Large Jet Research Articles

A Physical Model Study of Two-Phase Gas–Liquid Flows in a Ladle Shroud

Argon-steel flows inside a ladle shroud during teeming from a ladle to a tundish have been modelled physically. To this end, full-scale Perspex models of bloom as well as slab casting shrouds (BCS and SCS), operating with air and water, have been applied. Both open to air as well as immersed conditions were investigated with and without gas injection. Flows inside a ladle shroud under open to air and immersed conditions were found to be substantially different with a strong function of gas and liquid flow rates, collector nozzle and shroud diameters. Depending on the volumetric gas injection rate relative to liquid flow rate, different flow regimes have been observed in an immersed shroud $$ \left[ {i.e.,\,\,0 < \left( {\frac{{d_{\text{s}} }}{{L_{\text{s}} }}} \right) \le 0.24} \right]. $$ At extremely low gas flow rates, $$ \left[ {i.e.,\,\,\left( {\frac{{Q_{\text{g}} }}{{Q_{\text{L}} }}} \right) \le 0.02} \right], $$ injected gas is completely entrained as bubbles by the down-flowing liquid resulting in a bubbly two-phase flow over the entire length of a shroud. However, with an increasing gas flow rate, two distinctly different regions start to develop within the shroud body: a free liquid jet in the upper part and a gas–liquid mixing zone below. The length of the free jet increases with an increasing gas flow rate and at significantly higher gas to liquid flow rates $$ \left[ {viz.,\,\,\left( {\frac{{Q_{\text{g}} }}{{Q_{\text{L}} }}} \right)_{\text{BCS}} \ge 0.42} \right] $$ and $$ \left[ {viz.,\,\,\left( {\frac{{Q_{\text{g}} }}{{Q_{\text{L}} }}} \right)_{\text{SCS}} \ge 0.30} \right] $$ , and the free jet is found to prevail over the entire length of the shroud. Within the range of conditions studied, it is observed that the free jet length or the line of demarcation between the jetting and two-phase mixing zone depends on gas and liquid flow rates and is specific to a particular shroud-collector nozzle system. Physical model results further indicate that a sufficiently large free jet length (~ shroud length) tends to create a high pressure region inside a shroud and prevent ingression of air. Possible implications of the present findings with reference to industrial teeming practices are also discussed in the text.

Probing the B-fields of AGN jets on kiloparsec scales - NGC 6251

AbstractBy constructing images of the Faraday rotation measure (RM) of large scale astrophysical jets, the line-of-sight magnetic field component and electron density in the region of Farady rotation can be investigated. A significant gradient in the RM transverse to the jet direction may indicate a corresponding gradient in the line-of-sight magnetic field, implying a toroidal or helical magnetic field, which would, in turn, imply the presence of an associated electrical current in the jet. The detection of such large scale gradients can reliably demonstrate that helical or toroidal fields can persist to large distances from the central AGN. We present a kiloparsec-scale Faraday rotation map of NGC 6251 that shows statistically significant transverse RM gradients across its kiloparsec scale jet structure that imply an outward current.

The effect of jet speed on large volume jet injection

Jet injection presents a promising alternative to needle and syringe injection for transdermal drug delivery. The controllability of recently-developed jet injection devices now allows jet speed to be modulated during delivery, and has enabled efficient and accurate delivery of volumes up to 0.3 mL. However, recent attempts to inject larger volumes of up to 1 mL using the same methods have highlighted the different requirements for successful delivery at these larger volumes. This study aims to establish the jet speed requirements for delivery of 1 mL of liquid using a controllable, voice coil driven injection device. Additionally, the effectiveness of a two-phase jet speed profile is explored (where jet speed is deliberately decreased toward the end of the injection) and compared to the constant jet speed case.A controllable jet injection device was developed to deliver volumes of 1 mL of liquid at jet speeds >140 m/s. This device was used to deliver a series of injections into post-mortem porcine tissue in single and two-phase jet speed profiles. Single-phase injections were performed over the range 80 m/s to 140 m/s. Consistent delivery success (>80% of the liquid delivered) was observed at a jet speed of 130 m/s or greater. Consistent penetration into the muscle layer coincided with delivery success. Two-phase injections of 1 mL were performed with a first phase volume of 0.15 mL, delivered at 140 m/s, while the injection of the remainder of fluid was delivered at a second phase speed that was varied over the range 60 m/s to 120 m/s. Ten two-phase injections were performed with a second phase speed of 100 m/s producing a mean delivery volume of 0.8 mL ± 0.2 mL, while the single-phase injections at 100 m/s achieved a mean delivery volume of 0.4 mL ± 0.3 mL. These results demonstrate that a reduced jet speed can be used in the later stages of a 1 mL injection to achieve delivery success at a reduced energy cost. We found that a jet speed approaching 100 m/s was required following initial penetration to successfully deliver 1 mL, whereas speeds as low as 50 m/s have been used for volumes of <0.3 mL. These findings provide valuable insight into the effect of injection volume and speed on delivery success; this information is particularly useful for devices that have the ability to vary jet speed during drug delivery.

