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The $p$ -GaN gate technology is commonly implemented to achieve normally OFF gallium nitride (GaN) devices. Nonetheless, the threshold voltage instability under OFF-state stress remains a concern. In this article, the characterization technique of threshold voltage shift is proposed and the $V_{\text {th}}$ shift’s impact on device performance is investigated. Specifically, a fast $V_{\mathrm {th}}$ the measurement circuit is introduced and validated to successfully characterize both the magnitude and the time-constant of the $V_{\mathrm {th}}$ shift. According to the experimental results, the $V_{\mathrm {th}}$ increases by more than 50% within several $\mu \text{s}$ after the high drain voltage is applied. In contrast, the $V_{\mathrm {th}}$ slowly (tens of seconds) gets back to the static value after the stress is removed. Following the characterization, the threshold voltage instability’s impact on the device’s static/switching performance is studied experimentally. A knee point shift is observed at low gate voltage, and the static ON-resistance value remains unchanged. Regarding the switching performance, the turn-ON loss increases by >20% after the high drain voltage stress. The change in turn-ON loss can be reduced when the gate resistance is decreased from 20 to $0~\Omega $ . In terms of the turn-OFF loss, the impact of the $V_{\mathrm {th}}$ shift is negligible. It is concluded that time-dependent threshold voltage shift needs to be considered in $p$ -GaN device’s modeling, and high gate drive voltage together with low gate resistance is recommended to mitigate the $V_{\mathrm {th}}$ instability’s effect on $p$ -GaN high-electron-mobility transistor’s performance.

Avalanche ruggedness is one of the key factors for safe and reliable power converters deployed in various automotive subsystems. In this article, the avalanche capability of power MOSFETs is tested under different repetitive avalanche conditions to differentiate the die degradation and package degradation. While examining the degradation mechanisms, the corresponding electrical parameter shifts are analyzed to better understand the structural changes and root causes and identify potential precursors for condition monitoring. For this purpose, a high-resolution and cost-effective nanosecond current pulse generator (CPG) is designed. Due to the high-resolution pulsewidth modulation function of a digital signal processor (DSP), short current pulses can be generated in the order of 100 ps where the magnitude and duration of the current pulsewidth can be adjusted precisely. During the experiments, power MOSFETs are stressed under two different pulsewidths. It is observed that the ON-state resistance gradually increases in both cases, yet the roots of the degradations are different. The die degradation and package degradation are responsible for the changes in short pulse and long pulse, respectively. In the short pulse case, some devices show saturation in drain leakage current and ON-state resistance, while some others show a significant threshold voltage drop, which leads to a noticeable shift of transfer and output characteristics. The electrical parameter shifts indicate a possible gate degradation after the device aging. At the end of the tests, failure analyses are conducted on both devices under test (DUTs) under different stress conditions, revealing different failure mechanisms.

Herein, the influence of platinum (Pt) catalyst on the interface between SiO 2 nanofiller and addition cure silicone rubber (ALSR) matrix is investigated with different concentrations of Pt catalyst. It is found through various tests that Si–O–Si covalent bonds and hydrogen bonds form at the interface with a moderate amount of Pt catalyst. Based on these observations, a model for the interfacial structure of ALSR/SiO 2 nanocomposites is proposed. In particular, it is demonstrated, without changing the mass fraction and surface modifier of the filler, a more compact interface is obtained by increasing the amount of added Pt catalyst by a few ppm, resulting in a 25% increase of breakdown strength, 10% increase in thermal conductivity, 50% increase in tensile strength, and a 31% increase in the elongation at break.

An unusual tensile deformation behaviour in the form of a propagating band along the sample gauge was observed in two neutron-irradiated 316 stainless steel samples during room-temperature tests, leading to a combination of high strength and high ductility. These bands were not observed in an unirradiated counterpart. With the help of in situ high-energy synchrotron x-ray diffraction, the phase-specific crystal information was tracked at different deformation levels in each sample. Post-irradiation and post-deformation samples were examined using electron microscopy to characterize various microstructural features. All samples displayed a deformation-induced martensitic phase transformation, which was identified as a second strain-hardening mechanism accompanying the dislocation hardening. The deformation-induced martensitic transformation was rationalized by the effect of applied stress on the effective martensite start temperature. The results showed that the irradiation did not alter the dislocation hardening and the martensitic transformation mechanisms, but the increased yield strength in irradiated materials facilitated the localized phase transformation at the onset of plastic deformation, in contrast to the unirradiated material which required pre-straining. The hardening effect of the martensitic transformation reduced the tendency towards necking and mitigated the loss of ductility in the irradiated material by carrying the deformation in the form of a propagating band. Despite the beneficial effect from the martensitic transformation, this study indicates that this mechanism cannot not be activated at typical operating temperatures of nuclear reactors.

Food consumption has been identified as a major pathway for human exposure to short-chain chlorinated paraffins (SCCPs) and medium-chain chlorinated paraffins (MCCPs), but evaluations of SCCP and MCCP intake from major dietary sources are limited. We used the sixth Chinese Total Diet Study to perform a comprehensive investigation of SCCPs and MCCPs in cereals, vegetables, potatoes, legumes, eggs, milk, meats, and aquatic foods from nine southern provinces. The geographical distribution of CP concentrations showed higher levels in Jiangsu, Hubei, and Zhejiang provinces. The CP concentrations in most animal-origin foods were higher than those in foods of plant origin. The total estimated daily intakes (EDIs) of SCCPs and MCCPs, with average values of 7.0 × 102 and 4.7 × 102 ng kg-1 day-1, respectively, were mostly contributed by cereals, vegetables, and meats. Risk assessment indicated the EDIs of CPs posed no significant risk to residents in South China.

