbed hemodynamics. Magn Reson Med 50:164–174, 2003. © 2003 Wiley‐Liss, Inc.
Detection of the anoxic depolarization of focal ischemia using manganese‐enhanced MRI
Authors: Aoki Ichio , Ebisu Toshihiko , Tanaka Chuzo , Katsuta Kiyotaka , Fujikawa Akihiko , Umeda Masahiro , Fukunaga Masaki , Takegami Tetsuro , Shapiro Erik M. , Naruse Shoji
Published: June 2003

Mismatch between diffusion‐ and perfusion‐weighted MRI was used to indicate a treatable area following focal ischemia, called the penumbra. Activity‐induced manganese contrast MRI has been reported as a new visualization method for neural activation using manganese ions as a depolarization‐dependent contrast agent. It is well known that energy failure induced by cerebral ischemia produces anoxic depolarization. The purpose of this study was to detect manganese accumulation caused by permanent middle cerebral artery occlusion (MCAO) of rat brain and to compare regional differences between manganese accumulation and decreased apparent diffusion coefficient (ADC). The ratios of signal intensity of manganese‐enhanced MRI in the ipsilateral cortex to that in the contralateral cortex were 171.0 ± 17.5% in MCAO group and 108.4 ± 13.2% in the sham group. In addition, the enhanced region was much smaller than the area which was detected as having a reduced ADC. Magn Reson Med 50:7–12, 2003. © 2003 Wiley‐Liss, Inc.
Jaco J.M. Zwanenburg, Joost P.A. Kuijer, J. Tim Marcus, Robert M. Heethaar. Steady‐state free precession with myocardial tagging: CSPAMM in a single breathhold, Magnetic Resonance in Medicine (2003)49(4):722‐730
Authors: Zwanenburg Jaco J.M. , Kuijer Joost P.A. , Marcus J. Tim , Heethaar Robert M.
Published: June 2003

The original article to which this Erratum refers was published in Magnetic Resonance in Medicine (2003) 49(4):722–730
Modified perturbation method for transverse electromagnetic (TEM) coil tuning and evaluation
Authors: Avdievich Nikolai I. , Krymov Vladimir N. , Hetherington Hoby P.
Published: June 2003

A modified perturbation method for tuning and testing volume head coils was developed. The common perturbation method, utilizing the change in resonance frequency of a resonator in response to the presence of a small dielectric or magnetic probe, was modified to modulate the frequency shift due to rotation of a probe. This modification enabled the RF magnetic and electric fields as well as the angular distribution of current in the longitudinal elements of the coil to be mapped. The latter serves as a quick test of magnetic field homogeneity by comparing the measured distribution with the sinusoidal function required for the field to be homogenous. The method was experimentally applied to tune and test a transverse electromagnetic (TEM) head coil. Magn Reson Med 50:13–18, 2003. © 2003 Wiley‐Liss, Inc.
Mortuary patterns in burial caves on Mangaia, Cook Islands
Authors: Antón S. C. , Steadman D. W.
Published: June 2003

The behavioural, cultural, and political implications of archaeological human remains in non‐mortuary, possibly culinary, contexts requires that we understand the range of mortuary practices in a particular region. Although several rockshelter sites on Mangaia, Cook Islands have yielded burned, fragmentary human bones in earth ovens that seem to support archaeological models and ethnohistoric accounts of ritual sacrifice and cannibalism, the absence of data on the range of Mangaian mortuary patterns obscures these interpretations. We describe burial patterns based on 40 above‐ground interments representing at least 92 individuals in caves of Mangaia, Cook Islands, in order to begin to develop an island‐wide perspective on mortuary patterns. Sampling both pre‐ and post‐European contact sites we found that multiple interments dominate probable pre‐contact burials (73%, 19 of 26) and single interments dominate post‐contact contexts (80%, eight of ten burials), probably reflecting the influence of Christianity on mortuary ritual. Subadults were more frequent in all post‐contact contexts suggesting alternative burial places, probably church cemeteries, for adults. Burial cave remains are broadly consistent with ethnohistoric accounts of interment in caves, however, they also illustrate additional burial practices and differences between time periods, such as primary body position and the role of multiple‐individual interments, which are not discussed ethnohistorically. The mortuary practices in Mangaian burial caves differ from burials associated with marae and seem completely unrelated to the presence of highly fragmentary and burnt human remains in pre‐contact rockshelter middens elsewhere on the island. Copyright © 2003 John Wiley & Sons, Ltd.
Lessons from temporal variation in the mammalian faunas from two collections of owl pellets in Columbia County, Washington
Authors: Lyman R. L. , Lyman R. J.
Published: June 2003

