International Journal of Modern Physics B

The configurations, electronic and spin of the FeO–HCNO clusters are calculated at the PW91 level. The results show that the Fe atom of FeO molecule prefers to interact with the O and N atoms of HCNO molecule and the corresponding FeO–HCNO cluster possesses highest kinetic stability. For this lowest-energy FeO–HCNO clusters, the 2p3d orbitals of O and N atoms obtain more electrons than the 2s orbital of the two atoms loss. In the isomer (6) which O atoms occur at the same ends of the FeO and HCNO fragments, it leads to increase the dipole moment. As for the axisymmetric isomer (1), the total spin is zero due to upward spin is perfectly offset by the downward spin.

We introduce a new (2+1)-dimensional equation by modifying the potential form of the Calogero–Bogoyavlenskii–Schiff (CBS) equation. By applying the Hirota bilinear method, we construct explicit lump solutions to this new equation and establish necessary and sufficient conditions that guarantee that the solutions are analytic and rationally localized in all directions in space. We also depict the evolution of the profiles of some selected lump solutions with three-dimensional and contour plots. It is immediately observed that the lump solutions generated are solitary wave type solutions as is the case with the KP equation.

We investigated the structural and electronic properties of Sr${}_{1-x}$M${}_x$Si₂ (M=Ca and Ba) (x=0, 0.25, 0.5, 0.75 and 1) by the first-principles calculation in the frame work of density-functional theory. It was found that the structure of Sr${}_{1-x}$Ca${}_x$Si₂ is evidently compressed with increasing the Ca content. On the other hand, the incorporation of Ba cause the swelling crystal structure. A structure transition for Sr${}_{1-x}$M${}_x$Si₂ (M=Ca and Ba) from cubic to tetragonal appear when the doping concentration is 0.5. Band structure calculations indicated that the bandgap decrease or even disappear with increasing Ca atoms, which suggesting the transition from the semiconductor to the metal for SrSi₂. Whereas, the semiconducting bandgap increases with the incorporation of Ba atoms. Our results imply that the thermoelectric properties of SrSi₂-based alloys can be further enhanced by increasing Ca doping content, Ca-doped SrSi₂ is a promising thermoelectric material.

This paper reports the stress and frequency analysis of dynamic silicon diaphragm during the simulation of micro-electro-mechanical-systems (MEMS) based piezoresistive pressure sensor with the help of finite element method (FEM) within the frame work of COMSOL software. Vibrational modes of rectangular diaphragm of piezoresistive pressure sensor have been determined at different frequencies for different pressure ranges. Optimal frequency range for particular applications for any diaphragm is a very important so that MEMS sensors performance should not degrade during the dynamic environment. Therefore, for the MEMS pressure sensor having applications in dynamic environment, the diaphragm frequency of 280 KHz has been optimized for the diaphragm thickness of 50 $\mu$m and hence this frequency can be considered for showing the better piezoresistive effect and high sensitivity. Moreover, the designed pressure sensor shows the high linearity and enhanced sensitivity of the order of ($\sim$0.5066 mV/psi).

Water pollution has always been an important issue threatening human health. Water quality monitoring is an important step to ensure water quality safety. Water quality parameters such as pH, temperature and conductivity are important indicators in water quality monitoring. In this paper, a multi-parameter water quality detection integrated chip system is studied, and multiple sensors are integrated on the same chip to realize the monitoring of conventional parameters such as pH, temperature and conductivity in drinking water. The chip system was processed by MEMS technology. A ruthenium oxide (RuO₂) film is used for pH detection, and the sensor exhibits a super-Nernst response (62.88 mV/pH) in the range of pH 1.92–11.74. The patterned micro Pt film is used as the temperature sensor, and the three-wire orthogonal structure is used for temperature detection. The sensitivity of this temperature sensor is 5.517 $\mathrm{\Omega }$/${}^{\circ }$C in the range of 6 to 80${}^{\circ }$C. Conductivity was measured by a four-electrode system, and the electrode constant was 1.667 cm${}^{-1}$ measured between 0.994 and 21.167 mS/cm. The test results show that the multi-parameter integrated chip system can realize the simultaneous detection of pH, temperature and conductivity in water, and has the characteristics of miniaturization and low cost, and provides an effective way for simultaneous detection of water quality.

