Rigidity of tube sheet structure

The shear displacement of a tube sheet relative to a parallel stationary sheet depends not only on the stiffness of the tubes connecting the two sheets, but also on the play of the tubes within the holes of the sheets. This dependence is non-linear and extremely sensitive.     

The consequences of UV-induced immunosuppression for human health

Exposure to UV radiation can cause suppression of specific immune responses. The pathways leading to the down-regulation are complex, starting from the absorption of UV photons by chromophores in the skin and ending with local and systemic changes in immune mediators, the generation of T and B regulatory cells and inhibition of effector and memory T cell activation. The consequences for human health are thought to be both beneficial and adverse. The former are illustrated by protection against polymorphic light eruption, and possible protection against T cell-mediated autoimmune diseases and asthma. The latter are illustrated by skin cancer, cutaneous lupus erythematosus and infectious diseases including vaccination. Many outstanding questions remain in this rapidly developing and controversial area, not least what advice to give the general public regarding their sun exposure. While considerable advances have been made in the development of strategies that preserve the health benefits of sunlight exposure and decrease its detrimental effects, further research is required before optimal levels of protection are achieved.     

Non-planar smoulder propagation governed by diffusion

The steady propagation of a thin smouldering front in a half-spacehas been considered. A suitable coordinate transformation hasallowed the region near the leading edge of the front to beexamined for both a maintained planar surface and with surfacecollapse due to material shrinkage. The change in the oxidizerconcentration for a small increment in the propagation speedfor large time and surface collapse has been determined. Theinfluence of two types of nonlinear diffusion on the shape ofthe smouldering front has been found; other cases can be dealtwith in a similar manner.     

Signature and unitary in the multi-Regge model

In a previous paper it was shown how factorisation and signature properties for production processes arose from a well-defined set of singularities in complex angular momentum and helicity. These arose for Feynman diagrams without crossed channel singularities. In this paper we show how the general case gives rise to a sum of terms of this form. We also show how these precise singularities are crucial to prevent the occurence of terms in inclusive pionisation cross sections which are much greater than the canonical pomeron terms.     

The role of twinning in the fatigue behaviour of α-titanium

Coarse grained (0·3 mm) -titanium has been fatigued in tension-compression about a zero mean load to 100 cycles/sec at normal temperature. Sections through fatigued specimens revealed that twin formation had occurred in grains completely constrained by surrounding material during cyclic loading and that fatigue damage was associated with some of these twins. A micro-beam X-ray and single face sterographic analysis technique combined with metallographic observations of the specimens revealed that {10¯12}, {11¯21} and {11¯22} twins had formed and that the internal fatigue damage was preferentially formed at the twin-matrix interface of the {11¯21} twins.The authors wish to thank Professor G. V. Raynor, F.R.S., for the provision of laboratory facilities. This research has been sponsored in part by the Air Force Materials Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio U.S.A. through the European Office of Aerospace Research under Contract No. F61052.67.C.0007.     

A field theory model for fixed angle proton-proton scattering

It is argued that the sum of the leading terms to each order in the coupling constant in massive Q.E.D. at fixed angle leads to the elastic cross-section dσ/dt = A(θ)s^?2exp (a ln²s + b(θ)lns). This gives good agreement with the data for wide angle proton-proton scattering.     

The cutting rules for the 4-reggeon amplitude

We derive the s-channel cutting rules for the four-pomeron amplitude in the context of a ø³ weak coupling model.     

Inflammatory doses of UV may not be necessary for skin carcinogenesis

The UV wavelengths in sunlight are the main cause of skin cancer in humans. Sunlight causes gene mutations, immunosuppression and, at higher doses, inflammation. While it is clear that immunosuppression and gene mutations are essential biologic events via which UV causes skin cancer, the requirement for UV-induced inflammation is less certain. Both the UVB (290-320 nm) and UVA (320-400 nm) wavebands within sunlight can cause skin cancer, gene mutations and immunosuppression. However, UVB, but not UVA, at realistic doses can cause inflammation, and UVB induces skin cancer, immunosuppression and gene mutations at doses much lower than those required to cause inflammation. Inflammation enhances skin carcinogenesis, but may not be UV induced, and inflammatory mediators at doses too low to cause inflammation may be required. UV-induced mutations can cause epidermal cells to make proinflammatory factors or to induce them in the surrounding stroma, creating an oxidizing environment in which additional oncogenic mutations are likely to take place, even in the absence of UV. Our hypothesis is therefore that subinflammatory doses of both UVA and UVB cause benign skin tumors. One of the effects of sunlight-induced mutations may be the production of inflammatory mediators that enhance carcinogenesis.     

The induction of immunity to a protein antigen using an adjuvant is significantly compromised by ultraviolet A radiation

Ultraviolet (UV) radiation from sunlight causes skin cancer and inhibits priming of the immune system during vaccination. However the dose related effects of the different components of sunlight (UVA and UVB) are complex and require further investigation. Using ovalbumin as a model protein vaccine with saponin as adjuvant we show that both UVA and UVB can suppress the DTH response to a poorly immunogenic protein. Increasing doses of UVB induced increased levels of immunosuppression and tolerance. UVA however, caused a bi-phasic dose response with intermediate but not low or high doses causing primary immunosuppression. No dose of UVA caused significant tolerance. Similar results were observed in both C57BL/6 and Balb/c mice. Our data confirms the complex immunomodulatory dose effects of UVA and UVB for a protein antigen, and shows that both UVB and UVA can suppress immunity induced by a protein with adjuvant. This highlights the importance of considering sun exposure patterns in the future success of both preventing skin cancer development and enhancing vaccination regimes.     

Covalent attachment of antagonists to the α7 nicotinic acetylcholine receptor: synthesis and reactivity of substituted maleimides

The 3-methylmaleimide congeners of the natural product methyllycaconitine (MLA) and an analogue covalently attach to functional cysteine mutants of the α7 nicotinic acetylcholine receptor (nAChR).