137 research outputs found
Late to Post-Variscan tectonics in the Sardinia Einstein Telescope candidate site (Italy): insights from Structural Survey and Electrical Resistivity Tomography
No full textThe geological characterization preceding the construction of a large-scale underground structure, such as the Einstein Telescope (ET), is a mandatory step of civil engineering studies. The ET Italian candidate site is located in the Variscan basement of Sardinia because of its geodynamic quietness, very low seismicity and anthropogenic seismic noise. The ET layout is currently projected as an underground triangular infrastructure (10 km long sides), whose vertices are located between the villages of Lula, Bitti and Onanì, and is confined within an area not crossed by main regional faults.
The geological features of the Palaeozoic metamorphic rocks are the result of ductile deformation with folds and related planar and linear anisotropies. This polydeformed metamorphic basement was intruded by several granitic bodies and by mafic to acidic dykes, mostly of early Permian age. A brittle to ductile fault network affects the metamorphic-plutonic ensemble. Within such a structural frame it is difficult to accurately predict lithologies at depth by means of the geological survey alone. Thus, we started an integrated multidisciplinary cartographic, structural and Electrical Resistivity Tomography (ERT) study. The results as far obtained are useful to highlight the structural elements at depth, particularly lithological contacts and fault zones, which are relevant for the prediction of mechanic behaviour of the rocks along the tunnels tracks as well as the groundwater occurrence.
We have merged the lithologic information from published maps (also by comparing satellite images) and new data collected in the field. Newly traced morphostructural lineaments mark the distribution of fault zones from the areas that surround the boreholes drilled at two vertices. The analysis of satellite images has thus allowed to define the segmentation of principal faults, whose length is limited at surface to a few kilometers (2.5 km max).
Field structural results provided evidence of at least two ductile phases (D2+3) almost completely transposing the original bedding and the oldest schistosity (S0+1). Faults are mainly NNW-, and WSW-striking and are associated with either more altered bedrock and/or cataclastic bands. The WSW-striking faults are often conjugated with E- to NE-striking faults. Fault zones can be associated with thick quartz veins, or thin chlorite fibers. Locally, they are crossed by intense fracture arrays, pseudotachilites and gouge that can be as thick as a meter.
Near the vertices that were site of drilling (ca. 250 m total depth), ERT tomography was carried out, providing a complex internal resistivity stratification, that consists of up to three levels with variable distribution and thickness. As supported by field observation, we have interpreted the more conductive electrolayer as regolith and alluvial units, while the most resistive electro-layers correspond with the less-altered granitoids. The sudden trend of the isoresistivity line, that also recognized from satellite images or field evidence, was related to saturated fractured zones.
Thus, matching the vertical information provided by the 2D ERT results and the geological information from the study area, we provide a more accurate estimate of satured fault geometry at depth. Beside the ET vertices, similar approach can be adopted in predicting zone of hazards during the tunnel drillings
LOW FREQUENCY NOISE SUPPRESSION FOR THE DEVELOPMENT OF GRAVITATIONAL ASTRONOMY
No full textThe existence of gravitational radiation, predicted by the General Relativity theory, was indirectly demonstrated by the observation of the orbital decay in the binary pulsar 1913+16, for which R.A. Hulse and J.H. Taylor were awarded with the Nobel Prize in 1993. From then on, the direct detection of gravitational waves became a main issue in the experimental physics, not only for the verification of the theory itself but, most important, because it can open a new "observation window" of the universe. In fact, many astronomical objects, such as neutron stars and black holes, can be directly studied only through their gravitational emission. Moreover, since its interaction with matter is intrinsically weak, the degradation of informations carried by gravitational waves is negligible, and their revelation will allow us to understand the internal structure of massive objects which emit them, and will also provide a complementary point of view to the traditional astronomy and cosmology.
