Size Dispersion Research Articles

Structures of alkaline earth metal oxides supported on MCF and the enhanced catalytic performance for methanolysis of polycarbonate

Mesoporous solid bases catalysts were prepared by impregnation of a certain amount of alkaline-earth metals species on the synthesized MCF support and used in the methanolysis of PC. Compared with the synthesized SBA-15 solid base catalysts, CaO/MCF catalysts with larger pore size, pore volume and higher active species dispersion exhibited higher catalytic activity. The influences of supported catalyst physicochemical properties and methanolysis conditions were also investigated. The results indicated that methanolysis rate of PC was closed to 100%, and yield of BPA was over 95% under the proper reaction conditions with the excellent performance of 12%CaO/MCF catalyst. The catalyst stability study showed that 12%CaO/MCF had good catalytic activity after five circles. At the same time, the possible methanolysis mechanism of PC was proposed.

A note on size– biased new quasi Poisson– Lindley distribution

In this paper some important properties including coefficients of variation, skewness, kurtosis and index of dispersion of size–biased new quasi Poisson–Lindley distribution (SBNQPLD) have been discussed and their behaviors have been explained graphically for varying values of parameters. Some applications of SBNQPLD have also been discussed.

Microstructural analysis of sheared polydisperse polyhedral grains.

This article presents an analysis of the shear strength of numerical samples composed of polyhedra presenting a grain size dispersion. Previous numerical studies using, for instance, disks, polygons, and spheres, have consistently shown that microstructural properties linked to the fabric and force transmission allow granular media to exhibit a constant shear resistance although packing fraction can dramatically change as a broader grain-size distribution is considered. To have a complete picture of such behavior, we developed a set of numerical experiments in the frame of the discrete element method to test the shear strength of polydisperse samples composed of polyhedral grains. Although the contact networks and force transmission are quite more complex for such generalized grain shape, we can verify that the shear strength independence still holds up for 3D regular polyhedra. We make a particular focus upon the role of different contact types in the assemblies and their relative contributions to the granular connectivity and sample strength. The invariance of shear strength at the macroscopic scale results deeply linked to fine compensations at the microstructural level involving geometrical and force anisotropies of the assembly.

Photoluminescence of CdTe/ZnTe Heterostructures with Nominal CdTe Layer Thickness from One to Eight Monolayers Grown by Atomic Layer Deposition

We studied the luminescence of CdTe layers with a nominal thickness of one, two, four, and eight monolayers (MLs) grown by atomic layer deposition in a ZnTe matrix. The layers with a thickness of one and two monolayers exhibit the properties of homogeneous layers, while the layers with a thickness of four and eight monolayers are planar arrays of quantum dots (QDs). The sizes of QDs and their size dispersion increase with an increase in the nominal thickness of the CdTe layer. The shape of the luminescence excitation spectra of the CdTe layer in these samples varies greatly. Depending on the energy distance between the exciton levels of the CdTe layers and the ZnTe matrix, the ratio of the contributions of the ZnTe exciton and charge carriers unbound to the exciton to the energy transfer varies significantly.

Lipid-Based Nano Formulation Approach to Target Brain for the Management of Tuberculosis through Intranasal Delivery: Formulation Development and Evaluation

