1,722,575 research outputs found
FEKO/GRASP Simulations of Super-Resolution with a Reflective Metal-Mesh Toraldo Pupil on the 32m Medicina Radio Telescope
No full textWe are currently carrying out a project devoted to the implementation of super-
resolution on single-dish radio telescopes, aimed to obtain an angular resolution better than
the classical diffraction limit. A feasible method to achieve this goal consists of using variable
transmittance pupils, and specifically the simplest version of these pupils which consists of a
binary phase shift mask, also known as Toraldo pupil (TP). An attractive method to design
and fabricate TPs is to use the metal mesh-filter technology, which allows to fabricate both
transmissive and reflective TPs. In this work we show, through EM numerical simulations,
that super-resolution can indeed be achieved on a Cassegrain radio telescope using a previously
designed and tested reflective mesh-filter TP
Millimiter CBR polarimetry: the POLCBR experiment at M.I.T.O.
No full textCBR polarization may provide many information about the history of the universe. We study a polarimeter configuration that minimizes the spurious polarization introduced by the telescope-polarimeter optics and that reduces noise from atmospheric fluctuations
A statistical theory of the strength of epidemics: An application to the Italian COVID-19 case.
No full textThe proposed theory defines a relative index of epidemic lethality that compares any two configurations in different observation periods, preferably one in the acute and the other in a mild epidemic phase. Raw mortality data represent the input, with no need to recognize the cause of death. Data are categorized according to the victims' age, which must be renormalized because older people have a greater probability of developing a level of physical decay (human damage), favouring critical pathologies and co-morbidities. The probabilistic dependence of human damage on renormalized age is related to a death criterion considering a virus spread by contagion and our capacity to cure the disease. Remarkably, this is reminiscent of the Weibull theory of the strength of brittle structures containing a population of crack-like defects, in the correlation between the statistical distribution of cracks and the risk of fracture at a prescribed stress level. Age-of-death scaling laws are predicted in accordance with data collected in Italian regions and provinces during the first wave of COVID-19, taken as representative examples to validate the theory. For the prevention of spread and the management of the epidemic, the various parameters of the theory shall be informed on other existing epidemiological models
Statistical micro-macro approach for the strength of aged brittle materials
No full textFailure of brittle materials is due to the unstable propagation of a dominant crack and, therefore, their macroscopic strength is governed by the presence of surface microdefects. The defectiveness scenario continuously changes during the service life due to natural aging, mainly associated with processes of abrasion and corrosion. Developing the original idea by Freudenthal [1], we propose a micromechanically-motivated approach to pass, in statistical terms, from the population of micro-cracks to the population of macroscopic strengths. Assuming a uniform distribution of non-interacting flaws without preferred orientation, whose size statistically follows a Pareto distribution, the population of strengths shall vary according to a 2-parameter Weibull distribution. This is the most used statistics for brittle materials, even though its ability to interpret the left-hand-side tails of the population is a subject of debate. Furthermore, an upper-Truncation of the Pareto distribution for crack lengths leads to a left-Truncated Weibull distribution, which can much better interpret the tails of the population of strengths for some brittle materials, such as structural float glass [2]. The micro-macro approach can also interpret the observed variation of material strength during service life due to abrasion or corrosion. In fact, such phenomena are associated with a modification of the defectiveness scenario. In particular, corrosion leads to a surface dissolution and, hence, to a constant length reduction for all the surface micro-cracks. This effect is beneficial, especially for the highest fractiles of strength, associated with the smallest crack lengths. On the other hand, abrasion produces new surface cracks. A very hard abrasion process can overtake the initial defectiveness scenario, so that the strength population shall be governed by the new micro-cracks population. Instead, if the abrasion is "mild", the new crack population superimposes on the original one, resulting in a bi-modal Weibull distribution of strengths. Finally, some abrasion processes, such as sandblasting, can originate additional semi-spherical defects, which could provoke the shielding of pre-existing cracks. Here, this approach is used to justify the observed modification in the statistical strength population for corroded or abraded glass, induced also during the float production process. Further applications may include ceramics, glass-ceramics and polycrystalline silicon ME
Which Kind of Collaboration is Right for You? The new leaders in innovation will be those who figure out the best way to leverage a network of outsiders
No full textSystematic polarisation effects introduced by lenses and by axial birefringent half-wave plates used in CMB experiments in the millimeter region
No full textA lot of effort is currently devoted to the design of ground based experiments dedicated to the detection of the Cosmic Microwave Background Radiation Polarisation. The very low level of the expected signals requires a detailed study of the spurious effects introduced by each element of the optics. We use the well-known general formulae for the reflection and transmission coefficients in isotropic medium-uniaxial birefringent crystal interfaces for any angle of incidence and arbitrary birefringence optical axis orientation. Ordinary and extraordinary ray tracings are carried out and arbitrary incoming polarisation is used to calculate instrumental polarisation and depolarisation effects
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
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