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With the development of cloud computing, more and more resource constrained data owners tend to store their images in the cloud and rely on image retrieval services to get back images they want. However, this process raises huge privacy leakage risks. Privacy-preserving image retrieval (PPIR) can prevent privacy leakage during the retrieval process. Using convolutional neural networks for image feature extraction can significantly improve retrieval accuracy and has become a common trend in PPIR, but it also brings a new problem of network model parameter leakage, which is often ignored by most PPIR schemes. Besides, existing PPIR schemes often adopt centralized image retrieval service, which typically require frequent interactions between the cloud server and users during the retrieval process, resulting in excessive computational overhead for resource-limited users. Aiming to solve these problems, a distributed privacy-preserving image retrieval scheme is proposed in this paper. Three collaborative cloud servers utilize three neural network models split and outsourced by the data owner to extract features of the query image and perform subsequent retrieval tasks. A new secure Euclidean distance calculation protocol is designed for cloud servers to measure feature similarity, and secure sort pair protocol, secure sorting protocol, secure search protocol are utilized to achieve secure image retrieval. Additionally, a hierarchical index tree is employed to narrow down the search scope and improve search efficiency. This approach avoids the problem of network model parameter leakage caused by using neural networks to extract image features at the users' side, reduces the computational burden on users, and improves the accuracy and the efficiency of the retrieval process while ensuring retrieval security. Security analysis and experimental results demonstrate the security and retrieval performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

To investigate the potential utilization of MOF templates in hydrodesulfurization (HDS) of large sulfur-containing compounds, MOF-derived Ni2P was prepared and characterized by XRD, TG, SEM, TEM, XPS and Raman. The findings indicate that MOF-derived Ni2P catalyst exhibits significantly enhanced Hydrodesulfurization (HDS) activity compared to conventional unsupported Ni2P. A modified pyrolysis and phosphiding condition allowed the stacking of central Ni atoms to be aggregated loosely, and morphology of MOF-derived Ni2P can be controllably transmitted from polyhedral to petal-like. A lower pyrolysis temperature tends to reduce density of Ni aggregates and cluster size of Ni2P(111), thereby facilitating the phosphiding of Ni aggregates and enhancing the catalytic activity of MOF-derived Ni2P in HDS process. Increasing the duration time of pyrolysis at lower temperatures does not accelerate the aggregation of particles, but makes petals on surface of MOF-derived Ni become thinner and eventually disappear, until coral-like nanosphere aggregates with uniform size are formed. The gradually elimination of MOF framework renders nickel aggregates more susceptible to phosphiding. The collapse of pore structure of MOF template can impact HDS activity of MOF-derived Ni2P. Prolonging pyrolysis time causes the spacing between Ni2P clusters to diminish, thereby significantly decreasing reactivity of Ni2P-400-4-275 compared to Ni2P-400-2-275 in DBT–HDS. [ABSTRACT FROM AUTHOR]

The Convention on Biological Diversity seeks to conserve at least 30% of global land and water areas by 2030, which is a challenge but also an opportunity to better preserve biodiversity, including flowering plants (angiosperms). Herein, we compiled a large database on distributions of over 300,000 angiosperm species and the key functional traits of 67,024 species. Using this database, we constructed biodiversity-environment models to predict global patterns of taxonomic, phylogenetic, and functional diversity in terrestrial angiosperms and provide a comprehensive mapping of the three diversity facets. We further evaluated the current protection status of the biodiversity centers of these diversity facets. Our results showed that geographical patterns of the three facets of plant diversity exhibited substantial spatial mismatches and nonoverlapping conservation priorities. Idiosyncratic centers of functional diversity, particularly of herbaceous species, were primarily distributed in temperate regions and under weaker protection compared with other biodiversity centers of taxonomic and phylogenetic facets. Our global assessment of multifaceted biodiversity patterns and centers highlights the insufficiency and unbalanced conservation among the three diversity facets and the two growth forms (woody vs. herbaceous), thus providing directions for guiding the future conservation of global plant diversity. [ABSTRACT FROM AUTHOR]

Global climate change has led to the decline of species and functional diversity in ecosystems, changing community composition and ecosystem functions. However, we still know little about how species with different resource-use strategies (different types of resource usage and plant growth of plants as indicated by the spectrum of plant economic traits, including acquisitive resource-use strategy and conservative resource-use strategy) would change in response to climate change, and how the changes in the diversity of species with different resource-use strategies may influence community-level productivity. Here, using long-term (1982–2017) observatory data in a temperate grassland in Inner Mongolia, we investigated how climate change had affected the species richness (SR) and functional richness (FRic) for the whole community and for species with different resource-use strategies. Specifically, based on data for four traits representing leaf economics spectrum (leaf carbon concentration, leaf nitrogen concentration, leaf phosphorus concentration, and specific leaf area), we divided 81 plant species appearing in the grassland community into three plant functional types representing resource-acquisitive, medium, and resource-conservative species. We then analyzed the changes in community-level productivity in response to the decline of SR and FRic at the community level and for different resource-use strategies. We found that community-level SR and FRic decreased with drying climate, which was largely driven by the decline of diversity for resource-acquisitive species. However, community-level productivity remained stable because resource-conservative species dominating this grassland were barely affected by climate change. Our study revealed distinctive responses of species with different resource-use strategies to climate change and provided a new approach based on species functional traits for predicting the magnitude and direction of climate change effects on ecosystem functions. [ABSTRACT FROM AUTHOR]

