共查询到20条相似文献,搜索用时 62 毫秒
1.
构造两个曲面的拼接曲面 总被引:1,自引:1,他引:1
给出了当两个待拼接曲面的拼接线具有参数化形式或者可以参数化时,它们之间 G1光滑拼接曲面的构造方法。所得的拼接曲面是由一个空间曲线集定义的,每一条空间曲线由拼接线上的点对确定。并且拼接曲面都是参数曲面,它们的形状可以通过预设的参数很好地调整和控制。作为实例,讨论了两个截口是平面的或非平面的(由两个二次曲面定义)的二次曲面之间的拼接曲面的构造和一般的参数曲面的拼接曲面的构造。 相似文献
2.
分别推导和分析了环境大气氦分压对压氦法的影响,地球干洁大气氦分压对预充氦法和预充氦密封器件压氦法复检的影响.证明对于压氦法,不需要考虑地球干洁大气氦分压的影响.但是如果候检室环境大气氦分压显著升高,对于内腔有效容积大,且等效标准漏率小的密封器件,会加大测量漏率值,所以压氦后,被检器件应尽快离开压氦设备所在的房间.对于预充氦法,地球干洁大气氦分压会使测量漏率通过极大值后出现极小值,且当候检时间与内腔有效容积之比大于100 h/cm3时,极小值点的气流仍处于分子流状态,不能靠粗检鉴别,所以需压氦法复检加粗检,才能防止漏检.另外,地球干洁大气氦分压会使预充氦法候检时间的第一特征点变大,从而扩大了需压氦法复检加粗检的范围,但第二特征点不变,也不影响压氦法复检加粗检的结果. 相似文献
3.
4.
不同材料拼接半平面的周期裂缝问题 总被引:4,自引:0,他引:4
带周期裂缝的不同材料拼接平面弹性基本问题,马道玮作过讨论,本文将用复变方法讨论拼接半平面上带周期分布裂缝时的弹性基本问题,把在满足一定边界条件下寻求复应力函数的问题归结为求解某种正则型奇异积分方程,并证明这种方程的解存在且唯一。 相似文献
5.
氦制冷机节流级的最佳工作点 总被引:3,自引:0,他引:3
在氦制冷机/液化器中,最末级的冷却一般采用节流方式.节流级的各参数的选择必然会影响氦制冷机的制冷量或氦液化率.讨论了节流级节流前压力、末级换热器的热端温度及其效率对制冷量或液化率的影响,得出了不同模式下的节流级的最佳工作点. 相似文献
6.
密封器件氦质谱细检漏包括压氦法(即背压法)和预充氦法.对于压氦法,通常靠粗检鉴别是否有大漏孔,但候检时间不可过长,以免可能存在的大漏孔处于分子流状态,不能靠粗检鉴别.本文给出了最长候检时间表达式,以便既避免漏检又做好被检器件表面的净化工作.预充氦法的优点是可检测的最小等效标准漏率比压氦法低好几个量级.但用户复检时,候检时间往往已很长,如果仅靠通常的压氦法复检加粗检则发挥不出预充氦法的优点.本文改进了预充氦法:提出候检时间存在两个特征点,并给出了表达式;还对压氦法复检加粗检赋于新的重要功能,从而可以针对各种情况,用不同方法和判据,判断漏率是否合格.因此,即使候检时间已很长,仍有可能充分发挥预充氦法优点,并在漏率合格时给出被检器件的等效标准漏率. 相似文献
7.
8.
9.
许多使用透平膨胀机的中等功率的低温氦装置正在运转。考虑到低温氦装置用于大型低温系统的前景,研究和分析这些装置的运行和使用经验乃是一项迫切任务。我们对《氦机器》科学生产联合公司出产的新系列低温氦装置第一台样机—КГУ—500/4.5—140的工作进 相似文献
10.
11.
Su Kong Chong Vikram V. Deshpande 《Current Opinion in Solid State & Materials Science》2021,25(5):100939
Three-dimensional (3D) topological insulators (TIs) have generated tremendous research interest over the past decade due to their topologically-protected surface states with linear dispersion and helical spin texture. The topological surface states offer an important platform to realize topological phase transitions, topological magnetoelectric effects and topological superconductivity via 3D TI-based heterostructures. In this review, we summarize the key findings of magneto and quantum transport properties in 3D TIs and their related heterostructures with normal insulators, ferromagnets and superconductors. For intrinsic 3D TIs, the experimental evidences of the topological surface states and their coupling effects are reviewed. Whereas for 3D TI related heterostructures, we focus on some important phenomenological magnetotransport activities and provide explanations for the proximity-induced topological and quantum effects. 相似文献
12.
