High-speed Holographic Microscopy Research Articles

Splash behaviour and oily marine aerosol production by raindrops impacting oil slicks

The high-speed impact of a droplet on a bulk fluid at high Weber number (We) is not well understood but is relevant to the production of marine aerosol by raindrop impact on the sea surface. These splashes produce a subsurface cavity and a crown which closes into a bubble canopy, but a floating layer of immiscible oil, such as a crude oil slick, alters the splash dynamics. The effects of oil layer fluid properties and thickness, droplet size and impact speed are examined by high-speed visualization. Oil layer rupture and crown behaviour are classified by dimensional scaling. The subsurface cavity volume for impact on thick layers is shown to depend on the Reynolds number (Re), although canopy formation at highReintroduces a competingWeeffect since rapid canopy closure is found to retard cavity expansion. Time-resolved kinematic measurements show that thin crude oil slicks similarly alter crown closure and cavity growth. The size and spatial distributions of airborne droplets are examined using high-speed holographic microscopy. The droplets have a bimodal distribution with peaks at 50 and$225~{\rm\mu}\text{m}$and are clustered by size at different elevation angles. Small droplets ($50~{\rm\mu}\text{m}$) are ejected primarily at shallow angles, indicating production by splashing within the first$100~{\rm\mu}\text{s}$and by breakup of microligaments. Larger droplets ($225~{\rm\mu}\text{m}$) are found at steeper elevation angles, indicating later production by capillary instability acting on large ligaments protruding upward from the crown. Intermittent droplet release while the ligaments grow and sweep upward is thought to contribute to the size-dependent spatial ordering. Greater numbers of small droplets are produced at high elevation angles when a crude oil layer is present, indicating satellite droplet formation from ligament breakup. A crude oil layer also increases the target fluid Ohnesorge number, leading to creation of an intact ejecta sheet, which then ruptures to form aerosolized oil droplets.

The Role of Central Microtubules in the Beating of Eukaryotic Flagella, Revealed by High-Speed Holographic Microscopy

Understanding the mechanics of the eukaryotic flagellum is a key challenge in biophysics. As well as being of scientific interest, there are clear therapeutic applications, not least in reproductive medicine. The axoneme lies at the heart of the flagellum, and its structure is known: nine microtubule doublets surround a central pair of microtubule singlets. The role of the central pair in this canonical ‘9+2’ arrangement has been the subject of speculation for some time, though they are known to assist in regulating the flagellar beat. Our group has developed high-speed holographic microscopy that allows us to numerically refocus a digital image off-line. By generating a stack of refocused images from each frame in a video, we obtain scans of the sample volume at the frame rate of our video camera. Effectively, this allows us to image 500-1000 volumes per second. By analyzing this volumetric data, we can measure the waveform of a eukaryotic flagellum to within 200 nm in three dimensions, and with millisecond time resolution. We have previously used this method to measure the waveform of a naturally occurring, isolated flagellum: the microgamete of the rodent malaria parasite Plasmodium berghei. In order to assess the role of the central pair, we take advantage of a newly-available mutant strain that is lacking one or both central microtubules. By comparing the three-dimensional shape and movement observed in mutant flagella to that in the wild-type, we can get some insight into how the central pair helps to regulate the beating action.

Three-Dimensional Dynamics of a Eukaryotic Flagellum Revealed by High-Speed Holographic Microscopy

Understanding the mechanics of the eukaryotic flagellum is a key challenge in biophysics. As well as being of scientific interest, there are clear therapeutic applications, not least in reproductive medicine. The physics of swimming sperm has been studied for some time and there are several competing hypotheses for the underlying mechanics of the axoneme. A key aspect of this work remains unaddressed, however: almost all flagellar waveforms are three-dimensional. Comparing 2D theories with 2D images has met with some success, but for a complete understanding, the 3D nature of the beating must be considered. We have employed digital holographic microscopy to record the 3D beating of a gamete of Plasmodium berghei (a parasite associated with malaria in rodents). When coupled with high-speed imaging we are able to obtain a complete record of the flagellar waveform with excellent temporal and spatial resolution. This sperm is an interesting limiting case: it has no head, and almost no other accessory structures. Our analysis of the 3D beating pattern has implications for the proposed link between structural chirality in the axoneme and the chirality of flagellar waveforms.View Large Image | View Hi-Res Image | Download PowerPoint Slide

