Search

Herein, an efficient lithium tert‐butoxide/DMSO‐mediated rapid synthesis of naphthalenes, benzofurans, and indoles is reported. The anticipated aromatics and heteroaromatics are obtained in high yields within a few minutes, even in a decagram‐scale reaction. [ABSTRACT FROM AUTHOR]

Achieving the accurate perception of occluded objects for autonomous vehicles is a challenging problem. Human vision can always quickly locate important object regions in complex external scenes, while other regions are only roughly analysed or ignored, defined as the visual attention mechanism. However, the perception system of autonomous vehicles cannot know which part of the point cloud is in the region of interest. Therefore, it is meaningful to explore how to use the visual attention mechanism in the perception system of autonomous driving. In this paper, we propose the model of the spatial attention frustum to solve object occlusion in 3D object detection. The spatial attention frustum can suppress unimportant features and allocate limited neural computing resources to critical parts of the scene, thereby providing greater relevance and easier processing for higher-level perceptual reasoning tasks. To ensure that our method maintains good reasoning ability when faced with occluded objects with only a partial structure, we propose a local feature aggregation module to capture more complex local features of the point cloud. Finally, we discuss the projection constraint relationship between the 3D bounding box and the 2D bounding box and propose a joint anchor box projection loss function, which will help to improve the overall performance of our method. The results of the KITTI dataset show that our proposed method can effectively improve the detection accuracy of occluded objects. Our method achieves 89.46%, 79.91% and 75.53% detection accuracy in the easy, moderate, and hard difficulty levels of the car category, and achieves a 6.97% performance improvement especially in the hard category with a high degree of occlusion. Our one-stage method does not need to rely on another refining stage, comparable to the accuracy of the two-stage method. [ABSTRACT FROM AUTHOR]

In order to solve the problem of overheating of the engine and cooling system of the vehicle in the plateau low-pressure environment, it is necessary to study air-side thermal-hydraulic performance of the vehicle cooling system heat exchanger under low-pressure environment. In this paper, the experimental study on the louvered fin and flat tube heat exchanger of the vehicle is carried out on the low-pressure wind tunnel test bench. The results show that at a gauge pressure of −44 kPa, the air-side convective heat transfer coefficient is reduced by 33.5%~23.3% compared with 0 kPa; the Colburn j-factor is increased by 36.8% on average; the f factor is increased by 51.2% on average. Based on this, numerical simulations are carried out to study the heat transfer and flow characteristics of louvered fins with different structural parameters under low-pressure environment. The empirical correlations of Colburn j-factor and Friction factor f are fitted by multiple linear regression. In the range of gauge pressure from 0 kPa to −44 kPa, the average deviation of the correlation calculation result of Colburn j-factor is 3.4%, and the average deviation of the correlation calculation result of f factor is 5.5%. The research results can provide a basis for the design of louvered fin heat exchangers utilized in the plateau environment. [ABSTRACT FROM AUTHOR]

Nanocomposite AgBr@HPU-4 was synthesized based on a 3D Cu-MOF, {[Cu(L) 0.5 (H 2 O) 2 ]·4H 2 O} n (HPU-4) through a facile reaction route and confirmed by XRD, TEM, SEM. UV–Vis absorption spectrum indicates that AgBr@HPU-4 nanocomposite has strong optical capability nearly in the whole range of visible light spectrum. The as-prepared AgBr@HPU-4 photocatalyst, as compared to AgBr or HPU-4 , exhibits enhanced photocatalytic activity towards the degradation of Methylene Blue and Methyl Orange dyes. [ABSTRACT FROM AUTHOR]

A Cu(I)/Cu(II) 3D framework, {[(CuII) 3 (CuI) 3 (pbt) 3 Cl 2 ]·ClO 4 ·H 2 O} n ( HPU-3 ) (H 2 pbt = 5′-(pyridin-2-yl)–2H,4′H-3,3′-bi(1,2,4-triazole)), has been synthesized by using solvothermal method. UV–Vis absorption spectrum indicates that HPU-3 has strong optical capability nearly in the whole range of visible light spectrum. HPU-3 photocatalyst exhibits good photocatalytic activity toward the degradation of Methylene Blue and Methyl Orange dyes. [ABSTRACT FROM AUTHOR]

Fused polycyclic furans are privileged structural scaffolds in materials chemistry, including organic semiconductors. Specifically, indeno[1,2- c ]furans are an interesting type of polycyclic furans featuring a fused furan and indenone framework. Unfortunately, limited studies on their photophysical properties have been performed, probably owing to the lack of efficient and straightforward approaches to those compounds. Herein, we have developed a cobalt-catalyzed radical-polar crossover cyclization of the readily available o -alkynylaryl β-carbonyls to afford diverse indeno[1,2- c ]furans. Photophysical and DFT calculations were also carried out, suggesting that the obtained indeno[1,2- c ]furans exhibit promising electronic and optical properties.

The generation of smart responsive materials that can perform multiple drastic optical outputs upon different triggers provides a good platform to encode and hide the information and create multilevel security. In this paper, a smart multiresponsive MOF-on-MOF material was reported using one MOF ( HPU-14 ) as a platform to grow ZIF-8 on the outer layer, combining different emitter centers such as anthracene (ANT) and lanthanide ions (Ln 3+ ) confined into two MOFs. Due to the existence of ANT in the pores of ZIF-8 , this composite material can exhibit reversible photoswitching behavior under a 365 nm ultraviolet (UV) lamp and enable "resetting and reusing" dynamic anticounterfeiting application. Meanwhile, when treated by an acid/alkali gas, this material can also display reversible switching behavior under 254 nm UV irradiation, which is attributed to the loading of Ln 3+ on HPU-14 . We demonstrated that this excellent practical anticounterfeiting material can decipher the right information only by following a strict stimuli sequence. Therefore, this MOF-on-MOF material synthesis technology for sophisticated counterfeiters, which makes the protected information highly secure, could open a new way to design multilevel anticounterfeiting materials.

Active species were introduced into MOFs to prepare multifunctional fluorescent probes by a stepwise postsynthetic modulation strategy. First, two-dimensional HPU-16 (HPU = Henan Polytechnic University; HPU-16 = Zn(L) 2 (H 2 O); HL = 2-(5-pyridin-4-yl-5 H -[1,2,4]triazol-3-yl)-pyrazine) was transformed into three-dimensional HPU-17 ({Zn 3 (L) 2 (btc) 2 (H 2 O)} n ) through a crystal dissolution-recrystallization process. Second, linker replacement was used to introduce -NH 2 into the HPU-17 to generate functional NH 2 -HPU-17 via a single-crystal to single-crystal transformation. The functional amino groups caused NH 2 -HPU-17 to show a significant response to ClO - . Because of the interaction of amino groups and ClO - , the fluorescence of NH 2 -HPU-17 gradually changed from blue to yellow-green. More interestingly, NH 2 -HPU-17 could encapsulate Tb 3+ and sensitize the visible-emitting characteristic fluorescence of Tb 3+ in aqueous solution. Then, newly generated Tb 3+ @NH 2 -HPU-17 could serve as an effective probe for the determination of DPA. This work paves a new way for the design and modulation of ratiometric fluorescence probes for the selective and sensitive detection of special molecules.