Sensitivity of He Flames in X-ray Bursts to Nuclear Physics

Through the use of axisymmetric 2D hydrodynamic simulations, we further investigate laterally propagating flames in X-ray bursts (XRBs). Our aim is to understand the sensitivity of a propagating helium flame to different nuclear physics. Using the Castro simulation code, we confirm the phenomenon of enhanced energy generation shortly after a flame is established after by adding ${}^{12}$C(p, ${\gamma}$)${}^{13}$N(${\alpha}$, p)${}^{16}$O to the network, in agreement with the past literature. This sudden outburst of energy leads to a short accelerating phase, causing a drastic alteration in the overall dynamics of the flame in XRBs. Furthermore, we investigate the influence of different plasma screening routines on the propagation of the XRB flame. We finally examine the performance of simplified-SDC, a novel approach to hydrodynamics and reaction coupling incorporated in Castro, as an alternative to operator-splitting.Comment: 18 pages, 17 figure

Dynamics of Laterally Propagating Flames in X-ray Bursts. I. Burning Front Structure

We investigate the structure of laterally-propagating flames through the highly-stratified burning layer in an X-ray burst. Two-dimensional hydrodynamics simulations of flame propagation are performed through a rotating plane-parallel atmosphere, exploring the structure of the flame. We discuss the approximations needed to capture the length and time scales at play in an X-ray burst and describe the flame acceleration observed. Our studies complement other multidimensional studies of burning in X-ray bursts.Comment: Submitted to Ap

Individualized Pain Plans for Pediatric Sickle Cell Patients

Background: Vaso-occlusive (VOC) pain crisis in sickle cell pediatric patients is a hallmark symptom, and both unpredictable and crippling. There is a lack of evidence as to what is best practice to avoid a VOC pain crisis in pediatric sickle cell patients. Individualized Pain Plans were created and trialed based off the format asthma action plans with goals to improve overall pain management and to prevent or decrease emergency department visits and hospitalizations. Aims: This is a cross-sectional and quality improvement study designed to evaluate the effectiveness of previously implemented Individualized Sickle Cell Pain Plans in a midwestern children’s hospital. The primary aim was to evaluate the physical and psychosocial risk factors related to the pain experiences in the post implementation timeline of receiving their individualized pain plan. The second aim was to evaluate the satisfaction and use by both parent and child of the pain plans. Methods: Evaluation of outcomes of these plans were done by survey using the Pediatric Pain Screening Tool (PPST), satisfaction questionnaires, and chart audits of Emergency Department (ED) visits due to pain crisis pre and post implementation administered by the Hematology/Oncology (H/O) team. Settings: This study was conducted at a midwestern children’s hospital and associated H/O clinic. Participants/Subjects: Sample population included pediatric patients, aged four to 18 years old, who are diagnosed with sickle cell disease who have an individualized pain plan created by their Hematology provider, and their parent(s) and/or caregivers. Each patient/parent/caregiver gave verbal consent to participate. Design: The data was collected at a routine follow up appointment at the H/O clinic. Surveys were administered at the appointments including the PPST, demographics, and a satisfaction/use survey for the patient and parent. A chart audit of ED visits due to pain crisis pre and post pain plan implementation was also performed. Results: A total of eleven patients and eleven parents were captured in this study that qualified based on the inclusion criteria. 73% of responses being mostly satisfied and very satisfied with the pain plans, 27% of responses were sometimes satisfied and satisfied, and one response with no satisfaction. Eleven parents were asked how often the pain plans were being used and/or referenced, 18% said they were not using it and needed help with how to use it better, 9% use it when their child cannot sleep at night due to pain, 45% use it when their child cannot play or go to school due to pain, and 27% said they use it when their child tells them they have pain. Six patients were then asked how often they were using the pain plans, one said they do not use it because he lost it, one said they do not know how to use the pain plan, one said they use it when they cannot play, and three (50%) say they use it when an adult tells them to. When compared, the number of ED and inpatient hospital admissions (IHA) for each patient pre and post pain plan implementation, it was found that ED visits increased from pre (16 of 74 patients) to post (29 of 74 patients). Conclusions: Individualized pain plans provide guidance for patients and families when a pain crisis begins. It is recommended that these pain plans be implemented at other pediatric hospitals across the nation to support patients with sickle cell disease and their families. It would be recommended that the clinic continue to collect data indefinitely due to the small sample population of this study as this could provide stronger evidence for the use of the individualized pain plans

White Dwarf Mergers on Adaptive Meshes I. Methodology and Code Verification

The Type Ia supernova progenitor problem is one of the most perplexing and exciting problems in astrophysics, requiring detailed numerical modeling to complement observations of these explosions. One possible progenitor that has merited recent theoretical attention is the white dwarf merger scenario, which has the potential to naturally explain many of the observed characteristics of Type Ia supernovae. To date there have been relatively few self-consistent simulations of merging white dwarf systems using mesh-based hydrodynamics. This is the first paper in a series describing simulations of these systems using a hydrodynamics code with adaptive mesh refinement. In this paper we describe our numerical methodology and discuss our implementation in the compressible hydrodynamics code CASTRO, which solves the Euler equations, and the Poisson equation for self-gravity, and couples the gravitational and rotation forces to the hydrodynamics. Standard techniques for coupling gravitation and rotation forces to the hydrodynamics do not adequately conserve the total energy of the system for our problem, but recent advances in the literature allow progress and we discuss our implementation here. We present a set of test problems demonstrating the extent to which our software sufficiently models a system where large amounts of mass are advected on the computational domain over long timescales. Future papers in this series will describe our treatment of the initial conditions of these systems and will examine the early phases of the merger to determine its viability for triggering a thermonuclear detonation.Comment: Accepted for publication in the Astrophysical Journa

MAESTROeX: A Massively Parallel Low Mach Number Astrophysical Solver

We present MAESTROeX, a massively parallel solver for low Mach number astrophysical flows. The underlying low Mach number equation set allows for efficient, long-time integration for highly subsonic flows compared to compressible approaches. MAESTROeX is suitable for modeling full spherical stars as well as well as planar simulations of dynamics within localized regions of a star, and can robustly handle several orders of magnitude of density and pressure stratification. Previously, we have described the development of the predecessor of MAESTROeX, called MAESTRO, in a series of papers. Here, we present a new, greatly simplified temporal integration scheme that retains the same order of accuracy as our previous approaches. We also explore the use of alternative spatial mapping of the one-dimensional base state onto the full Cartesian grid. The code leverages the new AMReX software framework for block-structured adaptive mesh refinement (AMR) applications, allowing for scalability to large fractions of leadership-class machines. Using our previous studies on the convective phase of single-degenerate progenitor models of Type Ia supernovae as a guide, we characterize the performance of the code and validate the new algorithmic features. Like MAESTRO, MAESTROeX is fully open source