Modern Physics Letters B

A series of Ti${}_{1-x}$Co${}_x$O${}_{2-\delta }$ ($x$ = 0.01, 0.03, 0.05, 0.07) nanoparticles were synthesized by sol–gel method. The X-ray diffraction, transmission electron microscopy, Raman analysis and X-ray photoelectron spectroscopy ruled out the signatures of Ti${}^{3+}$, Co-clusters or any other oxides of Co. The ferromagnetic behavior was clearly observed at room temperature in doped samples with saturation magnetization $(M_s)$ of the order of 0.008–0.035 emu/g depending on doping concentrations. The saturation magnetization is found to be increased with the Co contents increasing from 1% to 7%. From the plot of the M–T curve, we obtain the $T_c$ as $\sim$515 K for 5% Co-doped TiO₂. Oxygen vacancies were detected from the photoluminescence (PL) measurement. Magnetic properties analyses and PL analyses showed that oxygen vacancies probably played a major role in ferromagnetism of the Ti${}_{1-x}$Co${}_x$O₂ system with Co substituting for Ti. The first-principles calculation was performed to investigate the magnetic properties of Co-doped TiO₂ nanoparticles. It can be found that the major magnetic moment is from the 3d electron of Co. The experiment results are consistent with the first-principles calculation. The ferromagnetism derived from the spin-split of O-2p and Co-3d electron states caused by p–d orbit hybridization.

${\mathrm{\text{Cu}}}_x{\mathrm{\text{Ni}}}_{(1-x)/2}{\mathrm{\text{Zn}}}_{(1-x)/2}{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_4$ ($x$ = 0.1, 0.3 and 0.5) nanoparticles were prepared by chemical co-precipitation method. The developed nanoparticles were characterized for structural properties by powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. Peak position in the X-ray diffraction pattern confirmed the single spinel phase of the developed particles. Infrared (IR) spectroscopy in mid-IR range showed the presence of characteristic absorption bands corresponding to octahedral and tetrahedral bonds in the spinel structure of prepared samples. Thermo-gravimetric analysis (TGA) measurements showed a considerable weight loss in the developed samples above 700${}^{\circ }$C. Frequency dependence of the electrical properties of the developed material pellets was studied in the frequency range of 1 kHz–5 MHz. Temperature dependence of the dielectric constant of ${\mathrm{\text{Cu}}}_{0.1}{\mathrm{\text{Ni}}}_{0.45}{\mathrm{\text{Zn}}}_{0.45}{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_4$ was studied at different temperatures, i.e. at 425, 450 and 475 K, in the frequency range of 1 kHz–5 MHz. It was found that the electrical conductivity decreases with increasing Cu${}^{2+}$ ion content while it increases with the increase in temperature.

We report the comparison of electrode metals for LiNbO₃ surface acoustic wave (SAW) devices. Palladium (Pd) was systematically studied as a SAW electrode metal for the first time, compared with gold (Au). Simulations were first conducted to gain an understanding of the differences of the materials and the metallization ratio. Two sets of identical SAW devices were then fabricated using Au and Pd as electrodes with different electrode widths and same SAW period. The insertion losses, types of resonance mode, the resonance frequencies, peak amplitudes, quality factors and trends with different metallization ratios were systematically compared and analyzed. We found that Pd electrode devices only exhibit the parallel resonance frequency and have higher resonance frequency for both the first-order and third-order harmonics. Au electrode devices tend to have a smooth response and a quality factor two times higher than Pd. Both Pd and Au electrode devices have nearly identical electromechanical coupling coefficients, and the quality factor and third-order harmonics both improve with increasing metallization ratio.

Uncovering community structures is a fundamental and important problem in analyzing the complex networks. While most of the methods focus on identifying node communities, recent works show the intuitions and advantages of detecting link communities in networks. In this paper, we propose a non-negative matrix factorization (NMF) based method to detect the link community structures. Traditional NMF-based methods mainly consider the adjacency matrix as the representation of network topology, while the adjacency matrix only shows the relationship between immediate neighbor nodes, which does not take the relationship between non-neighbor nodes into consideration. This may greatly reduce the information contained in the network topology, and thus leads to unsatisfactory results. Here, we address this by introducing multi-step similarities using the graph random walk approach so that the similarities between non-neighbor nodes can be captured. Meanwhile, in order to reduce impact caused by self-similarities (similarities between nodes themselves) and increase importance gained from similarities between other different nodes, we add a penalty term to our objective function. Then an efficient optimization scheme for the objective function is derived. Finally, we test the proposed method on both synthetic and real networks. Experimental results demonstrate the effectiveness of the proposed approach.

