Distinct Gradient Research Articles

Spatiotemporal Controls on the Delivery of Dissolved Organic Matter to Streams Following a Wildfire

AbstractWarmer and drier climate has contributed to increased occurrence of large, high severity wildfires in the Pacific Northwest, drawing concerns for water quality and ecosystem recovery. While nutrient fluxes generally increase post‐fire, the composition of organic matter (OM) transported to streams immediately following a fire is poorly constrained, yet can play an integral role in downstream water quality and biogeochemistry. Here, we quantified the spatiotemporal patterns of dissolved OM (DOM) chemistry for five streams burned by wildfires in Oregon, USA in 2020. We sampled over a 24 hr storm event 1 month after the fire revealing DOM dynamics were temporally variable, but spatially linked with burn severity. Specifically, nitrogen and aromatic character of DOM increased in streams burned at greater severity. Our results suggest spatially distinct gradients of burn severity impact DOM dynamics immediately following fire activity and highlight a key gap in our knowledge of post‐fire DOM transport to streams.

Divergent prokaryotic microbial assembly, co-existence patterns and functions in surrounding river sediments of a Cu-polymetallic deposit in Tibet

The exploitation of polymetallic deposits produces large amounts of mine drainage, which poses great challenges to the surrounding aquatic ecosystem. However, the prokaryotic microbial community assembly and co-existence patterns in the polluted area are poorly understood, especially in high-altitude localities. Herein, we investigated the prokaryotic microbial assembly, co-existence patterns and their potential functional responses in surrounding river sediments of a Cu-polymetallic deposit in Tibet. The sediments from mine drainage and surrounding tributaries exhibited distinct geochemical gradients, especially the changes in Cu content. The microbial community structure changed significantly, accompanied by decreased richness and diversity with increased Cu content. Interestingly, the relative abundances of some potential functional bacteria (e.g., Planctomycetota) actually increased as the Cu levels raised. In low contaminated area, ecological drift was the most important assembly process, whereas deterministic processes gained importance with pollution levels. Meanwhile, negative interactions in co-occurrence networks were more frequent with higher modularity and reduced keystone taxa in high contaminated area. Notably, the functions related to ABC transporters and quorum sensing (QS) were more abundant with high Cu content, which helped bacteria work together to cope with the stressful environment. Taken together, the physicochemical gradients dominated by Cu content drove the distribution, assembly and co-existence patterns of microbial communities in surrounding river sediments of a Cu-polymetallic deposit. These findings provide new insights into the maintenance mechanisms of prokaryotic microbial communities in response to heavy metal stress at high altitudes.

Driving factors of phytoplankton trace metal concentrations and distribution along anthropogenically-impacted estuaries of southern Taiwan

Phytoplankton are key marine components in global primary productivity and ocean biogeochemistry. However, anthropogenic activities impact phytoplankton through toxic metal dispersion—threatening the food web with increased metal bioaccumulation. This study assessed the phytoplankton trace metal concentrations, distribution, and relationship with community structure. Environmental parameters (temperature, salinity, pH, dissolved oxygen, biological oxygen demand, suspended solids, chlorophyll-a, ammonium, nitrate, nitrite, phosphate, silicate, total phosphorus) and phytoplankton were collected in southern Taiwan; from five transects (estuaries; T1–T5), composed of estuarine (Es) and offshore (Os) sites. This study respectively used size and density fractionation to accurately measure phytoplankton trace metals. Results showed that anthropogenically-impacted rivers and marine outfall discharges drive community structure and phytoplankton trace metal distribution. Among sites, T3–T5Es differed in its environmental characteristics. Significant differences on environmental characteristics and trace metals in phytoplankton were found between transects—indicating higher anthropogenic impacts in T3 (Dianbao–Houjin estuary) and T4 (Kaohsiung Harbor estuary). Phytoplankton trace metals follows an order of Fe >> Mn > Cr > Cu > Ni > Co > As > Pb > Hg. Metals in estuarine phytoplankton were higher compared offshore, but not significantly different (p > 0.05), highlighting the role of marine outfalls in offshore pollutant diffusion. Phytoplankton metal distribution showed a distinct spatial gradient between agriculture- and industry-associated areas. Significantly high Cr bioaccumulation factor (BCF > 100) were also found in transects T2 and T4. Overall, this study presents an accurate trace metal data and BCF in phytoplankton of southern Taiwan. Further, insights on the potential relationship between phytoplankton community structure and trace metal concentrations are presented – with nutrients mainly impacting phytoplankton community, initiating a ripple effect which likely favored blooming of metal-tolerant species (high dominance) – increasing the trace metal bioaccumulation.

