bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of thermooxidative stability of non‐edible vegetable oils of Indian origin for biodegradable lubricant application
Authors: Joseph P. V. , Sharma D. K.
Published: April 2010

For environmental reasons, as well as the dwindling source of petroleum, a new class of environmentally acceptable and renewable lubricants based on vegetable oils is available. Even though vegetable oils possess excellent lubricant‐related properties, there are some concerns about using it as lubricant base oil. Still, unmodified and modified varieties of soybean, rapeseed, sunflower and canola oils have been in use in the USA and Europe. In India, with the shortage of edible oil, alternate sources of vegetable oils stocks are being explored. With this aim, a comprehensive study has been conducted earlier in the authors' laboratory. In this study, numerous options of non‐edible vegetable oil sources were explored, and a few potential vegetable oils were studied in the laboratory. It was found that even though the oils performed much better in comparison with other vegetable oils, it still required improvement in thermooxidative stability. Therefore, in the later part of the study, different options were explored to improve thermooxidative stability. With a background on the initial studies of the authors as described above, the present paper deals with the studies on improvement of these non‐edible candidate vegetable oils of Indian origin for lubricant by treating with selected antioxidants for applying them in lubricants. Copyright © 2010 John Wiley & Sons, Ltd.
Simulation of hydraulic fracture propagation near a natural fracture using virtual multidimensional internal bonds
Authors: Zhang Z. , Ghassemi A.
Published: April 2010

A virtual multidimensional internal bond (VMIB) model developed to simulate the propagation of hydraulic fractures using the finite‐element method is formulated within the framework of the virtual internal bond theory (VIB) that considers a solid as randomized material particles in the micro scale, and derives the macro constitutive relation from the cohesive law between the material particles with an implicit fracture criterion. Hydraulic pressure is applied using a new scheme that enables simulation of hydraulically driven cracks. When the model is applied to study hydraulic fracture propagation in the presence of a natural fracture, the results show the method to be very effective. It shows that although the in situ stress ratio is the dominant factor governing the propagation direction, a natural fault can also strongly influence the hydraulic fracture behavior. This influence is conditioned by the shear stiffness of the fault and the distance to the original hydraulic fracture. The model results show that when the fault is strong in shear, its impact on hydraulic fracture trajectory is weak and the hydraulic fracture will likely penetrate the fault. For a weak fault, however, the fracture tends to be arrested at the natural fault. The distance between the fault and the hydraulic fracture is also important; the fault influence increases with decreasing distance. The VMIB does not require selection of a fracture criterion and remeshing when the fracture propagates. Therefore, it is advantageous for modeling fracture initiation and propagation in naturally fractured rock. Copyright © 2010 John Wiley & Sons, Ltd.
Numerical and analytical observations on long and infinite slopes
Authors: Griffiths D. V. , Huang Jinsong , deWolfe Giorgia F.
Published: April 2010

Interest in the mechanics of landslides has led to renewed evaluation of the infinite slope equations, and the need for a more general framework for estimating the factor of safety of long and infinite slopes involving non‐homogeneous soil profiles. The paper describes finite element methods that demonstrate the potential for predicting failure in long slope profiles where the critical mechanism is not necessarily at the base of the soil layer. The influence of slope angle is also examined in long slopes, leading to some counter‐intuitive conclusions about the impact of slope steepness on the factor of safety. Copyright © 2010 John Wiley & Sons, Ltd.
Diffuse and localized failure modes: Two competing mechanisms
Authors: Nicot François , Darve Félix
Published: April 2010

The concept of failure is one of the most debated in soil mechanics, for two reasons essentially. First, this is a crucial issue in the engineering of structures and geotechnical project design. Second, this is still a challenging academic issue mobilizing significant scientific interest in the development of a unique framework to describe the different failure modes. In this respect, this paper revisits the localized failure mode, replacing the well‐known Rice criterion within the wider context of bifurcation. Considering a micro‐mechanical model, the main theoretical results are covered. In particular, it is established that localized failure is a particular case of failures observed within the so‐called bifurcation domain: the incremental strain within the localization band is associated with a vanishing value of the second‐order work. Copyright © 2010 John Wiley & Sons, Ltd.
A fixed grid algorithm for simulating the propagation of a shallow hydraulic fracture with a fluid lag
Authors: Gordeliy E. , Detournay E.
Published: April 2010

This paper describes a fixed grid algorithm to simulate the propagation of shallow hydraulic fractures, under plane strain or axisymmetric conditions. Because of the low stress environment that exists near a free surface, these fractures are generally characterized by a fluid front that lags behind the fracture edge. The simulation of shallow hydraulic fractures requires therefore the tracking of two distinct fronts. The proposed algorithm, which traces its roots to the one described by Zhang et al. (Int. J. Numer. Anal. Methods Geomech. 2005; 29:1317–1340), advances the fracture by a constant step and computes the corresponding time required to reach this new fracture configuration as well as the matching location of the fluid front within the fixed grid. For any trial value of the time and of the front position, a non‐linear system of algebraic equations is solved using either Newton's method or a fixed point iteration scheme, with preconditioning. The non‐linear system is formulated by combining an implicit finite volume method for solving the lubrication equation and the displacement discontinuity method for solving the elasticity equation. The critical difference with the algorithm of Zhang et al. lays in the approach chosen to update the fluid front position. Rather than using a filling fraction method, the new algorithm adopts a velocity treatment of the fluid‐front location that is akin to a one‐dimensional implementation of a level set algorithm for front tracking. This conversion from a fluid volume to a fluid velocity‐based approach to update the front position increases the degree of implicitness of the algorithm, which is responsible for a significant reduction of the CPU time by about two orders of magnitude. Copyright © 2010 John Wiley & Sons, Ltd.
Cauchy problem of three‐dimensional critical slip surfaces of slopes
Authors: Zheng Hong , Sun Guan Hua , Li Chun Guang
Published: April 2010

