Clusters Of Spherical Particles Research Articles

A Structural Analysis of Host-Parasite Interactions in Achatina fulica (Giant African Snail) Infected with Angiostrongylus cantonensis.

Angiostrongylus cantonensis is a nematode parasite that resides in the pulmonary arteries of rodents, serving as its definitive hosts. The life cycle involves several species of non-marine gastropods as intermediate hosts, and the African giant snail Achatina fulica is considered one of the most important around the world. Experimental data concerning A. cantonensis infection in the African giant snail remains notably limited. This helminth causes eosinophilic meningitis or meningoencephalitis in humans, representing an emergent zoonosis in Brazil. Understanding the host-parasite relationship through the application of new tools is crucial, given the complex interaction between zoonosis and the intricate mechanisms involving wild/human hosts, parasite adaptation, and dispersion. The objective of this study was to employ SEM as a novel methodology to understand the structural organization of the host tissue, particularly the granuloma formation. This sheds light on the complex balance between A. fulica and A. cantonensis. Nine three-month-old snails were randomly selected and exposed for 24 h to a concentration of 2000 L1/dose of A. cantonensis. A necropsy was performed 37 days after the infection, and the samples were examined using light and scanning electron microscopy (SEM). The histopathological results revealed third-stage larvae of A. cantonensis associated with granulomas distributed throughout the head-foot mass, mantle, and kidney. Scanning electron microscopy of the histological section surface showed that the granuloma is surrounded by a cluster of spherical particles, which are distributed in the region bordering the larvae. This reveal details of the nematode structure, demonstrating how this methodology can enhance our understanding of the role of granulomas in molluscan tissue. The structural characteristics of granuloma formation in A. fulica suggest it as an excellent invertebrate host for A. cantonensis. This relationship appears to provide protection to the parasite against the host's immune defense system while isolating the snail's tissue from potential exposure to nematode antigens.

Effect of Bi3+co-doping on the up-converting and photocatalytic properties of SrGd2O4:Yb3+/Ho3+ phase

In this investigation, samples of strontium-gadolinium-oxide (SrGd2O4) doped with different Yb3+ (2, 4 and 6 at%) and constant Ho3+ (1 at%) contents and co-doped with Bi3+ (2 at%) were prepared using the glycine-assisted sol–gel method. The pure orthorhombic SrGd2O4 phase, space group Pnma, was revealed using X-ray diffraction in all samples. Transmission electron microscopy discovered agglomerated clusters of spherical particles measuring approximately 150 nm in size. The inclusion of Bi3+ ions into the structure influenced the morphology since the formation of larger grains was observed, with sizes reaching up to ∼1.7 μm. The uniform distribution of all constitutive elements was confirmed by energy-dispersive X-ray spectroscopy. In all samples, up-conversion emission spectra revealed two dominant green (540 and 550 nm), red (671 nm), and infrared (758 nm) emission lines, due to the 5F4,5S2→5I8, 5F5→5I8, and 5F4,5S2 → 5I7 transitions, respectively. The sample co-doped with Bi3+ showed the most intense photoluminescent emissions, shorter luminescence decay, and the highest quantum yield. Additionally, a significant decrease in the energy band gap value was detected using diffuse reflectance spectroscopy for this sample. Methylene blue was used as a test pollutant to investigate its photocatalytic efficiency under simulated sunlight irradiation. The results show that Bi3+ co-doping deteriorates the photocatalytic efficiency of the SrGd2O4:Yb3+/Ho3+ phase by reducing hydroxyl radical formation.

