Dissipation Region Research Articles

Electromagnetic draping of merging neutron stars.

We first derive a set of equationsdescribing general stationary configurations of relativistic force-free plasma, without assuming any geometric symmetries. We then demonstrate that electromagnetic interaction of merging neutron stars is necessarily dissipative due to the effect of electromagnetic draping-creation of dissipative regions near the star (in the single magnetized case) or at the magnetospheric boundary (in the double magnetized case). Our results indicate that even in the single magnetized case we expect that relativistic jets (or "tongues") are produced, with correspondingly beamed emission pattern.

A steel bracing system dissipating energy through moment-rotation hysteresis loops

According to the capacity design method, earthquake-resistant structures should be able to dissipate energy through dissipative regions, which are expected to yield while the other structural members remain in the elastic field during seismic excitation. The non-linear response of a bracing system, in which energy dissipation relies on a fuse, is investigated through experimental tests and numerical analyses. Loading on the fuse is a combination of bending moment, axial, and shear load. Results provide valuable information on the influence of several design parameters, such as the member cross-section compactness, shape, and member slenderness. The stability of the moment-rotation hysteresis loops and the energy dissipation are assessed through cyclic tests.To promote the utilization of the proposed bracing system in earthquake resistant steel structures, the work concludes by highlighting that the fuses are easily replaceable while ensuring ductile system response.

An innovative ductile bracing system easily repairable after a seismic event

According to the capacity design method, earthquake-resistant structures should have the ability to dissipate energy through dissipative regions, which are expected to yield while the other structural members remain in the elastic field during seismic excitation. The nonlinear response of an innovative bracing system, in which the dissipation of energy relies on a fuse, is investigated through experimental tests. The fuse is subject to a combination of bending moment, axial, and shear force. Results provide useful information on the influence of several design parameters, such as the fuse cross-section compactness and shape, on the mechanical behavior of the system. The stability of the moment-rotation hysteresis loops and the energy dissipation are investigated through cyclic tests. The work highlights the fuse to be easily replaceable while ensuring ductile system response.

3D chemical structure of the diffuse turbulent interstellar medium

Aims. The high abundances of CH+ in the diffuse interstellar medium (ISM) are a long-standing issue of our understanding of the thermodynamical and chemical states of the gas. We investigate here the formation of CH+ in turbulent and multiphase environments, where the heating of the gas is almost solely driven by the photoelectric effect. Methods. The diffuse ISM is simulated using the magnetohydrodynamic (MHD) code RAMSES which self-consistently computes the dynamical and thermal evolution of the gas along with the time-dependent evolutions of the abundances of H+, H, and H2. The rest of the chemistry, including the abundance of CH+, is computed in post-processing, at equilibrium, under the constraint of out-of-equilibrium H+, H, and H2. The comparison with the observations is performed taking into account an often neglected yet paramount piece of information, namely the length of the intercepted diffuse matter along the observed lines of sight. Results. Almost all of the mass of CH+ originates from unstable gas, in environments where the kinetic temperature is higher than 600 K, the density ranges between 0.6 and 10 cm−3, the electronic fraction ranges between 3 × 10−4 and 6 × 10−3, and the molecular fraction is smaller than 0.4. Its formation is driven by warm and out-of-equilibrium H2 initially formed in the cold neutral medium (CNM) and injected in more diffuse environments, and even the warm neutral medium (WNM) through a combination of advection and thermal instability. The simulation that displays the closest agreement with the HI-to-H2 transition and the thermal pressure distribution observed in the solar neighborhood is found to naturally reproduce the observed abundances of CH+, the dispersion of observations, the probability of occurrence of most of the lines of sight, the fraction of nondetections of CH+, and the distribution of its line profiles. The amount of CH+ and the statistical properties of the simulated lines of sight are set by the fraction of unstable gas rich in H2, which is controlled on Galactic scales by the mean density of the diffuse ISM (or, equivalently, its total mass), the amplitude of the mean UV radiation field, and the strength of the turbulent forcing. Conclusions. This work offers a new and natural solution to an 80-yr-old chemical riddle. The almost ubiquitous presence of CH+ in the diffuse ISM likely results from the exchange of matter between the CNM and the WNM induced by the combination of turbulent advection and thermal instability, without the need to invoke ambipolar diffusion or regions of intermittent turbulent dissipation. Through two-phase turbulent mixing, CH+ might thus be a tracer of the H2 mass loss rate of CNM clouds.

