bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of intracellular accumulation of anthracyclines in cancerous cells by direct injection of cell lysate in MEKC/LIF detection
Authors: Mbuna Julius , Kaneta Takashi , Imasaka Totaro
Published: March 2010

Anthracyclines are chemotherapeutic drugs that are broadly used in the treatment of various types of solid cancers and leukemia. Herein, we report on a novel analytical method for intracellular accumulation of anthracyclines using MEKC/LIF detection. An aqueous separation system permitted the injection of cell lysates directly into the capillary. The MEKC migrating solution was made up of borate buffer at pH 9.22 containing sodium taurodeoxycholate, (2‐hydroxypropyl)‐γ‐CD, and SDS. The anthracyclines, Doxorubicin (DOX) and epirubicin (EPI) were detected by LIF using a Nd:YAG laser (532 nm) or an argon ion laser (488 nm) for excitation. Two cell lines, human humerus tumor cells (RDES) and human lung tumor cells (A549), were treated with a mixture of the two anthracyclines for fixed periods of time, and then intracellular concentrations were determined by injecting cell lysates directly. Recovery values of 96.0–100.8% were obtained for DOX and EPI. Reproducibility quantified by RSD was less than 3.9% intraday and 6.7% interday at concentrations ranging between 50 and 500 nM. The uptake of EPI was found to be slightly less than that of DOX for A549, but higher levels of EPI were observed in RDES. Intracellular accumulation of anthracyclines was greater in RDES than in A549, but both types of cells excreted anthracyclines after 12 h. These results indicate that MEKC with an aqueous medium is useful for investigating intracellular uptake and accumulation of drugs, since cell lysates can be used directly with no pretreatment such as deproteination or solvent extraction of analytes.
Are there limits to collectivism? Culture and children's reasoning about lying to conceal a group transgression
Authors: Sweet Monica A. , Heyman Gail D. , Fu Genyue , Lee Kang
Published: March 2010

This study explored the effects of collectivism on lying to conceal a group transgression. Seven‐, 9‐, and 11‐year‐old US and Chinese children (N=374) were asked to evaluate stories in which protagonists either lied or told the truth about their group's transgression and were then asked about either the protagonist's motivations or justification for their own evaluations. Previous research suggests that children in collectivist societies such as China find lying for one's group to be more acceptable than do children from individualistic societies such as the United States. The current study provides evidence that this is not always the case: Chinese children in this study viewed lies told to conceal a group's transgressions less favourably than did US children. An examination of children's reasoning about protagonists' motivations for lying indicated that children in both countries focused on an impact to self when discussing motivations for protagonists to lie for their group. Overall, results suggest that children living in collectivist societies do not always focus on the needs of the group. Copyright © 2010 John Wiley & Sons, Ltd.
Metastasis suppressor function of NM23‐H1 requires its 3′‐5′ exonuclease activity
Authors: Zhang Qingbei , McCorkle Joseph R. , Novak Marian , Yang Mengmeng , Kaetzel David M.
Published: March 2010

The metastasis suppressor NM23‐H1 possesses 3 enzymatic activities in vitro, a nucleoside diphosphate kinase (NDPK), a protein histidine kinase and a more recently characterized 3′‐5′ exonuclease. Although the histidine kinase has been implicated in suppression of motility in breast carcinoma cell lines, potential relevance of the NDPK and 3′‐5′ exonuclease to metastasis suppressor function has not been addressed in detail. To this end, site‐directed mutagenesis and biochemical analyses of bacterially expressed mutant NM23‐H1 proteins have identified mutations that disrupt the 3′‐5′ exonuclease alone (Glu5 to Ala, or E5A), the NDPK and histidine kinase activities tandemly (Y52A, H118F) or all 3 activities simultaneously (K12Q). Although forced expression of NM23‐H1 potently suppressed spontaneous lung metastasis of subcutaneous tumor explants derived from the human melanoma cell line 1205LU, no significant metastasis suppressor activity was obtained with the exonuclease‐deficient variants E5A and K12Q. The H118F mutant, which lacked both the NDPK and histidine kinase while retaining the 3′‐5′ exonuclease, also exhibited compromised suppressor activity. In contrast, each mutant retained the ability to suppress motility and invasive characteristics of 1205LU cells in culture, indicating that the NM23‐H1 molecule possesses an additional activity(s) mediating these suppressor functions. These studies provide the first demonstration that the 3′‐5′ exonuclease activity of NM23‐H1 is necessary for metastasis suppressor function and further indicate cooperativity of the 3 enzymatic activities of the molecule on suppression of the metastatic process.
Rab4 interacts with the human P‐glycoprotein and modulates its surface expression in multidrug resistant K562 cells
Authors: Ferrándiz‐Huertas Clotilde , Fernández‐Carvajal Asia , Ferrer‐Montiel Antonio
Published: March 2010

