Assessment of MISR and MODIS cloud top heights through inter-comparison with a back-scattering lidar at SIRTA

One year of back-scattering lidar cloud boundaries and optical depth were analysed for coincident inter-comparison with the latest processed versions of the NASA-TERRA MISR stereo and MODIS CO2-slicing operational cloud top heights. Optically thin clouds were found to be accurately characterised by the MISR cloud top height product as long as no other cloud was present at lower altitude. MODIS cloud top heights were generally found within the cloud extent retrieved by lidar; agreement improved as cloud optical depth increased and when CO2-slicing was the only technique used for the retrieval. The difference between Lidar and MISR cloud top heights was found to lie between −0.1 and 0.4 km for low clouds and between 0.1 and 3.1 km for high clouds. The difference between Lidar and MODIS cloud top heights was found to lie between −1.2 and 1.5 km for low clouds and between −1.4 and 2.7 km for high clouds

Aharonov-Bohm cages in the GaAlAs/GaAs system

Aharonov-Bohm oscillations have been observed in a lattice formed by a two dimensional rhombus tiling. This observation is in good agreement with a recent theoretical calculation of the energy spectrum of this so-called T3 lattice. We have investigated the low temperature magnetotransport of the T3 lattice realized in the GaAlAs/GaAs system. Using an additional electrostatic gate, we have studied the influence of the channel number on the oscillations amplitude. Finally, the role of the disorder on the strength of the localization is theoretically discussed.Comment: 6 pages, 11 EPS figure

Electron states of mono- and bilayer graphene on SiC probed by STM

We present a scanning tunneling microscopy (STM) study of a gently-graphitized 6H-SiC(0001) surface in ultra high vacuum. From an analysis of atomic scale images, we identify two different kinds of terraces, which we unambiguously attribute to mono- and bilayer graphene capping a C-rich interface. At low temperature, both terraces show $(\sqrt{3}\times \sqrt{3})$ quantum interferences generated by static impurities. Such interferences are a fingerprint of $\pi$-like states close to the Fermi level. We conclude that the metallic states of the first graphene layer are almost unperturbed by the underlying interface, in agreement with recent photoemission experiments (A. Bostwick et al., Nature Physics 3, 36 (2007))Comment: 4 pages, 3 figures submitte

