Simulation numérique de la sédimentation dans les retenues de barrages : cas de la retenue de Zardezas, Algérie

La construction d'un modèle numérique destiné à prédire la formation et l'évolution de dépôts de sédiments à l'amont d'un barrage est présentée. A partir d'informations sur les apports en eau et en sédiments en provenance du bassin versant consolidées par une analyse hydrologique en QdF, un modèle hydraulique bidimensionnel horizontal couplant équations de Saint Venant et une équation de convection-diffusion est mis en œuvre. L'application de ce modèle sur la retenue de Zardezas de la région de Skikda (Algérie) montre, à la fois, les difficultés pratiques rencontrées dans la mise en œuvre et l'apport possible d'une telle méthode pour la gestion des retenues algériennes.Sedimentation rates are often very high in Algeria, reaching about 1% of the reservoir volume per year in most cases. The management of existing reservoirs and the choice of location of new reservoirs may be improved by using a numerical model that simulates sediment deposition. The proposed method was developed on a selected case for which a convenient set of data had been gathered.Initially, the Zardezas reservoir had a capacity of 34 million m3, but presently, the capacity is only 17 million m3. Due to the levelling of two topographies in 1975 and 1986 and discharge data available from 1968 to 1993, the numerical model could be calibrated for the period 1975-1986.As the cross-distribution of sediments is thought to be a main factor for the reservoir deposition rate, a 2-D horizontal hydrodynamic model was selected. Sediments were modelled by a concentration that was calculated using an advection-diffusion equation. A source term determining the exchange rate between the flow and the bottom as proportional to an equilibrium concentration was used. Calculation of this source term followed a simplified version of the method developed by VAN RIJN (1984). The set of 4 equations ((8) + (9) + (10) + (11)) was solved by a second-order explicit finite volume scheme of the Godunov type, which allows the modelling of very unsteady flows (PAQUIER, 1998). The bottom elevation was modified at every time step by distributing the calculated deposits inside one cell among the neighbouring vertices.Globally, the proposed method should be carried out in two steps. The first step involved model calibration including a hydrological analysis in order to determine the inputs (water and sediments) during the calibration period and calculation of the features of the hydrological regime for the extrapolation periods. The second step involved use if the model to define management strategies. The hydrological scenarios are built from the hydrological regime and the 2-D model is used to calculate the sediment deposits for every scenario. This second step is not described in the present paper.The hydrological analysis involved building QdF (flood-duration-frequency) curves (JAVELLE et al., 2000) from the daily discharges and from the maximum discharges of the rarest floods. Some flood discharge hydrographs were considered and were used to determine the duration of typical floods. Results from this hydrological analysis are summarised by curves in V(d,T) (Table 2) (maximum mean stream flows during the duration d for a return period T) and Q(d,T) (Table 3) (maximum over-threshold during stream flows for T) which were built from the converging QdF model developed by JAVELLE et al. (1999). The main catchment parameters D (characteristic flood duration) and the instantaneous peak discharge over a return period of 10 years were respectively equal to 4 hours and 362 m3 /s. For the estimate of the curves over a return period of 10 years, the gradex of maximum 24 hour rainfalls (estimated to be 24.7 mm) was used. From Table 3 of Q(d,T), mono frequency synthetic discharge hydrographs (HSMF) can be built (e.g. Figure 4) using a rising time equal to D. These hydrographs can be used to define hydrological scenarios by fixing the successive return periods (of the HSMF).For the calibration period 1975 to 1986, the observed or reconstituted discharge hydrographs were used to be closer to real events (Table 4). Because concentrations were not registered precisely enough, simplified assumptions were used for the calibration period and should be kept for future scenarios (peak concentration was fixed to 100 kg/m3 and a linear relation between discharge and concentration was assumed during the flood (see Figure 5)). Only one class of sediment with a mean diameter of 0.1 mm was considered. The 2-D calculations were performed on a grid of 1005 cells (Figure 6) with a space step between 10 and 80 metres. Model calibration consisted of selecting a suitable coefficient a (in equation (12)), which is equivalent to the average distance required to reach the equilibrium concentration. For the period 1975-1986, the calculation provides 4 m thick deposits through the entire reservoir bottom (Figure 8). The discrepancies with measurements were mainly too few deposits near the dam and too much sediment accumulated on the banks of the reservoir (Figures 7 to 9). It can be concluded that the proposed method provides useful results although some improvements are required such as: sediment exchange relations between the flow and the bottom; refining the calculation grid and reducing the uncertainty about the inputs by accurately and regularly measuring both discharge and sediment concentrations. The method should be further validated on other existing reservoirs in the same hydroclimatic context

Aurora kinase A drives the evolution of resistance to third-generation EGFR inhibitors in lung cancer.

