147 research outputs found

    La lagune de Ghar El Melh : Diagnostic écologique et perspectives d'aménagement hydraulique

    Get PDF
    La lagune de Ghar El Melh, situĂ©e au Nord de la Tunisie (dans le Golfe de Tunis), est caractĂ©risĂ©e par une superficie de 28,5 km2, une faible profondeur et une faible communication avec la mer. Actuellement, sous l'effet des actions anthropiques (les rejets terrestres), elle connaĂźt une dĂ©gradation progressive de la qualitĂ© de ses eaux et sĂ©diments dont les consĂ©quences sont la chute de la richesse biologique et la rĂ©duction des ressources halieutiques de la lagune.Dans ce travail, nous prĂ©sentons les rĂ©sultats de l'analyse des caractĂ©ristiques physico-chimiques et biologiques des eaux de la lagune. Ces analyses montent bien l'hyper-eutrophisation du milieu caractĂ©risĂ© par de fortes concentrations des eaux en azote total et en phosphore total. Les rĂ©sultats de simulation du fonctionnement hydrodynamique, que nous avons rĂ©alisĂ©e Ă  l'aide d'un modĂšle Ă  2 dimensions intĂ©grĂ© sur la hauteur, montrent une stagnation des eaux dans environ 80% de surface de la lagune qui a fortement amplifiĂ© la dĂ©gradation de la qualitĂ© de l'Ă©cosystĂšme. Parmi plusieurs scĂ©narios d'amĂ©nagements simulĂ©s, nous proposons la crĂ©ation d'une nouvelle communication avec la mer dont la simulation hydrodynamique montre une nette augmentation des Ă©changes d'eau mer-lagune. Nous prĂ©sentons ensuite un modĂšle Ă©cologique homogĂšne de la lagune de Ghar El Melh qui a Ă©tĂ© mis au point et calibrĂ© en s'appuyant sur les mesures de terrain. Les simulations, avec ce modĂšle, montrent que l'arrĂȘt total des rejets terrestres et la crĂ©ation d'un nouveau grau rĂ©duisent considĂ©rablement l'eutrophisation du milieu ce qui conduiraient certainement Ă  une nette amĂ©lioration de la production halieutique dans la lagune.The Ghar El Melh lagoon is a Mediterranean water body, situated in Northeastern Tunisia, on the Northwestern side of the Gulf of Tunis. The Ghar El Melh lagoon is a vestigial part of the Utique Sea, and this lagoon was largely open at the time of the Roman invasion. Due to a combination of the shape of the coastline and alluvium deposits from the Medjerda River, this small gulf has become progressively closed from the Utique Sea, causing the lagoon to become progressively shaped to its present morphology. The coastal barrier separating the lagoon from the Mediterranean Sea was interrupted, allowing a permanent hydraulic communication across a local opening. The lagoon has an elliptical shape of approximately 28.5 km2 and an average depth of 0.8 m. Due to human activities within the lagoon itself and in the surrounding area, the lagoon ecosystem has suffered a progressive deterioration. This deterioration has led to a reduction in biodiversity resulting mainly in a decrease in fish resources and production.In order to improve the water quality of the lagoon for ecological and economical purposes, a diagnostic survey was carried out to characterize the present site conditions and to provide data for calibration of hydrodynamic and ecological models. The main results of the annual survey of biotic and non-biotic parameters demonstrated the existence of zones within the lagoon, with some seasonal variation. Thus, a decreasing biotic and non-biotic gradient was measured from the area of the lagoon under marine influence towards the bottom of the lagoon, under the continental and anthropogenic influence of the west side. The lagoon could be considered hypereutrophic with an annual average concentration of total phosphorus of 350 mg/m3. In order to conceptualize and optimise hydraulic structures for water quality improvement in the lagoon, a numerical model of the velocity fields (depth averaged) and water depth was used. The hydrodynamic model used was bi-dimensional, adapted for use in shallow lagoons. After model calibration using in-situ measurements, simulations were carried out to analyse the present hydrodynamic condition of the lagoon. Several stagnation zones were detected, which contributed to the altered water quality that was observed. Several management practices were proposed and simulated, aiming to control and improve the internal circulation and water exchange between the lagoon and the Mediterranean Sea. The main goal of these simulations was to improve water mobility inside the lagoon, and thus improve the water quality. The proposed hydraulic development measures consisted mainly of the creation of a new hydraulic communication in the south-eastern area of the lagoon, by dredging the south part of the lake or by channel creation in front of the new communication, reaching the stagnation zones of the lagoon. The impact assessment of the proposed development was verified with simulations using the bi-dimensional hydrodynamic model.An ecological model based on nitrogen and phosphorus cycling, was also developed for Ghar El Melh lagoon. It took into account one ecological compartment, the macro algae, that included Cladophora sp., Ulva sp. and Enteromorpha sp. Algae (A), inorganic nitrogen (NA), inorganic phosphorus (PA), organic nitrogen (NEorg) and organic phosphorus (PEorg), were the main variables of this model. After calibration of the model, a 10-yr simulation showed that all variables demonstrated a steady behaviour and that the lagoon eutrophication level remained. Model sensitivity analysis allowed the choice of some restoration scenarios and the prediction of their impacts on the ecological behaviour of the ecosystem. The simulations showed that wastewater load deviation combined with an increase in the sea-lagoon water exchange, instead of a decrease of nutrient diffusion from the sediments, led to a substantial decrease in the eutrophication level of the lagoon. Indeed, the annual average nutrient concentrations decreased from 270 to 60 mg/m3 for total nitrogen and from 350 to 20 mg/m3 for total phosphorus in the Ghar El Melh lagoon

