bluuebunny/crossref_metadata_2025 huggingface dataset:
Phenolic diterpene and α‐tocopherol contents in leaf extracts of 60 Salvia species
Authors: Abreu Maria E , Müller Maren , Alegre Leonor , Munné‐Bosch Sergi
Published: October 2008

BACKGROUND: Carnosic acid and carnosol, the two major phenolic diterpenes present in rosemary and sage extracts, have received attention in food science and biomedicine because of their potent antioxidant properties. In plants, these compounds have been identified as being present in some species of the family Lamiaceae, but there is still little information about their distribution within the plant kingdom. The aim of the present study was to gain a better understanding of the occurrence of these compounds within leaf extracts of the genus Salvia and also to examine to what extent leaf senescence may influence their accumulation in relation to that of α‐tocopherol (vitamin E).

RESULTS: Methanolic leaf extracts of 60 species of the genus Salvia were tested for the presence of carnosic acid and carnosol. These two diterpenes were detected in 48 and 27 species respectively. In contrast, α‐tocopherol was present in all species examined. Leaf senescence in Salvia officinalis resulted in α‐tocopherol increases by up to 5.5‐fold, while carnosic acid and carnosol increased by up to 18 and 290% respectively. Isorosmanol, an oxidation product of carnosic acid, increased by up to 2.1‐fold in senescing leaves.

CONCLUSION: It was found that, while α‐tocopherol is ubiquitous in the genus Salvia, phenolic diterpenes are present in several but not all species. It was also shown that leaf senescence may increase the yield of both phenolic diterpenes and α‐tocopherol in sage extracts. Copyright © 2008 Society of Chemical Industry
Protein interactions with cyanidin‐3‐glucoside and its influence on α‐amylase activity
Authors: Wiese Stefanie , Gärtner Sonja , Rawel Harshadrai M. , Winterhalter Peter , Kulling Sabine E.
Published: October 2008

BACKGROUND: Recent studies indicate that the bioavailability of anthocyanins is extremely low. One of the possible reasons could be their binding to proteins. Therefore, the binding affinity of cyanidin‐3‐glucoside (Cy3glc) to HSA and α‐amylase was investigated by the quenching of protein tryptophan fluorescence. From data obtained, the binding constants and the free Gibbs energy were calculated. The changes in conformation of the proteins tested were studied with circular dichroism and the influence of binding on α‐amylase activity determined.

RESULTS: Cy3glc quenched the tryptophan fluorescence and upon ligand binding a change in protein structure was observed related to the corresponding decrease in the α‐amylase activity. The association constants of 25 to 77 × 103 L mol−1 were calculated for different proteins, indicating weak interactions of non‐covalent nature. Competitive binding with HSA in the presence of 8‐anilino‐1‐naphthalene sulfonic acid suggest involvement of hydrophobic interactions, in the case of HSA the possible site being subdomain IIA.

CONCLUSION: The strongest affinity of Cy3glc for HSA being at pH 7 underlines its potential in transport and distribution of the phenolic compounds in organisms. An influence on salivary amylase activity is possible when drinking berry juices with high anthocyanins content. Copyright © 2008 Society of Chemical Industry
Chemical composition and in vitro control of agricultural plant pathogens by the essential oil and various extracts of Nandina domestica Thunb.
Authors: Bajpai Vivek K , Lee Tae Jong , Kang Sun Chul
Published: October 2008

BACKGROUND: The aims of this study were to examine the chemical composition of the essential oil isolated from the floral parts of Nandina domestica Thunb. by hydrodistillation, and to test the efficacy of essential oil and various leaf extracts (n‐hexane, chloroform, ethyl acetate and methanol) as an antifungal potential against a panel of agricultural plant pathogens.

RESULTS: The GC‐MS analysis determined that 79 compounds, which represented 87.06% of total oil, were present in the oil containing mainly 1‐indolizino carbazole (19.65%), 2‐pentanone (16.4%), mono phenol (12.1%), aziridine (9.01%), methylcarbinol (4.6%), ethanone (3.3%), furfural (2.96%), 3,5‐dimethylpyrazole (1.29%) and 2(5H)‐furanone (1.32%). The oil (1000 ppm disc−1) and the leaf extracts (1500 ppm disc−1) revealed remarkable antifungal effect against Fusarium oxysporum, Fusarium solani, Phytophthora capsici, Colletotrichum capsici, Sclerotinia sclerotiorum, Botrytis cinerea and Rhizoctonia solani in the growth inhibition range of 53.3–64.3% and 33.3–56.0%, respectively, along with their respective values for mimimum inhibitory concentration (MIC) ranging from 125 to 1000 µg mL−1 and 500 to 2000 µg mL−1. The values for minimal fungicidal concentration (MFC) of the oil and extracts were obtained in the range of 125 to 1000 µg mL−1 and 500 to 2000 µg mL−1, respectively. The essential oil also had a strong detrimental effect on spore germination of all the plant pathogens tested along with concentration as well as time‐dependent kinetic inhibition of B. cinerea.

