bluuebunny/crossref_metadata_2025 huggingface dataset:
Optisch reine, monodisperse cis‐Oligodiacetylene: Chiralitätsverstärkung durch Aggregation
Authors: Chernick Erin T. , Börzsönyi Gabor , Steiner Christian , Ammon Maximilian , Gessner David , Frühbeißer Sabine , Gröhn Franziska , Maier Sabine , Tykwinski Rik R.
Published: November 2013

Konformationsänderungen des konjugierten Rückgrats von Poly‐ und Oligodiacetylenen (PDAs und ODAs) spielen bei der Bestimmung der elektronischen Eigenschaften dieser Verbindungen eine wichtige Rolle. Gleichzeitig können Konformationsänderungen auch zu gefalteten Strukturen führen, die helikale Chiralität aufweisen. Durch Verwendung von D‐Campher als chiraler Baustein konnten monodisperse, optisch reine cis‐Oligodiacetylene (ODAs) in hoher Ausbeute erhalten werden. cis‐ODAs bis zur Länge des Tridecamers wurden synthetisiert, was dem längsten bisher bekannten monodispersen cis‐ODA entspricht. UV/Vis‐Spektroskopie deutet auf eine hohe effektive Konjugationslänge in THF hin, vermutlich aufgrund einer linearen planaren Konformation in diesem Lösungsmittel. Hochauflösende STM/AFM‐Messungen von Filmen des Nonamers, abgeschieden aus einer THF‐Lösung auf HOPG, zeigen eine lineare Struktur. In iPrOH gemessene Zirkulardichroismus(CD)‐Spektren legen die Bildung chiraler Aggregate der ODAs mit mindestens neun D‐Campher‐Einheiten nahe. Die CD‐Resonanz ist konzentrations‐ und temperaturabhängig.
Penta‐ und hexakoordinierte Tris(pentafluorethyl)fluorosilicate
Authors: Steinhauer Simon , Stammler Hans‐Georg , Neumann Beate , Ignat'ev Nikolai , Hoge Berthold
Published: November 2013

Das Forschungsgebiet der Perfluoralkylsilane ist noch jung. Zwar sind bereits mehrere Beispiele für Difluorotriorganylsilicate bekannt, hier stellen wir allerdings mit dem Dianion [Si(C2F5)3F3]2− das erste Beispiel für ein vollständig charakterisiertes Trifluorotriorganylsilicat vor. Der stark elektronenziehende Einfluss der Pentafluorethylgruppen scheint wesentlich für die Stabilisierung dieser Verbindung zu sein. Des Weiteren ist dieses Dianion das erste strukturell charakterisierte Beispiel einer Tris(pentafluorethyl)siliciumverbindung. Uns gelang die Herstellung und vollständige Charakterisierung von [PPh4]2[Si(C2F5)3F3] und [PPh4][Si(C2F5)3F2] sowie der Vorstufe [H(OEt2)2][Si(C2F5)3F2] ausgehend von SiCl4 und LiC2F5.
Gold‐Catalyzed Heterogeneous Aerobic Dehydrogenative Amination of α,β‐Unsaturated Aldehydes to Enaminals
Authors: Jin Xiongjie , Yamaguchi Kazuya , Mizuno Noritaka
Published: November 2013

Although enaminals (β‐enaminals) are very important compounds and have been utilized as useful synthons for various important compounds, they have been synthesized through non‐green and/or limited procedures until now. Herein, we have successfully developed a green synthetic procedure using a heterogeneous catalyst. In the presence of gold nanoparticles supported on manganese‐oxide‐based octahedral molecular sieves OMS‐2 (Au/OMS‐2), dehydrogenative amination of α,β‐unsaturated aldehydes with amines proceeded efficiently, with the corresponding enaminals isolated in moderate to high yields (50–97 %). The catalysis was truly heterogeneous, and Au/OMS‐2 could be reused. Furthermore, the formal Wacker‐type oxidation of α,β‐unsaturated aldehydes to enaminones has been realized.
Total Synthesis of Pectenotoxin‐2
Authors: Fujiwara Kenshu , Suzuki Yuki , Koseki Nao , Aki Yu‐ichi , Kikuchi Yuta , Murata Shun‐ichi , Yamamoto Fuyuki , Kawamura Mariko , Norikura Toshio , Matsue Hajime , Murai Akio , Katoono Ryo , Kawai Hidetoshi , Suzuki Takanori
Published: November 2013

Pectenotoxin‐2 (PTX2) is a shellfish toxin and has a non‐anomeric spiroacetal, which is not stabilized by an anomeric effect. The selective construction of the non‐anomeric spiroacetal has been a major problem in the synthesis of PTX2. Described herein is the stereoselective total synthesis of PTX2 via the isomerization of anomeric spiroacetal pectenotoxin‐2b (PTX2b). The synthesis of PTX2b was achieved by a simple process including sulfone‐mediated assembly of spirocyclic and bicyclic acetals and subsequent macrocyclization by ring‐closing olefin metathesis. Finally, the selective construction of PTX2 was accomplished by the early termination of a dynamic transition process to equilibrium in the acid‐catalyzed isomerization of anomeric PTX2b. [6,6]‐Spiroacetal pectenotoxin‐2c (PTX2c) was also synthesized from PTX2b. The cytotoxicity assay of the synthetic compounds against HepG2 and Caco2 cancer cells showed a potency of the order: PTX2≫PTX2b>PTX2c.
Structure of a Complex Formed by a Protein and a Helical Aromatic Oligoamide Foldamer at 2.1 Å Resolution
Authors: Buratto Jérémie , Colombo Cinzia , Stupfel Marine , Dawson Simon J. , Dolain Christel , Langlois d'Estaintot Béatrice , Fischer Lucile , Granier Thierry , Laguerre Michel , Gallois Bernard , Huc Ivan
Published: November 2013

