bluuebunny/crossref_metadata_2025 huggingface dataset:
The hematopoietic stem cell niche: Low in oxygen but a nice place to be
Authors: Eliasson Pernilla , Jönsson Jan‐Ingvar
Published: September 2009

The enormous regenerative capacity of the blood system to sustain functionally mature cells are generated from highly proliferative, short‐lived progenitors, which in turn arise from a rare population of pluripotent and self‐renewing hematopoietic stem cells (HSC). In the bone marrow, these stem cells are kept in a low proliferative, relatively quiescent state in close proximity to stromal cells and osteoblasts, forming specialized niches. The interaction in particular to bone is crucial to prevent exhaustion of HSCs from uncontrolled cell‐cycle entry and to excessive proliferation. In addition, the niche and its components protect stem cells from stress, such as accumulation of reactive oxygen species and DNA damage. One of the key issues is to identify conditions to increase the number of HSCs, either in vivo or during ex vivo growth cultures. This task has been very difficult to resolve and most attempts have been unsuccessful. However, the mechanistic insights to HSC self‐renewal and preservation are gradually increasing and there is now hope that future research will enable scientists and clinicians to modulate the process. In this review, we will focus on the molecular mechanisms of self‐renewal and HSC maintenance in the light of novel findings that HSCs reside at the lowest end of an oxygen gradient. Hypoxia appears to regulate hematopoiesis in the bone marrow by maintaining important HSC functions, such as cell cycle control, survival, metabolism, and protection against oxidative stress. To improve the therapeutic expansion of HSCs we need to learn more about the molecular mechanisms of hypoxia‐mediated regulation. J. Cell. Physiol. 222:17–22, 2010. © 2009 Wiley‐Liss, Inc.
Mesenchymal stem cells in regenerative medicine: Opportunities and challenges for articular cartilage and intervertebral disc tissue engineering
Authors: Richardson Stephen M. , Hoyland Judith A. , Mobasheri Reza , Csaki Constanze , Shakibaei Mehdi , Mobasheri Ali
Published: September 2009

Defects of load‐bearing connective tissues such as articular cartilage and intervertebral disc (IVD) can result from trauma, degenerative, endocrine, or age‐related disease. Current surgical and pharmacological options for the treatment of arthritic rheumatic conditions in the joints and spine are ineffective. Cell‐based surgical therapies such as autologous chondrocyte transplantation (ACT) have been in clinical use for cartilage repair for over a decade but this approach has shown mixed results. This review focuses on the potential of mesenchymal stem cells (MSCs) as an alternative to cells derived from patient tissues in autologous transplantation and tissue engineering. Here we discuss the prospects of using MSCs in regenerative medicine and summarize the advantages and disadvantages of these cells in articular cartilage and IVD tissue engineering. We discuss the conceptual and practical difficulties associated with differentiating and pre‐conditioning MSCs for subsequent survival in a physiologically harsh extracellular matrix, an environment that will be highly hypoxic, acidic, and nutrient deprived. Implanted MSCs will be exposed to traumatic physical loads and high levels of locally produced inflammatory mediators and catabolic cytokines. We also explore the potential of culture models of MSCs, fully differentiated cells and co‐cultures as “proof of principle” ethically acceptable “3Rs” models for engineering articular cartilage and IVD in vitro for the purpose of replacing the use of animals in arthritis research. J. Cell. Physiol. 222:23–32, 2010. © 2009 Wiley‐Liss, Inc.
A model for predicting pathologist's velocity profiles when navigating virtual slides
Authors: Gómez Francisco , Romero Eduardo
Published: September 2009

Navigation through large microscopic images is a potential benefit for histology or pathology teaching, for improving the quality of diagnosis in pathology, or for communicating pathologists in some telemedicine applications. However, the size of this kind of images is prohibitive for navigation with conventional techniques. This article presents a soft computing model, which permits to anticipate the pathologist trajectories in diagnosis tasks when exploring virtual slides. The Bayesian strategy combines an offline model of a baseline pathologist knowledge (the prior) and a prediction online module (the likelihood) that captures a particular pathologist navigation pattern. While optimal parameters for the biologically inspired offline model are calculated using an Expectation‐Maximization strategy, prediction is carried out by a particle filter. Parameters are estimated from several series of actual navigations performed by several pathologists in different virtual slides. The present approach is compared with other conventional prediction methods and decreases the calculated MSE in about a 50% for the entire group of pathologists. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc.
A novel method for shape from focus in microscopy using Bezier surface approximation
Authors: Muhammad Mannan Saeed , Choi Tae‐Sun
Published: September 2009

In this article, we introduce a novel shape from focus method to compute 3D shape of microscopic objects, based on modified‐pixel intensities and Bezier surface approximations. A new and simple but effective focus measure is proposed. In our focus measure, the original intensities of a sequence of small neighborhood are modified by subtracting the maximum of the values of first and last frames. An initial depth map is calculated by finding the maximum of the pixel's focused energy and its corresponding frame number. Missing information between two consecutive frames, false depth detection, and enhancement of noise related intensities may provide inaccurate depth map. To overcome these problems and to produce an accurate depth map, we proposed Bezier surface approximation. The proposed method is tested using synthetic and real image sequences. The comparative analysis demonstrates the effectiveness of the proposed method. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc.
Histometric and histomorphologic comparison of combustion and ambustion using in vivo reflectance‐confocal microscopy
Authors: Altintas Ahmet Ali , Amini Peymaneh , Altintas Mehmet Ali , Perbix Walter , Phan Vu , Stasch Tilman , Spilker Gerald
Published: September 2009