Affordable Uncertainty Quantification for Industrial Problems: Application to Aero-Engine Fans

Uncertainty quantification (UQ) is an increasingly important area of research. As components and systems become more efficient and optimized, the impact of uncertain parameters is likely to become critical. It is fundamental to consider the impact of these uncertainties as early as possible during the design process, with the aim of producing more robust designs (less sensitive to the presence of uncertainties). The cost of UQ with high-fidelity simulations becomes therefore of fundamental importance. This work makes use of least-squares approximations in the context of appropriately selected polynomial chaos (PC) bases. An efficient technique based on QR column pivoting has been employed to reduce the number of evaluations required to construct the approximation, demonstrating the superiority of the method with respect to full-tensor quadrature (FTQ) and sparse-grid quadrature (SGQ). Orthonormal polynomials used for the PC expansion are calculated numerically based on the given uncertainty distribution, making the approach optimal for any type of input uncertainty. The approach is used to quantify the variability in the performance of two large bypass-ratio jet engine fans in the presence of shape uncertainty due to possible manufacturing processes. The impacts of shape uncertainty on the two geometries are compared, and sensitivities to the location of the blade shape variability are extracted. The mechanisms at the origin of the change in performance are analyzed in detail, as well as the differences between the two configurations.

Constraints on particle acceleration in SS433/W50 from MAGIC and H.E.S.S. observations

Context. The large jet kinetic power and non-thermal processes occurring in the microquasar SS 433 make this source a good candidate for a very high-energy (VHE) gamma-ray emitter. Gamma-ray fluxes above the sensitivity limits of current Cherenkov telescopes have been predicted for both the central X-ray binary system and the interaction regions of SS 433 jets with the surrounding W50 nebula. Non-thermal emission at lower energies has been previously reported, indicating that efficient particle acceleration is taking place in the system.Aim. We explore the capability of SS 433 to emit VHE gamma rays during periods in which the expected flux attenuation due to periodic eclipses (Porb~ 13.1 days) and precession of the circumstellar disk (Ppre ~ 162 days) periodically covering the central binary system is expected to be at its minimum. The eastern and western SS 433/W50 interaction regions are also examined using the whole data set available. We aim to constrain some theoretical models previously developed for this system with our observations.Methods. We made use of dedicated observations from the Major Atmospheric Gamma Imaging Cherenkov telescopes (MAGIC) and High Energy Spectroscopic System (H.E.S.S.) of SS 433 taken from 2006 to 2011. These observation were combined for the first time and accounted for a total effective observation time of 16.5 h, which were scheduled considering the expected phases of minimum absorption of the putative VHE emission. Gamma-ray attenuation does not affect the jet/medium interaction regions. In this case, the analysis of a larger data set amounting to ~40–80 h, depending on the region, was employed.Results. No evidence of VHE gamma-ray emission either from the central binary system or from the eastern/western interaction regions was found. Upper limits were computed for the combined data set. Differential fluxes from the central system are found to be ≲ 10−12–10−13 TeV−1 cm−2 s−1 in an energy interval ranging from ~few × 100 GeV to ~few TeV. Integral flux limits down to ~ 10−12–10−13 ph cm−2 s−1 and ~ 10−13–10−14 ph cm−2 s−1 are obtainedat 300 and 800 GeV, respectively. Our results are used to place constraints on the particle acceleration fraction at the inner jetregions and on the physics of the jet/medium interactions.Conclusions. Our findings suggest that the fraction of the jet kinetic power that is transferred to relativistic protons must be relatively small in SS 433, qp ≤ 2.5 × 10−5, to explain the lack of TeV and neutrino emission from the central system. At the SS 433/W50 interface, the presence of magnetic fields ≳10 μG is derived assuming a synchrotron origin for the observed X-ray emission. This also implies the presence of high-energy electrons with Ee− up to 50 TeV, preventing an efficient production of gamma-ray fluxes in these interaction regions.

