基于前后测的课例研究——以《周长》为例

在课例研究中,常使用前测与后测的方法收集实证数据来评价学生在课堂上的真实获得,其作用是知道学生“已经知道了什么”、获取学习资源和用数据评价教学的效果。通过《周长》课例研究中前后测的使用,明确前后测可以通过研究学生来设计和开展教学,从数据分析中反思教学中的问题,有助于丰富对学生学习的看法。而要准确知道每个学生或不同学力水平学生的学习困难并将相应举措融入教学设计中,还需要结合质性资料的分析。

感知·体验·理解——《周长》的教学片断与评析

本案例教学的是人教版义务教育课程标准实验教科书《数学》三年级上册第41页的内容：

关注概念本质 在操作体验中发展数学概念——以《周长的认识》教学为例

数学概念是数学知识的核心和数学思想方法的有效载体,正确理解和掌握概念是学生能力提升的保证。本文以《周长的认识》一课为例,从影响概念教学的因素和开展概念教学的策略两个方面入手,阐述教师如何开展概念教学。

“直观-开放、启智”教学法让难点不攻自破——《周长的认识》教学实录与评析

在教学比较抽象的知识时,采用＂直观—开放、启智＂教学法,合理运用直观的教学手段,将抽象的数学问题具体化、形象化,并通过开放式教学,开放、启发学生思维,往往能激发学生学习的积极性,使学生自主理解与建构知识,让教学难点不攻自破,达到事半功倍的效果。下面以《周长的认识》教学实录为案例进行分析。一、创设情境,引出课题师：同学们喜欢上体育课吗？体育课上常会有哪些比赛？生：……

多维度呈现 积累空间表象——《周长的认识》课堂教学实践及思考

在小学数学教学中，如何才能将抽象的数学问题具体化、形象化呢？笔者认为，教师要采用开放的课堂教学，多维度呈现，帮助学生积累空间表象，让学生自主理解和建构数学知识，达到对抽象概念的理解。现根据自己在《周长的认识》一课的教学实践谈几点粗浅的认识和思考。

Microstructure and tribological behavior of Mg-Gd-Zn-Zr alloy with LPSO structure

A Mg-14.28Gd-2.44Zn-0.54Zr （mass fraction, %） alloy was prepared by conventional ingot metallurgy （I/M）. The microstructure differences in as-cast and solution-treated alloys were investigated. Sliding tribological behaviors of the as-cast and solution-treated alloys were investigated under oil lubricant condition by pin-on-disc configuration. The wear loss and friction coefficients were measured at a load of 40 N and sliding speeds of 30-300 mm/s with a sliding distance of 5000 m at room temperature. The results show that the as-cast alloy is mainly composed ofα-Mg solid solution, the lamellar 14H-type long period stacking ordered （LPSO） structure within matrix, andβ-[（Mg,Zn）3Gd] phase. However, most of theβ-phase transforms to X-phase with 14H-type LPSO structure after solution heat treatment at 773 K for 35 h （T4）. The solution-treated alloy presents low wear-resistance, because the hard β-phase is converted into thermally-stable, ductile and soft X-Mg12GdZn phase with LPSO structure in the alloy.

Microstructure and mechanical properties of Mg_(94)Zn_2Y_4 extruded alloy with long-period stacking ordered structure

The microstructure and mechanical properties of Mg94Zn2Y4 extruded alloy containing long-period stacking ordered structures were systematically investigated by SEM and TEM analyses. The results show that the 18R-LPSO structure and α-Mg phase are observed in cast Mg94Zn2Y4 alloy. After extrusion, the LPSO structures are delaminated and Mg-slices with width of 50-200 nm are generated. By ageing at 498 K for 36 h, the ageing peak is attained andβ′phase is precipitated. Due to this novel precipitation, the microhardness ofα-Mg matrix increases apparently from HV108.9 to HV129.7. While the microhardness for LPSO structure is stabilized at about HV145. TEM observations and SAED patterns indicate that the β′ phase has unique orientation relationships betweenα-Mg and LPSO structures, the direction in the close-packed planes ofβ′precipitates perpendicular to that ofα-Mg and LPSO structures. The ultimate tensile strength for the peak-aged alloy achieves 410.7 MPa and the significant strength originates from the coexistence ofβ′precipitates and 18R-LPSO structures.

