This paper studies the mechanical characteristics of SALTATION of bed-load particles in turbulent flows.Experiments have been carried out by means of high speed photography to obtain SALTATION characteristics such as length, height, velocity, impacting and rebounding angles for different hydraulic conditions, particle size, density and bed roughness by analyzing and processing pictures taken at 250 frames per second. The measured values of the parameters showed that increases in turbulence parameters of the flow increase SALTATION length, height, and velocity but decrease the impacting and rebounding angles. It was also found that SALTATION length and height tended to increase as the average size of the bed material (d50) increased. To solve numerical trajectory equations, the initial velocity component of the particle must be known. The initial longitudinal particle velocity was found to range from 3u* to 8u* and its vertical velocity ranged from 1.5u* to 3.5u*, which were different from the values reported in the literature. The longitudinal and vertical components of the restitution coefficient were also measured and it was seen that the Shields parameter (t*) had no meaningful effect on these components, remaining almost constant with increasing.

In this paper, spinning rate of sediment particle during SALTATION in turbulent flow was measured by means of high speed photography technique. Experiments have been carried out for different hydraulic conditions, particle sizes and densities. Particle spin was measured in five stage of SALTATION step by analyzing and processing picture taken at 250 frame per seconds. The results showed that increasing turbulence parameter of flow will cause increase in angular velocity and under the same flow condition, particles with larger sizes and specific gravities spin more rapidly.

In our present research, we focus on the modeling of airflow related to natural disasters, such as sand accumulation, with urban form studies. The objective is to find which urban form can promote sand passing and reduce as much as possible stagnation of sand in the building area (streets, alleys, etc. ). The urban form design will be discussed through the simulation of airflow by using Computational Fluid Dynamics (CFD). In terms of simulation, we simulated the airflow behavior, which is responsible of sand stagnation in some specific configurations. A flat ground was chosen with a first configuration, which was varied to test each time a current airflow behavior in this configuration. This modeling is made possible following an appropriate turbulence model. In this study, a correlation was made between urban wind speed and morphological parameters such as aspect ratio, building geometry and building density. According to our theoretical references, this correlation shows that urban wind speed can help reduce sand stagnation with proper values of these parameters. Therefore, through the urban form study we can promote wind speed and blow away the accumulated sand till the urban limits.

The diffusion and transfer of dust particles in the atmospheric area were investigated with experimental and image processing methods. In a flat field, the rising of dust particles into the   air by plowing the field with a tractor and their spreading along the  surrounding environment as  a  real model of dust diffusion in the atmospheric area. The experiments carried out for specifying the particle-size distribution of the bed dust and its density. The experimental photos of dust diffusion were analyzed by image processing. The intensity of the diffusion of dust particles in the atmospheric area at the different roughness of surfaces for the different speeds of the tractor movement was obtained. The roughness of the surface increases the impact threshold and reduce the number of splashing particles. As particles velocities increase, the particles height increases and the proportion slope decreases at the high velocities. A relative concentration parameter Cα was defined. The results of this study compared with previous works based on this relative concentration. The concentration of dust particles decreases exponentially by increasing up to a certain height and after this height, changes in concentration are minor. Also, the role of mid-air collisions is significant, especially at high speeds.

