جستجوی مقالات مرتبط با کلیدواژه « زمان » در نشریات گروه « آب و خاک »

In regard to wide piers, the pile group rather than single pile is used frequently to bear the loading of the structure in a particular arrangement; piles group composed of only one column of piles in the flow direction has a great effect on supporting the bridge deck. In this study, local scour at a single column arrangement of the piles group made up of four rows of piles characterized by different piles spacing was studied for clear-water conditions with two flow discharges of 20 and 35 l/s (the effect of increasing the flow depth with the same flow intensity). The results indicated that an increase in the flow depth not only greatly enhanced the scour depth and the width of the scour hole. Besides, the investigation of the relative flow depth on scour extent showed the need for revision in deep water conditions, as reported in the literature. The results of the pile group experiments revealed the noticeable impacts of piles spacing on the local scour. The bigger pile spacing caused a feeble interaction of wake-horseshoe vortices, leading to a decrease of the scour depth; the separate view of the scour holes was generated at individual piles. Finally, the results were compared with commonly used comprehensive models. The findings of this study can be applied for the appropriate selection and positioning for the countermeasure of the scour at bridge piers.

Hydrological modeling plays a valuable role in watershed management. In order to advance this important, in this study, a combination of linear programming, cross-wavelet transform and Kalman filter as a control model for the analysis of nine compound rainfall and runoff events were used in Sufi Chay Basin. The results were compared with modified time area unit hydrograph, and e geomorphologic unit hydrograph. Finally, using the evaluation criteria used in the research, the final performance of these methods was investigated and analyzed. it was revealed that the modified time area method has a relatively weaker performance than the other two methods, which is due to the assumptions used in drawing the isochrones lines. The LP-CW-KF method showed the best performance among the studied methods, which simulated the compound events in the calibration and validation stage with a mean squared error of 2.47 and 2.7, respectively. On average, in all the events and the three studied methods, the mean absolute relative error (MARE) was 0.069 in the time to peak, 0.131 in the peak discharge and 0.125 in the base time. Therefore, on average, all methods showed a better performance in estimating time to peak.

Effects of two organic amendments, cow manure and bagasse compost of sugarcane, on the chemical fractions of cadmium in soil were investigated at three incubation times in the present study. Soil sample was polluted with 50 mg kg-1 of cadmium by spraying the cadmium salt and after 90 days 25 and 50 tons’ ha-1 of the organic amendments were added to the soil. Some of the soil chemical properties and contents of chemical fractions of cadmium were determined by sequential extraction method of Tessier after 1, 30 and 60 days from the date of adding the organic amendments. The most fraction of cadmium in the all of the treatments was observed in the carbonate- fraction and the soluble and exchangeable- and organic matter- fractions of cadmium were significantly (p

In this study, effects of heavy metal of chromium on microbial and eco physiological indices of soil in presence of vermicompost were evaluated using a complete randomized design. This experiment was carried out in five levels of chromium (0, 100, 200, 300 and 400 mg Cr kg-1 soil from potassium dichromate) and seven incubation periods (5, 30,60,90,100,110 and 120 days) in three replicates and for decreasing the adverse effects of pollutant in soil, in the 90th day, vermicompost was added to all of the treatments. At the end of each period, dehydrogenase enzyme activity, basal respiration and microbial biomass carbon as microbial indices and also metabolic and microbial quotient as eco physiological indices were measured. The results showed that with increasing chromium concentration in soil, the microbial indices were decreased up to the 90th day. Dehydrogenase enzyme activity decreased by 100 percent in concentrations of 100 mg Cr kg- and then it was increased, therefore application of the vermicompost compensated the adverse effects of the pollutant. Metabolic quotient in concentration of 300 mg kg- Cr the 90th day reached to 5.43 and then decreased to 0.164 in the 100th day. This decrease happened in concentration of 400 mg kg- Cr, severely. By adding organic matter, the microbial quotient increased 56 and 44 percent in control and in the highest concentration of the chromium respectively. Based on result of this research, in concentrations higher than 100 mg Cr kg- in soil negative effects of the metal on microbial indices was revealed and usage of vermicompost in improvement of this indices in presence of chromium was efficient.