    Analyse de sensibilitĂ© du systĂšme oasien et mesures de sauvegarde de l’oasis de MĂ©touia (Tunisie)

    Get PDF
    L’oasis de MĂ©touia, situĂ©e au sud‑est de la Tunisie, est caractĂ©risĂ©e par un climat aride oĂč les prĂ©cipitations sont rares et irrĂ©guliĂšres. L’oasis doit donc son existence aux eaux souterraines qui, autrefois, provenaient de sources artĂ©siennes actuellement taries suite Ă  une surexploitation de la nappe profonde. La pĂ©dogenĂšse actuelle est dominĂ©e par l’évolution des processus de salinisation et d’hydromorphie affectant en totalitĂ© ou en partie le profil pĂ©dologique. Cette salinisation est la rĂ©sultante des effets cumulĂ©s de la salinitĂ© des eaux d’irrigation et celle de la nappe phrĂ©atique proche de la surface dont la remontĂ©e capillaire gĂ©nĂšre des efflorescences salines. Ce facteur est accentuĂ© par l’absence de lessivage des sols et le dysfonctionnement du rĂ©seau de drainage. Le suivi des paramĂštres abiotiques de l’oasis durant quatre annĂ©es successives (2001 – 2004), a rĂ©vĂ©lĂ© une interdĂ©pendance Ă©troite entre la qualitĂ© des eaux prĂ©cĂ©demment dĂ©crite et les processus gĂ©ochimiques qui en rĂ©sultent, d’une part, et la dĂ©gradation de la zone non saturĂ©e, siĂšge des accumulations gypseuses, d’autre part. Par ailleurs, aux facteurs prĂ©cĂ©demment signalĂ©s, viennent s’ajouter la mauvaise exploitation des parcelles et l’absence de rĂšgles de gestion du systĂšme oasien dans sa globalitĂ©. Afin de contrecarrer ces phĂ©nomĂšnes qui affectent profondĂ©ment la sensibilitĂ© du systĂšme oasien, on a Ă©laborĂ© des recommandations visant l’optimisation des besoins dynamiques en eau, du mode de distribution, ainsi que du rĂ©seau de drainage freinant la remontĂ©e de la nappe et amĂ©liorant l’aĂ©ration et le lessivage de la zone non saturĂ©e.The MĂ©touia oasis is situated in south-eastern Tunisia near the coast of GabĂšs City. The climate is arid with rare and irregular precipitation events. The oasis originated from a confined subsurface that was hydraulically connected to surface springs that had already been exhausted by human activities. The soil features are presently dominated by the evolution of salinization and water-saturation processes either partially or totally affecting the soil profile. The visible salt deposits and soil salinization processes are generated by the salinity of irrigation water and the shallow water table as well as the rising capillarity head. These processes are strongly influenced by the weak soil leaching mechanisms, on the one hand, and the poor drainage schemes, on the other hand. The four-year monitoring programme (2001 – 2004) focussed on important abiotic water and soil parameters and showed a close relationship between water quality and the generated geochemical processes parallel to the degradation of the non-saturated zone, in which gypsum accumulation processes are taking place. In addition to the above mentioned factors, the poor land exploitation system and the lack of integrated management of the oasis system are also important. Due to the high sensitivity of the oasis and in order to overcome the problems, several recommendations were proposed concerning the optimization of the irrigation scheme, the water supply network and drainage schemes. The recommended hydraulic infrastructure, combined with the proposed management rules for the oasis, would lead to better control of ground-water fluctuations and improvement of leaching and aeration processes in the unsaturated zone

    Heat and fluid flow in a scraped-surface heat exchanger containing a fluid with temperature-dependent viscosity

