130,558 research outputs found
Energy efficiency and HVAC systems in existing and historical buildings
No full textRefurbishment of existing and historical buildings is a priority in many European countries. Due to the need of developing a harmonized approach focusing on historical buildings, in 2014 AiCARR (Italian Association for air conditioning, heating, refrigeration) published a specific Guidelines entitled “Energy efficiency in historic buildings” (de Santoli et al., 2014) intended for both design engineers and superintendents to support the energy retrofit actions in historical buildings. The Guidelines provide the design engineers with a tool for the energy audit of the historic building and offer a framework for the design of possible energy upgrades, appropriately tailored to the needs and peculiarities of the cultural heritage. In this chapter, the energy efficiency in historical buildings and the new CEN Standard on this topic will be examined and discussed
Supersymmetric solutions of SU(2)-Fayet–Iliopoulos-gauged N=2, d=4 supergravity
No full textWe explore the construction of supersymmetric solutions of theories of N=2,d=4 supergravity with a SU(2) gauging and SU(2) Fayet–Iliopoulos terms. In these theories an SU(2) isometry subgroup of the Special-Kähler manifold is gauged together with a SU(2) R-symmetry subgroup. We construct several solutions of the CP‾3 quadratic model directly in four dimensions and of the ST[2,6] model by dimensional reduction of the solutions found by Cariglia and Mac Conamhna in N=(1,0),d=6 supergravity with the same kind of gauging. In the CP‾3 model, we construct an AdS2×S2 solution which is only 1/8 BPS and an R×H3 solutions that also preserves 1 of the 8 possible supersymmetries. We show how to use dimensional reduction as in the ungauged case to obtain Rn×Sm and also AdSn×Sm-type solutions (with different radii) in 5- and 4-dimensions from the 6-dimensional AdS3×S3 solution
BPS black holes in a non-homogeneous deformation of the stu model of N = 2, D = 4 gauged supergravity
No full textWe consider a deformation of the well-known stu model of ,
supergravity, characterized by a non-homogeneous special K\"ahler manifold,
and by the smallest electric-magnetic duality Lie algebra consistent with its
upliftability to five dimensions. We explicitly solve the BPS attractor
equations and construct static supersymmetric black holes with radial symmetry,
in the context of \textU(1) dyonic Fayet-Iliopoulos gauging, focussing on
axion-free solutions. Due to non-homogeneity of the scalar manifold, the model
evades the analysis recently given in the literature. The relevant physical
properties of the resulting black hole solution are discussed
Prescrizioni antisismiche per impianti tecnologici. La Normativa Europea, la vigente Normativa Italiana di cui al D.M. 14 gennaio 2008 e la Normativa Americana
No full textLa funzionalità degli impianti tecnologici a seguito di un evento calamitoso di tipo sismico concorre, al pari della agibilità della struttura portante, a garantire un adeguato livello di sicurezza e un idoneo livello di operatività dell’edificio. Da ciò la occorrenza di un approccio progettuale antisismico per gli impianti tecnologici similare a quello operato per le strutture portanti, e di conseguenza la necessità di standards progettuali minimi specifici per gli impianti tecnologici.
Nel presente lavoro sono state analizzate alcune prescrizioni inerenti la progettazione antisimica degli impianti tecnologici presenti a livello Comunità Europea, Nazionale ed Extraeuropeo, al fine di definire inizialmente uno stato dell’arte in tale ambito e successivamente impostare un confronto a carattere generale delle disposizioni trattate
Non-Abelian black string solutions of N = (2,0), d = 6 supergravity
No full textWe show that, when compactified on a circle, N=(2,0),d=6 supergravity coupled
to 1 tensor multiplet and nV vector multiplets is dual to N=(2,0),d=6
supergravity coupled to just nT=nV+1 tensor multiplets and no vector
multiplets. Both theories reduce to the same models of N=2,d=5 supergravity
coupled to nV5=nV+2 vector fields. We derive Buscher rules that relate
solutions of these theories (and of the theory that one obtains by dualizing
the 3-form field strength) admitting an isometry. Since the relations between
the fields of N=2,d=5 supergravity and those of the 6-dimensional theories are
the same with or without gaugings, we construct supersymmetric non-Abelian
solutions of the 6-dimensional gauged theories by uplifting the recently found
5-dimensional supersymmetric non-Abelian black-hole solutions. The solutions
describe the usual superpositions of strings and waves supplemented by a BPST
instanton in the transverse directions. One of the solutions obtained
interpolates smoothly between two AdS3xS3 geometries with different radii
University of Wisconsin solution and human saphenous vein graft preservation: preliminary anatomic report.
