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991.
An Alternating Direction Method of Multipliers for MCP-penalized Regression with High-dimensional Data 下载免费PDF全文
The minimax concave penalty (MCP) has been demonstrated theoretically and practically to be effective in nonconvex penalization for variable selection and parameter estimation. In this paper, we develop an efficient alternating direction method of multipliers (ADMM) with continuation algorithm for solving the MCP-penalized least squares problem in high dimensions. Under some mild conditions, we study the convergence properties and the Karush–Kuhn–Tucker (KKT) optimality conditions of the proposed method. A high-dimensional BIC is developed to select the optimal tuning parameters. Simulations and a real data example are presented to illustrate the efficiency and accuracy of the proposed method. 相似文献
992.
Considered in this paper is a class of singular boundary value problem, arising in hydrodynamics and nonlinear field theory, when centrally bubble-type solutions are sought: \((p(t)u0)0 = c(t)p(t)f(u); u0(0) = 0; u(+1) = L > 0\) in the half-line \([0;+1)\), where \(p(0) = 0\). We are interested in strictly increasing solutions of this problem in \([0;1)\) having just one zero in \((0;+1) \)and finite limit at zero, which has great importance in applications or pure and applied mathematics. Su±cient conditions of the existence of such solutions are obtained by applying the critical point theory and by using shooting argument [9,10] to better analysis the properties of certain solutions associated with the singular di®erential equation. To the authors' knowledge, for the first time, the above problem is dealt with when f satis¯es non-Lipschitz condition. Recent results in the literature are generalized and signi¯cantly improved. 相似文献
993.
Feilong Yang Xiaoyu Liu Xiang Shi Yong Wang Guoru Hu Sheng Lin Xiaozhen Jiao Ping Xie 《Tetrahedron》2019,75(23):3101-3107
Bysspectin A (1), an unusual polyketide-derived octaketide dimer, has highly selective inhibitory activities against human carboxylesterase 2 (hCE2) with an IC50 value of 2.01 μM. Herein, we report the first synthesis of this natural product. The synthesis relies upon a key Cu-catalysed domino Sonogashira-cyclization process. 相似文献
994.
Ping Cheng Kuang Xu Yan Chi Chen Ting Ting Wang Yu Chen Cheng Long Yang Shi Ying Ma Yong Liang Hui Ming Ge Rui Hua Jiao 《Tetrahedron letters》2019,60(26):1706-1709
Chemical study of the insect-derived bacterium, Streptomyces sp. NA4286, led to the discovery of four new polyketides, murayaquinones B-E (1–4), together with a known compound, murayaquinone (5). The structures of new compounds (1–4) were determined by extensive analysis of their NMR and HRESIMS data. The absolute configuration of (+)-1 and (?)-1 was assigned through comparison of experimental and calculated ECD spectra. Murayaquinone D (3) exhibited potent cytotoxic activities against six human cancer cell lines with IC50 values ranging from 1.03 to 9.99 μM. 相似文献
995.
Na Li Feng Jiao Xiulian Pan Yuxiang Chen Jingyao Feng Gen Li Xinhe Bao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(22):7478-7482
Despite significant efforts towards the direct conversion of syngas into liquid fuels, the selectivity remains a challenge, particularly with regard to high‐quality gasoline with a high octane number and a low content of aromatic compounds. Herein, we show that zeolites with 1D ten‐membered‐ring (10‐MR) channel structures such as SAPO‐11 and ZSM‐22 in combination with zinc‐ and manganese‐based metal oxides (ZnaMnbOx) enable the selective synthesis of gasoline‐range hydrocarbons C5–C11 directly from syngas. The gasoline selectivity reached 76.7 % among hydrocarbons, with only 2.3 % CH4 at 20.3 % CO conversion. The ratio of isoparaffins to n‐paraffins was as high as 15, and the research octane number was estimated to be 92. Furthermore, the content of aromatic compounds in the gasoline was as low as 16 %. The composition and structure of ZnaMnbOx play an important role in determining the overall activity. This process constitutes a potential technology for the one‐step synthesis of environmentally friendly gasoline with a high octane number from a variety of carbon resources via syngas. 相似文献
996.
