Jet Mode Research Articles

Inferring the star formation histories of massive quiescent galaxies with bagpipes: evidence for multiple quenching mechanisms

We present Bayesian Analysis of Galaxies for Physical Inference and Parameter EStimation, or BAGPIPES, a new Python tool which can be used to rapidly generate complex model galaxy spectra and to fit these to arbitrary combinations of spectroscopic and photometric data using the MultiNest nested sampling algorithm. We extensively test our ability to recover realistic star-formation histories (SFHs) by fitting mock observations of quiescent galaxies from the MUFASA simulation. We then perform a detailed analysis of the SFHs of a sample of 9289 quiescent galaxies from UltraVISTA with stellar masses, $M_* > 10^{10}\ \mathrm{M_\odot}$ and redshifts $0.25 < z < 3.75$. The majority of our sample exhibit SFHs which rise gradually then quench relatively rapidly, over $1{-}2$ Gyr. This behaviour is consistent with recent cosmological hydrodynamic simulations, where AGN-driven feedback in the low-accretion (jet) mode is the dominant quenching mechanism. At $z > 1$ we also find a class of objects with SFHs which rise and fall very rapidly, with quenching timescales of $< 1$ Gyr, consistent with quasar-mode AGN feedback. Finally, at $z < 1$ we find a population with SFHs which quench more slowly than they rise, over $>3$ Gyr, which we speculate to be the result of diminishing overall cosmic gas supply. We confirm the mass-accelerated evolution (downsizing) trend, and a trend towards more rapid quenching at higher stellar masses. However, our results suggest that the latter is a natural consequence of mass-accelerated evolution, rather than a change in quenching physics with stellar mass. We find $61\pm8$ per cent of $z > 1.5$ massive quenched galaxies undergo significant further evolution by $z = 0.5$. BAGPIPES is available at https://bagpipes.readthedocs.io

Jet extraction and characterization in an inertial electrostatic confinement device

Characterization of IEC tight jet mode is achieved through Faraday probe measurements. Preliminary results indicate that the tight jet is a highly energetic electron beam with scattering of secondary ions and electrons, which result from electron beam impact ionization. A novel analytical model is proposed to evaluate this non-Maxwellian plasma beam, including a compensation of the secondary electron emission effect on the probe's surface. The results show prominent features on the extracted jet's kinetic energy and the respective (electron) current of IEC. In addition, they demonstrate a practical method to characterise non-Maxwellian plasma jets through Faraday probes.

Influence of the laser plasma-expansion specific on a cathode jet formation and the current stability in a laser-ignited vacuum discharge

The formation of a current-plasma shell is studied during the expansion of a laser-ignited low-power vacuum-discharge cathode plasma jet into the interelectrode gap. The shell geometry is found to be determined by the mode of laser-plasma expansion at the discharge ignition stage. It is shown that the increase in the laser-beam focal spot area on the cathode surface leads to the increase in the matter density and the decrease in the density gradient in the discharge gap and to transition from the spherical laser-plasma expansion mode to the jet mode. The latter considerably stabilizes the current transfer in the discharge plasma, even during the development of the hydrodynamic sausage instability in it.

Comparison of downstream scour of single and combined free-fall jets in co-axial and non-axial modes

Downstream plunge pools of dams have been exposed to erosion caused by falling jets of the hydraulic structure’s outlets. This damages the foundation and body of the dam and its constituent structures. Therefore, investigating the scouring phenomenon of plunge pools is one of the important issues in hydraulic engineering. The present research investigates the characteristics of scour holes by single jets and combined jets in different operational modes of dam spillway and outlet. Using experimental modeling, 36 experiments were conducted with various discharges and two tail water depths in single and combined jet modes. The results show that combined jet has lower scour depth and hill height than single jets in all conditions. Comparing the depth and length of the hole and hill height caused by scouring reveals that combined jet is approximately between 5 and 10% greater for a co-axial than for non-axial combined jets in all tail water conditions. But the width of the scour hole of the non-axial combined jets is more than the co-axial one. With the aid of dimensional analysis, an equation is proposed for calculating the scouring characteristics of the combined jets, which is a good determination coefficient between calculated and observational data. Also, the dimensionless results show that the length of the scour hole and the length of mound are about one and a half times the position where the maximum scour depth is formed. Thus, a unit non-dimensional curve can be obtained for the longitudinal profile of scour. The results of the study indicate that, given the case of combining jets as non-axial, the depth and length of the scour holes are lower than the single mode, and that downstream scour can be controlled and reduced relative to the co-axial state by combining the non-axial spillway outlet jet with the orifice jet.

