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The Experimental Herbicide CGA 325′615 Inhibits Synthesis of Crystalline Cellulose and Causes Accumulation of Non-Crystalline β-1,4-Glucan Associated with CesA Protein1

Peng, Liangcai; Xiang, Fan; Roberts, Eric; Kawagoe, Yasushi; Greve, L. Carl; Kreuz, Klaus; Delmer, Deborah P.
Fonte: American Society of Plant Physiologists Publicador: American Society of Plant Physiologists
Tipo: Artigo de Revista Científica
Publicado em /07/2001 EN
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279.54564%
Developing cotton (Gossypium hirsutum) fibers, cultured in vitro with their associated ovules, were used to compare the effects of two herbicides that inhibit cellulose synthesis: 2,6-dichlorobenzonitrile (DCB) and an experimental thiatriazine-based herbicide, CGA 325′615. CGA 325′615 in nanomolar concentrations or DCB in micromolar concentrations causes inhibition of synthesis of crystalline cellulose. Unlike DCB, CGA 325′615 also causes concomitant accumulation of non-crystalline β-1,4-glucan that can be at least partially solubilized from fiber walls with ammonium oxalate. The unusual solubility of this accumulated glucan may be explained by its strong association with protein. Treatment of the glucan fraction with protease changes its size distribution and leads to precipitation of the glucan. Treatment of the glucan fraction with cellulase digests the glucan and also releases protein that has been characterized as GhCesA-1 and GhCesA-2—proteins that are believed to represent the catalytic subunit of cellulose synthase. The fact that cellulase treatment is required to release this protein indicates an extremely tight association of the glucan with the CesA proteins. In addition, CGA 325′615, but not DCB, also causes accumulation of CesA protein and a membrane-associated cellulase in the membrane fraction of fibers. In addition to the effects of CGA 325′615 on levels of both of these proteins...

Solid-State 13C Nuclear Magnetic Resonance Characterization of Cellulose in the Cell Walls of Arabidopsis thaliana Leaves.

Newman, R. H.; Davies, L. M.; Harris, P. J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1996 EN
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278.54148%
Solid-state 13C nuclear magnetic resonance was used to characterize the molecular ordering of cellulose in a cell-wall preparation containing mostly primary walls obtained from the leaves of Arabidopsis thaliana. Proton and 13C spin relaxation time constants showed that the cellulose was in a crystalline rather than a paracrystalline state or amorphous state. Cellulose chains were distributed between the interiors (40%) and surfaces (60%) of crystallites, which is consistent with crystallite cross-sectional dimensions of about 3 nm. Digital resolution enhancement revealed signals indicative of triclinic and monoclinic crystalline forms of cellulose mixed in similar proportions. Of the five nuclear spin relaxation processes used, proton rotating-frame relaxation provided the clearest distinction between cellulose and other cell-wall components for purposes of editing solid-state 13C nuclear magnetic resonance spectra.

Molecular Rigidity in Dry and Hydrated Onion Cell Walls.

Ha, M. A.; Apperley, D. C.; Jarvis, M. C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1997 EN
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287.47559%
Solid-state nuclear magnetic resonance relaxation experiments can provide information on the rigidity of individual molecules within a complex structure such as a cell wall, and thus show how each polymer can potentially contribute to the rigidity of the whole structure. We measured the proton magnetic relaxation parameters T2 (spin-spin) and T1p (spin-lattice) through the 13C-nuclear magnetic resonance spectra of dry and hydrated cell walls from onion (Allium cepa L.) bulbs. Dry cell walls behaved as rigid solids. The form of their T2 decay curves varied on a continuum between Gaussian, as in crystalline solids, and exponential, as in more mobile materials. The degree of molecular mobility that could be inferred from the T2 and T1p decay patterns was consistent with a crystalline state for cellulose and a glassy state for dry pectins. The theory of composite materials may be applied to explain the rigidity of dry onion cell walls in terms of their components. Hydration made little difference to the rigidity of cellulose and most of the xyloglucan shared this rigidity, but the pectic fraction became much more mobile. Therefore, the cellulose/xyloglucan microfibrils behaved as solid rods, and the most significant physical distinction within the hydrated cell wall was between the microfibrils and the predominantly pectic matrix. A minor xyloglucan fraction was much more mobile than the microfibrils and probably corresponded to cross-links between them. Away from the microfibrils...

Expansin mode of action on cell walls. Analysis of wall hydrolysis, stress relaxation, and binding.

