Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Fe

  • dissolved fe
  • santa fe
  • total fe

  • Terms modified by Fe

  • fe abundance
  • fe accumulation
  • fe analysis
  • fe atom
  • fe availability
  • fe catalyst
  • fe complex
  • fe concentration
  • fe content
  • fe crystal
  • fe film
  • fe formulation
  • fe ion
  • fe k
  • fe mesh
  • fe method
  • fe model
  • fe models
  • fe nanoparticle
  • fe oxide
  • fe ratio
  • fe simulation
  • fe solution

  • Selected Abstracts

    Reagentless Biosensor for Hydrogen Peroxide Based on the Immobilization of Hemoglobin in Platinum Nanoparticles Enhanced Poly(chloromethyl thiirane) Cross-linked Chitosan Hybrid Film

    ELECTROANALYSIS, Issue 12 2009
    Shanshan Jia
    Abstract An unmediated hydrogen peroxide (H2O2) biosensor was prepared by co-immobilizing hemoglobin (Hb) with platinum nanoparticles enhanced poly(chloromethyl thiirane) cross-linked chitosan (CCCS-PNs) hybrid film. CCCS could provide a biocompatible microenvironment for Hb and PNs could accelerate the electron transfer between Hb and the electrode. Spectroscopic analysis indicated that the immobilized Hb could maintain its native structure in the CCCS-PNs hybrid film. Entrapped Hb exhibited direct electrochemistry for its heme Fe(III)/Fe(II) redox couples at ,0.396,V in the CCCS-PNs hybrid film, as well as peroxidase-like activity to the reduction of hydrogen peroxide without the aid of an electron mediator. [source]

    Properties of Poly(sodium 4-styrenesulfonate)-Ionic Liquid Composite Film and Its Application in the Determination of Trace Metals Combined with Bismuth Film Electrode

    ELECTROANALYSIS, Issue 5 2008
    Jianbo 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]

    Photogalvanic effect in aqueous Methylene blue nickel mesh systems: Conversion of light into electricity

    Ilker S. Bayer
    Abstract The photogalvanic effect in electrochemical cells, employing aqueous Methylene blue and Fe(II)/Fe(III) couple electrolyte and nickel-mesh electrodes, were experimentally investigated. Five different standard H-cell configurations were set-up by modifying the electrolyte. Long-term open-circuit voltage measurements were conducted in order to test the stability of the cells. Light on,off reproducibility experiments were also carried out during lengthy cell operations. By comparing experimental quantum yield with theoretical predictions, it was found that the cells operate on differential electrode kinetics. Oxidation of the illuminated electrode was detected. This affected the current,voltage characteristics of the cells after a sufficiently long cell operation. Schottky junction treatment was used to model the electrolyte,electrode junction. After calculating the ratio between the majority carrier (electron) current density and minority carrier (hole) current density, we concluded that the oxidation of the electrodes contributes positively to the cell performance since the electrode,electrolyte interface shows unipolar Schottky diode characteristics. Copyright 2001 John Wiley & Sons, Ltd. [source]

    An optimized H, index for disentangling stellar population ages

    J. L. Cervantes
    ABSTRACT We have defined a new H, absorption index definition, H,o, which has been optimized as an age indicator for old and intermediate age stellar populations. Rather than using stellar spectra, we employed for this purpose a library of stellar population spectral energy distributions of different ages and metallicities at moderately high resolution. H,o provides us with improved abilities for lifting the age,metallicity degeneracy affecting the standard H, Lick index definition. The new index, which has also been optimized against photon noise and velocity dispersion, is fully characterized with wavelength shift, spectrum shape, dust extinction and [,/Fe] abundance ratio effects. H,o requires spectra of similar qualities as those commonly used for measuring the standard H, Lick index definition. Aiming at illustrating the use and capabilities of H,o as an age indicator we apply it to Milky Way globular clusters and to a well selected sample of early-type galaxies covering a wide range in mass. The results shown here are particularly useful for applying this index and understand the involved uncertainties. [source]