In the search of molecules that could recognize sizeable areas of protein surfaces, a series of ten helical aromatic oligoamide foldamers was synthesized on solid phase. The foldamers comprise three to five monomers carrying various proteinogenic side chains, and exist as racemic mixtures of interconverting right‐handed and left‐handed helices. Functionalization of the foldamers by a nanomolar ligand of human carbonic anhydrase II (HCA) ensured that they would be held in close proximity to the protein surface. Foldamer–protein interactions were screened by circular dichroism (CD). One foldamer displayed intense CD bands indicating that a preferred helix handedness is induced upon interacting with the protein surface. The crystal structure of the complex between this foldamer and HCA could be resolved at 2.1 Å resolution and revealed a number of unanticipated protein–foldamer, foldamer–foldamer, and protein–protein interactions.
Bacteria‐Triggered Release of Antimicrobial Agents
Authors: Komnatnyy Vitaly V. , Chiang Wen‐Chi , Tolker‐Nielsen Tim , Givskov Michael , Nielsen Thomas E.
Published: November 2013

Medical devices employed in healthcare practice are often susceptible to microbial contamination. Pathogenic bacteria may attach themselves to device surfaces of catheters or implants by formation of chemically complex biofilms, which may be the direct cause of device failure. Extracellular bacterial lipases are particularly abundant at sites of infection. Herein it is shown how active or proactive compounds attached to polymeric surfaces using lipase‐sensitive linkages, such as fatty acid esters or anhydrides, may be released in response to infection. Proof‐of‐concept of the responsive material is demonstrated by the bacteria‐triggered release of antibiotics to control bacterial populations and signaling molecules to modulate quorum sensing. The self‐regulating system provides the basis for the development of device‐relevant polymeric materials, which only release antibiotics in dependency of the titer of bacteria surrounding the medical device.
Synthesis of Five‐ and Six‐Coordinate Tris(pentafluoroethyl)fluorosilicates
Authors: Steinhauer Simon , Stammler Hans‐Georg , Neumann Beate , Ignat'ev Nikolai , Hoge Berthold
Published: November 2013

The research area of perfluoroalkylsilanes is still in its infancy. Although there are already many examples of difluorotriorganylsilicates, the first example of a completely characterized trifluorotriorganylsilicate is presented, the dianion [Si(C2F5)3F3]2−. The strongly electron‐withdrawing influence of the pentafluoroethyl groups appears to be a fundamental cause of the stability of this compound. This dianion is also the first structurally characterized example of a tris(pentafluoroethyl)silicon compound. The synthesis and complete characterization of [PPh4]2[Si(C2F5)3F3] and [PPh4][Si(C2F5)3F2] along with the precursor [H(OEt2)2][Si(C2F5)3F2] was achieved from SiCl4 and LiC2F5.
Pt‐Pd‐Co Trimetallic Alloy Network Nanostructures with Superior Electrocatalytic Activity towards the Oxygen Reduction Reaction
Authors: Liu Xinyu , Fu Gengtao , Chen Yu , Tang Yawen , She Peiliang , Lu Tianhong
Published: November 2013

Pt alloy nanostructures show great promise as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes. Herein, three‐dimensional (3D) Pt‐Pd‐Co trimetallic network nanostructures (TNNs) with a high degree of alloying are synthesized through a room temperature wet chemical synthetic method by using K2PtCl4/K3Co(CN)6–K2PdCl4/K3Co(CN)6 mixed cyanogels as the reaction precursor in the absence of surfactants and templates. The size, morphology, and surface composition of the Pt‐Pd‐Co TNNs are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected‐area electron diffraction (SAED), energy dispersive spectroscopy (EDS), EDS mapping, X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). The 3D backbone structure, solid nature, and trimetallic properties of the mixed cyanogels are responsible for the 3D structure and high degree of alloying of the as‐prepared products. Compared with commercially available Pt black, the Pt‐Pd‐Co TNNs exhibit superior electrocatalytic activity and stability towards the ORR, which is ascribed to their unique 3D structure, low hydroxyl surface coverage and alloy properties.
Evaluation of nucleation rate by in‐situ focused beam reflectance measurement in an unseeded batch cooling crystallization
Authors: Kim Jun‐Woo , Kim Jungwook , Lee Keun‐Deuk , Koo Kee‐Kahb
Published: November 2013

