1,721,354 research outputs found
New estimates of secular sealevel rise from tide gauge data and GIA modeling
No full textDuring the last three decades, at least thirty independent estimates of the secular
global mean sea–level rise (GMSLR) have been published, based on sufficiently long
tide gauge records. Despite its apparent simplicity, the problem of GMSLR is fraught
with a number of difficulties, which make it one of the most challenging questions
of climate change science. Not surprisingly, published estimates show considerable
scatter, with rates ranging between 1 and 2 mm/yr for observations on the century
time scale. In previous work, the importance of Glacial Isostatic Adjustment (GIA)
upon the assessment of the GMSLR has been clearly demonstrated. In particular,
starting from the 80s, GIA models have been routinely employed to decontaminate
tide gauge observations from the effects of melting of the late–Pleistocene ice sheets,
in order to fully highlight the sea–level variations driven by climate change. However,
uncertainties associated with the Earth’s rheological profile and the time history of
the past continental ice sheets can propagate into the GIA corrections. After revisit-
ing previous work and estimates, we suggest a significant modification of the criteria
for the selection of the tide gauges which are most suitable for the robust assessment
of the secular GMSLR. In particular, we seek a set of tide gauges for which GIA
corrections are essentially independent of the parameterization of the rheological
profile of the Earth’s mantle and of the detailed time–chronology of surface loading.
This insensitivity is established by considering predictions based upon three GIA
models widely employed in the recent literature (namely, ICE–3G, ICE–5G and the
one developed at the Research School of Earth Sciences of the National Australian
University). Applying this approach and selection criteria previously proposed in
the literature, we identify a set of 22 sufficiently evenly distributed tide gauges.
By simple statistical methods, these records yield a “preferred”, GIA–independent
GMSLR estimate since 1880, namely 1.5 ± 0.1 mm/yr (rms=0.4 mm/yr, wrms=0.3
mm/yr). This value is consistent with various previous estimates based on secular
tide gauge observations and with that proposed, for the 20th century, by the IPCC
Fourth Assessment Report (1.7 ± 0.5 mm/yr)
Results of RELAP4/MOD6 code applications", Lectures L8, L9, L10, L13, L16 at Course on Thermal-hydraulic Phenomena in Nuclear Reactor Technology - Sofia (BG),
No full textA Course in Nuclear thermal-hydraulics was organized by UNIPI in Sofia at the time of the cold war (Soviet Union collapsed in 1991). Contacts crossing the iron curtain were extremely complex. The entire Course consists of several hundred slides (all preserved in paper format by the corresponding author) and a couple dozen lectures (see copies below). Two pages from the Course are reported below. The current lecture deals with the selected topics relevant in nuclear thermal-hydraulics –more details can be found in the copied program below
IgM MGUS anti myelin-associated glycoprotein neuropathy can rarely express as a predominantly distal motor neuropathy
No full textSpectral analysis of sea level during the altimetry era, and evidence for GIA and glacial melting fingerprints
No full textWe study the spatial patterns of the mass and steric components of sea-level change during the "altimetry era" (1992-today), and we characterize them at different scales by the orthonormal functions method. The spectrum of the altimetry-derived rate of sea-level rise is red and decays with increasing wavenumber nearly following a power law with exponent ≈. 2. By analyzing the degree correlation and the admittance function, we find that the altimetric rate of sea-level change is coherent with the total steric field in the whole range of wavelengths considered (down to ≈. 1000 km), but particularly for wavelengths exceeding ≈. 2000 km. Thermosteric and halosteric components are moderately anti-correlated within the range of wavelengths 1000-4000 km. Their power spectrum varies significantly with the wavelength and, for ≈. 2000 km, it is equally partitioned between the two components. The power of regional sea-level variations driven by Glacial Isostatic Adjustment and the melting of continental ice sheets is small compared to that held by the steric component, which explains most of the regional variability shown by the altimetry record. This causes the elusiveness of the "static" sea-level fingerprints, which at present are hidden in the pattern of the residual sea-level (i.e., the altimetry-derived sea-level minus the steric component). However, we find that at harmonic degree 2, mainly associated with rotational variations, the power of glacial melting is significant and it will progressively increase during next century in response to global warming. We also estimate that at the end of the Mid-Holocene the strength of the glacial isostatic readjustment fingerprints was ≈. 10 times larger than today, well above the long-wavelength component of residual sea-level. © 2016 Elsevier B.V
Modeling, Validation, Scaling, Uncertainty and Application in Nuclear Thermal Hydraulics
No full textNuclear Thermal Hydraulics (NTH) implies a universe of knowledge, which, among the other things, is not easy to summarize and can be described (correctly) from different viewpoints. Resulting pictures are not necessarily consistent among each other and may prevent an optimal planning of researches, definitely slowing down the progress in understanding. Current generation and forthcoming water-cooled nuclear reactors are at the center of the attention; however, a few statements in Conclusions deal with thermal hydraulics in ‘other’ types of reactors. Rather than suggesting way-outs in future investigations, an interpretation of the state of the art constitutes the target for the paper. Referring to the words in the title, we try to substantiate the following evaluations, obvious or well established: (a) modeling is imperfect; (b) validation is essential; (c) scaling is controversial; (d) uncertainty is a guru-type of matter; (e) applications need proper strategy and consideration of research outcomes, including connections with different technologies. The Best Estimate Plus Uncertainty (BEPU) approach embeds the topics above and fixes the links between NTH on the one side and the Probabilistic Safety Assessment (PSA) and licensing on the other side
"Analysis of natural circulation test A2-77 performed in LOBI facility, by RELAP5/MOD2 code"
No full textThe document deals with the analysis of an experiment to be performed in LOBI ITF in the configuration Mode2. LOBI was a Pressurized Water Reactor (PWR) simulator installed in the EC center of Ispra Italy financially supported by EURATOM.