McQueen-Mason, S J; Cosgrove, D J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1995 EN
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278.91926%
The biochemical mechanisms underlying cell wall expansion in plants have long been a matter of conjecture. Previous work in our laboratory identified two proteins (named "expansins") that catalyze the acid-induced extension of isolated cucumber cell walls. Here we examine the mechanism of expansin action with three approaches. First, we report that expansins did not alter the molecular mass distribution or the viscosity of solutions of matrix polysaccharides. We conclude that expansins do not hydrolyze the major pectins or hemicelluloses of the cucumber wall. Second, we investigated the effects of expansins on stress relaxation of isolated walls. These studies show that expansins account for the pH-sensitive and heat-labile components of wall stress relaxation. In addition, these experiments show that expansins do not cause a progressive weakening of the walls, as might be expected from the action of a hydrolase. Third, we studied the binding of expansins to the cell wall and its components. The binding characteristics are consistent with this being the site of expansin action. We found that expansins bind weakly to crystalline cellulose but that this binding is greatly increased upon coating the cellulose with various hemicelluloses. Xyloglucan...

Immersion Refractometry of Isolated Bacterial Cell Walls

Marquis, Robert E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1973 EN
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282.82873%
Immersion-refractometric and light-scattering measurements were adapted to determinations of average refractive indices and physical compactness of isolated bacterial cell walls. The structures were immersed in solutions containing various concentrations of polymer molecules that cannot penetrate into wall pores, and then an estimate was made of the polymer concentration or the refractive index of the polymer solution in which light scattering was reduced to zero. Because each wall preparation was heterogeneous, the refractive index of the medium for zero light scattering had to be estimated by extrapolation. Refractive indices for walls suspended in bovine serum albumin solutions ranged from 1.348 for walls of the rod form of Arthrobacter crystallopoietes to 1.382 for walls of the teichoic acid deficient, 52A5 strain of Staphylococcus aureus. These indices were used to calculate approximate values for solids content per milliliter, and the calculated values agreed closely with those estimated from a knowledge of dextran-impermeable volumes per gram, dry weight, of the walls. When large molecules such as dextrans or serum albumin were used for immersion refractometry, the refractive indices obtained were for entire walls, including both wall polymers and wall water. When smaller molecules that can penetrate wall pores to various extents were used with Micrococcus lysodeikticus walls...

X-Ray Diffraction Studies on Selected Bacterial Cell Walls

Carito, Sebastian L.; Bazil, Stephen L.; DiGiacomo, Giulio
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1967 EN
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276.6137%
The cell walls of selected bacteria were studied by X-ray diffraction analysis to determine and characterize crystalline components. The walls were isolated by mechanical disruption and purified by enzymatic and washing procedures. The X-ray diffraction lines which appeared from the gram-positive cell walls were shown to be due to the constituent “mucopeptide” fraction. No diffraction lines could be obtained from the gram-negative bacterium studied. The results show that crystallinity is associated with mucopeptide.

Carbohydrate-binding modules promote the enzymatic deconstruction of intact plant cell walls by targeting and proximity effects

Hervé, Cécile; Rogowski, Artur; Blake, Anthony W.; Marcus, Susan E.; Gilbert, Harry J.; Knox, J. Paul
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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278.91926%
Cell wall degrading enzymes have a complex molecular architecture consisting of catalytic modules and noncatalytic carbohydrate-binding modules (CBMs). The function of CBMs in cell wall degrading processes is poorly understood. Here, we have evaluated the potential enzyme-targeting function of CBMs in the context of intact primary and secondary cell wall deconstruction. The capacity of a pectate lyase to degrade pectic homogalacturonan in primary cell walls was potentiated by cellulose-directed CBMs but not by xylan-directed CBMs. Conversely, the arabinofuranosidase-mediated removal of side chains from arabinoxylan in xylan-rich and cellulose-poor wheat grain endosperm cell walls was enhanced by a xylan-binding CBM but less so by a crystalline cellulose-specific module. The capacity of xylanases to degrade xylan in secondary cell walls was potentiated by both xylan- and cellulose-directed CBMs. These studies demonstrate that CBMs can potentiate the action of a cognate catalytic module toward polysaccharides in intact cell walls through the recognition of nonsubstrate polysaccharides. The targeting actions of CBMs therefore have strong proximity effects within cell wall structures, explaining why cellulose-directed CBMs are appended to many noncellulase cell wall hydrolases.

