Stable Dust Research Articles

Observation of self-excited oscillations in DC glow discharge dusty plasma

We present a detailed experimental study of discharge current oscillations in a planar cathode plasma with poly dispersed alumina dust particles. Our experimental measurements suggest that surface density of dust particles play an important role together with cathode spots, in deciding self excited oscillating regime or stable dust cloud regime. Experiments conducted with dust particles density below the critical limit shows self excited oscillations. Operating above the critical limit, a dust cloud levitated in the sheath region was observed.

Slowly Expanding Stable Dust Spacetimes

We establish the future nonlinear stability of a large class of FLRW models as solutions to the Einstein-Dust system. We consider the case of a vanishing cosmological constant, which, in particular implies that the expansion rate of the respective models is linear, i.e. has zero acceleration. The resulting spacetimes are future globally regular. These solutions constitute the first generic class of future regular Einstein-Dust spacetimes not undergoing accelerated expansion and are thereby the slowest expanding generic family of future complete Einstein-Dust spacetimes currently known.

Design of Experiments (DoE) approach for the development and optimisation of an extraction method for steroid hormones and coccidiostats from stable dust

Design of Experiments (DoE) approach for the development and optimisation of an extraction method for steroid hormones and coccidiostats from stable dust

Experimental study of discharge current oscillations with dust particles

We present a detailed experimental study of discharge current oscillations in a planar cathode plasma with poly-dispersed alumina dust particles. The dominant frequency of oscillation depends on the discharge voltage, operating pressure, and amount of dust particles placed on the cathode. The power-law variation in the dominant frequency with different external operating parameters is presented. Experimental observations suggest that the dominant mechanism behind the generation of these oscillations is the cathode spot injection of sub-micron-sized dust particles. The cathode spots also aid in the generation of fine dust particles. The threshold limit on dust particle density dispersed on the cathode suggests that below the threshold limit, the fine particles depleting the electrons play an important role and lead to the generation of self-excited oscillations. Operating above the threshold limit, a stable dust cloud was observed together with the suppression of self-excited oscillations.

A self-consistent model for dust settling and the vertical shear instability in protoplanetary disks

Abstract The spatial distribution of dust particles in protoplanetary disks affects dust evolution and planetesimal formation processes. The vertical shear instability (VSI) is one of the candidate hydrodynamic mechanisms that can generate turbulence in the outer disk region and affect dust diffusion. Turbulence driven by the VSI has a predominant vertical motion that can prevent dust settling. On the other hand, the dust distribution controls the spatial distribution of the gas cooling rate, thereby affecting the strength of VSI-driven turbulence. Here, we present a semi-analytic model that determines the vertical dust distribution and the strength of VSI-driven turbulence in a self-consistent manner. The model uses an empirical formula for the vertical diffusion coefficient in VSI-driven turbulence obtained from our recent hydrodynamical simulations. The formula returns the vertical diffusion coefficient as a function of the vertical profile of the cooling rate, which is determined by the vertical dust distribution. We use this model to search for an equilibrium vertical dust profile where settling balances with turbulent diffusion for a given maximum grain size. We find that if the grains are sufficiently small, there exists a stable equilibrium dust distribution where VSI-driven turbulence is sustained at a level of αz ∼ 10−3, where αz is the dimensionless vertical diffusion coefficient. However, as the maximum grain size increases, the equilibrium solution vanishes because the VSI can no longer stop the settling of the grains. This runaway settling may explain highly settled dust rings found in the outer part of some protoplanetary disks.

