Dust distribution and dynamics in the coma of 67P/Churyumov-Gerasimenko

2021 ◽  
Author(s):  
Pablo Lemos
Keyword(s):  
Imaging System ◽  
Solar Radiation Pressure ◽  
Dust Particles ◽  
Transform Method ◽  
Additional Information ◽  
Novel Approach ◽  
Synthetic Images ◽  
Strict Requirement ◽  
Dust Distribution ◽  
Comet 67P

<p>In this work, the motion of dust particles in the coma of the comet 67P/Churyumov-Gerasimenko is investigated. This is done by analyzing sets of images taken by OSIRIS, the main imaging system on board Rosetta, in which these dust particles can be seen as bright tracks instead of points sources, as result of the combination of motions of both particles and spacecraft. A fundamental obstacle to deriving the dust size and velocity distribution from such data is that without additional information, the apparent brightness of a particle constrains only the ratio of size and distance, but neither quantity individually.</p> <p>While previous works in this area focused on obtaining the distance to individual detected particles in the image, a novel approach to analyze the dynamics of the dust is introduced in this work. This new approach is based on the statistical comparison between the images obtained by the camera, and synthetic images created by modeling the dynamics of the dust in the coma. The main advantage of this approach is to bypass the mentioned distance determination to the particles, which lifts the strict requirement on the observation conditions that were imposed by the earlier methods. This allows us to analyze a much larger set of images, and then, characterize the dust distribution and dynamics at the coma in a variety of conditions.</p> <p>Our method can be divided in three main parts. First, dust tracks on the OSIRIS images are detected using an algorithm based on the Hough transform method. Secondly, the trajectories of dust particles under the influence of gas drag, nucleus gravity, and solar radiation pressure are modeled. These trajectories vary depending on the dust properties, such as density and size. The combination of the trajectories and the information about spacecraft position and orientation allows us to generate synthetic images for each type of modeled dust. Lastly, the distribution of selected track properties, like orientation, length and total brightness, obtained from the real images, is fitted by combining the ones obtained from the synthetic images. This allows us to estimate the contents of each type of dust in the coma. </p>

scholarly journals Functional prediction of environmental variables using metabolic networks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Adèle Weber Zendrera ◽  
Nataliya Sokolovska ◽  
Hédi A. Soula
Keyword(s):  
Machine Learning ◽  
Growth Temperature ◽  
Environmental Variables ◽  
Metabolic Networks ◽  
Machine Learning Techniques ◽  
Underlying Structure ◽  
Glutathione Biosynthesis ◽  
Additional Information ◽  
Cold Environments ◽  
Novel Approach

AbstractIn this manuscript, we propose a novel approach to assess relationships between environment and metabolic networks. We used a comprehensive dataset of more than 5000 prokaryotic species from which we derived the metabolic networks. We compute the scope from the reconstructed graphs, which is the set of all metabolites and reactions that can potentially be synthesized when provided with external metabolites. We show using machine learning techniques that the scope is an excellent predictor of taxonomic and environmental variables, namely growth temperature, oxygen tolerance, and habitat. In the literature, metabolites and pathways are rarely used to discriminate species. We make use of the scope underlying structure—metabolites and pathways—to construct the predictive models, giving additional information on the important metabolic pathways needed to discriminate the species, which is often absent in other metabolic network properties. For example, in the particular case of growth temperature, glutathione biosynthesis pathways are specific to species growing in cold environments, whereas tungsten metabolism is specific to species in warm environments, as was hinted in current literature. From a machine learning perspective, the scope is able to reduce the dimension of our data, and can thus be considered as an interpretable graph embedding.

scholarly journals Configuration of the Martian dust rings: shapes, densities, and size distributions from direct integrations of particle trajectories

