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Search Results: 1 - 10 of 147596 matches for " B. ROSSI "
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Risultati e prospettive delle ricerche spaziali
B. ROSSI
Annals of Geophysics , 1963, DOI: 10.4401/ag-5244
Abstract: Sarebbe una presunzione da parte degli scienziati il pensare che i grandiosi e costosissimi programmi di attività spaziale in cui, una dopo l'altra, si vanno imbarcando le maggiori nazioni del mondo siano motivati esclusivamente, od anche principalmente, da ragioni scientifiche. Vi sono importanti ragioni pratiche, come lo sviluppo di una rete globale di comunicazioni e la raccolta di dati meteorologici che permetta sicure predizioni del tempo. Vi sono questioni di prestigio nazionale. E vi è infine l'indomabile spirito d'avventura che obbliga l'uomo a tentare tutto ciò che è umanamente possibile, a spingersi sempre più lontano nel mondo che lo circonda. Eppure è assai probabile che, in ultima analisi, il risultato più importante e più durevole di questa attività saranno appunto quelle scoperte scientifiche che oggi passano quasi inosservate. è probabile che il periodo iniziato quasi cinque anni fa col lancio del primo sputnick passerà alla storia come quello in cui l'umanità ha compiuto uno sbalzo di eccezionale portata verso la conoscenza del pianeta su cui vive e dell'universo che circonda questo pianeta. La terra è parte del sistema solare, e l'esplorazione diretta del sistema solare ha già avuto inizio. Non v'è dubbio che durante il prossimo decennio strumenti sempre pili complessi e raffinati verranno lanciati a distanze sempre più grandi dal nostro pianeta. E, con ogni probabilità, in questo periodo assisteremo pure ai primi viaggi di astronauti oltre i limiti di quella regione dello spazio che è sotto l'influenza diretta della terra.
Interventi
B. De' Rossi
Aestimum , 1977,
Abstract:
A Hybrid Angular/Energy Dispersive Method to Improve Some Characteristics of Laboratory X-Ray Diffraction  [PDF]
V. Rossi Albertini, D. Bailo, A. Generosi, B. Paci
Modern Instrumentation (MI) , 2012, DOI: 10.4236/mi.2012.11001
Abstract: The Energy Dispersive X-ray Diffraction, generally referred as EDXD, has shown to be a valid alternative to the conventional Angular Dispersive X-ray Diffraction, the ADXD. EDXD exhibits several advantages to its AD counterpart, mainly related to the properties of the polychromatic X-ray beam utilized for diffracting, such as higher signal intensities, a wider accessible region of the reciprocal space, a greater transparency of samples, and a parallel data collection of the q-points in the diffraction pattern acquisition. However, the main drawback of poly-chromaticity lays in the fact that the quantities that modulate the scattered intensity in a diffraction measurement depend on the energy. These quantities are the primary X-ray beam spectrum, polarization, and X-ray absorption, the last producing by far the most critical effect because it rapidly changes as a function of energy. Therefore, a detailed knowledge of the energy dependence of all these quantities is required in EDXD in order to process the data correctly and prevent systematic errors. The difficulty in handling the energy-dependent factors complicates the experimental procedure and may make the measurements unreliable. In the present paper, a hybrid method between the ED and AD X-ray Diffraction is proposed to maintain the advantages of the polychromatic nature of the radiation utilized in EDXD, while preventing the problems produced by the energy-dependent quantities.
The surface properties of SOA generated from limonene and toluene using specific molecular probes: exploration of a new experimental technique
B. Demirdjian,M. J. Rossi
Atmospheric Chemistry and Physics Discussions , 2005,
Abstract: A new experimental technique of characterizing the aerosol-atmosphere surface has been explored using three examples: the secondary organic aerosols (SOA) resulting from the reaction of limonene with O3 and from the photooxidation of toluene in comparison with the combustion aerosol (soot) from a toluene diffusion flame. Rather than investigating the bulk composition of the aerosol by complete chemical analysis and identification of the many dozens if not more of constituent compounds we have interrogated the type and number of functional groups located at the aerosol surface by interacting them with specific molecular probes such as O3, NO2, N(CH3)3, and NH2OH to probe for the presence of oxidizable sites, acidic sites and carbonyl functionalities, respectively, that are present on the surface of the aerosol particle. In practice, typical amounts of one to a few mg of laboratory-generated SOA of limonene, toluene and soot have been deposited on a PTFE membrane filter that subsequently has been transferred to a molecular flow reactor used for the titration reaction of the surface functional groups by the molecular probes. Absolute amounts Ni with i=O3, NO2, N(CH3)3, NH2OH of probe molecules taken up by the filter sample measured using molecular beam sampling mass spectrometry have been converted into the number of surface group functionalities per unit surface area S using the aerosol particle distribution function (PDF) of limonene and toluene SOA and the BET total surface area of toluene flame soot to result in Ni/S. Arguments are presented that support the transfer of the PDF of the suspended to the aerosol collected on the Teflon filter.
