bluuebunny/crossref_metadata_2025 huggingface dataset:
Fast Bayesian approach for parameter estimation
Authors: Jin Bangti
Published: March 2008

This paper presents two techniques, i.e. the proper orthogonal decomposition (POD) and the stochastic collocation method (SCM), for constructing surrogate models to accelerate the Bayesian inference approach for parameter estimation problems associated with partial differential equations. POD is a model reduction technique that derives reduced‐order models using an optimal problem‐adapted basis to effect significant reduction of the problem size and hence computational cost. SCM is an uncertainty propagation technique that approximates the parameterized solution and reduces further forward solves to function evaluations. The utility of the techniques is assessed on the non‐linear inverse problem of probabilistically calibrating scalar Robin coefficients from boundary measurements arising in the quenching process and non‐destructive evaluation. A hierarchical Bayesian model that handles flexibly the regularization parameter and the noise level is employed, and the posterior state space is explored by the Markov chain Monte Carlo. The numerical results indicate that significant computational gains can be realized without sacrificing the accuracy. Copyright © 2008 John Wiley & Sons, Ltd.
Non‐linear coupled multi‐field mechanics and finite element for active multi‐stable thermal piezoelectric shells
Authors: Varelis Dimitris , Saravanos Dimitris A.
Published: March 2008

In this paper, a coupled multi‐field mechanics framework is presented for analyzing the non‐linear response of shallow doubly curved adaptive laminated piezoelectric shells undergoing large displacements and rotations in thermal environments. The mechanics incorporate coupling between mechanical, electric and thermal fields and encompass geometric non‐linearity effects due to large displacements and rotations. The governing equations are formulated explicitly in orthogonal curvilinear coordinates and are combined with the kinematic assumptions of a mixed‐field shear‐layerwise shell laminate theory. A finite element methodology and an eight‐node coupled non‐linear shell element are developed. The discrete coupled non‐linear equations of motion are linearized and solved, using an extended cylindrical arc‐length method together with a Newton–Raphson technique, to enable robust numerical predictions of non‐linear active shells transitioning between multiple stable equilibrium paths. Validation and evaluation cases on laminated cylindrical strips and cylindrical panels demonstrate the accuracy of the method and its robust capability to predict non‐linear response under thermal and piezoelectric actuator loads. Moreover, the results illustrate the capability of the method to model piezoelectric shells undergoing large shape changes by actively jumping between stable equilibrium states and quantify the strong relationship between shell curvature, applied electric potential, applied temperature differential and induced shape change. Copyright © 2008 John Wiley & Sons, Ltd.
High‐frequency response analysis via algebraic substructuring
Authors: Ko Jin Hwan , Bai Zhaojun
Published: March 2008

High‐frequency response analysis (Hi‐FRA) of large‐scale dynamical systems is critical to predict the resonant behavior of modern micro‐devices and systems operated over MHz or GHz frequency range. Algebraic substructuring (AS) is a powerful technique to extract a large number of natural frequencies. In this work, we extend the AS technique for FRA between two specified cutoff frequencies ωmin and ωmax. The technique is referred to as ASFRA. ASFRA can be efficiently applied to Hi‐FRA, as demonstrated by two examples of microelectromechanical sensors operated at 1–2 and 200–250 MHz ranges. To some extent ASFRA generalizes the underlying numerical algorithm and functionality of commercially viable automated multi‐level substructuring (AMLS) technique. AMLS is designed for FRA up to a specific frequency ωmax, starting from the lowest, and is inefficient for Hi‐FRA. Copyright © 2008 John Wiley & Sons, Ltd.
Nodal velocity derivatives of finite element solutions: The FiND method for incompressible Navier–Stokes equations
Authors: Ilinca F. , Pelletier D.
Published: March 2008

This paper presents the development and application of the finite node displacement (FiND) method to the incompressible Navier–Stokes equations. The method computes high‐accuracy nodal derivatives of the finite element solutions. The approach imposes a small displacement to individual mesh nodes and solves a very small problem on the patch of elements surrounding the node. The only unknown is the value of the solution (u, p) at the displaced node. A finite difference between the original and the perturbed values provides the directional derivative. Verification by grid refinement studies is shown for two‐dimensional problems possessing a closed‐form solution: a Poiseuille flow and a flow mimicking a boundary layer. For internal nodes, the method yields accuracy slightly superior to that of the superconvergent patch recovery (SPR) technique of Zienkiewicz and Zhu (ZZ). We also present a variant of the method to treat boundary nodes. The local discretization is enriched by inserting an additional mesh point very close to the boundary node of interest. Computations show that the resulting nodal derivatives are much more accurate than those obtained by the ZZ SPR technique. Copyright © 2008 John Wiley & Sons, Ltd.
An analysis of monotonicity conditions in the mixed hybrid finite element method on unstructured triangulations
Authors: Mazzia Annamaria
Published: March 2008

In this paper we consider the mixed hybrid finite element method on unstructured triangular grids and evaluate its monotonicity properties by using a non standard set of basis functions for the velocity approximation space.

