سال:1393 | دوره: | شماره: |تعداد مقالات:18

New activated carbon was produced from pulp and paper mill sludge as a low cost precursor via chemical activation by zinc chloride. The activated carbon was successfully used for the adsorption of phenol and two of its derivatives, i.e. 2-chlorophenol and 4-nitrophenol from aqueous solutions. The characterization of the prepared activated carbon demonstrated high textural properties for the synthesized activated carbon. The results revealed superior adsorption performance of the prepared activated carbon in this study compared to the commercial one. The effect of main affecting parameters such as pH, contact time, concentration and temperature on adsorption of phenolic compounds was experimentally investigated in discontinuous system. The adsorption capacities followed the order of 4-nitrophenol>2-chlorophenol>phenol which was attributed to the property of substituent groups in their chemical structure. Amongst the isotherm models used to describe experimental equilibrium data, the best match was obtained by Sips isotherm which revealed the heterogeneous behavior of the adsorption sites on the adsorbent surface. Kinetic study demonstrated that the adsorption kinetics followed pseudo-second-order kinetic model. Based on thermodynamical analysis, the negative values obtained for Gibbs free energy, enthalpy and entropy indicated spontaneous, exothermic and random behavior of the adsorption process.

Enzyme cost is the major problem for industrial scale application. Immobilization is a promising approach to moderate the enzyme cost factor and increase its stability and activity. In this study, sol-gel method was used to prepare the immobilization platform and entrapped lipase as one of the most used enzyme in dairy processing, cosmetics and pharmaceutical industries. Lipase from Candida rugosa was immobilized onto glycidoxypropyltrimethoxysilane (GPTMS) and tetramethoxysilane (TMOS) derived sol-gels and its characteristics and hyrdrolytic activity were investigated. Michaelis-Menten kinetic properties reveal that although free enzyme can catalyze the reaction faster, but it has lower affinity for substrate molecules compared to sol-gel immobilized lipase. Entrapped lipase retained 67% of its initial activity after six reaction cycles. It showed 100% activity compared to free lipase powder at 40-45°C. In pH 9, as free enzyme lost 90% of its initial activity, immobilized lipase lost only 29% of its activity. Immobilized enzyme was more stable toward different pHs (100% activity at pH 7.5 compared to free form). Morphological characteristics of the immobilized enzyme were investigated by SEM images and BET. The sample had specific surface area and mean pore diameter of 2.599 m2/g and 46.13 nm, respectively.

Heat exchangers are widely used in power engineering and industrial applications. Many techniques such as coiled tube, surface tension devices, rough surfaces and extended surfaces have been investigated to enhancethermal performance and minimize the cost and size of the heat exchanger equipment. One of the most important techniques is tube insert. In general, tube inserts can be classified into two broad categories: stationary inserts and self-rotating inserts. Compared with stationary inserts, the self-rotating inserts can rotate in the tube by fluid and the comprehensive performance of self-rotating inserts is improved significantly. This paper mainly focuses on reviewing the large number of experimental and numerical works taken by researchers on self-rotating inserts such as twisted tapes, miniature hydraulic turbine, turbine-type swirl generators, etc. To improve the thermal efficiency of heat exchanger and serviceable to designers implemention of passive enhancement techniques in heat exchanger are required. The authors found that self-rotating inserts can streng then the heat transfer efficiency, meanwhile achieve on-line automatic anti-scaling and descaling effect. When the fluid velocity is more than 0.2m/s, most of self-rotating inserts can be applied. The heat transfer performance and frictional loss have been discussed to get the optimal configuration of self-rotating inserts. The convective heat transfer correlations have also been discussed. Determining how to find the optimal self-rotating insert is the main objective of this paper.

MCM-41 particles were synthesized using inorganic raw materials and Cetyltrimethylammonium bromide (CTAB). The textural properties and structure of MCM-41 particles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and N2 adsorption-desorption methods. To study performance of Dubinin-Astakhov and Dubinin-Raduchkevic isotherm models in evaluating mesopore volume and pore size of MCM-41, the mesopore volume and pore size of several MCM-41 samples were calculated by means of the two- mentioned isotherm models and by utilizing N2 adsorption isotherms and XRD data. The results were compared with the mesopore volume and pore size calculated by other methods. The results showed that the calculated mesopore volume and pore size on the samples with the fraction of mesopore volume>0.9 had not good consistency with XRD data and the results obtained by other methods. However, the calculated mesopore volume and pore size on the samples with the fraction of mesopore volume£0.9 were in good agreement with XRD data and other advanced simulation techniques.