LED nanosecond pulsed imaging for electrohydrodynamic liquid breakup of a modified nozzle

The behavior of an electrified liquid jet breakup and modes of disintegration were investigated at different flow rates and voltages. The current phenomenology belongs to a new injector introduced recently by Morad et al. (2016). This injector has proven to highly extend the stability and flow rate of electrospray particularly in the Taylor cone-jet mode. The experimental investigation was performed using a high-power light-emitting diode (LED) illumination as the light source. The light source was developed to operate in the pulsing condition when synchronized with a digital camera and was particularly designed to function properly in the presence of high electromagnetic interference (EMI). The details of the light source development were observed through the images captured from the jet breakup at different modes. Finally, the operational map of the new injector was obtained, and the physical mechanisms of different behaviors were examined.

The mass transfer at Taylor cones

Electrospraying is a highly attractive method for generation of small particles and also for measurement applications of particles in suspensions. In the cone jet mode, the particle generation rate increases with decreasing flow rate. For applications in the field of aerosol technology flow rates of less than 10µl/h are attractive as particle sizes of less than 200nm can be obtained in this flow rate range. At the same time generation frequency of drops reaches the values required for size measurements by Scanning Mobility Particle Sizers (SMPS). A special challenge in operation of electrosprays at small flow rates is the change of liquid composition due to mass transfer processes between the Taylor cone and the surrounding gas phase. Typically used organic solvents such as alcohols, acetone or acetonitrile evaporate fast (or even evaporate completely) and mixtures containing such volatile species will change their composition significantly due to evaporation from the Taylor cone. Based on key experiments we showa)that the evaporating solvent can be reduced by as much as a factor of 20 by controlling the gas phase saturation. This allows spraying volatile solvents such as e.g. methanol at flow rates down to less than 1µl/h and makes the attractive sub-10µl/h flow rate range accessible to quite volatile solvents as well.b)that changes in the liquid composition by not considering the mass transfer (evaporation) problem lead to significant differences in liquid properties between the feed liquid and the Taylor cone. For example, an increase of surface tension by a factor of 2 is observed for water and t-butanol feed liquid.c)that employing a saturated sheath gas flow allows for very effective manipulation of the solvent composition in the Taylor cone. Based on water as feed liquid we show that a sufficient amount of organic solvent is easily transferred to the Taylor cone liquid from the gas phase to allow spraying the water without electron scavenging gases.Measurement results of the Taylor cone liquid composition are in good agreement with predictions by the presented new model describing the mass transfer between the Taylor cone and the surrounding gas phase. The efficiency of the mass transfer, the predictability of the process and the opportunity of comparably quick changes of the Taylor cone liquid by changing the gas phase saturation state result in a powerful tool for the entire field of electrospraying at low rates.

The effect of ethanol gas impurity on the discharge mode and discharge products of argon plasma jet at atmospheric pressure

Argon is a widely used working gas of plasmas, which is much cheaper than helium but on the other hand much more difficult to generate diffuse discharge at atmospheric pressure. In order to meet the application requirements, plenty of researches have been reported to facilitate the diffuse discharge happening for argon plasmas, and in this paper an approach of using ethanol gas (EtOH) impurity is investigated. The discharge characteristics of Ar + EtOH plasma jet are studied as a function of the applied voltage and the concentration of EtOH, from which the concentration of EtOH between ∼200 and ∼3300 parts per million (ppm) is determined necessary for the generation of diffuse discharge. Compared with the helium plasma jet in literature, it is deduced that the diffuse discharge is probably caused by the Penning ionization happening between the metastable argon and EtOH. The discharge products of Ar + EtOH (672 ppm) plasma jet are measured and the corresponding chemistry pathways are analyzed. About 20% of EtOH is decomposed via complex chemical reactions to form more than a dozen of neutral species, such as CH3CHO, CH3COOH, CO, H2O, and CnH2n+2 (n ≥ 3), and various kinds of ionic species, including C+, CH+, ArH+, CH3CH2O−, etc.

