Showing 39 results for Omidvar
Volume 1, Issue 1 (3-2013)
Abstract
In order to determine effects of chicken and cattle manures in culture of Chlorococcum, an experiment was designed in six treatments including; 0.1, 0.4, 0.8 g/l of chicken manure and 0.1, 0.4, 0.8 g/l of cattle manure as completely randomize design with three replicates for 28 days. Results showed that the mean maximum density (87.1 × 105 cell/ml), specific growth rate (0.054 day-1), algal dry biomass (0.644 g/l), and chlorophyll a (9.42 mg/l) were obtained with 0.8 mg/l chicken manure. In order to compare performance of these manures with other culture media, second experiment with five treatments including; BBM (control) (Bold’s Basal Medium), BBM + soil extract, 0.8 g/l chicken manure, 0.8 g/l cattle manure and mixture of all treatment (BBM, BBM + soil extract, chicken manure and cattle manure) was designed as completely randomize design with three replicates for 15 days. Comparative results showed that BBM + soil extract had highest algal density (11.6 x 106 cells/ml), highest algal dry biomass (0.81 mg/ml), maximum SGR (0.13 /day), highest chlorophyll a (10.15 mg/l) and minimum doubling time (4.97 days). In conclusion, performance of BBM + soil extract was better in terms of biomass and growth parameters of Chlorococcum.
Volume 2, Issue 1 (3-2014)
Abstract
Drought is a climatic phenomenon that causes much detrimental influence on ecological environments. This research investigates the performance of meteorological drought indices in different time scales in theTajan basin in Iran. Indices undergone in this study include: Percent Normal Precipitation Index (PNPI), Z-Score Index (ZSI), Standard Precipitation Index (SPI), China Z Index (CZI), Modified CZI (MZCI), and Decile Precipitation Index (DPI). In this study, we used data of annual and monthly precipitation from meteorological stations in the basin. Drought indices were determined at time scales of 1, 3, 6, 9, 12, 18, 24 year of minimum precipitation with very intense drought and the method of correlation coefficients between drought indices values and monthly precipitation. The results showed that DPI was the best index at annual time scale, while at the time scale of 1,6,12 and 24-months, PNPI was the best index. MCZI was the best index for time scales of 9 and 48-months, and the ZCI had the maximum efficiency for a three-month scale.
Volume 2, Issue 3 (Issue 3 - 2014)
Abstract
Aim: School bullying is a worldwide problem and crosses national boundaries. Students involved in bullying have a greater chance of developing emotional and behavioral disorders, as well as a higher risk of engaging in criminal behavior later in their lives. This study aims to examine the prevalence of bullying behavior and some of its associated factors among male middle school students in Tehran, Iran.
Methods: Overall, 1803 middle school students, aged 11 to 15, were enrolled in the study between January and March, 2012. Bullying behavior of and on participants was evaluated using Persian version of the revised Olweus Bully/Victim Questionnaire (OBVQ). Findings: More than 55% of students reported being involved in bullying behaviors in school, either as a victim (51%), a bully (31%) or both a bully and a victim (18%). The most common subtypes of bullying were verbal (61.3%), physical (47.6%), and indirect (50.3%) bullying. In a regression analysis, the number of students' close friends, their age, their father's education level and home atmosphere were the only significant predictors of bullying behavior.
Conclusion: The prevalence of bullying among Iranian middle school students is highly concerning; hence, implementation of a comprehensive, school-based anti-bullying program is an urgent need because students, who are involved in bullying behavior, are at higher risk for developing psychosocial disorders and engaging in criminal behavior later in their lives.
