Controller Synthesis for Positive Linear Systems With Bounded Controls

This brief solves some synthesis problems for a class of linear systems for which the state takes nonnegative values whenever the initial conditions are nonnegative. In particular, the synthesis of state-feedback controllers is solved in terms of linear programming problem, including the requirement of positiveness of the controller and its extension to uncertain plants. In addition, the synthesis problem with nonsymmetrical bounds on the stabilizing control is treated     

A Concept in Bactericidal Materials: The Entrapment of Chlorhexidine within Silver

A new concept in bactericidal agents is described: the entrapment of an organic biocidal agent within a bactericidal metal, which leads to synergism between the two components. Specifically this concept is demonstrated for the entrapment of chlorhexidine digluconate (CHD) within an aggregated silver matrix, a metal known for its own biocidal qualities, forming the CHD@silver composite. The bactericidal efficacy against E. coli is evaluated and compared with the separate components. While the bactericidal efficacy of the individual ingredients (CHD and metallic silver) is very low, CHD@silver exhibits a markedly enhanced efficacy. This enhanced bactericidal effect is partially attributed to the simultaneous release and presence of the active biocidal ingredients CHD and Ag⁺ in the solution. Detailed composite characterization is provided.     

Thermoelastic and infrared-thermography methods for surface strains in cracked orthotropic composite materials

Two quantitative thermoelastic strain analysis (TSA) experimental methods are proposed to determine the surface strain fields in mechanically loaded orthotropic materials using the spatial distribution of temperature gradient measured from the surface. Cyclic loadings are applied to orthotropic composite specimens to achieve adiabatic conditions. The small change in surface temperatures that resulted from the change in the elastic strain energy is measured using a high sensitivity infrared (IR) camera that is synchronized with the applied loading. The first method is applied for layered orthotropic composites with a coat layer made of isotropic or in-plane transversely isotropic material. In this case, one material parameter (pre-calibrated from the surface) is required to map the strain invariant to the temperature gradients. The proposed method can be used together with Lekhnitskii’s elasticity solution to quantify the full strain field and determine mixed-mode stress intensity factors (SIFs) for crack tips in composite plates subjected to off-axis loading. The second method is formulated for orthotropic layers without a coat and it requires thermo-mechanical calibrations for two material parameters aligned with the material axes. The virtual crack closure technique (VCCT), Lekhnitskii’s and Savin’s elasticity solutions, and finite element (FE) analyses are used for demonstrations and validations of the second experimental method. The SIFs from the TSA methods are very sensitive to the uncertainty in the location of the crack tip and the unknown inelastic or damage zone size around the crack tip. The two experimental methods are effective in generating the strain fields around notched and other FRP composites.     

Controlling surfaces and interfaces of semiconductors using organic molecules

Control over semiconductor surface energetics can be achieved using different chemisorbed organic molecules with diverse electronic properties. We find evidence of such control over CdTe upon adsorption of dicarboxylic acid derivatives with different substituted phenyl rings. FT-IR measurements show that the dicarboxylic acid derivatives bind as carboxylates to form approximately one monolayer. Such chemisorption modifies both the band bending and the electron affinity (up to 500 and 700 mV, respectively), as measured by contact potential difference WPM Changes in band bending result from a coupling between molecular orbitals and surface states close to the valence band and depend on the withdrawing character of the phenyl substituent. A model is presented to interpret and explain the data.     

Kinetics of hydrogen evolution on Ni-Al alloy electrodes

The kinetics of the hydrogen evolution reaction have been studied on Ni-Al alloy electrodes. The electrodes after leaching aluminium in alkaline solution, are very active despite their large Tafel slopes. The SEM studies show a formation of deep pores on the electrode surface. The kinetics were studied using an ac impedance technique. It was found that the impedance plots may be explained assuming a fractal model. The logarithm of the charge transfer resistance is a linear function of the overpotential. Using a nonlinear least square approximation it was found that the reaction proceeds through the Volmer-Heyrovsky mechanism and the kinetic parameters were estimated.     

DYNAMIC ANALYSIS OF CONTINUOUS WELL-MIXED FLUIDIZED/SPOUTED BED DRYERS

A diffusion-based mathematical model is presented for the prediction of the dynamics of drying in continuous well-mixed fluidized/spouted beds. Numerical techniques are used to solve the model equations. The outlet solids moisture content, the outlet air humidity and solids temperature are predicted as a function of time for the falling rate drying period. The model is helpful in describing the drying process during the startup periods and in studying open loop behavior of drying process. The model is also useful in designing control system for fluidized/spouted bed dryers.     

Plasticity-based model for circular concrete columns confined with fibre-composite sheets

This paper presents analytical stress–strain curves that describe the axial and the lateral behaviour of externally and internally confined concrete in circular columns. The solution to the problem of an elastic cylinder confined by internal and external elastic confining materials is derived. Following the elastic solution, the analytical curves are derived based on the full elastoplastic behaviour of the confined concrete column and by using the well-known Drucker–Prager failure criterion to represent concrete behaviour. Application of the Drucker–Prager model does not require an iterative procedure in order to solve the problem and thus an explicit solution is obtained. The proposed model can be applied to describe the behavior of concrete confined by transverse steel reinforcement, by fibre-reinforced polymer (FRP) composites, or by both transverse steel reinforcement and FRP composites. It is shown that the analytical results are in good agreement with both experimental and the finite element method results.     

Temperature influence on the excess interaction parameter of styrene-methyl methacrylate copolymer

Intrinsic viscosity data for polystyrene, poly(methyl methacrylate) and styrene-methyl methacrylate copolymer of azeotropic composition have been used to evaluate the excess interaction parameters at different temperatures in γ-butyrolactone and dimethylformamide. It is found that these values are positive and show a negligible increase with increase in temperature, indicating therefore that the hetero-contact interactions are not influenced by temperature, contrary to the results obtained by Dondos and Benoit for the same copolymer system in p-xylene and iso-amyl acetate.