Effect of axial eccentricity on the performance of a cylindrical differential mobility classifier

A differential mobility classifier (DMC) is one of the core components in electrical mobility particle sizers for sizing sub-micrometer particles. A DMC in the cylindrical configuration (i.e., constructed by axial aligning of the inner and outer cylinders) is typically included in the sizers. The knowledge of construction tolerance is required in the design of a cylindrical DMC. The numerical approach was applied in this study. Our study shows that the DMC transfer function deteriorated as the axial eccentricity was increased (i.e., the peak is reduced and the width at the half peak height is broaden). At high axial eccentricity, the transfer function peak would split into two. In addition to the flow parameters such as the sheath-to-aerosol flow rate ratio and total flow rate, the effect of geometrical parameters (i.e., the length and aspect ratio of the particle classification channel, and the ratio of outer-to-inner cylinder radii) on the transfer function of an eccentric DMC were also investigated. It is found that the classification length and the sheath-to-aerosol flow rate ratio have obvious impact on the transfer function of an eccentric DMC. Furthermore, the particle diffusivity reduced the effect of axial eccentricity on DMC transfer function, especially for particles with the sizes less than 10?nm.

Copyright © 2019 American Association for Aerosol Research     

Numerical modeling of the performance of high flow DMAs to classify sub-2 nm particles

While there are several computational studies on differential mobility analyzers (DMA), there is none for high flow DMA to classify nanoparticles less than 3?nm. A specific design of a high flow DMA, a half mini DMA, is investigated to predict its performance through numerical modeling in the incompressible flow regime. The governing equations for flow field, electric field and aerosol transport are solved using COMSOL 5.3. The transfer function of the half mini DMA is compared with that of a nano DMA (TSI 3085). The results show that both the height of the transfer function and resolution (R) of the half mini DMA are much better than those of nano DMA in sub-2?nm particle size range. Finally, the transfer function of half mini DMA is evaluated for different values of aerosol flow rate to the sheath flow rate (q/Q). Comparison of the simulated transfer function with existing models from Knutson–Whitby and Stolzenburg is also elucidated. It is found that the former model overestimates the resolution; whereas the latter is close to the simulation results for q/Q above 0.067. This work provides a useful method to study the flow regimes and transfer function of a high flow DMA.

Copyright © 2018 American Association for Aerosol Research     

Investigation of the size of the incandescent incipient soot particles in premixed sooting and nucleation flames of n-butane using LII,HIM, and 1 nm-SMPS

Laser-induced incandescence (LII) measurements were conducted to explore the ability of LII to detect small soot particles of less than 10 nm in two sooting flat premixed flames of n-butane: a so-called nucleation flame obtained at a threshold equivalence ratio Φ = 1.75, in which the incipient soot particles undergo only minor soot surface growth along the flame, and a more sooting flame at Φ = 1.95. Size measurements were obtained by modeling the time-resolved LII signals detected using 1064 nm laser excitation. Spectrally-resolved LII signals collected in the nucleation flame display a similar blackbody-like behavior as mature soot. Soot particle temperature was determined from spectrally-resolved detection. LII modeling was conducted using parameters either relevant to those of mature soot or derived from fitting the modeled results to the experimental LII data. Particle size measurements were also carried out using (1) ex situ analysis by helium-ion microscopy (HIM) of particles sampled thermophoretically and (2) online size distribution analysis of microprobe-sampled particles using a 1 nm-SMPS. The size distributions of the incipient soot particles, found in the nucleation flame and in the early soot region of the Φ = 1.95 flame, derived from time-resolved LII signals are in good agreement with HIM and 1 nm-SMPS measurements and are in the range of 2–4 nm. The thermal and optical properties of incipient soot were found to be not radically different from those of mature soot commonly used in LII modeling. This explains the ability of incipient soot particles to produce continuous thermal emissions in the visible spectrum. This study demonstrates that LII is a promising in situ optical particle sizing technique that is capable of detecting incipient soot as small as about 2.5 nm and potentially 2 nm and resolving small changes in soot sizes below 10 nm.

