Aspect Ratio (aspect + ratio)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Aspect Ratio

  • different aspect ratio
  • high aspect ratio
  • large aspect ratio
  • low aspect ratio
  • various aspect ratio

  • Selected Abstracts

    Polymer Films Composed of Surface-Bound Nanofilaments with a High Aspect Ratio, Molecularly Imprinted with Small Molecules and Proteins

    Ana Valvanuz Linares
    Abstract Hierarchically nanostructured materials that combine two or more levels of structuring and that exhibit a combination of useful features have gained considerable interest over recent years. Here, the generation of surface-bound nanofilaments with a high aspect ratio by nanomolding on a nanoporous template surface is described. The filaments, at the same time, carry molecularly imprinted binding sites. The dye fluorescein and the protein myoglobin are used as model templates for imprinting. The surfaces exhibit specific binding as revealed by fluorescence microscopy. The wetting properties of the surfaces depend on the dimensions of the nanofilaments and on the nature of the polymer. It is believed that these materials can potentially be useful for applications in biosensors and biochips. [source]

    Ultrathin Te Nanowires: An Excellent Platform for Controlled Synthesis of Ultrathin Platinum and Palladium Nanowires/Nanotubes with Very High Aspect Ratio

    ADVANCED MATERIALS, Issue 18 2009
    Hai-Wei Liang
    Uniform ultrathin Pt nanotubes, Pt and Pd nanowires with diameters of only several nanometers and a very-high aspect ratio of ,10,000 can be fabricated using ultrathin Te nanowires as both reducing agent and sacrificial template in ethylene glycol. The valences of metal precursors have a crucial effect on the morphology of the nanostructures. [source]

    A Simple Approximate Formula for the Aspect Ratio of Oblate Particles

    Willi Pabst
    Abstract A simple approximative formula is derived, which can be used to quantify the shape of oblate particles or an average shape of the corresponding particle system, when the results of sedimentation analysis (Stokes equivalent diameters) are known and results from either microscopic image analysis (assuming stable orientation, i.e., with the plane perpendicular to the direction of observation) or laser diffraction (assuming random orientation) are available for the same sample. In the latter case Cauchy's stereological theorem is applied to account for random orientation. Furthermore, it is shown that for sufficiently large aspect ratios, this formula is very close to the well-known Jennings-Parslow relation and can replace this more complicated expression in many practical cases, e.g., in the routine characterization of ceramic raw materials (kaolins and oxide or non-oxide platelet powders). [source]

    Shape and Size Determination by Laser Diffraction: Average Aspect Ratio and Size Distributions by Volume; Feasibility of Data Analysis by Neural Networks

    Luc Deriemaeker
    Abstract A new strategy for the recovery of the average shape factor and the volume weighted size distribution from laser diffraction data using neural networks is presented. The method yields reliable estimates for both the shape factor and the volume weighted size distribution. [source]

    Highly Ordered Arrays of Mesoporous Silica Nanorods with Tunable Aspect Ratios from Block Copolymer Thin Films,

    ADVANCED MATERIALS, Issue 4 2008
    A. Chen
    Highly ordered arrays of mesoporous silica nanorods with a tunable aspect ratio can be fabricated using PEOm - b -PMA(Az)n block copolymer thin films as templates. Together, penetration of the films by the silica precursor and the film thickness control the SiO2 nanorod growth, and heights of almost 200,nm can be achieved. Inside the SiO2 nanorods, mesochannels with a diameter of ,,2,nm are formed that are aligned along the longitudinal axis of the rod. [source]

    Fabrication of Metal Nanohole Arrays with High Aspect Ratios Using Two-Step Replication of Anodic Porous Alumina

    ADVANCED MATERIALS, Issue 18 2005
    T. Yanagishita
    Metal nanohole arrays with straight holes of high aspect ratio have been fabricated using a new replication process based on the preparation of polymer pillars, both sides of which are supported and can therefore be maintained upright. These nanopillar arrays are demonstrated as negatives for the preparation of metal (Ni) nanohole arrays (see Figure). [source]

