Extreme Gradients Research Articles

LC/8YSZ TBCs Thermal Cycling Life and Failure Mechanism under Extreme Temperature Gradients

The purpose of this paper is to study the thermal shock resistance and failure mechanism of La2Ce2O7/8YSZ double-ceramic-layer thermal barrier coatings (LC/8YSZ DCL TBCs) under extreme temperature gradients. At high surface temperatures, thermal shock and infrared temperature measuring modules were used to determine the thermal cycling life and insulation temperature of LC/8YSZ DCL TBCs under extreme temperature gradients by an oxygen–acetylene gas flame testing machine. A viscoelastic model was used to obtain the stress law of solid phase sintering of a coating system using the finite element method. Results and Conclusion: (1) Thermal cycling life was affected by the surface temperature of LC/8YSZ DCL TBCs and decreased sharply with the increase of surface temperature. (2) The LC ceramic surface of the failure coating was sintered, and the higher the temperature, the faster the sintering process. (3) Accelerated life test results showed that high temperature thermal cycling life is not only related to thermal fatigue of ceramic layer, but is also related to the sintering degree of the coating. (4) Although the high temperature thermal stress had great influence on the coating, great sintering stress was produced with sintering of the LC ceramic layer, which is the main cause of LC/8YSZ DCL TBC failure. The above results indicate that for new TBC ceramic materials, especially those for engines above class F, their sinterability should be fully considered. Sintering affects the thermal shock properties at high temperature. Our research results can provide reference for material selection and high temperature performance research.

Metabolic potential and survival strategies of microbial communities across extreme temperature gradients on Deception Island volcano, Antarctica.

Active volcanoes in Antarctica have remarkable temperature and geochemical gradients that could select for a wide variety of microbial adaptive mechanisms and metabolic pathways. Deception Island is a stratovolcano flooded by the sea, resulting in contrasting ecosystems such as permanent glaciers and active fumaroles, which creates steep gradients that have been shown to affect microbial diversity. In this study, we used shotgun metagenomics and metagenome-assembled genomes to explore the metabolic potentials and survival strategies of microbial communities along an extreme temperature gradient in fumarole and glacier sediments on Deception Island. We observed that communities from a 98 °C fumarole were significantly enriched in genes related to hyperthermophilic (e.g. reverse gyrase, GroEL/GroES and thermosome) and oxidative stress responses, as well as genes related to sulfate reduction, ammonification and carbon fixation. Communities from <80 °C fumaroles possessed more genes related osmotic, cold- and heat-shock responses, and diverse metabolic potentials, such as those related to sulfur oxidation and denitrification, while glacier communities showed abundant metabolic potentials mainly related to heterotrophy. Through the reconstruction of genomes, we were able to reveal the metabolic potentials and different survival strategies of underrepresented taxonomic groups, especially those related to Nanoarchaeota, Pyrodictiaceae and thermophilic ammonia-oxidizing archaeal lineages.

Gyrokinetic benchmark of the electron temperature-gradient instability in the pedestal region

Transport from turbulence driven by the electron temperature-gradient (ETG) instability is likely a major source of electron heat losses through the pedestal. Due to extreme gradients and strong shaping, ETG instabilities in the pedestal are distinct from those in the core, having, for example, multiple branches (toroidal and slab) in different wavenumber ranges. Due to its importance for pedestal transport, and its rather exotic character, a rigorous multi-code benchmarking exercise is imperative. Here, we describe such an exercise, wherein we have carried out a detailed comparison of local linear pedestal ETG simulations using three gyrokinetic codes, CGYRO, GEM, and GENE and testing different geometric parameters (such as circular, Miller, and equilibrium EFIT geometry). The resulting linear frequencies, growth rates, and eigenfunctions show very good agreement between the codes in the three types of employed geometries. A nonlinear benchmark between CGYRO and GENE is also described, exhibiting good agreement (a maximum of 20% difference in the heat fluxes computed) at two locations in the pedestal. This lays the foundation for confidently modeling ETG turbulence in the pedestal.

