Search

The primary acoustic signal of the voice is generated by the complex oscillation of the vocal folds (VFs), whereby physicians can barely examine the medial VF surface due to its anatomical inaccessibility. In this study, we investigated possibilities to infer medial surface dynamics by analyzing correlations in the oscillatory behavior of the superior and medial VF surfaces of four human hemilarynges, each in 24 different combinations of flow rate, VF adduction, and elongation. The two surfaces were recorded synchronously during sustained phonation using two high-speed camera setups and were subsequently 3D-reconstructed. The 3D surface parameters of mean and maximum velocities and displacements and general phonation parameters were calculated. The VF oscillations were also analyzed using empirical eigenfunctions (EEFs) and mucosal wave propagation, calculated from medial surface trajectories. Strong linear correlations were found between the 3D parameters of the superior and medial VF surfaces, ranging from 0.8 to 0.95. The linear regressions showed similar values for the maximum velocities at all hemilarynges (0.69–0.9), indicating the most promising parameter for predicting the medial surface. Since excessive VF velocities are suspected to cause phono-trauma and VF polyps, this parameter could provide added value to laryngeal diagnostics in the future. [ABSTRACT FROM AUTHOR]

Due to the poor surface characteristics of additively manufactured parts, the necessity for post-process surface enhancement is crucial. Among the prevalent post-processing techniques, the acoustic cavitation-based surface finishing technique has recently emerged. Despite a considerable amount of focused research on the material removal mechanisms of this technique, less attention has been devoted to addressing its limitations associated with enhancing the process capability towards achieving a better surface finish. The driving force behind the acoustic cavitation technique is the bubble implosion through cavitation streaming, and the cessation of the acoustic cavitation streaming beyond a certain length is the main limitation. It has restrained the process capability towards finishing both external and internal surfaces. Hence, this research aims to unravel novel ways of employing the acoustic cavitation-generating parameters and achieving better-quality surface finishing of additively manufactured (AM) components. A study has been conducted on different AM materials, including Inconel 625 and aluminum alloy, by introducing various methods associated with acoustic amplitude, working mediums, temperature, and external vibration. The results reveal a significant reduction in average surface roughness for both materials. The topographical and morphological observations confirm the qualitative improvement on the surfaces. In addition, the conical bubble structures that frame the acoustic cavitation streaming are elucidated by implementing high-speed imaging techniques, and their enhancement at different parametric conditions is delineated. Henceforth, the findings suggest a notable insight into the potential of the employed approaches in enhancing the acoustic cavitation streaming for achieving a better surface finish of AM components. [Display omitted] • Surface finishing of AM components by enhanced acoustic cavitation. • Overcoming the limitations of acoustic cavitation for surface quality improvement. • Acoustic cavitation: factors affecting acoustic streaming and AM surface quality. • Thermal effect on bubble structures in free-field and confined acoustic cavitation. • A study on parametric investigation of acoustic cavitation: a different approach. [ABSTRACT FROM AUTHOR]

Photoacoustic microscopy (PAM) enables label‐free imaging of the 3D vasculature and functional information with 2D lateral scan. The unique capacity in probing metabolism makes it ideal for animal research and clinical application. However, the high‐excitation power impedes the high‐speed monitoring of hemodynamics due to thermal accumulation and photon damage. To address this challenge, a self‐supervised photoacoustic single volume denoising (PSVD) approach, which combines 3D random sampling and noise augmentation to achieve 6 dB signal‐to‐noise‐ratio and contrast‐to‐noise‐ratio increases for the customized optical‐resolution photoacoustic microscope, is developed. Using PSVD, high‐quality PAM images of the mouse ear are acquired with only 10% fluence of normal excitation. Functional imaging is validated with this PSVD‐empowered low‐fluence PAM. Accurate oxygen saturation maps and high‐contrast flow kymographs are obtained. Moreover, the capability of this approach in the live mouse ear under hypercapnia is demonstrated. Further transformation into clinical imaging with low fluence will broaden the application of PAM. [ABSTRACT FROM AUTHOR]

This experimental study investigated the influence of different turbine guide vane parameters on the ignition limit and light-round processes in a triple-dome combustor. It was found that for the triple-dome combustor, the minimum fuel/air ratios at the ignition limit all show a trend of initial decrease followed by subsequent increase with the growth of incoming air mass flow rate. The ignition fuel/air ratio decreases with the increase in turbine blockage ratio, and the optimal scheme is achieved with a blockage ratio of 0.8. Under the condition where the incoming air mass flow rate is 0.089 kg/s, the light-round time decreases with the increase in fuel/air ratio, and the light-round time of the combustor without guide vanes is shorter than that of the other schemes. With the increase in incoming air mass flow rate, the light-round time of the schemes with guide vanes is shortened. Under the same incoming air mass flow rate and fuel/air ratio, the increase in the blockage ratio will lead to an increase in the light-round time of the triple-dome combustor. [ABSTRACT FROM AUTHOR]

Mesoscopic carbon‐based perovskite solar cells (C‐PSCs) have the potential to be manufactured at an industrial scale by utilizing screen‐printing, a simple, affordable, and commercially mature process. As such, many recent publications have focused on enhancing performance through modifying cell architecture and perovskite chemistries. This work examines how ink rheology can be tuned to optimize cell performance through reducing the occurrence of common print defects to create higher quality m‐TiO2 films. Inks with different solvent dilutions and rheological profiles are assessed using high‐speed imaging through the screen‐printing visualization (SPV) technique, to investigate the impact of the viscosity and elasticity on ink separation mechanisms. The resultant film quality and its influence on device performances are then assessed. Ink separation lengths are minimized, and the formation of filaments ceases during printing, leading to improved TiO2 film topography and homogenous infiltration of the perovskite precursor. Consequently, PCE is improved by over 10% of the original efficiency in cells and 224 cm2 active area modules due to enhanced Voc and FF. These results not only provide key insights into tailoring ink rheology, to achieve improved print homogeneity and higher performing cells, but also aid further work on enhancing the performance of other screen‐printed functional films. [ABSTRACT FROM AUTHOR]

