2,365 research outputs found
The truncated and evolving inner accretion disc of the black hole GX 339-4
The nature of accretion onto stellar mass black holes in the low/hard state
remains unresolved, with some evidence suggesting that the inner accretion disc
is truncated and replaced by a hot flow. However, the detection of relativistic
broadened Fe emission lines, even at relatively low luminosities, seems to
require an accretion disc extending fully to its innermost stable circular
orbit. Modelling such features is however highly susceptible to degeneracies,
which could easily bias any interpretation. We present the first systematic
study of the Fe line region to track how the inner accretion disc evolves in
the low/hard state of the black hole GX 3394. Our four observations display
increased broadening of the Fe line over two magnitudes in luminosity, which we
use to track any variation of the disc inner radius. We find that the disc
extends closer to the black hole at higher luminosities, but is consistent with
being truncated throughout the entire low/hard state, a result which renders
black hole spin estimates inaccurate at these stages of the outburst.
Furthermore, we show that the evolution of our spectral inner disc radius
estimates corresponds very closely to the trend of the break frequency in
Fourier power spectra, supporting the interpretation of a truncated and
evolving disc in the hard state.Comment: Accepted for publication in A&A. Some typos corrected from version
Revealing accretion onto black holes: X-ray reflection throughout three outbursts of GX 339-4
Understanding the dynamics behind black hole state transitions and the
changes they reflect in outbursts has become long-standing problem. The X-ray
reflection spectrum describes the interaction between the hard X-ray source
(the power-law continuum) and the cool accretion disc it illuminates, and thus
permits an indirect view of how the two evolve. We present a systematic
analysis of the reflection spectrum throughout three outbursts (500+
observations) of the black hole binary GX 339-4, representing the largest study
applying a self-consistent treatment of reflection to date. Particular
attention is payed to the coincident evolution of the power-law and reflection,
which can be used to determine the accretion geometry. The hard state is found
to be distinctly reflection weak, however the ratio of reflection to power-law
gradually increases as the source luminosity rises. In contrast the reflection
is found dominate the power-law throughout most of the soft state, with
increasing supremacy as the source decays. We discuss potential dynamics
driving this, favouring inner disc truncation and decreasing coronal height for
the hard and soft states respectively. Evolution of the ionisation parameter,
power-law slope and high-energy cut-off also agree with this interpretation.Comment: Accepted for publication in MNRA
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Results of an aqueous source term model for a radiological risk assessment of the Drigg LLW Site, U.K.
A radionuclide source term model has been developed which simulates the biogeochemical evolution of the Drigg low level waste (LLW) disposal site. The DRINK (DRIgg Near field Kinetic) model provides data regarding radionuclide concentrations in groundwater over a period of 100,000 years, which are used as input to assessment calculations for a groundwater pathway. The DRINK model also provides input to human intrusion and gaseous assessment calculations through simulation of the solid radionuclide inventory. These calculations are being used to support the Drigg post closure safety case. The DRINK model considers the coupled interaction of the effects of fluid flow, microbiology, corrosion, chemical reaction, sorption and radioactive decay. It represents the first direct use of a mechanistic reaction-transport model in risk assessment calculations
Millisecond accuracy video display using OpenGL under Linux
To measure peopleâs reaction times to the nearest millisecond, it is necessary to know exactly when
a stimulus is displayed. This article describes how to display stimuli with millisecond accuracy on a
normal CRT monitor, using a PC running Linux. A simple C program is presented to illustrate how this
may be done within X Windows using the OpenGL rendering system. A test of this system is reported
that demonstrates that stimuli may be consistently displayed with millisecond accuracy. An algorithm
is presented that allows the exact time of stimulus presentation to be deduced, even if there are relatively
large errors in measuring the display time
Reading ecosystem services at the local scale through a territorial approach: The case of peri-urban agriculture in the thau Lagoon, Southern France
© 2015 by the author(s). In recent years, the ecosystem services (ES) concept has become a major paradigm for natural resource management. While policy-makers demand âhardâ monetary evidence that nature conservation would be worth investing in, ongoing attempts are being made to formalize the concept as a scientifically robust âone size fits allâ analytical framework. These attempts have highlighted several major limitations of the ES concept. First, to date, the concept has paid little attention to the role of humans in the production of ES. Second, the ongoing formalization of the ES concept is turning it into a âtechnology of globalization,â thereby increasingly ignoring the socio-cultural context and history within which ecosystems emerge. Third, economic valuation has been shown to limit local stakeholders in expressing their daily and immediate ways of interacting with their environment over and beyond extrinsic motivation provided by financial gains. We address these three limitations by analyzing a social evaluation of the roles of peri-urban farmland from a territorial perspective. Our case study is the Thau lagoon in southern France. We conducted in-depth interviews with a broad range of stakeholders and ran two participatory workshops. Using a territorial meta-model that distinguishes three levelsâ physical, logical, and existentialâstakeholder data were analyzed to unravel the interplay of territorial elements at these three levels that gives rise to ES in two broad categories: food production and aesthetic landscape. The coupling of ES and territory concepts opens up several novel analytical perspectives. It allows partitioning of ES in a manner that âre-contextualizesâ them and gives insight about both their physical constituents and their meaning at the territorial level. Additional research should incorporate the dynamics of service demand and supply, and further investigate options for implementation
