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Single Particles (single + particle)
Selected AbstractsHighly Surface-roughened "Flower-like" Silver Nanoparticles for Extremely Sensitive Substrates of Surface-enhanced Raman ScatteringADVANCED MATERIALS, Issue 45 2009Hongyan 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] Particulate flow simulations using lubrication theory solution enrichmentINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2003G. J. Wagner Abstract A technique for the numerical simulation of suspensions of particles in fluid based on the extended finite element method (X-FEM) is developed. In this method, the particle surfaces need not conform to the finite element boundaries, so that moving particles can be simulated without remeshing. The finite element basis is enriched with the Stokes flow solution for flow past a single particle and the lubrication theory solution for flow between particles. The latter enrichment allows the simulation of particles that come arbitrarily close together without refining the mesh in the gap between them. Example problems illustrating both types of enrichment are shown, along with a study of a 50% solution in channel flow. Copyright © 2003 John Wiley & Sons, Ltd. [source] HEAT TRANSFER TO CANNED PARTICULATES IN HIGH-VISCOSITY NEWTONIAN FLUIDS DURING AGITATION PROCESSINGJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 6 2006YANG MENG ABSTRACT Heat transfer to canned particulate-laden Newtonian high-viscous fluids (Nylon particles suspended in aqueous glycerin solution [40, 60, 80, 90 and 100%, v/v] and motor oil [85W140]) during end-over-end rotation was studied in a pilot-scale, full water-immersion single-cage rotary retort. Computations of conventional fluid-to-particle heat transfer coefficient (hfp) and overall heat transfer coefficient (U) were successful with multiple particles for an entire range of viscosity, but the predicted particle lethality was underestimated. With a single particle in the can, hfpand U calculations were successful only for low-viscosity fluids (40 and 60% glycerin solutions), but again resulted in underestimation of particle lethality. Apparent heat transfer coefficients (hap) between retort and particle surface and apparent overall heat transfer coefficient (Ua) were also evaluated, and this methodology worked well for all cases. Further, the particle lethality predicted using hap better matched the measured values. With a single particle in the can, the associated hap was significantly (P < 0.05) influenced by rotation speed, retort temperature, liquid viscosity, particle material and can size. Ua was significantly (P < 0.05) influenced by rotation speed and liquid viscosity. The effects of headspace, radius of rotation and particle size were not significant (P > 0.05) on hap and Ua values. [source] Phase Separation and Organisation of Colloidal Spheres Suspended in Sheared Lyotropic Liquid-Crystalline PolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 11 2005Shanju Zhang Abstract Summary: Organisation behaviours of spherical particles suspended in sheared, lyotropic, liquid-crystalline polymer solutions have been investigated using polarizing optical microscopy. We find that in a nematic phase the particles phase separate and adopt anisotropic chain-like structures along the director. An earring defect is observed around a single particle whereas a cross or strings defect between neighbouring particles is found to serve as a repulsive barrier to prevent the particles from contacting each other. A theoretical analysis is presented to explain this new phenomenon. An optical micrograph of 0.01 wt.-% glass spheres suspended in a nematic solution of 40 wt.-% ethyl cellulose in chloroform under an external shear force. [source] Hydrodynamic Cell Model: General Formulation and Comparative Analysis of Different ApproachesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2007Emiliy K. Zholkovskiy Abstract This paper is concerned with the Cell Model method of addressing hydrodynamic flow through system of solid particles. The starting point of the analysis is the general problem formulation intended for describing a pressure driven flow through a diaphragm which can be considered as a set of representative cells having arbitrary shape and containing any number of particles. Using the general problem formulation, the hydrodynamic field inside an individual representative cell is interrelated with the applied pressure difference and the external flow velocity. To this end, four relationships containing integrals over the outer boundary of a representative cell are derived in the paper. Assuming that the representative cell is a sphere containing a single particle in the centre, the derived general relationships are transformed into outer cell boundary conditions employed in the literature by different authors. The general number of the obtained outer boundary conditions is more than the required number. Accordingly, by choosing different sets of the outer boundary conditions, different models are considered and compared with each other and with the results obtained by others for regular particle arrays. The common and different features of the hydrodynamic and electrodynamic versions of the Cell Model approaches are analyzed. Finally, it is discussed which version of the cell model gives the best approximation while describing pressure and electrically driven flows through a diaphragm and sedimentation of particles. On s'intéresse dans cet article à la méthode du Modèle de Cellules pour traiter l'écoulement à travers un système de particules solides. Le point de départ de l'analyse consiste à formuler le problème général dans le but de décrire un écoulement sous pression dans un diaphragme qui peut être considéré comme un ensemble de cellules représentatives de forme arbitraire et contenant un nombre quelconque