CONCLUSION: The results obtained in this study demonstrate that N. domestica mediated oil and extracts could become potential alternatives to synthetic fungicides for controlling certain important agricultural plant pathogenic fungi. Copyright © 2008 Society of Chemical Industry
Determination of estrogens and their metabolites in water using C30 SPE‐LC‐MS
Authors: Yan Wei , Zhao Lixia , Feng Qinzhong , Lin Jin‐Ming
Published: October 2008

Triacontyl bonded silica (C30) material was applied as solid‐phase extraction (SPE) sorbent and an SPE‐LC‐MS method was established for the determination of eight estrogens and their metabolites in water samples. Compared to commercial C18 SPE cartridge, the performance of C30 was evaluated in various important SPE conditions, such as sorbent mass, elution solvent and its volume, loading flow rate, and sample loading volume. The results showed a superior performance of C30–C18 by the shorter treatment time and fewer required elution solvent. In the optimum conditions, the results showed good recoveries (80.5–109.4%), excellent linear relationships (0.02–1 ng/mL, except 2‐MeO‐E2), high precisions (lower than 10.0% RSD for both low and high spiked concentration), and low LODs (1–16 ng/L). Method validation using C30 packed cartridge was also testified with spiked real water samples, including tap water and river water. Satisfy results demonstrated the feasibility of C30 SPE to the analysis for real environmental waters.
Identification of collagen types in tissues using HPLC‐MS/MS
Authors: Pataridis Statis , Eckhardt Adam , Mikulíková Katerina , Sedláková Pavla , Mikšík Ivan
Published: October 2008

A method for the determination and quantification of collagen types I–V in rat tissues has been developed. This method is based on collagen fragmentation by cyanogen bromide followed by trypsin digestion. After that, HPLC‐MS/MS (HPLC coupled to an IT mass spectrometer) analyses of the resulting peptide mixtures (peptide maps) were performed. Specific peptides for each collagen type were selected. According to online databases, these peptides are present in human, bovine, and rat collagens. As a result, this method can be potentially applied to other species' tissues as well, such as human tissues, and provides a universal and simple method of quantifying collagen types. The applicability of this method for analyzing collagen types was demonstrated on rat tissues (skin, tendon, and aorta).
Separation and analysis of acylglycerols by chromatographic methods
Authors: De Clercq Nathalie , Foubert Imogen , Dewettinck Koen
Published: October 2008

Many studies in lipid analysis require separation and isolation of various acylglycerol classes for subsequent analysis, research and use. Different chromatographic techniques can be used for this purpose. The most desirable method should be rapid, convenient and inexpensive, provide a high yield and supply as much information as possible about each compound with minimal interference or overlaps with other similar components. This article discusses some methods that can be used to separate acylglycerols.
Influence of Clay Modification on the Properties of Resol Nanocomposites
Authors: Manfredi Liliana B. , Puglia Debora , Tomasucci Annalisa , Kenny José M. , Vázquez Analía
Published: October 2008

Two organically modified (Cloisite® 30B and 10A) and one unmodified clay (Cloisite® Na) were added to a resol‐type phenolic prepolymer. The modified montmorillonites showed a better dispersion in the prepolymer. The dispersion of the clay, the chemical structure as well as the thermal degradation behavior of the cured polymer and nanocomposites were studied. It was observed that the addition of Cloisite® Na leads to enhanced crosslinking of the cured polymer, leading to a higher activation energy for thermal degradation. The resol with Cloisite® 10A contained a higher percentage of voids, which seems to be one of the major factors that reduce hardness and adhesive strength when the nanocomposite was applied to a metal substrate.

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An analogue method for simultaneous prediction of surface weather parameters at a specific location in the Western Himalaya in India
Authors: Singh D. , Dimri A. P. , Ganju A.
Published: October 2008

Avalanches in the Western Himalaya cause loss of life and damage property every year. To reduce such losses avalanche forecasting is practiced. This technique requires information about various surface weather parameters at least a couple of days in advance. In view of the above requirement, an analogue method has been employed to predict maximum, minimum and ambient temperatures, average wind speed, surface pressure and relative humidity at a specific location in the Western Himalaya. Predictions for surface weather parameters 3 days in advance have been attempted using information of past synoptic situations corresponding to the current situation searched from a database through Euclidean distance. Surface weather observations of the past 16 winters (1989–1990 to 2005–2006) have been used to develop the model. The model has been tested with independent data set of 166 days of winter 2006–2007. The forecast accuracy for maximum, minimum and ambient temperature falls in the range 74.7–85.5, 64.2–81.8 and 58.5–79.9% within an error limit of 3 °C for day 1, day 2 and day 3. Forecast accuracy for prediction of average wind speed is in the range 65.7–70.9% and it is in the range 73.7–82.5% for atmospheric pressure with same error limit as temperature (with respective units) for day 1, day 2 and day 3. Accuracy for the prediction of relative humidity is in the range 58.5–69.3%, within an error limit of 20% for all three days. The root mean square error (RMSE) and mean absolute error (MAE) of each weather parameter have been computed to test the prediction error of the model. The results suggest that the analogue method holds promise for simultaneous prediction of surface weather parameters with reasonable accuracy. Predicted surface weather parameters have been used for assessing future avalanche situations with reasonable confidence. Copyright © 2008 Royal Meteorological Society
Modulation of the postprandial phase by β‐glucan in overweight subjects: Effects on glucose and insulin kinetics
Authors: Nazare Julie‐Anne , Normand Sylvie , Oste Triantafyllou Angeliki , Brac de la Perrière Aude , Desage Michel , Laville Martine
Published: October 2008

