Home About us Contact
|
Home About us Contact | ||
|
|
||
Cleavage Planes (cleavage + plane)
Selected AbstractsSpace-demanding intramolecular isomerizations in the solid stateJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2002G. Kaupp Abstract The thermal isomerizations of meso - and rac -3,4-dibromo-1,6-diphenyl-1,6-bis(p -tolyl)-1,2,4,5-hexatetraene (1) to give stereospecifically the 3,4-bis(phenyl- p -tolylmethylene)-1,2-dibromocyclobutenes 3 and 5,+,6 were studied in the solid state using atomic force microscopy (AFM) and interpreted on the basis of known crystal structural data. These isomerizations run to completion in the bulk and include highly space-demanding internal rotations around the central bond. Far-reaching anisotropic molecular movements are detected on the major faces that align the surface features along cleavage planes in the initial phase rebuilding stage. Only one of three identified cleavage planes of meso - 1 is successful, owing to closer interactions of the bromine substituents in the non-used cleavage planes. Thus, very fine details can be correlated and predicted for the occurrence of internal rotations and molecular movements in the crystal lattice. The second stage in these intramolecular isomerizations, the phase transformation, produces very high features up to 100,nm and still parallel to the preferred cleavage plane of meso - 1 but in the,µm range without relation to the initial crystal structure in the case of rac - 1. Copyright © 2002 John Wiley & Sons, Ltd. [source] Estimation of screened plasma resonance frequencies of a layered semiconductor using a single oblique incidence reflectance spectrumPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007O. Foltin Abstract The second derivative of a simulated oblique incidence specular reflectance spectrum of infrared radiation, polarized parallel to the plane of incidence, shows the possibility of estimating the values of two screened plasma resonance frequencies of an optically uniaxial semiconductor by knowledge of a single spectrum. The use of a basal plane reflection surface enables us, in a case of a layered semiconductor, to avoid a troublesome production and a poor spectroscopic quality of the reflection surface oriented normal to the easy cleavage plane, otherwise needed for one of the normal incidence reflectance measurements. For the calculations the parameters of a Bi2Se3 crystal were used. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reining in cytokinesis with a septin corralBIOESSAYS, Issue 1 2005Fern P. Finger Septins are a family of conserved GTP-binding proteins that function in cytokinesis in fungi and animals. In budding yeast, septins form scaffolds for assembly of the actomyosin contractile ring at the cleavage plane, a role that does not appear to be conserved in other organisms. The septins form an hourglass-shaped collar at the mother-bud neck, which splits into two rings flanking the division plane at cytokinesis. A recent study1 demonstrates that these two septin rings constitute diffusion barriers that create a cytokinetic compartment to retain cortical cytokinetic factors in proximity to the cleavage plane. BioEssays 27:5,8, 2005. © 2004 Wiley Periodicals, Inc. [source] Alcohol vs. mechanical delamination in the treatment of corneal erosion: an electron microscopic studyACTA OPHTHALMOLOGICA, Issue 2009I PALADINI Purpose To performed an electron microscopy study to investigate the cleavage plane and the efficacy of alcohol delamination in recurrent corneal erosion (RCE). Methods By electron microscopy we analysed the epithelium of: seven controls treated with mechanical debridment, seven controls treated with alcohol delamination, ten cases of traumatic RCE and seven RCE due to MDFP treated with alcohol delamination, with special regard to the epithelial cells and the cleavage plane. Moreover we analysed four corneas from penetrating keratoplastys that were treated by alcohol delamination on the bench and both the epithelium and stroma were studied. Results In traumatic RCE the basement membrane remained in situ, a precondition for quick epithelial healing . In MDFP the whole basement membrane was detached from the stroma and remained adherent to the epithelium, therefore after alcohol delamination the healing process should be different between MDFP and traumatic RCE. Conclusion The present findings give strenght to alcohol delamination as a promising treatment for RCE [source] Mechanical properties of single crystalline and glassy lithium triborateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2008I. P. Shakhverdova Abstract Mechanical properties of LiB3O5 single crystal plates with different orientation as well as of glass with the same composition have been investigated. The nano- (H) and microhardness (HM), the reduced Young's modulus (Er) and the crack behaviour of the samples were studied. Both hardness and Young's modulus of glass appeared smaller in comparison to corresponding single crystal data (H , 7 , 8 GPa, HM , 6 GPa, Er , 70 , 80 GPa for glass and H , 10 , 15 GPa, HM , 6 ,11 GPa, Er , 93 , 155 GPa for single crystal). H, Er, and the plane of crack propagation proved orientation-dependent. Cracks in the glass sample were not observed up to 0.49 N microindentation load, whereas for the single crystal the cracks appeared already at 0.098N. In single crystals the observed cleavage planes {211} and/or {412} are oriented nearly parallel to planes of B-O rings. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal growth of mixed-valence ammonium vanadatesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2007Tie-Zhen Ren Abstract A new method has been developed for the synthesis of mixed-valence ammonium vanadate crystals. Single crystals of (NH4)2V3O8 were synthesized on a large scale by hydrothermal reduction of NH4VO3 in ethanol-H2O solutions in the presence of triblock copolymer Pluronic P123. The crystals are shining thin plates with (001) cleavage planes. Calcination of the (NH4)2V3O8 crystals at 300°C or above resulted in pure phases of V2O5. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AFM study of the surface morphology of the {100} cleavage planes of L-arginine phosphate monohydrate single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2004Y. L. Geng Abstract Surface morphology of the {100} cleavage planes of L-arginine phosphate monohydrate single crystals grown from aqueous solutions is described and discussed. Different from the previous studies, dislocations are not frequently detected and most of them don't have hollow cores on the emergence points. Various step patterns are also described. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Some aspects of spiralian developmentACTA ZOOLOGICA, Issue 1 2010Claus Nielsen Abstract Nielsen, C. 2010. Some aspects of spiralian development. ,Acta Zoologica (Stockholm) 91: 20,28 Spiralian development is not only a characteristic early cleavage pattern, with shifting orientations of the cleavage planes, but also highly conserved cell lineages, where the origin of several organs can be traced back to identifiable cells in the lineage. These patterns are well documented in annelids, molluscs, nemertines, and platyhelminths and are considered ancestral of a bilaterian clade including these phyla. Spiral cleavage has not been documented in ecdysozoans, and no trace of the spiral development pattern is seen in phoronids and brachiopods. Origin of the spatial organization in spiralian embryos is puzzling, but much of the information appears to be encoded in the developing oocyte. Fertilization and "pseudofertilization" apparently provides the information defining the secondary, anterior-posterior body axis in many species. The central nervous system consists of three components: an apical organ, derived from the apical blastomeres 1a111 -1d111, which degenerates before or at metamorphosis; the cerebral ganglia derived from other blastomeres of the first micromere quartet and retained in the adult as a preoral part of the brain; and the originally circumblastoporal nerve cord, which has become differentiated into a perioral part of the brain, the paired or secondarily fused ventral nerve cords, and a small perianal nerve ring. [source] Space-demanding intramolecular isomerizations in the solid stateJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2002G. Kaupp Abstract The thermal isomerizations of meso - and rac -3,4-dibromo-1,6-diphenyl-1,6-bis(p -tolyl)-1,2,4,5-hexatetraene (1) to give stereospecifically the 3,4-bis(phenyl- p -tolylmethylene)-1,2-dibromocyclobutenes 3 and 5,+,6 were studied in the solid state using atomic force microscopy (AFM) and interpreted on the basis of known crystal structural data. These isomerizations run to completion in the bulk and include highly space-demanding internal rotations around the central bond. Far-reaching anisotropic molecular movements are detected on the major faces that align the surface features along cleavage planes in the initial phase rebuilding stage. Only one of three identified cleavage planes of meso - 1 is successful, owing to closer interactions of the bromine substituents in the non-used cleavage planes. Thus, very fine details can be correlated and predicted for the occurrence of internal rotations and molecular movements in the crystal lattice. The second stage in these intramolecular isomerizations, the phase transformation, produces very high features up to 100,nm and still parallel to the preferred cleavage plane of meso - 1 but in the,µm range without relation to the initial crystal structure in the case of rac - 1. Copyright © 2002 John Wiley & Sons, Ltd. [source] Role of Internal Friction in Indentation Damage in a Mica-Containing Glass-CeramicJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Anthony C. Fischer-Cripps The indentation response of a mica-containing glass-ceramic that exhibits shear-driven yield in an indentation test is interpreted in terms of events occurring on the microstructural scale. It is proposed that shear-driven damage within the specimen occurs via internal sliding along cleavage planes within the mica platelets. The sliding surfaces in this case are considered to be atomically smooth so the real and apparent areas of contact coincide. The frictional shear stress is thus independent of the normal forces arising from thermal mismatch stresses and only depends on the work of adhesion of the interface and the scale of the contacts. The scale of contacts for these materials lies within an intermediate zone in which the frictional shear stress arises from the stress required to nucleate dislocation-like discontinuities within the material. This leads to a size effect similar to that experienced by a crack in Mode II loading and is in accordance with previous work in which a connection between such a size effect and the macroscopic response of the material was identified. This work has particular relevance to the design and manufacturing of ceramics in machining, wear, bearings, and coatings applications. [source] | |||||||||||||