Thickness Of Zone Research Articles

Comparing Recovery Volumes of Steady and Unsteady Injections into an Aquifer Storage and Recovery Well

Aquifer Storage and Recovery (ASR) can involve injecting available surface water into an unconfined aquifer and then extracting it to provide secondary water for irrigation. This study demonstrates a method for evaluating the appropriateness of steady injection versus unsteady injection for an assumed situation. In design, it can be important to affect the transient: the proportion of the injected water that would be subsequently extracted (versus that remaining in the aquifer) and the proportion within the extracted water that would be an injectate (versus ambient groundwater). These proportions can be predicted from the predicted value of an ASR well’s Recovery Effectiveness (REN)—the time-varying proportion of injectate that is extracted subsequently from the same fully penetrating well. Applying the demonstrated procedure with appropriately detailed data and simulation models can predict the REN values resulting from steady versus unsteady injection, followed by steady extraction. For convenience in displaying and computing REN, the injectate was assumed to have a 100 ppm conservative solute concentration. For this demonstration, a homogenous isotropic unconfined one-layer aquifer was assumed. The scenarios involved steady or unsteady injection for 61 days via a fully penetrating ASR well. Then, 91 days of steady pumping led to the extraction of a total volume equal to that injected. For the assumed hydrogeologic data—31 years of Salt Lake City, Utah, rainfall data and estimated captured runoff—the results show that steady injection is more likely to cause a predictable REN but might not cause a higher REN than daily varying injection of the same total volume. Assuming different runoff or hydrogeologic flows would lead to different REN values. Steady injection causes a predictable groundwater mound and can assure a sufficient vadose zone thickness for overlying plants. Augmentation and storage of captured rainwater can help to provide a steady injection rate. For a situation that requires REN management, appropriate simulations can help water managers design ASR systems that will achieve REN goals and increase sustainable groundwater availability.

Significant changes of area, length and terminus of Sikkim Himalayan glaciers within the Kanchenjunga national park from 1990 - 2022

In this study, we have investigated four glaciers, namely Zemu, Talung, Alukthang and Rathong within Kanchenjunga national park. This study evaluates physical and morphometric parameters (area, length, perimeter, area of accumulation zone, ablation zone length, snout position, thickness and specific mass balance) of multiple glaciers and to ascertain the poorly understood glaciers of western Sikkim region under Kanchenjunga national park. The principal objective of this research is to find out the changes of glacial mass and other physical parameters of the selected glaciers using multi sources digital elevation model data.Various techniques of statistics, including Mann-Kendall and Sen’s slope tests have been applied at different confidence interval. We have identified that climate change is responsible for the alterations of the physical characteristics of the glaciers. Result shows that during the study period, Zemu glacier has faced highest amount of deglaciation in terms of area (20.79 sq.km) along with maximum 30 meter elevation reduction, 24m increase of snout elevation and 200m retreat of terminus. Furthermore, it is observed that terminus of the each selected glaciers retreated during the study period. Rathong experienced maximum retreat rate, approximately 550m, and it is accompanied by a notable 163% increase in the ablation zone. Alukthang and Talung reduced their areas 0.56 and 4.06 sq.km respectively, along with 2.75m and 9.10m thickness respectively. Maximum 36.39m/y-1 flow rate has been observed over Zemu glacier. The flow rate of Talung, Rathong and Alukthang glacier is 26.4m/y-1, 34.1m/y-1, and 23.7m/y-1 respectively.

Magmatic activity in incipient continental break-up as revealed by coupling melt and fluid inclusions

