PROPERTIES OF UV-CURED POLYURETHANE ACRYLATES: EFFECT OF POLYOL TYPE AND MOLECULAR WEIGHT

Several families of UV-cured polyurethane acrylates were synthesized and the effects of polyol type and molecular weight on their physical properties were investigated. Increasing polyol molecular weight led to a lower polyol glass transition temperature, a smaller amount of a separate urethane acrylate phase, and a larger chain length between crosslinks. The first two effects were reflected in lower modulus and strength at room temperature while the larger chain length between crosslinks led to higher elongation at break (room temperature) and lower modulus at high temperatures. The use of different polyols (polycarbonate, polytetramethylene oxide, polypropylene oxide, and polycaprolactone) primarily affected the room temperature modulus due to differences in the position and breadth of the polyol glass transition. The properties of materials based on isocyanatoethyl methacrylate (IEM) and toluene diisocyanate-2-hydroxyethyl melhacrylate (TDI-HEMA) were also compared.     

APPLICATION OF GELATIN FOR ENCAPSULATING ASPIRIN INTO ETHYL CELLULOSE MICROCAPSULE IN AN O/W EMULSION

The application of gelatin protective colloid for microencapsulating aspirin in ethylcellulose was demonstrated using an oil-in-water emulsification/solvent evaporation technique. The gelatin concentration, alcohol co-solvent amount, and ethylcellulose viscosity were investigated by analyzing the recovered weight, particle size distribution, drug loading efficiency, aspirin release rate, surface characteristics, and release kinetics. Results showed that recovery increased with greater concentrations of gelatin (up to 1%). Adding co-solvent (ethanol) also changed the microcapsule particle size distribution. Higher recovery and release rates were obtained when the ethanol content in polymer solvent was at 25% and the viscosity of ethylcellulose was low (45cps). The release rate followed Higuchi matrix release kinetics, suggesting a monolithic system with aspirin uniformly distributed over the microcapsule.     

USING GELATIN-BASED ANTIMICROBIAL EDIBLE COATING TO PROLONG SHELF-LIFE OF TILAPIA FILLETS

Skinless tilapia (Dreochromis niloticus x D. aureus) fillets were covered with a gelatin coating containing benzoic acid as an antimicrobial agent. Benzoic acid content of fish fillets was used to estimate the amount of gelatin coated on fillet surface, and it was found that the gelatin contents were between 16.3 mg and 17.3 mg per g of fillets. Aerobic and anaerobic microbial loads, volatile basic nitrogen (VBN) contents, and sensory evaluation were used as indicators to survey the feasibility of an antimicrobial gelatin coating to prolong the shelf‐life of tilapia fillets under refrigeration. After 7 days of storage under refrigeration, tilapia fillets coated with gelatin containing benzoic acid had acceptable VBN contents, increased moderately in microbial loads, and showed no significant sensory difference (P < 0.05) from fresh fillets. The results indicate that an antimicrobial gelatin coating is suitable for preservation of tilapia fillets.     

Analysis and optimal control of linear time-varying systems via general orthogonal polynomials

The operational matrix consisting of the product of two time functions, and the operational matrices for forward or backward integration consisting of general orthogonal polynomials are derived, respectively, for the analysis and optimal control of linear time-varying systems with a quadratic performance measure. The present results include results obtained via Chebyshev, Legendre, Laguerre, Jacobi, Hermite and ultraspherical polynomials as special cases.     

Solutions of integral equations via Taylor series

The Taylor operational matrix of integration and the Taylor product operational matrix are introduced. These two operational matrices are applied to approximation of solutions of Fredholm and Volterra integral equations. The proposed method reduces solution of integral equations to the successive solution of a set of linear algebraic equations in matrix form. Owing to the simplicity of the operational matrix of integration, and the product operational matrix of the Taylor series, the algorithms derived possess considerable computational advantages over the orthogonal-polynomial approximation, provided that both input and output are analytic functions of t.     

Analysis of linear time-varying systems and bilinear systems via shifted Chebyshev polynomials of the second kind

Linear time-varying systems and bilinear systems are analysed via shifted Chebyshev polynomials of the second kind. Using the operational matrix for integration and the product operational matrix, the dynamical equation of a linear time-varying system (or bilinear system) is reduced to a set of simultaneous linear algebraic equations. The coefficient vectors of shifted Chebyshev polynomials of the second kind can be determined by using the least-squares method. Illustrative examples show that shifted Chebyshev polynomials of the second kind having a finite number of terms are more accurate than either the Legendre or Laguerre methods.     

Taylor series analysis and identification of scaled systems

The Taylor series is introduced to analyse and approximate the solution of a class of scaled systems. Using the operational matrix of integration, together with the derived scaled operational matrix, the dynamical equation of a scaled system is reduced to a set of simultaneous linear algebraic equations. The coefficient vectors of the Taylor series expansion can be determined recursively by the derived algorithm. The parameter identification problems of scaled systems are also investigated. Owing to the simplicity of the operational matrix of integration and the scaled operational matrix, the Taylor series presents considerable computational advantages when compared with the other possible polynomial series, provided that both the input and output signals are analytic functions of t.     

Optimal control of linear time-delay systems via general orthogonal polynomials

A Padé approximation is introduced to transform the delay differential equation into an ordinary equation. The optimal control of a linear time delay system with quadratic performance index is then derived via general orthogonal polynomials. The adjoint equation is also extracted using a maximum principle. The state and adjoint equations can be solved by using the general orthogonal polynomials and the difficulty encountered when using a two-point boundary condition is circumvented. Examples are given to demonstrate the usefulness of the proposed method.     

Solution of discrete scaled systems via general discrete orthogonal polynomials

General discrete orthogonal polynomials are introduced to analyse and approximate the solution of a class of discrete scaled systems. Using the general discrete shift transformation matrix, together with the general discrete scale matrix, the discrete scaled system can be reduced to a set of simultaneous linear algebraic equations. The coefficient vectors of general discrete orthogonal polynomials can be determined simply by the derived algorithm. Examples are included to show the applicability of the general discrete orthogonal polynomial approximations.     

Application of general discrete orthogonal polynomials to optimal-control systems

The shift-transformation matrix of general discrete orthogonal polynomials is introduced. General discrete orthogonal polynomials are adopted to obtain the modified discrete Euler-Lagrange equations. Then general discrete orthogonal polynomials are applied to simplify the discrete Euler-Lagrange equations into a set of linear algebraic ones for the approximation of state and control variables of digital systems. An example is included to demonstrate the simplicity and applicability of the method. Also, a comparison of the results obtained via several classical discrete orthogonal polynomials for the same problem is given.