Modern Physics Letters B

Following the scheme proposed by Eberly and Wodkiewicz for the physical spectrum, we calculate the fluorescence spectrum of the Jaynes–Cummings model when the two-level system interacts with an electromagnetic field that initially is in a squeezed coherent state. We show the appearing of “ringing lines” in the fluorescence spectrum that are echoes of the oscillations in the photon distribution of the compressed field. These ringing lines may be a similar effect as the ringing revivals of the atomic inversion that are a signature of squeezed states.

In this article, some novel optical and periodic wave structures are studied to the fractional Schrödinger–Hirota equation with a truncated $M$-fractional derivative. For this purpose, the integration scheme, which was adopted is fractional extended Fan sub-equation. The optical solitons are observed in single and combined forms, and some other solutions are also fall out during the derivation. Subsequently, the exact solutions demonstrate the effectiveness, efficiency and reliability of the proposed methods, which can be useful for exploring various kind of solutions in the diverse fields of contemporary sciences and engineering. The constraint conditions are utilized, as well as the gained solutions are plugged into the model to verify the results.

The semilinear space-time-fractional Schrödinger equation is solved numerically using one-step and two-step exponential time differencing methods in time, and a fractional centered difference scheme in space. The two-parametric Mittag–Leffler function arising in the time integral is computed with Padé approximations, which improves the efficiency of the scheme markedly. Numerical experiments for well-known models from literature are performed to show the effectiveness and efficiency of the proposed methods.

Designing a discrete chaotic system via fractal transformation has become a new method for engineering applications. This method generates new discrete chaotic system through external mechanisms, instead of the traditional way of internal mechanisms. The way of building novel discrete chaotic system is enriched by fractal and mathematical operation. Taking one-dimensional ICMIC map and two-dimensional Hénon map as the seed maps, dynamics of the generated chaotic map is analyzed by bifurcations, complexity and spectrum distribution characteristics. The results show that the new discrete chaotic map has the advantages in complexity and distribution in the parameter space. Finally, the digital circuit of fractal chaotic system is implemented based on DSP technique. The feasibility of the circuit is verified. Therefore, it has good application prospects in secure communication.

The transmission of vibration waves in specific frequency bands can be suppressed by the local resonance and the multi-layer transmission structure. A composite non-periodic isolator containing a local resonance structure is proposed in this paper. The transmission performance of vibration waves is studied using the modal displacement, and the main vibration control frequency band is picked up for vibration wave transmission. Meanwhile, the total power distribution, frequency quality loss factor and total power loss density are calculated in main frequency band. Further, the energy transmission and loss performance of vibration waves are studied in the composite non-periodic isolator. The transmission ratio of the vibration wave is also discussed, the evolution of the vibration transmission ratio is compared in each metal frame of the composite non-periodic isolator, and the vibration isolation performance is evaluated. Research shows that the vibration isolation energy can be effectively increased and the vibration isolation performance can be effectively improved in the proposed composite non-periodic isolator.

As an environmental vegetable insulation oil, camellia oil will be decomposed into dissolvable gases in the presence of electric field. In this work, the characteristic gases of camellia oil were measured by experiments with partial discharge and breakdown discharge, and the decomposition process of triglyceride, which is the main component of camellia oil, was investigated using molecular simulations (MSs). The experimental results demonstrate that H₂ is the main characteristic gas caused by the partial discharge while C₂H₂ is the main decomposition products for the breakdown discharge. According to the MS results, the C–O bond connected to the center carbon in glycerol breaks initially when the electric field strength is lower, and the C–(O–C) bond in the triglyceride molecule breaks while the electric field strength exceeded critical value with increase of voltage. The decomposition gas generates gradually through decomposition and recombination of radicals, H₂ and CH₄ are the main gas products generated by triglyceride with low electric field strength, while the C₂H₂ increases gradually and becomes the main gas product with the energy of the system accumulated.

Non-local symmetries in forms of square spectral function and residue over the (2+1)-dimensional Korteweg–de Vries (KdV) equation are studied in some detail. Then, we present $N$-soliton solution to this equation with the help of symmetry transformation.

In this paper, the BKP hierarchy is viewed as the Kupershmidt reduction of the modified KP hierarchy. Then based upon this fact, the gauge transformation of the BKP hierarchy are obtained again from the corresponding results of the modified KP hierarchy. Also the constrained BKP hierarchy is constructed from the constrained modified KP hierarchy, and the corresponding gauge transformations are investigated. Particularly, it is found that there is a new kind of gauge transformations generated by the wave functions in the constrained BKP hierarchy.

