初中化学项目式教学实践——以“质量守恒定律”为例

文章以“质量守恒定律”为例,首先阐述了初中化学项目式教学实践,然后分析了初中化学项目式教学实践效果,其中教学实践部分包括立足课程标准,明确教学方向;关注实际学情,设计教学项目;科学组建实验小组,实施项目探究;组织汇报交流,提升学生能力四个方面。

“质量守恒定律”的说课

一、教材分析，1．本节内容在教材中的地位和作用，“质量守恒定律”是2004年课标教材(人教版)初中三年化学第五单元《化学方程式》第1课题内容。在学习本课题之前，学生已学过化学反应的文字表达式，这种表示方法只能表示反应物和生成物是何种物质，无法表示反应物和生成物的组成，也无法反映各个物质之间的量的关系，使用亦不方便，不利于进一步深入学习化学。而元素符号、化学式、化学方程式是初中化学入门的三种重要化学用语，掌握了它们，才有可能学好化学，故其重要性可想而知。前两者已经学过，这为本单元化学方程式的教学作了知识准备。

Theoretical analysis of minimum metal foil thickness achievable by asymmetric rolling with fixed identical roll diameters

A novel approach is proposed for computing the minimum thickness of a metal foil that can be achieved by asymmetric rolling using rolls with identical diameter. This approach is based on simultaneously solving Tselikov equation for the rolling pressure and the modified Hitchcock equation for the roller flattening. To minimize the effect of the elastic deformation on the equal flow per second during the ultrathin foil rolling process, the law of conservation of mass was employed to compute the proportions of the forward slip, backward slip, and the cross shear zones in the contact arc, and then a formula was derived for computing the minimum thickness for asymmetric rolling. Experiment was conducted to find the foil minimum thickness for 304 steel by asymmetric rolling under the asymmetry ratios of 1.05, 1.15 and 1.30. The experimental results are in good agreement with the calculated ones. It was validated that the proposed formula can be used to calculate the foil minimum thickness under the asymmetric rolling condition.

Responses of wind-induced internal pressure in a two-compartment building with a dominant opening and background porosity Part 1:Theoretical formulation and experimental verification

The equations governing wind-induced internal pressure responses for a two-compartment building with a dominant opening and background porosity were derived.The unsteady form of the Bernoulli equation,the law of mass conservation,and adiabatic equation were used for the derivation.The precision of the governing equations was verified by a wind tunnel test on a rigid model of a low-rise building.The results show that the governing equations can effectively analyze the wind-induced internal pressure responses.The internal pressure responses in both compartments are suppressed due to the additional damping provided by background porosity.The responses of internal pressure in both compartments,especially in the compartment without an external opening,decrease with increased lumped leakage area.

A numerical simulation of seepage structure surface and its feasibility

According to Cubic law and incompressible fluid law of mass conservation, the seepage character of the fracture surface was simulated with the simulation method of fractal theory and random Brown function. Furthermore, the permeability coefficient of the single fracture was obtained. In order to test the stability of the method, 500 simulations were conducted on each different fractal dimension. The simulated permeability coefficient was analyzed in probability density distribution and probability cumulative distribution statistics. Statistics showed that the discrete degree of the permeability coefficient increases with the increase of the fractal dimension. And the calculation result has better stability when the fractal dimension value is relatively small. According to the Bayes theory, the characteristic index of the permeability coefficient on fractal dimension P（Dfi｜ Ri） is established. The index, P（Dfi｜ Ri）, shows that when the simulated permeability coefficient is relatively large, it can clearly represent the fractal dimension of the structure surface, the probability is 82%. The calculated results of the characteristic index verify the feasibility of the method.

Study on the propagation law of shock wave resulting from coal and gas outburst

According to the formation of shock wave resulting from coal and gas outburst, the gas flow of coal and gas outburst was transformed from an unsteady flow to a steady one based on selected appropriate reference coordinates, and the mathematical expressions were then established by applying mass conservation, momentum conservation equation, and energy conservation equation. On this basis, analyzed gas flow mitigation of variable cross-section area and the outburst intensity, and the relations between cross-section area, velocity, and density; the relations between overpressures and outburst intensity were deduced. Furthermore, shock waves resulting from coal and gas outburst and outburst intensity were measured by experimental setup, the overpressure and outburst intensity of different gas pressures were obtained, and the similar conditions of the experiment were numerically simulated. The averaged overpressure and gas flow velocity of variable cross-section under different gas pressures were numerically derived. The results show that the averaged overpressure and outburst intensity obtained from simulation are in good agreement with the experimental results. Moreover, the gas flow velocity of variable cross-sections approximates to the theoretical analysis.

