Multimodal Size Distribution Research Articles

Luminescent Colloidal InSb Quantum Dots from In Situ Generated Single-Source Precursor.

Despite recent advances, the synthesis of colloidal InSb quantum dots (QDs) remains underdeveloped, mostly due to the lack of suitable precursors. In this work, we use Lewis acid–base interactions between Sb(III) and In(III) species formed at room temperature in situ from commercially available compounds (viz., InCl3, Sb[NMe2]3 and a primary alkylamine) to obtain InSb adduct complexes. These complexes are successfully used as precursors for the synthesis of colloidal InSb QDs ranging from 2.8 to 18.2 nm in diameter by fast coreduction at sufficiently high temperatures (≥230 °C). Our findings allow us to propose a formation mechanism for the QDs synthesized in our work, which is based on a nonclassical nucleation event, followed by aggregative growth. This yields ensembles with multimodal size distributions, which can be fractionated in subensembles with relatively narrow polydispersity by postsynthetic size fractionation. InSb QDs with diameters below 7.0 nm have the zinc blende crystal structure, while ensembles of larger QDs (≥10 nm) consist of a mixture of wurtzite and zinc blende QDs. The QDs exhibit photoluminescence with small Stokes shifts and short radiative lifetimes, implying that the emission is due to band-edge recombination and that the direct nature of the bandgap of bulk InSb is preserved in InSb QDs. Finally, we constructed a sizing curve correlating the peak position of the lowest energy absorption transition with the QD diameters, which shows that the band gap of colloidal InSb QDs increases with size reduction following a 1/d dependence.

Apparent crystallite domain size growth in metal oxide nanocrystal ensembles: The importance of surface reactivity of powders for processing

A major challenge related to metastable oxide nanoparticles as starting materials for ceramics is to achieve control over their processing related property changes. We compared MgO nanoparticles with those of Ba2+-admixtures exhibiting enhanced surface reactivity. The enhanced surface reactivity promotes particle coarsening and gives rise to a multimodal particle size distribution with a fine fraction of nanocubes (d ​< ​10 ​nm) and a coarse fraction of larger particles. Water adsorption from the ambient has a key influence on sintering and resulting microstructures. After sample exposure to water vapor there arise significant changes in structure and crystallite domain size that originate from size dependent dissolution effects transforming only the fine fraction of particles (<10 ​nm) into hydroxides. Thus, controlled Ba-admixture and segregation at the single particle level provides means to address the impact of surface basicity, hydration and consecutive surface chemistry on microstructure evolution during processing.

Uranium Aerosol Activity Size Distributions at a Nuclear Fuel Fabrication Plant.

Inhalation of uranium aerosols is a concern in nuclear fuel fabrication. Determination of committed effective doses and lung equivalent doses following inhalation intake requires knowledge about aerosol characteristics; e.g., the activity median aerodynamic diameter (AMAD). Cascade impactor sampling of uranium aerosols in the breathing zone of nuclear operators was carried out at a nuclear fuel fabrication plant producing uranium dioxide via ammonium uranyl carbonate. Complementary static sampling was carried out at key process steps. Uranium on impaction substrates was measured using gross alpha counting and alpha spectrometry. Activity size distributions were evaluated for both unimodal and bimodal distributions. When a unimodal distribution was assumed, the average AMAD in the operator breathing zone at the workshops was 12.9–19.3 μm, which is larger than found in previous studies. Certain sampling occasions showed variable isotope ratios (234U/238U) at different impactor stages, indicating more than one population of particles; i.e., a multimodal activity size distribution. When a bimodal distribution (coarse and fine fraction) was assumed, 75–88% of the activity was associated with an AMAD of 15.2–18.9 μm (coarse fraction). Quantification of the AMAD of the fine fraction was associated with large uncertainties. Values of 1.7–7.1 μm were obtained. Static sampling at key process steps in the workshops showed AMADs of 4.9–17.2 μm, generally lower than obtained by breathing zone sampling, when a unimodal distribution was assumed. When a bimodal distribution was assumed, a smaller fraction of the activity was associated with the coarse fraction compared to breathing zone sampling. This might be due to impactor positioning during sampling and sedimentation of large particles. The average committed effective dose coefficient for breathing zone sampling and a bimodal distribution was 1.6–2.6 μSv Bq−1 for 234U when Type M/S absorption parameters were assumed (5.0 μSv Bq−1 for an AMAD of 5 μm). The corresponding lung equivalent dose coefficient was 3.6–10.7 μSv Bq−1 (29.9 μSv Bq−1 for an AMAD of 5 μm). The predicted urinary excretion level 100 d after inhalation intake was found to be 13-34% of that corresponding to an AMAD of 5 μm. Uranium aerosols generated at a nuclear fuel fabrication plant using ammonium uranyl carbonate route of conversion were associated with larger AMADs compared to previous work, especially when sampling of aerosols was carried out in the operator breathing zone. A bimodal activity size distribution can be used in calculations of committed effective doses and lung equivalent doses, but parameters associated with the fine fraction must be interpreted with care due to large uncertainties.

