Showing 31 results for Jafari
Reza Jafari Nodoushan, Mostafa Azimzadeh, Sahar Bagheri, Arefeh Dehghani Tafti,
Volume 11, Issue 4 (12-2021)
Abstract
Introduction: In recent years tend to use of natural fibers has increased in making sound absorbers. Fiber-based natural materials have low density, low production costs, and are biodegradable.
Material and Methods: In this study, the effect of nanoclay and the behavior of the nanocomposite specimens containing tea waste, polypropylene, and nanoclay in the sound absorption coefficient are investigated.
Results: The results showed the sound absorption coefficient increases by increasing the tea waste weight percent of the polypropylene. 60% increase in tea waste has a special role in the absorption of sound waves at a frequency of 1000 Hz and 2500 to 6300 Hz frequency range as the TW60 N5 sample has the sound absorption coefficient 0.94 and 0.84 in 1000 and 6300 Hz frequencies, respectively. Comparison of the sound absorption coefficient of composite and nanocomposite showed that sound absorptions increase by adding nanoclay to the 5%, at frequencies above 2000 Hz.
Conclusion: Tea waste-based sound absorbers can be used in noise control due to the high acoustic absorption and no harmful effects on human health.
Ehsan Garosi, Adel Mazloumi, Amir Homayoun Jafari, Ahmadreza Keihani, Ali Sharifnezhad, Mansour Shamsipour, Ramin Kordi,
Volume 12, Issue 2 (6-2022)
Abstract
Introduction: The use of exoskeletons as a new ergonomics intervention to reduce musculoskeletal disorders risk factors and increase human performance has emerged in the fourth-generation industrial revolution. The aim of this study was to assess the cervical exoskeleton effect on the neck and shoulder muscles electrical activity.
Material and Methods: In this experimental study, 14 male participants were asked to perform the simulated overhead work with and without using the cervical exoskeleton at two neck postural angles randomly. During the task, electromyography of the target muscles in the neck and shoulders was recorded. In addition, at the end of each task, participants completed a perceived discomfort questionnaire. Electromyographic signals were processed with Matlab 2017b software and the level of the electrical activity of the target muscles was normalized to the maximum muscle activity. Data analysis was performed using Random intercept mix model in STATA 14 software.
Results: Mean perceived discomfort in the neck and shoulders regions significantly reduced by the exoskeleton device, but there was no statistically significant difference in other areas. Also, the mean activity level of sternocleidomastoid and splenius capitis muscles on the right and left was significantly decreased during the use of the cervical exoskeleton. However, this difference showed a significant increase in trapezius muscles.
Conclusion: The use of the neck exoskeleton was associated with a reduction of muscle electrical activity and the perceived discomfort in the neck area. These results may be related to transferring neck and head weight by the exoskeleton retaining jack during the neck extension to other areas of the body. The exoskeleton design did not provide support for the shoulder and arm area, which explains the reason for the non-significant results in the shoulder area. Using the exoskeleton with the additional support in shoulder area could be considered as an ergonomic intervention in such overhead works.
Masoud Feyzi, Ali Jafari, Hojat Ahmadi,
Volume 12, Issue 2 (6-2022)
Abstract
Introduction: Due to the non-developed mechanization situation, chainsaw is a widely used tool in Iranian forests. This tool can trigger unwelcome disorders (e.g., white finger syndrome) due to the transmitted vibrations from its handle to the body members. Characterizing these vibrations can result in minimizing the intensity of these disorders. This study aims to investigate the effect of different hardwood species (Beech, Hornbeam, and Alder) on the vibrations transmitted to the wrist and arm.
Material and Methods: Experiments are conducted during four operations including Beech-, Hornbeam-, and Alder-cross-cutting and without cutting as the control sample. Vibration accelerations in three directions of a local Cartesian coordinate system are measured at three points including chainsaw handle, operator's arm and wrist. Using the time and frequency spectra of vibration accelerations, root mean square (RMS), total vibration acceleration, total vibration transmissibility, and frequency-weighted vibration acceleration are calculated based on ISO 5349 (2001) and ISO 10819 (2013) standards. The calculated parameters were statistically analyzed in SAS.
Results: The results showed that variations in wood species could significantly affect the RMS at all three points. The RMS magnitude decreases from handle towards the arm. Interestingly, a significant variation in vibration transmissibility is observed in different frequencies. This study confirms that body organs can damp the high-frequency vibrations better than the low frequency ones.
Conclusion: Although the RMS for cutting operations is less than the control sample, frequency-weighted vibration acceleration and consequently the risk of white finger syndrome is higher in cutting regimes. Furthermore, some vibration accelerations (below 40 Hz for wrist and below 25 Hz for arm) are amplified during transmission despite significant damping in total vibrations.
