Hojjat Ahmadi | University of Tehran (original) (raw)

Papers by Hojjat Ahmadi

Research paper thumbnail of A practical approach to electromotor fault diagnosis of Imam Khomaynei silo by vibration condition monitoring

African Journal of Agricultural Research, Apr 30, 2009

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Research paper thumbnail of Prediction Of Watermelon Consumer Acceptability Based On Vibration Response Spectrum

It is difficult to judge ripeness by outward characteristics such as size or external color. In t... more It is difficult to judge ripeness by outward characteristics such as size or external color. In this paper a nondestructive method was studied to determine watermelon (Crimson Sweet) quality. Responses of samples to excitation vibrations were detected using laser Doppler vibrometry (LDV) technology. Phase shift between input and output vibrations were extracted overall frequency range. First and second were derived using frequency response spectrums. After nondestructive tests, watermelons were sensory evaluated. So the samples were graded in a range of ripeness based on overall acceptability (total desired traits consumers). Regression models were developed to predict quality using obtained results and sample mass. The determination coefficients of the calibration and cross validation models were 0.89 and 0.71 respectively. This study demonstrated feasibility of information which is derived vibration response curves for predicting fruit quality. The vibration response of watermelon...

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Research paper thumbnail of Surveying and Comparing Thermal Conductivity and Physical Properties of Oil Base Nanofluids Containing Carbon and Metal Oxide Nanotubes

Journal of Nanostructures, 2012

In this research, nano materials with tubular structures are added to SAE 20W50 engine oil to stu... more In this research, nano materials with tubular structures are added to SAE 20W50 engine oil to study the rate of their effects on the properties of engine oil. Multi-walled carbon nanotubes (MWCNTs) and vanadium oxide nanotubes (VONTs) has been used as two different additive materials, one of them is carbonic and the other is metallic oxides and their effect on different parameters containing viscosity, thermal conductivity coefficient, flash point and pour point of engine oil as the quality properties of engine oil has been studied and compared. The samples of two concentrations 0.1 and 0.2 wt% with using planetary ball mill were made. The obtained results show that MWCNTs in all cases, which have been evaluated, had better functionality with respect to vanadium oxide nanotubes. In the 0.1 wt% concentration, flash point of MWCNTs/oil and VONTs/oil increased about 9.3% and 5.8% respectively. In addition, thermal conductivity of them increased 13.2% and 10.2% respectively.

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Research paper thumbnail of Experimental Research on Variation of Pore Water Pressure in Constant Rate of Strain Consolidation Test

Acta Geotechnica Slovenica, 2014

Constant rate of strain (CRS) consolidation is a rapid test method which is used for determinatio... more Constant rate of strain (CRS) consolidation is a rapid test method which is used for determination of compressibility of clayey soils. In a CRS test, the appropriate strain rate is selected based on pore water pressure ratio, i.e. the ratio of pore pressure to total stress. In the present study, to investigate the effect of strain rate on variation of pore water pressure ratio, four different clay samples of different plasticity were tested by CRS apparatus. The results of the experiments showed that the trend of variation of pore water pressure is dependent on the drained water flow regime which may be either Darcy or non-Darcy. The results also indicated that the plasticity of clay does not have considerable effect on variation of pore water pressure.

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Research paper thumbnail of An Appropriate Approach for Misalignment Fault Diagnosis Based on Feature Selection and Least Square Support Vector Machine

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Research paper thumbnail of Runoff and sediment yield modeling using WEPP in a semi-arid environment (Case study: Orazan Watershed)

Desert, 2011

Water erosion is a major environmental problem in many parts of the world. Majority of semi-arid ... more Water erosion is a major environmental problem in many parts of the world. Majority of semi-arid countries are concerned because of their specific climate and soils sensitivity, but also because of the recent intensification of human activities and agricultural practices. Accurate estimation of water erosion for various land-use and climate scenarios is so an important key to define sustainable management policies. In the last decades, several studies have been carried out to build models suitable for quantifying sedimentation. Among these models, the Water Erosion Prediction Project (WEPP), is a physically based, distributed-parameter model that has been developed and mainly validated in America. Only few studies have investigated its applicability to environmental conditions that differs from those where the model was developed. The aim of this work is to test the efficiency of WEPP model to predict runoff and sediment yield at catchment scale in a semi-arid area. Continuous simul...

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Research paper thumbnail of Some Physical and Mechanical Properties of Iranian Wild Pistachio (Pistachio mutica L.)

