Finite depth Stokes’ first problem of thixotropic fluid

This paper presents a study of the finite depth Stokes' first problem for a thixotropic layer. The yield behavior of the thixotropic fluid in this problem is investigated for the first time. The main physical features of this problem are discussed, including the flow field, the wall stress, and the depth of the yield region. It is shown that the yield region appears near the wall, and the yield surface moves from the wall into the flow region and moves back to the wall finally. In contrast to the solution of the Newtonian fluid,the velocity of the thixotropic layer generally does not increase with time monotonously during the start-up process. The classical solution of the Newtonian fluid can be recovered from our results in extreme cases.     

Inhibitory Effect of Fisetin on α-Glucosidase Activity: Kinetic and Molecular Docking Studies

The inhibition of α-glucosidase is a clinical strategy for the treatment of type 2 diabetes mellitus (T2DM), and many natural plant ingredients have been reported to be effective in alleviating hyperglycemia by inhibiting α-glucosidase. In this study, the α-glucosidase inhibitory activity of fisetin extracted from Cotinus coggygria Scop. was evaluated in vitro. The results showed that fisetin exhibited strong inhibitory activity with an IC₅₀ value of 4.099 × 10⁻⁴ mM. Enzyme kinetic analysis revealed that fisetin is a non-competitive inhibitor of α-glucosidase, with an inhibition constant value of 0.01065 ± 0.003255 mM. Moreover, fluorescence spectrometric measurements indicated the presence of only one binding site between fisetin and α-glucosidase, with a binding constant (lgKa) of 5.896 L·mol⁻¹. Further molecular docking studies were performed to evaluate the interaction of fisetin with several residues close to the inactive site of α-glucosidase. These studies showed that the structure of the complex was maintained by Pi-Sigma and Pi-Pi stacked interactions. These findings illustrate that fisetin extracted from Cotinus coggygria Scop. is a promising therapeutic agent for the treatment of T2DM.     

Prediction of Stability for Polychlorinated Biphenyls in Transformer Insulation Oil Through Three-dimensional Quantitative Structure-activity Relationship Pharmacophore Model and Full Factor Experimental Design

Based on the obtained data of half-lives(t_1/2) for 31 polychlorinated biphenyl congeners(PCBs), 3D quantitative structure-activity relationship(QSAR) pharmacophore was used to establish a 3D QSAR model to predict the t_1/2 values of the remaining 178 PCBs, using the structural parameters as independent variables and lgt_1/2 values as the dependent variable. Among this process, the whole data set(31 compounds) was divided into a training set(24 compounds) for model generation and a test set(7 compounds) for model validation. Then, the full factor experimental design was used to research the potential second-order interactional effect between different substituent positions, obtaining the final regulation scheme for PCB. At last, a 3D QSAR pharmacophore model was established to validate the reasonable regulation targeting typical PCB with respect to half-lives and thermostability. As a result, the cross-validation correlation coefficient(q²) obtained by the 3D QSAR model was 0.845(>0.5) and the coefficient of determination(r²) obtained was 0.936(>0.9), indicating that the models were robust and predictive. CoMSIA analyses upon steric, electrostatic and hydrophobic fields were 0.7%, 85.9%, and 13.4%, respectively. The electrostatic field was determined to be a primary factor governing the t_1/2. From CoMSIA contour maps, t_1/2 increased when substi- tuents possessed electropositive groups at the 2'-, 3-, 3'-, 5- and 5'- positions and electronegative groups at the 3-, 3'-, 5-, 6- and 6'- positions, which could increase the PCB stability in transformer insulation oil. Modification of two typical PCB congeners(PCB-77 and PCB-81) showed that the lgt_1/2for three selected modified compounds increased by 13%(average ratio) compared with that of each congener and the thermostability of them were higher, validating the reasonability of the regulatory scheme obtained from the 3D QSAR model. These results are expected to be beneficial in predicting t_1/2 values of PCB homologues and derivatives and in providing a theoretical foundation for further elucidation of the stability of PCBs.     

QuEChERS净化-液相色谱-串联质谱法测定茶叶中氯噻啉

建立了茶叶中农药氯噻啉残留的液相色谱-串联质谱检测方法。茶叶样品用乙腈提取,提取液经QuEChERS法净化,利用PSA(N-丙基乙二胺)、C₁₈、GCB(石墨化炭黑)等吸附剂材料进一步去除杂质,净化液经过离心后取上清液以水等体积稀释。以乙腈-0.1%(v/v)甲酸水溶液为流动相,在0.30 mL/min流速下梯度洗脱,用C₁₈色谱柱进行液相色谱分离,电喷雾正离子模式电离(ESI⁺),选择反应监测(SRM)模式检测,外标法定量。结果表明:氯噻啉在1~500 μ g/L范围内线性关系良好(相关系数r为0.9999),定量限为0.01 mg/kg(S/N≥10),在乌龙茶和绿茶中3个添加水平(0.01、0.3和3 mg/kg)的平均回收率为87.0%~101.0%,相对标准偏差(RSD, n=7)在2.1%~13.1%之间。对多种茶叶的测定结果表明,该方法操作简便、成本低、准确性高、特异性好、分析速度快,可以对茶叶中氯噻啉残留进行定性和定量检测。     

