Multi objective simulation-optimization operation of dam reservoir in low water regions based on hedging principles.

The high level of reliability of water resources is always an advantage for consumers, but in arid and semi-arid regions where the inflow to the reservoir is faced with severe fluctuations, it makes sense to decrease the percentage of reliability of the system and allocate less water to consumption zones to prevent critical conditions such as emptying of the reservoir. In this research, the employed operation model is based on the simulation-optimization combination by considering the objectives of minimizing the violation of the allowed capacity of the reservoir and maximizing the percentage of supplying the demands. The optimal hedging variables are specified by linking the WEAP (Water Evaluation and Planning System) to the MOPSO multi-objective optimization algorithm. According to the available data, the duration of the simulation and optimization period in the model is 360 months. After 1000 iterations, the optimal reservoir volume values are obtained at the hedging level and hedging coefficient in different months. Finally, the model results are compared with the results obtained from the standard operation policy (SOP). The results show that the proposed model is able to manage the allocation to needs in the dry months and prevent the reservoir from emptying. Also, by storing a part of the flow in the reservoir in watery months and consuming it in low water months, it increases the supply of needs by 20 to 35% and reduces the failure rate in dry months.

Hospitalizations and its related factors in HIV/AIDS patients in Tehran, Iran.

BACKGROUND: HIV/AIDS patients are mainly hospitalized for HIV-related diseases and opportunistic infections.ions. This study was performed to determine the causes of hospitalization and its related factors in HIV/AIDS patients in Tehran's Imam Khomeini Hospital during 2009-2012. METHODS: This study was a descriptive cross-sectional study. HIV patients admitted to the Imam Khomeini Hospital were included in the study through census method, during the study. Demographic variables, hepatitis co-infection, CD4 count, history of receiving anti- retroviral therapy (ART), cause of admission, length of hospitalization and patient's outcome were recorded. Data were analyzed by SPSS software and by means of Chisquare and Mann Whitney U tests. RESULTS: During the study, 555 HIV patients were included in, 84.9% of whom were male, with the mean age of 36.59±8.51 years and the average length of hospitalization for 16.04±18.82 days. Opportunistic infections were the most common cause of hospitalization (46.5%) with prevalent of which was pulmonary tuberculosis being the most prevalent (37.6%). Patients suffering from opportunistic infections had significantly lower CD4 count and longer hospitalization than the other diseases. A significant difference was detected between patients outcome and the history of ART. CONCLUSION: Low CD4 count may contribute to an increase in number and length of hospitalization in HIV/AIDS patients. Accordingly, it appears to affect outcome of their treatment and ART was accompanied by a drop in the death rate of hospitalized patients.