Skin Aging Clock and Its Resetting by Light-Emitting Diode Low-Level Light Therapy
Shamim I. Ahmad in Aging: Exploring a Complex Phenomenon, 2017
Light, comprising minute particles of pure energy without mass known as photons, is classed by its wavelength measured in nanometers (1 nm = 1 × 10−9 m). Figure 27.2a illustrates a typical sinusoid waveform of a beam of light, and the wavelength (λ in the figure) is measured from the beginning to the end of one complete cycle. In Figure 27.2b there are several waveforms with different wavelengths. It can be noted that, as the wavelength gets shorter, so the waveform alters over time on the x-axis with more cycles per given unit of time. This is referred to as the frequency of light, and is measured in cycles per second, or hertz (Hz). One cycle per second is 1 Hz, 10 cycles is 10 Hz and so on, and it can be noted in Figure 27.2b that the frequency increases in direct proportion to the decreasing wavelength: in other words, shorter wavelengths have higher frequencies [5,6]. Because of this, UV radiation, and to a lesser extent shorter wavelengths of visible light, are more damaging to the skin than the rest of the visible and infrared energy [7]. This is because of the energy level of the photons which make up a beam of light, so light can be said to comprise photons propagating linearly in a waveform path (Figure 27.2), and each photon has its own photon energy.
Physical concepts
Stanley A. Gelfand in Hearing, 2017
It has already been noted that the oscillating air particle is moving back and forth around its resting or average position. In other words, the air particle's displacement changes over the course of each cycle. The magnitude of the air particle's displacement is called amplitude. Figure 1.8 illustrates a difference in the amplitude of a sinusoid, and contrasts this with a change in its frequency. In both frames of the figure, the tone represented by the lighter curve has an amplitude greater than the one portrayed by the heavier line. This is shown by the greater vertical distance from the baseline (amplitude) at any point along the horizontal axis (time). (Obviously, exceptions occur at those times when both curves have zero amplitudes.)
Physiology of Hearing
John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed in Paediatrics, The Ear, Skull Base, 2018
The above examples show the effect of adding sinusoids that are in phase. Since sinusoids are periodical sounds, their summation will produce a repeating pattern, the frequency of which (repetition frequency) is known as the fundamental frequency (F0). In the above examples, 0.1 kHz is the highest common factor between each of the constituent components (i.e. the highest integer that all components will divide into). The period (and therefore the repetition frequency) of the complex periodical sound is equal to the highest common factor. The higher-frequency components, which are exact integer multiples of the fundamental frequency, are known as harmonics.
Effect of intracardiac blood flow pulsatility during radiofrequency cardiac ablation: computer modeling study
Published in International Journal of Hyperthermia, 2021
Cristina Parés, Enrique Berjano, Ana González-Suárez
The first pulsatile profile (P1) consisted of an absolute value of a sinusoid wave, i.e. A is the peak value, t is time and f the frequency of the cardiac rhythm. In the context of electrical engineering this waveform is a full wave rectified sine wave. We assumed f = 1 Hz, which is equivalent to a heart rate of 60 beats per minute (bpm). In order to compare the use of a continuous blood velocity value vs. a pulsatile profile under equal conditions, the value of A was chosen so that the waveform associated with the pulsatile profile had an average value (Vavg) equivalent to the continuous value. Since the average value of an absolute value of a sinusoid wave can be calculated as A associated with each average value. For instance, for a continuous value of 8.5 cm/s, the peak value of the waveform associated with the P1 profile will be A = 8.5/0.636 = 13.37 cm/s (see blue line in Figure 4).
Genetic polymorphisms for BDNF, COMT, and APOE do not affect gait or ankle motor control in chronic stroke: A preliminary cross-sectional study
Published in Topics in Stroke Rehabilitation, 2021
Rehab Aljuhni, Brice T. Cleland, Stephen Roth, Sangeetha Madhavan
Participants performed a motor tracking task with the paretic ankle using a custom ankle tracking device. As described previously,4,30 participants were seated and the paretic ankle was secured to the device with the foot in a neutral position. Ankle dorsiflexion and plantarflexion were performed to track a computer-generated sinusoidal waveform visually displayed on a monitor. Participants performed three familiarization/pretest trials and 12 tracking trials (60 s in duration each). There was a one-minute break after every four trials. The amplitude of the sinusoid was determined individually based on the maximal ankle range of motion for each participant. Ankle position was measured with Spike2 software (Cambridge Electronic Design, Milton, Cambridge, UK). To quantify ankle motor control accuracy, we calculated the root-mean-square error (RMSE) between the sine wave and the ankle position and normalized the RMSE value to the participant-specific sine wave amplitude.4,30 Accuracy was presented as a percentage: accuracy = (1-RMSE)*100, and averaged across the 12 tracking trials. Data from one participant were excluded as an outlier (more than 3 standard deviations below the mean).
Facing Repeated Stressors in a Motor Task: Does it Enhance or Diminish Resilience?
Published in Journal of Motor Behavior, 2021
Yannick Hill, Nico W. Van Yperen, Ruud J. R. Den Hartigh
In order to measure resilience, the level of functioning to which the system seeks to return to needs to be defined. Because the performance aim of the task is to oscillate as quickly and precisely as possible between the targets, we identified the time point and its according x-axis position when the direction of the movement changed from left to right or vice versa. These turning points represent peaks in an oscillatory movement profile, which approximates a sinusoid curve when mapped over time. The peaks were chosen to represents the movement accuracy and speed because they 1) indicate the onset and endpoint of a movement cycle, and 2) represent the time point when the cursor was aimed to have been successfully moved into a target, before the participants starts aiming at the subsequent target.