化学教学中应如何培养学生的问题意识

当前,中学生问题意识较差,不能发现并提出问题。这种状况不能适应新课程改革的需要。笔者总结自己在化学教学中培养学生问题意识的几种做法：唤醒“问”的意识,使学生想问;营造“问”的氛围,使学生敢问;创设“问”的情境,使学生能问;传授“问”的技巧,使学生会问;教师要正确面对学生的提问。     

Bi3.25Nd0.75Ti3O12纳米结构: 可控合成及其可见光催化活性

用水热法制备不同形貌的掺钕钛酸铋(Bi3.25Nd0.75Ti3O12,BNdT)纳米粉体.透射电子显微镜(TEM)结果表明,通过控制OH-浓度可以得到不同形貌的纳米粉体.基于不同条件下制备的样品微结构分析,提出了这些不同形貌的形成机制.紫外-可见漫反射光谱(UV-Vis DRS)表明BNdT样品的带隙能(Eg)约为1.984 eV.利用可见光照射下甲基橙降解实验评价了BNdT样品的光催化性能.结果表明,BNdT的光催化活性比商用TiO2催化剂P25和掺氮TiO2高得多.OH-浓度为10 mol·L-1时制备的BNdT纳米线光催化效率最高,经可见光照射360min,浓度为0.01 mmol·L-1甲基橙溶液的降解率可达到93.0%,且循环使用4次后,其光催化活性并没有明显降低,表明BNdT是一种稳定有效的可见光催化剂.     

A new approach to variable selection in least squares problems

The title Lasso has been suggested by Tibshirani (1996) as acolourful name for a technique of variable selection which requiresthe minimization of a sum of squares subject to an l₁ bound on the solution. This forces zero components in the minimizingsolution for small values of . Thus this bound can functionas a selection parameter. This paper makes two contributionsto computational problems associated with implementing the Lasso:(1) a compact descent method for solving the constrained problemfor a particular value of is formulated, and (2) a homotopymethod, in which the constraint bound becomes the homotopyparameter, is developed to completely describe the possibleselection regimes. Both algorithms have a finite terminationproperty. It is suggested that modified Gram-Schmidt orthogonalizationapplied to an augmented design matrix provides an effectivebasis for implementing the algorithms.     

一类含临界增长的多重调和方程组非平凡解的存在性

本文研究了带临界指标的多重调和半线性椭圆方程组.利用变分法,得到了此类方程组非平凡解的存在性和非存在性的条件.     

Above-Threshold Dissociation of HD+ in Femtosecond Laser Field

The above-threshold dissociation （ATD） of the HD＋ molecular ion in femtosecond laser field is investigated theoretically. The energy-dependent distribution of the dissociated fragments is calculated using an asymptoticflow expression in the momentum space. The calculations show that the ATD of HD＋ is sensitive to the initial vibrational level of ground electronic state. Multiphoton ATDs can be observed in the dissociation processes. The dynamics phenomena are interpreted by using the concept of light-dressed potential.     

An auditory periphery model for improving narrow-band noise recognition rate of underwater targets

The recognition rate of the auditory periphery features decreases when the model is used to identify underwater targets in practice. To solve this problem, an improved method based on Gammatone filter bank is proposed. Firstly, after the reason of the decreasing of the recognition results is analyzed,the mechanism of multichannel data acquisition in acoustic engineering may narrow down signal frequency range, which leads to time-frequency features distortion. Secondly, the Gammatone filter bank is implemented to simulate frequency decomposition characteristics of human ear basilar membrane. Since the class information of the underwater noise signal is mostly contained in low frequency range, the auditory features of the conventional model are interpolated and the channel number of the filter bank and the central frequency of each frequency band are adjusted accordingly to obtain a 27-dimensional feature vector of the narrow-band target signal. The adjusted model may reflect the target's timefrequency feature more precisely. Finally, the performance of the auditory features is tested by a Neural Network classifier. The experiment results show that the modified auditory model is more effective than the conventional ones. The major information contained in broadband signals is reserved and the classification ability for real targets is further enhanced. The recognition results are increased from 82.59% to 88.80%. The modified auditory features effectively improve the recognition rate for underwater target radiated noise signals.     

