RELATIONSHIP BETWEEN EROSION AND ACCUMULATION OF SEDIMENTS IN COASTAL ZONE OF BINH THUAN PROVINCE-SOUTH CENTRAL OF VIETNAM

Joint Research on Environmental Science and Technology for the Eart

Existence and Decay of Solutions of a Nonlinear Viscoelastic Problem with a Mixed Nonhomogeneous Condition

We study the initial-boundary value problem for a nonlinear wave equation given by u_{tt}-u_{xx}+\int_{0}^{t}k(t-s)u_{xx}(s)ds+ u_{t}^{q-2}u_{t}=f(x,t,u) , 0 < x < 1, 0 < t < T, u_{x}(0,t)=u(0,t), u_{x}(1,t)+\eta u(1,t)=g(t), u(x,0)=\^u_{0}(x), u_{t}(x,0)={\^u}_{1}(x), where \eta \geq 0, q\geq 2 are given constants {\^u}_{0}, {\^u}_{1}, g, k, f are given functions. In part I under a certain local Lipschitzian condition on f, a global existence and uniqueness theorem is proved. The proof is based on the paper [10] associated to a contraction mapping theorem and standard arguments of density. In Part} 2, under more restrictive conditions it is proved that the solution u(t) and its derivative u_{x}(t) decay exponentially to 0 as t tends to infinity.Comment: 26 page

Large time behavior of differential equations with drifted periodic coefficients modeling Carbon storage in soil

This paper is concerned with the linear ODE in the form $y'(t)=\lambda\rho(t)y(t)+b(t)$, $\lambda <0$ which represents a simplified storage model of the carbon in the soil. In the first part, we show that, for a periodic function $\rho(t)$, a linear drift in the coefficient $b(t)$ involves a linear drift for the solution of this ODE. In the second part, we extend the previous results to a classical heat non-homogeneous equation. The connection with an analytic semi-group associated to the ODE equation is considered in the third part. Numerical examples are given.Comment: 18 page

Vortex flow generator utilizing synthetic jets by diaphragm vibration

This paper develops a millimeter scale fully packaged device in which a vortex flow of high velocity is generated inside a chamber. Under the actuation by a lead zirconate titanate (PZT) diaphragm, a flow circulates with increasing velocity after each actuating circle to form a vortex in a cavity named as the vortex chamber. At each cycle, the vibration of the PZT diaphragm creates a small net air flow through a rectifying nozzle, generates a synthetic jet which propagates by a gradual circulation toward the vortex chamber and then backward the feedback chamber. The design of such device is firstly conducted by a numerical analysis whose results are considered as the base of our experimental set-up. A vortex flow generated in the votex chamber was observed by a high-speed camera. The present approach which was illustrated by both the simulation and experiment is potential in various applications related to the inertial sensing, fluidic amplifier and micro/nano particle trapping and mixing

The regularity and exponential decay of solution for a linear wave equation associated with two-point boundary conditions

This paper is concerned with the existence and the regularity of global solutions to the linear wave equation associated with two-point type boundary conditions. We also investigate the decay properties of the global solutions to this problem by the construction of a suitable Lyapunov functional.Comment: 18 page

Existence, blow-up and exponential decay estimates for a nonlinear wave equation with boundary conditions of two-point type

This paper is devoted to study a nonlinear wave equation with boundary conditions of two-point type. First, we state two local existence theorems and under suitable conditions, we prove that any weak solutions with negative initial energy will blow up in finite time. Next, we give a sufficient condition to guarantee the global existence and exponential decay of weak solutions. Finally, we present numerical resultsComment: 2

Criteria and Indicators to Define Priority Areas for Biodiversity Conservation in Vietnam

Balancing biodiversity conservation with land use for agricultural production is a major societal challenge. Conservation activities must be prioritized since funds and resources for conservation are insufficient in the context of current threats, and conservation competes with other societal priorities. In order to contribute to conservation priority-setting literature, we applied an environmental model, Pressure–State–Response (PSR), to develop a set of criteria for identifying priority areas for biodiversity conservation in Vietnam. Our empirical data have been compiled from 185 respondents and categorized into three groups: Governmental Administration and Organizations, Universities and Research Institutions, and Protected Areas. The Analytic Hierarchy Process (AHP) theory was used to identify the weight of all criteria. Our results show that the priority levels for biodiversity conservation identified by these three factors are 41% for “Pressure”, 26% for “State”, and 33% for “Response”. Based on these three factors, seven criteria and seventeen indicators were developed to determine priority areas for biodiversity conservation. Besides, our study also reveals that the groups of Governmental Administration and organizations and Protected Areas put a focus on the “Pressure” factor, while the group of Universities and Research Institutions emphasized the importance of the “Response” factor in the evaluation process. We suggest that these criteria and indicators be used to identify priority areas for biodiversity conservation in Vietnam

Corona based air-flow using parallel discharge electrodes

A novel air-flow generator based on the effect of ion wind has been developed by the simultaneous generation of both positive and negative ions using two electrodes of opposite polarity placed in parallel. Unlike the conventional unipolar-generators, this bipolar configuration creates an ion wind, which moves away from both electrodes and yields a very low net charge on the device. The electro-hydrodynamic behavior of air-flow has been experimentally and numerically studied. The velocity of ion wind reaches values up to 1.25 m/s using low discharge current 5 mu-A with the kinetic conversion efficiency of 0.65% and the released net charge of �30 fA, 8 orders of magnitude smaller compared with the discharge current. Due to easy scalability and low net charge, the present configuration is beneficial to applications with space constraints and/or where neutralized discharge process is required, such as inertial fluidic units, circulatory flow heat transfer, electrospun polymer nanofiber to overcome the intrinsically instability of the process, or the formation of low charged aerosol

A study of ion wind generator using parallel arranged electrode configuration for centrifugal flow mixer

Ion wind is recently applied in various research areas such as the biomedical engineering, microfluidic mixing and particle manipulation. In this work, a bipolar ion wind generator configured by parallel arranged electrodes is used for centrifugal mixing applications. With the proposed configuration, negative and positive ion winds are simultaneously generated, mixed and then neutralized by each other while travelling toward liquid surface. The efficiency of the device was investigated both computationally and experimentally. The mixing of liquid occurred in different ways when the system is activated by either direct or alternating currents. Furthermore, the mixing is dependent on the dimension of electrode tip

A closed device to generate vortex flow using PZT

This paper reports for the first time a millimeter scale fully packaged device which generates a vortex flow of high velocity. The flow which is simply actuated by a PZT diaphragm circulates with a higher velocity after each actuating circle to form a vortex in a desired chamber. The design of such device is firstly conducted by a numerical analysis using OpenFOAM. Several numerical results are considered as the base of our experiment where a flow vortex is observed by a high speed camera. The present device is potential in various applications related to the inertial sensing, fluidic amplifier and micro/nano particle trapping and mixing