Volume 2, Issue 4 (Winter 97 2019)
Abstract
The control of bacterial diseases of fish has always been one of the most important problems of aquaculteriets in recent years. One of these problems is bacterial resistance. Using antibiotics can cause problems for consumers. Therefore, the use of new antimicrobial agents with minimal complications is common. In the present study, using the acid-thermal method, the bentonite structure was modified and the chitosan and bentonite hybrids were modified in the stage of development. The structure of the compounds was studied using the Infrared Fourier Transform Spectrometry (FTIR), Surface Electron Scanning Microscopy (FE-SEM) and X-ray diffraction spectroscopy (EDX). Antimicrobial activity of two types of modified bentonite on gram negative bacterium Aeromonas hydrophila was studied in vitro using two methods of disk diffusion and microdilution. The results of the disc diffusion method showed that the antimicrobial compounds produced had antibacterial properties in experimental conditions against the Aeromonas hydrophilia bacteria. Antimicrobial activity (MIC and MBC) was determined using microdilution and clonal counting in Agar culture medium. The results showed that the modified compound with the acidic method had MBC of 28.57 and 14.28 mg / L for Aeromonas hydrophila bacteria in 10 minutes and 30 minutes. For chitosan and modified bentonite composite, MBC was 14.28 mg / ml for Aeromonas hydrophila bacteria in 10 and 30 minutes. The results of this study showed that modified bentonite and composite compounds have strong antimicrobial effects and can remove pathogens in laboratory conditions and can be used as new compounds to control pathogens in breeding systems.
Volume 3, Issue 1 (6-2014)
Abstract
The effect of six diets including Scenedesmus quadricauda), manure (cattle+poultry, 1:1 ratio), vegetable (spinach+parsely+coriander, 1:1:1 ratio), algae+soil, vegetable+soil, and manure+soil were examined on culture of freshwater copepod, Acanthocyclopsrobustus, under the experimental conditions of 23±1ºC, 12 hours dark: 12 hours light photoperiod, and light intensity of 60 µmol photons/m2/s. The maximum population density (1282.6±163.7 individuals/L), maximum specific growth rate (SGR) (0.17±0.0 /day) and minimum doubling time (Dt) (4.0±0.1 days) were obtained when A. robustus fed on algae+soil. The nauplii production was 727.3±42.4 (±SE), 272.0±23.5, 267.6±17.7, 147.0±18.2, 33.6±3.8 and 25.0±7.1 ind./L and copepodit production was 311.3±26.8, 124.3±11.1, 183.0±13.0, 59.0±7.1, 14.3±8.1, and 17.6±3.6 ind./L in algae, algae+soil, vegetable, vegetable+soil, manure+soil, and manure, respectively. Correspondingly, the adult production was 208.5±26.8, 51.6±16.5, 192.7±23.7, 91.7±28.4, 8.7±5.4 and 8.7±3.6 ind./L, respectively. The maximum body length (663.8±29.1 µm) and width (526.2±23.7 µm) of A. robustus were recorded when fed with vegetable+soil and vegetable, respectively. The number of nauplii, copepodit, adults, length and width were significantly correlated with EC, BOD and COD. According to results, the A. robustus has suitable potential culture on algal and non-algal diets based on production, growth, body size, BOD and COD, but the better performance obtain on algae+soil and vegetable.
Mehdi Maerefat, Amir Omidvar,
Volume 8, Issue 1 (10-2008)
Abstract
Internal thermal conditions and cooling load of the buildings intensely depend on outdoor conditions. Outdoor conditions of the building are not constant during a day, so assumption of constant thermal conditions for indoor is not proper. It seems that using adaptive temperature panels proportional to the variations of outdoor conditions decreases the energy consumption in comparison with constant temperature cooling panels. In this paper the effects of adaptive temperature metal panels are investigated on energy consumption of the buildings and thermal comfort conditions of the occupants. Results of hourly analysis show that, in Tehran with maximum relative humidity of 65%, in buildings with north and south orientations, we do not need cooling systems in nearly 10 hours of a day, in remains we can provide thermal comfort conditions by radiant ceiling cooling panels with natural ventilation and without any anxiety about condensation on the panels. However, in buildings with east or west orientations we do not need to air conditioning and cooling systems in only 7 hours of a day. In these buildings condensation is inevitable in some intervals of system operation during a day. In these periods, we can decrease the probability of condensation by using mechanical ventilation. Results also demonstrate that cooling energy consumption is decreased of 29 to 45% depending on the orientation of building.
