Showing papers on "Particle published in 2000"
TL;DR: In this article, the authors describe an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and demonstrate quantitative mea surement capability for a laboratory-generated pure component NH4 NO3 aerosol.
Abstract: The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition We describe here an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative mea surement capability for a laboratory-generated pure component NH4 NO3 aerosol The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques A unique aerodynamic aerosol inlet (developed at the University of Minnesota) focuses particles into a narrow beam and efficiently transports them into vacuum where aerodynamic particle size is determined via a particle time-of-flight (TOF) measurement Time-resolved particle mass detection is performed mass spectrometrically following particle flash
1,357 citations
TL;DR: The hypothesis that ultrafine particles are causally involved in adverse responses seen in sensitive humans is based on several studies summarized in this brief review, and the studies performed so far support the ultrafine particle hypothesis.
Abstract: Introduction and Objectives: Recent epidemiological studies have shown an association between increased particulate urban air pollution and adverse health effects on susceptible parts of the population, in particular the elderly with pre-existing respiratory and cardiovascular diseases. Urban particles consist of three modes: ultrafine particles, accumulation mode particles (which together form the fine particle mode) and coarse mode particles. Ultrafine particles (those of <0.1 μm diameter) contribute very little to the overall mass, but are very high in number, which in episodic events can reach several hundred thousand/cm3 in the urban air. The hypothesis that ultrafine particles are causally involved in adverse responses seen in sensitive humans is based on several studies summarized in this brief review. Methods and Results: Studies on rodents demonstrate that ultrafine particles administered to the lung cause a greater inflammatory response than do larger particles, per given mass. Surface properties (surface chemistry) appear to play an important role in ultrafine particle toxicity. Contributing to the effects of ultrafine particles is their very high size-specific deposition when inhaled as singlet ultrafine particles rather than as aggregated particles. It appears also that ultrafine particles, after deposition in the lung, largely escape alveolar macrophage surveillance and gain access to the pulmonary interstitium. Inhaled low doses of carbonaceous ultrafine particles can cause mild pulmonary inflammation in rodents after exposure for 6 h. Old age and a compromised/sensitized respiratory tract in rodents can increase their susceptibility to the inflammatory effects of ultrafine particles significantly, and it appears that the aged organism is at a higher risk of oxidative stress induced lung injury from these particles, compared with the young organism. Results also show that ultrafine particle effects can be significantly enhanced by a gaseous co-pollutant such as ozone. Conclusions: The studies performed so far support the ultrafine particle hypothesis. Additional studies are necessary to evaluate mechanistic pathways of responses.
1,314 citations
TL;DR: In this article, the influence of the wettability of spherical, nanometer-sized silica particles on the type and stability of water−toluene emulsions is described.
Abstract: A systematic investigation into the influence of the wettability of spherical, nanometer-sized silica particles on the type and stability of water−toluene emulsions is described. The particles rang...
1,229 citations
TL;DR: In this article, an updated detailed chemical kinetic model for soot formation is presented, which combines recent developments in gas phase reactions, aromatic chemistry, soot particle coagulation, and particle aggregation, and develops a new submodel for surface growth.
1,083 citations
IBM1
TL;DR: In this paper, the authors examined the consequence of spin-current-induced angular momentum deposition in a monodomain Stoner-Wohlfarth magnetic body using the Landau-Lifshitz-Gilbert equation with a phenomenological damping coefficient.
Abstract: I examined the consequence of a spin-current-induced angular momentum deposition in a monodomain Stoner-Wohlfarth magnetic body. The magnetic dynamics of the particle are modeled using the Landau-Lifshitz-Gilbert equation with a phenomenological damping coefficient $\ensuremath{\alpha}.$ Two magnetic potential landscapes are studied in detail: One uniaxial, the other uniaxial in combination with an easy-plane potential term that could be used to model a thin-film geometry with demagnetization. Quantitative predictions are obtained for comparison with experiments.
1,075 citations
TL;DR: A review of the current state of organic aerosol sampling, analysis, and simulation, examines the limitations of current technology, and presents prospects for the future is provided in this article, where the emphasis is on distilling findings from recent atmospheric, smog chamber, and theoretical studies to provide a coherent picture of what has been accomplished, especially during the last five years.
967 citations
TL;DR: In this paper, a laser ablation of a metal silver plate in an aqueous solution of sodium dodecyl sulfate, C12H25OSO3Na, was shown to be essentially the same as that of silver nanoparticles chemically prepared in a solution.