Development of Cellulosic Secondary Walls in Flax Fibers Requires β-Galactosidase1[C][W][OA]

Roach, Melissa J.; Mokshina, Natalia Y.; Badhan, Ajay; Snegireva, Anastasiya V.; Hobson, Neil; Deyholos, Michael K.; Gorshkova, Tatyana A.
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
EN
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276.6137%
Bast (phloem) fibers, tension wood fibers, and other cells with gelatinous-type secondary walls are rich in crystalline cellulose. In developing bast fibers of flax (Linum usitatissimum), a galactan-enriched matrix (Gn-layer) is gradually modified into a mature cellulosic gelatinous-layer (G-layer), which ultimately comprises most of the secondary cell wall. Previous studies have correlated this maturation process with expression of a putative β-galactosidase. Here, we demonstrate that β-galactosidase activity is in fact necessary for the dynamic remodeling of polysaccharides that occurs during normal secondary wall development in flax fibers. We found that developing stems of transgenic (LuBGAL-RNAi) flax with reduced β-galactosidase activity had lower concentrations of free Gal and had significant reductions in the thickness of mature cellulosic G-layers compared with controls. Conversely, Gn-layers, labeled intensively by the galactan-specific LM5 antibody, were greatly expanded in LuBGAL-RNAi transgenic plants. Gross morphology and stem anatomy, including the thickness of bast fiber walls, were otherwise unaffected by silencing of β-galactosidase transcripts. These results demonstrate a specific requirement for β-galactosidase in hydrolysis of galactans during formation of cellulosic G-layers. Transgenic lines with reduced β-galactosidase activity also had biochemical and spectroscopic properties consistent with a reduction in cellulose crystallinity. We further demonstrated that the tensile strength of normal flax stems is dependent on β-galactosidase-mediated development of the phloem fiber G-layer. Thus...

Comprehensive Compositional Analysis of Plant Cell Walls (Lignocellulosic biomass) Part II: Carbohydrates

Foster, Cliff E.; Martin, Tina M.; Pauly, Markus
Fonte: MyJove Corporation Publicador: MyJove Corporation
Tipo: Artigo de Revista Científica
Publicado em 12/03/2010 EN
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280.58441%
The need for renewable, carbon neutral, and sustainable raw materials for industry and society has become one of the most pressing issues for the 21st century. This has rekindled interest in the use of plant products as industrial raw materials for the production of liquid fuels for transportation2 and other products such as biocomposite materials6. Plant biomass remains one of the greatest untapped reserves on the planet4. It is mostly comprised of cell walls that are composed of energy rich polymers including cellulose, various hemicelluloses, and the polyphenol lignin5 and thus sometimes termed lignocellulosics. However, plant cell walls have evolved to be recalcitrant to degradation as walls contribute extensively to the strength and structural integrity of the entire plant. Despite its necessary rigidity, the cell wall is a highly dynamic entity that is metabolically active and plays crucial roles in numerous cell activities such as plant growth and differentiation5. Due to the various functions of walls, there is an immense structural diversity within the walls of different plant species and cell types within a single plant4. Hence, depending of what crop species, crop variety, or plant tissue is used for a biorefinery, the processing steps for depolymerisation by chemical/enzymatic processes and subsequent fermentation of the various sugars to liquid biofuels need to be adjusted and optimized. This fact underpins the need for a thorough characterization of plant biomass feedstocks. Here we describe a comprehensive analytical methodology that enables the determination of the composition of lignocellulosics and is amenable to a medium to high-throughput analysis (Figure 1). The method starts of with preparing destarched cell wall material. The resulting lignocellulosics are then split up to determine its monosaccharide composition of the hemicelluloses and other matrix polysaccharides1...

Powerful regulatory systems and post-transcriptional gene silencing resist increases in cellulose content in cell walls of barley

