Transition Zone Research Articles

Utilization of construction and demolition waste in ultra-high performance concrete: Macro-micro properties and environmental impacts

To further improve the utilization of recycled fine aggregates (RFA) obtained from construction and demolition in ultra-high performance concrete (UHPC), this work aims to adopting the nano-silica (NS) to develop a UHPC incorporating RFA with high strength and low shrinkage. A series of experiment evaluation on the workability, compressive strength, autogenous shrinkage and resistance to chloride penetration of UHPC are conducted. The hydration products, pore structure, and microstructure of UHPC are analyzed using isothermal calorimetry, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry, respectively. Results indicate that the addition of RFA decreases the flowability and early compressive strength of UHPC. However, it effectively mitigates autogenous shrinkage and compensates for the later-stage strength loss. NS significantly enhances the early compressive strength and resistance to chloride penetration in UHPC containing RFA. The combined incorporation of 20 % RFA and 3 % NS leads to 65.6 % reduction in the autogenous shrinkage within 7 days, 12.1 % improvement in compressive strength and 16.5 % decrease chloride diffusion coefficient of UHPC specimens at 28 days. Furthermore, the synergistic effects of RFA and NS promote the cement hydration, reduce the porosity and further refine the pore structure, and improve the interface transition zone in UHPC. This provides valuable insights for advancing the development of environmentally sustainable which collaborative utilization of RFA and NS in the manufacture of UHPC with reducing carbon footprint.

Effect of curing regimes on mechanical properties and microstructure of engineered cementitious composites with full desert sand

To establish a curing regime that facilitates the rapid enhancement and stable progression of early-age strength and tensile ductility in engineered cementitious composites with full desert sand (DSECC), aligning with production efficiency, this study examines the effects of different curing regimes (standard curing, natural curing, 20℃ water curing, and 90℃ water bath curing) on DSECC 's the mechanical properties and microstructure. The findings indicate that 90℃ water bath curing is beneficial to enhance the mechanical properties of DSECC, and its early 7 days strength and tensile deformation capacity (up to 7.05 %) can reach or exceed the standard curing 28 days level. In the uniaxial tensile test, samples cured in 20℃ water exhibit increased crack widths and reduced crack numbers, resulting in a sharp decline in the ultimate tensile strain from 4.96 % at 14 days to 1.57 % at 28 days. Natural curing leads to regression in strength at 28 days. The microstructure analysis revealed that 90℃ water bath curing fostered the development of high-density C-S-H gel and the dissolution of desert sand, while preserving the integrity of the fibers, enhancing the fiber-matrix interface transition zone (ITZ). The pore characteristic parameters under 90℃ water bath curing are superior, which has a notable refinement of the DSECC matrix's pore size. 20℃ Water curing can make up for the defects caused by desert sand and improve the compactness of matrix-aggregate ITZ. Natural curing yields the lowest degree of matrix hydration, with porosity reaching as high as 41.90 %, and pores smaller than 50 nm accounting for only 8.97 %.

Tidal triggering of seismic swarm associated with hydrothermal circulation at Blanco ridge transform fault zone, Northeast Pacific

Seismicity associated with hydrothermal systems (e.g., submarine volcanoes, mid-oceanic ridges, oceanic transform faults, etc.) share a complex relationship with the tidal forcing and induced fluid flow process under different tectonic settings. The hydrothermal circulation drives the deformation at the brittle-ductile transition zone within a permeable brittle crust. Although the tidal loading amplitudes are too small to generate a brittle deformation, the incremental pressure exerted by the tidal loading can modulate the flow of hydrothermal fluid circulation and trigger the critically stressed faults or fracture zones. We present a compelling case of tidal modulation in seismicity along the Blanco Ridge Transform Fault Zone (BRTFZ), in the northeast Pacific. The strong diurnal and fortnightly periodicity has been observed in the deeper seismic swarm (7–15 km), whereas the shallow seismic swarm (0–7 km) does not exhibit any such tidal periodicity. The dominance of diurnal and fortnightly periodicity in the deeper seismic swarm is explained by the high amplitude tidal cycles providing additional stress on the fluid circulation at the crust-mantle boundary. Moreover, our robust statistical correlation of seismicity with tidal stress and resonance destabilization model under rate-and-state friction formalism suggests that the fault segments are conditionally unstable and more sensitive to periodic tidal stress perturbation.