Abstract: Silver nanoparticles were produced by laser ablation of a metal silver plate in an aqueous solution of sodium dodecyl sulfate, C12H25OSO3Na. The absorption spectrum of the silver nanoparticles is found to be essentially the same as that of silver nanoparticles chemically prepared in a solution. The size distribution of the nanoparticles measured by an electron microscope shifts to a smaller size with increase in the concentration of sodium dodecyl sulfate and with a decrease in the irradiation laser power. These findings are explained by a scheme that the nanoparticles are formed via rapid formation of an embryonic silver particle and a consecutive slow particle growth in competition with termination of the growth due to SDS coating on the particle.
768 citations
TL;DR: The real-space dynamics in a model system of colloidal hard spheres was studied by means of time-resolved fluorescence confocal scanning microscopy for direct experimental evidence for the presence of dynamical heterogeneities in a dense liquid.
Abstract: The real-space dynamics in a model system of colloidal hard spheres was studied by means of time-resolved fluorescence confocal scanning microscopy. Direct experimental evidence for the presence of dynamical heterogeneities in a dense liquid was obtained from an analysis of particle trajectories in two-dimensional slices of the bulk sample. These heterogeneities manifest themselves as a non-Gaussian probability distribution of particle displacements and also affect the onset of long-time diffusive behavior.
715 citations
TL;DR: This article is devoted to an overview, comparison and discussion of recent results (both theoretical and experimental) about lateral capillary forces, when the contact of particles or other bodies with a fluid phase boundary causes perturbations in the interfacial shape.
655 citations
TL;DR: In this article, a high performance LiCoO2 cathode was fabricated by a sol−gel coating of Al2O3 to the particle surfaces and subsequent heat treatment at 600 °C for 3 h.
Abstract: A high-performance LiCoO2 cathode was successively fabricated by a sol−gel coating of Al2O3 to the LiCoO2 particle surfaces and subsequent heat treatment at 600 °C for 3 h. Unlike bare LiCoO2, the ...
639 citations
TL;DR: Results from an aerosol dynamics model with a ternary nucleation scheme indicate that nucleation in the troposphere should be ubiquitous, and yield a reservoir of thermodynamically stable clusters 1–3 nm in size.
Abstract: The formation of new atmospheric particles with diameters of 3–10 nm has been observed at a variety of altitudes and locations. Such aerosol particles have the potential to grow into cloud condensation nuclei, thus affecting cloud formation as well as the global radiation budget. In some cases, the observed formation rates of new particles have been adequately explained by binary nucleation, involving water and sulphuric acid1, but in certain locations—particularly those within the marine boundary layer1,2 and at continental sites1,3—observed ambient nucleation rates exceed those predicted by the binary scheme. In these locations, ambient sulphuric acid (H2SO4) levels are typically lower than required for binary nucleation1, but are sufficient for ternary nucleation4 (sulphuric acid–ammonia–water). Here we present results from an aerosol dynamics model with a ternary nucleation scheme which indicate that nucleation in the troposphere should be ubiquitous, and yield a reservoir of thermodynamically stable clusters 1–3 nm in size. We suggest that the growth of these clusters to a detectable size (> 3 nm particle diameter) is restricted by the availability of condensable vapour. Observations of atmospheric particle formation and growth from a continental and a coastal site support this hypothesis, indicating that a growth process including ternary nucleation is likely to be responsible for the formation of cloud condensation nuclei.
TL;DR: It is shown that light affects the assembly processes, and how to produce patterns using electrophoretic deposition in the presence of an ultraviolet (UV) illumination motif is demonstrated.
Abstract: The production of materials with micrometre- and submicrometre-scale patterns is of importance in a range of applications, such as photonic materials, high-density magnetic data storage devices, microchip reactors and biosensors. One method of preparing such structures is through the assembly of colloidal particles. Micropatterned colloidal assemblies have been produced with lithographically patterned electrodes or micromoulds. Here we describe a different method that combines the well-known photochemical sensitivity of semiconductors with electric-field-induced assembly to create ordered arrays of micrometre-sized colloidal particles with tunable patterns. We show that light affects the assembly processes, and demonstrate how to produce patterns using electrophoretic deposition in the presence of an ultraviolet (UV) illumination motif. The distribution of current across an indium tin oxide (ITO) electrode can be altered by varying the illumination intensity: during the deposition process, this causes colloidal particles to be swept from darkened areas into lighted regions. Illumination also assists in immobilizing the particles on the electrode surface. Although the details of these processes are not well understood, the patterning effects of the UV light are discussed in terms of alterations in the current density that affects particle assembly on an ITO electrode.