This paper aims to study the traffic flow characteristics considering drivers’ distraction behavior, which is common and lasts for stochastic duration time. The distribution of distraction duration time and the influence of distraction on traffic flow are analyzed. The relationship among distraction duration time, probability of distraction occurrence and proportion of distraction is established by stochastic model. Then a modified optimal velocity model was proposed to simulate a two-lane road, taking the effect of distraction behavior into account. A survey was conducted to collect maximum speed, average speed, lane change frequency and headway of vehicle when distracted. The results suggest that distraction behavior has significant negative influence on traffic flow rate and increases the lane changing frequency. Short-time distraction seems to have smaller impact on traffic flow than long-time distraction. This model simulates the distraction behavior very well and distracted drivers have lower mean speed, lower lane changing frequency, longer headway and are overtaken by more vehicles in simulation. This study provided a good model to analyze distraction behavior in traffic flow and pointed out an important factor affecting the traffic flow efficiency.

A new Lax pair is introduced for a perturbed Kaup–Newell equation and used to construct two series of conservation laws through a Riccati equation that a ratio of eigenfunctions satisfies. Both series of conservation laws are defined recursively, and the first two in each series are presented explicitly.

We studied the holographic characteristics of acrylamide-based photopolymer layers ranging in thickness from 300 $\mu \mathrm{\text{m}}$ to 1000 $\mu \mathrm{\text{m}}$. Scattering patterns of various materials were presented, and both transmittance and scattering ratio were measured. Then, theoretical and experimental Bragg selectivity curves of two samples with thicknesses of 300 $\mu \mathrm{\text{m}}$ and 510 $\mu \mathrm{\text{m}}$ were analyzed, demonstrating the effective optical thickness inside photopolymer, which was responsible for the width of Bragg selectivity curve. Through the simulation for the spatial dynamics of refractive index distribution inside materials with different thicknesses, the attenuation of grating along the direction of thickness inside photopolymer was presented. Moreover, the photo-induced polymer chain length was evaluated, and a growing tendency of polymer chain length as increasing depth of material thickness was presented for the first time, in other words, there were polymers with longer chain length in deeper layer of material.

Under investigation in this paper is a generalized variable-coefficient Boussinesq system, which describes the propagation of the shallow water waves in the two-layered fluid flow. Bilinear forms, Bäcklund transformation and Lax pair are derived by virtue of the Bell polynomials. Hirota method is applied to construct the one- and two-soliton solutions. Propagation and interaction of the solitons are illustrated graphically: kink- and bell-shape solitons are obtained; shapes of the solitons are affected by the variable coefficients ${\alpha }_1$, ${\alpha }_3$ and ${\alpha }_4$ during the propagation, kink- and anti-bell-shape solitons are obtained when ${\alpha }_3>0$, anti-kink- and bell-shape solitons are obtained when ${\alpha }_3<0$; Head-on interaction between the two bidirectional solitons, overtaking interaction between the two unidirectional solitons are presented; interactions between the two solitons are elastic.

The in-plane electron mobility has been calculated in InAs/GaSb type-II superlattices (SLs) at low temperatures. The interface roughness scattering and ionized impurity scattering are investigated as the dominant scattering mechanisms in limiting the electron transport at low temperatures. For this purpose, the band structures and wave functions of electrons in such SLs are calculated by solving the K.P Hamiltonian using the numerical Finite Difference method. The scattering rates have been obtained for different temperatures and structural parameters. We show that the scattering rates are high in thin-layer SLs and the mobility rises as the temperature increases in low-temperature regime.

Sodium-ion batteries (NIBs) as an alternative to lithium-ion batteries (LIBs) have recently received great attentions because of the relatively high abundance of sodium. Searching for suitable anode materials has always been a hot topic in the field of NIB study. Recent reports show that phosphorus-based materials are potential as the anode materials for NIBs. Using first-principles calculations, herein, we study the atomic and electronic structures, diffusion dynamics and intrinsic elastic properties of various Na–P alloy compounds (NaP₅, Na₃P${}_{11}$, NaP and Na₃P) as the intermediate phases during Na extraction/insertion in phosphorus-based anode materials. It is found that all the crystalline phases of Na–P alloy phases considered in our study are semiconductors with band gaps larger than that of black phosphorus (BP). The calculations of Na diffusion dynamics indicate a relatively fast Na diffusion in these materials, which is important for good rate performance. In addition, the diffusion channels of sodium ions are one-dimensional in NaP₅ phase and three-dimensional in other three phases (Na₃P${}_{11}$, NaP and Na₃P). Elastic constant calculations indicate that all four phases are mechanically stable. Among them, however, NaP₅, Na₃P${}_{11}$ and NaP alloy phases are ductile, while the fully sodiated phase Na₃P is brittle. In order to improve the electrochemical performance of Na–P alloy anodes for NIBs, thus, promoting ductility of Na–P phase with high sodium concentration may be an effective way.

