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1.
本文研究了磷酸铝单晶的旋光特性.用偏光显微镜观察了晶体的锥光干涉图、埃拉螺旋图;测量了晶体的旋光率、旋光率随波长和温度的变化.指出该晶体旋光性质是受晶体中Al-O及P-O四面体的旋向和随温度的变化所制约.  相似文献   

2.
云中客 《物理》2003,32(7):493-493
在自然界或实验室内 ,“理想化”总是一个难以实现的概念 .但最近美国休斯顿大学的P .Vekilov教授及其同事们发现 ,他们常常可以将胰岛素晶体生长成理想的晶体形式 .他们让胰岛素蛋白质在一个已有的胰岛素晶体的螺旋位错缺陷处进行生长 ,蛋白质将绕着这个缺陷发生晶化并形成一个理想晶状胰岛素 .这是因为螺旋位错常常使晶层间产生一个微小的角度偏差 .对于大多数的晶体来说 ,晶层间的相互作用能促进晶体生长时界面间的配置 ,并导致晶层阶跃发生束缚和形成一个有条纹的晶体 .除此之外 ,在溶液中输入被溶解物质也能引起晶层阶跃的约束 .胰岛…  相似文献   

3.
罗薇  蔡强 《光散射学报》1999,11(4):351-354
无机介孔材料MCM41是高有序,直孔道介孔分子筛,具有孔径约4nm的一维均匀孔道,孔壁厚约1nm,介孔体积可达40%,是一种很理想的组装材料主体。半导体碲位于第Ⅵ族,其六方相的晶格排列呈螺旋链状结构。本文采用固相合成反应方法,将单质半导体碲成功地组装在MCM41介孔分子筛中。在组装体中,单质半导体碲保持着六方相的晶体结构,其拉曼晶体振动表现出纳米晶体的结构特征。真空热处理实验表明,组装体具有良好的热稳定性。Te的六方相和所具有的独特的螺旋链状结构使Te分子很容易进入MCM41的直孔道内,同时MCM41均匀而规则的直孔道限制了Te螺旋链的随机排列,因而被组装在直孔道内的Te能螺旋链式生长,形成一维半导体纳米晶体,排列均匀,尺寸单一,具有稳定的空间构型  相似文献   

4.
《现代物理知识》2014,(3):56-56
<正>最近,中国科学技术大学微尺度物质科学国家实验室和化学与材料科学学院教授曾杰研究组在拓扑绝缘体二维层状纳米材料Bi2Se3的结构设计、合成与生长机理研究方面取得新进展。研究人员对Bi2Se3晶体的成核及生长进行了动力学调控,通过引入螺旋位错首次实现了二维层状材料的螺旋生长,将材料由分立的层状转变成连续性的螺旋条带,从而获得了一  相似文献   

5.
碳纳米管内金纳米线的结构与热稳定性   总被引:1,自引:0,他引:1       下载免费PDF全文
采用分子动力学模拟方法, 研究了填充在(8,8)单壁碳纳米管内的Au纳米线的结构和热稳定性. 研究表明, 经高温退火至室温, Au在碳纳米管内能生成多样而稳定的结构上明显区别于自由状态Au纳米线的壳层螺旋结构Au纳米线, 其螺旋结构会随着温度的变化而转变. 束缚在碳纳米管内的壳层螺旋结构Au纳米线有非常好的热稳定性, 稳定温度高于块体Au晶体的熔化温度. 关键词: 纳米线 碳纳米管 热稳定性 分子动力学模拟  相似文献   

6.
因其独特的结构特点,纳米材料的螺旋生长一直备受关注。在本综述中,主要采用分子动力学方法来模拟指定材料间的相互作用。模拟结果证明,石墨烯纳米带能够自发螺旋嵌入碳纳米管,亦能螺旋缠绕在碳纳米管外壁,而这一结果已被实验证实。同时,封闭的石墨烯纳米环可填充到碳纳米管空腔中形成类似DNA的双螺旋结构,亦能螺旋塌陷在碳纳米管外壁形成大螺距双层螺旋结构。模拟发现,石墨烯纳米带与石墨烯纳米环均可螺旋缠绕在金属纳米线外壁形成碳-金属壳核结构,这一机理可用于制备壳核复合结构。另外,我们论述了硅纳米粒子在碳纳米锥与碳纳米管表面的螺旋形核机制。通过相互作用机制和热力学模型的建立来进一步研究纳米材料的螺旋生长。据推断,螺旋结构具有最低的能量且具有最高的空间利用率。同时,实验证明,极性面以及螺旋位错的存在也可驱动晶体结晶过程中的螺旋生长。到目前,尽管涉及纳米材料螺旋生长的研究非常广泛,但还需要更详实的后续研究来解释螺旋生长的作用机制。  相似文献   

