Localization of the inner body in jumbo phage phiK601 by Cryo-EM and high-dose imaging

Abstract. Particles in the atmosphere are of concern due to their toxic properties and effects on climate. In coastal areas, ship emissions can be a significant anthropogenic source. In this study we investigated the contribution from ship emissions to the total particle number and mass concentrations at a remote location. We studied the particle number concentration (12 to 490 nm in diameter), the mass concentration (12 to 150 nm in diameter) and number and volume size distribution of aerosol particles in ship plumes for a period of 4.5 months at Høvsøre, a coastal site on the western coast of Jutland in Denmark. During episodes of western winds, the site is about 50 km downwind of a major shipping lane and the plumes are approximately 1 hour old when they arrive at the site. We have used a sliding percentile-based method for separating the plumes from the measured background values and to calculate the ship plume contribution to the total particle number and PM0.15 mass concentration (mass of particles below 150 nm in diameter, converted from volume assuming sphericity) at the site. The method is not limited to particle number or volume concentration, but can also be used for different chemical species in both particle and gas phase. The total number of analyzed ship plumes was 726, covering on average 19% of the time when air masses were arriving at the site over the shipping lane. During the periods when plumes were present, the particle concentration exceeded the background values on average by 790 cm−3 by number and 0.10 μg m−3 by mass. The corresponding daily average values were 170 cm−3 and 0.023 μg m−3, respectively. This means that the ship plumes contributed between 11 and 19% to the particle number concentration and between 9 and 18% to PM0.15 during days when air was arriving over the shipping lane. The estimated annual contribution from ship plumes, where all wind directions were included, was in the range of 5–8% in particle number concentration and 4–8% in PM0.15.

Systems for studying the toxicity of metal aggregates on the airways are normally not suited for evaluating the effects of individual particle characteristics. This study validates a set-up for toxicological studies of metal aggregates using an air–liquid interface approach. The set-up used a spark discharge generator capable of generating aerosol metal aggregate particles and sintered near spheres. The set-up also contained an exposure chamber, The Nano Aerosol Chamber for In Vitro Toxicity (NACIVT). The system facilitates online characterization capabilities of mass mobility, mass concentration, and number size distribution to determine the exposure. By dilution, the desired exposure level was controlled. Primary and cancerous airway cells were exposed to copper (Cu), palladium (Pd), and silver (Ag) aggregates, 50–150 nm in median diameter. The aggregates were composed of primary particles <10 nm in diameter. For Cu and Pd, an exposure of sintered aerosol particles was also produced. The doses of the particles were expressed as particle numbers, masses, and surface areas. For the Cu, Pd, and Ag aerosol particles, a range of mass surface concentrations on the air–liquid interface of 0.4–10.7, 0.9–46.6, and 0.1–1.4 µg/cm2, respectively, were achieved. Viability was measured by WST-1 assay, cytokines (Il-6, Il-8, TNF-a, MCP) by Luminex technology. Statistically significant effects and dose response on cytokine expression were observed for SAEC cells after exposure to Cu, Pd, or Ag particles. Also, a positive dose response was observed for SAEC viability after Cu exposure. For A549 cells, statistically significant effects on viability were observed after exposure to Cu and Pd particles. The set-up produced a stable flow of aerosol particles with an exposure and dose expressed in terms of number, mass, and surface area. Exposure-related effects on the airway cellular models could be asserted.Graphical Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-016-3389-y) contains supplementary material, which is available to authorized users.

