Packing and Uniaxial Alignment of Liquid Crystalline Oligofluorenes

Summary: Liquid crystalline oligomers of 9,9‐bis(2‐ethylhexyl)fluorene of defined degree of polymerization 4, 5, 6, and 7 were investigated by X‐ray diffraction in the non‐oriented and in the aligned state. The diffraction data give evidence for a smectic B type phase for all of the oligomers. Quenching below the glass transition does not change the structure of the liquid crystalline phase. This allows to align spin‐coated films of these oligomers on rubbed polyimide substrates to give monodomain films. These are stable against thermal disordering below T_g, e.g. at room temperature. The degree of alignment is characterized by the dichroic spectra and polarized fluorescence spectra. Dichroic ratios and polarization ratios increase substantially with the chain length and values as high as D = 23 and P = 41 are obtained for the heptamer. The type of packing of the oligomers in the LC phase is discussed based on the X‐ray single crystal structure of models. In one such model the packing of the 2‐ethylhexyl side chains could be fully resolved, while the other model reveals the torsional angle between adjacent fluorene units in the same molecule as 144.2° which corroborates earlier work based on fiber diffraction of corresponding polyfluorenes.

     

3D MRI-Based Multicomponent FSI Models for Atherosclerotic Plaques

A three-dimensional (3D) MRI-based computational model with multicomponent plaque structure and fluid-structure interactions (FSI) is introduced to perform mechanical analysis for human atherosclerotic plaques and identify critical flow and stress/strain conditions which may be related to plaque rupture. Three-dimensional geometry of a human carotid plaque was reconstructed from 3D MR images and computational mesh was generated using Visualization Toolkit. Both the artery wall and the plaque components were assumed to be hyperelastic, isotropic, incompressible, and homogeneous. The flow was assumed to be laminar, Newtonian, viscous, and incompressible. The fully coupled fluid and structure models were solved by ADINA, a well-tested finite element package. Results from two-dimensional (2D) and 3D models, based on ex vivo MRI and histological images (HI), with different component sizes and plaque cap thickness, under different pressure and axial stretch conditions, were obtained and compared. Our results indicate that large lipid pools and thin plaque caps are associated with both extreme maximum (stretch) and minimum (compression when negative) stress/strain levels. Large cyclic stress/strain variations in the plaque under pulsating pressure were observed which may lead to artery fatigue and possible plaque rupture. Large-scale patient studies are needed to validate the computational findings for possible plaque vulnerability assessment and rupture predictions.     

Separate and variably shaped chromosome arm domains are disclosed by chromosome arm painting in human cell nuclei

Fluorescence in situ hybridization (FISH) with microdissection probes from human chromosomes 3 and 6 was applied to visualize arm and subregional band domains in human amniotic fluid cell nuclei. Confocal laser scanning microscopy and quantitative three-dimensional image analysis showed a pronounced variability of p- and q-arm domain arrangements and shapes. Apparent intermingling of neighbouring arm domains was limited to the domain surface. Three-dimensional distance measurements with pter and qter probes supported a high variability of chromosome territory folding.     

Regional differences in the compaction of chromatin in human G0/G1 interphase nuclei

The large-scale structure of chromatin corresponding to G- and R-bands in human G₀/G₁ interphase nuclei was compared. Fluorescence in situ hybridization (FISH) was used to measure the interphase distance between 42 pairs of probes separated by 0.1–1.5Mbp. The probe pairs were derived from 21q22.2 and Xp21.3, G-band positive regions, and from 4p16.3, 6p21.3, and Xq28, R-band positive regions. Distributions of measured interphase distances in all regions approximated a Rayleigh distribution, suggesting that the chromatin follows a random-walk path over this range. A linear correlation of mean-square interphase distance and genomic separation, also indicative of random-walk folding, was observed in all regions. The slope of the correlation observed using probes from G-band regions was systematically lower than that from R-band regions. The difference in the slope between Xp21.3 and Xq28 was particularly striking and was observed in normal fibroblast cells, fixed alternatively with methanol and acetic acid or paraformaldehyde, and HeLa cells. These results demonstrate regional differences in large-scale chromosome structure during interphase, with the more openly configured chromatin corresponding to R-bands.This revised version was published online in November 2005 with corrections to the Cover Date.     