Wind erosion is the most important agent of environmental degradation, poverty of soil, air pollution and the dust spread. Wind erosion is causing a lot of damage to crops, buildings, facilities and vehicles. The first step of the wind erosion control is the stabilization of soil particles. Soil stabilizing methods to control wind erosion can be classified into mechanical, biological and chemical stabilization. Mechanical soil stabilization type is relatively time-consuming and costly. Biological stabilization is a traditional way that exhibits a long-term validity but sandy soil cannot provide essential water and nutrition elements needed by plant. Recently, chemical stabilization such as high-molecular-weight anionic polyacrylamide (PAM) has attracted the attention of researchers because of its advantages in easy and quick construction, and the improvement of the growing conditions for plant. However PAM has been mainly used to control water erosion and there is still little available information regarding the effectiveness of PAM on preventing soil loss by wind erosion. The main objective of this study was to investigate the feasibility of using PAM in wind erosion controlling. Also, effects of PAM on some soil physical and chemical properties and their temporal variability were evaluated.
In this study polyacrylamide polymer was used as a restoration of soil and soil structure stabilizer on sandy soil of Azadegan Plain (Khuzestan province, Iran). Consequently, an experiment was conducted as factorial based on completely randomized design with three replicates. The experimental treatments were consist polyacrylamide polymer (PAM) at three levels (0, 0.5, and 1 %), soil moisture at two levels (80% FC and dry) and time duration at three levels (15, 30 and 45 days). The emulsion of PAM was sprayed homogeneously on the soil surface. After passing each time treatment, penetration resistance and some physical and chemical properties of soil was measured. Finally after doing all measurements, the treatment with maximum penetration resistance were selected and the sample was prepared for wind tunnel testing. The wind erosion experiments were conducted in a wind tunnel. Soil samples were located in removable trays. The width and length of the trays was 30 and 100 cm, respectively. The wind erosion experiments were performed under wind velocity of 12 m s−1 according to the actual situation of study area.
The results indicated that in comparison to control, soil acidity decreased at both levels of the polymer with increasing time. The decreasing of soil acidity in wet treatments was more than dry treatment. The lowest amount of pH was obtained in the 30-day wet treatment at 1% polymer level. The results show from the 30th day onwards, soil pH increased, which is probably due to the polymer degradation. With passing time, soil electrical conductivity (EC) at both levels of the polymer (0.5 and 1%) increased and decreased respectively after 30 days. These observations are probably because after 30 days the properties of polymer-hydrophilic units gradually decrease and water adsorption was reduced or that soil soluble salts were adsorbed by polymer particles. The results also showed with passing time, Mean Weight-Diameter of Soil Aggregates (MWD) increased and then after 30 days declined. The largest MWD was observed in 30 days treatment at 1% polymer level. After thirty days, its effect has probably diminished due to polymer degradation. Furthermore, the results showed no significant difference of bulk density among treated soil with different level of polymer, but application of polymer caused to decrease bulk density comparison to control. Polymer application increased soil penetration resistance significantly. Using 1% of polymer increased it to 6 kg/m2. The results also indicated that the soil resistance at first increased with time and then decreased significantly. The amount of soil penetration resistance at 45-day was less than 15-day. The results of wind tunnel with a maximum 12 m/s wind velocity showed that application of the polymer reduced the erosion of sands samples to zero.
The research results indicated that PAM application increased soil penetration resistance and MWD. The polymer could improve the structure of soil aggregates and increase the amount of dry-stable aggregates and therefore decrease soil bulk density. Spraying PAM solution on the surface of soil significantly decreased the wind erosion amounts. Therefore, this inexpensive and easily usable polymer can be considered as a soil stabilizer to control wind erosion in arid and semiarid areas.

Texture fractal dimension is a physical index to describe soil particle size distribution having a variety of applications. Fractal dimension may be calculated from three relations of mass-time, mass-diameter and modified mass-diameter (Kravchenko-Zhang) with two linear and nonlinear options for fittings. The aim of the present study was to compare methods and select an appropriate one and fitting option for determining the fractal dimension using hydrometer data. Sixty soil samples were collected from four fields of Taqanak, near Shahrekord. After removal of organic matter and other initial treatments, hydrometer readings were obtained at 0.67, 1, 2, 5, 15, 30, 60, 120, 180, 1440 and 2880 minutes and were converted to mass-time or mass-diameter data. Nonlinear fitting of the Kravchenko-Zhang mass-diameter relation was selected as the most appropriate method of calculating the fractal dimension of solid particles, due to its highest coefficient of determination and smallest mean square error and lowest Akaike Information Criteria. Error analysis also confirmed this conclusion. There was a significant, though not very strong, relationship between the fractal dimension obtained by linear and nonlinear fitting of mass- diameter and Kravchenko-Zhang mass-diameter methods. These relationships can be used to correct the fractal dimension determined by other methods and fitting options.

