International Journal of Modern Physics B

This paper presents a digital MEMS gyroscope with 40${}^{\circ }$/h instability variation in −40${}^{\circ }$C to 85${}^{\circ }$C, performing 5${}^{\circ }$/h instability variation at normal temperature and 0.01% nonlinearity in the range of ±400${}^{\circ }$/s. This stability was achieved by using temperature compensation for the zero-output value changed after the temperature signal. As the resonant frequency of the mechanical structure varied according to the temperature linearly, a frequency calculator was adopted to detect the temperature of the mechanical structure. And the resolution of the frequency could be up to 0.01 Hz with a 1 MHz clock frequency used, obtaining a 10 Hz bandwidth. The driving mode used a PI controller to control a VGA to maintain at a fixed effective value of the driving signal. The sensing mode contained a low noise C/V convertor and a switch demodulation, which could give the angular velocity signal to the A/D convertor. Then the output data of A/D will be compensated in the digital domain. Finally, the digital output of the gyroscope will be available through a normal SPI serial port. The whole circuit was realized on one chip with an active circuit area of 3.5 mm × 5.2 mm fabricated in a 0.35 $\mu$m CMOS technology. And the MEMS structure and circuit are packaged in a 2.5 cm × 2.5 cm × 2.5 cm aluminum mold. The digital output of the gyroscope earned a noise floor of 0.0024${}^{\circ }$/s.

The influence of the surface electric field on the edge photoconductivity (PC) in undoped and ytterbium-doped (N${}_{\mathrm{\text{Yb}}}$$\sim$ 10${}^{18}$ cm${}^{-3}$) layered GaS crystals at T = 77 K irradiated with gamma quanta was investigated. It was found that the PC of layered crystals in the absorption edge region due to charge exchange of surface levels is formed as a result of electric smoothing of fluctuations in the potential of surface energy bands. The degree of smoothing of the surface bending of the zones depends on the dose of $\gamma$-irradiation, the concentration of impurity atoms and also on the magnitude and direction of the transverse electric field.

In this paper, the structural, mechanical and thermal properties of the four structures of Cu₂ZnSiS₄ were studied on the basis of density functional theory (DFT). The generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE) was used to treat the exchange related energy and potential of total energy calculation. The independent elastic constants of the four structures are calculated, which prove that they are mechanically stable. The bulk modulus, Poisson’s ratios and universal anisotropy indices of Cu₂ZnSiS₄ can be calculated from the obtained elastic constants. In addition, the variation of the bulk modulus with the pressure (0–25 GPa) and temperature (0–700 K) have been reported. In order to further study the compound, the thermal properties of the compound were analyzed by using the quasi-harmonic Debye model, including specific heat, thermal expansion coefficient and Debye temperature.

A multiband tunable electromagnetic induced transparency (EIT) effect in metamaterial at microwave frequency range is investigated. The sandwich structure contains silicon dioxide and gold layers. The metamaterial structure has multiband EIT phenomenon due to coupling with U-Shaped split-ring resonators (SRRs) and cut wire (CW). Two different modes can be obtained in CW and a single band EIT effects in SRRs. Results show that the different resonances in the structure lead to multiband EIT. By adding the finding of the graphene layer on top of the structures, EIT window can be changed obviously. It is shown that the graphene can adjust EIT phenomenon. The group index is calculated to exhibit the slow light effect. The demonstrated phenomenon can provide valuable variety of important applications, including microwave communication technology, microwave devices, slow light and switch devices.

When virus spreads in a network, individuals may adaptively change their contact relationships to reduce risk of infection. In order to describe the interaction between a time varying network topology and the dynamics of the nodes, here we propose a susceptible–infected–susceptible (SIS) model on a weighted adaptive heterogeneous network where the dynamics of and on the networks are described. Rewiring strategies are designed to inhibit the epidemic spreading. Our results show that network topology and individual behaviors have significant influence on virus spreading in a weighted adaptive heterogeneous network. The adaptive rewiring process during the dynamics can effectively inhibit virus spreading. Large dispersion of weights can significantly decrease the final epidemic size. Moreover, our proposed rewiring strategies based on the individual spontaneous behaviors are effective for the inhibition of epidemics.

