1,028 research outputs found
Vacuum phototriodes for the CMS electromagnetic calorimeter endcap
The measurement of scintillation light from the lead tungstate crystals of the Compact Muon Solenoid (CMS) electromagnetic calorimeter (ECAL) poses a substantial technical challenge, particularly in the endcap regions, where the radiation levels are highest. The photodetectors must be fast, sensitive, radiationhard, and operate with significant internal gain in a magnetic field of 4 Tesla. The measured performance characteristics of the first batches of series production vacuum phototriodes (VPT), developed to satisfy the needs of CMS, will be described
The response to high magnetic fields of the vacuum phototriodes for the compact muon solenoid endcap electromagnetic calorimeter
The endcap electromagnetic calorimeter of the Compact Muon Solenoid (CMS) detects particles with the dense fast scintillator lead tungstate (PbWO4). Due to the low light yield of this scintillator photodetectors with internal gain are required. Silicon avalanche photodiodes cannot be used in the endcap region due to the intense neutron flux. Following an extensive R&D programme 26 mm diameter single-stage photomultipliers (vacuum phototriodes) have been chosen as the photodetector in the endcap region. The first 1400 production devices are currently being evaluated following recent tests of a pre-production batch of 500 tubes. Tubes passing our acceptance tests have responses, averaged over the angular acceptance of the endcap calorimeter, corresponding to the range 20 to 55 electrons per MeV deposited in PbWO4. These phototriodes operate, with a typical gain of 10, in magnetic fields up to 4T.PPARC, EC(INTAS-CERN scheme 99-424
Spitzer spectral line mapping of the HH211 outflow
Aims: We employ archival Spitzer slit-scan observations of the HH211 outflow
in order to investigate its warm gas content, assess the jet mass flux in the
form of H2 and probe for the existence of an embedded atomic jet. Methods:
Detected molecular and atomic lines are interpreted by means of emission line
diagnostics and an existing grid of molecular shock models. The physical
properties of the warm gas are compared against other molecular jet tracers and
to the results of a similar study towards the L1448-C outflow. Results: We have
detected and mapped the v=0-0 S(0) - S(7) H2 lines and fine-structure lines of
S, Fe+, and Si+. H2 is detected down to 5" from the source and is characterized
by a "cool" T~300K and a "warm" T~1000 K component, with an extinction Av ~ 8
mag. The amount of cool H2 towards the jet agrees with that estimated from CO
assuming fully molecular gas. The warm component is well fitted by C-type
shocks with a low beam filling factor ~ 0.01-0.04 and a mass-flux similar to
the cool H2. The fine-structure line emission arises from dense gas with
ionization fraction ~0.5 - 5 x 10e-3, suggestive of dissociative shocks. Line
ratios to sulfur indicate that iron and silicon are depleted compared to solar
abundances by a factor ~10-50. Conclusions: Spitzer spectral mapping
observations reveal for the first time a cool H component towards the CO
jet of HH211 consistent with the CO material being fully molecular and warm at
~ 300 K. The maps also reveal for the first time the existence of an embedded
atomic jet in the HH211 outflow that can be traced down to the central source
position. Its significant iron and silicon depletion excludes an origin from
within the dust sublimation zone around the protostar. The momentum-flux seems
insufficient to entrain the CO jet, although current uncertainties on jet speed
and shock conditions are too large for a definite conclusion.Comment: 13 pages, 10 figures, accepted for publication in A&
Discovery of interstellar mercapto radicals (SH) with the GREAT instrument on SOFIA
We report the first detection of interstellar mercapto radicals, obtained
along the sight-line to the submillimeter continuum source W49N. We have used
the GREAT instrument on SOFIA to observe the 1383 GHz Doublet Pi 3/2 J = 5/2 -
3/2 lambda doublet in the upper sideband of the L1 receiver. The resultant
spectrum reveals SH absorption in material local to W49N, as well as in
foreground gas, unassociated with W49N, that is located along the sight-line.