A procedure for preparing the semi-activated carbon fiber (SACF) at low temperature is proposed. The first step of the procedure is coating of an inorganic fiber (E-glass fiber) by an adsorbent mixture (powder activated carbon) using methyl cellulose and water as gluing material. In this work, a set of experiments were performed to attain appropriate adsorbent mixture for good quality coating. The best composition was investigated based on the adsorption and the mechanical properties of the coated fibers. The results showed that an adsorbent mixture containing 3 to 4 wt% of methyl cellulose, and 15-20 wt% of activated carbon renders good quality coating. The adsorption property of the coated fibers was studied by determination of iodine number for the adsorbent mixture. In this work, the weight percent of the coated adsorbent mixture on the fibers have also been measured and reported. The mechanical properties were examined by flow of air through a packing of the coated fibers. BET surface area of the samples was also examined and compared to other reported works. The results showed that the surfaces area of the samples were either equal to or higher than other disclosed works. In order to test the weight loss of the coated fibers, the weight of packing was measured after 20, 40 and 60 min flowing of air through the packing. The weight loss in all cases was very low (up to 0.001g); thus good quality of coating was occurred.

The possibility of employing internal wall as mass absorber in rectangular water storage tanks subjected to harmonic ground motion excitation is investigated in this paper. Internal walls are usually used to lengthen the water path in the tank that could also be used as mass absorber to control seismic demand on tank's exterior walls. Derivation of the response of the coupled system including rigid external walls, flexible internal wall and fluid field is in frequency domain. The responses of the tank are evaluated subjected to harmonic excitations. By tuning the dynamic behavior of the tank and the sloshing liquid by changing the mass and stiffness of internal flexible wall, it is shown that wave elevation and water pressure on external rigid walls can be significantly reduced.

One of the main steps in regional rainfall analysis is to determine the most appropriate of several potentially possible probability distributions of rainfall data. For this purpose, the chi-square, the Kolmogrov-Smirnov and the Probability Plot Correlation Coefficient (PPCC) methods as goodness of fit tests are usually used. Recently, L-moment ratio diagrams have been recommended to verify the goodness of fit of various probability distributions to regional hydrological data such as rainfall. Therefore, the PPCC and L-moment procedure were applied to examine the most appropriate probability distributions of regional rainfall data investigation with 95% acceptance regions in north west of Iran. For this purpose, 50 years of monthly and annual rainfall data records at 12 synoptic stations were applied based on different evaluating criteria. The results of both PPCC procedure and L-moment diagram indicate that Pearson type three probability distribution is the best probability distribution for fitting rainfall data in north west of Iran, while the L-moment approach is able to test fitness of many samples using a single diagram.

An analytical approach is presented to assess the response of offshore structures under seismic excitation. This paper evaluates the impacts of different fluid field models and the mass of equipment at the top of offshore structure which is simulated as lumped mass on the responses of offshore structures. To do this, two and three dimensional fluid field models are developed. In three dimensional models different approximation regarding the free surface boundary condition associated with high and low frequency excitations are adopted. Then the alternation of response of structure with changing in the value of lumped mass is calculated. Finally the impacts of different models on the value of maximum displacement for Kobe earthquake are evaluated. It is shown that different approximations regarding the fluid field could largely change the value of maximum displacement evaluated by the models.

Soft computing techniques play an important role for decision-making applications with imprecise and uncertain knowledge. The application of fuzzy soft computing applications is rapidly emerging in the medical diagnosis and prognosis. A fuzzy expert system models knowledge as a set of explicit linguistic rules and performs reasoning with words. Although there are several technology-oriented studies reported for breast cancer diagnosis, few studies have been reported for the breast cancer prognosis. However, prognosis of breast cancer suffers from uncertainty and imprecision associated to imprecise input measures and incompleteness of knowledge as well as diagnosis. This research presents a fuzzy expert system for breast cancer prognosis. This approach is capable enough to capture ambiguity and imprecision prevalent in the characterization of the breast cancer. For this, the paper utilizes a Mamdani fuzzy inference model, which is more intuitive and has high interpretability for interacting with human experts during prognosis process. The main advantage of this work compared to other related studies, mostly presented for assessing the risk of the cancer development stage, is using unbiased input variables in the prognosis process; i.e., this model has the potential to predict the risk of developing breast cancer even in healthy females. Furthermore, the fuzzy expert system was evaluated on real dataset and the results of system were compared to an obstetrician decisions. The performance results on real dataset reveals superiority of the fuzzy expert system in the prognosis process with an average accuracy of 95%, compared to other related works. This approach is optimistic for prediction of breast cancer risk and early diagnosis of the cancer and can consequently improve survival rate.