Microstructure evolution and mechanical properties of Mg-7Gd-3Y-1Nd-1Zn-0.5Zr alloy

X-ray diffraction （XRD）, optical microscopy （OM）, scanning electronic microscopy （SEM）, transmission electron microscopy （TEM） and tensile tests at room temperature （RT） were performed to investigate the effect of homogenization on microstructure evolution and mechanical properties of Mg-7Gd-3Y-1Nd-1Zn-0.5Zr （mass fraction,%） alloy. The results indicate that the microstructure of the as-cast alloy is composed of α-Mg, （Mg, Zn）3RE phase and stacking fault （SF）, the homogenization results in the disappearance of （Mg, Zn）3RE phase and stacking fault （SF） as well as the emergence of 14H-type long-period stacking ordered （LPSO） phase. The ultimate tensile strength （UTS）, yield strength （YS） and elongation of the as-cast alloy are 187 MPa, 143 MPa and 3.1%, and the UTS, YS and elongation of the as-homogenized alloy are 229 MPa, 132 MPa and 7.2%, respectively.

Immunohistochemical Analysis of IAA in Anthers of the Photoperiod-sensitive Genic Male-sterile Rice

The immunohistochemical localization of IAA and the comparison of their relative levels were carried out for the first time in the anthers of Nongken 58S and its wild type Nongken 58 (Oryza sativa subsp. japonica) after long_day and short_day treatments. The distribution of free_IAA in anthers and its dynamic variation could be reflected by this method. The results showed that the IAA level in the anthers of Nongken 58S after long_day treatment was much lower than that in short_day_treated Nongken 58S and those in wild type Nongken 58 in five stages from pistil and stamen primordia formation to late uninucleate stage. The possible reasons for IAA deficiency in Nongken 58S_LD anthers and its relationship with fertility alteration were also discussed.

Microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr alloys

The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5, there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg24（Er, Y, Zn）5 phase decreases, but the Mg12Zn（Y, Er） phase and lamellar phases continuously increase. When Zn content reaches 4% （normal mass fraction）, the Mg12Zn（Y, Er） phase mainly exists as large bulks, and some a-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mgl2Zn（Y, Er） and Mg24（Er, Y, Zn）5 phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.

Long-period stacking ordered structures in Mg-3Cu-1Mn-2Zn-1Y damping alloy

14H, 18R and 24R long-period stacking ordered （LPSO） structures were observed in the as-cast Mg-3Cu-1Mn-2Zn-1Y damping alloy using transmission electron microscopy （TEM）. These LPSO structures contained Mg, Y, Cu and Zn and thus they were quaternary phases. Sharp diffraction pattern of the 24R structure was obtained and the angle between and g10024R was measured to be 5.03°. During high resolution TEM observations, lattice fringes with two characteristic spacings were observed within the 24R structure. Based on the experimental results, 6H, 7H and three 8H are suggested as the building blocks of 18R, 14H and 24R structures, respectively. The 24R unit cell can be interpreted as the stacking of 8H building blocks in the same shear direction with a shear angle of about 5.03°. The imperfect 24R structures are in order or disorder arrangements of principal 8H and minor 6H blocks. This double-block structure model is also applicable to other reported defects in LPSO structures.

Pacing and predictors of performance during cross-country skiing races:A systematic review

Background： Cross-country skiing （XCS） racing, a popular international winter sport, is complex and challenging from physical, technical, and tactical perspectives. Despite the vast amount of research focusing on this sport, no review has yet addressed the pacing strategies of elite XCS racers or the factors that influence their performance. The aim was to review the scientific literature in an attempt to determine the effects of pacing strategy on the performance of elite XCS racers. Methods： Four electronic databases were searched using relevant subject headings and keywords. Only original research articles published in peerreviewed journals and the English language and addressing performance, biomechanics, physiology, and anthropometry of XCS racers were reviewed. Results： All 27 included articles applied correlative designs to study the effectiveness of different pacing strategies. None of the articles involved the use of an experimental design. Furthermore, potential changes in external conditions （e.g.,weather, ski properties） were not taken into consideration. A comparable number of studies focused on the skating or classical technique. In most cases, positive pacing was observed, with certain indications that higher-level athletes and those with more endurance and strength utilized a more even pacing strategy. The ability to achieve and maintain a long cycle length on all types of terrain was an important determinant of performance in all of the included studies, which was not the case for cycle rate. In general, uphill performance was closely related to overall race performance, with uphill performance being most closely correlated to the success of female skiers and performance on flat terrain being more important for male skiers. Moreover, pacing was coupled to the selection and distribution of technique during a race, with faster skiers employing more double poling and kick double poling, less diagonal stride, and more V2 （double dance） than V1 （single dance） skating across a race. Conclusion： We propose that skiers at all levels can improve their performance with more specific training in techniques （i.e., maintaining long cycles without compromising cycle rate and selecting appropriate techniques） in combination with training for endurance and more strength. Furthermore, we would advise less experienced skiers and/or those with lower levels of performance to apply a more even pacing strategy rather than a positive one （i.e., starting the race too fast）.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.