Extinction and Independent Scattering Criterion for Clusters of Spherical Particles Embedded in Absorbing Host Media

In practical applications, the independent scattering approximation (ISA) is widely used to analyze light transfer in nanoparticle systems. However, the traditional independent scattering criterion is obtained under the assumption that the host medium surrounding particles is nonabsorbing, and thus may be invalid in certain circumstances. In this work, to explore the applicability of the ISA for small particles in absorbing host media, we calculate the extinction efficiency of particle clusters by direct solutions of macroscopic Maxwell equations. Using the far-field and distance-independent definitions of extinction, the computational efficiency multi-sphere method is applied for particle clusters in absorbing host, and its accuracy is verified with the discrete dipole approximation method. It is well known that for small particles, the dependent scattering in transparent host always enhances the extinction of the cluster and the criterion for the ISA is nearly independent of the particle refractive index and particle size. We show, however, that when the host medium is absorbing, the dependent scattering between particles can lead to a decreased or even negative extinction, and thus the ISA criterion depends on the particle refractive index, size, and host medium absorption index. In this result, the generalized criteria for absorbing host media may differ significantly from the conventional ones for transparent host media. The results can provide guidance in solving problems related to light transfer in nanoparticle systems, particularly in the presence of absorption in the host medium.

T-matrix method for calculation of second-harmonic generation in clusters of spherical particles

In this article, we present a T-matrix method for numerical computation of second-harmonic generation from clusters of arbitrarily distributed spherical particles made of centrosymmetric optical materials. The electromagnetic fields at the fundamental and second-harmonic (SH) frequencies are expanded in series of vector spherical wave functions, and the single sphere T-matrix entries are computed by imposing field boundary conditions at the surface of the particles. Different from previous approaches, we compute the SH fields by taking into account both local surface and nonlocal bulk polarization sources, which allows one to accurately describe the generation of SH in arbitrary clusters of spherical particles. Our numerical method can be used to efficiently analyze clusters of spherical particles made of various optical materials, including metallic, dielectric, semiconductor, and polaritonic materials.

Collective Effects in the Formation of an Ensemble of Photonic Nanojets by an Ordered Microassembly of Dielectric Microparticles

The results of theoretical studies of spatially localized near-field light structures (photonic nanojets) formed when laser radiation is scattered on a meta-surface having the form of an ordered single-layer assembly of dielectric microparticles (spheres, cones) embedded in a transparent matrix (silicone film) are presented. The behavior of the main parameters of the localized light structures (length, width, and peak intensity) under the effects of light fields of neighboring microparticles is thoroughly analyzed by using computational electrodynamics to solve Maxwell’s equations with the finite-difference time-domain method (FDTD). It is ascertained that the main factors which affect the parameters of photonic nanojets under study are the spatial orientation of the microcones and the depth of their immersion in the silicone matrix. It is shown that several spatial configurations of the microassembly of the cones allow the creation of an ensemble of photonic nanojets with specific parameters, which are unattainable for isolated microcones. Ordered clusters of spherical particles have an advantage in terms of a comprehensive assessment of the parameters of photonic nanojets.

Structure and thermal properties of stearic acid/silica composites as form-stable phase change materials

In this study, stearic acid/silica phase change composites were prepared by the sol-gel method using stearic acid as phase change materials (PCMs). The effects of mass fraction of stearic acid were comprehensively investigated. The structures and thermal properties of the obtained composites were characterized by various methods, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), leakage tests, and thermogravimetry analysis (TG). The results indicated that composite containing 76% stearic acid had the best thermal properties and low mass leakage, making 76% stearic acid as the maximum content that silica matrix could protect in the composites. The latter was further confirmed by morphological analyses of the silica matrix. Silica matrix exhibited spherical particle clusters, following big–small–big–small size pattern as stearic acid rose. The composite with 76% stearic acid was at the key point of change in particle size. These findings look promising for future to prepare silica-based phase change composites with good thermal properties easily.

Magnetic field-induced enhancement of thermal conductivities in polymer composites by linear clustering of spherical particles

Abstract We developed linearly linked spherical fillers in polymer composites with incorporating Al2O3-Fe3O4 hybrid particles under a magnetic field to form thermal networks for high thermal conductivity. The Al2O3-Fe3O4 hybrid particles were prepared by a simple precipitation method and their magnetic properties were characterized with magnetic hysteresis. The Al2O3-Fe3O4 hybrid particles were well aligned through direction of magnetic field as confirmed by microscopic observation. The polymer composites obtained with Al2O3-Fe3O4 hybrid particles possessed high thermal conductivity in a parallel magnetic alignment direction at low filler loading, which is more than 240% outperformed the composites with randomly dispersed fillers.

