bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of macromolecules and nuclear magnetic relaxation: Application of mode‐coupling diffusion theory to DNA, proteins and their complexes
Authors: Fausti Simone , La Penna Giovanni , Perico Angelo , Pratolongo Roberto
Published: March 2011

A mode‐coupling approach has been used to solve the Smoluchowski diffusion equation describing the correlation functions relevant in nuclear magnetic relaxation experiments on biological molecules like protein and DNA. A good reproduction of relaxation patterns for molecules that are fluctuating about three‐dimensional structures imposed by secondary motives has been found. Important differences can be explained with the poor statistics collected by numerical simulations that do not contain fluctuations contributing to rates in the ns time‐scale, therefore comparable with rotational rates.
Electron crystallography and organic materials with non‐linear optical properties
Authors: Voigt‐Martin Ingrid G. , Kolb Ute , Kothe Hans , Yakimanski Alexander V. , Yu Ri‐Cheng , Matveeva Galina N. , Tenkovtsev Andrey V.
Published: March 2011

Results of electron microscopic studies of crystal structures of a number of bis‐benzylidene cyclohexanones are presented. It is shown that some of these compounds are efficient crystalline non‐linear optically active (NLO) chromophores with second harmonic generation (SHG) properties. Appropriately functionalized chromophores of this type can be used as a polycondensation comonomer to produce partly crystalline main‐chain NLO‐active polymers. Electron diffraction crystal structural data, obtained for very small crystals, allowed us to get reasonable estimations of macroscopic crystal NLO‐coefficients, relating quantum‐chemically calculated molecular first hyperpolarizability components to crystal axes.
Influence of salts on hydrophobically end‐capped polyethylene oxides in aqueous solution
Authors: Beaudoin Emmanuel , Gourier Christine , Lapp Alain , François Jeanne
Published: March 2011

The influence of four different salts (NaCl, KBr, CaCl2 and MgCl2) on the associative behaviour of poly(ethylene oxide) (POE with M=32000g/mol) hydrophobically end‐capped with hexadecyl groups in aqueous solutions was investigated. Phase diagrams were obtained, structural properties were established by small angle neutron scattering (SANS) measurements and studies on the viscoelastic properties of the solutions were performed by low‐shear viscosity and dynamic stress experiments. The influence of the four salts is compared as well as the difference of the interactions obtained with and without salts.
Comparative study of the poly‐dimethylsiloxane monolayer with styrene and polystyrene
Authors: Marchenko Svetlana B. , Gritskova Inessa A. , Zaitsev Sergei Yu.
Published: March 2011

Polydimethylsiloxane (PDS) and it mixtures with styrene and polystyrene (PSt) are able to form stable monolayers at the liquid‐gas interfaces in contrast to pure styrene or PSt. The surface pressure — molecular area isotherms of PDS monolayers have two regions at low and high pressures with pronounced transition plateau in between. The area per PDS molecule in the liquid‐expanded state is about 1.60 nm2 (at 5 mN/m) that can be explained by twisting of polymer chain into the helical conformation. The area per PDS molecule in the liquid‐condensed state is about 0.48 nm2 (at 20 mN/m) that can be explained by PDS reorientation in the helical conformation from the horizontal to the vertical position with respect to the air‐water interface. The addition of styrene in the PDS monolayer drastically changes the π‐A isotherms (no transition plateau) with area increase from 0.47 till 2.70 nm2 per PDS with the increasing of polymer concentration from 1 to 10 mass %. In contrast, there are only small quantitative changes in the isotherms in the presence of PSt in the PDS monolayer. Thus, the formation of the polymer adsorption layers at the interface has been studied, modeling the initial and final step of the styrene polymerization in emulsion.
Simulation of intermediate order in polymeric glasses
Authors: Ludovice Peter J. , Ahmed Savant , van Order Jon , Jenkins Jerry
Published: March 2011

The glass phase of most polymers is typically considered amorphous. However, many commercially important polymer glasses do contain a subtle level of structural order intermediate between the crystalline and truly amorphous phases. These include a number of commercially important polymers. This “Intermediate Order” is distributed homogeneously throughout the glass phase and is therefore quite different than the morphology of semi‐crystalline materials. Typical computer simulation methods can fail to accurately reproduce the structure of polymers with intermediate order, because they are often based on the assumption that the polymer structure is truly amorphous. Given the subtle nature of this order, computer simulation is important in understanding this structural order and the unique material properties commonly associated with it. We outline the critical issues required for the successful simulation of polymer glasses with intermediate order, and discuss the results of some continuing research designed to improve the accuracy of such simulations.
Morphology and mechanical properties of low‐molecular ‐ weight polyethylene and ultrahigh‐molecular‐weight polyethylene films drawn up to 200‐fold
Authors: Bin Yuezhen , Fukuda Miwako , Kurosu Hiromichi , Matsuo Masaru
Published: March 2011

