scholarly journals Spectrophotometric characterization of the Philae landing site and surroundings with the Rosetta/OSIRIS cameras

2020 ◽  
Vol 498 (1) ◽  
pp. 1221-1238
Author(s):  
Hong Van Hoang ◽  
S Fornasier ◽  
E Quirico ◽  
P H Hasselmann ◽  
M A Barucci ◽  
...  
Keyword(s):  
Total Mass ◽  
Morphological Changes ◽  
Landing Site ◽  
Spectral Slope ◽  
Water Ice ◽  
Total Mass Loss ◽  
Before And After ◽  
Comet 67P ◽  
Cometary Activity

ABSTRACT We investigate Abydos, the final landing site of the Philae lander after its eventful landing from the Rosetta spacecraft on comet 67P/Churyumov–Gerasimenko on 2014 November 12. Over 1000 OSIRIS-level 3B images were analysed, which cover the 2014 August–2016 September timeframe, with spatial resolution ranging from 7.6 m pixel−1 to approximately 0.06 m pixel−1. We found that the Abydos site is as dark as the global 67P nucleus and spectrally red, with an average albedo of 6.5 per cent at 649 nm and a spectral slope value of about 17 per cent/(100 nm) at 50° phase angle. Similar to the whole nucleus, the Abydos site also shows phase reddening but with lower coefficients than other regions of the comet, which may imply a thinner cover of microscopically rough regolith compared to other areas. Seasonal variations, as already noticed for the whole nucleus, were also observed. We identified some potential morphological changes near the landing site implying a total mass-loss of (4.7–7.0) × 105 kg. Small spots ranging from 0.1 to 27 m2 were observed close to Abydos before and after perihelion. Their estimated water ice abundance reaches 30–40 per cent locally, indicating fresh exposures of volatiles. Their lifetime ranges from a few hours up to three months for two pre-perihelion spots. The Abydos surroundings showed a low level of cometary activity compared to other regions of the nucleus. Only a few jets are reported originating nearby Abydos, including a bright outburst that lasted for about 1 h.

scholarly journals Time evolution of dust deposits in the Hapi region of comet 67P/Churyumov-Gerasimenko

2020 ◽  
Vol 636 ◽  
pp. A91
Author(s):  
P. Cambianica ◽  
M. Fulle ◽  
G. Cremonese ◽  
E. Simioni ◽  
G. Naletto ◽  
...  
Keyword(s):  
Time Evolution ◽  
Southern Hemisphere ◽  
Loss Rate ◽  
Dust Layer ◽  
Water Ice ◽  
Narrow Angle ◽  
Dust Deposit ◽  
Erosion And Accretion ◽  
Comet 67P ◽  
Cometary Activity

Aims. We provide a measurement of the seasonal evolution of the dust deposit erosion and accretion in the Hapi region of comet 67P/Churyumov-Gerasimenko with a vertical accuracy of 0.2–0.9 m. Methods. We used OSIRIS Narrow Angle Camera images with a spatial scale of lower than 1.30 m px−1 and developed a tool to monitor the time evolution of 22 boulder heights with respect to the surrounding dust deposit. The tool is based on the measurement of the shadow length projected by the boulder on the surrounding pebble deposit. Assuming the position of the boulders does not change during the observational period, boulder height variations provide an indication of how the thickness of the surrounding dust layer varies over time through erosion and accretion phenomena. Results. We measured an erosion of the dust deposit of 1.7 ± 0.2 m during the inbound orbit until 12 December, 2014. This value nearly balances the fallout from the southern hemisphere during perihelion cometary activity. During the perihelion phase, the dust deposit then increased by 1.4 ± 0.8 m. This is interpreted as a direct measurement of the fallout thickness. By comparing the erosion rate and dust volume loss rate at the Hapi region measured in the coma, the fallout represents ~96% in volume of the ejecta. The amount of the eroded pristine material from the southern hemisphere, together with its subsequent transport and fallout on the nucleus, led us to discuss the pristine water ice abundance in comet 67P. We determine that the refractory-to-ice mass ratio ranges from 6 to 110 in the perihelion-eroded pristine nucleus, providing a pristine ice mass fraction of (8 ± 7)% in mass.