Fluid–thermal–structure interaction of three heated circular cylinders in tandem at a low Reynolds number of 150

The fluid–thermal–structure interaction of three identical, heated circular cylinders in tandem with a variable spacing ratio ranging from 4.0 to 10.0 is numerically investigated using the finite element method in this work. The vibration response and vorticity–temperature distribution are examined at the Prandtl number of Pr = 0.71 and the Reynolds number of Re = 150 in the reduced velocity range of 1.0 ≤ Ur ≤ 15.0. The numerical results indicate that the temperature distribution generally follows the vorticity clusters, presenting a distinct gradient in the wake. Four flow regimes are identified in terms of the interference of shear layers and vortex shedding, that is, continuous reattachment, alternate reattachment, quasi-identical shedding, and co-identical shedding, which are related to the reduced velocity and the spacing ratio. The middle and downstream cylinders experience the wake-induced vibration, and the wake-induced galloping occurs when Ur > 6. Compared with an isolated cylinder, the tandem configuration contributes to the drag reduction in the considered range of spacing ratio. Due to the wake interference, the time-averaged Nusselt number Numean is lower than that of an isolated cylinder. The heat transfer of the tandem cylinders is closely associated with their hydrodynamic behaviors.

Effects of land use and environmental gradients on the taxonomic and functional diversity of rotifer assemblages in lakes along the Yangtze River, China

Anthropogenic pressures are the main drivers of freshwater biodiversity loss. Lakes can act as sentinels of both local and regional changes and experience increased anthropogenic disturbances. Functional traits have been developed to elucidate the consequential functional progression of community changes, yet only a few studies on rotifer functional approaches exist compared with other biotic community attributes. Here, we investigate the responses of rotifer taxonomic and functional diversity metrics to an environmental gradient representing changing lake morphology, land use and physicochemical conditions in 30 lakes along the Yangtze River, China. Based on the distinct lake morphological gradient, land use patterns and environmental conditions, the 30 lakes were clustered into three groups with decreasing anthropogenic stress from Group 1 to Group 3. Our findings indicated that both species and functional richness decreased from Group 1 to Group 3 and that functional richness exhibited better correspondence with multiple stressors than did taxonomic richness. Moreover, we found that the rotifer assemblages varied significantly among the three lake groups along land use and environmental gradients, and the community-weighted means (CWM) of trait expression of the corresponding communities changed simultaneously. Types of trophi and corona were considered as the most variable traits among the three lake groups. We highlight that trait-based approaches are more sensitive, responsive and informative than taxonomic approaches in indicating human-induced environmental alterations in freshwater ecosystems.

Research on the field aging gradient behavior of SBS-modified bitumen at different depths of pavement by rheological and microscopic characterization

This study investigated the aging behavior of styrene–butadienestyrene copolymer (SBS)-modified bitumen with different depth after exposure in the field. The SBS-modified bitumen after construction aging (CA), field aging for 1 year (1Y) and field aging for 5 years (5Y) was obtained and analyzed. Samples were divided into three layers (upper/middle/lower) according to depth. Dynamic shear rheometer (DSR), infrared spectroscopy (IR), bending beam rheometer (BBR) and fluorescence microscopy (FM) experiments were used to observe the trends and changes of the rheological properties and microscopic performance of SBS-modified bitumen with depth. The test results showed that in the CA stage, the SBS-modified bitumen had no aging gradient behavior in the depth direction. The SBS-modified bitumen had a gradient change with depth direction during the 1Y, but the gradient behavior had not evolved to the middle and lower layers. After 5Y the effects of deep aging behavior gradually emerged, showing a distinct gradient behavior. The molecular change characteristics of SBS modified bitumen showed obvious gradient behavior after 5Y, and the change trend was consistent with the aging trend of bitumen. Compared with the aging index of rheological properties, it was found that the most serious degree of aging was on 5Y-upper, followed by 1Y-upper, 5Y-middle and 1Y-middle. It can be seen that the influence of direct contact with aging factors on the degree of aging was greater than the influence of aging time on the depth of aging. Therefore, in the road maintenance process, only the milling surface could be considered for the restoration of the SBS modified bitumen pavement after 5 years of field aging.