Ultrahigh‐molecular‐weight polyethylene (UHMWPE) and low‐molecular‐weight polyethylene (LMWPE) blend films were prepared by gelation/crystallization from solutions. UHMWPE with the viscosity‐average molecular weight (Mv) of 6×106 and three kinds of LMWPE with (Mv) <5×104 were used. The LMWPE/ UHMWPE compositions chosen were 1/1, 2/1, 4/1 and 9/1. The resulting blend gels with the 9/1 composition (10% UHMWPE content) became films by evaporating the solvents, although LMWPE homopolymer gels have no ability to form films. The films with the above compositions could be readily elongated up to 200‐fold in a hot oven. Such high elongation is assumed to be due to the existence of a suitable level of entanglements between UHMWPE and LMWPE chains. The orientational degree of LMWPE crystallites became poorer as the LMWPE content in the blend film increased, indicating a decrease in the number of entanglements. The storage modulus of the blend films at the same draw ratio decreased as the LMWPE content increased. The storage modulus of the 1/1 blend film with λ = 200 reached about 50 GPa at 20°C but the storage modulus decreased drastically with further increase in the LMWPE content: The value of the 9/1 blend film with λ = 200 was less than 10 GPa. This means that a suitable level of entanglements between LMWPE and UHMWPE chains plays an important role in transmitting the drawing force effectively and promoting the orientational degree of the c‐axis, owing to the crystal transformation from a folded to a fibrous type.
Relationship of hierarchical structure to mechanical properties
Authors: Baer E. , Hiltner A. , Jarus D.
Published: March 2011

The mechanical properties in complex systems are explained based on the hierarchical structures present in the system. Hierarchical structures designed for specific mechanical responses are best exemplified by examples from biology. Collagen, a main component in soft connective tissues, is organized into hierarchical structures in the form of tendons or intervertebral discs as examples. Understanding these structures is vital in relating the structures to the intended properties. This approach is also used to characterize organic/inorganic natural composites such as human bone, reindeer antler and nacre. Another example of a hierarchical structure in biology with excellent mechanical properties is that of cellulose, when organized into wood. The importance of hierarchical structures also applies to synthetic polymers for a clearer understanding of the structure‐property relationships. Solid‐state biaxially oriented polypropylene has excellent tensile and impact properties, which are explained by the hierarchical structure induced during the processing. Thermotropic liquid crystalline polymers develop a hierarchical structure during injection molding that influence the final properties. Furthermore, the impact modification of polycarbonate is more easily understood when the system is explained in a hierarchical manner. It is also now possible to create or force hierarchical structures in synthetic polymers by microlayering technology. Several systems are outlined in which a hierarchical structure is created to enhance specific properties. SAN, a brittle polymer, can be microlayered with PC to create tough materials due to the scale, interaction and architecture of the microlayered composite. Another example is the effect of microlayered composite of PC/SAN on the interfacial adhesion mechanisms. Furthermore, toughening mechanisms in filled microlayers are examined based on the hierarchical structure.
Application of the crack resistance concept to the toughness characterization of high‐impact thermoplastics
Authors: Seidler Sabine , Grellmann Wolfgang
Published: March 2011

Heterophasic reactor‐grade polypropylene‐ethylene copolymers were diluted with a propylene‐ethylene random copolymer to obtain materials with a constant EPR/PE‐particle diameter but various interparticle distances. In addition to these copolymers, PP/EPR blends were investigated. According to the results of instrumented impact tests, brittle‐to‐tough transitions were found at different temperatures. In the materials with PP matrix, two transitions in the load‐deflection behaviour were seen. The first transition occurs from the elastic to the elastic‐plastic material behaviour, the second from the unstable to stable crack growth. “Critical” interparticle distances could be determined in the region of predominantly unstable crack growth as well as in the region of predominantly stable crack growth. With increasing test temperature, both transitions shift to higher interparticle distances. From this theoretically similar behaviour of fracture mechanical values quantifying different proportions of the crack growth process, one can conclude that different processes must be occurring.
Mechanical properties of crosslinked polyolefin‐based materials
Authors: Chodák Ivan , Nógellová Zuzana , Kokta Bohuslav V.
Published: March 2011

The effect of crosslinking on mechanical properties of various polyethylene‐based materials is compared. In virgin polyethylene, higher strength results from formation of spatial network, especially at increased temperatures. On the other hand, decreased crystalline portion leads to lower Young's modulus values compared with the uncrosslinked polymer. Crosslinking of LDPE/PP blends leads to a dramatic increase in elongation at break and impact resistance. The reason is seen in an in situ formation of very efficient compatibilizers via co‐crosslinking on the phase boundary. In LDPE filled with silica, the main effect consists in higher elongation at break and increased toughness, although the effect is lower than that in LDPE/PP blends. Increased resistance to the crack growth rate was demonstrated to be a reason for the observed behaviour. In LDPE filled with organic fillers, formation of direct covalent bonds on the interface and a significant increase in adhesion is suggested to be the reason for the enormous increase in Young's modulus and tensile strength observed.
Deformation behavior and mechanical properties of hard elastic and porous films of polyethylene
Authors: Elyashevich Galina , Karpov Evgenii , Kozlov Alexandr
Published: March 2011

Hard elastic samples of linear polyethylene were prepared by melt extrusion at a high velocity of the melt flow and by subsequent annealing of crystallized samples. The deformation behavior of hard elastic samples obtained by annealing of as‐spun samples at different temperatures has been analyzed at uniaxial extension resulting in formation of porous structure. Mechanical properties of microporous films in the longitudinal and transverse directions have been investigated. Composite systems consisting of a microporous polyethylene film and a thin layer of an electroconducting polymer have been prepared. Mechanical properties of composite systems, such as elastic modulus, tensile strength, and break elongation, have been compared with the properties of polyethylene substrates.
From dynamic mechanical properties to plastic strain behavior of epoxy networks. Effect of the network architecture
Authors: Pierre A. , Sindt O. , Thorne N. , Perez J. , Gérard J. F.
Published: March 2011

