bluuebunny/crossref_metadata_2025 huggingface dataset:
3D Plotted PCL Scaffolds for Stem Cell Based Bone Tissue Engineering
Authors: Yilgor Pinar , Sousa Rui A. , Reis Rui L. , Hasirci Nesrin , Hasirci Vasif
Published: August 2008

The ability to control the architecture and strength of a bone tissue engineering scaffold is critical to achieve a harmony between the scaffold and the host tissue. Rapid prototyping (RP) technique is applied to tissue engineering to satisfy this need and to create a scaffold directly from the scanned and digitized image of the defect site. Design and construction of complex structures with different shapes and sizes, at micro and macro scale, with fully interconnected pore structure and appropriate mechanical properties are possible by using RP techniques. In this study, RP was used for the production of poly(ε‐caprolactone) (PCL) scaffolds. Scaffolds with four different architectures were produced by using different configurations of the fibers (basic, basic‐offset, crossed and crossed‐offset) within the architecture of the scaffold. The structure of the prepared scaffolds were examined by scanning electron microscopy (SEM), porosity and its distribution were analyzed by micro‐computed tomography (µ‐CT), stiffness and modulus values were determined by dynamic mechanical analysis (DMA). It was observed that the scaffolds had very ordered structures with mean porosities about 60%, and having storage modulus values about 1 × 107 Pa. These structures were then seeded with rat bone marrow origin mesenchymal stem cells (MSCs) in order to investigate the effect of scaffold structure on the cell behavior; the proliferation and differentiation of the cells on the scaffolds were studied. It was observed that cell proliferation was higher on offset scaffolds (262000 vs 235000 for basic, 287000 vs 222000 for crossed structure) and stainings for actin filaments of the cells reveal successful attachment and spreading at the surfaces of the fibers. Alkaline phosphatase (ALP) activity results were higher for the samples with lower cell proliferation, as expected. Highest MSC differentiation was observed for crossed scaffolds indicating the influence of scaffold structure on cellular activities.
Evaluation of Chitosan/Biphasic Calcium Phosphate Scaffolds for Maxillofacial Bone Tissue Engineering
Authors: Urkmez Aylin Sendemir , Clark Sherrie G. , Wheeler Matthew B. , Goldwasser Michael S. , Jamison Russell D.
Published: August 2008

Porous, 3D chitosan/biphasic calcium phosphate (BCP) scaffolds were used to prepare tissue engineering constructs for maxillofacial bone tissue reconstruction. Mesenchymal stem cells (MSC's) were seeded and cultured on clinically relevant sized scaffolds.In vitroengineered constructs facilitated the healing of mandibular defects in pigs if accompanied with delivery of basic fibroblast growth factor (bFGF).
Characterization of Poly(vinyl alcohol)/Chitosan Hydrogels as Vascular Tissue Engineering Scaffolds
Authors: Vrana Nihal Engin , Liu Yurong , McGuinness Garret Brian , Cahill Paul Aidan
Published: August 2008

In this study, PVA/Chitosan hydrogels were fabricated by freeze/thaw cycles and further crosslinking with a KOH/Na2SO4 coagulation bath and the effect of freeze/thaw cycle number on cell behaviour was evaluated. The surface of the hydrogels were further modified with Collagen type I adsorption and seeded with bovine aortic vascular smooth muscle and endothelial cells. Increasing the number of freeze/thaw cycles resulted in a marked change in surface morphology, hydrophilicity and protein adsorption. Collagen coating caused an increase in initial attachment and proliferation. We concluded that hydrogels that have undergone 3 freeze/thaw cycles were optimum for cell attachment both in the presence and the absence of coating.
Novel Biologically Inspired Collagen Nanofibers Reconstituted by Electrospinning Method
Authors: Foltran Ismaela , Foresti Elisabetta , Parma Bruna , Sabatino Piera , Roveri Norberto
Published: August 2008

The possibility to prepare bioinspired collagen nanofibers by electrospinning from aqueous suspension of telopeptide‐free collagen molecules avoiding both organic solvents and blends with any synthetic and natural polymers has been investigated. The results have highlighted the need for a basic atmosphere between the needle and the ground collector in order to increase the environmental pH during the collagen molecules self‐assembly along the electrostatic force lines. Morphological, spectroscopic and calorimetric analyses carried out on the electrospun collagen nanofibers have opened the possibility to take advantage of this new approach in order to prepare an ideal biomimetic reinforcing component of new biomedical and surgical biomaterials.
Phospholipids Bilayers as Molecular Models for Drug‐ Membrane Interactions. The Case of the Antiepileptics Phenytoin and Carbamazepine
Authors: Suwalsky Mario , Mennickent Sigrid , Villena Fernando , Sotomayor Carlos P.
Published: August 2008

With the aim to better understand the molecular mechanisms of the interaction of phenytoin and carbamazepine with cell membranes we utilized a well‐established model consisting in intact human erythrocytes, isolated unsealed human erythrocyte membranes (IUM) and molecular models of its membrane. The latter consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidyl‐ethanolamine (DMPE), representative of phospholipid classes respectively located in the outer and inner monolayers of erythrocytes and other cell membranes. This report presents the following evidence that phenytoin and carbamazepine interact with membrane phospholipids: a) X‐ray diffraction and fluorescence spectroscopy showed that both drugs preferentially interacted with DMPC; b) in IUM, the drugs induced a disordering effect on the polar head groups and acyl chains of the eryhrocyte membrane lipid bilayers; c) electron microscopy observations of human erythrocytes showed the echinocyte formation, an effect due to phenytoin and carbamazepine insertion in the outer monolayer of the red cell membrane.
Influence of Oxygen Plasma Modification on Surface Free Energy of PMMA Films and Cell Attachment
Authors: Ozcan Canturk , Zorlutuna Pınar , Hasirci Vasıf , Hasirci Nesrin
Published: August 2008

