117 research outputs found
Discussioni sulla contingenza da Boezio a Leibniz. Introduzione
No full textSi tratta dell'introduzione al fascicolo mongrafico 1/2013 della Rivista di Storia della Filosofia. L'introduzione presenta una breve rassegna delle posizioni storiografiche e filosofiche più aggiornate sul tema della contingenza, dei futuri contingenti da Boezio a Leibni
Evolutionary dynamics of populations structured by dietary diversity and starvation: cross-diffusion systems
No full textIn questa tesi presentiamo alcuni progressi nell'analisi di problemi parabolici non lineari, derivanti dalla biologia e dall'ecologia. In particolare, studiamo l'esistenza, la regolarità e la stabilità delle soluzioni di equazioni alle derivate parziali (PDE), che descrivono l'evoluzione di due specie interagenti tra loro che si diffondono in un dominio spazialmente omogeneo. Le PDE considerate sono fortemente accoppiate, cioè accoppiate attraverso termini con derivata di secondo ordine, e danno luogo a sistemi che rientrano nella classe di sistemi di reazione-diffusione non lineari, chiamati sistemi di diffusione incrociata. Più precisamente, studiamo una classe di sistemi triangolari di diffusione incrociata, indotta dalla diversità alimentare delle popolazioni nell'ecosistema. Le tecniche usate nell'analisi riguardano metodi di entropia, stime a priori, argomenti di punto fisso e di compattezza. Inoltre, studiamo la stabilità lineare degli equilibri omogenei per analizzare l'instabilità di Turing e la conseguente formazione di motivi (pattern). Infine, completiamo l'analisi con simulazioni numeriche a supporto dei risultati teorici ottenuti.This thesis aims to present some recent results and advances in the analysis of nonlinear parabolic problems arising in biology and ecology. More precisely, we study the existence, regularity and stability of solutions of partial differential equations (PDEs), describing the evolution of two species that diffuse in a homogeneous environment and interact with each other. The PDEs we consider are strongly coupled and the system they give rise to belongs to a class of non-linear reaction-diffusion systems, called cross-diffusion systems. More precisely, we study a class of triangular starvation driven cross-diffusion systems arising in population dynamics. The tools employed are entropy methods, a priori estimates, fixed point and compactness arguments. Moreover, we analyze the linear stability of homogeneous equilibria to investigate Turing instability and pattern formation. Numerical simulations are performed to complement the theoretical results
Il dio viandante. Appunti per una ricerca su Vittorio Beonio Brocchieri scrittore per ragazzi
No full textVittorio Beonio Brocchieri (1902-1979) was an Italian scholar with a very unique personality. Po-litical Scientist, scholar of Nietzsche and Spengler, he studied with Gaetano Mosca at university of Turin before reaching Pavia where he taught history of political thought from 1926 until 1972. A draftsman and engraver, in a special way he was a traveler, a kind of modern nomad. His travels inspired him a rich bibliography composed of books and newspaper articles. Particularly for the Corriere della Sera, with which he collaborated during the Thirties. In his contribution, Adolfo Scotto di Luzio addresses a lesser known topic of the activity of Beonio Brocchieri as a writer of books for young people. Starting from a text published at the end of the Thirties, Scotto di Luzio ex-amines themes, symbols and imagery of political scientist Beonio Brocchieri
Effect of different platelet agonists on intracellular free Ca++ concentrations in human tumor cells: possible role in tumor growth
No full textModulation of cytoplasmic Ca++ concentration is a mechanism common to signal transduction pathways regulating many cellular phenomena, including the interactions of tumors with the hemostatic system. We have investigated the pro-aggregating and pro-coagulant activities of human tumor cell lines cultured in vitro and the ability of different platelet agonists to induce Ca++ transients in these cells. Cells of a malignant mesothelioma line activated platelets by a thrombin-dependent mechanism; on the contrary, HeLa cells, derived from a uterine cervical cancer, possessed ADP-dependent pro-aggregating activity, and DND-IA melanoma cells did not stimulate platelet aggregation. All cell lines showed a tissue-factor-like procoagulant property, more pronounced in mesothelioma cells. Furthermore, ADP was able to induce a transient increase in cytoplasmic Ca++ concentration in tumor cells from all lines; collagen showed this effect in mesothelioma cells and in HeLa cells, and thrombin was effective only in mesothelioma cells. PAF never induced Ca++ fluxes in any of the cell lines investigated. Finally, the calcium-channel blocker verapamil inhibited agonist-induced Ca++ transients in tumor cells and in vitro tumor-cell growth. These data may help to identify new possible mechanisms of the 2-way interaction of tumors with the hemostatic system
Thickness determination of the gilding on brass materials by XRF technique