Using the continuum‐based finite element approach in conjunction with the strength reduction technique, one can easily find out the factor of safety of a slope with rather high precision, but will encounter some obstacles in the accurate location of the corresponding three‐dimensional critical slip surface (CSS). On the basis of the Mohr–Coulomb failure criterion and the stress field in the limit equilibrium state of the slope, it is deduced that the three‐dimensional CSS is the solution of the Cauchy problem of a quasi‐linear partial differential equation (PDE) of first order. By means of the method of characteristics for the problem, the three‐dimensional CSS that may take any shape can be determined without the specification of its geometry. Copyright © 2010 John Wiley & Sons, Ltd.
Coupling of BEM with a large displacement and rotation algorithm
Authors: Asadollahi Pooyan , Tonon Fulvio
Published: April 2010

In stability analysis of rock blocks, the deformability of the blocks can conveniently be simulated using the boundary element method (BEM). However, all boundary conditions are given as stresses. Thus, the displacement solution is not unique. In this paper, an algorithm is proposed to remove rigid body motions in the solution of the boundary form of Somigliana identity discretized by the direct BEM formulation. The algorithm is applied to the calculation of the normal stiffness of rock blocks and coupled with BS3D, large displacement and rotation algorithm for the general stability of rock blocks. Copyright © 2010 John Wiley & Sons, Ltd.
A simulation study of microstructure evolution inside the shear band in biaxial compression test
Authors: Mahmood Zafar , Iwashita Kazuyoshi
Published: April 2010

We study the development of microstructure inside the shear band in granular media consisting of elliptical‐shaped particles. Plane strain biaxial compression test was simulated using two‐dimensional distinct element method. The generation of large voids and concentration of excessive particle rotation inside a shear band are found in a quite similar manner to those observed in natural soils. Evolution of the microstructure inside and outside the shear band is studied. The magnitude and direction of particle rotation inside the shear band is influenced by orientation of long axes of elliptical particles. Because of such particle rotations inside the shear band, the preferred alignment of particles becomes horizontal in the residual state, which results in a more anisotropic contact normal distribution oriented along the major principal stress axis. Copyright © 2010 John Wiley & Sons, Ltd.
A non‐coaxial and unbalanced plastic flow rule for geomaterials and its application to the shear band orientation prediction
Authors: Wang G. S. , Kong L. W.
Published: April 2010

In this paper, the non‐coaxial relation between the principal plastic strain increments and the principal stresses, which results from the internal friction in geomaterials, is analyzed, and the phenomenon of the unbalanced development of plastic flow in two conjugate directions is discussed. A non‐coaxial, unbalanced plastic flow model for Coulomb frictional materials is developed and used to determine the orientation of shear band in geomaterials. It is shown that the unbalanced indexrof plastic flow has important effect on the orientation of the shear band, and the orientation determined by the conventional plastic flow theory is only a special case of the proposed model whenr=0. This result soundly explains the reason that the geomaterials with the same internal friction angle and dilatancy angle can have very different shear band orientations. In addition, the difference between the intrinsic and apparent dilatancy angles is analyzed, and it is emphasized that the dilatancy angle commonly used in practice is indeed the apparent dilatancy angle. Copyright © 2010 John Wiley & Sons, Ltd.
Application of extended Kalman filter to back analysis of the natural stress state accounting for measuring uncertainties
Authors: Yang Cheng Xiang , Wu Yong Hong , Hon Tung , Feng Xia‐Ting
Published: April 2010

In this work, we present a numerical procedure for determining the nature stress state in the rock mass around a tunnel. A finite element method is applied for analyzing the direct problems of tunneling during the back analysis of parameter estimation, in which a no‐tension elastic–plastic model is used to simulate the elastic–tensile and elastic–plastic‐tensile failure states which often occur in the cases of underground excavation in heavily jointed rock masses. By considering the natural stress state as random parameters of the tunneling system, the Kalman filter method is employed for feedback analysis to modify the parameter values in a statistical context, which uses the prior information in the process of estimation and employs a set of displacements obtained from field measurements. To verify the effectiveness of the proposed method of inverse analysis, the developed numerical procedure is applied to a synthetic example of deep tunnels in yielding rock masses. The relative importance of the a priori and updating information is investigated, as is the importance of their uncertainty. The results show great potential of the proposed approach. Copyright © 2010 John Wiley & Sons, Ltd.
Elastoplastic modelling of diffuse instability response of geomaterials
Authors: Wan R. G. , Pinheiro M. , Guo P. J.
Published: April 2010

