Fraction Of Large Particles Research Articles

Temperature Dependences of the Magnetic Susceptibility of Water-Based Magnetic Fluids

This paper presents the results of a study of the temperature dependences of the magnetic susceptibility of water-based magnetic fluids (magnetic colloids) with magnetite particles stabilized by their electrostatic interaction. The average size of dispersed particles was 8 nm, and the volume concentration of particles in the selected samples under study was 1.4% and 1.6%. The investigations were carried out over a wide temperature range. The temperature dependence of the susceptibility, for the first time, was obtained in the region of the colloidal phase transition under supercooling of the dispersion medium (water). Significant differences were found between the temperature dependences of the magnetic susceptibility of such magnetic fluids, where as similar dependences have been found for the susceptibility of magnetic hydrocarbon-based fluids. The observed behavior of such dependences near the water phase transition temperature is determined by the changes in the water phase state, heat release and structuring of the colloid as a result of water crystallization. Moreover, it is suggested that a certain impact on the dependence behavior in the region of the colloidal solidification temperature can also come from the process of blocking the Brownian degrees of freedom of a small fraction of large dispersed particles. It is concluded that the observed maxima in the investigated susceptibility temperature dependences in the lower temperature region are due to magnetic transformations in the colloidal zones formed at the solidification front of the disperse medium with a dense packing of single-domain colloidal particles.

Thermal Stability and Grain Growth Kinetics of Ultrafine-Grained W with Various Amount of La2O3 Addition

In this study, ultrafine-grained W alloys with various amount of La2O3 addition (0.5 ~ 5.0 wt pct) have been prepared by pressureless sintering. The influence of the addition of La2O3 particles on the grain growth of ultrafine-grained W alloys have been studied. The results showed that the addition of La2O3 particles can significantly decrease the grain growth rate, but it seems counterintuitive that the ultrafine-grained W alloy with 2.0 wt pct La2O3 addition, rather than 5.0 wt pct, has the smallest grain size (1.23 μm) after annealing at 1900 °C for 6 h. To reveal the abnormal grain growth behavior, the inhibition effect of the size and distribution of La2O3 particles on grain growth was analyzed, suggesting that the excessive addition of La2O3 particles can cause an abnormal increase in grain size duo to the large fraction of intergranular particles, the small-particle spacing and the high mass transfer rate at the grain boundary.

Fluidization of a Multicomponent Bed in a Reactor for Co-Torrefaction of Waste Coal and Biomass

A study has been made of the hydrodynamic characteristics of the transition of a multicomponent bed consisting of coal sludge and straw pellets to a fluidized state. It has been shown that increase in the fraction of large particles (pellets) in the bed leads to a decrease in its relative height and in the amplitude of pulsations of the pressure difference in it; this contributes to the rise in the degree of conversion of chemical reations occurring in the bed. The possibility of assessing the minimum fluidization velocity of a multicomponent bed from the dependence of the standard deviation of a pulsation of the pressure difference in it on the velocity of air blown though the bed has been proved.

Packing void ratios of very dense ternary mixtures of similar ellipsoids

The paper presents a numerical study on the void ratio of a ternary mixture of similar ellipsoids. The effect of particle size distribution on the void ratio was investigated through samples of various volume fractions of large, medium, and small particles. The particle size ratio of large, medium, and small particles is 16:4:1. The ratio between the major and minor axes of an ellipsoid is 1.5. Thirty-nine very dense ternary samples and sixteen samples of very dense binary samples have been created using the discrete element method. The void ratios of the ternary samples are similar to those of the round washed sands of broader particle sizes. The void ratios of these numerical samples were estimated by an existing model of ternary mixtures of spheres without adjusting the constants to examine the effect of particle shape. A novel phenomenological model is suggested for the void ratio of a ternary mixture. The model is applied to the ternary mixture of similar ellipsoids, and the ternary mixture of round washed sands. A good agreement is observed in both cases.