For any biomaterial placed into a biological medium, the surface properties of the material, such as porosity, crystallinity, presence and distribution of electrical charge and functional groups are very critical parameters that determine the acceptance or rejection of the material. Applications, especially tissue engineering require some surface modifications at the molecular level without disturbing the bulk properties of the implants in order to enhance the cell attachment on the material. An appropriate technique is the application of glow discharge plasma which employs no solvents, takes place at ambient temperatures, and alterations take place only at the surface by changing the surface chemistry along with surface free energy (SFE) and efficiency for cell‐material interaction. In this study, poly(methyl methacrylate) (PMMA) film surfaces were modified with oxygen plasma. SFE and its dispersive and polar (acidic‐basic) components of the modified surfaces were calculated by means of several theoretical approaches including geometric mean, harmonic mean and acid‐base equations. The relation between SFE and its dispersive and polar components and cell attachment on surfaces were studied. The highest 3T3 cell attachment was obtained for the surface with the total SFE of 61.77 mJ/m2 and polar component of 50.91 mJ/m2 according to Geometric mean. The total SFE of this surface was calculated to be 61.06 mJ/m2 and the polar component as 40.96 mJ/m2 using the Harmonic mean method.
Surface Modification of Polyurethanes with Covalent Immobilization of Heparin
Authors: Aksoy Ayse E , Hasirci Vasif , Hasirci Nesrin
Published: August 2008

Thrombus formation and blood coagulation is a major problem associated with blood contacting products such as catheters, vascular grafts, arteries, artificial hearts and heart valves. An intense research is being conducted towards the synthesis of new hemocompatible materials and modifications of surfaces with biological molecules. In this study, polyurethane (PU) films were synthesized in medical purity from diisocyanate and polyol without using any other ingredients and their surfaces were modified by covalent immobilization of heparin. Two types of heparin, unfractionated (UFH) and low molecular weight heparin (LMWH), were immobilized to investigate their effect on cell adhesion. The surface properties of the modified PUs were examined with ESCA, ATR‐FTIR and AFM. ESCA results demonstrated sulfur peaks indicating the presence of heparin and AFM results showed the alteration of surface structure after coating with heparin. Cell adhesion studies were conducted with heparinized whole human blood. The surfaces of the UFH immobilized films resulted in lesser red blood cell adhesion in comparison to LMWH demonstrating strong anti‐thrombogenic activity of the latter.
Autooxidized Polyunsaturated Oils/Oily Acids: Post‐it Applications and Reactions with Fe(III) and Adhesion Properties
Authors: Keleş Elif , Hazer Baki
Published: August 2008

Soybean oil, sesame oil, linoleic acid and linolenic acid were epoxidized, peroxidized and hydroperoxidized via autooxidation under air oxygen and sunlight at room temperature to obtain novel post‐it materials. Polymeric soybean oil peroxide and sesame oil peroxide were containing soluble part of 60%(w/w) together with crosslinked part of 40%(w/w) while polymeric linoleic and polymeric linolenic acids were completely soluble. The autooxidized soluble products with Mn varying between 800 and 3100 Daltons were used as post‐it adhesive. The highest adhesion was observed in the case of polymeric soybean oil (3.0 Newton), while adhesion of commercial epoxidized soybean oil, polymeric linoleic and polymeric linolenic acid were 0.8, 0.5 and 0.5 Newton, respectively. Reactions of the autooxidized soluble products with Fe(NO3)3. 4H2O in the presence of ethanol, glycerol and diethyleneglycol gave the hydroxy functionalized products with the same Mn values and indicating no adhesive properties. When the commercial epoxidized soybean oil was reacted with Fe(NO3)3. 4H2O in the presence of the alcohols, Mn of the hydroxy functionalized polymeric oil was found to be unchanged. 1H NMR, FT‐IR, SEM and GPC techniques were used in the characterization of the products obtained.
Post Polymerization of Saturated and Unsaturated Poly(3‐hydroxy alkanoate)s
Authors: Erduranlı Haydar , Hazer Baki , Borcaklı Mehlika
Published: August 2008

Summary: Chemical modification is useful to diversify poly(3‐hydroxyalkanoate)s, for medical and industrial applications. In this manner, transesterification reactions of poly(3‐hydroxy butyrate) were carried out under reflux condition of 1,2‐dichlorobenzene in the presence of 1,4‐butane diol, poly(ethylene glycol) bis(2‐aminopropyl ether) with molecular weights of 1000 and 2000, poly(ethylene glycol)methacrylate or glycerol at 180 °C. Addition reactions of bromine and –SH groups of 3‐mercaptopropionic acid to the double bond of poly(3‐hydroxy‐10‐undecenoate) were also carried out. Functionalized poly(3‐hydroxyalkanoate)s were characterized using 1H NMR, FTIR, GPC and thermal analysis techniques.
Structure elucidation and NMR spectral assignments of four neolignan glycosides with enantiometric aglycones from Osmanthus ilicifolius
Authors: Machida Koichi , Sakamoto Shigeaki , Kikuchi Masao
Published: August 2008

