bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis and reduction of quadrature errors in the material point method (MPM)
Authors: Steffen Michael , Kirby Robert M. , Berzins Martin 
Published: April 2008

AbstractThe material point method (MPM) has demonstrated itself as a computationally effective particle method for solving solid mechanics problems involving large deformations and/or fragmentation of structures, which are sometimes problematic for finite element methods (FEMs). However, similar to most methods that employ mixed Lagrangian (particle) and Eulerian strategies, analysis of the method is not straightforward. The lack of an analysis framework for MPM, as is found in FEMs, makes it challenging to explain anomalies found in its employment and makes it difficult to propose methodology improvements with predictable outcomes.In this paper we present an analysis of the quadrature errors found in the computation of (material) internal force in MPM and use this analysis to direct proposed improvements. In particular, we demonstrate that lack of regularity in the grid functions used for representing the solution to the equations of motion can hamper spatial convergence of the method. We propose the use of a quadratic B‐spline basis for representing solutions on the grid, and we demonstrate computationally and explain theoretically why such a small change can have a significant impact on the reduction in the internal force quadrature error (and corresponding ‘grid crossing error’) often experienced when using MPM. Copyright © 2008 John Wiley & Sons, Ltd.
Preparation of microwave radiation induced graft copolymers and their applications as reinforcing material in phenolic composites
Authors: Kaith B.S. , Kalia Susheel 
Published: April 2008

AbstractFlax fiber was modified through grafting of binary vinyl monomers mixtures such as methyl methacrylate (MMA)/vinyl acetate (VA), MMA/acrylamide (AAm), and MMA/styrene (Sty) under the influence of microwave radiations. 24.64% grafting was found at 210 W microwave power under optimum reaction conditions. Graft copolymers obtained were characterized with FTIR spectroscopy, scanning electron microscopy, and TGA/DTA techniques. Graft copolymers were found to be moisture retardant with better tensile strength. Phenolic composites using graft copolymers vis‐à‐vis flax as reinforcing material were subjected for the evaluation of different mechanical properties such as wear resistance, tensile strength, compressive strength, modulus of rupture (MOR), modulus of elasticity (MOE), and stress at the limit of proportionality (SP). Composites reinforced with graft copolymers showed better mechanical properties in comparison to composites reinforced with flax. Phenolic composites reinforced with Flax‐g‐poly(MMA/Sty) showed maximum wear resistance followed by reinforcement with flax, Flax‐g‐poly (MMA/AAm), and Flax‐g‐poly(MMA/VA). Composites reinforced with Flax‐g‐poly(MMA/Sty) and flax fibers have been found to show 150 N tensile strength with extension of 3.94 and 2.17 mm, respectively. It has also been found that composites reinforced with Flax‐g‐poly(MMA/Sty) showed maximum compressive strength (1,000 N) with compression of 3.71 mm in comparison to other graft copolymers and flax fibers reinforcement. Reinforcement of phenolic resin with Flax‐g‐poly(MMA/Sty) and flax fibers could improve the MOR and MOE. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
On the application of liquid‐crystal thermography for the nondestructive detection of delamination in composite structures
Authors: Khatibi Akbar Afaghi , Maleki Hadi Rezghi 
Published: April 2008

AbstractTo prevent the catastrophic failure of composite structures, several nondestructive testing methods have been developed. In this study, a new technique to evaluate these structures by using thermochromic liquid crystal (TLC) thermography is presented. Temperature gradients produced by sensitive liquid‐crystals are used to detect delamination in composite specimens. The effects of constituent materials and delamination size/location are investigated. The results from TLC thermography are compared to those from infrared thermography. Finally, advantages/disadvantages of the new method are discussed. On the basis of the results from this study, it could be concluded that the TLC thermography can be used as an inexpensive nondestructive testing method in inspection of composite structures. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Mechanical properties and morphologies of polypropylene with different sizes of glass bead particles
Authors: Yang Kun , Yang Qi , Li Guangxian , Kuang Junjie , Jiang Ziqiang 
Published: April 2008

