Graphene on Ru(0001): a 25 x 25 supercell

The structure of a single layer of graphene on Ru(0001) has been studied using surface x-ray diffraction. A surprising superstructure containing 1250 carbon atoms has been determined, whereby 25 x 25 graphene unit cells lie on 23 x 23 unit cells of Ru. Each supercell contains 2 x 2 crystallographically inequivalent subcells caused by corrugation. Strong intensity oscillations in the superstructure rods demonstrate that the Ru substrate is also significantly corrugated down to several monolayers and that the bonding between graphene and Ru is strong and cannot be caused by van der Waals bonds. Charge transfer from the Ru substrate to the graphene expands and weakens the C-C bonds, which helps accommodate the in-plane tensile stress. The elucidation of this superstructure provides important information in the potential application of graphene as a template for nanocluster arrays.     

(BN)25团簇的结构与性能

采用密度泛函理论的杂化密度泛函（B3LYP）方法,在6-31G （d）基组水平上,对（BN）₂₅团簇进行结构优化和频率计算,得到基态构型,并对其稳定性、自然键轨道（NBO）、振动光谱和NICS进行计算.结果表明：（BN）₂₅团簇的能隙值较高,具有良好的化学稳定性;B原子和N原子的内部及原子之间都会发生s、p轨道杂化,原子之间有少量电荷转移;（BN）₂₅团簇的红外光谱和拉曼光谱都有较多振动峰;（BN）₂₅团簇具有芳香性.     

Solid-state 25Mg QCPMG NMR of bis(cyclopentadienyl)magnesium

Application of the "quadrupolar Carr-Purcell Meiboom-Gill" (QCPMG) sequence permits the first natural abundance solid-state 25Mg NMR study of an organometallic magnesium compound, bis(cyclopentadienyl)magnesium. Analytical and numerical simulations of both static and magic-angle spinning QCPMG NMR spectra beget an axially symmetric 25Mg electric field gradient (EFG) tensor (quadrupolar asymmetry parameter, eta(Q)=0.01(1)) with a nuclear quadrupole coupling constant of C(Q)=5.80(5)MHz. Restricted Hartree-Fock and hybrid density functional theory (B3LYP) calculations are in good agreement with experimental EFG values and predict a chemical shielding anisotropy of about 40-50 ppm, which we attempt to elucidate by numerical simulations. The parameters and orientation of the 25Mg EFG tensor are rationalized from examination of the crystal structure and molecular symmetry. The NMR properties of the cyclopentadienyl rings are examined by 13C[1H] CPMAS NMR, RHF and hybrid-DFT (B3LYP) calculations, and simulations of the effects of chemical exchange on the 13C powder pattern.     

Second-harmonic generation in Ge(20)As(25)S(55) glass irradiated by an electron beam

Second-harmonic generation was observed in Ge(20)As(25)S(55) chalcogenide glass irradiated by an electron beam. The second-harmonic intensity increased with increasing electron-beam current and accelerating voltage. The second-harmonic generation in Ge(20)As(25)S(55) glass was caused by the space-charge electrostatic field that was generated by irradiation of an electron beam. Second-order nonlinearity X((2)) as great as 0.8 pm/V was obtained. The results of measurements of thermally stimulated depolarization current indicated that the glass was poled in the thin layers of its surface (several micrometers) and that the nonlinearity was stable.     

《核聚变与等离子体物理》2005 年第25 卷总目次

第1期HL-2A等离子体边界识别的研………………………………………………究袁保山,刘莉,游天雪,…李芳著,杨青巍,严龙文,洪文玉(1)空间傅里叶分析法识别MHD振动模……………………………………………………式冯北滨,杨青巍(7)轴向剪切流对Z箍缩等离子体瑞利-泰勒不稳定性的抑………………………………制张扬,丁宁(15)低杂波控制电流分布与改善约束研…………………………………究沈慰慈,匡光力,单家芳,丁伯江(22)托卡马克等离子体中的电子回旋波电流驱……………………………………动彭晓炜,龚学余,刘文艳(29)HL-2A装置LHCD天线波谱测…     

Fe和Co元素在铁磁性形状记忆合金Mn50Ni25－xFe(Co)xGa25中的作用

为了进一步改善材料的性能和探索新的材料，将Mn₂NiGa合金中的Ni元素分别用Fe和Co替代，制备了Mn₅₀Ni_25-xFe(Co)_xGa₂₅系列合金. 研究了Fe和Co元素对Mn₂NiGa合金的结构、马氏体相变行为、磁性和机械性能等方面的影响. 关键词： 铁磁形状记忆合金 Heusler合金 50Ni_25-xFe(Co)_xGa₂₅')" href="#">Mn₅₀Ni_25-xFe(Co)_xGa₂₅     

Super S_(25)与New S_(25)光电阴极的光谱响应特性的数值模拟

根据多碱光电阴极的光谱响应理论表达式 ,对荷兰DEP公司和日本Hamamatsu公司美国分公司开发的两种SuperS2 5阴极的光谱响应曲线进行了理论模拟 ,得到了这些阴极的有关特性参量 ,并通过对模拟结果的分析以及与美国夜视实验室研制的NewS2 5光电阴极特性的比较 ,揭示了两种SuperS2 5光电阴极内在机理和可能采用的工艺处理方法 ,对多碱光电阴极的理论研究和实际操作具有指导意义     

Spins in 23Na from 25Mg(d, α)

The ²⁵Mg(d, α)²³Na reaction has been investigated at bombarding energies of 12.07,11.82 and 11.57 MeV. Angular distributions are approximately symmetric about 90° and for states of known J^π angle-integrated cross sections $\text{σ}$ averaged over bombarding energy, are roughly proportional to $\text{2J + 1:}\text{σ}\text{/(2J + 1) = 25±4 μ}\text{b}$. Measured cross sections for other states, up to E_x = 7.9 MeV, have been used to place limits on J.     