© 2017 American Association for Aerosol Research     

Modification of the TSI 3081 differential mobility analyzer to include three monodisperse outlets: Comparison between experimental and theoretical performance

Differential mobility analyzers (DMAs) are widely used to determine the size of aerosol particles, and to probe their size-dependent physicochemical properties when two are employed in tandem. A limitation of tandem DMA (TDMA) systems is their long measuring cycle when the properties of more than one monodisperse population of particles need to be probed. In this work, we propose a simple modification of the classical cylindrical DMA by including three monodisperse-particle outlets in its central electrode (namely, the 3MO-DMA), with the objective of using it as the first DMA in TDMA systems for reducing their measuring cycle. The performance of the 3MO-DMA at different flow conditions was evaluated using laboratory-generated aerosol particles, and compared with theoretical predictions. The theory predicted accurately (i.e., within 3%) the geometric mean diameters of the three distinct populations, as well as the resolutions of the first and the third outlet, under all experimental conditions. For the second outlet, the resolution was 10% to 74% lower than that predicted theoretically depending on the sheath-to-aerosol flow ratio. Nevertheless, the geometric standard deviation of the monodisperse aerosol from all the outlets was less than 1.09, which is sufficient for using the 3MO-DMA designed and tested in this work as a first DMA to produce a monodisperse aerosol flow containing three distinct particle populations in TDMA systems.

Copyright © 2016 American Association for Aerosol Research     

Humidity,density, and inlet aspiration efficiency correction improve accuracy of a low-cost sensor during field calibration at a suburban site in the North-Western Indo-Gangetic plain (NW-IGP)

Abstract

Low-cost particulate matter (PM) sensors are now widely used by concerned citizens to monitor PM exposure despite poor validation under field conditions. Here, we report the field calibration of a modified version of the Laser Egg (LE), against Class III US EPA Federal Equivalent Method PM₁₀ and PM_2.5 β-attenuation analyzers. The calibration was performed at a site in the north-western Indo-Gangetic Plain from 27 April 2016 to 25 July 2016. At ambient PM mass loadings ranging from <1–838?µg m^?3 and <1–228?µg m^?3 for PM₁₀ and PM_2.5, respectively, measurements of PM₁₀, PM_2.5 from the LE were precise, with a Pearson correlation coefficient (r) >0.9 and a percentage coefficient of variance (CV) <12%. The original Mean Bias Error (MBE) of ～?90?µg m^?3 decreased to ?30.9?µg m^?3 (Sensor 1) and ?23.2?µg m^?3 (Sensor 2) during the summer period (27 April–15 June 2016) after correcting for particle density and aspiration losses. During the monsoon period (16 June–25 July 2016) the MBE of the PM_2.5 measurements decreased from 19.1?µg m^?3 to 8.7?µg m^?3 and from 28.3?µg m^?3 to 16.5?µg m^?3 for Sensor 1 and Sensor 2, respectively, after correcting for particle density and hygroscopic growth. The corrections reduced the overall MBE to <20?µg m^?3 for PM₁₀ and <3?µg m^?3 for PM_2.5, indicating that modified version of the LE could be used for ambient PM monitoring with appropriate correction and meteorological observations. However, users of the original product may underestimate their PM₁₀ exposure.