Background: When combustion and ambustion induce a superficial injury, they are summarized as superficial burns, regardless of the underlying cause. Reflectance‐confocal microscopy (RCM) allows noninvasive imaging of the human skin on morphological features. We hypothesized that combustion and ambustion have different histomorphological effects on the human skin. Methods: Superficial burns caused by combustion (CO‐group, five females, three males; aged 26.8 ± 14.2 years) and caused by ambustion (AM‐group, four females, four males; aged 28.1 ± 13.8 years) were evaluated 24 h after injury. The following parameters were obtained using RCM on injured and noninjured (control) site: horny layer thickness, epidermal thickness, granular cell size, basal layer thickness. Results: Compared with the controls (12.8 ± 2.5 μm), horny layer thickness decreased significantly to 10.6 ± 2.1 μm in the CO‐group, whereas it increased significantly to 17.8 ± 2.8 μm in the AM‐group. The epidermal thickness did not differ significantly in CO‐group (47.9 ± 2.1 μm) and AM‐group (49.0 ± 3.1 μm), however, both increased significantly compared with the controls (42.7 ± 1.6 μm). The basal layer thickness increased more in AM‐group (17.0 ± 1.2 μm) compared to CO‐group (15.4 ± 1.1 μm). Both differed significantly compared with their controls (13.9 ± 0.9 μm). The granular cell size increased significantly in both groups ompared to the controls (721 ± 42 μm), however, a significantly higher increase was observed in CO‐group compared to AM‐group (871 ± 55 μm vs. 831 ± 51 μm). Conclusions: RCM evaluates significant histomorphological differences in superficial burns caused by combustion and ambustion. The term “superficial burn” should consider the underlying cause and thus supplemented by the term “combustion” or “ambustion.” Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc.
Cortactin/tyrosine‐phosphorylated cortactin interaction with connexin 43 in mouse seminiferous tubules
Authors: Vitale María Leiza , Akpovi Casimir D. , Pelletier R.‐Marc
Published: September 2009

Deletion of the cortactin gene leads to male infertility. Considering that cortactin is an actin filament (F‐actin)‐binding protein associated with intercellular junctions, we measured changes in the expression and distribution of cortactin and tyrosine phosphorylated cortactin (P‐cortactin) in the seminiferous epithelium of developing and adult mice to address the physiological significance of cortactin to germ cell differentiation. Cortactin was expressed in neonatal and developing Sertoli cells. Cortactin levels decreased early during puberty, while P‐cortactin increased. Cortactin labeling was intense in the basal and apical thirds of the epithelium. Sertoli cell cytoplasmic processes facing spermatogonia, preleptotene spermatocytes, and step 8–13 spermatids were intensely labeled by both cortactin and P‐cortactin. In contrast, the middle region of Sertoli cells exhibited diffuse cortactin labeling but no P‐cortactin. This is consistent with the view that plasma membrane segments facing germ cells are part of the continuum of Sertoli cell junctional complexes that extend over lateral and apical membranes of supporting cells. Moreover, F‐actin and P‐cortactin share a common location in the seminiferous epithelium. The increased P‐cortactin levels detected during puberty may be related to the modulatory effect of cortactin tyrosine phosphorylation on actin assembly at sites of selected Sertoli cell‐germ cell contacts. Cortactin and connexin 43 (Cx43) were physically linked in seminiferous tubule homogenates and their colocalization in the basal and apical thirds of the seminiferous epithelium was stage‐dependent. Our results suggest that cortactin‐Cx43 interaction helps coordinate formation of cell‐to‐cell junctions and organization of the subsurface actin cytoskeleton in specific regions of the epithelium. Microsc. Res. Tech., 2009. © 2009 Wiley‐Liss, Inc.
Methodological assessment of acid‐etching for visualizing the osteocyte lacunar‐canalicular networks using scanning electron microscopy
Authors: Kubek Daniel J. , Gattone Vincent H. , Allen Matthew R.
Published: September 2009

Osteocytes are the most abundant of the bone cells. Each osteocyte is contained within its own lacuna and connected to adjacent osteocytes via fillipodial processes, which form an intricate network of canaliculi within the matrix. Studying this intricate network of cells and their processes is difficult, because it exists embedded within a densely mineralized matrix. Scanning electron microscopy (SEM) has been shown to be a useful tool for visualizing this cellular network, yet the techniques involved for preparing specimens has not been systematically explored. The goal of this study was to investigate how variations in acid‐etching, both etching media and etching duration, affect SEM‐based visualization of the osteocyte lacunar–canalicular network. Bone samples were embedded in plastic and then acid etched in either 9% (10, 20, 40, and 60 s durations) or 37% (5, 10, and 15 s) phosphoric acid. Specimens were imaged using SEM, and qualitative evaluation of the lacunar–canalicular network was undertaken. Our findings show acid etchingwith a 9% phosphoric acid solution for 20 s provided the most favorable visualization of the osteocyte lacunar–canalicular network. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc.
Parallel deconvolution of large 3D images obtained by confocal laser scanning microscopy
Authors: Pawliczek Piotr , Romanowska‐Pawliczek Anna , Soltys Zbigniew
Published: September 2009

