China 
Africa 
Explore chapters and articles related to this topic
Optical fiber sensors
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
John P. Dakin, Kazuo Hotate, Robert A. Lieberman, Michael A. Marcus
To measure tiny phase differences, of the order of micro-radians, between the two lightwaves traveling in the fiber coil of Figure 11.18, a special processing scheme had to be established. When the system is in the rest state, the signals interfering at the detector in Figure 11.18 would normally give rise to a maximum in the sinusoidal response (dashed curve). At this peak, the gradient is of course zero, so there is no initial response to small phase changes, so hence zero sensitivity for a small rotation rate. In order to solve this problem, a phase biasing scheme is needed, in order to drive the state of the interferometer to a region of the phase response curve where the gradient is nonzero. To achieve this, a phase modulator, driven by a signal of sinusoidal or square waveform, is applied at, or near, the end of the sensing fiber coil. Due to the timing difference of the modulation between the clockwise (CW) and the counter-clockwise (CCW) waves, the two lightwaves now have a periodic phase difference when they impinge on the detector, and give a “mixed” or detected output signal having the same frequency as the applied phase-modulation waveform.
Circadian System and Diurnal Activity
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
A range of both nocturnal and diurnal species has been studied (Pittendrigh and Daan, 1976; Pittendrigh, 1981). Remarkably, all have shown the same basic ‘phase response curve’ to light (Figure 2.1), though the precise shape varies between species. In all organisms studied to date, including humans, light around dusk will delay the clock, and light around dawn will advance the clock, and in this way activity is broadly aligned to the expanding and contracting light–dark cycle throughout the year. The phase response curve (PRC) model of entrainment has been helpful in searching for entrainment mechanisms and the molecular components of the circadian system. However, it does not provide a complete description of entrainment. It is not fully understood how light intensity, wavelength, the phase of exposure, the length of the free-running period, the magnitude of the advances and delays or even how photic and non-photic cues might interact to generate stable entrainment (Foster and Helfrich-Forster, 2001).
Use of melatonin in recovery from jet-lag following an eastward flight across 10 time-zones
Published in Thomas Reilly, Julie Greeves, Advances in Sport, Leisure and Ergonomics, 2003
B. J. Edward, G. Atkinson, J. Waterhouse, T. Reilly, R. Godfrey, R. Budgett
These results do not support the view that melatonin had acted as a chronobiotic, but there are other factors that complicate the position. First, the size and direction of shifts in the circadian system depend upon the time of administration of melatonin, in accord with a phase response curve. Two such curves for melatonin have been reported, but they are not identical (Zaidan et al. 1994, Lewy et al. 1998), and this causes some difficulties of interpretation. For example, in the current study, melatonin was ingested at the time recommended by Arendt and Deacon (1997) to promote the hypnotic effect of melatonin; this was at about 22:00-23:00 h local time, and corresponds to 12:00 – 13:00 h on unadjusted ‘body time’. This time appears to fall either in the phase-delay portion of the phase response curve (Zaidan et al. 1994), or in the phase-advance portion (Lewy et al. 1992, 1998). Second, giving melatonin at 18:00-19:00 h on the plane was equivalent to giving it at 08:00 – 09:00 h UK time. This would promote either a delay (Zaidan et al. 1994) or have no effect or a slight phase-advancing effect (Lewy et al. 1998). Third, there is the problem that timing of administering melatonin on the days after arrival does not change; this would be appropriate for a hypnotic effect, but is inappropriate for a chronobiotic effect upon a body clock that is adjusting to local time. Finally, the subjects’ exposure to, and avoidance of, bright light must be controlled in such a way that any phase-shifting effects due to this zeitgeber (Waterhouse et al. 1997) act synergistically with those promoted by melatonin. No such control was exerted in the current study, both on the day of arrival and on subsequent days. Therefore, it is plausible that any effect of melatonin on the process of readjustment of the body clock would have been ‘swamped’ by the effects of the subjects’ haphazard exposure to the light-dark cycle.
Uncertainty propagation of frequency response of viscoelastic damping structures using a modified high-dimensional adaptive sparse grid collocation method
Published in Mechanics of Advanced Materials and Structures, 2022
Tianyu Wang, Chao Xu, Ning Guo, Mohamed Hamdaoui, E. I. Mostafa Daya
Figure 18 shows the deterministic responses of amplitude and phase in the frequency domain of 0-400 Hz. As can be seen from Figure 18a, there are five resonance peaks in the amplitude response within this frequency range, and the corresponding resonance frequencies are respctively 56 Hz, 127 Hz, 215 Hz, 229 Hz and 395 Hz. Figure 18b presents the phase response curve. It can be seen that the curve has a drastic change near the resonance frequencies. Table 4 shows the first six nature frequencies and loss factors obtained from the modal analysis. Note that the 3rd-order mode is not activated on the response node B.
Tutorial: Theoretical Considerations When Planning Research on Human Factors in Lighting
Published in LEUKOS, 2019
In the literature, the NIF effects are generally categorized as circadian or acute. The first category pertains to entrainment of our internal clock to the Earth’s 24-hour rhythm and the induction of phase shifts in which the timing of the central endogenous pacemaker relative to external clock time is changed. Literature shows that light is crucial for a healthy entrainment of our biological clock. Experts in the field agree that it affects circadian rhythms “more powerfully than any drug” (Czeisler 2013, p. S13). Light exposure can shift and entrain the internal clock but, importantly, these effects depend on many characteristics of the exposure. First, because these effects are driven mainly (though not entirely; e.g., see Gooley et al. 2010) by melanopic (ipRGC) activation, the intensity and spectrum of the light falling on the retina are crucial determinants. Responses typically follow a compressive nonlinear function, where the shift induced by exposure initially rises fast with increasing light levels and then saturates (Boivin et al. 1996; Zeitzer et al. 2000) and where light near the peak sensitivity of the ipRGCs exerts greater effects than light outside their sensitive range (Warman et al. 2003). Effects are mildly, and nonlinearly, dependent on the duration of light exposure (Duffy and Wright 2005), but much more important is the timing of exposure: circadian shifts vary not only in size but even in direction depending on whether light exposure occurs early or late in one’s subjective morning, afternoon, or evening. The dynamics of this phenomenon are captured in the so-called phase-response curve (Khalsa et al. 2003; Minors et al. 1991), which sketches whether a bout of light exposure will result in a phase advance, resulting in earlier wake and sleep propensity, or a phase delay, causing one to become sleepy later in the day and also wanting to rise later the following day.
Island detection methods and grid current control methods in SPV-based energy systems
Published in International Journal of Ambient Energy, 2022
If the utility is tripped and the frequency of PCC voltage is distorted, the inverter phase response curve increases the phase error and hence causes instability in the frequency. This instability further amplifies the perturbation of the frequency of PCC voltage and the frequency is eventually driven away until it hits ULFL protection.