TL;DR: In this article, a review of DLS techniques for studying sizes and shapes of nanoparticles in liquids is presented. But the authors focus on the time fluctuations in the intensity of light scattered by the particle dispersion.
Abstract: Dynamic light scattering (DLS) techniques for studying sizes and shapes of nanoparticles in liquids are reviewed. In photon correlation spectroscopy (PCS), the time fluctuations in the intensity of light scattered by the particle dispersion are monitored. For dilute dispersions of spherical nanoparticles, the decay rate of the time autocorrelation function of these intensity fluctuations is used to directly measure the particle translational diffusion coefficient, which is in turn related to the particle hydrodynamic radius. For a spherical particle, the hydrodynamic radius is essentially the same as the geometric particle radius (including any possible solvation layers). PCS is one of the most commonly used methods for measuring radii of submicron size particles in liquid dispersions. Depolarized Fabry-Perot interferometry (FPI) is a less common dynamic light scattering technique that is applicable to optically anisotropic nanoparticles. In FPI the frequency broadening of laser light scattered by the particles is analyzed. This broadening is proportional to the particle rotational diffusion coefficient, which is in turn related to the particle dimensions. The translational diffusion coefficient measured by PCS and the rotational diffusion coefficient measured by depolarized FPI may be combined to obtain the dimensions of non-spherical particles. DLS studies of liquid dispersions of nanometer-sized oligonucleotides in a water-based buffer are used as examples.
TL;DR: The presented carrier of colloidal lipid particles with improved payloads and enhanced storage stability was investigated and adds additional benefits to the well-known opportunities of conventional SLN and is suited for topical use.
TL;DR: A novel code system, TRiP, dedicated to the planning of radiotherapy with energetic ions, in particular 12C, designed to cooperate with three-dimensional active dose shaping devices like the GSI raster scan system is described.
Abstract: We describe a novel code system, TRiP, dedicated to the planning of radiotherapy with energetic ions, in particular 12C. The software is designed to cooperate with three-dimensional active dose shaping devices like the GSI raster scan system. This unique beam delivery system allows us to select any combination from a list of 253 individual beam energies, 7 different beam spot sizes and 15 intensity levels. The software includes a beam model adapted to and verified for carbon ions. Inverse planning techniques are implemented in order to obtain a uniform target dose distribution from clinical input data, i.e. CT images and patient contours. This implies the automatic generation of intensity modulated fields of heavy ions with as many as 40 000 raster points, where each point corresponds to a specific beam position, energy and particle fluence. This set of data is directly passed to the beam delivery and control system. The treatment planning code has been in clinical use since the start of the GSI pilot project in December 1997. Forty-eight patients have been successfully planned and treated.
TL;DR: In this paper, a survey on nano-particles and nanocomposites and the importance of small particle sizes on their optical properties is presented, focusing on results from a laboratory concerning nanocom composites with extremely high or low refractive indices and dichroic nanocomposition and their application in bicolored liquid crystal displays.
Abstract: Upon transmission of visible light through composites comprising of a transparent polymer matrix with embedded particles, the intensity loss by scattering is substantially reduced for particle diameters below 50-100 nm (nanoparticles, nanosized particles). As a consequence, related materials (nanocomposites) have found particular interest in optical studies. The first part of this article deals with a historical survey on nano-particles and nanocomposites and the importance of small particle sizes on their optical properties. The second part focuses on results from our laboratory concerning nanocomposites with extremely high or low refractive indices and dichroic nanocomposites and their application in bicolored liquid crystal displays (LCD). The inorganic colloids required for these studies (lead sulfide, iron sulfides, gold, and silver) were prepared in situ in presence of a polymer or isolated as redispersable metal colloids modified at the surface with a self-assembled monolayer (SAM) of an alkanethiol. The nanocomposites themselves were finally obtained by coprecipitation, spin coating, solvent casting or melt extrusion, with poly(ethylene oxide), gelatin, poly(vinyl alcohol) and polyethylene as matrix polymers.
TL;DR: The diffusive behavior of colloidal particles which are confined to one-dimensional channels generated by scanning optical tweezers is studied and the mean-square displacement is found to scale as t(1/2), which is expected for systems where single-file diffusion occurs.