Ion flow and dust charging at the sheath boundary in dusty plasma with an electron-emitting surface: applications to laboratory and lunar dusty plasmas

In laboratory and space plasmas, the emission of electrons from the surface significantly affects the characteristics of the plasma sheath that forms at that surface, which is crucial to understanding the overall plasma-wall interaction mechanism. In this work, the collisional fluid model is used for laboratory dusty plasma, whereas the collisionless model is used for lunar dusty plasma. We have extended the Bohm sheath criterion for the formation of the stable plasma sheath due to electron emission from the surface, loss of ion flux, and the gas pressure of the collisional laboratory dusty plasmas. It is found that ion flow at the sheath boundary is considerably influenced by the concentration of electron emission, the ion loss term, and gas pressure. The evolution of the dust charge explicitly determines the magnitude of the ion flow at the sheath boundary. The plasma parameters adopted in the present case are reliable in laboratory and space dusty plasmas, especially the dusty plasma environment on the lunar surface. The lunar surface and dust grains on the Moon become electrically charged as a result of the interaction between solar wind plasma and photoemission electrons emitted from the lunar surface. In addition, the lunar plasma sheath characteristics, dust-charging process, and stable dust levitation in the sheath region have been studied.

Observation of non-planar dust acoustic solitary wave in a strongly coupled dusty plasma

The nonlinear evolution and propagation of a stable dust acoustic solitary wave (DASW) in a non-planar geometry is investigated here. The experiment is performed in a strongly coupled dusty plasma consisting of monodisperse micrometer sized particles levitated in the sheath of a capacitively coupled radio frequency argon plasma. The non-planar waves are generated with the help of a cylindrical conducting exciter pin placed at the center of the homogeneous dust cloud. A negative excitation pulse is used to create a dust void and a dust density perturbation simultaneously around the exciter. From the edge of the void, the density perturbation propagates as a nonlinear (cylindrical) non-planar DASW. The characteristics of the solitary wave are measured using image analysis of the recorded video of wave propagation. The numerical solution of the modified Korteweg–de Vries equation with an additional term to take care of the non-planar geometry is compared with the experimental observation. The wave amplitude and width are measured as a function of time and compared with the theoretical predictions.

Self-excited converging shock structure in a complex plasma medium.

We report the study of a self-excited converging shock structure observed in a complex plasma medium. A high-density dust cloud of melamine formaldehyde particles is created and horizontally confined by a circular ring in a dc glow discharge plasma at a particular discharge voltage and pressure. Later, as the discharge voltage is increased, a circular density crest is spontaneously generated around the outer boundary of the dust cloud. This nonlinear density structure is seen to propagate inward towards the center of the dust cloud. The properties of the excited structure are analyzed and found to follow the characteristics of a converging shock structure. A three-dimensional molecular dynamics simulation has also been performed in which a stable dust cloud is formed and levitated by the balance of forces due to gravity and an external electric field mimicking the cathode sheath electric field in the experiment. Particles are also horizontally confined by an external electric field, representing the sheath electric field of the circular ring present in the experiment. A circular shock structure has been excited by applying an external perturbation in the horizontal electric field around the outer boundary of the dust cloud. The characteristic properties of the shock are analyzed in the simulation and qualitatively compared with the experimental findings. This paper is not only of fundamental interest but has many implications concerning the study of converging shock waves excited in other media for various potential applications.

Stable stadial and interstadial states of the last glacial's climate identified in a combined stable water isotope and dust record from Greenland

Abstract. During the last glacial interval, the Northern Hemisphere climate was punctuated by a series of abrupt changes between two characteristic climate regimes. The existence of stadial (cold) and interstadial (milder) periods is typically attributed to a hypothesised bistability in the glacial North Atlantic climate system, allowing for rapid transitions from the stadial to the interstadial state – the so-called Dansgaard–Oeschger (DO) events – and more gradual yet still fairly abrupt reverse shifts. The physical mechanisms driving these regime transitions remain debated. DO events are characterised by substantial warming over Greenland and a reorganisation of the Northern Hemisphere atmospheric circulation, which are evident from concomitant shifts in the δ18O ratios and dust concentration records from Greenland ice cores. Treating the combined δ18O and dust record obtained by the North Greenland Ice Core Project (NGRIP) as a realisation of a two-dimensional, time-homogeneous, and Markovian stochastic process, we present a reconstruction of its underlying deterministic drift based on the leading-order terms of the Kramers–Moyal equation. The analysis reveals two basins of attraction in the two-dimensional state space that can be identified with the stadial and interstadial regimes. The drift term of the dust exhibits a double-fold bifurcation structure, while – in contrast to prevailing assumptions – the δ18O component of the drift is clearly mono-stable. This suggests that the last glacial's Greenland temperatures should not be regarded as an intrinsically bistable climate variable. Instead, the two-regime nature of the δ18O record is apparently inherited from a coupling to another bistable climate process. In contrast, the bistability evidenced in the dust drift points to the presence of two stable circulation regimes of the last glacial's Northern Hemisphere atmosphere.