Flow behaviour of drop and jet modes of a laminar falling film on horizontal tubes

The flow behaviour of a falling film on horizontal tubes has significant impacts on the efficiency of heat and mass transfer for the horizontal tubular evaporators and absorbers. Thus it is crucial to investigate the effect of contact angle and specific flow rate on the hydrodynamics of films and droplets in the drop and jet modes, which are the most important modes for evaporators and absorbers. A three-dimensional CFD model, using the volume of fluid (VOF) method, has been built to capture the gas-liquid interface. By employing mesh refinement and independence tests, the film spreading and droplet formation, liquid bridge breakup, droplet detachment, impact and fluctuation waviness of the simulations at the completely wetting condition are found to be in good agreement with experimental data and theory. In the drop mode, the behaviours of the droplets alternately falling from neighboring sites, including unstable slender liquid bridge and complex saddle waves were observed. This indicates that the wave propagation speed at first is higher than the impaction speed. In the in-line jet mode, the flow pattern is almost stationary but it is perturbed weakly by the impaction wave. The circumferential ring film has its maximum thickness located at the middle of the two-column in-line jet due to the wave interaction. In addition, the wetting area, spreading speed and instability time of the falling film are reduced with an increase in the contact angle, while the first two parameters increase at higher specific flow rates. In particular, an overshoot occurred at the larger contact angle. Finally, the results showed that the falling film flow pattern is sensitive to the initial wetting condition. Further, it reveals that the final steady wetted region depends on the receding contact angle, thus the introduction of the dynamic contact angle is the best approach for accurately determining the behaviour of falling films.

TAYLOR CONE–JET MODE IN THE FABRICATION OF ELECTROSPRAYED MICROSPHERES

In this study, electrospray modes were investigated to clarify their effects on the morphology and size of polycaprolactone (PCL) particles. The result indicated that electrosprayed microspheres with homogeneous and stable morphology were fabricated by using cone–jet mode and suitable electrospray processing parameters. Besides, the PCL solution was created by dissolving in dichloromethane with different concentrations such as 3.5%, 4%, 4.5% and 5%. The scanning electron microscopy (SEM) micrographs pointed that electrosprayed PCL microspheres were formed by using 4.5 % polymer solution. In addition, the reproducible and homogeneous morphology of PCL microparticles were obtained at the following set of parameters: applied voltage of 18 kV, flow rate of 1.5 mL/h and distance tip to collector of 20 cm. Moreover, at the collecting distance of 15–25 cm, the flow rate of 1.2–1.8 mL/h and applied voltage of 18 kV the cone–jet mode was generated. It was an effective electrospray mode to create stable and homogeneous microspheres.

Numerical simulation, PIV measurements and analysis of air movement influenced by nozzle jets and heat sources in underground generator hall

A research project was undertaken, using Computational Fluid Dynamic (CFD) numerical simulations and Particle Image Velocimetry (PIV) experimental techniques, to investigate air movement influenced by nozzle jets and heat sources in large generator hall of underground hydropower station. The interaction between supply nozzle air jet (inertia force) and thermal plume from heat source (thermal buoyancy) was studied under the design heat source and five different nozzle jet modes: Case1 = V/V0 = 0.5, Case2 = V/V0 = 0.75, Case3 = V/V0 = 1, Case4 = V/V0 = 1.25 and Case5 = V/V0 = 1.5 (V is the actual velocity of the nozzle jets, V0 is the design nozzle jet velocity). The air distribution was assessed based on the evaluation indexes. The accuracy and reliability of the CFD prediction was verified by the theoretical formula and PIV experiment. The results show that the first three cases (Ar≤0.00048) could meet the requirements of industry standards. After comparing with Case1 and Case2, Case3's velocity uniformity coefficient can be reduced by 24.96% and 13.63%; temperature uniformity coefficient can be decreased by 5.10% and 3.77%; energy efficiency coefficient can be raised by 22.61% and 6.83%; the average value of Air Diffusion Performance Index can be raised by 34.51% and 3.98% respectively. It is found that a larger jets velocity does not always ensure better replacement of the indoor air, and vice versa.