To enhance the glucaric acid (GA) production in Saccharomyces cerevisiae, the Vitreoscilla hemoglobin was employed to reinforce cellular oxygen supplement. Additionally, the pH-free fermentation strategy was engaged to lower the cost brought by base feeding during the acid-accumulated and long-period glucaric acid production. Recombinant yeast Bga-4 was constructed harboring Vitreoscilla hemoglobin on the basis of previous Bga-3. Higher glucose uptake rate, growth rate, and ethanol reuse rate were achieved in Bga-4 in shake-flask fermentation than those in Bga-3. Furthermore, the fed-batch fermentation in a 5-L bioreactor was performed without pH control, resulting in a final glucaric acid titer of 6.38 g/L. Both the GA titer and biomass were enhanced along with the efficiency of ethanol re-utilization in the presence of VHb. Moreover, the absence of base feeding for long-period fermentation reduced production cost, which is meaningful for industrial applications.

Orientation-controlled growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs) may enable many new electronic and optical applications. However, previous studies reporting aligned growth of WSe2 usually yielded very small domain sizes. Herein, we introduced gold vapor into the chemical vapor deposition (CVD) process as a catalyst to assist the growth of WSe2 and successfully achieved highly aligned monolayer WSe2 triangular flakes grown on c-plane sapphire with large domain sizes (130 µm) and fast growth rate (4.3 µm·s−1). When the aligned WSe2 domains merged together, a continuous monolayer WSe2 was formed with good uniformity. After transferring to Si/SiO2 substrates, field effect transistors were fabricated on the continuous monolayer WSe2, and an average mobility of 12 cm2·V−1·s−1 was achieved, demonstrating the good quality of the material. This report paves the way to study the effect of catalytic metal vapor in the CVD process of TMDCs and contributes a novel approach to realize the growth of aligned TMDC flakes.

LiAl-layered double hydroxide (LiAl-LDH) has been reported as a potential hardening accelerator of calcium sulfoaluminate (CSA) cement. Until now, little has been known about the effect of synthesis conditions and post-synthetic treatments of LiAl-LDH on the performance of CSA cement. The present work shows two methods for the synthesis of LiAl-LDH – a solvothermal method and a separate nucleation and aging steps method (SNAS) – and two methods for the post-synthetic treatments of LiAl-LDH, with and without drying process. The effect of the resultant LiAl-LDH on the performance of CSA cement was studied in relation to the strength, hydration process and products. Results indicate that specimens containing LiAl-LDH showed a greatly enhanced performance with regard to setting time and compressive strength at early and later ages. Compared to LiAl-LDH prepared with the solvothermal method, LiAl-LDH from SNAS synthesis is more effective to increase the compressive strength and shorten setting time. Moreover, the post-synthetic treatments affect the performance of LiAl-LDH. LiAl-LDH without a drying process has better dispersion stability, higher compressive strength and a shorter setting time. Owing to the crystal seed effect, LiAl-LDH enhanced the hydration rate and improved the amount of hydration products, resulting in a higher compressive strength.

Nonwoven-based microfluidics is an emerging field in low-cost microfluidics as another alternative to paper-based microfluidics. Comparing with the conventional paper material that has been widely used in low-cost microfluidics, the cost of nonwoven fabric material is the same range, but with the advantages of higher mechanical strength and a wider choice of chemical/physical properties. In this study, we proposed a novel method for defining a programmable and single-use wax valve on nonwoven-based microfluidic devices. The nonwoven-based microfluidic devices were fabricated using wax-printing and thermal reflow approach to define the basic microchannels for fluid penetration. Then, another layer of wax material contain valve structures were deposited on the surface of the microchannels, each wax valve structure has a corresponding heater resistor that can trigger the wax penetration to block (close) the microchannel. With the controlled thermal actuator operation, the fluid penetration inside the porous media of nonwoven fabric microchannel can be programmed with the control of wax valves. A chemical method for reopening the microchannels was also introduced in this study. The proposed programmable wax valve on nonwoven-based microfluidics is easily accessible with low-cost for point-of-care applications in biological and medical fields.

Nanographenes (NGs) with tunable electronic and magnetic properties have attracted enormous attention in the realm of carbon-based nanoelectronics. In particular, NGs with biradical character at the ground state are promising building units for molecular spintronics. However, most of the biradicaloids are susceptible to oxidation under ambient conditions and photolytic degradation, which hamper their further applications. Herein, we demonstrated the feasibility of tuning the magnetic properties of zigzag-edged NGs in order to enhance their stability via the controlled Diels-Alder reactions of peri-tetracene (4-PA). The unstable 4-PA (y0 =0.72; half-life, t1/2 =3 h) was transformed into the unprecedented benzo-peri-tetracenes (BPTs) by a one-side Diels-Alder reaction, which featured a biradical character at the ground state (y0 =0.60) and exhibited remarkable stability under ambient conditions for several months. In addition, the fully zigzag-edged circumanthracenes (CAs) were achieved by two-fold or stepwise Diels-Alder reactions of 4-PA, in which the magnetic properties could be controlled by employing the corresponding dienophiles. Our work reported herein opens avenues for the synthesis of novel zigzag-edged NGs with tailor-made magnetic properties.

In this article, an in situ SiC mosfet degradation monitoring method using readily available converter sensors is presented. Device's drain-source resistance in saturation and ohmic regions are employed as aging precursors to, respectively, indicate die and package-related degradations. The presented findings in this article are essential for low-cost and practical early warning systems in power electronics applications. To verify the effectiveness of the proposed method, a number of power-cycling tests are conducted to analyze aging process and fatigue mechanism. Device static parameters are measured throughout accelerated aging tests and the physical causes behind them are discussed in detail. It is shown that the drain-source resistance within saturation region at low gate bias can be used to indicate die-related degradation. Similarly, at full positive gate bias, device on -state drain-source resistance can be used to detect package-related degradation. In order to find out optimal variables such as applied gate bias, pulse duration, etc., a comprehensive single pulse test is conducted and the results are reported. Finally, the proposed degradation monitoring method is experimentally validated in the context of a three-phase inverter considering different sensor configurations and load types.