The mixed hybrid discretization of the steady‐state diffusion equation produces a system matrix that depends only on the inner product of the outward normals to the edges of the triangulation and not on the choice of the velocity space basis. This property is used to study the characteristics of the system matrix. It is well known that this matrix is of type M if the angles of the triangulation are not bigger than π/2. An M‐matrix has a nonnegative inverse, i.e. all the elements are nonnegative. This implies the existence of a discrete maximum principle and thus monotonicity of the discretization. We show that, when the triangulation is of Delaunay type and satisfies the property that no circumcenters of boundary elements with Dirichlet conditions lie outside the domain, the inverse of the final matrix is always positive, even in the presence of obtuse angles. Copyright © 2008 John Wiley & Sons, Ltd.
A second‐order accurate difference scheme for the two‐dimensional Burgers' system
Authors: Xu Pei‐Pei , Sun Zhi‐Zhong
Published: March 2008

In this article, a Crank‐Nicolson‐type finite difference scheme for the two‐dimensional Burgers' system is presented. The existence of the difference solution is shown by Brouwer fixed‐point theorem. The uniqueness of the difference solution and the stability and L2 convergence of the difference scheme are proved by energy method. An iterative algorithm for the difference scheme is given in detail. Furthermore, a linear predictor–corrector method is presented. The numerical results show that the predictor–corrector method is also convergent with the convergence order of two in both time and space. At last, some comments are provided for the backward Euler scheme. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009
The method of fundamental solutions with eigenfunctions expansion method for 3D nonhomogeneous diffusion equations
Authors: Young D.L. , Chen C.H. , Fan C.M. , Shen L.H.
Published: March 2008

After the successful applications of the combination of the method of fundamental solutions (MFS), the method of particular solutions (MPS), and the eigenfunctions expansion method (EEM) to solve 2D homogeneous and nonhomogeneous diffusion equations by Young et al. (Young et al., Numer Meth Part Differ Equat 22 (2006), 1173), this article intends to extend the same fundamental concepts to calculate more challenging 3D nonhomogeneous diffusion equations. The nonhomogeneous diffusion equations with time‐independent source terms and boundary conditions are analyzed by the proposed meshless MFS‐MPS‐EEM model. Nonhomogeneous diffusion equation in any complex domains can be decomposed into a Poisson equation and a homogeneous diffusion equation by the principle of linear superposition. This approach is proved to be far better off than solutions by using classic method of separation of variables with inefficient multisummation of very sophisticated series expansion from special functions, which can only limit to treat very simple 3D geometries such as cube, cylinder, or sphere. Poisson equation is solved by using the MPS‐MFS model, in which the source term in the Poisson equation is first handled by the MPS based on the compactly‐supported radial basis functions and the Laplace equation is solved by the MFS. On the other hand, by utilizing the EEM, the homogeneous diffusion equation is first transformed into a Helmholtz equation, which is then solved by the MFS together with the technique of singular value decomposition (SVD) to acquire the eigenvalues and eigenfunctions. After the eigenfunctions are obtained, we can synthesize the diffusion solutions like the orthogonal Fourier series expansions but with only one summation for the series even for multidimensional problems. Numerical results for four case studies of 3D homogeneous and nonhomogeneous diffusion problems show good agreement with the analytical and other numerical solutions, such as finite element method (FEM). Thus, the present numerical scheme has provided a promising meshfree numerical approach to solve 3D nonhomogeneous diffusion equations with time‐independent source terms and boundary conditions for very irregular domains. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009
Most low‐level microsatellite instability in colorectal cancers can be explained without an elevated slippage rate
Authors: Graham T , Halford S , Page KM , Tomlinson IPM
Published: March 2008

Many cancers show a low level of microsatellite slippage and are labelled MSI‐L (microsatellite instability—low). However, it is unclear whether this slippage can be attributed to some underlying genetic change that results in a mutator phenotype, analogous to mismatch repair deficiency in MSI‐H cancers, or whether the apparent instability is the result of relatively frequent normal somatic slippage. Here, we have used a mathematical model of microsatellite slippage during cancer growth to estimate the degree of microsatellite slippage expected in a cancer due to normal somatic slippage. We compared the model to the slippage observed in 42 non‐MSI‐H cancers that were macro‐dissected into four distinct regions and genotyped at N = 9 microsatellite loci. When the slippage rate was set at µ = 10−5 per locus per division, ten cancers showed a level of slippage in at least one region that was too severe to be expected from normal somatic slippage alone, suggesting that these cancers had acquired MSI‐L. Only one of these ten cancers had putative MSI‐L in all four regions. When we considered a slightly higher slippage rate of µ = 5 × 10−5, none of the cancers showed a degree of slippage that could not be reasonably explained by normal somatic slippage. Counting the number of ‘unstable’ loci was a poor indicator of putative MSI‐L status. We conclude that most low‐level microsatellite instability in colorectal cancers can be explained without requiring an elevated slippage rate during neoplastic development, and hence there is little evidence for a discrete MSI‐L group of cancers. Putative MSI‐L status is indicated by the presence of at least one locus that has multiple alleles that differ by at least five motif repeats from the germline. If an underlying genetic change does cause MSI‐L, it appears to be a relatively uncommon event that occurs late in oncogenesis. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Experimental characterization of the impact‐damage tolerance of a cross‐ply graphite‐fiber/epoxy laminate
Authors: Wu Xiang‐Fa , Ghoshal Goutam , Kartashov Mikhail , Aslan Zuleyha , Turner Joseph A. , Dzenis Yuris A.
Published: March 2008