Approach to increasing the quality of pressure-relieved gas drained from protected coal seam using surface borehole and its industrial application

During mining of lower protective coal seam, a surface borehole can efficiently extract not only the pressure-relieved gas from the protected layer, but also the gas from the mining layer gob. If the distance between the borehole and gob is too large, the quantity of gas drained from the protected layer decreases substantially. To solve this problem, a mathematical model for extracting pressure-relieved gas from a protected coal seam using a surface borehole was established, based on the radial gas flow theory and law of conservation of energy. The key factors influencing the quantity of gas and the drainage flow network using a surface borehole were presented. The results show that the quantity of pressure-relieved gas drained from the protected layer can be significantly increased by increasing the flow resistance of the borehole bottom. Application of this method in the Wulan Coal Mine of the Shenhua Group significantly increased the flow of pure gas and the gas concentration （by factors of 1.8 and 2.0, respectively）, thus demonstrating the remarkable effects of this method.

A Redemptive Analysis of Suffering

The notion of suffering carries with it aspects which are private and individual on the one hand, and social and lingual on the other. I would pay attention to the latter part of the suffering notion, where the notion of suffering is recognized to be primitive by almost all the theories of human values. This primitive character allows a commensurable basis on the basis of which most plural theories share something in common to talk objectively to each other. In this paper, I would like to offer three arguments in order to advance a thesis that one＇s suffering is redemptive of others. First, the conservation law of mass says that matter of a closed system can neither be created nor destroyed, although it may be differently rearranged. This may be applied to the experience of suffering, to allow the conservation law of suffering： My unjust self-interest costs pains in others to the level of the same amount but if I voluntarily suffer a sacrifice, others will have their pains lightened to the analogous level. Second, notion of yin-yang helps to support the redemptive thesis of suffering. The notion says that all things in the reality consist of two complementary opposite Capacities that interact within a greater whole, as part of a dynamic system. Then, my acceptance of suffering and the decrease of other＇s pain are two complementary capacities of one reality. Third, any person is responsible for his own act, so is a society as a whole. Then, as an individual restores his damaged person, when he commits a crime, by being suffered or punished, a society restores itself to its own proper state, when any member of the society is wronged, by suffering communally in one way or other.

A mass-conservative average flow model based on finite element method for complex textured surfaces

A mass-conservative average flow model based on the finite element method(FEM) is introduced to predict the performances of textured surfaces applied in mechanical seals or thrust bearings.In this model,the Jakobsson-Floberg-Olsson(JFO) boundary conditions are applied to the average flow model for ensuring the mass-conservative law.Moreover,the non-uniform triangular grid is utilized,which can deal with the problem of complex geometric shapes.By adopting the modeling techniques,the model proposed here is capable of dealing with complex textured surfaces.The algorithm is proved correct by the numerical experiment.In addition,the model is employed to gain further insight into the influences of the dimples with different shapes and orientations on smooth and rough surfaces on the load-carrying capacity.

Application of Lagrange＇s equation to rigid-elastic coupling dynamics

A consistent focus in theoretical mechanics has been on how to apply Lagrange's equation to continuum mechanics.This paper uses the concept of a variational derivative and its laws of operation to investigate the derivation of Lagrange's equation,which is then applied to nonlinear elasto-dynamics.In accordance with the work-energy principle and the energy conservation law,kinetic and potential energies are proposed for rigid-elastic coupling dynamics,whose governing equation is established by manipulating Lagrange's equation.In addition,case studies are used to demonstrate the application of the proposed method to spacecraft dynamics.

Gravitational Energy-Momentum and Conservation of Energy-Momentum in General Relativity

Based on a general variational principle, Einstein–Hilbert action and sound facts from geometry, it is shown that the long existing pseudotensor, non-localizability problem of gravitational energy-momentum is a result of mistaking different geometrical, physical ob jects as one and the same. It is also pointed out that in a curved spacetime, the sum vector of matter energy-momentum over a finite hyper-surface can not be defined. In curvilinear coordinate systems conservation of matter energy-momentum is not the continuity equations for its components. Conservation of matter energy-momentum is the vanishing of the covariant divergence of its density-flux tensor field. Introducing gravitational energy-momentum to save the law of conservation of energy-momentum is unnecessary and improper. After reasonably defining "change of a particle's energy-momentum", we show that gravitational field does not exchange energy-momentum with particles. And it does not exchange energy-momentum with matter fields either. Therefore, the gravitational field does not carry energy-momentum, it is not a force field and gravity is not a natural force.