Geochemical anomalies of hydrocarbon gases in bottom sediments of eostructures of the Laptev-Siberian transition zone of the East Arctic shelf

Geochemical anomalies of hydrocarbon gases in bottom sediments of eostructures of the Laptev-Siberian transition zone of the East Arctic shelf

Nano-micrometer scale characterization of PWSCC crack tips in the transition zone of 52M overlay and the implication to intergranular cracking

This study examines the microstructural characteristics of the primary water stress corrosion cracking (PWSCC) crack tip in the transition zone (TZ) of the 52 M overlay and its implications for intergranular cracking. In the TZ, the Cr content at grain boundaries near the fusion boundary (FB) is lower than those farther from the FB. Additionally, residual strain at grain boundaries near the FB is higher than that farther away, with the fine-grained zone around the FB showing higher local deformation than the surrounding columnar grains. Stress corrosion cracking (SCC) crack growth rate (CGR) test results indicate that the TZ showed certain SCC sensitivity, and the closer to the FB, the lower the SCC resistance. Analysis of the SCC crack tip found that the distinctive composition distribution of the 52 M overlay TZ, characterized by low Cr and high Fe near the FB, is prone to intergranular oxidation, thereby reducing SCC resistance. Conversely, higher Cr and lower Fe content at grain boundaries in the TZ farther from the FB form dense, Cr-rich oxides ahead of the crack tip that slow SCC crack growth, resulting in the diffusion of oxidation along the dislocation structure into the grains and forming a fibrous oxidation zone.

Repair of ordinary concrete using basalt fiber reinforced geopolymer: High temperature resistance and micro structure evolution of adhesive interface

Good bonding properties in the interfacial transition zone (ITZ) between the substrate and the repair material are critical to the success of the repair, and a good repair material can act as a protective layer to reduce the impact of fire on the structure. In this paper, Ordinary concrete (OP), geopolymer mortar (GP), and basalt fiber reinforced geopolymer mortar (GPb) were poured as the three repair materials on the roughened surface of the old substrate. The bonded specimens were exposed to temperatures of 23 °C, 200 °C, 400 °C, 600 °C and 800 °C for 1 h. The interfacial bond strength of the bonded specimens was tested by slant shear test, and the physical phase change of the repair material and the microstructure of the ITZ were analyzed by microscopic test. The results showed that the mechanical properties and high temperature resistance of ITZ were best when the old substrate interfaces were grinded and grooved and GPb was used as the repair material. Compared with S-OP, the bond strength of S-GPb was 26.92 %, 27.43 %, 46.50 %, 44.26 %, and 97.02 % higher at different temperatures. The increase in interfacial bond strength can be attributed to three mechanisms: (1) Mechanical interlocking with the old substrate with a rough surface. (2) The increase in temperature accelerates the volcanic ash reaction, and the formation of hydration products further fills the voids at the ITZ, maintaining the strength and compactness of the ITZ. (3) The addition of basalt fibers can form an anchoring effect at the interface, reducing the risk of interfacial spalling and cracking caused by material shrinkage in the ITZ.

Data-driven prediction of drilling strength ahead of the bit

This paper compares the performance of two data-driven methods, Signal-Matching Predictor (SMP) and Long Short-Term Memory (LSTM), for predicting drilling strength (Es) ahead of the bit based on drilling data from nearby offset wells. The comparison is based on the accuracy, applicability, complexity, and computational cost of the methods with the objective of suggesting the most appropriate tool for look-ahead drilling strength prediction. The methods were tested using data from offshore wells in Newfoundland. The SMP used a fixed-size sliding-window of real-time Es data from the target well to find a match in the offset well within similar geological formations and chose the scaled value from the offset well as the prediction. In the second approach, twelve LSTM models were trained using the drilling data of twelve offset wells, and the drilling data of the thirteenth well was used for blind testing. Results showed that the SMP achieved a coefficient of determination (R2) of 0.92, 0.92, and 0.79 for predicting 1.5, 3, and 5 feet ahead of the bit, respectively, while the LSTM reached an R2 of 0.95, 0.92, and 0.80 for the respective prediction intervals. The R2 of the LSTM models was further increased to 0.96, 0.94, and 0.83 after retraining it with weighted samples in formation transition zones. Also, a post-processing technique was proposed that further enhanced the R2 of the LSTM-based approach to 0.98, 0.97, and 0.93, respectively. The strength of the LSTM-based approach was to use measurable drilling parameters as the only inputs and not the Es itself. According to the results, the LSTM-based method can be reliably used to predict the Es ahead of the bit allowing drillers to identify upcoming drilling dysfunctions.