de particules. À l'aide de cette formulation générale du problème, l'hydrodynamique dans une cellule représentative donnée est reliée à la différence de pression appliquée et à la vitesse d'écoulement externe. À cette fin, quatre relations contenant des intégrales sur la frontière d'une cellule représentative sont établies dans cette étude. Si l'on suppose que la cellule représentative est une sphère contenant une particule unique en son centre, les relations générales calculées peuvent être transformées en conditions à la frontière des cellules semblables à celles employées dans la littérature scientifique par différents auteurs. Le nombre général de conditions limites obtenues dépasse le nombre requis. Par conséquent, en choisissant différents ensembles de conditions limites, différents modèles sont considérés et comparés entre eux ainsi qu'avec les résultats obtenus pour des arrangements réguliers de particules. Les caractéristiques des versions hydrodynamiques et électrodynamiques des approches du Modèle de Cellules sont analysées. Finalement, on examine quelle version de modèle de cellule donne la meilleure approximation des écoulements sous pression et des écoulements électrodynamiques à travers un diaphragme et pour la sédimentation des particules. [source] Dynamics of protein uptake within the adsorbent particle during packed bed chromatographyBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2002Jürgen Hubbuch Abstract A new experimental set-up for on-line visualization of the intra-particle uptake kinetics during packed bed chromatography has been designed and tested. Confocal laser scanning microscopy was used to analyze the dynamics of protein adsorption to porous stationary phases. In combination with this, a flow cell was developed that could be packed with chromatography media and operated as a fully functional mini-scale chromatography column. Adsorption profiles of single- and two-component mixtures containing BSA and IgG 2a during packed bed cation-exchange chromatography were investigated. The two proteins appear to exhibit different transport characteristics. For BSA a classical "shrinking core" behavior could be detected. The profiles obtained during IgG 2a adsorption point toward a different transport mode, which deviates from the classical pore-diffusion picture. For the two-component system, a superposition of the single-component profiles combined with a classical displacement of the weaker bound protein species was found. The results indicate that depending on the adsorbed protein the uptake can vary tremendously, even for adsorption to the same chromatographic support. It is clearly shown that the new microcolumn allows in situ quantitative investigations of protein adsorption dynamics within a single particle, which adds a new tool to the available methods for characterizing and optimizing protein adsorption chromatography. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 359,368, 2002. [source] Volumetric Filtering, Modeling and Visualization for Nano-MedicineCOMPUTER GRAPHICS FORUM, Issue 3 2003Chandrajit Bajaj The 3D structures of individual proteins or small complexes, such as most of the Protein Data Bank entries, are still unable to yield the "full picture" of a functional biological complex. The study of large macromolecular complexes, such as viruses, ion channels, the ribosome and other macromolecular machines of various types, offer more complete structural and functional description of the nano-machinery of life. In addition to x-ray crystallography. NMR spectroscopy, electron cryomicroscopy (cryoEM) imaging of single particles, and in-vivo molecular tomographic imaging has become indispensable at revealing the structures of large macromolecular complexes at subnanometer resolutions. In this talk, I shall describe some of the recent computational advances in filtering, modeling, analysis and visualization, that have propelled structure determination by cryoEM and tomographic imaging, to steadily increasing accuracy. [source] Analysis of proteins stained by Alexa dyesELECTROPHORESIS, Issue 6 2004Shijun Huang Abstract Alexa dye staining of proteins is used for the fluorescence microscopy of single particles that are sometimes multimolecular protein complexes. To characterize the staining, post-staining determination must be made of which protein(s) in a complex have been Alexa-stained. The present communication describes the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for performing this determination. The Alexa-stained proteins are observed directly in gels by illumination with an ultraviolet transilluminator. The test multimolecular particle is bacteriophage T7. The protein capsid of T7 is a multimolecular complex that has both external and internal proteins. SDS-PAGE of Alexa-stained bacteriophage T7 produces fluorescent capsid proteins each of which usually comigrates with an unstained protein. However, one Alexa-induced modification of protein migration was observed by SDS-PAGE. Mass spectrometry shows that the protein with modified migration is the major protein of the outer shell of the T7 capsid. The procedures used are generally applicable. The distribution of Alexa staining among T7 capsid proteins depends on the size of the dye molecule used. The larger the dye molecule is, the greater the preference for external proteins. [source] Mammalian Mcm2/4/6/7 complex forms a toroidal structureGENES TO CELLS, Issue 5 2003Norikazu Yabuta Background: The Mcm proteins are a family of six homologous proteins (Mcm2,7) that play an important role in DNA replication. They form Mcm4/6/7 and Mcm2/4/6/7 complexes, but their structures are not known. Results: We found that the human Mcm2/4/6/7 tetramer forms a toroidal structure, with a central cavity about 3,4 nm in diameter. Observations were made using electron microscopy, employing the image analysis of single