bluuebunny/crossref_metadata_2025 huggingface dataset:
Nicotinic acid/laropiprant: a new lipid‐modifying therapy
Authors: Chaplin Steve , Evans Marc
Published: February 2009

Cardiovascular disease (CVD) is a leading cause of death in the UK.1 Blood choleserol levels are a key risk factor for CVD, and can be modified by both drug treatment and lifestyle changes. In this article, Steve Chaplin considers the available clinical data on a new lipid‐modifying therapy, a modified‐release formulation of nicotinic acid and laropiprant; and Marc Evans comments on its potential contribution to reducing the risk of CVD. Copyright © 2009 John Wiley & Sons, Ltd.
Taphonomy and abundance of birds from the Lower Eocene Fur Formation of Denmark
Authors: Dyke Gareth , Lindow Bent
Published: February 2009

The pattern, pace and extent of the evolutionary radiation of modern birds (Neornithes) by the end‐Cretaceous (65 Ma) has long been debated. Well‐dated, taphonomically understood and phylogenetically constrained fossil birds from both sides of the Cretaceous–Paleogene (K–Pg) boundary are required to quantify the shape of this radiation, but have largely been lacking. Here we report on a large collection of fossil birds from the Lower Eocene of Denmark (ca. 54 Ma) that includes three‐dimensionally preserved, articulated specimens from carbonate concretions as well as skeletal imprints and feathers. These birds are from a marine diatomite sequence (the Fur Formation), a low‐energy deep‐water preservational environment unique to the Cretaceous and Paleogene avian fossil record. We present taphonomic and palaeoecological information gleaned from these birds that in combination with phylogenetic data have implications for unravelling avian survivorship across the K–Pg boundary as well as for the pattern of the neornithine evolutionary radiation. Copyright © 2009 John Wiley & Sons, Ltd.
Neural activation of swallowing and swallowing‐related tasks in healthy young adults: An attempt to separate the components of deglutition
Authors: Malandraki Georgia A. , Sutton Bradley P. , Perlman Adrienne L. , Karampinos Dimitrios C. , Conway Charles
Published: February 2009

Understanding the underlying neural pathways that govern the highly complex neuromuscular action of swallowing is considered crucial in the process of correctly identifying and treating swallowing disorders. The aim of the present investigation was to identify the neural activations of the different components of deglutition in healthy young adults using functional magnetic resonance imaging (fMRI). Ten right‐handed young healthy individuals were scanned in a 3‐Tesla Siemens Allegra MRI scanner. Participants were visually cued for both a “Swallow” task and for component/control tasks (“Prepare to swallow”, “Tap your tongue”, and “Clear your throat”) in a randomized order (event‐related design). Behavioral interleaved gradient (BIG) methodology was used to address movement‐related artifacts. Areas activated during each of the three component tasks enabled a partial differentiation of the neural localization for various components of the swallow. Areas that were more activated during throat clearing than other components included the posterior insula and small portions of the post‐ and pre‐central gyri bilaterally. Tongue tapping showed higher activation in portions of the primary sensorimotor and premotor cortices and the parietal lobules. Planning did not show any areas that were more activated than in the other component tasks. When swallowing was compared with all other tasks, there was significantly more activation in the cerebellum, thalamus, cingulate gyrus, and all areas of the primary sensorimotor cortex bilaterally. Hum Brain Mapp 2009. © 2009 Wiley‐Liss, Inc.
Estimating health insurance impacts under unobserved heterogeneity: the case of Vietnam's health care fund for the poor
Authors: Wagstaff Adam
Published: February 2009

Vietnam's health care fund for the poor (HCFP) uses government revenues to finance health care for the poor, ethnic minorities living in selected mountainous provinces, and all households living in communes officially designated as highly disadvantaged. As of 2006, the program, which started in 2003, covered around 60% of those eligible. Those who were covered (about 20% of the population) were disproportionately poor, and around 80% of those covered were eligible. Estimates of the program's impact were obtained using a method that takes into account unobserved heterogeneity – including unobserved idiosyncratic returns – but requires minimal assumptions. The downside is that it provides an estimate only of the program's impact on those covered by it; it cannot therefore answer the question of how those currently uncovered will fare when they are eventually covered. The results suggest that HCFP has had no impact on use of services, but has substantially reduced out‐of‐pocket spending. Copyright © 2009 John Wiley & Sons, Ltd.
CD26 expression in mature B‐cell neoplasia: its possible role as a new prognostic marker in B‐CLL
Authors: Cro Lilla , Morabito Fortunato , Zucal Nadia , Fabris Sonia , Lionetti Marta , Cutrona Giovanna , Rossi Francesca , Gentile Massimo , Ferrario Andrea , Ferrarini Manlio , Molica Stefano , Neri Antonino , Baldini Luca
Published: February 2009

