Properties of pore structure of thin-layer external plasters under ageing in simulated environment

The basic and commonly used four types of thin-layer facade plasters on cement and silicate binders were subjected to 400 cycles of accelerated ageing in the simulate chamber. The main attention was focused on the character of pore structure evolution during of ageing process. To reach this objective, examinations of the microstructure by the mercury intrusion method and total porosity by the densitometry method were carried out in time per 100 cycles. During the study, the main emphasis was put on the open porosity and changes of dimensional groups of pores. On the ground of the hysteresis of the mercury pressure by mercury intrusion porosimetry testing, the presence of pores with capillary entrance was suggested. In view of this, the cylindrical and spherical model of porous structure has been defined. The contribution of capillary and spherical pores vary in time together with properties such as: average pore radius, length of cylindrical pores and their tortuosity. The changes of these values confirm that atmospherical ageing influences plasters’ binders in two zones. It appears on the one hand by the decrease of total porosity, length and diameter of capillaries but on the other hand by the increase of open porosity and the decrease of pores’ tortuosity. It indicates the tightening character of the inside pore structure of the examined plasters and at the same time it gives diverse effect in its external zone.     

Depth Dependence of Nanoindentation Pile-Up Patterns in Copper Single Crystals

A study of the dependence of nanoindentation pile-up patterns on the indentation load and crystallographic orientation is presented. Three different orientations—(001), (011), and (111)—of single crystal copper were investigated. Experiments were conducted on a CSM ultra-nanoindentation tester using a Berkovich tip. The topographic images were obtained using an atomic force microscope. The evolution of pile-up patterns with different applied loads was observed. The results show that for applied loads equal to 0.45 mN and smaller the pile-up patterns do not depend on the crystallographic orientation of the indented surface; instead, they depend on the tip’s geometry. On the other hand, in the case of indentation loads bigger than 2 mN, pile-up patterns on the surfaces of (001)-, (011)-, and (111)-oriented single crystals have fourfold, twofold, and sixfold (or threefold) symmetry, respectively. An intermediate state was also reported. Furthermore, a detailed analysis of residual impressions with maximal applied loads equal to 2 mN and bigger reveals that both pile-up and sink-in patterns are present.     

Elastohydrodynamic lubrication and finite configuration changes in reciprocating elastomeric seals

A computational framework has been developed for a fully coupled analysis of elastohydrodynamic lubrication and finite deformations of elastomeric reciprocating seals in hydraulic actuators. The relevant formulation is provided, which consistently treats finite configuration changes of the seal modelled as a hyperelastic (Mooney-Rivlin) solid. The steady-state hydrodynamic lubrication is modelled using the classical Reynolds equation. Coupling of the solid and fluid parts is fully accounted for, including friction due to shear stresses in the lubricant film. Detailed results of finite element simulations are provided for two benchmark problems of O-ring and rectangular rod seals in a wide range of process parameters.     

Investigation of Serine‐Proteinase‐Catalyzed Peptide Splicing in Analogues of Sunflower Trypsin Inhibitor 1 (SFTI‐1)

Serine‐proteinase‐catalyzed peptide splicing was demonstrated in analogues of the trypsin inhibitor SFTI‐1: both single peptides and two‐peptide chains (C‐ and N‐terminal peptide chains linked by a disulfide bridge). In the second series, peptide splicing with catalytic amount of proteinase was observed only when formation of acyl–enzyme intermediate was preceded by hydrolysis of the substrate Lys–Ser peptide bond. Here we demonstrate that with an equimolar amount of the proteinase, splicing occurs in all the two‐peptide‐chain analogues. This conclusion was supported by high resolution crystal structures of selected analogues in complex with trypsin. We showed that the process followed a direct transpeptidation mechanism. Thus, the acyl–enzyme intermediate was formed and was immediately used for a new peptide bond formation; products associated with the hydrolysis of the acyl–enzyme were not observed. The peptide splicing was sequence‐ not structure‐specific.     

The kinetics of coal chars hydrogasification

Hydrogasification reaction of chars produced from two rank coals was investigated in temperature up to 1173 K and pressure up to 8 MPa. The reactivity of the lignite Szczerców char has been found to be slightly higher than of the subbituminous coal Janina char produced at the same conditions. A high value of the char reactivity was observed to certain carbon conversion, above which a sharp drop takes place. It has been shown that to achieve proper carbon conversion the hydrogasification reaction must proceed at temperature above 1200 K. Based on the active centres theory the kinetic equations of the hydrogasification process were developed and the kinetic constants at the maximum reaction rate evaluated for the analyzed chars.     

A method for fast simulation of multiple catastrophic faults in analogue circuits

The paper offers an efficient method for simulation of multiple catastrophic faults in linear AC circuits. The faulty elements are either open circuits or short circuits. The method exploits the well‐known Householder formula in matrix theory to find the node voltages deviations due to the perturbations of some circuit elements. The main achievement of the paper is a systematic method for performing the simulation of all combinations of the multiple catastrophic faults. The method includes two new procedures enabling us to find very efficiently the node impedance matrix of the nominal circuit and inverses of some matrices corresponding to different fault combinations. The procedures are the crucial point of this approach and make it very efficient. Consequently, the amount of the computing power needed to carry out all the simulations is significantly reduced. Numerical examples illustrating the proposed approach are provided. Copyright © 2008 John Wiley & Sons, Ltd.     

Semi-empirical model of efficiency of wire electrical discharge machining of hard-to-machine materials

In this study, the efficiency of wire electrical discharge machining of hard-to-machine materials was investigated experimentally. Uncoated brass wire, 0.25 mm diameter, zinc oxide coated brass wire and brass CuZn20 coated brass CuZn50 wire were utilized in the conducted research. The following variables were chosen as important WEDM parameters: discharge time t_on, average working voltage U. The following properties of machined materials, such as: melting point T_t, electrical conductivity σ, thermal conductivity K, thermal expansion coefficient k, density ρ, heat capacity c_p, were selected to develop the semi-empirical model of volumetric efficiency of WEDM. The variation of the WEDM efficiency in cutting different materials and applying different wire electrodes and different process parameters was modelled semi-empirically by employing dimensional analysis.     

Stress singularities in a periodically layered composite near interface crack tips

The paper deals with the asymptotic analysis of stresses near interface crack tips in the periodically two-layered elastic composites. The problem is investigated for the plane state of strain within the framework of the homogenized model with microlocal parameters. The angular dependence of stresses at the crack tip is presented for different mechanical and geometrical properties of the composite.     

High-mobility modulation-doped SiGe-channel p-MOSFETs

A novel subsurface SiGe-channel p-MOSFET is demonstrated in which modulation doping is used to control the threshold voltage without degrading the channel mobility. A novel device design consisting of a graded SiGe channel, an n⁺ polysilicon gate, and p⁺ modulation doping is used. A boron-doped layer is located underneath the graded and undoped SiGe channel to minimize process sensitivity and maximize transconductance. Low-field hole mobilities of 220 cm²/V-s at 300 K and 980 cm²/V-s at 82 K were achieved in functional submicrometer p-MOSFETs