Population Of Small Particles Research Articles

Microwave Emission from Spinning Dust in Circumstellar Disks

In the high-density environments of circumstellar disks dust grains are expected to grow to large sizes by coagulation. Somewhat unexpectedly, recent near-IR observations of PAH features from disks around Herbig Ae/Be stars demonstrate that a substantial amount of dust mass in the surface layers of these disks (up to several tens of percent of the local carbon content) can be locked up in small nanometer-sized particles. We investigate the possibility of detecting the electric dipole emission produced by these nanoparticles (sizes ~1 nm) as they spin at thermal rates (tens of GHz) in cold gas. We show that such emission peaks in the microwave range and dominates over the thermal disk emission at ν 50 GHz typically by a factor of several if 5% of the total carbon abundance is locked up in nanoparticles. We test the sensitivity of this prediction to various stellar and disk parameters and show that if the potential contamination of the spinning dust component by the free-free and/or synchrotron emission can be removed, then the best chances of detecting this emission would be in disks with small opacities, having SEDs with steep submillimeter slopes (which minimize thermal disk emission at GHz frequencies). Detection of the spinning dust emission would provide important evidence for the existence, properties, and origin of the population of small dust particles in protoplanetary disks, with possible ramifications for planet formation.

A modelling of the interaction between electromagnetic radiation and West Ford needles clusters: a preliminary study

Radar observations of small space debris made with the Goldstone radar facility have shown that a population of small particles do exist at an altitude larger than 2000 km. This population has been identified with clusters of copper needles created upon the deployment of the West Ford needles project, by MIDAS satellites in 1961 and 1963. This set of particles is either not taken into account in the debris models or only added to other populations. But owing to their specific physical and geometrical properties, the sunlight they scatter could affect, for instance, the spaceborne astronomical experiments. In order to assess this threat it is necessary to model their physical and geometric characteristics. A preliminary modelling using spheres suggests that some improvement is needed. We propose a better approach with long conductive cylinders as a model for the clusters. The interaction of solar light with these particles allows us to estimate the spurious flux scattered inside spaceborne instruments. We conclude that for a given spatial configuration light flashes can affect seriously the operating mode of high sensitivity instruments.

Electrically charged small soot particles in the exhaust of an aircraft gas-turbine engine combustor: comparison of model and experiment

Abstract The emission of electrically charged soot particles by an aircraft gas-turbine combustor is investigated using a theoretical model. Particular emphasis is placed on the influence of the fuel sulfur content (FSC). The model considers the production of primary “combustion” electrons and ions in the flame zone and their following interaction with molecular oxygen, sulfur-bearing molecules (e.g. O 2 , SO 2 , SO 3 , etc.) and soot particles. The soot particle size distribution is approximated by two different populations of mono-dispersed large and small soot particles with diameters of 20–30 and 5–7 nm, respectively. The effect of thermal ionization of soot and its interaction with electrons and positive and negative ions is included in the model. The computed positive and negative chemiion (CI) concentrations at the combustor exit and relative fractions of small neutral and charged soot particles were found to be in satisfactory agreement with experimental data. The results show that the FSC indeed may influence the concentration of negative CI at low fuel flow into combustor. Importantly the simulation indicates a very efficient mutual interaction of electrons and ions with soot particles with a large effect on both ion and charged soot particle concentrations. This result may be interpreted as a possible indirect effect of FSC on the growth and size distribution of soot particles.

Environmentally-induced debris sources

Resident spacecraft and rocket bodies are known to spontaneously produce large fragments (>10 cm), usually released at low velocities in small numbers and normally exhibiting large area-to-mass ratios. Potential causes of these anomalous events, which are not related to the more dramatic satellite breakups, include material degradation due to environmental stresses and impact by small natural or man-made particles. An examination of known and previously undocumented anomalous events was undertaken to gain better insight into the frequency of such events and the resultant consequences to the overall orbital debris environment. Some space vehicle types, e.g., US Transit spacecraft and former Soviet Vostok orbital stages, demonstrate a propensity for debris generation, while other satellite designs appear less vulnerable. Some satellites are known to produce numerous debris over a period of many years, and the debris exhibit wide-ranging characteristics. It is concluded that such debris currently account for a small portion of the large orbital debris population, but the number of smaller debris cannot yet be estimated. Better identification and analysis of anomalous events might indicate the degree to which small particle impacts are responsible and whether the frequency of anomalous events in given orbital regimes can be used to monitor changes in the small particle population. Modifications to some satellite designs might mitigate anomalous event debris generation.

