Guilin University of Technology

Using the financial data of listed Chinese companies, we study the impact of COVID-19 on corporate performance. We show that COVID-19 has a negative impact on firm performance. The negative impact of COVID-19 on firm performance is more pronounced when a firm’s investment scale or sales revenue is smaller. We show, in an additional analysis, that the negative impact of COVID-19 on firm performance is more pronounced in serious-impact areas and industries. These findings are among the first empirical evidence of the association between pandemic and firm performance.

Since the successful synthesis of the first MXenes, application developments of this new family of two-dimensional materials on energy storage, electromagnetic interference shielding, transparent conductive electrodes and field-effect transistors, and other applications have been widely reported. However, no one has found or used the basic characteristics of greatly changed interlayer distances of MXene under an external pressure for a real application. Here we report a highly flexible and sensitive piezoresistive sensor based on this essential characteristics. An in situ transmission electron microscopy study directly illustrates the characteristics of greatly changed interlayer distances under an external pressure, supplying the basic working mechanism for the piezoresistive sensor. The resultant device also shows high sensitivity (Gauge Factor ~ 180.1), fast response (<30 ms) and extraordinarily reversible compressibility. The MXene-based piezoresistive sensor can detect human being's subtle bending-release activities and other weak pressure.

In large-scale applications of portable and wearable electronic devices, high-performance supercapacitors are important energy supply sources. However, since the reliability and stability of supercapacitors are generally destroyed by mechanical deformation and damage during practical applications, the stretchability and self-healability must be exploited for the supercapacitors. Preparing the highly stretchable and self-healable electrodes is still a challenge. Here, we report reduced graphene oxide fiber based springs as electrodes for stretchable and self-healable supercapacitors. The fiber springs (diameters of 295 μm) are thick enough to reconnect the broken electrodes accurately by visual inspection. By wrapping fiber springs with a self-healing polymer outer shell, a stretchable and self-healable supercapacitor is successfully realized. The supercapacitor has 82.4% capacitance retention after a large stretch (100%), and 54.2% capacitance retention after the third healing. This work gave an essential strategy for designing and fabricating stretchable and self-healable supercapacitors in next-generation multifunctional electronic devices.

Abstract 2D/2D heterostructures can combine the collective advantages of each 2D material and even show improved properties from synergistic effects. 2D Transition metal carbide Ti 3 C 2 MXene and 2D 1T‐MoS 2 have emerged as attractive prototypes in electrochemistry due to their rich properties. Construction of these two 2D materials, as well as investigation about synergistic effects, is absent due to the instability of 1T‐MoS 2 . Here, 3D interconnected networks of 1T‐MoS 2 /Ti 3 C 2 MXene heterostructure are constructed by magneto‐hydrothermal synthesis, and the electrochemical storage mechanisms are investigated. Improved extra capacitance is observed due to enlarged ion storage space from a synergistically interplayed effect in 3D interconnected networks. Outstanding rate performance is realized because of ultrafast electron transport originating from Ti 3 C 2 MXene. This work provides an archetype to realize excellent electrochemical properties in 2D/2D heterostructures.

Global resources of heavy Rare Earth Elements (REE) are dominantly sourced from Chinese regolith-hosted ion-adsorption deposits in which the REE are inferred to be weakly adsorbed onto clay minerals. Similar deposits elsewhere might provide alternative supply for these high-tech metals, but the adsorption mechanisms remain unclear and the adsorbed state of REE to clays has never been demonstrated in situ. This study compares the mineralogy and speciation of REE in economic weathering profiles from China to prospective regoliths developed on peralkaline rocks from Madagascar. We use synchrotron X-ray absorption spectroscopy to study the distribution and local bonding environment of Y and Nd, as proxies for heavy and light REE, in the deposits. Our results show that REE are truly adsorbed as easily leachable 8- to 9-coordinated outer-sphere hydrated complexes, dominantly onto kaolinite. Hence, at the atomic level, the Malagasy clays are genuine mineralogical analogues to those currently exploited in China.

