Amplitude Of Applied Pressure Research Articles

Flexible hybrid eu3+ doped P(VDF-HFP) nanocomposite film possess hypersensitive electronic transitions and piezoelectric throughput

A novel red light-emitter made of Eu3+ doped self-poled electroactive poly(vinylidene fluoride–hexafluoropropylene) [P(VDF-HFP)] hybrid nanocomposite film possesses piezoelectric throughput that is suitable for flexible piezoelectric nanogenerator (PNG) fabrication. We observed that PNG is enabled to generate an open-circuit voltage of 5 V and 0.35 μA of short-circuit current under an applied pressure amplitude of ∼10.4 kPa. By simple mechanical energy scavenging, PNG demonstrates an ability to light more than ten blue commercial light emitting diodes instantly, without using an energy-storage device. Additionally, it successfully charges up capacitors by simple repeating finger touch motion, which indicates its potency as an efficient energy harvesting power source. The high performance of PNG is due to well-coated Eu3+ with P(VDF-HFP) in a hybrid nanocomposite so it displays improved dielectric permittivity and energy storage capacity. This flexible composite film also possesses a hypersensitive electronic transition as it responds by an intense red light-emission confirmed by the CIE 1931 chart. This enables applications in piezo-photonics as a high-performance, energy-saving, flexible solid-state red light emitter. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2335–2345.

The effect of airway pressure and oscillation amplitude on ventilation in pre-term infants

We determined the effect of lung recruitment and oscillation amplitude on regional oscillation volume and functional residual capacity (FRC) in high-frequency oscillatory ventilation (HFOV) used in pre-term infants with respiratory distress syndrome (RDS). Changes in lung volume, oscillation volume and carbon dioxide levels were recorded in 10 infants during a stepwise recruitment procedure, and an increase in pressure amplitude of 5 cmH(2)O was measured using electrical impedance tomography and transcutaneous monitoring. The pressures at maximal respiratory system compliance, maximal oscillation volume and minimal carbon dioxide levels were determined. Impedance data were analysed for the chest cross-section and predefined regions of interest. Despite the fixed pressure amplitude, the oscillation volume changed during the incremental pressure steps following a parabolic pattern, with an inverse relationship to the carbon dioxide pressures. The pressures corresponding with maximal compliance, maximal oscillation volume and minimal carbon dioxide were similar and highly correlated. Regional analysis showed similar findings. The increase in pressure amplitude resulted in increased oscillation volumes and decreased carbon dioxide levels, while FRC remained unchanged. In HFV pre-term infants with RDS, oscillation volumes are closely related to the position of ventilation in the pressure-volume envelope and the applied pressure amplitude. Changes in pressure amplitude do not seem to affect FRC.

On the impact of vessel size on the threshold of bubble collapse

A series of experiments involving microbubbles in narrow tubes is presented. The threshold for bubble collapse has been investigated as a function of the applied pressure and tube diameter. The threshold has been found to be dependent not only on the applied pressure amplitude but also on the tube size with an increase for smaller tubes. The data have been interpreted in terms of a simple damped harmonic oscillator model. The motivation of this study lies in the possibility of obtaining a better understanding of microbubble behavior in blood vessels in order to optimize applications of microbubbles in medical ultrasound.

On the impact of vessel size on the threshold of bubble collapse

Most of the studies investigating the physical properties of ultrasound contrast agents have addressed situations in which the microbubbles are contained in vessels much larger than the bubble size. Since contrast agents are normally injected into blood vessels, the investigation of their behavior in a confined environment may reveal useful information for the optimization of diagnostic and therapeutic applications of ultrasound. A series of experiments involving an ultrasound contrast agent in different sized silica and polyester tubes ranging from 50 to 400 microns in internal radius is presented. It is shown that the threshold for bubble collapse, as recorded by broadband acoustic emission, is not only dependent on the applied pressure amplitude but also on the tube size with an increase for smaller vessels. These data are interpreted and rationalized on the basis of a simple physical model. These findings may have implications for the evaluation of the risk of inertial cavitation in blood vessels. [Work supported by NIH RO1-EB003268 and by the Brigham Radiology Research and Education grant.]

FORCED OSCILLATIONS OF NONSPHERICAL BUBBLES

The oscillation of a gas bubble in liquid under externally applied sinusoidal pressure field is studied. When the applied pressure amplitude is small and the forcing frequency is not in the neighborhood of the resonance frequency of the bubble, the familiar linear results are obtained. When the applied amplitude is not small, there is a tendency to generate both the subharmonic oscillations of the spherical mode and the surface waves on the bubble. The theoretical study is carried out by using both the normal mode analysis and the variational method. It is found that the variational method can lead to approximate solutions in a simpler way than other conventional methods. Experimental implication of the theoretical results is also discussed.

Forced oscillations of nonspherical bubbles

The oscillation of a gas bubble in liquid under externally applied sinusoidal pressure field is studied. When the applied pressure amplitude is small and the forcing frequency is not in the neighborhood of the resonance frequency of the bubble, the familiar linear results are obtained. When the applied amplitude is not small there is a tendency to generate both the subharmonic oscillations of the spherical mode and the surface waves on the bubble. The theoretical study is carried out mainly by the variational method. Experimental implication of the theoretical results is also discussed.

Forced oscillations of nonspherical bubbles

The oscillation of a gas bubble in liquid under externally applied sinusoidal pressure field is studied. When the applied pressure amplitude is small and the forcing frequency is not in the neighborhood of the resonance frequency of the bubble, the familiar linear results are obtained. When the applied amplitude is not small, there is a tendency to generate both the subharmonic oscillations of the spherical mode and the surface waves on the bubble. The theoretical study is carried out by using both the normal mode analysis and the variational method. It is found that the variational method can lead to approximate solutions in a simpler way than other conventional methods. Experimental implication of the theoretical results is also discussed.