Suppressing Boring Bar Vibrations by Parametric Excitation

Machine tool chatter causes an instability that can occur in tool-workpiece-machine system. Hence surface roughness and tool wear in metal cutting processes. This instability caused by interaction between current tool positions and surface left by previous tool passes. Many methods have been developed to minimize the effects of regenerative chatter in machine tools and to enhance the damping capability minimizing the loss in static stiffness through implementation of device uses PZT actuators or MR fluid. The possibility of suppressing self-excited vibrations of boring process using parametric excitation is discussed. We consider a two-mass system of which the main mass is excited by a self excited force (cutting force). A single mass which acts as a dynamic absorber is attached to the main mass and, by varying the stiffness between the main mass and the absorber mass, represents a parametric excitation

Modelling of thermal ageing effect on elastic-viscoplastic behaviour of semi-cristallin polymers by D.N.L.R approach

AbstractThis work is devoted to the numerical and experimental study of thermal ageing effect on microstructure and mechanical properties of HDPE. Uniaxiale tension tests were conducted at 25 0C in order to characterize the large deformation response of HDPE. The influence of thermal ageing on the alteration of the large deformation response of HDPE was examined. A Distribution of Non Linear Relaxation (D.N.L.R) Approach was used to describe the mechanical response of virgin HDPE. The thermal ageing effect was incorporated into the constitutive model to capture the stress-strain behaviour up to failure of aged HDPE. The model is shown to be in good agreement with experimental results

Élimination des colorants des eaux résiduaires de l'industrie textile par la bentonite et des sels d'aluminium

L'industrie textile utilise des colorants de synthèse toxiques qui polluent ses eaux résiduaires avec, parfois, des flux importants. Les procédés traditionnels les éliminent mal : ils sont peu iodégradables et la seule floculation, par exemple par des sels de fer, donne des résultats insuffisants. Or, en Algérie, la réutilisation agricole des eaux usées même industrielles est devenue une impérieuse nécessité. Le procédé proposé repose sur l'utilisation de sels d'aluminium ou, mieux encore, un polyhydroxyaluminium, associés à une bentonite de forage très fine présentant l'avantage d'être localement disponible et peu coûteuse. Quatre colorants ont été testés. Ils appartiennent à deux grandes familles : les colorants acides d'une part, Jaune Supranol 4GL et Vert Nylomine C8B et les colorants dispersifs d'autre part, Rouge Foron RDGL et Violet Foron S3RL. Les essais montrent que, si la bentonite seule ou les sels d'aluminium seuls présentent des efficacités insuffisantes, ces derniers du fait d'une mauvaise décantabilité des microflocs formés, l'association bentonite-aluminium permet d'éliminer les colorants en quasi totalité avec une excellente décantabilité. Les concentrations optimales à mettre en oeuvre sont relativement basses, de l'ordre de 13 mg/l de Al3+ et 250 mg/l de bentonite. Les coûts d'exploitation sont donc très raisonnables. Sur un effluent industriel réel, le procédé permet de passer d'une DCO de 770 mg/l à moins de 30 mg/l.The textile industry uses synthetic dyes, most of them being toxic. In Algeria, the agricultural reuse of treated wastewater, even of industrial origin, is becoming commonplace. It is therefore compulsory to drastically reduce pollutant fluxes. The presently operated conventional processes cannot meet the water quality requirements: bioelimination of dyes is negligible and flocculation with iron salts, as currently carried out in the SOITEX plant located in Tlemcen, Algeria, is not effective enough. The use of aluminum salts in the flocculation of such wastewaters is well known (FIESSINGER AND BERSILLON, 1977; LAHAV et al., 1978) but the resulting microflocs are not easily settleable. Bentonite, locally available at a low cost, can also eliminate micropollutants (LAHAV et al., 1978). Associated with polyhydroxyaluminum, it can reduce such compounds as benzene or toluene, favoring simultaneously the liquid-solids separation. This paper evaluates the treatability of dyes by bentonite associated with aluminum salts.All the runs were carried out in a 200 cm3 batch reactor, mechanically stirred and thermoregulated at 20·C. The main physico-chemical characteristics of the bentonite are given in Table 1. The flocculant was aluminum chloride, previously neutralized with sodium hydroxide (mass ratio OH-/Al=1.85). The solutions were used immediately or left to polymerize during 6 days leading to polyhydroxyaluminum PHAl (LAHAV et al., 1978). When the reactor was operated with bentonite and aluminum, the mass ratio Al/bentonite was maintained at 53.10-3 (KACHA, 1994). Four dyes belonging to two main families were tested: Supranol Yellow 4GL and Nylomine Green (acid dyes) and Foron Red RDGL and Foron Violet S3RL (dispersive dyes). Their concentrations were obtained by spectrophotometry.Bentonite alone does not induce a significant abatement excepted for low pH values around 4 (Figs. 1 and 2). Dye elimination appears to require a previous protonation step followed by cation exchange. The equilibrium can be modeled by a Freundlich equation (Fig. 3 and Table 2). The dyes can also be eliminated by aluminum salts alone (Fig. 4). The efficiency is then better with polyhydroxyaluminum, i.e. more than 90 % of the initial concentration is removed. Nevertheless, the dyes abatement probably results from an adsorption or chemical reaction on microflocs which are not easily settleable. By assuming that all the aluminum ions are precipitated as aluminum hydroxide, the equilibrium is modeled by the Langmuir equation which would indicate a monolayer adsorption (Fig. 5). When the reactor is operated with bentonite and aluminum salts, dye abatement is nearly complete and the liquid-solids separation is particularly efficient (Figs. 6 and 7). The best results are obtained with PHAl but the use of the monomer can be sufficient. The required concentrations are relatively low and the process is then economically feasible (Table 3). However, the experimental data can no longer be modeled by the Freundlich equation nor by the Langmuir equation. When the aluminum salts react alone with the dyes, the conductance displayed against the aluminum concentration shows two straight lines of different slopes (Fig. 8). The abscissa of the points where the slopes change are proportional to the initial dye concentration, suggesting a chemical reaction between the dye and the aluminum salts (Fig. 9). However, the final pH value lies at the limit value of aluminum hydroxide precipitation; an adsorption on aluminum hydroxide or an aluminum salt precipitation cannot then be assumed. In presence of bentonite, such changes of slope are not observed and, moreover, the final pH value does not correspond either to a precipitation value (Figs. 11 and 12). At this stage, a comprehensive mechanism cannot thus be proposed. However, the process using bentonite/PHAl is particularly efficient and easy to operate (Fig. 13 and Table 3). The results were confirmed with a true industrial effluent, the Chemical Oxygen Demand (COD) of which was reduced from 770 mg/l to less than 30 mg/l (Fig. 14). As a matter of comparison, the actual process, which includes an activated sludge treatment followed by an iron sulfate/lime flocculation, leads to an effluent containing only 140 mgCOD/l

