Clustering of galaxies around GRB sight-lines

There is evidence of an overdensity of strong intervening MgII absorption line systems distributed along the lines of sight towards GRB afterglows relative to quasar sight-lines. If this excess is real, one should also expect an overdensity of field galaxies around GRB sight-lines, as strong MgII tends to trace these sources. In this work, we test this expectation by calculating the two point angular correlation function of galaxies within 120$^{\prime\prime}$ ($\sim470~h_{71}^{-1}~\mathrm{Kpc}$ at $\langle z\rangle \sim0.4$) of GRB afterglows. We compare the Gamma-ray burst Optical and Near-infrared Detector (GROND) GRB afterglow sample -- one of the largest and most homogeneous samples of GRB fields -- with galaxies and AGN found in the COSMOS-30 photometric catalog. We find no significant signal of anomalous clustering of galaxies at an estimated median redshift of $z\sim0.3$ around GRB sight-lines, down to $K_{\mathrm{AB}}<19.3$. This result is contrary to the expectations from the MgII excess derived from GRB afterglow spectroscopy, although many confirmed galaxy counterparts to MgII absorbers may be too faint to detect in our sample -- especially those at $z>1$. We note that the addition of higher sensitivity Spitzer IRAC or HST WFC3 data for even a subset of our sample would increase this survey's depth by several orders of magnitude, simultaneously increasing statistics and enabling the investigation of a much larger redshift space.}Comment: 10 pages, 6 figures. A&A accepte

GRB 091127: The cooling break race on magnetic fuel

Using high-quality, broad-band afterglow data for GRB 091127, we investigate the validity of the synchrotron fireball model for gamma-ray bursts, and infer physical parameters of the ultra-relativistic outflow. We used multi-wavelength follow-up observations obtained with GROND and the XRT onboard the Swift satellite. The resulting afterglow light curve is of excellent accuracy, and the spectral energy distribution is well-sampled over 5 decades in energy. These data present one of the most comprehensive observing campaigns for a single GRB afterglow and allow us to test several proposed emission models and outflow characteristics in unprecedented detail. Both the multi-color light curve and the broad-band SED of the afterglow of GRB 091127 show evidence of a cooling break moving from high to lower energies. The early light curve is well described by a broken power-law, where the initial decay in the optical/NIR wavelength range is considerably flatter than at X-rays. Detailed fitting of the time-resolved SED shows that the break is very smooth with a sharpness index of 2.2 +- 0.2, and evolves towards lower frequencies as a power-law with index -1.23 +- 0.06. These are the first accurate and contemporaneous measurements of both the sharpness of the spectral break and its time evolution. The measured evolution of the cooling break (nu_c propto t^-1.2) is not consistent with the predictions of the standard model, wherein nu_c propto t^-0.5 is expected. A possible explanation for the observed behavior is a time dependence of the microphysical parameters, in particular the fraction of the total energy in the magnetic field epsilon_B. This conclusion provides further evidence that the standard fireball model is too simplistic, and time-dependent micro-physical parameters may be required to model the growing number of well-sampled afterglow light curves.Comment: accepted to A&A, 13 pages, 5 figure

The Lantern, 2022-2023

The Genie and the Scotsman • Taxi Driver Savior Complex • Midnight Waltz • Eulogy of Caution • Don\u27t cry over spilled milk!! • I am the spider • The Lamb • The Witch and the Shepherd • Nostalgia • In the Summer I Want Light • I Am (Not) • Thanatophobia • We\u27re not children anymore • Hamlet\u27s Fool • Lemon • the last two people in the world • Amongst Chaos (what captivated me) • How About Now, Billy Joel • Bug Trap • Spring, Musser Hall, Room 219 • Time\u27s Denial • A Song of History • A Haiku for You • Hello! My Name Is: • Toilet Humor • Waterfalls • Communion • Shift • Mama Told Me Not To Waste My Life • Writer\u27s Block • Sharp-Tongued Women • Off Trail • Paper Bag Town • Serenity • Landscape of Ursinus Courtyard • Image #07, Affinist designer • Love Birds • Discount Narnia • False Security • Stripes and Illusions • The Burning of Ophelia • Molly\u27s Folly • The Son of Bethany • Meta • Little Blue Sailboats • Grease Trap • Hitchhiking With My Eyes Closed • The Donna of Our Time • The Magic of Cooking • The Closing Shift • A Baptism of Teeth • Dear Beloved • How Kansas Got to Chicago • Anywhere, if you look hard enoughhttps://digitalcommons.ursinus.edu/lantern/1191/thumbnail.jp

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Do tutors make a difference in online learning? A comparative study in two Open Online Courses

Two free fully online courses were offered by Peoples-uni on its Open Online Courses site, both as self-paced courses available any time and as courses run over four weeks with tutor-led discussions. We tested the hypothesis that there are no measurable differences in outcomes between the two delivery methods. Similar numbers attended both versions of each course; students came from multiple countries and backgrounds. Numbers of discussion forum posts were greater in tutor-led than self-paced courses. Measured outcomes of certificates of completion, quiz completion and marks gained were very similar and not statistically significantly different between the tutor-led and the self-paced versions of either course. In light of little discernible difference in outcome between self-paced learning compared with courses including tutor-led discussions, the utility of the time cost to tutors is in question. The findings may be relevant to others designing online courses, including MOOCs

Data set for "Automated Wafer-Level Characterisation of Electrochemical Test Structures for Wafer Scanning"

This paper presents an automated system for the electrochemical characterization of micro-scale test structures at the wafer level, with the objective to identify good devices suitable for full characterization and packaging. The integration of the on-wafer characterization enables a quality assessment of the devices prior to packaging ensuring the development of this technology minimizes the packaging of faulty sensors. The prototype system integrates all the elements for automated on-wafer in-line characterization of electrochemistry based systems thereby confirming the suitability of this approach for implementation on commercial automated probers, which are generally available for parametric testing. The system's capabilities are demonstrated on a three-electrode cell design typically employed in electrochemical sensing applications. Finally, the system is integrated with a semi-automatic probe station and its potential demonstrated by wafer mapping the performance of electrochemical microelectrode devices.Schmueser, Ilka; Mackay, Logan; Moore, Fiona; Doherty, Kayleigh; Elliott, Justin P.; Mount, Andrew R.; Walton, Anthony J.; Smith, Stewart; Terry, Jonathan G.. (2020). Data set for "Automated Wafer-Level Characterisation of Electrochemical Test Structures for Wafer Scanning", [dataset]. University of Edinburgh. School of Engineering. https://doi.org/10.7488/ds/2759

COS Ambassadors

A collection of materials and resources for COS ambassadors