The influence of lateral and terminal substitution on the structure of a liquid crystal dendrimer in nematic solution: A computer simulation study

The choice of lateral and terminal substitution can have a major influence on the structure of a liquid crystalline supermolecule, which in turn can induce radically different phase behaviour. In this study we use molecular dynamics simulations to investigate the shape of a liquid crystal dendrimer within a liquid crystalline solvent. A coarse-grained (CG) simulation model is employed to represent a third generation dendrimer in which 32 mesogenic groups are bonded to chains at the end of each branch of the dendrimer. In this CG-model the liquid crystal groups can be appended either terminally or laterally. This bonding option is used to generate the structure of four separate systems: (a) a dendrimer with 32 terminal mesogens, (b) a dendrimer with 32 laterally appended mesogens, (c) and (d) dendrimers with 16 lateral and 16 terminal groups represented with laterally bonded sites on one side of the molecule, model (c) or next to terminally bonded sites, model (d). The simulations show that the dendrimer is able to change shape in response to molecular environment and that the molecular shape adopted depends critically on the nature of the lateral/terminal susbstitution.     

Quantitative cerebral magnetic resonance imaging during ACTH treatment of multiple sclerosis

Serial MR scans were performed with the 2DFT imaging method and the filtered backprojection imaging method on 12 patients with multiple sclerosis in acute phase, 4 in a relapsing/remitting form, and 8 in a progressive form, before, during and after ACTH treatment. Both T₁ and T_2mono relaxation times, obtained by fitting transverse magnetization decay curves with a monoexponential function within the apparently normal white matter and the areas of increased signal, were measured. With the backprojection method it was possible to fit the transverse magnetization decay curve with a biexponential function and obtain T_2long and T_2short relaxation times. The T_2mono and T₁ relaxation times of the apparently normal white matter were significantly different from those obtained for volunteers, but no significant differences were found before, during, or after treatment. The transverse magnetization decay curves of the areas of increased signal were better fitted by a biexponential function. No significant changes in these relaxation times were observed after ACTH treatment. These results argue against an anti-oedematous action of ACTH and may suggest that it has an immunosuppressant effect.     

Acoustic analysis of voice in multiple sclerosis patients

The objective is to investigate the presence of dysphonic symptoms in multiple sclerosis (MS) patients and to compare quantitative acoustic parameters in multiple sclerosis patients and normal individuals. The method of study was an 8-month controlled cross-sectional that was carried out with 106 individuals (30 MS, 76 controls). Both groups included males and females from 20 to 55 years. Exclusion criteria were prior vocal disorder, laryngeal microsurgery, recent endotracheal intubation, tumors, laryngeal, lung or mediastinal metastases, respiratory disease, and other associated neurological diagnoses. For dysphonic symptoms (qualitative variables), associations were assessed using Mantel-Haenszel's chi2 test, with Yates correction or the Fisher exact test when necessary. Statistical significance was set at p< or =0.05. Dysphonia was observed in 70% of MS individuals versus 33% of controls (p=0.01). Association was found between MS and dysphonia (OR: 2.2, CI 95%: 1.13-4.25). Fundamental frequency was higher among MS patients (p=0.01). Fundamental frequency deviation was significantly higher in MS women (but not men) than controls (p=0.00). Jitter was higher in MS men than in all other groups (p=0.00). Results suggest that evaluation and treatment of MS patients should be revised, evaluating voice alterations in relation to other signs. MS seems to intensify gender effect on fundamental frequency deviation, noise, and jitter, with MS women presenting fewer voice variations than men.     

Cornerning radial tyres

An angular difference between direction of wheel motion and wheel plane produced a lateral force on a rolling tyre. A simple mechanism of shear stress generation in the contact area of tread is used. The coefficient of friction plays a limiting role. The resulting lateral force and self-aligning torque are computed by means of the belt model of a radial tyre. Finally, some numerical results are given to illustrate the theory.     