Closed epoxy networks with various architectures, i.e., crosslink density and chain flexibility between crosslinks, were considered in this study. The crosslink density can be varied by preparing epoxy‐amine networks from a mixture of primary amines having different functionalities using mixtures of poly(oxypropylene)amines or a monofunctional amine having the same chemical structure acting as a chain extender. The chain flexibility is modified by considering aliphatic epoxy prepolymers instead of aromatic. The influence of the architecture of the epoxy networks on the low‐ and high‐stress mechanical properties is discussed. The dynamic mechanical spectroscopy conducted in wide ranges of frequency and temperature gives insight into the molecular level analyzing the data in both the glass transition region (α‐relaxation) and sub‐Tg relaxation zones. A model described by Perez and based on the existence of nanofluctuations of density or quasi‐point defects and the concept of hierarchically correlated molecular motions are also used to describe the low‐stress mechanical behaviour. The same theory is extended by taking into account the large‐stress effects and used to analyze the stress‐strain curves recorded in compression at various temperatures and strain rates. This modeling can describe variation of the flow stress with temperature and gives a unique description of the yielding of all the epoxy networks. From this model, the main physical parameter determining the flow stress is the cohesion of the solid state resulting from intermolecular interactions; the loss of cohesion, as temperature increases, corresponds to the α‐process which depends on the network architecture. Finally, the strain and stress at break (sr and ϵr) recorded in tension at various temperatures and strain rates for epoxy networks having various crosslink densities are correlated with the low‐stress behavior from the shift factors, aT, determined in the glass transition region.
Short predicting the strength and toughness of fiber composites
Authors: Kardos J. L. , Halpin J. C.
Published: March 2011

Predictions of strength and toughness for short‐fiber‐reinforced plastic systems are complex but industrially crucial problems. In this contribution, we utilize a new approach which accounts for the large stress concentration penalties in a perfectly aligned short‐fiber composite. Although empirical, the approach permits calculation of a strength reduction factor which can then be utilized with an appropriate failure criterion to calculate the strength of a wide range of short‐fiber composite systems. A similar approach is used for the toughness problem, with the fracture toughness of an isotropic, random‐in‐a‐plane, short‐fiber composite being expressed in terms of the fracture toughness of single unidirectionally oriented plies with cracks oriented along the two orthotropic axes. For both strength and toughness, a laminate analogy approach is used. The short‐fiber system is thought of as being composed of several plies or layers, each containing uniaxially aligned short fibers. The plies are oriented in the laminate to replicate the actual system fiber orientation distribution, and the linear stress‐strain or fracture toughness properties are calculated by analyzing the individual ply responses to the overall applied stress. Comparison with experimental data for random‐in‐a‐plane fiber orientation and for biased in‐plane orientations at practical fiber volume loadings shows good agreement. In the case of fracture toughness, there was qualitative agreement between theory and experiment, but the data scatter precluded a rigorous comparison.
Comparative study of mechanical and dielectric properties of glassy acrylic polymers containing 1,3‐dioxane rings in their structures
Authors: Díaz‐Calleja Ricardo , Riande Evaristo
Published: March 2011

A comparative study of mechanical and dielectric relaxation behaviour in the glassy region of some acrylic polymers containing 1,3‐dioxane rings in the side chain is reported. Earlier results for similar polymers containing cycloaliphatic rings are used to interpret the results obtained. This study suggests that simple mechanisms based on chair‐to‐chair inverse conformational transitions are not able to explain in a unified way the responses of these polymers in the glassy region to mechanical and electric perturbation fields.
Yielding and fracture in crosslinked epoxies
Authors: Tcharkhtchi Abbas , Trotignon Jean‐Pierre , Verdu Jacques
Published: March 2011

From a comparison of tensile properties of two epoxy networks crosslinked, respectively, with an aromatic diamine or an anhydride and from the available literature data on the fracture properties of thermosets, it has been tried to establish structure‐property relationships in this field. Attention was focused on possible specific aspects of the crosslinked polymers. Surprisingly, the crosslink density does not seem to play a crucial direct role in fracture. In contrast, there is a relation between toughness and Tg: Aliphatic networks of low Tg are generally tougher than aromatic ones. The local mobility plays a very important role because it partly controls the value of Poisson's ratio (which determines the relative importance of dilatant stresses and shear stresses responsible, respectively, for brittle rupture and yielding) and, presumably, the activation volume of yielding (which partly determines the broadness of the temperature interval of ductility).
Epoxy networks modified by unsaturated oligoesters and acrylates or methacrylates
Authors: Bratychak Mihailo , Brostow Witold , Yatczyshyn Yozef
Published: March 2011