Investigations on the formation of multi-modal size distribution of mechanochemically processed Cu-Y-CuO powders

Abstract In order to improve the high-temperature stability of copper (Cu) alloys, which have a range of applications because of their high conductivity, an in-situ mechanochemical process based on Mechanical Alloying (MA) and Hot Isostatic Pressing (HIP) was proposed and Cu-Y2O3 alloys were prepared. An interesting multi-modal distribution of particle size was observed in the high yttria (3/ 5 wt%) doped MA powders. Understanding the mechanism behind the above phenomenon will be important for preparing ODS-Cu by MA process. Thus, this paper investigates the formation of multi-modal distribution of particle size in the Cu-Y-CuO system. It was found that the finer the powder, the larger its lattice parameter, hardness, and oxygen content will be. On the basis of these data and the microstructural evolution of the powders with MA time, it was suggested that after CuO powder is mixed with Cu-Y alloyed powder, the high energy ball-milling will induce the formation of a hard and brittle O-rich shell on the surface of Cu-Y particles. With the continuing of MA, the high-energy collision between the balls will make the hard/brittle O-rich layer break into pieces. These results can provide helpful information to optimize the preparation of copper-based materials through process control.

Multimodal γ′ precipitation in Inconel-738 Ni-based superalloy during electron-beam powder bed fusion additive manufacturing

Additive manufacturing is a promising alternative method for fabricating components of Ni-based superalloys which are difficult to cast, form and join. However, typical thermal cycles associated with laser powder bed-fusion techniques suppress the formation of desirable microstructures containing γ′ particles, necessitating long-time post-process heat treatments. Here we report in-situ precipitation of γ′ (L12-ordered) particles and carbides during electron-beam powder bed-fusion of Inconel-738. The γ′ particles are homogenously distributed across the build and exhibit a multimodal size distribution. Based on atom-probe microscopy, we propose a eutectic reaction and multiple nucleation, growth, coarsening and dissolution bursts during thermal cycling as formation mechanism.

Pore structure characterization and permeability estimation with a modified multimodal Thomeer pore size distribution function for carbonate reservoirs

Pore structure of carbonate reservoirs is complex and multimodal. In order to characterize the pore structure of complex carbonate, a modified multimodal Thomeer pore size distribution (PSD) function was developed, which was based on the multimodal Gaussian density function and three controlling parameters including peak position, peak height and full width at half maximum (FWHM). The Expectation-Maximization algorithm for Gaussian mixture model was utilized to obtain three controlling parameters for the calculation of Thomeer parameters, namely the extrapolated displacement pressure, the percent bulk volume occupied by mercury at infinite capillary pressure and the pore geometrical factor. Three permeability models were proposed based on the Thomeer parameters and compared with the previous models. The results show that PSD curve of 55% samples need more than two Gaussian density function, which illustrates the multimodal characteristic. Thomeer parameters relate to the controlling parameters of Gaussian density function. The peak position moved toward larger capillary pressure with the increase of extrapolated displacement pressure and pore geometrical factor. The peak height has positive correlation with the percent bulk volume occupied by mercury at infinite capillary pressure and negative correlation with pore geometrical factor respectively. FWHM has positive correlation with pore geometrical factor. The extrapolated displacement pressure derived from the first Gaussian density function has a high correlation with permeability, which demonstrates that permeability is mainly controlled by the maximum pore throat radius. We found that when the sample has the percentage occupied by the first porous system larger enough than 21.64%, its permeability is dominated by the first porous system with the maximum pore throat radius; otherwise, it would be influenced by the second porous system. The comparative study shows that permeability models that has considered the influence of second porous system could improve the accuracy of permeability estimation for the complicated carbonate samples.

