Scale Jet Research Articles

Early Hotspot Detection in Photovoltaic Modules using Deep Learning Methods

Photovoltaic (PV) energy systems have been widely used in energy production especially in recent years due to their clean, reliable, environmentally friendly and resource continuity. The electrical energy to be obtained must be uninterrupted and of high quality. For this reason, faults that may cause production losses in PV power plants should be detected quickly and accurately. In this study, an approach that can automatically detect hotspot fault in solar PV modules is presented. In the proposed approach, firstly, Jet colormap based colored image transformation process is applied to gray scale infrared image data. Then, using three different deep learning models such as MobilNetV2, ResNet-18, InceptionV3, both original grey scale data and Jet colormap data are detected and evaluation metric values are obtained. The importance of this research lies in the potential of deep learning-based effective detection, especially in the early and rapid diagnosis of PV hotspot faults.

X-ray emission from large scale jets of AGNs at high redshifts

The limited angular resolution of the existing telescopes, operating in radio, optical and X-ray wavebands, hinder the study on multi-spectral component (MSC) emissions from the large scale jet of AGNs. This is particularly strenuous for the sources located at high redshifts. Though a few of them were resolved in radio-optical wavebands, their X-ray counterparts have been rarely discovered. This poses a bigger challenge in understanding their emission mechanism. At high redshifts, the X-ray emission from the large scale jets are generally interpreted as inverse-Compton scattering of cosmic microwave background photons (IC/CMB), due to the increase in CMB photon density. However, recent Fermi γ-ray flux upper limit estimates on two high redshift (z>3.5) AGN jets (J1510+5702 and J1421-0643), question the validity of the IC/CMB model. Here, we propose a model by considering the advection of electrons from the sites of particle acceleration (Rahman et al., 2022), to interpret the MSC emission from these sources. We show that observed radio/optical/X-ray emissions can be explained by the synchrotron emission from the advected and accelerated electron distribution. We also show that the IC/CMB spectrum of this composite electron distribution satisfies the constraints drawn from Fermi observations.

Magnetosheath jets at Jupiter and across the solar system

The study of jets in the Earth’s magnetosheath has been a subject of extensive investigation for over a decade due to their profound impact on the geomagnetic environment and their close connection with shock dynamics. While the variability of the solar wind and its interaction with Earth’s magnetosphere provide valuable insights into jets across a range of parameters, a broader parameter space can be explored by examining the magnetosheath of other planets. Here we report the existence of anti-sunward and sunward jets in the Jovian magnetosheath and show their close association with magnetic discontinuities. The anti-sunward jets are possibly generated by a shock–discontinuity interaction. Finally, through a comparative analysis of jets observed at Earth, Mars, and Jupiter, we show that the size of jets scales with the size of bow shock.

Theoretically assisted and empirical scalings in the problem of determination of internal inductance in tokamaks

The problem of inferring the internal inductance from external magnetic measurements in tokamaks is considered. It was practically resolved in JET (Barana O et al 2002 Plasma Phys. Control. Fusion 44 2271), but several questions remain to be addressed before extrapolation of that method on other tokamaks. These naturally arise because of the integral nature of determined by unknown distribution of the magnetic field inside the plasma. Without universal solutions, the quality of approximations should be examined along with potential experimental enforcements of the existing procedures. This is the main goal of the study that is fully analytical. Several relevant quantities are calculated for the large-aspect-ratio plasma with elliptical shifted magnetic surfaces. Usually the plasma elongation is mentioned as a key factor in the task. Here it is explicitly shown that not only , but its radial derivative too plays a role. The latter parameter did not appear in the JET scaling and in the accompanying discussions. It is also shown that the -dependent term representing there the first iteration actually brings a systematic error. Therefore, several improvements to that scaling can be proposed. The study is based on the use of virial relations for the toroidal axisymmetric configurations.

