Small Dust Particles Research Articles

Interaction force in a vertical dust chain inside a glass box.

Small number dust particle clusters can be used as probes for plasma diagnostics. The number of dust particles as well as cluster size and shape can be easily controlled employing a glass box placed within a Gaseous Electronics Conference (GEC) rf reference chamber to provide confinement of the dust. The plasma parameters inside this box and within the larger plasma chamber have not yet been adequately defined. Adjusting the rf power alters the plasma conditions causing structural changes of the cluster. This effect can be used to probe the relationship between the rf power and other plasma parameters. This experiment employs the sloshing and breathing modes of small cluster oscillations to examine the relationship between system rf power and the particle charge and plasma screening length inside the glass box. The experimental results provided indicate that both the screening length and dust charge decrease as rf power inside the box increases. The decrease in dust charge as power increases may indicate that ion trapping plays a significant role in the sheath.

Seeding cirrus clouds could drive global net cooling

Cirrus clouds—thin, wispy streamers that form in the upper troposphere when ice crystals nucleate around small dust or metallic particles—have a net warming effect on climate. Previous studies have suggested that seeding cirrus clouds with an overload of dust particles reduces their formation and lifespan, thus leading to a net cooling effect on global climate. Recently, however, research has raised questions regarding how exactly cirrus clouds form, which has implications for seeding strategies.

Using Multiple-Phase Nozzles to Produce Water Droplets for Removing Smaller Dust Particles of Below MRT-BTS Saphan Khwai Station in Bangkok Thailand

The research is intentionally aimed to employ the multiple-phase nozzles to produce the 10-micrometer water droplets in gas form to remove less 100-micrometer smaller dust particles by agglomeration process inside street tunnel on heavy traffic point sources at sky train MRT-BTS Saphan Khwai station in Bangkok. The four sets of 100-m hoses with 52 multiple-phase nozzles (208 nozzles) were established on 100-m beams (four beams), which are 21-m wide (5-m apart) and 5.575-m high, and connecting with high pressure pump (1,000 lbs/min) to press clean water 0.076 liters/min through the 10-micrometer orifice nozzles. The spraying time was about every 10 minutes during collecting TSP and PM10 dust by Hi-Volume Air Sampler on five periods of 05:00-08:00, 08:00-11:00, 11:00-14:00, 14:00-17:00, and 17:00-20:00 for 5-consecutive days, 30 November to 4 December 2008. Also, the air temperature, actual vapor pressure, and speed-direction wind measured at 1.5 and 5.0 meters in height underneath of the ceiling and above the roof of MRT-BTS Saphan Khwai station. Results found that the multiple-phase nozzles showed effectiveness to remove the smaller 100-micrometer dust particles underneath of MRT-BTS Saphan Khwai station by spraying 10-micrometer water droplets through 10-micrometer orifice nozzles. The decreasing concentration of TSP northerly 30.25 %, southerly 26.21 %; and also for PM10 northerly 39.96 %, southerly 40.39 %. Moreover, the concentration between street tunnel and northerly were decreased in both TSP (30.38%) and PM10 (40.17 %), and southerly were decreased in both TSP (30.05%) and PM10 (40.88 %). In case, on the central line effects between street tunnel and northerly found the decreases of TSP (30.64%) and PM10 (37.65%), southerly decreases of TSP (33.71%) and PM10 (43.78%). An increase of the 10-micrometer water droplets spraying frequency through multiple-phase nozzles (208 nozzles) is expected to gain more decreasing concentration down to under standard values. In addition, an applying the concentration of smaller 100-micrometer dust particles is useful for setting the automatic pumping operation that would be acceptable to the public.