CD26 (dipeptidyl peptidase IV, DPP IV) is widely expressed by T and natural killer (NK) cells, epithelial and endothelial cells of different tissues, and it is strongly upregulated in activated B‐cells; moreover it plays a regulatory role in the neoplastic transformation and progression of various types of tumours. CD26 expression was evaluated by means of flow cytometry in various peripheral B‐cell lymphoid tumours: 12 follicular and 12 mantle cell lymphomas, 20 multiple myelomas (MMs), 12 hairy cell leukaemias (HCLs), 112 chronic lymphocytic leukaemias (CLLs), 20 CD5negative B‐cell chronic lymphoproliferative diseases (CD5neg B‐CLPDs) and 12 diffuse large cell lymphomas (DLCLs). CD26 expression was absent or barely detectable in follicular and mantle cell lymphomas, high in MMs and HCLs, and variable in CLLs, in CD5neg B‐CLPDs and in DLCLs. CD26 significantly correlated with CD49d and CD38 expressions (p < 0.0001) in B‐CLLs, and there was a significant correlation between CD26 and ZAP‐70 expressions or IgVH mutational status (p < 0.0001). After a median follow‐up of 36 months, 65 B‐CLL patients were treated; taking 10% as the best CD26 cut‐off value, Kaplan–Meier curves revealed a significantly shorter time to treatment in the CD26‐positive cases (p < 0.0001). Overall, our data indicate that CD26 expression may identify subsets of B‐CLL patients with an unfavourable clinical outcome in terms of therapeutic need, thus suggesting its potential role as a marker (together with CD38 and CD49d) in a future routine cytofluorimetric panel to be validated for the prognostic stratification of B‐CLLs. Copyright © 2009 John Wiley & Sons, Ltd.
ChIP‐based methods for the identification of long‐range chromatin interactions
Authors: Fullwood Melissa J. , Ruan Yijun
Published: February 2009

Chromatin immunoprecipitation (ChIP) is an important technique for studying protein–DNA interactions. Whole genome ChIP methods have enjoyed much success, but are limited in that they cannot uncover important long‐range chromatin interactions. Chromosome conformation capture (3C) and related methods are capable of detecting remote chromatin interactions, but are tedious, have low signal‐to‐noise ratios, and are not genome‐wide. Although the addition of ChIP to 3C (ChIP–3C) would conceivably reduce noise and increase specificity for chromatin interaction detection, there are concerns that simple mixing of the ChIP and 3C protocols would lead to high levels of false positives. In this essay, we dissect current ChIP‐ and 3C‐based methodologies, discuss the models of specific as opposed to non‐specific chromatin interactions, and suggest approaches to separate specific chromatin complexes from non‐specific chromatin fragments. We conclude that the combination of sonication‐based chromatin fragmentation, ChIP‐based enrichment, chromatin proximity ligation and Paired‐End Tag ultra‐high‐throughput sequencing will be a winning implementation for genome‐wide, unbiased and de novo discovery of long‐range chromatin interactions, which will help to establish an emerging field for studying human chromatin interactomes and genome regulation networks in three‐dimensional spaces. J. Cell. Biochem. 107: 30–39, 2009. © 2009 Wiley‐Liss, Inc.
In vitro evaluation of a ‘stealth’ adenoviral vector for targeted gene delivery to adult mammalian neurones
Authors: Sims Karen , Ahmed Zubair , Read Martin L. , Cooper‐Charles Lisa , Gonzalez Ana Maria , Fisher Kerry D. , Berry Martin , Seymour Leonard W. , Logan Ann
Published: February 2009

Background

Polymer coating of adenovirus type 5 (Ad5) particles produces a ‘stealth’ Ad5 (sAd5) that confers protection from immune recognition, blocks receptor‐mediated uptake, and favours uptake into pinocytic cells.

Methods

In mixed cultures of primary adult rat dorsal root ganglion neurones (DRGN), rat C6 glioma cells, A9 non‐Coxsackie and Ad Receptor (CAR)‐ and CAR‐expressing fibroblasts, reporter gene expression after sAd5 pinocytotic uptake was monitored using the green fluorescent protein (gfp) gene, and viral particle trafficking and polymer coat dismantling was followed using Yoyo‐1 tagged Ad5 DNA and Texas Red (TR) to label the coat.

Results

sAd5.gfp was pinocytosed by significantly higher proportions of neurones, than other cells, but GFP was not expressed. The TR‐labelled coat remained co‐localised with tagged viral DNA within transfected DRGN, showing that sAd5 did not uncoat and viral DNA did not traffic to the nucleus. Noncoated Ad5 transduced non‐neuronal DRG cells more efficiently than DRGN, whereas A9CAR cells were more significantly transduced than any other cell type. Retargeting of the sAd5.gfp with either fibroblast growth factor‐2 or nerve growth factor (NGF) enhanced internalisation by DRGN into endocytic vesicles allowing uncoating and thus GFP expression. Retargeting with NGF resulted in significantly higher numbers of DRGN expressing GFP than non‐neuronal DRG cells.

