We continue studying convection as a possible factor of episodic accretion in protoplanetary disks. Within the model of a viscous disk, the accretion history is analyzed at different rates and regions of matter inflow from the envelope onto the disk. It is shown that the burst-like regime occurs in a wide range of parameters. The long-term evolution of the disk is modeled, including the decreasing-with-time matter inflow from the envelope. It is demonstrated that the disk becomes convectively unstable and maintains burst-like accretion onto the star for several million years. The general conclusion of the study is that convection can serve as one of the mechanisms of episodic accretion in protostellar disks, but this conclusion needs to be verified using more consistent hydrodynamic models.

In this work we applied the previously developed self-consistent 1D model of hydrogen-helium atmosphere with suprathermal electrons to close-in hot neptune GJ 436 b. The obtained height profile of density shows the two-scale structure of the planetary atmosphere. The mass-loss rate is found to be about .

We have studied the input of the exothermic photochemistry into the formation of the non-thermal escape flux in the transition H2 − H region of the extended upper atmosphere of the hot exoplanet - the sub-neptune π Men c. The formation rate and the energy spectrum of hydrogen atoms formed with an excess of kinetic energy due to the exothermic photochemistry forced by the stellar XUV radiation were calculated using a numerical kinetic Monte Carlo model of a hot planetary corona. The escape flux was estimated to be equal to 2.5×1012 cm−2s−1 for the mean level of stellar activity in the XUV radiation flux. This results in the mean estimate of the atmospheric loss rate due to the exothermic photochemistry equal to 6.7×108 g s−1. The calculated estimate is close to the observational estimates of the possible atmospheric loss rate for the exoplanet π Men c in the range less than 1.0×109 gs−1.

Acid mine drainage (AMD) commonly contains elevated concentrations of As(III) and/or As(V) due to oxidation of arsenic-containing sulfides. Bone char has been used as a low-cost filling material for passive treatment. The breakthrough curves of As(III) and As(V) were studied in column experiments conducted at different flow rates, adsorption cycle times, and with different coexisting cations and anions to compare their transport behaviours. The experimental data were fitted by the Convection- Diffusion Equation (CDE) and Thomas model with the aim of obtaining retardation factors of As(III) and As(V) and their maximum adsorption capacities, respectively. The maximum adsorption capacities of As(III) and As(V) are 0.214 and 0.335 mg/g, respectively. Coexisting Mn2+ and Al3+ ions can shorten the equilibrium time of As(V) adsorption from 25 h to 8 h, but they have little effect on As(III). The retardation factors of As(III) and As(V) calculated by the CDE model decrease with adsorption cycles from 37 to 20 and 51 to 32, respectively. The Mn2+ and Al3+ ions could enhance retention ability with adsorption cycle time, especially Mn2+ for As(V). Secondary adsorption phenomena were observed only in breakthrough curves of As(V) in the presence of Mn2+ and Al3+. The competitive influences of coexisting arsenic species is As(V) > As(III). Regeneration experiments using distilled water and NaOH solution were completed to quantify the degree of desorption of both As(III) and As(V). The results show that As(V) adsorbed on bone char has better desorption performance than As(III), and the average degrees of desorption of As(III) and As(V) for three desorption experiments are 75% and 31%, respectively.

Glaciers in the southern Himalayas advanced in the early Holocene despite an increase in incoming summer solar insolation at the top of the atmosphere. These glacier advances are in contrast to the smaller alpine glaciers in the western and northern regions of Central Asia. Two different glacier mass-balance models are used to reconcile this Holocene glacier history with climate by quantifying the change in equilibrium-line altitudes (ELA) for simulated changes in Holocene climate. Both ELA models clearly show that the lowering of ELAs in the southern Himalayas is largely due to a decrease in summer temperatures, and that an increase in monsoonal precipitation accounts for less than 30% of the total ELA changes. The decrease in summer temperatures is a dynamic response to the changes in solar insolation, resulting in both a decrease in incoming shortwave radiation at the surface due to an increase in cloudiness and an increase in evaporative cooling. In the western and northern zones of Central Asia, both ELA models show a rise in ELAs in response to a general increase in summer temperatures. This increase in temperatures in the more northern regions is a direct radiative response to the increase in summer solar insolation.

The actuation mechanism is a crucial aspect in the design of morphing structures due to the very stringent requirements involving actuation torque, consumed power, and allowable size and weight.

In the framework of the CRIAQ MD0-505 project, novel design strategies are investigated to enable morphing of aeronautical structures. This paper deals with the design of a morphing aileron with the main focus on the actuation technology. The morphing aileron consists of segmented 'finger-like' ribs capable of changing the aerofoil camber in order to match target aerodynamic shapes. In this work, lightweight and compact actuation kinematics driven by electromechanical actuators are investigated to actuate the morphing device. An unshafted distributed servo-electromechanical actuation arrangement is employed to realise the transition from the baseline configuration to a set of target aerodynamic shapes by also withstanding the aerodynamics loads. Numerical investigations are detailed to identify the optimal actuation architecture matching as well as the system integratability and structural compactness.