Effect of Preannealing on Microstructural Evolution and Tensile Properties of a Novel Nickel‐Based Superalloy

The effect of preannealing (PA) on microstructural evolution and tensile properties of a novel nickel‐based alloy GH4065 is investigated. Particularly, the study of PA in disc superalloys is reported herein for the first time. The detailed strengthening mechanisms of specimens under different heat treatment cycles are identified by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) observations. The results reveal that the PA treatment after deformation improves the homogeneity of the microstructure due to static recrystallization (SRX). Multimodal size distributions and the morphology of γ′ precipitates are found after the PA + solution + aging (PASA). Also, the distributions of secondary and tertiary γ′ precipitates are optimized due to the PA. The tensile strength of GH4065 alloy after PASA is higher than that of as‐forged (AF) alloy and solution + aging (SA) alloy attributed to the improved microstructure during PA treatment. Compared with the SA specimens, the specimens of GH4065 alloy after PASA treatment lead to significant strengthening as the yield strength increased to more than 150 MPa, which is mainly due to the contribution from annealing twins and microtwins strengthening, as well as the grain refinement and γ′ precipitation strengthening.

Synthesis of macroporous ceramic with enhanced sound absorption capability in low and medium frequency

We propose a novel hybrid method to produce macroporous ceramic with excellent sound absorption coefficient at medium and low frequency noise and multimodal pore size distribution. Macroporous ceramics with pore sizes from 100 nm to 2000 μm and apparent porosity in the range 85%–90% were fabricated by twice-foaming method and two pore-forming agents. These ceramics display a sound absorption coefficients from 0.11 to 0.99 in the sound-wave frequency range of 200–2000 Hz with sufficient connectivity rate above 99%. This ceramic represents a highly expected industrialization of properties for noise control and reduction at corrosive environments and high temperatures.

Fabrication, Characterization, and Formation Mechanism of Zein-Gum Arabic Nanocomposites in Aqueous Ethanol Solution with a High Ethanol Content.

The antisolvent precipitation method is widely applied to produce zein colloidal particles. The process involves dissolving zein in 55-90% (v/v) alcohol/water mixtures and then shearing such solutions into deionized water to lower the ethanol content. In the present work, on the basis of the preliminary result that gum arabic (GA) was able to well disperse in 70% (v/v) alcohol/water mixtures, a new way was created to produce zein-GA nanocomposites by simply mixing their aqueous alcohol solution with a high alcohol level of 70% (v/v) at pH 8.0. Findings showed that the multimodal size distribution of zein or GA alone was shifted to be the monomodal peak after zein and GA aqueous ethanol solution was mixed, indicating the successful formation of zein-GA nanocomposites. A core-shell structure was observed for zein-GA nanocomposites, with zein as a core and GA as a shell. In addition, the incorporation of GA caused the conformational and second structural changes of zein. A two-step mechanism was involved to explain the formation of zein-GA nanocomposites. The first step was that GA addition changed the polarity of zein aqueous ethanol solution and zein nanoparticles formed, and the second step was that hydrogen bonds and hydrophobic interactions promoted the adsorption of GA onto the particle surfaces. Results in this work would provide a new sight into the design of zein-based nanocomplexes, which may have potential applications, such as constructing delivery systems, for bioactive compounds.

Patterns of somatic structural variation in human cancer genomes

A key mutational process in cancer is structural variation, in which rearrangements delete, amplify or reorder genomic segments that range in size from kilobases to whole chromosomes1–7. Here we develop methods to group, classify and describe somatic structural variants, using data from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA), which aggregated whole-genome sequencing data from 2,658 cancers across 38 tumour types8. Sixteen signatures of structural variation emerged. Deletions have a multimodal size distribution, assort unevenly across tumour types and patients, are enriched in late-replicating regions and correlate with inversions. Tandem duplications also have a multimodal size distribution, but are enriched in early-replicating regions—as are unbalanced translocations. Replication-based mechanisms of rearrangement generate varied chromosomal structures with low-level copy-number gains and frequent inverted rearrangements. One prominent structure consists of 2–7 templates copied from distinct regions of the genome strung together within one locus. Such cycles of templated insertions correlate with tandem duplications, and—in liver cancer—frequently activate the telomerase gene TERT. A wide variety of rearrangement processes are active in cancer, which generate complex configurations of the genome upon which selection can act.

The structure of gold nanoparticles: molecular dynamics modeling and its verification by X-ray diffraction

Noble metal nanoparticles exhibit unique physical, chemical, biomedical, catalytic and optical properties. Understanding these properties and further development of production methods entail detailed knowledge of the structure at the atomic scale. Gold nanoparticles with multimodal size distribution were synthesized on porous silica and their atomic scale structure was studied by X-ray diffraction. The obtained experimental data are compared with molecular dynamics simulations. Spherical models of the Au nanoparticles, defined by ensembles of the Cartesian coordinates of constituent atoms, were generated and their geometry was optimized by applying the LAMMPS software. The comparison was performed in both reciprocal and real space. A good agreement is achieved for the models with disorder that can be related to surface relaxation effects and vacancy defects. The approach adopted here may have wider applications for further structural studies of other nanomaterials, offering direct verification of simulation results by experiment.