Although targeted therapies often elicit profound initial patient responses, these effects are transient due to residual disease leading to acquired resistance. How tumors transition between drug responsiveness, tolerance and resistance, especially in the absence of preexisting subclones, remains unclear. In epidermal growth factor receptor (EGFR)-mutant lung adenocarcinoma cells, we demonstrate that residual disease and acquired resistance in response to EGFR inhibitors requires Aurora kinase A (AURKA) activity. Nongenetic resistance through the activation of AURKA by its coactivator TPX2 emerges in response to chronic EGFR inhibition where it mitigates drug-induced apoptosis. Aurora kinase inhibitors suppress this adaptive survival program, increasing the magnitude and duration of EGFR inhibitor response in preclinical models. Treatment-induced activation of AURKA is associated with resistance to EGFR inhibitors in vitro, in vivo and in most individuals with EGFR-mutant lung adenocarcinoma. These findings delineate a molecular path whereby drug resistance emerges from drug-tolerant cells and unveils a synthetic lethal strategy for enhancing responses to EGFR inhibitors by suppressing AURKA-driven residual disease and acquired resistance

The apparent eta Carinae's long-term evolution and the critical role played by the strengthening of P Cygni absorption lines

Over the entire 20th century, Eta Carinae (\ec) has displayed a unique spectrum, which recently has been evolving towards that of a typical LBV. The two competing scenarios to explain such evolution are: (1) a dissipating occulter in front of a stable star or (2) a decreasing mass loss rate of the star. The first mechanism simultaneously explains why the central star appears to be secularly increasing its apparent brightness while its luminosity does not change; why the Homunculus' apparent brightness remains almost constant; and why the spectrum seen in direct light is becoming more similar to that reflected from the Homunculus (and which resembles a typical LBV). The second scenario does not account for these facts and predicts an increase in the terminal speed of the wind, contrary to observations. In this work, we present new data showing that the P Cygni absorption lines are secularly strengthening, which is not the expected behaviour for a decreasing wind-density scenario. CMFGEN modelling of the primary's wind with a small occulter in front agrees with observations. One could argue that invoking a dissipating coronagraphic occulter makes this object even more peculiar than it already appears to be. However, on the contrary, it solves the apparent contradictions between many observations. Moreover, by assigning the long-term behaviour to circumstellar causes and the periodic variations due to binarity, a star more stable after the 1900s than previously thought is revealed, contrary to the earlier paradigm of an unpredictable object.Comment: 17 pages, 12 figures, submitted to MNRA

Selenium Toxicity to Honey Bee (Apis mellifera L.) Pollinators: Effects on Behaviors and Survival

We know very little about how soil-borne pollutants such as selenium (Se) can impact pollinators, even though Se has contaminated soils and plants in areas where insect pollination can be critical to the functioning of both agricultural and natural ecosystems. Se can be biotransferred throughout the food web, but few studies have examined its effects on the insects that feed on Se-accumulating plants, particularly pollinators. In laboratory bioassays, we used proboscis extension reflex (PER) and taste perception to determine if the presence of Se affected the gustatory response of honey bee (Apis mellifera L., Hymenoptera: Apidae) foragers. Antennae and proboscises were stimulated with both organic (selenomethionine) and inorganic (selenate) forms of Se that commonly occur in Se-accumulating plants. Methionine was also tested. Each compound was dissolved in 1 M sucrose at 5 concentrations, with sucrose alone as a control. Antennal stimulation with selenomethionine and methionine reduced PER at higher concentrations. Selenate did not reduce gustatory behaviors. Two hours after being fed the treatments, bees were tested for sucrose response threshold. Bees fed selenate responded less to sucrose stimulation. Mortality was higher in bees chronically dosed with selenate compared with a single dose. Selenomethionine did not increase mortality except at the highest concentration. Methionine did not significantly impact survival. Our study has shown that bees fed selenate were less responsive to sucrose, which may lead to a reduction in incoming floral resources needed to support coworkers and larvae in the field. If honey bees forage on nectar containing Se (particularly selenate), reductions in population numbers may occur due to direct toxicity. Given that honey bees are willing to consume food resources containing Se and may not avoid Se compounds in the plant tissues on which they are foraging, they may suffer similar adverse effects as seen in other insect guilds

A systematic review of clinical trials of pharmacological interventions for acute ischaemic stroke (1955-2008) that were completed, but not published in full

<p>Abstract</p> <p>Background</p> <p>We assessed the prevalence, and potential impact of, trials of pharmacological agents for acute stroke that were completed but not published in full. Failure to publish trial data is to be deprecated as it sets aside the altruism of participants' consent to be exposed to the risks of experimental interventions, potentially biases the assessment of the effects of therapies, and may lead to premature discontinuation of research into promising treatments.</p> <p>Methods</p> <p>We searched the Cochrane Stroke Group's Specialised Register of Trials in June 2008 for completed trials of pharmacological interventions for acute ischaemic stroke, and searched MEDLINE and EMBASE (January 2007 - March 2009) for references to recent full publications. We assessed trial completion status from trial reports, online trials registers and correspondence with experts.</p> <p>Results</p> <p>We identified 940 trials. Of these, 125 (19.6%, 95% confidence interval 16.5-22.6) were completed but not published in full by the point prevalence date. They included 16,058 participants (16 trials had over 300 participants each) and tested 89 different interventions. Twenty-two trials with a total of 4,251 participants reported the number of deaths. In these trials, 636/4251 (15.0%) died.</p> <p>Conclusions</p> <p>Our data suggest that, at the point prevalence date, a substantial body of evidence that was of relevance both to clinical practice in acute stroke and future research in the field was not published in full. Over 16,000 patients had given informed consent and were exposed to the risks of therapy. Responsibility for non-publication lies with investigators, but pharmaceutical companies, research ethics committees, journals and governments can all encourage the timely publication of trial data.</p

