Dissipative Region Research Articles

The Energy-dependent Gamma-Ray Light Curves and Spectra of the Vela Pulsar in the Dissipative Magnetospheres

We study the pulsar energy-dependent γ-ray light curves and spectra from curvature radiation in the dissipative magnetospheres. The dissipative magnetospheres with the combined force-free (FFE) and Aristotelian are computed by a pseudo-spectral method with a high-resolution simulation in the rotating coordinate system, which produces a near-FFE field structure with the dissipative region only near the equatorial current sheet outside the light cylinder. We use the test-particle trajectory method to compute the energy-dependent γ-ray light curves and phase-average and phase-resolved spectra by including both the accelerating electric field and radiation reaction. The predicted energy-dependent γ-ray light curves and spectra are then compared with those of the Vela pulsar observed by Fermi. Our results can generally reproduce the observed trends of the energy-dependent γ-ray light curves and spectra for the Vela pulsar.

Multilevel resistive switching memory in lead-free double perovskite La_{2}NiFeO_{6} films

Dense and flat La_{2}NiFeO_{6} (LNFO) films were fabricated on the indium tin oxide-coated glass (ITO/glass) substrate by sol–gel method. The bipolar resistive switching behavior (BRS) could be maintained in 100 cycles and remained after 30 days, indicating that the LNFO-based RS device owned good memory stability. Surprisingly, the multilevel RS characteristics were firstly observed in the Au/LNFO/ITO/glass device. The high resistance states (HRSs) and low resistance state (LRS) with the maximum ratio of sim 500 could be remained stably in 900 s and 130 cycles, demonstrating the fine retention and endurance ability of this LNFO-based RS device. The BRS behavior of Au/LNFO/ITO/glass devices primarily obeyed the SCLC mechanism controlled by oxygen vacancies (OVs) dispersed in the LNFO layer. Under the external electric field, injected electrons were captured or discharged by OVs during trapping or detrapping process in the LNFO layer. Thus, the resistive state switched between HRS and LRS reversibly. Moreover, the modulation of Schottky-like barrier formed at the Au/LNFO interface was contributed to the resistive states switchover. It was related to the change in OVs located at the dissipative region near the Au/LNFO interface. The multilevel RS ability of LNFO-based devices in this work provides an opportunity for researching deeply on the high density RS memory in lead-free double perovskite oxides-based devices.

A unified framework for non-linear reconstruction schemes in a compact stencil. Part 1: Beyond second order

Discretization of the convection term in a three-cell compact stencil has been widely used in Computational Fluid Dynamics (CFD) of engineering because the second-order interpolation scheme is considered to be more robust and algorithmically simple than very high-order schemes. However, according to Godnunov's theorem, it has never been trivial to design an accurate and oscillation-free discretization scheme in a compact stencil. Over decades, various kinds of schemes have been proposed to increase accuracy beyond second-order without producing non-physical numerical oscillations. Representative schemes are polynomial-based non-linear interpolations such as TVD (Total Variation Diminishing), NVD (Normalized Variable Diagram) and third-order WENO (Weighted Essentially Non-oscillatory); and non-polynomial-based interpolations including RBF (Radial Basis Functions), LDLR (Local Double Logarithmic Reconstruction) and Tangent of Hyperbola for INterface Capturing (THINC). Within the semi-discretization finite volume method, existing reconstruction schemes suffer from different issues to some extent. For example, existing TVD schemes tend to cause smearing, clipping and squaring effects. Most WENO schemes and inconsistent RBF schemes are not scale-invariant. Especially, the improved WENO-Z scheme is neither scale-invariant nor mesh-size-independent. Computationally expensive non-polynomial-based interpolations usually have singularity and are dependent on tunable parameters. Thus, this work reviews reconstruction schemes by reformulating or calculating the reconstructed boundary value in the normalised-variable space where the characteristics of reconstruction schemes can be read directly. Through the accuracy analysis and the induction of existing schemes, this work proposes a Unified Normalised-variable Diagram (UND) where the following properties of a reconstruction scheme can be given diagrammatically: 1) the second-order and the third-order accuracy condition, 2) the TVD and CBC (Convection Boundedness Criterion) constrain, 3) the ENO condition, 4) the High Resolution (HR) property, 5) and the numerical dissipation and anti-dissipation error.The proposed UND framework is firstly demonstrated by the improvement of the existing schemes with a shape-preserving TVD limiter and a scale-invariant WENO scheme. Then, by defining the normalised reconstruction operator, a brand-new scheme named ROUND (Reconstruction Operator on Unified Normalised-variable Diagram) is proposed. The ROUND scheme is devised by directly configuring the normalised reconstruction operator of favourable properties on UND. This work presents a dissipative ROUND scheme in which normalised reconstruction operators are fully in the dissipative region of UND, and a low-dissipative ROUND scheme where rigorously adjusted anti-dissipation errors are introduced. Different formulations of ROUND schemes are presented to show the flexibility of designing schemes within the UND framework. The proposed dissipative and low-dissipative ROUND schemes are evaluated via benchmark tests which show the superior performance of ROUND on accuracy and resolution. Especially, in some cases, the low-dissipative ROUND schemes obtain comparable and even better resolution than classic fifth-order WENO. The significance of this work is further demonstrated by the preliminary results of applying ROUND on the FDM-IBM (Finite Difference Method and Immersed Boundary Method) framework.

