Large Range Of Particle Sizes Research Articles

Potential of powder metallurgical methods to fabricate Fe-6.5Si soft magnetic components

The soft magnetic Fe-6.5Si alloy is well known for its excellent soft magnetic properties but its usage is limited due to fabricational constrains by conventional methods. Powder metallurgical processing of Fe-6.5Si is possible by a variety of different methods shown here, sinter-based screen printing (SP), electron beam powder bed fusion (E-PBF) and field-assisted sintering (field-assisted sintering/spark plasma sintering, FAST/SPS). The microstructure of the components varies strongly by process and powder used which is directly influencing their soft magnetic properties. The correlation between powder properties and processing parameters on the structural and magnetic properties is established. Lowest coercivity ( H c = 7 A m−1) is achieved by E-PBF due to large grain size minimising hysteresis losses necessary for direct current applications. SP can provide sheets with low coercivity ( H c = 21 A m−1) and adjustable thickness reducing eddy current losses especially suitable for alternating current application at higher frequencies. FAST/SPS can be used for a large range of powder particle sizes which is suitable to tune the soft magnetic properties in a wide range between 40 and 210 A m−1.

A novel method for measuring and analyzing the characteristics of coarse aggregates in concrete

The characteristic of coarse aggregate is an important factor affecting the building performance of concrete, so it is of great significance to measure and characterize it. In this paper, a method of measuring the characteristics of coarse aggregate in concrete buildings by using borehole camera technology is proposed. For the obtained borehole wall image, the corresponding image processing method is proposed, which can accurately recognize the coarse aggregate structure in the image. On this basis, the characteristics of coarse aggregate in the borehole wall image are calculated and analyzed. The calculation parameters include uniformity, gradation, aspect ratio, inclination angle, shape index, angularity and surface texture. The results show that the coarse aggregate in the borehole wall image used in this paper is not evenly distributed at different depths, the gradation continuity is good, and there are some coarse aggregates with large particle size. The aspect ratio of most coarse aggregates is less than 3 (AR1:97.71%; AR2:96.26%), and the content of needle flake coarse aggregate is less. The inclination angle is mostly distributed in the horizontal direction, accounting for more than 50%. The distribution of shape index and angularity has obvious correlation with the particle size range, and the shape index and angularity in the large particle size range are richer and more uniform. The distribution characteristics of surface texture of coarse aggregate in different particle size range are basically the same, and there is no obvious correlation with particle size. In this paper, a new in-situ measurement and multi characteristic parameter analysis of coarse aggregate in borehole is carried out, which provides a new idea for the evaluation of concrete building performance.

Properties of ZrO2 and Ag–ZrO2 nanopowders prepared by pulsed electron beam evaporation

ZrO2 and Ag doped ZrO2 powders were prepared from mixtures of ZrO2 and AgNO3 commercial powders (99:1 and 95:5 wt %) by pulsed electron beam evaporation (PEBE) in vacuum. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), textural and magnetic analysis, photocatalytic test, photoluminescence spectroscopy (PL) and cell cytology (Vero and Hela). XRD analysis confirmed the presence of monoclinic ZrO2 phase and cubic Ag phase in the final product. НRTEM pictures showed a large range of particle sizes approximately from 10 to 500 nm; the spherical silver nanoparticles (NPles) (10 nm) were observed on the ZrO2 particle surfaces. Ferromagnetic contribution in pure ZrO2 powder was 0,002 emu/g, and in Ag doped ZrO2 powders it reached 0,016 emu/g. It was found that Ag doped ZrO2 powders showed increased photocatalytic activity in methyl orange (MO) compared with pure ZrO2 NPles. The produced powders can be used to kill Hela cancer cells, as low (<0.1 wt) Ag photocatalysts and in other applications.