Prediction of marginal rock mass stability in clays of Quaternary deposits including the effect of filtration reservoir by the example of the Bachat coal mine

Introduction. During opencast mining, the development of mine workings in clays of Quaternary deposits is often accompanied by stability loss. As a rule, the reason for the development of geomechanical processes 46 "Izvestiya vysshikh uchebnykh zavedenii. Gornyi zhurnal". No. 3. 2021 ISSN 0536-1028 is the mismatch between the accepted geometry and physical-mechanical characteristics of soils. In case strength characteristics and moisture content are strongly related in the conditions of lacking water saturation sources, slopes remain stable for a long time. However, in the case of water saturation, soils change to plastic or liquid consistency, and the strength properties are reduced. In engineering practice, to prevent hazardous geomechanical processes, electrophysical methods are applied that make it possible to build the boundaries of soil moisture anomalies through electrical contrast. In the instances when the water-saturated strata occurrence depth and thickness is known from drilling and vertical electrical sounding data, electrical profiling makes it possible to promptly determine the variability of these characteristics of the anomaly. The authors proposed an algorithm of water-saturated strata thickness variability determination from the point of electrical profiling. Research aim is to predict the stability of the marginal rock mass in clays of Quaternary deposits, taking into account the effect of filtration reservoirs by combining engineering-geological databases and geophysical measurement results based on the 3D geological-geophysical model. Methodology includes the analysis of the engineering-geological databases and geophysical measurement results. Results. A 3D geological-geophysical model of the marginal rock mass with the boundaries of the watersaturated stratum was built from the results of the research to predict the stability of the marginal rock mass’s actual position. Slope stability analysis established the following: at design sections О3у3–О5у5 after deformation, retaining forces exceed shearing forces significantly (safety factor) because the weight of the base wedge grows due to landslide masses; potential landslide hazard area is associated with the design section О1у1, which is due to smooth fall of the stability factor from 1.38 (section О2у2) to 1.06, close to ultimate. Conclusions. For the extension of the marginal rock physical-mechanical properties variation it is appropriate to apply the method of electrical prospecting (sounding and profiling) determining watersaturated areas by local negative anomalies of effective electrical resistivity and establishing the function of loose Quaternary deposits thickness variation by the inversion of electrical profiling graphs with the use of the least square procedure and the golden section method. If landslide hazard areas are vast, the variation of the stability factor design values, which were determined based on 3D geological-geophysical models, may possess the non-monotonic character with several extreme values and significant gradients. For that reason, it is appropriate to carry out computerized analysis with a cyclic extension of the most hazardous areas by the coordinate of the profile and the direction of the design section in a plan.

Non stretching NMO (Normal-Moveout) correction with DTW (Dynamic Time Warping) algorithm, study case: shallow target seismic

Normal Move Out (NMO) Correction using Common Mid-Point (CMP) data based on shallow target seismic. It has several problems for NMO correction. This constraint is caused by changes in extreme velocity gradients, resulting in less optimum value shallow target Common Mid-Point (CMP). The increased velocity causes a stretch in the Normal moveout (NMO) process which can reduce the S/N ratio. To minimize the stretch effect on NMO processing, we use a dynamic time warping algorithm analysis seismic signal with dynamic time warping algorithm based calculation time shift at time series sequence. The results of the NMO-DTW show that there is no change phase and frequency in the trace seismic with the far offset. Because algorithm calculation is based on the initial trace on CMP.

