Maximum Particle Concentration Research Articles

Optimizing Energy Efficiency in Deep-Sea Mining: A Study on Swirling Flow Transportation of Double-Size Mineral Particles

Deep-sea minerals are regarded as the most economically viable and promising mineral resource. Vertical hydraulic lifting represents one of the most promising methods for deep-sea mining lifting systems. To mitigate the potential for clogging due to the aggregation of particles in vertical pipe transport during deep-sea mining operations, this paper employs numerical simulations utilizing the computational fluid dynamics and discrete element method (CFD-DEM) model to investigate the swirling flow transportation of mineral particles. The characteristics of the swirling flow field and the motion law of double-size particles at different swirling ratios are investigated. The findings demonstrate that, in comparison to axial transport within the pipeline, the particle movement observed in swirling flow transport exhibits an upward spiral trajectory. This phenomenon facilitates the orderly movement of particles, thereby enhancing the fluidization of particles within the pipeline. An increase in the swirling ratio (SR) has a considerable impact on the velocity within the pipe. The tangential velocity distribution undergoes a gradual transition from centrosymmetric to non-centrosymmetric as the distance from the inlet increases. An increase in the SR results in an enhanced aggregation of particles at the wall, accompanied by a notable rise in the local particle concentration. The value of SR = 0.3 represents a critical threshold. When SR exceeds this value, the distribution of particles in the cross-section reaches a relatively stable state, rendering it challenging to further alter the distribution and concentration of particles, even if the SR is augmented. Furthermore, the maximum local particle concentration in the vicinity of the wall tends to be stable. These results provide valuable insights into vertical pipe swirling flow transport for deep-sea mining.

Quantitative evaluation of the impact of indoor relative humidity on deposition of aerosols generated during tooth grinding in a real-world clinical setting.

Exposure to aerosol particles generated from tooth grinding has a negative impact on the health of dental personnel. The aim of this study was to quantitatively analyze the impact of indoor relative humidity (IRH) on the deposition of these suspended particles in a well-controlled dental environment. In this study, a humidity control system was employed to effectively regulate and maintain indoor relative humidity (IRH). A novel computer-assisted numerical control system was developed to pre-treat the molar specimens, and accurately simulate clinical tooth grinding procedures. Each procedure was performed in triplicate, with an online real-time particle counter (ORPC; TR-8301, TongrenCo.) measuring aerosol production. All testing devices were controlled remotely. The data obtained were statistically analyzed using descriptive statistics and non-parametric tests (Kruskal-Wallis/ Dunn's post hoc test with Bonferroni correction, p < 0.05). The findings showed that with increasing IRH, the maximum peak concentration of aerosol particles decreased by 397% from 6.51 × 107 particles/m3 at 30% to 1.64 × 107 particles/m3 at 80%. The Kruskal-Wallis test results indicated a statistically significant effect of IRH on the aerosol increment (p < 0.05). Increasing the IRH level can effectively promote the deposition of aerosol particles, with a return to baseline within 15min after reaching 60% or above. Our study suggested that maintaining IRH above 70% during the cleaning process, allowing natural recovery to ambient humidity levels within 15min after cleaning, and taking basic precautions, may lead to an adequate reduction in the possible health risks of aerosol contamination.

Effect of electric field on separation characteristics of oil–water–solid three phases separating device

Lubricating oil can decay as a result of the mixing of water with solid impurities in the working process, and this process can adversely affect the performance of the machinery. Therefore, desolidification and dewatering are key steps in overall oil purification. In general, a basic swirl device cannot sustain efficient dewatering and desolidification. Thus, a three-phase separating device enhanced by an electric field has been proposed. To study the performance of the oil-water-solid separation process, a numerical model of the device was conceived based on combining the governing equations of the flow field and the electric field with the particle-tracking equation giving due consideration to the population balance model. The tangential velocity and the distribution of solid particles at various voltage amplitudes were analyzed, and the effect of the electric field on the oil, water and particle separation process was studied. The results show that at 3 kV, the tangential velocity increased by 5.06%, compared with that at 12 kV. Application of an electric field to the device was found to accelerate more solid particles which assembled near the wall of the device, and where the number of the particles near the axial plane decreased. The maximum particle concentration near the wall at the z = 630 mm plane is 20.24%. Moreover, the average residence time of the solid particles initially exhibited an increasing and then a decreasing trend. Additionally, the increase in the droplet size and enhancement of the oil-water separation process are promoted through the action of the electric field. The rate for desolidification, deoiling and dewatering at 3 kV are 93.60%, 93.30% and 95.59%, respectively.