Smoc2 potentiates proliferation of hepatocellular carcinoma cells via promotion of cell cycle progression

AIM To determine the influence of Smoc2 on hepatocellular carcinoma(HCC) cell proliferation and to find a possible new therapeutic target for preventing HCC progression.METHODS We detected expression of Smoc2 in HCC tissues and corresponding non-tumor liver(CNL) tissues using PCR, western blot, and immunohistochemistry methods. Subsequently, we down-regulated and upregulated Smoc2 expression using siR NA and lentivirus transfection assay, respectively. Then, we identified the effect of Smoc2 on cell proliferation and cell cycle using CCK-8 and flow cytometry, respectively. The common cell growth signaling influenced by Smoc2 was detected by western blot assay. RESULTS The expression of Smoc2 was significantly higher in HCC tissues compared with CNL tissues. Overexpression of Smoc2 promoted HCC cell proliferation and cell cycle progression. Down-regulation of Smoc2 led to inhibition of cell proliferation and cell cycle progression. Smoc2 had positive effect on ERK and AKT signaling.CONCLUSION Smoc2 promotes the proliferation of HCC cells through accelerating cell cycle progression and might act as an anti-cancer therapeutic target in the future.

Effect of Zn addition on microstructure and mechanical properties of cast Mg-Gd-Y-Zr alloys

The effects of Zn addition on the microstructure and mechanical properties of Mg.10Gd.3Y.0.6Zr(wt.%)alloys in the as-cast,solution-treated,and peak-aged conditions were investigated.Experimental results reveal that the microstructure of the as-cast alloy without Zn consists ofα-Mg and Mg24(Gd,Y)5 phases,and the alloy with 0.5 wt.%Zn consists ofα-Mg,(Mg,Zn)3(Gd,Y)and Mg24(Gd,Y,Zn)5 phases.With the addition of Zn increasing to 1 wt.%,the Mg24(Gd,Y,Zn)5 phase disappears and some needle-like stacking faults distribute along the grain boundaries.Moreover,the 18R long-period stacking ordered(LPSO)phase is observed in the as-cast alloy with 2 wt.%Zn.After solution treatment,the Mg24(Gd,Y)5 and Mg24(Gd,Y,Zn)5 eutectic phases are completely dissolved,and the(Mg,Zn)3(Gd,Y)phase,needle-like stacking faults and 18R LPSO phase all transform into 14H LPSO phase.Both the suitable volume fraction of 14H LPSO phases and the fine ellipsoidal-shapedβ′phases make the peak-aged alloy with 0.5 wt.%Zn exhibit excellent comprehensive mechanical properties and the UTS,YS and elongation are 338 MPa,201 MPa and 6.8%,respectively.

Correlation between growth differentiation factor-15 and collagen metabolism indicators in patients with myocardial infarction and heart failure