Probing the jet size of two black hole X-ray binaries in the hard state

ABSTRACT Using multifrequency very long baseline interferometry (VLBI) observations, we probe the jet size in the optically thick hard state jets of two black hole X-ray binary (BHXRB) systems, MAXI J1820+070 and V404 Cygni. Because of optical depth effects, the phase-referenced VLBI core positions move along the jet axis of the BHXRB in a frequency-dependent manner. We use this ‘core shift’ to constrain the physical size of the hard state jet. We place an upper limit of 0.3 au on the jet size measured between the 15 and 5 GHz emission regions of the jet in MAXI J1820+070, and an upper limit of 1.0 au between the 8.4 and 4.8 GHz emission regions of V404 Cygni. Our limit on the jet size in MAXI J1820+070 observed in the low-hard state is a factor of 5 smaller than the values previously observed in the high-luminosity hard state (using time lags between multifrequency light curves), thus showing evidence of the BHXRB jet scaling in size with jet luminosity. We also investigate whether motion of the radio-emitting region along the jet axis could affect the measured VLBI parallaxes for the two systems, leading to a mild tension with the parallax measurements of Gaia. Having mitigated the impact of any motion along the jet axis in the measured astrometry, we find the previous VLBI parallax measurements of MAXI J1820+070 and V404 Cygni to be unaffected by jet motion. With a total time baseline of 8 yr, due to having incorporated 14 new epochs in addition to the previously published ones, our updated parallax measurement of V404 Cygni is 0.450 ± 0.018 mas (2.226 ± 0.091 kpc).

Mode decomposition and simulation of cloud cavity behaviors around a composite hydrofoil

Numerical investigation of the cavity dynamics around a composite hydrofoil with a blunt trailing edge in the cloud cavitating flow is carried out using a tightly coupled fluid–structure interaction method. The hydrofoil is made of a carbon-fiber-reinforced polymers with a ply angle of −45∘(CFRP −45). The results of a stainless-steel hydrofoil with the same geometry and conditions are used as a reference. Simulation results have been validated carefully against experimental data. Several fundamental mechanisms are dictated through simulation results and mode decomposition, including the multistage shedding process, the influence of the bend–twist coupling effect on cavity behaviors, cavitation–vortex interaction, and kinematics of coherent structures. The main reason for the generation of a secondary re-entrant jet is that the primary cloud cavity collapse leads to high pressure, which spreads to the residual sheet cavity closure and then induces a high-pressure gradient. The negative bend–twist coupling effect causes the CFRP −45 hydrofoil to exhibit a smaller cloud cavity scale and non-uniform re-entrant jet strength in the spanwise direction compared to the stainless-steel hydrofoil. Modal decomposition via proper orthogonal decomposition and dynamic mode decomposition indicates that the dominant coherent structures in the cloud cavitating flow include the large-scale cloud cavity, rotating structures due to the re-entrant jet, attached cavity, and small-scale vortex in the wake. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to complex cloud cavitating flow around a composite hydrofoil.

Intermittent flame lengths of buoyant jet flames in reduced and normal pressures: Experiments and theoretical analysis

Quantifying the intermittent flame length scale of buoyant jets is valuable for the understanding of the physical mechanisms of flame stabilization, risk assessment of fuel leakage fire in storage facilities, as well as the practical design of effective industrial burners. In this work, experimental studies are conducted to study the intermittent flame lengths in both reduced (0.64 atm) and normal (1.0 atm) pressures. The intermittent flame lengths are quantified by flame probability contours of propane flame using five nozzles with different diameters ranging from 4 to 10 mm with different heat release rates ranging from 4.31 kW to 49.52 kW. The intermittent flame lengths are found to be positively related to the heat release rate Q˙ and nozzle diameter d. Besides, results show that lower ambient pressure can bring about significantly higher intermittent flame lengths as compared with the results obtained in normal pressure. Moreover, based on physical analysis of the flow character of unburned fuel pressure dependence of flame length scale, a general model coupling with Froude number and nozzle diameter (d) and pressure effect (P∞/1.0atm)2/3 is established as Δlf/d(P∞/1.0atm)2/3=C1Frm−0.4(2−C2Frm−0.6) for the quantification of the intermittent flame lengths in both pressures. And the correlating results show that all the data in both pressures and those from previous literature can be well normalized with a satisfactory agreement. The current work can provide some supplemental knowledge on flame instability in the reduced pressure environment, a scientific evaluation model of fire length scale in fire safety strategies in fuel storage facility leakage cases, and good data reference for CFD validation.