The Daqingshan gold deposit, located in the Beishan orogenic belt, northwestern China, is hosted in a Carboniferous greenschist facies metavolcanic-sedimentary sequence. Three periods of metamorphic and deformational events were recognized, corresponding with the three types of quartz veins in the deposit area. Quartz veins formed in the second period (D2) are the main auriferous ones that are strictly controlled by the subsidiary structures of the Kuluke shear zone. Gold mineralization occurs both as quartz veins and as enveloping altered wall rocks. Native gold, pyrite, and arsenopyrite are the primary ore minerals, while quartz and sericite are the main gangue minerals. Wall-rock alteration predominantly consists of silicification, sericitization, arsenopyritization, and pyritization. Systematic fluid inclusion investigation shows that CO2-H2O three-phase inclusions are the dominant type of fluid inclusions in the auriferous quartz veins, suggesting that the ore-forming fluids belong to a CO2-H2O ± CH4 ± N2 system that is particularly rich in CO2. The ore fluids are characterized by medium to high temperature (230~380 °C), low salinity (2~8% NaCleqv.), and medium density (0.8~0.9 g/cm3). Oxygen isotopes (δ18Ofluid = 11.3‰ to 13.9‰) indicate that the ore-forming fluids were most likely derived from metamorphic water. Fluid immiscibility might be the critical mechanism leading to the deposition of gold. The U-Pb dating results of hydrothermal zircons from auriferous quartz veins indicated that the maximum timing of the gold mineralization at Daqingshan was 295 Ma, the Early Permian. Comprehensive studies suggest that the Daqingshan deposit is a typical orogenic gold deposit formed during the subduction-accretionary phase of the Beishan orogenic belt. Significantly, recognizing the ore genesis of the Daqingshan gold deposit has an important implication for deep and regional mining exploration of southern Beishan.

Nanocarbons have emerged as low-cost, efficient and durable nonmetallic catalysts for H2S selective oxidation. However, the most efficient active sites for H2S activation remain elusive, which restricts further development of high-performance catalysts for industrial application. Herein, we report on the synthesis of N-doped carbon nanoflakes with tunable nitrogen dopants and abundant structural defects for H2S selective oxidation. These defect enriched N-doped carbon nanoflakes exhibited significantly enhanced catalytic performance (>740 gsulfur kgcat.−1 h−1), stability (>110 h) and decent tolerance to impurity gas (CO2) and steam toward continuous H2S selective oxidation. Combined advanced characterization, control experiments and theoretical simulation showed that the N species along with defects on N-doped carbon nanoflakes could enhance significantly the catalytic activity, and further confirmed that the pyridinic N was the most active species and the C atoms adjacent to N atoms exhibit strong interaction with HS−. Our study provides predictive guidelines for the rational design of highly efficient and durable carbocatalysts for continuous catalytic oxidative desulfurization.

Interspecific root separation is an important example of spatial niche differentiation that drives species coexistence in many ecosystems. Particularly under water-stressed conditions, it is believed to be an inevitable outcome of species interactions. However, evidence for and against this idea has been found. So far, studies aiming at reconciling the debate have mainly focused on abiotic determinants. It remains unclear if and to what extent root separation depends on the type and growth form of interacting plants. We conducted a detailed field study in three adjacently located (with pairwise distances

In this paper, a graphical tuning method for controllers parameters based on the open-loop fractional transfer function (FO-EOTF) method is proposed for fractional-order parameter uncertain multivariable system. The FO-EOTF method is proposed to transform the parameter uncertain fractional-order multivariable system into a set of independent parameter uncertain fractional-order univariate systems and determine the parameters regions of the univariate systems. The gain phase margin tester is used to further guarantee the robust performance of the controlled system. Finally, simulation result from the numerical simulation is presented to demonstrate the effectiveness of this method.

This study proposed a novel method for the fabrication of non-woven based microfluidic devices with a wax hydrophobic barrier. Current microfluidic devices were fabricated with glass or polymer material, and paper is also widely used for the fabrication of low-cost microfluidic devices. The application of non-woven fabric based microfluidic devices provides a new option of bulk materials for microfluidics. Compared with the glass or polymer material used in microfluidics, non-woven fabric is low-cost, easy to process and disposable. Fluid can penetrate through the non-woven fabric material with capillary force without the requirement of external pumps. As fiber-based material, comparing with paper, non-woven fabric material is more durable with higher mechanical strength, and various types of non-woven fabric material also provide a board choice of surface chemical/physical properties for microfluidic applications. In this study, the hydrophilic non-woven fabric is chosen as the bulk material for microfluidic devices, a wax pattern transfer protocol is also proposed in this study for the deposition of hydrophobic barriers. For a demonstration of the proposed fabrication technique, a microfluidic mixer was also fabricated in this study.

A unique class of crystalline Ge1–ySny alloys with ultrahigh Sn concentrations reaching 33% as well as Si-doped analogues have been synthesized directly on large-area Si wafers by chemical vapor de...

The dynamic on -resistance in gallium nitride (GaN) devices is problematic as it can impair the converter's efficiency due to the increased conduction loss. In this paper, the hard-switching transient's effect on the dynamic on -resistance is, for the first time, evaluated experimentally on a commercial high-voltage GaN high electron mobility transistor. A new ${R_{{\rm{dyn}} - {\rm{ds}},{\rm{on}}}}$ measurement circuit with fast sensing speed is designed, and an accurate measurement of ${R_{{\rm{dyn}} - {\rm{ds}},{\rm{on}}}}$ can be realized experimentally within 49.6 ns after the device's current reaches to the load current. A double-pulse-test setup is designed to comprehensively evaluate the switching transient's effect on ${R_{{\rm{dyn}} - {\rm{ds}},{\rm{on}}}}$ under different operating conditions. From the experimental results, it is found that the turn- on and turn- off gate resistance have a significant impact on the dynamic on -resistance whereas the cross-talk effect on ${R_{{\rm{dyn}} - {\rm{ds}},{\rm{on}}}}$ is negligible. Specifically, at 400 V/25 A, more than 27% (28.2%) increase in ${R_{{\rm{dyn}} - {\rm{ds}},{\rm{on}}}}$ is observed when the external turn -on (turn- off ) gate resistance increases from 0 to 20 Ω. Detailed discussion and quantitative analysis are provided to explain the experimental results. In terms of the turn -on process, it is concluded that the ${R_{{\rm{dyn}} - {\rm{ds}},{\rm{on}}}}$ variation is mainly caused by the different numbers of generated hot electrons. For the turn -off transient, it is confirmed the variation of drain current at different dv/dt slew rate leads to the ${R_{{\rm{dyn}} - {\rm{ds}},{\rm{on}}}}$ difference.