Ali Jafari, Mohammad Reza Monazzam, Ali Khavanin, Maede Lashgari, Seyed Ali Ghoreyshi,
Volume 13, Issue 1 (3-2023)
Abstract
Introduction: Wood-Wool Cement Panels (WWCPs) are environmentally friendly sound absorbers also used as heat, energy, and moisture insulators. WWCPs have suitable mechanical properties due to using Portland cement and wood strands as raw materials. In this study, the acoustic performance of WWCP absorbents will be investigated.
Material and Methods: The mixed raw materials were molded under pressure through a hydraulic press to fabricate the WWCP samples. Samples were demolded after 24 hours. Samples were created with two thicknesses of 2 and 4 cm and three bulk densities of 400, 500, and 600 kg/m3 to examine the impact of thickness and bulk density on the acoustic absorption coefficient. The sound absorption coefficients were determined as a function of frequency for two frequency ranges: low (63-500 Hz) and high (630-6300 Hz).
Results: In the low-frequency range, increasing the thickness from 2 to 4 cm increased the absorption coefficient at 500 Hz by 0.16 and 0.23 for densities of 400 and 500 kg/m3, respectively. Increasing the thickness added an absorption peak and increased the value of these absorption peaks to 0.9 in the high-frequency range. When the bulk density of the 4-cm-thick samples increased from 400 to 600 kg/m3, the low-frequency absorption peak increased by 0.33. In the high-frequency range, the same density change increased the absorption peak by 0.26 for the 2-cm-thick sample.
Conclusion: Increasing the thickness of WWCP improves both its high- and low-frequency acoustic absorption coefficients. In addition, increasing the bulk density to approximately 500 kg/m3 boosts the sound absorption efficiency in both frequency ranges.
Adel Jafari, Farshid Ghorbani Shahna, Abdulrahman Bahrami, Majid Habibi Mohraz,
Volume 13, Issue 2 (6-2023)
Abstract
Introduction: With the spread of the COVID-19 pandemic and the lack of adequate protection by existing protective equipment, many researchers’ attention has turned to developing improved respiratory protection equipment. Considering their special properties and nanoscale dimensions, electrospun nanofibers are a suitable option for improving operational characteristics of substrates used in conventional facemasks. This study aimed to optimize the electrospinning process of polyacrylonitrile nanofibers (PAN) containing ZIF8 and use the optimized substrate in medical facemasks to increase their protective performance.
Material and Methods: This study employed an environmentally friendly method to synthesize ZIF8 in an aqueous environment. Then, PAN/ZIF8 polymer solutions were prepared in dimethylformamide. The effects of electrospinning parameters, including electrospinning voltage, polymer solution concentration, electrospinning distance, and polymer injection flow rate on diameter and uniformity of nanofibers were investigated. Electrospinning conditions were optimized using response surface methodology (RSM) and central composite design (CCD) to obtain desired values for response (dependent) variables. Finally, optimized PAN/ZIF8 and PAN nanofibers were electrospun on spun-bond substrate. Base weight, average diameter of fibers, filtration performance, pressure drop, and quality factor of fabricated substrates were assessed.
Results: According to results, optimal conditions for electrospinning of PAN/ZIF8 polymeric solution for polymer concentration (A), electrospinning voltage (B), electrospinning distance (C), and polymer injection flow rate (D) were respectively 70 w/v%, 20 kV, 18 cm, and 0.4 ml/h. Moreover, despite lower base weight of PAN/ZIF8 nanofiber mask, it displayed higher filtration performance (98.51%), lower pressure drop (31.42 Pa), and higher quality factor (0.140 Pa-1) in comparison to other studied masks.
Conclusion: Experimental models developed in this study provide acceptable values for filtration efficiency and quality factor for filtration applications. Additionally, they serve as a guideline for subsequent experiments to produce uniform and continuous nanofibers with desired diameter for future applications in absorbent media (intermediate absorbent layers) of respirators.
Marzieh Izadi Laybidi , Adel Mazloumi , Jebraeil Nasl Saraji, Faramarz Gharagozlou, Amir Homayoun Jafari, Zahra Shirzhiyan, Kamal Azam ,
Volume 13, Issue 3 (9-2023)
Abstract
Introduction: Air traffic control is a very complex process, including multiple human-machine interactions. Human mental workload plays an important role in this process. Nowadays, electroencephalography indexes are considered as new indicators in the field of assessment of mental workload. The purpose of the present study was to investigate the relationship between EEG theta power and mental workload in air traffic control simulation.
Material and Methods: Fourteen air traffic controllers participated in this study. Controllers carried out two scenarios, including low and high workload, based on task load factors in an air traffic control simulator. Mental workload was assessed in these two scenarios by the NASA-TLX questionnaire. EEG signals were continuously recorded during air traffic control tasks. Afterward, absolute theta power was extracted from participants’ EEG using Fast Fourier Transform (FFT) by the MATLAB software and was compared with each other in terms of high and low workload.
