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Individual Particles (individual + particle)

Distribution by Scientific Domains

Polymers and Materials Science	40%
Chemistry	32%
Engineering	16%
Earth and Environmental Science	8%

Selected Abstracts

Standardized analysis of UHMWPE wear particles from failed total joint arthroplasties

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 5 2002
Jay D. Mabrey
Abstract Periprosthetic tissue obtained at revision surgery from eight total hip replacement cases was hydrolyzed, and polyethylene debris particles were isolated from each case. Individual particles were analyzed by scanning electron microscopy (SEM) and computerized image analysis in accordance with ASTM F1877-98, a standard for quantitative description of wear debris. For comparison, periprosthetic tissues from eight total knee revision and four total shoulder revision cases were processed and analyzed with identical methods. A total of 2599 hip, 4345 knee, and 1200 shoulder particles were analyzed. The morphologies of the isolated polyethylene particles from the total hip specimens were distinctly different from the total knee and total shoulder particles. The mean equivalent circle diameter (ECD) for hip particles was 0.694 ,m ± 0.005; knee particles measured 1.190 ,m ±0.009; and shoulder particles 1.183 ,m ± 0.017. The ECD was significantly different between hip particles and those from the shoulder and knee. The mean aspect ratio (AR) for the hip particles was 1.626 ± 0.015, compared to the knee particles at 1.935 ± 0.015 and shoulder particles at 2.082 ± 0.033. The AR was statistically different among all three groups. Other descriptors from the ASTM standard, elongation (E), form factor (FF), and roundness (R) were all significantly different among the three groups of joints. This study demonstrates the utility of ASTM F1877-98 in differentiating wear debris particles from different sources. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 475,483, 2002 [source]

Highly Surface-roughened "Flower-like" Silver Nanoparticles for Extremely Sensitive Substrates of Surface-enhanced Raman Scattering

ADVANCED MATERIALS, Issue 45 2009
Hongyan Liang
Abstract Surface-enhanced Raman scattering (SERS) is a new optical spectroscopic analysis technique with potential for highly sensitive detection of molecules. Recently, many efforts have been made to find SERS substrates with high sensitivity and reproducibility. In this Research News article, we provide a focused review on the synthesis of monodispersed silver particles with a novel, highly roughened, "flower-like" morphology by reducing silver nitrate with ascorbic acid in aqueous solutions. The nanometer-scale surface roughness of the particles can provide several hot spots on a single particle, which significantly increases SERS enhancement. The incident polarization-dependent SERS of individual particles is also studied. Although the different "hot spots" on a single particle can have a strong polarization dependency, the total Raman signals from an individual particle usually have no obvious polarization dependency. Moreover, these flower-like silver particles can be measured by SERS with high enhancement several times, which indicates the high stability of the hot spots. Hence, the flower-like silver particles here can serve as highly sensitive and reproducible SERS substrates. [source]

Soil creep and convex-upward velocity profiles: theoretical and experimental investigation of disturbance-driven sediment transport on hillslopes

