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Parallel Arrangement (parallel + arrangement)

Distribution by Scientific Domains
Medical Sciences40%

Selected Abstracts

Study of order and dynamic processes in tendon by NMR and MRI

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2007
G. Navon PhD
Abstract Tendons are composed of a parallel arrangement of densely packed collagen fibrils that results in unique biomechanical properties of strength and flexibility. In the present review we discuss several advanced magnetic resonance spectroscopy (MRS) and imaging (MRI) techniques that have allowed us to better understand the biophysical properties of tendons and ligaments. The methods include multiple quantum and T2 filtering combined with NMR and MRI techniques. It is shown in detail how these techniques can be used to extract a number of useful parameters: 1) the 1H- 1H and 1H- 2H dipolar interactions; 2) the proton exchange rates between water and collagen, and between water molecules; 3) the distribution of fibril orientations; and 4) the anisotropy of diffusion. It is shown that relaxation data as a function of angular dependence can be obtained in vivo using mobile NMR sensors. Finally, this article describes how double quantum filtered (DQF) MRI can be used to image and monitor the healing process in injured tendons. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [source]

Ultrastructural and MRI study of the substantia nigra evolving exofocal post-ischemic neuronal death in the rat

NEUROPATHOLOGY, Issue 3 2002
Fengyu Zhao
To clarify the morphological characteristics of exofocal post-ischemic neuronal death (EPND) in the substantia nigra (SN), we investigated the course of light- and electron-microscopic changes of the SN of rats subjected to occlusion of the left middle cerebral artery (MCA) for 1, 2, 4, 7 and 12 days. To assess cellular edema, sequential magnetic resonance (MR) mapping of the apparent diffusion coefficient (ADC) and the T2 value test was performed. Histological and electron-microscopic examination on day 1 showed dotted chromatin clumps in the nuclei of some neurons and mild swelling of the perivascular endfeet of astrocytes in the ipsilateral SN. On day 2, a few cells of the ipsilateral SN pars reticulata (SNr) revealed key morphological signs of apoptosis , apoptotic body-like condensation and segregation of the chromatin and DNA fragmentation-like nuclear remnants. On day 4, 38% of neurons became swollen (pale neurons) with cytoplasmic microvacuoles, which appeared to originate from rough endoplasmic reticulum (rER), mitochondria and Golgi apparatus. Twenty percent of neurons showed massive proliferation of the cisternae of the rER, some of which were fragmented or had lost their normal parallel arrangement. In addition, MR mapping revealed a transient ADC decrease with a T2 increase (signifying a phase of cellular edema), which coordinated with the phase of ultrastructural cellular swelling. Further, the total number of neurons started to decrease gradually, the perivascular endfeet of astrocytes were markedly swollen, and the neuropil became loose on day 4. On day 7, reactive astrocytes and dark neurons occurred most frequently. These results suggest that the EPND in the SN after occlusion of the MCA in adult rats is due to both apoptosis and necrosis, although necrosis seems to be the dominant mechanism of the EPND. However, the morphologic resemblances of EPND to delayed neuronal death suggest these processes have a common pathomechanism. [source]

An unusual three-dimensional chiral threefold polycatenating network self-assembled from inclined two-dimensional (4,4) layer motifs

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2010
Suna Wang
In the coordination compound poly[diaqua(,2 -4,4,-bipyridine)(,2 -4-carboxylatocinnamato)nickel(II)], [Ni(C10H6O4)(C10H8N2)(H2O)2]n, both the 4-carboxylatocinnamate and 4,4,-bipyridine (4,4,-bpy) ligands act as bidentate bridges, connecting the NiII centres in an octahedral coordination geometry into a two-dimensional (4,4) layer. Each layer polycatenates two other identical layers, thus giving a rare 2D , 3D polycatenating network (2D and 3D are two- and three-dimensional, respectively), with a mutually parallel arrangement of the layers. The chiral 4,4,-bpy ligands link the NiII centres into chiral chains, thus introducing chirality into the layer and the resulting 3D network. [source]

Two crystal forms of mesogenic bis(4,-cyanobiphenyl-4-yl) butanedioate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009
Kayako Hori
The title compound, C30H20N2O4, exhibits a nematic phase in the wide temperature range between 498.5 and 538.6,K, in spite of the short linker moiety. Two crystal forms have been found. In both forms, the molecule is centrosymmetric. Form I has a planar biphenyl group, while form II has a twisted biphenyl group with a twist angle of 34.75,(6)°. The packing modes are also different. In form I the long molecular axes are tilted with respect to each other at about 30°, while in form II the long molecular axes have an almost parallel arrangement. [source]

The first metalloporphyrin dimer linked by a bridging phenylenedicarbene ligand

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2006
Hidetaka Yuge
In the first bis­[ruthenium(II),porphyrin],dicarbene complex, ,-[1,4-phenyl­ene­bis(phenyl­methyl­idene-,C)]bis­[(ethanol-,O)(5,10,15,20-tetra- p -tolyl­porphyrinato-,4N)ruthenium(II)] 1,2-di­chloro­ethane trisolvate, [Ru2(C20H14)(C48H36N4)2(C2H6O)2]·3C2H4Cl2, an inversion center is located at the center of the ,-phenyl­ene group, leading to a parallel arrangement for the pair of porphyrin ring systems. The bond lengths and angles compare favourably with literature values for ruthenium,porphyrin,monocarbene complexes; the Ru=C(carbene) bond length and the C(phenyl),C(carbene),C(phenyl­ene) angle are 1.865,(3),Å and 112.3,(3)°, respectively. The RuII ion is displaced out of the C20N4 porphyrin least-squares plane (by 0.2373,Å) toward the bridging ligand of the Ci -symmetry dimer. The porphyrin ring systems of the dimer thus exhibit mildly domed conformations. [source]