Light Detection and Ranging (lidar) technology has been applied in military and civil areas and shows great potential. However, in coherent lidar detection, significant Doppler Effect and velocity uncertainty result a bad influence on moving target ranging. In this study, the authors demonstrate a velocity compensation method based on both Doppler shift evaluation and velocity searching and matching method. The authors used dot-linear frequency modulation signal for detection in order to achieve both velocity and distance information in the same period. Further by using searching and matching processing based on Shannon entropy can give a better-compensated velocity to extract more accurate distance information of targets. The authors applied this method on passive and self-driving moving targets, which fit the actual characteristics of both kinds of targets. Especially in self-driving moving target, there exists a significant target fluctuation in movement during detection that causes the splitting of Doppler peaks. The blurry in velocity estimation restricts the accuracy of sensing. The authors found the Shannon entropy searching method could reduce this effect. On the other hand, the feature of fluctuation in micro movement may give a way to identify the targets in the future.

A planar and broadband cholesteric liquid crystal (CLC) lens is designed, fabricated, and hybridized with a refractive lens to form a catadioptric pancake lens for virtual reality (VR) displays. Due to their opposite optical dispersion behaviors, the chromatic aberration of the assembled pancake lens is dramatically suppressed, as verified by both ray-tracing analysis and experimental results. The demonstrated catadioptric pancake lens has great potential for next-generation VR displays.

Autonomous driving, which can free our hands and feet, is of increasing importance in our daily lives. However, the capacity of onboard computation and communication limits the rapid development of autonomous driving. To address this issue, this paper proposes a novel model named the edge computing-based lanes scheduling system (ECLSS) to study lane scheduling for each vehicle around crossroads with real-time edge devices. There are several edge computing devices (ECD) deployed around crossroads in ECLSS that can collect information from vehicles and road conditions with short-range wired/wireless transmissions. Based on the strong computing power of ECDs and their real-time transmission performance, we propose two centralized management lane scheduling methods: the searching for efficient switching algorithm (SESA) and special vehicles lane switching algorithm (SVLSA). These edge computing-based autonomous driving methods aim to achieve high speed passing through crossroads and guarantee that special vehicles can pass through crossroads within a certain time. Extensive simulations are conducted, and the simulation results demonstrate the superiority of the proposed approaches over competing schemes in typical lane switching scenarios.

The fabrication of a bionic super-hydrophobic metallic surface without any low-surface-energy modification is investigated, in which picosecond laser ablation, electropolishing and electrodeposition are used sequentially. The micro-cone structure is formed via laser ablation, and then the nano-pyramid structure is electrodeposited on the micro-cone structure, resulting in a hierarchical structure that is important for achieving super-hydrophobicity on an intrinsically hydrophilic material surface. In this study, the surface morphology and material removal mechanism are discussed with respect to the laser-ablated surface and the subsequent electropolished/electrodeposited surfaces. The condensation experiments results show that both types of surfaces are associated with relatively high contact angles (CAs) at normal temperatures, and the CAs are 147° and 160°, respectively. However, the CA on the laser-ablated surfaces at low temperatures decreases to as less as 107°, which may be owing to the easy transition from Cassie state to a metastable state or even the Wenzel state, leading to a degraded hydrophobic surface. By contrast, the CA on the sequentially processed surfaces still maintains at 150°, which should be attributed to the densely distributed nano-scale structures. The sequentially processed surfaces also show excellent long-term durability. Furthermore, this technique has been employed for fabricating super-hydrophobic surfaces with CAs > 151° and the sliding angles (SAs)

A novel EMD-based denoising method, referred to as EMD with soft thresholding and Savitzky-Golay, is proposed for single photon lidar denoising. After the discrimination of the high-frequency and low-frequency IMFs, the soft thresholding and Savitzky-Golay filter are applied, respectively. The proposed denoising method has a better denoising performance and less signal distortion on simulated single photon lidar data than that of EMD partial reconstruction and wavelet transform method. With the proposed method, the SNR of real single photon lidar increased from 12.36 to 15.32 dB and false alarm rate is reduced obviously.

In the present work, we show the preparation of (In,Ga,Mn)As films with different Ga concentration by Mn ion implantation and pulsed laser melting. All films are confirmed to be well recrystallized by Rutherford backscattering spectrometry/channeling and to be ferromagnetic by magnetometry measurements, respectively. Their Curie temperatures depend on the Ga concentration. Our results show the perspective of ion implantation in the preparation of different III-Mn-V quaternary alloys as new members of diluted ferromagnetic semiconductors.

Severe lithium (Li) dendrite growth during the plating/stripping process, which results in low Coulombic efficiency and safety issues, strongly hinders the practical applications of Li metal anodes. Herein, we propose a novel design of three-dimensional (3D) interconnected graphene (IG) framework synthesized with the help of nickel (Ni) microspheres for stable Li metal anodes. The as-prepared IG framework consists of multiple stacks of two-dimensional (2D) graphene layers and plenty of hollow graphene microspheres in between, and thus provides protective layers on the top to suppress lithium dendrites, sufficient surface area to reduce the effective current density, as well as ion channels for fast Li transport, which is confirmed by post-cycle morphology characterization. When Li foil was used as the counter electrode for Li deposition, the assembled coin cell maintained an average Coulombic efficiency of more than 97.5% for 100 cycles at current density of 1 mA cm−2 with a Li loading of 1 mAh cm−2. Furthermore, we achieved stable cycling for more than 300 h at a current density of 1 mA cm−2 with a Li loading of 2 mAh cm−2 when assembled as symmetric cells. This strategy of vertically stacking 2D materials provides a novel approach towards dendrite-free Li metal anodes for the next-generation energy storage systems.