In this study, the impact‐damage tolerance of a graphite‐fiber/epoxy composite laminate is studied by examining the correlation between the impact force and the resulting delamination area in the laminate. The cross‐ply [02/902/02]s composite laminate was made of thermosetting P7051S‐20Q‐1000 prepregs (Toray Composites America). A Hopkinson pressure bar (HPB) was employed to create the impulsive loading with varying magnitude. Transient impact force, displacement, impact power, and transmitted impact energy were calculated using the transient signals recorded from the strain gage mounted on the HPB. Impulsive loads with controllable magnitude were used to induce delamination damage with varying size in the composite samples. Nondestructive evaluation based on a novel ultrasonic pulse‐echo reflector technique was used successfully for characterizing the delamination areas in the thin composite samples with thickness ∼2 mm. The present experimental results indicate that there exists a very good linear correlation between the impact force (e.g. the peak force, impact impulse, peak impact power, and the transmitted impact energy of the first impact force pulse exerted by the HPB) and the delamination area of the composite samples. This correlation can be used to determine the threshold of the impact force that initiates the delamination damage in the composite laminate. In contrast to the weight‐drop test, the present experimental method successfully examined the impact damage tolerance of polymer matrix composites (PMCs) subjected to impulsive loading with very high force magnitude and ultra short duration such as the typical ballistic impact. The present method and results can be used for the study of impact damage tolerance of PMCs with varying lay‐ups and interface modifications. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Effect of Attapulgite filler on the properties of Nylon‐6
Authors: Subramani Chandramouleeswaran , Jamnik Vijay S. , Mhaske S.T.
Published: March 2008

Nylon‐6/Attapulgite (ATP) composites were prepared by melt blending in a twin screw extruder. Nylon‐6/ATP composites were tested for its mechanical, rheological, thermal and morphological properties. The results have shown drastic improvement in the flexural modulus by 74% at the loading level of 4% of ATP. The tensile strength was also increased at the 3–4% loadings of ATP. The impact strength was doubled even at the 2% loading of ATP. The strength and stiffness of Nylon‐6/ATP composites were both improved significantly in the presence of attapulgite. In addition, the incorporation of ATP gave rise to the increase in the storage modulus. The extensional viscosities were studied and found to increase as the loading level was increased. Scanning electron microscopy (SEM) was used to assess the clay morphology and the dispersion of the attapulgite. SEM revealed the addition of attapulgite showed fibrillar structure of Nylon‐6/ATP composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Preparation of a xanthate‐terminated dextran by click chemistry: Application to the synthesis of polysaccharide‐coated nanoparticles via surfactant‐free ab initio emulsion polymerization of vinyl acetate
Authors: Bernard Julien , Save Maud , Arathoon Benoit , Charleux Bernadette
Published: March 2008

Stable monodisperse poly(vinyl acetate) (PVAc) submicronic latex particles were synthesized by ab initio batch emulsion polymerization using a dextran derivative from renewable resource as an efficient steric stabilizer. The dextranend‐functionalized by a xanthate moiety was synthesized by Huisgen's 1,3‐dipolar cycloaddition (click chemistry). It was applied as a macromolecular RAFT (reversible addition fragmentation chain transfer) agent in surfactant‐free emulsion polymerization of vinyl acetate to form in situ an amphiphilic block copolymer able to efficiently stabilize the latex particles. The method afforded the preparation of high solids content (27%) latices coated by dextran. Both the kinetic study and the molar mass analyses confirmed the involvement of the dithiocarbonate group in the emulsion polymerization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2845–2857, 2008
Precise Measurement of the Size of Nanoparticles by Dynamic Light Scattering with Uncertainty Analysis
Authors: Takahashi Kayori , Kato Haruhisa , Saito Takeshi , Matsuyama Shigetomo , Kinugasa Shinichi
Published: March 2008

Dynamic light scattering (DLS) is a powerful technique for the sizing of nanoparticles and characterization of their properties in the liquid phase. However, the precision of this technique remains unclear and therefore, in the current work, the precision of the DLS technique for sizing polystyrene latex suspensions and the uncertainty of the DLS data are estimated. Precise measurements of the short time correlation function at seven scattering angles and five different concentrations are performed for four kinds of polystyrene latex suspensions with diameters of 30–100 nm. The extrapolations of apparent diffusion coefficients to infinite dilution and to lower angles yield more precise values than those obtained at one angle and one concentration. The extrapolated particle size measured by DLS is compared to the size determined by a differential mobility analyzer (DMA) in air. Before the comparison, the intensity‐averaged size measured by DLS is recalculated to the number‐averaged size in the case of DMA from the particle size distribution. After the recalculation, consistent values of mean particle diameter are found to be between those obtained by DLS and DMA within the estimated uncertainties.
Particle Size Classification of Glass Particles Using Aerodynamic Jet Vectoring
Authors: Humes Zachary E. , Smith Barton L.
Published: March 2008

An experimental demonstration of a new, non‐contact particle characterization technique called Aerodynamic Vectoring Particle Sorting (AVPS) is presented. AVPS uses secondary blowing and suction control flows–flows that are a fraction of the jet flow rate–to sharply change the direction of a planar, particle‐laden jet. As the jet is vectored, particles present in the flow experience a resultant drag force, dependent upon their size, that balances inertia. Since this balance determines the particle's trajectory, vectoring the flow leads to a separation of particles downstream. This simple, low‐pressure‐drop sorting technique classifies particles with less risk of damage or contamination than currently available sorting devices.

