Mechanical Stress Effects on 550 °C Hot Corrosion Propagation Rates in Precipitation Hardened Ni-Base Superalloys: CMSX-4, CM247LC DS and IN6203DS

Combinations of temperature, stress and hot corrosion may cause environmentally-assisted cracking in precipitation-hardened Ni-base superalloys, which is little understood. This research aims to increase current understanding by investigating the effects of mechanical stress on the hot corrosion propagation rate during corrosion-fatigue testing of CMSX-4, CM247LC DS and IN6203DS. The parameters used during the tests included a high R-ratio, high frequency, and a temperature of 550 °C. The results showed CMSX-4 experienced a predictable increase in the hot corrosion rate, CM247LC DS also experienced increased rates, but no obvious trend was apparent; whilst IN6203DS showed no evidence of an increased rate. These different behaviours appear to be a result of an interaction between the mechanical stress and microstructural features, which include gamma-prime volume fractions in both the matrix and eutectic regions, along with the distribution of the eutectic structure. The different behaviours in the hot corrosion propagation rate subsequently affected the respective corrosion fatigue results, with both CMSX-4 and CM247LC DS experiencing fracture but with significantly more scatter involved in the CM247LC DS results. All IN6203DS corrosion-fatigue specimens completed the respective tests without fracture and showed no evidence of cracking. It, therefore, appears that precipitation hardened Ni-base superalloys, which are susceptible to environmentally-assisted cracking, also experience increased hot corrosion propagation rates.

Understanding of an Iceberg Breaking Off Event Based on Ice-Front Motion Analysis of Amery Ice Shelf, Antarctica

On 26 September 2019, a massive iceberg broke off the west side of the Amery Ice Shelf (AIS) in East Antarctica. Since 1973, the AIS calving front has steadily advanced at a rate of 1.0 km yr−1. However, the advancement rate of the central portion of the AIS increased dramatically during 2012–2015, which indicates a velocity increase prior to the calving event. Eight calving front locations from 1973 to 2018 were mapped to investigate the advancement rate of AIS over the entire observational period. Additionally, the propagation of rift A was observed unstable from 2012 to 2015. The westward propagation rate of rift A1 increased to 3.7 km yr−1 from 2015 to 2017, which was considerably faster than the other rifts near the AIS calving front. The increased advancement rate and the increasing propagation magnitude of at least one active rift appear to be precursors of this large calving event.

The fate of continuous input of relatively heavy fluid at the base of a porous medium

We evaluate theoretically and confirm experimentally the shape of the fluid envelope resulting from the input of relatively heavy fluid at a constant rate from a point source at the base of a homogeneous porous medium. In three dimensions an initially expanding hemisphere transitions into a gravity current flowing over the assumed rigid, horizontal and impermeable bottom of the porous medium. A range of increasing transition times occurs if defined by extrapolation of the relationships in the two extreme regimes (hemispherical shape and thin-layer gravity current) so that they intersect, for: the ratio of buoyancy to fluid resistance; the horizontal extent of the fluid; the ratio of height at the centre to the radius; and just the height at the centre. Corresponding results are derived for two-dimensional geometries. In this case, we conduct a series of laboratory experiments demonstrating the transition between the radial and gravity current regimes both in terms of form and propagation rate. The results are extrapolated briefly to two-layer systems, in order to begin to understand effects due to vertically heterogeneous pore structures. We sketch, and verify by experiment, that an expanding hemisphere in a lower layer can reach a much more permeable upper layer and flow through it as a gravity current, thereby uniting the two regimes.

Variability of Time and Amplitude ECG Indicators in Older Adults

The purpose of this article was to determine the effect of the clinostatic test on the electrical properties of the myocardium in older adults leading an active lifestyle. Materials and methods. The study involved 38 people aged between 70 and 90 years living in a northern city (Syktyvkar, 61°N) and leading an active lifestyle. The indicators of the electrical properties of the cardiac muscle were determined before and after the clinostatic test. For this purpose, an ECG was recorded in the standard lead II in the standing and lying positions. Results. Using the method of paired comparisons, we showed a decrease in heart rate under the influence of the clinostatic test from 76 ± 10 beats/min to 64 ± 10 beats/min. The variability of ECG components according to pNN50 (the percentage of successive NN intervals differing from each other by more than 50 ms) in older adults in the standing position was, on average, two times lower than in the lying position. The PP interval increased from 0.81 ± 0.12 s (in the standing position) to 0.90 ± 0.10 s (in the lying position). The PT interval remained practically unchanged, staying at the level of (0.46 ± 0.07) – (0.49 ± 0.07) s. The TP segment grew from 0.35 to 0.42 ± 0.10 s. The RD amplitude was 1.04 ± 0.43 mV in the standing and 0.88 ± 0.30 mV in the lying position; the propagation rate of depolarization in the cardiac muscle was 245 ± 137 and 205 ± 106 mm/s, respectively. In addition, the paper discussed the mechanism of opposite reactions to the clinostatic test, i.e. increasing duration of cardiointervals and decreasing amplitude indicators. For citation: Irzhak L.I., Russkikh N.G., Parshukova A.N. Variability of Time and Amplitude ECG Indicators in Older Adults. Journal of Medical and Biological Research, 2021, vol. 9, no. 4, pp. 355–365. DOI: 10.37482/2687-1491-Z073

