130,538 research outputs found
Innovative research for coating thermal noise reduction in gravitational wave detectors and other high precision experiments
No full textMechanical and optical thermal noise is a limiting source of noise in many high precision opto-mechanical experiments that involve stabilized optical cavities. Most of the theoretical and experimental research in this field was driven by gravitational wave physics and interferometric detectors. The Virgo-LIGO collaboration was able to detect for the first time gravitational wave on September 14th, 2015 opening the gravitational wave astronomy era. Since then, many other signals followed, during the successive observing runs. Nowadays the possible upgrades of different subsystems is ongoing and will be implemented in order to increase more and more the sensitivity, and then observing volume and detection rates. The mid frequency band, from few to hundreds Hz, has proven to be the most fruitful bandwidth of gravitational signals, until now. In this region the thermal noise of the multi-layered dielectric coating of the mirrors is become the most limiting noise. Being able to reduce it, is an essential step in achieving the desired sensitivity goals. Coating thermal noise arises from fluctuations of the mirror surface under thermally activated transitions between equilibrium configurations of structure in coatings. Its amplitude is linked to the amount of internal friction and stresses inside the multilayer dielectric coatings. In this framework, it is important to accelerate their investigation and optimization. Coating thermal noise is an issue common to all experiments that strive for really small movement measures. The mission is pursued mainly in gravitational wave community by Virgo Coating Research and Development Collaboration and in LIGO Optical Working Group, by exploiting the recent advances in amorphous thin film synthesis, by utilizing high throughput characterization of elastic loss, by drawing on a new theoretical understanding of atomic scale mechanism of elastic loss, and by employing non-destructive methods to determine the short and medium range atomic arrangement of sub-micron amorphous films. The goal is to develop coatings that meet the thermal noise requirements, preserving outstanding optical properties. Present coatings are ion-beam sputtering multi-layers, alternatively made of titanium dioxide-doped tantalum pentoxide (Ti:Ta2O5, high refractive index) and fused silica (SiO2, low refractive index). They are deposited by the Laboratoire de Mat ́eriaux Avanc ́es, on massive, large-area fused silica substrates. Ti:Ta2O5 layer is the dominant source of thermal noise in coatings. For this reason, there is interest in finding new possible high-index material or new deposition techniques that allows the production of coatings with lower internal frictions. I II Acronyms This theses work is framed inside this perspective, especially involving characterization of substrates’ (both amorphous like fused silica, and crystalline, like silicon) and coatings’ mechanical losses, along with morphological and optical characterizations. Main analysed coatings are examples of possible new coatings, under investigation inside the Virgo Coating Research and Development Collaboration. In the first chapter a general introduction to thermal noise, starting from thermodynamic equilibrium in systems at a temperature different from zero, passing through fluctuation dissipation theorem up to inelastic behaviour and mechanical dissipations in solids, is shown. In the second chapter the more specific topic of mirror’s thermal noise is faced. The main contributions of all the system’s part are analysed, highlighting the more relevant contribution of coating thermal noise. Two sections are dedicated to two high precision experiments that suffer for coating thermal noise: optical cavities’ experiments and gravitational wave detector experiments. In the third chapter the state of the art of nowadays gravitational wave detector coatings is illustrated; after this, the general guidelines of the research plans devoted to the coating thermal noise reduction are presented. The three main sections shown are metrology, deposition techniques and treatments, and new materials. This chapter lay the foundation for the next experimental chapters, introducing the method to measure mechanical losses in coatings. In the fourth and fifth chapters the main issues regarding the substrates upon which coatings can be deposited are shown. A general description of the constituent material comes with a specific treatment of the substrates experimentally measured and characterized. Analytical models of their inelastic behaviour are presented and compared with experimental results. In the sixth chapter the topic of new coatings is faced in a twofold way. Through the study and characterization of a candidate material for coating research, the zinc sulphide (ZnS). Furthermore, the nano-layered coating technique is illustrated, together with initial morphological and mechanical characterization of some samples
Geomorphology hazard assessment of giampilieri and briga river basins after the rainfall event on the october 1, 2009 (sicily, Italy)