Phenanthrene release-migration characteristics and potential influencing mechanisms from paddy soil to overlying water under bioturbation in a rice-fish coculture agroecosystem

Currently, polycyclic aromatic hydrocarbons (PAHs) such as phenanthrene (Phe) in rice-fish (RF) coculture paddy fields in Northeast China pose widespread environmental pollution risks. This study constructed experimental microcosm systems to explore the release-migration rules and reveal the potential influencing mechanisms of Phe from paddy soil to overlying water under bioturbation in an RF coculture agroecosystem in this area. (1). The release of particulate Phe (P-Phe) and dissolved Phe (D-Phe) was significantly promoted by bioturbation (p<0.05). The results of Pearson correlation analysis revealed strong correlations between P-Phe and total suspended solids (TSS), D-Phe and dissolved organic carbon (DOC) (p<0.05). (2). The adsorption process of Phe at the paddy soil-overlying water interface conformed to the competitive adsorption-solubilization (CAS) model of large-molecule biological dissolved organic matter (Bio-DOM) at low concentrations (7 mg/L) (L-CBio-DOM-LM-CAS) and the coadsorption and accumulation model of small-molecule Bio-DOM at high concentrations (45 mg/L) (H-CBio-DOM-SM-CAA). (3). Ultraviolet fluorescence (UV-FS) tracing technology and reaction diffusion modeling were used to qualitatively and quantitatively simulate the migration pathway of Phe-containing paddy soil particles. The maximum fluorescent particle (f-ps) concentration of Phe migration in paddy soil was 8.23%, and the maximum bioturbation diffusion coefficient (Db) was 23.6 × 10−3 cm2/d. Bioturbation significantly altered the physicochemical properties of paddy soil (p<0.05). The results of principal component analysis (PCA) showed that particle size (<0.05 mm) is the key factor causing the Phe maximum migration concentration to be 68.39 ng/g in paddy soil. This study will provide an important research basis for the prevention and control of secondary release and migration of pollutants under bioturbation in RF coculture agroecosystems.

Investigation of particle laden gravity currents using the light attenuation technique

An extensional use of the light attenuation technique is described to study the dynamics of particle laden flows. The method is validated against an analytical absorption/scattering model. It is then applied to particle laden gravity currents (PLGCs) and provides access to quantitative measurements of the particle mass fraction field. The influence of particle concentration on the turbulent dynamics of the flow and the front velocity are evaluated and discussed. In all experiments heterogeneities in the particle distribution are measured, with the maximum particle concentration in the PLGC front and intermediate particle concentration at the turbulent interface. The results highlight two regimes. In the dilute case, particles have no measurable impact on the turbulent structures observed in the flow nor on the bulk velocity. Particle sedimentation occurs due to mixing between the carrier and surrounding fluids. In the dense case, turbulent structures strongly weaken and the bulk velocity of the PLGC quantitatively decreases as the effective flow viscosity grows.

Балқаш қаласының атмосфералық ауасының ауыр металдармен ластануы

Мақалада Балқаш қаласының атмосфералық ауасының химиялық элементтермен ластану жағдайы талқыланған. Қалқыма бөлшектердің мөлшері РМ-10 стационарлық бақылау нәтижелері бойынша сынамалар 99,6% шаң бөлшектерінің шоғырлануы (құрамы бойынша сараланбаған шаң/аэрозоль) кезінде — 0,8 РШК о.т құрады, РШК о.т. нормасы 0,05 мг/м3, Балқаш қаласының атмосфералық ауасында қатты бөлшектердің бір реттік концентрациясының ең жоғары мөлшері 0,2 РШК болды. Қалқыма бөлшектердің концентрациясының мөлшері РМ-2.5. Нормалар бойынша РМ 2.5 орташа тәуліктік деңгейі 0,25 мг/м3 аспауы керек. Мәліметтер бойынша РМ 2.5 орташа тәуліктік деңгейінің асу еселігі 0,7 мг/м3қатты бөлшектердің бір реттік шоғырлануының ең жоғары РМ-2,5-0,2 РШК болды. Жалпы қала бойынша озонның орташа концентрациясы 1,5 РШК о.т. құрады; күкірт диоксиді-5,4 РШК м.бр.ш.; көміртегі оксиді-2,2 РШК м.бр.ш; азот диоксиді — 2,0 РШК м.бр.ш.; күкіртсутегі-20,1 РШК м.бр.ш. рұқсат етілген ең жоғары бір реттік шоғырлану 0,5 мг/м3 кезінде қолайсыз метеорологиялық жағдайлар кезеңінде күкіртті ангидридтің нақты концентрациясы тиісті РШК-дан 23,7 есе асып түскендігі анықталды.

