Nadir compromise programming: A model for optimization of multi-objective portfolio problem

In problem of portfolio selection, financial Decision Makers (DMs) explain objectives and investment purposes in the frame of multi-objective mathematic problems which are more consistent with decision making realities. At present, various methods have introduced to optimize such problems. One of the optimization methods is the Compromise Programming (CP) method. Considering increasing importance of investment in financial portfolios, we propose a new method, called Nadir Compromising Programming (NCP) by expanding a CP-based method for optimization of multi-objective problems. In order to illustrate NCP performance and operational capability, we implement a case study by selecting a portfolio with 35 stock indices of Iran stock market. Results of comparing the CP method and proposed method under the same conditions indicate that NCP method results are more consistent with DM purposes.     

An experimental study of forced convective heat transfer for fully developed Al2O3–water nanofluid in an annulus tube

Nanofluids have been known as practical materials to ameliorate heat transfer within diverse industrial systems. The current work presents an empirical study on forced convection effects of Al₂O₃–water nanofluid within an annulus tube. A laminar flow regime has been considered to perform the experiment in high Reynolds number range using several concentrations of nanofluid. Also, the boundary conditions include a constant uniform heat flux applied on the outer shell and an adiabatic condition to the inner tube. Nanofluid particle is visualized with transmission electron microscopy to figure out the nanofluid particles. Additionally, the pressure drop is obtained by measuring the inlet and outlet pressure with respect to the ambient condition. The experimental results showed that adding nanoparticles to the base fluid will increase the heat transfer coefficient (HTC) and average Nusselt number. In addition, by increasing viscosity effects at maximum Reynolds number of 1140 and increasing nanofluid concentration from 1% to 4% (maximum performance at 4%), HTC increases by 18%.     

Strength evaluation of granite block samples with different predictive models

Over the last decade, application of soft computing techniques has rapidly grown up in different scientific fields, especially in rock mechanics. One of these cases relates to indirect assessment of uniaxial compressive strength (UCS) of rock samples with different artificial intelligent-based methods. In fact, the main advantage of such systems is to readily remove some difficulties arising in direct assessment of UCS, such as time-consuming and costly UCS test procedure. This study puts an effort to propose four accurate and practical predictive models of UCS using artificial neural network (ANN), hybrid ANN with imperialism competitive algorithm (ICA–ANN), hybrid ANN with artificial bee colony (ABC–ANN) and genetic programming (GP) approaches. To reach the aim of the current study, an experimental database containing a total of 71 data sets was set up by performing a number of laboratory tests on the rock samples collected from a tunnel site in Malaysia. To construct the desired predictive models of UCS based on training and test patterns, a combination of several rock characteristics with the most influence on UCS has been used as input parameters, i.e. porosity (n), Schmidt hammer rebound number (R), p-wave velocity (V_p) and point load strength index (Is(50)). To evaluate and compare the prediction precision of the developed models, a series of statistical indices, such as root mean squared error (RMSE), determination coefficient (R²) and variance account for (VAF) are utilized. Based on the simulation results and the measured indices, it was observed that the proposed GP model with the training and test RMSE values 0.0726 and 0.0691, respectively, gives better performance as compared to the other proposed models with values of (0.0740 and 0.0885), (0.0785 and 0.0742), and (0.0746 and 0.0771) for ANN, ICA–ANN and ABC–ANN, respectively. Moreover, a parametric analysis is accomplished on the proposed GP model to further verify its generalization capability. Hence, this GP-based model can be considered as a new applicable equation to accurately estimate the uniaxial compressive strength of granite block samples.

     

Effects of layup sequences on stresses of thick composite cantilever tubes

In this study, a new simple-input displacement-based method is used to study effects of layup sequences on stresses, strains, and deformations of thick laminated orthotropic cantilever straight tubes under transverse loading. Three-dimensional stress distributions are obtained based on the most general displacement field of elasticity. A layer-wise theory which includes the full three-dimensional constitutive relations is used. A non-dimensional simple coefficient is introduced to compare interlaminar radial stresses of different layup sequences. Finally, some design guidelines are proposed to consider effects of layup sequences of laminated thick composite tubes subjected to shearing load.     

Production of Al–20 wt.% Al2O3 composite powder using high energy milling

High energy ball milling was used to produce a nanostructured Al matrix composite reinforced by submicron α-alumina particles. Scanning electron microscopy analysis as well as tap and green density measurements were used to optimize the milling time needed for the completion of the mechanical milling process. Results show that addition of alumina particles as the reinforcement has a drastic effect on the size, morphology and pressability of the powder. Scanning electron microscopy shows that distribution of alumina particles in the Al matrix reaches a full homogeneity after steady state. This would increase the hardness of powder due to a nano-structured matrix and oxide dispersion strengthening.     

