![]() In 2013, a study involving 312,944 people in nine European countries revealed that there was no safe level of particulates and that for every increase of 10 μg/m 3 in PM 10, the lung cancer rate rose 22% (95% CI ). Particulates are the most harmful form (other than ultra-fines) of air pollution due to their ability to penetrate deep into the lungs, blood streams and brain, causing health problems including heart attacks, respiratory disease, and premature death. The IARC and WHO designate airborne particulates as a Group 1 carcinogen. Types of atmospheric particles include suspended particulate matter thoracic and respirable particles inhalable coarse particles, designated PM 10, which are coarse particles with a diameter of 10 micrometers (μm) or less fine particles, designated PM 2.5, with a diameter of 2.5 μm or less ultrafine particles, with a diameter of 100 nm or less and soot. They have impacts on climate and precipitation that adversely affect human health, in ways additional to direct inhalation. Sources of particulate matter can be natural or anthropogenic. The term aerosol commonly refers to the particulate/air mixture, as opposed to the particulate matter alone. The number at the upper left states the time in microseconds.Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter ( PM) or suspended particulate matter ( SPM) – are microscopic particles of solid or liquid matter suspended in the air. The movie is taken at approximately 1 million frames/s. They are visible as blurry shadows in the upper right corner and the second cavitation event leads to a dark fuzzy object just below the in-focus cavity. Two additional out-of-focus cavitation events are recorded in this series, too. Then a second attached cavity on the particle becomes visible and grows in the following frames into a void of size comparable to that of the particle. The re-expanding cavity obtains a funnel-like shape, which indicates that a liquid jet has developed during the cavity collapse. Moreover, the volume centre of the cavity shifts slightly to the left. During the detachment process the cavity develops a mushroom shape, and collapses. ![]() As the growth decelerates the particle moves away from the cavity and forms a neck which breaks. A cavitation bubble expanding on the left side of the particle becomes visible and grows explosively. Initially an isolated particle is visible. ![]() Example of a cavitation event on a particle and the successive dynamics, see figure 3. in the context of drug delivery into tissue. Finally, an example is presented to demonstrate the potential application of the cavity–particle system as a particle cannon, e.g. Moreover, after collapse of the primary cavity, a second inception was often observed. In several cases we observed inception at two or more locations on a single particle. ![]() The cavity shapes obtained from the BEM calculations compare well with the photographs until neck formation occurs. The model then allows us to calculate the resulting particle trajectory. The input for both models is a pressure pulse, which is obtained from the observed radial cavity dynamics during an individual experiment. The experimental observations are simulated with (i) a spherical cavity model and (ii) with an axisymmetric boundary element method (BEM). When the volume growth of the cavity slows down, the particle detaches from the cavity through a process of neck-breaking, and the particle is shot away. They reach velocities of ~40 ms −1 and even higher. Particles, which serve as nucleation sites for cavitation bubbles, are set into a fast translatory motion during the explosive growth of the cavity. The cavity–particle dynamics at cavitation inception on the surface of spherical particles suspended in water and exposed to a strong tensile stress wave is experimentally studied with high-speed photography.
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