Abstract: Single-file diffusion, prevalent in many processes, refers to the restricted motion of interacting particles in narrow micropores with the mutual passage excluded. A single-filing system was developed by confining colloidal spheres in one-dimensional circular channels of micrometer scale. Optical video microscopy study shows evidence that the particle self-diffusion is non-Fickian for long periods of time. In particular, the distribution of particle displacement is a Gaussian function.
TL;DR: In this article, a theoretical expression for the depth of the two-dimensional measurement plane is derived and it is shown that the particle concentration must be chosen judiciously in order to balance the desired spatial resolution and signal-to-noise ratio of the particle-image field.
Abstract: In particle image velocimetry experiments where optical access is limited or in microscale geometries, it may be desirable to illuminate the entire test section with a volume of light, as opposed to a two-dimensional sheet of light. With volume illumination, the depth of the measurement plane must be defined by the focusing characteristics of the recording optics. A theoretical expression for the depth of the two-dimensional measurement plane is derived and it is shown to agree well with experimental observations. Unfocused particle images, which lie outside the measurement plane, create background noise that decreases the signal-to-noise ratio of the particle-image fields. Results show that the particle concentration must be chosen judiciously in order to balance the desired spatial resolution and signal-to-noise ratio of the particle-image field.
TL;DR: Microstructured particles were synthesized by growing colloidal crystals in aqueous droplets suspended on fluorinated oil to allow control of particle size and shape from spheres through ellipsoids to toroids by varying the droplet composition.
Abstract: Microstructured particles were synthesized by growing colloidal crystals in aqueous droplets suspended on fluorinated oil. The droplets template highly ordered and smooth particle assemblies, which diffract light and have remarkable structural stability. The method allows control of particle size and shape from spheres through ellipsoids to toroids by varying the droplet composition. Cocrystallization in colloidal mixtures yields anisotropic particles of organic and inorganic materials that can, for example, be oriented and turned over by magnetic fields. The results open the way to controllable formation of a wide variety of microstructures.
TL;DR: In this article, the authors extended the theory of microscopic particle image velocimetry (PIV) to encompass this situation and derived an equation for a particle image intensity function that yields image diameter and intensity as a function of distance from the object plane.
Abstract: In microscopic particle image velocimetry (μPIV) the entire volume of a flowfield is illuminated, resulting in all of the particles in the field of view contributing to the image, either by forming discrete particle images or contributing to a background glow. The theory of PIV is expanded to encompass this situation. Equations are derived for a particle image intensity function that yields image diameter and intensity as a function of distance from the object plane, as well as an equation for a new quantity, termed particle visibility. The effect of changing experimental parameters is discussed. Next, the contribution of out-of-focus particles to the correlation function is addressed. A weighting function that can be used to calculate either velocity measurement bias or the distance from the object plane beyond which particles no longer significantly contribute to the correlation function is derived. A new experimental parameter, the depth of correlation, is then introduced, and its dependence on experimental parameters is discussed.
TL;DR: A mechanism for attraction which is based on nonuniform wetting causing an irregular shape of the particle meniscus is proposed, including the cluster dissolution caused by addition of detergent to the subphase and the formation of linear aggregates.
Abstract: Recent observations of charged colloidal particles trapped at the air-water interface revealed long-range interparticle attractive forces, not accounted for by the standard theories of colloidal interactions. We propose a mechanism for attraction which is based on nonuniform wetting causing an irregular shape of the particle meniscus. The excess water surface area created by these distortions can be minimized when two adjacent particles assume an optimum relative orientation and distance. Typically, for spheres with diameter of 1 mm at an interparticle distance of 2 mm, deviations from the ideal contact line by as little as 50 nm result in an interaction energy of the order of 10(4)kT. Roughness-induced capillarity explains the experimental findings, including the cluster dissolution caused by addition of detergent to the subphase and the formation of linear aggregates. This kind of interaction should also be of importance in particle-stabilized foams and emulsions.
TL;DR: A suspension of plate-like colloids that shows isotropic, nematic and columnar phases on increasing the particle concentration is described, finding that the columnar two-dimensional crystal persists for a polydispersity of up to 25%, with a cross-over to smectic-like ordering at very high particle concentrations.