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2004
Joshua J. Roering
Abstract The movement of unconsolidated materials near the Earth's surface is often driven by disturbances that occur at a range of spatial and temporal scales. The nature of these disturbances ranges from highly variable, such as tree turnover, to periodic and predictable, such as frost heave or creep. To explore the effect of probabilistic disturbances on surface processes, we formulated a granular creep model with analogy to rate process theory (RPT) used for chemical reactions. According to the theory, individual particles must be energized to a height greater than adjacent particles in order for grain dilation and transport to occur. The height of neighbouring particles (which is akin to activation energy in chemical reactions) varies with slope angle such that energy barriers get smaller in the downslope direction as slopes steepen. When slopes approach the friction-limited angle of repose, the height of energy barriers approaches zero and grains ,ow in the absence of disturbance. An exponential function is used to describe the probability distribution of particle excitation height although alternative distributions are possible. We tested model predictions of granular dynamics in an experimental sandpile. In the sandpile, acoustic energy serves as the disturbance agent such that grains dilate and shear in response. Particle velocities are controlled by the frequency of energy pulses that result in grain displacement. Using tracer particles, we observed a convex-upward velocity pro,le near the surface of the sandpile, consistent with predictions of our RPT-based velocity model. In addition, we depth-integrated the velocity model to predict how ,ux rates vary with inclination of the sandpile and observed non-linear ,ux,gradient curves consistent with model predictions. By varying the acoustic energy level in the experimental sandpile, we documented changes in the rate of grain movement; similar changes in modelled velocities were achieved by varying the exponent of the particle excitation probability distribution. The general agreement between observed and modelled granular behaviour in our simple laboratory sandpile supports the utility of RPT-based methods for modelling transport processes (e.g. soil creep, frost heave, and till deformation), thus enabling us to account for the probabilistic nature of disturbances that liberate sediment in natural landscapes. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Consolidation of Particles by Severe Plastic Deformation: Mechanism and Applications in Processing Bulk Ultrafine and Nanostructured Alloys and Composites,

ADVANCED ENGINEERING MATERIALS, Issue 8 2010
Kenong Xia
Severe plastic deformation (SPD) can be used to consolidate particles into bulk ultrafine and nanostructured materials. SPD consolidation relies on plastic deformation of individual particles, rather than diffusion, to achieve bonding and thus can be carried out at much lower temperatures. Using examples of consolidation of Al particles by back pressure equal channel angular pressing (BP-ECAP), it is demonstrated that full consolidation is achieved when the particles are sheared to disrupt the surface oxide layer whereas consolidation is impossible or incomplete in the case of particles sliding over each other. The effects of particle characteristics such as size, shape, strength and surface condition, as well as processing parameters including temperature and back pressure, are discussed to shed light on the mechanism of SPD consolidation. Potential applications of SPD in powder consolidation and processing of bulk ultrafine and nanostructured materials are discussed. [source]

Temporal and spatial monitoring of mobile nanoparticles in a vineyard soil: evidence of nanoaggregate formation

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2010
N. Perdrial
Mechanisms of formation, stabilization, liberation, transport and deposition of nanoparticles and their relationship to contaminant transport remain scarcely investigated in natural porous media. This study investigated nanoparticles mobilized in the pore space of a French vineyard soil by observing mobile soil-derived organic matter (SOM) and minerals in pore fluids over an 8-month monitoring period. Samples were collected in situ and investigated by transmission electron microscopy coupled to electron-dispersive spectroscopy. The main types of nanoparticles transported within the soil were clay, bacteria, SOM and nanoaggregates. Nanometric clay particles were enriched in various metals (Fe, Zn, As and Pb) and organically-derived constituents. Analyses of bacteria showed enrichments in Pb. SOM consisted of small carbon-based particles (<200 nm) with slight enrichments in various metals. The fourth dominant particle type consisted of the association of particles forming organo-mineral nanoaggregates. Based on the study of more than 22 500 individual particles, we propose a schematic interpretation of the evolution of the distribution of particles with depth in a soil profile. The increase of nanoaggregates with depth in the soil seemed to be largely controlled by the ionic strength of soil water and soil hydrodynamics. Seasonal variations in temperature also appear to affect nanoaggregation. Based on the architecture of the nanoaggregates, we propose an improvement of pre-existing models of microaggregation by focusing on early aggregation stages suggesting the importance of bacteria and electrostatic interactions. The process of nanoaggregation can enhance the net reactivity of soil with respect to transported suspended matter, including heavy metals, and can initiate the process of C sequestration. [source]

