Kinetic and potential energies available in water dissipating using structures like drops can be used for generating electricity on small scale. To this aim, the Archimedes screw turbine, as an emerging turbine, can be employed for converting kinetic and potential energies to mechanical energy in irrigation canals. However, there is no literature in this regard. In this research, the effect of tailwater on turbine performance was investigated. To this end, an Archimedes screw turbine was designed and validated using FLOW-3D, and the effect of different submersion ratios was investigated. The results showed that there needs 0.5 to 0.75 submersion ratio in the downstream canal to avoid extra power loss, resulting in maximum power and efficiency in the same conditions.

Labyrinth weirs are often a favorable design option to regulate water surface elevation in upstream canal and increase flow capacity. Due to their hydraulic performance and geometric versatility, labyrinth weirs have been used extensively in canals, rivers, ponds, and reservoirs as energy dissipaters, flow aerators, and spillways. Nevertheless, it can be difficult for engineer to optimally design, labyrinth weirs due to the complexities of nappe behavior and many geometric and hydraulic variables. A level of sedimentation in upstream and submergence in downstream of the weirs are effective parameters which affects the discharge coefficient, and the performance of these structures. In this investigation effects of 408 tests of different levels of tail water (increase of downstream canal bed level to one third and two third of weir height) and upstream sedimentation level (non-sedimentation and sedimentation level of 90 percent of weir height) on the discharge coefficient of different geometers of trapezoidal labyrinth weirs was investigated experimentally. The analysis of results indicated that increase of tail water level to one third of weir height didn’taffect on the discharge coefficient of weirs. By increasing tail water depth to two third of weir height, air cavity volume under nappe decreased. Therefore, the flow pattern of the nappe changed from leaping to clinging condition and upstream head decreased. As a result, the labyrinth weirs discharge coefficient in non-sedimentation and sedimentation level of 90 percent of weir height increased about 3.3 to 12.2 and 2.1 to 9.2 in comparison with non submergence tail water for maximum discharge respectively. Finally, the statistical equation for estimation of the discharge coefficient of trapezoidal labyrinth weirs for upstream sedimentation and submerged conditions was developed.

Grade control structures are used to control bed erosion in steep small rivers mostly in the mountains. Scour downstream of this structure can lead to failure. Over the past years, the effect of different variables on this phenomena have been studied, however the effect of upward seepage  which is common due to head difference of the banks water table or water surface level between the upstream and downstream reaches of a grade control structure has not been studied. In this paper, results of an experimental investigation on the maximum scour depth downstream of a grade control structure with and without upward seepage through bed sediments are presented. Experiments were run for the conditions of free falling jets, over sedimentary beds (median sizes=1.5, 2.4 and 3.15 mm). Our data for the case of existing upward seepage shows that D' Agostino and Ferro (2004) expression significantly overestimates the scour depth. New finding of this study indicates that with the presence of upward seepage the scour depth decreases significantly which confirms the results of Sarker and Dey (2006) on scour downstream of horizontal jet with no horizontal apron.

Accurate assessment of systematic risks in financial markets can lead to favorable capital allocation. Systematic tail risk is adverse events that, if they occur, can affect stock returns. Therefore, the purpose of this study is to investigate the effect of tail risk on excess stock returns. In the present study, two criteria of cumulative tail risk and combined tail covariance risk were used to measure tail risk. For this purpose, using the systematic removal method, a sample of 136 companies listed on the Tehran Stock Exchange (TSE) in the period 2009 to 2019 was selected. Research hypotheses were tested using the five-factor model of Fama and French regression. The results showed that the combination of size portfolio and tail risk and the combination of value portfolio and tail risk have a negative effect on excess stock returns. In addition, the results indicate that the combination of profitability portfolio and tail risk and the combination of investment portfolio and tail risk does not lead to excess stock returns. In general, the results showed that tail risk can be added to asset pricing models in addition to the variables of the five-factor model of Fama and French.

The low (high) abnormal returns of stocks with a high (low) left tail risk is a financial anomaly studied in empirical capital asset pricing research. This anomaly is caused by undesirable and unexpected events that incur severe losses for investors, and this loss has the characteristic of continuity. Since the prediction of left-tail risk can help formulate an appropriate trading strategy, this study aims to predict the left-tail risk through past left tail risk information via portfolio analysis and Fama and Macbeth's (1973) regression. To this end, the data of 307 companies of Tehran Stock Exchange and Iran Fara Bourse from 2005 to 2020 were used. The results revealed the ability to predict the left tail risk by past risk information in the research sample. Further exploration by additional portfolio analysis suggested that the future left-tail risk prediction power by past information left-tail risk is greater among stocks with small size characteristics and high unsystematic volatility, but only a small portion of the market is devoted to stocks with these characteristics.

