1,721,009 research outputs found
Nomina degli amministratori di società di capitali, regime dell’ineleggibilità e profili formali
No full textThe essay analyzes the space of new rules relating the disqualification of directors of companies according Italian Companies Law and the new formal duties of directors concerning their appointmentIl contributo analizza la portata delle nuove norme in tema di ineleggibilità degli amministratori delle società di capitali e sui nuovi obblighi formali
An Explicit Threshold for the Appearance of Lift on the Deck of a Bridge
Full text linkWe set up the analytical framework for studying the threshold for the appearance of a lift force exerted by a viscous steady fluid (the wind) on the deck of a bridge. We model this interaction as in a wind tunnel experiment, where at the inlet and outlet sections the velocity field of the fluid has a Poiseuille flow profile. Since in a symmetric configuration the appearance of lift forces is a consequence of non-uniqueness of solutions, we compute an explicit threshold on the incoming flow ensuring uniqueness. This requires building an explicit solenoidal extension of the prescribed Poiseuille flow and bounding some embedding and cutoff constants
Time and frequency GPR waveforms analysis for clay content evaluation in soils
No full textThe mechanical behaviour of soils is partly affected by their clay content, which exerts some considerable effects in many applications in the fields of civil engineering, geology and environmental engineering. This study focuses on pavement engineering, but the approach can be extended to other purposes.
The presence of clay in the bearing structural layers of pavements frequently causes damages and defects, such as transversal and longitudinal cracks, deformations and rutting. Consequently, the road safety and operability decrease, while the expected number of accidents increases.
In this work Ground Penetrating Radar (GPR) laboratory inspections are carried out in order to predict the presence of clay in pavement structural layers. Data are post-processed in the frequency domain, according to the Rayleigh scattering method based on the Fresnel theory. This new technique can be supported by other survey methods, improving the quality of the results.
Analysis are carried out using two different GPR systems.
A Radar is used with ground-coupled antennae in a bistatic configuration and common offset; the transmitter and receiver are linked by optic fiber electronic modules and operate at 500 MHz central frequency. The received signal is sampled in the time domain at time steps of 7.8125 x 10-2 ns.
A Vector Network Analyzer (VNA) acquires ultra-wide band data in a bandwidth from 500 MHz to 3000 MHz. The signal is sampled in the frequency domain with approximately 1.56 MHz frequency steps. A double-ridged broadband horn antenna is connected via a high-quality coaxial cable to the VNA pulse generator and illuminates the analyzed target in a monostatic off-ground configuration.
The experimental setting required the use of road material, typically employed for sub-grade and sub-base layers. Three kind of soils, classified as A1, A2, A3 by AASHTO are used and adequately compacted in electrically and hydraulically isolated boxes. Bentonite clay is gradually added from 2% to 25% in weight, according to mixing and compaction laboratory procedures. A metal plate supports the experimental boxes, so that the GPR signal is totally reflected.
GPR surveys are carried out for each clay content. The signals are analyzed in both time and frequency domains.
In the time domain the reliability of results is validated by the electromagnetic theory, in terms of signal amplitude, electric permittivity and time delay . In the frequency domain the results are highly consistent for all the investigated soils . Assuming a residual water content of the dry clay that is due to its hygroscopic capability, frequency spectra shift not linearly, as expected from the scattering theory. The modulation depends on the water content and, indirectly, on the clay content. The correlation between the central frequency values of the spectra and the clay content is negative: decreasing values of the central frequency correspond to increasing values in the clay content, from 0% up to 25%. A comparative analysis of the three soil spectra for different clay contents has shown a different behaviour of the clay, both for the ground-coupled radar and the broadband analyzer. In general, in fine grain size soils lower central frequency value intensities are registered
On the long-time behaviour of solutions to unforced evolution Navier–Stokes equations under Navier boundary conditions
Full text linkWe study the asymptotic behaviour of the solutions to Navier-Stokes unforced equations under Navier boundary conditions in a wide class of merely Lipschitz domains of physical interest. The paper draws its main motivation from celebrated results by Foias and Saut (1984) under Dirichlet conditions; here the choice of the boundary conditions requires carefully considering the geometry of the domain Ω, due to the possible lack of the Poincaré inequality in presence of symmetries. In non-axially symmetric domains we show the validity of the Foias-Saut result about the limit at infinity of the Dirichlet quotient, in axially symmetric domains we provide two invariants of the flow which completely characterize the motion and we prove that the Foias-Saut result holds for initial data belonging to one of the invariants
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Enrico Sertoli and the supporting cells of the testis "Morphology is function"
Full text linkIn 1865, Enrico Sertoli, at the age of 23, published an article in his own name entitled: 'About the existence of special branched cells in the seminiferous tubules of the human testis.''These were Sertoli's ideal cells; in this paper he arrived at a perspicacious description of the morphology and function of these cells and in the subsequent articles he investigated the topic of spermatogenesis. Despite the importance of Sertoli's discovery, the attention of the scientific literature remained very limited after Sertoli's death for half a century and the partial eclipse finished only in the 1970s of the twentieth century
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Electric characterization of construction materials through radar data inversion
