279 research outputs found
Corrigendum
No full textBiazar E, Heidari M, Asefnezhad A, Montazeri N. The relationship between cellular adhesion and surface roughness in polystyrene modified by microwave plasma radiation. International Journal of Nanomedicine. 2011;6:631-639.The correct spelling of the third author's name is "Asefnejad."Original articl
Corrigendum
No full textHeidari S, Azhdadi SN, Asefnezhad A, Sadraeian M, Montazeri M, Biazar EThe relationship between cellular adhesion and surface roughness for polyurethane modified by microwave plasma radiation. International Journal of Nanomedicine. 2011;6:641-647.The correct spelling of the third author's name is "Asefnejad."Original Articl
Multi-strategy Gaussian Harris hawks optimization for fatigue life of tapered roller bearings
No full textBearing is one of the most fundamental components of rotary machinery, and its fatigue life is a crucial factor in designing. The design optimization of tapered roller bearing (TRB) is a complex design problem because various arrays of designing parameters and functional requirements should be fulfilled. Since there are many design variables and nonlinear constraints, presenting an optimal design of TRBs poses some challenges for metaheuristic algorithms. The Harris hawks optimization (HHO) algorithm is a robust nature-inspired method with unique exploitation and exploration phases due to its time-varying structure. However, this metaheuristic algorithm may still converge to local optima for more challenging problems such as the design of TRBs. Therefore, this study aims to improve the accuracy and efficiency of the shortcomings of this algorithm. The performance of the proposed algorithm is first evaluated for the TRB optimization problem. The TRB optimization design has nine design variables and 26 constraints because of geometrical dimensions and strength conditions. The productivity of the proposed method is compared with diverse metaheuristic algorithms in the literature. The results demonstrate the significant development of dynamic load capacity in comparison to the standard value. Furthermore, the enhanced version of the HHO algorithm presented in this study is benchmarked with various well-known engineering problems. For supplementary materials regarding algorithms in this research, readers can refer to https://aliasgharheidari.com.Ozyegin Universit
Active vibration control of rotor-bearing system by virtual dynamic absorber
No full textThe main sources of the vibration in rotor dynamic systems are unbalanced masses and manufacturing defects of bearings used in the rotor system. In this study, magnetic absorber as a new method brings the rotor system out of resonance state by applying a dynamic absorber system force and creating two new natural frequencies. This study virtually reconstructed magnetic absorber controller software as a combined active and passive dynamic absorber to reduce vibration amplitude, efficiently. In this approach, combined routes are defined for the rotor frequency response, so that the optimal values of the parameters of dynamic absorber system are calculated using H∞ method and maximum damping for frequencies lower and higher than resonance frequencies, respectively. The results confirm that transient response overshoot is less, and transient response attenuation is more in maximum damping method. Hence, the controller system easily recognizes initial overshoots and determines the parameters of the dynamic absorber system in accordance with maximum damping state if it is struck at any rotor frequency and any rotation angle. It is also observed that for all rotor rotation frequencies, the system overshoot reduces in comparison with H∞ method by using this control method
Vibration control of imbalanced Jeffcott rotor by virtual passive dynamic absorber with optimal parameter values
No full text Today, dynamic absorbers are widely used to control vibrations of the systems that are being excited by the harmonic forces. In this paper, the usage of the magnetic force as virtual dynamic absorber for vibration control in rotary systems is investigated. In order to examine this new method, two different types of passive dynamic absorber systems are applied to control imbalanced Jeffcott rotor vibrations. In the first type of the absorber system, damper is located between the absorber mass and the disk and in the second type, it is located between the absorber mass and the ground. Then, the optimal parameters of absorber system, stiffness and damping have been analytically achieved by using two fixed points theory. Moreover, for further reduction of the vibration amplitude, combined paths have been designed for rotor frequency response. Finally, in order to evaluate the obtained results, the experimental data of our virtual dynamic absorbers were compared with simulation results and it is found that the vibration amplitude of rotor was efficiently limited in this case. Furthermore, the second type of the absorber system with equal mass ratio to the first type of the absorber system was more efficient than the first one in reduction of the amplitude of vibrations. Our findings show that the second absorber transfer more force than the first one since the second absorber connects chasis of system with damper. Therefore, it is recommended to apply the first absorber after the first resonance. </jats:p
Relationship between Urolithiasis and Nutrition in Patients with Urinary Stones in Ardabil City
No full textBackground & Objectives: Urolithiasis is the third common urinary disease. While,
relationship between the urinary stones and diet is known to some extent, but there are
controversies about it. The aim of this study was to determine the association between food
habit, nutrients intake and kinds of urinary stone disease.
Methods: This cross-sectional and descriptive analytical study was performed on 150 patients
(91 male and 59 females) with urinary stone disease in Ardabil during 2008-2009. Data of
urinary stones analysis, type of stone in the graph, type of stone, preventive emprise and type
of drinking water were recorded. Food data were recorded using 24-hour dietary recalls three
days in week and food frequency questionnaires. Data were analyzed using SPSS, Food
Processor III software, and ANOVA Statistical program.
Results: Findings showed that the most common and lowest form of urinary stone disease in
men and women were calcium oxalate and ammonium phosphate, respectively. There was
significant inverse association between beta-carotene intake and the percentage of uric acid
stone disease (p<0.05). We observed significant relationship between vitamin A and folacin
intake with percentage of uric acid stone disease (p<0.05). There was significant relationship
between consumption of cheese and pickles with calcium phosphate stone disease (p<0.05).