Analysis of influence of acoustic wave disturbance on internal and external scale and refractive index power spectrum function of atmospheric turbulence

Sound wave is a kind of mechanical wave, and as the carrier of energy, its transmission in the atmospheric turbulence environment will “disturb” the change of turbulence dissipation rate, thus affecting the evolution of turbulence physical structure. Using the acoustic energy and turbulent energy balance equations and combining the inner and outer scales of turbulence and the atmospheric refractive index power spectral function, this work studies the variation characteristics of the inner and outer scales and refractive index power spectral functions of atmospheric turbulence under different acoustic disturbances. The results show that the propagation of different acoustic waves can cause the internal and external scales of turbulence to change. The greater the sound source power, the stronger the influence on the scale of turbulence is. However, the greater the sound source frequency, the less significant the influence on the scale of turbulence is. The propagation of different sound waves can change the atmospheric refractive index power spectrum function. In the inertial region, considering the effects of sound waves on the inner and outer scales of turbulence, the influences of different sound sources on the atmospheric refractive index power spectrum are different. In a dissipative region, the atmospheric refractive index power spectrum fluctuates with the transmission distance of sound wave. This work explores the acoustic-wave caused variation of the characteristic parameters of the refractive index power spectrum function of atmospheric turbulence, providing a theoretical basis for studying the laser propagation characteristics and acoustooptic coupling in atmospheric turbulence caused by acoustic waves.

Rectangular C-Device with Circular Transitions: Modelling Approaches and Development of an Equivalent Nonlinear Inelastic Spring for Seismic Analysis

Yield devices of “C” shape, known as C-devices, supplement the energy dissipation sources when installed in earthquake resistant structures. However, the explicit modelling of C-devices is time consuming. Accordingly, this paper presents a new reliable methodology to define and calibrate an equivalent uniaxial inelastic spring that effectively reproduces the expected hysteretic response of a C-device. The shape of the C-device under study resembles that of a rectangular portal frame with circular interior corner transitions to avoid stress concentration and to control the extension of the dissipative region. The characterization of the properties of the equivalent spring is supported by both, finite element (FE) analyses of a family of C-devices and by experimental validation. Two types of FE models are used to predict the response of the C-device. A simple FE model idealizes the device as an inelastic frame with pinned supports, whereas the more elaborate model analyses the device as a C-shaped inelastic plate under in-plane actions and explicitly reproduces the boundary conditions of the plate at the device connections. Results indicate that the FE analysis results and those obtained with the equivalent inelastic spring are in a good agreement with experimental tests for monotonic and reversed cyclic loading.

Passivity-Based Multisampled Converter-Side Current Control of LCL-Filtered VSCs

With the gradually decreasing cost of high-performance digital processors, multisampling current control is a potential method to reduce the control delay and improve the stability in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered grid-connected converters. In the practical implementation, an antialiasing filter is required to remove the sampled switching harmonics and suppress the low-order aliasing. However, due to the phase lag from the antialiasing filter, the dissipative region of converter output admittance still cannot be lifted to switching frequency, which leads to a risk of system instability under wide grid admittance variation. In order to tackle this challenge, a filter capacitor voltage feedforward scheme using multisampling is proposed in this article. Consequently, the dissipation below the switching frequency is harvested for a three-phase converter. Furthermore, by doubling the multisampling rate, the proposed method can extend the dissipative region to the apparent switching frequency for a single-phase converter using unipolar modulation. The experimental results validate the effectiveness of the proposed method on a down-scaled single/three-phase converter.