A response has been made to concerns raised about the data quality underlying a recent floristic map of the world. The concerns suggested that non-native distribution records and incomplete sampling may have biased the findings. However, after re-analyzing the data and updating the databases, it was found that these issues were not as serious as suggested. The proportion of non-native distributions in the database was lower than reported, and the regionalization map remained largely unchanged. The study used a wide range of data sources and addressed the issue of incomplete sampling. The authors conclude that non-native distributions did not bias the results of the study. [Extracted from the article]

Floristic regions reflect the geographic organization of floras and provide essential tools for biological studies. Previous global floristic regions are generally based on floristic endemism, lacking a phylogenetic consideration that captures floristic evolution. Moreover, the contribution of tectonic dynamics and historical and current climate to the division of floristic regions remains unknown. Here, by integrating global distributions and a phylogeny of 12,664 angiosperm genera, we update global floristic regions and explore their temporal changes. Eight floristic realms and 16 nested sub-realms are identified. The previously-defined Holarctic, Neotropical and Australian realms are recognized, but Paleotropical, Antarctic and Cape realms are not. Most realms have formed since Paleogene. Geographic isolation induced by plate tectonics dominates the formation of floristic realms, while current/historical climate has little contribution. Our study demonstrates the necessity of integrating distributions and phylogenies in regionalizing floristic realms and the interplay of macroevolutionary and paleogeographic processes in shaping regional floras. This study updates the floristic realms of the world by integrating global distributions and mega-phylogenies of 12,664 angiosperm genera. Eight realms and 16 sub-realms are identified, most of which have formed since the Paleogene, and their formation is dominated by geographic isolation induced by plate tectonics rather than current or historical climate. [ABSTRACT FROM AUTHOR]

Fast spin-flipping is the key to exploit the triplet excitons in thermally activated delayed fluorescence based organic light-emitting diodes toward high efficiency, low efficiency roll-off and long operating lifetime. In common donor-acceptor type thermally activated delayed fluorescence molecules, the distribution of dihedral angles in the film state would have significant influence on the photo-physical properties, which are usually neglected by researches. Herein, we find that the excited state lifetimes of thermally activated delayed fluorescence emitters are subjected to conformation distributions in the host-guest system. Acridine-type flexible donors have a broad conformation distribution or bimodal distribution, in which some conformers feature large singlet-triplet energy gap, leading to long excited state lifetime. Utilization of rigid donors with steric hindrance can restrict the conformation distributions in the film to achieve degenerate singlet and triplet states, which is beneficial to efficient reverse intersystem crossing. Based on this principle, three prototype thermally activated delayed fluorescence emitters with confined conformation distributions are developed, achieving high reverse intersystem crossing rate constants greater than 106 s−1, which enable highly efficient solution-processed organic light-emitting diodes with suppressed efficiency roll-off.The distribution of dihedral angles in film state has significant influence on excited state lifetimes of thermally activated delayed fluorescence emitters. Here authors report conformation distribution confinement strategy to achieve fast spin-flipping for efficient organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

Soil microbes assemble in highly complex and diverse microbial communities, and microbial diversity patterns and their drivers have been studied extensively. However, diversity correlations and co-occurrence patterns between bacterial, fungal, and archaeal domains and between microbial functional groups in arid regions remain poorly understood. Here we assessed the relationships between the diversity and abundance of bacteria, fungi, and archaea and explored how environmental factors influence these relationships. We sampled soil along a 1500-km-long aridity gradient in temperate grasslands of Inner Mongolia (China) and sequenced the 16S rRNA gene of bacteria and archaea and the ITS2 gene of fungi. The diversity correlations and co-occurrence patterns between bacterial, fungal, and archaeal domains and between different microbial functional groups were evaluated using α-diversity and co-occurrence networks based on microbial abundance. Our results indicate insignificant correlations among the diversity patterns of bacterial, fungal, and archaeal domains using α-diversity but mostly positive correlations among diversity patterns of microbial functional groups based on α-diversity and co-occurrence networks along the aridity gradient. These results suggest that studying microbial diversity patterns from the perspective of functional groups and co-occurrence networks can provide additional insights on patterns that cannot be accessed using only overall microbial α-diversity. Increase in aridity weakens the diversity correlations between bacteria and fungi and between bacterial and archaeal functional groups, but strengthens the positive diversity correlations between bacterial functional groups and between fungal functional groups and the negative diversity correlations between bacterial and fungal functional groups. These variations of the diversity correlations are associated with the different responses of microbes to environmental factors, especially aridity. Our findings demonstrate the complex responses of microbial community structure to environmental conditions (especially aridity) and suggest that understanding diversity correlations and co-occurrence patterns between soil microbial groups is essential for predicting changes in microbial communities under future climate change in arid regions. [ABSTRACT FROM AUTHOR]

