2,846 research outputs found
Does R&D Expenditure Boost Economic Growth in Lagging Regions?
No full textWe assess the impact of the EU Regional Policy on regional economic growth by applying a new evaluation strategy, which integrates mediation analysis with a quasi-experimental framework. Using the R&D expenditure as an indicator of innovation capability, we evaluate how much of the total effect of the EU Regional Policy is due to R&D in the poorest EU regions. Consistently with the previous literature, we found a positive impact of the overall policy on economic growth, but, among the convergence regions, those investing a higher proportion of funds in R&D have the same convergence rate as regions investing more in other priorities. These findings confirm that the EU Regional Policy played an important role in the economic recovery of the poorest regions in the aftermath of the Great Recession. However, focusing resources on R&D does not seem to provide additional economic benefits, at least in the short run
Long-range pair potential from the low density S(k) of 4He around 6 K
No full textThe static structure factor S(k) of gaseous 4He at various densities along the T=6.13 K isotherm has been determined with the G4.1 diffractometer at LLB (Saclay, F). Thanks to the explored k-values (1<k/nm^-1<34), the long range behaviour of the interatomic interaction potential U(r^N) can be conveniently investigated. The resulting structure factors S(k) are presented and compared with previous determinations obtained at almost the same thermodynamic conditions using the D4B and D11 diffractometers at ILL (Grenoble, F). By means of a well known low-k expansion of the Fourier transform of the direct correlation function c(k), the London dispersion coefficient C6 of the r^-6 tail in U(r^N) has been experimentally evaluated for the first time and compared with the values present in literature
Chinese or Not Chinese? Investigating Early Bronze Buddhas
No full textThis article reopens the discussion on two celebrated early Buddhist bronzes, one in the
Harvard Art Museums seated in dhyanamudra and with flaming shoulders, and the
other in the Asian Art Museum of San Francisco, dated to 338. The article suggests that
the Harvard Buddha is not Chinese, as generally believed, in light of a series of
iconographical details, the most important of which—the dhyana mudra—has been
overlooked in the previous scholarly research. Focusing on the form this mudra takes in
India and China, the author shows that it underwent significant modifications as it
moved east, which has important implications for the wider field of the transfer of
Buddhist art to China
Solitary plasmacytoma of the spine: relationship of IGM to tumour progression and recurrence.
No full textAbstract
The authors report a retrospective study of 15 patients with solitary vertebral plasmacytoma. 15 patients were considered in this study on the basis of the following characteristics: 1) histologically confirmed plasmacytoma following surgical removal; 2) existence of a single vertebral lesion, documented by skeletal and MRI scan; 3) no signs, at diagnosis of disseminated disease by blood laboratory test, urine analysis, sternal puncture, iliac bone marrow biopsy, a total-body CT scan. The clinical course of the patients has been analysed on the basis of the following factors: age, sex, length of clinical history before diagnosis, site, presence/absence of the M component. The M component is an electrophoretically homogeneous immunoglobin. The most significant factors for predicting development of multiple myeloma proved to be the presence /absence of the M component at diagnosis and, to a lesser degree, the age of the patient. In the light of other reports too, it would seem that the presence of the M component at diagnosis is a reflection of aggressive biological and clinical tumour behaviour
La «Longevità di una democrazia comunale». Bormio e le sue valli nell’opera di Roberto Celli (1984)
No full textIl saggio considera i fattori, le condizioni di lungo periodo e le diverse circostanze storiche che hanno promosso e consentito la formazione di un’entità politica, sociale, economica e territoriale che, sviluppatasi nel pieno Medioevo in un cantone delle Alpi Retiche a cavallo dello spartiacque, rimane vitale e funzionante nelle sue forme tradizionali fino all’età napoleonica, che costituisce l’avvento della contemporaneità istituzionale, economica, sociale
Gamma-ray and neutrino signatures of Galactic cosmic-ray accelerators
No full textSupernova remnants are believed to be the major contributors to the observed Galactic cosmic-ray flux, though indisputable observational pieces of evidence of such statement are still missing. A crucial aspect of the supernova remnant para- digm for the origin of Galactic cosmic rays is that particle acceleration, as due to diffusive shock acceleration, requires effective confinement of particles in the shock region to let them achieve energies up to the so-called knee, around 1015 1016 eV. However, the current theoretical description of cosmic-ray acceleration and propagation within and around supernova remnants suffers from certain limitations, which also affect the predictions on the shape of the energy spectra of secondary gamma rays and neutrinos. In particular, in this thesis, two relevant aspects of this theory are investigated: the particle acceleration at shocks propagating in clumpy non-homogeneous environments and the particle escaping process from the acceleration site. The standard diffusive shock acceleration model usually assumes that shocks expand into ideally uniform environments, while a more realistic picture should consider an inhomogeneous gas distribution where supernova remnants develop. In this work, I conducted a detailed study on the particle acceleration and propagation through non-homogenous structures and its effect on the resulting secondary radiation. Regarding the particle escape from the acceleration site, I developed a phenomenological model to investigate this process and its impact on the gamma-ray emission from middle-aged supernova remnants, where particle escape is expected to be effective. I will show that spectroscopic and morphological studies of the gamma rays coming from both inside and immediately outside of those remnants can provide insight into the escaping process in general, and in particular, will shed light on their ability to act as cosmic-ray PeVatrons. So far, the only hint of the presence of a PeVatron has been found in the Galactic Center region, whose nature is, however, unclear. Under the assumption that the observed gamma-ray flux originates from hadronic interactions, I calculated the expected flux of multi-TeV neutrinos in order to investigate its detectability with future km3-scale neutrino telescopes. Finally, a comparative analysis of the performances of the two major upcoming detectors, namely CTA and KM3NeT, is presented in the context of future studies on the origin of Galactic cosmic rays through respectively gamma-ray and neutrino observations.
