Constitutive equations are reviewed and presented for low alloy ferritic steels which undergo creep deformation and damage at high temperatures; and, a thermodynamic framework is provided for the deformation rate potentials used in the equations. Finite element continuum damage mechanics studies have been carried out using these constitutive equations on butt-welded low alloy ferritic steel pipes subjected to combined internal pressure and axial loads at 590 and 620 8C. Two dominant modes of failure have been identified: firstly, fusion boundary failure at high stresses; and, secondly, Type IV failure at low stresses. The stress level at which the switch in failure mechanism takes place has been found to be associated with the relative creep resistance and lifetimes, over a wide range of uniaxial stresses, for parent, heat affected zone, Type IV and weld materials. The equi-biaxial stress loading condition (mean diameter stress equal to the axial stress) has been confirmed to be the worst loading condition. For this condition, simple design formulae are proposed for both 590 and 620 8C.
Summary Photodynamic therapy (PDT) has been reported to be useful in treating certain nonmelanoma skin cancers and a variety of benign skin conditions. We examined whether PDT might be effective in the treatment of disseminated superficial actinic porokeratosis. Three patients with classical disseminated superficial actinic porokeratosis had a small test area treated with topical aminolaevulinic acid PDT. Following the first treatment, the disorder cleared in the test area in one patient, but failed to respond in the other two patients. After subsequent treatment, the initial benefit seen in the first patient was not sustained, and no response was seen in the second patient, while the third patient was not retreated due to hyperpigmentation induced by the procedure. The results obtained in this small case series suggest that topical PDT is not a promising treatment for disseminated superficial actinic porokeratosis.
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