Nonlinear buckling and post-buckling analysis of eccentrically stiffened functionally graded circular cylindrical shells under external pressure

The nonlinear buckling and post-buckling behavior of functionally graded stiffened thin circular cylindrical shells subjected to external pressure are investigated by the analytical approach in this paper. The shells are reinforced by eccentrically rings and stringers attached to the inside and material properties of shell and stiffeners are assumed to be continuously graded in the thickness direction. Fundamental relations, equilibrium equations are derived based on the smeared stiffeners technique and the classical shell theory with the geometrical nonlinearity in von Karman sense. Approximate three-terms solution of deflection is more correctly chosen and explicit expression to finding critical load and post-buckling pressure-deflection curves are given by using the Galerkin’s method. The numerical results show the effectiveness of stiffeners in enhancing the stability of shells
http://repository.vnu.edu.vn/handle/VNU_123/32875

Removal of As(V) from aqueous solutions by iron coated rice husk

A lignocellulosic material extracted from rice husk (Oryza sativa), Vietnam, was modified as a new adsorbent for the removal of As(V) ions from aqueous solution. Iron was coated onto this adsorbent by hydrolization of ferric nitrate while adding an alkaline solution drop wise into the batch type reactor. The adsorption of As(V) ions from aqueous solution on coated rice husk was then studied at varying pH, As(V) concentrations, contact times, ionic strength, and adsorbent amounts. The minimum contact time to reach equilibrium is about 6 h. The adsorption of As(V) anions on the coated rice husk was found to be highly pH dependent due to Coulomb interactions between As(V) species in solution and positively charged surface groups RH-FeOOH, as well as formation of chelate complexes with naturally occurring carboxyl and carbonyl functional groups in the ma-trix. As(V) adsorption on Fe(III)-coated rice husk (RH-FeOOH) from aqueous solution was studied in the pH range 2–10. The main effects of pH on adsorption are estimated by considering both the behavior of As(V) ions (hydrolysis and hydroxide precipitation) and the effect of pH on coordination. A strong effect of pH was demonstrated at pH 4.0 with a maximum percentage for removal of As(V) ions 94%. Although both Langmuir and Freundlich isotherms have been used to characterize the adsorption of As(V), the Langmuir modelfitted the equilibrium data better than Freundlich model and confirmed the surface homogeneity of adsorbent. The maximum adsorption capacity is determined as 2.5 mg/g of adsorbent at pH 4.0 for the Fe(III)-coated rice husk. It is concluded that initial As(V) concentration has an effect on the removal efficiency of RH-FeOOH. Higher adsorption of As(V) was observed at lower initial concentrations. RH-FeOOH as a low cost material is effective for the removal of As(V) ions and may become a valuable adsorbent to improve the ground water quality in Vietnam

http://repository.vnu.edu.vn/handle/VNU_123/32877

STABILITY AND ROBUST STABILITY OF LINEAR TIME-INVARIANT DELAY DIFFERENTIAL-ALGEBRAIC EQUATIONS

Necessary and sufficient conditions for exponential stability of linear time-invariant delay differential-algebraic equations are presented. The robustness of this property is studied when the equation is subjected to structured perturbations and a computable formula for the structured stability radius is derived. The results are illustrated by several example
http://repository.vnu.edu.vn/handle/VNU_123/32988

Design of photocontrolled biomolecules based on azobenzene derivatives

This review focuses on methods of designing photocontrolled proteins and nucleic acids. Data on prep-aration and modification of proteins and nucleic acids with azobenzene derivatives are summarized. Examples of using photoswitchable proteins, their substrates, inhibitors and ligands containing azobenzene, as well as azobenzene deriv-atives of nucleic acids, for design of nanomachines are considered. The bibliography includes 122 references

http://repository.vnu.edu.vn/handle/VNU_123/32990

Vectored DSL: Potential, Implementation Issues and Challenges

This paper investigates specific techniques suitable for Vectored DSL, their performance, complexity and practical implementation. More specifically, various Vectored DSL tech-niques for both upstream and downstream transmission are discussed, including the Tomlinson-Harashima Pre-coder (THP), Diagonalizing Pre-coder (DP), Zero-Forcing (ZF) canceller, and Decision-Feedback (DF) canceller. A thorough discussion on some of the practical implementation aspects of Vectored DSL is provided. In particular, various implementation challenges are discussed, including computational load, memory storage, line management, partial crosstalk cancellation, and the effect of imperfect channel knowledge. As well, the potential gains and challenges of combining Phantom DSL and Vectored DSL are also discussed. Illustrative examples are provided based on both measured data and channel models to compare the various Vectored DSL techniques and their practical implementation challenges.
http://repository.vnu.edu.vn/handle/VNU_123/32991

Treatment of tapioca starch wastewater by a novel combination of physical and biological processes

A pilot plant combining dissolved airflotation, anaerobic degradation in an expanded granular sludge bed (EGSB) reactor and aerobic post-treatment in a verticalflow constructed wetland has been used to treat tapioca starch wastewater for more than 2.25 years. It is demonstrated that organic matter (chemical oxygen demand by>98%), nitrogen (Kjeldahl-N by>90%) and cyanide (total cyanide by>99%) can be removed very efficiently under stable operating conditions. The removal efficiency for phosphorus is lower (total-P by 50%). The treatment concept, which includes several sustainable aspects, e.g. production of energy to be used on-site, low operation demands and minimal use of chemicals, could be interesting for small- and middle-sized tapioca processing plant

http://repository.vnu.edu.vn/handle/VNU_123/32994

Treatment of tapioca starch wastewater by a novel combination of physical and biological processes

A pilot plant combining dissolved airflotation, anaerobic degradation in an expanded granular sludge bed (EGSB) reactor and aerobic post-treatment in a verticalflow constructed wetland has been used to treat tapioca starch wastewater for more than 2.25 years. It is demonstrated that organic matter (chemical oxygen demand by>98%), nitrogen (Kjeldahl-N by>90%) and cyanide (total cyanide by>99%) can be removed very efficiently under stable operating conditions. The removal efficiency for phosphorus is lower (total-P by 50%). The treatment concept, which includes several sustainable aspects, e.g. production of energy to be used on-site, low operation demands and minimal use of chemicals, could be interesting for small- and middle-sized tapioca processing plants

http://repository.vnu.edu.vn/handle/VNU_123/32995