AbstractA commercial grade of isotactic polypropylene (PP) was used to study the mechanical properties and morphologies of the PP composites filled with four sizes of glass bead particles. The glass bead particles used were with average particle sizes of 15 μm (GB15), 10 μm (GB10), 5 μm (GB5), and 2.5 μm (GB2.5), respectively. It was clear that the glass bead size was an important factor on the determination of mechanical properties of the composites. As a whole, in view of the scatter in the data, under the condition of same filler content, the yield strength and impact strength of the composites filled with smaller glass bead particles was higher than those of the composites filled with bigger ones. And the flexural strength and modulus of the composites filled with GB10, GB5, or GB2.5 particles could be regarded as the same. The flexural strength and modulus of the composites filled with GB15 particles were higher than those of the composites filled with other three sizes of particles. Among four sizes of glass bead particles, GB2.5 had the best toughening effect to improve the impact strength of PP matrix. And the major toughening mechanism of the PP/GB2.5 composites was the pinning effect introduced by GB2.5. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Phase transition studies of polymer–liquid crystal composite using dielectric and optical transmittance techniques
Authors: Agarwalla N.K. , Madhusudanan K.P. , Srivastava Abhishek Kumar , Manohar Rajiv , Shukla J.P. 
Published: April 2008

AbstractDielectric properties of polymer–liquid crystal composite comprised of the polymer poly(methyl methacrylate) and low‐molecular mass liquid crystal, cholesteryl palmitate are investigated in the frequency range from 1 kHz to 10 MHz and in the temperature range of 27–120°C. The dielectric permittivity and dielectric loss shows substantial changes with the addition of polymer. The significant feature is that the pure liquid crystal exhibits broad absorption, showing dielectric relaxation in the range of 10 – 100 kHz whereas the composite shows relaxation peaks at 10 MHz. The percentage optical transmittance of pure liquid crystal and composite have also been measured and compared to study its phase transition behavior. The smectic phase observed in the pure liquid crystal is suppressed on formation of polymer composites. The mass spectrometry measurement does not show any abduct formation between the pure liquid crystal and the composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Preparation and characterization of carboxymethyl polyvinyl alcohol–graphite nanosheet composites
Authors: Yu Chaosheng , Li Bin 
Published: April 2008

AbstractCarboxymethyl polyvinyl alcohol (CMPVA) was prepared by introducing carboxymethyl groups to polyvinyl alcohol (PVA) with chloroacetic acid. Graphite nanosheets (NanoG) were obtained by treating expandable graphite at a high temperature in a muffle furnace, and then sonicating it in an aqueous ethyl alcohol solution. Nanocomposites of CMPVA with NanoG were prepared by dispersing NanoG in a CMPVA aqueous solution with the aid of sonication and then casted on plastic film to remove water. Carboxymethyl groups were proved to be linked to PVA by Fourier transform infrared (FTIR) spectra and the degree of carboxymethyl substitution on the PVA was 2.77% determined by conductometric titration. Experimental results show that carboxylate anions in introduced carboxymethyl groups facilitate the dispersal of NanoG with positive charges in the CMPVA solution. The CMPVA matrix was detected by X‐ray diffraction (XRD) and FTIR spectra to be less crystal, into which NanoG tend to disperse. Scanning electron microscopy was used to characterize the structure of the graphite and morphology of the composites to prove that NanoG was 40–70 nm thick. The percolation threshold of CMPVA/NanoG composites at room temperature was as low as 0.80 wt%. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Continuous subcutaneous insulin infusion (CSII insulin pump therapy) for type 1 diabetes: a Bournemouth perspective
Authors: Kerr D , Nicholls H , James J 
Published: April 2008

AbstractThe first patient in Bournemouth to use insulin pump therapy started in 1998. Subsequently, meta‐analyses have supported our clinical experience that, for carefully selected individuals with type 1 diabetes, insulin pump therapy is associated with: reductions in HbA1c of 0.5–0.9% compared to multiple injection therapy; fewer glycaemic excursions above and below target levels compared to traditional injection therapy with patients reporting marked improvements in well‐being; reduction in the risk of severe hypoglycaemic episodes, particularly at night; and improved quality of life.Starting insulin pump therapy requires a specialist multidisciplinary team for selection of patients for continuous subcutaneous insulin infusion, and to provide the on‐going education. Before starting pump therapy, patients should have participated in a structured group education programme whilst on multiple daily injections of insulin.Once established, the use of additional technologies including continuous glucose monitoring and the pump download facilities give significant added value to the clinical care of people with type 1 diabetes opting for this form of insulin delivery.It is important that all patients with type 1 diabetes are made aware of these technologies in diabetes care and, if appropriate, have access to them. Copyright © 2008 John Wiley & Sons.
Autumn 2007 Meeting of the Association of British Clinical Diabetologists
Authors: Wroe J 
Published: April 2008