Λ\Lambda CDM jerk parameter in symmetric teleparallel cosmology

In this paper, we have examined the recently proposed modified symmetric teleparallel gravity, in which gravitational Lagrangian is given by an arbitrary function of non-metricity scalar $Q$. We have considered the $\Lambda$CDM jerk parameter to express the Hubble rate. Moreover, we have used 57 points of Hubble $H\left( z\right)$ and 1048 points of Pantheon datasets to constraint our model parameters by means of the Markov Chain Monte Carlo analysis. The mean values and the best fit obtained give consistent Hubble rate and deceleration parameter compared to the observation values. In order to study the current accelerated expansion scenario of the Universe with the presence of the cosmological fluid as a perfect fluid, we have considered two forms of teleparallel gravity. We have studied the obtained field equations with the proposed forms of $f(Q)$ models, specifically, linear $f\left( Q\right) =\alpha Q+\beta$ and non-linear $f\left( Q\right) =Q+mQ^{n}$ models. Next, we have discussed the physical behavior of cosmological parameters such as energy density, pressure, EoS parameter, and deceleration parameter for both model. To ensure the validity of our proposed cosmological models, we have checked all energy conditions. The properties of these parameters confirm that our models describe the current acceleration of the expansion of the Universe. This result is also corroborated by the energy conditions criteria. the Finally, the EoS parameter for both models indicates that the cosmological fluid behaves like a quintessence dark energy model.Comment: 12 pages, 10 figure

Utilisation des lichens comme bio-indicateurs de la pollution atmosphérique par le plomb, cadmium et zinc de la région de Rabat-Sale-Zemmour-Zaêr (Maroc)

Au Nord-Ouest du Maroc, la région de Rabat-Salé-Zemmour-Zaêr présente une importance socioéconomique pour le royaume. En effet, elle est sujette à deux sources de pollution; le trafic routier et les rejets des poteries. Considérant le risque de contamination métallique de l’Homme et de l’environnement, une étude a été conduite pour évaluer la pollution métallique de l’atmosphère. Elle a porté sur les bioindicateurs lichens (Xanthoria Parietina). C’est ainsi que des échantillons de thalle de Xanthoria Parietina ont été prélevés au cours de la période située entre janvier et juillet 2007 et trois éléments métalliques Plomb(Pb), Cadmium(Cd) et Zinc(Zn) ont été détectés. Les résultats de suivi spatial obtenus au niveau des quatre stations étudiées (Kamra, Centre ville, Oulja et Allal Behraoui) ont révélé des concentrations moyennes mensuelles dépassant les normes requises à l’exception de la station de Allal Behraoui. Les résultats de suivi temporel obtenus au niveau des lichens montrent que la variation saisonnière atmosphérique des métaux est très marquée avec des teneurs plus élevées en hiver et plus basses en été.Mots-clés : métaux lourds, lichens, plomb, cadmium, zinc, Rabat, salé, Zemmour, Zaêr, Maroc

Cryptococcose neuroméningée et tuberculose osseuse chez un immunocompétent: un cas

Les auteurs rapportent un cas de cryptococcose neuroméningée (CNM) chez un patient de 39 ans, non infecté par le VIH suivi pour une tuberculose de hanche. Le tableau clinique était celui d'une méningite subaiguë. Le  diagnostic a été possible grâce à la mise en évidence de cryptocoques dans le LCR. L'évolution a été satisfaisante sous fluconazole

Méningo-vascularite bactérienne révélant un adénome hypophysaire

Un macroadénome à prolactine se présente généralement par un syndrome hormonal associé à un syndrome tumoral. Une méningite bactérienne compliquant un macroprolactinome en dehors de toute thérapie médicale ou chirurgicale est rarement rapporté dans la littérature. Mme R.C âgée de 48 ans s'est présentée aux urgences pour trouble de conscience fébrile. La ponction lombaire a révélé une méningite  bactérienne. L'imagerie cérébrale a mis en évidence un aspect de vascularite cérébrale et un processus de la loge sellaire avec lyse du plancher faisant évoquer une brèche ostéoméningée. Le bilan biologique a montré une hyperprolactinémie à 200 mg/dl. La patiente est mise sous antibiothérapie à dose méningée et une corticothérapie associée à un traitement par la Cabergoline. Le traitement chirurgical de la brèche ostéoméningée s'est fait par voie endonasale. L'évolution est marquée par une nette amélioration clinique et biologique et l'absence de récidive de la méningite après un recul de 14 mois. Un macroprolactinome peut  provoquer une brèche ostéoméningée en dehors de tout traitement médical ou chirurgical et avoir comme première manifestation une méningite infectieuse