Assessing colloidal stability of long term MWCNT based nanofluids

This report presents an assessment on colloidal stability of functionalized multiwalled carbon nanotubes based nanofluids. To this end, an innovative technique that allows for measurement of settling velocity during centrifugation is applied. This method also enables measurements without dilution, inferring further accuracy to the experimental study. The results suggest that functionalization techniques enable the production of highly stable nanofluids. It is also found, that the colloidal stabilities of these nanofluids are characterized by hindered settling. The settling velocity decreases when the nanoparticles volume fraction rises from 0.25% to 1.50% due to the increase of interparticle interaction. Furthermore, a high aspect ratio of nanoparticles directly contributed to an increase in colloidal stability. It is expected that these results may significantly contribute to proper tailor of nanofluids engineering, ensuring a long term stable dispersion enhancing industrial application suitability.     

A holomorphic extension theorem from a fractal hypersurface in ℂ<Superscript>2</Superscript>

We consider the problem of identifying boundary values of holomorphic functions on bounded domains in ℂ². We use the quaternionic analysis techniques to extending the CR structure to a pure function theoretical nature. The advantage of our procedure lies in the fact that it also runs for domains with fractal boundary.     

Measurement of the forward-backward asymmetry ofe+e?→Z→ b[`(b)]b\bar b using prompt leptons and a lifetime tag

An analysis of inclusive production of K⁰ and the meson resonances K^*±(892), ⁰(770),f ₀(975) andf ₂(1270) in hadronic decays of the Z⁰ is presented, based on about 973,000 multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. Overall multiplicities have been determined as 1.962±0.060 K⁰ mesons, 0.712±0.067 K^*±(892) and 1.21±0.15⁰(770) per hadronic Z⁰ decay. The average multiplicities off ₀(975) for scaled momentum,x _p , in the range 0.05x _p 0.6 and off ₂(1270) for 0.05x _p 1.0 are 0.098±0.016 and 0.170±0.043 respectively. Thef ₀(975) and ⁰(770)x _p -spectra have similar shapes. Thef ₂(1270)/⁰(770) ratio increases withx _p . The average multiplicities and the differential cross sections are compared with the JETSET Parton Shower model. The model with default parameters fails to reproduce the experimental K⁰ momentum spectrum at low momentum, describes the K^*±(892) and ⁰(770)x _p -spectrum shapes, but significantly overestimates their production rates.(CICYT-AEN93-0832)     

Theoretical studies of manganese and iron superoxide dismutases: superoxide binding and superoxide oxidation

Density-functional calculations indicate that the second sphere of coordination around the metal centers of manganese and iron superoxide dismutases (MnSODs and FeSODs) plays an important role in the binding of O2(-). In these systems, O2(-) prefers to bind to Mn or Fe in end-on configurations. For human and E. coli MnSODs, the bound O2(-) forms hydrogen bonds with the tyrosine and glutamine amino acid residues in the second sphere of coordination. In the cases of E. coli and T. elongates FeSODs, hydrogen bonding occurs between the bound O2(-) and the tyrosine amino acid only because the glutamine is too far away for an effective bonding interaction. The manner in which the O2(-) binds to the metal center in MnSODs and FeSODs can affect the rate of subsequent protonation and determine the mechanism for the formation of H2O2. Both Mn- and Fe-containing superoxide dismutases contain a metal-bound solvent molecule that has been suggested to be involved in the uptake of a H+ upon reduction of the metal center [Bull, C.; Fee, J. A. J. Am. Chem. Soc. 1985, 107, 3295; Miller, A.-F.; Padmakumar, K.; Sorkin, D. L.; Karapetian, A.; Vance, C. K. J. Inorg. Biochem. 2003, 93, 71]. Using density-functional theory, we confirm this suggestion and show the involvement of the second sphere of coordination in the process. We show that the oxidation of superoxide by Mn- or Fe-containing superoxide dismutases is facilitated by a cooperative effect between superoxide binding, protonation of the OH- bound to the metal, and electron transfer from the superoxide molecule to the oxidized metal. In particular, proton transfer through tyrosine-34 on the absence of a bound superoxide is uphill while, once superoxide is bound, the energetic barrier is lowered. It is this barrier that likely keeps the resting state (Mn(III)SOD) of the enzyme with a bound hydroxide, instead of a water. This work provides a model for the mechanism of reaction of superoxide with the oxidized form of the metal within Mn- and FeSODs.     

Spotlight on Photoinduced Aryl Migration Reactions

Rearrangement reactions are certainly one of the most useful approaches towards complex structures in organic chemistry. With efficient conditions, it is indeed possible to convert simple substrates into highly functionalized products. Moreover, combining this approach with an attractive initiation process, such as visible-light catalysis, makes these reactions particularly powerful. Recently, tremendous improvements have been made, owing to a better understanding of photoredox mechanisms. In this review, recent progress on visible-light aryl migration reactions is discussed, focusing especially on Smiles rearrangement and related reactions.     

The electrochemical behavior of core-shell CdSe/CdS magic-sized quantum dots linked to cyclodextrin for studies of the encapsulation of bioactive compounds

Semiconductor nanocrystal quantum dots have been the subject of extensive investigations in different areas of science and technology in the past years. In particular, there are few studies of magic-sized quantum dots (MSQDs), even though they exhibit features such as extremely small size, fluorescence quantum efficiency, molar absorptivity greater than traditional QDs, and highly stable luminescence in HeLa cell cultures, thereby enabling monitoring of biological or chemical processes. The present study investigated the electrochemical behavior of free CdSe/CdS MSQDs using glassy carbon electrode and CdSe/CdS MSQDs immobilized on a gold electrode modified with a self-assembled cyclodextrin monolayer. The MSQDs showed two peaks in aprotic medium. The functionalized film modifier was prepared and characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy using ferricyanide ions as a redox probe. The prepared modified electrode exhibited a stable behavior. The proposed method was successfully applied to encapsulation studies of mangiferin, a natural antioxidant compound, and cyclodextrin associated with the quantum dot, and the response was compared with that of the modified electrode without QD. The fluorescence study revealed that CdSe/CdS quantum dots emit blue light when excited by an optical source of wavelength of 350 nm and a significant increase in fluorescence and absorbance intensity is observed from the core-shell CdSe/CdS MSQDs when quantities of mangiferin are added to the solution containing thiolated cyclodextrin. CdSe/CdS MSQDs are optically and electrochemically sensitive and can be used for the detection and interaction of compounds encapsulated in cyclodextrin.     

Boundary value problems for quaternionic monogenic functions on non-smooth sureaces

In this paper, analogous of the Compound Riemann-Hilbert boundary value problems are investigate for quaternionic monogenic functions. The solution (explicitly) of the problem is established over continuous surface, with little smoothness, which bounds a bounded domain of R³. In particular, smoothness property for high-dimensional Cauchy type integral are computed. We also use Zygmund type estimates to adapt existing one-variable complex results to ilustrate the Hölder-boundedness of the singular integral operator on 2-dimensional Ahlfors regular surfaces. At the end, uniqueness of solution for the Riemann boundary value problem have already built taking as a base the general Operator Theory.