In order to obtain compact epoxy-based organic coatings with superior corrosion resistance and self-healing performance, a novel Ti3C2Tx/LDH-epoxy hybrid coating was prepared on AZ31 magnesium alloy in this work. The layered double hydroxide (LDH) adopted here is MgAl-LDH intercalated by the cysteine acid (Cys), an environmentally friendly organic acid anions, as corrosion inhibitors, and the MXene (Ti3C2Tx)/MgAl-LDH (TML) heterostructure nanosheets were grown by a facile in situ assembled method. The morphology, composition, structure and the corrosion protection of the Ti3C2Tx/MgAl-LDH-epoxy (EP-TML) composite coatings were systematically investigated and compared with the other three epoxy-based coatings: bare waterborne epoxy resin (EP), Ti3C2Tx pigmented in EP (EP-T), MgAl-LDH in EP (EP-ML). It is found that the TML heterostructure has good dispersion and compatibility with the epoxy resin. The corrosion current density and the impedance value at low frequency (|Z|0.01 Hz) of the EP-TML composite coating are 1.4 × 10–9 A/cm2 and 1.66 × 107 Ω cm2, which is 4 orders of magnitude lower than that of the uncoated Mg substrate and 1–2 orders of magnitude higher than that of EP (8.7 × 105 Ω cm2), respectively, indicating its excellent corrosion resistance. And the self-healing efficiency of EP-TML composite coating is found to be higher as 56.17% after 6 days immersion in a corrosive environment. The significant improvement of the anti-corrosion and self-healing performance of the EP-TML composite coating are mainly ascribed to the synergistic effect of "barrier effect" of TML and the corrosion inhibition effect of the cysteine acid encapsulated in MgAl-LDH. This work provides some valuable insights to widen the functional application of Ti3C2Tx and the design of highly corrosion-resistant and self-healing organic coatings for Mg alloys. [ABSTRACT FROM AUTHOR]

Reliable estimates of groundwater recharge are crucial for the groundwater resources evaluating and sustainable utilization plans formulating. To protect the precious karst groundwater resources, this paper critically reviewed the previous studies on karst groundwater recharge in northern China karst regions from the perspective of diffuse recharge and focused recharge, and took Niangziguan Spring catchment as a case study. It is concluded that for the 119 karst groundwater systems, 52% occur diffuse recharge through precipitation infiltration, 48% occur both diffuse recharge through precipitation infiltration and focused recharge through surface water leakage. The mean annual precipitation, diffuse recharge and infiltration coefficient (IC, as percentage of precipitation) are 560 mm, 136 mm and 23.1%, respectively. A high correlation was observed between annual precipitation and annual diffuse recharge with a nonlinear relationship. The IC can vary substantially even with the same annual precipitation between 9.3 and 38.0%, with an evidently increasing trend eastward. This reflects a significant difference in the degree of karstification for the northern karst regions. The most commonly applied for recharge assessment in northern China karst regions is equal volume spring flow method, the chloride mass balance method is highly recommended for groundwater recharge estimation of the regions based on the case study. This work provides reference for recharge estimation, assessment and management of karst groundwater resources in northern China. [ABSTRACT FROM AUTHOR]

Deep learning has been increasingly recognized as a promising tool in solving kinds of physical problems beyond powerful approximations. A multi-domain physics-informed neural network (mPINN) is proposed to solve the non-uniform heat conduction and conjugate natural convection with the discontinuity of temperature gradient on the interface. Local radial basis function method (LRBF) is applied to compute the case without the analytical solution and is regarded as the benchmark solver. Each physical domain matches a private neural network and all neural networks are connected by the shared information of temperature and heat flux on the interface. Joint training and separate training are utilized to minimize the loss function, which usually consists of the residual of boundary conditions, interface conditions and governing equations. Joint training minimizes the sum of all losses from neural networks with one shared optimizer, while separate training owns its private optimizer. Local adaptive activation function (LAAF) is used to accelerate the convergence and acquire a lower loss value when compared with its fixed counterpart. The numerical experiments on three types of residual points, uniform, Gauss-Lobatto and random, are conducted and it can be concluded that the uniform residual points can obtain the most accurate solution than the random and Gauss-Lobatto. Joint training is more accurate than the separate training when the number of residual points is relatively small, while the separate training performs better than the joint training for the large number of residual points. Numerous test cases on multi-domain heat transfer and fluid flow show the accuracy of the proposed mPINN. Local and global heat transfer rates show good agreements with the results from LRBF. Excepting the forward problems, the thermal conductivity ratio, the constant source and the characteristic parameters of natural convection are accurately learned from sparsely distributed data points. [ABSTRACT FROM AUTHOR]

Multilayered, spatially ordered and highly permeable three-dimensional cross-network porous carbons were prepared from waste superabsorbent polymer (SAP) and were used as supports for NiMo hydrodesulfurization (HDS) catalysts. The acidified SAP-based carbon support and the corresponding catalyst were characterized by FT-IR, XRD, N2 adsorption–desorption, NH3-TPD, TG, SEM, TEM, XPS and H2-TPR. The results show that the acidification of the SAP-based carbon support optimizes the pore structure, increases the acidic surface functional groups, enhances the interaction between the metal and the support, and significantly improves the catalytic hydrodesulfurization performance of the catalyst. Liquid phase acidification can produce defects and wrinkles on surfaces of carbon material and form interconnected voids on spongy catalyst. Further acidification with nitric acid vapor is helpful to form a three-dimensional cross-network structure with multilayer, spatial order and high permeability. Under the same metal Mo loading and high reaction temperature, HDS performance of DBT and 4,6-DMDBT of the NiMo catalyst supported on acidified SAP is better than that of the commercial NiMo catalyst. [ABSTRACT FROM AUTHOR]

Traditional centralized cloud services face challenges, such as high communication delay, single point of failure, etc. Edge computing is one of distributed computing services in which resources are placed closer to users, and thus is more robust and can reduce communication delay. Although outsourcing data to the edge servers can bring great convenience, it also brings serious security threats. In order to provide image retrieval while ensuring users' data privacy, a privacy-preserving content-based image retrieval scheme in edge environment is proposed. Considering the distributed characteristics of edge environment and the requirement of lightweight computing, we design a secure interaction protocol completed through the collaborative cooperation of two or more edge servers. This scheme not only protects data privacy, but also has low communication overhead and delay as well as low computing complexity, therefore it is more suitable for edge computing environment. Theoretical analysis and experiments show that our scheme has high security, retrieval accuracy and efficiency. [ABSTRACT FROM AUTHOR]