Accumulation et fonte de la neige en milieux boisé et déboisé

Les auteurs présentent une étude des caractéristiques physiques du couvert de neige en relation avec l'altitude, l'exposition et le couvert forestier. L'expérience s'est déroulée à la forêt Montmorency, sise à 80 km au nord de Québec. Au cours des hivers 1981 et 1982, l'équivalent en eau maximal de la neige, pour l'ensemble du bassin du lac Laflamme, a été de 28 et 29 cm, respectivement. Durant cette période, les mesures effectuées n'ont pas permis de détecter l'effet des faibles différences d'altitude (50 m) sur l'accumulation de la neige. L'équivalent en eau de la neige était maximal dans les milieux découverts et apparaissait plus important sous les jeunes peuplements que sous les vieux. Les jeunes sapinières, entourées d'arbres plus hauts, agissent comme des pièges à neige. L'influence de l'exposition ne ressort que durant la période de fonte, accélérée d'une semaine sur les flancs sud. La fonte en sous-bois dure un mois et demi en moyenne et est écourtée d'une à deux semaines dans les sites découverts. Un modèle de fonte, basé sur les degrés-jours, est finalement adapté. Le coefficient de fonte est rajusté en fonction de deux périodes distinctes par la densité du manteau nival ou les degrés-jours cumulés.A study of physical characteristics of the snow cover in relation to altitude, aspect and forest cover, is presented in this paper. The experimental site is located at Montmorency forest, 80 km north of Québec City. During the winters of 1981 and 1982, the snow water equivalent for the lake Laflamme watershed reached a maximum of 28 and 29 cm, respectively. The effect on snow accumulation by the small elevation range (50 m) was not detectable by our measurements. The snow water equivalent was greatest in open areas and appeared greater under the young than the older stands. The young fir associations, surrounded by higher trees, act as snow traps. The aspect plays a role during the melting period only, which is shortened by one week on south exposures. Snowmeit lasts one and a half month in average under the cover and is shortened by one to two weeks in the open. A snowmeit model, based on degree-days, is finally calibrated. The melt coefficient is readjusted for two periods separated by snow density or cumulative degree-days.Die Autoren legen eine Studie vor, die die Beziehung der physischen Merkmale der Schneedecke zu Hôhe, Himmelsrichtung und Bewaldung untersucht. Der Versuch wurde im WaId Montmorency, der 80 km nôrdlich von Québec liegt, durchgefùhrt. Wàhrend der Winter 1981 und 1982 war das maximale Wasserâquivalent der Schneemenge 28 cm bzw. 29 cm fur das gesamte Becken des Laflamme-Sees. Wahrend dieser Période konnten die durchgefuhrten Messungen keinerlei Einflup der schwachen Hôhenunterschiede (50 m) auf die Menge des angesammelten Schnees feststellen. Das der Schneemenge entsprechende Wasserâquivalent war maximal in den freien Gebieten und schien grosser unter den jungen Baumbestanden als unter den alten. Die jungen Tannenwâlder, die von hôheren Baurnen umgeben sind, wirken wie Schneefallen. Der EinfluB der Himmelsrichtung wird erst wâhrend der Zeit der Schneeschmelze spurbar, die auf den Sudflanken urn eine Woche kùrzer ist. Die Schneeschmelze im WaId dauert im Durchschnitt eineinhalb Monate und ist ein bis zwei Wochen kurzer in den offenen Gelànden. Ein Schneeschmelze-Modell auf der Basis Grade-Tage wird schlieplich geeicht. Der Schmelzkoeffizient wird zwei Perioden angepaBt, die sich durch die Dichte der Schneedecke oder die kumulierten Grade-Tage unterscheiden

Caractérisation des sous-produits d'oxydation des boues en conditions sous-critiques et supercritiques