Cirrus cloud iridescence: a rare case study.

On the evening of 25 November 1998, a cirrus cloud revealing the pastel colors of the iridescence phenomenon was photographed and studied by a polarization lidar system at the University of Utah Facility for Atmospheric Remote Sensing (FARS). The diffraction of sunlight falling on relatively minute cloud particles, which display spatial gradients in size, is the cause of iridescence. According to the 14-year study of midlatitude cirrus clouds at FARS, cirrus rarely produce even poor iridescent patches, making this particularly long-lived and vivid occurrence unique. In this unusually high (13.2-14.4-km) and cold (-69.7 degrees to -75.5 degrees) tropopause-topped cirrus cloud, iridescence was noted from approximately 6.0 degrees to approximately 13.5 degrees from the Sun. On the basis of simple diffraction theory, this indicates the presence of particles of 2.5-5.5-microm effective diameter. The linear depolarization ratios of delta = 0.5 measured by the lidar verify that the cloud particles were nonspherical ice crystals. The demonstration that ice clouds can generate iridescence has led to the conclusion that iridescence is rarely seen in midlatitude cirrus clouds because populations of such small particles do not exist for long in the presence of the relatively high water-vapor supersaturations needed for ice-particle nucleation.

Void coalescence within periodic clusters of particles

The effect of particle clustering on void damage rates in a ductile material under triaxial loading conditions is examined using three-dimensional finite element analysis. An infinite material containing a regular distribution of clustered particles is modelled using a unit cell approach. Three discrete particles are introduced into each unit cell while a secondary population of small particles within the surrounding matrix is represented using the Gurson–Tvergaard–Needleman (GTN) constitutive equations. Deformation strain states characteristic of sheet metal forming are considered; that is, deep drawing, plane strain and biaxial stretching. Uniaxial tensile stress states with varying levels of superimposed hydrostatic tension are also examined. The orientation of a particle cluster with respect to the direction of major principal loading is shown to significantly influence failure strains. Coalescence of voids within a first-order particle cluster (consisting of three particles) is a stable event while collapse of inter-cluster ligaments leads to imminent material collapse through void-sheeting.

Juice Clarification by Thermostable Fractions of Marsh Grapefruit Pectinmethylesterase

ABSTRACT: Orange juice clarification by thermostable pectinmethylesterase (TS‐PME), isolated from grapefruit pulp by ammonium sulfate precipitation, and ion‐exchange and affinity chromatography was investigated. TSPME, having different specific activities, induced different clarification behavior of reconstituted orange juice at 2 units/ml. Based on percent transmittance, TS‐PME fraction with the lower specific activity clarified juices earlier than TS‐PME at higher specific activity. Particle size distribution of the cloud‐soluble fraction showed that TS‐PME increased the average particle size from 0.7 μm to 1 mm and maintained a monomodal distribution. After 27 d of storage at 4 °C, samples of clarified juice still showed a large population of small cloud particles when measured by diffraction light scattering.

Inhibition of hepadnaviral replication by polyethylenimine-based intravenous delivery of antisense phosphodiester oligodeoxynucleotides to the liver.

