Journal articles on the topic 'Multiple Nucleation Sites'
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1
Seltzer, V. "Multiple microtubule nucleation sites in higher plants." Cell Biology International 27, no. 3 (2003): 267–69. http://dx.doi.org/10.1016/s1065-6995(02)00345-1.
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Nisany, Stav, and Dan Mordehai. "A Multiple Site Type Nucleation Model and Its Application to the Probabilistic Strength of Pd Nanowires." Metals 12, no. 2 (February 4, 2022): 280. http://dx.doi.org/10.3390/met12020280.
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Pristine specimens yield plastically under high loads by nucleating dislocations. Since dislocation nucleation is a thermally activated process, the so-called nucleation-controlled plasticity is probabilistic rather than deterministic, and the distribution of the yield strengths depends on the activation parameters to nucleate. In this work, we develop a model to predict the strength distribution in nucleation-controlled plasticity when there are multiple nucleation site types. We then apply the model to molecular dynamics (MD) simulations of Pd nanowires under tension. We found that in Pd nanowires with a rhombic cross-section, nucleation starts from the edges, either with the acute or the obtuse cross-section angles, with a probability that is temperature-dependent. We show that the distribution of the nucleation strain is approximately normal for tensile loading at a constant strain rate. We apply the proposed model and extract the activation parameters for site types from both site types. With additional nudged elastic bands simulations, we propose that the activation entropy, in this case, has a negligible contribution. Additionally, the free-energy barriers obey a power-law with strain, with different exponents, which corresponds to the non-linear elastic deformation of the nanowires. This multiple site type nucleation model is not subjected only to two site types and can be extended to a more complex scenario like specimen with rough surfaces which has a distribution of nucleation sites with different conditions to nucleate dislocations.
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Erhardt, Mathieu, Virginie Stoppin-Mellet, Sarah Campagne, Jean Canaday, Jérôme Mutterer, Tanja Fabian, Margret Sauter, et al. "The plant Spc98p homologue colocalizes with γ-tubulin at microtubule nucleation sites and is required for microtubule nucleation." Journal of Cell Science 115, no. 11 (June 1, 2002): 2423–31. http://dx.doi.org/10.1242/jcs.115.11.2423.
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The molecular basis of microtubule nucleation is still not known in higher plant cells. This process is better understood in yeast and animals cells. In the yeast spindle pole body and the centrosome in animal cells,γ-tubulin small complexes and γ-tubulin ring complexes,respectively, nucleate all microtubules. In addition to γ-tubulin,Spc98p or its homologues plays an essential role. We report here the characterization of rice and Arabidopsis homologues of SPC98. Spc98p colocalizes with γ-tubulin at the nuclear surface where microtubules are nucleated on isolated tobacco nuclei and in living cells. AtSpc98p-GFP also localizes at the cell cortex. Spc98p is not associated with γ-tubulin along microtubules. These data suggest that multiple microtubule-nucleating sites are active in plant cells. Microtubule nucleation involving Spc98p-containing γ-tubulin complexes could then be conserved among all eukaryotes, despite differences in structure and spatial distribution of microtubule organizing centers.
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Roudsari, Golnaz, Olli H. Pakarinen, Bernhard Reischl, and Hanna Vehkamäki. "Atomistic and coarse-grained simulations reveal increased ice nucleation activity on silver iodide surfaces in slit and wedge geometries." Atmospheric Chemistry and Physics 22, no. 15 (August 8, 2022): 10099–114. http://dx.doi.org/10.5194/acp-22-10099-2022.
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Abstract. Ice clouds can form at low and moderate supercooling through heterogeneous ice nucleation on atmospheric particles. Typically, the nucleation requires active sites with special chemical and physical properties, including surface topology and roughness. This paper investigates microscopic mechanisms of how combinations of confinement by the surface topology and lattice match induced by the surface properties can lead to enhanced ice nucleation. We perform molecular dynamics simulations using both atomistic and coarse-grained water models, at very low supercooling, to extensively study heterogeneous ice nucleation in slit-like and concave wedge structures of silver-terminated silver iodide (0001) surfaces. We find that ice nucleation is greatly enhanced by slit-like structures when the gap width is a near-integer multiple of the thickness of an ice bilayer. For wedge systems we also do not find a simple linear dependence between ice nucleation activity and the opening angle. Instead we observe strong enhancement in concave wedge systems with angles that match the orientations of ice lattice planes, highlighting the importance of structural matching for ice nucleation in confined geometries. While in the slit systems ice cannot grow out of the slit, some wedge systems show that ice readily grows out of the wedge. In addition, some wedge systems stabilize ice structures when heating the system above the thermodynamics melting point. In the context of atmospheric ice-nucleating particles, our results strongly support the experimental evidence for the importance of surface features such as cracks or pits functioning as active sites for ice nucleation at low supercooling.
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Dong, Fu, and Liao Tao. "Vapour-to-Liquid Nucleation in Associating Lennard-Jones Fluids with Multiple Association Sites." Chinese Physics Letters 24, no. 10 (September 28, 2007): 2804–7. http://dx.doi.org/10.1088/0256-307x/24/10/025.
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Lee, Sooheyong, Haeng Sub Wi, Wonhyuk Jo, Yong Chan Cho, Hyun Hwi Lee, Se-Young Jeong, Yong-Il Kim, and Geun Woo Lee. "Multiple pathways of crystal nucleation in an extremely supersaturated aqueous potassium dihydrogen phosphate (KDP) solution droplet." Proceedings of the National Academy of Sciences 113, no. 48 (October 24, 2016): 13618–23. http://dx.doi.org/10.1073/pnas.1604938113.
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Solution studies have proposed that crystal nucleation can take more complex pathways than previously expected in classical nucleation theory, such as formation of prenucleation clusters or densified amorphous/liquid phases. These findings show that it is possible to separate fluctuations in the different order parameters governing crystal nucleation, that is, density and structure. However, a direct observation of the multipathways from aqueous solutions remains a great challenge because heterogeneous nucleation sites, such as container walls, can prevent these paths. Here, we demonstrate the existence of multiple pathways of nucleation in highly supersaturated aqueous KH2PO4(KDP) solution using the combination of a containerless device (electrostatic levitation), and in situ micro-Raman and synchrotron X-ray scattering. Specifically, we find that, at an unprecedentedly deep level of supersaturation, a high-concentration KDP solution first transforms into a metastable crystal before reaching stability at room temperature. However, a low-concentration solution, with different local structures, directly transforms into the stable crystal phase. These apparent multiple pathways of crystallization depend on the degree of supersaturation.
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Arafin, Muhammad A., and Jerzy A. Szpunar. "A Markov Chain Fracture Model for Intergranular Crack Propagation in Polycrystalline Materials." Advanced Materials Research 89-91 (January 2010): 29–34. http://dx.doi.org/10.4028/www.scientific.net/amr.89-91.29.
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A model for intergranular damage propagation in polycrystalline materials is proposed, based on Markov Chain theory, Monte Carlo simulation and percolation concept. The model takes into account crack branching and coalescence, multiple crack nucleation sites, crack-turning etc., as well as the effect of grain boundary plane orientations with respect to the external stress direction. Both honeycomb and voronoi microstructures were utilized as the input microstructures. The effect of multiple crack nucleation sites has been found to have great influence on the crack propagation length. It has been observed that percolation threshold reported in the literature based on hexagonal microstructure is not applicable when the effect of external stress direction on the susceptibilities of grain boundaries is considered. The successful integration of voronoi algorithm with the Markov Chain and Monte Carlo simulations has opened up the possibilities of evaluating the intergranular crack propagation behaviour in a realistic manner.
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Pach, Ladislav, Rustum Roy, and Sridhar Komarneni. "Nucleation of alpha alumina in boehmite gel." Journal of Materials Research 5, no. 2 (February 1990): 278–85. http://dx.doi.org/10.1557/jmr.1990.0278.
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Transformation of boehmitc-derived alumina gel to α–Al2O3 in unseeded gels is strongly influenced by the parent phase, θ-Al2O3. In seeded gels the perfect structure of the epitaxial substrate (α–Al2O3, 0.3 wt. %) influences the surrounding defect θ-phase resulting in (a) fewer imperfections due to lower transformation enthalpy to α–Al2O3, and (b) multiple nucleation sites of α–Al2O3 at the α–Al2O3 seed surface. The rate of transformation expressed for the same number of α–Al2O3 nuclei in unseeded and seeded gels indicates that it is faster in the unseeded gel than in the seeded gel.
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Broadley, S. L., B. J. Murray, R. J. Herbert, J. D. Atkinson, S. Dobbie, E. Condliffe, and L. Neve. "Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust." Atmospheric Chemistry and Physics Discussions 11, no. 8 (August 12, 2011): 22801–56. http://dx.doi.org/10.5194/acpd-11-22801-2011.
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Abstract. Atmospheric dust rich in illite is transported globally from arid regions and may impact cloud properties through the nucleation of ice. We present measurements of ice nucleation in water droplets containing known quantities of an illite rich powder under atmospherically relevant conditions. The illite rich powder used here, NX illite, has a similar mineralogical composition to atmospheric mineral dust sampled in remote locations, i.e. dust which has been subject to long range transport, cloud processing and sedimentation. Arizona Test Dust has a significantly different mineralogical composition and we suggest that NX illite is a better surrogate of natural atmospheric dust. Heterogeneous nucleation by NX illite was observed, using optical microscopy, to occur dominantly between 246 K and the homogeneous freezing limit and higher freezing temperatures were observed with larger surface areas of NX illite present within the droplets. It is shown that there is strong particle to particle variability in terms of ice nucleating ability with a few particles dominating ice nucleation at high surface areas. In fact, this work suggests that the bulk of atmospheric mineral dust particles are less efficient at nucleating ice than assumed in parameterisation currently used in models. For droplets containing ≤2 × 10−6 cm2 of NX illite, freezing temperatures did not noticeably change when the cooling rate was varied by an order of magnitude. The data obtained during cooling experiments (with surface areas ≤2 × 10−6 cm2) is shown to be inconsistent with the single component stochastic model, but is well described by the singular model (ns(236.2 K ≤ T ≤ 247.5 K) = exp(6.53043 × 104 − 8.2153088 × 102 T + 3.446885376 T 2 − 4.822268 × 10−3 T3). However, droplets continued to freeze when the temperature was held constant, which is inconsistent with the time independent singular model. We show that this apparent discrepancy can be resolved using a multiple component stochastic model in which it is assumed there are many types of nucleation sites, each with a unique temperature dependent nucleation coefficient. Cooling rate independence can be achieved with this time dependent model if the nucleation rate coefficients increase very rapidly with decreasing temperature, thus reconciling our measurement of nucleation at constant temperature with the cooling rate independence.