Nucleation kinetics in the cooling crystallization of hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) from γ‐butyrolactone was studied by converting total counts/s measured by in situ focused beam reflectance measurement (FBRM) into number of crystals. The classical nucleation rate model, which is derived exclusively from the thermodynamic state for the nucleation and molecular collision frequency, was found to be inadequate to describe the experimentally measured nucleation rates. However, the nucleation rates predicted by the modified classical nucleation rate model, inclusive of an additional temperature term, were found to be in good agreement with those measured in the present work. Furthermore, the metastable zone widths are also found to be more accurately predicted by the modified classical nucleation rate model than the classical approach, which assumes that the mass‐based nucleation rate is an exponential function of supersaturation and is equal to the supersaturation rate.
Downregulation of microRNA‐107 in intestinal CD11c+ myeloid cells in response to microbiota and proinflammatory cytokines increases IL‐23p19 expression
Authors: Xue Xiaochang , Cao Anthony T. , Cao Xiaocang , Yao Suxia , Carlsen Eric D. , Soong Lynn , Liu Chang‐Gong , Liu Xiuping , Liu Zhanju , Duck L. Wayne , Elson Charles O. , Cong Yingzi
Published: November 2013

Commensal flora plays an important role in the development of the mucosal immune system and in maintaining intestinal homeostasis. However, the mechanisms involved in regulation of host‐microbiota interaction are still not completely understood. In this study, we examined how microbiota and intestinal inflammatory conditions regulate host microRNA expression and observed lower microRNA‐107 (miR‐107) expression in the inflamed intestines of colitic mice, compared with that in normal control mice. miR‐107 was predominantly reduced in epithelial cells and CD11c+ myeloid cells including dendritic cells and macrophages in the inflamed intestines. We demonstrate that IL‐6, IFN‐γ, and TNF‐α downregulated, whereas TGF‐β promoted, miR‐107 expression. In addition, miR‐107 expression was higher in the intestines of germ‐free mice than in mice housed under specific pathogen‐free conditions, and the presence of microbiota downregulated miR‐107 expression in DCs and macrophages in a MyD88‐ and NF‐κB‐dependent manner. We determined that the ectopic expression of miR‐107 specifically repressed the expression of IL‐23p19, a key molecule in innate immune responses to commensal bacteria. We concluded that regulation of miR‐107 by intestinal microbiota and proinflammatory cytokine serve as an important pathway for maintaining intestinal homeostasis.
Gold(I) Complexes of Phosphaalkynes
Authors: Sanguramath Rajashekharayya A. , Townsend Nell S. , Lynam Jason M. , Russell Christopher A.
Published: November 2013

Cationic gold(I) complexes of phosphaalkynes are formed by the interaction of [PtBu2(o‐biphenyl)AuCl] with AgSbF6 and an excess amount of RC≡P in CH2Cl2 at room temperature. Free and coordinated phosphaalkyne readily exchange through an associative mechanism. In the solid state, the phosphaalkyne binds in a π fashion and slips towards the carbon end of the triple bond.
Impact of extent of parotid resection on postoperative wound complications: A prospective study
Authors: Tuckett Joel , Glynn Ronan , Sheahan Patrick
Published: November 2013

Background

Sialocele and salivary fistula are common complications after parotidectomy. The purpose of the present study was to investigate whether extent of parotidectomy influences the incidence of these complications.

Methods

We conducted a prospective study of 66 consecutive parotidectomies. Cases undergoing skin or bone resection or flap reconstruction were excluded. Patients were divided into 2 groups based on extent of surgery: group 1 (extracapsular dissection or partial superficial parotidectomy); and group 2 (superficial parotidectomy or more extensive resection). The incidence of postoperative sialocele, salivary fistula, and facial weakness was studied.

Results

Eleven patients (16.7%) developed a sialocele, and 4 (6.1%) developed a salivary fistula. Group 1 had a significantly higher incidence of wound complications (p = .008), but a significantly lower incidence of facial weakness (p = .004).

Conclusion

Less extensive parotid resection seems to be associated with a higher incidence of postoperative sialocele and salivary fistula, but is also associated with less postoperative facial nerve dysfunction. © 2014 Wiley Periodicals, Inc. Head Neck 37: 64–68, 2015
Passive sampling methods for contaminated sediments: Practical guidance for selection, calibration, and implementation
Authors: Ghosh Upal , Kane Driscoll Susan , Burgess Robert M , Jonker Michiel TO , Reible Danny , Gobas Frank , Choi Yongju , Apitz Sabine E , Maruya Keith A , Gala William R , Mortimer Munro , Beegan Chris
Published: November 2013

This article provides practical guidance on the use of passive sampling methods (PSMs) that target the freely dissolved concentration (Cfree) for improved exposure assessment of hydrophobic organic chemicals in sediments. Primary considerations for selecting a PSM for a specific application include clear delineation of measurement goals for Cfree, whether laboratory-based “ex situ” and/or field-based “in situ” application is desired, and ultimately which PSM is best-suited to fulfill the measurement objectives. Guidelines for proper calibration and validation of PSMs, including use of provisional values for polymer–water partition coefficients, determination of equilibrium status, and confirmation of nondepletive measurement conditions are defined. A hypothetical example is described to illustrate how the measurement of Cfree afforded by PSMs reduces uncertainty in assessing narcotic toxicity for sediments contaminated with polycyclic aromatic hydrocarbons. The article concludes with a discussion of future research that will improve the quality and robustness of Cfree measurements using PSMs, providing a sound scientific basis to support risk assessment and contaminated sediment management decisions. Integr Environ Assess Manag 2014;10:210–223. © 2014 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC.