Antisense oligodeoxynucleotides (ODNs) appear as attractive anti-hepatitis B virus (HBV) agents. We investigated in vivo, in the duck HBV (DHBV) infection model, whether linear polyethylenimine (lPEI)-based intravenous delivery of the natural antisense phosphodiester ODNs (O-ODNs) can prevent their degradation and allow viral replication inhibition in the liver. DHBV-infected Pekin ducklings were injected with antisense O-ODNs covering the initiation codon of the DHBV large envelope protein, either in free form (O-ODN-AS2) or coupled to lPEI (lPEI/O-ODN-AS2). Following optimization of lPEI/O-ODN complex formulation, complete O-ODN condensation into a homogenous population of small (20-60 nm) spherical particles was achieved. Flow cytometry analysis showed that lPEI-mediated transfer allowed the intrahepatic delivery of lPEI/O-ODN-AS2 to increase three-fold as compared with the O-ODN-AS2. Following 9-day therapy the intrahepatic levels of both DHBV DNA and RNA were significantly decreased in the lPEI/O-ODN-AS2-treated group as compared with the O-ODN-AS2-treated, control lPEI/O-ODN-treated, and untreated controls. In addition, inhibition of intrahepatic viral replication by lPEI/O-ODN-AS2 was not associated with toxicity and was comparable with that induced by the phosphorothioate S-ODN-AS2 at a five-fold higher dose. Taken together, our results demonstrate that phosphodiester antisense lPEI/O-ODN complexes specifically inhibit hepadnaviral replication. Therefore we provide here the first in vivo evidence that intravenous treatment with antisense phosphodiester ODNs coupled to lPEI can selectively block a viral disease-causing gene in the liver.

ApoE-containing high density lipoproteins and phospholipid transfer protein activity increase in patients with a systemic inflammatory response

High density lipoproteins (HDL) mediate reverse cholesterol transport as well as the clearance of oxidation products or inflammatory mediators, thereby contributing to tissue integrity. The decrease in HDL in inflammation has been attributed to decreased lecithin:cholesterol acyltransferase activity, whereas the role of phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein has not been analyzed in detail. We have studied the activities of HDL-modifying proteins and the heterogeneity of HDL in healthy control subjects and three groups of postsurgery patients: no bacterial infection (group 1), bacterial focus and systemic inflammatory response (group 2), and severe sepsis (group 3). For all patients, a decrease in total HDL could be demonstrated, with a loss of mainly large, apolipoprotein A-I (apoA-I) HDL particles, an almost total loss of apoC-I, and an increase in apoE HDL (200–500 kDa), which did not contain significant amounts of apoA-I, apoA-II, or apoC-I. PLTP activity was increased in patients of groups 2 and 3, paralleled by a redistribution of PLTP into a population of small (120- to 200-kDa) particles, probably representing PLTP homodimers or lipid-complexed PLTP. In summary, the increase in apoE HDL and PLTP activity may improve the delivery of energy substrates and phospholipids to tissues that must maintain cellular membrane homeostasis under conditions of inflammatory stress. —Barlage, S., D. Fröhlich, A. Böttcher, M. Jauhiainen, H. P. Müller, F. Noetzel, G. Rothe, C. Schütt, R. P. Linke, K. J. Lackner, C. Ehnholm, and G. Schmitz. ApoE-containing high density lipoproteins and phospholipid transfer protein activity increase in patients with a systemic inflammatory response.

Cosmic dust and micro-debris measurements on the MIR space station

During the last ten years, investigation of impact features found on material retrieved from low earth orbit, after exposure to space for a long period of time, has provided us with a great deal of data on the particulate environment, either natural or man-made. Between 1987 and 1997, several detection devices have been deployed outside the Russian MIR space station. Passive sensors are composed primarily of stacked thin metal foils (gold and aluminum). Depending on the size of the particles, they are either decelerated or fragmented upon high velocity impact. The size of holes or impact craters give information on the size or shape of the impacting particles. Samples have been retrieved for laboratory analysis. In addition, solar cells from a solar array retrieved by a Shuttle-MIR mission have been searched for impact craters. Comparison with data from LDEF, and HST provides insight in the long-term evolution of small particle population and in the debris environment of a permanently manned station. Several samples show evidence of secondary impact cratering: an attempt is made to locate the origin of primary impact sites. Some results about the possible origin of the impactors are provided by the chemical identification of particle remnants inside the craters.