Copyright © 2020 American Association for Aerosol Research     

Formation of submicron particulate matter (PM1) during coal combustion and influence of reaction temperature

Combustion of pulverized coals was conducted in a lab-scale drop tube furnace to investigate the formation of submicron particulate matters less than 1.0 μm in diameter (PM₁). Three temperatures, 1473, 1573 and 1723 K were tested. PM₁ was collected by a low-pressure-impactor, which automatically segregates particulates into seven sizes ranging from 0.03 to 0.76 μm. Each size was subjected to several techniques for elemental composition and morphology analysis. The results indicate that there are two major portions formed for PM₁: particulates smaller than 0.1 μm and those larger ones. The former portion, termed as PM_0.1 in this study, was formed by aggregation of elemental vapors generated by either decomposition of organically bound elements in coal pyrolysis or vaporization of inorganic compounds in char combustion. Sulfates and phosphates dominate this portion. On the other hand, the latter portion in PM₁, termed as PM_0.1+, was generated containing two kinds of typical particles: one is in a molten solid shape and rich in Al-silicates and another one in the fractal agglomerate form. Liberation of inherent fine minerals (≤1 μm) and aggregation of nucleates containing vaporized elements are the two major routes for their formation. PM_0.1+ was mainly formed in char combustion. Additionally, both coal type and reaction temperature affected the formation of PM₁ greatly. Combustion of bituminous coals produced more the PM₁ than the anthracite coal did. Increasing temperature produced more the PM₁ as well.     

High performance size exclusion chromatography of poly(organo)phosphazenes

The determination of the molecular weights of polyorganophosphazenes can only be achieved with great care. The nature of the substituents, the proportion of residual chlorine atoms after substitution, and also any traces of hydrolysis can considerably modify the behavior of these polymers in solution and thus lead to erroneous results. In our current research we have been developing a characterization method based on steric exclusion chromatography, coupled with a light scattering detector. We have used columns with styrene–divinylbenzene organic micropacking as the stationary phase and THF with added LiBr (0.1 mol/L) as the eluent. This method has enabled us to establish accurate correlations between molecular weight, hydrodynamic volume, and viscosimetric measurements for polyaryloxyphosphazenes of varying structures and origins. The method also provides results which agree very well with the variables for the preparation of polyphosphazenes, which is based on polycondensation of P-trichloro-N-dichlorophosphoryl monophosphazene Cl₃P = N? P(O)Cl₂. Finally this method allows us to show that, despite their mineral backbone, these polymers obey Benoit's universal calibration concept.     

Revisiting the thermal relaxations of poly(vinyl alcohol)

The molecular dynamics of poly(vinyl alcohol) (PVA) were studied by dielectric spectroscopy and dynamic mechanical analysis in the 20–300°C range. The well-established plasticizing effect of water on the glass-transition temperature (T_g) of PVA was revisited. Improper water elimination analysis has led to a misinterpretation of thermal relaxations in PVA such that a depressed T_g for wet PVA films (ca. 40°C) has been assigned as a secondary β relaxation in a number of previous studies in the literature. In wet PVA samples, two different Vogel–Fulcher–Tammann behaviors separated by the moisture evaporation region (from 80 to 120°C) are observed in the low- (from 20 to 80°C) and high- (>120°C) temperature ranges. Previously, these two regions were erroneously assigned to two Arrhenius-type relaxations. However, once the moisture was properly eliminated, a single non-Arrhenius α relaxation was clearly observed. X-ray diffraction analysis revealed that the crystalline volume fraction was almost constant up to 80°C. However, the crystallinity increased approximately 11% when temperature increased to 180°C. A secondary β_c relaxation was observed at 140°C and was related to a change in the crystalline volume fraction, as previously reported. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development of a new personal air filter test system using a low-cost particulate matter (PM) sensor

