Introduction to the Anthropocene

https://nanocrit.com/issues/issue13/Editors-Introduction-for-NANO-Special-Issue-13-The-Anthropocenehttps://nanocrit.com/issues/issue13/Editors-Introduction-for-NANO-Special-Issue-13-The-AnthropoceneAccepted manuscrip

The role of dredge-up in double white dwarf mergers

We present the results of an investigation of the dredge-up and mixing during the merger of two white dwarfs with different chemical compositions by conducting hydrodynamic simulations of binary mergers for three representative mass ratios. In all the simulations, the total mass of the two white dwarfs is $\lesssim1.0~{\rm M_\odot}$. Mergers involving a CO and a He white dwarf have been suggested as a possible formation channel for R Coronae Borealis type stars, and we are interested in testing if such mergers lead to conditions and outcomes in agreement with observations. Even if the conditions during the merger and subsequent nucleosynthesis favor the production of $^{18}{\mathrm O}$, the merger must avoid dredging up large amounts of $^{16}{\mathrm O}$, or else it will be difficult to produce sufficient $^{18}{\mathrm O}$ to explain the oxygen ratio observed to be of order unity. We performed a total of 9 simulations using two different grid-based hydrodynamics codes using fixed and adaptive meshes, and one smooth particle hydrodynamics (SPH) code. We find that in most of the simulations, $>10^{-2}~{\rm M_\odot}$ of $^{16}{\mathrm O}$ is indeed dredged up during the merger. However, in SPH simulations where the accretor is a hybrid He/CO white dwarf with a $\sim 0.1~{\rm M_\odot}$ layer of helium on top, we find that no $^{16}{\mathrm O}$ is being dredged up, while in the $q=0.8$ simulation $<10^{-4}~{\rm M_\odot}$ of $^{16}{\mathrm O}$ has been brought up, making a WD binary consisting of a hybrid CO/He WD and a companion He WD an excellent candidate for the progenitor of RCB stars.Comment: Accepted for publication in Ap

Intracranial Hemorrhage Secondary to Newly Diagnosed Acute Promyelocytic Leukemia: A Cautionary Tale

Acute promyelocytic leukemia (APL) typically presents with complications from pancytopenia, generalized weakness, and hemorrhagic findings, with a distinguishing feature being the associated predilection of disseminated intravascular coagulation (DIC). APL is characterized by the halting of cellular differentiation in the promyelocyte stage, and balanced chromosomal translocation t(15;17) (q24;q21) that forms the promyelocytic leukemia-retinoic acid receptor-α (PML-RARA) fusion protein present in 95% of cases. APL has a high rate of early mortality secondary to coagulopathy, lending to the imperative need to begin a differentiation agent as soon as the disease is suspected, with all-trans retinoic acid (ATRA) being the most common differentiation agent. Herein, we present the case of a 32-year-old man presenting with non-specific symptoms of fatigue and scattered bruising, who was found to have an intracranial hemorrhage (ICH) in the setting of suspected APL. This case illuminates the importance of early brain imaging in suspected cases of APL to conceivably lessen the severity of hemorrhagic complications and represents a cautionary tale for similar cases in the future