How strong are the Rossby vortices?

The Rossby wave instability, associated with density bumps in differentially rotating discs, may arise in several different astrophysical contexts, such as galactic or protoplanetary discs. While the linear phase of the instability has been well studied, the nonlinear evolution and especially the saturation phase remain poorly understood. In this paper, we test the non-linear saturation mechanism analogous to that derived for wave-particle interaction in plasma physics. To this end we perform global numerical simulations of the evolution of the instability in a two-dimensional disc. We confirm the physical mechanism for the instability saturation and show that the maximum amplitude of vorticity can be estimated as twice the linear growth rate of the instability. We provide an empirical fitting formula for this growth rate for various parameters of the density bump. We also investigate the effects of the azimuthal mode number of the instability and the energy leakage in the spiral density waves. Finally, we show that our results can be extrapolated to 3D discs.Comment: Accepted for publication in MNRA

Spinning-Down of Moving Magnetars in the Propeller Regime

We use axisymmetric magnetohydrodynamic simulations to investigate the spinning-down of magnetars rotating in the propeller regime and moving supersonically through the interstellar medium. The simulations indicate that magnetars spin-down rapidly due to this interaction, faster than for the case of a non-moving star. From many simulation runs we have derived an approximate scaling laws for the angular momentum loss rate, \dot{L} \propto \~\eta_m^{0.3}\mu^{0.6}\rho^{0.8}{\cal M}^{-0.4} \Omega_*^{1.5}, where \rho is the density of the interstellar medium, \cal M is Mach number, \mu is the star's magnetic moment, \Omega_* is its angular velocity, and \eta_m is magnetic diffusivity. A magnetar with a surface magnetic field of 10^{13} - 10^{15} G is found to spin-down to a period P > 10^5-10^6 s in \sim 10^4 - 10^5 years. There is however uncertainty about the value of the magnetic diffusivity so that the time-scale may be longer. We discuss this model in respect of Soft Gamma Repeaters (SGRs) and the isolated neutron star candidate RXJ1856.5-3754.Comment: 10 pages, 4 figures, accepted by MNRAS. See version with better resolution figures and animation at http://astrosun2.astro.cornell.edu/us-rus/propeller.ht

Relativistic Jets from Accretion Disks

The jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, hydromagnetic jets, which have a significant mass flux and have energy and angular momentum carried by both matter and electromagnetic field and, Poynting jets, where the mass flux is small and energy and angular momentum are carried predominantly by the electromagnetic field. Here, we describe recent theoretical work on the formation of relativistic Poynting jets from magnetized accretion disks. Further, we describe new relativistic, fully-electromagnetic, particle-in-cell simulations of the formation of jets from accretion disks. Analog Z-pinch experiments may help to understand the origin of astrophysical jets.Comment: 7 pages, 3 figures, Proc. of High Energy Density Astrophysics Conf., 200

An evaluation of the 1974 Forestry Incentives Program in twelve East Tennessee Counties

In order to evaluate the effectiveness of the 1974 Forestry Incentives Program (FIP), interviews were conducted with Agricultural Stabilization and Conservation Service (ASCS) county executive direc-tors, district foresters, area foresters, and FIP applicants in 12 East Tennessee counties. Administrator questionnaires were designed to determine the extent of FIP activity in the various administrators\u27 areas of responsibility; the administrators\u27 knowledge of FIP and its procedures; attitudes and opinions which influenced administrators; and administrative problems that occurred. Applicant questionnaires were designed to learn the applicants\u27 characteristics, past land management practices, FIP accomplishments, and problems that prevented project completions. FIP was not successful in the study area. Less than 1% of the eligible landowners applied for assistance. Completed projects affected slightly more than 100 acres and comprised just 28% of the approved applications. FIP had numerous inherent problems that retarded its effectiv- ness. Tennessee made no provisions to directly assist landowners in completing their projects. A ten-acre minimum tree planting require-ment in Tennessee prevented several applications from being approved for FIP. Maximum cost-sharing rates set by the state were often substantially inadequate. ASCS had no established procedure for screening applicants; therefore, many ineligible owners were enrolled in FIP, and administrative duties were unnecessarily increased. Disinterest in forestry by ASCS county executive directors and Extension Service county agents appeared to be the outstanding administrator problem that reduced FIP success. These personnel often promoted non-forestry programs and neglected FIP. Another administrator problem was limited understanding of the program, caused by the pro-gram\u27s newness and numerous amendments. Foresters often could not efficiently administer their areas due to a heavy workload. Landowners faced financial difficulties and problems of allocating their time to work on their projects. The compounded problems of the high percentage of absentee-owner applicants also prevented many pro-ject completions. Suggestions were offered to aid improvement of the Forestry Incentives Program and similar programs that may be developed in the future. These suggestions include the following: 1. start the program early in the year; 2. adjust and regulate cost-shares; 3. provide state labor assistance and promote vendor services; 4. increase the forestry-awareness of extension agents and ASCS county directors; 5. improve communications

