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Mechanical Stability (mechanical + stability)
Selected AbstractsMicrostructured Arrays of TiO2 Nanotubes for Improved Photo-Electrocatalysis and Mechanical StabilityADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Daoai Wang Abstract The preparation of micropatterned TiO2 nanotubes (NTs) with tunable morphologies by combining laser micromachining technology and an anodization method is reported. The micropatterned structure can be easily designed and fabricated by laser micromachining a titanium substrate, further anodization of which gives nanotube arrays perpendicularly oriented to the titanium surface. The patterned TiO2 NTs show dramatically improved photocurrent and photocatalytic performances because of their enhanced surface area and light-harvesting capability. The photocurrent density and incident-photon-to-current efficiency at the peak absorption increases by 48 and 39%, respectively, compared to a TiO2 NT array without a patterned structure. It was also found that micropatterning dramatically improves the mechanical stability of the TiO2 NTs on the substrate, which otherwise were liable to peel off from the substrate surface. The strategy will reasonably expand the application of TiO2 NTs in a variety of fields that require enhanced photo-electrocatalysis and mechanical stability. [source] Direct Synthesis of Highly Stable Mesoporous Molecular Sieves Containing Zeolite Building Units,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2005A. Sakthivel Abstract A novel, one-step synthesis of a highly stable mesoporous molecular sieve (MMS-H), which has a structure analogous to MCM-48 but which contains zeolite building units, is reported. A variety of experimental techniques,X-ray diffraction (XRD), N2 adsorption/desorption, transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, hyperpolarized 129Xe,NMR, and solid-state 27Al and 31P,magic-angle spinning (MAS) NMR spectroscopies,have been used to characterize the framework structure, porosity, and acidity of this novel mesoporous/microporous composite material, which is also found to possess superior thermal, hydrothermal, steam, and mechanical stabilities. [source] Application of nano-modified surfaces for fouling mitigationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2009M. R. Malayeri Abstract Energy lost due to fouling of heat exchangers accounts for at least 2% of the total world energy production per year. The overwhelming proportion of these losses is compensated by additional consumption of fossil energy carriers. Not surprisingly, this comes with an enormous energy price-tag as well as considerable green-house gas emissions, acidification of water resources and release of chemical fouling inhibitors. Any solution towards the mitigation of fouling will, therefore, provide significant economic and environmental benefits. In the present paper, the performance of innovative nano-modified surfaces is described when subjected to calcium sulphate scale deposition during convective heat transfer. Two types of non-structured and structured nano-modified surfaces are examined. The experimental results demonstrate that such coatings will significantly increase the induction time before fouling starts and also reduce the subsequent fouling rate, in comparison with untreated stainless steel surfaces. Considering these promising results and the potential application of nanotechnology to combat fouling, the paper continues by discussing the demands on thermal and mechanical stabilities that such coatings will have to satisfy. Copyright © 2009 John Wiley & Sons, Ltd. [source] Compaction of cell shape occurs before decrease of elasticity in CHO-K1 cells treated with actin cytoskeleton disrupting drug cytochalasin DCYTOSKELETON, Issue 4 2009Christian Schulze Abstract The actin filaments of the cytoskeleton form a highly dynamic polymer scaffold which is actively involved in many essential mechanisms such as cell migration, transport, mitosis, and mechanosensitivity. We treated CHO-K1 cells with different concentrations of the actin cytoskeleton disrupting drug cytochalasin D. Then investigating the cells' elastic behaviour by scanning force microscopy-based rheology we confirmed for high cytochalasin D concentrations (,1.5 ,M) a significant decrease of mechanical stability. At lower concentrations we measured no significant softening, but flattening and a horizontal contraction was observable even at low concentrations (,0.3 ,M) of cytochalasin D. The observed changes in cell shape resulted in a lower cell volume, showing that there is compensation by volume for small decreases in cytoskeletal strength resulting from reduced numbers or lengths of actin filaments. These results suggest that the characteristic functions defining a cell's mechanical stability such as mechanosensitivity can be maintained via small changes in cell volume in order to counter fluctuations in cytoskeletal composition. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] Properties of Poly(sodium 4-styrenesulfonate)-Ionic Liquid Composite Film and Its Application in the Determination of Trace Metals Combined with Bismuth Film ElectrodeELECTROANALYSIS, Issue 5 2008Jianbo Jia Abstract A new kind of bismuth film modified electrode to sensitively detect trace metal ions based on incorporating highly conductive ionic liquids 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF6) in solid matrices at glassy carbon (GC) was investigated. Poly(sodium 4-styrenesulfonate) (PSS), silica, and Nafion were selected as the solid matrices. The electrochemical properties of the mixed films modified GC were evaluated. The electron transfer rate of Fe(CN)64,/Fe(CN)63, can be effectively improved at the PSS-BMIMPF6 modified GC. The bismuth modified PSS-BMIMPF6 composite film electrodes (GC/PSS-BMIMPF6/BiFEs) displayed high mechanical stability and sensitive stripping voltammetric performances for the determination of trace metal cations. The GC/PSS-BMIMPF6/BiFE exhibited well linear response to both Cd(II) and Pb(II) over a concentration range from 1.0 to 50,,g L,1. And the detection limits were 0.07,,g L,1 for Cd(II) and 0.09,,g L,1 for Pb(II) based on three times the standard deviation of the baseline with a preconcentration time of 120,s, respectively. Finally, the GC/PSS-BMIMPF6/BiFEs were successfully applied to the determination of Cd(II) and Pb(II) in real sample, and the results of present method agreed well with those of atomic absorption spectroscopy. [source] Electroanalysis at Diamond-Like and Doped-Diamond ElectrodesELECTROANALYSIS, Issue 17 2003Richard Abstract Diamond as a high performance material occupies a special place due to its in many ways extreme properties, e.g., hardness, chemical inertness, thermal conductivity, optical properties, and electric characteristics. Work mainly over the last decade has shown that diamond also occupies a special place as an electrode material with interesting applications in electroanalysis. When made sufficiently electrically conducting for example by boron-doping, ,thin film' and ,free,standing' diamond electrodes exhibit remarkable chemical resistance to etching, a wide potential window, low background current responses, mechanical stability towards ultrasound induced interfacial cavitation, a low ,stickiness' in adsorption processes, and a high degree of ,tunability' of the surface properties. This review summarizes some of the recent work aimed at applying conductive (boron-doped) diamond electrodes to improve procedures in electroanalysis. [source] High-buffering capacity, hydrolytically stable, low-pI isoelectric membranes for isoelectric trapping separationsELECTROPHORESIS, Issue 20 2004Sanjiv Lalwani Abstract Hydrolytically stable, low-pI isoelectric membranes have been synthesized from low-pI ampholytic components, poly(vinyl alcohol), and a bifunctional cross-linker, glycerol-1,3-diglycidyl ether. The low-pI ampholytic components used contain one amino group and at least two weakly acidic functional groups. The acidic functional groups are selected such that the pI value of the ampholytic component is determined by the pKa values of the acidic functional groups. When the concentration of the ampholytic component incorporated into the membrane is higher than a required minimum value, the pI of the membrane becomes independent of variations in the actual incorporation rate of the ampholytic compound. The new, low-pI isoelectric membranes have been successfully used as anodic membranes in isoelectric trapping separations with pH < 1.5 anolytes and replaced the hydrolytically less stable polyacrylamide-based isoelectric membranes. The new low-pI isoelectric membranes have excellent mechanical stability, low electric resistance, good buffering capacity, and long life time, even when used with as much as 50 W power and current densities as high as 33 mA/cm2 during the isoelectric trapping separations. [source] Functionalized-Silk-Based Active Optofluidic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Konstantinos Tsioris Abstract Silk protein from the silkworm Bombyx mori has excellent chemical and mechanical stability, biocompatibility, and optical properties. Additionally, when the protein is purified and reformed into materials, the biochemical functions of dopants entrained in the protein matrix are stabilized and retained. This unique combination of properties make silk a useful multifunctional material platform for the development of sensor devices. An approach to increase the functions of silk-based devices through chemical modifications to demonstrate an active optofluidic device to sense pH is presented. Silk protein is chemically modified with 4-aminobenzoic acid to add spectral-color-responsive pH sensitivity. The functionalized silk is combined with the elastomer poly(dimethyl siloxane) in a single microfluidic device. The microfluidic device allows spatial and temporal control of the delivery of analytic solutions to