“第三教学”的核心学力形成与个性发展

最旧式的、教师中心的、灌输教科书知识的教学,谓之“第一教学”。“第一教学”存在种种问题,从新的视角加以修正、改进,确立新的教学型态,称之为“第二教学”。“第二教学”的着眼点有两个:第一,面向学生;第二,针对不同学科探讨合理的教学方法,以此为据展开教学便能提高学生的学力。不过,“第二教学”终究未能摆脱“第一教学”的轨道,在“第二教学”中,应试教育的体制与机制依然未变。“第三教学”是立足于儿童本性的教学;是培养未来世纪新人的生存能力的教学;是真正实现教育中的重心转移、旨在人人成功的教学;是培养学生自主学习的教学。不同于“

Crack elimination and strength enhancement mechanisms of selective laser melted Si-modified Al−Mn−Mg−Er−Zr alloy

In order to increase the processability and process window of the selective laser melting(SLM)-fabricated Al−Mn−Mg−Er−Zr alloy,a novel Si-modified Al−Mn−Mg−Er−Zr alloy was designed.The effect of Si alloying on the surface quality,processability,microstructure,and mechanical properties of the SLM-fabricated alloy was studied.The results showed that introducing Si into the Al−Mn−Mg−Er−Zr alloy prevented balling and keyhole formation,refined the grain size,and reduced the solidification temperature,which eliminated cracks and increased the processability and process window of the alloy.The maximum relative density of the SLM-fabricated Si/Al−Mn−Mg−Er−Zr alloy reached 99.6%.The yield strength and ultimate tensile strength of the alloy were(371±7)MPa and(518±6)MPa,respectively.These values were higher than those of the SLM-fabricated Al−Mn−Mg−Er−Zr and other Sc-free Al−Mg-based alloys.

淡化形式注重实质——工科数学教学漫谈之一

在工科数学教学中,应淡化知识、概念的形式化描述,注重实质掌握;应淡化知识的量的积累,注重学力形成;注重数学的人文价值。

“第三教学”的探索与实践

新世纪,基础教育面临着新的挑战,以培养学生创新精神和实践能力为重点的素质教育迫切要求人才培养模式的改革.由于受传统教育理念、教育思想和教育模式惯性的影响,一些学校在实际教育中,以教师为中心的讲解模式仍占据着统治地位.这种教育模式低效高耗,培养的学生层次不高,教师教得辛苦,学生学得痛苦.教学最大的浪费在课堂,浪费的根源在教师.为寻求最优的教学方式,笔者先后尝试过"中学物理导学模式"和"创新教育的物理问题教学法的研究",均收到了良好的效果,但自感美中不足,仍有许多方面需要研究和完善,试想能否冲破传统理念的束缚呢?为此立项申报了"十五"省级课题:探索"第三教学",提高学生学力的研究.

Effect of process parameters on microstructure and properties of AM50A magnesium alloy parts formed by double control forming

Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting （DC） due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength （YS）, ultimate tensile strength （UTS） and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 ＆#176;C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 ＆#176;C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.

Effect of minor Fe addition on glass forming ability and mechanical properties of Zr_(55)Al_(10)Ni_5Cu_(30) bulk metallic glass

A series of rod samples with diameter of 3 mm（Zr0.55Al0.10Ni0.05Cu0.30）100-xFex（x=0,1,2,3,4） were prepared by magnetic suspend melting and copper mold suction casting method.The effects of a small amount of Fe on glass forming ability（GFA） and mechanical properties of Zr55Al10Ni5Cu30 bulk metallic glass（BMG） were investigated.The results show that the addition of an appropriate amount（less than 3%,mole fraction） of Fe enhances GFA,as indicated by the increase in the reduced glass transition temperature Trg（=Tg/Tl） and the parameter γ（=Tx/（Tg＋Tl）） with increasing Fe content,and GFA gets deteriorated by further Fe addition（4%）.The addition of Fe also effectively improves the compressive plasticity and increases the compressive fracture strength in these Zr-based BMGs.Compressive tests on BMG sample with 3 mm in diameter and 6 mm in length reveal work-hardening and a certain plastic strain in the alloy containing 2% Fe.The BMG composite containing 4% Fe also exhibits a high fracture strength along with significant plasticity.

