中学化学教学中的科学思维与逻辑辨析

化学是一门具有创造性的基础科学,是环境、生命、医药、材料等科学的基础,在思维逻辑上彰显和蕴含了丰富的科学思维方法。系统总结化学科学思维方法,可以有效破解中学化学学习中的“繁,难,乱”。在多年的教学实践中,提出了化学科学多向思维方法体系,强调多层次思维过程中对多因素的立体逻辑思维辨析。重点介绍了与中学化学教学相关的零阶、初阶、中阶和高阶逻辑思维辨析的内涵,期望化学教学中重视化学思维逻辑过程,实现化学教与学在思维模式上的深层次发展与提升。     

物理化学混合式教学设计与实践——以“单组分系统相变热力学”为例*

以“单组分系统相变热力学”为例介绍了物理化学混合式教学设计与教学实践。围绕课程教学目标,在课前、课中、课后的每一个教学环节中践行课程教学理念,通过“问题+案例”方式突出物理化学基本方法的应用性、普适性与前沿性,让学生在教学过程中获取原理、体验探究、发展思维、生成智慧。教学评价结果显示,绝大部分学生对混合式教学模式给予了积极的评价。     

A Districtwide Study of Automaticity When Included in Concept‐Based Elementary School Mathematics Instruction

While conceptual understanding of properties, operations, and the base‐ten number system is certainly associated with the ability to access math facts fluently, the role of math fact memorization to promote conceptual understanding remains contested. In order to gain insight into this question, this study looks at the results when one of three elementary schools in a school district implements mandatory automaticity drills for 10 minutes each day while the remaining two elementary schools, with the same curriculum and very similar demographics, do not. This study looks at (a) the impact that schoolwide implementation of automaticity drills has on schoolwide computational math skills as measured by the ITBS and (b) the relationship between automaticity and conceptual understanding as measured by statewide standardized testing. The results suggest that while there may be an association between automaticity and higher performance on standardized tests, caution should be taken before assuming there are benefits to promoting automaticity drills. These results are consistent with those that support a process‐driven approach to automaticity based on familiarity with properties and strategies associated with the base‐ten number system; they are not consistent with those that support an answer‐driven approach to automaticity based on memorization of answers.     

二甲基亚砜对乙酸气相色谱保留时间的影响及其机理

通过气相色谱、红外光谱分析和量子化学计算,探究溶于二甲基亚砜（DMSO）中乙酸保留时间发生波动的原因。 结果显示,乙酸保留时间变化与DMSO体积等量递增呈线性关系,R²=0.99301;根据红外光谱分析得出,DMSO和乙酸之间生成了氢键,以DMSO-乙酸分子的形式通过色谱柱;根据Gaussian09程序计算结果,DMSO电子密度大的部分给予电子,与乙酸之间形成了氢键,而DMSO电子密度小的部分容易获得电子与具有强偶极矩的色谱柱固定液聚乙二醇产生作用力,吸附在固定液上。因此,在上述一系列复杂的分子间作用力的共同影响下,乙酸保留时间发生了波动,且随着溶剂DMSO体积比增加,乙酸保留时间不断延长。     

The die swell phenomenon

Summary A polymer melt or solution undergoes an increase in its cross-section when it is forced out of an orifice into air. The normal stress effects and elastic effects shown by these materials are frequently invoked to explain this die swell phenomenon. These explanations are here discussed and criticised. The analogous situation for a Newtonian jet is also discussed and the solution to a related problem of two-dimensional lowReynolds number flow is given.

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Zusammenfassung Kunststoffschmelzen oder -lösungen zeigen nach dem Austritt aus einer Mündung in Luft eine Aufweitung des Querschnitts. Häufig wird dieses Schwell-Phänomen als Folge von Normalspannungen und Elastizität erklärt. Erklärungen dieser Art werden hier kritisch untersucht.Ebenso wird der entsprechende Fall einer Newtonschen Düsenströmung diskutiert. Für das verwandte Problem einer zweidimensionalen Strömung bei niedrigerReynolds-Zahl wird die Lösung gegeben.

     

Injection moulding of thermoplastics: Freezing of variable-viscosity fluids.

