Optimization of Crushing Strength and Disintegration Time of a High-Dose Plant Extract Tablet by Neural Networks

Optimization of crushing strength and disintegration time of a high-dose plant extract tablet was reached after extensive experimentation. Effects of the processing parameters, like compression force and tooling, and also of the excipients were found to be significant. Best results for both disintegration time and crushing strength were obtained with a plant extract that was granulated by roller compaction before compression. To gain more information about the different effects, artificial neural networks (ANNs) and a conventional multivariate method (partial least squares [PLS]) were used for data analysis. The topologies of the neural networks of the feed-forward type were optimized manually and by pruning methods. All methods were tested for contemplated parameters, crushing strength, and disintegration time. In general, ANNs were found to be more successful in characterizing the effects that influence crushing strength and disintegration time than the conventional multivariate methods.     

A Macromechanical Damage Model of Fibrous Laminated Composites

A new model for the damage factor in terms of strain energy densities is derived and proposed. The damage factor values can be predicted directly from the stress–strain data using the aforementioned model. Moreover, an expression of crack density ratios in terms of total strain energy densities is inferred. Their validity has been shown by comparing their results with the limited experimental data. The proposed model compares well with the model and the experimental data of Voyiadjis performed on metal-matrix laminates. A new technique, used to predict reasonably the values of crack density ratios at any fiber orientation angle using measured data in the principal material directions, is also developed. Due to difficulties encountered in the evaluation of amount of damage in composite materials up to failure, especially, when using experimental techniques, it was shown that the proposed method for finding the damage factor and crack-density ratios is sufficient and gives reasonable predictions.     

Local feedback stabilization and bifurcation control, I. Hopf bifurcation

Local bifurcation control problems are defined and employed in the study of the local feedback stabilization problem for nonlinear systems in critical cases. Sufficient conditions are obtained for the local stabilizability of general nonlinear systems whose linearizations have a pair of simple, nonzero imaginary eigenvalues. The conditions show, in particular, that generically these nonlinear critical systems can be stabilized locally, even if the critical modes are uncontrollable. The analysis also yields a direct method for computing stabilizing feedback controls. Use is made of bifurcation formulae which require only a series expansion of the vector field.     

Drilling in mudrocks: rock behavior issues

Borehole stability analyses use different analytical models to evaluate stresses, pressures, and temperatures around boreholes. Mudrocks do not possess spatio-temporally constant material properties: mechanical properties are time-dependent because of the continuous change in pore pressure, moisture content, and temperature near the borehole. Mudrocks with high specific surface areas also exhibit high sensitivity to changes in physical and chemical properties of their pore fluids. Pressure and concentration diffusion during drilling continuously change the ionic composition of pore fluids and, accordingly, the engineering properties of those fine-grained argillaceous materials. Such fine-grained materials are considered “reactive”; it is shown that a “reactivity coefficient” can be used to assess the physico-chemical sensitivity of mudrocks. Coupling between chemical and mechanical properties may develop in reactive mudrocks, leading to further changes in their mechanical parameters. Experimental data from triaxial and oedometer tests are presented for several materials to illustrate their time-dependent mechano-chemical properties in borehole environments. A discussion of coupled diffusivity processes in mudrocks is included, and the concept of large micro-scale strains that can lead to deterioration of properties is introduced.Finally, we speculate on the degree of complexity required for constitutive modeling of borehole stability analysis of shales in practical situations.     

Successful Derivation of Hepatoblasts,Cholangiocytes and Hepatocytes from Simian Induced Pluripotent Stem Cells

The use of primary cells in human liver therapy is limited by a lack of cells. Induced pluripotent stem cells (iPSCs) represent an alternative to primary cells as they are infinitely expandable and can be differentiated into different liver cell types. The aim of our work was to demonstrate that simian iPSCs (siPSCs) could be used as a new source of liver cells to be used as a large animal model for preclinical studies. We first differentiated siPSCs into a homogenous population of hepatoblasts (siHBs). We then separately differentiated them into hepatocytes (siHeps) and cholangiocytes (siChols) expressing respective specific markers and displaying epithelial polarity. Moreover, we showed that polarized siChols can self-organize into 3D structures. These results should facilitate the deciphering of liver development and open the way to exploring co-culture systems that could be assessed during preclinical studies, including in autologous monkey donors, for regenerative medicine purposes.     