On the post-processing techniques for elastoplastic axisymmetrical problems

In this paper, superconvergent patch recovery techniques [see Refs Zienkiewicz and Zhu (1992); Blacker and Belytschko (1994)] which have been proposed for linear elliptic problems are generalized here to the elastoplastic axisymmetrical problems. Numerical examples for axisymmetrical problems (using 4-node quadrilateral elements) are presented to illustrate the reliability of this generalization. As an outcome of our study, the superior performance of the modified post-processing technique, Blacker and Belytschko (1994), in comparison with the standard one, Zienkiewicz and Zhu (1992), is found through the numerical results.     

Corrosion of Steel Reinforcement in Carbon Fiber-Reinforced Polymer Wrapped Concrete Cylinders

The rehabilitation, repair, and strengthening of concrete structures has increased worldwide with a growing number of systems employing externally applied fiber-reinforced polymer (FRP) composites. However, the service life and effectiveness of FRP repair and strengthening techniques when applied to concrete in corrosive marine environments is still not well understood. This paper presents the results of an experimental study on the corrosion performance of embedded steel reinforcement in cylindrical reinforced concrete specimens with 13 different surface treatment options. Samples were subjected to an impressed current and a high salinity solution. Test variables included the type of epoxy, wrap fiber orientation, and the number of wrap layers. Samples were evaluated for corrosion activity by monitoring corrosion potentials and impressed current flow levels, and by examining reinforcement mass loss and concrete chloride content among samples. Test results indicated that FRP wrapped specimens had prolonged test life, decreased reinforcement mass loss, and reduced concrete chloride content. The performance of wrapped specimens was superior to that of either control samples or those coated only with epoxy. Epoxy type had a significant effect on the performance of samples regarding their resistance to corrosion. It was concluded that carbon FRP wraps were able to confine concrete, slowing deterioration from cracking and spalling and inhibiting the passage of salt water.     

Spatial Structure of a Single Mn Impurity State on GaAs (110) Surface

Using a low temperature scanning tunneling microscope (STM), we have manipulated individual Mn adatoms at the GaAs (110) surface to apparently bond with two surface As atoms. In this configuration the Mn atoms, which either are at an interstitial site or have substituted for a surface Ga atom, give rise to strong in-gap levels as probed by spatially resolved STM spectroscopy measurements. Mapping the Mn-induced in-gap bound state shows an unusual spatial structure, with highly anisotropic character. The bound state shares some characteristic features with subsurface Mn and Zn dopants.     

One-pot synthesis of hematite-alumina hollow sphere composite by ultrasonic spray pyrolysis technique with high adsorption capacity toward PAHs

A hybrid nanocomposite of alumina and hematite was synthesized by ultrasonic spray pyrolysis technique. The study of microscopic images, mapping analysis, and XRD patterns revealed that the Al₂O₃ – Fe₂O₃ nanocomposite was composed of separated spherical particles with a thin layer ball-shaped structure that metal oxides are uniformly distributed in the wall of hollow sphere particles, led to a coherent and monotonous construction. A series of coefficients of equilibrium sorption of polycyclic aromatic hydrocarbons (PAHs) as hazardous materials were measured on the prepared composite material in a batch technique. The free or pure Al₂O₃ or Fe₂O₃ showed negligible removal efficiency for the mentioned analytes. The various significant variables, such as initial analyte concentration, solution pH, adsorbent dose, and contact time to remove analyte, were studied in the aqueous solutions. Adsorption data were modeled to Langmuir, Freundlich, and Temkin isotherms, and a good correlation found in the case of Langmuir isotherm and adsorption capacity for anthracene, phenanthrene, and naphthalene were 370, 333, and 322 mg g^?1, respectively. Investigation of the kinetic models proved a pseudo-second-order, and the prepared adsorbent can be reused more than 7 times without a significant decrease of adsorption performance.     

Application-aware virtual paths insertion for NOCs

Network-on-chip (NoC) has rapidly become a promising alternative for complex system-on-chip architectures including recent multicore architectures. Additionally, optimizing NoC architectures with respect to different design objectives that are suitable for a particular application domain is crucial for achieving high-performance and energy-efficient customized solutions. Despite the fact that many researches have provided various solutions for different aspects of NoCs design, a comprehensive NoCs system solution has not emerged yet. This paper presents a novel methodology to provide a solution for complex on-chip communication problems to reduce power, latency and area overhead. Our proposed NoC communication architecture is based on setting up virtual source–destination paths between selected pairs of NoCs cores so that the packets belonging to distance nodes in the network can bypass intermediate routers while traveling through these virtual paths. In this scheme, the paths are constructed for an application based on its task-graph at the design time. After that, the run time scheduling mechanism is applied to improve the buffer management, virtual channel and switch allocation schemes and hence, the constructed paths are optimized dynamically. Moreover, in our design the router complexity and its overheads are reduced. Additionally, the suggested router has been implemented on Xilinx Virtex-5 FPGA family. The evaluation results captured by SPLASH-2 benchmark suite reveal that in comparison with the conventional NoC router, the proposed router takes 25% and 53% reduction in latency and energy, respectively besides 3.5% area overhead. Indeed, our experimental results demonstrate a significant reduction in the average packet latency and total power consumption with negligible area overhead.