Key Points

Specific guidance is provided for the use of passive sampling methods for measuring freely dissolved concentrations in contaminated sediment site assessments. Guidelines are provided for proper calibration and validation of passive sampling methods including use of provisional values for polymer-water partition coefficients. Determination of equilibrium status and confirmation of non-depletive measurement conditions are defined. Further development is needed for the use of non-equilibrium passive sampling methods in the field and the validation of performance reference compound use in static sediment environments.
Polycaprolactone/oligomer compound scaffolds for cardiac tissue engineering
Authors: Srinivasa Reddy Chaganti , Reddy Venugopal Jayarama , Ramakrishna Seeram , Zussman Eyal
Published: November 2013

Polycaprolactone (PCL), a synthetic biocompatible and biodegradable polymer generally used as a scaffold material for tissue engineering applications. The high stiffness and hydrophobicity of the PCL fiber mesh does not provide significant cell attachment and proliferation in cardiac tissue engineering. Towards this goal, the study focused on a compound of PCL and oligomer hydrogel [Bisphenol A ethoxylated dimethacrylate (BPAEDMA)] processed into electrospun nanofibrous scaffolds. The composition, morphology and mechanical properties of the compound scaffolds, composed of varying ratios of PCL and hydrogel were characterized by scanning electron microscopy, infrared spectroscopy and dynamic mechanical analyzer. The elastic modulus of PCL/BPAEDMA nanofibrous scaffolds was shown to be varying the BPAEDMA weight fraction and was decreased by increasing the BPAEDMA weight fraction. Compound fiber meshes containing 75 wt % BPAEDMA oligomer hydrogel exhibited lower modulus (3.55 MPa) and contact angle of 25o. Rabbit cardiac cells cultured for 10 days on these PCL/BPAEDMA compound nanofibrous scaffolds remained viable and expressed cardiac troponin and alpha‐actinin proteins for the normal functioning of myocardium. Cell adhesion and proliferations were significantly increased on compound fiber meshes containing 75 wt % BPAEDMA, when compared with other nanofibrous scaffolds. The results observed that the produced PCL/BPAEDMA compound nanofibrous scaffolds promote cell adhesion, proliferation and normal functioning of cardiac cells to clinically beneficial levels, relevant for cardiac tissue engineering. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3713–3725, 2014.
Analysis of an electromagnetic tube placement device versus a self‐advancing nasal jejunal device for postpyloric feeding tube placement
Authors: Boyer Nathan , McCarthy Mary S. , Mount Cristin A.
Published: November 2013

BACKGROUND

Initiation of enteral feeding is an important part of the best practice model for critically ill patients. Although nasogastric feeding is appropriate for the majority of patients requiring short‐term nutrition support, certain patients benefit greatly from postpyloric feeding.

OBJECTIVE

To determine which of 2 specialized enteral tube systems achieved postpyloric placement on initial insertion attempt most efficiently.

DESIGN

Retrospective study comparing the Tiger 2 tube (T2T) and Cortrak Enteral Access System (C‐EAS).

SETTING

Academic medical center, mixed intensive care unit (ICU).

PATIENTS

All patients admitted to the ICU between 2009 and 2013 who had either a C‐EAS or T2T placed.

MEASUREMENTS

Success rate for postpyloric placement, congruency of real‐time tube placement with x‐ray confirmation for C‐EAS, and complication rates.

RESULTS

Seventy‐one T2T and 74 C‐EAS patients were included. The T2T was postpyloric 62% (44/71) of attempted placements. C‐EAS was postpyloric 43% (32/74) of attempted placements (P = 0.03). C‐EAS tracings accurately reflected chest x‐ray findings 83% and 82% for postpyloric and non‐postpyloric insertion, respectively. During the entire study period, no adverse events were recorded.

CONCLUSION

Our institution evaluated 2 different systems designed to ensure postpyloric placement of a small bore feeding tube. No literature exists directly comparing the 2 systems. Our retrospective review, although limited, showed that the T2T was more effective at postpyloric placement on first attempt. Although 1 benefit of the C‐EAS system may be real‐time visualization, our practice showed this system to be user dependent, which likely led to less success with postpyloric placement. Journal of Hospital Medicine 2014;9:23–28. Published 2013 Society of Hospital Medicine
Re-evaluation of the predictive score for 6-month graft survival in living donor liver transplantation in the modern era
Authors: Yoshizumi Tomoharu , Ikegami Toru , Bekki Yuki , Ninomiya Mizuki , Uchiyama Hideaki , Iguchi Tomohiro , Yamashita Yo-Ichi , Kawanaka Hirofumi , Shirabe Ken , Maehara Yoshihiko
Published: November 2013

The limitations of donor age, graft size, and the Model for End-Stage Liver Disease (MELD) score have not been apparent in living donor liver transplantation (LDLT). Our team developed a formula for predicting graft survival after LDLT; the formula includes the graft weight, donor age, MELD score, and portosystemic shunt status. The aims of this study were to re-evaluate the reliability of our formula and to assess whether our modified treatment strategy has improved 6-month graft survival. Two hundred seventeen patients were allocated into 2 groups: patients with predictive scores ≥ 1.30 (n = 162) and patients with predictive scores < 1.30 (n = 55). The latter group was also divided into subgroups of patients with scores of 1.15 to 1.30 (n = 37) and patients with scores < 1.15 (n = 18). Survival rates for patients with scores < 1.30 were significantly worse than rates for patients with scores ≥ 1.30 (P = 0.006). Survival rates for patients with scores < 1.15 were significantly worse than rates for patients with scores of 1.15 to <1.30 (P < 0.001). A multivariate analysis showed that a predictive score < 1.15 (odds ratio = 7.87, P = 0.006) and a body mass index ≥ 30 kg/m2 (odds ratio = 13.3, P < 0.001) were independent risk factors for 6-month graft mortality. In conclusion, predictive scores reliably predict 6-month graft survival and could allow a widening of the safe ranges for donor ages and graft sizes. Liver Transpl 20:323-332, 2014. © 2013 AASLD.
Collective Dynamics and Transient Behavior of Partially Hydrophobic Hyaluronic Acid Chains
Authors: Finelli Ivana , Chiessi Ester , Oddo Letizia , Galesso Devis , Renier Davide , Paradossi Gaio
Published: November 2013