Jet behaviors and ejection mode recognition of electrohydrodynamic direct-write

By introducing image recognition and micro-current testing, jet behavior research was conducted, in which the real-time recognition of ejection mode was realized. To study the factors influencing ejection modes and the current variation trends under different modes, an Electrohydrodynamic Direct-Write (EDW) system with functions of current detection and ejection mode recognition was firstly built. Then a program was developed to recognize the jet modes. As the voltage applied to the metal tip increased, four jet ejection modes in EDW occurred: droplet ejection mode, Taylor cone ejection mode, retractive ejection mode and forked ejection mode. In this work, the corresponding relationship between the ejection modes and the effect on fiber deposition as well as current was studied. The real-time identification of ejection mode and detection of electrospinning current was realized. The results in this paper are contributed to enhancing the ejection stability, providing a good technical basis to produce continuous uniform nanofibers controllably.

A new insight of temperature distribution on superhydrophilic surface horizontal tubes falling film at low spray density

Falling film on horizontal tube banks is widely used in heat and mass transfer processes, because it leads to a higher heat and mass transfer performance. In this paper, a series of experiments were conducted to investigate the temperature distribution and local temperature evolution feature of liquid film at low spray density on superhydrophilic surfaces by thermal tracing method. The experimental results revealed that the temperature distribution of liquid film on the superhydrophilic surfaces presented a sub-region effect for different flow mode, a uniform and repeated distribution for jet mode and two totally different zones for droplet mode. Besides, for there existed a new high temperature band, which was first observed in the center of saddle-shaped lamella for droplet mode and a lower temperature region coinciding with the interaction ring between each pair of jets for local temperature feature due to the effect of the collision and overlap of spread film on superhydrophilic surfaces.

Instability waves and low-frequency noise radiation in the subsonic chevron jet

Spatial instability waves associated with low-frequency noise radiation at shallow polar angles in the chevron jet are investigated and are compared to the round counterpart. The Reynolds-averaged Navier–Stokes equations are solved to obtain the mean flow fields, which serve as the baseflow for linear stability analysis. The chevron jet has more complicated instability waves than the round jet, where three types of instability modes are identified in the vicinity of the nozzle, corresponding to radial shear, azimuthal shear, and their integrated effect of the baseflow, respectively. The most unstable frequency of all chevron modes and round modes in both jets decrease as the axial location moves downstream. Besides, the azimuthal shear effect related modes are more unstable than radial shear effect related modes at low frequencies. Compared to a round jet, a chevron jet reduces the growth rate of the most unstable modes at downstream locations. Moreover, linearized Euler equations are employed to obtain the beam pattern of pressure generated by spatially evolving instability waves at a dominant low frequency St=0.3, and the acoustic efficiencies of these linear wavepackets are evaluated for both jets. It is found that the acoustic efficiency of linear wavepacket is able to be reduced greatly in the chevron jet, compared to the round jet.

External confinement and surface modes in magnetized force-free jets

External confinement and surface modes in magnetized force-free jets

Onset of global instability in low-density jets

In low-density axisymmetric jets, the onset of global instability is known to depend on three control parameters, namely the jet-to-ambient density ratio $S$, the initial momentum thickness $\unicode[STIX]{x1D703}_{0}$ and the Reynolds number $Re$. For sufficiently low values of $S$ and $\unicode[STIX]{x1D703}_{0}$, these jets bifurcate from a steady state (a fixed point) to a self-excited oscillatory state (a limit cycle) when $Re$ increases above a critical value corresponding to the Hopf point, $Re_{H}$. In the literature, this Hopf bifurcation is often regarded as supercritical. In this experimental study, however, we find that under some conditions, there exists a hysteretic bistable region at $Re_{SN}&lt;Re&lt;Re_{H}$, where $Re_{SN}$ denotes a saddle-node point. This shows that, contrary to expectations, the Hopf bifurcation can also be subcritical, which we explore by evaluating the coefficients of a truncated Landau model. The existence of subcritical bifurcations implies the potential for triggering and the need for weakly nonlinear analyses to be performed to at least fifth order if one is to be able to predict saturation and bistability. We conclude by proposing a universal scaling for $Re_{H}$ in terms of $S$ and $\unicode[STIX]{x1D703}_{0}$. This scaling, which is insensitive to the super/subcritical nature of the bifurcations, can be used to predict the onset of self-excited oscillations, providing further evidence to support Hallberg &amp; Strykowski’s concept (J. Fluid Mech., vol. 569, 2006, pp. 493–507) of universal global modes in low-density jets.

