2,307 research outputs found
Neutrons from Piezonuclear Reactions
We report the results obtained by cavitating water solutions of iron salts
(iron chloride and iron nitrate) with different concentrations at different
ultrasound powers. In all cases we detected a neutron radiation well higher
than the background level. The neutron production is perfectly reproducible and
can at some extent be controlled. These evidences for neutron emission
generated by cavitation support some preliminary clues for the possibility of
piezonuclear reactions (namely nuclear reactions induced by pressure and shock
waves) obtained in the last ten years. We have been able for the first time to
state some basic features of such a neutron emission induced by cavitation,
namely: 1) a marked threshold behavior in power, energy and time; 2) its
occurring without a concomitant production of gamma radiation.Comment: 8 figures; we added some more important references; we replaced some
figures with more detailed ones; we added more comprehensive details which
could not be desclosed before as part of private patents which have been
published no
Excised acoustic black holes: the scattering problem in the time domain
The scattering process of a dynamic perturbation impinging on a draining-tub
model of an acoustic black hole is numerically solved in the time domain.
Analogies with real black holes of General Relativity are explored by using
recently developed mathematical tools involving finite elements methods,
excision techniques, and constrained evolution schemes for strongly hyperbolic
systems. In particular it is shown that superradiant scattering of a
quasi-monochromatic wavepacket can produce strong amplification of the signal,
offering the possibility of a significant extraction of rotational energy at
suitable values of the angular frequency of the vortex and of the central
frequency of the wavepacket. The results show that theoretical tools recently
developed for gravitational waves can be brought to fruition in the study of
other problems in which strong anisotropies are present.Comment: 8 pages, 9 figure
Competing mechanisms of stress-assisted diffusivity and stretch-activated currents in cardiac electromechanics
We numerically investigate the role of mechanical stress in modifying the
conductivity properties of the cardiac tissue and its impact in computational
models for cardiac electromechanics. We follow a theoretical framework recently
proposed in [Cherubini, Filippi, Gizzi, Ruiz-Baier, JTB 2017], in the context
of general reaction-diffusion-mechanics systems using multiphysics continuum
mechanics and finite elasticity. In the present study, the adapted models are
compared against preliminary experimental data of pig right ventricle
fluorescence optical mapping. These data contribute to the characterization of
the observed inhomogeneity and anisotropy properties that result from
mechanical deformation. Our novel approach simultaneously incorporates two
mechanisms for mechano-electric feedback (MEF): stretch-activated currents
(SAC) and stress-assisted diffusion (SAD); and we also identify their influence
into the nonlinear spatiotemporal dynamics. It is found that i) only specific
combinations of the two MEF effects allow proper conduction velocity
measurement; ii) expected heterogeneities and anisotropies are obtained via the
novel stress-assisted diffusion mechanisms; iii) spiral wave meandering and
drifting is highly mediated by the applied mechanical loading. We provide an
analysis of the intrinsic structure of the nonlinear coupling using
computational tests, conducted using a finite element method. In particular, we
compare static and dynamic deformation regimes in the onset of cardiac
arrhythmias and address other potential biomedical applications
Use of the Natural Circulation Flow Map for Natural Circulation Systems Evaluation
The aim of this paper is to collect and resume the work done to build and develop, at the University of Pisa, an engineering tool related to the natural circulation. After a brief description of the different loop flow regimes in single phase and two phase, the derivation of a suitable tool to judge the NC performance in a generic system is presented. Finally, an extensive comparison among the NC performance of various nuclear power plants having different design is done to show a practical application of the NC flow map
SELSE, vers. 1.0â. Un Database in formato Microsoft ACCESS per la digitalizzazione dei dati raccolti con la Scheda âgeologicaâ di II livello per la âValutazione degli effetti locali nei siti di ubicazione di singoli edifici (edilizia ordinaria, strategica e monumentale)â
Ă stato realizzato un database relazionale (figura 1), denominato SELSE (Scheda Effetti
Locali per il Singolo Edificio), che consente la digitalizzazione delle informazioni rilevate con la scheda âgeologicaâ per la âValutazione degli effetti locali nei siti di ubicazione di singoli edificiâ (di seguito indicata come scheda âEffetti Localiâ; Compagnoni et al., 2009)
Superradiance from BEC vortices: a numerical study
The scattering of sound wave perturbations from vortex excitations of
Bose-Einstein condensates(BEC) is investigated by numerical integration of the
associated Klein-Gordon equation. It is found that, at sufficiently high
angular speeds, sound wave-packets can extract a sizeable fraction of the
vortex energy through a mechanism of superradiant scattering. It is conjectured
that this superradiant regime may be detectable in BEC experiments.Comment: 4 pages, 4 figure
Accident Management in VVER-1000
The present paper deals with the investigation study on accident management in VVER-1000 reactor type conducted in the framework of a European Commission funded project. The mentioned study involved both experimental and computational fields. The purpose of this paper is to summarize the main findings from the execution of a wide-range analysis focused on AM in VVER-1000 with main regard to the qualification of computational tools and the proposal for an optimal AM strategy for this kind of NPP
Thermal-Hydraulic Analysis of Coolant Flow Decrease in Fuel Channels of Smolensk-3 RBMK during GDH Blockage Event
One of the transients that have received considerable attention in the safety evaluation of RBMK reactors is the partial break of a group distribution header (GDH). The coolant flow rate blockage in one GDH might lead to excessive heat-up of the pressure tubes and can result in multiple fuel channels (FC) ruptures. In this work, the GDH flow blockage transient has been studied considering the Smolensk-3 RBMK NPP (nuclear power plant). In the RBMK, each GDH distributes coolant to 40â43âFC. To investigate the behavior of each FC belonging to the damaged GDH and to have a more realistic trend, one (affected) GDH has been schematized with its forty-two FC, one by one. The calculations were performed using the 0-D NK (neutron kinetic) model of the RELAP5-3.3 stand-alone code. The results show that, during the event, the mass flow rate is disturbed differently according to the power distribution established for each FC in the schematization. The start time of the oscillations in mass flow rate depends strongly on the attributed power to each FC. It was also observed that, during the event, the fuel channels at higher thermal power values tend to undergo first cladding rupture leaving the reactor to scram and safeguarding all the other FCs connected to the affected GDH
Consistent Posttest Calculations for LOCA Scenarios in LOBI Integral Facility
Integral test facilities (ITFs) are one of the main tools for the validation of best estimate thermalhydraulic system codes. The experimental data are also of great value when compared to the experiment-scaled conditions in a full NPP. The LOBI was a single plus a triple-loop (simulated by one loop) test facility electrically heated to simulate a 1300âMWe PWR. The scaling factor was 712 for the core power, volume, and mass flow. Primary and secondary sides contained all main active elements. Tests were performed for the characterization of phenomenologies relevant to large and small break LOCAs and special transients in PWRs. The paper presents the results of three posttest calculations of LOBI experiments. The selected experiments are BL-30, BL-44, and A1-84. They are LOCA scenarios of different break sizes and with different availability of safety injection components. The goal of the analysis is to improve the knowledge of the phenomena occurred in the facility in order to use it in further studies related to qualifying nodalizations of actual plants or to establish accuracy data bases for uncertainty methodologies. An example of procedure of implementing changes in a common nodalization valid for simulating tests occurred in a specific ITF is presented along with its confirmation based on posttests results
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