Small Dust Particles Research Articles

Numerical simulation of dust deposition characteristics of photovoltaic arrays taking into account the effect of the row spacing of photovoltaic modules

Dust deposition on the surfaces of Photovoltaic (PV) arrays during their operation markedly affects their power generation efficiency. Previous research has overlooked the impact of the row spacing of PV modules on the actual dust deposition on PV arrays. This study investigates the dust deposition process and its behavior on PV arrays considering variations in row spacings, inlet wind speeds, dust particle sizes, and dust particle counts. By employing commercial Computational Fluid Dynamics (CFD) software, incorporating the SST k-ω turbulence model and discrete particle model, numerical simulations were performed to analyze the airflow field, dust particle trajectories, dust deposition patterns, and deposition rates on the PV array through grid-independent verification and numerical validation. At the same time, we performed a comparative analysis of the deposition rate considering the rebound of dust particles on the PV module surface versus the case where rebound is not considered. Results revealed that the maximum dust deposition rates at different inlet wind speeds were 6.84 %, 8.84 %, 11.0 %, and 14.6 %, corresponding to dust sizes of 50 μm, 100 μm, 120 μm, and 300 μm, respectively. Smaller dust particles exhibited lower deposition rates, while larger particles were influenced more by mass inertia and gravity, leading to predominant deposition on the front row of PV modules. Larger dust particles are more likely to deposit primarily on the front row of PV modules in a PV array. The tilt angles of 30°, 45°, and 60° were chosen to study the effects of different tilt angles on the dust deposition of PV arrays, and the results show that the dust deposition rate decreases as the tilt angle increases, and it is worth noting that the larger the tilt angle, the larger the dust deposition rate is when the dust particles are especially small as 5 μm. When wind speeds are low and dust particles are small, the dust deposition rate gradually rises as the row spacing increases. However, at higher wind speeds with small dust particles, the row spacing has minimal impact on the dust deposition rate. Conversely, with larger dust particles, increasing the row spacing results in a lower dust deposition rate. These findings underscore the significance of optimizing PV array design for enhanced power generation efficiency.

Observations of circumstellar disks in scattered light with SPHERE at the VLT

The technological developments initiated in the early 21 st century have led to the implementation of “planet finders” instruments on 8-m class telescopes which are in operation since 2014-2015. Such facilities are at the inception of significant progresses in the study of exoplanetary systems by enabling high contrast imaging of the environment of young nearby stars. One of the most productive science in this field is certainly the observations at high angular resolution of circumstellar disks, from the very young gas-rich protoplanetary disks all the way to more elusive dust-rich debris disks. In this paper, we summarize the main results obtained for these two categories of objects focusing on their morphological characteristics, as well as on the measurement of optical properties of the small dust particles to which the near IR spectral range is sensitive to. We mostly provide exemples based on observations performed with the SPHERE instrument at the VLT.

Parameters of dust particle chains levitated vertically in a gas discharge plasma

The structural parameters of the dust particle chains suspended vertically in the electric field of a gas discharge are studied here. The investigations are performed by a numerical multi-block model based on a mean field approximation. The model describes the movement of ions and dust particles under the action of an external electric field, the electric field (Coulomb) of each charged dust particle, and the field of bulk plasma charge (ions and electrons) that screens the charges of dust particles. The gravity and the ion drag forces acting on the dust particles are also taken into account. Self-consistent chain parameters are calculated and compared for different number (1, 3, 5, and 7) and two different diameters (3.4 and 8.94 mcm) of dust particles in the chains. It is shown that an “ion wake” is formed behind the dust structures, and it grows with the number of dust particles and their size. With an increase in the number of dust particles in the chain, the charge of the first (top) dust particle increases. In the case of small dust particles, with an addition of new particles into the chain, the centers of the chains almost remain at the position of a single particle in the vertical direction. The chains of big dust particles move as a whole down in the direction of gravity with an increase in the number of particles.

