947 research outputs found
La liturgia ynglesa o el libro de la oracion comun y administracion de los sacramentos y uso de la yglesia anglicana juntamente con el psalterio [Texto impreso] ...]
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UV and EUV Instruments
We describe telescopes and instruments that were developed and used for
astronomical research in the ultraviolet (UV) and extreme ultraviolet (EUV)
regions of the electromagnetic spectrum. The wavelength ranges covered by these
bands are not uniquely defined. We use the following convention here: The EUV
and UV span the regions ~100-912 and 912-3000 Angstroem respectively. The
limitation between both ranges is a natural choice, because the hydrogen Lyman
absorption edge is located at 912 Angstroem. At smaller wavelengths,
astronomical sources are strongly absorbed by the interstellar medium. It also
marks a technical limit, because telescopes and instruments are of different
design. In the EUV range, the technology is strongly related to that utilized
in X-ray astronomy, while in the UV range the instruments in many cases have
their roots in optical astronomy. We will, therefore, describe the UV and EUV
instruments in appropriate conciseness and refer to the respective chapters of
this volume for more technical details.Comment: To appear in: Landolt-Boernstein, New Series VI/4A, Astronomy,
Astrophysics, and Cosmology; Instruments and Methods, ed. J.E. Truemper,
Springer-Verlag, Berlin, 201
Modeling the architecture of the regulatory system controlling methylenomycin production in Streptomyces coelicolor
The antibiotic methylenomycin A is produced naturally by Streptomyces coelicolor A3(2), a model organism for streptomycetes. This compound is of particular interest to synthetic biologists because all of the associated biosynthetic, regulatory and resistance genes are located on a single cluster on the SCP1 plasmid, making the entire module easily transferable between different bacterial strains. Understanding further the regulation and biosynthesis of the methylenomycin producing gene cluster could assist in the identification of motifs that can be exploited in synthetic regulatory systems for the rational engineering of novel natural products and antibiotics
Recognition of Intentional Violations of Active Constraints in Cooperative Manipulation Tasks
Active Constraints (ACs) are high-level control algorithms deployed to assist a human operator in man-machine cooperative tasks [1], and define regions within which it is safe for the robot to move and cut [2]. To enhance the performance in cooperative surgical tasks,
adaptive constraints have been exploited to optimally adjust the provided level of assistance according to some knowledge of the task, hardware or user. In [3] Hidden Markov Models were used for the run-time detection of the user intention to leave a guidance
constraint to circumvent an obstacle. In this work, we present a novel, Neural Network (NN)-based method for the runtime classification of intentional and unintentional violations of ACs, that is trained on either statistical or frequency features from the enforced
constraint forces. We investigate which set of parameters yield faster and more reliable classification results, both for guidance and regional constraints
Kinetic and Dynamic Delaunay tetrahedralizations in three dimensions
We describe the implementation of algorithms to construct and maintain
three-dimensional dynamic Delaunay triangulations with kinetic vertices using a
three-simplex data structure. The code is capable of constructing the geometric
dual, the Voronoi or Dirichlet tessellation. Initially, a given list of points
is triangulated. Time evolution of the triangulation is not only governed by
kinetic vertices but also by a changing number of vertices. We use
three-dimensional simplex flip algorithms, a stochastic visibility walk
algorithm for point location and in addition, we propose a new simple method of
deleting vertices from an existing three-dimensional Delaunay triangulation
while maintaining the Delaunay property. The dual Dirichlet tessellation can be
used to solve differential equations on an irregular grid, to define partitions
in cell tissue simulations, for collision detection etc.Comment: 29 pg (preprint), 12 figures, 1 table Title changed (mainly
nomenclature), referee suggestions included, typos corrected, bibliography
update
X-ray observations of PKS 0745-191 at the virial radius: Are we there yet?
We wish to reassess the properties of the ICM at large radii in the galaxy
cluster PKS 0745-191 in light of the recent Suzaku measurements. We analyze an
archival 10.5 ksec ROSAT/PSPC observation to extract the surface-brightness
profile of PKS 0745-191 and infer the deprojected density profile. We then
compare the ROSAT surface-brightness profile with the Suzaku result. We perform
a mass analysis combining the ROSAT density profile and the published
temperature profiles from different instruments. We find that the ROSAT
surface-brightness profile is statistically inconsistent (7.7 sigma) with the
Suzaku result around and beyond the value of r200 estimated by Suzaku. We argue
that, thanks to its large field of view and low background, ROSAT/PSPC is to
the present day the most sensitive instrument to low surface-brightness X-ray
emission in the 0.4-2.0 keV band. We also note that the Suzaku temperature and
mass profiles are at odds with the results from at least two other satellites
(XMM-Newton and Swift). The difference in surface brightness between ROSAT and
Suzaku is most likely explained by the existence of additional foreground
components at the low Galactic latitude of the source, which were not taken
into account in the Suzaku background modeling. In light of our mass analysis,
we conclude that any estimate of the fraction of the virial radius reached by
X-ray measures is affected by systematic errors of the order of 25%. As a
result, the properties of the ICM at the virial radius are still uncertain, and
the Suzaku results should be considered with caution.Comment: 6 pages, 5 figures, accepted for publication in A&
Far Ultraviolet Spectra of B Stars near the Ecliptic
Spectra of B stars in the wavelength range of 911-1100 A have been obtained
with the EURD spectrograph onboard the Spanish satellite MINISAT-01 with ~5 A
spectral resolution. IUE spectra of the same stars have been used to normalize
Kurucz models to the distance, reddening and spectral type of the corresponding
star. The comparison of 8 main-sequence stars studied in detail (alpha Vir,
epsilon Tau, lambda Tau, tau Tau, alpha Leo, zeta Lib, theta Oph, and sigma
Sgr) shows agreement with Kurucz models, but observed fluxes are 10-40% higher
than the models in most cases. The difference in flux between observations and
models is higher in the wavelength range between Lyman alpha and Lyman beta. We
suggest that Kurucz models underestimate the FUV flux of main-sequence B stars
between these two Lyman lines. Computation of flux distributions of
line-blanketed model atmospheres including non-LTE effects suggests that this
flux underestimate could be due to departures from LTE, although other causes
cannot be ruled out. We found the common assumption of solar metallicity for
young disk stars should be made with care, since small deviations can have a
significant impact on FUV model fluxes. Two peculiar stars (rho Leo and epsilon
Aqr), and two emission line stars (epsilon Cap and pi Aqr) were also studied.
