模型图法在数学教学中的应用

新加坡学生在TIMSS中屡次表现突出.引起了不同国家教育工作者对新加坡数学教育的极大关注.问题解决一直是新加坡数学课程的核心,考虑到问题解决的重要作用,新加坡数学大纲建议,为中小学学生列出问题解决策略来帮助他们解决问题.在所有的策略中,模型图法是最为突出的策略.且看小学里的一个运用模型图法解应用题的例子.如图1,一把尺子和两支铅笔共需1.40元,一把尺子花费要比一支铅笔多20分,那么一把尺子花费     

Spatial Characteristics of Thomson Scattering Spectra in Laser and Magnetic Fields

Spatial characteristics of Thomson scattering spectra are studied for an electron moving in the circularly polarized laser field in the presence of a strong uniform magnetic field. The results show that the angular distributions of the spectra with respect to the azimuthal and polar angles exhibit different symmetries, respectively, which depend on the fields and electron parameters sensitively and significantly. Moreover, for relatively large parameters such as high laser intensity, high magnetic resonance parameter as well as large initial momentum of electron, the two lobes in spectra tend to the laser-propagating direction so that the radiation can be collimated in the forward direction. Furthermore, an important finding is that by choosing the appropriate fields and initial momentum of electron, the high frequency part of the Thomson scattering spectra can reach the frequency range of soft x-ray,in which a high radiation power per solid angle as ～10~(11) a.u. can be obtained.     

单克隆抗体依那西普融合蛋白的活性结构保护

采用拉伸模拟和伞状采样的方法, 利用Gromacs软件和Amber99sb-ildn分子力场研究了不同浓度的海藻糖体系和海藻糖-甘露醇复合体系中单克隆依那西普融合蛋白二聚体的解离过程. 结果表明, 海藻糖能显著增强依那西普二聚体活性结构的稳定性, 且海藻糖-甘露醇的复合保护优于海藻糖的单一保护; 保护剂的种类及其选择性吸附保护的特定位置对依那西普蛋白二聚体活性结构保护效果的影响显著.     

Modified Bubble Core Fields and Bubble Shape in Laser Driven Plasma

Bubble core fields as well bubble shape modification due to the nondepleted electrons inside the bubble is investigated theoretically. It is found that the slope of transverse fields are reduced significantly, however, the slope of longitudinal electric field, which plays a key role on electrons acceleration in bubble, changes little. Moreover a modified longitudinal compressed bubble shape leads to a shorter dephasing distance which makes the electrons acceleration energy reduced to some extent. As a comparison we perform particle-in-cell simulations whose results are consistent with that of our theoretical consideration.     

Generation of high quality ion beams through the stable radiation pressure acceleration of the near critical density target

In order to generate high quality ion beams through the stable radiation pressure acceleration(RPA) of the near critical density(NCD) target, we propose a new type of target where an ultra-thin high density(HD) layer is attached to the front surface of an NCD target, which has a preferable self-supporting property in the RPA experiments than the ultra-thin foil target. It is found that in one-dimensional particle-in-cell(PIC) simulation, by the block of the HD layer in the new target,there emerges the hole-boring process rather than propagation in the NCD layer when the intense laser pulse impinges on this target. As a result, a typical RPA structure that the compressed electron layer overlaps the ion layer as a whole is formed and a high quality ion beam is obtained, e.g., a circularly polarized laser pulse with normalized amplitude a_0= 120 impinges on this new target and a 1.2 GeV monoenergetic ion beam is generated through the RPA of the NCD layer. Similar results are also found in the two-dimensional PIC simulation.     

Enhancement of electron-positron pairs in combined potential wells with linear chirp frequency

Effect of linear chirp frequency on the process of electron-positron pairs production from vacuum is investigated by the computational quantum field theory. With appropriate chirp parameters, the number of electrons created under combined potential wells can be increased by two or three times. In the low frequency region, frequency modulation excites interference effect and multiphoton processes, which promotes the generation of electron-positron pairs. In the high frequency region, high frequency suppression inhibits the generation of electron-positron pairs. In addition, for a single potential well, the number of created electron-positron pairs can be enhanced by several orders of magnitude in the low frequency region.     