Conclusions

These findings indicate that DRGN pinocytose atropic genetic particles at higher levels than non‐neuronal DRG cells and the environment of pinocytic vesicles is not conducive to sAd5 uncoating and capsid dismantling, requiring reformulation of sAd5 with either a neurone specific ligand or a self‐dismantling coat to target sAd5 transgene expression to neurones. Copyright © 2009 John Wiley & Sons, Ltd.
Synthesis of the perdeuterated cellulose solvents 1‐ethyl‐3‐methylimidazolium acetate (EMIM‐OAc‐d14) and 1‐butyl‐3‐methylimidazolium acetate (BMIM‐OAc‐d18) and of 2‐13C‐butyl‐3‐methylimidazolium acetate
Authors: Yoneda Yuko , Ebner Gerald , Takano Toshiyuki , Nakatsubo Fumiaki , Potthast Antje , Rosenau Thomas
Published: February 2009

The syntheses of two perdeuterated ionic liquids (ILs), which have found use as solvents for cellulose derivatization and processing in addition, are described: 1‐ethyl‐3‐methylimidazolium acetate (EMIM‐OAc‐d14) and 1‐butyl–3‐methylimidazolium acetate (BMIM‐OAc‐d18). The targets were obtained from imidazole in three‐step sequences starting with butylation and ethylation, respectively. The resulting 1‐alkyl imidazoles were purified, and subsequently methylated according to a novel protocol using dimethylcarbonate‐d6. To obtain the 1‐alkyl‐3‐methylimidazolium moiety, methylation of 1‐alkylimidazoles proved to be superior to the conventional approach of alkylating 1‐methylimidazole. Addition of acetic acid‐d4 caused traceless degradation of the methylcarbonate counter anions, which were neatly exchanged for acetate. The IL 2‐13C‐butyl‐3‐methylimidazolium acetate, in which the isotopically enriched C‐2 is a good NMR‐indicator of side reactions and solvent–solute interactions, was synthesized according to the same reaction sequence, starting from 2‐13C‐1‐alkylimidazole which, in turn, was obtained by reaction of glyoxale, alkylamine, ammonia and paraformaldehyde‐13C. Copyright © 2009 John Wiley & Sons, Ltd.
The intraruminal papillation gradient in wild ruminants of different feeding types: Implications for rumen physiology
Authors: Clauss Marcus , Hofmann Reinhold R. , Fickel Jörns , Streich W. Jürgen , Hummel Jürgen
Published: February 2009

Browsing and grazing ruminants are thought to differ in the degree their rumen contents are stratified—which may be due to different characteristics of their respective forages, to particular adaptations of the animals, or both. However, this stratification is difficult to measure in live animals. The papillation of the rumen has been suggested as an anatomical proxy for stratification—with even papillation indicating homogenous contents, and uneven papillation (with few and small dorsal and ventral papillae, and prominent papillae in the atrium ruminis) stratified contents. Using the surface enlargement factor (SEF, indicating how basal mucosa surface is increased by papillae) of over 55 ruminant species, we demonstrate that differences between the SEFdorsal or SEFventral and the SEFatrium are significantly related to the percentage of grass in the natural diet. The more a species is adapted to grass, the more distinct this difference, with extreme grazers having unpapillated dorsal and ventral mucosa. The relative SEFdorsal as anatomical proxy for stratification, and the difference in particle and fluid retention in the rumen as physiological proxy for stratification, are highly correlated in species (n = 9) for which both kind of data are available. The results support the concept that the stratification of rumen contents varies among ruminants, with more homogenous contents in the more browsing and more stratified contents in the more grazing species. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.
The surface radiation budget over North America: gridded data assessment and evaluation of regional climate models
Authors: Markovic Marko , Jones Colin G. , Winger Katja , Paquin Dominique
Published: February 2009

While surface station observations of downwelling radiation offer accuracy at high temporal resolution, they do not easily allow an evaluation of model surface radiation budgets (SRB) over a wide geographical area. We evaluate three gridded SRB data sets against detailed observations from six surface radiation sites from the US surface radiation (SURFRAD) network. We subsequently use the most accurate surrogate observational data set for evaluation of model‐simulated SRB. The data sets assessed are: ERA40—reanalysis of European Centre for Medium‐Range Weather Forecasts (ECMWF), North American Regional Reanalysis (NARR)—regional reanalysis of National Centres for Environmental Prediction (NCEP) and the surface radiative budget (SRB) from the International Satellite Cloud Climatology Project (ISCCP). Due to varying constraints with respect to temporal coverage of each data set, the evaluation period used in this study is 1996–2001, inclusive.

The ERA40 downwelling longwave radiation (DLR) appears the most accurate surrogate observation, while both ERA40 and ISCCP show accurate results when the incoming shortwave radiation (ISR) is considered across the annual cycle. Winter DLR is less accurate in ISCCP with a positive bias and lack of very low (<200 Wm−2) flux values. The NARR SRB shows a large positive bias in the ISR throughout the annual cycle, linked to a significant underestimate of cloud cover.

