DICHLODIPHENYLTRICHLOETHANES (DDTS) RESIDUES IN TAM GIANG-CAU HAI AND LANG CO LAGOONS, VIETNAM

Joint Research on Environmental Science and Technology for the Eart

An Efficient Spectral Leakage Filtering for IEEE 802.11af in TV White Space

Orthogonal frequency division multiplexing (OFDM) has been widely adopted for modern wireless standards and become a key enabling technology for cognitive radios. However, one of its main drawbacks is significant spectral leakage due to the accumulation of multiple sinc-shaped subcarriers. In this paper, we present a novel pulse shaping scheme for efficient spectral leakage suppression in OFDM based physical layer of IEEE 802.11af standard. With conventional pulse shaping filters such as a raised-cosine filter, vestigial symmetry can be used to reduce spectral leakage very effectively. However, these pulse shaping filters require long guard interval, i.e., cyclic prefix in an OFDM system, to avoid inter-symbol interference (ISI), resulting in a loss of spectral efficiency. The proposed pulse shaping method based on asymmetric pulse shaping achieves better spectral leakage suppression and decreases ISI caused by filtering as compared to conventional pulse shaping filters

Double-Curvature Test of Reinforced Concrete Columns Using Shaking Table: A New Test Setup

This paper proposes a new test setup to study the double-curvature behavior of reinforced concrete (RC) columns using shaking table. In this setup, the seismic action is simulated by the horizontal movement of a long-heavy rigid mass sitting on the top of only one test specimen. The double-curvature mechanism of specimen is affected by the movement of the concrete mass on a test rig consisting four steel hollow-section columns fully anchored to the shaking table. Application of axial load on the specimen is made possible through a pre-stressing equipment connecting to its top and bottom bases. The current setup offers two improvements over the previous ones. First, it makes available greater ranges of test data for conducting bigger sizes of the specimens. Second, it allows to directly measure the variation of axial force in the test specimens while the test implementation can be fast and easy with a high safety margin even until the complete collapse of the test units. The current test setup has been successfully applied on two ½ scaled V-shaped columns. It has been shown that the column specimen with a low axial load level of 0.05f’cAg, where f’c is the concrete strength and Ag is the cross-sectional area of the specimen, can well survive at a ground peak acceleration up to 5.5 (m/s2) with a drift ratio of approximately 2.91%. Meanwhile, the column subjected to moderate axial load level of 0.15f’cAg can survive at a higher ground peak acceleration of 8.0 (m/s2) with a drift ratio of 3.75%. Furthermore, it is experimentally evidenced that the V-shaped cross-section does not deform in-plane under seismic action. The angle between two planes corresponding to the column web and flange are up to 0.03 (rad). This finding is significant since it contradicts the plane strain assumption available in the current design practice

Optimization Parameters of Milling Process of Mould Material for Decreasing Machining Power and Surface Roughness Criteria

Improving milling performances is an effective solution to decrease the costs required. This paper addressed a multi-response optimization to simultaneously decrease the machining power consumed Pm, arithmetical roughness Ra, and ten-spot roughness Rz. The Grey-Response Surface Method-Multi Island Genetic Algorithm (GRMA) consisting of grey relational analysis (GRA), response surface method (RSM), and multi-island genetic algorithm (MA) was proposed to predict the optimal parameters and yield optimum milling performances. The experimental trials were conducted with the support of a CNC milling center. The influences of spindle speed (S), depth of cut (ap), feed rate (fz), and tip radius (r) were explored using GRA. The nonlinear relationship between machining parameters and grey grade (GG) model was developed using RSM. Finally, two optimization techniques, including desirability approach (DA) and MA were performed to observe the optimal values. The results indicated that the machining power was greatly affected by processing factors and the radius has a significant impact on the roughness criteria. The measured reductions using optimal parameters of Pm, Ra, and Rz are approximately 77.05%, 50.00%, and 58.02%, respectively, as compared to initial settings. The GRMA can be considered as an effective approach to generate reliable values of processing conditions and technological performances in the milling process

ADSORPTIVE CATHODIC STRIPPING VOLTAMMETRIC DETERMINATION OF SEVERAL HEAVY METALS (Ni, Co, Cu, Pb) IN NATURAL WATERS

Joint Research on Environmental Science and Technology for the Eart