6,399 research outputs found
Garigliano nuclear power plant: seismic evaluation of the turbine building
The Italian Garigliano Nuclear Power Plant (NPP) started its energy production in 1963. At present it is in the decommissioning stage. In order to get a proper management of the radioactive waste that will be produced during the dismantling operations it has been considered convenient to convert the turbine building of the plant into a temporary waste repository. This decision posed a remarkable seismic safety assessment issue. As a matter of fact, the challenge was to extend, in satisfactory safety conditions, the use of an important facility that has reached the end of its designed lifetime and to have this extended use approved by nuclear safety agencies. In this context many tasks have been accomplished, of which the most important are:
(a) a new appraisal of site seismic hazard;
(b) the execution of many investigations and testing on the
construction materials;
(c) the set up of a detailed 3D finite element model including the explicit representation of foundation piles and soil;
(d) consideration of soil structure kinematic and dynamic nteraction effects.
This paper describes the adopted seismic safety assessment criteria which are based on a performance objectives design approach. While performance based design is the approach currently recommended by European Regulations to manage seismic risk and it is fully incorporated in the Italian code for conventional buildings, bridges and plants, NPP are not explicitly considered. Therefore it was necessary to delineate a consistent interpretation of prescribed rules in order to properly select the maximum and operating design earthquakes on one side and corresponding acceptable limit states on the other side. The paper further provides an outline of the numerical analyses carried out, of the main results obtained and of the principal retrofitting actions that will be realized
Synthesis and characterisation of iron platinum nanoparticles
This thesis investigates the synthesis and characterization of FePt nanoparticles, a material which is a promising candidate for use as an ultra-high density magnetic storage medium; relevant literature is reviewed in chapter one. Chapter two gives full details of the characterisation techniques and physical property measurements employed throughout the work described in the following chapters. This includes powder X-ray diffraction, SQUID magnetometry, transmission electron microscopy, extended X- ray fluorescence spectroscopy and Rutherford backscattering. Chapter three describes the synthesis and characterisation of FePt nanoparticles prepared by a route presented in the literature as well as one developed during this study. Chapter four describes a systematic investigation into the Rietveld refinement of powder X-ray diffraction data of iron platinum nanoparticles. From the study it is concluded which of the methodologies presented is most suitable for use in further work on iron platinum nanoparticle studies. Chapter five describes a number of in-situ variable temperature X-ray diffraction studies designed to investigate the order-disorder transition in FePt nanoparticles. A comparison between this transition in samples made via both synthetic routes discussed in chapter three is made before analysing in-depth data in order to provide information about the phase transition and its relationship with precise synthetic conditions. Chapter six describes work done on FePt nanoparticles to determine if EXAFS measurements can be obtained and modelled such that conclusions can be drawn as to the degree of order of samples prepared via different methods. Chapter seven describes a variety of magnetic studies designed to investigate the structure and properties of FePt nanoparticles. The first part of the chapter focuses on typical experiments and what use they are whilst the second part discusses the methodology and equipment required to study the phase transition of iron platinum nanoparticles, i.e. variable temperature magnetic studies
On the ergoregion instability in rotating gravastars
The ergoregion instability is known to affect very compact objects that
rotate very rapidly and do not possess a horizon. We present here a detailed
analysis on the relevance of the ergoregion instability for the viability of
gravastars. Expanding on some recent results, we show that not all rotating
gravastars are unstable. Rather, stable models can be constructed also with
J/M^2 ~ 1, where J and M are the angular momentum and mass of the gravastar,
respectively. The genesis of gravastars is still highly speculative and
fundamentally unclear if not dubious. Yet, their existence cannot be ruled out
by invoking the ergoregion instability. For the same reason, not all
ultra-compact astrophysical objects rotating with J/M^2 <~ 1 are to be
considered necessarily black holes.Comment: 10 pages, 7 figure
Analyzing Trails in Complex Networks
Even more interesting than the intricate organization of complex networks are
the dynamical behavior of systems which such structures underly. Among the many
types of dynamics, one particularly interesting category involves the evolution
of trails left by moving agents progressing through random walks and dilating
processes in a complex network. The emergence of trails is present in many
dynamical process, such as pedestrian traffic, information flow and metabolic
pathways. Important problems related with trails include the reconstruction of
the trail and the identification of its source, when complete knowledge of the
trail is missing. In addition, the following of trails in multi-agent systems
represent a particularly interesting situation related to pedestrian dynamics
and swarming intelligence. The present work addresses these three issues while
taking into account permanent and transient marks left in the visited nodes.