In-situ detection of micrometeoroids and orbital debris: The PIE experiment on MIR

During the last few years, investigation of impact features found on material retrieved after exposure to space for a long period of time, in low earth orbits, has provided us with a great deal of data on the particulate environment, either natural or man-made. The PIE detection device presented here has been deployed outside the Kvant-2 module attached to the Russian MIR station, between June 1996 and April 1997. Part of the experiment uses a detection technique similar to the one used in previous experiments flown on LDEF and MIR. Passive sensors are composed primarly of stacked thin metal foils (gold and aluminium). According to the size of the particles, they are either decelerated or fragmented upon high velocity impact. The size of holes or impact craters give information on the size or shape of the impacting particles. Samples have been retrieved for laboratory analysis. Comparison with data from LDEF, EuReCa, HST and previous experiments on MIR provides insight in the long term evolution of small particle population and in the debris environment of a permanently manned station. Some of the samples show evidence of secondary impact cratering: an attempt is made to locate the origin of the primary impact site. Some results about the possible origin of the impactors are provided by the chemical identification of particle remnants inside the craters.

Identification of a U8 snoRNA-specific Binding Protein

Eukaryotic nucleoli contain a large and diverse population of small nucleolar ribonucleoprotein particles (snoRNPs) that play diverse and essential roles in ribosome biogenesis. We previously demonstrated that U8 snoRNP is essential for processing of both 5.8 and 28 S rRNA. The RNA component of the U8 RNP particle is necessary but not sufficient for processing. Using an electrophoretic mobility sift assay, we enriched for U8-specific binding proteins from Xenopus ovary extracts. UV cross-linking reactions with partially purified fractions implicated a 29-kDa protein directly binding to U8 RNA. This protein interacted specifically and with high affinity with U8 snoRNA; it did not bind other snoRNAs and is probably not a common component of all snoRNPs. This is the first report of a protein component specific to an snoRNP essential for processing of the large ribosomal subunit in vertebrates.

Phase Formation Kinetics in a Glass Ceramic Studied by Small-Angle Scattering of X-rays and Neutrons and by Visible-Light Scattering

The kinetics of the primary phase formation in a glass ceramic base glass near the cordierite composition in the MgO–Al2O3–SiO2 system, with additions of ZrO2 and TiO2 as nucleating agents, have been investigated by combining different small-angle scattering techniques. Phase formation in the base glass heated isothermally at 1093 K has been studied in order to elucidate the structural processes that take place during controlled nucleation before volume crystallization begins. Complementary results of X-ray diffraction, transmission electron microscopy and electron microprobe analysis reveal that in the final stages of annealing, different crystalline phases, which are dispersed in the residual glassy phase, are developed. The largest particles have sizes of the order of several hundreds of nanometers and consist of magnesium petalite as well as a high-quartz solid solution. Besides these crystals, two populations of smaller particles, the sizes of which can be resolved by small-angle scattering, were detected and found to be enriched with TiO2 and/or ZrO2. The growth of particles of intermediate size was studied in situ. The radius, R, of each of these particles increases with increasing treatment time, t, according to the power law R ∝ t1/2, indicating diffusion-limited independent growth. The scattering patterns are modified by diffusion zones surrounding the growing particles. The characteristics of the diffusion zones are evaluated by fitting appropriate model scattering curves to the experimental scattering data. The structural arrangement of the Ti and Zr ions was studied by contrast variation with the help of anomalous small-angle X-ray scattering and small-angle neutron scattering. As revealed by the contrast variation experiments, Ti ions are concentrated in the interface between the intermediate-sized particles and the glass matrix, whereas Zr is homogeneously distributed in these particles. Additionally, the Zr ions participate in the formation of the smallest particles, which are crystallites enriched with ZrO2. Finally, the catalyzing effect of TiO2 and ZrO2 on the nucleation and volume crystallization of the glass ceramic is discussed.

