Bondi-Hoyle-Lyttleton Accretion onto Star Clusters

An isolated star moving supersonically through a uniform gas accretes material from its gravitationally-induced wake. The rate of accretion is set by the accretion radius of the star and is well-described by classical Bondi-Hoyle-Lyttleton theory. Stars, however, are not born in isolation. They form in clusters where they accrete material that is influenced by all the stars in the cluster. We perform three-dimensional hydrodynamic simulations of clusters of individual accretors embedded in a uniform-density wind in order to study how the accretion rates experienced by individual cluster members are altered by the properties of the ambient gas and the cluster itself. We study accretion as a function of number of cluster members, mean separation between them, and size of their individual accretion radii. We determine the effect of these key parameters on the aggregate and individual accretion rates, which we compare to analytic predictions. We show that when the accretion radii of the individual objects in the cluster substantially overlap, the surrounding gas is effectively accreted into the collective potential of the cluster prior to being accreted onto the individual stars. We find that individual cluster members can accrete drastically more than they would in isolation, in particular when the flow is able to cool efficiently. This effect could potentially modify the luminosity of accreting compact objects in star clusters and could lead to the rejuvenation of young star clusters as well as globular clusters with low-inclination and low-eccentricity.Comment: 15 pages, 12 figures. Accepted to Ap

Using the Kalman filter to smooth the shocks of a dynamic stochastic general equilibrium model

This paper shows how to use the Kalman filter (Kalman 1960) to back out the shocks of a dynamic stochastic general equilibrium model. In particular, we use the smoothing algorithm as described in Hamilton (1994) to estimate the shocks of a sticky-prices and sticky-wages model using all the information up to the end of the sample.

Robotic Arm Manipulation to Perform Rock Skipping in Simulation

Rock skipping is a highly dynamic and relatively complex task that can easily be performed by humans. This project aims to bring rock skipping into a robotic setting, utilizing the lessons we learned in Robotic Manipulation. Specifically, this project implements a system consisting of a robotic arm and dynamic environment to perform rock skipping in simulation. By varying important parameters such as release velocity, we hope to use our system to gain insight into the most important factors for maximizing the total number of skips. In addition, by implementing the system in simulation, we have a more rigorous and precise testing approach over these varied test parameters. However, this project experienced some limitations due to gripping inefficiencies and problems with release height trajectories which is further discussed in our report

Reciprocal Frames: The Flat Beam Grillage

This report follows the pursuit of attaining information and researching academic resources regarding the elusive reciprocal frame structures throughout history, in particular the flat beam grillage. In the following pages, the reader should expect to learn about reciprocal frames in a historical context throughout the globe, as well as, gain insight on how to potentially analyze these frames when they span two-dimensionally. As seen in Figure 1 (Pugnale 2011) and Figure 2 (Godthelp 2019), reciprocal frame structures consist of multiple groups of three or more members that are mutually supported. Along the perimeter of the structure, the members are supported by walls, columns, or the ground; where members meet to a certain extent from the ends of an adjacent member, they are supported by such subsequent members. In structural engineering, it is an intuitive instinct to attempt to follow the load path of a structure until the load is safely distributed into the ground. Only considering gravity, when looking at a planar reciprocal frame layout, it is difficult to visualize exactly how the loading is being transferred within the structure. Furthermore, how does one go about doing statics on a problem that is undergoing a perpetual cycle of load transfer? Hopefully, with the data that has been gathered within this research paper, a path can begin to be paved in regard to the design and analysis of two-dimensional reciprocal frames

A Thoughtful Discourse on Sexuality Education: A Review of \u3cem\u3eThe Sexuality Curriculum and Youth Culture\u3c/em\u3e

The present article reviews Carlson and Roseboro\u27s (2011) The Sexuality Curriculum and Youth Culture. The book analyzes factors that influence the sexuality curriculum within today\u27s heteronormative culture, and it is particularly useful for teachers, school administrators, and educators in training. Overall, this book thoughtfully raises awareness about the influences of heterosexist norms and homophobia within the context of traditional education systems