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Research paper thumbnail of Development of a New Threshold Based Classification Model for Analyzing Thermal Imaging Data to Detect Fungal Infection of Pistachio Kernel

Agricultural Research, 2013

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Research paper thumbnail of An Assessment of Specific Sediment Yield of Geological Formations Using Investigated Sedimentary Deposits in Reservoirs and Fingerprinting

Journal of Agricultural Science and Technology

Sediment yield data, collected for most regions in Iran has been insufficient and not so reliable... more Sediment yield data, collected for most regions in Iran has been insufficient and not so reliable and there is still not any sufficiently reliable methodology available for sediment yield assessment in the country as a whole. On the other hand, an attainment of reliable sediment yield data is a must and key requirement for the design of effective sediment management as well as control strategies. Sediment deposition in reservoirs is assumed as a very useful tool in providing such data. The main objective of the present research was to discuss a combination of both source fingerprinting technique and reservoir sediment survey to provide reliable data on sediment yield of geological formations for three small catchments in Semnan Province, Iran. Throughout the study, the volume and mass of deposited sediments in reservoirs were initially assessed. Fingerprinting technique was employed to identify the contribution to, as well as the specific sediment deposition yield of each geological...

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Research paper thumbnail of Application of Remote Sensing in the Agricultural Land-Use Assessment

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Research paper thumbnail of Determining the reliability function of farm tractors

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Research paper thumbnail of Energy use and economic analysis of strawberry production in Sanandaj zone of Iran

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Research paper thumbnail of Application of Vibration Response for the Nondestructive Ripeness Evaluation of Watermelons

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Research paper thumbnail of Fuzzy-Rule-Based faults classification of gearbox tractor

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Research paper thumbnail of Investigation of Effective Factors on Runoff Generation and Sediment Yield of Loess Deposits Using Rainfall Simulator

Soil Erosion Studies, 2011

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Research paper thumbnail of An Efficient Iris Coding Based on Gauss-Laguerre Wavelets

Lecture Notes in Computer Science

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Research paper thumbnail of Estimation of the anesthetic depth using wavelet analysis of electroencephalogram

2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society

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Research paper thumbnail of Energy inputs and outputs in a chickpea production system in Kurdistan, Iran

African Crop Science Journal, 2011

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Research paper thumbnail of Optimization and Efficient Purification in Production of Brucella melitensis Recombinant HSP A and TF Proteins With Low Endotoxin Contents

Jundishapur Journal of Microbiology, 2013

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Research paper thumbnail of Determination of Optimum Life (Economic Life) for Mf285 Tractor: A Case Study in Center Region of Iran

American-Eurasian J. Agric. …, 2008

Abstract: Making use of tractor to do agricultural mechanized operations is responsible for a fun... more Abstract: Making use of tractor to do agricultural mechanized operations is responsible for a fundamental and important role to mechanize agricultural section. Replacement of farm machinery with a new similar machine is one of the most important objects of farm ...

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Research paper thumbnail of A practical approach to electromotor fault diagnosis of Imam Khomaynei silo by vibration condition monitoring

African Journal of Agricultural Research, Apr 30, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Prediction Of Watermelon Consumer Acceptability Based On Vibration Response Spectrum

It is difficult to judge ripeness by outward characteristics such as size or external color. In t... more It is difficult to judge ripeness by outward characteristics such as size or external color. In this paper a nondestructive method was studied to determine watermelon (Crimson Sweet) quality. Responses of samples to excitation vibrations were detected using laser Doppler vibrometry (LDV) technology. Phase shift between input and output vibrations were extracted overall frequency range. First and second were derived using frequency response spectrums. After nondestructive tests, watermelons were sensory evaluated. So the samples were graded in a range of ripeness based on overall acceptability (total desired traits consumers). Regression models were developed to predict quality using obtained results and sample mass. The determination coefficients of the calibration and cross validation models were 0.89 and 0.71 respectively. This study demonstrated feasibility of information which is derived vibration response curves for predicting fruit quality. The vibration response of watermelon...

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Research paper thumbnail of Surveying and Comparing Thermal Conductivity and Physical Properties of Oil Base Nanofluids Containing Carbon and Metal Oxide Nanotubes

Journal of Nanostructures, 2012

In this research, nano materials with tubular structures are added to SAE 20W50 engine oil to stu... more In this research, nano materials with tubular structures are added to SAE 20W50 engine oil to study the rate of their effects on the properties of engine oil. Multi-walled carbon nanotubes (MWCNTs) and vanadium oxide nanotubes (VONTs) has been used as two different additive materials, one of them is carbonic and the other is metallic oxides and their effect on different parameters containing viscosity, thermal conductivity coefficient, flash point and pour point of engine oil as the quality properties of engine oil has been studied and compared. The samples of two concentrations 0.1 and 0.2 wt% with using planetary ball mill were made. The obtained results show that MWCNTs in all cases, which have been evaluated, had better functionality with respect to vanadium oxide nanotubes. In the 0.1 wt% concentration, flash point of MWCNTs/oil and VONTs/oil increased about 9.3% and 5.8% respectively. In addition, thermal conductivity of them increased 13.2% and 10.2% respectively.