Hadronic signatures from magnetically dominated baryon-loaded AGN jets

ABSTRACT Blazars are a rare class of active galactic nuclei (AGNs) with relativistic jets pointing towards the observer. Jets are thought to be launched as Poynting-flux dominated outflows that accelerate to relativistic speeds at the expense of the available magnetic energy. In this work, we consider electron–proton jets and assume that particles are energized via magnetic reconnection in parts of the jet where the magnetization is still high (σ ≥ 1). The magnetization and bulk Lorentz factor Γ are related to the available jet energy per baryon as μ = Γ(1 + σ). We adopt an observationally motivated relation between Γ and the mass accretion rate into the black hole $\dot{m}$, which also controls the luminosity of external radiation fields. We numerically compute the photon and neutrino jet emission as a function of μ and σ. We find that the blazar SED is produced by synchrotron and inverse Compton radiation of accelerated electrons, while the emission of hadronic-related processes is subdominant except for the highest magnetization considered. We show that low-luminosity blazars (Lγ ≲ 1045 erg s−1) are associated with less powerful, slower jets with higher magnetizations in the jet dissipation region. Their broad-band photon spectra resemble those of BL Lac objects, and the expected neutrino luminosity is $L_{\nu +\bar{\nu }}\sim (0.3-1)\, L_{\gamma }$. High-luminosity blazars (Lγ ≫ 1045 erg s−1) are associated with more powerful, faster jets with lower magnetizations. Their broad-band photon spectra resemble those of flat spectrum radio quasars, and they are expected to be dim neutrino sources with $L_{\nu +\bar{\nu }}\ll L_{\gamma }$.

Numerical simulations of the laser-driven Petschek-type magnetic reconnection

This paper describes a numerical study of the magnetic reconnection between two magnetic fields of opposite polarity. The magnetic fields are created by an electric current in a coil connected to two metal disks. One of the disks is irradiated by a strong laser beam, whereby large amounts of free electrons flow toward the other disk, constituting a closed circuit for the electric current flowing through the coil. Two parallel coils are arranged to connect the two disks, and irradiation of the laser beam on one disk results in parallel electric currents in the two coils, inducing two magnetic fields of opposite polarity in the region between them. The magnetic reconnection that occurs in this region is three-dimensional. This three-dimensional magnetic reconnection is investigated via magnetohydrodynamic numerical simulations. The characteristics of the Petschek-type magnetic reconnection are observed for the first time in such numerical simulations of magnetic reconnection. Changes in the shape of the magnetic field lines form the boundary of the dissipation region and the outflow region. Moreover, the thermal plasma generated by reconnection is strongly confined to the region where the reconnecting current sheet and the slow-mode shock are located, and no leaks of thermal plasma are observed. Comparisons with existing laboratory experiment results confirm that our numerical simulations reproduce the experimental outcomes and provide reasonable explanations for the results observed in laboratories.

