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Showing 619 results for Type of Study: Research

Rabie Mosaad Rabie, Hegazy Zaher, Naglaa Ragaa Saied, Heba Sayed,
Volume 0, Issue 0 (10-2024)
Abstract

Harris Hawks Optimization (HHO) algorithm is a new metaheuristic algorithm, inspired by the cooperative behavior and chasing style of Harris' Hawks in nature called surprise pounce. HHO demonstrated promising results compared to other optimization methods. However, HHO suffers from local optima and population diversity drawbacks. To overcome these limitations and adapt it to solve feature selection problems, a modified Harris hawks optimization (MHHO) is proposed for solving global optimization problems. a Modified Harris hawks optimization (MHHO) algorithm is proposed using mutation- selection approach. Results from systematic experiments conducted on 23 benchmark functions demonstrated that the proposed method can provide a more reliable solution than other well-known algorithms. The MHHO shows completely superiority than the basic HHO with the best average values and standard deviations and obtains the smallest average values compared to other algorithms and improve the convergence speed. The experiments show competitive results compared to other meta-heuristic algorithms, which prove that MHHO has better optimization performance than others.
 
Amirmohammad Larni-Fooeik, Hossein Ghanbari, Seyed Jafar Sadjadi, Emran Mohammadi,
Volume 0, Issue 0 (10-2024)
Abstract

In the ever-evolving realm of finance, investors have a myriad of strategies at their disposal to effectively and cleverly allocate their wealth in the expansive financial market. Among these strategies, portfolio optimization emerges as a prominent approach used by individuals seeking to mitigate the inherent risks that accompany investments. Portfolio optimization entails the selection of the optimal combination of securities and their proportions to achieve lower risk and higher return. To delve deeper into the decision-making process of investors and assess the impact of psychology on their choices, behavioral finance biases can be introduced into the portfolio optimization model. One such bias is regret, which refers to the feeling of remorse that can induce hesitation in making significant decisions and avoiding actions that may lead to unfavorable investment outcomes. It is not uncommon for investors to hold onto losing investments for extended periods, reluctant to acknowledge mistakes and accept losses due to this behavioral tendency. Interestingly, in their quest to sidestep regret, investors may inadvertently overlook potential opportunities. This research article aims to undertake an in-depth examination of 41 publications from the past two decades, providing a comprehensive review of the models and applications proposed for the regret approach in portfolio optimization. The study categorizes these methods into accurate and approximate models, scrutinizing their respective timeframes and exploring additional constraints that are considered. Utilizing this article will provide investors with insights into the latest research advancements in the realm of regret, familiarize them with influential authors in the field, and offer a glimpse into the future direction of this area of study.  The extensive review findings indicate a growth in the adoption of the regret approach in the past few years and its advancements in portfolio optimization.

La Sinaini, Saptana, Sri Bananiek, Bungati,
Volume 0, Issue 0 (10-2024)
Abstract

Cashew nuts, a plantation commodity from Indonesia, come with a high economic value. Cashew nut processing enterprises are crucial in elevating the value added, broadening the work field, and enhancing labor absorption. This research provides an analysis of the performance and marketing strategy of micro, small, and medium enterprises (MSMEs) of cashew nut processing in Muna. It was a case study using explorative, descriptive, and qualitative methods and involved an informant, i.e., the owner of CV Hukasari Semesta. Results demonstrated that CV Hukasari Semesta contributed to the household economic sector, especially in espousing the cashew nut supply chain, which consisted of cashew nut farmers as the key material suppliers, village collecting traders, transport workers, transportation entrepreneurs, processing workers, and store employees. In operating the cashew nut processing business, parties concerned applied strategies for staple ingredient procurement, processing process, management, packaging, capital procurement, more labor recruitment, processing technology procurement, product innovation by varying product packaging and flavors, market network expansion by distributing products to supermarkets and retailers, and market segmentation. Additionally, among the marketing strategies to escalate cashew nut processing MSMEs in Muna were improving product innovation by developing more attractive product packaging based on national standards, carrying out well-planned branding, developing digital-based product information and marketing systems, honing processing and marketing labor skills, increasing processing industrial tool technology, and bolstering business capital.
Renny Rochani, Wahyudi Sutopo, Satrio Fachri Chaniago,
Volume 0, Issue 0 (10-2024)
Abstract

Electric motorcycles (EM) are the solution for eco-friendly vehicles, but there are some dilemmas caused by the source of the energy used to charge EM and its limited charging facilities. This article aimed to answer the dilemma of EM usage by designing the Mobile Battery Swap Charging Station (MBSCS) initial design based on using solar power plants as its source of energy. The initial design was developed using the design thinking method. The results of this study provide the MBSCS initial design, technical indicators to assess the MBSCS system, and simulation results using PVSyst software. The findings of this study serve as a benchmark for designing mobile and environmentally friendly electric vehicle charging facilities in the future and demonstrating the potential use of portable solar power generators.

