Date issued
Has File(s)


Current filters:

Search Results

Item hits:
  • 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: 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: Nguyen, Thi Thanh Phuong;  Co-Author: 2005 (Institutional accreditation is an excellent vehicle for facilitating change toward the improvement of quality in higher education. It is fulfilled by three phases: (a) a self-study, (b) a peer review, and (c) a decision by the accrediting agency. Self-study is at the heart of institutional accreditation; however, it is not always favored. Some participants consider it to be a waste of time and resources. Yet, self-study, if properly approached and packaged, can help ensure a high-quality future for the institution. This qualitative case study research explored the internal review (self-study) processes used by a Level VI public university, United States Sigma University (USSU) (a pseudonym), that successfully went through reaffirmation in 2004 under the Southern Association of Colleges and Schools - Commission on Colleges (SACS-COC) new Principles of Accreditation: Foundations for Quality Enhancement, which was approved in December 2001. Data were collected from reviewing online and other documents; a fieldwork trip to USSU where interviews, observations, documents, and archival materials were gathered; and follow-up correspondence that increased the validity, reliability, and utility of the research study. The data analysis strategy used in this research study was the constant comparative method and the theoretical framework was open systems theory. Because the Principles of Accreditation were new, this research study addressed two fundamental problems: (a) how to deal with this new reaffirmation approach and the associated need for change and (b) how to integrate other quality improvement mechanisms with the internal review processes. Results of the study indicate that sixteen critical elements contributed to the success of the internal review processes at USSU: 1. Adapting to the new Principles; 2. Selecting the right Accreditation Liaison; 3. Selecting the right Leadership Team; 4. Starting early and using timelines; 5. Training and preparing the participants and the university community; 6. Using unique strategies for developing the Compliance Certification and the Quality Enhancement Plan (QEP); 7. Having a well-written Compliance Certification and QEP; 8. Preparing well for the on-site review; 9. Having university leadership commitment, support, and belief in accreditation; 10. Communicating effectively; 11. Using technology effectively; 12. Leveraging available resources and matching the reaffirmation with the institutional circumstances; 13. Establishing an effective relationship and regular communication with the SACS-COC staff liaison; 14. Having competent reviewers; 15. Using internal review findings for improvement; and 16. Having a strong institutional effectiveness program. This study also indicates that the more reaffirmation requirements are integrated into institutional processes (e.g., strategic planning and budgeting), the better the institution will do in carrying out its internal review. Sixteen critical elements of the USSU internal review processes and insights gained from this case study are potentially useful to other SACS-COC universities. This research contributes to knowledge for improvement of educational practices. It also meets the SACS-COC universities’ needs for understanding effective ways of conducting internal reviews for quality improvement while simultaneously satisfying the SACS-COC new requirements for reaffirmation.)

  • Thesis

  • Authors: Lê, Văn Thăng.;  Advisor: Baptist, Robert.;  Co-Author: 2008 (This thesis is focussed on the chemical vapour deposition method to produce single wall carbon nanotubes.The purposes of this research are to understand exactly the role of the various chemical components presented in catalyst for the producing of SWNTs, to control process conditions, to develop synthesis techniques for SWNTs on patterned catalyst that allow the integration for electronic devices and to transfer process to industrial CVD instrument. Experimental investigations are resented which allow getting a comprehensive picture of the powder catalyst growth of carbon nanotubes film. The role of each element in catalyst and the optimal amount of them are illustrated. Based on the electron microscopy, Raman spectroscopy, X-Ray diffraction, X-Ray photoelectron spectroscopy and microbalance results, a new component, (FexAly)(Al2-yFe1-x)O4, is detected. Subsequent studies of the properties of the produced carbon nanotubes grown by CVD reveal significant features of the product. Based on those experimental results, a mechanism for the growth of carbon nanotubes on the powder catalyst is suggested. Furthermore, a purification method of as-grown SWCNT has been developed that provides for the removal of catalyst nanoparticles and impurity carbon. Complementary, by varying global growth parameters such as synthesis temperature, flow ratio of carbonaceous/hydrogen gas and growth time, this study attempts to control the process condition for the synthesis high yield of SWNTs. Furthermore, we present the results of the transfer of the synthesis process of SWNTs from the EASYTUBE system (small tubular CVD reactor) to industrial CENTURA tool (compatible wafer 200 mm) and the patterned growth of SWNTs for electrical devices.)

  • Luận văn, Luận án (Theses)

  • Authors: La, Thị Thái Hà;  Advisor: Nguyễn, Hữu Niếu.; Nguyễn, Đắc Thành.;  Co-Author: 2005 (- Tổng hợp các nhựa vinyleste :VESO, VEPB và VE-331 từ dầu đậu nành epoxy hóa (ESO), polybutadien lỏng epoxy hóa (EPB) và nhựa epoxy DER 331 theo thứ tự với axít metacrylic. - Xác định các thông số động học như nhiệt phản ứng , năng lượng hoạt hóa và bậc của phản ứng trùng hợp theo cơ chế gốc tự do của nhựa vinyleste đã tổng hợp là: VESO, VEPB và VE-331. - Khảo sát phản ứng đồng trùng hợp của từng loại nhựa vinyleste tổng hợp ở trên với styren. - Đánh giá các tính chất cơ học và nhiệt của tổ hợp giữa VE-331 với các hàm lượng VESO khác nhau sau đóng rắn. - Nghiên cứu tổ hợp vật liệu từ VE-331 với VESO để làm lớp bọc lót (primer) liên diện cho vật liệu compozit trên nền kim loại là thép.; - To synthesize the vinyl ester resins: VESO, VEPB and VE-331 from Epoxydized Soya Oil (ESO), Epoxydized liquid Polybutadiene (EPB) and Epoxy DER-331 respectively by using methacrylic acid. - To determine the kinetic parameters such as heat of reaction, activation energy and reaction orders of free radical polymerization of the vinyl ester resins synthesized: VESO, VEPB and VE-331. - To investigate the kinetics of copolymerization of each vinyl ester synthesized above with styrene (S). - To evaluate mechanical and thermal properties of cured combinations of VE-331 with different VESO contents. - To study the material mixture from VE-331 with VESO for using as a primer for composite material over steel surface.)