Van der Waals versus dipolar forces controlling mesoscopic organizations of magnetic nanocrystals 总被引:2,自引:0,他引:2
The structure, thermodynamics and dynamics in many physical and chemical systems are determined by interplay of short-range isotropic and long-range anisotropic forces. Magnetic nanoparticles dispersed in solution are ideal model systems to study this interplay, as they are subjected to both isotropic van der Waals and anisotropic dipolar forces. Here we show from experiment an abrupt transition of maghemite nanocrystal organization from chain-like to random structures when nanoparticle solutions are evaporated under a magnetic field. This is explained by brownian dynamics simulations in terms of a variation of the strength of van der Waals interactions with the particle contact distance, which is tuned by the length of the molecules coating the particles. The weak dipole-dipole interactions between the maghemite particles are usually not sufficient to result in the chain formation observed here. However, due to the van der Waals interactions, when the nanocrystal contact distance is short enough, clusters of nanocrystals are formed during the evaporation process. These clusters exhibit large dipole moments compared with a single particle, which explains the formation of chain-like structures. Conversely, when the nanocrystal contact distance is too long, no nanocrystal aggregation occurs, and a random distribution of maghemite nanocrystals is obtained. 相似文献
13.
S. S. Batsanov 《Inorganic Materials》2001,37(9):871-885
The available data on the van der Waals radii of atoms in molecules and crystals are summarized. The nature of the continuous variation in interatomic distances from van der Waals to covalent values and the mechanisms of transformations between these types of chemical bonding are discussed. 相似文献
14.
15.
We explore the role which the van der Waals field plays in the behavior of the superfluid density of confined helium near T. This effect can be calculated in the context of -theory. The influence of a solid wall is incorporated into the equation for the order parameter via a spatially-dependent transition temperature. The equation is solved numerically. We first calculate the scaling function without wall interactions for the case of 2D, 1D, and 0D dimensionality crossover. We find that upon introducing the van der Waals field, its influence is too small, and in the wrong direction to explain experimental observations. 相似文献
16.
A van der Waals model of dusty plasma is suggested, which enables one to determine the phase diagram of a system of dust particles with free boundaries in thermal plasma. 相似文献
17.
Bikash Das Subrata Ghosh Shamashis Sengupta Pascale Auban-Senzier Miguel Monteverde Tamal Kumar Dalui Tanima Kundu Rafikul Ali Saha Sujan Maity Rahul Paramanik Anudeepa Ghosh Mainak Palit Jayanta K. Bhattacharjee Rajib Mondal Subhadeep Datta 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(39):2302240
Manipulation of long-range order in 2D van der Waals (vdW) magnetic materials (e.g., CrI3, CrSiTe3 ,etc.), exfoliated in few-atomic layer, can be achieved via application of electric field, mechanical-constraint, interface engineering, or even by chemical substitution/doping. Usually, active surface oxidation due to the exposure in the ambient condition and hydrolysis in the presence of water/moisture causes degradation in magnetic nanosheets that, in turn, affects the nanoelectronic /spintronic device performance. Counterintuitively, the current study reveals that exposure to the air at ambient atmosphere results in advent of a stable nonlayered secondary ferromagnetic phase in the form of Cr2Te3 (TC2 ≈160 K) in the parent vdW magnetic semiconductor Cr2Ge2Te6 (TC1 ≈69 K). The coexistence of the two ferromagnetic phases in the time elapsed bulk crystal is confirmed through systematic investigation of crystal structure along with detailed dc/ac magnetic susceptibility, specific heat, and magneto-transport measurement. To capture the concurrence of the two ferromagnetic phases in a single material, Ginzburg-Landau theory with two independent order parameters (as magnetization) with a coupling term can be introduced. In contrast to the rather common poor environmental stability of the vdW magnets, the results open possibilities of finding air-stable novel materials having multiple magnetic phases. 相似文献
18.
研究了低温砷化镓的外延lift-off和基于范德华力在石英新衬底上贴附的实验方法:腐蚀掉100 nm厚的AlAs牺牲层,将外延生长的500 nm厚的低温砷化镓(LT-GaAs)从生长衬底上揭下(lift-off),借助于范德华力将LT-GaAs外延膜贴附在新衬底上.Lift-off之前在LT-GaAs表面上滴附黑蜡,以增强在lift-off过程中对LT-GaAs的保护,和加快反应气体扩散离开反应区的过程.针对500 nm厚的LT-GaAs外延薄膜的揭起和贴附,给出了低温砷化镓的最佳lift-off尺寸和提高范德华力贴附质量的实验技术.此外还给出了利用所得到的lift-off后的LT-GaAs制备的共平面条形结构光导开关的时间特性:上升时间小于1.5ps,FWHM小于2 ps. 相似文献
19.
20.
C H Satyanarayana 《Bulletin of Materials Science》1981,3(4):409-414
The cohesive energies of PbS PbSe and PbTe, having NaCl type of crystal structure, are calculated using the generalized Huggins-Mayer
form (GHM) for the Born repulsion energy. The van der Waals interactions (VDW) are estimated from the London and Mayer formulae
and compared with those estimated from the Slater-Kirkwood variational method. The cohesive energies calculated adopting the
VDW coefficients calculated from the later method are in good agreement with the experimental values. The difference between
the experimental cohesive energies and the calculated, assuming variational method, are 2·26, 2·97 and 3·75 eV respectively
for PbS, PbSe and PbTe which are in good agreement with the reported values for the covalent bonding correction using Heitler-London-Lowdin
method (HLL) which are respectively 2·1, 2·9 and 3·3 eV (Tanaka and Morita 1979). 相似文献