Abstract. Combustion of fossil fuel in gasoline and diesel powered vehicles is a major source of aerosol particles in a city. In a street canyon, the number concentration of particles smaller than 300 nm in diameter, which can be inhaled and cause serious health effects, is dominated by particles originating from this source. In this study we measured both, particle number size distribution and traffic density continuously in a characteristic street canyon in Germany for a time period of 6 months. The street canyon with multistory buildings and 4 traffic lanes is very typical for larger cities. Thus, the measurements also are representative for many other street canyons in Europe. In contrast to previous studies, we measured and analyzed the particle number size distribution with high size resolution using a Twin Differential Mobility Analyzer (TDMPS). The measured size range was from 3 to 800 nm, separated into 40 size channels. Correlation coefficients between particle number concentration for integrated size ranges and traffic counts of 0.5 were determined. Correlations were also calculated for each of the 40 size channels of the DMPS system, respectively. We found a maximum of the correlation coefficients for nucleation mode particles in the size range between 10 and 20 nm in diameter. Furthermore, correlations between traffic and particles in dependence of meteorological data were calculated. Relevant parameters were identified by a multiple regression method. In our experiment only wind parameters have influenced the particle number concentration significantly. High correlation coefficients (up to 0.8) could be observed in the lee side of the street canyon for particles in the range between 10 and 100 nm in diameter. These values are significantly higher than correlation coefficients for other wind directions and other particle sizes. A minimum was found in the luff side of the street. These findings are in good agreement with theory of fluid dynamics in street canyons.

The fine structure of both the afferent and efferent hair cell synapses in the sensory epithelium of guinea pig organ of Corti was examined by freeze-fracture electron microscopy. In the afferent synapse, barlike aggregates of intramembrane particles (IMPs) of about 10 nm in diameter were seen on the P-face of the afferent presynaptic membrane directly beneath the presynaptic dense projection which is located in the active zone of the presynaptic membrane. Small and large depressions have been seen on the presynaptic membrane. The former were observed in the proximity of the barlike aggregates, while the latter were observed some distance from the aggregate. In outer hair cells, IMPs of about 10 nm in diameter were seen on the P-face of the afferent postsynaptic membrane at a density of 3,000/microns 2. In the efferent synapse, many aggregates composed of from several to tens of large IMPs of 13 nm in diameter were observed on the presynaptic membrane. These aggregates were localized to small membrane depressions, which tended to be deeper as particle number per aggregate increased. Dense populations of IMPs of about 9 nm in diameter were observed on the P-face of the efferent postsynaptic membrane at a density of 4,000/microns 2. A fenestrated subsynaptic cistern completely covers the efferent postsynaptic membrane. Moreover, the subsynaptic cistern spans several efferent postsynaptic membranes when efferent synapses are gathered in a group. In the afferent and efferent synapses of hair cells, specializations of the synaptic membranes were represented by marked aggregates characteristic of IMPs. In the efferent synapse, IMP movement inside the synaptic membrane was proposed in relationship to retrival of synaptic vesicle membrane. Structural relationship between the subsynaptic cistern and efferent postsynaptic membrane was revealed.

The ultrastructure of Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus-8 (HHV-8) has not yet been fully elucidated, although some findings have been reported using primary effusion lymphoma (PEL) cell lines, KS-1, harboring no Epstein-Barr virus (EBV) coinfection. In the present study, detailed fine structural examination of KSHV/HHV-8 was performed after stimulation of the PEL-derived cell line KS-1 with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in vitro. While unstimulated KS-1 cells contained a small number of intranuclear virus particles associated with no extracellular mature particles, KS-1 cells stimulated with TPA produced many extracellular mature particles as well as intranuclear particles, in addition to interesting tubulo-reticular structures and aggregated tubular structures in vesicles. The induced intranuclear particles were empty, doughnut shaped, and dense cored, with outer and inner diameters of 100-110 nm and 60-70 nm, respectively. Dense-cored extracellular mature particles were 150-160 nm in diameter, and some contained doughnut-shaped cores, together with a few megaloviruses, 260 nm in outer diameter. These findings indicate that KS-1 cells treated with TPA can produce extracellular mature particles as well as intranuclear particles, which were proven to be KSHV/HHV-8.

