Ruthenium nanoparticles in ionic liquids: structural and stability effects of polar solutes

Ionic liquids are a stabilizing medium for the in situ synthesis of ruthenium nanoparticles. Herein we show that the addition of molecular polar solutes to the ionic liquid, even in low concentrations, eliminates the role of the ionic liquid 3D structure in controlling the size of ruthenium nanoparticles, and can induce their aggregation. We have performed the synthesis of ruthenium nanoparticles by decomposition of [Ru(COD)(COT)] in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(1)C(4)Im][NTf(2)], under H(2) in the presence of varying amounts of water or 1-octylamine. For water added during the synthesis of metallic nanoparticles, a decrease of the solubility in the ionic liquid was observed, showed by nanoparticles located at the interface between aqueous and ionic phases. When 1-octylamine is present during the synthesis, stable nanoparticles of a constant size are obtained. When 1-octylamine is added after the synthesis, aggregation of the ruthenium nanoparticles is observed. In order to explain these phenomena, we have explored the molecular interactions between the different species using (13)C-NMR and DOSY (Diffusional Order Spectroscopy) experiments, mixing calorimetry, surface tension measurements and molecular simulations. We conclude that the behaviour of the ruthenium nanoparticles in [C(1)C(4)Im][NTf(2)] in the presence of 1-octylamine depends on the interaction between the ligand and the nanoparticles in terms of the energetics but also of the structural arrangement of the amine at the nanoparticle's surface.     

Adsorption energetics of CO on supported Pd nanoparticles as a function of particle size by single crystal microcalorimetry

The heat of adsorption and sticking probability of CO on well-defined Pd nanoparticles were measured as a function of particle size using single crystal adsorption microcalorimetry. Pd particles of different average sizes ranging from 120 to 4900 atoms per particle (or from 1.8 to 8 nm) and Pd(111) were used that were supported on a model in situ grown Fe(3)O(4)/Pt(111) oxide film. To precisely quantify the adsorption energies, the reflectivities of the investigated model surfaces were measured as a function of the thickness of the Fe(3)O(4) oxide layer and the amount of deposited Pd. A substantial decrease of the binding energy of CO was found with decreasing particle size. Initial heat of adsorption obtained on the virtually adsorbate-free surface was observed to be reduced by about 20-40 kJ mol(-1) on the smallest 1.8 nm sized Pd particles as compared to the larger Pd clusters and the extended Pd(111) single crystal surface. This effect is discussed in terms of the size-dependent properties of the Pd nanoparticles. The CO adsorption kinetics indicates a strong enhancement of the adsorbate flux onto the metal particles due to a capture zone effect, which involves trapping of adsorbates on the support and diffusion to metal clusters. The CO adsorption rate was found to be enhanced by a factor of ～8 for the smallest 1.8 nm sized particles and by ～1.4 for the particles of 7-8 nm size.     

The proton relaxation of CH3OD in the presence of Co(II) ions,as studied by spin-echo techniques

By measurement of the proton relaxation times T ₁ and T ₂ of CH₃OD containing Co⁺⁺ ions in dilute solution and the dependence of the observed decay time (T ₂ ^?) on t _ep the separation between pulses in a Carr-Purcell sequence the coordination number is shown to be six. Since this result has previously been obtained by an independent method, the use of the dependence of T ₂ ^? on t _ep to determine coordination numbers is justified for solutions of paramagnetic ions. The validity of analytical expressions derived previously has been checked by numerical methods, and the analytical expression is shown to be valid even in the presence of H ₀ and H ₁ inhomogeneity and inaccurate pulses of finite duration, provided that the Meiboom-Gill method is used. In an Appendix insight derived from the results of the numerical solutions is used to give a brief derivation of the dependence of T ₂ ^? on H ₀, exchange rate and t _ep.     

The Application of 2D NMR Techniques in the Structural Assignment of the Diterpenoid Alkaloid,Delphinine

The two dimensional inverse detected heteronuclear correlation experiment HMQC and the homonuclear correlation experiments COSY and ROESY were performed on the natural alkaloid, delphinine enabling complete assignments of the ¹H and ¹³C spectra. The stereochemistry of ring A and B have been determined in solution. The results suggest that the application of direct correlation multipulse NMR techniques allows for unambiguous structural assignment of delphinine.     

Random telegraph noise in carbon nanotubes and peapods

The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs) and C₆₀-filled SWNTs (the so-called peapods). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with ballistic electrons. On the other hand, the noise for peapods can be attributed to the motion of C₆₀ molecules in hollow space of SWNTs.     

Atomic force microscopy evidence for K domains on freshly cleaved mica

The unit cell height in the c-direction of muscovite mica is well established at 10 Å. However, we have observed steps much lower than this whilst imaging freshly cleaved mica surfaces in an atomic force microscope. The steps, 1.0±0.05 Å high, are unstable and disappear in a period of minutes after cleavage. We propose that they are due to the presence of domains of residual K⁺ ions that form two matching patchworks on the cleaved faces. Upon cleavage, they relax inwards from the bulk equilibrium position 1.6 Å above the oxygen atoms of the tetrahedral silicate. Possible mechanisms for the disappearance of the steps are discussed.     

Magnetic field effects on the magnetism of Zr3FeH5.3

Zr₃FeH_5.3 exhibits hydrogen-induced magnetism below an ordering temperatureT ₀=135 K. Comparison of three fit models for analysis of the zero field Mössbauer spectra belowT ₀ is presented. The models are based on discrete and distributed static hyperfine fields and magnetic relaxation. The response of Zr₃FeH_5.3 to an applied field of 6.9 T indicates that antiferromagnetic interactions are present with spin canting also possible.     

Nachweis und colorimetrische Bestimmungsmethoden des Molybd?ns

Ohne Zusammenfassung     

What is the complexity of a distributed computing system?

Distributed computing systems are becoming bigger and more complex. Although the complexity of large‐scale distributed systems has been acknowledged to be an important challenge, there has not been much work in defining or measuring system complexity. Thus, today, it is difficult to compare the complexities of different systems, or to state that one system is easier to program, to manage, or to use than another. In this article, we try to understand the factors that cause computing systems to appear very complex to people. We define different aspects of system complexity and propose metrics for measuring these aspects. We also show how these aspects affect different kinds of people—viz. developers, administrators, and end‐users. On the basis of the aspects and metrics of complexity that we identify, we propose general guidelines that can help reduce the complexity of systems. © 2007 Wiley Periodicals, Inc. Complexity 12: 37–45, 2007