In this paper, we study material instabilities in geomaterials through an elastoplastic constitutive model endowed with appropriate attributes, such as stress, density and fabric dependencies. The analyses reveal the possibility of having diffuse instability, bifurcation and loss of uniqueness within the plastic limit surface. The resulting domain of bifurcation encompasses the intrinsic effects of stress–strain history, direction of loading, type of loading and fabric. The computations start at a material point level and are later on extended to an initial boundary value setting where diffuse failure of a three‐dimensional sand specimen with a random distribution of void ratio is examined. We restrict our simulations to the study of a q‐constant laboratory experimental test under different sets of control parameters. Diffuse failure is also revealed in a slope analysis under water infiltration following similar loading paths as in the q‐constant test. The analysis shows common material instability features observed in the above test. Copyright © 2010 John Wiley & Sons, Ltd.
A new method to calculate the equivalent Mohr–Coulomb friction angle for cohesive and frictional materials
Authors: Jiang Hua , Wang Xiaowo
Published: April 2010

In this note, a new method to calculate the equivalent Mohr–Coulomb friction angle ϕ′mc for cohesive and frictional materials is presented. This method makes a transformation from the failure surface for cohesive materials to the failure surface for cohesionless materials and obtains ϕ′mc as well as the principal stress ratio σ′1/σ′3 for cohesionless materials in the transformed space first, then obtains ϕ′mc for cohesive materials by linking σ′1/σ′3 in the transformed space and in the original space. In the application example, an analytical solution of the invariant stress ratio L is derived from the failure function in the transformed space. The influence of the intermediate effective principal stress σ′2 is also demonstrated using the already calculated ϕ′mc. Copyright © 2010 John Wiley & Sons, Ltd.
Seismic wave propagation analysis in vertical arrays at Kashiwazaki–Kariwa nuclear power plant site by using modified normalized input–output minimization (mod‐NIOM) method
Authors: Shrestha Santa Man , Kawakami Hideji
Published: April 2010

A new approach on numerical modeling of wave propagation is introduced and is used to analyze the effect of earthquake magnitudes (ground motion amplitudes) on wave propagation. In this method, the sum of the maximum amplitudes of the first output model at time 0 s and rest of the output models at different times are normalized to unity. Considering this as a constraint, the sum of the weighted‐squared Fourier amplitudes is minimized by using the Lagrange multiplier method. The proposed method can reveal the relationship of actual time histories by showing simple clear peaks. This method is used to analyze the time histories of various earthquake events at different vertical array sites of the Kashiwazaki–Kariwa nuclear power plant of Tokyo electric power company (TEPCO). The wave arrival times obtained from this method and down‐hole measurements are compared. The results show increase in the arrival times at surface layer when the magnitude of earthquake is large. The results reveal that the amplitudes of small magnitude earthquakes at depths are small and are largely amplified at surface, whereas in case of large magnitude earthquakes, the amplitudes are large at depths and are deamplified at surface reflecting the effects of the strain‐dependent soil properties that result in non‐linear site response to strong shaking. The results also show that the reflected peak amplitudes are higher for small magnitude earthquakes than for large magnitude earthquakes. Copyright © 2010 John Wiley & Sons, Ltd.
Investigation of model uncertainty for block stability analysis
Authors: Bagheri Mehdi , Stille Håkan
Published: April 2010

The application of probabilistic design, such as FORM, is expanding rapidly in the design of geotechnical structures. The analytical solution proposed by Crawford and Bray for analyzing block stability can be used as a performance function to carry out probabilistic design. The solution benefits from considering both clamping forces and joint stiffness. However, imperfect assumptions and simplifications in the solution generate model uncertainties. The amount of model uncertainty must be considered in order to assess a reliable design. The purpose of this paper is to identify when the analytical solution is applicable and quantify the model uncertainty of the solution. The amount of model uncertainty for the analytical solution has been assessed for different conditions. The results show that at a shallow depth with a low value of in situ stress ratio (horizontal stress/vertical stress), the analytical solution predicts that the block is stable whereas DEM shows that the block is unstable. The results of the analyses indicate that in cases with low stress ratio, cases with high anisotropy of joint stiffness or the case of a semiapical angle close to the friction angle, the accuracy of the analytical solution is low. Neglecting key parameters, such as the absolute value of joint shear and normal stiffness, vertical in situ stress and its influence on joint relaxation generate model uncertainty in the analytical solution. The analyses show that by having more information about the key parameters, the model uncertainty factor could be identified more precisely. Copyright © 2010 John Wiley & Sons, Ltd.
A fully integrated noise robust strategy for the identification of constitutive laws from digital images
Authors: Réthoré Julien
Published: April 2010