P‐glycoprotein (P‐gp) is a plasma membrane glycoprotein that has been signaled as a primary cause of multidrug resistance (MDR) in tumors. We performed a yeast 2‐hybrid screen using the C‐terminal domain of P‐gp and identified 2 small GTPases involved in vesicular trafficking, Rab4 and Rab14, which complex with P‐gp. The overexpression of GFP‐Rab4, either transiently or stably, but not of Rab14, in K562ADR cells decreased the presence of P‐gp in the cell surface. As a result, expression of this GTPase reduced the MDR phenotype of K562ADR cells, by augmenting the intracellular accumulation of daunomycin (DNM). This effect was mimicked by the constitutively active Rab4Q72L mutant, but not by the dominant negative Rab4S27N mutant. Rab4 regulated excocytotic P‐gp trafficking to the plasma membrane from intracellular compartments, and this modulation required the interaction of both proteins and the GTPase activity. Noteworthy, K562ADR cells exhibited a significant reduction of Rab4 levels, but not of other Rab GTPases, as compared with the sensitive parental cell line, suggesting that the development of the MDR phenotype in these cells involves upregulation of P‐gp and a concomitant downregulation of proteins that regulate its surface expression. Attenuation of endogenous Rab4 levels in K562ADR by RNA interference enhanced the expression of P‐gp in the cell surface, and reduced the uptake of DNM. Accordingly, these findings substantiate the notion that modulation of the temporal and spatial distribution of P‐gp in cancer cells may be a valid therapeutic strategy to alleviate the MDR phenotype, and signal to Rab4 as a potential target.
pFARs, Plasmids free of antibiotic resistance markers, display high‐level transgene expression in muscle, skin and tumour cells
Authors: Marie Corinne , Vandermeulen Gaëlle , Quiviger Mickaël , Richard Magali , Préat Véronique , Scherman Daniel
Published: March 2010

Background

Nonviral gene therapy requires a high yield and a low cost production of eukaryotic expression vectors that meet defined criteria such as biosafety and quality of pharmaceutical grade. To fulfil these objectives, we designed a novel antibiotic‐free selection system.

Methods

The proposed strategy relies on the suppression of a chromosomal amber mutation by a plasmid‐borne function. We first introduced a nonsense mutation into the essential Escherichia coli thyA gene, resulting in thymidine auxotrophy. The bacterial strain was optimized for the production of small and novel plasmids free of antibiotic resistance markers (pFARs) and encoding an amber suppressor t‐RNA. Finally, the potentiality of pFARs as eukaryotic expression vectors was assessed by monitoring luciferase activities after electrotransfer of LUC‐encoding plasmids into various tissues.

Results

The introduction of pFARs into the optimized bacterial strain restored normal growth to the auxotrophic mutant and allowed an efficient production of monomeric supercoiled plasmids. The electrotransfer of LUC‐encoding pFAR into muscle led to high luciferase activities, demonstrating an efficient gene delivery. In transplanted tumours, transgene expression levels were superior after electrotransfer of the pFAR derivative compared to a plasmid carrying a kanamycin resistance gene. Finally, in skin, whereas luciferase activities decreased within 3 weeks after intradermal electrotransfer of a conventional expression vector, sustained luciferase expression was observed with the pFAR plasmid.

Conclusions

Thus, we have designed a novel strategy for the efficient production of biosafe plasmids and demonstrated their potentiality for nonviral gene delivery and high‐level transgene expression in several tissues. Copyright © 2010 John Wiley & Sons, Ltd.
Performance of HPLC/MS microchips in isocratic and gradient elution modes
Authors: Ehlert Steffen , Trojer Lukas , Vollmer Martin , van de Goor Tom , Tallarek Ulrich
Published: March 2010

We analyzed the chromatographic performance of particle‐packed, all‐polyimide high‐performance liquid chromatography/mass spectrometry (HPLC/MS) microchips in terms of their hydraulic permeabilities and separation efficiency under isocratic and gradient elution conditions. The separation channels of the chips (with ca 50 µm × 75 µm trapezoidal cross‐section and a length of 43 mm) were slurry packed with either 3.5 or 5 µm spherical porous C18‐silica particles. A custom‐built holder enveloped the chip during packing to prevent channel deformation and delamination from high pressures. It is shown that the packing conditions significantly impact the packing density of the HPLC/MS chips, which determines their performance in both, isocratic and gradient elution modes. Even with steep solvent gradients, peak shape and chromatographic resolution for the densely packed HPLC/MS chips are much improved. Our data show that the analytical power of the HPLC/MS chip is limited by the quality of the chromatographic separation. Copyright © 2010 John Wiley & Sons, Ltd.
Geochemical evidence (C, N and Pb isotopes) of recent anthropogenic impact in south‐central Chile from two environmentally distinct lake sediment records
Authors: Fagel Nathalie , Bertrand Sebastien , Mattielli Nadine , Gilson Delphine , Chirinos Luis , Lepoint Gilles , Urrutia Roberto
Published: March 2010