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Monk, P. N., and P. Banks. "Evidence for the involvement of multiple signalling pathways in C5a-induced actin polymerization and nucleation in human monocyte-like cells." Journal of Molecular Endocrinology 6, no. 3 (June 1991): 241–47. http://dx.doi.org/10.1677/jme.0.0060241.
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ABSTRACT The signal transduction mechanisms involved in complement fragment C5a-induced recruitment of actin to the cytoskeleton have been investigated using U-937 cells differentiated by exposure to dibutyryl cyclic AMP. Two parameters of cytoskeletal activation were compared: F-actin formation and nucleation of polymerization of pyrenyl-actin in whole cell lysates. The dose dependency of these responses to C5a was clearly different to that observed for [3H]inositol phosphate formation and also markedly different from that observed for the production of reactive oxygen intermediates (ROI). Further evidence to dissociate inositol lipid hydrolysis from these cytoskeletal responses was obtained by treating cells with neomycin, phorbol myristate acetate and pertussis toxin and by modulating the levels of intracellular Ca2+ using quin 2. Inhibition of [3H]inositol phosphate and ROI production was not correlated with effects on actin recruitment or nucleation. In addition, these agents had differing effects on F-actin formation and nucleation activity. The results show that the production of inositol phosphates is not required for stimulating either F-actin formation or nucleation activity and also that ligand-induced polymerization of actin depends primarily upon an increase in the availability of G-actin rather than nucleation sites. These cytoskeletal responses are apparently controlled by different signalling pathways which diverge at an early stage.
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She, Yihong, Zhen Wu, Shengdong You, Quan Du, Xiaohong Chu, Lijuan Niu, Changchun Ding, Kenan Zhang, Lijie Zhang, and Shaoming Huang. "Multiple-Dimensionally Controllable Nucleation Sites of Two-Dimensional WS2/Bi2Se3 Heterojunctions Based on Vapor Growth." ACS Applied Materials & Interfaces 13, no. 13 (March 26, 2021): 15518–24. http://dx.doi.org/10.1021/acsami.1c00377.
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Broadley, S. L., B. J. Murray, R. J. Herbert, J. D. Atkinson, S. Dobbie, T. L. Malkin, E. Condliffe, and L. Neve. "Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust." Atmospheric Chemistry and Physics 12, no. 1 (January 5, 2012): 287–307. http://dx.doi.org/10.5194/acp-12-287-2012.
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Abstract. Atmospheric dust rich in illite is transported globally from arid regions and impacts cloud properties through the nucleation of ice. We present measurements of ice nucleation in water droplets containing known quantities of an illite rich powder under atmospherically relevant conditions. The illite rich powder used here, NX illite, has a similar mineralogical composition to atmospheric mineral dust sampled in remote locations, i.e. dust which has been subject to long range transport, cloud processing and sedimentation. Arizona Test Dust, which is used in other ice nucleation studies as a model atmospheric dust, has a significantly different mineralogical composition and we suggest that NX illite is a better surrogate of natural atmospheric dust. Using optical microscopy, heterogeneous nucleation in the immersion mode by NX illite was observed to occur dominantly between 246 K and the homogeneous freezing limit. In general, higher freezing temperatures were observed when larger surface areas of NX illite were present within the drops. Homogenous nucleation was observed to occur in droplets containing low surface areas of NX illite. We show that NX illite exhibits strong particle to particle variability in terms of ice nucleating ability, with ~1 in 105 particles dominating ice nucleation when high surface areas were present. In fact, this work suggests that the bulk of atmospheric mineral dust particles may be less efficient at nucleating ice than assumed in current model parameterisations. For droplets containing ≤2 × 10−6 cm2 of NX illite, freezing temperatures did not noticeably change when the cooling rate was varied by an order of magnitude. The data obtained during cooling experiments (surface area ≤2 × 10−6 cm2) is shown to be inconsistent with the single component stochastic model, but is well described by the singular model (ns(236.2 K ≤ T ≤ 247.5 K) = exp(6.53043 × 104− 8.2153088 × 102T + 3.446885376T2 − 4.822268 × 10−3T3). However, droplets continued to freeze when the temperature was held constant, which is inconsistent with the time independent singular model. We show that this apparent discrepancy can be resolved using a multiple component stochastic model in which it is assumed that there are many types of nucleation sites, each with a unique temperature dependent nucleation coefficient. Cooling rate independence can be achieved with this time dependent model if the nucleation rate coefficients increase very rapidly with decreasing temperature, thus reconciling our measurement of nucleation at constant temperature with the cooling rate independence.
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Zamoum, Mohammed, Lounes Tadrist, Herve Combeau, and Mohand Kessal. "Experimental Study of Boiling Heat Transfer on Multiple and Single Nucleation Sites Using a Boiling-Meter." Heat Transfer Engineering 35, no. 5 (November 2013): 508–16. http://dx.doi.org/10.1080/01457632.2013.833052.
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Turn, Rachel E., Michael P. East, Rytis Prekeris, and Richard A. Kahn. "The ARF GAP ELMOD2 acts with different GTPases to regulate centrosomal microtubule nucleation and cytokinesis." Molecular Biology of the Cell 31, no. 18 (August 15, 2020): 2070–91. http://dx.doi.org/10.1091/mbc.e20-01-0012.
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The ELMOD2 gene has been linked to a number of human pathologies and encodes an ∼32 kDa protein that acts from multiple sites in mammalian cells. Knocking out the protein in fibroblasts causes defects in microtubules and cell division.
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Thuvander, Mattias, Marcus Andersson, and Krystyna Stiller. "Multiple Influences of Molybdenum on the Precipitation Process in a Martensitic PH Stainless Steel." Metals 9, no. 10 (October 19, 2019): 1118. http://dx.doi.org/10.3390/met9101118.
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Molybdenum has been found to influence the complex precipitation process in a martensitic precipitation hardening stainless steel during aging at 475 °C in several different ways. Three steels with different Mo content (0, 1.2 and 2.3 at.%) were investigated. Studies of the microstructure were performed with atom probe tomography and energy filtered transmission electron microscopy. It is shown that, at the initial stage of aging, a faster nucleation of Cu-rich clusters takes place with increasing Mo content. The Cu-clusters act as precipitation sites for other solute elements and promote the nucleation of Ni-rich phases. During further aging, a higher Mo content in the material instead slows down the growth and coarsening of the Ni-rich phases, because Mo segregates to the interface between precipitate and matrix. Additionally, Mo promotes decomposition of the matrix into α and α′ regions. After longer aging times (>40 h) quasicrystalline Mo-rich R′ phase forms (to a greater extent in the material having the highest Mo content). The observations serve to understand the hardness evolution during aging.
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Modesti, Mauro, Dejan Ristic, Thijn van der Heijden, Cees Dekker, Joost van Mameren, Erwin J. G. Peterman, Gijs J. L. Wuite, Roland Kanaar, and Claire Wyman. "Fluorescent Human RAD51 Reveals Multiple Nucleation Sites and Filament Segments Tightly Associated along a Single DNA Molecule." Structure 15, no. 5 (May 2007): 599–609. http://dx.doi.org/10.1016/j.str.2007.04.003.
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Huang, Chunfeng, Qi Sun, Zhiling Chen, Dongping Wen, Zongqian Tan, Yaxian Lu, Yuelan He, and Ping Chen. "Controlled Synthesis and Growth Mechanism of Two-Dimensional Zinc Oxide by Surfactant-Assisted Ion-Layer Epitaxy." Crystals 13, no. 1 (December 20, 2022): 5. http://dx.doi.org/10.3390/cryst13010005.
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Two-dimensional (2D) zinc oxide (ZnO) has attracted much attention for its potential applications in electronics, optoelectronics, ultraviolet photodetectors, and resistive sensors. However, little attention has been focused on the growth mechanism, which is highly desired for practical applications. In this paper, the growth mechanism of 2D ZnO by surfactant-assisted ion-layer epitaxy (SA-ILE) is explored by controlling the amounts of surfactant, temperature, precursor concentration, and growth time. It is found that the location and the number of nucleation sites at the initial stages are restricted by the surfactant, which absorbs ions via electrostatic attraction at the water-air interface. Then, the growth of 2D ZnO is administered by the temperature, precursors, and growth time. In other words, the temperature is connected with the diffusion of solute ions and the number of nucleation sites. The concentration of precursors determines the solute ions in solution, which plays a dominant role in the growth rate of 2D ZnO, while growth time affects the nucleation, growth, and dissolution processes of ZnO. However, if the above criteria are exceeded, the nucleation sites significantly increase, resulting in multiple 2D ZnO with tiny size and multilayers. By optimizing the above parameters, 2D ZnO nanosheets with a size as large as 20 μm are achieved with 10 × 10−5 of the ratio of sodium oleyl sulfate to , 70 °C, 50 mM of precursor concentration, and 50 min of growth time. 2D ZnO sheets, are confirmed by scanning electron microscope (SEM), energy-dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and Raman spectrum. Our work might guide the development of SA-ILE and pave the platform for practical applications of 2D ZnO on photodetectors, sensors, and resistive switching devices.