    Spectral models for solar-scaled and ,-enhanced stellar populations

    P. Coelho
    ABSTRACT We present the first models allowing one to explore in a consistent way the influence of changes in the ,-element-to-iron abundance ratio on the high-resolution spectral properties of evolving stellar populations. The models cover the wavelength range from 3000 to 1.34 ,m at a constant resolution of full width at half-maximum (FWHM) = 1 and a sampling of 0.2 , for overall metallicities in the range 0.005 ,Z, 0.048 and for stellar population ages between 3 and 14 Gyr. These models are based on a recent library of synthetic stellar spectra and a new library of stellar evolutionary tracks, both computed for three different iron abundances ([Fe/H]=,0.5, 0.0 and 0.2) and two different ,-element-to-iron abundance ratios ([,/Fe]= 0.0 and 0.4). We expect our fully synthetic models to be primarily useful for evaluating the differential effect of changes in the ,/Fe ratio on spectral properties such as broad-band colours and narrow spectral features. In addition, we assess the accuracy of absolute model predictions in two ways: first, by comparing the predictions of models for scaled-solar metal abundances ([,/Fe]= 0.0) to those of existing models based on libraries of observed stellar spectra; and secondly, by comparing the predictions of models for ,-enhanced metal abundances ([,/Fe]= 0.4) to observed spectra of massive early-type galaxies in the Sloan Digital Sky Survey Data Release 4. We find that our models predict accurate strengths for those spectral indices that are strongly sensitive to the abundances of Fe and , elements. The predictions are less reliable for the strengths of other spectral features, such as those dominated by the abundances of C and N, as expected from the fact that the models do not yet allow one to explore the influence of these elements in an independent way. We conclude that our models are a powerful tool for extracting new information about the chemical properties of galaxies for which high-quality spectra have been gathered by modern surveys. [source]

    The age, metallicity and ,-element abundance of Galactic globular clusters from single stellar population models

    Jon T. Mendel
    ABSTRACT Establishing the reliability with which stellar population parameters can be measured is vital to extragalactic astronomy. Galactic globular clusters (GCs) provide an excellent medium in which to test the consistency of single stellar population (SSP) models as they should be our best analogue to a homogeneous (single) stellar population. Here we present age, metallicity and ,-element abundance measurements for 48 Galactic GCs as determined from integrated spectra using Lick indices and SSP models from Thomas, Maraston & Korn, Lee & Worthey and Vazdekis et al. By comparing our new measurements to independent determinations we are able to assess the ability of these SSPs to derive consistent results , a key requirement before application to heterogeneous stellar populations like galaxies. We find that metallicity determinations are extremely robust, showing good agreement for all models examined here, including a range of enhancement methods. Ages and ,-element abundances are accurate for a subset of our models, with the caveat that the range of these parameters in Galactic GCs is limited. We are able to show that the application of published Lick index response functions to models with fixed abundance ratios allows us to measure reasonable ,-element abundances from a variety of models. We also examine the age,metallicity and [,/Fe],metallicity relations predicted by SSP models, and characterize the possible effects of varied model horizontal branch morphology on our overall results. [source]

    The NOAO Fundamental Plane Survey , III.

    Variations in the stellar populations of red-sequence galaxies from the cluster core to the virial radius
    ABSTRACT We analyse absorption line-strength indices for ,3000 red-sequence galaxies in 94 nearby clusters to investigate systematic variations of their stellar content with location in the host cluster. The data are drawn from the National Optical Astronomy Observatory (NOAO) Fundamental Plane Survey. Our adopted method is a generalization of that introduced by Nelan et al. to determine the global age,mass and metallicity,mass relations from the same survey. We find strong evidence for a change in galaxy properties, at fixed mass, over a range from the cluster centre to the virial radius, R200. For example, red-sequence galaxies further out in the clusters have weaker Mgb5177 (at ,8, significance) and stronger H, and H, absorption (,3,, ,4,) than galaxies of the same velocity dispersion in the cluster cores. The Fe5270 and Fe5335 indices show only very weak trends with radius. Using a total of 12 indices, the pattern of cluster-centric gradients is considered in light of their different dependences on stellar age and chemical composition. The measured gradients for all 12 indices can be reproduced by a model in which red-sequence galaxies at ,1 R200 have on average younger ages (by 15 4 per cent) and lower ,-element abundance ratios (by 10 2 per cent) than galaxies of the same velocity dispersion but located near the cluster centres. For the total metallicity, Z/H, no significant gradient is found (2 3 per cent larger at R200 than in the cores). There are hints that the age trend may be stronger for galaxies of lower mass and/or for galaxies with more discy morphology. We show, however, that the trends cannot be driven primarily by changes in the morphological mix as a function of radius. The cluster-centric age and [,/Fe] gradients are in the sense expected if galaxies in the cluster core were accreted at an earlier epoch than those at larger radii, and if this earlier accretion contributed to an earlier cessation of star formation. The size of the observed age trend is comparable to predictions from semi-analytic models of hierarchical galaxy formation. [source]

    Testing stellar population models with star clusters in the Large Magellanic Cloud