The effect of heat treatment on the mechanical and tribological properties of dual size SiC reinforced A357 matrix composites

In the present work, the effect of aging temperature and particle size ratio of SiC particles on the mechanical and tribological properties of A357 composites reinforced with dual particle size SiC were investigated. The composites were prepared by melt-stirring assisted permanent mold casting technique with different weight fractions (3% coarse +3% fine, 4% coarse +2% fine, and 2% coarse +4% fine) of large and small size SiC particles. These three prepared composites are referred as DPS1, DPS2 and DPS3 composites. The solutionizing temperature was maintained constant at 540°C for 9h while the aging was done at 160°C, 180°C and 200°C (T6 treatment) for 6h. Optical and scanning electron microscopy studies showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. High-resolution transmission electron microscopy images showed formation of uniformly dispersed needle-like β″ phase and spherical shaped β-Mg2Si precipitates under peak aging conditions. Compared to T6 treated A357 alloy, the T6 treated DPS A357 composites showed improved yield strength, tensile strength, hardness and wear resistance. Among the three composites, hardness and wear resistance of T6 treated DPS2 composite was found to be significantly higher when compared to the other two composites (DPS1 and DPS3). Ratio of large particles to small particles also seems to effect the mechanical and tribological properties. Presence of more small particles was found to be good for strength and ductility whereas more large particles were found to be good for hardness and wear resistance.

Manufacturing high strength aluminum matrix composites by friction stir processing: An innovative approach

Abstract Shape Memory Alloys (SMA), e.g., NiTi (nitinol), are good candidates of reinforcement agents for the improvement of mechanical properties of aluminum alloys. Friction Stir Processing (FSP) has been shown to be an appropriate manufacturing process for particulate Aluminum Matrix Composites (AMCs), due to the mitigation of critical intermetallic formation between particles and matrix. However, AMCs processed by FSP with the matrix material made of high strength alloys, in particular 7xxx series, have systematically shown severe defects, such as clusters and cavities that result from poor material flow. Herein, we present an innovative strategy to manufacture Al7075/NiTi composites via FSP avoiding this unacceptable particle clustering. The strategy involves the addition of 7xxx series Al powder in a groove or multi-holes to be stirred together with the NiTi particles, leading to dissociation of the latter. The X-ray computed tomography acquisitions allow for 3D quantitative assessment of the size and spatial distribution of the embedded reinforcements. It is revealed that the groove filling method results in a more homogenous distribution compared to the multi-holes filling method. Moreover, the distribution is found to be dependent on the particle size, as a higher volume fraction of large particles is observed at the upper part of the FSP stir zone. These new AMCs, with a good Al-NiTi interface, present a potential to tailor the composite mechanical properties by exploiting the shape memory effect of the NiTi reinforcements.

Summertime and wintertime atmospheric processes of secondary aerosol in Beijing

Abstract. Secondary aerosol constitutes a large fraction of fine particles in urban air of China. However, its formation mechanisms and atmospheric processes remain largely uncertain despite considerable study in recent years. To elucidate the seasonal variations in fine-particle composition and secondary aerosol formation, an Aerodyne quadrupole aerosol chemical speciation monitor (Q-ACSM), combined with other online instruments, was used to characterize the sub-micrometer particulate matter (diameter < 1 µm, PM1) in Beijing during summer and winter 2015. Our results suggest that photochemical oxidation was the major pathway for sulfate formation during summer, whereas aqueous-phase reaction became an important process for sulfate formation during winter. High concentrations of nitrate (17 % of the PM1 mass) were found during winter, explained by enhanced gas-to-particle partitioning at low temperature, while high nitrate concentrations (19 %) were also observed under the conditions of high relative humidity (RH) during summer, likely due to the hydrophilic property of NH4NO3 and hydrolysis of N2O5. As for organic aerosol (OA) sources, secondary OA (SOA) dominated the OA mass (74 %) during summer, while the SOA contribution decreased to 39 % during winter due to enhanced primary emissions in the heating season. In terms of the SOA formation, photochemical oxidation perhaps played an important role for summertime oxygenated OA (OOA) formation and less-oxidized wintertime OOA (LO-OOA) formation. The wintertime more-oxidized OOA (MO-OOA) showed a good correlation with aerosol liquid water content (ALWC), indicating a more important contribution of aqueous-phase processing over photochemical production to MO-OOA. Meanwhile, the dependence of LO-OOA and the mass ratio of LO-OOA to MO-OOA on atmospheric oxidative tracer (i.e., Ox) both degraded when RH was greater than 60 %, suggesting that RH or aerosol liquid water may also affect LO-OOA formation.