ACCRETING PLANETS AS DUST DAMS IN “TRANSITION” DISKS

We investigate under what circumstances an embedded planet in a protoplanetary disc may sculpt the dust distribution such that it observationally presents as a `transition' disc. We concern ourselves with `transition' discs that have large holes ($\gtrsim 10$ AU) and high accretion rates ($\sim 10^{-9}-10^{-8}$ M$_\odot$ yr$^{-1}$). Particularly, those discs which photoevaporative models struggle to explain. Assuming the standard picture for how massive planets sculpt their parent discs, along with the observed accretion rates in `transition' discs, we find that the accretion luminosity from the forming planet is significant, and can dominate over the stellar luminosity at the gap edge. This planetary accretion luminosity can apply a significant radiation pressure to small ($s\lesssim 1\mu$m) dust particles provided they are suitably decoupled from the gas. Secular evolution calculations that account for the evolution of the gas and dust components in a disc with an embedded, accreting planet, show that only with the addition of the radiation pressure can we explain the full observed characteristics of a `transition' disc (NIR dip in the SED, mm cavity and high accretion rate). At suitably high planet masses ($\gtrsim 3-4$ M$_J$), radiation pressure from the accreting planet is able to hold back the small dust particles, producing a heavily dust-depleted inner disc that is optically thin (vertically and radially) to Infra-Red radiation. We use our models to calculate synthetic observations and present a observational evolutionary scenario for a forming planet, sculpting its parent disc. The planet-disc system will present as a `transition' disc with a dip in the SED, only when the planet mass and planetary accretion rate is high enough. At other times it will present as a disc with a primordial SED, but with a cavity in the mm, as observed in a handful of protoplanetary discs.

Subsonic Motion of Projectile in a Fluid Complex Plasma under Microgravity Conditions

Subsonic motion of a large particle moving through the bulk of a dust crystal formed by negatively charged small particles is investigated, by using the PK-3 Plus laboratory on the board of the International Space Station. Tracing the particle trajectories shows that the large particle moves almost freely through the bulk of a plasma crystal, while dust particles move along characteristic a-shaped pathways near the large particle. We develop a theory of the nonviscous motion of dust particles near a large particle and calculate particle trajectories. The deformation of a cavity around a large projectile moving with subsonic velocity in the cloud of small dust particles is investigated with a due regard for the friction between dust particles and atoms of a neutral gas. The pressure of a dust cloud at the surface of a cavity around the projectile can become negative, which entails the emergence of a considerable asymmetry of the cavity, i.e., the cavity deformation. The corresponding threshold velocity is calculated, which is found to decrease with increasing the cavity size. A good agreement with experiment validates our approach.

A quantification of hydrodynamical effects on protoplanetary dust growth

Context. The growth process of dust particles in protoplanetary disks can be modeled via numerical dust coagulation codes. In this approach, physical effects that dominate the dust growth process often must be implemented in a parameterized form. Due to a lack of these parameterizations, existing studies of dust coagulation have ignored the effects a hydrodynamical gas flow can have on grain growth, even though it is often argued that the flow could significantly contribute either positively or negatively to the growth process. Aims. We intend to provide a quantification of hydrodynamical effects on the growth of dust particles, such that these effects can be parameterized and implemented in a dust coagulation code. Methods. We numerically integrate the trajectories of small dust particles in the flow of disk gas around a proto-planetesimal, sampling a large parameter space in proto-planetesimal radii, headwind velocities, and dust stopping times. Results. The gas flow deflects most particles away from the proto-planetesimal, such that its effective collisional cross section, and therefore the mass accretion rate, is reduced. The gas flow however also reduces the impact velocity of small dust particles onto a proto-planetesimal. This can be beneficial for its growth, since large impact velocities are known to lead to erosion. We also demonstrate why such a gas flow does not return collisional debris to the surface of a proto-planetesimal. Conclusions. We predict that a laminar hydrodynamical flow around a proto-planetesimal will have a significant effect on its growth. However, we cannot easily predict which result, the reduction of the impact velocity or the sweep-up cross section, will be more important. Therefore, we provide parameterizations ready for implementation into a dust coagulation code.

