Flexible power sources with high energy density are crucial for the realization of next-generation flexible electronics. Theoretically, rechargeable flexible zinc–air (Zn–air) batteries could provide ...high specific energy, while their large-scale applications are still greatly hindered by high cost and resources scarcity of noble-metal-based oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) electrocatalysts as well as inferior mechanical properties of the air cathode. Combining metallic Co4N with superior OER activity and Co–N–C with perfect ORR activity on a free-standing and flexible electrode could be a good step for flexible Zn–air batteries, while lots of difficulties need to be overcome. Herein, as a proof-of-concept experiment, we first propose a strategy for in situ coupling of strung Co4N and intertwined N–C fibers, by pyrolyzation of the novel pearl-like ZIF-67/polypyrrole nanofibers network rooted on carbon cloth. Originating from the synergistic effect of Co4N and Co–N–C and the stable 3D interconnected conductive network structure, the obtained free-standing and highly flexible bifunctional oxygen electrode exhibits excellent electrocatalytic activity and stability for both OER and ORR in terms of low overpotential (310 mV at 10 mA cm–2) for OER, a positive half-wave potential (0.8 V) for ORR, and a stable current density retention for at least 20 h, and especially, the obtained Zn–air batteries exhibit a low discharge–charge voltage gap (1.09 V at 50 mA cm–2) and long cycle life (up to 408 cycles). Furthermore, the perfect bendable and twistable and rechargeable properties of the flexible Zn–air battery particularly make it a potentially power portable and wearable electronic device.
In recent years, researchers pay growing attention to the few-shot learning (FSL) task to address the data-scarce problem. A standard FSL framework is composed of two components: i) Pre-train. Employ ...the base data to generate a CNN-based feature extraction model (FEM). ii) Meta-test. Apply the trained FEM to the novel data (category is different from base data) to acquire the feature embeddings and recognize them. Although researchers have made remarkable breakthroughs in FSL, there still exists a fundamental problem. Since the trained FEM with base data usually cannot adapt to the novel class flawlessly, the novel data's feature may lead to the distribution shift problem. To address this challenge, we hypothesize that even if most of the decisions based on different FEMs are viewed as weak decisions , which are not available for all classes, they still perform decent in some specific categories. Inspired by this assumption, we propose a novel method Multi-Decision Fusing Model (MDFM), which comprehensively considers the decisions based on multiple FEMs to enhance the efficacy and robustness of the model. MDFM is a simple, flexible, non-parametric method that can directly apply to the existing FEMs. Besides, we extend the proposed MDFM to two FSL settings (e.g., supervised and semi-supervised settings). We evaluate the proposed method on five benchmark datasets and achieve significant improvements of 3.4%-7.3% compared with state-of-the-arts.
At present, nonparametric subspace classifiers, such as collaborative representation-based classification (CRC) and sparse representation-based classification (SRC), are widely used in many ...pattern-classification and -recognition tasks. Meanwhile, the spatial pyramid matching (SPM) scheme, which considers spatial information in representing the image, is efficient for image classification. However, for SPM, the weights to evaluate the representation of different subregions are fixed. In this paper, we first introduce the spatial pyramid matching scheme to remote-sensing (RS)-image scene-classification tasks to improve performance. Then, we propose a weighted spatial pyramid matching collaborative-representation-based classification method, combining the CRC method with the weighted spatial pyramid matching scheme. The proposed method is capable of learning the weights of different subregions in representing an image. Finally, extensive experiments on several benchmark remote-sensing-image datasets were conducted and clearly demonstrate the superior performance of our proposed algorithm when compared with state-of-the-art approaches.
This paper attempts to improve the identification accuracy of traffic flow states, and disclose the impacts of different evaluation indices on the identification results. To this end, a multi-index ...fusion clustering strategy is proposed in this research. Firstly, flow, velocity and occupancy were selected as the evaluation indices. Then, the weights of the three indices were initialized by a group of experts. After that, the objective function of a weight optimization model was set up to maximize the distance between projection centers of samples under different traffic flow states and to minimize the projection variance between samples under the same traffic flow state. The model was solved by the method of Lagrange multipliers, producing the optimal weight combination. Then, the optimal weights were introduced to the fuzzy c-means (FCM) clustering, forming the multi-index fusion clustering method. The results of example analysis show that our method differentiated between traffic flow states more accurately than the original FCM clustering. And the traffic flow identification accuracy improved from 94.0% to 96.6%. This is because the improved method retains most of the original features of the evaluation indices, which further facilitates the accurate clustering of traffic flow states.