In this paper, we compare the elemental and isotopic (C, N, Pb) geochemistry of lake sediments from two contrasted environments in south‐central Chile. The first lake, Laguna Chica de San Pedro (LCSP), is situated in the urbanised area of the Biobio Region (36°S). The second lake, Lago Puyehue (40° S), is located 400 km to the southeast of LCSP and within an Andean national park. Our aim is to identify environmental impacts associated with increasing industrial activities and land degradation during the last 150 a. In LCSP, shifts in C/N atomic ratios, δ13C and δ15N from 1915–1937 to the late 1980s are attributed to successive land degradation episodes in the lake watershed. Based on a Pb isotopic mixing model, we estimate that up to 20% of lead in LCSP sediments is supplied from urban atmospheric pollution. By contrast, human impact in the watershed of Lago Puyehue is very limited. We observe no change in organic geochemistry during the last 150 a and lead contamination remains lower than 5%, even during the last decades. Although contamination levels are much higher in LCSP than in Lago Puyehue, a peak in anthropogenic Pb is recorded during the same period (1974–1976) at both sites. This maximum contamination level is consistent with increased industrial activity in the vicinity of Concepción. Copyright © 2010 John Wiley & Sons, Ltd.
Purification and biochemical characterisation of a novel glutamate decarboxylase from rice bran
Authors: Wang Li , Xu Dong Xia , Lv Ying Guo , Zhang Hui
Published: March 2010

BACKGROUND: Glutamate decarboxylase (GAD) is a useful enzyme whose main function is to catalyse the irreversible α‐decarboxylation of L‐glutamate to produce γ‐aminobutyric acid. The cheap and abundant rice‐processing by‐product rice bran contains a high amount of GAD, the purification and characterisation of which have not yet been reported. In this study, research on rice bran GAD was initiated.

RESULTS: Rice bran GAD was purified to homogeneity via a combined purification protocol of ammonium sulfate fractionation, ion exchange chromatography and two gel filtrations, with a purification fold of 128.6 and an activity recovery of 21.3%. The enzyme was active at pH 5.5 and 40 °C and retained 80% of its original activity in the pH range 5–9 and the temperature range 30–50 °C. GAD activity was significantly enhanced in the presence of Ca2+ but strongly inhibited by Ag+, Hg2+, sodium dodecyl sulfate and CH3COOH. Kinetic determination of the apparent Km for L‐glutamate and pyridoxal 5′‐phosphate gave values of 27.4 mmol L−1 and 1.16 µmol L−1 respectively.

CONCLUSION: Considering that rice bran is cheap and commercially available and that rice bran GAD is relatively stable, the development of cost‐effective rice bran GAD‐related functional foods would seem to be feasible. Copyright © 2010 Society of Chemical Industry
Cholesterol and lipid oxidation in raw and pan‐fried minced beef stored under aerobic packaging
Authors: Ferioli Federico , Dutta Paresh C , Caboni Maria F
Published: March 2010

BACKGROUND: The type of packaging atmosphere has been reported as a technological factor that consistently affects the quality of lipid fraction in meat. Oxidation of cholesterol and lipids was evaluated before and after pan frying in commercial refrigerated minced beef stored under aerobic atmosphere for 1 and 8 days.

RESULTS: In raw beef, cholesterol and lipid oxidation developed at a slow rate. Cholesterol oxidation products (COPs) did not significantly vary (∼8 µg COPs g−1 of fat) over 8 days, while in the same period thiobarbituric acid reactive substances (TBARS) less than doubled (from 0.7 to 1.2 malondialdehyde equivalents kg−1 of muscle). Pan frying did not influence the oxidative degree in the fresh product but consistently catalyzed cholesterol oxidation in stored beef. A significant increase was assessed in beef at the end of storage: from 8.6 to 30.0 µg COPs g−1 of fat in raw and cooked beef, respectively.

CONCLUSION: Aerobic packaging did not appear as a pro‐oxidant factor in fresh minced beef with a good oxidative quality during a short period of refrigerated storage. Copyright © 2010 Society of Chemical Industry
Biochemical, biological and histological evaluation of some culinary and medicinal herbs grown under greenhouse and field conditions
Authors: Yi Weiguang , Wetzstein Hazel Y
Published: March 2010

BACKGROUND: Increasing evidence supports the potential health benefits of herbal extracts displaying antioxidant, anti‐inflammatory and antitumour activities. Environment can have a pronounced effect on phenolic content and antioxidant capacity. The objectives of this study were to evaluate the total phenolic contents and antioxidant capacities of five different herbs grown under greenhouse and field conditions and to assess their potential anti‐inflammatory effects.

RESULTS: High total polyphenolic (TPP) content (measured by the Folin‐Ciocalteu reagent method) and high Trolox equivalent antioxidant capacity (TEAC) were observed in all herbs evaluated. Leaves from thyme, sage, spearmint and peppermint grown in the greenhouse showed significantly higher TPP content and TEAC than those grown under field conditions, with a threefold difference being observed in peppermint. Rosemary, spearmint and peppermint extracts showed stronger inhibition of cyclooxygenase COX‐2 than of COX‐1.

CONCLUSION: The results show that producing herbs under greenhouse conditions can improve their biological activities by increasing TPP contents and antioxidant capacities. The selective inhibition of COX‐2 activity by rosemary, spearmint and peppermint suggests that they may be useful as anti‐inflammatory agents with fewer side effects than regular non‐steroidal drugs. Copyright © 2010 Society of Chemical Industry
Influence of the Doping Level on the Interactions between Poly(3,4‐ethylenedioxythiophene) and Plasmid DNA
Authors: Teixeira‐Dias Bruno , Zanuy David , del Valle Luis J. , Estrany Francesc , Armelin Elaine , Alemán Carlos
Published: March 2010