No full textMud and debris flows constitute a serious threat for several Italian regions as attested by recent several disasters attributable to such phenomena. The adoption of effective mitigation measures is complicated by the difficulty in predicting spatial and intensity features of future events. This paper applies a practical application of debris/mud flows hazard assessment in the area of Messina province. The study was based on an inventory of several debris flows triggered by heavy rainfall occurred in the Giampilieri and Briga catchments after the event of October 1, 2009. Data elaboration was focused on mapping source areas and on assessing the runout of landslides and their intensity. An evaluation of the factors that make the area prone to these events was used as input for a GIS based hazard prediction model. © Springer-Verlag Berlin Heidelberg 2013
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Les éléments de parure en verre du site de Lumaca (Âge du Fer, Centuri, Haute-Corse) : compositions et typochronologie
No full textLumaca, an open air settlement located at the northern end of Cap Corse, was occupied from the Early Neolithic until historic times. This long occupation is explained by the presence of a little sheepfold; all the stratigraphic levels are strongly disturbed. During the excavation of the site eight glass beads and rings were discovered. Analyses reveal that these ancient glass beads were all manufactured with Near-Eastern soda glasses. These glasses, obtained by fusing calcareous sands together with a mineral
soda flux, characterise the production of the Syro-Palestinian glass
factories and are found throughout the Mediterranean Basin from the
beginning of the first millennium B. C. to the end of the first millennium
A. D. The analytical data allow the beads from Lumaca to be divided in three groups which are essentially attributed to the Iron Ages (from Hallstatt to the 1st century A. D.). It is important to note that these beads were discovered in a dwelling and not (as often) in a tomb.Lumaca, établissement de plein air situé à l’extrémité nord du cap Corse, a été fréquenté depuis le Néolithique ancien jusqu’aux périodes historiques. Cette longue fréquentation due à la présence d’une petite bergerie a entraîné une très forte perturbation des différents niveaux d’occupation. Néanmoins, il nous a paru intéressant d’analyser un lot de huit perles et anneaux en pâte de verre qui y a été recueilli. L’analyse a mis en évidence l’origine proche-orientale de la pâte de verre utilisée comme matière première. Il s’agit d’un verre à fondant sodique très répandu dans le Bassin
méditerranéen jusqu’à la fin du premier millénaire de notre ère et caractéristique
des productions des centres verriers syro-palestiniens. Les perles se répartissent en trois lots attribuables pour l’essentiel aux premier et deuxième Âges du Fer (depuis la phase de Hallstatt jusqu’au début de notre ère). On notera également que ces perles proviennent non pas d’une sépulture, mais d’un habitat, ce qui renvoie à d’autres questionnements.Gratuze Bernard, Lorenzi Françoise. Les éléments de parure en verre du site de Lumaca (Âge du Fer, Centuri, Haute-Corse) : compositions et typochronologie . In: Bulletin de la Société préhistorique française, tome 103, n°2, 2006. pp. 379-384
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Scholarly Communication and Publishing Lunch and Learn Talk #11: The ULS Open Access Author Fee Fund
No full textAt the May 2014 talk, you will learn about the ULS Open Access Author Fee Fund--what it is, why we do it, how it works, and how the program is going so far
Adaptive optics methods in gravitational wave interferometric detectors, a perspective
No full textThe performance of present and future gravitational wave detectors is limited by fundamental
factors, such as thermal noise, seismic or newtonian noise and quantum nature of light. Besides,
technological factors impact the reach of advanced detectors in that upgrade strategies are
limited by state-of-art performances. In the realm of optics, the quantum limit to sensitivity
will be addressed by injecting higher laser power and by exploiting the capabilities of squeezed
light. In turn, technological efforts in the preparation of suitable optics able to meet more and
more demandig requirements are ongoing. Moreover, solutions to mitigate the effect of known
showstoppers such as parametric instablities are being studied.
The present day strategy to correct for residual cold defects in the core optics and to counteract
the thermal effects due to power absorption is embedded in a set of sensors and actuators
integrated in the Advanced Virgo design, the so called Thermal Compensation System (TCS).
This system is designed to be focused on the needs of high power operation of the detector,
nonetheless it is highly versatile and can deal with foreseen and unexpected issues. We discuss
the features of the TCS with emphasis on its versatility and portability to upgraded detectors; we
also present the status of the R&D activity in the Tor Vergata labs, highlighting new applications
where the methods of TCS can have a relevant impact, such as adaptive mode matching for
squeezing and damping of parametric instabilities
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