The ERA40 data are subsequently used to evaluate the simulated SRB in three regional climate models across North America. With respect to solar radiation, cloud cover biases are seen to be crucial, while for longwave fluxes both cloud fraction and in‐cloud water content are important to simulate correctly. Inclusion of trace gases beyond H2O, CO2 and O3 appears necessary for an accurate calculation of clear‐sky longwave radiation. Error compensation frequently occurs between the various components contributing to a model total‐sky SRB. This is important to consider when trying to identify the underlying causes of errors in the simulated total SRB. Copyright © 2009 Royal Meteorological Society
Influence of ENSO on multi‐annual temperature variations at Hongyuan, NE Qinghai‐Tibet plateau: evidence from δ13C of spruce tree rings
Authors: Xu Hai , Hong Yetang , Hong Bing , Zhu Yongxuan , Wang Yu
Published: February 2009

Influence of ENSO on global temperature variations has aroused wide attention. However, little is known about this effect at regions where different monsoons prevail. In this study, we measured δ13C of spruce trees (picea likiangensis var. rubescens) and reconstructed temperature variations during the past 270 years at Hongyuan, the Zoige plateau where Indian summer monsoon (ISM) dominates. Temperature variation inferred from δ13Ctreering at the Zoige plateau shows anti‐teleconnection on multi‐annual timescales to the sea‐surface temperature (SST) anomaly in the Niño3 region (SSTANiño3 for short) which has been widely used as an indicator of the “El Niño–South Oscillation” (ENSO). We speculate that the ENSO may modulate the regional surface temperature by influencing the intensity of the ISM, which affects the influx of warm/moist air mass to the study region and subsequently changes the latent heating. On multi‐annual scales, when the SSTANiño3 is high (low), the ISM is weak (strong), monsoon precipitation decreases (increase), the latent heating is weakened (strengthened) and surface air temperature is lower (higher). Copyright © 2009 Royal Meteorological Society
Effects of vertical hedge interval of vetiver grass on erosion on steep agricultural lands
Authors: Donjadee S. , Clemente R. S. , Tingsanchali T. , Chinnarasri C.
Published: February 2009

Vetiver grass is widely used to reduce soil erosion and has been applied in many areas of the world. However, studies of the effect of vertical hedge intervals on runoff, soil loss and outflow sediment size distribution under a steep slope area are rare. The vetiver grass system (VGS) with three vertical hedge intervals (0·75, 1·5 and 3 m) and no hedgerow were tested at three land slopes (30, 40 and 50 per cent) under three simulated rainfall intensities (60, 85 and 110 mm h−1). It has been observed that vetiver grass (Vetiveria nemoralis) has great potential for reducing runoff and soil loss by about 38·7–68·6 and 56·2–87·9 per cent, respectively. The vetiver strips delayed incipient runoff and reduced peak runoff rate and steady erosion rate. The land slope affected soil loss but did not have a significant effect on runoff. A narrow vetiver hedge interval slightly reduced runoff and soil loss more than a wider one. The soil loss equation obtained in this study revealed that runoff has a higher effect on soil loss. The median sediment size that passed through the vetiver strip increased with rainfall intensity and was mostly dominated by very fine sand, silt and clay. Copyright © 2009 John Wiley & Sons, Ltd.
Combined peroneal and proximal tibial nerve palsies
Authors: Williams Eric H. , Williams Christopher G. , Rosson Gedge D. , Dellon A. Lee
Published: February 2009

Combined compression of both the common peroneal nerve and the proximal tibial nerve at the level of the popliteal fossa is rare. Recently, an anatomic site of compression of the proximal tibial nerve at the soleal sling (originating arch for the soleus muscle) has been described in cadavers. The present report includes three patients who had a combined compression of the common peroneal nerve at the fibular neck (fibular tunnel syndrome) and compression of the proximal tibial nerve at the soleal sling (soleal sling syndrome). In each case, blunt trauma was the precipitating event. Neurolysis of both nerves resulted in restoration of motor and sensory function in each ofthese three patients. This is the first clinical report illustrating combined neurolysis of the common peroneal at the knee and the proximal tibial nerve in the soleal sling. © 2009 Wiley‐Liss, Inc. Microsurgery, 2009.
A new model updating method for damped structural systems
Authors: Jiang Jiashang , Yuan Yongxin
Published: February 2009

In this paper, the following two are considered:

Problem IQEP

Given Ma∈SRn×n, Λ=diag{λ1, …, λp}∈Cp×p, X=[x1, …, xp]∈Cn×p, and both Λ and X are closed under complex conjugation in the sense that \documentclass{article}\footskip=0pc\pagestyle{empty}\begin{document}$\lambda_{2j} = \bar{\lambda}_{2j-1} \in {\mathbf{C}}$\end{document}, x2j=x̄2j−1∈Cn for j = 1,…,l, and λk∈R, xk∈Rn for k=2l+1,…,p, find real‐valued symmetric (2r+1)‐diagonal matrices D and K such that ∥MaXΛ2+DXΛ+KX∥=min.

Problem II

Given real‐valued symmetric (2r+1)‐diagonal matrices Da, Ka∈Rn×n, find
\documentclass{article}\footskip=0pc\usepackage{amssymb}\usepackage[mathscr]{euscript}\pagestyle{empty}\begin{document}$(\hat{D},\hat{K}) \in {\mathscr{S}}_{DK}$\end{document} such that \documentclass{article}\usepackage{amssymb}\usepackage[mathscr]{euscript}\footskip=0pc\pagestyle{empty}\begin{document}$\|\hat{D}-D_a \|^2+ \| \hat{K}-K_a \|^2=\rm{inf}_{(D,K) \in {\mathscr{S}}_{DK}}(\|D-D_a\|^2+\|K-K_a\|^2)$\end{document}, where 𝒮DK is the solution set of IQEP.

