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  • Thesis


  • Authors: Lưu, Trường Văn.;  Co-Author: 2009 (The major objective of this research is to describe how the BSC and trength-Weakness-Opportunity -Thread (SWOT) matrix can be used to formulate the business strategies and to measure the strategic performance of construction. Angiang Construction Enterprise (ACE) is selected as a case study to measure the strategic performance. An applicable simulation model of a construction enterprise was built using system dynamics methodology. The DBSC model was calibrated to a construction enterprise to measure the strategic performance and to formulate and evaluate practical policies to improve its performance. In order to considerably improve performance, some integrated policies combining the separate policies having the most effects were evaluated. This research reveals that the DBSC model should be considered as a promising tool for the construction enterprise to experiment with the effects of its strategies and policies prior to implementing them in the real project. This also proves that the integration between SD and BSC has enormous potentials in the performance measurement of construction organizations. The findings imply that the low training frequency of human resource and high proportion of direct costs and administrative expenses to turnover are generally “Achilles’ heel” of medium-sized construction enterprises in Vietnam and very likely in other developing countries. The findings from this case study provide valuable lessons for practitioners in the application of new management frameworks (i.e. BSC and SWOT) in managing their strategic performance in other developing countries and region. The integration of BSC approach and SWOT analysis can help medium-sized construction enterprises in developing countries identify short-term objectives and longterm strategies, establish the performance measurement.)

  • Thesis


  • Authors: Huỳnh, Kỳ Phương Hạ.;  Co-Author: 2008 (The Supercritical Fluid Extraction (SCFE) process is a powerful technique to develop for separating products with high added value. In this study, Supercritical fluid Carbon Dioxide (SC CO2) was used in the extraction of essential oil from two different parts of the lemongrass plant, the leaves and the stems. The batch extraction process was carried out in a stand alone compact unit of SCFE system. The lemongrass was loaded into the 500m1 extractor with an up flow rate of 0.5 m3 per hour of CO2. The extraction temperature was varied from 35°C to 50°C while the extraction pressure applied was from 90 to 110 atmospheres and the length of material was varied from 4 mm to 8 mm. The extraction time was set at 3.0 hours. This study intends to compare the composition of essential oil extracted from lemongrass leaves and lemongrass stems using SC CO2 and Steam Distillation. The extracts from both methods were analyzed by GC-MS and the variations of the compositions were reported. Furthermore, the study attempts to formulate statistical experimental design using Design-Expert Software (version 7.0.1). The effects of temperature, pressure and length of material were analyzed employing the Response Surface Methodology (RSM) technique. The models of extraction for both leaves and stems were established with the extraction yield and citral content of the essential oil at the established responses. The optimum yields of essential oil from leaf and stem at the given extraction conditions were also determined.)

  • Thesis


  • Authors: Dương, Như Hùng.;  Co-Author: 2008 (The studies of hedge fund performance are hindered by the lack of quality returns data and the complicated nature of hedge fund returns. This study contributes to the literature in three ways. First, I reinvestigate the performance of hedge funds from different aspects. Second, I develop a new framework to evaluate fund of hedge funds managers’ skills. Finally, I exam the performance persistence of funds of hedge funds by using various performance measures. In the first study, I find that the annual survivorship and backfilled biases for funds of hedge funds are 0.66% and 0.21%, respectively, during the period 1994-2004. I confirm that hedge funds’ monthly returns tend to have low standard deviations, negative skewness and high kurtosis. Hedge funds often underperform the equity market in terms of absolute returns, but outperform the equity market in terms of traditional performance measures like the Jensen alpha, Treynor, and Sharpe ratios. However, when accounting for downside risks, the Omega and Sortino ratios both indicate that the performance of hedge funds is not as superior as the traditional performance measures suggest. I also find that hedge funds usually have low exposures to risk factors identified by Fama and French (1993), and Fung and Hsieh (2004). The subperiod analysis indicates that hedge funds tend to underperform the equity market during a bullish stock market, but outperform the equity market during a bearish stock market. I also find some evidence of stale price when returns are measured monthly, quarterly or semiannually. However, it appears that the stale price does not affect the performance rankings. In the second study, I am able to replicate funds of funds returns by using hedge fund strategy indices. I find that fund of hedge funds managers have neither the ability of picking winning hedge funds on the net basis nor the ability of predicting winning hedge fund strategies. In the third study, I find strong evidence of performance persistence when returns are measured monthly, quarterly or semiannually. The evidence of persistence is substantially weakened when returns are measured annually. The quintile analysis indicates that the winners based on the past alpha tend to have the highest return while the losers based on the past Sortino ratio have the lowest return.)

