627 research outputs found
GAIA accuracy on radial velocities assessed from a synthetic spectra database
Spectrograph aboard the GAIA satellite operates in the near-IR, in the 8490--
8740 \AA window accessible also from the ground. The most important parameter
yet to be determined is the spectral resolution. Realistic estimates of the
zodiacal light background are obtained and a total of
correlation runs are used to study the accuracy of radial velocity measured by
the spectrograph as a function of resolution, magnitude of the target, its
spectral type and luminosity class. Accuracy better than 2 km/s is achievable
for bright stars if a high enough dispersion is chosen. Radial velocity error
of 5 km/s is at for Cepheids and at 17.7 for horizontal branch stars.
Even for very faint objects, with spectra dominated by background and readout
noise, the optimal dispersion is still in the 0.25 / 0.75 \AA/pix range. This
is also true for complicated cases such as spectroscopic binaries or if
information other than radial velocity, i.e. abundances of individual elements
or stellar rotation velocity, is sought after. The results can be scaled to
assess performance of future ground based instruments.Comment: accepted for publication in Astronomy and Astrophysics, 8 pages, 4
figure
Rethinking African development: Beyond impasse, towards alternatives
ASC – Publicaties niet-programma gebonde
Comparison of the COBE FIRAS and DIRBE Calibrations
We compare the independent FIRAS and DIRBE observations from the COBE in the
wavelength range 100-300 microns. This cross calibration provides checks of
both data sets. The results show that the data sets are consistent within the
estimated gain and offset uncertainties of the two instruments. They show the
possibility of improving the gain and offset determination of DIRBE at 140 and
240 microns.Comment: Accepted for publication in the Astrophysical Journal 11 pages, plus
3 figures in separate postscript files. Figure 3 has three part
Submillimeter wavelength survey of the galactic plane from l = -5 deg to l = +62 deg: Structure and energetics of the inner disk
Results from a large scale survey of the first quadrant of the Milky Way galactic plane at wavelengths of 150, 250, and 300 microns with a 10x10 arcmin beam are presented. The emission detected in the survey arises from compact sources, most of which are identified with known peaks of 5 GHz and/or CO emission, and from an underlying diffuse background with a typical angular width of approximately 0.9 deg (FWHM) which accounts for most of the emission. A total of 80 prominent discrete sources were identified and characterized, of which about half were not previously reported at far infrared wavelengths. The total infrared luminosity within the solar circle is approximately 1 to 2x10 to the 10th power L sub 0, and is probably emitted by dust that resides in molecular clouds
Structural and magnetic properties of an InGaAs/FeSi superlattice in cylindrical geometry
The structure and the magnetic properties of an InGaAs/Fe3Si superlattice in
a cylindrical geometry are investigated by electron microscopy techniques,
x-ray diffraction and magnetometry. To form a radial superlattice, a
pseudomorphic InGaAs/Fe3As bilayer has been released from its substrate
self-forming into a rolled-up microtube. Oxide-free interfaces as well as areas
of crystalline bonding are observed and an overall lattice mismatch between
succeeding layers is determined. The cylindrical symmetry of the final radial
superlattice shows a significant effect on the magnetization behavior of the
rolled-up layers
Coupled monoubiquitylation of the co-E3 ligase DCNL1 by Ariadne RBR E3 ubiquitin ligases promotes cullin-RING ligase complex remodeling
Cullin-RING E3 ubiquitin ligases (CRLs) are large and diverse multisubunit protein complexes that contribute to about one-fifth of ubiquitin-dependent protein turnover in cells. CRLs are activated by the attachment of the ubiquitin-like protein neural precursor cell expressed, developmentally down-regulated 8 (NEDD8) to the cullin subunits. This cullin neddylation is essential for a plethora of CRL-regulated cellular processes and is vital for life. In mammals, neddylation is promoted by the five co-E3 ligases, defective in cullin neddylation 1 domain-containing 1-5 (DCNL1-5); however, their functional regulation within the CRL complex remains elusive. We found here that the ubiquitin-associated (UBA) domain-containing DCNL1 is monoubiquitylated when bound to CRLs and that this monoubiquitylation depends on the CRL-associated Ariadne RBR ligases TRIAD1 (ARIH2) and HHARI (ARIH1) and strictly requires the DCNL1's UBA domain. Reconstitution of DCNL1 monoubiquitylation in vitro revealed that autoubiquitylated TRIAD1 mediates binding to the UBA domain and subsequently promotes a single ubiquitin attachment to DCNL1 in a mechanism previously dubbed coupled monoubiquitylation. Moreover, we provide evidence that DCNL1 monoubiquitylation is required for efficient CRL activity, most likely by remodeling CRLs and their substrate receptors. Collectively, this work identifies DCNL1 as a critical target of Ariadne RBR ligases and coupled monoubiquitylation of DCNL1 as an integrated mechanism that affects CRL activity and client-substrate ubiquitylation at multiple levels
Two 'transitions': the political economy of Joyce Banda's rise to power and the related role of civil society organisations in Malawi
This is an Accepted Manuscript of an article published by Taylor & Francis in Review of African Political Economy on 21/07/2014, available online: http://www.tandfonline.com/doi/abs/10.1080/03056244.2014.90194
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High-temperature phase transitions in dense germanium.
Through a series of high-pressure x-ray diffraction experiments combined with in situ laser heating, we explore the pressure-temperature phase diagram of germanium (Ge) at pressures up to 110 GPa and temperatures exceeding 3000 K. In the pressure range of 64-90 GPa, we observe orthorhombic Ge-IV transforming above 1500 K to a previously unobserved high-temperature phase, which we denote as Ge-VIII. This high-temperature phase is characterized by a tetragonal crystal structure, space group I4/mmm. Density functional theory simulations confirm that Ge-IV becomes unstable at high temperatures and that Ge-VIII is highly competitive and dynamically stable at these conditions. The existence of Ge-VIII has profound implications for the pressure-temperature phase diagram, with melting conditions increasing to much higher temperatures than previous extrapolations would imply
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