Amal Qassim,
Volume 0, Issue 0 (10-2024)
Abstract

The aim of this study is to explore gender differences in occupational stress sources, coping strategies, and emotional well-being among academic staff in Saudi public universities. The leading theory of transactional stress and coping implies the impact of stress and coping strategies on the health and well-being of people. The study surveyed 475 academic staff, 340 females and 137 males employed in Saudi public universities. They were invited to participate in the study by responding to the questionnaire. The study's significant findings reveal distinct variations in occupational stress levels between male and female academic staff. Additionally, it highlights gender-based differences in coping strategies employed by academic staff. Furthermore, the study identifies a prevalent issue of suboptimal levels of emotional well-being among academic staff at public universities in Saudi Arabia. These findings underscore the importance of addressing gender-specific stressors and promoting strategies for enhancing emotional well-being within the academic environment. The presented results consider relevant research, and the practical implications indicate that when Saudi-based universities implement policies and support systems for their staff members, they should consider the gender-based differences emphasized in this study. This could involve providing resources and training for stress management while fostering a healthy work-life balance.

F.d. Javanroodi , K. M. Nikbin ,
Volume 17, Issue 3 (9-2006)
Abstract

There is an increasing need to assess the service life of components containing defect which operate at high temperature. This paper describes the current fracture mechanics concepts that are employed to predict cracking of engineering materials at high temperatures under static and cyclic loading. The relationship between these concepts and those of high temperature life assessment methods is also discussed. A model for predicting creep crack growth initiation and growth in terms of C* and the creep uniaxial ductility is presented and it is shown that this model gives good agreement with the experimental results. The effects of cyclic loading on crack growth behaviour are considered and fractography evidence is shown to back a simple cumulative damage concept when dealing with creep/fatigue interaction. Finally a discussion is presented which highlights the important aspect of life assessment methodology for high temperature plant.


H. Yarjiabadi, M. H. Shojaeefard, A.r. Noorpoor, H.yarjiabadi, , M. Habibian , A.r. Noorpoor ,
Volume 17, Issue 3 (9-2006)
Abstract

The hydrocyclone has a very important roll in industrial separation. The consideration of its behavior is very important for design. In this investigation, behavior of water flow and particles trajectory inside a hydrocyclone has been considered by means of numerical and experimental methods, and results have been compared together. To have a numerical simulation, a CFD software was used, and for modeling flow the RNG k – model applied. Finally, the effect of particle size on hydrocyclone performance has been studied. It was found that the grade efficiency and number of particle that exit from underflow of the hydrocyclone is increased when bigger particles is used.

A series of experiments has been carried out in a laboratory with a hydrocyclone. Comparison shows that, there is a good agreement between the CFD models and experimental result.


M. Haghpanahi, H. Pirali ,
Volume 17, Issue 3 (9-2006)
Abstract

Finite element analysis of a tubular T-joint subjected to various loading conditions including pure axial loading, pure in-plane bending (IPB) and different ratios of axial loading to in-plane bending loading has been carried out. This effort has been established to estimate magnitudes of the peak hot spot stresses (HSS) at the brace/chord intersection and to find the corresponding locations as well, since, in reality, offshore tubular structures are subjected to combined loading, and hence fatigue life of these structures is affected by combined loading. Therefore in this paper, at the first step, stress concentration factors (SCFs) for pure axial loading and in-plane bending loading are calculated using different parametric equations and finite element method (FEM). At the next step, the peak HSS distributions around the brace/chord intersection are presented and verified by the results obtained from the API RP2A Code procedure. Also the locations of the peak hot spot stresses which are the critical points in fatigue life assessment have been predicted. 


M. M. Shokrieh, R. Rafiee ,
Volume 17, Issue 3 (9-2006)
Abstract

The main goal of this research is to extract the full mechanical properties of stitch biax and triax composite materials which are necessary for finite element analysis, based on limited available experimental data and without performing full static characterization tests. Utilized experimental data are limited to elastic modulus of two 0o and 45o directions. Using presented technique and aforementioned data, mechanical properties of unidirectional fabrics of biax and triax are obtained and consequently mechanical properties of biax and triax composites are calculated. Evaluation of the results proved proper performance of the technique in this research.


M.r. Modarres Razavi, S.h. Seyedein, P.b. Shahabi , S.h Seyedein,
Volume 17, Issue 3 (9-2006)
Abstract

In this paper hemodynamic wall parameters which play an important role to diagnose arterial disease were studied and compared for three different rheology models (Newtonian, Power law and Quemada). Also because of the pulsatile behavior of blood flow the results were obtained for three Womersley numbers which represent the frequencies of the applied pulses. Results show that Quemada model always located between Newtonian and Power law models however its behavior is closer to Power law model. Concerning this behavior and better agreement between Quemada and experimental blood viscosity, it can be expected that Quemada results are more realistic and accurate.