Various deconvolution algorithms are often used for restoration of digital images. Image deconvolution is especially needed for the correction of three‐dimensional images obtained by confocal laser scanning microscopy. Such images suffer from distortions, particularly in the Z dimension. As a result, reliable automatic segmentation of these images may be difficult or even impossible. Effective deconvolution algorithms are memory‐intensive and time‐consuming. In this work, we propose a parallel version of the well‐known Richardson–Lucy deconvolution algorithm developed for a system with distributed memory and implemented with the use of Message Passing Interface (MPI). It enables significantly more rapid deconvolution of two‐dimensional and three‐dimensional images by efficiently splitting the computation across multiple computers. The implementation of this algorithm can be used on professional clusters provided by computing centers as well as on simple networks of ordinary PC machines. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc.
Elaborate regulations of the predator‐induced polyphenism in the water flea Daphnia pulex: kairomone‐sensitive periods and life‐history tradeoffs
Authors: Imai Maki , Naraki Yuka , Tochinai Shin , Miura Toru
Published: September 2009

Adaptive polyphenism produces alternative phenotypes depending on environmental stimuli. The water flea Daphnia pulex shows predator‐induced polyphenism, facultatively forming neckteeth in response to kairomones released by Chaoborus larvae. This study was designed to reveal the regulatory systems producing the defensive morph during embryonic and postembryonic development. As noted previously, the crest epithelium at the site of neckteeth is shown to thicken earlier the neckteeth formation, and the neckteeth number increased until the third instar, and later disappeared. Exposure to kairomone at various time points and intervals during development showed that the signal was required even at early postembryonic stages to maintain neckteeth. Moreover, two different induction methods, i.e. embryonic and maternal exposures, enabled us to discriminate maternal and zygotic effects in response to kairomone. Direct embryonic exposure is shown to be sufficient to form neckteeth without maternal effect although their growth was diminished; namely, there is a trade‐off for neckteeth production. However, maternal exposures resulted in larger progenies in smaller numbers, suggesting that the mother daphnids change their reproductive strategy depending on kairomone signals. Taken together, the developmental responses to the presence of predators are regulated elaborately at various levels. J. Exp. Zool. 311A:788–795, 2009. © 2009 Wiley‐Liss, Inc.
Efficient synthesis of 14‐substituted‐14‐H‐dibenzo[a,j]xanthenes using silica supported sodium hydrogen sulfate or amberlyst‐15 catalyst
Authors: Kumar Chebolu Naga Sesha Sai Pavan , Srinivas Chiguru , Sadhu Partha Sarathi , Rao Vaidya Jayathirtha , Palaniappan Srinivasan
Published: September 2009

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Silica supported sodium hydrogen sulfate (NaHSO4·SiO2) or amberlyst‐15 acts as an efficient heterogeneous catalyst for the preparation of 14‐alkyl and aryl‐14‐H‐dibenzo[a,j]xanthenes with various aldehydes and β‐naphthol in dichloroethane solvent in excellent yields. Synthesis of three new compounds are reported using this methodology. Recyclable nature of the amberlyst‐15 catalyst was also studied and the catalyst can be reused. J. Heterocyclic Chem., (2009).
Dimethylformamide dimethyl acetal as a building block in heterocyclic synthesis
Authors: Abu‐Shanab Fathi A. , Sherif Sherif M. , Mousa Sayed A. S.
Published: September 2009

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This review focuses on the use of dimethylformamide dimethyl acetal in the preparation of heterocyclic compounds via formylation of active methylene groups, methyl groups to give enamines, and formylation of amino groups to give amidines. These compounds are found to be useful intermediates in the formation and modification of heterocyclic compounds. J. Heterocyclic Chem., (2009).
Modelling CoolMOSC3 transistor characteristics in SPICE
Authors: Górecki Krzysztof , Zarębski Janusz
Published: September 2009

In this paper three models of CoolMOSC3 transistors worked out by Infineon Technologies, dedicated for SPICE, are presented and investigated. These models are verified experimentally both for dc and ac device operating conditions. The advantages and drawbacks of the investigated models are shown and discussed. The device operating conditions, at which the models are of acceptable accuracy, are identified. Copyright © 2009 John Wiley & Sons, Ltd.
The compact d.c. electrothermal model of power MOSFETs for SPICE
Authors: Zarębski Janusz
Published: September 2009

This paper concerns the problem of modelling of power MOS transistors in SPICE. In the paper the new form of the electrothermal d.c. model (ETM) of the considered class of power devices is proposed. The ETM is based on the modified Shichman–Hodges model, in which the generation current, the breakdown voltage, the sub‐threshold region, the thermally dependent series resistances and self‐heating are included. The device inner temperature calculated from the thermal model is the sum of the ambient temperature and the product of the electrical power dissipated inside the device and its thermal resistance. The presented model has been verified experimentally. The results of calculations and measurements of MTD15N06V (ON Semiconductor) and IRF840 (International Rectifier) transistors are given as well. Copyright © 2009 John Wiley & Sons, Ltd.
A three‐dimensional mesh refinement algorithm with low boundary reflections for the finite‐difference time‐domain simulation of metallic structures
Authors: Pernice W. H. P. , Payne F. P. , Chaloulos K. , Gallagher D. F. G.
Published: September 2009