Tan, H.T.; Shirley, N.J.; Singh, R.R.; Henderson, M.; Dhugga, K.S.; Mayo, G.M.; Fincher, G.B.; Burton, R.A.
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
Publicado em //2015 EN
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384.0721%
BACKGROUND: The ability to increase cellulose content and improve the stem strength of cereals could have beneficial applications in stem lodging and producing crops with higher cellulose content for biofuel feedstocks. Here, such potential is explored in the commercially important crop barley through the manipulation of cellulose synthase genes (CesA). RESULTS: Barley plants transformed with primary cell wall (PCW) and secondary cell wall (SCW) barley cellulose synthase (HvCesA) cDNAs driven by the CaMV 35S promoter, were analysed for growth and morphology, transcript levels, cellulose content, stem strength, tissue morphology and crystalline cellulose distribution. Transcript levels of the PCW HvCesA transgenes were much lower than expected and silencing of both the endogenous CesA genes and introduced transgenes was often observed. These plants showed no aberrant phenotypes. Although attempts to over-express the SCW HvCesA genes also resulted in silencing of the transgenes and endogenous SCW HvCesA genes, aberrant phenotypes were sometimes observed. These included brittle nodes and, with the 35S:HvCesA4 construct, a more severe dwarfing phenotype, where xylem cells were irregular in shape and partially collapsed. Reductions in cellulose content were also observed in the dwarf plants and transmission electron microscopy showed a significant decrease in cell wall thickness. However...

Morphological studies of polymeric systems with liquid crystalline order

O'Rourke, Mary Jane Elizabeth.
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (260, [3] leaves); 13118425 bytes; 13118226 bytes; application/pdf; application/pdf
ENG
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280.58441%
This thesis addresses the structure, properties, and processing of various liquid crystal polymer systems. Morphologies of microphase separated side chain liquid crystal block copolymers are determined, both in the bulk and when confined to thin films. We show for the first time how these materials could potentially be used as a novel kind of surface stabilized liquid crystal display device. Magnetic field induced structures in a thermotropic main chain liquid crystal homopolymer were also examined. Defects in orienting fields are of interest because liquid crystal displays must be defect free over large areas. A study of the interaction of defects in an applied field yields information towards optimally processing these materials in order to minimize or completely eliminate these defects. The basic building block of the systems investigated is a liquid crystal mesogen. Liquid crystal mesogens are easily oriented by electric, magnetic, and flow fields and interact with polarized light such that they are desirable materials for display devices. Additionally, these systems are all polymeric, lending the complexity of the molecules' long-chain nature to the material properties, and the resulting processing challenges and mechanical advantages inherent to polymers. Polarized light microscopy (PLM)...

Distribution and conformation of crystalline nigeran in hyphal walls of Aspergillus niger and Aspergillus awamori.

Bobbitt, T F; Nordin, J H; Roux, M; Revol, J F; Marchessault, R H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1977 EN
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289.7617%
Hyphal walls of Aspergillus awamori containing increased amount of the alpha-glucan, nigeran, became correspondingly more opaque when viewed in the electron microscope as shadowed preparations. However, increased polymer deposition was not accompanied by any significant change in wall thickness. The nigeran of both A. awamori and Aspergillus niger occurred in situ in a crystalline conformation identical to that of single crystals prepared with pure polysaccharide. Furthermore, this polymer was the dominant crystalline material in the hyphae whether or not they were enriched in nigeran. Enzymic digestion of nigeran in A. niger and A. awamori revealed that the bulk of the polymer was exposed to the cell's exterior. However, a certain fraction was accessible to enzymic attack only after the wall was treated with boiling water. A third portion, detectable only by x-ray diffraction, was associated with other components and could not be extracted, even with prolonged boiling. It was removed by hot, dilute alkali and was associated in the wall with another glucan fraction. Dry heating of A. niger walls altered their susceptibility to enzymic digestion of nigeran in situ. It is proposed that this treatment introduces interstices in the crystal surface that facilitate attack.

Charge-order domain walls with enhanced conductivity in a layered manganite

Ma, Eric Yue; Bryant, Benjamin; Tokunaga, Yusuke; Aeppli, Gabriel; Tokura, Yoshinori; Shen, Zhi-Xun
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 03/07/2015 EN
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278.91926%
Interfaces and boundaries in condensed-matter systems often have electronic properties distinct from the bulk material and thus have become a topic of both fundamental scientific interest and technological importance. Here we identify, using microwave impedance microscopy, enhanced conductivity of charge-order domain walls in the layered manganite Pr(Sr0.1Ca0.9)2Mn2O7. We obtain a complete mesoscopic map of surface topography, crystalline orientation and electronic phase, and visualize the thermal phase transition between two charge-ordered phases. In both phases, charge-order domains occur with domain walls showing enhanced conductivity likely due to local lifting of the charge order. Finite element analysis shows that the resolved domain walls can be as narrow as few nanometres. The domain walls are stabilized by structural twins and have a strong history dependence, suggesting that they may be manipulated to create novel devices.