Detecting communities is one of the important research directions in social network analysis currently. However, complexity and size of real world networks makes it practically impossible to develop a unique mechanism for finding communities, which will show satisfactory results in almost any network. In this paper, we have proposed a genetic method that can detect communities in social networks extracted from the Web. Advantage of the method is that we can set an upper boundary to the number of clusters in the network. This is achieved by means of information centrality. When we choose top $p$ nodes, which shall be used in the algorithm iteration, we know that the number of clusters in the network is less that the number $p$. Yet another advantage of the method is that it is fast with computational complexity equals $O(n^{2}p)$. This is a huge improvement compared to most algorithms with convergence speed $O(n^3)$. The experimental results verify the superior performance of the proposed method.

This paper investigates the effects of interparticle distance and heating rate on the aggregation characteristics of Cu/Au nanoparticles using molecular dynamics (MD) simulations, and focuses on discussing the effects of the two above-mentioned factors on the entire system. Our results suggested that the reduction in heating rate and increasing the initial distance of the particles would both contribute to raising the initial sintering temperature. However, when the particles’ initial distance was greater than the cut-off radius of the system, the initial sintering temperature was not increased any longer, but fluctuated within a certain range. Furthermore, the sintering force of the nanoparticles at the initial sintering temperature was investigated, and it was found that the heating rate made no obvious difference to it. Nonetheless, the sintering force varied under different initial distance of the particles (at the same heating rate) due to system energy changes.

Poisson’s ratios of two-dimensional (2D) all-inorganic perovskites Cs₂PbX₄ (X = Cl, Br, I) have been calculated by the first-principles calculations. The contribution of each geometric parameter (bond length $L$, bond angle $\mathrm{\Phi }$, rotation angle ${𝜃}_1$, and tilt angle ${𝜃}_2$) to Poisson’s ratio is obtained analytically. Through a comprehensive analysis of the geometric deformations of the perovskite under the uniaxial strain, we find that Poisson’s ratios of the perovskites are sensitive to the change of the bond length $L$ and the bond angle $\mathrm{\Phi }$. In addition, the value of the bond angle ${\mathrm{\Phi }}_0$ in the strain-free structure mainly determines the high in-plane anisotropy of Poisson’s ratios in Cs₂PbX₄.

In addition to Dirac and Weyl fermions, exotic massless fermions with non-zero Berry curvature fluxes may exist in condensed matter systems under the protection of crystal symmetry, for example, spin-1 excitations with threefold degeneracy and spin-3/2 Rarita–Schwinger–Weyl fermions with fourfold degeneracy. More recently, the theory of topological quantum chemistry has provided us with a convenient way to find the existence of these quasi-particles. Herein, we have found a space group (No. 199) that may have both spin-1 excitations and spin-3/2 Rarita–Schwinger–Weyl fermions near the Fermi level. By using the ab initio density functional theory, we show that these unconventional quasi-particles mentioned above coexist in Bi₄Ni₆S₄ in space group $I{2}_{1}3$ (No. 199), when spin-orbit coupling is considered. Their non-trivial topology results in a series of Fermi arcs connecting the projection of these excitations on (001) surface.

The coalescence of particles extensively exists in the industrial production and nature, which is of great research significance. This paper examined the alloying process of Cu/Au nanoparticles with different sizes by molecular dynamics (MDs) simulations. The coalescence process presents three stages which can be divided by the contact and fusion. The alloying processes of Cu/Au nanoparticles with different sizes had contacted with each other before the heating at 300 K. The Au atoms diffused through the outer area of the sintering neck before the nanoparticles were fused into one particle. The coalescence had become severe after the systems reached the melting temperature. The different systems showed different sintering rate.

