A new role-switching mechanism optimizing the coexistence of?bluetooth and Wi-Fi networks

Unlicensed ISM band is used by various wireless technologies. Therefore, issues related to ensuring the required efficiency and quality of operation of coexisting networks become essential. The paper addresses the problem of mutual interferences between IEEE 802.11b transmitters (commercially named Wi-Fi) and Bluetooth (BT) devices. An optimization approach to modeling the topology of BT scatternets is introduced, resulting in more efficient utilization of ISM environment consisting of BT and Wi-Fi networks. To achieve it, the Integer Linear Programming approach has been proposed. Example results presented in the paper illustrate significant benefits of using the proposed modeling strategy.     

Tocopherol composition of deodorization distillates and their antioxidative activity

During the last stage of plant oil refining, deodorization distillates containing very important biological substances such as tocopherols, sterols, terpenoids or hydrocarbons are formed as a by-products. This study aimed at evaluating the content and antioxidant capacity of tocopherol concentrates from deodorization distillates obtained after the refining of rapeseed, soybean and sunflower oil. The majority of the matrix substances were eliminated from deodorization distillates by freezing with an acetone solution at -70 degrees C. The tocopherol concentrates obtained in this way contained approximately fivefold more tocopherols than the quantity in condensates after deodorization. Antioxidant activity was investigated by observing the peroxide value at 25 degrees C and using the Oxidograph test. The test medium was lard enriched with the tocopherol concentrates of the three plant oils versus single, synthetic alpha-, gamma- and delta-tocopherols (-T), which served for comparison. In these model systems, all investigated tocopherol concentrates exhibited antioxidant capacity. Their antioxidant effect was significantly lower than that of single delta-T and gamma-T, but significantly higher than alpha-T. The results prove that natural tocopherol concentrates obtained from plant oils are valuable food antioxidants and they also increase the biological and nutritional value of food especially when administered to animal fats or food of animal origin. Tocopherol concentrates can fully replace synthetic antioxidants that have been used thus far.     

Design and scaling of wheat dough extrusion by numerical simulation of flow and heat transfer

This paper proposes a computational method to obtain simultaneous scale-up of mixing and heat transfer in single screw extruders by several parametric 3D non-isothermal numerical simulations. The numerical experiments of flow and heat transfer modeling studies are conducted using the Mackey and Ofoli [Cereal Chem. 67 (1990) 221] viscosity model for low to intermediate moisture wheat doughs in the metering section of a single screw extruder. The non-isothermal flow model includes viscous dissipation and the complete three-dimensional flow geometry including leakage flows without any simplifications such as unwinding the screw. Based on Rauwendaal [Polymer Extrusion, Hanser Publishers, New York, 1986] residence time distribution (RTD) and specific mechanical energy (SME) were chosen as the design parameters for the scale-up of mixing and heat transfer respectively. Parametric numerical simulations were conducted by varying screw geometric variables such as helix angle, channel depth, screw diameter to channel depth ratio, screw length to screw diameter ratio, and the clearance between the screw flights and barrel. SME and RTD curves vs. screw parameters were developed from the numerical simulations. From the design charts two differently sized extruders were obtained which had a scale-up of about 10 times based on throughput rates but had the same RTD and SME.     

Post-mortem changes in the concentration of lactic acid, phosphates and pH in the muscles of wild rabbits (Oryctolagus cuniculus) according to the perimortal situation

In this study changes in the concentrations of lactate, phosphates, and pH values of water extracts of muscles of transported and hunted rabbits during ripening were determined. Concentrations of lactate were higher in the muscles of hunted rabbits. The highest differences were obtained 24h after kill/hunt. Concentrations of lactate in the muscles of hunted rabbits were decreasing, while in the muscles of transported rabbits we observed it to increase in the 7th day and then decrease in the 14th day. Higher concentrations of phosphates were found in the muscles of transported wild rabbits. During the ripening process concentrations of phosphates were decreasing in muscles of both groups. Muscles of hunted rabbits had lower pH values during the whole ripening process. Our research showed that concentrations of lactate, phosphates and pH value post-mortem depended on the perimortal situations.     

