AlGaN/GaN heterostructure devices are capable of delivering high‐frequency power amplifiers and power switches with performances far superior than those offered by the mainstream silicon technology ...and other advanced semiconductor technologies. Primarily driven by applications' need, the last few years have witnessed major effort in the development of AlGaN/GaN enhancement‐mode (E‐mode) HEMTs and MIS‐HEMT. This paper attempts to review the latest progresses in this technology, including alternative approaches and device characteristics. Application examples of the E‐mode HEMT technology are also discussed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•Synthesis of γ-PGA-Fe3O4-GO-(o-MWCNTs) nanocomposite via a simple one-pot reaction.•γ-PGA-Fe3O4-GO-(o-MWCNTs) show obvious adsorption capacity for metal ions.•γ-PGA-Fe3O4-GO-(o-MWCNTs) can be ...separated more easily from solution systems.•Addition of o-MWCNTs solves the serious aggregation problem of GO.
A novel hybrid adsorbent, anionic polypeptide poly(γ-glutamic acid)—(γ-PGA) functionalized magnetic Fe3O4-GO-(o-MWCNTs) hybrid nanocomposite was successfully prepared via a simple one-pot reaction. The as-prepared γ-PGA-Fe3O4-GO-(o-MWCNTs) composites were characterized via SEM, TEM, FTIR, XRD, TGA, AFM, zeta potential analysis and magnetic properties analysis. The results indicate that the addition of o-MWCNTs solves the serious aggregation problem of GO and thus makes the GO exposed more grafted sites bonded to large amount of γ-PGA molecule chains. The prepared γ-PGA-Fe3O4-GO-(o-MWCNTs) composites not only have a higher specific surface area to offer abundant surface adsorption sites, but also can be separated more easily from solution systems. Furthermore, the adsorption tests of the γ-PGA-Fe3O4-GO-(o-MWCNTs) were analyzed in Cd(II), Cu(II) and Ni(II) solutions at various pH values, contact time, and initial concentrations of ions. This work indicates that the hybrid adsorbent can be the suitable absorbent materials for various types of heavy metal ions pollution removal and exhibit higher adsorbing capacities in the pH range of 2–10. Its maximum removal capacity calculated by Langmuir model under the optimal conditions toward Cd(II), Cu(II) and Ni(II) is 625.00, 574.71 and 384.62 mg/g, respectively. The adsorption process was well described by the pseudo-second-order kinetics model and the Langmuir isotherm model, respectively. The adsorption mechanism may involve characteristic coordination bonding and electrostatic attraction between γ-PGA-Fe3O4-GO-(o-MWCNTs) and metal ions. Additionally, anionic polypeptide γ-PGA-Fe3O4-GO-(o-MWCNTs) composite can be easily regenerated and recycled at least for three adsorption–desorption recycles. The unique characteristics render the composite highly promising as an advanced adsorbent material for the removal of heavy metal ions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Photon recycling and carrier diffusion are the two plausible processes that primarily affect the carrier dynamics in halide perovskites, and therefore the evaluation of the performance of their ...photovoltaic and photonic devices. However, it is still challenging to isolate their individual contributions because both processes result in a similar emission redshift. Herein, it is confirmed that photon recycling is the dominant effect responsible for the observed redshifted emission. By applying one‐ and two‐photon confocal emission microscopy on Ruddlesden–Popper type 2D perovskites, of which interplane carrier diffusion is strictly suppressed, the substantial PL redshift (72 meV) is well reproduced by the photon transport model. A comparison of 3D bulk CH3NH3PbBr3 single crystal to 2D perovskite by depth‐resolved two‐photon PL spectra reveals the contribution of carrier diffusion on energy transport at a distance beyond diffusion length is constantly negligible, though the carrier diffusion indeed exists in the 3D crystal. The investigation resolves the fundamental confusion and debate surrounding the issue and provides significant insights into carrier kinetics in perovskites, which is important for future developments in solar cells and other optoelectronic devices.
