Interplay of internal stresses, electric stresses and surface diffusion in polymer films

We investigate two destabilization mechanisms for elastic polymer films and put them into a general framework: first, instabilities due to in-plane stress and second due to an externally applied electric field normal to the film's free surface. As shown recently, polymer films are often stressed due to out-of-equilibrium fabrication processes as e.g. spin coating. Via an Asaro-Tiller-Grinfeld mechanism as known from solids, the system can decrease its energy by undulating its surface by surface diffusion of polymers and thereby relaxing stresses. On the other hand, application of an electric field is widely used experimentally to structure thin films: when the electric Maxwell surface stress overcomes surface tension and elastic restoring forces, the system undulates with a wavelength determined by the film thickness. We develop a theory taking into account both mechanisms simultaneously and discuss their interplay and the effects of the boundary conditions both at the substrate and the free surface.Comment: 14 pages, 7 figures, 1 tabl

Development of a helium gas balloon flying system for aerial photographing and observation

Abstract: This paper describes the implementation of a helium gas balloon flying system equipped with a camera and tracking subsystem for aerial photography. This is partially the results of a successful project conducted in November 2012 by a group of electrical and electronic students from the University of Johannesburg. The goal of this project was to take aerial pictures at the highest possible altitude above the sea level from the flying system while tracking its position in real-time. The solution proposed was based on a low cost unmanned system for a reliable and optimal aerial observation and tracking, suitable for start-ups companies or research groups

ATP-Binding Cassette Systems of Brucella

Brucellosis is a prevalent zoonotic disease and is endemic in the Middle East, South America, and other areas of the world. In this study, complete inventories of putative functional ABC systems of five Brucella species have been compiled and compared. ABC systems of Brucella melitensis 16M, Brucella abortus 9-941, Brucella canis RM6/66, Brucella suis 1330, and Brucella ovis 63/290 were identified and aligned. High numbers of ABC systems, particularly nutrient importers, were found in all Brucella species. However, differences in the total numbers of ABC systems were identified (B. melitensis, 79; B. suis, 72; B. abortus 64; B. canis, 74; B. ovis, 59) as well as specific differences in the functional ABC systems of the Brucella species. Since B. ovis is not known to cause human brucellosis, functional ABC systems absent in the B. ovis genome may represent virulence factors in human brucellosis

Low-temperature alkaline activation of feldspathic solid solutions: Development of high strength geopolymers

Most of the natural solid solutions, as a result of the history of their formation and crystallization, present a fraction of amorphous or metastable materials that may easily be dissolved or activated in alkaline media. In this work, trachyte, granite, pegmatite and sand for comparison are used as principal solid precursors for the design of high strength geopolymers. The particularity of the solid-solution based geopolymers is the high fraction of crystalline phases incongruently dissolved that may react essentially at the surface, thus developing very resistant bonds. While working with 100 wt% of solid solution is almost unrealistic for the production of geopolymers, it was found that 15 to 30 wt% of metakaolin in replacement of the solid-solution powder conducts to low porosity (10 vol.%), high flexural strength (20-30 MPa) and compact microstructure. Preliminary resonance-based mechanical tests showed that the elastic modulus of the investigated samples ranged between 11-15 GPa, as also confirmed by instrumented micro-indentations. It was concluded that a high strength and durable matrix are a result of chemico-mechanical equilibrium of phases contained within the composites including the pore volume and pore-size distribution, which are significant for the life cycle of geopolymer composites

On the mechanical, thermoelectric, and excitonic properties of Tetragraphene monolayer

Two-dimensional carbon allotropes have attracted much attention due to their extraordinary optoelectronic and mechanical properties, which can be exploited for energy conversion and storage applications. In this work, we use density functional theory simulations and semi-empirical methods to investigate the mechanical, thermoelectric, and excitonic properties of Tetrahexcarbon (also known as Tetragraphene). This quasi-2D carbon allotrope exhibits a combination of squared and hexagonal rings in a buckled shape. Our findings reveal that tetragraphene is a semiconductor material with a direct electronic bandgap of 2.66 eV. Despite the direct nature of the electronic band structure, this material has an indirect exciton ground state of 2.30 eV, which results in an exciton binding energy of 0.36 eV. At ambient temperature, we obtain that the lattice thermal conductivity for tetragraphene is approximately 118 W/mK. Young's modulus and the shear modulus of tetragraphene are almost isotropic, with maximum values of 286.0 N/m and 133.7 N/m, respectively, while exhibiting a very low anisotropic Poisson ratio value of 0.09

Monitoring of the medication distribution and the refrigeration temperature in a pharmacy based on internet of things (IoT) technology

Abstract: For the past 15 years since its appearance, Internet of Things (IoT) technology has been leading the planet towards a smart world where all devices and physical objects, referred to as “things”, will be connected via electronic sensors through the Internet. The distribution of medication to patients at a pharmacy in certain regions is still very traditional and outdated. Patients wait for a long time in queues to receive their medications, this is mostly due to the absence of an efficient distribution system. Also, the refrigeration temperature within several pharmacies is a huge problem, as medications must be kept at a constant temperature for an optimal results..

Physico-chemical properties of crude oil of Khaya senegalensis (Desr.) A. Juss according to bioclimatic zones in Chad

The mature seeds of Khaya senegalensis are from 2 to 2.5 cm long and weigh 289 g per 1000 seeds. These seeds contain about 67% oil by weight. This oil, which is fairly rich in oleic acid (66%), is used in West Africa for cooking, for cosmetics, as an insecticide and in traditional medicine. Prospecting to enhance the development of this oil in Chad, the present study aims to determine the physico-chemical properties of this oil according to bioclimatic zones. The density, acidity, peroxide value, moisture content and percentage of impurities were the parameters studied. The results showed that the crude oil of the seeds of K. senegalensis has the qualities close to those of other edible oils. The study also revealed that climate has influenced the physico-chemical parameters of this oil. Further and more research investigations are necessary to guide decisions on the valorisation and large-scale production of this oil. Keywords: Khaya senegalensis, seed crude oil, physico-chemical parameters, valorisation, bioclimatic zone, Cha