1,849 research outputs found
Radiation environment along the INTEGRAL orbit measured with the IREM monitor
The INTEGRAL Radiation Environment Monitor (IREM) is a payload supporting
instrument on board the INTEGRAL satellite. The monitor continually measures
electron and proton fluxes along the orbit and provides this information to the
spacecraft on board data handler. The mission alert system broadcasts it to the
payload instruments enabling them to react accordingly to the current radiation
level. Additionally, the IREM conducts its autonomous research mapping the
Earth radiation environment for the space weather program. Its scientific data
are available for further analysis almost without delay.Comment: 5 pages, 7 figures, accepted for publication in A+A letter
Gamma-Ray Burst Polarization: Limits from RHESSI Measurements
Using the RHESSI satellite as a Compton polarimeter, a recent study claimed
that the prompt emission of GRB021206 was almost fully linearly polarized. This
was challenged by a subsequent reanalysis. We present an novel approach,
applying our method to the same data. We identify Compton scattering candidates
by carefully filtering events in energy, time, and scattering geometry. Our
polarization search is based on time dependent scattering rates in
perpendicular directions, thus optimally excluding systematic errors. We
perform simulations to obtain the instrument's polarimetric sensitivity, and
these simulations include photon polarization. For GRB021206, we formally find
a linear polarization degree of 41% (+57% -44%), concluding that the data
quality is insufficient to constrain the polarization degree in this case. We
further applied our analysis to GRB030519B and found again a null result.Comment: 39 pages, 11 figures, accepted for publication by the Astrophysical
Journa
RHESSI as Gamma Ray Burst Polarimeter
The Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) was designed to measure hard X-rays and Îł-rays from solar flares. With its big detection area and thin side shielding it also proved to be well suited for studying
Gamma Ray Bursts (GRB). Polarization analysis is feasible as well, due to a big modulation factor (MF), though serious constraints on the minimum detectable polarization
(MDP) come from detection efficiency of double scattered photons. More constraints are given by background of accidental and real coincidences
Spectral Analysis of GRBs Measured by RHESSI
The Ge spectrometer of the RHESSI satellite is sensitive to Gamma Ray Bursts
(GRBs) from about 40 keV up to 17 MeV, thus ideally complementing the Swift/BAT
instrument whose sensitivity decreases above 150 keV. We present preliminary
results of spectral fits of RHESSI GRB data. After describing our method, the
RHESSI results are discussed and compared with Swift and Konus.Comment: 4 pages, 4 figures, conference proceedings, 'Swift and GRBs:
Unveiling the Relativistic Universe', San Servolo, Venice, 5-9 June 2006, to
appear in Il Nouvo Ciment
Modelling the energy gap in transition metal/aluminium bilayers"
We present an application of the generalised proximity effect theory.Comment: 15 pages, 11 figures, presented at workshop on low temperature
superconducting electronics at the University of Twente, The Netherland
The role of VEGF receptors in angiogenesis; complex partnerships
Abstract.: Vascular endothelial growth factors (VEGFs) regulate blood and lymphatic vessel development and homeostasis but also have profound effects on neural cells. VEGFs are predominantly produced by endothelial, hematopoietic and stromal cells in response to hypoxia and upon stimulation with growth factors such as transforming growth factors, interleukins or platelet-derived growth factor. VEGFs bind to three variants of type III receptor tyrosine kinases, VEGF receptor 1, 2 and 3. Each VEGF isoform binds to a particular subset of these receptors giving rise to the formation of receptor homo- and heterodimers that activate discrete signaling pathways. Signal specificity of VEGF receptors is further modulated upon recruitment of coreceptors, such as neuropilins, heparan sulfate, integrins or cadherins. Here we summarize the knowledge accumulated since the discovery of these proteins more than 20years ago with the emphasis on the signaling pathways activated by VEGF receptors in endothelial cells during cell migration, growth and differentiatio
Polarization from GRB021206: No constraints from reanalysis of RHESSI data
The determination of a polarization signal in Gamma Ray Bursts (GRBs) would give new information about their nature and mechanism. Using the RHESSI satellite as a Compton polarimeter, Coburn W. and Boggs S. E. (Nature, 423 (2003) 415) reported that GRB021206 was highly linearly polarized. This was contradicted by Rutledge R. E. and Fox D. B. (Mon. Not. R. Astron. Soc., 350 (2004) 1288) who found about 10 times less scattering events suitable for measuring