No full textEndothelial damage of human saphenous vein (HSV) during the preparation for bypass grafting could affect graft patency. Improving the preservation of HSV could provide a longer and better patency of coronary artery bypass grafts. An electron microscopic comparative analysis of the effects of three different preservatives on HSV morphology was carried on in order to determine the best method to prevent or minimize possible endothelial damage. Distal segments of HSVs were harvested from 15 patients with a "no-touch" technique. Each segment was divided into seven specimens after a low pressure distension with saline solution. The first of them was fixed immediately after harvesting with 2.5% glutaraldehyde solution, for basal evaluation. Three were fixed after 30 min and three after 5 h preservation at 4 degrees C in a) autologous, oxygenated, and heparinized blood (AOHB), b) heparinized saline solution with papaverine (HSSP) and c) University of Wisconsin solution (UWS). The specimens preserved in AOHB showed marked endothelial cell detachment and endothelial cell loss after both preservation times (30 min and 5 h). The specimens preserved in HSSP for 30 min showed no alteration in endothelium in 12 cases, while a partial endothelial detachment with intracellular edema was present in the last 3 cases; all 5 h specimens showed only a few remnants of endothelial cells. The specimens preserved in UWS for 30 min showed a morphology comparable to specimens preserved in the saline solution for the same time; in the 5 h specimens a well preserved endothelium was found in 11 cases and partial endothelial detachment and subendothelial edema in the other 4.(ABSTRACT TRUNCATED AT 250 WORDS
University of Wisconsin solution and human saphenous vein graft preservation: preliminary anatomic report
No full text
SOLUTIONS OF N=2 GAUGED SUPERGRAVITY IN 4, 5 AND 6 DIMENSIONS
No full textThe main goal of the work we are presenting is the exploration of some sectors of the space of the supersymmetric solutions of supergravity theories with 8 supercharges, in 4, 5 and 6 dimensions, which led to the new solutions.
We are firstly reviewing the supergravity theories of our interest, paying attention to their geometrical structure and to their possible gaugings. While discussing the 4-dimensional case, we are also introducing a couple of solutions generating techniques.
We then introduce the idea of dimensionally reducing a theory and its solutions on a circle, as the necessary tool to relate 4, 5 and 6-dimensional ungauged supergravity theories among themselves. An interesting feature emerges from this treatment: there are two classes of 6-dimensional theories that lead, when compactified, to the same 5-dimensional model; the two 6-dimensional theories are therefore dual. In the present context, the main reason to treat dimensional reduction is given by the possibility of generating new solutions, reducing or uplifting known ones.
Finally, we apply these techniques to generate the first 4-dimensional solution of U(1)-Fayet-Iliopoulos gauged supergravity coupled to vector multiplets, whose scalars parametrize a non-homogeneous Kähler manifold. It is a black hole solution, with AdS4 asymptotes. We then explore the SU(2)-Fayet-Iliopoulos gauged sector, in 4 dimensions. Once a simple model is chosen, some solutions for this setting are found. More solutions for the same theory are obtained through dimensional reduction -that has been generalized to relate gauged theories- of a couple of known solutions for the 6-dimensional, FI-gauged theory. 5-dimensional solutions are obtained in the procedure, as well. Finally, a known 5-dimensional solution, an extremal black hole sourced by a BPST instanton, is uplifted to 6 dimensions
Gravity gradiometers for planetary geodesy: requirements and concept for a space instrument
No full textThe measurement of the gravitational field of Solar System bodies is becoming ever and ever crucial in the physical description of their composition, state and evolution. Indeed, many planetary processes at large scale are ruled by their internal structure, where surface
and tectonic features are mainly the result of heat exchanges from the interior to the surface. Gravity field measurements are one of the observational methods to investigate those processes and to place constraints on the structure of the planetary interiors and on the
formation and geologic evolution of a planet. The retrieval of the spherical harmonic coefficients used to describe the gravitational field of a body gives insights into e.g. its polar oblateness, moment of inertia and deviations from hydrostatic equilibrium. With geologic assumptions and other remote sensing data, significant geophysical parameters, related e.g. to crust and mantle density and thickness, core size and structure, mantle/core coupling can be obtained. These parameters are used in planetary models to address topics such as planets differentiation, thermal evolution, characteristics and composition of the interiors. Moreover, the internal structure can be further investigated (wherever possible)
through seismometers on the surface, exploiting the analysis of seismic waves travelling through the interior (as performed by Apollo missions EASEP and ALSEP packages and currently by Mars Insight).
Until now, the Radio-Tracking technique (RT), part of the Radio Science (RS) observations, jointly with POD (Precise Orbit Determination), has been de-facto the main technique for gathering this type of information. It has been implemented in several deep-space missions, such as Magellan (Venus), MRO (Mars), Cassini (Saturn), Messenger (Mercury), Juno (Jupiter), and, in the forthcoming future, BepiColombo (Mercury) and JUICE (Jupiter and its moons).