Mega-scale glacial lineations (MSGLs) are highly elongate subglacial bedforms associated with ice streaming. However, the link between MSGLs and rapid ice flow is largely qualitative, and there have been few attempts to quantitatively link their formation to ice flow characteristics (e.g. ice velocity, thickness, basal shear stress). We take measurements of MSGLs from a palaeo-ice stream that once occupied Marguerite Trough, Antarctic Peninsula and explore a range of possible correlations with ice dynamics generated from an ensemble of numerical modelling experiments that reproduce the deglaciation of the ice stream. Our results confirm that high mean ice velocities and a weak bed correlate with longer MSGLs. Furthermore, the height of MSGLs are low (2–3 m) where modelled basal shear stress is low, but their height tends to be higher and more variable where basal shear stress is larger. The mean density of MSGLs decreases as ice flux increases. Our analysis further suggests that the length of MSGLs is a function of basal ice velocity and time. Although our data/model correlations confirm the importance of ice velocity in MSGL formation, a significant challenge remains if we are to employ MSGLs as a quantifiable measure of past ice stream velocity.

We study a depth-averaged model of gravity-driven flows made ofsolid grains and fluid, moving over variable basal surface. In particular, we are interested in applicationsto geophysical flows such as avalanches and debris flows,which typically contain both solid material and interstitial fluid.The model system consists of mass and momentum balance equations for thesolid and fluid components, coupled together by both conservative and non-conservative terms involving the derivatives of the unknowns,and by interphase drag source terms. The system is hyperbolic at leastwhen the difference between solid and fluid velocities is sufficiently small.We solve numerically the one-dimensional model equations by a high-resolution finite volume scheme based on a Roe-type Riemann solver. Well-balancing oftopography source terms is obtained via a technique that includesthese contributions into the wave structure of the Riemann solution. We present and discuss several numerical experiments, including problemsof perturbed steady flows over non-flat bottom surface that show the efficient modeling of disturbances of equilibrium conditions.

Une étude de l'écoulement dans une soupape de décharge de turbocompresseur de suralimentation, est présentée dans ce travail. Une modélisation numérique tridimensionnelle de l'écoulement turbulent à travers la soupape a été entreprise en s'appuyant sur la résolution des équations de Navier-Stokes et d'énergie couplées à un modèle de turbulence de type k−ε. Cette modélisation a permis de fournir une connaissance fine des structures de l'écoulement à travers la soupape, et de prédire ses courbes caractéristiques de fonctionnement. À partir des résultats locaux de l'écoulement, le coefficient de débit de la soupape a été déterminé en fonction de sa levée. De même, à partir des données géométriques de la soupape, une modélisation analytique a été établie, en vue de donner le débit en fonction du taux de détente. Pour valider aussi bien le calcul par voie de simulation numérique que celui fourni par l'approche analytique proposée, nous avons utilisé un banc d'essai équipé d'un turbocompresseur à soupape de décharge pour automobile. La comparaison des courbes caractéristiques de fonctionnement obtenues à partir de notre travail avec celles des travaux expérimentaux antérieurs, a montré une bonne concordance.

The current status of the Haplosporidia is reviewed as well as recent information on Haplosporidium nelsoni, the causative agent of MSX disease in oysters. Recent molecular phylogenetic analyses with greatly increased taxon sampling support monophyly of the Haplosporidia and hypothesize placement of the group as sister taxon to the phylum Cercozoa. Oyster pathogens in the genus Bonamia should be considered haplosporidians based on molecular sequence data. Thus, the group contains 4 genera: Uropsoridium, Haplosporidium, Bonamia and Minchinia. Molecular phylogenetic analyses support monophyly of Urosporidium, Bonamia and Minchinia, but Haplosporidium forms a paraphyletic clade. Reports of haplosporidia worldwide are reviewed. Molecular detection assays have greatly increased our ability to rapidly and specifically diagnose important pathogens in the phylum and have also improved our understanding of the distribution and biology of H. nelsoni and H. costale. Much of the data available for H. nelsoni has been integrated into a mathematical model of host/parasite/environment interactions. Model simulations support hypotheses that recent H. nelsoni outbreaks in the NE United States are related to increased winter temperatures, and that a host other than oysters is involved in the life cycle. Evidence is presented that natural resistance to H. nelsoni has developed in oysters in Delaware Bay, USA. However, in Chesapeake Bay, USA H. nelsoni has intensified in historically low salinity areas where salinities have increased because of recent drought conditions. Efforts to mitigate the impact of H. nelsoni involve selective breeding programs for disease resistance and the evaluation of disease resistant non-native oysters.