Volume 8, Issue 1 (No. 8 (Tome 36), (Articles in Persian) 2017)
Abstract
speaker`s attitude toward her/his statement. Aikhenvald (2004) presented a model for evidential in about 500 languages around the world. She introduce 2 types of evidentiality. Grammatical evidentiality including obligatory affixes and clitics and ungrammatical evidentiality including optional syntactic and lexical strategies. Aikhenvald refers to direct and indirect evidentials from a semantic view point. This study show that there aren`t any grammatical evidentials in Persian and like the other Indo- European languages , Persian has linguistic items which fulfill evidential function in addition to their first roles in language. Some of evidential structures in Persian include impersonal passive forms, modal expressions , tense- aspect features, reports and quotations and sensory and perception verbs.
Volume 8, Issue 4 (3-2019)
Abstract
Today, developed and developing countries are focusing more on environmental issues and development. The present study aims to provide a model for the establishment of green human resources management in the entrepreneurship ecosystem. The purpose of this research is in the field of applied research, and since it describes the variables and relationships between them, the recognition of the status quo and finally the presentation of the pattern of deployment, is descriptive-survey method. The statistical population of this research includes relevant experts. In order to reach the consensus, 27 people were studied by interview method and the required information was collected. To analyze qualitative data and to extract factors affecting HRM and its influential factors, the method of analysis of the theme (theme analysis) was used. Structural-interpretive modeling has been used to identify the relationships between variables and the deployment of green human resources in the entrepreneurship ecosystem. The findings of the research include explaining the green human resources management model in the entrepreneurship ecosystem and analyzing the results of infiltration-correlation; the existing model is a model for different businesses with the aim of establishing a green human resource management in the entrepreneurship ecosystem. The research findings show 18 dimensions for the establishment of green human resources management. The research results indicate the impact of green human resource management on entrepreneurship ecosystems and green thinking and sustainable development, and ultimately globalization.
Mehdi Maerefat, Amir Omidvar,
Volume 9, Issue 1 (12-2009)
Abstract
In cold season, draught or undesired local cooling sensation in ankle and neck region is one of the most frequent cases of complaint of the occupants. A person who are subjected to draughts in winter, tend to elevate the room temperature to counteract the cooling sensation, thereby increasing the energy consumption. In naturally ventilated buildings, draught is due to windows and other cold surfaces in the room. Draught is dependent on the air speed and on the magnitude of turbulence intensity. Serious draught complaints can often occur at mean speeds lower than those recommended by standards when turbulence intensity is high. So investigation of undesired local cooling in floor heating systems is very important, although in these systems the mean air speed is not significant. In this paper, the effects of size of window on draught are investigated in floor heating systems. Results demonstrated that, undesired thermal discomfort caused by local cooling phenomenon in floor heating systems is negligible. At the end, the probability of occurrence of local cooling phenomenon in floor heating systems is compared to vertical heating panels. Thereby the floor heating systems are more effective than the vertical heating panels in aspect of thermal comfort and energy consumption.
Volume 9, Issue 17 (Spring & Summer 2022)
Abstract
Ignoring the precise meaning and implications of Quranic lexicons appended to its text in various styles or registers may cause misunderstanding and inaccuracy in determining the connotation of the holy Quranic verses. The same problem has driven many Quranic commentators and translators to disregard the original meaning of the Quranic phrase Alqa al-Alwah [Tossed the Tablets] (Al-A'raf/105) and instead conceive it as a phrase that relates to Moses' (PBUH) violence and rebellion. However, this misinterpretation vividly contradicts the chastity of the holy prophets, and as a result, some scholars, following the Israiliyyat hadiths, have portrayed Moses as an impatient and furious prophet. Using a descriptive-analytical approach and dictionary and commentary resources, this research seeks to reveal the true meaning of this Quranic phrase and correct misconceptions about the holy prophet as someone who disregards God's commandments. The findings demonstrate that the root "La-qa-ya" does not have the connotation of "throwing," and the meaning retrieved from employing it in the pattern of If'al (Alqa) does not necessarily give it the sense of "throwing." The underlying practical meaning of Alqa al-Alwah is "to put down or toss," which refers to putting something from up to down in a non-insulting manner. This Quran phrase has a metaphoric connotation of "refusing to explain The Ten Commandments." An accurate translation may include both of the above-mentioned meanings. However, many Quran translators have failed to reflect both meanings simultaneously.