Decreasing the postprandial glucose response is potentially of major importance to public health when low‐glycemic index or high‐fibre content foods are associated with a decreased risk of diabetes. We investigated in overweight subjects the effect of adding β‐glucan (BG) to a polenta (Pol) meal on postprandial metabolism and glucose bioavailability using stable isotopes. In this single‐blind, randomized, crossover trial, 12 subjects ate two meals containing Pol with (Pol + BG) or without (Pol) 5 g BG. Concentrations of glucose, insulin, C‐peptide, nonesterified fatty acids, triacylglycerol, total and exogenous glucose kinetics were assessed for 6 h postprandially. The kinetics of total and exogenous glucose importantly differed between the meals, but not the quantity of total and exogenous glucose appearing in plasma. Less total and exogenous glucose appeared during the first 120 min after the Pol + BG meal; the phenomenon was then reversed (both p < 0.0001). After 120 min, glucose and insulin responses declined, but remained higher after the Pol + BG meal (p < 0.05) in parallel to the inhibition of lipolysis. The endogenous glucose production (EGP) was significantly more inhibited after the Pol + BG meal. The addition of BG slowed the appearance of glucose in plasma, resulting in longer‐lasting insulin secretion which exerted a prolonged inhibition of EGP and lipolysis.
Regulation of β‐catenin and connexin‐43 expression: Targets for sphingolipids in colon cancer prevention
Authors: Simon Kirk W. , Roberts Paul C. , Vespremi Michael J. , Manchen Steve , Schmelz Eva M.
Published: October 2008

Sphingolipid metabolites are generated throughout the intestinal tract after hydrolysis of orally administered complex sphingolipids and significantly suppress colon cancer in carcinogen‐treated CF1 mice. In the present study, the mechanisms of tumor suppression by dietary sphingolipids were investigated. Changes in select genes that are critical in early stages of colon cancer were analyzed in the colonic mucosa of dimethylhydrazine‐treated CF1 mice fed AIN76A diet with or without 0.05% sphingomyelin (SM). Supplementation with SM did not significantly alter mRNA levels of most of the selected genes. However, a downregulation of β‐catenin (p = 0.007) and increased protein levels of connexin‐43 (p = 0.017) and Bcl‐2 (p = 0.033) were observed in SM‐fed animals. This suggests that sphingolipids may be regulating specific post‐transcriptional events to reverse aberrant expression of individual proteins. Since the dysregulation of β‐catenin metabolism and its transcriptional activity in addition to a decreased intercellular communication has been causally linked to the development of colon cancer while a low Bcl‐2 expression is associated with a worse prognosis in colon cancer, the reversal of these early changes may be important events in the prevention of colon cancer by orally administered sphingolipids, and may provide specific molecular biomarkers for sphingolipid efficacy in vivo.
Acute urodynamic effects of percutaneous posterior tibial nerve stimulation on neurogenic detrusor overactivity in patients with Parkinson's disease
Authors: Kabay Sibel Canbaz , Kabay Sahin , Yucel Mehmet , Ozden Hilmi
Published: October 2008

Aims

Lower urinary tract dysfunction is often occurs in patients with Parkinson's disease (PD), that is primarily induced by neurogenic detrusor overactivity (NDO) and negatively effect the quality of the patient's life. The aim of this study is to evaluate the acute effects of posterior tibial nerve stimulation (PTNS) on the urodynamic findings in the PD patients with NDO.

Methods

Thirty‐two patients with PD (19 [59.3%] men and 13 [40.6%] women) with NDO were included in the study. Mean age of the patients was 64.2 ± 8.7 years (range 44–78). Urodynamic studies before and during PTNS were performed. Electrical stimulation was applied unilaterally from the medial malleolus and posterior to the edge of the tibia by using charge‐compensated 200 µsec pulses with a pulse rate of 20 Hz. Mean first involuntary detrusor (1st IDCV) contractions and means maximum cystometric capacity (MCC) before and during PTNS was compared.

Results

Mean 1st IDCV on standard cystometry was 145.2 ± 41.1 (55–265) ml, while it was 244.7 ± 51.7 (145–390) ml during PTNS. MCC on standard cystometry was 204.8 ± 40.5 (115–320) ml, while it was 301.2 ± 51.5 (230–395) ml during stimulation. Mean 1st IDC and mean MCC were significantly improved during PTNS.

