Modern Physics Letters B

Flexible surface enhanced Raman scattering (SERS) substrate was prepared by modification of sandpaper with silver nanoparticles. Under 633 nm excitation wavelength, the SERS enhancement effect of sandpapers which were treated with silver nanoparticles were evaluated by collecting Raman signals of probed molecules. The results demonstrate that the SERS enhancement effect of white (12,000 meshes) is better than that of pink (8000 meshes) sandpaper under the same condition; when the concentration of probe molecules is $10^{-4}$ mol/L, white sandpaper has the best SERS enhancement; the Raman scattering spectrum has better signal when the silver sol is 15 $\mu \mathrm{\text{L}}$.

The purpose of this work is to introduce a novel 4D chaotic system and investigate its multistability. The novel system has an unstable origin and two stable symmetrical hyperbolic equilibria. When the parameter increases across a critical value, the equilibria lose their stability and double Hopf bifurcations occur with the appearance of limit cycles. A pair of point, periodic, chaotic attractors are observed in the system from different initial values for given parameters. The chaos of the system is yielded via period-doubling bifurcation. A double-scroll chaotic attractor is numerically observed as well. By using the electronic circuit, the chaotic attractor of the system is realized. The control problem of the system is reported. An effective controller is designed to stabilize the system.

The influences of second-order dispersion (SOD) and third-order dispersion (TOD) on spectral properties of wavelength conversion based on FWM at mid-infrared region (mid-IR) are theoretically investigated in a silicon nitride waveguide. It is found that the SOD and TOD can affect the frequency shift and temporal profiles of idler pulses. Moreover, the temporal and frequency spectrum of output signal are also discussed with different SODs and TODs. Meanwhile, the numerical simulation results imply that the efficiency of FWM process will be reduced and the wavelength range of phase-match will be shifted due to the change of SOD or TOD.

The results of calculations of the electron structure for Ag₂S and Ag₂Se crystals from first-principle in the framework of density functional theory (DFT) are presented in this work. The origin of the bands from $s,p$ and $d$ electron states of Ag, S and Se atoms are investigated. It was established that the orthorhombic Ag₂Se crystal shows semiconductor properties in P222₁ and P2₁2₁2₁ space groups and semimetallic properties in Im-3m space groups with cubic crystal system. Monoclinic crystal type of Ag₂S shows semiconductor properties in P2₁/c space group. However, semimetallic properties manifested itself in monoclinic Ag₂S in P2₁ and cubic Ag₂S structure in Im-3m phases.

The formation and characterization of multiferroic Gadolinium Ferrite (GdFeO₃) nanoparticles has been demonstrated in detail. The structural, magnetic, magnetodielectric, ferroelectric, optical and electrical properties are studied at different temperature ranges. Dielectric properties, DC and AC transport properties and dielectric relaxation behavior are analyzed in electrical characterization. XRD pattern confirms the phase formation where crystallite size, lattice strain, etc. are carried out by Rietveld refinement and Williamson–Hall plot. Average particle size is 64 nm, which is calculated from TEM image. Mixed ferroic order of ferromagnetism and antiferromagnetism along with exchange bias are detected in the nanoparticles. Ferroelectric nature of the sample is confirmed by the P-E hysteresis loops. Positive magnetodielectric coupling is observed in GdFeO₃ nanoparticles, which is a signature of multifunctionality nature. Charge transport mechanism of DC and AC applied electric field is successfully analyzed with Mott’s variable range hopping (VRH) and correlated barrier hopping (CBH) theoretical models, respectively. Non-Debye type relaxation behavior is observed with activation energy of 0.37 eV. Optical band gap is calculated from the Tauc plot (2.98 eV) which confirms the semiconducting nature of the sample. Existence of ferromagnetic/antiferromagnetic (FM/AFM) and ferroelectric along with magnetodielctric coupling ensures the multiferroic property of GdFeO₃ nanoparticles, which may enhance potentiality in spintronic device applications.

We show the possibility of describing fractional exclusion statistics (FES) as an occupancy process with global and local exclusion constraints. More specifically, using combinatorial identities, we show that FES can be viewed as “ball-in-box” models with appropriate weighting on the set of occupancy configurations (merely represented by a partition of the total number of particles). As a consequence, the following exact statement of the generalized Pauli principle is derived: for an $N$-particles system exhibiting FES of extended parameter $g=q/r$ ($q$ and $r$ are co-prime integers such that $0<q\le r$), (1) the allowed occupation number of a state is less than or equal to $r-q+1$ and not to $1/g$ whenever $q\ne 1$ and (2) the global occupancy shape is admissible if the number of states occupied by at least two particles is less than or equal to $(N-1)/r$ ($N\equiv 1modr$). These counting rules allow distinguishing infinitely many families of FES systems depending on the parameter $g$ and the size $N$.

Moments play an important role in image analysis and invariant pattern recognition. There are two types: orthogonal moments and non-orthogonal moments. Orthogonal moments perform better than non-orthogonal moments, they have properties such as robustness to image noise and geometrical invariant properties such as scale, rotation and translation. In this paper, an improvement in fingerprint recognition is done by using the Non-subsampled contourlet transform (NSCT) and the Zernike moments (ZMs). NSCT decomposes the fingerprint images into NSCT subbands. Thereafter, ZMs are used to evaluate the features of fingerprint images. Thereafter, feature selection technique is applied to select potential features from the obtained features using coefficient of determination. Thereafter, a well-known weighted-support vector machine is also used to train and test the evaluated features. Extensive experiments reveal that the proposed technique achieves significant improvement over the existing techniques in terms of accuracy, sensitivity, specificity, $f$-measure, kappa statistics and execution time.

