First Observational Signature of Rotational Deceleration in a Massive, Intermediate-age Star Cluster in the Magellanic Clouds

While the extended main-sequence turn-offs (eMSTOs) found in almost all 1--2 Gyr-old star clusters in the Magellanic Clouds are often explained by postulating extended star-formation histories, the tight subgiant branches (SGBs) seen in some clusters challenge this popular scenario. Puzzlingly, the SGB of the eMSTO cluster NGC 419 is significantly broader at bluer than at redder colors. We carefully assess and confirm the reality of this observational trend. If we would assume that the widths of the features in color--magnitude space were entirely owing to a range in stellar ages, the star-formation histories of the eMSTO stars and the blue SGB region would be significantly more prolonged than that of the red part of the SGB. This cannot be explained by assuming an internal age spread. We show that rotational deceleration of a population of rapidly rotating stars, a currently hotly debated alternative scenario, naturally explains the observed trend along the SGB. Our analysis shows that a `converging' SGB could be produced if the cluster is mostly composed of rapidly rotating stars that slow down over time owing to the conservation of angular momentum during their evolutionary expansion from main-sequence turn-off stars to red giants.Comment: 11 pages, preprint format (uses aastex6.cls); ApJ Letters, in pres

A measurement of circumgalactic gas around nearby galaxies using fast radio bursts

The distribution of gas in the circumgalactic medium (CGM) of galaxies of all types is poorly constrained. Foreground CGMs contribute an extra amount to the dispersion measure (DM) of fast radio bursts (FRB). We measure this DM excess for the CGMs of $10^{11}-10^{13}\ M_\odot$ halos using the CHIME/FRB first data release, a halo mass range that is challenging to probe in any other way. Because of the uncertainty in the FRBs' angular coordinates, only for nearby galaxies is the localization sufficient to confidently associate them with intersecting any foreground halo. Thus we stack on galaxies within 80 Mpc, optimizing the stacking scheme to approximately minimize the stack's variance and marginalize over uncertainties in FRB locations. The sample has 20-30 FRBs intersecting halos with masses of $10^{11}-10^{12}\ M_\odot$ and also of $10^{12}-10^{13}\ M_\odot$, and these intersections allow a marginal $1-2\,\sigma$ detection of the DM excess in both mass bins. The $10^{11}-10^{12}\ M_\odot$ halos bin also shows a DM excess at 1-2 virial radii. By comparing data with different models for the CGM gas profile, we find that all models are favored by the data up to 2-$\sigma$ level compared to the null hypothesis of no DM excess. With 2000-3000 more bursts from a future CHIME data release, we project a 4-$\sigma$ detection of the CGM. Distinguishing between viable CGM models by stacking FRBs with CHIME-like localization would require tens of thousands of bursts.Comment: submitted to Ap

Markovian bulk-arrival and bulk-service queues with general state-dependent control

We study a modified Markovian bulk-arrival and bulk-service queue incorporating general state-dependent control. The stopped bulk-arrival and bulk-service queue is first investigated, and the relationship between this stopped queue and the full queueing model is examined and exploited. Using this relationship, the equilibrium behaviour for the full queueing process is studied and the probability generating function of the equilibrium distribution is obtained. Queue length behaviour is also examined, and the Laplace transform of the queue length distribution is presented. The important questions regarding hitting times and busy period distributions are answered in detail, and the Laplace transforms of these distributions are presented. Further properties regarding the busy period distributions including expectation and conditional expectation of busy periods are also explored

Implementing Controlled Digital Lending with Google Drive and Apps Script: A Case Study at the NYU Shanghai Library

The unexpected outbreak of COVID-19 near the beginning of 2020 has significantly interrupted the daily operation of a wide range of academic institutions worldwide. As a result, libraries faced a challenge of providing their patrons access to physical collections while the campuses may remain closed. Discussions on the implementation of Controlled Digital Lending (CDL) among libraries have been trending ever since. In theory, CDL enables libraries to digitize a physical item from their collections and loan the access-restricted file to one user at a time based on the “owned to loaned” ratio in the library’s collections, for a limited time. Despite all the discussions and enthusiasm about CDL, there is, however, still a lack of technical infrastructure to support individual libraries to manage their self-hosted collections. With COVID-19 still very much a presence in our lives, many libraries are more than eager to figure out the best approach to circulating materials that only exist in print form to their users in a secure and legitimate way. This article describes the author's temporary but creative implementation of CDL amid the COVID-19 pandemic. We managed to work out a technical solution in a very short time, to lend out digital versions of library materials to users when the library is physically inaccessible to them. By collaborating with our campus IT, a Google Spreadsheet with Google Apps Scripts was developed to allow a team of Access Services Staff to do hourly loans, which is a desired function for our reserve collection. Further, when the access to a file expires, staff will be notified via email. We hope our experience can be useful for those libraries that are interested in lending their physical materials using CDL and are in urgent need for an applicable solution without a cost