Aerosol particles from metalorganic vapor phase epitaxy bubblers

Separation and detection of individual submicron polystyrene spheres using capillary electrophoresis with laser-light-scattering detection has been demonstrated. Electrophoretically separated particles were passed through a focused laser beam and light scattered from individual particles was collected at 90 degrees. Each diameter of polystyrene spheres injected (from 110 to 992 nm) resulted in the observation of a well-defined migration window containing multiple peaks, each arising from the light scattered by an individual particle. The migration time window for individual particles of a particular size corresponded well to the migration time of a peak from a population of particles of the same size detected using a UV absorbance detector. The electrophoretic mobility and scattered light intensity were determined for each particle detected. The average scattered light intensity for each particle size was consistent with Mie scattering theory. Particles as small as 110 nm in diameter were detected individually using this method, but particles with a diameter of 57 nm could not be individually detected. The number of single particle scattering events was counted and compared to the theoretical number of particles injected electrokinetically, and the detection efficiency determined ranged from 38 to 57% for polystyrene spheres of different sizes. The laser-light-scattering detection method was directly compared to laser-induced fluorescence detection using fluorescent polystyrene microspheres. The number of particles detected individually by each method was in agreement.

Indoor and outdoor particle size characterization at a family house in Espoo–Finland

Seamless transition: New hybrid fullerene-like nanostructures of MoS2 are comprised of a nanoscale octahedral core with a smooth transition to quasi-spherical outer shells (see picture). The particles were generated by ultra-high irradiance solar ablation and their structures confirmed by modeling studies. MoS2, a layered compound with tribological and catalytic applications, is known to form a range of hollow closed nanostructures1–5 and nanoparticles, including graphene-like structures.6 These have been demonstrated experimentally through high-temperature synthesis and pulsed laser ablation (PLA), and theoretically with quantum chemical calculations. The smallest allowed structures are nanooctahedra of 3 to 8 nm size. Nicknamed the "true inorganic fullerene" in analogy to carbon fullerenes,4 they differ from larger multi-walled MoS2 fullerene-like nanoparticles both in their morphology and predicted electronic properties. The larger fullerene-like particles are quasi-spherical (polyhedral) or nanotubular, typically with diameters of 20 to 150 nm.3 Above a few hundred nm in size, these nanoparticles transform into 2H-MoS2 platelets. Fullerene-like particles have been recognized as superior solid lubricants7 with numerous commercial applications, and MoS2 nanooctahedra may have catalytic applications. Understanding the fundamental commonality of these two morphologies might prove essential in the development of new materials. The research on hollow MoS2 nanostructures of minimal size (<10 nm in diameter) was initiated in 1993 upon the first independent proposal of the formation of nanooctahedra of MoS23, 5 (and BN)8 with six rhombi in their corners. In 1999, it was demonstrated4 that two- to four-walled MoS2 nanooctahedra, 3–5 nm in size and up to ca. 104 atoms, could be obtained by PLA. Similar results were subsequently reported in Ref. 1, 2 as illustrated in Figure 1 a. Recent studies of high energy density methods such as laser ablation and arc–discharge9–13 resulted in small structures with only a limited number of atoms: Mo–S clusters or double-walled nanooctahedra. a) Transmission electron microscope (TEM) image that includes MoS2 nanooctahedra generated from MoS2 powder by PLA as reported in Ref. 1, 2. Note the large number of nanooctahedra with two or three layers and <8 nm in size. b) Ball-and-stick models showing assorted projections of the nanooctahedra in (a), where Mo atoms are red and S atoms are yellow. On the other hand, theoretical modeling1, 2 suggested that the stability limit for nanooctahedra should be almost an order of magnitude larger than the largest structures produced by PLA (see Figure 3 of Ref. 1). Therefore, nanooctahedra with more than five layers were not considered in modeling procedures. A principal insight from the PLA studies was that the low density of the