Anisotropic Optical Properties of Semitransparent Coatings of Gold Nanocaps,

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2006
J. Liu
Abstract An ordered array of cap-shaped gold nanoparticles has been prepared by vapor deposition onto polystyrene nanospheres supported on a glass substrate. The method of fabrication used imparts a significant anisotropy to the geometric and optical properties of the coating. The optical-absorption properties of these deposits have been measured using UV-vis spectrometry and simulated using a code based on the discrete dipole approximation. Because the nanocaps are not interconnected, they interact with incident light as individual particles with a plasmon resonance that depends upon wavelength and the polarization vector of the light. The resulting extinction peaks manifest in the upper visible and near-infrared regions of the electromagnetic spectrum. Surprisingly, varying the angle of incidence of the light (for a fixed polarization) has no effect on the optical properties of individual nanocaps. Calculations show that these phenomena may be readily interpreted in terms of dipole resonances excited across the longitudinal, transverse, and short-transverse directions of the nanocaps. Coatings comprised of arrays of these particles have the potential to serve as angularly and spectrally selective filters. [source]

Highly Surface-roughened "Flower-like" Silver Nanoparticles for Extremely Sensitive Substrates of Surface-enhanced Raman Scattering

Soluble Graphene: Soluble Graphene: Generation of Aqueous Graphene Solutions Aided by a Perylenebisimide-Based Bolaamphiphile (Adv. Mater.

ADVANCED MATERIALS, Issue 42 2009
42/2009)
Single-layer graphene (SLG) can be deposited onto Si/SiO2 substrates from aqueous dispersions using a scalable and quick detergent-based method that takes advantage of the availability and low cost of graphite as a feedstock, report Andreas Hirsch and co-workers on p. 4265. The deposits were analyzed using absorption and Raman spectroscopy and atomic force and optical microscopy. Evaluation of the two-phonon defect-induced Raman peak of individual particles on the substrate was then used to confirm exfoliation into graphene monolayers. [source]

Soluble Graphene: Generation of Aqueous Graphene Solutions Aided by a Perylenebisimide-Based Bolaamphiphile

ADVANCED MATERIALS, Issue 42 2009
Jan M. Englert
Single-layer graphene (SLG) is deposited onto Si/SiO2 substrates from aqueous dispersions using a scalable and quick detergent-based method (see figure). The deposits are analyzed using absorption and Raman spectroscopy and atomic force and optical microscopy. Evaluation of the two-phonon defect-induced Raman peak of individual particles on the substrate is used to confirm exfoliation into graphene monolayers. [source]

Radio-tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by Einstein

HYDROLOGICAL PROCESSES, Issue 3 2001
H. M. Habersack
Abstract Hans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio-tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain-diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain-diameters and 6·1 m or 120 grain-diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D50 of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Neural network approach to stereoscopic correspondence of three-dimensional particle tracking velocimetry

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 6 2008
Achyut Sapkota Student Member
Abstract Particle tracking velocimetry (PTV) is a reliable measurement technique for the quantitative study of fluid flows by observing the motion of the particles seeded in them and is widely used in several industrial applications. The nature of the flow can be precisely observed only if all the three components of the velocity are computed. In 3-D PTV system, particles viewed by two (or more than two) stereoscopic cameras with a parallax have to be correctly paired at every synchronized time step. This is important because the 3-D coordinates of individual particles cannot be computed without the knowledge of the correct stereo correspondence of the particles. In the present work, a neural network,based algorithm has been proposed for the stereoscopic particle pairing process. The correspondence between the particle pairs is modeled as a constrained optimization problem. The constraints are provided on the basis of the epipolar geometry of the particle images and on the basis of the uniqueness of the matched pairs. The results are tested with various standard images. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

An experimental method for determining the effects of strain gradients in a granular material

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 8 2003
Matthew R. Kuhn
Abstract The paper presents an algorithm for use with the discrete element method to study possible strain-gradient effects in granular materials. The algorithm produces an intentionally non-uniform displacement pattern by applying external (body) forces to the particles within a simulated granular assembly. The paper describes a method for adjusting the external forces to attain the intended gross displacement pattern, but while allowing individual particles to be in equilibrium among neighbouring particles. The performance of the algorithm is tested in an example of quasi-static deformation, and the algorithm's performance is measured in three respects. The algorithm is shown to enforce the intended displacement pattern, to allow particles to equilibrate among neighbouring particles, and to produce a smooth distribution of the external forces among particles. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A novel approach to the analysis of distributed shear banding in polymer blends

