Two-dimensional analysis of a negative differential conductance gate transistor as a THz emitter

We investigate plasma modes in a transistor including a negative differential conductance in the gate.The analytical results show that the plasma wave generation is substantially influenced by the lateral direction (width of the transistor),gate leakage current and viscosity.The injection from the gate (opposed to the gate leakage current) can improve the plasma oscillations and their amplitude with respect to ordinary transistors.We also estimate,which to our best knowledge has been derived for the first time,the total power emitted by the transistor and the emitted pattern which qualitatively gives reasonable agreement with the experimental data.The results show that the radiated power depends on various parameters such as drift velocity,momentum relaxation time,gate leakage current and especially the lateral direction.A negative gate current enhances the power while the gate leakage current decreases the power.     

Microstructure and mechanical properties in nano and microscale SiC-included dissimilar friction stir welding of AA6061-AA2024

This work investigates the effect of SiC particles on the microstructure and mechanical properties of dissimilar friction stir welding between AA6061-T6 and AA2024-T351. Two variations in the size of SiC particles, along the joint line, various groove width, and tool offset, were used for the welding. It was found that the joints made by rotational speed of 800?rev?min^?1, travelling speed of 31.5?mm?min^?1, groove width of 0.3?mm, and tool offset of 0.5?mm exhibited the most uniform distribution of particles for both micro- and nano-scale SiC particles. Additionally, the smaller and rounded equiaxed particles result in easier material flow, a more uniform metal matrix composite, the smallest grain size in the stir zone and the highest tensile strength.     

Combination of neural network and ant colony optimization algorithms for prediction and optimization of flyrock and back-break induced by blasting

Blasting is the process of use of explosives to excavate or remove the rock mass. The main objective of blasting operation is to provide proper rock fragmentation and to avoid undesirable environmental impacts such as ground vibration, flyrock and back-break. Therefore, proper predicting and subsequently optimizing these impacts may reduce damage on facilities and equipment. In this study, an artificial neural network (ANN) was developed to predict flyrock and back-break resulting from blasting. To do this, 97 blasting works in Delkan iron mine, Iran, were investigated and required blasting parameters were collected. The most influential parameters on flyrock and back-break, i.e. burden, spacing, hole length, stemming, and powder factor were considered as model inputs. Results of absolute error (Ea) and root mean square error (RMSE) (0.0137 and 0.063 for Ea and RMSE, respectively) reveal that ANN as a powerful tool can predict flyrock and back-break with high degree of accuracy. In addition, this paper presents a new metaheuristic approximation approach based on the ant colony optimization (ACO) for solving the problem of flyrock and back-break in Delkan iron mine. Considering changeable parameters of the ACO algorithm, blasting pattern parameters were optimized to minimize results of flyrock and back-break. Eventually, implementing ACO algorithm, reductions of 61 and 58 % were observed in flyrock and back-break results, respectively.     

Flutter and bifurcation instability analysis of fluid-conveying micro-pipes sandwiched by magnetostrictive smart layers under thermal and magnetic field

International Journal of Mechanics and Materials in Design - Fluid-conveying micro/Nano structures are key tools in MEMS and NEMS applications especially for drug delivery systems to attack a...     

The Role of Surface Preparation Parameters on Cold Roll Bonding of Aluminum Strips

It is the objective of this article to investigate the influence of surface preparation on the cold roll bonding (CRB) process. In this context, the effects of surface preparation parameters consisting of surface preparation method, surface roughness, scratch-brushing parameters, and the delay time between surface preparation and rolling are investigated on the bond strength of aluminum strips. The bond strength of two adjacent aluminum strips produced by the CRB process is evaluated by the peeling test. Furthermore, the interface region is investigated by metallographic observations. Our findings indicate that higher surface roughness values and shorter delay times improve the bond strength. It is also found that degreasing followed by scratch-brushing yield the best bonding properties.     

Numerical Study of Pressure Drop and Thermal Characteristics of Al2O3–Water Nanofluid Flow in Horizontal Annuli

In this paper the results of numerical study of the mixed convection heat transfer of Al₂O₃–water nanofluid in a horizontal annuli are presented. Steady, laminar flows in symmetric configurations are considered. Single-phase fluid approach is adopted for nanofluid modeling. The governing equations are discretized using the finite-volume method. A SIMPLE-like algorithm has been applied for pressure–velocity coupling on the collocated arrangement. In order to validate the code performance, the numerical results are compared with those available in the literature and good agreement is achieved. The effects of some important parameters such as nanoparticle volume fraction, aspect ratio, Grashof number, and heat flux ratio are studied and discussed in detail. In general, it is observed that the local Nusselt number increases with increase in nanoparticle concentration, Grashof number, and radius ratio. However, when increasing the nanoparticle concentration there are considerable increments in pressure drop and pumping power, which are not desirable. On the other hand, changes in the skin friction coefficient are negligible.     

Effect of SiC Nanoparticles on Bond Strength of Cold Roll Bonded IF Steel

In this study, cold roll bonding process characteristics of IF steel strips, such as bond strength, threshold deformation, undulation of peeling force, and peeled surface, in the presence of SiC nanoparticles were examined and compared to those of an IF steel strip without nanoparticles. The bond strength was evaluated by the peeling test and scanning electron microscopy. It was found that when the thickness reduction was increased, the peeling force of IF steel strips improved. The results also indicated that the presence of silicon carbide nanoparticles decreased the bond strength of IF steel strips when compared to the strips without nanoparticles for the same thickness reduction. When the thickness reduction was increased, the undulation of average peeling force values increased at a constant nanoparticle content. Also, the strips without nanoparticles had a lower undulation value as compared to the strips with SiC nanoparticles. In addition, in the presence of silicon carbide, when the nanoparticles’ content was increased, the undulation of average peeling force values decreased at a constant thickness reduction. Finally, it was found that the bond strength of IF steel strips was less than that of aluminum and copper strips. This was attributed to their crystal structure.     

Texture Evolution of Nanostructured Aluminum/Copper Composite Produced by the Accumulative Roll Bonding and Folding Process

In this study, the accumulative roll bonding and folding (ARBF) process was used for manufacturing nanostructured aluminum/copper multilayered composites. Textural evolution during the ARBF process of composites was evaluated using X-ray diffraction. Microstructural observation of some samples was evaluated by scanning electron microscopy and transmission electron microscopy. The ARBF process induced formation of a strong preferred orientation along the β-fiber and also to the pronounced copper texture component. In the aluminum side, occurrence of dynamic recovery reduced the intensity of the β-fiber rolling texture due to change in dislocation structure and decrease in the degree of strain hardening. On the other hand, occurrence of discontinuous dynamic recrystallization at the third and fourth ARBF cycles led to decreasing the intensity of fibers and texture components in the copper side. The average grain sizes of the final sample for the copper and aluminum sides were ~50 and ~200 nm, respectively.     

Fabrication of MMC Strip by CRB Process

In this study, Al/Al₂O₃ composite strips were produced by the cold roll bonding (CRB) process. Microhardness, tensile strength, and elongation of composite strips were investigated as a result of changes in thickness reduction, quantity of alumina particles, and the production method used. It was found that higher values of reduction and quantities of alumina improved microhardness and tensile strength but decreased elongation. Furthermore, as-received strips exhibited the highest values for microhardness and tensile strength but the lowest for elongation. In contrast, post-rolling annealed strips recorded the lowest values for microhardness and tensile strength but the highest for elongation. Finally, it was found that pre-rolling annealing was the best method for producing this composite via the CRB process.