Decrease in volcano jet noise peak frequency as crater expands

Volcanic jet noise is the sound, often <20 Hz and termed infrasound, generated by momentum-driven fluid flow through a volcanic vent. Assuming the self-similarity of jet flows and audible jet noise extends to infrasonic volcanic jet noise, the Strouhal number, St, connects frequency changes to those in jet length (expanded jet diameter) and/or velocity scale (jet velocity). We examine the infrasound signals from the June 2019 eruptions of Raikoke, Kuril Islands and Ulawun, Papua New Guinea volcanoes with changes in crater geometry. We use data from the International Monitoring System infrasound network and pre- and post-eruption satellite data (PlanetScope imaging). We observe a decrease in infrasound peak frequency during the transition to a more intense phase, which remains through the end of both eruptions. With the PlanetScope data, we measured a crater area increase of ∼50 000 m2 at Raikoke and ∼31 000 m2 at Ulawun. We use crater diameter as a proxy for expanded jet diameter. Our analysis suggests that the increases in crater diameter alone cannot account for the decreases in peak frequency for a constant St. This suggests the jet velocity also increased, which fits satellite data, and or the fluid properties (e.g., particle loading, nozzle characteristics, etc.) changed. This is reasonable as the eruptions intensified, which likely involved an increase in jet velocity and erosion of the crater walls. This is the first study to corroborate the decrease in infrasound peak frequency with documented increase in crater area.

A multimessenger study of the blazar PKS 0735+178: a new major neutrino source candidate

ABSTRACT The blazar PKS 0735+178 is possibly associated with multiple neutrino events observed by the IceCube, Baikal, Baksan, and KM3NeT neutrino telescopes while it was flaring in the γ-ray, X-ray, ultraviolet, and optical bands. We present a detailed study of this peculiar blazar to investigate the temporal and spectral changes in the multiwavelength emission when the neutrino events were observed. The analysis of Swift-XRT snapshots reveal a flux variability of more than a factor 2 in about 5 × 103 s during the observation on 2021 December 17. In the γ-ray band, the source was in its historical highest flux level at the time of the arrival of the neutrinos. The observational comparison between PKS 0735+178 and other neutrino source candidates, such as TXS 0506+056, PKS 1424+240, and GB6 J1542+6129, shows that all these sources share similar spectral energy distributions, very high radio and γ-ray powers, and parsec scale jet properties. Moreover, we present strong supporting evidence for PKS 0735+178 to be, like all the others, a masquerading BL Lac. We perform comprehensive modelling of the multiwavelength emission from PKS 0735+178 within one-zone lepto-hadronic models considering both internal and external photon fields and estimate the expected accompanying neutrino flux. The most optimistic scenario invokes a jet with luminosity close to the Eddington value and the interactions of ∼ PeV protons with an external UV photon field. This scenario predicts ∼0.067 muon and anti-muon neutrinos over the observed 3-week flare. Our results are consistent with the detection of one very high-energy neutrino like IceCube-211208A.

A multi-scale model for impingement drying of porous slab

Air impingement drying of a planar sheets of porous materials offers advantages of high and controllable heat and mass transfer rates. The governing heat and mass transfer phenomena involve multi-scale physical mechanisms ranging from mesoscopic pore scale to macroscopic jet scale. This work presents a pore-scale heat and mass transfer model of an unsaturated porous material based on statistically self-similar fractal scaling laws of pore structures. Furthermore, the effective transport coefficients are derived and applied to develop a cross-scale mathematical model for hot air impingement drying of a slab made of an unsaturated porous material. The flow and thermal fields of jet impingement and drying characteristics of unsaturated porous material are modeled numerically. The quantitative correlations between the mesoscopic pore structure and macroscopic heat and mass transfer properties are explored. The proposed fractal pore-scale model of porous material and cross-scale mathematical model of jet impingement show good agreement with experimental data. The effects of jet velocity, porosity as well as pore and tortuosity fractal dimensions on drying rate are discussed in detail. The computational results show that the mesoscopic pore structures indicate significant effect on the drying rate during later stage of drying. Results of this study provide useful guidance for efficient design of impingement of porous materials. • Meso-scale heat and mass transfer model of unsaturated porous material is proposed. • Multi-scale model for laminar impingement drying of porous slab is developed. • Impingement drying performance of porous slab is predicted. • Effect of mesoscopic structure on drying kinetics of porous material is explored.

