Optimization of the fatigue life of threaded connections by the positioning method

The presented paper addresses the problem of optimization of the fatigue life of threaded connections by the positioning method. This method presents a technique operating upon the periodic mutual change of nut and stud positions in order to increase the fatigue life. The modelling of the fatigue life of threaded connections using the positioning method is based on concept of damageability curve. A mathematical model is formulated in terms of mathematical programming taking into account technological and operation constraints. The performance and possibilities of the model are demonstrated by numerical experiments. The influence of weighting and constraints on the fatigue life of threaded connection, the influence of the heights of inter-turnings on threaded connection fatigue life and the influence of a number of positioning periods on threaded connection fatigue life when the height of inter-turnings is constant are presented.     

Evaluation of ischemic injury of the cardiac tissue by using the principal component analysis of an epicardial electrogram

Monitoring and control of the heart tissue viability is of crucial importance during heart surgery operations. In most cases the heart tissue suffers from an ischemic injury that causes a decrease in the velocity of electrical excitation propagation in it and influences the shape of the excitation wave front that spreads over the injured area. It is reflected in a more complex shape of the registered epicardial electrogram as compared to normal. A method for quantitative evaluation of the complexity of the shape of the epicardial electrogram based on the principal component analysis is here proposed for evaluation of the ischemic injury of the cardiac tissue. A minimal, yet sufficient, number of the principal components (the optimal basis functions) for truncated expansion of the epicardial electrogram signals could be used as an estimate of signal complexity. The method for determination of such a minimal, yet sufficient, number of principal components were developed by using epicardial electrograms registered during in situ experiments on dogs in which local ischemia was evoked by ligation of a coronary vessel.     

Chemical and sensory characterisation of aroma of Viburnum opulus fruits by solid phase microextraction-gas chromatography-olfactometry

The aroma profile of four cultivars of Viburnum opulus and one cultivar of V. opulus var. sargentii fruits was studied by solid phase microextraction of headspace volatiles and subsequent analysis by gas chromatography, mass spectrometry and olfactometry (SPME-HS-GC-MS-O). In total, 41 compounds were identified, 3-methyl-butanoic acid (63.0-71.8% of identified volatile organic compounds) being the major constituent in the three V. opulus cultivars, while 2-octanone was dominant in one cultivar of V. opulus and in V. opulus var. sargentii, amounting to 28.1% and 25.6% of identified volatile compounds, respectively. Ten odour active compounds were detected and characterised by the trained panel of judges in the course of GC-O by using detection frequency analysis (DFA). 3-Methyl-butanoic and 2-methyl-butanoic acids as well as linalool and ethyl decanoate were found to be the main odour active components for V. opulus aroma.     

Tracking coefficients of a nonstationary system,followed by static nonlinearity jointly with the time delay

This paper considers a block-oriented nonlinear Wiener system that consists of a linear block with real time-varying unknown coefficients and pure time delay followed by a static invertible nonlinearity. Consideration is concentrated on the joint linear block coefficients and time delay tracking by processing observation samples. Two problems are analyzed. The first one is the avoidance of mean-squares prediction error function multiextremality for time delay while seeking the global minimum. The other problem consists of the applicability of unified adaptive algorithms, based on the schema with corrective operators for the Wiener system. An approach used to transform the multiextremal criterion into a unimodal function for a nonstationary linear system, in respect of the time delay, is developed and analyzed for a block-oriented nonlinear Wiener system with time-varying coefficients and a time delay. The recursive parametric identification approach, based on the method of corrective operators, is developed for the nonstationary dynamic Wiener system. Applicability of algorithms is supported by various simulation tests solved by a computer.     

A Crucial Role of Mitochondrial Dynamics in Dehydration Resistance in Saccharomyces cerevisiae

Mitochondria are dynamic organelles as they continuously undergo fission and fusion. These dynamic processes conduct not only mitochondrial network morphology but also activity regulation and quality control. Saccharomyces cerevisiae has a remarkable capacity to resist stress from dehydration/rehydration. Although mitochondria are noted for their role in desiccation tolerance, the mechanisms underlying these processes remains obscure. Here, we report that yeast cells that went through stationary growth phase have a better survival rate after dehydration/rehydration. Dynamic defective yeast cells with reduced mitochondrial genome cannot maintain the mitochondrial activity and survival rate of wild type cells. Our results demonstrate that yeast cells balance mitochondrial fusion and fission according to growth conditions, and the ability to adjust dynamic behavior aids the dehydration resistance by preserving mitochondria.     

Sol–gel synthesis,characterization and application of lanthanide-doped cobalt chromites (CoCr2–xLnxO4; Ln = Tm3+ and Yb3+)

Cobalt chromite based pigments CoCr_2–xLn_xO₄ (Ln?=?Tm³⁺ and Yb³⁺) with different substitutional level of lanthanide (x?=?0–0.5) have been synthesized using aqueous sol–gel synthetic approach. The XRD analysis revealed that single phase spinel was obtained only with low content of lanthanide ions (x?=?0.01–0.04). The sol–gel derived powders with higher concentration of lanthanide (x?=?0.05–0.2) contained minor amount of orthochromite phase. At the highest substitutional level (x?≥?0.2) the perovskite phase became the main crystalline phase. The colour of obtained pigments and corresponding ceramic glazes were analogous. Depending on the dominant phase, the colour varied from bluish-green (prevailing spinel phase) to dark brownish green (the main perovskite phase). This study proved that the replacement of chromium ions by thulium and ytterbium was successful at low content of lanthanides influencing the shade of pigment and corresponding glazes.     

Piezoelectric resonator and high-frequency admittance study of viscosity and density changes in a thin water layer adjacent to the electrode surface

Analysis of the admittance of quartz resonator in contact with water has shown that the viscosity-density product of water at a metallic electrode surface decreases during the positive potential scan. This decrease is more pronounced when the electrode surface is coated by a thin layer of polymer. Literature data provide evidence that the density of water in the first layer attached to the surface increases when the potential is shifted into the positive direction. It is concluded that during such potential scan the decrease of viscosity is larger than the increase of density.     

Three-dimensional Correction of the Stress Intensity Factor for Plate with a Notch

The 3D effects of the 2D mode I stress intensity factor for the plate with a V-shaped straight through-thickness notch are investigated by the finite element method and three-dimensional thicknessdependent correction of SIF is suggested. The correction relies on the assumed relationship between the SIF and the constraint factor (out-of-plane degree of freedom). The 3D finite element mesh generator combining the 2D in-plane adaptive unstructured mesh with the structured through-thickness mesh Is developed and applied for the analysis purposes. Three-dimensionality was examined by using two independent indicators, namely, stress- or strain-based constraint factors. The three-point bend and tensile center-cracked plates are investigated. The results demonstrated that the developed 3D corrections may be treated as upper bound estimates of the SIF for three-point bend plate,while directly obtained numerical values are considered as lower bound estimates. Analysis of the tensile center-cracked plate demonstrated a different nature of the 3D SIF profile, which cannot be simply explained as a transitional state between plain strain and plain stress. Therefore, the suggested 3D correction concept is of a particular character.