Abstract The added value of biochar when applied along with fertilizers, beyond that of the fertilizers themselves, has not been summarized. Focusing on direct comparisons between biochar additions (≤20 t ha −1 ) – separately considering the addition or not of inorganic fertilizers ( IF ) and/or organic amendments ( OA ) along with biochar – and two different controls (with and without the addition of IF and/or OA ), we carried out a meta‐analysis to explain short‐term (1‐year) field responses in crop yield across different climates, soils, biochars and management practices worldwide. Compared with the non‐fertilized control, a 26% ( CI : 15%–40%) increase in yield was observed with the use of IF only, whereas that of biochar along with IF caused a 48% ( CI : 30%–70%) increase. Compared with the use of IF only, the addition of biochar along with IF caused a 15% ( CI : 11%–19%) increase in yield, indicating that biochar was as effective as fertilizers in increasing crop yields when added in combination. The use of biochar alone did not increase crop yield regardless of the control considered. Whereas in the short term, liming may have partly contributed to the beneficial effect of biochar (&gt;90% was plant‐derived) when added along with IF , a separate meta‐analysis – using those studies that reported crop yields for different years after a single biochar application – showed a 31% ( CI : 17%–49%) increase in crop yield over time (≥ 3 years), which denotes the influence of biochar properties other than liming (i.e. an increase in CEC ). Our results also suggest that biochar application rates &gt; 10 t ha −1 do not contribute to greater crop yield (at least in the short term). Data limitations precluded identification of the influence of feedstock, production conditions or climatic conditions without bias. As the response of crop yield to biochar addition was less a result of climatic zones or soil type than fertilizer use (chiefly N additions), the choice of nutrient addition along with biochar should be priorities for future research and development regardless of the region.

Abstract Heteroatom‐doping in metal‐nitrogen‐carbon single‐atom catalysts (SACs) is considered a powerful strategy to promote the electrocatalytic CO 2 reduction reaction (CO 2 RR), but the origin of enhanced catalytic activity is still elusive. Here, we disclose that sulfur doping induces an obvious proton‐feeding effect for CO 2 RR. The model SAC catalyst with sulfur doping in the second‐shell of FeN 4 (Fe 1 −NSC) was verified by X‐ray absorption spectroscopy and aberration‐corrected scanning transmission electron microscopy. Fe 1 −NSC exhibits superior CO 2 RR performance compared to sulfur‐free FeN 4 and most reported Fe‐based SACs, with a maximum CO Faradaic efficiency of 98.6 % and turnover frequency of 1197 h −1 . Kinetic analysis and in situ characterizations confirm that sulfur doping accelerates H 2 O activation and feeds sufficient protons for promoting CO 2 conversion to *COOH, which is also corroborated by the theoretical results. This work deepens the understanding of the CO 2 RR mechanism based on SAC catalysts.

Aliovalent A-site engineering enables superior energy storage density in AgNbO₃ lead-free antiferroelectric ceramics.

As an important parameter in recent and numerous environmental studies, soil moisture (SM) influences the exchange of water and energy at the interface between the land surface and atmosphere. Accurate estimate of the spatio-temporal variations of SM is critical for numerous large-scale terrestrial studies. Although microwave remote sensing provides many algorithms to obtain SM at large scale, such as SMOS and SMAP etc., resulting in many data products, they are almost low resolution and not applicable in small catchment or field scale. Estimations of SM from optical and thermal remote sensing have been studied for many years and significant progress has been made. In contrast to previous reviews, this paper presents a new, comprehensive and systematic review of using optical and thermal remote sensing for estimating SM. The physical basis and status of the estimation methods are analyzed and summarized in detail. The most important and latest advances in soil moisture estimation using temporal information have been shown in this paper. SM estimation from optical and thermal remote sensing mainly depends on the relationship between SM and the surface reflectance or vegetation index. The thermal infrared remote sensing methods uses the relationship between SM and the surface temperature or variations of surface temperature/vegetation index. These approaches often have complex derivation processes and many approximations. Therefore, combinations of optical and thermal infrared remotely sensed data can provide more valuable information for SM estimation. Moreover, the advantages and weaknesses of different approaches are compared and applicable conditions as well as key issues in current soil moisture estimation algorithms are discussed. Finally, key problems and suggested solutions are proposed for future research.

