Nanofiltration de solutions de nitrate d'ammonium. Etude des paramètres influents

Cet article propose une étude de la rétention du nitrate d'ammonium par une membrane commerciale de nanofiltration (Nanomax 50). Les effets de la pression, de la concentration et de la vitesse d'écoulement tangentiel ont été étudiés avec le souci d'une meilleure compréhension du mécanisme de transport des ions nitrate et en vue d'une optimisation de la rétention. Le taux de rétention des ions nitrate augmente dans un premier temps avec la pression, atteint un maximum puis diminue. La rétention, pour des pressions élevées, peut cependant être améliorée en augmentant la vitesse d'écoulement tangentiel. La séparation résulterait d'un rapport de différentes forces : une force d'entraînement radial dans le pore (illustrée par l'effet de la pression transmembranaire), une force d'entraînement tangentiel vers le rétentat (illustrée par l'effet de la vitesse d'écoulement tangentiel) et une force de surface traduisant les interactions membrane-soluté (illustrée par l'effet de la concentration). L'équation de Spiegler et Kedem est proposée en première approche de modélisation pour une valeur limite de pression.Many water sources deal with the problem of increasing nitrate concentrations above authorised levels for drinking water. In order to minimise this amount of pollution and to achieve high quality of water and reused water in the distribution system, membrane processes are becoming a promising technology. Indeed, they present the major advantages of a small land area requirement, low temperature operation, continuous separation, better effluent quality, little or no sludge production and a large reduction in the quantities of chemical additives. Reverse osmosis has already been used to remove most of the nitrates together with the other solutes, but the disadvantage is that this technique induces a total demineralisation of the treated water. Another possible filtration process, nanofiltration, has been investigated in this study while no extensive research has been carried out on its nitrate removal potential. Theories cannot adequately predict the influence of operating parameters on membrane performance. Consequently, new membranes and modules must be experimentally evaluated for each new application. The main objective of this study was to provide fundamental data for designing an operation of nanofiltration under various operating conditions such as transmembrane pressure, cross-flow velocity and initial feed concentration for drinking water and water reuse purposes.The retention rate rises with an increase of the applied pressure, reaches a maximum and then decreases. Such a result is quite different from those usually mentioned in the literature where the retention increases and reaches a plateau when the pressure grows. The singular decrease of the retention rate observed in this study could be explained in terms of a concentration polarization phenomenon. However, since the volumetric flux increased linearly with the pressure and remained close to the pure water flux, it might be thought that such an assumption is not valid in the case of this work. Therefore, another hypothesis has to be provided to explain the variation of the retention with transmembrane pressure. As the size of NH4+ ion (ionic radius=0.148 nm) is lower than that of the pore of membrane (diameter=1 nm), cations can enter the pores where they are partially retained due to surface forces (electrostatic and friction forces). When the pressure increases, these forces remain constant while drag forces increase due to the flux in the pore. At low pressure (∆P < 5 bars), the surface forces are stronger than the drag forces. Therefore, the solute flux remains low while the solvent flux increases with the pressure, leading to an increase in the solute retention. Above a given pressure (≅ 5 bars), the drag forces become higher than the surface forces. Consequently, the retention rate decreases.As can be observed in the obtained results, the retention rate decreased when the feed concentration was increased regardless of the operating pressure. This effect is mainly attributed to the cation shielding of the effective charge of the membrane. This characteristic can be explained by the fact that the electric repulsion becomes less efficient at higher concentration. It has been recognized that the effective charge density of the membrane decreases with an increase in the feed concentration of an ionic solution. Consequently, the retention rate of the co-ion due to charge effect is reduced. It follows that a greater amount of nitrate ions could permeate when feed solutions of higher concentration are applied.The effect of cross-flow velocity on the fluxes is insignificant since the permeate flux depends only on transmembrane pressure. However, the retention performance increases with velocity. The lower the cross-flow velocity, the higher the interaction between the solute and the membrane. Therefore, at low cross-flow rate, the solute amount that enters the membrane pores is high. When the drag forces become stronger than the surface forces, as explained above, the retention sharply decreases. At high cross-flow velocity, the feed circulation transports a large solute amount and therefore, the solute amount that enters the pores is reduced and is less sensitive to operating pressure. In consequence, the sensitivity of the retention to transmembrane pressure is not so marked. It might be thought that for a very high cross-flow velocity, the retention increases and then remains constant.It was demonstrated in this work that nanofiltration can be successfully used to remove nitrates from water. The retention was shown to depend strongly on operating parameters such as feed solution concentration, applied pressure and circulation cross-flow rate. In fact, the retention is mainly determined by the intensity of the solute / membrane interaction. This interaction comes from two main forces: a tangential one due to the feed solute flow (illustrated by the cross-flow velocity effect) and a radial one in the pores due to drag forces (illustrated by the transmembrane pressure effect). Moreover, it was observed that the valence of the associated ions is an important factor that can affect nitrate retention. It can be expected that the optimization of the separation performance will result of the best combination of all these parameters. Therefore, with a view to a future industrial application, it will be necessary to take into consideration the chemical composition of the resource and to adapt the operating conditions to the desired objectives

