The Effects of Acidosis on eNOS in the Systemic Vasculature: A Focus on Early Postnatal Ontogenesis

The activity of many vasomotor signaling pathways strongly depends on extracellular/intracellular pH. Nitric oxide (NO) is one of the most important vasodilators produced by the endothelium. In this review, we present evidence that in most vascular beds of mature mammalian organisms metabolic or respiratory acidosis increases functional endothelial NO-synthase (eNOS) activity, despite the observation that direct effects of low pH on eNOS enzymatic activity are inhibitory. This can be explained by the fact that acidosis increases the activity of signaling pathways that positively regulate eNOS activity. The role of NO in the regulation of vascular tone is greater in early postnatal ontogenesis compared to adulthood. Importantly, in early postnatal ontogenesis acidosis also augments functional eNOS activity and its contribution to the regulation of arterial contractility. Therefore, the effect of acidosis on total peripheral resistance in neonates may be stronger than in adults and can be one of the reasons for an undesirable decrease in blood pressure during neonatal asphyxia. The latter, however, should be proven in future studies.     

Protective properties of petroleum lubricating oils

Chemistry and Technology of Fuels and Oils -     

An ultrasonic method of mixing powders of refractory metal dichalcogenides with gallium-base low-melting-point alloys

Conclusions The investigation has shown that ultrasonic treatment is the only effective mechanical method of mixing the components of systems consisting of tungsten and molybdenum disulfides (or diselenides) and gallium-base low-melting-point alloys. Ultrasonic treatment results in the formation of homogeneous mixtures of MoS₂, WS₂, MoSe₂, and WSe₂ with gallium alloys in a wide range of concentrations of the latter component (from 5 to 50 wt.%).Translated from Poroshkovaya Metallurgiya, No. 11(179), pp. 42–45, November, 1977.     

MODELLING FOR TRANSCRYSTALLINE AND INTERCRYSTALLINE FRACTURE BY VOID NUCLEATION AND GROWTH

A criterion has been formulated for transcrystalline and intercrystalline fracture caused by the evolution of voids located both in a grain and on grain boundaries. The criterion is based on the idea of plastic collapse for a unit cell that is a regular structural mezovolume of polycrystalline material. The criterion does not require the introduction of any empirical parameters, such as critical void size, critical size of ligament between voids and critical void volume fraction, which are used in most models.
Modelling has been performed for void nucleation and growth in a grain and on grain boundaries for elastic–plastic deformation and under creep conditions. A scheme is proposed to describe the transition from transcrystalline to intercrystalline cavitation fracture as a function of strain rate and temperature.
The effect of stress triaxiality on the critical strain and the lifetime for both transcrystalline and intercrystalline fracture has been investigated. A comparison of the results predicted by the suggested criterion with available empirical data has been performed.     

Effect of cyclic deformation on the resistance of a material to brittle failure

A physicomechanical model is suggested for determining the critical brittle failure stress S_c in statically and cyclically deformed material. The model is based on ideas about retardation of microcracks in a deformed substructure which changes during material loading. The effect is determined by experiment of prior cyclic material deformation on resistance to cleavage. The calculated dependence of S_c on the Odquist parameter is compared with the experimental results obtained. Model ideas about the effect of material substructure on brittle failure are confirmed by fractographic studies. Unstable fatigue crack growth is studied on the basis of models for brittle and fatigue failure of BCC-metals.Translated from Problemy Prochnosti, No. 1, pp. 14–21, January, 1991.     

The effect of various factors on the strength of hard-alloy balls

Conclusions The compressive strength of hard-alloy balls depends mainly on the peening regimes; it is therefore necessary to inspect the products thoroughly at the given production stage.The mechanical strength of hard-alloy balls with a hole depends substantially on the orientation of the hole relative to the axis of loading: when the hole is oriented parallel to the axis of load application, the compressive strength of the balls is about 3.5 times higher than that of balls with arbitrary orientation of the holes.Additional heat treatment of specimens increases their mechanical strength on an average by 12–18%.The strength of the balls depends to a considerable extent on their surface roughness.Translated from Poroshkovaya Metallurgiya, No. 10 (346), pp. 101–103, October, 1991.     

An analysis of the conditions of brittle fracture origin

A modified criterion of brittle fracture, a necessary condition of which, the condition of origin of microcracks, is plastic deformation until some value of ₀ dependent upon temperature, is experimentally substantiated. An experimental-calculation method is developed for determination of the relationship of ₀ to temperature T, on the basis of which the ₀(T) relationship is obtained for type 15Kh2MFA steel. It is shown that the proposed formulation of the criterion of brittle fracture makes it possible to consistently describe the fracture processes with different stressed and strained states of the material.Leningrad Branch, Institute of Mechanical Engineering. Translated from Problemy Prochnosti, No. 11, pp. 9–13, November, 1989.     

Brittle fracture local criterion and radiation embrittlement of reactor pressure vessel steels

The application of local criteria for predicting brittle fracture of reactor pressure vessel steels is discussed with an emphasis on radiation embrittlement. An association of the radiation-induced damages and the processes of initiation and propagation of cleavage microcracks is analyzed from the standpoint of the local criterion for fracture. Physical-mechanical models are put forward to describe the influence of radiation damages on the cleavage microcrack initiation. The influence of the material hardening caused by neutron irradiation and plastic deformation on the fracture toughness is studied.     

Radiation embrittlement modelling in multi-scale approach to brittle fracture of RPV steels

The purpose of the present article is to develop a multi-scale brittle fracture modelling for irradiated RPV materials. For this development, applicability of local brittle fracture criteria for radiation embrittlement modelling is analysed through comparison of the predicted and test results on radiation embrittlement of RPV steels in terms of ductile-to-brittle transition temperature and fracture toughness. The influence of radiation-induced defects on the processes of cleavage microcrack nucleation and propagation is clarified. The physical-and-mechanical models of the effect of irradiation-induced defects on cleavage microcrack nucleation are developed on the basis of dislocation and brittle fracture theories. Stress-and-strain controlled fracture criterion is developed that allows the adequate prediction of radiation embrittlement by various mechanisms. The differences and commonalities are revealed in the nature of material embrittlement due to cold work and neutron irradiation. The mechanism is explained of significant recovery of fracture resistance properties with simultaneous increase of fraction of intercrystalline fracture after post-irradiation annealing. Engineering approach for prediction of the temperature dependence of fracture toughness as a function of neutron fluence is justified.