Conclusions

These results have demonstrated the objective acute effect of PTNS on urodynamic parameters. PTNS is acutely effective to suppress detrusor overactivity in PD patients. Neurourol. Urodynam. 28:62–67, 2009. © 2008 Wiley‐Liss, Inc.
1H and 31P NMR studies indicate reduced bile constituents in patients with biliary obstruction and infection
Authors: Bala Lakshmi , Tripathi Pratima , Bhatt Ganesh , Das Kshaunish , Roy Raja , Choudhuri Gourdas , Khetrapal C. L.
Published: October 2008

Patients with extrahepatic biliary obstruction present with impairment of the normal bile flow, with jaundice and cholangitis as common complications. 1H and 31P NMR quantitative analysis of bile specimens from patients with extrahepatic biliary obstruction (n = 80) (with/without jaundice and cholangitis separately and together) was carried out for the chief biliary constituents to determine the relationship between biliary constituents and jaundice (serum bilirubin concentration ≥1.0 mg/dL) and cholangitis (total leucocyte count >11 000 cells/mm3 and/or fever >38.5°C with/without bile culture positivity). Compared with controls (patients without jaundice and cholangitis), median indices of the chief biliary constituents (total bile acids, cholesterol, phosphatidylcholine and inorganic phosphate) were significantly suppressed in patients with cholangitis and/or jaundice. Quantities of total bile acids, cholesterol and phosphatidylcholine correlated negatively with the quantity of bilirubin and with cholangitis, i.e. total leucocyte count. Suppression of biliary constituents correlated significantly with the severity of jaundice and cholangitis. The decrease in biliary constituents in the presence of jaundice and cholangitis is possibly the result of downregulation of the function of transporters located at the canalicular side of hepatocytes, leading to their suppressed indices in bile. This information may have implications in the examination of bile for clinical studies. Copyright © 2008 John Wiley & Sons, Ltd.
An SPH shell formulation for plasticity and fracture analysis in explicit dynamics
Authors: Maurel B. , Combescure A.
Published: October 2008

This paper introduces a new modeling method suitable for the simulation of shell fracture under impact. This method relies on an entirely meshless approach based on the smoothed particle hydrodynamics (SPH) method. The paper also presents the SPH shell formulation being used as well as the different test cases used for its validation. A plasticity model of the global type throughout the thickness is also proposed and validated. Finally, in order to illustrate the capabilities of the method, fracture simulations using a simplified fracture criterion are presented. Copyright © 2008 John Wiley & Sons, Ltd.
A random field model for generating synthetic microstructures of functionally graded materials
Authors: Rahman Sharif
Published: October 2008

This article presents a new level‐cut, inhomogeneous, filtered Poisson random field model for representing two‐phase microstructures of statistically inhomogeneous, functionally graded materials with fully penetrable embedded particles. The model involves an inhomogeneous, filtered Poisson random field comprising a sum of deterministic kernel functions that are scaled by random variables and a cut of the filtered Poisson field above a specified level. The resulting level‐cut field depends on the Poisson intensity, level, kernel functions, random scaling variables, and random rotation matrices. A reconstruction algorithm including model calibration and Monte Carlo simulation is presented for generating samples of two‐phase microstructures of statistically inhomogeneous media. Numerical examples demonstrate that the model developed is capable of producing a wide variety of two‐ and three‐dimensional microstructures of functionally graded composites containing particles of various sizes, shapes, densities, gradations, and orientations. An example involving finite element analyses of random microstructures, leading to statistics of effective properties of functionally graded composites, illustrates the usefulness of the proposed model. Copyright © 2008 John Wiley & Sons, Ltd.
Simultaneous untangling and smoothing of moving grids
Authors: López Ezequiel J. , Nigro Norberto M. , Storti Mario A.
Published: October 2008

In this work, a technique for simultaneous untangling and smoothing of meshes is presented. It is based on an extension of an earlier mesh smoothing strategy developed to solve the computational mesh dynamics stage in fluid–structure interaction problems. In moving grid problems, mesh untangling is necessary when element inversion happens as a result of a moving domain boundary. The smoothing strategy, formerly published by the authors, is defined in terms of the minimization of a functional associated with the mesh distortion by using a geometric indicator of the element quality. This functional becomes discontinuous when an element has null volume, making it impossible to obtain a valid mesh from an invalid one. To circumvent this drawback, the functional proposed is transformed in order to guarantee its continuity for the whole space of nodal coordinates, thus achieving the untangling technique. This regularization depends on one parameter, making the recovery of the original functional possible as this parameter tends to 0. This feature is very important: consequently, it is necessary to regularize the functional in order to make the mesh valid; then, it is advisable to use the original functional to make the smoothing optimal. Finally, the simultaneous untangling and smoothing technique is applied to several test cases, including 2D and 3D meshes with simplicial elements. As an additional example, the application of this technique to a mesh generation case is presented. Copyright © 2008 John Wiley & Sons, Ltd.
Point vortex models of bluff body wakes
Authors: Stremler Mark A. , Brøns Morten
Published: October 2008