Based on laboratory direct shear tests and discrete element theory, the crack propagation mechanism and numerical simulation of rock-like specimens with preexisting flaws considering combined actions of internal hydraulic pressure and shear force were carried out in this paper. We completed the filling of the internal hydraulic pressure in the rock-like specimens with preexisting flaws, and performed direct shear tests on the specimens. Furthermore, we explored the crack propagation process of rock-like specimens with flaws under internal hydraulic pressure and shear load. In the numerical analysis, the pipe domain model in the two-dimensional particle flow code (PFC2D) was modified owing to the high brittleness and low permeability of the cement mortar particles in the numerical model. We modified the calculation rules of the interaction between the fluid and cement mortar particles, and proposed an improved fluid–solid coupling model which is more suitable for the crack propagation analysis in the high brittle cement mortar specimens. Under the action of internal hydraulic pressure, a tensile region existed at the tip of the preexisting flaws of the cement mortar specimen, which can also explain the crack initiation and propagation along the horizontal shear direction during the stage of crack initiation. When cracks progressively propagated, concentrated tensile stress and internal hydraulic pressure were released, leading to the appearance of a large number of tensile cracks, and the release of transverse shear force and internal hydraulic pressure resulted in the appearance of a large number of shear cracks. In the presence of internal hydraulic pressure, the increased number of pre-existing flaws would reduce the shear strengths of cement mortar specimens. Compared with the shear strength of the specimen with single flaw, the shear strength of the specimen with double flaws was reduced by 7.6%, and the specimen with triple flaws was reduced by 10.2%. [ABSTRACT FROM AUTHOR]

The 3-replica redundancy strategy is widely used to solve the problem of data reliability in large-scale distributed storage systems. However, its storage capacity utilization is only 33%. In this paper, a data placement algorithm based on fault-tolerant domain (FTD) is proposed. Owing to the fine-grained design of the FTD, the data reliability of systems using two replicas is comparable to that of current mainstream systems using three replicas, and the capacity utilization is increased to 50%. Moreover, the proposed FTD provides a new concept for the design of distributed storage systems. Distributed storage systems can take FTDs as the units for data placement, data migration, data repair and so on. In addition, fault detection can be performed independently and concurrently within the FTDs. [ABSTRACT FROM AUTHOR]

Protected areas (PAs) play a pivotal role in maintaining viable populations of species and minimizing their habitat loss. Globally, there are currently over 200,000 PAs that cover approximately 15% of land area. The post-2020 global biodiversity framework aims to expand this coverage to 30% by 2030. However, focusing only on the percentage coverage of PAs without evaluating their effectiveness may fail to achieve conservation goals. Here, we use a multidimensional approach incorporating species, climate and anthropogenic vulnerabilities to assess the threat levels in over 2500 PAs in China. We identify nearly 10% of PAs as the most threatened PAs in China and about one-fifth PAs as hotspots of climate and anthropogenic vulnerabilities. We also find high climate instability in species vulnerability hotspots, suggesting an elevated likelihood of species' extirpation therein. Our framework could be useful in assessing resiliency of global protected lands and also in selecting near optimal areas for their future expansion. Proected areas (PA) expansion is a major conservation goal, but its effectiveness is debated. Here, the authors propose a multi-dimensional framework to assess PA vulnerability and select areas suitable for expansion, demonstrating it for 2572 PAs in China under a low-emission scenario. [ABSTRACT FROM AUTHOR]

Steric hindrance of methyl on reaction pathway of hydrodesulfurization in presence of quinoline was investigated over a NiMo/Al2O3 catalyst at 4.0 MPa and 320 °C. The results show that steric hindrance of methyl changed the main pathway of HDS while presence of quinoline further exacerbated this transformation. Changes in inhibitory factor curve show that quinoline poisoning on DBT HDS is a relatively mild. When adjacent methyl is present, even at low concentration, the inhibitory factor of quinoline on 4,6-DMDBT HDS is still greater than 85%. At high levels, the inhibitory factor of quinoline on DDS pathway even exceeds 99%. Quinoline poisons HYD pathway of DBT HDS to a stable level in a short time (30 to 60 min). However, after 6 h of reaction, HYD pathway yield of 4,6-DMDBT HDS is still increasing. Quinoline simultaneously poisons HYD and DDS pathways of 4,6-DMDBT HDS to a stable level within 120 min, and then DDS pathway will continue to be poisoned, thereby increasing HYD pathway yield. Regardless of presence of adjacent methyl in sulfur-containing molecules, an increase in quinoline concentration will lead to an increase in HYD/DDS pathway yield ratio. Addition of quinoline inhibits conversion of hydrogenated intermediates to DDS products by poisoning C–S bond dissociation center (such as CUS active site) and leads to formation of deep hydrogenated products. [ABSTRACT FROM AUTHOR]