Collections of owl pellets deposited before and after a change in nearby habitats from producing wheat fields only to producing wheat fields and a patchy grass field were obtained from Columbia County, southeastern Washington. Pellets deposited before the change contained more than three times as many deer mice (Peromyscus maniculatus) as montane vole (Microtus montanus); pellets deposited after the change contained more than three times as many voles (M. montanus, M. longicaudus) as deer mice. The change in the ratio of deer mice to voles mirrors changes in rodent faunas in nearby areas caused by altered agricultural practices and resulting changes in vegetation. Because biologists correctly suggest the change in prey ratios could reflect variation in predation behaviours or prey availability, it is apparent that multiple lines of evidence are necessary to establish that changes in rodent faunas reflect changes in habitats. Copyright © 2003 John Wiley & Sons, Ltd.
Differential diagnosis of a prehistoric biological object from the Koster (Illinois) Site
Authors: Komar Debra , Buikstra Jane E.
Published: June 2003

This paper details the differential diagnosis of a biological artifact recovered from a burial within the Koster Middle Archaic site in Illinois. The burial was excavated from the Middle Archaic 3, Helton Phase component (∼5800–4900 BP). The artifact was a calcified nodule of unequivocal biological origin recovered from the pelvic region of an adult (50+ years) female. Morphological and radiographic analysis of the object resulted in the consideration of 19 possible diagnoses; all but four could be eliminated. Possible interpretations of the object as a lithopaedion, calcified lymph node, amputated ovary or simple ovarian cyst are examined in detail. Of these, calcified lymph node or amputated ovary remain most probable. Copyright © 2003 John Wiley & Sons, Ltd.
Determination of a controllable set for a class of non‐linear stochastic control systems
Authors: Liu Yazeng , Peng Shige
Published: June 2003

A controllable set of a class of non‐linear stochastic control systems to a given set is defined. A value function associated with an optimal control problem is introduced. Under some reasonable conditions, the controllable set is characterized by a level set of the viscosity solution of a Hamilton–Jacobi–Bellman equation. Copyright © 2003 John Wiley & Sons, Ltd.
Discrete‐time polynomial systems approach to combined fault monitoring and control
Authors: Grimble M. J.
Published: June 2003

The combined fault monitoring and control problem is discussed, using an H2 optimization framework. The main aim is to investigate the frequency‐domain and pole‐zero properties of the combined control and fault estimation compensator. The solution of the LQG stochastic optimal multivariable control and fault estimation problem is obtained using a polynomial matrix systems approach. The combined control and fault estimation problem involves a performance index including the usual regulating error and control weighting terms and also fault estimation error terms. The system model includes input disturbances, reference, coloured noise signals and actuator/sensor fault signals. The proposed numerical algorithm has common polynomial terms, so that the computation of the fault estimates and control law, is not significantly more difficult than the calculation of the control law alone. Copyright © 2003 John Wiley & Sons, Ltd.
A new method for mixedH2/H∞control with regional pole constraints
Authors: Wu Jenq‐Lang , Lee Tsu‐Tian
Published: June 2003

In this paper, the problem of state feedback mixedH2/H∞control with regional pole constraints is studied. The constraint region is represented by several algebraic inequalities. This constrained optimization problem cannot be solved via the LMI approach. Based on the barrier method, we instead solve an auxiliary minimization problem to get an approximate solution. We shall show that the obtained minimal solution of the auxiliary minimization problem can be arbitrarily close to the infimal solution of the original problem. An example is provided to illustrate the benefits of the approach. Copyright © 2003 John Wiley & Sons, Ltd.
Simulation of pedestrian flows by optimal control and differential games
Authors: Hoogendoorn Serge , H.L. Bovy Piet
Published: June 2003

