Recovery of second-order optical nonlinearity in annealedproton-exchanged LiNbOx

The second-order nonlinear coefficients measured in proton-exchanged LiNbO₃ as a function of annealing time are discussed. Measurements of reflected second-harmonic power indicate that the second-order nonlinear coefficient d₃₃ is reduced to 60% of the bulk value as a result of proton exchange in pure benzoic acid. It is also shown that annealing restores the d-coefficients to almost the original value of the virgin crystal. For example, recovery to ~90% of the bulk value was obtained for a sample with a 0.3-μm-bulk proton-exchanged layer, annealed for 10 h at 350°C     

Using directed hypergraphs to verify rule-based expert systems

Rule-based representation techniques have become popular for storage and manipulation of domain knowledge in expert systems. It is important that systems using such a representation are verified for accuracy before implementation. In recent years, graphical techniques have been found to provide a good framework for the detection of errors that may appear in a rule base. The authors present a graphical representation scheme that: 1) captures complex dependencies across clauses in a rule base in a compact yet intuitively clear manner and 2) is easily automated to detect structural errors in a rigorous fashion. Their technique uses a directed hypergraph to accurately detect the different types of structural errors that appear in a rule base. The technique allows rules to be represented in a manner that clearly identifies complex dependencies across compound clauses. Subsequently, the verification procedure can detect errors in an accurate fashion by using simple operations on the adjacency matrix of the directed hypergraph. The technique is shown to have a computational complexity that is comparable to that of other graphical techniques. The graphical representation coupled with the associated matrix operations illustrate how directed hypergraphs are a very appropriate representation technique for the verification task     

Adhesive and thermal characteristics of maleimide-functional novolac resins

A novel, addition-curable maleimide-functional novolac phenolic resin was evaluated for adhesive properties such as lap shear strength and T-peel strength using aluminium adherends, when thermally self-cured and cocured with epoxy resins. The adhesive properties of the self-cured resin, although inferior at ambient temperature, improved at high temperature and were found to depend on the cure conditions. When cocured with epoxy resin, the adhesive properties improved significantly and showed a strong dependence on the nature of the epoxy resin used, on the stoichiometry of the reactants, on the concentration of imide groups in the phenolic resin, and on the extent of polymerization of the maleimide groups. Optimum adhesive properties were obtained for novolac resins with a moderate concentration of maleimide groups, taken on a 1 : 1 hydroxyl–epoxy stoichiometry with a novolac epoxy resin. In comparison to the conventional novolac, the imide–novolac contributed to improved adhesion and better adhesive property retention at higher temperature when cured with the novolac–epoxy resin. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 695–705, 1999     

ANALYSIS OF HEAT AND MASS TRANSFER DURING DRYING OF PAPER/BOARD

A mathematical model has been successfully developed to study the heat and mass transfer process during paper drying. This model takes into account the consective transfer of vapor and liquid apart from the known transport mechanisms of capillary flow of liquid, diffusion, vaporization-condensation, and heat conduction. The partial differential equations describing temperature, saturation and pressure change within the web during drying with associated boimdary conditions and initial conditions were solved using finite difference method. The model predictions show that during the drying process the web can be conveniently divided into three different zones, namely dry zone, wet zone and an intermediate zone. The movement of liquid and vapor in opposite directions in the intermediate zone is similar to the action of a heat pipe. Also, as drying proceeds the location of the intermediate zone and hence the heat pipe advances progressively through the thickness of the web.     

