凝胶渗透色谱法测定聚丙烯腈共聚物分子量中宽分布校正法的应用

应用宽分布校正法对凝胶渗透色谱(GPC)进行了校正，将校正曲线用于聚丙烯腈(PAN)共聚物分子量的计算。对扣除色谱峰扩展效应前后的测试结果与乌氏粘度法测得的数据进行比较。结果表明，应用宽分布校正法时，必须扣除色谱峰扩展效应，才能得到较为准确的测试结果。     

基本不变量神经网络解析梯度方法的研究

提升势能面的运行速度对于动力学模拟至关重要. 相对于计算简单、 但耗时更长的数值梯度计算, 直接求解势能面梯度的解析公式能够大幅提高势能面的运行效率. 本文发展了基本不变量神经网络解析梯度的生成方法. 计算解析梯度的代码可以通过程序自动生成. 对大量数据点进行测试后, 证明了该方法可以得到正确的势能面梯度输出结果. 通过测试不同势能面的调用时间, 发现采用解析梯度方法能够带来10倍以上的性能提升. 随着体系的增大, 这种性能提升也会越明显.     

化学滴定法测定甲基β-环糊精的平均取代度

借助甲基β-环糊精依次与氢碘酸、溴及碘化钾的定量化学反应关系,设计了测定甲基β-环糊精平均取代度n值的一种化学滴定法,并根据滴定原理探讨了计算n值的方程式。结果表明,该法测试结果与标计值(基于分子质谱法测得的数据)更接近,明显优于以D2O为溶剂、以Me4Si为内标、在AM-400 NMR仪上利^1H NMR谱图计算得到的结果。     

计算机辅助有机元素分析研究共聚物的组成

本文提出了计算机辅助有机元素分析计算高分子共聚物组成的一般公式,并以丙烯酰胺-丙烯酸钠共聚物为例予以验证。同时测试了AP-20系列共聚物及AT-430共聚物的共聚组成,其结果与~(13)C NMR测定数据一致。     

粘度法测定水溶液中裂褶多糖分子量

通过对Takashi试验数据的分析和计算,完善了粘度法测定裂褶多糖(SPG)分子量的Mark-Hou-wink公式,即在25℃的SPG水溶液中,当[η]≤445 cm-3/g时,[η]=5.19×10-7M1w.59。根据Ah-Hyun用扫描电镜(SEM)和原子力显微镜(AFM)获得SPG结构的最新数据,结合Yamakawa推导的[η]-M模型对公式进行分析。通过模型计算、粘度公式计算和凝胶过滤色谱(GPC)获得的SPG的重均分子量(Mw)分别为3.7×105、5.8×105、2.5×107,其中采用理论模型和粘度公式计算的结果较一致,而GPC测试的结果相差较大的原因可能与样品和标准分子量范围不同有关。IR和13C-NMR的数据表明该多糖具有-β(1-6)葡萄糖苷分支的-β(1-3)-D葡聚糖结构。     

结合神经网络方法和扩大训练基组构建新B3LYP泛函

神经网络方法成功地应用于修正密度泛函理论B3LYP方法中的三个参数(a0、ax和ac)以构建新B3LYP交换相关泛函.本文采用包含输入层、隐藏层和输出层的三层式神经网络结构.总电子数、多重度、偶极矩、动能、四极矩和零点能被选为物理描述符.296个能量数据被随机地分成两组,246个能量数据作为训练集以确定神经网络的最优结构和最优突触权重,50个能量数据作为测试集以测试神经网络的预测能力.修正后的三个参数觔0、觔x、觔c从输出层处得到,并用于计算体系的热化学性质如原子化能(AE)、电离势(IP)、质子亲合能(PA)、总原子能(TAE)和标准生成热(ΔfH苓).修正后的计算结果优于传统B3LYP/6-311+G(3df,2p)方法的计算结果.经过神经网络修正后,296个物种的总体均方根偏差从41.0 kJ.mol-1减少到14.2 kJ.mol-1.     

丝氨酸热分解机理的研究

用热重法(TG)、差热分析(DTA)和红外光谱(IR)方法测试了丝氨酸的热分解过程,用量子化学方法在RHF/6-21G水平上全优化计算了丝氨酸及其热分解中间产物、产物分子的几何构型,得到其总能量和Mulliken集居数等数据.从理论上证明了环氧中间产物的存在.通过对实验结果和计算结果如Mulliken集居数的分析,提出了丝氨酸的热分解反应机理是先失去CO2为主要反应通道,同时伴有先失去NH3而生成环氧中间产物的副反应发生.     