Predicting Effective Electromechanical Properties of Pb-Free Polymer Composite Using Finite Element Method

Polyvinylidene fluoride (PVDF) – Lead Zirconate Titanate (PZT) is a polymer composite that is becoming increasingly popular in micro-scale sensors and actuators because of its unique properties such as high flexibility, low density and high piezoelectric constants. However, lead-based piezoceramics, despite their superior properties, are toxic and are known to damage the environment, and as such a conscientious effort is being made by the scientific community towards replacing lead-containing piezoceramics with environmentally-friendlier and lead-free piezoceramics. Barium Titanate (BaTiO3) is one such piezoceramics that is widely studied today to be a potential replacement of PZT in many applications. As such, in this work, effort has been made to predict the effective mechanical, dielectric and piezoelectric properties of PVDF-BaTiO3 composite system using Finite Element Method (FEM). Kinematic Uniform Boundary Conditions (Displacement and Voltage) are used for this analysis. For evaluation of the effective material constants of the composite, several types of representative volume elements are considered. The effects of volume fraction, effect of the size of the micro-particles i.e. mono-modal versus multi-modal size distribution, effect of periodic versus quasi-random distribution of microparticles in the matrix, the effect of clustering of the particles, effect of orientation of the microparticles i.e. unidirectional or randomly oriented are discussed. Finally, a comparison of properties between PVDF-PZT and PVDF-BaTiO3 is made, so as to see whether PVDF-BaTiO3 can be a potential replacement for PVDF-PZT composite.

Defect-induced activity enhancement of enzyme-encapsulated metal-organic frameworks revealed in microfluidic gradient mixing synthesis.

Mimicking the cellular environment, metal-organic frameworks (MOFs) are promising for encapsulating enzymes for general applications in environments often unfavorable for native enzymes. Markedly different from previous researches based on bulk solution synthesis, here, we report the synthesis of enzyme-embedded MOFs in a microfluidic laminar flow. The continuously changed concentrations of MOF precursors in the gradient mixing on-chip resulted in structural defects in products. This defect-generating phenomenon enables multimodal pore size distribution in MOFs and therefore allows improved access of substrates to encapsulated enzymes while maintaining the protection to the enzymes. Thus, the as-produced enzyme-MOF composites showed much higher (~one order of magnitude) biological activity than those from conventional bulk solution synthesis. This work suggests that while microfluidic flow synthesis is currently underexplored, it is a promising strategy in producing highly active enzyme-MOF composites.

基于人工蜂群算法的多峰颗粒粒度分布反演

基于人工蜂群算法的多峰颗粒粒度分布反演

Microstructural and hydro-mechanical behaviour of bentonite pellets and powder mixtures

Binary mixtures of high-density MX-80 bentonite pellets (80%) and bentonite powder (20%) at hygroscopic water content have been recently considered as an alternative engineered barrier system for the long-term disposal of radioactive wastes. These mixtures display a dry density of around 1.49 Mg/m3 on pouring and present components with multi-modal pore size distributions that significantly evolve during the hydro-mechanical paths. To better understand the hydro-mechanical behaviour of this multiple porosity mixture, the contribution initially focuses on describing the initial state, as well as the main microstructural features determined by mercury intrusion porosimetry tests for the mix and each of the components (pellets and powder). Afterwards, hydro-mechanical results of both components and the mixture are presented. The hydraulic results focus on the water retention and water permeability, while the mechanical tests concentrate on the compressibility properties on loading.

基于人工蜂群算法的多峰颗粒粒度分布反演

基于人工蜂群算法的多峰颗粒粒度分布反演

Method of protection of cathode blocks of aluminium electrolysis cells

Cathode wear is one of the main lifetime limiting factors of an aluminium electrolysis cell. In the present work the composition of the wettable TiB2-based coating and the cost-effective method of its application to protect the most defenseless areas of the cell bottom are proposed in relation with the cathode blocks wear profile and failure mechanisms. The protective coating composition comprises a mixture of TiB2 powders with bimodal or multimodal grain size distribution (65-40 wt. %) and a water-soluble environmentally friendly binder (35-60 wt. %). The proposed TiB2-C protective coating is characterised by high adhesion to the cathode block material, as well as wear resistance, resistance to cracks initiation and their propagation, wettability by liquid aluminium. That leads to a contact electrical resistance decrease and an increase of a chemical resistance at the Al-TiB2-C interface. The developed method of the cathode blocks protection was tested in operating conditions on an industrial electrolysis cell. The expected lifetime of cathode blocks was increased at least for 4 mounts. The results are promising and show the efficiency of the proposed method for cathode blocks protection.

