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Tanoue R.,Kumamoto University | Higuchi R.,Kumamoto University | Ikebe K.,Kumamoto University | Uemura S.,Kumamoto University | And 9 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2014

Two-dimensional-conjugated metal-porphyrin covalent organic frameworks were produced in aqueous solution on an iodine-modified Au(111) surface by "on-site" azomethine coupling of FeIII- 5,10,15,20-tetrakis(4- aminophenyl)porphyrin (FeTAPP) with terephthal dicarboxaldehyde and investigated in detail using in-situ scanning tunneling microscopy. Mixed covalent organic porphyrin frameworks consisting of FeTAPP and metal-free TAPP (H2TAPP) were prepared through simultaneous adsorption in a mixed solution as well as partial replacement of FeTAPP by H2TAPP in an as-prepared metal-porphyrin framework. In the mixed framework, the relative distribution of FeTAPP to H2TAPP was not random and revealed a preference for homo-connection rather than heteroconnection. The construction of substrate-supported,-conjugated covalent frameworks from multiple building blocks, including metal centers, will be of significant utility in the design of functional molecular nanoarchitectures Copyright © 2014 American Scientific Publishers All rights reserved.

Arora A.,Arizona State University | Vance K.,Arizona State University | Sant G.,University of California at Los Angeles | Sant G.,California Nano Systems Institute | Neithalath N.,Arizona State University
Construction and Building Materials | Year: 2016

This paper compares the performance of commercial interground Portland-limestone cements (PLC) to those of blended limestone systems. Limestone of four different median sizes is mixed with ordinary portland cement (OPC) to create blends in an attempt to match the particle size distribution of the PLCs. The interground systems are found to outperform the blended systems, plausibly because of the difference in size distributions of the clinker and limestone fractions between the PLCs and the blended systems. A novel methodology to extract the particle size distributions of the components in the interground systems is reported. This method, applicable for several types of multi-component powder systems, considers Rosin-Rammler size distributions for the ground clinker and limestone, and optimizes the parameters of the distribution to obtain a composite distribution of the same fineness as the interground system. The model is verified using a cement hydration and microstructure model. © 2016 Elsevier Ltd. All rights reserved.

Arora A.,Arizona State University | Sant G.,University of California at Los Angeles | Sant G.,California Nano Systems Institute | Neithalath N.,Arizona State University
Construction and Building Materials | Year: 2016

The influence of high volume cement replacement using a combination of slag and limestone, on the hydration, reaction products and pore structure, and strength of cementitious systems is reported in this paper. Total replacement levels vary from 20% to 50% by volume. Slag is blended with: (i) Portland-limestone cement (PLC) that contains limestone interground with cement, or (ii) OPC and limestone of four different sizes in such a way that the resulting particle size distribution of the composite matches that of the corresponding PLC-based mixture. The hydration response of cement and cement-slag mixtures are found to be modified in the presence of limestone. It is observed from calorimetric and thermogravimetric analysis that a favorable slag-limestone synergy exists, that enables high volume replacement of cement without concomitant loss in properties. The early-age compressive strengths are beneficially impacted by the presence of limestone whereas the clinker factor does not play a significant role in later-age strengths in both the blended and interground systems. The study paves the way for development of multiple-material binders containing higher levels of cement replacement that demonstrate early and later age properties that are comparable to or better than that of traditional straight cement systems. © 2015 Elsevier Ltd. All rights reserved.

Dadras J.,University of California at Los Angeles | Jimenez-Izal E.,University of California at Los Angeles | Alexandrova A.N.,University of California at Los Angeles | Alexandrova A.N.,California Nano Systems Institute
ACS Catalysis | Year: 2015

Immobilized Pt clusters are interesting catalysts for dehydrogenation of alkanes. However, surface-deposited Pt clusters deactivate rapidly via sintering and coke deposition. The results reported here suggest that adding boron to oxide-supported Pt clusters could be a magic bullet against both means of deactivation. The model systems studied herein are pure and B-doped Pt clusters deposited on MgO(100). The nonstoichiometric boride cluster obtained via such alloying is found to anchor to the support via a covalent B-O bond, and the cluster-surface binding is much stronger than in the case of pure Pt clusters. Additionally, B introduces covalency to the intracluster bonding, leading to structural distortion and stabilization. The energy required to dissociate a Pt atom from a boride cluster is significantly larger than that of pure Pt clusters. These energetic arguments lead to the proposal that sintering via both Ostwald ripening and particle coalescence would be discouraged relative to pure Pt clusters. Finally, it is shown that the affinity to C also drops dramatically for borated clusters, discouraging coking and increasing the selectivity of potential cluster catalysts. © 2015 American Chemical Society.

Maier B.,University of Cologne | Wong G.C.L.,California Nano Systems Institute
Trends in Microbiology | Year: 2015

The bacterial type IV pilus (T4P) is a versatile molecular machine with a broad range of functions. Recent advances revealed that the molecular components and the biophysical properties of the machine are well conserved among phylogenetically distant bacterial species. However, its functions are diverse, and include adhesion, motility, and horizontal gene transfer. This review focusses on the role of T4P in surface motility and bacterial interactions. Different species have evolved distinct mechanisms for intracellular coordination of multiple pili and of pili with other motility machines, ranging from physical coordination to biochemical clocks. Coordinated behavior between multiple bacteria on a surface is achieved by active manipulation of surfaces and modulation of pilus-pilus interactions. An emerging picture is that the T4P actively senses and responds to environmental conditions. © 2015 Elsevier Ltd.

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