Constitutive parameter identification has been greatly improved by the achievement of full‐field measurements. In this context, noise sensitivity has been shown to be of great importance. It is crucial to incorporate noise sensitivity minimization in the design of robust identification procedures. In this paper, we investigate noise sensitivity reduction techniques for constitutive parameter identification based on Finite Element Model Updating. After examining the existing strategies, we propose a single step algorithm based on a mixed optical/mechanical cost function. The key point of this novel procedure is that no boundary conditions are needed. A first example on a real case illustrates the advantages of the proposed methodology in terms of noise sensitivity. A second example shows its capabilities to identify a non‐linear consitutive law. Copyright © 2010 John Wiley & Sons, Ltd.
A partition of unity finite element method for obtaining elastic properties of continua with embedded thin fibres
Authors: Radtke F. K. F. , Simone A. , Sluys L. J.
Published: April 2010

The numerical analysis of large numbers of arbitrarily distributed discrete thin fibres embedded in a continuum is a computationally demanding process. In this contribution, we propose an approach based on the partition of unity property of finite element shape functions that can handle discrete thin fibres in a continuum matrix without meshing them. This is made possible by a special enrichment function that represents the action of each individual fibre on the matrix. Our approach allows to model fibre‐reinforced materials considering matrix, fibres and interfaces between matrix and fibres individually, each with its own elastic constitutive law. Copyright © 2010 John Wiley & Sons, Ltd.
The skeleton of a medieval male with multiple traumatic fractures from Piazza della Signoria, Florence, Italy
Authors: Boccone S. , Chilleri F. , Pacciani E. , Cecchi J. Moggi , Salvini M.
Published: April 2010

We report on the palaeopathology of a medieval skeleton of a young adult male with multiple traumatic fractures found in 1989 in Piazza della Signoria, Florence, Italy. The skeleton presents ante mortem fractures of the right ulna and femur, and left tibia and fibula. We reconstruct the dynamics of the accident based on the location and type of fractures. Then we discuss the impact of this severe trauma on the subject's living conditions based on articular and enthesic modifications of the skeleton. Copyright © 2010 John Wiley & Sons, Ltd.
Application of capillary electrophoresis in anion binding studies: complexation and separation of nitrate and nitrite by an azacryptand
Authors: Wu Hao , Saeed Musabbir A. , Hwang Huey‐Min , Zhao Shulin , Liu Yi‐Ming , Hossain Md. Alamgir
Published: April 2010

Capillary electrophoresis (CE) was employed to study the complexation of an azacryptand with nitrate and nitrite in aqueous solution. CE separation of a mixture of nitrate and nitrite with 10 mM acetate buffer (pH 3.3) showed two peaks at the retention times of 2.8 and 3.1 min for nitrate and nitrite, respectively. However, when the ligand (2 mM) was added to the running buffer, the peaks emerged in the reverse order and at shorter retention times of 2.7 and 2.5 min for nitrate and nitrite, respectively. The longer retention time for nitrate compared with nitrite indicates a stronger complex formation between the ligand and nitrate, which reduces the migration speed of nitrate as compared with the less strongly bound nitrite. The 1H NMR titrations of L with these two anions at the pH 3.3 gave the binding constants (log K), 3.75 and 4.23, for nitrite and nitrate, respectively which were consistent with the results obtained from the CE method. Copyright © 2010 John Wiley & Sons, Ltd.
Kinetics of the gas‐phase homogeneous unimolecular elimination of selected ethyl esters of 2‐oxo‐carboxylic acids
Authors: Reyes Andreina , Domínguez Rosa M. , Tosta Maria , Herize Armando , Chuchani Gabriel
Published: April 2010

The gas‐phase elimination kinetics of selected ethyl esters of 2‐oxo‐carboxylic acid have been studied over the temperature range of 270–415 °C and pressures of 37–114 Torr. The reactions are homogeneous, unimolecular, and follow a first‐order rate law in a seasoned static reaction vessel, with an added free radical suppressor toluene. The observed overall and partial rate coefficients are expressed by the following Arrhenius equations:

Ethyl oxalyl chloride

log koverall (s−1) = (13.22 ± 0.45) − (179.4 ± 4.9) kJ mol−1 (2.303 RT)−1

Ethyl piperidineglyoxylate

log k(CO2) (s−1) = (12.00 ± 0.30) −  (191.2 ± 3.9) kJ mol−1 (2.303 RT)−1

log k(CO) (s−1) = (12.60 ± 0.09) − (210.7 ± 1.2) kJ mol−1 (2.303 RT)−1

log kt(overall) (s−1) = (12.22 ± 0.26) − (193.4 ± 3.4) kJ mol−1 (2.303 RT)−1

Ethyl benzoyl formate

log k(CO2) (s−1) = (12.89 ± 0.72) − (203.8 ± 9.0) kJ mol−1 (2.303 RT)−1

log k(CO) (s−1) = (13.39 ± 0.31) − (213.3 ± 3.9) kJ mol−1 (2.303 RT)−1

log kt(overall) (s−1) = (13.24 ± 0.60) − (205.8 ± 7.6) kJ mol−1 (2.303 RT)−1

The kinetic and thermodynamic parameters of these reactions, together with those reported in the literature, lead to consider three different mechanistic pathways of elimination. Copyright © 2010 John Wiley & Sons, Ltd.
The crystal structure of ribonuclease A in complex with thymidine‐3′‐monophosphate provides further insight into ligand binding
Authors: Doucet Nicolas , Jayasundera Thusitha B. , Simonović Miljan , Loria J. Patrick
Published: April 2010

