Behavioural alterations induced by chronic exposure to 10 nm silicon dioxide nanoparticles

Silicon dioxide nanoparticles (SiO₂ NPs) are widely invested in medicine, industry, agriculture, consuming products, optical imaging agents, cosmetics, and drug delivery. However, the toxicity of these NPs on human health and the ecosystem have not been extensively studied and little information is available about their behavioural toxicities. The current study aimed to find out the behavioural alterations that might be induced by chronic exposure to 10 nm SiO₂ NPs. BALB/C mice were subjected to 36 injections of SiO₂ NPs (2 mg/kg Bw) and subjected to 11 neurobehavioural tests: elevated plus‐maze test, elevated zero‐maze test, multiradial maze test, open field test, hole‐board test, light‐dark box test, forced swimming test, tail‐suspension test, Morris water‐maze test, Y‐maze test and multiple T‐maze test. Treated mice demonstrated anxiety‐like effect, depression tendency, behavioural despair stress, exploration and locomotors activity reduction with error induction in both reference and working memories. The findings may suggest that silica NPs are anxiogenic and could aggravate depression affecting memory, learning, overall activity and exploratory behaviour. Moreover, the findings may indicate that these nanomaterials (NMs) may induce potential oxidative stress in the body leading to neurobehavioural alterations with possible changes in the vital organ including the central nervous system.     

Towards a classification of energy aware MAC protocols for wireless sensor networks

Power management is an important issue in wireless sensor networks (WSNs) because wireless sensor nodes are usually battery powered, and an efficient use of the available battery power becomes an important concern specially for those applications where the system is expected to operate for long durations. This necessity for energy efficient operation of a WSN has prompted the development of new protocols in all layers of the communication stack. Provided that, the radio transceiver is the most power consuming component of a typical sensor node, large gains can be achieved at the link layer where the medium access control (MAC) protocol controls the usage of the radio transceiver unit. MAC protocols for sensor networks differ greatly from typical wireless networks access protocols in many issues. MAC protocols for sensor networks must have built‐in power conservation, mobility management, and failure recovery strategies. Furthermore, sensor MAC protocols should make performance trade‐off between latency and throughput for a reduction in energy consumption to maximize the lifetime of the network. This is in general achieved through duty cycling the radio transceiver. Many MAC protocols with different objectives were proposed for wireless sensor networks in the literature. Most of these protocols take into account the energy efficiency as a main objective. There is much more innovative work should be done at the MAC layer to address the hard unsolved problems. In this paper, we first outline and discuss the specific requirements and design trade‐offs of a typical wireless sensor MAC protocol by describing the properties of WSN that affect the design of MAC layer protocols. Then, a typical collection of wireless sensor MAC protocols presented in the literature are surveyed, classified, and described emphasizing their advantages and disadvantages whenever possible. Finally, we present research directions and identify open issues for future medium access research. Copyright © 2009 John Wiley & Sons, Ltd.     

Neural network modelling for shear strength of concrete members reinforced with FRP bars

This paper investigates the feasibility of using artificial neural networks (NNs) to predict the shear capacity of concrete members reinforced longitudinally with fibre reinforced polymer (FRP) bars, and without any shear reinforcement. An experimental database of 138 test specimens failed in shear is created and used to train and test NNs as well as to assess the accuracy of three existing shear design methods. The created NN predicted to a high level of accuracy the shear capacity of FRP reinforced concrete members.Garson index was employed to identify the relative importance of the influencing parameters on the shear capacity based on the trained NNs weightings. A parametric analysis was also conducted using the trained NN to establish the trend of the main influencing variables on the shear capacity. Many of the assumptions made by the shear design methods are predicted by the NN developed; however, few are inconsistent with the NN predictions.     

Three-Dimensional Modeling of a Helixchanger® Heat Exchanger Using CFD

Abstract

Detailed three-dimensional computational fluid dynamics (CFD) simulations have been performed to explore the performance of a helically baffled heat exchanger, commercially referred to as the Helixchanger ® heat exchanger. The CFD simulations employ the HEATX computer simulation program, which is designed for the simulation of shell-and-tube heat exchangers. The simulation accounts for the complex helical geometry of baffles, leakages, and nozzle entrance and exit. Three cases are presented that correspond to helix angles of 10°, 25°, and 40°, defined with respect to the radial axis. Inspection of the computed flows reveals distinct inner and outer regions, with the outer region showing a very desirable plug flow characteristic. The inner region, however, displays recirculation zones due to back mixing at the small helix angle, which suggests potential vibration problems but also creates a desirable temperature uniformity. A comparison with plug flow showed that the helically baffled heat exchanger had a fluid turn ratio of 0.64, 0.78, and 0.77 for the 10°, 25°, and 40° helix angles, indicating more overall plug-like flow for the higher helix angles. Computed pressure drops compare reasonably well with ABB Lummus Heat Transfer correlation results, although nozzle entrance and exit losses require further study.     

