Calculation of Confined Phonon Spectrum in Narrow Silicon Nanowires Using the Valence Force Field Method

We study the effect of confinement on the phonon properties of ultra-narrow silicon nanowires of side sizes of 1 nm to 10 nm. We use the modified valence force field (MVFF) method to compute the phononic dispersion and extract the density of states, the transmission function, the sound velocity, the ballistic thermal conductance, and boundary-scattering-limited diffusive thermal conductivity. We find that the phononic dispersion and the ballistic thermal conductance are functions of the geometrical features of the structures, i.e., the transport orientation and confinement dimension. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical features of the channel. The 〈110#x232A; nanowire has the highest group velocity and thermal conductance, whereas the 〈111#x232A; has the lowest. The 〈111#x232A; channel is thus the most suitable orientation for thermoelectric devices based on Si nanowires since it also has a large power factor. Our findings could be useful in the thermal transport design of silicon-based devices for thermoelectric and thermal management applications.     

The Microstructural, Textural, and Mechanical Properties of Extruded and Equal Channel Angularly Pressed Mg-Li-Zn Alloys

The microstructural and textural evolution of the Mg-6Li-1Zn (LZ61), Mg-8Li-1Zn (LZ81), and Mg-12Li-1Zn (LZ121) alloys were investigated in the as-extruded condition and after being equal channel angularly pressed (ECAPed) for one, two, and four passes. The shear punch testing technique was employed to evaluate the room-temperature mechanical properties of the extruded and ECAPed materials. Microstructural analysis revealed that the grain refinement in both LZ61 and LZ121 alloys could be achieved after multipass ECAP through the continuous dynamic recovery and recrystallization process. For the LZ81 alloy, however, the occurrence of Li loss in the four passes of ECAP condition partly offsets the grain refining effect of the ECAP process by increasing grain size and volume fraction of the α phase. Textural studies in both LZ61 and LZ81 alloys indicated that the developed fiber texture after extrusion could be replaced by a typical ECAP texture, where the basal planes are mainly inclined about 45 deg to the extrusion axis. The increased volume fraction of the β phase in LZ81 significantly affected the α-phase texture by decreasing the intensity of the maximum orientations of the basal and prismatic planes in all deformation conditions, compared with the LZ61 alloy. It was also observed that the abnormal grain growth might be promoted by the strong texture developed in the extruded LZ121 alloy. This texture became more randomized when the number of ECAP passes increased. The SPT results showed that the shear yield stress, ultimate shear strength and normalized displacement in all studied alloys were improved through the grain refinement strengthening caused by ECAP. It was also established that increasing Li content decreased the shear strength and enhanced the shear elongation in all deformation conditions.     

Dyeing properties of the atmospheric pressure plasma-treated polypropylene fabric subjected to butane tetra carboxylic acid

In this paper, dyeing properties of dielectric barrier discharge (DBD)-treated polypropylene (PP) fabrics padded with butanetetracarboxylic acid (BTCA) were evaluated. We have used a DBD, working in an atmospheric pressure air. More polar functional groups were presented on the substrate surface after DBD pretreatment. After DBD treatment, BTCA was applied to PP fabrics by pad–dry–cure system. Both treated and untreated fabrics were dyed using acidic and basic dyestuffs. The surface morphology was investigated by scanning electron microscopy images. Treated samples were also characterized by means of Fourier transform infrared spectroscopy. The wettability of the samples was evaluated by water drop test according to AATCC 79-2000 standard. Color intensities of the dyed fabrics with both acidic and basic dyestuffs were measured using a UV–vis–NIR reflective spectrophotometer, over the range of 400–700 nm. The results showed that, by treating the fabric, the relative color strength (K/S values) of the dyed fabrics has been increased. From the results of tensile strength test, both weft and warp directions, no significant difference was obtained within the accuracies of the measurement. Also, the fastnesses properties of samples were measured.     

A Novel Detection Algorithm Efficient for Turbo Coded CDMA Signals in Detect and Forward Cooperative Channels

In this paper, a new detection algorithm is proposed for turbo coded Code Division Multiple Access (CDMA) signals in detect and forward cooperative channels. Use of user cooperation makes much improvement in the performance of CDMA systems. Due to the special structure of CDMA systems, cooperative schemes increase the sum and cutoff capacities of CDMA based wireless systems and improve the quality of user-partner link which enhances the overall performance of the system. In this paper, a new combining scheme is proposed that makes the receiver more robust against the decision errors in the partner link. This structure is simulated for punctured 1/2 rate 4 states turbo code in a channel with first order Markov time variation and different Rice factor variances. Through various simulations, it is shown when the channel estimates are available in the partner and receiver, the cooperation between users provides much diversity gain especially while using the new proposed combining algorithm.     