Particles from 10–40 μm and 2.5 times the density of water have been sorted to an accuracy of 1.5 μm. Sorting of heavy particles such as these is accomplished at very low speeds, reducing the tendency of damage to the particles. Lighter particles are sorted at higher speeds. Particles from 5–40 μm and 0.6 times the density of water were sorted to an accuracy of 6.6 μm.

AVPS is also shown to be capable of concentrating aerosols. Our measurements indicate that an air sample containing water‐like particles can be concentrated by a factor of 10 using AVPS.
Lag effect of particulate air pollution on lung function in children
Authors: Min Jin‐Young , Min Kyoung‐Bok , Cho Sung‐Il , Paek Domyung
Published: March 2008

We assessed the relationship between particle air pollution and changes in lung function in children as measured by spirometry over time. Data were collected from air pollution and family health examinations of 181 subjects, aged 9–19 years, in a Korean community. The children performed lung function tests, and their height and weight were measured. Their parents responded to an interview regarding the children's history of disease. Data on air pollution were obtained from the Environmental Management Corporation, which is part of the Korean Ministry of the Environment. We found evidence that the declines in forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1) were significantly associated with the PM10 concentration for 37–60 hr preceding the lung function tests. The associations were consistent in the two‐pollutant models. Our findings suggest that exposure to PM10 may increase the risk of adverse health effects in children with respiratory symptoms or diseases. Pediatr Pulmonol. 2008; 43:476–480. © 2008 Wiley‐Liss, Inc.
The effect of gadolinium addition on the surface structure of Bi2O3–GeO2 glasses and vitroceramics
Authors: Simon V. , Ponta O. , Simon S. , Udvar D. A. , Neumann M.
Published: March 2008

Heavy metal oxide glasses and vitroceramics belonging to the Bi2O3–GeO2–Gd2O3 system are investigated. The changes induced by heat treatment in the elemental composition on sample surfaces are related to the local order changes. O 1s and Bi 4f core level X‐ray photoelectron spectra evidence the local order changes caused by gadolinium addition to the Bi2O3–GeO2 matrix and by partial crystallisation of the precursor glass samples. The addition of gadolinium to the Bi2O3–GeO2 glass matrix leads to a reduction of the number of bridging oxygens and a depolymerisation of the glass structure. The number of bridging oxygens increases on heat treatment of the samples. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
White‐beam synchrotron topographic characterization of antiparallel 180° domains in MgO doped near‐stoichiometric LiNbO3
Authors: Gao Lei , Wang Ji Yang , Liu Hong , Hu Xiao Bo , Zhu Pei Ping , Tian Yu Lian , Huang Wan Xia
Published: March 2008

The Czochralski grown MgO‐doped near‐stoichiometric LiNbO3 (N‐SLN) crystals have been investigated by using white‐beam synchrotron radiation topography. It was found that quasi‐periodic antiparallel 180° domains appeared frequently in y ‐cut (10$ \bar 1 $0) slice. Due to the different structure factors between positive and negative domains, at the wavelengths near the absorption edge of Nb atom, antiparallel 180° domains in MgO‐doped N‐SLN were revealed by anomalous scattering and the domain boundaries were visible by black‐white contrast from positive and negative domains. In the case of occurrence of anomalous scattering the ratio of |F (0006)|2 to |F (000$ \bar 6 $)|2 was calculated. The mechanisms of this quasi‐periodic domain inversion and the growth characteristics in MgO‐doped N‐SLN are also discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ag‐YBCO compounds as thermoelectric material
Authors: Rodríguez J. E.
Published: March 2008

In order to improve their thermoelectric properties, the transport properties of polycrystalline YBa2Cu3O7–δ (YBCO) perovskites were modified by partial substitutions of Cu by silver atoms and by submitting the samples to a thermal process at 600 °C. The Seebeck coefficient S (T), electrical resistivity ρ (T) and thermal conductivity κ (T) were measured in the temperature range between 77 K and 300 K. The Seebeck coefficient in all samples is positive in the measured temperature range and its magnitude increases with the Ag content from 30 μV/K to 130 μV/K. The behavior of the electrical resistivity changes from semiconducting to metallic as the Ag doping increases; its magnitude is always less than 0.9 mΩ cm. The thermal conductivity shows a weak linear temperature behavior and its magnitude decreases with Ag doping, which suggest that Ag atoms are efficient phonon‐scattering centers. In all samples κ (T) is less than 5 W/K m and in highly doped samples it reaches values close to 3.5 W/K m. From S (T), ρ (T) and κ (T) data the dimensionless thermoelectric figure of merit ZT (T) and the thermoelectric power factor PF(T) were calculated; these parameters reach maximum values close to 0.4 and 60 μW/K2cm, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
DFT studies on structure, mechanics and phase behavior of magnetic shape memory alloys: Ni2MnGa
Authors: Özdemir Kart S. , Uludog˘an M. , Karaman I. , Çag˘ın T.
Published: March 2008

