Search for: temporal-variation
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    Characterizing the effect of traffic density on ambient CO, NO2, and PM2.5 in Tehran, Iran: an hourly land-use regression model

    , Article Transportation Letters ; 2017 , Pages 1-11 ; 19427867 (ISSN) Hassanpour Matikolaei, S. A. H ; Jamshidi, H ; Samimi, A ; Sharif University of Technology
    Economic development and population growth in Tehran has increased demand for goods movement and road transportation. This trend has increased mobile source emissions and citizens’ exposure, imposing severe health risks. We used the framework of Land-Use Regression models to quantify the effect of real-time traffic, within buffer distance, on hourly exposure of CO, NO2, and PM2.5. Effect of residential, industrial, and governmental land-use in addition to the effect of pollution sources, such as construction sites and airport were assessed on air pollution. Meteorological variables were also employed to adjust between day variations. R-squared of the models were 38, 27, and 38% for CO, NO2,... 

    General solution to wave propagation in media undergoing arbitrary transient or periodic temporal variations of permittivity

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 35, Issue 11 , 2018 , Pages 29232932- ; 07403224 (ISSN) Chegnizadeh, M ; Mehrany, K ; Memarian, M ; Sharif University of Technology
    OSA - The Optical Society  2018
    A novel and general formulation for wave propagation in time-varying media is presented. Unlike previousreports, our formalism is able to solve propagation in media with arbitrary time variations of permittivity orpermeability, for both transient and steady-state periodic variations. The formulation is approximate yet strikingly accurate in most practical cases. The provided closed-form expressions show that the normalized averagepower after the transition of the permittivity does not depend on the details of the transition, while the energydensity does. Some important discussions are made about time-periodic media, and it is shown that there is anaccumulation of energy when the temporal... 

    Scour hole depth prediction around pile groups: review, comparison of existing methods, and proposition of a new approach

    , Article Natural Hazards ; Volume 88, Issue 2 , 2017 , Pages 977-1001 ; 0921030X (ISSN) Amini Baghbadorani, D ; Beheshti, A. A ; Ataie Ashtiani, B ; Sharif University of Technology
    A dataset of 365 laboratory tests for scour hole depth (SHD) around pile groups (PGs) under unidirectional aligned flow is compiled, and the performances of the existing equations are comparatively evaluated on the dataset using several statistical indices. A formulation based on a correction of HEC-18 equation provides the best estimate with a correlation factor of 0.58. The test durations of the considered data ranged between 4 and 389 h. A time factor (Kt) is proposed to take into account the temporal variation of the SHD around different PGs. Among the datasets, 51 long-duration experiments are scrutinized to show the temporal variation of scour depth toward equilibrium state. The time... 

    A weighting scheme for mining key skeletal joints for human action recognition

    , Article Multimedia Tools and Applications ; Volume 78, Issue 22 , 2019 , Pages 31319-31345 ; 13807501 (ISSN) Shabaninia, E ; Naghsh Nilchi, A. R ; Kasaei, S ; Sharif University of Technology
    Springer New York LLC  2019
    A novel class-dependent joint weighting method is proposed to mine the key skeletal joints for human action recognition. Existing deep learning methods or those based on hand-crafted features may not adequately capture the relevant joints of different actions which are important to recognize the actions. In the proposed method, for each class of human actions, each joint is weighted according to its temporal variations and its inherent ability in extension or flexion. These weights can be used as a prior knowledge in skeletal joints-based methods. Here, a novel human action recognition algorithm is also proposed in order to use these weights in two different ways. First, for each frame of a... 

    An area-scalable human-based mobility model

    , Article Computer Networks ; Volume 177 , 2020 Gharib, M ; Foroozani, A ; Rezaei, S ; Hemmatyar, A. M. A ; Movaghar, A ; Sharif University of Technology
    Elsevier B.V  2020
    Mobile networks have been growing rapidly, where it is of paramount importance to evaluate the performance of any protocol designed for such networks before deployment. Mobility is one of the main mobile network issues that directly affects performance metrics. Since mobile nodes are often carried by their owners, nodes movement should be modeled according to humans movement. In this paper, we extend our previously published human mobility model based on real collected data. The real human movement is traced, cleaned up and analyzed. To the best of our knowledge, our collected data set is the only one that contains the detail of both walking and driving nodes. The analysis shows several... 

