1,721,108 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
The microscopic origin of the anomalous isotopic properties of ice relies on the strong quantum anharmonic regime of atomic vibration
Full text linkWater ice is a unique material presenting intriguing physical properties, such as negative thermal expansion and anomalous volume isotope effect (VIE). They arise from the interplay between weak hydrogen bonds and nuclear quantum fluctuations, making theoretical calculations challenging. Here, we employ the stochastic self-consistent harmonic approximation to investigate how thermal and quantum fluctuations affect the physical properties of ice XI with ab initio accuracy. Regarding the anomalous VIE, our work reveals that quantum effects on hydrogen are so strong to be in a nonlinear regime: When progressively increasing the mass of hydrogen from protium to infinity (classical limit), the volume first expands and then contracts, with a maximum slightly above the mass of tritium. We observe an anharmonic renormalization of about 10% in the bending and stretching phonon frequencies probed in IR and Raman experiments. For the first time, we report an accurate comparison of the low-energy phonon dispersion with the experimental data, possible only thanks to high-level accuracy in the electronic correlation and nuclear quantum and thermal fluctuations, paving the way for the study of thermal transport in ice from first-principles and the simulation of ice under pressure
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Methodology for the evaluation of fission gas release in lead fast reactor
Full text linkThe Lead cooled Fast reactor is a reactor design option selected within GEN-IV initiative. GEN-IV reactor concepts have to fulfill four strategic goals, namely: sustainability, economics, safety and reliability, proliferation resistance and physical protection. Fast spectrum nuclear reactors enable a much more reduction of uranium consumption. To increase the operability of the reactor, sufficient reactivity reserve has to be assured by the core designer. Hence the nuclear fuel has to be designed to withstand high burn up. Increasing the burn up the gas release issue become more and more important, thus a correct and reliable evaluation of fission gas release during normal operation and in case of accident is of a major importance. In the former case statistical analysis may complement more classical mechanistic evaluations; in the latter case different computational tools may be involved.
Best estimate methodology may imply use of different codes. Namely to perform a realistic assessment of the fuel behavior, especially in case of accident conditions, a chain of codes has to be adopted if an analyst wants to adopt a suitable tool per different disciplines
Relevance of Thermo-Fluid Dynamics for Establishing the Safety of Nuclear Power Plants
No full textAccident Management, and related terms ‘procedures’ and ‘strategies’ (instead of Management), constitutes
a branch of the nuclear reactor safety. The understanding of the meaning and of the objectives of the AM
branch requires the knowledge of the safety/licensing concepts like Design Basis Accident (DBA), Beyond
DBA (BDBA), and Severe Accident (SA), as well as Probabilistic Safety Assessment (PSA) and role of
Human Factors (HF) within nuclear reactor safety. Based on this terminology, the AM branch occupies a
virtual region before or upstream the SA area and aims at forming an additional boundary to the progression
of accidents that eventually escaped the DBA boundary. This is done consistently with findings and
requirements of the PSA branch, taking into account of the HF and of the available NPP components and
systems and of their actual status.