AbstractOver 100 members attended the Autumn 2007 Meeting of ABCD to hear state of the art lectures on diabetes‐related clinical topics and to debate the pros and cons of the Quality and Outcomes Framework for Diabetes. As always, professional discussion and exchange of views and experiences outside the official programme of the Meeting were as important as the set lectures. These bi‐annual meetings afford an important insight into the state of affairs in the specialist diabetes service, not an altogether happy one at present. Copyright © 2008 John Wiley & Sons.
Preparation and characterization of multi‐walled carbon nanotubes/polymer gradient composite films
Authors: Hu Nantao , Zhou Hongwei , Dang Guodong , Chen Chunhai , Jing Jing , Zhang Wanjin 
Published: April 2008

AbstractBACKGROUND: Recently, much work has focused on the efficient dispersion of carbon nanotubes (CNTs) throughout a polymer matrix for mechanical and/or electrical enhancement. However, there are still only few reports about gradient distribution of CNTs in polymer matrices. In the work reported here, CNTs embedded in a polymer film with a gradient distribution were successfully obtained and studied.RESULTS: For composite films with gradient distributions of CNTs, the upper surface behaves as an intrinsic insulator, while the lower one behaves as a semiconductor, or even as a conductor. It is also found that with an increase of 1 wt% CNTs, the resistance of the bottom surface decreases by 2–3 orders of magnitude, as compared with pure polyarylene ether nitrile; furthermore, when the proportion of CNTs increases up to 5 wt%, the resistance of the bottom surface shows only very little change. As a result, sufficient matrix conductivity of the bottom surface could be achieved at a lower filler concentration with CNTs in a gradient distribution. Meanwhile, the thermal stability, glass transition temperature and tensile properties of the matrix are maintained.CONCLUSION: There is considerable interest in such gradient composite films, which could be applied in the electrical engineering, electronics and aerospace fields, for their excellent mechanical properties, thermal stability and novel electrical properties. Copyright © 2008 Society of Chemical Industry
Bis(2‐(6‐methylpyridin‐2‐yl)‐benzimidazolyl)titanium dichloride and titanium bis(6‐benzimidazolylpyridine‐2‐carboxylimidate): Synthesis, characterization, and their catalytic behaviors for ethylene polymerization
Authors: Liu Shaofeng , Zuo Weiwei , Zhang Shu , Hao Peng , Wang Deligeer , Sun Wen‐Hua 
Published: April 2008

AbstractA series of 6‐(benzimidazol‐2‐yl)‐N‐organylpyridine‐2‐carboxamide were synthesized and transformed into 6‐benzimidazolylpyridine‐2‐carboxylimidate as dianionic tridentate ligands. Bis(2‐(6‐methylpyridin‐2‐yl)‐benzimidazolyl)titanium dichloride (C1) and titanium bis(6‐benzimidazolylpyridine‐2‐carboxylimidate) (C2–C8) were synthesized in acceptable yields. These complexes were systematically characterized by elemental and NMR analyses. Crystallographic analysis revealed the distorted octahedral geometry around titanium in both complexes C1 and C4. Using MAO as cocatalyst, all complexes exhibited from good to high catalytic activities for ethylene polymerization. The neutral bis(6‐benzimidazolylpyridine‐2‐carboxylimidate)titanium (C2–C8) showed high catalytic activities and good stability for prolonged reaction time and elevated reaction temperature; however, C1 showed a short lifetime in catalysis as being observed at very low activity after 5 min. The elevated reaction temperature enhanced the productivity of polyethylenes with low molecular weights, whereas the reaction with higher ethylene pressure resulted in better catalytic activity and resultant polyethylenes with higher molecular weights. At higher ratio of MAO to titanium precursor, the catalytic system generated better activity with producing polyethylenes with lower molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3411–3423, 2008
Effect of annealing on magnetic and magnetotransport properties of Fe84Zr3.5Nb3.5Cu1B8 ribbons
Authors: Celegato F. , Coïsson M. , Kane S. N. , Mazaleyrat F. , Modak S. S. , Tiberto P. , Varga L. K. , Vinai F. 
Published: April 2008