Shuang Zhu Xue‐Jiao Dai Xiu‐Guang Wang Ying‐Yu Cao Xiao‐Jun Zhao En‐Cui Yang 《无机化学与普通化学杂志》2019,645(5):516-522
Two new layered complexes with the formulas of {[Cu(H2O)(HL)2Cl](NO3)}n ( 1 ) and {[Cu(H2O)2(HL)2](NO3)2}n ( 2 ) were solvothermally synthesized by the reactions of the bulky conjugated 4′‐(4‐hydroxyphenyl)‐4,2′:6′,4′′‐terpyridine ligand (HL) with different CuII salts, which were further used as photocatalysts to achieve hydrogen production from water splitting. Single‐crystal structural analyses reveal that both complexes feature coplanar (4 4) layers with different connection manners between the HL extended Z‐shaped chains. More interestingly, 1 possessing more negative conduction band potential and higher structural stability exhibits a large hydrogen production rate of 2.43 mmol · g–1 · h–1, which is four times higher than that of 2 . Thus, the CuII‐based coordination polymers modified by the bulky conjugated organic ligand can become potentially promising non‐Pt photocatalysts for hydrogen production from water splitting. 相似文献
997.
Xu Zhang Jiao Sun Guangfeng Wei Zhipan Liu Huimin Yang Kaimin Wang Honghan Fei 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(9):2870-2875
The reported metal–organic framework (MOF) catalyst realizes CO2 to methanol transformation under ambient conditions. The MOF is one rare example containing metal‐free N‐heterocyclic carbene (NHC) moieties, which are installed using an in situ generation strategy involving the incorporation of an imidazolium bromide based linker into the MOF by postsynthetic ligand exchange. Importantly, the resultant NHC‐functionalized MOF is the first catalyst capable of performing quantitative hydrogen transfer from silanes to CO2, thus achieving quantitative (>99 %) methanol yield. Density‐functional theory calculations indicate the high catalytic activity of the NHC sites in MOFs are attributed to the decreased reaction barrier of a reaction route involving the formation of an NHC‐silane adduct. In addition, the MOF‐immobilized NHC catalyst shows enhanced stability for up to eight cycles without base activation, as well as high selectivity towards the desired silyl methoxide product. 相似文献
998.
Novel expanded porphyrinoids with advanced structure features(such as multiple-inner-ring-fusion)have a wide range of benefits(such as multi-metal coordination and facile tunable aromaticity) not offered by their normal porphyrin analogues,and have found wide applications as sensors,fluorescent probes,novel ligands and functionalized NIR organic dyes in various research fields.However,the structures of these expanded porphyrinoids are scarce due to their limited synthetic accessibility.Herein,we summarized the lately reported efficient synthesis of novel expanded porphyrinoids with multipleinner-ring-fusion(up to six-inner-ring-fusion) and smaragdyrins with tunable aromaticity.Their synthesis is either based on an oxidative ring cyclization on linear/macrocyclic oligopyrroles containing N-confused pyrrole unit(s) or a straightforward double SNAr reaction on readily available 3,5-dibromoBODIPY,respectively. 相似文献
999.
In this paper, a new type of flame retardant (AF‐Fe) based on para‐aramid fiber (AF) which was modified with iron diethyl phosphinate was applied for thermoplastic polyurethane elastomer (TPU). The flame‐retardant properties of TPU were tested using cone calorimeter test, smoke density test, and thermogravimetric analysis/infrared spectrometry. The cone calorimeter test showed that AF‐Fe can greatly reduce the heat release rate, total heat release, smoke factor, and other parameters of TPU composites compared with the sample of TPU/AF. For example, the pHRR of the composite with 1.0 wt% AF‐Fe was reduced by 15.19% compared with the sample with the same content of pure AF. In addition, the smoke factor of TPU/AFFe3 was reduced by 50.52% and 15.63% compared with TPU0 and TPU/AF respectively. The results of smoke density test showed that the luminous flux of TPU/AFFe3 was increased by 79.26% compared with the sample of TPU/AF. The TG results revealed that the sample with TPU/AFFe3 had lower weight loss rate and higher char residue content at 700°C compared with the sample of TPU/AF. 相似文献
1000.
Thermoplastic polyurethane (TPU) elastomer has a widely application because of its perfect physical and chemical properties. However, it was limited by its low reliability in fire safety. In this paper, a new fire agent integrated with molecular sieve and tetrafluoroborate ionic liquid ([EOOEMIm][BF4]) was used to improve fire safety of TPU. The fire safety of TPU composites was investigated by cone calorimeter test, smoke density test, and thermogravimetric/infrared spectroscopy, respectively. The results showed that modified molecular sieve (MMS) can improve fire safety of TPU effectively. The luminous flux increased to 10.10%, total smoke release decreased by 58%, and heat release rate declined of 65% than pure TPU when the addition of MMS was 0.5 wt%. In addition, MMS can improve thermal stability of TPU even in nitrogen according to thermogravimetric/infrared spectroscopy test. These proved that MMS has a satisfactory application prospect in fire safe polymer materials. 相似文献