Experimental Investigation into the Effect of Fin Shapes on Heat Dissipation Performance of Phase Change Heat Sink

In this paper, the thermal management of missile-borne components in a flight state is studied. Avoiding excessive component temperatures under the high-temperature circumstances brought by aerodynamic heat is a requirement to guarantee the equipment’s safe and reliable operation. In this work, we designed four finned shell constructions for a phase change module using the phase change temperature control method and then studied their effects on the module’s ability to dissipate heat using an experimental approach. Three sizes of 30 mm, 40 mm, and 50 mm heating pads were used to replicate heat sources with various heat flux densities and heat dissipation regions, with reference to the heating characteristics of various chips. The results demonstrated that the square-shaped fin had the best heat dissipation effect after operating for 10 min under the power of 10 W and 20 W, while the strip-shaped fins exhibited the highest performance under the power of 30 W. The square-shaped fins had the best heat dissipation effect when reducing working time to 5 min. This paper proposes the optimal fin scheme under different power densities, as well as an enhanced heat dissipation idea for the melting process of the phase change materials based on the test results.

Variability and Spectral Behavior of Gamma-Ray Flares of 3C 279

3C 279 showed enhanced flux variations in Fermi-LAT γ-ray observations from 2018 January to June. We present a detailed Fermi-LAT analysis to investigate the variability and spectral behaviors of 3C 279 during the γ-ray flares in 2018. In this work, we analyzed the γ-ray spectra and found that the spectra in either the flaring or quiescent states do not show any clear breaks (or cutoffs). This indicates that the dissipation region is outside the broad-line region, and the energy dissipation may be due to the inverse Compton process of scattering the dust torus infrared photons, this result is also consistent with that in Tolamatti et al. An external inverse Compton scattering of dusty torus (DT) photons is employed to calculate the broadband spectral energy distribution (SED). This model was further supported by the fact that we found flare decay timescale was consistent with the cooling time of relativistic electrons through DT photons. During the SED modeling, a relatively harder spectrum for the electron energy distribution is found and suggests these electrons may not be accelerated by the shock that happened in the dissipation region. Besides, the magnetic reconnection is also ruled out due to a low magnetization ratio. Thus, we suggest an injection of higher-energy electrons from outside the blob and raising the flare.

A Statistical Comparison of EUV Brightenings Observed by SO/EUI with Simulated Brightenings in Nonpotential Simulations

The High Resolution Imager (HRIEUV) telescope of the Extreme Ultraviolet Imager (EUI) instrument onboard Solar Orbiter has observed EUV brightenings, so-called campfires, as fine-scale structures at coronal temperatures. The goal of this paper is to compare the basic geometrical (size, orientation) and physical (intensity, lifetime) properties of the EUV brightenings with regions of energy dissipation in a nonpotential coronal magnetic-field simulation. In the simulation, HMI line-of-sight magnetograms are used as input to drive the evolution of solar coronal magnetic fields and energy dissipation. We applied an automatic EUV-brightening detection method to EUV images obtained on 30 May 2020 by the HRIEUV telescope. We applied the same detection method to the simulated energy dissipation maps from the nonpotential simulation to detect simulated brightenings. We detected EUV brightenings with a density of 1.41 times 10^{-3} brightenings/Mm2 in the EUI observations and simulated brightenings between 2.76times 10^{-2} – 4.14times 10^{-2} brightenings/Mm2 in the simulation, for the same time range. Although significantly more brightenings were produced in the simulations, the results show similar distributions of the key geometrical and physical properties of the observed and simulated brightenings. We conclude that the nonpotential simulation can successfully reproduce statistically the characteristic properties of the EUV brightenings (typically with more than 85% similarity); only the duration of the events is significantly different between observations and simulation. Further investigations based on high-cadence and high-resolution magnetograms from Solar Orbiter are under consideration to improve the agreement between observation and simulation.

