Placement Of Particles Research Articles

Study of the morphology of solidified binder in spray fluidized bed agglomerates by X-ray tomography

Properties of agglomerated products depend on the materials used (primary particles, binder) and on their internal structure. Previous studies have characterized the internal structure of spray fluidized bed agglomerates in terms of the placement of primary particles, but binder morphology has not been investigated until now. Therefore, solidified binder morphology in spray fluidized bed agglomerates is discussed in the present work on data gained by X-ray micro-computed tomography. The main results refer to glass beads as the primary particles and to HPMC with contrast agent as the binder. Gas temperature and drying rate are shown to have a very strong influence not only on the morphology of the bridges that connect primary particles, specifically on the macroscopic porosity (hollowness) of such bridges, but also on the microscopic porosity of seemingly full bridge parts. Individual bridge volume, bridge clustering, binder volume distribution and agglomerate filling ratio with binder are discussed, and a classification is proposed for the various solidified binder elements observed. A critical view to systematic errors stemming from limitations in spatial resolution of the applied imaging technique is provided.

Redirection and channelization of power-law fluid flow in a rough-walled fracture

Flow of non-Newtonian fluids in rough-walled rock fractures is common in many technological processes in oil and gas industry. A numerical study of power-law fluid flow in rough-walled fractures is carried out under the assumptions of the lubrication theory approximation. It is shown that, in a self-affine fracture, varying the exponent of the power-law fluid may lead to a redirection of flow compared to a Newtonian fluid flow field. This effect is observed even though the fracture landscape is isotropic, i.e. no preferential flow paths have been created in the model by e.g. relative displacement of the fracture faces. In another fracture, one that contains an obstacle represented by a spot of zero aperture, the spread of the flow around the obstacle is again controlled by the power exponent of the fluid. The fluid being more shear-thinning leads to a channelization of the flow in such a fracture. “Channelization” here refers to the fluid velocity component in the direction of the applied pressure gradient becoming larger as compared to the velocity component in the direction normal to the overall flow direction as the fluid becomes more shear-thinning. A channelization is also observed in a fracture containing a local zone of an elevated aperture. The effects of rheology on the spread and redirection of flow in a fracture of variable aperture are crucial for optimization of transport and placement of particles or tracers in natural and man-made fractures.

Jammed disks in a narrow channel: criticality and ordering tendencies

A system of identical disks is confined to a narrow channel, closed off at one end by a stopper and at the other end by a piston. All surfaces are hard and frictionless. A uniform gravitational field is directed parallel to the plane of the disks and perpendicular to the axis of the channel. We employ a method of configurational statistics that interprets jammed states as configurations of floating particles with structure. The particles interlink according to set rules. The two jammed microstates with smallest volume act as a pseudo-vacuum. The placement of particles is subject to a generalized Pauli principle. Jammed macrostates are generated by random agitations and specified by two control variables. They are inferred from measures for expansion work against the piston, gravitational potential energy, and intensity of random agitations. In this two-dimensional space of variables there exists a critical point. The jammed macrostate realized at the critical point depends on the path of approach. We describe all jammed macrostates by volume and entropy. Both are functions of the average population densities of particles. Approaching the critical point in an extended space of control variables generates two types of jammed macrostates: states with random heterogeneities in mass density and states with domains of uniform mass density. Criticality is shown to be robust against some effects of friction.

Semiregular Solid Texturing from 2D Image Exemplars

Solid textures, comprising 3D particles embedded in a matrix in a regular or semiregular pattern, are common in natural and man-made materials, such as brickwork, stone walls, plant cells in a leaf, etc. We present a novel technique for synthesizing such textures, starting from 2D image exemplars which provide cross-sections of the desired volume texture. The shapes and colors of typical particles embedded in the structure are estimated from their 2D cross-sections. Particle positions in the texture images are also used to guide spatial placement of the 3D particles during synthesis of the 3D texture. Our experiments demonstrate that our algorithm can produce higher quality structures than previous approaches; they are both compatible with the input images, and have a plausible 3D nature.

Decomposable Statistics and Random Placement of Particles over a Countable Set of Cells*

In the paper, the scheme of independent particle allocation is considered. A connection is demonstrated between finite-dimensional distributions for the process of the number of particles assigned to the k-th cell and the conditional distribution of independent Poisson distributed random variables. Conditions are specified for the convergence of these distributions to finite-dimensional distributions of the Gaussian process. A certain scheme of dependent particle allocation on a countable set of cells is introduced and investigated.