Using flip buckets as a part of the flow dissipaters in vertical case in dams would lead to dissipation of the energy from the flood passage. This structure is used to reduce costs in comparison with other energy dissipaters. Water jet collision with the river bed leads to the creation of scouring hole which can reduce the stability of dams and relevant structures. In the present study, the scouring phenomenon of the downstream of a flip bucket in free conditions and also in the presence of slots with rectangular and triangular shapes in various intervals distances with 9 flow rates and a total of 45 tests have been investigated. The results of this study showed that the presence of a slot would have a lot of effects on the depth and extent of scouring, so that a flip bucket with alternate rectangular slot compared to a non-slotted case causes about 13 percent less scour. Also, the maximum scour depth in bucket mode with alternate rectangular slots occurred in a more favorable range than the rest of the models. Then, the obtained results were compared with a number of empirical formulas and it was determined that Martinez B relation provides closer results to real values.

Objective: Left-tailed risk illustrates the probability of unfavorable events that could occur in a range wider than three variances of the distribution function. Although such events have a very low occurrence probability, they would cause significant losses in case of occurrence. This research aims at examining the cross-sectional effects of left-tailed risk on expected excess returns. The present research also examines the probability of the persistence of left-tiled risk in the future. Methods: In this research two proxies of value at risk and expected shortfall are used to measure left-tailed risk. For this purpose, a sample of 120 companies listed in the Tehran stock market in the period of the years 2010-2017 have been selected. Research hypotheses were examined with the use of Fama and Macbeth regression. Transition matrix was used to determine the probability of left-tailed risk persistence in the future. Results: According to the findings of the research, left-tailed risk has a significant and negative effect on the expected excess returns. The findings also suggested that the negative returns of the left tail will have a persistence probability of over 50% in the future. Conclusion: The findings of the present research illustrate a new anomaly in the financial area, which is the negative effect of left-tail risk on the expected excess returns, and persists in the future.

Objective: This research aims to explore the applicability of the long-tail theory within the context of electronic bookstores, using the Taaghche bookstore (Taaghche.com) as the main study case. The long-tail theory posits that cultural products, especially books with low sales but wide variation, occupy the tail of the distribution, while high-selling items with limited variation are situated at the head of the distribution. The objective of this research is to demonstrate that as the tail becomes heavier, there is an increase in variation among low-sales products. Furthermore, it posits that the revenue generated from the tail could equal or even surpass the income from the head of the distribution.Methodology: This research relies on quantitative data and employs an analytical survey method for analysis. The sample, drawn from the Taaghche electronic bookstore, consists of literature storybooks that are generally well-received. The data was collected in collaboration with Taaghche and subjected to statistical analysis.Findings: The results indicate that as the number of books increases, the long-tail distribution becomes a more appropriate fit. Furthermore, by identifying the point where sales rates in the head and tail are equal, the tail of the plot lengthens and approximates the 98 percent Anderson rule. This suggests that 98 percent of the books have been sold at least once a year.Conclusion: The results present a counter-example to the Pareto principle, which suggests that an increase in the number of available books leads to increased sales of other books. It is recommended that electronic bookstores expand their range of books, as this has a positive and direct impact on the visibility of other books. The findings clearly demonstrate that increasing the number of books not only creates a long tail in sales but also enhances the visibility of other available books, which is an intriguing observation. Generally, it can be inferred that as the number of books in an electronic bookstore increases, the findings align more closely with the long tail principle. Achieving the long tail implies an increase in the variety of books, which benefits the readership. Given today’s technological advancements and the proliferation of online communication networks and electronic bookstores, many limitations of physical bookstores, such as product storage space and accessibility, have been reduced. This development allows people worldwide, with diverse interests, tastes, and fields of study, to access electronic bookstores in the shortest possible time. Now that electronic bookstores are not constrained by physical space for book storage, it is advantageous to collaborate with publishers to expand the diversity of their books as much as possible, ensuring the satisfaction and welfare of a broader audience.