Periodic point vortex configurations can be used as reduced‐order models of vorticity‐dominated wakes behind bluff bodies. The staggered Kármán street is considered the canonical representation of these vortex wakes. However, the streamline topology of this configuration is structurally unstable. Slight variations in the intervortex separations cause fluid to wind through the street, which has implications for transport and mixing in vortex wakes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element differential forms
Authors: Arnold Douglas N. , Falk Richard S. , Winther Ragnar
Published: October 2008

A differential form is a field which assigns to each point of a domain an alternating multilinear form on its tangent space. The exterior derivative operation, which maps differential forms to differential forms of the next higher order, unifies the basic first order differential operators of calculus, and is a building block for a great variety of differential equations. When discretizing such differential equations by finite element methods, stable discretization depends on the development of spaces of finite element differential forms. As revealed recently through the finite element exterior calculus, for each order of differential form, there are two natural families of finite element subspaces associated to a simplicial triangulation. In the case of forms of order zero, which are simply functions, these two families reduce to one, which is simply the well‐known family of Lagrange finite element subspaces of the first order Sobolev space. For forms of degree 1 and of degree n − 1 (where n is the space dimension), we obtain two natural families of finite element subspaces, unifying many of the known mixed finite element spaces developed over the last decades. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectral filtering for ultra‐fast mode‐locking in the normal dispersive regime
Authors: Bale Brandon G. , Kutz J Nathan
Published: October 2008

A theoretical model is developed which characterizes the physical process responsible for generating ultra‐short, high‐energy, mode‐locked pulses in a normal GVD laser cavity with spectral filtering. Two physical parameters are critical to achieving optimal performance: the ratio of the filter bandwidth to the gain bandwidth and the placement of the output coupler in the laser cavity. The spectral filtering allows for the high‐energy of typical normal GVD laser cavities to be maintained while the pulse intensity doubles and the FWHM reduces by an order of magnitude. This phenomenon is generic and ubiquitous to normal GVD mode‐locking. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SPSA vs Simplex in statistical machine translation optimization
Authors: Lambert Patrik , Banchs Rafael E.
Published: October 2008

Most statistical machine translation systems are combinations of various models and tuning scaling factors is an important step. However, this optimisation problem is hard because the objective function has many local minima and the available algorithms cannot achieve a global optimum. Consequently, optimisations starting from different initial settings can converge to fairly different solutions. We present tuning experiments with the Simultaneous Perturbation Stochastic Approximation (SPSA) algorithm, and compare them with the widely used downhill simplex method. With IWSLT 2005 Chinese‐English data, both methods showed similar performance, but SPSA was more robust to the choice of initial settings. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On some topological and variational properties of a model for reconstructing three‐dimensional transparent images with self‐occlusions
Authors: Bellettini Giovanni
Published: October 2008

We discuss a variational model for reconstructing an image taking into account the depth of the various objects in the threedimensional space, based on the properties of the apparent contour. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A mortar method for thermomechanically coupled problems
Authors: Berend E. , Wriggers P. , Nackenhorst U.
Published: October 2008

In the foundry industry a reliable prediction of quality defects of the products like residual stresses or size alterations requires detailed constitutive material equations along with a precise modelling of the cast/mould interaction. In this contribution we focus on the description of a contact‐dependent heat transfer between the metal and the mould. Within this approach the contact formulation is based on the mortar finite element scheme. This strategy has turned out to be more stable for contact problems than other schemes like node‐to‐segment discretizations, see e.g.[1]. Due to the significant difference in the stiffness of the mould and the cast in the liquid or semi‐solid state a formulation is proposed that works without additional parameters like a penalty parameter or Lagrange multipliers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Updating preconditioners for permuted non‐symmetric linear systems
Authors: Birken Philipp , Tebbens Jurjen Duintjer , Meister Andreas , Tuma Miroslav
Published: October 2008

We consider the solution of a sequence of nonsymmetric linear systems arising from a supersonic model problem by exploiting triangular preconditioner updates. In addition, we demonstrate how the power of the updates can be enhanced by permuting the entire sequence beforehand with a physically motivated reordering of unknowns. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Three‐dimensional continuum mechanical modeling of the Portevin‐Le Châtelier effect
Authors: Bondár G. , Böhlke T. , Estrin Y.
Published: October 2008

In many Al, Cu, Fe and Ni based alloys jerky flow associated with the Portevin‐Le Châtelier (PLC) effect occurs within a specific range of temperatures and strain‐rates. This effect which reduces the ductility and the surface quality of sheet materials is caused by dynamic interaction of mobile dislocations with solute atoms [1]. A three‐dimensional continuum mechanical model of this effect, also known as dynamic strain ageing, is presented. Furthermore, the predictions of the three‐dimensional model are compared with experimental data. Special emphasis is put on the determination of the instability region in the strain and strain‐rate space [2]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of the incompressible Navier‐Stokes equations with explicit integration of the pressure term
Authors: Bonfigli G.
Published: October 2008