Sustainable Slope Stability Analysis: A Critical Study on Methods

When studying the stability of a slope, the first issue that needs to be clarified is the slip surface, which determines the minimum safety factor. The slopes investigated here are homogenous with three distinct gradients (1:1.5; 1:1; 2:1), two defined heights (H-3 m; H-8 m), and four different soil characteristics (S1—clayey silt, S2—sandy clayey silt, S3—sandy silty clay, S4—clay). The purpose of this paper is to develop a new methodology capable of estimating the safety factor and the shape and centre of the critical slip surface, delivering an improved estimate of slope probability of failure, which can represent a significant component in a more precise risk assessment. This paper compares distinct methods used in the slope stability analysis, examining their hypotheses and effects on the estimated safety factor and the centre and shape of the critical slip surface. The study compares the limit equilibrium results with those determined by the shear strength reduction method using an approach based on the upper-bound limit analysis to compare the predictions extracted from these methods with those from the finite element method (FEM) analysis. The finite element method discretizes the soil mass into finite elements. Hence, it establishes a kinematically admissible velocity field searching for the failure mechanism of the slope. Results for FEM show the influence of the slope geometry and the mesh size and density on the safety factor. In the study, plots of the regression curves of five different critical slip surface shapes, including a circular slip surface (benchmark), show that the shape of the failure surface depends on the shape and material of the slope. Furthermore, they show that the critical slip surface layout can approach a logarithmic spiral, damped sinusoid, parabola, etc.; the slip surface is not always circular. The analysis reveals that none of the approaches can consider all uncertainties concerning the factor of safety and the interpretations of critical slip surfaces.

The hyporheic zone as an invertebrate refuge during a fine sediment disturbance event

AbstractSubsurface sediments offer an important refuge that support the survival and persistence of river invertebrates during adverse surface conditions. Access to refuges for invertebrates varies with differing hydrological and substrate characteristics, especially the proportion of fine sediment. This study examines whether substrate characteristics influence the use of the hyporheic zone as an invertebrate refuge during a fine sediment disturbance event. We used 12 outdoor stream mesocosms to examine the vertical migration of benthic and hyporheic invertebrates to fine sediment loading. Each mesocosm was filled with coarse or experimentally colmated sediments. After 69 days, a fine sediment pulse of three varying fine sediment concentrations was added to the stream mesocosms. Both before and after the fine sediment pulse, a distinct gradient in the abundance and richness of hyporheic invertebrates was apparent with depth. Hyporheic abundance and taxonomic richness decreased at 5 cm and increased at 18 cm during fine sediment loading, indicating vertical migration of invertebrates from the benthic to hyporheic zone. Our study provides support for the hyporheic zone as a refuge for benthic invertebrates during fine sediment disturbance events. We also found evidence that movement pathways within subsurface sediments were still accessible and permitted bidirectional migration of individuals between the benthic and hyporheic zone in the coarse and colmated sediments during fine sediment loading. Understanding how increased fine sediment deposition affects streambed porosity will be increasingly important with ongoing climate change and anthropogenic sedimentation.

Quantitative determination of environmental factors governing the snow melting: a geodetector case study in the central Tienshan Mountains

Because of the distinctive vertical climate and topography gradients in the alpine region, the snow cover of the Tienshan Mountains possesses complex spatiotemporal heterogeneity, particularly during the melting process. Quantifying the environmental factors is therefore crucial to understanding the melting process and for predicting and managing snowmelt runoff. Herein, the snow cover area, grain size, and contamination extent were determined to characterize the detailed melting status based on surface reflectance data of MOD09A1 in the central Tienshan Mountains from 2013 to 2017. The environmental factors collected include relief (elevation, slope, and aspect); meteorology (surface air temperature, land surface temperature, solar radiation, and wind speed); and land surface vegetation. Analysis of the geodetector results indicated the following. (1) Patterns of changes in the overall dominant environmental variables were consistent for the pre-, mid-, and post-melting periods defined according to the decline of snow cover area over five years. (2) The overall major environmental factors were wind speed and radiation (pre-period), land surface temperature and elevation (mid-period), and elevation and land surface types (post-period), respectively. (3) Regional distinctions were detected of the dominant environmental factors. In the pre-melting period, the effects of solar radiation and wind speed were noticeable in the north and south regions, respectively. The effects of elevation, land surface temperature, and land cover types became more prominent in all regions during the mid- and post-melting periods. (4) Interaction between the major environmental factors was significantly enhanced on both the overall and regional scales, thus affecting the snow-melting process. Finally, the energy distribution mismatch resulted in the snowmelt. Multiple environmental factors substantially affect heat redistribution at different spatiotemporal scales, resulting in the snowmelt as a complex manifestation of the factors and their interactions. The findings highlight regional differences in various environmental factors of the melting process and offer a theoretical foundation for the melting process at various scales over multiple years.

