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Significance of rigorous fluid-foundation interaction in dynamic analysis of concrete gravity dams
Lotfi, Vahid Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.2
Dynamic analysis of dam-reservoir-foundation system is usually carried out by employing a simplified and approximate one-dimensional model to account for fluid-foundation interaction. The approximation introduced on this basis is examined thoroughly in this paper by comparing the method with the rigorous approach. It is concluded that the errors due to approximate method could be very significant both for horizontal and vertical ground motions.
Lotfi, Vahid,Zenz, Gerald Techno-Press 2018 Coupled systems mechanics Vol.7 No.3
The Wavenumber or more accurately Wavenumber-FD approach was initially introduced for two-dimensional dynamic analysis of concrete gravity dam-reservoir systems. The technique was formulated in the context of pure finite element programming in frequency domain. Later on, a variation of the method was proposed which was referred to as Wavenumber-TD approach suitable for time domain type of analysis. Recently, it is also shown that Wavenumber-FD approach may be applied for three-dimensional dynamic analysis of concrete arch dam-reservoir systems. In the present study, application of its variation (i.e., Wavenumber-TD approach) is investigated for three-dimensional problems. The method is initially described. Subsequently, the response of idealized Morrow Point arch dam-reservoir system is obtained by this method and its special cases (i.e., two other well-known absorbing conditions) for time harmonic excitation in stream direction. All results for various considered cases are compared against the exact response for models with different values of normalized reservoir length and reservoir base/sidewalls absorptive conditions.
An efficient three-dimensional fluid hyper-element for dynamic analysis of concrete arch dams
Lotfi, Vahid Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.24 No.6
The accurate dynamic analysis of concrete arch dams relies heavily on employing a three-dimensional semi-infinite fluid element. The usual method for calculating the impedance matrix of this fluid hyper-element is dependent on the solution of a complex eigen-value problem for each frequency. In the present study, an efficient procedure is proposed which simplifies this procedure amazingly, and results in great computational time saving. Moreover, the accuracy of this technique is examined thoroughly and it is concluded that efficient procedure is incredibly accurate under all practical conditions.
Cross-Validation Probabilistic Neural Network Based Face Identification
Lotfi, Abdelhadi,Benyettou, Abdelkader Korea Information Processing Society 2018 Journal of information processing systems Vol.14 No.5
In this paper a cross-validation algorithm for training probabilistic neural networks (PNNs) is presented in order to be applied to automatic face identification. Actually, standard PNNs perform pretty well for small and medium sized databases but they suffer from serious problems when it comes to using them with large databases like those encountered in biometrics applications. To address this issue, we proposed in this work a new training algorithm for PNNs to reduce the hidden layer's size and avoid over-fitting at the same time. The proposed training algorithm generates networks with a smaller hidden layer which contains only representative examples in the training data set. Moreover, adding new classes or samples after training does not require retraining, which is one of the main characteristics of this solution. Results presented in this work show a great improvement both in the processing speed and generalization of the proposed classifier. This improvement is mainly caused by reducing significantly the size of the hidden layer.
Lotfi, Fezeh,Chekli, Laura,Phuntsho, Sherub,Hong, Seungkwan,Choi, Joon Young,Shon, Ho Kyong Elsevier Scientific Pub. Co 2017 Desalination Vol. No.
<P><B>Abstract</B></P> <P>We investigated the possible underlying mechanism of the low fouling potential in the forward osmosis (FO) process during the osmotic dilution of seawater as part of the simultaneous desalination and wastewater reuse by FO and reverse osmosis hybrid system. Long-term experiments revealed an interesting water flux pattern highly dependent on the different operating parameters. The most interesting observation made was the spontaneous increase in the FO permeate flux at regular time interval during the FO operation using synthetic wastewater as feed and seawater. This sinusoidal FO flux pattern related well with the build-up of loose fouling layer and their natural peel-off from the membrane surface upon reaching certain layer thickness due to crossflow velocity shear. This flux pattern was more prominent at higher cross-flow velocity rates, lower feed water pH, for a smoother membrane surface and at lower operating pressure during pressure assisted osmosis (PAO) mode. Based on these results, membrane cleaning strategies were proposed by targeting a higher cross-flow velocity shear at a time when the permeate flux started to just increase. The approach of physical membrane cleaning was observed efficient and was able to almost fully restore the initial flux even under the PAO operation at 4bar.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An interesting water flux pattern was observed during osmotic dilution of seawater. </LI> <LI> It was related to the build-up of loose fouling layer peeled-off from the surface. </LI> <LI> This sinusoidal flux pattern was highly dependent on the operating parameters. </LI> <LI> Intrinsic membrane cleaning strategies can be adopted; avoiding plant down time. </LI> <LI> Increasing the feed cross-flow velocity at specific time was found most efficient. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lotfi, Alireza,Mohammadi, Ghodrat,Saniee, Lale,Mousaviagdas, Mehrnoosh,Chavoshi, Hadi,Tavassoli, Atena Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.15
Background: Laryngeal cancer is an important malignancy in head and neck area and squamous cell carcinoma (SCC) is the most common type accounting for 95% of cases. Increase in matrix metalloproteinases (MMPs) in different tumors and their correlation with tumor invasiveness has been documented. However, most studies have evaluated MMP-2 and MMP-9 expression and few have evaluated serum levels. The aim of current study was to evaluate serum levels in patients with laryngeal SCC compared to normal subjects and assess any relation with tumor clinicopathological findings. Materials and Methods: In this case control study, 20 patients with oral SCC and 20 healthy subjects were included. Serum levels of MMP-2 and MMP-9 were compared between groups and correlations with findings including grade (T) and node involvement (N) were evaluated. Results: Patients with laryngeal SCC had significantly higher serum levels of MMP-2 (p=0.01) and MMP-9 (p=0.03) compared to healthy subjects. Patients with higher T stage (T3,4) had significantly higher MMP-2 (p=0.04) and MMP-9 (p=0.01). There was significant positive correlation between serum levels of MMP-2 with T stage (r=0.45, p=0.04) and lymph node involvement (r=0.563, p=0.01) and between levels of MMP-9 with T stage (r=0.527, p=0.01). Conclusions: Our results showed that compared to healthy subjects, both MMP-2 and MMP-9 are significantly increased in serum of laryngeal SCC cases. MMP-2 was correlated with lymph node involvement while MMP-9 has stronger correlation with T stage compared to MMP-2.
Direct frequency domain analysis of concrete arch dams based on FE-BE procedure
Lotfi, Vahid Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.26 No.4
A FE-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by finite elements, while foundation rock is handled by three dimensional boundary element formulation. This would allow a rigorous inclusion of dam-foundation rock interaction, with no limitations imposed on geometry of canyon shape. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various ratios of foundation rock to dam concrete elastic moduli under an empty reservoir condition. Furthermore, the effects of canyon shape on response of dam, is also discussed.