    Solid-Based Hydrothermal Synthesis and Characterization of Alumina Nanofibers with Controllable Aspect Ratios

    Shou-Cang Shen
    Nanofibers of AlOOH with controllable aspect ratios have been synthesized by a facile steam-assisted solid-phase crystallization route. The morphology and aspect ratios of resulting AlOOH nanofibers were significantly influenced by the alkaline medium used in the preparation of solid precipitates from Al(NO3)3 solution. When tetramethylammonium hydroxide was used for precipitation, straight rod-like nanofibers with aspect ratios of 10,20 were obtained. The use of other tetra-alkylated ammonium hydroxides, such as tetraethylammonium hydroxide, tetrapropylammonium hydroxide or tetrabutylammonium hydroxide, led to the formation of long wire-like nanofibers with aspect ratios up to 150. After thermal treatment at 600C, the morphologies of the one-dimensional nanostructures were well preserved while the crystal structure was converted to ,-alumina. The wire-like nanofibers of alumina possessed higher thermal stability than alumina nanorods, and both exhibited much higher stability as compared with alumina micropowder. [source]

    Low-Temperature Synthesis of Zinc Oxide Nanoparticles

    Po-Yi Wu
    Crystalline zinc oxide nanoparticles have been prepared by mixing aqueous solutions of zinc nitrate and hexamethylenetetramine (HMT) at 60C and 80C. Transmission electron microscopy and X-ray diffraction show that the ZnO nanoparticles of diameters ranging from 15,33 nm and 25,43 nm long are formed. Aspect ratio is observed to range from 1.18 to 1.74 at 60C and 1.22 to 1.70 at 80C as the HMT to zinc nitrate concentration ratio increases from 10 to 150. Nanoparticle size decreases as the concentration of HMT increases. Much larger ZnO particles are formed with ammonium hydroxide as a hydrolysis agent without HMT. In summary, HMT is an ammonium-hydroxide source in the reaction, a surfactant for retaining nanosize, and not necessarily a template for ZnO nucleation. [source]

    Wear particle analysis of highly crosslinked polyethylene isolated from a failed total hip arthroplasty

    Yukihide Minoda
    Abstract Polyethylene wear particles are one of the most important factors affecting the results of total hip arthroplasty (THA). To reduce wear generation and to achieve better long-term results of THA, highly crosslinked polyethylene (HXPE) has recently been introduced and come into wide use. Thus far, however, there have been no reports on in vivo analysis of HXPE wear particles. We isolated HXPE wear particles from periprosthetic tissue of a failed THA and analyzed using scanning electron microscope. The number of particles was 5.33 107 g,1. Particle size (equivalent circle diameter) was 0.66 0.40 ,m (mean standard error). Aspect ratio and roundness were 1.37 0.26 and 1.44 0.67, respectively. All the particles were round shaped, and "fibrils" or "shreds" were not detected. Thus far, this was the first report on in vivo wear particle analysis of HXPE. HXPE generated less, smaller, and rounder particles, compared with the corresponding reported values for particles generated from conventional polyethylene. These characteristics might affect macrophage response, osteolysis, and long-term results of THA with HXPE. 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]

    Flow energy and channel adjustments in rills developed in loamy sand and sandy loam soils