We have studied the formation of networks on the basis of an epoxy resin called ED‐20, the same resin modified with tert ‐butylhydroperoxide (called ED‐20P), unsaturated oligoesters and polyethylenepolyamine in the presence of acrylates and methacrylates at 20°C, 100°C and 130°C. The gel‐fraction contents in the blends and the pendulum damping hardness of films made from the blends have been determined. The progress of gelation has been related to the composition, time and crosslinking temperature. The presence of peroxide groups enhances the extent of gelation. When those groups are present, acrylates and methacrylates provide still higher values of the ultimate gel fractions, acting as diluents (lowering viscosity of the initial blends) and simultaneously as crosslinking agents. The pedulum damping hardness tests for organic films performed as a function of time provide results parallel to those obtained by the gel fraction determination via Soxhlett extraction with acetone. Thus, both methods can be used to pursue the progress of gelation.
Properties of in‐situ filled polyethylene
Authors: Bolz Andreas , Hess Michael , Veeman Wiebren S.
Published: March 2011

Polyethylene‐filler composites (kaolin, BaSO4, and TiO2) have been prepared by in‐situ polymerization using a metallocene catalyst and by extrusion mixing in the melt. TiO2 influences the polymerization process. In‐situ polymerization was found to be advantageous with respect to encapsulation, dispersion of the filler particles leading to improved mechanical properties, except for TiO2 containing composites. No significant influence on crystallization was observed.
Biodegradation of poly (vinylalcohol) with enzymatic extracts of phanerochaete chrysosporium
Authors: Mejía G. Amanda Inés , López O. Betty Lucy , Mulet P. Antonio
Published: March 2011

Commercial poly(vinylalcohol) samples (PVOH) of average molecular mass (Mw) 120,000 g/mol, were subjected to biodegradation with enzymatic extracts of the Phanerochaete chrysosporium fungus, in which the lignine peroxidase activity (LiP) was detected. The results of differential refractive index and ultraviolet (UV) absorption Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography coupled to a Mass Detector (GC‐MS) allow to deduce that in 15 days, under the conditions of this study, the average molar mass of the polymer decreases in 79.3 %. The benzaldehyde was detected as the main degradation product.
Mobility and orientation of semi‐rigid polyesters
Authors: Baxmann Rita , Hess Michael , Woelke Ralf , Veeman Wiebren
Published: March 2011

Mobility and orientational behavior of semi‐flexible polyesters from diphenyl‐dicarbonic acid and some branched propyl‐and butyl spacers have been investigated using static NMR techniques. Increasing molar mass of the polymers was found to influence the mobility of the rigid parts of the polymer chain while the spacer remains almost unaffected by the degree of polymerization. The mobility of the spacer carbons depends, however, on the length of the side chains. Even a magnetic field of 7 Tesla was not able to cause a reasonable macroscopic orientation in most of the samples, probably hindered by the high viscosity of the melts.
Characterization of short glass fiber filled polystyrene by fiber orientation and mechanical properties
Authors: Lee Seok Won , Youn Jae Ryoun
Published: March 2011

A quasi‐steady state, non‐isothermal, compressible, inelastic, and creeping flow of polymer melt into a thin cavity is analyzed to predict fiber orientation states. Modified Cross model and Tait's state equation are adopted to consider shear‐thinning behavior and compressibility of the polymer melt. Second order tensors are introduced to describe 3‐dimensional fiber orientation. Flow‐induced fiber orientation can be predicted by solving the equations of change for the orientation tensor with a suitable closure approximation. The orthotropic closure is applied except for the case of low interaction coefficient. Fiber orientation develops mainly due to shear flow in the skin layer and due to stretching effect in the core layer. It turns out that the compressibility, which induces additional velocity gradients during packing, reduces development of the fiber orientation. Results are dependent upon the magnitude of the interaction coefficient. The larger the interaction coefficient, the smaller the orientation development and the effect of compressibility. To predict orientation dependent mechanical properties, the orientation averaging for an arbitrary orientation is carried out from the properties of a transversely isotropic unit cell. The compressibility reduces the axial modulus and increases the transverse modulus. Opposite trends are observed for thermal expansion coefficients. It is also observed that the consideration of compressibility reduces the overall anisotropy of the molded product. Effects of compressibility on mechanical properties of the parts are reduced as the interaction coefficient becomes larger.
Element‐containing fibers with epoxy binders: Structures and properties of hardened compositions
Authors: Dubkova Valentina I.
Published: March 2011

New types of composites based on element‐containing carbon fibers (ECFs) and an epoxy binder have been developed. The results show that the presence of functional groups within the ECF structure affects significantly the reaction mechanism of the epoxy matrix. Connections between processes occuring in the interphase zone (the boundary layer) and the properties of hardened composites have been revealed. The factors controlling the binder hardening reactions occuring on surfaces of interphases when creating composites with improved physical and mechanical properties as well as with predermined service properties (polishing, anion‐exchange, anti‐corrosion, flame‐resistance, controlled range of electrical resistance etc) are defined.