L'élimination de la matière organique et la réduction de volume des boues peuvent être obtenues par incinération, par oxydation sous pression en milieu humide ("wet air oxidation") ou par combustion en eau supercritique ("supercritical water oxidation"). Une étude en autoclave agité a permis de comparer sur une même boue d'épuration les performances des deux techniques d'oxydation voie humide et d'oxydation supercritique, en mettant l'accent sur les sous-produits résiduels en phase liquide et la composition de la phase gaz. Les résultats obtenus montrent que l'élimination de la DCO dépend fortement de la température: l'abattement de la DCO passe de 70 % à 235 °C à 94 % à 430 °C. L'azote organique de la boue est transformé en NH4+ mais seule une élimination limitée de l'azote totale est obtenue à 430 °C. Les sous-produits résiduels dans la phase liquide sont constitués en majorité d'acides gras, d'aldéhydes et de cétones, l'acide acétique étant prédominant. Hormis le CO2, les sous-produits gazeux majeurs formés par des réactions complexes comme la pyrolyse, le réformage et la méthanation sont CO, H2 et CH4. Dans les conditions supercritiques, tous les sous-produits gazeux sont fortement oxydés. L'augmentation de la température de traitement permet d'obtenir un résidu solide de plus en plus inerte, les cendres obtenues en conditions supercritiques contenant moins de 1 % de matière organique. Les performances des deux procédés étudiés laissent envisager leur développement à moyen terme comme voies alternatives d'élimination des boues.ContextAs the number of wastewater treatment plants increases, and the efficiency of treatment improves, the problem of how to dispose of the ever increasing amounts of generated sludge has intensified. For the beginning of the next century 1 million tons of sludge will be produced annually in France; disposal in landfills will be impossible and agricultural use could be limited by tight quality standards. Therefore, the development of effective and acceptable sludge processes is urgently needed.Destruction of organic matter in sludge and large reductions in sludge volume are achieved either by incineration or by wet air oxidation (WAO), which needs no fuel and generates no smoke, fly ash or emissions of NOx and SO2. Supercritical water oxidation (SCWO) offers an attractive alternative. Water, above its vapor-liquid critical point of 374°C and 221 bar, is an excellent solvent for organic compounds and becomes completely miscible with oxygen. Reported results of sewage sludge SCWO demonstrate rapid and effective treatment. The objective of this study was to compare sub- and supercritical water oxidation of sludge in terms of organic matter destruction and formation of by-products in both gas and liquid phases. MethodologyOxidation of sludge was studied in a 0.5 L batch reactor rated for 450°C-300 bar. The raw material was a biological sludge containing 4% solids with a chemical oxygen demand (COD) value of 52 g/L. In the standard experimental procedure, 100 mL sludge were heated up to reaction temperature and oxygen was then introduced in 50% excess with respect to COD. Heating was maintained during 1 hour before slow cooling to room temperature. The overall organic destruction was quantified in terms of total organic carbon (TOC) and COD. Gas and liquid phases sampled at room temperature after reaction were analyzed by gas chromatography (GC). Sulfur and nitrogen species were also analyzed.ResultsWhen the temperature increased from 210 to 383°C, COD destruction increased significantly (Table 1). At 383°C, a COD destruction efficiency of 94.3% was obtained. However, at 430°C, organic matter oxidation was only marginally improved. In WAO tests, considerable acetic acid was produced and remained in the substrate. The produced acetic acid was oxidized rapidly under SCWO conditions. Surprisingly, the concentrations of the other volatile fatty acids (VFA) remained approximately constant between 310 and 430°C (Table 2). In addition to VFA, which represent ca. 50% of the residual COD, oxygenated organic compounds such as aldehydes, ketones and alcohols were produced (Table 3). The data in Table 4 show that decomposition of organic nitrogen compounds into ammonia was completed at 383°C, while nitrates were reduced to N2 by reaction with organic matter and ammonia. NOx were not detected in the gas phase. The low reactivity of ammonia in supercritical water had been previously demonstrated. At 430°C, ammonia removal from sludge was limited to 15%. On the other hand, even in WAO conditions all sulfur species were totally converted to sulfate. Under subcritical conditions, the gas phase contained significant concentrations of hydrogen and carbon monoxide in addition to water, residual oxygen and carbon dioxide. Traces of methane and C2-C3 hydrocarbons were also detected (Figs. 1 and 2). These gases result from a complex chemistry including pyrolysis, steam reforming and water-gas shift. Under supercritical conditions, all these compounds were extensively eliminated by oxidation. Under supercritical conditions the residual solids contained less than 1% organic matter. By X-ray diffraction hydroxyapatite, quartz and kaliophilite were identified in the residual solids.These results confirm that supercritical water oxidation is a new sludge treatment concept of great interest. The degree of conversion of organic carbon is high, while liquid and especially gaseous by- products are produced in minor amounts compared to subcritical conditions. Temperatures higher than 430°C would be needed for substantial nitrogen removal

A V-shape superconducting artificial atom based on two inductively coupled transmons

Circuit quantum electrodynamics systems are typically built from resonators and two-level artificial atoms, but the use of multi-level artificial atoms instead can enable promising applications in quantum technology. Here we present an implementation of a Josephson junction circuit dedicated to operate as a V-shape artificial atom. Based on a concept of two internal degrees of freedom, the device consists of two transmon qubits coupled by an inductance. The Josephson nonlinearity introduces a strong diagonal coupling between the two degrees of freedom that finds applications in quantum non-demolition readout schemes, and in the realization of microwave cross-Kerr media based on superconducting circuits.Comment: 5 pages, 3 figure

Kerr non-linearity in a superconducting Josephson metamaterial

We present a detailed experimental and theoretical analysis of the dispersion and non-linear Kerr frequency shifts of plasma modes in a one-dimensional Josephson junction chain containing 500 SQUIDs in the regime of weak nonlinearity. The measured low-power dispersion curve agrees perfectly with the theoretical model if we take into account the Kerr renormalisation of the bare frequencies and the long-range nature of the island charge screening by a remote ground plane. We measured the self- and cross-Kerr shifts for the frequencies of the eight lowest modes in the chain. We compare the measured Kerr coefficients with theory and find good agreement