Concerning scientific targets of interest, it needs to be highlighted that gravity field models are available (section 2), besides the Earth and the Moon, just for few planetary bodies such as the terrestrial planets Mercury, Venus and Mars. However, often such models are restricted only to large spatial resolutions, about one or more hundreds of kilometers, not enough to understand the geophysical processes that have driven formation and evolution of those bodies. The accuracy of these models is good enough as well but just for the lower part of the gravity field spectra, where a sufficient signal-to-noise ratio is achieved.
Moreover, there is much more lack of data for the external planets, where only few gravity field parameters have been derived for some of the gaseous planets and their main moons.
Any improvement on those targets, with a special attention to Venus, Mars and Galilean moons, would be very helpful in understanding their interior and the geophysical and geological processes that operated on them.
To answer the need for higher space resolution and accuracy in planetary gravity fields, two different approaches can be pursued:
1. to improve the measurement performance of the instrumentation used for RS; in these experiments the gravity field to be studied is inferred by the orbit of a spacecraft (that can be considered a ‘proof mass’ falling in the overall external gravity field) and an accelerometer is used to measure the Non-Gravitational Perturbations (NGP) perturbing the spacecraft free-fall, i.e. its motion from a pure (in principle) geodesic of space-time. An improvement of the accelerometer performance and its integration within an enhanced tracking system used to measure the spacecraft position and velocity, are needed conditions to improve the performance of gravity field reconstruction.
2. to introduce innovative measurement concepts, allowing to overcome some of the bottlenecks of the current methods (non-continuous monitoring, field attenuation with the altitude, disturbances mitigation, etc. In a roadmap definition, one of the more promising is the gravity gradiometry technique, which would allow to directly sense the gravity field by measuring the gravity gradients, and not just indirectly, as for RT, through monitoring the spacecraft gravitational perturbations. Unlike the radio-tracking, spacebased gravity gradiometry has still to unfold its potentialities; indeed, the ESA’s GOCE mission is the first and unique till now that has flown a gravity gradiometer to explore Earth’s gravity in 2009-13. The planetary gradiometry still awaits achievements outside the Earth System.
Satellite gradiometry refers to the measurement of acceleration differences, ideally in all three spatial directions, between the test-masses of an ensemble of accelerometers inside one satellite. The differentiation of gravity accelerations allows to highlight small-scale surface and sub-surface features, making such a technique, differently wrt RT, inherently sensitive to medium and large degrees (i.e. high resolutions) of the spherical harmonic representation of the gravity field. Therefore, the use of gradiometry would allow to improve the gravity field knowledge by measuring medium and large degrees, filling the gap above depicted and fostering the investigation on the structure and evolution of the planets.
The activity of this PhD Thesis starts from the definition of the planetary gravity field state of the art and the identification of the needs of the scientific community to improve the planetary bodies knowledge. Based on this result, a selection of targets of interest will be operated. A
review of the gravity field measurement techniques will be carried out, identifying advantages and drawbacks, pointing out innovative techniques such as gradiometry. On the basis of these activities, a series of numerical simulations will be implemented to produce the time series of gradiometric signals foreseen in a set of case studies. The choice of the case studies will be based on the preliminary studies about the science needs. The main outcome will be a set of requirements to be matched by a typical gradiometric instrument/mission, aiming at fulfilling the scientific needs. An important requirement would be, for instance, the typical instrument sensitivity and spectral band, as well as the expected
acceleration or gravity gradient amplitude of a signal sensed with a reasonable signal-tonoise ratio. Different scenarios will be simulated on the basis of the science needs.
In chapter 2 the gravity field is faced from the theoretical point of view and a snapshot of the current understanding of gravity field of planetary bodies is carried out. At last, science needs are identified and planetary bodies of interest are selected.
In chapter 3 measurement techniques of the gravity field are described, focusing the attention on the gravitational gradiometry. Advantages and drawbacks are considered. Moreover, spaceborne, airborne and groundborne gradiometric instruments have been identified and analysed to identify the current state of the art.
In chapter 4 gravity mission needs are identified in terms of science and mission requirements. Afterwards, a matlab code developed to compute the gravity gradient signal expected in some case studies is described and evaluated. At last, analysis of ways to increase the sensitivity of gradiometers is carried out.
In chapter 5, based on analysis of previous chapters, an instrument concept is introduced and analysed to match the requirements identified. The basic performance are derived, discussed and compared to the signal that is expected to be measured according to the computation carried out with the matlab code. Future work foresees to further develop the concept and to further deep the analysis of the identified gradiometer configurations
- …