The influence of the doping level in the formation of specific interactions between plasmid DNA and PEDOT is investigated using experimental assays and theoretical calculations. Electrochemical methods are used to prepare polymer samples with oxidation degrees ranging from 0.14 to 1.05 positive charges per repeating unit. A combination of experimental and theoretical results are used to propose a mechanism for the formation of DNA/conducting polymer complexes, which consists of the initial stabilization of the adducts through non‐specific interactions followed by small structural re‐arrangements that allow to be established specific hydrogen bonds involving the polar groups of the conducting polymer and selected DNA bases.

magnified image
Degradation of Poly(methyl methacrylate) Model Compounds Under Extreme Environmental Conditions
Authors: Bennet Francesca , Hart‐Smith Gene , Gruendling Till , Davis Thomas P. , Barker Philip J. , Barner‐Kowollik Christopher
Published: March 2010

There is a significant knowledge gap in the degradation of poly(methyl methacrylate) (pMMA) under conditions experienced by surface coatings in the harsh Australian environment. In the current study pMMA model compounds were exposed to 95 °C temperatures and high UV radiation (1 kW · m−2), separately as well as in combination. Contrary to the findings of previous studies, degradation proceeds in these conditions via a non‐radical cyclic mechanism. The mechanism was further confirmed by synthesis and degradation of ethylene‐oxide‐terminated pMMA, an intermediate product in the cycle. Electrospray ionisation mass spectrometry analysis of thermally degraded samples after 155 weeks shows degradation consistent with the proposed cycle in vinyl‐terminated pMMA, while saturated pMMA was shown to be stable after the same period. Saturation delayed the UV‐induced degradation, yet these compounds still displayed some slight degradation after 52 weeks, confirming the terminal vinyl bond in pMMA as a weak point. Combined UV and thermal radiation after 56 weeks showed degradation of both pMMA samples, with the vinyl‐terminated sample also exhibiting crosslinking. The combination of thermal and UV radiation also caused acceleration of degradation, shown by a comparison of the polymer samples after ≈60 weeks.

magnified image
State of Order of the Crosslinker in Main‐Chain Liquid Crystalline Elastomers
Authors: Zander Frank , Finkelmann Heino
Published: March 2010

Rigid anisotropic crosslinkers have been shown to decrease the nematic order and the transition temperatures of main‐chain liquid crystalline elastomers (MCLCEs). In order to look into this phenomenon, the state of order of an anisotropic crosslinker in an MCLCE was investigated separately from that of the matrix. For this purpose, multifunctional perylene derivatives were synthesized and used as a crosslinker and as a reference mesogen probe. Their states of order were measured by their dichroism, and were compared to that of the MCLCE matrix. A systematically lower degree of order was observed for the crosslinker in comparison to the matrix, both when attached to and dissolved in the network.

magnified image
Polyamide‐12/Functionalized Carbon Nanofiber Composites: Evaluation of Thermal and Mechanical Properties
Authors: Chávez‐Medellín Ricardo , Prado Luis A. Sanchez de Almeida , Schulte Karl
Published: March 2010

This work aims at improving the interfacial bonding between polyamide‐12 and CNFs. CNFs were oxidized and dispersed in polyamide‐12 giving rise to polymer nanocomposites. The oxidation caused an increase in the specific surface area and structural defects of the fibers, as indicated by surface area and Fourier‐transform Raman spectroscopy. The nanocomposites exhibited improved thermal and thermo‐oxidative stabilities. The oxidized nanofibers had marginal effect on the crystallinity and crystallization of the polyamide‐12. An over‐proportional enhancement of stiffness due to the fibers could be achieved. In spite of these improvements the fiber/polymer adhesion should be further improved.

magnified image
Ensemble Rule‐Based Classification of Substrates of the Human ABC‐Transporter ABCB1 Using Simple Physicochemical Descriptors
Authors: Demel Michael A. , Kraemer Oliver , Ettmayer Peter , Haaksma Eric , Ecker Gerhard F.
Published: March 2010

Within the last decades, the detailed knowledge on the impact of membrane bound drug efflux transporters of the ATP binding cassette (ABC) protein family on the pharmacological profile of drugs has enormously increased. Especially, ABCB1 (P‐glycoprotein, P‐gp, MDR1) has attracted particular interest in medicinal chemistry, since it determines the clinical efficacy, side effects and toxicity risks of drug candidates. Based on this, the development of in silico models that provide rapid and cost‐effective screening tools for the classification of substrates and nonsubstrates of ABCB1 is an urgent need in contemporary ADMET profiling. A characteristic hallmark feature of this transporter is its polyspecific ligand recognition pattern. In this study we describe a method for classifying ABCB1 ligands in terms of simple, conjunctive rules (RuleFit) based on interpretable ADMET features. The retrieved results showed that models based on large, very diverse data sets gave better classification performance than models based on smaller, more homogenous training sets. The best model achieved gave a correct classification rate of 0.90 for an external validation set. Furthermore, from the interpretation of the best performing model it could be concluded that in comparison to nonsubstrates ABCB1 substrates generally show a higher number of hydrogen‐bond acceptors, are more flexible and exhibit higher logPvalues.
Quantitative Prediction of Regioselectivity Toward Cytochrome P450/3A4 Using Machine Learning Approaches
Authors: Hasegawa Kiyoshi , Koyama Michio , Funatsu Kimito
Published: March 2010

