Breakdown Zone Research Articles

Effect of the anti-Alzheimer drug GSK-3β antagonist on numerical modeling of the energy dissipation through the resin-dentin interface

ObjectivesThe aim of this study was to determine the viscoelastic performance and energy dissipation of conditioned dentin infiltrated with polymeric nanoparticles (NPs) doped with tideglusib (TDg) (TDg-NPs). MethodsDentin conditioned surfaces were infiltrated with NPs and TDg-NPs. Bonded interfaces were created, stored for 24 h and submitted to mechanical and thermal challenging. Resin-dentin interfaces were evaluated through nano-DMA/complex-loss-storage moduli-tan delta assessment and atomic force microscopy (AFM) analysis. ResultsDentin infiltrated with NPs and load cycled attained the highest complex modulus at hybrid layer and bottom of hybrid layer. Intertubular dentin treated with undoped NPs showed higher complex modulus than peritubular dentin, after load cycling, provoking energy concentration and breakdown at the interface. After infiltrating with TDg-NPs, complex modulus was similar between peri-intertubular dentin and energy dissipated homogeneously. Tan delta at intertubular dentin was higher than at peritubular dentin, after using TDg-NPs and load cycling. This generated the widest bandwidth of the collagen fibrils and bridge-like mineral structures that, as sight of energy dissipation, fastened active dentin remodeling. TDg-NPs inducted scarce mineralization after thermo-cycling, but these bridging processes limited breakdown zones at the interface. SignificanceTDg-based NPs are then proposed for effective dentin remineralization and tubular seal, from a viscoelastic approach.

A hydrous sub-arc mantle domain within the northeastern Neo-Tethyan ophiolites: Insights from cumulate hornblendites

Being a part of the large-scale Indus-Tsangpo suture zone ophiolites of the Alpine-Himalayan orogenic system, the Neo-Tethyan ophiolites of eastern Arunachal Himalaya, northeast India, are important in understanding the formation and evolution of the Neo-Tethyan lithosphere. This study focuses on the hornblendite dykes occurring within serpentinized peridotites of the Mayodia ophiolites in eastern Arunachal Himalaya, to ascertain the origin and evolution of such hydrous mineral cumulates within the ophiolite complex. Texturally and chemically, the hornblendites contain three types of amphiboles, Amp1 (pargasite), Amp2 (Mg-hornblende), and Amp3 (actinolite). The pargasites occur as large cm-sized phenocrysts and show cumulate textures while Mg-hornblende appears as both intercumulus grains between cumulus pargasites and surrounding partially resorbed clinopyroxene grains. Actinolite occurs along the breakdown zone of pargasite and is associated with other secondary minerals. The hornblendites are characterized by high MgO (~12–20 wt%) and low SiO2 (~42–44 wt%) with depleted light rare earth elements (REE) [(La/Sm)N = 0.29–0.52] and almost flat heavy REE [(Gd/Yb)N) = 0.89–1.11]. Moreover, the samples are characteristically depleted in high field strength elements (Nb, Ta, Ti, Hf) while being enriched in Pb. Geothermobarometric calculations yield high magmatic temperatures of ~950 and ~840 °C for pargasite and Mg-hornblende, respectively, and variable pressures with pargasite having the highest pressures (1.6–1.7 GPa) followed by Mg-hornblende (1.1–1.2 GPa) and finally actinolite (~0.55 GPa). Furthermore, fO2 calculations for the cumulus pargasites revealed highly oxidizing conditions (ΔNNO+2) and water content of parental melts (H2Omelt% = ~14.25 %). Parental melt calculations using whole-rock REE concentrations suggest formation from a hydrous sub-alkaline basaltic melt. Whole-rock initial SrNd isotopic ratios of the hornblendites reveal a primary signature for them, falling in the mantle array in proximity to the high-μ (HIMU) mantle reservoir. All these signatures point towards a magmatic arc affinity for these hornblendites. The host peridotite unit shows highly enriched REE concentrations (ƩREE = 18.13 ppm) with flat REE patterns compared to the other peridotites of the locality, which show depleted signatures. Olivine chemistry of the host peridotite unit depicts primary compositions falling in the mantle array. The olivine-liquid thermometer yields temperatures ~1000 °C, which are much lower than those of peridotites occurring in spreading centers (MOR or back-arc). These evidence suggest that the hornblendites and their host peridotite unit represent an island arc root complex, which further imply the hydrous nature of the Neo-Tethyan sub-arc mantle.