On the Origin of Dust Structures in Protoplanetary Disks: Constraints from the Rossby Wave Instability

High-resolution submillimeter observations of protoplanetary disks with ALMA have revealed that dust rings are common in large, bright disks. The leading explanation for these structures is dust trapping in a local gas pressure maximum, caused by an embedded planet or other dynamical process. Independent of origin, such dust traps should be stable for many orbits to collect significant dust. However, ringlike perturbations in gas disks are also known to trigger the Rossby wave instability (RWI). We investigate whether axisymmetric pressure bumps can simultaneously trap dust and remain stable to the RWI. The answer depends on the thermodynamic properties of pressure bumps. For isothermal bumps, dust traps are RWI stable for widths from ∼1 to several gas scale heights. Adiabatic dust traps are stable over a smaller range of widths. For temperature bumps with no surface density component, however, all dust traps tend to be unstable. Smaller values of disk aspect ratio allow stable dust trapping at lower bump amplitudes and over a larger range of widths. We also report a new approximate criterion for RWI. Instability occurs when the radial oscillation frequency is ≲75% of the Keplerian frequency, which differs from the well-known Lovelace necessary (but not sufficient) criterion for instability. Our results can guide ALMA observations of molecular gas by constraining the resolution and sensitivity needed to identify the pressure bumps thought to be responsible for dust rings.

Experimental investigation of aluminum-air burning velocity at elevated pressure

Aluminum is an energy-dense metal that reacts exothermically with a range of oxidizers, making it a potentially useful fuel for certain thermal energy and power applications (e.g., boilers, swirl-stabilized burners, rockets, etc.). In addition to its reactive properties, aluminum is naturally abundant and commercially available in fine powders that are relatively inexpensive and chemically stable. Fine aluminum dusts, with particle diameters on the order of micrometers, can be aerosolized and mixed with a gaseous oxidizer such as air to create stable dust flames and heat for a thermodynamic cycle. In order to realize the potential utility of aluminum-air dust flames, the fundamental combustion behavior, such as the burning velocity, must be understood. In this work, an experimental system was developed that allows metal dust flames to be observed within an optically-accessible pressurized chamber. Using a high-speed camera, fuel-rich premixed aluminum-air jet flames were imaged through narrowband interference filters, and the data were used to calculate burning velocity. A single polydisperse size distribution of particles was tested at pressures ranging from 1 to 7.2 bar. Burning velocity was found to decrease with increased pressure (P), with an approximate proportionality to P−0.6 over the range of pressures tested (∼P−0.3 for only the laminar flow conditions). This reduction in burning velocity with increased pressure is hypothesized to occur due to increased oxidizer density along with a decrease in interparticle spacing, which may result in asymmetric particle heating and increased competition for oxidizer.

Characteristics and Impact Factors of Number Concentration of Primary Biological Aerosol Particles in Beijing