particles. The most predominant averaged image displayed a toroid harbouring four bulges forming corners, one of which was larger than the others. This structure was very similar to the mouse Mcm2/4/6/7 tetramer that was independently prepared and analysed by electron microscopy. These toroidal structures are distinct from that of the Mcm4/6/7 hexamer, which was also examined by electron microscopy. GST(glutathione S-transferase)-pull down and two hybrid experiments suggest that a putative Mcm6-Mcm6 hinge contributes to the formation of the Mcm7/4/6/6/4/7 heterohexamer. Conclusions: The Mcm2/4/6/7 tetramer forms a toroidal structure that is distinct from that of the Mcm4/6/7 hexamer in size and shape. [source] Small-angle neutron and X-ray scattering of dispersions of oleic-acid-coated magnetic iron particlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004Karen Butter This paper describes the characterization of dispersions of oleic-acid-coated magnetic iron particles by small-angle neutron and X-ray scattering (SANS and SAXS). Both oxidized and non-oxidized dilute samples were studied by SANS at different contrasts. The non-oxidized samples are found to consist of non-interacting superparamagnetic single dipolar particles, with a lognormal distribution of iron cores, surrounded by a surfactant shell, which is partially penetrated by solvent. This model is supported by SAXS measurements on the same dispersion. Small iron particles are expected to oxidize upon exposure to air. SANS was used to study the effect of this oxidation, both on single particles, as well as on interparticle interactions. It is found that on exposure to air, a non-magnetic oxide layer is formed around the iron cores, which causes an increase of particle size. In addition, particles are found to aggregate upon oxidation, presumably because the surfactant density on the particle surfaces is decreased. [source] Particle size distributions from small-angle scattering using global scattering functionsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2004G. Beaucage Control and quantification of particle size distribution is of importance in the application of nanoscale particles. For this reason, polydispersity in particle size has been the focus of many simulations of particle growth, especially for nanoparticles synthesized from aerosols such as fumed silica, titania and alumina. Single-source aerosols typically result in close to a log-normal distribution in size and micrograph evidence generally supports close to spherical particles, making such particles ideal candidates for considerations of polydispersity. Small-angle X-ray scattering (SAXS) is often used to measure particle size in terms of the radius of gyration, Rg, using Guinier's law, as well as particle surface area, S/V, from the Porod constant B and the scattering invariant Q. In this paper, the unified function is used to obtain these parameters and various moments of the particle size distribution are calculated. The particle size obtained from BET analysis of gas adsorption data directly agrees with the moment calculated from S/V. Scattering results are also compared with TEM particle-counting results. The potential of scattering to distinguish between polydisperse single particles and polydisperse particles in aggregates is presented. A generalized index of polydispersity for symmetric particles, PDI = BRg4/(1.62G), where G is the Guinier prefactor, is introduced and compared with other approaches to describe particle size distributions in SAXS, specifically the maximum-entropy method. [source] SPEDEN: reconstructing single particles from their diffraction patternsACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2004Stefan P. Hau-Riege SPEDEN is a computer program that reconstructs the electron density of single particles from their X-ray diffraction patterns, using a single-particle adaptation of the holographic method in crystallography [Szöke, Szöke & Somoza (1997). Acta Cryst. A53, 291,313]. The method, like its parent, is unique because it does not rely on `back' transformation from the diffraction pattern into real space and on interpolation within measured data. It is designed to deal successfully with sparse, irregular, incomplete and noisy data. It is also designed to use prior information for ensuring sensible results and for reliable convergence. This article describes the theoretical basis for the reconstruction algorithm, its implementation, and quantitative results of tests on synthetic and experimentally obtained data. The program could be used for determining the structures of radiation-tolerant samples and, eventually, of large biological molecular structures without the need for crystallization. [source] Following the path of hydrophobic and hydrophilic particles in a Denver Cell using positron emission particle trackingASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009K. E. Waters Abstract Positron emission particle tracking (PEPT) has been used to track the movement of single particles of galena and quartz in a Denver Cell batch flotation system. The particles were labeled with a radionuclide, 18F, and using an ADAC Forte positron camera the positions of the particles were determined during mixing, and once air was added to the cell at a constant rate. The hydrophobic galena particle entered the froth readily, attached to air bubbles, and overflowed the weir. Detachment from an air bubble in the froth was also observed, and this is presumed to be due to coalescence events occurring. The hydrophilic quartz particle did not overflow the weir when the air flow was on. When the particle did enter the froth, it was along the sides of the vessel following the flow of the water. This gives a potential indication of one of the methods of the entrainment of gangue minerals in froth flotation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||