Thymidine‐3′‐monophosphate (3′‐TMP) is a competitive inhibitor analogue of the 3′‐CMP and 3′‐UMP natural product inhibitors of bovine pancreatic ribonuclease A (RNase A). Isothermal titration calorimetry experiments show that 3′‐TMP binds the enzyme with a dissociation constant (Kd) of 15 μM making it one of the strongest binding members of the five natural bases found in nucleic acids (A, C, G, T, and U). To further investigate the molecular properties of this potent natural affinity, we have determined the crystal structure of bovine pancreatic RNase A in complex with 3′‐TMP at 1.55 Å resolution and we have performed NMR binding experiments with 3′‐CMP and 3′‐TMP. Our results show that binding of 3′‐TMP is very similar to other natural and non‐natural pyrimidine ligands, demonstrating that single nucleotide affinity is independent of the presence or absence of a 2′‐hydroxyl on the ribose moiety of pyrimidines and suggesting that the pyrimidine binding subsite of RNase A is not a significant contributor of inhibitor discrimination. Accumulating evidence suggests that very subtle structural, chemical, and potentially motional variations contribute to ligand discrimination in this enzyme. Proteins 2010. © 2010 Wiley‐Liss, Inc.
Predicting order of conformational changes during protein conformational transitions using an interpolated elastic network model
Authors: Tekpinar Mustafa , Zheng Wenjun
Published: April 2010

The decryption of sequence of structural events during protein conformational transitions is essential to a detailed understanding of molecular functions ofvarious biological nanomachines. Coarse‐grained models have proven useful by allowing highly efficient simulations of protein conformational dynamics. By combining two coarse‐grained elastic network models constructed based on the beginning and end conformations of a transition, we have developed an interpolated elastic network model to generate a transition pathway between the two protein conformations. For validation, we have predicted the order of local and global conformational changes during key ATP‐driven transitions in three important biological nanomachines (myosin, F1 ATPase and chaperonin GroEL). We have found that the local conformational change associated with the closing of active site precedes the global conformational change leading to mechanical motions. Our finding is in good agreement with the distribution of intermediate experimental structures, and it supports the importance of local motions at active site to drive or gate various conformational transitions underlying the workings of a diverse range of biological nanomachines. Proteins 2010. © 2010 Wiley‐Liss, Inc.
Preparation of ZnO thin films by MO‐CVD method using bis(acetylacetonato) zinc(II) anhydrate fiber
Authors: Seki Shigeyuki , Onodera Hisashi , Sekizawa Takumi , Sakuma Mio , Haga Koichi , Seki Yoshiyuki , Sawada Yutaka , Shishido Toetsu
Published: April 2010

The MO‐CVD method as a deposition process corresponding to the mass production of the high‐quality ZnO film that can be used as an active layer in the thin film transistor is paid to attention. Bis(acetylacetonato) zinc(II) (Zn(acac)2) which has chemical stability and low toxicity is promising as the inexpensive raw material for CVD. The problem includes (1) pollution with water in process by character to easily take water of crystallization, and (2) the supply of the gas‐phase raw material by sublimation should be not able to be controlled easily because it is a fine particle. In this study, Zn(acac)2 anhydrate fiber was prepared from Zn(acac)2 monohydrate powder by the sublimation process. Melting point of this fiber was almost same (∼134 °C) as the monohydrate powder in N2 atmosphere. ZnO film was deposited on r‐face sapphire substrate by MO‐CVD process using Zn(acac)2 anhydrate fiber, successfully. RMS of the film flatness was 0.48 nm. This film had resistivity of 4.6 × 10–1 Ω·cm, carrier electron density of 9.1 × 1017 cm–3 and Hall mobility of 15 cm2·V–1·s–1. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact of Al2O3 incorporation on device performance of HfO2 gate dielectric AlGaN/GaN MIS‐HFETs
Authors: Tian Feng , Chor Eng Fong
Published: April 2010

We report the effects of Al2O3 interfacial layer incorporation on the dc performance of AlGaN/GaN metal‐insulator‐semiconductor field effect transistors (MIS‐HFETs) using HfO2 as the gate dielectric and surface passivation layer. The HfO2/Al2O3 bi‐layer MIS‐HFETs exhibit a larger maximum drain current by ∼8.5%, larger gate voltage swing by ∼6.3%, and smaller gate leakage by 4∼5 times, compared to the HfO2 single layer MIS‐HFETs at room temperature. Furthermore, the HfO2/Al2O3 transistors are observed to have better thermal stability than the HfO2 transistors, and the estimated lifetime (in hour) of the former is longer than that of the latter by over an order of magnitude from 25 to 150 °C (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of growth temperature on Eu‐doped GaN layers grown by organometallic vapor phase epitaxy
Authors: Kawasaki Takashi , Nishikawa Atsushi , Furukawa Naoki , Terai Yoshikazu , Fujiwara Yasufumi
Published: April 2010