Spectral and Timing Analysis of the Black Hole Transient MAXI J1631–479 During its 2019 Outburst Observed with Insight-HXMT

We report spectral and timing analysis of the black hole transient MAXI J1631–479 during the hard intermediate state of its 2019 outburst from the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) observations. We find that the energy dependence of the type-C quasi-periodic oscillation (QPO) frequency evolves with time: during the initial rise of a small flare (∼MJD 58526.0-58527.1), the QPO frequency increases with increasing energy from ∼1 to ∼100 keV, and then the frequency remains constant after MJD 58527.1. We discover a possible new phenomenon of Fe line’s QPO frequency jump that has never been observed for other black hole transients: during the small flare, the QPO frequency around the Fe line energy is higher than any other energy band, with the frequency difference Δf = 0.25 ± 0.08 Hz between 5.5–7.5 keV and other energy bands. The spectral analysis shows that the evolution of QPOs is related to the equivalent width of the narrow Fe line, and its equivalent width increases during this small flare. We propose that the QPO frequency difference results from the differential precession of a vertically extended jet, and the higher QPO frequency of Fe line could be caused by the layered jet when the jet scale increases. At the same time, the evolution of QPOs is related to the accretion rate, while the energy dependence of QPOs supports the existence of deceleration in the vertically distributed jet.

Statistical Equilibrium Principles in 2D Fluid Flow: From Geophysical Fluids to the Solar Tachocline

An overview is presented of several diverse branches of work in the area of effectively 2D fluid equilibria which have in common that they are constrained by an infinite number of conservation laws. Broad concepts, and the enormous variety of physical phenomena that can be explored, are highlighted. These span, roughly in order of increasing complexity, Euler flow, nonlinear Rossby waves, 3D axisymmetric flow, shallow water dynamics, and 2D magnetohydrodynamics. The classical field theories describing these systems bear some resemblance to perhaps more familiar fluctuating membrane and continuous spin models, but the fluid physics drives these models into unconventional regimes exhibiting large scale jet and eddy structures. From a dynamical point of view these structures are the end result of various conserved variable forward and inverse cascades. The resulting balance between large scale structure and small scale fluctuations is controlled by the competition between energy and entropy in the system free energy, in turn highly tunable through setting the values of the conserved integrals. Although the statistical mechanical description of such systems is fully self-consistent, with remarkable mathematical structure and diversity of solutions, great care must be taken because the underlying assumptions, especially ergodicity, can be violated or at minimum lead to exceedingly long equilibration times. Generalization of the theory to include weak driving and dissipation (e.g., non-equilibrium statistical mechanics and associated linear response formalism) could provide additional insights, but has yet to be properly explored.

Advection of accelerated electrons in radio/X-ray knots of AGN jets

ABSTRACT The X-ray emission from the knots of the kiloparsec scale jet of active galactic nuclei (AGN) suggests the high energy emission process is different from the radio/optical counterpart. Interpretation based on the inverse Compton scattering of cosmic microwave photons has been ruled out through Fermi γ-ray observations for low-redshift sources. As an alternate explanation, synchrotron emission from a different electron population is suggested. We propose a model considering the advected electron distribution from the sites of particle acceleration in AGN knots. This advected electron distribution is significantly different from the accelerated electron distribution and satisfies the requirement of the second electron population. The synchrotron emission from the accelerated and the advected electron distribution can successfully reproduce the observed radio-to-X-ray fluxes of the knots of 3C 273. For the chosen combination of the model parameters, the spectrum due to inverse Compton scattering of cosmic microwave photons falls within the Fermi γ-ray upper limits.