High-dose pantoprazole continuous infusion is superior to somatostatin after endoscopic hemostasis in patients with peptic ulcer bleeding

BACKGROUND: The best antisecretory treatment after endoscopic hemostasis in patients with ulcer bleeding is still in quest. OBJECTIVES: To compare pantoprazole and somatostatin continuous infusion after endoscopic hemostasis in patients with bleeding peptic ulcers. PATIENTS AND METHODS: A total of 164 consecutive patients with a bleeding peptic ulcer, after successful endoscopic hemostasis, were randomly assigned to receive, double blindly, continuous IV infusion of pantoprazole 8 mg/h for 48 h after a bolus of 40 mg (group P) or somatostatin 250 μg/h for 48 h after a bolus of 250 μg (group-S). Twenty-four-hour pH-metry was performed in the last 30 patients in each group. Endoscopy was performed, in case of bleeding nonrecurrence, every 48 h until disappearance of stigmata. RESULTS: Bleeding recurrence: group S 14 patients (17%) versus group P 4 (5%) (P = 0.046). In multivariate analysis, bleeding recurrence was 4.57 (CI 1.31-15.91) times more frequent in group S (P = 0.02). There was no difference in the need for surgery and mortality. Acid suppression over pH 6: group S 82.9% of the time versus group P 81.5% (P = 0.97). Acid suppression over pH 6 for >85% of the time: group S 14 (47%) patients versus group P 17 (57%) (P = 0.44). Disappearance of endoscopic stigmata after 48 h: group S 25/68 patients (37%) versus group P 72/78 (92%) (P < 0.0001). No major side effects identified in either study group. CONCLUSIONS: In patients with a bleeding ulcer, after successful endoscopic hemostasis, despite equipotent acid suppression, pantoprazole continuous infusion was superior to somatostatin to prevent bleeding recurrence and quick disappearance of the endoscopic stigmata. Nevertheless, no differences were seen in the need for surgery and mortality. © 2007 by Am. Coll. of Gastroenterology

The Expansion of the X-Ray Nebula Around η Car

The massive colliding wind binary system η Car is embedded in an X-ray emitting region having a characteristic temperature of a few million degrees, associated with ejecta produced during the 1840s, and in earlier outbursts. We use CHANDRA X-ray imaging observations obtained over the past two decades to directly measure the expansion of the X-ray nebula for the first time. A combined CHANDRA/ACIS image shows a faint, nearly uniform elliptic structure. This faint elliptical “shell” has a similar orientation and shape as the Homunculus nebula but is about 3 times larger. We measure proper motions of brighter regions associated with the X-ray emitting ring. We compare spectra of the soft X-ray emitting plasma in CHANDRA/ACIS and XMM-Newton PN observations and show that the PN observations indicate a decline in X-ray flux which is comparable to that derived from NICER observations. We associate the diffuse elliptical emission surrounding the bright X-ray “ring” with the blast wave produced during the Great Eruption. We suggest that the interaction of this blast wave with pre-existing clumps of ejecta produces the bright, broken X-ray emitting ring. We extrapolate the trend in X-ray energy back to the time of the Great Eruption using a simple model and show that the X-ray energy was comparable to the kinetic energy of the Homunculus, suggesting equipartition of energy between fast, low-density ejecta and slower, dense ejecta. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

RIT1 oncoproteins escape LZTR1-mediated proteolysis.

RIT1 oncoproteins have emerged as an etiologic factor in Noonan syndrome and cancer. Despite the resemblance of RIT1 to other members of the Ras small guanosine triphosphatases (GTPases), mutations affecting RIT1 are not found in the classic hotspots but rather in a region near the switch II domain of the protein. We used an isogenic germline knock-in mouse model to study the effects of RIT1 mutation at the organismal level, which resulted in a phenotype resembling Noonan syndrome. By mass spectrometry, we detected a RIT1 interactor, leucine zipper-like transcription regulator 1 (LZTR1), that acts as an adaptor for protein degradation. Pathogenic mutations affecting either RIT1 or LZTR1 resulted in incomplete degradation of RIT1. This led to RIT1 accumulation and dysregulated growth factor signaling responses. Our results highlight a mechanism of pathogenesis that relies on impaired protein degradation of the Ras GTPase RIT1