The injection moulding of thermoplastics involves, during mould filling, flows of hot polymer melts into mould networks, the walls of which are so cold that frozen layers form on them. An analytical study of such flows is presented here for the case when the Graetz and Nahme numbers are large and the Pearson number is small. Thus the flows are developing and temperature differences due to heat generation by viscous dissipation are sufficiently large to cause significant variations in viscosity (but the difference between the entry temperature of the polymer to a specific part of the mould network and the melting temperature of the polymer is not). Br Brinkman number - Gz Graetz number - h half-height of channel or disc - h ^* half-height of polymer melt region in channel or disc - L length of channel or pipe - m viscosity shear-rate exponent - Na Nahme number - p pressure - P pressure drop - Pe Péclet number - Pn Pearson number - Q volumetric flowrate - r radial coordinate in pipe or disc - R radius of pipe - Re Reynolds number - R _i inner radius of disc - R _o outer radius of disc - R ^* radius of polymer melt region in pipe - T temperature - T _ad adiabatic temperature rise - T _e entry polymer melt temperature - T _m melting temperature of polymer - T _max maximum temperature - T ₀ reference temperature - T _w wall temperature - flow-average temperature rise - u _r radial velocity in pipe or disc - u _x axial velocity in channel - u _y transverse velocity in channel or disc - u _z axial velocity in pipe - w width of channel - x axial coordinate in channel or modified radial coordinate in disc - y transverse coordinate in channel or disc - z axial coordinate in pipe - thermal conductivity of molten polymer - thermal conductivity of frozen polymer - scaled dimensionless axial coordinate in channel or pipe or radial coordinate in disc - ₀ undetermined integration constant - heat capacity of molten polymer - viscosity temperature exponent - dimensionless transverse coordinate in channel or disc - ^* dimensionless half-height of polymer melt region in channel or disc - H ^* scaled dimensionless half-height of polymer melt region in channel or disc or radius of polymer melt region in pipe - dimensionless temperature - ^* dimensionless wall temperature - scaled dimensionless temperature - numerical constant - µ viscosity of molten polymer - µ ₀ consistency of molten polymer - dimensionless pressure gradient - scaled dimensionless pressure gradient - density of molten polymer - dimensionless radial coordinate in pipe or disc - _i dimensionless inner radius of disc - ^* dimensionless radius of polymer melt region in pipe - dimensionless streamfunction - scaled dimensionless streamfunction - dummy variable - streamfunction - similarity variable - similarity variable     

Injection moulding of thermoplastics: Freezing of variable-viscosity fluids.

The injection moulding of thermoplastics involves, during mould filling, flows of hot polymer melts into mould networks, the walls of which are so cold that frozen layers form on them. An analytical study of such flows is presented here for the case when the Graetz number is small and the Nahme number is non-zero and can be large. Thus the flows are fully-developed and temperature differences due to heat generation by viscous dissipation are sufficiently large to cause significant variations in viscosity. Gz Graetz number - h half-height of channel or disc - h ^* half-height of polymer melt region in channel or disc - L length of channel or pipe - m viscosity shear-rate exponent - Na _Q Nahme number based on flowrate - Na _P Nahme number based on pressure drop - Na _PL lower critical value of Nahme number based on pressure drop - Na _PU upper critical value of Nahme number based on pressure drop - Na _P Nahme number based on pressure gradient - p pressure - P pressure drop - Q volumetric flowrate - r radial coordinate in pipe or disc - R radius of pipe - Re Reynolds number - R _i inner radius of disc - R ₀ outer radius of disc - R ^* radius of polymer melt region in pipe - T temperature - T _m melting temperature of polymer - T ₀ reference temperature - T _w wall temperature - u axial velocity in pipe or channel or radial velocity in disc - w width of channel - x axial coordinate in channel - y transverse coordinate in channel or disc - z axial coordinate in pipe - thermal conductivity of molten polymer - thermal conductivity of frozen polymer - heat capacity of molten polymer - viscosity temperature exponent - dimensionless transverse coordinate in channel or disc - ^* dimensionless half-height of polymer melt region in channel or disc - dimensionless temperature - ^* dimensionless wall temperature - µ viscosity of molten polymer - µ ₀ consistency of molten polymer - dimensionless pressure drop - dimensionless pressure gradient - density of molten polymer - dimensionless radial coordinate in pipe or disc - _i dimensionless inner radius of disc - ^* dimensionless radius of polymer melt region in pipe - dimensionless velocity