Diffusion and memory effect in a stochastic process and the correspondence to an information propagation in a social system

A generalized Langevin equation is suggested to describe a diffusion particle system with memory. The equation can be transformed into the Fokker–Planck equation by using the Kramers–Moyal expansion. The solution of Fokker–Planck equation can describe not only the diffusion of particles but also that of opinion particles based on the similarities between the two. We find that the memory can restrain some non-equilibrium phenomena of velocity distribution in the system, without memory, induced by correlation between the noise and space (Wang et al., 2021). However, the memory can enhance the effective collision among particles as shown by the variation of diffusion coefficients, and changes the diffusion mode between the dissipative and pumping region by comparing with that in the aforementioned system without memory. As the discussions in this physical system is paralleled to a social system, the random diffusion of social ideology, such as the information propagation, can be suppressed by the correlation between the noise and space.

The Fundamental Plane Relation for Gamma-Ray Pulsars Implied by 4FGL

We explore the validity of the recently reported fundamental plane (FP) relation of γ-ray pulsars using 190 pulsars included in the latest 4FGL-DR3 catalog. This sample number is more than twice as large as that of the original study. The FP relation incorporates four parameters, i.e., the spin-down power, , the surface magnetic field, B ⋆, the total γ-ray luminosity, L γ , and a spectral cutoff energy, ϵ cut. The derivation of ϵ cut is the most intriguing one because ϵ cut depends on the proper interpretation of the available phase-averaged spectra. We construct synthetic phase-averaged spectra, guided by the few existing phase-resolved ones, to find that the best-fit cutoff energy, ϵ c1, corresponding to a purely exponential cutoff (plus a power-law) spectral form, is the parameter that optimally probes the maximum cutoff energy of the emission that originates from the core of the dissipative region, i.e., the equatorial current sheet. Computing this parameter for the 190 4FGL pulsars, we find that the resulting FP relation, i.e., the γ-ray luminosity in terms of the other observables, reads as this is in good agreement with both the empirical relation reported by Kalapotharakos et al. and the theoretically predicted relation for curvature radiation. Finally, we revisit the radiation reaction limited condition, to find it is a sufficient but not necessary condition for the theoretical derivation of the FP relation. However, the assumption of the radiation reaction limited acceleration reveals the underlying accelerating electric field component and its scaling with .

Electrostatic and tribological properties of hydrogenated diamond-like carbon on anodic aluminium oxide

The electrostatic and tribological properties of three types of anodic aluminium oxide (alumite) and hydrogenated Diamond-Like Carbon (DLC) on alumites were investigated. It was first proven that an ultrathin DLC at 5 nm on an insulative surface exhibits slow discharge. For alumites, clear electrostatic discharge behaviour was not observed in spite of the fact that surface resistance was in the dissipative region of 1010 Ω. Upon coating alumites with a hydrogenated DLC, slow charge and discharge were observed. DLC coatings on alumites significantly improved dielectric strength and hardness due to DLC's intrusion into the porous structure of the alumites. The coefficient of friction on alumites, which stood at 0.9 against Al2O3 and E52100 balls, was much improved to 0.1 with a DLC coating, and so was wear loss and life time.

The Pulsar Gamma-Ray Emission from High-resolution Dissipative Magnetospheres

Abstract The pulsar light curves and energy spectra in dissipative pulsar magnetospheres are explored with Aristotelian electrodynamics (AE), where particle acceleration is fully balanced with the radiation reaction. AE magnetospheres with nonzero pair multiplicity are computed using a pseudo-spectral method in the co-moving frame. The dissipative region near the current sheet outside the light cylinder is accurately captured by a high-resolution simulation. The pulsar light curves and spectra are computed using the test particle trajectory method, including the influence of both the consistent accelerating electric field and radiation reaction. Our results can generally reproduce the double-peak light curves and the GeV cutoff energy spectra in agreement with the Fermi observations for the pair multiplicity κ ≳ 1.