Primary biological aerosol particles (PBAP) are an important part of ambient aerosols. Both living and dead organisms not only influence human health and air quality but also play important roles in regulating certain atmospheric processes and affect the hydrological cycle and climate change. In this study, flow cytometry (FCM) was utilized in combination with the simultaneous use of permeant (SYBR Green I) and impermeant (propidium iodide, PI) nucleic acid fluorescent staining to detect and quantify the viable and dead airborne biological particles. At the same time, based on this method, the dead/viable PBAP in a Beijing urban area was detected and quantified. Moreover, the influence of environmental factors on the concentrations of primary biological aerosol particles was illuminated. The results showed that the media number concentration of dead and alive PBAP in the Beijing urban area during summer (1.03×106 m-3 and 7.43×105 m-3, respectively) were higher than those during winter (7.34×105 m-3and 6.18×105 m-3, respectively). Statistical analysis showed that there was no significant correlation between PBAP number concentration and environmental factors, i.e., meteorological conditions and air quality, showing a weak positive correlation with temperature and humidity and weak negative correlations with O3, maximum wind speed, and sunshine duration. The number concentration of PBAP was weakly correlated with the mass concentration of PM2.5 but positively correlated with that of coarse particulate matter (PM2.5-10). Both stable weather and dust transport could increase the number concentration of PBAP in Beijing.

Dust Evolution in the Coma of Distant, Inbound Comet C/2017 K2 (PANSTARRS)

C/2017 K2 (PANSTARRS) is an Oort Cloud comet previously observed to be active at heliocentric distances r > 20 au on what is likely its first passage through the inner solar system. We observed the comet on 2021 March 19–20 at r = 6.82 au preperihelion and 8.°35 phase angle with the Hubble Space Telescope (HST), and obtained high spatial resolution photometry and polarimetry mapping the properties of dust over the coma prior to the onset of water ice sublimation activity on the nucleus. We found clear radial gradients in the color and polarization of the coma: the F475W–F775W () reflectance slope increased from ∼4.5% per 100 nm within ∼10,000 km of the nucleus up to ∼7% per 100 nm by ∼50,000 km, while the negative polarization in F775W () strengthened from about −2% to −3.5% over the same range. The radial intensity profiles moreover strongly deviate from profiles simulated for stable dust grains. Near-infrared imagery obtained with the Palomar Hale Telescope on 2021 May 18 at r = 6.34 au revealed a continued absence of micron-sized grains in the tail, but showed no clear spatial gradient in JHKs colors. The observed patterns collectively appear consistent with the inner coma being optically dominated by sublimating, micron-sized water ice grains, unlike the tail of more stable, millimeter-sized grains. Finally, we evaluated these results alongside other Oort Cloud comets, and found in a reanalysis of HST observations of C/2012 S1 (ISON) that the near-nucleus polarimetric halo reported for that comet is likely an observational artifact.

Secretory protein beta-lactoglobulin in cattle stable dust may contribute to the allergy-protective farm effect.

BackgroundGrowing up on a cattle farm and consuming raw cow's milk protects against asthma and allergies. We expect a cattle‐specific protein as active component in this farm effect.MethodsDust was collected from cattle and poultry stables and from mattresses of households. Urine was obtained from cattle, and ambient aerosols were sampled. Samples were analysed for BLG by SDS PAGE/immunoblot and mass spectrometry, and for association with metals by SEC‐ICP‐MS. PBMC of healthy donors were incubated with BLG +/− zinc, and proliferation and cytokines determined. BALB/c mice were pre‐treated intranasally with stable dust extract containing BLG or depleted of BLG, and subsequent allergy response after sensitization was evaluated on antibody and symptom level.ResultsA major protein in dust from cattle farms and ambient air was identified as BLG. Urine from female and male cattle is a major source of BLG. In dust samples, BLG was associated with zinc. In vitro, zinc‐BLG provoked significantly lower proliferation of CD4+ and CD8+ cells while inducing significantly higher levels of IFN‐γ and IL‐6 than the apo‐BLG devoid of zinc. In vivo, pre‐treatment of mice with dust extract containing BLG resulted in lower allergy symptom scores to BLG and unrelated Bet v 1 than pre‐treatment with extract depleted of BLG. These in vitro and in vivo effects were independent of endotoxin.ConclusionThe lipocalin BLG is found in large amounts in cattle urine, accumulates in bovine dust samples and is aerosolized around farms. Its association with zinc favorably shapes the human cellular immune response towards Th1‐cytokines in vitro. BLG together with zinc in stable dust protects mice from allergic sensitization. BLG with its associated ligands may in an innate manner contribute to the allergy‐protective farm effect.