The thesis is organized as follows:
• In Chap. 1, the supernova remnant paradigm for the origin of cosmic rays is introduced and a discussion concerning possible Galactic PeV accelerators is presented. As gamma rays and neutrinos constitute observational signatures of particle acceleration and propagation, a review of their properties and detection techniques is provided.
• In Chap. 2, the propagation of accelerated particles within supernova remnants is investigated in the presence of strong shocks evolving through non-homogeneous media. A numerical approach to the particle transport under these conditions is here provided for the first time, conditions that represent realistic situations for the environments where sources as supernova remnants usually expand. Since dense molecular clumps constitute ideal targets for accelerated protons, enhanced gamma-ray and neutrino emissions are expected. The model is shown to provide an adequate description of the broadband gamma-ray emission of the Galactic supernova remnant RX J1713.7-3946 both in terms of total flux and spectral shape.
• In Chap. 3, a phenomenological description of particle escape from middle-aged supernova remnants is presented, and it represents the first attempt of studying this process within the context of extended sources. A proper description of this phenomenon is extremely relevant for the correct interpretation of the radiation spectrum observed in these sources, which reflects not only the acceleration mechanism and the interaction processes, but also the particle escape from the acceleration site. The model is applied to three interesting middle-aged Galactic supernova remnants, namely IC 443, W 51C, and W 28N. A major implication of the presence of particle escape is represented by the possible production of high-energy radiation also outside of the remnant shock, characterized by a very peculiar bump-like energy spectrum. This feature is interesting from the point of view of both gamma-ray and neutrino emissions, being experimentally con- nected to potentially background-free regions. Moreover, the escaping process is particularly relevant for a correct understanding of the cosmic-ray spectrum observed at Earth and to disentangle the propagation effects through the Galaxy.
• In Chap. 4, a candidate source of PeV cosmic rays located at the center of the Galaxy is discussed. The Galactic Center, as recently observed in multi-TeV gamma rays, shows a central emission with spectral cut-off energy at an energy of about 10 TeV. Nonetheless, a diffuse emission surrounding the central source shows no visible cut-off up to the energies currently probed by H.E.S.S.: the possibility of an intense infrared radiation field absorbing gamma rays from the central source is investigated for the first time. The detection of very high-energy neutrinos in angular correlation with the electromagnetic radiation would confirm the hadronic hypothesis for the origin of gamma rays. Hence, expectations from current and next-generation neutrino instruments are provided, indicating the relevance of a Northern Hemisphere detector for the
observation of this region with a clean event sample.
• In Chap. 5, the performances of the next-generation gamma-ray and neutrino
detectors are investigated, and differential sensitivities of CTA and KM3NeT for extended sources are derived. This study represents one of the first attempts towards the understanding of instrumental performances for extended sources related to spectroscopic detection of gamma rays through the imaging technique and capabilities of neutrino telescopes. Sensitivity analyses are, hence, applied to some interesting PeV cosmic-ray candidate sources, as the Galactic Center Ridge and the aforementioned supernova remnant RX J1713.7-3946.
• The main results of the work are summarized and discussed in Chap. 6.
The thesis contains three appendices, specifically separated from the text in order to facilitate its reading. In Appendix A, an overview of the equations regulating the magnetohydrodynamical properties of astrophysical plasma is presented, together with an insight into the numerical code adopted for the solution of this system of equations. In Appendix B, a detailed description of the numerical methods adopted for the solution of the particle transport equation in the presence of molecular clumps is provided. It is a technical appendix, intended to support the interested reader in reproducing the physical results discussed in Chap. 2. Its content repre- sents an original work developed by the author. Finally, Appendix C provides the mathematical framework developed in order to derive the analytical solution of the diffusive transport equation, satisfied by the escaping particle density function and presented in Chap. 3
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