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The Luchedu rock avalanche (LRA) that occurred in 1935 at the junction of Sichuan and Yunnan in Southwest China is a disaster chain of the rock slide, debris avalanche, and river blocking induced by heavy rainfall. The rock slide originated from the wedge formed by sheet metamorphic rocks on the fault zone on the left bank of the Jinsha River. After breaking away from the slope, the wedge disintegrated and cracked rapidly, forming debris and causing them to flow in fluidization along a 7.3 km path. After the obvious entrainment process and curve superelevation in the proximal area, the deposition reached 50.5 × 10 6 m3 in the distal area. The sedimentary structure of clasts has typical stratification characteristics. The types of sedimentary facies include carapace facies, body facies, and mixed facies. Inside the sedimentary structure, dense shear zones, liquefied intercalations, jigsaw structures, and directional arrangement of particles are observed. Through a detailed geological survey and DEM spatial analysis, the avalanche entrainment rate of LRA was determined as 1.2. The morphological fluctuation of basement lithology and gully path plays an important role in the long-distance movement. The rock fragments formed by metamorphic rocks with a primary schistosity structure can effectively reduce the energy loss in the internal shear process and significantly promote the laminar flow movement in the distal region of the avalanche. Therefore, as a giant rock avalanche formed by the evolution of specific metamorphic rocks, LRA results from the combination of macrohydrodynamics and microrock failure properties.

The thermal insulation effect of snow on the active layer thickness of permafrost cannot be ignored. Under the dual influence of snow cover and roadbed construction, this paper studies the influence of snow cover on the temperature field and permafrost upper limit under the permafrost roadbed in the alpine mountains. Through the application of PDE module in Comsol software, the hydrothermal coupling analysis of roadbed is carried out by means of numerical analysis. The results show that the permafrost degradation is accelerated by the snow on the subgrade surface, the temperature increases significantly, the thickness of the active layer increases, and the permafrost upper limit moves downward. With the increase of seasonal snow thickness, the permafrost temperature under the subgrade increases, the low-temperature permafrost under the subgrade has the risk of changing to high-temperature permafrost. The melting groove is formed under the subgrade on the right side, and with the increase of snow thickness, the area of the melting groove expands and develops towards the center of the subgrade. Permafrost upper limit on the left and right shoulder is lower than that on the right shoulder, and snow cover has a greater impact on permafrost upper limit on the right shoulder.

Adaptive video multicasting has been widely studied due to its effectiveness in transmitting live videos over wireless networks. The key challenges in live video multicasting include how to properly form multicast groups, select video versions and allocate wireless resources, in order to guarantee the quality of experience (QoE) while ensuring low latency delivery. Few prior works have jointly considered the above three problems, which are actually coupled. In this paper, to address these challenges, a novel multicast framework that leverages the advantages of network-assisted dynamic adaptive streaming over HTTP (DASH) and cloud radio access networks (CRANs) is proposed, where a multicast assistant server is deployed at the edge of a mobile network. Under this architecture, a joint user grouping, version selection, and bandwidth allocation method is designed to optimize the sum of user utilities. In particular, a two-step scheme is proposed to solve this complex problem. The number of multicast groups is first automatically determined and a user clustering method is presented. Then, group-level version selection and spectrum assignment algorithms are performed at different time scales. Simulation results demonstrate that our proposed scheme has at least a 7% improvement of QoE over the best performance of all baseline methods.

Due to the fact that the permeability coefficient of salinized frozen soil is difficult to measure through experimental test, this paper develops a model of the permeability coefficient of salinized frozen soil by using SFCC curves, which takes into account the effects of velocity slip on pore wall and seepage of unfrozen water film. This model is on the basis of capillary bundle model, and combines with phase diagram theory of water-salt binary system. For the silty clay from Qinghai-Tibet Plateau and silts from Onedia, the permeability coefficient fluctuation vs. temperature is calculated using the model. The estimated calculations of the permeability coefficient model were all found to be in good agreement with the experimental data by comparison. Additionally, the variation trend of permeability coefficient of NaCl, Na2SO4, and Na2CO3 type saline soils containing different salt contents is examined. The results indicate that before saline soils freeze, NaCl does not crystallize and thus has little impact on the permeability coefficient, whereas Na2SO4 and Na2CO3 both crystallize and block the pores, the permeability coefficient decreases with decreasing temperature. Once the saline soils have frozen, the freezing temperature has a larger impact on the permeability coefficient. During the early stage of freezing, the lower the freezing temperature is, the larger the permeability coefficient is. In the late stage of freezing, the permeability coefficients with various salt contents tended to be the same.