    Jovan R. Stefanovic
    Abstract The storms usually associated with rill development in nature are seldom prolonged, so development is often interrupted by interstorm disturbances, e.g. weathering or tillage. In laboratory simulated rainfall experiments, active rill development can be prolonged, and under these conditions typically passes through a period of intense incision, channel extension and bifurcation before reaching quasi-stable conditions in which little form change occurs. This paper presents laboratory experiments with coarse textured soils under simulated rainfall which show how channel adjustment processes contribute to the evolution of quasi-stability. Newly incised rills were stabilized for detailed study of links between rill configuration and flow energy. On a loamy sand, adjustment towards equilibrium occurred due to channel widening and meandering, whereas on a sandy loam, mobile knickpoints and chutes, pulsations in flow width and flow depth and changes in stream power and sediment discharge occurred as the channel adjusted towards equilibrium. The tendency of rill systems towards quasi-stability is shown by changes in stream power values which show short-lived minima. Differences in energy dissipation in stabilized rills indicate that minimization of energy dissipation was reached locally between knickpoints and at the downstream ends of rills. In the absence of energy gradients in knickpoints and chutes, stabilized rill sections tended toward equilibrium by establishing uniform energy expenditure. The study confirmed that energy dissipation increased with flow aspect ratio. In stabilized rills, flow acceleration reduced energy dissipation on the loamy sand but not on the sandy loam. On both soils flow deceleration tended to increase energy dissipation. Understanding how rill systems evolve towards stability is essential in order to predict how interruptions between storms may affect long-term rill dynamics. This is essential if event-based physical models are to become effective in predicting sediment transport on rilled hillslopes under changing weather and climatic conditions. Copyright 2008 John Wiley and Sons, Ltd. [source]

    Seismic control of smart base isolated buildings with new semiactive variable damper

    S. Nagarajaiah
    Abstract A new semiactive independently variable damper, SAIVD, is developed and shown to be effective in achieving response reductions in smart base isolated buildings in near fault earthquakes. The semiactive device consists of four linear visco-elastic elements, commonly known as Kelvin,Voigt elements, arranged in a rhombus configuration. The magnitude of force in the semiactive device can be adjusted smoothly in real-time by varying the angle of the visco-elastic elements of the device or the aspect ratio of the rhombus configuration. Such a device is essentially linear, simple to construct, and does not present the difficulties commonly associated with modelling and analysing nonlinear devices (e.g. friction devices). The smooth semiactive force variation eliminates the disadvantages associated with rapid switching devices. Experimental results are presented to verify the proposed analytical model of the device. A H, control algorithm is implemented in order to reduce the response of base isolated buildings with variable damping semiactive control systems in near fault earthquakes. The central idea of the control algorithm is to design a H, controller for the structural system that serves as an aid in the determination of the optimum control force in the semiactive device. The relative performance of the SAIVD device is compared to a variable friction device, recently developed by the authors in a separate study, and several key aspects of performance are discussed regarding the use of the two devices for reducing the responses of smart base isolated buildings in near fault earthquakes. Copyright 2006 John Wiley & Sons, Ltd. [source]

    Influence of dynamic soil,structure interaction on the nonlinear response and seismic reliability of multistorey systems

    Armando Brcena
    Abstract A set of reinforced concrete structures with gravitational loads and mechanical properties (strength and stiffness) representative of systems designed for earthquake resistance in accordance with current criteria and methods is selected to study the influence of dynamic soil,structure interaction on seismic response, ductility demands and reliability levels. The buildings are considered located at soft soil sites in the Valley of Mexico and subjected to ground motion time histories simulated in accordance with characteristic parameters of the maximum probable earthquake likely to occur during the system's expected life. For the near-resonance condition the effects of soil,structure interaction on the ductility demands depend mainly on radiation damping. According to the geometry of the structures studied this damping is strongly correlated with the aspect ratio, obtained by dividing the building height by its width. In this way, for structures with aspect ratio greater than 1.4 the storey and global ductility demands increase with respect to those obtained with the same structures but on rigid base, while for structures with aspect ratio less than 1.4 the ductility demands decrease with respect to those for the structures on rigid base. For the cases when the fundamental period of the structure has values very different from the dominant ground period, soil,structure interaction leads in all cases to a reduction of the ductility demands, independently of the aspect ratio. The reliability index , is obtained as a function of the base shear ratio and of the seismic intensity acting on the nonlinear systems subjected to the simulated motions. The resulting reliability functions are very similar for systems on rigid or on flexible foundation, provided that in the latter case the base rotation and the lateral displacement are removed from the total response of the system. Copyright 2006 John Wiley & Sons, Ltd. [source]

    Pseudo-dynamic seismic response of reinforced concrete frames infilled with non-structural brick masonry

