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Search Results: 1 - 10 of 596074 matches for " M. J. Rossi "
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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.
Analytic Isomorphisms of compressed local algebras
J. Elias,M. E. Rossi
Mathematics , 2012,
Abstract: In this paper we consider Artin local K-algebras with maximal length in the class of Artin algebras with given embedding dimension and socle type. They have been widely studied by several authors, among others by Iarrobino, Fr\"oberg and Laksov. If the local K-algebra is Gorenstein of socle degree 3, then the authors proved that it is canonically graded, i.e. analytically isomorphic to its associated graded ring. This unexpected result has been extended to compressed level K-algebras of socle degree 3 by A. De Stefani. In this paper we end the investigation proving that extremal Artin Gorenstein local K-algebras of socle degree s \le 4 are canonically graded, but the result does not extend to extremal Artin Gorenstein local rings of socle degree 5 or to compressed level local rings of socle degree 4 and type >1. As a consequence we present results on Artin compressed local K-algebras having a specified socle type.
Depression storage and infiltration effects on overland flow depth-velocity-friction at desert conditions: field plot results and model
M. J. Rossi ,J. O. Ares
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2012,
Abstract: Water infiltration and overland flow are relevant in considering water partition among plant life forms, the sustainability of vegetation and the design of sustainable hydrological models and management. In arid and semi-arid regions, these processes present characteristic trends imposed by the prevailing physical conditions of the upper soil as evolved under water-limited climate. A set of plot-scale field experiments at the semi-arid Patagonian Monte (Argentina) were performed in order to estimate the effect of depression storage areas and infiltration rates on depths, velocities and friction of overland flows. The micro-relief of undisturbed field plots was characterized at z-scale 1 mm through close-range stereo-photogrammetry and geo-statistical tools. The overland flow areas produced by controlled water inflows were video-recorded and the flow velocities were measured with image processing software. Antecedent and post-inflow moisture were measured, and texture, bulk density and physical properties of the upper soil were estimated based on soil core analyses. Field data were used to calibrate a physically-based, mass balanced, time explicit model of infiltration and overland flows. Modelling results reproduced the time series of observed flow areas, velocities and infiltration depths. Estimates of hydrodynamic parameters of overland flow (Reynolds-Froude numbers) are informed. To our knowledge, the study here presented is novel in combining several aspects that previous studies do not address simultaneously: (1) overland flow and infiltration parameters were obtained in undisturbed field conditions; (2) field measurements of overland flow movement were coupled to a detailed analysis of soil microtopography at 1 mm depth scale; (3) the effect of depression storage areas in infiltration rates and depth-velocity friction of overland flows is addressed. Relevance of the results to other similar desert areas is justified by the accompanying biogeography analysis of similarity of the environment where this study was performed with other desert areas of the world.
Estimation of overland flow metrics at semiarid condition: Patagonian Monte
M. J. Rossi,J. O. Ares
Hydrology and Earth System Sciences Discussions , 2012, DOI: 10.5194/hessd-9-5837-2012
Abstract: Water infiltration and overland flow (WIOF) processes are relevant in considering water partition among plant life forms, the sustainability of vegetation and the design of sustainable hydrological management. WIOF processes in arid and semiarid regions present regional characteristic trends imposed by the prevailing physical conditions of the upper soil as evolved under water-limited climate. A set of plot-scale field experiments at the semi-arid Patagonian Monte (Argentina) was performed in order to estimate infiltration-overland descriptive flow parameters. The micro-relief of undisturbed field plots at z-scale <1 mm was characterized through close-range stereo-photogrammetry and geo-statistical modelling. The overland flow areas produced by experimental runoff events were video-recorded and the runoff speed was measured with ortho-image processing software. Antecedent and post-inflow moisture were measured, and texture, bulk density and physical properties of the soil at the upper vadose zone were estimated. Field data were used to calibrate a physically-based, time explicit model of water balance in the upper soil and overland flows with a modified Green-Ampt (infiltration) and Chezy's (overland flow) algorithms. Modelling results satisfy validation criteria based on the observed overland flow areas, runoff-speed, water mass balance of the upper vadose zone, infiltration depth, slope along runoff-plume direction, and depression storage intensity. The experimental procedure presented supplies plot-scale estimates of overland flow and infiltration intensities at various intensities of water input which can be incorporated in larger-scale hydrological grid-models of arid regions. Findings were: (1) Overland flow velocities as well as infiltration-overland flow mass balances are consistently modelled by considering variable infiltration rates corresponding to depression storage and/or non-ponded areas. (2) The statistical relations presented allow the estimation of theoretical hydrodynamic parameters (Chezy's frictional C, average overland flow depth d*) through measurable characteristics of the surface soil and overland flow kinetics. (3) A protocol of field experiments and coupled time-distributed modelling to 1–2 above is described. The methodology and results obtained in this study are probably relevant to similar arid-semiarid areas of the world.
