Modern Physics Letters B

The study of bonding mechanism is important for the application of graphene in micro-electro-mechanical system (MEMS). Using molecular dynamics (MD) simulation, the adhesion behavior of graphene on silicon substrate was observed, by applying a constant vertical upward exfoliation velocity to graphene. The effects of silicon substrate size, graphene layer number and exfoliation velocity on adhesion properties of graphene were studied. The minimum velocity to exfoliate monolayer graphene was 4.3 Å/ps, and the maximum adhesive force was 25.04 nN. For two-layer graphene, velocity was applied on the top layer, 5.2 Å/ps and 12 Å/ps were the critical velocities: when the velocity was no more than 5.2 Å/ps, the top layer cannot be exfoliated; as the velocity was in the range of 5.2–12 Å/ps, the second layer was driven upward together with the top layer, because of interlayer interaction between graphene layers; when the velocity increased greater than 12 Å/ps, the top layer graphene was broken through the bonding forces of substrate and the second layer, and exfoliated alone. It can be concluded that the velocity to exfoliate graphene was extremely high, and the adhesion energy was 299.81 mJ/m² and 323.41 mJ/m² for exfoliating monolayer and two-layer graphene respectively, thus the adhesive strength between graphene and silicon was very strong.

A hard-sphere model strictly guaranteeing the uncrossability of polymer chains is used to simulate the relaxation process of the linear and ring polymers. The statistical and dynamic properties of both linear and ring chains are obtained by using Monte Carlo algorithm. We find that the relaxation time of a self-avoiding ring polymer is smaller than the time required for the polymer to move a distance of order of its own size. Moreover, the stretching properties of linear and ring polymers are also studied, and the results show that the elongation curve of a ring polymer is almost identical to that of a linear polymer except under the situation of small external force.

We describe in great generality features concerning constrained entropic, functional variational problems that allow for a broad range of applications. Our discussion encompasses not only entropies but, potentially, any functional of the probability distribution, like Fisher-information or relative entropies, etc. In particular, in dealing with generalized statistics in straightforward fashion one may sometimes find that the celebrated relation between entropic small changes and mean energy ones, $\frac{dS}{d\beta }=\beta \frac{d〈U〉}{d\beta }$, does not seems respected. We show here that, on the contrary, it is indeed obeyed by any system subject to a Legendre extremization process, i.e. in all constrained entropic variational problems.

The main purpose of this paper is to further explore the complexity of fuzzified dynamical systems. Especially, we study several kinds of specification properties of Zadeh’s extension. Among other things, we discuss the “stronger” sensitivity on product dynamical systems of g-fuzzification. There are two major ingredients. Firstly, it is proved that the specification (respectively almost specification) property of the original system and its Zadeh’s extension is equivalent, when the original system has the shadowing property. Moreover, we study the $\mathcal{ℱ}$-sensitivity (respectively multi-sensitivity) of g-fuzzification and its induced product dynamical system.

The impact of molybdenum ditelluride (p-type MoTe₂) transition metal dichalcogenide (TMDC) material formation as an interfacial layer between CdTe absorber layer and Mo back contact is investigated. The simulation is conducted using the solar cell capacitance simulator (SCAPS) software. Band gap energy, carrier concentration, and layer thickness of the p-MoTe₂ have been varied in this study to investigate the possible influences of p-MoTe₂ on the electrical properties and the photovoltaic parameters of CdTe thin film solar cells. It has been observed that a thickness of the p-MoTe₂ interfacial layer less than 60 nm leads to a decrease in the cell performance. In regard to the effect of the band gap, a maximum efficiency of 16.4% at the optimum energy gap value of 0.95 eV has been obtained at a doping of $10^{19}{\mathrm{\text{cm}}}^{-3}$. Additionally, increasing the acceptor carrier concentration $(N_A)$ of MoTe₂ enhances the solar cell performance. The solar cell efficiency reaches 15.5% with $N_A$ of $10^{18}{\mathrm{\text{cm}}}^{-3}$ with layer thicknesses above 80 nm. This might be attributed to the possibility of forming a back surface field for the photogenerated electrons, which reduces recombination at the back contact and hence provides a low resistivity contact for holes. The results justify that the MoTe₂ interfacial layer mediates an ohmic contact to CdTe films.