scholarly journals Rosetta/OSIRIS observations of the 67P nucleus during the April 2016 flyby: high-resolution spectrophotometry

2019 ◽  
Vol 630 ◽  
pp. A9 ◽  
Author(s):  
C. Feller ◽  
S. Fornasier ◽  
S. Ferrari ◽  
P. H. Hasselmann ◽  
A. Barucci ◽  
...  
Keyword(s):  
High Resolution ◽  
Source Region ◽  
Spectral Slope ◽  
Shape Model ◽  
Water Ice ◽  
Narrow Angle ◽  
Average Reflectance ◽  
The One ◽  
Phase Angles ◽  
Comet 67P

Context. From August 2014 to September 2016, the Rosetta spacecraft followed comet 67P/Churyumov–Gerasimenko along its orbit. After the comet passed perihelion, Rosetta performed a flyby manoeuvre over the Imhotep–Khepry transition in April 2016. The OSIRIS/Narrow-Angle-Camera (NAC) acquired 112 observations with mainly three broadband filters (centered at 480, 649, and 743 nm) at a resolution of up to 0.53 m/px and for phase angles between 0.095° and 62°. Aims. We have investigated the morphological and spectrophotometrical properties of this area using the OSIRIS/NAC high-resolution observations. Methods. We assembled the observations into coregistered color cubes. Using a 3D shape model, we produced the illumination conditions and georeference for each observation. We mapped the observations of the transition to investigate its geomorphology. Observations were photometrically corrected using the Lommel–Seeliger disk law. Spectrophotometric analyses were performed on the coregistered color cubes. These data were used to estimate the local phase reddening. Results. The Imhotep–Khepry transition hosts numerous and varied types of terrains and features. We observe an association between a feature’s nature, its reflectance, and its spectral slopes. Fine material deposits exhibit an average reflectance and spectral slope, while terrains with diamictons, consolidated material, degraded outcrops, or features such as somber boulders present a lower-than-average reflectance and higher-than-average spectral slope. Bright surfaces present here a spectral behavior consistent with terrains enriched in water-ice. We find a phase-reddening slope of 0.064 ± 0.001%/100 nm/° at 2.7 au outbound, similar to the one obtained at 2.3 au inbound during the February 2015 flyby. Conclusions. Identified as the source region of multiple jets and a host of water-ice material, the Imhotep–Khepry transition appeared in April 2016, close to the frost line, to further harbor several potential locations with exposed water-ice material among its numerous different morphological terrain units.

scholarly journals Surface evolution of the Anhur region on comet 67P/Churyumov-Gerasimenko from high-resolution OSIRIS images

2019 ◽  
Vol 630 ◽  
pp. A13 ◽  
Author(s):  
S. Fornasier ◽  
C. Feller ◽  
P. H. Hasselmann ◽  
M. A. Barucci ◽  
J. Sunshine ◽  
...  
Keyword(s):  
High Resolution ◽  
Imaging System ◽  
Morphological Changes ◽  
Surface Evolution ◽  
Water Ice ◽  
Narrow Angle ◽  
Highly Active ◽  
Rosetta Mission ◽  
High Resolution Images ◽  
Comet 67P

Context. The southern hemisphere of comet 67P/Churyumov-Gerasimenko (67P) became observable by the Rosetta mission in March 2015, a few months before cometary southern vernal equinox. The Anhur region in the southern part of the comet’s larger lobe was found to be highly eroded, enriched in volatiles, and highly active. Aims. We analyze high-resolution images of the Anhur region pre- and post-perihelion acquired by the OSIRIS imaging system on board the Rosetta mission. The Narrow Angle Camera is particularly useful for studying the evolution in Anhur in terms of morphological changes and color variations. Methods. Radiance factor images processed by the OSIRIS pipeline were coregistered, reprojected onto the 3D shape model of the comet, and corrected for the illumination conditions. Results. We find a number of morphological changes in the Anhur region that are related to formation of new scarps; removal of dust coatings; localized resurfacing in some areas, including boulders displacements; and vanishing structures, which implies localized mass loss that we estimate to be higher than 50 million kg. The strongest changes took place in and nearby the Anhur canyon-like structure, where significant dust cover was removed, an entire structure vanished, and many boulders were rearranged. All such changes are potentially associated with one of the most intense outbursts registered by Rosetta during its observations, which occurred one day before perihelion passage. Moreover, in the niche at the foot of a new observed scarp, we also see evidence of water ice exposure that persisted for at least six months. The abundance of water ice, evaluated from a linear mixing model, is relatively high (>20%). Our results confirm that the Anhur region is volatile-rich and probably is the area on 67P with the most pristine exposures near perihelion.

