Small Size Ratio Research Articles

Stochastic modeling of kaolinite transport through a sand filter

Accurately modeling the transport of clay particles through coarse-grained porous media is essential to engineering applications ranging from filtration and drainage, groundwater flow modeling, to contaminant transport. However, predicting the retention and clogging behavior of clay particles within a coarse-grained soil matrix is extremely challenging because clay particles can aggregate and form clusters with a variety of fabrics depending on the prevailing geochemistry of the pore fluid (i.e., pH and ionic strength). The work performed in this study developed a stochastic model to investigate the uncertainty of clay particle transport in porous media using random sampling at a given grain-size distribution to account for inherent uncertainty of the size of clay clusters being transported. Results demonstrated that the model proposed in this work can evaluate upper and lower boundaries of retention profiles of clay particles in a sand medium at given mean and standard deviation of grain-size distributions. In addition, the deterministic approach (using median sizes of sand and clay particles in the simulation) underestimated the mass of retained particles at small size ratios of clay particle size/sand particle size when compared with the stochastic prediction, which would result in nonconservative design.

Hazard Assessment of Polymeric Nanobiomaterials for Drug Delivery: What Can We Learn From Literature So Far.

The physicochemical properties of nanobiomaterials, such as their small size and high surface area ratio, make them attractive, novel drug-carriers, with increased cellular interaction and increased permeation through several biological barriers. However, these same properties hinder any extrapolation of knowledge from the toxicity of their raw material. Though, as suggested by the Safe-by-Design (SbD) concept, the hazard assessment should be the starting point for the formulation development. This may enable us to select the most promising candidates of polymeric nanobiomaterials for safe drug-delivery in an early phase of innovation. Nowadays the majority of reports on polymeric nanomaterials are focused in optimizing the nanocarrier features, such as size, physical stability and drug loading efficacy, and in performing preliminary cytocompatibility testing and proving effectiveness of the drug loaded formulation, using the most diverse cell lines. Toxicological studies exploring the biological effects of the polymeric nanomaterials, particularly regarding immune system interaction are often disregarded. The objective of this review is to illustrate what is known about the biological effects of polymeric nanomaterials and to see if trends in toxicity and general links between physicochemical properties of nanobiomaterials and their effects may be derived. For that, data on chitosan, polylactic acid (PLA), polyhydroxyalkanoate (PHA), poly(lactic-co-glycolic acid) (PLGA) and policaprolactone (PCL) nanomaterials will be evaluated regarding acute and repeated dose toxicity, inflammation, oxidative stress, genotoxicity, toxicity on reproduction and hemocompatibility. We further intend to identify the analytical and biological tests described in the literature used to assess polymeric nanomaterials toxicity, to evaluate and interpret the available results and to expose the obstacles and challenges related to the nanomaterial testing. At the present time, considering all the information collected, the hazard assessment and thus also the SbD of polymeric nanomaterials is still dependent on a case-by-case evaluation. The identified obstacles prevent the identification of toxicity trends and the generation of an assertive toxicity database. In the future, in vitro and in vivo harmonized toxicity studies using unloaded polymeric nanomaterials, extensively characterized regarding their intrinsic and extrinsic properties should allow to generate such database. Such a database would enable us to apply the SbD approach more efficiently.

Cast-and-Use Super Black Coating Based on Polymer-Derived Hierarchical Porous Carbon Spheres.

Super black materials with extremely low reflectance and high absorption of incident light are crucial in various applications with strict optical requirements. However, the existing super black materials suffer from technical complexity in practical use whereas the underlying physics of their ultralow reflectance is still unclear. Herein, hierarchical porous carbon spheres are prepared using poly(vinylidene chloride- co-vinyl chloride) as a precursor. Dehydrochlorination treatment has proved to be very crucial for the morphology robustness of the porous polymer spheres during carbonization process. Coatings cast from the dispersion of these carbon spheres exhibit a hemispherical reflectance of <0.2% in the visible region and <0.3% in the range of 300-2000 nm, and the lowest reflectance of 0.14% can be reached. This super black coating has great advantages in its easy availability of starting materials, low equipment requirement, and high adaptability onto various substrates. Besides, a theoretical investigation suggests that a small scatterer size and low volume-filling ratio are the two most essential factors in realizing ultralow reflectance, which also offers an instructive guidance for the rational design of super black materials.