By applying the Kronecker product and the stretching function of matrices, the general form of the solution of Problem IQEP is presented. The expression of the unique solution of Problem II is derived. A numerical algorithm for solving Problem II is provided. Copyright © 2009 John Wiley & Sons, Ltd.
The growth factor of a Hadamard matrix of order 16 is 16
Authors: Kravvaritis Christos , Mitrouli Marilena
Published: February 2009

In 1968 Cryer conjectured that the growth factor of an n × n Hadamard matrix is n. In 1988 Day and Peterson proved this only for the Hadamard–Sylvester class. In 1995 Edelman and Mascarenhas proved that the growth factor of a Hadamard matrix of order 12 is 12. In the present paper we demonstrate the pivot structures of a Hadamard matrix of order 16 and prove for the first time that its growth factor is 16. The study is divided in two parts: we calculate pivots from the beginning and pivots from the end of the pivot pattern. For the first part we develop counting techniques based on symbolic manipulation for specifying the existence or non‐existence of specific submatrices inside the first rows of a Hadamard matrix, and so we can calculate values of principal minors. For the second part we exploit sophisticated numerical techniques that facilitate the computations of all possible (n − j) × (n − j) minors of Hadamard matrices for various values of j. The pivot patterns are obtained by utilizing appropriately the fact that the pivots appearing after the application of Gaussian elimination on a completely pivoted matrix are given as quotients of principal minors of the matrix. Copyright © 2009 John Wiley & Sons, Ltd.
Friction induced flutter instability ‐ on modeling and simulation of brake‐squeal ‐
Authors: Hetzler Hartmut , Seemann Wolfgang
Published: February 2009

The issue of this contribution are self–excited vibrations due to sliding friction between moving elastic bodies. Starting from Hamiltons principle, the normal contact is implemented by two different approaches. Assuming discretizations in a spatial coordinate frame, the structure of the resulting equations of motions is outlined. For a simple model of a disc–brake, stability charts of the steady–state are presented, which show a considerable influence of the motion of the disc on the stability behavior. Finally, the influence of penalty approaches to the normal contact is addressed shortly. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Untersuchung von Schwingungen und Stößen an Systemen mit adhäsiven Kontakten
Authors: Kröger M.
Published: February 2009

In vielen technischen Anwendungen treten Kontakte auf, die sich bilden und wieder lösen, insbesondere bei Stößen zwischen Körpern. Besteht ein Kontaktpartner aus einem Elastomer, so ergibt sich durch das niedrige Elastizitätsmodul eine relativ große wahre Kontaktfläche, die dazu führt, dass intermolekulare Wechselwirkungen wie Van–der–Walls Bindungen zu großen adhäsiven Kräften führen können. Dadurch wird aus der einseitigen Bindung ein Kontakt, der auch Zugkräfte übertragen kann. Um diesen Vorgang sinnvoll zu beschreiben, muss die Dynamik des Gesamtsystems mit der adhäsiven Kontaktbeschreibung, inklusive der Beschreibung der Dynamik der Kontaktflächenbildung bzw. deren Abbau verknüpft werden. Die Grenze der Kontaktfläche kann als Rissspitze aufgefasst werden, wobei die Rissgeschwindigkeit von den viskoelastischen Materialeigenschaften abhängig ist. Sind die adhäsiven Effekte hinreichend groß, so wird der Kontakt nicht mehr gelöst und es kommt zu abklingenden Schwingungen. Hier werden experimentelle Untersuchungen an einem Adhäsionspendel und Ergebnissen aus der Simulation dargestellt. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Grundlagen zur Beschreibung der Wärmeleitung mit Zellulären Automaten
Authors: Müller Michael , Ostermeyer Georg‐Peter
Published: February 2009

Für die Beschreibung der Temperaturleitung werden oftmals die für die Zeitintegration stabilen impliziten Lösungsverfahren (zum Beispiel in Form von Finite–Elemente–Modellen) verwendet, was für ein Zelluläre–Automaten–Modell jedoch aufgrund der dann extremen Zunahme der Rechenzeit nicht zweckmäßig ist. Stattdessen wird die Dynamik der Wärme im Sinne des Zellulären Automaten mit einem expliziten Algorithmus wiedergegeben, der auf dem lokalen Austausch von Energiemengen, also auf Bilanzgleichungen zwischen den Zellen basiert. Dieses Paper zeigt Aussagen zur numerischen Stabilität in Hinblick auf Zeit– wie Ortsdiskretisierung auf. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Existence and approximation for a 3D model of thermally‐induced phase transformations in shape‐memory alloys
Authors: Mielke Alexander , Paoli Laetitia , Petrov Adrien
Published: February 2009

This note deals with a three–dimensional model for thermal stress–induced transformations in shape–memory materials. Microstructure, like twined martensites, is described mesoscopically by a vector of internal variables containing the volume fractions of each phase. The problem is formulated mathematically within the energetic framework of rate–independent processes. An existence result is proved and we study space–time discretizations and establish convergence of these approximations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐Asymptotic Modelling of Medium Thickness Plates with Plane Periodic Structure
Authors: Baron Eugeniusz
Published: February 2009