Mo–S vapor, coupled with the rapid temperature quench, prevented the nanooctahedra from growing to sizes large enough to realize their stability limit. It was concluded that a two-step process of PLA at 2000 °C, followed by in situ annealing at 500–750 °C, is advantageous for improving the yield of MoS2 nanooctahedra.1, 2, 14 In contrast, substantial amounts of larger multi-walled quasi-spherical or nanotubular structures were produced by oven-driven reactions, but without nanooctahedra. Most likely the internal energy of the process was insufficient for the required transformation,15–20 the nature of which has not been elucidated to date. The confluence of these results, and the success of purely photothermal PLA, prompted the development of alternative optical systems (such as solar and discharge lamp concentrators),21 and culminated in the development of a high-irradiance solar furnace22 shown in Figure 2. This experimental facility provides high power densities (ca. 15 000 suns, i.e., 15 W mm−2) on sizable areas (of the order of several mm2) in a continuous fashion. Relative to PLA systems, the solar furnace provides a larger reaction volume and higher vapor pressure of reactants, with peak reactor temperatures >2700 K.23 Thermal radiation from the heated precursor powder provides a natural, extensive, and hot annealing environment. High-irradiance solar furnace. a) Schematic. b) Side photograph. Ambient sunlight is reflected into the laboratory from an outdoor flat dual-axis tracking mirror, and redirected by a flat 45° mirror (A) to a downward-facing specular paraboloidal dish (B) with its focus just below the tilted mirror. Flux concentration is boosted to ca. 15 000 suns by a specular ellipsoidal dish (C) of high numerical aperture NA at its proximate focus F (attainable flux density is proportional to NA2). The quartz ampoule was inserted to F horizontally from the right, and translated horizontally by 1 mm each minute toward irradiating as much of the distributed precursor powder as possible. Figure 3 shows representative nanoparticles obtained by ablating MoS2 powder in a sealed, evacuated quartz ampoule in the above mentioned solar furnace. These MoS2 nanostructures likely start growing from the inside out (Figure 3 a–e). This growth mode is typical for a nucleation and growth mechanism from the vapor phase,24 and differs markedly from the outside–in growth mode where molybdenum oxide nanoparticles serve as a template for the reaction with H2S.18 When the nanooctahedra exceed a critical size, the layers should start to fold evenly and transform into quasi-spherical shape. The TEM images reveal multi-walled nanooctahedra at the core up to a diameter slightly above 10 nm or ca. 105 atoms beyond which the elastic strain is better accommodated by adopting an even folding of the layers into quasi-spherical shells. Tilted structures (Figure 3 c,d) reveal the inner core morphology, which is similar to that reported earlier for the smaller nanooctahedra.1, 4 The size of the hybrid nanoparticles' hollow core is determined by the maximum strain the MoS2 nanooctahedra can accommodate, i.e., their minimum size, which is ca. 3 nm.1, 4 Typical MoS2 closed nanoparticles in which a nanooctahedral core undergoes morphology change to quasi-spherical outer shells, obtained in the solar furnace. a,b) Two hybrid nanoclusters of roughly the same diameter (ca. 26 nm) and number of layers (ca. 20). c,d) TEM tilting experiment of an individual hybrid MoS2 nanoparticle of diameter 43 nm and 28 layers, substantially larger than those in (a) and (b), and reinforcing the clarity of the transition from core octahedra to surrounding quasi-spherical shells. e) High-resolution TEM images of a hybrid nanoparticle. The marked frame is enlarged in (f), showing atomic resolution of the MoS2 layers. The atomic model is overlaid in red (Mo) and yellow (S), and detailed in (g) with black lines as visual guides to their appearance in the TEM image. The chevron motif correlates with a prismatic coordinated MoS2 layer, which as a bulk phase is semiconducting. The pattern of diagonal lines indicates the 1T phase, which has been predicted to be metallic.25 A detailed phenomenological model that incorporates semi-empirical density functional methods1, 2 and has been shown to account for experimentally observed MoS2 nanostructures ranging from fundamentally small (ca. 3 nm) to large closed-cage fullerene-like and nanotubular configurations (diameters up to 100 nm) was adopted for gaining insight into, and predicting, nanostructure stability and