Correction to : The effect of a blue enriched white light on salivary antioxidant capacity and melatonin among night shift workers : a field study

Reza Kazemi,Rasoul Hemmatjo,Hamidreza Mokarami 대한직업환경의학회 2019 대한직업환경의학회지 Vol.30 No.-

Field Study of Effects of Night Shifts on Cognitive Performance, Salivary Melatonin, and Sleep

Kazemi, Reza,Motamedzade, Majid,Golmohammadi, Rostam,Mokarami, Hamidreza,Hemmatjo, Rasoul,Heidarimoghadam, Rashid Occupational Safety and Health Research Institute 2018 Safety and health at work Vol.9 No.2

Background: Night shift work is associated with many problems such as sleep deprivation, sleepiness, decreased cognitive performance, increased human errors, and fatigue. This study set out to measure cognitive performance, melatonin rhythms, and sleep after different consecutive night shifts (7 vs. 4) among control room operators (CORs). Methods: The participants included 60 CORs with a mean age of 30.2 years (standard deviation, 2.0) from a petrochemical complex located in Southern Iran. Cognitive performance was assessed using the n-back task and continuous performance test. To evaluate melatonin, saliva was collected and tested by enzyme-linked immunosorbent assay. To assess sleep and sleepiness, the Pittsburgh Sleep Quality Index and Karolinska Sleepiness Scale were used, respectively. Results: Individuals who worked 7 consecutive night shifts had a significantly better cognitive performance and sleep quality than those who worked 4 consecutive night shifts. However, salivary melatonin profile and sleepiness trend were not affected by shift type. Conclusion: The main duty of CORs working night shifts at the studied industry included managing safety-critical processes through complex displays; a responsibility that demands good cognitive performance and alertness. It is suggested that an appropriate number of consecutive night shifts in a rotating shift system should be planned with the ultimate aim of improving CROs performance/alertness and enhancing safety.

Field Study of Effects of Night Shifts on Cognitive Performance, Salivary Melatonin, and Sleep

Reza Kazemi,Majid Motamedzade,Rostam Golmohammadi,Hamidreza Mokarami,Rasoul Hemmatjo,Rashid Heidarimoghadam 한국산업안전보건공단 산업안전보건연구원 2018 Safety and health at work Vol.9 No.2

Background: Night shift work is associated with many problems such as sleep deprivation, sleepiness, decreased cognitive performance, increased human errors, and fatigue. This study set out to measure cognitive performance, melatonin rhythms, and sleep after different consecutive night shifts (7 vs. 4) among control room operators (CORs). Methods: The participants included 60 CORs with a mean age of 30.2 years (standard deviation, 2.0) from a petrochemical complex located in Southern Iran. Cognitive performance was assessed using the n-back task and continuous performance test. To evaluate melatonin, saliva was collected and tested by enzymelinked immunosorbent assay. To assess sleep and sleepiness, the Pittsburgh Sleep Quality Index and Karolinska Sleepiness Scale were used, respectively. Results: Individuals who worked 7 consecutive night shifts had a significantly better cognitive performance and sleep quality than those who worked 4 consecutive night shifts. However, salivary melatonin profile and sleepiness trend were not affected by shift type. Conclusion: The main duty of CORs working night shifts at the studied industry included managing safety-critical processes through complex displays; a responsibility that demands good cognitive performance and alertness. It is suggested that an appropriate number of consecutive night shifts in a rotating shift system should be planned with the ultimate aim of improving CROs performance/alertness and enhancing safety.

The effect of a blue enriched white light on salivary antioxidant capacity and melatonin among night shift workers

Reza Kazemi,Rasoul Hemmatjo,Mokarami Hamidreza 대한직업환경의학회 2018 대한직업환경의학회지 Vol.30 No.-

Background: Because of their positive impact on individuals’ performance and alertness, blue enriched white light sources are gaining popularity in households and industries. However, these sources of blue light spectrum may cause oxidative stress. On the other hand, there are no empirical studies investigating the negative effect of blue enriched white light on oxidative stress. Thus, the current study aimed at empirical assessment of the effect of such light sources on oxidative stress among night shift workers. Methods: The study, which adopted a cross-sectional design, focused on 30 control room operators of a petrochemical complex. The subjects followed a shift-work schedule comprising 7 night shifts, 7 day shifts, and 7 days off. The subjects were exposed to 6500 K, 3000 K, and 17,000 K light sources (which have various degrees of blue light) during three consecutive work cycles, with each cycle lasting for 7 nights. In each light condition, three salivary measurements were conducted (at the beginning, in the middle, and at the end of the shift). The measurements were used to assess catalase (CAT), total thiol molecules (TTG), and total antioxidant capacity (TAC), and melatonin. Results: The results of repeated measures ANOVA showed that there was no significant difference among various light conditions with regard to salivary biomarkers (catalase, total thiol molecules, and total antioxidant capacity). There was however a significant difference between 3000 K and 17,000 K conditions with regard to the concentration of salivary melatonin (p = 0.001). Conclusion: Given that there was no significant difference among various light conditions in terms of biomarkers, it is concluded that using sources of light with high color temperature can be recommended. Nonetheless, because of the limitations of the present study (e.g. short period of intervention), it is suggested that care should be exercised in using such light sources.

