188 research outputs found
Carbon isotopic composition and its implications on paleoclimate of the underground ancient forest ecosystem in Sihui, Guangdong
No full textWe present the carbon isotopic composition of the total organic carbon (TOC) and fine roots in the sedimentary profile from the underground ancient forest in Sihui to study the climatic and environmental changes from 4.5 ka BP to 0.6 ka BP. Results show that C(3) plant was the main vegetation from 4.5 ka BP to 0.6 ka BP in this region. The ancient forest began to develop in the wetland at around 4 ka BP and disappeared together with the wetland at about 3.0 ka BP, implying that the climate had changed greatly at around 3.0 ka BP. As indicated by the simulation results, the content of atmospheric CO(2) increased slightly during 3.5 ka BP to 3.0 ka BP, implying climate warming during that period. The interval of radiocarbon age between 3.0 ka BP to 1.2 ka BP was possibly caused by the strong erosion when the block was lifted in the neotectonic movement. From 1.2 ka BP to 0.6 ka BP, the region remained in terrestrial sedimentary environment, and the surface plant biomass declined gradually. Drought caused by the climate change was the likely cause for the disappearance of the ancient forest. South transition of Intertropical Convergence Zone (ITCZ) was probably the main mechanism for the climate change.Geosciences, MultidisciplinarySCI(E)EI3ARTICLE5638-6465
On the Northern Zhou Dynasty Post of Sihui 司会: The Relationship Between the Six Ministries System 六官制 and the Bafu 覇府
No full textAfter the fall of the Northern Wei Dynasty in 534, the Western Wei and subsequent Northern Zhou Dynasties abolished the current bureaucratic system in favor of the six ministries system (Liuguan-Zhi 六官制) originally laid out in the Zhouli 周礼.However, even today there are many things we do not know about this system, although in recent years research comparing the Liuguan and Sui Dynasty bureaucracies has progressed. Unfortunately, our insufficient knowledge about the former has posed a hindrance to such comparative research.Moreover, in order to improve our understanding about the political history of the Northern Zhou Dynasty, it is necessary to clarify the relationship between the Liuguan system and the Bafu 覇府, the military headquarters from which Yuwen Tai, Yuwen Hu and Yang Jian (founder of the Sui Dynasty) wielded actual power.Although research is progressing on the institutions close to the emperor, like the Neishi 内史(governor of the capital) and Yuzheng 御正 (chancellors of the imperial household), during the first half of the Dynasty’s reign, these posts did not form the core of governance, due to the hegemony of Yuwen Hu. In order to contribute to the growing research, the present article takes up the Imperial Ministry’s (Tianguan天官) post of Sihui Zhongdaifu 司会中大夫, who during the era of Yuwen Hu acted as his assistant in coordinating the affairs of the Liuguan ministries.The research to date had understood Sihui as the minister of fiscal affairs and its control over the Liuguan System was thought to have been a temporaryone. On the other hand, Jiao Peimin 焦培民, identifies the Northern Zhou Sihui as performing the same duties as the head of the Executive Branch (Shangshu-Sheng 尚書省) of the Northern Wei’s three ministry system; however, since the Northern Zhou purposefully dismantled that ministry, it is difficult to conceive of the Sihui performing the same function.Instead, the purpose of this article is to analyze the functions of and appointees to the post of Sihui, in an attempt to clarify the relationship between the Northern Zhou’s Liuguan system and the Bafu.Based on the main text of the Zhouli and commentaries on it written by Zheng Xuan 鄭玄 during the last decades of the Later Han Dynasty, the author concludes that while the Northern Zhou Sihui was an appointment similar in function to the head of the former Shengshu Ministry, his authority was much diminished compared to his Northern Wei counterpart and consisted of coordinating proposals submitted by the Liuguan bureaus and reporting back the policy decisions made concerning them.Nevertheless, the post of Sihui was indispensable to the maintenance of the regime, ensuring the smooth functioning of government.For this reason, the Sihui was also appointed by the Yuwens and Yang Jian as a trusted member of the Bafu general staff and put in charge of administrative affairs, clearly showing an intimate relationship between the Liuguan system and the Bafu, as well as revealing one important characteristic of the Northern Zhou Dynasty’s bureaucratic structure.journal articl
PEPTIDOMIMICRY: DESIGN, SYNTHESIS AND CONFORMATIONAL STUDY OF C2-SYMMETRIC OLIGOUREAS