Abstract Deciphering deep magmatic processes driving the onset of continental break-up is fundamental to constrain our understanding of plate tectonics. The East African Rift System (EARS) is the only currently active system on Earth to study distinct stages of rift evolution. We present a coupled analysis of melt and fluid inclusions in the Virunga Volcanic Province (VVP) offering an unprecedented insight into the dynamics of incipient rifting and its evolution. Our study highlights that melting of distinct metasomes in the deep lithosphere is a common feature of immature rifts. In the VVP, it leads to the emission of nephelinitic and basanitic melts at Nyiragongo and Nyamulagira volcanoes, respectively. Additionally, the chemical composition of melt and fluid inclusions supports the identification of another magmatic series in the area. Related alkali basaltic melts would be produced by contemporary melting of a less enriched domain in the upper lithosphere, more classically documented in mature rifts. Various extents of mixing and crystallisation of these three distinct magmatic series occur in the lower crust beneath the VVP where the barometric estimates are consistent with the presence of a thick seismic low velocity zone (LVZ). The involvement of alkali basaltic melts in the regional magma production could be also detected in the spread of gas emissions in the rift valley and in the fumaroles of the main active volcanoes. Melting of the corresponding mantle domain is an added source of gas release that may largely contribute to CO2 emissions along the EARS.

Advanced Scanning Technology for Volume Change Measurement of Residual Soil

Weathering processes of rocks lead to the formation of residual soil layers, which are typically characterized by a deep groundwater table and a thick unsaturated zone. Hence, the calculation of a slope’s safety factor under the influences of climatic circumstances is a function of unsaturated characteristics, such as the soil–water characteristic curve (SWCC). To determine the SWCC, the volume of the soil specimen must be determined in order to compute the void ratio and degree of saturation. The drying processes of the soil specimen led to uneven soil volume change during laboratory SWCC testing, demanding the development of a soil shrinkage curve. Several methods for measuring soil volume change have been developed over the years. However, there are significant limitations, and it is rarely used due to the difficulty linked to accurately measuring the soil volume during drying processes. In this study, a revised scanning approach is developed to evaluate residual soil volume change utilizing 3D scanning technology. The proposed method is applied in a case study on residual soil from the Old Alluvium in Singapore. The laboratory data and analysis results suggested that 3D scanning technology should be required to provide a correct estimation of the air-entry value of soil.

Anatomy of a deep Piedmont critical zone: Evaluating hypotheses on regolith depth controls through comparison of ridge and valley boreholes

AbstractControls on the physical and chemical architecture of the subsurface critical zone are somewhat controversial, with multiple hypotheses proposed to account for variations in the depth of weathering between sites, and with landscape position at a site. In the Piedmont region of the Mid‐Atlantic US weathering of crystalline bedrock has been observed to extend tens of meters below the surface and groundwater in a'bow‐tie’ shape – i.e. weathering extends to lower elevations below ridges than below channels. The chemical and physical structure of a hillslope transect in the Maryland Piedmont was explored with a 45 m borehole in the ridge, as well as shallow bedrock boreholes at the toe of the slope and valley. Chemical weathering fronts were characterized using elemental abundances and mineralogical analysis. The ridge borehole did not extend deeper than the chemically and physically weathered rock. Surface and borehole geophysics and density measurements were used to characterize the weathered rock and saprolite. Na and Ca results suggest that plagioclase feldspar weathering is similar between samples collected from 45 m under the ridge and 2.2 m under the valley bottom. A narrow Fe oxidation garnet weathering front co‐insides with the transition from weathered bedrock to saprolite, suggesting that this reaction may generate initial saprolite porosity. Muscovite weathering co‐occurs with complete depletion of plagioclase a few meters above the Fe oxidation front. These nested weathering fronts in the saprolite appear to follow a subdued version of the surface topography. The location and shape of the nested saprolite weathering fronts may be controlled by the feedback between the transport of reactants and solutes and reaction‐generated porosity, consistent with the conceptual “valve” hypothesis. Differing dominant control mechanisms on deep bedrock weathering and saprolite initiating reactions may explain the thickness and structure of the critical zone at our site.