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Szakáll, Miklós, Michael Debertshäuser, Christian Philipp Lackner, Amelie Mayer, Oliver Eppers, Karoline Diehl, Alexander Theis, Subir Kumar Mitra, and Stephan Borrmann. "Comparative study on immersion freezing utilizing single-droplet levitation methods." Atmospheric Chemistry and Physics 21, no. 5 (March 4, 2021): 3289–316. http://dx.doi.org/10.5194/acp-21-3289-2021.
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Abstract. Immersion freezing experiments were performed utilizing two distinct single-droplet levitation methods. In the Mainz vertical wind tunnel, supercooled droplets of 700 µm diameter were freely floated in a vertical airstream at constant temperatures ranging from −5 to −30 ∘C, where heterogeneous freezing takes place. These investigations under isothermal conditions allow the application of the stochastic approach to analyze and interpret the results in terms of the freezing or nucleation rate. In the Mainz acoustic levitator, 2 mm diameter drops were levitated while their temperature was continuously cooling from +20 to −28 ∘C by adapting to the ambient temperature. Therefore, in this case the singular approach was used for analysis. From the experiments, the densities of ice nucleation active sites were obtained as a function of temperature. The direct comparison of the results from two different instruments indicates a shift in the mean freezing temperatures of the investigated drops towards lower values that was material-dependent. As ice-nucleating particles, seven materials were investigated; two representatives of biological species (fibrous and microcrystalline cellulose), four mineral dusts (feldspar, illite NX, montmorillonite, and kaolinite), and natural Sahara dust. Based on detailed analysis of our results we determined a material-dependent parameter for calculating the freezing-temperature shift due to a change in cooling rate for each investigated particle type. The analysis allowed further classification of the investigated materials to be described by a single- or a multiple-component approach. From our experiences during the present synergetic studies, we listed a number of suggestions for future experiments regarding cooling rates, determination of the drop temperature, purity of the water used to produce the drops, and characterization of the ice-nucleating material. The observed freezing-temperature shift is significantly important for the intercomparison of ice nucleation instruments with different cooling rates.
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Mustapa, Izan R., Robert A. Shanks, and Ing Kong. "Multiple melting behavior of poly(lactic acid)-hemp-silica composites using modulated-temperature differential scanning calorimetry." Journal of Polymer Engineering 34, no. 9 (December 1, 2014): 895–903. http://dx.doi.org/10.1515/polyeng-2013-0161.
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Abstract Poly(lactic acid) (PLA)-hemp-nanosilica (PHS) composites were prepared by impregnation of hemp woven fabric with PLA solution. Nanosilica was dispersed in the PLA solution to introduce a matrix reinforcing nanophase within the composite. The melting behavior of PLA composites was obtained by using differential scanning calorimetry (DSC) and modulated-temperature DSC (mT-DSC). Multiple melting which appeared in the non-isothermal heating curve showed that the temperature of a low melting peak increased when using a slower scanning rate. The incorporation of nanosilica in PLA composites affected the melting temperature (Tm) and sufficiently formed nucleation sites that promoted the growth of PLA crystals. Composites analyzed by a temperature-modulated program showed a broad exothermic peak before the melting peak in the non-reversing heat capacity and endothermic melting in the reversing heat capacity curve. This behavior was explained by a process of partial melting, recrystallization and remelting (mrr). The mT-DSC resolved that hemp fiber induced recrystallization and nanosilica acted as an effective nucleating agent, which promoted small and imperfect crystals that changed successively into more stable crystals through a melt-recrystallization process.
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Elhebeary, Mohamed, Tristan Harzer, Gerhard Dehm, and M. Taher A. Saif. "Time-dependent plasticity in silicon microbeams mediated by dislocation nucleation." Proceedings of the National Academy of Sciences 117, no. 29 (July 1, 2020): 16864–71. http://dx.doi.org/10.1073/pnas.2002681117.
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Understanding deformation mechanisms in silicon is critical for reliable design of miniaturized devices operating at high temperatures. Bulk silicon is brittle, but it becomes ductile at about 540 °C. It creeps (deforms plastically with time) at high temperatures (∼800 °C). However, the effect of small size on ductility and creep of silicon remains elusive. Here, we report that silicon at small scales may deform plastically with time at lower temperatures (400 °C) above a threshold stress. We achieve this stress by bending single-crystal silicon microbeams using an in situ thermomechanical testing stage. Small size, together with bending, localize high stress near the surface of the beam close to the anchor. This localization offers flaw tolerance, allowing ductility to win over fracture. Our combined scanning, transmission electron microscopy, and atomic force microscopy analysis reveals that as the threshold stress is approached, multiple dislocation nucleation sites appear simultaneously from the high-stressed surface of the beam with a uniform spacing of about 200 nm between them. Dislocations then emanate from these sites with time, lowering the stress while bending the beam plastically. This process continues until the effective shear stress drops and dislocation activities stop. A simple mechanistic model is presented to relate dislocation nucleation with plasticity in silicon.
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Hayes, Garret L., Frank C. Brown, Alexander K. Haas, Ryan M. Nottingham, Francis A. Barr, and Suzanne R. Pfeffer. "Multiple Rab GTPase Binding Sites in GCC185 Suggest a Model for Vesicle Tethering at the Trans-Golgi." Molecular Biology of the Cell 20, no. 1 (January 2009): 209–17. http://dx.doi.org/10.1091/mbc.e08-07-0740.
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GCC185, a trans-Golgi network-localized protein predicted to assume a long, coiled-coil structure, is required for Rab9-dependent recycling of mannose 6-phosphate receptors (MPRs) to the Golgi and for microtubule nucleation at the Golgi via CLASP proteins. GCC185 localizes to the Golgi by cooperative interaction with Rab6 and Arl1 GTPases at adjacent sites near its C terminus. We show here by yeast two-hybrid and direct biochemical tests that GCC185 contains at least four additional binding sites for as many as 14 different Rab GTPases across its entire length. A central coiled-coil domain contains a specific Rab9 binding site, and functional assays indicate that this domain is important for MPR recycling to the Golgi complex. N-Terminal coiled-coils are also required for GCC185 function as determined by plasmid rescue after GCC185 depletion by using small interfering RNA in cultured cells. Golgi-Rab binding sites may permit GCC185 to contribute to stacking and lateral interactions of Golgi cisternae as well as help it function as a vesicle tether.
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Vali, Gabor. "Exploratory experiments on pre-activated freezing nucleation on mercuric iodide." Atmospheric Chemistry and Physics 21, no. 4 (February 19, 2021): 2551–68. http://dx.doi.org/10.5194/acp-21-2551-2021.
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Abstract. Pre-activation of freezing nucleation (PFN) with mercuric iodide was first reported by Edwards, Evans, and Zipper (Edwards et al., 1970). They found that freezing, followed by melting just a few degrees Celsius above the melting point, leads to subsequent freezing of the sample more than 10 ∘C above the temperature of the initial nucleation temperature. Results presented in this paper are from laboratory experiments that followed the procedure designed by Edwards, Evans, and Zipper (1970) but employed multiple sample drops and many repetitions of the pre-activation cycle. The results obtained confirm the basic findings of the earlier work and refine them. It is shown that the pre-activation effect is lost gradually as the sample is heated above the melting point and that some effect is still seen with heating above +5 ∘C. Instrumental limitation in these experiments precluded detection of pre-activated freezing above −2 ∘C, but that possibility is not excluded. Some PFN was noted down to at least −6 ∘C. By also drawing on the results of Seeley and Seidler (2001), PFN is analyzed in search of constraints that help define the process responsible for it. No firm conclusions are reached, but the accumulated evidence points quite clearly to the role of surface sites in leading to PFN. Thus, sites are seen to play the same role as they do in heterogeneous freezing nucleation in general. PFN differs from pore condensation and freezing described by Marcolli (2020) and David et al. (2020), in that PFN is observed in liquid water while that process takes place in the vapor phase. Further explorations of the process leading to PFN can help in understanding ice nucleation and its practical manifestations at a basic level. The results call attention to an ice nucleation pathway hitherto barely explored that can be expected to have consequences in how ice nucleation occurs in atmospheric clouds and in other systems. PFN is also a potential tool for deliberate initiation of freezing in clouds and other systems.
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van Giessen, Alan E., and John E. Straub. "Coarse-Grained Model of Coil-to-Helix Kinetics Demonstrates the Importance of Multiple Nucleation Sites in Helix Folding." Journal of Chemical Theory and Computation 2, no. 3 (May 2006): 674–84. http://dx.doi.org/10.1021/ct0503318.
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Costabile, F., W. Birmili, S. Klose, T. Tuch, B. Wehner, A. Wiedensohler, U. Franck, K. König, and A. Sonntag. "Spatio-temporal variability and principal components of the particle number size distribution in an urban atmosphere." Atmospheric Chemistry and Physics 9, no. 9 (May 15, 2009): 3163–95. http://dx.doi.org/10.5194/acp-9-3163-2009.
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Abstract. A correct description of fine (diameter <1 μm) and ultrafine (<0.1 μm) aerosol particles in urban areas is of interest for particle exposure assessment but also basic atmospheric research. We examined the spatio-temporal variability of atmospheric aerosol particles (size range 3–800 nm) using concurrent number size distribution measurements at a maximum of eight observation sites in and around Leipzig, a city in Central Europe. Two main experiments were conducted with different time span and number of observation sites (2 years at 3 sites; 1 month at 8 sites). A general observation was that the particle number size distribution varied in time and space in a complex fashion as a result of interaction between local and far-range sources, and the meteorological conditions. To identify statistically independent factors in the urban aerosol, different runs of principal component (PC) analysis were conducted encompassing aerosol, gas phase, and meteorological parameters from the multiple sites. Several of the resulting PCs, outstanding with respect to their temporal persistence and spatial coverage, could be associated with aerosol particle modes: a first accumulation mode ("droplet mode", 300–800 nm), considered to be the result of liquid phase processes and far-range transport; a second accumulation mode (centered around diameters 90–250 nm), considered to result from primary emissions as well as aging through condensation and coagulation; an Aitken mode (30–200 nm) linked to urban traffic emissions in addition to an urban and a rural Aitken mode; a nucleation mode (5–20 nm) linked to urban traffic emissions; nucleation modes (3–20 nm) linked to photochemically induced particle formation; an aged nucleation mode (10–50 nm). Additional PCs represented only local sources at a single site, or infrequent phenomena. In summary, the analysis of size distributions of high time and size resolution yielded a surprising wealth of statistical aerosol components occurring in the urban atmosphere over one single city. A paradigm on the behaviour of sub-μm urban aerosol particles is proposed, with recommendations how to efficiently monitor individual sub-fractions across an entire city.