Magnetic domain walls in nanostrips of single-crystalline $\mathrm{Fe}_4\mathrm{N}(001)$ thin films with fourfold in-plane magnetic anisotropy

Ito, Keita; Rougemaille, Nicolas; Pizzini, Stefania; Honda, Syuta; Ota, Norio; Suemasu, Takashi; Fruchart, Olivier
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/11/2015
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282.82873%
We investigated head-to-head domain walls in nanostrips of epitaxial $\mathrm{Fe}_4\mathrm{N}(001)$ thin films, displaying a fourfold magnetic anisotropy. Magnetic force microscopy and micromagnetic simulations show that the domain walls have specific properties, compared to soft magnetic materials. In particular, strips aligned along a hard axis of magnetization are wrapped by partial flux-closure concertina domains below a critical width, while progressively transforming to zigzag walls for wider strips. Transverse walls are favored upon initial application of a magnetic field transverse to the strip, while transformation to a vortex walls is favored upon motion under a longitudinal magnetic field. In all cases the magnetization texture of such fourfold anisotropy domain walls exhibits narrow micro-domain walls, which may give rise to peculiar spin-transfer features.; Comment: 7 pages, 6 figures

Inducing magnetism onto the surface of a topological crystalline insulator

Assaf, Badih A.; Katmis, Ferhat; Wei, Peng; Chang, Cui-Zu; Satpati, Biswarup; Moodera, Jagadeesh S.; Heiman, Don
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/04/2015
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278.54148%
Inducing magnetism onto a topological crystalline insulator (TCI) has been predicted to result in several novel quantum electromagnetic effects. This is a consequence of the highly strain-sensitive band topology of such symmetry-protected systems. We thus show that placing the TCI surface of SnTe in proximity to EuS, a ferromagnetic insulator, induces magnetism at the interface between SnTe and EuS and thus breaks time-reversal-symmetry in the TCI. Magnetotransport experiments on SnTe-EuS-SnTe trilayer devices reveal a hysteretic lowering of the resistance at the TCI surface that coincides with an increase in the density of magnetic domain walls. This additional conduction could be a signature of topologically-protected surface states within domain walls. Additionally, a hysteretic anomalous Hall effect reveals that the usual in-plane magnetic moment of the EuS layer is canted towards a perpendicular direction at the interface. These results are evidence of induced magnetism at the SnTe-EuS interfaces resulting in broken time-reversal symmetry in the TCI.; Comment: Accepted for publication in Physical Review B

Homogeneous Alignment of Liquid Crystalline Dendrimers Confined in a Slit-Pore: Computational Simulation Study

Workineh, Zerihun G.; Vanakaras, Alexandros G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/11/2015
Relevância na Pesquisa
278.54148%
In this work we present results from NPT(isobaric-isothermal) Monte Carlo Simulation studies of Liquid Crystalline Dendrimer (LCDr) systems confined in a slit-pore made of two parallel flat walls. We investigate the substrate induced conformational and alignment properties of the system at different thermodynamic state points under uniform (unidirectional) anchoring condition. Tractable coarse grained force fields to model both monomer-monomer and monomer-substrate interaction potentials have been used from our previous work. In this anchoring condition, at lower pressure almost all the monomers are anchored to the substrates and mesogens are perfectly aligned with the aligning direction. This alignment is not uniformly transmitted to the bulk region as the pressure grows, instead, it decays with distance from the surface to the bulk region. Due to this reason, the global orintational order parameter decreases with increasing pressure (density). In the neighborhood (2-3 mesogenic diameter) of upper and lower walls, mesogenic units form smectic A like structure whose layers are separated by layers of spherical beads. In this region individual LCDrs possess a rod like shape.; Comment: 10 pages, 15 JPEG figures

Defects on cylinders: superfluid helium films and bacterial cell walls

Nelson, David R.; Amir, Ariel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/03/2013
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278.54148%
There is a deep analogy between the physics of crystalline solids and the behavior of superfluids, dating back to pioneering work of Phillip Anderson, Paul Martin and others. The stiffness to shear deformations in a periodic crystal resembles the superfluid density that controls the behavior of supercurrents in neutral superfluids such as He^4. Dislocations in solids have a close analogy with quantized vortices in superfluids. Remarkable recent experiments on the way rod-shaped bacteria elongate their cell walls have focused attention on the dynamics and interactions of point-like dislocation defects in partially ordered cylindrical crystalline monolayers. In these lectures, we review the physics of superfluid helium films on cylinders and discuss how confinement in one direction affects vortex interactions with supercurrents. Although there are similarities with the way dislocations respond to strains on cylinders, important differences emerge, due to the vector nature of the topological charges characterizing the dislocations.; Comment: Lectures given by D. R. Nelson at the Les Houches School on "Soft Interfaces", July 2-27, 2012