Metalearning and data augmentation for mass-generalized jet taggers

Deep neural networks trained for jet tagging are typically specific to a narrow range of transverse momenta or jet masses. Given the large phase space that the LHC is able to probe, the potential benefit of classifiers that are effective over a wide range of masses or transverse momenta is significant. In this work we benchmark the performance of a number of methods for achieving accurate classification at masses distant from those used in training, with a focus on algorithms that leverage metalearning. We study the discrimination of jets from boosted ${Z}^{\ensuremath{'}}$ bosons against a QCD background. We find that a simple data augmentation strategy that standardizes the angular scale of jets with different masses is sufficient to produce strong generalization. The metalearning algorithms provide only a small improvement in generalization when combined with this augmentation. We also comment on the relationship between mass generalization and mass decorrelation, demonstrating that those models which generalize better than the baseline also sculpt the background to a smaller degree.

Investigation for Effects of Jet Scale on Flame Stabilization in Scramjet Combustor

Jet scale affects the mixing and combustion of fuel and inflow. With the increase in the scale of scramjet combustors, the study of large-scale jets is particularly significant. The effects of jet scale on flame stability in scramjet combustors were studied by direct-connect combustion experiments. In this paper, the flame distribution characteristics of different jet scales were compared by using similar jet/inflow momentum ratios. The inflow Mach numbers were 2.4 and 3.0, and the total temperature was 1265 K and 1600 K, respectively. The results show that, when the equivalence ratio increases, the combustion intensity increases. Under the condition of same momentum ratio, the increase of jet scale is conducive to fuel injection into the core mainstream, increasing heat release, and the flame stabilization mode will change from cavity stabilization mode to jet-wake stabilization mode. Increasing the distance between jet orifices is not beneficial to combustion, and may even lead to blowoff.

Global oscillations in low-density round jets with parabolic velocity profiles

Experiments and spatiotemporal stability analysis are carried out to study the global oscillations in laminar low-density round jets with parabolic velocity profiles. The experimental results of laminar low-density jets with parabolic velocity profiles exhibit global axisymmetric oscillations. The spatiotemporal stability results based on base profiles from numerical simulations are consistent with the present experimental results. These results differ from the prediction of stability study by Coenen et al. (Phys. Fluids, vol. 20, 2008, p. 074104). They reported that the low-density jets with near parabolic velocity profiles show global helical oscillations. It is observed that the method used by Coenen et al. is not able to predict the nature of global oscillations observed in experiments for low-density jets with near parabolic profiles. The present spatiotemporal stability results demonstrate that the base flows from Navier–Stokes equations are required to predict the critical conditions observed in experiments for low-density jets with near parabolic velocity profiles. The breakdown distance of globally unstable low-density jets scales with $(Re-Re_c)^{-1/2}$ ( $Re_c$ is the critical Reynolds number), consistent with the scaling law obtained from the nonlinear global mode of the Ginzburg–Landau equation.

Intermediate length scale of water jets under gravity: An experimental result

Intermediate length scale of water jets under gravity: An experimental result

Development and scaling of turbulent, twin round jets

The velocity field of stationary, turbulent, twin round jets has been found to scale with an intrinsic velocity $U_0$ and length $L_0$ , both depending linearly on inflow plane parameters – jet velocity $U_j$ , diameter $d$ and distance between jets $S$ . Flow fields were obtained from large-eddy simulations at these conditions in two experiments: (1) at Reynolds number ${Re}=230\,000$ based on $U_j$ and $d$ , and $S/d=5$ ; and (2) at ${Re} = 25\,000$ , $S/d = 2, 4, 8$ . Each jet develops independently and then merges into a single jet with an elliptic cross-section. Downstream, the jet becomes circular after a mild overshoot. Close quantitative agreement with experiment was obtained in all cases. As the merged jets develop, fluctuation levels over a central half-width are nearly uniform and scale with the local maximum mean velocity. In all cases, the mean streamwise velocity along the centreline of the configuration, $U_c$ , rises to a peak $U_0$ at a distance $L_0$ from the inflow plane. The velocity $U_0$ decreases and $L_0$ increases with $S$ . For all nozzle spacings, a similar development was observed: $U_c/U_0$ is a function of distance $x/L_0$ only, and is essentially independent of $S/d$ and ${Re}$ . Further, these intrinsic and input quantities are connected by simple relations: $U_0 = U_j/(1.02S/d + 0.44)$ and $L_0/d = 5.58S/d - 1.16$ . The far field development of the merged jet can also be scaled with $U_0$ and $S$ , analogous to round jet scaling with $U_j$ and $d$ . Thus all twin round jets may be described by these new intrinsic scales.