Hybrid small-molecule organic semiconductor / quantum dot blend films are attractive for high efficiency low-cost solar energy harvesting devices. Understanding and controlling the self-assembly of the organic semiconductor and quantum...

BACKGROUND: Real-time shear wave elastography (SWE) is non-invasive and reliable for quantitatively evaluate stiffness of tissues and organs. Until now, little researches have applied SWE to evaluate brain tissue of premature neonates. This study sought to compare differences in the average brain tissue elasticity modulus (Emean) values of neonates, and explore the factors affecting these differences. METHODS: In total, 159 neonates admitted from December 2019 to February 2021 were taken as the study subjects and divided into 2 groups based on their time of birth. Premature neonates, full-term neonates, and neonates with neonatal pneumonia were included in this study. Of the 159 neonates, 76 were premature and 83 were full-term. SWE was used to quantitatively evaluate the Emean of bilateral paraventricular white matter, thalamus, and choroid, and to analyze the relationship between body mass index (BMI) and Emeans in both groups of neonates. RESULTS: The Emeans of the paraventricular white matter, thalamus, and choroid of the premature neonates were lower than those of the full-term neonates (P

Understanding carrier dynamics and transport in quantum dot based heterostructures is crucial for unlocking their full potential for optoelectronic applications. Here we report the direct visualization of carrier propagation in PbS CQD solids and quantum-dot-in-perovskite heterostructures using femtosecond transient absorption microscopy. We reveal three distinct transport regimes: an initial superdiffusive transport persisting over hundreds of femtoseconds, an Auger-assisted subdiffusive transport before thermal equilibrium is achieved, and a final hopping regime. We demonstrate that the superdiffusive transport lengths correlate strongly with the degree of energetic disorder and carrier delocalization. By tailoring the perovskite content in heterostructures, we obtained a superdiffusive transport length exceeding 90 nm at room temperature and an equivalent diffusivity of up to 106 cm2 s-1, which is 4 orders of magnitude higher than the steady-state values. These findings introduce promising strategies to harness nonequilibrium transport phenomena for more efficient optoelectronic devices.

Heptoses are important structural components of Gram-negative bacterium cell wall and participate in bacterial colonization, infection, and immune recognition. Current knowledge of NDP-heptose originating from d-sedoheptulose 7-phosphate in Grampositive bacterium remains limited. Here, in silico analysis suggested that the special tridomain NDP-heptose synthetases with isomerase, kinase, and nucleotidyltransferase activities are conservatively distributed in Actinobacteria class of Gram-positive bacterium. Enzymatical characterization of the tridomain proteins from different strains showed that they are involved in ADP-d-glycero-β-d-manno-heptose biosynthesis despite the unexpected discovery of kinase activities deficient in some proteins. The presence of three types of NDP-heptose synthetases in Gram-positive bacterium suggests that it is also a rich source of heptoses and the heptose moieties may play important roles in vivo. Our work updates the understanding of NDP-heptose biosynthesis in Gram-positive bacterium and lays a solid foundation for further physiological function explorations. Supporting Information The supporting information is available online at 10.1007/s11427-021-2000-2. The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.

