The Effect of Age, Sex, Strain, Species and Dose Level Differences Upon the Metabolism of 2-Naphthylamine in Rodents

THE production of bladder tumours by aromatic amines has been correlated with the excretion of ortho-hydroxylated metabolites (Clayson, 1962). In the case of 2-naphthylamine, Bonser, Clayson and Jull (1951) showed that the susceptibility of a species to bladder tumour induction on feeding this agent appeared to depend on the proportion of a dose metabolised to give 2-amino-1-naphthol and its conjugates. It was further shown that 2-amino-i-naphthol was highly carcinogenic upon implantation into the bladders of mice whilst the amine itself was only feebly carcinogenic under these circumstances (Bonser

The Attempted In Vivo Inhibition of the Ortho-hydroxylation of 2-Naphthylamine

CLAYSON suggested that certain aromatic amines act as bladder carcinogens as a consequence of their metabolic conversion to ortho-hydroxylated derivatives and considerable evidence has accumulated in support of this view (Claysoii, 1962). Amongst the ortho-hydroxylated amines believed to be bladder carcinogens are certain tryptophan metabolites such as, 3-hydroxykynurenine and 3-hydroxyanthranilic acid, and it has been suggested that the urinary excretion of these compounds may cause " spontaneous " bladder tumours in main (Allein, Boyland, Dukes, Horning and Watson, 1957). Abul-Fadl and Khalafallah (1961) have shown an association of ain abnormally high incidence of bladder tumours and a raised level of urinary excretion of 3-hydroxyanthranilic acid in bilharziasis. In view of the possible importance of ortho-aminophenols in the induction of bladder tumours in man, Boyland, Wallace and Williams (1957) suggested that glucosaccharo-l1 4-lactone might be used to inhibit urinary glucuronidase aild thus minimise the formation of free ortho-aminophenols in the bladder. Unfortunately the glucuronides are not the only conjugates, which coul

Diffusive processes in polyacrylic acid hydrogels

The aim of this work was to characterise the diffusive properties of superabsorbent polymer systems prepared by free radical crosslinking polymerisation of acrylic acid. The polyelectrolyte nature of these hydrogels gives rise to high swelling capacities, and their ability to absorb and retain water is highly dependent on the precise network structure. Modifying the synthesis formulation results in considerable changes to the dynamic and structural properties of these gels, providing the motive for the work presented here. The influence of two factors, namely the extent of monomer neutralisation and the level of crosslinker in the pre-gel solution, were investigated. The dynamic properties of gels were examined using Quasi-Elastic Light Scattering (QELS), from which the cooperative diffusion coefficient and degree of heterogeneity could be determined. The former was found to increase linearly with neutralisation, due to the introduction of electrostatic interactions. The diffusion coefficient initially remained constant with the addition of crosslinker, due to the dominating influence of physical entanglements, but increased above a threshold crosslinking degree, corresponding to a reduction of the network mesh size. The extent of large-scale inhomogeneity increased for higher ionisations, as both the crosslinker solubility and the efficiency of monomer-crosslinker reaction decreased. However, there was a tendency for concentration fluctuations to be minimised for higher neutralisations, making the gel more microscopically homogeneous. Kinetics of swelling experiments were used to investigate gels of varying composition. The macroscopic diffusion coefficient was found to increase rapidly with increasing neutralisation until the monomer was approximately 35% neutralised, beyond which point counterion condensation caused insignificant variation. This trend was also reflected in the equilibrium swelling ratios, and mode of diffusion. For the majority of gels, the diffusion process was characterised as case II transport. Variation of crosslinking degree caused an overall increase in the diffusion coefficient, reflecting the trend observed in the QELS studies. Nuclear Reaction Analysis (NRA) was used to probe the penetration of heavy water into dry network slabs. The concentration-depth profiles revealed a discontinuity in the diffusion coefficient, corresponding to the transition between glassy and rubbery states, for which the diffusivities differed by several orders of magnitude. The kinetics of plasticisation was assumed to be the rate determining factor in the swelling process, on the timescale of the NRA experiments. The diffusion coefficient for the swollen rubbery region, representative of the macroscopic diffusion process, was found to increase linearly with neutralisation, and decrease with crosslinking degree. The latter observation was explained as due to a reduction in the free volume available for solvent diffusion with higher levels of crosslinker

Structuralism, indiscernibility, and physical computation

Structuralism about mathematical objects and structuralist accounts of physical computation both face indeterminacy objections. For the former, the problem arises for cases such as the complex roots i and -i, for which a (non-trivial) automorphism can be defined, thus establishing the structural identity of these importantly distinct mathematical objects (see e.g. Keranen in Philos Math 3:308-330, 2001). In the case of the latter, the problem arises for logical duals such as AND and OR, which have invertible structural profiles (see e.g. Shagrir in Mind 110(438):369-400, 2001). This makes their physical implementations indeterminate, in the sense that their structural profiles alone cannot establish whether a given physical component is an AND-gate or an OR-gate. Doherty (PhilPapers, https:// philpapers.org/ rec/DOHCI-3, 2021) has recently shown both problems to be analogous, and has argued that computational structuralism is threatened with the absurd conclusion that computational digits might be indiscernible, such that, if structural properties are all that we have to go on, the binary digit 0 must be treated as identical to the binary digit 1 (rendering pure structuralism absurd). However, we think that a solution to the indiscernibility problem for mathematical structuralists, drawing on the work of David Hilbert, can be adapted for the analogous problem in the computational case, thereby rescuing the structuralist approach to physical computation

Extended skyrmion lattice scattering and long-time memory in the chiral magnet Fe1−x_{1-x}Cox_xSi

Small angle neutron scattering measurements on a bulk single crystal of the doped chiral magnet Fe$_{1-x}$Co$_x$Si with $x$=0.3 reveal a pronounced effect of the magnetic history and cooling rates on the magnetic phase diagram. The extracted phase diagrams are qualitatively different for zero and field cooling and reveal a metastable skyrmion lattice phase outside the A-phase for the latter case. These thermodynamically metastable skyrmion lattice correlations coexist with the conical phase and can be enhanced by increasing the cooling rate. They appear in a wide region of the phase diagram at temperatures below the $A$-phase but also at fields considerably smaller or higher than the fields required to stabilize the A-phase

Theoretical Investigation of Optical Conductivity in Ba [Fe(1-x)Co(x)]2 As2

We report on theoretical calculations of the optical conductivity of Ba [Fe(1-x)Co(x)]2 As2, as obtained from density functional theory within the full potential LAPW method. A thorough comparison with experiment shows that we are able to reproduce most of the observed experimental features, in particular a magnetic peak located at about 0.2 eV which we ascribe to antiferromagnetic ordered magnetic stripes. We also predict a large in-plane anisotropy of this feature, which agrees very well with measurements on detwinned crystals. The effect of Co doping as well as the dependence of plasma frequency on the magnetic order is also investigated