Optimization of palm shell pyrolysis parameters in helical screw fluidized bed reactor: Effect of particle size, pyrolysis time and vapor residence time

The production of bio-oil from palm shell pyrolysis was investigated using a helical screw fluidized bed reactor setup. This study was done by investigating the effects of particle size, pyrolysis time and vapor residence time on pyrolysis product yields. The pyrolysis experiments were performed at different particle sizes, pyrolysis times and vapor residence times from 0.25 mm to 10 mm; 20 min to 60 min and 0.25 s to 15 s, respectively. The optimum condition for PS pyrolysis in helical screw fluidized bed reactor is at 2 mm particle size, 30 min pyrolysis time and 0.25 s vapor residence time to produce PS derived bio-oil of the highest yield of 73.86 wt% and higher heating value of 43.14 MJ/kg. Here, we report of the capability of helical screw fluidized bed reactor in handling large biomass particle size ranging up to 10 mm with marginal deteriorations of less than 1% and 3% for bio-oil yield and higher heating value respectively. This feature was attributed to the screw propeller design system in helical screw fluidized bed reactor which provided high mass and heat transfer at large particle size range which is 5 times of the particle size limit as recommended in previous studies. This finding would enable the possibility of helical screw fluidized based pyrolysis to be done in the absence of biomass size reduction processes to reduce process cost and complexity.

A CFD study of particle–bubble collision efficiency in froth flotation

To improve understanding of the interaction between bubbles and particles during the flotation process, the interaction between the various factors that affect the collision efficiency has been analyzed in this paper. Four kinds of mineral particles (quartz, chalcopyrite, copper sulfide and galena) were investigated. Particle–bubble collisions between bubbles with size ranging from 0.6 mm to 2.0 mm and particles with diameter from 31 μm to 150 μm were examined. Representative analytical mathematical models (Generalised Sutherland Equation (GSE) model and Schulze model) are studied in depth, and errors in the equations for the GSE model reported in a review paper are corrected. Simultaneously, a computational fluid mechanics (CFD) technique was used to establish a fluid mechanics model which can directly reflect the relative motion of bubbles and particles during flotation. The results of the CFD model are compared with the existing mathematical models to analyze the advantages and disadvantages of the existing models as a description of collisions in the flotation process. The GSE model accounts for the centrifugal inertial effect (neglected in the Schulze model), but comparison with the CFD results suggests that it greatly over-estimates this effect. On the other hand, the Schulze model appears to overestimate the collision efficiency at the larger particle size range, giving values greater than unity in some cases. It would be expected that the CFD model would be more exact than either semi-theoretical model, given that it involves fewer assumptions. Therefore, it is recommended that the Schulze model (limited to a value less than unity) should be used as a sub-model for bubble–particle collision rate in macro-scale CFD models of flotation cells rather than the GSE model.

The distribution, composition, and particle properties of Mars mesospheric aerosols: An analysis of CRISM visible/near-IR limb spectra with context from near-coincident MCS and MARCI observations