Aeroacoustic simulation of transient vortex dynamics subjected to high-intensity acoustic waves

The transient vortex dynamics within a microsecond-level acoustic cycle were numerically investigated when an orifice–cavity structure, which is a unit component of an acoustic liner, was subjected to high-intensity acoustic waves. Three-dimensional vortex-acoustic coupling fields were determined by solving the compressible linearized Navier–Stokes equations (LNSEs) and considering the nonlinear thermoviscous effect around the micro-orifice. First, the LNSE results were well validated by literature results in terms of the sound absorption coefficient, reflection coefficient, acoustic resistance, acoustic reactance, acoustic impedance, and the spatial features of acoustically induced vortex structures. Subsequent cross correlation analysis demonstrated that attenuated standing-waves were generated inside the back cavity when the incident acoustic wave propagated across the orifice. Aeroacoustic energy analysis revealed that the periodic production of vortex kinetic energy contributed more to the sound attenuation in the orifice structure than the viscous dissipation effect. Then, the acoustically induced vortex dynamics were characterized in terms of a phase-dependent evolution process, and the formation, convection, and dissipation regions were classified. Finally, dynamic mode decomposition analyses were conducted to extract the dominant vortex structures by determining their frequency spectra. The dominant modes contained large-scale vortices around the orifice, while the high-order modes contained a series of small-scale vortices toward the upstream incident tube and downstream cavity.

Hot deformation characteristics and mechanism understanding of Ti–6Al–2Sn–4Zr–6Mo titanium alloy

Two-phase titanium alloy Ti–6Al–2Sn–4Zr–6Mo (TC19) has an excellent application prospect in aerospace field. In order to study its hot deformation behavior and the microstructure evolution mechanism of TC19 titanium alloy, hot compression tests were carried out. The flow behavior of this alloy was predicted by the constitutive models. Besides, the hot processing map of TC19 alloy was drawn according to the dynamic material model (DMM) theory. The peak efficiency of energy dissipation region occurred in the temperature range of 850–1000 °C with the strain rate of 0.001–0.1 s−1. The main deformation mechanisms were dynamic recovery (DRV) and dynamic recrystallization (DRX). It seems that the region of deformation instability was concentrated in high strain rate. The main deformation mechanisms in the structure were deformation band (DB), flow localization (FL), and recrystallized grains produced by continuous dynamic recrystallization (CDRX). Deformation mechanism of TC19 alloy was mainly controlled by the deformation rate. When the deformation rate was low, the deformation mechanism was mainly DRV and the strain-induced grain boundary migration, which led to the bulging of the grain boundary and resulted in discontinuous dynamic recrystallization (DDRX) with the increasing deformation rate. Furthermore, the sub-grain rotated continuously to transform from low angle grain boundaries (LAGBs) into high angle grain boundaries (HAGBs) at the high deformation rate continuously. Recrystallized grains packed with HAGBs were observed in the microstructure. The existence of ω phase in the precipitated phase observed by diffraction pattern, which indicated that phase transition was related to the deformation rate.

Force-free magnetic flux ropes: String confinement of super-strong magnetic fields and flare energy release

ABSTRACT A new class of force-free solutions for a horizontal magnetic filament with a circular cross-section is found, in which the magnetic field strength on the axis significantly (up to 2–3 orders of magnitude and more) exceeds the strength of the longitudinal external field that keeps the rope from lateral expansion. A weak transverse field leads to a small deviation from the force-free field structure and results in a density deficit and an increase in temperature on the rope axis. The possibility of a flare release of magnetic energy is shown when critical values ​​of the longitudinal electric current density in the filament are reached at which ‘anomalous resistance’ occurs, caused by the development of the current ion-sound plasma instability. It turns out to be much larger than the usual Coulomb resistance. The following values are determined: the scale of the current dissipation region, the electric field strength in it, which significantly exceeds the Dreicer value, and the possible energy of accelerated charged particles (up to hundreds of MeV). The critical density of the longitudinal current at which the plasma turbulence is excited does not depend on the presence of a super-strong field on the flux-rope axis, so that the current density depends only on the electron concentration, temperature, and anomalous conductivity. However, super-strong magnetic fields can manifest themselves in the fact that, in their presence, the excitation of plasma instabilities can occur at sufficiently high electron concentrations. This effect may explain the large number of accelerated particles sometimes observed in solar flares.

