Carbon nanotube synthesis from alcohols by a novel aerosol method

Single- and multiwalled carbon nanotubes (CNTs) were synthesised by a novel aerosol method using alcohols, namely ethanol and octanol, as carbon precursors. Preformed iron and nickel aerosol nanoparticles, produced by evaporation from resistively heated metal wire, were used as catalysts. Multiwalled CNTs were initiated by 10 nm sized catalyst particles and produced in the presence of ethanol vapour with the partial pressure of 7072 Pa, while combination of 2.4 nm particles and decreased alcohol vapour pressure (123 Pa) resulted in the formation of mainly single-walled and a small fraction of double-walled CNTs. The effect of a promoter (thiophene) in the system was found to be very important for the synthesis of multiwalled CNTs, while only a 30% number concentration increase was found for the single-walled CNT production.     

Hyper‐Archimedean BL‐algebras are MV‐algebras

Generalizations of Boolean elements of a BL‐algebra L are studied. By utilizing the MV‐center MV(L) of L, it is reproved that an element x ∈ L is Boolean iff x ∨ x * = 1 . L is called semi‐Boolean if for all x ∈ L, x * is Boolean. An MV‐algebra L is semi‐Boolean iff L is a Boolean algebra. A BL‐algebra L is semi‐Boolean iff L is an SBL‐algebra. A BL‐algebra L is called hyper‐Archimedean if for all x ∈ L, xⁿ is Boolean for some finite n ≥ 1. It is proved that hyper‐Archimedean BL‐algebras are MV‐algebras. The study has application in mathematical fuzzy logics whose Lindenbaum algebras are MV‐algebras or BL‐algebras. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A theory for the construction of the irreducible representations of finite groups

It is shown how the irreducible representations of a finite group can be calculated from the irreducible characters (the latter can be calculated exactly by using Dixon's method). All elements of the matrix, representing a group element, lie in the rational field of polynomials of ξ = exp (2πi/e), where e is the exponent of the group.     

Linear viscoelastic models: Part IV. From molecular dynamics to temperature and viscoelastic relations using control theory

Viscoelasticity and temperature dependences are explained using molecular dynamics and control theory. We have previously (Borg and Pääkkönen, 2009 [1], [2], [3]) applied control theory to model the relationship between the relaxation modulus, dynamic and shear viscosity, transient flow effects, power law and Cox–Merz rule related to the molecular weight distribution (MWD), and here these topics are discussed more generally. In this paper we show the direct simple relation to molecular dynamics using structural models comprising dumb-bells (Bird et al., 1987 [4]) with internal viscosity and elasticity in a statistical tube. The dumb-bell model is used to obtain the linear relation to the elasticity P′ value of function P′(ω) and the relation to the viscosity P″ value of function P″(ω) from chain friction. The applied principle is also valid for the relaxation modulus or shear viscosity. A new principle is presented for obtaining absolute values such as zero viscosity by modelling, which is first used to obtain absolute values for a target point at a high rate for unentangled chains (since close relaxed states of chain topology are much more complicated). An analytical model for the temperature dependency of viscoelastic flows is presented, which is many times more accurate than WLF or Arrhenius equations. Control theory and variations of tube diameter as a function of temperature gives linear relation between chain dynamics and viscoelastic properties. New compact formulas are presented to simultaneously model different polymer flows and temperatures. We have also found that the MWDs computed from the relaxation modulus or complex and the shear viscosity are not temperature sensitive, in contrast to what time–temperature superposition (TTS) suggests, although absolute viscoelastic values make them appear very temperature-dependent. TTS is verified for thermorheologically simple materials, and the reasons for it not holding are explained.     