Potential for Exposure to Particles and Gases throughout Vat Photopolymerization Additive Manufacturing Processes.

Vat photopolymerization (VP), a type of additive manufacturing process that cures resin to build objects, can emit potentially hazardous particles and gases. We evaluated two VP technologies, stereolithography (SLA) and digital light processing (DLP), in three separate environmental chambers to understand task-based impacts on indoor air quality. Airborne particles, total volatile organic compounds (TVOCs), and/or specific volatile organic compounds (VOCs) were monitored during each task to evaluate their exposure potential. Regardless of duration, all tasks released particles and organic gases, though concentrations varied between SLA and DLP processes and among tasks. Maximum particle concentrations reached 1200 #/cm3 and some aerosols contained potentially hazardous elements such as barium, chromium, and manganese. TVOC concentrations were highest for the isopropyl alcohol (IPA) rinsing, soaking, and drying post-processing tasks (up to 36.8 mg/m3), lowest for the resin pouring pre-printing, printing, and resin recovery post-printing tasks (up to 0.1 mg/m3), and intermediate for the curing post-processing task (up to 3 mg/m3). Individual VOCs included, among others, the potential occupational carcinogen acetaldehyde and the immune sensitizer 2-hydroxypropyl methacrylate (pouring, printing, recovery, and curing tasks). Careful consideration of all tasks is important for the development of strategies to minimize indoor air pollution and exposure potential from VP processes.

Modelling submerged biofouled microplastics and their vertical trajectories

Abstract. The fate of (micro)plastic particles in the open ocean is controlled by biological and physical processes. Here, we model the effects of biofouling on the subsurface vertical distribution of spherical, virtual plastic particles with radii of 0.01–1 mm. The biological specifications include the attachment, growth and loss of algae on particles. The physical specifications include four vertical velocity terms: advection, wind-driven mixing, tidally induced mixing and the sinking velocity of the biofouled particle. We track 10 000 particles for 1 year in three different regions with distinct biological and physical properties: the low-productivity region of the North Pacific Subtropical Gyre, the high-productivity region of the equatorial Pacific and the high mixing region of the Southern Ocean. The growth of biofilm mass in the euphotic zone and loss of mass below the euphotic zone result in the oscillatory behaviour of particles, where the larger (0.1–1.0 mm) particles have much shorter average oscillation lengths (&lt;10 d; 90th percentile) than the smaller (0.01–0.1 mm) particles (up to 130 d; 90th percentile). A subsurface maximum particle concentration occurs just below the mixed-layer depth (around 30 m) in the equatorial Pacific, which is most pronounced for larger particles (0.1–1.0 mm). This occurs because particles become neutrally buoyant when the processes affecting the settling velocity of a particle and the seawater's vertical movement are in equilibrium. Seasonal effects in the subtropical gyre result in particles sinking below the mixed-layer depth only during spring blooms but otherwise remaining within the mixed layer. The strong winds and deepest average mixed-layer depth in the Southern Ocean (400 m) result in the deepest redistribution of particles (&gt;5000 m). Our results show that the vertical movement of particles is mainly affected by physical (wind-induced mixing) processes within the mixed-layer and biological (biofilm) dynamics below the mixed layer. Furthermore, positively buoyant particles with radii of 0.01–1.0 mm can sink far below the euphotic zone and mixed layer in regions with high near-surface mixing or high biological activity. This work can easily be coupled to other models to simulate open-ocean biofouling dynamics, in order to reach a better understanding of where ocean (micro)plastic ends up.

