Critical crater diameter and asteroid impact seismology

AbstractInadvertent Er:YAG laser irradiation occurs in dentistry and may harm restorative materials in teeth. The aim of this in vitro study was to quantify Er:YAG laser-induced damage to a nanohybrid composite in simulated clinical scenarios for inadvertent direct and indirect (reflection) laser irradiation. The simulation was performed by varying the output energy (OE;direct˃indirect) reaching the specimen and the operating distance (OD;direct˂indirect). Composite specimens were irradiated by an Er:YAG laser. The ablation threshold was determined and clinically relevant parameters were applied (n = 6 for each OE/OD combination) for direct (OE: 570 mJ/OD: 10 mm, OE: 190 mJ/OD: 10 mm) and indirect irradiation (OE: 466 mJ/OD: 15 mm, OE: 57 mJ/OD: 15 mm, OE: 155 mJ/OD: 15 mm, OE: 19 mJ/OD: 15 mm). The extent of damage in the form of craters was evaluated using a laser scanning microscope (LSM) and a conventional light microscope (LM). The ablation threshold was determined to be 2.6 J/cm2. The crater diameter showed the highest value (LM: 1075 ± 18 µm/LSM: 1082 ± 17 µm) for indirect irradiation (reflectant:dental mirror) (OE: 466 mJ/OD: 15 mm). The crater depth showed the highest and comparable value for direct (OE: 570 mJ/OD: 10 mm; LSM: 89 ± 2 µm) and indirect irradiation (OE: 466 mJ/OD: 15 mm; LSM: 90 ± 4 µm). For each OD, the crater diameter, depth, and volume increased with higher laser fluence. However, the OD—and thus the laser spot diameter—also had an enlarging effect. Thus, indirect irradiation (reflectant:dental mirror) with only 47% of the laser fluence of direct irradiation led to a larger diameter and a comparable depth. The three-dimensional extent of the crater was large enough to cause roughening, which may lead to plaque accumulation and encourage caries, gingivitis, and periodontitis under clinical conditions. Clinicians should be aware that reflected irradiation can still create such craters.

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Jadeite and its relatives: fake news or a real tool to constrain shock conditions?

10.21203/rs.3.rs-575896/v1 ◽

2021 ◽

Author(s):

Ioannis Baziotis ◽

Stamatios Xydous ◽

Angeliki Papoutsa ◽

Jinping Hu ◽

Chi Ma ◽

...

Keyword(s):

First Principles ◽

Chemical Space ◽

Formula Unit ◽

First Principles Calculations ◽

Fake News ◽

State Transformation ◽

Solid State Transformation ◽

Crater Diameter ◽

Grain Sizes ◽

New Occurrences

Abstract Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Sometimes, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently identify jadeite and distinguish it from related species. Based on chemical and spectral analysis of three new occurrences, complemented by first-principles calculations, we show that related pyroxenes in the chemical space (Na)M2(Al)M1(Si2)TO6 – (Ca)M2(Al)M1(AlSi)TO6 – (□)M2(Si)M1(Si2)TO6 with up to 2.25 atoms Si per formula unit have spectral features similar to jadeite. However, their distinct stability fields and synthesis pathways, considered together with textural constraints, have specific implications for precursor phases and estimates of impactor size, encounter velocity, and crater diameter. A reassessment of reported jadeite occurrences puts in a new light many previous conclusions about the shock histories preserved in particular meteorites.

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The mass impacts on chemosynthetic primary producers: potential implications on anammox communities and their consequences

International Journal of Astrobiology ◽

10.1017/s1473550418000411 ◽

2018 ◽

Vol 18 (05) ◽

pp. 440-444

Author(s):

Noel Pérez ◽

Jorge Luis Velazco-Vargas ◽

Osmel Martin ◽

Rolando Cardenas ◽

Jesús Martínez-Frías

Keyword(s):

Water Column ◽

Deposition Rate ◽

Extreme Case ◽

Chemical Compounds ◽

Global Scale ◽

Biogeochemical Cycle ◽

Potential Influence ◽

Asteroid Impact ◽

Global Cooling ◽

The Impact

AbstractThe potential of a mass asteroid impact on Earth to disturb the chemosynthetic communities at global scale is discussed. Special emphasis is made on the potential influence on anammox communities and their implications in the nitrogen biogeochemical cycle. According to our preliminary estimates, anammox communities could be seriously affected as a consequence of global cooling and the large process of acidification usually associated with the occurrence of this kind of event. The scale of affectations could vary in a scenario like the Chicxulub as a function of the amount of soot, depth of the water column and the deposition rate for sulphates assumed in each case. The most severe affectations take place where the amount of soot and sulphates produced during the event is higher and the scale of time of settlements for sulphates is short, of the order of 10 h. In this extreme case, the activity of anammox is considerably reduced, a condition that may persist for several years after the impact. Furthermore, the impact of high levels of other chemical compounds like sulphates and nitrates associated with the occurrence of this kind of event are also discussed.

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Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning

Handbook of Cosmic Hazards and Planetary Defense ◽

10.1007/978-3-319-03952-7_42 ◽

2015 ◽

pp. 569-581 ◽

Cited By ~ 1

Author(s):

Harold J. Reitsema ◽

Edward T. Lu

Keyword(s):

Space Telescope ◽

Asteroid Impact

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Numerical study of asteroid impact on the earth’s surface with allowance for gravitation and radiation energy transfer

Journal of Engineering Physics and Thermophysics ◽

10.1007/bf02699461 ◽

1999 ◽

Vol 72 (6) ◽

pp. 1131-1141

Author(s):

G. S. Romanov ◽

A. S. Smetannikov

Keyword(s):

Energy Transfer ◽

Numerical Study ◽

Radiation Energy ◽

Asteroid Impact

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Friction Characteristics with Pin-on-Disc Friction Test on Microstructured Surface Using Whirling Electrical Discharge Texturing

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1017.417 ◽

2014 ◽

Vol 1017 ◽

pp. 417-422

Author(s):

Vitchuda Lertphokanont ◽

Takayuki Sato ◽

Masahiro Oi ◽

Minoru Ota ◽

Keishi Yamaguchi ◽

...

Keyword(s):

Friction Coefficient ◽

Electrical Discharge ◽

Area Ratio ◽

Mixed Lubrication ◽

Optimal Conditions ◽

Friction Test ◽

Crater Diameter ◽

Microstructured Surface ◽

Pin On Disc ◽

Lubrication Condition

A microstructured surface was created on a steel surface by whirling electrical discharge texturing (WEDT) since it was considered that the microstructures could act as lubricant reservoirs to assist the formation of a lubricating film, resulting in reduced friction. In this study, friction tests under engine oil were carried out over a range of loads and sliding speeds. In addition, the surface characteristics of the microstructured surface were also investigated to optimize the friction characteristics of the textured surface through pin-on-disc friction tests. It was found that under the mixed lubrication condition near the boundary condition, textured surfaces with texture-area ratio of approximately 6% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient. However, a texture-area ratio of approximately 4% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient under the mixed lubrication condition near the elastohydrodynamic lubrication condition. It was considered that when the normal load decreased, the lubrication region changed from the mixed lubrication condition to the hydrodynamic lubrication condition, which meant that the actual contact surface area decreased. The decrease in the actual contact surface area with decreasing texture-area ratio led to a reduction in the friction coefficient. Finally, it was clarified that the friction coefficient was reduced under the optimized conditions of the microstructured surface through a pin-on-disc friction test.

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