Диагностика электротехнических компонентов гидротехнического оборудования: эффективность комплексного подхода

Diagnostics of electrical components of hydrotechnical equipment used in agricultural production within the planned maintenance intervals with continuous analysis of residual resource is useful for reducing equipment operation costs. The use of inexpensive universal diagnostic equipment in conjunction with primary analysis of the state of units makes it possible to detect 60 to 80% of pre-failure states. To ensure efficient application of complex approach to primary diagnostics of electrical components of hydraulic equipment used in agricultural production, the authors considered the most common electric motors of pumping units, electrohydraulic distributors and switching equipment. Complex diagnostics included the use of a thermal imager, vibration signal processing systems and current signal control systems. The vibrograms of equipment control points were analyzed, the state of bearing units, cavitation characteristics of pumps were assessed by methods of acoustic and vibration diagnostics, hydraulic equipment leaks were searched, power cables breakdown zones were detected in accordance with methodical instructions for determining the breakdowns of power cables with voltage up to 10 kV RD34.20.516‑90. The article shows the possibilities of applying the diagnostics methodology based on surface thermograms to determine typical defects. Particularly discussed are the parameters of current signals from the electromagnet coils observed in case of distribution equipment malfunction. The authors give comparative evaluation of diagnostics methods with calculated efficiency determination. It is established that the method of combined diagnostics using the analysis of external thermal fields can halve the time of preliminary diagnostics of faults with a stable forecast of the failure time 2‑3 months before the critical state. This reduces the costs for detection of unit failures and simplifies the planning of maintenance procedures.

The device for monitoring the insulation breakdown zone of power cable lines in distribution networks with isolated neutral system during high-voltage diagnostic

The article considers an electrical device designed for diagnostic work in distribution networks of 6-10 kV, namely, the determination of damage zones in case of failure of insulating materials of cable lines during high-voltage diagnostics with a rectified voltage of negative polarity. The novelty of the developed device is its ability to connect directly to a high-voltage cable line without additional matching devices. The device is capable of detecting damage zones in lines up to 10 km remotely with an error of up to 0.2% of the cable length. The prefix allows you to fix any variants of damage to single-phase and three-phase cable lines with high transient resistance at the site of damage without the operation of “burning” insulation, which significantly reduces the time of repair work at the controlled facility.

The effects of match circuit on the breakdown process of capacitively coupled plasma driven by radio frequency

The breakdown process of capacitively coupled plasma (CCP) in the presence of a matching network is rarely studied, even though it is the indispensable part of the most laboratory and industrial devices of CCP. Based on the method of Verboncoeur, the solution method of the general “L”-type match circuit coupled with a particle-in-cell/Monte Carlo code is deduced self-consistently. Based on this method, the electrical breakdown process of CCP is studied. Both the plasma parameters and the electric parameters of the matching network during the breakdown are given and analyzed. In the pre-breakdown phase, the entire circuit can be considered as a linear system. However, the formation of the sheath during breakdown significantly enhanced the capacitance of the discharge chamber, which changed the electric signal amplitude of the external circuit. With the stabilization of plasma, the equivalent capacitance of CCP increases, which continues to change the electrical signal until the steady-state is reached. Accompanied by plasma stabilization is the appearance of high-order harmonics of discharge current caused by the gradually oscillating CCP capacitance. The breakdown characteristics can be obviously affected by the capacitance of the matching network. In the case of a breakdown zone, some breakdowns with special characteristics can be obtained by choosing the different capacitors. These works might be a reference for understanding the interaction between the plasma and the external circuit during the breakdown process and how to modulate the gas breakdown by controlling the external circuit.

