FGM micro-gripper under electrostatic and intermolecular Van-der Waals forces using modified couple stress theory

Reza Jahangiri,Hadi Jahangiri,Hamed Khezerloo 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.6

In this paper mechanical behavior of the functional gradient materials (FGM) micro-gripper under thermal load and DC voltage is numerically investigated taking into account the effect of intermolecular forces. In contrary to the similar previous works, which have been conducted for homogenous material, here, the FGM material has been implemented. It is assumed that the FGM micro-gripper is made of metal and ceramic and that material properties are changed continuously along the beam thickness according to a given function. The nonlinear governing equations of the static and dynamic deflection of microbeams have been derived using the coupled stress theory. The equations have been solved using the Galerkin based step-by-step linearization method (SSLM). The solution procedure has been evaluated against available data of literature showing good agreement. A parametric study has been conducted, focusing on the combined effects of important parameters included DC voltage, temperature variation, geometrical dimensions and ceramic volume concentration on the dynamic response and stability of the FGM micro-gripper.

Introducing the Innovative Post-tensioned Connection with the Rigid Steel Node

Ali Jahangiri,Farhad Behnamfar,Mohammad Jahangiri 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.4

Securing strength, stiffness, and ductility in connections is one of the most important goals in structural design. After the Northridge earthquake, most steel moment resistant frames were damaged due to sudden fractures in beam-to-column connections. This resulted in the reconsideration of connection design and performance. As an alternative to weld connections, some researchers proposed the implementation of post-tensioned connections. In the present paper, the innovative connection is a combination of high strength steel frames which, through a rigid steel node above and below the beam flanges, provide the required stiffness, strength and ductility. Advantages of this connection include self-centering capability, lack of residual deformations, and energy dissipation which are analyzed using numerical and experimental methods. The modeling procedure and the cyclic behavior of the connection are studied and the analytical and the experimental results are compared. The results show that the cyclic responses observed in numerical simulations are in agreement with those from the experimental task and that the connection is superior to conventional moment resisting connections. The assumptions employed in simplifying simulations demonstrated high accuracy revealing an improvement in the seismic behavior of the connection.

Needle Stick Injuries and their Related Safety Measures among Nurses in a University Hospital, Shiraz, Iran

Jahangiri, Mehdi,Rostamabadi, Akbar,Hoboubi, Naser,Tadayon, Neda,Soleimani, Ali Occupational Safety and Health Research Institute 2016 Safety and health at work Vol.7 No.1

Background: This study aimed to determine the prevalence and factors related to needle stick injuries (NSIs) and to assess related safety measures among a sample of Iranian nurses. Methods: In this cross-sectional study, a random sample of 168 registered active nurses was selected from different wards of one of the hospitals of Shiraz University of Medical Sciences (SUMS). Data were collected by an anonymous questionnaire and a checklist based observational method among the 168 registered active nurses. Results: The prevalence of NSIs in the total of work experience and the last year was 76% and 54%, respectively. Hollow-bore needles were the most common devices involved in the injuries (85.5%). The majority of NSIs occurred in the morning shift (57.8%) and the most common activity leading to NSIs was recapping needles (41.4%). The rate of underreporting NSIs was 60.2% and the major reasons for not reporting the NSIs were heavy clinical schedule (46.7%) and perception of low risk of infection (37.7%). A statistically significant relationship was found between the occurrence of NSIs and sex, hours worked/week, and frequency of shifts/month. Conclusion: The study showed a high prevalence of NSIs among nurses. Supportive measures such as improving injection practices, modification of working schedule, planning training programs targeted at using personal protective equipment, and providing an adequate number of safety facilities such as puncture resistant disposal containers and engineered safe devices are essential for the effective prevention of NSI incidents among the studied nurses.

HARMONIC MEROMORPHIC STARLIKE FUNCTIONS

Jahangiri, Jay, M. Korean Mathematical Society 2000 대한수학회보 Vol.37 No.2

We give sufficient coefficient conditions for a class of meromorphic univalent harmonic functions that are starlike of some order. Furthermore, it is shown that these conditions are also necessary when the coefficients of the analytic part of the function are positive and the coefficients of the co-analytic part of the function are negative. Extreme points, convolution and convex combination conditions for these classes are also determined. Fianlly, comparable results are given for the convex analogue.

Human Error Analysis in a Permit to Work System: A Case Study in a Chemical Plant

Jahangiri, Mehdi,Hoboubi, Naser,Rostamabadi, Akbar,Keshavarzi, Sareh,Hosseini, Ali Akbar Occupational Safety and Health Research Institute 2016 Safety and health at work Vol.7 No.1

Background: A permit to work (PTW) is a formal written system to control certain types of work which are identified as potentially hazardous. However, human error in PTW processes can lead to an accident. Methods: This cross-sectional, descriptive study was conducted to estimate the probability of human errors in PTWprocesses in a chemical plant in Iran. In the first stage, through interviewing the personnel and studying the procedure in the plant, the PTW process was analyzed using the hierarchical task analysis technique. In doing so, PTWwas considered as a goal and detailed tasks to achieve the goal were analyzed. In the next step, the standardized plant analysis risk-human (SPAR-H) reliability analysis method was applied for estimation of human error probability. Results: The mean probability of human error in the PTW system was estimated to be 0.11. The highest probability of human error in the PTW process was related to flammable gas testing (50.7%). Conclusion: The SPAR-H method applied in this study could analyze and quantify the potential human errors and extract the required measures for reducing the error probabilities in PTW system. Some suggestions to reduce the likelihood of errors, especially in the field of modifying the performance shaping factors and dependencies among tasks are provided.