Sequential irradiation does not improve fatigue crack propagation resistance of human cortical bone at 15 kGy

Sequential irradiation has been advocated for mitigating the reduction in fatigue properties of tendon compared to a single dose. However, to our knowledge, its capability of mitigating fatigue losses in bone is unknown. Recently, we reported that sequential irradiation did not mitigate losses in high-cycle S-N fatigue life of cortical bone at 15 kGy; however, it is unclear if sequential irradiation provides a benefit to fatigue crack propagation resistance. Our previous study also showed that radiation-induced collagen chain fragmentation and crosslinking increased from 0 to 15 kGy, suggesting that both likely contribute to the reduction in high-cycle S-N fatigue life within this dose range. Our objectives were: 1) to evaluate the fatigue crack propagation resistance of cortical bone and the effect of radiation on fracture plane damage zone thickness (DZT) at the crack tip in the dose range of 0–15 kGy, and 2) to evaluate whether sequential irradiation at 15 kGy mitigates the loss of fatigue crack propagation resistance of cortical bone compared to a single irradiation dose. Compact tension specimens from four male donor femoral pairs (ages 21–61 years old) were divided into 5 treatment groups (0 kGy, 5 kGy, 10 kGy, 15 kGy, and a 15 kGy sequential irradiation dose of 5 kGy sequentially irradiated with 10 kGy) and subjected to fatigue crack propagation testing (n = 3–4 specimens per group) where fatigue crack growth rate da/dN and cyclic stress intensity factor ΔK were determined. Following testing, specimens were bulk stained in basic fuchsin, embedded in poly(methylmethacrylate), sectioned, and mounted on acrylic slides to evaluate fracture plane DZT at known crack lengths. Sections were then imaged with a fluorescence microscope, and fracture plane DZT was measured using ImageJ (n = 3–4 specimens per group) and analyzed as a function of ΔK. We observed a decrease in fatigue crack propagation resistance at 15 kGy compared to doses of 10 kGy or lower (p ≤ 0.013). Fracture plane DZT decreased overall with increasing radiation dose from 0 to 15 kGy. Sequential irradiation offered no improvement in fatigue crack propagation resistance (p = 0.98). Radiation-induced collagen chain fragmentation and crosslinking in this dose range likely contribute to a decrease in energy dissipation capability with increasing radiation dose. Other alternative radiation sterilization methods besides sequential irradiation may be warranted to mitigate radiation-induced tissue damage and extend the functional lifetime of structural cortical bone allografts.

HISTOLOGICAL CHANGES IN THE RAT SPLEEN IN THE EARLY STAGES OF EXPERIMENTAL STREPTOZOTOCIN-INDUCED DIABE-TES MELLITUS

Diabetes is a systemic disorder that has a significant impact on a number of different organ systems within the body. Studying changes in the spleen in diabetic rats aids in understanding these changes and their effect on immune function. The objective of the study is to investigate the characteristics of morphological changes in the structural components of the spleen in the early stage of experimental diabetes.Results. Morphological changes in the spleen during the early stages of streptozotocin-induced experimental diabetes mellitus were observed. Diabetes was induced by a single intraperitoneal injection of streptozotocin. Histological examination of the spleen was conducted 14 and 28 days after diabetes induction. In healthy rats, the spleen exhibited a normal structure with a clear distinction between red and white pulp. Morphometric analysis showed that lymphoid nodules had a diameter of (445.92±12.6) μm and a marginal zone thickness of (76.22±5.12) μm. After 14 days of experimental diabetes, histological preparations revealed reduced lymphoid nodules of white pulp with a diameter of (435.83±14.28) μm and germinal centers (139.97±5.74) μm. After 28 days, lymphoid nodules further decreased to (392.37±10.29) μm, and germinal centers - to (125.93±5.71) μm. The width of the periarterial lymphoid sheaths decreased to (67.91±3.62) μm, indicating early changes in T-cell zones.Conclusion. During the initial stages of diabetes mellitus in experimental settings, notable structural modifications occur in the spleen. Specifically, there is a reduction in the size of lymphoid nodules, germinal centers, and various zones of the spleen, as well as a decrease in the density of lymphocytes. These alterations may suggest a severe immunological dysfunction in rats used for experimentation.