No full textThe gold coating layer of the gold-plated brass objects was estimated using calibration curves obtained with a handheld X-ray fluorescence spectrometer (XRF). Calibration curves were obtained using reference materials (Au and brass) and intensity ratios of the X-ray fluorescence peaks generated in both the gold coating and the brass substrate. In addition, a calibration was also performed with the PLS (Partial Least Squares) multivariate analysis method. Good agreement was obtained by comparing the results of the different methods. The calibrations were successfully applied to gold-plated brass jewels and samples
Coating thickness of plated objects using XRF technique concentrations
No full textThe coating layer thickness of the double-layer objects was estimated using the concentration value of an element of the covering layer or of the substrate after obtaining suitable calibration curves using reference materials. The x-ray fluorescence technique was used with a handheld instrument to determine the concentration of elements. Various experimental configurations were built using gold- and silver-plated materials. The concentration calibrations curve as a function of coating layer thickness were successfully applied to gold-plated brass and copper jewelry, gold-plated samples and an ancient silver coin. The results obtained using the concentrations are in good agreement with those of other more elaborate methods
Type of housing affects social and feeding behaviour of captive buzzards (_Buteo buteo_)
No full textThe animals used in this study were observed in captivity for along time during recovery from injuries before their release. Their social behaviour was studied under two housing conditions: one group (20 animals) was kept in a 9x9x4 m pen on the ground floor together with 10 individuals of different species but of similar size; another group (40 animals) was kept in a pen of equal size to the first, on the upper floor, with a lower level of disturbance by stockpersons. The intra- and interspecific interactions were recorded continuously in both groups
Il dio viandante. Appunti per una ricerca su Vittorio Beonio Brocchieri scrittore per ragazzi
No full textVittorio Beonio Brocchieri (1902-1979) was an Italian scholar with a very unique personality. Po-litical Scientist, scholar of Nietzsche and Spengler, he studied with Gaetano Mosca at university of Turin before reaching Pavia where he taught history of political thought from 1926 until 1972. A draftsman and engraver, in a special way he was a traveler, a kind of modern nomad. His travels inspired him a rich bibliography composed of books and newspaper articles. Particularly for the Corriere della Sera, with which he collaborated during the Thirties. In his contribution, Adolfo Scotto di Luzio addresses a lesser known topic of the activity of Beonio Brocchieri as a writer of books for young people. Starting from a text published at the end of the Thirties, Scotto di Luzio ex-amines themes, symbols and imagery of political scientist Beonio Brocchieri
Estimation of Ag coating thickness by different methods using a handheld XRF instrument
No full textPrecious objects are often made from a thin layer of metal (gold or silver) superimposed on another metal or alloy. Non-invasive XRF analysis is widely used on these objects to determine the composition and thickness of the surface layer. Here, silver surface thickness of two-layered metal samples using an ED-XRF handheld spectrometer is estimated by different methods whose results are compared. These methods involved the relationships between the intensities of the characteristic lines of Kα, Kβ, Lα and Lβ of Ag and of elements present in the substrate (Cu, Fe, Pb) and some of their combinations, as well as the PLS regression. Reference layers were used to derive the calibration curves of each methodology. PLS method was the most accurate, but the other methods were also found suitable for the purpose. Applications have been successfully made on an ancient Roman coin and a modern silver-plated object
Gold-coating thickness determination on Ag, Cu, Fe, and Pb using a handheld X-ray instrument
No full textHere, the X-ray fluorescence technique is used to determine the thickness of a coating layer as well as to analyze the surface of objects. Four metals (Ag, Cu, Fe, Pb) were covered with increasing thicknesses of gold. The measurements were performed with a commercial handheld instrument, X-SORT (Spectro). In double layers, the thickness of the covering layer was assessed by (a) the ratio between the most intense fluorescence lines of the covered element, (b) a cross-ratio between two lines of the elements in the two layers, and (c) the ordinary partial least squares (PLS) regression method. In all cases, the curves obtained could be used for the quantitative determination of the thickness. The experimental data followed the theoretical trend even though the values of the attenuation parameters were not always in agreement with the theoretical ones. Comparisons and discussion of the results of the different approaches and also with models in the literature are made. The methods studied were applied to determine the nature of the coating layers of some gilded objects and proved to be suitable for estimating the thickness of gold by providing results that were in good agreement with each other
- …