Insight into TiN inclusion induced pit corrosion of interstitial free steel exposed to aerated NaCl solution

Abstract The mechanism of step-like corrosion pit induced by TiN inclusion in Ti-stabilized interstitial free steel was systematically investigated. There was neither micro-crevice nor local stress in the steel matrix adjacent to the TiN inclusion, but a significant Volta potential difference was detected between the conductive TiN and steel matrix. The corrosion pits induced by the TiN inclusion had a step-like structure, composed of an inner pit and a shallow ring-like corroded region (RCR). Three stages, initiation, transition, and propagation stages, involved in the formation of the step-like corrosion pits were observed. The three stages were manifested with the initiation of inner pit, the deepening of inner pit, and RCR formation, respectively. The inner pit was triggered by the Volta potential difference in the initiation stage. In the transition stage, the extreme gradients of H+ and Cl− occurred through the hydrolysis of Fe2+ and electromigration of Cl− in the deepening inner pit. Finally, the extreme gradients of aggressive ions between the inner pit and NaCl bulk solution resulted in the formation of RCR surrounding the inner pit in the propagation stage.

In-Situ Calibrated Modeling of Residual Stresses Induced in Machining under Various Cooling and Lubricating Environments

Although many functional characteristics, such as fatigue life and damage resistance depend on residual stresses, there are currently no industrially viable ‘Digital Process Twin’ models (DPTs) capable of efficiently and quickly predicting machining-induced stresses. By leveraging advances in ultra-high-speed in-situ experimental characterization of machining and finishing processes under plane strain (orthogonal/2D) conditions, we have developed a set of physics-based semi-analytical models to predict residual stress evolution in light of the extreme gradients of stress, strain and temperature, which are unique to these thermo-mechanical processes. Initial validation trials of this novel paradigm were carried out in Ti-6Al4V and AISI 4340 alloy steel. A variety dry, cryogenically cooled and oil lubricated conditions were evaluated to determine the model’s ability to capture the tribological changes induced due to lubrication and cooling. The preliminarily calibrated and validated model exhibited an average correlation of better than 20% between the predicted stresses and experimental data, with calculation times of less than a second. Based on such fast-acting DPTs, the authors envision future capabilities in pro-active surface engineering of advanced structural components (e.g., turbine blades).

Extreme gradients in CO2 losses downstream of karstic springs.

Rivers are significant sources of CO2 to the atmosphere, and karstic watersheds are particularly important in this respect due to their large availability of inorganic carbon. This study examines characteristics of dissolved inorganic carbon (DIC) and excess partial pressures of CO2 (epCO2) in the source springs and headwaters of four watersheds in a Central European karstic region, via dissolved inorganic carbon concentration and stable carbon isotope measurements. Our results show the most 13C-depleted δ13CDIC values at the source springs, which become rapidly enriched downstream due to CO2 degassing. Concurrently, epCO2 values, while consistently in excess of atmospheric concentrations at the spring sources, show decreases of up to 92% within only 50m downstream distance. In conjunction with the large observed flux estimates of up to 88g C m-2day-1, these findings suggest that karstic springs are major CO2 sources to the atmosphere. Because headwater streams constitute the bulk of the surface area of most watersheds, they may provide a disproportionately large contribution to CO2 effluxes in carbonate-dominated basins, in which source springs play a particularly important role.

Incorporation of GTR (generation–transport–recombination) in semiconductor simulations

With the emergence of phase change memory, where the devices experience extreme thermal gradients (∼100 K/nm) during transitions between low and high resistive states, the study of thermoelectric effects at small scales becomes particularly relevant. We had earlier observed asymmetric melting of self-heated nano-crystalline silicon micro-wires, where current densities of ∼107 A/cm2 were forced through the wires by 1 μs, ∼30 V pulses. The extreme asymmetry can be explained by the generation of considerable amount of minority carriers, transport under the electric field, and recombination downstream, a heat transfer process we termed as generation–transport–recombination, which is in opposite direction of the electronic-convective heat carried by the majority carriers. Here, we present a full semiconductor physics treatment of this carrier-lattice heat transport mechanism and the contribution of the minority carriers on the evolution of the melt–solid interface, which can be applied to various high-temperature electronic devices.