A dinoflagellate exploits toxins to immobilize prey prior to ingestion

Toxins produced by the harmful algal bloom (HAB) forming, mixotrophic dinoflagellate Karlodinium veneficum have long been associated with fish kills. To date, the perceived ecological role for toxins has been relief from grazing pressures. Here, we demonstrate that karlotoxins also serve as a predation instrument. Using high-speed holographic microscopy, we measure the swimming behavior of several toxic and nontoxic strains of K. veneficum and their prey, Storeatula major, within dense suspensions. The selected strains produce toxins with varying potency and dosages, including a nontoxic one. Results clearly show that mixing the prey with the predatory, toxic strains causes prey immobilization at rates that are consistent with the karlotoxins' potency and dosage. Even prey cells that continue swimming slow down after exposure to toxic predators. The swimming characteristics of predators vary substantially in pure suspensions, as quantified by their velocity, radii of helical trajectories, and direction of helical rotation. When mixed with prey, all toxic strains that are involved in predation slow down. Furthermore, they substantially reduced their predominantly vertical migration, presumably to remain in the vicinity of their prey. Conversely, the nontoxic control strain does not alter its swimming and does not affect prey behavior. In separate experiments, we show that exposing prey to exogenous toxins also causes prey immobilization at rates consistent with potency. Clearly, the toxic predatory strains use karlotoxins as a means of stunning their prey, before ingesting it. These findings add a substantiated critical understanding for why some HAB species produce such complex toxin molecules.

動的破壊力学の研究と光計測(基調講演)

When solid materials break under external forces, fast propagating cracks often appear and propagate at a speed more than several hundred meters per second. The fast propagating crack often bifurcates into two cracks, and it is necessary to measure the energy release rate of the bifurcating crack to figure out the mechanism of crack bifurcation. The present paper describes the Moire interferometiy used to develop the measurement method and high-speed holographic microscopy to measure the energy release rate of rapidly bifurcating cracks.

Measurement of energy release rate and energy flux of rapidly bifurcating crack in Homalite 100 and Araldite B by high-speed holographic microscopy

High-speed holographic microscopy is applied to take three successive photographs of fast propagating cracks in Homalite 100 or in Araldite B at the moment of bifurcation. Crack speed at bifurcation is about 540 m/s on Homalite 100, and about 450 m/s on Araldite B. From the photographs, crack speeds immediately before and after bifurcation are obtained, and it is found that discontinuous change of crack speed does not exist at the moment of bifurcation in the case of Homalite 100, but exists in the case of Araldite B. From the photographs, crack opening displacement (COD) is also measured along the cracks as a function of distance r from the crack tips. The measurement results show that the CODs are proportional to √ r before bifurcation. After bifurcation, the CODs of mother cracks are proportional to √ r, though the CODs of branch cracks are not always proportional to √ r. The energy release rate is obtained from the measured CODs, and it is found that energy release rate is continuous at bifurcation point in both cases of Homalite 100 and Araldite B. Energy flux that shows the energy flow toward a crack tip is also obtained.

618 アラルダイトB中における高速分岐き裂のき裂速度とエネルギー解放率の測定(OS10(3) 拡大する実験力学・光学的手法の拡大)

High speed holographic microscopy is applied to take three successive microscopic photographs of rapidly bifurcating cracks in Araldite B. Crack tip positions are measured from the photographs, and the crack speeds before and after bifurcation are obtained by assuming that crack speeds are kept constant before and after the bifurcation respectively. Energy release rate is also obtained by measuring the crack opening displacement of the cracks on the photographs. The results say that there exists the discontinuity of crack speed at bifurcation, and the crack speed after bifurcation is slower than that before bifurcation. On the other hand, the energy release rate is continuous at the bifurcation, and increases gradually with crack extension.