The unique performance of a partially hydrophobic derivative of hyaluronic acid, HYADD4, bearing 2–3 hexadecylic side chains every 100 repeating units, enables hydrogels based on this polymer to be suitably used as a viscosupplement to replace synovial fluid in stressed or injured articular joints. This contribution addresses: i) as to whether there is a self‐assembly process driving the HYADD4 hydrogel stabilization and ii) what the characteristics of the long‐range dynamics governing the macroscopic viscoelastic behavior are, and to what extent these features are different from those present in the parent polymer (i.e., hyaluronic acid). Mesoscale dynamic and static properties are interpreted in the light of “sticky reptation theory” and evaluated in combination with small‐angle neutron scattering results.

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Energy and CO2 Savings: Systematic Approach and Examples in Polymer Production
Authors: Bachmann Rolf , Drumm Christian , Garg Vijay Kumar , Heijl Jan , Ruytinx Bert , Eynde Johan Vanden , Wolf Aurel
Published: November 2013

The chemical industry has set ambitious targets for the reduction of greenhouse gas emissions and energy consumption. In the present work, a systematic approach for a successful reduction of energy consumption and emissions is presented. A Structured Efficiency System for Energy (STRUCTese®) helps to identify, monitor and manage energy efficiency. The method fosters and accompanies energy saving measures as shown in the first two examples from polymer production: energy savings through operational efficiency and raw material savings with a new plant design. In addition, such a systematic approach pushes the development of innovative processes and provides a vision for an energy efficient future as shown in the third example: the use of CO2 as a raw material in the copolymerization with epoxides.
Dynamics of Network Formation in Aqueous Suspension RAFT Styrene/Divinylbenzene Copolymerization
Authors: Gonçalves Miguel A. D. , Pinto Virgínia D. , Dias Rolando C. S. , Hernándes‐Ortiz Julio C. , Costa Mário Rui P. F. N.
Published: November 2013

Experimental studies concerning the RAFT copolymerization of styrene and commercial divinylbenzene were performed in order to assess the use of controlled radical polymerization for the production of non‐conventional polymer networks. Aqueous suspension polymerizations were carried out in stirred batch reactor and changes of a few operation parameters were tried in order to assess their effect on key product properties: reaction temperature, initial ratio monomer/RAFT agent, monomer dilution in the organic phase and crosslinker content in the monomer mixture were changed along the experimental program. Polymerizations were extended beyond the gel point in order to synthesize gel beads. The effect of different commercially available RAFT agents (e.g. S‐thiobenzoyl thioglycolic acid and two trithiocarbonates) on network process formation was also studied. Dynamics of gel formation was measured using size exclusion chromatography with refractive index and light scattering detection. Iodine chloride titration yielded pendant double bonds concentration. In‐line and off‐line FTIR‐ATR measurements were also performed in order to obtain information concerning the kinetics of formation and final structure of the gels.
An In‐Situ NMR Study of Radical Copolymerization Kinetics of Acrylamide and Non‐Ionized Acrylic Acid in Aqueous Solution
Authors: Preusser Calista , Hutchinson Robin A.
Published: November 2013

An in‐situ NMR technique has been developed to study the aqueous phase copolymerization of non‐ionized acrylic acid (AA) and acrylamide (AM) under near‐isothermal conditions at much higher monomer contents than previously reported in the literature. The composition data obtained over the entire conversion range provides a precise estimate of monomer reactivity ratios not available from low conversion data. The set of experiments, with initial monomer content in aqueous solution varied between 5 and 40%, were well‐fit over the complete conversion range by rAA = 1.24 ± 0.02, and rAM = 0.55 ± 0.01. It was found that the rate of monomer conversion increases with increasing monomer concentration, a trend contrary to the known decrease in the AA and AM chain‐end propagation rate coefficients.
New Reactor for Polyester Polyols Continuous Synthetic Process
Authors: Chen Like , Xi Zhenhao , Qin Zhen , Zhao Ling , Yuan Weikang
Published: November 2013

Based on the kinetic and thermodynamic equations, a comprehensive mathematical model for the continuous synthetic process of polyester polyols was developed, which was carried out in two innovational bubbling reactive distillation towers (BRDTs). In this new type of reactor, condensation reactions among oligomers of polyester polyols were accomplished efficiently and rapidly. Two bench BRDTs with the height of 2 m were applied for the continuous process of poly(ethylene adipate) (PEA). In the first continuous esterification operation at atmospheric pressure, linear oligomers were discharged from the bottom of the column, while water and ethylene glycol (EG) passed a few column trays and a packing section and reached the top of the column. Then water was discharged as byproducts and EG was sent back to the first tray for further reaction. In the second continuous polycondensation operated in the second BRDT under partial vacuum, PEA was discharged from the bottom of the column, while water and ethylene glycol passed a few column trays, they were discharged as byproducts. The influence of major operating conditions on reactor performance was also simulated. Simulation results provided a strategy for developing and optimizing this process.
Experimental and Modeling Study of Melt Polycondensation Process of PA‐MXD6
Authors: Xi Zhenhao , Chen Like , Zhao Yong , Zhao Ling
Published: November 2013