The Basel Accord requires commercial banks to meet a capital requirement for operational risk. Therefore, a reliable operational risk measurement is of great significance for financial institutions. In this paper, based on the framework of LDA, we propose a more appropriate model (Double Correlation model) in correlation structure construction, which considers both frequency correlation and mean severity correlation simultaneously. On this basis, annual loss scenarios for each risk cell are restored and VaR is also estimated by Monte Carlo simulation. Empirical study adopts the data of Chinese commercial banks disclosed to the public and contains the comparison of double correlation model and the other four correlation models. The result indicates that the VaR estimated by the double correlation model is significantly lower than that upon the assumption of comonotonicity, proving the existence of risk diversification. Meanwhile, the VaR estimated by double correlation model is significantly lower than that of the other two correlation models when confidence level is lower than 99% but the relationships between them will reverse if the confidence level rises to more than 99%.

Livestock grazing is the most extensive human land use and one of the key drivers of the conversion of tropical forests into grasslands. Livestock effects on vegetation structure are complex, as they can prevent tree recruitment and growth through browsing and trampling, but they can also affect vegetation indirectly through fire interactions. However, a systematic analysis of the overall effects of livestock across the global tropics is lacking. We analyzed remote sensing data on vegetation height and cover, climate, and fire as well as ground data on livestock density. We used generalized linear models and structural equation models to analyze the effects of livestock on fire regimes and vegetation structure. Across the global tropics, higher livestock densities are associated to lower fire frequency and a higher cover of shrubs and dwarf trees. This pattern occurs across continents, and is particularly pronounced at intermediate precipitation levels (1000–1500 mm y−1) where fire frequency is highest. In those regions, fire frequency is on average 49% lower in areas with high versus low livestock densities. South America has much higher livestock density and lower fire frequency than Africa and Asia–Australia across the whole precipitation gradient. Our findings suggest that livestock grazing reduces fire incidence through grass consumption and favors shrubs and a sparse cover of trees in regions where forests could potentially exist. Livestock can thus be a strong modifier of the climatic effect on vegetation structure, and livestock management changes can impact the structure and functioning of savannas and grasslands throughout the global tropics.

Studies on the highly pathogenic avian influenza (HPAI) H5N1 suggest that wild bird migration may facilitate its long-distance spread, yet the role of wild bird community composition in its transmission risk remains poorly understood. Furthermore, most studies on the diversity–disease relationship focused on host species diversity without considering hosts’ phylogenetic relationships, which may lead to rejecting a species diversity effect when the community has host species that are only distantly related. Here, we explored the influence of waterbird community composition for determining HPAI H5N1 occurrence in wild birds in a continental-scale study across Europe. In particular, we tested the diversity–disease relationship using both host species diversity and host phylogenetic diversity. Our results provide the first demonstration that host community composition—compared with previously identified environmental risk factors—can also effectively explain the spatial pattern of H5N1 occurrence in wild birds. We further show that communities with more higher risk host species and more closely related species have a higher risk of H5N1 outbreaks. Thus, both host species diversity and community phylogenetic structure, in addition to environmental factors, jointly influence H5N1 occurrence. Our work not only extends the current theory on the diversity–disease relationship, but also has important implications for future monitoring of H5N1 and other HPAI subtypes., SCOPUS: ar.j, info:eu-repo/semantics/published

Optically pumped Ge1-ySny lasers operating at low temperature have been recently demonstrated. This article reviews the challenges to efficient lasing that arise from the intrinsic properties of alloys in the Si-Ge-Sn system. The first such challenge is the possibility that even in nominally direct gap Ge1-ySny materials, a significant fraction of pumped carriers reside in the valleys associated with the indirect gap, and therefore are not available for lasing. We find theoretically that this is indeed the case at room temperature, possibly explaining the strong temperature dependence of lasing. A second challenge is finding appropriate barrier materials to reduce the lasing threshold power via spatial confinement. We show that strained layer Ge1-ySny/Ge1-y'Sny' multilayers are unlikely to produce the required direct gap Type-I alignment, and that even the introduction of ternary Ge1-x-ySixSny layers may not lead to suitable lasing structures due to giant bowing parameters in the compositional dependences of their interband transition energies.

The glass forming ability, microstructure, magnetism and magnetocaloric effect (MCE) in two quinary rare-earth rich amorphous ribbons of Tm20Ho20Gd20Co20Ni20 and Tm20Ho20Gd20Co20Cu20 are reported. Both amorphous ribbons exhibit excellent glass forming ability and a table-like MCE. In addition to large magnetic entropy change of ∼14.0 J/kg-K, an extremely high refrigerant capacity of ∼790 J/kg are achieved which can almost cover the temperature range from liquid hydrogen to liquid nitrogen for the magnetic field change of 0–7 T for both ribbons. Therefore, the quinary rare-earth rich amorphous ribbons can be proposed as a new class of promising magnetic refrigeration materials.

Irradiation induced microstructural changes in the NF709 austenitic stainless steel were investigated under 1 MeV Kr ion irradiations to a dose of 3 dpa at room temperature (RT), 300, 400, 500 and 600 °C, and a dose of 20 dpa at RT. The irradiation-induced defects and the stability of precipitates were characterized with transmission electron microscopy (TEM). Frank dislocation loops were observed in all the irradiated samples, and the loop sizes were much larger at 600 °C than those at lower temperatures. “Raft” defect structures, formed through self-alignment of small dislocation loops, were also observed in all irradiated samples. M23C6 precipitates were amorphorized under irradiations at RT and 300 °C, but remained to be crystalline at 400 °C and above. MX precipitates were stable under irradiations at RT up to 20 dpa, and at temperatures below 600 °C to 3 dpa. At 600 °C, some MX precipitates were observed to dissolve during in-situ irradiation, suggesting possible precipitate instability at this irradiation temperature.

