Study of the effect of contact force model on the dynamic response of mechanical systems with dry clearance joints : computational and experimental approaches

The main objective of this work is to present a computational and experimental study on the contact forces developed in revolute clearance joints. For this purpose, a well-known slider-crank mechanism with a revolute clearance joint between the connecting rod and slider is utilized. The intra-joint contact forces that generated at this clearance joints are computed by considered several different elastic and dissipative approaches, namely those based on the Hertz contact theory and the ESDU tribology-based for cylindrical contacts, along with a hysteresis-type dissipative damping. The normal contact force is augmented with the dry Coulomb’s friction force. In addition, an experimental apparatus is use to obtained some experimental data in order to verify and validate the computational models. From the outcomes reported in this paper, it is concluded that the selection of the appropriate contact force model with proper dissipative damping plays a significant role in the dynamic response of mechanical systems involving contact events at low or moderate impact velocities.Fundação para a Ciência e a Tecnologia (FCT

Modelling and bioinformatics analysis of the dimeric structure of house dust mite allergens from families 5 and 21 : Der f 5 could dimerize as der p 5

Allergy represents an increasing thread to public health in both developed and emerging countries and the dust mites Dermatophagoides pteronyssinus (Der p), Blomia tropicalis (Blo t), Dermatophagoides farinae (Der f), Lepidoglyphus destructor (Lep d) and Suidasia medanensis (Sui m) strongly contribute to this problem. Their allergens are classified in several families among which families 5 and 21 which are the subject of this work. Indeed, their biological function as well as the mechanism or epitopes by which they are contributing to the allergic response remain unknown and their tridimensional structures have not been resolved experimentally except for Blo t 5 and Der p 5. Blo t 5 is a monomeric three helical bundle, whereas Der p 5 shows a three helical bundle with a kinked N-terminal helix that assembles in an entangled dimeric structure with a large hydrophobic cavity. This cavity could be involved in the binding of hydrophobic ligands, which in turn could be responsible for the shift of the immune response from tolerance to allergic inflammation. We used molecular modelling approaches to bring out if other house dust mite allergens of families 5 and 21 (Der f 5, Sui m 5, Lep d 5, Der p 21 and Der f 21) could dimerize and form a large cavity in the same way as Der p 5. Monomeric models were first performed with MODELLER using the experimental structures of Der p 5 and Blo t 5 as templates. The ClusPro server processed the selected monomers in order to assess their capacity to form dimeric structures with a positive result for Der p 5 and Der f 5 only. The other allergens (Blo t 5, Sui m 5, Lep d 5, Der p 21 and Der f 21) did not present such a propensity. Moreover, we identified mutations that should destabilize and/or prevent the formation of the Der p 5 dimeric structure. The production of these mutated proteins could help us to understand the role of the dimerization process in the allergic response induced by Der p 5, and if Der p 5 and Der f 5 behave similarl

Isolation and Identification of Entomopathogenic Bacteria from Algerian Desert Soil and their Effects against the Migratory Locust, Locusta migratoria (Linnaeus, 1758) (Orthoptera: Acrididae)

After isolation and characterization of some bacteria in the rhizosphere soil of the Algerian desert plants, a total of 17 bacterial strains were isolated. They are mobile, aerobic, with a positive catalase. From these bacterial strains, four were selected for their entomopathogenic potential and identified based on their genetic traits. The rDNA16S sequences of these named strains (B3, B4, B5 and B6) were recorded in the EMBL/EBI data bank and their phylogenetic analysis revealed that they belong to the genera; Pseudomonas, Bacillus and Enterobacter. This study was highlighted on their entomopathogenic activity against the 5th instar larvae of the migratory locust, Locusta migratoria (Linnaeus, 1758) (Orthoptera: Acrididae). The results obtained, one week after treatment, showed that the treated nymphs were highly sensitive to the tested isolates of bacteria, with mortality rates of 100, 98, 71 and 65% for Pseudomonas sp. strain B3 (HF911369), Pseudomonas sp. strain B4 (HF911366) Enterobacter sp. strain B6 (HF911368) and Bacillus sp. strain B5 (HF911367), respectively, in comparison to the control (3.33%

Isolation of an extremely halophilic arhaeon Natrialba sp. C21 able to degrade aromatic compounds and to produce stable biosurfactant at high salinity