Below 1 µV cm−1: determining the geometrically-saturated critical transport current of a superconducting tape

In the critical state model, the critical current, , of a superconductor defines the upper limit of dissipation-free current flow. However conventional transport measurements of practical superconductors rely on the detection of a voltage drop along the length of the conductor. This requires that the superconductor has entered the dissipative regime, and hence inherently over-estimates the current at which geometric saturation occurs. Nonetheless, the convenience of the 1 µV cm−1 criterion means that it has become the widely adopted definition of transport . Here, we present an alternative definition for the transport critical current of a superconducting tape under self-field conditions, which is based on the concept of geometric current saturation across the full cross-sectional area. This saturation threshold can be experimentally determined through simple Hall sensor measurements of the evolving perpendicular magnetic field at the tape surface. The surface field exhibits a signature transition when the transport current increases beyond the current-saturation threshold. We present an analytical model which describes this effect and defines the critical saturated current as a function of . This definition is first validated using finite element (FE) modelling, and then experimentally demonstrated through measurements on a variety of commercial REBCO and Bi-2223 tapes of differing widths. It is found that the 1 µV cm−1 criterion consistently leads to an overestimation of the saturated critical current by ∼15% in REBCO tapes, and up to 30% in a Bi-2223 tape. FE modelling indicates that this overestimate is most prominent in superconductors exhibiting a low n-value (i.e. n ≲ 20). A key advantage of the measurement approach presented here is that it allows the unambiguous measurement of a transport value to be completed at lower currents, without entering the dissipative region in which sample damage can occur. There are also implications as to the correct choice of value which should be employed within the well-known Norris and Brandt equations for AC loss.

Three-dimensional Dissipative Pulsar Magnetospheres with Aristotelian Electrodynamics

Abstract A good compromise between the resistive model and the particle-in-cell model is Aristotelian electrodynamics, which can include the back-reaction of the radiative photons onto particle motion and allow for a local dissipation where the force-free condition is violated. We study the dissipative pulsar magnetosphere with Aristotelian electrodynamics where particle acceleration is fully balanced by radiation. The expression for the current density is defined by introducing a pair multiplicity. The 3D structure of the pulsar magnetosphere is then presented by solving the time-dependent Maxwell equations using a pseudo-spectral algorithm. It is found that the dissipative magnetosphere approaches the force-free solution and the dissipative region is more restricted to the current sheet outside the light cylinder (LC) as the pair multiplicity increases. The spatial extension of the dissipative region is self-consistently controlled by the pair multiplicity. Our simulations show the high magnetospheric dissipation outside the LC for the low pair multiplicity.

Soliton transmutations in KdV–Burgers layered media

We study the behaviour of the soliton which, while travelling in non-dissipative medium encounters a barrier with dissipation. New effects are presented in the case of numerically finite barrier on the soliton path: first, if the dissipation distribution has a form of a frozen soliton, the wave leaving the dissipative barrier emerges as a bi-soliton and a reflection wave is a comparatively small oscillation. Second, if the dissipation is negative (the wave, instead of loosing energy, is pumped with it) the passed wave is a soliton of a greater amplitude and velocity. Third, when the travelling wave solution of the KdV–Burgers (it is a shock wave in a dissipative region) enters a non-dissipative layer this shock wave transforms into a quasi-harmonic oscillation.

Dissipative dynamic output feedback control for switched systems via multistep Lyapunov function approach

The conservatism reduction problem of dissipative dynamic output feedback (DOF) control for a class of average dwell time switched system is investigated via a multistep Lyapunov function (LF) approach. First, a larger dissipative region with guaranteed stability and specifically, smaller [Formula: see text] level can be achieved by increasing a predictive step N, which means the monotonic requirement of LF is relaxed. Then, based on the results of dissipative analysis, a robust dissipative DOF controller is further designed. Unlike the traditional method that introduces equality constraint to obtain numerical testable conditions with heuristic nature, a less conservative controller is designed, where the LF matrix is formulated without structural constraint.

Automatic cells generation algorithms for two-dimensional physically non-linear BEM analysis

The integral equations used by the boundary element method (BEM) in physically non-linear analysis of solid mechanics present a remaining domain integral term, involving the inelastic field. The most direct way to treat this term is by the introduction of internal cells. However, this procedure represent a drawback in the BEM context, since not only the boundary is being discretized. On the other hand, an opportunity to develop algorithms that optimize such analyses emerges from the fact that only the inelastic regions of the domain need to be divided into cells. In this way, this paper presents new methodologies to progressively generate two-dimensional cells, with triangular or quadrilateral geometries, following the growth of the dissipative region. Moreover, a unified constitutive modeling framework is used in order that different material behaviors can be addressed by a unique computational structure. Numerical examples considering elastoplatic and isotropic damage constitutive models are presented.