Quasi-two-dimensional (2D) β-Ga2O3 is a rediscovered metal-oxide semiconductor with an ultra-wide bandgap of 4.6–4.9 eV. It has been reported to be a promising material for next-generation power and radio frequency electronics. Field effect transistors (FETs) that can switch at high voltage are key components in power and radio frequency devices, and reliable Ohmic contacts are essential for high FET performance. However, obtaining low contact resistance on β-Ga2O3 FETs is difficult since reactions between β-Ga2O3 and metal contacts are not fully understood. Herein, we experimentally demonstrate the importance of reactions at the metal/β-Ga2O3 interface and the corresponding effects of these reactions on FET performance. When Ti is employed as the metal contact, annealing of β-Ga2O3 FETs in argon can effectively transform Schottky contacts into Ohmic contacts and permit a large drain current density of ~ 3.1 mA/μm. The contact resistance (Rcontact) between the Ti electrodes and β-Ga2O3 decreased from ~ 430 to ~ 0.387 Ω·mm after annealing. X-ray photoelectron spectroscopy (XPS) confirmed the formation of oxygen vacancies at the Ti/β-Ga2O3 interface after annealing, which is believed to cause the improved FET performance. The results of this study pave the way for greater application of β-Ga2O3 in electronics.

The tensile deformation behavior of a high-temperature, ultrafine-precipitate strengthened (HT-UPS) stainless steel was characterized in-situ with high-energy X-ray diffraction at 20 and 400 °C. The HT-UPS samples were neutron irradiated to 3 dpa at 400 °C. Significant irradiation hardening and ductility loss were observed at both temperatures. Lattice strain evolutions of the irradiated samples showed a strong linear response up to near the onset of the macroscopic yield, in contrast to the unirradiated HT-UPS which showed a pronounced non-linear behavior well below the macroscopic yield. While the room-temperature diffraction elastic moduli in the longitudinal direction increased after irradiation, the 400 °C moduli were similar before and after irradiation. The evolution of the {200} lattice strain parallel to the loading axis ( e { 200 } L ) showed unique characteristics: in the plastic regime, the evolution of e { 200 } L after yield is temperature-dependent in the unirradiated specimens but temperature-independent in the irradiated specimens; and the value of e { 200 } L at the yield is an irradiation-sensitive, temperature-independent parameter. The evolution of e { 200 } L corresponds well with the dislocation density evolution, and is an effective probe of the deformation-induced long-range internal stresses in the HT-UPS steel.

Dietary intake is an important route of human exposure to chlorinated paraffins (CPs). Cup instant noodles are widely popular food and millions packet of instant noodles are consumed every year. To investigate the levels, congener groups, and health risk of SCCPs and MCCPs in each component of cup instant noodles, samples of nine common brands were collected and analyzed by comprehensive two dimensional gas chromatography coupled with mass spectrometry. The mean concentrations in the noodles were 1.2 × 103 ng/g wet weight (ww) (SCCPs) and 1.2 × 102 ng/g ww (MCCPs), the mean concentrations in the seasoning were 1.4 × 103 ng/g ww (SCCPs) and 1.3 × 102 ng/g ww (MCCPs), and the mean concentrations in the soup were 5.6 × 102 ng/L (SCCPs) and 5.4 × 102 ng/L (MCCPs). The SCCP to MCCP ratio were similar in the soup and soup container, which means CPs in the soup might be migrated from the soup container. Seasoning and noodles from the same brands have similar congener profiles of SCCPs and MCCPs, which may be raised from the manufacturing process or food packaging materials. The dominant SCCP congener groups were C10–11Cl6–7 in noodles and seasoning, and C10,13Cl6–7 in soup. The dominant MCCP congener groups were C14–15Cl6–7 in noodles and seasoning, and C14–15Cl6–7 in soup. A preliminary health risk assessment indicated that the current intakes of SCCPs and MCCPs through cup instant noodles in China did not pose a significant risk to human health.

There is a rising prospective in harvesting energy from the environment, as in situ energy is required for the distributed sensors in the interconnected information society, among which the water flow energy is the most potential candidate as a clean and abundant mechanical source. However, for microscale and unordered movement of water, achieving a sustainable direct-current generating device with high output to drive the load element is still challenging, which requires for further exploration. Herein, we propose a dynamic PN water junction generator with moving water sandwiched between two semiconductors, which outputs a sustainable direct-current voltage of 0.3 V and a current of 0.64 μ A. The mechanism can be attributed to the dynamic polarization process of water as moving dielectric medium in the dynamic PN water junction, under the Fermi level difference of two semiconductors. We further demonstrate an encapsulated portable power-generating device with simple structure and continuous direct-current voltage output of 0.11 V, which exhibits its promising potential application in the field of wearable devices and the IoTs.

Lead–sCO2 intermediate heat exchanger (IHX) was designed for lead-cooled fast reactor (LFR). The reactor coolant is lead and flowing through a circular straight channel, meanwhile, sCO2 is heated through 5 channels with different geometries were investigated respectively, including straight channel, zigzag 52° channel, S-shaped fins, offset rectangular fins, and airfoil fins. Considering the thermal-hydraulics characteristics, mechanical structure, corrosion, and flow blockage in the IHX designs, the performance, total cost, and power density of several heat exchanger designs were evaluated and compared. Finally, a printed circuit heat exchanger (PCHE) design using the circular straight (lead) - offset rectangular fins (sCO2) channels was proposed. The straight and S-shaped channels for sCO2 flow were recommended as alternative designs under certain circumstances. However, S-shaped fins and zigzag channels will dramatically increase the cost while straight and airfoil channels will greatly increase the volume.