2020 ◽  
Vol 500 (3) ◽  
pp. 2979-2985
Author(s):  
Xiaodong Liu ◽  
Jürgen Schmidt
Keyword(s):  
Size Range ◽  
Solar Radiation Pressure ◽  
Dust Particles ◽  
Size Distributions ◽  
Grain Sizes ◽  
Gravitational Perturbations ◽  
Ring Configuration ◽  
Upper Limits ◽  
Configuration Simulation ◽  
Fifth Order

ABSTRACT It is expected since the early 1970s that tenuous dust rings are formed by grains ejected from the Martian moons Phobos and Deimos by impacts of hypervelocity interplanetary projectiles. In this paper, we perform direct numerical integrations of a large number of dust particles originating from Phobos and Deimos. In the numerical simulations, the most relevant forces acting on the dust are included: Martian gravity with spherical harmonics up to fifth degree and fifth order, gravitational perturbations from the Sun, Phobos, and Deimos, solar radiation pressure, as well as the Poynting–Robertson drag. In order to obtain the ring configuration, simulation results of various grain sizes ranging from submicrometres to 100 μm are averaged over a specified initial mass distribution of ejecta. We find that for the Phobos ring grains smaller than about 2 μm are dominant; while the Deimos ring is dominated by dust in the size range of about 5–20 μm. The asymmetries, number densities, and geometric optical depths of the rings are quantified from simulations. The results are compared with the upper limits of the optical depth inferred from Hubble observations. We compare to previous work and discuss the uncertainties of the models.

scholarly journals CO-driven activity constrains the origin of comets

2020 ◽  
Vol 636 ◽  
pp. L3 ◽  
Author(s):  
M. Fulle ◽  
J. Blum ◽  
A. Rotundi
Keyword(s):  
Loss Rate ◽  
Dust Particles ◽  
Mass Ratio ◽  
Cometary Nuclei ◽  
Nucleus Surface ◽  
Activity Onset ◽  
Gas Loss ◽  
Open Question ◽  
Comet 67P ◽  
Co Gas

Context. An open question in the study of comets is the so-called cohesion bottleneck, that is, how dust particles detach from the nucleus. Aims. We test whether the CO pressure buildup inside the pebbles of which cometary nuclei consist can overcome this cohesion bottleneck. Methods. A recently developed pebble-diffusion model was applied here to comet C/2017K2 PANSTARRS, assuming a CO-driven activity. Results. (i) The CO-gas pressure inside the pebbles erodes the nucleus into the observed dust, which is composed of refractories, H2O ice and CO2 ice. (ii) The CO-driven activity onset occurs up to heliocentric distances of 85 au, depending on the spin orientation of the comet nucleus. (iii) The activity onset observed at ≈26 au suggests a low obliquity of the nucleus spin axis with activity in a polar summer. (iv) At 14 au, the smallest size of the ejected dust is ≈0.1 mm, consistent with observations. (v) The observed dust-loss rate of ≈200 kg s−1 implies a fallout ≥30%, a nucleus surface active area ≥10 km2, a CO-gas loss rate ≥10 kg s−1, and a dust-to-gas ratio ≤20. (vi) The CO-driven activity never stops if the average refractory-to-all-ices mass ratio in the nucleus is ≤4.5 for a nucleus all-ices-to-CO mass ratio ≈4, as observed in comets Hale–Bopp and Hyakutake. These results make comet C/2017K2 similar to the Rosetta target comet 67P/Churyumov–Gerasimenko. (vii) The erosion lifetime of cometary planetesimals is a factor 103 shorter than the timescale of catastrophic collisions. This means that the comets we observe today cannot be products of catastrophic collisions.

scholarly journals Measuring Vascular Recovery Rate After Exercise

Proceedings ◽  
2018 ◽  
Vol 4 (1) ◽  
pp. 12 ◽  
Author(s):  
Halil Dijab ◽  
Jordi Alastruey ◽  
Peter Charlton
Keyword(s):  
Heart Rate ◽  
Recovery Rate ◽  
Wearable Sensors ◽  
Cardiovascular Fitness ◽  
Wave Shape ◽  
Future Studies ◽  
Additional Information ◽  
Novel Approach ◽  
Pulse Waves ◽  
Future Work