Characterization of aerosol particles at Cabo Verde close to sea level and at the cloud level – Part 1: Particle number size distribution, cloud condensation nuclei and their origins

Abstract. In the framework of the MarParCloud (Marine biological production, organic aerosol particles and marine clouds: a Process Chain) project, measurements were carried out on the islands of Cabo Verde (a.k.a. Cape Verde) to investigate the abundance, properties and sources of aerosol particles in general, and cloud condensation nuclei (CCN) in particular, both close to sea level and at the cloud level. A thorough comparison of particle number concentration (PNC), particle number size distribution (PNSD) and CCN number concentration (NCCN) at the Cape Verde Atmospheric Observatory (CVAO, sea-level station) and Monte Verde (MV, cloud-level station) reveals that during times without clouds the aerosols at CVAO and MV are similar and the boundary layer is generally well mixed. Therefore, data obtained at CVAO can be used to describe the aerosol particles at cloud level. Cloud events were observed at MV during roughly 58 % of the time, and during these events a large fraction of particles was activated to cloud droplets. A trimodal parameterization method was deployed to characterize PNC at CVAO. Based on number concentrations in different aerosol modes, four well-separable types of PNSDs were found, which were named the marine type, mixture type, dust type1 and dust type2. Aerosol particles differ depending on their origins. When the air masses came from the Atlantic Ocean, sea spray can be assumed to be one source for particles besides new particle formation. For these air masses, PNSDs featured the lowest number concentration in Aitken, accumulation and coarse modes. Particle number concentrations for sea spray aerosol (SSA, i.e., the coarse mode for these air masses) accounted for about 3.7 % of NCCN,0.30 % (CCN number concentration at 0.30 % supersaturation) and about 1.1 % to 4.4 % of Ntotal (total particle number concentration). When the air masses came from the Sahara, we observed enhanced Aitken, accumulation and coarse mode particle number concentrations and overall increased NCCN; NCCN,0.30 % during the strongest observed dust periods is about 2.5 times higher than that during marine periods. However, the particle hygroscopicity parameter κ for these two most different periods shows no significant difference and is generally similar, independent of air mass. Overall, κ averaged 0.28, suggesting the presence of organic material in particles. This is consistent with previous model work and field measurements. There is a slight increase in κ with increasing particle size, indicating the addition of soluble, likely inorganic, material during cloud processing.

Indoor persistent organic pollutants in agricultural areas from Argentina

Persistent Organic Pollutants (POPs) are anthropogenic chemicals extensively used in the past for industrial and agricultural purposes, characterized by their lipophilicity, ubiquity, volatility and environmental persistence. By other hand, chlorpyrifos is the most widely used current pesticide (CUPs) being the main insecticide used for crops in Argentina. The aim of this work was to assess levels of POPs and CUPs in different fractions of airborne particles collected indoor in agricultural areas from Argentina. Particles higher than 2.5µm were trapped in polyurethane foams (PUF) while particles smaller than 1µm and volatile compounds were adsorbed on activated charcoal. Compounds were analyzed by gas chromatograph with electron capture detector (GC-ECD). Endosulfans, chlordanes, PCBs, and HCHs were detected in all PUF samples, while endosulfans, chlorpyrifos, PCBs, and HCHs were the most abundant in smaller particles. Majority of pesticides showed higher concentrations during the summer season (1397.7 vs 832.5pg/m3 ). Even adding up all measured organic compounds, no sample reaches the threshold limit value for indoor pesticides levels (0.1pg/m3 ), neither in the large or small particle fraction. However, the fact that chronic exposure to POPs has been linked to several diseases raises concern for human health.