Impact of discontinuous grain size distributions on the spectral energy distribution of debris disks

Context. The collisional evolution of debris disks is expected to cause the characteristic wavy pattern, that is, an under- or overabundance of particles of specific sizes, of grain size distributions. This perturbed grain size distribution potentially leaves characteristic patterns in the spectral energy distribution (SED) of the disk system. Aims. We aim to quantify and understand the specific influence of discontinuous particle size distributions on the appearance of debris disks. For this purpose, we considered dust emission models based on two different grain size distributions, namely, one with a single power law and one with a broken power law. In particular, our study is focused on the impact of an overabundance of small grains and an underabundance of medium-sized grains on the far-IR and (sub-)millimeter regime on the dust reemission radiation and the potential to constrain discontinuities in the grain size distribution from (sub-)millimeter photometric measurements of debris disks. Methods. We compared the spectral index α (Fν ∝ να) in the case of a continuous grain size distribution with that of a discontinuous grain size distribution. We performed this comparison for central stars with different spectral types and two different disk structures (e.g., slim and broad debris dust rings). Results. Within the considered parameter space, we found a characteristic difference between the spectral slopes of the SED in the different scenarios. In particular, the overabundance of small grains resulting from collisional events and thus parameters defining the outcome of disk events in debris disks is potentially observable by comparison with the SED corresponding to a grain size distribution resulting from an ideal collisional cascade. More specifically, the overabundance of small grains leads to a steeper slope in the far-IR and sub-millimeter regime, while the spectral index in the millimeter regime is hardly affected. On the other hand, the underabundance of medium-sized grains results in a slight steepening of the far-IR slope of the SED, but its primary effect is on the millimeter slope of the SED, causing it to become shallower. We also found that the impact of an overabundance of small dust particles is more pronounced than that of an underabundance of medium-sized dust particles. We also found that the difference between the spectral indices for the two different grain size distributions is largest for debris disks around brighter central stars and broader disks. However, the impact of the considered spatial distributions described by the fractional width of the disk system is weak. Our results also show that the dust composition is not the sole physical mechanism responsible for the spectral inversion observed in the far-IR to millimeter part of the SED of debris disk systems. Furthermore, the location of the spectral break is placed at different wavelength regimes if the grain size distribution is considered as a function of blowout size and stellar type.

자율주행 카메라 인지성능에 작은 오염이 미치는 영향 연구

The environmental awareness sensors of self-driving cars include cameras, radars, and lidar. While various cognitive sensors are employed in combinations as per self-driving manufacturers' unique development strategies, the camera is a consistently utilized sensor. Camera sensors are the only ones capable of capturing texture, color, and contrast information, as well as recognizing objects such as road lanes, signals, signs, pedestrians, bicycles, and surrounding vehicles. Due to the ever-increasing pixel resolution and relatively low prices, camera sensors are gaining importance in autonomous vehicles. However, they are susceptible to environmental changes like dust, sun, rain, snow, or darkness. Furthermore, due to their relatively small, lens-like shape in comparison to radar and lidar sensors, camera sensor performance can be compromised by visual obstructions such as small dust particles (referred to as ‘blockage’ hereafter), which can significantly impact the safety of autonomous driving. In this study, a camera simulator was employed to simulate a virtual accident scenario based on an actual accident, projecting the virtual scenario screen directly through a camera. Object recognition delay time was assessed based on the density and color of the blockage. This study demonstrates that cognitive delays caused by blockage can lead to major accidents and draws a parallel with the idea that a small speck of dust in one's faith can cause significant trials. In addition to emphasizing the importance of cleaning the camera lens to prevent blockage, I would like to suggest the periodic purification of one's faith from external temptations.