The Compact Reconnaissance Imaging Spectral Mapper (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) obtains pole-to-pole observations (i.e., full MRO orbits) of vertical profiles for visible/near-IR spectra (λ= 0.4–4.0 μm), which are ideally suited to identifying the composition and particle sizes of Mars ice and dust aerosols over 50–100 km altitudes in the Mars mesosphere. Within the coverage limitations of the CRISM limb data set, a distinct compositional dichotomy is found in Mars mesospheric ice aerosols. CO2 ice clouds appear during the aphelion period of Mars orbit (Solar Longitudes, Ls ∼ 0–160°) at low latitudes (∼20S–10N) over specific longitude regions (Meridiani, Valles Marineris) and at typical altitudes of 55–75 km. Apart from faint water ice hazes below 55 km, mesospheric H2O ice clouds are primarily restricted to the perihelion orbital range (Ls∼160 – 350°) at northern and southern mid-to-low latitudes with less apparent longitudinal dependences. Mars mesospheric CO2 clouds are presented in CRISM spectra with a surprisingly large range of particle sizes (cross section weighted radii, Reff = 0.3 to 2.2 μm). The smaller particle sizes (Reff ≤1 μm) appear concentrated near the spatial (latitude and altitude) boundaries of their global occurrences. CRISM spectra of mesospheric CO2 clouds also show evidence of iridescence, indicating very narrow particle size distributions (effective variance, Veff ∼ 0.03) and so very abrupt CO2 cloud nucleation. Furthermore, these clouds are sometimes accompanied by altitude coincident peaks in 1.27 μm O2 dayglow, which indicates very dry, cold regions of formation. Mesospheric water ice clouds generally exhibit small particle sizes (Reff = 0.1–0.3 μm), although larger particle sizes (Reff = 0.4–0.7 μm) appear infrequently. On average, water ice cloud particle sizes decrease with altitude over 50–80 km in the perihelion mesosphere. Water ice mass appears similar in clouds over a large range of observed cloud particle sizes, with particle number densities increasing to ∼10 cm−3 for Reff = 0.2 μm. Near coincident Mars Climate Sounder (MCS) temperature and aerosol profile measurements for a subset of CRISM mesospheric aerosol measurements indicate near saturation (H2O and CO2) conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading. Dayside (3 pm) mesospheric CO2 clouds with larger particle sizes (Reff ≥0.5 μm) scatter surface infrared emission in MCS limb infrared radiances, as well as solar irradiance in the MCS solar band channel. Scattering of surface infrared emission is most strikingly presented in nighttime (3 am) MCS observations at 55–60 km altitudes, indicating extensive mesospheric nighttime CO2 clouds with considerably larger particle sizes (Reff∼7 μm). Mesospheric CO2 ice clouds present cirrus-like waveforms over extensive latitude and longitude regions (10°×10°), as revealed in coincident Mars Color Imager (MARCI) nadir imaging. Solar tides, gravity waves, and the large orbital variation of the extended thermal structure of the Mars atmosphere influence all of these behaviors. Mesospheric dust aerosols appear infrequently over the non-global (planet encircling) dust storm era of the CRISM limb data set (2009–2016), and exhibit smaller particle sizes (Reff = 0.2–0.7 μm) relative to dust in the lower atmosphere. One isolated case of an aphelion (Ls = 96°) mesospheric dust layer with large dust particle sizes (Reff ∼2 μm) over Syria Planum may reflect high altitude, non-local transport of dust over elevated regions.

Parametric study of fluid–solid interaction for single-particle dissipative particle dynamics model

In this paper, a parametric study of fluid–solid interaction for single-particle dissipative particle dynamics (DPD) model is conducted to describe the hydrodynamic interactions in a large range of particle sizes. To successfully reproduce the hydrodynamics for different particle sizes, and overcome the problem that effective radius of solid sphere does not match its real radius, the cut-off radius and conservative force coefficient of single-particle DPD model have been modified. The cut-off radius and conservative force coefficient are related to the drag force and radial distribution function, so that, for each particle size, they can be determined by DPD simulations. Through numerical fitting, two empirical formulas as a function of spherical radius are developed to calculate the cut-off radius and conservative force coefficient. Numerical results indicate that the single-particle DPD model is, indeed, capable of capturing low Reynolds number hydrodynamic interactions for different particle sizes by selecting these model parameters reasonably. Specifically, the model can not only insure that drag force and torque are quantitatively consistent with theoretical results, but also guarantee the effective radius matches well its real radius. In addition, the shear dissipative force is the major part of drag force and should not be ignored. This study will help to improve the application range of single-particle DPD model to make it suitable for different particle sizes and provide parameter guidance for studying fluid–solid interaction using single-particle DPD model.