Pollution Trends in China from 2000 to 2017: A Multi-Sensor View from Space

Satellite sensors can provide unique views of global pollution information from space. In particular, a series of aerosol and trace gas monitoring instruments have been operating for more than a decade, providing the opportunity to analyze temporal trends of major pollutants on a large scale. In this study, we integrate aerosol products from MODIS (MODIS Resolution Imaging Spectroradiometer, all abbreviations and their definitions are listed alphabetically in Abbreviations) and MISR (Multi-angle Imaging Spectroradiometer), the AAI (Absorbing Aerosol Index) product from OMI (Ozone Monitoring Instrument), column SO2 and NO2 concentrations from OMI, and tropospheric column ozone concentration from OMI/MLS (Microwave Limb Sounder) to study temporal changes in major pollutants over China. MODIS and MISR consistently revealed that column AOD (Aerosol Optical Depth) increased from 2000, peaked around 2007, and started to decline afterward, except for northwest and northeast China, where a continuous upward trend was found. Extensive negative trends in both SO2 and NO2 have also been found over major pollution source regions since ~2005. On the other hand, the OMI AAI exhibited significant increases over north China, especially the northeast and northwest regions. These places also have a decreased Angstrom exponent as revealed by MISR, indicating an increased fraction of large particles. In general, summer had the largest AOD, SO2, and NO2 trends, whereas AAI trends were strongest for autumn and winter. A multi-regression analysis showed that much of the AOD variance over major pollution source regions could be explained by SO2, NO2, and AAI combined, and that the SO2 and NO2 reduction was likely to be responsible for the negative AOD trends, while the AOD increase over NE and NW China may be associated with an increase of coarse particles revealed by increased AAI and decreased AE. In contrast to aerosols, tropospheric ozone exhibited a steady increase from 2005 throughout China. This indicates that although the recent emission control effectively reduced aerosol pollutants, ozone remains a challenging issue and may dominate future air pollution.

Characterisation of suspended and sedimented particulate matter in blue-green infrastructure ponds

Abstract Blue-green infrastructure (BGI) ponds have an important function of alleviating flood risk and provide water quality improvements among other multiple benefits. Characterisation of bottom sediments and suspended particulate matter (SPM) is understudied, but is indispensable for assessing the ponds' functioning because of their role in biogeochemical cycling and pollutant adsorption. Here we report on the analysis of particle sizes and chemistry from multiple locations. The results have shown that SPM in these ponds includes particles of both biological and abiotic origin, and the in situ produced organic matter constitutes a major part of SPM. The relevance of biological processes is often overlooked, but a combination of scanning electron microscopy (SEM) observations and chemical analysis highlights its primary importance for characterisation of the particulate matter. A considerable proportion of both suspended and sedimented particulates is smaller than 100 microns. There is normally a large fraction of small silt-sized particles, and often a considerable proportion of very fine particles (clay-size). Although for some spectra unimodal distribution has been observed, in many cases the revealed particle size distribution (PSD) was bimodal, and in some instances more than two modes were revealed. A complex PSD would be expected to result from a combination of simple unimodal distributions. Hence the multimodality observed may have reflected contributions from different sources, both abiotic and biological. Furthermore, many smaller particles appear to be interconnected by detrital matter. Among chemical elements routinely detected within the SPM in significant concentrations were Si, Al, Ca, Mg, Fe, K, Mn, P, Cl and S. In a number of cases, however, there were less expected elements such as Ti, Y, Mo, Cr and even Au; these may have reflected the effect of car park and road runoff and/or industrial pollution. Most of these elements (except Mo and Au) and up to 30 others were also routinely detected in sediment samples. Such pollutants as Co, Cu, Ni, Zn and As were detected in bottom sediments of all ponds. There were a number of correlations between pollutants in sediments and the particle's median diameter. However, aggregation leads to large low density flocks and masks correlation of chemicals with SPM particle size. Statistical associations among the elements aided the understanding of their sources and pathways, as well as the underlying biological and abiotic processes. Specifically, our analysis implicated contributions from such sources as allochthonous and autochthonous detritus, roadside and industrial pollution, biologically induced precipitation, and discarded electronics. Elevated levels of rare earth elements (REE) and other trace elements open a possibility of their recovery from the sediments, which should be considered among the multiple benefits of BGI.