The rate at which an individual recovers from exercise is known to be indicative of cardiovascular risk. It has been widely shown that the reduction in heart rate immediately after exercise is predictive of mortality. However, little research has been conducted into whether the time taken for the blood vessels to return to normal is also indicative of risk. In this study, we present a novel approach to assess vascular recovery rate (VRR) using the photoplethysmogram (PPG) signal, which is monitored by smart wearables. The VORTAL dataset (http://peterhcharlton.github.io/RRest/) was used for this study, containing PPG signals from 39 healthy subjects before (baseline) and after exercise. 31 VRR indices were extracted from the PPG pulse wave shape, as well as heart rate for comparison. The rate at which indices returned to baseline after exercise was quantified, and the consistency of changes between subjects was assessed statistically. Many VRR indices exhibited changes after exercise which were consistent between subjects. Indices derived from the timings and second derivative of pulse waves were identified as candidates for future work. The rate at which the indices returned to baseline differed between indices and subjects, indicating that they may provide additional information beyond that of heart rate, and that they may be useful for stratifying subjects. This study demonstrated the feasibility of assessing VRR after exercise from the PPG. Future studies should investigate whether VRR indices are associated with cardiovascular fitness, and the potential utility of incorporating the indices into wearable sensors.

scholarly journals Extracellular and intracellular DNA for bacterial profiling of long-ripened cheeses

2020 ◽  
Vol 367 (13) ◽  
Author(s):  
Tommaso Bardelli ◽  
Lia Rossetti ◽  
Miriam Zago ◽  
Domenico Carminati ◽  
Giorgio Giraffa ◽  
...  
Keyword(s):  
Lactobacillus Rhamnosus ◽  
Streptococcus Thermophilus ◽  
Lactobacillus Helveticus ◽  
Extracellular Dna ◽  
Intact Cells ◽  
Additional Information ◽  
Buffer Solutions ◽  
Novel Approach ◽  
Three Samples ◽  
Bacterial Profiling

ABSTRACT A novel approach was developed to extract the extracellular DNA (eDNA), i.e. the free DNA outside the microbial cell, compared to the intracellular DNA (iDNA). The two DNA fractions were investigated in seven long-ripened cheeses. Among different buffer solutions tested, EDTA 0.5 M at pH 8 enabled a mild homogenization of cheese samples and the highest eDNA recovery. The extraction protocol was tested on single strains of lactic acid bacteria characterizing many Italian long-ripened cheeses, such as Streptococcus thermophilus, Lactobacillus helveticus, and Lactobacillus rhamnosus. The method resulted suitable for eDNA extraction because it minimized cell-lysis, avoiding the leakage of iDNA from the cells. The yields of eDNA, ranging from 0.01 to 0.36 µg g−1 cheese, were generally higher than the iDNA, indicating that autolytic phenomena prevailed over intact cells after 8–12 months of ripening. In four of the seven cheeses, the same LAB species were detected in the eDNA and iDNA fractions by length-heterogeneity PCR, while in the remaining three samples, a higher number of species was highlighted in the eDNA compared to the corresponding iDNA. The sequential extraction of eDNA and iDNA can be applied to obtain additional information on the composition of the bacterial community in long-aged cheeses.

Optical and Thermal Properties of Zodiacal Dust

1996 ◽  
Vol 150 ◽  
pp. 301-308 ◽  
Author(s):  
A.C. Levasseur-Regourd
Keyword(s):  
Thermal Properties ◽  
Physical Properties ◽  
Bulk Density ◽  
Thermal Emission ◽  
Symmetry Plane ◽  
Dust Particles ◽  
Orbital Inclination ◽  
Zodiacal Dust ◽  
Dust Distribution