Optoelectronic properties of alkaline-earth calcium-barium chalcogenide ternary alloys Ca${}_x$Ba${}_{1-x}$S, Ca${}_x$Ba${}_{1-x}$Se and Ca${}_x$Ba${}_{1-x}$Te have been calculated using first principle-based FP-LAPW methodology employing modified Becke–Johnson (mBJ) exchange-correlation functional. Both the lattice parameter and the bulk modulus vary nonlinearly with dopant concentration in each of these alloy systems. The evolution of a series of thermodynamically stable wide-direct-bandgap ternary alloys as a result of amalgamation of indirect-bandgap homo-chalcogen CaX and BaX at Ca-concentrations $x$ = 0.25, 0.50 and 0.75 is observed. Bonding between calcium and chalcogen is ionic, while that between barium and chalcogen is covalent in nature. Each of the alloy systems show substantial nonlinearity in the concentration dependence of bandgap and the dominant role is played by the volume deformation effect in total bandgap bowing. It is observed that the chalcogen-p of valence band as initial states and Ca-3d as well as Ba-5d states of conduction band as final states play the dominant role in optical transitions. Nature of nonlinear concentration dependence of each of the static optical constants is opposite and critical point is similar to that of bandgap in each of the alloy systems. Several calculated properties are found to agree well with the corresponding experimental findings.

We present the number of dimer coverings N_d(n) on the Tower of Hanoi graph TH_d(n) at n stage with dimension 2 $\le$d$\le$ 5. When the number of vertices v(n) is even, N_d(n) gives the number of close-packed dimers; when the number of vertices is odd, it is impossible to have a close-packed configurations and one of the outmost vertices is allowed to be unoccupied. We define the entropy of absorption of diatomic molecules per vertex as S${}_{{\mathrm{\text{TH}}}_d}$=${lim}_{n\to \infty }ln$ N_d(n)/v(n), that can be shown exactly for TH₂, while its lower and upper bounds can be derived in terms of the results at a certain n for TH_d(n) with 3 $\le$d$\le$ 5. We find that the difference between the lower and upper bounds converges rapidly to zero as n increases, such that the value of S${}_{{\mathrm{\text{TH}}}_d}$ with d=3 and 5 can be calculated with at least 100 correct digits.

The Linked Cluster Theory in the spin polaron formulation is investigated in this paper using the finite temperature (Matsubara) Green’s function method. We use a representation where holes and spins are described as spinless fermions and normal bosons, respectively. An analytic expression of the thermodynamic potential of high-temperature superconductors in the superconducting state was obtained using the Linked Cluster theory and an expression for its normal state by setting the energy gap to zero. The expression of the thermodynamic potential enabled us to calculate two bulk thermodynamic properties of high-temperature superconductors, entropy and specific heat, both in the normal and superconducting states.

First-principles calculations of the structural, electronic, optical and thermal properties of chalcopyrite CuXTe₂ (X=Al, Ga, In) have been performed within density functional theory using the full-potential linearized augmented plane wave (FP-LAPW) method, by employing for the exchange and correlation potential the approximations WC-GGA and mBJ-GGA. The effect of X cations replacement on the structural, electronic band structure, density of states and optical properties were highlighted and explained. Our results are in good agreement with the previous theoretical and experimental data. As far as we know, for the first time we find the effects of temperature and pressure on thermal parameters of CuAlTe₂ and CuGaTe₂ compounds. Thermal properties are very useful for optimizing crystal growth, and predict photovoltaic applications on extreme thermodynamic conditions.

X-ray diffraction (XRD) method and structural refinement were used to characterize the sample of $\alpha$-Si₃N₄. Rietveld analyses of XRD data confirmed that the sample belongs to hexagonal crystal (space group of P31c, No:159). The refined structural parameters are in agreement with the available theoretical and synchrotron radiation experimental results. Then, the infrared (IR) spectra of $\alpha$-Si₃N₄ under 22 GPa were investigated with the diamond anvil cell (DAC). According to the IR absorption spectra at 296.3 K and 2 hPa (Observation range from 400 cm${}^{-1}$ to 12,500 cm${}^{-1}$), we observed 23 IR active peaks. Normalized Fourier transform infrared (FTIR) absorption spectra under high pressure and room-temperature (296.3 K) show that $\alpha$-Si₃N₄ undergoes a phase transition at 16.3 GPa and changes from hexagonal to cubic phase, namely, $\gamma$-Si₃N₄, which is very close to the result of our theoretical calculations, i.e., the phase transition pressure is 16.3 GPa.