Metasurface-Based Wide-Angle Beam Steering for Optical Trapping

Metasurfaces become increasingly important for wavefront shaping and beam steering with high efficiency. We propose a wide-angle beam steering device based on all-dielectric metasurfaces consisting of two symmetrical blazed gratings for optical trapping of particles, which can convert the input Gaussian beam to a special beam with intensity gradient along the propagation direction. Two major types of metasurfaces (Pancharatnam-Berry phase and nanoposts) are compared, and dramatic difference is found between them, especially at oblique incidence. We show that the Pancharatnam-Berry phase-based metasurface is more tolerant to the incident angle and that significant optical gradient force can be generated over a large angle range of -50° to 50°, and the maximum attractive force is up to tens of pN/W, with a trapping range of 14 gym for particles of 2.5 μym in diameter. The proposed scheme exhibits great potential to trap a large fraction of particles floating in a microfluidic channel when the beam is dynamically steered.

The mesoscopic collective motion of self-propelling active particle suspension confined in two-dimensional micro-channel

The mesoscopic collective motion of self-propelling active particle suspension confined in high aspect ratio two-dimensional micro-channel is numerically studied through coupled equation by considering background thermal fluctuation, inter-particle interaction, self-propulsion and micro-channel confinement. Both the self-propulsion and micro-channel confinement are the factors driving the system away from equilibrium and sustaining heterogeneous motion. In such system, the propulsion induced particle accumulation around the channel walls is a universal phenomenon with spatial heterogeneity, where large fraction of particles are caged inside the accumulated cluster with local oscillation coexisting with few fast propelling particles in the center region. Although the formation mechanism of the induced accumulation is well studied, post the cluster formation, how the cluster evolves and its dynamical properties is rarely discussed. Based on the merits of equation, the dynamical evolution of induced accumulation is revealed by particle trajectories. It is found that the induced accumulation can be dissociated through the slow re-orientation process of few jammed particles. By using the idea of force chain network, how the transverse confinement couples the transverse displacement with the longitudinal displacement is evidenced. It is further verified by the statistical measurement of correlation probability between transverse and longitudinal displacements. The suppressed displacements in both directions is the origin leading to the slow dynamics of cluster evolution. Temporally, within the orientational relaxation time, this system exhibits non-trivial anomalous diffusion under the competition between the counter effects of self-propulsion (enhanced diffusion) and micro-channel confinement (suppressed diffusion). Additionally, by considering the orientational coupling, the deep hysteresis of accumulation has been found even for very weak orientational coupling strength.

Impact of field ramp rate on magnetic field assisted thermal transport in ferrofluids

The impact of magnetic field ramp rate and the resulting aggregation kinetics on thermal transport in three different oil based ferrofluids of similar properties but with different particle size distributions is reported here. The volume fraction of the surfactant capped magnetite nanoparticles, in all three cases were kept constant at 0.037(20 wt%). For 17 G/s ramp thermal conductivity enhancement of 180% at 200 G improved to 230% with 33 G/s ramp in the ferrofluid system with the least fraction of larger particles. Our results show that faster magnetic field ramps have a profound influence on thermal conductivity enhancement. The phase contrast optical microscopy images show that the slower ramps resulted in thicker aggregates leading to a substantial decrease in their number density. On the other hand, faster ramps resulted in simultaneous formation of large number density of finer aggregates which proved to be extremely beneficial for thermal transport. In a ferrofluid with moderately high number of larger particles, faster ramps were found to be very effective in improving thermal transport. On sudden exposure to magnetic field, particularly for higher strengths, substantial improvement in thermal conductivity was observed initially, which decreased with time due to coarsening of aggregates and reduced number density of chains, but leveled off to a lower time independent value. Our findings provide a way to improve field induced thermal transport of a ferrofluid without altering their physical properties. Alternate magnetic field on-off cycles and faster field ramps were found to be particularly helpful in improving thermal transport of a ferrofluid possessing modest amount of larger particles, which will enable development of superior smart cooling devices.