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Berland, Kevin, Clémence Rose, Jorge Pey, Anais Culot, Evelyn Freney, Nikolaos Kalivitis, Giorgios Kouvarakis, et al. "Spatial extent of new particle formation events over the Mediterranean Basin from multiple ground-based and airborne measurements." Atmospheric Chemistry and Physics 17, no. 15 (August 9, 2017): 9567–83. http://dx.doi.org/10.5194/acp-17-9567-2017.
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Abstract. Over the last two decades, new particle formation (NPF), i.e., the formation of new particle clusters from gas-phase compounds followed by their growth to the 10–50 nm size range, has been extensively observed in the atmosphere at a given location, but their spatial extent has rarely been assessed. In this work, we use aerosol size distribution measurements performed simultaneously at Ersa (Corsica) and Finokalia (Crete) over a 1-year period to analyze the occurrence of NPF events in the Mediterranean area. The geographical location of these two sites, as well as the extended sampling period, allows us to assess the spatial and temporal variability in atmospheric nucleation at a regional scale. Finokalia and Ersa show similar seasonalities in the monthly average nucleation frequencies, growth rates, and nucleation rates, although the two stations are located more than 1000 km away from each other. Within this extended period, aerosol size distribution measurements were performed during an intensive campaign (3 July to 12 August 2013) from a ground-based station on the island of Mallorca, as well as onboard the ATR-42 research aircraft. This unique combination of stationary and mobile measurements provides us with detailed insights into the horizontal and vertical development of the NPF process on a daily scale. During the intensive campaign, nucleation events occurred simultaneously both at Ersa and Mallorca over delimited time slots of several days, but different features were observed at Finokalia. The results show that the spatial extent of the NPF events over the Mediterranean Sea might be as large as several hundreds of kilometers, mainly determined by synoptic conditions. Airborne measurements gave additional information regarding the origin of the clusters detected above the sea. The selected cases depicted contrasting situations, with clusters formed in the marine boundary layer or initially nucleated above the continent or in the free troposphere (FT) and further transported above the sea.
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Gherasimova, Maria, See Wee Chee, Robert Hull, Mark C. Reuter, and Frances M. Ross. "Controlled Nucleation of Ge Islands on Si and Self-Assembly of Nanoscale Island Clusters." International Journal of High Speed Electronics and Systems 23, no. 01n02 (March 2014): 1420003. http://dx.doi.org/10.1142/s0129156414200031.
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Germanium nucleation on a silicon surface typically proceeds via spontaneous formation of nanoscopic islands, or quantum dots (QDs), at random locations. However, potential applications of epitaxial QDs, such as quantum cellular automata, require precise control of Ge island positions on Si in clusters with the individual islands' separation of tens of nanometers or less. Controlled Ge island placement with an inter-island separation down to 100 nm can be reliably obtained by depositing Ge onto a Si(001) surface modified with a low dose focused ion beam (FIB) pattern to create preferred nucleation sites for individual islands. Here we investigate QD self-assembly of multiple islands on single topographical features intended to obtain clusters of QDs with smaller separations. We observe formation of 50 nm clusters on a single location defined by the FIB patterning of a larger and shallower feature, where cluster formation is promoted by reduced surface diffusion. We also discuss cluster formation on single sites defined by residual trenches on a footprint of a larger island that has been desorbed. We propose that controlled placement of islands during the first deposition may result in greater control over subsequent cluster size and placement fidelity due to improved uniformity of target features.
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Li, Zhi. "X‐Ray Spectromicroscopy Investigation of Heterogeneous Sodiation in Hard Carbon Nanosheets with Vertically Oriented (002) Planes." ECS Meeting Abstracts MA2022-01, no. 7 (July 7, 2022): 658. http://dx.doi.org/10.1149/ma2022-017658mtgabs.
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Hard carbon (HC) is a promising anode material for sodium-ion batteries, but the performance remains unsatisfactory and the sodiation mechanism in HC is one of the most debated topics. Here, from self-assembled cellulose nanocrystal sheets with crystallographic texture, unique HC nanosheets with vertically oriented (002) planes are fabricated and used as a model HC to investigate the sodiation mechanisms using synchrotron scanning transmission X-ray microscopy (STXM) coupled with analytical transmission electron microscopy (TEM). The model HC simplifies the 3D sodiation in a typical HC particle into a 2D sodiation, which facilitates the visualization of phase transformation at different states of charge. The results for the first time unveil that the sodiation in HC initiates heterogeneously, with multiple propagation fronts proceeding simultaneously, eventually merging into larger aggregates. The spatial correlation between the preferential adsorption and nucleation sites suggests that the heterogeneous nucleation is driven by the local Na-ion concentration, which is determined by defects or heteroatoms that have strong binding to Na ions. By identifying intercalation as the dominant sodium storage mechanism in the model HC, the findings highlight the importance of engineering the graphene layer orientation and the structural heterogeneity of edge sites to enhance the performances. Figure 1
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Kadlecova, Zuzana, Stephanie J. Spielman, Dinah Loerke, Aparna Mohanakrishnan, Dana Kim Reed, and Sandra L. Schmid. "Regulation of clathrin-mediated endocytosis by hierarchical allosteric activation of AP2." Journal of Cell Biology 216, no. 1 (December 21, 2016): 167–79. http://dx.doi.org/10.1083/jcb.201608071.
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The critical initiation phase of clathrin-mediated endocytosis (CME) determines where and when endocytosis occurs. Heterotetrameric adaptor protein 2 (AP2) complexes, which initiate clathrin-coated pit (CCP) assembly, are activated by conformational changes in response to phosphatidylinositol-4,5-bisphosphate (PIP2) and cargo binding at multiple sites. However, the functional hierarchy of interactions and how these conformational changes relate to distinct steps in CCP formation in living cells remains unknown. We used quantitative live-cell analyses to measure discrete early stages of CME and show how sequential, allosterically regulated conformational changes activate AP2 to drive both nucleation and subsequent stabilization of nascent CCPs. Our data establish that cargoes containing Yxxφ motif, but not dileucine motif, play a critical role in the earliest stages of AP2 activation and CCP nucleation. Interestingly, these cargo and PIP2 interactions are not conserved in yeast. Thus, we speculate that AP2 has evolved as a key regulatory node to coordinate CCP formation and cargo sorting and ensure high spatial and temporal regulation of CME.
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Sun, Yunkai, and Giovanni Zangari. "Streamlined Derivations and Explanations of the Scharifker-Hills Model." ECS Meeting Abstracts MA2022-01, no. 23 (July 7, 2022): 1204. http://dx.doi.org/10.1149/ma2022-01231204mtgabs.
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Despite being very popular in the analysis of experimentally measured potentiostatic transients during the initial stage of electrodeposition of metallic single-element coatings, the derivations and the assumptions of the Scharifker-Hills (S-H) model are not well understood. Important details and assumptions are scattered in different original papers. Meanwhile, some of the simplifications in derivations are somewhat intuitive, rather than being rigorously derived from a set of governing equations. It is important to understand the derivations, the assumptions, and the successfulness of the S-H model first before moving forward to an advanced model for the potentiostatic transient at the initial stage of metal or alloy electrodeposition. In this presentation, we will provide rigorous derivation for each step and each assumption, thus achieving a complete demonstration of the physics of the S-H model. References: [1] G.J. Hills, D.J. Schiffrin, J. Thompson, Electrochemical nucleation from molten salts—I. Diffusion controlled electrodeposition of silver from alkali molten nitrates, Electrochim. Acta, 19 (1974) 657-670. [2] B. Scharifker, G. Hills, Theoretical and experimental studies of multiple nucleation, Electrochim. Acta, 28 (1983) 879-889. [3] G. Gunawardena, G. Hills, I. Montenegro, B. Scharifker, Electrochemical nucleation: Part I. General considerations, J. Electroanal. Chem., 138 (1982) 225-239. [4] B.R. Scharifker, J. Mostany, Three-dimensional nucleation with diffusion controlled growth: Part I. Number density of active sites and nucleation rates per site, J. Electroanal. Chem., 177 (1984) 13-23. [5] B.R. Scharifker, J. Mostany, Electrochemical Nucleation and Growth, in: A.J. Bard (Ed.) Encyclopedia of Electrochemistry2007, pp. 512-539. [6] M. Sluyters-Rehbach, J.H.O.J. Wijenberg, E. Bosco, J.H. Sluyters, The theory of chronoamperometry for the investigation of electrocrystallization: Mathematical description and analysis in the case of diffusion-controlled growth, J. Electroanal. Chem., 236 (1987) 1-20.
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Luan, Qing, Alex Zelter, Michael J. MacCoss, Trisha N. Davis, and Brad J. Nolen. "Identification of Wiskott-Aldrich syndrome protein (WASP) binding sites on the branched actin filament nucleator Arp2/3 complex." Proceedings of the National Academy of Sciences 115, no. 7 (January 31, 2018): E1409—E1418. http://dx.doi.org/10.1073/pnas.1716622115.