With the development of mathematics as well as natural sciences and with the improvement of the human cognitive level, a new discipline dealing with complexity of different and complex natural systems has been recognized. Therefore, several complexity measures have been developed. Complexity measures provided to scientific community new insights into environmental processes that cannot be discovered by the traditional mathematical methods. Spatial distribution of heavy metals and radionuclides (HM&RN further) is formed by acting natural processes as well as human activities. Despite the fact that this distribution plays an important role in environmental processes, it has not been analyzed with deserving attention. The usual way to present the results obtained by some measurements having an objective to describe environmental properties is by creating a map of spatial distributions of some chosen quantities or indices. Attempts to introduce some quantitative measure, which characterizes measured areal distribution (and corresponding map) of physical quantity, cannot be frequently encountered in scientific community. In this paper, we invested an effort to introduce some numerical indices as a new measure which can describe spatial distributions of physical quantity based on the complexity computed by the Lempel–Ziv algorithm (LZA) or Lempel–Ziv complexity (LZC).

In this paper, we have proposed a new chaotic megastable oscillator which has both conservative and dissipative characters depending on the selection of parameters. Various dynamical characteristics including megastability of the new system are investigated and presented. The bifurcation plots and the corresponding Lyapunov exponents (LEs) confirm the existence of both dissipative and conservative oscillations in the system. The proposed megastable oscillator is used as a carrier generator in a differential chaos shift keying (DCSK). Another application of the new chaotic oscillator is shown by using it in developing a random number generator (RNG) and the NIST test results are presented to show the statistical complexity of the new system.

For the fabricated AlGaN/GaN high electron mobility transistors (HEMTs) with different Ohmic contact widths, the gate-channel electron mobility is obtained experimentally. Mobility curves show very different values and trends. This phenomenon is investigated with the scattering theory in AlGaN/GaN HEMTs. The reason for the different mobility curves is found to be attributed to the different polarization charge distributions at the AlGaN/GaN interface. The AlGaN/GaN HEMT with a smaller Ohmic contact width corresponds to positive additional polarization charge near the Ohmic contact. The AlGaN/GaN HEMT with a larger Ohmic contact width corresponds to negative additional polarization charge near the Ohmic contact. Changing the Ohmic contact width will be a new dimension to optimize the characteristics of AlGaN/GaN HEMTs effectively.

Modification of surface of natural fibers by high energy electron beam irradiation (6 MeV) is a process for enhancing the adhesion between fiber and matrix. Composites reinforced with natural fiber have gained a prominent place in the field of research and innovation due to the advantages such as low cost, light weight and environment friendly factors. We have studied the thermal properties such as thermal degradation and crystallinity behavior of biodegradable composites using biodegradable polymer poly (lactic) acid (PLA) and fiber of luffa cylindrica (LC) fabricated by using injection molding technique. First, reinforcement LC fibers are irradiated with electron beam of 0.5, 1.0, 2.0, 4.0 and 10.0 Gy using 6 MeV linear accelerator at room temperature in presence of air. The thermal properties like glass transition temperature $(T_g)$, cold crystallization temperature $(T_{cc})$, melting peak temperature $(T_m)$ and thermal stability of the composites are studied using differential scanning calorimetry (DSC) in the temperature range from 30${}^{\circ }$C to 250${}^{\circ }$C and thermogravimetric analysis (TGA) in temperature range from 20${}^{\circ }$C to 700${}^{\circ }$C. The variation of these properties in response to the irradiation dose is analyzed in detail. It is observed that with increase in irradiation dose, glass transition temperature and crystallization temperature increase. However, the thermal stability of the composites is found to increase with increase in irradiation dose.

In this study, we constructed the exact traveling and soliton solutions for unstable nonlinear Schrödinger equation (UNLSE) by a modified mathematical method. The UNLSE explains the disorder of a time period in slightly unstable and stable medium, and also accomplishes the instability for modulated carrier wave. The demonstrated soliton solutions represent to bright-dark solitons, periodic solitary wave, and traveling waves. This technique is more efficient and powerful to investigate various kinds of soliton solutions for higher order unstable nonlinear PDEs. By applying symbolic computations, the physical interpretations of soliton solutions represent by two- and three-dimensions graphical. Our obtained results may helpful in the study of nonlinear optics, fiber optics, solitonic dynamic, and various kinds of physical sciences.