Characteristics of heavy metals in road dust: An overview of South Korean cases

The urbanization and industrialization of our society necessitate the extension of road traffic systems. Road dust generated by road traffic is harmful to the human respiratory system. In particular, heavy metals adsorbed on road dust can pose substantial risks to human health owing to their toxicity, environmental longevity, and ability to accumulate in the human body. Although the evaluation of the concentration of heavy metals in road dust is essential for understanding their sources and risks to human health, there is a lack of comprehensive information on the heavy metal content in road dust in South Korea. In this review, sampling methods and analytical techniques for characterizing the contents of various heavy metals in road dust collected from different regions of South Korea are discussed. Cu, Zn, Cd, Pb, Ni, Cr, As, and Hg are the most frequently found heavy metals in road dust, and their concentrations are strongly associated with the sampling locations (e.g., industrial vs. residential sites and rural vs. urban areas) and particle size of the road dust. Road dust samples collected from more industrialized regions tend to contain more heavy metals. Further, smaller dust particles are likely apt to contain more heavy metals. The application of non-destructive analytical techniques is also necessary for the accurate characterization of heavy metals in road dust.

Mitigating dust particle contamination in an afterglow plasma by controlled lifting with a DC electric field

Particle contamination due to plasma processing motivates the design of a method of electrically lifting particles in a time interval after a plasma’s power is turned off. Small solid dust particles have electric charges that are not frozen until a late stage of the plasma afterglow. Beyond that time, before they fall to a surface below and cause defects, particles can be lifted in a controlled manner by applying an appropriate direct-current (DC) electric field, as we demonstrate experimentally. A few milliseconds after an argon plasma’s capacitively coupled radio-frequency power is switched off, a vertical DC electric field is applied. Thereafter, video imaging shows that the falling of the particles is slowed or stopped altogether, depending on the magnitude of the upward electric force.

The effect of turbulent motions on particle spatial distribution in high-Reynolds-number particle-laden flows

The spatial relationship between turbulent and particle concentration structures is investigated based on the turbulent velocity and particle concentration data obtained synchronously at the Qingtu Lake Observation Array site. In addition to the observation of particle concentration structures that contain not only large-scale coherence but also significant energy in the high-Reynolds-number atmospheric surface layer (ASL), the scale of turbulent motions that have the most significant coherence with particle concentration is found to follow a 1/2 power scaling law with the local height and ASL thickness. Moreover, large-scale turbulent velocity fluctuations have a significant amplitude modulation effect on particle concentration fluctuations, but the modulating influence is different for small dust particles and large saltating particles. Based on the interphase amplitude modulation, there exists a particle–turbulence structure phase difference that varies with height, which further makes the structure inclination angle of the particle concentration larger than that of the turbulence. In this scenario, a conceptual model reflecting the relationship between the two is proposed, and a quantitative formulation is further derived and found to be in good agreement with the experimental results. These findings and the proposed model contribute insights into particle–turbulence interactions, thereby providing theoretical support for a unified model of turbulence dynamics and particle kinematics.

The growth and decay of nonlinear wave in polytropic reacting gas with small solid dust particles

The aim of this study is to examine the evolutionary process of shock waves along the characteristic path under the effect of dust particles in a polytropic reacting gas. Testing the nature of the governing quasilinear of this system as a coordinate, we reconstruct the governing equations as Bernoulli’s differential equation and obtain the results. The results in the characteristic plane can display a non-linear behavior in the physical plane. It is shown how the reacting gas parameter influences the evolutionary process of the compressive and expansive waves, respectively, in reacting gas flows. Also, it is shown how the existence of dust in reacting gas influences the growth and decay of the compressive and expansive waves. The transport equation leading to the evolution of shock waves is determined and used to derive the condition for the shock formation. The comparative study of the effect of reacting gas parameters and dust particles on the flow patterning and distorting of shock waves for planar, cylindrically and spherically symmetric flows is also performed.