M. Nikian, , M. Naghashzadegan, S. K. Arya ,
Volume 17, Issue 3 (9-2006)
Abstract

The cylinder working fluid mean temperature, rate of heat fluxes to combustion chamber and temperature distribution on combustion chamber surface will be calculated in this research. By simulating thermodynamic cycle of engine, temperature distribution of combustion chamber will be calculated by the Crank-Nicolson method. An implicit finite difference method was used in this code. Special treatments for piston movement and a grid transformation for describing the realistic piston bowl shape were designed and utilized. The results were compared with a finite element method and were verified to be accurate for simplified test problems. In addition, the method was applied to realistic problems of heat transfer in an Isuzu Diesel engine, and gave good agreement with available experimental.


M. H. Shojaeefard, F. A. Boyaghchi , M. B. Ehghaghi ,
Volume 17, Issue 4 (11-2006)
Abstract

In this paper the centrifugal pump performances are tested when handling water and viscous oils as Newtonian fluids. Also, this paper shows a numerical simulation of the three-dimensional fluid flow inside a centrifugal pump. For these numerical simulations the SIMPLEC algorithm is used for solving governing equations of incompressible viscous/turbulent flows through the pump. The k-ε turbulence model is adopted to describe the turbulent flow process. These simulations have been made with a steady calculation using the multiple reference frames (MRF) technique to take into account the impeller- volute interaction. Numerical results are compared with the experimental characteristic curve for each viscous fluid. The data obtained allow the analysis of the main phenomena existent in this pump, such as: head, efficiency and power changes for different operating conditions. Also, the correction factors for oils are obtained from the experiment for part loading (PL), best efficiency point (BEP) and over loading (OL). These results are compared with proposed factors by American Hydraulic Institute (HIS) and Soviet :::union::: (USSR). The comparisons between the numerical and experimental results show good agreement.


Gh. Yari , M. D Jafari ,
Volume 17, Issue 4 (11-2006)
Abstract

Main result of this paper is to derive the exact analytical expressions of information and covariance matrix for multivariate Pareto, Burr and related distributions. These distributions arise as tractable parametric models in reliability, actuarial science, economics, finance and telecommunications. We showed that all the calculations can be obtained from one main moment multidimensional integral whose expression is obtained through some particular change of variables. Indeed, we consider that this calculus technique for that improper integral has its own importance.


 


A. Shidfar, Ali Zakeri,
Volume 17, Issue 4 (11-2006)
Abstract

This paper considers a linear one dimensional inverse heat conduction problem with non constant thermal diffusivity and two unknown terms in a heated bar with unit length. By using the WKB method, the heat flux at the end of boundary and initial temperature will be approximated, numerically. By choosing a suitable parameter in WKB method the ill-posedness of solution will be improved. Finally, a numerical example will be presented.


M.r. Alirezaee, S.a Mir-Hassani,
Volume 17, Issue 4 (11-2006)
Abstract

In the evaluation of non-efficient units by Data Envelopment Analysis (DEA) referenced Decision Making Units (DMU’s) have an important role. Unfortunately DMU’s with extra ordinary output can lead to a monopoly in a reference set, the fact called abnormality due to the outliers' data. In this paper, we introduce a DEA model for evaluating DMU’s under this circumstance. The layer model can result in a ranking for DMU’s and obtain an improving strategy leading to a better layer.


M. Nadjafikhah, H. R. Salimi Moghaddam ,
Volume 17, Issue 4 (11-2006)
Abstract

In this article, we generalize the concept of the Lie algebra of vector fields to the set of smooth sections of a T-bundle which is by definition a canonical generalization of the concept of a tangent bundle. We define a Lie bracket multiplication on this set so that it becomes a Lie algebra. In the particular case of tangent bundles this Lie algebra coincides with the Lie algebra of vector fields.


A. Aghajani , V. Roomi ,
Volume 18, Issue 1 (1-2007)
Abstract

Abstract: This paper investigates the problem of whether all trajectories of the system and cross the vertical isocline, which is very important for the existence of periodic solutions and oscillation theory. Sufficient conditions are given for all trajectories to cross the vertical isocline.

 


M.b Ghaemi , P. Spain ,
Volume 18, Issue 1 (1-2007)
Abstract

Abstract: In this paper, we exhibit new conditions for the sum of two commuting AC-operators to be again an AC-operator. In particular, this is satisfied on Hilbert space when one of them is a scalar-type spectral operator.

 


M. Nadjafikhah , A.r. Forough ,
Volume 18, Issue 1 (1-2007)
Abstract

Abstract : Let be a 2nd order ODE. By Cartan equivalence method, we will study the local equivalence problem under the transformations group of time-fixed coordinates. We are going to solve this problem by an applicable method which has been recognized by R. Gardner, and classify them.

  


K. Maleknejad , M. Rabbani ,
Volume 18, Issue 1 (1-2007)
Abstract

 Abstract: There are some methods for solving integro-differential equations. In this work, we solve the general-order Feredholm integro-differential equations. The Petrov-Galerkin method by considering Chebyshev multiwavelet basis is used. By using the orthonormality property of basis elements in discretizing the equation, we can reduce an equation to a linear system with small dimension. For numerical examples, the solutions may be produced with good accuracy, by choosing suitable trial and test spaces in Petrov-Galerkin method.

 



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