Rare Dissipative Transitions Punctuate the Initiation of Chemical Denaturation in Proteins

Protein unfolding dynamics are bound by their degree of entropy production, a quantity that relates the amount of heat dissipated by a nonequilibrium process to a system’s forward and time-reversed trajectories. We here explore the statistics of heat dissipation that emerge in protein molecules subjected to a chemical denaturant. Coupling large molecular dynamics datasets and Markov state models with the theory of entropy production, we demonstrate that dissipative processes can be rigorously characterized over the course of the urea-induced unfolding of the protein chymotrypsin inhibitor 2. By enumerating full entropy production probability distributions as a function of time, we first illustrate that distinct passive and dissipative regimes are present in the denaturation dynamics. Within the dissipative dynamical region, we next find that chymotrypsin inhibitor 2 is strongly driven into unfolded states in which the protein’s hydrophobic core has been penetrated by urea molecules and disintegrated. Detailed analyses reveal that urea’s interruption of key hydrophobic contacts between core residues causes many of the protein’s native structural features to dissolve.

A long cavity passive mode-locking fibre laser with the reflective non-linear optical loop mirror

In this paper, we report a long cavity passively mode-locked fibre laser. The proposed mode locker is a reflective long cavity non-linear optical loop mirror (NOLM) which consists of a 50:50 coupler and 2-km single-mode fibres. The laser achieves stable mode locking at a fundamental repetition rate of 100 kHz. The rectangular pulses operating in dissipative soliton resonance region is generated in the laser. The relationship between the pulse duration and the pump power is investigated in detail. When the pump power is 200 mW, the laser generates rectangular pulses at 1565.57 nm (central wavelength) with pulse duration of 81.5 ns. The single pulse energy as high as 33.34 nJ is obtained. The results show that the reflective NOLM is an efficient mode locker and useful for the generation of high energy pulse.

Dissipative Soliton Resonance in a Wavelength-Tunable Thulium-Doped Fiber Laser With Net-Normal Dispersion

We demonstrate an all-fiber figure-eight mode-locked thulium-doped fiber laser with a wide tunable range in both pulsewidth and wavelength. A 45-m-long ultrahigh numerical aperture fiber is used to manage the cavity dispersion, and the net cavity dispersion is calculated to be 0.8585 ps 2 at 1900 nm. With net-normal dispersion, the experimental laser, operating in a dissipative soliton resonance region, generates stable rectangular pulses. The pulsewidth varies from 480 ps to 6.19 ns with the increasing pump power, and its center wavelength has a 28.95-nm tunable range (from 1940.22 to 1969.17 nm) by properly adjusting the polarization controllers. The maximum of average output power and pulse energy is 60.73 mW and 19.51 nJ, respectively. The rectangular pulses have a clamped peak power of about 3.16 W. The wavelength-tunable fiber laser with high-energy output operating at 2 μm has great potential in various application fields.

Stabilization of hyperbolic equations with mixed boundary conditions

This paper is devoted to study decay properties of solutions to hyperbolic equations in a bounded domain with two types of dissipative mechanisms, i.e. either with a small boundary or an internal damping. Both of the equations are equipped with the mixed boundary conditions. When the Geometric Control Condition on the dissipative region is not satisfied, we show that sufficiently smooth solutions to the equations decay logarithmically, under sharp regularity assumptions on the coefficients, the damping and the boundary of the domain involved in the equations. Our decay results rely on an analysis of the size of resolvent operators for hyperbolic equations on the imaginary axis. To derive this kind of resolvent estimates, we employ global Carleman estimates for elliptic equations with mixed boundary conditions.

Fractional entropy decay and the third law of thermodynamics.

We report in this paper a theoretical study on the quantum thermodynamic properties of a fractional damping system. Through the analysis, few nontrivial characteristics are revealed, which include (1) a fractional power-law decay entropy function, which provides an evidence for the validity of the third law of thermodynamics in the quantum dissipative region and (2) the varying of the entropy from a nonlinear divergent function to a semilinear decay function with a fractional exponent as the temperature approaches absolute zero.