Using MBPE technique to accelerate solving the thin-wire EFIE used in numerical simulation of lightning

The antenna theory (AT) model is widely used to numerically simulate the propagation of current wave along lightning return-stroke channels and compute the radiated electromagnetic fields. In this model, the return stroke channel is considered as a vertical monopole antenna above perfectly conducting ground for which the numerical solution of the governing electric field integral equation (EFIE) in the frequency domain by the conventional method of moment (MoM) is prohibitively slow. In this paper, a model-based parameter estimation (MBPE) technique is proposed to reduce the number of frequency-domain calculation points required for the evaluation of space-time current distribution along a lightning return stroke channel. In applying this technique to a rational function model for the channel current distribution, a uniform-like sampling strategy is investigated. In order to accelerate the building of the moment impedance matrix, the reciprocal closed-form mutual impedance of sinusoidal electric dipoles and the symmetry of the model are used. The proposed technique is validated against the conventional inverse fast Fourier transform algorithm which uses a MoM solution for all frequencies within the channel base current spectrum. It is shown that considerable computation efficiency is achieved in terms of CPU time without losing accuracy.     

Microstructural changes in fat during the ripening of Iranian ultrafiltered Feta cheese

In this study, fat globules in Iranian ultrafiltered Feta cheese (3 to 60 d) were directly observed during the ripening period by scanning electron microscopy. According to images of ultrafiltered Feta cheese samples obtained by scanning electron microscopy, individual fat globules and aggregates of fat were easily distinguishable on d 3 and had completely disappeared within 20 d of storage. On d 20, only the fingerprints of the fat globules and pools of free fat in the casein matrix remained. After 40 d of ripening, the texture was homogeneous and no fat globules or fat voids were detected. Chemical analysis of cheese samples showed that with an increase in the ripening period, the contents of dry matter and fat decreased significantly, whereas the pH values and salt content did not indicate any significant changes.     

Thermoelastic Characterization and Evaluation of Residual Stresses in Bi-Directional Fibrous Composites

The thermoelastic behavior of bi-directional fibrous composites will be studied through the use of a finite element-based micromechanical model. The model is used to study the effect of the crossing angle of the fibers on the composite’s coefficient of thermal expansion (CTE) and the residual thermal stresses that develop after a temperature change. The effect of the fiber volume fraction (V _f ) on the same results is also studied. For anisotropic materials, one can see that in addition to normal strains, shear strains will also be developed due to temperature change. This method will lend itself to evaluate the coefficients of thermal expansions not only due to normal expansion, but also due to shear expansion for composites with no principal directions. In this micromechanical model, parallelepiped unit cells incorporating the fibers at different cross angles are created to represent the periodic microstructure of the angular bi-directional composite. The volume averaged stresses per unit temperature of the individual constituents are used to study the residual thermal stresses that develop. Two different sets of materials are used to test this model. Results show that when the fiber’s cross angle is not 0^o or 90^o, shear strains are created. Also, residual stresses in the unit cell are functions of the cross angle between the fibers.     

Reservoir Optimization for Energy Production Using a New Evolutionary Algorithm Based on Multi-Criteria Decision-Making Models

The study applies kidney algorithm for the optimization of reservoir operation for hydropower generation. The objective function defined for optimization is to minimize the hydroelectric power deficiency. Results of kidney algorithm are compared with those of bat algorithm (BA), water cycle algorithm (WCA), biogeography-based optimization algorithm (BBO), genetic algorithm (GA), particle swarm optimization algorithm (PSOA), and scatter matters search algorithm (SMSA). All algorithms are evaluated by Complex proportional assessment (COPRAS), Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), modified TOPSIS, and Weighted Aggregated Sum Product Assessment (WASPAS), as well as Borda count social choice theory. Then, vulnerability, time and volumetric reliability, as well as resiliency indices are used for comparison and multi-criteria decision-making indicators for selecting the best algorithm. It is found that no algorithm is ranked uniformly the best. Results indicate that kidney and particle swarm algorithms are ranked higher than other algorithms by most indices. Results of 10 random implementations of the objective function indicate that KA has a lower coefficient of variation and is computationally moe efficient. Further, most of the multi-criteria decision making models allocate the first rank to KA.