A potential for using ECFs in a role unusual for them, namely as hardeners for epoxide binders, has been established. Applications of reactive ECFs which may function both as a filler and as a hardener provides longer service life of the composites and minimizes the amount of volatile products released in the process of hardening.
Molecular motions in a polycarbonate composite as studied by thermally stimulated recovery and dynamic mechanical analysis
Authors: Alves Natália M. , Mano João F. , Ribelles José L. Gómez
Published: March 2011

The viscoelastic properties of a short carbon‐fibre reinforced polycarbonate are studied in the glassy state and in the glass transition region by means of Thermally Stimulated Recovery (TSR) and Dynamic Mechanical Analysis (DMA) techniques in the flexural mode. The temperature calibration of the apparatus is discussed. Each thermal sampling experiment is analysed according to a simple Voigt‐Kelvin model in which the temperature dependence of the retardation time follows the Arrhenius equation with two adjustable thermokinetic parameters. Non‐linear fittings of the experimental data are performed with the corresponding constitutive equation. Both the activation energy and the pre‐exponential factor follow the usual trends with temperature and present the well‐known compensation phenomena. A divergence between the TSR results of the two materials is found above ± 145°C and may be a result of the effect of the interface. The observed movements in the glassy state which are still found to have a cooperative character are analysed according to the Adam‐Gibbs theory. Dynamic‐mechanical relaxation properties of the composite are reported and analysed in terms of Takayanagi's block model.
Hodgkin lymphoma risk: Role of genetic polymorphisms and gene–gene interactions in DNA repair pathways
Authors: Monroy Claudia M. , Cortes Andrea C. , Lopez Mirtha , Rourke Elizabeth , Etzel Carol J. , Younes Anas , Strom Sara S. , El‐Zein Randa
Published: March 2011

DNA repair variants may play a potentially important role in an individual's susceptibility to developing cancer. Numerous studies have reported the association between genetic single nucleotide polymorphisms (SNPs) in DNA repair genes and different types of hematologic cancers. However, to date, the effects of such SNPs on modulating Hodgkin lymphoma (HL) risk have not yet been investigated. We hypothesized that gene–gene interaction between candidate genes in direct reversal, nucleotide excision repair (NER), base excision repair (BER) and double strand break (DSB) pathways may contribute to susceptibility to HL. To test this hypothesis, we conducted a study on 200 HL cases and 220 controls to assess associations between HL risk and 21 functional SNPs in DNA repair genes. We evaluated potential gene–gene interactions and the association of multiple polymorphisms in a chromosome region using a multi‐analytic strategy combining logistic regression, multi‐factor dimensionality reduction and classification and regression tree approaches. We observed that, in combination, allelic variants in the XPC Ala499Val, NBN Glu185Gln, XRCC3 Thr241Me, XRCC1 Arg194Trp, and XRCC1 399Gln polymorphisms modify the risk for developing HL. Moreover, the cumulative genetic risk score revealed a significant trend where the risk for developing HL increases as the number of adverse alleles in BER and DSB genes increase. These findings suggest that DNA repair variants in BER and DSB pathways may play an important role in the development of HL. © 2011 Wiley Periodicals, Inc.
Hypodipsia discriminates progressive supranuclear palsy from other parkinsonian syndromes
Authors: Stamelou Maria , Christ Helena , Reuss Alexander , Oertel Wolfgang , Höglinger Günter
Published: March 2011

Background:

The objective of this study was to evaluate whether the sensation of thirst differs between patients with progressive supranuclear palsy (PSP), multiple system atrophy with predominant parkinsonism (MSA‐P), and Parkinson's disease (PD).

Methods:

We administered a standardized thirst questionnaire to age‐, sex‐, and stage‐matched patients with probable PSP, PD, and MSA‐P and healthy controls (HC), n = 15/group. In an independent cohort (n = 10/group), we provoked thirst by infusing hypertonic NaCl in age‐, sex‐, and stage‐matched patients with PSP, PD, and MSA‐P and recorded plasma osmolality and thirst (visual analog scale).

Results:

On questioning, 73% of PSP patients reported a reduced sensation of thirst (hypodipsia) compared with previous years (HC, 0%; PD, 7%; MSA‐P, 7%; P < .0001). On NaCl infusion, PSP patients reported significantly lower thirst than did PD and MSA‐P patients for all times from 20 to 95 minutes (P < .05). The thirst score at 25 minutes discriminated individual PSP patients well from PD and MSA‐P patients.

Conclusions:

Hypodipsia appears helpful in differentiating PSP from PD and MSA‐P. © 2011 Movement Disorder Society
Fast concomitant gradient field and field inhomogeneity correction for spiral cardiac imaging
Authors: Cheng Joseph Y. , Santos Juan M. , Pauly John M.
Published: March 2011

Non‐Cartesian imaging provides many advantages in terms of flexibility, functionality, and speed. However, a major drawback to these imaging methods is off‐resonance distortion artifacts. These artifacts manifest as blurring in spiral imaging. Common techniques that remove the off‐resonance field inhomogeneity distortion effects are not sufficient, because the high order concomitant gradient fields are nontrivial for common imaging conditions, such as imaging 5 cm off isocenter in an 1.5 T scanner. Previous correction algorithms are either slow or do not take into account the known effects of concomitant gradient fields along with the field inhomogeneities. To ease the correction, the distortion effects are modeled as a non‐stationary convolution problem. In this work, two fast and accurate postgridding algorithms are presented and analyzed. These methods account for both the concomitant field effects and the field inhomogeneities. One algorithm operates in the frequency domain and the other in the spatial domain. To take advantage of their speed and accuracy, the algorithms are applied to a real‐time cardiac study and a high‐resolution cardiac study. Both of the presented algorithms provide for a practical solution to the off‐resonance problem in spiral imaging. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Transcriptional deficits in oxidative phosphorylation with statin myopathy
Authors: Hubal Monica J. , Reich Kimberly A. , De Biase Andrea , Bilbie Cherie , Clarkson Priscilla M. , Hoffman Eric P. , Thompson Paul D.
Published: March 2011