Abstract: Objectives: Development of nano-emulsion based drug delivery as combined drug loaded form for the possible management of meningitis. Intranasal delivery of nano-emulsion to the brain and study the nasal irritancy. Methodology: Spontaneous emulsification method was used in preparing the nanoemulsion. The compatibility studies i.e., Differential Scanning Colorimetry and Fourier Transform Infrared Spectroscopy were carried out for Isoniazid, Rifampicin, Resveratrol and physical mixture. Pseudoternary phase diagrams were constructed in various ratios. The formulations which passed the thermodynamic stability studies were evaluated for particle size, zeta potential and poly dispersity index. Cytotoxicity of the pure drugs and formulations were measured in in vitro cell line. The formulations were given for histopathological studies. Then these formulations were administered to rats intranasally and the brain of the rats was collected. Then the brain tissue was minced and was given for LCMS analysis to know the amount of drug reaching the brain. Results: The DSC and FTIR graphs state that the drugs were compatible with each other. The formulations which passed the thermodynamic stability studies were A7, A9, J8 and G9. Among these formulations A7 was selected as it had lower particle size when compared to other formulations. The formulations showed low nasal irritancy and no malignancy. From the LCMS analysis it was found that 82.6% of Isoniazid with Resveratrol nanoemulsion and 78.48% of Rifampicin with Resveratrol nanoemulsion has reached the targeted area the brain. Conclusion: From the studies it can be concluded that when the formulations were administered intranasally maximum amount of the drugs had reached the targeted area the brain. So, when the drugs are given intranasally there could be decrease in the dose of the drug, increased bioavailability at the site of action and increased therapeutic efficacy. Key words: Tuberculous meningitis, Intranasal delivery, Nanoemulsion, Blood Brain Barrier, Mycobacterium tuberculosis.

Comparison of Two Gas Injection Methods for Generating Bubbles in a T-junction

In this work, we compare the performance of two different methods for generating bubbles in conditions relevant to microgravity. A T-junction formed by two cylindrical (1 mm of internal diameter) and perpendicular channels is used to generate trains of non-wetting bubbles. Air and distilled water are used as dispersed and continuous phases, respectively. The difference between both methods lies in the strategy used to inject the fluids. In one case (here referred to as TJ-A configuration), the gas is injected into the side channel. In the other case (referred to as TJ-B), the gas is injected into the main channel. Bubble size dispersion is analyzed and quantified with the polydispersity index. The increase of the capillary number (based on the continuous phase) has shown a strong influence on the regularity of the bubble generation process. The TJ-A method can produce monodisperse bubbles at higher capillary numbers than configuration TJ-B. The limits of monodispersity, as far as the capillary number is concerned, are studied. These limits determine the optimal operating range of the T-junction for generating highly monodisperse bubbles. Beyond these limits, polydispersity increases, although much more abruptly in TJ-B than in TJ-A. The bubble generation frequency is also studied, with special attention to the two main regimes that characterize the frequency, i.e. the linear regime (at very low gas flow rate) and the saturation regime (at high gas flow rates). A new dimensionless expression of the bubble generation frequency is proposed in this work.

Analytical Modeling Based on Modified Effective Medium Theories for Optical Properties of Photovoltaic Material-Incorporated Plasmonic Nanoparticles

Theoretical guidance on the optical properties of plasmonic nanoparticles (NPs) is of significant importance in tremendous numbers of fields like photovoltaics. The incorporation of plasmonic NPs into photovoltaic material can promote optical absorption either via the excitation of localized surface plasmon resonance (LSPR) modes or due to multiple light scattering. Since most fabrication techniques for the incorporation of NPs into photovoltaic material result in a random array of NPs with various sizes, numerical simulations based on solving the Maxwell equations are computationally expensive and prohibitively slow for this large number of NPs. Therefore, in this paper, based on modified effective medium theories, taking into account finite size of NPs, size dispersion for NPs, extrinsic dynamic effect, and intrinsic confinement effect, fast and cost-effective analytical modeling, considering both LSPR and scattering effects, is presented to obtain the optical properties of photovoltaic material incorporated by spherical NPs with nonuniform size and random distribution. Then, by means of presented analytical modeling, considering reasonably low and high volume fractions of NPs in addition to small and large size of NPs, the effect of different parameters of embedded NPs into organic and inorganic photovoltaic materials is explored.