We present a method for including areas of high grid density into a general grid for the finite‐difference time‐domain method in three dimensions. Reflections occurring at the boundaries separating domains of different grid size are reduced significantly by introducing appropriate interpolation methods for missing boundary points. Several levels of refinement can be included into one calculation using a hierarchical refinement architecture. The algorithm is implemented with an auxiliary differential equation technique that allows for the simulation of metallic structures. We illustrate the performance of the algorithm through the simulation of metal nano‐particles included in a coarser grid and by investigating gold optical antennas. Copyright © 2009 John Wiley & Sons, Ltd.
Collective psychological ownership within the work and organizational context: Construct introduction and elaboration
Authors: Pierce Jon L. , Jussila Iiro
Published: September 2009

The construct collective psychological ownership is introduced. Reflecting the psychology of “us” and “ours,” collective psychological ownership emerges through interactive dynamics whereby individuals come to a single and shared mind‐set as it relates to a sense of ownership for a particular object. After providing a conceptual definition for the construct, we turn our attention to a detailed elaboration of the construct, offering comments on its genesis, emergent context, underlying motives, and a discussion of what can and cannot be owned. We also provide a discussion of the dynamics associated with its formation, highlighting the paths down which groups travel that influence the emergence of this psychological state. Next, we turn our attention to the emergence of collective psychological ownership within the organizational and teamwork context paying particular attention to the role of work environment structure. We conclude with a discussion of a set of work‐related attitudinal, motivational, behavioral, and stress‐related outcomes that stem from this psychological state. Copyright © 2009 John Wiley & Sons, Ltd.
Retracted: Authentically leading groups: The mediating role of collective psychological capital and trust
Authors: Walumbwa Fred O. , Luthans Fred , Avey James B. , Oke Adegoke
Published: September 2009

Although there have been recent theoretical advances in what is increasingly being recognized as authentic leadership, research testing possible mediating processes and the impact on group‐level outcomes has not received attention. To help address this need, this study examined at the group level of analysis the role that collective psychological capital and trust may play in the relationship between authentic leadership and work groups' desired outcomes. Utilizing 146 intact groups from a large financial institution, the results indicated a significant relationship between both their collective psychological capital and trust with their group‐level performance and citizenship behavior. These two variables were also found to mediate the relationship between authentic leadership and the desired group outcomes, even when controlling for transformational leadership. Implications for future research and practice conclude the paper. Copyright © 2009 John Wiley & Sons, Ltd.
Toll‐like receptors and aseptic loosening of hip endoprosthesis—a potential to respond against danger signals?
Authors: Lähdeoja Tuomas , Pajarinen Jukka , Kouri Vesa‐Petteri , Sillat Tarvo , Salo Jari , Konttinen Yrjö T.
Published: September 2009

Bacterial remnants and subclinical biofilms residing on prosthesis surfaces have been speculated to play a role in hip implant loosening by opsonizing otherwise relatively inert wear particles. The innate immune system recognizes these microbial pathogen‐associated molecular patterns (PAMPs) using Toll‐like receptors (TLRs). Our objective was to evaluate the possible presence of TLRs in aseptic synovial membrane‐like interface tissue. Bacterial culture‐negative, aseptic (n = 4) periprosthetic synovial membrane‐like tissue was compared to osteoarthritis synovial membrane (n = 5) for the presence of cells positive for all known human functional TLRs, stained using specific antibodies by immunohistochemistry, and evaluated using morphometry. In comparison to osteoarthtritic synovium, the number of TLR‐positive cells was found to be increased in the aseptic setting, reflecting the considerable macrophage infiltration to the tissues investigated. Thus aseptic periprosthetic tissue seems to be very reactive to PAMPs. It has been recently recognized that TLR do not only respond to traditional PAMPs, but also to endogenous alarmings or danger signals released from necrotic and activated cells. Alarming‐TLR interaction in the periprosthetic tissue might be a novel mechanism of aseptic loosening of endoprosthesis. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:184–190, 2010
GDF‐5/7 and bFGF activate integrin α2‐mediated cellular migration in rabbit ligament fibroblasts
Authors: Date Hirokazu , Furumatsu Takayuki , Sakoma Yoshimasa , Yoshida Aki , Hayashi Yuko , Abe Nobuhiro , Ozaki Toshifumi
Published: September 2009