The effect of 3D structure design on fire behavior of polyethylene terephthalate glycol containing aluminum hypophosphite and melamine cyanurate

Effect of the shape of 3D printed samples on fire behavior of polyethylene terephthalate glycol (PET-G) and PET-G additivated with a mix of aluminum hypophosphite (AHP) and melamine cyanurate as flame retardant, was investigated. The additives improved fire performance (e.g., maximum average rate of heat emission, total oxygen consumption, heat release rate indices) irrespective of structural complexity, favoring carbonaceous char formation. However, at increasing structural complexity, they promoted higher release of smoke, compared to neat PET-G, because of a change in the prevalent retardation mechanism, which became dominated by the flame inhibition action of AHP. Consequently, the synergistic effect obtained combining the two additives, was hindered. Impact of product design on mechanisms of fire retardation helps in devising engineering solutions aimed at meeting required level of fire-safety performance, which should be tailored to the specific product.     

Effect of SiC reinforcement particles on the grain density in a magnesium-based metal–matrix composite: Modelling and experiment

The aim of this work is to develop a numerical model capable of predicting the grain density in the Mg-based matrix phase of an AZ91/SiC composite, as a function of the diameter and total mass fraction of the embedded SiC particles. Based on earlier work in a range of alloy systems, we assume an exponential relationship between the grain density and the maximum supercooling during solidification. Analysis of data from cast samples with different thicknesses, and mass fractions and particle diameters of added SiC, permits conclusions to be drawn on the role of SiC in increasing grain density. By fitting the data, an empirical nucleation law is derived that can be used in a micro–macro model. Numerical simulations based on the model can predict the grain density of magnesium alloys containing SiC particles, using the diameter and mass fraction of the particles as inputs. These predictions are compared with measured data.     

Mechanical response of metallic glasses: Insights from in-situ high energy X-ray diffraction

The term “metallic glass” usually refers to a metallic alloy rapidly quenched in order to “freeze” its structure from the liquid state. A metallic glass is a metastable alloy, which lacks the symmetry typical for crystalline materials and at room temperature shows an amorphous liquid-like structure. Bulk metallic glasses (BMGs) represent a class of amorphous alloys. The most notable property of BMGs is their ultrahigh (near theoretical) strength and hardness. Because the known BMGs usually miss tensile plasticity and thus exhibit catastrophic failure upon tension it is important to understand deformation mechanisms involved and thus improve their performance. This aricle analyzes the use of synchrotron radiation for evaluating the elastic-plastic response of such materials.     

Desertification? Northern Ethiopia re-photographed after 140 years

A collection of sepia photographs, taken during Great Britain's military expedition to Abyssinia in 1868, are the oldest landscape photographs from northern Ethiopia, and have been used to compare the status of vegetation and land management 140 years ago with that of contemporary times. Thirteen repeat landscape photographs, taken during the dry seasons of 1868 and 2008, were analyzed for various environmental indicators and show a significant improvement of vegetation cover. New eucalypt woodlands, introduced since the 1950s are visible and have provided a valuable alternative for house construction and fuel-wood, but more importantly there has also been locally important natural regeneration of indigenous trees and shrubs. The situation in respect to soil and water conservation measures in farmlands has also improved. According to both historical information and measured climatic data, rainfall conditions around 1868 and in the late 19th century were similar to those of the late 20th/early 21st century. Furthermore, despite a ten-fold increase in population density, land rehabilitation has been accomplished over extensive areas by large-scale implementation of reforestation and terracing activities, especially in the last two decades. In some cases repeat photography shows however that riparian vegetation has been washed away. This is related to river widening in recent degradation periods, particularly in the 1970s-1980s. More recently, riverbeds have become stabilized, and indicate a decreased runoff response. Environmental recovery programmes could not heal all scars, but this study shows that overall there has been a remarkable recovery of vegetation and also improved soil protection over the last 140 years, thereby invalidating hypotheses of the irreversibility of land degradation in semi-arid areas. In a highly degraded environment with high pressure on the land, rural communities were left with no alternative but to improve land husbandry: in northern Ethiopia such interventions have been demonstrably successful.     

Modelling of Heat Transfer in the Evaporator and Condenser of the Working Fluid in the Heat Pipe

The aim of this paper is to point out possible solutions to the further development of heat pipes by numerical modelling of phase-change heat transfer. Numerical modelling has now become a standard method that helps to reduce the economic costs of research and development of new and innovative devices. The article describes the procedures for using numerical simulation in phase-change heat transfer that occurs due to evaporation and condensation of the working fluid. The suggested procedure enables modelling of gravitational heat pipe under different changes in its geometry or under changes in the working fluid. From the simulation results we can find out how the heat pipe behaves under different geometric changes and how much heat output it transfers. The paper presents results obtained from modelling of heat pipes, such as classical gravitational heat pipe, heat pipe with capillary geometry, and closed loop pulsating heat pipe. The results gathered from numerical simulation of heat pipes were compared with measurement results.