Analysis of the permeability tensor and the correlation length of heterogeneities in paper using X-ray microtomography

A technique to determine the permeability from X-ray microtomographic images was developed and applied to paper structures. The images are thresholded and a skeleton of the pore space is obtained from the images. The skeleton is represented by means of a network of resistances. The total resistance of the network along the principal directions is now determined both in the in-plane (X, Y) as well as through the plane (Z) directions. The network resistance for structures at each section is determined. From this data, a correlation length for the network resistance is obtained. Correlation length data are used for determining the effect of heterogeneities on transport properties of paper structures. From this analysis, it is possible to analyze and simulate the moisture transport processes such as wicking and drying in paper, reproducing smaller-scale variations. Permeabilities in the thickness direction were calculated from the X-ray microtomographic reconstructions of the pore space. A set of paper samples prepared with different amounts of fines but with similar porosity and density was analyzed. The permeabilities of the X-ray reconstructions were reduced significantly in papers with fines in agreement with macroscopic measurements of flow through the same sheets. This demonstrated the higher tortuosities of the papers and their increased flow resistance, although the macroscopic porosity and density were relatively unchanged. The same analysis was repeated for a set of pilot machine sample papers to demonstrate variations in permeability predicted by X-ray microtomographic analyses in agreement with expected increases due to refining of pulps.     

Construction of Barrettes for High‐Rise Foundations

Barrettes are huge concrete piers, basically rectangular. The cross‐sectional areas of barrettes have often been more than 75 sq ft (7?m2) and they have been used for depths exceeding 260 ft (80?m) facilitating heavy vertical loads of the order of 3,000 tons∕barrette to be transmitted to the bearing layer. Barrettes are used also as Moscovite wall for deep basements of high‐rise buildings to resist both vertical and lateral loads. The fact that a single barrette can replace a group of conventional piles results in a more compact, economical, and reliable foundation system. The installation technique of barrettes follows closely the method of constructing diaphragm wall using bentonite slurry, reinforcing cage, and tremie concreting with careful quality control. Although there are certain reservations for using barrettes instead of conventional piles and diaphragm walls, the inherent advantages and the confidence gained by experience have been responsible for their increased usage, especially as heavy load‐bearing elements for high‐rise foundations and basements.     

Multiobjective Optimal Fuzzy Logic Control System for Response Control of Wind-Excited Tall Buildings

Performance of the structure includes both the safety as well as comfort level for the user. The safety of the structure mainly depends on the displacement response, while the comfort level of occupants depends on the acceleration response. In this paper, an approach for multiobjective optimal design of a fuzzy logic controller (FLC)-driven active tuned mass damper (ATMD) has been proposed. The evaluation criteria for both the acceleration and displacement responses have been used as the two objective functions for this multiobjective optimization problem. As a multiobjective optimization approach provides a set of Pareto-optimal solutions, the user is allowed to select an appropriate design for the specific performance requirement. The effectiveness and performance of the proposed FLC-driven ATMD has been investigated for the third-generation benchmark problem for the response control of wind-excited tall buildings. A multiobjective optimization version of the genetic algorithm has been used for obtaining the FLC and ATMD design parameters, as this approach is more effective in handling a discontinuous and nonconvex domain. Performance of the proposed control system has been found to be better than the sample controller given in the benchmark problem. The proposed controller is less sensitive than the sample controller for the variation in the stiffness of the structure.     

Rheological properties of black gram (Phaseolus mungo) batter: characterisation of flour from native and modified rice and their effect on batter viscosity

Rheological properties of black gram batter as a function of soaking time, and effect of flour from native and thermally modified rice on black gram batter have been studied. Greater increase in hydration capacity of black gram dhal was observed during 5–15 min of soaking, a gradual increase up to 90 min and a marginal increase beyond this period. Apparent viscosity of batter showed 100% increase up to 90 min and less than 20% increase beyond 120 min, and shear‐thinning nature of batter indicated that they were pseudo‐plastic in nature. Yield stress and consistency index showed greater changes after 90 min, while flow behaviour index did not show significant change beyond 90 min of soaking. Compared with the addition of native rice flour, incorporation of flaked rice flour and expanded rice flour into black gram batter significantly increased the cold paste viscosity of the batter, probably because of their greater water‐holding capacity, compared with that from native rice. Differences in physicochemical characteristics and pasting behaviour of these flour slurries, as studied by Rapid Visco Analyser, corroborated these results by the typical profile of pregelatinised products for flaked rice and expanded rice in comparison to native rice.