Gravity current is a phenomenon caused by density difference between two fluids and due to this phenomenon the fine sediments can be moved to the body dam and as a result causes for many serious problems for dam intake. Therefore, controlling the flow can reduce the potential problems. In this study a permeable obstacle was used to evaluate the performance of permeable obstacles for control of turbidity current. The variables were the porosity percentage of the obstacle and different concentrations of the currents. The gravity current discharges and concentrations were measured upstream and downstream of the obstacle. The results of the measured discharges showed that the obstacle efficiency in control of gravity current reduces with increasing porosity. The results of the measured concentrations also showed the same conclusion. The final results of the review sediment load and view similar trend was confirmed. After calculating water entrainment to the gravity current passing through the permeable obstacle, it was observed that with increasing porosity of permeable obstacle, the volume of water entrainment is reduced. Therefore it can be concluded due to lower volume of water entrainment, processing efficiency in controlling the gravity current using the permeable obstacle is reduced. Also, the maximum efficiency of the controlling the gravity current was measured about 73.2%.

Flood flow in rivers is often of density current type. Hence, recognizing and exploring these currents can solve some problems of sedimentation. In this study, the effect of porosity and the angle of permeable obstacles on the control and trapping of density current have been investigated in the laboratory. For this purpose, an expanded polystyrene (EPS) polymer was used with 1. 135 g/L density and average diameter of 1. 15 mm. The experiments were carried out with two concentrations (10 and 20%) and 5 porosity and 4 angles. The obstacles were made of palsy glass plates and two types of groove and cavity with 8. 2 mm width of the groove and the diameter of the cavity. The results showed that, with an increase in porosity ratio, the amount of trapping to optimum porosity decreases and then increases. The optimal porosity of the cavity and groove is 22 % and 19%, respectively. In experiments, the cavity trapping was observed more than the groove, in the concentrations of 10. 20% it was 0. 13 and 0. 14%, respectively. In addition, with the increase of the angle, the amount of trapping has reduced and its value was observed in the groove more than the cavity. The correlation coefficient in the grooves and cavities was 0. 996 and 0. 937, respectively. The major effect of obstacles, reducing velocity and slowing flow were identified as the average velocity in the cavity was 62. 3% higher than the groove. Accordingly, in the same conditions, the cavity obstacles have better performance than the groove obstacles.

This study explored the effect of porosity and installation angle, thickness (dimension) and second layer of permeable obstacles on density current control and trapping in the laboratory. For this purpose, an insoluble suspended polymer and two types of groove and cavity obstacles made from plexiglass sheets were selected. The experiments were conducted with two different concentrations, five different porosities, four different angles, four different thicknesses and two obstacle layers. The results showed that the optimum porosities for cavity and groove obstacles were 22 and 19%, respectively. In all experiments, the cavity trapping rates of 0.13% and 0.14% at 10% and 20% concentrations were higher than those of groove trapping. In addition, by increasing the angle, the rate of trapping decreased and its value was observed in the groove with the correlation coefficients of 0.995 and 0.981 compared to the cavity. The major effect of obstacles was found to be the flow deceleration where the average velocity in the cavity was obtained 3.62% higher than that in the groove. For the increased thickness with 10% porosity and groove type, the passage of materials from the obstacle further increased. By creating the second layer of obstacle, the passage of materials from the obstacle in the both groove and cavity increased, and the optimal distance of the second obstacle was 2.25 m from the first one.

Detecting and preventing incidents with obstacles is a challenging problem. Most of the common obstacle detection techniques are currently sensor-based. Mobile robots like Small Unmanned Aerial Vehicles (UAVs) are not able to carry obstacle detection sensors such as radar; therefore, vision-based methods are considered, which can be divided into stereo and mono techniques. Mono methods are classified into two groups: Foreground-background separation, and brain-inspired methods. Brain-inspired methods are highly efficient in obstacle detection. A recent research in this field has focused on matching the Scale- Invariant Feature Transform (SIFT) points along with SIFT size-ratio factor and area-ratio of convex hulls in two consecutive frames to detect obstacles. However, this method is not able to distinguish between near and far obstacles nor the obstacles in a complex environment and, thus, is sensitive to wrong matched points. This paper aims to solve the aforementioned problems through using the distance-ratio of matched points. Then, every point is investigated for distinguishing between far and near obstacles. The results demonstrated the high efficiency of the proposed method in complex environments. The least achieved accuracy of the algorithm was 60.0%, and the overall accuracy was 79.0%.