Four new 8‐O‐4′ type neolignan glycosides with enantiometric aglycones, (7S,8R)‐erythro‐guaiacylglycerol‐β‐O‐4′‐sinapyl ether 9‐O‐β‐D‐glucopyranoside (1), (7R,8S)‐erythro‐guaiacylglycerol‐β‐O‐4′‐sinapyl ether 9‐O‐β‐D‐glucopyranoside (2), (7S,8R)‐erythro‐ syringylglycerol‐β‐O‐4′‐sinapyl ether 9‐O‐β‐D‐glucopyranoside (3) and (7R,8S)‐erythro‐ syringylglycerol‐β‐O‐4′‐sinapyl ether 9‐O‐β‐D‐glucopyranoside (4), were isolated from the leaves of Osmanthus ilicifolius. Their structures were established on the basis of NMR, circular dichroism (CD), MS and chemical data. The NMR assignments for the compounds were carried out using 1H, 13C, COSY, HMQC, HMBC and NOESY NMR experiments. Copyright © 2008 John Wiley & Sons, Ltd.
hp‐Generalized FEM and crack surface representation for non‐planar 3‐D cracks
Authors: Pereira J. P. , Duarte C. A. , Guoy D. , Jiao X.
Published: August 2008

A high‐order generalized finite element method (GFEM) for non‐planar three‐dimensional crack surfaces is presented. Discontinuous p‐hierarchical enrichment functions are applied to strongly graded tetrahedral meshes automatically created around crack fronts. The GFEM is able to model a crack arbitrarily located within a finite element (FE) mesh and thus the proposed method allows fully automated fracture analysis using an existing FE discretization without cracks. We also propose a crack surface representation that is independent of the underlying GFEM discretization and controlled only by the physics of the problem. The representation preserves continuity of the crack surface while being able to represent non‐planar, non‐smooth, crack surfaces inside of elements of any size. The proposed representation also provides support for the implementation of accurate, robust, and computationally efficient numerical integration of the weak form over elements cut by the crack surface. Numerical simulations using the proposed GFEM show high convergence rates of extracted stress intensity factors along non‐planar curved crack fronts and the robustness of the method. Copyright © 2008 John Wiley & Sons, Ltd.
Combined modification of asphalt by waste PE and rubber
Authors: Fang Changqing , Li Tiehu , Zhang Zengping , Wang Xin
Published: August 2008

Waste PE (WPE) and rubber were combined to modify the ordinary oil asphalt in order to improve the performance of asphalt. In this study, the recycled waste packing polymer replacing the ordinary polymer modifiers modified the road asphalt through mechanical mixing for the first time. Results showed that softening point and ductility of asphalt increased, while the penetration degree decreased after the modification. The overall performance of the asphalt/WPE/RU system was superior to that of the asphalt/WPE system. FT‐IR analysis indicated that the modification actually was a physical process. The microstructure of the modified asphalt indicated that the shear yield and crack‐branching caused by the waste rubber powder were the main reasons for the improvement of the performance of asphalt. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
A fatigue damage model for composite materials
Authors: Chen Hsing‐Sung , Hwang Shun‐Fa
Published: August 2008

Composite materials using polymer resins as matrices possess viscoelastic properties such that the fatigue behavior of the composite could be changed by different stress levels, stress ratio, stress frequency, or temperature. Based on a physical phenomenon of damage growth, this work develops a fatigue damage model including the nonlinear effects of stress ratio and stress frequency on the damage processes for carbon/epoxy composites. A damage index is defined and used to confirm the damage evolution behavior, and a series of fatigue tests of unidirectional specimens under monotonous loading and two‐stress level loading are conducted to test the proposed fatigue damage model. The results reveal that the proposed model could reasonably predict the fatigue life of composite materials under complicated loading conditions and it also includes the sequence effect of cyclic block loadings. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Grafting of polystyrene chains on surfaces of nanosilica particles via peroxide bulk polymerization
Authors: Suckeveriene R.Y. , Tzur A. , Narkis M. , Siegmann A.
Published: August 2008

This article describes an in situ bulk polymerization process of styrene in the presence of silica nanoparticles. In this peroxide bulk polymerization process, two polystyrene fractions are formed: A polystyrene (PS) fraction attached to the particle's surface, which cannot be detached by hot xylene extraction, and an unattached PS fraction which dissolves in xylene. Solvent extraction and TGA measurements have confirmed the existence of grafted PS chains to the silica surfaces. FTIR measurements have indicated the existence of SiOC bonds connecting the PS grafts to the silica surface. Polypropylene (PP) was blended with the extracted PS‐g‐silica particles to produce concentrations of 1–3% nanoparticles in the PP composites. A remarkably improved dispersability of the nanoparticles was achieved, thus grafting reduces re‐agglomeration and increases the affinity of the grafted surface to the polymer matrix. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Preparation and insulation property studies of thermoplastic PMMA‐silica nanocomposite foams
Authors: Yeh J.M. , Chang K.C. , Peng C.W. , Chand B.G. , Chiou S.C. , Huang H.H. , Lin C.Y. , Yang J.C. , Lin H.R. , Chen C.L.
Published: August 2008