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.
The heterogeneous chemical kinetics of N2O5 on CaCO3 and other atmospheric mineral dust surrogates
F. Karagulian, C. Santschi,M. J. Rossi
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2006,
Abstract: Uptake experiments of N2O5 on several mineral dust powder samples were carried out under continuous molecular flow conditions at 298±2 K. At [N2O5]0=(4.0±1.0)×1011 cm 3 we have found γss values ranging from (3.5±1.1)×10 2 for CaCO3 to (0.20±0.05) for Saharan Dust with γss decreasing as [N2O5]0 increased. The uptake coefficients reported in this work are to be regarded as upper limiting values owing to the fact that they are based on the geometric (projected) surface area of the mineral dust sample. We have observed delayed production of HNO3 upon uptake of N2O5 for every investigated sample owing to hydrolysis of N2O5 with surface-adsorbed H2O. Arizona Test Dust and Kaolinite turned out to be the samples that generated the largest amount of gas phase HNO3 with respect to N2O5 taken up. In contrast, the yield of HNO3 for Saharan Dust and CaCO3 is lower. On CaCO3 the disappearance of N2O5 was also accompanied by the formation of CO2. For CaCO3 sample masses ranging from 0.33 to 2.0 g, the yield of CO2 was approximately 42–50% with respect to the total number of N2O5 molecules taken up. The reaction of N2O5 with mineral dust and the subsequent production of gas phase HNO3 lead to a decrease in [NOx] which may have a significant effect on global ozone.
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.
Afterglow lightcurves, viewing angle and the jet structure of gamma-ray bursts
E. Rossi,D. Lazzati,M. J. Rees
Physics , 2001, DOI: 10.1046/j.1365-8711.2002.05363.x
Abstract: Gamma ray bursts are often modelled as jet-like outflows directed towards the observer; the cone angle of the jet is then commonly inferred from the time at which there is a steepening in the power-law decay of the afterglow. We consider an alternative model in which the jet has a beam pattern where the luminosity per unit solid angle (and perhaps also the initial Lorentz factor) decreases smoothly away from the axis, rather than having a well-defined cone angle within which the flow is uniform. We show that the break in the afterglow light curve then occurs at a time that depends on the viewing angle. Instead of implying a range of intrinsically different jets - some very narrow, and others with similar power spread over a wider cone - the data on afterglow breaks could be consistent with a standardized jet, viewed from different angles. We discuss the implication of this model for the luminosity function.
On the Hilbert function of one-dimensional local complete intersections
J. Elias,M. E. Rossi,G. Valla
Mathematics , 2012,
Abstract: The Hilbert function of standard graded algebras are well understood by Macaulay's theorem and very little is known in the local case, even if we assume that the local ring is a complete intersection. An extension to the power series ring $R$ of the theory of Gr\"{o}bner bases (w.r.t. local degree orderings) enable us to characterize the Hilbert function of one dimensional quadratic complete intersections $A=R/I$, and we give a structure theorem of the minimal system of generators of $I$ in terms of the Hilbert function. We find several restrictions for the Hilbert function of $A$ in the case that $I$ is a complete intersection of type $(2,b). $ Conditions for the Cohen-Macaulyness of the associated graded ring of $A$ are given.
The blow-up problem for a semilinear parabolic equation with a potential
C. Cortazar,M. Elgueta,J. D. Rossi
Mathematics , 2006, DOI: 10.1016/j.jmaa.2007.01.079
Abstract: Let $\Omega$ be a bounded smooth domain in $\RR^N$. We consider the problem $u_t= \Delta u + V(x) u^p$ in $\Omega \times [0,T)$, with Dirichlet boundary conditions $u=0$ on $\partial \Omega \times [0,T)$ and initial datum $u(x,0)= M \phi (x)$ where $M \geq 0$, $\phi$ is positive and compatible with the boundary condition. We give estimates for the blow up time of solutions for large values of $M$. As a consequence of these estimates we find that, for $M$ large, the blow up set concentrates near the points where $\phi^{p-1}V$ attains its maximum.
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