Reflectance model for densely packed media: Estimates of the surface properties of the high-albedo satellites of Saturn

Interpretation of photometric and polarimetric observations of atmosphereless celestial bodies faces the problems connected with both the insufficient accuracy and level of details in groundbased observations and the current state of the theory of the multiple scattering of light. In application to sparse media, where the electromagnetic waves, propagating between the scatterers, can be considered as spherical (the socalled far-field approximation), this theory is rather well developed for both the diffuse and coherent components of the scattered radiation. In this paper, we show that this theory can be also successfully applied to the measurements of polarization of light scattered by densely packed, though nonabsorbing or weakly absorbing, media. For this purpose, we calculated the models for a semi-infinite layer of the medium composed of randomly oriented clusters of spherical particles and compared them with the data of laboratory and astronomical measurements. The potential of the present approach is illustrated by an example of the interpretation of the polarization measurements of the ice satellites of Saturn—Rhea and Enceladus—which allowed some properties of the surface of these celestial bodies to be estimated. In particular, the ratio of the surface area that makes no contribution to the negative polarization of light reflected at small phase angles to the area producing the negative polarization branch was found. Under the assumption of the same albedo of these areas, this ratio turned out to be 3.31–3.66 and 1.7–3.8 for Rhea and Enceladus, respectively. For Enceladus, it is difficult to obtain a sufficiently narrow range of the estimated parameters, since the number of measurement points in the phase dependence of polarization of this satellite is small. For the surface of Rhea, the estimated packing density of particles, participating in the opposition effects, is approximately 15%, while their smallest size is of the order of the wavelength of visible light.

Scattering of electromagnetic waves by a cluster of charged spherical nanoparticles

The interaction of light with a cluster of charged spherical particles is studied. The electromagnetic field is expanded in terms of the vector multipole fields, and the expansion of the scattered field is related to that of the incident field. The dimer and the chainlike and disordered arrangements of ten particles are studied. Features of the absorption and scattering signals can be used to measure the charge. This paves the way for the optical measurement of a nonspherical dust particle charge in a plasma since a cluster of spherical particles may approximate a nonspherical one.

Segregation of "isotope" particles within colloidal molecules.

Clusters of spherical particles are called "colloidal molecules" because they adopt structures that resemble those of true molecules. In this analogy, the particles are the atoms, the attractive interactions between them are bonds, and the different structures that appear in equilibrium are isomers. We take this analogy a step further by doping colloidal molecules with colloidal "isotopes," particles that have the same size but different bonding energies from the other particles in the system. Our molecules are two-dimensional clusters consisting of polystyrene and silica microspheres held together by depletion interactions. Using a combination of optical microscopy and particle tracking, we examine an ensemble of 4- and 5-particle molecules at different isotope ratios. We find that the isotopes tend to segregate to particular positions in the various isomers. We explain these findings using a statistical mechanical model that accounts for the rotational entropy of the isomers and the different interaction potentials between the different types of particles. The model shows how to optimize the yield of any particular isomer, so as to put the isotopes in desired locations. Our experiments and models show that even in systems of particles with isotropic interactions, the structures of self-assembled molecules can in principle be controlled to a surprisingly high extent.

