Cylindrical Magnets and Ideal Solenoids

Both wire-wound solenoids and cylindrical magnets can be approximately modeled as ideal, azimuthally symmetric solenoids. We present here an exact solution for the magnetic field of an ideal solenoid in an especially easy to use form. The field is expressed in terms of a single function that can be rapidly computed by means of a compact, highly efficient algorithm, which can be coded as an add-in function to a spreadsheet, making field calculations accessible even to introductory students. In computational work these expressions are not only accurate but also just as fast as most approximate expressions. We demonstrate their utility by numerically simulating the experiment of dropping a cylindrical magnet through a nonmagnetic conducting tube and then comparing the calculation with data obtained from experiments suitable for an undergraduate laboratory.Comment: 12 pages, 5 figures, revTe

A Bow Shock Nebula Around a Compact X-Ray Source in the Supernova Remnant IC443

We present spectra and high resolution images of the hard X-ray feature along the southern edge of the supernova remnant IC443. Data from the Chandra X-ray Observatory reveal a comet-shaped nebula of hard emission, which contains a softer point source at its apex. We also present 20cm, 6cm, and 3.5cm images from the Very Large Array that clearly show the cometary nebula. Based on the radio and X-ray morphology and spectrum, and the radio polarization properties, we argue that this object is a synchrotron nebula powered by the compact source that is physically associated with IC443. The spectrum of the soft point source is adequately but not uniquely fit by a black body model (kT=0.71 +/- 0.08 keV, L=(6.5 +/- 0.9) * 10^31 erg/s). The cometary morphology of the nebula is the result of the supersonic motion of the neutron star (V_NS=250 +/- 50 km/s), which causes the relativistic wind of the pulsar to terminate in a bow shock and trail behind as a synchrotron tail. This velocity is consistent with an age of 30,000 years for the SNR and its associated neutron star.Comment: 9 pages, 5 figures, accepted for publication in the ApJ Letter

Routine frailty assessment predicts postoperative complications in elderly patients across surgical disciplines – a retrospective observational study

BACKGROUND: Frailty is a frequent and underdiagnosed functional syndrome involving reduced physiological reserves and an increased vulnerability against stressors, with severe individual and socioeconomic consequences. A routine frailty assessment was implemented at our preoperative anaesthesia clinic to identify patients at risk. OBJECTIVE: This study examines the relationship between frailty status and the incidence of in-hospital postoperative complications in elderly surgical patients across several surgical disciplines. DESIGN: Retrospective observational analysis. SETTING: Single center, major tertiary care university hospital. Data collection took place between June 2016 and March 2017. PATIENTS: Patients 65 years old or older were evaluated for frailty using Fried's 5-point frailty assessment prior to elective non-cardiac surgery. Patients were classified into non-frail (0 criteria, reference group), pre-frail (1-2 positive criteria) and frail (3-5 positive criteria) groups. MAIN OUTCOME MEASURES: The incidence of postoperative complications was assessed until discharge from the hospital, using the roster from the National VA Surgical Quality Improvement Program. Propensity score matching and logistic regression analysis were performed. RESULTS: From 1186 elderly patients, 46.9% were classified as pre-frail (n = 556), and 11.4% as frail (n = 135). The rate of complications were significantly higher in the pre-frail (34.7%) and frail groups (47.4%), as compared to the non-frail group (27.5%). Similarly, length of stay (non-frail: 5.0 [3.0;7.0], pre-frail: 7.0 [3.0;9.0], frail 8.0 [4.5;12.0]; p < 0.001) and discharges to care facilities (non-frail:1.6%, pre-frail: 7.4%, frail: 17.8%); p < 0.001) were significantly associated with frailty status. After propensity score matching and logistic regression analysis, the risk for developing postoperative complications was approximately two-fold for pre-frail (OR 1.78; 95% CI 1.04-3.05) and frail (OR 2.08; 95% CI 1.21-3.60) patients. CONCLUSIONS: The preoperative frailty assessment of elderly patients identified pre-frail and frail subgroups to have the highest rate of postoperative complications, regardless of age, surgical discipline, and surgical risk. Significantly increased length of hospitalisation and discharges to care facilities were also observed. Implementation of routine frailty assessments appear to be an effective tool in identifying patients with increased risk. Now future studies are needed to investigate whether patients benefit from optimization of patient counselling, process planning, and risk reduction protocols based on the application of risk stratification