Stability of an Electrically Conducting Fluid Flow between Coaxial Cylinders under Magnetic field

This research aims to investigate the vortex breakdown zone, the stability margin, and the fluid layers of the rotating flow between two vertical coaxial cylinders under the effect of thermal gradient and an axial magnetic field. The governing Navier-Stokes, temperature, and potential equations are solved using the finite-volume method. Three combinations of aspect ratios (γ) and Reynolds numbers (Re) are compared. The pumping action sets up a secondary circulation along the meridional plane of the annular gap. For certain combinations, the vortex breakdown bubble occurred near the inner wall. Bifurcation in form of multiple fluid layers becomes apparent when the temperature difference exceeds a critical value. These fluid layers play the role of thermal insulation and limit the heat transfer between the hot top and cold bottom of the coaxial cylinders. Both the vortex breakdown and fluid layers could be suppressed by the magnetic field; the increasing of Hartmann number (Ha) would reduce the number of fluid layers. Diagrams represent the effect of increasing Richardson number (Ri) on fluid layers are established. Then stability diagrams corresponding to the transition from the multiple fluid layers zone to the one fluid layer zone for increasing Prandtl number (Pr) are obtained.

Subnanosecond breakdown of air-insulated coaxial line initiated by runaway electrons in the presence of a strong axial magnetic field

Flow of runaway electrons (RAEs) propagating in a radial, air-filled gap of coaxial line (CL) changes the dynamics of breakdown in the field of traveling voltage pulse. However, despite the effect of RAEs, breakdown does not occur if subnanosecond pulse is less in duration and amplitude than some values. In this work, we study the influence of an external axial magnetic field (B z) on the breakdown development. We demonstrate the transformation of the voltage pulse reflection from the ionized (breakdown) zone with changing B z. Due to gyration of fast electrons in an applied magnetic field, the gas region ionized by RAEs does not reach the anode. The ionized bridge between the cathode and anode is gradually replaced by a near-cathode plasma layer representing a discrete, reflecting/absorbing inhomogeneity in the CL.

Characteristics of Stress Drop and Energy Budget from Extended Slip-Weakening Model and Scaling Relationships

The extended slip-weakening model was investigated by using a compiled set of source-spectrum-related parameters, i.e. seismic moment Mo, S-wave velocity Vs, corner-frequency fc, and source-controlled high-cut frequency fmax, for 113 shallow crustal earthquakes (focal depth less than 25 km, MW 3.0~7.5) that occurred in Japan from 1987 to 2016. The investigation was focused on the characteristics of stress drop, radiation energy-to-seismic moment ratio, radiation efficiency, and fracture energy release rate, Gc. The scaling relationships of those source parameters were also investigated and compared with those in previous studies, which were based on generally used singular models with the dimensionless numbers corresponding to fc given by Brune and Madariaga. The results showed that the stress drop from the singular model with Madariaga’s dimensionless number was equivalent to the breakdown stress drop, as well as Brune’s effective stress, rather than to static stress drop as has been usually assumed. The scale dependence of stress drop showed a different tendency in accordance with the size category of the earthquakes, which may be divided into small-moderate earthquakes and moderate-large earthquakes by comparing to Mo = 1017~1018 Nm. The scale dependence was quite similar to that shown by Kanamori and Rivera. The scale dependence was not because of a poor dynamic range of recorded signals or missing data as asserted by Ide and Beroza, but rather it was because of the scale dependent Vr-induced local similarity of spectrum as shown in a previous study by the authors. The energy release rate Gc with respect to breakdown distance Dc from the extended slip-weakening model coincided with that given by Ellsworth and Beroza in a study on the rupture nucleation phase; and the empirical relationship given by Abercrombie and Rice can represent the results from the extended slip-weakening model, the results from laboratory stick-slip experiments by Ohnaka, and the results given by Ellsworth and Beroza simultaneously. Also the energy flux into the breakdown zone was well correlated with the breakdown stress drop,   and peak slip velocity of the fault faces. Consequently, the investigation results indicate the appropriateness of the extended slip-weakening model.

Extended Slip-Weakening Model and Inference of Rupture Velocity

The slip-weakening model developed by Ohnaka and Yamashita is extended over the breakdown zone by equating the scaling relationships for the breakdown zone and the whole rupture area. For the extension, the study uses the relationship between rupture velocity and radiation efficiency, which was derived in the theory of linear elastic fracture mechanics, and the definition of fmax given in the specific barrier model proposed by Papageorgiou and Aki. The results clearly show that the extended scaling relationship is governed by the ratio of rupture velocity to S wave velocity, and the velocity ratio can be determined by the ratio of characteristic frequencies of a Fourier amplitude spectrum, which are corner frequency, fc, and source-controlled cut-off frequency, fmax, or vice versa. The derived relationship is tested by using the characteristic frequencies extracted from previous studies of more than 130 shallow crustal events (focal depth less than 25 km, MW 3.0~7.5) that occurred in Japan. Under the assumption of a dynamic similarity, the rupture velocity estimated from fmax/fc and the modified integral timescale give quite similar scale-dependence of the rupture area to that given by Kanamori and Anderson. Also, the results for large earthquakes show good agreement to the values from a kinematic inversion in previous studies. The test results also indicate the unavailability of the spectral self-similarity proposed by Aki because of the scale-dependent rupture velocity and the rupture velocity-dependent fmax/fc; however, the results do support the local similarity asserted by Ohnaka. It is also remarkable that the relationship between the rupture velocity and fmax/fc is quite similar to Kolmogorov’s hypothesis on a similarity in the theory of isotropic turbulence.