In the drug discovery process, it is important to know the properties of both drug candidates and their metabolites. Fast and precise prediction of metabolites is essential. However, it has been difficult to predict metabolites because of the complexity of the mechanism of cytochrome P450/3A4 (CYP 3A4), which is the main metabolite enzyme of drugs. In this study, we focus on the regioselectivity of CYP 3A4, i.e., the selectivity of metabolic sites. We have developed a model to predict the regioselectivity of drug candidates by using machine learning (ML) approaches.
Linearly tapered slotline antenna array for quasi‐optical molecular spectroscopy
Authors: Lukes Zbynek , Lacik Jaroslav , Raida Zbynek
Published: March 2010

In this article, a novel design of a millimeter‐wave antenna array consisting of linearly tapered slotline antenna elements is presented. The antenna array was designed for the frequency range from 50 to 600 GHz. A numerical model of the antenna array was developed in CST microwave studio. To optimize the antenna model, a novel real‐coded genetic algorithm was proposed. The optimized antenna was fabricated from a low‐loss dielectric substrate ARLON CuClad 217, and its parameters were experimentally verified. The antenna was designed for quasi‐optical terahertz spectroscopy applications. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1043–1046, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25110
Festkörperchemie 2009
Authors: Höppe Henning , Indris Sylvio , Schmedt auf der Günne Jörn
Published: March 2010

Spektroskopie und Chemie der Festkörper — wie ein Stein mit vielen Facetten: intelligente Synthesen, die mit den Aggregatzuständen flüssig, gasförmig oder fest spielen, anspruchsvolle Strukturanalytik, Dynamik und Reaktionskinetik, Theorie der chemischen Bindung, reine Grundlagenforschung und der von Gesellschaft und Politik geforderte Transfer in die Anwendung.
Physikalische Chemie 2009: Zellen im Mikrochip
Authors: Kuhn Phillip , Dittrich Petra S.
Published: March 2010

Mit mikrofluidischen Plattformen lassen sich Veränderungen an einzelnen Zellen durch externe Einflüsse oder Zell‐Zell‐Kommunikation untersuchen. Das gewonnene Wissen wird nicht nur unser Verständnis für biologische Abläufe in lebenden Organismen erweitern, sondern kann auch helfen, Krankheiten besser zu verstehen und Medikamente zu entwickeln.
Makromolekulare Chemie 2009
Authors: Rehahn Matthias , Buchmeiser Michael R.
Published: March 2010

Polymere fassen in der Solarenergie Fuß und interagieren mit biologischen Systemen. Definierte Polymerarchitekturen sind der Schlüssel zu organischen und anorganischen Nanomaterialien.
Chemiedidaktik 2009
Authors: Becker Hans‐Jürgen , Stäudel Lutz
Published: March 2010

Die Chemiedidaktik belebt die Diskussion um Differenzierung im Unterricht zurzeit neu: Erkenntnisse werden aktualisiert, variiert und unter diagnostischer Perspektive problematisiert und reflektiert. Diese Diskussion liefert Lösungen für grundlegende Probleme von Chemieunterricht.
Optimization of magnetosonoporation for stem cell labeling
Authors: Xie Daohai , Qiu Bensheng , Walczak Piotr , Li Xubin , Ruiz‐Cabello Jesus , Minoshima Satoshi , Bulte Jeff W. M. , Yang Xiaoming
Published: March 2010

Recent advances in magnetic cell labeling have taken place with the development of a magnetosonoporation (MSP) technique. The aim of this study was to optimize the MSP protocol in order to achieve high cell viability and intracellular uptake of MR contrast agents. First, we determined the sub‐optimal MSP parameters by evaluating the viabilities of C17.2 neural stem cells without Feridex using various MSP intensities ranging from 0.1 to 1 w/cm2, duty cycles at 20%, 50% or 100%, and exposure times from 1–15 min. The sub‐optimized MSP parameters with cell viabilities greater than 90% were further optimized by evaluating both cell viability and intracellular iron uptake when Feridex was used. We then used the optimized MSP parameters to determinate the optimal concentration of Feridex for magnetic cell labeling. Subsequently, we validated the feasibility of using MRI to track the migration of neural stem cells from the transplanted sites to glioma masses in four mouse brains when the cells had been labeled with Feridex using the optimized MSP protocol. The MRI findings were confirmed by histological correlations. In vitro experiments demonstrated that the optimal MSP protocol was achieved at 20% duty cycle, 0.3 w/cm2 ultrasound intensity, 5‐min exposure time and 1mg/mL Feridex. This study demonstrated that the optimized MSP cell labeling technique can achieve both high cell viability and intracellular uptake of MR contrast agents, and has the potential to be a useful cell labeling technique to facilitate future clinical translation of MRI‐integrated cell therapy. Copyright © 2010 John Wiley & Sons, Ltd.
The generalized minimum edge‐biconnected network problem: Efficient neighborhood structures for variable neighborhood search
Authors: Hu Bin , Leitner Markus , Raidl Günther R.
Published: March 2010

