4,289 research outputs found
The X-ray Emissions from the M87 Jet: Diagnostics and Physical Interpretation
We reanalyze the deep Chandra observations of the M87 jet, first examined by
Wilson & Yang (2002). By employing an analysis chain that includes image
deconvolution, knots HST-1 and I are fully separated from adjacent emission. We
find slight but significant variations in the spectral shape, with values of
ranging from . We use VLA radio observations, as well
as HST imaging and polarimetry data, to examine the jet's broad-band spectrum
and inquire as to the nature of particle acceleration in the jet. As shown in
previous papers, a simple continuous injection model for synchrotron-emitting
knots, in which both the filling factor, , of regions within which
particles are accelerated and the energy spectrum of the injected particles are
constant, cannot account for the X-ray flux or spectrum. Instead, we propose
that is a function of position and energy and find that in the inner
jet, , and
in knots A and B, , where is the emitted photon energy and and is the
emitting electron energy. In this model, the index of the injected electron
energy spectrum () is at all locations in
the jet, as predicted by models of cosmic ray acceleration by ultrarelativistic
shocks. There is a strong correlation between the peaks of X-ray emission and
minima of optical percentage polarization, i.e., regions where the jet magnetic
field is not ordered. We suggest that the X-ray peaks coincide with shock waves
which accelerate the X-ray emitting electrons and cause changes in the
direction of the magnetic field; the polarization is thus small because of beam
averaging.Comment: Accepted for publication in ApJ; 21 pages, 9 figures, 2 tables;
abstract shortened for astro-ph; Figures 1, 7 and 8 at reduced resolutio
Entrepreneurship Education: Engineering a Pracademic Approach
Innovation and entrepreneurship are becoming increasingly important as we rely on economies to create jobs around the globe. And yet, considering the myriad and dynamic business environments of the 21st century and ever increasing consumer power, the risk of entrepreneurial activity has increased considerably. Consequently, we need to educate engineers in an innovative manner and fundamentally change the teaching methods, curriculum, and research in entrepreneurship education. Applying the scholarship of teaching and learning (SoTL) to entrepreneurship with similar rigor can increase the odds of being successful engineering entrepreneurs. Still, faculty and administrators of engineering programs are hesitant to introduce courses into an engineering curriculum outside of engineering fundaments. The paradox, however, is that non-core engineering courses including leadership and engineering management can help students develop highly desired attributes that contribute to career and industry success.
In this paper, the authors look at current trends in entrepreneurship education and will propose a potential new approach to innovation and entrepreneurship education for engineers in the 21st century. This approach will focus on pracademic (practical / professional and academic) learning concepts that are both engaging and worthwhile for student-centered learning. Supplementary pedagogical approaches are necessary to augment classroom learning for aligning active-learning topics within innovative course frameworks. This new approach will focus on four topics: innovation in teaching methods, introducing leadership education into the entrepreneurship curriculum, quality within systems engineering management, and using rigorous research to drive transformational change in entrepreneurship education. The pracademic approach will be taught as a workshop series or as courses in the entrepreneurship domain and will be presented as part of this paper where methods, leadership, quality, and rigorous research are the central tenets the authors propose for serious and thrivable consideration
Exploring the Dynamics of Fungal Cellular Automata
Cells in a fungal hyphae are separated by internal walls (septa). The septa
have tiny pores that allow cytoplasm flowing between cells. Cells can close
their septa blocking the flow if they are injured, preventing fluid loss from
the rest of filament. This action is achieved by special organelles called
Woronin bodies. Using the controllable pores as an inspiration we advance one
and two-dimensional cellular automata into Elementary fungal cellular automata
(EFCA) and Majority fungal automata (MFA) by adding a concept of Woronin bodies
to the cell state transition rules. EFCA is a cellular automaton where the
communications between neighboring cells can be blocked by the activation of
the Woronin bodies (Wb), allowing or blocking the flow of information
(represented by a cytoplasm and chemical elements it carries) between them. We
explore a novel version of the fungal automata where the evolution of the
system is only affected by the activation of the Wb. We explore two case
studies: the Elementary Fungal Cellular Automata (EFCA), which is a direct
application of this variant for elementary cellular automata rules, and the
Majority Fungal Automata (MFA), which correspond to an application of the Wb to
two dimensional automaton with majority rule with Von Neumann neighborhood. By
studying the EFCA model, we analyze how the 256 elementary cellular automata
rules are affected by the activation of Wb in different modes, increasing the
complexity on applied rule in some cases. Also we explore how a consensus over
MFA is affected when the continuous flow of information is interrupted due to
the activation of Woronin bodies.Comment: 31 pages, 30 figure
Numerical models of irrotational binary neutron stars in general relativity
We report on general relativistic calculations of quasiequilibrium
configurations of binary neutron stars in circular orbits with zero vorticity.