Threat belief determines the degree of costly safety behavior: Assessing rule-based generalization of safety behavior with a dimensional measure of avoidance

Excessive generalization of safety behavior to innocuous stimuli that resemble a feared stimulus is oftentimes pathological especially with inflicted impairments. Safety behavior is conventionally assessed dichotomously, requiring multiple presentations of each test stimulus for assessing the proportion of safety behavior executed. Thus, the generalization gradient confounds with ongoing extinction learning during non-reinforced test trials. The present study employed a recently developed dimensional measure of avoidance to examine the extent of safety behavior generalization. We found that a dimensional measure of avoidance was able to assess the generalization gradients of safety behavior even when each test stimulus was presented once, thus minimizing the effect of ongoing extinction learning. Of equal importance is whether higher-order cognitive processes shape generalization of safety behavior. We found a range of distinct generalization gradients in safety behavior, which were highly consistent with participants’ verbally reported relational rules. This rule-based generalization parallels to how clinically anxious individuals develop different threat beliefs after trauma exposure, and models how these distinct threat beliefs determine the extent of safety behavior engagement.

Shift from soil chemical to physical filters in assembling riparian floristic communities along a flooding stress gradient

Understanding community assembly is a key issue in recognizing community succession and guiding the restoration of degraded ecosystems. Based on the stress-dominance hypothesis (SDH), along a gradient of increasing environmental stress, the relative importance of environmental filtering is supposed to be dominant but species interaction could be a minor process in assembling communities. However, this hypothesized model of the assembly-rule shift was equivocally supported by various studies. In this study, by examining riparian plant communities with the zonation distribution of species composition along a markedly contrast flooding-stress gradient, a general aim was to clarify whether assembly rules of the communities would be also sorted into the zonation pattern as expected by the SDH. Another aim was to identify how edaphic factors associate with the assembly processes. Firstly, we found that even under the distinct stress gradient, community assembly was not stratified into different rules as the SDH expected, but environmental filtering appeared as a dominant assembly process across the stress gradient. Secondly, although filtering holds as a dominant assembly rule, environmental filters were found different along the gradient. By disentangling the filters of edaphic attributes, we found that the filters significantly shifted from soil physical properties to chemical nutrients governing the filtering process along the gradient. This result revealed that, across the contrast gradient, the environmental deterministic process on assembly is so strong that the other assembly processes became weaker. By synthesizing our results, the SDH may not be applied even under the context of a contrast stress gradient, which suggests that environmental context may be a key in testing and applying the SDH. Finally, in guiding riparian restoration under strong stress, we suggest that soil physical structure rather than chemical nutrients shall be given a priority for consideration in rebuilding the degraded riparian communities.

Shifts in dominance and complementarity between sessile oak and beech along ecological gradients

Abstract Whether tree species benefit from growing in a mixed forest depends on the relative importance of positive versus negative interactions, which varies according to abiotic conditions. In mixture with sessile oak Quercus petraea [Matt.] Liebl., European beech Fagus sylvatica L. is often competitively dominant. Sessile oak, however, is more resistant to water deficit stress. Under water‐limiting conditions, facilitation or even competition exerted by oak may gain in importance. We investigated the relative importance of dominance and complementarity in seven triplets of pure and mixed forests in Belgium's temperate oceanic climate. We analysed ring width data of 145 oaks and 138 beech trees along three distinct gradients: a spatial (i) and a temporal (ii) water availability gradient and a temporal gradient in growing conditions (iii). Gradient (ii) was represented by a precipitation variable, obtained by defining a large set of candidate climate variables over variable time frames, narrowed down using a species and site‐specific lasso model. Growing conditions on a temporal gradient (iii) were represented by standardized tree growth. Two sets of linear mixed‐effects models were used. Growth models assess mixing effects on ring width along gradients (i) and (ii). Mixing index models test for all three gradients how they affect the relative difference in average ring width of trees in mixed and pure stands. Beech trees grew faster than oak trees, and mixing further increased beech growth while decreasing oak growth, except on drier sites where the negative effect on oak growth disappeared. Low precipitation years, in contrast, reduced the beneficial effect of mixing on beech. In years of low growth, the positive mixing effect on beech growth was reinforced, and the negative mixing effect on oak growth decreased. Synthesis. Mixing buffered against growth limitations in general, though this depends on the nature of the limitation and the gradient over which it is measured. On dry sites, competitive dominance of beech was replaced by higher complementarity between species. During dry years, however, oak did not profit from a decreased mixing benefit of beech.