Accurate and efficient layered-medium modeling of wave propagation in inshore seawater for ground penetrating radar detection

The electromagnetic (EM) wave-based ground penetrating radar (GPR) finds extensive applications due to its ability to propagate through various media with significant penetration power. In the inshore shallow sea regions, the water has a low salinity and high sediment content with a nonuniform distribution. Leveraging GPR in these regions presents a novel approach to acquiring seafloor topographic knowledge. Although the oceanic environment exhibits continuous stratification, we propose a layered-medium model method (LMMM) for simplification. Through meticulous analysis of EM wave propagation within this model, GPR enables the identification of interfaces between water-suspended sediment transition zones and marine sediments, along with effective discrimination of sediment types. The wave propagation at the frequency of f = 9.0 MHz in the GPR is simulated in the environment of the shallow coast and the distribution of the magnetic field is obtained in different directions. The simulation results are compared with those of the well-known HFSS, thus validating the effectiveness of the proposed approach.

The impact of benign tissue within cancerous regions in the prostate: Characterizing sparse and dense prostate cancers on whole-mount histopathology and on multiparametric MRI

PurposeTo establish the incidence, size, zonal location and Gleason Score(GS)/Gleason Grade Group(GG) of sparse versus dense prostate cancer (PCa) lesions and to identify the imaging characteristics of sparse versus dense cancers on multiparametric MRI (mpMRI). MethodsSeventy-six men with untreated PCa were scanned prior to prostatectomy with endorectal-coil 3 T MRI including T2-weighted imaging, diffusion-weighted imaging and dynamic contrast-enhanced MRI. Cancerous regions were outlined and graded on the whole-mount, processed specimens, with tissue compositions estimated. Regions with cancer comprising <50 % and ≥ 50 % of the tissue were considered sparse and dense respectively. Regions of interest (ROI) were manually drawn on T2-weighted MRI. Within each patient, area-weighted ROI averages were calculated for each imaging measure for each tissue type, GS/GG, and sparse/dense composition. ResultsA large number of cancer regions were identified on histopathology (n = 1193: 939 (peripheral zone (PZ)) and 254 (transition zone (TZ))). Thirty-seven percent of these lesions were sparse. Sparse lesions were primarily low-grade with the majority of PZ and 100 % of TZ sparse lesions ≤GS3 + 3/GG1. Dense lesions were significantly larger than sparse lesions in both PZ and TZ, p < 0.0001. On imaging, 246/45 PZ and 109/8 TZ dense/sparse 2D cancerous ROIs were drawn. Sparse GS3 + 3 and sparse ≥GS3 + 4 cancers did not have significantly different MRI intensities to dense GS3 + 3 cancers, while sparse GS3 + 3/GG1 cancers differed from benign, p < 0.05. ConclusionHistopathologically identified prostate cancer lesions were sparse in 37 % of cases. Sparse cancers were entirely low grade in TZ and predominantly low-grade in PZ and generally small, thus likely posing lower risk for spread and progression than dense lesions. Sparse lesions were not distinguishable from dense lesions on mpMRI, but could be distinguished from benign tissues.

Arthrobrachus crassicornis sp. nov (Coleoptera: Melyridae), a new species from the South American Transition Zone in Argentina

Arthrobrachus Solier, 1849 is a genus of Melyridae distributed in the southern cone of South America, with twenty valid species. A new species of the genus was recognized in the study of collection material. Artrobrachus crassicornis sp. nov. is described from Argentina and distributed in the South American Transition Zone.