Abstract

The extensive use of air filters has encouraged advances in both the fabrication and characterization of air filter technology. An affordable and accessible means of assessing the quality of air filters is greatly needed because of the high demand for these filters. We developed a personal air filter test (PAFT) system for measuring filter pressure drop, efficiency, and quality of filtration. The PAFT system utilizes a PM sensor (Sharp, GP2Y1010AU0F) to measure filtration efficiency. PM sensor performance was evaluated and optimized to guarantee its suitability for this application. The sensor performance evaluation studied the output responses to sampling flow, particle diameter, and PM sources. We also improved the sensor’s sensitivity. The experimental results show that the sensor had no significant influence on the sampling flow. The sensor output was highly dependent on the particle size and PM source, but its response curves remained linear, which was an advantage for filter efficiency measurement. We measured the efficiency of nanofiber filters of various efficiencies, comparing the results to a reference efficiency as measured by a CPC (TSI, 3772). The test resulted in a filtration coefficient (K_f), which was used to correct the PAFT efficiency measurement results. We also conducted filtration efficiency tests on commercial mask filters and the results showed good agreement to the reference, with a small average error of about 2.5%. The complete design of the PAFT and experimental methods is discussed in detail.

Copyright © 2020 American Association for Aerosol Research     

Structural origin of size effect on piezoelectric performance of Pb(Zr,Ti)O3

Grain size effect plays a vital role in piezoelectric performance from both scientific and technological view. However, the underlying structural mechanism related to grain size is still unclear. In the present study, the structural mechanism of grain size effect on piezoelectric performance has been revealed in the prototype Pb(Zr,Ti)O₃ system by using in-situ synchrotron X-ray diffraction. The miniaturization of grain size tends to favor the appearance of higher symmetric tetragonal phase, while a single monoclinic phase is determined in the coarse-grained ceramics. The direct structural evidence reveals that both tetragonal and monoclinic phases in the fine-grained ceramics are less sensitive to the electric field, corresponding to the inferior piezoelectric performance, while the single monoclinic phase in the coarse-grained ceramics is more active to be driven by the electric field, generating good piezoelectric behavior. Both domain switching ability and lattice strain are suppressed with decreasing grain size, which directly leads to the deterioration in piezoelectric performance. The current results will benefit the structural understanding of the size effect of piezoelectric and other related systems.     

Distribution of uranium in the production of triple superphosphate (TSP) fertilizer and phosphoric acid

In this study the distribution of uranium, which is one of the radioactive elements present in phosphate fertilizers was investigated in different steps of the triple superphosphate (TSP) production process. The uranium in phosphate rock, phosphoric acid, phosphogypsum and TSP was extracted into the organic phase by using the TOPO extraction method. The uranium contents of these materials were determined by measuring the absorbance of the formed (pH 7.6) uranyl bromo-PADAP [uranyl(2-(5-bromo-2-pyridylazo)-5-diethylaminophenol)] complex solutions at 574 nm against blank. It was found that 50% of the uranium is dissolved in the acid during the production of phosphoric acid while the remainder is precipitated with phosphogypsum residue. The observations showed that in the second step, the sum of uranium in phosphate rock and phosphoric acid completely passed into TSP in the TSP manufacturing process.     

Development and field evaluation of an online monitor for near-continuous measurement of iron,manganese, and chromium in coarse airborne particulate matter (PM)

A novel air sampling monitor was developed for near-continuous (i.e., 2-h time resolution) measurement of iron (Fe), manganese (Mn), and chromium (Cr) concentrations in ambient coarse particulate matter (PM) (i.e., PM_10–2.5). The developed monitor consists of two modules: (1) the coarse PM collection module, utilizing two virtual impactors (VIs) connected to a modified BioSampler to collect ambient coarse PM into aqueous slurry samples; (2) the metal concentration measurement module, which quantifies the light absorption of colored complexes formed through the reactions between the soluble and solubilized target metals and pertinent analytical reagents in the collected slurries using a micro volume flow cell (MVFC) coupled with UV/VIS spectrophotometry. The developed monitor was deployed in the field for continuous ambient PM collection and measurements from January to April 2016 to evaluate its performance and reliability. Overall, the developed monitor could achieve accurate and reliable measurements of the trace metals Fe, Mn, and Cr over long sampling periods, based on the agreement between the metal concentrations measured via this online monitor and off-line parallel measurements obtained using filter samplers. Based on our results, it can be concluded that the developed monitor is a promising technology for near-continuous measurements of metal concentrations in ambient coarse PM. Moreover, this monitor can be readily configured to measure the speciation (i.e., water-soluble portion as well as specific oxidation states) of these metal species. These unique abilities are essential tools in investigations of sources and atmospheric processes influencing the concentrations of these redox-active metals in coarse PM.