Quantum dots (QDs) have a wide range of applications in the field of optoelectronics. They have been playing multiple roles within the configuration of a device, by serving as the building blocks for both the active layer and the carrier transport layer. While the performance of various optoelectronic devices has been steadily improving via developments in passivating the QD active layer, the possible improvement via passivation of the QD-based carrier transport layer has been largely overlooked. Here, with lead sulfide QD photovoltaics as the platform of study, we demonstrate that the device performance can be significantly improved by passivating the QD hole transport layer (HTL) with zinc salt post-treatments. The power conversion efficiency is improved from 8.7% of the reference device to 10.2% and 9.5% for devices with zinc acetate (ZnAc)- and zinc iodide (ZnI2)-treated HTLs, respectively. Transient absorption spectroscopy confirms that both treatments effectively reduce band-tail states and increase carrier lifetime of the HTLs. Further elemental analysis shows that ZnAc provides a higher amount of Zn2+ for passivation while maintaining the function of HTL by allowing essential p-doping oxidation. In contrast, the additional I- passivation from ZnI2 inhibits p-doping oxidation and limits the function of HTL. This work demonstrates the potential of improving device performance by passivating the QD-based HTLs, and the method developed is likely applicable to other optoelectronic devices.

Funder: AiF Project, no: ZIM-KK5085302DF0, Funder: Polish National Agency for Academic Exchange within the Bekker programme (grant no. PPN/BEK/2020/1/00264/U/00001), Funder: Royal Society Te Apārangi and the Cambridge Commonwealth European and International Trust, Funder: Hans Fischer Senior Fellowship from the Technical University of Munich's Institute for Advanced Study, funded by the German Excellence Initiative, I-V-VI2 ternary chalcogenides are gaining attention as earth-abundant, nontoxic, and air-stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slowly-rising absorption onsets, and their charge-carrier transport is not well understood yet. Herein, we investigate cation-disordered NaBiS2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching >105 cm-1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (picosecond-time scale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS2 nanocrystals. These unusual features arise because of the localised, non-bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially-separated electrons and holes, as well as the slow decay of trapped holes. This work reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics.

Quantum dot-organic semiconductor hybrid materials are gaining increasing attention as spin mixers for applications ranging from solar harvesting to spin memories. Triplet energy transfer between the inorganic quantum dot (QD) and organic semiconductor is a key step to understand in order to develop these applications. Here we report on the triplet energy transfer from PbS QDs to four energetically and structurally similar tetracene ligands. Even with similar ligands we find that the triplet energy transfer dynamics can vary significantly. For TIPS-tetracene derivatives with carboxylic acid, acetic acid and methanethiol anchoring groups on the short pro-cata side we find that triplet transfer occurs through a stepwise process, mediated via a surface state, whereas for monosubstituted TIPS-tetracene derivative 5-(4-benzoic acid)-12-triisopropylsilylethynyl tetracene (BAT) triplet transfer occurs directly, albeit slower, via a Dexter exchange mechanism. Even though triplet transfer is slower with BAT the overall yield is greater, as determined from upconverted emission using rubrene emitters. This work highlights that the surface-mediated transfer mechanism is plagued with parasitic loss pathways and that materials with direct Dexter-like triplet transfer are preferred for high-efficiency applications.

A three-dimensional stratum model stratum model is a useful auxiliary tool for geotechnical engineering and other exploration work. The existing methods for stratum model construction lack complete topological descriptions of entities, so it is difficult to apply them to 3D geological modeling with complex geometric structures and complex topological relationships between modules. To solve the above problem, in this paper, the boundary representation method is used to represent the arbitrarily-shaped geological entities, and the half winged-edge-face structure topological structure is proposed to describe the topological information of the stratum model for a complex entity. The topological structure can record the topological information of the solid stratum model completely, thereby providing the basis for operations with the model and the applications of various algorithms. Based on this topological structure, the construction process for a 3D solid stratum model is proposed. The reliability and effectiveness of the constructed 3D solid stratum model are verified by an engineering case. The solid stratum model not only solves the geological modeling problem with respect to complex geometric and topological relations, but also provides a new method and idea for 3D geological modeling.

In order to reduce the interference, a novel, cluster-based medium access control (MAC) protocol with load aware for VANETs is proposed in this paper. First, all vehicles on roads are grouped into stable clusters in the light of their direction, number of neighbors, link reliability, and traffic load. By utilizing the advantages of centralized control in software defined VANETs (SDVN), cluster stability can be maintained in real-time. Second, a contention-free MAC mechanism composed of inter-cluster multi-channel allocation and intra-cluster dynamic TDMA frame allocation is proposed to prevent co-channel interference and hidden terminal interference. Simulation results show that the proposed protocol outperforms some existing protocols in cluster stability, delivery ratio, throughput and delay performance.

