Study the flashover voltage for outdoor polymer insulators under desert climatic conditions

This work presents a study of flashover voltage for outdoor polyester and composite insulators under some desert climatic conditions. Cylindrical polyester composite samples have been prepared after incorporated with different concentrations of inorganic fillers e.g., alumina trihydrate [ATH], boric acid [H₃BO₃] and magnesium hydroxide [Mg(OH)₂] to improve the electrical, mechanical and thermal properties in addition to maximize the surface flashover voltage and decrease the tracking phenomena.Results showed that flashover voltage reaches to 38 kV for samples without filler and 47 kV for samples containing 50% of ATH filler in dry condition. A comparison between inorganic fillers under various environmental conditions showed higher flashover voltage values for samples containing ATH filler than that of samples containing H₃BO₃ and Mg(OH)₂ fillers at all filler concentrations. Flashover voltage increases 24% by adding ATH filler for polyester samples under sandstorm conditions. Also, in this study, the effects of sandstorm, ultra violet (UV) radiation, mechanical strength (compressive and tensile strengths) and thermal performance with respect to surface of the sample under test have been investigated in detail.     

In vitro bioactivity and biocompatibility of lithium substituted 45S5 bioglass

In this study, different concentrations of Li₂O (0–12 wt.%) were substituted for Na₂O in 45S5 bioglass® and the effect of these substitutions on both in vitro apatite formation ability and osteoblastic cell responses was studied. For these purposes, the structural and topographical properties of the glasses were studied using, XRD, FTIR, SEM/EDXA and AFM techniques, before and after storing in simulated body fluid for different time intervals. Additionally, the proliferation rate and activity of newborn rat calvaria-derived osteoblastic cells on different samples were examined by using dimethylthiazol diphenyl tetrazolium bromide (MTT) and alkaline phosphatase (ALP) assessment methods. From XRD and FTIR data, it was found that poor crystalline carbonated nanoapatite phase was formed on the surface of glasses with maximum concentration of Li or without Li, while at low substitutions an inhibition of apatite formation was observed. The apatite layer formed on the surfaces of the glasses had similar morphology, flakes which tightly entangled to others. All samples had the same surface roughness before soaking but different values after that. It was found that both proliferation rate and alkaline phosphatase activity of the cells cultured on Li-substituted glasses were higher than those of Li-free sample in a dose-dependent manner. The results suggest that lithia-modified glasses may be successfully used as bone defect filler even with more effectiveness than 45S5 bioglass®.     

Analysis of interaction between tunnels in soft ground by 3D numerical modeling

Tunnels are increasingly being excavated in soft ground conditions when services are required in urban environments, and it is now common to have tunnels crossing at various elevations. As the tunnel excavations are undertaken at different levels, there will be an interaction which can have a significant influence on stress distributions and consequently deformations within the tunnels and surface settlement. As multi-layer tunnelling is a three dimensional phenomenon in nature, 3D numerical solutions must be utilized for perpendicularly crossing tunnels at various levels. This paper reports the investigations into the changes in stress distribution, deformations and surface settlements which may be expected when the twin Tohid Tunnels pass beneath the Line 4 metro tunnel in Tehran.     

A coupled bending-torsion model for electrostatically actuated torsional nano/micro-actuators with considering influence of van der Waals force

In the current paper, a coupled two degree of freedom model which considers both bending and torsion of the supporting torsion beams is presented for electrostatically actuated torsional nano/micro-actuators under the effect of van der Waals (vdW) force. Newton’s second law is utilized for finding the normalized equations governing the static behavior of the actuator. The implict function theorem is then utilized for finding the equations governing the pull-in state of the actuator. The related results show that torsion model considerably overestimates the pull-in parameters of the nano/micro-actuator. The concept of the instability mode is introduced, and it is shown that when the ratio of the bending stiffness to the torsion stiffness of the supporting torsion beams is relatively low, the dominant instability mode of the actuator would be the bending mode and otherwise the dominant instability mode would be the torsion mode. It is also observed that the presence of the vdW force can significantly reduce the pull-in angle and pull-in deflection of the nano/micro-actuator. The presented results also show that the vdW force can lead to considerable reduction in the pull-in voltage of the actuator. The equilibrium behavior of the actuator is studied, and it is observed that the vdW force and also bending of the supporting torsion beams greatly reduce the maximum allowable voltage which can be applied to the actuator. Results of this paper can be used for successful design of electrostatically actuated torsional nano/micro-actuators where the size of the actuator is sufficiently small, and as a result, the vdW force plays a major role in the system.     