The main polycondensation reaction of poly(m‐xylene adipamide) (PA‐MXD6) is a reversible reaction strongly coupled with mass transfer in melt polycondensation process. In this work, a realistic model for melt polycondensation of PA‐MXD6 has been proposed taking in to account the kinetics data, equilibrium data and diffusion process for major by‐product water in the melts. The characteristics of reaction and the effects of mass‐transfer of polycondensation process have been studied by using stagnant film experiments. It is observed that the apparent rate of the polycondensation process increases with higher temperature, lower degree of vacuum and thinner film thickness with reduced specific interfacial area. Based on the experimental data, the model parameters including the kinetics data, equilibrium data and mass transfer coefficient of volatile have been estimated by the nonlinear least squares method. The model predictions are in a quite satisfactory agreement with the experimental data that all of the relative deviations are almost less than 2%.
Certified Nonlinear Parameter Optimization with Reduced Basis Surrogate Models
Authors: Dihlmann Markus , Haasdonk Bernard
Published: November 2013

PDE‐constrained parameter optimization problems suffer from the high dimensionality of the corresponding discretizations, which results in long optimization runtimes. One possible approach to solve such large scale optimization problems more rapidly is to replace the PDE constraint by a low‐dimensional model constraint obtained via model reduction. We present a general technique for certification of such surrogate optimization results by a‐posteriori error estimation based on Reduced Basis (RB) models. We allow arbitrary PDEs and optimization functionals, in particular cover nonlinear optimization problems. Experiments on a stationary heat‐conduction problem demonstrate the applicability of the error bound. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling Dislocation‐Stacking Fault Interaction Using Molecular Dynamics
Authors: Rezaei Mianroodi Jaber , Svendsen Bob
Published: November 2013

In a number of fcc materials such as copper or aluminum, as well as more complex materials such as twinning induced plasticity (TWIP) steels, the interaction between dislocations and other defects such as stacking faults or twins plays an important role in the hardening behavior of such materials. Interactions of dislocation and twin or stacking fault layers have been studied in this work using molecular dynamics. Depending on the material and the loading conditions, possible interaction modes include (i) penetration of the dislocation into the faulted layer, (ii) reduction of the faulted layer after interaction, (iii) growth of the faulted layer after interaction. Such studies up to this point have been performed without temperature control near zero K (0 to 2 K). In this work, we extend the previous studies to higher temperature with the help of two methods, both based on molecular dynamics (MD) modeling. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterisation of bubble clusters in simulations of upward turbulent channel flow
Authors: Santarelli Claudio , Fröhlich Jochen
Published: November 2013

The paper reports on Direct Numerical Simulations of bubble‐laden flows performed to investigate the interaction of bubbles with turbulence in an upward flow between two parallel vertical plates. Two simulations are presented with uniform bubble diameter and a third one with bi‐disperse bubbles. Three different approaches are used to characterize bubble clustering in the investigated configuration. Horizontal pairing and tendency to form cluster has been found for all reported cases, slightly less pronounced in the bi‐disperse swarm. Among other results, a 60°‐alignment has been found by means of the angular pair correlation function for the mixed pairs in the bi‐disperse swarm. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On frequency estimations in phase fitted variational integrators for the general N‐body problem
Authors: Kosmas Odysseas , Leyendecker Sigrid
Published: November 2013

In the present work, the advantages of high order variational integrator methods are combined with phase lag properties for the numerical integration of the general N‐body problem. Expressing the action integral at any intermediate points along the curve segment using a discrete Lagrangian that depends only on the end points of the interval, high order integrators can be obtained by defining the discrete Lagrangian in any time segment as a weighted sum on intermediate points, whose expressions for positions and velocities use Galerkin interpolation techniques. When oscillatory behavior is taken into account, the methods derived use trigonometric interpolation functions that depend on a frequency, which needs to be estimated. For that, using phase lag analysis, a new way to derive methods has been developed, that uses frequency estimation for each body at every time step. Results on special cases of the N‐body problem show more stable orbits and less energy error when compared with the linear interpolation scheme. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elements on the Concept and Design of a Tracked Mini Robot – “ROBO GENIU” – Destined for Special Applications
Authors: Petrişor Silviu Mihai , Bârsan Ghiţă , Ioan Diana Andreea Aniela
Published: November 2013

The authors of this paper aim to highlight issues related to the organology and the integration of the hardware component in the mechanical structure of a tracked mini robot, called Robo Geniu, part of the unmanned ground vehicles category having the ability to act autonomously and enabling its endowment with means of observation, listening, tapping, relaying and jamming. This paper reveals, in detail, the composing parts of the hardware component, as well as the way they are assembled in the mechanical structure of the mini robot under study. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Mechanics of a High‐G Human Centrifuge
Authors: Dančuo Zorana , Rašuo Boško , Vidaković Jelena , Kvrgić Vladimir , Bućan Mirko
Published: November 2013