Experimental investigation of the dynamic behavior of railway track with sleeper voids

The deterioration of the sleeper support on the ballasted track begins with the accumulation of sleeper voids. The increased dynamic loading in the voided zone and the ballast contact conditions cause the accelerated growth of the settlements in the voided zones, which results in the appearance of local instabilities like ballast breakdown, white spots, subgrade defects, etc. The recent detection and quantification of the sleeper voids with track-side and onboard monitoring can help to avoid or delay the development of local instabilities. The present paper is devoted to the study of the dynamic behavior of railway track with sleeper voids in the ballast breakdown zone. The result of the experimental track-side measurements of rail acceleration and deflection is presented. The analysis shows the existence of the dynamic impact during wheel entry in the voided zone. However, the measured dynamic impact is subjected to the bias of the track-side measurement method. Both the mechanism of the impact and the measurement aspects are explained by using the one-beam model on viscoelastic foundation. The void features in the dynamic behavior are analyzed for the purpose of track-side and onboard monitoring. A practical method of the void parameter quantification is proposed.

Opto-Acoustic Effects by Laser Breakdown of Seawater in an Ultrasonic Field

Studies of the opto-acoustic effects accompanying laser breakdown in water generated by focused laser and ultrasonic radiation are performed. For the first time, the experimental results were obtained showing sharply increasing effects of acoustic emission from the breakdown zone under the combined influence of laser and ultrasonic irradiation. Experiments were performed using the nanosecond pulses of a Nd:YAG laser operating at a wavelength of 532 nm. Acoustic radiation was generated by acoustic focusing systems at various frequencies. It is shown that recording of acoustic emission from the breakdown zone makes it possible to study the thresholds and dynamics of the laser breakdown, which coincide with the high-speed optical methods. The results obtained make it possible to find applications of the acoustic method of diagnostics of laser breakdown and cavitation in opaque environments for which optical methods are not applicable. The effect of the increase in the resolution of the spectral lines of chemical elements in seawater under the action of an ultrasonic field is established. This effect indicates the possibility of development of a combined method of laser–spark spectroscopy using ultrasound, which will make it possible to approach the sensitivity of the precision chemical analysis, and which should be more practical and advanced because it yields a high efficiency and detailed measurements.

Experimental and numerical investigations of double pulse laser energy deposition in air

This study focuses on the laser energy deposition characteristics through single and double pulse at short and long pulse intervals in quiescent air, both experimentally and numerically. A frequency-doubled and Q-switched Nd: YAG laser is used to create the spark in the air. High-speed schlieren imaging technique is used to visualize the shock-wave evolution and plasma kernel expansion. To estimate the energy available for ignition, the energy absorbed is measured and the energy loss through the shock-wave is estimated by using Jones blast wave model. Two-dimensional numerical simulations are carried out by solving the Navier-Stokes equations along with the species conservation equations in finite volume framework. After cessation of the laser pulse, the breakdown zone assumed to consists of seven species (O2, O, N2, N, NO, NO+ and e−). For double pulse at short pulse interval, the second pulse absorbed more energy than the first pulse, and the shock loss is relatively higher. The lifetime of plasma is found to have increased by 13.56 % due to the jump in temperature and pressure after the introduction of the second pulse. Same total energy two successive laser pulses at short time interval are found to be a promising alternative of single pulse for lean limit of combustion. The amount of energy left in the kernel for ignition is 16.02 % and 15.78 % of the absorbed energy in 50 + 50 mJ and 100 + 100 mJ double pulse respectively. In case of double laser pulse deposition at long pulse interval, along with multiple layers of shock-wave, a third lobe and a fourth lobe are observed on either side (upstream and downstream) of the plasma kernel enhancing the kernel surface area and mixing process.

