2,766 research outputs found
Human Factors Considerations in System Design
Human factors considerations in systems design was examined. Human factors in automated command and control, in the efficiency of the human computer interface and system effectiveness are outlined. The following topics are discussed: human factors aspects of control room design; design of interactive systems; human computer dialogue, interaction tasks and techniques; guidelines on ergonomic aspects of control rooms and highly automated environments; system engineering for control by humans; conceptual models of information processing; information display and interaction in real time environments
Micropulsations in the electric field near the plasmapause, observed by ISEE-1
The occurrence of micropulsations near and inside the plasmapause was surveyed. The observed pulsations, classified as Pc3 and Pi2, are discussed. In addition one single event of Pc1 was observed. The frequencies in the Pc3 and Pi2 bands, the amplitude ranges, and the direction of rotation for the electric field vector are reported
Resolved Kinematics of Runaway and Field OB Stars in the Small Magellanic Cloud
We use GAIA DR2 proper motions of the RIOTS4 field OB stars in the Small
Magellanic Cloud (SMC) to study the kinematics of runaway stars. The data
reveal that the SMC Wing has a systemic peculiar motion relative to the SMC Bar
of (v_RA, v_Dec) = (62 +/-7, -18+/-5) km/s and relative radial velocity +4.5
+/- 5.0 km/s. This unambiguously demonstrates that these two regions are
kinematically distinct: the Wing is moving away from the Bar, and towards the
Large Magellanic Cloud with a 3-D velocity of 64 +/- 10 km/s. This is
consistent with models for a recent, direct collision between the Clouds. We
present transverse velocity distributions for our field OB stars, confirming
that unbound runaways comprise on the order of half our sample, possibly more.
Using eclipsing binaries and double-lined spectroscopic binaries as tracers of
dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers
of runaways accelerated by supernova kicks, we find significant contributions
from both populations. The data suggest that HMXBs have lower velocity
dispersion relative to dynamically ejected binaries, consistent with the former
corresponding to less energetic supernova kicks that failed to unbind the
components. Evidence suggests that our fast runaways are dominated by
dynamical, rather than supernova, ejections.Comment: Accepted to ApJ Letters. 10 pages, 4 figure
Determining the Locations of Dust Sources in FeLoBAL Quasars
We conduct a spectroscopic search of quasars observed by the Sloan Digital
Sky Survey (SDSS) with broad absorption line (BAL) troughs due to Mg II and
troughs due to Fe II that simultaneously exhibit strong Balmer narrow emission
lines (NELs). We find that in a redshift range of 0.4 less than or equal to z
less than or equal to 0.9 approximately 23 of the 70 Mg II BALs and 4 of a
subset of 15 Fe II BALs exhibit strong Balmer emission. We also find
significant fractions of Mg II BALs (approximately 23%) and those Mg II BALs
with Fe II troughs (approximately 27%) have strong continuum reddening, E(B -
V) greater than or equal to 0.1. From measurements of the Balmer decrement in
three objects, we find similarly significant reddening of the NEL region in
three of the four objects; the NELs in the fourth object are not measurable. We
also include one object in this study not taken from the SDSS sample that shows
Fe II absorption and strong narrow emission, but due to measurement uncertainty
and low continuum reddening the comparison is consistent but inconclusive. We
find a trend in both the Mg II and Fe II BAL samples between the NEL reddening
and continuum reddening. Because the narrow line reddening is consistent with
the continuum reddening in every object in the two SDSS samples, it suggests
that the reddening sources in these objects likely exist at larger radial
distances than the narrow line regions from the central nucleus.Comment: 40 manuscript pages, accepted in ApJ (July
A New Class of Majoron-Emitting Double-Beta Decays
Motivated by the excess events that have recently been found near the
endpoints of the double beta decay spectra of several elements, we re-examine
models in which double beta decay can proceed through the neutrinoless emission
of massless Nambu-Goldstone bosons (majorons). Noting that models proposed to
date for this process must fine-tune either a scalar mass or a VEV to be less
than 10 keV, we introduce a new kind of majoron which avoids this difficulty by
carrying lepton number . We analyze in detail the requirements that
models of both the conventional and our new type must satisfy if they are to
account for the observed excess events. We find: (1) the electron sum-energy
spectrum can be used to distinguish the two classes of models from one another;
(2) the decay rate for the new models depends on different nuclear matrix
elements than for ordinary majorons; and (3) all models require a (pseudo)
Dirac neutrino, having a mass of a several hundred MeV, which mixes with
.Comment: 43 pages, 10 figures (included), [figure captions are now included
Segre Classes on Smooth Projective Toric Varieties
We provide a generalization of the algorithm of Eklund-Jost-Peterson for
computing Segre classes of closed subschemes of projective k-space. The
algorithm is here generalized to computing the Segre classes of closed
subschemes of smooth projective toric varieties.Comment: 19 pages, 1 figure, added references, corrected typos, minor text
replacement
Dynamical mechanism of atrial fibrillation: a topological approach
While spiral wave breakup has been implicated in the emergence of atrial
fibrillation, its role in maintaining this complex type of cardiac arrhythmia
is less clear. We used the Karma model of cardiac excitation to investigate the
dynamical mechanisms that sustain atrial fibrillation once it has been
established. The results of our numerical study show that spatiotemporally
chaotic dynamics in this regime can be described as a dynamical equilibrium
between topologically distinct types of transitions that increase or decrease
the number of wavelets, in general agreement with the multiple wavelets
hypothesis. Surprisingly, we found that the process of continuous excitation
waves breaking up into discontinuous pieces plays no role whatsoever in
maintaining spatiotemporal complexity. Instead this complexity is maintained as
a dynamical balance between wave coalescence -- a unique, previously
unidentified, topological process that increases the number of wavelets -- and
wave collapse -- a different topological process that decreases their number.Comment: 15 pages, 14 figure
Face-to-face: Social work and evil
The concept of evil continues to feature in public discourses and has been reinvigorated in some academic disciplines and caring professions. This article navigates social workers through the controversy surrounding evil so that they are better equipped to acknowledge, reframe or repudiate attributions of evil in respect of themselves, their service users or the societal contexts impinging upon both. A tour of the landscape of evil brings us face-to-face with moral, administrative, societal and metaphysical evils, although it terminates in an exhortation to cultivate a more metaphorical language. The implications for social work ethics, practice and education are also discussed
Mathematical retroreflectors
Retroreflectors are optical devices that reverse the direction of incident
beams of light. Here we present a collection of billiard type retroreflectors
consisting of four objects; three of them are asymptotically perfect
retroreflectors, and the fourth one is a retroreflector which is very close to
perfect. Three objects of the collection have recently been discovered and
published or submitted for publication. The fourth object - notched angle - is
a new one; a proof of its retroreflectivity is given.Comment: 32 pages, 19 figure
Influence of silicon doping on vacancies and optical properties of AlxGa1-xN thin films
The authors have used positron annihilation spectroscopy and photoluminescence measurements to study the influence of silicon doping on vacancy formation in AlGaN:Si structures. The results show a correlation between the Doppler broadening measurements and the intensity from 510nm photoluminescence transition. The reduction in the W parameter when the [Si]∕[Al+Ga] fraction in the gas phase is above 3×10exp−4 indicates that the positrons annihilate in an environment where less Ga 3d electrons are present, i.e., they are trapped in group-III vacancies. The observation of vacancies at these silicon concentrations coincides with the onset of the photoluminescence transition at 510 nm.Peer reviewe
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