Q. Dorosti, M. Maerefat, A. Omidvar,
Volume 10, Issue 3 (12-2010)
Abstract
- The effect of panel height on performance of ceiling radiant cooling system has been studied. Investigation has been done by employing solution of conservative equations, together with the radiant and thermal comfort equations. Calculation is performed for the typical hottest day of Tehran. Vapour condensation is one of the most important problems whit these systems. Therefore effect of panel height on condensation has been also studied, in a residential place with several different ranges of ventilation rate. The results show that appropriate design of the panel height can significantly reduce the rate of condensation.
Volume 10, Issue 4 (12-2010)
Abstract
Abstract:
Direct calculation of free term coefficients for linear isotropic problems in three dimensional
displacement boundary integral equations is presented in details. In addition, the shape
functions of 9 node non-continuous and semi-continuous elements for modeling the crack
surfaces, layers interface, infinite boundary and other similar problems have been
demonstrated. This proposed method for calculating cij coefficients has been verified
comparing with some solved problems.
, Amir Omidvar, ,
Volume 13, Issue 2 (5-2013)
Abstract
This paper presents a comparative study of turbulence models performance in prediction the oscillating characteristics of naturally excited jet flows. The unsteady averaged Navier-Stoks equations for turbulent incompressible flow and five variant turbulence closures are used in this study. A large family of turbulence models exists in the literature which is far too extensive to be reviewed here. The models are ranged from simple algebraic expressions for the eddy viscosity to more elaborated formulations which introduce a separate transport equation for each component of the Reynolds stresses. The software, FLUENT 6.3.26, was employed for solving the governing equations. Computational results compared with reported experimental data. The standard k-ε and SST k-ω models clearly showed better results than the others. The accuracy of standard k-ε model decreases with decreasing the nozzle inlet velocity and it failed to predict the minimum excitation velocity (minimum excitation kinetic energy) in the self excited fluidic nozzle.
, Amir Omidvar, ,
Volume 13, Issue 8 (11-2013)
Abstract
In this research, validity of temperature-independent thermophysical properties assumption of water-Al203 nanofluid in natural convection problems within the enclosures is investigated. The numerical results are obtained utilizing an in-house finite volume code based on the SIMPLE algorithm. In order to do the validation the numerical results and those of existing correlations are compared. In order to evaluate the thermal performance of the enclosure, the average Nusselt number on the hot side wall in both temperature-independent and dependent cases is compared Results show that, in the all considered solid volume fractions, the difference in the Nusselt number in the case of temperature-independent properties is less than 10 percent in comparison with the case in which the properties are temperature-dependent when temperature difference is less than 5 ○C. As the temperature increases, the difference between Nusselt number in both cases increases and the effect of increase in solid volume fraction is to increase this difference. Results also show that the difference between these two cases is dependent solely on temperature differences between the hot and cold walls regardless of the temperature they have.
Amir Omidvar, ,
Volume 13, Issue 10 (1-2014)
Abstract
Ali Alavi Nia, Hamid Omidvar, Hassan Nourbakhsh,
Volume 13, Issue 15 (Third Special Issue 2014)
Abstract
Friction stir process is one of the severe plastic deformation techniques which causes microstructure refinement and hence change in mechanical properties of the specimen. Temperature, strain and strain rate which are the results of this process, causing dynamic recrystallization and followed by shift in mechanical properties. Magnesium is the lightest structural alloy which is used in a wide range, in the automobile and aerospace industries. In this research, the overlapping friction stir process is applied on the surface of AZ31 alloy. The overlapping is conducted in 50 and 0 percentages. In order to reduce the temperature which is generated in the process, rapid cooling was used. After friction stir processing in the 0 percent overlapping the grains refine from 18 micrometer in the base metal to 7 micrometer with a uniformer structure than the base metal, ultimate tensile strength and elongation increased 29.9% and 19.8%, respectively with respect to the base metal. The structural uniformity of 50 percent overlapping was less than that of 0 percent overlapping, ultimate tensile strength and elongation increased 19.98% and 3.9%, respectively with respect to the base metal.