The Effect of Storage Conditions on the Content of Molecules in Malus domestica ‘Chopin’ cv. and Their In Vitro Antioxidant Activity

The apple fruit is one of the most widely cultivated temperate fruits and a rich source of bioactive compounds. Since a growing number of consumers are increasingly seeking safe and healthy food production, organic apple production provides this possibility. In this study, the content of bioactive compounds in organic apples depending on temperature and storage time were determined. ‘Chopin’ apples were stored for 7, 14 and 21 days at 5 °C and 20 °C. All analyses were performed using the HPLC method. The control samples of fresh apples contained the highest content of vitamin C (21.87 mg/100 g FW), L-ascorbic (11.50 mg/100 g FW), DHA (10.37 mg/100 g FW), total carotenoids (2.82 mg/100 g FW), β-carotene (0.21 mg/100 g FW) and lutein (2.41 mg/100 g FW). Samples stored at 20 °C had the highest content of total carotenoids and lutein, but samples stored at 5 °C contained the most β-carotene and zeaxanthin. Apples stored at 20 °C contained significantly more chlorophyll a (0.05 g/100 g FW). The samples stored at 5 °C contained the most total polyphenols. Samples stored for 14 days were characterized by the highest content of total flavonoids. Samples stored for 21 days were characterized by the highest content of epigallocatechin and quercetin-3-O-rutinoside, but the highest content of quercetin and kaempferol was found in control samples. The highest content of total flavonoids was found in apples stored at 5 °C.     

Statistical theory for hydrogen bonding fluid system of AaDd type (Ⅱ): Properties of hydrogen bonding networks

Making use of the invariant property of the equilibrium size distribution of the hydrogen bonding clusters formed in hydrogen bonding system of AaDd type, the analytical expressions of the free energy in pregel and postgel regimes are obtained. Then the gel free energy and the scaling behavior of the number of hydrogen bonds in gel phase near the critical point are investigated to give the corresponding scaling exponents and scaling law. Meanwhile, some properties of intermolecular and intramolecular hydrogen bonds in the system, sol and gel phases are discussed. As a result, the explicit relationship between the number of intramolecular hydrogen bonds and hydrogen bonding degree is obtained.     

多层岩土环境的溶洞智能识别方法研究

提出了一种基于双向长短期记忆(bidirectional long short-term memory, BiLSTM) 神经网络的多层岩土环境溶洞三维定量智能识别方法。首先,借鉴浅层地震反射波法原理,建立含有单个无填充球形孔洞的多层岩土结构模型,并计算桩锤激振下地表的加速度响应信号;其次,针对不同溶洞工况大量建模,以获取不同工况下的响应信号作为数据集;最后,基于BiLSTM设计了双数据通道分离架构网络模型,实现了对多层岩土环境下不同溶洞工况的定量识别。研究表明,本文所提出方法能够对不同岩土体结构下溶洞的三维位置和直径进行定量识别,且在3 m容差范围内的识别准确率达到了98%以上。

     

支化高分子溶胶-凝胶相变的热力学

以典型的Aa-Bb型缩聚反应为例, 应用统计力学和热力学的基本原理对反应体系的一些平衡特征进行研究. 基于从两种不同角度所构造的正则配分函数, 导出反应体系的平衡自由能以及质量作用定律的解析形式, 同时指出获得数量分布函数的新方法, 并通过计算反应体系的等温压缩系数从而得到反应体系的凝胶化条件. 进一步利用数量分布函数的不变性, 给出临界点后溶胶相和凝胶相的平衡自由能, 探讨了溶胶-凝胶相变的相关问题.