Electronic beam steering is an essential feature of state-of-the-art radar systems. Conventional phased array (PA) radars with fixed carrier frequencies are well-known for electronically steering ...their beam with high directivity. However, the resulting beampattern is angle-dependent but range-independent. Recently, a new electronic beam steering concept, referred to as frequency diverse array (FDA) radar, has attracted increasing attention due to its unique range-angle dependent beampattern. More importantly, the FDA radar employs a small frequency increment across the array elements to achieve beam steering as a function of angle, range, and time. In this paper, we review the development of the FDA radar since its inception in 2006. Since the frequency offset attaches great importance in FDAs to determine the beampattern shape, initially much of the research and development were focused on designing the optimal frequency offsets for improved beampattern synthesis. Specifically, we analyze characteristics of the FDA beampattern synthesis using various frequency offsets. In addition to analyzing the FDA beampattern characteristics, this study also focuses on the neglected propagation process of the transmitted signals in the early FDA literature, and discuss the time-variant perspective of FDA beampatterns. Furthermore, FDA can also play a significant role in wireless communications, owing to its potential advantages over the conventional PAs. Therefore, we highlight its potential applications in wireless communication systems. Numerical simulations are implemented to illustrate the FDA beampattern characteristics with various frequency offset functions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Mechanoluminescence（ML） refers to the light emission from various organic and inorganic materials upon mechanical stimulus. As a new class of smart materials, mechanoluminescent materials are widely ...applicable for fluorescence switches, mechanosensors, security papers, optoelectronic devices and data storage etc. In the past few years, systematic investigations have been carried out, resulting in the production of a variety of mechanoluminescent materials. In this review, recent progress in pure organic mechanoluminescent materials is summarized, including mechanofluorescent and triboluminescent effects from conjugated small molecules.
Heterodimeric tryptophan‐containing diketopiperazines (HTDKPs) are an important class of bioactive secondary metabolites. Biosynthesis offers a practical opportunity to access their bioactive ...structural diversity, however, it is restricted by the limited substrate scopes of the HTDKPs‐forming P450 dimerases. Herein, by genome mining and investigation of the sequence‐product relationships, we unveiled three important residues (F387, F388 and E73) in these P450s that are pivotal for selecting different diketopiperazine (DKP) substrates in the upper binding pocket. Engineering these residues in NasF5053 significantly expanded its substrate specificity and enabled the collective biosynthesis, including 12 self‐dimerized and at least 81 cross‐dimerized HTDKPs. Structural and molecular dynamics analysis of F387G and E73S revealed that they control the substrate specificity via reducing steric hindrance and regulating substrate tunnels, respectively.
The biosynthesis of heterodimeric tryptophan‐containing diketopiperazines (HTDKPs) is restricted by the limited substrate scopes of the HTDKP‐forming P450 dimerases. Engineering of three important residues (F387, F388, and E73) in NasF5053 significantly expanded its substrate specificity and enabled the collective biosynthesis of at least 93 HTDKPs.
This study uses geochemical mohometers to investigate the paleo‐crustal thickness and elevation of western Tibet through the Cretaceous to Eocene. The northern Lhasa Block and southern Qiangtang ...Block (QB) had a similar paleo‐crustal thickness of ∼55 km during the Late Cretaceous, but the latter had reached its present‐day thickness (∼70 km) and elevation (∼5.5 km) by the mid‐Eocene, which was not caused by underthrusting of Indian crust according to isotopic evidence. Our study demonstrates the western and central QB shared a similar early Paleogene tectonomagmatic evolution with the formation of a continues proto‐plateau in central Tibet, resulting from crustal shortening and subsequent lithospheric foundering. This in turn implies underthrusting of the Indian lithosphere beneath the western QB after Eocene, given the present‐day lithospheric difference between the western and central QB. Our reconstruction of paleo‐crustal thickness and elevation, however, suggests the Indian underthrusting caused minimal further crustal thickening and uplift.