In this paper, a novel fractional-order charge-pump-phase-locked-loop (FO-CPPLL) using a fractional-order loop filter (FO-LF) is proposed to improve the overall system performance. The FO-CPPLL is obtained by extending the traditional CPPLL order from integer domain to real domain by using the FO-LF. Specifically, a fractional-order capacitor is applied to replace the integer-order capacitor in the traditional second-order LF, and the constructed FO-LF is inserted between PFD/CP and VCO to form the FO-CPPLL. The FO-LF actualizes fine tuning accuracy in seeking the orders between [0,1] for FO-CPPLL to improve the tracking speed and reducing the system phase loss. Also, the proposed FO-CPPLL can obtain lower jitter and better stability. Finally, simulation results verify the analysis and effectiveness of the proposed FO-CPPLL.

Hyperdoping Si with chalcogens is a topic of great interest due to the strong sub-bandgap absorption exhibited by the resulting material, which can be exploited to develop broadband room-temperature infrared photodetectors using fully Si-compatible technology. Here, we report on the critical behavior of the impurity-driven insulator-to-metal transition in Te-hyperdoped Si layers fabricated via ion implantation followed by nanosecond pulsed-laser melting. Electrical transport measurements reveal an insulator-to-metal transition, which is also confirmed and understood by density functional theory calculations. We demonstrate that the metallic phase is governed by a power law dependence of the conductivity at temperatures below 25 K, whereas the conductivity in the insulating phase is well described by a variable-range hopping mechanism with a Coulomb gap at temperatures in the range of 2-50 K. These results show that the electron wave-function in the vicinity of the transition is strongly affected by the disorder and the electron-electron interaction., Comment: 19 pages, 6 figures

The dynamical behavior of broken symmetric coupled cavity lasers is theoretically investigated. The frequency response of this class of lasers is obtained using small signal analysis under direct modulation. Our model predicts a modulation bandwidth enhancement as a broken symmetric laser, operating in the parity-time (PT) symmetry and non-PT symmetry domains. This theoretical prediction is numerically examined in a laser system based on an InGaAs quantum dot platform. Our results clearly show that in these structures, in addition to the injection current, the gain-loss contrast can be used as a new degree of freedom in order to control the characteristic poles of the frequency response function.

The emergence of the new coronavirus (nCoV-19) has brought global impact on human health, whilst the interaction between the virus and the host is the foundation of the disease. The viral genome codes a cluster of proteins, each with a unique function in the event of host invasion or viral development. Under current adverse situation, we employ virtual screening tools in searching for drugs and nature products which have been already deposited in the DrugBank in attempt to accelerate the drug discovery process. This study provides an initial evaluation of current drug candidates from various reports using our systemic in silico drug screening based on structures of viral proteins and human ACE2 receptor. Besides, we built an interactive online platform (https://shennongproject.com:11443/#/home) for browsing these results with the visual display of small molecule docked on its potential target protein, without installing any specialized structural software. With continuous maintenance and incorporation of data from laboratory works, it may serve not only as the assessment tool for the new drug discovery but also an educational website to meet general interest from the public.

Coastal wetlands provide many critical ecosystem services including carbon storage. Soil organic carbon (SOC) is the most important component of carbon stock in coastal salt marshes. However, there are large uncertainties when estimating SOC stock in coastal salt marshes at large spatial scales. So far, information on the spatial heterogeneity of SOC distribution and determinants remains limited. Moreover, the role of complex ecological interactions in shaping SOC distribution is poorly understood. Here, we report detailed field surveys on plant, soil and crab burrowing activities in two inter-tidal salt marsh sites with similar habitat conditions in Eastern China. Our between-site comparison revealed slight differences in SOC storage and a similar vertical SOC distribution pattern across soil depths of 0&minus, 60 cm. Between the two study sites, we found substantially different effects of biotic and abiotic factors on SOC distribution. Complex interactions involving indirect effects between soil, plants and macrobenthos (crabs) may influence SOC distribution at a landscape scale. Marked differences in the SOC determinants between the study sites indicate that the underlying driving mechanisms of SOC distribution are strongly system-specific. Future work taking into account complex interactions and spatial heterogeneity is needed for better estimating of blue carbon stock and dynamics.

In this work, a systematic investigation on magnetic critical behavior is performed for the first time on an antiperovskite-type Mn3GaN, which is prepared by intentionally modifying stoichiometry. According to the XRD results, the antiperovskite structure is well preserved, even though all lattice parameters shrink upon reducing Ga and N content down to 60%. The sample exhibits a ferromagneticlike feature with a Curie temperature (T-C) of 394K rather than frustrated behavior in stoichiometric Mn3GaN. Most importantly, the modified Arrott plots, Kouvel-Fisher plots, as well as critical isotherm method self-consistently co-confirm the critical exponents of beta=0.33, gamma=1.23, and delta=4.7, unambiguously indicating that the critical behavior follows the 3D-Ising model around T-C. Published under license by AIP Publishing.

Urban natural surfaces and non-surface human activities are key factors determining the urban heat island (UHI), but their relative importance remains highly controversial and may vary at different spatial scales and focal urban systems. However, systematic studies on the scale-dependency system-specificity remain largely lacking. Here, we selected 32 major Chinese cities as cases and used Landsat 8 images to retrieve land surface temperature (LST) and quantify natural surface variables using point of interest (POI) data as a measure of the human activity variable and using multiple regression and relative weight analysis to study the contribution and relative importance of these factors to LST at a range of grain sizes (0.25–5 km) and spatial extents (20–60 km). We revealed that the contributions and relative importance of natural surfaces and human activities are largely scale-dependent and system-specific. Natural surfaces, especially vegetation cover, are often the most important UHI determinants for a majority of scales, but the importance of non-surface human activities is increasingly pronounced at a coarser spatial scale with respect to both grain and spatial extent. The scaling relations of the UHI determinants and their relative importance were mostly linear-like at the city-collective level, but highly diverse across individual cities, so reducing non-surface heat emissions could be the most effective measure in particular cases, especially at relatively large spatial scales. This study advances the understanding of UHI formation mechanisms and highlights the complexity of the scale issue underpinning the UHI effect.

