Graphs with three distinct eigenvalues and largest eigenvalue less than 8

In this paper we consider graphs with three distinct eigenvalues and, we characterize those with the largest eigenvalue less than 8. We also prove a simple result which gives an upper bound on the number of vertices of graphs with a given number of distinct eigenvalues in terms of the largest eigenvalue.     

Synthesis and properties of aromatic polyamides containing the cyclohexane structure

1,1-Bis[4-(4-carboxyphenoxy)phenyl]cyclohexane (III) and 1,1-bis[4-(4-aminophenoxy)phenyl]cyclohexane (V) were prepared in two main steps starting from the aromatic nucleophilic substitution of p-fluorobenzonitrile and p-chloronitrobenzene, respectively, with 1,1-bis(4-hydroxyphenyl)cyclohexane in the presence of potassium carbonate in N,N-dimethylformamide (DMF). Using triphenyl phosphite and pyridine as condensing agents, two series of polyamides with cyclohexylidene cardo groups were directly polycondensated from dicarboxylic acid III with various aromatic diamines or from diamine V with various aromatic dicarboxylic acids in an N-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride. The polyamides exhibited inherent viscosities in the range of 0.45 to 1.78 dL/g. Almost all of the polymers were readily soluble in polar aprotic solvents such as NMP and N,N-dimethylacetamide (DMAc) and could afford transparent, flexible, and tough films by solution casting. The glass transition temperatures (T_g) of these aromatic polyamides were in the range of 180–243°C by DSC, and the 10% weight loss temperatures in nitrogen and air were all above 450°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3575–3583, 1999     

Type II Intramolecular [5+2] Cycloaddition: Facile Synthesis of Highly Functionalized Bridged Ring Systems

A type II intramolecular oxidopyrylium‐mediated [5+2] cycloaddition reaction allows the efficient and diastereoselective formation of various highly functionalized and synthetically challenging bridged seven‐membered ring systems (such as bicyclo[4.4.1]undecane, bicyclo[4.3.1]decane, bicyclo[5.4.1]dodecane, and bicyclo[6.4.1]]tridecane). This simple, thermal, direct transformation has a broad substrate scope and is high yielding, with high functional‐group tolerance and unique endo selectivity. The highly strained tricyclic cores of ingenol mebutate (picato) and cyclocitrinol are synthesized efficiently and diastereoselectively using this methodology.     

Syntheses and Characterization of Organoimido Complexes of Niobium(V); Potential CVD Precursors

New niobium imido complexes (RN)Nb(NEt₂)₃ (R = Prⁿ, Prⁱ and Bu^t), potential precursors to grow niobium containing thin films by chemical vapor deposition (CVD), were prepared by reacting the corresponding (RN)NbCl₃py₂ complexes (R = Prⁿ, Prⁱ and Bu^t; py = pyridine) with LiNEt₂ in hydrocarbon solvents. The structures of (RN)NbCl₃py₂ (R = Prⁱ and Bu^t), determined by X-ray crystallography, are mononuclear with distorted octahedral geometries, For each complex, three chloride ligands are cis to the imido ligand and occupy meridional positions. One of two py ligands is cis to and the other is trans to the imido ligand. For (PrⁱN)NbCl₃py₂, the Nb=NPrⁱ bond distance (Å) is 1.733(3) and the ∠Nb=N-Prⁱ angle (°) is 178.0(3). Crystal data: monoclinic, space group P2₁/n, a = 8.805(2), b = 14.930(4), c = 13, 407(3) Å, β = 93.37(2)°, V = 1759.5(7) ų, Z = 4, D_c = 1.565 g cm³. For (Bu^tN)NbCl₃py₂, the Nb=NBu^t bond distance (Å) is 1.734(4) and the ∠Nb=N-Bu^l angle (°) is 174.8(4). Crystal data: monoclinic, space group P2₁/c, a = 9.609(1), b = 13.591(6), c = 14.615(2) Å, β = 90.05(1)°, V = 1908.5(9) ų, Z = 4, D_c = 1.492 g cm^?3.     

多介质五方程简化模型及界面捕捉的人工压缩算法

根据两介质五方程简化模型的基本假设,发展了适用于任意多种介质的体积分数方程.为了捕捉多介质界面,将HLLC-HLLCM混合型数值通量的计算格式推广应用于二维平面和柱几何的多介质复杂流动问题,在高阶精度的数据重构过程中采用斜率修正型人工压缩方法ACM.通过一维、二维多介质黎曼问题算例测试,结果表明:发展的计算格式能够较好...     

