DRAG ON SUBMICRON NANOPARTICLE AGGREGATES

A new procedure was developed for estimating the effective collision diameter of an aggregate composed of primary particles of any size. The coagulation coefficient of two oppositely charged particles was measured experimentally and compared with classic Fuchs theory, including a new method to account for particle non-sphericity. A second set of experiments were performed on well-defined nanoparticle aggregates at different stages of sintering, i.e. from the aggregate to the fully sintered stage. Here, electrical mobility was used to characterize the particle drag. The aggregates are being built from two different size-fractionated nanoparticle aerosols, the non-aggregated particles are discarded by an electrofilter and then they are passed through a furnace at concentrations low enough not to induce coagulation.     

Spectral element solution of steady incompressible viscous free-surface flows

In this paper we present a new approach for the solution of the steady incompressible Navier-Stokes equations in a domain bounded in part by a free surface. In the spatial discretization procedure, a Legendre spectral element method is used to generate the discrete equations. For effective solution of the set of algebraic equations, the geometry is decoupled from the fluid velocity and pressure. In addition, two different algorithms are proposed depending on the importance of surface tension effects. Numerical results are presented to demonstrate the effectiveness of the proposed algorithms.     

E.S.R. of sulphur-substituted purines and nucleosides; carbon-centred radicals in mercaptopurine crystals at 77 K

Single crystals of the sulphur-containing DNA-base analogue 6-methylmercaptopurine (6MeMP) and its riboside 6-methylmercaptopurine riboside (6MeMPR) have been prepared and irradiated by 4·0 MeV electrons at 77 K. Electron spin resonance techniques have been used to study the radiation-induced radicals at 77 K. The primary carbon-centred radical, common to both molecules, has been identified as a species formed by hydrogen atom abstraction from the methyl group. The principal values of the two α-proton hyperfine coupling tensors and the g-tensors were almost the same for both molecules and for 6MeMPR were: α1, -28·8, -17·9 and -6·4 G; α2, -28·2, -15·7 and -9·8 G; and g, 2·0063, 2·0024 and 2·0018. These data indicate a spin density of 0·77 on the methyl carbon atom. Molecular orbitals determined from CNDO/2 methods were used in calculations of the directions and magnitude of the g-tensor principal values. Comparison of these calculated values and experimental data suggests that contribution of spin density in d-orbitals on the sulphur atom is important in describing the g-tensor. Methyl H-abstraction radicals trapped in pairs were also detected in 6MeMP and the data are consistent with an effective interspin distance of 4·67 Å.     

Eine Reaktion auf Mangan

Ohne Zusammenfassung     

A chromatic partition polynomial

A polynomial in two variables is defined by C_n(x,t)=Σ_πΠnx(Gπ,x)t^|π|, where Π_n is the lattice of partitions of the set {1, 2, …, n}, G_π is a certain interval graph defined in terms of the partition gp, χ(G_π, x) is the chromatic polynomial of G_π and |π| is the number of blocks in π. It is shown that , where S(n, i) is the Stirling number of the second kind and (x)_i = x(x − 1) ··· (x − i + 1). As a special case, C_n(−1, −t) = A_n(t), where A_n(t) is the nth Eulerian polynomial. Moreover, A_n(t)=Σ_πΠna_πt^|π| where a_π is the number of acyclic orientations of G_π.     

Secondary isotope effect on kinetic energy release and reaction symmetry

A secondary deuterium isotope effect on the kinetic energy release has been observed for the loss of molecular hydrogen from protonated formaldehyde and protonated methylimine. The results have been used to show that the centre of the reactions lies towards the carbon atom.     

Turbidimetric ultramicro titration of potassium

Summary A method has been worked out for the determination of ultramicro quantities of potassium. The potassium is precipitated with sodium tetraphenylborate and the excess of the reagent is determined by turbidimetric titration with cetyltrimethylammomum bromide.

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Zusammenfassung Eine Methode zur Bestimmung von Ultramikromengen Kalium wurde ausgearbeitet. Dieses wird mit Natriumtetraphenylborat gefällt und der Uberschuß des Fällungsmittels durch turbidimetrische Titration mit Cetyltrimethylammoniumbromid bestimmt.

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Résumé Mise au point d'une méthode pour le dosage d'ultramicroquantités de potassium. Le potassium est précipité par le tétraphénylborate de sodium et l'excès de réactif est dosé par titrage turbidimétrique avec le bromure de cétyltriméthylammonium.

     

Reactions of platinum clusters Pt(n)(+/-), n = 1-21, with CH4: to react or not to react

The relative reactivity of any given neutral platinum cluster falls in-between that of the corresponding anion and cation.