    F. Colangelo
    Abstract This paper presents pseudo-dynamic test results on the in-plane seismic behaviour of infilled frames. Thirteen single-storey, single-bay, half-size-scale, reinforced concrete-frame specimens, most of which infilled with non-structural masonry made of perforated bricks and cement mortar are tested. The infills are in contact with frames, without any connector; openings are not covered. The frames are different in their strength and details, reinforcement grade, and aspect ratio. Seismic input is the 1976 Tolmezzo (Friuli, Italy) ground acceleration, to which specimens are subjected two times: virgin and damaged by the previous test. The global seismic response of initially virgin infilled specimens considerably differs from that of bare specimens. This follows a dramatic change of properties: compared to a bare frame, the initial stiffness increases by one order of magnitude, and the peak strength more than doubles. The peak drift lessens; however, the displacement ductility demand does not. The energy demand is greater. Nevertheless, the influence of infill decreases as damage proceeds. Displacement time histories of damaged specimens are quite similar. At the local level, infill causes asymmetry and concentration of the frame deformation. Copyright 2005 John Wiley & Sons, Ltd. [source]

    Earthquake behavior of structures with copper energy dissipators

    Juan C. De la Llera
    Abstract The earthquake behavior of structures with supplemental copper dampers is evaluated in this study. The investigation is divided into two parts: (i) an experimental work with seven pairs of hourglass copper dampers of different aspect ratios and side profiles; and (ii) a parametric study of 6-, 12-, and 25-story planar structures with elastic as well as inelastic behavior in the primary structure and copper dampers. The copper used in this study is electrolytic tough pitch (ETP) copper C11000; probably the most commonly used of all coppers; ductile, with a low-yield, and highly resistant to corrosion. Experimental results demonstrate that all copper plates reached stable angular distortions of the order of ,=25%, which implies transverse distortions in the devices larger than 40mm. The behavior of the devices is highly dependent on the aspect ratio of the plate, h/t, and a recommendation is made to use plates in the range 11 h/t,18. Plates beyond this range exhibit either large stress and strain concentrations in the neck of the device or a strong influence of axial deformations in their cyclic behavior. The inelastic earthquake response of structures with such devices shows that drift reduction factors of the order of 30 to 40% can be achieved with reasonably economic designs. It is also shown that the efficiency of these devices depends on the soil conditions and flexibility of the primary structure. Finally, it is concluded that supplemental copper dampers are a good alternative for drift reduction in a wide range of structural layouts, ranging from coupled shear-wall systems to moment-resisting frames, and for impulsive as well as non-impulsive ground motions. Copyright 2003 John Wiley & Sons, Ltd. [source]

    Factors influencing the partitioning and toxicity of nanotubes in the aquatic environment,,

    Alan J. Kennedy
    Abstract Carbon nanotubes (NTs) may be among the most useful engineered nanomaterials for structural applications but could be difficult to study in ecotoxicological evaluations using existing tools relative to nanomaterials with a lower aspect ratio. Whereas the hydrophobicity and van der Waals interactions of NTs may suggest aggregation and sedimentation in aquatic systems, consideration regarding how engineered surface modifications influence their environmental fate and toxicology is needed. Surface modifications (e.g., functional groups and coatings) are intended to create conditions to make NTs dispersible in aqueous suspension, as required for some applications. In the present study, column stability and settling experiments indicated that raw, multiwalled NTs (MWNTs) settled more rapidly than carbon black and activated carbon particles, suggesting sediment as the ultimate repository. The presence of functional groups, however, slowed the settling of MWNTs (increasing order of stability: hydroxyl > carboxyl > raw), especially in combination with natural organic matter (NOM). Stabilized MWNTs in high concentrations of NOM provided relevance for water transport and toxicity studies. Aqueous exposures to raw MWNTs decreased Ceriodaphnia dubia viability, but such effects were not observed during exposure to functionalized MWNTs (>80 mg/L). Sediment exposures of the amphipods Leptocheirus plumulosus and Hyalella azteca to different sizes of sediment-borne carbon particles at high concentration indicated mortality increased as particle size decreased, although raw MWNTs induced lower mortality (median lethal concentration [LC50], 50 to >264 g/kg) than carbon black (LC50, 18,40 g/kg) and activated carbon (LC50, 12,29 g/kg). Our findings stress that it may be inappropriate to classify all NTs into one category in terms of their environmental regulation. [source]