Understanding the Fundamental Plane and the Tully Fisher Relation

The relation between early type galaxy size, surface brightness and velocity dispersion, "the fundamental plane", has long been understood as resulting from equilibrium in their largely pressure supported stellar dynamics. The dissipation and feedback involved in reaching such an equilibrium through merger formation of these galaxies over cosmic time can be responsible for the orientation of the plane. We see a correlation between surface brightness enhancement and youth in the 6dF Galaxy Survey. Correlations of this `tilt' with stellar mass, age, concentration, shape and metallicity now point the direction for further work on the resolved kinematics and structure of these nearby galaxies and on their initial mass function and dark matter component. On the face of it, the Tully Fisher relation is a simpler one dimensional scaling relation. However, as late type galaxies have bulges as well as disks, and, as the surface density of disks is only standard for the more massive galaxies, additional parameters are involved.

Microstructure and physicochemical properties: Effect of pre-chilling and storage time on the quality of Channel catfish during frozen storage

The objective this research was to investigate pre-chilling time (1, 4, 8 and 24 h) on the histomorphology and physicochemical properties of catfish fillets during frozen storage (1, 4, 12 and 24 weeks). With the extended pre-chilling (4 °C) and frozen storage (−18 °C) time, cells of catfish fillet were gradually dissociated in three aspects: size change, dispersion and breakage by ice crystals. Catfish fillets pre-chilled for 24 h or stored for more than 12 weeks showed apparent higher cell structure damage than other treated groups. The Magnetic resonance imaging (MRI) results showed that the activity of hydrogen protons was progressively enhanced with the storage time up to the 4 weeks and then decreased. With the increasing frozen storage period, pH of catfish samples were transferred from weakly alkali to weakly acid, shear force and whiteness of frozen channel catfish fillets was progressively decreased (P < 0.05), while the total volatile base-nitrogen (TVB-N), K value, expressible moisture and thiobarbituric acid-reactivate substance (TBARS) contents were increased (P < 0.05). Therefore, the maximum pre-chilling time and shelf-life of frozen catfish fillets should be recommended as 8 h and 12 weeks, respectively. This research provided theoretical support for aquatic processing industrially.

Formulation of peppermint oil nanoemulsion using conjugates of whey proteins with maltodextrin and its characterization

Whey protein-maltodextrin conjugate is used as emulsifier and stabilizer to prepare peppermint (Mentha piperita L.) oil (PO) nanoemulsion. The mean particle size, zeta potential and poly dispersity index (PDI) of stable PO nanoemulsion (5% oil+8% conjugate+0.5% Tween 80) was 144.8±5.32 nm, -24.40±0.42 mV and 0.217±0.05 respectively and this formulation was not unstable to food processing conditions like pH 3.0 to pH 7.0, heat treatments and ionic strength 0.1 M to 1.0 M. The emulsion was stable at 25°C for 15 days and its particle size is 332.2±4.66 nm at 15th day of storage. Agar well diffusion method is used to assess the antimicrobial efficacy of PO (5%) dissolved in dimethyl sulphoxide (DMSO) and 5% PO nanoemulsion against microorganisms like E. coli ATCC 25922, B. cereus ATCC 14459, Salmonella typhi NCDC 6017 and E. faecalis NCDC 115. The formulation prepared in the present study will have the application in preservation of various foods against spoilage microorganisms.

Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures.

We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on Pb4S3Br2, a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS–PbBr2 phase diagram. The Pb4S3Br2 nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to ∼30 nm), an indirect bandgap, photoconductivity (responsivity = 4 ± 1 mA/W), and stability for months in air. A crystal structure is proposed for this new material by combining the information from 3D electron diffraction and electron tomography of a single nanocrystal, X-ray powder diffraction, and density functional theory calculations. Such a structure is closely related to that of the recently discovered high-pressure chalcohalide Pb4S3I2 phase, and indeed we were able to extend our synthesis scheme to Pb4S3I2 colloidal nanocrystals, whose structure matches the one that has been published for the bulk. Finally, we could also prepare nanocrystals of Pb3S2Cl2, which proved to be a structural analogue of the recently reported bulk Pb3Se2Br2 phase. It is remarkable that one high-pressure structure (for Pb4S3I2) and two metastable structures that had not yet been reported (for Pb4S3Br2 and Pb3S2Cl2) can be prepared on the nanoscale by wet-chemical approaches. This highlights the important role of colloidal chemistry in the discovery of new materials and motivates further exploration into metal chalcohalide nanocrystals.

