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RISS 인기검색어
- 검색키워드
- 저자 : Sajjad Tohidi (검색결과 4 건)
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Sajjad Tohidi,Yasser Sharifi 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.4
Half-through girders are not affected by conventional lateral-torsional buckling. I-section beams of simply supported half-through girders experience compression in their top flanges and tension in their bottom flanges. In this condition, the compression flange is restrained only by the stiffness of the web, and the buckling mode is generally restrained distortional. In this study, new and efficient model is derived to predict the Restrained Distortional Buckling (RDB) strength of half-through I-section bridge girders utilizing an Artificial Neural Network (ANN). The model is developed based on a reliable database obtained from the nonlinear finite element (FE) method. To verify the accuracy of the derived model, it is applied to estimate the RDB strength of parts of the FE analysis results that were not included in the modeling process. A sensitivity analysis has been also developed to determine the importance of each input parameters. ANN model is further compared to the some existing design codes. The results indicate that the proposed model is effectively capable of evaluating the RDB load of the half-through girders. The prediction performance of the ANN model is markedly better than prediction of the AISC/LRFD and the AS4100 specifications. The ANN-based design equation can reliably be employed for pre-design applications.
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Association between Dietary Acid Load and Insulin Resistance
Sajjad Khalili Moghadam,Zahra Bahadoran,Parvin Mirmiran,Maryam Tohidi,Fereidoun Azizi 한국식품영양과학회 2016 Preventive Nutrition and Food Science Vol.21 No.2
In the current study, we investigated the longitudinal association between dietary acid load and the risk of insulin resistance (IR) in the Tehranian adult population. This longitudinal study was conducted on 925 participants, aged 22∼80 years old, in the framework of the third (2006∼2008) and fourth (2009∼2011) phases of the Tehran Lipid and Glucose Study. At baseline, the dietary intake of subjects was assessed using a validated semi-quantitative food frequency questionnaire, and the potential renal acid load (PRAL) and net endogenous acid production (NEAP) scores were calculated at baseline. Fasting serum insulin and glucose were measured at baseline and again after a 3-year of follow-up; IR was defined according to optimal cut-off values. Multiple logistic regression models were used to estimate the risk of IR according to the PRAL and NEAP quartile categories. Mean age and body mass index of the participants were 40.3 years old of 26.4 ㎏/㎡, respectively. Mean PRAL and NEAP scores were −11.2 and 35.6 mEq/d, respectively. After adjustment for potential confounders, compared to the lowest quartile of PRAL and NEAP, the highest quartile was accompanied with increased risk of IR [odds ratio (OR)=2.81, 95% confidence interval (CI)=1.32∼5.97 and OR=2.18, 95% CI=1.03∼4.61, respectively]. Our findings suggest that higher acidic dietary acid-base load, defined by higher PRAL and NEAP scores, may be a risk factor for the development of IR and related metabolic disorders.
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Association between Dietary Acid Load and Insulin Resistance: Tehran Lipid and Glucose Study
Moghadam, Sajjad Khalili,Bahadoran, Zahra,Mirmiran, Parvin,Tohidi, Maryam,Azizi, Fereidoun The Korean Society of Food Science and Nutrition 2016 Preventive Nutrition and Food Science Vol.21 No.2
In the current study, we investigated the longitudinal association between dietary acid load and the risk of insulin resistance (IR) in the Tehranian adult population. This longitudinal study was conducted on 925 participants, aged 22~80 years old, in the framework of the third (2006~2008) and fourth (2009~2011) phases of the Tehran Lipid and Glucose Study. At baseline, the dietary intake of subjects was assessed using a validated semi-quantitative food frequency questionnaire, and the potential renal acid load (PRAL) and net endogenous acid production (NEAP) scores were calculated at baseline. Fasting serum insulin and glucose were measured at baseline and again after a 3-year of follow-up; IR was defined according to optimal cut-off values. Multiple logistic regression models were used to estimate the risk of IR according to the PRAL and NEAP quartile categories. Mean age and body mass index of the participants were 40.3 years old of $26.4kg/m^2$, respectively. Mean PRAL and NEAP scores were -11.2 and 35.6 mEq/d, respectively. After adjustment for potential confounders, compared to the lowest quartile of PRAL and NEAP, the highest quartile was accompanied with increased risk of IR [odds ratio (OR)=2.81, 95% confidence interval (CI)=1.32~5.97 and OR=2.18, 95% CI=1.03~4.61, respectively]. Our findings suggest that higher acidic dietary acid-base load, defined by higher PRAL and NEAP scores, may be a risk factor for the development of IR and related metabolic disorders.
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ESS equipped DFIG wind farm with coordinated power control under grid fault conditions
Mazgar, Farshid Najaty,Hagh, Mehrdad Tarafdar,Tohidi, Sajjad The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.1
A new structure for doubly fed induction generator (DFIG) wind farms with coordinated power control under grid fault conditions are proposed in this paper. The proposed structure uses one grid side converter (GSC) and one energy storage system (ESS) for the entire wind farm unlike conventional structures, which have one GSC for each of the DFIGs. A converter loss decrease and a reliability enhancement are some of the advantages of the proposed wind farm, under normal operating conditions. The proposed wind farm follows the new grid codes to remain connected to the grid. In addition, it supports the network voltage and frequency stability by generating reactive and active power during and after faults. The ESS is coordinated with the wind farm to generate smooth active power under normal operation. This improves the low voltage ride-through capability of the wind farm under-voltage fault conditions and enhances the frequency response of the wind farm under frequency faults. MATLAB/Simulink software was used to simulate the proposed wind farm structure. An experimental setup was also provided to test the operation of the proposed power circuit topology.
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