BUILDING USER TASK SPACE BY MINING TEMPORALLY PROXIMATE DESKTOP ACTIONS

Awareness of the user's current context, that is, the task the user resides in, can allow for various ways of supporting their work. In this article we present a novel approach for mining user's regular tasks on the basis of temporal proximity of users’ desktop actions without user intervention in a completely automatic, unobtrusive, and unsupervised manner. The proposed method is based on time-based clustering of a user's desktop actions and, in contrast to previous approaches, it does not enforce fixed time constraints on the mined actions, and typical transition times, when they exist, emerge from the logged activity data for that specific user. The performance of our technique was evaluated on a large data set of 724 days of desktop work by five knowledge workers. The results showed that our approach performed very well and was able to cluster those temporally proximate user actions that commonly used fix time window techniques fail to deal with. Notably, the main improvement is in the recall of the tasks, where our approach recalled 10.18% more actions than the predefined time window technique.     

Compatibilization mechanisms of nanoclays with different surface modifiers in UCST blends: Opposing effects on phase miscibility

The effects of organically modified and pristine nanoclays on the kinetics of thermodynamic equilibrium state attainment for semicrystalline binary blends of polyethylene (PE)/ethylene-vinyl acetate copolymer (EVA) have been investigated. Due to the non-equilibrium compatibilization mechanism, intercalated organoclay results in a slower rate of phase miscibility change at lower annealing temperatures, thereby worsening the PE/EVA compatibility state. In contrast to poorly dispersed pristine nanoclay, the homogeneous state is obtained at higher or equal rates by adding organoclay at higher annealing temperatures because of the dominant role of nanofiller equilibrium compatibilization mechanism. Phase diagrams of these UCST blends determined by a dynamic method shifts to higher temperatures by the incorporation of nanofillers and the unexpected reduction in miscibility window area is much more noticeable for nanocomposites having highly restricted molecular movements. This can verify that dynamic methods lose their efficiency for measuring the equilibrium phase diagram of polymer blends containing nanoparticles.     

Evaluation of hydrogen sorption models for AB5-type metal alloys by employing a gravimetric technique

This paper is concerned with hydrogen absorption and desorption in AB₅-type hydrogen storage metal alloys. We give a brief overview on models which have been proposed for hydrogen sorption in metals over the past decades. We choose three models based on different perspectives, i.e. thermodynamics, reaction kinetics, and mere observation (empiricism), and evaluate their applicability in order to describe the sorption behaviour. Additionally, we propose a model which is based on a cumulative distribution function. In order to evaluate the models, the hydrogen absorption and desorption isotherms of LaNi₅ and LaNi_4.5Co_0.5 are measured by means of a gravimetric technique. A nonlinear regression is performed to fit the models to experimental data. The computed model parameters are compared to values reported in the literature. The emphasis is given to the applicability of the models with respect to describing the non-ideality of the plateau region and the continuity/smoothness of phase transition regions.     

Preparation of nanocomposite dispersions based on cellulose whiskers and acrylic copolymer by miniemulsion polymerization: Effect of the silane content

A one‐step method was used to prepare stable aqueous nanocomposite dispersions based on cellulose whiskers extracted from the rachis of the date palm tree and a poly(styrene‐co‐2‐ethyl hexylacrylate) copolymer via miniemulsion polymerization. A reactive silane, i.e., methacryloxypropyl triethoxysilane was added to stabilize the dispersion and favor the anchoring of the whiskers on polymer particles. Dynamic light scattering was used to study the effect of the silane and whiskers contents on the average particle size of the polymer. Nanocomposites materials were prepared from these dispersions using a casting/evaporation method. The effect of the silane and whiskers contents on the thermal and mechanical properties were studied using differential scanning calorimetry and dynamic mechanical analysis. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

New parametric study of nugget size in resistance spot welding process using finite element method

Resistance spot welding process (RSW) is one of important manufacturing processes in automotive industry for assembling bodies. Quality and strength of the welds and therefore body mainly are defined by quality of the weld nuggets. The most effective parameters in this process are: current intensity, welding time, sheet thickness and material, geometry of electrodes, electrode force, and current shunting. In present research, a mechanical–electrical–thermal coupled model in a finite element analysis environment is made using. Via simulating this process, the phenomenon of nugget formation and the effects of process parameters on this phenomenon are studied. Moreover, the effects of welding parameters on temperature of faying surface are studied. Using this analysis, shape and size of weld nuggets are computed and validated by comparing them with experimental results from published articles. The methodology developed in this paper provides prediction of quality and shape of the weld nuggets with variation of each process parameter. Utilizing this methodology assists in adjusting welding parameters so that costly experimental works can be avoided. In addition, the process can be economically optimized to manufacture quality automotive bodies.