Ultra‐high‐speed synchrotron‐based hard X‐ray (i.e. above 10 keV) imaging is gaining a growing interest in a number of scientific domains for tracking non‐repeatable dynamic phenomena at spatio‐temporal microscales. This work describes an optimized indirect X‐ray imaging microscope designed to achieve high performance at micrometre pixel size and megahertz acquisition speed. The entire detector optical arrangement has an improved sensitivity within the near‐ultraviolet (NUV) part of the emitted spectrum (i.e. 310–430 nm wavelength). When combined with a single‐crystal fast‐decay scintillator, such as LYSO:Ce (Lu2−xYxSiO5:Ce), it exploits the potential of the NUV light‐emitting scintillators. The indirect arrangement of the detector makes it suitable for high‐dose applications that require high‐energy illumination. This allows for synchrotron single‐bunch hard X‐ray imaging to be performed with improved true spatial resolution, as herein exemplified through pulsed wire explosion and superheated near‐nozzle gasoline injection experiments at a pixel size of 3.2 µm, acquisition rates up to 1.4 MHz and effective exposure time down to 60 ps. [ABSTRACT FROM AUTHOR]

Ultra-high-speed synchrotron-based hard X-ray (i.e. above 10 keV) imaging is gaining a growing interest in a number of scientific domains for tracking non-repeatable dynamic phenomena at spatio-temporal microscales. This work describes an optimized indirect X-ray imaging microscope designed to achieve high performance at micrometre pixel size and megahertz acquisition speed. The entire detector optical arrangement has an improved sensitivity within the near-ultraviolet (NUV) part of the emitted spectrum (i.e. 310–430 nm wavelength). When combined with a single-crystal fast-decay scintillator, such as LYSO:Ce (Lu2−xYxSiO5:Ce), it exploits the potential of the NUV light-emitting scintillators. The indirect arrangement of the detector makes it suitable for high-dose applications that require high-energy illumination. This allows for synchrotron single-bunch hard X-ray imaging to be performed with improved true spatial resolution, as herein exemplified through pulsed wire explosion and superheated near-nozzle gasoline injection experiments at a pixel size of 3.2 µm, acquisition rates up to 1.4 MHz and effective exposure time down to 60 ps.

Ultrasound-triggered bubble-mediated local drug delivery has shown potential to increase therapeutic efficacy and reduce systemic side effects, by loading drugs into the microbubble shell and triggering delivery of the payload on demand using ultrasound. Understanding the behavior of the microbubbles in response to ultrasound is crucial for efficient and controlled release. In this work, the response of microbubbles with a coating consisting of poly(2-ethyl-butyl cyanoacrylate) (PEBCA) nanoparticles and denatured casein was characterized. High-speed recordings were taken of single microbubbles, in both bright field and fluorescence. The nanoparticle-loaded microbubbles show resonance behavior, but with a large variation in response, revealing a substantial interbubble variation in mechanical shell properties. The probability of shell rupture and the probability of nanoparticle release were found to strongly depend on microbubble size, and the most effective size was inversely proportional to the driving frequency. The probabilities of both rupture and release increased with increasing driving pressure amplitude. Rupture of the microbubble shell occurred after fewer cycles of ultrasound as the driving pressure amplitude or driving frequency was increased. The results highlight the importance of careful selection of the driving frequency, driving pressure amplitude and duration of ultrasound to achieve the most efficient ultrasound-triggered shell rupture and nanoparticle release of protein-and-nanoparticle–stabilized microbubbles. [ABSTRACT FROM AUTHOR]

Vibration measurement is crucial in fields like aviation, aerospace, and automotive engineering, which are trending towards larger, lighter, and more complex structures with increasingly complicated dynamics. Consequently, measuring a structure's dynamic characteristics has gained heightened importance. Among non-contact approaches, those based on high-speed cameras combined with laser interferometry or computational imaging have gained widespread attention. These techniques yield sequences of images that form a three-dimensional space-time data set. Effectively processing these data is a prerequisite for accurately extracting dynamic deformation information. This paper presents two examples to illustrate the significant advantages of signal processing along the time axis in dynamic interferometric and digital speckle-image-based dynamic measurements. The results show that the temporal process effectively minimizes speckle and electronic noise in the spatial domain and dramatically increases measurement resolutions. [ABSTRACT FROM AUTHOR]

To address safety and labour-intensive challenges in laser powder bed fusion, a novel Metal Additive Manufacturing using Powder Sheets (MAPS) method is employed. By examining the formation mechanism of the melt pool, we discovered that MAPS printing utilising a negative defocus strategy achieves a favourable conduction mode. This approach results in the fabrication of crack-free SS304 samples with over 99.65% relative density and elongated grains. These phenomena are caused by diverged laser power density distribution and decreased entrainment of byproducts such as vapour into the melt pool, as observed by the laser-powder sheet in-situ interaction. Furthermore, the productivity of MAPS increases when printing using the negative defocus setting compared to the scenario without defocus and productivity also increases with the decrease in scanning speed, attributed to a larger amount of metal particles entrained into the melt pool. This study provides insights into the novel MAPS manufacturing for functional metal components.

The standard multi-dose nasal spray pump features an integrated actuator and nozzle, which inevitably causes a retraction of the nozzle tip during application. The retraction stroke is around 5.5 mm and drastically reduces the nozzle's insertion depth, which further affects the initial nasal spray deposition and subsequent translocation, potentially increasing drug wastes and dosimetry variability. To address this issue, we designed a new spray pump that separated the nozzle from the actuator and connected them with a flexible tube, thereby eliminating nozzle retraction during application. The objective of this study is to test the new device's performance in comparison to the conventional nasal pump in terms of spray generation, plume development, and dosimetry distribution. For both devices, the spray droplet size distribution was measured using a laser diffraction particle analyzer. Plume development was recorded with a high-definition camera. Nasal dosimetry was characterized in two transparent nasal cavity casts (normal and decongested) under two breathing conditions (breath-holding and constant inhalation). The nasal formulation was a 0.25% w/v methyl cellulose aqueous solution with a fluorescent dye. For each test case, the temporospatial spray translocation in the nasal cavity was recorded, and the final delivered doses were quantified in five nasal regions. The results indicate minor differences in droplet size distribution between the two devices. The nasal plume from the new device presents a narrower plume angle. The head orientation, the depth at which the nozzle is inserted into the nostril, and the administration angle play crucial roles in determining the initial deposition of nasal sprays as well as the subsequent translocation of the liquid film/droplets. Quantitative measurements of deposition distributions in the nasal models were augmented with visualization recordings to evaluate the delivery enhancements introduced by the new device. With an extension tube, the modified device produced a lower spray output and delivered lower doses in the front, middle, and back turbinate than the conventional nasal pump. However, sprays from the new device were observed to penetrate deeper into the nasal passages, predominantly through the middle-upper meatus. This resulted in consistently enhanced dosing in the middle-upper turbinate regions while at the cost of higher drug loss to the pharynx. [ABSTRACT FROM AUTHOR]