Influence of temporal variations in plasma conditions on the electric potential near self-organized dust chains

Self-organization of dust grains into stable filamentary dust structures (or “chains”) largely depends on dynamic interactions between individual charged dust grains and complex electric potential arising from the distribution of charges within a local plasma environment. Recent studies have shown that the positive column of the gas discharge plasma in the Plasmakristall-4 (PK-4) experiment at the International Space Station supports the presence of fast-moving ionization waves, which lead to variations of plasma parameters by up to an order of magnitude from the average background values. The highly variable environment resulting from ionization waves may have interesting implications for the dynamics and self-organization of dust particles, particularly concerning the formation and stability of dust chains. Here, we investigate the electric potential surrounding dust chains in the PK-4 experiment by employing a molecular dynamics model of the dust and ions with boundary conditions supplied by a particle-in-cell with Monte Carlo collision simulation of the ionization waves. The model is used to examine the effects of the plasma conditions within different regions of the ionization wave and compare the resulting dust structure to that obtained by employing the time-averaged plasma conditions. The comparison between simulated dust chains and experimental data from the PK-4 experiment shows that the time-averaged plasma conditions do not accurately reproduce observed results for dust behavior, indicating that more careful treatment of plasma conditions in the presence of ionization waves is required. It is further shown that commonly used analytic forms of the electric potential do not accurately describe the electric potential near charged dust grains under these plasma conditions.

Generation of the fluctuations by a charged dust beam in the ionosphere

Different kinds of waves and instabilities in the F-region of the ionosphere excited by the relative streaming of the dust beam to the background plasma are studied in the present paper. The dispersion relations of different waves are obtained on different time scales. It is found from our numerical results that there are both a stable upper hybrid wave on the electron vibration time scale and a stable dust ion cyclotron wave on the ion vibration time scale. However, the chaotic behaviour appears on the dust particles vibration time scale due to the relative streaming of the dust particles to the background plasma. Such instabilities may drive plasma irregularities that could affect radar backscatter from the clouds.

The extended farm effect: The milk protein β-lactoglobulin in stable dust protects against allergies.

Background: The allergy- and asthma-protective farm effect is mediated by numerous factors. Especially dust from cattle stables and raw cow’s milk show beneficial properties, suggesting a bovine protein to be involved. As a major milk protein and member of the lipocalin family, β-lactoglobulin (BLG) binds small, hydrophobic ligands and thereby modulates the immune response. Empty BLG promotes allergy development, whereas BLG in association with ligands shows allergy-preventive as well as allergy-reducing effects in vivo and in vitro. Results: BLG has been identified as a major protein in stable dust (therein bound to zinc) as well as in the air around cattle stables. This association with zinc favors an allergy-protective immune profile. Conclusion: Its immune-modulating, allergy-protective characteristics together with its presence in raw cow’s milk as well as in stable dust and ambient air render BLG an essential contributor to the farm effect.

Detrital zircon U–Pb age analysis of last glacial loess sources and proglacial sediment dynamics in the Northern European Plain

