Atmospheric Chemistry for Astrophysicists: A Self-consistent Formalism and Analytical Solutions for Arbitrary C/O

We present a self-consistent formalism for computing and understanding the atmospheric chemistry of exoplanets from the viewpoint of an astrophysicist. Starting from the first law of thermodynamics, we demonstrate that the van't Hoff equation (which describes the equilibrium constant), Arrhenius equation (which describes the rate coefficients) and procedures associated with the Gibbs free energy (minimisation, rescaling) have a common physical and mathematical origin. We address an ambiguity associated with the equilibrium constant, which is used to relate the forward and reverse rate coefficients, and restate its two definitions. By necessity, one of the equilibrium constants must be dimensionless and equate to an exponential function involving the Gibbs free energy, while the other is a ratio of rate coefficients and must therefore possess physical units. We demonstrate that the Arrhenius equation takes on a functional form that is more general than previously stated without recourse to tagging on ad hoc functional forms. Finally, we derive analytical models of chemical systems, in equilibrium, with carbon, hydrogen and oxygen. We include acetylene and are able to reproduce several key trends, versus temperature and carbon-to-oxygen ratio, published in the literature. The rich variety of behavior that mixing ratios exhibit as a function of the carbon-to-oxygen ratio is merely the outcome of stoichiometric book-keeping and not the direct consequence of temperature or pressure variations.Comment: Accepted by ApJ. 9 pages, 4 figure

Tegument Protein BNRF1 Regulation of Epstein-Barr Virus Genome Chromatinization During Early Infection

Epstein-Barr virus (EBV) is a ubiquitously prevalent human herpesvirus whose persistent latent infection is associated with many lymphomas. The prevalence of this virus can be attributed to its ability to establish a persistent latent infection in host cells, during which only a small number of viral genes are expressed from a highly regulated viral genome. However, it is not completely understood how EBV evades cellular antiviral defenses and regulates chromatin assembly to establish latent infections. The EBV major tegument protein BNRF1 was found to be required for the establishment of latent infections, and contains sequence homology to cellular purine biosynthesis enzymes, yet neither the functional mechanism nor link to purine metabolism is known. We have found that BNRF1 interacts with the cellular transcription co-repressor Daxx, and disrupts the binding between Daxx and its interaction partner, the chromatin remodeler ATRX. By ectopically complimenting BNRF1-null virus with mutant BNRF1, we found that the interaction with Daxx is essential for BNRF1 to support viral gene expression and infection. Furthermore, knockdown studies show that Daxx and ATRX are involved in the maintenance of viral chromatin during latency. With the Daxx-ATRX complex recently found to function as a histone variant H3.3 chaperone, we found that BNRF1 forms a complex with Daxx together with histones H3.3 and H4, suggesting potential modulation of a histone pre-deposition complex. In support of this, we show that BNRF1 can increase the release of histone H3.3 into the cellular free histone pool. We then show in primary infection of B lymphocytes that BNRF1-knockdown virus failed to prevent Daxx-ATRX access to the viral chromatin. This results in enriched H3.3 and decreased active histone H3K4me3 markers on the viral DNA, coinciding with deficient expression of viral latent genes. Our findings demonstrate that EBV BNRF1, by interacting with Daxx and displacing ATRX, prevents repressive histone variant H3.3 chromatin formation on viral DNA. Thus, BNRF1 is essential for the formation of viral chromatin permissive for expressing viral latent genes. This is the first demonstration of a viral tegument FGARAT-homology protein involved in the regulation of chromatin assembly. Most importantly, our findings suggest that active manipulation of a histone pre-deposition complex could turn chromatin-based host antiviral resistances into a mechanism of establishing viral latent chromatin

THOR 2.0: Major Improvements to the Open-Source General Circulation Model

THOR is the first open-source general circulation model (GCM) developed from scratch to study the atmospheres and climates of exoplanets, free from Earth- or Solar System-centric tunings. It solves the general non-hydrostatic Euler equations (instead of the primitive equations) on a sphere using the icosahedral grid. In the current study, we report major upgrades to THOR, building upon the work of Mendon\c{c}a et al. (2016). First, while the Horizontally Explicit Vertically Implicit (HEVI) integration scheme is the same as that described in Mendon\c{c}a et al. (2016), we provide a clearer description of the scheme and improved its implementation in the code. The differences in implementation between the hydrostatic shallow (HSS), quasi-hydrostatic deep (QHD) and non-hydrostatic deep (NHD) treatments are fully detailed. Second, standard physics modules are added: two-stream, double-gray radiative transfer and dry convective adjustment. Third, THOR is tested on additional benchmarks: tidally-locked Earth, deep hot Jupiter, acoustic wave, and gravity wave. Fourth, we report that differences between the hydrostatic and non-hydrostatic simulations are negligible in the Earth case, but pronounced in the hot Jupiter case. Finally, the effects of the so-called "sponge layer", a form of drag implemented in most GCMs to provide numerical stability, are examined. Overall, these upgrades have improved the flexibility, user-friendliness, and stability of THOR.Comment: 57 pages, 31 figures, revised, accepted for publication in ApJ

