Temperature effects on the radiation damage morphology in nanocrystalline iron
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Vetterick, G.↗
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Results for “C-Y”
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Characterizing the magnetic fields of nearby molecular clouds using submillimeter polarization observations
Of all the factors that influence star formation, magnetic fields are perhaps the least well understood. The goal of this paper is to characterize the 3D magnetic field properties of nearby molecular clouds through various methods of statistically analysing maps of polarized dust emission. Our study focuses on nine clouds, with data taken from the Planck Sky Survey as well as data from the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry observations of Vela C. We compare the distributions of polarization fraction (p), dispersion in polarization angles ($\mathcal {S}$), and hydrogen column density (N H ) for each of our targeted clouds. To broaden the scope of our analysis, we compare the distributions of our clouds’ polarization observables with measurements from synthetic polarization maps generated from numerical simulations. We also use the distribution of polarization fraction measurements to estimate the inclination angle of each cloud’s cloud-scale magnetic field. We obtain a range of inclination angles associated with our clouds, varying from 16° to 69°. We establish inverse correlations between p and both $\mathcal {S}$ and NH in almost every cloud, but we are unable to establish a statistically robust $\mathcal {S}$ versus NH trend. By comparing the results of these different statistical analysis techniques, we are able to propose a more comprehensive view of each cloud’s 3D magnetic field properties. These detailed cloud analyses will be useful in the continued studies of cloud-scale magnetic fields and the ways in which they affect star formation within these molecular clouds.
79 ASTRONOMY AND ASTROPHYSICS↗
The Davis–Chandrasekhar–Fermi method revisited
ABSTRACT Despite the rich observational results on interstellar magnetic fields in star-forming regions, it is still unclear how dynamically significant the magnetic fields are at varying physical scales, because direct measurement of the field strength is observationally difficult. The Davis–Chandrasekhar–Fermi (DCF) method has been the most commonly used method to estimate the magnetic field strength from polarization data. It is based on the assumption that gas turbulent motion is the driving source of field distortion via linear Alfvén waves. In this work, using MHD simulations of star-forming clouds, we test the validity of the assumption underlying the DCF method by examining its accuracy in the real 3D space. Our results suggest that the DCF relation between turbulent kinetic energy and magnetic energy fluctuation should be treated as a statistical result instead of a local property. We then develop and investigate several modifications to the original DCF method using synthetic observations, and propose new recipes to improve the accuracy of DCF-derived magnetic field strength. We further note that the biggest uncertainty in the DCF analysis may come from the linewidth measurement instead of the polarization observation, especially since the line-of-sight gas velocity can be used to estimate the gas volume density, another critical parameter in the DCF method.
79 ASTRONOMY AND ASTROPHYSICS↗
Survey of Gravitationally lensed objects in HSC Imaging (SuGOHI). VIII. New galaxy-scale lenses from the HSC SSP
Abstract We conduct a search for galaxy-scale strong gravitational lens systems in Data Release 4 of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP), consisting of data taken up to the S21A semester. We select 103191 luminous red galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) sample that have deep multiband imaging from the HSC SSP and use the YattaLens algorithm to identify lens candidates with blue arc-like features automatically. The candidates are visually inspected and graded based on their likelihood of being a lens. We find eight definite lenses, 28 probable lenses, and 138 possible lenses. The new lens candidates generally have lens redshifts in the range 0.3 ≲ zL ≲ 0.9, a key intermediate redshift range to study the evolution of galaxy structure. Follow-up spectroscopy will confirm these new lenses and measure source redshifts to enable detailed lens modeling.
Astronomy & Astrophysics↗
Materials Data on Y2C by Materials Project
Y2C is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Y2C sheets oriented in the (0, 0, 1) direction. Y is bonded in a distorted T-shaped geometry to three equivalent C atoms. All Y–C bond lengths are 2.48 Å. C is bonded to six equivalent Y atoms to form edge-sharing CY6 octahedra.
36 MATERIALS SCIENCE↗
Materials Data on Y2C3 by Materials Project
Y2C3 is Plutonium carbide structured and crystallizes in the cubic I-43d space group. The structure is three-dimensional. Y3+ is bonded in a 9-coordinate geometry to nine equivalent C2- atoms. There are a spread of Y–C bond distances ranging from 2.52–2.83 Å. C2- is bonded to six equivalent Y3+ and one C2- atom to form a mixture of distorted edge, face, and corner-sharing CY6C trigonal bipyramids. The C–C bond length is 1.34 Å.
36 MATERIALS SCIENCE↗
Materials Data on YC2 by Materials Project
YC2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Y is bonded in a distorted q4 geometry to ten equivalent C atoms. There are two shorter (2.45 Å) and eight longer (2.69 Å) Y–C bond lengths. C is bonded in a 6-coordinate geometry to five equivalent Y and one C atom. The C–C bond length is 1.30 Å.