On the discourse function of particles in post-initial position

The paper presents a corpus-based information-structural analysis of the German discourse particles aber and auch in the so-called post-initial position, i.e. between the pre-field constituent and the finite verb in main clauses. Based on corpus data, I argue that aber and auch in this position mark the boundary between the focus and the background of the sentence that hosts them. By doing this, they essentially contribute to identifying relevant alternatives involved in focus interpretation and discourse interpretation in general. In this way, the placement of particles in post-initial position facilitates interpretation by providing processing instructions to the reader/hearer and by ruling out ambiguities. The analysis thus argues against existing accounts of the discourse function of post-initial particles in terms of indicating association with topic and topic shift.

Measuring the effects of artificial viscosity in SPH simulations of rotating fluid flows

A commonly cited drawback of SPH is the introduction of spurious shear viscosity by the artificial viscosity term in situations involving rotation. Existing approaches for quantifying its effect include approximate analytic formulae and disc-averaged be- haviour in specific ring-spreading simulations, based on the kinematic effects produced by the artificial viscosity. These methods have disadvantages, in that they typically are applicable to a very small range of physical scenarios, have a large number of simplifying assumptions, and often are tied to specific SPH formulations which do not include corrective (e.g., Balsara) or time-dependent viscosity terms. In this study we have developed a simple, generally applicable and practical technique for evaluating the local effect of artificial viscosity directly from the creation of specific entropy for each SPH particle. This local approach is simple and quick to implement, and it al- lows a detailed characterization of viscous effects as a function of position. Several advantages of this method are discussed, including its ease in evaluation, its greater accuracy and its broad applicability. In order to compare this new method with ex- isting ones, simple disc flow examples are used. Even in these basic cases, the very roughly approximate nature of the previous methods is shown. Our local method pro- vides a detailed description of the effects of the artificial viscosity throughout the disc, even for extended examples which implement Balsara corrections. As a further use of this approach, explicit dependencies of the effective viscosity in terms of SPH and flow parameters are estimated from the example cases. In an appendix, a method for the initial placement of SPH particles is discussed which is very effective in reducing numerical fluctuations.

Controlling the size and the activity of Fe particles for synthesis of carbon nanotubes

The properties of carbon nanotubes (CNTs) are controlled by their structure and morphology. Therefore, their selective synthesis, using catalytic chemical vapor deposition, requires precise control of a number of parameters including the size and activity of the catalyst nanoparticles. Previously, an environmental scanning transmission electron microscope (ESTEM) has been used to demonstrate that electron beam-induced decomposition (EBID) of Fe containing precursor molecules can be used to selectively deposit Fe catalyst nanoparticles that are active for CNT growth. We have extended these in situ ESTEM observations to further our understanding of the EBID parameters, such as deposition time, and substrate temperature, that control the size and placement of Fe catalyst particles for two precursors, namely diiron nonacarbonyl (Fe2(CO)9) and ferrocene (Fe(C5H5)2). We found that the diameter of deposited particles increased with increasing deposition time. Electron energy-loss spectra, collected during deposition, show the incorporation of C in the Fe particles. The C content decreased as the substrate temperature was increased and was negligible at 100°C for Fe2(CO)9. However, C and Fe were co-deposited at all temperatures (up to 450°C) when Fe(C5H5)2 was used as an iron source. After deposition, the substrate was heated to the CNT growth temperature in flowing hydrogen to remove the co-deposited C, which was an important step to activate the deposited Fe catalyst for the growth using acetylene. Our measurements revealed that the Fe nanoparticles fabricated from Fe2(CO)9 had higher activity for CNT growth compared to the ones fabricated using Fe(C5H5)2. We also found that the co-deposited carbon could not be removed by heating in hydrogen in the case of Fe(C5H5)2. The particles deposited from Fe(C5H5)2 at 300°C to 450°C formed a core–shell structure with Fe surrounded by graphitic carbon. We speculate that the reduced activity for Fe(C5H5)2 is due to the C content in the deposit.