ПЕРШІ РЕЗУЛЬТАТИ ІНТЕРПРЕТАЦІЇ ЗА СЕЙСМОТОМОГРАФІЧНИМ ГЕОТРАВЕРСОМ "ВІННИЦЯ – ТАГАНРОГ"

Methodological aspects and results of studying of the stratigraphic section of the upper mantle along the seismic tomographic geotraverse "Vinnytsia – Taganrog" are considered in the article. To localize mantle anomalies associated with changes in the composition, density of the substrate, temperature, etc., an analysis of the curves of the first and second velocity gradients was used to search for the inflection points of the vp curve. A velocity curve was obtained by constructing a seismotomographic model using the Taylor approximation method. Before the curvature analysis, a smoothing procedure was carried out in accordance with the wavelength. This procedure is important for screening false anomalies, the size of which is responsible for Fresnel zones, since the resolution of the seismic wave has the dimension of the Fresnel zones. According to this technique, the curves of the first and second velocity gradients vp were calculated for the upper mantle under the main tectonic structures of the Ukrainian Shield along the "Vinnytsia – Taganrog" geotraverse. The profile crosses the Podol, Bug megablocks, Golovanev suture zone, Ingul megablock, Kryvyy-Rig-Kremenchug suture zone, Middle-Dnipro megablock, Orekhovo-Pavlograd suture zone and Azov megablock. According to the results, the most significant features of the mantle structure were identified in the depth interval of 50–750 km. A transregional tectonic zone was distinguished (between points 30.0E, 49N and 32.0E, 48.25N), over which the Golovan suture zone (GSZ) and the eastern part of the Bug-Ros megablock and the western part of Ingul, where significant violations of the common mantle border of 660 km are observed – a border between the upper and middle mantle. Under the Podol megablock, this border is located at a depth of 550–560 km. Under GSZ it rises to 450–460 km, and to the east of the suture zone it drops sharply to 660-670 km, where it takes a subhorizontal position. A sharp jump to marks of 450–460 km shows the global breakdown zone and the nature of the contact between different geodynamic mantle regions under the modern platform.

A dielectric breakdown model for an electrode along an interface between two piezoelectric materials

A plane strain problem for an interface electrically charged thin electrode in a bimaterial piezoelectric space is considered. Remote in-plane mechanical loading and an electrical field parallel to the electrode faces are applied. The known solution of this problem demonstrates the electromechanical field singularities at the electrode tips. To remove these singularities the dielectric breakdown model is applied. Using the presentations of electromechanical quantities via sectional analytic functions the Riemann-Hilbert problem with discontinuous right side is formulated and solved exactly. The dielectric breakdown zone lengths are found from the electric field finiteness at the end points of these zones. It is shown that this length depends on the external electric field and the electrode net charge. The variations of electromechanical characteristics along the electrode and its continuation are presented in graphical form. Particular cases of an uncharged electrode and homogeneous material are considered and compared with previously obtained results. A verification of the obtained solutions by means of the ABAQUS code is carried out and good agreement of analytical and numerical results is revealed.

Influence of Axial Magnetic Field on Swirling Flow and Vortex Breakdown Zones in a Cylindrical Cavity with a Rotating Lid

In this study, behavior of swirling flow under the influence of axial magnetic field in a cylindrical container with a top rotating disk has been probed. The flow is assumed to be axisymmetric for the parameters considered. The domain consists of a cylindrical cavity packed with viscous and electrically conducting metallic liquid. The qualitative effect of magnetic field is manifested in terms of torque coefficient evaluated on the rotating lid as well as the fixed end wall. Effects of the magnetic field on the zones of vortex breakdown, in the Aspect ratio (AR), Reynolds number (Re) plane, for the top rotating lid with all sides electrically insulated have been developed. Moreover, it is found that one can control the behavior of flow with help of a proper choice of the electric conducting wall.