Gaining insights into pedestrian flow operations and assessment tools for pedestrian walking speeds and comfort is important in, for instance, planning and geometric design of infrastructural facilities, as well as for management of pedestrian flows under regular and safety‐critical circumstances. Pedestrian flow operations are complex, and vehicular flow simulation modelling approaches are generally not applicable to pedestrian flow modelling. This article focusses on pedestrian walking behaviour theory and modelling. It is assumed that pedestrians are autonomous predictive controllers that minimize the subjective predicted cost of walking. Pedestrians predict the behaviour of other pedestrians based on their observations of the current state as well as predictions of the future state, given the assumed walking strategy of other pedestrians in their direct neighbourhood. As such, walking can be represented by a (non‐co‐operative or co‐operative) differential game, where pedestrians may or may not be aware of the walking strategy of the other pedestrians. Copyright © 2003 John Wiley & Sons, Ltd.
Self‐diffusion of styrene, 2,2′‐azobisisobutyronitrile, and polystyrene in bulk polymerization by pulsed‐gradient spin‐echo nuclear magnetic resonance spectroscopy
Authors: Arcos‐Casarrubias José Antonio , Olayo Roberto
Published: June 2003

The self‐diffusion of styrene, polystyrene, and 2,2′‐azobisisobutyronitrile has been determined in the bulk polymerization of styrene with pulsed‐gradient spin‐echo nuclear magnetic resonance at 25 °C. Data on small molecules are discussed with respect to recent diffusion models. They can fit self‐diffusion coefficient data of small molecules in dilute or semidilute polymer solutions; in concentrated solutions, however, there is a breakdown. A semiempirical model based on scaling laws is used to describe the self‐diffusion of styrene and 2,2′‐azobisisobutyronitrile over the whole range of concentrations studied. The dependence of the polystyrene self‐diffusion coefficient on the polymer concentration is described with a stretched exponential function, D = D0 exp(−αcν), where α depends on the molecular weight of the polymer and ν depends on the kind of solvent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1605–1614, 2003
Network structure and swelling behavior of poly(acrylamide/crotonic acid) hydrogels in aqueous salt solutions
Authors: Çaykara Tuncer , Bozkaya Uğur , Kantoğlu Ömer
Published: June 2003

Hydrogels with various ionic group contents were prepared from acrylamide and crotonic acid (CrA) monomers with 0–12.9 mol % CrA in aqueous solutions by radiation‐induced polymerization and gelation with γ rays from a 60Co source. The volume swelling ratio of the poly(acrylamide/crotonic acid) hydrogels was investigated as a function of the pH and ionic strength of the swelling medium and the type of counterion in the swelling medium. The volume swelling ratio increased with an increase in pH and a decrease in the ionic strength. The volume swelling ratio of these hydrogels was evaluated with an equation, based on the Flory–Huggins thermodynamic theory, the James–Guth phantom network theory, and the Donnan theory of swelling of weakly charged ionic gels, that was modified here for the determination of the molecular weight between crosslinks (Mc) and the polymer–solvent interaction parameter (χ). The modified equation described very well the swelling behavior of the charged polymeric network. The same equation also provided the simultaneous measurement of these parameters for the systems investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1656–1664, 2003
Viscoelastic properties of nanostructured natural rubber/polystyrene interpenetrating polymer networks
Authors: Mathew Aji P. , Groeninckx Gabriel , Michler G. H. , Radusch H. J. , Thomas Sabu
Published: June 2003

The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of −80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (Tg's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, theTgvalues showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003
Effect of annealing on the viscoelastic and viscoplastic responses of low‐density polyethylene
Authors: Drozdov Aleksey D. , Yuan Qiang
Published: June 2003

Two series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low‐density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 °C. Constitutive equations were derived for the time‐dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress‐strain relations involve five material constants that were found by fitting the observations. Fair agreement was demonstrated between the experimental data and the results of numerical simulation. This study focuses on the effects of strain rate and annealing temperature on the adjustable parameters in the constitutive equations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1638–1655, 2003
Energy migration in poly(N‐vinyl carbazole) and its copolymers with methyl methacrylate: Fluorescence polarization, quenching, and molecular dynamics
Authors: Gallego Javier , Mendicuti Francisco , Mattice Wayne L.
Published: June 2003

Fluorescence polarization and quenching measurements were used to examine intramolecular energy migration for poly(N‐vinyl carbazole) and copolymers of N‐vinyl carbazole with methyl methacrylate. Quenching measurements of the carbazole fluorescence by CCl4 were performed in dilute solution in toluene, and fluorescence anisotropy, r, was measured for the chains dispersed in a solid matrix of poly(methyl methacrylate) (PMMA). The results suggested that the chains with a high carbazole content, that is, a high content of excimer trapping sites, do not show the highest values of the singlet energy‐migration rate. Isotropies, r−1, of the samples in vitrified PMMA corroborated such conclusions. Molecular dynamics simulations on isotactic and syndiotactic trichromophoric copolymer fragments were used to obtain parameters related to the energy‐transfer process as a function of the methyl methacrylate content. The parameters from the simulations supported the interpretation of the experiments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1615–1626, 2003
Study of the phase transition of poly(N,N‐diethylacrylamide) in water by rheology and dynamic light scattering
Authors: Lessard D. G. , Ousalem M. , Zhu X. X. , Eisenberg A. , Carreau P. J.
Published: June 2003