Hypothalamic EAP1 (Enhanced at Puberty 1) Is Required for Menstrual Cyclicity in Nonhuman Primates

Mammalian reproductive cyclicity requires the periodic discharge of GnRH from hypothalamic neurons into the portal vessels connecting the neuroendocrine brain to the pituitary gland. GnRH secretion is, in turn, controlled by changes in neuronal and glial inputs to GnRH-producing neurons. The transcriptional control of this process is not well understood, but it appears to involve several genes. One of them, termed enhanced at puberty 1 (EAP1), has been postulated to function in the female hypothalamus as an upstream regulator of neuroendocrine reproductive function. RNA interference-mediated inhibition of EAP1 expression, targeted to the preoptic region, delays puberty and disrupts estrous cyclicity in rodents, suggesting that EAP1 is required for the normalcy of these events. Here, we show that knocking down EAP1 expression in a region of the medial basal hypothalamus that includes the arcuate nucleus, via lentiviral-mediated delivery of RNA interference, results in cessation of menstrual cyclicity in female rhesus monkeys undergoing regular menstrual cycles. Neither lentiviruses encoding an unrelated small interfering RNA nor the placement of viral particles carrying EAP1 small interfering RNA outside the medial basal hypothalamus-arcuate nucleus region affected menstrual cycles, indicating that region-specific expression of EAP1 in the hypothalamus is required for menstrual cyclicity in higher primates. The cellular mechanism by which EAP1 exerts this function is unknown, but the recent finding that EAP1 is an integral component of a powerful transcriptional-repressive complex suggests that EAP1 may control reproductive cyclicity by inhibiting downstream repressor genes involved in the neuroendocrine control of reproductive function.

Tatuagem extensa por amálgama em mucosa gêngivo-alveolar

Amalgam tattoos are common exogenous pigmented lesions of the oral mucosa occurring mainly by inadvertent placement of amalgam particles into soft tissues. The diagnosis of amalgam tattoo is simple, usually based on clinical findings associated with presence or history of amalgam fillings removal. Intraoral X-rays may be helpful in detecting amalgam-related radiopacity. In cases where amalgam tattoo cannot be differentiated from other causes of oral pigmentation, a biopsy should be performed. This article deals with an extensive amalgam tattoo lesion which required a biopsy for a definitive diagnosis.

Controlling the Motion and Placement of Micrometer-Sized Metal Particles Using Patterned Polymer Brush Surfaces

In this paper, we show that silicon surfaces patterned with poly(methacrylic acid) brushes are able to control the Brownian motion of 2-3 μm iron particles, which sediment onto the surface in aqueous solution and experience differences in repulsive force depending upon their position. Differences in repulsion lead to different gravitational potential energies across the surface, which gives bias to the Brownian motion taking place. Three regimes have been identified depending upon the brush height: (i) no control of Brownian motion when the brush height is small, (ii) Brownian motion that is influenced by the polymer brush when the brush 17 height is intermediate, (iii) Brownian motion that is confined by polymer brush barriers when the brush height is greatest. The height of brush found necessary to significantly influence iron particle motion was small at 39 nm or 2% of the particle diameter.

Real‐Time Template‐Assisted Manipulation of Nanoparticles in a Multilayer Nanofluidic Chip

The ability to control dynamically the flow and placement of nanoscale particles and biomolecules in a biocompatible, aqueous environment will have profound impact in advancing the fields of nanoplasmonics, nanophotonics, and medicine. Here, an approach based on electrokinetic forces is demonstrated that enables dynamically controlled placement of nanoparticles into a predefined pattern. The technique uses an applied voltage to manipulate nanoparticles in a multilayer nanofluidic chip architecture. Simulations of the nanoparticles' motion in the nanofluidic chip validate the approach and are confirmed by experimental demonstration to produce uniform 200-nm-diameter spherical nanoparticle arrays. The results are important as they provide a new method that is capable of dynamically capturing and releasing nanoscale particles and biomolecules in an aqueous environment, which could lead to the creation of reconfigurable nanostructure patterns for nanoplasmonic, nanophotonic, biological sensing, and drug-delivery applications.

Vertical Structure of Hurricane Eyewalls as Seen by the TRMM Precipitation Radar

AbstractStatistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones, shown by the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR), shows that the eyewall contains high reflectivities and high echo tops, with deeper and more intense but highly intermittent echo perturbations superimposed on the basic structure. The overall echo strength, height of echo top, and presence of intense echo perturbations all increase with vortex strength. Intense echo perturbations decrease in frequency with low sea surface temperatures. When the PR data are normalized by the amount of radar echo in each sample and examined quadrant by quadrant relative to the direction of the environmental shear, the nature of convective processes in different parts of the eyewall becomes apparent. The normalized statistics of the echo intensity, brightband structure, and maximum echo-top height show that processes generating convective precipitation are generally favored in the downshear-right region of the eyewall, while the nonnormalized statistics indicate that the vertical wind shear determines the placement of precipitation particles downwind of the generation zone such that the precipitation maximum occurs about one quadrant downwind of the convective generation zone. When the track speed exceeds the magnitude of the shear vector, this pattern modifies such that the asymmetry rotates one quadrant to the right. The statistics, moreover, indicate that vertical wind shear is the factor determining the placement of precipitation particles around the storm, while other factors determine the location, intensity, and means of their generation.