Quantifying Dynamical Predictability： the Pseudo-Ensemble Approach

The ensemble technique has been widely used in numerical weather prediction and extended-range forecasting. Current approaches to evaluate the predictability using the ensemble technique can be divided into two major groups. One is dynamical, including generating Lyapunov vectors, bred vectors, and singular vectors, sampling the fastest error-growing directions of the phase space, and examining the dependence of prediction efficiency on ensemble size. The other is statistical, including distributional analysis and quantifying prediction utility by the Shannon entropy and the relative entropy. Currently, with simple models, one could choose as many ensembles as possible, with each ensemble containing a large number of members. When the forecast models become increasingly complicated, however, one would only be able to afford a small number of ensembles, each with limited number of members, thus sacrificing estimation accuracy of the forecast errors. To uncover connections between different information theoretic approaches and between dynamical and statistical approaches, we propose an （ε, T）-entropy and scale-dependent Lyapunov exponent--based general theoretical framework to quantify information loss in ensemble forecasting. More importantly, to tremendously expedite computations, reduce data storage, and improve forecasting accuracy, we propose a technique for constructing a large number of ＂pseudo＂ ensembles from one single solution or scalar dataset. This pseudo-ensemble technique appears to be applicable under rather general conditions, one important situation being that observational data are available but the exact dynamical model is unknown.     

Preparation of Zn2+–Ni2+–Fe3+–CO32−LDHs and study of photocatalytic activities for decomposition of Methyl Orange solution

New type photocatalytic materials of Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs were prepared by complexing agent-assisted homogeneous precipitation technique and Zn(NO₃)₂·6H₂O, Ni(NO₃)·6H₂O, Fe(NO₃)₃·9H₂O used as raw materials in the case of molar ratio of Zn²⁺/Ni²⁺/Fe³⁺ = 1:6:2. Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs having a specific surface area of 96.5 m²/g. The structure and catalytic properties of the material were systematically studied. The experimental results show that the Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs has a higher adsorption performance and lower band gap which make it an excellent catalyst for reducing the degradation of the methyl orange. Study on the process of photocatalytic reaction shows that Methyl Orange was adsorbed to the layer of Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs, and then it was photodecomposed to inorganic molecules and ions by Zn²⁺, Ni²⁺, and Fe³⁺ on the surface of Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs.     

Material Tensors and Pseudotensors of Weakly-Textured Polycrystals with Orientation Distribution Function Defined on the Orthogonal Group

A representation theorem on material tensors of weakly-textured polycrystals was recently established by Man and Huang, which delineates quantitatively the effect of crystallographic texture on the material tensor in question. Man and Huang’s theorem is based on the classical assumption in texture analysis that ODFs are defined on the rotation group SO(3), which strictly speaking makes it applicable only to polycrystals with crystallite symmetry defined by one of the 11 proper point groups. In this paper we let ODFs be defined on the orthogonal group O(3) and extend the representation theorem of Man and Huang to cover pseudotensors and polycrystals with crystallite symmetry defined by any of the 21 improper point groups. In SO(3)-based texture analysis, as a result of the inherent limitation imposed by the restricted definition of the ODF, each improper group of crystallite symmetry in question is routinely treated as if it were its peer proper group in the same Laue class. In light of the extended representation theorem, we examine the conditions under which this ad hoc practice will still work as far as effects of texture on material tensors and pseudotensors are concerned and the circumstances under which it won’t.     

气相色谱-四极杆飞行时间质谱准确鉴定常见水果蔬菜中的农药残留

建立了一种新型农药多残留检测方法。采用气相色谱-四极杆飞行时间质谱（GC-QTOF MS）结合Carbon NH₂柱固相萃取净化可对不同类别的152种农药残留进行准确的鉴定。一级（MS¹）精确质量数据库评价3~5个特征离子,以3个及以上特征离子检出且离子丰度比（Q/q_i）合适作为一级质谱定性依据。对部分特征离子数不足及特征离子检出情况不符合条件的农药进行二级（MS²）确证,应用二级谱图库检索及镜像结果对比分析实现疑似农药确证。本文对梨、甘蓝、番茄3种代表性果蔬在5.0和10.0 μg/kg 2个添加水平的152种农药进行测定,回收率在70%~120%范围的比例分别为甘蓝91.45 %、94.08%,番茄88.20%、88.80%,梨86.84%、92.10%。本方法为常见果蔬中农药残留的准确判断提供了可靠依据,扩大了分析范围。     

超细二氧化硅粉体对淀粉火焰抑制的实验研究

为了探究不同粒径二氧化硅粉体抑制效果上的差异,采用小尺寸竖直燃烧管道系统,研究添加10 μm和30 nm二氧化硅粉体时,不同粒径小麦淀粉燃烧的火焰传播、温度、速度等参数特性的变化。实验结果表明:超细二氧化硅粉体能减弱小麦淀粉燃烧反应强度;30 nm二氧化硅粉体抑制效果优于10 μm二氧化硅,当小麦淀粉粒径小于25 μm时,质量浓度为0.43 kg/m3、粒径30 nm的超细二氧化硅粉体可使小麦淀粉火焰亮度明显下降,最高温度下降38.07%,最大速度和平均速度分别下降42.25%、65.59%;超细二氧化硅粉体主要起物理抑制作用,抑制效果与小麦粒径成反比关系,小麦粒径越小,二氧化硅抑制效果越好。