36 MATERIALS SCIENCE↗
Materials Data on Y4C5 by Materials Project
Y4C5 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to five C+2.40- atoms to form YC5 trigonal bipyramids that share corners with two equivalent CY5C octahedra, corners with four equivalent YC5 trigonal bipyramids, and edges with two equivalent YC5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 36–48°. There are a spread of Y–C bond distances ranging from 2.42–2.70 Å. In the second Y3+ site, Y3+ is bonded in a 7-coordinate geometry to nine C+2.40- atoms. There are a spread of Y–C bond distances ranging from 2.45–2.90 Å. There are three inequivalent C+2.40- sites. In the first C+2.40- site, C+2.40- is bonded to six Y3+ atoms to form CY6 octahedra that share corners with four equivalent CY5C octahedra and edges with six CY6 octahedra. The corner-sharing octahedral tilt angles are 61°. In the second C+2.40- site, C+2.40- is bonded to five Y3+ and one C+2.40- atom to form CY5C octahedra that share corners with six CY6 octahedra, corners with two equivalent YC5 trigonal bipyramids, and edges with six CY6 octahedra. The corner-sharing octahedra tilt angles range from 29–61°. The C–C bond length is 1.33 Å. In the third C+2.40- site, C+2.40- is bonded in a 5-coordinate geometry to six Y3+ and one C+2.40- atom.
36 MATERIALS SCIENCE↗
Materials Data on Y4C7 by Materials Project
Y4C7 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to seven C+1.71- atoms to form distorted YC7 octahedra that share corners with two equivalent YC7 octahedra, a cornercorner with one CY4C trigonal bipyramid, and edges with five equivalent YC7 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Y–C bond distances ranging from 2.50–3.01 Å. In the second Y3+ site, Y3+ is bonded in a 9-coordinate geometry to nine C+1.71- atoms. There are a spread of Y–C bond distances ranging from 2.44–2.85 Å. There are four inequivalent C+1.71- sites. In the first C+1.71- site, C+1.71- is bonded to six Y3+ atoms to form CY6 octahedra that share corners with two equivalent CY4C trigonal bipyramids, edges with two equivalent CY6 octahedra, and edges with four equivalent CY4C trigonal bipyramids. In the second C+1.71- site, C+1.71- is bonded to four Y3+ and one C+1.71- atom to form distorted CY4C trigonal bipyramids that share a cornercorner with one YC7 octahedra, a cornercorner with one CY6 octahedra, corners with six equivalent CY4C trigonal bipyramids, and edges with two equivalent CY6 octahedra. The corner-sharing octahedra tilt angles range from 33–61°. The C–C bond length is 1.33 Å. In the third C+1.71- site, C+1.71- is bonded in a 6-coordinate geometry to four Y3+ and two C+1.71- atoms. The C–C bond length is 1.33 Å. In the fourth C+1.71- site, C+1.71- is bonded in a 5-coordinate geometry to five Y3+ and one C+1.71- atom.
36 MATERIALS SCIENCE↗
Materials Data on YC by Materials Project
YC is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Y3+ is bonded to six equivalent C3- atoms to form a mixture of corner and edge-sharing YC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Y–C bond lengths are 2.55 Å. C3- is bonded to six equivalent Y3+ atoms to form a mixture of corner and edge-sharing CY6 octahedra. The corner-sharing octahedral tilt angles are 0°.
36 MATERIALS SCIENCE↗
Materials Data on YC by Materials Project
YC is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Y3+ is bonded to four equivalent C3- atoms to form corner-sharing YC4 tetrahedra. All Y–C bond lengths are 2.37 Å. C3- is bonded to four equivalent Y3+ atoms to form corner-sharing CY4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on YC by Materials Project
YC is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Y3+ is bonded in a body-centered cubic geometry to eight equivalent C3- atoms. All Y–C bond lengths are 2.69 Å. C3- is bonded in a body-centered cubic geometry to eight equivalent Y3+ atoms.
36 MATERIALS SCIENCE↗
Crystallization Age of NWA 1460 Shergottite: Paradox Revisited
We have determined the Rb-Sr age of basaltic shergottite NWA 1460 to be 312 +/- 3 Ma, and the Sm-Nd age to be 352 +/- 30 Ma. The initial Sr and Nd isotopic compositions of NWA 1460 suggest it is an earlier melting product of a Martian mantle source region similar to those of the Iherzolitic shergottites and basaltic shergottite EETA79001, lithology B. The new ages of NWA 1460 and other recently analyzed Martian meteorites leads us to reexamine the paradox that most of the Martian meteorites appear to be younger from the majority of the Martian surface. This paradox continues to pose a challenge to determining a reliable Martian chronology.