Abstract: Colloidal suspensions that form periodic self-assembling structures on sub-micrometre scales are of potential technological interest; for example, three-dimensional arrangements of spheres in colloidal crystals might serve as photonic materials, intended to manipulate light. Colloidal particles with non-spherical shapes (such as rods and plates) are of particular interest because of their ability to form liquid crystals. Nematic liquid crystals possess orientational order; smectic and columnar liquid crystals additionally exhibit positional order (in one or two dimensions respectively). However, such positional ordering may be inhibited in polydisperse colloidal suspensions. Here we describe a suspension of plate-like colloids that shows isotropic, nematic and columnar phases on increasing the particle concentration. We find that the columnar two-dimensional crystal persists for a polydispersity of up to 25%, with a cross-over to smectic-like ordering at very high particle concentrations. Our results imply that liquid crystalline order in synthetic mesoscopic materials may be easier to achieve than previously thought.
TL;DR: It was found that a linear relationship between the degradation rate and particle size existed, with the larger particles degrading fastest, and the rate of polymer degradation was found to increase with increasing incubation temperature.
TL;DR: In this article, a simple, fast, and flexible technique to measure optical scattering spectra of individual metallic nanoparticles was developed to measure the effect of particle diameter on the dephasing time of the particle plasmon resonance in gold nanoparticles.
Abstract: We have developed a simple, fast, and flexible technique to measure optical scattering spectra of individual metallic nanoparticles. The particles are placed in an evanescent field produced by total internal reflection of light from a halogen lamp in a glass prism. The light scattered by individual particles is collected using a conventional microscope and is spectrally analyzed by a nitrogen-cooled charge-coupled-device array coupled to a spectrometer. This technique is employed to measure the effect of particle diameter on the dephasing time of the particle plasmon resonance in gold nanoparticles. We also demonstrate the use of this technique for measurements in liquids, which is important for the potential application of particle plasmons in chemical or biological nanosensors.
Book•
31 May 2000
TL;DR: In this article, the background information of particle counting and scattering is discussed. But the focus is on the counting and scaling of the number of particles and not on the light scattering process.
Abstract: Preface. Acknowledgements. 1. Particle Characterization - An Overview. 2. Light Scattering - The Background Information. 3. Laser Diffraction - Sizing from Nanometers to Millimeters. 4. Optical Particle Counting - Counting and Sizing. 5. Photon Correlation Spectroscopy - Submicron Particle Characterization. 6. Electrophoretic Light Scattering - Zeta Potential Measurement. Appendices. Author Index. Subject Index.
TL;DR: A novel, sensitive electrochemical immunoassay has been developed using a colloidal gold label that, after oxidative gold metal dissolution in an acidic solution, was indirectly determined by anodic stripping voltammetry (ASV) at a single-use carbon-based screen-printed electrode (SPE).
Abstract: A novel, sensitive electrochemical immunoassay has been developed using a colloidal gold label that, after oxidative gold metal dissolution in an acidic solution, was indirectly determined by anodic stripping voltammetry (ASV) at a single-use carbon-based screen-printed electrode (SPE). The use of disposable electrodes allows for simplified measurement in 35 μL of solution. The method was evaluated for a noncompetitive heterogeneous immunoassay of an immunoglobulin G (IgG) and a concentration as low as 3 × 10-12 M was determined, which is competitive with colorimetric ELISA or with immunoassays based on fluorescent europium chelate labels. The high performance of the method is related to the sensitive ASV determination of gold(III) at a SPE (detection limit of 5 × 10-9 M) and to the release of a large number of gold(III) ions from each gold particle anchored on the immunocomplex (e.g., 1.7 × 105 gold atoms are theoretically contained in a 18-nm spherical gold particle).
TL;DR: The rheological data of weakly attractive colloidal particles are shown to exhibit a surprising scaling behavior as the particle volume fraction, straight phi, or the strength of the attractive interparticle interaction, U, are varied.
Abstract: The rheological data of weakly attractive colloidal particles are shown to exhibit a surprising scaling behavior as the particle volume fraction, straight phi, or the strength of the attractive interparticle interaction, U, are varied. There is a critical onset of a solid network as either straight phi or U increase above critical values. For all solidlike samples, both the frequency-dependent linear viscoelastic moduli, and the strain-rate dependent stress can be scaled onto universal master curves. A model of a solid network interspersed in a background fluid qualitatively accounts for this behavior.
TL;DR: In this article, a simulation of gas/particle flow behavior in the riser section of a circulating fluidized bed (CFB) was simulated using a computational fluid dynamics (CFD) package by Fluent.
TL;DR: In this article, a model describing the evolution of microstructure has been developed for WC-Co coatings in high velocity oxy-fuel thermal spraying of conventional and nanocomposite powders which contain WC grains in the size range 2-5μm and 70-250nm, respectively.