Magnetic shape memory alloys (MSMAs) are the smart materials which can undergo a reversible structural phase transition when a magnetic field is applied. The experimentally most studied MSMA, Ni2MnGa, undergoes a martensitic phase transition from a high temperature cubic phase to a low temperature tetragonal phase. In this work, a detailed study of structure, magnetic and mechanical properties of Ni2MnGa in these phases were performed using density functional theory (DFT). The predicted lattice constant, bulk modulus, magnetic moments and elastic constants of the initial L21 structure are in good agreement with experimental results and previous calculations. We report the martensitic phase at c /a = 1.26 for non‐modulated and c /a = 0.93 for 5M modulated structures which are consistent with the experiments. Analysis of electronic density of states showed that the double minority spin peak appeared at the Fermi level is due to the hybridization of Ga 4p and Ni 3d states. The peaks in the minority spin in the cubic structure reverse their order during martensitic transformation. The elastic constants of martensitic phases were also calculated to encourage measurements of these quantities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effective dielectric response of nanostructured layers
Authors: Wormeester Herbert , Kooij E. Stefan , Poelsema Bene
Published: March 2008

The Maxwell Garnett effective medium theory was originally developed for a very small volume fraction of metal particles in a transparent medium. In contrast to the bulk situation, it can be applied to high coverages for thin metal particulate films and predicts the plasmon resonance energy accurately in contrast to the Bruggeman effective medium theory. The comparison of the Maxwell Garnett approach to a more rigorous analysis of particulate films with the Thin Island Film theory shows that also the plasma energy of the plasmon resonance is very accurately obtained with the simple effective medium theory. Also a quite accurate splitting of the resonance energy through particle interaction is obtained. However, interband transitions and the optical coupling of the layer with the effective medium response to the substrate lead to substantial differences compared to the dipole approximation of the rigorous Thin Island Film theory. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Etching‐back of uniaxially strained silicon on insulator investigated by spectroscopic ellipsometry
Authors: Himcinschi C. , Singh R. , Moutanabbir O. , Scholz R. , Reiche M. , Christiansen S. H. , Gösele U. , Zahn D. R. T.
Published: March 2008

Spectroscopic Ellipsometry was employed to study the etching process of uniaxially strained Si (sSi) layers obtained by direct wafer bonding of Si wafers in a mechanically bent state followed by thinning one of the Si wafers, the donor wafer, by the smart‐cut process, keeping the other, the handle wafer intact. The smart‐cut process requires a high dose hydrogen implantation into the donor wafer prior to bonding. As a result of the implantation conditions a ∼600 nm uniaxially sSi layer could be transferred onto the handle wafer. In order to thin down and smooth the surface damage of the transferred layer induced by the implantation and splitting process, the samples were dipped in a solution of tetra‐methyl ammonium hydroxide (TMAH). The thicknesses of the transferred sSi layers determined from ellipsometry were in good agreement with those obtained from Transmission Electron Microscopy (TEM), while the roughness values were matching those obtained from Atomic Force Microscopy (AFM). The etching rate has also been determined. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Depolarizing Mueller matrices: how to decompose them?
Authors: Ossikovski R. , Anastasiadou M. , Ben Hatit S. , Garcia‐Caurel E. , De Martino A.
Published: March 2008

The various decompositions of depolarizing Mueller matrices into products of basic optical devices, i.e. retarders, diattenuators and depolarizers, are critically revisited and discussed. Both classic as well as recently proposed factorizations are reviewed. Physical and calculation aspects such as depolarization and matrix singularity are comparatively addressed. The problems of physical realizability and matrix filtering are treated in connection with the sum decomposition of a depolarizing Mueller matrix. Experimental matrices are factorized using the different decompositions and physically interpreted. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rayleigh–Mie scattering ellipsometry as an in situ diagnostic for the production of “smart nanoparticles”
Authors: Weiß Raphaela , Hong Suk‐Ho , Ränsch Jens , Winter Jörg
Published: March 2008

We have utilised in situ Rayleigh–Mie scattering ellipsometry to analyse the growth process of amorphous hydrogenated carbon nitride (a‐C:H:N) nanoparticles synthesised in a plasma of nitrogen and acetylene. The validity of the measurements is shortly discussed. The complex refractive indices in dependence of the particle radius are carefully determined and compared with a‐C:H(:N) films which are deposited under similar conditions and analysed via multiple wavelength ellipsometry. Internal structures of the nanoparticles are then deduced from the change of optical constants during the growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical functions of AlAsSb characterized by spectroscopic ellipsometry
Authors: Mozume T. , Tanaka M. , Yoshimi A. , Susaki W.
Published: March 2008

Nominally undoped AlAsx Sb1–x layers with a thickness of 200 nm to 370 nm and arsenic mole fraction x of 0.325–0.872 were grown on Fe‐doped (001) InP substrates by solid‐source molecular beam epitaxy. Their optical properties were investigated over a wide photon range of 0.7 eV to 5 eV at room temperature using variable angle spectroscopic ellipsometry. The obtained data were analyzed using standard multilayer calculation schemes. The determined thicknesses of these layers were in good agreement with the calibrated normal growth rate. For photon energies below the AlAsSb band gap, which is the transparency region of the AlAsSb layer, pronounced Fabry–Perot interference oscillations due to the multiple internal reflections in the AlAsSb layer were observed. A clear blue shift of the energy gap of AlAsSb was observed as the As concentration increased. The refractive index decreased with an increase of the bandgap energy in the energy range of 0.7 eV to 2.1 eV. This trend is the same as that observed in conventional III–V alloy semiconductors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectroscopic ellipsometry study of Co‐doped TiO2 films
Authors: Águas H. , Popovici N. , Pereira L. , Conde O. , Branford W. R. , Cohen L. F. , Fortunato E. , Martins R.
Published: March 2008

