二维叶片襟翼增升的试验研究

本文在雷诺数为0.24×106，0°－40°攻角范围内测定了带有90°，45°，135°三种不同偏转角的位于压力面后缘的襟翼的NACA632—215叶片的表面压力分布．根据压力分布求得的升力系数和阻力系数（压差）表明，襟翼能在不同程度上起到增升的效果，且当襟翼高度相同时，偏转角为90°时增升效果最佳；当偏转角为90°时，襟翼高度越大，升力系数增加越多．     

用MAEAM法计算Ag/Ni的界面能

采用改进分析型嵌入原子法计算了Ag(111)//Ni(001)和Ag(001)//Ni(111)扭转界面的能量，结果表明：对Ag(111)//Ni(001)界面，当扭转角等于0°（或30°）时界面能最小，这一择优扭转角取向和Gao等人的实验结果一致；同样，对Ag(001)//Ni（111）界面，当扭转角等于0°（或30°）时界面能最小；从界面能最小化考虑，Ag(001)//Ni(111)扭转界面的择优扭转角也为0°（或30°）. 关键词： Ag/Ni界面 界面能 计算 改进分析型嵌入原子法 近重合位置点阵     

用单光纤光栅实现扭转与温度的双参量传感测量

采用一种新颖的扭梁设计结构 ,利用单光纤光栅成功地实现了扭转 (扭转角或扭矩 )与温度的双参量同时测量。该方法能够有效地解决扭转角与温度的交叉敏感问题 ,且光纤光栅波长的变化对扭转角、扭矩及扭应力 (力臂一定时 )均呈线性关系。在 - 40°～ +32°范围内 ,扭转角、扭矩和温度的传感灵敏度分别达到 0 .19nm (°)、3.2 9nm Nm和 0 .0 3nm ℃ ,波长线性调谐范围可达 14.2 0nm。     

新型光纤光栅扭转传感器研究

报道了一种新型光纤光栅扭转传感器的基本原理和传感结构,推导了扭转测量的理论公式,该传感器的扭角与光纤光栅中心波长的变化呈线性关系.在±40°扭角范围内,技术上实现了灵敏度为10.715°/nm的扭转传感.     

用低能电子衍射研究ⅢA—VA化合物{110}表面吸附Sb和Bi的表…

用低能电子衍射研究了Ｓｂ和Ｂｉ吸附在ＩｎＰ｛１１０｝和ＧａＡｓ｛１１０｝表面上表面结构。结果显示出：对Ｓｂ／ＩｎＰ｛１１０｝，表面原子层间距：ｄ１＝０．２７±０．２３Ａ（膨胀９．４％±０．０２Ａ）；旋转角ω１为－１０．７７°±２．２９°和ω２为１５．２６°±０．８２°；吸附键长ｌｃ１－Ａ＝２．８４±０．０５Ａ，ｌｃ２－Ｂ＝２．７５±０．０２Ａ，其键角α＝１０１．２１°±２．１°，β＝１０７．８６°     

几种前缘流动控制的实验研究

在低速风洞中，以NACA0012翼型为例，采用对比实验的方法，研究了三种改善翼型大攻角气动性能的流动控制措施，即（1）在翼型上表面安装小三角翼涡发生器；（2）在翼型前缘安装矩形涡发生器；（3）利用前缘切口．实验雷诺数分别为4．9×105到6．5×105，攻角范围为-10°至20°．实验结果表明三种措施均可不同程度地改善原翼型在其失速区域的性能，不仅可以提高翼型的升力，而且可以提高其升阻比；但常用攻角范围内翼型气动性能有不同程度的下降，三种措施各有优缺点．几种前缘流动控制的实验研究@刘宝杰$北京航空航天大学404教研室!北京,1…     

氢气放电源打靶的较完整新谱系实验测量

 为了能够实现明确和清晰地同时测出氢气放电源打靶的较完整新谱系，使用氢气放电中的电子和X射线等直接打靶，在衍射角和测量角均为45°时，测量氢气放电源打靶的较完整新谱系。实验同时测到了3组6条氢气放电源打靶的新谱系，它们是：（2.25±0.07）和（2.56±0.08） keV；（3.25±0.10）和（3.62±0.11） keV；（4.42±0.13）和（4.79±0.15） keV。这6条新谱线表征了未知粒子的能级特性，是未知粒子存在的标志。未知粒子在靶中能储存一年以上，测得的未知粒子能级谱线能量为keV量级，氢气放电源中粒子为已知粒子，据此可以认为未知粒子是一种新原子态氢原子。     

康普顿相机图像重建中的快速滤波反投影算法

提出一个由CZT像素探测器与NaI闪烁体阵列组成的康普顿相机，计算探测器系统的几何参数、散射体探测器的能量分辨率及多普勒展宽等因素对相机空间分辨率的影响.相机的总体角分辨率为5.1°~5.6°，主要影响因素为探测器系统的几何参数.首先用解析方法研究图像重建中的滤波反投影算法，不考虑展宽影响时点源重建图像的角分辨率可达1.7°，考虑展宽影响时角分辨率可达4.2°；然后利用Geant4程序进行模拟，用实际应用方法对模拟数据进行重建，不考虑展宽影响时的角分辨率为1.7°，考虑展宽影响时角分辨率可达5.1°.采用滤波反投影算法进行图像重建时，在OpenCL框架下利用GPU实现并行加速，加速比为79倍.     

