Geometrothermodynamics of black holes with a nonlinear source

General Relativity and Gravitation - Based on the generalized Tsallis entropy and holographic hypothesis, the Tsallis agegraphic dark energy (TADE) was proposed by introducing the timescale as...     

构建低成本的Ni3C/孪晶Zn0.5Cd0.5S异质结/同质结纳米杂化体系来实现高效的光催化分解水产氢

开发低成本的半导体光催化剂以实现可见光下高效、持久的光催化分解水产氢化是一个非常具有挑战性的课题.近年来,具有孪晶结构的ZnxCd1-xS(ZCS)固溶体引起了人们的研究兴趣,这主要是由于孪晶相之间形成了同质结,同质结可以通过提高体相光生电子-空穴对的分离效率,从而提高原始硫化物光催化剂的光催化分解水产氢活性.但由于孪晶ZCS固溶体表面超快载流子复合以及活性位点不足,进一步提高其光催化析氢活性还需解决这些不足.负载助催化剂被认为是加速产氢动力学和促进表面光生电子空穴分离最有效策略之一.因此,我们将低成本的类金属Ni3C助催化剂与孪晶ZCS固溶体通过简单的研磨方法结合来实现高效的可见光催化分解水产氢.合成的Zn0.5Cd0.5S-1%Ni3C(ZCS-1)异质结/同质结最高的可见光光催化分解水产氢速率可达783μmol h–1,是纯ZCS的2.88倍.在420 nm时,ZCS和ZCS-1的表观量子效率分别为6.13%和19.25%.这是由于孪晶ZCS固溶体中闪锌矿段和纤锌矿段的同质结连接可以显著提高光生电子空穴对的体相转移和分离.同时,ZCS与金属Ni3C助催化剂间的异质结可以有效地增加孪晶ZCS固溶体的光捕获及表面载流子分离,增强产氢活性位,从而提高催化活性.本文以乙酸镉、乙酸锌和氢氧化钠为原料合成了CdZn(OH),后者与硫代乙酰胺水热合成了孪晶CZS,并用超声研磨方法合成CZS-Ni3C.在可见光下进行了产氢测试,实验结果证实了优化的ZCS-1在Na2S·9H2O和Na2SO3的水溶液中光催化析氢活性最高.经过4次连续的循环反应,ZCS-1二元复合体系展现出良好的稳定性.为深入探讨高效产氢机制,对纳米级ZCS复合材料的光催化物化性能及载流子分离机制进行了表征.通过X射线衍射确定了ZCS和ZCS-1的晶体结构.用高分辨电子显微镜和X射线光电子能谱证实合成了ZCS和Ni3C助催化剂的成功复合.用紫外-可见漫反射光谱法对制备的ZCS和ZCS-1复合样品的光吸收特性进行了表征.结果表明,在ZCS上负载Ni3C以后,样品的可见光吸收能力显著提升.利用稳态及瞬态荧光光谱研究了ZCS-1光催化剂的电荷载流子复合和转移行为.进一步对纯ZCS和ZCS-1复合光催化剂的瞬态光电流响应(I-t曲线)进行了研究,确定了光生载体的分离效率.阻抗是深入研究电荷载流子迁移和界面转移的最有力技术,利用阻抗技术证实ZCS-1界面高效的载流子分离性能.极化曲线结果表明,加入Ni3C可以降低ZCS的产氢过电势,因此加速表面产氢动力学.由此可见,本文所构建的ZCS同质结与Ni3C助催化剂的协同作用可以明显促进体相及表面光生电子空穴对的分离,从而显著增强光催化分解水产氢活性.该文所采用基于ZCS纳米孪晶与异质助催化剂耦合策略可以作为一种通用策略扩展到各种传统半导体的改性,从而极大地推进高效光催化产氢材料的持续进步.     

Effects of time-periodic intercoupling strength on burst synchronization of a clustered neuronal network

In this paper, we investigate the effect of time-periodic intercoupling strength on burst synchronization of a clustered neuronal network. We mainly focus on discussing the effects of amplitude and frequency of the time-periodic intercoupling strength on burst synchronization. We found that by tuning the frequency, burst synchrony of the clustered neuronal network could change from higher synchronized states to low synchronized states, and vice versa. While for the amplitude, we surprisingly found that with increasing of the amplitude, burst synchrony of the clustered neuronal network is not always enhanced. We know that synchronization has close relationship with cognitive activities and brain disorders. Thus, our results could give us some useful insight on the important role of time-dependent couplings in neuronal systems.     

Influence of proton beam Coulomb explosion in laser proton acceleration

To further understand proton acceleration driven by the interaction between ultra-intense laser pulse and foil targets, the influence of proton beam Coulomb explosion has been analyzed theoretically and investigated using two-dimensional particle-in-cell (2D-PIC) simulations. Employing different proton layer sizes in the simulations, it is found that proton beam Coulomb explosion plays an important role on proton acceleration, in particular on proton cut off energy. Proton dynamics including the effect of both sheath field and proton beam Coulomb explosion was proposed and discussed in detail. This work may serve to improve the understanding of proton acceleration driven by intense laser-foil interactions.     