Modelling of oedometer tests on pellet-powder bentonite mixtures to support mock-up test analysis

Bentonite mixtures of MX-80 (80% of high-density pellets and 20% of bentonite powder on a mass basis) have been recently proposed as a candidate material for sealing deep geological disposals of high-level radioactive waste. A loading/unloading oedometer test at constant water content has been performed on this mixture, which has been modelled using the finite element Code_Bright. The constitutive model used to represent the mechanical response is the Barcelona Expansive Model (BExM), since a multi-modal pore size distribution characterises the pore network of the mixture. During compression at constant water content, an increase in the degree of saturation and a consequent reduction of suction is induced. Consequently, two competing effects occur at different pore-size scales: (a) compression due to mean net stress increase; and (b) expansion on induced suction reduction that mainly affects the micro-porosity level inside aggregates. A sensitivity analysis has been performed to explore these effects, in which the elastic compressibility parameter at the micro-porosity scale for changes in mean effective stress plays an important role.

The superior role of coagulation factor FX over FVII in adenoviral-mediated innate immune induction of the hepatocyte: an in vitro experiment.

Aim of the studyTo better understanding the contribution of coagulation factors to the extent of adenovirus-mediated innate toxicity on the hepatocyte.Material and methodsAdenovirus-36 (AD) and adenovector type 5-GFP (Ad5-GFP) were propagated and titered; then, they were loaded with coagulation factors VII or X. The complex of adenovirus with coagulation factor VII and X were for size and charge parameters. After adding AD-VII and AD-X complexes, the expression levels of innate inflammatory genes including protein kinase R (PKR), interleukin (IL)-1β, IL-8 and IL-18 were measured by Real-time PCR on a hepatocellular carcinoma cell line, HepG2.ResultsThe loading of coagulation factors VII and X on Ad5-GFP enhanced the transduction rate up to 50% and 60% (p < 0.05), respectively, compared to the adenovector alone (30%) (p < 0.05). The formation of the coagulation factor-virus complex leads to multimodal size distribution with an increase in average hydrodynamic size and absolute zeta potential. The qPCR results showed that PKR expression increased significantly after treatment with all adenoviruses. These findings also showed that AD had a significant (p = 0.0152) inflammatory impact on Hep-G2. However, AD which was loaded with FX (AD-X) exhibited the most inflammatory effect (p = 0.0164). Significantly, the expression of IL-1β (p = 0.0041), IL-8 (p = 0.0107) and IL-18 (p = 0.0193) were also enhanced following FX loading. On the other hand, the AD-VII complex showed the least effect of innate immune induction when compared to the negative control (p < 0.05).ConclusionsThe loading of coagulation factors, particularly FX, could enhance the transduction efficiency of Ad5-GFP. Furthermore, adenovirus loaded with FX exhibited more innate toxicity on the hepatocytes, while it was not the case for FVII.

Improved biofilm adhesion and electrochemical properties of a graphite-cement composite with silica nanoflowers versus two benchmark carbon felts

Low cost graphite-cement composite (GC70S) is prepared by blending graphite, cement and fumed SiO2 to obtain nanoflowers and proposed as an alternative to common carbon-based materials in the anode of biodevices with biofilm growth. The selected anodic benchmarks are carbon felt (CF) that is cheap, flexible, porous, and conductive three-dimensional support and a modified CF with polyethyleneimine (CF-PEI), where PEI is used to coat the carbon fibers. In spite of such advantages, CF has drawbacks, such as deformation by pore compression, hydrophobicity, low biofilm adhesion, and easy fragility by aging. Compared to these benchmarks, the GC70S has a multi-modal pore size distribution with micro (1–7 μm) and nano (20 nm) pores, whereas CF and CF-PEI only show macroscopic (55–60 μm) pores. The comparative results also show that the new composite provides better wettability, higher specific surface area (4.53·107 m2·m−3), and good electrical conductivity (2.04 ± 0.18 S·m−1). In half-cell tests, the yeast biofilm is firmly attached to GC70S anode, while its charge transfer resistance is greatly reduced. From the biofilm resistance contribution, the inhabitancy appears more abundant than in CF or CF-PEI.