The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
N Nanninga - One of the best experts on this subject based on the ideXlab platform.
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the relation between cell size chromosome length and the orientation of chromosomes in dividing root cortex cells
Plant and Soil, 1994Co-Authors: N NanningaAbstract:Cells in the root meristem are organised in longitudinal files. Repeated transverse cell divisions in these files are the prime cause of root growth. Because of the orientation of the cell divisions, we expected to find mitoses with an Spindle Axis parallel to the file Axis. However, we observed in the root cortex ofVicia faba large number of oblique chromosome orientations. From metaphase to telophase there was a dramatic increase of the rotation of the Spindle Axis. Measurements of both the size of the cortex cells and the chromosome configurations indicated that most cells were too small for an orientation of the Spindle parallel to the file Axis. Space limitation force the Spindle into an oblique position. Despite this Spindle Axis rotation, most daughter cells remained within the original cell file. Only in extremely flat cells did the position of the daughter nuclei forced the cell to set a plane of division parallel to the file Axis, which result in side-by-side orientation of the daughter cells. Telophase Spindle Axis rotations are also observed inCrepis capillaris andPetunia hybrida.. These species have respectively medium and small sized chromosomes compared toVicia. Since space limitation, which causes the rotation, depends both on cell and chromosome size, the frequency and extent of the phenomenon in former two species is comparatively low.
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cell shape chromosome orientation and the position of the plane of division in vicia faba root cortex cells
Journal of Cell Science, 1992Co-Authors: N NanningaAbstract:Three-dimensional chromosome orientation was studied in thick sections of Vicia faba root meristem, using confocal microscopy and digital image analysis techniques. In the proliferative part of the root meristem, where the cells are organized in longitudinal files, it was expected to find dividing cells with a Spindle Axis parallel to the file Axis and, occasionally, perpendicular to the file Axis (resulting in a local file bifurcation). However, we observed a large number of oblique Spindle axes. From metaphase to telophase there was a progressive increase in the rotation of the Spindle Axis. A 90° turn of the metaphase equator plane was never observed. Three-dimensional measurements of both the space occupied by the ana- and telophase chromosome configurations, and the size of the corresponding cortex cells, showed that most cells were too flat for an orientation of the Spindle parallel to the file Axis. Apparently, cell size limitations forced the Spindle to rotate during mitosis. Consequently, the nuclei in the daughter cells were positioned diagonally in opposite directions, instead of on top of each other. In the majority of these cells, a transverse plane of division would intersect the nuclei. Therefore, the new cell wall was sigmoid shaped or oblique. Most daughter cells remained within the original cell file but, occasionally, in extremely flat cells the position of the daughter nuclei forced the cell to set a plane of division parallel to the file Axis. This resulted in file bifurcation. It has been concluded that cell shape, the extent of Spindle rotation and the position of the division plane are related.
Jiri Vyroubal - One of the best experts on this subject based on the ideXlab platform.
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Compensation of machine tool thermal deformation in Spindle Axis direction based on decomposition method
Precision Engineering, 2012Co-Authors: Jiri VyroubalAbstract:One of the fundamental areas in high precision cutting is represented by the machine's thermal state monitoring. Understanding of this state gives significant information about the overall machine condition such as proper performance of cooling system as well as software compensation of machine's thermal deformation during manufacturing. This paper presents a method focused on compensation of machine's thermal deformation in Spindle Axis direction based on decomposition analysis. The machine decomposition is performed with the help of specially developed measuring frame, which is able to measure deformation of machine column, headstock, Spindle and tool simultaneously. Compensation is than calculated as a sum of multinomial regression equations using temperature measurement. New placements of temperature measurement like Spindle cooling liquid or workspace are used to improve the accuracy of this calculation. Decomposition process allows describing each machine part's thermal dynamic more precisely than the usual deformation curve usually used one deformation curve for the complete machine. The residual thermal deformation of the machine is considerably reduced with this cheap and effective strategy. The advantage is also in the simplicity of presented method which is clear and can be used also on older machines with slower control systems without strong computing power. ?? 2011 Elsevier Inc. All Rights Reserved.