A multiplexed high‐resolution imaging spectrometer for resonant inelastic soft X‐ray scattering spectroscopy

The optical design of a two‐dimensional imaging soft X‐ray spectrometer is described. A monochromator will produce a dispersed spectrum in a narrow vertical illuminated stripe (～2 µm wide by ～2 mm tall) on a sample. The spectrometer will use inelastically scattered X‐rays to image the extended field on the sample in the incident photon energy direction (vertical), resolving the incident photon energy. At the same time it will image and disperse the scattered photons in the orthogonal (horizontal) direction, resolving the scattered photon energy. The principal challenge is to design a system that images from the flat‐field illumination of the sample to the flat field of the detector and to achieve sufficiently high spectral resolution. This spectrometer provides a completely parallel resonant inelastic X‐ray scattering measurement at high spectral resolution (～30000) over the energy bandwidth (～5 eV) of a soft X‐ray absorption resonance.     

Bioactive Agent Discovery from the Natural Compounds for the Treatment of Type 2 Diabetes Rat Model

Diabetes mellitus is a well-known chronic metabolic disease that poses a long-term threat to human health and is characterized by a relative or absolute lack of insulin, resulting in hyperglycemia. Type 2 diabetes mellitus (T2DM) typically affects many metabolic pathways, resulting in β-cell dysfunction, insulin resistance, abnormal blood glucose levels, inflammatory processes, excessive oxidative reactions, and impaired lipid metabolism. It also leads to diabetes-related complications in many organ systems. Antidiabetic drugs have been approved for the treatment of hyperglycemia in T2DM; these are beneficial for glucose metabolism and promote weight loss, but have the risk of side effects, such as nausea or an upset stomach. A wide range of active components, derived from medicinal plants, such as alkaloids, flavonoids, polyphenol, quinones, and terpenoids may act as alternative sources of antidiabetic agents. They are usually attributed to improvements in pancreatic function by increasing insulin secretions or by reducing the intestinal absorption of glucose. Ease of availability, low cost, least undesirable side effects, and powerful pharmacological actions make plant-based preparations the key player of all available treatments. Based on the study of therapeutic reagents in the pathogenesis of humans, we use the appropriate animal models of T2DM to evaluate medicinal plant treatments. Many of the rat models have characteristics similar to those in humans and have the advantages of ease of genetic manipulation, a short breeding span, and access to physiological and invasive testing. In this review, we summarize the pathophysiological status of T2DM rat models and focus on several bioactive compounds from herbal medicine with different functional groups that exhibit therapeutic potential in the T2DM rat models, in turn, may guide future approach in treating diabetes with natural drugs.     

Studies on photochemical rearrangement of non-oxygenated bicyclo[2.2.2]octenones and mono-oxygenated bicyclo[2.2.2]octenones from masked o-benzoquinones: Access to protoilludane and marasmane skeletons

In this work, we described flexible approaches to protoilludane-like (5,6,4-tricyclic ring) and marasmane-like (5,6,3-tricyclic ring) skeletons with naturally occurring cis/anti/cis stereochemistry using photochemical rearrangement of bicyclo[2.2.2]octenones and Diels-Alder reaction of masked o-benzoquinones as the key steps.     

碳点在润滑领域中的应用

各种形式的摩擦和磨损不仅消耗了全球20%以上的能源,而且造成大量设备损坏。因此,开发减摩抗磨润滑材料对节约能源、延长机械设备使用寿命具有重要意义。碳点是一种新型的碳纳米材料,被广泛应用于化学传感、生物成像、催化、光电器件等领域。近年来,大量研究探索了碳点在工业润滑、微/纳米电子机械系统润滑、生物润滑等润滑领域的应用,证明了碳点具有优异的摩擦学性能,具备巨大潜力成为下一代绿色高效的减摩抗磨润滑材料。然而,至今仍缺乏碳点在润滑领域应用的系统性总结论述。因此,本文对碳点在润滑领域应用的研究进展作了全面系统综述。首先,详细介绍了碳点作为纳米添加剂和润滑涂层的润滑效果及提升其润滑性能的3种策略(尺寸形状控制、表面修饰、杂原子掺杂);然后,全面分析了碳点的润滑机理;最后概述了碳点在润滑领域应用所面临的主要挑战。     

准固相转化机制硫正极

随着电动汽车及便携式电子产品的迅速发展,对于高能量密度电池体系的需求越来越迫切,然而传统锂离子电池正极材料的能量密度发展逼近理论极限,因此发展下一代电池体系迫在眉睫。硫正极具有理论比容量高、来源广泛和成本低廉等优点,成为研究热点之一。硫正极在常规醚类电解液中为溶解-沉积机制,会产生“穿梭效应”,造成活性物质不可逆损失、电池库仑效率低和循环寿命短等问题。为了缓解“穿梭效应”,通常采用物理限域、化学吸附和反应加速剂等方式,但都没有从根本解决该问题。准固相转化机制可以彻底避免多硫化物溶解流失,受到研究者的广泛关注。本文综述了微孔碳、正极表面SEI膜和电解液调控等途径构建准固相转化机制硫正极的代表性工作,总结了研究意义和电化学特征;针对准固相转化硫正极本征动力学慢的问题,提出加快反应动力学的方案;有助于提高长循环性能,从而促进锂硫电池实用化。