Porosity changes in progressively pulverized anthracite subsamples: Implications for the study of closed pore distribution in coals

Coal samples for low-pressure nitrogen (N2) adsorption measurement in previous work cover a large particle size range (from 0.075 to 4.75 mm). However, minimal attention has been paid to the effect of coal particle size on pore structure using gas adsorption methods. Anthracite coal collected from the Zhina Coalfield, China, was crushed, subsampled, and sieved to eight particle size ranges: 1–2 mesh (8000–25400 µm), 40–50 mesh (270–380 µm), 50–70 mesh (212–270 µm), 70–90 mesh (160–212 µm), 90–160 mesh (96–160 µm), 160–200 mesh (75–96 µm), 200–300 mesh (48–75 µm), and >300 mesh (<48 µm). The adsorption–desorption isotherms of each subsample were measured using N2 at 77.35 K to compare differences in pore structure characteristics. The results of the N2 adsorption tests show that particle size has a significant effect on pore volume, specific surface area, and pore size distribution of coal. Specifically, decreasing coal particle size results in continuous increase in macro- and mesopore volumes and specific surface areas. This can be attributed to the fact that smaller-sized coal particles open more of the previously closed pores, which are then accessible to adsorping gas. The contribution of closed pores to the total pore volume is 94.94% in the pore aperture range of 3.1–370 nm. The volume of closed macropores varies from 48.96 to 84.69% of the total closed pore volume. According to optical microscope and SEM observations of the Zhina Coalfield subsamples, massive gas pores exist in an isolated form with poor connectivity; some plant tissue pores are filled by pyrites and clay minerals, and may be totally occluded. Thus, gas pores contribute the dominant amount of the closed pore volume. In addition, different Zhina Coalfield subsamples show varied hysteresis loop shapes, indicating that closed pores in coal possess a variety of pore morphologies and sizes. To improve the accuracy and comparability of the pore structure of coal, we propose >300 mesh as the preferred particle size of coal for all low-pressure N2 adsorption measurement in future work. Furthermore, caution must be used in evaluating coal bed methane resource recovery potential as coal possesses high closed porosity; failure to account for this will result in an overestimation of the amount of gas that can be recovered from coal seams during production.

Novel Nanofluids Based on Magnetite Nanoclusters and Investigation on Their Cluster Size-Dependent Thermal Conductivity

To probe the effect of particle size on thermal conductivity (k) enhancement in nanofluids, especially in a very large particle size range, we study the cluster size-dependent k in novel nanofluids containing magnetite (Fe3O4) nanoclusters. The Fe3O4 nanoclusters in the size range of 115 to 530 nm were synthesized by a facile and cost-effective solvothermal approach. The structural, surface, and magnetic characteristics of Fe3O4 nanoclusters were investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). Thermal conductivity studies in diethylene glycol (DEG)-based Fe3O4 cluster nanofluids showed an enhancement in k with an increase in nanocluster size. With a fixed volume fraction (ϕ) = 0.0193, the k enhancement was about 5.3% and 12.6%, respectively, for nanofluids having cluster size of 115 and 530 nm. The observed increase in nanofluid k with increase...

Alcohol Solvent Effects in the Synthesis of Co3O4 Metal-Oxide Nanoparticles: Disproof of a Surface-Ligand Thermodynamic Effect en Route to Alternative Kinetic and Thermodynamic Explanations.