electronic properties. The predicted electronic properties, derived from the structural features, showed that the lattice defects associated with the formation of the nanooctahedra may induce a metallic-like nature, while quasi-spherical structures are semiconducting. where c is the lattice parameter for bulk 2H-MoS2 (1.23 nm),26 and εvdW is the van der Waals energy of interlayer interaction (−0.2 eV per atom).25 A simplifying assumption was that the outer MoS2 walls are perfectly spherical, which neglects the contribution of the cusps where the folding is uneven. This simplification is deemed accurate enough for this investigation, given the agreement between model predictions and experimental observations (see below). The predictions plotted in Figure 4 confirm that the model can indeed account for the coexistence of nested MoS2 octahedra and peripheral spherical shells, with a smooth transition from nanoclusters dominated by octahedra to those dominated by spherical shells as the particle size and number of layers increase. For a fixed total number of layers (taken to be 10, 20, and 30) and nanoparticle diameter (ranging from 13 to 60 nm), there is a thermodynamically preferred mix of octahedral and spherical shells, i.e., a minimum in the curves of Figure 4, all of which are more stable than the monolayer. The existence and sharpness of these minima become less pronounced, and the nanoparticles become dominated by spherical layers, as the nanostructures grow larger. For example, if a MoS2 nanoparticle reaches a diameter of at least 44 nm, then its most stable composition becomes solely spherical shells. Note that the 44 nm curves for nanoparticles with a total of 10, 20, and 30 layers exhibit a broad range of essentially equal-stability hybrid compositions rather than an evident minimum. Energy (relative to that of a monolayer) of hollow hybrid MoS2 nanostructures comprising nested nanooctahedra inside spherical shells, as a function of the number of spherical shells, for a range of values of the 1) total number of layers (10 (black), 20 (green), and 30 (red)), and 2) outer diameter (nm label to the right of each curve). The schematics below the graph illustrate the extremes of pure octahedral and pure spherical structures (in this instance for 12 layers). The properties of the experimentally generated nanoparticles of Figure 3 are indicated by arrows. The nanostructure of Figure 3 a is close to the model's energetic minimum for a total of ca. 20 layers of which ca. 10 are spherical, and a diameter of 26 nm, for which the model indicates 720 000 atoms, i.e., 240 000 stoichiometric MoS2 units. The nanostructure of Figure 3 c,d, with a diameter of 44 nm and ca. 20 spherical shells, is consistent with the model's broad range of equally low-energy configurations for a total of 30 layers and the same diameter. The consistency of model predictions with experimental findings is highlighted in Figure 4 with indicators for the nanostructures of both Figure 3 a (26 nm in diameter and ca. 20 shells of which 10 are spherical) and Figure 3 c,d (44 nm in diameter and 30 shells of which 20 are spherical). The indistinctness in deciphering the fraction of octahedral layers in the nanostructures of Figure 3 is reflected in the broad theoretical minima of Figure 4. Another consideration is that the model is purely thermodynamic, disregarding kinetic effects that may not be insubstantial for rapidly evolving structures, and could result in hollow hybrid nanostructures other than those of the local minima in Figure 427—especially given the non-equilibrium reactor conditions. This may also play a role in explaining the production of nanoparticles such as in Figure 3 b, where, for approximately the same size and total number of layers as in Figure 3 a, the octahedral core layers dominate to a noticeably greater degree. Band-structure calculations2 indicate that the corners and edges of the pure nanooctahedra induce states within the Fermi level, rendering a metallic character to a pure nanooctahedral shell. In contrast, both theory28, 29 and experiment30, 31 have shown that, in analogy to the bulk material, larger fullerene-like and nanotubular MoS2 nanostructures are semiconductors irrespective of their chirality vector. Consequently, the transition from inner nanooctahedra to quasi-spherical outer shells may mark a transition from metallic-like layers to semiconducting ones. A second structural feature to be considered is that MoS2 has multiple bulk phases which exhibit different electronic properties. MoS2 layers form two