The prototype X-ray binary GX 339–4: using TeV γ-rays to assess LMXBs as Galactic cosmic ray accelerators

ABSTRACT Since the discovery of cosmic rays (CRs) over a century ago, their origin remains an open question. Galactic CRs with energy up to the knee (1015 eV) are considered to originate from supernova remnants, but this scenario has recently been questioned due to lack of TeV γ-ray counterparts in many cases. Extragalactic CRs, on the other hand, are thought to be associated with accelerated particles in the relativistic jets launched by supermassive accreting black holes at the centre of galaxies. Scaled down versions of such jets have been detected in X-ray binaries hosting a stellar black hole (BHXBs). In this work, we investigate the possibility that the smaller scale jets in transient outbursts of low-mass BHXBs could be sources of Galactic CRs. To better test this scenario, we model the entire electromagnetic spectrum of such sources focusing on the potential TeV regime, using the ‘canonical’ low-mass BHXB GX 339–4 as a benchmark. Taking into account both the leptonic radiative processes and the γ-rays produced via neutral pion decay from inelastic hadronic interactions, we predict the GeV and TeV γ-ray spectrum of GX 339–4 using lower frequency emission as constraints. Based on this test-case of GX 339–4, we investigate whether other, nearby low-mass BHXBs could be detected by the next-generation very-high-energy γ-ray facility the Cherenkov Telescope Array, which would establish them as additional and numerous potential sources of CRs in the Galaxy.

The AGN fuelling/feedback cycle in nearby radio galaxies – IV. Molecular gas conditions and jet–ISM interaction in NGC 3100

ABSTRACT This is the fourth paper of a series investigating the AGN fuelling/feedback processes in a sample of 11 nearby low-excitation radio galaxies (LERGs). In this paper, we present follow-up Atacama Large Millimeter/submillimeter Array (ALMA) observations of one source, NGC 3100, targeting the 12CO(1-0), 12CO(3-2), HCO+(4-3), SiO(3-2), and HNCO(6-5) molecular transitions. 12CO(1-0) and 12CO(3-2) lines are nicely detected and complement our previous 12CO(2-1) data. By comparing the relative strength of these three CO transitions, we find extreme gas excitation conditions (i.e. Tex ≳ 50 K) in regions that are spatially correlated with the radio lobes, supporting the case for a jet–ISM interaction. An accurate study of the CO kinematics demonstrates that although the bulk of the gas is regularly rotating, two distinct non-rotational kinematic components can be identified in the inner gas regions: one can be associated to inflow/outflow streaming motions induced by a two-armed spiral perturbation; the second one is consistent with a jet-induced outflow with vmax ≈ 200 km s−1 and $\dot{M}\lesssim 0.12$ M⊙ yr−1. These values indicate that the jet-CO coupling ongoing in NGC 3100 is only mildly affecting the gas kinematics, as opposed to what expected from existing simulations and other observational studies of (sub-)kpc scale jet–cold gas interactions. HCO+(4-3) emission is tentatively detected in a small area adjacent to the base of the northern radio lobe, possibly tracing a region of jet-induced gas compression. The SiO(3-2) and HNCO(6-5) shock tracers are undetected: this – along with the tentative HCO+(4-3) detection – may be consistent with a deficiency of very dense (i.e. ncrit > 106 cm−3) cold gas in the central regions of NGC 3100.