We investigated the effect of growth temperature on the luminescence properties of Eu‐doped GaN layers grown by organometallic vapor phase epitaxy (OMVPE). The dominant photoluminescence (PL) peak intensity at 621 nm, due to the intra‐4f shell transitions of 5D0‐7F2 in Eu3+ ions, became the highest when the sample was grown at 1000 °C. We consider three reasons for this temperature dependence. Firstly, Eu concentration became the highest when the sample was grown at 1000 °C. Secondly, Eu‐doped GaN layer grown at 1000 °C had the local structure of Eu3+ ions, which emitted at 621 nm preferentially. Thirdly, the density of screw and mixed dislocations decreased with increasing growth temperature. These results indicated that an appropriate growth temperature exists for strong Eu‐related luminescence from Eu‐doped GaN layer grown by OMVPE. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards a deeper understanding of the reduced efficiency droop in low defect‐density GaInN wide‐well LEDs
Authors: Maier Markus , Passow Thorsten , Kunzer Michael , Pletschen Wilfried , Köhler Klaus , Wagner Joachim
Published: April 2010

A series of 400 nm emitting GaInN/GaN single‐well light‐emitting diodes, grown on ultra‐low dislocation density GaN templates with well widths varying between 3 and 18 nm, were investigated by pulsed and time resolved electroluminescence measurements using small signal modulation technique for the latter. A reduction of the efficiency droop at high current densities with increasing well width was observed. The highest overall external quantum efficiency was obtained for LEDs with 11 nm thick double‐heterostructure (or wide well) active region at current densities above 70 A/cm2. Furthermore, carrier lifetime and volume carrier density in the wells were determined. A model based on the interplay between defect assisted recombination, depending on dislocation density, and strongly carrier density dependent loss processes is presented explaining the well‐thickness dependence of the efficiency droop. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Q‐factor measurements on planar nitride cavities
Authors: Collins Daniel P. , Holmes Mark J. , Taylor Robert A. , Oliver Rachel A. , Kappers Menno J. , Humphreys Colin J.
Published: April 2010

To enable the study of cavity quantum electro‐dynamical effects in nitride systems, it is essential to be able to fabricate high quality cavity structures that exhibit large Q‐values of the order of several thousands. A promising candidate for such a realisation is based around the micro‐pillar distributed Bragg reflector (DBR) cavity. The growth of nitride stacks is problematic due to such material issues as lattice mismatch and dislocation propagation which seem to be more pronounced when compared to similar arsenide structures. In this paper we report on our efforts to characterize the homogeneity of our first generation planar DBR structures through both reflectivity measurements using the broadband output of a photonic crystal fiber (PCF) and cryogenic photoluminescence under ultraviolet (UV) excitation. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deep etch of GaN by laser micromachining
Authors: Mak Giuseppe Y. , Lam Edmund Y. , Choi H. W.
Published: April 2010

Trench formation for device isolation on GaN light‐emitting diode (LED) wafers via nanosecond ultraviolet laser micromachining is demonstrated. Owing to the dissimilar ablation thresholds between GaN and sapphire, the etch process terminates automatically at the GaN/sapphire interface. It was found that optimal focus offset, optimal pulse energy and high repetition rate are essential for obtaining a trench with tapered sidewall and smooth bottom surface, which is suitable for the conformal deposition of interconnects across the trench. This technique has been successfully applied to the rapid prototyping of interconnected LED arrays on a single chip. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN‐based light emitting diodes with periodic nano‐structures on the surface fabricated by nanoimprint lithography technique
Authors: Naoi Yoshiki , Matsumoto Masakazu , Tan Tianya , Tohno Mistuaki , Sakai Shiro , Fukano Atsuyuki , Tanaka Satoru
Published: April 2010

We investigated the characteristics of GaN‐based light emitting diodes (LEDs) with periodic nano‐structures on the surface by nanoimprint lithography technique. We measured the intensity emitted through nano‐structure on the p‐GaN surface into the forward side in an air/GaN‐LED/sapphire configuration, and also the intensity through nano‐structure fabricated between GaN/sapphire interfaces into the back side. Angular spatial distribution of electroluminescence intensity from GaN‐based 380 nm UV and 410 nm blue LED with nano‐structures were considerably different from that for the sample without nano processing, and the lobe near the horizontal direction in the surface side profile was observed. The results can be explained by a combination of diffracted light by the fabricated grating by NIL and transmitted light though the sidewall at the interface of the periodic structure. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Making available information from studies sponsored by the pharmaceutical industry: some current practices
Authors: O'Kelly Michael , Julious Steven A. , Pyke Stephen , Day Simon , Todd Sue , Seldrup Jorgen , Matcham James
Published: April 2010

Since the web‐based registry ClinicalTrials.gov was launched on 29 February 2000, the pharmaceutical industry has made available an increasing amount of information about the clinical trials that it sponsors. The process has been spurred on by a number of factors including a wish by the industry to provide greater transparency regarding clinical trial data; and has been both aided and complicated by the number of institutions that have a legitimate interest in guiding and defining what should be made available. This article reviews the history of this process of making information about clinical trials publicly available. It provides a reader's guide to the study registries and the databases of results; and looks at some indicators of consistency in the posting of study information. Copyright © 2010 John Wiley & Sons, Ltd.
The effect of variability and carryover on average bioequivalence assessment: A simulation study
Authors: Sánchez O María Pilar , Ocaña Jordi , Carrasco Josep L.
Published: April 2010

The purpose of this study was to evaluate the effect of residual variability and carryover on average bioequivalence (ABE) studies performed under a 2×2 crossover design. ABE is usually assessed by means of the confidence interval inclusion principle. Here, the interval under consideration was the standard ‘shortest’ interval, which is the mainstream approach in practice.