Tensile and shear strength of porous dust agglomerates

Context.Within the sequential accretion scenario of planet formation, planets are build up through a sequence sticking collisions. The outcome of collisions between porous dust aggregates is very important for the growth from very small dust particles to planetesimals. In this work we determine the necessary material properties of dust aggregates as a function the porosity. Aims: Continuum models such as SPH that are capable of simulating collisions of macroscopic dust aggregates require a set of material parameters. Some of them such as the tensile and shear strength are difficult to obtain from laboratory experiments. The aim of this work is to determine these parameters from ab-initio molecular dynamics simulations. Methods: We simulate the behavior of porous dust aggregates using a detailed micro-physical model of the interaction of spherical grains that includes adhesion forces, rolling, twisting, and sliding. Using different methods of preparing the samples we study the strength behavior of our samples with varying porosity and coordination number of the material. Results: For the tensile strength, we can reproduce data from laboratory experiments very well. For the shear strength, there are no experimental data available. The results from our simulations differ significantly from previous theoretical models, which indicates that the latter might not be sufficient to describe porous dust aggregates. Conclusions: We have provided functional behavior of tensile and shear strength of porous dust aggregates as a function of the porosity that can be directly applied in continuum simulations of these objects in planet formation scenarios.

Recently Deglaciated High-Altitude Soils of the Himalaya: Diverse Environments, Heterogenous Bacterial Communities and Long-Range Dust Inputs from the Upper Troposphere

BackgroundThe Himalaya with its altitude and geographical position forms a barrier to atmospheric transport, which produces much aqueous-particle monsoon precipitation and makes it the largest continuous ice-covered area outside polar regions. There is a paucity of data on high-altitude microbial communities, their native environments and responses to environmental-spatial variables relative to seasonal and deglaciation events.Methodology/Principal FindingsSoils were sampled along altitude transects from 5000 m to 6000 m to determine environmental, spatial and seasonal factors structuring bacterial communities characterized by 16 S rRNA gene deep sequencing. Dust traps and fresh-snow samples were used to assess dust abundance and viability, community structure and abundance of dust associated microbial communities. Significantly different habitats among the altitude-transect samples corresponded to both phylogenetically distant and closely-related communities at distances as short as 50 m showing high community spatial divergence. High within-group variability that was related to an order of magnitude higher dust deposition obscured seasonal and temporal rearrangements in microbial communities. Although dust particle and associated cell deposition rates were highly correlated, seasonal dust communities of bacteria were distinct and differed significantly from recipient soil communities. Analysis of closest relatives to dust OTUs, HYSPLIT back-calculation of airmass trajectories and small dust particle size (4–12 µm) suggested that the deposited dust and microbes came from distant continental, lacustrine and marine sources, e.g. Sahara, India, Caspian Sea and Tibetan plateau. Cyanobacteria represented less than 0.5% of microbial communities suggesting that the microbial communities benefitted from (co)deposited carbon which was reflected in the psychrotolerant nature of dust-particle associated bacteria.Conclusions/SignificanceThe spatial, environmental and temporal complexity of the high-altitude soils of the Himalaya generates ongoing disturbance and colonization events that subject heterogeneous microniches to stochastic colonization by far away dust associated microbes and result in the observed spatially divergent bacterial communities.