Wafer-scale on-chip synthesis and field emission properties of vertically aligned boron nitride based nanofiber arrays

One dimensional boron nitride (BN) nanomaterials with a high aspect ratio are of great interest due to their unique properties and potential applications. However, BN nanomaterials are generally difficult to synthesize. Here, we describe the creation of arrays of vertically aligned pure BN nanofibers and BN coated carbon nanofibers, fabricated on-chip via a straightforward template-assisted chemical conversion reaction. The template, a glassy carbon nanofiber array, is produced by plasma processing of conventional photoresists. The method is highly controllable, patternable, and scalable, and the final arrays can be fabricated over large areas with a controlled fiber length. We characterize the electron field emission properties of the BN-coated carbon nanofiber array and find a large field enhancement factor, low turn-on voltage, and good stability. The outstanding field emission performance results from the small tip size and high aspect ratio of the nanofiber as well as the high chemical stability and high thermal conductivity of the BN coating.

Optimization of the catalytic performance of Pd/Fe3O4 nanoparticles prepared via microwave-assisted synthesis for pharmaceutical and catalysis applications

Microwave assisted synthesis technique was used to prepare palladium supported on iron oxide nanoparticles. The advantage of using microwave irradiation as a synthetic tool is due to its unique features as a one step, simple, versatile, and rapid process. The reactants are added simply at room temperature without using high-temperature injection. Hydrazine hydrate was added by the following ratios (0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1, 1.6, and 3) ml to the different prepared samples at room temperature in order to investigate its effect on the catalytic performance of the prepared catalysts. The prepared catalyst could be used as an ideal candidate not only for Pharmaceutical industry through cross-coupling reactions but also for low temperature oxidation catalysis of carbon monoxide and pharmaceutical applications as well. The experimental results showed that Pd/Fe3O4 catalyst has a remarkable catalytic activity for carbon monoxide oxidation catalysis due to the strong interaction between palladium and iron oxide nanoparticles. This may be due to the small particle size (7-14 nm) and concentration ratio of the Pd nanoparticles dispersed on the surface of magnetite (Fe3O4). Those nanoparticles were characterized by various spectroscopic techniques including; X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Vibrating Sample Magnetometer (VSM) and transmission electron microscopy (TEM).

Strategy to control CO2 diffusion in polystyrene microcellular foaming via CO2-philic additives

The introduction of suitable CO2-philic additives, enabling high CO2 concentration retained in the polymer matrix, might be a promising strategy to obtain foams with small cell size and large volume expansion ratio. The effect of molecular weight (Mn) (2000–17000 g/mol) of CO2-philic additives (PDMS and PVAc) on the diffusion of supercritical CO2 into and out of polystyrene (PS) was investigated via experiments and dissipative particle dynamics simulations. The CO2 diffusion coefficient increased with the presence of additives especially with PDMS (2000 g/mol, from 1.2 × 10−9 m2/s to 2.8 × 10−9 m2/s). Meanwhile, the saturation solubility of CO2 increase with the incorporation additives. Compared with high Mn additives, the slower CO2 desorption rate with additives with Mn of 2000 g/mol enabled higher amount of CO2 retained in PS, resulting in higher cell density. The incorporation of PDMS (2000 g/mol) decreased the cell size (from 11.67 to 7.57 μ m) and increased volume expansion ratio of PS foams.