电磁辐射作用于计算机主板的模拟及效应评估

 提出了一种电磁辐射（EMR）效应评估的方法：通过区域分解并且引入子域敏感因子，采用电场强度的加权平均作为EMR效应评估的参考指标。以一款普通计算机主板作为研究对象，使用时域有限差分法（FDTD）进行模拟计算，得到了EMR作用下计算机主板耦合的电磁场分布。基于该效应评估方法，比较了3~12 GHz 的平面电磁波在0°~90°入射时对计算机主板的效应。数值模拟结果表明：随着平面电磁波入射角度的增加，EMR对计算机主板的影响趋于减弱；EMR频率的变化对效应没有显著影响。当EMR入射角度为40°时，最高主板表面耦合的电场强度达到最大值；0°入射时，主板上平均电场强度达到最大值；随着入射EMR频率的升高，主板表面的最大电场强度趋于减弱。     

究竟能成多少个像

在物理教学杂志、课外辅导习题册上常会遇到这样一道光学选择题：两相交平面镜反射面间夹角恰为６０°,在其中任一位置放置一点光源Ｓ．那么,它所成的像共有［Ｃ］ Ａ．３个 　Ｂ．４个 　Ｃ．５个 　Ｄ．６个 答案是 Ｃ．５个．有些竞赛辅导书上还给出了特殊角（如９０°、６０°、４５°、３０°等）成像个数计算式：（３６０°／θ）－１（θ为两相交平面镜反射面特殊夹角度数）． 如果两相交平面镜反射面间夹角θ是任意角,如 ５５°、４０°、３６°……,能成多少个像哪？究竟有没有规律哪？我进行了实验研究,得到了如下结论： １…     

Energy calculation of (0 1 1) twist grain boundary in noble metals

With modified analytical embedded atom method (MAEAM), the energy of (0 1 1) twist grain boundary (GB) has been calculated for three noble metals Cu, Ag and Au. The results show that the unrelaxed energy keeps almost constant with twist angle θ except several cusps at low Σ boundaries. The GB energies drop significantly after expansion perpendicular to the boundary. In-boundary translation results in a periodic energy variation and the rectangular period is 1/Σ of their own CSL smallest unit cell. Three specific positions, the corners or centre of the periodic rectangle, or the midpoints of the sides, are preferable in GB translation.     

钢中小角度晶界区的电子结构及掺杂效应

根据位错的弹性理论,建立了9Ni钢中53°掺杂小角度晶界的原子模型,利用Recursion方法,计算了杂质在53°小角度晶界典型环境中的能量和电子结构,由此得出,钢中小角度晶界的强度敏感地依赖于隔离杂质的类型,S,P杂质使晶粒间结合减弱,从而导致晶界疏松 ;相反,B,C,N则会使晶界间的结合加强.在所有的杂质中,B显示出独特的性质,在钢中B 不仅能增强晶界的结合,而且由于占位竞争效应会使其他杂质远离晶界,具有净化晶界的作用. 关键词： 小角晶界 杂质 占位竞争 晶界隔离     

Solute-atom segregation at symmetric twist and tilt boundaries in binary metallic alloys on an atomic-scale

Monte Carlo and overlapping distributions Monte Carlo (ODMC) techniques are employed to simulate grain boundary (GB) segregation in a number of single-phase binary metallic alloys—the Au-Pt, Cu-Ni, Ni-Pd, and Ni-Pt systems. For a series of symmetric [001] twist and [001] tilt boundaries, with coincident site lattice (CSL) structures, we demonstrate that the Gibbsian interfacial excess of solute is a systematic function of the misorientation angle. We also explore in detail whether the GB solid solution behavior is ideal or nonideal by comparing the results of Monte Carlo and ODMC simulations. The range of binding free energies of specific atomic sites at GBs for solute atoms is also studied. The simulational results obtained demonstrate that the thermodynamic and statistical thermodynamic models commonly used to explain GB segregation are too simple to account for the microscopic segregation patterns observed, and that it is extremely difficult. If not impossible, to extract the observed microscopic information employing macroscopic models.     

Theoretical study of broadband near-field optical spectrum of twisted bilayer graphene

We theoretically study the broadband near-field optical spectrum of twisted bilayer graphene (TBG) at various twist angles near the magic angle using two different models. The spectrum at low Fermi energy is characterized by a series of peaks that are almost at the same energies as the peaks in the far-field optical conductivity of TBG. When the Fermi energy is near a van Hove singularity, an additional strong peak appears at finite energy in the near-field spectrum, which has no counterpart in the optical conductivity. Based on a detailed calculation of the plasmon dispersion, we show that these spectroscopic features are associated with interband and intraband plasmons, which can provide critical information about the local band structure and plasmonic excitations in TBG. The near-field peaks evolve systematically with the twist angle, so they can serve as fingerprints for identifying the spatial dependent twist angle in TBG samples. Our findings pave the way for future experimental studies of the novel optical properties of TBG in the nanoscale.     

