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Topic Review
Leo
Leo, the Lion, is one of the zodiac constellations, known for its distinctive shape resembling a lion's mane and head. It is one of the oldest recognized constellations, dating back to ancient civilizations such as the Mesopotamians, Egyptians, and Greeks. Leo is home to several bright stars and notable deep-sky objects.
  • 411
  • 15 Mar 2024
Topic Review
Osmium-172
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 411
  • 19 Oct 2022
Topic Review
Laser Interference Lithography
Laser interference lithography (LIL) is a technique that allows for the simple, flexible, and rapid fabrication of high-resolution periodic structures over large areas without the use of masks. Different interference conditions can produce a wide range of light fields. When an LIL system is used to expose the substrate, a variety of periodic textured structures, such as periodic nanoparticles, dot arrays, hole arrays, and stripes, can be produced. The LIL technique can be used not only on flat substrates, but also on curved or partially curved substrates, taking advantage of the large depth of focus.
  • 410
  • 26 Jun 2023
Topic Review
Electron Elastic-Collisions with Multi-Electron Atoms and Fullerene Molecules
The Regge pole-calculated low-energy electron elastic total cross sections (TCSs) of complex heavy multi-electron systems are characterized generally by dramatically sharp resonances manifesting negative-ion formation. These TCSs yield directly the anionic binding energies (BEs), the shape resonances (SRs) and the Ramsauer–Townsend(R-T) minima. From the TCSs unambiguous and reliable ground, metastable and excited states negative-ion BEs of the formed anions during the collisions are extracted and compared with the measured and/or calculated electron affinities (EAs) of the atoms and fullerene molecules. The novelty and generality of the Regge pole approach is in the extraction of rigorous negative-ion BEs from the TCSs, without any assistance whatsoever from either experiment or any other theory. The EA provides a stringent test of theoretical calculations when their results are compared with those from reliable measurements. For ground states collisions, the Regge pole-calculated negative ion BEs correspond to the challenging to calculate theoretically EAs, yielding outstanding agreement with the standard measured EAs for Au, Pt and the highly radioactive At atoms as well as for the C60 and C70 fullerenes.
  • 409
  • 12 Aug 2022
Topic Review
Centaurus
Centaurus, a prominent southern hemisphere constellation, is one of the largest and most recognizable constellations in the night sky. Named after the centaur Chiron from Greek mythology, Centaurus features the bright Alpha Centauri system, one of the closest star systems to Earth.
  • 408
  • 29 Feb 2024
Topic Review
Europa Thermal Emission Imaging System
The Europa Thermal Emission Imaging System (E-THEMIS) instrument is designed to scan the surface of Europa and identify areas of geologically recent resurfacing through the detection of subtle thermal anomalies. This 'heat detector' will provide high spatial resolution, multi-spectral thermal imaging of Europa to help detect active sites such as outflows and plumes. E-THEMIS will be launched on board the planned Europa Clipper astrobiology mission to Jupiter's moon Europa in 2025. The E-THEMIS uses technology inherited from the THEMIS camera flown on board the 2001 Mars Odyssey orbiter, and the OSIRIS-REx OTES instruments.
  • 407
  • 18 Oct 2022
Topic Review
On Sizes and Distances
On Sizes and Distances (of the Sun and Moon) (Περὶ μεγεθῶν καὶ ἀποστημάτων [ἡλίου καὶ σελήνης], Peri megethon kai apostematon) is a text by the ancient Greek astronomer Hipparchus. It is not extant, but some of its contents have been preserved in the works of Ptolemy and his commentator Pappus of Alexandria. Several modern historians have attempted to reconstruct the methods of Hipparchus using the available texts.
  • 406
  • 20 Oct 2022
Topic Review
SMC AB8
AB8, also known as SMC WR8, is a binary star in the Small Magellanic Cloud (SMC). A Wolf-Rayet star and a main sequence companion of spectral type O orbit in a period of 16.638 days. It is one of only nine known WO stars, the only Wolf-Rayet star in the SMC not on the nitrogen sequence, and the only Wolf-Rayet star in the SMC outside the main bar.
  • 405
  • 26 Oct 2022
Topic Review
The Phase Field Approach
The phase field approach was developed in the last 20 years to handle radiation damage in materials. This approach bridges the gap between atomistic simulations extensively used to model first step of radiation damage at short time and continuum approach at large time. The main advantage of such an approach lies in its ability to compute not only the microstructure at the nanometric scale but also to calculate generalized susceptibilities such as elastic constants under irradiation.
  • 405
  • 05 May 2022
Topic Review
Properties of MXene Products
MXenes are two-dimensional layered materials containing early transition metal carbides, nitrides, and carbonitrides. 
  • 404
  • 03 Apr 2023
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