42,886 research outputs found
Characterisation and Interpretation of On‐Surface Chemical Reactions Studied by Ultra‐High‐Resolution Scanning Probe Microscopy
No full textThe investigation of supramolecular self-assembly at surfaces requires detailed characterisation at the molecular or even sub-molecular level. The primary technique that has been employed to ensure a detailed understanding of self-assembled structures is based on high-resolution scanning probe microscopy (SPM). Such techniques, notably scanning-tunnelling microscopy (STM) and atomic force microscopy (AFM) have been widely used and such techniques allow the resolution of the geometric structure of organic molecules with intramolecular resolution. The development of noncontact atomic force microscopy (ncAFM) over recent years has allowed sub-molecular imaging of the chemical, electronic, and electrostatic properties of single molecules. This chapter focuses on the use of this technique to track complex on-surface chemical reactions, investigate novel reaction products, and even synthesise new molecular structures one bond at a time
New trends in crystal engineering.
No full textThe articles and highlights presented at the second CrstEngComm meeting, held in Nottingham in Sept. 2004 are reviewed. The discussion has highlighted the current development of crystal engineering and allowed to emerge some of its future potentials. In particular. the papers described in this highlight focus on four fundamental aspects: (i) intermol. interactions: evaluation and application to crystal design; (ii) networks: design and applications: (iii) approaches to crystal synthesis; (iv) polymorphism, solvates and chiral crystal resol
Synthesis of hydrophobic MIL-53(Al) nanoparticles in low molecular weight alcohols: systematic investigation of solvent effects
No full textThe effects of using low-weight alcohols, methanol and ethanol, for the synthesis of MIL-53(Al) are investigated and the results directly compared with analogous synthesis in water and N,N-dimethylformamide (DMF). When methanol is employed in the synthesis of MIL-53(Al), termed MIL 53(MeOH), several unique properties are observed. The breathing phenomenon which is known for MIL-53(Al) derivatives, prepared using water or DMF as reaction solvent, is not observed for samples prepared from methanol and the framework adopts, and remains in, the large-pore form. Thus, measurement of N2-isotherms and calculation of internal surface areas have verified that the synthesis of MIL-53(MeOH) leads to a product which is highly porous without the requirement for an energy-consuming activation process. Furthermore, X-ray diffraction measurements and scanning electron microscopy at different humidity levels reveal a reversible loss of crystallinity at high humidity levels for MIL-53(MeOH) which was not observed previously for any other known MIL-53 derivative. In contrast the synthesis of MIL-53(Al) in ethanol leads of a product with low crystallinity
Laguerre geometry of hypersurfaces in R-n
No full textLaguerre geometry of surfaces in R-3 is given in the book of Blaschke [Vorlesungen uber Differentialgeometrie, Springer, Berlin Heidelberg New York (1929)], and has been studied by Musso and Nicolodi [Trans. Am. Math. soc. 348, 4321-4337 (1996); Abh. Math. Sem. Univ. Hamburg 69, 123-138 (1999); Int. J. Math. 11(7), 911-924 (2000)], Palmer [Remarks on a variation problem in Laguerre geometry. Rendiconti di Mathematica, Serie VII, Roma, vol. 19, pp. 281-293 (1999)] and other authors. In this paper we study Laguerre differential geometry of hypersurfaces in R-n. For any umbilical free hypersurface x:M -> R-n with non-zero principal curvatures we define a Laguerre invariant metric g on M and a Laguerre invariant self-adjoint operator S:TM -> TM, and show that {g,S} is a complete Laguerre invariant system for hypersurfaces in R-n with >= 4. We calculate the Euler-Lagrange equation for the Laguerre volume functional of Laguerre metric by using Laguerre invariants. Using the Euclidean space R-n, the semi-Euclidean space R-1(n) and the degenerate space R-0(n) we define three Laguerre space forms URn, UR1n and UR0n and define the Laguerre embeddings URn1 -> URn and UR0n -> URn, analogously to what happens in the Moebius geometry where we have Moebius space forms S-n, H-n and R-n (spaces of constant curvature) and conformal embeddings H-n -> S-n and R-n -> S-n[cf. Liu et al. in Tohoku Math. J. 53, 553-569 (2001) and Wang in Manuscr. Math. 96, 517-534 (1998)]. Using these Laguerre embeddings we can unify the Laguerre geometry of hypersurfaces in R-n, R-1(n) and R-0(n). As an example we show that minimal surfaces in R-1(3) or R-0(3) are Laguerre minimal in R-3.MathematicsSCI(E)0ARTICLE173-9512