Strength and microstructure of geopolymer recycled brick aggregate concrete after high temperatures

Geopolymer recycled brick aggregate concrete (GRBC), as a new environmentally friendly material, exhibits excellent mechanical performance at ambient temperature, but its properties after exposure to high temperatures are not clear. In this paper, the strength and microstructure of GRBC after high temperatures were investigated and compared with ordinary recycled brick aggregate Portland cement concrete (ORBC) through compressive strength, splitting tensile strength, and microscopic tests. The main parameters varied in the strength tests were temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and recycled brick aggregate (RBA) replacement ratio (0 %, 25 %, 50 %, 75 %, and 100 %). The results indicated that the strength of GRBC decreased less than that of ORBC after high temperatures. The compressive strength retention rate of GRBC after exposure to 800 °C was 0.359−0.456, and the tensile strength retention rate was 0.415−0.442. The strength of GRBC with 50 % RBA replacement ratio was about 0.70 that of the case without RBAs. The microscopic test results showed that the structure of GRBC was denser than that of ORBC, and the interfacial transition zone (ITZ) between matrix and RBAs was less affected by the temperature. The first weak zone after high temperatures was RBA itself for GRBC, but ITZ between matrix and RBAs for ORBC. The X-ray diffraction analysis indicated that the phase composition of GRBC and ORBC after high temperatures was basically similar to that at ambient temperature. The strength of GRBC was mainly provided by the N-A-S-H and C-A-S-H gels, while the strength of ORBC was mainly relied on the C-S-H gel.

Factors Affecting the Physical Properties of Microbial Induced Calcium Carbonate Precipitation (MICP) Enhanced Recycled Aggregates

Microbial-induced calcium carbonate precipitation (MICP) can enhance the physical properties of recycled aggregates. Compared to traditional technologies, MICP offers environmental benefits and produces no pollution. However, its mineralization efficacy is significantly influenced by the process parameters. To investigate this, an MICP mineralization test was conducted by manipulating various process parameters throughout the mineralization process. The water absorption rate, apparent density, and calcium carbonate content of the mineralized recycled aggregates were assessed to discern the impact of these parameters on the mineralization outcome. Further analysis using techniques such as thermogravimetric analysis (TG), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) were employed to elucidate the mineralization mechanism of the recycled aggregates at a micro-level. The findings indicated that the MICP treatment induced bacteria to precipitate CaCO3, forming calcite crystalline CaCO3 within the pores and microcracks. This led to a denser interfacial transition zone and, consequently, improved the physical properties of the recycled aggregates. Optimal mineralization was achieved when the bacterial solution concentration was 1.4, the temperature and pH were 35 °C and 9, respectively, and the urea concentration, Ca+ concentration, and mineralization time were 0.5 mol/L, 0.5 mol/L, and 7 days, respectively. Under these conditions, the mineralized recycled aggregate exhibited a 16.07% reduction in water absorption, a 1.07% increase in apparent density, and a 2.28% change in mass.

Enhancing toughness in cement-based composites: Unraveling the composite effect mechanisms of polymers and fibers through physic testing and molecular dynamics simulations

To reveal the toughening mechanism of polymers and fibers in composite applications, a combination of physical tests (uniaxial compression, flexural fracture, single fiber pull-out, scanning electron microscopy, and X-ray diffraction (XRD)) and molecular dynamics simulations have been carried out. Three polymers, i.e. ethylene-vinyl acetate copolymer (EVA), styrene-acrylate copolymer (SAE), and styrene-butadiene copolymer (SB), and two fibers, i.e. polypropylene fiber (PP) and polyvinyl alcohol fiber (PVA) are considered. Their composite effect mechanisms are explained in the viewpoint of three scales. At the macro-scale, the pull-out tests of single fiber show that the polymer increased the equivalent bond strength between the fiber and the mortar matrix. At micro-scale, it was observed from the SEM experiments that the fiber and polymer film inhibited the crack extension at different scales, besides the polymer could absorb on the fiber surface to improve the interfacial transition zone (ITZ) density around the fiber and increase the roughness of the fiber surface. At nano-scale, MD simulations demonstrate that three polymers facilitated the bond strength between PP fiber and C–S–H at the nano-scale, mainly because of the formation of Ca–O coordination bond and H-bonds between the polymers and C–S–H, and the presence of van der Waals forces between the polymers and PP fiber. However, SAE facilitated the bonding between the PVA fibers and the C–S–H, which originated from the coordination bonds formed between Ca ions on the surface of SAE and O atoms in PVA. In addition, the large number of H-bonds formed between SAE and PVA.