A molecularly imprinted polymer as the sorptive phase immobilized in a rotating disk extraction device for the determination of diclofenac and mefenamic acid in wastewater

The microextraction of diclofenac and mefenamic acid from water samples was performed by using rotating disk sorptive extraction (RDSE) with molecularly imprinted polymer (MIP) as the sorptive phase. The MIP was synthesized from the monomer 1-vinylimidazol (VI) together with the cross-linker divinylbenzene (DVB) using diphenylamine as the template molecule. Scanning electron microscopy (SEM) analyses of the MIP revealed clusters of spherical particles having a narrow size distribution, with diameters of approximately 1 μm.The optimized extraction conditions involved a disk rotation velocity of 3000 rpm, an extraction time of 120 min, a sample volume of 50 mL, and a sample pH of 2 as well as 25 mg of MIP immobilized in the disk. Desorption of the extracted analytes was performed with 5 mL of methanol for 10 min. Analysis by gas chromatography-mass spectrometry (GC–MS) was carried out after derivatization of the analytes with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA).Nonmolecularly imprinted polymer (NIP) was also synthesized for comparison. It was observed that under the same conditions, MIP extracted significantly more NSAIDs containing diphenylamine (or part of this molecule) in their structure than NIP. Higher significant differences between MIP and NIP were observed for diclofenac, mefenamic acid and paracetamol, clearly indicating the effect of the template on the extraction.Recoveries of the method were between 100 and 112%, with relative standard deviations of 5–6%. The limits of detection were between 60 and 223 ng L−1. Water samples from a wastewater treatment plant (WWTP) of Santiago de Chile, were found to contain concentrations of these acidic drugs between 1.6 and 4.3 μg L−1 and between 1.4 and 3.3 μg L−1 in the influent and effluent, respectively.

Polarized backscattering by clusters of spherical particles.

The linear and circular polarization ratios for clusters of spherical particles averaged over multiple orientations show a systematic pattern as a function of the refractive index and the size parameter. We show that, at backscattering, the depolarizing behavior of orientation-averaged clusters of spheres can be approximated by second-order scattering of bispheres. The pattern is relatively invariable in terms of the number of particles. We also demonstrate the significance of the near-field effects for polarization at backscattering.

Analytical Modeling of Effective Diffusivity in Micro-Porous Layers

The membrane electrode assembly (MEA) used in polymer electrolyte fuel cells consists of a membrane, two electrodes (anode and cathode), and two gas diffusion layers (GDLs). The GDL is responsible for providing the pathways for transport of the reactant gases from the flow channels to the catalyst layers. Hence, the mass transport resistance of this layer should be minimized for high performance operation. The GDL is typically a dual-layer carbon-based material composed of a macro-porous substrate, which usually contains carbon fibers, binder, and PTFE, and a thin delicate micro-porous layer (MPL), which is usually made of carbon nano-particles and PTFE. Spherical carbon nano-particles of 20-100 nm in diameter construct the complex structure of MPL. Small pore sizes and highly hydrophobic characteristics are the two main specifications of the MPL. The effective diffusivity of the MPL is a key property in determining the fuel cell performance. However, since the MPL is a recently developed material, the number of published works with focus on its diffusivity is limited. Measuring the MPL diffusivity is a challenging task since the MPL needs a physical support and cannot be analyzed as a separate object. Similar to its measurements, modeling the MPL diffusivity is also a difficult task (Nanjundappa et al., Electrochimica Acta 110:349-57), since it involves the reconstruction of the complex structure numerically and solving the diffusion equations in the nano-scale pores where the continuum assumption may be invalid and Knudsen diffusion may prevail. Usually, complex numerical algorithms are employed to reconstruct a small portion of the MPL. This step is followed by a computationally intensive stage to solve the diffusion equations inside the void spaces of the reconstructed domain. Although this approach leads to reliable and accurate results, an analytical relationship that correlates certain design parameters to the MPL diffusivity could be helpful. A fully analytical solution of the mass transport equation inside a randomly structured porous material is however not feasible. Simplifying assumptions are therefore required to derive an analytical model for predicting the transport properties of porous structures. The unit cell approach is one way of simplifying the structure. A unit cell is a hypothetical, periodic domain that represents the entire structure. Hence, optical observations can aid the selection of the optimal unit cell arrangement. In this work a unit cell is chosen based on cross-sectional SEM images of a standard MPL material. Generally, two main regions can be observed in the MPL: i) clusters of spherical particles; and ii) pores. The considered unit cell, which is devised based on these observations, is shown in Figure 1. The analogy between the heat and mass transfer is employed to solve the diffusion equation in the unit cell and a relationship is proposed to calculate the effective MPL diffusivity. The obtained values from this relationship are compared with the experimental data available in the literature and another stochastic model which is under development in our group. The proposed relationship is able to predict the MPL diffusivity with an acceptable accuracy, i.e., with less than 10% deviation. The required input parameters of the model are particle diameter, MPL porosity, and average pore size. A parametric study is then performed to examine the effects of these parameters on the MPL diffusivity. The proposed relationship is expected to be useful to the fuel cell community, especially for the purposes of performance modeling. Furthermore, the results from the parametric study c provide valuable information on the effects of carbon particle size, the MPL porosity, and the MPL pore size distribution on its effective diffusivity. Acknowledgments:This research was supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada.