Like other complex systems, sand dunes alternate between stable states, which have coexisted for 12,000 years in northern China., Dune systems can have alternative stable states that coexist under certain environmental conditions: a vegetated, stabilized state and a bare active state. This behavior implies the possibility of abrupt transitions from one state to another in response to gradual environmental change. Here, we synthesize stratigraphic records covering 12,000 years of dynamics of this system at 144 localities across three dune fields in northern China. We find side-by-side coexistence of active and stabilized states, and occasional sharp shifts in time between those contrasting states. Those shifts occur asynchronously despite the fact that the entire landscape has been subject to the same gradual changes in monsoon rainfall and other conditions. At larger scale, the spatial heterogeneity in dune dynamics averages out to produce relatively smooth change. However, our results do show different paths of recovery and collapse of vegetation at system-wide scales, implying that hysteretic behavior occurs in spatially extended systems.

Two-dimensional (2D) semiconductors have been extensively explored as a new class of materials with great potential. In particular, black phosphorus (BP) has been considered to be a strong candidate for applications such as high-performance infrared photodetectors. However, the scalability of BP thin film is still a challenge, and its poor stability in the air has hampered the progress of the commercialization of BP devices. Herein, we report the use of hydrothermal-synthesized and air-stable 2D tellurene nanoflakes for broadband and ultrasensitive photodetection. The tellurene nanoflakes show high hole mobilities up to 458 cm2/V·s at ambient conditions, and the tellurene photodetector presents peak extrinsic responsivity of 383 A/W, 19.2 mA/W, and 18.9 mA/W at 520 nm, 1.55 μm, and 3.39 μm light wavelength, respectively. Because of the photogating effect, high gains up to 1.9 × 103 and 3.15 × 104 are obtained at 520 nm and 3.39 μm wavelength, respectively. At the communication wavelength of 1.55 μm, the tellurene photodetector exhibits an exceptionally high anisotropic behavior, and a large bandwidth of 37 MHz is obtained. The photodetection performance at different wavelength is further supported by the corresponding quantum molecular dynamics (QMD) simulations. Our approach has demonstrated the air-stable tellurene photodetectors that fully cover the short-wave infrared band with ultrafast photoresponse.

Hand detection is a crucial pre-processing procedure for many human hand related computer vision tasks, such as hand pose estimation, hand gesture recognition, human activity analysis, and so on. However, reliably detecting multiple hands from cluttering scenes remains to be a challenging task because of complex appearance diversities of dexterous human hands (e.g., different hand shapes, skin colors, illuminations, orientations, and scales, etc.) in color images. To tackle this problem, an accurate hand detection method is proposed to reliably detect multiple hands from a single color image using a hybrid detection/reconstruction convolutional neural networks (CNN) framework, in which regions of hands are detected and appearances of hands are reconstructed in parallel by sharing features extracted from a region proposal layer, and the proposed model is trained in an end-to-end manner. Furthermore, it is observed that the generative adversarial network (GAN) could further boost the detection performance by generating more realistic hand appearances. The experimental results show that the proposed approach outperforms the state-of-the-art on public challenging hand detection benchmarks.

Thin films of Si1−xMnx were deposited on Al2O3 substrate using pulsed laser deposition(PLD)technique employing time-of-flight separation of the ejected particles with different laser fluence (E = 3.8–7.6 J/cm2). Magnetic properties of these films reveal that the variation in the laser fluence has engineered several magnetic phases in Si1−xMnx films: high temperature (HT) ferromagnetic (FM) phase Si1−xMnx(x = 0.51–0.52) with uniformly distributed Si vacancies, and the low-temperature (LT) FM phases MnSi and Mn4Si7 with Curie temperature ≤40 K. At small fluence, the mesoscopic size MnSi and Mn4Si7 crystallites are formed in the upper layer of Si1−xMnx films with Si excess (x ≈ 0.4–0.5), yielding to inhomogeneous magnetic phase distribution along the film growth direction, while the high and optimal fluence has resulted in uniform distribution of the HT FM phase during the film growth. The XPS, magnetotransport and ferromagnetic resonance (FMR) measurements confirm the presence of several FM phases in the samples and the amplifying role of LT FM for films grown at E ≤ 4.4 J/cm2.

In this paper, we perform a comparison of magnetic and electrical properties between Mn-doped and (Mn, Zn) co-doped GaP dilute ferromagnetic semiconductors. Due to the shallow Zn impurity level (∼20–40 meV above the top of the III-V compounds valence band), the Zn co-doping leads to the increase of conductivity of (Ga,Mn)P, however both the Curie temperature and magnetization reduce, which is probably due to the suppression of active Mn substitution by Zn co-doping.

Microstructural changes resulted from neutron irradiation and post-irradiation annealing in a high-temperature ultra-fine precipitate strengthened (HT-UPS) stainless steel were characterized using transmission electron microscopy (TEM) and atom probe tomography (APT). Three HT-UPS samples were neutron-irradiated to 3 dpa at 500 °C, and after irradiation, two of them were annealed for 1 h at 600 °C and 700 °C, respectively. Frank dislocation loops were the dominant defect structure in both the as-irradiated and 600 °C post-irradiation-annealed (PIAed) samples, and the loop sizes and densities were similar in these two samples. Unfaulted dislocation loops were observed in the 700 °C PIAed sample, and the loop density was greatly reduced in comparison with that in the as-irradiated sample. Nano-sized MX precipitates were observed under TEM in the 700 °C PIAed sample, but not in the 600 °C PIAed or the as-irradiated samples. The titanium-rich clusters were identified in all three samples using APT. The post-irradiation annealing (PIA) caused the growth of the Ti-rich clusters with a stronger effect at 700 °C than at 600 °C. The irradiation caused elemental segregations at the grain boundary and the grain interior, and the grain boundary segregation behavior is consistent with observations in other irradiated austenitic steels. APT results showed that PIA reduced the magnitude of irradiation induced segregations.