床边屏蔽辅助板的设计

目的　制作具有升降调节功能的床边屏蔽辅助板 ,防范等高散射线 ,增加近台操作的安全防护系数 ,使腹部以下透射剂量率下降至最小程度。方法　制作带有内铅层的空腔竖立直板 ,内层铅板可在竖立直板空腔内上 下移动 ,满足不同的床边屏蔽高度。结果　屏蔽床边位屏蔽辐射实验测定值与市防站的实际测定值分别为 2 .5 0× 10 8μGy/h和 2 .5 8× 10 8μGy/h,符合最优化设计及国家标准要求。结论　本研究研制的床边屏蔽辅助板具有较高的临床实用价值     

大鼠三叉神经本体觉中枢通路二级神经元中继咬肌本体觉传入的微超结构证据

将Ricin注入大鼠咬肌神经,存活2周左右,再将HRP分别定位电泳于作为三叉神经本体觉中枢通路三级传入神经元所在地的三叉神经感觉主核背内侧部(Vpdm)和三叉神经运动核腹侧区(AVM)。电镜观察结果表明,在三叉神经本体觉中枢通路二级传入神经元所在地的三叉神经脊束核吻侧亚核背内侧部(Vodm),初级传入的溃变终末与HRP逆标的树突间形成非对称型突触,确证了Vodm是三叉神经本体觉中枢通路的中继核团。突触后树突多为中间树突和近侧树突。此外,在Vodm区还发现来自Vpdm的顺行标记终末与非标记的树突形成突触。本研究证明Vodm区超微结构有以下几个特征:(1)轴-体突触极少见;(2)轴-棘突触少见;(3)突触小球结构少见;(4)大扇贝形终末较少见;(5)这一区域也有小颗粒泡和大颗粒泡终末。这些超微结构特征,可能是Vodm与三叉神经感觉核簇其它部位区别之点,也可能是本体感觉中继核团特有的结构特征。     

Cloning and characterization of the cDNA encoding the HA protein of a hemagglutination-defective measles virus strain

cDNA clones corresponding to the mRNA for the hemagglutinin of the hemagglutination-defective strain AK-1 of measles virus were isolated and characterized. Compared with the prototype Edmonstron strain, 60 nucleotide substitutions that resulted in 18 amino acid changes were detected. An additional potential N-linked glycosylation site was added by point mutation, which was supported by the observation that the hemagglutinin of the AK-1 strain was stained more heavily after NaDodSO₄PAGE and periodic acid-Schiff (PAS) staining than the Edmonston strain. Computer-assisted analysis revealed that three reverse turns in the secondary structure had disappeared in the hemagglutinin of the AK-1 strain. Moreover, one of these structural changes occurred in the closely glycosylated region at amino acid residues 168–240, which appeared to be a biologically important functional domain. The isoelectric point calculated from the predicted amino acid sequence became about 1 pH unit more basic in the AK-1 strain than the Edmonston strain. This present study is the first sequence analysis of the hemagglutinin gene in a hemagglutination-defective strain of the measles virus.     

An Analytic Model of Subminiature Auditory Sensation System for Sound Source Localization

It is reported that some types of insects have a remarkable ability to detect the direction of an incident sound even though its acoustic sensory organs are in very close proximity each other. Maybe the ears are jointed by a cuticular structure with which the separated motions can be coupled mechanically and thus be magnified. In this paper, a detailed model is setup to describe the principle of this type of localization using a mechanical coupled structure. The transfer functions and the responses of the model in terms of time and frequency are analyzed to describe the mechanism of its ability of directional hearing. This analytical model provides a method to design the experimental model for the predetermined incident sound pressure, and the analysis of this model shows that this structure have the ability to determine the direction of the incident stimulus.     

高频电刀对家兔活体肌肉组织的作用

目的 :探讨高频电刀对肌肉组织结构的作用。方法 :用高频电极在不同输出功率时测定大白家兔活体肌肉组织的电流强度 ,灼伤中心区汽化深度和汽化表面积 ,光镜和电镜下观察创面下 0～ 6mm深度的组织结构变化。结果 :随着电流输出功率的增强 ,肌肉组织的电流强度 ,中心区汽化深度和汽化表面积也随之增加 ,创面深部组织显微和超微结构发生了热凝固性改变 ,损伤程度随着离中心区距离的延长而减弱 ,但在 6mm深处仍有较明显的损伤性改变。结论 :用高频电刀操作时应注意对深部肌肉组织的损伤性作用 ,为减少损伤应注意操作时的电流强度和电灼时间。