A compact microstrip-fed antenna with dual notched bands is proposed. First, a simple basic configuration is presented for Ultra Wide Band (UWB) applications and then the dual band notched structure is extended from the UWB one. The basic structure of the UWB antenna consists of a simple square radiating patch and a ground plane with a wide square slot on back of the substrate. A semi-circle shaped slot is cut from the ground plane to improve the antenna impedance matching. In the sequel, with the aim at filtering Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN), via-fed inverted T-shaped element and two rectangular stubs are embedded in the antenna structure. The presented antenna is printed on a 20×20×0.8 mm3 FR4 substrate and operates over the frequency range of 2.9-16 GHz with WiMAX and WLAN notched. To compare the performance of the proposed UWB antenna to some previous designs, a novel framework based on the Analytical Hierarchy Process (AHP) is proposed. Using AHP methodology, the important operational aspects of antennas are taken into account simultaneously, resulting in a comprehensive comparison. Expert Choice software is used to apply the AHP technique.

A set of hybrid microstrip patch and semi-circular cavity antennas is introduced. The semi-circular cavity is implemented using Half-mode Substrate Integrated Waveguide (HMSIW) technique. Different shapes of the patch including rectangular, semi-circular and equilateral triangular are excited using proximity effect by the semi-circular SIW cavity at its TM010 mode. The proposed antenna structures have been excited using an inset 50 W microstrip line that leads to a facility of planar circuit integration. The inherent limited bandwidth of the conventional microstrip patch antenna and SIW cavity-backed slot antenna is improved about 6 to 10% depending on the type of the patch using the proposed structure. Additionally, the proposed hybrid antenna enhanced the antenna gain by about 1.5 dB in comparison with the half-mode cavity without patch. Meanwhile, the proposed hybrid antennas made on a single-layer substrate has a low fabrication cost using printed circuit board (PCB) process. Three hybrid antennas are numerically and experimentally investigated. A comparative study between the three different structures contains gain, bandwidth, Cross Polarization Level (CPL) and Front to Back Ratio (FBR) is presented.

Radar Signal Processing has been an interesting area of research for realization of programmable digital signal processor using VLSI design techniques. Digital Signal Processing (DSP) algorithms have been an integral design methodology for implementation of high speed application specific real-time systems especially for high resolution radar. In recent times, CORDIC algorithm is turned out to be a huge researched outcome for its easy realizability in on-chip design in the field of vector rotated DSP applications. In this paper, we propose a pipelined CORDIC architecture for digital demodulation in high performance, low power frequency modulated CW Radar. A complex Digital Phase Locked Loop (DPLL) has been used for digital demodulation with pipelined CORDIC module as its core processing element. The FPGA implementation of CORDIC based design has been chosen because of its inherent high throughput of system due to its pipelined architecture where latency is reduced in each of the pipelined stage. Substantial amount of resource utilization has been reduced in proposed design. For better loop performance of first order complex DPLL during demodulation, the convergence of the CORDIC architecture is also optimized. Multiplierless BOXCAR filter has been incorporated at the final stage of the design for better information recovery from narrow samples with little energy signal and easy realization. Hardware synthesized result using Cadence design tools are presented.

Cumulative Count of Conforming (CCC) charts are utilized for monitoring the quality characteristics in high-quality processes. Executive cost of control charts is a motivation for researchers to design them with the lowest cost. Usually, in most researches, only one objective named cost function is minimized subject to statistical constraints, which is not effective method for economic-statistical design of control charts. In this paper, a multi-objective model for the economic-statistical design of the CCC control chart is developed. Then, multi-objective evolutionary algorithm (NSGA-II) for obtaining the Pareto optimal solution of the model is proposed. A numerical example is applied to illustrate the effectiveness of the proposed model. This model leads to lower cost and smaller probability of Type I and Type II errors, compared with economic model. In addition, a sensitivity analysis is done to investigate the effect of input parameters on the best solutions of the proposed model.