Co‐doped TiO2 films were characterized by spectroscopic ellipsometry to determine their thickness, deposition rate and optical properties as function of substrate temperature and background gas composition. To fit the data we used a combination of a single Tauc–Lorentz oscillator with the Drude free electron model to take in account the free electrons present in the film. The Co doping and the addition of H2 to the gas phase during film growth cause the formation of a titanium oxide which containsfree electrons that absorb the energy of the red part of the spectrum, causing k to increase. The n of the films at 1.5 eV is about 2.3 eV. The fittings also show that the n of films decreases and k increases at the surface. This can be related to a segregation of Co to the surface, which in some cases, of high substrate temperature and high H2 flow during deposition, can lead to an even higher concentration of free electrons at the surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ellipsometric measurements of quantum confinement effects on higher interband transitions of Ge nanocrystals
Authors: Alonso M. I. , Garriga M. , Bernardi A. , Goñi A. R. , Lopeandia A. F. , Garcia G. , Rodríguez‐Viejo J. , Lábár J. L.
Published: March 2008

We studied the dielectric functions of Ge nanocrystals obtained by crystallization of amorphous Ge thin films embedded in SiO2. Partial crystallization of films was induced by thermal annealing. Crystalline regions gave rise to clear spectral features due to interband transitions whose critical point parameters correlated with the initial a‐Ge thickness. These changes were clearly attributed to quantum confinement effects. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of O2 partial pressure and substrate temperature on the plasma emission spectra and ZnO growth behavior
Authors: Liu M. , Ma C. Y. , Zhang Q. Y.
Published: March 2008

An on‐line measurement of optical emission spectrum (OES) was used to study the variation of Zn and O components in the plasma of ZnO film growth with reactive radio‐frequency magnetron sputtering method. It was found that the decline of all the Zn emission lines shows three different stages with the increase of oxygen partial pressure (PO), corresponding to metal sputtering (PO < 6.0 × 10–3 Pa), the compound sputtering (PO > 5.0 × 10–2 Pa), and the transition range (6.0 × 10–3 Pa to 5.0 × 10–2 Pa), respectively. In the stage of compound sputtering, a critical oxygen pressure is found at about 1.5 × 10–1 Pa. At the oxygen pressures below and above the critical pressure, the film growth is found to be O‐controlled and Zn‐controlled, respectively. Similarly, a critical substrate temperature is found at about 550 °C. At the temperatures above the critical temperature, the variation of Zn472.6 intensity is more obvious, suggesting the deposited films is more close to the stoichiometric ratio than the films deposited at the lower temperatures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Antitumor effects of saponin extract from Patrinia villosa (Thunb.) Juss on mice bearing U14 cervical cancer
Authors: Zhang Tao , Li Qingwang , Li Kun , Li Yurong , Li Jian , Wang Guijie , Zhou Shaobo
Published: March 2008

Saponin extracted from Patrinia villosa (Thunb.) Juss (SPVJ) is a Chinese medicine which is used widely by traditional medicine doctors. In this study, the antitumor effects and the possible mechanisms of SPVJ were investigated in mice bearing U14 cervical cancer. The results showed that SPVJ (50 mg/kg and 100 mg/kg) effectively reduced the weight of U14 cervical tumor (35.1% and 57.1%, respectively). Compared with the control group, SPVJ (100 mg/kg) significantly increased tumor cells in the G0/G1 phase (38.1% vs 68.5%), increased the number of cells in apoptosis (9.4% vs 28.9%) and G0/G1 phase and decreased the number of cells in S phase (41% vs 26.2%) and G2/M (20.9% vs 5.3%), inhibited proliferating cell nuclear antigen (PCNA) of tumor cell (80.6% vs 21.8%), decreased the expression of mutant p53 (66.4% vs 33.5%) and bcl‐2 protein (78.2% vs 20.3%). The mechanism of the SPVJ antitumor effect might be associated with inhibition of tumor cells in G0/G1 phase, inducing apoptosis and inhibiting the expression of PCNA, mutant P53 and Bcl‐2 protein. Copyright © 2008 John Wiley & Sons, Ltd.
Effect of green tea and (‐)‐epigallocatechin gallate on ethanol‐induced toxicity in HepG2 cells
Authors: Lee Sang Il , Kim Hyo Jung , Boo Yong Chool
Published: March 2008

Despite the continuing reports supporting the hepatoprotective effects of green tea against ethanol intoxication, there remain controversies regarding the active compound(s) and molecular mechanism. These issues were addressed in the present study using cultured HepG2 cells exposed to a lethal dose of ethanol. Gamma‐glutamyl transferase (GGT) was chosen as a marker of ethanol toxicity because it is widely used in clinics. When the cells were treated with ethanol at various concentrations, there was a dose‐dependent increase of GGT activity in the culture media and loss of cell viability. Pretreatment of the cells with green tea extract attenuated the changes significantly. Among the green tea constituents, (‐)‐epigallocatechin gallate (EGCG) attenuated the ethanol cytotoxicity effectively, whereas l‐theanine and caffeine had no effects. The ethanol cytotoxicity was also attenuated by alcohol dehydrogenase inhibitor 4‐methyl pyrazol and GGT inhibitor acivicin as well as by thiol modulators such as S‐adenosyl‐l‐methionine, N‐acetyl‐l‐cysteine and glutathione. EGCG failed to prevent the intracellular glutathione loss caused by ethanol, but it appeared to be a strong GGT inhibitor. Therefore the cytoprotective effects of green tea could be attributed to the inhibition of GGT activity by EGCG. This study suggests that GGT inhibitors including EGCG may provide a novel strategy for attenuating ethanol‐induced liver damage. Copyright © 2008 John Wiley & Sons, Ltd.
A novel function of bamboo extract in relieving lipotoxicity
Authors: Panee Jun , Liu Wanyu , Lin Yanling , Gilman Christy , Berry Marla J.
Published: March 2008

