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Reduced skin blood flow of older and subjects with diabetes, decreased thickness of the dermal layer, and increased subcutaneous fat, as well as damage to transient receptor potential vanilloid 1 receptors, may account for some of the differences between the groups.

Applications that have coupling among shaft, disk, and blades are investigated. A shaft-disk-blades unit often seen in engineering is presented. The governing relations for shaft torsion, disk bending, and blade bending are derived. Free vibration is then studied and the results show that shaft-blade (SB), shaft-disk-blades (SDB), disk-blades (DB), and blade-blade (BB) type coupling modes exist. The SDB and DB modes are observed to be evolved from the original SB and BB modes in a previously studied case of a rigid disk case. The effects of stagger angle (β) on the coupling of the components are also examined. In the two extremes at β=0, the disk is uncoupled, and at β=π∕2, the shaft is uncoupled. In between, the three components are coupled. As β increases, the disk participates more strongly, but the shaft behaves in exactly the opposite way. A SB mode at β=0 will transfer into a SDB mode as β increases, eventually becoming a DB mode at β=π∕2. Basically, as β increases, the disk flexibility contributes more and reduces the natural frequencies. The effect of rotation is the last to be discussed and the results show that frequency bifurcation and loci veering occur as the rotation rate increases because of disk flexibility. For SD and SDB modes, the frequency loci veer and merge at certain rotational speeds. In these regions, there exist mode exchange and instability problems.

SummaryBackgroundWhen heat is applied to the skin, it is dissipated due to conductive heat flow in the tissue and the blood. While heat flow has been studied after applying a single heat exposure, the physiology of repeated exposures to local heat has not been well investigated.Material/MethodsTwenty male and female subjects in the age range of 20–65 years old participated in a series of experiments during which a thermode was placed on their leg above the quadriceps muscle for 20 minutes, and on 3 sequential days, to see the effect of repeated local heat on skin blood flow, skin temperature, and on caloric transfer from a thermode used to raise skin temperature.ResultsThe results of the experiment showed that, for young subjects, to raise skin temperature to 40 degrees C required more than double the calories required in older subjects. Further, in the younger subjects, the blood flow response in the first 20 minutes of heat exposure was over 30% higher than that seen in the older subjects. However, on the 2nd and 3rd day, the blood flow response of the younger subjects, was not significantly different between day 2 and 3, but was significantly less than day 1. There was no statistical difference in the blood flow response between day 1, 2 and 3 in the older subjects. In the younger subjects, in the 2 and 3rd day, the number of calories needed to warm the skin was also significantly less than that seen in the first day.ConclusionsIn younger subjects but not older subjects, there appears to be some degree of acclimatization with an enhanced blood flow response in the first day that was protective to the skin which was not seen in repeated heat exposure.

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