The comparative studies for the effect of vinyl‐modified silica (VMS) and raw silica (RS) particles on the cell structure, insulation (dielectric and thermal transport) properties, and thermal stability of thermoplastic PMMA‐silica nanocomposite (PSN) foams are described. The VMS particles were synthesized by the conventional acid‐catalyzed sol‐gel reactions of tetraethyl orthosilicate (TEOS) in the presence of 3‐(trimethoxysilyl)propyl methacrylate (MSMA) molecules. The as‐prepared VMS particles were then characterized through fourier transform infrared (FTIR), solid‐state 13C‐nuclear magnetic resonance (13C‐NMR) and 29Si‐NMR spectroscopy. Subsequently, the PSN materials were prepared via in‐situ bulk polymerization. The dispersion of silica particles in PMMA matrix was observed by transmission electron microscopy (TEM) studies. Gel permeation chromatography (GPC) was used to determine the molecular weights of as‐prepared samples. The PSN materials were used to produce foams by a batch process in an autoclave using nitrogen as foaming agent. The effect of VMS and RS particles on the cell structure, insulation properties and thermal stability of PSN foams were investigated by scanning electron microscopy (SEM), LCR meter, Transient plane source (TPS) technique and thermal gravimetric analysis (TGA), respectively. The better dispersion capability of VMS particles in PSN foams was found to lead enhanced nucleation efficiency, thermal stability and decreased dielectric constant (ε′), dielectric loss (ε″) and thermal conductivity (k). POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Improving the properties of LDPE/glass fiber composites with silanized‐LDPE
Authors: Fabris Felipe W. , Cardozo Nilo S.M. , Mauler Raquel S. , Nachtigall Sônia M.B.
Published: August 2008

Low density polyethylene (LDPE) is a widely used thermoplastic. The dispersion of inorganic fillers in thermoplastic matrices such as polyethylene has been largely employed to improve some of its properties. However, interaction between both components is a major issue so the presence of a coupling agent is usually necessary to increase the interaction among the phases. In this study, LDPE chemically modified with vinyltriethoxysilane (VTES) was used as a coupling agent in glass fiber‐reinforced LDPE. The composites were prepared in a mixing chamber and subsequently analyzed by tensile tests, rotational rheometry, and scanning electron microscopy (SEM). The mechanical properties were significantly increased by the use of small amounts of the coupling agent. Moreover, the rheological behavior and the SEM micrographs showed higher interaction between the matrix and the reinforcing phase in the composites containing LDPE modified with VTES, confirming the suitability of using this coupling agent in these systems. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Biodegradable nanocomposites from maleated polycaprolactone/soy protein isolate blend with organoclay: Preparation, characterization, and properties
Authors: Sasmal Abhisek , Sahoo Debasish , Nanda Rajashree , Nayak Preetishree , Nayak Padma L. , Mishra Joy K. , Chang Young‐Wook , Yoon Joon‐Yong
Published: August 2008

New biobased, eco‐friendly nanocomposites were prepared from maleated polycaprolactone/soy protein isolate blend (50/50 wt/wt) with organo‐modified clay by melt compounding. The XRD, TEM, tensile, DMTA, and rheological properties of the nanocomposites were investigated. X‐ray diffraction and transmission electron microscopy analysis revealed that the intercalated nanocomposite is formed and the silicate layers of the clay are uniformly dispersed at a nanometer scale in the polymer matrix. There is a great enhancement in tensile and dynamic mechanical properties of the nanocomposites. Rheological study revealed that the nanocomposite exhibits strong shear thinning behavior and clay particles form network in the melted state of the composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Maleated polypropylene film and wood fiber handsheet laminates
Authors: Lee Sangyeob , Shupe Todd F. , Groom Leslie H. , Hse Chung Y.
Published: August 2008

The grafting effect of maleic anhydride (MA) as an interfacial bonding agent and its influence on the tensile strength properties of thermomechanical pulp handsheet‐isotactic polypropylene (iPP) film laminates was studied. For the MA treated with benzoyl peroxide (BPO) as an initiator, tensile strength properties increased 76% with PP film over untreated laminates. The optimal strength properties were obtained with a MA and BPO ratio of 2:1. A strong correlation was observed between the number of fibers in the web and tensile strength properties for both handsheet drying conditions. The R2 values were 0.95 for air‐dry conditions and 0.94 from oven‐dry conditions. Scanning electron microscopy images also showed the effectiveness of MA loading on the surface of thermomechanical pulp fibers due to increased fiber failure, which occurred without fiber being pulled out from the PP matrixes. Crystallinity and heat flow were determined using differential scanning calorimetry (DSC) and increased as expected as the ratio of MA and BPO increased from 0:0 to 2:1. These results were also in accordance with the morphological observations at the fracture surface, Fourier transform infrared spectra, and thermal analysis. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Hospitalization for peptic ulcer and bleeding in users of selective COX‐2 inhibitors and nonselective NSAIDs with special reference to celecoxib
Authors: Patterson M. Kay , Castellsague Jordi , Walker Alexander M.
Published: August 2008

Purpose

To assess the relative incidence of peptic ulcer bleeding and perforation (PUBP) in users of selective cyclooxygenase‐2 (COX‐2) inhibitors and nonselective nonsteroidal anti‐inflammatory drugs (NSAIDs).

Methods

This was a retrospective case–control study based on insurance claims, with chart review to confirm cases. The base population consisted of 2.2 million adult users of celecoxib, diclofenac, ibuprofen, naproxen, rofecoxib, or valdecoxib who were covered by commercial health insurance in the United States from 1999–2003. For 790 persons hospitalized for PUBP and 7887 controls, most recent NSAID/COX‐2 use and a variety of medical and pharmacy risk factors were ascertained from the insurance files and analyzed by conditional logistic regression. The main outcome measure was the odds ratio (OR) associated with use of each drug by comparison to naproxen, and in successive intervals after last dispensing.

