Thermally altered subsurface material of asteroid (162173) Ryugu

2021 ◽  
Author(s):  
K. Kitazato ◽  
R. E. Milliken ◽  
T. Iwata ◽  
M. Abe ◽  
M. Ohtake ◽  
...  
Keyword(s):  
Subsurface Material

scholarly journals The Variation of Riverbed Material due to Tropical Storms in Shi-Wen River, Taiwan

2014 ◽  
Vol 2014 ◽  
pp. 1-12
Author(s):  
Chin-Ping Lin ◽  
Yu-Min Wang ◽  
Samkele S. Tfwala ◽  
Ching-Nuo Chen
Keyword(s):  
Grain Size ◽  
Geometric Mean ◽  
Size Variation ◽  
Annual Rainfall ◽  
Geometric Standard Deviation ◽  
Roughness Coefficient ◽  
Bed Form ◽  
Subsurface Material ◽  
Typhoon Season ◽  
Bed Material

Taiwan, because of its location, is a flood prone region and is characterised by typhoons which brings about two-thirds to three quarters of the annual rainfall amount. Consequently, enormous flows result in rivers and entrain some fractions of the grains that constitute the riverbed. Hence, the purpose of the study is to quantify the impacts of these enormous flows on the distribution of grain size in riverbeds. The characteristics of riverbed material prior to and after the typhoon season are compared in Shi-Wen River located at southern Taiwan. These include grain size variation, bimodality, and roughness coefficient. A decrease (65%) and increase (50%) in geometric mean size of grains were observed for subsurface and surface bed material, respectively. Geometric standard deviation decreased in all sites after typhoon. Subsurface material was bimodal prior to typhoons and polymodal after. For surface material, modal class is in the gravel class, while after typhoons it shifts towards cobble class. The reduction in geometric mean resulted to a decrease in roughness coefficient by up to 30%. Finally, the relationship of Shields and Froude numbers are studied and a change in the bed form to antidunes and transition form is observed, respectively.

Characterisation of the Rietvlei wetland: Implications for spatial distribution of groundwater recharge

2019 ◽  
Vol 122 (3) ◽  
pp. 369-378 ◽  
Author(s):  
G. Mahed ◽  
N. Gariremo ◽  
S. Lehlohonolo ◽  
R. Campbell ◽  
E. Swartbooi
Keyword(s):  
Spatial Distribution ◽  
Groundwater Recharge ◽  
Silty Sand ◽  
Factors Affecting ◽  
Shallow Wells ◽  
Subsurface Material ◽  
Dug Wells ◽  
Water Table Fluctuation Method ◽  
Fluctuation Method ◽  
Recharge Rates

Abstract The current study aimed to determine the factors affecting groundwater recharge and its spatial distribution in the Rietvlei wetland located near Cape Town. To achieve this, the subsurface material was logged during the construction of eight shallow wells, complimented with field observations, and surveying the dug wells. The water stemming from these wells was sampled and analysed for Oxygen 18 and Deuterium to determine the source of groundwater in Rietvlei wetland. Downhole salinity logs of the wells were also undertaken, and rainfall samples were analysed for the stable isotopes. Isotopic results indicate that groundwater stems from rainfall, with the exception of Well 8 which has been influenced by the river due to its proximity to the surface water body. Additionally, results obtained indicate a distinct relationship between elevation and soil structure. Shallow profiles were mainly dominated by medium to fine sands, silty sand, and clay. Using the water table fluctuation method, this was found to have a direct impact on the spatial distribution of groundwater recharge on an event basis. It was therefore concluded that both lithology and topography have a direct effect on recharge rates and water quality.

scholarly journals Asteroid–comet continuum objects in the solar system

2017 ◽  
Vol 375 (2097) ◽  
pp. 20160259 ◽  
Author(s):  
Henry H. Hsieh
Keyword(s):  
Solar System ◽  
Royal Society ◽  
Sample Material ◽  
Society Meeting ◽  
Solar System Objects ◽  
Subsurface Material ◽  
Solar System Bodies ◽  
Dynamical Properties ◽  
Continuous Range ◽  
Asteroids And Comets

In this review presented at the Royal Society meeting, ‘Cometary science after Rosetta’, I present an overview of studies of small solar system objects that exhibit properties of both asteroids and comets (with a focus on so-called active asteroids). Sometimes referred to as ‘transition objects’, these bodies are perhaps more appropriately described as ‘continuum objects’, to reflect the notion that rather than necessarily representing actual transitional evolutionary states between asteroids and comets, they simply belong to the general population of small solar system bodies that happen to exhibit a continuous range of observational, physical and dynamical properties. Continuum objects are intriguing because they possess many of the properties that make classical comets interesting to study (e.g. relatively primitive compositions, ejection of surface and subsurface material into space where it can be more easily studied, and orbital properties that allow us to sample material from distant parts of the solar system that would otherwise be inaccessible), while allowing us to study regions of the solar system that are not sampled by classical comets. This article is part of the themed issue ‘Cometary science after Rosetta’.