Effetto delle dimensioni del cordone di saldatura sulla resistenza a fatica dei giunti a croce
B. Atzori,B. Rossi,G. Demelio
Frattura ed Integrità Strutturale , 2009,
Abstract: La scelta della dimensione da assegnare al cordone di saldatura nel caso di giunzioni saldate a croce può presentarsi problematica, specie quando gli spessori delle lamiere che formano il giunto sonodifferenti tra loro. Le normative di tipo tecnologico suggeriscono in genere di prevedere uno spessore del cordone di saldatura inferiore al minimo spessore della lamiera da collegare, mentre le normative di tipo strutturale non prevedono una dipendenza della resistenza del giunto, sia statica che a fatica, dalle dimensioni del cordone di saldatura, a meno che queste non siano tanto ridotte da portare a rotture che si inneschino e si propaghino non più nella lamiera base ma nel cordone di saldatura. Scopo del presente lavoro è la verifica,teorica e sperimentale, della variazione della resistenza a fatica al variare del rapporto tra lo spessore del cordone di saldatura e quello minimo delle lamiere da saldare.
Resistenza a fatica di strutture in leghe di alluminio: normative a confronto e verifica sperimentale
B. Atzori,G. Meneghetti,B. Rossi
Frattura ed Integrità Strutturale , 2009,
Abstract: Le problematiche relative all’utilizzo delle normative nell’ambito della progettazione a fatica di strutture in leghe di alluminio sono state di recente affrontate in numerosi lavori che hanno messo in luce sia le difficoltà legate al passaggio da normative oramai obsolete ad altre di nuova concezione, ma di caratteristiche e struttura completamente diverse, che la sostanziale carenza anche all’interno delle più recenti normative europee, quale l’Eurocodice 9, di molti risultati e metodi sviluppati in anni di ricerca scientifica e ormai indiscutibilmente consolidati. Il presente lavoro si propone di approfondire entrambe le tematiche tramite il confronto tra risultati sperimentali tratti da letteratura e le corrispondenti curve di resistenza proposte rispettivamente dalla normativa italiana UNI 8634, di recente ritirata, e dall’Eurocodice 9. In questo modo verranno messe in luce le differenze tra i valori di resistenza proposti dalle due norme e verrà illustrata sia la corrispondenza a volte poco soddisfacente con i risultati sperimentali che le conseguenze dovute alla mancata applicazione di assodati risultati teorici.
The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: implications for the lifetime of atmospheric ice particles
C. Delval, B. Fluckiger,M. J. Rossi
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2003,
Abstract: Using a multidiagnostic approach the rate Rev [ molec cm-3 s-1] or flux Jev [ molec cm-2 s-1] of evaporation of H2O and its corresponding rate constant for condensation, kcond [s-1 ], on a 1 μm thick ice film have been studied in the temperature range 190 to 240 K as well as in the presence of small amounts of HCl and HBr that left the vapor pressure of H2O on ice unchanged. The resulting Arrhenius expressions for pure ice are Jev = 1.6 · 10 28 ± 1 · exp (- 10.3 ± 1.2/ RT) [ molec cm-2 s-1] , kcond = 1.7 · 10 - 2 ± 1 · exp (+ 1.6 ± 1.5/ RT ) [s -1], in the presence of a HCl mole fraction in the range 3.2 · 10 - 5 - 6.4 · 10 - 3 : Jev = 6.4 · 10 26 ± 1 · exp (- 9.7 ± 1.2/ RT) [ molec cm-2 s-1] , kcond = 2.8 · 10 - 2 ± 1 · exp ( + 1.5 ± 1.6 /RT) [s -1], and a HBr mole fraction smaller than 6.4 · 10 - 3 : Jev = 7.4 · 10 25 ± 1 · exp ( - 9.1 ± 1.2 /RT) [ molec cm-2 s-1] , kcond = 7.1 · 10 - 5 ± 1 · exp (+ 2.6 ± 1.5/ RT) [s -1]. The small negative activation energy for H2O condensation on ice points to a precursor mechanism. The corresponding enthalpy of sublimation is DHsubl = Eev - Econd = 11.9 ± 2.7 kcal mol-1 , DHsubl = 11.2 ± 2.8 kcal mol-1, and DHsubl = 11.7 ± 2.8 kcal mol-1 whose values are identical within experimental uncertainty to the accepted literature value of 12.3 kcal mol-1 . Interferometric data at 633 nm and FTIR absorption spectra in transmission support the kinetic results. The data are consistent with a significant lifetime enhancement for HCl- and HBr-contaminated ice particles by a factor of 3–6 and 10–20, respectively, for submonolayer coverages of HX once the fraction of the ice not contaminated by HX has evaporated.