    Michael A. Beasley
    Abstract We present high signal-to-noise ratio integrated spectra of 24 star clusters in the Large Magellanic Cloud (LMC), obtained using the FLAIR spectrograph at the UK Schmidt telescope. The spectra have been placed on to the Lick/IDS system in order to test the calibration of Simple Stellar Population (SSP) models. We have compared the SSP-predicted metallicities of the clusters with those from the literature, predominantly taken from the Ca-triplet spectroscopy of Olszewski et al. (1991). We find that there is good agreement between the metallicities in the range ,2.10 ,[Fe/H], 0. However, the Mg2 index (and to a lesser degree Mg b) systematically predict higher metallicities (up to +0.5 dex higher) than ,Fe,. Among the possible explanations for this are that the LMC clusters possess [,/Fe] > 0. Metallicities are presented for eleven LMC clusters which have no previous measurements. We compare SSP ages for the clusters, derived from the H,, H, and H, Lick/IDS indices, with the available literature data, and find good agreement for the vast majority. This includes six old globular clusters in our sample, which have ages consistent with their HST colour-magnitude diagram (CMD) ages and/or integrated colours. However, two globular clusters, NGC 1754 and NGC 2005, identified as old (,15 Gyr) on the basis of HST CMDs, have H, line-strengths which lead ages that are too low (,8 and ,6 Gyr respectively). These findings are inconsistent with their CMD-derived values at the 3, level. Comparison between the horizontal branch morphology and the Balmer line strengths of these clusters suggests that the presence of blue horizontal branch stars has increased their Balmer indices by up to ,1.0 . We conclude that the Lick/IDS indices, used in conjunction with contemporary SSP models, are able to reproduce the ages and metallicities of the LMC clusters reassuringly well. The required extrapolations of the fitting functions and stellar libraries in the models to lower ages and low metallicities do not lead to serious systematic errors. However, owing to the significant contribution of horizontal branch stars to Balmer indices, SSP model ages derived for metal-poor globular clusters are ambiguous without a priori knowledge of horizontal branch morphology. [source]

    Copper- or Iron-Catalyzed Arylation of Phenols from respectively Aryl Chlorides and Aryl Iodides

    Ning Xia
    The first general entry into copper-catalyzed arylation of phenols from aryl chlorides is the principal outcome of the study presented in this article. The use of the 2,2,6,6-tetramethyl-3,5-heptanedione (1) as ligand is the key to the success of this reaction. An additional finding of this study, touched upon only briefly here, is the 1/Fe-catalyzed arylation of phenols from aryl iodides (R=a donating or an electron-withdrawing group). [source]

    A new bismuth iron oxyphosphate, Bi6(Bi0.32Fe0.68)(PO4)4O4

    Nachiappan Arumugam
    Iron was inserted into the known crystal structure of the bismuth phosphate oxide Bi6.67(PO4)4O4 to ascertain its location in the vacancies associated with the bismuth ion located at the origin of the unit cell. Single-crystal X-ray diffraction refinements converged to a model of composition Bi6(Bi0.32Fe0.68)(PO4)4O4 (hexabismuth iron tetraphosphate tetraoxide), in which Bi and Fe are displaced from the origin giving rise to a random distribution over the 2i sites instead of 1a, the origin of space group P. The isotropic displacement parameter for Bi/Fe has a reasonable value in this model. This structure establishes for the first time that Fe substitutes in the Bi-deficient site in this series of materials and that Fe and Bi are disordered around the center of symmetry. These results enhance understanding of the crystal chemistry of these main group phosphates that are of interest in ion transport. [source]

    An online thermodynamics courseware

    C. C. Ngo
    Abstract This article presents an online Thermodynamics courseware and how it can be used to enhance the learning experience of students. The courseware has been developed to present the materials in a dynamic and interactive fashion. It also includes a review section to help students in the preparation of the Fundamentals of Engineering (FE) Exam. Since its first implementation in summer 2000, this courseware has received overwhelming response from our students. 2003 Wiley Periodicals, Inc. Comput Appl Eng Educ 11: 75,82, 2003; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.10039 [source]

    Uncertainty and Sensitivity Analysis of Damage Identification Results Obtained Using Finite Element Model Updating