We consider the generalized minimum edge‐biconnected network problem where the nodes of a graph are partitioned into clusters and exactly one node from each cluster is required to be connected in an edge‐biconnected way. Instances of this problem appear, for example, in the design of survivable backbone networks. We present different variants of a variable neighborhood search approach that utilize different types of neighborhood structures, each of them addressing particular properties as spanned nodes and/or the edges between them. For the more complex neighborhood structures, we apply efficient techniques—such as a graph reduction—to essentially speed up the search process. For comparison purposes, we use a mixed integer linear programming formulation based on multi‐commodity flows to solve smaller instances of this problem to proven optimality. Experiments on such instances indicate that the variable neighborhood search is also able to identify optimal solutions in the majority of test runs, but within substantially less time. Tests on larger Euclidean and random instances with up to 1,280 nodes, which could not be solved to optimality by mixed integer programming, further document the efficiency of the variable neighborhood search. In particular, all proposed neighborhood structures are shown to contribute significantly to the search process. © 2010 Wiley Periodicals, Inc. NETWORKS, 2010
SGBEM with Lagrange multipliers applied to elastic domain decomposition problems with curved interfaces using non‐matching meshes
Authors: Vodička R. , Mantič V. , París F.
Published: March 2010

An original approach to the solution of linear elastic domain decomposition problems by the symmetric Galerkin boundary element method is developed. The approach is based on searching for the saddle‐point of a new potential energy functional with Lagrange multipliers. The interfaces can be either straight or curved, open or closed. The two coupling conditions, equilibrium and compatibility, along an interface are fulfilled in a weak sense by means of Lagrange multipliers (interface displacements and tractions), which enables non‐matching meshes to be used at both sides of interfaces between subdomains. The accuracy and robustness of the method is tested by several numerical examples, where the numerical results are compared with the analytical solution of the solved problems, and the convergence rates of two error norms are evaluated for h‐refinements of matching and non‐matching boundary element meshes. Copyright © 2010 John Wiley & Sons, Ltd.
Modelling of reinforced‐concrete structures providing crack‐spacing based on X‐FEM, ED‐FEM and novel operator split solution procedure
Authors: Ibrahimbegovic Adnan , Boulkertous Amor , Davenne Luc , Brancherie Delphine
Published: March 2010

In this work, we present a novel approach to the finite element modelling of reinforced‐concrete (RC) structures that provides the details of the constitutive behavior of each constituent (concrete, steel and bond‐slip), while keeping formally the same appearance as the classical finite element model. Each component constitutive behavior can be brought to fully non‐linear range, where we can consider cracking (or localized failure) of concrete, the plastic yielding and failure of steel bars and bond‐slip at concrete steel interface accounting for confining pressure effects. The standard finite element code architecture is preserved by using embedded discontinuity (ED‐FEM) and extended (X‐FEM) finite element strain representation for concrete and slip, respectively, along with the operator split solution method that separates the problem into computing the deformations of RC (with frozen slip) and the current value of the bond‐slip. Several numerical examples are presented in order to illustrate very satisfying performance of the proposed methodology. Copyright © 2010 John Wiley & Sons, Ltd.
A stable explicit fractional step procedure for the solution of heat and fluid flow through interfaces between saturated porous media and free fluids in presence of high source terms
Authors: Arpino F. , Massarotti N. , Mauro A.
Published: March 2010

In this paper, porous medium‐free fluid interface problems in the presence of high source terms are studied for the first time by using a stable, accurate and efficient Artificial Compressibility (AC) Characteristic‐Based Split (CBS) algorithm. The interest in the AC‐CBS scheme has increased, as its matrix‐inversion free procedure offers the possibility of an easy and efficient parallelization. The present algorithm, recently introduced for the solution of porous media flows, presented some difficulties in solving complex interface problems. In this paper, the AC‐CBS scheme has been specifically developed to overcome such difficulties and produce an accurate, stable, and efficient solution for the generalized porous medium flow equations for forced, free, and mixed convection through interfaces. In order to obtain the present results, a stability analysis for the AC‐CBS scheme for the solution of problems with high source terms is carried out for the first time. The efficiency and the accuracy of the AC‐CBS algorithm are verified through comparison with analytical, numerical, and experimental data available in the literature. The authors consider three different types of interface benchmark problems: (i) forced convection in a horizontal channel; (ii) mixed convection in a vertical channel; and (iii) natural convection in a vertically divided cavity. Copyright © 2010 John Wiley & Sons, Ltd.
Simulation of transient heat conduction using one‐dimensional mapped infinite elements
Authors: Motley M. R. , Prévost J. H.
Published: March 2010

Many engineering problems exist in physical domains that can be said to be infinitely large. A common problem in the simulation of these unbounded domains is that a balance must be met between a practically sized mesh and the accuracy of the solution. In transient applications, developing an appropriate mesh size becomes increasingly difficult as time marches forward. The concept of the infinite element was introduced and implemented for elliptic and for parabolic problems using exponential decay functions. This paper presents a different methodology for modeling transient heat conduction using a simplified mesh consisting of only two‐node, one‐dimensional infinite elements for diffusion into an unbounded domain and is shown to be applicable for multi‐dimensional problems. A brief review of infinite elements applied to static and transient problems is presented. A transient infinite element is presented in which the element length is time‐dependent such that it provides the optimal solution at each time step. The element is validated against the exact solution for constant surface heat flux into an infinite half‐space and then applied to the problem of heat loss in thermal reservoirs. The methodology presented accurately models these phenomena and presents an alternative methodology for modeling heat loss in thermal reservoirs. Copyright © 2010 John Wiley & Sons, Ltd.
An improved cohesive element for shell delamination analyses
Authors: Yang Q. D. , Fang X. J. , Shi J. X. , Lua J.
Published: March 2010