Effects of human and tectonic activities on groundwater in the upper Yellow River terraces of the loess Plateau

Terraces of the Yellow River are among the most crucial geomorphological landforms pertaining to human survival on the Loess Plateau. After more than half a century of surface flood irrigation, rapid rises in groundwater levels have led to frequent geological disasters, causing a rapid short-term evolution of Yellow River terraces, and an increasingly serious contradiction between this rapid evolution and human survival. However, the process by which water transfers through the thick loess vadose zone and causes a rapid groundwater response within months or years remains controversial. Using the Heitai platform of Yellow River terrace IV as an example, we found, on the basis of regional geological surveys, that at least 112 tectonically-induced cracks have developed in this area. We contend that the superimposed effects of earthquake ground motions from historical and ancient earthquakes since the Late Pleistocene have driven the development of such densely distributed cracks in the loess layer. These cracks, together with a series of fault planes generated by NE-directed extrusive stress at the regional scale, constitute a potential network of preferential channels for water transport within the Heitai platform. Combined with the results of a large-scale in situ ponding test and electrical resistivity tomography, we found that this network of cracks helps to establish catchment areas within the loess layer, thereby increasing soil saturation at a more extensive spatial scale, which may then increase the overall movement velocity of the wetting front. We semi-quantified the efficiency of the crack network in enhancing the recharge of surface water to groundwater, and suggested that the impact of human and tectonic activities substantially shortens the response time of groundwater to surface water, with the reduced time far exceeding one order of magnitude. The results of a field investigation of structural traces and terrace groundwater after the Ms 6.2 Jishishan earthquake on 18 December 2023 further emphasize that a causal mechanism of human and tectonic activities leading to the rapid short-term evolution of groundwater distribution patterns may be universally applicable to all Yellow River terraces on the Loess Plateau. This study mitigates the long-standing controversy concerning the mode of surface water infiltration, including piston flow and preferential flow, and the infiltration medium by which rapid surface water recharge to groundwater occurs in loess areas over short time periods.

To Investigate the Impact of Land Use Change on the Potential Groundwater Recharge on Hillslope With Deep Loess Deposits

ABSTRACTAccurately estimating groundwater recharge in hilly areas with limited water and thick vadose zones is challenging. This study investigated the impact of land use changes on groundwater recharge at a hillslope scale of Yuanzegou Watershed in China's Loess Plateau. Three adjacent hillslopes were selected for three different land uses: arbor (jujube, Ziziphus jujuba Mill.), subshrub (native grass, Artemisia gmelinii), and crop (millet, Setaria italica). Soil cores (as deep as 10–16/18 m) were collected at each of the three landscape positions on a hillslope. Reported tritium profiles in the watershed were used to estimate the net chloride input into vadose zone on hillslope associated with inverse chloride mass balance (CMB) method/chloride accumulation method (CAM). Soil water content and chloride profiles in the study were measured to determine recharge rates at each landscape position beneath different vegetation types. For the first time, we evaluated the actual chloride input into vadose zone on hillslopes as 540.2 ± 23.8 mg m−2 yr.−1, excluding the impact of runoff. Then, estimated recharge rates ranged from 42.7 ± 3.5 to 62.4 ± 4.7 mm yr.−1, consistent with nearby studies. Results showed that groundwater recharge does not change with landscape position except for higher value on upslope beneath subshrub hillslope. In contrast, groundwater recharge did significantly reduce by 12.9% ± 5.4% and 26.5% ± 4.5% after conversion from cropland to subshrub/arbor on the hillslope, respectively. Our findings contribute to understanding the ecohydrological effects of land use changes on groundwater recharge on hillslope and help to select suitable afforested vegetation for greening efforts in water‐limited hilly areas, with a priority on groundwater safety.

Can Large Strains Be Accommodated by Small Faults: “Brittle Flow of Rocks” Revised

AbstractBrittle deformation in the upper crust is thought to occur primarily via faulting. The fault length‐frequency distribution determines how much deformation is accommodated by numerous small faults versus a few large ones. To evaluate the amount of deformation due to small faults, we analyze the fault length distribution using high‐quality fault maps spanning a wide range of spatial scales from a laboratory sample to an outcrop to a tectonic domain. We find that the cumulative fault length distribution is well approximated by a power law with a negative exponent close to 2. This is in agreement with the earthquake magnitude‐frequency distribution (the Gutenberg‐Richter law with b‐value of 1), at least for faults smaller than the thickness of the seismogenic zone. It follows that faulting is a self‐similar process, and a substantial fraction of tectonic strain can be accommodated by faults that don't cut through the entire seismogenic zone, consistent with inferences of “hidden strain” from natural and laboratory observations. A continued accumulation of tectonic strain may eventually result in a transition from distributed fault networks to localized mature faults.