    A simple model for the prediction of the fatigue delamination growth of impacted composite panels

    ABSTRACT The fatigue behaviour of composite panels that have been subjected to low-velocity impact was studied. Impacted specimens were tested under compression,compression fatigue. A delamination propagation model based on the derivation of the strain energy release rate was used. The stress distribution around the initially induced delamination was derived analytically. The shape of the delamination was experimentally monitored by c-scan imaging and is assumed to be an ellipse. The orientation and aspect ratio of the ellipse were used to calculate the corresponding strain energy-release rates, which were subsequently used to predict the direction of delamination propagation. [source]

    Fatigue life prediction and failure analysis of a gas turbine disc using the finite-element method

    R. A. CLUDIO
    ABSTRACT A numerical prediction of the life of a gas turbine model disc by means of the finite-element technique is presented and the solution is compared with an experimental rim-spinning test. The finite-element method was used to obtain the K solution for a disc with two types of cracks, both at the notch root of the blade insert and located in the corner and in the centre. A crack aspect ratio of (a/c) = 1 was assumed. The fracture mechanics parameters J -integral and K were used in the assessment, which were computed with linear elastic and elastic,plastic material behaviour. Using a crack propagation program with appropriate fatigue-creep crack growth-rate data, previously obtained in specimens for the nickel-based superalloy IN718 at 600 C, fatigue life predictions were made. The predicted life results were checked against experimental data obtained in real model discs. The numerical method, based on experimental fatigue data obtained in small laboratory specimens, shows great potential for development, and may be able to reduce the enormous costs involved in the testing of model and full-size components. [source]

    Growth and Transfer of Monolithic Horizontal ZnO Nanowire Superstructures onto Flexible Substrates

    Sheng Xu
    A method of fabricating horizontally aligned ZnO nanowire (NW) arrays with full control over the width and length is demonstrated. A cross-sectional view of the NWs by transmission electron microscopy shows a "mushroom-like" structure. Novel monolithic multisegment superstructures are fabricated by making use of the lateral overgrowth. Ultralong horizontal ZnO NWs of an aspect ratio on the order of ten thousand are also demonstrated. These horizontal NWs are lifted off and transferred onto a flexible polymer substrate, which may have many great applications in horizontal ZnO NW-based nanosensor arrays, light-emitting diodes, optical gratings, integrated circuit interconnects, and high-output-power alternating-current nanogenerators. [source]

    Flame height correlation and upward flame spread modelling

    FIRE AND MATERIALS, Issue 6 2002
    Kuang- Chung Tsai
    Previous work has demonstrated that flame height is one of the two most important parameters determining the rate of vertical flame spread on a wall. Flame spread models rely on empirical flame height correlations of the form Xf=KQ,,n, but there have been no carefully controlled experiments designed to establish the validity of such correlations and there are no data for values of Q,,< c.25 kW/m. Two new sets of data are presented here, one based on experiments with 6 mm thick PMMA slabs (heights 25,250 mm, width 50,150 mm) as the fire source, measuring Q,, and Xf simultaneously. This set relates to the early stages of a wall fire when Q,,< 30 kW/m. The other set of data was obtained with a vertical gas-fired panel which consisted of an array of 14 independent burners arranged to allow the aspect ratio of the burning surface to be varied. The data confirm that the flame height correlates with Q,,, but reveal (inter alia) that there are two regions, for values of Q,, greater than and less than c. 20 kW/m. An existing upward flame spread model was modified to allow these two correlations to be incorporated to predict the development of a small fire on a vertical surface for these two regions, which would provide more realistic modelling information. Copyright 2002 John Wiley & Sons, Ltd. [source]

    Conductivity and Methanol Permeability of Nafion,Zirconium Phosphate Composite Membranes Containing High Aspect Ratio Filler Particles,

