Modern Physics Letters B

We study in this paper the Blume–Emery–Griffiths model in a thin film of stacked triangular lattices. The model is described by three parameters: bilinear exchange interaction between spins $J$, quadratic exchange interaction $K$ and single-ion anisotropy $D$. The spin $S_i$ at the lattice site $i$ takes three values $(-1,0,+1)$. This model can describe the mixing phase of He-4 $(S_i=+1,-1)$ and He-3 $(S_i=0)$ at low temperatures. Using Monte Carlo simulations, we show that there exists a critical value of $D$ below (above) which the transition is of second-(first-)order. In general, the temperature dependence of the concentrations of He-3 is different from layer by layer. At a finite temperature in the superfluid phase, the film surface shows a deficit of He-4 with respect to interior layers. However, effects of surface interaction parameters can reverse this situation. Effects of the film thickness on physical properties will be also shown as functions of temperature.

A series of Ta(4 nm)/Y₂O${}_3(t)$/Ni${}_{81}$Fe${}_{19}$(20 nm)/Y₂O${}_3(t)$/Ta(3 nm) films were prepared on glass substrates by magnetron sputtering under appropriate conditions. AMR value, phase composition and magnetic hysteresis hoop of Ni${}_{81}$Fe${}_{19}$ films were measured and analyzed by four-point probe technology, X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. Influence of Y₂O₃ which work as oxidation intercalation on AMR values of Ni${}_{81}$Fe${}_{19}$ films was investigated. The experiment results show that, at the substrate temperature of 450${}^{\circ }$C, the AMR value of the film with Y₂O₃ layer thickness of 2.5 nm can reach 4.61%, increasing by 71.3% compares with the film without Y₂O₃ layer.

Passively Q-switching performance of the composite Nd:YVO₄ laser was experimentally investigated by using V:YAG as saturable absorber. The comparisons between the temperature distributions and thermal focal lengths in Nd:YVO₄ crystals were numerically analyzed by using a finite element method. The maximum CW output power of 1.65 W with an optical slope efficiency of 25.6% was obtained by YVO₄/Nd:YVO₄ composite crystal under an incident pump power of 7.1 W. For Q-switching regime, the highest output power was 664 mW with a pulse repetition rate of 30 kHz and pulse duration of 35 ns.

In this work, CdSe QDs were synthesized using a microwave assisted method and chemical reaction between NaHSe, CdSO₄ at the presence of TGA as capping molecule. Thereafter without CdSe extraction, CdS shell was grown subsequently around CdSe cores by a reaction based on the heat sensitivity of Na₂S₂O₃ dissociation. Synthesized QDs were characterized by means of X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV–Vis and photoluminescence (PL) spectroscopy. All of these analyzes confirmed formation of CdSe QDs and successfully growth of CdS shell on surface of CdSe to forming CdSe/CdS core-shell structure.

Our analytical method uses a linear combination of the Hankel functions $H_1$ and $H_2$ to represent the field in the gold region of a fiber-based plasmonic sensor. This method is applied for different structures made from three, four and five layers. When the analyte is distilled water, the difference between the resonant wavelengths calculated with the finite element method and the analytical method is very small (0.00 nm for three layers, 0.19 nm for four layers and 0.07 nm for five layers with two gold layers). The important characteristics of the Bessel and Hankel functions at the loss matching point are analyzed.

Based on a ternary quantum logic circuit, four symmetric weak ternary quantum homomorphic encryption (QHE) schemes were proposed. First, for a one-qutrit rotation gate, a QHE scheme was constructed. Second, in view of the synthesis of a general $3\times 3$ unitary transformation, another one-qutrit QHE scheme was proposed. Third, according to the one-qutrit scheme, the two-qutrit QHE scheme about generalized controlled $X$ (GCX($m,n$)) gate was constructed and further generalized to the $n$-qutrit unitary matrix case. Finally, the security of these schemes was analyzed in two respects. It can be concluded that the attacker can correctly guess the encryption key with a maximum probability $p_k=1/3^{3n}$, thus it can better protect the privacy of users’ data. Moreover, these schemes can be well integrated into the future quantum remote server architecture, and thus the computational security of the users’ private quantum information can be well protected in a distributed computing environment.

We developed the method of calculation of the temperature dependence of the magnetic susceptibility. We considered the de Haas–van Alphen (dHvA) effect in semiconductors at high temperatures and low magnetic fields. The effect of temperature on dHvA effect is explained with respect to the temperature dependence of the thermodynamic density of states in a magnetic field.