Barium molybdate (BMO) powders doped with Re${}^{3+}$ (Eu, Sm, Tb, Dy) were successfully synthesized by the solid-state reaction with the assistance of polyvinyl alcohol (PVA). The effects of the reaction conditions and activator ions on the structural and luminescence properties of BMO were extensively investigated. The results of powder X-ray diffraction (XRD) and Raman spectra exhibited the structures of the phosphors, which demonstrate that the Eu${}^{3+}$ have been effectively doped into the BaMoO₄ (BMO) lattice. The factors of PVA amount, Eu${}^{3+}$-doped concentration and different dopants on phosphor samples were investigated via photoluminescence (PL) measurements. The as-synthesized samples degrade as a two-step degradation by thermogravimetric analysis. BMO phosphors show strong multicolor emission with different dopant RE${}^{3+}$ ions: red–orange (Eu${}^{3+}$), red (Sm${}^{3+}$), green (Tb${}^{3+}$) and green–yellow (Dy${}^{3+}$) under ultraviolet excitation, which may find potential applications in light phosphor powders, light-emitting diodes (LEDs) and device in photochemical field.

We have designed and developed a metamaterial (MTM)-based multipurpose sensor structure capable of sensing moisture, liquid (ethyl alcohol-ethanol-in our case) density in pure water and the concrete aging. The structure is composed of a rectangular shape MTM cell resonator which can be adjusted to any desired frequency range depending on the application area and the material to be sensed. The material is put into a plastic rectangular pipe placed in a hole located in the middle of the structure. Depending on the response of the proposed model to the electromagnetic properties of the material under test (MUT), overall resonance frequency shifts providing the information to accurately estimate the soil moisture, concrete age and density rate of the sensed liquid samples in real time. The resonance frequency has been carefully chosen so that the MUT has a linear variation in its electromagnetic response behaviors. It is aimed for future studies to adjust the structure for designing a portable multipurpose sensor device and even adjust it to smart phones and sense the materials by simply using smart phones and a small amount of sample in high efficiency.

The purpose of this paper is to lessen the deviation of printing and to predict the nucleus size of binder droplet infiltration in three-dimensional printing (3DP) technology. The industrial CT is used to scan powders and the parameters of materials are calculated. A spherical model, which is based on the data from industrial CT scanning, predicts the nucleus size. The radius of the sphere is equal to the average radius of the sand particles. The spreading radius of binder droplet on the material is obtained by using the experimental method, and then the nucleus size is calculated by the equations. In order to do research on the process of droplet infiltration more intuitively, we analyze the effects of contact angle, porosity and drop height on the infiltration by using the software Comsol in the simulation. To verify the results of the simulation, the processes of infiltration are recorded by the high-speed digital video camera, and the nucleus size is observed by electron microscope. The study is important to conduct the infiltration experiments and provides a theoretical basis for optimization of process parameters in practical application.

When the hydrogen atom moves, the proton current generates a magnetic field which interacts with the hydrogen electron. A simple analysis shows that for the hydrogen velocity $\frac{v}{c}\ll \alpha$ the dominant interaction between the hydrogen momentum and the electron is of order of ${\alpha }^3\frac{v}{c}m$, where $\alpha$ is the fine structure constant, v is the atom velocity, c is the speed of light and m is the electron mass. Using the Bethe–Salpeter equation, the two velocity-dependent operators of this order are derived. As is well known, the degeneracy of the energy levels with the same principal quantum number, n, and the same quantum number of the total angular momentum, j, but the different orbital angular momenta $l=j\pm 1/2$ is removed by the radiative corrections (the Lamb shift) that are proportional to ${\alpha }^{5}m$. It is shown that the velocity-dependent perturbation interactions remove this degeneracy as well. There is, however, an important difference between the Lamb shifts and the energy-level shifts induced by the atom motion. The Lamb shift is the diagonal correction to the energy separately for each of the degenerate states. The velocity-dependent perturbation interactions result in the off-diagonal energy corrections between the mutually degenerate states. The joint effect of these two perturbations, which are essentially different in their origin, is analyzed. Given their order of magnitude, the crossover from the Lamb shifts to the motion-induced shifts should occur at the atom velocity $v=k{\alpha }^{2}c$, where $k\gg 1$ is a numerical factor dependent on n and j. An experiment using the orbital motion of the Earth is proposed to test the developed theory.

