Stagnation temperature measurement using thin-film platinum resistance sensors

This article was published in the journal, Measurement Science & Technology [© IOP Publishing] and the definitive version is available at: http://dx.doi.org/10.1088/0957-0233/25/1/015101The measurement of stagnation temperature in high-speed flows is an important aspect of gas turbine engine testing. The ongoing requirement to improve the accuracy of such measurements has led to the development of probe systems that use a thin-film platinum resistance thermometer (PRT) as the sensing element. For certain aspects of engine testing this type of sensing device potentially offers superior measurement performance to the thermocouple, the temperature sensor of choice in most gas turbine applications. This paper considers the measurement performance of prototype PRT-based stagnation temperature probes, up to high-subsonic flow conditions, using passively aspirated probe heads. The relatively poor temperature recovery performance of a simply constructed probe has led to the development of a new design that is intended to reduce the impact of thermal conduction within the probe assembly. The performance of this so-called dual-skin probe has been measured through a series of tests at a range of Mach numbers, incidence angles and Reynolds numbers. The data reveal that a high probe recovery factor has been achieved with this device, and that the application of this design to engine tests would yield the measurement performance benefits of the PRT whilst requiring small levels of temperature recovery compensation

Mechanisms of peripheral tolerance and suppression induced by monoclonal antibodies to CD4 and CD8.

Over the last five years it has become increasingly clear that the peripheral immune system can maintain tolerance to both self and non-self antigens through a variety of mechanisms. Although clonal deletion may play an important part in limiting rapidly expanding responses, there are many examples where antigen reactive T cells remain. It has been proposed that tolerance is maintained in this situation either by the induction of anergy or by ongoing suppression. The phenomenon known as immune deviation, where non-inflammatory Th2 responses could suppress Th1 and positively reinforce themselves provided an attractive explanation for infectious tolerance, where tolerant T cells could guide further naive T cells also to tolerance. However, experiments to test this hypothesis in the models of CD4 and CD8 antibody-induced tolerance have given conflicting data, with no clear evidence of Th2 responses in tolerant mice. In this paper we review recent data that IL-4 plays a role in suppression, but that the source of IL-4 may not be the tolerant/suppressor T cell. We also discuss how infectious tolerance can operate on third party antigens if they are linked on the same antigen presenting cell and how CD4+ T cells can suppress CD8+ T-cell responses. Finally, we suggest a model of infectious anergy that is compatible with the available data