2008年天津高考物理试题评析

2008年天津高考是天津市自2004年以来自主命题后的第五年高考,也是天津在高中实施新课程改革之前应用原教材教学的最后一次高考,本次高考物理试题符合<教育部考试中心普通高等学校招生全国统一考试大纲>和天津市教育招生考试院<天津卷考试说明>的要求;沿用了全国统一高考物理试卷的模式,试卷结构稳定,突出了对主干知识和能力考查;知识覆盖面广,基础知识,重点、难点知识考核突出,具有较好区分度,本次试题尤其注重了对中学教学的正面导向作用,得到了广大物理教师的认可.     

Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2

We have performed low temperature resistivity p（T） and specific heat C（T） measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is -4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat γn=4.51 mJmol^-1K^2 and the Debye temperature θD=419 K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/γnTc = 2.84 exp（-1.21Tc/T）. This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.     

非中心对称超导体Mg10±δIr19B16?δ的超导电性研究

Mg_10±δIr₁₉B_16δ是具有非中心对称性的超导材料. 通过对两种组分的样品Mg_9.3Ir₁₉B_16.7和Mg₁₁Ir₁₉B₁₅的比热测量, 得到了这类超导体的超导态和正常态的特征参数：包括转变温度T_C, 正常态态密度N(E_F), 德拜温度Θ_D, 上临界场H_C2等. 并由此求出Ginzburg-London相干长度ξ_GL, 穿透深度λ_GL, 下临界场H_C1和热力学临界场H_C. 这些参数因化学组分不同而变化. 高的N(E_F)和Θ_D对应高的T_C, 因此也具有较高的H_C2. 另外比热跃变ΔC/γ_nT_C=1.66 和电声子耦合常数λ=0.58不随化学组分变化, 表明此超导体是中等强度耦合的第二类超导体. 关键词： 非中心对称超导体 比热     

INFLUENCE OF RELATIVE DENSITY AND PARTICLE SIZE ON THE SPECIFIC HEAT OF NANOCRYSTALLINE IRON

The specific heats of two nanocrystalline iron samples with different structures have been measured in the temperature range from 2 to 26 K. Experimental results show that the specific heat of nanocrystalline iron samples exhibits abnormal characteristic compared with that of standard bulk iron. The contributions of quantum size effect, surface mode and Einstein mode have been observed in the measurement. Through analyses, it is discovered that the relative density and particle size have a great influence on specific heat of nanocrystalline iron at low temperature.     

Anisotropy Properties of Mn_2P Single Crystals with Antiferromagnetic Transition

Single crystals of hexagonal structure Mn₂P are synthesized by Sn flux for the first time. Transport and magnetic properties have been performed on the single crystals, which is an antiferromagnet with Neel temperature 103 K.Obvious anisotropy of resistivity is observed below the Neel temperature, which is manifested by metallic behavior with a current along the C-axis and semiconducting behavior with a current along the α-axis. The negative slope of temperature-dependent resistivity ...     

Generation of UV radiation at 335.5 nm based on frequency-quadrupling of a diode-pumped Nd:YVO4 laser

The generation of ultraviolet （UV） light at 335.5 nm based on frequency quadrupling of a diode-end- pumped Q-switched Nd：YVO4 laser at 1342 nm was demonstrated. KTP crystal was used for generation of wavelength of 671 nm by intracavity doubling and LBO （BBO） crystal was exploited for the subsequent external fourth harmonic generation （FHG）. With 6.3-W absorbed pump power and 10-kHz frequency repetition rate, the UV output power of 35 and 63 mW were obtained by using LBO and BBO as frequency quadrupling nonlinear crystals, respectively. The experimental results show that the conversion efficiency （red-UV） of 6.4% for BBO crystal is higher than that of 3.5% for LBO crystal, but the UV beam quality obtained by LBO crystal is better than by BBO crystal.     

Lasiodonin Acetonide的NMR数据解析

对lasiodonin acetonide进行了¹H和¹³C NMR检测,参考lasiodonin, maoecrystal T, wikstroemioidin B和rabdocoetsin A的¹H、¹³C NMR数据,通过DEPT和¹H-¹H COSY、HSQC、HMBC等2D NMR技术对该化合物所有的¹H和¹³C NMR信号进行了全归属和详细解析.     

“变与不变”的思想方法在小学数学中的渗透

数学思想方法是基于具体数学内容,又高于具体数学内容的一种指导思想和普遍适用的方法.数学思想方法从数学知识产生发展的过程抽象而成,又更具效率地指导数学的学习与研究,并促成个体思维品质的提升,对人生的成长与发展都具有重要意义.数学思想方法应及早渗透于小学生的数学学习过程中,在具体数学知识点的学习中,凝练重要的数学思想方法,化隐为显,让学生去感悟,以提升学生的数学素养.本文以“变与不变”这一思想方法为例,在比例法、奇偶分析、列方程解题等知识方法学习中,去感悟与运用这一数学思想方法,提升解题能力与思维品质.     

磁场对重电子金属材料CeCu6-xCdx电阻的影响

介绍了重电子金属CeCu6-x_6-xCdx_x（x=010，015，020，0 30，050）在18—300K温度范围内,在磁场(μ0₀H=0，5，10T)下电阻 随温度的变化规律 及低温（19 ，15K）下的磁电阻（μ0₀H=0—10T）.实验表明所有样品在 零场下的Tmax_max（对应于电阻极大值的温度）都低于18K.加磁场后，Tmax _max随磁场和掺杂量 关键词： 重电子系统 低温电阻 近藤散射 相干散射     

Polymer White-Light-Emitting Diodes with High Work Function Cathode Based on a Novel Phosphorescent Chelating Copolymer

Polymer white-light-emitting diodes are fabricated based on the blend of poly[9,9-di-（2-ethylhexyl）-fluorenyl-2, 7- diyl]-end capped with polysilsesquioxane （PFO） and a chelating copolymer of poly[（9,9-bis（3′-（N,N-dimethylamino） propyl）-2, 7-fluorene-alt-2, 7-（9,9-dioctylfluorene） ）-co- [2, 7-（9,9-dioctlyfluorene）-alt-5,5-bis（2-（4-methyl-l-naphtha- lene） pyridine-C^2,N） iridium （III） acethylacetonate]] （PFN-NaIr）. The device with the sole aluminium cathode is able to produce a comparably white electroluminescence efficiency of 1.31 cd/A to that of the device using low work function cathodes （such as Ba, Ca, etc.）. The CIE coordinates of the white light emission consisting of red, green and blue three components are nearly at （0.34, 0.35）. The mechanism of the white light emission from the device with the AI cathode is investigated, which is related to the efficient injection of electrons through the interface of PFN-Nalr/AI.