Hirota equation is a modified nonlinear Schrödinger (NLS) equation, which takes into account higher order dispersion and delay correction of cubic nonlinearity. The propagation of the waves in the ocean is described, and the optical fiber can be regarded as a more accurate approximation than the NLS equation. Using the algebraic reductions from the Lie algebra $gl(n,ℂ)$ to its commutative subalgebra $Z_n$, we construct the general $Z_n$-Hirota systems. Considering the potential applications of two-mode nonlinear waves in nonlinear optical fibers, including its Lax pairs, we use the algebraic reductions of the Lie algebra $gl(2,ℂ)$ to its commutative subalgebra $Z_2=ℂ[\mathrm{\Gamma }]/({\mathrm{\Gamma }}^2)$. Then, we construct Darboux transformation of the strongly coupled Hirota equation, which implies the new solutions of $(q^{[1]},r^{[1]})$ generated from the known solution $(q,r)$. The new solutions $(q^{[1]},r^{[1]})$ furnish soliton solutions and breather solutions of the strongly coupled Hirota equation. Furthermore, using Taylor series expansion of the breather solutions, the rogue waves of the strongly coupled Hirota equation can be given demonstrably. It is obvious that different images can be obtained by choosing different parameters.

Velocity–temperature correlations in a high-temperature supersonic turbulent channel flows, including thermally perfect gas (TPG) and calorically perfect gas (CPG), are investigated based on the direct numerical simulation database [Chen et al., J. Turbul. 19 (2018) 365] to study the gas model effects. The results show that in fully developed turbulent channel flow, the Reynolds analogy factor remains close to 1.2 for both gas models. The “recovery enthalpy” is better than Walz’s equation to connect the mean stream-wise velocity with mean static temperature because it is independent with gas models. The modified strong Reynolds analogy for TPG is more accurate scaling than that for CPG, and the turbulent Prandtl number is insensitive to gas models. In addition, the influence of gas model on the probability density functions of stream-wise velocity and static temperature concentrate on the corresponding right tails.

It is well known that Fano effect usually requires the introduction of asymmetric (or breaking) in their structure designs. The smaller the degree of breaking, the more obvious the Fano effect. However, the small degree of breaking demands extremely precise manufacturing capabilities and levels. This paper proposes a novel robust metallic array structure that can achieve a Fano-like effect with a high $Q$-factor as 73, consisting of a square patch and a closed-ring resonator. This distinct Fano-like resonance originates from the interactions of quadrupole resonance mode and dipole resonance mode. Moreover, the effect of the size and conductivity of the square patch on the Fano effect are discussed, and the sensing performance of this structure is also discussed. These results will pave the way for designing practical sensors and optical switches in the terahertz frequency range.

As regards the copper oxide nanowire growth process, our experiment was consistent with the proposal of copper ions surface diffusion on a nanowire. Simply in the atmospheric pressure it is possible to synthesize CuO nanowires by annealing a copper sheet. Under a general copper oxide nanowires occurring condition, pouring the flow rate of a slight amount of air into an enclosed electric furnace in the atmospheric pressure, copper oxide nanowires adhering copper particles were synthesized on copper sheet successfully. In the growth process of the CuO wire, when the Cu substrate was heated in the air, stresses caused grain boundaries of Cu₂O and CuO layers in the Cu substrate. Ultimately Cu ions formed a wire tip diffusing on the surface of a CuO wire in the vertical direction to the top surface of the CuO layer, while assembling to the tip. In this report, we describe characteristics of the structure of the CuO nanowire obtained by lowering the air flow rate.

The optical transmission properties in a three-slit metal grating with different mediums are studied. The results show that the tunable phase resonances and multiple phase resonances can be obtained by filling different mediums into the three slits of the straight channel grating. When the medium in the three slits is extremely asymmetric, the phenomenon of multiphase splitting becomes very obvious. In addition, based on the field distributions, multiphase resonant mechanisms have been proposed for the physical origins of the observations. In addition, a multi-channel selector is described by flexibly controlling the light through any slit of the grating. Compared with the conventional compound grating, this grating with different mediums has obvious advantages, such as simple structure, and ease of implementation.

In this paper, using the Bernoulli sub-equation function method, we obtain new dark, complex and singular soliton solutions for the longitudinal wave equation in a magneto-electro-elastic circular rod with $M$-derivative. Many new complex singular soliton solutions are successfully extracted. For better understanding of physical meanings, we plotted 2D and 3D graphs along with contour simulations.

In this paper, the phenomenon of inverse stochastic resonance (ISR) induced by Levy noise is investigated in a single neuron. Firstly, the discharge of Hodgkin–Huxley neuron at different current strengths without noise is studied. Then we cite the concept of average spiking rate and use it as a scale to measure the discharge of neuron. Under the influence of Levy noise, it is found that the average firing rate can reach a minimum caused by stability index and a scale parameter of Levy noise. The conclusion is that ISR could be induced by Levy noise when the input current strength reaches the critical threshold. Besides, in order to further prove that Levy noise can produce ISR, interspike intervals (ISIs) histogram is used for studying discharge patterns in voltage. Finally, we find that with the increase of stability index and scale parameter of Levy noise, the total number of ISIs decreases first and then increases, which implies the appearance of ISR.