High-Resolution X-ray Study of the Smectic A-Smectic B Phase Transition and the Smectic B Phase in Butyloxybenzylidene Octylaniline

We have carried out a high resolution X-ray study of the smectic phases of Butyloxybenzylidene Octylaniline. We find that the phase previously identified as Smectic-B in this material is crystalline with in-plane order extending over at least 1.4 μm. The in-plane Bragg peaks are accompanied by anomalously strong diffuse scattering that can be described by a form 1/(q ²⊥ + γ² q ² _z). Unless the elastic constant C₄₄ is more than an order of magnitude smaller than previously reported values of ～ 10⁸ ergs/cm³ the diffuse scattering can not be due to acoustic phonons. The crystalline-B to Smectic-A melting transition is strongly first order with no observable pre-transition effects on either side of the transition.     

Surface Plasmon Enhanced Vibrational Spectra of Monolayer Assemblies on Gratings and Rough Metal Surfaces

The vibrational spectra of monolayer assemblies of cadmium arachidate on smooth and rough silver substrates were obtained by surface infrared and surface plasmon enhanced Raman spectroscopy. The assemblies were laid down by the Langmuir-Blodgett deposition technique. For Raman scattering the intensity of the incident light was enhanced by grating coupling to surface plasmon optical modes of the metal or to localized plasmon modes in the case of rough surfaces. It was found that the different vibrational frequency regions corresponding, for example, to C-C and C-H stretching modes, were enhanced by selecting different scattering angles for collecting the inelastically scattered light. The Raman spectra of monolayer assemblies in contact with silver islands showed evidence of conformational disorder, i.e., the alkyl chains of some molecules were not in the all-trans configuration. In contrast, the infrared spectra did not show evidence of similar disorder. These observations were explained by assuming that the infrared photons sensed the majority undistorted molecular species, while the Raman photons came from a distorted minority species located in regions where optical electromagnetic fields were enhanced by shape plasmon resonances of the rough silver surface.     

三向受压混凝土的动态特性研究

为探究混凝土在三向受压状态下的动态特性,利用自行研制的大型多功能三轴材料试验机,进行不同应变速率(10-5/s、10-4/s、10-3/s、10-2/s)下混凝土不同定侧压比(1∶1、2∶1、3∶1、4∶1)的动态真三轴抗压试验,研究了混凝土在动态抗压下的强度和变形特性.结果表明:混凝土在三向受压状态下表现出明显的应变...     

杆件在横向力和轴向压力共同作用下的内力计算

针对杆件在横向力和轴向压力共同作用下的内力计算问题进行了研究．在考虑杆件变形因素的情形下,推导出了杆件在横向力和轴向压力共同作用下的内力和正应力的计算公式,并与材料力学中未考虑杆件变形因素的对应公式进行了比较,说明了二者之间不同之处．     

薄板结构加筋布局优化设计方法研究

提出一种两步优化策略,以加筋板结构的固有频率最大化为目标函数,以结构所受外载荷作用的最大静变形为约束条件,开展薄板结构加筋构件的布局优化设计研究。为了降低加筋布局优化的难度,提高优化设计的效率,将加筋等效为一系列弹性铰（点）支撑,以便快速获得加筋横向移动的灵敏度信息。在基本不改变结构重量的情形下,通过合理布局加筋位置,能显著改善结构的刚度分布,提高结构的整体承载能力。随后,小幅调整加筋的截面尺寸,以满足对结构最大变形的设计要求。最后,用两个算例验证了所提优化方法的可行性和有效性。     

考虑侧面摩擦的侧限压缩模型的数值解法

海上箱筒型基础结构下沉到位后,舱内土体的受力变形可以看作是侧限压缩模型问题,上部荷载引起的侧壁摩擦力与土体应力之间的关系较为复杂。本文通过简化模型,列出了侧限压缩模型的平衡微分方程,分析了方程解析计算时存在的难点,结合摩擦应力边界条件的特点,构造函数迭代法对该方程进行数值求解,展示了计算的收敛过程,得到接触侧面上水平应力和土体表面位移的非线性分布规律,并将其结果与ABAQUS数值模拟结果进行了对比。结果表明,函数迭代法收敛速度较快,计算过程稳定,对其他存在变量耦合边界条件的微分方程数值求解有一定的参考价值。