Wetting of droplets on homogeneous and spherical concave rough surfaces is investigated based on thermodynamics. In this study, neglecting the droplet gravity and the thickness of the precursor film of the liquid–vapor interface, the three-phase system is divided into six parts using Gibbs concept of dividing surface. The system Helmholtz free energy is established based on thermodynamics. Supposing the temperature and chemical potential to be constant, a new generalized Young’s equation of the equilibrium contact angle for a spherical droplet on a spherical concave rough surfaces is obtained including the line tension effects. Under certain conditions, this generalized Young’s equation is the same as the Rusanov’s equation.

A dual-band bandpass filter at X-band is proposed using composite metamaterial resonator consisting of an outer square closed-ring resonator (SCRR) and two inner electric inductance–capacitance (ELC) resonators. Numerical simulation and microwave measurement reveal that the filter exhibits two passbands centered at 8.76 GHz and 11.04 GHz, with 3 dB bandwidths of 130 MHz and 290 MHz, respectively. The complex dispersion relation of the filter is further derived based on the effective medium theory, where two balanced composite right-/left-handed bands are found, i.e. lines exhibiting two left-handed and two right-handed bands alternating. The proposed filter may find useful in dual-band or multi-band wireless communication systems.

Detecting community is a challenging task in analyzing networks. Solving community detection problem by evolutionary algorithm is a heated topic in recent years. In this paper, a multi-objective discrete cuckoo search algorithm with local search (MDCL) for community detection is proposed. To the best of our knowledge, it is first time to apply cuckoo search algorithm for community detection. Two objective functions termed as negative ratio association and ratio cut are to be minimized. These two functions can break through the modularity limitation. In the proposed algorithm, the nest location updating strategy and abandon operator of cuckoo are redefined in discrete form. A local search strategy and a clone operator are proposed to obtain the optimal initial population. The experimental results on synthetic and real-world networks show that the proposed algorithm has better performance than other algorithms and can discover the higher quality community structure without prior information.

In this paper, ZnO nanostructures have been synthesized by thermal evaporation process using metallic zinc powder in the presence of oxygen on $p$-Si (100) at different distances from the boat. The structural and optical characterizations have been carried out. The morphological study shows various shape nanostructures. XRD data indicate that all samples have a polycrystalline wurtzite hexagonal structure in such a way that the closer sample has a preferred orientation along (101) while the ones farther are grown along (002) direction. From the structural and optical data analysis, we found that the induced strains are the main parameter controlling the UV/green peaks ratios in the PL spectra of the studied samples.

This communication is involved in providing, via a modern approach, a direct derivation that, with 100% probability, none of the atomic electrons falls to the center of multi-electron atoms — a problem which has been around historically in the quantum mechanics of atoms since the birth of the former and has, undoubtedly, come across every learner of the subject since then. No need arises for explicit eigenfunctions.

Rear earth (RE) ions-doped 12CaO$\cdot$7Al₂O₃ single crystal has been successfully prepared by Czochralski method. Under 980 nm excitation, a strong green upconversion emission at 548 nm and a weaker red upconversion emission at 662 nm were observed. The green upconversion emission is corresponding to the transition of ⁵F ₄/⁵S${}_2\to {}^5$I₈ of Ho${}^{3+}$, and the red one is corresponding to the transition of ⁵F${}_5\to {}^5$I₈ of Ho${}^{3+}$. A much weaker NIR band at 762 nm is also observed, which corresponds to the ⁵F ₄/⁵S${}_2\to {}^5$I₇ transition of Ho${}^{3+}$. The pump dependence and luminescence decay dynamics spectra show the green and red upconversion are populated by two-photon process, and the upconversion mechanisms are analyzed in detail. The color of the upconversion luminescence can be changed by simply adjusting the excitation power. RE ions-doped 12CaO$\cdot$7Al₂O₃ single crystal with these properties is expected to have broad application prospects in solid-state multicolor display and instrument integration. RE ions-doped 12CaO$\cdot$7Al₂O₃ single crystal has the ability to replace some traditional single crystals such as LiNbO₃ in many applications.

In this paper, we use car-following theory to study the traditional vehicle’s running cost and the electric vehicle’s running cost. The numerical results illustrate that the traditional vehicle’s running cost is larger than that of the electric vehicle and that the system’s total running cost drops with the increase of the electric vehicle’s proportion, which shows that the electric vehicle is better than the traditional vehicle from the perspective of the running cost.