    Babak Moaveni
    The shake table tests were designed so as to damage the building progressively through several historical seismic motions reproduced on the shake table. A sensitivity-based finite element (FE) model updating method was used to identify damage in the building. The estimation uncertainty in the damage identification results was observed to be significant, which motivated the authors to perform, through numerical simulation, an uncertainty analysis on a set of damage identification results. This study investigates systematically the performance of FE model updating for damage identification. The damaged structure is simulated numerically through a change in stiffness in selected regions of a FE model of the shear wall test structure. The uncertainty of the identified damage (location and extent) due to variability of five input factors is quantified through analysis-of-variance (ANOVA) and meta-modeling. These five input factors are: (1,3) level of uncertainty in the (identified) modal parameters of each of the first three longitudinal modes, (4) spatial density of measurements (number of sensors), and (5) mesh size in the FE model used in the FE model updating procedure (a type of modeling error). A full factorial design of experiments is considered for these five input factors. In addition to ANOVA and meta-modeling, this study investigates the one-at-a-time sensitivity analysis of the identified damage to the level of uncertainty in the identified modal parameters of the first three longitudinal modes. The results of this investigation demonstrate that the level of confidence in the damage identification results obtained through FE model updating, is a function of not only the level of uncertainty in the identified modal parameters, but also choices made in the design of experiments (e.g., spatial density of measurements) and modeling errors (e.g., mesh size). Therefore, the experiments can be designed so that the more influential input factors (to the total uncertainty/variability of the damage identification results) are set at optimum levels so as to yield more accurate damage identification results. [source]

    Assessment of Protection Systems for Buried Steel Pipelines Endangered by Rockfall

    Bernhard Pichler
    First, a gravel-based protection system (GBPS) is investigated, that is, a pipeline buried in sandy gravel is considered. To assess the load-carrying behavior of this structure when subjected to rockfall, a finite element (FE) model has been developed. The development and the validation of this structural model are strictly separated, that is, they are based on two physically and statistically independent sets of experiments. Subsequently, scenarios of rockfall onto a gravel-buried steel pipe are analyzed considering different boundary conditions and structural dimensions. Following the conclusions drawn from these numerical analyses, an enhanced protection system (EPS) is proposed. It consists of gravel as an energy-absorbing and impact-damping system and a buried steel plate resting on walls made of concrete representing a load-carrying structural component. The potential and the limitations of both protection systems are discussed in detail. [source]

    An experimentally calibrated finite element study of maxillary trauma

    Michael J Casas
    Abstract,,, A baseball injury to an instrumented human cadaver maxillae was simulated with a regulation (142 g) baseball traveling at 14 m s,1. Measurements of strain were obtained with three-axis strain gauge rosettes located at the medial palate and both canine fossae. A three-dimensional finite element (FE) model of a dentate human maxilla was constructed from computed tomography scans of the skull of an adolescent. This three-dimensional mathematical model of the maxilla was deemed geometrically accurate by convergence testing when the model's degrees of freedom approximated 74 000. The simulated load case involved a transient dynamic impact to the medial maxilla with boundary conditions imposed at skeletal buttresses of the model. The model was calibrated through direct comparison with the displacements and principal strains gathered from experimental and epidemiological data. The comparison of experimental and calculated principal strains as a result of the simulated impacts revealed a 1.7,11.4% difference. [source]

    Novel Sensitive Voltammetric Detection of Trace Gallium(III) with Presence of Catechol Using Mercury Film Silver Based Electrode

    ELECTROANALYSIS, Issue 16 2009
    Robert Piech
    Abstract A new adsorptive stripping voltammetric method for the determination of trace gallium(III) based on the adsorption of gallium(III)-catechol complex on the cyclic renewable mercury film silver based electrode (Hg(Ag)FE) is presented. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 2,nM (0.14,,g L,1) to 100,nM (6.97,,g L,1) for a preconcentration time of 30,s, with correlation coefficient of 0.9993. For a Hg(Ag)FE with a surface area of 9.7,mm2 the detection limit for a preconcentration time of 90,s is as low as 7,ng L,1. The repeatability of the method at a concentration level of the analyte as low as 0.05,,g L,1, expressed as RSD is 3.6% (n=5). The proposed method was successfully applied by studying the natural samples and simultaneous recovery of Ga(III) from spiked water and sediment samples. [source]

    Renewable Copper and Silver Amalgam Film Electrodes of Prolonged Application for the Determination of Elemental Sulfur Using Stripping Voltammetry

    ELECTROANALYSIS, Issue 7 2008
    Robert Piech
    Abstract New, renewable copper (Hg(Cu)FE) and silver (Hg(Ag)FE) based amalgam film electrodes applied for the determination of elemental sulfur using differential pulse cathodic stripping voltammetry are presented. With surface areas adjustable from 1 to 12,mm2, both electrodes are characterized by very good surface reproducibility (,2%) and long-term stability (a few thousand measurement cycles). The mechanical refreshing of the amalgam film takes about 1,2 seconds. The effects of various factors such as instrumental parameters and the supporting electrolyte composition were optimized. Interferences from sulfides are easily removed by the addition of acid, and bubbling with argon, for Hg(Ag)FE. In the case of Hg(Cu)FE, sulfides did not interfere. The calibration graph is linear within the studied range from 16,ng L,1 to 4.8,,g L,1 for Hg(Cu)FE, and up to 6.4,,g L,1 for Hg(Ag)FE (tacc=15,s). The correlation coefficients for the two electrodes were at least 0.997. The detection limits for a low concentration of S(0) and tacc=60,s are as low as 14,ng L,1 for Hg(Cu)FE and 4,ng L,1 for Hg(Ag)FE. The proposed method was successfully applied and validated by studying the recovery of S(0) from spiked river water. [source]