Graphene oxide (GO) is emerging as a potential adsorbent for environmental cleanup due to its attractive attributes associated with high removal efficiency toward water pollutants. However, it is difficult to separate GO from water after adsorption. Until now, the development of an effective approach that can simultaneously take advantage of the adsorption feature of GO and overcome the separation problem is still a challenge. Herein, we demonstrate a simple one-step approach to fabricate magnetic GO/poly(vinyl alcohol) (PVA) composite gels (mGO/PVA CGs), which not only exhibit convenient magnetic separation capability but also show remarkably enhanced adsorption capacity for cationic methylene blue (MB) and methyl violet (MV) dyes as compared with the one without GO (e.g., the adsorption capacities of mGO/PVA-50% and mGO/PVA-0% for MB are 231.12 and 85.64 mg/g, respectively). Detailed adsorption studies reveal that the adsorption kinetics and isotherms can be well-described by pseudo-second-order model and Langmuir isotherm model, respectively. Moreover, the adsorbent could be well regenerated in an acid solution without obvious compromise of removal efficiency. Considering the facile fabrication process and robust adsorption performance of the mGO/PVA CG, this work opens up enormous opportunities to bring GO from experimental research to practical water treatment applications. In addition, the mGO/PVA CG can act as a magnetic support for in situ growth of noble metal nanocatalyst with excellent catalytic performance, as exemplified by the synthesis of mGO/PVA-Pt catalyst in this paper.

For improving the capability, cycling stability and rate capacity of anatase TiO2-based electrode, Mo-doped TiO2 anatase encapsulated in nitrogen-doped amorphous carbon (denoted for Mo-TiO2@NC) were synthesized through a facile hydrothermal method and followed by coating with polyaniline (PANI) and heating treatment. When tested as anode for lithium ion batteries, the Mo-TiO2@NC electrode showed initial discharge and charge capacities of 850.7 and 548.3 mAh g-1 at a current density of 85 mA g-1, respectively, with a remarkable discharge capacity maintained at 449.2 mAh g-1 after 100 cycles. Even at high current density of 850 mA g-1, a reversible capacity of 154 mAh g-1 after 200 cycles is obtained, displaying good rate capacity and long-term cycling stability. The outstanding electrochemical performance of Mo-TiO2@NC could be attributed to the synergistic effect of aliovalent ions doping and carbon coating.

Fluorescent carbon dots (CDs) hold great promise for a myriad applications due to their fascinating attributes. However, the development of CDs with high fluorescence quantum yield (QY) and unique surface property is still in its infancy. Herein, we report a simple and green strategy to produce water-soluble nitrogen-doped CDs (N-CDs) via the one-pot hydrothermal carbonization of the mixture of natural peach gum polysaccharide (PGP) and ethylenediamine. The resulting N-CDs exhibit a remarkably enhanced QY (28.46%) as compared with that of undoped CDs (5.31%). In addition, the N-CDs show stable fluorescence against ionic strength variation and pH change. Preliminary biological studies reveal that N-CDs possess low cytotoxicity and high fluorescent contrast in cells. Moreover, we present here for the first time that the obtained N-CDs can exhibit a fast and highly sensitive and selective fluorescence quenching effect toward Au3+ ions. The detection limit can reach 6.4 × 10–8 M, which compares favorably to other reported fluorescent probes. We have also demonstrated that the N-CDs can be employed to sense Au3+ ions in real river water. Considering the easy synthetic process and excellent performance of the N-CDs, this investigation opens up new opportunities for preparing high-quality fluorescent CDs to meet the requirement of many applications.