Antarctic Water Tracks: Microbial Community Responses to Variation in Soil Moisture, pH, and Salinity

Ice-free soils in the McMurdo Dry Valleys select for taxa able to cope with challenging environmental conditions, including extreme chemical water activity gradients, freeze-thaw cycling, desiccation, and solar radiation regimes. The low biotic complexity of Dry Valley soils makes them well suited to investigate environmental and spatial influences on bacterial community structure. Water tracks are annually wetted habitats in the cold-arid soils of Antarctica that form briefly each summer with moisture sourced from snow melt, ground ice thaw, and atmospheric deposition via deliquescence and vapor flow into brines. Compared to neighboring arid soils, water tracks are highly saline and relatively moist habitats. They represent a considerable area (∼5–10 km2) of the Dry Valley terrestrial ecosystem, an area that is expected to increase with ongoing climate change. The goal of this study was to determine how variation in the environmental conditions of water tracks influences the composition and diversity of microbial communities. We found significant differences in microbial community composition between on- and off-water track samples, and across two distinct locations. Of the tested environmental variables, soil salinity was the best predictor of community composition, with members of the Bacteroidetes phylum being relatively more abundant at higher salinities and the Actinobacteria phylum showing the opposite pattern. There was also a significant, inverse relationship between salinity and bacterial diversity. Our results suggest water track formation significantly alters dry soil microbial communities, likely influencing subsequent ecosystem functioning. We highlight how Dry Valley water tracks could be a useful model system for understanding the potential habitability of transiently wetted environments found on the surface of Mars.

Mixed Convection in Pipe and Duct Flows With Strong Magnetic Fields

Abstract An imposed strong magnetic field suppresses turbulence and profoundly changes the nature of the flow of an electrically conducting fluid. We consider this effect for the case of mixed convection flows in pipes and ducts, in which unique regimes characterized by extreme temperature gradients and high-amplitude fluctuations (the so-called magnetoconvective fluctuations) have been recently discovered. The configuration is directly relevant to the design of the liquid-metal components of future nuclear fusion reactors. This review presents the general picture of the flow transformation emerging from the recent studies, illustrates the key known facts, and outlines the remaining open questions. Implications for fusion reactor technology and novel experimental and numerical methods are also discussed.

Capturing Velocity Gradients and Particle Rotation Rates in Turbulence.

Turbulent fluid flows exhibit a complex small-scale structure with frequently occurring extreme velocity gradients. Particles probing such swirling and straining regions respond with an intricate shape-dependent orientational dynamics, which sensitively depends on the particle history. Here, we systematically develop a reduced-order model for the small-scale dynamics of turbulence, which captures the velocity gradient statistics along particle paths. An analysis of the resulting stochastic dynamical system allows pinpointing the emergence of non-Gaussian statistics and nontrivial temporal correlations of vorticity and strain, as previously reported from experiments and simulations. Based on these insights, we use our model to predict the orientational statistics of anisotropic particles in turbulence, enabling a host of modeling applications for complex particulate flows.

Statistical Modeling with a Hidden Markov Tree and High-resolution Interpolation for Spaceborne Radar Reflectivity in the Wavelet Domain

With the increasing availability of precipitation radar data from space, enhancement of the resolution of spaceborne precipitation observations is important, particularly for hazard prediction and climate modeling at local scales relevant to extreme precipitation intensities and gradients. In this paper, the statistical characteristics of radar precipitation reflectivity data are studied and modeled using a hidden Markov tree (HMT) in the wavelet domain. Then, a high-resolution interpolation algorithm is proposed for spaceborne radar reflectivity using the HMT model as prior information. Owing to the small and transient storm elements embedded in the larger and slowly varying elements, the radar precipitation data exhibit distinct multiscale statistical properties, including a non-Gaussian structure and scale-to-scale dependency. An HMT model can capture well the statistical properties of radar precipitation, where the wavelet coefficients in each sub-band are characterized as a Gaussian mixture model (GMM), and the wavelet coefficients from the coarse scale to fine scale are described using a multiscale Markov process. The state probabilities of the GMM are determined using the expectation maximization method, and other parameters, for instance, the variance decay parameters in the HMT model are learned and estimated from high-resolution ground radar reflectivity images. Using the prior model, the wavelet coefficients at finer scales are estimated using local Wiener filtering. The interpolation algorithm is validated using data from the precipitation radar onboard the Tropical Rainfall Measurement Mission satellite, and the reconstructed results are found to be able to enhance the spatial resolution while optimally reproducing the local extremes and gradients.