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Arp2/3 complex nucleates branched actin filaments important for cellular motility and endocytosis. WASP family proteins are Arp2/3 complex activators that play multiple roles in branching nucleation, but little is known about the structural bases of these WASP functions, owing to an incomplete understanding of how WASP binds Arp2/3 complex. Recent data show WASP binds two sites, and biochemical and structural studies led to models in which the WASP C segment engages the barbed ends of the Arp3 and Arp2 subunits while the WASP A segment binds the back side of the complex on Arp3. However, electron microscopy reconstructions showed density for WASP inconsistent with these models on the opposite (front) side of Arp2/3 complex. Here we use chemical cross-linking and mass spectrometry (XL-MS) along with computational docking and structure-based mutational analysis to map the two WASP binding sites on the complex. Our data corroborate the barbed end and back side binding models and show one WASP binding site on Arp3, on the back side of the complex, and a second site on the bottom of the complex, spanning Arp2 and ARPC1. The XL-MS-identified cross-links rule out the front side binding model and show that the A segment of WASP binds along the bottom side of the ARPC1 subunit, instead of at the Arp2/ARPC1 interface, as suggested by FRET experiments. The identified binding sites support the Arp3 tail release model to explain WASP-mediated activating conformational changes in Arp2/3 complex and provide insight into the roles of WASP in branching nucleation.
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Costabile, F., W. Birmili, S. Klose, T. Tuch, B. Wehner, A. Wiedensohler, U. Franck, K. König, and A. Sonntag. "Spatio-temporal variability and principal components of the particle number size distribution in an urban atmosphere." Atmospheric Chemistry and Physics Discussions 8, no. 5 (October 16, 2008): 18155–217. http://dx.doi.org/10.5194/acpd-8-18155-2008.
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Abstract. Due to the presence of diffusive anthropogenic sources in urban areas, the spatio-temporal variability of fine (diameter <1 μm) and ultrafine (<0.1 μm) aerosol particles has been a challenging issue in particle exposure assessment as well as atmospheric research in general. We examined number size distributions of atmospheric aerosol particles (size range 3–800 nm) that were measured simultaneously at a maximum of eight observation sites in and around a city in Central Europe (Leipzig, Germany). Two main experiments were conducted with different time span and number of observation sites (2 years at 3 sites; 1 month at 8 sites). A general observation was that the particle number size distribution varied in time and space in a complex fashion as a result of interaction between local and far-range sources, and the meteorological conditions. To identify statistically independent factors in the urban aerosol, different runs of principal component analysis were conducted encompassing aerosol, gas phase, and meteorological parameters from the multiple sites. Several of the resulting principal components, outstanding with respect to their temporal persistence and spatial coverage, could be associated with aerosol particle modes: a first accumulation mode ("droplet mode", 300–800 nm), considered to be the result of liquid phase processes and far-range transport; a second accumulation mode (centered around diameters 90–250 nm), considered to result from primary emissions as well as aging through condensation and coagulation; an Aitken mode (30–200 nm) linked to urban traffic emissions in addition to an urban and a rural Aitken mode; a nucleation mode (5–20 nm) linked to urban traffic emissions; nucleation modes (3–20 nm) linked to photochemically induced particle formation; an aged nucleation mode (10–50 nm). A number of additional components were identified to represent only local sources at a single site each, or infrequent phenomena. In summary, the analysis of size distributions of high time and size resolution yielded a surprising wealth of statistical aerosol components occurring in the urban atmosphere over one single city. Meanwhile, satisfactory physical explanations could be found for the components with the greatest temporal persistence and spatial coverage. Therefore a paradigm on the behaviour of sub-μm urban aerosol particles is proposed, with recommendations how to efficiently monitor individual sub-fractions across an entire city.
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Daneu, Nina, Goran Dražič, Matjaž Mazaj, Fabrice Barou, and José Alberto Padrón-Navarta. "Formation of contact and multiple cyclic cassiterite twins in SnO2-based ceramics co-doped with cobalt and niobium oxides." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 78, no. 4 (July 27, 2022): 695–709. http://dx.doi.org/10.1107/s2052520622006758.
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Contact and multiple cyclic twins of cassiterite commonly form in SnO2-based ceramics when SnO2 is sintered with small additions of cobalt and niobium oxides (dual doping). In this work, it is shown that the formation of twins is a two-stage process that starts with epitaxial growth of SnO2 on CoNb2O6 and Co4Nb2O9 seeds (twin nucleation stage) and continues with the fast growth of (101) twin contacts (twin growth stage). Both secondary phases form below the temperature of enhanced densification and SnO2 grain growth; CoNb2O6 forms at ∼700°C and Co4Nb2O9 at ∼900°C. They are structurally related to the rutile-type cassiterite and can thus trigger oriented (epitaxial) growth (local recrystallization) of SnO2 domains in different orientations on a single seed particle. While oriented growth of cassiterite on columbite-type CoNb2O6 grains can only result in the formation of contact twins, the Co4Nb2O9 grains with a structure comparable with that of corundum represent suitable sites for the nucleation of contact and multiple cyclic twins with coplanar or alternating morphology. The twin nucleation stage is followed by fast densification accompanied by significant SnO2 grain growth above 1300°C. The twin nuclei coarsen to large twinned grains as a result of the preferential and fast growth of the low-energy (101) twin contacts. The solid-state diffusion processes during densification and SnO2 grain growth are controlled by the formation of point defects and result in the dissolution of the twin nuclei and the incorporation of Nb5+ and Co2+ ions into the SnO2 matrix in the form of a solid solution. In this process, the twin nuclei are erased and their role in the formation of twins is shown only by irregular segregation of Co and Nb to the twin boundaries and inside the cassiterite grains, and Co,Nb-enrichment in the cyclic twin cores.
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Heerman, Luc, Edward Matthijs, and Steven Langerock. "The concept of planar diffusion zones. Theory of the potentiostatic transient for multiple nucleation on active sites with diffusion-controlled growth." Electrochimica Acta 47, no. 6 (December 2001): 905–11. http://dx.doi.org/10.1016/s0013-4686(01)00792-7.
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Nakamura, Masafumi, Hirohisa Masuda, Johji Horii, Kei-ichi Kuma, Nobuhiko Yokoyama, Tomoyuki Ohba, Hideo Nishitani, Takashi Miyata, Masao Tanaka, and Takeharu Nishimoto. "When Overexpressed, a Novel Centrosomal Protein, RanBPM, Causes Ectopic Microtubule Nucleation Similar to γ-Tubulin." Journal of Cell Biology 143, no. 4 (November 16, 1998): 1041–52. http://dx.doi.org/10.1083/jcb.143.4.1041.
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A novel human protein with a molecular mass of 55 kD, designated RanBPM, was isolated with the two-hybrid method using Ran as a bait. Mouse and hamster RanBPM possessed a polypeptide identical to the human one. Furthermore, Saccharomyces cerevisiae was found to have a gene, YGL227w, the COOH-terminal half of which is 30% identical to RanBPM. Anti-RanBPM antibodies revealed that RanBPM was localized within the centrosome throughout the cell cycle. Overexpression of RanBPM produced multiple spots which were colocalized with γ-tubulin and acted as ectopic microtubule nucleation sites, resulting in a reorganization of microtubule network. RanBPM cosedimented with the centrosomal fractions by sucrose- density gradient centrifugation. The formation of microtubule asters was inhibited not only by anti- RanBPM antibodies, but also by nonhydrolyzable GTP-Ran. Indeed, RanBPM specifically interacted with GTP-Ran in two-hybrid assay. The central part of asters stained by anti-RanBPM antibodies or by the mAb to γ-tubulin was faded by the addition of GTPγS-Ran, but not by the addition of anti-RanBPM anti- bodies. These results provide evidence that the Ran-binding protein, RanBPM, is involved in microtubule nucleation, thereby suggesting that Ran regulates the centrosome through RanBPM.
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Kong, Guang Ming, Xu Dong Li, and Zhi Tao Mu. "Fracture Analysis of 6A02 Aluminum Alloy Subjected to Corrosion Fatigue Damage." Advanced Materials Research 998-999 (July 2014): 59–62. http://dx.doi.org/10.4028/www.scientific.net/amr.998-999.59.
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With the aid of scanning electron microscope and energy spectrum analysis, the present thesis made a research on the fatigue fracture surface of AA 6A02 with corrosion damage as well as the effect of alloy element Si, Mg and the corrosion damage on the fracture process. Results indicate that the fatigue fracture surface is tough fracture with multiple fatigue sources. Pits introduced by corrosion damage will weaken the material property, which serve as crack nucleation sites. Proper hardening constituent element introduced during alloying process such as Si, Mg, who are in proper ratio of component to form strengthening phase Mg2Si without the excess phase of single crystal Si, will make strength and plasticity match, thus improve fatigue performance of materials.
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Robson, Joseph D., Nicolas Kamp, A. Sullivan, and Hugh R. Shercliff. "Modelling Precipitate Evolution during Friction Stir Welding of Aerospace Aluminium Alloys." Materials Science Forum 519-521 (July 2006): 1101–6. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.1101.
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Two models to predict the microstructural evolution and post-weld properties of friction stir welds in aerospace aluminium alloys are presented. The first model is a develop- ment of an existing semi-empirical method for the prediction of hardness profiles after welding, calibrated using isothermal hardness data. Post-weld natural ageing is accounted for, and a new method that predicts natural ageing kinetics is introduced. Once calibrated, the model is shown to accurately predict weld hardness profiles. However, this model does not explicitly predict the microstructure and therefore cannot readily be extended to model other properties. It can also only be applied to alloys welded in peak or overaged conditions. The second model aims to explicitly predict the heterogeneous precipitate distributions obtained after welding for any initial condition. It is based on classical kinetic theory and the numerical framework of Kampmann and Wagner. Multiple nucleation sites and multiple phases are accounted for. This model provides detailed microstructural information required for prediction of complex properties.
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Hiranuma, N., S. Augustin-Bauditz, H. Bingemer, C. Budke, J. Curtius, A. Danielczok, K. Diehl, et al. "A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of seventeen ice nucleation measurement techniques." Atmospheric Chemistry and Physics Discussions 14, no. 15 (August 28, 2014): 22045–116. http://dx.doi.org/10.5194/acpd-14-22045-2014.