Treating severe dermal disruptions often presents significant challenges. Recent advancements have explored biological cell sprays as a promising treatment, but their success hinges on efficient cell delivery and complete wound coverage. This requires a good spray distribution with a small droplet size, high particle number, and ample surface coverage. The type of nozzle used with the spray device can impact these parameters. To evaluate the influence of different nozzles on spray characteristics, we compared air-assisted and unassisted nozzles. The unassisted nozzle displayed small particle size, high particle number, good overall coverage, high cell viability, preserved cell metabolic activity, and low cytotoxicity. Air-assisted nozzles did not perform well regarding cell viability and metabolic activity. Flow visualization analysis comparing two different unassisted nozzles using high-speed imaging (100 kHz frame rate) revealed a tulip-shaped spray pattern, indicating optimal spray distribution. High-speed imaging showed differences between the unassisted nozzles. One unassisted nozzle displayed a bi-modal distribution of the droplet diameter while the other unassisted nozzle displayed a mono-modal distribution. These findings demonstrate the critical role of nozzle selection in successful cell delivery. A high-quality, certified nozzle manufactured for human application omits the need for an air-assisted nozzle and provides a simple system to use with similar or better performance characteristics than those of an air-assisted system. [ABSTRACT FROM AUTHOR]

Additive manufacturing of AlSi10Mg has obtained increased attention due to its lightweight feature. However, handling of loose powder, efficient usage of feedstock, and powder recycling still remain major open challenges. Herein, a novel additive manufacturing method based on metal additive manufacturing using powder sheet (MAPS) is proposed, which leverages composite flexible films made of the feedstock of metal powder and a polymeric binder, aiming to extend the range of applicability of AlSi10Mg-based additive manufacturing technologies, for example, vehicle components. In situ high-speed imaging is used to explore the underlying manufacturing mechanisms of the proposed MAPS concept and investigate the laser–powder sheet interaction. In addition, a representative computational thermo-mechanical model was used to evaluate the substrate deformation due to the printing process, a critical aspect that must be minimized in order to transfer this technology to larger scale applications. [ABSTRACT FROM AUTHOR]

Liquid jet quenching of metals is typically adopted to achieve specific material properties of metals, thereby making them suitable for advanced engineering applications. In this process, a metal plate is heated and cooled rapidly by impinging water jets. The temperature history during cooling leads to a microstructural transformation thereby improving the material properties such as hardness. During liquid jet quenching, since the plate surface temperature is above the Leidenfrost temperature, the boiling heat transfer dominates. This is associated with an intense cooling and water vapor generation, where the Leidenfrost effect impedes the immediate wetting of the surface. The resulting uneven cooling over the plate surface tends to potential deformation and cracking. To control this process, a detailed understanding of the spatial and the temporal heat transfer behavior is imperative. Experiments in this context are limited and therefore investigating the conjugate heat transfer process is to be combined with a multi-phase numerical model. The two-phase numerical model based on the Euler-Euler approach is developed and validated to simulate the jet quenching of a stationary plate considering all the boiling regimes within a single framework. This model consists of two phases, the liquid water which is the continuous phase (primary) and the water vapor modeled as the dispersed phase (secondary). In this study, a circular water jet (tap water) impact is considered and the plate materials under investigation are aluminum alloy (Al-alloy) and stainless steel (St-steel). Experiments are performed using infrared and high-speed imaging. The validated numerical model provides the technical parameters such as wetting front behavior, heat flux, HTC (heat transfer coefficient) etc. The influence of the jet Reynolds number and the plate material properties on the heat transfer is analysed. The study emphasizes that the plate material has a significantly higher influence on the heat transfer during jet quenching. [ABSTRACT FROM AUTHOR]

The flow generated in a gas-liquid stirred tank reactor highly depends on the design of the impeller and sparger. To better understand the contact between the phases and the mass and heat transfer rates, especially when the mass transfer is the limiting step, it is crucial to investigate the hydrodynamics generated by the impellers and its impact on the bubble size and their distribution, and gas volume fraction. In this work, experimental and numerical studies are performed with a novel mixed impeller in a pilot scale (T = 0.486 m) gas-liquid stirred tank reactor. The Sauter mean diameter, mean bubble diameter and bubble size distribution is determined at the different radial and axial regions by using high-speed imaging technique. Further, Euler-Euler simulations are performed to find the detailed flow field of novel mixed impeller used in the current study. Finally, the gassed power to impeller swept volume ratio is determined from the CFD and correlated with the Sauter mean diameter measured in the experiment in the impeller discharge region. It is found that the novel mixed impeller used in current work shows the similar behavior as the Rushton impeller in the impeller discharge region and it also provide good axial mixing. [ABSTRACT FROM AUTHOR]

Boiling is a high-performance heat dissipation process that is central to electronics cooling and power generation. However, there exists a practical limit of boiling heat transfer known as the critical heat flux (CHF), beyond which significant performance degradation is observed. Understanding the physical mechanism that triggers CHF is essential to meet the increasing cooling demands driven by power densification and device miniaturization. However, the high dimensionality, stochasticity, and dynamicity of the boiling process have led to strong challenges in the experimental characterization and modeling of boiling CHF. As such, high-frame rate, high-resolution, multi-physics boiling datasets are critical to advancing the fundamental understanding of boiling heat transfer. To this end, this paper presents a multimodal boiling dataset consisting of synchronized thermal, acoustic, and optical signals collected from five different heater surfaces under two distinct heat load conditions. With its high sampling frequency, diverse signal types, large data volume, and detailed recorded information, this dataset provides valuable ''data blood'' for the field of thermal crisis monitoring. This dataset will not only promote fundamental research on bubble dynamics during boiling but also support the implementation of advanced monitoring technologies in industrial applications such as power electronics, motors, data centers, and power plants.