Results

Hospitalization for PUBP was highest from the date of NSAID/COX‐2 dispensing through the end of an exposure period that corresponded to the days supply; the rate dropped steadily thereafter. The covariate‐adjusted ORs by comparison to naproxen were: ibuprofen 0.86 (95% confidence interval (CI) 0.68, 1.09), rofecoxib 0.79 (0.62, 1.02), diclofenac 0.66 (0.47, 0.94), valdecoxib 0.50 (0.26, 0.97), and celecoxib 0.45 (0.35, 0.58). The nonselective NSAIDs had an OR for PUBP of 1.51 (1.26, 1.98) compared to the selective COX‐2 inhibitors.

Conclusion

Nonselective NSAIDs convey half again as much risk of hospitalization for PUBP as do COX‐2 inhibitors. Celecoxib users had about half the hospitalization rate of users of naproxen. Copyright © 2008 John Wiley & Sons, Ltd.
‘Yours is potentially serious but most of these are cured’: optimistic communication in UK outpatient oncology consultations
Authors: Leydon Geraldine M.
Published: August 2008

Objective: To describe how experienced doctors discuss radiotherapy and chemotherapy with cancer patients about to undergo such treatment.

Methods: Qualitative analysis of 27 consultations between consultant oncologists and patients with breast, head, and neck cancer or gastrointestinal cancer. Set in outpatient oncology clinics: one in the South West, one in the Midlands, and a large London teaching hospital. Participants included three experienced consultant oncologists and 27 patients diagnosed with cancer attending outpatient oncology consultations to discuss radiotherapy or chemotherapy.

Results: Doctors repeatedly invoked optimism when discussing bad and uncertain information about radiotherapy and chemotherapy. This was achieved by following relatively bad or uncertain information with some good information. Patients tended to collaborate in the construction of optimism.

Conclusions: Doctors talked optimistically while sharing information about chemotherapy and radiotherapy with patients about to undergo such treatment. Research indicates that patients want their doctors to openly share bad and uncertain information, but to do so sensitively. Following uncertain or bad tidings with relatively better news was one way in which doctors delivered information honestly without diminishing opportunities for hope in the consultation room or optimism about the future. Findings from qualitative empirical studies, such as that described, provide a valuable educational adjunct to the role play and simulated patient interactions, often used in conventional communication skills training and research. Copyright © 2008 John Wiley & Sons, Ltd.
SWNT probed by multi‐frequency EPR and nonresonant microwave absorption
Authors: Corzilius B. , Dinse K.‐P. , Hata K. , Haluška M. , Skákalová V. , Roth S.
Published: August 2008

In addition to g = 2.00 signals seen frequently in EPR spectra of SWNT, signals at g = 2.07 of SWNT prepared by CVD were detected, exhibiting a Pauli susceptibility temperature dependence. This Pauli magnetism in combination with the large g shift is taken as evidence that these signals originate from itinerant electrons of metallic nanotubes. At temperatures below 150 K, a dominant narrow signal develops at g = 2.00. By applying multifrequency EPR up to 319 GHz, its inhomogeneous nature was confirmed. This signal is assigned to defects of the carbon network of the tubes.

Comparing room temperature EPR spectra of CVD and arc‐grown SWNT, we found a much lower concentration of metallic tubes in arc material. No g = 2.07 signals of itinerant spins could be observed, which might be also caused by the high amount of residing catalyst. A drastic increase in nonresonant microwave absorption is observed below 10 K for both types of samples, if a threshold microwave power level is passed. In the same temperature range a drop in EPR intensity is also detected. These observations are taken as evidence for a transition into a superconducting phase of part of the sample. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hybrid grid/particle filter for Lagrangian data assimilation. II: Application to a model vortex flow
Authors: Salman H.
Published: August 2008

We apply our hybrid filter to a regularised vortex model of a co‐rotating vortex pair. To illustrate the main advantages of our formulation over existing filters, we compare our method to the perturbed observation Ensemble Kalman filter and a particle filter with Gaussian resampling. Our numerical simulations show that both the hybrid and particle filters can track the true vortex positions even when tracer position data is assimilated infrequently into our model. In contrast, the Ensemble Kalman filter diverges in this parameter range as was recently observed in the more realistic shallow‐water model simulations of Salman et al. We have found that our hybrid method can track the true system with as few as 20 members for the vortex model flow. The particle filter on the other hand requires an ensemble comprising in excess of 160 members. The hybrid filter, therefore, provides one solution to the filter divergence problem that has been identified in recent work on Lagrangian data assimilation. Copyright © 2008 Royal Meteorological Society
Influence of regional factors on zooplankton structure in a saline lowland river: the Salado River (Buenos Aires province, Argentina)
Authors: Claps María C. , Gabellone Néstor A. , Neschuk Nancy C.
Published: August 2008