Observation on Liutex similarity in the dissipation subrange of turbulent boundary layer

The motion of the small vortices in the dissipation region (large wave number) is not fully understood due to the influence of the kinematic viscosity and energy dissipation rate. Studying the motion law of small vortices is of great significance to understand the physical mechanism of turbulence. It is well known that the motion of small vortices is statistically isotropic in the dissipation region. Liutex is a new physical quantity recently found to define the rigid rotation of fluids in turbulent flow. In this study, the turbulent flow of boundary layer on a flat plate at freestream Mach number of 0.5 was studied based on a high-order direct numerical simulation (DNS). Using our DNS of flat plate and one DNS of plane turbulent channels of Fluid Dynamics Group UPM, the spectrum of Liutex is analyzed, and the similarity law of Liutex in the dissipation region is obtained. The study results show that the wavenumber spectrum of Liutex exactly follows the -5/3 law, i.e. EL(κ)∼Cκ−5/3, where κ=1/l is the wavenumber and EL is the amplitude of the Liutex spectrum. The scaling of Liutex with the frequency shows a same law of -5/3, since turbulent vortices propagate downstream with almost equal speeds. This paper reports the Liutex similarity for the dissipation subrange of different areas in fully developed turbulent boundary layers at low Reynolds number. Meanwhile, the vorticity and Q-criteria are found having no such similarity in boundary layers due to the shear contamination.

Probing the nature of dissipation in compressible MHD turbulence

Context. An essential facet of turbulence is the space–time intermittency of the cascade of energy that leads to coherent structures of high dissipation. Aims. In this work, we aim to systematically investigate the physical nature of the intense dissipation regions in decaying isothermal magnetohydrodynamical (MHD) turbulence. Methods. We probed the turbulent dissipation with grid-based simulations of compressible isothermal decaying MHD turbulence. We took unprecedented care in resolving and controlling dissipation: we designed methods to locally recover the dissipation due to the numerical scheme. We locally investigated the geometry of the gradients of the fluid state variables. We developed a method to assess the physical nature of the largest gradients in simulations and to estimate their travelling velocity. Finally, we investigated their statistics. Results. We find that intense dissipation regions mainly correspond to sheets; locally, density, velocity, and magnetic fields vary primarily in one direction. We identify these highly dissipative regions as fast and slow shocks or Alfvén discontinuities (Parker sheets or rotational discontinuities). On these structures, we find the main deviation from a 1D planar steady-state is mass loss in the plane of the structure. We investigated the effect of initial conditions, which yield different imprints at an early time on the relative distributions among these four categories. However, these differences fade out after about one turnover time, at which point they become dominated by weakly compressible Alfvén discontinuities. We show that the magnetic Prandtl number has little influence on the statistics of these discontinuities, but it controls the ohmic versus viscous heating rates within them. Finally, we find that the entrance characteristics of the structures (such as entrance velocity and magnetic pressure) are strongly correlated. Conclusions. These new methods allow us to consider developed compressible turbulence as a statistical collection of intense dissipation structures. This can be used to post-process 3D turbulence with detailed 1D models apt for comparison with observations. It could also be useful as a framework to formulate new dynamical properties of turbulence.

Wake Vortices and Dissipation in a Tidally Modulated Flow Past a Three‐Dimensional Topography

AbstractLarge eddy simulations are employed to investigate the role of tidal modulation strength on wake vortices and dissipation in flow past three‐dimensional topography, specifically a conical abyssal hill. The barotropic current is of the form Uc + Ut sin(Ωtt), where Uc and Ut are the mean and oscillatory components, respectively, and Ωt is the tidal frequency. A regime with strong stratification and weak rotation is considered. The velocity ratio R = Ut/Uc is varied from 0 to 1. Simulation results show that the frequency of wake vortices reduces gradually with increasing R from its natural shedding frequency at R = 0 to Ωt/2 when R ≥ 0.2. The ratio of R and the excursion number, denoted as , controls the shift in the vortex frequency. When , vortices are trapped in the wake during tidal deceleration, extending the vortex shedding cycle to two tidal cycles. Elevated dissipation rates in the obstacle lee are observed in the lateral shear layer, hydraulic jet, and the near wake. The regions of strong dissipation are spatially intermittent, with values exceeding during the maximum‐velocity phase, where D is the base diameter of the hill. The maximum dissipation rate during the tidal cycle increases monotonically with R in the downstream wake. Additionally, the normalized area‐integrated dissipation rate in the hydraulic response region scales with R as (1 + R)4. Results show that the wake dissipation energetically dominates the internal wave flux in this class of low‐Froude number geophysical flows.