Due to the difference of the spatial and temporal distribution of rainfall and the complex diversity of the disaster-prone environment (topography, geological, fault, and lithology), it is difficult to assess the hazard of landslides at the regional scale quantitatively only considering rainfall condition. Based on detailed landslide inventory and rainfall data in the hilly area in Sichuan province, this study analyzed the effects of both rainfall process and environmental factors on the occurrence of landslides. Through analyzing environmental factors, a landslide susceptibility index (LSI) was calculated using multiple layer perceptron (MLP) model to reflect the regional landslide susceptibility. Further, the characteristics of rainfall process and landslides were examined quantitatively with statistical analysis. Finally, a probability model integrating LSI and rainfall process was constructed using logistical regression analysis to assess the landslide hazard. Validation showed satisfactory results, and the inclusion of LSI effectively improved the accuracy of the landslide hazard assessment: Compared with only considering the rainfall process factors, the accuracy of the landslide prediction model both considering the rainfall process and landslide susceptibility is improved by 3%. These results indicate that an integration of susceptibility index and rainfall process is essential in improving the timeliness and accuracy of regional landslide early warning. [ABSTRACT FROM AUTHOR]

UV Raman, TG-MS (TPO) and nitrogen physisorption characterization were used to characterize deactivated Mo/HZSM-5 catalysts from coupling reaction of methane CO2 autothermal reforming (MCAR) and methane dehydroaromatization (MDA). The results show that MCAR/MDA maintains the Mo-oxo species throughout the process, reducing the maximum C6H6 yield, but extending the reaction life by at least 4 time. As O/CH4 increases, MCAR/MDA changes from oxygen-deficient to oxygen-rich state. For MCAR/MDA under oxygen-deficient condition, O2 can only delay the accumulation of aromatics. Grown of coke on Brӧnsted acid eventually leads to complete blockage of the micropores of the catalyst. Slowly deposited graphite coke in MCAR/MDA extended the critical time by nearly 4 times. For MCAR/MDA under oxygen-rich condition, a 70% C6H6 selectivity was maintained throughout the process. After 3700 min of operation, the remaining micropore volume and micropore surface of the deactivated catalyst remained above 1/3. The timely removal of graphite coke at the pore mouth by the MCAR/MDA reaction under oxygen-rich conditions can eliminate the limitation of C6H6 diffusion, thereby effectively preventing the acceleration of the coke deposit micropores which cause the MDA reaction to be rapidly deactivated. [ABSTRACT FROM AUTHOR]

The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence of flow instability such as stall and surge. The paper experimentally examines the developing process of surge and stall occurring in a centrifugal compressor to advance the understanding on flow mechanism of flow instability. It is found that three types of pressure fluctuation can be observed at low flowrate region. At the critical point, the local stall firstly occurs in some specific diffuser passages and the enlarged local diffuser stall eventually induces the mild surge of compression system indicated by the sinusoidal pressure fluctuation. At lower mass flow rate, the diffuser stall cell begins to circumferentially propagate along the impeller rotating direction at 11% of rotor speed with the existence of mild surge. In comparative analysis of IGV pre-swirl angle on the occurrence of mild surge, the mild surge still occurs at the operating condition when the slope of the characteristic map of test stage is still obviously negative, in which the compression system is supposed to be stable in previous study. And a new suggested criterion for the prediction of mild surge is demonstrated that the occurrence of mild surge depends on the destabi-lization effect of downstream components about diffuser and volute. Combined with the experimental data, the streamwise distribution characteristic of diffuser stall can be used to develop the simplified model of lumped parameters for the analysis on the generation mechanism of the diffuser rotating stall. The quantitative investigation on the relation between the pressure-rise characteristic of subcomponents and the occurrence of mild surge and diffuser rotating stall not only advances the prediction of stability limit but also lays the theoretic foundation for controlling these unsteady behaviors to improve the operating range. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is considered as an advanced sheet metal-forming process for flexibly producing complex sheet metal parts. Numerical simulation is supposed to be able to effectively track the forming process, which is beneficial for ISF process optimization. Accuracy and efficiency in ISF process simulation have always been a research focus, especially for friction stir-assisted ISF (FS-ISF) with local friction heat involved, which brings a challenge to FS-ISF process simulation: how can this forming process be effectively simulated with acceptable accuracy? In order to accurately and efficiently predict the impact of local friction heat on FS-ISF process, a new thermal-mechanical coupling simulation method was developed. Based on a new equivalent method of the thermal field on the geometrically compressed tool and scaling of thermal conductivity of sheet metal, the simulation model was proposed and verified. Comparison with the experiment results of AA2024-T3 FS-ISF demonstrates that the optimal simulation model can improve computational efficiency by 316% and simulate FS-ISF process with promising accuracy, which provides a potential tool for virtual check of the feasibility of FS-ISF process design and optimization with thermal field involved. [ABSTRACT FROM AUTHOR]

Friction stir-assisted incremental sheet forming with synchronous bonding is developed as a novel variant of incremental sheet forming, by which the two sheet metals form incrementally and get bonded simultaneously. Numerical simulation of this process is crucial in revealing the forming mechanism and optimizing the process compared with expensive physical tryouts. A coupled thermo-mechanical finite element model was established to take the contact and heat transformation in every interface into consideration, and VUINTER contact subroutine which can express the heat partition coefficient and coefficient of friction was complied, validated and revised by groove tests. The effectiveness of the numerical simulation was verified by experiments. Furthermore, a comparative study based on numerical simulation is conducted to analyze the effects of process variables including feed rate, spindle speed, wall angle and vertical step size on temperature, thickness, and central bulge. [ABSTRACT FROM AUTHOR]

