The investigation of industrial plant processes using radiotracer techniques

Additional plant has been commissioned at the Springfields Works of BNFL to obtain increased production of uranium tetrafluoride. A programme of investigational work was undertaken during production to improve our understanding of the process. This paper describes some of the radiometric techniques used in the project, including passive gamma and neutron measurements and experiments using radioactive tracers.     

Determination of aflatoxins B1, B2, G1 and G2 by high-performance liquid chromatography with electrochemical detection

A new approach to the determination of afiatoxins B₁, B₂, G₁ and G₂ is given; the method involves high-performance liquid chromatography with amperometric detection in the differential-pulse mode at the dropping mercury electrode with 1-s drop time. These aflatoxins can be determined simultaneously with good resolution but with some compromise in sensitivity. The detection limit of underivatized aflatoxin standards is around 5 ng. Average recoveries of aflatoxins from peanut butter by the Beebe method were G₂ 81%, G₁ 87%, B₂ 77% and B₁ 76%.     

Turbulence measurements in a resonance tube

Experimental investigations of acoustically induced turbulence in a resonance tube have been performed. Frequency (f) and sound pressure level (I_p) effects have been studied. Measurements were made at various spatial locations on loops and nodes. Sampled data were processed to estimate the characteristics of turbulence. It is found that the acoustically induced turbulence appears when I_p exceeds 160 dB under the experimental conditions of f = 680–2740 Hz and I_p = 160–166 dB. The turbulent spectrum (F) and the wave number (κ) are found to satisfy a power law F ∝ K^s with $\text{s ? ?1·6}\text{to}\text{? 2·1}$. The r.m.s. turbulent velocity ($\text{u}\text{?}$) is experimentally found to have an $\text{I}{}_{\mathrm{p}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ dependence, yet is relatively insensitive to the variation of f. Throughout the whole measuring range of f and I_p, the rate of energy dissipation per unit mass (ε) is estimated to be in the order of 10⁶–10⁷cm²/s³.     

Measurements of some reaction rates of importance in KrF lasers

A flowing afterglow method has been used to study a number of reactions of importance in KrF lasers using NF₃ as the fluorine donor. Total rate constants are reported for Kr^*(³ P ₂)+NF₃ and Kr⁺+NF₃. The thermal energy attachment coefficient has been measured for NF₃ and the cross section for the electron excitation process Kr^*(³ P ₂) +e→Kr^*(³ P ₁)+e has been estimated. The relevance of these results to discharge pumped KrF lasers is discussed.     

Ergodic properties of operator semigroups in general weak topologies

The aim of this paper is to study ergodic properties (i.e., properties about the limit of Cesàro averages) of a semigroup of bounded linear operators on a Banach space X, which is assumed to be continuous and locally integrable in the sense of a certain general weak topology of X. Then the results are applied to particular examples, such as locally strongly integrable semigroups, their dual semigroups, and the tensor product semigroup of two (C₀)-semigroups.     

Some complexes of rhodium and iridium with 2-(di-t-butylphosphinomethyl)-1-methoxy-4-methylbenzene

Summary The new tertiary phosphine t-13u₂(2-MeO-5-MeC₆H₃CH₂)P, L, was prepared by the base treatment of the phosphonium salt, LH⁺I^–, which was in turn prepared from t-Bu₂PH, 2-MeO-5-MeC₆H₃CH₂Cl and sodium iodide. This phosphine, L, reacts with various chloro-rhodium and -iridium species without O-demethylation. This contrasts with the behaviour of t-Bu₂PC₆H₄OMe-2 which demethylates readily on similar treatment to give chelate complexes. The completely different behaviour between this new 2-methoxybenzylphosphine, L, and the 2-anisylphosphine, t-Bu₂PC₆H₄OMe-2, is explained in terms of steric effects.No reprints are available.     

Quantitative determination of alkylated quaternary amines and their n-hydroxylated metabolites in an enzyme incubation matrix by liquid chromatography electrospray ionization mass spectrometry

A simple, rapid and sensitive reversed-phase liquid chromatography method coupled to electrospray ionization mass spectrometry has been developed for studying the in vitro metabolism of the long-chain quaternary ammonium compounds dodecyltrimethylamine, tetradecyltrimethylamine and hexadecyltrimethylamine. Samples were prepared from the biological matrix by a simple protein precipitation stage. The separation was performed using a BDS Hypersil C8 3 microm particle size (100 x 3 mm i.d.) column with a fast gradient separation (60% B to 100% B) using a mobile phase of 10 mm aqueous ammonium acetate (pH 4.0, with 0.06% triethylamine; (A)-acetonitrile (B) at 0.7 mL min(-1). To minimize contamination of the MS source a switching value was used to divert the solvent front to waste. Decylammonium bromide was used as the internal standard and analytes were identified and quantified by positive ion electrospray selected ion monitoring of their intact molecular cations. The assay had a limit of quantitation of 0.25 microm (6.25 pmol on column) and was linear over the range 0.25--100 microm assay concentration for this series of long-chain quaternary amines. The precision of intra- and inter-day assays was better than 19% and the accuracy was between 93 and 109%. The method was used to assess the in vitro metabolism of the quaternary amines by wild-type cytochrome P450 enzyme CYP 4 A 1 and mutants in an artifical membrane system.     

Technical considerations for the use of 15N-DNA stable-isotope probing for functional microbial activity in soils

Stable-isotope DNA probing is a culture-independent technique that may provide a link between function and phylogeny of active microorganisms. The technique has been used in association with 13C substrates while here we evaluate feasibility and limitations of 15N-DNA stable-isotope probing (SIP) using labelled and unlabelled pure microbial cultures or soil extracts. Our results showed that (15)N-DNA probing is feasible for cultures as well as soil samples. Limitations of 15N-DNA-SIP are (a) the need for relatively large quantities of DNA to visualise bands (although molecular resolution is much higher) and (b) 15N-DNA enrichment needed to ideally be >50 at%; however, this requirement can be lowered to approx. 40 atom% 15N with pure cultures using a modified CsCl centrifugation method (140K g for 69 h). These advances in 15N-DNA-SIP methodology open new opportunities to trace active microbial populations utilising specific N substrates in situ.     

The Classification of Flats in {\boldsymbol {PG}}({\bf 9,2}) which are External to the Grassmannian {\cal G}_{\bf 1,4,2}

Constructions are given of different kinds of flats in the projective space $PG(9,2)={\mathbb P}(\wedge^{2}V(5,2))$ which are external to the Grassmannian ${\cal G}_{\bf 1,4,2}$ of lines of PG(4,2). In particular it is shown that there exist precisely two GL(5,2)-orbits of external 4-flats, each with stabilizer group ?31:5. (No 5-flat is external.) For each k=1,2,3, two distinct kinds of external k-flats are simply constructed out of certain partial spreads in PG(4,2) of size k+2. A third kind of external plane, with stabilizer ?2³:(7:3), is also shown to exist. With the aid of a certain ‘key counting lemma’, it is proved that the foregoing amounts to a complete classification of external flats.