Intersubband resonance polarons in Al/δ-GaAs tunneling junctions

Tunneling spectra of the A1/δ-GaAs junctions fabricated by molecular-beam epitaxy in the regime of “intimate” contact of A1 with GaAs (100) were studied at 1.6 K in a magnetic field B parallel to the two-dimensional electron-gas layer. The concentration of 2D electrons in the δ-layer grown at a distance of 20 nm from the A1/GaAs interface was 1.1 × 10¹² cm^?2 and corresponded to a partial filling of only the lowest subband E ₀. The tunneling spectra exhibited many-particle features, viz., a zero-bias anomaly, lines of longitudinal optical (LO) phonons, and characteristic “dips” corresponding to the energies E _i of the 2D subbands. In the B fields below the critical value B _c ?11 T, the levels of 2D subbands underwent the usual diamagnetic shifts. At B≥B _c , the E ₁ (B) term pinning and the anticrossing of the E ₁(B) and E ₀(B)+2?ω_LO terms were observed, where ?ω_LO is the LO-phonon energy in GaAs. The observed effects are interpreted as manifestations of resonance intersubband polarons arising in the δ-layer upon reaching the E ₁(B _c )?E ₀(B _c )=2?ω_LO resonance.     

Ba(n,x)134Cs,134Ba(n,2n)133Ba,140Ce(n,2n)139Ce,142Ce(n,2n)141)Ce和23Na(n,2n)22Na反应截面的测量

用中子活化法相对于⁵⁴Fe(n,P)⁵⁴Mn反应,在13.50—14.80MeV中子能区测量了Ba(n,x)¹³⁴Cs,¹³⁴Ba(n,2n)¹³³Ba,¹⁴⁰Ce(n,2n)¹³⁹Ce,¹⁴²Ce(n,2n)¹⁴¹Ce和²³Na(n,2n)²²Na的反应截面.并将所测的结果和其他作者的结果进行了比较,中子能量是用⁹⁰Zr(n,2n)^89m+gZr反应和⁹³Nb(n,2n)^92mNb反应截面比法测定的.     

Cesium adsorption on the β2-GaAs(001) surface

The results of first-principles calculations of the cesium adsorption energy on the β2-GaAs(001) surface performed within approaches of the density functional theory are presented for two possible terminations of the surface. It is shown that, among the considered high-symmetry positions, the energy-preferred position for cesium is position T ₃ when the surface layer contains arsenic and position T ₄ for gallium terminated surface. Cesium introduces insignificant perturbations in the positions of surface-layer atoms, and surface dimers do not break even in the case of adsorption at the dimer bridge and top positions. It is shown that cesium bonding to the GaAs (001) substrate can be explained by sp hybridization of arsenic and gallium orbitals as well as by formation of cesium states mixed with delocalized states of a clean surface. At low coverage, more preferable adsorbate sites are those with nearest neighbor arsenic atoms for both surface terminations.     

应把n/4与n/6的矛盾和解释写进教材

现行高校热学教材中的分子物理学部分,都明显地存在一个问题——“1/4 n(?)与“1/6 n(?)”的矛盾。每当讲到这部分内容时,学生总是质疑,争论不休,教材中存在着明显的矛盾,但教师在讲课时又不能迥避这个问题,与其让老师各自分别写补充材料解答,不如把对这一矛盾的统一解释明确地写入再版的热学教材里。现在笔者把对这一问题的认识写出来与各位同仁商榷。以求得认识的统一。 在讲气体分子速率分布律时,我们曾根据麦克斯韦速度分布律,准确地推算出单位时间内碰到单位面积器壁(即基准面 dA)上的气体分子数为n(?)/4=0个(这一结果一般作为公式来应用。有的教材则把这一结果作为一道练习题来处理,但在作完题之后,仍把     

107Ag(n,2n)106mAg反应截面测量

本文报告了E_n=13.50—14.73MeV中子能区用活化法以²⁷Al(n,2)²⁴Na截面为中子注量标准得的¹⁰⁷Ag(n,2n)^106mAg的反应截面.在E_n=13.50,13.60,13.90,14.10,14.35,和14.73MeV处的截面分别为469±22,480±22,503±24,538±25,555±25和572±26mb.在文中还列举了一些国外已发表的截面数据以作比较.中子能量用铌锆活度比法测定.     