No full textThe non-destructive evaluation with the aim of characterizing objects before or after treatment has taken place, and the monitoring of long-term performance is analyzed in this thesis. Generally, these test methods measure material properties or changes in these properties that decision makers are interested in. There is a variety of non-destructive testing (NDT) methods to choose from, depending on the aim of the analysis. Generally speaking, different non-destructive testing methods can be used for investigating the inner structure of materials. It is worth noticing that there is not one single analytical method able to provide all the necessary information. Therefore, a combined test series capable of providing complementary information is usually adopted. Most of the methods used in NDT generate pictures of the object interior that can help locate structural flaws. Even though not common, these methods can give quantitative results. The use of electromagnetic waves within the radio frequency bandwidth, in particular, can be valuable in detecting defects, for assessing the deterioration and the success of refurbishment activities. A particular radar technology was used in this study as a tool for assessing the ability to characterize materials in specific built environments. Numerical and laboratory studies were carried out to evaluate the feasibility of the proposed methodology for the mentioned applications. A secondary objective was to provide a contribution to the road safety, preventing the risk of severe damage of pavement, induced by clay content in sub-asphalt layers, and to improve the operations of rehabilitation and maintenance through an effective inspection. In Chapter 2 the electric properties of multiphase aggregate mixtures were evaluated for a given mineralogic composition at frequencies between 300 kHz and 3 GHz. Two measurement techniques were employed: a coaxial transmission line and a monostatic stepped-frequency ground-penetrating radar. The propagation matrices analytical method was used to retrieve the electrical permittivity and conductivity of the mixtures from the measured scattering parameters in the coaxial transmission line. The effect of increasing water content was analyzed in several sand-clay mixtures. For the end-member case of maximum clay (25% by weight) and increasing water content, investigations were compared between the two measurement techniques. The electrical properties of materials are influenced by the amount of water, but clay affects the frequency dependency of soils showing distinctive features regardless of the mineralogy. The microwave attenuation, expressed by the quality factor Q, is partly dependent on frequency and on water content. The performance of one empirical and one volumetric mixing model was evaluated to assess the capability of indirectly retrieving the volumetric water content for a known mixture. The results obtained were encouraging for applications in the field of pavement engineering with the aim of clay detection. The models used show similar behaviors, but measured data were better modeled using third order polynomial equations. High-frequency, ultra-wideband penetrating radar has the potential to be used as a non-invasive inspection technique for buildings, providing high-resolution images of structures and possible fractures affecting constructions. To test this possibility, in Chapter 3 numerical and laboratory experiments were conducted using a proximal, stepped-frequency continuous-wave radar system operating in zero-offset mode, spanning the 3-8 GHz frequency range. The reconstruction of material electrical properties is achieved by resorting to full-waveform inverse modeling. Numerical experiments showed that for typical electric permittivity and electrical conductivity values of concrete and plaster, it is possible to retrieve the physical properties of the material and to detect fractures less than 1 mm thick. Laboratory experiments were conducted on non-reinforced concrete and plaster test slabs in different configurations. The results showed the good potential of this method: (1) to provide a thorough fracture response model in buildings or artworks and (2) to non-invasively characterize the samples in terms of their electromagnetic properties. The characterization of the subsurface can be performed by full-waveform inversion of electromagnetic data relating to a particular model. The modeling process relies on the ability of retrieving the scattered field Green’s function from the measured data. This is achieved using sets of antenna characteristic global reflection and transmission coefficients to describe the media in terms of their scattered field impulse response. As described in Chapter 4, crucial for a successful implementation of this technique is the understanding of uncertainties involved in the acquisition of the antenna calibration and survey measurements, and how these propagate in the parameter estimation results. It was found that averaging a number of possible Green’s functions obtained from one measurement with several antenna characteristic coefficients sets works remarkably well in reducing the uncertainties. The accuracy of the inversions improved using characteristic coefficients acquired as close as possible to the measurement conditions. Moreover, a clear relation between dynamic range and system resolution was highlighted, based on the number of effective bits contained in the data. The presence of cohesive soils as bearing courses of road pavement frequently causes damages and defects (e.g., transversal and longitudinal cracks, deformations and ruts). In Appendix A, different ground-penetrating radar (GPR) methods and techniques were used to non-destructively investigate the clay content in sub-asphalt compacted soils. The experimental layout provided the use of typical road materials, employed for road bearing courses construction. Three types of soils classified as A1, A2, A3 by the American Association of State Highway and Transportation Officials (AASHTO) were used and adequately compacted in electrically and hydraulically isolated test boxes. Analyses were carried out for each clay content using two different GPR instruments. A pulse radar with ground-coupled antennae at 500 MHz center frequency and a vector network analyzer (VNA) with a 1–3 GHz bandwidth were used. Signals were processed in both time and frequency domains, and the consistency of results was validated by the Rayleigh scattering method, the full-waveform inversion and the signal picking techniques. Promising results were obtained for the detection of clay content or cohesive soils affecting the bearing capacity of sub-asphalt layers.Geoscience & EngineeringCivil Engineering and Geoscience
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