Results: The results showed a significant relationship in absolute theta power during low and high workload scenarios in all regions of the brain (p < 0.05). Absolute theta power increased primarily in the frontal region during the high workload scenario. Also, there was a significant increase in the relationship between work experience and absolute theta power at the F3 region during the high workload scenario (P=0.021, r=0.607).
Conclusion: Absolute theta power provides a good parameter to assess mental workload at different levels of air traffic control tasks. Therefore, it can be used as a tool for the design of human-machine complex systems.
Mahdi Alinia Ahandani, Saba Kalantary, Monireh Khadem, Fatemeh Jafari, Kamal Azam, Farideh Golbabaei,
Volume 13, Issue 4 (12-2023)
Abstract
Introduction: VOCs are harmful air pollutants that must be detected, monitored and eliminated. Adsorber tubes are standard tools for this task, specifically activated carbon tubes with high adsorption and selectivity. This research aims to compare the structural and functional characteristics of domestically produced activated carbon tubes with the conventional commercial ones for sampling toluene, a volatile organic compound.
Material and Methods: The characteristics of each adsorbent, such as structure, morphology, porosity, and element composition, were examined by SEM photography, BET testing, and EDAX analysis. The central composite design (CCD) method was employed to investigate the adsorption properties of the adsorbents. The input concentration and readsorption time of the samples were the variables considered in this study. Additionally, a field phase of personal air sampling was performed to evaluate the effectiveness of adsorbent tubes.
Results: SEM and BET analyses indicated that the porous structure of domestic activated carbon was comparable to the model produced by SKC. EDAX analysis detected a minor impurity (1%) in the domestic activated carbon adsorbent. The adsorption performance was significantly influenced by the variations in readsorption time and pollutant input concentration. The accuracy and precision of the performance of the domestic adsorbent tube were obtained as 90.77% and 91.76%. The field phase results demonstrated that the amount of pollutant adsorbed in the SKC-activated charcoal adsorber did not differ significantly during 0 to 30 days. However, the domestic adsorber showed a significant difference in the same period. The overall performance of the two adsorbers did not exhibit a significant difference between 0 and 30 days.
Conclusion: Despite minor structural differences, the adsorption efficiency of toluene by domestic adsorbent tubes in sampling high concentrations is very similar to its commercial type. However, it is not recommended for use in low-concentration environments (10 ppm and less).
Rohollah Fallah Madvari, Reyhaneh Sefidkar, Reza Raeisi, Gholamhossein Halvani, Reza Jafari Nodoushan,
Volume 14, Issue 2 (6-2024)
Abstract
Introduction: Considering the abundance and the large number of workers employed in micro and small industrial workshops in Iran and the importance of workers’ health, the present study aimed to investigate the mediating role of chronic fatigue in the relationship between mental workload and work ability with cognitive failure using path analysis.
Material and Methods: This study was conducted using a cross-sectional design on a sample of workers employed in micro and small industrial workshops in the city of Eghlid. Data were collected utilizing various measures, including demographic and occupational information questionnaires, the NASA Task Load Index (NASA-TLX), the Work Ability Index (WAI), and questionnaires for chronic fatigue and cognitive failure. The correlation test and path analysis modeling were used in SPSS (version 24) and AMOS softwares to investigate the relationship between variables.
Results: The mean scores of mental workload, work ability, chronic fatigue, and cognitive failure
were 69.63, 35.20, 15.58, and 53.30, respectively. The values of the goodness of fit indices lead to
the confirmation of the conceptual model by the research data. Also, based on the findings of the path analysis, the current research model has a good fit (CFI=1.00, GFI=0.998, NFI=0.999, AGFI=0.98 and RMSEA=0.003(0.00,0.169)).
Conclusion: The path analysis results indicate that chronic fatigue plays a significant mediating role
in the relationship between mental workload and work ability with cognitive failure. A better understanding of the mediating mechanisms and complex effects of these relationships can contribute to improving the management of chronic fatigue and enhancing cognitive performance in the workplace.
Ali Jafari, Mohammad Reza Monazzam Esmaeelpour, Fardin Zandsalimi,
Volume 14, Issue 2 (6-2024)
Abstract
Introduction: A wood-wool cement panel (WWCP) is wood wool combined with Portland cement mortar. This environmentally friendly acoustic material can be used as a thermal insulator and fire-resistance material with desired mechanical properties. This study aimed to determine the mechanism by which WWCP absorbs sound and the effect of production and application parameters on absorption
Material and Methods: The samples were prepared from poplar wood wool and white Portland cement as a binder in two Cement Fiber Ratios (CFR), namely 2:0.7 and 2:0.95, with bulk densities of 400, 500, and 600 Kg/m3 and thicknesses of 2 and 4 cm. Three layers of backing: air, polyurethane foam, and glass wool were examined separately. Acoustic absorption coefficient was measured using an impedance tube based on ISO 10534-2.