MEROMOR0PHIC UNIVALENT HARMONIC FUNCTIONS WITH NEGATIVE COEFFICIENTS

Jahangiri, Jay M.,Silverman, Herb Korean Mathematical Society 1999 대한수학회보 Vol.36 No.4

The purpose of this paper is to give sufficient coefficient conditions for a class of univalent harmonic functions that map each $$\mid$z$\mid$$ = r >1 onto a curve that bounds a domain that is starlike with respect to origin. Furthermore, it is shown that these conditions are also necessary when the coefficients are negative. Extreme points for these classes are also determined. Finally, comparable results are given for the convex analgo.

A Descriptive Study of Occupational Health Services in Self-employed Enterprises (Nanoscale Enterprises), Shiraz, Iran

Jahangiri, Mehdi,Rostamabadi, Akbar,Yekzamani, Parvaneh,Abadi, Bahare Mahmood,Behbood, Fariborz,Ahmadi, Seyyedeh Fatemeh,Momeni, Zahra Occupational Safety and Health Research Institute 2016 Safety and health at work Vol.7 No.4

Background: This study was conducted with aim of providing an overview of the current status of occupational health services and identifying the most common harmful agents at workplaces of Iranian self-employed enterprises (Nano-Scale Enterprises). Methods: A cross-sectional study was performed among a random sample including 1,758 employees engaging in self-employed enterprises with 5 and less employees. Results: Coverage of occupational health surveillance was very poor, annual health examinations were been conducted only for 64 (3.64%) of males and 31 (1.76%) of females, and occupational health trainings were not included of the services at all. Personal Protective Equipment were available in 462 (26.3%) of the enterprises. only in 0.4% of the enterprises working processes were been equipped by a local exhaust ventilation system. Difficult postures were the most common (81.5%) adverse working conditions. Conclusion: This study revealed a poor level of the implementation of occupational health services in Iranian self-employed enterprises. Based on the findings, providing basic training on the occupational health, more enforcing in conduction of health examinations and providing PPE, and taking appropriate strategies aimed at eliminating or minimizing work environment harmful agents are the major factor that should be considered to improve the level of occupational health services among the studied enterprises.

Failure analysis of gas turbine generator cooling fan for 14o and 19o - blades angle of attack

Ali Jahangiri,Seyed Ebrahim Moussavi Torshizi,Seyed Majid Yadavar Nikravesh 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.4

In gas turbine power plants, a fan is used as a cooling system to dissipate generated heat in coils (copper conductors) and generator electric circuits at the end sides of its rotor. In some cases, fracture of blades causes short circuit between rotor and stator and consequently generator explosion and made lot of financial problems. The fracture of cooling fan blades has been occurred five times at the turbine side of the generator in our case of study, just 100 hr after resuming operation after overhaul. Using numerical analysis as well as laboratory investigation - includes visual inspections, metallography and SEM - can help better finding failure problems that cause blade failures. A series of numerical analysis was performed to diagnose the cause of failure possibility. CFD analysis is used to study the airflow distribution in order to observe probable separation phenomenon and pressure forces that they are imposed to fan blades due to operation. A finite element method was utilized to determine the stresses and dynamic characteristics of the fan blade (natural frequencies,stresses and vibrations).

Using microwave heating for synthesis of SrCO3 nanostructures with different morphologies

Hasan Jahangiri,Mehdi Ranjbar,Mohammad Ali Taher,Hanif kazerooni 한국공업화학회 2015 Journal of Industrial and Engineering Chemistry Vol.21 No.1

Strontium carbonate (SrCO3) nanostructures were synthesized successfully via simple microwaveapproach by Sr(NO3)2, carbonate powder and sodium hydroxide (NaOH) as reagents. The effects ofmicrowave time and power were investigated on product size and morphology. The products werecharacterized with X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmissionelectron microscopy (TEM), Ultraviolet–visible (UV–vis) and room temperature photoluminescencespectroscopy (PL).

Numerical simulation of hemodynamic parameters of turbulent and pulsatile blood flow in flexible artery with single and double stenoses

Mehdi Jahangiri,Mohsen Saghafian,Mahmood Reza Sadeghi 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.8

This article investigates the pulsatile and turbulent blood flows in flexible artery with single and double stenoses. The changes in pressuredrop, mean wall shear stress (WSS), radial displacement of the artery, and oscillating shear index are investigated. Similar to experimentaldata, the results of the present study show that a laminar flow occurs for stenosis of up to 70%, and for 80% stenosis the flowis turbulent. The mean WSS analysis shows that assuming the flow is laminar causes more errors than assuming the walls are solid. Thecomparison of the results for single stenosis with those for double stenosis reveals that the dilation in the arterial walls in double stenosesis much more common than in single stenosis. Therefore, the maximum mean WSS in double stenoses is less than that in single stenosis. The results also indicate that the axial pressure drop in double stenoses is higher than that in single stenosis.