Poly(N,N‐diethylacrylamide) (PDEA) possesses a lower critical solution temperature (LCST) in aqueous media. The solution properties of PDEA at various temperatures have been characterized with techniques such as rheology and dynamic light scattering. There is a decrease in the coil size before the phase transition due to a coil‐to‐globule transition. At the LCST, rheological and dynamic light scattering studies have also confirmed an aggregation phenomenon. This aggregation modifies the rheological properties of the polymer solutions. High frequencies hinder the phase‐transition process and reduce the LCST of the polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1627–1637, 2003
Effects of the oriented mesophase on the cold crystallization of syndiotactic polystyrene and its blend with poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Dikshit A. K. , Kaito A.
Published: June 2003

The effects of molecular orientation on the crystallization and polymorphic behaviors of syndiotactic polystyrene (sPS) and sPS/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) blends were studied with wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry. The oriented amorphous films of sPS and sPS/PPO blends were crystallized under constraint at crystallization temperatures ranging from 140 to 240°C. The degree of crystallinity was lower in the cold‐crystallized oriented film than in the cold‐crystallized isotropic film. This was in contrast to the case of the cold crystallization of other polymers such as poly(ethylene terephthalate) and isotactic polystyrene, in which the molecular orientation induced crystallization and accelerated crystal growth. It was thought that the oriented mesophase was obtained in drawn films of sPS and that the crystallization of sPS was suppressed in that phase. The WAXD measurements showed that the crystal phase was more ordered in an sPS/PPO blend than in pure sPS under the same annealing conditions. The crystalline order recovered in the cold‐crystallized sPS/PPO blends in comparison with the cold‐crystallized pure sPS because of the decrease in the mesophase content. The crystal forms depended on the crystallization temperature, blend composition, and molecular orientation. Only the α′‐crystalline form was obtained in cold‐crystallized pure sPS, regardless of molecular orientation, whereas α′, α″, and β′ forms coexisted in the cold‐crystallized sPS/PPO blends prepared at higher crystallization temperatures (200–240°C). The β′‐form content was much lower in the oriented sPS/PPO blend than in the isotropic blend sample at the same temperature and composition. It was concluded that the oriented mesophase suppressed the crystallization of the stable β′ form more than that of the metastable α′ and α″ forms during the cold crystallization of sPS/PPO blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1665–1675, 2003
Thermal transitions of benzene in copolymers and interpenetrating polymer networks based on hydrophilic and hydrophobic components: Experimental evidence of hydrophobic interaction
Authors: Salmerón Sánchez M. , Monleón Pradas M. , Gómez Ribelles J. L.
Published: June 2003

Thermal transitions of benzene in a hydrophobic polymer network have been explained by us in terms of the phase diagram of the polymer‐solvent system. In this work, we executed a similar study on copolymers and interpenetrating polymer networks (IPNs) with controllable hydrophilic/hydrophobic ratios. Copolymers and IPNs were swollen with different amounts of benzene and subjected to cooling and heating scans with differential scanning calorimetry (DSC). Synthesis of the IPNs was carried out in such a way that phase separation appeared, and three qualitatively different types of DSC thermograms were identified depending on the benzene content of IPN. Thermal transitions of benzene in the hydrophilic/hydrophobic copolymers can also be explained as a consequence of the phase diagram of the system, but an increase in the glass‐transition temperature of the system can be correlated with the interactions among the hydrophilic groups of the copolymer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1713–1721, 2003
Chain dynamics in entangled polymers: Diffusion versus rheology and their comparison
Authors: Wang Shi‐Qing
Published: June 2003