Proton fixed-target scintillation experiment to search for millicharged dark matter

We propose a low-cost and movable setup to probe minicharged particles using high-intensity proton fixed-target facilities. This proposal, FerMINI, consists of a scintillator-based detector, requiring multicoincident scintillation signatures within a small time window, located downstream of the proton target of a neutrino experiment. During the collisions of a large number of protons on the target, intense minicharged particle beams may be produced via meson photo-decays and Drell-Yan production. We take advantage of the high statistics, shielding, and potential neutrino-detector-related background reduction to search for minicharged particles in two potential sites: the MINOS near detector hall and the proposed DUNE near detector hall, both at Fermilab. We also explore several alternative designs, including modifications to increase signal yield, and combining this detector technology with existing and planned neutrino detectors to better search for minicharged particles. FerMINI can achieve unprecedented sensitivity for minicharged particles in the MeV to few GeV regime with fractional charge $\epsilon=Q_χ/e$ as low as $10^{-4}$

Hybrid Infant Warmer

ME450 Capstone Design and Manufacturing Experience: Winter 2015An estimated 15 million babies are born preterm each year (before 37 weeks of pregnancy are complete). Preterm birth complications are the leading cause of death among children under 5 years of age, responsible for nearly 1 million deaths in 2013. The World Health Organization recommends that Kangaroo Mother Care (KMC), where the baby is carried by the mother with skin-to-skin contact and frequent breastfeeding, is a particularly effective and safe alternative to conventional neonatal care for the management of low birth weight infants, especially in underresourced settings. KMC has been shown to prevent infections, promote breastfeeding, regulate the baby’s temperature, breathing, and brain activity, and encourage mother and baby bonding. Initiated in hospitals, KMC has the potential to reduce reduce newborn deaths by 51% for preterm babies who are stable. Current uptake of the practice is however low. The goal of this project is to design a low cost and hybrid infant warming device for use in low-resource settings that promotes Kangaroo Mother Care and transitions to a standalone incubator when the mother cannot maintain skin-to-skin contact.http://deepblue.lib.umich.edu/bitstream/2027.42/111314/1/17_Report.pd

Ultrafast all-optical switching via coherent modulation of metamaterial absorption

We report on the demonstration of a femtosecond all-optical modulator providing, without nonlinearity and therefore at arbitrarily low intensity, ultrafast light-by-light control. The device engages the coherent interaction of optical waves on a metamaterial nanostructure only 30 nm thick to efficiently control absorption of near-infrared (750-1040 nm) femtosecond pulses, providing switching contrast ratios approaching 3:1 with a modulation bandwidth in excess of 2 THz. The functional paradigm illustrated here opens the path to a family of novel meta-devices for ultra-fast optical data processing in coherent networks.Comment: 5 pages, 4 figure

The Peculiar Atmospheric Chemistry of KELT-9b

The atmospheric temperatures of the ultra-hot Jupiter KELT-9b straddle the transition between gas giants and stars, and therefore between two traditionally distinct regimes of atmospheric chemistry. Previous theoretical studies assume the atmosphere of KELT-9b to be in chemical equilibrium. Despite the high ultraviolet flux from KELT-9, we show using photochemical kinetics calculations that the observable atmosphere of KELT-9b is predicted to be close to chemical equilibrium, which greatly simplifies any theoretical interpretation of its spectra. It also makes the atmosphere of KELT-9b, which is expected to be cloudfree, a tightly constrained chemical system that lends itself to a clean set of theoretical predictions. Due to the lower pressures probed in transmission (compared to emission) spectroscopy, we predict the abundance of water to vary by several orders of magnitude across the atmospheric limb depending on temperature, which makes water a sensitive thermometer. Carbon monoxide is predicted to be the dominant molecule under a wide range of scenarios, rendering it a robust diagnostic of the metallicity when analyzed in tandem with water. All of the other usual suspects (acetylene, ammonia, carbon dioxide, hydrogen cyanide, methane) are predicted to be subdominant at solar metallicity, while atomic oxygen, iron and magnesium are predicted to have relative abundances as high as 1 part in 10,000. Neutral atomic iron is predicted to be seen through a forest of optical and near-infrared lines, which makes KELT-9b suitable for high-resolution ground-based spectroscopy with HARPS-N or CARMENES. We summarize future observational prospects of characterizing the atmosphere of KELT-9b.Comment: Accepted by ApJ. 9 pages, 6 figures. Corrected minor errors in Figures 1a and 1b (some line styles were switched by accident), text and conclusions unchanged, these minor changes will be updated in final ApJ proo