449 research outputs found
The Supernova Remnant G11.2-0.3 and its central Pulsar
The plerion inside the composite Supernova Remnant G11.2-0.3 appears to be
dominated by the magnetic field to an extent unprecedented among well known
cases. We discuss its evolution as determined by a central pulsar and the
interaction with the surrounding thermal remnant, which in turn interacts with
the ambient medium. We find that a plausible scenario exists, where all the
observations can be reproduced with rather typical values for the parameters of
the system; we also obtain the most likely period for the still undetected
pulsar.Comment: 10 pages, to be published on ApJ Letters. Formatted using AASTe
A Combinational Digital Logic Design Tool for Practice and Assessment in Engineering Education
As technology advances, computers are being used almost everywhere. In a 2013 US Census report (File and Ryan, 2014), 83.8% (up from 78.9% in 2012) of U.S. households reported owning a computer with 74.4% reporting internet use (73.4% high speed internet). In recent years, the shift in educational technologies has been moving towards gaming, more specifically serious gaming. Although this is an important trend, there is still much to be said about e-learning through a step-by-step interactive process using an online practice tool. This paper presents a detailed description of the Combinational Logic Design Tool (CLDT) (Morsi and Russell (2007). CLDT was designed and developed under the CCLI project, #0737242, funded by the National Science Foundation, which aimed to develop and disseminate a novel online practice tool for on demand review and assessment in Electrical and Computer Engineering education. The paper also reports on a formal assessment conducted in a Digital Logic Design Classroom and presents the results of this assessment
Syntax circuitry: a mobile game for practicing programming language syntax
According to the U.S. Bureau of Labor Statistics [1], computer science professions are
among the fastest growing occupations in the U.S., and computer science occupations will add more
than half a million new jobs in the next ten years. A similar need for computer professionals is expected
in Kazakhstan. Simultaneously, universities in the U.S. and worldwide are seeing poor retention rates
in computer science, a major reason being that students often view the early courses in the subject as
uninteresting and dull [2]. Game-based learning is one of many techniques proposed to address this
issue [2,3,4,5]. We have developed a mobile game that provides an engaging way for students to practice
(not learn) the basic syntax of C, C++ and Java (since these languages share the same syntax for basic
constructs like declarations, selection and iteration). Learning programming language syntax is a tedious
process. Practicing by programming is, of course, ideal, but we believe that a game which is fun to play in
their spare time will help students get used to distinguishing correct syntactical constructs quickly
Problems for the WELS classification of planetary nebula central stars: Self-consistent nebular modelling of four candidates
IFU spectroscopy of southern planetary nebulae - III
In this paper, we describe integral field spectroscopic observations of four southern Galactic planetary nebulae (PNe), M3-4, M3-6, Hen2-29 and Hen2-37 covering the spectral range 3400–7000 Å. We derive the ionization structure, the physical conditions, the chemical compositions and the kinematical characteristics of these PNe and find good agreement with previous studies that relied upon the long-slit technique in their co-spatial area. From their chemical compositions as well as their spatial and kinematic characteristics, we determined that Hen2-29 is of the Peimbert type I (He- and N-rich), while the other three are of type II. The strength of the nebular He II line reveals that M3-3, Hen2-29 and Hen2-37 are of mid to high excitation classes while M3-6 is a low-excitation PN. A series of emission-line maps extracted from the data cubes were constructed for each PN to describe its overall structure. These show remarkable morphological diversity. Spatially resolved spectroscopy of M3-6 shows that the recombination lines of C II, C III, C IV and N III are of nebular origin, rather than arising from the central star as had been previously proposed. This result increases doubts regarding the weak emission-line star (WELS) classification raised by Basurah et al. In addition, they reinforce the probability that most genuine cases of WELS arise from irradiation effects in close binary central stars
DA495 - an aging pulsar wind nebula
We present a radio continuum study of the pulsar wind nebula (PWN) DA 495
(G65.7+1.2), including images of total intensity and linear polarization from
408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations
with the Effelsberg 100-m Radio Telescope. Removal of flux density
contributions from a superimposed \ion{H}{2} region and from compact
extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz,
with a spectral index below the break and
above it (). The
spectral break is more than three times lower in frequency than the lowest
break detected in any other PWN. The break in the spectrum is likely the result
of synchrotron cooling, and DA 495, at an age of 20,000 yr, may have
evolved from an object similar to the Vela X nebula, with a similarly energetic
pulsar. We find a magnetic field of 1.3 mG inside the nebula. After
correcting for the resulting high internal rotation measure, the magnetic field
structure is quite simple, resembling the inner part of a dipole field
projected onto the plane of the sky, although a toroidal component is likely
also present. The dipole field axis, which should be parallel to the spin axis
of the putative pulsar, lies at an angle of {\sim}50\degr east of the North
Celestial Pole and is pointing away from us towards the south-west. The upper
limit for the radio surface brightness of any shell-type supernova remnant
emission around DA 495 is OAWatt
m Hz sr (assuming a radio spectral index of ), lower than the faintest shell-type remnant known to date.Comment: 25 pages, accepted by Ap
SOLUBILITY OF SUNFLOWER PROTEINS AND GEL FILTRATION CHROMATOGRAPHY OF THEIR WATER-SOLUBLE FRACTIONS
Aeolian transport layer
We investigate the airborne transport of particles on a granular surface by
the saltation mechanism through numerical simulation of particle motion coupled
with turbulent flow. We determine the saturated flux and show that its
behavior is consistent with a classical empirical relation obtained from wind
tunnel measurements. Our results also allow to propose a new relation valid for
small fluxes, namely, , where and
are the shear and threshold velocities of the wind, respectively, and
the scaling exponent is . We obtain an expression for the
velocity profile of the wind distorted by the particle motion and present a
dynamical scaling relation. We also find a novel expression for the dependence
of the height of the saltation layer as function of the wind velocity.Comment: 4 pages, 4 figure
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