Lettuce is a perishable vegetable that its shelf life is limited by detrimental texture changes and enzymatic activities during postharvest storage.One of solutions that can be used in storage and distribution of this...Lettuce is a perishable vegetable that its shelf life is limited by detrimental texture changes and enzymatic activities during postharvest storage.One of solutions that can be used in storage and distribution of this product is modified atmosphere packaging(MAP).But its effects on the mechanical properties of the product have not been studied.This information would be beneficial in inspection of eating quality and later processing such as cutting and shredding.This research aimed to study effect of active MAP technology on the postharvest mechanical properties of lettuce at different storage periods.It was found that MAP had a significant effect on the tension property of the lettuce leaf.MAP treatment preserved the brittleness of the specimens during storage,but the control ones lost their brittleness and tolerated greater tension.Stiffness and rupture energy were significantly affected by MAP with P values of 0.01 and 0.05,respectively.Also,stiffness of the MAPtreated samples was higher than the control at the same storage time.The findings are due to reducing respiration,transpiration and bacterial growth by MAP which delays nutrient decomposition and maintains the original color and texture.展开更多
The goal of the modern farming systems is to economize energy consumption and to reduce farming costs.Proper selection and use of agricultural machines are important factors to achieve this end.Rotary tillers are till...The goal of the modern farming systems is to economize energy consumption and to reduce farming costs.Proper selection and use of agricultural machines are important factors to achieve this end.Rotary tillers are tillage tools that are used for accomplishment of both the primary and secondary tillage practices.Considering the widespread application of rotary tillers and wide use of modern tractors in Iran,optimal design of these machines is mandatory.Therefore in this study,the optimal working width and optimal diameter of the rotary tiller's rotor proportionate with the power of the MF 399 tractor was delineated based on the energy method.This theoretical method is based on the specific works of tractor and rotary tiller.Results showed that the optimal working width and optimal diameter of the rotary tiller’s rotor with maximum of forward speed 1 m/s for tractor was 240 cm and 6.27 cm,respectively.展开更多
Apart from number and size of machines in a farm,operations scheduling can also affect timeliness costs.In this study a new equation was presented for determination of timeliness costs and it was proven that the new e...Apart from number and size of machines in a farm,operations scheduling can also affect timeliness costs.In this study a new equation was presented for determination of timeliness costs and it was proven that the new equation is a generalization of the well-known ASABE standard equation.Based on the new equation,a parameter namely,timeliness index was defined that indicates the distribution of an operation around the optimum time of performing the operation.By minimizing the index,the whole timeliness cost is minimized.Since the planting operation is highly sensitive to its time of accomplishment,timeliness cost was determined accordingly.In this study the optimum planting starting date(opls)regarding the concept of timeliness costs,was determined.If for any reason,the planting operation cannot be performed in the minimum planting period,an optimization method is required to determine opls.For this,a numerical approach and an analytical method were presented for determination of opls and a computer model was developed based on the numerical method.opls was determined for the Research Farm of the University of Tehran in Karaj–Iran and both methods showed good agreement with each other.展开更多
基金Authors are grateful to Iran National Science Foundation(INSF)(Research Project Reference Number:9230796)for provided financial support and assistance.
文摘Lettuce is a perishable vegetable that its shelf life is limited by detrimental texture changes and enzymatic activities during postharvest storage.One of solutions that can be used in storage and distribution of this product is modified atmosphere packaging(MAP).But its effects on the mechanical properties of the product have not been studied.This information would be beneficial in inspection of eating quality and later processing such as cutting and shredding.This research aimed to study effect of active MAP technology on the postharvest mechanical properties of lettuce at different storage periods.It was found that MAP had a significant effect on the tension property of the lettuce leaf.MAP treatment preserved the brittleness of the specimens during storage,but the control ones lost their brittleness and tolerated greater tension.Stiffness and rupture energy were significantly affected by MAP with P values of 0.01 and 0.05,respectively.Also,stiffness of the MAPtreated samples was higher than the control at the same storage time.The findings are due to reducing respiration,transpiration and bacterial growth by MAP which delays nutrient decomposition and maintains the original color and texture.
文摘The goal of the modern farming systems is to economize energy consumption and to reduce farming costs.Proper selection and use of agricultural machines are important factors to achieve this end.Rotary tillers are tillage tools that are used for accomplishment of both the primary and secondary tillage practices.Considering the widespread application of rotary tillers and wide use of modern tractors in Iran,optimal design of these machines is mandatory.Therefore in this study,the optimal working width and optimal diameter of the rotary tiller's rotor proportionate with the power of the MF 399 tractor was delineated based on the energy method.This theoretical method is based on the specific works of tractor and rotary tiller.Results showed that the optimal working width and optimal diameter of the rotary tiller’s rotor with maximum of forward speed 1 m/s for tractor was 240 cm and 6.27 cm,respectively.
文摘Apart from number and size of machines in a farm,operations scheduling can also affect timeliness costs.In this study a new equation was presented for determination of timeliness costs and it was proven that the new equation is a generalization of the well-known ASABE standard equation.Based on the new equation,a parameter namely,timeliness index was defined that indicates the distribution of an operation around the optimum time of performing the operation.By minimizing the index,the whole timeliness cost is minimized.Since the planting operation is highly sensitive to its time of accomplishment,timeliness cost was determined accordingly.In this study the optimum planting starting date(opls)regarding the concept of timeliness costs,was determined.If for any reason,the planting operation cannot be performed in the minimum planting period,an optimization method is required to determine opls.For this,a numerical approach and an analytical method were presented for determination of opls and a computer model was developed based on the numerical method.opls was determined for the Research Farm of the University of Tehran in Karaj–Iran and both methods showed good agreement with each other.
