Groundwater and River Interaction Parameter Estimation in Saigon River, Vietnam

The Saigon River system is one of the largest resources contributing water supply for domestic and industrial fields in the Ho Chi Minh City and Binh Duong Province where the drought issue are occurring at downstream area in recent years. To manage the water resources in Saigon Basin effectively, the groundwater and river interaction parameter needs to be assessed systematically. However, in the past researches, the parameters seem to be less described with full understandings. In this study, a groundwater modeling of the main stream of Saigon River was applied to analyze groundwater and river interaction parameter along the river. The interaction layer was defined as a combined layer by materials of riverbed and materials of aquitard or aquifer. The values of conductance, through groundwater model calibration by piezometric heads during 2000 to 2007 at three cross-sections in Saigon River, were used to estimate the interaction parameter (KiM-1) at correlative cross-section. A function of interaction parameter with ratio of wetted length (Rw) was developed to estimate interaction parameter at each cross-section along Saigon River. When river cross-sections has no penetration to the aquifer and the materials of interaction layer consists of materials of riverbed and aquitard, the value of interactions is equal to 0.0003 d-1. In the other hand, the value will be reach to 0.254 d-1 when river cross-section has fully penetration to the aquifer. The interaction parameter function developed was applied to investigate the flow in and out between river and aquifer in the study area. In the upper part of Saigon River, river gained water from inflow of groundwater through riverbed (river gain) and lost water to groundwater (river loss) by outflow through the riverbed in the lower part during 2000 to 2007 and the river recharge to the first aquifer supplies to the second aquifer to supplement the aquifer storage discharged from the pumping

On the Asymptotic Behavior of Solutions of Differential Systems

There are many studies on the asymptotic behavior of solutions of differential equations. In the present paper, we consider another aspect of this problem, namely, the rate of the asymptotic convergence of solutions.Асимптотичній поведінці розв'язків диференціальних рівнянь присвячено чимало досліджень. У даній роботі проблему розглянуто з іншого боку, а саме, з точки зору швидкості асимптотичної збіжності розв'язків

Estimation of Groundwater Use Pattern and Distribution in the Coastal Mekong Delta, Vietnam via Socio-Economical Survey and Groundwater Modelling

In many provinces of Mekong delta, excessive groundwater extraction has resulted in many serious groundwater-related problems. To solve problems relevant to increasing water demand as well as other negative influence of groundwater depletion, an exigent question was raised whether at what time in future is the limits to local groundwater use reached? Hence, there is a need to know groundwater use (GWU) pattern and distribution in the study area for future groundwater management. In this study, firstly, the study used socio-economic data of Tra Vinh Province to classify groups of revenue, potential of water resources and population distributed in each district in order to design and conduct the socio-economic survey and to explore information relevant to GWU for each purpose. Secondly, the data set of 419 survey questionnaires per 9 surveyed communes were analysed by SPSS tool to estimate ratio of household using groundwater (RHHUG) for each purpose as well as average pumping rate (APR) per household for domestic use and per ha for agriculture use, respectively. Thirdly, the APRs were extended to propose the total GWU pattern and distribution during 2007-2016 by using socio-economic data of the province and expand to spatial distribution by using correlation with land surface temperature (LST) which was estimated from Landsat 8 images. Besides, the groundwater flow model of the study area was developed to verify the estimated amount of groundwater pumping (pattern and distribution) in the period. The study found that the annual GWU of Tra Vinh Province in 2016 was 347,793 m3/d in which two coastal districts occupied more than 50 percentages, i.e., about 188,551 m3/d. RHHUG increased from 2 to 3 times during the period of 2007 to 2016 in this area. LST distribution performed a good correlation (adj-R2 = 0.646) with GWU distribution in Tra Cu district. Results of groundwater modelling also showed that the discharge from aquifer (mainly pumping) was always higher than the recharge to aquifer

Parameter Estimation and Predictive Speed Control of Chopper-Fed Brushed DC Motors

This paper presents an effective speed control method for brushed DC motors fed by a DC chopper using the concept of Finite Control Set-Model Predictive Control (FCS-MPC). As this control algorithm requires the parameters of the controlled object, the estimation of motor parameters is first performed by using two types of data. The first data includes the output speed response corresponding to the step input voltage to obtain the transfer function in the no-load regime. The second data consists of the motor speed and armature current when a load torque is applied to the motor shaft. The discrete-time equation of the motor armature circuit is used to obtain the future values of the armature circuit current and the motor speed. A cost function is defined based on the difference between the reference and predicted motor speed. The optimal switching states of the DC chopper are selected corresponding to the maximum value of the cost function. The performance of the proposed speed control algorithm is validated on an experimental system. The simulation and experimental results obtained show that the MPC controller can outperform the conventional proportional-integral (PI) controller

Impact of Agency Costs on Firm Performance: Evidence from Vietnam

An assumption in agency costs theory is that agency costs can exert a negative impact on firm performance. In this study, we examine the impact of agency costs on firm performance of Vietnamese listed companies. Our sample includes 736 companies in Vietnam during the period om 2010 to 2015. We find that agency costs exert a negative impact on firm performance. Our results are robust to alternative econometric models, including an instrumental variables technique and a system generalized method of moment model. In addition, we show that a debt instrument can be a useful tool to reduce the negative impact of agency costs on firm performance