Cellular activities responding to growth factors are important in ligament healing. The anterior cruciate ligament (ACL) has poor healing potential compared to the medial collateral ligament (MCL). To assess the differences, we investigated the proliferation, migration, adhesion, and matrix synthesis responding to growth factors in rabbit ACL and MCL fibroblasts. ACL cell proliferation to basic fibroblast growth factor (bFGF), bone morphogenetic protein‐2, growth and differentiation factor (GDF)‐5, and GDF‐7 treatment was similar to that of MCL cells. GDF‐5 enhanced Col1a1 expression in ACL and MCL fibroblasts up to 4.7‐ and 17‐fold levels of control, respectively. MCL fibroblasts showed stronger migration activities in response to bFGF and GDF‐5 than ACL cells. GDF‐5/7 and bFGF also changed the stress fiber formation and cellular adhesion by modulating the distribution of integrin α2. Functional blocking analyses using anti‐integrin α2 antibodies revealed that cellular migration responding to growth factors depended on the integrin α2‐mediated adhesion on type I collagen. The expression of integrin α2 was also increased by growth factors in both cells. Our results demonstrate that GDF‐5/7 and bFGF stimulate cellular migration by modulating integrin α2 expression and integrin α2‐dependent adhesion, especially in MCL fibroblasts. These findings suggest that the different healing potential between ACL and MCL may be caused by different cellular behavior in the integrin α2‐mediated cellular migration in response to growth factors. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:225–231, 2010
Inhibition of ectopic bone formation by a selective retinoic acid receptor α‐agonist: A new therapy for heterotopic ossification?
Authors: Shimono Kengo , Morrison Tiffany N. , Tung Wei‐en , Chandraratna Roshantha A. , Williams Julie A. , Iwamoto Masahiro , Pacifici Maurizio
Published: September 2009

Heterotopic ossification (HO) consists of formation of ectopic cartilage followed by endochondral bone and is triggered by major surgeries, large wounds, and other conditions. Current therapies, including low‐dose irradiation, are not always effective and do not target the skeletogenic process directly. Because chondrogenesis requires a decrease of nuclear retinoic acid receptor α (RARα) action, we reasoned that pharmacologic activation of this receptor pathway should inhibit HO. Thus, we selected the synthetic retinoid NRX195183, a potent and highly selective RARα‐agonist, and found that it did inhibit chondrogenesis in mouse limb micromass cultures. We established a mouse HO model consisting of subcutaneous implantation of Matrigel mixed with rhBMP‐2. Control mice receiving daily oral doses of vehicle (peanut oil) or retinol (a natural nonactive retinoid precursor) developed large HO‐like masses by days 9–12 that displayed abundant cartilage, endochondral bone, vessels, and marrow. In contrast, formation of HO‐like masses was markedly reduced in companion mice receiving daily oral doses of α‐agonist. These ectopic masses contained sharply reduced amounts of cartilage and bone, blood vessels, and TRAP‐positive osteoclasts, and expressed markedly lower levels of master chondrogenic genes including Sox9, cartilage genes such as collagen XI and X, and osteogenic genes including Runx2. The data provide proof‐of‐principle evidence that a pharmacological strategy involving a selective RARα‐agonist can indeed counteract an ectopic skeletal‐formation process effectively and efficiently, and could thus represent a novel preventive treatment for HO. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:271–277, 2010
Parabolic mirror‐assisted tip‐enhanced spectroscopic imaging for non‐transparent materials
Authors: Zhang Dai , Wang Xiao , Braun Kai , Egelhaaf Hans‐Joachim , Fleischer Monika , Hennemann Laura , Hintz Holger , Stanciu Catrinel , Brabec Christoph J. , Kern Dieter P. , Meixner Alfred J.
Published: September 2009

A versatile and efficient tip‐enhanced spectroscopic imaging technique based on a parabolic mirror (PM) assisted near‐field optical microscope is demonstrated. The replacement of the conventional objective lens with a parabolic mirror allows the non‐restricted investigation of sample materials regarding their opacity. In addition, an improved signal collection efficiency and effective excitation of the longitudinal plasmonic oscillation in the tip apex are obtained. The capabilities of PM‐assisted tip‐enhanced Raman (TER) and photoluminescence (PL) imaging in distinguishing the individual domains made of different chemical components in poly (3‐hexythiophene)/[6, 6]‐penyl‐C61 butyric acid methyl ester (P3HT/PCBM) solar cell blend film and in the investigation of the plasmonic properties of geometrically well‐defined Au cones are demonstrated. Copyright © 2009 John Wiley & Sons, Ltd.
A pigment (CuS) identified by micro‐Raman spectroscopy on a Chinese funerary lacquer ware of West Han Dynasty
Authors: Jin Pu‐Jun , Yao Zheng‐Quan , Zhang Mao‐Lin , Li Yu‐Hu , Xing Hui‐Ping
Published: September 2009

A blue pigment was identified by micro‐Raman spectroscopy, X‐ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX) and X‐ray diffraction (XRD). The test sample, a funerary lacquer tray, belongs to West Han Dynasty (206 BC–AD 8) of China and was decorated with faint blue patterns. The result from Raman spectroscopy showed that the faint blue is covellite (CuS) due to the presence of a characteristic peak at 474.5 cm−1, which further was confirmed by XRF, SEM–EDX and XRD. This research indicated that CuS had been used as a blue pigment to decorate lacquer wares from the West Han Dynasty in China. Copyright © 2009 John Wiley & Sons, Ltd.
Tip‐enhanced Raman spectroscopy of 6H‐SiC with graphene adlayers: selective suppression of E1 modes
Authors: Domke Katrin F. , Pettinger Bruno
Published: September 2009