Optimizing swirl in compact uniflow cyclones

This paper presents an experimental examination of the velocity field distribution in the separation chamber of a uniflow cyclone with closed particle outlet to evaluate the swirl characteristics in the vortex finder region based on stereoscopic particle image velocimetry. A cold flow model with a closed particle outlet was used to assess different angles of attack and core size ratios at typical Reynolds numbers for the separation of low loaded gas‐solid flows. The focus of the study was on the relationship between swirl strength as well as performance data. At higher angles, the parabolic swirl strength distribution changed to a region with constant high acceleration of the particles in the separation zone. Integral and differential swirl numbers were correlated with the ratio of tangential to radial velocity and to the calculated cut size diameter. At low angles of attack, implying a strong redirection of flow perpendicular toward the main flow direction and small core size ratios, defined by the radial distance between hub and tip, the local differential swirl number can be more than twice as large as in the base configuration. Yet, the integral swirl number hardly changed. The velocity fields showed mean tangential to radial velocity ratios ranging from 0.73 to 6.85 at swirl vane angles of 15 °–60 °; core size ratios between 0.125 and 0.625 at vortex finder diameter were measured and calculated cut size diameters between 10 and 90 μm were derived. This data provides the foundation for further validation studies and the development of new design criteria. © 2018 American Institute of Chemical Engineers AIChE J, 65: 766–776, 2019

Identifying Inflated Super-Earths and Photo-evaporated Cores

Abstract We present empirical evidence, supported by a planet formation model, to show that the curve approximates the location of the so-called photo-evaporation valley. Planets below that curve are likely to have experienced complete photo-evaporation, and planets just above it appear to have inflated radii; thus we identify a new population of inflated super-Earths and mini-Neptunes. Our N-body simulations are set within an evolving protoplanetary disk and include prescriptions for orbital migration, gas accretion, and atmospheric loss due to giant impacts. Our simulated systems broadly match the sizes and periods of super-Earths in the Kepler catalog. They also reproduce the relative sizes of adjacent planets in the same system, with the exception of planet pairs that straddle the photo-evaporation valley. This latter group is populated by planet pairs with either very large or very small size ratios (R out/R in ≫ 1 or R out/R in ≪ 1) and a dearth of size ratios near unity. It appears that this feature could be reproduced if the planet outside the photo-evaporation valley (typically the outer planet, but sometimes not) has its atmosphere significantly expanded by stellar irradiation. This new population of planets may be ideal targets for future transit spectroscopy observations with the upcoming James Webb Space Telescope.

Analysis of slot-based radiators using TCM and its application in MIMO antennas

In this article, with the help of the theory of characteristic modes (TCM), it is found that the introduction of circular slots in a chassis modifies the chassis modes. Based on the location of the slot, different chassis modes will be affected. For a fixed location, the slot to chassis size ratio plays an important role in its effect on the radiating bandwidth (BW). For a small size ratio, a modified chassis mode will be created without affecting the radiating BW. The current concentration across the slot depends on the shape of the slot (circular, rectangular, triangular, or square) and its location on the chassis. Moreover, the effect of multiple circular slots on the chassis modes is investigated. For slots introduced in a symmetrical fashion, that is, four elements, the modes are not affected and are similar to the original chassis ones. We also investigate the principle behind frequency reconfigurability using TCM analysis. The varactors used for frequency reconfigurability do not alter the radiating BW (Modal Significance plots) but only help in the input impedance matching at different frequency bands of the same mode. If a mode is excited purely using a proper feeding arrangement, the same frequency reconfigurable antenna will behave as a wide band one. Based on the detailed analysis presented in this work, a compact multiple-input-multiple-output annular slot frequency reconfigurable antenna operating between 1.8 and 2.45 GHz is presented. Frequency tuning is achieved using varactor diodes.

Effect of filler content, size, aspect ratio and morphology on thermal, morphological and permeability properties of porous talc filled—Polypropylene obtained through MEAUS process

AbstractSeveral commercial grades of talc were selected to develop polypropylene based microporous membranes through MEAUS process (melt extrusion—annealing—uniaxial strain). Talc commercial grades differed in particle size, aspect ratio, and crystalline morphology. Different filler percentages were added to polypropylene (1, 5, 10 wt.%) Parameters such as draw ratio during extrusion, annealing temperature strain rate, and strain extension were kept as constant to analyze the effect of the talc characteristics and content of the obtained membranes. Small particle size and high aspect ratio tend to provide membranes with small pore size, high porous area, and high Gurley permeability values.