The plasma bulk velocity is one of the key parameters describing the behavior of a plasma jet and is relevant for applications such as plasma spraying or electric propulsion. Therefore, different measurement techniques to determine the velocity were developed in the past. This paper presents a novel, non-invasive method for spatially resolved velocity measurements. The method is based on tracking of characteristic features in tomographic reconstructions of the plasma plume. A high-speed image recording system combined with tomographic acquisition is therefore the backbone of this method. The proposed setup captures the object under study from six different directions at a frame rate up to one million frames per second, providing high spatial and temporal resolution. The tomographic reconstructions are then calculated using the ART algorithm to track features in the plasma fluctuations, from which the bulk velocity is determined. The setup was tested with a DC plasma torch operated at reduced pressures in the range of tens of millibars. For the analyzed parameters, the axial velocity reached a maximum of 1061 m/s at a distance of three centimeters from the plasma torch exit and decreased to 919 m/s further downstream at a distance of seven centimeters, which is in good accordance with previous work. Therefore, the proposed diagnostic method can serve as a non-invasive alternative to velocity measurements, providing additional information in the form of a 3D model of the plasma bulk.

The primary acoustic signal of the voice is generated by the complex oscillation of the vocal folds (VFs), whereby physicians can barely examine the medial VF surface due to its anatomical inaccessibility. In this study, we investigated possibilities to infer medial surface dynamics by analyzing correlations in the oscillatory behavior of the superior and medial VF surfaces of four human hemilarynges, each in 24 different combinations of flow rate, VF adduction, and elongation. The two surfaces were recorded synchronously during sustained phonation using two high-speed camera setups and were subsequently 3D-reconstructed. The 3D surface parameters of mean and maximum velocities and displacements and general phonation parameters were calculated. The VF oscillations were also analyzed using empirical eigenfunctions (EEFs) and mucosal wave propagation, calculated from medial surface trajectories. Strong linear correlations were found between the 3D parameters of the superior and medial VF surfaces, ranging from 0.8 to 0.95. The linear regressions showed similar values for the maximum velocities at all hemilarynges (0.69–0.9), indicating the most promising parameter for predicting the medial surface. Since excessive VF velocities are suspected to cause phono-trauma and VF polyps, this parameter could provide added value to laryngeal diagnostics in the future.

This experimental study investigated the influence of different turbine guide vane parameters on the ignition limit and light-round processes in a triple-dome combustor. It was found that for the triple-dome combustor, the minimum fuel/air ratios at the ignition limit all show a trend of initial decrease followed by subsequent increase with the growth of incoming air mass flow rate. The ignition fuel/air ratio decreases with the increase in turbine blockage ratio, and the optimal scheme is achieved with a blockage ratio of 0.8. Under the condition where the incoming air mass flow rate is 0.089 kg/s, the light-round time decreases with the increase in fuel/air ratio, and the light-round time of the combustor without guide vanes is shorter than that of the other schemes. With the increase in incoming air mass flow rate, the light-round time of the schemes with guide vanes is shortened. Under the same incoming air mass flow rate and fuel/air ratio, the increase in the blockage ratio will lead to an increase in the light-round time of the triple-dome combustor.

The onset and early stages of dynamic wetting on different hydrophobic surfaces is investigated experimentally for aqueous solutions of two commercial trisiloxane surfacants of similar chemical structure, one of which exhibits superspreading behaviour, in order to investigate the spreading dynamics independently of the surface activity. Superspreading, or the ability of a surfactant solution to spread on a surface beyond the state determined by thermodynamic equilibrium, has been investigated for more than 30 years however its physical mechanism remains poorly understood to date despite its important applications in the formulation of agrochemicals. Surfactant solutions were prepared by dissolving S233 and S240 surfactants (Evonik Industries AG, Essen, Germany) into de-ionised water at a weight concentration of 0.1%. Drops of surfactant solutions and pure water were deposited on three horizontal substrates with different wettability (equilibrium contact angle of water ranging between 55 ∘ and 100 ∘ ), and observed from below with a high-frame rate camera to visualise the advancing contact line. The spreading ratio of drops as a function of time was extracted from high-speed videos by digital image processing. Results reveal that the superspreading solution exhibits an intermittent spreading rate, as well as peculiar features of the contact line, which are not observed for the non-superspreading solution, and confirm the superspreading effect becomes less significant when the surface energy of the substrate is decreased. [ABSTRACT FROM AUTHOR]

This research explores the two-phase flow behavior involved in enhanced dense phase carbon dioxide inactivation of E. coli DH5α, which has been shown to possess a high microbial reduction efficiency of up to 3.7 ± 0.4 log. We present an experiment in which the liquid sample was pressurized with liquid carbon dioxide to 8.2 MPa and, after saturation, was forced to flow through a mini tube. An experimental setup was developed to visualize the flow patterns (plug, slug and churn flows) occurring in the mini tube by means of high-speed imaging. The values of the wall shear stress were estimated within the mini tube with the help of the gas slug velocities (8–9 m/s) and were compared with threshold shear stress values reported for the disruption of fresh E. coli cells. The results suggest that the preliminary pressurization phase may cause a substantial destabilization of the cell wall of E. coli DH5α. [ABSTRACT FROM AUTHOR]

Vibration measurement is crucial in fields like aviation, aerospace, and automotive engineering, which are trending towards larger, lighter, and more complex structures with increasingly complicated dynamics. Consequently, measuring a structure’s dynamic characteristics has gained heightened importance. Among non-contact approaches, those based on high-speed cameras combined with laser interferometry or computational imaging have gained widespread attention. These techniques yield sequences of images that form a three-dimensional space-time data set. Effectively processing these data is a prerequisite for accurately extracting dynamic deformation information. This paper presents two examples to illustrate the significant advantages of signal processing along the time axis in dynamic interferometric and digital speckle-image-based dynamic measurements. The results show that the temporal process effectively minimizes speckle and electronic noise in the spatial domain and dramatically increases measurement resolutions.