Nyquist, L. E.↗
Sm-Nd and Rb-Sr Ages for MIL 05035: Implications for Surface and Mantle Sources
The Sm-Nd and Rb-Sr ages and also the initial Nd and Sr isotopic compositions of MIL 05035 are the same as those of A-881757. Comparing the radiometric ages of these meteorites to lunar surface ages as modeled from crater size-frequency distributions as well as the TiO2 abundances and initial Sr-isotopic compositions of other basalts places their likely place of origin as within the Australe or Humboldtianum basins. If so, a fundamental west-east lunar asymmetry in compositional and isotopic parameters that likely is due to the PKT is implied.
Nyquist, L. E.↗
Prospects for Chronological Studies of Martian Rocks and Soils
Chronological information about Martian processes comes from two sources: Crater-frequency studies and laboratory studies of Martian meteorites. Each has limitations that could be overcome by studies of returned Martian rocks and soils. Chronology of Martian volcanism: The currently accepted chronology of Martian volcanic surfaces relies on crater counts for different Martian stratigraphic units [1]. However, there is a large inherent uncertainty for intermediate ages near ~2 Ga ago. The effect of differing preferences for Martian cratering chronologies [1] is shown in Fig. 1. Stoeffler and Ryder [2] summarized lunar chronology, upon which Martian cratering chronology is based. Fig. 2 shows a curve fit to their data, and compares to it a corresponding lunar curve from [3]. The radiometric ages of some lunar and Martian meteorites as well as the crater-count delimiters for Martian epochs [4] also are shown for comparison to the craterfrequency curves. Scaling the Stoeffler-Ryder curve by a Mars/Moon factor of 1.55 [5] places Martian shergottite ages into the Early Amazonian to late Hesperian epochs, whereas using the lunar curve of [3] and a Mars/Moon factor ~1 consigns the shergottites to the Middle-to-Late Amazonian, a less probable result. The problem is worsened if a continually decreasing cratering rate since 3 Ga ago is accepted [6]. We prefer the adjusted St ffler-Ryder curve because it gives better agreement with the meteorite ages (Fig.
Nyquist, L. E.↗
Sm-Nd for Norite 78236 and Eucrite Y980318/433: Implications for Planetary and Solar System Processes
Here, we compare Sm-147-Nd-143 and Sm-146-Nd-142 data for lunar norite 78236 to those for approximately 4.54-4.56 Ga old cumulate eucrite Yamato 980318/433 and show that the norite data are compatible with its derivation from an isotopic reservoir similar to that from whence the eucrite pair came. Thus, lunar-like Sm-Nd isotopic systematics are not unique to the Earth-Moon system.
Nyquist, L. E.↗
Concordant Rb-Sr and Sm-Nd Ages for NWA 1460: A 340 Ma Old Basaltic Shergottite Related to Lherzolitic Shergottites
Preliminary Rb-Sr and Sm-Nd ages reported by [1] for the NWA 1460 basaltic shergottite are refined to 336+/-14 Ma and 345+/-21 Ma, respectively. These concordant ages are interpreted as dating a lava flow on the Martian surface. The initial Sr and Nd isotopic compositions of NWA 1460 suggest it is an earlier melting product of a Martian mantle source region similar to those of the lherzolitic shergottites and basaltic shergottite EETA79001, lithology B. We also examine the suggestion that generally "young" ages for other Martian meteorites should be reinterpreted in light of Pb-207/Pb-206 - Pb-204/Pb-206 isotopic systematics [2]. Published U-Pb isotopic data for nakhlites are consistent with ages of approx.1.36 Ga. The UPb isotopic systematics of some Martian shergottites and lherzolites that have been suggested to be approx.4 Ga old [2] are complex. We nevertheless suggest the data are consistent with crystallization ages of approx.173 Ma when variations in the composition of in situ initial Pb as well as extraneous Pb components are considered.
Nyquist, L. E.↗
Mn-53-Cr-53 Systematics of R-Chondrite NWA 753
Chondrules and chondrites are interpreted as objects formed in the early solar system, and it is important to study them in order to elucidate its evolution. Here, we report the study of the Mn-Cr systematics of the R-Chondrite NWA753 and compare the results to other chondrite data. The goal was to determine Cr isotopic and age variations among chondrite groups with different O-isotope signatures. The Mn-53-Cr-53 method as applied to individual chondrules [1] or bulk chondrites [2] is based on the assumption that 53Mn was initially homogeneously distributed in that portion the solar nebula where the chondrules and/or chondrites formed. However, different groups of chondrites formed from regions of different O-isotope compositions. So, different types of chondrites also may have had different initial Mn-53 abundances and/or Cr isotopic compositions. Thus, it is important to determine the Cr isotopic systematics among chondrites from various chondrite groups. We are studying CO-chondrite ALH83108 and Tagish Lake in addition to R-Chondrite NWA753. These meteorites have very distinct O-isotope compositions (Figure 1).
Jogo, K.↗