This paper reports two basic microfluidic strategies for the magnetic manipulation of unlabeled nonmagnetic particles/cells. One is the deflection induced by a single magnet, and the other is the confusing effect produced by two magnets of opposite polarity. They can be combined into more completed particle manipulations like continuous flow separation, counting and detection, which are essential steps in biomedical applications. We experimentally studied the dynamics of 10.4 and 20 $\mu$m nonmagnetic polystyrene particles within a flow rate range of 30, 50, 70 and 90 $\mu$L/min in a straight channel. We defined the cross-section length that the particles occupy as the “particle bandwidth” to characterize the extent of deflection and focusing. To predict the trajectories of the particles, we established a simple theoretical model by considering the magnetic force and viscous drag force. Compared with the experimental results, the maximum deviation of the simulation is 9.28%. The influences of magnetic nanoparticle concentration, magnetic field parameters, size of microparticles and flow rate are systematically investigated. We also demonstrated that the effective deflection and focusing could be realized at low Fe₃O₄ nanoparticle concentrations, which means that this method can reduce the damage on cells in the practical applications.

We have investigated the interference of the dipolar Bose–Einstein condensates (DBECs) released from a double-well potential and studied the effects of dipole–dipole interaction (DDI) on the interference phenomena. We find that the DDI plays an important role in the interference process. When the effective polarization direction of the dipolar atoms is in the normal direction of the condensate plane, with the increasing of the strength of DDI, the visibility of fringes reduces and the width of fringes becomes larger. When the strength of DDI is fixed and the effective polarization direction of the dipolar atoms deviates from the normal direction of the condensate plane, the interference fringes become bent. Especially, for the situation of polarization parallel to the condensate plane, the interference fringes in the central regions become wave-shaped and vortex–antivortex pairs can be formed due to the anisotropic DDI. In addition, vortex–antivortex pairs could also be created by the spatial and temporal control of the DDI.

Local minimum appearing in the interionic pair potentials, when derived from local model pseudopotential, for Al (and some other polyvalent metals) remains as a long standing problem of clear understanding of its origin, although some attempts have been made by a few authors. The origin of this feature of local minimum is systematically investigated for the first time in this paper considering both the core size and the conduction electron density as variables. Interionic pair potential is derived from Ashcroft’s empty core model because it depends on these two variables only. Results of this investigation show monovalent metals do not exhibit a local minimum at all but trivalent Al and some other polyvalent metals do exhibit at their normal densities. Here, the combined effect of the core size and the conduction electron density results whether the local minimum will appear or not. More interestingly, for smaller core size, conduction electron density plays major role and for larger core size the core radius plays the major role in determining the depth of the local minimum.

Reduction of transconductance related to the junctionless silicon (JL-Si) transistor shows challenges to its performance for analog/radio frequency (RF) applications. An effective way to increase the transconductance of JL-Si device without reducing its performance is to use III–V semiconductor materials with a high carrier mobility/velocity instead of silicon. In the present study, the application of In${}_x$Ga${}_{1-x}$As/GaAs structures is proposed in order to enhance the transconductance of double gate JL (DG-JL) with channel length of 10 nm and body thickness of 5 nm. The importance of the thickness of In${}_x$Ga${}_{1-x}$As layer as well as the indium mole fraction on the electrical characteristics of the proposed device is shown in terms of the transconductance by a numerical simulator. By decreasing the thickness of the In${}_x$Ga${}_{1-x}$As layer down to 1 nm for a specified mole fraction of 0.3, a maximum transconductance of 1.7 mS/um was obtained. Comparing the results of JL-In${}_{0.3}$Ga${}_{0.7}$As/GaAs device with JL-GaAs, JL-In${}_{0.3}$Ga${}_{0.7}$As and JL-Si structures, an increase of 21%, 18% and 44% in transconductance, respectively, was found. Moreover, simulation results show that the proposed structure exhibits output resistance of 300 G$\mathrm{\Omega }$, intrinsic gain of 32.5 dB and unity gain cut-off frequency of 513 GHz. Thus, the JL-In${}_{0.3}$Ga${}_{0.7}$As/GaAs device can be a good candidate for analog/RF applications.