A novel incremental sheet forming process, friction-stir-assisted incremental sheet forming with synchronous bonding (FS-ISF&SB) using aluminum alloy and steel sheets was developed. The influences of stacking sequence, wall angle, ratio of rotational speed to feeding rate and step down on the forming and bonding quality, geometric profile, interface morphology and thickness distribution were investigated through a series of experiments. Experimental results demonstrate that FS-ISF&SB is specifically suitable for the fabrication laminated sheet metal parts. The part with good forming and bonding quality can be obtained with the stacking sequence as of S-A, wall angle as of 40°, rotational speed as of 3000 RPM, feeding rate as of 750 mm/min and step down as of 0.4 mm, respectively. Based on the scoring of various failure modes, five factors are listed in descending order of significance in forming and bonding quality as wall angle, step down, stacking sequence, rotational speed and ratio of rotational speed to feeding rate. A special geometric feature named as "bump structure" reveals the heterogeneous deformation. Results also indicate that the thickness distribution of the formed part does not conform to sine law, and the deviation from design model increases with the increasing of wall angle. [ABSTRACT FROM AUTHOR]

The use of quantitative measures to select priority areas for conservation has been in practice since the early 1980s. However, the relative efficiency of different methods for identifying priority areas is still the subject of debate. Here, using the distribution data of 556 Rhododendron species in China with high spatial resolution, we evaluated the performance of the two commonly used methods, i.e. hotspot and complementarity and selected the efficient method to select priority areas for the conservation of Rhododendron in China. By overlaying the priority areas map with the locations of protected areas, we also identified the regions not covered by current protected areas (i.e. conservation gaps). We found that the complementarity method selected less number of grid cells to capture an equivalent number of species and hence had higher efficiency and representativeness than the commonly used hotspot method. Moreover, the complementarity method was better at capturing the range-restricted species than the hotspot method. Based on the complementarity method, we identified 61 grid cells of 50 × 50 km as priority areas for Rhododendron conservation in China. Among these priority areas, only about 50% grid cells were located in the hotspot areas (e.g. Hengduan Mountains), and 14% grid cells were outside the current protected area network. Our findings suggest that, despite its popularity and ease of implementation, the sites selected by hotspot algorithm may not necessarily be the best sites to allocate conservation efforts. Since the identification of priority areas in China has largely been based on the hotspot method, the current study has revived the need to reassess the priority areas for other taxonomic groups too. More importantly, our findings have emphasized the need to expand the conservation priorities from Hengduan Mountains to south and southeast China as well. [ABSTRACT FROM AUTHOR]

In Northern China, karst systems in widely distributed carbonate rocks are one of the most important water supplies for local inhabitants. Constrained by the specific geological and geomorphological conditions, most karst water in this region is discharged as individual or groups of springs. This paper summarizes the characteristics, chemistry, and environmental quality of these karst systems in Northern China. Five structural models of karst water systems were identified based on the relationships between the karst geological strata and karst groundwater flow fields. These specific structural models may closely relate to the attendant environmental geological issues and consistent risks from pollution. Over the past 40 years, the karst water systems in Northern China have suffered from various environmental problems, including deteriorating water quality, the drying up of springs, a continuous decline in the level of karst water, and so on. Based on the field investigation and previous data, a preliminary summary is provided of the environmental problems related to the development and evolutionary trends of karst water in this region. The results highlight the significant challenges associated with karst water, and it is essential that all segments of society be made aware of the situation in order to demand change. In addition, the study provides a scientific basis for the management, protection, and sustainable utilization of karst water resources. [ABSTRACT FROM AUTHOR]

An organic compound exhibiting simultaneously reversible switch between its emission colors and luminescence mechanisms, possessing high contrast from deep blue normal fluorescence (NF) to yellow thermally activated delayed fluorescence (TADF), is reported. Based on these two complementary colors, white-light emission combining NF and TADF from a single compound can be achieved in various states. Experimental results and density functional theory calculations indicate that the controllable conformational distribution under thermal and mechanical activation is the mechanism responsible for the reversible switching behavior. [ABSTRACT FROM AUTHOR]

The research on microfluidic droplet size prediction has been extensive and fruitful, while the droplet deforming process has been seldom studied. In this paper, a frying-oil-assessing microfluidic device was designed to study the droplet deforming and recovering processes, which were dominated by channel geometry, flow rates, sheath flow viscosity and interfacial tension of the two phases. Theoretical expressions of the deforming process and its extreme value were obtained for the first time, supported by simulation and experiments. Theoretical, simulation and experimental results indicated that the steady-state droplet length could be a useful parameter for frying oil assessment. [ABSTRACT FROM AUTHOR]

The vaned-diffuser usually brings compressor instability problems under the small flow rate, for instance the spike-type rotating stall phenomenon which restricts the operation range and may cause the trouble of blade fatigue. Since it is difficult to mathematically predict the spike-type stall for its randomness, finding out a practical method to warning this stall precursor appears to be meaningful. The paper explains the relationship between the spike-type precursor and the blade passing irregularity coefficient to analyze whether this coefficient is appropriate for the spike-stall warning inside a centrifugal compressor with the vaned-diffuser. The advanced wireless measurements were conducted on a 1.5 stages test centrifugal compressor to capture the unsteady behavior progressing from the design to stall inception within the region between the impeller trailing edge (TE) and diffuser leading edge (LE). The circumferential distribution of the blade passing irregularity has been quantitatively revealed. The steep increase of the blade passing irregularity at some “special locations”, which is responsible for the onset of the spike-type precursor, is highlighted. Also, to further understand the spike precursor inside the diffuser passage corresponding to the circumferential “special location” with maximum irregularity, the high-response transient measurement within this passage is presented. With the help of full-annulus computational fluid dynamics (CFD) simulation and the mathematical model, it is proved that the blade passing irregularity precisely reflects the flow characteristics during the spike precursor, which presents the guidance for this stall warning method. [ABSTRACT FROM AUTHOR]