scholarly journals Degradable dual co-electrospun polyester based nonwovens for guided tissue regeneration

2020 ◽  
Vol 6 (3) ◽  
pp. 168-171
Author(s):  
Stefan Oschatz ◽  
Thomas Reske ◽  
Klaus-Peter Schmitz ◽  
Sabine Illner ◽  
Jana Markhoff ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Composite Materials ◽  
Tissue Regeneration ◽  
Total Mass ◽  
Morphological Changes ◽  
Guided Tissue Regeneration ◽  
In Vitro Degradation ◽  
Total Mass Loss

AbstractIn this study, initial experiments are presented regarding the suitability of polyester based nonwoven composite materials for guided tissue regeneration based on degradation. The in vitro degradation of poly(lactic-coglycolic acid)/polydioxanone and polycaprolactone/ polydioxanone mats has been performed under accelerated condition in alkaline glycine buffer at 50 °C for 21 days. The degradation of the materials has been characterized regarding total mass loss and macroscopic morphological changes, as well as determination of the molecular weight degradation via GPC experiments.

scholarly journals Some Remarks on the Liberation of Gases from Cometary Nuclei

1972 ◽  
Vol 45 ◽  
pp. 260-264
Author(s):  
B. Yu. Levin
Keyword(s):  
Total Mass ◽  
Physical Theory ◽  
Point Of View ◽  
Reactive Force ◽  
Cometary Nuclei ◽  
Water Ice ◽  
Total Mass Loss ◽  
Order Of Magnitude ◽  
Perihelion Passage ◽  
Nongravitational Forces

According to modern data water ice is the main constituent of cometary nuclei. The rate of its evaporation determines the rate of liberation of other constituents, including those that determine the photometric properties of comets. The estimates of the total mass loss per perihelion passage seem to give values about one order of magnitude smaller than those necessary to explain the nongravitational forces as due to the reactive force of material leaving the nuclei. Thus the conventional explanation of the nongravitational forces deserves further study from the point of view of the physical theory of comets.

scholarly journals Morphological Changes and Component Characterization of Coffee Silverskin

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 4914
Author(s):  
Xia Wang ◽  
De-Fu Hong ◽  
Gui-Lin Hu ◽  
Zhong-Rong Li ◽  
Xing-Rong Peng ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Morphological Changes ◽  
2D Nmr ◽  
Coffee Silverskin ◽  
Before And After ◽  
2D Nmr Spectra ◽  
Main Components ◽  
First Time ◽  
Non Destructive

Nuclear magnetic resonance (NMR) spectroscopy was used for the qualitative and quantitative analysis of aqueous extracts of unroasted and roasted coffee silverskin (CS). Twenty compounds were identified from 1D and 2D NMR spectra, including caffeine, chlorogenic acid (CGA), trigonelline, fructose, glucose, sucrose, etc. For the first time, the presence of trigonelline was detected in CS. Results of the quantitative analysis showed that the total amount of the main components after roasting was reduced by 45.6% compared with values before roasting. Sugars in the water extracts were the main components in CS, and fructose was the most abundant sugar, its relative content accounting for 38.7% and 38.4% in unroasted and roasted CS, respectively. Moreover, 1D NMR combined with 2D NMR technology shows application prospects in the rapid, non-destructive detection of CS. In addition, it was observed by optical microscopy and scanning electron microscopy (SEM) that the morphology of CS changed obviously before and after roasting.

