673 research outputs found
Modal characteristics of a flexible cylinder in turbulent axial flow from numerical simulations
The BeppoSAX WFC X-ray source catalogue
We present the catalogue of X-ray sources detected by the two Wide Field
Cameras (WFCs) in complete observations on board BeppoSAX during its 6 years of
operational lifetime, between April 1996 and April 2002. The BeppoSAX WFCs were
coded mask instruments sensitive in the 2-28 keV energy band with a 40x40
square degree fields of view, pointing in opposite directions and
perpendicularly to the BeppoSAX Narrow Field Instruments (NFI). The WFCs were
usually operated simultaneously to NFI observations, each lasting up to several
days. WFCs observed thus the entire sky several times with a typical
sensitivity of 2 to 10 mCrab. A systematic analysis of all WFC observations in
the BeppoSAX archive has been carried out using the latest post-mission release
of the WFC analysis software and calibrations. The catalogue includes 253
distinct sources, obtained from a total sample of 8253 WFC detections. We
describe the basic statistical properties of the sample and present a six-year
history of two celestial calibration X-ray sources.Comment: 15 pages, 11 figures, Catalogue, Accepted for publication on A&
Effect of spatial distribution of daily rainfall on interior catchment response of a distributed hydrological model
International audienceWe investigate the effect of spatial variability of daily rainfall on soil moisture, groundwater level and discharge using a physically-based, fully-distributed hydrological model. This model is currently in use with the district water board and is considered to represent reality. We focus on the effect of rainfall spatial variability on day-to-day variability of the interior catchment response, as well as on its effect on the general hydrological behaviour of the catchment. The study is performed in a flat rural catchment (135 km2) in the Netherlands, where the climate is semi-humid (average precipitation 800 mm/year, evapotranspiration 550 mm/year) and rainfall is predominantly stratiform (i.e. large scale). Both range-corrected radar data (resolution 2.5Ă—2.5 km2) as well as data from a dense network of 30 raingauges are used, observed for the period March?October 2004. Eight different rainfall scenarios, either spatially distributed or spatially uniform, are used as input for the hydrological model. The main conclusions from this study are: (i) using a single raingauge as rainfall input carries a great risk for the prediction of discharge, groundwater level and soil moisture, especially if the raingauge is situated outside the catchment; (ii) taking into account the spatial variability of rainfall instead of using areal average rainfall as input for the model is needed to get insight into the day-to-day spatial variability of discharge, groundwater level and soil moisture content; (iii) to get insight into the general behaviour of the hydrological system it is sufficient to use correct predictions of areal average rainfall over the catchment
Report on the selection of the reference XT-ADS target design and specifications
The XT-ADS is an experimental accelerator driven system (ADS) that is being developed in the framework of the European FP6 EUROTRANS project. In this deliverable, the specifications of the spallation target and the selection of its reference design are discussed. Justification of the design options, in relation to the performance requirements of the XT-ADS and the interlinking with the design of the sub-critical core and the primary system, are given
Solar-Driven Continuous CO<sub>2</sub> Reduction to CO and CH<sub>4</sub> using Heterogeneous Photothermal Catalysts:Recent Progress and Remaining Challenges
The urgent need to reduce the carbon dioxide level in the atmosphere and keep the effects of climate change manageable has brought the concept of carbon capture and utilization to the forefront of scientific research. Amongst the promising pathways for this conversion, sunlight-powered photothermal processes, synergistically using both thermal and non-thermal effects of light, have gained significant attention. Research in this field focuses both on the development of catalysts and continuous-flow photoreactors, which offer significant advantages over batch reactors, particularly for scale-up. Here, we focus on sunlight-driven photothermal conversion of CO2 to chemical feedstock CO and CH4 as synthetic fuel. This review provides an overview of the recent progress in the development of photothermal catalysts and continuous-flow photoreactors and outlines the remaining challenges in these areas. Furthermore, it provides insight in additional components required to complete photothermal reaction systems for continuous production (e. g., solar concentrators, sensors and artificial light sources). In addition, our review emphasizes the necessity of integrated collaboration between different research areas, like chemistry, material science, chemical engineering, and optics, to establish optimized systems and reach the full potential of this technology.</p
Modal characteristics of a flexible tube in turbulent axial flow: a numerical approach and validation with experimental data
Flow-induced vibration is an important concern in the design of tube bundles.
Due to the coupling of fluid motion and structural motion, instabilities such as
flutter and divergence can arise. Next to the instabilities caused by the coupling of fluid
motion and structural motion, turbulence could cause small amplitude vibrations, which
in turn could give rise to long-term damage. Currently, the dynamical behavior of a tube
in axial flow is studied by splitting the flow forces into inviscid and viscous components.
The inviscid flow forces are determined from potential flow theory while the viscous flow
forces come from empirical formulations.
In this paper, a computational methodology is proposed to improve the accuracy of the
predicted dynamical behaviour. In this methodology partitioned fluid-structure interaction
simulations are performed to calculate the free vibration decay of a tube in axial
flow. The tube is initially deformed according to an eigenmode in vacuum. Modal characteristics
are then derived from the free vibration decay of the tube surrounded by the
turbulent water flow. To validate this computational methodology a series of experiments
is reproduced. In these experiments the frequency and damping of the fundamental mode
of a solid brass cylinder were measured
On the absence of appreciable half-life changes in alpha emitters cooled in metals to 1 Kelvin and below
The recent suggestion that dramatic changes may occur in the lifetime of
alpha and beta decay when the activity, in a pure metal host, is cooled to a
few Kelvin, is examined in the light of published low temperature nuclear
orientation (LTNO) experiments, with emphasis here on alpha decay. In LTNO
observations are made of the anisotropy of radioactive emissions with respect
to an axis of orientation. Correction of data for decay of metallic samples
held at temperatures at and below 1 Kelvin for periods of days and longer has
been a routine element of LTNO experiments for many years. No evidence for any
change of half life on cooling, with an upper level of less than 1%, has been
found, in striking contrast to the predicted changes, for alpha decay, of
several orders of magnitude. The proposal that such dramatic changes might
alleviate problems of disposal of long-lived radioactive waste is shown to be
unrealistic.Comment: 27 pages, 12 figures, accepted for publication in Nucl.Phys.A.
Revised version, including quantitative analysis of the sensitivity of
nuclear orientation experiments, discussed in this work, to changes of
alpha-decay lifetimes in metals at low temperatures. Conclusions remain
unchange
- …