Detecting trends of extreme rainfall series in Sicily
B. Bonaccorso, A. Cancelliere,G. Rossi
Advances in Geosciences (ADGEO) , 2005,
Abstract: The objective of the study is to assess the presence of linear and non linear trends in annual maximum rainfall series of different durations observed in Sicily. In particular, annual maximum rainfall series with at least 50 years of records starting from the 1920’s are selected, and for each duration (1, 3, 6, 12 and 24 h) the Student’s t test and theMann- Kendall test, respectively, for linear and non linear trend detection, are applied also by means of bootstrap techniques. The effect of trend on the assessment of the return period of a critical event is also analysed. In particular, return periods related to a storm, recently occurred along the East Coast of Sicily, are computed by estimating parameters based on several sub-series extracted from the whole observation period. Such return period estimates are also compared with confidence intervals computed by bootstrap. Results indicate that for shorter durations, the investigated series generally exhibit increasing trends while as longer durations are considered, more and more series exhibit decreasing trends.
Adaptive regridding in 3D reflection tomography
G. B?hm,G. Rossi,A. Vesnaver
Annals of Geophysics , 1997, DOI: 10.4401/ag-3936
Abstract: 3D reflection tomography allows the macro-model of complex geological structures to be reconstructed. In the usual approach, the spatial distribution of the velocity field is discretized by regular grids. This choice simplifies the development of the related software, but introduces two serious drawbacks: various domains of the model may be poorly covered, and a relevant mismatch between the grid and a complex velocity field may occur. So the tomographic inversion becomes unstable, unreliable and necessarily blurred. In this paper we introduce an algorithm to adapt the grid to the available ray paths and to the velocity field in sequence: so we get irregular grids with a locally variable resolution. We can guide the grid fitting procedure interactively, if we are going to introduce some geological a priori information; otherwise, we define a fully automatic approach, which exploits the Delauny triangles and Voronoi polygons.
The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: Implications for the lifetime of atmospheric ice particles
C. Delval,B. Fluckiger,M. J. Rossi
Atmospheric Chemistry and Physics Discussions , 2003,
Abstract: Using a multidiagnostic approach the rate Rev or flux Jevof evaporation of H2O and its condensation, kcond, on a 1mm thick ice film have been studied in the temperature range 190 to 240 K as well as in the presence of small amounts of HCl and HBr that left the vapor pressure of H2O on ice unchanged. The resulting Arrhenius expressions with RT in kcal mol-1 for pure ice are Jev=1.6×1028+/ 1·exp({ 10.3+ 1.2}/{RT}) [molec cm 2 s 1], kcond=1.7×10 2+-1×exp({+1.6+ 1.5}/{RT}) [s 1], in the presence of an HCl mole fraction in the range 3.2×10 5-6.4×10 3: Jev=6.4×1026+/ 1×exp({ 9.7+/ 1.2}/{RT}) [molec cm 2 s 1], kcond=2.8×10 2+/-1×exp({+1.5+/ 1.6}/{RT}) [s 1], and an HBr mole fraction smaller than 6.4×10 3:Jev=7.4×1025+/ 1×exp({ 9.1+/ 1.2}/{RT}) [molec cm 2 s 1], kcond=7.1×10 5+ 1×exp({+2.6+/ 1.5}/{RT}) [s 1]}. The small negative activation energy for H2O condensation on ice points to a precursor mechanism. The corresponding enthalpy of sublimation is DHsubl=Eev-Econd=11.9+/ 2.7 kcal mol 1, DHsubl=11.2+/ 2.8 kcal mol 1, and DHsubl=11.7+/ 2.8 kcal mol 1 whose values are identical within experimental uncertainty to the accepted literature value of 12.3 kcal mol 1. Interferometric data at 633 nm and FTIR absorption spectra in transmission support the kinetic results. The data are consistent with a significant lifetime enhancement for HCl- and HBr-contaminated ice particles by a factor of 3–6 and 10–20, respectively, for submonolayer coverages of HX.
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