Non-hookean stress-strain response and changes in crystallite orientation of carbon fibres

The non-hookean stress-strain response of carbon fibres was investigated in relation to changes in crystallite orientation with tensile stress. Various one-dimensional array models and a mosaic model were examined. Amongst these models, only the mosaic model in which the stress of the crystallites can be transmitted in both the transverse and the axial directions showed any quantitative agreement with the measured increases in the tensile modulus and the crystallite orientation with tensile stress. This suggests that deformation of the crystallites is constrained with increasing tensile stress. It was also found that the ratio of the tensile stress of the fibre to that of the crystallites is close to the crystallite volume fraction rather than the ratio of the fibre density to the crystallite density.     

The effect of the framework structure on the chemical properties of the vanadium oxide species incorporated within zeolites

V-silicalite catalysts (VS-1 and VS-2) prepared by hydrothermal synthesis have been studied by ESR, XAFS (XANES and EXAFS) and photoluminescence spectroscopy. The in situ characterization of these V-silicalites shows that vanadium is present within the zeolitic framework as a highly dispersed tetrahedrally coordinated V-oxides, VO₄ unit, having a short V=O bond length. Photoluminescence spectroscopy in static and dynamic mode, as well as XAFS studies allow to detect in the V-silicalites different V species than that present in V-HMS or V/SiO₂, in terms of V=O bond length, vibrational energy, bond angle and lifetime of the excited triplet state. It is suggested that the combined contribution of the neighboring Si---OH group attached to the VO₄ unit and the zeolitic rigid framework structure of V-silicalites cause a more significant and pronounced effect on the chemical properties of the VO₄ unit than the flexible structure of V-HMS or V/SiO₂. Moreover, the dynamic quenching of the phosphorescence by the addition of reactant molecules such as NO or propane indicates that the V species in the excited triplet state can be expected to be the active sites for the photocatalytic reactions.     

A rate-dependent cohesive model for simulating dynamic crack propagation in brittle materials

Numerical investigations are conducted to simulate high-speed crack propagation in pre-strained PMMA plates. In the simulations, the dynamic material separation is explicitly modeled by cohesive elements incorporating an initially rigid, linear-decaying cohesive law. Initial attempts using a rate-independent cohesive law failed to reproduce available experimental results as numerical crack velocities consistently overestimate experimental observations. As proof of concept, a phenomenological rate-dependent cohesive law, which bases itself on the physics of microcracking, is introduced to modulate the cohesive law with the macroscopic crack velocity. We then generalize this phenomenological approach by establishing a rate-dependent cohesive law, which relates the traction to the effective displacement and rate of change of effective displacement. It is shown that this new model produces numerical results in good agreement with experimental data. The analysis demonstrates that the simulation of high-speed crack propagation in brittle structures necessitates the use of rate-dependent cohesive models, which account for the complicated rate-process of dynamic fracture at the propagating crack tip.     

Supramolecular morphology of two-step melt-spun poly(dioxanone) fibers

Structure of poly(dioxanone) (PPDX) fibers produced through a two-step melt-spinning process with an additional short-period annealing above the melting temperature of PPDX was investigated and the effect of annealing on the degradation behavior was discussed. The morphological study carried out by etching the fibers using a phosphate or permanganate solution suggested that the fibers take a skin–core structure, and both the skin layer and the core region consist of a bundle of microfibrils. The micro-beam X-ray diffraction analysis revealed that the short-period annealing in the production process only slightly promotes the crystallization in the skin layer but contributes to increasing the packing of amorphous chains near the skin, which seems to be the controlling factor of the hydrolytic degradation behavior of the fibers.     

Data preprocessing and output evaluation of an autoassociative neural network model for online fault detection in virginiamycin production

In this study, an artificial autoassociative neural network (AANN) was used online to detect deviations from normal antibiotic production fermentation using conventional process variables. To improve the efficiency of extracting hidden information contained in multidimensional process variables, and to finally render the AANN adequate for fault detection, we explored the following methods: selection of process variables; preprocessing of data that involved normalizing the training data of the AANN; and evaluation of data that involved assessing the output of the AANN. A method for fault detection in virginiamycin M and S production by Streptomyces virginiae was successfully developed based on these techniques.     

Instability of plastic flow in mild steel

Plastic flow localization in the yielding of mild steel is theoretically studied in terms of the instability of the uniform mode of yielding. The instability is judged by the small perturbation theory in which the development of non-uniform modes superimposed upon the basic uniform mode is examined. The constitutive equation of rate-dependent type and the criterion of yield initiation at the plastic-zone front are employed as the constitutive relations of mild steel. The results of the analysis show the relation between the instability and the characteristic nature of mild steel.     

On-line recognition of physiological state in a yeast fed-batch culture

The physiological states with respect to cell growth and ethanol production in a yeast fed-batch culture can be recognized on-line by fuzzy inferencing. The error vector is newly defined in a macroscopic elemental balance equation and utilized for the on-line recognition of the physiological state of the micro-organisms. Fuzzy membership functions are constructed from the error vectors and state recognition is performed successfully by fuzzy inferencing. In particular, a usual physiological state for yeast cultivation in which aerobic ethanol production is accompanied by very low cell growth can be recognized accurately.     

Small-angle X-ray scattering of long-period structures forming bundles

Small-angle X-ray scattering (SAXS) patterns have been calculated based on a structure model, which consisted of the bundles of long-period structures. The proposed model has produced various scattering patterns of polymers, such as the equatorial, layer line, four-spot, droplet-shaped and triangular scattering. The 0.5th order scattering has arisen when the disorder in or between the long-period structures was large even though the structure did not have the periodicity directly related to the scattering maximum. A slight decrease in the disorder due to slip between the long-period structures has accounted for the sudden change of the SAXS pattern of a poly(ethylene terephthalate) fiber from the four-spot to the layer line scattering which was caused by a slight tensile deformation.     

Bidirectional cell-surface anchoring function of C-terminal repeat region of peptidoglycan hydrolase of Lactococcus lactis IL1403

With the aim of constructing an efficient protein display system for lactic acid bacteria (LABs), the effect of fusion direction on the cell-surface binding activity of the C-terminal region of the peptidoglycan hydrolase (CPH) of Lactococcus lactis IL1403 was studied. CPH fused to the alpha-amylase (AMY) of Streptococcus bovis 148 either at its C-terminus (CPH-AMY) or at its N-terminus (AMY-CPH) was expressed intracellularly in Escherichia coli. This domain was able to direct binding of AMY to the surface of L. lactis ATCC 19435 in both constructs. However, the number of bound molecules per cell and the specific activity for starch digestion in the case of CPH-AMY were 3 and 14 times greater than those in the case of AMY-CPH, respectively. Of the LABs tested, L. lactis ATCC 19435 showed the highest binding capability for CPH-AMY, up to 6 x 10(4) molecules per cell, with a dissociation rate constant of 5.00 x 10(-5) s(-1). The binding of CPH-AMY to the surface of Lactobacillus delbrueckii ATCC 9649 cells was very stable with a dissociation rate constant of 6.96 x 10(-6) s(-1). The production of CPH-AMY in the soluble form increased 3-fold as a result of coexpression with a molecular chaperone, trigger factor. The results of this study suggest the usefulness of CPH as a bidirectional anchor protein for the production of cell-surface adhesive enzymes in E. coli. Furthermore, the importance of the fusion direction of CPH in determining cell-surface binding and enzymatic activities was shown.