Abstract The recharge ability of zinc metal‐based aqueous batteries is greatly limited by the zinc anode. The poor cycling durability of Zn anodes is attributed to the dendrite growth, shape change and passivation, but this issue has been ignored by using an excessive amount of Zn in the past. Herein, a 3D nanoporous (3D NP) Zn–Cu alloy is fabricated by a sample electrochemical‐assisted annealing thermal method combined, which can be used directly as self‐supported electrodes applied for renewable zinc‐ion devices. The 3D NP architectures electrode offers high electron and ion transport paths and increased material loading per unit substrate area, which can uniformly deposit/strip Zn and improve charge storage ability. Benefiting from the intrinsic materials and architectures features, the 3D NP Zn–Cu alloy anode exhibits high areal capacity and excellent cycling stability. Further, the fabricated high‐voltage double electrolyte aqueous Zn–Br 2 battery can deliver maximum areal specific capacity of ≈1.56 mAh cm −2 , which is close to the level of typical commercial Li‐ion batteries. The excellent performance makes it an ideal candidate for next‐generation aqueous zinc‐ion batteries.

Electrical characterizations of Nb2O5 doped 0.65BiFeO3–0.35BaTiO3 (0.65BF–0.35BT) ceramic were carried out over broad temperature and frequency ranges through dielectric spectroscopy, impedance spectroscopy, and ac conductivity measurements. The dielectric constant and loss tangent are drastically reduced with introducing Nb2O5 into the 0.65BF–0.35BT system. Two dielectric anomalies are detected in the temperature regions of 100 °C ≤ T ≤ 280 °C and 350 °C ≤ T ≤ 480 °C, and the Curie temperature (TC) was confirmed in higher temperature region. A dielectric relaxation with large dielectric constants was detected near the TC. This dielectric relaxation becomes even stronger with the gradual increase in the Nb2O5 content. Impedance spectroscopy results clearly show the contributions of grains and grain boundaries in the frequency range of 100 Hz ≤ f ≤ 1 MHz, and the relaxation processes for grains and grain boundaries are non-Debye-type. The grain boundaries are more resistive than that of the grains, revealing the inhomogeneity in samples. The experimental results are well fitted based on a Maxwell-Wagner (MW) interfacial polarization model below 100 kHz, and the MW interfacial polarization effect becomes more and more obvious with the increase in the Nb2O5 content. The increase in dielectric constant is possibly related to space charge polarization, which is caused by charges accumulated at the interface between the grain and grain boundaries. Frequency dependence of the ac conductivity confirms the MW interfacial polarization effect below 100 kHz.

This letter investigates the problem of anti-jamming communications in a dynamic and intelligent jamming environment through machine learning. Different from existing studies which need to know (estimate) the jamming patterns and parameters, we use the temporal and spectral information, i.e., the spectrum waterfall, directly. First, to cope with the challenge of infinite state of spectrum waterfall, a recursive convolutional neural network is designed. Then, an anti-jamming deep reinforcement learning algorithm is proposed to obtain the optimal anti-jamming strategies. Finally, simulation results validate the proposed approach. The proposed algorithm does not need to model the jamming patterns, and naturally has the ability to explore the unknown environment, which implies that it can be widely used for combating dynamic and intelligent jamming.

UAV cooperative control has been applied in many complex UAV communication networks. It remains challenging to develop UAV cooperative coverage and UAV energy-efficient communication technology. In this paper, we investigate current works about UAV coverage problem and propose a multi-UAV coverage model based on energy-efficient communication. The proposed model is decomposed into two steps: coverage maximization and power control, both are proved to be exact potential games (EPG) and have Nash equilibrium (NE) points. Then the multi-UAV energy-efficient coverage deployment algorithm based on spatial adaptive play (MUECD-SAP) is adopted to perform coverage maximization and power control, which guarantees optimal energy-efficient coverage deployment. Finally, simulation results show the effectiveness of our proposed approach, and confirm the reliability of proposed model.