The main aim of this contribution are presented a certain selected problems (aspects) of non–asymptotic modelling of medium thickness (or Reissner–type) rectangular plates with a plane periodic in–homogeneous structure. In course of non–asymptotic modeling, by using tolerance averaging technique (TAT), apart from the known separation for biperiodic and uniperiodic plates, it is necessary to introduce extra partitions. The four non–asymptotic models of plates with plane periodic structure can be led out independently (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of a combined process of thermomechanical treatment of 304 stainless steel
Authors: Bontcheva Nikolina , Parashkevova Ludmila , Petzov Georgi
Published: February 2009

Grain refinement due to phase transformation is an effective method for improving the mechanical properties of steel. An approach is proposed in the present work based on the FEM, for numerical simulation of the microstructure evolution. Grain refinement in 304 stainless steel is considered. Coupling of the thermoplastic deformation with microstructure evolution is realized. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the complexity and analysis of auxetic systems
Authors: Munteanu Ligia
Published: February 2009

A challenge in creating a model for an auxetic system based on a formalism that is fully computable, is the aim of this paper. Two major levels of complexity are discussed in a way of understanding the structure and processes that define an auxetic system. The auxeticity and structural complexity are interpreted in the light of Cosserat elasticity which admits degrees of freedom not present in classical elasticity, i.e. the rotation of points in the material, and a couple per unit area or the couple stress. The Young'modulus computing for a laminated periodic system made up of alternating aluminum and an auxetic material is an example of computing complexity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Symmetric Cauchy stresses do not imply symmetric Biot strains in weak formulations of isotropic hyperelasticity with rotational degrees of freedom.
Authors: Fischle Andreas , Neff Patrizio , Münch Ingo
Published: February 2009

We show that symmetric Cauchy stresses do not imply symmetric Biot strains in relaxed weak formulations of finite isotropic hyperelasticity with exact rotational degrees of freedom. This is contrary to claims in the literature. It is noted that in the linear isotropic case with skew symmetric infinitesimal rotational degrees of freedom a similar discrepancy does not arise. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards Modeling the Curing Processes of Thermosets
Authors: Hossain Mokarram , Possart Gunnar , Steinmann Paul
Published: February 2009

This contribution presents a newly developed phenomenological model to describe the curing processes of thermosets undergoing small strain deformations [1]. The governing equations are derived from a number of physical and chemical assumptions. Some numerical examples demonstrate the model's capability to correctly represent the evolution of elastic and inelastic material properties as well as the volume shrinkage taking place during the curing process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material Forces in elasto‐plastic Materials
Authors: Maatouki Ismail , Müller Ralf , Gross Dietmar
Published: February 2009

In this contribution the concept of configurational forces, also called material forces, is applied to rate–independent, elasto–plastic materials. The theory of configurational forces is briefly recast. Zones of plastic deformation can be interpreted as distributed inhomogeneities. With this background the theory of configurational forces can be applied in many situations, including plastic zones at crack tips, elastic inclusions in elasto–plastic materials and localized deformation. The numerical evaluation is done with the Finite Element Method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of the states of deformation and stress in the compact tension specimen (CT)
Authors: Malag Leszek , Kukielka Leon
Published: February 2009

This work presents a new method of determination of the states of stresses and strains in the compact tension specimen (CT). The numerical analysis was carried out in ANSYS/LS–DYNA programme. The Cowper–Symond's material model was applied in the computational analysis. Selected mechanical properties executed from the uniaxial tension test were used in the numerical calculations. The main aim of this paper is to determinate the influence of the dimensions and vertical notch angle of CT on the stresses and strains states. The present application allows a calculation of the states of stresses and strains in arbitrarily specimen place, and at any time of the duration of the tensile test process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature and Rate effects in Finite Viscoplasticity of Glassy Polymers at Different Deformation Modes: Experiments and Simulations
Authors: Méndez Diez Joel , Göktepe Serdar , Miehe Christian
Published: February 2009

The non–linear inelastic response of glassy polymers is highly influenced by the three–dimensional deformation state, the temperature and the strain rate at which they are deformed. The contribution presents new experiments for different deformation modes which are carried out at different temperatures and rates on commercial bis–phenol A polycarbonate. Emphasis is put not only on the experimental results by themselves but also on the setup and the technique employed in the obtention of the data. The effect of temperature on the velocity with which the neck propagates along the gaged section of a flat specimen under tension is studied means a facility based on photogrammetry. From the homogeneous compression experiments a single set of material parameters appearing in a constitutive model based on the distributed free volume theory under the frame work of additive kinematics will be identified. The inhomogeneous experimental results serve then as a validation for 3–D simulations since the non–uniform strain distribution on the surfaces of both, simulations and experiments, can be compared. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization of Unidirectional and Arbitrarily Oriented Fiber‐Reinforced Materials by the Method of Conditional Moments
Authors: Khoroshun Leonid , Nazarenko Lidija , Müller Wolfgang H. , Wille Ralf
Published: February 2009

In this paper the method of conditional moments is developed for the case of a two–component matrix composite with randomly distributed unidirectional and arbitrarily oriented ellipsoidal inclusions. The algorithm for determination of the effective elastic properties of composites from the given elastic constants of the components and geometrical parameters and orientation of inclusions is discussed. It is assumed that the components of the composite show orthotropic symmetry of thermoelastic properties. As a numerical example arbolite (straw particle inclusions in a cement matrix) is considered. The dependencies of Young's moduli, Poisson's ratios and shear moduli from the concentration of inclusions and for certain orientations of the inclusions are predicted and discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical treatment of a finite strain viscoplasticity model based on a double multiplicative split
Authors: Shutov A. V. , Kreißig R.
Published: February 2009