Heat flux measurements from a human forearm under natural convection and isothermal jets

Heat transfer from a human forearm to a large jet, representative of a building HVAC vent/outlet was studied using both an IR camera and a heat flux sensor. The isothermal jet was discharged horizontally from a wind tunnel, at the same temperature as the ambient air. A model cylinder was used to validate the heat transfer results with results from previous studies, using both an IR camera and heat flux sensors. The same jet was used for studies from a human forearm at various Reynolds numbers (Re = 9500–41,000) and impinging distances of four and eight jet diameters The results were compared with heat transfer due to natural convection under both open and controlled environments. A significant increase in convection heat transfer with Reynolds number and distance from the jet outlet was observed. A nearly fourfold increase in convection heat transfer coefficient was obtained when a jet with Reynolds number of 9500 was impinged on a human arm when compared to that obtained under natural convection in an open environment. Empirical correlations for predicting the stagnation and average Nusselt number from a human arm were also developed with high values of correlation coefficients for future studies. Overall, impingement jets were found to be an effective means to transfer heat from human bodies and could potentially be used for creating thermally conditioned microenvironments.

Adaptive predictors based on probabilistic SVM for real time disruption mitigation on JET

Detecting disruptions with sufficient anticipation time is essential to undertake any form of remedial strategy, mitigation or avoidance. Traditional predictors based on machine learning techniques can be very performing, if properly optimised, but do not provide a natural estimate of the quality of their outputs and they typically age very quickly. In this paper a new set of tools, based on probabilistic extensions of support vector machines (SVM), are introduced and applied for the first time to JET data. The probabilistic output constitutes a natural qualification of the prediction quality and provides additional flexibility. An adaptive training strategy ‘from scratch’ has also been devised, which allows preserving the performance even when the experimental conditions change significantly. Large JET databases of disruptions, covering entire campaigns and thousands of discharges, have been analysed, both for the case of the graphite and the ITER Like Wall. Performance significantly better than any previous predictor using adaptive training has been achieved, satisfying even the requirements of the next generation of devices. The adaptive approach to the training has also provided unique information about the evolution of the operational space. The fact that the developed tools give the probability of disruption improves the interpretability of the results, provides an estimate of the predictor quality and gives new insights into the physics. Moreover, the probabilistic treatment permits to insert more easily these classifiers into general decision support and control systems.

Magnetic Reconnection at a Thin Current Sheet Separating Two Interlaced Flux Tubes at the Earth's Magnetopause

AbstractThe occurrence of spatially and temporally variable reconnection at the Earth's magnetopause leads to the complex interaction of magnetic fields from the magnetosphere and magnetosheath. Flux transfer events (FTEs) constitute one such type of interaction. Their main characteristics are (1) an enhanced core magnetic field magnitude and (2) a bipolar magnetic field signature in the component normal to the magnetopause, reminiscent of a large‐scale helicoidal flux tube magnetic configuration. However, other geometrical configurations which do not fit this classical picture have also been observed. Using high‐resolution measurements from the Magnetospheric Multiscale mission, we investigate an event in the vicinity of the Earth's magnetopause on 7 November 2015. Despite signatures that, at first glance, appear consistent with a classic FTE, based on detailed geometrical and dynamical analyses as well as on topological signatures revealed by suprathermal electron properties, we demonstrate that this event is not consistent with a single, homogenous helicoidal structure. Our analysis rather suggests that it consists of the interaction of two separate sets of magnetic field lines with different connectivities. This complex three‐dimensional interaction constructively conspires to produce signatures partially consistent with that of an FTE. We also show that, at the interface between the two sets of field lines, where the observed magnetic pileup occurs, a thin and strong current sheet forms with a large ion jet, which may be consistent with magnetic flux dissipation through magnetic reconnection in the interaction region.

Inclusive Search for a Highly Boosted Higgs Boson Decaying to a Bottom Quark-Antiquark Pair.