trigonal prismatic bulk phases: 2H (anti-parallel) and 3R (parallel), the former being more stable. Both phases are semiconducting.32 An octahedrally coordinated phase (1T) also exists and was predicted to be metallic,25 but is not stable in the bulk form, and is associated solely with MoS2 monolayers. Both the 2H and 3R phases have been observed in closed-cage structures; but so far not the 1T phase. Therefore, the internal structure of the particle may also have a distinct influence on the electronic properties of the hybrid particle. The X-ray diffraction measurements are strongly affected by disorder and strain, which encumbers the delicate differentiation between the 2H and 3R phases. Hence the focus here was on straightforward direct imaging. The diffraction data comprise a basis for future research that will take into account strain effects within these closed-cage structures, and will be complemented by electron diffraction data. The question of atomic-scale coordination prompted examining the hybrid nanostructures by aberration-corrected TEM33 (Figure 3 f). The aberration-corrected TEM revealed first-ever 1T coordination of layers embedded within nanoparticles (Figure 3 e–g), with Figure 3 f clearly showing the different MoS2 layers. Figures 3 f,g reveal a single 1T layer between prismatic layers: to its right is an anti-parallel alignment of the prismatic layers, and to its left a single prismatic layer. The scarcity of the 1T phase in previously reported structures may be related either to the number of layers lying below the detection limit of XRD or Raman measurements, or to the relative instability of the 1T phase, which prevents the formation of multiple 1T shells. The occurrence of the 1T phase may be the result of a transformation from the 3R to the 2H phase by an intermediate 1T phase that is trapped by fast quenching. Nevertheless, the incorporation of a single 1T layer might have substantial effects on the electronic properties of the whole particle, since the phase multiplicity may induce inner metal–semiconductor junctions. The two structural features contributing to the formation of such "buried" junctions in a spherical geometry raise new, fundamental questions regarding their electronic properties. These features are the focus of ongoing experimental and theoretical research. The discovery of these hybrid particles bridges the gap between the two limits of pure, fundamentally small nanooctahedra and markedly larger quasi-spherical nanoparticles. The two nanostructures coexist within an individual nanoparticle, with a near-seamless transition from a core of octahedral layers to a peripheral region of quasi-spherical shells. Such nanostructures, if produced in large amounts, could reveal new electrical, optical, and possibly catalytic characteristics. Other applications, including the well-established one for solid lubrication, remain to be investigated when larger amounts of such nanoparticles can be synthesized. The solar concentrator optics depicted here created reactor conditions of continuous ultra-high irradiance, high temperature, large reaction volumes, and extended hot annealing conditions that produced an unpredicted, fundamental, and previously unobserved family of hybrid MoS2 nanostructures. An extended phenomenological model was used to calculate their critical sizes, the number of MoS2 layers, and the mix of octahedral and quasi-spherical layers for this transition, and found to agree with the experimental observations. The hybrid nanoparticles are 25 to 45 nm in diameter, with the fraction of the layers comprising the inner octahedra decreasing as the nanoparticles grow larger. Kinetically controlled nanostructures dominated by the octahedral core layers were also observed. In addition, atomic-scale features identified by aberration-corrected high-resolution TEM suggest that the hybrid particle has a complex unprecedented electronic structure. To summarize, a fundamentally new MoS2 fullerene-like nanostructure was realized exhibiting a smooth transition from a nanooctahedral core to quasi-spherical outer shells within individual nanoparticles, with corroborating theoretical modeling and atomic resolution transmission electron microscopy. The transformations are driven by an ultra-high irradiance solar concentrator that produces the requisite high temperatures, large reaction volumes, and naturally hot annealing environments. Unraveling the internal structure of these hybrid nanoparticles suggests the existence of metal–semiconductor junctions within individual nanoparticles.