    FUEL CELLS, Issue 4 2009
    M. Casciola
    Abstract Gels of exfoliated ,-zirconium phosphate (ZrPexf) in dimethylformamide (DMF) were used to prepare Nafion/ZrPexf composite membranes with filler loadings up to 7,wt.-% by casting mixtures of Nafion 1100 solutions in DMF and suitable amounts of 2,wt.-% ZrP gels in DMF. TEM pictures showed that the ZrPexf particles had aspect ratio of at least 20. All samples were characterised by methanol permeability (P) and through-plane (,thp) and in-plane (,inp) conductivity measurements at 40,C and 100% RH. The methanol permeability of Nafion membranes containing in situ grown ZrP particles with low aspect ratio (Nafion/ZrPisg) was also determined. The methanol permeability and the swelling behaviour of the composite membranes turned out to be strongly dependent on the filler morphology. As a general trend, both permeability and swelling decreased according to the sequence: Nafion/ZrPisg > Nafion > Nafion/ZrPexf. The maximum selectivity (,thp/P,=,1.4,,105,S,cm,3,s) was found for the membrane filled with 1,wt.-% ZrPexf: this value is seven times higher than that of Nafion. For the Nafion/ZrPexf membranes, the ratio ,inp/,thp increases with the filler loading, thus indicating that the preferred orientation of the ZrP sheets is parallel to the membrane surface. [source]

    Synthesis and Characterization of Ferroferriborate (Fe3BO5) Nanorods

    Yi Liu
    Abstract Fe3BO5 nanorods with diameters from 4,nm to 16,nm and length from 43,nm to 60,nm are synthesized by a facile thermal decomposition of iron acetylacetonate and t -butylamine borane (TBAB). TBAB is used to control the 1D growth and the aspect ratio of the nanorods. These Fe3BO5 nanorods are antiferromagnetic with TN,=,174,K, which is higher than that of bulk Fe3BO5 (114,K). [source]

    Adhesive, Flexible, and Robust Polysaccharide Nanosheets Integrated for Tissue-Defect Repair

    Toshinori Fujie
    Abstract Recent developments in nanotechnology have led to a method for producing free-standing polymer nanosheets as a macromolecular organization. Compared with bulk films, the large aspect ratio of such nanosheets leads to unique physical properties, such as transparency, noncovalent adhesion, and high flexibility. Here, a biomedical application of polymer nanosheets consisting of biocompatible and biodegradable polysaccharides is reported. Micro-scratch and bulge tests indicate that the nanosheets with a thickness of tens of nanometers have sufficient physical adhesiveness and mechanical strength for clinical use. A nanosheet of 75,nm thickness, a critical load of 9.1,,104,N m,1, and an elastic modulus of 9.6,GPa is used for the minimally invasive repair of a visceral pleural defect in beagle dogs without any pleural adhesion caused by wound repair. For the first time, clinical benefits of sheet-type nano-biomaterials based on molecular organization are demonstrated, suggesting that novel therapeutic tools for overlapping tissue wounds will be possible without the need for conventional surgical interventions. [source]

    Amplitude fluctuations due to diffraction and refraction in anisotropic random media: implications for seismic scattering attenuation estimates

    T. M. Mller
    SUMMARY We calculate the variance of the log-amplitude within the Rytov approximation for plane waves propagating in weakly inhomogeneous and statistically anisotropic random media. Since there is a simple relation between the log-amplitude variance and the attenuation coefficient of seismic primaries in the weak wavefield fluctuation regime, we also obtain scattering attenuation estimates that additionally depend on the aspect ratio of longitudinal and transverse correlation scales of the inhomogeneities. These estimates can be useful for the statistical characterization of anisotropic, large-scale inhomogeneities (large compared with the wavelength of the probing pulse) in the Earth crust and mantle, such as fault zones. With the help of plane-wave-transmission numerical experiments using the finite-difference method we compute the log-amplitude variance as a function of the propagation distance and observe reasonable agreement with the analytical results. We discuss the implications of our results in the context of seismic scattering attenuation estimations. [source]

    An approach to combined rock physics and seismic modelling of fluid substitution effects