Different topologies are considered for trail reconstruction and trail source
identification, including four complex networks models and four real networks,
namely the Internet, the US airlines network, an email network and the
scientific collaboration network of complex network researchers. Our results
show that the topology of the network influence in trail reconstruction, source
identification and agent dynamics.Comment: 10 pages, 16 figures. A working manuscript, comments and criticisms
welcome
Controllability of a viscoelastic plate using one boundary control in displacement or bending
In this paper we consider a viscoelastic plate (linear viscoelasticity of the
Maxwell-Boltzmann type) and we compare its controllability properties with the
(known) controllability of a purely elastic plate (the control acts on the
boundary displacement or bending). By combining operator and moment methods, we
prove that the viscoelastic plate inherits the controllability properties of
the purely elastic plate
WhiskyMHD: a new numerical code for general relativistic magnetohydrodynamics
The accurate modelling of astrophysical scenarios involving compact objects
and magnetic fields, such as the collapse of rotating magnetized stars to black
holes or the phenomenology of gamma-ray bursts, requires the solution of the
Einstein equations together with those of general-relativistic
magnetohydrodynamics. We present a new numerical code developed to solve the
full set of general-relativistic magnetohydrodynamics equations in a dynamical
and arbitrary spacetime with high-resolution shock-capturing techniques on
domains with adaptive mesh refinements. After a discussion of the equations
solved and of the techniques employed, we present a series of testbeds carried
out to validate the code and assess its accuracy. Such tests range from the
solution of relativistic Riemann problems in flat spacetime, over to the
stationary accretion onto a Schwarzschild black hole and up to the evolution of
oscillating magnetized stars in equilibrium and constructed as consistent
solutions of the coupled Einstein-Maxwell equations.Comment: minor changes to match the published versio
The uterine junctional zone: A 3-dimensional ultrasound study of patients with endometriosis
The uterine junctional zone (JZ) alterations are correlated with adenomyosis. An accurate evaluation of the JZ may be obtained by 3-dimensional transvaginal sonography (TVS). The aim of the present prospective study was to assess the value of detectable alterations by 3-dimensional TVS of the JZ in patients with pelvic endometriosis (diagnosed by laparoscopy and histologic condition) and to compare these findings with those of women without pelvic endometriosis
High-contrast imaging of HD 29992 and HD 196385 with GPI
Based on high contrast images obtained with the Gemini Planet Imager (GPI),
we report the discovery of two point-like sources at angular separations of
and from the stars HD 29992 and HD 196385. A
combined analysis of the new GPI observations and images from the literature
indicates that the source close to HD 29992 could be a companion to the star.
Concerning HD 196385, the small number of contaminants () suggests
that the detected source may be gravitationally bound to the star. For both
systems, we discarded the presence of other potential companions with
M at . From stellar model atmospheres and
low-resolution GPI spectra, we derive masses of - M
for these sources. Using a Markov-chain Monte Carlo approach, we performed a
joint fit of the new astrometry measurements and published radial velocity data
to characterize the possible orbits. For HD 196385B, the median dynamic mass is
in agreement with that derived from model atmospheres, whilst for HD 29992B,
the orbital fit favors masses close to the brown dwarf regime(
M). HD 29992 and HD 196385 might be two new binary systems with
M-type stellar companions. However, new high angular resolution images would
help to definitively confirm whether the detected sources are gravitationally
bound to their respective stars, and permit tighter constraints on the orbital
parameters of both systems
Table of Contents
Table of contents for Volume 10, Issue 3 of the Linfield Magazin
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