AbstractRecent progress has been reported in the determination of the zodiacal thermal emission, brightness and polarization. These results, of interest to estimate the foreground sources in astrophysical observations, do not provide immediately information on the dust distribution, and on its optical and thermal properties. To infer local information about the bulk density, and the physical properties of the dust particles, it is necessary to compare the observations with realistic models or to invert the line-of-sight data. The latter approach typically suggests that the bulk density is (in the symmetry plane) inversely proportional to the solar distance, that the particles are not spheroidal, but rather irregular in shape, that their physical properties change with their distance to the Sun and their orbital inclination, and finally that they do not emit like a blackbody. The heterogeneity noticed in the cloud is due to various sources of dust particles, the size, shape or albedo of which evolve as a function of time, under collision and/or evaporation processes.

scholarly journals Dust of comet 67P/Churyumov-Gerasimenko collected by Rosetta/MIDAS: classification and extension to the nanometer scale

2019 ◽  
Vol 630 ◽  
pp. A26 ◽  
Author(s):  
T. Mannel ◽  
M. S. Bentley ◽  
P. D. Boakes ◽  
H. Jeszenszky ◽  
P. Ehrenfreund ◽  
...  
Keyword(s):  
Interplanetary Dust ◽  
Dust Particles ◽  
Nanometer Scale ◽  
Early Solar System ◽  
Interplanetary Dust Particles ◽  
Surface Features ◽  
Cometary Dust ◽  
Log Normal ◽  
Resolution Of Imaging ◽  
Comet 67P

Context. The properties of the smallest subunits of cometary dust contain information on their origin and clues to the formation of planetesimals and planets. Compared to interplanetary dust particles or particles collected during the Stardust mission, dust collected in the coma of comet 67P/Churyumov-Gerasimenko (67P) during the Rosetta mission provides a resource of minimally altered material with known origin whose structural properties can be used to further the investigation of the early solar system. Aims. The cometary dust particle morphologies found at comet 67P on the micrometer scale are classified, and their structural analysis is extended to the nanometer scale. Methods. We present a novel method for achieving the highest spatial resolution of imaging obtained with the MIDAS Atomic Force Microscope on board Rosetta. 3D topographic images with resolutions down to 8 nm were analyzed to determine the subunit sizes of particles on the nanometer scale. Results. Three morphological classes can be determined: (i) fragile agglomerate particles of sizes larger than about 10 μm comprised of micrometer-sized subunits that may themselves be aggregates and show a moderate packing density on the surface of the particles. (ii) A fragile agglomerate with a size of about a few tens of micrometers comprised of micrometer-sized subunits that are suggested to be aggregates themselves and are arranged in a structure with a fractal dimension lower than two. (iii) Small micrometer-sized particles comprised of subunits in the size range of hundreds of nanometers that show surface features that are again suggested to represent subunits. Their differential size distributions follow a log-normal distribution with means of about 100 nm and standard deviations between 20 and 35 nm. Conclusions. The properties of the dust particles found by MIDAS represent an extension of the dust results of Rosetta to the micro- and nanometer scale. All micrometer-sized particles are hierarchical dust agglomerates of smaller subunits. The arrangement, appearance, and size distribution of the smallest determined surface features are reminiscent of those found in chondritic porous interplanetary dust particles. They represent the smallest directly detected subunits of comet 67P.

scholarly journals 5.3 Modeling of the Orbital Evolution of Vaporizing Dust Particles Near the Sun

1976 ◽  
Vol 31 ◽  
pp. 434-436 ◽  
Author(s):  
Zdenek Sekanina
Keyword(s):  
Interplanetary Space ◽  
Solar Radiation Pressure ◽  
Orbital Evolution ◽  
Critical Distance ◽  
Dust Particles ◽  
Dynamical Effect ◽  
The Sun ◽  
Particle Collisions ◽  
Rate Of Evaporation ◽  
Small Dust