This review article scrutinizes and reanalyzes the extensively available literature data on the tracer and self chain diffusion coefficients Dtr and Ds along with the corresponding zero‐shear viscosity η0 to show that Ds ∝ M−ν starts with ν > 2.0 and converges to the asymptotic scaling exhibited by Dtr ∝ M−2.0 as the molecular weight M increases beyond M/Me = 10–20, in contrast to the onset of the asymptotic scaling M3 for η0 taking place typically for M/Me ≫ 10–20. A coherent analysis of these observations leads to the suggestion that the observed crossover in Ds is due to the constraint release effect, which diminishes around M/Me = 10–20 and is negligible in measurements of Dtr when the matrix molecular weight P is much greater than M. The contour length fluctuation (CLF) effect, which is believed to cause the molecular weight scaling of η0 to deviate significantly from its limiting behavior of M3, has little direct influence on the chain diffusion. The absence of the CLF effect on Ds leads to a much stronger than linear dependence of the product η0Ds on M, which has been observed previously. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1589–1604, 2003
Effect of annealing on the structure and properties of poly(vinylidene fluoride) β‐form films
Authors: Nakamura Koh , Sawai Daisuke , Watanabe Yuuji , Taguchi Daisuke , Takahashi Yoshiyuki , Furukawa Takeo , Kanamoto Tetsuo
Published: June 2003

Oriented poly(vinylidene fluoride) (PVDF) films consisting of β crystals were prepared by the solid‐state coextrusion (SC) of a gel film near the melting temperature (Tm) and by conventional cold tensile drawing (TD) of a melt‐quenched film. These films were annealed over the temperature range of 75–190 °C (below and above the static Tm) while the sample length was kept constant or constant loads were applied. After annealing with the sample length kept constant, the dynamic Young's modulus markedly decreased because of the relaxation of oriented amorphous chains, as shown by infrared spectroscopy. In contrast, annealing under a constant load improved the chain orientation in both the crystalline and amorphous regions, resulting in an increase in the modulus from an initial 10.5 to 14.3 GPa for the SC and from an initial 3.3 to 4.8 GPa for the TD. The SC, annealed at 190 °C with a constant load corresponding to an initial tension of 200 MPa, exhibited an extreme crystalline‐chain orientation of 0.998 and a modulus of 14.3 GPa, among the highest values ever reported for PVDF. Although the remanent polarization (Pr) of the TD increased slightly from the initial 62 to 68 mC/m2, Pr of the SC stayed constant at 100 mC/m2 independently of the annealing conditions. This suggests that the Pr value of 100 mC/m2 approached the equilibrium value for this PVDF sample containing 3.5 mol % structural defects. Therefore, although the modulus and Pr of the TD increased slightly with annealing, the maximum values achieved by annealing were markedly lower than those of the SC and annealed SC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1701–1712, 2003
Infrared spectroscopic study of the interactions of nylon‐6 with water
Authors: Iwamoto Reikichi , Murase Hiroshi
Published: June 2003

We studied the interactions of nylon‐6 with water by following the Fourier transform infrared spectra of a hydrated thin film during dehydration. Very small changes in the spectra caused by the interactions were clearly revealed by the application of spectral subtraction. The water was found to interact with amide groups to form hydrogen bonds with non‐hydrogen‐bonded or free CO and NH groups in the amorphous portion in the first hydration sphere. This was deduced from an analysis of minus and plus peaks appearing around the absorptions of the NH stretching, amide I band, and amide II bands in the difference spectra between the spectra during dehydration and the one at the most dehydration. The interactions of the amide groups with water were significantly stronger than the hydrogen bond between CO and NH in the crystalline portion, according to the magnitude of the frequency shift of relevant bands. Water, as the interacting counterpart, showed a distorted OH stretching absorption with two close peaks at about 3450 cm−1. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1722–1729, 2003
Effect of the premelting temperature and sample thickness on the polymorphic behavior of syndiotactic polystyrene/clay nanocomposites
Authors: Wu Tzong‐Ming , Hsu Sung‐Fu , Wu Jeng‐Yue
Published: June 2003