All‐optical NOT and XOR logic gates using photonic crystal nano‐resonator and based on an interference effect

In this study, a small size, low power, simple and high contrast ratio (CR) structure was designed and simulated to use in photonic crystal-based all-optical logic gates. This structure can be used for both all-optical logic NOT and XOR gates. The suggested structure is composed of three waveguides and a nano-resonator. The nano-resonator was designed by removing two dielectric rods. For use as an optical NOT logic gate, one of the input ports enters the control signal. In this case, the CR between logic levels `0' and `1' is 20.53 dB, which is higher than that of the provided gates based on structures published recently. The CR for the XOR gate is 19.95 dB. The response time to the input signal of the designed gate is 0.466 ps. The simplicity of the structure, small size, and high CR are the advantages of this structure compared to previously provided logic gates. The results have proven a superior prospect for the proposed structure to use in all optical integrated circuits.

(Invited) Electro/Electroless Grafting of Organic Dielectric Film on Silicon Surface and Its Application on through Silicon Via

With the rapid development of electronic industry, the packaging technology requires higher density and integration, which is a great challenge for semiconductor manufacturing. In order to continue the acknowledged “Moore's law”, the three-dimensional through silicon via (TSV) packaging of stacked chips has become the focus of attention, providing fresh ideas for the industry. The preparation of insulators is one of the key technologies for TSV. However it is difficult for conventional methods to prepare SiO2 insulators with high coverage in TSV with small size and high aspect ratio. In addition, higher performance of TSV proposes a big challenge for SiO2. Organic polymers can replace SiO2 used as an insulator for TSV, because their lower dielectric constant can greatly improve the properties of TSV. Electrografting is a novel technology for polymer film preparation, which has the advantages of being simple, low cost and does not required special equipment.. In recent years, the modification of the Si surface with the electrochemical reduction of diazonium salts has become attractive because it can be performed in aqueous media, which is more acceptable for industrial applications. In the best understood reaction, a diazonium salt with an electrolyte such as tetrabutylammonium cations is reduced by an externally applied potential, typically at around −1 V versus the saturated calomel electrode. In our study, the electrografting technology is used to graft polymer film onto a Si surface, and its mechanism and the effects of pulsed voltage and composition of the solution are investigated. In the process of electrografting, 4-nitrobenzene diazonium (NBD) tetrafluoroborate is reduced by electrons provided by an electric source, forming nitrophenyl radicals. These radicals covalently bond to the Si surface to form a polynitrophenyl (PNP) primer layer, and initiate the polymerization of vinyl monomers. The radical-terminated polyvinyl chains formed in the solution and nitrophenyl radicals are then added to the aromatic rings of the primer layer to form the expected polyvinyl film. Consequently the grafted film is composed of PNP and the polymer of monomers. Furthermore, we propose an easier chemical grafting method based on the finding that diazonium salt can be spontaneously reduced at the Si surface when HF is present in the aqueous solution even without an externally applied potential., and study the influence factors of structure, morphology and component of the polymer film. This process is conducted in acidic aqueous media containing HF. From the mechanistic point of view, Si atoms at the Si surface are oxidized by HF, providing electrons for the reduction of NBD cations at the open circuit potential. The mechanism of the grafting of the polymer of monomers is the same as that of an electrografting process. The polymer films prepared by either the electrografting or chemical grafting methods have good adhesion, dielectric properties and thermal properties. Then the polymer film is applied in TSV. As far as we know, insufficient film thickness and low coverage are still serious problems for plasma-enhanced chemical vapor deposition methods. However, both electrografting and chemical grafting overcome these problems. In addition, the narrow diameter and high aspect ratio (≥1:10) are not limitations for grafting methods. Poly(methyl methacrylate) film has a coverage of 76%, while poly(acrylic acid) film has a coverage as high as 100%.

Evidence of Stratification in Binary Colloidal Films from Microbeam X-ray Scattering: Toward Optimizing the Evaporative Assembly Processes for Coatings

Colloidal films have many important applications where a layered configuration is desirable, including flexible electronics, antireflective coatings, and antimicrobial paints. We report stratification during evaporative film formation in binary colloidal dispersions, probed using a novel microbeam small-angle X-ray scattering (SAXS) technique. To our knowledge, SAXS approaches have not been used to experimentally obtain quantitative data of concentration profiles in multicomponent colloidal films. We measured the local scattering of a film at different vertical locations using a microfocused X-ray beam and determined particle concentrations at different film depths using a linear combination analysis of the mixed film and pure film scattering data. Using small particle size ratios ranging from 2.6 to 1.2, we experimentally observed and quantify three distinct stratification configurations: inverted small-on-top, large-on-top, and no stratification. Our results show some agreement with a previously proposed stratification state diagram, although there are some limitations. Experimental verification of these stratification phenomena is critical to fully understanding the physics of particle movement and structure development during film formation, which is crucial for optimizing evaporative assembly processes for coatings.