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Abstract. Immersion freezing is the most relevant heterogeneous ice nucleation mechanism through which ice crystals are formed in mixed-phase clouds. In recent years, an increasing number of laboratory experiments utilizing a variety of instruments have examined immersion freezing activity of atmospherically relevant ice nucleating particles (INPs). However, an inter-comparison of these laboratory results is a difficult task because investigators have used different ice nucleation (IN) measurement methods to produce these results. A remaining challenge is to explore the sensitivity and accuracy of these techniques and to understand how the IN results are potentially influenced or biased by experimental parameters associated with these techniques. Within the framework of INUIT (Ice Nucleation research UnIT), we distributed an illite rich sample (illite NX) as a representative surrogate for atmospheric mineral dust particles to investigators to perform immersion freezing experiments using different IN measurement methods and to obtain IN data as a function of particle concentration, temperature (T), cooling rate and nucleation time. Seventeen measurement methods were involved in the data inter-comparison. Experiments with seven instruments started with the test sample pre-suspended in water before cooling, while ten other instruments employed water vapor condensation onto dry-dispersed particles followed by immersion freezing. The resulting comprehensive immersion freezing dataset was evaluated using the ice nucleation active surface-site density (ns) to develop a representative ns(T) spectrum that spans a wide temperature range (−37 °C < T < −11 °C) and covers nine orders of magnitude in ns. Our inter-comparison results revealed a discrepancy between suspension and dry-dispersed particle measurements for this mineral dust. While the agreement was good below ~ −26 °C, the ice nucleation activity, expressed in ns, was smaller for the wet suspended samples and higher for the dry-dispersed aerosol samples between about −26 and −18 °C. Only instruments making measurement techniques with wet suspended samples were able to measure ice nucleation above −18 °C. A possible explanation for the deviation between −26 and −18 °C is discussed. In general, the seventeen immersion freezing measurement techniques deviate, within the range of about 7 °C in terms of temperature, by three orders of magnitude with respect to ns. In addition, we show evidence that the immersion freezing efficiency (i.e., ns) of illite NX particles is relatively independent on droplet size, particle mass in suspension, particle size and cooling rate during freezing. A strong temperature-dependence and weak time- and size-dependence of immersion freezing efficiency of illite-rich clay mineral particles enabled the ns parameterization solely as a function of temperature. We also characterized the ns (T) spectra, and identified a section with a steep slope between −20 and −27 °C, where a large fraction of active sites of our test dust may trigger immersion freezing. This slope was followed by a region with a gentler slope at temperatures below −27 °C. A multiple exponential distribution fit is expressed as ns(T) = exp(23.82 × exp(−exp(0.16 × (T + 17.49))) + 1.39) based on the specific surface area and ns(T) = exp(25.75 × exp(−exp(0.13 × (T + 17.17))) + 3.34) based on the geometric area (ns and T in m−2 and °C, respectively). These new fits, constrained by using an identical reference samples, will help to compare IN measurement methods that are not included in the present study and, thereby, IN data from future IN instruments.
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Hiranuma, N., S. Augustin-Bauditz, H. Bingemer, C. Budke, J. Curtius, A. Danielczok, K. Diehl, et al. "A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of 17 ice nucleation measurement techniques." Atmospheric Chemistry and Physics 15, no. 5 (March 6, 2015): 2489–518. http://dx.doi.org/10.5194/acp-15-2489-2015.
Full textAbstract:
Abstract. Immersion freezing is the most relevant heterogeneous ice nucleation mechanism through which ice crystals are formed in mixed-phase clouds. In recent years, an increasing number of laboratory experiments utilizing a variety of instruments have examined immersion freezing activity of atmospherically relevant ice-nucleating particles. However, an intercomparison of these laboratory results is a difficult task because investigators have used different ice nucleation (IN) measurement methods to produce these results. A remaining challenge is to explore the sensitivity and accuracy of these techniques and to understand how the IN results are potentially influenced or biased by experimental parameters associated with these techniques. Within the framework of INUIT (Ice Nuclei Research Unit), we distributed an illite-rich sample (illite NX) as a representative surrogate for atmospheric mineral dust particles to investigators to perform immersion freezing experiments using different IN measurement methods and to obtain IN data as a function of particle concentration, temperature (T), cooling rate and nucleation time. A total of 17 measurement methods were involved in the data intercomparison. Experiments with seven instruments started with the test sample pre-suspended in water before cooling, while 10 other instruments employed water vapor condensation onto dry-dispersed particles followed by immersion freezing. The resulting comprehensive immersion freezing data set was evaluated using the ice nucleation active surface-site density, ns, to develop a representative ns(T) spectrum that spans a wide temperature range (−37 °C < T < −11 °C) and covers 9 orders of magnitude in ns. In general, the 17 immersion freezing measurement techniques deviate, within a range of about 8 °C in terms of temperature, by 3 orders of magnitude with respect to ns. In addition, we show evidence that the immersion freezing efficiency expressed in ns of illite NX particles is relatively independent of droplet size, particle mass in suspension, particle size and cooling rate during freezing. A strong temperature dependence and weak time and size dependence of the immersion freezing efficiency of illite-rich clay mineral particles enabled the ns parameterization solely as a function of temperature. We also characterized the ns(T) spectra and identified a section with a steep slope between −20 and −27 °C, where a large fraction of active sites of our test dust may trigger immersion freezing. This slope was followed by a region with a gentler slope at temperatures below −27 °C. While the agreement between different instruments was reasonable below ~ −27 °C, there seemed to be a different trend in the temperature-dependent ice nucleation activity from the suspension and dry-dispersed particle measurements for this mineral dust, in particular at higher temperatures. For instance, the ice nucleation activity expressed in ns was smaller for the average of the wet suspended samples and higher for the average of the dry-dispersed aerosol samples between about −27 and −18 °C. Only instruments making measurements with wet suspended samples were able to measure ice nucleation above −18 °C. A possible explanation for the deviation between −27 and −18 °C is discussed. Multiple exponential distribution fits in both linear and log space for both specific surface area-based ns(T) and geometric surface area-based ns(T) are provided. These new fits, constrained by using identical reference samples, will help to compare IN measurement methods that are not included in the present study and IN data from future IN instruments.
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Wilbur, J. C., S. D. Phillips, T. G. Donoghue, D. L. Alvarenga, D. A. Knaus, P. J. Magari, and J. C. Buckey. "Signals consistent with microbubbles detected in legs of normal human subjects after exercise." Journal of Applied Physiology 108, no. 2 (February 2010): 240–44. http://dx.doi.org/10.1152/japplphysiol.00615.2009.
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Exercise may produce micronuclei (presumably gas-filled bubbles) in tissue, which could serve as nucleation sites for bubbles during subsequent decompression stress. These micronuclei have never been directly detected in humans. Dual-frequency ultrasound (DFU) is a resonance-based, ultrasound technique capable of detecting and sizing small stationary bubbles. We surveyed for bubbles in the legs of six normal human subjects (ages 28–52 yr) after exercise using DFU. Eleven marked sites on the left thigh and calf were imaged using standard imaging ultrasound. Subjects then rested in a reclining chair for 2 h before exercise. For the hour before exercise, a series of baseline measurements was taken at each site using DFU. At least six baseline measurements were taken at each site. Subjects exercised at 80% of their age-adjusted maximal heart rate for 30 min on an upright bicycle ergometer. After exercise, the subjects returned to the chair, and multiple postexercise measurements were taken at the marked sites. Measurements continued until no further signals consistent with bubbles were returned or 1 h had elapsed. All subjects showed signals consistent with bubbles after exercise at at least one site. The percentage of sites in a given subject showing signals significantly greater than baseline ( P < 0.01) at first measurement ranged from 9.1 to 100%. Overall, 58% of sites showed signals consistent with bubbles at the first postexercise measurement. Signals decreased over time after exercise. These data strongly suggest that exercise produces bubbles detectable using DFU.
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Adair, W. S., S. A. Steinmetz, D. M. Mattson, U. W. Goodenough, and J. E. Heuser. "Nucleated assembly of Chlamydomonas and Volvox cell walls." Journal of Cell Biology 105, no. 5 (November 1, 1987): 2373–82. http://dx.doi.org/10.1083/jcb.105.5.2373.
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The Chlamydomonas reinhardtii cell wall is made up of hydroxyproline-rich glycoproteins, arranged in five distinct layers. The W6 (crystalline) layer contains three major glycoproteins (GP1, GP2, GP3), selectively extractable with chaotropic agents, that self-assemble into crystals in vitro. A system to study W6 assembly in a quantitative fashion was developed that employs perchlorate-extracted Chlamydomonas cells as nucleating agents. Wall reconstitution by biotinylated W6 monomers was monitored by FITC-streptavidin fluorescence and quick-freeze/deep-etch electron microscopy. Optimal reconstitution was obtained at monomer concentrations (0.2-0.3 mg/ml) well below those required for nonnucleated assembly. Assembly occurred from multiple nucleation sites, and faithfully reflected the structure of the intact W6 layer. Specificity of nucleated assembly was demonstrated using two cell-wall mutants (cw-2 and cw-15); neither served as a substrate for assembly of wild-type monomers. In addition, W6 sublayers were assembled from purified components: GP2 and GP3 coassembled to form the inner (W6A) sublayer; this then served as a substrate for self-assembly of GP1 into the outer (W6B) sublayer. Finally, evolutionary relationships between C. reinhardtii and two additional members of the Volvocales (Chlamydomonas eugametos and Volvox carteri) were explored by performing interspecific reconstitutions. Hybrid walls were obtained between C. reinhardtii and Volvox but not with C. eugametos, confirming taxonomic assignments based on structural criteria.