Diagnostic accuracy of AI for bpMRI screening of prostate cancer: a systematic review and meta-analysis

The primary objective of this systematic literature review and meta-analysis is to evaluate the quality of prognostic models created for screening of prostate cancer (PCa). Methods: The systematic search of publications from January 2019 to September 2023 in the electronic databases ELibrary, PubMed, Google Scholar, Web of Science and Research Gate was used in accordance with the PRISMA protocol. Two authors independently assessed the need for inclusion or exclusion of the relevant studies Results: This meta-analysis included 21 studies. In total, 3,630 patients, of which 47% were with prostate cancer and 53% with benign prostate tumors. The average age of patients was 67.1 (mainly from 36 to 90 years). Eighty one percent (81%) of studies were based on T2-weighted imaging (T2-WI), 57% on diffusion-weighted imaging (DWI), and 76% on the apparent diffusion coefficients imaging (ADC). Forty three percent (43%) of studies were devoted to a malignancy formation in the transitional zone (TZ), 33% to the peripheral zone (PZ) of the prostate gland. Fifty two percent (52%) of authors conducted research on the entire organ, without dividing it into zones. The analysis showed that the researchers used machine learning (ML) algorithms: MLR (multiple logistic regression, in 76%), SVM (support vector machine, in 38%) and RF (random forest, in 24%). According to a meta-analysis of ROC-AUC assessment in 73 prognostic models described in the publications we studied, using methodological random effects, a final ROC-AUC value of 0.793 [95%CI 0.768; 0.818], I2 = 86.71%, p0.001. The most predictive models are based on T2-WI + ADC protocol: 0.860 [95%CI 0.813; 0.907], and those models that were created according to the “white box” principle (0.834 [95%CI 0.806; 0.861]). For comparison the values for “black box” are (0.733 [95%CI 0.695; 0.771]). Models using MRI and physiological features were slightly more accurate than the MRI parameters alone (0.869 [95% CI 0.844, 0.895] vs. 0.779 [95% CI 0.751, 0.807]). Model accuracy was virtually the same across PZ and/or TZ studies. Conclusion: The results reveal the most promising AI models. However, the clinical applicability may require more rigorous institutional validation and evaluation of efficacy in the prospective studies.

Brown patch on tall fescue as influenced by nitrogen and fungicide applications

AbstractTall fescue (Festuca arundinacea Schreb.) is a cool‐season turfgrass species commonly used in the transition zone. Brown patch (Rhizoctonia solani Kuhn) can have a significant impact on quality of tall fescue between late spring and late summer and is impacted by management strategies including fertilization and fungicide use. The objective of this study was to evaluate the influence of four nitrogen (N) sources and two application rates (0, 74 kg ha−1 [low], or 220 kg ha−1 [high] annually) along with fungicide application (azoxystrobin applied or not applied) on tall fescue brown patch infection. Highest quality occurred when tall fescue received the highest level of N and fungicide treatment. If high levels of N were applied and no fungicide was used, quality was reduced significantly when brown patch was observed in tall fescue. For example, on July 21, 2023, when most intense brown patch occurred, tall fescue had variable brown patch levels: low N levels 2%–23% and high N levels 48%–66%. Across three rating dates in summer 2023, tall fescue receiving the low N level exhibited statistically similar brown patch among all N sources. Conversely, brown patch treated with high levels of N had lower brown patch in urea compared to humic‐coated urea and slow‐release N on at least one of the three dates. Applying N at a level of 220 kg ha−1 annually or higher can result in significant brown patch in some summers; lower N levels will reduce brown patch. Desiring high tall fescue quality requires the high N level and inclusion of preventive fungicide applications.