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compensation of machine tool thermal deformation in Spindle Axis direction based on decomposition method
Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 2012Co-Authors: Jiri VyroubalAbstract:One of the fundamental areas in high precision cutting is represented by the machine's thermal state monitoring. Understanding of this state gives significant information about the overall machine condition such as proper performance of cooling system as well as software compensation of machine's thermal deformation during manufacturing. This paper presents a method focused on compensation of machine's thermal deformation in Spindle Axis direction based on decomposition analysis. The machine decomposition is performed with the help of specially developed measuring frame, which is able to measure deformation of machine column, headstock, Spindle and tool simultaneously. Compensation is than calculated as a sum of multinomial regression equations using temperature measurement. New placements of temperature measurement like Spindle cooling liquid or workspace are used to improve the accuracy of this calculation. Decomposition process allows describing each machine part's thermal dynamic more precisely than the usual deformation curve usually used one deformation curve for the complete machine. The residual thermal deformation of the machine is considerably reduced with this cheap and effective strategy. The advantage is also in the simplicity of presented method which is clear and can be used also on older machines with slower control systems without strong computing power.
C. Park - One of the best experts on this subject based on the ideXlab platform.
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Parallelism measurement of the slide Axis with respect to the Spindle Axis of a diamond turning machine
Proceedings of the 5th International Conference on Leading Edge Manufacturing in 21st Century LEM 2009, 2009Co-Authors: Jiye Lee, Y. Noh, W. Gao, Y. Arai, J Hwang, C. ParkAbstract:To measure the parallelism error between the Z-slide Axis and the Spindle Axis of the ultra precision diamond turning machine which has a T-base design with a Spindle, an X-slide and a Z-slide, the rotating reversal method is carried out. Two capacitance probes are employed for the measurement of the cylinder workpiece(for rotating) which was installed on the Spindle. The straightness error of the Z-slide of the ultra-precision diamond turning machine was measured to be about 100 nm and parallelism error was evaluated to be approximately 0.84 arc-second of the Z-slide by the rotating reversal method over a movement range of 126 mm.
Jiye Lee - One of the best experts on this subject based on the ideXlab platform.
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Parallelism measurement of the slide Axis with respect to the Spindle Axis of a diamond turning machine
Proceedings of the 5th International Conference on Leading Edge Manufacturing in 21st Century LEM 2009, 2009Co-Authors: Jiye Lee, Y. Noh, W. Gao, Y. Arai, J Hwang, C. ParkAbstract:To measure the parallelism error between the Z-slide Axis and the Spindle Axis of the ultra precision diamond turning machine which has a T-base design with a Spindle, an X-slide and a Z-slide, the rotating reversal method is carried out. Two capacitance probes are employed for the measurement of the cylinder workpiece(for rotating) which was installed on the Spindle. The straightness error of the Z-slide of the ultra-precision diamond turning machine was measured to be about 100 nm and parallelism error was evaluated to be approximately 0.84 arc-second of the Z-slide by the rotating reversal method over a movement range of 126 mm.
Kerry Bloom - One of the best experts on this subject based on the ideXlab platform.
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ChromoShake: a chromosome dynamics simulator reveals that chromatin loops stiffen centromeric chromatin
Molecular Biology of the Cell, 2015Co-Authors: Josh Lawrimore, Joseph K. Aicher, Patrick J. Hahn, Alyona Fulp, Ben Kompa, Leandra Vicci, Michael R. Falvo, Russell M. Taylor, Kerry BloomAbstract:ChromoShake is a three-dimensional simulator designed to find the thermodynamically favored states for given chromosome geometries. The simulator has been applied to a geometric model based on experimentally determined positions and fluctuations of DNA and the distribution of cohesin and condensin in the budding yeast centromere. Simulations of chromatin in differing initial configurations reveal novel principles for understanding the structure and function of a eukaryotic centromere. The entropic position of DNA loops mirrors their experimental position, consistent with their radial displacement from the Spindle Axis. The barrel-like distribution of cohesin complexes surrounding the central Spindle in metaphase is a consequence of the size of the DNA loops within the pericentromere to which cohesin is bound. Linkage between DNA loops of different centromeres is requisite to recapitulate experimentally determined correlations in DNA motion. The consequences of radial loops and cohesin and condensin binding are to stiffen the DNA along the Spindle Axis, imparting an active function to the centromere in mitosis.
