螺栓扭矩系数影响因素的试验研究

在螺栓连接结构中,为保证连接的可靠性,必须为螺栓提供合适的预紧力。工程中通常采用扭矩法装配螺栓连接结构,因此需要确定预紧力与扭矩之间的关系(即扭矩系数),以施加合适的装配扭矩。本文对输电塔中常用的M16镀锌螺栓进行预紧力试验研究,测试分析了螺栓强度等级、有无垫圈和有无润滑对螺栓连接副扭矩系数的影响。研究结果表明,高强度螺栓比普通螺栓的扭矩系数小,数据离散性也小;无垫圈的螺栓比有垫圈的螺栓扭矩系数小,但数据离散性大;有润滑的螺栓比无润滑的螺栓扭矩系数小,数据离散性也小。本文同时探讨了如何控制、调整扭矩系数,以及螺栓连接中要注意的问题,为设计和施工单位提供参考。     

Numerical study on three-dimensional flow field of continuously rotating detonation in a toroidal chamber

Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonationshock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interesting properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.     

弹体高速侵彻混凝土质量侵蚀实验研究

为研究弹体高速侵彻混凝土过程中质量侵蚀规律及特性,开展了一系列实验研究,进行了不同速度(800～1500m/s)侵彻不同强度(C30～C80)混凝土试验,根据试验结果拟合出了既定材料弹体质量侵蚀同侵彻速度之间的对应关系。试验结果还表明:(1)对于该种材料弹体,当侵彻速度小于1200m/s时,弹体侵蚀量不仅同Vs2(动能)呈线性关系,也随混凝土强度的提高而增加;(2)对于材料为60Si2Mn的弹体,其理想侵彻速度为1100m/s～1200m/s之间;高于该速度,质量侵蚀严重,弹体侵彻能力急剧下降;(3)弹体质量侵蚀主要发生在头部,当侵彻速度较低时,磨损是导致弹体质量损失的主要因素;当侵彻速度逐步提高,超过某临界值时,熔融和磨损是导致弹体质量损失主导因素。     

3D-QSAR and Docking Studies of Pyrido[2,3-d]pyrimidine Derivatives as Wee1 Inhibitors

In order to investigate the inhibiting mechanism and obtain some helpful information for de-signing functional inhibitors against Wee1, three-dimensional quantitative structure-activity relationship (3D-QSAR) and docking studies have been performed on 45 pyrido[2,3-d] pyrim-idine derivatives acting as Wee1 inhibitors. Two optimal 3D-QSAR models with significant statistical quality and satisfactory predictive ability were established, including the CoMFA model (q²=0.707, R²=0.964) and CoMSIA model (q²=0.645, R²=0.972). The external val-idation indicated that both CoMFA and CoMSIA models were quite robust and had high predictive power with the predictive correlation coefficient values of 0.707 and 0.794, essen-tial parameter r²_m values of 0.792 and 0.826, the leave-one-out r²_m(LOO) values of 0.781 and 0.809, r²_m(overall) values of 0.787 and 0.810, respectively. Moreover, the appropriate binding orientations and conformations of these compounds interacting with Wee1 were revealed by the docking studies. Based on the CoMFA and CoMSIA contour maps and docking analyses, several key structural requirements of these compounds responsible for inhibitory activity were identified as follows: simultaneously introducing high electropositive groups to the sub-stituents R1 and R5 may increase the activity, the substituent R2 should be smaller bulky and higher electronegative, moderate-size and strong electron-withdrawing groups for the substituent R3 is advantageous to the activity, but the substituent X should be medium-size and hydrophilic. These theoretical results help to understand the action mechanism and design novel potential Wee1 inhibitors.     

Magnetic and magneto-optical studies on Zn1−xCrxTe (x=0.05) films grown on glass substrate

Zn_1−xCr_xTe (x=0.05) films were prepared by thermal evaporation onto glass substrates. X-ray diffraction (XRD) was used to determine the crystalline quality of the ZnTe:Cr film. Magnetic force microscopy (MFM) investigation has shown a non-uniform distribution of magnetic domains with an average size of 4 nm at room temperature. SQUID measurements have further shown that the non-uniform distribution of domains does not affect the room temperature ferromagnetism of this material. Electron spin resonance spectroscopy (ESR) was done to determine the Cr valence state in the ZnTe lattice. Magnetic circular dichroism (MCD) analysis was used to confirm the ZnCrTe phase contributing to the ferromagnetic behavior.     