Nowadays, in majority of academic contexts, it has been tried to consider the highest possible level of similarities to the real world. Hence, most of the problems have complicated structures. Traditional methods for solving almost all of the mathematical and optimization problems are inefficient. As a result, meta-heuristic algorithms have been employed increasingly during recent years. In this study, a new algorithm, namely Seeker Evolutionary Algorithm (SEA), is introduced for solving continuous mathematical problems, which is based on a group seeking logic. In this logic, the seeking region and the seekers located inside are divided into several sections and they seek in that special area. In order to assess the performance of this algorithm, from the available samples in papers, the most visited algorithms have been employed. The obtained results show the advantage of the proposed SEA in comparison to these algorithms. At the end, a mathematical problem is designed, which is unlike the structure of meta-heuristic algorithms. All the prominent algorithms are applied to solve this problem, and none of them is able to solve.

In this paper, a new methodology in the area of cost of quality (COQ) is proposed to determine the optimal investment allocation to all costs. The goal is to minimize costs involved in achieving a required level of quality. The contribution of this paper is fivefold: (I) considering two types of weights for each part of COQ, in which the first type is determined by the cost volume and the second is obtained by applying a decision-making technique; (II) participating shareholders’ opinions through the balanced scorecard method; (III) presenting a mathematical programming model to maximize the investment effectiveness; (IV) considering a continuous improvement cycle to tune the model parameters, and (V) developing COQ technique in fuzzy environment to enhance the accuracy of traditional methods of employing linguistic variables. To demonstrate the applicability of the presented methodology, a case study is investigated in automotive parts industry in Asia.

New approaches to extracting natural hydroxyl carbonate apatite from bio waste of bovine bones cortical femur have been developed. To extract pure and natural bio ceramics, three different treatments have been applied: (1)-Calcination heat treatment at temperature of 700°C, (2)-Alkaline hydrothermal at temperature of 275°C and (3)- Pressurized low polarity water hydrothermal at temperature of 250°C. Raw bovine bone and obtained apatite have been characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction, differential thermal analysis (DTA), thermogravimetric analysis (TGA), fluorescent microscopy and scanning electron microscopy (SEM). Under heat treatment process, mainly all the organic component such as collagen was removed at temperature of 600°C and a hydroxyl carbonate apatite was obtained. The presence of carbonate groups led to increasing the biocompatibility and will be preferable for orthopedic and medical usages. The degree of crystallization of powders is increased by increasing of temperature from 250°C for pressurized low polarity water processing to 600°C for calcinations treatment. Growth behavior and adhesion of cultured umbilical cord mesenchymal stem cells on the surface of 2-D hydroxyapatite scaffolds derived by these three different methods have been investigated. The results show that the stem cells could survive and attach on surface of derived carbonated hydroxyapatite scaffolds by calcinations.

Electrochemical depositions of calcium phosphide layer on Ni-Ti alloy in concentrated simulated body flood (SBF×5) were carried out by cathodic electrodeposition. This layer was deposited on Ni-Ti alloy substrate under 10mA/cm2 current density for 2 hours at room temperature. Then, in order to investigate the bioactivity of the pre-calcified samples, they were put in SBF for 1 and 3 days at room temperature. The microstructure, chemical composition, and bioactivity of the coatings were evaluated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. Results showed that the activation of the surface of the Ni-Ti alloy by electrochemical process can significantly enhance the biomimetic deposition during time. On the other hand, by increasing immersion time of pre-calcified samples in SBF from 1 to 3 days, the biomimetic coating uniformly covered the surface of the sample. The ratio of the Ca/P for the pre-calcified sample after immersion in SBF for 3 days was about 1.5 which is very close to the Ca/P ratio of stoichiometric hydroxyapatite.

In this paper, experimental responses of the clamped mild steel, copper, and aluminium circular plates are presented subjected to blast loading. The GMDH-type (Group Method of Data Handling) neural networks are then used for the modelling of the mid-point deflection thickness ratio of the circular plates using those experimental results. The aim of such modelling is to show how the mid-point deflection varies with the variations of the important parameters. Further, it is shown that the use of dimensionless input variables, rather than the actual physical parameters, in such GMDH-type network modelling leads to simpler polynomial expressions which can be used for modelling and prediction purposes. It is also demonstrated that Singular Value Decomposition (SVD) can be effectively used to find the vector of coefficients of quadratic sub-expressions embodied in such GMDH-type networks. Such application of SVD will highly improve the performance of GMDH-type networks to model the nonlinear dynamic behavior of circular plates.