The synthesis of Co3O4 core nanoparticles from cobalt acetate is explored in alcohol solvents plus limited water using O2 as oxidant and NH4OH as the base, all in comparison to controls in water alone employing the otherwise identical synthetic procedure. Syntheses in EtOH or t-BuOH cosolvents with limited water yield phase-pure and size-controlled (3 ± 1 nm) Co3O4-core nanoparticles. In marked contrast, the synthesis in water alone yields mixed phases of Co3O4 and β-Co(OH)2 with a very large particle-size range (14-400 nm). Importantly, acidic reductive digestion of the Co3O4 particles followed by 1H NMR on the resultant solution yields no detectable EtOH in nanoparticles prepared in EtOH, nor any detectable t-BuOH in nanoparticles prepared in t-BuOH (∼5% detection limits for each alcohol), despite the dramatic effect of each alcohol cosolvent on the resultant cobalt-oxide product. Instead, in both cases HOAc is detected and quantified, indicative of OAc- as a surface ligand-and not EtO- or t-BuO- as the surface ligand. The resultant ROH cosolvent-derived particles were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, plus elemental analysis to arrive at an approximate, average molecular formula in the case of the particles prepared in EtOH, {[Co3O4(C2H3O2)]-[(NH4+)0.3(H+0.7)]+·(H2O)}∼216. The key finding is that, because EtOH and t-BuOH have a substantial effect on the phase- and size-dispersion of the cobalt-oxide nanoparticle product, yet the intact alcohol does not show up in the final Co3O4 nanoparticle product, the effect of these alcohols cannot be a surface-ligand thermodynamic effect on the net nanoparticle formation reaction. A careful search of the literature provided scattered, but consistent, literature in which anions or other additives have large effects on metal-oxide nanoparticle formation reactions, yet also do not show up in the nanoparticle products-that is, where the observed effects are again not due to binding by that anion or other additive in a surface-ligand thermodynamic effect on the overall reaction. Alternative hypotheses are provided as to the origin of ROH solvent effects on metal-oxide nanoparticles.

Co-firing of coal and rice straw pellet in a circulating fluidized-bed reactor

This paper presents the experimental investigation of co-firing of coal with rice straw pellet in terms of combustion efficiency, gaseous emissions (CO, NOx and SO2) and occurrence of bed agglomeration. The influence of excess air ratio (EA) and mass share of rice straw in the mixed fuel were investigated in a lab-scale circulating fluidized bed (CFB) reactor. The fuel feed rate was fixed at 14 kg/hr, while the air supply was varied to achieve EA 1.28-1.94. Rice straw pellet was mixed with coal at 25% and 50% mass fraction. The results show that increasing EA generally reduced CO emission. However, at excessively high EA, CO emission started to rise due to the insufficient residence time for complete combustion and the cooling effect. The CO emission clearly reflected the combustion efficiency trend. Higher CO emission was also found when increasing biomass, which may be influenced by the lower combustion temperature and the incomplete combustion of biomass volatiles. NOx and SO2 emission strongly depended on N and S content in the fuel that is the higher rice straw addition the lower NOx and SO2. At lower EA, the observed lower NOx emission could be the effect of reduction by CO and carbon present; while the opposite effect was found at high EA. SO2 emission was more temperature dependent and continuously decreased with increasing EA. System pressure monitoring and visual observation of the spent bed showed no occurrence of bed agglomeration even at 50% addition of rice straw pellet. However, the size distribution of spent bed moved slightly towards a larger particle size range indicating a tendency of agglomeration.

Assessing Guest-Molecule Diffusion in Heterogeneous Powder Samples of Metal-Organic Frameworks through Pulsed-Field-Gradient (PFG) NMR Spectroscopy.

Investigation of guest diffusion in porous metal-organic frameworks (MOFs) is of major importance, because many porosity-related properties of MOFs are influenced by diffusion effects. The diffusion of dimethyl sulfoxide (DMSO) in the MOF MIL-53-NH2 (Al) was investigated through pulsed-field-gradient (PFG) NMR spectroscopy. The microporous material was synthesized in small crystallites (under 500 nm), which agglomerated in a large range of particle sizes (from hundreds of nanometers to tens of micrometers), giving a morphologically very heterogeneous sample. No special agglomeration pattern could be observed, which makes a PFG NMR investigation very challenging, yet it represents a realistic situation for the diffusion of guest molecules in porous materials. We were able to distinguish between two diffusion regimes existing in parallel with each other over the total range from 15 to 200 ms of observation times as accessible in the experiments: In the large crystal agglomerates (diameters above 20 μm), guest movement was found to be subdiffusive, with a time exponent κ =0.8 (rather than one as for normal diffusion). Guest diffusion in the remaining, smaller host particles followed the pattern of normal diffusion within a bed of spheres of impenetrable external surfaces, with a size distribution in good agreement with that of the material under study. Diffusion in a rather complex system could thus be referred to a two-region model with new potentials for application to systems of intricate topology.