Abstract It is a textbook knowledge that protein photoluminescence stems from the three aromatic amino acid residues of tryptophan(Trp), tyrosine (Tyr), and phenylalanine (Phe), with predominant contributions from Trp. Recently, inspired by the intrinsic emission of nonaromatic amino acids and poly(amino acids) in concentrated solutions and solids, we revisited protein light emission using bovine serum albumin (BSA) as a model. BSA is virtually nonemissive in dilute solutions (≤0.1 mg mL −1 ), but highly luminescent upon concentration or aggregation, showing unique concentration‐enhanced emission and aggregation‐induced emission (AIE) characteristics. Notably, apart from well‐documented UV luminescence, bright blue emission is clearly observed. Furthermore, persistent room‐temperature phosphorescence ( p ‐RTP) is achieved even in the amorphous solids under ambient conditions. This visible emission can be rationalized by the clustering‐triggered emission (CTE) mechanism. These findings not only provide an in‐depth understanding of the emissive properties of proteins, but also hold strong implications for further elucidating the basis of tissue autofluorescence.

It is of great difficulty to obtain deep-UV transparent materials with enhanced second harmonic generation (SHG), mainly limited by the theoretically poor transparency of these materials in the deep-UV spectral region. Here we report a new noncentrosymmetric, deep-UV transparent phosphate RbNaMgP 2 O 7, which undergoes a thermo-induced reversible phase transition (at a high temperature of 723 K) and correspondingly an evident SHG enhancement up to ∼1.5 times. The phase transition is aroused by the twist of [P 2 O 7 ] 4– dimers with deviation from the P–O–P equilibrium positions. Theoretical analyses reveal that the enhanced SHG can be ascribed to the thermo-induced collective alignment of SHG-active [P 2 O 7 ] 4– dimers along the polar axis of high-temperature phase. This work provides an unprecedented physical routine (to SHG-enhanced materials) that is distinguished from the traditional one by chemical design and synthesis.

In this technical note, we describe a facile method for one-step fabrication of paper-based microfluidic devices, by simply using commercially available permanent markers and metal templates with specific patterns. The fabrication process involves only a single step of plotting pattern in paper; it can be typically finished within 1 min. The ink marks formed in the patterned paper will act as the hydrophobic barriers to define the hydrophilic flow paths or separate test zones. Various paper devices can be created by using different templates with corresponding patterns. Transparent adhesive tape-sandwiched devices could protect their assay surfaces from potential contamination. In the proof-of-concept experiments, circular paper test zones (~3 mm diameter) were fabricated for colorimetric and quantification detection of prostate-specific antigen (PSA) as a model target, based on dot-immunogold staining assays coupled with gold enhancement amplification. Several serum specimens were additionally evaluated with this new approach and the results were compared with the commercial chemiluminescence immunoassay, validating its feasibility of practical applications. Such a one-step plotting method for paper patterning does not require any specialized equipments and skills, is quite inexpensive and rapid, and thus holds great potential to find wide applications especially in remote regions and resource-limited environments such as small laboratories and private clinics.

MXenes, or transition metal carbides or nitrides, as an advanced 2D materials have already attracted extensive attention due to their high conductivity and large specific surface area for applications in the field of energy storage. MXenes also have many other advanced properties such as good transmittance and adjustable work function over a large range. However, few works study the properties of MXenes in the field of optoelectronics. Here, the optoelectronic properties of Ti 3 C 2 T X (with a work function of 4.37 eV) on n‐type silicon (n‐Si) of vertical van der Waals heterostructures are studied. The Ti 3 C 2 T X not only functions as the transparent electrode but also contributes to the separation and transport of photo‐induced carriers. After investigations on the influence of annealing, temperature, illumination, and applied voltage on the performance of Ti 3 C 2 T X /n‐Si Schottky junction heterostructures, this study fabricates a self‐driven vertical junction photodetectors with high response and recovery speeds. It is believed that the excellent photoelectric properties of MXenes will attract many researchers' attention to the application of MXenes in the photoelectrical field.