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Research paper thumbnail of Experimental Research on Variation of Pore Water Pressure in Constant Rate of Strain Consolidation Test

Acta Geotechnica Slovenica, 2014

Constant rate of strain (CRS) consolidation is a rapid test method which is used for determinatio... more Constant rate of strain (CRS) consolidation is a rapid test method which is used for determination of compressibility of clayey soils. In a CRS test, the appropriate strain rate is selected based on pore water pressure ratio, i.e. the ratio of pore pressure to total stress. In the present study, to investigate the effect of strain rate on variation of pore water pressure ratio, four different clay samples of different plasticity were tested by CRS apparatus. The results of the experiments showed that the trend of variation of pore water pressure is dependent on the drained water flow regime which may be either Darcy or non-Darcy. The results also indicated that the plasticity of clay does not have considerable effect on variation of pore water pressure.

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Research paper thumbnail of An Appropriate Approach for Misalignment Fault Diagnosis Based on Feature Selection and Least Square Support Vector Machine

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Runoff and sediment yield modeling using WEPP in a semi-arid environment (Case study: Orazan Watershed)

Desert, 2011

Water erosion is a major environmental problem in many parts of the world. Majority of semi-arid ... more Water erosion is a major environmental problem in many parts of the world. Majority of semi-arid countries are concerned because of their specific climate and soils sensitivity, but also because of the recent intensification of human activities and agricultural practices. Accurate estimation of water erosion for various land-use and climate scenarios is so an important key to define sustainable management policies. In the last decades, several studies have been carried out to build models suitable for quantifying sedimentation. Among these models, the Water Erosion Prediction Project (WEPP), is a physically based, distributed-parameter model that has been developed and mainly validated in America. Only few studies have investigated its applicability to environmental conditions that differs from those where the model was developed. The aim of this work is to test the efficiency of WEPP model to predict runoff and sediment yield at catchment scale in a semi-arid area. Continuous simul...

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Research paper thumbnail of Some Physical and Mechanical Properties of Iranian Wild Pistachio (Pistachio mutica L.)

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Development of a New Threshold Based Classification Model for Analyzing Thermal Imaging Data to Detect Fungal Infection of Pistachio Kernel

Agricultural Research, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of An Assessment of Specific Sediment Yield of Geological Formations Using Investigated Sedimentary Deposits in Reservoirs and Fingerprinting

Journal of Agricultural Science and Technology

Sediment yield data, collected for most regions in Iran has been insufficient and not so reliable... more Sediment yield data, collected for most regions in Iran has been insufficient and not so reliable and there is still not any sufficiently reliable methodology available for sediment yield assessment in the country as a whole. On the other hand, an attainment of reliable sediment yield data is a must and key requirement for the design of effective sediment management as well as control strategies. Sediment deposition in reservoirs is assumed as a very useful tool in providing such data. The main objective of the present research was to discuss a combination of both source fingerprinting technique and reservoir sediment survey to provide reliable data on sediment yield of geological formations for three small catchments in Semnan Province, Iran. Throughout the study, the volume and mass of deposited sediments in reservoirs were initially assessed. Fingerprinting technique was employed to identify the contribution to, as well as the specific sediment deposition yield of each geological...

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Research paper thumbnail of Application of Remote Sensing in the Agricultural Land-Use Assessment

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Determining the reliability function of farm tractors

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Energy use and economic analysis of strawberry production in Sanandaj zone of Iran

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Application of Vibration Response for the Nondestructive Ripeness Evaluation of Watermelons

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Fuzzy-Rule-Based faults classification of gearbox tractor

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Investigation of Effective Factors on Runoff Generation and Sediment Yield of Loess Deposits Using Rainfall Simulator

Soil Erosion Studies, 2011

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Research paper thumbnail of An Efficient Iris Coding Based on Gauss-Laguerre Wavelets

Lecture Notes in Computer Science

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Research paper thumbnail of Estimation of the anesthetic depth using wavelet analysis of electroencephalogram

2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society

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Research paper thumbnail of Energy inputs and outputs in a chickpea production system in Kurdistan, Iran

African Crop Science Journal, 2011

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Optimization and Efficient Purification in Production of Brucella melitensis Recombinant HSP A and TF Proteins With Low Endotoxin Contents

Jundishapur Journal of Microbiology, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Determination of Optimum Life (Economic Life) for Mf285 Tractor: A Case Study in Center Region of Iran

American-Eurasian J. Agric. …, 2008

Abstract: Making use of tractor to do agricultural mechanized operations is responsible for a fun... more Abstract: Making use of tractor to do agricultural mechanized operations is responsible for a fundamental and important role to mechanize agricultural section. Replacement of farm machinery with a new similar machine is one of the most important objects of farm ...

Bookmarks Related papers MentionsView impact