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003
K. G. W. Pijnenburg
Abstract The toughness of glassy polymers can be enhanced by blending with rubber particles. The consensus is that this toughening is due to massive plastic deformation of the matrix that takes place once the particles have cavitated. Micromechanical studies of regular stackings of particles in a polymer matrix have provided much insight into the localized plastic flow in blends at the microscale of individual particles (or voids, once cavitated). Even some steps towards macroscopic constitutive models have been made. However, at intermediate length scales (i.e. larger than several particles, but smaller than the scale at which the material may be regarded as homogeneous) the situation is unclear. It is this length scale that becomes important around crack tips, for example, where a thorough understanding of the toughening effect has to be derived from. In this paper, we therefore present a novel approach to the analysis of distributed shear banding in polymer,rubber blends. A coarse-grain description, in which much of the morphology is retained but the local shear banding is idealized into ,shear surfaces', will enable us to analyse ensembles with large numbers of particles. The parameters of this model will be validated with results from detailed cell analyses. Copyright © 2003 John Wiley Sons, Ltd. [source]

Cover Picture: Programmable Motion and Separation of Single Magnetic Particles on Patterned Magnetic Surfaces (Adv. Mater.

ADVANCED MATERIALS, Issue 14 2005
14/2005)
Abstract Structured magnetic surfaces enabling programmable motion of single micrometer-sized magnetic particles are reported on p.,1730 by Gunnarsson and co-workers. Patterns of thin-film magnetic elements are tailored to form transport lines with junctions for the separation of individual particles. This method has the potential to improve and generate new applications in biotechnology. The cover shows a schematic of the transportation and separation of magnetic particles functionalized with antibodies capable of selectively capturing the corresponding analytes from a sample. [source]

Simultaneous light and small-angle neutron scattering on aggregating concentrated colloidal suspensions

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2003
Sara Romer
A new sample environment has been developed in order to perform light and small-angle neutron scattering (SANS) simultaneously on colloidal systems. The combination of SANS and diffusing wave spectroscopy (DWS) is of particular use in the high-concentration regime. DWS provides information on the local dynamic properties of the individual particles, whereas SANS gives access to the structural properties on similar length scales. The combination of both methods thus allows one to obtain structural and dynamic information over a very large range of length and time scales. Using this new setup, the onset of aggregation and the sol,gel transition in concentrated destabilized polystyrene sphere suspensions have been investigated. At the gel point, a dramatic change of the particle dynamics from diffusion to a subdiffusive arrested motion is observed. However, while the DWS measurements indicate that dramatic changes in the local dynamics occur over a long period, the SANS pattern quickly reaches its final appearance. The SANS experiments thus indicate that a fluid-like structure is arrested in the course of the gel formation. The data are found to be in good qualitative agreement with computer simulations. [source]

Synthesis and properties of organic/inorganic hybrid nanoparticles prepared using atom transfer radical polymerization

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Tzong-Liu Wang
Abstract The synthesis of organic/inorganic hybrid materials was conducted by atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate (MMA) from the surface of silica colloids. Colloidal initiators were prepared by the functionalization of silica nanoparticles with (3-(2-bromoisobutyryl)propyl) dimethylethoxysilane (BIDS). Well-defined polymer chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined outer polystyrene (PS) or poly(methyl methacrylate) (PMMA) layer. Fourier transform infrared (FTIR) and solid state 13C and 29Si-NMR spectroscopy confirmed the successful modification of nanosilica surfaces. Subsequent grafting of polymers on silica surfaces by ATRP was also performed with success based on FTIR and NMR data. Scanning electron microscopy (SEM) and silicon mapping showed both hybrid materials were homogeneous dispersion systems. Energy dispersive X-ray spectrometer (EDS) analysis indicated that the BIDS initiator was covalently attached on surfaces of silica nanoparticles and ATRP of styrene and MMA were accomplished. Thermogravimetric analysis (TGA) results displayed higher thermal stabilities for both nanohybrids in comparison with the linear-type vinyl polymers. Contact angle measurements revealed the nanomaterials character for both silica-based hybrid materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Electrostatic energies and forces computed without explicit interparticle interactions: A linear time complexity formulation