Copyright © 2016 American Association for Aerosol Research     

The effect of particle size of fly ash (FA) on the interfacial interaction and performance of PVC/FA composites

In this study, the effect of particle size of fly ash (FA) on the interfacial interaction between the filler particles and the polymer matrix is investigated. Structural and physical characterization of FA with different particle sizes show that its chemical composition is highly dependent on the particle size. The mechanical, dynamic‐mechanical, structural, and microstructural properties of the composites are evaluated. Interfacial interaction between FA particles and the polymer matrix is assessed experimentally using a nanoindenter and numerically using two different models developed by Pukanszky and Kubat. The composites reinforced with smaller particles exhibit better mechanical, viscoelastic, and microstructural properties. Structural and interfacial studies show that, although the characterized amount of silicon oxide in the small particles is lower than the large particles, the concentration of –OH group in SiO₂ is particle‐size and surface‐area dependent. Therefore, smaller particle inclusions result in better interfacial interaction and improved properties. This observation is consistent with the numerically estimated interfacial interaction. J. VINYL ADDIT. TECHNOL., 25:134–143, 2019. © 2018 Society of Plastics Engineers     

Controlled reduction for size selective synthesis of thiolate-protected gold nanoclusters Aun (n = 20, 24, 39, 40)

ABSTRACT: This work presents a controlled reduction method for the selective synthesis of different sized gold nanoclusters protected by thiolate (SR = SC2H4Ph). Starting with Au(III) salt, all the syntheses of Aun(SR)m nanoclusters with (n, m) = (20, 16), (24, 20), (39, 29), and (40, 30) necessitate experimental conditions of slow stirring and slow reduction of Au(I) intermediate species. By controlling the reaction kinetics for the reduction of Au(I) into clusters by NaBH4, different sized gold nanoclusters are selectively obtained. Two factors are identified to be important for the selective growth of Au20, Au24, and Au39/40 nanoclusters, including the stirring speed of the Au(I) solution and the NaBH4 addition speed during the step of Au(I) reduction to clusters. When comparing with the synthesis of Au25(SC2H4Ph)18 nanoclusters, we further identified that the reduction degree of Au(I) by NaBH4 also plays an important role in controlling cluster size. Overall, our results demonstrate the feasibility of attaining new sizes of gold nanoclusters via a controlled reduction route.     

Effect of pore size on the performance of mesoporous material supported chiral Mn(III) salen complex for the epoxidation of unfunctionalized olefins

A series of mesoporous MCM-41 and MCM-48 materials with different pore sizes were synthesized and used as supports to immobilize chiral Mn(III) salen complex. The heterogeneous catalysts were characterized by XRD, FT-IR, DR UV–vis, and N₂ sorption, and the results indicated the successful immobilization of chiral Mn(III) salen complex. The confinement effect of pore size on the catalytic performance of the heterogeneous catalysts was studied for the asymmetric epoxidation of unfunctionalized olefins with m-chloroperoxybenzoic acid as an oxidant. It was found that the conversions and enantiomeric excess (ee) values were closely correlated with the pore sizes of parent supports. The catalysts immobilized on the large-pore mesoporous supports exhibited higher conversions, and for the catalysts immobilized on MCM-41 materials, the ee values improved with increasing pore size. However, for the MCM-48 material-supported catalysts, the compatible pore size of the support with the substrate was beneficial for obtaining higher enantioselectivity in olefin epoxidation.     