88Y(n,2n)反应截面研究

本工作用相同复合系统的核反应替代法获得了入射中子能量在10.3MeV到17.4MeV区间不稳定靶核⁸⁸Y(n,2n)核反应截面,并把该结果同我们的理论计算结果及Prestwood等人的实验和理论计算结果进行了比较,比较结果表明这种替代测量法值得研究.     

87Sr(n, n′)87mSr非弹散射

本文测量了满壳缺一个中子的⁸⁷Sr(n, n′)^87mSr, E_n<2 MeV的非弹散射截面值, 把原有的激发曲线延伸到了低能部分, 构成了一条完整的激发曲线.     

50,40,46的(n,p)(n,α)和58Ni的(n,2n)(n,p)反应截面的测量

本文叙述了从13.50MeV到14.81MeV中子能区用活化法相对²⁷Al(n,α²⁴Na的反应截面,对⁵⁰Ti(n,α)⁴⁷Ca、⁴⁸Ti(n,p)⁴⁸Sc、⁴⁶Ti(n,p)⁴⁶Sc、⁵⁸Ni(n,2n)⁵⁷Ni、⁵⁸Ni(n,p)^58m+gCo五个反应截面的测量.并将所得的结果和其他作者的结果进行了比较.     

160Gd(n,2n)159Gd和158Gd(n,p)158Eu反应截面测量

报道了在13.5—14.6MeV中子能区用活化法测得的¹⁶⁰Gd(n,2n)¹⁵⁹Gd和¹⁵⁸Gd(n,p)¹⁵⁸Eu的 反应截面值. 中子注量用⁹³Nb(n, 2n)⁹²m Nb反应截面得到. 由(13.5±0.2)MeV,(14.1±0.1)MeV和(14.6±0.2)MeV中子引起的¹⁶⁰Gd(n, 2n) ¹⁵⁹Gd反应截面值分别为(1940±83)mb, (2324±92)mb和(1983±77)mb, ¹⁵⁸Gd(n, p) ¹⁵⁸Eu反应截面值分别为(1.9±0.1)mb, (2.1±0.1)mb和(3.5±0.1)mb. 单能中子由T(d, n)⁴He反应获得.文中还列举了已收集到的数据以作比较.     

Existence theorems for π/n vortex scattering

The analysis of 90° vortex-vortex scattering is extended to /n scattering in all head-on collisions ofn vortices in the Abelian Higgs model. A Cauchy problem with initial data that describe the scattering ofn vortices is formulated. It is shown that this Cauchy problem has a unique global finite-energy solution. The symmetry of the solution and the form of the local analytic solution then show that /n scattering is realized.     

59Co(n,p)59Fe,59Co(n,α)56Mn,59Co(n,2n)58Co反应截面的测量

本实验用活化法测量了中子能量在12.8MeV到17.8MeV的⁵⁹Co(n,p)⁵⁹Fe,⁵⁹Co(n,α)⁵⁶Mn,⁵⁹Co(n,2n)⁵⁸Co三个反应道的反应截面值,实验的测量误差在3.3%—6.9%范围内.     

100Mo(n2n)99Mo,96Mo(n,p)96Nb和92Mo(n,α)89m+gZr反应截面测量

本文报告了在E_n=13.40—14.79MeV中子能区用活化法以²⁷Al(n,α)²⁴Na截面为中子注量标准测行的¹⁰⁰Mo(n2n)⁹⁹Mo,⁹⁶Mo(n,p)⁹⁶Nb和⁹²Mo(n,α)^89m+gZr的反应截面,中子能量是用铌锆截面比法测定的.文中将实验测量值与理论计算值进行了比较,还对上述三个反应的截面进行了编评,给出了推荐的激发曲线.     

1/4n和1/6等几率假设

一般在普通物理教学中,讨论气体的迁移现象时,都假定分子向各方向运动的机会均等,因而向前、后、左、右、上、下运动的分子各占总数的1/6,得到单位时间内碰撞单位壁面的分子数为1/6n,推导出粘滞系数η=1/3ρ. 李椿等编的《热学》一书中,在第三章讨论麦克斯韦速度分布律后,有一个计算分子碰壁数的例题,给出结果为了1/4nv.而在第四章中又用1/6nv来研究输运过程,有些学生提出“既然已精确地计算出碰壁数为了1/4nv,为什么还用古。否来研究迁移现象”?认为今的等几率假设太粗糙,提出了怀疑.虽然可以指明了。否是限定为垂面运动的分子,二n否则包含…     

14MeV中子引起的185Re(n,2n)184g,mRe和191Ir(n,2n)190Ir的核反应截面测量

利用活化方法测量了1?4MeV中子引起的¹⁸⁵Re(n,2n)^184gRe,¹⁸⁵Re(n,2n)^184mRe和¹⁹¹Ir(n,2n)¹⁹⁰Ir核反应的截面.中子能量E_n=(14.7±0.2)MeV时的实验结果分别为:(1817±85)mb,(390±18)mb和(2038±82)mb.并利用HFTT程序计算了中子能量在7—18MeV范围内的截面值,给出了其中两个核反应的激发函数曲线.     