Методика оценки концентрации мелкодисперсных частиц PM10 при работе центробежных фрикционных роликов

One of the solutions to increase the storage capacity and speed of handling palletized goods in warehouses is the use of gravity pallet racking. As elements of the safe operation of such conveyors, centrifugal friction rollers are widely used, which ensure the speed of the pallet within the limits that do not exceed the permissible values. During the operation of centrifugal friction rollers, wear products — brake dust, which have an adverse effect on the human body, may enter the atmosphere. Therefore, an urgent task is to study the operation of friction-type brake rollers from the point of view of the environmental assessment of the released brake dust. The paper assesses the concentration of fine particles with dimensions from 10 micrometers to 2.5 micrometers during the operation of centrifugal friction rollers in gravity pallet racks, and proposes a method for estimating their concentration in the warehouse working area. The coefficient of environmental friendliness of the design of the brake roller of the friction type has been introduced, which is one of the factors determining the maximum number of braking, and takes values from 0 to 1.0 for various designs of the friction roller — closed type, ventilated and open type. The results of an experimental study of materials for friction pairs of brake rollers show that the maximum amount of braking is provided at a pressure on the friction lining of 0.1 MPa, which corresponds to a pallet weight of 1000 kg. An example of using the methodology for estimating the concentration of particles in the working area for a warehouse consisting of one block of gravity racks for pallets 1200x800x1500 mm (length x width x height), weighing 1000 kg, with a total number of 546 pallet places is considered. Analysis of the results showed that the maximum number of pallet braking at which the maximum permissible concentration of particles with a dimension of 10 micrometers to 2.5 micrometers is reached and the maximum turnover of the warehouse can serve as a comprehensive assessment of its environmental friendliness.

Role of particle dynamics in processing of terrestrial nitrogen and phosphorus in the estuarine mixing zone

AbstractMultiple biogeochemical processes in estuaries modulate the flux of nutrients from land to sea, thus contributing to the coastal filter. The role of particle dynamics in regulating the fate of terrestrial nutrients in estuaries is poorly constrained. To address this issue, we resolved the particle size distribution of suspended material, and quantified size‐fractionated particulate nitrogen (PN) and phosphorus (PP), in a stratified mesotrophic estuary (Pojoviken, Finland). We also carried out a mixing experiment where the effects of salt‐induced flocculation on particle size distribution and concentrations of PN and PP were examined. The experimental results showed that salt‐induced flocculation at already very low salinities increases the total particle concentration and mean particle size, indicating transfer of dissolved material into particulates. Correspondingly, a significant increase in PP and particulate iron (Fe) was observed in the experiment results, suggesting coupled flocculation of P‐containing organic matter (OM) and ferrihydrite. Particle dynamics in the field data were dominated by processes occurring downstream of the flocculation zone. Primary production created a downward flux of autochthonous OM particles, promoting passive aggregation by random collisions with terrestrial material in the water column. Maximum particle concentrations were observed at and below the halocline. The highest PN and PP concentrations were observed in the subhalocline layer, 3.5 and 0.14 μmol L−1, respectively. Molar ratios of N:P in this material were &gt;40, consistent with typical marine snow in the early stages of microbial processing. Our study provides a mechanistic overview of the biogeochemical drivers of particulate nutrient dynamics in stratified estuarine environments.

Preferential concentration by mechanically driven turbulence in the two-fluid formalism

Preferential concentration is thought to play a key role in promoting particle growth, which is crucial to processes such as warm rain formation in clouds, planet formation, and industrial sprays. In this work, we investigate preferential concentration using 3D Direct Numerical Simulations adopting the Eulerian-Eulerian two-fluid approach, where the particles are treated as a continuum field with its own momentum and mass conservation laws. We consider particles with Stokes number $St \lesssim O(0.01)$ in moderately turbulent flows with fluid Reynolds number $Re \leq 600$. In our previous work (Nasab & Garaud, Physical Review Fluids. doi: 10.1103/PhysRevFluids.5.114308, 2020), we established scaling laws to predict maximum and typical particle concentration enhancements in the context of the particle-driven convective instability. Here we verify that the same results apply when turbulence is externally driven, extending the relevance of our model to a wider class of particle-laden flows. We find in particular that (i) the maximum particle concentration enhancement above the mean scales as $u_{rms}^2 \tau_p / \kappa_p$, where $u_{rms}$ is the rms fluid velocity, $\tau_p$ is the particle stopping time, and $\kappa_p$ is the assumed particle diffusivity from the two-fluid equations; (ii) the typical particle concentration enhancement over the mean scales as $(u_{rms}^2 \tau_p / \kappa_p)^{1/2}$; and (iii) the probability distribution function of the particle concentration enhancement over the mean has an exponential tail whose slope scales like $(u_{rms}^2 \tau_p /\kappa_p)^{-1/2}$. We conclude by discussing the caveats of our model and its implications in a relevant cloud application.