Based on a diesel engine fuelled with BD20 biodiesel, particle number (PN) emission characteristics of the engine equipped with DOC, DOC+DPF and none after-treatment device were investigated respectively by engine bench tests. Results showed that both of DOC and DOC+DPF reduced PN emissions, DOC mainly reduced PN in size range of 30nm~50nm smaller diameter, DPF reduced PN of particles larger than 10nm diameter obviously. PN reduction rate of DOC and DOC+DPF were 5%~35% and 60%~98%, DPF contributed 35%~90% of PN reduction rate on the base of DOC. The after-treatment combination of DOC+DPF was recommended as the device with high efficiency in particle number emission control of biodiesel engine.

The serum from one case of acute hepatitis contained large numbers of hollow particles of hepatitis B antigen (HB Ag). Particles had diameters of 15–20 nm, occurred frequently in compact masses, and were sometimes connected by bridges. This form may be the precursor of normal HB Ag.

A giant-cell glioblastoma was examined by electron microscopy and by the freeze-fracture technique. The cell membranes bordering the extensive extracellular space often showed complicated undulations and peripheral vacuoles as well as occasional microvilli or filopodia. The undulations were mainly composed of plasmalemmal vesicles as well as of large (400--800 nm in diameter) and small (30--50 nm in diameter) localized protrusions and invaginations of the cell membrane. Deep invaginations of the cell membrane apparently resulted in two separate cytoplasmic portions. Locking of protruded cytoplasmic tongues and adherens junctions were sometimes seen in closely approximated cell membranes. The average number of membrane particles per micrometer2 was 630 +/- 130 on the P face and 180 +/- 30 on the E face. The membrane particles were occasionally aggregated to form clusters about 30 to 150 micrometer in diameter. Gap junctions were occasionally found, but there were no tight junctions. Large particles about 30 nm in diameter were found in places.

Spectra of absorption (400–800 nm) by the aggregates of colloidal gold (5, 15, and 30 nm in diameter) and silver (20 nm in diameter) particles were studied experimentally and theoretically. It was revealed that, during fast aggregation corresponding to the diffusion-limited cluster aggregation (DLCA), the pattern of spectra is dependent on the size of primary particles. Spectra with the additional absorption maximum in the red region are observed for 15 and 30 nm gold and 20 nm silver particles, while the absorption spectrum for 5 nm particles is characterized by only one maximum shifted to the red region. The slow aggregation resulted in a decrease in plasmon absorption peak with no marked shift to the red region and to the broadening of long-wave absorption wing. From data on electron microscopy, typical branched DLCA-clusters were formed during fast aggregation, whereas small compact aggregates and a noticeable number of single particles were observed in a system during slow aggregation. The computer model of the diffusion-limited cluster-cluster aggregation was used to explain these results. Optical properties of aggregates were calculated using coupled dipole method (CDM or DDA) and the exact method of a multipole expansion. Corrections for the size effect were introduced into the bulk optical constants of metals for nanosized particles. It was shown that a modified version of DDA (Markel et al.,Phys. Rev. B, 1996, vol. 53, no. 5, p. 2425) allows us to explain the pattern of experimental spectra of DLCA-aggregates and their dependence on a monomer size. The exact method was applied to calculate the extinction cross sections of metallic aggregates demonstrating strong electrodynamic interaction between particles. The number of higher multipoles that are required to adequately describe this interaction is much larger than the number of terms of an ordinary Mie series and is the main obstacle to the exact calculation of the spectra of metallic aggregates with a large number of particles.

SiO 2 , Al 2 O 3 , and 3Al 2 O 3 .2SiO 2 powders were synthesized by combustion of SiCl 4 or/and AlCl 3 using a counterflow diffusion flame. The SiO 2 and Al 2 O 3 powders produced under various operation conditions were all amorphous and the particles were in the form of agglomerates of small particles (mostly 20 to 30 nm in diameter). The 3Al 2 O 3 .2SiO 2 powder produced with a low‐temperature flame was also amorphous and had a similar morphology. However, those produced with high‐temperature flames had poorly crystallized mullite and spinel structure, and the particles, in addition to agglomerates of small particles (20 to 30 nm in diameter), contained larger, spherical particles 150 to 130 nm in diameter). Laser light scattering and extinction measurements of the particle size and number density distributions in the flame suggested that rapid fusion leading to the formation of the larger, spherical particles occurred in a specific region of the flame.

Modal structure and spatial?temporal variations of urban and suburban aerosols in Helsinki?Finland