图的无符号拉普拉斯和距离无符号拉普拉斯特征值

Let G be a simple graph. We first show that ■, where δiand di denote the i-th signless Laplacian eigenvalue and the i-th degree of vertex in G, respectively.Suppose G is a simple and connected graph, then some inequalities on the distance signless Laplacian eigenvalues are obtained by deleting some vertices and some edges from G. In addition, for the distance signless Laplacian spectral radius ρQ(G), we determine the extremal graphs with the minimum ρQ(G) among the trees with given diameter, the unicyclic and bicyclic graphs with given girth, respectively.     

Solvent Impedes CO2 Cycloaddition on Metal–Organic Frameworks

The catalytic performance of metal–organic frameworks (MOFs) for the synthesis of cyclic carbonate from carbon dioxide and epoxides has been explored under solvent and solvent‐free conditions, respectively. It was found that MOF catalysts have significantly improved catalytic activities in solvent‐free CO₂ cycloaddition reactions than those in solvent. The mechanism was discussed with regard to the competition of solvent with substrate to adhere MOF catalysts during the reaction process.     

Electrochemical study of the use of tin(II) complexed by sorbitol in volumetric analysis

The possibility of using the sorbitoi complex of divalent tin in volumetric analysis was studied. Potassium dichromate and potassium hexacyanoferrate were used for standardization. The dependences on the pH and ionic strength indicate that the most suitable titration medium is sat. Na₂CO₃. The titrant is stable for 14 days in an inert atmosphere. It was found polarographically and voltammetrically that the Sn(IV)-sorb./Sn(II) sorb, system is irreversible. Standard solutions of Sn(II)-sorb. were used to determine K₂Cr₂O₇, K₃Fe(CN)₆, H₂O₂, and inorganic and organic peroxides, I₂ Hg(II), Ag(I). chloramine T, chlorinated lime. n-bromosuccinimide, and TAR. Potentiometry, bipotentiometry, and biamperometry were used for determination of the equivalence point.     

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2 + ethanol and CO2 + methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.     

NORMAL VIBRATIONAL ANALYSIS OF TRANS-POLYACETYLENE

The results of normal vibrational analyses of trans, trans-2, 4-hexadiene and the backbone of trans, trans-1, 4-diphenyl-butadiene were used in the normal mode computation of trans-polyacetylene (PA). Only 8 non-zero calculated frequencies were obtained which obeys the rule of 3N-4. The potential energy distribution (PED) data were in good agreement with the empirical assignment of Shirakawa et al. and Kozmany, but most of the vibrational frequencies of trans-PA had contributions from several empirical modes, indicationg the more complieacy in trans-PA molecular vibration than in the model molecule case. The calculated C=C and C—C stretching frequencies of trans-PA were over 200cm~(-1) higher and lower than the observed ones, respectively, due to the longer effective conjugate length in the trans-PA. This was shown by the dependence of the PED-weighted average frequencies of C=C and C—C stretchings on the force constants f(C=C)~2 and f(C—C)~2.     

氮掺杂超薄碳纳米片复合铂钌单原子合金催化剂的电化学析氢性能

为了减少贵金属的用量, 降低成本, 提高大规模生产的可能性, 构建单原子合金(SAA)是一个非常可行的解决方案. 设计了一种超小PtRu单原子合金物种均匀分散在掺氮超薄碳纳米片上的电催化剂(PtRu SAA/NC), 并通过基于同步辐射的X射线吸收精细结构(XAFS)光谱进行了结构确认. 与纯Ru团簇和氮掺杂的碳片相比, PtRu SAA/NC具有更高的析氢反应(HER)催化活性和特殊的稳定性, 在0.5 mol/L H₂SO₄溶液中进行HER时, 表现出较小的Tafel斜率(43 mV/dec), 且在10 mA/cm²电流密度下过电位仅为54 mV.     

热敏电阻位置与超辐射发光二极管光源温控参数的关系研究

针对某陀螺生产厂家新引入的超辐射发光二极管光源在原光源驱动设备上的功率变化异常的问题,对光源温控环节的传递函数和相应控制参数进行了理论和试验分析。相比陀螺常用SLD光源,新引入SLD光源内部热敏电阻与SLD管芯间距大得多,且不在同一热沉上,这使得该厂光源温控部分的传递函数出现明显时间滞后,表现为其对微分环节依赖性增强。通过对原光源驱动设备上微分环节的优化设计,可使热敏电阻位置相差较大的不同厂家的光源同时获得良好温控效果。上述结果对于理解SLD光源温控PID(比例-积分-微分)参数差异性、提高SLD光源温度控制适应性提供了客观依据。     

Time‐Dependent Aggregation‐Induced Enhanced Emission,Absorption Spectral Broadening,and Aggregation Morphology of a Novel Perylene Derivative with a Large D–π–A Structure

Strong aggregation‐caused quenching of perylene diimides (PDI) is changed successfully by simple chemical modification with two quinoline moieties through C?C at the bay positions to obtain aggregation‐induced enhanced emission (AIEE) of a perylene derivative ( Cya‐PDI ) with a large π‐conjugation system. Cya‐PDI is weakly luminescent in the well‐dispersed CH₃CN or THF solutions and exhibits an evident time‐dependent AIEE and absorption spectra broadening in the aggregated state. In addition, morphological inspection demonstrates that the morphology of the aggregated form of Cya‐PDI molecules changed from plate‐shaped to rod‐like aggregates under the co‐effects of time and water. An edge‐to‐face arrangement of aggregation was proposed and discussed. The fact that the Cya‐PDI aggregates show a broad absorption covering the whole visible‐light range and strong intermolecular interaction through π–π stacking in the solid state makes them promising materials for optoelectric applications.