Dry wear behavior of A356-SiCp functionally graded composite in unidirectional and reciprocating contacts

PurposeThe purpose of this study is to distinguish the difference in tribological behavior of functionally graded composites in two sliding modes, namely, unidirectional and reciprocating.Design/methodology/approachA356-(10 Wt.%)SiCp functionally graded composite material (FGM) was prepared by vertical centrifugal casting and then a comparison was made between the tribological characteristics using pin-on-disk and pin-on-reciprocating plate configurations under identical operating conditions (sliding distance (s): 350 m; load (W): 30 = W = 120 N, in steps of 30 N; and velocity (v): 0.2 = v = 1.2 m/s, in steps of 0.2 m/s). Two types of test pins were considered, namely, a test pin taken from the outer zone of the FGM with maximum particle concentration and a test pin taken from the inner zone of the FGM in a matrix-rich region.FindingsThe study revealed that, for the test pin taken from the outer zone of the FGM in the low-velocity range (0.2–0.4 m/s), the reciprocating wear of the friction pair was dominant, while unidirectional wear was dominant in the velocity range of 0.6–0.8 m/s for the entire load range investigated. However, when the velocity was increased from 1.0 to 1.2 m/s, conflicting nature of dominancy in the wear characteristics of the friction pair was observed, depending on the loading condition. In addition, the inner zone FGM pin underwent seizure in the reciprocating mode, whereas this phenomenon was not seen in the unidirectional mode.Originality/valueDifferences in wear and friction characteristics of FGM friction pairs in two different sliding modes were investigated over a wide range of operating parameters.

Numerical Characterization of the Solid Particle Accumulation in a Turbulent Flow through Curved Pipes by Means of Stokes Numbers

The accumulation of particles in a turbulent flow of incompressible air with mono-dispersed solid particles inside a 90° pipe bend was simulated using ANSYS® Fluent (CFD), taking into account the effect of gravity, drag force and a bidirectional fluid-particle coupling. An analysis of the geometrical parameters and the structures of the secondary flow generated in a curved pipe (Dean vortices) was developed, thus determining the characteristic time scales of the flow. Four Stokes numbers (Stk) were formulated, whose values are calculated and studied from the numerical simulations performed. Two different particle sizes (d1 = 50 μm y d2 = 150 μm), at two different flow conditions (Re1 = 61,500 y Re2 = 173,972), and for three curvature ratios Rc/R = 1, 4 and 8 were studied. The flow was solved using a Eulerian–Lagrangian approach with a RNG k-ε turbulence model. Once the multiphase flow was solved and validated, the distribution and maximum particle concentration inside the 90° bend were presented. Additionally, the Stk numbers were calculated to estimate the possible particle concentration level for the different system configurations (dp, Re and Rc/R). It is concluded that, if all Stk numbers are less than one, relative concentration levels reach a minimum, while for Stk numbers larger than one, an increase in the maximum concentration inside the pipe bend was noticed.

Formation of Molybdenum Blue Nanoparticles in the Organic Reducing Area.

Molybdenum blue dispersions were synthesized by reducing an acidic molybdate solution with glucose, hydroquinone and ascorbic acid. The influence of the H/Mo molar ratio on the rate of formation of molybdenum particles was established. For each reducing agent, were determined the rate constant and the order of the particle formation and were established the conditions for the formation of aggregative stable dispersion with the maximum concentration of particles. The dispersed phase is represented by toroidal molybdenum oxide nanoclusters, which was confirmed by the results of UV/Vis, FTIR, XPS spectroscopy and DLS.