Structure factors in a two-dimensional binary colloidal hard sphere system

ABSTRACTHard disks are one of the simplest interacting many-body model system in two dimensions (2D). Here, we present a comprehensive set of measurements of the static structure factors for quasi-2D monodisperse fluids and two different binary colloidal hard sphere mixtures: a small size ratio (SSR) system with a negligibly small negative non-additivity and a large size ratio system with a significantly larger non-additivity. We compare the experimental results for the monodisperse and SSR systems to those calculated using density functional theory (DFT) for additive mixtures. Furthermore, we determine the zero-wavevector limits of the static structure factors for the monodisperse and binary hard sphere fluids directly from an analysis of number and concentration fluctuations. For the monodisperse case, this leads to the isothermal compressibility, which agrees very well with DFT, and is consistent with the scaled particle theory equation of state for hard disks. For the binary fluids, the partial static structure factors are used to calculate the Bhatia–Thornton structure factors, and we find qualitative agreement with DFT for the SSR mixture. Finally, the zero-wavevector limits of the Bhatia–Thornton structure factors are determined and directly related to the thermodynamic factor, the dilatation factor and the isothermal compressibility.

Design and Optimization Techniques of Over-Chip Bond-Wire Microtransformers With LTCC Core

This paper describes the realization of bond-wire micromagnetics by using standard bonding wires and a toroidal ferromagnetic low-temperature co-fired ceramic core with high resistivity. The proposed fabrication procedure is suitable for the development of magnetic components on the top of an integrated circuit with a small profile and a small size ( $\sim 33~\mu \text{H}$ ) and high effective turns ratio (~20). Applications include bootstrap circuits and micropower conversion for energy harvesting. Measurements demonstrate a maximum secondary Q-factor of 11.6 at 1.3 MHz, and a coupling coefficient of 0.65 with an effective turns ratio of 19, which are among the highest values reported for toroidal miniaturized magnetics. The achieved inductance density is $2~\mu \text{H}$ /mm2, along with an inductance per unit core volume of 15.6 $\mu \text{H}$ /mm3, and a dc inductance-to-resistance ratio of 2.23 $\mu \text{H}/\Omega $ . The presented technique allows to obtain over-chip magnetics trough a postprocessing of the core, and it is also suitable for high-density power supply in package and power supply on-chip. Finally, a series of optimization techniques for planar core magnetic devices in order to maximize the inductance per unit area is discussed and applied to the considered case.

Reinforcement Parameter Effect on Properties of Three-Phase Composites

AbstractIn this study, a micromechanics model has been proposed for predicting the effects of particle size and aggregation on elastic properties of nanocomposites, and the interphase between the particle and matrix is also taken into account. Inherent characteristics of nanoparticle, such as small size and high surface area ratio, make nanoparticle in a state of unstable energy and easy to agglomerate in matrix. The analytical expressions for the effective elastic modulus of nanocomposites are derived, which can consider the effect of particle agglomeration. The dispersion state or degree of agglomeration of nanoparticle and the thickness and stiffness of interphase are known to have a significant influence on nanocomposites. The results show that the increase of particle radius and agglomeration volume fractions reduces the elastic stiffness of nanocomposites. Moreover, the composite reinforcement can be improved by increases of interphase thickness and stiffness.

Study on the fabrication of composite photonic crystals with high structural stability by co-sedimentation self-assembly on fabric substrates

The Silica/Poly(methylmethacrylate-butylacrylate)[SiO2/P(MMA-BA)] photonic crystals(PCs) with brilliant structural colors were fabricated on fabric substrates by co-sedimentation self-assembly, in which the relatively smaller P(MMA-BA) copolymer particles filled in the interstices among the larger SiO2 microspheres. The fabricated composite PCs were mechanically robust and strongly bonded to the substrate because of the cementing effect caused by the soft P(MMA-BA) copolymer particles filling in the interstices of the SiO2 microspheres like cement filling in the gap and tightly holding stones in a sturdy cement wall. The volume fraction and the size ratios of the two components significantly influenced the structural colors of the composite PCs, and the larger volume fraction could improve the structural stability of the composite PCs, while the smaller size ratios could enhance the brightness of the structural colors of the composite PCs. The composite PCs with both high structural stability and brilliant structural colors have great application prospect for structural coloration of textiles.