Seasonal changes in subsurface characteristics in the Lower Bengal Basin: Potential impacts on groundwater

The risk of groundwater depletion is most significant if anthropogenic withdrawals are high in regions where the subsurface characteristics do not favor surface water infiltration and natural recharge. However, such regions have not been identified systematically in the Indo-Gangetic basin, one of the most fertile alluvial aquifers in the world. This identification may be enabled by a study of how seasonal changes in subsurface characteristics affect groundwater levels. We conducted a resistivity survey in Nanoor block of the Lower Ganges Basin, where groundwater levels have declined steeply in recent decades, to determine how subsurface characteristics controlling infiltration and groundwater quality may change seasonally. Vertical Electrical Soundings (VES) using the Schlumberger electrode array were conducted over an 8 km² area with an electrode spacing of 180-200 meters during the pre-monsoon (April 2018) and post-monsoon (October 2018) seasons. Seasonal variations in the Dar- Zarrouk parameters: longitudinal conductance, transverse resistance, and the coefficient of anisotropy were evaluated. While the average longitudinal conductance remained unchanged across seasons, it increased in certain locations in post-monsoon, indicating potential risks of contamination from the surface. The transverse resistance significantly increased in the post-monsoon, suggesting reduced groundwater potential. Additionally, in some areas, the coefficient of anisotropy indicated increased compaction of overburden layers in the post-monsoon, suggesting decreased natural recharge potential. Finally, the thickness of the unsaturated zone increased significantly from pre-monsoon to post-monsoon, which may be attributed to groundwater withdrawal for irrigation during the Kharif cropping season. These results indicate that this region, heavily reliant on groundwater for irrigation, is characterized by subsurface properties that allow limited natural recharge potential. This study may provide a framework for managing groundwater resources in developing countries where anthropogenic withdrawals are likely to have a more significant impact on groundwater levels than reduced natural recharge due to changing rainfall characteristics.

Oxidation and interdiffusion behavior of NiAlY/AlCrTaTiZr coating on Fe–Cr alloy prepared by magnetron sputtering

An AlCrTaTiZr high-entropy alloy (HEA) as a diffusion barrier was prepared by sputtering to suppress interdiffusion across the NiAlY/Fe–Cr alloy interface. The oxidation and interdiffusion behavior of NiAlY coatings with and without the HEA diffusion barrier were investigated at 850 °C. The results indicate the oxidation mass gain of NiAlY and NiAlY/AlCrTaTiZr coatings were 0.45 and 0.39 mg cm−2 after 100 h, respectively. The thickness of the interdiffusion zone (IDZ) in the composite coating was thinner than that in the HEA-free layer. The HEA layer serves as an effective barrier against the interdiffusion between the NiAlY coating and the substrate, maintaining the high aluminium content in the coating and inhibiting the formation of brittle intermetallic phases in IDZ. Consequently, oxidation resistance of the composite coating is increased.

AHP and geospatial technologies for identifying groundwater exploration target regions in Dindigul, southern India