South–North and Radial Traverses through the Interplanetary Dust Cloud

Identicalin situdust detectors are flown on board the Galileo and Ulysses spacecraft. They record impacts of micrometeoroids in the ecliptic plane at heliocentric distances from 0.7 to 5.4 AU and in a plane almost perpendicular to the ecliptic from −79° to +79° ecliptic latitude. The combination of both Ulysses and Galileo measurements yields information about the radial and latitudinal distributions of micron- and sub-micron-sized dust in the Solar System. Two types of dust particles were found to dominate the dust flux in interplanetary space. Interplanetary micrometeoroids covering a wide mass range from 10−16to 10−6g are recorded mostly inside 3 AU and at latitudes below 30°. Interstellar grains with masses between 10−14and 10−12g have been positively identified outside 3 AU near the ecliptic plane and outside 1.8 AU at high ecliptic latitudes (>50°). Interstellar grains move on hyperbolic trajectories through the planetary system and constitute the dominant dust flux (1.5 × 10−4m−2sec−1) in the outer Solar System and at high ecliptic latitudes.To compare and analyze the Galileo and Ulysses data sets, a new model is developed based onJ. Geophys. Res.98,17029–17048, Divine's (1993, “five populations of interplanetary meteoroids” model. Both models describe the interplanetary meteoroid environment in terms of dust populations on distinct orbits. Taking into account the measured velocities and the effect of radiation pressure on small particles (described by the ratio of radiation pressure force to gravity, β), we define four populations of meteoroids on elliptical orbits and one population on hyperbolic orbit that can fit the micrometeoroid flux observed by Galileo and Ulysses. Micrometeoroids with masses greater than 10−10g and negligible radiation pressure (β = 0) orbit the Sun on low to moderately eccentric orbits and with low inclinations (≤30°). Populations of smaller particles with mean masses of 10−11g (β = 0.3), 10−13g (β = 0.8), and 5 × 10−15g (β = 0.3), respectively, have components with high eccentricities and have increasingly wider inclination distributions with decreasing mass. Similarities among the orbit distributions of the small particle populations on bound orbits suggest that all are genetically related and are part of an overall micrometeoroid complex that prevails in the inner Solar System. The high-eccentricity component of the small particle populations may actually be β-meteoroids which are not well characterized by our measurements. Our modeling suggests further that the interstellar dust flux is not reduced at Ulysses' perihelion distance (1.3 AU) and that it contributes about 30% of the total dust flux observed there.

The characterization of small emulsion droplets made from milk proteins and triglyceride oil

Measurements have been made of the light scattering properties of emulsion droplets produced using a Microfluidizer. The droplet size distributions were measured by both Integrated Light Scattering (ILS) over a wide range of scattering angles, and by Dynamic Light Scattering (DLS) at a fixed angle of 90°. From the former, it was possible to derive number distributions, whereas the latter was used to give intensity distributions of the droplets. The calculated distributions from light scattering were also compared with samples studied by transmission electron microscopy. A range of samples was studied, including whole milks, and emulsions prepared from soya oil and stabilized by sodium caseinate; fractions containing the smaller droplets from these emulsions were also collected and studied. The results confirmed that it was possible to isolate a population of small ( < 100 nm) particles from microfluidized milk or from the emulsions; larger particles were also present. Both ILS and electron microscopy confirmed these results. DLS also confirmed the presence of the small particles in the emulsions, but principally was useful in the analysis of the separated fractions. To improve the sensitivity of the method, it is necessary to use non-linear channel times in DLS experiments.

ICE Particle Size and Shape Effect on Solar Energy Scattering Angular Distribution

The rare occurrence of te halos produced by cirrus ice crystals in nature has been investigated by modelling the incident solar (visible) light scattering angular distribution using the Monte Carlo/ray tracing method. The results show that the irregular shapes of ice crystals and large population of small ice particles in cirrus are responsible for the rare occurrence of halos.