In this paper, an improved cohesive element is proposed for accurate quantification of delamination in laminar composites. The improved cohesive element employs a mixed Gaussian and sub‐domain integration scheme for cohesive stress integration. Level set description of crack front geometry is used to accurately track the evolving delamination crack front. The new element offers significant improvement in solution accuracy and numerical stability, as compared with conventional cohesive elements using either Gaussian integration or Newton–Cotes integration. The much enhanced numerical accuracy and stability permit the use of bonded structural element size as large as 1∼1.5 times the cohesive zone size without significantly compromising numerical accuracy and efficiency. This greatly alleviates the strict mesh size requirement imposed by conventional cohesive elements that require the bonded structural element size be smaller than \documentclass{article}\footskip=0pc\pagestyle{empty}\begin{document}$\frac{1}{3}\sim\frac{1}{5}$\end{document} of the cohesive zone size. Furthermore, the new element offers the benefit of easy insertion of arbitrary initial crack geometry for a structured mesh. Copyright © 2010 John Wiley & Sons, Ltd.
Numerical aspects associated with the implementation of a finite strain, elasto‐viscoelastic–viscoplastic constitutive theory in principal stretches
Authors: Holmes D. W. , Loughran J. G.
Published: March 2010

This paper treats the numerical implementation of a finite strain, elasto‐viscoelastic–viscoplastic constitutive model for semi‐crystalline polymers, written in principal stretches. A parallel configuration of the three model elements is used that enables the decoupled algorithmic treatment of each response within a stress update numerical scheme. The numerical aspects associated with the use of principal stretch constitutive expressions in a tensor space numerical environment are initially developed for the general cases of any elastic or inelastic constitutive element. Included is the formulation of the closed‐form, consistent tangential modulus tensor. The principal space algorithmic treatments of the elastic, viscoelastic and viscoplastic elements are then used as specific examples. Of particular importance is the development of a principal space, closest point projection return mapping algorithm for viscoplasticity including isotropic strain hardening. Preliminary numerical examples are presented to illustrate the versatility of the model. Copyright © 2010 John Wiley & Sons, Ltd.
Evaluation of Green's function derivatives for exponentially graded elasticity
Authors: Sallah Omar M. , Gray L. J. , Nintcheu Fata S.
Published: March 2010

Effective formulas for computing Green's function of an exponentially graded three‐dimensional material have been derived in previous work. The expansion approach for evaluating Green's function has been extended to develop corresponding algorithms for its first‐ and second‐order derivatives. The resulting formulas are again obtained as a relatively simple analytic term plus a single double integral, the integrand involving only elementary functions. A primary benefit of the expansion procedure is the ability to compute the second‐order derivatives needed for fracture analysis. Moreover, as all singular terms in this hypersingular kernel are contained in the analytic expression, these expressions are readily implemented in a boundary integral equation calculation. The computational formulas for the first derivative are tested by comparing with results of finite difference approximations involving Green's function. In turn, the second derivatives are then validated by comparing with finite difference quotients using the first derivatives. Published in 2010 by John Wiley & Sons, Ltd.
Algebraic multigrid for finite element elasticity equations: Determination of nodal dependence via edge‐matrices and two‐level convergence
Authors: Karer E. , Kraus J. K.
Published: March 2010

We study an algebraic multigrid (AMG) method for solving elliptic finite element equations of linear elasticity problems. In this method, which has been proposed in (Kraus, SIAM J Sci Comput 2008; 30: 505–524), the coarsening is based on the so‐called edge‐matrices, which allows to generalize the concept of strong and weak connections, as used in the classical AMG, to ‘algebraic vertices’ that accumulate the nodal degrees of freedom in case of vector‐field problems. The major contribution of this work is related to the investigation of a measure for the nodal dependence and on the generation of the edge‐matrices, which are the basic building blocks of this method. A natural measure is the cosine of the abstract angle between the two subspaces spanned by the basis functions corresponding to the respective algebraic vertices. Another original contribution of this work is a two‐level convergence analysis of the method. The presented numerical results cover also problems with jumps in Young's modulus of elasticity and orthotropic materials. Copyright © 2010 John Wiley & Sons, Ltd.
Coupling of finite element and boundary integral methods for a capsule in a Stokes flow
Authors: Walter J. , Salsac A.‐V. , Barthès‐Biesel D. , Le Tallec P.
Published: March 2010

We introduce a new numerical method to model the fluid–structure interaction between a microcapsule and an external flow. An explicit finite element method is used to model the large deformation of the capsule wall, which is treated as a bidimensional hyperelastic membrane. It is coupled with a boundary integral method to solve for the internal and external Stokes flows. Our results are compared with previous studies in two classical test cases: a capsule in a simple shear flow and in a planar hyperbolic flow. The method is found to be numerically stable, even when the membrane undergoes in‐plane compression, which had been shown to be a destabilizing factor for other methods. The results are in very good agreement with the literature. When the viscous forces are increased with respect to the membrane elastic forces, three regimes are found for both flow cases. Our method allows a precise characterization of the critical parameters governing the transitions. Copyright © 2010 John Wiley & Sons, Ltd.
Subdomain radial basis collocation method for fracture mechanics
Authors: Wang Lihua , Chen Jiun‐Shyan , Hu Hsin‐Yun
Published: March 2010