MINDS

Context. The Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) on board the James Webb Space Telescope (JWST) allows us to probe the inner regions of protoplanetary disks, where the elevated temperatures result in an active chemistry and where the gas composition may dictate the composition of planets forming in this region. The disk around the classical T Tauri star Sz 98, which has an unusually large dust disk in the millimetre with a compact core, was observed with the MRS, and we examine its spectrum here. Aims. We aim to explain the observations and put the disk of Sz 98 in context with other disks, with a focus on the H2O emission through both its ro-vibrational and pure rotational emission. Furthermore, we compare our chemical findings with those obtained for the outer disk from Atacama Large Millimeter/submillimeter Array (ALMA) observations. Methods. In order to model the molecular features in the spectrum, the continuum was subtracted and local thermodynamic equilibrium (LTE) slab models were fitted. The spectrum was divided into different wavelength regions corresponding to H2O lines of different excitation conditions, and the slab model fits were performed individually per region. Results. We confidently detect CO, H2O, OH, CO2, and HCN in the emitting layers. Despite the plethora of H2O lines, the isotopo-logue H218O is not detected. Additionally, no other organics, including C2H2, are detected. This indicates that the C/O ratio could be substantially below unity, in contrast with the outer disk. The H2O emission traces a large radial disk surface region, as evidenced by the gradually changing excitation temperatures and emitting radii. Additionally, the OH and CO2 emission is relatively weak. It is likely that H2O is not significantly photodissociated, either due to self-shielding against the stellar irradiation, or UV shielding from small dust particles. While H2O is prominent and OH is relatively weak, the line fluxes in the inner disk of Sz 98 are not outliers compared to other disks. Conclusions. The relative emitting strength of the different identified molecular features points towards UV shielding of H2O in the inner disk of Sz 98, with a thin layer of OH on top. The majority of the organic molecules are either hidden below the dust continuum, or not present. In general, the inferred composition points to a sub-solar C/O ratio (<0.5) in the inner disk, in contrast with the larger than unity C/O ratio in the gas in the outer disk found with ALMA.

Study on the transport and deposition of micron-sized particles with different densities in the coal mine environment in miners

To address the health problems caused by the long-term intrusion of high-concentration dust generated in coal mining operations into the human respiratory tract, this study reconstructed a 3D digital model of the upper airway based on fine industrial CT scanning images, and established the micron particle migration calculation model by Euler-Lagrange method. The transport and deposition mechanisms of dust with different densities under different inspiratory intensities were simulated and analyzed. The simulated results were compared with the results of dust exposure experiments in the upper airway combined with 3D printing technology, and the relative errors obtained were in the range of 2.9% to 6.3%. The results showed that the airflow volume peaked in the nasopharynx, oropharynx, epiglottis, and larynx, leading to the airflow separation and formation of circulation that tend to cause dust deposition in these regions. As the dust density and inspiratory airflow volume increased, the deposition fraction of small dust particles (<1μm) in the upper airway slightly changed, and most of them escaped to the lung. For 7.07 μm dust particles, as the dust density increased from 1210 kg/m3 to 2750 kg/m3, the escape rate decreased from 31.43% to 0.48%, and this trend can be seen in the fitting function of escape rate and inspiratory airflow volume Y7.07μm=(80–1.37ν + 0.0064ν2) × 100%. When the dust particle diameter exceeded 20 μm, the impact of dust density was weakened by the large size of the dust, and the escape rate was close to 0% when the inspiratory airflow volume was 50–110 L/min. This study can provide theoretical support for the research and development of respiratory dust sensors and targeted dust prevention technologies.

Occurrence and risk associated with urban road-deposited microplastics

An in-depth understanding of urban road-deposited MPs is important for the accurate prediction of the risk posed by MPs in different exposure scenarios. This study provides new insights into the intrinsic/extrinsic factors in terms of the variability of concentration and species in urban road-deposited MPs. The study results confirmed that a considerable abundance of road-deposited MPs can be identified with the average concentration ranging from 0.33 to 3.64 g m-2. Land use types and sediment particle size are the important factors that contribute to MPs abundance. The majority of detected MPs including polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) are mainly derived from anthropogenic activities in commercial and residential land uses while rubber MP particles in urban road surfaces are mainly derived from tyre wear. The significant correlation (p < 0.05) between MPs and fine dust particles (< 150 µm) indicated the high affinity of small dust particles for MPs. The risk scores from MPs varied greatly from 10 to 11,000 among the study sites, which indicated the significant spatial variation of potential environmental risks posed by road-deposited MPs. The hotspots of risks posed by MPs were in areas with a high fraction of industrial, commercial and residential land uses. Specifically, the highest risk from MPs was found in mixed industrial and residential areas.