Introduction: Hydroxymethylglutaryl–coenzyme A (HMG‐CoA) reductase inhibitors, or statins, are widely used drugs for hyperlipidemia and are generally well‐tolerated, but the can produce skeletal muscle toxicity. The molecular mechanisms driving statin myopathy are unknown. We investigated the effects of statin treatment and eccentric (damaging) exercise on transcriptional patterns between statin myopathy (Sym; N = 9) and statin‐tolerant subjects (Asym; N = 6). Methods: Skeletal muscle biopsies were collected 6 h post‐exercise at baseline and after statin treatment. Subjects performed concentric (non‐damaging) exercise with one leg and concentric + eccentric exercise with the other leg using a cross‐over design between time‐points. Results: Sym as compared with Asym demonstrated decreased skeletal muscle gene expression for oxidative phosphorylation–related and mitochondrial ribosomal protein genes before and after statin treatment with eccentric exercise. Conclusions: These results suggest that pre‐existing deficiencies in energy production may contribute to the development of symptoms during statin therapy, especially when muscle is exposed to eccentric exercise. Muscle Nerve 44: 393–401, 2011
Role of RNA binding protein HuR in ductal carcinoma in situ of the breast
Authors: Heinonen Mira , Hemmes Annabrita , Salmenkivi Kaisa , Abdelmohsen Kotb , Vilén Suvi‐Tuuli , Laakso Marko , Leidenius Marjut , Salo Tuula , Hautaniemi Sampsa , Gorospe Myriam , Heikkilä Päivi , Haglund Caj , Ristimäki Ari
Published: March 2011

HuR is a ubiquitously expressed RNA‐binding protein that modulates gene expression at the post‐transcriptional level. It is predominantly nuclear, but can shuttle between the nucleus and the cytoplasm. While in the cytoplasm HuR can stabilize its target transcripts, many of which encode proteins involved in carcinogenesis. While cytoplasmic HuR expression is a marker of reduced survival in breast cancer, its role in precursor lesions of malignant diseases is unclear. To address this we explored HuR expression in atypical ductal hyperplasia (ADH) and in ductal in situ carcinomas (DCIS). We show that cytoplasmic HuR expression is elevated in both ADH and DCIS when compared to normal controls, and that this expression associated with high grade, progesterone receptor negativity and microinvasion and/or tumour‐positive sentinel nodes of the DCIS. To study the mechanisms of HuR in breast carcinogenesis, HuR expression was silenced in an immortalized breast epithelial cell line (184B5Me), which led to reduction in anchorage‐independent growth, increased programmed cell death and inhibition of invasion. In addition, we identified two novel target transcripts (CTGF and RAB31) that are regulated by HuR and that bind HuR protein in this cell line. Our results show that HuR is aberrantly expressed at early stages of breast carcinogenesis and that its inhibition can lead to suppression of this process. ArrayExpress Accession No. E‐MEXP‐3035. Copyright © 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Effect of processing procedures and conditions on structural, morphological, and rheological properties of polyethylene/polyamide/nanoclay blends
Authors: Médéric Pascal , Ville Julien , Huitric Jacques , Moan Michel , Aubry Thierry
Published: March 2011

The article deals with the effect of processing procedures and conditions on structural, morphological, and rheological properties of ternary blends composed of polyethylene (PE), polyamide (PA)‐12, and organically modified montmorillonite nanoclay with selective affinity. Samples were prepared from PE/PA and PA/PE blends, either by simultaneous mixing or from a polymer/clay masterbatch, using two processing conditions. The results have shown the existence of a weight fraction threshold, above which no significant processing effect was observed. Below this weight fraction threshold, the results tend to underline the significant role of two parameters that depend on processing procedures and/or conditions: the contact time between PE and PA phases and the contact time between clay and PA. Clay structure, blend morphology, and rheological properties were all shown to depend on these two parameters, and also on the nature of the matrix (PE or PA), because of the selective affinity of clay toward polymer phases. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Melting and crystallization behavior of copolymer from cyclic butylene terephthalate and polycaprolactone
Authors: Wu Chang‐Mou , Huang Cheng‐Wei
Published: March 2011

In this study, we investigated the nonisothermal crystallization kinetics, crystallization morphology, and melting behavior of polymerized cyclic butylene terephthalate (pCBT) copolymerized with polycaprolactone (PCL). The results of this experiment indicated that the Ozawa exponent varied between 2 and 3 for pCBT, but between 1 and 2 for blends of pCBT/PCL. At the same temperature (185°C), the crystallization rate constant KT for pCBT/PCL blend was much lower than for pCBT homopolymer. These results indicated a strong hindrance on the crystallization of pCBT/PCL blends. The pCBT and pCBT/PCL samples exhibited no visible difference in morphology or microstructure. However, the crystallization and melting peak temperature of pCBT/PCL blends was ∼20°C lower than that of pCBT homopolymer. Crystal morphology confirmed that the mechanism of simultaneous polymerization and crystallization found applicable to pCBT homopolymer did not apply for blends of pCBT/PCL. It therefore appears that crystallization should be delayed until after the completion of pCBT/PCL copolymerization. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Electrospinning of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibrous tissue engineering scaffolds in two different electric fields
Authors: Tong Ho‐Wang , Wang Min
Published: March 2011

Poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) was electrospun into ultrafine fibrous nonwoven mats. Different from the conventional electrospinning process, which involves a positively charged conductive needle and a grounded fiber collector (i.e., positive voltage (PV) electrospinning), pseudo‐negative voltage (NV) electrospinning, which adopted a setup such that the needle was grounded and the fiber collector was positively charged, was investigated for making ultrafine PHBV fibers. For pseudo‐NV electrospinning, the effects of various electrospinning parameters on fiber morphology and diameter were assessed systematically. The average diameters of PHBV fibers electrospun via pseudo‐NVs were compared with those of PHBV fibers electrospun via PVs. With either PV electrospinning or pseudo‐NV electrospinning, the average diameters of electrospun fibers ranged between 500 nm and 4 μm, and they could be controlled by varying the electrospinning parameters. The scientific significance and technological implication of fiber formation by PV electrospinning and pseudo‐NV electrospinning in the field of tissue engineering were discussed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Structure–reactivity relationship for alcohol oxidations via hydride transfer to a carbocationic oxidizing agent
Authors: Lu Yun , Bradshaw Joshua , Zhao Yu , Kuester William , Kabotso Daniel
Published: March 2011

Second‐order rate constants were determined for the oxidation of 27 alcohols (R1R2CHOH) by a carbocationic oxidizing agent, 9‐phenylxanthylium ion, in acetontrile at 60 °C. Alcohols include open‐chain alkyl, cycloalkyl, and unsaturated alcohols. Kinetic isotope effects for the reaction of 1‐phenylethanol were determined at three H/D positions of the alcohol (KIEα‐D = 3.9, KIEβ‐D3 = 1.03, KIEOD = 1.10). These KIE results are consistent with those we previously reported for the 2‐propanol reaction, suggesting that these reactions follow a hydride‐proton sequential transfer mechanism that involves a rate‐limiting formation of the α‐hydroxy carbocation intermediate. Structure–reactivity relationship for alcohol oxidations was deeply discussed on the basis of the observed structural effects on the formation of the carbocationic transition state (Cδ+OH). Efficiencies of alcohol oxidations are largely dependent upon the alcohol structures. Steric hindrance effect and ring strain relief effect win over the electronic effect in determining the rates of the oxidations of open‐chain alkyl and cycloalkyl alcohols. Unhindered secondary alkyl alcohols would be selectively oxidized in the presence of primary and hindered secondary alkyl alcohols. Strained C7C11 cycloalkyl alcohols react faster than cyclohexyl alcohol, whereas the strained C5 and C12 alcohols react slower. Aromatic alcohols would be efficiently and selectively oxidized in the presence of aliphatic alcohols of comparable steric requirements. This structure–reactivity relationship for alcohol oxidations via hydride‐transfer mechanism is hoped to provide a useful guidance for the selective oxidation of certain alcohol functional groups in organic synthesis. Copyright © 2011 John Wiley & Sons, Ltd.
Substituent effects on the pH‐dependent multiequilibria of flavylium salt analogs of anthocyanins
Authors: Freitas Adilson A. , Dias Luis G. , Maçanita António A.L. , Quina Frank H.
Published: March 2011

Substituent effects on the hydration, tautomerization, and isomerization equilibria of flavylium salts can be described by a series of linear free energy relationships (LSER) based on Hammett correlations. The positions on the flavylium rings were classified as either activated (para‐like) or nonactivated (meta‐like) to decide which σ value to employ (σR or σm, respectively), while the steric effects of substituents at C‐3 were included via the ES parameter. Based on these relationships, we then show that it is possible to predict values of the “apparent pKa” (pKap) of flavylium ions that were not included in the original data set, as well as those of several naturally occurring anthocyanins. The value of pKap provides a measure of the thermodynamic stability of the flavylium cation as a function of pH and is directly related to the pH range in which the color of the flavylium cation form of anthocyanins persists in aqueous solution. Copyright © 2011 John Wiley & Sons, Ltd.
Polypeptide binding specificities of Saccharomyces cerevisiae oligosaccharyltransferase accessory proteins Ost3p and Ost6p
Authors: Jamaluddin M. Fairuz B. , Bailey Ulla‐Maja , Tan Nikki Y.J. , Stark Anthony P. , Schulz Benjamin L.
Published: March 2011

Asparagine‐linked glycosylation is a common and vital co‐ and post‐translocational modification of diverse secretory and membrane proteins in eukaryotes that is catalyzed by the multiprotein complex oligosaccharyltransferase (OTase). Two isoforms of OTase are present in Saccharomyces cerevisiae, defined by the presence of either of the homologous proteins Ost3p or Ost6p, which possess different protein substrate specificities at the level of individual glycosylation sites. Here we present in vitro characterization of the polypeptide binding activity of these two subunits of the yeast enzyme, and show that the peptide‐binding grooves in these proteins can transiently bind stretches of polypeptide with amino acid characteristics complementary to the characteristics of the grooves. We show that Ost6p, which has a peptide‐binding groove with a strongly hydrophobic base lined by neutral and basic residues, binds peptides enriched in hydrophobic and acidic amino acids. Further, by introducing basic residues in place of the wild type neutral residues lining the peptide‐binding groove of Ost3p, we engineer binding of a hydrophobic and acidic peptide. Our data supports a model of Ost3/6p function in which they transiently bind stretches of nascent polypeptide substrate to inhibit protein folding, thereby increasing glycosylation efficiency at nearby asparagine residues.
Local models of heterotic flux vacua: spacetime and worldsheet aspects
Authors: Israël D. , Carlevaro L.
Published: March 2011