The evaluation was performed by means of a simulation study under different combinations of carryover and residual variability besides of formulation effect and sample size. The evaluation was made in terms of percentage of ABE declaration, coverage and interval precision.

As is well known, high levels of variability distort the ABE procedures, particularly its type II error control (i.e. high variabilities make difficult to declare bioequivalence when it holds). The effect of carryover is modulated by variability and is especially disturbing for the type I error control. In the presence of carryover, the risk of erroneously declaring bioequivalence may become high, especially for low variabilities and large sample sizes. We end up with some hints concerning the controversy about pretesting for carryover before performing ABE analysis. Copyright © 2010 John Wiley & Sons, Ltd.
Organizing matters: how ‘the social dimension’ gets lost in sustainability projects
Authors: Vifell Åsa Casula , Soneryd Linda
Published: April 2010

This paper explores the conditions for taking the social dimension into consideration when trying to aim for increased sustainability through activities organized in projects. Among the three commonly accepted pillars of sustainable development – economic, ecological and social – the social dimension is often the most vague and least explicit in practical attempts to shape sustainable development. The aim with this study is to explore the role of organizing in shaping the balance between the pillars. The two cases examined are projects explicitly related to sustainable development goals set by the national government or parliament and implemented by other actors. The cases concern two topics: food production and electromagnetic fields. On the basis of relevant organizational dimensions and case analyses, the paper shows how the organization of sustainability shapes the ways in which the projects articulate the social dimension. This leads to practical advice for organizing new projects in the future. Copyright © 2010 John Wiley & Sons, Ltd and ERP Environment.
Strength of evidence of non‐inferiority trials—The adjustment of the type I error rate in non‐inferiority trials with the synthesis method
Authors: Kang Seung‐Ho , Tsong Yi
Published: April 2010

In non‐inferiority trials that employ the synthesis method several types of dependencies among test statistics occur due to sharing of the same information from the historical trial. The conditions under which the dependencies appear may be divided into three categories. The first case is when a new drug is approved with single non‐inferiority trial. The second case is when a new drug is approved if two independent non‐inferiority trials show positive results. The third case is when two new different drugs are approved with the same active control. The problem of the dependencies is that they can make the type I error rate deviate from the nominal level. In order to study such deviations, we introduce the unconditional and conditional across‐trial type I error rates when the non‐inferiority margin is estimated from the historical trial, and investigate how the dependencies affect the type I error rates. We show that the unconditional across‐trial type I error rate increases dramatically as does the correlation between two non‐inferiority tests when a new drug is approved based on the positive results of two non‐inferiority trials. We conclude that the conditional across‐trial type I error rate involves the unknown treatment effect in the historical trial. The formulae of the conditional across‐trial type I error rates provide us with a way of investigating the conditional across‐trial type I error rates for various assumed values of the treatment effect in the historical trial. Copyright © 2010 John Wiley & Sons, Ltd.
Likelihood‐based methods for estimating the association between a health outcome and left‐ or interval‐censored longitudinal exposure data
Authors: Wannemuehler Kathleen A. , Lyles Robert H. , Manatunga Amita K. , Terrell Metrecia L. , Marcus Michele
Published: April 2010

The Michigan Female Health Study (MFHS) conducted research focusing on reproductive health outcomes among women exposed to polybrominated biphenyls (PBBs). In the work presented here, the available longitudinal serum PBB exposure measurements are used to obtain predictions of PBB exposure for specific time points of interest via random effects models. In a two‐stage approach, a prediction of the PBB exposure is obtained and then used in a second‐stage health outcome model. This paper illustrates how a unified approach, which links the exposure and outcome in a joint model, provides an efficient adjustment for covariate measurement error. We compare the use of empirical Bayes predictions in the two‐stage approach with results from a joint modeling approach, with and without an adjustment for left‐ and interval‐censored data. The unified approach with the adjustment for left‐ and interval‐censored data resulted in little bias and near‐nominal confidence interval coverage in both the logistic and linear model setting. Published in 2010 by John Wiley & Sons, Ltd.
Space–time latent component modeling of geo‐referenced health data
Authors: Lawson Andrew B. , Song Hae‐Ryoung , Cai Bo , Hossain Md Monir , Huang Kun
Published: April 2010

Latent structure models have been proposed in many applications. For space–time health data it is often important to be able to find the underlying trends in time, which are supported by subsets of small areas. Latent structure modeling is one such approach to this analysis. This paper presents a mixture‐based approach that can be applied to component selection. The analysis of a Georgia ambulatory asthma county‐level data set is presented and a simulation‐based evaluation is made. Copyright © 2010 John Wiley & Sons, Ltd.
Combining stratified and unstratified log‐rank tests in paired survival data
Authors: Oakes David , Feng Changyong
Published: April 2010