Combination effect of activated carbon with TiO2 for the photodegradation of binary pollutants at typical indoor air level

Previously we identified that residence time and water vapor are the vital parameters that affect the photodegradation of indoor air pollutants at parts-per-billion (ppb) levels using TiO₂. The presence of water vapor competes with pollutants for adsorption sites on TiO₂ thus reducing the pollutant removal rate. By immobilizing TiO₂ on activated carbon (AC), a satisfactory pollutant removal rate is achieved even at high water vapor levels. This study further examines the effect of TiO₂ immobilized on AC by co-injecting binary pollutants simultaneously since the presence of other pollutants might have an inhibition effect on the photocatalytic activity under different humidity levels. 200 parts-per-billion NO, 20 ppb BTEX and 200 ppb SO₂ were co-injected under different residence time and humidity levels to investigate their mutual effect on TiO₂ and TiO₂ immobilized on AC. Results showed that no significant pollutant removal difference was observed between TiO₂ and TiO₂ immobilized on AC at longer residence time. The presence of BTEX only reduced NO conversion by 5%. At evaluated humidity levels, however, a significant different pollutant removal rate was observed. The presence of BTEX reduced NO conversion by more than 10%. The use of TiO₂ on AC, reduced both the competition effect of the pollutant and water vapor on TiO₂. The inhibition effect of BTEX and SO₂ on NO conversion was significantly reduced when TiO₂ immobilized on AC compared to TiO₂ only. The by-product, NO₂, from the photodegradation of NO, was also reduced despite the presence of SO₂ and BTEX under high humidity level.     

Infrared dim moving target tracking via sparsity-based discriminative classifier and convolutional network

Infrared dim and small target tracking is a great challenging task. The main challenge for target tracking is to account for appearance change of an object, which submerges in the cluttered background. An efficient appearance model that exploits both the global template and local representation over infrared image sequences is constructed for dim moving target tracking. A Sparsity-based Discriminative Classifier (SDC) and a Convolutional Network-based Generative Model (CNGM) are combined with a prior model. In the SDC model, a sparse representation-based algorithm is adopted to calculate the confidence value that assigns more weights to target templates than negative background templates. In the CNGM model, simple cell feature maps are obtained by calculating the convolution between target templates and fixed filters, which are extracted from the target region at the first frame. These maps measure similarities between each filter and local intensity patterns across the target template, therefore encoding its local structural information. Then, all the maps form a representation, preserving the inner geometric layout of a candidate template. Furthermore, the fixed target template set is processed via an efficient prior model. The same operation is applied to candidate templates in the CNGM model. The online update scheme not only accounts for appearance variations but also alleviates the migration problem. At last, collaborative confidence values of particles are utilized to generate particles' importance weights. Experiments on various infrared sequences have validated the tracking capability of the presented algorithm. Experimental results show that this algorithm runs in real-time and provides a higher accuracy than state of the art algorithms.     

Tuning the electronic and magnetic properties of germanene by surface adsorption of small nitrogen-based molecules

The structural, energetic and electronic properties of germanene adsorbed with small nitrogen-based molecules, including N₂, NH₃, NO₂ and NO, have been investigated by using first-principles calculations. The results show that all nitrogen-based molecules considered bind much stronger to germanene than to graphene due to the hybridized sp²-sp³ bonding of Ge atoms. The N₂, NO and NO₂ molecules all act as an acceptor, while the NH₃ molecule donates electrons to germanene. We also found sizable band gaps (2–158 meV) are opened at the Dirac point of germanene through N₂, NH₃, and NO₂ adsorptions, but with only slightly destroying its Dirac cone shape. The NO₂ molecule also shows a heavy p-type doping character and makes germanene to be metallic. Moreover, when adsorbed by NO molecule, the germanene can change to be a ferromagnetic half-metal with 100% spin-polarization at the Fermi level. Overall, the different adsorption behaviors of small nitrogen-based gas molecules on germanene provide a feasible way to exploit chemically modified germanene for a wide range of practical applications, such as field-effect transistors, gas sensors and spintronic devices.     

2020 Roadmap on two-dimensional nanomaterials for environmental catalysis

Environmental catalysis has drawn a great deal of attention due to its clean ways to produce useful chemicals or carry out some chemical processes. Photocatalysis and electrocatalysis play important roles in these fields. They can decompose and remove organic pollutants from the aqueous environment, and prepare some fine chemicals. Moreover, they also can carry out some important reactions, such as O₂ reduction reaction (ORR), O₂ evolution reaction (OER), H₂ evolution reaction (HER), CO₂ reduction reaction (CO₂RR), and N₂ fixation (NRR). For catalytic reactions, it is the key to develop high-performance catalysts to meet the demand for targeted reactions. In recent years, two-dimensional (2D) materials have attracted great interest in environmental catalysis due to their unique layered structures, which offer us to make use of their electronic and structural characteristics. Great progress has been made so far, including graphene, black phosphorus, oxides, layered double hydroxides (LDHs), chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks (MOFs), covalent organic frameworks (COFs), and others. This content drives us to invite many famous groups in these fields to write the roadmap on two-dimensional nanomaterials for environmental catalysis. We hope that this roadmap can give the useful guidance to researchers in future researches, and provide the research directions.     

Conjugated polymers based on new thienylene – PPV derivatives for solar cell applications

Two π-conjugated monomers based on bis-(1-cyano-2-thienyl-vinylene)phenylene derivatives were synthesized by Knoevenagel condensation. Both monomers are found to form electroactive polymers upon electrochemical oxidation. The withdrawing effect due to the cyano-substituent allows for the reversible n-doping of the polymer. Thus, the band gap E_g was measured using electrochemical techniques and compared with that obtained by UV–VIS–NIR spectroscopy. Based on the measured band gap of 1.87 and 1.58 eV, these polymers appear to be interesting candidates for solar-cell applications.