Profile split of DIB 6196 in Sco OB2 association objects

ABSTRACT This paper describes the specific profile of the diffuse interstellar band (DIB) 6196 Å in objects belonging to the Sco OB2 association. The investigated feature is the narrowest known strong diffuse band. Reddened Sco OB2 association objects show slightly broadened and split (W-shaped) 6196 DIB profiles. The split cannot be explained by the presence of two (or more) clouds of different radial velocities along the line of sight because it is not observed in the much narrower identified atomic/molecular features. The observed DIB profile may (in some cases) be a composition of the band centre and its head of a still unknown molecule. Our estimation of the rotational temperature of C2 exhibits systematically higher values for objects with the observed split effect (Sco OB2 members). These split profiles are observed in both ζ and σ types of clouds, although in Sco OB2 objects only, suggesting that the phenomenon originates in some specific and currently unclear physical/chemical conditions inside the Sco OB2 association. It could be that a lower amount of small dust particles in Sco OB2 affects the flux of ultraviolet photons, providing a higher rotational temperature of DIB 6196 carriers, which is seen as a profile split.

The impact of dust evolution on the dead zone outer edge in magnetized protoplanetary disks

Context. The dead zone outer edge corresponds to the transition from the magnetically dead to the magnetorotational instability (MRI) active regions in the outer protoplanetary disk midplane. It has been previously hypothesized to be a prime location for dust particle trapping. A more consistent approach to access such an idea has yet to be developed, since the interplay between dust evolution and MRI-driven accretion over millions of years has been poorly understood. Aims. We provide an important step toward a better understanding of the MRI–dust coevolution in protoplanetary disks. In this pilot study, we present a proof of concept that dust evolution ultimately plays a crucial role in the MRI activity. Methods. First, we study how a fixed power-law dust size distribution with varying parameters impacts the MRI activity, especially the steady-state MRI-driven accretion, by employing and improving our previous 1+1D MRI-driven turbulence model. Second, we relax the steady-state accretion assumption in this disk accretion model, and partially couple it to a dust evolution model in order to investigate how the evolution of dust (dynamics and grain growth processes combined) and MRI-driven accretion are intertwined on million-year timescales, from a more sophisticated modeling of the gas ionization degree. Results. Dust coagulation and settling lead to a higher gas ionization degree in the protoplanetary disk, resulting in stronger MRI-driven turbulence as well as a more compact dead zone. On the other hand, fragmentation has an opposite effect because it replenishes the disk in small dust particles which are very efficient at sweeping up free electrons and ions from the gas phase. Since the dust content of the disk decreases over millions of years of evolution due to radial drift, the MRI-driven turbulence overall becomes stronger and the dead zone more compact until the disk dust-gas mixture eventually behaves as a grain-free plasma. Furthermore, our results show that dust evolution alone does not lead to a complete reactivation of the dead zone. For typical T-Tauri stars, we find that the dead zone outer edge is expected to be located roughly between 10 au and 50 au during the disk lifetime for our choice of the magnetic field strength and configuration. Finally, the MRI activity evolution is expected to be crucially sensitive to the choice made for the minimum grain size of the dust distribution. Conclusions. The MRI activity evolution (hence the temporal evolution of the MRI-induced α parameter) is controlled by dust evolution and occurs on a timescale of local dust growth, as long as there are enough dust particles in the disk to dominate the recombination process for the ionization chemistry. Once that is no longer the case, the MRI activity evolution is expected to be controlled by gas evolution and occurs on a viscous evolution timescale.