XMM-Newton observations of the supernova remnant IC 443: II. evidence of stellar ejecta in the inner regions

We investigate the spatial distribution of the physical and chemical properties of the hot X-ray emitting plasma of the supernova remnant IC 443, in order to get important constraints on its ionization stage, on the progenitor supernova explosion, on the age of the remnant, and its physical association with a close pulsar wind nebula. The hard X-ray thermal emission (1.4-5.0 keV) of IC 443 displays a centrally-peaked morphology, its brightness peaks being associated with hot (kT>1 keV) X-ray emitting plasma. A ring-shaped structure, characterized by high values of equivalent widths and median photon energy, encloses the PWN. Its hard X-ray emission is spectrally characterized by a collisional ionization equilibrium model, and strong emission lines of Mg, Si, and S, requiring oversolar metal abundances. Dynamically, the location of the ejecta ring suggests an SNR age of ~4,000 yr. The presence of overionized plasma in the inner regions of IC 443, addressed in previous works, is much less evident in our observations.Comment: 9 pages, 7 figures, accepted for publication in A&A. For hi-res figures, see http://www.astropa.unipa.it/Library/OAPA_preprints/aa20079123.pd

Six Years of Chandra Observations of Supernova Remnants

We present a review of the first six years of Chandra X-ray Observatory observations of supernova remnants. From the official "first-light" observation of Cassiopeia A that revealed for the first time the compact remnant of the explosion, to the recent million-second spectrally-resolved observation that revealed new details of the stellar composition and dynamics of the original explosion, Chandra observations have provided new insights into the supernova phenomenon. We present an admittedly biased overview of six years of these observations, highlighting new discoveries made possible by Chandra's unique capabilities.Comment: 82 pages, 28 figures, for the book Astrophysics Update

Milagro Observations of Multi-TeV Emission from Galactic Sources in the Fermi Bright Source List

We present the result of a search of the Milagro sky map for spatial correlations with sources from a subset of the recent Fermi Bright Source List (BSL). The BSL consists of the 205 most significant sources detected above 100 MeV by the Fermi Large Area Telescope. We select sources based on their categorization in the BSL, taking all confirmed or possible Galactic sources in the field of view of Milagro. Of the 34 Fermi sources selected, 14 are observed by Milagro at a significance of 3 standard deviations or more. We conduct this search with a new analysis which employs newly-optimized gamma-hadron separation and utilizes the full 8-year Milagro dataset. Milagro is sensitive to gamma rays with energy from 1 to 100 TeV with a peak sensitivity from 10-50 TeV depending on the source spectrum and declination. These results extend the observation of these sources far above the Fermi energy band. With the new analysis and additional data, multi-TeV emission is definitively observed associated with the Fermi pulsar, J2229.0+6114, in the Boomerang Pulsar Wind Nebula (PWN). Furthermore, an extended region of multi-TeV emission is associated with the Fermi pulsar, J0634.0+1745, the Geminga pulsar.Comment: Accepted for publication in Astrophysical Journal Letters June 30, 200

Why NS and BH mass distribition is bimodal?

The observed mass distribution for the compact remnants of massive stars (neutron stars and black holes) and its relationship to possible mechanisms for the ejection of the envelopes of type II and Ib/c supernovae is analyzed. The conclusion is drawn that this distribution can be obtained only by a magneto-rotational mechanism for the supernovae with sufficiently long time of the field amplification, and a soft equation of state for neutron stars with limiting masses \sim1.5-1.6M_\odot. Some consequences of this hypothesis are discussed.Comment: latex, 4 pages, 5 figures, Talk given at 5th Int. Tsessevich Conf. "Variable Stars", Odessa, Ukraine, August 200