    Tor Arne Johansen
    ABSTRACT The aim of seismic reservoir monitoring is to map the spatial and temporal distributions and contact interfaces of various hydrocarbon fluids and water within a reservoir rock. During the production of hydrocarbons, the fluids produced are generally displaced by an injection fluid. We discuss possible seismic effects which may occur when the pore volume contains two or more fluids. In particular, we investigate the effect of immiscible pore fluids, i.e. when the pore fluids occupy different parts of the pore volume. The modelling of seismic velocities is performed using a differential effective-medium theory in which the various pore fluids are allowed to occupy the pore space in different ways. The P-wave velocity is seen to depend strongly on the bulk modulus of the pore fluids in the most compliant (low aspect ratio) pores. Various scenarios of the microscopic fluid distribution across a gas,oil contact (GOC) zone have been designed, and the corresponding seismic properties modelled. Such GOC transition zones generally give diffuse reflection regions instead of the typical distinct GOC interface. Hence, such transition zones generally should be modelled by finite-difference or finite-element techniques. We have combined rock physics modelling and seismic modelling to simulate the seismic responses of some gas,oil zones, applying various fluid-distribution models. The seismic responses may vary both in the reflection time, amplitude and phase characteristics. Our results indicate that when performing a reservoir monitoring experiment, erroneous conclusions about a GOC movement may be drawn if the microscopic fluid-distribution effects are neglected. [source]

    Polymer Films Composed of Surface-Bound Nanofilaments with a High Aspect Ratio, Molecularly Imprinted with Small Molecules and Proteins

    Ana Valvanuz Linares
    Abstract Hierarchically nanostructured materials that combine two or more levels of structuring and that exhibit a combination of useful features have gained considerable interest over recent years. Here, the generation of surface-bound nanofilaments with a high aspect ratio by nanomolding on a nanoporous template surface is described. The filaments, at the same time, carry molecularly imprinted binding sites. The dye fluorescein and the protein myoglobin are used as model templates for imprinting. The surfaces exhibit specific binding as revealed by fluorescence microscopy. The wetting properties of the surfaces depend on the dimensions of the nanofilaments and on the nature of the polymer. It is believed that these materials can potentially be useful for applications in biosensors and biochips. [source]

    Textured Microstructure and Dielectric Properties Relationship of BaNd2Ti5O14 Thick Films Prepared by Electrophoretic Deposition

    Zhi Fu
    Abstract An alternative approach to tailor the temperature coefficient of permittivity (TC,r) of high Q dielectric BaO,Re2O3,TiO2 (Re: rare earth elements) thick films is presented. 10- to 80-m-thick BaNd2Ti5O14 (BNT) films are fabricated by electrophoretic deposition on Pt foils under different processing conditions. Observed anisotropic grain growth is facilitated by constrained sintering. The increase of the sintering temperature increases markedly the aspect ratio of the grains, decreases the dielectric permittivity and TC,r changes from ,114 to +12,ppm C,1. By controlling the sintering temperature, near-zero TC,r, high Q thick films can be fabricated with 45,<,,r,<,70. These findings are of technological relevance since they demonstrate that control of substrate constraint and sintering conditions can be used to control grain anisotropy and thus microwave properties of the BaO,Re2O3,TiO2. The thick films facilitate scaling to small device sizes for high frequency operation. Similar observations are expected in other microwave systems thus opening further technological opportunities. [source]

    Effects of Measurement Error on Horizontal Hydraulic Gradient Estimates

    GROUND WATER, Issue 1 2007
    J.F. Devlin
    During the design of a natural gradient tracer experiment, it was noticed that the hydraulic gradient was too small to measure reliably on an ,500-m2 site. Additional wells were installed to increase the monitored area to 26,500 m2, and wells were instrumented with pressure transducers. The resulting monitoring system was capable of measuring heads with a precision of 1.3 10,2 m. This measurement error was incorporated into Monte Carlo calculations, in which only hydraulic head values were varied between realizations. The standard deviation in the estimated gradient and the flow direction angle from the x-axis (east direction) were calculated. The data yielded an average hydraulic gradient of 4.5 10,425% with a flow direction of 56 southeast 18, with the variations representing 1 standard deviation. Further Monte Carlo calculations investigated the effects of number of wells, aspect ratio of the monitored area, and the size of the monitored area on the previously mentioned uncertainties. The exercise showed that monitored areas must exceed a size determined by the magnitude of the measurement error if meaningful gradient estimates and flow directions are to be obtained. The aspect ratio of the monitored zone should be as close to 1 as possible, although departures as great as 0.5 to 2 did not degrade the quality of the data unduly. Numbers of wells beyond three to five provided little advantage. These conclusions were supported for the general case with a preliminary theoretical analysis. [source]