No full textMimicking the structure and even the function of an ??-peptide with artificial chainmolecules such as ??-peptides, ??-peptides and other unnatural oligomers has shown early success.The structural similarities between natural peptides and oligoureas lead to the belief that C2-symmetric oligoureas could be a good candidate for peptidomimicry. Molecular modelingindicates that both homochiral (all monomers have the same absolute configuration) andalternate chiral (absolute configuration of the residues alternate) C2-symmetric oligoureas canform helix- and sheet-like structures in solution conditionally.Several C2-symmetric 1,2-diamines were chosen as the building blocks for the synthesisof chiral oligoureas, and all diamines except for one were prepared in lab. Homochiral andheterochiral oligoureas based on the same diamine or mixed diamines were synthesized in thesolution phase, growing a chain by adding one unit at a time to one terminus or two units at atime to both termini with 4-nitrophenoxycarbonyl (PNP)- activated and t-butoxycarbonyl (Boc)- protected diamines as the intermediates. All the chiral oligoureas were purified by eitherrecrystallization and /or column chromatography and/ or HPLC and characterized by NMR andMALDI-MS. For some oligoureas, crystal structures were obtained. Fragment condensation wasattempted to improve the efficiency of the synthesis, but this approach led to cyclized oligoureasinstead of the desired concatenated residues.Conformational studies of chiral oligoureas were done in both the solid state and thesolution state. The crystal structures of some homochiral oligoureas and some alternate chiraloligoureas indicate that both helix-like structures and extended structures exist for these C2-symmetric oligoureas. NMR and Circular Dichroism (CD) were used to study the conformationof oligoureas in solution, but the conformational study by NMR was not conclusive. CD studyshowed that these oligoureas have multiple conformations in solution and that some of theconformations are sensitive to solvents and temperature. Also, short homochiral and alternatechiral oligoureas based on trans-1,2-diaminocyclohexane (DACH) exhibit signs of cooperativebehavior in solution as gauged by a series of experiments
4-[(2-Phenylethyl)amino]benzoic acid
No full textThe title compound, C15H15NO2, crystallizes with two molecules in the asymmetric unit. In the crystal, the two molecules associate to form an acid–acid dimer by pairwise O—H...O hydrogen bonds
Influence of Tempering on the Microstructure & Properties of Martensite and Bainite developed in a Low-C High-Si Steel
No full textMartensitic and bainitic steels are two types of widely used steels with excellent mechanical behaviors in automatic industry. It’s universally acknowledged that as- quenched martensite possesses poor ductility and impact toughness, which should be tempered before putting into application. During tempering, as-quenched martensite changes from a hard and brittle microstructure to more ductile and softer microstructure, leading to improved mechanical properties for manufacturing. Bainitic microstructures is less sensitive to tempering in the improvement of mechanical properties, while the explicit tempering effects are still unknown.The primary goal of the current research is to study the effect of tempering on the microstructure and properties of martensitic and bainitic microstructures developed in the same low carbon steel with high content of silicon and manganese (0.2wt.%C- 2wt.%Si-3wt.%Mn). Results show that for tempered martensite, the hardness, yield strength and tensile strength have a decreasing tendency with higher tempering temperatures. Through tempering, martensite became more ductile at the expense of strength. Based on the literatures, transitional carbide precipitation is expected to take place instead of cementite at early stage of tempering due to the retarding effect of high silicon content. Investigations also show that bainite is less sensitive to tempering compared to martensite. The yield strength and elongation firstly increase due to the TRIP effect of retained austenite and then decrease with higher tempering temperature. Hardness and tensile strength have a similar decreasing tendency as martensite during tempering. The fracture modes of tempered martensite for all temperatures show a typical ductile fracture, while for bainite, a morphology of quasi-cleavage fracture is observed
4-Oxo-N-phenyl-1,4-dihydropyridine-3-carboxamide
No full textThe title compound, C12H10N2O2, shows a nearly planar conformation. The crystal structure is sustained by hydrogen bonds between the NH and the carbonyl O function of the 4-oxo-1,4-dihydropyridine ring of the molecules, forming infinite chains along the b-axis direction
N-(2,6-Dichlorophenyl)-2-oxo-1,2-dihydropyridine-3-carboxamide
No full textCrystals of the title compound, C12H8Cl2N2O2, were obtained by slow evaporation of an ethanolic solution. An intramolecular amideN—H...O=Clactam hydrogen bond is observed. In the crystal, two molecules pair up to form a centrosymmetric lactam–lactam dimers (LLD) by N—H...O=C hydrogen bonds, whereas the O=Camide group of the molecule does not participate in hydrogen bonding
2-Methyl-4-[(4-methylphenyl)amino]benzoic acid
No full textIn the title compound, C15H15NO2, which was prepared using a Buchwald–Hartwig cross-coupling reaction followed by ester hydrolysis, the dihedral angle between the aromatic rings is 42.44 (7)°. In the crystal, the molecules associate to form centrosymmetric acid–acid dimers
3-Methyl-2-(4-methylphenoxy)benzoic acid
No full textIn the title compound, C15H14O3, the dihedral angle between the aromatic rings is 86.7 (9)°. In the crystal, carboxylic acid inversion dimers linked by pairwise O—H...O hydrogen bonds are formed
Redetermined structure of 4-(benzyloxy)benzoic acid
No full textIn the title compound, C14H14O3, the dihedral angle between the aromatic rings is 39.76 (9)°. In the crystal, the molecules associate to form centrosymmetric acid–acid dimers linked by pairwise O—H...O hydrogen bonds. The precision of the geometric parameters in the present single-crystal study is about an order of magnitude better than the previous powder diffraction study [Chattopadhyay et al. (2013). CrystEngComm, 15, 1077–1085]
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