BackgroundGrowth differentiation factor （GDF）-15, a divergent member of the transforming growth factor beta super-family does appear to be up-regulated in response to experimental pressure overload and progression of heart failure （HF）. HF frequently develops after myocardial infarction （MI）, contributing to worse outcome. The aim of this study is to assess the correlation between GDF-15 levels and markers related to collagen turnover in different stages of HF.MethodsThe study consists of a cohort of 179 patients, including stable angina pectoris patients （AP group,n= 50）, old MI patients without HF （OMI group,n = 56）, old MI patients with HF （OMI-HF group,n= 38） and normal Control group （n = 35）. Both indicators reflecting the synthesis and degradation rates of collagen including precollagen I N-terminal peptide （PINP）, type I collagen carboxy-terminal peptide （ICTP）, precollagen III N-terminal peptide （PIIINP） and GDF-15 were measured using an enzyme-linked inmunosorbent assay.ResultsThe plasma GDF-15 level was higher in OMI-HF group （1373.4 ± 275.4 ng/L） than OMI group （1036.1 ± 248.6 ng/L）, AP group （784.6 ± 222.4 ng/L） and Control group （483.8 ± 186.4 ng/L） （P〈 0.001）. The indi-cators of collagen turnover （ICTP, PINP, PIIINP） all increased in the OMI-HF group compared with Control group （3.03 ± 1.02μg/Lvs. 2.08 ± 0.95μg/L, 22.2 ± 6.6μg/Lvs. 16.7 ± 5.1μg/L and 13.2 ± 7.9μg/Lvs. 6.4 ± 2.1μg/L, respectively;P〈 0.01）. GDF-15 positively cor-related with ICTP and PIIINP （r = 0.302,P〈 0.001 andr= 0.206,P= 0.006, respectively）. GDF-15 positively correlated to the echocardio-graphic diastolic indicators E/Em and left atrial pressure （r= 0.349 and r= 0.358, respectively;P〈 0.01）, and inversely correlated to the systolic indicators left ventricular ejection fraction and the average of peak systolic myocardial velocities （Sm） （r=-0.623 and r=-0.365, respectively;P〈 0.01）.ConclusionPlasma GDF-15 is associated with the indicators of type I and III collagen turnover.

3-restricted connectivity of graphs with given girth

Let G = （V, E） be a connected graph. X belong to V（G） is a vertex set. X is a 3-restricted cut of G, if G- X is not connected and every component of G- X has at least three vertices. The 3-restricted connectivity κ3（G） （in short κ3） of G is the cardinality of a minimum 3-restricted cut of G. X is called κ3-cut, if ｜X｜ = κ3. A graph G is κ3-connected, if a 3-restricted cut exists. Let G be a graph girth g ≥ 4, κ3（G） is min{d（x） ＋ d（y） ＋ d（z） - 4 ： xyz is a 2-path of G}. It will be shown that κ3（G） = ξ3（G） under the condition of girth.

Analysis of the characteristics of gravity waves during a local rainstorm event in Foshan,China

A detailed analysis of the dynamic frequency spectrum characteristics of gravity waves(GWs)during a local heavy rainfall event on 20–21 November 2016 in Foshan,China,is presented.The results of this analysis,which was based on high-precision microbarograph data,indicate that GWs played a key role in generating the rainstorm.The GWs experienced two intermittent periods of amplitude enhancement and period widening.The largest amplitudes of the GWs were 80–160 Pa,with a corresponding period range of 140–270 min,which were approximately 4 h ahead of the rainstorm.The severe storms appeared to affect the GWs by augmenting the wave amplitudes with center amplitudes of approximately 80–100 Pa and periods ranging between 210 and 270 min;in particular,the amplitudes increased to approximately 10 Pa for GWs with shorter periods(less than 36 min).The pre-existing large-amplitude GWs may be precursors to severe storms;that is,these GWs occurred approximately 4 h earlier than the time radars and satellites identified convections.Thus,these results indicate that large-amplitude GWs constitute a possible mechanism for severe-storm warning.

Microstructure evolution during heat treatment of Mg-Gd-Y-Zn-Zr alloy and its low-cycle fatigue behavior at 573K

In as-cast Mg?2.1Gd?1.1Y?0.82Zn?0.11Zr(mole fraction,%)alloy,lamellar microstructures that extend from grain boundaries to the interior ofα-Mg grains are identified as clusters ofγ′using a scanning transmission electron microscope equipped with a high-angle annular dark-field detector.Under a total strain-controlled low-cyclic loading at573K,the mechanical response and failure mechanism of Mg?2.1Gd?1.1Y?0.82Zn?0.11Zr alloy(T6peak-aging heat treatment)were investigated.Results show that the alloy exhibits cyclic softening response at diverse total strain amplitudes and573K.The experimental observations using scanning electron microscopy show that the micro-cracks initiate preferentially at the interface between long-period stacking order structures andα-Mg matrix and extend along the basal plane ofα-Mg.The massive long-period stacking order structures distributed at grain boundaries impede the transgranular propagation of cracks.