the system to provide the optical response of the optofluidic device. The modified silk is stable and spectrally responsive over a wide pH range from alkaline to acidic. [source] Comparison between Nafion® and a Nafion® Zirconium Phosphate Nano-Composite in Fuel Cell ApplicationsFUEL CELLS, Issue 3-4 2006F. Bauer Abstract A comparative investigation of the electrical, mechanical, and chemical behaviour of zirconium phosphate-Nafion® composite membranes and Nafion® by means of ex-situ measurements, as well as with fuel cell operation, reveals a slight reduction of ionic conductivity, a significant improvement of mechanical stability, and increased water retention for the composite materials. The overall efficiency at 130,°C is increased during direct methanol fuel cell (DMFC) operation because the reduction in the ionic conductivity is overcompensated for by the decrease in methanol crossover. With H2 as the fuel, the slight reduction in overall efficiency corresponds to the decrease in ionic conductivity. The dimensional stability of the membrane and the membrane electrode assembly (MEA) is significantly improved for operating temperatures above 100,°C. A model for the microstructure-property relation for PFSA-Zr(HPO4)2,·,n,H2O composite membranes is presented, based on the experimental results from membranes with varying filler contents and distributions, obtained through different synthesis routes. It is aimed at the improvement of water distribution in the membrane upon fuel cell operation. [source] Reversibly Deformable and Mechanically Tunable Fluidic AntennasADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Ju-Hee So Abstract This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ,90% efficiency over a broad frequency range (1910,1990,MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (±0.1,0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna. [source] Microstructured Arrays of TiO2 Nanotubes for Improved Photo-Electrocatalysis and Mechanical StabilityADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Daoai Wang Abstract The preparation of micropatterned TiO2 nanotubes (NTs) with tunable morphologies by combining laser micromachining technology and an anodization method is reported. The micropatterned structure can be easily designed and fabricated by laser micromachining a titanium substrate, further anodization of which gives nanotube arrays perpendicularly oriented to the titanium surface. The patterned TiO2 NTs show dramatically improved photocurrent and photocatalytic performances because of their enhanced surface area and light-harvesting capability. The photocurrent density and incident-photon-to-current efficiency at the peak absorption increases by 48 and 39%, respectively, compared to a TiO2 NT array without a patterned structure. It was also found that micropatterning dramatically improves the mechanical stability of the TiO2 NTs on the substrate, which otherwise were liable to peel off from the substrate surface. The strategy will reasonably expand the application of TiO2 NTs in a variety of fields that require enhanced photo-electrocatalysis and mechanical stability. [source] Biomimetic Surfaces for High-Performance OpticsADVANCED MATERIALS, Issue 46 2009Yunfeng Li High-performance antireflective and antifogging surfaces are fabricated on planar silica substrates and planconvex lenses. Such surfaces dramatically suppress reflection over a large range of wavelengths and a large field of view. Additionally, the ARS surfaces exhibit high-quality superhydrophilic properties. For antireflective and antifogging applications, the ARS surfaces exhibit more high-quality mechanical stability and better durability than multilayered films. [source] DNA Sensors: Highly Sensitive, Mechanically Stable Nanopore Sensors for DNA Analysis (Adv. Mater.ADVANCED MATERIALS, Issue 27 200927/2009) A new solid state nanopore biosensor for the analysis of individual DNA molecules is reported by Rashid Bashir and co-workers on p. 2771. The cover illustrates the passage of double-stranded DNA through an Al2O3 nanopore sensor fabricated using ALD and e-beam-induced sputtering processes. Hexagonal ,-phase Al2O3 nanocrystallites form during pore formation as shown, improving the mechanical stability and sensitivity of these nanopore sensors. The CMOS-compatible nature of this process establishes this technology as a potential candidate for next-generation DNA sequencing. [source] Chemical modification of polyethersulfone nanofiltration membranes: A reviewJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009B. Van der Bruggen Abstract Polysulfone (PS) and poly(ether)sulfone (PES) are often used for synthesis of nanofiltration membranes, due to their chemical, thermal, and mechanical stability. The disadvantage for applying PS/PES is their high hydrophobicity, which increases membrane fouling. To optimize the performance of PS/PES nanofiltration membranes, membranes can be modified. An increase in membrane hydrophilicity is a good