We report on some recent progress in understanding heterotic flux compactifications, from a worldsheet perspective mainly. We consider local models consisting in torus fibration over warped Eguchi‐Hanson space and non‐Kähler resolved conifold geometries. We analyze the supergravity solutions and define a double‐scaling limit of the resolved singularities, defined such that the geometry is smooth and weakly coupled. We show that, remarkably, the heterotic solutions admit solvable worldsheet CFT descriptions in this limit. This allows in particular to understand the important role of worldsheet non‐perturbative effects.
Charged particle‐like branes in ABJM: A summary
Authors: Gutierrez N. , Lozano Y. , Rodriguez‐Gomez D.
Published: March 2011

We study the effect of adding lower dimensional brane charges to the 't Hooft monopole, di‐baryon and baryon vertex configurations in AdS4 × ℙ3. We show that these configurations capture the background fluxes in a way that depends on the induced charges, requiring additional fundamental strings to cancel the worldvolume tadpoles. The dynamics reveal that the charges must lie inside some interval, a situation familiar from the baryon vertex in AdS5 × S5 with charges. For the baryon vertex and the di‐baryon the number of fundamental strings must also lie inside an allowed interval. Some ideas about the existence of these bounds in relation to the stringy exclusion principle are given.
Cosmic strings in string perturbation theory
Authors: Skliros D.
Published: March 2011

Fundamental cosmic superstrings are defined in string perturbation theory in terms of vertex operators, which are loosely identified with arbitrarily excited macroscopic string states. We construct explicit normal ordered cosmic string vertex operators, which are given in terms of covariant coherent string states. We also write down the general expression for arbitrarily excited mass‐eigenstate covariant vertex operators, and discuss the construction of string wavepackets.
Mg and Si dopant incorporation and segregation in GaN
Authors: Schmidt Th. , Siebert M. , Flege J. I. , Figge S. , Gangopadhyay S. , Pretorius A. , Lee T.‐L. , Zegenhagen J. , Gregoratti L. , Barinov A. , Rosenauer A. , Hommel D. , Falta J.
Published: March 2011

The surface segregation of Mg and Si dopant species and their atomic incorporation sites in GaN films grown by metal‐organic vapour phase epitaxy (MOVPE) on sapphire (0001) substrates have been analysed by X‐ray photoemission spectro‐microscopy and X‐ray standing waves (XSW). As revealed by spectro‐microscopy, both Mg and Si tend to segregate to the surface. In case of Mg, an enhanced surface dopant concentration is found even after sputter‐removal of several tens of nanometres, which confirms a segregation mechanism proposed earlier [S. Figge et al., Appl. Phys. Lett. 81, 4748 (2002)]. Si doping has been found to result in the formation of facetted grooves in the GaN films. The surface silicon concentration at the facets is determined to be about 2.5 times higher as compared to the planar (0001) surface by micro‐spectroscopy. XSW results show that with increasing Mg dopant concentration, non‐substitutional lattice sites are progressively occupied. The results can quantitatively be explained by Mg atoms incorporated in an anti‐bixbyite‐like structure and is related to inversion domain boundaries. For Si doping, no evidence is found for the occupation of non‐substitutional sites. However, a decrease in crystal quality is observed with increasing Si concentration.

magnified image

X‐ray photoemission micrograph of a Si doped GaN film showing a facetted groove at the lower left corner of the image. The local spectra (see inset) reveal Si enrichment at the facets.
Designing polymeric nanorod arrays for optical waveguide‐based biosensors
Authors: Gitsas Antonis , Lazzara Thomas D. , Yameen Basit , Steinhart Martin , Knoll Wolfgang , Duran Hatice
Published: March 2011

The optical waveguiding capabilities of polycyanurate thermoset nanorod (PCNs) arrays mounted on planar gold substrates were investigated using optical waveguide spectroscopy (OWS). The nanorods, with diameter of 60 and 150 nm, and length of 650 nm, are formed by thermal polymerization of cyanate ester oligomers within porous anodic aluminium oxide templates. We discuss the waveguiding properties of the PCNs arrays when the nanorod diameter is much smaller (<1/10) than the wavelength of the guided light. We monitored the changes in the waveguiding modes by exchanging the interrod filling environment with water, ethanol, and isopropanol. This study led to a sensing figure of merit as high as 196 reciprocal refractive index units, which is higher than that of other previously studied sensors based on angular modulation. Furthermore, numerical simulations were performed by applying an Effective Medium Theory (EMT) based on the Maxwell‐Garnett approximation for the prediction of the optical properties of anisotropic nanorod arrays. Simulations based on Fresnel equations were used for estimating the optimal fabrication geometry, with varying the nanorod diameter and the interrod distance. Based on these results, we introduce the applicability of the PCNs arrays platform as a concept in optical biosensors and other related applications (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)