Correlation of Thermal Conduction Properties With Mechanical Deformation Characteristics of a Set of SiC–Si3N4 Nanocomposites

New developments in high temperature ceramic materials technology have focused on obtaining nanocomposite materials with nanoscale features for an optimal control of thermal and mechanical properties. One example is the silicon carbide (SiC)–silicon nitride (Si3N4) nanocomposites with nanosized SiC particles placed either in microsized Si3N4 grains or along Si3N4 grain boundaries (GBs). This work focuses on analyzing the influence of GBs, interfaces, and impurities on thermal and mechanical properties of a set of SiC–Si3N4 nanocomposites at three different temperatures (300 K, 900 K, and 1500 K). Nanocomposite thermal conductivity values predicted in this study are smaller in comparison to the bulk Si3N4 values (∼30 W/m K). Even with the volume fraction of SiC phase being limited to maximum 40%, it is shown that the thermal conductivity values could be reduced to less than those of the bulk SiC phase (∼3 W/m K) by microstructural feature arrangement. Nanocomposite phonon spectral density values show a short rage structural order indicating a high degree of diffused phonon reflection. Visual analyses of the atomistic arrangements did not reveal any loss of crystallinity in the nanocomposites at high temperatures. This indicates that structural arrangement, not the phase change, is a factor controlling thermal conduction as a function of temperature. The nanocomposite deformation mechanism is a trade-off between the stress concentration caused by SiC particles and Si3N4–Si3N4 GB sliding. The temperature increase tends to work in favor of GB sliding leading to softening of structures. However, microstructural strength increases with increase in temperature when GBs are absent. GBs also contribute to reduction in thermal conductivity as well as increase in fracture strength. Replacement of sharp GBs by diffused GBs having C/N impurities, lowered thermal conductivity, and increased fracture strength. Decrease in SiC–Si3N4 interfaces by removal of SiC particles tends to favor an increase in thermal conductivity as well as fracture resistance. Overall, it is shown that for high temperature mechanical strength improvement, judicious placement of SiC particles and optimal control of GB atomic volume fraction are the main controlling factors.

Steady state conduction through 2D irregular bodies by smoothed particle hydrodynamics

This paper uses a Lagrangian formulation namely smoothed particle hydrodynamics (SPH) technique for the prediction of conduction heat transfer in irregular geometries. Suitable schemes for the placement of particles inside irregular computational domain have been described. Organization and locations for virtual particles are also discussed for both Dirichlet and Neumann boundary conditions. Three different problems having typical geometries that pose numerical complications in grid based technique, are tackled by SPH efficiently. Conduction shape factor (CSF) for all the problems calculated through SPH shows a good agreement with published results or analytical solutions. Further, the temperature profiles computed by SPH depict close matches with those obtained through numerical software Fluent. The present exercise opens up the possibility of using SPH in varied geometries using different schemes of particle positioning and their judicial combinations.

Experimental Study on Transport of Ultra-Dispersed Catalyst Particles in Porous Media

In situ upgrading of heavy oil by catalytic hydrogenation using submicrometer sized dispersed catalysts during thermal recovery is a promising new idea to achieve an environmentally sustainable method for unlocking heavy oil and bitumen resources. This requires placement of the ultradispersed catalyst particles deep into the formation where it can accelerate the high-temperature upgrading reactions. The objective of this work was to investigate the feasibility of transporting such ultradispersed catalyst particles through porous rock formations. This paper presents the results of experiments carried out to systematically examine the propagation of ultradispersed catalyst suspensions in sand packs. These experiments involved the injection of submicrometer-sized catalyst particles suspended in oil into a sand pack and analysis of the produced fluid samples and the sand bed. The results show that it is possible to propagate the ultradispersed catalyst suspension through sand beds. However, a fraction of the catalyst particles are retained by the sand (around 14 to 18%), and much higher retention occurs in the entrance region of the bed. Particles appear to be deposited on sand surfaces by an attachment mechanism deep inside the bed, but larger particles appear to be strained by mechanical trapping near the inlet face. The deposition of particles was found to be almost irreversible in the sense that the deposited particles could not be remobilized by reverse flow of the suspending medium.