We have characterized 6H‐SiC substrates with tip‐enhanced Raman spectroscopy in a broad spectral range between 100 and 3000 cm−1. A few adlayers of graphene previously grown on the semiconductor's C surface enabled us to approach the Au tip of a scanning tunneling microscope (STM) into tunnelling contact. In the recorded STM images of the substrate, we discern the height of the carbon adlayers in different sample regions. We compare tip‐enhanced Raman (TER) spectra of the sample to normal Raman spectra recorded with the field vector of the linearly polarized light oriented at 30° or 90° with respect to the surface normal. All spectra show the phonon fingerprint of SiC and of graphene. We find the E1 modes of 6H‐SiC selectively suppressed in the TER spectra whereas they are present in the normal Raman spectra excited at 30°. This effect is explained by a tip‐induced symmetry change. Copyright © 2009 John Wiley & Sons, Ltd.
Assessment of polymer composites for hydrodynamic journal‐bearing applications
Authors: McCarthy D. M. C. , Glavatskih S. B.
Published: September 2009

Polymer composites are used as facing materials in hydrodynamic bearings for their low friction and ‘compliant’ properties, which play an important role during machinery operation. In journal bearings, this low friction property can be of significant importance during start and stop cycles when insufficient oil is available to fully separate the surfaces in relative motion. Current work is aimed at determining a suitable material for use in hydrodynamic journal bearings for applications in hydroelectric power plants. This study investigates friction and wear encountered during the transition from the stationary state to operational speed (acceleration) during initial start‐up. This is examined for virgin poly‐tetra‐fluoro‐ethylene (PTFE) together with a series of commercially available PTFE‐based composites and a babbitt material in boundary/mixed lubrication conditions. Tests are performed using standard laboratory block‐on‐ring test apparatus with a VG32 mineral oil. Copyright © 2009 John Wiley & Sons, Ltd.
Syntheses of Polyesters from Succinic Anhydride and Various Diols Catalyzed by Metal Triflates
Authors: Yashiro Takao , Kricheldorf Hans R. , Huijser Saskia
Published: September 2009

Succinic anhydride (SuAh) was polymerized with various α,ω‐alkanediols from 1,3‐propanediol up to 1,10‐decanediol. Most polycondensations were conducted in bulk at temperatures of 80 °C with bismuth triflate as catalyst and number average molecular weights ($\overline M _{\rm n} {\rm s}$, uncorrected SEC data) up to 35 000 Da were obtained. Polycondensations of SuAh with 1,6‐hexanediol were also catalyzed with aluminum, tin(II), scandium, lanthanium, samarium, and hafnium triflate. Whereas, poor results were achieved with La‐triflate, aluminum and tin(II) triflate yielded $\overline M _{\rm n} {\rm s}$ comparable to those obtained with Bi‐triflate. With exception of the basic lanthanum triflate, all other catalysts generated small amounts of ether groups. The MALDI‐TOF mass spectra proved that the molecular weights depended on the conversion and on the extent of cyclization. The polycondensations of 1,4‐butanediol at temperatures up to 120 °C were affected by the formation of tetrahydrofuran, and even with an excess of the diol $\overline M _{\rm n} {\rm s}$ <10 000 Da were not obtained. Yet, BiCl3 and Bi‐triflate catalyzed polycondensations in refluxing decalin gave satisfactory results ($\overline M _{\rm n} {\rm s}$ ≈ 30 000 Da, uncorrected SEC data).

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Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization with a Polymeric RAFT Agent Containing Multiple Trithiocarbonate Groups
Authors: Liu Yuqing , Cavicchi Kevin A.
Published: September 2009

Polytrithiocarbonates were prepared by the condensation polymerization of a dicarboxylic acid functional trithiocarbonate and a diol. These polymers were effective reversible addition fragmentation chain transfer (RAFT) agents for the bulk polymerization of polystyrene homopolymers and a poly[styrene‐block‐(tert‐butylstyrene)] block copolymer. Size exclusion chromatography (SEC) analysis of the original and amine cleaved polymers showed that the polydispersity of the polymer tended toward two with increasing polymerization time, but the polydispersity of the polymer units between trithiocarbonate groups was narrow (ca. 1.1–1.3) Also, the average number of trithiocarbonate groups per chain was found to be proportional to the number of trithiocarbonate groups in the starting RAFT agent. These polytrithiocarbonate RAFT agents will be useful for preparing multiblock copolymers over a range of chemistries, block numbers and molecular weights.

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Micellization Phenomena in Semicrystalline Block Copolymers: Reflexive and Critical Views on the Formation of Cylindrical Micelles
Authors: Lazzari Massimo , López‐Quintela M. Arturo
Published: September 2009

Investigations on the self‐assembly of block copolymers in solution have in some way a less well‐studied history than the study of their phase separation in the solid state, and many aspects are yet not completely understood. Here we focus on the behavior of a specific class of copolymers, namely semicrystalline block copolymers, capable of forming cylindrical aggregates in a solvent selective for the non‐crystalline, complementary block. A common model of micellization is proposed, in principle applicable to most of these copolymeric systems.

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A Main‐Chain de Vries Smectic Liquid Crystal Polymer Prepared by Hoveyda–Grubbs Catalyst Initiated Acyclic Diene Metathesis Polymerization
Authors: Walba David M. , Yang Hong , Keller Patrick , Zhu Chenhui , Shao Renfan , Coleman David A. , Jones Christopher D. , Clark Noel A.
Published: September 2009

A main‐chain liquid crystalline polymer has been obtained by applying a Hoveyda–Grubbs 2nd generation catalyst in acyclic diene metathesis polymerization (ADMET) of a monomer containing on one end a terminal dimethylvinylsilyl group and at the other end a terminal CC double bond. This material showed an interesting Iso‐de Vries SmA* – SmC* – Glass phase transition with a very small layer shrinkage on progressing from the SmA* phase into the SmC* phase. Will this material present a helical structure along the fiber axis in the SmC* temperature range? Several physical characterization methods including XRD, optical observation, and microtome technique have been used to investigate the internal structural organization in this liquid crystalline fiber.