Results: The highest increase in the average absorption coefficient due to the increase in thickness was observed for the sample with a density of 400 kg/m3 and CFR = 2: 0.95, equal to 0.3. Increasing the bulk density to 500 kg/m3 for most samples and in the high-frequency range led to rising absorption efficiency. The optimal backing effect was due to the placement of 4 cm of polyurethane foam behind the sample, which in both thicknesses led to an absorption peak with an absorption coefficient higher than 0.95 at frequencies between 400 and 500 Hz. Selected samples showed that painting WWCPs led to a limited drop in absorption coefficients at high frequencies, comparing the before and after painting results with oil-based paints.
Conclusion: Tuning the absorption frequencies of these absorbers can be achieved by altering factors such as the thickness or density. It has been demonstrated that the effects of thickness and bulk density on the sound absorption of WWCP are related to each other. Concerning the CFR values, increasing the density did not significantly affect absorption in the two frequency ranges.
Akram Tabrizi, Mostafa Jafarizaveh, Hamid Shirkhanloo, Farideh Golbabaeie,
Volume 14, Issue 4 (12-2024)
Abstract
Introduction: Volatile organic compounds (VOCs) are hazardous toxic pollutants in the air, which are released from various industrial sources. Due to the adverse effects of xylene on health, the effective removal of VOCs from the air by nano sorbents is crucial. In this study, nanographene (NG) and nanographene oxide (NGO) were used as adsorbents to investigate the efficiency of xylene removal.
Material and Methods: In this study, in order to investigate the absorption efficiency of nanographene and nanographene oxide after the synthesis of nano absorbents in a dynamic system, xylene vapor was produced in a chamber in pure air and stored in a Tedlar sampling bag and then transferred to the adsorbent. Subsequently, the effect of various parameters such as xylene concentration, inlet air flow rate, and absorbent mass values at 32% humidity and 25°C temperature on the absorption rate and performance of the desired absorbents was investigated. Finally, the gas chromatographic flame ion detector (GC-FID) determined the concentration of xylene in air after the adsorption-desorption process.
Results: The average adsorption efficiencies for NG and NGO were found to be 96.8% and 17.5%, respectively. The characteristics of the NG and NGO adsorbents indicated that the particle size range was less than 100 nanometers.
Conclusion: The results demonstrated that the adsorption efficiency of NG for the removal of xylene from the air is higher than that of NGO. The GC-MS method validated the proposed approach in real air samples.
Soqrat Omari Shekaftik, Jamal Biganeh, Maedeh Hosseinzadeh, Hamidreza Jafari Nodoushan, Neda Mehrparvar,
Volume 14, Issue 4 (12-2024)
Abstract
Introduction: Workplaces often contain potential risks, such as exposure to toxic chemicals. Conducting a thorough health risk assessment helps employers recognize these dangers and implement necessary controls. In the 20th century, modern risk assessment frameworks began to be established with the rise of public health agencies.
Material and Methods: The present study is a narrative review. In order to obtain necessary information, Persian and English texts were searched in Web of Science, PubMed, Scopus, SID and Magiran databases. Keywords such as “health risk assessment”, “chemicals” and “nanomaterials” were used in this study.
Results: Both quantitative and qualitative health risk assessments play critical roles in occupational health, with each method providing different levels of depth and accuracy depending on the situation. EPA Model, Monte-Carlo Simulation, Physiologically Based Pharmacokinetic (PBPK) Modeling, Quantitative Structure-Activity Relationship (QSAR) Models, Probabilistic Risk Assessment (PRA), Life Cycle Impact Assessment (LCIA), and Biologically Based Dose-Response (BBDR) Models, are among the most important quantitative methods for assessing the health risk of chemicals. COSHH Model, ICCT Model, ICMM Model, Australian Model, and Romanian Model, are the most important qualitative methods for health risk assessment of chemicals. In addition to the quantitative and qualitative methods, semi-quantitative methods like Singapore Model, LEC Method, and SEP Model, have also been proposed for assessing the health risk of chemicals. The preference for qualitative over quantitative methods in the risk assessment of activities involving nanomaterials stems from substantial uncertainties, limited data availability, and the unique and complex behaviors of nanomaterials in the workplaces.
Conclusion: Overall, the evolution of health risk assessment methods reflects a continuous drive towards greater accuracy, reliability, and relevance. As we continue to innovate and expand our knowledge, the field is well-positioned to address the complex and evolving landscape of chemical and material risks, ensuring the protection of human health and the environment.
