220 research outputs found
Flow characterisation using fibre Bragg gratings and their potential use in nuclear thermal hydraulics experiments
With the ever-increasing role that nuclear power is playing to meet the aim of net zero carbon emissions, there is an intensified demand for understanding the thermal hydraulic phenomena at the heart of current and future reactor concepts. In response to this demand, the development of high-resolution flow analysis instrumentation is of increased importance. One such under-utilised and under-researched instrumentation technology, in the context of fluid flow analysis, is fibre Bragg grating (FBG)-based sensors. This technology allows for the construction of simple, minimally invasive instruments that are resistant to high temperatures, high pressures and corrosion, while being adaptable to measure a wide range of fluid properties, including temperature, pressure, refractive index, chemical concentration, flow rate and void fraction—even in opaque media. Furthermore, concertinaing FBG arrays have been developed capable of reconstructing 3D images of large phase structures, such as bubbles in slug flow, that interact with the array. Currently a significantly under-explored application, FBG-based instrumentation thus shows great potential for utilisation in experimental thermal hydraulics; expanding the available flow characterisation and imaging technologies. Therefore, this paper will present an overview of current FBG-based flow characterisation technologies, alongside a systematic review of how these techniques have been utilised in nuclear thermal hydraulics experiments. Finally, a discussion will be presented regarding how these techniques can be further developed and used in nuclear research
Protective vascular coagulation in response to bacterial infection of the kidney is regulated by bacterial lipid A and host CD147
Bacterial infection of the kidney leads to a rapid cascade of host protective responses, many of which are still poorly understood. We have previously shown that following kidney infection with uropathogenicEscherichia coli (UPEC), vascular coagulation is quickly initiated in local perivascular capillaries that protects the host from progressing from a local infection to systemic sepsis. The signaling mechanisms behind this response have not however been described. In this study, we use a number ofin vitro andin vivo techniques, including intravital microscopy, to identify two previously unrecognized components influencing this protective coagulation response. The acylation state of the Lipid A of UPEC lipopolysaccharide (LPS) is shown to alter the kinetics of local coagulation onsetin vivo. We also identify epithelial CD147 as a potential host factor influencing infection-mediated coagulation. CD147 is expressed by renal proximal epithelial cells infected with UPEC, contingent to bacterial expression of the α-hemolysin toxin. The epithelial CD147 subsequently can activate tissue factor on endothelial cells, a primary step in the coagulation cascade. This study emphasizes the rapid, multifaceted response of the kidney tissue to bacterial infection and the interplay between host and pathogen during the early hours of renal infection
Results from the Commissioning of the n-TOF Spallation Neutron Source at CERN
The new neutron time-of-flight facility (n_TOF) has been built at CERN and is now operational. The facility is intended for the measurement of neutron induced cross sections of relevance to Accelerator Driven Systems (ADS) and to fundamental physics. Neutrons are produced by spallation of the 20 GeV/c proton beam, delivered by the Proton Synchrotron (PS), on a massive target of pure lead. A measuring station is placed at about 185 m from the neutron producing target, allowing high-resolution measurements. The facility was successfully commissioned with two campaigns of measurements, in Nov. 2000 and Apr. 2001. The main interest was concentrated in the physical parameters of the installation (neutron flux and resolution function), along with the target behavior and various safety-related aspects. These measurements confirmed the expectations from Monte Carlo simulations of the facility, thus allowing to initiate the foreseen physics program
Measurement of the (90,91,92,93,94,96)Zr(n,gamma) and (139)La(n,gamma) cross sections at n_TOF
Open AccessNeutron capture cross sections of Zr and La isotopes have important implications in the field of nuclear astrophysics as well as in the nuclear technology. In particular the Zr isotopes play a key role for the determination of the neutron density in the He burning zone of the Red Giant star, while the (139)La is important to monitor the s-process abundances from Ba up to Ph. Zr is also largely used as structural materials of traditional and advanced nuclear reactors. The nuclear resonance parameters and the cross section of (90,91,92,93,94,96)Zr and (139)La have been measured at the n_TOF facility at CERN. Based on these data the capture resonance strength and the Maxwellian-averaged cross section were calculated
Measurement of the neutron capture cross section of the s-only isotope 204Pb from 1 eV to 440 keV
The neutron capture cross section of 204Pb has been measured at the CERN
n_TOF installation with high resolution in the energy range from 1 eV to 440
keV. An R-matrix analysis of the resolved resonance region, between 1 eV and
100 keV, was carried out using the SAMMY code. In the interval between 100 keV
and 440 keV we report the average capture cross section. The background in the
entire neutron energy range could be reliably determined from the measurement
of a 208Pb sample. Other systematic effects in this measurement could be
investigated and precisely corrected by means of detailed Monte Carlo
simulations. We obtain a Maxwellian average capture cross section for 204Pb at
kT=30 keV of 79(3) mb, in agreement with previous experiments. However our
cross section at kT=5 keV is about 35% larger than the values reported so far.
The implications of the new cross section for the s-process abundance
contributions in the Pb/Bi region are discussed.Comment: 8 pages, 3 figures, article submitted to Phys. Rev.
New measurement of neutron capture resonances of 209Bi
The neutron capture cross section of Bi209 has been measured at the CERN n
TOF facility by employing the pulse-height-weighting technique. Improvements
over previous measurements are mainly because of an optimized detection system,
which led to a practically negligible neutron sensitivity. Additional
experimental sources of systematic error, such as the electronic threshold in
the detectors, summing of gamma-rays, internal electron conversion, and the
isomeric state in bismuth, have been taken into account. Gamma-ray absorption
effects inside the sample have been corrected by employing a nonpolynomial
weighting function. Because Bi209 is the last stable isotope in the reaction
path of the stellar s-process, the Maxwellian averaged capture cross section is
important for the recycling of the reaction flow by alpha-decays. In the
relevant stellar range of thermal energies between kT=5 and 8 keV our new
capture rate is about 16% higher than the presently accepted value used for
nucleosynthesis calculations. At this low temperature an important part of the
heavy Pb-Bi isotopes are supposed to be synthesized by the s-process in the He
shells of low mass, thermally pulsing asymptotic giant branch stars. With the
improved set of cross sections we obtain an s-process fraction of 19(3)% of the
solar bismuth abundance, resulting in an r-process residual of 81(3)%. The
present (n,gamma) cross-section measurement is also of relevance for the design
of accelerator driven systems based on a liquid metal Pb/Bi spallation target.Comment: 10 pages, 5figures, recently published in Phys. Rev.
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