A computational study of the interaction noise from a small axial-flow fan

Time-of-day-dependent adaptation of the HPA axis to predictable social defeat stress

In modern societies, the risk of developing a whole array of affective and somatic disorders is associated with the prevalence of frequent psychosocial stress. Therefore, a better understanding of adaptive stress responses and their underlying molecular mechanisms is of high clinical interest. In response to an acute stressor, each organism can either show passive freezing or active fight-or-flight behaviour, with activation of sympathetic nervous system and the hypothalamus-pituitary-adrenal (HPA) axis providing the necessary energy for the latter by releasing catecholamines and glucocorticoids (GC). Recent data suggest that stress responses are also regulated by the endogenous circadian clock. In consequence, the timing of stress may critically affect adaptive responses to and/or pathological effects of repetitive stressor exposure. In this article, we characterize the impact of predictable social defeat stress during daytime versus nighttime on bodyweight development and HPA axis activity in mice. While 19 days of social daytime stress led to a transient reduction in bodyweight without altering HPA axis activity at the predicted time of stressor exposure, more detrimental effects were seen in anticipation of nighttime stress. Repeated nighttime stressor exposure led to alterations in food metabolization and reduced HPA axis activity with lower circulating adrenocorticotropic hormone (ACTH) and GC concentrations at the time of predicted stressor exposure. Our data reveal a circadian gating of stress adaptation to predictable social defeat stress at the level of the HPA axis with impact on metabolic homeostasis underpinning the importance of timing for the body's adaptability to repetitive stress.

Frequency-domain model of tonal blade thickness and loading noise

A tonal thickness noise and loading noise model of rotating blades has been developed as an extension of the exact frequency-domain solutions for rotating monopole and dipole point sources. The present model has two advantages over the previous methods and models for noise prediction. The first is the unified expression for sources in subsonic and supersonic rotation even at rest. The second is that the present model has no limit on the location of the observer and no interpolation error. Two test cases are carried out to validate the present model and emphasize its advantage at the noise prediction for sources in supersonic rotation. Moreover, as a specified application of the present model for the rotating blades whose tip radius is acoustically compact, acoustic energy distribution at different frequencies and in different directions is analyzed. Result shows that the acoustic energy of acoustically compact rotating blades is mainly concentrated at the source frequency while propagating along the axial direction, leaving the rest propagating along the radial direction at the other frequencies.