Adding heavy metals to soils leads to change of their original distribution pattern. Heavy metals distribution in soils depends upon heavy metal، application level، application time and soil characteristics as well. This investigation was conducted to assess the time effect on distribution of different fractions of Lead in soils. The experiment conducted as a factorial in a completely randomized design with three replications and two levels of cow manure (0 and 5%) and two levels of Lead using Lead nitrate (0 and 200 mg kg-1). Samples were incubated at 250C and 60% of field capacity for 120 days with different time intervals (0-30، 0-60، 0-90 and 0-120 day) to determine Lead fractions using sequential extraction methods. The results showed that Lead concentration decrease in exchangeable، carbonated and residual fractions during the time. Also the interactions between cow manure and time cause of decreases in the exchangeable and residual fractions and increases in the carbonated، Fe-Mn oxides-bound as well as organic matter-bond fractions. The interactions between time and Lead concentration lead to decrease in the exchangeable، carbonated and residual fractions and increase in the Fe-Mn oxides-bound and organic matter-bond Lead fractions. Since the most availability and toxic potential of lead is in the exchangeable-solution، the advantage of the this study is to reduce potion of this section during the time.

A study was conducted to evaluate the effect of incubation time, sewage sludge and clay content on the distribution of nickel and cadmium in different fractions of selected calcareous soils. To meet this purpose, an experiment with two different soils (4 and 30 percent CaCO3), two different textures (8 and 40 percent clay), two levels of nickel (0 and 100 mg.kg-1), two levels of cadmium (0 and 25 mg.kg-1) and organic matter in the form of sewage sludge in two levels (0 and 50 t ha-1) was carried out. Two incubation times (0 and 60 days) and three replications in a completely randomized design were mentioned. The samples were incubated for two months at temperature of 25±2 °C and soil moisture condition close to field capacity. Distribution of Cd and Ni in fractions soluble+exchangeable, organically bound, carbonate bound and residual fractions was determined by a sequential extraction method. The results illustrated that, in both soils, residual form of Ni and carbonate form of Cd were dominant and showed a significant change with sewage sludge treatment and time. Sewage sludge application increased the amount of organic and carbonate bound of Ni and Cd significantly. The proportion of organic and carbonate bond Cd and Ni was higher in soil with 33 percent lime. In contrast, in soil with 4 percent lime, the percentage of Ni and Cd in the residual fractions was higher. Residual fraction of Ni and Cd in Clay soil was significantly higher than sandy loam soil. Increasing the amount of Ni and Cd increased all fractions of these metals significantly. The organic forms of Ni and Cd decreased significantly in the course of time. In general, based on the results, it may be concluded that calcium carbonate, clay percent and sewage sludge treatment play a key role in the distribution of Ni and Cd in different fractions of soils.

Chromium is among the metals that has numerous applications in various industries due to its specifications. Widespread use of this metal in different industries has unfortunately been accompanied by its increased release into environment and this entails numerous environmental hazards. In the first phase of the research that was conducted to evaluate the effect of the leather processing companie's sewage on chromium behavior on soil, samples of soil affected by the sewage of leather processing companies were studied Hexavalent chromium and chromium distribution ratio in exchangeable organic, carbonated and residual fractions of these soils were examined. The second phase of this research was conducted to assess the effect of time, chromium, soil texture and soil organic mater on chromium distribution in soil fractions. In this phase of the research also the reduction process of hexavalent chromium with time was evaluated. In the evaluation of the soils affected with chromium in Charmshahr area of Mashhad the contamination was observed in 45-centimeter depth of the soil. In sequential extractions of these soils it was shown that 90% of the chromium was in the residual fraction. The chromium distribution order in various fractions of these soils was as follows: Exchange fraction> Organic fraction> Carbonated fraction> residual fraction The results showed that time had an important effect on the chromium distribution in various soil fractions especially in short term. Treatments of this section had not a significant effect on the chromium distribution in various fractions statistically except in limited cases. Among the most important results of this phase, we can cite the increased contribution (percentage) of chromium to exchangeable fraction with increased level of chromium in soil and this is so important from the environmental point of view.

Baking is obviously one of the most important stages of bread production. Baking time and oven temperature have greatest effects on bread quality. The aim of this study was to investigate the effect of baking time and temperature on bread quality and its shelf life. In this study, the effect of three rates of oven temperature (top and under bread surface) and baking time levels on bread quality and its shelf life was investigated. Baking temperature and time were 300 and 280 °C for 3 minutes and 20 seconds, 300 and 350 °C for 2 minutes and 30 seconds and 350 and 380 °C for 2 minutes respectively. Soluble starch and staling factors of the samples were measured. The data was statistically analyzed by complete randomized design and comparison was made between the means via Duncan,s multiple range test at 5% level. The results showed that the bread baked in various time–temperature conditions were different in moisture content. The bread baked at lower temperature and longer time had the lowest moisture. Also, the result showed that the amount of soluble starch increased by increasing the baking time and decreasing the baking temperature. The bread baked in various baking conditions showed significant differences in staling rates. Lower baking time and higher baking temperature caused the lowest bread staling rates.