用偏最小二乘法—荧光光谱法定量分析芳烃混合物

本文用偏最小二乘法方法来解析荧光的激发发射和左阵，直接定量分析荧光混合物试样。文中分析了ＥＥＭ的特点，介绍了用ＥＥＭ－ＰＬＳ定量分析试样的思路和方法，并对５个模拟混合物和４个实际混合物进行了测试和计算，获得了满意的结果。本文还用实例讨论了数据中的异常点，对结果的影响及晚年剔除的方法。     

"分光光度法测定碘化铅溶度积常数"实验存在的问题及改进

针对"分光光度法测定碘化铅溶度积常数"实验测定方法中存在的问题,提出了改进方法。用改进后的方法测定碘化铅溶度积常数,减少了实验药品和污染,简化了实验环节和数据处理过程,使实验测定的数据更准确。并且根据热力学公式推导、计算和作图,给出了lnK_(sp)~θ与1/T关系的直线方程,可以判断不同温度时测试结果的准确程度。     

胶体粒子Boltzmann分布对测试结果产生的误差分析

胶体粒子是自然科学中一类非常重要的研究对象。由于重力势场的作用,胶体粒子并不是均匀分布的(假设为Boltzmann分布)。为了考察Boltzmann分布对测试结果产生的影响,通过理论计算讨论了3种粒径(20 nm、50 nm、100 nm)的二氧化硅在重力势场作用下的Boltzmann分布,即浓度随高度的变化,并与平均浓度相比较。结果表明,粒子越大,重力势场对粒子分布的影响越大,对测试结果产生的误差也越大。最后,通过理论计算指出合理选择粒子种类和粒子大小,可以降低Boltzmann分布对测试结果产生的影响。     

Comparison of the effectiveness of various procedures for the rejection of outlying results and assigning consensus values in interlaboratory programs involving determination of trace elements or radionuclides

Rejection of outlying results is usually necessary in the evaluation of interlaboratory comparisons, especially those involving trace elements and low-level activity measurements. The performance of several criteria (Dixon's test, Grubbs' test, coefficient of skewness test, and coefficient of kurtosis test) is described; authentic data sets from intercomparison runs on trace element or radionuclide determinations in spiked samples are used. The existence of “masking effects” in certain cases is demonstrated. It is shown that concurrent use of all four criteria at small (0.01) or moderate (0.05) significance levels gives better results than the use of any single test. The use of all four criteria at α = 0.05 followed by calculation of overall mean and pertinent confidence limits is suggested as a general method of data handling in interlaboratory comparison. This method normally ensures good selectivity of outlier rejection while avoiding excessive rejections, and results in generally good agreement between the “true” value and the final overall mean. The use of this approach for the establishment of recommended values in candidate reference materials is demonstrated and its advantages and limitations are discussed. The results are further compared with those obtained by other methods of data evaluation (Student's test, dominant cluster mode and gamma transformation).     

Thermodynamic consistency of experimental VLE data for asymmetric binary mixtures at high pressures

A thermodynamic consistency of isothermal vapor–liquid equilibrium data for 9 non-polar and 8 polar binary asymmetric mixtures at high pressures has been evaluated. A method based on the isothermal Gibbs–Duhem equation was used for the test of thermodynamic consistency using a Φ–Φ approach. The Peng–Robinson equation of state coupled with the Wong–Sandler mixing rules were used for modeling the vapor–liquid equilibrium (VLE) within the thermodynamic consistency test. The VLE parameters calculations for asymmetric mixtures at high pressures were highly dependent on bubble pressure calculation, making more convenient to eliminate the data points yielding the highest deviations in pressure. However the results of the thermodynamic consistencies test of experimental data for many cases were found not fully consistent. As a result, the strategies for solving these problems were discussed in detailed.     

Intrinsic viscosity of solutions of rigid particles at high shear rates

The results of a numerical calculation which extends Scheraga's calculation on the non-Newtonian behavior of the viscosity factor v of rigid ellipsoid solutions are given here and compared to experimental data obtained on different poly(γ-benzyl L -glutamate) samples in helical configuration, over a wide range of molecular weight, up to 980,000. Relations for the axial ratio p, the rotary diffusion constant D, and a test of the deformability of the polymer under shear, are given as functions of the shear-rate dependence of the intrinsic viscosity. The experimental behavior under shear shows that PBLG becomes somewhat flexible in dichloroethane, but not in m-cresol. The dimensions calculated from the viscometric results suggest discrete changes in the length per monomeric unit of the helix at different well defined molecular weights.     