Coupled Oceanic and Atmospheric Controls of Deglacial Southeastern South America Precipitation and Western South Atlantic Productivity

Various mechanisms were proposed as substantial drivers of (sub)tropical South American hydroclimate changes during the last deglaciation. However, the interpretation of past precipitation records from the regions affected by the South American Summer Monsoon, the dominant hydroclimatic system in (sub)tropical South America, still insufficiently consider feedbacks between oceanic and atmospheric processes evident in modern observational data. Here, we evaluate ocean-atmosphere feedbacks active in the region from 19 to 4 ka based on a multi-proxy record comprising lipid biomarker, bulk sediment elemental composition and foraminiferal geochemistry from a sediment core retrieved from the tropical western South Atlantic offshore eastern Brazil at ~22°S. Our proxy data together with existing paleoclimate records show that the consideration of large scale synoptic climatic features across South America is crucial for understanding the past spatio-temporal rainfall variability, especially during the last deglaciation. While the paleohydrological data from our study site show relatively stable precipitation across the deglaciation in the core region of the South Atlantic Convergence Zone, distinct hydroclimatic gradients developed across the continent during Heinrich Stadial 1, which climaxed at ~16 ka. By then, the prevalent atmospheric and oceanic configuration caused more frequent extreme climatic events associated with positive rainfall in the northern portion of eastern South America and in the southeastern portion of the continent. These climatic extremes resulted from substantial warming of the sub(tropical) western South Atlantic sea surface that fostered oceanic moisture transport towards the continent and the reconfiguration of quasi-stationary atmospheric patterns. We further find that enhanced continental precipitation in combination with low glacial sea level strongly impacted marine ecosystems via enhanced terrigenous organic matter input in line with augmented nutrient release to the ocean. Extreme rainfall events similar to those that occurred during Heinrich Stadial 1 are likely to recur in South America as a consequence of global warming, because the projected reduction of the intra-hemispheric temperature gradient may lead to the development of atmospheric patterns similar to those in force during Heinrich Stadial 1.

Holocene bidirectional river system along the Kenya Rift and its influence on East African faunal exchange and diversity gradients

East Africa is a global biodiversity hotspot and exhibits distinct longitudinal diversity gradients from west to east in freshwater fishes and forest mammals. The assembly of this exceptional biodiversity and the drivers behind diversity gradients remain poorly understood, with diversification often studied at local scales and less attention paid to biotic exchange between Afrotropical regions. Here, we reconstruct a river system that existed for several millennia along the now semiarid Kenya Rift Valley during the humid early Holocene and show how this river system influenced postglacial dispersal of fishes and mammals due to its dual role as a dispersal corridor and barrier. Using geomorphological, geochronological, isotopic, and fossil analyses and a synthesis of radiocarbon dates, we find that the overflow of Kenyan rift lakes between 12 and 8 ka before present formed a bidirectional river system consisting of a "Northern River" connected to the Nile Basin and a "Southern River," a closed basin. The drainage divide between these rivers represented the only viable terrestrial dispersal corridor across the rift. The degree and duration of past hydrological connectivity between adjacent river basins determined spatial diversity gradients for East African fishes. Our reconstruction explains the isolated distribution of Nilotic fish species in modern Kenyan rift lakes, Guineo-Congolian mammal species in forests east of the Kenya Rift, and recent incipient vertebrate speciation and local endemism in this region. Climate-driven rearrangements of drainage networks unrelated to tectonic activity contributed significantly to the assembly of species diversity and modern faunas in the East African biodiversity hotspot.

Physiological Adaptation and Plant Distribution along a Steep Hydrological Gradient.