The configuration Mod2 of LOBI was designed as a consequence of the Three Mile accident in US and is the follow-up of the configuration Mod1. Mod2 was designed to simulate stratification phenomena and natural circulation which are important during Small Break Loss of Coolant Accidents (SBLOCA); as a difference Mod1 was designed to simulate phenomena expected during Large Break Loss of Coolant (LBLOCA) scenarios. Namely downcomer size in Mod2 was much smaller than in the case of Mod1 and a large number of Emergency Core Cooling Systems (ECCS) were installed in Mod2. The concerned A2-77 Natural Circulation (NC) experiment was performed to model as far as possible the PWR performance. Various phase of NC were identified and brought to important findings in Nuclear Reactor Safety, including the characterization of instabilities and the reflux condensing mode.
The work was discussed in a specific meeting in Ispra of the so-called LPTF research group where University of Pisa represented Italy
Accuracy quantification by the FFT method in FARO L-14 (ISP 39) open calculations, Ispra (I), April 22-23, 1997
No full textThe Fast Fourier Transform Based Method (FFTBM) was developed at University of Pisa to achieve a quantitative evaluation of the accuracy of thermal-hydraulic system code calculations. International cooperation was established to transfer the method with various Institutions all over the world. In the case documented in this report one scientists from University of Pisa (Mario Leonardi) has been invited at the European Commission (EC) Joint Research Center (JRC) of Ispra (Varese, Italy) to implement and to apply the method. The present document has been issued by JSI and describes the application of the method to the severe accident (corium interaction with water) FARO L-14 carried out in the framework of EC EURATOM researches. The L-14 experiment was selected at the basis of International Standard Problem 39 (ISP-39) by the Organization for Economic Cooperation and Development / Nuclear Energy Agency / Committee on the Safety of Nuclear Installations (OECD/NEA/CSNI)
Outline of User effect on Codes Predictions, 7th Meet. of CSNI THSB Task Group, Paris (F), June 26-28, 1990
No full textThe execution of a large number of pre-test and post-test analyses concerning (not only) International Standard Problems (ISP) each one with several participants with many of them using the same code version, showed an important impact on the code prediction which is not (or better, not entirely) associated with the nature of the code. This was called user effect. The user effect became a dominating topic in discussions and plant to improve the technology. The present report constitutes the origin of the ‘user-effect’ wording
Best Estimate Analysis and Uncertainty evaluation of the Angra-2 LBLOCA DBA
No full textThe licensing is a legal process to transfer the nuclear safety technology (developed and supported by researches) into a legal-fixed environment. Competences in the legal nuclear safety framework (typically part of the Atomic Act in each Country) and of nuclear reactor safety are needed in such a context.
University of Pisa had the opportunity and the challenge to participate, on the behalf of the local Regulatory body (a Governmental Institution) in Brazil, to the review of the safety report submitted by the German Industry (namely, KWU-Siemens) for the licensing of the Angra-2, 1400 Mwe (the largest Nuclear Power plant in the world in terms of reactor power) o Nuclear Power Plant.
The present document deals with the independent analysis of the Large Break Loss of Coolant Accident (LBLOCA) performed at University of Pisa and to be compared with the results for the same accident obtained by the industry
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