Recent advances in space technology are being widely utilized in resource mapping and management as they provide a high level of accuracy over a short duration and at a lower cost, when compared to traditional methods. Remote sensing and the geographical information system (GIS) play a vital role in collecting and analyzing information used to map resources and earth surface features. For example, anthropogenic activities and climate change affect the natural interaction between the surface and ground water making the monitoring and management of groundwater resources mandatory for future sustainable development. In this study, we attempt to identify the groundwater potential zones in the Dindigul district of Tamil Nadu, India using these emerging technologies. To map regions with groundwater potential, the analytical hierarchical process (AHP) was used to assign weights to all classes in each thematic layer based on groundwater-influencing factors. The sub-features of every parameter were also ranked, using a pairwise comparison method, based on the groundwater-influencing factors and expert knowledge. The parameters selected for the analysis were geology, geomorphology, soil, land-use/land-cover, drainage density, lineament density, slope, rainfall, thickness of top-soil, thickness of fractured zone, thickness of weathered zone, topographic wetness index, roughness and curvature. The weighted overlay analysis method was adopted for all the thematic layers, with technical support from the AHP for assigning weightages. The results were classified into five categories viz., very high, high, moderate, low, and very low potential zones, and used to prepare a groundwater potential map. This map revealed a nuanced distribution of groundwater potential across the district, with varying degrees of potentiality in different regions. Very high potential zones occupy a minimal area (0.07%) but are strategically located in areas characterized by high weathered zone thickness and conducive soil characteristics. High potential zones cover a significant area (22.33%) and are dispersed throughout the district, with specific concentrations in regions featuring highly fractured zones and favorable geological attributes. Moderate potential zones (35.12%) are primarily located in the northeastern part of the study area, while low and very low potential regions cover 19.56% and 22.92% of the study area. The low and very low potential zones appear particularly in hilly terrains, with unfavorable top soil and geological conditions. The validation of the groundwater potential zone (GWPZ) map using the annual average water level data demonstrates a substantial match (60.53%) between the identified groundwater conditions and actual well depths, affirming the reliability and significance of the findings from this study.

Gas hydrates on New Zealand’s Chatham Rise: An Indicator of Gondwanan Thermogenic Gas Expulsion?

High amplitude bottom simulating reflections (BSRs) interpreted in seismic reflection data are common proxy indicators for gas hydrates, while the spatial relationship of BSRs with fault systems can provide an indication for the source of gas bound within hydrates. The spatial correlation of fault zones with strong BSRs and thick free gas zones (FGZs) has sometimes been recognised as a common feature of thermogenic hydrate systems. We investigate the seismic stratigraphy and reflectivity of New Zealand’s Chatham Rise northwestern slope (CRNWS), which is a remnant section of the ancient East Gondwana subduction margin’s accretionary wedge. Seismic interpretation indicates the presence of a partially subducted, Cretaceous-aged sedimentary unit beneath the inactive, ∼6 km-thick East Gondwana accretionary wedge. Heat flow estimation and calculation of temperature profiles suggests that the ∼1–2 km-thick downgoing Mesozoic sedimentary sequence (MES) is situated within a thermal window conducive to thermogenic methane generation. As the downgoing MES may contain source rocks similar to the Glenburn Formation, a well-known thermogenic source, which is proposed to span the neighbouring Pegasus and East Coast Basins, we propose the presence of a sub-Gondwanan wedge thermogenic gas zone. Overlying the proposed Gondwanan thermogenic zone by ∼6–8 km, seismically-distinct shallow BSRs and hydrate-related features are interpreted spanning ∼1400 km2 of the CRNWS. BSRs often terminate against and are associated with deeply-rooted CRNWS faults, which penetrate the Gondwana wedge. These BSRs mark previously-undefined hydrate accumulations situated ∼50–100 km SW from the active Hikurangi subduction margin. We interpret the presence of thermogenic methane within the CRNWS hydrate zone, supplied from the ∼8–10 km deep downgoing MES by Gondwanan thrust faults, and BSR-proximal fault asperities. The close association of BSRs with a shallow, unit-bound polygonal fault complex may be further distributing free gas, up-dip across the CRNWS, resulting in concentrated hydrate accumulations and thick (∼100–150 m) FGZs.

Diminished retinal microcirculation in mild preeclampsia without obvious retinopathy in high-altitude native Tibetans by OCTA

