Materials Sliding Wear Model Based on Energy Dissipation

A mathematical model is developed to correlate the volumetric wear of materials with the dissipation energy in sliding contacts. In the analysis, the wear of contacting materials originating from the energy loss due to friction process in the contact is studied. Two mechanisms responsible for energy loss at contact are considered. The first is the amount of energy spent to import plastic deformation and the second is the elastic energy of the particulate. The energy loss due to elastic and plastic deformation is calculated. The statistical loss of energy is calculated for two rough surfaces by the assumption that there is negligible change in the statistical parameters of the surface during wear. The model can be useful to predict the service lifetime of components and eventually structures. The results showed that the amount of dissipated energy and the volumetric loss increased with increasing normal load. Also, changing the normal load changed the rate of energy dissipation per unit sliding distance.     

Geochemistry of thermal springs around Lake Abhe,Western Djibouti

The Republic of Djibouti, occupying an area of 23,180 km², falls within the arid zone of East Africa and is located above the ‘Horn of Africa’, adjacent to the Red Sea. This country has several thermal springs and fumaroles distributed over three regions – Lake Assal, Lake Hanle and Lake Abhe. The most characteristic feature of Lake Abhe is the presence of several linear chains of travertine chimneys. The thermal waters are typical of the Na-Cl type near neutral waters rich in CO₂. These waters show an oxygen shift, indicating reservoir temperatures>200°C. The chemical signature of the thermal springs and the geology of the Lake Abhe region are very similar to the Tendaho geothermal area of Ethiopia. The geology, temperature gradient and its proximity to Damah Ale volcano make the Lake Abhe region a potential site for geothermal power development.     

In-vitro anticancer and antimicrobial activities of PLGA/silver nanofiber composites prepared by electrospinning

In the present work, a series of 0, 1 and 7 wt% silver nano-particles (Ag NPs) incorporated poly lactic-co-glycolic acid (PLGA) nano-fibers were synthesized by the electrospinning process. The PLGA/Ag nano-fibers sheets were characterized using SEM, TEM and DSC analyses. The three synthesized PLGA/silver nano-fiber composites were screened for anticancer activity against liver cancer cell line using MTT and LDH assays. The anticancer activity of PLGA nano-fibers showed a remarkable improvement due to increasing the concentration of the Ag NPs. In addition to the given result, PLGA nano-fibers did not show any cytotoxic effect. However, PLGA nano-fibers that contain 1 % nano silver showed anticancer activity of 8.8 %, through increasing the concentration of the nano silver to 7 % onto PLGA nano-fibers, the anticancer activity was enhanced to a 67.6 %. Furthermore, the antibacterial activities of these three nano-fibers, against the five bacteria strains namely; E.coli o157:H7 ATCC 51659, Staphylococcus aureus ATCC 13565, Bacillus cereus EMCC 1080, Listeria monocytogenes EMCC 1875 and Salmonella typhimurium ATCC25566 using the disc diffusion method, were evaluated. Sample with an enhanced inhibitory effect was PLGA/Ag NPs (7 %) which inhibited all strains (inhibition zone diameter 10 mm); PLGA/Ag NPs (1 %) sample inhibited only one strain (B. cereus) with zone diameter 8 mm. The PLGA nano-fiber sample has not shown any antimicrobial activity. Based on the anticancer as well as the antimicrobial results in this study, it can be postulated that: PLGA nanofibers containing 7 % nano silver are suitable as anticancer- and antibiotic-drug delivery systems, as they will increase the anticancer as well as the antibiotic drug potency without cytotoxicity effect on the normal cells. These findings also suggest that Ag NPs, of the size (5–10 nm) evaluated in the present study, are appropriate for therapeutic application from a safety standpoint.     

Active vibration damping of composite structures using a nonlinear fuzzy controller

The present paper presents a comprehensive methodology for the structural active vibration damping using a fuzzy logic control. The proposed application setup consists of a cantilever beam equipped with two pairs of collocated piezoceramic (PZT) actuators and sensors. The investigated carbon composite beam is modeled using a shell 2D-model on Abaqus commercial finite element code. The PZT patches are modeled as additional layers with a coupled electromechanical effect. Experimental data corresponding to the controlled and to the uncontrolled systems are also presented considering fixed frequency and pulse force excitation.     

Reliability analysis of reverse osmosis plant

The increasing complexity of desalting plants demands consideration of operational and maintenance factors in the design phase. Applications of the fault tree techniques to RO sea water desalination systems are illustrated; critical failure problem areas are identified and methods of improving the performance of the RO desalination plants are recommended. Failure data has been extracted from operation and maintenance reports of the operating RO desalination plants in Jeddah, Saudi Arabia. An assessment is also made of the impact of failures and outages on the availability of the plant.     

Comparative study of different approaches for preparation of chlorzoxazone orodispersible tablets

Abstract

Context: Muscle spasm is a painful involuntary contraction of muscles, which causes involuntary movement and distortion. Chlorzoxazone is a centrally acting muscle-relaxant with sedative properties, but given orally, it is hepatically metabolized leading to decreased bioavailability.

Objective: Orodispersible tablets (ODTs) of chlorzoxazone were formulated using two different approaches; by coprocessed excipients (CE) or by liquisolid (LS) technique.

Materials and methods: Pharmaburst^® 500, Starlac^®, Pearlitol flash^®, Prosolv^® odt and F-melt^® were used as coprocessed superdisintegrants, whereas in LS, Avicel^® PH101, Microcelac^® 100 and Cellactose^® 80 were used as carriers, while Aerosil^® 200 was the coating material. ODTs were evaluated in terms of weight and thickness variations, drug content, hardness, friability, wetting time, dissolution, disintegration time (DT) and palatability.

Results: In vitro DT of CE-ODTs ranged from 26.43?±?1.693?s to >180?s, whereas it was between 25.42±?0.203?s to >180?s in LS-ODTs. Complete drug release within 15?min was attained by CE1 prepared with 92.5?mg Pharmaburst^® 500. In vivo DT of CE1 and LS3 were 19.779?±?0.810 and 18.105?±?0.423?s, respectively, using six volunteers. Volunteers found that CE1 had more acceptable taste and was more palatable than LS3.

Conclusion: It was concluded that chlorzoxazone ODTs could be successfully formulated using either CE or LS techniques and be used as novel dosage forms for pediatrics and geriatrics showing improved drug release. Moreover, CE technique was superior to LS technique in terms of palatability.     

Optimal design of a multilayered piezoelectric transducer based on a special unit cell homogenization method

Piezoelectric transducers with high directional-dependent response are of interest in several applications because of their ability to sense and actuate along specific directions where they can distinguish individual principal strain components. This paper presents an improved unidirectional sensor obtained using a multi-laminate piezocomposite that maximizes the electromechanical coupling factor or the piezoelectric strain constant in one direction with respect to the other directions. Furthermore, multi-laminate structures provide significant design potential by the variation of the orientation and stacking sequence of fibers to obtain the desired properties. The effective properties depend on the number of layers, the fibers orientation as well as the thickness of each layer, and they are estimated by the variational asymptotic method for unit cell homogenization. A design that guarantees maximum directional dependence in terms of piezoelectric strain constant is determined by a global optimization technique using a genetic algorithm. Layered transducers composed of several orthotropic passive layers and a single active layer are considered.