International Journal of Modern Physics B

In this paper, we address the influence of Dzyaloshinskii Moriya (DM) interaction on the thermodynamic properties of a multiferroic antiferromagnetic spin system using the spin wave theory (SWT) as a diagonalization method which, associated to the statistical physics, helps to evaluate the statistical sum. The basic factors in thermodynamics, such as the Boltzmann entropy and the specific heat capacity at thermal equilibrium, are obtained. Analyzing the numerical results, it follows that the DM interaction is the best candidate that can help to maintain in long time the system in its coherent state. Furthermore, we find that the influence of the DM interaction is more accentuated at low-temperature and that it enables the system to release heat energy. On the other hand, the fact that the specific heat capacity tends to the constant clearly shows that the system obeys the Dulong–Petit law. In addition, our results also show that for high magnetic field (greater than B=30 Tesla), the magnetic field dependence of both entropy and specific heat shows a peak-like behavior and that the DM interaction raises the corresponding critical magnetic field but lowers the peak amplitude. It follows that the spin-flop transition occurs in the system and that the strong magnetic field withdraw the antiferromagnetic phase. Overall, we find that the DM interaction is a promising candidate for the control of our system.

The elemental sulfur solubility in sour gas plays an important role in H₂S-rich gas reservoir development and transportation. While the solubility of elemental sulfur in sour gas can be measured in macroscopical respect, the interaction of solid deposition is not clear at microscale. In this work, molecular dynamic simulation (MD) was adopted to predict the solubility of elemental sulfur in hydrogen sulfide at nanoscale. It is found that the results of new nanoscale solubility model are close to the reported experimental data. The average relative error of the solubility of elemental sulfur in hydrogen sulfide by using the new model is 11.05% compared with the experimental data. Therefore, the new model can be used to predict the solubility of elemental sulfur in hydrogen sulfide.

Noise and delay are ubiquitous in brain and they have significant effects on neuronal network synchronization and even brain functions. Based on a small-world neuronal network of delayed FitzHugh–Nagumo (FHN) neurons subjected to sine-Wiener (SW) bounded noise, the effects of delay and SW noise on synchronization and synchronization transition are numerically investigated by calculating a synchronization measure R and plotting spatiotemporal patterns. The phenomenon of delay-induced synchronization transition is observed as delay $\tau$ is increased. And large self-correlation time and strength of SW noise can increase the number of delay-induced synchronization transition. In addition, delay-induced synchronization transition is robust against the change of topology structure of neuronal network and this phenomenon becomes much easier to see for small nearest neighbors k in the small-world network. Since synchronization transition may imply functional switch, our results may have important implications, and inspire future studies.

30-pair AlAs/GaAs distributed Bragg reflector (DBR), which has 1030 nm center reflectivity, is studied extensively by means of High Resolution X-ray Diffraction (HR-XRD) and reflectivity measurements. Theta/2-Theta measurements and dynamical simulations have been done for (002), (004) and (006) planes to determine strain and thickness of AlAs and GaAs layers in the DBR stack. Reciprocal space mappings (RSMs) are measured for same planes and also for (224) plane to find out tilt and relaxation of the DBR stack. Relaxation is not observed and it is confirmed with symmetric in-plane (400) Theta/2-Theta and RSM measurements. This is a first study in the literature according to the best of our knowledge. Finally, we have shown sensitivity of high angle diffraction planes to disorders in crystal. Angle-dependent reflectivity simulations have been also done and compared with measurements. 99.99% reflectivity is obtained with 99.5 nm stop bandwidth and 482.7 nm penetration depth.

A key property for the design of new shape memory alloys is their working temperature range that depends on their transformation temperature T₀. In previous works, T₀ was predicted using a simple linear regression with respect to the energy difference between the parent and the martensitic phases, $\mathrm{\Delta }$E${}_{p-m}$. In this paper, we developed an accurate method to predict T₀ based on machine learning assisted by the first-principles calculations. First-principles calculations were performed on 15 shape memory alloys; then, we proposed an artificial neural network method that used not only computed $\mathrm{\Delta }$E${}_{p-m}$ but also bulk moduli as input variables to predict T₀. The prediction error of T₀ was improved to 49 K for the proposed artificial neural network compared with 188 K for simple linear regression.

In this study, a novel metamaterial absorber (MA) is designed and numerically demonstrated for solar energy harvesting. The structure is composed of three layers with different thicknesses. The interactions of three layers bring about the plasmonic resonances. Although the main operation frequency of the structure is chosen between 430 and 770 THz, which is the visible light regime, the proposed structure is also investigated in the ultra-violet (UV) region. One can see from the results that the proposed structure carries nearly perfect absorption capacity that is more than 91% at the whole visible light spectrum. The proposed structure even has the absorption capacity of 99% between 556 and 657 THz. In addition, the designed MA is also investigated in terms of its polarization and angle independency. Results show that the proposed structure is independent from the polarization and incident angles. Lastly, the designed structure can be considered to be used in solar energy applications as a harvester since it has an ultra-broadband absorption characteristic in visible light regime.

Quantum Hall devices for primary resistance metrology based on the GaAs/Al${}_x$Ga${}_{1-x}$As heterostructure were fabricated and compared with the devices from international metrology organization International Bureau of Weights and Measures (BIPM) by calibrating the same 100 $\mathrm{\Omega }$ transfer standard resistor with a cryogenic current comparator. Relative deviation between NIM-made device NIM-C1 and BIPM-made device BIPM-1 was −4.49 parts in 10⁹ with an uncertainty of 3.63 parts in 10⁹ which indicated NIM-C1 satisfied the requirement for the primary resistance standard.