method to improve membrane performance. This article reviews chemical (and physicochemical) modification methods applied to increase the hydrophilicity of PS/PES nanofiltration membranes. Modification of poly(ether)sulfone membranes in view of increasing hydrophilicity can be carried out in several ways. Physical or chemical membrane modification processes after formation of the membrane create more hydrophilic surfaces. Such modification processes are (1) graft polymerization that chemically attaches hydrophilic monomers to the membrane surface; (2) plasma treatment, that introduces different functional groups to the membrane surface; and (3) physical preadsorption of hydrophilic components to the membrane surface. Surfactant modification, self-assembly of hydrophilic nanoparticles and membrane nitrification are also such membrane modification processes. Another approach is based on modification of polymers before membrane formation. This bulk modification implies the modification of membrane materials before membrane synthesis of the incorporation of hydrophilic additives in the membrane matrix during membrane synthesis. Sulfonation, carboxylation, and nitration are such techniques. To conclude, polymer blending also results in membranes with improved surface characteristics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Effect of particle size of an amorphous calcium phosphate filler on the mechanical strength and ion release of polymeric composites,JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Soo-Young Lee Abstract The random clustering of amorphous calcium phosphate (ACP) particles within resin matrices is thought to diminish the strength of their polymerized composites. The objective of this study was to elucidate the effect of ball-milling on the particle size distribution (PSD) of ACP fillers and assess if improved dispersion of milled ACP in methacrylate resin sufficiently enhanced filler/matrix interactions to result in improved biaxial flexure strength (BFS), without compromising the remineralizing potential of the composites. Unmilled and wet-milled zirconia-hybridized ACP (Zr-ACP) fillers were characterized by PSD analysis, X-ray diffraction, thermogravimetric and chemical analysis, infrared spectroscopy, and scanning electron microscopy. Composite specimens made from a photoactivated, ternary methacrylate resin admixed with a mass fraction of 40% of un-milled or milled Zr-ACP were evaluated for the BFS (dry and wet) and for the release of calcium and phosphate ions into saline solutions. While having no apparent effect on the structure, composition, and morphology/topology of the fillers, milling significantly reduced the average size of Zr-ACP particulates (median diameter, dm = 0.9 ± 0.2 ,m) and the spread of their PSD. Better dispersion of milled Zr-ACP in the resins resulted in the improved BFS of the composites, even after aqueous soaking, and also gave a satisfactory ion release profile. The demonstrated improvement in the mechanical stability of anti-demineralizing/remineralizing ACP composites based on milled Zr-ACP filler may be beneficial in potentially extending their dental utility. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Biodegradable poly(D,L -lactide) coating of implants for continuous release of growth factorsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 4 2001G. Schmidmaier Abstract Local application of growth factors like insulin like growth factor-I (IGF-I) and transforming growth factor-beta 1 (TGF-,1) from a biodegradable thin layer of poly(D,L -lactide) (PDLLA) coated implants could stimulate fracture healing. A new "cold coating technique" for metallic implants was established to produce a biodegradable coating with a high mechanical stability that provides a continuous release of incorporated growth factors. The properties of this bioactive coating were investigated in vitro and in vivo. Scanning electron microscope analysis revealed a coating thickness of in average 14.8 ,m on titanium and 10.7 ,m on steel wires. Intramedullary implantation and extraction experiments depicted a loss of PDLLA coating from titanium and steel implants of less than 5%. After explantation of the implants, the coating displayed a complete and regular layer without any defects of PDLLA uncovering the metallic surface. Smear tests demonstrate that the coating can be performed under sterile conditions. The PDLLA depicted a reduction of about 8% within 6 weeks in vitro and in vivo. The growth factors were incorporated in a stable form and demonstrated a loss of stability of less than 3% within 42 days and less than 5% within one year. In an elution experiment, 54% IGF-I and 48% TGF-,1 were released within the first 48 h. After 42 days, 76% of IGF-I and 71% of TGF-,1 were detected in the elution fluid by ELISA. Comparable results were obtained in the in vivo experiments after 42 days. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 449,455, 2001 [source] The initial phase of fracture healing is specifically sensitive to mechanical conditionsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2003Petra Klein Abstract Interfragmentary movements affect the quality and quantity of callus formation. The mounting plane of monolateral external fixators may give direction to those movements. Therefore, the aim of this study was to determine the influence of the fixator mounting plane on the process of fracture healing. Identically configured fixators were mounted either medially or anteromedially on the tibiae of sheep. Interfragmentary movements and ground reaction forces were evaluated in vivo during a nine week period. Histomorphological and biomechanical parameters described the bone healing processes. Changing only the mounting plane led to a modification of interfragmentary movements in the initial healing phase. The difference in interfragmentary movements between the groups was only significant during the first post-operative period. However, these initial differences in mechanical conditions influenced callus tissue formation significantly. The group with the anteromedially mounted fixator, initially showing significantly more interfragmentary movements, ended up with a significantly smaller callus diameter and a significantly higher callus stiffness as a result of advanced fracture healing. This demonstrates that the initial phase of healing is sensitive to mechanical conditions and influences the course of healing. Therefore, initial mechanical stability of an osteosynthesis should be considered an important factor in clinical fracture treatment. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Release mechanisms from gentamicin loaded poly(lactic- co -glycolic acid) (PLGA) microparticlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2002Wolfgang Friess Abstract To provide local gentamicin delivery for 1 week based on a biodegradable system, poly(lactic- co -glycolic acid) (PLGA) microparticles were developed utilizing a 50/50 blend of Resomer® RG 502H, an uncapped variety of 13.5 kD, and Resomer® RG 503, an endcapped polymer of 36.2 kD. The liberation mechanism was investigated by analysis of morphological changes and thermal analysis focusing on the polymer glass transition temperature (Tg) and the mechanical properties. The release of gentamicin was related to a structural breakdown of the particles reaching a critical molecular weight. A Tg of <,37°C in the hydrated state was not indicative of collapse and agglomeration of the particles because the mechanical strength of the polymer structures in the rubbery state may still render sufficient support. As the gap between incubation temperature and Tg widened, the mechanical stability of the PLGA microparticles decreased and became decisive. Particles prepared with RG 502H show a lower ability to bear mechanical stress than RG 503 and 50/50 RG 502H/RG 503 microparticles. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 845,855, 2002 [source] Poly(styrene- co -glycerol dimethacrylate): Synthesis, characterization, and application as a resin for gel-phase peptide synthesisJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2005Michael Roice Abstract An efficient cross-linked polymer support for solid-phase synthesis was prepared by introducing glycerol dimethacrylate cross-linker to polystyrene network using free radical aqueous suspension polymerization. The support was characterized by various spectroscopic methods. Morphological feature of the resin was analyzed by microscopy. The polymerization reaction was investigated with respect to the effect of amount of cross-linking agent, which in turn vary the swelling, loading, and the mechanical stability of the resin. The solvent uptake of the polymer was studied in relation to cross-linking and compared with Merrifield resin. The stability of the resin was tested in different synthetic conditions used for solid-phase peptide synthesis. Hydroxy group of the support was derivatized to chloro and then amino groups using different reagents and reaction conditions. Efficiency of the support was tested and compared with TentaGelÔ resin by following different steps involved in the synthesis of the 65,74 fragment of acyl carrier protein. The results showed that the poly(styrene- co -glycerol dimethacrylate) (GDMA-PS) is equally efficient as TentaGel resin in peptide synthesis. The purity of the peptides was analyzed by HPLC and identities were determined by mass spectroscopy and amino acid analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4382,4392, 2005 [source] New method for bonding an adsorbent film to the walls of capillary columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2003Wawrzyniak Abstract A new method for immobilisation of an adsorbent on the wall of a capillary column ensures high thermal and mechanical stability of the resulting coating. The method can be applied to a variety of adsorbents of natural or synthetic origin. Its effectiveness is illustrated by results obtained for coating