Volume 75, Issue 11

In this paper, the half-cycle harmonic generation process has been controlled by using the asymmetric inhomogeneous chirped pulse combined with the ultraviolet (UV) pulse. It is found that by properly optimizing the chirps and chirp delays of the fundamental two-color pulse, the optimal negative and positive half-cycle laser profiles for the harmonic cutoff extension can be obtained. Further, with the introduction of the negative and positive inhomogeneous effect, respectively, the harmonic cutoff from the negative and positive half-cycle laser profiles can be further improved. Next, with the assistance of the UV pulse, the harmonic intensity can be enhanced due to the UV resonance ionization. Moreover, the single and double UV photon resonance ionizations are much better for generating the higher harmonic intensity. As a result, the stronger and broader harmonic plateaus with the larger harmonic cutoff can be obtained, which can support the generation of the high-intensity ultrashort attosecond pulses with the pulse durations of sub-45 as.

The nonlinear wave excitations arising from the spatially varying magnetic field in the quantum plasma environment are investigated in the frame work of quantum hydrodynamic model. In the weakly nonlinear, dispersive and dissipative limit it is shown that the varying magnetic field and collision-induced excitations can be described by a modified form of Korteweg-de Vries–Burgers’ type model equation. It is found that the dissipation terms (Burgers’ and collisional term) arise due to spatially varying magnetic field and the ion-neutral collisions. The numerical solutions of this equation predict that the localized soliton solutions decay algebraically due to the combined effect of varying magnetic field and collision by radiating oscillatory pulses behind the propagating soliton.

Nonlinear rarefactive isothermal ion-acoustic periodic travelling waves (RIIAPTWs) are examined in a magnetized ultrarelativistic degenerate plasma, containing warm fluid ions and ultrarelativistic degenerate inertialess electrons as well as positrons and immobile heavy negative ions. In the linear regime, the excitation of an isothermal ion-acoustic mode and its evolution are investigated. The physical behavior of nonlinear rarefactive isothermal ion-acoustic waves (RIIAWs) in this plasma model is governed by a Zakharov–Kuznetsov (ZK) equation. The analytical solutions for the nonlinear rarefactive isothermal ion-acoustic solitary waves (RIIASWs) and RIIAPTWs are performed by the bifurcation analysis. A careful discussion demonstrates the excitations of RIIASWs and RIIAPTWs are amplified (i.e., the amplitudes become deeper), as the chemical potential (or the Fermi energy at zero temperature) of electrons is decreased. It is found physically that the presence of the ultrarelativistic degenerate positrons and stationary heavy negative ions have strong effects on features of nonlinear RIIASWs and RIIAPTWs. The implications of the present finding in compact astrophysical objects, such as white dwarf stars, have been discussed.

In 2005, we proposed that the nerve pulse is an electromechanical soliton (T. Heimburg and A. D. Jackson. “On soliton propagation in biomembranes and nerves,” Proc. Natl. Acad. Sci. U.S.A. , vol. 102, pp. 9790–9795, 2005). This concept represents a challenge to the well-known electrochemical Hodgkin–Huxley model. The soliton theory was criticized by Nimtz and Aichmann in a recent article in Zeitung für Naturforschung A (G. Nimtz and H. Aichmann. “On biological signaling,” Z. Naturforsch. A , vol. 75, pp. 507–509, 2020). Here, we wish to comment on some statements that we regard as misinterpretations of our views.

We consider the solution of the equation of motion of a classical/quantum spin subject to a monochromatical, elliptically polarized external field. The classical Rabi problem can be reduced to third-order differential equations with polynomial coefficients and hence solved in terms of power series in close analogy to the confluent Heun equation occurring for linear polarization. Application of Floquet theory yields physically interesting quantities like the quasienergy as a function of the problem’s parameters and expressions for the Bloch–Siegert shift of resonance frequencies. Various limit cases are thoroughly investigated.