Use of Artificial Intelligence as an Innovative Method for Liver Graft Macrosteatosis Assessment

The worldwide implementation of a liver graft pool using marginal livers (ie, grafts with a high risk of technical complications and impaired function or with a risk of transmitting infection or malignancy to the recipient) has led to a growing interest in developing methods for accurate evaluation of graft quality. Liver steatosis is associated with a higher risk of primary nonfunction, early graft dysfunction, and poor graft survival rate. The present study aimed to analyze the value of artificial intelligence (AI) in the assessment of liver steatosis during procurement compared with liver biopsy evaluation. A total of 117 consecutive liver grafts from brain-dead donors were included and classified into 2 cohorts: ≥30 versus &lt;30% hepatic steatosis. AI analysis required the presence of an intraoperative smartphone liver picture as well as a graft biopsy and donor data. First, a new algorithm arising from current visual recognition methods was developed, trained, and validated to obtain automatic liver graft segmentation from smartphone images. Second, a fully automated texture analysis and classification of the liver graft was performed by machine-learning algorithms. Automatic liver graft segmentation from smartphone images achieved an accuracy (Acc) of 98%, whereas the analysis of the liver graft features (cropped picture and donor data) showed an Acc of 89% in graft classification (≥30 versus &lt;30%). This study demonstrates that AI has the potential to assess steatosis in a handy and noninvasive way to reliably identify potential nontransplantable liver grafts and to avoid improper graft utilization

Insertion as an alternative to workfare: active labour market schemes in the Parisian suburbs

Many governments have tightened the link between welfare and work by attaching conditionality to out-of-work benefits, extending these requirements to new client groups, and imposing market competition and greater managerial control in service delivery – principles typically characterised as ‘workfare’. Based on field research in Seine-Saint-Denis, we examine French ‘insertion’ schemes aimed at disadvantaged but potentially job-ready clients, characterized by weak conditionality, low marketization, strong professional autonomy, and local network control. We show that insertion systems have resisted policy attempts to expand workfare derived principles, reflecting street-level actors’ belief in the key advantages of the former over the latter. In contrast with arguments stressing institutional and cultural stickiness, our explanation for this resistance thus highlights the decentralized network governance of front-line services and the limits to central government power

Early enteral nutrition in critically ill patients: ESICM clinical practice guidelines.

To provide evidence-based guidelines for early enteral nutrition (EEN) during critical illness. We aimed to compare EEN vs. early parenteral nutrition (PN) and vs. delayed EN. We defined "early" EN as EN started within 48 h independent of type or amount. We listed, a priori, conditions in which EN is often delayed, and performed systematic reviews in 24 such subtopics. If sufficient evidence was available, we performed meta-analyses; if not, we qualitatively summarized the evidence and based our recommendations on expert opinion. We used the GRADE approach for guideline development. The final recommendations were compiled via Delphi rounds. We formulated 17 recommendations favouring initiation of EEN and seven recommendations favouring delaying EN. We performed five meta-analyses: in unselected critically ill patients, and specifically in traumatic brain injury, severe acute pancreatitis, gastrointestinal (GI) surgery and abdominal trauma. EEN reduced infectious complications in unselected critically ill patients, in patients with severe acute pancreatitis, and after GI surgery. We did not detect any evidence of superiority for early PN or delayed EN over EEN. All recommendations are weak because of the low quality of evidence, with several based only on expert opinion. We suggest using EEN in the majority of critically ill under certain precautions. In the absence of evidence, we suggest delaying EN in critically ill patients with uncontrolled shock, uncontrolled hypoxaemia and acidosis, uncontrolled upper GI bleeding, gastric aspirate &gt;500 ml/6 h, bowel ischaemia, bowel obstruction, abdominal compartment syndrome, and high-output fistula without distal feeding access