Reactivity of natural phenols in radical reactions

Activation enthalpies and energies and the rate constants of reactions with peroxyl, alkyl, and thiyl radicals (76 reactions) were calculated for a group of natural antioxidants (19 monohydroxy and polyhydroxy phenols). The calculation was performed with the use of the model of a radical abstraction reaction as the intersection of two parabolic potential curves. The results of the calculation were compared with experimental data: the average discrepancy in the activation energies of the reactions RO ₂ ^? + ArOH was 0.8 kJ/mol. Interatomic distances in the reaction centers of the transition states of the test reactions were calculated. Factors affecting the reactivity of these compounds are discussed.     

对BJH方法计算孔径分布过程的解读

This paper introduces the geometric assumptions and neglects of the pore size distribution calculated by BJH method, the arithmetic approximation for simplified calculation, the derivation process of each parameter, the calculation steps and key points of the pore size distribution. This paper also introduces the application scope of BJH method at the current instrument level, and how to further integrate the data. In order to get the required analysis and test report, references are provided for the subsequent adjustment of test parameters and improvement of test methods. Some problems often encountered in reading experimental reports are also discussed.     

Do proficiency tests always verify laboratories’ performance? The case of FAPAS PT 0270

In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted. Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in PT 0270 are questionable.     

Surface states and resonances in field emission from low-index facets of clean tungsten

The energies, widths, and shapes of features observed in the total energy distributions in field emission from W(1 0 0) and W(1 1 1) are compared with the results of a full-potential LAPW calculation of the surface density of states based on a supercell model of the crystal structure at the metal–vacuum interface. The Swanson hump on W(1 0 0) is attributed to two bands of surface states and surface resonances of d_z² symmetry that are highly localised at , and a second peak observed at lower energy is attributed to a band of surface resonances, also of d_z² symmetry, centred at from along . The energy scale of the calculated total energy distribution is compressed by about 20% relative to the experimental data. The present calculation yields strong evidence that the broad asymmetric peak observed on W(1 1 1) is due to emission from a band of surface resonances. Further calculations for W(1 1 1) are proposed both to test the accuracy of the band model and to take into account the velocity factor that enters in a calculation of the emission current.     

Net analyte signal-based simultaneous determination of ethanol and water by quartz crystal nanobalance sensor

Net analyte signal (NAS)-based method called HLA/GO was applied for the selectively determination of binary mixture of ethanol and water by quartz crystal nanobalance (QCN) sensor. A full factorial design was applied for the formation of calibration and prediction sets in the concentration ranges 5.5-22.2 μg mL⁻¹ for ethanol and 7.01-28.07 μg mL⁻¹ for water. An optimal time range was selected by procedure which was based on the calculation of the net analyte signal regression plot in any considered time window for each test sample. A moving window strategy was used for searching the region with maximum linearity of NAS regression plot (minimum error indicator) and minimum of PRESS value. On the base of obtained results, the differences on the adsorption profiles in the time range between 1 and 600 s were used to determine mixtures of both compounds by HLA/GO method. The calculation of the net analytical signal using HLA/GO method allows determination of several figures of merit like selectivity, sensitivity, analytical sensitivity and limit of detection, for each component. To check the ability of the proposed method in the selection of linear regions of adsorption profile, a test for detecting non-linear regions of adsorption profile data in the presence of methanol was also described. The results showed that the method was successfully applied for the determination of ethanol and water.     

Proficiency testing in the light of a new rationale in metrology

The novel proposed definition of measurement result in the international metrology vocabulary requires a revision of standards and guidelines for proficiency testing (PT), and a new approach to processing proficiency data is needed to test the ability of laboratories to present not only unbiased quantity values, but reliable estimates of their uncertainty. Hence, an accepted reference value with the smallest possible uncertainty is needed to ascertain the proficiency of laboratories reporting results with lower than average uncertainty. A strategy based on the T-statistic is proposed leading to an accepted reference value that fully reflects the uncertainties reported by participants in a PT scheme and permits calculation of E _n numbers to distinguish whether or not measurement results are consistent with the accepted definition of the measurand. The strategy is applied to PT data from a recent international laboratory intercomparison of uranium isotopic ratios.