Of these, only epsilon Aqr has a flux in agreement with the models. The rest
have strong variability in the IUE range and/or uncertain reddening, which
makes the comparison with models difficult.Comment: 25 pages, 6 figures, to be published in The Astrophysical Journa
Coronal properties of G-type stars in different evolutionary phases
We report on the analysis of XMM-Newton observations of three G-type stars in
very different evolutionary phases: the weak-lined T Tauri star HD 283572, the
Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Com.
They all have high X-ray luminosity (10^31 erg/s for HD 283572 and 31 Com and
10^30 erg/s for EK Dra). We compare the Emission Measure Distributions (EMDs)
of these active coronal sources, derived from high-resolution XMM-Newton
grating spectra, as well as the pattern of elemental abundances vs. First
Ionization Potential (FIP). We also perform time-resolved spectroscopy of a
flare detected by XMM from EK Dra. We interpret the observed s as the
result of the emission of ensembles of magnetically confined loop-like
structures with different apex temperatures. Our analysis indicates that the
coronae of HD 283572 and 31 Com are very similar in terms of dominant coronal
magnetic structures, in spite of differences in the evolutionary phase, surface
gravity and metallicity. In the case of EK Dra the distribution appears to be
slightly flatter than in the previous two cases, although the peak temperature
is similar.Comment: 15 pages, 13 Postscript figures, to be published in A&
Chandra measurements of non-thermal-like X-ray emission from massive, merging, radio-halo clusters
We report the discovery of spatially-extended, non-thermal-like emission
components in Chandra X-ray spectra for five of a sample of seven massive,
merging galaxy clusters with powerful radio halos. The emission components can
be fitted by power-law models with mean photon indices in the range 1.5 < Gamma
< 2.0. A control sample of regular, dynamically relaxed clusters, without radio
halos but with comparable mean thermal temperatures and luminosities, shows no
compelling evidence for similar components. Detailed X-ray spectral mapping
reveals the complex thermodynamic states of the radio halo clusters. Our
deepest observations, of the Bullet Cluster 1E 0657-56, demonstrate a spatial
correlation between the strongest power-law X-ray emission, highest thermal
pressure, and brightest 1.34GHz radio halo emission in this cluster. We confirm
the presence of a shock front in the 1E 0657-56 and report the discovery of a
new, large-scale shock front in Abell 2219. We explore possible origins for the
power-law X-ray components. These include inverse Compton scattering of cosmic
microwave background photons by relativistic electrons in the clusters;
bremsstrahlung from supra-thermal electrons energized by Coulomb collisions
with an energetic, nonthermal proton population; and synchrotron emission
associated with ultra-relativistic electrons. Interestingly, we show that the
power-law signatures may also be due to complex temperature and/or metallicity
structure in clusters particularly in the presence of metallicity gradients. In
this case, an important distinguishing characteristic between the radio halo
clusters and control sample of predominantly cool-core clusters is the
relatively low central X-ray surface brightness of the former.Comment: Accepted for publication in MNRAS (24 pages, 13 figures). Improved
discussion includes a new, possible explanation for `soft excess' X-ray
emission from clusters as an artifact of metallicity/temperature structure
and projection effects. Other physical explanations for the observed
non-thermal-like X-ray emission also remai
The Structure of Stellar Coronae in Active Binary Systems
A survey of 28 stars using EUV spectra has been conducted to establish the
structure of stellar coronae in active binary systems from the EMD, electron
densities, and scale sizes. Observations obtained by the EUVE during 9 years of
operation are included for the stars in the sample. EUVE data allow a
continuous EMD to be constructed in the range log T~5.6-7.4, using iron
emission lines. These data are complemented with IUE observations to model the
lower temperature range. Inspection of the EMD shows an outstanding narrow
enhancement, or ``bump'' peaking around log T~6.9 in 25 of the stars, defining
a fundamental coronal structure. The emission measure per unit stellar area
decreases with increasing orbital (or photometric) periods of the target stars;
stars in binaries generally have more material at coronal temperatures than
slowly rotating single stars. High electron densities (Ne>10^12 cm^-3) are
derived at ~10 MK for some targets, implying small emitting volumes. The
observations suggest the magnetic stellar coronae of these stars are consistent
with two basic classes of magnetic loops: solar-like loops with maximum
temperature around log T~6.3 and lower electron densities (Ne>10^9-10.5), and
hotter loops peaking around log T~6.9 with higher electron densities
(Ne>10^12). For the most active stars, material exists at much higher
temperatures (log T>6.9) as well. However, current ab initio stellar loop
models cannot reproduce such a configuration. Analysis of the light curves of
these systems reveals signatures of rotation of coronal material, as well as
apparent seasonal changes in the activity levels.Comment: 45 pages, 9 figures (with 20 eps files). Accepted for its publication
in ApJ
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