Knowledge of regional factors influencing zooplankton structure in a semiarid river must include both the main channel and any tributaries in order to identify spatial and temporal patterns along with the main factor that affect the zooplankton community. Accordingly, seasonal samples were taken during 1997–1999 at 15 stations in the Salado River basin, where 172 species were identified (53 protozoans, 88 rotifers and 31 crustaceans). Conductivity and temperature optima and tolerances were calculated for the evident taxa. Different assemblages were recognized by cluster analysis, on the basis of their temperature and conductivity preferences. With respect to the zooplankton assemblages, three zones can be distinguished along the longitudinal axis of the basin: (1) the headwaters (the effluent from large saline shallow lakes), (2) the inter‐tributaries, and (3) the lower basin and associated shallow lakes. The spatial distribution of the assemblages was a result of the combined action of factors always promoting the dominance of rotifers. The influence of floodplain waters (backwater ponds, waterlogged depressions, flushing lakes) was attenuated progressively downstream, thus producing disadvantages for the crustaceans. The food availability and high nutrient concentrations related to land use in the headwaters favoured the co‐dominance of cladocerans and copepods along with the rotifers in that region. Copyright © 2008 John Wiley & Sons, Ltd.
Interactive effects of abiotic, hydrological and anthropogenic factors on fish abundance and distribution in natural run‐of‐the‐river shallow lakes
Authors: Rosso Juan José , Quirós Rolando
Published: August 2008

Ecological processes in lowland rivers are mostly dominated by hydrology and its interactions with other environmental factors. Fish–habitat relationships in rivers are also influenced by human impacts.

In this study, we describe patterns of abundance and distribution of fish species in a group of natural lowland river lakes along spatial anthropogenic and abiotic gradients when four hydrologically different summers are compared. We also describe the proportion of the total variances in fish species abundances that can be accounted for by selected abiotic (water conductivity), hydrological (water residence time) and human activity‐derived (total phosphorus (TP) concentration and NO3:NH4) variables. Consequently, our main purpose is to explore how abiotic and anthropogenic factors interact to affect fish abundance and distribution together with consistent results across different hydrological conditions. We conclude with a briefly discussion of some management implications.

The anthropogenic impacts on water quality, the extreme hydrological variability and the fluctuating abiotic environment affected fish abundance and distribution. Pampa inland silverside Odontesthes bonariensis was benefited from a less human disturbed environment with higher water residence time and total salinity, whereas species as Cyphocharax voga, Parapimelodus valenciennis and Cyprinus carpio found these conditions largely disadvantageous. On the other hand, while most species showed stronger—either negative or positive—response to anthropogenic, hydrological or abiotic factors Oligosarcus jenynsii was only slightly affected.

This paper identified the ecological function of a lowland river under its natural flow regime. There are not many opportunities to study unmodified rivers worldwide. Therefore, our findings may help in assessment programmes of fish communities in flow altered and human disturbed aquatic ecosystems. Copyright © 2008 John Wiley & Sons, Ltd.
Simulating the hydrology and total dissolved solids (TDS) of an ephemeral river in South Africa for environmental water requirement determinations
Authors: Hughes D. A.
Published: August 2008

Existing hydrological approaches to support the determination of environmental water requirements (EWRs) were largely developed for perennial rivers and may not be applicable to ephemeral rivers, where the quantity and quality dynamics of pool storage and frequency of connection can be more important than flow rates. The current understanding of semi‐arid hydrological processes and how best to apply hydrological models in ephemeral systems is less well developed than for more humid regions. The paper reports on the application of monthly and daily time‐step rainfall‐runoff models to simulating the hydrology (including pool storage) of the Seekoei River basin, a tributary of the Orange River in the Northern Province, South Africa. The hydrological response of the basin is spatially variable, a relatively small part of the basin generating a large proportion of the total stream flow. The outputs from the hydrological models have been used as inputs to a simple water quality mass balance model designed to simulate the total dissolved solids (TDS) of both flow and pool storage. The results from both the water quantity and quality models are encouraging when compared with the available observed data. While there are no data to confirm the simulation results at sub‐basin scales, they do appear to be conceptually acceptable. The conclusion is that the results are adequate to support ecological studies in the determination of EWRs. Copyright © 2008 John Wiley & Sons, Ltd.
Does ice matter? Site fidelity and movements by Atlantic salmon (Salmo salar L.) parr during winter in a substrate enhanced river reach
Authors: Linnansaari Tommi , Alfredsen Knut , Stickler Morten , Arnekleiv Jo Vegar , Harby Atle , Cunjak Richard A.
Published: August 2008

In‐stream habitat enhancement is a common remedial action in rivers where degradation/lack of suitable fish habitat can be diagnosed. However, post‐project monitoring to assess the response of the biota to modification is rare particularly during winter. We conducted in situ monitoring during the winters of 2004–2006 in the regulated Dalåa River, central Norway, in order to determine if winter habitat requirements of Atlantic salmon (Salmo salar L.) parr were realized in an enhanced (substrate and mesohabitat modification) reach. In total, 140 parr were marked with passive integrated transponder (PIT) tags and the fish were followed by carrying out active tracking surveys under variable ice conditions throughout the winter. Highest emigration (44%) occurred before ice formation started. Emigration was reduced after ice formed and was largely offset by parr re‐entering the enhanced area. Dispersal into the non‐enhanced, small substrate control area was observed only when the study reach was ice covered, and no parr were subsequently encountered in the control section after ice had melted. In the enhanced area, declining water temperature and surface ice conditions did not affect the spatial distribution of the resident salmon parr at the studied scale. Areas with ‘solid’ anchor ice precluded access for salmon parr whilst areas with ‘patchy’ anchor were used throughout the winter. Our results indicate that surface ice creates conditions that allow salmon parr to use stream habitats that otherwise provide only a limited amount of in‐stream cover. Ice processes should be taken into consideration when habitat enhancement projects are carried out and subsequently assessed for effectiveness. Copyright © 2008 John Wiley & Sons, Ltd.
Functional trait differences between extant exotic, native and extinct native plants in the Hunter River, NSW: a potential tool in riparian rehabilitation
Authors: Kyle Garreth , Leishman Michelle R.
Published: August 2008