The direct approximation of strong form using radial basis functions (RBFs), commonly called the radial basis collocation method (RBCM), has been recognized as an effective means for solving boundary value problems. Nevertheless, the non‐compactness of the RBFs precludes its application to problems with local features, such as fracture problems, among others. This work attempts to apply RBCM to fracture mechanics by introducing a domain decomposition technique with proper interface conditions. The proposed method allows (1) natural representation of discontinuity across the crack surfaces and (2) enrichment of crack‐tip solution in a local subdomain. With the proper domain decomposition and interface conditions, exponential convergence rate can be achieved while keeping the discrete system well‐conditioned. The analytical prediction and numerical results demonstrate that an optimal dimension of the near‐tip subdomain exists. The effectiveness of the proposed method is justified by the mathematical analysis and demonstrated by the numerical examples. Copyright © 2010 John Wiley & Sons, Ltd.
Imposing Dirichlet boundary conditions with Nitsche's method and spline‐based finite elements
Authors: Embar Anand , Dolbow John , Harari Isaac
Published: March 2010

A key challenge while employing non‐interpolatory basis functions in finite‐element methods is the robust imposition of Dirichlet boundary conditions. The current work studies the weak enforcement of such conditions for B‐spline basis functions, with application to both second‐ and fourth‐order problems. This is achieved using concepts borrowed from Nitsche's method, which is a stabilized method for imposing constraints on surfaces. Conditions for the stability of the system of equations are derived for each class of problem. Stability parameters in the Nitsche weak form are then evaluated by solving a local generalized eigenvalue problem at the Dirichlet boundary. The approach is designed to work equally well when the grid used to build the splines conforms to the physical boundary of interest as well as to the more general case when it does not. Through several numerical examples, the approach is shown to yield optimal rates of convergence. Copyright © 2010 John Wiley & Sons, Ltd.
Stochastic simulations based on mixed finite elements for solute transport in groundwater
Authors: Radu Florin A. , Suciu Nicolae
Published: March 2010

An accurate mixed finite element method to solve both flow and transport is developed for stochastic simulations of transport in saturated aquifers characterized by random log‐hydraulic conductivity fields. The main advantage of the mixed finite element is that it is local mass conservative. Unlike in stochastic finite element methods, this approach yields concentration fields and concentration moments for samples of the random field. In this way, it will be possible to analyze the behavior of different ensemble average observables of the transport process as well as the behavior of their fluctuations. Results of the stochastic simulations described here can be used to assess the reliability for real cases of the ensemble average quantities provided by stochastic modeling of transport in groundwater. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A constitutive model for continuous fiber reinforced polymer plies
Authors: Flatscher Thomas , Schuecker Clara , Pettermann Heinz E.
Published: March 2010

In the present paper a constitutive model is reviewed which can be used to predict the non‐linear behavior of continuous fiber reinforced laminates with polymeric matrix materials. The constitutive model considers stiffness degradation and plastic strain accumulation at the length scale of the individual plies (laminae). These effects are modeled via two different phenomenological approaches, however, their interaction is considered when the constitutive equations are solved by an implicit integration scheme. To demonstrate the predictive capabilities of the individual model parts, examples are given where the above mentioned effects are decoupled. This way, their impact on the laminate's response can be studied independently. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A multiphase finite element simulation of biological conversion processes in landfills
Authors: Ricken Tim , Robeck Markus , Widmann Renatus
Published: March 2010

Worldwide, landfills are the most common way to dispose of waste, but have an impact on the environment as a result of harmful gas and leachate production. Estimating the long‐term behaviour of a landfill in regard to this gas production and organic degrading, as well as to settlement and waste water production, is of high importance. Therefore, a model has been developed to simulate these processes. This constitutive model is based on the multiphase Theory of Porous Media. The body under investigation consists of an organic and an inorganic phase as well as a liquid and a gas phase. The equations of the model are developed on the basis of a consistent thermo‐mechanical approach including the momentum balance for the solid phase and the mixture, the energy balance for the mixture and the mass balance for the gas phase. All interactions between the constituents such as mass transfers, interaction forces and energy fluxes are taken into consideration. The strongly coupled set of partial differential equations is implemented in the finite element code FEAP. The theoretical framework and the results of meantime successfully performed simulation of a real landfill body will be shown. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inverse dynamics of underactuated multibody systems
Authors: Quasem Mahmud , Uhlar Stefan , Betsch Peter
Published: March 2010

The present work deals with controlled mechanical systems subject to holonomic constraints. In particular, we focus on underactuated systems, defined as systems in which the number of degrees of freedom exceeds the number of inputs. The governing equations of motion can be written in the form of differential‐algebraic equations (DAEs) with a mixed set of holonomic and control constraints. The rotationless formulation of multibody dynamics will be considered [1]. To this end, we apply a specific projection method to the DAEs in terms of redundant coordinates. A similar projection approach has been previously developed in the framework of generalized coordinates by Blajer & Kołodziejczyk [2]. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)