The direct detection must face the extreme weakness of gravitational radiation, hence very high sensitive detectors are required in order to reveal the quadrupolar effect produced by the passage of gravitational waves. The first attempts in this field were based on massive resonant bars, relying on the pioneering technique developed by J. Weber. In recent decades a more promising strategy based on interferometry was developed, providing the advantage of a wide-frequency detection-band (from few Hz to some kHz) jointly to an extreme sensitivity (the detectable strain is smaller than the size of a proton). The global network of first generation interferometric detectors, composed of Virgo, LIGO, GEO600 and TAMA300, demonstrated the feasibility of such a technique; in particular the kilometric-scale detectors Virgo and LIGO achieved a sensitivity high enough to determine the first upper limits for the gravitational emission of some known neutron stars, such as the Crab and Vela pulsars. In the next few years the upgraded version of these detectors, namely the second generation of detectors (such as Advanced Virgo and Advanced LIGO) will become operational and are expected to achieve the first direct detections of gravitational waves.
However, the signal-to-noise ratio (SNR) of these first detections will be too low for precise astronomical studies of the gravitational wave sources and for complementing optical, radio and X-ray observations in the study of fundamental systems and processes in the Universe.
For this reason the investigation on the design of a new, namely third, generation of detectors is already started, leading to the proposal of the European Einstein Telescope (ET). With a considerably improved sensitivity these new machines will open the era of routine gravitational wave astronomy, leading to the birth of a complete multimessenger astronomy. In particular, to enlarge the detector bandwidth in the range of 1 Hz, where interesting gravitational signals, such as those emitted by rotating neutron stars, can be detected, a further reduction of the so-called low-frequency noise, with respect to the second generation detectors, is required.
In this low-frequency band the main limitation to the sensitivity of an interferometric detector arises from the thermal noise, and at lower frequencies, from the seismic and Newtonian noises. The suppression of the thermal noise will require the implementation of a cryogenic apparatus, in order to cool the test masses down to about 10 K, so that the development of position-control devices capable of cryogenic operations will be also necessary for the suspension and payload control. The seismic attenuation was already obtained in first generation detectors by means of long suspension chains of vertical and horizontal oscillators (e.g. the superattenuator of Virgo), so that a further reduction requires a smaller seismic noise at the input of the suspension system; moreover, mass density fluctuations produced by the seismic motion induce also a stochastic gravitational field (the so-called Newtonian or gravity-gradient noise) which shunts the suspension and couples directly to the mirrors of the interferometer. In order to suppress these two seismically-generated noises, third generation interferometers will be constructed in underground sites, where Rayleigh surface waves are attenuated, and the surrounding rock layers are more homogeneous and stable, reducing the density fluctuations. The feasibility of a cryogenic and underground interferometer was already tested by the Japanese prototype-detector CLIO, in the same site where is currently under construction KAGRA (formerly known as LGCT), the first full-scale interferometric detector based on these approaches. For these aspects, this second generation detector will be the forerunner of third generation interferometers such as ET, therefore a collaboration between the two scientific collaborations has been established.
My experimental work is focused on the suppression of these low noise sources, so that this thesis is structured in two parallel fields of research: the seismic characterization of a potential site for the construction of the Einstein Telescope, and the development, calibration and test of a cryogenic vertical accelerometer, which can be used as a position control device, analogously to those used in the actual room-temperature superattenuator of Virgo, but also to check the vibrations introduced by the cryogenic apparatus, as I did with the measurements I performed on the cryostats of KAGRA, presented at the end of this thesis.
The scheme of this thesis is subdivided in three main parts: in the first part I introduce the foundations of the gravitational astronomy, from the theory and the astrophysical sources to the experiments which will lead to the gravitational observations; in the second part I discuss the theory of low frequency noise sources and their suppression; in the third part I present the experimental work I performed in this context.
Every part is composed of two chapters, structured as follows.
In the first chapter I describe the derivation of gravitational waves from the Einstein's field equations, discussing their properties and the astrophysical and cosmological sources, especially those whose emission is expected at low frequencies.
In the second chapter I describe the direct interferometric detection of gravitational waves and the main noise sources which limit the sensitivity, concluding with an overview of present and future detectors.
In the third chapter I discuss the main features of the seismic and Newtonian noises, and the strategies necessary to suppress them, especially in third generation detectors.