An inclusive search for the standard model Higgs boson (H) produced with large transverse momentum (p_{T}) and decaying to a bottom quark-antiquark pair (bb[over ¯]) is performed using a data set of pp collisions at sqrt[s]=13 TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb^{-1}. A highly Lorentz-boosted Higgs boson decaying to bb[over ¯] is reconstructed as a single, large radius jet, and it is identified using jet substructure and dedicated b tagging techniques. The method is validated with Z→bb[over ¯] decays. The Z→bb[over ¯] process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of H→bb[over ¯] with reconstructed p_{T}>450 GeV and in the pseudorapidity range -2.5<η<2.5 is 74±48(stat)_{-10}^{+17}(syst) fb, which is consistent within uncertainties with the standard model prediction.

Ionized-gas Kinematics Along the Large-scale Radio Jets in Type-2 AGNs

Abstract To investigate the connection between radioactivity and active galactic nucleus (AGN) outflows, we present a study of ionized-gas kinematics based on an [O iii] λ5007 emission line along the large-scale radio jet for six radio AGNs. These AGNs are selected based on the radioactivity (i.e., ) as well as optical emission-line properties as type-2 AGNs. Using the Red Channel Cross Dispersed Echellette Spectrograph at the Multiple Mirror Telescope, we investigate in detail the [[O iii]] and stellar kinematics. We spatially resolve and probe the central AGN-photoionization sizes, which is important in understanding the structures and evolutions of galaxies. We find that the typical central AGN-photoionization radius of our targets are in range of 0.9–1.6 kpc, consistent with the size–luminosity relation of [O iii] in previous studies. We investigate the [O iii] kinematics along the large-scale radio jets to test whether there is a link between gas outflows in the narrow-line region and extended radio-jet emissions. Contrary to our expectation, we find no evidence that the gas outflows are directly connected to the large-scale radio jets.

Search for new phenomena with large jet multiplicities and missing transverse momentum using large-radius jets and flavour-tagging at ATLAS in 13 TeV pp collisions

A search is presented for particles that decay producing a large jet multiplicity and invisible particles. The event selection applies a veto on the presence of isolated electrons or muons and additional requirements on the number of b-tagged jets and the scalar sum of masses of large-radius jets. Having explored the full ATLAS 2015-2016 dataset of LHC proton-proton collisions at sqrt{s}=13 TeV, which corresponds to 36.1 fb−1 of integrated luminosity, no evidence is found for physics beyond the Standard Model. The results are interpreted in the context of simplified models inspired by R-parity-conserving and R-parity-violating supersymmetry, where gluinos are pair-produced. More generic models within the phenomenological minimal supersymmetric Standard Model are also considered.

Characterizing dynamic behavior of carbon dioxide nano-jets using molecular dynamics simulation

This paper reports on the use of molecular dynamics (MD) simulations to elucidate the dynamic behavior of CO2 through a Graphene/Au(111) nano-injector. We investigated the effects of jet diameter (d), system temperature (T), and the extrusion velocity (v) of a graphite piston plate on the jet pattern, system pressure (P), and the number of molecules (Nm) in the outflow. Simulation results show that the combined effects of high v and small d induced a larger jet angle, resulting in an increase in the number of CO2 molecules attached to the surface of the outlet. Increasing d enhanced the formation of the T-junction molecular geometry of CO2 molecules, due to the effects of electrostatic attraction between C (0.5888e) and O (− 0.2944e) of CO2, which caused the formation of larger agglomerations of CO2 molecules in the vicinity of the nano-injector orifice in the final extrusion stage. The increase in P within the cylinder of the nano-injector was more pronounced during middle and final stages of extrusion, compared with the effects observed during the initial stages. Despite the fact that Nm increased noticeably with an increase in T, the value of Nm at d = 1.5 nm and T ≥ 300 K greatly exceeded that at d = 1.0 nm and T = 500 K, regardless of the value of v. The numerical simulations presented in this study could be helpful in the design of nano-injectors for a diversity of applications associated with engineering systems and biomedicine at the nano-scale.

Extended proper orthogonal decomposition of non-homogeneous thermal fields in a turbulent pipe flow