    Effect of local analgesia on movement of the equine back

    Summary Reasons for performing study: Diagnostic infiltration of local anaesthetic solution is commonly used in cases of equine back pain. Evaluation is subjective and it is not known how local analgesia of the back affects horses without clinical signs of back pain. Objectives: To evaluate the effect of infiltration of local anaesthetics on the movement of the back in horses without clinical signs of back pain, and to evaluate the usefulness of kinematic studies as an objective and quantitative tool in evaluating local analgesia in clinical practice. Methods: The kinematics of the back in 10 clinically sound horses were measured on 2 occasions at walk and trot before and after injections with mepivacaine and sodium chloride around the interspinous spaces between T16 and L2. The kinematics were compared between the 2 occasions before injections and before and after each injection. Results: The range of motion (ROM) for dorsoventral flexion-extension (FE) of the back was increased significantly in all measured segments other than T10 at walk, as was lateral bending (LB) at T10, L3 and L5 after injection of mepivacaine. For lateral excursion (LE), total movement increased at all measured segments. At trot the only affected segment was L3, where the injection with mepivacaine decreased the ROM for FE. After injection of sodium chloride the ROM for FE increased at T13 and T17 at walk. Lateral bending and LE were not affected at walk. At trot, LB increased at L3 and L5. Conclusions and potential relevance: Diagnostic infiltration of local anaesthetic solution affects the function of the back in clinically sound horses, which must be considered when interpreting the use of this clinical aid in assessing clinical cases of back dysfunction. Kinematics can qualitatively and quantitatively evaluate the effect of local analgesia of the back. [source]

    Constituent Particle Break-Up During Hot Rolling of AA 5182,

    Nicolas Moulin
    Aluminum sheet is currently used for body panels on a number of mass-produced vehicles, in particular for closure panels. AA5xxx alloys always contain coarse inter-metallic particles (Alx(Fe,Mn)ySi, Mg2Si) after casting. In the present work inter-metallic particle break-up during hot reversible rolling of AA5182 alloy sheets has been analyzed. The sizes and shapes of inter-metallic particles in as-cast and industrially hot rolled AA5182 alloys sheets were characterized by 3D X-ray tomography observations. The relation between particle break-up and particle morphology was then analyzed statistically and by a micromechanical finite element (FE)-based model. The essential outcomes of the statistical approach may be summarized as follows. The inter-metallic particle population may be described by five morphological parameters. Secondly the comparison of the particle morphology in as cast and industrially rolled sheets leads to the definition of five classes. The evolution of each particle class as function of the rolling strain is provided. The statistical analysis shows which particles break-up. The stresses and strains in inter-metallic particles, embedded in an elasto-viscoplastic aluminum matrix submitted to plane strain compression, were analyzed by an FE model. A new failure criterion was proposed. The essential outcomes of the mechanical approach are as follows: a precise description of stress concentration mechanisms in nonconvex particles, a close description of the parameters controlling particle break-up, and finally a simplified classification of the failure behavior. [source]

    Fatigue Crack Propagation and History Effects Induced by Plasticity,

    Sylvie Pommier
    Abstract For security-relevant components, a fracture mechanics assessment has to be carried out. When complex loading conditions are encountered, various problems arise. Among them the prediction of history effects induced by plasticity remains a difficult task and is the object of this paper. After an overload, for instance, plasticity-induced crack closure is known to decelerate the crack growth. This effect is known to be related to residual stresses ahead of and behind the crack tip. Since residual stresses are related to the material stress,strain behavior, the overload effect may vary significantly from one material to another. Finite-element (FE) methods are commonly employed to model plasticity and were shown to give very satisfactory results. However, if millions of cycles need to be modeled to predict the fatigue behavior of an industrial component, the method becomes computationally too expensive. By employing a multiscale approach, very precise analyses computed by FE methods can be brought to a global scale. The data generated using the FE method enables the identification of a global cyclic elastic-plastic model for the crack tip region. Once this model is identified, it can be employed directly with no need of additional FE computations, resulting in fast computations. This method was employed so as to predict fatigue crack growth under variable amplitude fatigue in steels at room temperatures and correlates well with experimental data. It was also extended so as to model fatigue crack growth in a nickel base superalloy under non-isothermal fatigue-dwell conditions. At present, the method is being extended to mixed-mode variable-amplitude loading conditions. [source]