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Highly Active Syndiospecific Living Polymerization of Higher 1‐Alkene with ansa‐Fluorenylamidodimethyltitanium Complex
Authors: Cai Zhengguo , Ohmagari Masayoshi , Nakayama Yuushou , Shiono Takeshi
Published: September 2009

1‐Hexene polymerization was conducted by [t‐BuNSiMe2(3,6‐t‐Bu2Flu)]TiMe2 (1) using trialkylaluminum‐free modified methylaluminoxane (dMMAO) as a cocatalyst in toluene. The system produced living syndiotactic poly(1‐hexene) with high turnover frequency of propagation (TOF, 98 s−1) at 0 °C. The propagation rate was increased linearly against the 1‐hexene concentration, which indicates that the first‐order dependence of the propagation rate on monomer concentration. Polymerizations of 1‐octene, 1‐decene and 1‐dodecene were also conducted for investigating the effect of chain length of 1‐alkene on propagation rate by means of the livingness of this system. The propagation rate decreased according to the chain length until 1‐decene but almost unchanged in longer 1‐alkene: TOF, 1‐octene (62 s−1)>1‐decene (32 s−1) ≈ 1‐dodecene (31 s−1).

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Intrinsic mono‐component decomposition of functions: An advance of Fourier theory
Authors: Qian Tao
Published: September 2009

We propose a function decomposition model, called intrinsic mono‐component decomposition (IMD). It is a continuation of the recent study on adaptive decomposition of functions into mono‐components (MCs). It is a further improvement of two recent results of which one is adaptive decomposition of functions into modified inner functions, and the other is decomposition by using adaptive Takenaka‐Malmquist systems. The proposed new decomposition model is of less restriction and thus gains more adaptivity. The theory is valid to both the unit circle and the real line contexts. Copyright © 2009 John Wiley & Sons, Ltd.
Mechanical and transport constitutive models for fractures subject to dissolution and precipitation
Authors: Elsworth Derek , Yasuhara Hideaki
Published: September 2009

Transient changes in the permeability of fractures in systems driven far‐from‐equilibrium are described in terms of proxy roles of stress, temperature and chemistry. The combined effects of stress and temperature are accommodated in the response of asperity bridges where mineral mass is mobilized from the bridge to the surrounding fluid. Mass balance within the fluid accommodates mineral mass either removed from the flow system by precipitation or advection, or augmented by either dissolution or advection. Where the system is hydraulically closed and initially at equilibrium, reduction in aperture driven by the effects of applied stresses and temperatures will be augmented by precipitation on the fracture walls. Where the system is open, the initial drop in aperture may continue, and accelerate, where the influent fluid is oversaturated with respect to the equilibrium mineral concentration within the fluid, or may reverse, if undersaturated. This simple zero‐dimensional model is capable of representing the intricate behavior observed in experiments where the feasibility of fracture sealing concurrent with net dissolution is observed. This zero‐order model is developed as a constitutive model capable of representing key aspects of changes in the transport parameters of the continuum response of fractured media to changes in stress, temperature and chemistry. Copyright © 2009 John Wiley & Sons, Ltd.
Exponential basis functions in solution of static and time harmonic elastic problems in a meshless style
Authors: Boroomand B. , Soghrati S. , Movahedian B.
Published: September 2009

In this paper, exponential basis functions (EBFs) are used in a boundary collocation style to solve engineering problems whose governing partial differential equations (PDEs) are of constant coefficient type. Complex‐valued exponents are considered for the EBFs. Two‐dimensional elasto‐static and time harmonic elasto‐dynamic problems are chosen in this paper. The solution procedure begins with first finding a set of appropriate EBFs and then considering the solution as a summation of such EBFs with unknown coefficients. The unknown coefficients are determined by the satisfaction of the boundary conditions through a collocation method with the aid of a consistent and complex discrete transformation technique. The basis and various forms of the transformation have been addressed and discussed. We shall propose several strategies for selection of EBFs with the aid of the basis explained for the transformation. While using the transformation, the number of EBFs should not necessarily be equal to (or less than) the number of boundary information data. A library of EBFs has also been presented for further use. The effect of body forces is included in the solution via construction of particular solution by the use of the discrete transformation and another series of EBFs. A number of sample problems are solved to demonstrate the capabilities of the method. It has been shown that the time harmonic problems with high wave number can be solved without much effort. The method, categorized in meshless methods, can be applied to many other problems in engineering mechanics and general physics since EBFs can easily be found for almost all problems with constant coefficient PDEs. Copyright © 2009 John Wiley & Sons, Ltd.
Energy–momentum consistent finite element discretization of dynamic finite viscoelasticity
Authors: Groß M. , Betsch P.
Published: September 2009