This manuscript analyzes the role of coherent structures in turbulent thermal transport in pipe flows. A Proper Orthogonal Decomposition (POD) analysis is performed on a direct numerical simulation dataset with non-homogeneous boundary conditions, heated on the upper side, representative of solar receivers (Antoranz et al., 2015, Int. J. Heat Fluid Flow, 55). Three flow conditions are analyzed: with friction Reynolds number equal to 180 and Prandtl number equal to 0.7 and 4 and with friction Reynolds number equal to 360 and Prandtl number equal to 0.7. Both POD and extended POD modes are presented and compared. This allows to visualize the main flow modes in terms of both turbulent kinetic energy and temperature fluctuations, analyzing their contribution to the turbulent transport of heat. The POD analysis shows that the temperature fluctuations are described by a more compact modal subspace than the turbulent kinetic energy. The effect of increasing the Reynolds number is to produce a thinner boundary layer, with a slightly less compact representation of both kinetic energy and temperature fluctuations. The increase of the Prandtl number, instead, results in a thinner thermal boundary layer with a greater scale separation between thermal fluctuations and kinetic energy. Temperature POD modes together with velocity extended POD modes are used to analyze and quantify the mode contribution to turbulent thermal transport. Results show that the correlation between velocity and temperature is such that it is possible to describe roughly 100% of the turbulent heat transport and temperature fluctuations with only 40% of the kinetic energy. For the cases with Pr=0.7, the first extended POD mode is a large vertical jet flanked by a pair of counter-rotating vortices near the heated part of the pipe. This single structure accounts for up to 10% of the turbulent heat transport.

Investigation on film cooling with swirling coolant flow by optimizing the inflow chamber

Three different kinds of coolant chamber configuration for film cooling are proposed to develop the swirling coolant flow at blowing ratios ranging from 0.5 to 2.0. The results show that the difference of film cooling effectiveness for three kinds of coolant chamber configuration is little at low blowing ratio, but the advantage of swirling film cooling becomes obviously with the increase of blowing ratio. When the blowing ratio is 2.0, the jet momentum of original coolant chamber configuration is large and uniform, which leads to the lowest cooling effectiveness due to the formation of a strong kidney vortex. The first coolant chamber configuration has a low jet momentum region at upstream of the film hole, the coolant in this region interacts with high temperature mainstream and bypasses the large jet momentum coolant to attach cooling surface at downstream. The second coolant chamber configuration is sprayed with the structure of unidirectional vortex, which forms a vortex pressing on other vortex, making the coolant in pressed vortex attach surface better, producing the best coverage and the higher film cooling effectiveness.

Design of Stable Nonlinear Pitch Control System for a Jet Aircraft by Using Artificial Intelligence

The principal objective of this paper is to present the design of a Swarm Optimized Proportional Integral Derivative controller to obtain the desired pitch angle for a nonlinear pitch control system of a Delta Aircraft (four engine very large cargo jet aircraft). The Bacterial Foraging Optimization technique is applied to optimize the PID controller. A fine-tuned Particle Swarm Optimization PID (PSOPID) controller and a Radial basis function neural controller (RBFNC) for flight control system are designed to compare and establish the superiority of our proposed system. It is established that Bacterial Foraging Optimized PID controller provides better performance in comparison to RBFNC and PSOPID controller in terms of early settling time and overshoot. Finally, it was established that the designed controller along with the Flight control system is robust stable with the help of Kharitonov Stability Criterion.

Role of tumbling in bacterial swarming.

Typical wild-type bacteria swimming in sparse suspensions exhibit a movement pattern called "run and tumble," characterized by straight trajectories (runs) interspersed by shorter, random reorientation (tumbles). This is achieved by rotating their flagella counterclockwise, or clockwise, respectively. The chemotaxis signaling network operates in controlling the frequency of tumbles, enabling navigation toward or away from desired regions in the medium. In contrast, while in dense populations, flagellated bacteria exhibit collective motion and form large dynamic clusters, whirls, and jets, with intricate dynamics that is fundamentally different than trajectories of sparsely swimming cells. Although collectively swarming cells do change direction at the level of the individual cell, often exhibiting reversals, it has been suggested that chemotaxis does not play a role in multicellular colony expansion, but the change in direction stems from clockwise flagellar rotation. In this paper, the effects of cell rotor switching (i.e., the ability to tumble) and chemotaxis on the collective statistics of swarming bacteria are studied experimentally in wild-type Bacillus subtilis and two mutants-one that does not tumble and one that tumbles independently of the chemotaxis system. We show that while several of the parameters examined are similar between the strains, other collective and individual characteristics are significantly different. The results demonstrate that tumbling and/or flagellar directional rotor switching has an important role on the dynamics of swarming, and imply that swarming models of self-propelled rods that do not take tumbling and/or rotor switching into account may be oversimplified.