    Correlation between concentrations of chlorophyll-a and satellite derived climatic factors in the Persian Gulf

    , Article Marine Pollution Bulletin ; Volume 161, Part A , December , 2020 Moradi, M ; Moradi, N ; Sharif University of Technology
    Elsevier Ltd  2020
    Monthly mean satellite derived Chl-a, aerosols, wind, SST, PAR, and turbidity datasets were used to investigate the possible factors regulating phytoplankton variability in the Persian Gulf. The spatial correlation analysis revealed two distinct regions of SST and PAR, and a relatively uniform spatial correlation pattern of the other parameters. The cross correlation between aeolian dusts and Chl-a was significantly positive with 1–3 months offset. The pattern of spatial correlation between Chl-a and SST was positive in the shallow regions without time lag, and was negative with time offset of 3–5 months in deeper regions. The cross correlation between Chl-a and north-ward winds were... 

    Rotation rate estimation in parametrically excited micro gyroscopes

    , Article Mechatronics ; Volume 31 , October , 2015 , Pages 264-275 ; 09574158 (ISSN) Fazlyab, M ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    Elsevier Ltd  2015
    This paper reports the estimation of angular velocity in micro gyroscopes with parametric excitation. The identification procedure is done into two consecutive steps: In the first step, the physical parameters of the gyroscope (stiffness, damping, and actuator parameters) are estimated via continuous time Extended and Unscented Kalman filter. In the second step, a separate Kalman filter is dedicated to estimate the time varying rotation rate, using the output of the first step. Using numerical simulations, it is found that by introducing an artificial noise in the observer equations and tuning its variance, arbitrary temporal variation of angular velocity can be well tracked by the proposed... 

    Monitoring temperature changes in a hypersaline lake using MODIS-derived water temperatures (the case of Urmia Lake, Iran)

    , Article 6th International Symposium on Environmental Hydraulics, Athens, 23 June 2010 through 25 June 2010 ; Volume 2 , 2010 , Pages 881-886 ; 9780415595469 (ISBN) Sima, S ; Tajrishy, M ; Sharif University of Technology
    Lake surface temperature is an important indicator of the lake state and a driver of regional weather and climate near large lakes. The objective of this study is to use thermal imagery from the MODIS on board the Earth Observing System Terra and Aqua platforms to assess the spatial and temporal variations in Urmia lake temperature. Urmia Lake, located in northwestern Iran is one of the largest permanent hypersaline lakes in the world. The surface temperature of Urmia Lake is examined between 2008 and 2009, as dry years. MODIS-derived lake SWT then was calibrated with monthly observations. MODIS-derived lake SWT exhibits a cool bias (-0.72°C) relative to in situ temperature observations in... 

    Characterizing the effect of traffic density on ambient CO, NO2, and PM2.5 in Tehran, Iran: an hourly land-use regression model

    , Article Transportation Letters ; Volume 11, Issue 8 , 2019 , Pages 436-446 ; 19427867 (ISSN) Hassanpour Matikolaei, S. A. H ; Jamshidi, H ; Samimi, A ; Sharif University of Technology
    Taylor and Francis Ltd  2019
    Economic development and population growth in Tehran has increased demand for goods movement and road transportation. This trend has increased mobile source emissions and citizens’ exposure, imposing severe health risks. We used the framework of Land-Use Regression models to quantify the effect of real-time traffic, within buffer distance, on hourly exposure of CO, NO2, and PM2.5. Effect of residential, industrial, and governmental land-use in addition to the effect of pollution sources, such as construction sites and airport were assessed on air pollution. Meteorological variables were also employed to adjust between day variations. R-squared of the models were 38, 27, and 38% for CO, NO2,... 

    Wave propagation in metallic slab waveguides undergoing arbitrary temporal variations of permittivity

    , Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 1529-1533 ; 9781728115085 (ISBN) Chegnizadeh, M ; Memarian, M ; Mehrany, K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    A general and closed form solution of wave propagation in a metallic slab waveguide undergoing any arbitrary, time-varying function of permittivity is presented. The formulation is general and accurate to account for all temporal variations of permittivity. Parametric amplification and frequency conversion is demonstrated using this closed form formulation. Moreover, all results are validated and confirmed using full wave FDTD simulation. The in-house FDTD MATLAB code takes into account time variations of the permittivity  

    Mapping surface temperature in a hyper-saline lake and investigating the effect of temperature distribution on the lake evaporation

    , Article Remote Sensing of Environment ; Volume 136 , 2013 , Pages 374-385 ; 00344257 (ISSN) Sima, S ; Ahmadalipour, A ; Tajrishy, M ; Sharif University of Technology
    Remote sensing is an effective tool for capturing spatial and temporal variations of water surface temperature (WST) in large lakes. The WST of Urmia Lake in northwestern Iran was examined from 2007 to 2010, using MODIS land surface temperature (LST) products. Spatial and temporal (diurnal, monthly, seasonal and inter-annual) variations of Urmia Lake WST were also investigated. Results indicate that the MODIS-derived WSTs are in a good agreement with the in situ data (R2=0.92 and bias=-0.27). Spatial analysis of WST revealed that there are three thermal zones along the lake: the shallow region in barriers of the causeway, islands and the shoreline; the south part; and the deep north parts.... 

