Exploring the Origins of Deuterium Enrichments in Solar Nebular Organics

Deuterium-to-hydrogen (D/H) enrichments in molecular species provide clues about their original formation environment. The organic materials in primitive solar system bodies have generally higher D/H ratios and show greater D/H variation when compared to D/H in solar system water. We propose this difference arises at least in part due to 1) the availability of additional chemical fractionation pathways for organics beyond that for water, and 2) the higher volatility of key carbon reservoirs compared to oxygen. We test this hypothesis using detailed disk models, including a sophisticated, new disk ionization treatment with a low cosmic ray ionization rate, and find that disk chemistry leads to higher deuterium enrichment in organics compared to water, helped especially by fractionation via the precursors CH$_2$D$^+$/CH$_3^+$. We also find that the D/H ratio in individual species varies significantly depending on their particular formation pathways. For example, from $\sim20-40$ AU, CH$_4$ can reach $\rm{D/H\sim2\times10^{-3}}$, while D/H in CH$_3$OH remains locally unaltered. Finally, while the global organic D/H in our models can reproduce intermediately elevated D/H in the bulk hydrocarbon reservoir, our models are unable to reproduce the most deuterium-enriched organic materials in the solar system, and thus our model requires some inheritance from the cold interstellar medium from which the Sun formed.Comment: 11 pages, 7 figures, accepted for publication in Ap

The ancient heritage of water ice in the solar system

Identifying the source of Earth's water is central to understanding the origins of life-fostering environments and to assessing the prevalence of such environments in space. Water throughout the solar system exhibits deuterium-to-hydrogen enrichments, a fossil relic of low-temperature, ion-derived chemistry within either (i) the parent molecular cloud or (ii) the solar nebula protoplanetary disk. Utilizing a comprehensive treatment of disk ionization, we find that ion-driven deuterium pathways are inefficient, curtailing the disk's deuterated water formation and its viability as the sole source for the solar system's water. This finding implies that if the solar system's formation was typical, abundant interstellar ices are available to all nascent planetary systems.Comment: 33 pages, 7 figures including main text and supplementary materials. Published in Scienc

Reentrant nu = 1 quantum Hall state in a two-dimensional hole system

We report the observation of a reentrant quantum Hall state at the Landau level filling factor nu = 1 in a two-dimensional hole system confined to a 35-nm-wide (001) GaAs quantum well. The reentrant behavior is characterized by a weakening and eventual collapse of the nu = 1 quantum Hall state in the presence of a parallel magnetic field component B||, followed by a strengthening and reemergence as B|| is further increased. The robustness of the nu = 1 quantum Hall state during the transition depends strongly on the charge distribution symmetry of the quantum well, while the magnitude of B|| needed to invoke the transition increases with the total density of the system

Even-denominator Fractional Quantum Hall Effect at a Landau Level Crossing

The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D) charged particles at high magnetic fields, is one of the most fascinating, macroscopic manifestations of a many-body state stabilized by the strong Coulomb interaction. It occurs when the filling factor ($\nu$) of the quantized Landau levels (LLs) is a fraction which, with very few exceptions, has an odd denominator. In 2D systems with additional degrees of freedom it is possible to cause a crossing of the LLs at the Fermi level. At and near these crossings, the FQHE states are often weakened or destroyed. Here we report the observation of an unusual crossing of the two \emph{lowest-energy} LLs in high-mobility GaAs 2D $hole$ systems which brings to life a new \emph{even-denominator} FQHE at $\nu=1/2$

Guidelines for initiation of anti-tumour necrosis factor therapy in rheumatoid arthritis: similarities and differences across Europe.

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Spacecraft Geometry Effects on Kinetic Impactor Missions

The DART (Double Asteroid Redirection Test) mission will impact a spacecraft on the secondary (Dimorphos) of the binary asteroid system Didymos in 2022 September, with the goal of altering the orbital period of Dimorphos about Didymos sufficiently to be observed from ground-based observations. Numerical impact modeling is a crucial component in understanding the outcome of the DART experiment, and while many have investigated the effects of target properties, such as material strength and porosity (which remain unknown), an often overlooked factor is the importance of accurately representing the spacecraft itself in such models. Most impact modeling to date has considered simple impactor geometries such as a solid uniform sphere, but in reality the spacecraft is a complex shape full of different components, open spaces, and thin walled structures. At a minimum, a simple solid representation underestimates the surface area of the impact: for a small body such as Dimorphos (approximately 160 m in diameter), the difference between a spacecraft spanning 20 m (including solar arrays) impacting and a sub-1 m idealized shape may be important. In this paper, we compare models impacting high-fidelity models of the spacecraft based on the CAD geometry with various simplified impactors, in order to assess the potential importance of this effect. We find that the difference between the simplest impactor geometries (such as a uniform sphere) and the real spacecraft is measurable, and has an interesting dependence on the material properties of the asteroid itself