We propose a formulation of the incompressible Navier‐Stokes equations considering a Poisson equation with Neumann boundary conditions for the pressure, and innovative boundary conditions for the velocity. Numerical tests show that the proposed formulation ensures solenoidality of the velocity field. If the initial condition is not divergence‐free, exponential decay is observed in time for the error in the fulfillment of the continuity equation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of scattering problems using pseudo‐differential impedance operators
Authors: Calvo David C. , Soukup Raymond J.
Published: October 2008

Direct numerical solutions of scattering problems based on boundary‐integral equations are computationally costly at high frequencies. A numerical method is presented that efficiently computes accurate approximations to unknown surface quantities given known surface data (an approximate Dirichlet‐to‐Neumann map). The method is based on a pseudo‐differential impedance operator (PIO) numerically implemented using rational approximations. An example of a PIO is the so‐called on‐surface radiation condition (OSRC) method. For a convex obstacle, the method can be viewed as applying a parabolic equation directly on the surface of a scatterer. In contrast to past OSRCs, the use of rational approximations provides accuracy for wide scattering angles which is needed for grazing angles of incidence. Generalization to impedance operators for two‐dimensional acoustic scatterers with concave parts is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time series modelling of the Singapore population data
Authors: Cheang Wai Kwong
Published: October 2008

Trends in population have important implications for a government in formulating its manpower‐related policies. A business may also need to adjust its long‐term market strategies according to these trends. This paper analyses the Singapore population data using time series regression model with autoregressive error term. In addition to a linear trend, other regressors included in the model are (i) a seasonal component of period 12 to account for the effect of the auspicious “dragon” years in the Chinese calendar; (ii) level‐shift interventions to account for the effect of the government campaigns on family planning. Two methods of estimating the autoregressive parameter are considered: maximum likelihood (ML) and restricted maximum likelihood (REML). For a time series of short or moderate sample length, it is shown in Cheang and Reinsel (2000) that the REML estimator is generally much less biased than the ML estimator. Consequently, the REML approach leads to more accurate inferences for the regression parameters. This paper compares the ML and REML estimation results, and examines the implications for the nature of nonstationarity (deterministic or stochastic trend component) exhibited by the Singapore population data series. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Challenges for mathematical and statistical modelling for metrology
Authors: Cox Maurice G , Forbes Alistair B , Harris Peter M
Published: October 2008

There are challenges in disseminating information concerning mathematical and statistical modelling for metrology. We specify these challenges and consider ways they are being met. In addition to journal papers, the value of supporting software and other aspects are indicated. Relevant work in the UK Software Support for Metrology programme is outlined. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of 3D free surface flows using implicit methods
Authors: Oishi Cassio M. , Cuminato José A. , Tomé Murilo F.
Published: October 2008

This work presents an implicit technique for simulating three‐dimensional unsteady low Reynolds number free surface flows of non‐Newtonian fluids. It is based on the Marker‐and‐Cell technique and it employs finite differences on a staggered grid. Validation results and the numerical simulation of complex free surface flows are presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of exit times and positions for Brownian motions and Diffusions
Authors: Deaconu Madalina , Lejay Antoine
Published: October 2008

We present in this note some variations of the Monte Carlo method for the random walk on spheres which allow to solve many elliptic and parabolic problems involving the Laplace operator or second‐order differential operators. In these methods, the spheres are replaced by rectangles or parallelepipeds. Our first method constructs the exit time and the exit position of a rectangle for a Brownian motion. The second method exhibits a variance reduction technique. The main point is to reduce the problem only to the use of some distributions related to the standard one‐dimensional Brownian motion. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computing the radiating source term in the system of radiation magnetohydrodynamics
Authors: Dedner Andreas
Published: October 2008

In this paper we present results for the extended short‐characteristics method (ESC) for computing the radiation source term Qrad with special focus on using this method in combination with a finite‐volume scheme for solving the equations of radiation magnetohydrodynamics (RMHD). Since the approximation of the radiation source term takes up a large amount of the computational cost, the efficiency of this part of the numerical scheme is an essential consideration. We compare this method with other methods from the literature with respect to their computational efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mixed‐integer models for topology optimization in sheet metal design
Authors: Fügenschuh Armin , Martin Alexander
Published: October 2008

Topology optimization lies at the heart of many design tasks in mechanical engineering. For those sheet metal products that consist of a bundle of separate channels (such as conduits) we formulate the design task as a linear mixed‐integer optimization problem. The design goal is to find a topology where each channel has a given cross section area, using a minimum amount of sheet met al. In addition to a light‐weight design, stiffness should also be taken into account. The entire approach is demonstrated in the design of a conduit with five separate channels. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An efficient distance algorithm for interval‐based octree‐encoded CSG objects with time‐space coherence utilization
Authors: Dyllong Eva , Grimm Cornelius
Published: October 2008