    Two-dimensional finite element thermal modeling of an oil-immersed transformer

    Jawad Faiz
    Abstract Finite element (FE) modeling of a typical transformer indicates that the hot spot position is always on the top most part of the transformer. The hot spot temperature of winding depends on the load and the type of loading and is changed by loading. A number of the generated magnetic flux lines of windings close to their paths perpendicular to the internal channel of the windings and therefore the flux density in the middle of the channel is considerably larger than the beginning and ending of the winding. Two models of windings are employed and different temperature distributions are obtained. The computation results show that the time constant of high voltage (HV) winding is lower than that of the low voltage (LV) winding. A good agreement between the test and computed results has been achieved. Copyright 2007 John Wiley & Sons, Ltd. [source]

    The one-level functional equation of multi-rate loss systems

    Harro L. Hartmann
    Motivated by the discrete multi-rate Kaufmann,Roberts recurrence relations, we derive a functional equation (FE), which covers nonintegral states. This FE implies a unique effective step parameter d, which defines an equivalent one-level recurrence depth, or bit-rate, at each state under progress. This state-dependent depth results from the equality requirement of the multi-rate and the one-level model in the moment-generating function transform domain. By this method it is possible to model d by a few moments of the original multi-rate statistic. In this case we obtain an explicit FE solution covering the entire (global) state space. Next we verify that the resulting state probability density incorporates iteratively enumerated discrete state probabilities, including the state-dependent depth. With a system capacity C the iterations then need time complexities between O(C) and O(C2). In contrast to this each FE state, is performed at a time complexity O(1). By the efficient coverage of the whole state space, fast optimizations of multi-rate networks and multi-resource systems can be improved. Copyright 2003 AEI. [source]

    Fatigue crack growth and life prediction of a single interference fitted holed plate

    ABSTRACT To understand the different aspects of fatigue behaviour of complex structural joints it will be much helpful if the effects of different parameters are studied separately. In this article, to study the isolated effect of interference fit on fatigue life a pined hole specimen is investigated. This specimen is a single-holed plate with an oversized pin which force fitted to the hole. The investigation was carried out both experimentally and numerically. In the experimental part, interference fitted specimens along with open hole specimens were fatigue tested to study the experimental effect of the interference fit. In the numerical part, three-dimensional finite element (FE) simulations have been performed in order to obtain the created stresses due to interference fit and subsequent applied longitudinal load at the holed plate. The stress distribution obtained from FE simulation around the hole was used to predict crack initiation life using Smith,Watson,Topper method and fatigue crack growth life using the NASGRO equation with applying the AFGROW computer code. The predicted fatigue life obtained from the numerical methods show a good agreement with the experimental fatigue life. [source]

    Determining the life cycle of bolts using a local approach and the Dang Van criterion

    Y. FARES
    ABSTRACT The fatigue behaviour of bolts under axial load has always been considered from the component point of view for which fatigue limit is usually taken equal to 50 MPa, and few results are available to designers for limited lifetimes. Here, we take up this problem from a material point of view using a local approach. For each case of fatigue testing, using finite-element (FE) model of the bolt, we determine the stabilized local stress at the root of the first thread in contact with the nut. To characterize bolt behaviour with these numerical results, we use Dang Van multiaxial fatigue criterion for which we extend application to the medium fatigue life. These results can be correlated with the experimental numbers of cycles to failure to determine material parameters of the generalized criterion. Using statistical Gauss method, we can make lifetime predictions for any level of risk of failure. In addition, we propose an analytical model to rapidly determine the local stress condition from nominal loading data (mean stress and alternating stress). This model dispenses us from a new modelling if the bolt is stressed in the same manner as the bolts used for behaviour characterization. Using this model and the generalized criterion, it is extremely easy to make lifetime predictions whatever the risk considered. [source]

    Standing contact fatigue with a cylindrical indenter

    ABSTRACT A hardened steel cylinder was repeatedly pressed against a flat case-hardened steel specimen that was equally wide as the cylinder was long. Some contact end effects were noted as a result of limited plastic deformation. A strain gauge on the contact surface, just outside the contact and oriented perpendicular to the cylinder detected a surface strain when the cylinder was loaded. The non-zero surface strain was the result of boundary effects of the finite specimen. Four different types of contact fatigue cracks developed in and below the specimen contact surface. The cracks were named lateral, median, contact end and edge cracks. Changes in the measured surface strain values could be used to determine when the lateral and edge cracks developed. The order in which all four crack types typically developed was determined from optical crack observation at test termination, strain measurements and stress computations. Numerical computations using finite-element (FE) analyses were used to verify the surface strain behaviour due to loading and cracking; to verify contact end effects; crack locations and crack orientation by aid of the Findley multi-axial fatigue criterion. [source]