从“问学”走向“学问”

'儿童问学课堂'是新常态下语文教学改革的新尝试,它顺应儿童好问的天性,把'问'和'学'的权利还给儿童,优化儿童的学习过程。问学,生成问题是前提,自主实践是基础,形成学力是归宿。问学课堂,要唤醒儿童问学的动机,营造民主的问学氛围,采用贴近儿童天性的评价来保持问学的动力,让儿童在快乐学习中形成'学问'。

Mechanical behavior of Al-Zn-Mg-Cu alloy under tension in semi-solid state

In order to study the hot fractures in relation to the semi-solid processing, the tensile tests of an extruded 7075 aluminum alloy which is based on Al?Zn?Mg?Cu system were carried out in the high temperature solid and semi-solid states at different strain rates. The results show that the tensile behavior can be divided into three regimes with increasing the liquid fraction. The alloy first behaves in a ductile character, and as the temperature increases, the fracture mechanism changes from ductile to brittle which is determined by both of liquid and solid, and lastly the fracture mechanism is brittle which is totally dominated by liquid. At strain rates of 1×10?4, 1×10?3 and 1×10?2 s?1, the brittle temperature ranges are 515?526, 519?550 and 540?580 °C, respectively. Two equations which are critical for tensile behavior are proposed.

Preparation, formation mechanism and mechanical properties of multilayered TiO_2-organic nanocomposite film

Ti O2-organic multilayered nanocomposite films were deposited on a self-assembled monolayer-coated silicon substrate based on layer-by-layer technique and chemical bath deposition method by a hydrolysis of Ti Cl4 in an acid aqueous solution. The chemical compositions, surface morphologies and mechanical properties of the films were investigated by X-ray photoelectron spectrometer(XPS), scanning electron microscopy(SEM) and nanoindentation depth-sensing technique, respectively. The results indicate that the major chemical compositions of the films are Ti and O. The principal mechanism for the nucleation and growth of the films is homogeneous nucleation, and the layer number of films has great influence on the surface morphology and roughness of the films. In addition, mechanical nanoindentation testing presents a significant increase in hardness and fracture toughness of titanium dioxide multilayered films compared with single-layer titanium dioxide thin film.

Preparation and properties of novel Cu-based bulk metallic glasses Cu_(55-x)Zr_(37)Ti_8In_x

The glassy rods were successfully fabricated in the Cu-Zr-Ti-In alloy system by casting into a copper mold. The value of ATx reaches a maximum of 66 K for the BMG CusoZraTTi8In5 alloy. The reasons for enhancing glass forming ability of Cu-based BMGs with the addition of indium were discussed from atomic size and thermodynamics. Alternatively, the BMG Cu52Zra7Ti8In3 exhibits the highest compressive strength （1981 MPa） and the best plasticity among glassy Cu55-xZra7TisInx （x_〈5）. The total plastic deformation of Cu52Zr37TisIn3 before fracture approaches 1.2%.

Design of high strength Fe-(P,C)-based bulk metallic glasses with Nb addition

Bulk metallic glass（BMG） rods Fe71Mo5-xNbxP12C10B2（x=1,2,3,4 and 5） with diameter of 1 or 2 mm were synthesized by copper mold casting.The effects of Nb substitution for Mo on the structure,thermal and mechanical properties of Fe71Mo5-xNbxP12C10B2 alloys were studied by X-ray diffraction,differential scanning calorimetry and compressive testing.The results show that the substitution of Nb for Mo leads to a decreased glass forming ability,but with plasticity of 1.0%,the fracture strength of Fe71Mo2Nb3P12C10B2 alloy increases up to 4.0 GPa.The improvement of the fracture strength is discussed in terms of the enhancement of atomic bonding nature and the favorite formation of a network-like structure due to the substitution of Nb for Mo.