不凝气体对R123凝结换热的影响

对氟利昂 R123 在水平单管外的凝结换热性能进行了试验研究,试验管为光管和五根强化管.目的是获得不凝气体对 R123 蒸气凝结时最佳肋密度的影响.试验结果表明:光管管外 Nusselt 理论值与实验数据偏差在±5%以内.对于含 8%不凝气体的 R123 在低肋管外的凝结换热,在肋密度为 1475 翅/米时可以获得最佳的换热性能.含不凝气体的 R123凝结换热系数显著下降,其管外换热系数约为纯蒸气的 20%～25%.随着肋密度的减小,不凝气体对凝结换热的影响逐渐减弱,但其最佳肋间隙仍保持不变,均为 0.32 mm.     

The archaeometry study of the chemical and mineral composition of pottery from Brazil’s Northeast

Chemical and mineralogical analysis was performed on ceramics and clay samples from Barracão archaeological site located in Baixo São Francisco River by means of instrumental neutron activation analysis (INAA) and by differential scanning calorimetry (DSC). The data set was studied by means of cluster analysis (CA) and discriminant analysis (DA). The results showed that the raw material used in ceramics is not local. By using DSC it was possible to discover that the principal minerals in the samples are quartz, feldspars, mica and kaolinite.     

A New Target for Synthesis: Theoretical Prediction for the Reaction between Boron Nitride Nanotube and Dichlorocarbene

Understanding the chemistry of BNNT is a crucial step toward their ultimate practical use. A comparative study of Reactions A （ASWCNT （5,5） and CCl2） and B （ASWBNNT （5,5） and CCl2） have been performed by using ONIOM （B3LYP/6-31G＊： AM1） method in Gaussian03 program package. The results show that （1） the two reactions are both exothermic; （2） the mechanism of Reaction B is a two-step mechanism; （3） the difference in energy barriers suggests that the reaction of CCl2 with BNNT is easier than with CNT; （4） in reaction B, CCl2 prefers to attack the boron atom of BNNT first.     

Bonding and correlation analysis of various Si2CO isomers on the potential energy surface

At various levels of theory, singlet and triplet potential energy surfaces (PESs) of Si₂CO, which has been studied using matrix isolation infrared spectroscopy, are investigated in detail. A total of 30 isomers and 38 interconversion transition states are obtained at the B3LYP/6‐311G(d) level. At the higher CCSD(T)/6‐311+G(2d)//QCISD/6‐311G(2d)+ZPVE level, the global minimum ¹1 (0.0 kcal/mol) corresponds to a three‐membered ring singlet O‐cCSiSi (¹A′). On the singlet PES, the species ¹2 (0.2 kcal/mol) is a bent SiCSiO structure with a ¹A′ electronic state, followed by a three‐membered ring isomer Si‐cCSiO (¹A′) ¹3 (23.1 kcal/mol) and a linear SiCOSi ¹4 (¹Σ⁺) (38.6 kcal/mol). The isomers ¹1, ¹2, ¹3 , and ¹4 possess not only high thermodynamic stabilities, but also high kinetic stabilities. On the triplet PES, two isomers ³1 (³B₂) (18.8 kcal/mol) and ³7 (³A″) (23.3 kcal/mol) also have high thermodynamic and kinetic stabilities. The bonding natures of the relevant species are analyzed. The similarities and differences between C₃O, C₃S, SiC₂O, and SiC₂S are discussed. The present results are also expected to be useful for understanding the initial growing step of the CO‐doped Si vaporization processes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical study on reaction mechanism of isocyanate radical NCO with ethene

The NCO + C₂H₄ reaction is simple and prototype for reaction of the NCO radical with unsaturated hydrocarbons, and it is considered to be important in fuel‐rich combustion. In this article, we for the first time perform detailed theoretical investigations for its reaction mechanism based on Gaussian‐3//B3LYP scheme covering various entrance and decomposition channels. The most favorable channel is firstly the NCO and C₂H₄ approach each other, forming a weakly‐bound complex L1 OCN···C₂H₄, followed by the formation of isomer L2 OCNCH₂CH₂ via a small barrier of 1.3 kcal/mol. Transition states of any decomposable or isomeric channels for L2 in energy are much higher than reactants, which indicate that adduct L2 has stabilization effect in this NCO + C₂H₄ reaction. The direct H‐abstraction channel leading to P1 HNCO + C₂H₃, might have an important contribution to the eventual products in high temperature. These results can well explain available kinetic experiment. Moreover, reaction mechanism for the title reaction is significantly different from the NCO + C₂H₂ reaction which proceeds on most favorably to generate the products HCN + HCCO and OCCHCN + H via a four‐membered ring intermediate. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009