Riparian and riverine systems around the world are subject to human mediated degradation. It is increasingly recognized that rehabilitation of these systems is important to retain biodiversity and important ecosystem services. Plant functional traits represent a potentially useful but underutilized tool in the restoration or rehabilitation of ecosystems such as riparian systems. This study uses a functional trait approach to provide insight into the changes in ecosystem function that have occurred with the loss of native plant species and their replacement by exotics. We examined the plant functional traits associated with extinct native, extant native and extant exotic species in the riparian margin of the Hunter River, New South Wales, Australia. Comparisons of 11 traits were conducted using univariate (analysis of variance and χ
2) and multivariate (principal component analysis and analysis of similarity) methods. Both extant native and extant exotic species had traits associated with a short lived, ruderal strategy: high specific leaf area (SLA), soft leaves, herbaceous growth forms and therophyte life form. In contrast, extinct native species had traits such as low SLA, tough leaves, tree and shrub growth form and phanerophyte life form. This shift in plant trait assemblages associated with the transition from a native to predominately exotic flora has important implications for ecosystem processes in this riverine system. We suggest that such a functional trait approach can be integrated with knowledge of other ecosystem components to provide an understanding of ecosystem function that can be used to guide rehabilitation initiatives. Copyright © 2008 John Wiley & Sons, Ltd.
Sharp thresholds for constraint satisfaction problems and homomorphisms
Authors: Hatami Hamed , Molloy Michael
Published: August 2008

We determine under which conditions certain natural models of random constraint satisfaction problems have sharp thresholds of satisfiability. These models include graph and hypergraph homomorphism, the (d,k,t)‐model, and binary constraint satisfaction problems with domain size three. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2008
A percolating hard sphere model
Authors: Cotar Codina , Holroyd Alexander E. , Revelle David
Published: August 2008

Given a homogeneous Poisson point process in ℝd, Häggström and Meester (Random Struct Algorithms 9 (1996) 295–315) asked whether it is possible to place spheres (of differing radii) centred at the points, in a translation‐invariant way, so that the spheres do not overlap but there is an unbounded component of touching spheres. We prove that the answer is yes in sufficiently high dimension. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2009
Targeted Delivery of Nanoparticles Bearing Fibroblast Growth Factor‐2 by Ultrasonic Microbubble Destruction for Therapeutic Arteriogenesis
Authors: Chappell John C. , Song Ji , Burke Caitlin W. , Klibanov Alexander L. , Price Richard J.
Published: August 2008

Therapeutic strategies in which recombinant growth factors are injected to stimulate arteriogenesis in patients suffering from occlusive vascular disease stand to benefit from improved targeting, less invasiveness, better growth‐factor stability, and more sustained growth‐factor release. A microbubble contrast‐agent‐based system facilitates nanoparticle deposition in tissues that are targeted by 1‐MHz ultrasound. This system can then be used to deliver poly(D,L‐lactic‐co‐glycolic acid) nanoparticles containing fibroblast growth factor‐2 to mouse adductor muscles in a model of hind‐limb arterial insufficiency. Two weeks after treatment, significant increases in both the caliber and total number of collateral arterioles are observed, indicating that the delivery of nanoparticles bearing fibroblast growth factor‐2 by ultrasonic microbubble destruction may represent an effective and minimally invasive strategy for the targeted stimulation of therapeutic arteriogenesis.
Innovative Stahltragwerke für das Museo del Acero in Mexiko
Authors: Sobek Werner , Schmid Angelika , Heinlein Frank
Published: August 2008

Das ehemalige Industriegelände “Parque Fundidora” in Monterrey (Mexiko) ist in den letzten Jahren zu einem Museumsstandort mit Unterhaltungsangeboten umgewandelt worden. In diesem Rahmen wurde ein stillgelegtes Stahlwerk zu einem Stahl‐Museum umgebaut, in dem Vergangenheit und Gegenwart der Stahlindustrie in der Region aufgezeigt werden (Bild 1). Das Museum öffnete im Herbst 2007 seine Tore für die Öffentlichkeit und erhielt aufgrund seiner großen baulichen Qualitäten sofort den Titel “Monumento Nacional de Mexico”. Für die Errichtung des Museo del Acero wurde zum einen der vorhandene Baukörper des alten Stahlwerks restauriert und über Laufstege von außen zugänglich gemacht. Zum anderen wurde ein Neubau erstellt, der auf Höhe des Erdgeschosses an den Bestand anschließt und im weiteren Verlauf aufgrund der Geländetopographie teilweise unterirdisch liegt. Wichtiger Teil des Neubaus sind zwei filigrane Sonderstrukturen aus Stahl – das facettierte Dach der sogenannten Stahlgalerie und eine frei schwebende Wendeltreppe – sowie eine leicht und transparent anmutende Glasfassade. Diese Tragwerke werden im folgenden Artikel beschrieben.
Große Teleskope und der Brückenbau
Authors: Kärcher Hans Jürgen
Published: August 2008

In den letzten Jahren hat die Entwicklung von extrem großen bodengebundenen optischen Teleskopen einen unvorhergesehenen Aufschwung genommen. Die technologische Entwicklung wird vorangetrieben durch die immer komplexere aktive und adaptive Optik. Dabei gewinnt aber auch die Gestaltung der Teleskopstruktur immer stärker an Bedeutung – sie ist schließlich das Rückgrat für die Optik, und hat entsprechenden Einfluss auf die Teleskopeigenschaften, insbesondere aber auch auf die Kosten.