Characterizing submicron vesicles with wavelength-resolved fluorescence in flow cytometry

Individual synthetic vesicles 0.1-1.0 micron in diameter are sized by using single-particle fluorescence emission spectra obtained in a custom sheath flow cell with an imaging spectrograph and a charge-coupled device. Data are acquired at 1 Hz, with limits of detection (3 sigma) less than 6.0 x 10(3) and 1.0 x 10(4) molecules of free sulforhodamine 101 and fluorescein, respectively, and with a spectral range for fluorescence emission collection from 350 to 800 nm (0.45 nm/pixel resolution). The system is used for small-particle population analysis by analyzing a suspension of submicron, unilamellar, synthetic vesicles prepared by standard procedures with phosphatidylserine and Texas red- or fluorescein head-group-conjugated dihydropalmitoylphosphatidylethanolamine. The submicron particles are individually identified, sized, and discriminated based on single-particle fluorescence emission spectra. Excellent agreement is found between fluorescence sizing data and transmission electron microscopic measurements.

Dynamic Populations of Dust in Interplanetary Space

AbstractInformation on the dynamics of interplanetary dust is obtained by observations of radio-meteors, zodiacal light, thermal infrared emission, and by measurements with in-situ detectors on board Earth satellites and deep spaceprobes. These methods are sensitive to different meteoroid sizes (mm- to sub-micron sized) and refer to different regions of space. Bigger particles (&gt; 10-9 g) move on bound Keplerian orbits and are dynamically dominated by solar gravity, while the trajectories of particles smaller than 10-10 g are strongly influenced by radiation pressure and electromagnetic interactions. Modelling interplanetary dust is done by dividing the whole meteoritic complex into dynamically distinct populations. Divine's (1993) model identifies five dynamically different populations of interplanetary meteoroids: bigger particles are described by the “core”, and “asteroidal”-populations, intermediate sizes by the “halo”-population, and small particles are included in the “eccentric” and the “inclined”-populations. The intermediate and the small particle populations, in particular, have to be redefined for several reasons: new data are available which require the consideration of hyperbolic orbits and the inclusion of radiation pressure and electromagnetic forces. New small particle populations are interstellar dust and beta-meteoroids.

Measurement of Particle Size Distributions in Milk Homogenized by a Microfluidizer: Estimation of Populations of Particles with Radii Less Than 100 nm

Different light-scattering techniques (integrated and dynamic) were used to study the overall distribution of particle sizes in milk homogenized using a microfluidization technique. This demonstrated that only integrated light scattering was able to show clearly that a population of small fat droplets, with radii less than 100 nm, was produced during the homogenization. This population of small particles had not previously been detected, nor were they clearly demonstrated using dynamic light scattering, but their presence was confirmed by physical separation using centrifugation and study of the separated fractions by light scattering. The presence of these particles may require revision of the methods used to determine size distributions in homogenized systems. It will also affect the analyses of adsorbed layers or protein in emulsions and of the kinetics of particle aggregation in emulsions which are undergoing destabilization.

Pig plasma phospholipid transfer protein facilitates HDL interconversion.

Phospholipid transfer protein (PLTP) from pig plasma was purified to homogeneity using ultracentrifugation and a combination of hydrophobic-, heparin-Sepharose-, and anti-pig-PLTP-affinity chromatography techniques. The molecular weight of PLTP is 78,000 as estimated by SDS-PAGE and by gel filtration. The effect of pig plasma PLTP on the particle size distribution of either human or pig high density lipoprotein (HDL) was studied by incubating HDL with PLTP. Incubation of human HDL3 or pig HDL with the highly purified preparations of PLTP induced a conversion of the homogeneous HDL into two main populations of particles. The conversion products were isolated by ultracentrifugation at density 1.21 g/ml. The size changes were evident as analyzed by native gradient gel electrophoresis and by high resolution gel filtration. The diameters of the large and small particles formed were 10.8 nm and 7.6-7.9 nm, respectively. In addition, pig HDL conversion products included a third population of particles with a diameter of 11.5 nm. The degree of conversion was dependent on time and PLTP activity. Neither cholesteryl ester transfer protein nor lecithin:cholesterol acyltransferase activity could be detected in the PLTP preparations. The present study demonstrates that purified pig PLTP can act as a conversion factor: it has the ability to convert HDL into populations of large and small particles. The release of apoA-I is an essential part of the conversion process.