In many Iranian languages including Persian, the past tense stem of some verbs terminates with – š t, while their present stem ends with a /r/ which in fact exists in the root; but this /r/ does not appear in the past stem. These verbs are /æ nbaš tæ n/, /engaš tæ n/, /pendaš tæ n/, /daš tæ n/, /kaš tæ n/, /gozaš tæ n/, /gaš tæ n/, /gozæ š tæ n/, /gomaš tæ n/, /negaš tæ n/ and their combinations. Concerning the basic morpheme of │ T│ for the past tense of verbs represented in different allomorphs (t, d, st, š t, xt, ft, ɑ d, ud and id), this research aims to detect the process of formation the-š t form of this morpheme in the mentioned verbs. The question is what phonemic processes have led to the deletion of a consonant (r) from the root (which is athwart the definition of "root” ) and appearance of /š / in the past stem. The main motivation for this investigation was the lack of convincing reason, explanation or even analysis for the issue. This research based on phonetic factors for sound change containing the elements of motor planning, aerodynamic constraints, gestural mechanics, and especially interactive-phonetic (IP) on one hand, and historical studies on the other hand, has applied both diachronic and synchronic evidences for analysis and explanation of the sound change, and ultimately morpheme formation in the discussed subject. The absence of a consonant in the stem of a verb, in Persian is a token for being stem constructor, but the presence of a consonant in the root and its absence in only one of the stems indicates that there must be a reason for disappearing the consonant of the root; particularly in past stems due to their construction. In the base of all past stems, “ t” or “ d” (depending on their voicing the environment) is seen, whilst the presence of /š / (the only phoneme without any vestige neither in the root nor in the base form of stems, unlike other phonemes than “ t/d” in the stems) in /š t/ has been regarded as the sole “ exceptional” past stem morpheme by the scholars, due to the lack of any reason for it. The assumption of this study was that the initial allomorph of past stem constructor should have been /st/ which had make the ending consonant cluster /rst/, and then through the telescoping process of the /r/ (unvoiced [ɾ /ɹ ]) with [s] has triggered to emerge /š /. The question here is about the fount of /s/ in the stem. Some investigations have pointed out that in the aorist paradigm of the Old Iranian languages including Old Persian, /s/ had been the aorist stem constructor; therefore some stems were ended with / rst/. According to researchers, this /s/ is still seen in some verbs, despite vanishing of aorist inflection, and in some cases, it has been changed into /š /. This statement improves our presupposition about the initial allomorph of past stem constructor /st/ instead of /š t/ to make ending consonant cluster /rst/ in the past stem. Moreover, one of the most frequent past tense morpheme of many stems in Iranian * languages is /-st/, and based on diachronic (e. g. in Indo-European and Indo-Iranian Languages) and synchronic (German dialects and Scandinavian Languages) studies there is a universal sound change of s→ š in an especial context. Hereupon, it seems reasonable to emerge such phoneme in the discussed stems if the condition is fulfilled. One of the triggering conditions has been reported in ruki rule (s → š / r, u, k, i-). Concerning the adjacency of /r/ (the last consonant of the root) and /s/ of the morpheme /st/, the condition is acquired, but the data in Iranian Persian language show that a /t/ or /n/ is needed for the change to occur. The process of this phonemic change seems to be a phasic telescoping process via SALTATION (conversion of sound A to C, leaping over a phonetically intermediate sound B) as follows. In order to articulate /r/ at the end of the root and the /s/ of the past tense morpheme, respectively the tip and the blade of the tongue touches the back and the front of the alveolar ridge. In this companion, /s/ gets regressive assimilation with /r/ and becomes retroflex ([ʂ ]: intermediate of SALTATION) by pulling back the tip of the tongue into the hard palate, but the alveolar /t/ in /st/ (which is articulated by blade of the tongue in Persian language) removes immediately the retroflex feature by pulling up the tip of the tongue toward the blade to form /š /. Thus based on telescoping process, contrary to the opinion of most scholars, the /r/ of the root has not been omitted but has been merged into /s/ to emerge the sole phoneme /š /: CVr+st → CVš t. The results not only explain the sound change in the above mentioned verbs, but also in some other words in Persian (e. g. /goš ne/ hungry, /teš ne/ thirsty and etc. ); and in dialects of Iranian languages (e. g. /š uš tan/ in Mahabadi Kurdish and /š iš tan/ in Davani dialect for /š ostan/ to wash in Persian). As previously mentioned, in all of the samples of this change a /t/ or /n/ must be after /rs/ (Vrsn/t). Moreover, the appearance of this phenomenon in simple words (free morphemic structure) like goš ne (hungry), teš ne (thirsty), Paš tu (Pashto), paš ne (heel) and so forth, indicates that this change cannot be a morphophonemic change. Therefore, this view does not consent to most of the studies in this case which remark it as a morphophonemic change; athwart, it accords with all studies and findings in IP model on phonemic change of /s/ to /š /.

The understanding soil erosion processes and the development of accurate erosion prediction models require understanding of detachment, deposition and sediment transport in rills. To evaluate the effect of soil type and flow stream power on the relative importance of flow driven processes of sediment transport, and on the boundary between the processes regarding to particle size, experiments were performed under six flow stream powers at the slope of 2% in the laboratory condition. A 0.05×0.05×2.5 m flume was used and time changes in sediment size distribution were measured during 40 minutes to evaluate sediment transport processes. The results supported: i) a hydraulically-dependent size selective pattern for particle transportation, and ii) transportation of different sizes of particles by different mechanisms including Suspension-SALTATION and Rolling. The results also showed that the particle size with minimum transportation, which has been considered as boundary between the suspension-SALTATION and rolling processes is unique for each soil, depends on its particle size distribution. This boundary is not changed by increasing flow stream power from 0.12 to 0.8 Wm-2.