The purpose of this paper is to summarize the main findings from the execution of a wide range analysis
focused to AM in VVER-1000 (within a European Commission funded Project) with main regard to the
qualification of computational tools and the proposal for a optimal AM strategy for this kind of NPP
Safety of evolutionary reactors: feasibility study for the experimental program of SPES facility
Full text linkIl documento riguarda uno studio di fattibilità condotto dal San Piero a Grado Nuclear Research Group dell'Università di Pisa per un programma sperimentale da svolgersi presso l'impianto SPES- 2. Data la rilevanza dell 'argomento della diluizione del boro relativamente alla sicurezza dei reattori nucleari, è stata esaminata la possibilità di effettuare un tale esperimento nell' apparecchiatura SPES. In particolare, l'obiettivo dell'attività è stato quello di investigare la distribuzione di diluizione boro in condizione di quantità massa ridotta, ad esempio, durante un evento di 'Small Break LOCA' (SB-LOCA). Come riferimento per uno studio di fattibilità è stato scelto il test OECD-PKL E2.2, che analizza la distribuzione di boro all'interno dell'apparecchiatura sperimentale PKL durante l'iniezione asimmetrica degli ECCS (HPIS e LPIS nei loop l e 2) e il seguente riempimento dell'apparecchiatura. Per verificare la riproducibilità di tale test in SPES-2 è stato utilizzato un modello RELAP5 dell 'impianto disponibile presso l'Università di Pisa. I risultati dei calcoli dimostrano che i principali aspetti termo-idraulici, che sono stati osservati nel test E2.2 presso l'apparecchiatura PKL, sono presenti anche nel test eseguito sullo SPES: modalità "reflux-condenser" e riempimento dell'impianto tramite l'intervento del sistema ECC, circolazione naturale in tutti i loop durante l'iniezione asimmetrica degli ECC e variazione della distribuzione boro, confermando così la fattibilità del test. Sono stati identificati anche alcuni requisiti per il sistema di misura SPES, poichè l'impianto deve essere dotato di dispositivi di misurazione della concentrazione e della portata di boro allo scopo di fornire informazioni significative per le successive analisi
Thirty Years’ Experience in RELAP5 Applications at GRNSPG & NINE
No full textThe application of RELAP5 at GRNSPG & NINE (Nuclear Research Group of San Piero a Grado–Nuclear and Industrial Engineering) started more than 30 years ago during which several versions of the code have been applied for the analysis of a very large variety of scenarios occurring in facilities and nuclear installations. The present paper has two goals: (1) to summarize the results and main outcomes achieved through the application of RELAP5 to international projects and benchmarks in which GRNSPG & NINE was involved and (2) to qualify the system’s thermal-hydraulic code calculations through the systematic application of a set of developed procedures.
Among the analyses performed, this paper will provide insights into the code results and, whenever possible, into the comparison with the reference/experimental data of scenarios measured in (1) integral test facilities: PSB-VVER, ATLAS, PKL, LOBI, LOFT, SPES, PACTEL; (2) separate effect test facilities: BFBT, Neptun, PANDA; (3) research reactors: Experimental Breeder Reactor (EBR); and (4) nuclear power plants: Atucha-II [pressurized heavy water reactor (PHWR)-Konvoi], VVER-1000, Darlington (CANDU).
In relation to the methodology developed for qualifying a system thermal-hydraulic code calculation, this paper provides a short description and spot results of the systematic application to the cases mentioned above in respect to some of the following steps: (1) demonstration of the geometrical fidelity; (2) demonstration of the steady-state achievement; (3) qualification at the on-transient level, which implies the characterization of (a) phenomenological windows and (b) relevant thermal-hydraulic aspects; and (4) quantitative analysis to evaluate the accuracy of the code calculation using the fast Fourier transform based method.
Finally, the main outcomes of the analyses summarized in this paper are the characterization of the level of assessment of RELAP5 and the demonstration of existence of a robust procedure to qualify system thermal-hydraulic code calculations
Relap5 Thermal Hydraulic Analysis 11% upper plenum leakage for PSB VVER test facility and VVER NPP
No full textThe presented paper considers the behavior of PSB-WWER facility and WWER 1000 NPP during 11% leakage transient in the upper plenum of the reactor vessel. RELAP 5/3.2 is applied for the analyzes. PSB-WWER facility is a 1/300 volume scale model of a WWER-1000, reactor installed at Electrogorsk Researc & Engineering Centre in 1998. Both nodalization are qualified, the WWER 1000 nodalization is a generic, no special NPP reference is used. In order to evaluate the nodalization performance, the comparing procedure set up at the DIMNP of Pisa University (UNIPI) has been applied that foresees two comparison levels: a ‘steady state’ level and an ‘on transient’ level. The transient is 11% equivalent break in Upper Plenum with the actuation of one high pressure injection system, connected to the hot leg of the loop #4, and 4 passive systems (ECCS hydro-accumulators), connected to the outlet plenum and to the inlet chamber of the downcomer. The low-pressure injection system is not available. The target is to compare calculation results for the test facility and the NPP and to reconsider the scaling and its influence on the transient results
- …