Complete genome sequence of Marinomonas arctica BSI20414, a giant antifreeze protein-producing bacterium isolated from Arctic sea ice.

Sea ice in the polar oceans is a dynamic and challenging environment for life to survive, with extreme gradients of temperature, salinity and nutrients etc., as well as formation of ice crystals. Bacteria surviving in sea ice attract broad attention from academia and industry, due to fascinating mechanisms for adaptation. Here we described the complete genome sequence of Marinomonas arctica BSI20414, isolated from Arctic sea ice. The strain tolerated high salinity and low temperature. Genetic features commonly related to adaptation to oxidative stress, osmotic stress and cold stress were detected in the genome. In addition, a large adhesion protein containing a putative antifreeze protein (AFP) domain was detected in the genome, similar with the giant AFP MpIBP from M. primoryensis. The presence of the putative AFP could facilitate M. arctica BSI20414 to bind to sea ice for favorable conditions and protect it from freezing. The genome sequence and the AFP reported here can provide insights into adaptation to sea ice and can be explored further for biotechnological applications.

Extreme dissipation and intermittency in turbulence at very high Reynolds numbers.

Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation probability density function (PDF) based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers, these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume-weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds numbers, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.

Adaptation and molecular evidence for convergence in decapod crustaceans from deep-sea hydrothermal vent environments.

Hydrothermal vents are unique deep-sea environments exhibiting extreme temperature gradients and toxic concentrations of H2 S that limit the growth of biological communities. Notably, some decapod crustaceans are the dominant organisms inhabiting these environments, and share similar phenotypic and physiological traits, such as white body coloration and chemosynthetic capacity. However, a lack of genomic information has precluded an understanding of these convergent phenotypes. Here, comparative transcriptomic analyses were performed in 14 decapod species, including four deep-sea hydrothermal vent species and 10 shallow-water relatives. Phylogenetic analysis suggested that the four deep-sea species stemmed from different ancestors despite being geographically close, and therefore their similar traits were probably the product of convergent evolution rather than lineal inheritance. A total of 391 positively selected genes, 109 parallel substituted genes and 33 significantly expanded gene families were identified in the deep-sea decapods. Among these, only the SNARE interactions in vesicular transport pathway was significantly enriched, with both positively selected genes and parallel substituted genes, suggesting that specific macromolecule transport might be a strong convergent evolution trait in deep-sea decapods. Furthermore, many genes involved in protein synthesis, processing and energy metabolism were detected under convergent evolution, suggesting a role for adaptive evolution in association with a specific metabolic pathway in response to chemosynthetic nutrition patterns. Moreover, our study suggests that convergently evolved white body colour might have resulted from the contraction of the crustacyanin gene family and the low content of astaxanthin in the body of deep-sea decapods. Therefore, this study provides valuable genetic evidence for convergent evolution in deep-sea decapods.

Monitoring Intense Oceanic Fronts Using Sea Surface Roughness: Satellite, Airplane, and In Situ Comparison

AbstractSea surface roughness is affected by surface current gradients, which provides a means of monitoring from satellite sharp oceanic fronts. This paper is the second report of an experiment designed to compare observations of sea surface roughness and surface currents at an unprecedented accuracy, owing to the conjunction of numerous deployed drifters and roughness instruments. About 200 drifters sampled a thin 10 km elongated submesoscale front, also monitored by a high density of roughness instruments: satellite synthetic aperture radar, satellite, and airborne multiangle sunglint radiometers. The first paper focused on the retrieval of the current gradient direction (convergence and cyclonic vorticity) at the front, using roughness observations at multiple angle from airplane. This second paper focuses on the retrieval of the current gradient magnitude and scale, using roughness observations at different scales, from airplane and from satellite. Two main results are obtained: (i) Trajectories of selected drifters show that the front is only 50 m wide and unambiguously exhibits convergence and cyclonic vorticity up to 100f (with f the Coriolis frequency). This far exceeds previously documented values for submesoscale deep ocean fronts. (ii) Correct estimation of such extreme current gradients using surface roughness hinges on instruments with sufficiently high spatial resolution. Lower‐resolution roughness sensors can still detect the front, as demonstrated from observations and a simplified model, but cannot properly estimate the current gradient magnitude and the frontal width. Those results provide guidelines for monitoring intense current gradients from space using sea surface roughness.