The log‐rank test is the most widely used nonparametric method for testing treatment differences in survival between two treatment groups due to its efficiency under the proportional hazards model. Most previous work on the log‐rank test has assumed that the samples from the two treatment groups are independent. This assumption is not always true. In multi‐center clinical trials, survival times of patients in the same medical center may be correlated due to factors specific to each center. For such data, we can construct both stratified and unstratified log‐rank tests. These two tests turn out to have very different powers for correlated samples. An appropriate linear combination of these two tests may give a more powerful test than either of the individual test. Under a bivariate frailty model, we obtain closed‐form asymptotic local alternative distributions and the correlation coefficient between these two tests. Based on these results we construct an optimal linear combination of the two test statistics to maximize the local power. Simulation studies with Hougaard's model confirm our construction. We also study the robustness of the combined test by simulations. Copyright © 2010 John Wiley & Sons, Ltd.
A linear exponent AR(1) family of correlation structures
Authors: Simpson Sean L. , Edwards Lloyd J. , Muller Keith E. , Sen Pranab K. , Styner Martin A.
Published: April 2010

In repeated measures settings, modeling the correlation pattern of the data can be immensely important for proper analyses. Accurate inference requires proper choice of the correlation model. Optimal efficiency of the estimation procedure demands a parsimonious parameterization of the correlation structure, with sufficient sensitivity to detect the range of correlation patterns that may occur. Many repeated measures settings have within‐subject correlation decreasing exponentially in time or space. Among the variety of correlation patterns available for this context, the continuous‐time first‐order autoregressive correlation structure, denoted AR(1), sees the most utilization. Despite its wide use, the AR(1) structure often poorly gauges within‐subject correlations that decay at a slower or faster rate than required by the AR(1) model. To address this deficiency we propose a two‐parameter generalization of the continuous‐time AR(1) model, termed the linear exponent autoregressive (LEAR) correlation structure, which accommodates much slower and much faster decay patterns. Special cases of the LEAR family include the AR(1), compound symmetry, and first‐order moving average correlation structures. Excellent analytic, numerical, and statistical properties help make the LEAR structure a valuable addition to the suite of parsimonious correlation models for repeated measures data. Both medical imaging data concerning neonate neurological development and longitudinal data concerning diet and hypertension [DASH (Dietary Approaches to Stop Hypertension) study] exemplify the utility of the LEAR correlation structure. Copyright © 2010 John Wiley & Sons, Ltd.
Effect of two horizontal components of earthquake on nonlinear response of torsionally coupled base isolated structures
Authors: Khoshnoudian Faramarz , Azad Ali Imani
Published: April 2010

Torsion in base‐isolated structures using bilinear rubber isolators effected by two horizontal components of earthquake simultaneously is investigated under various principal parameters including number of storeys; ratio of uncoupled torsional frequency to lateral frequency in the superstructure; ratio of uncoupled torsional frequency to lateral frequency in the isolation system; mass eccentricity in the superstructure and isolation system; and, in addition, the direction of eccentricity. Structure was supposed a shear structure and it was modeled by using concentrated mass and springs. Isolators are modelled by using nonlinear springs considering the interaction of isolator behaviour in two directions. The effect of variation in considered parameters on the behaviour of the superstructure and isolation system is investigated under seven ground motions. It is demonstrated that the parameters affect asymmetric structure behaviour with respect to symmetric one. The results of our investigations help us to understand the asymmetric structure behaviour under bidirectional earthquake by comparing it with a symmetric one. These results demonstrate that asymmetry in the superstructure or isolation system could have a significant effect on the torsional behaviour of isolated structures. In addition, the results show that the use of rigid superstructures and calculation of dynamic torsion by multiplying eccentricity by the dynamic base shear are unacceptable assumptions. Torsional effect on the isolated structural behaviour is amplified by considering two horizontal components of earthquake and comparing them with just one horizontal component. Copyright © 2010 John Wiley & Sons, Ltd.
Dual criterion equivalent linearization approach for yielding structures under earthquake excitation
Authors: Rahmatabadi Payman , Khaloo Alireza
Published: April 2010

In order to estimate both maximum displacement and maximum inertia force of bilinear hysteretic system subjected to earthquake motions, an equivalent linearization approach with new effective parameters is presented. Effective mass and effective damping ratio as pair of effective parameters instead of the effective period and effective damping ratio in existing equivalent linear systems are introduced. Two error measures for displacement and inertia force are defined. Error distributions over a two‐dimensional parameter space of effective parameters are analysed, and the parameters are determined through a statistical approach with a dual optimization criterion for displacement and inertia force errors applicable to structural design. Single‐degree‐of‐freedom systems with bilinear hysteretic model; natural periods from 0.1 to 3.0 s; linear damping ratios from 3 to 50%; ductility ratios from 1.5 to 6; and post‐yield slope ratios 0, 0.05, 0.1 are considered. Analytical expressions for the effective parameters, and the ratio of the maximum inertia force to the maximum restoring force as functions of response ductility, elastic damping ratio and natural period of inelastic system are proposed for different site conditions and post‐yield slope ratios. Evaluation of proposed equations is performed, which reveals that the linear parameters lead to permissible error ranges. Copyright © 2010 John Wiley & Sons, Ltd.