Numerical simulation of the effect of fine fraction on the flowability of powders in additive manufacturing

Additive manufacturing (AM) is a rapid and flexible technique for the production of metal parts and prototypes from metal powders. The quality of parts manufactured using AM is a strong function of powder physical and mechanical properties. Previous work has shown that powders with a large fraction of fine particles produce better parts in terms of smooth finished surface and high mass density. However, an excessive fine fraction in the source powder causes serious flowability issues, leading to unexpected voids or discontinuities in the finished product. This effect of the fine fraction on the flowability of metal powder is widely encountered but poorly understood in the AM industry. This study presents a three-dimensional (3D) discrete element method (DEM) model to simulate the microscale mechanisms of powder flow considering the effects of van der Waals force. This microscale force has a negligible influence on the flowability of coarse grains, but the effect becomes the dominant factor governing the behavior of fine fractions (micrometer scale). The results show that the numerical model presented in this paper is capable of reproducing the experimental dependency of the powder flowability on the fine fraction. Moreover, it also successfully captures the characteristics of particle flow under the influence of microscale van der Waals force.

Solid Nucleation Mode Engine Exhaust Particles Detection at High Temperatures with an Advanced Half Mini DMA

<div class="section abstract"><div class="htmlview paragraph">Diesel and gasoline direct injection engines emit nucleation mode particles either under special conditions or as part of their normally emitted size distribution, respectively. Currently, European legislation excludes nucleation mode particles as particle number vehicle emission measurements are limited down to 23 nm. The rationale behind such a cut-off size is based on the avoidance of significant uncertainties inherent in the sampling and measuring of sub-23 nm solid particles. However, the sub-23 nm particles have drawn increased attention since a large fraction of particles emitted by modern vehicles lies in this size range. In this study we investigate the possibility of accurate nucleation mode particles detection by using the Advanced Half Mini Differential Mobility Analyzer (HM-DMA). The Advanced HM-DMA system is able to classify aerosol particles in the mobility size range 5 - 30 nm with high resolution and fast spectrum acquisition that can accommodate a sample flow maintained at up to 200°C. The unique ability to classify particles at high temperatures permits engine exhaust measurements without the need for aerosol conditioning. Initially, the Advanced HM-DMA hot operation mode accuracy is tested with reference aerosols against State-of-the-Art instruments. Thereafter, the Advanced HM-DMA is employed for measuring nucleation mode particles generated by a diesel engine using a single hot dilution step. Advanced HM-DMA measurements are compared to measurements performed with PMP protocol-compliant volatile particle removal system. The excellent agreement between the two measurements confirms the reliability of the Advanced HM-DMA hot operation mode and indicates the possibility of using a simplified conditioning setup for solid nucleation-mode particles measurement.</div></div>

Organic Aerosol Processing During Winter Severe Haze Episodes in Beijing

AbstractOrganic aerosol (OA) constituted a large fraction of aerosol particles during severe haze episodes in winter in northern China, yet our understanding of its physical and chemical processing was limited. Here we investigate the sources and processes of OA during four haze episodes in winter in 2016 using high‐resolution aerosol mass spectrometer. The PM2.5 reached 400 μg/m3 during the severest episode (Ep1) when Beijing issued a red alert and implemented strict emission controls. Our results showed that secondary OA (SOA) dominated OA during haze episodes on average accounting for 46–66% of OA and was comparable to secondary inorganic aerosol (SIA) with the SOA/SIA ratios being 0.51–0.72. Primary OA from fossil‐fuel combustion, biomass burning, and cooking presented very strong diurnal variations during haze episodes and contributed up to 60% in OA at night. Comparatively, the changes in semivolatile and low‐volatility SOA were relatively small except a substantial increase in aqueous phase‐related oxidized OA (aq‐OOA) during Ep1 with high relative humidity and aerosol water content. aq‐OOA fell well into a small region in the middle of the triangle plot of f44 versus f43 (fraction of m/z 44 and 43 in OA, respectively), which can be used as a diagnostic for the presence of aqueous phase processing of SOA. In addition, the increases of SO2+/SO3+ as a function of relative humidity, the triangle plot of versus , and high nitrogen‐to‐carbon ratio in aq‐OOA suggest the potential formation of sulfur‐ and nitrogen‐containing organic compounds through aqueous phase processing.