A viscoplastic material model of overstress type is analyzed. The model is based on the kinematic assumption of a double multiplicative split in order to simulate a nonlinear kinematic hardening. We investigate theoretically and numerically two implicit time–stepping methods, which were used lately in engineering literature to integrate the evolution equations in the context of multiplicative plasticity/viscoplasticity. A common feature of both methods is that the plastic incompressibility constraint is exactly satisfied. Moreover, we show that both methods preserve the symmetry of internal variables, which is inherent to the problem. According to testing results, both methods are equivalent regarding robustness, accuracy, and computational efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modellierung und Simulation thermo‐mechanisch gekoppelter Umformprozesse
Authors: Bröcker C. , Matzenmiller A.
Published: February 2009

Die thermomechanisch konsistente Materialmodellierung des viskoplastischen Werkstoffverhaltens der Metalle bei thermomechanischer Kopplung wird beschrieben. Dabei beinhaltet die Wärmeleitungsgleichung auf natürliche Weise die Wärmeproduktion aufgrund der dissipativen Vorgänge während der plastischen Deformation. Ein konkretes Materialmodell wird angegeben und anhand von Experimenten validiert. Abschließend wird ein Anwendungsbeispiel zur gleichzeitigen Warm–/ Kaltumformung einer Flanschwelle mit LS–DYNA thermo–mechanisch gekoppelt simuliert. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized EVI‐space‐time Galerkin method for dynamical modeling in porous media
Authors: Chen Z. , Steeb H. , Diebels S.
Published: February 2009

We investigate a generalized space–time discontinuous Galerkin formulation for modeling dynamical phenomena in porous media. The finite element approximation is based on a coupled space–time discretization. An advanced Embedded Velocity Integration (EVI) technique is applied to circumvent the direction solution of the displacement fields but to solve the rate term of the unknowns. Moverover, a stabilization factor α is introduced to modify the integration scheme of the velocities, which further contributes to the numerical stabilization of the overall solution. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite Element Analysis of General Magnetomechanical Coupling Phenomena
Authors: Kiefer Björn , Rosato Daniele , Miehe Christian
Published: February 2009

In this paper we consider the derivation of a finite element model for fully–coupled magneto–mechanical boundary value problems based on a vector–valued magnetic potential. The formulation allows for the incorporation of nonlinear, anisotropic and hysteretic constitutive response. A piezomagnetic inclusion problem is computed to test the implementation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical model for tsunami generation by subaerial landslides
Authors: Pasenow Frithjof , Zilian Andreas , Dinkler Dieter
Published: February 2009

A discretization method based on stabilized space–time finite elements is presented for the numerical analysis of three–fluid flows of immiscible and incompressible fluids. Signed distance functions are used to assign the material properties to each spatial point in the domain. The motion and the change in topology of fluid–fluid interfaces are implicitly described by the level–set method. Strong and weak discontinuities in the fields of the physical state variables are captured by locally enriched approximations based on the partition–of–unity concept. An interior penalty method enforces interfacial conservation of mass and momentum. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation der aktiven Schwingungskontrolle von Fluid‐Struktur Wechselwirkung durch piezoelektrische Materialien
Authors: Sun Peng , Dinkler Dieter , Zilian Andreas
Published: February 2009

Ein numerisches Modell zur aktiven Kontrolle des dynamischen Verhaltens von Tragwerken unter transienter Windeinwirkung wird vorgestellt. Auf der Oberschicht passiver Tragstrukturen werden piezoelektrische Sensoren und Aktoren appliziert. Die resultierenden adaptierbaren Strukturen sind mit einem Regler gekoppelt. Die Modellierung der elektroelastischen Struktur erfolgt mit der geometrisch nichtlinearen Elastizitätstheorie und der Maxwell–Faraday–Theorie der Elektrostatik. Die Windumströmung der Struktur ist als inkompressibles, Newton'sches Fluid mit den Navier–Stokes–Gleichungen beschrieben. Die Diskretisierung der gekoppelten Modellgleichungen beider Kontinua erfolgt mit finiten Raum–Zeit–Elementen. Zeitliche Änderungen der Zustandsgrößen werden mit dem diskontinuierlichen Galerkin–Verfahren approximiert. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some basic ideas for the reconstruction of statistically similar microstructures for multiscale simulations
Authors: Balzani Daniel , Schröder Jörg
Published: February 2009

In this contribution we propose a method for the generation of statistically similar representative volume elements (RVE's). These RVE's are obtained by assuming that given real microstructures may be represented by periodic ones. Then an optimization problem has to be solved where the side condition of equal spectral density of the real microstructure and the statistically similar RVE is taken into account. First numerical results show that the proposed method works in principle and leads to more efficient direct multiscale simulations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Macroscopic mechanical properties of metal foam in dependence on the inhomogenities of the mesoscale
Authors: Schwarzer Daniel , Vogt Harald , Proppe Carsten
Published: February 2009