Productive restructuring and the reallocation of work and employment: a survey of the “new” forms of social inequality

O propósito do presente artigo consiste em questionar a inevitabilidade dos processos de segmentação e precarização das relações de trabalho e emprego, responsáveis pela inscrição de “novas” formas de desigualdade social que alicerçam o actual modelo de desenvolvimento das economias e sociedades. Visa-se criticar os limites da lógica econômica e financeira, de contornos globais, que configuram um “novo espírito do capitalismo”, ou seja, uma espécie de divinização da ordem natural das coisas. Impõe-se fazer, por isso, um périplo analítico pelas transformações em curso no mercado de trabalho, acompanhado pela vigilância epistemológica que permita enquadrar e relativizar as (di)visões neoliberais e teses tecnodeterministas dominantes. A perspectivação de cenários sobre o futuro do trabalho encerrará este périplo, permitindo-nos alertar para os condicionalismos histórico-temporais, para a urgência de se desocultar o que de ideológico e político existe nas actuais lógicas de racionalização e para os processos de ressimbolização do trabalho e emprego enquanto “experiência social central” na contemporaneidade.The scope of this paper is to question the inevitability of the processes of segmentation and increased precariousness of the relations of labor and employment, which are responsible for the introduction of “new” forms of social inequality that underpin the current model of development of economies and societies. It seeks to criticize the limits of global financial and economic logic, which constitute a “new spirit of capitalism,” namely a kind of reverence for the natural order of things. It is therefore necessary to conduct an analytical survey of the ongoing changes in the labor market, accompanied by epistemological vigilance which makes it possible to see neoliberal (di)visions and dominant technodeterministic theses in context. The enunciation of scenarios on the future of work will conclude this survey and will make it possible to draw attention to both the historical and temporal constraints and to the urgent need to unveil what is ideological and political in the prevailing logic of rationalization and processes to reinstate work and employment as a “central social experience” in contemporary times

Multiple Deprivation, Severity and Latent Sub-Groups:Advantages of Factor Mixture Modelling for Analysing Material Deprivation

Material deprivation is represented in different forms and manifestations. Two individuals with the same deprivation score (i.e. number of deprivations), for instance, are likely to be unable to afford or access entirely or partially different sets of goods and services, while one individual may fail to purchase clothes and consumer durables and another one may lack access to healthcare and be deprived of adequate housing . As such, the number of possible patterns or combinations of multiple deprivation become increasingly complex for a higher number of indicators. Given this difficulty, there is interest in poverty research in understanding multiple deprivation, as this analysis might lead to the identification of meaningful population sub-groups that could be the subjects of specific policies. This article applies a factor mixture model (FMM) to a real dataset and discusses its conceptual and empirical advantages and disadvantages with respect to other methods that have been used in poverty research . The exercise suggests that FMM is based on more sensible assumptions (i.e. deprivation covary within each class), provides valuable information with which to understand multiple deprivation and is useful to understand severity of deprivation and the additive properties of deprivation indicators

Travelers With Cutaneous Leishmaniasis Cured Without Systemic Therapy

Guidelines recommend wound care and/or local therapy as first-line treatment for cutaneous leishmaniasis. An analysis of a referral treatment program in 135 travelers showed that this approach was feasible in 62% of patients, with positive outcome in 83% of evaluable patient

Vascular clamping in liver surgery: physiology, indications and techniques

This article reviews the historical evolution of hepatic vascular clamping and their indications. The anatomic basis for partial and complete vascular clamping will be discussed, as will the rationales of continuous and intermittent vascular clamping