Plant species often separate strongly along steep environmental gradients. Our objective was to study how coupling between plant physiology and environmental conditions shapes vegetation characteristics along a distinct hydrological gradient. We therefore investigated species photosynthesis in air and under water within a limited area from dry-as-dust to complete submergence in a nutrient-poor limestone habitat on Öland’s Alvar, Sweden. We found structural and physiological adaptations of species to endure water limitation at the dry end (e.g., moss cushions and CAM-metabolism) and diffusive carbon limitation (e.g., bicarbonate use) at the submerged end of the gradient. As anticipated, mean photosynthesis in air increased 18-fold from the species-poor assembly of cushion-mosses and Sedum CAM-species on mm-thin limestone pavements to the species-rich assembly of C-3 terrestrial plants in deeper and wetter soils. A GLM-model indicated that 90% of the variation in species richness could be explained by a positive effect of soil depth, a negative effect of the duration of water cover and their interaction. In water, mean photosynthesis was highest among aquatic species, low among Sedum species and cushion mosses, and negligible among C-3 terrestrial plants. While aquatic species dried out in air, drought-resistant small species were probably competitively excluded from the more suitable terrestrial habitats on deeper soils with moderate flooding by taller species of high photosynthetic capability. In conclusion, the clear distribution of species along the steep hydrological gradient reflects distinct structural and physiological adaptations, environmental filtering and interspecific competition.

Controlling of Avalanche Dark Carriers in Realizing Hot Single Photon Detector

HgCdTe avalanche photodiode operating at high temperature in mid-infrared emerges as an indispensable device in ultra-weak light detection. However, the dramatically increased dark current as the temperature rises imposes an insurmountable challenge to achieve high performance detectors. Here, we propose a novel structure for high-temperature operation with the introduction of a barrier in the gradient-doped absorption layer. This forms dual-avalanche areas for photogenerated carriers and enables the band manipulations, thus allowing the simultaneous dark current suppression and photoelectric gain enhancement. Dark carriers outside the absorption area are blocked from the multiplication layer while the rebuilt electric field with distinct gradients enhances the photogenerated carriers’ avalanche effect. Simulations of electric potentials and carrier distributions are performed to further clarify the mercury-interstitial dynamic transporting mechanism. With dedicated design of the device which can be manufactured with current material growth technology, our results reveal that dark current can be selectively controlled without the sacrifice of the photoelectric gain at hot temperature. Dark current is suppressed 10 times lower and the maximum gain up to 130 at 240K is achieved with the optimized device.

Quantitative palaeobiogeography of the Kungurian–Roadian brachiopod faunas in the Tethys: Implications of allometric drifting of Cimmerian blocks and opening of the Meso-Tethys Ocean

Benthic faunas and their palaeobiogeographic affinities related to climate gradient can provide insightful information to unravel the tectonic histories of their hosted blocks if they moved across different latitude zones. In this study, three different quantitative analyses (network, cluster and non-metric multi-dimensional scaling analyses) are employed to carry out a palaeobiogeographic study of the Kungurian–Roadian brachiopod faunas of the Cimmerian blocks. A spin-glass algorithm that enables network community detection is here used for the first time and its six groups-partition is considered as the optimal solution. Two new palaeobiogeographic subprovinces, the Southern and Northern Cimmerian subprovinces in the Southern Transitional Zone, are first recognised besides the previously perceived Cathaysian, Transhimalayan, Westralian and Austrazean provinces. Based on distinct palaeobiogeographic discrepancies, it is suggested that the Lhasa, Tengchong and Irrawaddy blocks, constituting the main parts of the Southern Cimmerian Subprovince, were probably situated near the peri-Gondwanan region; whereas the South Qiangtang, Baoshan and Sibuma blocks of the Northern Cimmerian Subprovince probably were located in the temperate region of the southern hemisphere during the Cisuralian to Guadalupian transition. Such discrepancies in palaeobiogeographic affinitites between two continental slices imply that the Meso-Tethys Ocean had existed before the late Cisuralian and its present oceanic remnants are represented by the Bangong-Nujiang Suture Zone in central Tibet, the Gaoligongshan shear zone in western Yunnan and the Medial-Myanmar Suture Zone in southern Myanmar and Peninsula Thailand. Moreover, the Neo-Tethys Ocean had likely co-existed with the Meso-Tethys Ocean during that time. Given that all these blocks were attached to the northern peri-Gondwanan margin during the early Cisuralian, the Kungurian-Roadian faunal discrepancies among different continental slices with a distinct latitude gradient can be interpreted by the allometric northward drifting of the Cimmerian blocks, which led to the formation of the Meso-Tethys and Neo-Tethys oceans.