Stress transmission in cemented bidisperse granular materials.

We analyze stress distributions in a two-dimensional bidisperse cemented granular packing for a broad range of the values of particle-size ratio, the volumes of large and small particles, and the amount of cementing matrix. In such textured porous materials, the stress concentration, which controls the fracture and fragmentation of the material under tensile loading or in grinding processes, reflects not only the porosity but also the contact network of the particle phase and the resulting stress chains. By means of peridynamic simulations under tensile loading, we show how both the texture and stress distribution depend on size ratio, volume ratio, and the amount of the cementing matrix. In particular, the volume fraction of the class of small particles plays a key role in homogenizing stresses across the system by reducing porosity. Interestingly, the texture controls not only the porosity but also the distribution of pores inside the system with its statistical variability, found to be strongly correlated with the homogeneity of stresses inside the large particles. The most homogeneous stress distribution occurs for the largest size ratio and largest volume fraction of small particles, corresponding to the lowest pore size dispersion and the cushioning effect of small particles and its similar role to the binding matrix for stress redistribution across the packing. At higher porosity, the tensile stresses above the mean stress fall off exponentially in all phases with an exponent that strongly depends on the texture. The exponential part broadens with decreasing matrix volume fraction and particle-size ratio. These correlations reveal the strong interplay between size polydispersity and the cohesive action of the binding matrix for stress distribution, which is significant for the behavior of textured materials in grinding operations.

Room-Temperature Solid-State Preparation of CoFe2O4@Coal Composites and Their Catalytic Performance in Direct Coal Liquefaction

Iron-based catalysts are promising catalysts in the direct coal liquefaction (DCL) process as they are inexpensive and environmentally friendly. However, most such iron-based catalysts show relatively low activity in coal conversion and oil yield. Common techniques for the synthesis of these catalysts with excellent catalytic performance remain a substantial challenge. We present a simple solid-state synthesis strategy for preparing CoFe2O4 nanoparticles and CoFe2O4 nanoparticles supported on coal (CoFe2O4@coal) composites for DCL. The obtained bimetallic oxide CoFe2O4 nanoparticles show an enhanced catalytic performance in the DCL compared with monometallic components Fe2O3 and Co(OH)2 nanoparticles. The synergistic effect between Co and Fe of CoFe2O4 nanoparticles promotes the catalytic hydrogenation of coal during the DCL process. Moreover, the catalytic performance of CoFe2O4 nanoparticles is further improved when they are loaded on the coal. The conversion, oil yield, liquefaction degree, and gas yield of Dahuangshan lignite are 99.44, 56.01, 82.18 and 19.30 wt %, respectively, with the CoFe2O4@coal composites involved. The smaller particle size and high dispersion of CoFe2O4 supported on coal are of great benefit to full contact between coal and active components. The in-situ solid-state synthesis with coal as support shows great potential to prepare effective iron-based catalysts toward DCL in practice.