The sheet/cloud cavitating flow always contains complex multiscale vortex structures generated by the cavity cloud shedding and collapsing. In this study, the transient sheet/cloud cavitating flow around a Clark-Y hydrofoil is numerically investigated using the Large Eddy Simulation (LES) method coupled with the Zwart–Gerber–Belamri (ZGB) cavitation model. The simulation accurately reproduces the unsteady cavitation evolution process, and the predicted time-averaged lift and drag coefficients, total vapor volume variation and velocity distribution agree fairly well with the experimental measurements. The cavitation vortex dynamics are studied in detail with different vortex identification methods including the vorticity method, the $Q$-criterion method, the ${\lambda }_2$ method, the $\mathrm{\Omega }$ method and the Liutex method. The vortex identification ability of the different methods in the transient sheet/cloud cavitating flow is also discussed. Generally, the Liutex method combines the advantages of the other methods and can accurately identify both the vortex position and strength. Further analysis of cavitation-vortex interactions demonstrates that the cavity cloud shedding and collapsing have a pronounced influence on the vortex structure.

We use the Chern–Simons action for a $𝕊𝕆(3)$-connection for the description of point disclinations in the geometric theory of defects. The most general spherically symmetric $𝕊𝕆(3)$-connection with zero curvature is found. The corresponding orthogonal spherically symmetric $𝕊𝕆(3)$ matrix and $n$-field are computed. Two examples of point disclinations are described.

Temporal birefringent effects in the fibers change the crosstalk behaviors inside and between the fiber cores in the linear and non-linear optical power areas. This paper studies a non-linear Schrödinger system with the four-wave mixing term, which describes the optical solitons in a birefringent fiber. We construct the generalized Darboux transformation, and acquire the higher-order semirational solutions consisting of the second- and third-order semirational solutions, which represent the complex amplitudes of the electric fields in the two orthogonal polarizations. We acquire the interactions between/among the two/three solitons. Such interactions are elastic and generate the rogue waves around the interacting regions. We obtain the interactions among the second-/third-order rogue waves and two/three solitons, respectively. When $|dc-|b{|}^2|$ decreases, amplitude of the second-order rogue wave increases, with $d$ and $c$ accounting for the self-phase modulation and cross-phase modulation, respectively, while $b$ representing the four-wave mixing effect. With $|dc-|b{|}^2|$ kept invariant, when $c$ increases and ${\sigma }_1=0$, amplitudes of the second-order rogue wave and two bright solitons increase, while when $d$ increases and ${\sigma }_2=0$, amplitudes of the second-order rogue wave and two dark solitons increase, with ${\sigma }_1$ and ${\sigma }_2$ being the constants.

Local resonance structure (LRS) can effectively suppress wave transmission, but the design of LRS with tunable band gaps is still a challenge. This work proposes an LRS with two tunable band gaps, where the first bandwidth is successfully enlarged almost five times, and finally a low-frequency broadband with 60–420 Hz is obtained with the second disappearing because of the remarkable modification of band gaps obtained only by adjusting the stiffness rather than by large deformation or changing geometric configuration in traditional methods. The mechanism of tunable band gaps would have important implications for designing metamaterials with broadband, and potential applications for vibration and noise attenuation.

This paper is devoted to obtaining some new types of exact solutions of the (2+1)-dimensional Date–Jimbo–Kashiwara–Miwa (DJKM) equation utilizing the Lie symmetry method. All the Lie symmetries, infinitesimal generators, and possible geometric vector fields have been obtained by using the invariance condition of the group-theoretic method. Meanwhile, the Lie symmetry reductions and explicit exact solutions are obtained by a one-dimensional (1D) optimal system. All the obtained exact solutions are absolutely new and completely different from the earlier established results in the literature. Moreover, the dynamical behavior of obtained solitons like doubly solitons, dark solitons, kink wave, curved shaped multi-solitons, parabolic waves, solitary waves, and annihilation of elastic multi-soliton profiles is depicted graphically via interesting 3D-shapes. That will be widely used to provide many more attractive complex physical phenomena in the fields of plasma physics, statistical physics, fiber optics, fluid dynamics, condensed matter physics, and so on. Finally, we have verified all the achieved soliton solutions through symbolic computations with Mathematica.

The directed transport of inertial Lévy flights resulting from the superimposed roughness in a corrugated potential is investigated in this paper. The influence of the roughness on the transport is studied by calculating the mean velocity (MV) and the mean first escape time (MFET), with respect to the Lévy index $\mu$ and the asymmetry parameter $q$ which determines the asymmetry of the potential. The results indicate that the particles’ directed transport caused by the asymmetry of the potential will be counteracted by the roughness, which behaves as the absolute value of the MV decreases with roughness $𝜀$ increasing, and the MFET increases with $𝜀$ increasing, correspondingly. Though smaller Lévy index $\mu$ can produce more large jumps, which yield the enhancement of the directed transport, since the roughness superimposed on the corrugated potential supplies the hinder effect, the directed transport is also weakened after the appearance of the roughness.