Investigation of PM emissions in cellular automata model with slow-to-start effect

In this paper, combining with the empirical particulate emission model, we studied Particulate Matter (PM) emission of two typical cellular automata traffic models (VDR and TT models) with slow-to-start rules under periodic boundary condition and open boundary condition. Numerical simulations show the two slow-to-start models have different emissions under the same initial and boundary conditions. Under periodic boundary condition, the metastable traffic flow emits the most particulate matter for VDR model, and the traffic flow in decelerated state emits the most. For TT model, the vehicles with the most emissions are those in the state of traffic congestion and deceleration. Moreover, the emission characteristics of particulate matter in the two models are analyzed and compared. Under open boundary condition, the resulting phase diagram and flux diagram to reflect traffic congestion are obtained. Research shows that the injection probability and removal probability have a great impact on PM emissions. Numerical simulation displays that the trend of particulate emission varies with the different state of vehicle movements in spite of the same removal probability. For different removal probabilities, different maximum particle concentrations are emitted from traffic flows in the same movement state. Moreover, the emission of VDR model is significantly different from that of TT model in vehicle deceleration state.

Preferential concentration in the particle-induced convective instability

Heavy particles in turbulent flows have been shown to accumulate in regions of high strain rate or low vorticity, a process otherwise known as preferential concentration. This can be observed in geophysical flows, and is inferred to occur in astrophysical environments, often resulting in rapid particle growth which is critical to physical processes such as rain or planet formation. Here we study the effects of preferential concentration in a two-way coupled system in the context of the particle-driven convective instability. To do so, we use Direct Numerical Simulations and adopt the two-fluid approximation. We focus on a particle size range for which the latter is valid, namely when the Stokes number is $\lesssim O(0.1)$. For Stokes number above $\sim 0.01$, we find that the maximum particle concentration enhancement over the mean scales with the rms fluid velocity $u_{\rm{rms}}$, the particle stopping time $\tau_p$, and the particle diffusivity $\kappa_p$, as $u_{\rm{rms}}^2 \tau_p / \kappa_p$. We show that this scaling can be understood from simple arguments of dominant balance. We also show that the typical particle concentration enhancement over the mean scales as $(u_{\rm{rms}}^2 \tau_p/ \kappa_p)^{1/2}$. We finally find that the probability distribution function of the particle concentration enhancement over the mean has an exponential tail whose slope scales as $(u_{\rm{rms}}^2 \tau_p / \kappa_p)^{-1/2}$. We apply our model to geophysical and astrophysical examples, and discuss its limitations.

Effect of Electrocautery Settings on Particulate Concentrations in Surgical Plume during Tonsillectomy.

To describe the effect of monopolar electrocautery (EC) settings on surgical plume particulate concentration during pediatric tonsillectomy. Cross-sectional study. Tertiary medical center. During total tonsillectomy exclusively performed with EC, air was sampled with a surgeon-worn portable particle counter. The airborne mean and maximum particle concentrations were compared for tonsillectomy performed with EC at 12 W vs 20 W, with smoke evacuation system (SES) and no smoke evacuation (NS). A total of 36 children were included in this analysis: 9 cases with EC at 12 W and SES (12SES), 9 cases with EC at 20 W and SES (20SES), 9 cases with EC at 12 W without SES (12NS), and 9 cases with EC at 20 W without SES (20NS). Mean particle number concentration in the breathing zone during tonsillectomy was 1661 particles/cm3 for 12SES, 5515 particles/cm3 for 20SES, 8208 particles/cm3 for 12NS, and 78,506 particles/cm3 for 20NS. There was a statistically significant difference in the particle number concentrations among the 4 groups. The correlation between the particle number concentration and EC time was either moderate (for 12SES) or negative (for remaining groups). Airborne particle concentrations during tonsillectomy are over 9.5 times higher when EC is set at 20 W vs 12 W with NS, which is mitigated to 3.3 times with SES. Applying lower EC settings with SES during pediatric tonsillectomy significantly reduces surgical plume exposure for patients, surgeons, and operating room personnel, which is a well-known occupational health hazard.

Ash sedimentation by fingering and sediment thermals from wind-affected volcanic plumes

