Lunar accretion from a Roche-interior fluid disk

We use a hybrid numerical approach to simulate the formation of the Moon from an impact-generated disk, consisting of a fluid model for the disk inside the Roche limit and an N-body code to describe accretion outside the Roche limit. As the inner disk spreads due to a thermally regulated viscosity, material is delivered across the Roche limit and accretes into moonlets that are added to the N-body simulation. Contrary to an accretion timescale of a few months obtained with prior pure N-body codes, here the final stage of the Moon's growth is controlled by the slow spreading of the inner disk, resulting in a total lunar accretion timescale of ~10^2 years. It has been proposed that the inner disk may compositionally equilibrate with the Earth through diffusive mixing, which offers a potential explanation for the identical oxygen isotope compositions of the Earth and Moon. However, the mass fraction of the final Moon that is derived from the inner disk is limited by resonant torques between the disk and exterior growing moons. For initial disks containing < 2.5 lunar masses (ML), we find that a final Moon with mass > 0.8ML contains < 60% material derived from the inner disk, with this material preferentially delivered to the Moon at the end of its accretion.Comment: 42 pages, 10 figures, 5 tables. Accepted for publication in The Astrophysical Journa

A theoretical study of the propagation and attenuation of acoustic waves in the lunar surface Interim report

Acoustic wave propagation and attenuation in lunar space environmen

Giant impacts in the Saturnian System: a possible origin of diversity in the inner mid-sized satellites

It is widely accepted that Titan and the mid-sized regular satellites around Saturn were formed in the circum-Saturn disk. Thus, if these mid-sized satellites were simply accreted by collisions of similar ice-rock satellitesimals in the disk, the observed wide diversity in density (i.e., the rock fraction) of the Saturnian mid-sized satellites is enigmatic. A recent circumplanetary disk model suggests satellite growth in an actively supplied circumplanetary disk, in which Titan-sized satellites migrate inward by interaction with the gas and are eventually lost to the gas planet. Here we report numerical simulations of giant impacts between Titan-sized migrating satellites and smaller satellites in the inner region of the Saturnian disk. Our results suggest that in a giant impact with impact velocity > 1.4 times the escape velocity and impact angle of ~45 degree, a smaller satellite is destroyed, forming multiple mid-sized satellites with a very wide diversity in satellite density (the rock fraction = 0-92 wt%). Our results of the relationship between the mass and rock fraction of the satellites resulting from giant impacts reproduce the observations of the Saturnian mid-sized satellites. Giant impacts also lead to internal melting of the formed mid-sized satellites, which would initiate strong tidal dissipation and geological activity, such as those observed on Enceladus today and Tethys in the past. Our findings also imply that giant impacts might have affected the fundamental physical property of the Saturnian mid-sized satellites as well as those of the terrestrial planets in the solar system and beyond.Comment: 18 pages, 3 figures, Planetary and Space Science, in pres

Electronic Transfer: A Good Investment

Instead of debating whether use of computers in information offices is overrated or underrated, it may be more constructive for agricultural communicators to accept computerization as inevitable and weigh the advantages and disadvantages of jumping into different aspects of computerization now

Rotation of the Solar System planets and the origin of the Moon in the context of the tidal downsizing hypothesis

It has been proposed recently that the first step in the formation of both rocky and gas giant planets is dust sedimentation into a solid core inside a gas clump (giant planet embryo). The clumps are then assumed to migrate closer to the star where their metal poor envelopes are sheared away by the tidal forces or by an irradiation-driven mass loss. We consider the implications of this hypothesis for natal rotation rates of both terrestrial and gas giant planets. It is found that both types of planets may rotate near their break up angular frequencies at birth. The direction of the spin should coincide with that of the parent disc and the star, except in cases of embryos that had close interactions or mergers with other embryos in the past. Furthermore, the large repository of specific angular momentum at birth also allows formation of close binary rocky planets inside the same embryos. We compare these predictions with rotation rates of planets in the Solar System and also question whether the Earth-Moon pair could have been formed within the same giant planet embryo.Comment: latex typo corrected -- Fig2a and Fig3a were switched by error in the previous versio

Consideration of Why Some Chiropractic Students with Disabilities Choose Not to Utilize Academic Accommodations: A Transcendental Phenomenological Study

The purpose of this phenomenological study was to understand the experiences of students with disabilities (SWD) at a chiropractic college in the United States that led to their decision not to utilize the academic accommodations available to them. The theory that guided this study is Deci and Ryan’s self-determination theory. This qualitative study was conducted using the transcendental phenomenological approach. The research participants were students enrolled in a Doctor of Chiropractic (DC) program who had received a diagnosis that made them eligible for academic accommodations at any point in their academic career. The researcher conducted semi-structured interviews with participants, followed by focus groups, and the completion of journal prompts to triangulate and validate the data. The researcher practiced Epoché to see the participants\u27 experience more clearly and then analyzed the data with open coding and horizonalization to develop textural and structural descriptions. The study identifies personal, institutional, and social barriers to accommodations utilization by SWD enrolled in a DC program. The study offers implications for policy and practice that may improve the experiences of SWD enrolled in a DC program

Discovery of Novel Cross-Talk between Protein Arginine Methyltransferase Isoforms and Design of Dimerization Inhibitors

Protein arginine methyltransferase, PRMT, is a family of epigenetic enzymes that methylate arginine residues on histone and nonhistone substrates which result in a monomethylation, symmetric dimethylation or asymmetric dimethylation via the transfer of a methyl group from S-adenosyl-L-methionine (SAM). We discovered a novel interaction between two PRMT isoforms: PRMT1 interacts and methylates PRMT6. In this study site-directed mutagenesis was performed on selected arginines identified from tandem mass spectrometric analysis to investigate major methylation sites of PRMT6 by PRMT1. In combination with radiometric methyltransferase assays, we determined two major methylation sites. Methylations at these sites have significant effects on the nascent enzymatic activity of PRMT6 in H4 methylation. PRMTs have the ability to homodimerize which have been linked to methyltransferase activity. We designed dimerization inhibitors (DMIs) to further investigate the need for dimerization for enzyme activity. Preliminary results suggest that the monomeric form of PRMT1 retains methyltransferase activity comparable to that of the uninhibited PRMT1