    Numerical investigation on J -integral testing of heterogeneous fracture toughness testing specimens: Part I , weld metal cracks

    Y.-J. KIM
    ABSTRACT Based on extensive two-dimensional (2D) finite element (FE) analyses, the present work provides the plastic , factor solutions for fracture toughness J -integral testing of heterogeneous specimens with weldments. Solutions cover practically interesting ranges of strength mismatch and relative weld width, and are given for three typical geometries for toughness testing: a middle cracked tension (M(T)) specimen, single edge cracked bend (SE(B)) specimen and (C(T)) specimen. For mismatched M(T) specimens, both plane strain and plane stress conditions are considered, whereas for SE(B) and C(T) specimens, only the plane strain condition is considered. For all cases, only deep cracks are considered, and an idealized butt weld configuration is considered, where the weld metal strip has a rectangular cross section. Based on the present solutions for the strength mismatch effect on plastic , factors, a window is provided, within which the homogeneous J estimation procedure can be used for weldment toughness testing. The effect of the weld groove configuration on the plastic , factor is briefly discussed, concluding the need for further systematic analysis to provide guidance to practical toughness testing. [source]

    The validation of some methods of notch fatigue analysis

    This paper is concerned with the testing and validation of certain methods of notch analysis which the authors have developed theoretically in earlier publications. These methods were developed for use with finite element (FE) analysis in order to predict the fatigue limits of components containing stress concentrations. In the present work we tested and compared these methods using data from standard notches taken from the literature, covering a range of notch geometries, loading types, R -ratios and materials: a total of 47 different data sets were analysed. The greatest predictive success was achieved with critical-distance methods known as the point, line and area methods: 94% of these predictions fell within 20% of the experimental fatigue limits. This was a significant improvement on previous methods of this kind, e.g. that of Klesnil and Lucas [(1980) Fatigue of Metallic Materials, Elsevier Science]. Methods based on the Smith and Miller [(1978) Int. J. Mech. Sci. 20, 201,206] concept of crack-like notches were successful in 42% of cases; they experienced difficulties dealing with very small notches, and could be improved by using an ElHaddad-type correction factor, giving 87% success. An approach known as ,crack modelling' allowed the Smith and Miller method to be used with non-standard stress concentrations, where notch geometry is ill defined; this modification, with the same short-crack correction, had 68% success. It was concluded that the critical-distance approach is more accurate and can be more easily used to analyse components of complex shape, however, the crack modelling approach is sometimes preferable because it can be used with less mesh refinement. [source]

    Effect of Contact Mode on the Electrical Transport and Field-Emission Performance of Individual Boron Nanowires

    Fei Liu
    Abstract Vapor,liquid,solid processing of boron nanowires (BNWs) can be carried out either using a bottom-up or top-down growth mode, which results in different contact modes between the nanowire and the substrate. The contact mode may strongly affect the electrical transport and field-emission performance of the individual boron nanowires grown on a Si substrate. The electrical transport and field-emission characteristics of individual boron nanowires of different contact modes are investigated in situ using a scanning electron microscope. The contact barriers are very distinct for the different contact modes. Moreover, the transition from a "contact-limited" to a "bulk-limited" field-emission (FE) process is demonstrated in nanoemitters for the first time, and the proposed improved metal,insulator,vacuum (MIV) model may better illustrate the nonlinear behavior of the Fowler-Nordheim (FN) plots in these nanoscale systems. Individual BNWs with different contact modes have a discrepancy in their emission stability and vacuum breakdown characteristics though they have similar aspect ratios, which suggests that their electrical transport and field-emission performance are closely related to their contact mode. Boron nanowires grown in the base-up mode have better field-emission performances and are more beneficial than those grown in the top-down mode for various device applications. [source]

    Functional biodiversity of macroinvertebrate assemblages along major ecological gradients of boreal headwater streams

