1,557 research outputs found
The Cryogenic Target for the G Experiment at Jefferson Lab
A cryogenic horizontal single loop target has been designed, built, tested
and operated for the G experiment in Hall C at Jefferson Lab. The target
cell is 20 cm long, the loop volume is 6.5 l and the target operates with the
cryogenic pump fully immersed in the fluid. The target has been designed to
operate at 30 Hz rotational pump speed with either liquid hydrogen or liquid
deuterium. The high power heat exchanger is able to remove 1000 W of heat from
the liquid hydrogen, while the nominal electron beam with current of 40 A
and energy of 3 GeV deposits about 320 W of heat into the liquid. The increase
in the systematic uncertainty due to the liquid hydrogen target is negligible
on the scale of a parity violation experiment. The global normalized yield
reduction for 40 A beam is about 1.5 % and the target density fluctuations
contribute less than 238 ppm (parts per million) to the total asymmetry width,
typically about 1200 ppm, in a Q bin.Comment: 27 pages, 14 figure
Optical Link of the Atlas Pixel Detector
The on-detector optical link of the ATLAS pixel detector contains
radiation-hard receiver chips to decode bi-phase marked signals received on PIN
arrays and data transmitter chips to drive VCSEL arrays. The components are
mounted on hybrid boards (opto-boards). We present results from the irradiation
studies with 24 GeV protons up to 32 Mrad (1.2 x 10^15 p/cm^2) and the
experience from the production.Comment: 9th ICATPP Conference, Como, Ital
Radiation-Hard Optical Link for SLHC
We study the feasibility of fabricating an optical link for the SLHC ATLAS
silicon tracker based on the current pixel optical link architecture. The
electrical signals between the current pixel modules and the optical modules
are transmitted via micro-twisted cables. The optical signals between the
optical modules and the data acquisition system are transmitted via
radiation-hard/low-bandwidth SIMM fibres fusion spliced to
radiation-tolerant/medium-bandwidth GRIN fibres. The link has several nice
features. We have measured the bandwidths of the micro twisted-pair cables to
be ~ 1 Gb/s and the fusion spliced fibre ribbon to be ~ 2 Gb/s. We have
irradiated PIN and VCSEL arrays with 24 GeV protons and find the arrays can
operate up to the SLHC dosage. We have also demonstrated the feasibility of
fabricating a novel opto-pack for housing VCSEL and PIN arrays with BeO as the
substrate.Comment: 8th International Conference on Large Scale Applications and
Radiation Hardness of Semiconductor Detectors, Florence, Italy, 200
Selectivity and functional diversity in arbuscular mycorrhizas of co-occurring fungi and plants from a temperate deciduous woodland
1 The arbuscular mycorrhizal (AM) fungi colonizing plants at a woodland site in North Yorkshire (UK) have been characterized from the roots of five plant species (Rubus fruticosus agg. L., Epilobium angustifolium L., Acer pseudoplatanus L., Ajuga reptans L. and Glechoma hederacea L.), and identified using small-subunit rRNA (SSUrRNA) gene amplification and sequencing. 2 Interactions between five plant species from the site and four co-occurring glomalean fungi were investigated in artificial one-to-one AM symbioses. Three of the fungi were isolated from the site; the fourth was a culture genetically similar to a taxon found at the site. Phosphorus uptake and growth responses were compared with non-mycorrhizal controls. 3 Individual fungi colonized each plant with different spatial distribution and intensity. Some did not colonize at all, indicating incompatibility under the conditions used in the experiments. 4 Glomus hoi consistently occupied a large proportion of root systems and outperformed the other fungi, improving P uptake and enhancing the growth of four out of the five plant species. Only G. hoi colonized and increased P uptake in Acer pseudoplatanus, the host plant with which it associates almost exclusively under field conditions. Colonization of all plant species by Scutellospora dipurpurescens was sparse, and beneficial to only one of the host plants (Teucrium scorodonia). Archaeospora trappei and Glomus sp. UY1225 had variable effects on the host plants, conferring a range of P uptake and growth benefits on Lysimachia nummularia and T. scorodonia, increasing P uptake whilst not affecting biomass in Ajuga reptans and Glechoma hederacea, and failing to form mycorrhizas with A. pseudoplatanus. 5 These experimental mycorrhizas show that root colonization, symbiont compatibility and plant performance vary with each fungus-plant combination, even when the plants and fungi naturally co-exist. 6 We provide evidence of physical and functional selectivity in AM. The small number of described AM fungal species (154) has been ascribed to their supposed lack of host specificity, but if the selectivity we have observed is the general rule, then we may predict that many more, probably hard-to-culture glomalean species await discovery, or that members of species as currently perceived may be physiologically or functionally distinct
ATLAS Pixel Opto-Electronics
We have developed two radiation-hard ASICs for optical data transmission in
the ATLAS pixel detector at the LHC at CERN: a driver chip for a Vertical
Cavity Surface Emitting Laser (VCSEL) diode for 80 Mbit/s data transmission
from the detector, and a Bi-Phase Mark decoder chip to recover the control data
and 40 MHz clock received optically by a PIN diode. We have successfully
implemented both ASICs in 0.25 micron CMOS technology using enclosed layout
transistors and guard rings for increased radiation hardness. We present
results of the performance of these chips, including irradiation with 24 GeV
protons up to 61 Mrad (2.3 x 10e15 p/cm^2).Comment: 17 pages, 23 figures, submitted to NIM Added references. Added figure
15. Moved sec. IV to sec. I
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