We have recently proposed a new matrix dynamics at the Planck scale, building on the theory of trace dynamics. This is a Lagrangian dynamics in which the matrix degrees of freedom are made from Grassmann numbers, and the Lagrangian is trace of a matrix polynomial. Matrices made from even grade elements of the Grassmann algebra are called bosonic, and those made from odd grade elements are called fermionic. In the present article, we provide a basic definition of spin angular momentum in this matrix dynamics, and introduce a bosonic(fermionic) configuration variable conjugate to the spin of a boson(fermion). We then show that at energies below Planck scale, where the matrix dynamics reduces to quantum theory, fermions have half-integer spin (in multiples of Planck’s constant), and bosons have integral spin. We also show that this definition of spin agrees with the conventional understanding of spin in relativistic quantum mechanics. Consequently, we obtain an elementary proof for the spin-statistics connection.

The electronic structure of yttrium trihydride (YH 3 ) under pressure has been explored by using the first-principle calculation. The existence of semiconductor phase of YH 3 is predicted at low pressure with symmetry group p3¯c1$p\overline{3}c1$ (165). In the range of 10–24 GPa, electron- and hole-like bands near the Fermi level are overlapped and form a snake-like nodal ring around Γ point. Different from previous literature (D. Shao, T. Chen, Q. Gu, et al., “Nonsymmorphic symmetry protected node-line semimetal in the trigonal YH 3 ,” Sci. Rep. , vol. 8, 2018.; J. Wang, Y. Liu, K.-H. Jin, et al., Phys. Rev. B , vol. 98, p. 201112, 2018), which assumes the band degeneracy is protected by mirror symmetry, we argue that the nodal line is protected by the space inversion symmetry and the time reversal symmetry. For weak spin-orbital coupling (SOC), the fermion modes at the band crossings are real 3D Majorana fermions. This is a typical double charged nodal-line semimetal, meaning that there are two topological invariants of this nodal line: a 1D Berry’s phase and a Z 2 monopole charge, which are related to the first and the second Stiefel-Whitney classes of the Berry bundle and can be given by the first-principle calculation. It turns out that the 1D Berry’s phase is nontrivial, but the Z 2 monopole charge is trivial. Therefore, this nodal line can shrink to a point and gapped out without breaking the topological constraints.

Photocatalytic decomposition of methylene blue (BM) solution by Cu-doped ZnS nanoparticles in the presence of UV light has been studied. The effect of the molar ratio of Cu ions affecting the rate of degradation reaction has been investigated. Photocatalytic reactivity of ZnS:Cu nanoparticles could be tailored by the proper amount of Cu ions. The maximum decolorizing efficiency (85%) of 5 ppm MB was obtained by 30 mgL −1 nanoparticles containing 2 wt% Cu, which was ascribed to the most effective surface area of these particles. However, at more than 2 wt% Cu doping concentration, nanoparticles aggregated due to their high surface energy, and the decomposition efficiency was decreased.

We have calculated and analyzed the surface-state energies and wave functions in quasi-two dimensional (Q2D) organic conductors in a magnetic field parallel to the surface. Two different forms for the electron energy spectrum are used in order to obtain more information on the elementary properties of surface states in these conductors. In addition, two mathematical approaches are implemented that include the eigenvalue and eigenstate problem as well as the quantization rule. We find significant differences in calculations of the surface-state energies arising from the specific form of the energy dispersion law. This is correlated with the different conditions needed to calculate the surface-state energies, magnetic field resonant values and the surface wave functions. The calculations reveal that the value of the coordinate of the electron orbit must be different for each state in order to numerically calculate the surface energies for one energy dispersion law, but it has the same value for each state for the other energy dispersion law. This allows to determine more accurately the geometric characteristics of the electron skipping trajectories in Q2D organic conductors. The possible reasons for differences associated with implementation of two distinct energy spectra are discussed. By comparing and analyzing the results we find that, when the energy dispersion law obtained within the tight-binding approximation is used the results are more relevant and reflect the Q2D nature of the organic conductors. This might be very important for studying the unique properties of these conductors and their wider application in organic electronics.