Second‐order optimization methods for time‐delay Autoregressive eXogenous models: Nature gradient descent method and its two modified methods

This article proposes several second-order optimization methods for time-delay ARX model. Since the time-delay in the information vector makes the traditional identification algorithms be inefficient, a redundant rule based method is utilized to transformed the model into a redundant model. Then, the nature gradient descent (NGD) algorithm is developed for such a model. To reduce the computational efforts of the NGD algorithm and to adaptively update each element in the parameter vector, two modified NGD algorithms are also presented. The simulation examples verify the effectiveness of the proposed algorithms

Wet-chemical synthesis and applications of semiconductor nanomaterial-based epitaxial heterostructures

Semiconductor nanomaterial-based epitaxial heterostructures with precisely controlled compositions and morphologies are of great importance for various applications in optoelectronics, thermoelectrics, and catalysis. Until now, various kinds of epitaxial heterostructures have been constructed. In this minireview, we will first introduce the synthesis of semiconductor nanomaterial-based epitaxial heterostructures by wet-chemical methods. Various architectures based on different kinds of seeds or templates are illustrated, and their growth mechanisms are discussed in detail. Then, the applications of epitaxial heterostructures in optoelectronics, catalysis, and thermoelectrics are described. Finally, we provide some challenges and personal perspectives for the future research directions of semiconductor nanomaterial-based epitaxial heterostructures.Ministry of Education (MOE)Published versionThis work was supported by MOE under AcRF Tier 2 (ARC 19/15, No. MOE2014-T2-2-093; MOE2015T2-2-057; MOE2016-T2-2-103; MOE2017-T2-1-162) and AcRF Tier 1 (2016-T1-001-147; 2016-T1-002-051; 2017-T1001-150; 2017-T1-002-119) and NTU under Start-Up Grant (M4081296.070.500000) in Singapore. We would like to acknowl‑ edge the Facility for Analysis, Characterization, Testing and Simu‑ lation, Nanyang Technological University, Singapore, for use of their electron microscopy (and/or X-ray) facilities. Hua Zhang thanks the support from ITC via Hong Kong Branch of National Precious Metals Material Engineering Research Center, and the Start-Up Grant from City University of Hong Kong

Intramolecular hydrogen bonding-based topology regulation of two-dimensional covalent organic frameworks

Creating molecular networks with different topologies using identical molecular linkers is fundamentally important but requires precise chemistry control. Here, we propose an effective strategy to regulate the network topologies of two-dimensional (2D) covalent organic frameworks (COFs) through the conformational switching of molecular linkages. By simply altering the substituents of an identical molecular linker, the topology-selective synthesis of two highly crystalline 2D COFs can be readily achieved. Their distinct crystal structures are observed and determined by low-dose, high-resolution transmission electron microscopy imaging, indicating that the driving force for linkage conformation switching is intramolecular hydrogen bonding. Our strategy would greatly diversify the COF topologies and enable vast postsynthetic modifications such as boron complexation, endowing these structures with a unique optical property such as fluorescence turn on and aggregation-induced emission.Ministry of Education (MOE)This work was supported by MOE under AcRF Tier 2 (MOE2016-T2-2-103; MOE2017-T2-1-162) in Singapore. Y.Z. acknowledges financial support from the National Natural Science Foundation of China (grant no. 21771161) and the Thousand Talents Program for Distinguished Young Scholars. We acknowledge the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for the use of their electron microscopy (and/or X-ray) facilities. H.Z. is grateful for financial support from the ITC via the Hong Kong Branch of National Precious Metals Material Engineering Research Center (NPMM) and the start-up grant (project no. 9380100) and grants (project nos. 9610478 and 1886921) from the City University of Hong Kong

Isoreticular series of two-dimensional covalent organic frameworks with the kgd topology and controllable micropores

Two-dimensional (2D) covalent organic frameworks (COFs) possess designable pore architectures but limited framework topologies. Until now, 2D COFs adopting the kgd topology with ordered and rhombic pore geometry have rarely been reported. Here, an isoreticular series of 2D COFs with the kgd topology and controllable pore size is synthesized by employing a C6-symmetric aldehyde, i.e., hexa(4-formylphenyl)benzene (HFPB), and C3-symmetric amines i.e., tris(4-aminophenyl)amine (TAPA), tris(4-aminophenyl)trazine (TAPT), and 1,3,5-tris[4-amino(1,1-biphenyl-4-yl)]benzene (TABPB), as building units, referred to as HFPB-TAPA, HFPB-TAPT, and HFPB-TABPB, respectively. The micropore dimension down to 6.7 Å is achieved in HFPB-TAPA, which is among the smallest pore size of reported 2D COFs. Impressively, both the in-plane network and stacking sequence of the 2D COFs can be clearly observed by low-dose electron microscopy. Integrating the unique kgd topology with small rhombic micropores, these 2D COFs are endowed with both short molecular diffusion length and favorable host-guest interaction, exhibiting potential for drug delivery with high loading and good release control of ibuprofen.H.Z. acknowledges support from ITC via the Hong Kong Branch of National Precious Metals Material Engineering Research Center (NPMM), the Start-Up Grant (project no. 9380100), and grants (project nos. 7020013, 9678272, and 1886921) from the City University of Hong Kong. Y.Z. acknowledges financial support from the National Natural Science Foundation of China (Grant Nos. 21771161, 22122505, and 22075250). Y.P. thanks the financial support from the funding of the "Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang" (2020R01002) and the Class D of Qianjiang Talent Program (project no. ZD20011250001)

Base-Promoted, Aerobic, and Regioselective Carbon–Hydrogen Bond Activation of Thiophene with Group 9 Metalloporphyrins

Base-promoted aerobic carbon–hydrogen bond activation (CHA) of thiophene was achieved with high regioselectivity at the 2-position by group 9 metalloporphyrins in moderate to high yields. Mechanistic investigations suggest a homolytic aromatic substitution through M^II(ttp) (M = Rh, Ir) metalloradical addition, followed by β-elimination of a metal hydride pathway