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2005
Robert J. Petrella
Abstract A rapid method for the calculation of the electrostatic energy of a system without a cutoff is described in which the computational time grows linearly with the number of particles or charges. The inverse of the distance is approximated as a polynomial, which is then transformed into a function whose terms involve individual particles, instead of particle pairs, by a partitioning of the double sum. In this way, the electrostatic energy that is determined by the interparticle interactions is obtained without explicit calculation of these interactions. For systems of positive charges positioned on a face-centered cubic lattice, the calculation of the energy by the new method is shown to be faster than the calculation of the exact energy, in many cases by an order of magnitude, and to be accurate to within 1,2%. The application of this method to increase the accuracy of conventional truncation-based calculations in condensed-phase systems is also demonstrated by combining the approximated long-range electrostatic interactions with the exact short-range interactions in a "hybrid" calculation. For a 20-Å sphere of water molecules, the forces are shown to be six times as accurate using this hybrid method as those calculated with conventional truncation of the electrostatic energy function at 12 Å. This is accomplished with a slight increase in speed, and with a sevenfold increase in speed relative to the exact all-pair calculation. Structures minimized with the hybrid function are shown to be closer to structures minimized with an exact all-pair electrostatic energy function than are those minimized with a conventional 13-Å cutoff-based electrostatic energy function. Comparison of the energies and forces calculated with the exact method illustrate that the absolute errors obtained with standard truncation can be very large. The extension of the current method to other pairwise functions as well as to multibody functions, is described. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 755,787, 2005 [source]

Characterization of combustion-derived individual fine particulates by computer-controlled scanning electron microscopy

AICHE JOURNAL, Issue 11 2009
Lian Zhang
Abstract Particulate matter (PM) emission from the combustion of solid fuels potentially poses a severe threat to the environment. In this article, a novel approach was developed to examine the properties of individual particles in PM. With this method, PM emitted from combustion was first size-segregated. Subsequently, each size was characterized by computer-controlled scanning electron microscopy (CCSEM) for both bulk property and single particle analysis. Combustion of bituminous coal, dried sewage sludge (DSS) and their mixture were conducted at 1200°C in a laboratory-scale drop tube furnace. Three individual sizes smaller than 2.5 ,m were investigated. The results indicate that a prior size-segregation can greatly minimize the particle size contrast and phase contrast on the backscattered images during CCSEM analysis. Consequently, high accuracy can be achieved for quantifying the sub-micron particles and their inherent volatile metals. Regarding the PM properties as attained, concentrations of volatile metals including Na, K, and Zn have a negative relationship with particle size; they are enriched in the smallest particles around 0.11 ,m as studied here. Strong interactions can occur during the cofiring of coal and DSS, leading to the distinct properties of PM emitted from cofiring. The method developed here and results attained from it are helpful for management of the risks relating to PM emission during coal-fired boilers. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Heat conduction in granular materials

AICHE JOURNAL, Issue 5 2001
Watson L. Vargas
Heat transfer in particulate systems is important to a vast array of industries, yet is poorly understood even in the simplest case,conduction through the solid phase. This is due in part to the stress and contact heterogeneities inherent to these systems. Heat conduction in a packet bed of cylinders is investigated both experimentally and computationally. A novel model is developed based on the Discrete Element Method, which not only sheds light on fundamental issues in heat conduction in particles, but also provides a valuable test bed for existing theories. By explicitly modeling individual particles within the bulk material, bed heterogeneities are directly included, and dynamic temperature distributions are obtained at the particle level. Comparison with experiments shows that this model yields a quantitatively accurate temperature field without the need for adjustable parameters or detailed microstructural information. This simple system may also provide insight into such phenomena as reactor hot spot formation and spontaneous combustion of bulk reactive materials. [source]

