Surface damage resistance and yielding of chemically strengthened silicate glasses: From normal indentation to scratch loading

We report on surface elasticity, plastic deformation and crack initiation of chemically strengthened soda-lime silicate and sodium aluminosilicate glasses during lateral indentation and scratch testing. Instrumented indentation using a normal indenter set-up corroborated previous findings on the effects of chemical strengthening on surface Young's modulus, hardness, and indentation cracking. Using lateral indentation in the elastic-plastic regime, we find a pronounced increase in the scratch hardness as a result of chemical strengthening, manifest in higher work of deformation required for creating the scratch groove. Thereby, the glass composition is found to play a stronger role than the absolute magnitude of surface compressive stress. Using a blunt conical stylus for instrumented scratch testing reveals three distinct modes of scratch-induced surface fracture, which occur during scratching or after unloading. Occasional micro-cracking caused by pre-existing surface flaws at low scratching load can be completely suppressed through chemical strengthening. The intrinsic defect resistance to microcracking is reduced as a result of ion stuffing, depending on the initial glass composition, whereas the resistance to abrasive yielding is enhanced by several hundred MPa.     

The formation of BO 4 − tetrahedra and nonbridging oxygen ions in borosilicate glasses with low silica content

Alkali-, mixed alkali- and mixed alkali-alkaline earth aluminoborosilicate glasses with low silica content have been prepared and annealed. Molar volume measurements and structural analysis using X-ray diffraction, IR spectra, and UV-transmission were carried out. It is shown that the formation of nonbridging oxygen ions bonded with the silicon ions takes place during the formation of BO ₄ ^– tetrahedra for 0.4R0.8 whereR is the alkali oxide to the boron oxide ratio. From X-ray diffraction patterns, it is found that no crystalline phases can be detected. The UV-transmission spectra elucidated that the probability of formation of nonbridging oxygen ions in the glass with a single alkali ion (Li⁺) is higher than that in the glass with mixed alkali ions (Li⁺+K⁺) under the same conditions. It is assumed that the shift of the UV-edge to lower or longer wavelengths may be due to the phase separation process in these glasses.     

Roller bearings under radial and eccentric loads

The influence of the roller axial profile on the contact pressure distributions is discussed for the cases of aligned and misaligned rollers. The results of numerical solutions show that careful profiling using radial arcs can result in a more even distribution of pressure. A design method employed by Harris for predicting pressures on misaligned rollers can underestimate the maximum value. However, its use in a shaft and roller bearing system enables the maximum misalignment angle to be predicted for the worst loaded roller with fair accuracy. Numerical methods are then used to find the detailed pressure distribution, thus allowing bearing selection to be made, based upon the maximum pressure present     

Cryoprotectants-Free Vitrification and Conventional Freezing of Human Spermatozoa: A Comparative Transcript Profiling

Introduction: Spermatozoa cryopreservation is an important technique to preserve fertility for males. This study aimed at exploring the stability of epigenetics information in human spermatozoa, manipulated by two different technologies, freezing and vitrification. Methods: Spermatozoa samples were distributed into three groups: 1. Fresh spermatozoa (control group), 2. Frozen spermatozoa, 3. Vitrified spermatozoa. Epigenetic differences of fresh and cryopreserved spermatozoa were evaluated using high-throughput RNA sequencing. Results: Differentially expressed genes (DEGs) in frozen (1103 genes) and vitrified (333 genes) spermatozoa were evaluated. The bioinformatical analysis identified 8 and 15 significant pathways in groups of frozen and vitrified spermatozoa, respectively. The majority of these pathways are most relevant to immune and infectious diseases. The DEGs of the fertilization process are not detected during vitrification. The freezing process induces more down-regulation of genes and is relevant to apoptosis changes and immune response. Conclusion: Cryopreservation of human spermatozoa is an epigenetically safe method for male fertility preservation. Cryoprotectant-free vitrification can induce more minor biological changes in human spermatozoa, in comparison with conventional freezing.     

Low-Energy Laser-Driven Ultrashort Pulsed Electron Beam Irradiation-Induced Immune Response in Rats

The development of new laser-driven electron linear accelerators, providing unique ultrashort pulsed electron beams (UPEBs) with low repetition rates, opens new opportunities for radiotherapy and new fronts for radiobiological research in general. Considering the growing interest in the application of UPEBs in radiation biology and medicine, the aim of this study was to reveal the changes in immune system in response to low-energy laser-driven UPEB whole-body irradiation in rodents. Forty male albino Wistar rats were exposed to laser-driven UPEB irradiation, after which different immunological parameters were studied on the 1st, 3rd, 7th, 14th, and 28th day after irradiation. According to the results, this type of irradiation induces alterations in the rat immune system, particularly by increasing the production of pro- and anti-inflammatory cytokines and elevating the DNA damage rate. Moreover, such an immune response reaches its maximal levels on the third day after laser-driven UPEB whole-body irradiation, showing partial recovery on subsequent days with a total recovery on the 28th day. The results of this study provide valuable insight into the effect of laser-driven UPEB whole-body irradiation on the immune system of the animals and support further animal experiments on the role of this novel type of irradiation.     

The Mapping of Elastohydrodynamic Contacts

The paper describes an interferometric method of determining the shape and thickness of the clastohydrodynamic oil film formed between a rotating ball loaded against a diamond, sapphire, or glass plate, and a rotating roller loaded against a glass plate. The film shape for both point and line contact is found to depend critically on speed and load. It is found that considerable departure from the static Hertzian shape occurs at quite low speeds. The line contact results show the extent of the end closure and its dependence on the blend radius of the roller.     

Boundary Conditions for Elastohydrodynamics of Circular Point Contacts

The paper presents the solution of an elastohydrodynamic point contact condition using inlet and outlet lubricant entrainment with partial counter-flow. The inlet and outlet boundaries are determined using potential flow analysis for the pure rolling of contiguous surfaces. This shows that Swift–Stieber boundary conditions best conform to the observed partial counter-flow at the inlet conjunction, satisfying the compatibility condition. For the outlet region, the same is true when Prandtl–Hopkins boundary conditions are employed. Using these boundary conditions, the predictions conform closely to the measured pressure distribution using a deposited pressure-sensitive micro-transducer in a ball-to-flat race contact. Furthermore, the predicted conjunctional shape closely conforms to the often observed characteristic keyhole conjunction through optical interferometry. The combined numerical–experimental analysis with realistic boundary conditions described here has not hitherto been reported in the literature.     

The Functional and Application Possibilities of Starch/Chitosan Polymer Composites Modified by Graphene Oxide

This study describes functional properties of bionanocomposites consisting of starch/chitosan/graphene oxide (GO) obtained using the green synthesis method, such as water-barrier and optical properties, as well as the rate of degradation by enzymatic and acid hydrolysis. The toxicity of the composites and their effects on the development of pathogenic microflora during storage of meat food products was also investigated. Although the results showed that the barrier properties of the composites were weak, they were similar to those of biological systems. The studies carried out confirmed the good optical properties of the composites containing chitosan, which makes it possible to use them as active elements of packaging. The susceptibility of starch and chitosan films to enzymatic and acid hydrolyses indicates their relatively high biodegradability. The lack of toxicity and the high barrier against many microorganisms offer great potential for applications in the food industry.