This paper presents the kinematic characteristics of a human centrifuge for pilot training. The focus is placed on the influence of the tangential acceleration on human centrifuge performances. The main planetary motion is expressed with an ordinary first‐order nonlinear differential equation, which is solved numerically. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparative Study of the Influence of Statistically Distributed Microscopic Quantities on the Damage in Collagenous Tissues
Authors: Schmidt Thomas , Balzani Daniel , Holzapfel Gerhard A.
Published: November 2013

In this contribution we investigate the influence of dispersed microscopic quantities on the damage behavior in collagenous tissues. Therefore, we derive a damage model, that may take into account statistical distributions of collagen fiber properties. In detail, we regard distributions of the orientation of fibril‐interconnecting proteoglycan (PG) bridges and of an internal fibril length parameter. The damage model is embedded into the constitutive framework from [1] and a numerical example in a finite element framework is given. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of muscle paths in biomechanical simulations
Authors: Maas Ramona , Leyendecker Sigrid
Published: November 2013

Within dynamical simulations of biomechanical motion, the actuation of a multibody system (representing bones and joints) can be implemented via Hill‐type muscle models. The main task of these models is to describe the typical force‐length and force‐velocity relation of real muscles. Thus, it is crucial that the muscle path itself, which is dynamically changing during a motion, is represented correctly in the model, because its length and the change of its length in time, i.e. its concentric or eccentric velocity, are related to the scalar value of the muscle force amount and to the direction of the force acting on the multibody system. In our work, we assume that a muscle tone is always present, even at rest, which leads to the conclusion that tendons and muscles are supposed to follow the path of minimal distance between two insertion points not intersecting the bones. This problem can for example be formulated as a constrained nonlinear optimisation problem, or it can be solved with a more efficient algorithm that determines this path as a G1 (geometrical) continuous combination of given curves. Within this work, both procedures are compared concerning the resulting path length and force directions and their computational costs. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hyperelastic biphasic fiber reinforced model for articular cartilage considering the distribution and orientation of collagen fibers
Authors: Albrecht Daniel , Ricken Tim , Pierce David M. , Holzapfel Gerhard A.
Published: November 2013

Articular cartilage is a multiphase material consisting of fluids and electrolytes, which is described with the Theory of Porous Media. The mechanical characteristics of articular cartilage are porosity, incompressible material behavior combined with transversely isotropic behavior for solid and fluid phases. There are two central points to model articular cartilage: the poro‐viscosity of the porous matrix and the visco elasticity, and orientation of the collagen fibers. A numerical example is presented. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a FEM model for isotropic and transversely isotropic growth in biphasic materials
Authors: Werner Daniel , Ricken Tim , Ferreira Pfeiffer Anne
Published: November 2013

The presented continuum mechanical model describes isotropic and transversely isotropic growth in biphasic materials with focus on biological tissue. The model is capable to describe full isotropic growth, full transversely isotropic growth as well as a combination of both types. This approach is chosen to describe the most common occurring growth types, namely isotropic and transversely isotropic growth, but also to describe effects where the growth of the investigated body depends on multiple single growth effects that are difficult to distinguish among each other. For the description of growth a biphasic homogenized approach within the framework of the theory of porous media (TPM) is used. In this work we focus on the applied formulation of multiple multiplicative decoupling of the deformation gradient into elastic, growth, isotropic and transversely isotropic parts including the governing constitutive equations. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of microstructural damage evolution during very high cycle fatigue (VHCF) using the boundary element method
Authors: Hilgendorff P.‐M. , Fritzen C.‐P. , Grigorescu A. , Zimmermann M. , Christ H.‐J.
Published: November 2013

A simulation model for damage evolution in slip bands under VHCF condition is presented. By use of a numerical method it is applied to a real simulated microstructure of AISI304. It considers orientations of slip systems as well as individual anisotropic elastic properties in each grain. The numerical method is the two‐dimensional boundary element method which is based on two integral equations and implies fundamental solutions for anisotropic elastic solids. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Configurational‐Force‐Driven Crack Propagation and Adaptive Mesh Refinement in Finite Inelasticity
Authors: Böger Lukas , Miehe Christian
Published: November 2013

We introduce a consistent variational framework for inelasticity at finite strains, yielding dual balances in physical and material space as the Euler equations. The formulation is employed for the simultaneous usage of configurational forces as both driving forces for crack propagation as well as h‐adaptive mesh refinement. The theoretical basis builds upon a global balance of internal and external power, where the mechanical response is exclusively governed by two scalar functions, the free energy function and a dissipation potential. The resulting variational structure is exploited in the context of fracture mechanics and yields evolution equations for internal variables. In the discrete setting, we present a geometry model fully separated from the finite element mesh structure that represents structural changes of the material configuration due to crack propagation. Advanced meshing algorithms provide an optimal discretization at the crack tip. Local and global criteria are obtained via error estimators based on configurational forces being interpreted as indicators of an energetic misfit due to an insufficient discretization. The numerical handling is decomposed into a staggered algorithm scheme for the dual set of equilibrium equations in material and physical space and efficient mesh generation tools. Exemplary numerical examples are considered to illustrate the method and to underline the effects of inelastic material behaviour in the presented context. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A modified multistage fatigue model to study the fatigue life of forged HS6‐5‐3 tool steel under high cycle fatigue
Authors: Giang Ngoc Anh , Özden Utku Ahmet , Bezold Alexander , Broeckmann Christoph
Published: November 2013