Local neural-network-weighted models for occurrence and number of down wood in natural forest ecosystem

The natural forest ecosystem has been affected by wind storms for years, which have caused several down wood (DW) and dramatically modified the fabric and size. Therefore, it is very important to explain the forest system by quantifying the spatial relationship between DW and environmental parameters. However, the spatial non-stationary characteristics caused by the terrain and stand environmental changes with distinct gradients may lead to an incomplete description of DW, the local neural-network-weighted models of geographically neural-network-weighted (GNNWR) models are introduced here. To verify the validity of models, our DW and environmental factors were applied to investigate of occurrence of DW and number of DW to establish the generalized linear (logistic and Poisson) models, geographically weighted regression (GWLR and GWPR) models and GNNWR (GNNWLR and GNNWPR) models. The results show that the GNNWR models show great advantages in the model-fitting performance, prediction performance, and the spatial Moran’s I of model residuals. In addition, GNNWR models can combine the geographic information system technology for accurately expressing the spatial distribution of DW relevant information to provide the key technology that can be used as the basis for human decision-making and management planning.

Distinct body-size responses to warming climate in three rodent species.

In mammals, body-size responses to warming climates are diverse, and the mechanisms underlying these different responses have been little investigated. Using temporal and spatial datasets of three rodent species distributed across different climatic zones in China, we investigated temporal and spatial trends of body size (length and mass), identified the critical drivers of these trends, and inferred the potential causes underlying the distinct body-size responses to the critical drivers. We found that body mass of all species remained stable over time and across space. Body length, however, increased in one species over time and in two species across space. Generally, body-length variation was predicted best by minimum ambient temperature. Moreover, in two species, body length changed linearly with temperature differences between ancestral and colonization areas. These distinct temperature-length patterns may jointly be caused by species-specific temperature sensitivities and experienced magnitudes of warming. We hypothesize that species or populations distributed across distinct temperature gradients evolved different intrinsic temperature sensitivities, which affect how their body sizes respond to warming climates. Our results suggest that size trends associated with climate change should be explored at higher temporal and spatial resolutions, and include clades of species with similar distributions.

Effect of coating architecture on stress and energy relief efficiency of TiZrN coating on Si substrate

This study aims to investigate the extent of stress relief achieved by employing different types of coating architectures, and evaluate the energy relief efficiency in the coating architectures by an energy-balance physical model. TiZrN, TiZrN/Ti, TiZrN/TiN and TiZrN/TiN/Ti coatings with various thickness of TiN were deposited by unbalanced magnetron sputtering. Laser curvature method and the average X-ray strain method combined with nanoindentation were used to measure the residual stress of the entire coating and individual layers, respectively. Experimental results showed that higher stress relief in TiZrN coating could be attained by introducing an interlayer with TiN/Ti architecture than by adding a single Ti interlayer. The tri-layer specimen with a 300-nm TiN layer showed the largest stress relief among all specimens, where the TiZrN coating had the lowest residual stress, -2.01 GPa. The energy-balance model postulated that the release of stored elastic energy in the top coating and in the Si substrate were both converted into the plastic work of the Ti interlayer. The model analysis indicated that the TiN transitional layer served as a channel that effectively transferred the stored elastic energy in TiZrN to the Ti interlayer, by which the distinct stress gradient at the original TiZrN/Ti interface could be reduced, thereby increasing the plastic deformation capacity of the underlying Ti interlayer, and therefore a larger fraction of the residual stress in TiZrN was relieved compared to the TiZrN/Ti bilayer coating. Adding a TiN transitional layer into the TiZrN/Ti coating system only slightly changed the overall energy relief efficiency, while it increased the energy relief fraction in the TiZrN coating. The stress relief in an architectured coating, including transitional layer and metal interlayer, should be evaluated based on the measurements of overall stress and the stress in the major hard coating. The energy balance model could be employed to differentiate the fraction of energy relief in hard coating and in Si substrate, by which the efficiency of stress relief, or energy relief, could be correctly revealed.