There was no significant association between other foods and nutrients intake with types of
urinary stone disease.
Conclusion: This study showed the consumption of some nutrients including folacin, vitamin
A and some foods such as cheese was associated with the incidence of urinary stone disease.
Therefore, taking accurate diet could possibly prevent the incidence of urinary stone diseases
Investigating the effect real options on stock return a panel: Var approach
No full textIn this study, evidence is presented that shows the positive stock return-volatility relationship at the firm level is due to firm's real options. Therefore, the purpose of the study was to investigate the effect of real option on the relationship between stock returns and its volatility at the company level. In the real options theory, it can be deduced: a) that the positive stock return-volatility at the firm level for those firms with more real options is much stronger and that the level of the sensitivity of the firm's stock return in response to the changes in the stock return volatility is significantly reduced due to the use of real options. b) that the positive relationship between stock return and return volatility at the firm level for companies that have investment opportunities are stronger. While, this relationship for asset-based companies is weaker. In other words, the return – volatility relationship is stronger for newly established companies, small companies, companies with modern research and development and finally companies with high growth rates. c) That, the relationship between return – volatility for companies that have fewer restrictions and greater capabilities to better respond to uncertain demands (greater flexibility) are much stronger. In the real options models, managerial flexibility leads to greater firm's value convexity function. Thus, according to the theory of Jensen’s inequality, sensitivity of the firm's value due to volatility in firm's underlying assets, while increasing, it should help to strengthen the company's flexibility to the changes in investment decisions and operations
Business Process Quality Computation: Computing Non-Functional Requirements to Improve Business Processes
No full textBusiness process modelling is an important part of system design. When designing or redesigning a business process, stakeholders specify, negotiate, and agree on business requirements to be satisfied, including non-functional requirements that concern the quality of the business process. This thesis addresses the question of how to specify and compute the quality of a business process, given the model that stakeholders use. The motivation for this thesis is the increasing importance of the quality of business processes. Knowing the quality of specific business processes enables stakeholders to judge if these processes need improvement. Knowing the quality of the constructs of those processes (viz., events, inputs, activities, and outputs) and the way they are structured enables a more detailed analysis of their shortcomings and provides a basis for the design of improvements. The research challenge of this thesis is grounded in the assumption that: “Organisations need an appropriate means to effectively compute achievement of their goals and objectives by their business processes.” Given this challenge, the main research question on which this thesis focuses is: “Can the quality of a business process be computed quantitatively at different levels of granularity?” The research objective is: “To develop frameworks, factors, and metrics for computing non-functional requirements (quality) of business processes quantitatively at different levels of granularity.” The outcomes of this thesis are: 1) BPIMM, a language-independent business process integrating meta-model, based on the concepts of seven mainstream business process modelling languages: BPMN, EPC, RAD, UML AD, SADT, IDEF0, and IDEF3. 2) BPC-QC (Business Process Concept - Quality Computation), an approach to quality computation at the lowest level of granularity of a business process. The approach consists of: i. BPC-QEF (Business Process Concept - Quality Evaluation Framework), a language-independent generic framework and algorithm to compute the quality of the constructs of a business process: event, input, activity, and output. ii. A set of business process quality dimensions and factors. The following quality dimensions are distinguished: performance, efficiency, reliability, recoverability, permissibility, and availability. Each dimension categorises different quality aspects in terms of factors. A non-exhaustive set of sixteen quantitative factors is provided. iii. Quality metrics for each of the quality factors, to facilitate a quantitative computation of the quality of a specific construct of a business process. 3) BP-QC (Business Process - Quality Computation), an approach to compute the quality at the highest level of granularity of a business process. The approach consists of: i. BP-CQCF (Business Process - Compositional Quality Computation Framework), a language-independent generic framework and algorithm to compute the quality of a business process as a whole, given the quality of its constructs. ii. A set of generic business process modelling patterns to decompose a business process into more succinct parts, namely: sequential, parallel with synchronisation, exclusive, inclusive, simple loop, and complex loop. iii. A set of over one hundred computational formulae. For each combination of modelling pattern and a quality factor, there is a formula to compute the quality. 4) AAV (Approach to Application and Validation), an evaluation plan to evaluate BPIMM, BPC-QC and BP-QC in practice, together with expert stakeholders. The plan consists of the units of measure, a measurement model, and a case study procedure. To evaluate the applicability of the contributions of this thesis to real world business needs, four case studies have been conducted in different environments: a Dutch educational institution, a global financial institution, an international financial service provider, and a Dutch research project on crisis management. Each of these case studies concerns a different, single business process. This thesis shows that: 1) A quality computation approach can be adopted independent of a business process modelling language. 2) Quantitative quality factors can be introduced specifically for the constructs of a business process. 3) Quantitative metrics and computational formulae can be developed for specific quality factors, allowing the computation of different aspects of the quality of a business process quantitatively at different levels of granularity. 4) An evaluation plan can be developed to evaluate the applicability of the contributions of this thesis (viz., BPIMM, BPC-QC, and BP-QC). The contributions of this thesis are designed to be beneficial to the areas of business and management, requirements engineering, software engineering, and business process modelling. In the areas of requirements engineering and software engineering, these contributions are intended to help practitioners to consider non-functional requirements at the earliest stage. In the area of business process modelling, information systems, service computing, and cloud computing, the contributions can be used for quality-driven modelling, design, and redesign. To conclude, knowing the quality value of a business process at different levels of granularity provides a basis for its improvement.Multi Actor SystemsTechnology, Policy and Managemen
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