The Effect of the Active Component Content on the Catalytic Activity of Nickel Sulfide Catalysts in Olefin Synthesis from Stearic Acid

The effect of active component content on the catalytic activity of supported sulfide catalysts in the synthesis of C17 olefins from stearic acid has been studied. It has been shown that an increase in the nickel content leads to a decrease in the catalyst activity; in addition, there is a negative correlation between the activity and the fraction of large particles on the support surface. The highest heptadecene selectivity (50–60%) is observed for alumina-supported catalysts owing to the higher degree of dispersion of the active component.

Effect of selective catalytic reduction on exhaust nonvolatile particle emissions of Euro VI heavy-duty compression ignition vehicles

The nonvolatile particle number (PN) emissions of late technology diesel heavy-duty vehicles (HDV) are very low due to the introduction of Diesel Particulate Filters (DPF). Nevertheless, a large fraction (50%) of particles below the current lower regulated size (23 nm) was recently reported. Moreover, large differences between laboratory and PN Portable Emission Measurement Systems (PN-PEMS) have been observed. In order to better understand such differences, the physical properties of the exhaust aerosol from two Euro VI technology diesel heavy-duty engines were studied. It was found that urea injection leads to formation of nonvolatile particles. The produced particles covered a wide size range spanning from below 10 nm to above 100 nm. As such, they contribute to the regulated PN emissions, with measured concentrations corresponding to as high as 2 × 1011 #/kWh over a World Harmonized Transient Cycle (WHTC). However, a large fraction of them was undetected owing to their small particle size. Low-cutoff size (10 nm) Condensation Particle Counters (CPCs) (which are under discussion to be included in the regulations) measured up to twice as high concentrations. Considering the large particle losses in the sampling systems at this size range, the true concentrations can be two times higher from what the low-cutoff CPCs reported. When the temperature of the SCR system exceeded a threshold of 300 °C, the produced particles were found to be positively charged, increasing the average exhaust aerosol charge up to +3 elementary charges per particle. Scanning Mobility Particle Sizer (SMPS) measurements of non-neutralized samples revealed that even the smallest of them can carry more than one positive charge. The findings of this study can explain the differences reported between PEMS and laboratory systems and especially those based on diffusion charging. They also provide insight for a refinement of technical requirements prescribed in the European PEMS regulation to more accurately quantify the PN emissions from such technologies.

Self-Assembly of Amphiphilic Amylose Derivatives in Aqueous Media.

Six amylose derivative (C12CMA) samples with hydrophobic dodecyl ether groups and hydrophilic sodium carboxymethyl groups were synthesized from an enzymatically synthesized amylose for which the weight-average molar mass is 50 kg mol-1 to realize amylose-based amphiphilic polymer micelles. The degree of substitution of hydrophobic (DSC12) and hydrophilic (DSCM) groups ranges between 0.076 and 0.39 and between 0.35 and 1.83, respectively. Static and dynamic light scattering, small-angle X-ray scattering (SAXS), and fluorescence measurements with pyrene as a probe were carried out for the samples in 150 mM aqueous NaCl to characterize the higher-order structure in solution. The fluorescence from pyrene showed that all six samples have hydrophobic environment, while the hydrophobicity tends to increase with rising DSC12. All six samples have high scattering intensity owing to the relatively large concentrated droplets ranging in the hydrodynamic radius from 50 to 110 nm, whereas the weight fraction of such large particles is substantially small except for the highest DSC12 sample. Most polymer chains for relatively low DSC12 of 0.076 were molecularly dispersed with a very small amount of large droplets. The dispersed chain has a slightly smaller helix pitch per residue and a more rigid main chain than those for amylose in dimethyl sulfoxide, suggesting that the amylosic main chain of C12CMA has a helical structure with dodecyl groups at least locally. On the other hand, an anisotropic shaped micelle-like structure is only found for relatively high DSC12 (0.23 and 0.39) samples, which was detected by the SAXS profile at a high scattering vector range. The micelle structure for high DSC12 samples is consistent with the high chain stiffness.