To measure the bracelet automatically, a novel method based on feature energy is proposed. Firstly, the morphological method is utilized to preprocess the image, and the contour consisting of a concentric circle is extracted. Then, a feature energy function, which is relevant to the distances from one pixel to the edge points, is defined taking into account the geometric properties of the concentric circle. The input image is subsequently transformed to the feature energy distribution map (FEDM) by computing the feature energy of each pixel. The center of the concentric circle is thus located by detecting the maximum on the FEDM; meanwhile, the radii of the concentric circle are determined according to the feature energy function of the center pixel. Finally, with the use of a calibration template, the internal diameter and thickness of the bracelet are measured. The experimental results show that the proposed method can measure the true sizes of the bracelet accurately with the simplicity, directness and robustness compared to the existing methods. [ABSTRACT FROM AUTHOR]

To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain's impeller is investigated by using both steady and unsteady RANS solver techniques. It is found that the flow unsteadiness on the pressure side is much stronger than that on the suction side. The periodical frequency of the unsteady flow is around half of the blade passing frequency. The originating mechanism of the flow unsteadiness is illustrated with the time-dependent tip leakage flow and blade loading at the tip region. Due to the blockage caused by the joint effects of broken-downed tip leakage vortex, separated fluids and tip leakage flow at downstream, a low pressure region is formed on the pressure side, consequently the blade loadings is altered. In turn, the changed blade loadings will alter the intensity of tip leakage flow. Such alternative behavior finally results in the periodic process. By comparing the calculated flow field in the cases of single-passage and four-passage models, it is confirmed that the investigated flow unsteadiness is confined in each single passage, as no phase differences are found in the model of four passages. This is different from the situation in axial compressor when the rotating instability is encountered. The flow unsteadiness only occurs at the working conditions with small mass flow rates, and the oscillation intensity will be enhanced with the decrease of mass flow rate. When the mass flow rate is too small, the flow unsteadiness in a single passage may trigger rotating stall, as the disturbance propagates in the circumferential direction. [ABSTRACT FROM AUTHOR]

Vibration-assisted metal forming is one of the most recent and beneficial techniques used to improve material flow of the forming process. However, some technical challenges, such as the large power requirement of vibration generation and technical complexity of the metal forming process control, are difficult to solve. The main objective of this work is to investigate the possibility of applying electric-hydraulic chattering in the cold extrusion process. A series of forward cold extrusion experiments and finite element simulations were performed with and without electric-hydraulic chattering assistance. The experimental results showed that the maximum extrusion load was decreased by 5.1 % when electric-hydraulic chattering with an oil pressure of 8 MPa and a vibration frequency of 200 Hz was superimposed on the lower die. The effect of the oil pressure was more significant than the vibration frequency for the reduction of the extrusion load. A significant improvement in the surface finish of the formed parts was observed using the proposed design. The velocity of material flow during chattering extrusion process was changed cyclically, and the maximum velocity was higher than that achieved from the conventional extrusion process. The material flow at the corner area was improved. The effective stress distribution was altered periodically due to the chattering. However, the maximum effective stress was approximately equal to that attained by conventional method. Moreover, the effective strain distribution was more uniform compared to that produced by the conventional extrusion process. [ABSTRACT FROM AUTHOR]

In this paper, we study the necessary and sufficient conditions on the parameters for the boundedness of the multilinear fractional maximal operator $\mathcal{M}_{\Omega,\alpha}$ and the multilinear fractional integral operator $\mathcal{I}_{\Omega,\alpha}$ with rough kernels on Morrey spaces and modified Morrey spaces, respectively. This extends some recent results of Guliyev, Hasnov and Zeren; the necessary and sufficient conditions for the boundedness of $M_{\alpha}$ and $I_{\alpha}$ on modified spaces are considered. [ABSTRACT FROM AUTHOR]

The article presents a study that reveals the vulnerability of a dynamic identity based authentication scheme using chaotic maps for the telecare medicine information system and highlight its failure to provide user anonymity. Topics include Chebyshev chaotic maps, service misuse attack, smart card, and cryptographic mechanism.

A numerical investigation on the aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor is conducted through three-dimensional CFD analysis. The results show that the flow, especially near the diffuser inlet, is influenced by the axial misalignment obviously. When the impeller offsets to one side, the pressure at diffuser inlet close to this side will descend, and the vortex in the cavity on the other side will partially enter the diffuser and then result in the back flow. The performances of the stage and its components also change with the impeller-diffuser axial misalignment. There exists an optimum offset making the efficiency maximum at a given operating point. Furthermore, the effect of impeller-diffuser axial misalignment on the axial thrust is pronounced. The axial thrust is nearly increased linearly with the increase of axial misalignment. The aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor behaves more remarkably at the large flow rate. To alleviate the aerodynamic effects of impeller-diffuser misalignment, a rounding in the meridional plane at the diffuser inlet can be applied. [ABSTRACT FROM AUTHOR]

The low flow coefficient centrifugal impeller (LFCCI) gives a relatively low efficiency and a special treatment is required for the design of this kind of impeller. This paper investigates the influences of cavity leakage on the performance prediction and design of LFCCI based on Computational Fluid Dynamics (CFD) techniques. The results show that, the reduction in the efficiency of impeller due to the introduction of cavity leakage varies with the blade shape of impeller in a wide range since there is a strong and complex interaction of main flow and leakage flow in the LFCCI. To get a credible optimization result, the backside and foreside cavities should be considered in the CFD-based design of LFCCI. [ABSTRACT FROM AUTHOR]