Lipotoxicity is closely related to the etiology and complications of type 2 diabetes mellitus. This study investigated the protective effect of an extract from bamboo Phyllostachys edulis against palmitic acid (PA)‐induced lipoapoptosis. The lipo‐detoxification function of the bamboo extract (BEX) was evaluated using cell culture models. Cell viability was measured by MTT assay and cell apoptosis was monitored by Annexin V staining. Cellular uptake of fluorescent free fatty acid (FFA) analog was measured by flow cytometry. Protein levels of total protein kinase B (Akt) and phosphorylated Akt (p‐Akt) were measured by western blotting. The results show that co‐incubating BEX with mouse myoblast C2C12 cells had no effect on the cellular uptake of FFA, but dramatically decreased PA‐induced cell apoptosis and protected cell viability. A similar antilipotoxicity effect of BEX was observed in other mammalian cells. BEX significantly decreased the protein levels of both Akt and p‐Akt in C2C12 cells under normal cell culture conditions but not under lipotoxic conditions, indicating the regulatory effect of BEX on cell signaling pathways and its response to a high FFA environment. This study demonstrated a novel function of bamboo extract in preventing lipotoxicity in mammalian cells, implicating a promising phytotherapeutic approach for lipo‐detoxification. Copyright © 2008 John Wiley & Sons, Ltd.
Antimicrobial activity of some medicinal plants of the Cerrado, Brazil
Authors: Costa E. S. , Hiruma‐Lima C. A. , Lima E. O. , Sucupira G. C. , Bertolin A. O. , Lolis S. F. , Andrade F. D. P. , Vilegas W. , Souza‐Brito A. R. M.
Published: March 2008

In order to determine the potential of Cerrado plants as sources of antimicrobial activity, the phytochemical screening of ethanol extracts from Virola surinamensis, Qualea grandiflora, Alchornea castaneifolia, Hancornia speciosa and Curatella americana traditionally used in folk medicine are reported. Copyright © 2008 John Wiley & Sons, Ltd.
Cancer chemoprotective effects of Curcuma xanthorrhiza
Authors: Park Jae Hee , Park Kwang Kyun , Kim Mi Jeong , Hwang Jae Kwan , Park Sun Kyu , Chung Won Yoon
Published: March 2008

Curcuma xanthorrhiza Roxb. (Zingiberaceae) is a medicinal plant widely spread in South East Asia. In particular, it is commonly used not only for food and medicinal purposes in Indonesia, but also for the topical treatment of acne and skin inflammations as Thai traditional medicine. It was found that the methanol extract of C. xanthorrhiza inhibited significantly 7,12‐dimethylbenz[a]anthracene (DMBA)‐induced bacterial mutagenesis of Salmonella typhimurium TA98 and TA100 in the presence of S9, and the mutagenesis induced by H2O2 and tert‐butylhydroperoxide in S. typhimurium TA102, respectively. In addition, 12‐O‐tetradecanolyphorbol‐13‐acetate(TPA)‐induced mouse ear edema was markedly inhibited by pretreatment with C. xanthorrhiza extract. C. xanthorrhiza extract dose‐dependently reduced ODC expression in mouse skin with TPA‐induced acute inflammation. Furthermore, repeated treatment with 0.1% C. xanthorrhiza extract reduced the average number of tumors per mouse and the percentage of tumor‐bearing mice in a multistage mouse skin carcinogenesis induced by DMBA and TPA. These results demonstrate that the methanol extract of C. xanthorrhiza possesses cancer chemopreventive potential. Copyright © 2008 John Wiley & Sons, Ltd.
Hypericum perforatum and substance dependence: a review
Authors: Uzbay Tayfun I.
Published: March 2008

Substance abuse and dependence is a serious problem throughout the world. The development of several types of dependence remedies has medical, social and economical significance. In particular, alcohol and tobacco are the most commonly abused substances worldwide. An extract of Hypericum perforatum L. (HPE) displayed a clear antidepressant action and it has been used for the treatment of mild to moderate depression. Recent reports imply that HPE may be effective in the treatment of substance abuse. Studies have focused on alcohol and nicotine dependence. In this review, the effects of HPE on substance dependence and its possible benefit have been discussed in the light of current literature. Copyright © 2008 John Wiley & Sons, Ltd.
Carbon isotope determination for separate components of heterogeneous materials using coupled thermogravimetric analysis/isotope ratio mass spectrometry
Authors: Manning David A. C. , Lopez‐Capel Elisa , White Maggie L. , Barker Sam
Published: March 2008