These configurations are expected to represent realistic situations as opposed
to corotating configurations. The Einstein equations are solved under the
assumption of a conformally flat spatial 3-metric (Wilson-Mathews
approximation). The velocity field inside the stars is computed by solving an
elliptical equation for the velocity scalar potential. Results are presented
for sequences of constant baryon number (evolutionary sequences). Although the
central density decreases much less with the binary separation than in the
corotating case, it still decreases. Thus, no tendency is found for the stars
to individually collapse to black hole prior to merger.Comment: Minor corrections, improved figure, 5 pages, REVTeX, Phys. Rev. Lett.
in pres
Challenges in Monitoring Regional Trail
This study reports traffic monitoring results at 30 locations on a 972-mi shared-use trail network across the east-central United States. We illustrate challenges in adapting the principles in the Federal Highway Administration’s Traffic Monitoring Guide to a regional trail network. We make four contributions: 1) we use factor analysis and k-means clustering to implement a stratified random process for selecting monitoring sites; 2) we illustrate quality assurance procedures and the challenges of obtaining valid results from a multi-state monitoring system; 3) we describe variation in trail traffic volumes across five land use classes in response to daily weather and seasons; and 4) we report two performance measures for the network: annual average daily trail traffic and trail miles traveled. The Rails to Trails Conservancy deployed passive infrared traffic monitors in 2015 through 2017. Site-specific regression models were used to impute missing daily traffic volumes. The effects of weather were consistent across land use classes but the effects of temporal variables, including weekend and season of year, varied. A plan for short-duration monitoring is presented. Results confirm the FHWA monitoring principles and the difficulties of implementing them regionally
Chandra Observations of the Radio Galaxy 3C 445 and the Hotspot X-ray Emission Mechanism
We present new {\it Chandra} observations of the radio galaxy 3C 445,
centered on its southern radio hotspot. Our observations detect X-ray emission
displaced upstream and to the west of the radio-optical hotspot. Attempting to
reproduce both the observed spectral energy distribution (SED) and the
displacement, excludes all one zone models. Modeling of the radio-optical
hotspot spectrum suggests that the electron distribution has a low energy
cutoff or break approximately at the proton rest mass energy. The X-rays could
be due to external Compton scattering of the cosmic microwave background
(EC/CMB) coming from the fast (Lorentz factor ) part of a
decelerating flow, but this requires a small angle between the jet velocity and
the observer's line of sight (). Alternatively, the
X-ray emission can be synchrotron from a separate population of electrons. This
last interpretation does not require the X-ray emission to be beamed.Comment: 9 pages, 5 figures, ApJ, in pres
Measurement of low‐density lipoprotein cholesterol levels in primary and secondary prevention patients: Insights from the PALM registry
Background The 2013 American College of Cardiology/American Heart Association Guideline on the Treatment of Blood Cholesterol to Reduce Atherosclerotic Cardiovascular Risk in Adults recommended testing low-density lipoprotein cholesterol ( LDL -C) to identify untreated patients with LDL -C ≥190 mg/dL, assess lipid-lowering therapy adherence, and consider nonstatin therapy. We sought to determine whether clinician lipid testing practices were consistent with these guidelines. Methods and Results The PALM (Patient and Provider Assessment of Lipid Management) registry enrolled primary and secondary prevention patients from 140 US cardiology, endocrinology, and primary care offices in 2015 and captured demographic data, lipid treatment history, and the highest LDL -C level in the past 2 years. Core laboratory lipid levels were drawn at enrollment. Among 7627 patients, 2787 (36.5%) had no LDL -C levels measured in the 2 years before enrollment. Patients without chart-documented LDL -C levels were more often women, nonwhite, uninsured, and non-college graduates (all P\u3c0.01). Patients without prior lipid testing were less likely to receive statin treatment (72.6% versus 76.0%; P=0.0034), a high-intensity statin (21.5% versus 24.3%; P=0.016), nonstatin lipid-lowering therapy (24.8% versus 27.3%; P=0.037), and had higher core laboratory LDL -C levels at enrollment (median 97 versus 92 mg/dL; P\u3c0.0001) than patients with prior LDL -C testing. Of 166 individuals with core laboratory LDL -C levels ≥190 mg/dL, 36.1% had no LDL -C measurement in the prior 2 years, and 57.2% were not on a statin at the time of enrollment. Conclusions In routine clinical practice, LDL -C testing is associated with higher-intensity lipid-lowering treatment and lower achieved LDL -C level
Optical detection of the Pictor A jet and tidal tail : evidence against an IC/CMB jet
Date of Acceptance: 12/06/2015New images of the FR II radio galaxy Pictor A from the Hubble Space Telescope reveal a previously undiscovered tidal tail, as well as a number of jet knots coinciding with a known X-ray and radio jet. The tidal tail is approximately 5″ wide (3 kpc projected), starting 18″ (12 kpc) from the center of Pictor A, and extends more than 90″ (60 kpc). The knots are part of a jet observed to be about 4′ (160 kpc) long, extending to a bright hotspot. These images are the first optical detections of this jet, and by extracting knot flux densities through three filters, we set constraints on emission models. While the radio and optical flux densities are usually explained by synchrotron emission, there are several emission mechanisms that might be used to explain the X-ray flux densities. Our data rule out Doppler-boosted inverse Compton scattering as a source of the high-energy emission. Instead, we find that the observed emission can be well described by synchrotron emission from electrons with a low-energy index (p ∼ 2) that dominates the radio band, while a high-energy index (p ∼ 3) is needed for the X-ray band and the transition occurs in the optical/infrared band. This model is consistent with a continuous electron injection scenario.Peer reviewedFinal Accepted Versio
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