AbstractFe84Zr3.5Nb3.5Cu1B8 melt‐spun ribbons have been submitted to furnace annealing to relax quenched‐in stresses and, above the first crystallization temperature, to induce nanocrystallization. The volume fraction of the nanocrystalline phase and the crystallites average size have been monitored by means of X‐ray diffraction as a function of annealing temperature. Hysteresis loops have been measured on as‐quenched and annealed ribbons, revealing the expected softening of the magnetic properties (reduction of the coercive field) and increase of the saturation magnetization as long as the nanocrystalline phase grows to the expense of the amorphous matrix. Low frequency (100 kHz–30 MHz) giant magneto‐impedance is enhanced when the best soft magnetic properties of the alloy are exploited by suitable thermal treatments, but rapidly vanishes out on increasing the frequency of the exciting current. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diffusion simulation of Cr–Fe bcc systems at atomic level using a random walk algorithm
Authors: Sebastian I. San , Aldazabal J. , Capdevila C. , Garcia‐Mateo C. 
Published: April 2008

AbstractThis paper proposes a model to simulate the diffusion of impurities in bcc atomic lattices. It works with three‐dimensional volume, divided in small cubic elements (voxels), containing more than one atomic cell each.Once the domain is discretized, impurities jump from one voxel to another according to certain probability that takes into account the composition and geometry of the target voxel.In the present work, a model was applied to a prismatic volume and in order to deduce the relationship between the atomic jumping frequency and the temperature two different cases were studied. One consists of a Fe matrix with Cr impurities, and the other is based on a Cr matrix with Fe impurities. Results obtained from these simulations were compared with profiles obtained by Dictra software.Results for the atomic jumping frequencies were fitted to an Arrhenius type equation, as shown in following expressions:magnified imageFrom these equations it is possible to obtain an activation energy for the atomic jumping phenomenon of ∼306 kJ/mol and ∼411 kJ/mol for the Fe‐matrix and Cr‐matrix systems, respectively. These energies match the empirical measured values for the diffusion of Cr and Fe impurities, 250 kJ/mol and 407 kJ/mol, respectively.Results obtained in this work assure that the proposed model is suitable for simulating the three‐dimensional diffusion of substitutional impurities in Cr and Fe bcc systems. It could be easily expanded to other bcc matrix systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Narrow‐band photodetection based onM‐plane GaN films
Authors: Ghosh Sandip , Rivera C. , Pau J. L. , Muñoz E. , Brandt O. , Grahn H. T. 
Published: April 2008

AbstractRapid identification of a range of hazardous airborne biological and chemical agents requires simultaneous detection at several specific wavelengths, and consequently a set of photodetectors with very narrow‐band spectral responsivity. We demonstrate two ultraviolet photodetection configurations based on strainedM‐plane GaN films on LiAlO2(100) substrates grown by molecular‐beam epitaxy with a detection bandwidth below 8 nm. The optical band gap of the film depends on the orientation of the linear polarization of the incident light relative to thec‐axis of GaN, which lies in the film plane. The first configuration consists of a polarization‐sensitive planar Schottky photodetector and a filter. An orthogonal alignment of thec‐axis of the photodetector and the filter produces a detection system with a peak responsivity at 360 nm and a bandwidth of 6 nm. The second one consists of two planar Schottky photodetectors with theirc‐axes oriented perpendicular to each other. The difference signal between the two photodetectors produces a peak responsivity at 358 nm and a bandwidth of 7.3 nm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth, fabrication, and characterization of InGaN solar cells
Authors: Chen X. , Matthews K. D. , Hao D. , Schaff W. J. , Eastman L. F. 
Published: April 2008

