The extremal irregularity of connected graphs with given number of pendant vertices

Czechoslovak Mathematical Journal - The irregularity of a graph G = (V, E) is defined as the sum of imbalances ∣du ? dv∣ over all edges uv ∈ E, where du denotes the degree...     

基于钼酸盐光度法测定总磷的浊度去除方法

采取新的浊度去除方法,改进了测定总磷的钼酸盐光度法。测定过程中,消解液的浊度会对测定结果产生干扰。通过比较机械过滤法和试剂补偿法的浊度校正效果,建立了中速定性滤纸单次机械过滤的浊度去除方法,确定了最佳去除条件:控制待滤液温度不高于30℃,清洗纯水的体积不少于20 m L。选择消解液具有浊度干扰项的6种代表性水样,分别进行平行测定和加标回收试验,方法检出限为0.008 mg/L,测定结果的相对标准偏差为2.8%~7.9%(n=6),加标回收率为92.0%~106%。该方法灵敏度、准确度高,精密度良好,与现行国标法相比,试剂消耗量少,分析效率高,能够满足多种水环境样品中总磷的测定要求。     

Transport Coefficients of Two-temperature Lithium Plasma for Space Propulsion Applications

Lithium has been proposed as an attractive metal propellant for advanced electric propulsion. In our current work, transport coefficients including the viscosity, thermal conductivity, and electrical conductivity of lithium plasma under both the equilibrium and non-equilibrium conditions are calculated based on a two-temperature model. The collision integrals used in calculating the transport coefficients are significantly more accurate than values used in previous theoretical studies, resulting in more reliable values of the transport coefficients. Results are computed for different degrees of thermal non-equilibrium, i.e. the ratio of electron to heavy particle temperatures, from 1 to 15, with the electron temperature ranging from 300 to 60,000 K in a wide pressure range from 0.0001 to 100 atm. We compare our calculated results with existing published results and discrepancies are found and explained.     

Light-Driven Syngas Production over Defective ZnIn2S4 Nanosheets

Photocatalytic syngas (CO and H₂) production with CO₂ as gas source not only ameliorates greenhouse effect, but also produces valuable chemical feedstocks. However, traditional photocatalytic systems require noble metal or suffers from low yield. Here, we demonstrate that S vacancies ZnIn₂S₄ (V_S-ZnIn₂S₄) nanosheets are an ideal photocatalyst to drive CO₂ reduction into syngas. It is found that building S vacancies can endow ZnIn₂S₄ with stronger photoabsorption, efficient electron–hole separation, and larger CO₂ adsorption, finally promoting both hydrogen evolution reaction (HER) and CO₂ reduction reaction (CO₂RR). The syngas yield of CO and H₂ is therefore significantly increased. In contrast to pristine ZnIn₂S₄, the syngas yield over V_S-ZnIn₂S₄ can be improved by roughly ≈4.73 times and the CO/H₂ ratio is modified from 1:4.18 to 1:1. Total amount of syngas after 12 h photocatalysis is as high as 63.20 mmol g⁻¹ without use of any noble metals, which is even higher than those of traditional noble metal-based catalysts in the reported literatures. This work demonstrates the critical role of S vacancies in mediating catalytic activity and selectivity, and highlights the attractive ability of defective ZnIn₂S₄ for light-driven syngas production.     

Effects of imperfect experimental conditions on stress waves in SHPB experiments

Experimental and numerical simulations were undertaken to estimate the effects of imperfect conditions on stress waves in split Hopkinson pressure bar(SHPB)experiments. The photonic Doppler velocimetry(PDV) measurement results show that the rise and fall times of an incident wave increases with an increasing inclination angle;also, the fluctuations of the incident wave disappear gradually with the increase of inclination angle. The following characteristics for various defects in the SHPB were obtained by numerical simulation:(1) the influence of a curved bar was negligible;(2) misalignment modestly affects the fluctuation characteristics, and bending waves were generated at this condition;(3) inclination and indentation of the impact endsurface had a great impact on the incident waves, and both of them increase the rise time of the incident wave by increasing the degree of defects. In view of the results, misalignment,inclination, and indentation in SHPB experiments should be minimized.     

国家监测网方法测定地表水中总磷与国标法差异及改进

比较了国家地表水环境质量监测网总磷测定方法与国标法的差异。浊度补偿与过滤两种去除浊度方法测定结果的绝对偏差为-0.02~0.07 mg/L,其中含细颗粒物较多的样品绝对偏差较大,为0.04~0.07 mg/L,因此采用过滤法时,需对含较多细颗粒物的水样进行浊度补偿。对国家地表水环境质量监测网方法进行了改进,将原来的过滤后定容改为定容摇匀后过滤。方法改进前后,样品测定值的相对偏差不大于3.4%,绝对偏差为-0.01~0.02 mg/L。改进后的方法与原方法测定结果没有显著差异,但改进后方法浊度贡献减少,试剂用量减半,而且可操作性强,更加简便和环境友好。     

Reversal of elution order of N‐(2,4‐dinitrophenyl)‐proline and N‐(2,4‐dinitrophenyl)‐serine in HPLC by BSA chiral stationary phase

N‐(2,4‐dinitrophenyl)‐proline and N‐(2,4‐dinitrophenyl)‐serine were enantiomerically resolved on the BSA chiral stationary phase by HPLC in reversed‐phase mode. Effects of chromatographic conditions on enantioseparation and elution order have been investigated in detail. For these two samples, reversal of enantiomer elution order was observed by changing buffer pH, the content of acetonitrile, or alcohol modifiers in mobile phase, which is firstly reported in the BSA chiral stationary phase studies. More interestingly, combined effect between buffer pH and the content of acetonitrile was also observed. In addition, coelution range of enantiomers varied along with the content of acetonitrile in mobile phase.     

贫困地区农村中学化学教师专业发展的现状调查

选取了重庆市边缘几个国家级贫困县作为调查对象,从化学教师个人背景、化学教师教育理念、化学教师职业道德、化学教师专业知识结构及化学教师专业发展情意几个维度对贫困地区农村中学化学教师专业发展现状进行了调查。     

流动注射-石英晶体微天平中血清蛋白对扁桃酸的手性识别

采用流动注射-石英晶体微天平(FIA-QCM)和紫外光谱法研究了牛/羊血清蛋白(BSA和GSA)与扁桃酸的手性识别。 在QCM表面,BSA和GSA的浓度分别为4.9×10-12和8.8×10-12 mol/cm2。 血清蛋白与R-扁桃酸(R-MA)作用引起QCM振动频率变化值比S-扁桃酸(S-MA)大;相应紫外结合常数也比与S-MA大,说明血清蛋白对R-MA的作用强于与S-对映体。 从识别因子分析,GSA对扁桃酸的手性识别能力优于BSA。     

Dye-sensitized solar cells based on two-dimensional TiO2 nanosheets as the scattering layers

Research on Chemical Intermediates - Two-dimensional (2D) TiO2 nanosheets with high crystallinity and good light scattering properties were synthesized via a simple solvothermal process using...