Simulating Synchrotron Optical Flashes in the Reverse Shock of a Gamma Ray Burst

We construct a Monte Carlo simulation in Python to calculate optical flashes at 5x10¹⁴ Hz peaking at 6x10³¹ erg s⁻¹Hz⁻¹St⁻¹ due to synchrotron radiation from the reverse shock of a gamma-ray burst’s jet. While analytical solutions to this problem exist, they rely on sweeping simplifications of what is necessarily a highly variable and complex system. The simulation expands upon the well understood properties of single-electron synchrotron to predict observer-frame light curves from isotropic but analytically intractable outflows. The light curves produced compare favorably with theoretical predictions for simpler jets. Unfortunately, the simulation so far fails to resolve features associated with the geometry of our jet. Work continues toward a solution to this problem

Across the Tachocline Divide: Convection and Dynamo Action In M-Dwarf Stars

In this thesis, we explore the convective dynamics taking place in the interiors of M-dwarf stars across the transition from partial to full-sphere convection. Additionally, we search for theoretical explanations for the observed Tachocline Divide, whereby fully convective M-dwarfs seem to maintain their magnetic activity for longer and to flare more aggressively than more massive, partially convective M stars. To this end, we employ the open-source Rayleigh code on massively parallel supercomputers to simulate rotating spherical shells of anelastic magnetohydrodynamic convection in 3D with full nonlinearity. These shells include in their computational domains most of the modeled stars&rsquo; convection zones, as well as the underlying radiative zone and tachocline where applicable. We consider the dynamics of more than 80 simulations falling into three primary classes of models: partially convective spectral type M2 (0.4M) stars without underlying tachoclines, partially convective M2 stars with tachoclines, and fully convective M4 (0.3M) stars.&nbsp; We observe the broad characteristics of dynamo action in the convection zones of both spectral types of M-dwarfs to be shared not only between them, but also with more massive G- and K-stars. We find parity in parameter scalings for the efficiency of their dynamos, the timing of their cycles, and the strength of magnetic feedbacks upon the differential rotation. The effect on the differential rotation is of particular note &ndash; in many of the models we compute, the shear is strongly quenched by the intense magnetic fields, leading to nearly solid body rotation in the convection zone. We find that the most rapidly rotating models we considered tended to produce prograde traveling nests of enhanced convection. We observe these nests to interact strongly with the magnetic fields through their strong helical turbulence, triggering reversals of the magnetic field and accelerating flux emergence. In one particularly novel case, nest-driven field reversal sets the cycle period of the global dynamo. Among the M-dwarfs, we find a striking tendency toward single hemisphere iii dynamo states, which seem to grow more prominent with the increasing depth of the convection zone. We argue that these states result from weakly nonlinear coupling between even and odd eigenmodes of the dynamo solution. We find the generation of buoyant magnetic loops to be a general property of our simulations, despite their diffusivity. We develop a machine-learning pipeline for the autonomous isolation of these intricate magnetic structures, which we dub LoopNet.&nbsp; In consideration of the tachocline divide, we find that the presence of a tachocline in M2 stars significantly increases the prominence of large-scale axisymmetric fields in the global magnetic energy budget. We find that this in turn leads to surface fields which are much more dipolar. Through the spin-down interactions of these magnetic fields with the stellar wind, this trend implies shorter magnetic lifetimes than on M2 stars without tachoclines. However, we find that the surface fields of fully convective M4 stars in our simulations are both stronger and more dipolar than those of even the M2 stars with tachoclines. Even after accounting for stellar sizes, the implication of these findings is that the M4 stars should have shorter magnetic lifetimes than M2 stars. This comes as a surprise, due to the distinct inversion of this prediction in observations. We discuss various avenues by which the tension between our findings and observations might be resolved. Using LoopNet, we find that turbulent stirring by convection in the deep interiors of M4 stars allows them to produce significantly more buoyantly rising magnetic flux ropes than similarly active M2 stars. This result may possibly explain the cause for the enhanced flare rate exhibited by fully convective M-dwarfs when compared to more massive active stars. &nbsp;</p

An Institutional Theory Perspective on EHR Engagement: Mandates, Penalties, and Enforcement

Electronic Health Record (EHR) systems are the predominant information system (IS) used by healthcare clinicians and have been the source of both great success and pain. User engagement with EHR systems is unique from traditional IS contexts in significant ways. Prior research explains EHR usage and success primarily on traditional technology acceptance research (i.e., TAM, UTAUT). However, these models assume that EHR engagement is no different from IS systems in general business domains. Yet, the healthcare context is far more regulated than most. Based on qualitative focus group sessions with a leading healthcare analytics firm (KLAS Research), we identify the role of mandates, penalties, and enforcements from government, organizations, associations, and insurance companies in explaining EHR engagement. We validate a measurement instrument for these factors and demonstrate that their inclusion can improve model fit five times over a traditional UTAUT-based model (R2 = 54.8% versus 10.2%)

New physical characterization of the Fontana Lapilli basaltic Plinian eruption, Nicaragua