In this contribution, a way of simulating the influence of the mesoscopic irregular structure of metal foams on the macroscale is shown. To this end, mesoscopic periodic volume elements of a foam are derived in order to compute the mechanical properties including the effects of inhomogenities like imperfections, irregular structure and varying cell wall thicknesses. With the help of these volume elements, which are analysed via the finite element method, and their varying mechanical properties, a local varying stiffness can be computed and inserted into the macromechanical model. In this way the propagation of uncertainities from the mesoscale to the macroscale can be assessed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
About the projection of kinematical quantities within the FE2‐approach
Authors: Ebinger Tobias , Steeb Holger , Diebels Stefan
Published: February 2009

Within the FE2‐approach strain–like quantities are projected to the boundary of the attached microstructure yielding Dirichlet boundary conditions for the microscopic boundary value problem. By use of the divergence theorem one can show that the projection of gradient information to the boundary of the attached microstructure fulfills the condition that the volumetrical average of the strain–like quantities in the inner of the microstructure is exactly the same as the projected quantity, provided that the microstructure is continous. However, within the Cosserat continuum theory [1] the strain tensor depends directly on the extra rotation and not on the gradient of it. Thus, the projection can not be carried out in the same way as for gradient information. The present approach shows how to circumvent this problem by giving the extra–rotation within the Cosserat continuum theory a strong kinematical interpretation in the form of a displacement field, which shows the same effects as the extra–rotation itself. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Periodic three‐dimensional mesh‐generation for Voronoi tessellations with application to cubic crystal aggregates
Authors: Fritzen Felix , Böhlke Thomas , Schnack Eckart
Published: February 2009

We present a technique for the generation of unstructured periodic spatial discretizations of three–dimensional Voronoi tessellations. These define model microstructures for various polycrystalline aggregates. The elastic properties of cubic crystal aggregates are examined numerically using periodic displacement boundary conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical results for an elasto‐plastic Cosserat model with more than one million dof in 3D
Authors: Müller Wolfgang , Neff Patrizio , Wieners Christian
Published: February 2009

We present a finite element implementation of a infinitesimal elasto–plastic Cosserat model allowing for non–symmetric stresses. We use the von Mises yield criterion and restrict plastic effects to the classical elastic response as in the perfect plastic case. We review the nonlinear equations for the weak formulation of the problem. Numerical results are presented for 3D example with more than one million degrees of freedom. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructural behaviour of transversal isotropic material
Authors: Münch Ingo , Neff Patrizio , Wagner Werner
Published: February 2009

We discuss and simulate transversal isotropic material under tension loading. The preferential direction of the material is inclined under 45 degrees to the direction of the tensile resultant. In this configuration the deformation of a rectangular test specimen differ from the behaviour of isotropic material in the way, that beside Poissons effect additional displacement appear perpendicular to the tension direction. In classical continuum theories, this transverse deformations describe a typical S–shape. By using a non–local continuum theory, the effect of microstructural orientation is incorporated into the numerical model. Then, it depends on a phenomenological parameter of inner structure whether the energetically favoured configuration is classical or contains microstructural behaviour. In the second case, the transverse deformation is not described by the typical S–shape, but with higher forms of it. A simple experimental model will show the connection between the inner structure of the material and the rotational parameters within the non–local continuum theory. It is evident, that these parameters are responsible for the non–classical behaviour and give the possibility to find energetically favoured solutions. The results of the finite–element–analyses can help to understand constitutive parameters for the non–local continuum theory and to apply it to other specimens. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Continuum‐Atomistic Coupling based on Computational Homogenization
Authors: Ricker Sarah , Mergheim Julia , Menzel Andreas , Steinmann Paul
Published: February 2009

The objective of this work is the extension of the classical computational homogenization scheme for continuous micro–structures to the homogenization of atomistic systems. The atomistic setting is simulated by applying the so–called atomistic finite element method. In particular the influence of atomistic defects onto the macroscopic material behavior is highlighted. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical homogenization of foam‐like structures based on the FE2‐approach
Authors: Sehlhorst Hans‐Georg , Jänicke Ralf , Düster Alexander , Rank Ernst , Steeb Holger , Diebels Stefan
Published: February 2009

The computation of foam–like structures is still a topic of research. There are two basic approaches: the microscopic model where the foam–like structure is entirely resolved by a discretization (e.g. with Timoshenko beams) on a micro level, and the macroscopic approach which is based on a higher order continuum theory. A combination of both of them is the FE2‐approach where the mechanical parameters of the macroscopic scale are obtained by solving a Dirichlet boundary value problem for a representative microstructure at each integration point.

In this contribution, we present a two–dimensional geometrically nonlinear FE2‐framework of first order (classical continuum theories on both scales) where the microstructures are discretized by continuum finite elements based on the p‐version.

The p‐version elements have turned out to be highly efficient for many problems in structural mechanics. Further, a continuum–based approach affords two additional advantages: the formulation of geometrical and material nonlinearities is easier, and there is no problem when dealing with thicker beam–like structures.

In our numerical example we will investigate a simple macroscopic shear test. Both the macroscopic load displacement behavior and the evolving anisotropy of the microstructures will be discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)