Maintenance of nonviral vector particle size during the freezing step of the lyophilization process is insufficient for preservation of activity: Insight from other structural indicators

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2001
Marion d.C. Molina
Abstract The instability of nonviral vectors as liquid formulations has stimulated considerable interest in developing dehydrated formulations that would be resistant to shipping stresses and could be stored at room temperature. Recently, we reported that high sucrose/DNA ratios are capable of maintaining particle size during the freezing step of the lyophilization process and we suggested that the separation of individual particles within sugar matrices is responsible for the reported protection of nonviral vectors during the freezing step of a typical lyophilization protocol. The purpose of this study was to extend these observations to other nonviral vectors that incorporate different cationic components. Cationic lipid-based complexes composed of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), with helper lipid cholesterol (Chol) or dioleoylphosphatidyl-ethanolamine (DOPE), showed similar protection by sucrose. Formulations of a polyethylenimine (PEI)-based vector required much higher excipient/DNA ratios for size protection compared with protamine- and lipid-based vectors. At low sucrose/DNA ratios, zeta potentials for all complexes were significantly lowered during freezing. Similar results were obtained at high sucrose/DNA ratios, except for DOTAP,DOPE-containing vectors which maintained zeta potential values comparable to unfrozen controls. The changes in zeta potential values indicate that complexes are altered during freezing despite the maintenance of particle size as determined by light scattering. Furthermore, these changes might explain the observed reduction in transfection activity and provide new information about the effects of physicochemical changes of nonviral vectors during the freezing step of lyophilization. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1445,1455, 2001 [source]

MECHANICAL CHARACTERIZATION OF SHREDDED WHEAT

JOURNAL OF TEXTURE STUDIES, Issue 5 2008
J.B. LAURINDO
ABSTRACT The purpose of the study was to evaluate a methodology for mechanical characterization of brittle foods with strong anisotropy. Spoon-sized pieces of three commercial brands of dry shredded wheat were chosen for the demonstration. They were compressed along their three principal axes, individually and grouped in the same orientation. The force-displacement curves in the three directions were all irregular and irreproducible but had discernible features characteristic of the specimen's orientation. When tested as constrained groups, these features could change, depending on the compression direction, reflecting on the contribution of the broken structure's remnants to the specimen's mechanical resistance. The assemblies' force-displacement curves were all smoother than those of the individual particles, a result of the "averaging effect." The overall force level could not be predicted from the number of pieces because of differences in the specimens' post-failure response to added deformation. The jaggedness of the normalized (dimensionless) force oscillations record was quantified in terms of an apparent Kolmogorov (fractal) dimension, determined with the box counting algorithm. Its value strongly depended on the smoothing model's goodness fit if the fit was too close, but not if it only captured the general shape of the force-displacement curve. PRACTICAL APPLICATIONS Despite the irregular and irreproducible mechanical signature of shredded wheat and the dependence on the specimens' orientation, it is still possible to characterize the products' mechanical properties in a way that distinguishes between their overall strength and brittleness. The described method could help to quantify textural differences between these and other brittle food products, and probably identify the conditions under which crunchiness would be maintained or lost. [source]

Analysis of Particle Size Distribution by Particle Tracking

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2004
Christiane Finder
Abstract Particle tracking is performed using a combination of dark field or fluorescence video microscopy with automatic image analysis. The optical detection together with the image analysis software allows for the time resolved localization of individual particles with diameters between 100 and 1000,nm. Observation of their Brownian motion over a set of time intervals leads to the determination of their mean square displacements under the given room temperature and viscosity. Hereby, the radii of a set of particles visible within a given optical frame are derived simultaneously. Rapid data analysis leads to reliable particle size histograms. The applicability of this method is demonstrated on polystyrene latices and PMMA nanospheres with radii between 51,nm and 202,nm. [source]