In this paper, a new distance algorithm for octree‐encoded CSG objects is presented. Interval vectors are used to describe the nodes of the octree for a reliable and efficient realization of the hierarchical data structure. The algorithm yields the lower bounds of the distance between the objects and is based on accurate algorithms that have been shown in [1], but involves interval arithmetic for reliable handling of rounding errors. Furthermore, time‐space coherence is utilized to increase the efficiency of sequential distance calculations. Experiments validate the approach and show its range of applicability. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A globally well‐posed nonlinear nonlocal diffusion
Authors: Guidotti Patrick
Published: October 2008

Nonlinear diffusions have successfully been employed to perform a variety of tasks in image processing. In the context of denoising, the Perona‐Malik equation is a particularly successful example. In spite of its cherished qualities, it is mathematically ill‐posed and has some practical short‐comings. In this short paper a new nonlocal nonlinear diffusion is reported upon, which is globally well‐posed and shares with Perona‐Malik all its qualities even improving on its weaknesses. It can be viewed as a new kind of regularization. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Well modeling in the multi‐scale finite‐volume context
Authors: Jenny Patrick , Lunati Ivan
Published: October 2008

An extension of the multi‐scale finite‐volume (MSFV) method is devised, which allows to simulate flow and transport in reservoirs with complex well configurations. The new framework fits nicely into the data structure of the original MSFV method and it has the important property that no large patches covering the whole well are required. For each well, an additional degree of freedom is introduced. While the treatment of pressure‐constraint wells is trivial, since the well‐bore reference pressure is explicitly specified, additional equations have to be solved to obtain the unknown pressure values of rate‐constraint wells. Numerical simulations of a difficult test case with multiple complex wells demonstrate the ability of the new framework to capture the interference between the various wells and the reservoir accurately. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constraints on the convergence behavior of algorithms via reachable set analysis
Authors: Jordan J.
Published: October 2008

Many iterative algorithms can be interpreted as discrete‐time control systems evolving on manifolds. Here, shift parameters act as control inputs. The Adherence structure of the reachable sets provides fundamental limitations on the possible convergence behavior of the algorithm.

We analyse the reachable sets of inverse iteration schemes and rational iteration schemes. In particular we show a necessary conditions for the existence of local convergent shift strategies for inverse iteration. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Invariant manifolds and the interplanetary superhighway
Authors: Lo Martin W.
Published: October 2008

We propose a different model to study the Solar System by considering it as a series of Three Body Problems (Sun‐Planet‐Infinitesimal Body). The invariant manifolds of each Three Body System intersect in space to provide a transport mechanism spanning the entire Solar System which is popularly called the “Interplanetary Superhighway”. This concept is useful for designing space missions and for understanding the motions of minor bodies in the Solar System. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parareal in time approximation of the Korteveg‐deVries‐Burgers' equations
Authors: MahmoudKaber Sidi , Maday Yvon
Published: October 2008

The parareal in time algorithm is a predictor corrector method that allows to get parallelisation through the time. It consists in segmenting the interval of time integration into slabs, then propose iteratively seed values at the left hand side of each of the slabs. The derivation of the seed values is done sequentially and involves propagator that should mimic the equation to be solved but should be very cheap and parallel accurate propagations of each seed value over each slab. Various approaches have been proposed to get the coarse propagator, in this paper, we use the averaging approach developed by Barenblatt and Chorin for the Korteveg‐deVries‐Burgers' equations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Stefan problem related to a non‐equilibrium shrinking unreacted core model with fast reaction for the sphere
Authors: Muntean Adrian
Published: October 2008

The problem studied in this note refers to a substantial part of a larger system of partial differential equations modeling diffusion and fast reaction of a gaseous species A in a reactive spherical porous region. We report on the local existence and uniqueness of weak solutions to the corresponding moving‐boundary system containing two coupled mass‐balance equations in a moving annulus. Since the system incorporates an explicit description of the velocity of the moving boundary, our formulation resembles to the one‐phase Stefan‐like problem with kinetic condition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of building evacuation in emergency conditions
Authors: Camarena Alicia Guadalupe Ortega
Published: October 2008

In the present work, pedestrian behaviour in crowds is assumed to be a coupled phenomena. Therefore, the use of continuousand individual‐models in different regions according to its local density is suggested. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evolution equation for the sub‐grid heat flux in a finite volume Formulation
Authors: Otić Ivan
Published: October 2008

We derive an evolution equation for the sub‐grid heat flux vector for a filter that is consistent with finite volume representations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A geometrical multiscale approach to the evaluation of hemodynamic risk factors for internal carotid artery aneurysm development.
Authors: Passerini Tiziano , Veneziani Alessandro
Published: October 2008