Simulation of fluid-solid coexistence in finite volumes: A method to study the properties of wall-attached crystalline nuclei

Deb, Debabrata; Winkler, Alexander; Virnau, Peter; Binder, Kurt
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/03/2012
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277.17383%
The Asakura-Oosawa model for colloid-polymer mixtures is studied by Monte Carlo simulations at densities inside the two-phase coexistence region of fluid and solid. Choosing a geometry where the system is confined between two flat walls, and a wall-colloid potential that leads to incomplete wetting of the crystal at the wall, conditions can be created where a single nanoscopic wall-attached crystalline cluster coexists with fluid in the remainder of the simulation box. Following related ideas that have been useful to study heterogeneous nucleation of liquid droplets at the vapor-liquid coexistence, we estimate the contact angles from observations of the crystalline clusters in thermal equilibrium. We find fair agreement with a prediction based on Young's equation, using estimates of interface and wall tension from the study of flat surfaces. It is shown that the pressure versus density curve of the finite system exhibits a loop, but the pressure maximum signifies the "droplet evaporation-condensation" transition and thus has nothing in common with a van der Waals-like loop. Preparing systems where the packing fraction is deep inside the two-phase coexistence region, the system spontaneously forms a "slab state", with two wall-attached crystalline domains separated by (flat) interfaces from liquid in full equilibrium with the crystal in between; analysis of such states allows a precise estimation of the bulk equilibrium properties at phase coexistence.

A crustal-upper-mantle model for the Colorado Plateau based on observations of crystalline rock fragments in the Moses Rock Dike

McGetchin, Thomas R.; Silver, Leon T.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 10/12/1972
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284.0721%
On the basis of the size, the abundance, and the petrographic character of xenoliths in the Moses Rock dike, a model for the vertical stratigraphy of crystalline rocks beneath the dike is proposed extending from near the surface to a depth of about 200 km. Sedimentary clasts, whose original position in the undisturbed vent walls is known but which are now within the intrusive breccia of the Moses Rock dike, show a decrease in size with distance of upward transport from their original position in the vent walls. This inverse relationship between fragment size and known depth of origin provides an empirical basis for a reconstructed model for the distribution of rocks on the basis of the particle size of fragments in the intrusive breccia. Metabasalt, granite, and granite gneiss are abundant in the upper part of the crust along the dike walls; diorite, gabbro, and amphibole schists of basic composition constitute intermediate layers, and garnet-bearing metagabbro (basic granulite gneiss) and serpentine schist are present in the lower crust. The crustal rock suite is predominantly metavolcanic and metaplutonic and basic in composition. Dense ultramafic rocks, possibly derived from the mantle, constitute about 0.3% of the breccia filling the dike and include jadeite-rich clinopyroxenite...

Fractionation of carbohydrates in Arabidopsis root cell walls shows that three radial swelling loci are specifically involved in cellulose production.

Peng, L; Hocart, Charles; Redmond, J; Williamson, Richard
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
373.21023%
Three non-allelic radial swelling mutants (rsw1, rsw2 and rsw3) of Arabidopsis thaliana L. Heynh. were shown to be specifically impaired in cellulose production. Fractionation methods that identify, characterise and quantify some of the major cell wall polysaccharides in small quantities of seedlings demonstrated that changes in the production of cellulose are much more pronounced than changes in the production of non-cellulosic polysaccharides. A crude cell wall pellet was sequentially extracted with chloroform methanol (to recover lipids), dimethyl sulphoxide (starch), ammonium oxalate (pectins) and alkali (hemicelluloses). Crystalline cellulose remained insoluble through subsequent treatments with an acetic/nitric acid mixture and with trifluoroacetic acid. Cetyltrimethylammonium bromide precipitation resolved neutral and acidic polymers in the fractions, and precipitation behaviour, monosaccharide composition and glycosidic linkage patterns identified the major polysaccharides. The deduced composition of the walls of wild-type Seedlings and the structure and solubility properties of the major polymers were broadly typical of other dicots. The three temperature-sensitive, radial swelling mutants produced less cellulose in their roots than the wild type when grown at their restrictive temperature (31 °C). There were no significant differences at 21 °C where no radial swelling occurs: The limited changes seen in the monosaccharide compositions...