Illuminating black hole subsystems in young star clusters

There is increasing evidence that globular clusters retain sizeable black hole populations at present day. This is supported by dynamical simulations of cluster evolution, which have unveiled the spatial distribution and mass spectrum of black holes in clusters across cosmic age. However, black hole populations of young, high metallicity clusters remain unconstrained. Black holes hosted by these clusters mass segregate early in their evolutionary history, forming central subsystems of hundreds to thousands of black holes. We argue that after supernova feedback has subsided ($\gtrsim 50\,{\rm Myr}$), the host cluster can accumulate gas from its dense surroundings, from which the black hole subsystem accretes at highly enhanced rates. The collective accretion luminosity can be substantial and provides a novel observational constraint for young massive clusters. We test this hypothesis by performing 3D hydrodynamic simulations where we embed discretized potentials, representing our black holes, within the potential of a massive cluster. This system moves supersonically with respect to a gaseous medium from which it accretes. We study the accretion of this black hole subsystem for different subsystem populations and determine the integrated accretion luminosity of the black hole subsystem. We apply our results to the young massive clusters of the Antennae Galaxies and find that a typical subsystem accretion luminosity should be in excess of $\approx 10^{40}\,{\rm ergs\,\,s^{-1}}$. We argue that no strong candidates of this luminous signal have been observed and constrain the subsystem population of a typical cluster in the Antennae Galaxies to $\lesssim10-2\times10^2$ $10\,M_\odot$ black holes, given that feedback doesn't significantly impede accretion and that the gas remains optically thin.Comment: 15 pages, 8 figures. Accepted by Ap

The hydrodynamic evolution of binary black holes embedded within the vertically stratified disks of active galactic nuclei

Stellar-mass black holes can become embedded within the gaseous disks of active galactic nuclei (AGNs). Afterwards, their interactions are mediated by their gaseous surroundings. In this work, we study the evolution of stellar-mass binary black holes (BBHs) embedded within AGN disks using a combination of three-dimensional hydrodynamic simulations and analytic methods, focusing on environments in which the AGN disk scale height $H$ is $\gtrsim$ the BBH sphere of influence. We model the local surroundings of the embedded BBHs using a wind tunnel formalism and characterize different accretion regimes based on the local properties of the disk, which range from wind-dominated to quasi-spherical. We use our simulations to develop prescriptions for mass accretion and drag for embedded BBHs. We use these prescriptions, along with AGN disk models that can represent the Toomre-unstable outer regions of AGN disks, to study the long-term evolution of the BBHs as they migrate through the disk. We find that BBHs typically merge within $\lesssim 5-30\,{\rm Myr}$, increasing their mass significantly in the process, allowing BBHs to enter (or cross) the pair-instability supernova mass gap. The rate at which gas is supplied to these BBHs often exceeds the Eddington limit, sometimes by several orders of magnitude. We conclude that most embedded BBHs will merge before migrating significantly in the disk. Depending on the conditions of the ambient gas and the distance to the system, LISA can detect the transition between the gas-dominated and gravitational wave dominated regime for inspiraling BBHs that are formed sufficiently close to the AGN ($\lesssim$ 0.1 pc). We also discuss possible electromagnetic signatures during and following the inspiral, finding that it is generally unlikely but not inconceivable for the bolometric luminosity of the BBH to exceed that of the host AGN.Comment: 19 pages, 8 figures, submitted to Ap

Targeted long-read sequencing reveals clonally expanded HBV-associated chromosomal translocations in patients with chronic hepatitis B

Chronic HBV; Clonal expansion; Targeted sequencingVHB crónico; Expansión clónica; Secuenciación dirigidaVHB crònic; Expansió clonal; Seqüenciació dirigidaBackground & Aims HBV infects over 257 million people worldwide and is associated with the development of hepatocellular carcinoma (HCC). Integration of HBV DNA into the host genome is likely a key driver of HCC oncogenesis. Here, we utilise targeted long-read sequencing to determine the structure of HBV DNA integrations as well as full isoform information of HBV mRNA with more accurate quantification than traditional next generation sequencing platforms. Methods DNA and RNA were isolated from fresh frozen liver biopsies collected within the GS-US-174-0149 clinical trial. A pan-genotypic panel of biotinylated oligos was developed to enrich for HBV sequences from sheared genomic DNA (∼7 kb) and full-length cDNA libraries from poly-adenylated RNA. Samples were sequenced on the PacBio long-read platform and analysed using a custom bioinformatic pipeline. Results HBV-targeted long-read DNA sequencing generated high coverage data spanning entire integrations. Strikingly, in 13 of 42 samples (31%) we were able to detect HBV sequences flanked by 2 different chromosomes, indicating a chromosomal translocation associated with HBV integration. Chromosomal translocations were unique to each biopsy sample, suggesting that each originated randomly, and in some cases had evidence of clonal expansion. Using targeted long-read RNA sequencing, we determined that upwards of 95% of all HBV transcripts in patients who are HBeAg-positive originate from cccDNA. In contrast, patients who are HBeAg-negative expressed mostly HBsAg from integrations. Conclusions Targeted lso-Seq allowed for accurate quantitation of the HBV transcriptome and assignment of transcripts to either cccDNA or integration origins. The existence of multiple unique HBV-associated inter-chromosomal translocations in non-HCC CHB patient liver biopsies suggests a novel mechanism with mutagenic potential that may contribute to progression to HCC