The Effect of Tribofilm Formation and Humidity on the Friction and Wear Properties of Ceramic Materials

1992 ◽  
Vol 114 (1) ◽  
pp. 131-140 ◽  
Author(s):  
K. Komvopoulos ◽  
H. Li
Keyword(s):  
Steady State ◽  
Wear Debris ◽  
Friction And Wear ◽  
Ceramic Materials ◽  
Composition Analysis ◽  
Wear Properties ◽  
Qualitative Comparison ◽  
Wear Rates ◽  
Subsurface Material ◽  
Friction And Wear Properties

The processes of tribofilm formation and disruption and the predominant tribo-mechanisms of unlubricated ceramic materials were investigated experimentally. Sliding experiments in humidity controlled atmospheres revealed that the formation of interfacial tribofilms significantly affects the steady-state friction and wear properties of ceramics. Scanning electron microscopy and various composition analysis techniques demonstrated that although tribochemical reactions might occur, the principal mechanisms of tribofilm formation were the generation, agglomeration, and compaction of fine wear debris produced from both sliding surfaces. The tribofilms exhibited different tribological characteristics, depending on their elemental compositions and the humidity. For all the ceramic pairs tested, the steady-state coefficients of friction decreased with relative humidity. In contrast to the conventional fracture toughness approach, surface profilometry and microscopy studies showed that the highest wear rates were encountered with the toughest ceramic. Plowing grooves parallel to the direction of sliding, fine wear debris of round and cylindrical shapes, microcracking, and localized delamination of the tribofilms were identified. Microscopic observations suggested that damage of the subsurface material adjacent to the interface of the tribofilms was immeasurable. Qualitative comparison of the topographical features of worn surfaces indicated that, depending on the humidity and the type of ceramic, microplasticity, microfracture, and delamination of the tribofilms were the prevailing steady-state tribomechanisms.

scholarly journals Interpretasi Lingkungan Pengendapan Formasi Batuan Menggunakan Analisis Elektrofasies di Lokasi Tapak Puspiptek Serpong

EKSPLORIUM ◽  
2017 ◽  
Vol 38 (1) ◽  
pp. 29
Author(s):  
Heri Syaeful ◽  
Adi Gunawan Muhammad
Keyword(s):  
Depositional Environment ◽  
Gamma Ray ◽  
River System ◽  
Shape Variation ◽  
Point Bar ◽  
Meandering River ◽  
The North ◽  
Rock Formations ◽  
Subsurface Material ◽  
Crevasse Splay

ABSTRAKKegiatan karakterisasi material bawah permukaan penyusun pondasi tapak merupakan bagian dari studi tapak instalasi nuklir. Karakterisasi dilakukan dengan berbagai metode, diantaranya pemahaman tentang sistem pengendapan formasi batuan. Sebagai bagian dari metode interpretasi lingkungan pengendapan, analisis pemodelan fasies berdasarkan elektrofasies memberikan informasi yang cepat mengenai sistem pengendapan suatu formasi batuan. Metodologi yang digunakan adalah dengan interpretrasi log sinar gamma (log GR) menggunakan korelasi relatif antara variasi bentuk log dan fasies sedimentasi. Berdasarkan analisis diketahui Formasi Bojongmanik terbentuk pada lingkungan marine-lagoonal dengan pengaruh gelombang sangat rendah. Log GR yang menunjukan bentuk funnel, bergerigi dan simetris, mengindikasikan fasies shoreface, lagoon, dan tidal point bar. Arah sedimentasi, cekungan, dan suplai pada pengendapan sedimen Formasi Bojongmanik diinterpretasikan relatif ke utara. Formasi Serpong diendapkan pada sistem sungai bermeander dan tersusun atas endapan point bar, crevasse splay dan floodplain. Hasil analisis ini diharapkan dapat menjadi panduan dalam analisis lanjutan terkait karakterisasi material pondasi. ABSTRACTThe activity of subsurface material composing site foundation characterization is part of nuclear installation siting study. Characterization conducted by several methods, such as understanding the depositional environment of rock formations. As a segment of depositional environment interpretation method, facies model analysis based on electrofacies provides quicker information on depositional system of rock formation. Methodology applied is gamma ray log (log GR) interpretation using relative correlation between log shape variation and sedimentation facies. Based on the analysis, Bojongmanik Formation was deposited on marine-lagoonal environment with very low wave influence. Log GR that shows shape of funnel, serrated, and symmetry, indicate shoreface, lagoon, and tidal point bar facies. The direction of sedimentation, basin, and supply of Bojongmanik Formation interpreted relatively to the north. Serpong Formation deposited on meandering river system, and composed of point bar deposit, crevasse splay, and floodplain deposit. The result of analysis is expected to be guidance in further analysis related to the characterization of foundation materials.