Energie- und Winkelverteilung sekundärer Photonen bei der Wechselwirkung eines 6,2 GeV-Gammastrahls mit komplexen Kernen

The energy spectra of secondary photons from the interaction of a 6.2 GeV bremsstrahlung beam with targets of H₂, Be, C, Al and Cu are measured for laboratory angles from 35° to 120°. All spectra exhibit an exponential decrease of the photon yield with increasing momentum. Difference measurements with energies of the bremsstrahlung beam from 3.5 to 6.2 GeV for a center of mass angle of 90° are compared with the thermodynamical model of Fermi and the reaction temperature is determined to be 83MeV±8%. The results agree approximately with the measurements of p-Be-collisions at small laboratory angles.     

Nucleation and growth of helium bubble at(110) twist grain boundaries in tungsten studied by molecular dynamics

Migration of He atoms and growth of He bubbles in high angle twist grain boundaries(HAGBs) in tungsten(W) are investigated by atomic simulation method. The energy and free volume(FV) of grain boundary(GB) are affected by the density and structure of dislocation patterns in GB. The migration energy of the He atom between the neighboring trapping sites depends on free volume along the migration path at grain boundary. The region of grain boundary around the He bubble forms an ordered crystal structure when He bubble grows at certain grain boundaries. The He atoms aggregate on the grain boundary plane to form a plate-shape configuration. Furthermore, high grain boundary energy(GBE) results in a large volume of He bubble. Thus, the nucleation and growth of He bubbles in twist grain boundaries depend on the energy of grain boundary, the dislocation patterns and the free volume related migration path on the grain boundary plane.     

MOLECULAR DYNAMICS SIMULATION ON LOW ANGLE GRAIN BOUNDARIES

Molecular dynamics simulation has been performed to investigate the microstructure and properties of low angle grain boundaries, employing the embedded atom method(EAM) type interatomic potential for Ni-Al alloy. The energies of the low angle grain boundaries with different dislocation densities were calculated, and the results indicate that the low angle grain boundary energy varies as a function of misorientation angle. The simulation was found in good agreement with the calculation on the basis of the dislocation theories in the low angle scale. The low angle grain boundary energy goes up with the increase of misorientation angle and tends to go down after reaching a maximum. An energy cusp exists when the misorientation angle increases further, but in this scale the dislocation theories are invalid for energy calculation due to the strong interaction of the dislocations at the boundaries. The simulation results also indicate that the microstructure of low angle grain boundaries can still be described as dislocations when the misorientation angle is larger than 10°.     

Coupling to the elastic channel in electron impact spectroscopy: A simple second born model and its application to excitation of the 61P1 state of mercury and to the excitation of molecules

The matrix element in the infinite channel close coupling approximation responsible for coupling to the elastic channel in electron impact inelastic encounters is investigated. The contribution from the imaginary part of the energy denominator in the elastic coupling matrix element for dipole allowed transitions is shown to yield large angle differential cross sections in good agreement with experiment. This coupling mechanism predicts that the shape of the inelastic differential cross section will be dominated by the shape of the elastic cross section in the large angle high energy limit. In fact the coupling matrix element exhibits a dependence on incident energy, k², and momentum transfer, K, of the form 1/kK² which is in agreement with the theoretical predictions of Huo and means that in the limit of high incident energy the non-first-Born elastic coupling will dominate the angular dependence of the inelastic differential cross section at large scattering angles. In the case of molecular electron impact spectra it is shown that the analog of the Massey—Moore coherence features depending on the symmetry of the states involved in the excitation process will also occur in the coupling contribution. It is suggested that this new mechanism for producing coherent features in inelastic differential cross sections may be the explanation of the coherent features observed experimentally by Karle and Swick.It can be concluded on the basis of the results obtained here that the coupling to the elastic cross section provided by the imaginary contribution from the second Born energy denominator is sufficient to explain presently available experimental data on the large angle differential cross section and spin polarization. The simple coupling model was found to be inadequate to explain the small angle differential cross section in the range 10° < θ < 30° even at incident energies as high as 400 eV. The calculations also showed significant differences between first and second Born calculations at zero scattering angle. No conclusion can be drawn about this observation as all the omitted terms should make significant contributions in the small angle region. It is important to again emphasize that the large angle scattering even in the limit of high incident electron energy will be completely dominated by the coupling to the elastic channel^{7, 11}. On the basis of this work it appears that the coherent structure in the large angle inelastic differential cross section observed by Swick and Karle^{12, 13} at incident electron energies in the keV region may well be due to coupling to the elastic channel.     

Inelastic effect in low energy ion-surface collisions: He+Au,Ag

Energy distributions of He⁺ ions scattered by Au and Ag surfaces are measured by an ISS system with high energy resolution, at a scattering angle of 90° and at incident ion energies ranging from 277 to 977 eV. It is found that the observed peak energies deviate toward the low energy side by several electron-volts with respect to the calculated elastic single collision energies. Both the deviation Q' and the inelastic loss energy Q are plotted as a function of incident ion energy for the Au surface.