Numerical Simulation of Supersonic Twin-Jet Noise with High-Order Finite Difference Scheme

In this study, the noise generated from a cold supersonic circular twin jet is simulated with a high-order finite difference solver. The three-dimensional compressible Favre-filtered Navier–Stokes equations in Cartesian form are solved by computational aeroacoustics methods. To handle the complex geometry of two closely spaced circular nozzles, the grid block interface flux reconstruction method for high-order finite difference scheme is used. The supersonic twin jet with fully expanded Mach number 1.358 is simulated in this study. A single jet operating at the same condition is also computed for comparison. It is found that the two coupling jets are both oscillating in flapping mode but out of phase with each other. Therefore the near-field pressure is symmetric about two planes, the midplane separating the two nozzles and the plane involving the two jets’ axes. The computed noise spectra are compared with the experimental data of Walker [“Twin Jet Screech Suppression Concepts Tested for 4.7% Axisymmetric and Two-Dimensional Nozzle Configurations,” AIAA Paper 1990–2150, 1990]. The dominant and first harmonic modes in the twin jet are amplified dramatically comparing with the single jet. An increment of 12 dB for the dominant component is observed, whereas 17 dB for the first harmonic. The predicted amplitudes of the screech tone and its harmonic agree well with the experimental data. Comparing with the single jet, a frequency shift of the screech tone in the twin jet is observed. The pressure field of the jet plumes is analyzed with the dynamic mode decomposition (DMD) method. The eigenvalues and most energetic eigen-modes are presented. The coupling mechanism of the twin jet is analyzed based on the DMD results. The upstream shift of the DMD modes in the twin jet indicates stronger interactions between the instability waves and the shock cells, which generate stronger tone noise. The stronger interactions in turn alter the shock-cell length and the convective velocity of the instability waves and result in the frequency shift of the screech tone in the twin jet.

Wavepackets and trapped acoustic modes in a turbulent jet: coherent structure eduction and global stability

Coherent features of a turbulent Mach 0.9, Reynolds number$10^{6}$jet are educed from a high-fidelity large eddy simulation. Besides the well-known Kelvin–Helmholtz instabilities of the shear layer, a new class of trapped acoustic waves is identified in the potential core. A global linear stability analysis based on the turbulent mean flow is conducted. The trapped acoustic waves form branches of discrete eigenvalues in the global spectrum, and the corresponding global modes accurately match the educed structures. Discrete trapped acoustic modes occur in a hierarchy determined by their radial and axial order. A local dispersion relation is constructed from the global modes and found to agree favourably with an empirical dispersion relation educed from the simulation data. The product between direct and adjoint modes is then used to isolate the trapped waves. Under certain conditions, resonance in the form of a beating occurs between trapped acoustic waves of positive and negative group velocities. This resonance explains why the trapped modes are prominently observed in the simulation and as tones in previous experimental studies. In the past, these tones were attributed to external factors. Here, we show that they are an intrinsic feature of high-subsonic jets that can be unambiguously identified by a global linear stability analysis.