polarization. Applying our own method to thesamedata weconfirm them uch lower number of suitable scattering events. But we obtain three times smaller errors by using better selection criteria. Comparison with our Monte Carlo simulations shows that from the RHESSI data of GRB021206 we cannot distinguish between no and full polarization within less than 2 standard deviations. We also applied our method
to other GRBs observed by RHESSI. This shows that the probability to observe a GRB suitable for polarization search with such an instrument is small
Virtual water highway: water use efficiency in global food trade
International audienceAmid an increasing water scarcity in many parts of the world, virtual water trade as both a policy instrument and practical means to balance the regional, national and global water budget has received much attention in recent years. Built upon the knowledge of virtual water accounting in the literature, this study examines the efficiency of the resource use embodied in the global virtual water trade from the perspectives of exporting and importing countries. Different characteristics between "green" and "blue" virtual water corresponding to rainfed and irrigated agriculture are elaborated. The investigation reveals that the virtual water flows primarily from countries of high water productivity to countries of low water productivity, generating a global saving of water resources. Meanwhile, the domination of green virtual water in the total virtual water trade constitutes low opportunity costs and environmental impacts as opposed to blue virtual water. The results suggest efficiency gains in the global food trade in terms of water resource utilization. The study raises awareness of negative impacts of increasing reliance on irrigation for food production in many countries, including food exporting countries. The findings of the study call for a greater emphasis on rainfed agriculture to improve global food security and environmental sustainability
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Contribution of land use changes to near-surface air temperatures during recent summer extreme heat events in the Phoenix Metropolitan Area
The impact of 1973–2005 land use–land cover (LULC) changes on near-surface air temperatures during four recent summer extreme heat events (EHEs) are investigated for the arid Phoenix, Arizona, metropolitan area using the Weather Research and Forecasting Model (WRF) in conjunction with the Noah Urban Canopy Model. WRF simulations were carried out for each EHE using LULC for the years 1973, 1985, 1998, and 2005. Comparison of measured near-surface air temperatures and wind speeds for 18 surface stations in the region show a good agreement between observed and simulated data for all simulation periods. The results indicate consistent significant contributions of urban development and accompanying LULC changes to extreme temperatures for the four EHEs. Simulations suggest new urban developments caused an intensification and expansion of the area experiencing extreme temperatures but mainly influenced nighttime temperatures with an increase of up to 10 K. Nighttime temperatures in the existing urban core showed changes of up to 2 K with the ongoing LULC changes. Daytime temperatures were not significantly affected where urban development replaced desert land (increase by 1 K); however, maximum temperatures increased by 2–4 K when irrigated agricultural land was converted to suburban development. According to the model simulations, urban landscaping irrigation contributed to cooling by 0.5–1 K in maximum daytime as well as minimum nighttime 2-m air temperatures in most parts of the urban region. Furthermore, urban development led to a reduction of the already relatively weak nighttime winds and therefore a reduction in advection of cooler air into the city
Phase detection at the quantum limit with multi-photon Mach-Zehnder interferometry
We study a Mach-Zehnder interferometer fed by a coherent state in one input
port and vacuum in the other. We explore a Bayesian phase estimation strategy
to demonstrate that it is possible to achieve the standard quantum limit
independently from the true value of the phase shift and specific assumptions
on the noise of the interferometer. We have been able to implement the protocol
using parallel operation of two photon-number-resolving detectors and
multiphoton coincidence logic electronics at the output ports of a
weakly-illuminated Mach-Zehnder interferometer. This protocol is unbiased and
saturates the Cramer-Rao phase uncertainty bound and, therefore, is an optimal
phase estimation strategy.Comment: 4 pages, 5 figures replaced fig. 1 to correct graphics bu
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