In the fourth chapter I discuss the theory of thermal noise, from the ideal case of the damped harmonic oscillator to the real dissipative mechanical systems and optical components of the interferometer.
In the fifth chapter I present my experimental work on the long-period characterization of the Sos Enattos site in Sardinia (proposed for hosting the Einstein Telescope), from the construction and instrumentation of an underground array of sensors to the analysis of seismic and meteorological data collected in one year of observations.
Finally, in the sixth chapter I present my experimental work on the development of a cryogenic vertical accelerometer, from the designing to the cryogenic calibration and tests at T=20 K. In this chapter I also present the results of the implementation of this device into the cryostats dedicated to the test masses of KAGRA, where I verified the operations of the accelerometer at T=8 K and I measured the vibrations of the inner radiation shield of the cryostats. These measurements led to a first experimental estimate of the additional vibrational noise which will be injected by the cryogenic refrigerators to the detector test masses
Machine Learning to Optimize Newtonian Noise Cancellation in Third-Generation Gravitational Wave Detectors
No full textCorrection to: Seismic glitchness at Sos Enattos site: impact on intermediate black hole binaries detection efficiency (The European Physical Journal Plus, (2021), 136, 5, (511), 10.1140/epjp/s13360-021-01450-8)
No full textThe original version of this paper was inadvertently published with an incorrect author name for the author L. Naticchioni. The correct name is: L. Naticchioni. The original article has been corrected
A vertical accelerometer for cryogenics implementation in third-generation gravitational-wave detectors
No full textThe design of third-generation gravitational-wave detectors requires dedicated sensors to perform very accurate measurements of the residual motion of mechanical components cooled down at cryogenic temperatures and accommodated close to the test masses. For this reason, we developed a vertical accelerometer prototype derived by the classical scheme widely used in Virgo seismic suspension control. Thermal contractions are the main concern when cooling down such a device and the calibration check at low temperature, in the absence of commercial sensors working in parallel, plays a crucial role. The accelerometer was conceived to be used at low frequencies (0.3–3 Hz) in a quite specific environment, where the noise produced by cryocoolers has to be suppressed. However, it can be easily operated over a wider frequency band, up to ~100 Hz. The achieved sensitivity is ~10−8 m s−2 below 3 Hz. During 2013, the device was successfully installed in the KAGRA cryostat, where it was tested at low temperatures down to 8 K and provided the measurement of vertical vibrational modes of the inner thermal shield
Factor decomposition of cross-country income inequality with interaction effects
No full textIn this paper we propose a decomposition of the Theil measures of per capita income inequality which accounts for interaction effects between its multiplicative factors. Our theoretical findings, supported by an empirical application referring to EU-25 countries, suggest that neglecting these effects may strongly bias the relative importance of some factors, with consequent misleading policy implications.Inequality, Decomposition, Interaction Effects
Thermal noise study of a radiation pressure noise limited optical cavity with fused silica mirror suspensions
No full textIn this work we study the thermal noise of two monolithically suspended mirrors in a tabletop high-finesse optical cavity. We show that, given suitable seismic filters, such a cavity can be designed to be sensitive to quantum radiation pressure fluctuations in the audio band of gravitational wave interferometric detectors below 1 kHz. Indeed, the thermal noise of the suspensions and of the coatings constitutes the main limit to the observation of quantum radiation pressure fluctuations. This limit can be overcome with an adequate choice of mirror suspension and coating parameters. Finally, we propose to combine two optical cavities, like those modeled in this work, to obtain a tabletop quantum radiation pressure-limited interferometer
Mediterranean models of Welfare towards families and women