The effect of alumina particulate morphology on the properties of reinforced poly(propylene) and poly(ethylene-co-vinyl acetate) composites

The effect of alumina particulates on a thermoplastic matrix is investigated, in particular the effect altering the alumina particle size and morphology has on the mechanical properties. Different grades of alumina are used and two thermoplastic matrices; namely poly(propylene) and poly(ethylene-co-vinyl acetate). Investigations showed that optimum properties were achieved with the alumina of smallest particle size and lowest aspect ratio. Preliminary work has also been performed on the use of silane coupling agents and they have proved effective in increasing the tensile properties of the composites.     

Revisiting the Phylogenetic Relationship and Evolution of Gargarini with Mitochondrial Genome (Hemiptera: Membracidae: Centrotinae)

SummaryThis study attempts to elucidate the taxonomic complexities in tribe Gargarini using phylogenetic and evolutionary analysis based on the integrated morphological and molecular datasets: the shape of the pronotum and the complete mitochondrial genome, respectively. Despite being the largest tribe of the subfamily Centrotinae, with more than 400 species, the morphological similarities among the genera and complicated taxonomic history, the phylogenetic relationships among many species are still unknown. The phylogenetic relationships among some species of this tribe based on the mitochondrial genome were established in this study. Moreover, this study provides the possibility of establishing an evolutionary history. This study provides a basis for follow-up research on the phylogeny and evolution of more species of this tribe.AbstractIn this study, we newly sequenced and analyzed the complete mitochondrial genomes of five genera and six species in Gargarini: Antialcidas floripennae, Centrotoscelus davidi, Kotogargara minuta, Machaerotypus stigmosus, Tricentrus fulgidus, and Tricentrus gammamaculatus. The mitochondrial genomes contain 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, and a control region. The lengths of the mitochondrial genomes are 15,253 bp to 15,812 bp, and the AT contents of the obtained mitogenomes indicate a strong AT bias, ranging from 75.8% to 78.5%. The start codons of all PCGs show that most start with a typical ATN (ATA/T/G/C) codon and less start with T/GTG; the stop codon TAA is frequently used, and TAG and a single T are less used. In Gargarini mitogenomes, all tRNA genes can be folded into the canonical cloverleaf secondary structure, except for trnaS1, which lacks a stable dihydrouridine (DHU) stem and is replaced by a simple loop. At the same time, the phylogenetic analysis of the tribe Gargarini based on sequence data of 13 PCGs from 18 treehopper species and four outgroups revealed that the 10 Gargarini species form a steady group with strong support and form a sister group with Leptocentrini, Hypsauchenini, Centrotini, and Leptobelini. Diversification within Gargarini is distinguished by a Later Cretaceous divergence that led to the rapid diversification of the species. Moreover, the ancestral state reconstructions analysis showed the absence of the suprahumeral horn, which was confirmed as the ancestor characteristic of the treehopper, which has evolved from simple to complex. Our results shed new light specifically on the molecular and phylogenetic evolution of the pronotum in Gargarini.     

选择性催化还原NOx的反应机理研究

选择性催化还原法（SCR）脱除NOx具有较高的效率,是目前工业中应用最广泛的工艺。催化还原NOx的反应过程相当复杂。概括了H₂、CO、烃类、NH₃和尿素等作为还原剂选择性催化还原氮氧化物的各种反应机理,详细论述了催化还原过程中形成的中间体,如亚硝基甲烷、烯醇式物质[CH₂=O)、NO₂［NH₄+］₂、NO_y、C_xH_yO_zN、C_xH_yO_z、NO⁺、NCO或C_tH_xO_yN_z等,并讨论了催化剂和载体表面上的氧空缺和活性中心对SCR的影响,展望了这一领域的研究方向。     

Effect of coal rank on the composition of organic matter (Short Communication)

It was demonstrated that the ratios between the fractions of carbon and hydrogen in CH₃, CH₂, and CH groups regularly changed in the coal metamorphism series.