With the development of virtual reality (VR) technology, the future of VR systems is evolving from single-user wired connections to multi-user wireless connections. However, wireless online rendering and transmission incur extra processing and transmission latency, as well as higher bandwidth requirements. To meet the requirements of wireless VR applications and enhance the quality of the VR user experience, this paper designs a view synthesis-based 360° VR caching system over Cloud Radio Access Network (C-RAN), where both mobile edge computing (MEC) and hierarchical caching are supported. In the system, an MEC-Cache Server is deployed in the pooled Base band Units (BBU pool) and used for view synthesis and caching. In addition, the remote radio heads (RRHs) can also cache some video contents. If the requested content of a specific view is cached in the BBU pool or RRHs, or can be synthesized with the aid of the cached adjacent views, it is unnecessary to request the content from the remote VR video source server. Therefore, the transmission latency and backhaul traffic load for VR services can be decreased. We formulate a hierarchical collaborative caching problem aiming to minimize the transmission latency, which is proved NP-hard. To address the impractical expenses of the offline optimal method, an online MaxMinDistance caching algorithm with low complexity is proposed. Numerical simulation results demonstrate that the proposed caching strategy provides significantly improved cache hit rate, backhaul traffic load, transmission latency, and Quality of Experience (QoE) performances relative to conventional caching strategies.

Triplet energy transfer between inorganic quantum dots (QDs) and organic materials plays a fundamental role in many optoelectronic applications based on these nanocomposites. Attaching organic molecules to the QD as transmitter ligands has been shown to facilitate transfer both to and from QDs. Here we show that the often disregarded thiol anchoring group can achieve quantitative triplet energy transfer yields in a PbS QD system with 6,11-bis[(triisopropylsilyl)ethynyl]tetracene-2-methylthiol (TET-SH) ligands. We demonstrate efficient triplet transfer in a singlet fission-based photon multiplication system with 5,12-bis[(triisopropylsilyl)ethynyl]tetracene generating triplets in solution that transfer to the PbS QDs via the thiol ligand TET-SH. Importantly, we demonstrate the increased thermal stability of the PbS/TET-SH system, compared to the traditional carboxylic acid counterpart, allowing for higher photoluminescence quantum yields.

Maintaining efficient and reliable communication services in vehicle networks is challenging due to the high mobility of vehicle users. One of the key issues is to deal with the large amount of channel feedback and make better use of limited wireless resources in real time. In this letter, we propose a trajectory data driven method to maximize the total user utilities, which is characterized by intelligent channel state information (CSI) feedback reduction and vehicle-to-vehicle (V2V)/vehicle-to-infrastructure (V2I) mode switching. A deep neural network (DNN) model is trained using optimization approaches and vehicles’ trajectory data. Based on the well trained model, V2V/V2I mode is selected adaptively and bandwidth is allocated optimally with partial channel feedback. Simulation results show that our proposed method outperforms the comparison baseline and can achieve 96.23% of the performance obtained by exhausting searching with full CSI feedback.

PbS quantum dot solar cells (QDSCs) have emerged as a promising low-cost, solution-processable solar energy harvesting device and demonstrated good air stability and potential for large-scale commercial implementation. PbS QDSCs achieved a record certified efficiency of 12% in 2018 by utilizing an n+-n-p device structure. However, the p-type layer has generally suffered from low carrier mobility due to the organic ligand 1,2-ethanedithiol (EDT) that is used to modify the quantum dot (QD) surface. The low carrier mobility of EDT naturally limits the device thickness as the carrier diffusion length is limited by the low mobility. Herein, we improve the properties of the p-type layer through a two-step hybrid organic ligand treatment. By treating the p-type layer with two types of ligands, 3-mercaptopropionic acid (MPA) and EDT, the PbS QD surface was passivated by a combination of the two ligands, resulting in an overall improvement in open-circuit voltage, fill factor, and current density, leading to an improvement in the cell efficiency from 7.0 to 10.4% for the champion device. This achievement was a result of the improved QD passivation and a reduction in the interdot distance, improving charge transport through the p-type PbS quantum dot film.