The process map area of laser beam powder bed fusion for the nickel-based superalloy Inconel 718 is investigated using high laser power (600-1000 W) and scanning speeds (1500-3500 mm/s). The process map is defined by the surface morphologies (visually inspected) and relative densities of the as-built materials. The effects of the process parameters on the melting and solidification phenomena are observed by high-speed camera imaging, while those on the microstructure of the as-built parts are observed through the scanning electron micrograph (SEM). The process window to build specimens with smooth surfaces and high relative densities was in the laser power range of 700-1000 W and a scanning speed of 1500 mm/s. Notably, the relative density of the specimen built in this process window was slightly lower than that of the specimen built in the current process window of low power (100-400 W) and scanning speed (100-1500 mm/s). High-speed camera observation of the melt pool behavior revealed that the plasma plume was ejected backward in the laser scan direction, and many large spatters were ejected along the plume under the proposed higher power and scan speed conditions. Moreover, the melt pool was unstable, and the laser track displayed an irregular shape. The spatter and unstable melt pool were attributed to the keyhole evolution in the melt pool. The microstructure of the as-built parts presented features similar to those of materials built under the current process window. This research provided process parameters set under high power and scanning speed conditions and enabled the fabrication of dense materials like those produced within the conventional process window. The higher scanning velocity reduces the building time compared to the current process window.

The long-existing contradiction between cutting speed and surface quality in wire electrical discharge machining (WEDM) detrimentally hinders its further development and application. To address this problem, this work proposed a multi-channel discharge method that performs WEDM on several workpieces, each electrically insulated and connected to a pulse power supply with a resistor. As a result, the machining energy normally exerted on one plasma channel can be dispersed into multiple discharge channels when each pulse voltage is applied. Firstly, the mechanism of multi-channel discharge was theoretically illustrated. Secondly, machining waveforms and high-speed imaging of gap phenomena were captured to prove the feasibility of multi-channel discharge in high-speed WEDM (HSWEDM). Although the multi-channel discharge is stochastic, a certain probability exists due to the vibration of wire electrodes. Lastly, verification experiments were conducted to investigate the performance of multi-channel discharge. The results indicate that the multi-channel discharge can significantly improve surface quality without reducing cutting speed, thus achieving a better balance between productivity and surface quality. [ABSTRACT FROM AUTHOR]

Brittleness is an intrinsic mechanical property of rock materials that has attracted significant attention to be properly quantified as it plays an important role in characterization of brittle fracturing. Endeavors have led to the establishment of many Brittleness Indices (BIs) for various rock types and widespread engineering applications. Among them, assessing burst proneness as a serious challenge in underground mining has received considerable attention. Parallel to BIs' development, various Bursting Liability Indices (BLIs) have been proposed to specifically assess coal bursting phenomenon. Despite having different names, both BI and BLI in principle have aimed at evaluating the burst–brittleness level of different rocks for different applications. In this study, the principles of burst and brittleness were discussed followed by the development of a novel so-called burst–brittleness ratio (BBR) to assess the relative burst–brittleness of rock types irrespective of their applications. To do so, the proposed BBR was governed by point load testing (PLT) which has significant advantages over the other rock testing methods used in BI estimation such as direct or indirect tensile testing. To examine the suitability of the proposed ratio, three different rock types from various geological origins including coal, granite and sandstone were selected and tested under uniaxial compressive, indirect tensile Brazilian and point loadings. The high-speed imaging technique and Acoustic Emission (AE) were utilized to characterize the cracking process (e.g., failure under shear or tension) and to monitor the real-time failure behavior of samples under different loading conditions. The resulting data revealed that the severity of strength loss in coal samples was significantly higher than that observed in other rock types particularly under uniaxial compression endorsing the validity of the proposed BBR. Highlights: Comparing Brittleness index with Bursting Liability Index along with their pros and cons Development of a new Burst–Brittleness Ratio (BBR) based on UCS and point load strength index Validation of the proposed ratio through point load and UCS tests on granite, coal, and sandstone using high-speed imaging and Acoustic Emission (AE) techniques [ABSTRACT FROM AUTHOR]

An experimental study is performed to determine the head mechanics of American football helmets equipped with novel fiber energy absorbing material (FEAM). FEAM-based padding materials have substrates of textile fabrics and foam made with nylon fibers using electro-static flocking process. Both linear and angular accelerations of the sport helmets are determined under impact loads using a custom-built linear impactor and instrumented head. The effectiveness of padding materials and vinyl nitrile (VN) foam for impact loads on six different head positions that simulate two helmeted sport athletes in real-time helmet-to-helmet strike/impact is investigated. A high-speed camera is used to record and track neck flexion angles and compare them with pad effectiveness to better understand the head kinematics of struck players at three different impact speeds (6 m/s, 8 m/s, and 10 m/s). At impact speed of 6 m/s and 8 m/s, the FEAM-based padding material of 60 denier fibers showed superior resistance for angular acceleration. Although novel pads of VN foam flocked with 60 denier fibers outperformed with lowest linear acceleration for most of the head positions at low impact speed of 6 m/s, VN foam with no fibers demonstrated excellent performance for linear acceleration at other two speeds. [ABSTRACT FROM AUTHOR]

This paper provides quantitative information about the paths taken by blown powder particles during laser cladding. A proportion of the powder is "wasted" by bouncing off the solid areas surrounding the melt pool. This wastage reduces the productivity and profitability of the process. In this paper, specially developed software was used to analyze high-speed imaging videos of the cladding process, to monitor the directions of powder particle flight toward and away from the melt pool area. This information has been correlated to the geometry and position of the melt pool zone for three different cladding techniques: single track cladding (A tracks), standard overlapping track cladding (AAA cladding), and a recently developed technique called ABA cladding. The results show that the melt pool geometry, and particularly the overlap between the melt pool and the incoming powder stream, has a strong influence on powder catchment efficiency. ABA cladding was found to have considerably better powder catchment efficiency than standard AAA cladding and this improvement can be explained by consideration of the geometries and positions of the melt pools and surrounding solid material in each case. As powder costs are an important factor in industrial laser cladding, the adaption of the ABA technique, and/or control of pool/powder stream overlap (e.g., by making the powder stream not coaxial with the laser beam), could improve the profitability of the process. [ABSTRACT FROM AUTHOR]