Ash fallout and volcanic plume dispersion represent critical hazards for local and global human populations for minutes to years after the onset of an eruption. Understanding the key processes governing the sedimentation of ash particles is a major challenge in modern volcanology from modeling and risk management perspectives. Recent experiments predict that sedimentation from eruption clouds rich in fine-grained ash can be driven by convective phenomena in the form of ∼100 m to km-scale ash fingers related to the intermittent formation and detaching of ash-rich particle boundary layer. Remote sensing observations of mammatus and cloud veils from numerous eruptions over recent years as well as field observations of spatially discontinuous ash deposits are consistent with this prediction. Indeed, this mode of ash sedimentation is predicted to be the predominant mechanism of fine ash removal for a significant fraction of eruptions in the geological records. Here, we use a novel combination of 3 millimeter-wavelength Doppler radar observations and time series of optical disdrometer data to characterize for the first time in real-time the time-varying structure and sedimentation properties of volcanic ash plumes under steady wind conditions. As a case study, we apply this new method to weak short-lived plumes from Stromboli Volcano. 96% of the disdrometer proximal sedimentation data highlight pulsatory phases of increased sedimentation rate that are 20–60 s apart and characterized by particle size distribution variation with bulk concentrations up to 681 mg/m3. Radar data also record intermittent periods of higher reflectivity (i.e. a factor of 3 in mass concentration) inside the ash sedimentation interspersed by 30 to 50 s and interpreted as ash fingers crossing the radar beam. From time series of radar signals and ground-based disdrometer measurements, together with simple analog experiments, we develop a conceptual model for intermittent sedimentation from wind-affected ash plumes. In particular, we show that when wind speeds are comparable to or greater than ash settling velocities, the dynamics of wind-driven rolls in ash clouds can govern the production of gravitational instabilities and the occurrence and timing of ash fingers that form descending sediment thermals in turn. This study suggests that ambient wind should affect the maximum size and minimum concentration of ash particles needed to form fingers but also control where and when fingers form at the base of wind-drifted ash plumes. These novel predictions highlight the need for future work aimed at refining our understanding of ash finger formation under windy conditions from the perspectives of in-situ characterization, numerical modeling and risk assessment of fine ash dispersal from the most frequent style of eruptions on Earth.

Токсичность апконверсионных наночастиц. Обзор

Background and Objectives: The object of the study was the toxicity of upconversion nanoparticles. The aim is to overview the literature on the toxicity of various types of upconversion nanoparticles and to search for their maximum permissible concentration when administered to laboratory animals in vivo. Materials and Methods: The approach used has been the analysis of recent publications on the topic. Results: Upconversion particles are promising for visualization of the structure of biological tissues and organs in fluorescent light, as well as for use in diagnostics of diseases and photoinduced therapy. Nanoparticles with additional shells or functionalized by surface coating with targeted or photoactive molecules, allowing the creation of particles with several modalities, are considered. The phototoxicity of such particles is considered separately. When using nanoparticles for therapy or diagnostics of the state of living objects, the issue of toxicity is urgent. The toxic effect of upconversion nanoparticles on the body depends on their concentration upon administration, as well as on the total amount of nanoparticles correlated with the body weight. Conclusion: From the considered concentration dependences, based on the results of histological and biochemical studies, it was shown that, as a rule, no noticeable toxicity was observed in such particles, and the maximum permissible concentration of particles can be considered 2 mg/ml.

Classification of flavors in cigarillos and little cigars and their variable cellular and acellular oxidative and cytotoxic responses.

Flavored tobacco products are increasing in popularity but remain unregulated, with the exception of the ban on flavored conventional cigarettes. Lack of regulation of cigarillos and little cigars allows vendors to have their own version of popular flavors, each with different chemical components. A new classification system was created for flavored cigars in order to easily communicate our results with the scientific community. To understand the physicochemical characteristics of flavored little cigars and cigarillo smoke, size distribution and concentration of particulate matter in smoke were determined. Acellular reactive oxygen species generation was measured as an indirect measurement of the potential to cause oxidative stress in cells. In addition, cigarillo smoke extract treatment on bronchial epithelial (Beas-2b) cells were assessed to determine the flavor-induced cellular toxicity. Flavored cigars/cigarillos showed significant variability in the tested parameters between flavors as well as brands of the same flavor, but most of the cigars showed higher potential of generating oxidative stress, than research grade cigarettes. Flavored cigars produced maximum particle concentrations at 1.0μm and 4.0 μm compared with 3R4F reference research cigarettes. A differential cytotoxic response was observed with cigarillo smoke extract treatments, with "fruits/candy" and "drinks" being the most toxic, but were not more cytotoxic than smoke from cigarettes. These cigarillos with flavors must be well characterized for toxicity in order to prevent adverse effects caused by exposure to flavor chemicals. Our study provides insight into understanding the potential health effects of flavor-infused cigars/cigarillos and the need for the regulation of those flavoring chemicals in these products. Future research is directed to determine the flavoring toxicity of little cigars and cigarillos in vivo studies.