Evaluation the behavior of pre-fabricated moment connection with a new geometry of pyramidal end block under monotonic and cyclic loadings

Seyed Morteza Kazemi,Mohammad Reza Sohrabi,Hasan Haji-Kazemi 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.3

Researchers have been long studying new building implementation methods to improve the quality of construction, reduce the time of assembly, and increase productivity. One of these methods is the use of modular pre-fabricated structural forms that are composed of a beam, column, short column, pyramidal end block, and connection plates. In this study, a new geometry for the pyramidal end block was proposed that helps facilitate the assembly procedure. Since the proposed configuration affects the performance of this form of connection, its behavior was evaluated using finite element method. For this purpose, the connection was modeled in ABAQUS and then validated by comparing the outputs with experimental results. The research proceeded through analyzing 16 specimens under monotonic and cyclic loading. The results indicated that using the pyramidal end block not only makes the assembly process easier but also reduces the out-of-plane displacement of the short column webs and the vertical displacement of beam end. By choosing appropriate section properties for column and beam, the connection can bear a rotation up to 0.01 radians within its inelastic region and a total of 0.04 radians without any significant reduction in its bearing capacity.

The effect of beam section property on the behavior of modular prefabricated steel moment connection

Seyed Morteza Kazemi,Mohammad Reza Sohrabi,Hasan Haji Kazemi 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.6

The specially prefabricated steel moment connections with pyramid head is one of the significant innovations in the steel structures forms to improve the installation time and simplify the construction procedure. The beams in this structure form are supported by two top and bottom angles and web double angles. Such a configuration despite its advantages increases the welding operation and filed installation time and costs. In this paper, the effect of using beams with channel and I section in three classes of seismically compact, seismically non-compact, and slender section according to width-to-thickness ratio on the behavior of the connection was investigated under monotonic and cyclic loading. Modeling was performed by ABAQUS and verified by the results of an experimental specimen. The findings indicated that using I and channel section instead of angle section reduces the amount of welding materials as well as easing the installation procedure. However, it has no significant effect on the ultimate strength and ductility of the connection. Furthermore, if the beam section is seismically compact, this form is considered as a special moment frame that has a rotation capacity up to 0.04 radians without any reduction in connection moment resistance.

Design equations for prefabricated steel moment connections

Seyed Morteza Kazemi,Mohammad Reza Sohrabi,Hasan Haji Kazemi 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.80 No.3

Recently, modular prefabricated steel moment connections have been widely studied by several researchers. These connections are made of tubular columns that are ended to horizontal plates at both sides, an inter-story short column, and truss beams that are joined to the connecting plates using top and bottom plates. In this study, a series of equations have been developed and presented for designing each component of this type of connection. Then, to verify the proposed equations, the connection was modeled in ABAQUS and then the results extracted from the equations and modeling were compared. The findings indicated that the proposed equations have the required accuracy.

Seismic shear strengthening of R/C beams and columns with expanded steel meshes

Reza Morshed,Mohammad Taghi Kazemi 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.3

Numerical and experimental behavior of moment concrete frame retrofitted with TADAS metal yielding damper under lateral loading

Reza Nazeran,Ali Hemmati,Hasan Haji Kazemi 국제구조공학회 2024 Structural Engineering and Mechanics, An Int'l Jou Vol.89 No.5

Since the cost of reconstruction is very high and the structure may have been damaged by an earthquake, we must retrofit the structure. Therefore, the importance of studying this issue is very high in order to achieve the desired resistance against the regulations. The present study involved the numerical and experimental analysis of nine concrete frames, consisting of three concrete frames, three concrete frames with bracing, and three concrete frames with a TADAS damper. The purpose of this study is to strengthen the damaged concrete frame using braces and TADAS dampers. Observations were made of the frames as they were subjected to controlled displacement. Also, ABAQUS software was used to compare numerical and experimental results. According to the results, the software was sufficiently capable of modeling the studied frames. Additionally, a parametric study was conducted on the thickness and number of bending plates. Thickness increases from 8 mm to 12 mm, 8 mm to 15 mm, and 8 mm to 20 mm, increasing the base shear by about 6.7%, 11.1%, and 25%, respectively. Furthermore, increasing the number of plates from 4 to 5, 4 to 6, and 4 to 7 increased base shears by about 4.5%, 8.4%, and 14%, respectively.

Progressive collapse analysis of two existing steel buildings using a linear static procedure

Reza JalaliLarijani,Murude Celikag,Iman Aghayan,Mahdi Kazemi 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.2

In this study, the vulnerability of two existing asymmetric steel building frames to Progressive Collapse (PC) is assessed. The buildings have different frame systems, steel sections and number of stories (nine and six). An alternate path method (APM) with a linear static analysis (LS) is carried out according to General Services Administration (GSA) 2003 guidelines. The Demand Capacity Ratio (DCR) of each primary element (beams and columns) is given with its specific details for all frames. The results show that the nine-story building with a dual frame system (moment frame with bracing system) has a lower susceptibility and greater resistance to PC than the six-story building with a simple building frame system (gravity system with bracing system). Implementing built-up box-shaped sections for columns is a better choice than using built-up I-shaped sections because there is no weak axis for the box section.