Effects of technical parameters of continuous semisolid rolling on microstructure and mechanical properties of Mg-3Sn-1Mn alloy

A sloping semisolid rheo-rolling process of Mg-3Sn-1Mn alloy was developed, and the effects of process parameters on the microstructure and mechanical properties of Mg-3Sn-lMn alloy strip were studied. The results show that the primary grain average diameter of the strip increases with the increase of the roll speed. The primary grain average diameter decreases firstly and then increases with the increase of the vibration frequency, and the tensile strength and elongation of the strip increase firstly and then decrease with the increase of the vibration frequency. The primary grain average diameter increases with the increase of casting temperature, and the tensile strength and elongation of the strip decrease correspondingly. When the casting temperature is 670℃, the roll speed is 52 mm/s, and the vibration frequency is 60 Hz, Mg-3Sn-1Mn alloy strip with good properties is produced. The mechanical properties of the present product are higher than those of Mg-3Sn-lMn alloy casting with the addition of 0.87% Ce （mass fraction）.

Pharmacokinetics of Native r-SAK in Rabbit's Femoral Artery Thrombosis Model

Objective: To study the pharmacokinetics of native r SAK in rabbit's femoral artery thrombosis model, the “lytic circle' method was used to determine plasma levels of r SAK. Methods: Thirty New Zealand rabbits were randomly assigned to the control (saline 10 ml, 30 min), r SAK low dose (0.25 mg/kg, 30 min), medial dose (0.50 mg/kg, 30 min), high dose (1.00 mg/kg, 30 min), single bolus (0.50 mg/kg, 2 min) and conjunctive therapy (initiated with heparin 200 U/kg, followed by infusion of r SAK 0.50 mg/kg for 30 min, and subsequently infused heparin 50 U/(kg·h) to endpoint) groups. The right femoral artery thrombosis model in rabbit was made by balloon injury, then the thrombolytic agents were infused through parallel ear vein and the blood samples were collected pre thrombolysis and at different time post thrombolysis to determine the plasma levels of r SAK by “lytic circle' method, the plasma levels of r SAK were processed by pharmacokinetic computing procedure to fit the model. Results: The plasma levels of r SAK and the diameters of lytic circles showed a pretty good linear correlation under the scope of 2.0×10 4 2.0×10 6 U/L, and the averaged recycle rate was (96.05±11.35)%(RSD =±11.82%).All peak concentration time in each infusion group was 30 min, and the peak concentrations positively correlated with the doses administrated in infusion groups(r=0.999 98, P <0.000 1). In single bolus group, Peak concentration time was 2 min, and the peak concentration reached (5.16±1.02) mg/L, which was significant higher than that in the same dose r SAK infusion group ( P <0.01). In conjunctive therapy group, the peak concentration showed no significant difference from that in the same dose r SAK infusion group ( P >0.05). The plasma levels of r SAK fit in two compartment model as processed by pharmacokinetic computing procedure in each group. Conclusion: The “lytic circle' method is a simple, practical and reliable method to determine the plasma level of r SAK, and the pharmacokinetics of native r SAK infusion fits in two compartment model in rabbit's femoral artery thrombosis model.

Size effects on deformation behavior of C5210 phosphor bronze thin sheet

To investigate the effects of thickness and grain size on mechanical and deformation properties of C5210 phosphor bronze thin sheets, samples with different grain sizes were obtained through annealing heat treatment at different temperatures; and then tensile tests of samples with different thicknesses and grain sizes were conducted at room temperature. The results show that yield strength increases with decreasing thickness from 800 to 50 μm, but work hardening exponent and total elongation decrease, and a modified model was proposed to describe the relation between yield strength and thickness; yield strength decreases as the grain size increases, but work hardening exponent shows an increasing trend, total elongation increases to a peak and then decreases. Fracture morphology of tensile specimens was observed by SEM, which indicates that all tensile specimens are ductile fracture. The dimple intensity increases as the specimen thickness increases but reduces with the specimen grain size increasing.

Formation mechanism and growth kinetics of TiAl_(3) phase in cold-rolled Ti/Al laminated composites during annealing

Cold-rolled Ti/Al laminated composites were annealed at 525−625℃for 0−128 h,and the interfacial microstructure evolution was investigated.The results indicate that only the TiAl_(3) phase was formed at the Ti/Al interface;most of TiAl_(3) grains were fine equiaxed with average sizes ranging from hundreds of nanometers to several microns and the TiAl_(3) grain size increased with increasing annealing time and/or temperature,but the effect of annealing temperature on the TiAl_(3) grain size was far greater than that of annealing time.The growth of the TiAl_(3) phase consisted of two stages.The initial stage was governed by chemical reaction with a reaction activation energy of 195.75 kJ/mol,and the reaction rate constant of the TiAl_(3) phase was larger as the Ti/Al interface was bonded with fresh surfaces.At the second stage,the growth was governed by diffusion,the diffusion activation energy was 33.69 kJ/mol,and the diffusion growth rate constant of the TiAl_(3) phase was mainly determined by the grain boundary diffusion owing to the smaller TiAl_(3) grain size.