Loess deposits along the northern fringe of the European loess belt potentially record past changes in dust emission from areas proximal to former ice sheets. Recent chronologies from loess deposits across this region generally agree on greatly enhanced dust deposition rates when the Fennoscandian Ice Sheet reached its maximum extent during the late last glacial. However, uncertainties over the material's source and origin limit understanding of the causes of this enhanced dust activity. In particular, loess in southwestern Poland has been attributed to multiple origins, mainly involving glaciofluvial outwash plains along the Fennoscandian Ice Sheet margin and/or local sources in the mountainous areas of the Sudetes and Western Carpathians. Here we apply detrital zircon U–Pb age analyses for a large number of grains recovered from four loess samples taken from different stratigraphic units exposed at Biały Kościół in southwestern Poland, previously luminescence dated to MIS 4–2, to assess loess provenance as well as its temporal evolution during last glacial Fennoscandian Ice Sheet fluctuations. Furthermore, we analysed the detrital zircon U–Pb age spectra of five samples from potential source sediments to constrain the history of sediment recycling and mixing within the Northern European Plain prior to deflation and loess deposition. The broad range of zircon age components detected in the four loess samples suggests both Fennoscandian and closer Peri-Gondwanan proto-sources while a narrow, dominant Carboniferous age peak is consistent with sourcing from the local Strzelin Hills in the Sudetic foreland. However, the presence of both Fennoscandian and Peri-Gondwanan derived grains in samples from potential source sediments reveals that this mixture of sediment sources is widespread across the Northern European Plain, as a result of long-term glacial and fluvial reworking of cover sediments in the proglacial area throughout the Quaternary. Local rivers draining the Sudetic foreland transported this Fennoscandian-Peri-Gondwanan sediment mixture along with particles denuded from the Strzelin Hills, resulting in a nearby, temporally stable dust source for the Biały Kościół loess during MIS 4–2, while dust emission rates were substantially increased during the last glacial maximum. Given that our model for loess formation at Biały Kościół essentially involves sediment distribution via rivers prior to short distance aeolian transport, we infer that the proportion of northern ice sheet derived particles in European loess deposits is mainly controlled by the drainage pattern of major rivers in relation to Pleistocene ice margins where glaciofluvial sediment is abundant. Based on the presence of Fennoscandian derived zircon grains in European loess deposits, we constrain a southern limit of the influence of northern ice sheet dust sources along the central European highlands that currently divide drainage between the Northern European Plain and the Danube Basins.

Machine learning combined with Langmuir probe measurements for diagnosis of dusty plasma of a positive column

This paper reports the use of machine learning to enhance the diagnosis of a dusty plasma. Dust in a plasma has a large impact on the properties of the plasma. According to a probe diagnostic experiment on a dust-free plasma combined with machine learning, an experiment on a dusty plasma is designed and carried out. Using a specific experimental device, dusty plasma with a stable and controllable dust particle density is generated. A Langmuir probe is used to measure the electron density and electron temperature under different pressures, discharge currents, and dust particle densities. The diagnostic result is processed through a machine learning algorithm, and the error of the predicted results under different pressures and discharge currents is analyzed, from which the law of the machine learning results changing with the pressure and discharge current is obtained. Finally, the results are compared with theoretical simulations to further analyze the properties of the electron density and temperature of the dusty plasma.

A novel method for cleaning coal-dust-laden air and its application

During the green mining processes of coal energy, large amounts of coal-dust-laden air may be generated. This has caused serious health threats to mine workers. In this paper, a novel method for efficiently cleaning coal-dust-laden air was proposed. The method involved the use of air scrubbers composed of water inlet pipes, radial mixing impellers, water distribution plates, swirl vanes, and dehydrator. The radial mixing impellers were utilized to break up the water which flowed from the water inlet pipes to water distribution plates. As a result, water mist was formed, which then combined with the coal-dust-laden air, effectively sucking it using the negative pressure from the impeller rotation actions. The coal-dust-laden air and solid-liquid mixtures were moved along a certain trajectory by centrifugal force and gravity, and then discharged to the exterior. Experiments and field application processes were carried out in order to test the effectiveness of the proposed method. The experimental results showed that the dust removal efficiency of the method had reached 97.70 %. In addition, the proposed method was applied to a coal preparation plant in China’s Shanxi Province. The test results indicated that the average concentrations of total dust and respirable dust were found to have decreased from 71.11 to 2.89 mg/m3 and from 47.675 to 1.958 mg/m3, which met the requirements of environmental standards. Therefore, since the proposed method had not used conventional nozzles and filters, and had no requirements regarding the water quality of the coal mine, it had displayed strong adaptability and stable dust removal efficiency. The results obtained in this study showed that this new method of cleaning coal-dust-laden air was a promising measure by which to significantly improve the working environments of coal mines.