Strukturmechanik selbst ist eine sehr alte Kunst, beginnend vor langer Zeit mit dem Bau von Brücken oder gotischen Kathedralen. Grundlage dieser Kunst ist das Verständnis für Kräfte, Lastpfade, Gewicht und Balance sowie Beanspruchung und damit verbundene Verformungen. Der Beitrag entwickelt strukturmechanisches Verständnis für die Bauteile eines großen Teleskops (Tubus, Alidade) auf Grundlage des Denkens der Brückenbauer. Aktuelles Beispiel ist der Konzeptentwurf für ein 42 m Extrem Large Telescope (ELT).
Schwebefähren: Triumphbögen zwischen Festland und Meer – Versuch einer Chronologie
Authors: Stiglat Klaus
Published: August 2008

Die Schwebefähren waren eine überwiegend hängebrückenartige Konstruktion mit fest installierten Fahrgeräten, die dem Personen‐ und Gütertransport in See‐ und Flusshäfen dienten wie auch für innerbetriebliche Transporte in Industrieanlagen genutzt wurden.

Es wird versucht, ihre Entstehungsgeschichte chronologisch zu beschreiben und die wichtigsten technischen Merkmale und ihre Veränderungen aufzuzeigen. Insgesamt werden siebzehn bedeutende Fähren aus den Jahren 1893 bis 1920 besprochen.
Beurteilung bestehender Stahltragwerke: Empfehlungen zur Abschätzung der Restnutzungsdauer
Authors: Kühn Bertram , Helmerich Rosemarie , Nussbaumer Alain , Günther Hans‐Peter , Herion Stefan
Published: August 2008

Die zunehmende Bedeutung der Nachhaltigkeit im Bauwesen wird in Zukunft das Bauen im Bestand gegenüber Neubauten in den Vordergrund rücken. Dies gilt auch für den Brückenbau, wo das Qualitätsmanagement seit langem Brücken von ihrem Entstehungsgang über den Betrieb bis in die Entsorgung begleitet.

Die starke Vergrößerung der Frachtvolumina für Straße und Schiene und die zunehmende Überalterung des Brückenbestandes fragen danach, ob die bestehenden Brücken für die veränderten Betriebsbedingungen noch geeignet sind und wie sie und ob sie dafür instandgesetzt werden könnten.

Für die erforderlichen Instandhaltungs‐ und Instandsetzungsmaßnahmen oder einen eventuellen Ersatz durch einen Neubau ist aber die Frage der Restnutzungsdauer von entscheidender Bedeutung. Es ist daher nicht von ungefähr, dass sich Baulast‐träger auf nationaler und internationaler Ebene frühzeitig zusammengetan haben, um nach geeigneten Methoden der Bestimmung der Sicherheit und Restnutzungsdauer bestehender Brücken zu forschen. Auch die internationalen technisch‐wissenschaftlichen Verbände wie EKS und fib sowie die Standard‐Organisationen ISO und CEN sind der Frage eines internationalen Austauschs und der Vereinheitlichung der Methoden nachgegangen.

Für Stahlbrücken hat insbesondere das technische Komitee6 – Ermüdung – der EKS Anregungen aufgegriffen, aus den verschiedenen nationalen Erfahrungen und dem vorhandenen Wissen technische Empfehlungen für die Beurteilung bestehender Stahlbrücken zu entwickeln [1], die sich als Grundlage für die von CEN/TC 250 – das CEN‐Komitee für die Bearbeitung der Eurocode – geplante Erweiterung der Eurocode zur Instandhaltung und Instandsetzung des Brückenbestandes eignen.

Das Ergebnis ist ein technisch‐wissenschaftlicher Bericht, der im Rahmen der Zusammenarbeit der europäischen Kommission (DG‐Research – Joint Research Centre JRC) mit der EKS als Basispapier für eine zukünftige Eurocode‐Erweiterung veröffentlicht wurde und schon jetzt als Empfehlung für eine Vorgehensweise nach dem Stand der Technik verwendet werden kann.

Der vorliegende Beitrag behandelt die Grundzüge dieses Berichtes [1], der vom e‐bookshop der Kommission kostenfrei herunter geladen werden kann.
Graded response model based on the logistic positive exponent family of models for dichotomous responses
Authors: Samejima Fumiko
Published: August 2008

Samejima (Psychometrika 65:319–335, 2000) proposed the logistic positive exponent family of models (LPEF) for dichotomous responses in the unidimensional latent space. The objective of the present paper is to propose and discuss a graded response model that is expanded from the LPEF, in the context of item response theory (IRT). This specific graded response model belongs to the general framework of graded response model (Samejima, Psychometrika Monograph, No. 17, 1969 and No. 18, 1972; Handbook of modern item response theory, Springer, New York, 1997; Encyclopedia of Social Measurement, Academic Press, San Diego, 2004), and, in particular to the heterogeneous case (Samejima, Psychometrika Monograph, No. 18, 1972). Thus, the model can deal with any number of ordered polytomous responses, such as letter grades (e.g., A, B, C, D, F), etc.

For brevity, hereafter, the model will be called the LPEF graded response model, or LPEFG. This model reflects the opposing two principles contained in the LPEF for dichotomous responses, with the logistic model (Birnbaum, Statistical theories of mental test scores, Addison Wesley, Reading, 1968) as their transition, which provide a reasonable rationale for partial credits in LPEFG, among others.