with modified silica or molecular sieve 13X. [source] Coherence and wavefront characterization of Si-111 monochromators using double-grating interferometryJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2010Ana Diaz A study of the coherence and wavefront properties of a pseudo-channel-cut monochromator in comparison with a double-crystal monochromator is presented. Using a double-grating interferometer designed for the hard X-ray regime, the complex coherence factor was measured and the wavefront distortions at the sample position were analyzed. A transverse coherence length was found in the vertical direction that was a factor of two larger for the channel-cut monochromator owing to its higher mechanical stability. The wavefront distortions after different optical elements in the beam, such as monochromators and mirrors, were also quantified. This work is particularly relevant for coherent diffraction imaging experiments with synchrotron sources. [source] Dynamic performance of the beam position monitor support at the SSRFJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2009Xiao Wang Electron beam stability is very important for third-generation light sources, especially for the Shanghai Synchrotron Radiation Facility whose ground vibrations are much larger than those for other light sources. Beam position monitors (BPMs), used to monitor the position of the electron beam, require a greater stability than other mechanical structures. This paper concentrates on an investigation of the dynamic performance of the BPM support prototype. Modal and response analyses have been carried out by finite-element (FE) calculations and vibration measurements. Inconsistent results between calculation and measurement have motivated a change in the soft connections between the support and the ground from a ground bolt in the initial design to full grout. As a result the mechanical stability of the BPM support is greatly improved, showing an increase in the first eigenfrequency from 20.2,Hz to 50.2,Hz and a decrease in the ratio of the root-mean-square displacement (4,50,Hz) between the ground and the top of the support from 4.36 to 1.23 in the lateral direction. An example is given to show how FE analysis can guide the mechanical design and dynamic measurements (i.e. it is not just used as a verification method). Similar ideas can be applied to improve the stability of other mechanical structures. [source] Actively Q-switched all-fiber lasersLASER PHYSICS LETTERS, Issue 2 2008M.V. Andrés Abstract Q-switching of fiber lasers using bulk elements has important drawbacks as reduced mechanical stability and high insertion losses. The development of efficient all-fiber modulation techniques is the key to obtain robust, compact and efficient Q-switched all-fiber lasers. Certainly, the development of fiber Bragg gratings (FBG) has been crucial to make progress on fiber lasers. FBGs permit a simple way to assemble all-fiber laser cavities and can be written in the active fiber itself. The Q-factor of this type of cavities is determined by the reflectivity of the FBGs and the losses of the fiber. Here, we focus on the use of magnetostrictive materials and the acousto-optic interaction to develop efficient Q-factor modulators. Most of these modulators include an FBG and take advantage of the specific interaction of the magnetostrictive materials or the acoustic wave with the FBG itself. Fiber optic technologies permit the development of a rather unique type of fiber lasers, i.e., actively Q-switched distributed feedback (DFB) fiber lasers. In this case, both the use of magnetostrictive materials and the acousto-optic interaction permit the generation of dynamic defects in an FBG that has been previously written in a highly Er-doped fiber. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Evaluation of Modified CMC and CMC-PVA as Miscible Polymer Blend Membranes for HepatocytesMACROMOLECULAR BIOSCIENCE, Issue 5 2007Aysel Koç Abstract CMC and CMC-PVA were blended either with type I collagen, BSA or CS to obtain biocompatible membranes for evaluation as potential hepatocyte culture substrates. Pure and modified forms of CMC showed distinct surface, mechanical, and cell attachment properties. While the hydrophilicity decreased, the mechanical stability and the porosity of CMC membranes increased after blending. Serum proteins were adsorbed by all types of membranes. Among eight membranes tested, collagen-modified CMC was found to be a suitable membrane material for hepatocyte culture, in terms of mechanical and cell interaction properties. [source] Thermo-Responsive Organic/Inorganic Hybrid Hydrogels based on Poly(N -vinylcaprolactam)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2003Wouter Loos Abstract A new type of ,intelligent' hydrogels has been developed in the form of organic/inorganic hybrid materials by making use of the sol-gel technology. Poly(N -vinylcaprolactam) (PVCL) has been incorporated in these materials for its thermo-responsive