Quasi-static analysis of forces and stress for a novel two-step movable tooth drive

ABSTRACTFor sine movable tooth drive, the movable tooth number must be increased to obtain large speed ratio of the drive which increases largely radial size of the drive. Here, a novel two-step movable tooth drive is proposed. The drive can realize small size and large speed ratio simultaneously. For the two-step movable tooth drive, 3D design was done; the forces and the contact stress in the drive system were investigated; results show that the maximum force on the second step drive depends on radius of the movable teeth, size parameters of the second step drive, and radius of the sine ball track in the first step drive; the contact stresses between the meshing elements change periodically, the contact stress between the movable teeth and cap end is the maximum which can be taken as design factor for the load-carrying ability of the drive system.

Determination of dynamic dispersion coefficients for passive and reactive particles flowing in a circular tube

Using the moment analysis method and the Green’s function, mathematical formulations valid across the full-time scale have been derived to determine dynamic dispersion coefficients for passive and reactive particles flowing in a circular tube with fully-developed laminar flow under different source conditions. The newly proposed formulations were verified through agreements with both analytical solutions and random walk particle tracking (RWPT) simulations. The relationship between particle size and dispersion coefficient for passive particles varies with time and they are positively correlated if Peclet number is larger than its critical value; otherwise, they are negatively correlated. Furthermore, the critical Peclet number decreases as time increases. Compared to an instantaneous point source, the critical Peclet number for a volumetric planar source is much smaller. At a small size ratio, size-exclusion effects on passive particle dispersion can be neglected across the full-time scale for both instantaneous point and volumetric planar sources; whereas, at a large size ratio, its significance needs to be considered, depending upon time and source condition. Using Dre_diff=0.02 (Dre_diff=(D−Dnon_ad)/D, where D and Dnon_ad are dispersion coefficients with and without axial diffusion, respectively) as the critical value, axial-diffusion effects on dispersion are negligible for passive solutes at long times if Peclet number is not smaller than 50; however, due to size exclusion this is not applicable for passive particles. At early times, reaction rate, center-of-mass velocity, and dispersion coefficient are not sensitive to Damköhler number for reactive particles. At long times, reaction rate and enter-of-mass velocity increases in magnitude as the Damköhler number increases, while the dispersion coefficient decreases with increasing Damköhler number. Consequently, reaction at the tube walls greatly affects concentration distributions.

Elasticity of particle-loaded liquid foams.

Mixing solid particles with liquid foam is a common process used in industry for manufacturing aerated materials. Desire for improvement of involved industrial processes and optimization of resulting foamed materials stimulates fundamental research on those complex mixtures of grains, bubbles and liquid. In this paper, we generate well-controlled particle-loaded liquid foams and we determine their elastic behavior as a function of particle size (6-3000 μm) and particle volume fraction (0-6%). We focus on both the elastic modulus exhibited by the material at small strain and the strain marking the end of the linear elastic regime. Results reveal the existence of a critical particle-to-bubble size ratio triggering a sharp transition between two well-defined regimes. For small size ratios, the behavior is governed by the mechanical properties of the solid grains, which have been proved to pack in the shape of a foam-embedded granular skeleton. In contrast, bubbles elasticity prevails in the second regime, where isolated large particles contribute only weakly to the rheological behavior of the foamed material. The modeling of elasticity for each regime allows for this transition to be normalized and compared with previously reported particle size-induced effects for foam drainage (Haffner et al. J. Colloid Interface Sci., 2015, 458, 200-208) and solid foam mechanics (Khidas et al., Compos. Sci. Technol., 2015, 119, 62-67). This highlights that rheology and the other properties of particle-loaded foams are subjected to the same size-induced morphological transition.