Spatio-temporal effect of the breakdown zone in the laser-initiated ignition of atomized ethyl alcohol-air mixture

Laser initiated ignition would play a vital role in future gas turbine combustors. Two lasers of 270 μJ and 50 mJ pulse energy are used to study the laser-induced spark ignition of atomized ethyl alcohol-air mixture. With the low-energy pulse of 270 μJ energy, no display of ignition is observed even though it fulfills the threshold conditions to create breakdown. However, with the high-energy pulse of 50 mJ energy, ignition is observed if the plasma kernel was following certain conditions after the occurrence of the breakdown. It is observed that breakdown created by the low-energy pulse was unable to ignite the atomized ethanol-air mixture because the lifetime of the plasma kernel was very small (in microseconds). While performing the study with high-energy pulse, it is observed that the breakdown becomes a sufficient condition for ignition only when the lifetime of the kernel is couple of milliseconds. Additionally, the spatial location of the laser spark is found to play a vital role in successful ignition of the mixture. This work also discusses the spray formation process with its effect on ignition and the role of the third lobe on rapid development of the plasma kernel. The process of laser energy deposition to full scale combustion is categorized into three events. Finally, based on the experimental observations, this work has proposed some favourable conditions for initiating ignition with a laser spark. Knowledge of the proposed conditions can play a vital role for designing a practical laser ignition system.

Origin of High‐Frequency Radiation During Laboratory Earthquakes

AbstractWe monitor dynamic rupture propagation during laboratory stick‐slip experiments performed on saw‐cut Westerly granite under upper crustal conditions (10–90 MPa). Spectral analysis of high‐frequency acoustic waveforms provided evidence that energy radiation is enhanced with stress conditions and rupture velocity. Using acoustic recordings band‐pass filtered to 400–800 kHz (7–14 mm wavelength) and high‐pass filtered above 800 kHz, we back projected high‐frequency energy generated during rupture propagation. Our results show that the high‐frequency radiation originates behind the rupture front during propagation and propagates at a speed close to that obtained by our rupture velocity inversion. From scaling arguments, we suggest that the origin of high‐frequency radiation lies in the fast dynamic stress‐drop in the breakdown zone together with off‐fault coseismic damage propagating behind the rupture tip. The application of the back‐projection method at the laboratory scale provides new ways to locally investigate physical mechanisms that control high‐frequency radiation.

LES of Laser Initiation of Combustion of Gaseous Fuel-Air Mixture

Large Eddy Simulation has been carried out to understand the laser initiation of combustion of lean hydrogen-air mixture in homogeneous isotropic turbulence. Initially, the blast wave from the breakdown zone sweeps out most the mixture surrounding the hot core zone at high velocity preventing formation of burning zone. The combustion initiates only if the core zone contains enough heat to sustain a steady flame thereafter.

Stability boundaries for vortex breakdowns and boundaries between oscillatory and steady swirling flow in a cylindrical annulus with a top rotating lid

The present numerical simulation is carried out to analyze the behaviors of vortex breakdown in a lid-driven swirling flow in cylindrical cavity with a thin axial stationary or rotating rod. The range of aspect ratio (AR) of the cavity considered is to be from 1.0 to 2.5. However, Reynolds number (Re) value, for a given AR, ranges from 1000 to any value till the topmost point on the boundary of steady vortex breakdown zone is achieved. This enclosed flow region is also referred as annulus cylindrical cavity. A systematic study has been carried out involving a large number of simulations to obtain one-vortex or two-vortex breakdown zones for steady lid-driven swirling flow in the annulus cylindrical cavity. Cases within the inner wall, i.e., the axial rod being stationary or rotating, have been considered. It is observed that the boundaries of zones and of vortex breakdowns shift due to the presence of stationary/co-rotating thin axial rod. These zones of vortex breakdowns are represented with plots in AR–Re plane for various rotating speeds of the axial rod. These plots give quick information regarding overall influence of the presence of the thin axial rod. The direction of rotation of the rod is important; the co-rotating rod has stabilizing effects, whereas counter-rotating rod tends to create unsteady flow.

Swirl effect on flow structure and mixing in a turbulent jet

The paper reports on experimental study of turbulent transport in the initial region of swirling turbulent jets. The particle image velocimetry and planar laser-induced fluorescence techniques are used to investigate the flow structure and passive scalar concentration, respectively, in free air jet with acetone vapor. Three flow cases are considered, viz., non-swirling jets and swirling jets with and without vortex breakdown and central recirculation zone. Without vortex breakdown, the swirl is shown to promote jet mixing with surrounding air and to decrease the jet core length. The vortex core breakdown further enhances mixing as the jet core disintegrates at the nozzle exit.