    Influence of unsteady flow hydrograph shape on local scouring around bridge pier

    , Article Proceedings of the Institution of Civil Engineers: Water Management ; Volume 165, Issue 9 , October , 2012 , Pages 473-480 ; 17417589 (ISSN) Borghei, S. M ; Kabiri-Samani, A ; Banihashem, S. A ; Sharif University of Technology
    ICE Pub  2012
    Accurate estimation of scour depth is needed for economic and safe determination of bridge pier foundation depth. Most design criteria are based on maximum scour depth due to the steady design discharge without flow time limit. In this paper, the results are presented of an experimental investigation on local scouring around a single bridge pier under steady and unsteady flow regimes. For unsteady flow, triangular shape hydrographs with repeatable peaks have been chosen. Results show that both sharp and flat increases to the peak of hydrographs have a negligible effect on scour depth for the same base time. An equation is obtained to compute the scour depth due to a specific triangular... 

    Experimental investigation on aerodynamic performance of a flapping wing vehicle in forward flight

    , Article Journal of Fluids and Structures ; Volume 27, Issue 4 , 2011 , Pages 586-595 ; 08899746 (ISSN) Mazaheri, K ; Ebrahimi, A ; Sharif University of Technology
    The aerodynamic performance of a flexible membrane flapping wing has been investigated here. For this purpose, a flapping-wing system and an experimental set-up were designed to measure the unsteady aerodynamic forces of the flapping wing motion. A one-component force balance was set up to record the temporal variations of aerodynamic forces. The flapping wing was studied in a large low-speed wind tunnel. The lift and thrust of this mechanism were measured for different flapping frequencies, angles of attack and for various wind tunnel velocities. Results indicate that the thrust increases with the flapping frequency. An increase in the wind tunnel speed and flow angle of attack leads to... 

    In situ LIF temperature measurements in aqueous ammonium chloride solution during uni-directional solidification

    , Article Experiments in Fluids ; Volume 48, Issue 4 , April , 2010 , Pages 651-662 ; 07234864 (ISSN) Shafii, M. B ; Lum, C. L ; Koochesfahani, M. M ; Sharif University of Technology
    We present in situ whole-field measurements of the temperature field using laser-induced fluorescence in a study of bottom-chilled uni-directional solidification of aqueous ammonium chloride. We utilize a two-color, two-dye, ratiometric approach to address the significant spatial and temporal variations of laser sheet intensity field due to refractive index variations caused by the evolving concentration and temperature fields. In our work we take advantage of two temperature sensitive fluorescent dyes with opposite temperature sensitivities in order to increase the overall sensitivity and temperature resolution of the measurements. The resulting temperature sensitivity (about 4% K-1) is... 

    Investigating the temporal and spatial variations of water consumption in Urmia Lake River Basin considering the climate and anthropogenic effects on the agriculture in the basin

    , Article Agricultural Water Management ; Volume 213 , 2019 , Pages 782-791 ; 03783774 (ISSN) Taheri, M ; Emadzadeh, M ; Gholizadeh, M ; Tajrishi, M ; Ahmadi, M ; Moradi, M ; Sharif University of Technology
    Elsevier B.V  2019
    Urmia Lake River Basin (ULRB) is one of the most important habitats in the world and one of the major agricultural regions in Iran. On average, the ratio of irrigation to evapotranspiration in this basin is more than 73%. Investigating the irrigation water requirement pattern changes and the spatial distribution of evapotranspiration during the basin development period on a regional scale play important roles in understanding the basin situation. In this study, the actual evapotranspiration has been estimated by SEBAL model. By estimating the precipitation distribution in the basin, the agricultural irrigation water requirement pattern has been calculated using the land use map in 1995, 2010... 