Measurement of Crack Opening Displacement and Energy Release Rate of Rapidly Bifurcating Cracks in PMMA by High-Speed Holographic Microscopy

High-speed holographic microscopy is applied to take three successive photographs of fast propagating cracks at the moment of bifurcation. The cracks are propagated in PMMA plate specimens at a speed about 660m/s. From the photographs, crack opening displacement (COD) is measured along the cracks as a function of distance r from the crack tips. The measurement results show that the CODs are proportional to √r before bifurcation. After bifurcation, the CODs of mother cracks are proportional to √r, however, the CODs of branch cracks are not always proportional to √r. Crack speed is also measured from the photographs. As a result, discontinuous change of crack speed is not observed at the moment of bifurcation. The energy release rate and energy flux toward crack tips are obtained from the COD data, and are found to be continuous across the bifurcation point. The energy release rate and energy flux increase gradually across the bifurcation point.

OS1(1)-2(OS01W0244) Measurement of Crack Opening Displacement and Energy Release Rate of Rapidly Bifurcating Cracks by High-Speed Holographic Microscopy

OS1(1)-2(OS01W0244) Measurement of Crack Opening Displacement and Energy Release Rate of Rapidly Bifurcating Cracks by High-Speed Holographic Microscopy

OS01W0244 Measurement of crack opening displacement and energy release rate of rapidly bifurcating cracks by high-speed holographic microscopy

OS01W0244 Measurement of crack opening displacement and energy release rate of rapidly bifurcating cracks by high-speed holographic microscopy

Recent Progress of Experimental and Measuring Technology. Measurement of Opening Displacement of Bifurcated Cracks by High-Speed Holographic Microscopy and Moire Interferometry.

High-speed holographic microscopy is applied to take successive microscopic photographs of a fast propagating crack at bifurcation. The crack speed is about 650 m/s. From the photographs, crack opening displacements (CODs) of the mother crack and two bifurcated branches are measured along the crack. A specimen with a notch is also made, where the notch has the bifurcated notch tip same as the bifurcated fast propagating crack. Opening displacement of the notch is measured by Moire interferometry under static loading condition. The measurement results show that the opening displacements of both the mother crack of the bifurcated fast propagating crack and the mother notch of the bifurcated notch are proportional to square root of the distance r from the crack or the notch tip. The opening displacements of the two bifurcated branches of the notch are also proportional to √(r). But the CODs of the bifurcated branches of the fast propagating crack are not always proportional to √(r).

Reflection Type High-speed Holographic Microscopy to Photograph Bifurcation of Fast Propagating Cracks.

Reflection type high-speed holographic microscopy is applied to photograph the bifurcation of fast propagating cracks in PMMA. The cracks are of the opening mode. Spatial resolution is more than 180 lines/mm, frame interval is 5μs and the number of frames is three. A crack at bifurcation is recorded as three successive holograms on one photographic plate by means of angle-multiplexing holography. Lens assisted reconstruction method is used to reconstruct separately the three crack images from the holograms. The reconstructed crack images are magnified and photographed through a conventional microscope. The photographs show that, at bifurcation, several crack tips are running simultaneously in a small region about 1 mm in diameter. And also shown is dynamic three dimensional behavior of crack front edges or microcracks at bifurcation.

High-speed holographic microscopy for fast-propagating cracks in transparent materials

A method of high-speed holographic microscopy is developed to take three successive microscopic photographs of a crack tip propagating in a transparent poly(methyl methacrylate) specimen at a speed of several hundred meters per second. When a crack is propagating in a specimen, three Q-switched ruby lasers emit three laser pulses successively. The time interval between each laser pulse and the next is 1 mus or longer. An optical system of angle-multiplexing holography records the crack as three successive holograms on one photographic plate. Crack images are reconstructed and photographed through a conventional microscope. The spatial resolution of the reconstructed images is approximately 114 lines/mm. From the photographs, one can measure crack speed, crack opening displacement, and the dynamic stress intensity factor. The high-speed holographic microscopy makes it possible to study rapid crack propagation in microseconds.