In this paper, analysis, design and simulation of dual-band metasurfaces as the reflection-mode linear to circular polarization converters (RMCPs) consisting of single-buried-layer rectangular patches are carried out. The proposed structure for RMCPs can be realized for all frequency ranges from microwave to optical frequencies. However, two far-infrared frequencies, 2 THz and 10 THz, are considered for the design. Dimensions of the dual-band RMCP are obtained using equivalent transmission line circuit and defining a circular polarization (CP) indicator factor (RLI), which should be about ±1 for CP. An advantage of the proposed RMCP is the wide permitted angle of incidence $(𝜃)$ in both operating frequencies. Simulation results of the proposed RMCP indicate 41.2% and 39.1% bandwidths for 3-dB axial ratio (AR) at 2 THz and 10 THz, respectively with ${𝜃}_{min}=25^{\circ }$ and ${𝜃}_{max}=50^{\circ }$. In addition, higher quality of CP can be obtained by reducing the incident angle difference. For example, 2-dB AR bandwidths of the proposed metasurface are 28.4% and 42.1% at 2 THz and 10 THz, respectively, with ${𝜃}_{min}=25^{\circ }$ and ${𝜃}_{max}=45^{\circ }$.

A four-wave mixing effect on high-power continuous-wave fiber lasers has been demonstrated theoretically and experimentally. Detailed theoretical description of phase matching is presented and we found that the phase matching condition is satisfied at the frequency shift of 5.16 THz. While the intensity in fiber core region is more than about 394 MW/cm², the four-wave mixing products of 1100 nm and 1060 nm were also observed in high-power all-fiber laser. The comparison shows that the experiment result is in good agreement with the simulation result. In addition, the beam quality deterioration for the laser is caused by the four-wave mixing effect and the mode instability. The $M^2$ factor measured at maximal intensity of 478 MW/cm² is 2.80.

We introduced a rigid structure into the acoustic metasurface design, the proposed labyrinth structure is based on the equivalent medium theory and different media are replaced by curly labyrinth. Layered media theory and equivalent medium theory are combined to design the arbitrary acoustic metasurface structure. An acoustic metasurface studied in this paper realized simultaneous phase modulation and energy attenuation in the air, the effective phase modulation range covered from 30${}^{\circ }$ to 90${}^{\circ }$ and the energy attenuation is over 40%. According to layered media theory which could modulate the acoustic wave direction, the metasurface with same function can also be applied to underwater case. Corresponding simulation results are calculated by FEA. Finally, by introducing the curly labyrinth theory, the underwater acoustic metasurface with simultaneous phase modulation and energy attenuation is designed and verified. This paper has potential applications in rigid underwater acoustic metasurface designs with low frequency, adjustable direction and sound energy attenuation.

In this paper, we focus on the (2+1)-dimensional complex modified Korteweg–de Vries and Maxwell–Bloch (CMKdV-MB) equations. According to the relevant Lax pair, the n-fold Darboux transformation (DT) is constructed. In addition, via the DT and symbolic computation, two different kinds of soliton solutions are derived from trivial seed solutions. Meanwhile, the dynamic features of soliton solutions are graphically analyzed.

In the paper, a broadband CMOS active down-conversion mixer is presented. Specifically, a noise-canceling transconductor is developed to reduce the noise figure of the mixer. The current-reuse technique applied to the developed transconductor by stacked nMOS/pMOS architecture not only saves power consumption of the circuit, but also reduces the undesirable parasitics. Moreover, two passive $\pi$-type networks are exploited to absorb internal parasitics of the circuit and guarantee broadband operation. Implemented in an advanced 65-nm CMOS process, post-simulations show that, driven by 0 dBm sinusoidal LO signal, the proposed mixer provides a maximal conversion gain of 15 dB and a NF of 3.9–4.9 dB across RF input frequency range of 0.5–6.5 GHz. The IIP3 and IP1dB of 3.1 and −6.9 dBm are obtained, respectively. The mixer core consumes 7.2 mW from a 1 V supply.