The production of Antarctic Bottom Water is influenced by Ice Shelf Water which is formed due to the modification of shelf water masses under huge ice shelves. The coupling of inflow conditions, thermohaline processes at the ice shelf base and the sub-ice shelf circulation is studied with a two-dimensional thermohaline circulation model which has been developed for a section perpendicular to the ice shelf edge. Different boundary conditions appropriate to the Filchner Ice Shelf regime are considered. The model results indicate that, in general, shelf water is transported toward the grounding line, where at the ice shelf base melting occurs with a maximum rate of 1.5 my−1. Accumulation of ice takes place at the end of the melting zone close to the ice shelf edge with a rate on the order of 0.1 my−1. The location of this accumulation zone determines whether or not the density increase by salt rejection causes an upper circulation cell and the separation of the modified water mass from the ice shelf base at mid-range depth. At the ice shelf edge the simulated temperature, salinity, helium and δ18O values for the temperature minimum layer are typical for Ice Shelf Water. However the sub-ice shelf circulation is highly variable as well as sensitive to changes in boundary conditions. Moderate changes in the characteristics of the inflowing water or in sea-floor topography may double the intensity of the circulation. Non-linear processes in the accumulation zone cause variabilities which can be described by an ice shelf edge oscillator influencing the entire circulation regime.

In the Weddell Sea oceanographic data and numerical models demonstrate that Ice Shelf Water, one ingredient in the production of Weddell Sea Bottom Water, is formed by thermohaline interaction of High Salinity Shelf Water with the base of the Filchner-Ronne ice shelves. South of Berkner Island a passage with a water column thickness of about 300 m linking the Filchner and the Ronne regimes is important for the ventilation of the sub-ice shelf cavities. To simulate the flow we tested a two-dimensional thermohaline circulation model on several sections which approximate different geometries of a sub-ice shelf channel bounded by the ocean bottom and the ice shelf base. Temperature and salinity profiles measured in front of the Filchner-Ronne ice shelves are used to force the model. The results indicate that the circulation is sensitive to both salinity (density) forcing and depth of the shelf bottom prescribed at the open boundary representing the Ronne Ice Shelf edge. Where the shelf is shallow, 400 m deep, a closed circulation cell within the Ronne cavity acts like an ice pump with accumulation rates of marine ice at the ice shelf base up to 1.5 m y−1. The total outflow at the Ronne Ice Shelf edge is supported by an inflow from the Filchner regime. Where the shelf is deeper, a flow from the Ronne into the Filchner cavity develops if the bottom salinity at the Ronne Ice Shelf edge exceeds a critical value of 34.67. Seasonal variability imposed at both edges modifies the circulation pattern at the Filchner Ice Shelf edge such that the depth and magnitude of Ice Shelf Water outflow correspond with observations in the Filchner Depression.

Changes in water mass distribution and horizontal circulation due to seasonal influences on the Ross Sea continental shelf are investigated using a circumpolar numerical model. An anticyclonic circulation cell that extends across the open shelf and into the ice shelf cavity is formed in the model. The increased east–west density gradient caused by the strong brine release in the Ross Sea polynya in winter results in an intensification of this anticyclonic cell from 1.5 Sv to 2.5 Sv. This supports the concept of a thermohaline-driven horizontal circulation on the Ross Sea continental shelf. In addition to a temporal change in the circulation strength, the changes in the density structure lead to complex temporal and spatial variability in the circulation around Ross Island. Due to seasonal variation in circulation strength and water temperatures, the area averaged basal melt rate of 25 cm a−1 shows a bimodal seasonal cycle ranging from 20–28 cm a−1, with maxima in March and August.

Le modèle réalisé simule la dynamique d'une population phytoplanctonique composée de 8 espèces, sur le parcoursinférieur (310 km) d'une rivière eutrophe, en réponse aux conditions de température, lumière et nutriments. L'utilisationd'un modèle de type catastrophe appliqué aux conditions d'apparition d'un bloom de cyanophycées, de sa disparition et de ses effets sur les autres espèces est testé : celui-ci génère des phases de développement et de décroissance identiques à celles observées sur le milieu naturel considéré. De même, l'évolution de la composition du phytoplancton (Diatomées, Cyanophycées, Chlorophycées) est reproduite. Ce modèle basé sur des mesures en laboratoire de constantes spécifiques de croissance des algues permet une approche des conditions de développement et de succession des algues.

Un modèle de simulation numérique est proposé pour prédire en fonction du débit, de l'ensoleillement et des apports de nutriments, l'évolution de la biomasse de phytoplancton dans la série de plans d'eau qui se succèdent sur le cours canalisé de la rivière Lot. Ce modèle, basé sur les connaissances actuelles de la physiologie des algues, décrit en particulier les variations des constituants cellulaires (C, N , P, Chlorophylle) en fonction des conditions nutritives. La validité et la sensibilité du modèle sont testées par comparaison avec les résultats de deux séries de mesures réalisées sur une même masse d'eau, pendant son parcours vers l'aval, la première sur une distance de 50 km, la seconde sur une distance de 200 km.