For the foreground material at velocities in the range 37 - 44 km/s with
respect to the local standard of rest, we infer a total SH column density ~ 2.6
E+12 cm-2, corresponding to an abundance of ~ 7 E-9 relative to H2, and
yielding an SH/H2S abundance ratio ~ 0.13. The observed SH/H2S abundance ratio
is much smaller than that predicted by standard models for the production of SH
and H2S in turbulent dissipation regions and shocks, and suggests that the
endothermic neutral-neutral reaction SH + H2 -> H2S + H must be enhanced along
with the ion-neutral reactions believed to produce CH+ and SH+ in diffuse
molecular clouds.Comment: Accepted for publication in Astronomy and Astrophysics (SOFIA/GREAT
special issue
Quantitative optical and near-infrared spectroscopy of molecular hydrogen towards HH91A
Integral-field spectroscopy of molecular hydrogen in the optical wavelength
region and complementary long-slit near-infrared spectroscopy are presented
towards HH91A.The detection of some 200 H_2 lines arising from ro-vibrational
levels up to v'=8 ranging between 7700A and 2.3 microns is reported. The
emission arises from thermally excited gas where the bulk of the material is at
2750 K and where 1% is at 6000 K. The total column density of shocked gas is
N(H_2) = 10^{18} cm^{-2}. Non-thermal excitation scenarios such as
UV-fluorescence do not contribute to the excitation of H_2 towards HH91A. The
emission is explained in terms of a slow non-dissociative J-shock which
propagates into a low-density medium which has been swept-up by previous
episodes of outflows which have occurred in the evolved HH90/91 complex.Comment: A&A accepte
The CHESS survey of the L1157-B1 shock: the dissociative jet shock as revealed by Herschel--PACS
Outflows generated by protostars heavily affect the kinematics and chemistry
of the hosting molecular cloud through strong shocks that enhance the abundance
of some molecules. L1157 is the prototype of chemically active outflows, and a
strong shock, called B1, is taking place in its blue lobe between the
precessing jet and the hosting cloud. We present the Herschel-PACS 55--210
micron spectra of the L1157-B1 shock, showing emission lines from CO, H2O, OH,
and [OI]. The spatial resolution of the PACS spectrometer allows us to map the
warm gas traced by far-infrared (FIR) lines with unprecedented detail. The
rotational diagram of the high-Jup CO lines indicates high-excitation
conditions (Tex ~ 210 +/- 10 K). We used a radiative transfer code to model the
hot CO gas emission observed with PACS and in the CO (13-12) and (10-9) lines
measured by Herschel-HIFI. We derive 20010^5 cm-3. The CO
emission comes from a region of about 7 arcsec located at the rear of the bow
shock where the [OI] and OH emission also originate. Comparison with shock
models shows that the bright [OI] and OH emissions trace a dissociative J-type
shock, which is also supported by a previous detection of [FeII] at the same
position. The inferred mass-flux is consistent with the "reverse" shock where
the jet is impacting on the L1157-B1 bow shock. The same shock may contribute
significantly to the high-Jup CO emission.Comment: 7 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
Effect Of Plant Population Density On The Growth And Yield Of Sorghum Varieties Grown On A Vertisol
Sorghum (Sorghum bicolor (L.) Moench) is an important crop that is usually grown on the Vertisols of north eastern Nigeria during the dry season. The crop is grown on soils with residual moisture, and thus exposing it to terminal drought stress. Improvement of resource use efficiency and yields is probably possible through the use of appropriate plant densities. Field trials were therefore conducted to study the effects of four plant densities, varying from 2.0 to 12.5 plants m-2 on water and radiation use and performance of two Masakwa sorghum varieties grown on a Vertisol under residual soil moisture conditions. At higher plant densities the locally adapted Nigerian variety, Bulwalana produced higher grain yields than the selection from Cameroun, Bourgouri-28. It also had more efficient water use and better light interception. At low plant densities, Bourgouri-28 yielded higher than Bulwalana. Leaf area index and radiation interception increased with increasing plant density. Stem borer incidence decreased with increasing plant density. More stem borer holes and stem tunnelling were recorded in Bulwalana than in Bourgouri-28. Covered kernel smut [Sporisorium sorghi (Ehrenberg) Link] appeared to be a potentially serious disease of the crop. The study showed that the performance of the crop can be improved through manipulation of plant population and use of early maturing cultivars