Influence of trace Ca addition on texture and stretch formability of AM50 magnesium alloy sheet

The AM50,AM50-0.1 Ca,AM50-0.3 Ca and AM50-0.5 Ca(wt.%) alloys were hot-rolled and their mechanical properties were determined for the purpose of investigating the effect of trace Ca addition on the texture and stretch formability of AM50 alloy.The results show that the addition of trace Ca can effectively modify the basal texture,which is characterized by the split of basal poles deviated from the normal direction(ND) after the hot rolling,while a broad spread of the basal planes toward the transverse direction(TD) after the annealing.Such change of the basal texture is related to the prior formation of massive compression twins and the decrease of the c/a ratio.Erichsen value increases from 2.25 to 4.21 mm with the increase of Ca content.The enhancement of stretch formability is ascribed to the weakened basal texture,which results in the increase of n-value and the decrease of r-value.

Kinetics of Methane Hydrate Formation in Pure Water and Inhibitor Containing Systems

Kinetic data of methane hydrate formation in the presence of purewater, brines with single salt and mixed salts, and aqueous solutionsof ethylene glycol (EG) and salt + EG were measured. A new kineticmodel of hydrate formation for the methane + water systems wasdeveloped based on a four-step formation mechanism and reactionkinetics approach. The proposed kinetic model predicts the kineticbehavior of methane hydrate formation in pure water with goodaccuracy. The feasibility of extending the kinetic model to salt (s)and EG containing systems was explored.

Influence of process parameters on properties of AA6082 in hot forming process

The influences of process parameters on mechanical properties of AA6082in the hot forming and cold-die quenching(HFQ)process were analysed experimentally.Transmission electron microscopy was used to observe the precipitate distribution and to thus clarify strengthening mechanism.A new model was established to describe the strengthening of AA6082by HFQ process in this novel forming technique.The material constants in the model were determined using a genetic algorithm tool.This strengthening model for AA6082can precisely describe the relationship between the strengths of formed workpieces and process parameters.The predicted results agree well with the experimental ones.The Pearson correlation coefficient,average absolute relative error,and root-mean-square error between the calculated and experimental hardness values are0.99402,2.0054%,and2.045,respectively.The model is further developed into an FE code ABAQUS via VUMAT to predict the mechanical property variation of a hot-stamped cup in various ageing conditions.

Effect of alloy composition and heat treatment on mechanical performance of 6xxx aluminum alloys

The effect of alloy composition and heat treatment, including natural ageing and pre-ageing, on the mechanical performance of eight 6xxx alloys designed with systematically varying Si, Mg and Cu contents was studied. The results show that not only the alloy composition and heat treatment before forming influence the formability, but also they have an effect on the paint bake response of the alloys. Increasing the alloy Si content, decreasing Mg/Si ratio and adding 0.3% Cu （mass fraction） were generally found to improve the tensile ductility and formability of the alloys studied, while pre-ageing was found to decrease these properties. A full property profile of these alloys in terms of strength, tensile ductility, work hardening, strain rate sensitivity, forming limit and paint bake response was presented.

Decomposition Kinetics for Formation of CO_2 Hydrates in Natural Silica Sands

The decomposition kinetics for formation of CO2 hydrates in 90 cm 3wet natural silica sands were studied systematically using the depressurization method at the temperatures ranging from 273.2 to 277.2 K and the pressures from 0.5 to 1.0 MPa.The effects of temperature,pressure,particle diameter,porosity,and salinity of formation water on the decomposition kinetics were investigated.The results show that the dissociation percentage increases as temperature increases or as the initial decomposition pressure decreases.An increase in porosity or a decrease in particle diameter of silica sands accelerates the decomposition.Increasing the salinity of the formation water gives rise to a faster decomposition.However,a combination of the present results with the observations in literature reveals that the effect of the coexisting ionic solute depends on its chemical structure.