Global surface temperature has dramatically increased in the past decades. It is critical to evaluate such a change using appropriate approaches. The previous studies for assessment of the change usually used overall trends of temperature series (i.e. slopes of simple linear regression of temperature versus year based on a least-square analysis) for entire study period. Temperature trends, however, differ among different periods, i.e. there are often breakpoints in the temperature series. Therefore, the overall linear trend of a temperature series may conceal some of the temporal characteristics of the temperature change. To precisely characterize the temporal and spatial patterns of air temperature change in China, we analyze the annual mean temperature series between the year of 1961-2004 for 536 meteorological stations across China, using piecewise linear regression approach. We found remarkable breakpoints in the annual mean temperature during the study period across the country. The annual mean temperature started to increase in 1984 at a rate of 0.058°C/a at the country level. The year when warming started appeared to be gradually later from the north to the south: temperature increased since the 1970s in the north (north of 40°N), and did not rise until the 1980s in most areas of the south (south of 40°N), with warming starting in 1983 in the Tibetan Plateau. The trends in annual mean temperatures showed a large spatial heterogeneity across China: a relatively small rising with a rate of 0.025-0.05°C/a in the Sichuan Basin, Central China and South China; the greatest increase in some parts of northwest China (i.e. Xinjiang) with up to a rate of 0.1°C/a; and rising at a rate of >0.05°C/a for most regions of the country. The feedbacks of cold waves and snow may be responsible for such regional differences in the timing and rates of warming in China. [ABSTRACT FROM AUTHOR]

In this paper three perfect gas models with constant specific heat or with variable specific heat and one real gas model based on the gas property tables are respectively considered to implement into the three-dimensional CFD (computational fluid dynamics) analysis of a centrifugal refrigeration compressor stage. The results show that the gas models applied to the CFD code have significant influences on the performance of stage and the flow structures in the stage. Although the thermodynamics operating condition of evolving fluid in the centrifugal refrigeration compressor has a significant deviation from the perfect gas, the perfect gas model with the modified value of gas constant and the variable specific heat offers a good prediction of stage performance. To predict some basic fluid flow parameters and flow structure accurately, the real gas effects should be considered and the reasonably accurate thermodynamic properties based on the analytical gas equation of state or numerical interpolation of gas tables should be applied to the CFD code. [ABSTRACT FROM AUTHOR]

In the original version of this Article, the maps in Figs. The maps have now been updated according to the territorial map guidelines of the authors' institutions in both the PDF and HTML versions of the Article. [Extracted from the article]

Identifying drivers behind biodiversity recovery is critical to promote efficient ecological restoration. Yet to date, for secondary forests in China there is a considerable uncertainty concerning the ecological drivers that affect plant diversity recovery. Following up on a previous published meta-analysis on the patterns of species recovery across the country, here we further incorporate data on the logging history, climate, forest landscape and forest attribute to conduct a nationwide analysis of the main drivers influencing the recovery of woody plant species richness in secondary forests. Results showed that regional species pool exerted a positive effect on the recovery ratio of species richness and this effect was stronger in selective cutting forests than that in clear cutting forests. We also found that temperature had a negative effect, and the shape complexity of forest patches as well as the percentage of forest cover in the landscape had positive effects on the recovery ratio of species richness. Our study provides basic information on recovery and resilience analyses of secondary forests in China. [ABSTRACT FROM AUTHOR]

The means through which microbes and plants contribute to soil organic carbon (SOC) accumulation remain elusive due to challenges in disentangling the complex components of SOC. Here we use amino sugars and lignin phenols as tracers for microbial necromass and plant lignin components, respectively, and investigate their distribution in the surface soils across Mongolian grasslands in comparison with published data for other grassland soils of the world. While lignin phenols decrease, amino sugars increase with SOC contents in all examined grassland soils, providing continental-scale evidence for the key role of microbial necromass in SOC accumulation. Moreover, in contrast to clay’s control on amino sugar accumulation in fine-textured soils, aridity plays a central role in amino sugar accrual and lignin decomposition in the coarse-textured Mongolian soils. Hence, aridity shifts may have differential impacts on microbial-mediated SOC accumulation in grassland soils of varied textures. It remains unclear how microbes and plants contribute to soil organic carbon (SOC) accrual. Here, using biomarkers, the authors show that microbial necromass and plant-derived lignin components have divergent accumulation mechanisms and that microbial necromass plays a key role in SOC accumulation. [ABSTRACT FROM AUTHOR]

Ambient energy, niche conservatism, historical climate stability and habitat heterogeneity hypothesis have been proposed to explain the broad-scale species diversity patterns and species compositions, while their relative importance have been controversial. Here, we assessed the relative contributions of contemporary climate, historical climate changes and habitat heterogeneity in shaping Salix species diversity and species composition in whole eastern Asia as well as mountains and lowlands using linear regressions and distance-based redundancy analyses, respectively. Salix diversity was negatively related with mean annual temperature. Habitat heterogeneity was more important than contemporary climate in shaping Salix diversity patterns, and their relative contributions were different in mountains and lowlands. In contrast, the species composition was strongly influenced by contemporary climate and historical climate change than habitat heterogeneity, and their relative contributions were nearly the same both in mountains and lowlands. Our findings supported niche conservatism and habitat heterogeneity hypotheses, but did not support ambient energy and historical climate stability hypotheses. The diversity pattern and species composition of Salix could not be well-explained by any single hypothesis tested, suggesting that other factors such as disturbance history and diversification rate may be also important in shaping the diversity pattern and composition of Salix species. [ABSTRACT FROM AUTHOR]