46,841 research outputs found
X-Ray Absorption from the Milky Way Halo and the Local Group
Million degree gas is present at near-zero redshift and is due either to a
gaseous Galactic Halo or a more diffuse but very massive Local Group medium. We
can discriminate between these models because the column densities should
depend on location in the sky, either relative to the Galaxy bulge or to the
M31-Milky Way axis. To search for these signatures, we measured the OVII Kalpha
absorption line strength toward 25 bright AGNs, plus LMC X-3, using XMM-Newton
RGS archival data. The data are in conflict with a purely Local Group model,
but support the Galactic Halo model. The strongest correlation is between the
OVII equivalent widths and the ROSAT background emission measurement in the R45
band (0.4-1 keV), for which OVII emission makes the largest single
contribution. This suggests that much of the OVII emission and absorption are
cospatial, from which the radius of a uniform halo appears to lie the range
15-110 kpc. The present data do not constrain the type of halo gas model and an
equally good fit is obtained in a model where the gas density decreases as a
power-law, such as r^(-3/2). For a uniform halo with a radius of 20 kpc, the
electron density would be 9E-4 cm^(-3), and the gas mass is 4E8 Msolar. The
redshift of the four highest S/N OVII measurements is consistent with a Milky
Way origin rather than a Local Group origin.Comment: 32 pages (14 figures); ApJ, in pres
Attacks on midwives, attacks on womenâs choices
Nadine Edwards, Jo Murphy-Lawless, Mavis Kirkham and Sarah Davies ask whether recent attacks on midwives are a Human
Rights issu
Handling uncertainties in background shapes: the discrete profiling method
A common problem in data analysis is that the functional form, as well as the
parameter values, of the underlying model which should describe a dataset is
not known a priori. In these cases some extra uncertainty must be assigned to
the extracted parameters of interest due to lack of exact knowledge of the
functional form of the model. A method for assigning an appropriate error is
presented. The method is based on considering the choice of functional form as
a discrete nuisance parameter which is profiled in an analogous way to
continuous nuisance parameters. The bias and coverage of this method are shown
to be good when applied to a realistic example.Comment: Accepted by J.Ins
Supply chain integration, product modularity, and market valuation: evidence from the solar energy industry
Supply chain integration is increasingly seen as a method to obtain flexibility and, consequently, to provide competitive advantage for firms within a supply chain. Product modularity, either in concert with or independent of such integration, can also produce flexibility for firms within a supply chain. In this proof-of-concept research, we explore whether the supply chain network affects each constituent firm's market valuation and how decisions regarding the level of supply chain integration and the usage of product modularity are associated with the value of the supply chain. We develop a method to identify and measure the supply chain's effect on each constituent firm's market valuation. Results indicate that greater integration is associated with a higher supply chain valuation, whereas increasing aggregated product modularity across the supply chain relates to a lower supply chain value. However, when combined, the interaction of aggregated product modularity and supply chain integration is positively associated with the supply chain's valuation
Dust properties of external galaxies; NGC 891 revisited
We compare 850um SCUBA images of NGC 891 with the corresponding V-band
optical depth predicted from radiation transfer simulations. These two tracers
of dust show a very similar distribution along the minor axis and a reasonable
agreement along the major axis. Assuming that the grains responsible for
optical extinction are also the source of 850um emission we derive a
submillimeter emissivity (emission efficiency) for dust in the NGC 891 disk.
This quantity is found to be a factor of 2-3 higher than the generally-accepted
(but highly uncertain) values adopted for the Milky Way. It should be stated,
however, that if a substantial fraction of dust in NGC 891 is clumped, the
emissivity in the two galaxies may be quite similar. We use our newly-acquired
emissivity to convert our 850um images into detailed maps of dust mass and,
utilizing 21cm and CO-emission data for NGC 891, derive the gas-to-dust ratio
along the disk. We compute an average ratio of 260 -- a value consistent with
the Milky Way and external spirals within the uncertainties in deriving both
the dust mass and the quantity of molecular gas. The bulk of dust in NGC 891
appears to be closely associated with the molecular gas phase although it may
start to follow the distribution of atomic hydrogen at radii >9 kpc (i.e. >0.5
R_25). Using the optical depth of the NGC 891 disk, we quantify how light
emitted at high redshift is attenuated by dust residing in foreground spirals.
For B-band observations of galaxies typically found in the Hubble Deep Field,
the amount of light lost is expected to be small (~ 5%). This value depends
critically on the maximum radial extent of cold dust in spiral disks (which is
poorly known). It may also represent a lower limit if galaxies expel dust over
time into the intergalactic medium.Comment: 22 pages, 7 figures, A&A accepte
Curved planar quantum wires with Dirichlet and Neumann boundary conditions
We investigate the discrete spectrum of the Hamiltonian describing a quantum
particle living in the two-dimensional curved strip. We impose the Dirichlet
and Neumann boundary conditions on opposite sides of the strip. The existence
of the discrete eigenvalue below the essential spectrum threshold depends on
the sign of the total bending angle for the asymptotically straight strips.Comment: 7 page
Exploring the Design of Pay-Per-Use Objects in the Construction Domain
Equipment used in the construction domain is often hired in order to reduce cost and maintenance overhead. The cost of hire is dependent on the time period involved and does not take into account the actual use equipment has received. This paper presents our initial investigation into how physical objects augmented with sensing and communication technologies can measure use in order to enable new pay-per-use payment models for equipment hire. We also explore user interaction with pay-per-use objects via mobile devices. The user interactions that take place within our prototype scenario range from simple information access to transactions involving multiple users. This paper presents the design, implementation and evaluation of a prototype pay-per-use system motivated by a real world equipment hire scenario. We also provide insights into the various challenges introduced by supporting a pay-per-use model, including data storage and data security in addition to user interaction issues
The Low Surface Brightness Extent of the Fornax Cluster
We have used a large format CCD camera to survey the nearby Fornax cluster
and its immediate environment for low luminosity low surface brightness
galaxies. Recent observations indicate that these are the most dark matter
dominated galaxies known and so they are likely to be a good tracer of the dark
matter in clusters. We have identified large numbers of these galaxies
consistent with a steep faint end slope of the luminosity function (alpha~ -2)
down to MB ~ -12. These galaxies contribute almost the same amount to the total
cluster light as the brighter galaxies and they have a spatial extent that is
some four times larger. They satisfy two of the important predictions of N-body
hierarchical simulations of structure formation using dark halos. The
luminosity (mass ?) function is steep and the mass distribution is more
extended than that defined by the brighter galaxies. We also find a large
concentration of low surface brightness galaxies around the nearby galaxy
NGC1291.Comment: 16 pages, 6 figure
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