    Nucleation-Governed Reversible Self-Assembly of an Organic Semiconductor at Surfaces: Long-Range Mass Transport Forming Giant Functional Fibers,

    G. De, Luca
    Abstract The use of solvent-vapor annealing (SVA) to form millimeter-long crystalline fibers, having a sub-micrometer cross section, on various solid substrates is described. Thin films of a perylene-bis(dicarboximide) (PDI) derivative, with branched alkyl chains, prepared from solution exhibit hundreds of nanometer-sized PDI needles. Upon exposure to the vapors of a chosen solvent, tetrahydrofuran (THF), the needles re-organize into long fibers that have a remarkably high aspect ratio, exceeding 103. Time- and space-resolved mapping with optical microscopy allows the self-assembly mechanism to be unravelled; the mechanism is found to be a nucleation-governed growth, which complies with an Avrami-type of mechanism. SVA is found to lead to self-assembly featuring i),long-range order (up to the millimeter scale), ii),reversible characteristics, as demonstrated through a series of assembly and disassembly steps, obtained by cycling between THF and CHCl3 as solvents, iii),remarkably high mass transport because the PDI molecular motion is found to occur at least over hundreds of micrometers. Such a detailed understanding of the growth process is fundamental to control the formation of self-assembled architectures with pre-programmed structures and physical properties. The versatility of the SVA approach is proved by its successful application using different substrates and solvents. Kelvin probe force microscopy reveals that the highly regular and thermodynamically stable fibers of PDI obtained by SVA exhibit a greater electron-accepting character than the smaller needles of the drop-cast films. The giant fibers can be grown in,situ in the gap between microscopic electrodes supported on SiOx, paving the way towards the application of SVA in micro- and nanoelectronics. [source]

    Co3O4 Nanostructures with Different Morphologies and their Field-Emission Properties,

    B. Varghese
    Abstract We report an efficient method to synthesize vertically aligned Co3O4 nanostructures on the surface of cobalt foils. This synthesis is accomplished by simply heating the cobalt foils in the presence of oxygen gas. The resultant morphologies of the nanostructures can be tailored to be either one-dimensional nanowires or two-dimensional nanowalls by controlling the reactivity and the diffusion rate of the oxygen species during the growth process. A possible growth mechanism governing the formation of such nanostructures is discussed. The field-emission properties of the as-synthesized nanostructures are investigated in detail. The turn-on field was determined to be 6.4 and 7.7,V,,m,1 for nanowires and nanowalls, respectively. The nanowire samples show superior field-emission characteristics with a lower turn-on field and higher current density because of their sharp tip geometry and high aspect ratio. [source]

    Formation of Silver Nanoprisms with Surface Plasmons at Communication Wavelengths,

    V. Bastys
    Abstract Silver nanoprisms with strong absorption in the near-IR have been synthesized using a modification of the photoinduced method by illuminating preformed silver seeds under different illumination conditions. Low-intensity light-emitting diodes and white light combined with different color filters are used as light sources. The lateral dimensions of the nanoprisms are found to be correlated in a quasilinear fashion with the emission wavelength and the position of the main in-plane dipole plasmon band. The structural characterization of the Ag nanoparticles, carried out using scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and electron diffraction, reveal that the particles are flat and have a single-crystal face-centered-cubic structure. Time-resolved studies suggest that the nanoprisms are formed by steady consumption of the original Ag seeds with little variation of the aspect ratio after a short induction time. [source]