During laser fusion cutting, burr forms when the molten metal does not sufficiently exit the interaction zone. When it forms on the lower edge of the cut flank, burr becomes a factor limiting quality. Previous research has shown that a temporally regular and spatially localized melt flow can prevent the formation of burr. However, the high dynamics of the subprocesses involved can cause intrinsic instabilities that disrupt the flow and reduce the efficiency of the melt ejection. This paper presents a study on the correlation between process parameters, melt flow properties, and burr formation. It includes an experimental observation of the melt-flow dynamics using high-speed videography. In addition, a Computational Fluid Dynamics model was set up to examine fundamental flow properties, some of which are not observable experimentally. The dependency of the burr formation on the liquid Weber and Reynolds numbers is analyzed, and it is demonstrated how the magnitude and allocation of vapor pressure gradients in the kerf decisively affect melt ejection and burr formation. Additionally, a previously unknown melt ejection regime is identified in the thick section range, which occurs at feed rates close to the maximum cutting speed under specific high-power process conditions. This regime is characterized by a significantly increased process efficiency that could open up a new high-speed process window. [ABSTRACT FROM AUTHOR]

Microcantilever probes used for high-speed scanning probe microscopy are typically required to satisfy two mutually contradicting objectives: high eigenfrequency (ωn) and low flexural rigidity (kb). The conventional design approach shortens the microcantilever's length to increase the eigenfrequencies (as ωn∝1/L2); however, this also increases the probe's rigidity (as kb∝1/L3). This paper demonstrates—through experiments and physical modelling—the design of a novel high-eigenfrequency probe by redistributing the microcantilever's mass along its length. A 100% increase in the probe's eigenfrequency is achieved with this modified design, even while reducing its stiffness by 50%. Through experiments, this reduced stiffness has been found to enhance the probe's force sensitivity. Also, the probe's design facilitates redistributing the fluid pressure between its underside surface and the sample, thereby improving the quality factor by more than 100%. Significant reduction in 'overshoot' and 'parachute' is observed in contact mode scanning at the video rate. The improvements in the image resolution are proven for a variety of sample surfaces at very high scan rates up to 40 Hz (corresponding to a linear speed of 3.20 mm s−1) upon scanning over an area of 40×40 μm and are successfully demonstrated to map topographies with negligible image artefacts. [ABSTRACT FROM AUTHOR]

An externally wetted emitter array with longitudinally grooved structures for ionic liquid electrospray thrusters was fabricated to improve ionic liquid transport to the emitter tips. Two grooved emitter shapes with different groove depths were successfully fabricated using microelectromechanical system processing techniques. We evaluated the current–voltage characteristics, measured the mass spectra using time-of-flight (ToF) spectrometry, and conducted in-situ observations using a high-speed microscope. The experimental results of ion emission show that the absolute emission current increases compared with that of our previous emitter without grooves. This tendency is strengthened with deeper grooves. Moreover, the slope of the current–voltage curve for the grooved emitters does not decrease even when high voltages are applied, indicating that the grooved structure improves the ionic liquid transport to the emitter tips. This improvement is attributed to the low hydraulic impedance of the emitter structure. However, deeper grooving also increases the percentage of current intercepted by the extractor electrode, and electrochemical reactions are not avoided at an alternation frequency of 1 Hz. Although the first current–voltage measurement tended to have unstable characteristics, the ToF results indicated that the emission in the center line was in the pure-ion regime, composed mostly of monomer and dimer ions, under all the measured conditions. High-speed microscope observations showed that too much ionic liquid deposited on the extractor causes ion emission from the extractor to the emitter, known as backspray, and implies that no large droplets are emitted for either grooved emitter structure, which is consistent with the ToF results. [ABSTRACT FROM AUTHOR]

To explore the effect of conduit roughness on volcanic jet dynamics and on the related seismo‐acoustic radiation we performed a series of shock‐tube experiments using pipes with variable inner surface fractal dimension D. Variable starting pressure produced subsonic to supersonic jets visualized using high‐speed shadowgraph and recorded with an array of accelerometers and microphones. At all starting pressures, increasing D increases the energy transfer from the gas to the conduit walls, decreasing the jet exit velocity (Mach number) and, for supersonic cases, the related shock‐cell spacing, and increasing the seismic to acoustic radiation amplitude ratio. The roughness‐induced changes in jet velocity and turbulence affect the dominant sources of the jet noise and modulates the spectral properties of the acoustic signals. From our study we show that conduit wall roughness is an important and yet largely neglected factor in the dynamics of explosive volcanic eruptions and their monitored geophysical signals. Plain Language Summary: Volcanoes are amongst the most fascinating and mysterious subjects of science, for they allow no direct observation of what is happening within the conduit during eruptive activity. Indirect observations (such as measurements of the sound and vibration accompanying eruptions) are routinely performed for monitoring and research purposes. Laboratory studies mimicking the eruptive processes in small‐scale devices, are of great support for correctly interpreting such data. As such, we investigated the effect of the irregularity of conduit surface, amongst the most relevant and poorly known variables characterizing the eruptive processes, on volcanic jets and on their seismic and acoustic signals. We performed a series of laboratory experiments using conduits with different roughness of the internal surface and various starting pressures. Microphones and accelerometers, capable of measuring conduit sounds and vibration, respectively, in synch with high‐speed camera were used to constrain the characteristics of the generated subsonic and supersonic jets. Results show that conduit roughness controls: (a) the relative amplitude of seismic and acoustic signals; (b) the velocity, turbulence and properties of the sound of these jets. Our results will shed light on the link between observation at the surface and dynamic evolution of conduit geometry at depth. Key Points: Elastic radiation of analogue experimental volcanic subsonic to supersonic jets was compared against high‐speed shadowgraph analysisWe quantified variation in the spectral features, energy partitioning and jet structure due to differences in conduit roughnessDifferent behavior in subsonic versus supersonic regime was observed due to distinct dominating noise sources at different roughness [ABSTRACT FROM AUTHOR]