Multi‐scale spatial dynamics of the Chesapeake Bay nettle, Chrysaora chesapeakei

AbstractUntangling organisms' multi‐scale spatial distributions is challenging due to their interactions with environments at multiple spatial and temporal scales. We deployed an Adaptive Resolution Imaging Sonar (ARIS) in a Chesapeake Bay sub‐estuary to investigate multi‐scale spatial distributions of the bay nettle (Chrysaora chesapeakei) in May–September of 2016 and 2017. Nettles were found to be dispersed in aggregations of multiple individuals. The average density of bay nettles in 2017 was higher than in 2016. Small aggregations (&lt;5 m) were persistent in both years but only contributed &lt;10% of total observed nettles. Large patches (&gt;30 m) contributed ~40% of the total observed nettles. Large patches were more common in creek habitat where nettle density was higher. Nettle density was found to hit a peak value once in 2016, while there were two density peaks in 2017. Different aggregation patterns were observed during the second peak period in 2017 in which the number of large patches increased dramatically. Within the surveyed waterscape, the spatial patterns were consistent over time with higher abundance in the source creek than in the river channel, which underscores that C. chesapeakei requires hard substrate in shallow creeks for its benthic polyp stage. Using the ratio between nettles in the creek and near creek mouth as a proxy for dispersal rate, more nettles were transported out of the creek in 2017 than in 2016. The increase in patch size and high dispersion rate in peak periods in 2017 suggests that individuals were moving out of the creek habitat as density increased. Results highlight the complex spatial structure of bay nettles, which has major impacts on density estimates and subsequently affects our understanding of jellyfish population dynamics and long‐term trends.

Evaluation of the Mechanical Properties of Carbon Nanotube (CNT) Reinforced Aluminum (6061) Composites Using Closed Die Forging

In this study, the closed die forging of aluminium based compoistes reinfoced with CNTs (1vol% and 3vol%) were investigated. Initially, the composites were fabricated using high energy ball milling followed by compaction and sintering. The microstructural results showed that finer grain size and homogeneous dispersion of CNTs were obtained. Composites with up to 97% densification were produced when fine open porosities were removed by closed die forging. The results imply that the hardness and compressive strength of composites with 3vol.% of CNTs has improved without any deterioration. In addition, workability behaviors of composites were investigated by cold upsetting test. For that pore reopening test was performed to confirm the closure of micro-pores after the closed die forged, and to further analyze the densification of the composites. Typical cases, as the pores were not re-opened even after increasing the strain, additional forming is possible up to large deformations.

Influence of Precursor Concentration on the Formation of Silver Nanoparticles with Oligostyrylmonocarboxylate Ligands in ED-20 Epoxy Oligomer

Using transmission electron microscopy and UV–Vis spectroscopy, the effect of the concentration of the silver oligostyrylmonocarboxylate precursor in the range of 0.3–3.2 wt % in the reaction with the ED-20 epoxy resin on the formation of silver nanoparticles at a temperature of 75°C is studied. At the initial carboxylate concentration ≤0.3 wt %, silver nanoparticles with oligostyrylmonocarboxylate ligands having a spherical shape, small size, and narrow dispersion are produced. With an increase in the initial concentration of silver oligostyrylcarboxylate ≥0.3 wt %, the accumulation of nanoparticles is accompanied by the appearance of aggregates of arbitrary shape due to the van der Waals interaction of carboxylate ligands. The presence of aggregates leads to the broadening, splitting, and redshift of surface plasmon resonance peaks. Silver nanoparticles in aggregates are separated by ligand shells that reduce the probability of coalescence.

Analytical modeling for plasmonic graphene/GaAs solar cells with random distribution of nonuniform-sized nanoparticles

Numerical simulations based on solving the Maxwell equations provide a robust and efficient approach to obtaining optical properties of plasmonic metal nanoparticles (NPs), but they have high computational costs when considering the real conditions of incorporated NPs such as random distribution and nonuniform size. Therefore, an effective medium theory, taking into account light scattering on the surface of NPs and light concentration by localized surface plasmon resonance, has been employed to obtain optical properties of randomly embedded spherical NPs with nonuniform radii into GaAs. The results are input into an optoelectrical model of graphene/GaAs Schottky barrier solar cells (SCs), calibrated by the experimental data, to compare the performance of plasmonic graphene/GaAs SCs with the incorporation of different metal NPs of Au, Ag, Al, and Cu. Furthermore, the effects of the number of graphene layers, the radius of NPs, and the amount of size dispersion on the photovoltaic parameters of plasmonic graphene/GaAs SCs have been investigated. It is demonstrated that increasing the radius and size dispersion of NPs, by inducing an inhomogeneous broadening and an increase of plasmon band amplitude, enhances the efficiency of plasmonic graphene/GaAs SCs.