    FRESHWATER BIOLOGY, Issue 9 2005
    JANI HEINOArticle first published online: 3 AUG 200
    Summary 1. Biodiversity,environment relationships are increasingly well-understood in the context of species richness and species composition, whereas other aspects of biodiversity, including variability in functional diversity (FD), have received rather little rigorous attention. For streams, most studies to date have examined either taxonomic assemblage patterns or have experimentally addressed the importance of species richness for ecosystem functioning. 2. I examined the relationships of the functional biodiversity of stream macroinvertebrates to major environmental and spatial gradients across 111 boreal headwater streams in Finland. Functional biodiversity encompassed functional richness (FR , the number of functional groups derived from a combination of functional feeding groups and habit trait groups), FD , the number of functional groups and division of individuals among these groups, and functional evenness (FE , the division of individuals among functional groups). Furthermore, functional structure (FS) comprised the composition and abundance of functional groups at each site. 3. FR increased with increasing pH, with additional variation related to moss cover, total nitrogen, water colour and substratum particle size. FD similarly increased with increasing pH and decreased with increasing canopy cover. FE decreased with increasing canopy cover and water colour. Significant variation in FS was attributable to pH, stream width, moss cover, substratum particle size, nitrogen, water colour with the dominant pattern in FS being related to the increase of shredder-sprawlers and the decrease of scraper-swimmers in acidic conditions. 4. In regression analysis and redundancy analysis, variation in functional biodiversity was not only related to local environmental factors, but a considerable proportion of variability was also attributable to spatial patterning of environmental variables and pure spatial gradients. For FR, 23.4% was related to pure environmental effects, 15.0% to shared environmental and spatial effects and 8.0% to spatial trends. For FD, 13.8% was attributable to environmental effects, 15.2% to shared environmental and spatial effects and 5% to spatial trends. For FE, 9.0% was related to environmental variables, 12.7% to shared effects of environmental and spatial variables and 4.5% to spatial variables. For FS, 13.5% was related to environmental effects, 16.9% to shared environmental and spatial effects and 15.4% to spatial trends. 5. Given that functional biodiversity should portray variability in ecosystem functioning, one might expect to find functionally rather differing ecosystems at the opposite ends of major environmental gradients (e.g. acidity, stream size). However, the degree to which variation in the functional biodiversity of stream macroinvertebrates truly portrays variability in ecosystem functioning is difficult to judge because species traits, such as feeding roles and habit traits, are themselves strongly affected by the habitat template. 6. If functional characteristics show strong responses to natural environmental gradients, they also are likely to do so to anthropogenic environmental changes, including changes in habitat structure, organic inputs and acidifying elements. However, given the considerable degree of spatial structure in functional biodiversity, one should not expect that only the local environment and anthropogenic changes therein are responsible for this variability. Rather, the spatial context, as well as natural variability along environmental gradients, should also be explicitly considered in applied research. [source]

    Template Deformation-Tailored ZnO Nanorod/Nanowire Arrays: Full Growth Control and Optimization of Field-Emission

    Haibo Zeng
    Abstract Here, a facile and effective route toward full control of vertical ZnO nanorod (NR)/nanowire (NW) arrays in centimeter-scale areas and considerable improvement of field-emission (FE) performance is reported. Controlled deformation of colloidal crystal monolayer templates is introduced by heating near glass-transition temperature. The NR/NW density, uniformity, and tapering were all adjusted through selection of template size and deformation, and electrolyte composition. In line with the adjustments, the field-emission performance of the arrays is significantly improved. A low turn-on electric field of 1.8,V m,1, a field-enhancement factor of up to 5,750, and an emitting current density of up to 2.5,mA cm,2 were obtained. These improved parameters would benefit their potential application in cold-cathode-based electronics. [source]

    Periodic TiO2 Nanorod Arrays with Hexagonal Nonclose-Packed Arrangements: Excellent Field Emitters by Parameter Optimization

    Yue Li
    Abstract Periodic TiO2 nanorod arrays with hexagonal nonclose-packed (hncp) arrangements are synthesized by pulsed laser deposition (PLD) using polystyrene colloidal monolayers as templates and with subsequent annealing in air. The hncp-array formation is governed by in situ volume shrinkage of amorphous TiO2 nanorods in the crystallizing process during annealing. The array periodicity can easily be tuned by different sphere sizes of the colloidal template, whereas the distance between neighboring nanorods can be controlled by altering the background gas pressure during the PLD process, at a given periodicity for the nanorod array. Parameter-controlled growth is helpful for investigating and optimizing the parameter-dependent field-emission properties. The hncp nanorod array exhibits an enhanced field-emission (FE) performance compared to both particle films and nanorod arrays with top aggregation. With an increase in periodicity of a hncp nanorod array, the field-enhancement factor decreases and the turn-on FE field increases. FE characteristics can be further enhanced by increasing the distance between adjacent nanorods while maintaining the same periodicity. The parameter-optimized results suggest that the arrays with a smaller periodicity and a larger distance display the best FE performance and could be highly valuable for designing field-emission devices based on these periodic nanorod arrays. [source]