The Fontana Lapilli deposit was erupted in the late Pleistocene from a vent, or multiple vents, located near Masaya volcano (Nicaragua) and is the product of one of the largest basaltic Plinian eruptions studied so far. This eruption evolved from an initial sequence of fluctuating fountain-like events and moderately explosive pulses to a sustained Plinian episode depositing fall beds of highly vesicular basaltic-andesite scoria (SiO2 > 53 wt%). Samples show unimodal grain size distribution and a moderate sorting that are uniform in time. The juvenile component predominates (> 96 wt%) and consists of vesicular clasts with both sub-angular and fluidal, elongated shapes. We obtain a maximum plume height of 32 km and an associated mass eruption rate of 1.4 × 108 kg s−1 for the Plinian phase. Estimates of erupted volume are strongly sensitive to the technique used for the calculation and to the distribution of field data. Our best estimate for the erupted volume of the majority of the climactic Plinian phase is between 2.9 and 3.8 km3 and was obtained by applying a power-law fitting technique with different integration limits. The estimated eruption duration varies between 4 and 6 h. Marine-core data confirm that the tephra thinning is better fitted by a power-law than by an exponential trend

Biotic and environmental dynamics through the Late Jurassic-Early Cretaceous transition: evidence for protracted faunal and ecological turnover

The Late Jurassic to Early Cretaceous interval represents a time of environmental upheaval and cataclysmic events, combined with disruptions to terrestrial and marine ecosystems. Historically, the Jurassic/Cretaceous (J/K) boundary was classified as one of eight mass extinctions. However, more recent research has largely overturned this view, revealing a much more complex pattern of biotic and abiotic dynamics than has previously been appreciated. Here, we present a synthesis of our current knowledge of Late Jurassic–Early Cretaceous events, focusing particularly on events closest to the J/K boundary. We find evidence for a combination of short-term catastrophic events, large-scale tectonic processes and environmental perturbations, and major clade interactions that led to a seemingly dramatic faunal and ecological turnover in both the marine and terrestrial realms. This is coupled with a great reduction in global biodiversity which might in part be explained by poor sampling. Very few groups appear to have been entirely resilient to this J/K boundary ‘event’, which hints at a ‘cascade model’ of ecosystem changes driving faunal dynamics. Within terrestrial ecosystems, larger, more-specialised organisms, such as saurischian dinosaurs, appear to have suffered the most. Medium-sized tetanuran theropods declined, and were replaced by larger-bodied groups, and basal eusauropods were replaced by neosauropod faunas. The ascent of paravian theropods is emphasised by escalated competition with contemporary pterosaur groups, culminating in the explosive radiation of birds, although the timing of this is obfuscated by biases in sampling. Smaller, more ecologically diverse terrestrial non-archosaurs, such as lissamphibians and mammaliaforms, were comparatively resilient to extinctions, instead documenting the origination of many extant groups around the J/K boundary. In the marine realm, extinctions were focused on low-latitude, shallow marine shelf-dwelling faunas, corresponding to a significant eustatic sea-level fall in the latest Jurassic. More mobile and ecologically plastic marine groups, such as ichthyosaurs, survived the boundary relatively unscathed. High rates of extinction and turnover in other macropredaceous marine groups, including plesiosaurs, are accompanied by the origin of most major lineages of extant sharks. Groups which occupied both marine and terrestrial ecosystems, including crocodylomorphs, document a selective extinction in shallow marine forms, whereas turtles appear to have diversified. These patterns suggest that different extinction selectivity and ecological processes were operating between marine and terrestrial ecosystems, which were ultimately important in determining the fates of many key groups, as well as the origins of many major extant lineages. We identify a series of potential abiotic candidates for driving these patterns, including multiple bolide impacts, several episodes of flood basalt eruptions, dramatic climate change, and major disruptions to oceanic systems. The J/K transition therefore, although not a mass extinction, represents an important transitional period in the co-evolutionary history of life on Earth

Associations of physician burnout with organizational electronic health record support and after-hours charting.

In 2017, 43.9% of US physicians reported symptoms of burnout. Poor electronic health record (EHR) usability and time-consuming data entry contribute to burnout. However, less is known about how modifiable dimensions of EHR use relate to burnout and how these associations vary by medical specialty. Using the KLAS Arch Collaborative's large-scale nationwide physician (MD/DO) data, we used ordinal logistic regression to analyze associations between self-reported burnout and after-hours charting and organizational EHR support. We examined how these relationships differ by medical specialty, adjusting for confounders. Physicians reporting ≤ 5 hours weekly of after-hours charting were twice as likely to report lower burnout scores compared to those charting ≥6 hours (aOR: 2.43, 95% CI: 2.30, 2.57). Physicians who agree that their organization has done a great job with EHR implementation, training, and support (aOR: 2.14, 95% CI: 2.01, 2.28) were also twice as likely to report lower scores on the burnout survey question compared to those who disagree. Efforts to reduce after-hours charting and improve organizational EHR support could help address physician burnout