A two-channel pulsed power supply for an imaging system with brightness amplification and independent synchronous laser illumination is designed. The power supply generates synchronized high-voltage pulses with a frequency of 16-24 kHz, an average electrical power of up to 1.2 kW, and an adjustable amplitude of up to 6.2 kV to pump copper bromide gas discharge tubes with independent control of the temperature parameters of the active medium. To generate pumping pulses for laser media, we used a two-channel thyratron circuit with a common source of stabilized voltage provided by a step-down pulse stabilizer and a bridge inverter-based circuit for the pulsed charge of storage capacitors. The voltage equalization on the storage capacitors is carried out by means of magnetic coupling of the charging inductances wound on a common core. Adjustable delay lines based on variable inductances provide synchronous operation of two brightness amplifiers with a synchronization accuracy of lasing pulses of ±1 ns. The power supply demonstrated stable operation with two gas discharge tubes having different characteristics, including those with different types of electrodes. It has been integrated into a laboratory facility for the study of high-energy materials combustion. [ABSTRACT FROM AUTHOR]

Metalworking operations rely on the successful application of metalworking fluids (MWFs) for effective and efficient operation. Processes such as grinding or drilling often require the use of MWFs for cooling, lubrication, and chip removal. Electrochemical machining processes require electrolyte flow to operate. However, in those machining operations, a fundamental understanding of the mode of action of MWF is lacking due to the unknown flow dynamics and its interaction with the material removal during the process. Important information on the behaviour of MWFs during machining can be obtained from specific experimental flow visualisation studies. In this paper, promising flow visualisation analysis techniques applied to exemplary machining processes (grinding, sawing, drilling, and electrochemical machining) are presented and discussed. Shadowgraph imaging and flow measurements, e.g., particle image velocimetry, allow the identification of typical flow and MWF operating regimes in the different machining processes. Based on the identification of these regimes, efficient machining parameters and MWF applications can be derived. In addition, detailed experimental analyses of MWFs provide essential data for the input and validation of model development and numerical simulations within the Priority Programme SPP 2231 FluSimPro. [ABSTRACT FROM AUTHOR]

Abstract Stabilized microbubbles were commercialized over 30 years ago for use as contrast agents in ultrasound imaging. In recent years, interest in microbubble–acoustic interactions has expanded to applications not only in ultrasound imaging but also in drug and gene delivery. To understand the interaction of a microbubble and ultrasonic field, scientists optically observe the behavior of microbubbles during acoustic excitation. Because of the fast oscillations of microbubbles in ultrasound fields, the application of ultra‐high‐speed photography is required to capture bubble behavior. This manuscript reviews the approaches, challenges, and progress in high‐speed imaging systems utilized for microbubble analysis, focusing on innovations in camera technology.

Treating severe dermal disruptions often presents significant challenges. Recent advancements have explored biological cell sprays as a promising treatment, but their success hinges on efficient cell delivery and complete wound coverage. This requires a good spray distribution with a small droplet size, high particle number, and ample surface coverage. The type of nozzle used with the spray device can impact these parameters. To evaluate the influence of different nozzles on spray characteristics, we compared air-assisted and unassisted nozzles. The unassisted nozzle displayed small particle size, high particle number, good overall coverage, high cell viability, preserved cell metabolic activity, and low cytotoxicity. Air-assisted nozzles did not perform well regarding cell viability and metabolic activity. Flow visualization analysis comparing two different unassisted nozzles using high-speed imaging (100 kHz frame rate) revealed a tulip-shaped spray pattern, indicating optimal spray distribution. High-speed imaging showed differences between the unassisted nozzles. One unassisted nozzle displayed a bi-modal distribution of the droplet diameter while the other unassisted nozzle displayed a mono-modal distribution. These findings demonstrate the critical role of nozzle selection in successful cell delivery. A high-quality, certified nozzle manufactured for human application omits the need for an air-assisted nozzle and provides a simple system to use with similar or better performance characteristics than those of an air-assisted system.

The standard multi-dose nasal spray pump features an integrated actuator and nozzle, which inevitably causes a retraction of the nozzle tip during application. The retraction stroke is around 5.5 mm and drastically reduces the nozzle’s insertion depth, which further affects the initial nasal spray deposition and subsequent translocation, potentially increasing drug wastes and dosimetry variability. To address this issue, we designed a new spray pump that separated the nozzle from the actuator and connected them with a flexible tube, thereby eliminating nozzle retraction during application. The objective of this study is to test the new device’s performance in comparison to the conventional nasal pump in terms of spray generation, plume development, and dosimetry distribution. For both devices, the spray droplet size distribution was measured using a laser diffraction particle analyzer. Plume development was recorded with a high-definition camera. Nasal dosimetry was characterized in two transparent nasal cavity casts (normal and decongested) under two breathing conditions (breath-holding and constant inhalation). The nasal formulation was a 0.25% w/v methyl cellulose aqueous solution with a fluorescent dye. For each test case, the temporospatial spray translocation in the nasal cavity was recorded, and the final delivered doses were quantified in five nasal regions. The results indicate minor differences in droplet size distribution between the two devices. The nasal plume from the new device presents a narrower plume angle. The head orientation, the depth at which the nozzle is inserted into the nostril, and the administration angle play crucial roles in determining the initial deposition of nasal sprays as well as the subsequent translocation of the liquid film/droplets. Quantitative measurements of deposition distributions in the nasal models were augmented with visualization recordings to evaluate the delivery enhancements introduced by the new device. With an extension tube, the modified device produced a lower spray output and delivered lower doses in the front, middle, and back turbinate than the conventional nasal pump. However, sprays from the new device were observed to penetrate deeper into the nasal passages, predominantly through the middle-upper meatus. This resulted in consistently enhanced dosing in the middle-upper turbinate regions while at the cost of higher drug loss to the pharynx.

Abstract To explore the effect of conduit roughness on volcanic jet dynamics and on the related seismo‐acoustic radiation we performed a series of shock‐tube experiments using pipes with variable inner surface fractal dimension D. Variable starting pressure produced subsonic to supersonic jets visualized using high‐speed shadowgraph and recorded with an array of accelerometers and microphones. At all starting pressures, increasing D increases the energy transfer from the gas to the conduit walls, decreasing the jet exit velocity (Mach number) and, for supersonic cases, the related shock‐cell spacing, and increasing the seismic to acoustic radiation amplitude ratio. The roughness‐induced changes in jet velocity and turbulence affect the dominant sources of the jet noise and modulates the spectral properties of the acoustic signals. From our study we show that conduit wall roughness is an important and yet largely neglected factor in the dynamics of explosive volcanic eruptions and their monitored geophysical signals.