THE CROSS-SECTION MEASUREMENTS FOR 59Co(n,p)59Fe,59Co(n,α)56Mn AND 59Co(n,2n)58Co REACTIONS

The cross sections of ⁵⁹Co(n,p)⁵⁹Fe,⁵⁹Co(n,α)⁵⁶Mn AND ⁵⁹Co(n,2n)⁵⁸Co reactions have been measured at neutron energy region of 12.8MeV—17.8MeV by activation method.The coveriance matrix of measured errors was calculated,and the comparison between the values of measured and calculated using theory model was made.The evaluated excitation functions for the three reactions are given.     

n维固体带间光学性质与振子模型 n/2次积分关系

本文证明,n维固体临界点附近的带间介电函数及其微分谱可用n/2次积分分别从振子的介电函数及其微分谱求出。n维固体带间光谱中的振子物理特征通过n/2次积分算符的作用表现出来。文中讨论了带间跃迁与振子模型,光学性质与维度性之间的物理联系。在固体带间光谱的分数次积分表达式中,维度n可以推广到分数维数。 关键词：     

58Ni(n,p),60Ni(n,p),62Ni(n,α)和54Fe(n,p)反应截面的测量与评价

本实验用活化法测量了中子能量在13.60MeV—17.77MeV的⁵⁸Ni(n,p)^58m+gCo,⁶⁰Ni(n,p)⁶⁰Co和⁶²Ni(n,α)⁵⁹Fe三个反应道的反应截面值,并计算了反应截面测量误差的协方差矩阵.实验的测量误差在3%—7%范围内.     

The Cross Section Measurement for the Reactions of 48,46Ti(n,p) 48,46Sc 50Ti(n,α) 47Ca and 58Ni (n,2n) 57Ni 58Ni(n,p)58m+gCo

The cross sections for the ⁵⁰Ti(n,α)⁴⁷Ca,⁴⁶Ti(n,p)⁴⁶Sc、⁴⁸Ti(n,p)⁴⁸Sc and ⁵⁸Ni(n,2n)⁵⁷Ni ⁵⁸Ni(n,p)^58m+gCo reactions have been measured by using the activation method relative to the cross sections of the ²⁷Al(n,α)²⁴Na reaction in the neutron energy range of 13.50—14.81MeV.The neutron energies were determined by the cross section ratios of the ⁹⁰Zr(n,2N) ^89m+gZr and ⁹³Nb (n,2n) ^92mNb reactions.The results obtained are compared with the published and to be published data of several authors.     

The Cross Section Measurements for the 100Mo(n2n)99Mo,96Mo(n,p)96Nb and 92Mo(n,α)89m+gZr Reactions

The cross sections for ¹⁰⁰Mo(n2n)⁹⁹Mo,⁹⁶Mo(n,p)⁹⁶Nb and ⁹²Mo(n,α)^89m+gZr have been measured by using the activation method relative to the cross sections of ²⁷Al(n,α)²⁴Na in the neutron energy range 13.40—14.79MeV.The comparison between the values of measured and calculated using theory mode was made.The evaluated excition functions for the three reactions are given.     

The Cross-Section Measurements and Evaluations for 58Ni(n,p),60Ni(n,p),62Ni(n,α) and 54Fe(n,p) Reactions

Activation techniques have been used to measure the cross-section for ⁵⁸Ni(n,p),⁶⁰Ni(n,p) and ⁶²Ni(n,α) reactions in the neutron energy range 13.6—17.8MeV.The uncertainty of measured data has been aculated from 3%—7%.The covariance matrixes for measurement error are calculated.Evaluations for ⁵⁸Ni(n,p),⁶⁰Ni(n,p),⁶²Ni(n,α) and ⁵⁴Fe(n,p) crpss-section are made.