7.
一、晶体中的平面电磁波1.D0,E0,H0,K0,S0的几何关系 在本文中,我们只讨论电各向异性和磁各向同性的晶体,并且认为μ1,从而不考虑μ的影响. 众所周知,若晶体中传播着一平面单色波,令K0是波法线方向上的单位矢量,则由Maxwell方程可得它表明D,H,K0构成右手螺旋正交三矢族:H ×K0∞D.如果注意到能流密度的定义S=则 E,H,S0(以后用 S0表示S的方向上的单位矢量)也构成右手螺旋正交三矢族. 由于 D,E山介电张量 联系,D=E,这里为3×3矩阵,所以一般说来,D与E不平行,从而K0与S0不平行.但是,由于D K0,E,S0都与H垂直,所以 D,K0,E,S0共面,…  相似文献   

8.
本文报道了使用螺旋谐振腔技术在压电铌酸锂和石英晶体中直接激发频率低至10MHz的超声波的实验结果.谐振腔壁由一般的黄铜片或印刷电路板制成,腔体呈圆柱状或长方体,其Q值可达500以上.用插入腔体内的单股导线使信号源和谐振腔之间获得较满意的耦合.实验发现,腔体内螺旋线末端若与一块小铜片相联,可提高压电晶体内超声波的激发效率.本文也指出了该技术进一步改进的措施及在材料检测中可能的应用.  相似文献   

9.
针对螺旋扭曲的单包层-少芯光子晶体光纤在生成轨道角动量(orbital angular momentum, OAM)方面存在的不足,首次将三芯和内外空气孔不均匀的双包层结构引入光子晶体光纤,并通过螺旋扭曲实现了高阶OAM模式的生成.该光纤通过引入特殊设计的双包层结构有望降低生成的OAM模式的损耗,而围绕中心呈正三角分布的三个纤芯有望增加生成的OAM模式的数量.在光学变换原理的基础上,通过有限元方法对该光纤进行系统的分析,结果发现,当扭曲率a=7853.98 rad/m时,生成的OAM模式包括“OAM–4,1, OAM+9,1,OAM+10,1, OAM+11,1, OAM+13,1”,其中+13阶是目前利用螺旋扭曲光纤生成的OAM模式中最高的阶数,且OAM模式的损耗均小于1.64×10–3 d B/m,比已有文献中最低的OAM模式损耗(Napiorkowski M, Urbanczyk W S 2018 Opt. Express 26 12131)至少降低...  相似文献   

10.
羟基磷灰石结晶对牛血清白蛋白二级结构影响的光谱研究   总被引:1,自引:1,他引:1  
通过圆二色谱(CD)及傅里叶变换红外光谱及退卷积、曲线拟合等技术研究了羟基磷灰石结晶对牛血清白蛋白二级结构的影响.CD谱结果表明,在纯的牛血清白蛋白中,α-螺旋、β-折叠、β-转角及无规则卷曲等4种结构的含量分别为56.8%,5.8%,14.1%,23.9%;而在羟基磷灰石/牛血清白蛋白溶液中,4种结构的含量分别为25.4%,25.0%,20.0%和29.7%,红外光谱结果与其一致.由此可以看出,晶体的形成使牛血清白蛋白的α-螺旋结构含量减少,β-折叠结构含量增多,且随着反应时间的进行α-螺旋结构减少越来越明显,β-折叠结构增加越来越多,表明在溶液中部分α-螺旋结构转变为β-折叠结构.文章对这种变化的本质进行了初步探讨.  相似文献   

11.
应用液晶空间光调制器加载螺旋相位片的方法可以高效地生成涡旋光束,但由于液晶空间光调制器分辨率有限,在加载高阶螺旋相位片时其中心会出现相位失真,造成涡旋光束质量不高。通过在螺线相位片中心区域引入闪耀光栅的方法,得到了光束质量较高的高阶单模涡旋光束和多模涡旋光束,为生成高阶涡旋光束提供了一种很好的方法。  相似文献   

