Investigation of Er:YAG laser-activated irrigation for the removal of biofilm and observations of laser-induced cavitation behavior

Background We investigated the biofilm removal effects of LAI using a pig model, focusing on the impact of the fiber tip position, and used a high-speed camera to observe the occurrence and positioning of the cavitation associated with laser irradiation. Methods A total of 16 roots of deciduous mandibular second premolars from 4 pigs were used. After a pulpectomy, the canals were left open for two weeks and sealed for 4 weeks to induce intraradicular biofilm. Then, root canal irrigation was performed with Er:YAG laser activation. The fiber tip was inserted at two different positions, i.e., into the root canal in the intracanal LAI group and into the pulp chamber in the coronal LAI group. Intracanal needle irrigation with saline or 5% NaOCl was utilized in the positive control and CNI groups. SEM and qPCR were carried out to evaluate treatment efficacy. For qPCR, ANOVA and a Tukey-Kramer post hoc test were performed with α = 0.05. A high-speed camera was used to observe the generation of cavitation bubbles and the movement of the induced bubbles after laser irradiation. Results The intracanal and coronal LAI groups showed significantly lower amounts of bacteria than either the positive control or CNI groups. There was no significant difference found between the intracanal and coronal LAI groups. SEM images revealed opened dentinal tubules with the destruction of biofilm in both LAI groups. High-speed camera images demonstrated cavitation bubble production inside the root canal after a single pulse irradiation pulse. The generated bubbles moved throughout the entire internal multi-rooted tooth space. Conclusions Coronal LAI can generate cavitation in the root canal with a simply placed fiber inside the pulp chamber, leading to effective biofilm removal. This method could thus contribute to the future development of endodontic treatments for refractory apical periodontitis caused by intraradicular biofilm.

Design of a non circular gear Mechanism with Twice Unequal Amplitude Transmission Ratio

This study proposes a new non–circular gear transmission mechanism with an involute–cycloid composite tooth profile to realize the twice unequal amplitude transmission (In a complete rotation cycle of gear transmission, instantaneous transmission ratio has twice fluctuations obvious with unequal amplitude) of non–circular gears. The twice unequal amplitude transmission ratio curve was designed based on Fourier and polynomial functions, the change law of the Fourier coefficient on the instantaneous transmission ratio(In non-circular gear transmission, the transmission ratio changes with time, and the transmission ratio of non-circular gear should be instantaneous transmission ratio) was analyzed, and the pressure angle and contact ratio of the involute–cycloid composite tooth profile was calculated. The involute–cycloid composite tooth profile non–circular gear was machined by WEDM technology, while its meshing experiment was performed using high-speed camera technology. The results demonstrate that the instantaneous transmission ratio curve value obtained via the high-speed camera experiment was consistent with the simulation value of virtual software. Furthermore, the involute–cycloid composite tooth profile was applied in the seedling pickup mechanism of non–circular gear planetary gear train. The possibility of the application of the involute–cycloid composite tooth profile in the seedling pickup mechanism was verified by comparing the consistency of the theoretical and simulated seedling picking trajectory.

Comparisons of flow dynamics of dual-blade to single-blade beveled-tip vitreous cutters

Introduction: To compare the flow dynamics of the dual-blade to the single-blade beveled-tip vitreous cutters. Methods: The aspiration rates of balanced salt solution (BSS) and swine vitreous were measured for the 25-gauge and 27-gauge dual- and single-blade vitreous cutters. The flow dynamics of BSS and diluted vitreous mixed with fluorescent polymer at the maximal cutting rates and the reflux of BSS were measured in images obtained by a high-speed camera. The distal end of the cutter was defined as the head end. Results: The aspiration rates of BSS and vitreous by the 25- and 27-gauge dual-blade cutters were significantly higher than those of both single-blade cutters at the maximal cutting rate (all P≤0.01). The mean aspiration flow of BSS in front of the port from a lateral view was significantly faster for both dual-blade cutters than for both single-blade cutters (P=0.003, P=0.019). The angle of the mean flow of BSS of both dual-blade cutters was from the distal end (P<0.001, P<0.001) but that of the single blade-cutters was from the proximal end. The velocity and angle of the mean reflux flow of both types of cutters were not significantly different. The mean aspiration flow of diluted vitreous was significantly faster for 25-gauge dual-blade cutters with the angle more from the proximal end and 27-gauge dual-blade cutters more from the distal end than both single-blade cutters (P=0.018, P=0.048). Conclusion: The dual-blade beveled-tip vitreous cutters improve the efficiency of the vitrectomy procedures and maintain the distal aspirating flow by the beveled-tip.