Contact-Fatigue Resistance of PM Steel with Hard Coatings

Hard coatings applied by the Physical Vapor Deposition method often provide very good mechanical properties, especially when applied to metal parts that are mentioned to withstand certain level of wear. In this study, TiN coating combined with deep rolling were applied to the investigated steel samples, prepared by powder metallurgy and subjected to contact-fatigue stress. Computational analysis of stress states in samples by the finite element method helped to reveal the behavior and formation of fatigue failures when loading samples. The results, processed in the form of fatigue curves, probabilistic Weibull curves using metallography and electron microscopy, showed a positive effect of the used coatings and their combination with other surface treatments on the contact-fatigue strength of the examined samples. Microscopic study also showed the different mechanisms of crack formation and of crack propagation rate due to contact loading of material with a laser hardened surface, which has an obvious impact on material lifetime.

The influence of growth regulators and explant position on the growth and development of Mandevilla sanderi (Hemsl.) Woodson in vitro

Mandevilla is a valuable ornamental pot vine. However, due to a low propagation rate, it is difficult to keep up with the demand. Micropropagation would allow to produce lots of plants for the market. The aim of the study was to determine the effect of the growth regulators addition to the media and explants orientation on multiplication of Mandevilla sanderi, an exotic, ornamental pot plant. The shoot tips were placed vertically or horizontally on the Murashige and Skoog medium supplemented with benzyladenine (BA) or isopentenyladenine (2iP), at concentrations of 1, 2.5 or 5 mg·dm–3 singly or in combination with thidiazuron (TDZ) at concentrations of 0.01, 0.025 or 0.05 mg·dm–3. Maximum multiplication rate was noted on the media supplemented with 2.5 mg·dm–3 2iP + 0.025 mg·dm–3 TDZ or 5 mg·dm–3 2iP, when explants were placed horizontally. All the treatments resulted in callus formation. Medium supplemented with the highest concentration of BA combined with TDZ was the most active in callus growth.

Spatiotemporal Rates of Tectonic Deformation and Landscape Evolution above a Laterally Propagating Thrust Fault: Wheeler Ridge Anticline, California, USA

The Wheeler Ridge anticline, located in the southern San Joaquin Valley of California, USA, is a well-studied and classic example of a laterally growing fault propagation fold. New high-resolution lidar elevation data combined with nine infrared stimulated luminescence (IRSL) ages of discrete geomorphic surfaces that are bounded by prominent transverse wind and river gaps allow for investigation of tectonic topography through time. Luminescence ages from four of the six surfaces yield depositional ages that range from 32 ka to 153 ka, which are broadly consistent with a previously published soil chronosequence. Our graphical modeling indicates an average surface uplift rate of ~2.1 mm/yr and an average along-strike fold propagation rate of ~20 mm/yr. However, our probabilistic modelling and topographic analysis suggest a rate decrease of both uplift and lateral propagation toward the fault tip from ~2.4 to 0.7 mm/yr and from ~49 to 14 mm/yr, respectively. Rate decreases are not progressive but rather occur in punctuated deformational intervals across previously documented structural barriers (tear faults) resulting in a fold that is characterized by discrete segments that exhibit a systematic deformational decrease toward the east. The punctuated tectonic growth of Wheeler Ridge has also locally controlled the topographic evolution of the anticline by effecting the formational timing and position of at least seven wind and river gaps that result from multiple north-flowing antecedent streams that traverse the growing structure. We quantify the timing of wind and river gap formation, based on IRSL results and inferred incision rates, and present a model for the spatiotemporal evolution of transverse drainages and the topographic development of Wheeler Ridge. Our chronology of gap formation broadly correlates with regional Late Pleistocene dry climate intervals suggesting that both tectonics and climate were integral to the geomorphic development of the Wheeler Ridge anticline.