X‐ray diffraction methods and differential scanning calorimetry thermal analysis have been used to investigate the structural changes of syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay nanocomposites have been prepared by the mixing of sPS polymer solutions with organically modified montmorillonite. X‐ray diffraction data and differential scanning calorimetry results indicate that the dominating crystal forms and their relative fractions in sPS and sPS/clay nanocomposites are different for various premelting temperatures (Tmax's). Higher Tmax's favor the formation of the thermodynamically more stable β‐crystalline form, and its relative fraction has been obtained from the X‐ray diffraction data in the range of 11.5–13°. The intensity of the X‐ray diffraction data in the range of 11.5–13° decreases as the thickness of sPS/clay nanocomposites decreases from 150 to 20 μm. At the same time, the intensity of the X‐ray data in the range of 6–7° becomes sharper as the thickness of sPS/clay nanocomposites decreases. The calculation ratio based on the peak intensities at 6.2 and 6.8° for sPS/clay nanocomposites of equal thickness and crystallinity in the pure β and α forms has also been determined in this study. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1730–1738, 2003
Electrical and optical properties of ceramic–polymer nanocomposite coatings
Authors: Sun Jiakuan , Gerberich William W. , Francis Lorraine F.
Published: June 2003

Transparent, conductive composite coatings were fabricated from suspensions of poly(vinyl acetate‐acrylic) (PVAc‐co‐acrylic) copolymer latices (50–600 nm) and nanosized antimony‐doped tin oxide (ATO) particles (∼15 nm). The suspensions were deposited as coatings onto poly(ethylene terephthalate) substrates and dried at 50 °C. Microstructure studies using field emission scanning electron microscopy and tapping‐mode atomic force microscopy (TMAFM) indicated that the latex particles coalesced during drying and forced the ATO particles to segregate into the boundaries between the latex particles. Low phase contrast was observed with TMAFM; this result was consistent with the presence of PVAc‐co‐acrylic in the ATO‐rich phase of the composite. The conductivity of the composite coatings followed a percolation power‐law equation, with the percolation threshold between 0.05 and 0.075 volume fractions of ATO and the critical conductivity exponent ranging from 1.34 to 2.32. The highest direct‐current conductivity of the composite coatings was around 10−2 S/cm. The optical transmittance and scattering behavior of the coatings were also investigated. Compared with the PVAc‐co‐acrylic coating, the composite coatings had lower transparency because of the Rayleigh scattering. The transparency of the composite coatings was improved by a reduction in the coating thickness. The best transparency for the coatings with a direct‐current conductivity of approximately 10−2 S/cm was around 85% at a wavelength of 600 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1744–1761, 2003
Effect of operation parameters on temperature rising elution fractionation and crystallization analysis fractionation
Authors: Anantawaraskul Siripon , Soares João B. P. , Wood‐Adams Paula M.
Published: June 2003

Crystallization analysis fractionation and temperature rising elution fractionation are two techniques used to estimate the chemical composition distributions of semicrystalline copolymers. This study investigates the cooling rate and cocrystallization effects for both techniques with a series of ethylene/1‐olefin copolymers and their blends. Ideally, both techniques should operate in the vicinity of thermodynamic equilibrium so that crystallization kinetic effects are avoided. The results show that, in fact, crystallization kinetic effects play an important role at the typical cooling rate used with both techniques. Cocrystallization is significant when fast cooling rates are used. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1762–1778, 2003
Heats of Combustion and Formation of New Energetic Thermoplastic Elastomers Based on GAP, PolyNIMMO and PolyGLYN
Authors: Diaz Emmanuela , Brousseau Patrick , Ampleman Guy , Prud'homme Robert Emery
Published: June 2003

Heats of combustion and formation of various energetic thermoplastic elastomers (ETPE), corresponding to linear copolyurethanes based on an energetic prepolymer and a diisocyanate, were measured by a calorimetric method. These ETPEs were synthesized from three different molecular weights of glycidyl azide polymer, from poly(3‐nitratomethyl‐3‐methyloxetane) and from poly glycidyl nitrate. The prepolymers were also analyzed for comparison with the corresponding ETPEs. A significant difference of the heats of formation was observed between the prepolymers and their ETPEs, while the heats of combustion were similar.
An Investigation of Composite Propellant Accelerated Ageing Mechanisms and Kinetics
Authors: Judge Michael D.
Published: June 2003

The ageing kinetics and mechanisms of a composite solid rocket propellant were investigated by monitoring unstressed propellant samples during prolonged storage at elevated temperatures. For samples confined under air during ageing, it was determined that oxidative cross‐linking of the propellant binder was the main degradation mechanism over time. Plasticizer loss was a significant ageing mechanism only for those samples aged unconfined. In addition, there was an indication that ambient humidity had a significant but reversible effect on propellant mechanical properties. Arrhenius mathematical relationships were derived in order to ascertain the extent to which ageing was accelerated by increased propellant temperature. An activation energy for binder oxidation of between 71 and 74 kJ/mol was determined.