Present-day stress field, strain rate field and seismicity of the Pannonian region: overview and integrated analysis

We present an overview of recent findings on the seismicity, stress field and strain rate field of the Pannonian region. We furthermore show new inferences for deformation mechanisms and lithospheric rheology via an integrated analysis of the datasets. The N-NW motion of the Dinarides and the opposite, SW motion of the E-and S-Carpathians induce shortening in the western and central Pannonian Basin while leading to regional shearing around the basin's SE boundary. This induces moderate seismic activity related to strike-slip and reverse faulting. Maximum horizontal stress and geodetic shortening directions generally agree, implying that upper crustal stresses and surface deformation correspond to the same forces. 2D rheological models confirm that the shallow upper crust is the only brittle layer in the Pannonian lithosphere, while the brittle-ductile transition zone could be as shallow as 6-9.5 km in the Danube Basin. Comparison of seismic moment rates and moment rate predictions from geodetic strain rates show that deep Pannonian sub-basins accumulate major seismic deficits. This could be explained by dominantly aseismic deformation of the weak upper crust, as supported by a comparison with case studies from different geodynamic environments. Stronger mountainous regions in the study area show no to moderate seismic deficits.

Research on Spatiotemporal Continuous Information Perception of Overburden Compression-Tensile Strain Transition Zone during Mining and Integrated Safety Guarantee System.

The mining of deep underground coal seams induces the movement, failure, and collapse of the overlying rock-soil body, and the development of this damaging effect on the surface causes ground fissures and ground subsidence on the surface. To ensure safety throughout the life cycle of the mine, fully distributed, real-time, and continuous sensing and early warning is essential. However, due to mining being a dynamic process with time and space, the overburden movement and collapse induced by mining activities often have a time lag effect. Therefore, how to find a new way to resolve the issue of the existing discontinuous monitoring technology of overburden deformation, obtain the spatiotemporal continuous information of the overlying strata above the coal seam in real time and accurately, and clarify the whole process of deformation in the compression-tensile strain transition zone of overburden has become a key breakthrough in the investigation of overburden deformation mechanism and mining subsidence. On this basis, firstly, the advantages and disadvantages of in situ observation technology of mine rock-soil body were compared and analyzed from the five levels of survey, remote sensing, testing, exploration, and monitoring, and a deformation and failure perception technology based on spatiotemporal continuity was proposed. Secondly, the evolution characteristics and deformation failure mechanism of the compression-tensile strain transition zone of overburden were summarized from three aspects: the typical mode of deformation and collapse of overlying rock-soil body, the key controlling factors of deformation and failure in the overburden compression-tensile strain transition zone, and the stability evaluation of overburden based on reliability theory. Finally, the spatiotemporal continuous perception technology of overburden deformation based on DFOS is introduced in detail, and an integrated coal seam mining overburden safety guarantee system is proposed. The results of the research can provide an important evaluation basis for the design of mining intensity, emergency decisions, and disposal of risks, and they can also give important guidance for the assessment of ground geological and ecological restoration and management caused by underground coal mining.

Spatial distribution of shrubs and perennial plants under grazing disturbance in the desert steppe of Inner Mongolia

The desert steppe is unique as a transition zone from the steppe to the desert of the Eurasian Steppe. The spatial distribution of shrubs and perennial plants has changed due to long-term disturbance caused by overgrazing in the ecosystem. This study aimed to determine the degree of patchiness of shrubs and perennial plants under grazing disturbance, which is of great significance to better understand the succession mechanism of plant community in the desert steppe. This study investigated the spatial distribution of shrubs and perennial plants under four stocking rates (no grazing, CK, 0 sheep·hm−2·half year−1; light grazing, LG, 0.93 sheep·hm−2·half year−1; moderate grazing, MG, 1.82 sheep·hm−2·half year−1; heavy grazing, HG, 2.71 sheep·hm−2·half year−1) in the desert steppe of Inner Mongolia, primarily using geostatistical methods. The density of perennial grasses increased with increasing stocking rate, while its height decreased (except for HG). The density and height of the shrubs and the perennial forbs showed an exponential or gradual decline. The spatial distribution of shrubs and perennial plants is mainly affected by structural factors such as topography, soil parent material, and climate, and the density of shrubs and perennial plants is most sensitive to changes in stocking rate. An appropriate stocking rate increases the spatial heterogeneity of shrubs and perennial plants, but heavy grazing reduces the spatial heterogeneity of shrubs and perennial plants.