Photon recycling and carrier diffusion are the two plausible processes that primarily affect the carrier dynamics in halide perovskites, and therefore the evaluation of the performance of their photovoltaic and photonic devices. However, it is still challenging to isolate their individual contributions. Herein, it is confirmed that photon recycling is the dominant effect responsible for the observed redshifted emission.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Bulk traps in the high-resistivity buffer stack underneath the 2-dimensional electron gas (2DEG), which can interact with the high vertical electric field at OFF state, impose a critical challenge to ...the dynamic ON-resistance (RON) of AlGaN/GaN-on-Si power devices. In this paper, the impact of substrate bias polarity on carrier injection/transport and buffer-induced current collapse has been investigated by using ramped and transient back-gating characterizations as well as TCAD simulations. High voltage applied to the conductive Si substrate can modulate 2DEG conductivity through the back-gate effect, whereby the dynamics of both acceptor and donor buffer traps are identified. Distinct buffer trapping and asymmetric vertical leakage under opposite top-to-substratebias polarities have been observed, which are attributed to the fundamentally different carrier injection/transport mechanisms. It is suggested that the energy barrier at the nucleation-layer/Si interface can limit the electron injection from Si substrate into the buffer stack and consequently influence the bufferrelated current collapse.
In this study, we aimed to demonstrate the importance of diabatic heating in extreme rainstorm weather events induced by the Southwest China vortex (SWCV) in different precipitation regions with a ...similar circulation background. The results showed that atmospheric diabatic heating had indicative significance for the intensity evolution of the SWCV and the precipitation area. Changes in the diabatic heating intensity preceded the intensity evolution of the SWCV, and the diabatic heating region was consistent with the heavy precipitation region. The variation in diabatic heating was mainly due to the positive contribution of its vertical transport term. The two types of spatially non-uniform heating effects were similar; however, the western type was located southeast of the SWCV, with an asymmetric distribution on the southeastern and northwestern sides. The eastern type was located in the northeast of the SWCV, with an asymmetric distribution on the northeastern and southwestern sides. The vertically non-uniform heating effect played a decisive role in the distribution and evolution of the spatially non-uniform heating terms. The vertically non-uniform heating effect affected the intensity evolution of the SWCV. In contrast, the horizontally non-uniform heating effect, in opposition to the vertically non-uniform heating effect, had a slightly weaker intensity than the vertically non-uniform heating effect. For the SWCV system, which induces extreme rainstorms, the magnitude of the horizontally non-uniform heating effect could reach that of vertically non-uniform heating; thus, the possible impact of horizontally non-uniform heating should be considered.
An effective passivation technique for AlGaN/GaN high-electron-mobility transistors (HEMTs) is presented. This technique features an AlN thin film grown by plasma-enhanced atomic layer deposition ...(PEALD). With in situ remote plasma pretreatments prior to the AlN deposition, an atomically sharp interface between ALD-AlN and III-nitride has been obtained. Significant current collapse suppression and dynamic ON-resistance reduction are demonstrated in the ALD-AlN-passivated AlGaN/GaN HEMTs under high-drain-bias switching conditions.
Cell-fate decisions remain poorly understood at the chromatin level. Here, we map chromatin remodeling dynamics during induction of pluripotent stem cells. ATAC-seq profiling of MEFs expressing ...Oct4-Sox2-Klf4 (OSK) reveals dynamic changes in chromatin states shifting from open to closed (OC) and closed to open (CO), with an initial burst of OC and an ending surge of CO. The OC loci are largely composed of genes associated with a somatic fate, while the CO loci are associated with pluripotency. Factors/conditions known to impede reprogramming prevent OSK-driven OC and skew OC-CO dynamics. While the CO loci are enriched for OSK motifs, the OC loci are not, suggesting alternative mechanisms for chromatin closing. Sap30, a Sin3A corepressor complex component, is required for the OC shift and facilitates reduced H3K27ac deposition at OC loci. These results reveal a chromatin accessibility logic during reprogramming that may apply to other cell-fate decisions.