12.
The propagation of microwaves in the frequency range from 8.5 to 12GHz and acoustic radiation in the frequency range from 8.5 to 14 kHz in the same 2D periodic crystal formed by cylindrical spiral coils has been investigated. The frequency ranges in which the effective refractive index nef of the crystal is close to zero are found. In these ranges, microwaves are collimated and concentrated in a narrow lobe with an FWHM of about 9?. Focusing of divergent microwave and acoustic beams by a flat periodic structure has been observed in the frequency range where the effective refractive index of this structure is negative.  相似文献   

13.
14.
The elementary processes of crystal growth in the case of a low kink density on step edges have been studied by in situ atomic force microscopy. High-resolution images of the first turn of the polygonal dislocation spiral on the (101) face of monoclinic lysozyme crystals, which allow one to discern separate crystal cells, have been obtained. It has been shown that the dependence of the spiral segment velocity on its length is inconsistent with the Gibbs-Thomson law and is represented by several rectilinear sections. The results were explained by taking into account the features of the growth of crystals with a low kink density at low supersaturation.  相似文献   

15.
P.M. Martins  F. Rocha 《Surface science》2007,601(23):5466-5472
The effect of crystal size on the growth rate of sucrose (C12H22O11) at 40 °C is investigated from a theoretical and an experimental point of view. Based on new perspectives resulting from the recently introduced spiral nucleation model [P.M. Martins, F. Rocha, Surf. Sci. 601 (2007) 3400], crystal growth rates are expressed in terms of mass deposition per time and crystal volume units. This alternative definition is demonstrated to be size-independent over the considered supersaturation range. The conventional overall growth rate expressed per surface area units is found to be linearly dependent on crystal size. The advantages of the “volumetric” growth rate concept are discussed. Sucrose dissolution rates were measured under reciprocal conditions of the growth experiments in order to investigate the two-way effect of crystal size on mass transfer rates and on the integration kinetics. Both effects are adequately described by combining a well-established diffusion-integration model and the spiral nucleation mechanism.  相似文献   

16.
The dynamics of defects and their mutual transformation and annihilation in drops of a nematic-cholesteric mixture in the presence of quasistatic electric fields has been investigated by the birefringence method. Three basic independent configurations of the director distribution—static and dynamic with the right and left-handed twists of cholesteric layers around the axis parallel to the field—are formed above the threshold field. The possible mechanisms of the observed processes have been discussed. It has been shown that a certain symmetry of the causes (the nematic-cholesteric liquid crystal and field) does not necessarily lead to the corresponding symmetry of the induced structures and mechanical processes. An anisotropic distribution of the orientation of rotating spiral structures with respect to the normal to the nematic-cholesteric liquid crystal layer has been revealed.  相似文献   

17.
G. V. Kovalev 《JETP Letters》2009,89(6):265-270
The peak position, impact-parameter range, and optimal conditions for observing spiral scattering of relativistic particles in a uniformly bent crystal are estimated. The existence of spiral scattering with a square-root singularity is pointed out. In this case, the secondary process of volume capture to the channeling mode is absent and the conditions for observing this effect are most favorable.  相似文献   

18.
19.
The investigations performed in this work have demonstrated that an easy-axis frustrated non-Heisenberg magnet can contain homogeneous phases with the vector (ferromagnetic) and tensor (nematic) orderings, as well as a spatially inhomogeneous phase of the magnetic spiral type. Depending on the relationships between the material parameters, either a ferromagnetic spiral or a spiral of the quadrupole–ferromagnetic type with different periods of the spiral structures can be formed in the system. The phase diagram of the system has been constructed.  相似文献   

20.
P.M. Martins  F. Rocha 《Surface science》2007,601(16):3400-3408
Classical concepts of two-dimensional nucleation and spiral growth are used together with recent findings on the dynamics of dislocation spirals to derive a new crystal growth model. Initial growth nuclei result from the organization of adsorbed molecules in spirals around surface dislocations. The energetic barrier for the activation of the spiral nuclei is considerably lower than the admitted by classical two dimensional nucleation models. Stable nuclei evolve into bigger growth hillocks in supersaturated media through the incorporation of adsorbed units into their steps. The displacement velocity of steps during solution and vapour growth is calculated by different kinetic approaches, taking into consideration the distinct role of surface diffusion in each process, and avoiding known limitations of conventional theories. A generalized expression is obtained relating the crystal growth rate with main variables such as supersaturation, temperature, crystal size, surface topology and interfacial properties. At the end of the paper, the crystallization kinetics of sucrose measured at 40 °C is interpreted in the light of the new perspectives resulting from the proposed model. The application example illustrates how to estimate interfacial and topological properties from the experimental crystal growth results.  相似文献   

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