    Multi-site statistical downscaling of precipitation using generalized hierarchical linear models: a case study of the imperilled Lake Urmia basin

    , Article Hydrological Sciences Journal ; Volume 65, Issue 14 , 2020 , Pages 2466-2481 Abbasian, M. S ; Abrishamchi, A ; Najafi, M. R ; Moghim, S ; Sharif University of Technology
    Taylor and Francis Ltd  2020
    A downscaling model capable of explaining the temporal and spatial variability of regional hydroclimatic variables is essential for reliable climate change studies and impact assessments. This study proposes a novel statistical approach based on generalized hierarchical linear model (GHLM) to downscale precipitation from the outputs of general circulation models (GCMs) at multiple sites. GHLM partitions the total variance of precipitation into within- and between-site variability allowing for transferring information between sites to develop a regional downscaling model. The methodology is demonstrated by downscaling precipitation using the outputs of eight GCMs in Lake Urmia basin in... 

    MODSharp: Regional-scale numerical model for quantifying groundwater flux and contaminant discharge into the coastal zone

    , Article Environmental Modelling and Software ; Volume 22, Issue 9 , 2007 , Pages 1307-1315 ; 13648152 (ISSN) Ataie Ashtiani, B ; Sharif University of Technology
    In this paper the development of a quasi-three-dimensional numerical model that can be used for quantifying groundwater inputs and associated contaminant discharged from coastal aquifers into the coastal zone at a regional scale is presented. The present model is called MODSharp. In order to handle problems at a regional scale, the sharp interface approach which is used for conceptualising seawater intrusion, is applied to this model. This model can be used for the simulation of groundwater flow and contaminant transport in layered coastal aquifers at a regional scale. The method of characteristics is used to solve the advection-dispersion equation, which governs contaminant transport in... 

    Spatio-temporal variation of hydro-climatic variables and extreme indices over Iran based on reanalysis data

    , Article Stochastic Environmental Research and Risk Assessment ; Volume 36, Issue 11 , 2022 , Pages 3725-3752 ; 14363240 (ISSN) Malaekeh, S. M ; Safaie, A ; Shiva, L ; Tabari, H ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2022
    A comprehensive investigation of historical hydro-climatic changes at a county level is an essential prerequisite of developing any adaptation or mitigation strategies to deal with the destructive impacts of climate change. In this study, spatial distributions and trends in thirty-seven hydro-climatic mean and extreme indices across Iran were analyzed based on the state-of-the-art reanalysis datasets (ERA5-Land and AgERA5) at the county level from 1986 to 2015 using several nonparametric approaches such as multiple modified Mann–Kendall statistical tests and Sen’s Slope estimator. Their interannual oscillations were also examined using continuous wavelet transform to portray a complete... 

    Evaluation of spatial and temporal variation in water quality by pattern recognition techniques: A case study on Jajrood River (Tehran, Iran)

    , Article Journal of Environmental Management ; Volume 91, Issue 4 , 2010 , Pages 852-860 ; 03014797 (ISSN) Razmkhah, H ; Abrishamchi, A ; Torkian, A ; Sharif University of Technology
    In this paper, principal component analysis (PCA) and hierarchical cluster analysis (CA) methods have been used to investigate the water quality of Jajrood River (Iran) and to assess and discriminate the relative magnitude of anthropogenic and "natural" influences on the quality of river water. T, EC, pH, TDS, NH4, NO3, NO2, Turb., T.Hard., Ca, Mg, Na, K, Cl, SO4, SiO2 as physicochemical and TC, FC as biochemical variables have been analyzed in the water samples collected every month over a three-year period from 18 sampling stations along a 50 km section of Jajrood River that is under the influence of anthropogenic and natural changes. Exploratory analysis of experimental data has been... 

    Dynamic behavior of electric field in the microrings in the presence of Kerr and two-photon absorption

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 7 April 2008 through 10 April 2008, Strasbourg ; Volume 6996 , 2008 ; 0277786X (ISSN) ; 9780819471949 (ISBN) Keyvaninia, S ; Karvar, M ; Bahrampour, A ; Sharif University of Technology
    This paper a simple semi-analytical model for calculation of the time evolution and spatial variation of the electric field in microring resonators in the presence of The Kerr effect and two-photon absorption (TPA) is presented. The theoretical analysis is based on the delayed feedback model, which is well known in microring theory. The model is applied to the Chalcogenide glass and AlGaAs microrings to study the Kerr and TPA effects on the spatial and temporal variation of electric field respectively across the microring. The effects of microring parameters and input signal shapes on the transient behavior are taken into consideration. It is shown that, the results are in good agreement...