Finite element computational modelling and experimental investigation of perforated NiTi plates under tension

This paper explores the pseudoelastic deformation behaviour of perforated near-equiatomic NiTi plates by means of finite element modelling and tensile experimentation. The numerical modelling is based on an elastohysteresis model, which takes into account the hysteretic and hyperelastic contributions of material response in the global deformation. The effects of hole size, shape and number on stress–strain behaviour are discussed. The numerical results are compared and validated with experimental data.     

Compositional changes during guava fruit ripening

Compositional changes of fruit pulp and peel during ripening of white- and pink-fleshed guava fruits were studied. The white and pink guava fruits exhibited a typical climacteric pattern of respiration. Fruit tissue firmness decreased progressively, in a similar manner, in both guava fruit types. Total soluble solids (TSS) and total sugars increased in pulp and peel of both guava types with decrease in flesh firmness. More increase in total sugars was observed after the climacteric peak of respiration. Reducing sugars and titratable acidity increased up to the full-ripe stage and then decreased. Ascorbic acid and phenolic compounds decreased continuously during ripening of the two types. The peel showed higher values of ascorbic acid, total protein and phenolic compounds than the plup. The white-fleshed guavas had higher levels of TSS, total sugars, reducing sugars. titratable acidity, phenolic compounds and ascorbic acid content then the pink-fleshed fruits.     

Simulations of microfluidic droplet formation using the two-phase level set method

Microdroplet formation is an emerging area of research due to its wide-ranging applications within microfluidic based lab-on-a-chip devices. Our goal is to understand the dynamics of droplet formation in a microfluidic T-junction in order to optimize the operation of the microfluidic device. Understanding of this process forms the basis of many potential applications: synthesis of new materials, formulation of products in pharmaceutical, cosmetics and food industries. The two-phase level set method, which is ideally suited for tracking the interfaces between two immiscible fluids, has been used to perform numerical simulations of droplet formation in a T-junction. Numerical predictions compare well with experimental observations. The influence of parameters such as flow rate ratio, capillary number, viscosity ratio and the interfacial tension between the two immiscible fluids is known to affect the physical processes of droplet generation. In this study the effects of surface wettability, which can be controlled by altering the contact angle, are investigated systematically. As competitive wetting between liquids in a two-phase flow can give rise to erratic flow patterns, it is often desirable to minimize this phenomenon as it can lead to a disruption of the regular production of uniform droplets. The numerical simulations predicted that wettability effects on droplet length are more prominent when the viscosity ratio λ (the quotient of the viscosity of the dispersed phase with the viscosity of the continuous phase) is O(1), compared to the situation when λ is O(0.1). The droplet size becomes independent of contact angle in the superhydrophobic regime for all capillary numbers. At a given value of interfacial tension, the droplet length is greater when λ is O(1) compared to the case when λ is O(0.1). The increase in droplet length with interfacial tension, σ, is a function of with the coefficients of the regression curves depending on the viscosity ratio.     

Microstructural and Hardness Studies of Cu-10wt.%Sn Alloy Under Different Aging Conditions

Microstructure of Cu-10wt.%Sn alloy, prepared by powder metallurgy technique and sintered at 900 °C for 120 min in hydrogen atmosphere, was studied by optical microscopy and XRD technique as a function of aging time. Isothermal aging of the alloy specimens was performed at 250 °C for a period of 30, 60, 120, 300, and 1440 min after solution treatment at 500 °C for 60 min. Rockwell hardness of aged specimens was also measured at room temperature as a function of aging time. It was observed that microstructure of the as-sintered specimens consists of the grains of alpha Cu-Sn solid solution. Moreover, solution treatment of the alloy specimens followed by quenching in water increased the hardness of the as-sintered alloy specimens from 35.5 to 59.8 HRF due to the residual stresses generated by fast cooling. Aging at 250 °C for 30, 60, and 120 min was found to cause a decrease in hardness from 59.8 to 45.1 HRF, whereas the specimens aged for 300 and 1440 min show an increase in hardness from 45.1 to 75.7 HRF. The values of porosity calculated from XRD patterns of the alloy specimens referred to show that porosity varies with aging time in a manner opposite to that of hardness, e.g., porosity is maximum for 120 min aging time where hardness is minimum.