88,817 research outputs found
La collezione di ofidi ivoriani di Padre Giacomo Bardelli nella Società Missioni Africane di Feriole (PD)
No full textNel nostro Paese sono presenti numerosi esempi di collezioni erpetologiche poco note, non valorizzate, smembrate e/o abbandonate che a volte rischiano di andare perdute. Nel presente lavoro è stata rintracciata parte della raccolta di serpenti di Padre Bardelli, traslocata dalla sede della Società Missioni Africane di Genova a quella di Padova e soggetta a periodi alterni di valorizzazione e abbandono in cui si è avuta anche la perdita di esemplari. Gli ofidi, tutti provenienti dalla Costa d’Avorio, sono corredati di informazioni dettagliate per cui possono rappresentare importanti reperti di studio per numerose attività di ricerca
Local structure of Sr2FeMoxW1-xO6 double perovskites across the composition-driven metal to insulator transition
No full textSr2FeMoO6 oxides exhibit a half-metallic ferromagnetic (HM-FM) ground state and peculiar magnetic and magnetotransport properties, which are interesting for applications in the emerging field of spintronics and attractive for fundamental research in the field of heavily correlated electron systems. Sr2FeWO6 is an insulator with an antiferromagnetic (I-AFM) ground state. The solid solutions Sr2FeMoxW1-xO6 also have peculiar properties-W doping enhances chemical order which allows stabilization of the HM-FM state; as the W content exceeds a certain value a metal to insulator transition (MIT) occurs. The role of W indetermining the physical properties of Sr2FeMoxW1-xO6 systems has been a matter of intense investigation. This work deals with the problem of the structural and electronic changes related to the MIT from a local perspective by means of x-ray absorption spectroscopy (XAS). This technique allows one to probe in detail the local structure and electronic modifications around selected absorber ions (W, Mo, Fe and Sr in our case). The results of XAS analysis in the whole composition range (0 <= x <= 1), in the near edge (XANES) and extended (EXAFS)regions, demonstrate an abrupt change of the local structure around the Fe and Mo sites at the critical composition, x(c). This change represents the microstructural counterpart associated with the MIT. Conversely, the local structure and electronic configuration of W ions remain unaltered in the whole composition range, suggesting indirect participation of W in the MIT
EFFECT OF CROSSLINKING PROCESS PARAMETERS ON THE RHEOLOGICAL BEHAVIOR OF A POLYDIMETHYLSILOXANE
No full textPolydimethylsiloxane crosslinking kinetics: A systematic study on Sylgard184 comparing rheological and thermal approaches
No full textIn this work a systematic investigation of crosslinking kinetics of Sylgard184 polydimethylsiloxane is performed in both isothermal and dynamic conditions. The results are discussed in terms of two conversions, αC and αR determined by thermal and rheological analysis, respectively. Thermal analysis can well detect the first stage of the reaction, while rheological analysis starts being sensitive only at longer time. However, once the rheological response is observable, it changes with time faster than the calorimetric one. From rheology experiments it comes out that the gel point occurs at αR = 0.53, independently of the applied thermal history. At gel point, αC is around 0.30 indicating that about 30% of the bonds involved in the crosslinking process is enough to create an infinite network. A modified version of the Kamal's autocatalytic model allows to fit and predict the experimental findings from both the techniques; however, two distinct sets of parameters have been used. The results of this work may be a useful tool to design appropriate curing cycles for the preparation of Sylgard184
ESTRA-FitEXA: A software package for EXAFS data analysis
No full text""ESTRA and FitEXA are two programs for processing X-ray absorption spectroscopy data, extraction of extended X-ray absorption fine structure (EXAFS) signal, and EXAFS data analysis via least square refinement procedure (shell fitting). ESTRA and FitEXA propose useful options such as the analysis of the noise on the raw χ(k) data and a high flexibility in the choice of the model distribution function: harmonic, anharmonic (cumulants) and hard sphere models. The minimization routines underneath the FitEXA code allow ample choice\\\/control of the non-linear minimization procedure and check of the correlation among the parameters."
Influence of curing thermal history on cross-linking degree of a polydimethylsiloxane: Swelling and mechanical analyses
No full textIn this work, the change of the elastic properties induced by a change in cross-linking conditions of polydimethylsiloxane is investigated by measuring its shear modulus by dynamic mechanical analysis and correlating it to that predicted
from swelling measurements. Polymer cross-linking is performed at different curing temperatures reached with ramps at different heating rates. From both mechanical and swelling measurements, the molecular weight between cross-links, MC, is determined, and its dependency on the applied thermal history is analyzed. The main results are: (i) the elastic modulus of the cured material is not significantly affected by the heating rate adopted, while (ii) the curing temperature has a significant influence on the polydimethylsiloxane mechanical properties. In addition, (iii) MC evaluation from swelling measurements is in good agreement with that estimated from mechanical measurements when appropriate theories are considered. This last result suggests that swelling experiments can be considered as a reliable tool to predict the elastic modulus of the polydimethylsiloxane studied. The quantitative information reported in this paper, also obtainable by the suggested method if other thermal curing histories are applied, is extremely useful for the proper design of devices based on polydimethylsiloxane
Odierne possibilità cliniche di valutazione dell'indice di rischio per il danno radioterapico tardivo
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