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•ATAC-seq reveals chromatin accessibility dynamics during reprogramming•TFs associated with initial chromatin closing are barriers for reprogramming•OSK opens the pluripotent loci gradually through a direct process•OSK closes the somatic loci indirectly in part through SAP30
Li et al. show that Yamanaka factors remodel the nuclear architecture of MEFs following a binary logic that may guide further improvement in reprograming technology and be applicable for other cell-fate decisions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The double vertical explosive welding process produces two composites in one explosion and improves the energy utilization efficiency. However, the interface morphology at different positions shows ...obvious unevenness. 2D and 3D models of double vertical explosive welding were established by SPH. The interface morphology and process parameters were analysed. The relationship between the interface morphology and process parameters was discussed, and the pressure condition was the most suitable wave-forming condition in this paper. The interface morphology of the whole plate was predicted by combining the pressure condition with the contours of the flyer plate of the 3D model. A relevant experiment was carried out, and samples at different locations were observed under an OM. The results indicated that the wave interface and jetting were reproduced well in the 2D models. The distribution of the wave interface presented a butterfly shape. A straight interface existed at the detonation point and the boundary areas. The distribution of interface morphology in the experimental results was basically the same as those predicted by the numerical simulations. In addition, a discontinuous convex block was observed in the straight interface. Evidence of a vortex, jetting and an island region existed in the large wave interface.
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•Comparing the left-end detonation, the mid-point detonation had the higher pressure, shorter duration, and more uneven interface morphology.•The process parameters obtained in the three-dimensional model were slightly smaller than those in the two-dimensional models.•Due to unstable explosive detonation and boundary effect, the straight interface appeared near the detonation point and the boundaries.•The wave interface of the composite plates was butterfly-shaped after an explosion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Improving the carbon sequestration capacity (CSC) of an ecosystem by optimizing urban ecological networks is one of the effective ways to achieve the goal of “carbon neutrality” in the world. The ...contradiction between the irreplaceable ecological function and economic development of Yancheng City is prominent. Therefore, taking Yancheng City as an example, this paper adopted the morphological spatial pattern analysis–minimum cumulative resistance (MSPA-MCR) model to establish the ecological network of Yancheng City in 2020 and combined it with complex network theory to evaluate its ecological base, network quality, and CSC. The results show that the ecological network of Yancheng City has obvious characteristics of coastal cities. There is a significant positive correlation between CSC and the clustering efficiency of ecological sources, and improving the clustering efficiency of vegetation and water ecological nodes is conducive to enhancing the CSC of ecological networks. In terms of functional restoration of ecological networks, four types of 13 ecological stepping stones and 12 ecological corridors have been designed to strengthen the connectivity and balance of the network, and the improvement of network robustness before and after optimization verifies that the optimization scheme is reasonable and effective. This study improved the optimization method of ecological networks in Yancheng City based on enhancing the CSC of ecological nodes, which provided a theoretical framework and practical reference for the realization of global strategic goals of carbon neutrality.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Histogram-based thresholding is one of the widely applied techniques for conducting color image segmentation. The key to such techniques is the selection of a set of thresholds that can discriminate ...objects and background pixels. Many thresholding techniques have been proposed that use the shape information of histograms and identify the optimum thresholds at valleys. In this work, we introduce the novel concept of a hierarchical-histogram, which corresponds to a multigranularity abstraction of the color image. Based on this, we present a new histogram thresholding-Adaptive Hierarchical-Histogram Thresholding (AHHT) algorithm, which can adaptively identify the thresholds from valleys. The experimental results have demonstrated that the AHHT algorithm can obtain better segmentation results compared with the histon-based and the roughness-index-based techniques with drastically reduced time complexity.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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