  • Thesis


  • Authors: Hà, Tùng Anh.;  Co-Author: 2007 (Due to degradation during aging, most elastomers lose their particularly high extensibility as well as their ability to completely recover after deformation. In this study, the effect of thermo-oxidative aging on mechanical behaviors was investigated for neoprene (polychloroprene rubber). The results from tensile tests have shown that thermal aging resulted in an increase in crosslink density, tensile stress and modulus, as well as a decrease in ultimate elongation. The tensile stress-strain relationship at large strain obeys the eight-chains model. However, Mooney-Rivlin equation shows the best fit for the experimental data in the range of moderate strain and its parameters dependence on aging could be predicted using Arrhenius-type kinetic relation. With prolonged aging or/and at higher aging temperatures, the change in properties is more pronounced at the surface than in the bulk of the sample due to the effect of heterogeneous oxidation. Tearing energies measured at different tear rates and temperatures can be superimposed on a single master curve in accordance with the WLF (Williams-Landel-Ferry) rate-temperature relation, indicating that tearing in elastomers is governed by a viscoelastic process. During aging, the decrease in tearing energy can be associated with a decrease in the strain energy density in the crack tip region rather than with changes in the crack tip diameter. On the other hand, the fracture energy for cutting process is almost unchanged during aging due to a scale effect at the cut tip. The results from DMTA (Dynamic Mechanical Thermal Analysis) indicate an increase in Tg and a decrease in the damping value of neoprene after aging. In contrast, aging leads to a significant increase in the energy dissipation at high strain. This discrepancy can be attributed to the difference between the mechanisms of hysteresis of elastomers at low and high strain. A new theoretical model has been developed for predicting the hysteresis loss of elastomers under different aging and loading conditions. Finally, it has been found that the rate of thermo-oxidative aging in neoprene provides similar values of activation energy when measured either by the oxidative induction time (OIT), by the tearing energy or by the tensile ultimate elongation. For polychloroprene, the OIT corresponds to the moment when the elastomer reaches an optimized balance between strength enhancement from additional crosslink formation and the capability of the crosslinked network to dissipate deformation energy. The results show that thermal induction time tests at high temperatures can be used as a useful technique to predict the fracture performance of elastomers at lower temperatures.)

  • Thesis


  • Authors: Bùi, Trọng Vinh.;  Co-Author: 2009 (The main objective of this study is to investigate the erosion mechanism of cohesive bank in river and around river mouth to evaluate erosion resistance of cohesive soil and to establish the procedure for stabilizing and utilizing the coastal regions effectively. To achieve the aim, three research objectives have been carried out as following (1) Assess the effects of development, preservation and disaster prevention on coastal erosion in some Asian countries. (2) Establish procedure for evaluating critical shear stress of cohesive soils for erosion. (3) Study on erosion mechanism of cohesive bed, bank and shore and propose procedure for examining erosion resistance.)

  • Thesis


  • Authors: Hà, Hoàng Kha.;  Co-Author: 2008 (Digital filter banks have found in a wide variety of applications in data compression, digital communications, and adaptive signal processing. The common objectives of the filter bank design consist of frequency selectivity of the individual filters and perfect reconstruction of the filter banks. The design problems of filter banks are intrinsically challenging because their natural formulations are nonconvex constrained optimization problems. Therefore, there is a strong motivation to cast the design problems into convex optimization problems whose globally optimal solutions can be efficiently obtained. The main contributions of this dissertation are to exploit the convex optimization algorithms to design several classes of the filter banks. First, the two-channel orthogonal symmetric complex-valued filter banks are investigated. A key contribution is to derive the necessary and sufficient condition for the existence of complex-valued symmetric spectral factors. Moreover, this condition can be expressed as linear matrix inequalities (LMIs), and hence semi-definite programming (SDP) is applicable. Secondly, for two-channel symmetric real-valued filter banks, a more general and efficient method for designing the optimal triplet halfband filter banks with regularity is developed. By exploiting the LMI characterization of nonnegative cosine polynomials, the semi-infinite constraints can be efficiently handled. Consequently, the filter bank design is cast as an SDP problem. Furthermore, it is demonstrated that the resulting filter banks are applied to image coding with improved performance. It is not straightforward to extend the proposed design methods for two-channel filter banks to M-channel filter banks. However, it is investigated that the design problem of M-channel cosine-modulated filter banks is a nonconvex optimization problem with the low degree of nonconvexity. Therefore, the efficient semidefinite relaxation technique is proposed to design optimal prototype filters. Additionally, a cheap iterative algorithm is developed to further improve the performance of the filter banks. Finally, the application of filter banks to multicarrier systems is considered. The condition on the transmit filter bank and channel for the existence of zero-forcing filter bank equalizers is obtained. A closed-form expression of the optimal equalizer is then derived. The proposed filter bank transceivers are shown to outperform the orthogonal frequency-division multiplexing (OFDM) systems.)