Experimental investigation of a 25-MW microwave (3-cm range) compressor prototype

An experimental study of a resonance microwave (3-cm-range) compressor with gas insulation and energy output through a superdimensional coaxial interference switch is reported. The rated parameters of the compressor are output signal power ∼25 MW, signal duration 2 ns, gain 26 dB, and efficiency ∼57%. A gain of 20 dB was achieved at a peak output signal power of 12 MW, signal duration of 2 ns, efficiency of ∼24%, and traveling wave power of 24 MW.     

Resonance strength measurements and thermonuclear reaction rates for 25Mg(p, γ)26Al (II)

The strengths of resonances in ${}^{25}\text{Mg(p}\text{, γ)}{}^{26}\text{Al}$ have been measured in the energy range E_p = 600–1730 keV. Several serious disagreements with previously published results are reported. Thermonuclear reaction rates are calculated for the temperature range (0.5–10) × 10⁹ K for production of ²⁶Al in its ground state and in its isomeric first excited state. Total thermonuclear reaction rates are compared with those calculated from statistical-model cross sections and, even in energy ranges where the experimental cross section derives from widely spaced resonances, the agreement is very good. The establishment of a thermal population of ²⁶Al excited states in a stellar environment is discussed, with both electromagnetic transitions and proton inelastic and superelastic scattering as the thermalising processes.     

25MeV/u 40)Ar+209Bi裂变反应研究

实验对25MeV/u ⁴⁰Ar+²⁰⁹Bi体系的裂变反应,利用线性动量转移的分窗选择不同的激发能,研究裂变动能分布和质量分布与热核初始激发能的关系.实验证实激发能小于380MeV时裂变总动能分布与低激发能复合核相似.激发能大于380MeV时,最可几动能呈现出随激发增加而增加,并出现高能非对称性,而且质量分布宽度随激发能增加而迅速增大.     

Effect of the mechanical stretching on the ferroelectric properties of a (VDF/TrFE) (75/25) copolymer film

The transition phase behaviour of a vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer film was studied after being subjected to different mechanical stretching levels in both longitudinal (L) and transversal (T) directions relatively to the initial extrusion direction. Both ferroelectric-paraelectric (FE-PE) and melting transitions were detected in the films by differential scanning calorimetry, that were not affected by L stretching. This suggests that sliding mechanism along the c-axis of such films during plastic deformation influences slightly the all-trans chain conformations and the CF₂ dipole orientation. On the other hand, the FE-PE peak decreases in area and temperature upon T stretching, indicating a damage of the ferroelectric phase. However, the melting peak maintains unchanged. This fact provides evidence that the mechanical stretching do not change the total degree of crystallinity. The results suggest that the stretching induces a FE-PE phase transformation, without affecting the degree of crystallinity.     

NewS25与LEP光电阴极光谱响应特性的研究

研究了Ｎｅｗ Ｓ２５与ＬＥＰ＾＊光电阴极的光谱响应特性。从理论上分析了光电子逸出深度，光电阴极结构参量和光电阴极厚度对光谱响应特性的影响。并对实用三碱阴极的潜力进行了理论预测。明确指出集Ｎｅｗ Ｓ２５与ＬＥＰ＾＊之长获得的实用三碱阴极可以和Ⅲ－Ⅴ族ＮＥＡ阴极媲美。     

Direct capture in the 24Mg(p, γ)25Al reaction

Excitation functions for the ²⁴Mg(p, γ)²⁵Al capture reaction have been obtained for the beam energy range E_p = 0.2–2.3 MeV. The analysis of these data revealed the presence of the direct capture process to the low-lying states in ²⁵Al at , $\text{945(}\text{3}\text{2}{}^{\mathrm{+}}\text{), 2485(}\text{1}\text{2}{}^{\mathrm{+}}\text{)}\text{and}\text{3062}\text{keV}\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$. The presence of the weaker direct capture transitions is manifested through interference effects on the tails of the two broad resonances at E_p = 823 and 1623 keV. The deduced spectroscopic factors for these final states in ²⁵Al are compared with the corresponding values from stripping data as well as model calculations. An astrophysical S-factor of S(0) ≈ 30 keV· b for this reaction has been obtained.     

Search for low-energy resonances in25Mg(p,γ)26Al

The reaction²⁵Mg(p,γ)²⁶Al has been investigated atE _p (lab)=80-350keV. The existence of the resonance atE _p =317keV has been verified and new resonances have been found atE _p =198, 255 and 304 keV. TheE _p = 304keV resonance represents a new compound state in²⁶A1. Information on branching ratios,Ωγ values, total widths andJ ^π assignments for the observed resonances as well as upper limits on themy strengths for the expected resonances atE _p =97 and 134 keV are given. The astrophysical aspects of the data are discussed in the light of the renewed interest in the precise location of²⁶A1 nucleosynthesis.