Using symbolic execution and data flow criteria to aid test data selection

The utilization is described of a data flow path selection criterion in a symbolic execution system. The system automatically generates a subset of program paths according to a certain control flow criterion. This subset is called the ZOT-subset, since it requires paths that traverse loops zero, one and two times. Experience indicates that traversing this subset of program paths is enough to cover most control flow and data flow components of the program. The problem with the ZOT-subset is that it might contain, for large programs, a large number of paths. The number of paths in this subset can be reduced by concentrating on executable paths that cover vital components of programs such as data flow components. This object is achieved by employing a data flow path selection criterion in the system. The system symbolically executes the paths of the ZOT-subset, and creates a system of branch conditions for each one. The user determines infeasible paths by checking the consistency of each system of conditions. The system selects feasible paths from the ZOT-subset that cover the data flow criterion. Solving the systems of conditions of the selected paths provides the user with test data to fulfil the given data flow criterion.     

Multiparameter singular perturbation problems: Iterative expansions and asymptotic stability

Recursive formulae are derived which yield asymptotic expansions for the eigenvalues of multiparameter singular perturbation problems. These formulae follow readily from an exact expression for the eigenvalues which involves an implicit matrix function. The implicit function satisfies an algebraic matrix Riccati equation reminiscent of a similar equation of the single parameter theory. The results also explicate the ‘block D-stability’ criterion for asymptotic stability previously introduced by Khalil and Kokotovic.     

Decentralized collaborative business process execution using blockchain

World Wide Web - Blockchain technology enables several untrustworthy parties to execute inter-organizational business processes in a tamper-proof manner. Existing approaches are based on smart...     

Sampled-data modelling and analysis of the power stage of PWM DC-DC converters

The power stage of the PWM DC–DC converter is modelled and analysed using the sampled-data approach. The work addresses both continuous and discontinuous conduction mode under voltage mode control, and continuous conduction mode under current mode control. For each configuration, nonlinear and linearized sampled-data models, and control-to-output transfer functions are derived. Using this approach, both current mode control and discontinuous conduction mode can be handled systematically in a unified framework, making the modelling for these cases simpler than with the use of averaging. The results of this paper are similar to results of Tymerski, but they are presented in a simpler manner tailored to facilitate immediate application to specific circuits. It is shown how sampling the output at certain instants improves the obtained phase response. Frequency responses obtained from the sampled-data model are more accurate than those obtained from various averaged models. In addition, a new (‘lifted’) continuous-time switching frequency-dependent model of the power stage is derived from the sampled-data model. Detailed examples illustrate the modelling tools presented here and also provide a means for comparing results obtained from the sampled-data approach with those obtained from averaging.     

Influence of ageing on the internal friction of magnesium

The internal friction of cp- (99.8 wt.%) and hp- (99.99 wt.%) magnesium was determined by measuring the logarithmic decrement of free vibrations of bending beams, which were clamped at one end. Independently of the purity and the thermomechanical pretreatment, for all samples the logarithmic decrement increases with increasing strain amplitude. The damping in hp-magnesium is generally higher than in cp-magnesium. This can be explained by the model of Granato and Lücke, assuming that the successive unpinning of dislocation segments between weak pinning points is the reason of the increment of damping with increasing strain amplitude. The weak pinning points are assumed to be solute atoms or vacancies. Based on this model, other effects, found also in time and stress dependent internal friction measurements, can be explained qualitatively. The damping decreases at room temperature with ageing time and annealing temperatures up to 150°C. For higher annealing temperatures the damping increases monotonously with the temperature of the heat treatment. The effect of ageing can also be reverted by dynamic strain in the range of about 10⁻⁴–10⁻³, which increases the internal friction of aged samples before they can age again.