Investigation on physical characteristics of suspended sediment is an important subject in river studies. The Particle size distribution of the suspended sediment is one of these physical properties represents important links between sources and fluvial mechanisms in the watersheds. However, limited studies have been conducted in field of suspended sediment Particle size distribution. The present study therefore aimed to investigate the Particle size distribution of suspended sediments in Kojour River within the period of one year. Toward this attempt, 24 suspended sediment samples were collected at intervals of some 15 days. The Particle size distribution was determined after necessary preparations by laser scattering Particle size of HORIBA LA-950. The results showed that the suspended sediment diameter were in the range of 0.82 to 353.55 microns during time of sampling and in different conditions. Also, the silt Particles with partial contribution of 97.68 % had the largest contribution in the suspended sediment load. In addition, the results indicated that the precipitation and sand harvesting plays an important role in increasing the coarse Particles of suspended sediment load.

Particle size distribution is an important characteristic in suspension polymerization. Special condition must satisfy for achievement of an appropriate Particle size distribution. This condition is studied for some systems. In this work the effect of parameters affecting the suspension polymerization system of styrene was studied and then the approximate optimum range was determined to obtain narrow Particle size distribution mainly in the range of 200 to 400 microns. The studied parameters are: position of impeller, impeller type, impeller speed, baffles, stabilizer concentration, initiator concentration and divinylbenzene concentration as cross-linking agent.

Wind erosion is one of the phenomena which causes land degradation in arid and semiarid regions and is a serious challenge for sustainable production and farmland management. The rate of wind erosion depends on wind velocity and surface properties of the soil. Random roughness is one of the most important factor affecting wind erosion, which depends on soil Particle size distribution. Due to some limitations in field measurement of erosion, this study was carried out to investigate the effect of Particle size distribution on erosion rate using wind tunnel. For this purpose, two cropland soils and sandy soils were applied to create four different Particle size distributions. The largest aggregates on the surface of cropland soil were 2, 5 and 15 mm and on the sandy soil was 2 mm, which were subjected to different wind velocities of 2, 9, 15 and 18 m s-1 at the height of 20 cm with three replications. The results showed that by increasing wind velocity, erosion rate was intensified. The erosion rate depends on surface Particle size distribution. The results also indicated that the size of largest aggregates on soil surface has an important influence on erosion rate. The cropland soil had higher percentage of macroaggregates (> 0.25 mm) than the sandy soil, Consequently its erosion rate was significantly lower. In addition, increasing aggregate size from 2 to 5 mm for the velocity of 15 m s-1, led to 3-fold decrease in erosion rate.

In recent years, many researchers have attempted to estimate the soil hydraulic functions (e.g. soil moisture characteristics curve, and hydraulic conductivity function) using Particle-size distribution (PSD) curve. In these studies, an accurate mathematical representation of PSD is required for fitting the observed data. So far, some mathematical models were developed with different limitations. The goodness of fit is directly related to the number of the model parameters. However, estimating the parameters for higher-parameter models which have no mathematical or physical significance is a problem. Among the current models, 2-parameter Log-normal distribution model with mathematical significant parameters has been considered as a basis for many studies. In this study, it is indicated that the 2-parameter Log-normal distribution model can not be very accurate for representation of the PSD for all of soil textural classes. As an alternative, 2-parameter Gamma distribution model is proposed for more accurate representation of the PSD that its two parameters also are mathematical significant and readily computable. These two models have been compared in fitting the observed PSD data of 461 soil samples from UNSODA soil database. Gamma distribution model indicated a pronounced improvement in representation of the PSD. Based on Coefficient of determination (R2), in 362 samples and based on RMSE, in 323 samples, Gamma distribution model showed a better representation of the PSD than Log-normal. To evaluate the significance of the difference between two models, a t-test was performed. The results showed that, at confidence level of 1%, the R2-values of the Gamma model are significantly greater than those of Log-normal model. Also, at confidence level of 5%, a significant difference between the RMSE-values of two models was shown. Therefore, 2-parameter Gamma distribution model is judged to be better than 2-parameter Log-normal model for representation of PSD.

Introduction: Particle size distribution (PSD) is one of the most fundamental features of soil physics that is widely used as the most common input to predict several key soil attributes. The mathematically representing the PSD provides several benefits to soil mechanics, physics, and hydrodynamics as well as helps to convert PSD data of various Particle size classification systems to the desired one. Consequently, the correct and consistent descriptions of soil PSD using mathematical functions is necessary. …

The soil water retention curve (SWRC) is a basic characteristic of the determination of soil hydraulic properties, including unsaturated hydraulic conductivity. Measurement of this curve is essential to research, thus scientists have focused on indirect methods such as pedotransfer functions and empirical relationships to estimate SWRC easily. Since there is a close relationship between SWRC and Particle-size distribution (PSD), fractal geometry was used in this study to define a relationship between the fractal dimensions of these two curves. This helps to obtain an SWRC equation based on soil Particle size distribution as a readily available parameter. To achieve the above objective, 40 soil samples with seven different textures were used. Two logarithmic equations were presented for determination of the fractal dimensions of PSD and SWRC based on their clay percentages. Their correlation coefficients equaled 0.96 and 0.93, respectively. Finally, a cubic polynomial equation was obtained between the fractal dimension of SWRC (Ds) and the fractal dimension of PSD (Dp) with a goodness of fit of R2=0.94. The physical properties of another five soils collected from Pars province were used to evaluate this relationship. First, the Dp of the soils were calculated. Next, using the Ds-Dp relationship, the Ds and the SWRC equation were estimated using the Xu model. To increase the accuracy of the prediction of SWRC, a calibration model was used to adjust the predicted water content values by using two measured points on the SWRC. Comparison of the adjusted water content values with measured ones was done by statistical analysis and calculating the relative standard error (RSE) and Akaike's information criterion (AIC).  The results showed that the RSE and AIC values decreased 50% to 85% and 20% to 93%, respectively, using the calibration model.