Apocenter pileup and arcs: A narrow dust ring around HD 129590

Context. Observations of debris disks have significantly improved over the past decades, both in terms of sensitivity and spatial resolution. At near-infrared wavelengths, new observing strategies and post-processing algorithms allow us to drastically improve the final images and reveal faint structures in the disks. These structures inform us about the properties and spatial distribution of the small dust particles. Aims. We present new H-band observations of the disk around the solar-type star HD 129590, which display an intriguing arc-like structure in total intensity observations but not in total polarimetry, and we propose an explanation for the origin of this arc. Methods. Assuming geometric parameters for the birth ring of planetesimals, our model provides the positions of millions of particles of different sizes to compute scattered light images. The code can either produce images over the full size distribution or over several smaller intervals of grain sizes. Results. We demonstrate that if the grain size distribution is truncated or strongly peaks at a size larger than the radiation pressure blow-out size, we are able to produce an arc quite similar to the one detected in the observations. If the birth ring is radially narrow, given that particles of a given size have similar eccentricities, they will have their apocenters at the same distance from the star. Since this is where the particles spend most of their time, an “apocenter pileup” occurs that can look like a ring. Due to more efficient forward scattering, this arc only appears in total intensity observations and remains undetected in polarimetric data, which is in good agreement with our observations. Conclusions. For the secondary ring to be detected, sharp variations either in the grain size distribution or for the scattering efficiencies Qsca (or a combination of both) are required. We show that a wavy size distribution and a size-dependent phase function can strengthen the apocenter pileup. Overall, such arcs are rarely detected in other systems, which can mainly be explained by the fact that most parent belts are usually broad.

Impact of turbulence intensity and fragmentation velocity on dust particle size evolution and non-ideal magnetohydrodynamics effects

ABSTRACT We investigate the influence of dust particle size evolution on non-ideal magnetohydrodynamic (MHD) effects during the collapsing phase of star-forming cores, taking both the turbulence intensity in the collapsing cloud core and the fragmentation velocity of dust particles as parameters. When the turbulence intensity is small, the dust particles do not grow significantly, and the non-ideal MHD effects work efficiently in high-density regions. The dust particles rapidly grow in a strongly turbulent environment, while the efficiency of non-ideal MHD effects in such an environment depends on the fragmentation velocity of the dust particles. When the fragmentation velocity is small, turbulence promotes coagulation growth and collisional fragmentation of dust particles, producing small dust particles. In this case, the adsorption of charged particles on the dust particle surfaces becomes efficient and the abundance of charged particles decreases, making non-ideal MHD effects effective at high densities. On the other hand, when the fragmentation velocity is high, dust particles are less likely to fragment, even if the turbulence is strong. In this case, the production of small dust particles becomes inefficient and non-ideal MHD effects become less effective. We also investigate the effect of the dust composition on the star and disc formation processes. We constrain the turbulence intensity of a collapsing core and the fragmentation velocity of dust for circumstellar disc formation due to the dissipation of the magnetic field.

Методика подсчета общего числа гемоцитов австралийского красноклешневого рака

The optimal formula for calculating the total number of hemocytes (HTN) of the Australian red-claw crayfish (Cherax quadricarinatus) has been established, which allows optimizing the time of counting HTN without re-ducing accuracy. Methodical recommendations on preparing a hemolymph sample, HTN calculation and differentiated calculation of hemocytes are given. It was found out that the differences in HTN are minimal when using different formulas, which is con-firmed by the analysis of variance F = 0.011, p = 0.998, the average values of HTN range from 2 384 to 2 427 cell/µl. Conducting multiple comparisons also demonstrated that the differences between the formulas are minimal: the significance levels between the formulas were p = 0.99. The optimal formula for the Australian red-claw crayfish is: HTN in 1 µl = N • 10, where N is the total number of hemocytes in 25 large squares of Gorjaev’s chamber. The counting chamber should be clean, since when even small dust particles are found on the grid, hemocyte clusters can form and impede counting, or the result of the calculation will be incorrect, because the distribution &#x0D; of hemocytes on the grid will not be uniform. After filling the chamber with hemolymph, it is recommended to wait &#x0D; 1-1.5 minutes so that the movement of the hemolymph stops and the hemocytes stop moving. It is recommended to use an anticoagulant, which prevents the rapid decay of cells and promotes their uniform distribution on the grid of the chamber without developing clots (clusters) that affect the accuracy of counting. Working with the whole hemolymph implies the speed and accuracy of the researcher's actions, since it quickly coagulates and forms clusters of hemocytes. In order to avoid confusion when counting cells located on the border between squares, Egorov’s rule is applied. The optimal increase for counting is a 400-fold increase.