Size segregation of intruders in perpetual granular avalanches

Granular flows such as landslides, debris flows and avalanches are systems of particles with a large range of particle sizes that typically segregate while flowing. The physical mechanisms responsible for this process, however, are still poorly understood, and there is no predictive framework for ascertaining the segregation behaviour of a given system of particles. Here, we provide experimental evidence of individual large intruder particles being attracted to a fixed point in a dry two-dimensional flow of particles of otherwise uniform size. A continuum theory is proposed which captures this effect using only a single fitting parameter that describes the rate of segregation, given knowledge of the bulk flow field. Predictions of the continuum theory are compared with the experimental findings, both for the typical location and velocity field of a range of intruder sizes. For large intruder particle sizes, the continuum model successfully predicts that a fixed point attractor will form, where intruders are drawn to a single location.

Inter-comparison of personal monitors for nanoparticles exposure at workplaces and in the environment

Personal monitors based on unipolar diffusion charging (miniDiSC/DiSCmini, NanoTracer, Partector) can be used to assess the individual exposure to nanoparticles in different environments. The charge acquired by the aerosol particles is nearly proportional to the particle diameter and, by coincidence, also nearly proportional to the alveolar lung-deposited surface area (LDSA), the metric reported by all three instruments. In addition, the miniDiSC/DiSCmini and the NanoTracer report particle number concentration and mean particle size. In view of their use for personal exposure studies, the comparability of these personal monitors was assessed in two measurement campaigns. Altogether 29 different polydisperse test aerosols were generated during the two campaigns, covering a large range of particle sizes, morphologies and concentrations. The data provided by the personal monitors were compared with those obtained from reference instruments: a scanning mobility particle sizer (SMPS) for LDSA and mean particle size and a ultrafine particle counter (UCPC) for number concentration. The results indicated that the LDSA concentrations and the mean particle sizes provided by all investigated instruments in this study were in the order of ±30% of the reference value obtained from the SMPS when the particle sizes of the test aerosols generated were within 20–400nm and the instruments were properly calibrated. Particle size, morphology and concentration did not have a major effect within the aforementioned limits. The comparability of the number concentrations was found to be slightly worse and in the range of ±50% of the reference value obtained from the UCPC. In addition, a minor effect of the particle morphology on the number concentration measurements was observed. The presence of particles >400nm can drastically bias the measurement results of all instruments and all metrics determined.

A Parametric Model of the LARCODEMS Heavy Media Separator by Means of Multivariate Adaptive Regression Splines.

Modeling of a cylindrical heavy media separator has been conducted in order to predict its optimum operating parameters. As far as it is known by the authors, this is the first application in the literature. The aim of the present research is to predict the separation efficiency based on the adjustment of the device’s dimensions and media flow rates. A variety of heavy media separators exist that are extensively used to separate particles by density. There is a growing importance in their application in the recycling sector. The cylindrical variety is reported to be the most suited for processing a large range of particle sizes, but optimizing its operating parameters remains to be documented. The multivariate adaptive regression splines methodology has been applied in order to predict the separation efficiencies using, as inputs, the device dimension and media flow rate variables. The results obtained show that it is possible to predict the device separation efficiency according to laboratory experiments performed and, therefore, forecast results obtainable with different operating conditions.