A COMBINED VERY LARGE TELESCOPE AND GEMINI STUDY OF THE ATMOSPHERE OF THE DIRECTLY IMAGED PLANET, β PICTORIS b

We analyze new/archival VLT/NaCo and Gemini/NICI high-contrast imaging of the young, self-luminous planet $\beta$ Pictoris b in seven near-to-mid IR photometric filters, using advanced image processing methods to achieve high signal-to-noise, high precision measurements. While $\beta$ Pic b's near-IR colors mimick that of a standard, cloudy early-to-mid L dwarf, it is overluminous in the mid-infrared compared to the field L/T dwarf sequence. Few substellar/planet-mass objects -- i.e. $\kappa$ And b and 1RXJ 1609B -- match $\beta$ Pic b's $JHK_{s}L^\prime$ photometry, and its 3.1 $\mu m$ and 5 $\mu m$ photometry are particularly difficult to reproduce. Atmosphere models adopting cloud prescriptions and large ($\sim$ 60 $\mu m$) dust grains fail to reproduce the $\beta$ Pic b spectrum. However, models incorporating thick clouds similar to those found for HR 8799 bcde but also with small (a few microns) modal particle sizes yield fits consistent with the data within uncertainties. Assuming solar abundance models, thick clouds, and small dust particles ($<a>$ = 4 $\mu m$) we derive atmosphere parameters of log(g) = 3.8 $\pm$ 0.2 and $T_{eff}$ = 1575--1650 $K$, an inferred mass of 7$^{+4}_{-3}$ $M_{J}$, and a luminosity of log(L/L$_{\odot}$) $\sim$ -3.80 $\pm$ 0.02. The best-estimated planet radius, $\approx$ 1.65 $\pm$ 0.06 $R_{J}$, is near the upper end of allowable planet radii for hot-start models given the host star's age and likely reflects challenges with constructing accurate atmospheric models. Alternatively, these radii are comfortably consistent with hot-start model predictions if $\beta$ Pic b is younger than $\approx$ 7 Myr, consistent with a late formation, well after its host star's birth $\sim$ 12$^{+8}_{-4}$ Myr ago.

Effect of soiling on photovoltaic modules

In the past, the phenomenon of dust deposition on the glass cover of photovoltaic modules has been studied mainly in the Middle East, but little is known about the phenomenon in Central Europe. This paper focuses on the magnitude of the problem in Belgium (Köppen climate classification: Cfb). A variety of measurements were performed to determine the effect of dust settlement on the power output of photovoltaic modules. The physical properties of the collected dust were examined using a scanning electron microscope (SEM). A potential solution for the phenomenon, namely the usage of special coatings on the cover glass, was investigated. The results show that the problem of dust settlement on photovoltaic modules in Belgium is not as severe as in the Middle East. Nonetheless the problem exists and results in a constant power loss between 3% and 4% for the optimal tilt angle in Belgium which is 35° and with periods of regular rainfall. Please note that these results do not reflect a one year energy loss, further experiments are needed. Rain seems to have little cleaning effect on smaller dust particles (2–10μm), but on bigger particles (pollen, approx. 60μm) the cleaning effect is clearly visible. The use of special coatings on the glass have a potential reduction in power loss caused by dust settlement. However, at this moment, the extra cost associated with these coatings is not justified for photovoltaic modules in Belgium. Cleaning panels should only be done when soft tap water or demineralized water is available.

The production of activated carbon using the equipment of thermal power plants and heating plants

The production technology of activated carbon using the conventional equipment of the thermal power stations and boiler houses is proposed. The obtained product is directed into the systems of chemical water preparation and water drain of enterprises. The production cycle is invariable when producing the activated carbon by the proposed technology. The fuel consumption and heat losses are considerably reduced when implementing this technology compared with the known analogs of the carbon sorbent. The production efficiency increases if small dust particles are preliminary separated and coal is activated in narrow ranges of fraction sizes.

Onset of cavity deformation upon subsonic motion of a projectile in a fluid complex plasma

We study the deformation of a cavity around a large projectile moving with subsonic velocity in the cloud of small dust particles. To solve this problem, we employ the Navier-Stokes equation for a compressible fluid with due regard for friction between dust particles and atoms of neutral gas. The solution shows that due to friction, the pressure of a dust cloud at the surface of a cavity around the projectile can become negative, which entails the emergence of a considerable asymmetry of the cavity, i.e., the cavity deformation. Corresponding threshold velocity is calculated, which is found to decrease with increasing cavity size. Measurement of such velocity makes it possible to estimate the static pressure inside the dust cloud.

