Planet formation around low mass stars: the moving snow line and super-Earths

We develop a semi-analytic model for planet formation during the pre-main sequence contraction phase of a low mass star. During this evolution, the stellar magnetosphere maintains a fixed ratio between the inner disk radius and the stellar radius. As the star contracts at constant effective temperature, the `snow line', which separates regions of rocky planet formation from regions of icy planet formation, moves inward. This process enables rapid formation of icy protoplanets that collide and merge into super-Earths before the star reaches the main sequence. The masses and orbits of these super-Earths are consistent with super-Earths detected in recent microlensing experiments.Comment: accepted by ApJ Letter

A CA+ Pair Adjacent to a Sheared GA or AA Pair Stabilizes Size-Symmetric RNA Internal Loops†

ABSTRACT: RNA internal loops are often important sites for folding and function. Residues in internal loops can have pKa values shifted close to neutral pH because of the local structural environment. A series of RNA internal loops were studied at different pH by UV absorbance versus temperature melting experiments and imino proton nuclear magnetic resonance (NMR). A stabilizing CA pair forms at pH 7 in the CG CA AA and AA nearest neighbors when the CA pair is the first noncanonical pair (loop-terminal pair) in 3 3 nucleotide and larger size-symmetric internal loops. These CG C

Planet formation around stars of various masses: The snow line and the frequency of giant planets

We use a semi-analytic circumstellar disk model that considers movement of the snow line through evolution of accretion and the central star to investigate how gas giant frequency changes with stellar mass. The snow line distance changes weakly with stellar mass; thus giant planets form over a wide range of spectral types. The probability that a given star has at least one gas giant increases linearly with stellar mass from 0.4 M_sun to 3 M_sun. Stars more massive than 3 M_sun evolve quickly to the main-sequence, which pushes the snow line to 10-15 AU before protoplanets form and limits the range of disk masses that form giant planet cores. If the frequency of gas giants around solar-mass stars is 6%, we predict occurrence rates of 1% for 0.4 M_sun stars and 10% for 1.5 M_sun stars. This result is largely insensitive to our assumed model parameters. Finally, the movement of the snow line as stars >2.5 M_sun move to the main-sequence may allow the ocean planets suggested by Leger et. al. to form without migration.Comment: Accepted to ApJ. 12 pages of emulateap

Exact Results for the Bipartite Entanglement Entropy of the AKLT spin-1 chain

We study the entanglement between two domains of a spin-1 AKLT chain subject to open boundary conditions. In this case the ground-state manifold is four-fold degenerate. We summarize known results and present additional exact analytical results for the von Neumann entanglement entropy, as a function of both the size of the domains and the total system size for {\it all} four degenerate ground-states. In the large $l,L$ limit the entanglement entropy approaches $\ln(2)$ and $2\ln(2)$ for the $S^z_T=\pm 1$ and $S^z_T=0$ states, respectively. In all cases, it is found that this constant is approached exponentially fast defining a length scale $\xi=1/\ln(3)$ equal to the known bulk correlation length.Comment: 11 pages, 3 figure

Conformational ensembles of RNA oligonucleotides from integrating NMR and molecular simulations

RNA molecules are key players in numerous cellular processes and are characterized by a complex relationship between structure, dynamics, and function. Despite their apparent simplicity, RNA oligonucleotides are very flexible molecules, and understanding their internal dynamics is particularly challenging using experimental data alone. We show how to reconstruct the conformational ensemble of four RNA tetranucleotides by combining atomistic molecular dynamics simulationswith nuclear magnetic resonance spectroscopy data. The goal is achieved by reweighting simulations using a maximum entropy/Bayesian approach. In this way, we overcome problems of current simulation methods, as well as in interpreting ensemble- and time-averaged experimental data. We determine the populations of different conformational states by considering several nuclear magnetic resonance parameters and point toward properties that are not captured by state-of-the-art molecular force fields. Although our approach is applied on a set of model systems, it is fully general and may be used to study the conformational dynamics of flexible biomolecules and to detect inaccuracies in molecular dynamics force fields

The Characteristics of Occupational Students in Postsecondary Education

This Brief presents a profile of the enrollment, demographic, and educational characteristics, and the educational goals, of community college students in occupational programs. It compares their features with those of community college students in academic programs and with baccalaureate students. This analysis further considers the distinct features of occupational students enrolled in certificate degree programs. The Brief stands alone as a comparative description of these students, but also provides important background material for CCRC’s companion Briefs on postsecondary occupational students, Educational Outcomes of Postsecondary Occupational Students and Who Benefits from Postsecondary Occupational Education? Findings from the 1980s and 1990s

Listening and Negotiation II

This paper is based on a panel held in June, 2017 in Columbus, Ohio, jointly sponsored by the Women in Engineering Division and by the Minorities in Engineering Division. It is focused on negotiation, with an emphasis on providing practical strategies that are relevant in an academic setting. The panel featured academic leaders at multiple levels, including professor, chair and dean, from diverse engineering institutions, ranging from teaching-centric to heavily research-focused. Panelists discussed strategies for negotiation, with an emphasis on an approach that meets the interests of both parties to the extent possible. The panel was administrated with an opening lightning-round in which each panelist provided one strategy for negotiation; this was followed by a role-play of a negotiation, followed with questions and input from the audience. This paper, associated with the panel, provides several examples of negotiation that were presented in the panel discussion

Varicella-Zoster viruses associated with post-herpetic neuralgia induce sodium current density increases in the ND7-23 Nav-1.8 neuroblastoma cell line

Post-herpetic neuralgia (PHN) is the most significant complication of herpes zoster caused by reactivation of latent Varicella-Zoster virus (VZV). We undertook a heterologous infection in vitro study to determine whether PHN-associated VZV isolates induce changes in sodium ion channel currents known to be associated with neuropathic pain. Twenty VZV isolates were studied blind from 11 PHN and 9 non-PHN subjects. Viruses were propagated in the MeWo cell line from which cell-free virus was harvested and applied to the ND7/23-Nav1.8 rat DRG x mouse neuroblastoma hybrid cell line which showed constitutive expression of the exogenous Nav 1.8, and endogenous expression of Nav 1.6 and Nav 1.7 genes all encoding sodium ion channels the dysregulation of which is associated with a range of neuropathic pain syndromes. After 72 hrs all three classes of VZV gene transcripts were detected in the absence of infectious virus. Single cell sodium ion channel recording was performed after 72 hr by voltage-clamping. PHN-associated VZV significantly increased sodium current amplitude in the cell line when compared with non-PHN VZV, wild-type (Dumas) or vaccine VZV strains ((POka, Merck and GSK). These sodium current increases were unaffected by acyclovir pre-treatment but were abolished by exposure to Tetrodotoxin (TTX) which blocks the TTX-sensitive fast Nav 1.6 and Nav 1.7 channels but not the TTX-resistant slow Nav 1.8 channel. PHN-associated VZV sodium current increases were therefore mediated in part by the Nav 1.6 and Nav 1.7 sodium ion channels. An additional observation was a modest increase in message levels of both Nav1.6 and Nav1.7 mRNA but not Nav 1.8 in PHN virally infected cells