Biodegradation of Btex in Subsurface Materials Contaminated with Gasoline: Granger, Indiana

1990 ◽  
Vol 22 (6) ◽  
pp. 53-62 ◽  
Author(s):  
J. M. Thomas ◽  
V. R. Gordy ◽  
S. Fiorenza ◽  
C. H. Ward
Keyword(s):  
Hydrogen Peroxide ◽  
Liquid Scintillation ◽  
Scintillation Counting ◽  
Unleaded Gasoline ◽  
Subsurface Material ◽  
Benzene Toluene ◽  
Contaminated Area ◽  
Microbial Numbers ◽  
Core Materials

The microbial ecology and potential for biodegradation of benzene, toluene, ethylbenzene, and o- and m-xylene (BTEX) in core materials contaminated with unleaded gasoline were investigated. The site studied was unique because a portion of the contaminated area was biostimulated in a demonstration of the use of hydrogen peroxide as an oxygen source in in situ biorestoration. Two years after termination of the field demonstration, core samples were collected from uncontaminated, contaminated, and biostimulated areas at the site and analyzed for inorganic nutrients, microbial numbers, mineralization potential of glucose, benzene, and toluene using liquid scintillation counting, and biotransformation of BTEX using gas chromatography. The results indicated that the subsurface microflora at the site was active and capable of degrading a variety of compounds. Microbial numbers and contaminant biodegradation potential in samples from the biostimulated area were greater than in uncontaminated and contaminated zones. Toluene, ethylbenzene, and m-xylene were removed in all core materials, whereas o-xylene was recalcitrant. Mineralization experiments indicated that toluene was mineralized to a greater extent than benzene. These data indicated that the biodegradation potential of the subsurface material from the biostimulated zone, which still contained residual hydrocarbon, remained enhanced for at least 2 yr after the in situ biorestoration process had been terminated.

Characterization of the craters’ surface at Ryugu using NIR spectroscopy

2021 ◽  
Author(s):  
Lucie Riu ◽  
Cédric Pilorget ◽  
Ralph Milliken ◽  
Kohei Kitazato ◽  
Tomoki Nakamura ◽  
...  
Keyword(s):  
Near Infrared ◽  
Spectral Characteristics ◽  
Solar Heating ◽  
Absorption Feature ◽  
Space Weathering ◽  
Near Surface ◽  
Exposure Age ◽  
Reflectance Factor ◽  
Subsurface Material ◽  
Band Depth

<div> <p>Asteroid Ryugu was observed up close for almost a year and a half by the instruments on-board the Japanese Aerospace eXploration Agency (JAXA) Hayabusa2 spacecraft. It has been shown that in the near-infrared wavelength ranges, the asteroid exhibits relatively homogeneous spectral characteristics: including a very low reflectance factor, a slight red slope towards longer wavelengths, and a narrow and weak absorption feature centered at 2.72 <span>μ</span>m. Numerous craters have been identified at the surface of Ryugu. These features provide good candidates for studying more recently exposed near-surface material to further assess potential spectral/compositional heterogeneities of Ryugu. We present here the results of a spectral survey of all previously identified and referenced craters (Hirata et al. 2020) based on reflectance data acquired by the NIRS3 spectrometer. Globally, we find that the spectral properties inside and outside of craters are very similar, indicating that subsurface material is either compositionally similar to material at the surface that has a longer exposure age or that material at Ryugu’s optical surface is spectrally altered over relatively short timescales by external factors such as space weathering. The 2.72 <span>μ</span>m band depth, present on the overall surface, exhibits a slight anti-correlation with the reflectance factor selected at 2 <span>μ</span>m, which could indicate different surface properties (<em>e.g.</em>, grain size and/or porosity) or different alteration processes (<em>e.g.</em>, space weathering, shock metamorphism and/or solar heating). We identified four different spectral classes based on their reflectance factor at 2 <span>μ</span>m and 2.72 <span>μ</span>m absorption strength. The most commonly spectral behavior associated with crater floors, is defined by a slightly lower reflectance at 2 <span>μ</span>m and deeper band depth. These spectral characteristics are similar to those of subsurface material excavated by the Hayabusa2 small carry-on impactor (SCI) experiment, suggesting these spectral characteristics may represent materials with a younger surface exposure age. Conversely, these materials may have experienced significant solar heating and desiccation to form finer grains that subsequently migrated towards and preferentially accumulated in areas of low geopotential, such as craters floors. Detailed analyses of the returned samples of Ryugu that are now being investigated at the curation facility in ISAS will allow for further testing of these formation and alteration hypotheses.<span> </span></p> </div>

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