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Zhou, Changshan, Hezhi Zhang, Xudong Yuan, Kaikai Song, and Dan Liu. "Applicability of Pre-Plastic Deformation Method for Improving Mechanical Properties of Bulk Metallic Glasses." Materials 15, no. 21 (October 28, 2022): 7574. http://dx.doi.org/10.3390/ma15217574.
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Pre-plastic deformation (PPD) treatments on bulk metallic glasses (BMGs) have previously been shown to be helpful in producing multiple shear bands. In this work, the applicability of the PPD approach on BMGs with different Poisson’s ratios was validated based on experimental and simulation observations. It was found that for BMGs with high Poisson’s ratios (HBMGs, e.g., Zr56Co28Al16 and Zr46Cu46Al8), the PPD treatment can easily trigger a pair of large plastic deformation zones consisting of multiple shear bands. These PPD-treated HBMGs clearly display improved strength and compressive plasticity. On the other hand, the mechanical properties of BMGs with low Poisson’s ratios (LBMG, e.g., Fe48Cr15Mo14Y2C15B6) become worse due to a few shear bands and micro-cracks in extremely small plastic deformation zones. Additionally, for the PPD-treated HBMGs with similar high Poisson’s ratios, the Zr56Co28Al16 BMG exhibits much larger plasticity than the Zr46Cu46Al8 BMG. This phenomenon is mainly due to more defective icosahedral clusters in the Zr56Co28Al16 BMG, which can serve as nucleation sites for shear transformation zones (STZs) during subsequent deformation. The present study may provide a basis for understanding the plastic deformation mechanism of BMGs.
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Giribaskar, Sivaswamy, Gouthama, and Rajesh Prasad. "Dynamic Recrystallization in Al-Li Based Alloy during Equal Channel Angular Extrusion." Materials Science Forum 715-716 (April 2012): 286–91. http://dx.doi.org/10.4028/www.scientific.net/msf.715-716.286.
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Development of bulk ultra-fine grained (UFG) materials by severe plastic deformation to attain improved mechanical properties is becoming more attractive and extensively studied nowadays. Equal channel angular extrusion (ECAE) is one of technique used effectively for obtaining bulk UFG materials. Novelty of this technique is one can build up significant amount of plastic strain by increasing the number of passes without much dimensional change. In present investigation dynamic recrystallization at deformation zones around the non-shearable second phase particles in Al-Li based alloy processed by ECAE is reported. Transmission electron microscopy technique involving imaging the regions of such deformation zones with different specimen tilt conditions is used. It is shown that the dynamic recrystallisation occurring in the proximities of second phase particles during the deformation at room temperature, leads to very fine grained microstructure. Observation of multiple active nucleation sites around even sub-micrometer sized non-deformable particles in the as-processed material indicates that the system exhibits efficiency >1 based on the concept of particle stimulated nucleation (PSN). Crystallites of ultra-fine/nanocrystalline size ranges are formed in the deformation zones around the non-deformable particles during deformation itself. Effect of short term post deformation annealing to understand the recovery and recrystallization was undertaken. Based on these results effect of optimal post deformation heat treatment conditions on the thermal stability of the microstructures is emphasized. It is suggested that with significant fraction of non-shearable particles it might be possible to get grain size in the nanocrystalline or ultra-fine range with relatively low effective strain levels using ECAE.
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Syubaev, Sergey, Stanislav Gurbatov, Evgeny Modin, Denver P. Linklater, Saulius Juodkazis, Evgeny L. Gurevich, and Aleksandr Kuchmizhak. "Laser Printing of Plasmonic Nanosponges." Nanomaterials 10, no. 12 (December 4, 2020): 2427. http://dx.doi.org/10.3390/nano10122427.
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Three-dimensional porous nanostructures made of noble metals represent novel class of nanomaterials promising for nonlinear nanooptics and sensors. Such nanostructures are typically fabricated using either reproducible yet time-consuming and costly multi-step lithography protocols or less reproducible chemical synthesis that involve liquid processing with toxic compounds. Here, we combined scalable nanosecond-laser ablation with advanced engineering of the chemical composition of thin substrate-supported Au films to produce nanobumps containing multiple nanopores inside. Most of the nanopores hidden beneath the nanobump surface can be further uncapped using gentle etching of the nanobumps by an Ar-ion beam to form functional 3D plasmonic nanosponges. The nanopores 10–150 nm in diameter were found to appear via laser-induced explosive evaporation/boiling and coalescence of the randomly arranged nucleation sites formed by nitrogen-rich areas of the Au films. Density of the nanopores can be controlled by the amount of the nitrogen in the Au films regulated in the process of their magnetron sputtering assisted with nitrogen-containing discharge gas.
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Fedi, Baptiste, Aymeric Nevers, Marie-Pierre Gigandet, and Jean-Yves Hihn. "Modelling Nucleation during Electrodeposition By MODEL Method. Parametric Identification Considering Agitation By Rde or Ultrasound." ECS Meeting Abstracts MA2022-01, no. 23 (July 7, 2022): 1205. http://dx.doi.org/10.1149/ma2022-01231205mtgabs.
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Nowadays, 40% of the world wide used energy is provided by electric power and this share should reach about 60% by 2040. For environmental reasons, it is crucial to ensure low dissipation loss in power electronic devices by optimizing energy conversion. In the field of renewable energies and automotive electronics, possible energy savings are estimated to be between 20 and 35%. For that purpose, innovative power components and modules are required, with a growing interest for fast and simple joining processes in their fabrication management, in the case for example of the assembly of large-size double-side cooled modules. Several options are possible, including free sintering of metallic pastes or electroforming welding. In all cases, this requires a great control of both surfaces to be joined, mostly prepared by electrodeposition (microstructure, porosity, alloy composition). But the final properties of electrodeposited coatings are strongly dependent of the first nucleation steps, which influence the whole layer structure. In this frame, the modelling of a nucleation process followed by diffusion limited three dimensional growth is an area of promising interest. The study of potentiostatic current transients is a relevant methodology, allowing the determination of several parameters such as nucleation rate, nucleus density, and number of active sites. Different competing models are available, such as Scharifker and Hills [1] and Scharifker and Mostany [2]. By using the model method i.e. the identification of the model parameters by error minimization, it is possible to reach an accurate description of the first layer growth in the case of different metals such as silver and copper. Nevertheless, little attention have been paid to changes in hydrodynamic conditions, for example in the study of current response under forced convection [3]. The present work describes the extension of the model method to the modelling of the first steps of nucleation growth in the case of a sample exposed to an ultrasonic irradiation, which was compared to forced convection induced by a rotating disc electrode at the very same agitation level (equivalent velocity [4,5]. Eventually, the case of electrodeposited alloys was examined, as a function of their Brenner classifications (anomalous and normal codeposition [6]). The limitation of the data processing by the numerical approach are also discussed. [1] Scharifker, B. & Hills, G. Theoretical and experimental studies of multiple nucleation. Electrochimica Acta 28, 879–889 (1983). [2] Scharifker, B. R. & Mostany, J. Three-dimensional nucleation with diffusion controlled growth. J. Electroanal. Chem. Interfacial Electrochem. 177, 13–23 (1984). [3] Hyde, M. E. & Compton, R. G. Theoretical and experimental aspects of electrodeposition under hydrodynamic conditions. J. Electroanal. Chem. 581, 224–230 (2005). [4] Pollet B.G., Hihn J.-Y., Doche M.L, Mandroyan A., Lorimer J.P., Mason T.J “Transport limited currents close to an ultrasonic horn: equivalent flow velocity determination”, Journal of Electrochemistry Society, 154(10), E131-E138, (2007) [5] A. Nevers, L. Hallez, F. Touyeras, J.-Y. Hihn, Effect of ultrasound on silver electrodeposition: Crystalline structure modification, Ultrason. Sonochem. 40 (2018) [6] Brenner, A. Electrodeposition of alloys. Principles and practice Volume II, (1963).
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Sun, Qin, and William Margolin. "FtsZ Dynamics during the Division Cycle of LiveEscherichia coli Cells." Journal of Bacteriology 180, no. 8 (April 15, 1998): 2050–56. http://dx.doi.org/10.1128/jb.180.8.2050-2056.1998.
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ABSTRACT The dynamics and assembly of bacterial cell division protein FtsZ were monitored in individual, growing and dividing Escherichia coli cells in real time by microculture of a merodiploid strain expressing green fluorescent protein (GFP)-tagged FtsZ. Cells expressing FtsZ-GFP at levels less than or equivalent to that of wild-type FtsZ were able to grow and divide over multiple generations, with their FtsZ rings visualized by fluorescence. During the late stages of cytokinesis, which constituted the last one-fourth of the cell cycle, the lumen of the FtsZ ring disappeared as the whole structure condensed. At this time, loops of FtsZ-GFP polymers emanated outward from the condensing ring structure and other unstable fluorescent structures elsewhere in the cell were also observed. Assembly of FtsZ rings at new division sites occurred within 1 min, from what appeared to be single points. Interestingly, this nucleation often took place in the predivisional cell at the same time the central FtsZ ring was in its final contraction phase. This demonstrates directly that, at least when FtsZ-GFP is being expressed, new division sites have the capacity to become fully functional for FtsZ targeting and assembly before cell division of the mother cell is completed. The results suggest that the timing of FtsZ assembly may be normally controlled in part by cellular FtsZ concentration. The use of wide-field optical sectioning microscopy to obtain sharp fluorescence images of FtsZ structures is also discussed.
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Matsui, Hirotaka, Yuko Ozaki, Akiko Nagamachi, and Toshiya Inaba. "Abnormal Mitosis Due to Impairment of Centrosome Maturation by the Deletion of Candidate 7q- Responsible Genes." Blood 120, no. 21 (November 16, 2012): 1297. http://dx.doi.org/10.1182/blood.v120.21.1297.1297.