An Electron Microscope Study of Interdiffusion and Compound Formation in Ta-Au Thin Films

1973 ◽  
Vol 31 ◽  
pp. 32-33 ◽  
Author(s):  
T. C. Tisone ◽  
S. Lau
Keyword(s):  
Electron Microscope ◽  
Electron Microscope Study ◽  
Thermally Grown Oxide ◽  
Ion Milling ◽  
Compound Formation ◽  
Technology Application ◽  
Transmission Electron ◽  
Before And After ◽  
Au Thin Films

In a study of the properties of a Ta-Au metallization system for thin film technology application, the interdiffusion between Ta(bcc)-Au, βTa-Au and Ta2M-Au films was studied. Considered here is a discussion of the use of the transmission electron microscope(TEM) in the identification of phases formed and characterization of the film microstructures before and after annealing.The films were deposited by sputtering onto silicon wafers with 5000 Å of thermally grown oxide. The film thicknesses were 2000 Å of Ta and 2000 Å of Au. Samples for TEM observation were prepared by ultrasonically cutting 3mm disks from the wafers. The disks were first chemically etched from the silicon side using a HNO3 :HF(19:5) solution followed by ion milling to perforation of the Au side.

Thermal characterization of ABS-Graphene blended three dimensional printed functional prototypes for electro chemical energy storage

2018 ◽  
Vol 1 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Kamaljit Singh Boparai ◽  
Rupinder Singh
Keyword(s):  
Energy Storage ◽  
Structural Changes ◽  
Fused Deposition Modeling ◽  
Morphological Changes ◽  
Three Dimensional ◽  
Thermal Characterization ◽  
Chemical Energy ◽  
Flow Index ◽  
Fused Deposition

This study highlights the thermal characterization of ABS-Graphene blended three dimensional (3D) printed functional prototypes by fused deposition modeling (FDM) process. These functional prototypes have some applications as electro-chemical energy storage devices (EESD). Initially, the suitability of ABS-Graphene composite material for FDM applications has been examined by melt flow index (MFI) test. After establishing MFI, the feedstock filament for FDM has been prepared by an extrusion process. The fabricated filament has been used for printing 3D functional prototypes for printing of in-house EESD. The differential scanning calorimeter (DSC) analysis was conducted to understand the effect on glass transition temperature with the inclusion of Graphene (Gr) particles. It has been observed that the reinforced Gr particles act as a thermal reservoir (sink) and enhances its thermal/electrical conductivity. Also, FT-IR spectra realized the structural changes with the inclusion of Gr in ABS matrix. The results are supported by scanning electron microscopy (SEM) based micrographs for understanding the morphological changes.

Fullerene-like Nanoparticles of WS2 as a Promising Protection from Erosive Wear of Gun Bore Nozzles

2020 ◽  
Vol 16 (1) ◽  
pp. 62-70 ◽  
Author(s):  
Narimane Rezgui ◽  
Danica Simić ◽  
Choayb Boulahbal ◽  
Dejan Micković
Keyword(s):  
Mass Loss ◽  
Solid Lubricant ◽  
Erosive Wear ◽  
Mechanical Resistance ◽  
Protective Function ◽  
Protective Layers ◽  
Total Mass Loss ◽  
Mass Losses ◽  
Before And After ◽  
Tube Life

Background: Erosive wear causes increase in the bore diameter of firearms barrels and nozzles. Most responsible factors for this erosion are friction and heat generated during the shot. Protection from erosive wear is very important for gun tube life cycle, and various protection methods are used: adding phlegmatizers in gunpowder composition or applying protective layers on the gun bore inner surface. Objective: In this research, a possibility is examined to protect the surface of a nozzle exposed to gunpowder erosion applying a layer of tungsten disulfide fullerene-like nanoparticles, IF-WS2, known as outstanding solid lubricant of a great mechanical resistance. Methods: Nanoparticles on the nozzle surface before and after the gunfire tests were observed using scanning electron microscopy/energy dispersive X-ray spectroscopy. Gunfire tests were performed on designed erosion device. Temperatures in the defined position near the affected surface were measured with thermocouples and compared for the nozzles with and without nanoprotection, as well as the nozzle mass loss after each round. Results: For the sample with IF-WS2 lower temperatures after firing and lower mass losses were observed. Mass loss after first round was 25.6% lower for the sample with protective nanoparticles layer, and the total mass loss was about 5% lower after five rounds. After the first round the nozzle without IF-WS2 was heated up to a temperature which was for 150.8°C higher than the nozzle with IF-WS2. Conclusion: Protective function of IF-WS2 is the most pronounced for the first round. The observed results encourage its further application in firearms gun bores protection.

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