Structure,trend and prospect of operational research: a scientific analysis for publications from 1952 to 2020 included in Web of Science database

As an important research direction, operational research (OR) has always attracted scholars worldwide. We study the structure, trend and prospect in the OR field by conducting a bibliometric analysis of publications in the period of 1952–2020, which are included in the Web of Science (WoS) database. Using three effective bibliometric tools, namely, VOS viewer, CiteSpace, and Bibliometrix, a total of 5,353 publications were retrieved to show clear visual results using a series of scientific analyses. First, a performance analysis revealed the basic characteristics of publications considering the type distribution, annual trend, quantity and quality. Then, a cooperation analysis presented the influential countries/regions and showed the relationships among countries/regions, institutions and authors during different periods based on bibliometric indicators and co-authorship networks. Moreover, a keyword analysis was conducted to investigate the hot topics and development of the OR field, using co-occurrence analysis, timeline view analysis and evolution analysis. Finally, we discussed the implications and limitations, and summarized the main findings. This study hopes to provide important and valuable references for future research on the OR field.

     

A note on “small representations of finite distributive lattices as congruence lattices”

G. Grätzer, H. Lakser, and E. T. Schmidt proved that every distributive lattice with n join-irreducible elements can be represented as the congruence lattice of a small lattice L, that is, a lattice L with O(n ² ) elements. G. Grätzer, I. Rival, and N. Zaguia proved that, for any <2, O(n ² ) can not be improved to O(n ). In this note we show that the theorem about small representation can be improved further to get a more delicate result.     

Theoretical study of addition reactions of heavy carbenes to carbon and boron nitride nanotubes

In an effort to gain insight into the activation energies and reaction enthalpies of the chemical functionalization of carbon and boron nitride nanotubes, calculations using density functional theory have been carried out for the cycloaddition of a heavy carbene to a single-walled carbon (SWCNT; C(130)H(20)) and a boron nitride (SWBNNT; B(65)N(65)H(20)) nanotube. The (CH(3))(2)X + SWCNT and (CH(3))(2)X + SWBNNT (X = C, Si, Ge, Sn, and Pb) reactions are the subject of the present study. All the stationary points were determined at the B3LYP/LANL2DZ level of theory. The major conclusions that can be drawn from this work are as follows: (i) Considering both the activation barrier and reaction enthalpy based on the model calculations presented here, it is found that the order of (CH(3))(2)X reactivity is X = C > Si > Ge > Sn > Pb, irrespective of whether cycloaddition is to a SWCNT or a SWBNNT sidewall. That is to say, (CH(3))(2)C and (CH(3))(2)Si can readily add to the sidewalls of SWCNT and SWBNNT, whereas (CH(3))(2)Ge, (CH(3))(2)Sn, and (CH(3))(2)Pb are unreactive. (ii) Since the chemical reactivities of SWCNT and SWBNNT sidewalls closely resemble those of the small C(16)H(10) and B(8)N(8)H(10) molecules, at least in a qualitative sense, the use of the above small molecules as models is sufficient to provide qualitatively correct results. (iii) Our theoretical observations indicate that all the (5,5) SWCNT and SWBNNT cycloadducts favor opened rather than closed three-membered ring structures. (iv) The theoretical investigations demonstrate that the singlet-triplet splitting of the carbene species (R(2)X) as well as that of the small model molecules can be used as a diagnostic tool to predict the addition reactivities of carbene analogues and sidewalls of various nanotubes, respectively. Moreover, the results obtained in this work allow a number of predictions to be made.     

Highly regioselective rearrangement of 2-substituted vinylepoxides catalyzed by gallium(III) triflate

Gallium(III) triflate catalyzed the rearrangement of 2-substituted vinylepoxides into beta,gamma-unsaturated carbonyl compounds with high regio- and chemoselectivity (>97/3) in low catalyst loading (1-5 mol %). The alkyl-substituted trimethylsilylvinyl epoxides gave beta,gamma-unsaturated ketone, but aryl-substituted vinylepoxides gave the aldehydes instead.     

2型糖尿病患者血清钙镁与甲状腺激素含量变化及临床意义

为了监测 2型糖尿病人血清钙、镁和甲状腺激素含量 ,分析其临床意义及相关性 ,应用放射免疫分析法测定了 1 1 5例 2型糖尿病及 1 5 0例健康人血清甲状腺激素含量。同时用美国杜邦RXL自动生化仪测定了其血清钙、镁含量。结果表明 ,在 2型糖尿病伴有明显并发症者血镁、FT3水平明显降低 (P <0 0 5 ) ,钙镁两种元素与甲状腺激素水平无明显相关性。 2型糖尿病患者适当补镁对预防其并发症是有益的 ,测定FT3 等可作为判断 2型糖尿病严重程度和估计预后的参考指标。     

Calculation of avoided crossings for highly excited Stark states of Rb

Using the method of diagonalization, in which zero-field wavefunctions from a potential model are chosen as a basis, we calculate positions and widths of anticrossings for highly excited Stark states of Rb with principal quantum number n up to 49. We obtain the theoretical positions and widths in good agreement with available experimental values, and we present scaling laws of the field positions and widths of anticrossings that can be used to provide information for future experiments.     

Dye-sensitized solar cells based on composite solid polymer electrolytes

The ionic conductivity of polymer electrolytes and their interfacial contact with dye-attached TiO2 particles were enhanced markedly by the addition of amorphous oligomer into polymer electrolytes, resulting in very high overall energy conversion efficiency.