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Abstract Abstract 1297 Centrosomes acquire dense microtubule nucleation sites in the beginning of mitosis. Failure of this process (called centrosome maturation) impairs the function of mitotic centrosomes to create robust mitotic spindles, resulting in lagging and scattered chromosomes that subsequently cause abnormal nuclear morphology such as bi- tri- or multiple-nuclei with or without small nucleus, as seen routinely in MDS. We previously reported that the Miki (LOC253012) gene, located in 7q21.3, is frequently deleted in MDS patients, and that low levels of Miki are tightly associated with abnormal mitosis and nuclear morphology (BBRC 2009). Here we demonstrate that Miki plays critical roles in the formation of robust spindles required for the prompt movement of chromosomes in a poly(ADP) ribosylation (PARsylation)-dependent manner (a part of data was published in Mol. Cell 2012). While Miki was localized in the Golgi apparatus during interphase, it was relocated to centrosomes at the beggining of mitosis. Treatment of cells with Miki-specific siRNA induced ‘pseudometaphase’ condition, in which lagging chromosomes juxtaposed to, or even situated behind, spindle poles. Pseudometaphase was followed by apoptosis or abnormal exit from mitosis that creates cells with abnormal nuclear morphology. This phenotype of Miki-downregulation was caused by the reduced robustness of mitotic spindles. α -tubulin staining of siRNA-treated cells revealed curling and disorganized spindles, with an occasional chaotic centrosome at only one side of the alignment. In addition, Miki-downregulation reduced γ-tubulin signals in mitotic centrosomes and markedly inhibited microtubule nucleation, shown by the impaired accumulation of the EB1 microtubule tip-binding protein at centrosomes. In immnunoblot analysis of lysate extracted from isolated spindles/centrosomes using Miki antibody, we detected a dense 125 kDa band in addition to the expected 50 kDa band and found that the 125 kDa band represents PARsylated Miki. A recent report indicated that tankyrase-1, a PAR polymerase (PARP), is required for the progression of prometaphase. We found that the downregulation of tankyrase-1 prevents Miki from localizing to mitotic centrosomes. In addition, immunoblot analysis of immunoprecipitation revealed that Miki is a substrate for tankyrase-1. These data suggested that tankyrase-1 PARsylates and translocates Miki from the Golgi apparatus to mitotic centrosomes/spindles during the short period from late G2 to prophase. We also found that PARsylated Miki promotes CG-NAP, a major component of microtubule nucleation sites, to concentrate in mitotic centrosomes. Interestingly, the CG-NAP gene resides 1.2Mb centromeric to Miki in band 7q21, and approximately 20% of MDS patients lose one allele of both Miki and CG-NAP genes. This indicates that loss of 7q results in low expression of two crucial factors in the tankyrase-1/Miki-dependent system for centrosome maturation, and that this may cause miotic/nuclear abnormalities and chromosome instability characteristic of 7q- MDS. Disclosures: No relevant conflicts of interest to declare.
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Dall'Osto, M., X. Querol, A. Alastuey, M. C. Minguillon, M. Alier, F. Amato, M. Brines, et al. "Presenting SAPUSS: solving aerosol problem by using synergistic strategies at Barcelona, Spain." Atmospheric Chemistry and Physics Discussions 12, no. 7 (July 31, 2012): 18741–815. http://dx.doi.org/10.5194/acpd-12-18741-2012.
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Abstract. This paper presents the summary of the key objectives, instrumentation and logistic details, goals, and initial scientific findings of the Marie Curie Action FP7-EU SAPUSS project carried out in the Western Mediterranean Basin (WMB) from 20 September–20 October 2010. The experiment involved concurrent measurements of aerosols with multiple techniques occurring simultaneously. The key objective is to deduce point aerosol source characteristics and to understand the atmospheric processes responsible for their generations and transformations. The unique approach is the large variety of instrumentation deployed simultaneously in six monitoring sites in Barcelona (NE Spain) and around the city, including: a main road traffic site, two urban background sites, a regional background site and two tower sites (150 m and 545 m a.s.l., 150 m and 80 m above ground, respectively). The SAPUSS experiment allows us to interpret the variability of aerosols levels and composition in an Urban Mediterranean, an environment not well characterized so far. During SAPUSS different air mass scenarios were encountered, including warm Saharan, cold Atlantic, wet European and stagnant Regional ones and presenting different local meteorology and boundary layer conditions. Analysis of part of the data collected allows us to compare the monitoring sites as well as to draw scientific conclusions about relevant air quality parameters. High levels of traffic-related gaseous pollutants were measured at the urban ground level monitoring sites, whereas layers of tropospheric ozone were recorded at tower levels. Particularly, tower level night time average ozone concentrations (80 ± 25 μg m−3) were up to double than ground level ones. Particle number concentrations (N>5: 9980 ± 6500 cm−1, average of all measurements) were generally traffic dependent, although a contribution from two different types of nucleation events was also found. Analysis of the particulate matter (PM) mass concentrations shows an enhancement of coarse particles (PM2.5-10) at the urban ground level (+64%, average 11.7 μg m−3) but of fine ones (PM1) at urban tower level (+28%, average 14.4 μg m−3). Preliminary modeling findings reveal an underestimation of the fine accumulation aerosols. In summary, this paper lays the foundation of SAPUSS, an integrated study of relevance to many other similar urban Mediterranean coastal environment sites.
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Zhu, Jialin, Shifeng Liu, Xiaoli Yuan, and Qing Liu. "Comparing the Through-Thickness Gradient of the Deformed and Recrystallized Microstructure in Tantalum with Unidirectional and Clock Rolling." Materials 12, no. 1 (January 7, 2019): 169. http://dx.doi.org/10.3390/ma12010169.
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Controlling the microstructure homogeneity is crucial in achieving high quality tantalum (Ta) sputtering targets used in integrated circuit fabrication. Unluckily, traditional rolling easily generates a microstructure gradient along the thickness direction in Ta sheets. The deformation and recrystallization behavior of unidirectional and clock rolled Ta with an 87% strain were therefore systematically compared to investigate whether the change of strain-pass can effectively ameliorate the microstructure gradient along the thickness. Electron backscatter diffraction was used to analyze the misorientation characteristics of the deformed grains. A strong microstructure gradient exists in the unidirectional rolled (UR) sheets. Many microshear bands and well-defined microbands occurred in {111} deformed grains in the UR sheets, especially in the center region, while the grain fragmentation with {111} and {100} orientation in the clock rolled (CR) sheets was more homogenous along the thickness. The kernel average misorientation (KAM) and grain reference orientation deviation-hyper (GROD-Hyper) further confirmed these differences. X-ray line profile analysis (XLPA) indicated that the stored energy distribution was more inhomogeneous in the UR sheets. Schmid factor analysis suggested that the strain path changes due to clock rolling promoted the activation of multiple slip systems in {111} oriented grains. Upon static annealing, homogeneous nucleation combined with a slower grain growth rate resulted in finer and more uniform grain size for the CR sheet. In contrast, a strong recrystallization microstructure-gradient along the thickness formed in the UR sheets, which is attributed to the fact that the higher stored energy and more preferential nucleation sites led to faster recrystallization in the center region, as compared with the surface region. Thus, clock rolling can effectively improve the homogeneity of the through-thickness recrystallization microstructure of Ta sheets.
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Rimer, Jeffrey D., Aseem Chawla, and Thuy T. Le. "Crystal Engineering for Catalysis." Annual Review of Chemical and Biomolecular Engineering 9, no. 1 (June 7, 2018): 283–309. http://dx.doi.org/10.1146/annurev-chembioeng-060817-083953.
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Crystal engineering relies upon the ability to predictively control intermolecular interactions during the assembly of crystalline materials in a manner that leads to a desired (and predetermined) set of properties. Economics, scalability, and ease of design must be leveraged with techniques that manipulate the thermodynamics and kinetics of crystal nucleation and growth. It is often challenging to exact simultaneous control over multiple physicochemical properties, such as crystal size, habit, chirality, polymorph, and composition. Engineered materials often rely upon postsynthesis (top-down) processes to introduce properties that would otherwise be challenging to attain through direct (bottom-up) approaches. We discuss the application of crystal engineering to heterogeneous catalysts with a focus on four general themes: ( a) tailored nanocrystal size, ( b) controlled environments surrounding active sites, ( c) tuned morphology with well-defined facets, and ( d) hierarchical materials with disparate pore size and active site distributions. We focus on nonporous materials, including metals and metal oxides, and two classes of porous materials: zeolites and metal organic frameworks. We review novel synthesis methods involving synergistic experimental and computational design approaches, the challenges facing catalyst development, and opportunities for future advancement in crystal engineering.
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Chen, Huan, Bingyue Han, Chen Lang, Min Wen, Baitao Fan, and Zheyuan Liu. "Hydrates for Cold Storage: Formation Characteristics, Stability, and Promoters." Applied Sciences 11, no. 21 (November 8, 2021): 10470. http://dx.doi.org/10.3390/app112110470.
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The potential of hydrates formed from R141b (CH3CCl2F), trimethylolethane (TME), and tetra-n-butylammonium bromide/tetra-n-butylammonium chloride (TBAB/TBAC) to be used as working substances for cold storage was investigated to provide a solution for unbalanced energy grids. In this study, the characteristics of hydrate formation, crystal morphology of hydrates, and the stability of hydrate in cyclic formation under 0.1 MPa and at 5 °C were carried out. It found that the ice had a positive effect on the hydrate formation under same conditions. Upon the addition of the ice cube, the induction time of R141b, TME, and TBAB/TBAC hydrates decreased markedly, and significantly high formation rates were obtained. Under magnetic stirring, the rate at which TBAB/TBAC formed hydrates was significantly lower than that when ice was used. In microscopic experiments, it was observed that the TBAB/TBAC mixture formed hydrates with more nucleation sites and compact structures, which may increase the hydrate formation rate. In the multiple cycle formation of TBAB/TBAC hydrates, the induction time gradually decreased with the increasing number of formation cycles and finally stabilized, which indicated the potential of the TBAB/TBAC hydrates for application in cold storage owing to their good durability and short process time for heat absorption and release.