DIN type forged HS6‐5‐3 tool steel (AISI M3:2) is most commonly used in tooling industry and also in some engine parts. Those components are usually exposed to cyclic mechanical stresses and 90% of them failed by fatigue damage. For predicting the life time of this tool steel under high cycle fatigue (HCF) a modified multistage fatigue model found by McDowell is proposed, which leads to reduce effects and cost for predicting life time of this material. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparison between multi‐layered and functionally graded spherical pressure vessels
Authors: Arslan Eray
Published: November 2013

Two analytical models are developed for elastic multi‐layered and functionally graded thick walled spherical pressure vessels subjected to uniform internal pressure. Simple and comprehensive recursive algorithms are proposed for the multi‐layered vessel. In the model for functionally graded one, the modulus of elasticity is assumed to vary in radial direction according to a power law. Stress distributions of those vessels are compared and the results are presented in graphical form. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Developing a Simplified Surrogate Model for Structured Sheet Metals with Numerical and Experimental Comparisons
Authors: Mahler‐de Silva Tina , Kühhorn Arnold , Kober Markus
Published: November 2013

It is important to steadily refine lightweight designs with regard to saving resources and energy in common with good economic efficiency.

Thin structured sheet metals offer significantly improved component stiffnesses in addition to an upgraded buckling behavior compared to flat, unstructured sheet metals.

By using a distortion energy based homogenization method it is possible to develop a mechanical surrogate model which describes effective mean properties. The accurate selection of symmetric and periodic boundaries enables to determine the required parameters. The conditions are contemplated on elementary cells whose structural mechanical behavior is representative for the elastic behavior of large structures. By doing this, the amount of elements can be reduced and thus the calculating time of large components can considerably be saved.

For an efficient surrogate model it is required to analyze and compare numerical with experimental investigations. Some different versions of optimization will be tested to get better approximation of the data. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fraeijs de Veubeke variational principle‐based cylindrical shell finite element model
Authors: Kocsán Lajos György
Published: November 2013

In this paper a dimensionally reduced cylindrical shell model based on the dual‐mixed variational principle of Fraeijs de Veubeke will be presented. The fundamental variables of this variational principle are the not a priori symmetric stress tensor and the skew‐symmetric rotation tensor. The tensor of first‐order stress functions is applied to satisfy translational equilibrium. A shell model derived in this way makes the application of the classical kinematical hypotheses unnecessary, and enables us to use unmodified three‐dimensional constitutive equations. On the basis of this shell model, a new dual‐mixed cylindrical shell finite elements capable of both h‐ and p‐approximation can be derived. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improving the numerical efficiency for 3D enhanced assumed strain finite elements in explicit time integration
Authors: Schmied Christoph , Mattern Steffen , Schweizerhof Karl
Published: November 2013

Explicit time integration has proven to be highly suitable for the simulation of very fast processes and highly nonlinear applications. As is well known the time integration algorithm is only stable if the Courant‐Friedrichs‐Lewy criterion is fulfilled leading usually to very small time step sizes. As a result the efficiency of the time integration algorithm is dictated by the computational time of element operations. In structural mechanics low order finite elements are attractive due to their efficiency but introduce artificial stiffness effects. To resolve the so‐called locking effects a transient description – suitable for the solution in the context of explicit time integration – of the method of enhanced assumed strains (EAS) is formulated utilizing a generalization of the method of incompatible modes (IM). The element routines are computationally realised applying symbolic programming. The functionality and achieved efficiency are demonstrated on a numeric example. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical modeling of elliptical cylindrical shells, containing flowing fluid
Authors: Bochkarev Sergey , Lekomtsev Sergey , Matveenko Valery
Published: November 2013

The paper presents a finite‐element algorithm for investigation of the dynamic behavior of elastic shells with arbitrary cross sections containing a flowing fluid. A curvilinear surface of the structure is approximated by a set of plane elements, which are subjected to both membrane and bending forces. Description of the shell motion is based on the variable principle of virtual displacements, which includes the linearized Bernoulli equation for calculation of hydrodynamic pressure. A compressible non‐viscous fluid is considered in the framework of the potential theory, the equations of which are transformed with the use of the Bubnov‐Galerkin method. The performance of the algorithm is demonstrated by the example of two shells with a circular and elliptical cross section. Numerical simulation have been carried out to analyze the influence of the ratio of the ellipse semi‐axes, the linear dimensions of the structure and the level of shell filling on the hydrodynamic stability of the connected “shell‐fluid” system. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear Modeling of the Elastic Beam with Different Order Couplings
Authors: Luu Quang Khanh , Söffker Dirk
Published: November 2013

New structures become larger, lighter, and slender in practical applications. The problem of large elastic deformations undergoing overall motion in these structures has to be considered in the dynamic modeling. Using descriptions considering the nonlinear strain displacement relationships, the couplings between overall motions and the flexible deformations can be taken into account. Several approaches exist in the literature, but are not compared. These models are briefly introduced and explained with respect to the above mentioned problem. Effects of different couplings of different order combining nonlinear kinematics and higher order kinetics of flexible deformations are therfore investigated systematically. The results allow a deep insight and therfore understanding of related effects. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)