properties. The synthesis of the hybrid hydrogels was achieved by the in situ formation of an inorganic silica phase in the presence of an aqueous solution of high molecular weight PVCL. This methodology results in the preparation of micro-heterogeneous systems in which silica particles of nanometer dimensions act as physical cross-links for the PVCL molecules. Hydrogen bonds between the remaining non-condensed silanol groups and the PVCL carbonyl functions, together with physical entanglements, are responsible for the strong interactions between the organic and inorganic phases. Stress-strain tests on highly swollen materials demonstrated that the unique structure of these thermo-responsive hybrid hydrogels improves the mechanical stability to a great extent as compared to conventional hydrogels. Transmission measurements demonstrate that the presence of the inorganic phase does not influence the cloud point temperatures of PVCL significantly. On the other hand, the response of the reinforced hybrid hydrogels to temperature becomes less pronounced for increasing silica fractions. The reversibility of the swelling/deswelling process has been demonstrated by swelling experiments as a function of temperature. PVCL/SiO2 hybrid hydrogels. [source] Verhalten laserschockverfestigter und festgewalzter Randschichten der Ti-Legierung Ti-6Al-4V bei schwingender Beanspruchung unter erhöhten TemperaturenMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 6 2003I. Altenberger Laser Shock Peening; Deep Rolling; Residual Stresses; Ti-6-4 Abstract Es ist seit langem bekannt, dass mechanische Oberflächenbehandlungen wie etwa Festwalzen, Kugelstrahlen oder Laserschockoberflächenbehandlungen, um nur einige zu nennen, das Ermüdungsverhalten hochbeanspruchter metallischer Bauteile entscheidend verbessern können. Insbesondere Festwalzen und Laserschockoberflächenbehandlungen haben sich als besonders wirksam herausgestellt, da sie tiefe Druckeigenspannungs- und Verfestigungsprofile sowie eine vergleichsweise glatte Oberflächentopographie erzeugen. Tatsächlich wird z.,B. das Festwalzen bereits serienmässig zur Erhöhung der Schwingfestigkeit von Stählen, wie etwa beim Festwalzen von Kurbelwellen, eingesetzt. Obwohl die meisten Arbeiten zum Festwalzen sich mit Stählen beschäftigen, wurde dieses Verfahren in jüngerer Zeit auch auf eine Reihe von Titanwerkstoffen erfolgreich angewendet. Die vorliegenden Untersuchungen beschäftigen sich mit dem Einfluss von Festwalzbehandlungen auf das Niedrig- und Hochlastwechselermüdungsverhalten der wichtigsten kommerziellen Titanlegierung Ti-6Al-4V, wobei besonderes Augenmerk auf die thermische und mechanische Stabilität randnaher Eigenspannungszustände und Mikrostrukturen gerichtet wurde. Zusätzlich werden erste Ergebnisse zum Eigenspannungszustand und zur Schwingfestigkeit lasergeschockter Ti-6Al-4V-Proben präsentiert und mit Resultaten festgewalzter Zustände verglichen. Ausserdem wird untersucht, ob die Oberflächenbehandlungen auch bei erhöhten Temperaturen (bis 450,°C) ihre Wirksamkeit zur Verbesserung der Schwingfestigkeit behalten. Basierend auf Wechselverformungs- und Lebensdaueruntersuchungen, in Kombination mit Röntgendiffraktometrie und In-situ -Transmissionselektronenmikroskopie, lässt sich feststellen, dass Laserschockoberflächenbehandlungen und insbesondere Festwalzen die Rissbildung und Ausbreitung in hochtemperaturschwingbeanspruchtem Ti-6Al-4V trotz eines fast völligen Druckeigenspannungsabbaus wirkungsvoll hemmt. Daraus lässt sich ableiten, dass zusätzlich zu Eigenspannungen vor allem randnahe Mikrostrukturen, welche im Falle von mechanisch randschichtverfestigtem Ti-6Al-4V durch sehr hohe Versetzungsdichten und Nanokristallite gekennzeichnet ist, einen wesentlichen Einfluss bei der Lebensdauererhöhung durch Randschichtverfestigung haben. Residual stress stability and near-surface microstructures in high temperature fatigued mechanically surface treated Ti-6Al-4V It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of deep rolling on the low-cycle and high-cycle fatigue behavior of a Ti-6Al-4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti-6Al-4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ,450,°C, i.e., at an homologous temperature of ,0.4 T/Tm (where Tm is the melting temperature). Based on cyclic deformation and stress/life (S/N) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti-6Al-4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti-6Al-4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment. [source] Prediction of electronic, structural and elastic properties of the hardest oxide: TiO2PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009M. A. Caravaca Abstract This work combines the theory of elasticity with first principles quantum mechanic calculations to predict the electronic, structural and elastic properties: elastic constants, bulk moduli of the TiO2 (Titania) in the Pnma phase. Band-structure shows a direct gap in , which increases its value under hydrostatic pressure. It