Electrostatic dust remediation for future exploration of the Moon

Dust accumulation is one of the critical issues that must be mitigated on in-situ lunar explorations because an in-situ probe is exposed to small dust particles, which are easily attached to it, during its operations. The Lunar Dust Science Definition Team is organized by the Jet Propulsion Lab/California Institute of Technology through NASA’s Biological and Physical Sciences Division to define key science questions and assess dust remediation techniques. Here, we assess three electrostatic remediation technology concepts: electrostatic dust shield; surface electrostatically collecting dust, later called attractive surface; and electron beam — plasma jet inducing electrostatic dust lofting from a surface. We qualitatively investigate their maturity by defining six operational factors: Time and location; Amount of dust removal; Contamination of target surfaces; Operation duration; Installation; and Safety. In addition to these techniques, we discuss a supporting system that loads dust particles onto a test article to examine dust removal efficiency. The results show that further development increases the maturity of all the technologies. While laboratory and theoretical demonstrations reported whether each technology robustly work on the Moon, which hosts a complex, heterogeneous dust environment, we find that it is still uncertain if this is the case because none has been tested in the lunar environment. Particularly, operation duration and safety are critical to be addressed further on both laboratory and spaceflight scales.

An improved Representative Particle Monte Carlo method for the simulation of particle growth

Context. A rocky planet is formed out of the agglomeration of around 1040 cosmic dust particles. As dust aggregates grow by coagulation, their number decreases. But until they have grown to hundreds of kilometres, their number still remains well above the number of particles a computer model can handle directly. The growth from micrometres to planetesimal-sized objects therefore has to be modelled using statistical methods, often using size distribution functions or Monte Carlo methods. However, when the particles reach planetary masses, they must be treated individually. This can be done by defining two classes of objects: a class of many small bodies or dust particles treated in a statistical way, and a class of individual bodies such as one or more planets. This introduces a separation between small and big objects, but it leaves open how to transition from small to big objects, and how to treat objects of intermediate sizes. Aims. We aim to improve the Representative Particle Monte Carlo (RPMC) method, which is often used for the study of dust coagulation, to be able to smoothly transition from the many-particle limit into the single-particle limit. Results. Our new version of the RPMC method allows for variable swarm masses, making it possible to refine the mass resolution where needed. It allows swarms to consist of few numbers of particles, and it includes a treatment of the transition from swarm to individual particles. The correctness of the method for a simplified two-component test case is validated with an analytical argument. The method is found to retain statistical balance and to accurately describe runaway growth, as is confirmed with the standard constant kernel, linear kernel, and product kernel tests as well as by comparison with a fiducial non-representative Monte Carlo simulation.

METHODS OF PROTECTING THE ENVIRONMENT BY USING AUTOMATED AND COMPUTERIZED WORK TECHNIQUES IN THE CEREALS GRINDING PROCESS

The technological flow from a compound feed factory is a very complex one, starting from the storage of raw materials in special bunkers, then their movement to the processing installations with the help of conveyor belts, grinding the cereals, adding all the ingredients indicated by the assortment recipe, mixing and homogenization, and finally granulation and sterilization of the finished product obtained. As can be seen, one of the basic activities carried out during the production process of various types of compound feed is the grinding of cereal grains, which involves the release of small dust particles into the atmosphere. Therefore, it is aimed to use high-performance work installations in compound feed factories, with a high degree of mechanization, automation and computerization, with high productivity and low specific consumption, to ensure a rigorous monitoring of dust and other noxes according to accepted European norms. This article analyses the technical working parameters in the cereals grinding area and presents the results of the experimental measurements carried out in the dust discharge areas, which prove the advantage of using automated and computerized work installations, equipped with special filters which respect the optimal projected parameters and which ensure the rules imposed by the European Union for the protection of the environment.&#x0D;