Temperature mapping and thermal lensing in large-mode, high-power laser diodes
The authors use high-resolution charge-coupled device based thermoreflectance to derive two dimensional facet temperature maps of a λ = 1.55âÎŒmλ=1.55ÎŒm InGaAsP/InPInGaAsPâInP watt-class laser that has a large (>5Ă5âÎŒm2)(>5Ă5ÎŒm2) fundamental optical mode. Recognizing that temperature rise in the laser will lead to refractive index increase, they use the measured temperature profiles as an input to a finite-element mode solver, predicting bias-dependent spatial mode behavior that agrees well with experimental observations. These results demonstrate the general usefulness of high-resolution thermal imaging for studying spatial mode dynamics in photonic devices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87806/2/201110_1.pd
The Unseen Face of E-Business Project Development
The purpose of this paper is intent on identify and analyze the unseen factors of successful or failure of e-business project development. The IT managers must take into account both all costs involved in e-business development and all phases (analysis, design, testing, implementation, maintenance and operation) according to principle of project management for software/systems life cycle development. There are many solutions to exceed these factors of failure among could be counted outsourcing, a good project management, involvement of senior management, a real cost estimation etc.Zadanie pt. âDigitalizacja i udostÄpnienie w Cyfrowym Repozytorium Uniwersytetu ĆĂłdzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet ĆĂłdzkiâ nr 885/P-DUN/2014 zostaĆo dofinansowane ze ĆrodkĂłw MNiSW w ramach dziaĆalnoĆci upowszechniajÄ
cej nauk
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Bells and whistles of convection parameterization
The present workshop constitutes the 5th in the annual series on âConcepts for Convective Parameterizations in Large-Scale Modelsâ. The purpose of the workshop series has been to discuss the fundamental theoretical issues of convection parameterization with a small number of European scientists. The workshop series has been funded by European Cooperation in the Field of Scientific and Technical Research (COST) Action ES0905. The theme of the workshop for the year 2012 was decided from a main conclusion of the previous workshop, which focused on the convective organization problem, seeking a means for implementing such effects into convection parameterizations (Yano et al. 2012).
As it turned out, in order to discuss this implementation issue in any concrete manner, we have first to know very well the bells and whistles of convection parameterizations. This was the purpose of the 5th workshop. The title of the workshop is rather metaphorically tagged as âBulk or Spectrum?â, because this is a typical decision we have to face at the outset of any parameterization development. The following report discusses selected issues of bells and whistles addressed
during the meeting
Using size-selected gold clusters on graphene oxide films to aid cryo-transmission electron tomography alignment
A three-dimensional reconstruction of a nano-scale aqueous object can be achieved by taking a series of transmission electron micrographs tilted at different angles in vitreous ice: cryo-Transmission Electron Tomography. Presented here is a novel method of fine alignment for the tilt series. Size-selected gold clusters of ~2.7â
nm (Au(561 ± 14)), ~3.2â
nm (Au(923 ± 22)), and ~4.3â
nm (Au(2057 ± 45)) in diameter were deposited onto separate graphene oxide films overlaying holes on amorphous carbon grids. After plunge freezing and subsequent transfer to cryo-Transmission Electron Tomography, the resulting tomograms have excellent (de-)focus and alignment properties during automatic acquisition. Fine alignment is accurate when the evenly distributed 3.2â
nm gold particles are used as fiducial markers, demonstrated with a reconstruction of a tobacco mosaic virus. Using a graphene oxide film means the fiducial markers are not interfering with the ice bound sample and that automated collection is consistent. The use of pre-deposited size-selected clusters means there is no aggregation and a user defined concentration. The size-selected clusters are mono-dispersed and can be produced in a wide size range including 2â5â
nm in diameter. The use of size-selected clusters on a graphene oxide films represents a significant technical advance for 3D cryo-electron microscopy
Inclination and relativistic effects in the outburst evolution of black hole transients
We have systematically studied the effect of the orbital inclination in the
outburst evolution of black hole transients. We have included all the systems
observed by the Rossi X-ray timing explorer in which the thermal, accretion
disc component becomes strongly dominant at some point of the outburst.
Inclination is found to modify the shape of the tracks that these systems
display in the colour/luminosity diagrams traditionally used for their study.
Black hole transients seen at low inclination reach softer spectra and their
accretion discs look cooler than those observed closer to edge-on. This
difference can be naturally explained by considering inclination dependent
relativistic effects on accretion discs.Comment: 8 pages, 4 figures, accepted for publication in MNRA
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