has two regimes: in the range 0,50 GPa the band-gap has a negative second pressure derivative and changes its sign in the range 50,100 GPa. The band gap becomes indirect at pressures above 150 GPa. This phase improves its mechanical stability and insulator properties under extreme conditions of hydrostatic pressures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Flame retardancy mechanisms of metal phosphinates and metal phosphinates in combination with melamine cyanurate in glass-fiber reinforced poly(1,4-butylene terephthalate): the influence of metal cationPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2008Ulrike Braun Abstract The pyrolysis and fire behavior of glass-fiber reinforced poly(butylene terephthalate) (PBT/GF) with two different metal phosphinates as flame retardants in combination with and without melamine cyanurate (MC) were analyzed by means of thermogravimetry, thermogravimetry coupled with infrared spectroscopy, flammability, and cone calorimeter tests as well as scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray fluorescence spectroscopy. In PBT/GF, dosages of 13,20% of the halogen-free flame retardant aluminum phosphinate or aluminum phosphinate in combination with MC fulfill the requirements for electrical engineering and electronics applications (UL 94,=,V-0; LOI,>,42%), whereas the use of the same amount of zinc phosphinate or zinc phosphinate in combination with MC does not improve the fire behavior satisfactorily (UL 94,=,HB; LOI,=,27,28%). The performance under forced flaming conditions (cone calorimeter) is quite similar for both of the metal phosphinates. The use of aluminum and zinc salts results in similar flame inhibition predominantly due to the release of the phosphinate compounds in the gas phase. Both metal phosphinates and MC interact with the polymer changing the decomposition characteristics. However, part of the zinc phosphinate vaporizes as a complete molecule. Because of the different decomposition behavior of the metal salts, only the aluminum phosphinate results in a small amount of thermally stable carbonaceous char. In particular, the aluminum phosphinate-terephthalate formed is more stable than the zinc phosphinate-terephthalate. The small amount of char has a crucial effect on the thermal properties and mechanical stability of the residue and thus the flammability. Copyright © 2008 John Wiley & Sons, Ltd. [source] Cadaveric and Engineering Analysis of the Septal L-Strut,THE LARYNGOSCOPE, Issue 11 2007Ted Mau MD Abstract Objectives: To identify patterns of failure of the L-strut, to identify elements of the nasal framework that support the L-strut, and to investigate the effect of altering L-strut design on its stability. Study Design: Laboratory study with human cadaveric heads and computational modeling. Methods: Directional forces were applied to cadaveric L-struts and patterns of failure with incremental force were noted. Computational modeling using the finite element method (FEM) was employed to determine quantitatively the effect of various modifications on the stability of the L-strut. Results: The L-strut was found to respond to frontal force initially by buckling. This buckling was reversible until the force exceeded a certain threshold when the L-strut broke at the bony-cartilaginous junction. The threshold force varied depending on the length of the overlap with the bony vault. Intact mucoperichondrium provided significant stability. Modeling with FEM showed that the preservation of a triangular piece of cartilage at the dorsal anchor of a narrowed L-strut can offset some of the loss in mechanical stability. Conclusions: Intrinsic elasticity of the septal cartilage, the mucoperichondrial flap, and overlap with the bony vault all contribute to the stability of the L-strut, which is enhanced by preserving a small segment of cartilage at the bony-cartilaginous junction of the dorsal L-strut. [source] POST-MEDIEVAL CRUCIBLE PRODUCTION AND DISTRIBUTION: A STUDY OF MATERIALS AND MATERIALITIES,ARCHAEOMETRY, Issue 1 2009M. MARTINÓN-TORRES This paper is concerned with the manufacture and trade of post-medieval crucibles (14th,19th centuries). The analytical study of crucibles from different contexts in Europe and America employed optical microscopy and SEM,EDS, coupled with archaeological and historical data. We identified two major producers of crucibles, both of them in Central Europe, whose products appear widely distributed internationally. The analytical data allow an explanation of the technical reasons behind their superior reputation, as both crucible types shared comparable material properties, such as thermal, chemical and mechanical stability. Conversely, the two crucible types were radically different in their manufacture and appearance. We argue that, besides technical considerations, sensorial aspects such as texture and colour may have played an important role in the perception and choice of materials. [source] | |||||||||||||||||||||||||||||||||||||