Ignition and combustion of single particles of coal and biomass

Co-firing technology at large power plants can contribute to reducing emissions and maintaining stable and secure electricity supplies. Due to the higher reactivity of biomass, a larger particle size range is generally used for biomass fuels compared with pulverized coal. A single particle apparatus has been developed for rapid heating and combustion of individual fuel particles. This wire mesh apparatus is used as a heating element to heat the particle by radiation while optical access allows particle combustion characterization by high speed camera recording. A woody biomass and a bituminous coal were used in this study. Both fuels showed a sequential combustion of volatile matter followed by char combustion. High speed video image analysis showed differences in ignition and devolatilization behaviour. The biomass volatile flame was smooth along the overall particle, while coal volatile matter release was delivered by jets. Times for the volatile matter combustion were much shorter for the coal while pyrolysis seemed to be the dominant step for around half of total combustion time. During devolatilization, the bituminous coal showed a significant swelling that was not seen in the biomass. As particle mass increased the overall times required for drying, devolatilization and burnout increased for both samples, and this was the dominant parameter to predict burnout time. Impact of particle size and mass was much higher in coal, with a dramatic increase in burnout times for particles above 300µm, while biomass particle size can have a greater range of sizes for the same burnout times. During biomass particle combustion, the results showed that the surface tension on the biomass char particle plays a significant role due to partial melting of the char particle. This effect modifies the char particle shape during its combustion, with particles becoming more spherical even for the initial fibrous shape of the woody biomass particles.

Measuring winter precipitation and snow on the ground in northern polar regions

Measuring winter precipitation in cold and windy regions is recognized as a difficult task. Nonetheless, the accurate measurement of solid precipitation provides important input data for predicting snowmelt floods and avalanche danger and for monitoring climate change. The difficulties in measuring solid precipitation are associated with environmental factors and technological issues. Environmental factors that contribute to measurement errors include wind, freezing rain, rime, and a large range of solid particle shapes and sizes. Technological issues include gauge configuration, the need for remote, low-power-consumption operation, and difficult conditions for data transmission and retrieval. The objectives of this study were to review currently used gauges for measuring solid precipitation and snow on the ground, to summarize the positive and negative characteristics of each gauge, and to provide a discussion of best practices and design and performance criteria that might be used to stimulate research on new and/or improved precipitation gauges in Northern Research Basin (NRB) countries.

Retrieval method of cirrus microphysical parameters at terahertz wave based on multiple lookup tables

Cirrus is an important regulator for the flow of radiant energy in the earth-atmosphere system through the processes of scattering and absorption of radiation. In order to satisfy the urgent requirement for accurate retrieval of cirrus microphysical properties, terahertz wave is expected to be the best waveband for inverting cirrus particle size and ice water path, with terahertz wavelengths on the order of the size of typical cirrus particles. There is an urgent need for establishing stable and accurate inversion method. A new retrieval method for particle size and ice water path is developed based on multiple lookup tables for spaceborne measurements of brightness temperature spectrum of 183 GHz, 325 GHz, 462 GHz, 664 GHz, and 874 GHz channels. Five parameters are derived to quantify the effects of particle size and ice water path on terahertz radiation spectrum due to the scattering of ice clouds, manifested by brightness temperature difference, brightness temperature difference slope, etc. To retrieve cirrus microphysical parameters, a weighted least square fit that matches the modeled parameters is used. The analysis of retrieval errors are conducted by a simulated data series and the results are compared with those retrieved by the other two methods, i. e., difference method and slope method. The results retrieved by the multiple lookup table method are much closer to the simulated data series than those from the other two methods. It is indicated that the method introduced here is a stable and valid method of inverting particles between 50 and 500 m and ice water path between 10 and 500 g/m2. Compared with the errors from the difference-featured method and slope-featured method, the retrieval errors are reduced by 68.78% and 60.28% for particle size, 78.17% and 49.01% for ice water path. The analyses of retrieval uncertainties show that, in general, uncertainties of particle size and ice water path vary with particle size and ice water path. The ice water path uncertainties mainly spread in a range of 0-15 g/m2. The particle size uncertainties fluctuate within a range of 0-20 m. In other words, for small particle size range, the uncertainties are 0-5 m for thick clouds and 5-20 m for thin clouds. However, for large particle size range, the uncertainties are 0-5 m for particles larger than 300 m and 5-15 m for those smaller than 300 m. The results will be helpful for further developing the terahertz wave remote sensing of cirrus microphysical parameter technology. Moreover, it is also an important reference to the improvement of cirrus retrieval accuracy.

