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

Evidence for Model-based Computations in the Human Amygdala during Pavlovian Conditioning

Contemporary computational accounts of instrumental conditioning have emphasized a role for a model-based system in which values are computed with reference to a rich model of the structure of the world, and a model-free system in which values are updated without encoding such structure. Much less studied is the possibility of a similar distinction operating at the level of Pavlovian conditioning. In the present study, we scanned human participants while they participated in a Pavlovian conditioning task with a simple structure while measuring activity in the human amygdala using a high-resolution fMRI protocol. After fitting a model-based algorithm and a variety of model-free algorithms to the fMRI data, we found evidence for the superiority of a model-based algorithm in accounting for activity in the amygdala compared to the model-free counterparts. These findings support an important role for model-based algorithms in describing the processes underpinning Pavlovian conditioning, as well as providing evidence of a role for the human amygdala in model-based inference

γ-Hemolysin oligomeric structure and effect of its formation on supported lipid bilayers: An AFM Investigation.

γ-Hemolysins are bicomponent β-barrel pore forming toxins produced by Staphylococcus aureus as water-soluble monomers, which assemble into oligomeric pores on the surface of lipid bilayers. Here, after investigating the oligomeric structure of γ-hemolysins on supported lipid bilayers (SLBs) by atomic force microscopy (AFM), we studied the effect produced by this toxin on the structure of SLBs. We found that oligomeric structures with different number of monomers can assemble on the lipid bilayer being the octameric form the most stable one. Moreover, in this membrane model we found that γ-hemolysins can form clusters of oligomers inducing a curvature in the lipid bilayer, which could probably enhance the aggressiveness of these toxins at high concentrations

Memory, learning and language in autism spectrum disorder

Background and aims: The ‘dual-systems’ model of language acquisition has been used by Ullman and colleagues to explain patterns of strength and weakness in the language of higher-functioning people with autism spectrum disorder (ASD). Specifically, intact declarative/explicit learning is argued to compensate for a deficit in non-declarative/implicit procedural learning, constituting an example of the so-called ‘see-saw’ effect. Ullman and Pullman (2015) extended their argument concerning a see-saw effect on language in ASD to cover other perceived anomalies of behaviour, including impaired acquisition of social skills. The aim of this paper is to present a critique of Ullman and colleagues’ claims, and to propose an alternative model of links between memory systems and language in ASD. Main contribution: We argue that a 4-systems model of learning, in which intact semantic and procedural memory are used to compensate for weaknesses in episodic memory and perceptual learning, can better explain patterns of language ability across the autistic spectrum. We also argue that attempts to generalise the ‘impaired implicit learning/spared declarative learning’ theory to other behaviours in ASD are unsustainable. Conclusions: Clinically significant language impairments in ASD are under-researched, despite their impact on everyday functioning and quality of life. The relative paucity of research findings in this area lays it open to speculative interpretation which may be misleading. Implications: More research is need into links between memory/learning systems and language impairments across the spectrum. Improved understanding should inform therapeutic intervention, and contribute to investigation of the causes of language impairment in ASD with potential implications for prevention

Fracture Propagation Driven by Fluid Outflow from a Low-permeability Aquifer

Deep saline aquifers are promising geological reservoirs for CO2 sequestration if they do not leak. The absence of leakage is provided by the caprock integrity. However, CO2 injection operations may change the geomechanical stresses and cause fracturing of the caprock. We present a model for the propagation of a fracture in the caprock driven by the outflow of fluid from a low-permeability aquifer. We show that to describe the fracture propagation, it is necessary to solve the pressure diffusion problem in the aquifer. We solve the problem numerically for the two-dimensional domain and show that, after a relatively short time, the solution is close to that of one-dimensional problem, which can be solved analytically. We use the relations derived in the hydraulic fracture literature to relate the the width of the fracture to its length and the flux into it, which allows us to obtain an analytical expression for the fracture length as a function of time. Using these results we predict the propagation of a hypothetical fracture at the In Salah CO2 injection site to be as fast as a typical hydraulic fracture. We also show that the hydrostatic and geostatic effects cause the increase of the driving force for the fracture propagation and, therefore, our solution serves as an estimate from below. Numerical estimates show that if a fracture appears, it is likely that it will become a pathway for CO2 leakage.Comment: 21 page

Neural correlates of specific and general Pavlovian-to-Instrumental Transfer within human amygdalar subregions: a high-resolution fMRI study

It is widely held that the interaction between instrumental and Pavlovian conditioning induces powerful motivational biases. Pavlovian-Instrumental Transfer (PIT) is one of the key paradigms demonstrating this effect, which can further be decomposed into a general and specific component. Although these two forms of PIT have been studied at the level of amygdalar subregions in rodents, it is still unknown whether they involve different areas of the human amygdala. Using a high-resolution fMRI (hr-fMRI) protocol optimized for the amygdala in combination with a novel free operant task designed to elicit effects of both general and specific PIT, we demonstrate that a region of ventral amygdala within the boundaries of the basolateral complex and the ventrolateral putamen are involved in specific PIT, while a region of dorsal amygdala within the boundaries of the centromedial complex is involved in general PIT. These results add to a burgeoning literature indicating different functional contributions for these different amygdalar subregions in reward-processing and motivation