Structural and Magnetic Properties of Ultrafine Magnesium Ferrite Nanoparticles

Nanoparticles of MgFe2O4 with average crystallite size of ~ 8 nm have been synthesized employing non-aqueous combustion method. Structural properties of the nanoparticles are analyzed with the help of X-Ray Diffractometry (XRD), Scanning Electron Microscopy (SEM), Energy dispersive X-Ray analysis (EDX), Fourier Transform Infra-Red spectroscopy (FT-IR). X-Ray Diffraction pattern and FT-IR spectra reveal the formation of spinel structure of MgFe2O4 nanoparticles. The SEM micrographs of the sample show the formation of clusters of spherical particles with pores revealing the history of synthesis as combustion process. The constituent elements and chemical composition are analyzed using EDX spectrum. Magnetic study done using Vibrating Sample Magnetometer (VSM) reveals that the prepared nanoparticles remain unsaturated within the field of 15 kOe and have a very low coercivity of 20 Oe.

Towards controlling PCDD/F production in a multi-fuel fired BFB boiler using two sulfur addition strategies. Part III: Cu speciation in the fly ash

PCDD/F abatement strategies – sulfur pellet addition and peat co-combustion – were tested for a BFB boiler facility utilizing SRF-bark-sludge as fuel. In this paper chemical and physical analyses of electrostatic precipitator (ESP) fly ashes were used to explain the differences in the performance of these strategies. These analyses revealed a difference between the coarse and fine fly ashes collected in the ESP. Chemical analysis of the fine fly ashes revealed high concentration of easily volatilized elements while the SEM micrographs showed that fine ash are composed of clusters of spherical particles, thereby leading to a conclusion that fine ashes were originally in a gas phase in the high temperature zones of the boiler. Variation in the distribution of active and passive forms of Cu in fly ashes was revealed using X-ray absorption spectroscopy (XANES mode). It was also found that peat co-combustion led to increased formation of Cu oxides that may act as active catalysts in de novo synthesis. Furthermore, XANES revealed the formation of CuSO4 for all the test cases. By applying the empirical ratio between mole fractions of the active and passive species of Cu, the role of Cu speciation to PCDD/F production was emphasized. It is concluded that sulfur pellet addition is more effective than peat addition as a PCDD/F abatement strategy for the BFB facility understudy.

The motion of a cluster of spherical particles in an ideal fluid

The motion of a cluster of an arbitrary number of spherical particles, attached to one another, in an ideal incompressible fluid is considered. Using the previously developed self-consistent field method, an expression is obtained for the virtual mass of the cluster in the form of an explicit function of the coordinates of all the particles. It is shown that, for special cases, the solution obtained is identical with the corresponding results known in the literature. For a statistically uniform particle distribution, using an averaging procedure over all the different possible configurations in the fluid inside a spherical volume, a simple analytic relation is obtained for the average value of the virtual mass of the spherical cluster as a function of its radius in the first approximation with respect to the volume fraction of the particles.