BackgroundTo investigate the retinal microcirculation in mild preeclampsia (PE) without obvious retinopathy in high-altitude native Tibetans by optical coherence tomography angiography (OCTA). MethodsThis study enrolled 64 mild preeclamptic pregnant women without retinopathy (group PPW), 63 healthy pregnant women (group HPW), and 61 healthy non-pregnant women (group HNPW). All participants were high-altitude native Tibetans who underwent OCTA, retinal thickness (RT), vascular density (VD), perfusion density (PD) and foveal avascular zone (FAZ) parameters were measured in the macula. Differences in these parameters among the groups were compared, and the correlations of these parameters with blood pressure were evaluated. ResultsIn the entire macula, VD and PD were significantly lower in group PPW than in group HPW and HNPW (p < 0.05). In the subregions, VD was significantly different in fovea, parafovea and perifovea, PD was significantly different in parafovea and perifovea among the three groups (p < 0.05), the further pairwise comparisons showed VD and PD in parafovea and perifovea were lower in group PPW than in group HPW, and VD and PD in perifovea were lower in group PPW than in group HNPW (p < 0.05). RT and FAZ parameters did not differ among the groups (P > 0.05). VD and PD exhibited negative correlations with SBP and DBP (p < 0.05). ConclusionOCTA can objectively evaluate diminished microcirculation in mild PE without obvious retinopathy among high-altitude native Tibetans, and provide a crucial time window for early screening of PE-induced retinopathy.

Unnotched fatigue behavior of the laser powder bed fused and hot isostatic pressed Inconel 718 at 600 °C

The microstructure and mechanical properties of hot isostatically pressed (HIP) Inconel 718 additively manufactured using the laser beam powder bed fusion (LPBF) process were investigated at 600 °C, with emphasis on the high cycle fatigue behavior evaluated using the rotating bend fatigue tests, and elucidation of the role of γ” precipitate size on the fatigue resistance. Experimental results show that the unnotched fatigue strength (σf) of the peak aged alloy improves only by 7 % after HIP, as compared to that of the non-HIP peak aged alloy, despite a significant improvement in the ductility due to HIP. Over-aging the HIP alloy, however, led to a further enhancement (by ∼14 %) in σf. Fractographic analyses suggest that the fatigue crack initiation occurs from the intrusions and extrusions on the fracture surface of both versions of the aged alloy. Microstructural investigations reveal the presence of persistent slip bands (PSBs) with different morphologies in peak- and over-aged microstructures. A change in the deformation mechanism due to the size of precipitates was identified to be the reason for the formation of nano-grains (through dynamic recrystallization) within the PSBs of the alloy with a coarse γ” microstructure. In several {110} grains, ∼5 μm thick nanocrystalline grain zones formed on the specimen surface; they completely suppressed the formation of PSBs and enhanced the fatigue resistance of the HIP LPBF IN718 alloy in the over-aged condition.

Microstructure and mechanical properties of stainless steel 316L-Inconel 625 bimetallic structure fabricated by laser wire direct energy deposition

This study explores the laser wire direct energy deposition (LW-DED) process to manufacture bimetallic SS316L and Inconel 625 alloy. The microstructure and mechanical properties of as-printed SS316L, Inconel 625, and the bimetal were analyzed. Notably, the LW-DED bimetal exhibited superior mechanical properties and a robust metallurgical bond compared to wire arc additive manufacturing. The bimetallic interface demonstrated epitaxial grain growth, a columnar coarse grain structure, and a gradual transition with a zone thickness of 55 μm, as revealed by elemental mapping analysis. Electron backscatter diffraction (EBSD) analysis confirmed low angle grain boundaries leaning towards Inconel 625 deposition, ensuring uniform grain growth from SS316L to Inconel 625 with a consistent crystallographic direction. The EBSD analysis indicated a strong fabric texture with a <001> orientation towards the build direction. However, with increasing layer deposition, the morphology of δ-ferrite in SS316L transformed to skeletal, without interface defects and minimal laves phase. Higher layer deposition revealed the presence of laves phase, as observed in the SEM and EDAX analysis. Microhardness and nano-hardness measurements illustrated that the hardness values in the interfacial region fall between those of individual materials, showcasing a gradual transition at the interface. The tensile properties are higher in the Inconel 625, while SS 316L exhibits comparable properties to the bimetallic sample.