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dyskerin trna genes and condensin tether pericentric chromatin to the Spindle Axis in mitosis
Journal of Cell Biology, 2014Co-Authors: Chloe E Snider, Andrew D Stephens, Jacob G Kirkland, Omar Hamdani, Rohinton T Kamakaka, Kerry BloomAbstract:Condensin is enriched in the pericentromere of budding yeast chromosomes where it is constrained to the Spindle Axis in metaphase. Pericentric condensin contributes to chromatin compaction, resistance to microtubule-based Spindle forces, and Spindle length and variance regulation. Condensin is clustered along the Spindle Axis in a heterogeneous fashion. We demonstrate that pericentric enrichment of condensin is mediated by interactions with transfer ribonucleic acid (tRNA) genes and their regulatory factors. This recruitment is important for generating axial tension on the pericentromere and coordinating movement between pericentromeres from different chromosomes. The interaction between condensin and tRNA genes in the pericentromere reveals a feature of yeast centromeres that has profound implications for the function and evolution of mitotic segregation mechanisms.
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The spatial segregation of pericentric cohesin and condensin in the mitotic Spindle
Molecular Biology of the Cell, 2013Co-Authors: Andrew D Stephens, Russell M. Taylor, Julian Haase, Cory Quammen, Binny Chang, Kerry BloomAbstract:In mitosis, the pericentromere is organized into a spring composed of cohesin, condensin, and a rosette of intramolecular chromatin loops. Cohesin and condensin are en- riched in the pericentromere, with spatially distinct patterns of localization. Using model convolution of computer simulations, we deduce the mechanistic consequences of their spa- tial segregation. Condensin lies proximal to the Spindle Axis, whereas cohesin is radially dis- placed from condensin and the interpolar microtubules. The histone deacetylase Sir2 is re- sponsible for the axial position of condensin, while the radial displacement of chromatin loops dictates the position of cohesin. The heterogeneity in distribution of condensin is most accurately modeled by clusters along the Spindle Axis. In contrast, cohesin is evenly distrib- uted (barrel of 500-nm width × 550-nm length). Models of cohesin gradients that decay from the centromere or sister cohesin Axis, as previously suggested, do not match experimental images. The fine structures of cohesin and condensin deduced with subpixel localization ac - curacy reveal critical features of how these complexes mold pericentric chromatin into a functional spring.
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Cohesin, condensin, and the intramolecular centromere loop together generate the mitotic chromatin spring
Journal of Cell Biology, 2011Co-Authors: Andrew D Stephens, Leandra Vicci, Russell M. Taylor, Julian Haase, Kerry BloomAbstract:Sister chromatid cohesion provides the mechanistic basis, together with Spindle microtubules, for generating tension between bioriented chromosomes in metaphase. Pericentric chromatin forms an intramolecular loop that protrudes bidirectionally from the sister chromatid Axis. The centromere lies on the surface of the chromosome at the apex of each loop. The cohesin and condensin structural maintenance of chromosomes (SMC) protein complexes are concentrated within the pericentric chromatin, but whether they contribute to tension-generating mechanisms is not known. To understand how pericentric chromatin is packaged and resists tension, we map the position of cohesin (SMC3), condensin (SMC4), and pericentric LacO arrays within the Spindle. Condensin lies proximal to the Spindle Axis and is responsible for axial compaction of pericentric chromatin. Cohesin is radially displaced from the Spindle Axis and confines pericentric chromatin. Pericentric cohesin and condensin contribute to Spindle length regulation and dynamics in metaphase. Together with the intramolecular centromere loop, these SMC complexes constitute a molecular spring that balances Spindle microtubule force in metaphase.