Research on Cavitation Flow Dynamics and Entropy Generation Analysis in an Axial Flow Pump

The entropy generation theory is introduced to investigate the effects of different NPSH and tip clearance size on the cavitation flow dynamics and mechanical energy dissipation intuitively and quantitatively within an axial flow pump through numerical simulations. The results indicate that main mechanical energy dissipation of the pump gathers in part impeller and diffuser, and most are turbulent dissipation. Meanwhile, the impeller is the largest place of mechanical energy dissipation of the pump under cavitation conditions, accounting for more than 50%. NPSH has significant effects on the cavitation pattern, which reflects on the field that the areas of attached sheet cavitation and tip leakage vortex cavitation around blades increase obviously with NPSH reducing under the tip clearance of 0.1% span. With NPSH decreasing, high regions of turbulent dissipation in the impeller mainly expands along blades and move downstream, with span S0.98 near the shroud having larger turbulent dissipation. Besides, high regions of turbulent dissipation are mainly distributed at the rear part of the cavity for every corresponding span of the impeller, which indicates that the turbulent dissipation has a strong relation with the cavitation pattern. In the impeller, the unstable flows cause cavity shedding at the rear of the cavity and wake flows near the blade trail induce higher turbulent kinetic energy, finally resulting in higher turbulent dissipation there. Under the same NPSH, areas of tip leakage vortex cavitation and areas of tip clearance cavitation around the tip both expand with the tip clearance increasing from 0.1% span to 0.8% span. And high areas of turbulent dissipation also are distributed at the rear of the cavity and moving downstream along the blade suction side, especially at span S0.98. Therefore, the tip clearance width mainly affects the cavitation development and turbulent dissipation distribution near the impeller’s shroud under same NPSH.

Bright Light Decreases Peripheral Skin Temperature in Healthy Men: A Forced Desynchrony Study Under Dim and Bright Light (II).

Human thermoregulation is strictly regulated by the preoptic area of the hypothalamus, which is directly influenced by the suprachiasmatic nucleus (SCN). The main input pathway of the SCN is light. Here, thermoregulatory effects of light were assessed in humans in a forced desynchrony (FD) design. The FD experiment was performed in dim light (DL, 6 lux) and bright white light (BL, 1300 lux) in 8 men in a semi-randomized within-subject design. A 4 × 18 h FD protocol (5 h sleep, 13 h wake) was applied, with continuous core body temperature (CBT) and skin temperature measurements at the forehead, clavicles, navel, palms, foot soles and toes. Skin temperature parameters indicated sleep-wake modulations as well as internal clock variations. All distal skin temperature parameters increased during sleep, when CBT decreased. Light significantly affected temperature levels during the wake phase, with decreased temperature measured at the forehead and toes and increased navel and clavicular skin temperatures. These effects persisted when the lights were turned off for sleep. Circadian amplitude of CBT and all skin temperature parameters decreased significantly during BL exposure. Circadian proximal skin temperatures cycled in phase with CBT, while distal skin temperatures cycled in anti-phase, confirming the idea that distal skin regions reflect heat dissipation and proximal regions approximate CBT. In general, we find that increased light intensity exposure may have decreased heat loss in humans, especially at times when the circadian system promotes sleep.