Stochastic generation of particle structures with controlled degree of heterogeneity

The recently developed void expansion method (VEM) allows for an efficient generation of porous packings of spherical particles over a wide range of volume fractions. The method is based on a random placement of the structural particles under addition of much smaller "void-particles" whose radii are repeatedly increased during the void expansion. Thereby, they rearrange the structural particles until formation of a dense particle packing and introduce local heterogeneities in the structure. In this paper, microstructures with volume fractions between 0.4 and 0.6 produced by VEM are analyzed with respect to their degree of heterogeneity (DOH). In particular, the influence of the void- to structural particle number ratio, which constitutes a principal VEM-parameter, on the DOH is studied. The DOH is quantified using the pore size distribution, the Voronoi volume distribution and the density-fluctuation method in conjunction with fit functions or integral measures. This analysis has revealed that for volume fractions between 0.4 and 0.55 the void-particle number allows for a quasi-continuous adjustment of the DOH. Additionally, the DOH-range of VEM-generated microstructures with a volume fraction of 0.4 is compared to the range covered by microstructures generated using previous Brownian dynamics simulations, which represent the structure of coagulated colloidal suspensions. Both sets of microstructures cover similarly broad and overlapping DOH-ranges, which allows concluding that VEM is an efficient method to stochastically reproduce colloidal microstructures with varying DOH.

The placement of focus particles in Dutch

The placement of focus particles in Dutch

A Network-of-Voids Model to Assess Wall Flow Patterns and Heat Transfer for Low Aspect Ratio Packed-Bed Reactors

Exothermic packed bed catalytic reactors are usually characterised by a low diameter-aspect ratio to facilitate heat transfer. In operation, these reactors often exhibit localized regions with much higher temperatures referred to as hot spots. A new model based on a 2-D network-of voids (NoV) has been devised to explore wall heat transfer behaviour for such low aspect ratio packed tubes. Random placement of (packing) particles is used to provide a simple NoV framework for implicitly creating the tortuous fluid flows amongst the resulting randomized inter-connecting voids. This is a computationally tractable strategy for exploring the haphazard appearance of individual tube pin-hole burn-outs amongst the typically thousands, or tens of thousands, of tubes within high temperature industrial multi-tubular configurations. Although presently limited to 2-D, the model captures many natural features of the flow and heat transfer of randomly packed tubes, especially huge variations in wall and cross flows and consequently massive variations in local wall heat transfer coefficients along the length of individual tubes. The model is potentially superior to those based upon averaged properties, which do not properly distinguish the solid and fluid phases. The network-of-voids concept is readily extended to 3-D, in order to achieve geometric congruence of the model and assemblies of individual particles.

Analyses of the role of the second phase SiC particles in microstructure dependent fracture resistance variation of SiC-Si3N4 nanocomposites

One of the primary factors affecting the failure in high strength silicon carbide (SiC)–silicon nitride (Si3N4) nanocomposites is the placement of spherical nano-sized SiC particles in micro-sized Si3N4 grains. In order to analyze this issue, the cohesive finite element method (CFEM) based dynamic fracture analyses of SiC–Si3N4 nanocomposites at two different loading rates (0.5 and 2 m s−1) with an explicit account of the lengthscales associated with Si3N4 grain boundaries (GBs) (sizescale 100 nm), SiC particles (sizescale 200–300 nm), and Si3N4 grains (sizescale 0.8–1.5 µm) are performed. A range of CFEM meshes with selective placement of second phase particles placed exclusively along GBs, exclusively inside Si3N4 grains, and along GBs as well as inside Si3N4 grains are generated for analyses. Analyses of the damage progression and stress distribution as a function of microstructural morphology indicate that high strength and relatively small sized SiC particles act as stress concentration sites in Si3N4 matrix. The dominant mode of fracture in all microstructures, therefore, is intergranular Si3N4 matrix cracking. Crack density evolution and fracture energy dissipation results show loading rate dependence of failure with the role of phase morphology becoming prominent at the lower loading rate. Contrary to the belief that microstructures with second phase particles lying exclusively along GBs are the strongest against fracture, microstructures with SiC particles lying along GBs as well as inside Si3N4 grains in locations near GBs are found to be the strongest.