We investigate the effect of CaO/SiO₂ (molar ratio) and B₂O₃ content on the structure and sintering contraction behaviors of Calcium borosilicate (CaO–B₂O₃–SiO₂, CBS) glass-ceramic through the dilatometer and the Fourier transform infrared (FTIR) spectroscopy. The results show that the sintering-shrinkage of CBS glass-ceramics is promoted dramatically with the increase of CaO/SiO₂ to 1.14, and then keeps nearly constant as the CaO/SiO₂ further increases. This phenomenon is correlated with the degree of polymerization (DOP) of the Si–O network structure modulated by the CaO/SiO₂, additionally, two sintering shrinkage peaks, corresponding to two-step depolymerization, are detected in the sintering-shrinkage curves of the CBS glass-ceramic as the B₂O₃ content is elevated to 13.6 mol%. Meanwhile, the shrinking rate of CBS glass-ceramics is increased from 8 × 10${}^{-3}$ to 37 × 10${}^{-3}$ min${}^{-1}$ and the softening point is decreased from 736${}^{\circ }$C to 691${}^{\circ }$C with the increase of B₂O₃ content from 6.8 to 20.8 mol⋅%. This is due to the introduction of BO3 trihedral into Si–O–Si three-dimensional structure, which greatly reduces the uniformity and symmetry of the networks, inducing the decrease of the strength for the whole Si–O–Si network structures. The results obtained in this paper reveal the relationship between the glass structure and sintering behavior of the CBS glass-ceramic, which gives an avenue to improve its physical properties.

A novel traffic lattice hydrodynamic model considering the effect of density integration is proposed and analyzed in the paper. Via linear stability theory, linear stability condition of the new model is derived, which reveals an improvement of traffic stability by considering the integration of continuous historical density information. Moreover, the nonlinear properties of the extended model are revealed through nonlinear analysis. The propagating backwards kink–antikink waves are generated by deriving the mKdV equation near the critical point and verified by numerical simulation. All the results show that the density integration effect can suppress traffic congestion efficiently in traffic lattice hydrodynamic modeling.

Detailed first-principles calculations of the electronic structure and magnetic properties of alkali metal chlorides of the type A₂MCl₆ (A = K, Rb, Cs; M = Mn, Mo) have been performed using the density functional theory (DFT). The calculated optimized lattice constants show close agreement with experimental results. The electronic band structure and density of states (DOS) were investigated for the first time using different schemes of generalized gradient approximation (GGA) such as Wu–Cohen GGA, modified Becke Johnson potential and GGA plus Hubbard U parameter method. We found that the Hubbard U correction significantly improves the current DFT results. The calculated band structures of K₂MoCl₆ or Cs₂MoCl₆ indicate that the spin up electrons have metallic structure while the spin down configurations have semi-conducting nature together resulting in a half-metallic behavior. Finally, the analysis of magnetic properties indicates a ferromagnetic nature for all these compounds. These findings indicate that the alkali metal chlorides K₂MoCl₆ and Cs₂MoCl₆ are potentially promising candidates for future applications in the field of spintronics.

In this paper, high purity boron carbide samples were irradiated by ${}^{60}$Co gamma radioisotope source (0.27 Gy/s dose rate) with 50, 100, 150 and 200 irradiation hours at room-temperature. The unirradiated and irradiated boron carbide samples were heated from 30${}^{\circ }$C to 1000${}^{\circ }$C at a heating rate of 5${}^{\circ }$C/min under the argon gas atmosphere of flow rate 20 ml/min. Thermogravimetric (TG) and Differential Scanning Calorimetry (DSC) were carried out in order to understand the thermodynamic kinetics of boron carbide samples. The weight kinetics, activation energy and specific heat capacity of the unirradiated and irradiated boron carbide samples were examined in two parts, T $\le$ 650${}^{\circ }$C and T $\ge$ 650${}^{\circ }$C, according to the temperature. The dynamic of quantitative changes in both ranges is different depending on the irradiation time. While the phase transition of unirradiated boron carbide samples occurs at 902${}^{\circ }$C, this value shifts upto 940${}^{\circ }$C in irradiated samples depending on the irradiation time. The activation energy of the unirradiated boron carbide samples decreased from 214 to 46 J/mol in the result of 200h gamma irradiation. The reduction of the activation energy after the irradiation compared to the initial state shows that the dielectric properties of the irradiated boron carbide samples have been improved. After the gamma irradiation, two energy barrier states depending on the absorption dose of samples were formed in the irradiated samples. The first and second energy barriers occurred in 0.56–0.80 and 0.23–0.36 eV energy intervals, respectively. The existence of two energy levels in the irradiated boron carbide indicates that the point defects are at deep levels, close to the valence band.

