Search results for "atmosphere"
showing 10 items of 673 documents
Evidence of nonthermal particles in coronal loops heated impulsively by nanoflares
2014
The physical processes causing energy exchange between the Sun's hot corona and its cool lower atmosphere remain poorly understood. The chromosphere and transition region (TR) form an interface region between the surface and the corona that is highly sensitive to the coronal heating mechanism. High resolution observations with the Interface Region Imaging Spectrograph (IRIS) reveal rapid variability (about 20 to 60 seconds) of intensity and velocity on small spatial scales at the footpoints of hot dynamic coronal loops. The observations are consistent with numerical simulations of heating by beams of non-thermal electrons, which are generated in small impulsive heating events called "corona…
The precious treasure of Mariano Valenza: The history of Ludovico Sicardi and the birth of geochemical volcano monitoring
2020
I was lucky enough to meet Mariano Valenza in September 1995. I was hitchhiking on the highway that leads from Cefalu to Palermo to go back home. I had spent my summer holidays in the beautiful and wild Madonie mountains. An off-road vehicle (a Land Rover Defender) stopped and a refined gentleman with a curious and charismatic gaze offered me a ride. During our journey, we chatted pleasantly and he told he was originally from that area. When I told him, I was a Geology student, he smiled at me and said Then we will meet again soon, I am going to be your Teacher of Geochemistry!. After a few weeks the lessons began and I met again Professor Valenza in Via Archirafi 36, at the University of P…
Temperature dependence of sodium and ionized calcium resonance lines perturbed by helium
2014
International audience; Traces of heavy metals in cool DZ white dwarf stars may be attributed to the accretion of circumstellar dust thought to originate from tidal disruption of rocky parent bodies. Spectra of such stars therefore provide a unique opportunity to study the composition of extrasolar planetary systems. The determination of metal abundances from stellar spectra depends on stellar atmospheric parameters and an accurate prior knowledge of the collision broadening of the line profiles by the most common constituents of the stellar atmosphere. For this purpose, we present theoretical absorption spectra of Na and Ca+ broadened by He for the conditions prevailing in cool white dwarf…
Drawing and Project at the VChUTEMAS. Graphic Interpretations
2019
The article deals with the graphic study of the project for the Kominern Palace designed in 1929 by Lidija Komarova, one of the students of the Russian Laboratories known by the acronym VChUTEMAS, founded in 1920 in Moscow. Strongly characterized by the revolutionary atmosphere that was delineating the artistic progress based on the synthesis of all the plastic arts, the Russian Laboratories attributed to the architecture a position of the first order, a perfect association between the scientific possibility and the art technique. The redrawing of this project allows to deepen the compositional principles of the new architectural formation of the Eastern European avant-garde, providing digi…
Intrinsic generation of OH groups in dry silicon dioxide upon thermal treatments
2008
We show the existence of an intrinsic generation mechanism of OH groups in synthetic dry silica upon thermal treatments. Samples are treated for ~160 h at 390 °C in He at 2.7 or 180 bar, and the growth of the OH IR absorption band at 3670 cm−1 is observed. An OH concentration of ~10^18 cm^−3 is estimated. Possible contributions of reactions with molecules absorbed from the atmosphere are excluded. Reactions with H2O already contained in the samples are rejected by IR measurements. The observed OH generation is attributed to the reaction of network sites with H2 already present in the material. Possible reaction paths are examined
Influence of SMSI effect on the catalytic activity of a Pt(1%)/ Ce0.6Zr0.4O2 catalyst: SAXS, XRD, XPS and TPR investigations
2004
Abstract The steady-state activity of NO reduction by C3H6, in lean conditions, was studied on a Pt(1%)/Ce0.6Zr0.4O2 catalyst, in a plug-flow reactor, in the temperature range 100–500 °C. The influence of reductive pre-treatments on the catalytic performance at low temperature (250 °C) was investigated. Enhancement of the activity was found for the catalyst pre-treated in hydrogen at 350 °C as compared to the sample pre-treated in H2 at 800 and 1050 °C. Moreover, transient reactivity tests of NO reduction by hydrogen were also carried out. As previously observed, the sample reduced at 350 °C was the most active catalyst. In both types of reactions the temperature and the nature of pre-treat…
Short-term emissions of CO 2 and N 2 O in response to periodic flood irrigation with waste water in the Mezquital Valley of Mexico
2015
Irrigation with waste water adds labile carbon and nitrogen compounds to the soil, and when applied by flooding it rapidly changes the soil's atmosphere and redox potential. In the Mezquital Valley more than 90 000 ha is irrigated with waste water from Mexico City, and enhanced emissions of CO2 and N2O follow each flooding. We measured the emissions of these two gases from a field irrigated periodically with waste water and under three crops, namely alfalfa, rye-grass and maize, using static chambers for 21 months. We also measured emissions from a field growing rain-fed maize before and shortly after two rain events. The data from repeated measurements from the same chambers are correlated…
Application and evaluation of the SWAP model for simulating water and solute transport in a cracking clay soil
2005
In Sicily, the increasing scarcity of quality water is leading to irriga- from salinization (Crescimanno et al., 2004). tion with saline water in soils having a considerable susceptibility to In Sicily, the increasing scarcity of good quality water cracking. Irrigation systems involving high application rates are used coupled with intensive use of soil under semiarid to arid in these irrigated areas, and bypass flow during irrigation is thus climatic conditions, is leading to irrigation with saline prevalent. Adoption of management practices accounting for cracking water on soils having a high shrink-swell potential and is therefore necessary to prevent salinization and land degradation. su…
Carbon isotope exchange between gaseous CO2 and thin solution films: Artificial cave experiments and a complete diffusion-reaction model
2017
Abstract Speleothem stable carbon isotope (δ 13 C) records provide important paleoclimate and paleo-environmental information. However, the interpretation of these records in terms of past climate or environmental change remains challenging because of various processes affecting the δ 13 C signals. A process that has only been sparsely discussed so far is carbon isotope exchange between the gaseous CO 2 of the cave atmosphere and the dissolved inorganic carbon (DIC) contained in the thin solution film on the speleothem, which may be particularly important for strongly ventilated caves. Here we present a novel, complete reaction diffusion model describing carbon isotope exchange between gase…
A conceptual dynamic vegetation-soil model for arid and semiarid zones
2007
Plant ecosystems in arid and semiarid zones show high complexity from the point of view of water resources, since they depend on water availability to carry out their vital processes. In these climates, water stress is the main factor controlling vegetation development. The available water in the system results from a water balance where the soil, vegetation and the atmosphere are the key issues; but it is the vegetation which modulates (to a great extent) the total balance of water and the mechanisms of the feedback between soil and atmosphere, being the knowledge about soil moisture quite relevant for assessing available water and, as a consequence, for growth and plants maintenance and t…