Direct Numerical Simulation of Dense Gas-Solid Two-Phase Flows

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2000
Y. Zhulin
Based on Newton's law and the classical physical laws, Eulerian and Lagrangian methods are respectively used to deal with gas-field and discrete particles. The three-dimensional viscid air-field and three-dimensional discrete particle field are solved in each time step ,t. Collision and friction between individual particles are taken into account when establishing the mathematical models, including individual particle diameter, density, stiffness and friction coefficient. Particles mixing in ball mills, particles dropping from hoppers, and particles fluidizing in fluidized beds are used as examples of the simulations. Selected simulated results are compared to experimental results. [source]

Nanoparticles of [Fe(NH2 -trz)3]Br2,3,H2O (NH2 -trz=2-Amino-1,2,4-triazole) Prepared by the Reverse Micelle Technique: Influence of Particle and Coherent Domain Sizes on Spin-Crossover Properties

CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2009
Thibaut Forestier Dr.
Abstract By changing the surfactant/water ratio, nanoparticles of the iron(II) spin crossover material, [Fe(NH2 -trz)3]Br2,3,H2O (with NH2 -trz=4-amino-1,2,4-triazole), have been synthesised from 1,,m down to 30,nm (see figure). Magnetic and reflectivity experiments indicate that the critical size for observing a thermal hysteresis in this 1D polymer family is around 50,nm, and powder X-ray diffraction shows that particles of about 30,nm are constituted by about one coherent domain. This paper describes the synthesis of iron(II) spin-crossover nanoparticles prepared by the reverse micelle technique by using the non-ionic surfactant Lauropal (Ifralan D0205) from the polyoxyethylenic family. By changing the surfactant/water ratio, the size of the particles of [Fe(NH2 -trz)3]Br2,3H2O (with NH2trz=4-amino-1,2,4-triazole) can be controlled. On the macroscopic scale this complex exhibits cooperative thermal spin crossovers at 305 and 320,K. We find that when the size is reduced down to 50,nm, the spin transition becomes gradual and no hysteresis can be detected. For our data it seems that the critical size, for which the existence of a thermal hysteresis can be detected, is around 50,nm. Interestingly, the change of the particle size induces almost no change in the temperature of the thermal spin transition. A systematic determination of coherent domain size carried out on the nanoparticles by powder X-ray diffraction indicates that at approximately 30,nm individual particles consist of one coherent domain. [source]

Back-scattered electron imaging and elemental microanalysis of retrieved bone tissue following maxillary sinus floor augmentation with calcium sulphate

CLINICAL ORAL IMPLANTS RESEARCH, Issue 8 2008
Nicola Slater
Abstract Objectives: To investigate the presence and composition of residual bone graft substitute material in bone biopsies from the maxillary sinus of human subjects, following augmentation with calcium sulphate (CaS). Material and methods: Bone cores were harvested from the maxillary sinus of patients who had undergone a sinus lift procedure using CaS G170 granules 4 months after the initial surgery. Samples from seven patients, which contained residual biomaterial particles, were examined by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy was used to determine the composition of the remaining bone graft substitute material. Results: Residual graft material occurred in isolated areas surrounded by bone and consisted of individual particles up to 1 mm in length and smaller spherical granules. On the basis of 187 separate point analyses, the residual material was divided into three categories (A, B and C) consisting of: A, mainly CaS (S/P atomic% ratio ,2.41); B, a heterogeneous mixture of CaS and calcium phosphate (S/P=0.11,2.4) and C, mainly calcium phosphate (S/P,0.11; C), which had a mean Ca : P ratio of 1.63±0.2, consistent with Ca-deficient hydroxyapatite. Linescans and elemental maps showed that type C material was present in areas which appeared dense and surrounded, or were adjacent to, more granular CaS-containing material, and also occurred as spherical particles. The latter could be disintegrating calcium phosphate in the final stages of the resorption process. Conclusions: CaS resorption in the human maxillary sinus is accompanied by CaP precipitation which may contribute to its biocompatibility and rapid replacement by bone. [source]