Natrialba sp. strain C21 was isolated from oil contaminated saline water in Ain Salah (Algeria) and has exhibited a good potential for degrading phenol (3 % v/v), naphthalene (3 % v/v), and pyrene (3 % v/v) at high salinity with high growth, enzymatic activity and biosurfactant production. Successful metabolism of aromatic hydrocarbon compounds of the strain Natrialba sp. C21 appears to require the ortho-cleavage pathway. Indeed, assays of the key enzymes involved in the ring cleavage of catechol 1, 2-dioxygenase indicated that degradation of the phenol, naphthalene and pyrene by strain Natrialba sp. C21 was via the ortho-cleavage pathway. Cells grown on aromatic hydrocarbons displayed greater ortho-activities mainly towards catechol, while the meta-activity was very low. Besides, biosurfactants derived from the strain C21 were capable of effectively emulsifying both aromatic and aliphatic hydrocarbons and seem to be particularly promising since they have particular adaptations like the increased stability at high temperature and salinity conditions. This study clearly demonstrates for the first time that strain belonging to the genera Natrialba is able to grow at 25 % (w/v) NaCl, utilizing phenol, naphthalene, and pyrene as the sole carbon sources. The results suggest that the isolated halophilic archaeon could be a good candidate for the remediation process in extreme environments polluted by aromatic hydrocarbons. Moreover, the produced biosurfactant offers a multitude of interesting potential applications in various fields of biotechnology. © 2015 Springer Japa

EXTREMELY HALOPHILIC ARCHAEA FROM ALGERIAN SALT LAKES: ISOLATION, PHYLOGENETIC IDENTIFICATION AND BIOPROSPECTION OF HYDROLYTIC ENZYMES

International audienc

Isolation and characterization of halophilic archaea able to produce biosurfactants

Halotolerants microorganisms able to live in saline environments, offer a multitude of actual or potential applications in various fields of biotechnology. This is why some strains of Halobacteria from an Algerian culture collection were screened for biosurfactant production in a standard medium using the qualitative drop-collapse test and emulsification activity assay. Five of the Halobacteria strains reduced the growth medium surface tension below 40mNm-1 and two of them exhibited high emulsion-stabilising capacity. Diesel oil-in-water emulsions were stabilized over a broad range of conditions, from pH 2 to 11, with up to 35% sodium chloride or up to 25% ethanol in the aqueous phase. Emulsions were stable to three cycles of freezing and thawing. The components of the biosurfactant were determined; it contains sugar, protein and lipid. The two Halobacteria strains with enhanced biosurfactants producers designed strain A21 and strain D21 were selected to identify by phenotypic, biochemical characteristics and by partial 16S rRNA gene sequencing. The strains have Mg2+and salt growth requirements are always above 15% (w/v) salts with an optimal concentration of 15% to 20%. Analyses of partial 16S rRNA gene sequences of the two strains suggested that they were halophiles belonging to genera of the family Halobacteriaceae, Halovivax (strain A21) and Haloarcula (strain D21). To our knowledge, this a first report of biosurfactant production at such a high salt concentratio

Bacterial community issued from a Chlorophytum plant-microbial fuel cell for electricity generation

Some microorganisms, particularly bacteria, can adhere to conductive surfaces and grow as an electroactive biofilm, on which they communicate electrochemically and generate electricity. Here, a bacterial community isolated from anodic electroactive biofilms of a Microbial Fuel Cell planted with Chlorophytum comosom is studied. Seventeen different bacterial strains were isolated from electroactive biofilms and were identified using the 16S rRNA marker gene. The strains were affiliated to 8 bacteria families and 8 genera (Aeromonas, Enterobacter, Alcaligenes, Pseudomonas, Clostridium, Paraclostridium, Enterococcus and Kurthia spp.). After that, it was demonstrated using electrochemical methods, principally imposed potential chronoamperometry under +0.155 mV/SCE, that the consortium constituted of 17 strains was able to exchange electrons with conductive materials. A maximum current density of 345 µA/cm2 was revealed at 48h of the study, using acetate as the sole carbon source and without any additional external mediator.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Modeling and simulation of joint clearance effects on mechanisms having rigid and flexible links

In this study, kinematic and dynamic characteristics of a planar four-bar mechanism having joint clearance and link flexibility are investigated. Assuming that joint clearance as a virtual massless link, artificial clearances are developed at crank-coupler and coupler-follower joints. Contact model in joints with clearance is established using the nonlinear spring-damper model and the friction effect is considered using the Coulomb friction model. Then the simulation is implemented and the kinematic and dynamic characteristics of model mechanism are investigated. The computational methodology can predict the effects of clearance on planar mechanism having rigid and flexible links. The results are evaluated for the case of stationary phase, and naturally show that extreme values occur in output of the mechanism with clearances. Due primarily to the suspension effect of the flexible link, values of these peaks in the flexible mechanism decrease relative to that of the rigid mechanism. In addition, the flexibility has a significant effect on the vibration response of the mechanism with joint clearance