In this paper, various kinds of spontaneous dynamic patterns are investigated based on a two-layer nonlinearly coupled Brusselator model. It is found that, when the Hopf mode or supercritical Turing mode respectively plays major role in the short or long wavelength mode layer, the dynamic patterns appear under the action of nonlinearly coupling interactions in the reaction–diffusion system. The stripe pattern can change its symmetrical structure and form other graphics when influenced by small perturbations sourced from other modes. If two supercritical Turing modes are nonlinearly coupled together, the transition from Turing instability to Hopf instability may appear in the short wavelength mode layer, and the twinkling-eye square pattern, traveling and rotating pattern will be obtained in the two subsystems. If Turing mode and subharmonic Turing mode satisfy the three-mode resonance relation, twinkling-eye patterns are generated, and oscillating spots are arranged as square lattice in the two-dimensional space. When the subharmonic Turing mode satisfies the spatio-temporal phase matching condition, the traveling patterns, including the rhombus, hexagon and square patterns are obtained, which presents different moving velocities. It is found that the wave intensity plays an important role in pattern formation and pattern selection.

Ba₈Cu₆Ge${}_{15}$Si${}_{25}$ were successfully synthesized by a simple high pressure and high temperature (HPHT) method to investigate the microstructures and thermoelectric (TE) properties. After high pressure synthesis, a highly dense bulk material with lots of fine-layered structure, lattice defects and disorders has been obtained. As expected, the thermal conductivity decreased greatly and the ZT value has been improved significantly, which reaches up to 0.43 at around 773 K. Comparing with other methods, HPHT could shorten the synthesis time from several days to half an hour. It reveals that the HPHT method will become an effective approach for optimizing the TE performance of these materials.

In this paper, a possibility of use of the controlled decomposition of solid solutions of oxides with perovskite structure in the state of coexisting domains of the antiferroelectric (AFE) and ferroelectric (FE) phases for manufacturing materials with the negative refractive index is demonstrated. The lead zirconate titanate-based solid solutions are considered as an example of substances suitable for creation of such materials. Manufactured composites constitute a dielectric AFE matrix with a structure of conducting interphase boundaries separating domains of the FE and AFE phases. The electric conductivity of the interphase boundaries occurs as a result of the local decomposition of the solid solutions in the vicinity of these boundaries. The decomposition process and consequently the conductivity of the interphase boundaries can be controlled by means of external influences.

The main purpose of the present study is to explore the classes of the Schrödinger-like wave equations derived from Dirac equation, for which the similarity transformation and asymptotic iteration algorithms can assist in generating second-order differential equation that admit general exact solutions in the presence of nonsymmetrical potential terms. For illustration purposes, we extract the exact bound-state solutions of the Dirac equation with the noncentral Hartmann potential for the cases of exact $SU(2)$ spin and pseudospin symmetries. Also, we have shown that both Dirac-radial and Dirac-polar parts are sensitive to the variation of the involved parameters.

Based on density functional theory (DFT) calculations, the electronic structures and magnetic properties of $3d$ transition-metal phthalocyanine (TMPc, TM = Ti, V, Cr, Mn, Fe, Co, Ni and Cu), as well as Li-adsorbed phthalocyanines have been studied. The results show that the pristine TMPcs all have a good $D_{4h}$ symmetry. When there is one Li atom adsorbed on TMPcs directly over (LiTMPc-$\alpha$) or slantly above (LiTMPc-$\beta$) the TM atoms, the geometries and electronic structures will be changed. For LiTMPc-$\alpha$ systems, the central TM atoms will deviate from the molecular plane and the molecules exhibit good $C_{4v}$ symmetry. LiTMPc-$\beta$ systems are more stable than LiTMPc-$\alpha$ systems but it do not possess $D_{4h}$ and $C_{4v}$ symmetries. The total and local magnetic moments and the charge transfer are also presented. Finally, by using the orbit mixing and splitting theory under $D_{4h}$ and $C_{4v}$ symmetry, we get the ordering of the energy levels of the central TM atoms.

The optical properties of Yb-doped LaB₆ have been investigated by first-principles calculations within the framework of density functional theory. The results show that the Yb $4f$ states at near Fermi surface affect their optical properties and the Yb-doping leads to a reduction of the plasmon energy of LaB₆, i.e. a redshift of the position of transmission peak in the visible-near infrared region. This study offers a theoretical prediction for the design and application of Yb-doped LaB₆ as an optoelectronic material.