I-V-VI

In the future vehicular networks with an increased number of transceiver antennas and higher vehicle speeds, more frequent beam switching is required to ensure the quality of communication, which poses challenges to beam tracking speed and resource efficiency. Integrated sensing and communication (ISAC) provide a new solution to cope with this problem since radar echo can help to predict the vehicle’s future location and beam direction. Therefore, we present a radar-assisted beam tracking algorithm based on Extended Kalman filtering (EKF) and multi-road side unit (RSU) cooperation in this article. Each RSU uses EKF and radar echo to predict and track the vehicle position and upload the prediction information to the edge server (ES). By deploying multiple RSUs, the ES uses the uploaded distributed sensing information for joint estimation and thus improves the accuracy of vehicle location prediction, which is used for the beam tracking task at the next moment. Considering the real complex road conditions, we investigate two scenarios where vehicles move linearly or curvilinearly. Simulation results show that the proposed method with multiple base station cooperation improves the spectral efficiency by 34% and 20% over non-cooperative beam tracking in linear and curvilinear mobility, respectively. In addition, compared with traditional beam tracking based on beam scanning and signaling feedback, radar-assisted beam tracking significantly reduces the communication overhead.

Seed mass (SM) is a core functional trait of plant species. Thus, information of the effect of grazing and nitrogen addition on the occurrence of species with different SMs can help us understand the influence of grazing and fertilization on survival of species and community assembly. In alpine meadows with different grazing and nitrogen addition treatments on the eastern Tibet Plateau, we measured SM and plant height (H) of the most common plants and conducted a series of quadrat surveys. Overall, grazing promoted survival of small-seeded species, while fertilization suppressed their survival. At the community level, moderate grazing reduced the average community weighted mean (CWM) of SM and increased the coefficient of variation (CV) of SM. However, there was no significant difference between the functional diversity (FDrao, calculated as Rao's index) of SM in grazed and nongrazed meadows. Nitrogen addition significantly increased the CWM of SM, had a marginally significant effect on FDrao of SM, but had no significant effect on CV of SM. The impact of gazing and fertilization on occurrence of species with different SMs can be explained by their effect on vegetation height. From the perspective of SM selection, our study helps clarify the mechanism of species diversity loss due to fertilization, and that of species diversity increase by moderate grazing.

Quantum dot (QD) solids are an emerging platform for developing a range of optoelectronic devices. Thus, understanding exciton dynamics is essential towards developing and optimizing QD devices. Here, using transient absorption microscopy, we reveal the initial exciton dynamics in QDs with femtosecond timescales. We observe high exciton diffusivity (~10² cm² s¯¹) in lead chalcogenide QDs within the first few hundred femtoseconds after photoexcitation followed by a transition to a slower regime (~10¯¹–1 cm² s¯¹). QD solids with larger interdot distances exhibit higher initial diffusivity and a delayed transition to the slower regime, while higher QD packing density and heterogeneity accelerate this transition. The fast transport regime occurs only in materials with exciton Bohr radii much larger than the QD sizes, suggesting the transport of delocalized excitons in this regime and a transition to slower transport governed by exciton localization. These findings suggest routes to control the optoelectronic properties of QD solids.

Aiming at the low comprehensive utilization rate of corn straw resources, a straw kneading and cutting conveyor suitable for corn harvester was designed to improve the utilization rate of corn straw resources. The workbench module of ANSYS is used to carry out modal analysis of the two blades, and it is determined that the vibration frequency will not cause damage to the blade sweeping bore. By changing the structure of the movable blade shaft, the speed of the blade shaft can be reduced while ensuring the effect of straw crushing and collecting. In order to determine the best working parameters, three-factor and three-level orthogonal test was carried out with blade arrangement, blade shaft speed and length of feed straw as test factors, and the crushing rate of straw as evaluation index. The results show that the main factors influencing the crushing rate of straw are blade shaft speed, blade arrangement and the minor factor is the length of feed straw. Finally, the optimum combination parameters, blade arrangement, blade shaft speed 400 r/min and whole plant feed with straw, were determined. The corresponding straw crushing rate was 96.39%. The research meets the requirements of straw crushing and can provide technical scheme for comprehensive utilization of corn straw.