Numerical Simulation and Experimental Analysis of Volume Alternate Cavitation (VAC) - A new Cavitation Generation Method

Cavitation generation methods have been applied in multifarious directions due to their diversity. And scholars have carried out numerous researches and discussions on cavitation generation methods. The purpose of this study is to explore the generating mechanism and evolution law of volumetric alternate cavitation (VAC). In the VAC, the liquid water is placed in an airtight container with variable volume. With the volume alternately changes, the liquid water inside the container continues to cavitate. In this study, the mixture turbulence model and in-cylinder dynamic grid model were used to apply computational fluid dynamics (CFD) simulation of volume alternate cavitation. In the simulation, the cloud images at 7 heights on the central axis are monitored, and the phenomenon and mechanism of height and eccentricity are analyzed detailedly. By using the method of cavitation flow visualization (CFV), the generating mechanism and evolution law of cavitation are clarified. The synergistic effects of experiments and high-speed camera capture confirm the simulation. In the experiment, the volume change stroke of the airtight container is 20 mm, the volume change frequency is 18 Hz, and the shooting frequency of the high-speed camera is set to 10000 fps. The results show that the position of occurring cavitation phenomenon has a reasonable law during the whole evolution cycle of the cavitation cloud. It is evident that a cycle of volume alternation corresponds to the generation, development and collapse stages of cavitation bubbles.

Influence of Initial Temperature and Convective Heat Loss on the Self-Propagating Reaction in Al/Ni Multilayer Foils

A two-dimensional numerical model for self-propagating reactions in Al/Ni multilayer foils was developed. It was used to study thermal properties, convective heat loss, and the effect of initial temperature on the self-propagating reaction in Al/Ni multilayer foils. For model adjustments by experimental results, these Al/Ni multilayer foils were fabricated by the magnetron sputtering technique with a 1:1 atomic ratio. Heat of reaction of the fabricated foils was determined employing Differential Scanning Calorimetry (DSC). Self-propagating reaction was initiated by an electrical spark on the surface of the foils. The movement of the reaction front was recorded with a high-speed camera. Activation energy is fitted with these velocity data from the high-speed camera to adjust the numerical model. Calculated reaction front temperature of the self-propagating reaction was compared with the temperature obtained by time-resolved pyrometer measurements. X-ray diffraction results confirmed that all reactants reacted and formed a B2 NiAl phase. Finally, it is predicted that (1) increasing thermal conductivity of the final product increases the reaction front velocity; (2) effect of heat convection losses on reaction characteristics is insignificant, e.g., the foils can maintain their characteristics in water; and (3) with increasing initial temperature of the foils, the reaction front velocity and the reaction temperature increased.

Investigation of Hypersonic Conic Flows Generated by Magnetoplasma Light-Gas Gun Equipped With Laval Nozzle

This chapter introduces new approach of hypersonic flow generation and experimental study of hypersonic flows over cones with half- angles τ1 = 3◦ and τ2 = 12◦. Mach number of the of the incident flow was M1 = 18. Visualization of the flow structure was made by the schlieren method. Straight Foucault knife was located in the focal plane of the receiving part of a shadow device. Registration of shadow patterns was carried out using high- speed camera Photron Fastcam (300 000 fps) with an exposure time of 1 μs. The Mach number on the cone was calculated from inclination angle of shock wave in the shadowgraph.

Evaporation of levitating liquid microdroplets over a dry heated surface

The present work is devoted to the study of the evaporation process of micro-sized water droplets levitating over a heated dry substrate. The study of this process is relevant in connection with the development of spray cooling systems. Due to the extreme complexity of this phenomenon the mechanism of spray cooling is still not fully understood. In this work we studied the evaporation of micro-sized water droplets levitating over a dry substrate heated from below. The working area was open to the atmosphere. Evaporation was studied in the temperature substrate range from 23 to 95°C. During the experiment local values of the substrate temperature and geometric characteristics of the drop were determined. In the experiment a shadow method with high spatial resolution was used, shooting was performed with a high-speed camera.