The characteristic analysis of high-pressure gas jets for natural gas engine based on shock wave structure

High gas injection pressure leads to the formation of under-expanded gas jet at nozzle exit. The shock wave structure near the nozzle affects gas jet injection and mixing characteristics, which affects the combustion and emission performance of the engine. Gas jet injection process and shock wave structure evolution law under different nozzle pressure ratio (NPR) and orifice diameter have been investigated with the application of Schlieren imaging and numerical simulation. Results show that long injection duration exists in gas injection process after the end of injection. It is attributed to the slow pressure reduction velocity in the nozzle. This phenomenon is one of the key factors which influence the high HC emission of gas fuel port injection natural gas engines. The change of pressure inside the nozzle also affects the shock wave structure (Mach disk) near the nozzle. It is found that the increase of Mach disk width leads to a large jet near-field angle which promotes the spatial distribution and turbulent mixing of gas jet. In addition to experimental results, numerical simulation is used to analyze the injection characteristics of gas injection system. Increasing gas nozzle flow area and shortening gas nozzle length are regarded as effective ways to improve the responsiveness of gas injection system and reduce gas injection duration. The range of Reynolds number at exit of the nozzle is 0.5–2.5×105 under various gas injection pressures and orifice diameters. This presents that gas jet is easily influenced by air turbulence in intake manifold. Strong air turbulence in intake manifold is needed in a gas fuel port injection natural gas engine in order to obtain homogeneous gas/air mixture.

Searches for Exotic Physics in ATLAS using Substructure Techniques

The significant increase of the centre-of-mass energy of the Large Hadron Collider (LHC) from 8 to 13 TeV has allowed the LHC experiments to explore previously inaccessible kinematic regimes in their search for phenomena beyond the Standard Model. The sensitivity of these searches depends crucially on the efficient reconstruction and identification of hadronic decays of highly energetic (boosted) objects, the decay products of which are typically collimated into a single large jet with a characteristic substructure. In this contribution, the searches conducted by the ATLAS experiment on data recorded during 2015 and 2016 that rely on jet substructure techniques to identify signatures of interest are reviewed. A particular emphasis is placed on recent developments in the rapidly evolving field of boosted object tagging.

H2S nano-jetting through a p–n junction-like graphene/Au nano-injector: a molecular dynamics study

This paper uses fully atomistic molecular dynamics to outline the dynamics of H2S nano-jetting through a p–n junction-like graphene/Au nano-injector. We examined the effects of nano-injector diameter (d), system temperature (T), and the extrusion velocity (v) of a graphite piston plate on the formation of H2S nano-jets, system pressure, and the number of molecules (N m) in the outflow. The combined effects of high critical pressure and small orifice resulted in a larger jet angle, which increased the number of H2S molecules stuck to the graphene surface at the outlet. Moving the graphite piston plate toward the orifice of the nano-injector increased in the change in momentum and interactive forces between H2S molecules, resulting in three phases of pressure establishment in the nano-injector: incubation (phase I), steep pressure increase (phase II), and high pressure (phase III). When operated at T ≥ 300 K and v < 27.912 m/s, the proposed nano-jet device is able to produce a well-dispersed spray of H2S without H2S molecules sticking to the graphene surface at the outlet. The p–n junction-like Au-doped graphene surface provides an additional energy barrier preventing the transport of electrons from H2S molecule to the graphene. This inhibits the accumulation of H2S molecules and subsequent blockages at the exit of the nano-injector. Simulation results demonstrate the potential of using chemiresistive sensing to monitor H2S flow patterns during nano-jetting. The findings presented in this study could be transformative to the design of nano-injectors for other gases commonly used as biomarkers.

Asymmetric frequency dependence of plasma jet formation in resonator electrode

Large aspect ratio plasma jets with sub-mm diameter are produced by a microwave coaxial resonator electrode. The jet length shows a sharp asymmetric dependence on the drive frequency: the plasma jet suddenly turns off below a critical frequency while the jet length slowly decreases above the frequency. A general mechanism is proposed to explain the asymmetry based on a universal feedback relation among the plasma impedance, the power coupling efficiency and the plasma dimension in resonator type electrodes. The input impedance of the resonator electrode changes depending on the plasma size formed in the electrode. The degree of the impedance mismatch between the electrode-plasma and the power source determines the power coupling efficiency and the resistive loss in the electrode which in turn affects the plasma size. The asymmetric dependence on the drive frequency is a consequence of the fact that the resonance frequency decreases for increasing plasma size. The feedback model shows a good agreement with the experimental measurements, providing essential information for the plasma control.