The distribution, diversity and conservation of the Mexican herpetofauna among its biogeographic provinces

Mexico houses a substantial diversity of amphibians and reptiles, with a large number of endemics. We generated a checklist of Mexico’s herpetofauna and their distribution among its biogeographic regions and provinces. We found a total 435 species of amphibians (70.6% endemic to Mexico), and 964 species of reptiles (60.7% endemic to Mexico). The Transition Zone had the greatest herpetofaunal richness, housing 90.8% of the amphibian species and 71.1% of the reptile species that inhabit Mexico. Amphibian and reptile richness decreased from south to north, with the highest richness in the Sierra Madre del Sur, followed by the Trans-volcanic Belt and the Sierra Madre Oriental. According to the IUCN Red List, currently 28.4% of the native species of Mexican amphibians and reptiles are in a category of conservation concern. The Transition Zone, specifically the Sierra Madre del Sur, is of utmost importance due to the conservation status of its species, since this biogeographic province is home to a large number of endemic species. The Neotropical and Nearctic Regions both have around 13% of their species included in some category of conservation concern. The pairwise Jaccard distances among the biogeographic provinces for amphibians and reptiles are highly correlated suggesting parallel patterns of similarity between these two taxonomic groups. We found a positive correlation between Jaccard distances and the length of the shared border between provinces and a negative correlation between Jaccard distance and the distance between the geographic centroids of the provinces, suggesting that geographic proximity plays an important role in the similarity of herpetofauna among biogeographic provinces. The number of species in a province was not correlated with its area or longitude but showed a negative correlation with its latitude. Cluster analyses showed three main clusters of biogeographic provinces for both amphibians and reptiles, with subclusters reflecting geographic proximity and shared habitats. These results highlight the importance of considering geographic factors, such as geographic proximity and habitat similarities, in understanding the distribution and conservation of amphibians and reptiles in Mexico.

Distinct mechanisms controlling and influencing the supply of clay-sized sediments to the northern shelf of the Sea of Okhotsk since the Last Glacial Maximum

The Sea of Okhotsk is a transitional zone between East Asia and northwestern Pacific Ocean. As a result, its massive thick sediments contain numerous important records of geological past, such as the mechanisms of materials and energy exchanges. However, the scarcity of studies tracing the provenance of clay-sized sediments in the sea has limited the progress of reconstructing the paleoclimate of East Asia. In this study, clay mineral analysis was conducted on 31 surface stations and the LV87–54-1 core. These results were combined with grain-size to provide reliable evidence for distinct mechanisms controlling the influx of clay-sized sediments into the northern shelf of the Sea of Okhotsk since 23 ka. Results of provenance analyses suggested that clay-sized sediments in the northern shelf mainly originated from its northwestern shelf, the Okhotsk–Chukotka volcanic belt, and the Kamchatka Peninsula. Clay-sized sediments of the northern shelf was primarily transported from the northwestern shelf and the Okhotsk–Chukotka volcanic belt after 23 ka, while those analogues from the Kamchatka Peninsula increased after 11.7 ka. Based on variations in clay mineral ratios, sediments from the northwestern shelf were mainly transported by the North Okhotsk Countercurrent, wherein rapid millennial-scale variations were influenced by the high-latitude Arctic Oscillation (from the Last Glacial Maximum to the Last Deglaciation) and the low-latitude East Asian summer monsoon (including the Holocene), respectively. By contrast, the influx of clay-sized sediments from the western Kamchatka Peninsula might be mainly controlled by the intensity of the West Kamchatka Current. From the Last Glacial Maximum to the Last Deglaciation, north and northwest geostrophic winds dominated in winter, and the West Kamchatka Current shifted eastward. Since the Holocene, weakened north and northwest geostrophic winds, but strengthened east winds caused a series of rapid millennial-scale variations in the West Kamchatka Current.