This paper is concerned with energy–momentum consistent time discretizations of dynamic finite viscoelasticity. Energy consistency means that the total energy is conserved or dissipated by the fully discretized system in agreement with the laws of thermodynamics. The discretization is energy–momentum consistent if also momentum maps are conserved when group motions are superimposed to deformations. The performed approximation is based on a three‐field formulation, in which the deformation field, the velocity field and a strain‐like viscous internal variable field are treated as independent quantities. The new non‐linear viscous evolution equation satisfies a non‐negative viscous dissipation not only in the continuous case, but also in the fully discretized system. The initial boundary value problem is discretized by using finite elements in space and time. Thereby, the temporal approximation is performed prior to the spatial approximation in order to preserve the stress objectivity for finite rotation increments (incremental objectivity). Although the present approach makes possible to design schemes of arbitrary order, the focus is on finite elements relying on linear Lagrange polynomials for the sake of clearness. The discrete energy–momentum consistency is based on the collocation property and an enhanced second Piola–Kirchhoff stress tensor. The obtained coupled non‐linear algebraic equations are consistently linearized. The corresponding iterative solution procedure is associated with newly proposed convergence criteria, which take the discrete energy consistency into account. The iterative solution procedure is therefore not complicated by different scalings in the independent variables, since the motion of the element is taken into account for solving the viscous evolution equation. Representative numerical simulations with various boundary conditions show the superior stability of the new time‐integration algorithm in comparison with the ordinary midpoint rule. Both the quasi‐rigid deformations during a free flight, and large deformations arising in a dynamic tensile test are considered. Copyright © 2009 John Wiley & Sons, Ltd.
Scalar wave equation by the boundary element method: A D‐BEM approach with constant time‐weighting functions
Authors: Carrer J. A. M. , Mansur W. J.
Published: September 2009

A D‐BEM approach, based on time‐weighting residuals, is developed for the solution of two‐dimensional scalar wave propagation problems. The modified basic equation of the D‐BEM formulation is generated by weighting, with respect to time, the basic D‐BEM equation, under the assumption of linear and cubic time variation for the potential and for the flux. A constant time‐weighting function is adopted. The time integration reduces the order of the time‐derivative that appears in the domain integral; as a consequence, the initial conditions are directly taken into account. An assessment of the potentialities of the proposed formulation is provided by the examples included at the end of the work. Copyright © 2009 John Wiley & Sons, Ltd.
Model order reduction for hyperelastic materials
Authors: Niroomandi Siamak , Alfaro Icíar , Cueto Elías , Chinesta Francisco
Published: September 2009

In this paper, we develop a novel algorithm for the dimensional reduction of the models of hyperelastic solids undergoing large strains. Unlike standard proper orthogonal decomposition methods, the proposed algorithm minimizes the use of the Newton algorithms in the search of non‐linear equilibrium paths of elastic bodies.

The proposed technique is based upon two main ingredients. On one side, the use of classic proper orthogonal decomposition techniques, that extract the most valuable information from pre‐computed, complete models. This information is used to build global shape functions in a Ritz‐like framework.

On the other hand, to reduce the use of Newton procedures, an asymptotic expansion is made for some variables of interest. This expansion shows the interesting feature of possessing one unique tangent operator for all the terms of the expansion, thus minimizing the updating of the tangent stiffness matrix of the problem.

The paper is completed with some numerical examples in order to show the performance of the technique in the framework of hyperelastic (Kirchhoff–Saint Venant and neo‐Hookean) solids. Copyright © 2009 John Wiley & Sons, Ltd.
The multipliers‐free domain decomposition methods
Authors: Herrera Ismael , Yates Robert A.
Published: September 2009

This article concludes the development and summarizes a new approach to dual‐primal domain decomposition methods (DDM), generally referred to as “the multipliers‐free dual‐primal method.” Contrary to standard approaches, these new dual‐primal methods are formulated without recourse to Lagrange‐multipliers. In this manner, simple and unified matrix‐expressions, which include the most important dual‐primal methods that exist at present are obtained, which can be effectively applied to floating subdomains, as well. The derivation of such general matrix‐formulas is independent of the partial differential equations that originate them and of the number of dimensions of the problem. This yields robust and easy‐to‐construct computer codes. In particular, 2D codes can be easily transformed into 3D codes. The systematic use of the average and jump matrices, which are introduced in this approach as generalizations of the “average” and “jump” of a function, can be effectively applied not only at internal‐boundary‐nodes but also at edges and corners. Their use yields significant advantages because of their superior algebraic and computational properties. Furthermore, it is shown that some well‐known difficulties that occur when primal nodes are introduced are efficiently handled by the multipliers‐free dual‐primal method. The concept of the Steklov–Poincaré operator for matrices is revised by our theory and a new version of it, which has clear advantages over standard definitions, is given. Extensive numerical experiments that confirm the efficiency of the multipliers‐free dual‐primal methods are also reported here. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010
A new high accuracy finite difference discretization for the solution of 2D nonlinear biharmonic equations using coupled approach
Authors: Mohanty R. K.
Published: September 2009

In this article, using coupled approach, we discuss fourth order finite difference approximation for the solution of two dimensional nonlinear biharmonic partial differential equations on a 9‐point compact stencil. The solutions of unknown variable and its Laplacian are obtained at each internal grid points. This discretization allows us to use the Dirichlet boundary conditions only and there is no need to discretize the derivative boundary conditions. We require only system of two equations to obtain the solution and its Laplacian. The proposed fourth order method is used to solve a set of test problems and produce high accuracy numerical solutions. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010