Staphylococcal Panton-Valentine Leucocidin as a Major Virulence Factor Associated to Furuncles

Panton-Valentine Leucocidin (PVL), one of the β-barrel pore-forming staphylococcal leucotoxins, is known to be associated to furuncles and some severe community pneumonia. However, it is still uncertain how many other virulence factors are also associated to furuncles and what the risk factors of furuncles are in immuno-compromised status of patients, especially the HIV (+) patients. In this paper, we use antigen immunoprecipitation and multiplex PCR approach to determine the presence of 19 toxins, 8 adhesion factors and the PFGE profiles associated to furuncles in three independent patient study groups of S. aureus (SA) isolates collected from the Cayenne General Hospital (French Guiana). The patient groups were made of: 16 isolates from HIV (−) patients, 9 from HIV (+) patients suffering from furuncles, and 30 control isolates from patients with diverse secondary infected dermatitis. Our data reveals that the majority (96%) of SA strains isolated from HIV patient-derived furuncles significantly produced PVL (p<10−7), whereas only 10% of SA strains produced this toxin in secondary infected dermatosis. A high prevalence of LukE-LukD-producing isolates (56 to 78%) was recorded in patient groups. Genes encoding clumping factor B, collagen- and laminin-binding proteins (clfB, cna, lbp, respectively) were markedly frequent (30 to 55%), without being associated to a specific group. Pulse field gel electrophoresis evidenced 24 overall pulsotypes, whereas the 25 PVL-producing isolates were distributed into 15 non clonal fingerprints. These pulsotypes were not specific PVL-producing isolates. PVL appears to be the major virulence factor associated to furuncles in Europe and in South America regardless of the immune status of the HIV patients

Toxins and adhesion factors associated with Staphylococcus aureus strains isolated from diarrhoeal patients in Benin

Staphylococcus aureus is a causative agent of acute and infectious diarrhoea. In Africa, there is no sufficient information on the virulence and the degree of factors produced by its diarrhoea-isolated strains. Clinical features and virulence factors produced by S. aureus isolated from diarrhoeal-patients admitted at the Hospital Hubert Koutoukou Maga (HKM) in Cotonou was investigated. The virulence factors were screened by radial immunoprecipitation and multiplex polymerase chain reaction (PCR).Fifteen antibiotics were tested. Among independent 115 patients examined for diarrhoea, 32 had faeces positive for S. aureus isolated as pure culture. Most of these patients were hospitalized (21/32) and developed aqueous, bloody and painful diarrhoea, after antimicrobial therapy. About 62% were resistant to oxacillin. Genes encoding for clumping factor B and for laminin binding protein were detected in 62% of S. aureus isolates. About 94% of LukE-LukD producing strains have been isolated from patientsdeveloping post-antibiotic associated diarrhoea (PAAD). The Panton-Valentine Leucocidin (PVL) was produced by 19% of isolates, all from PAAD. This study points out new data concerning virulencefactors and adhesion factor produced by S. aureus strains isolated from diarrhoea in Benin. The culture of the faeces will not always allow the diagnosis. It is important to update a technique, which enablesresearchers to carry out the virulence factors produced by these bacteria

Analysis of steroid hormones and their conjugated forms in water and urine by on-line solid-phase extraction coupled to liquid chromatography tandem mass spectrometry

Background: In recent years, endocrine disrupting compounds (EDCs) have been found in rivers that receive significant inputs of wastewater. Among EDCs, natural and synthetic steroid hormones are recognized for their potential to mimic or interfere with normal hormonal functions (development, growth and reproduction), even at ultratrace levels (ng L-1). Although conjugated hormones are less active than free hormones, they can be cleaved and release the unconjugated estrogens through microbial processes before or during the treatment of wastewater. Due to the need to identify and quantify these compounds, a new fully automated method was developed for the simultaneous determination of the two forms of several steroid hormones (free and conjugated) in different water matrixes and in urine.Results: The method is based on online solid phase extraction coupled with liquid chromatography and tandem mass spectrometry (SPE-LC-MS/MS). Several parameters were assessed in order to optimize the efficiency of the method, such as the type and flow rate of the mobile phase, the various SPE columns, chromatography as well as different sources and ionization modes for MS. The method demonstrated good linearity (R-2 &gt; 0.993) and precision with a coefficient of variance of less than 10 %. The quantification limits vary from a minimum of 3-15 ng L-1 for an injection volume of 1 and 5 mL, respectively, with the recovery values of the compounds varying from 72 to 117 %.Conclusion: The suggested method has been validated and successfully applied for the simultaneous analysis of several steroid hormones in different water matrixes and in urine