In this paper, a receiver front-end in 180 nm CMOS operating at 28 GHz is presented. The receiver front-end consists of a cascade low-noise amplifier (LNA) with two gain stages and a current-bleeding active mixer with tunable loads. By embedding a quadrature coupler into the mixer, the circuit delivers in-phase and quadrature outputs. The proposed architecture avoids the traditional I/Q implementation by process-sensitive quadrature voltage control oscillators (VCOs) with larger power consumption at high frequencies. The adopted transformers and inductors are optimized by a momentum tool. The simulated results show that the receiver front-end provides an NF of 5.48 dB, a conversion gain of 18.1 dB, and an IIP3 around −8.5 dBm at 28 GHz. The circuit dissipates 17.3 mW under a 1.8 V supply.

Single crystals of AgCuS, ${\mathrm{\text{Ag}}}_{1.55}{\mathrm{\text{Cu}}}_{0.45}\mathrm{\text{S}}$, ${\mathrm{\text{Ag}}}_{1.55}{\mathrm{\text{Cu}}}_{0.45}\mathrm{\text{S}}$ and ${\mathrm{\text{Ag}}}_{1.55}{\mathrm{\text{Cu}}}_{0.45}\mathrm{\text{S}}$ compounds were synthesized using the Bridgman method. The crystal structures and phase transitions were studied by X-ray diffraction (XRD) method in the high temperature ranges. The monoclinic, orthorhombic, hexagonal and cubic phases were observed in the temperature range of $300\mathrm{\text{K}}\le T\le 870\mathrm{\text{K}}$. Thermal expansion coefficients were calculated for different phases according to the lattice parameters. It was determined that the values of thermal expansion coefficients differ in different planes depending on the space group and symmetry.

Quantum measurements based on mutually unbiased base (MUB) are commonly used in quantum information processing. Firstly, we construct two completed unextendible maximally entangled bases (UMEBs) in bipartite systems $C^d\otimes C^{q(d+1)}$. Then, the sufficient and necessary conditions of these two UMEBs develop into MUB can be obtained. Finally, we present some UMEBs that are mutually unbiased in concrete bipartite systems. These results provide a method to construct the best measurement bases.

The concept of geometric phase acquired by a quantum state during its evolution is generalized to the subspace of states of evolving quantum system. Physical motivation of this generalization comes from the effect of coherent population trapping. Under certain conditions, there exists a two-dimensional “dark” subspace of atomic ground states that does not interact with the external radiation. The structure of this “dark” subspace depends on the local field amplitude. We show that certain mathematical difficulties in finding the geometric phase for “dark” subspaces can be circumvented with the help of the orthogonal “bright” subspace.

The lower harmonic intensity is still the reason that limits the application of attosecond pulse. Thus, in this paper, on the basis of resonance ionization schemes, we propose the effective methods to improve the harmonic intensity of atomic and molecular systems. For atomic system (i.e. He atom), with the combination of chirped-UV pulse, not only the harmonic cutoff can be extended, but also the harmonic intensity can be enhanced, caused by the UV resonance ionization between ground state and excited state. As a result, the single harmonic energy peak (HEP) with the higher intensity and higher emitted photon energy can be obtained, which can support the attosecond pulses shorter than 40 as. For the molecular system (i.e. ${\mathrm{\text{H}}}_2^{+}$ and ${\mathrm{\text{D}}}_2^{+}$), by properly choosing the pulse duration of the fundamental pulse, the time region of charge resonance enhanced ionization (CREI) can be well controlled. Therefore, the maximum HEP with the higher intensity can be obtained. Second, by properly adding a half-cycle unipolar pulse, the selected maximum HEP in the CREI region can be further extended. Thus, an intense and broad spectral region can be produced, which can generate the attosecond pulses with durations of 36as.

The study focuses on the use of a direct algebraic approach to the analysis of the Triki–Biswas (TB) model. This model addresses the distribution of ultrashort pulses in optical fiber in the presence of non-Kerr dispersion concept and group velocity dispersion. However, using the new extended direct algebraic method, we have obtained various optical soliton solutions for the TB model. The optical soliton solutions are new and reliable compared to the existing methods.