THE FATE OF PLANETESIMALS IN TURBULENT DISKS WITH DEAD ZONES. I. THE TURBULENT STIRRING RECIPE

Turbulence in protoplanetary disks affects planet formation in many ways. While small dust particles are mainly affected by the aerodynamical coupling with turbulent gas velocity fields, planetesimals and larger bodies are more affected by gravitational interaction with gas density fluctuations. For the latter process, a number of numerical simulations have been performed in recent years, but a fully parameter-independent understanding has not been yet established. In this study, we present simple scaling relations for the planetesimal stirring rate in turbulence driven by magnetorotational instability (MRI), taking into account the stabilization of MRI due to Ohmic resistivity. We begin with order-of-magnitude estimates of the turbulence-induced gravitational force acting on solid bodies and associated diffusion coefficients for their orbital elements. We then test the predicted scaling relations using the results of recent Ohmic-resistive MHD simulations by Gressel et al. We find that these relations successfully explain the simulation results if we properly fix order-of-unity uncertainties within the estimates. We also update the saturation predictor for the density fluctuation amplitude in MRI-driven turbulence originally proposed by Okuzumi & Hirose. Combination of the scaling relations and saturation predictor allows to know how the turbulent stirring rate of planetesimals depends on disk parameters such as the gas column density, distance from the central star, vertical resistivity distribution, and net vertical magnetic flux. In Paper II, we apply our recipe to planetesimal accretion to discuss its viability in turbulent disks.

The different faces of transitional discs

AbstractRecent imaging observations of transitional discs have revealed discrepancies between the structure observed at different wavelengths. In some targets, the gap measured using sub-mm observations disappears when observed using near infrared polarimetry, suggesting that the empty region is actually filled with small particles of dust (Dong et al., 2012). Assuming the gapped structure observed in transitional discs is caused by the presence of a planet, we try to explain such discrepancies simulating observations of physical models of disc/planet systems with VLT/SPHERE-ZIMPOL, Subaru/HiCIAO, VLT/VISIR and ALMA.

Characterization of lead, chromium, and cadmium in dust emitted from municipal solid waste incineration plants

The dust is emitted from municipal solid waste incinerators (MSWIs). Volatile toxic heavy metals are abundant in smaller dust particles and influence the toxicity of particulate matter such as fine particles <2.5 μm (PM2.5). However, little is known about the properties of these metals in fine dust particles. Therefore, X-ray absorption fine structure (XAFS) spectroscopy was used to investigate the chemical states of lead (Pb), chromium (Cr), and cadmium (Cd) in MSWI dust collected for nine particle size fractions at the inlet of the dust collector and the stacks of two MSWI plants. XAFS spectroscopy of the dust in the inlet of the dust collectors showed that finer dust contained predominantly Pb as PbCl2 with some PbSiO3, coarser dust consisted of Cr forms, including more toxic Cr(VI) species, and all dust contained CdCl2. Although the dust collector removed almost all of the Pb, trace amounts of PbCl2 remained in the stack gas after passing through the dust collector.

Experimental demonstration of the role of cohesion in electrostatic dust lofting

The cohesion between small dust particles plays an important role in determining the electrostatic force required to loft charged dust off a surface. On airless, celestial bodies, the cohesive bond between dust particles can be stronger than the gravitational force. Assuming that the charge on dust particles is given by Gauss' law, a theoretical model considering both cohesive and gravitational forces has predicted that intermediate‐sized particles require the smallest electric field strength to loft. We experimentally confirm that, for a given electric field, intermediate‐sized particles are lofted, while smaller and larger particles do not move.