Volume 14, Issue 1 (Spring 2010)
Abstract
One of the natural disasters causing many damages in dry and desert areas of the world and especially in the Yazd region of Iran, is strong winds and storms. This region (Yazd), due to it is geographical situation and climatic conditions, is always subject to strong winds and dust storms. Therefore, understanding the storms and strong winds regime, in order to reduce the destructive effects of this phenomenon, especially in stabilizing the running sands, is necessary.
This study was accomplished using the data of horizontal vision, speed and direction of wind, relative humidity, temperature, pressure, cloud and dust event in Yazd and Kerman synoptic stations, as well as the atmosphere data of the above stations, and the synoptic maps during statistical period between 1983-2003.
The results of the study showed that more than 77 percent of strong winds in the area blow from 2500 to 3300, and its speed is between 15-29 m/sec during the fluctuation. These strong winds blow in the afternoons. The blow of dominant winds is from North -West and West. More than 5 percent of storms and strong winds in this region occur in Apirl and May.
In the begining of the hot period of the year and changing of the season, the atmospheric instability and the dust storms increase in the region. The main reason of this phenomena is the intensive winds that occur by the fast changes of the temperature and pressure in this time. Passing of a low pressure system with cold and dry front from the West-North Western along with the presence of trough in the 500 and 850 hpa levels, and also the local instabilities are the most important reasons of these strong winds in this region.
Amir Omidvar, Babak Afra,
Volume 14, Issue 3 (6-2014)
Abstract
Up to now, lots of thermal comfort models have been introduced to predict human being’s body thermal response to the changes in personal and environmental conditions. Among them, Gagge’s model because of its ability in estimating body physiological responses and thermal sensation in transient conditions has turned to one of the most used thermal comfort models. Although, this model uses transient mechanisms to determine body core and skin temperatures, but yet, simplified assumptions including steady heat and moisture transfer through clothing and disregarding thermal and mass inertia in the clothing is used in its structure. This study, by investigating various mechanisms of heat and moisture transfer in the clothing (steady heat and mass transfer, transient heat transfer-steady mass transfer, transient heat transfer-semi transient mass transfer) tries to compare upcoming results of these models with those of experiments. It was declared that considering transient heat transfer along with semi transient mass transfer in the clothing have positive effects on the results.
Amir Omidvar, Mohsen Ghazikhani, Mohammad Reza Razavi,
Volume 14, Issue 5 (8-2014)
Abstract
In this study, the theoretical design of a vapor ejector used in an air-conditioning system is performed and the designed ejector is then optimized via computational fluid dynamics. Based on the numerical simulations, two geometrical parameters, throat diameter and nozzle position, are optimized. Then, the effects of the operating parameters on the performance of the optimized ejector are investigated numerically. The optimized ejector geometry is used as a variable-geometry ejector by using a spindle in the primary throat and the performance of the system in various spindle positions is studied. The results show the importance of using a analytical design to obtain the overall geometry of the ejector and numerical simulation in order to achieve the optimal ejector performance. The variable-geometry ejector designed based on the proposed method in this study with using solar energy, in conjunction with a cold storage system, might be able to provide the necessary refrigeration for all day long.
Volume 15, Issue 1 (Spring 2015 2015)
Abstract
In this article, using two criteria of rivalry and excludability, the direct production factors are classified as physical capital, human capital and technology. Based on the new theories of economic growth, essential role of human capital in innovation, adoption and application of new technologies is emphasized. Then to explain differences of economic growth across countries, institutions as the fundamental causes of economic growth are discussed. It is argued that institutions provide circumstances in which proximate causes of production are accumulated and used. Institutions signal to the economic agents to pursue productive or rent seeking activities. In this regard, paradoxical findings of empirical studies as to effects of human capital on economic growth are analyzed. Using a cross-section data, based on 10-year average of output per worker for about 90 countries over the period 2001-2010, the interaction effect of human capital and institutional quality on growth is evaluated. The main implication of the model for Iranian economy is: Notwithstanding the huge investments in human capital, which mainly financed by oil revenues, low quality of institutions has led to slow economic growth.