No full textAfter tracing a Malta’s short historical excursus with its effects on female condition, family’s structure and concept, organizational model of non profit sector, the paper gives a survey of the most recent economic and demographic trends with special attention to families’ well-being and women’s working and social conditions, based not only on statistical data of Malta’s National Institute of Statistics and of Eurostat, but also on the results of some empirical studies based on some surveys carried out into the archipelago. The main islands’ social problems are outlined with the indication of the principal sources of aid to face peoples’ different needs (first of all family, followed by the State, while the Third Sector, with its strong component of foundations, heritage of English culture, is not pre-eminent yet). The paper also shows that the same citizens’ expectations of satisfaction of social needs are still mainly placed in the State, according to the collective image. After drawing this scenario, the paper makes a short history of Malta’s Welfare State specially considering legislation concerning families and women. In addition to the description of the legislative measures, a deeper investigation is also devoted to other programs realized at european and national level: Equal Program (2004-2006) and Malta’s latest “Action Plan”, alias the National Social Plan in its general lines of policy towards families and women. Besides the illustration of the services provided to families by the Ministry of Family and Social Solidarity in the context of the National Action Plan, three other articulations of the Plan are briefly examined: Gender Equity National Action Plan (2003-2004), National Action Plan on Poverty and Social Exclusion (2004-2006), National Action Plan for Employment (2004). The correlative institutional framework is also reviewed: the National Family Commission established in 2001 and the National Commission for the Promotion of Equality for Men and Women considered by the “Equality for Men and Women Act” of 2003. Finally the paper classifies Malta’s Welfare State among the Mediterranean models of social assistance for its specific characteristics though, differently from the evolutive tendencies of these last ones, the passage from Welfare State to Welfare Mix is still problematic and slow in Malta. In spite of the increasing forms of collaboration between public and non profit organizations, Malta’s Third Sector has still a too weak role, in comparison with family and State, in supporting people’s life on both factual and symbolic dimension. In this missing transition, specially as regards elderly care, Malta can not see yet the growth, inside Welfare Mix, of the more informal components formed by immigrated women to detriment of the services offered by private or non profit organizations (“care drain” phenomenon), which is very strongly in course in other Mediterranean countries (Italy, Spain, Greece).Family and Social Policy, Social Segregation, Poverty
The Youth Experience Gap: Explaining Differences across EU Countries
No full textThis note aims to provide a theoretical framework to think of the youthunemployment problem and a classification of EU countries according to the way they address it.The key factor to explain youth unemployment is what we call the youth experience gap. To helpyoung people fill it in and ease school-to-work transitions, every EU country provides a mix ofpolicy instruments, including different degrees and types of labour market flexibility, of educationaland training systems, of passive income support schemes and fiscal incentives. Five differentcountry groups are detected whose outcomes in terms of youth unemployment are dramaticallydifferent: a) the North-European; b) the Continental European; c) the Anglo-Saxon; d) the South-European; e) New Member States. The Lisbon strategy provides guidelines in line with thetheoretical framework discussed here, but it is costly and hard to implement.Youth Unemployment Problem, Youth Experience gap, Youth Employment Policy, Lisbon Strategy
The willingness to pay for Renewable Energy Sources (RES): the case of Italy with different survey approaches and under different EU “climate vision”. First results.
No full textIn reference to the “Renewable Sources” EU Directive 2001/77/CE the Italian goal, for 2010, is to attain the share of 22% in RES electricity production. In such context it becomes crucial to explore the existence of consumer’s Willingness to Pay (WTP) in order to use green energy in the electricity production. This study is founded on a national survey with 1601 phone interviews made, in Italy, at the end of November 2006. This paper focus much on three issues. First one, how the different elicitation affects respondents choices, second one on the relationship between a “single point value” and “a valuation distribution” and finally on the gaps between different formats as: bidding game and dichotomous referendum (single bounded) contingent valuation method. In all the elicitations formats we make a “certainty correction” proposing five degree of acceptance: definitely yes and no (DY, DN), probably yes and no (PY, PN) and don’t know (DK). In order to apply the quantitative analysis, the original dataset has been appropriately treated, recoding DK, PN and PY responses. With regard to the results we found a significant path dependences in respondents answers due to the elicitation formats. Another important result is that also in “conservative” way we found a substantial willingness of consumers to partially cover the cost of Italian RES goal.bidding game, contingent valuation, renewable energy sources, descending and ascending elicitation format
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