A gas‐tight thermal analysis system (Netzsch STA 449C Jupiter) has been connected to an isotope ratio mass spectrometer (PDZ Europa 20‐20) via an interface containing an oxidizing furnace, water trap, and gas‐sampling valve. Using this system, δ13C has been measured for CO2 derived from the thermal decomposition of carbonate and oxalate minerals and organic materials at temperatures that correspond to different decomposition events. There is close agreement between measured and published δ13C values for carbonate and oxalate minerals, which have simple decarbonation reactions on heating. Cellulose and lignin‐rich materials show much more complex thermal decomposition, reflecting differences in their purity and structure, and measured δ13C values vary with the temperature of gas sampling. Provided that measurements are made at temperatures that correspond to the decomposition of cellulose and lignin (indicated by maximum weight loss), internally consistent data can be obtained. However, measurements for cellulose and lignin are systematically enriched in δ13C (by up to 1.4‰) with respect to those reported for reference materials, possibly due to the slower combustion kinetics (compared with EA‐IRMS). Thermogravimetric analysis/isotope ratio mass spectrometry (TG‐IRMS) is ideal for materials and samples for which it is not possible to use other isotopic measurement techniques, for example because of sample heterogeneity. Copyright © 2008 John Wiley & Sons, Ltd.
On‐line measurements of δ15N in biological fluids by a modified continuous‐flow elemental analyzer with an isotope‐ratio mass spectrometer
Authors: Wang Xu , Feng Lianjun , Zhang Fusong , Ding Zhongli
Published: March 2008

A modified continuous‐flow elemental analyzer coupled to an isotope‐ratio mass spectrometer (modified EA‐IRMS) was tested for on‐line δ15N measurement on urea solution and biological fluids (e.g. urine). The elemental analyzer configuration was adapted by adding a U‐shaped cold trap and an X‐pattern four‐way valve for on‐line trapping/venting of water from the liquid samples. Results indicate that the δ15N ratios show little variation (standard deviation (SD) = 0.05‰) with a sample size above the equivalent N yield of 0.2 mg urea (0.092 mg N) when the mass spectrometer conditions were carefully optimized. By contrast, a significant logarithmic decrease in δ15N with sample size was observed but this can be offset by applying a linearity correction or blank correction when the sample size is between equivalent N yields of 0.05 and 0.2 mg urea. The blank corrected δ15N ratios give an overall precision of ∼0.16‰ whereas the average precision for δ15N corrected using combined linearity and shift correction is 0.05‰. The relatively large variation in blank corrected δ15N values may be attributed to the variability of the blank δ15N in the sequence. Therefore, the blank correction should be carefully performed in routine measurements. As a result, the linearity range of a modified EA‐IRMS can be extended to a minimum sample size of 0.023 mg N. In addition, the reproducibility of the new system is good, as indicated by the precision (<0.2‰) for a set of standards and unknowns. The data show that fluids containing nitrogen can be successfully analyzed in the modified EA‐IRMS. Copyright © 2008 John Wiley & Sons, Ltd.
Spiking of serum specimens with exogenous reporter peptides for mass spectrometry based protease profiling as diagnostic tool
Authors: Findeisen Peter , Peccerella Teresa , Post Stefan , Wenz Frederik , Neumaier Michael
Published: March 2008

Serum is a difficult matrix for the identification of biomarkers by mass spectrometry (MS). This is due to high‐abundance proteins and their complex processing by a multitude of endogenous proteases making rigorous standardisation difficult. Here, we have investigated the use of defined exogenous reporter peptides as substrates for disease‐specific proteases with respect to improved standardisation and disease classification accuracy. A recombinant N‐terminal fragment of the Adenomatous Polyposis Coli (APC) protein was digested with trypsin to yield a peptide mixture for subsequent Reporter Peptide Spiking (RPS) of serum. Different preanalytical handling of serum samples was simulated by storage of serum samples for up to 6 h at ambient temperature, followed by RPS, further incubation under standardised conditions and testing for stability of protease‐generated MS profiles. To demonstrate the superior classification accuracy achieved by RPS, a pilot profiling experiment was performed using serum specimens from pancreatic cancer patients (n = 50) and healthy controls (n = 50). After RPS six different peak categories could be defined, two of which (categories C and D) are modulated by endogenous proteases. These latter are relevant for improved classification accuracy as shown by enhanced disease‐specific classification from 78% to 87% in unspiked and spiked samples, respectively. Peaks of these categories presented with unchanged signal intensities regardless of preanalytical conditions. The use of RPS generally improved the signal intensities of protease‐generated peptide peaks. RPS circumvents preanalytical variabilities and improves classification accuracies. Our approach will be helpful to introduce MS‐based proteomic profiling into routine laboratory testing. Copyright © 2008 John Wiley & Sons, Ltd.
Strategic networks and entrepreneurial ventures
Authors: Stuart Toby E. , Sorenson Olav
Published: March 2008

Much research suggests that social networks shape the emergence and development of nascent ventures. Scholars have argued that founders' and firms' networks influence innovation and the identification of entrepreneurial opportunities, as well as facilitate the mobilization of resources for growth and the harvesting of value from fledgling firms. It is not an exaggeration to claim that existing empirical findings point to the centrality of networks in every aspect of the entrepreneurial process. However, with exceptions so few they may be counted on one hand, this research untenably treats network structures as exogenous—in other words, as if entrepreneurs and enterprises do not pursue valuable connections. In this article, we review the literature on networks in entrepreneurial contexts, argue that it disproportionately focuses on the consequences of networks at the expense of research on their origins, and consider the implications for the literature of the fact that most entrepreneurs and young ventures are strategic in their formation of relations. We then articulate a research agenda composed of five areas of inquiry we consider critical to a better understanding of networks and entrepreneurship. Copyright © 2008 Strategic Management Society.