Cooling dynamics of two titanium alloys during laser powder bed fusion probed with in situ X-ray imaging and diffraction

Metal parts produced by laser powder bed fusion (LPBF) additive manufacturing exhibit characteristic microstructures comparable to those observed in laser welding. The primary cause of this characteristic microstructure is rapid, localized heating and cooling cycles, which result in extreme thermal gradients where material solidification is followed by fast cooling in the solid state. The final microstructure and mechanical performance are also influenced by pore formation caused by melt pool fluid dynamics. Here, we use high speed, in situ X-ray diffraction to probe the kinetics of cooling and solid-solid phase transitions after laser melting in two aerospace titanium alloys: Ti-6Al-4V, an α + β alloy; and Ti-5Al-5V-5Mo-3Cr, a near-β alloy. We complement these diffraction studies with in situ X-ray imaging to probe melt pool dynamics and pore formation. From these two complementary probes, we quantify pore formation during melting and the subsequent microstructural evolution as the material rapidly cools after solidification. These results are critical for understanding defect formation and residual stress development in different titanium alloys under LPBF conditions and can help inform process models to predict final part performance.

Control selection for the assessment of protected areas in the Hengduan Mountains: A case study in Yunlong Tianchi National Nature Reserve, China

To assess whether a forest protected area (PA) is effective in preventing deforestation, it is common to compare the deforestation rate inside the PA with that of its surrounding area, defined using a buffer zone of a certain distance from the PA boundary. However, this methodology is often problematic for PAs located in mountainous regions because the resulting buffer area may present very different environmental features such as topography, introducing significant bias in the final assessment. We present a new approach to address these issues, based on the assumption that the control areas that best represent a given PA in terms of similarity are located along the same mountain ridge. The proposed approach is compared with commonly used methods (fixed buffers surrounding the PA), by taking the Yunlong Tianchi Nature Reserve located in the Hengduan Mountains of China, as a case study. The results showed that elevation, slope, and topographic position index of the PA were more similar to the control area defined using our approach than those defined using a fixed buffer of 3 km and 10 km. Moreover, when performing a covariate matching analysis with the aim to pair highly similar sub-samples of the PA with those of control areas, a greater number of pairs was found with our control area than the others. These findings demonstrate how our approach is able to define a control area more comparable with its corresponding PA then traditional methods. The proposed approach is particularly suitable for those mountainous regions characterized by extreme elevational gradients hosting a high diversity of landforms, vegetation, and climatic patterns coexisting in a relatively restrained area.

Quantifying microscale drivers for fatigue failure via coupled synchrotron X-ray characterization and simulations

During cyclic loading, localization of intragranular deformation due to crystallographic slip acts as a precursor for crack initiation, often at coherent twin boundaries. A suite of high-resolution synchrotron X-ray characterizations, coupled with a crystal plasticity simulation, was conducted on a polycrystalline nickel-based superalloy microstructure near a parent-twin boundary in order to understand the deformation localization behavior of this critical, 3D microstructural configuration. Dark-field X-ray microscopy was spatially linked to high energy X-ray diffraction microscopy and X-ray diffraction contrast tomography in order to quantify, with cutting-edge resolution, an intragranular misorientation and high elastic strain gradients near a twin boundary. These observations quantify the extreme sub-grain scale stress gradients present in polycrystalline microstructures, which often lead to fatigue failure.