    Get PDF
    Scraped-surface heat exchangers (SSHEs) are extensively used in a wide variety of industrial settings where the continuous processing of fluids and fluid-like materials is involved. The steady non-isothermal flow of a Newtonian fluid with temperature-dependent viscosity in a narrow-gap SSHE when a constant temperature difference is imposed across the gap between the rotor and the stator is investigated. The mathematical model is formulated and the exact analytical solutions for the heat and fluid flow of a fluid with a general dependence of viscosity on temperature for a general blade shape are obtained. These solutions are then presented for the specific case of an exponential dependence of viscosity on temperature. Asymptotic methods are employed to investigate the behaviour of the solutions in several special limiting geometries and in the limits of weak and strong thermoviscosity. In particular, in the limit of strong thermoviscosity (i.e., strong heating or cooling and/or strong dependence of viscosity on temperature) the transverse and axial velocities become uniform in the bulk of the flow with boundary layers forming either just below the blade and just below the stationary upper wall or just above the blade and just above the moving lower wall. Results are presented for the most realistic case of a linear blade which illustrate the effect of varying the thermoviscosity of the fluid and the geometry of the SSHE on the flow

    Change, stress and sustainability: aquatic ecosystem resilience in North Africa

    Get PDF
    Summary report of a workshop held at the Institute Scientifique, University Mohammed V, Rabat, Morocco, 2-5th December 1998. Cassarina report no. 4

    Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone : Insights from the Otway Basin, SE Australia

    Get PDF
    This research forms part of a PhD project supported by the Australian Research Council [Discovery Project DP160101158] and through an Australian Government Research Training Program Scholarship. Dave Healy acknowledges the support of the Natural Environment Research Council (NERC, UK) through the award NE/N003063/1 ‘Quantifying the Anisotropy of Permeability in Stressed Rock’. This study was also funded by scholarships from the Petroleum Exploration Society of Australia and the Australian Petroleum Production and Exploration Association. We thank Gordon Holm for preparing thin sections and Colin Taylor for carrying out particle size measurements and mercury injection capillary pressure analyses. Aoife McFadden and David Kelsey from Adelaide Microscopy, Braden Morgan, and Sophie Harland are acknowledged for their assistance with laboratory work. Field assistants James Hall, Rowan Hansberry, and Lachlan Furness are also gratefully acknowledged for their assistance with sample collection. Discussions with Ian Duddy on the mineralogy of the Eumeralla Formation are also greatly appreciated. This forms TRaX record 416.Peer reviewedPublisher PD

    A multiple spacecraft detection of the 2 April 2022 M-class flare and filament eruption during the first close Solar Orbiter perihelion

    Get PDF
    CONTEXT: The Solar Orbiter mission completed its first remote-sensing observation windows in the spring of 2022. On 2 April 2022, an M-class flare followed by a filament eruption was seen both by the instruments on board the mission and from several observatories in Earth’s orbit, providing an unprecedented view of a flaring region with a large range of observations. AIMS: We aim to understand the nature of the flaring and filament eruption events via the analysis of the available dataset. The complexity of the observed features is compared with the predictions given by the standard flare model in 3D. METHOD: In this paper, we use the observations from a multi-view dataset, which includes extreme ultraviolet (EUV) imaging to spectroscopy and magnetic field measurements. These data come from the Interface Region Imaging Spectrograph, the Solar Dynamics Observatory, Hinode, as well as several instruments on Solar Orbiter. RESULTS: The large temporal coverage of the region allows us to analyse the whole sequence of the filament eruption starting with its pre-eruptive state. Information given by spectropolarimetry from SDO/HMI and Solar Orbiter PHI/HRT shows that a parasitic polarity emerging underneath the filament is responsible for bringing the flux rope to an unstable state. As the flux rope erupts, Hinode EIS captures blue-shifted emission in the transition region and coronal lines in the northern leg of the flux rope prior to the flare peak. This may be revealing the unwinding of one of the flux rope legs. At the same time, Solar Orbiter SPICE captures the whole region, complementing the Doppler diagnostics of the filament eruption. Analyses of the formation and evolution of a complex set of flare ribbons and loops, of the hard and soft X-ray emissions with STIX, show that the parasitic emerging bipole plays an important role in the evolution of the flaring region. CONCLUSIONS: The extensive dataset covering this M-class flare event demonstrates how important multiple viewpoints and varied observations are in order to understand the complexity of flaring regions. While the analysed data are overall consistent with the standard flare model, the present particular magnetic configuration shows that surrounding magnetic activity such as nearby emergence needs to be taken into account to fully understand the processes at work. This filament eruption is the first to be covered from different angles by spectroscopic instruments, and provides an unprecedented diagnostic of the multi-thermal structures present before and during the flare. This complete dataset of an eruptive event showcases the capabilities of coordinated observations with the Solar Orbiter mission