Numerical determination of visible/NIR optical constants from laboratory spectra of HED meteorites

Radiative transfer models in particulate media (Hapke, 1981, 1993, 2012b; Shkuratov et al., 1999) are the most versatile tool that can be used to retrieve both composition and surface physical properties from observation of asteroids and other atmosphereless bodies of the Solar System. One caveat is that these methods require as input a sufficiently comprehensive set of optical constants of suitable template materials. These optical constants are the real and imaginary parts of the refractive indexes of the material as function of wavelength, and have to be derived from laboratory measurements of samples of minerals and meteorites. Optical constants can be calculated from a variety of types of measurements, and each has its problems and limitations. In particular, a problem with the determination of optical constants from measurement of reflectance is that the measurements need to be themselves interpreted using radiative transfer models. This is an issue because the number of parameters used in the most accurate versions of the radiative transfer models is large, and for most of the samples many of these parameters were not measured independently. As a result, attempts in the literature to retrieve optical constants from reflectance measurements tend to assume values for the unknown parameters, which can lead to uncertainties in the retrieved optical constants that can be difficult to quantify. In this work we propose a numerical method that allows the simultaneous inversion of the optical constant and the model parameters. This model is then applied to a set of reflectance spectra of 5 HED meteorites from the RELAB database that were measured with the same setup for samples with several particle size intervals. Our results indicate that our method is able to retrieve optical constants which are able to reproduce the measured reflectance of the samples over a large range (25–500 µm) of particle diameters. It is also found that the solutions obtained in this way are non-unique, in the sense that many combination of the model parameters can yield different sets of optical constants that fit equally well the reflectance spectra. Thus, in the absence of the independent determination of at least some of the model parameter the method is unable to decide which solution correspond to the physical optical constants of the materials. Even so, the dispersion of the model parameters (in particular effective particle diameter and porosity) for acceptable solutions (defined as the ones that reproduce the measured reflectance spectra at all size range with residues smaller than 10%) is within a radius of around 30% of the value of the best fit solution for each parameter. Given the ability of the optical constants derived with this method to reproduce the sample spectra over a large range of particle sizes, they can be used without other restriction to assess if a given meteorite assemblage is contributing to the observed spectra of asteroids. However, quantitative informations that can also be derived using these optical constants, like particle sizes, porosity and volumetric fractions of each end-member in a mixture should be regarded only as rough estimates.

Evaluation of N95 Filtering Facepiece Respirators Challenged with Engineered Nanoparticles

ABSTRACTNIOSH-certified respirators, including N95 respirators, are recommended when engineering and administrative controls do not adequately prevent exposures to airborne nanomaterials. Laboratory evaluations of filtering efficiency using standard test aerosols have been reported in the literature, but there is no information on penetration of engineered nanoparticles (1–100 nm) for N95 filtering facepiece respirators (FFR). This project evaluated the performance of two manufacturers’ N95 FFR filters challenged with engineered nanoparticle aerosols containing metal oxides (such as TiO2) and carbon (such as fullerenes and nanotubes) in contrast with a sodium chloride (NaCl) aerosol at flow rates of 30, 85, and 130 L min–1. For new respirator filters in general, NaCl aerosol penetration was less than 5% and the most penetrating particle size occurred at 40 nm. Overall penetration of the engineered nanoparticle aerosols exceeded 5% and was often greater than 5% at and near the most penetrating particle size (MPPS), which occurred at a larger particle size range (90–150 nm). For respirators treated with isopropanol in which the electrostatic force was removed, penetration of NaCl and engineered nanoparticles increased substantially and the MPPS increased to 150 nm for both types of aerosols. Our results indicated that a possible reason for higher maximum penetrations and shift of MPPS observed for these engineered nanoparticles in the new respirators was related to electrostatic collection processes.