Eyewitnesses about the Tunguska cosmic body

The analysis of 700 eyewitness’s stories about the Tunguska disaster enables to have an important information about the Tunguska cosmic body, its flight and destruction. Having compared the visual sizes of the flying object with the Sun, according to eyewitnesses stories, one can conclude that the visual size of the cosmic body considerably, more than 10 times, exceeded the real size of the Tunguska body. Dozens eyewitnesses noted sparkles scattering from the object, therefore the body’s substance was breaking to pieces strongly, its fragments flying out of the object at a speed close to that of the cosmic body. The flying object resembled an inflammation, both in its coloure and form, i.e. the substance that had separated from the object was undergoing a reaction of burning with atmospheric oxygen. Eyewitnesses neatly determined a head and a tile divided by a bottleneck in the contour of the flying object. Therefore, substance of the cosmic body must have comprised two components at least. Gases and small dust particles got burned down right at the moment of discharging from the object, thus forming “the head”. Larger fragments formed the burning tail of the flying object. In settlements at a distance of 200–350 km from the epicentre eyewitnesses noted that the flying object had a multicoloured iridescent tail. Duration of the flight of the body was more than 1 min inasmuch as people had enough time to go out from their houses to discern the phenomenon.

Methods for Simulating the Heavy Core Instability

Vortices have been proposed as the sites of planet formation, where dust col- lects and grows into planetesimals, the building blocks of planets. However, for very small dust particles that can be treated as a pressure-less fluid, we have recently discov- ered the heavy core instability, driven by the density gradient in the vortex. In order to understand the eventual outcome of this instability, we need to study its non-linear development. Here, we describe our ongoing work to develop highly accurate numerical models of a vortex with a density gradient embedded within a protoplanetary disk.

Case Study

Occupational exposure to silica in the construction industry has been well documented,(1–7) and respirable crystalline silica (quartz and cristobalite) has been associated with silicosis,(8,9) lung cancer,(10,11) pulmonary tuberculosis,(12,13) and airway diseases.(14,15) These concerns prompted a local construction union to request assistance from the National Institute for Occupational Safety and Health (NIOSH) for health hazard evaluations concerning exposures to dust and silica among roofers in Phoenix, Arizona. In response to these requests, NIOSH performed field studies to evaluate roofers’ exposures to silica. Health Effects Associated with Silica Exposure Silicosis is a disease of the lung caused by the deposition of fine crystalline silica particles (10 μm or less in diameter) in the lungs. The deposition of silica particles in the lungs triggers a chronic inflammatory response resulting in normal lung tissue being replaced with scar tissue (fibrosis). Symptoms of silicosis may include cough, shortness of breath, chest pain, early fatigue with exertion, and wheezing. Silicosis usually occurs after years of exposure (chronic) but may appear in a shorter period of time (acute) if exposure concentrations are very high. Acute silicosis is typically associated with a history of high exposures from tasks that produce small particles of airborne dust with a high silica content.(16) The International Agency for Research on Cancer (IARC) in 1996 concluded that there was “sufficient evidence in humans for the carcinogenicity of inhaled crystalline silica in the form of quartz or cristobalite from occupational sources.”(17) Workers diagnosed with silicosis are also at an increased risk of developing tuberculosis due to silica particles disabling the macrophages.(18) For a diagnosis of occupational silicosis, workers must have a history of exposure to respirable silica and a confirmatory test such as a chest X-ray, chest computed tomography (CT), or lung biopsy.

A New Cosmic Dust Detector with a Novel Method Using a Resistive Grid Sensitive to Hypervelocity Impacts

A new method is demonstrated to detect impacts of hypervelocity particles in real-time and to determine the size of particles. It uses a resistive grid on a thin substrate (here Duroid). Penetration of the substrate in an impact breaks lines on the grid, changing the overall resistance of the grid. The change in resistance is proportional to the width of the damaged area (i.e. number of resistive lines that are broken), which is in turn proportional to the impactor size. This method provides a large area, low mass, low power detector for measuring the flux of small dust particles in space. Based on experimental data (taken in a two-stage light gas gun), we show that impacts at 5km s-1 demonstrate that the principle works as described for particles 150μm and above and that in theory could work for impacts down to size scales as small as 50μm.