Ultrasound-induced cavitation in blood vessels is a common scenario in medical procedures. This paper focuses on understanding the mechanism of microscopic damage to vessel walls caused by the evolution of cavitation bubbles within the vessels. In this study, cavitation bubbles were generated using the low-voltage discharge method in 0.9% sodium chloride saline, and vessel models with wall thicknesses ranging from 0.7 mm to 2 mm were made using a 3D laminating process. The interaction between cavitation bubbles and vessel models with different wall thicknesses was observed using a combination of high-speed photography. Results show that cavitation bubble morphology and collapse time increased and then stabilized as the vessel wall thickness increased. When the cavitation bubble was located in vessel axial line, pair of opposing micro-jets were formed along the axis of the vessel, and the peak of micro-jet velocity decreased with increasing wall thickness. However, when the cavitation bubble deviated from the vessel model center, no micro-jet towards the vessel model wall was observed. Further analysis of the vessel wall deformation under varying distances from the cavitation bubble to the vessel wall revealed that the magnitude of vessel wall stretch due to the cavitation bubble expansion was greater than that of the contraction. A comparative analysis of the interaction of between the cavitation bubble and different forms of elastic membranes showed that the oscillation period of the cavitation bubble under the influence of elastic vessel model was lower than the elastic membrane. Furthermore, the degree of deformation of elastic vessel models under the expansion of the cavitation bubble was smaller than that of elastic membranes, whereas the degree of deformation of elastic vessel models in the contraction phase of the cavitation bubble was larger than that of elastic membranes. These new findings provide important theoretical insights into the microscopic mechanisms of blood vessel potential damage caused by ultrasound-induced cavitation bubble, as well as cavitation in pipelines in hydrodynamic systems.

In the EU funded SmartCHP project, biomass derived fast-pyrolysis bio-oil (FPBO) is used to fuel modified stationary diesel engines for combined heat and power applications. In this study, the spray combustion characteristics of fast-pyrolysis bio-oil and FPBO/ethanol blends are experimentally investigated in a combustion research unit. Due to the special physicochemical properties of fast-pyrolysis bio-oil, major modifications are made to the combustion research unit to facilitate testing this fuel, including the installation of a high-temperature chamber and a heavy-fuel oil injection system. Experimental tests are carried out at a chamber wall temperature of 750 °C and an ambient pressure of 50 bar. The pressure-based heat release analysis is used to evaluate fuel ignition and combustion characteristics, while a high-speed imaging technique is adopted to visualize natural luminosity of spray flames through a borescope.Results show that fast-pyrolysis bio-oil has lower sooting tendency than diesel, and it significantly alleviates the fuel dribble phenomenon. At injection pressure of 300 bar, the poor atomization of fast-pyrolysis bio-oil leads to rather grainy-looking spray flame images, and nozzle orifices becoming clogged within couple of injections. The increase of injection pressure to 900 bar results in an obvious improvement of the atomization quality and nozzle durability for fast-pyrolysis bio-oil. Adding ethanol into fast-pyrolysis bio-oil could improve fuel atomization and further reduce the natural luminosity. The ignition delay of fast-pyrolysis bio-oil is slightly retarded by 10% ethanol addition, while it is advanced by 30% ethanol addition.

Thermally-induced breakup of metal-precursor-laden droplets in spray-flame synthesis occurs via a rapid and disruptive disintegration, i.e., “puffing” and “micro-explosion”. To assess the temporal evolution and statistics of droplet disruption, LED-illuminated droplet shadowgraphs were imaged with a microscope onto a high-speed camera and morphological image analysis was applied. The atomized liquid was a mixture of 35 vol.-% ethanol and 65 vol.-% 2-ethylhexanoic acid mixed with iron(III) nitrate nonahydrate (INN) as a precursor. Droplet evaporation and disruption were also simulated with a population balance model. The model finds solid precipitates forming in the droplets because of the decomposition of the precursor intermediate iron(III) 2-ethylhexanoate. The precipitates form a particle shell, which favors the superheating of the droplets’ interior, and they facilitate heterogeneous bubble nucleation. Imaging experiments and modelling find that per 10 µs lifetime of a droplet, the probability for disruption increases from 5 to 13% and 5 to 19%, respectively, when increasing the INN concentration from 0.05 to 0.5 mole/l. The probability of disruption suggests that throughout their lifetime in the spray flame, nearly all droplets will undergo disruption and many of them multiple times. In the experiment, droplets before disruption are 15% smaller than regular, non-disrupting droplets. Once disrupted, the droplets have a 45% smaller mean diameter than regular droplets. Under all conditions, disrupting and disrupted droplets are slower than regular droplets while the disruption does not significantly accelerate disrupted droplets.

Porous microneedles (MNs) offer broad advantages such as fluid capture and filtration. Compared to hollow MNs, fluid injection through porous MNs causes a broader diffusion spread. Herein, three MN designs with a constant pore size and controlled pore locations are fabricated and compared, using two-photon polymerization (2PP), by examining factors such as diffusion spread, mixing capabilities, and mechanical resilience. Results show that the porous MN can cover 16 times the injection area than that of the hollow MN. Porous MNs also show good mixing capabilities with two fluids. Mechanical compression results reveal that one porous MN can withstand a load of 0.6 N. [ABSTRACT FROM AUTHOR]

An experimental evaluation of the flow field on two high‐gravity spiral concentrators is presented along with the analytical solutions. A digital depth gauge was used to measure the liquid level on the spiral troughs. The tracer particle trajectories and the free surface velocity of a spiral were determined with a high‐speed camera. An increase in the flow rate leads to an increase in the liquid depth and free surface velocity along the trough surface. Three full turns of the high gravity spiral concentrator are sufficient for achieving a stabilized flow. High‐gravity spirals show lower flow depths and free surface velocities but steeper depths on the outer trough zone than low‐gravity spirals. Higher flow depths contribute to larger circulation zones, which eventually help in greater separation of heavier minerals from gangue particles. [ABSTRACT FROM AUTHOR]