Micellar thermodynamics of voriconazole cyclodextrin-HS15 complex in glucose and NaCl solution

The hydrodynamic radius and size dispersion of cyclodextrin-micelle complexes loaded with voriconazole in glucose and NaCl solutions were studied in detail by dynamic light scattering technique. The critical micelle concentration (CMC) was determined by surface tension, and the relevant air–water interface parameters and micellization thermodynamic parameters were calculated. In the environment of glucose and NaCl, the CMC value decreases with the increase in the concentration of the additive. Glucose forms more stable hydrophilic ends by binding to the micelle hydrophilic group. NaCl acts as a water structure building ion to provide hydrophobic force to the gum surfactant molecules and promote the formation of micelles. The results of insoluble particles are consistent with the CMC results, which further supports the results obtained.

Factors defining the stability of poly(lactide-co-glycolide) spheres for the sustained release of a cysteine protease inhibitor.

Colloidal stability and the regularity of the release kinetics benefit from the high circularity and the narrow size dispersion of polymeric particles as drug delivery carriers. A method for obtaining such particles composed of poly(lactide-co-glycolide) (PLGA), averaging at 1.0±0.3µm in size, is reported here, along with the analysis of the effects of different synthesis parameters on their morphological characteristics. As in agreement with the classical nucleation theory, the particle size and the degree of cohesion were inversely proportional to supersaturation. Consequently, the optimal conditions for the precipitation of small and narrowly dispersed particles involved an abrupt elevation of supersaturation. Owing to the high colloidal stability of the particles, centrifugation exhibited a counterintuitive effect on them, refining their morphological features and promoting their individuation. Polyvinyl alcohol (PVA) was used as a steric repulsion additive and its effect on the stability of PLGA spheres was concentration-dependent, with the particles aggregating, partially coalescing and losing their distinct features both with no PVA in the system and at PVA concentrations higher than the optimal. At its narrowest, the particle size distribution was bimodal, exhibiting the average circularity of 0.997±0.003 and the average roundness of 0.913±0.054. PLGA spheres were loaded with an inhibitor of EhCP4, a cysteine protease from E. histolytica, a parasite causing amoebic dysentery in the tropical and developing world. The burst release of the drug at early time points was followed by a zero-order release period, yielding a biphasic profile that can be of benefit in the delivery of anti-infective agents. The release profile fitted poorly with the Hixson-Crowell kinetic model and excellently with the Higuchi and the Korsmeyer-Peppas ones, indicating that the release is conditioned by diffusion rather than by the degradation of the polymer. The release and the erosion proceeded independently from one another, suggesting that the pore formation, water penetration and swelling are the primary driving forces for the release of the drug.

Structure, Morphology, and Faceting of TiO2 Photocatalysts by the Debye Scattering Equation Method. The P25 and P90 Cases of Study.

Characterization of functional nanocrystalline materials in terms of quantitative determination of size, size dispersion, type, and extension of exposed facets still remains a challenging task. This is particularly the case of anisotropically shaped nanocrystals (NCs) like the TiO2 photocatalysts. Here, commercially available P25 and P90 titania nanopowders have been characterized by wide-angle X-ray total scattering techniques. Synchrotron data were modelled by the reciprocal space-based Debye scattering equation (DSE) method using atomistic models of NC populations (simultaneously carrying atomic and nanoscale structural features) for both anatase and rutile phases. Statistically robust descriptors are provided of size, morphology, and {101} vs. {001} facet area of truncated tetragonal bipyramids for anatase, jointly to polymorph quantification. The effects of using the proper NC shape on the X-ray diffraction pattern are analyzed in depth through DSE simulations by considering variable bipyramid aspect ratios (resulting in different {101} vs. {001} surface) and relative dispersion in a bivariate manner. We demonstrate that using prismatic NCs having equal volume and aspect ratio as bipyramids provides reasonably accurate sizes and {101} and {001} surface areas of the parent morphology.