The CORALIE survey for southern extra-solar planets XV. Discovery of two eccentric planets orbiting HD4113 and HD156846
We report the detection of two very eccentric planets orbiting HD4113 and
HD156846 with the CORALIE Echelle spectrograph mounted on the 1.2-m Euler Swiss
telescope at La Silla. The first planet, HD4113b, has minimum mass of
, a period of days and an
eccentricity of . It orbits a metal rich G5V star at
AU which displays an additional radial velocity drift of 28 m s/yr
observed during 8 years. The combination of the radial-velocity data and the
non-detection of any main sequence stellar companion in our high contrast
images taken at the VLT with NACO/SDI, characterizes the companion as a
probable brown dwarf or as a faint white dwarf. The second planet, \object{HD
156846 b}, has minimum mass of M, a period
of days, an eccentricity of and is located
at AU from its parent star. HD156846 is a metal rich G0 dwarf and is
also the primary of a wide binary system ( AU, years). Its
stellar companion, \object{IDS 17147-1914 B}, is a M4 dwarf. The very high
eccentricities of both planets can be explained by Kozai oscillations induced
by the presence of a third object.Comment: 4 pages, 5 figures, A&A Letter accepte
Dystrophin deficiency affects human astrocyte properties andresponse to damage
In addition to progressive muscular degeneration due to dystrophin mutations, 1/3 of Duchenne muscular dystrophy (DMD) patients present cognitive deficits. However, there is currently an incomplete understanding about the function of the multiple dystrophin isoforms in human brains. Here, we tested the hypothesis that dystrophin deficiency affects glial function in DMD and could therefore contribute to neural impairment. We investigated human dystrophin isoform expression with development and differentiation and response to damage in human astrocytes from control and induced pluripotent stem cells from DMD patients. In control cells, short dystrophin isoforms were up-regulated with development and their expression levels changed differently upon neuronal and astrocytic differentiation, as well as in 2-dimensional versus 3-dimensional astrocyte cultures. All DMD-astrocytes tested displayed altered morphology, proliferative activity and AQP4 expression. Furthermore, they did not show any morphological change in response to inflammatory stimuli and their number was significantly lower as compared to stimulated healthy astrocytes. Finally, DMD-astrocytes appeared to be more sensitive than controls to oxidative damage as shown by their increased cell death. Behavioral and metabolic defects in DMD-astrocytes were consistent with gene pathway dysregulation shared by lines with different mutations as demonstrated by bulk RNA-seq analysis. Together, our DMD model provides evidence for altered astrocyte function in DMD suggesting that defective astrocyte responses may contribute to neural impairment and might provide additional potential therapeutic targets
INDIGO : better geomagnetic observatories where we need them
The INDIGO project aims to improve the global coverage of digital observatories by deploying digital magnetometer systems in:
i) Observatories where existing analog recording equipment is in need of upgrading.
ii) Newly established digital observatories.
iii) Existing digital observatories for the purpose of quality control and redundancy.
In implementing the project and selecting suitable sites, special attention is paid to parts of the Earth devoid of magnetic observatories, increasing the reliability and long-term operation of existing observatories and cost-effective use of local resources.
The Poster reviews the current status of the project. We examine the different steps and initiatives taken since the initiation of INDIGO in 2004 and assess their effectiveness in achieving progress towards our aims of improving global coverage and enhanced data quality
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