Emerging applications of metal-organic frameworks
No full textMetal–organic frameworks are a unique class of materials well known for their crystallinity and ultra-high porosity. Since their first report over fifteen years ago, research in this area has sought to actively exploit these properties, especially in gas adsorption. In this article we canvass some emerging topics in the field of MOF research that show promise for new applications in areas such as biotechnology, catalysis, and microelectronics.Raffaele Ricco, Constance Pfeiffer, Kenji Sumida, Christopher J. Sumby, Paolo Falcaro, Shuhei Furukawa, Neil R. Champness and Christian J. Doona
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Experimental investigation into the effect of substrate clamping on the piezoelectric behaviour of thick-film PZT elements
No full textThis paper details an experimental investigation of the clamping effect associated with thick-film piezoelectric elements printed on a substrate. The clamping effect reduces the measured piezoelectric coefficient, d33, of the film. This reduction is due to the influence of the d31 component in the film when a deformation of the structure occurs, by either the direct or indirect piezoelectric effect. Theoretical analysis shows a reduction in the measured d33 of 62%, i.e. a standard bulk lead zirconate titanate (PZT)-5H sample with a manufacturer specified d33 of 593pC/N would fall to 227.8pC/N. To confirm this effect, the d33 coefficients of five thin bulk PZT-5H samples of 220µm thickness were measured before and after their attachment to a metallized 96% alumina substrate. The experimental results show a reduction in d33 of 74% from 529pC/N to 139pC/N. The theoretical analysis was then applied to existing University of Southampton thick-film devices. It is estimated that the measured d33 value of 131pC/N of the thick-film devices is the equivalent of an unconstrained d33 of 345pC/N
X-ray crystallography in open-framework materials
No full textOpen-framework materials, such as metal-organic frameworks (MOFs) and coordination polymers have been widely investigated for their gas adsorption and separation properties. However, recent studies have demonstrated that their highly crystalline structures can be used to periodically organize guest molecules and non-structural metal compounds either within their pore voids or by anchoring to their framework architecture. Accordingly, the open framework can act as a matrix for isolating and elucidating the structures of these moieties by X-ray diffraction. This concept has broad scope for development as an analytical tool where obtaining single crystals of a target molecule presents a significant challenge and it additionally offers potential for obtaining insights into chemically reactive species that can be stabilized within the pore network. However, the technique does have limitations and as yet a general experimental method has not been realized. Herein we focus on recent examples in which framework materials have been utilized as a scaffold for ordering molecules for analysis by diffraction methods and canvass areas for future exploration.Witold M. Bloch, Neil R. Champness and Christian J. Doona
Synthesis and structural characterisation of coordination polymers designed using discrete phosphonodithioato NiII complexes and dipyridyl donor ligands
No full textSquare-planar phosphonodithioato complexes [Ni(ROdtp)2] [ROdtp = (4-MeOPh)(RO)PS22; R = Me (1), Et (2)] have been treated with four different dipyridyl donors, namely 1-pyridyl-4-(4’-pyridyl-ethynyl)-benzene (I), 4,4’-bipyridine (II), 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (III), and 3,6-bis(3-pyridyl)-1,2,4,5-tetrazine (IV). The single crystal X-ray structures of the reaction products (1.I) (3), (1.III) (5), and (2.IV) (6), along with that of the previously reported compound (2.II) (4) prove the ability of dipyridyl donors to self-assemble with coordinatively unsaturated nickel-phosphonodithioates to give 1D coordination polymers whose topology, such as the shape and the separation between consecutive metal centres, can be tuned through structural modifications in the N-donor linkers. DFT calculations on the free ligands have been performed with the goal of elucidating the nature of the frontier orbitals of the ligands involved in the coordination of the nickel complexes
- …