Spatial deformation prediction method of fractured rock tunnel based on quantified GSI and its application

Determining rock mass mechanical parameters and accurately predicting tunnel deformation during tunnel construction remain challenging tasks. This study introduces a novel approach to calculate the Geological Strength Index by integrating indoor rock mechanics tests with geometric data from three-dimensional dense reconstruction. We utilized the Hoek-Brown strength criterion to develop a theoretical model for predicting tunnel deformation in fractured rock masses. Case studies reveal that the average value of Geological Strength Index for the Xiamen highway tunnel’s surrounding rock is 44. With support from the lining structure equivalent to 0.002–0.02 times the initial in-situ stress, the plastic zone thickness decreased by approximately 50%, and radial displacement was reduced by about 40%. Enhancing the lining structure’s support pressure significantly reduces the plastic zone radius and radial displacement. As the Geological Strength Index decreases, the nonlinearity between support pressure and plastic zone radius becomes more pronounced, with a similar trend observed for the relationship between support pressure and tunnel radial displacement. The relative deviation between predicted and measured values did not exceed 1.69%. The method accurately captures the effects of rock fragmentation and tunnel construction on plastic zone formation and displacement, offering an effective approach for the rapid and secure assessment of rock tunnel excavation stability using digital technology.

Evaluating the productivity of basement rock aquifers for sustainable groundwater development in sub-Sahara Africa using borehole pumping experiments and geophysical data

Ensuring all-year-round groundwater availability in the basement complex regions of sub-Sahara Africa requires careful combinations of strategies for exploration, development, and management of groundwater resources. The productivity of the basement aquifer of sub-Sahara Africa, SSA, was evaluated in terms of the volume of water produced per unit time, the aquifer transmissivity, hydraulic conductivity, specific capacity, and the thickness of the water-bearing zones using a suit of data from borehole pumping experiments, geophysical surveys, and lithologic logs from Opaque Field in sub-Sahara Africa. Findings from the study have been used to classify the basement complex aquifers of sub-Sahara Africa into three categories: marginally productive, low productive, and moderately productive. Weathered and fractured zones were found to be bright spots for groundwater storage, and aquifer productivity correlates with topography and the thickness of the weather zones. Most of the boreholes located on the low topographic heights were found to have the highest groundwater discharge, transmissivity, and hydraulic conductivity. Further, the study showed that the popular models used for estimating aquifer properties are unsuitable for basement complex aquifers. The results of the models are exaggerated when compared to the pumping test results. Cases of dry holes or poorly performing wells in the basement complex terrain may be attributed to the exaggeration. Consequently, two new and novel quantitative models were proposed and tested for evaluating the productivity parameters of basement aquifers of SSA for optimal selection of sites for groundwater development. The aquifer productivity maps computed with the new quantitative models show striking similarities to those computed from the pumping tests results and confirmed the appropriateness of the new quantitative models. The appropriate pumping device, pump operation time, and installation depth were recommended for the boreholes producing groundwater from the three categories of aquifers identified in this study.

Effects of corneal epithelial remodeling on corneal asphericity after FS-LASIK and Trans-PRK: A prospective study.

To observe the changes in corneal epithelial thickness after FS-LASIK and Trans-PRK surgery and to investigate the impact of corneal epithelial remodeling on Q-value and HOA. In this prospective cohort study, 50 patients (100 eyes) underwent FS-LASIK and 45 patients (90 eyes) underwent Trans-PRK. Anterior segment OCT was used to measure the corneal epithelial thickness in different corneal zones (central zone: 0-2 mm; paracentral zone: 2-5 mm; and mid-peripheral zone: 5-6 mm) preoperatively and postoperatively at 1 week, 1 month, 3 months, and 6 months. The correlation between ΔCET in the superior, nasal, inferior, and temporal region at 6 months postoperatively and ΔQ and ΔHOA was analyzed. At 6 months postoperatively, the epithelial thickness increased in the central, paracentral, and mid-peripheral zones in FS-LASIK and Trans-PRK. Central epithelial thickness and different regions of the paracentral zone and mid-peripheral exhibited significant thickening (P < 0.001). In the para-central zone and mid-peripheral zone, the ΔCET in different regions after LASIK and Trans-PRK was positively correlated with ΔQ (P < 0.05) and ΔHOA (P < 0.05). After FS-LASIK and Trans-PRK, significant epithelial thickening was observed. Epithelial changes in different regions lead to different Q-values in different regions and have different effects on HOA. This has a certain guiding significance for the design of refractive surgery, and minimizing the increase of Q-value may improve the postoperative visual quality.