Effect of laser shock processing on fatigue life of 2205 duplex stainless steel notched specimens

The effect laser shock processing (LSP) on high cycle fatigue behavior of 2205 duplex stainless steel (DSS) notched samples was investigated. The swept direction parallel (LSP 1) and perpendicular (LSP 2) to rolling were used in order to examine the sensitivity of LSP to manufacturing process since this steel present significantly anisotropy. The Nd:YAG pulsed laser operating at 10Hz frequency and 1064nm wavelength was utilized. The LSP configuration was the water jet mode without protective coating. Notched specimens 4mm thick were treated on both sides, and then fatigue loading was applied with R=0.1. The results showed that the LSP 2 condition induces higher compressive residual stresses as well as a higher fatigue life than the LSP 1 condition. By applying LSP 2 condition, an enhancement of fatigue life up to 402% is reported. In addition, the microhardness profiles showed different depths of hardening layer for each direction, according to the anisotropy observed.

A new view on the M 87 jet origin: Turbulent loading leading to large-scale episodic wiggling

Context. The nearby, giant radio galaxy M 87 hosts a supermassive black hole (BH) and is well-known for a bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large BH mass, M 87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. Many kinematic studies have been performed to determine the proper motions in the jet. Despite M 87 providing all proofs of being an active BH, the apparent jet speed remained puzzling, because proper motion measurements between 15 and 43 GHz for the same region of 1–10 mas core distance provided largely discrepant results. This source is a prime object to be studied in exquisite detail with the upcoming Event Horizon Telescope (EHT) observations because it promises to allow a direct view on the jet launching process itself. Aims. We aim to decipher some of the kinematic puzzles in the pc-scale jet with the analysis we present here.Methods. We re-modeled and re-analyzed 31 VLBA observations at 15 GHz obtained within the MOJAVE program. The data span a time range between Jul. 1995 and May 2011. We performed a detailed investigation of the pc-scale jet kinematics on different timescales, the shortest periods between the observations beeing 10 and 80 days, and in different jet modes, making use of VLBA observations. In addition, we studied the jet ridge line behavior as a function of time. Special care was taken to analyze the region close to the 15 GHz core, and the dynamics and distribution of newly emerging jet features in the jet.Results. We find an indication for apparent superluminal motion in the jet. Moreover, we present evidence for acceleration between 0.5 and 10 mas of core separation. The data suggest that the central part of M 87 at 15 GHz seems to be rotating. Jet components and counter-jet components are ejected in different directions under varying angles, explaining the impression of a broad opening angle. In this paper we present evidence for two different operating modes of the jet of M 87. The jet switches between two phases: i) the jet ridge line is at least double or the jet axis is displaced vertically, and ii) an unperturbed phase where the jet ridge line remains almost straight but is smoothly curved and the jet components are aligned along a classical jet axis. The mode change occurs every couple of years. Between the two operating modes, a transition phase is visible.Conclusions. The M 87 jet visible at 15 GHz probes a different physical zone compared to the standard blazar-zone we tend to see in AGN jets. The most likely scenario explaining the observed phenomena is a turbulent mass loading into the jet, most probably due to local, fast reconnection processes driven by turbulence of a tangled magnetic field, which is either generated in the accretion disk or the disk corona. In addition, on large scales, a global magnetic structure is required to channel the turbulent flow into what evolves into a large-scale jet. Large-scale jet instabilities may explain the curved pattern of the observed jet flow.

Experimental study on electrohydrodynamics (EHD) spraying of ethanol with double-capillary

This paper presents a visualization study on electrohydrodynamics (EHD) spraying of ethanol with double-capillary. The tilted dripping, spindle, pulsated-jet, whipping-jet, tilted straight jet and multi-jet modes are reported through off-line analyzing images captured by microscopy with photographingfrequency of 104Hz. The time-resolved evolution of each spraying mode has been thoroughly analyzed in a complete cycle. The repetition frequency, drops size and the angle between the direction of drop/jet movement and nozzle axis under non-continuous spraying modes have also been presented and discussed. The drop size is evidently associated with spraying mode and is larger for dripping and spindle modes, while smaller for jet modes. The drop size distribution follows the universal scaling laws in cone-jet mode. The repetition frequency increases with applied voltage increased and have a sharp jump with transition of dripping into spindle mode. The peak repetition frequency isrelatedtothe flow rate in present study. The angle strongly depends on repulsive force or electrical strength. For dripping and spindle modes, the angle increases with an increase in applied voltage and flow rate. In each complete cycle, the angle decreases as drop falling down. There are larger variations in angle for different modes because of electrical and gravity forces alternating.