17,361 research outputs found
Low-noise flow valve for air ducts
Valve assembly controls air flow from feeder into main duct, with minimum of turbulence, friction, pressure differential, and noise. Valve consists of damper, deflector, and spring. Streamlining of damper and deflector merges flow smoothly, while spring keeps damper and deflector in contact and eliminates valve chatter and damping vibrations
The effects of a comptonizing corona on the appearance of the reflection components in accreting black hole spectra
We discuss the effects of a comptonizing corona on the appearance of the
reflection components, and in particular of the reflection hump, in the X-rays
spectra of accreting black holes. Indeed, in the framework of a thermal corona
model, we expect that part (or even all, depending on the coronal covering
factor) of the reflection features should cross the hot plasma, and thus suffer
Compton scattering, before being observed. We have studied in detail the
dependence of these effects on the physical (i.e. temperature and optical
depth) and geometrical (i.e. inclination angle) parameters of the corona,
concentrating on the slab geometry . Due to the smoothing and shifting towards
high energies of the comptonized reflection hump, the main effects on the
emerging spectra appear above 100 keV. We have also investigated the importance
of such effects on the interpretation of the results obtained with the standard
fitting procedures. We found that fitting Comptonization models, taking into
account comptonized reflection, by the usual cut-off power law + uncomptonized
reflection model, may lead to an underestimation of the reflection
normalization and an overestimation of the high energy cut-off. We discuss and
illustrate the importance of these effects by analysing recent observational
results as those of the galaxy NGC 4258. We also find that the comptonizing
corona can produce and/or emphasize correlations between the reflection
features characteristics (like the iron line equivalent width or the covering
fraction) and the X-ray spectral index similar to those recently reported in
the literature. We also underline the importance of these effects when dealing
with accurate spectral fitting of the X-ray background.Comment: 11 pages, 14 figures accepted for publication in MNRAS. Version
printable on US 8.5x11 pape
Anti-slipping system improves wire saw performance
System prevents wire saw slippage by providing sufficient friction to turn idler spools even when turns of wire on spools do not provide sufficient friction. Low cost system is easily applied to existing equipment
Estimating total momentum at finite distances
We study the difficulties associated with the evaluation of the total Bondi
momentum at finite distances around the central source of a general
(asymptotically flat) spacetime. Since the total momentum is only rigorously
defined at future null infinity, both finite distance and gauge effects must be
taken into account for a correct computation of this quantity.
Our discussion is applicable in general contexts but is particularly relevant
in numerically constructed spacetimes for both extracting important physical
information and assessing the accuracy of additional quantities.Comment: 10 pages, 1 figure. Typos corrected. Comments added and a new
Appendix. To be published in PR
A longer XMM-Newton look at I Zwicky 1: Distinct modes of X-ray spectral variability
The short-term spectral variability of the narrow-line Seyfert 1 galaxy I
Zwicky 1 (I Zw 1) as observed in an 85 ks XMM-Newton observation is discussed
in detail. I Zw 1 shows distinct modes of variability prior to and after a flux
dip in the broad-band light curve. Before the dip the variability can be
described as arising from changes in shape and normalisation of the spectral
components. Only changes in normalisation are manifested after the dip. The
change in the mode of behaviour occurs on dynamically short timescales in I Zw
1. The data suggest that the accretion-disc corona in I Zw 1 could have two
components that are co-existing. The first, a uniform, physically diffuse
plasma responsible for the "typical'' long-term (e.g. years) behaviour; and a
second compact, centrally located component causing the rapid flux and spectral
changes. This compact component could be the base of a short or aborted jet as
sometimes proposed for radio-quiet active galaxies. Modelling of the average
and time-resolved rms spectra demonstrate that a blurred Compton-reflection
model can describe the spectral variability if we allow for pivoting of the
continuum component prior to the dip.Comment: 8 pages, 9 figures. Accepted by MNRA
Governance mechanisms for effective leadership: The case of Spain.
Most recent work on Boards of Directors has been focused on what can be considered best practices for effective governance in terms of roles, composition, process and style. Furthermore, this literature can be divided among very practically oriented managerial work, and more rigorous, theoretically based work. Most of the empirical research in this area has been centered on Anglo-Saxon countries. Some European countries, like Spain, have a very different governance tradition. Given this context, our present work pursues with three complementary objectives: 1. To ascertain the current status of governance practices in Spain. 2. To obtain evidence about which of these practices may be associated with effective governance. 3. To find out what factors account for the composition of General Managers’ compensation.leadership; effective governance;
Caught in the act: Measuring the changes in the corona that cause the extreme variability of 1H 0707-495
The X-ray spectra of the narrow line Seyfert 1 galaxy, 1H 0707-495, obtained
with XMM-Newton, from time periods of varying X-ray luminosity are analysed in
the context of understanding the changes to the X-ray emitting corona that lead
to the extreme variability seen in the X-ray emission from active galactic
nuclei (AGN). The emissivity profile of the accretion disc, illuminated by the
X-ray emitting corona, along with previous measurements of reverberation time
lags are used to infer the spatial extent of the X-ray source. By fitting a
twice-broken power law emissivity profile to the relativistically-broadened
iron K fluorescence line, it is inferred that the X-ray emitting corona expands
radially, over the plane of the accretion disc, by 25 to 30 per cent as the
luminosity increases, contracting again as the luminosity decreases, while
increases in the measured reverberation lag as the luminosity increases would
require also variation in the vertical extent of the source above the disc. The
spectrum of the X-ray continuum is found to soften as the total X-ray
luminosity increases and we explore the variation in reflected flux as a
function of directly-observed continuum flux. These three observations combined
with simple, first-principles models constructed from ray tracing simulations
of extended coron self-consistently portray an expanding corona whose average
energy density decreases, but with a greater number of scattering particles as
the luminosity of this extreme object increases.Comment: 12 pages, 4 figures. Accepted for publication in MNRA
Social Networks, Confirmation Bias and Shock Elections
In recent years online social networks have become increasingly prominent in political campaigns and, concurrently, several countries have experienced shock election outcomes. This paper proposes a model that links these two phenomena. In our set-up, the process of learning from others on a network is influenced by confirmation bias, i.e. the tendency to ignore contrary evidence and interpret it as consistent with one's own belief. When agents pay enough attention to themselves, confirmation bias leads to slower learning in any symmetric network, and it increases polarization in society. We identify a subset of agents that become more/less influential with confirmation bias. The socially optimal network structure depends critically on the information available to the social planner. When she cannot observe agents' beliefs, the optimal network is symmetric, vertex-transitive and has no self-loops. We explore the implications of these results for electoral outcomes and media markets. Confirmation bias increases the likelihood of shock elections, and it pushes fringe media to take a more extreme ideology
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