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In an attempt to regularize a previously known exactly solvable model (Yang and Zhang 2019 Eur. J. Phys. 40 035401), we find yet another exactly solvable toy model. The interesting point is that while the Hamiltonian of the model is parameterized by a function f(x) defined on [0, ∞), its spectrum depends only on the end values of f, i.e., f(0) and f(∞). This model can serve as a good exercise in quantum mechanics at the undergraduate level. [ABSTRACT FROM AUTHOR]

We explore the application of a two-component model of proton structure functions in the analysis of deep-inelastic scattering (DIS) data at low Q2 and small x. This model incorporates both vector meson dominance and the correct photo-production limit. The CJ15 parameterization is applied to the QCD component, in order to take into account effects of order 1/Q2 effects, such as target mass corrections and higher twist (HT) contributions. The parameters of the leading twist parton distribution functions (PDFs) and HT coefficient functions are determined by fitting DIS data. The second moments of the PDFs are extracted and compared with other global fits and lattice determinations. [ABSTRACT FROM AUTHOR]

We here present a new type of kinetic-scale (∼1 ion gyroradius) flux rope (KFR) in the Earth's dayside magnetosheath boundary layer with Magnetospheric Multiscale high temporal cadence data. This structure exhibits a slight twist of magnetic field that is possibly generated by a field-aligned current, which differs from typical dayside flux ropes usually observed within the current sheet where magnetic reconnection can occur. The perpendicular electron fluxes within 19–52 eV are increased ∼10% inside the KFR. Detailed analysis shows that these perpendicular electrons may encounter their mirror point (at the position of the KFR, strong field region) when traveling from the magnetosheath toward the ionosphere and will be reflected to the magnetosheath. A possible scenario is that this KFR is different from previous flux ropes that transfer electron flux to the magnetosphere but could intercept magnetosheath large pitch angle electron flux to the magnetosphere. [ABSTRACT FROM AUTHOR]

We examine the influence of noise and Alfvén wave turbulence on magnetic reconnection in a reduced magnetohydrodynamics model. We focus on the dynamics of magnetic helicity density. Helicity conservation is then used to calculate the global reconnection rate in terms of the helicity density flux. Two specific scenarios are explored—noisy reconnection and Alfvén wave turbulent reconnection. For noisy reconnection, the current sheet is assumed to sit in a noisy state, marginal to plasmoid formation instability. The scaling of the reconnection rate in the presence of noise is proportional to (S20/VAL2)1/11, where S20/VAL2 is the relative amplitude of the noise. We obtain this prediction using a symmetry analysis of the helicity density flux. For Alfvén wave turbulent reconnection, a mean field closure scheme is applied. A reconnection rate proportional to is obtained, where and 〈 B〉 are the relative energy of Alfvén wave turbulence and the reconnecting field. The constraint on reconnection rate enforced mean-square magnetic potential conservation is reexamined. A critical magnetic Reynolds number Rm, c is identified. For Rm ≫ Rm, c, the reconnection rate becomes independent of Spitzer resistivity and thus can be higher than the Sweet-Parker model prediction. Both cases exhibit a weak dependence of the reconnection rate on the amplitude of the turbulence. Therefore, even noise or weak turbulence can trigger fast reconnection if the system is marginally stable. The important distinction between turbulent reconnection and turbulent dissipation of magnetic energy is also discussed. [ABSTRACT FROM AUTHOR]