In this work we address morphological and fluid‐mechanical features of Internal Carotid Artery (ICA) which can be possibly related to the presence and the rupture of cerebral aneurysms. A classification is presented, based on geometrical characteristics (ICA radius and curvature). Fluid dynamics analyses of blood flow in vessels belonging to different classes show significant differences in mechanical behaviour, being the risk of rupture (a dramatic event) potentially quite different among the classes. Classification could have therefore a significant predictive role. Multiscale models can be exploited to take into account the mechanical effects of the circulatory system embodying the pathological vascular district. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards the computational homogenization of discrete microstructures
Authors: Ricker Sarah , Menzel Andreas , Steinmann Paul
Published: October 2008

The main objective of the current work is the extension of a computational homogenization scheme towards the simulation of discrete micro‐structures. On the micro‐level so‐called multiple particle systems (MPS) are introduced for which a continuization scheme, resulting in a formulation analogous to a homogenization scheme, is developed. Furthermore, three types of constitutive behavior are applied to these particle systems and their influence on the overall macro‐structure is studied. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of surfactant on bubble and thread dynamics
Authors: Booty M.R. , Siegel M.
Published: October 2008

Two examples from the dynamics of surfactant‐laden interfacial flow are considered. In the first example, a bubble is rapidly stretched by an imposed flow to form a dumb‐bell shape, then the imposed flow is relaxed, so that the bubble evolves solely under the action of surfactant‐modified surface tension. In the second example, a surfactant‐coated bubble is continually stretched by a steady extensional flow. At sufficiently small strain rates, steady bubble shapes are found, whereas at larger strain rates a long‐wave model of the dynamics predicts behavior that is reminiscent of experimentally observed tip‐streaming. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled system of Korteweg‐de Vries equation‐type in domains with oscillatory moving boundaries
Authors: Vera Octavio , Sepúlveda Mauricio , Bisognin Vanilde
Published: October 2008

We consider the initial‐boundary value problem in a bounded domain with oscillatory moving boundaries and nonhomogeneous boundary conditions for the coupled system of equations of KdV type modelling strong interactions between internal solitary waves. We give a result of global existence and uniqueness for strong solutions for the coupled system of equations of Korteweg – de Vries type as well as the exponential decay of small solutions in asymptotically cylindrical domains. We present a numerical examples based in semi‐implicit finite differences showing the numerical effect of the oscillatory moving boundaries for this kind of systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A positive and conservative second order finite volume scheme applied to a phosphor cycle in canals with sediment
Authors: Benz Joachim , Meister Andreas , Zardo Philipp Andrea
Published: October 2008

This paper is devoted to the description of a higher order finite volume scheme for the 2D shallow water equation with a specific focus on a complex phosphor cycle describing processes in lakes and rivers. The scheme guarantees the unconditional positivity and mass conservation of respectively modelled quantities, which are crucial properties for meaningful computed results in biochemical contexts. It works on secondary unstructured meshes which enables the application to arbitrary complex geometries. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Straight chains of interconnected mass points under the action of non‐symmetric dry friction
Authors: Zeidis I. , Zimmermann K. , Pivovarov M.
Published: October 2008

The motion of a chain of interconnected equal material points placed on a rough straight line and connected by equal kinematical constraints is considered. It is supposed that the system experiences a small non‐symmetric Coulomb dry frictional force acting from the line side upon each mass point and opposite to the direction of motion. The magnitude of this force depends on the direction of motion. To the equation of motion the procedure of averaging is applied. The expression for the stationary “on the average” velocity of the motion of the system as a single whole is found. The obtained theoretical results can be used for the design of worm‐like vibration robots. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cointegration applied to purchasing‐power analysis of mean Ukrainian total wages
Authors: Bardadym Tamara , Emmenegger Jean‐François
Published: October 2008

The main purpose of this study is to propose Johansen's [6] methodology of linear cointegration analysis as a tool to measure the purchasing power of the Ukrainian mean total wages (MTW) within the period of November 1993 to December 2004 expressed in terms of prices of some basic food products or of the Consumer Price Index (CPI). Nineteen monthly price time series of basic food products, the CPI and MTW published by the State Committee of Statistics of Ukraine (Derzhkomstat) have been selected. Preliminary studies of stationarity are undertaken to establish their degree of integratedness with a battery of adequate unit root tests. A cointegration analysis of couples of one of these price time series of some basic food products, respectively the CPI and the MTW time series are realised, yielding linear functions between both selected series, establishing tentative long‐run equilibrium relations for subperiods shorter than the interval 1993 to 2004. The results show that the purchasing power of the MTW, expressed in terms of the prices of some basic food products, respectively the CPI, gradually increased from 1993 to 2004. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of anisotropic atomic motions in biological macromolecules
Authors: Burden C. J. , Formont L. , Oakley A. J.
Published: October 2008

A compact and convenient graphical technique for assessing agreement between spatial atomic distributions in large molecules determined from alternate sources is presented. The procedure is available as downloadable software. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)