Bushehr is one of the famous and historical ports. it has an important place in economy politics history and sailing of Iran and Persian gulf. in duration of Afsharieh Zandieh Qajar and even initial Pahlavi Bushehr port was not the largest port in Sothern iran but also considered as the most important and famous ports of Persian gulf. Near about 20 consulates from different countriesare located in the region. In 19 th century economy of Bushehr was basedon Business and commercial sailing. In crease in Bushehr commercial sailing in 19 th century resulted in forming a powerful commercial societythere in a way that great businessmen and capital owners migrated from different parts of iran and resded in bushehr. Despite of this prominent historical place in second half of 20th century bushehr dropped behind and left its place to rivals. As the moment it is considerd as the second class ports in Persian gulf. this research aims at exploring historical obstacles in development of bushehrand consequently the key question would be as: what are the historical obstaclers in deveploment of busheh? The main hypothesis in this study is weakness and degeneration of bushehr commercial society along with some other factores which ended in bushehr decline part. Obviously other factores will be also be studied in this research. Results show that bushrhr development dependes on resolving historical obstacles.

In this everchanging world, any policy - makersand expertshave been focused on the problems of employment and it"s complexities. It is obvious that the frame of country"s youth population and increasing work inquiries, requires more attention to this phenomenon. The fact is that, in due to change in traditional economies, in providing imployment and generating production, some temporary industrial projects, are not efficient. In other words, in today"s country situations, which have been most affected by external elements, to decfease the problem of unemployment, the new job opportunities should be defined and introduced to the society. In this paper, the focus woutd be on analysing the infrastructure obstacles facing the problems of country"s unemployment. Finally, with more attention to the different economic sectors with high potential, educational system and production development, the ways that can get rid of this crisis, will be presented.

Hydraulic structures in some cases, cause to produce obstacles in path of the flow that create oscillating vortices in downstream of the obstacles. Vortices produce oscillating forces to the obstacle that are harmful for the stability of structure. In recent years this phenomenon is used to create clean energy. In this study, oscillation of an obstacle in the presence of a fixed obstacle at the upstream was examined. The experiments on triangular block were carried out under varying discharge and different upstream distances. The main objective of this study was to investigate the effect of parameters of velocity and upstream obstacle distance on the oscillation frequency. Using dimensional analysis, the dimensionless parameters of Strouhal number, Reynolds number and ratio of distance to diameter were obtained. The charts of the relationship of the Reynolds number and also the ratio of distance to diameter vs. the Strouhal numbers were plotted. Finally, a new relationship was presented using data analysis and spss20 software to estimate the Strouhal number. Verifying the proposed relation, confirmed a fairly good prediction of this relation.

Introduction: Regarding the role of research in developing and improving a better culture, society and economics, 95% to 97% world finance in research belongs to developed countries while only 3%-5% to developing countries. Although the universities as the major organizations are to do research works, it seems that there are some problems to bring this true. We tried to find out if a load of teaching hours could work as an obstacle to "research" or not.Methods: 413 academic staff from Hamadan, Kermanshah, Booshehr and Ahwaz universities was randomly selected in this descriptive research. Content validity and reliability were examined before approaching research. The data was collected through a questionnaire and analyzed.Results: The most teaching hours was in Ahwaz (11.59 hours) and the least was in Booshehr (5.32 hours). Reseach works was the most in Booshehr (96.8%), and the least in Hamadan (84.2%). 26.4% from Ahwaz, 17.8% from Kermanshah, Hamadan 47.8%, Booshehr 22.6%, agreed on the following obstacles: a) Intensive clinical education, b) Intensive teaching hours, c) Strong authoritical preference for clinical matters than to research work.Conclusion: A very significant correlation among the teachers views was not seen, but all of them agreed on intensivity of clinical education as am obstacle to do "research".

Monolithic aerogels of high molecular weight polyethylene (Mw=3×106- 6×106 g/mol) have been prepared by solvent extraction with supercritical carbon dioxide from thermoreversible gels prepared in decalin. These low density and highly porous aerogels present an apparent porosity up to 90%. The aerogel morphology observed by scanning electron microscopy (SEM) is characterized by spherulitic structures being interconnected by fibers. The X-ray diffraction experiments show that PE aerogels are highly crystalline with a degree of crystallinity of c.a.80% and PE chains being packed into the typical orthorombic unit cell. The combined SEM and N2 sorption investigations show that PE aerogels are essentially macroporous with a small amount of mesopores. The oil-sorption performance of polyethylene aerogels has been also evaluated in this study in order to assess a possible use of these materials for oil spillage recovery and results show that aerogel macropores allow a very fast sorption kinetics with a 100% oil weight uptake obtained in less than 1 min.