A novel design and analysis of a butt-coupler are presented to be coupled with an edge-emitting laser and a silicon waveguide. The coupler is fairly effective when used with an edge-emitting laser of a certain integrated size and a high refractive index core material. Butt-coupling is not sensitive to polarization as both TE and TM modes achieve similar efficiency. The laser alignment tolerance and silicon waveguide gap in both lateral and vertical positions were studied. Although the air gap between the laser and the silicon cladding reduces coupling efficiency greatly, gap filling can help solve this problem. This design is proved to be quite effective in dealing with high index contrast and huge size mismatch between the laser and semiconductor waveguide.

In this paper, a newly designed composite of magnetic nano-Co₃O₄ fiber coated on carbon fiber (Cf) is prepared and characterized for the electromagnetic interference (EMI) shielding properties. XRD, SEM and TEM are used to investigate the micromorphology and microstructure evolution during the preparation. By hydrothermal method, the flowerlike clusters of single crystal flake-Co(OH)₂ are first obtained on Cf. The firstly prepared Co(OH)₂ sheets then turn into Co₃O₄ fibers during the next calcination step. The continuous and loose coating of magnetic Co₃O₄ nanofibers is finally obtained on the Cf. The loose coating is in proportion to the weight loss, and the wirelike Co₃O₄ is good for the interface strength for the Cf composite preparation. Based on the above work, the loose magnetic fibers coating on the Cf could be a feasible composite structure for the EMI composite materials integrated with absorbing and reflecting.

The effect of semiconductor saturable absorber mirror (SESAM) on continuous-wave multi-wavelength fiber ring-cavity laser with semiconductor optical amplifier (SOA) is experimentally demonstrated. The evolutionary process of multi-wavelength oscillation and the decrease of oscillating mode number caused by an SESAM are discussed. It’s found that the free oscillating mode number of the multi-wavelength fiber ring-cavity laser with SOA can be upto three, and the lasing wavelengths are 1573.8 nm, 1578.09 nm and 1582.37 nm, respectively. When a SESAM is inserted in the fiber ring-cavity, it narrows the amplified spontaneous emission (ASE) spectrum of the SOA, and the oscillating mode number of the multi-wavelength fiber ring-cavity lasers with SOA decreases to two, a stable dual-wavelength lasing at 1560.91 nm and 1564.12 nm is obtained.

A novel numerical method of calculating the current transfer length (CTL) from several matrices to superconducting region has been proposed in this paper, there are two ways to calculate the CTL corresponding to two criteria of CTL: E-based criterion and I-based criterion, and the relationship between these criteria have been given again. The method of calculating the CTL from several matrices to superconducting region has high accuracy compared with the method introduced by Stenvall, and simulation and experiments of measuring the CTL have been carried out to compare with the ones calculated by the numerical method. The results show that the novel numerical method has high accuracy in calculating the CTL of superconducting tape and is useful for generalizing to calculate the CTL of superconducting cable.

The Hamiltonian and wavefunctions describing two-dimensional (2D) two-electron ZnO quantum dot in rigid confinement are developed. Then the Schrödinger equation is solved analytically and numerically for determining the ground and excited state energies. The ground state energy of 2D two-electron ZnO quantum dot (QD) in rigid confinement is studied using perturbation and variational methods. The obtained result show that our trial wavefunction is good enough to describe the 2D two-electron QD in rigid confinement. The wavefunction describing the ground state is the combination of symmetric spatial wavefunction and antisymmetric spin wavefunction which is a para-state. The ground state energy eigenvalue obtained by variational technique is a little above that of a perturbation technique. Based on this; the trial wavefunction for the excited state is developed. The excited state energy of 2D two-electron ZnO QD in rigid confinement is studied computationally using variational method. The wavefunction describing the excited state is the combination of symmetric spatial wavefunction with antisymmetric spin wavefunction (para-state) or vice versa (ortho-state). The para and ortho-state energies of the first excited state are calculated and their difference is twice of the exchange energy. Based on the obtained energy eigenvalues of the ground and the first excited state at the value of the coupling constant $\xi$ $\approx$ 1, the third-order nonlinear absorption coefficient and refractive index changes are investigated. The optical transition is only considered between the two lowest para states.