AbstractThe InGaN alloy system offers a unique opportunity to develop high efficiency multi‐junction solar cells. In this study, single junction solar cells made of Inx Ga1–x N are successfully developed, with x = 0, 0.2, and 0.3. The materials are grown on sapphire substrates by MBE, consisting of a Si‐doped InGaN layer, an intrinsic layer and an Mg‐doped InGaN layer on the top. The I –V curves indicate that the cell made of all‐GaN has low series resistance (0.12 Ω cm2) and insignificant parasitic leakage. Contact resistances of p and n contacts are 2.9 × 10–2 Ω cm2 and 2.0 × 10–3 Ω cm2, respectively. Upon illumination by a 200 mW/cm2, 325 nm laser, Voc is measured at 2.5 V with a fill factor of 61%. Clear photo‐responses are also observed in both InGaN cells with 0.2 and 0.3 Indium content when illuminated by outdoor sunlight. But it is difficult to determine the solar performance due to the large leakage current, which may be caused by the material defects. A thicker buffer layer or GaN template can be applied to the future growth process to reduce the defect density of InGaN films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ultraviolet GaN‐based nanocolumn light‐emitting diodes grown on n‐(111) Si substrates by rf‐plasma‐assisted molecular beam epitaxy
Authors: Sekiguchi Hiroto , Kato Kei , Tanaka Jo , Kikuchi Akihiko , Kishino Katsumi 
Published: April 2008

AbstractWe report the fabrication of GaN/AlGaN nanocolumn LEDs on n‐(111) Si substrates by RF‐MBE for the first time. Clear diode characteristics with a turn‐on voltage of 4 V and an ultraviolet emission spectrum with a peak wavelength of 354 nm were observed at room temperature. When the Al composition of p‐Alx Ga1–x N was changed from 8.8% to 25.1%, the high Al content led a narrowing of the FWHM compared withthat for low Al contents due to the suppression of carrier overflow. We measured the electroluminescence (EL) under dc and pulsed operations. The integrated EL intensity under the pulsed operation was 3 times as strong as that under the dc operation at 100 mA due to the reduced generation of heat. The thermal resistance was estimated to be 40 °C/W from the EL peak wavelength difference between the dc and pulsed operations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Performance of high‐power III‐nitride light emitting diodes
Authors: Chen G. , Craven M. , Kim A. , Munkholm A. , Watanabe S. , Camras M. , Götz W. , Steranka F. 
Published: April 2008

AbstractThe performance of III‐nitride based high‐power light emitting diodes (LEDs) is reviewed. Direct color high‐power LEDs with 1 × 1 mm2 chip size in commercial LUXEON® Rebel packages are shown to exhibit external quantum efficiencies at a drive current of 350 mA ranging from ∼60% at a peak wavelength of ∼420 nm to ∼27% at ∼525 nm. The short wavelength blue LED emits ∼615 mW at 350 mA and >2 W at 1.5 A. The green LED emits ∼110 lm at 350 mA and ∼270 lm at 1.5 A. Phosphor‐conversion white LEDs (1 × 1 mm2 chip size) are demonstrated that emit ∼126 lm of white light when driven at 350 mA and 381 lm when driven at 1.5 A (Correlated Color Temperature, CCT ∼ 4700 K). In a similar LED that employs a double heterostructure (DH) insign instead of a multi‐quantum well (MQW) active region, the luminous flux increases to 435 lm (CCT ∼ 5000 K) at 1.5 A drive current. Also discussed are experimental techniques that enable the separation of internal quantum efficiency and extraction efficiency. One technique derives the internal quantum efficiency from temperature and excitation‐dependent photoluminescence measurements. A second technique relies on variable‐temperature electroluminescence measurements and enables the estimation of the extraction efficiency. Both techniques are shown to yield consistent results and indicate that the internal quantum efficiency of short wavelength blue (λ ∼ 420 nm) high‐power LEDs is as high as 71% even at a drive current of 350 mA. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct observation of indium compositional fluctuation in GaInN/GaN multi‐quantum wells using an X‐ray micro‐beam from the 8‐GeV storage ring
Authors: Miyajima Takao , Uemura Shigeaki , Kudo Yoshihiro , Terada Yasuko , Fuutagawa Noriyuki 
Published: April 2008

AbstractWe measured the micrometer‐scale fluctuation of the indium contents in a 50 μm x 30 μm region of annealed Ga0.8In0.2N/GaN multi quantum wells by mapping the counts of indium fluorescent X‐rays excited by a 1.3 μm x 3.8 μm X‐ray micro‐beam. The mapping indicates that two distinct regions – indium‐rich and indium‐poor regions – are formed by the annealing. The indium contents in the island‐shaped low‐indium regions are 20% less than in the surrounding high‐indium region. As the island‐shaped low‐indium regions clearly coincide with the low‐radiative regions as observed by Hg‐lamp‐excited fluorescent microscopy, we believe that the low‐radiative regions are a result not of indium segregation but of the generation of defects such as plane defects. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)