GeV Signatures of Short Gamma-Ray Bursts in Active Galactic Nuclei

The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGNs), and we investigate the γ-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton, and external inverse Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN disks contribute to the EIC component. We show that a low-density cavity can be formed in the migration traps, leading to the embedded mergers producing successful GRB jets. We find that the EIC component would dominate the GeV emission for typical CBO mergers with an isotropic-equivalent luminosity of L j,iso = 1048.5 erg s−1 that are located close to the central supermassive black hole. Considering a long-lasting jet of duration T dur ∼ 102–103 s, we find that the future Cherenkov Telescope Array (CTA) will be able to detect its 25–100 GeV emission out to a redshift z = 1.0. In the optimistic case, it is possible to detect the on-axis extended emission simultaneously with GWs within one decade using MAGIC, H.E.S.S., VERITAS, CTA, and LHAASO-WCDA. Early diagnosis of prompt emissions with Fermi-GBM and HAWC can provide valuable directional information for the follow-up observations.

Long-term Optical Monitoring of the TeV BL Lacertae Object 1ES 2344 + 514

Variability is one of the main observational characteristics of blazars. Studying variability is an efficient method to reveal the nature of active galactic nuclei. In the present work, we report optical R-band photometry observations of a TeV blazar, 1ES 2344 + 514, carried out with a 70 cm telescope in the period of 1998 July–2017 November at Abastumani Observatory, Georgia. Based on the optical R-band observations, the optical variation behaviors on both short timescales and long timescales are investigated. Three methods (Jurkevich, discrete correlation function, and power spectrum analysis) are used to investigate periodicity in the light curve. In addition, combined with multiwavelength data, the jet physical properties are discussed. The following conclusions are drawn: (1) A variability of ΔR = 0.155 mag (15.356 − 15.201 mag) over a timescale of ΔT = 12.99 minutes is detected during our 628 days of monitoring. (2) According to the Kelvin–Helmholtz thermal instability, if the magnetic field intensity (B) for the source is greater than a critical value (B c ), it will reduce the incidence of intraday variations in the light curves. (3) The physical parameters of the dissipation region are obtained by fitting the spectral energy distribution with a one-zone synchrotron self-Compton model for the average and flare states. (4) The three methods show that there are periods of P = 2.72 ± 0.47 yr, P = 1.61 ± 0.18 yr, P = 1.31 ± 0.17 yr, and P = 1.05 ± 0.07 yr. When a binary black hole system is adopted with a period of P = 2.72 ± 0.41 yr, we obtain the orbital parameters for the binary black hole system as follows: M = 8.08 × 109 M ⊙, the sum of the semiaxes is r = 7.18 × 1016 cm, and the lifetime of the binary black hole is τ merge = 6.24 × 102 yr.

The effect of large-scale forcing on small-scale dynamics of incompressible turbulence

The subtle but crucial effects of large-scale forcing on the small-scale velocity-gradient (VG) dynamics is examined using direct numerical simulation (DNS) data of incompressible turbulence. The interplay among large-scale forcing, inertia, pressure and viscous effects is characterised as a function of local streamline geometry and VG magnitude (Frobenius norm). When conditioned on local topology, forcing: (i) counteracts inertial and viscous action in the strain-dominated nodal topologies; and (ii) balances pressure action in the rotation-dominated unstable focal topologies. Unexpectedly, forcing acts to reduce VG magnitudes in regions of strong dissipation. In these regions, forcing balances the non-local pressure effects whereas viscous action offsets the nonlinear inertial effects. In regions of very low dissipation, forcing combines with inertia and pressure effects to offset viscous action. With regard to the probability distribution of the normalised VG invariants, the primary role of forcing is to nullify certain features (dilatational probability currents) of inertia, pressure and viscous action. This results in the emergence of universal statistical features (solenoidal probability currents) that are determined largely by inertia–pressure–viscous interactions. These findings serve to enhance our understanding of small-scale processes in turbulence and guide VG model development.