Preparation and Characterization of A Composite Obtained through Ti (IV) and Phosphoric Acid

This paper describes the preparation and complementary characterization of a composite formed from the activation of titanium isopropoxide by phosphoric acid and deionized water (TiP).Techniques such as, X-ray diffraction (XRD), Raman , electronic (UV-vis) and Scanning electron microscopies (SEM) were used for characterization of this new composite formed. In the X-ray diffractogram of TIP was observed four intense peaks. A strong absorption was observed in the region 362-445 nm. The scanning electron microscopy of TiP, shows that the prepared material consists mostly of a cluster of spherical particles with diameters ranging from 2.35 to 2.60 μm.

Coherent backscattering by discrete random media composed of clusters of spherical particles

The approximate method of accounting for the weak localization effect in discrete random media makes it possible to calculate the intensity and the degree of linear polarization of radiation reflected by a semi-infinite layer containing randomly oriented clusters of identical nonabsorbing spherical particles. The paper is focused on the analysis of the influence of the medium properties – the concentration of the clusters, their structure, the sizes and the number of constituent monomers – on the phase dependence of the characteristics of the interference (coherent) component of radiation. Three types of clusters were chosen for the analysis: a fractal-like cluster and two random clusters with different packing densities of monomers. Three values of the size parameters of monomers were considered: 0.5, 1.0, and 1.5. The chosen values of the refractive index of monomers correspond to that of magnesium oxide in the visible spectral range. This allowed us to compare the theoretical phase curves of the degree of linear polarization of light reflected by the medium with the data of measurements by Lyot. For all of the considered cluster types, starting from some minimal number of constituent monomers, which is typical of the specified cluster's type and the monomer's size, the characteristics of the coherent component were found to be practically independent of the number of constituents. In particular, in the phase-angle range from 0° to 15°, the branch of negative polarization measured for a layer of magnesium oxide by Lyot can be well described with several models of the media containing either the fractal-like clusters or the random clusters with the packing density larger than 30%. In these models, the number and sizes of constituent monomers vary. To select from the whole set of “suitable” clusters those the optical characteristics of which actually correspond to characteristics of an elementary volume of the specified medium, additional information is required. For example, this can be the results of polarization measurements in a wider phase interval that includes a zone of the dominating influence of incoherent (diffuse) scattering.

Scattering of clusters of spherical particles—Modeling and inverse problem solution in the Rayleigh–Gans approximation

In this work, an exact scattering model for a system of clusters of spherical particles, based on the Rayleigh–Gans approximation, has been parameterized in such a way that it can be solved in inverse form using Thikhonov Regularization to obtain the morphological parameters of the clusters. That is to say, the average number of particles per cluster, the size of the primary spherical units that form the cluster, and the Discrete Distance Distribution Function from which the z-average square radius of gyration of the system of clusters is obtained. The methodology is validated through a series of simulated and experimental examples of x-ray and light scattering that show that the proposed methodology works satisfactorily in unideal situations such as: presence of error in the measurements, presence of error in the model, and several types of unideallities present in the experimental cases.

Foam-Film-Stabilized Liquid Bridge Networks in Evaporative Lithography and Wet Granular Matter

Evaporative lithography using latex particle templates is a novel approach for the self-assembly of suspension-dispersed nanoparticles into ordered microwire networks. The phenomenon that drives the self-assembly process is the propagation of a network of interconnected liquid bridges between the template particles and the underlying substrate. With the aid of video microscopy, we demonstrate that these liquid bridges are in fact the border zone between the underlying substrate and foam films vertical to the substrate, which are formed during the evaporation of the liquid from the suspension. The stability of the foam films and thus the liquid bridge network stability are due to the presence of a small amount of surfactant in the evaporating solution. We show that the same type of foam-film-stabilized liquid bridge network can also propagate in 3D clusters of spherical particles, which has important implications for the understanding of wet granular matter.