In this paper, the classical lattice dynamics for the two-dimensional diced and decorated honeycomb lattices in the harmonic approximation is studied. The numerical results for the vibrational mode frequencies are presented.

In this paper, fixed-time cluster synchronization of directed community networks (DCNs) with diverse coupling and different-order nodes is explored. For the DCN model, the inherent dynamics and state dimensions of the nodes in different communities can be nonidentical, and moreover, the interactive nodes can differ in their types of connections in different communities and the connections between any pair of different communities can be nonidentical as well. Two types of control strategies, state feedback control and adaptive feedback control, are adopted to force such DCNs to realize cluster synchronization in fixed-time. By utilizing reduction to absurdity, some sufficient conditions ensuring the fixed-time cluster synchronization are derived for the proposed two control schemes. Moreover, it is revealed theoretically that our estimated settling time is more precise and less conservative than that presented in the previous researches. Finally, the validity of the obtained fixed-time cluster synchronization criteria is verified via numerical simulations.

The current study investigates theoretically and numerically the entropy generation in time-dependent free-convective third-grade viscoelastic fluid convection flow from a vertical plate. The nondimensional conservation equations for mass, momentum and energy are solved using a Crank–Nicolson finite difference method with suitable boundary conditions. Expressions for known values of flow-variables coefficients are also derived for the wall heat transfer and skin friction and numerically evaluated. The effect of Grashof number, Prandtl number, group parameter (product of dimensionless temperature difference and Brinkman number) and third-grade parameter on entropy heat generation is analyzed and shown graphically. Bejan line distributions are also presented for the influence of several control parameters. The computations reveal that with increasing third-grade parameter, the entropy generation decreases and Bejan number increases. Also, the comparison graph shows that contour lines for third-grade fluid vary considerably from the Newtonian fluid. The study is relevant to non-Newtonian thermal materials processing systems.

In this paper, we present the results of the temperature dependence studies of the photoinduced phonon mode which appears in a ferroelectric-semiconductor Sn₂P₂S₆ (SPS) crystal under the influence of femtosecond laser pulses. We show that its behavior reminds the soft mode one near the phase transition. However, the observed decrease in the oscillation frequency in the vicinity of Curie temperature Tc is much weaker than previously reported. This can be explained by the shadowing of the pure soft mode by its interaction with other photoinduced modes.

Based on the density functional theory (DFT) and using the generalized gradient approximation (GGA) and GGA-mBJ approximations, the electronic and optical properties of the bulk and mono-layer Molybdenum sulphoselenide MoS${}_x$Se${}_{(2-x)}$ ($0\le x\le 2$) are calculated. In both bulk and mono-layer cases, the energy gap decreases by increasing the density of the Se atom, so that the reduction in the mono-layer case is more observable than the bulk case. Also, the variation of the exchange-correlation (XC) potential has the maximum and minimum effects on the bulk MoS₂ and the mono-layer MoSe₂ cases, respectively. The static dielectric function of MoS₂ in the ${𝜀}_1(\omega )$ as well as its optical conductivity is less than the other two compounds. In the mono-layer case along $x$-direction, the first response to the incident photon belongs to MoS₂ in the infrared region, while the other two compounds respond in the edge of the visible area. The intensity of the MoSSe response, unlike its bulk case, is less than the other compounds. Along $z$-direction, the first response is observed in the visible area. The remarkable point is that the optical stability in the bulk case is more than that in the mono-layer case.

In this research, LiMn₂O₄ nanopowders were synthesized via sol–gel method using gelatin as a novel chelating agent. The effect of temperature and pH on the structure, morphology and particle size of synthesized powders has been investigated by the differential thermal analysis (DTA), the X-ray diffraction (XRD), the Fourier transform infrared (FTIR) and the field-emission scanning electron microscope (FESEM). The crystal structure of LiMn₂O₄ was completely formed without any impurity phase at a calcination temperature of 750${}^{\circ }$C. The peak intensity ratio of I${}_{400}$/I${}_{311}$, which presents the stability of LiMn₂O₄ structure, is bigger for the sample with pH=4 than that of the samples with pH=7 and 8. The sample with pH=4 has smaller particles of about 70 nm, with more homogeneity and less agglomeration than that of the other samples. At calcination temperature to 850${}^{\circ }$C, the size of the particles has become bigger and the particle surfaces show more clarity in all samples. The effect of the pH value on electrochemical properties was studied by galvanostatic charge/discharge tests. The results show more capacity lost for the sample with pH=8 with regards to the other samples.

In order to effectively depict the queuing state of pedestrians at the exit of interior space, a new pedestrian evacuation model is proposed based on cellular automation and S-queue. This model firstly defines the calculation equation of the pedestrian movement probability based on the floor field and queue length, and derives the calculation equation of queue length according to the S-queue theory. Finally, pedestrians are organized for real evacuation in the interior space, and an experimental platform is constructed for simulation analysis according to the real environment, and the relationship between parameters, e.g., exit width, evacuation time, queue length, evacuation velocity and pedestrian density, etc. are studied in depth. The results show that the evacuation strategy that emphasizes the queuing effect helps to reduce the number of pedestrian in queue, especially when the crowd density is larger, such strategy can effectively reduce the evacuation time.