Diabetes Education Referral from the Emergency Department to Improve Patient Care and Health Literacy

Diabetes is a complex disease that can lead to increased morbidity and mortality. Inadequate disease management is considered when patients present to the emergency department (ED) for care related to this disease. Once out of the hospital or ED, it is imperative the patient receives timely follow-up care to effectively manage the disease to reduce morbidity and mortality and to decrease return visits to the ED. Primary care across the nation is facing a national shortage with provider time spent with patients decreasing and patients’ length of time spent waiting to get an appointment increasing (Medscape, 2017; Merritt Hawkins, 2017 ). Diabetes Education Centers are available in various settings throughout the Denver Metropolitan area. Diabetes education could provide acute self-management skills, lifestyle, and behavior modifications. Diabetes education is an intervention supported by the American Diabetes Association (2018) and paid for by most insurances including Medicaid and Medicare. Adding this modality to treatment helps diversify and intensify the patient’s own health literacy and ability in managing his/her diabetes disease. The Medical Center of Aurora (TMCA) is a Level II Trauma Center in a large suburb of Denver, Colorado. Discharge practice includes referring diabetic patients to follow up within days at their primary care provider; this time frame could be iv problematic for patients. This project evaluated current ED provider knowledge of outpatient follow-up care and outpatient diabetes services available to discharged ED patients. The Doctor of Nursing Practice student then provided an educational intervention to address identified gaps in knowledge and evidence regarding TMCA’s Diabetes Education Center as an adjunct in follow up the provider could then include in the discharge instructions. A post-intervention survey gauged providers’ new knowledge and probability of providing this referral to their ED patients in the future. Lastly, an initial implementation of making a referral to an outpatient diabetes center was observed and evaluation performed

Engaging Today’s Students: Current Topics 2.0

In this session we share a new version of a Current Topics assignment geared toward millennial students’ preferences for structure and hands-on learning. Participants will try-out the assignment by reading a short article and answering the three assignment prompts: 1) What are the main points of the article? 2) What points are the most interesting and/or useful to you? 3) What course concepts are illustrated in the article? Connections to student learning outcomes are discussed as well as ways to adapt this assignment. Article citations, grading practices and student feedback are shared

Relativistic Poynting Jets from Accretion Disks

A model is developed for relativistic Poynting jets from the inner region of a disk around a rotating black hole. The disk is initially threaded by a dipole-like magnetic field. The model is derived from the special relativistic equation for a force-free electromagnetic field. The ``head'' of the Poynting jet is found to propagate outward with a velocity which may be relativistic. The Lorentz factor of the head (Gamma) is found to be dependent on the magnetic field strength close to the black hole, B_0, the density of the external medium n_ext, and on the ratio R=r_0/r_g >1, where r_g is the gravitational radius of the black hole, and r_0 is the radius of the O-point of the initial dipole field threading the disk. For conditions pertinent to an active galactic nuclei, Gamma is approximately equal to 8 (10/R)^(1/3) (B_0/10^3 Gauss)^(1/3) (1/cm^3/n_ext)^(1/6). This model offers an explanation for the observed Lorentz factors which are of the order of 10 for the parsec-scale radio jets measured with very long baseline interferometry.Comment: 4 pages, 1 figur