Plain Language Summary
The Tibetan Plateau is a key locality to study large‐scale continental tectonics because of the well‐preserved Cenozoic geological records along with the validity of geophysical data. The western part of the Tibetan Plateau is not a simple extension of the central‐eastern part as demonstrated by numerous geophysical investigations on the lithospheric structure. The western Qiangtang Block (QB) in central Tibet is generally thought to be raised by the Miocene underthrusting of the Indian lithosphere, yet no palaeoaltimetry data are available to test this hypothesis. This provides the first quantitative constraint on the uplift history of the western QB. We use recently calibrated igneous geochemical proxies of continental thickness to investigate the paleo‐crustal thickness and elevation of western Tibet through the Early Cretaceous to Eocene. Our data demonstrate that the western Tibetan crust had reached its present‐day thickness (∼70 km) and elevation (∼5.5 km) by the Mid‐Eocene, as a result of crustal shortening and subsequent lithospheric foundering. Based on a synthesis of independent geological and seismic data, we contend that the post‐Eocene underthrusting of the Indian lithosphere beneath the western QB has caused minimal further crustal thickening and uplift.
Key Points
First quantitative constraint on the uplift history of the western Qiangtang Block (QB) in central Tibet
The western QB has reached its present‐day thickness and elevation by Eocene
Underthrusting of the Indian lithosphere caused minimal further thickening and uplift of the western Qiangtang crust
•A Gaussia luciferase EV71 reporter virus was constructed.•The reporter virus was infectious and stable in cell culture.•The reporter virus was suitable for antiviral test.
We report a stable Gaussia ...luciferase enterovirus 71 (Gluc-EV71) reporter virus to facilitate drug discovery. The Gluc-EV71 reporter virus was generated by engineering the Gaussia luciferase (Gluc) gene between the 5′ untranslated region and VP4 gene of the EV71 genome. We could recover Gluc-EV71 after transfection of Vero cells with the cDNA clone-derived RNA. The reporter virus efficiently infects and replicates in various cell types (Vero, human rhabdomyosarcoma, and HeLa cells), producing robust luciferase activity. The Gluc-EV71 virus replicates slower than the wild-type virus in cell culture. The reporter virus is stable in maintaining the Gluc gene after five rounds of continuous passaging in Vero cells. Using known EV71 inhibitors, we demonstrate that the reporter virus can be used for antiviral testing. However, the Gluc-EV71 infection assay cannot be adapted to a homogenous format for high throughput screen, mainly due to the secreted nature of the Gluc protein and the short half-life of the Gluc luminescence signal. The Gluc-EV71 and its infection assay could be useful for antiviral drug discovery as well as for studying EV71 replication and pathogenesis.
Ammonia synthesis is one of the most kinetically complex and energetically challenging chemical processes in industry and has used the Harber–Bosch catalyst for over a century, which is processed ...under both harsh pressure (150–350 atm) and hightemperature (623–823 K), wherein the energy and capital intensive Harber–Bosch process has a huge energy cost accounting for about 1%–3% of human's energy consumption. Therefore, there has been a rough and vigorous exploration to find an environmentally benign alternative process. As the amorphous material is in a metastable state and has many “dangling bonds”, it is more active than the crystallized one. In this paper, CeOx‐induced amorphization of Au nanoparticles anchored on reduced graphite oxide (a‐Au/CeOx–RGO) has been achieved by a facile coreduction method under ambient atmosphere. As a proof‐of‐concept experiment, a‐Au/CeOx–RGO hybrid catalyst containing the low noble metal (Au loading is 1.31 wt%) achieves a high Faradaic efficiency (10.10%) and ammonia yield (8.3 μg h−1 mg−1cat.) at −0.2 V versus RHE, which is significantly higher than that of the crystalline counterpart (c‐Au/RGO), and even comparable to the yields and efficiencies under harsh temperatures and/or pressures.
CeOx‐induced amorphization of Au nanoparticles anchored on reduced graphite oxide (a‐Au/CeOx–RGO) as a heterogeneous electrocatalyst shows excellent catalytic activity for electrochemical N2 reduction reaction with high Faradic efficiency (10.10%) and ammonia yield (8.3 μg h‐1 mg‐1cat.)
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