Ultrabright γ-ray emission from the interaction of an intense laser pulse with a near-critical-density plasma

An efficient scheme for generating ultrabright γ-rays from the interaction of an intense laser pulse with a near-critical-density plasma is studied by using the two-dimensional particle-in-cell simulation including quantum electrodynamic effects. We investigate the effects of target shape on γ-ray generation efficiency using three configurations of the solid foils attached behind the near-critical-density plasma: a flat foil without a channel (target 1), a flat foil with a channel (target 2), and a convex foil with a channel (target 3). When an intense laser propagates in a near-critical-density plasma, a large number of electrons are trapped and accelerated to GeV energy, and emit γ-rays via nonlinear betatron oscillation in the first stage. In the second stage, the accelerated electrons collide with the laser pulse reflected from the foil and emit high-energy, high-density γ-rays via nonlinear Compton scattering. The simulation results show that compared with the other two targets, target 3 affords better focusing of the laser field and electrons, which decreases the divergence angle of γ-photons. Consequently, denser and brighter γ-rays are emitted when target 3 is used. Specifically, a dense γ-ray pulse with a peak brightness of 4.6×10²⁶ photons/s/mm²/mrad²/0.1%BW (at 100 MeV) and 1.8×10²³ photons/s/mm²/mrad²/0.1%BW (at 2 GeV) are obtained at a laser intensity of 8.5×10²² W/cm² when the plasma density is equal to the critical plasma density n_c. In addition, for target 3, the effects of plasma channel length, foil curvature radius, laser polarization, and laser intensity on the γ-ray emission are discussed, and optimal values based on a series of simulations are proposed.     

4-芳亚甲基-2-羟基-3-蒎酮类化合物的合成及其紫外吸收特征研究

以(-)-α-蒎烯为原料合成了系列新型4-芳亚甲基-2-羟基-3-蒎酮类化合物.(-)-α-蒎烯经选择性氧化得到(+)-2-羟基-3-蒎酮;在碱催化作用下,(+)-2-羟基-3-蒎酮与苯甲醛、对甲基苯甲醛、对甲氧基苯甲醛、对羟基苯甲醛、对氯苯甲醛、对硝基苯甲醛和糠醛等芳香醛缩合,得到系列光学活性4-芳亚甲基-2-羟基-3-蒎酮类化合物a～g.采用1H NMR,13C NMR,GC-MS和FT-IR等分析手段对合成所得4-芳亚甲基-2-羟基-3-蒎酮类化合物的结构进行了表征,考察了它们的紫外吸收特性及光稳定性.结果表明,化合物a,b,e对UVB具有良好的吸收性能;而化合物c,d,f,g兼具长波紫外线(UVA)和中波紫外线(UVB)的吸收性能.化合物a～g的光稳定性顺序为d>c>e>f>b>a>g.     

新一代SiC功率MOSFET器件研究进展

自2017年报道SiC(碳化硅)功率金属-氧化物半导体场效应晶体管(MOSFET)技术进展以来,针对器件比导通电阻(RON,SP)高等问题不断优化器件结构设计,本课题组改进关键加工工艺,使1200 V SiC MOSFET的RON,SP从8 mΩ·cm2降低到4.8 mΩ·cm2.与此同时,本课题组采用新一代SiC MOSFET设计和工艺技术研制出6.5 kV、10 kV以及15 kV等高压低导通电阻SiC MOSFET,其中10 kV和15 kV器件的比导通电阻分别为144 mΩ·cm2和204 mΩ·cm2,接近单极型SiC器件的理论极限.     

Ga2O3/GaN/蓝宝石模板上β-Ga2O3薄膜的生长

为获得高质量的β-Ga2O3薄膜,将c面蓝宝石上生长的GaN薄膜进行高温氧化制成了Ga2O3/GaN/蓝宝石模板,进而在模板上利用金属有机化学气相沉积(MOCVD)工艺进行了β-Ga2O3薄膜的同质外延。通过X射线衍射仪、原子力显微镜、场发射扫描电子显微镜等方法对样品的晶体结构、表面形貌等性质进行测试与分析。结果表明,该方法获得的β-Ga2O3薄膜晶体质量受GaN薄膜氧化效果与MOCVD工艺条件等因素影响较大。通过优化实验条件,得到了质量较高的β-Ga2O3薄膜。与蓝宝石上或GaN薄膜上异质外延得到的β-Ga2O3薄膜相比,薄膜的晶体质量明显提高。通过对比不同样品的晶体质量、表面形貌和制备过程,发现该方法成功地将β-Ga2O3薄膜在蓝宝石衬底或GaN/蓝宝石模板上异质外延转化为了Ga2O3/GaN/蓝宝石模板上的同质外延,有效地减小了β-Ga2O3薄膜和蓝宝石、GaN之间较大的晶格失配和热失配,有利于提高β-Ga2O3薄膜的晶体质量。