Optical properties of thermally responsive amphiphilic gold nanoparticles protected with polymers

Amphiphilic thermally responsive gold nanoparticles have been prepared by protecting the particles with both polystyrene, PS, and poly(N-isopropylacrylamide), PNIPAM, chains. Particles form a monolayer on a water surface in a Langmuir trough, and according to in situ spectroscopic measurements, the surface plasmon resonance, SPR, band undergoes a blue-shift during the monolayer compression. The compression-induced blue-shift is related to a change in the conformation of tethered PNIPAM chains; the phenomenon is discussed on the basis of Mie-Drude theory. In contrast, a red-shift in the SPR of the multilayers of the same nanoparticles transferred at different temperatures has been observed with increasing the deposition cycle, attributed to the presence of a weak interparticle coupling in the multilayer.     

Enthalpies of formation and isomerization of cis‐ and trans‐decalin,and their oxa‐analogs by G3(MP2)//B3LYP calculations

G3(MP2)//B3LYP calculations have been carried out on trans‐ and cis‐decalin, and their mono‐, di‐, tri‐, and tetraoxa‐analogs. The main purpose of the work was to obtain enthalpies of formation for these compounds, and to study the relative stabilities of the cis–trans and positional isomers of the various (poly)oxadecalins. Comparison of the computational enthalpies of formation with the respective experimental ones, known only for the decalins and 1,3,5,7‐tetraoxadecalins, shows that in both cases the computational values are more negative than the experimental ones, the deviations being ?5 to ?7 kJ mol^?1 for the decalins and ?12 to ?17 kJ mol^?1 for the 1,3,5,7‐tetraoxadecalins. The respective computational enthalpies of cis–trans isomerization, however, are in excellent to satisfactory agreement with the experimental data. The cis–trans enthalpy differences vary from +11.0 kJ mol^?1 for decalin to ?15.4 kJ mol^?1 for 1,4,5,8‐tetraoxadecalin. Low relative enthalpy values were also calculated for the cis isomers of 1,8‐dioxadecalin (?3.7 kJ mol^?1), 1,3,6‐trioxadecalin (?4.6 kJ mol^?1), 1,3,8‐trioxadecalin (?9.7 kJ mol^?1), 1,4,5‐ trioxadecalin (?5.6 kJ mol^?1), 1,3,5,8‐tetraoxadecalin (?7.3 kJ mol^?1), and 1,3,6,8‐tetraoxadecalin (?14.5 kJ mol^?1). Copyright © 2009 John Wiley & Sons, Ltd.     

Enthalpies of formation and isomerization of aromatic hydrocarbons and ethers by G3(MP2)//B3LYP calculations

A computational method for estimation of the gas‐phase enthalpies of formation of aromatic hydrocarbons and ethers has been developed. The method is based on high‐level G3(MP2)//B3LYP calculations, atomization reactions, and structure‐dependent correction terms. By this method, enthalpies of formation Δ_fH_m°(g, 298.15 K) of 86 aromatic compounds were evaluated. The calculated enthalpies of formation raise questions of the reliability of several experimental enthalpies of formation reported in the literature. As an application of the computational enthalpies of formation, reaction enthalpies for several types of isomerization reactions of aromatic compounds were calculated. In cases in which experimental reaction enthalpies were available for comparison, the agreement between the computational and experimental data proved to be excellent. Copyright © 2008 John Wiley & Sons, Ltd.     

The hydrogen atom in a cubic field of electric dipoles

The full rotational symmetry of the hydrogen atom is lowered to that of the double group of O_h. This is done by a cubic field of electric dipoles. Symmetry-adapted spin orbitals have been calculated and with them the energies of the lowest states as functions of the distance from the dipoles to the atom, the dipole moment, and the size of the atoms forming the dipoles. The Hamiltonian used is obtained by starting with the Dirac equations and then making some simplifications and approximations.     

Electron transport in two-dimensional arrays of gold nanocrystals investigated by scanning electrochemical microscopy

This article reports the use of the scanning electrochemical microscope (SECM) to investigate the electronic properties of Langmuir monolayers of alkane thiol protected gold nanocrystals (NCs). A substantial increase in monolayer conductivity upon mechanical compression of the Au NC monolayer is reported for the first time. This may be the room temperature signature of the insulator to metal transition previously reported for comparable silver NC monolayers. Factors influencing the conductivity of the monolayer NC array are discussed.