AbstractThe Poynting-Robertson (P-R) effect (Robertson, 1937, Wyatt and Whipple, 1950), assisted by a pseudo P-R effect due to the sputtering (Whipple, 1955, 1967), is known to cause small dust particles in interplanetary space to spiral toward the sun. Evaporation from the surface of such particles thus increases progressively with time and their size is being reduced accordingly. When the rate of evaporation is no longer negligibly low, it induces on the particle a measurable dynamical effect, which is associated with the implied variations in the magnitude of solar radiation pressure relative to solar attraction. By gradually reducing solar attraction, the particle evaporation tends to increase the orbit dimensions, thus acting against P-R. The P-R inward spiraling, far exceeding the dynamical effect from evaporation at larger heliocentric distances, slows gradually down as the particle approaches the sun, and virtually ceases when the critical distance is reached, where the two forces approximately balance each other. Then, typically, the perihelion distance stabilizes, while the eccentricity starts increasing very rapidly until the particle is swept out of the solar system. This, in brief, is the orbital evolution of a vaporizing particle in the absence of other potentially important but rather poorly known processes, such as particle collisions, rotational bursting, electric charging and interactions with the solar wind and with the interplanetary magnetic field.

scholarly journals A novel approach to Verify air gap and SSD for proton radiotherapy using surface imaging

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Xiao Wang ◽  
Chi Ma ◽  
Rihan Davis ◽  
Rahul R. Parikh ◽  
Salma K. Jabbour ◽  
...  
Keyword(s):  
Body Surface ◽  
Imaging System ◽  
Air Gap ◽  
Surface Imaging ◽  
Proton Radiotherapy ◽  
Optical Surface ◽  
Air Gaps ◽  
Novel Approach ◽  
Proton Treatment ◽  
The Absolute

Abstract Purpose To develop a novel approach to accurately verify patient set up in proton radiotherapy, especially for the verification of the nozzle – body surface air gap and source-to-skin distance (SSD), the consistency and accuracy of which is extremely important in proton treatment. Methods Patient body surfaces can be captured and monitored with the optical surface imaging system during radiation treatment for improved intrafraction accuracy. An in-house software package was developed to reconstruct the patient body surface in the treatment position from the optical surface imaging reference capture and to calculate the corresponding nozzle – body surface air gap and SSD. To validate this method, a mannequin was scanned on a CT simulator and proton plans were generated for a Mevion S250 Proton machine with 20 gantry/couch angle combinations, as well as two different snout sizes, in the Varian Eclipse Treatment Planning Systems (TPS). The surface generated in the TPS from the CT scan was imported into the optical imaging system as an RT Structure for the purpose of validating and establishing a benchmark for ground truth comparison. The optical imaging surface reference capture was acquired at the treatment setup position after orthogonal kV imaging to confirm the positioning. The air gaps and SSDs calculated with the developed method from the surface captured at the treatment setup position (VRT surface) and the CT based surface imported from the TPS were compared to those calculated in TPS. The same approach was also applied to 14 clinical treatment fields for 10 patients to further validate the methodology. Results The air gaps and SSDs calculated from our program agreed well with the corresponding values derived from the TPS. For the phantom results, using the CT surface, the absolute differences in the air gap were 0.45 mm ± 0.33 mm for the small snout, and 0.51 mm ± 0.49 mm for the large snout, and the absolute differences in SSD were 0.68 mm ± 0.42 mm regardless of snout size. Using the VRT surface, the absolute differences in air gap were 1.17 mm ± 1.17 mm and 2.1 mm ± 3.09 mm for the small and large snouts, respectively, and the absolute differences in SSD were 0.81 mm ± 0.45 mm. Similarly, for patient data, using the CT surface, the absolute differences in air gap were 0.42 mm ± 0.49 mm, and the absolute differences in SSD were 1.92 mm ± 1.4 mm. Using the VRT surface, the absolute differences in the air gap were 2.35 mm ± 2.3 mm, and the absolute differences in SSD were 2.7 mm ± 2.17 mm. Conclusion These results showed the feasibility and robustness of using an optical surface imaging approach to conveniently determine the air gap and SSD in proton treatment, providing an accurate and efficient way to confirm the target depth at treatment.

Sign in / Sign up

Export Citation Format

Share Document