    Oral HPV infection and MHC class II deficiency (A study of two cases with atypical outcome)

    Get PDF
    <p>Abstract</p> <p>Background</p> <p>Major histocompatibility complex class II deficiency, also referred to as bare lymphocyte syndrome is a rare primary Immunodeficiency disorder characterized by a profondly deficient human leukocyte antigen class II expression and a lack of cellular and humoral immune responses to foreign antigens. Clinical manifestations include extreme susceptibility to viral, bacterial, and fungal infections. The infections begin in the first year of life and involve usually the respiratory system and the gastrointestinal tract. Severe malabsorption with failure to thrive ensues, often leading to death in early childhood. Bone marrow transplantation is the curative treatment.</p> <p>Case reports</p> <p>Here we report two cases with a late outcome MHC class II deficiency. They had a long term history of recurrent bronchopulmonary and gastrointestinal infections. Bone marrow transplantation could not be performed because no compatible donor had been identified. At the age of 12 years, they developed oral papillomatous lesions related to HPV (human papillomavirus). The diagnosis of HPV infection was done by histological examination. HPV typing performed on the tissue obtained at biopsy showed HPV type 6. The lesions were partially removed after two months of laser treatment.</p> <p>Conclusions</p> <p>Viral infections are common in patients with MHC class II and remain the main cause of death. Besides warts caused by HPV infection do not exhibit a propensity for malignant transformation; they can cause great psychosocial morbidity.</p

    Modelling credit spreads with time volatility, skewness, and kurtosis

    Get PDF
    This paper seeks to identify the macroeconomic and financial factors that drive credit spreads on bond indices in the US credit market. To overcome the idiosyncratic nature of credit spread data reflected in time varying volatility, skewness and thick tails, it proposes asymmetric GARCH models with alternative probability density functions. The results show that credit spread changes are mainly explained by the interest rate and interest rate volatility, the slope of the yield curve, stock market returns and volatility, the state of liquidity in the corporate bond market and, a heretofore overlooked variable, the foreign exchange rate. They also confirm that the asymmetric GARCH models and Student-t distributions are systematically superior to the conventional GARCH model and the normal distribution in in-sample and out-of-sample testing

    EnGraft: a multicentre, open-label, randomised, two-arm, superiority study protocol to assess bioavailability and practicability of Envarsus¼ versus Advagrafℱ in liver transplant recipients

    Get PDF
    Background Graft rejection and chronic CNI toxicity remain obstacles to organ transplant success. Current formulations of tacrolimus, such as Prograf¼ and Advagrafℱ, exhibit limitations in terms of pharmacokinetics and tolerability, related in part to suboptimal bioavailability. As dosing non-compliance can result in graft rejection, the once daily formulation of tacrolimus, Advagrafℱ, was developed (vs 2x/day Prograf¼). Benefits of Advagrafℱ are counterbalanced by delayed achievement of therapeutic trough levels and need for up to 50% higher doses to maintain Prograf¼-equivalent troughs. Envarsus¼ is also a prolonged-release once-daily tacrolimus formulation, developed using MeltDoseℱ drug-delivery technology to increase drug bioavailability; improved bioavailability results in low patient drug absorption variability and less pronounced peak-to-trough fluctuations. In phase III de novo kidney transplant studies, Envarsus¼ proved non-inferior to twice-daily tacrolimus; however, no phase IV studies show superiority of Envarsus¼ vs Advagrafℱ in de novo liver transplant (LTx) recipients. Methods The EnGraft compares bioavailability and tests superiority of Envarsus¼ (test arm) versus Advagrafℱ (comparator arm) in de novo LTx recipients. A total of 268 patients from 15 German transplant centres will be randomised 1:1 within 14 days post-LTx. The primary endpoint is dose-normalised trough level (C/D ratio) measured 12 weeks after randomisation. Secondary endpoints include the number of dose adjustments, time to reach first defined trough level and incidence of graft rejections. Additionally, clinical and laboratory parameters will be assessed over a 3-year period. Discussion C/D ratio is an estimate for tacrolimus bioavailability. Improving bioavailability and increasing C/D ratio using Envarsus could reduce renal dysfunction and other tacrolimus-related toxicities; previous trials have shown that a higher C/D ratio (i.e. slower tacrolimus metabolism) is not only associated with improved renal function but also linked to reduced neurotoxic side effects. A higher C/D ratio could improve clinical outcomes for LTx recipients; EnGraft has begun, with one third of patients recruited by January 2022

    Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

    Get PDF
    Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P &lt; 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely
    • 

    corecore