A new approach method to dealing with the puzzle of spectral analysis in prompt gamma neutron activation analysis (PGNAA) is developed and demonstrated. It consists of utilizing BP neural network to PGNAA energy spectrum analysis which is based on Monte Carlo (MC) simulation, the main tasks which we will accomplish as follows: (1) Completing the MC simulation of PGNAA spectrum library, we respectively set mass fractions of element Si, Ca, Fe from 0.00 to 0.45 with a step of 0.05 and each sample is simulated using MCNP. (2) Establishing the BP model of adaptive quantitative analysis of PGNAA energy spectrum, we calculate peak areas of eight characteristic gamma rays that respectively correspond to eight elements in each individual of 1000 samples and that of the standard sample. (3) Verifying the viability of quantitative analysis of the adaptive algorithm where 68 samples were used successively. Results show that the precision when using neural network to calculate the content of each element is significantly higher than the MCLLS.

Quantum speed limit (QSL) time for open systems driven by classical fields is studied in the presence of thermal bosonic environments. The decoherence process is quantitatively described by the time convolutionless master equation. The evolution speed of an open system can be accelerated by means of driving classical fields at finite temperatures. It is found out that the structural reservoir at low temperature may contribute to the acceleration of quantum evolution. The manifest oscillation of QSL time happens under the circumstance of classical driving field. The scaling property of QSL for entangled systems is also investigated. It is demonstrated that the entanglement of open systems can be considered as one kind of resource for improving the potential capacity of thermal quantum speedup.

Epitaxial CeO₂ seed layer and La₂Zr₂O₇ (LZO) buffer layers were deposited on biaxially-textured Ni–5 at.% W (NiW) tape substrate by liquid-phase polymer assisted nanoparticles deposition (PAND) method. LZO layers deposited by PAND have consistently shown tilting of the $c$-axis toward the direction of the sample’s surface normal. A new approach increasing the sharpening of the buffer texture by magnetic structural processing (MSP) of buffer layers was tested. The LZO layers, deposited on the seed and buffer layers after MSP, have dense and smooth surface structure, and more importantly, significantly improved out-of-plane texture, compared with the LZO layers that were deposited on a layer without MSP. Transmission electron microscopy study confirmed the $c$-axis tilting of CeO₂ and LZO layers and revealed the absence of interfaces between LZO layers which have been grown on the layers after MSP. There are very small (2–4 nm) gated pores in the single-crystal structure of LZO layers that are not typical for structure of LZO layers obtained by liquid-phase methods. Thus the LZO buffer layers can serve as an effective metal-ion diffusion barrier.

Spin-polarized electron transport through a zigzag zinc oxide nanoribbon (ZnONR) has been studied using first-principles transport simulations. Ribbons without edges passivated show 100% spin polarization at small bias voltage independently of width. The ribbons with edge zinc atoms passivated maintain absolute spin-filtering effect in much larger bias region. The results demonstrate that zigzag ZnONRs act as perfect spin-filters in the absence of magnetic electrodes and external fields.

Samples of pure zirconium (Zr) were irradiated by 18 MeV helium (He${}^{+}$) ions in the dose range 0.00162–0.0324 dpa at 373 K by using Cyclotron accelerator. The atomic force microscopy (AFM) results indicated an increase in average surface roughness of Zr by increasing the irradiation dose. The AFM images revealed nucleation and growth of nano- and micro-size hillocks at lower doses (0.00162–0.00324 dpa), whereas formation of a volcano-like cavities and craters was observed within these hillocks by increasing the radiation dose from 0.00324 to 0.0324 dpa. The high-resolution X-ray diffraction (XRD) results showed a variation in the intensities and positions of the diffraction peaks after the irradiation. The transmission electron microscopy (TEM) results reported a significant decrease in the grain size after the He${}^{+}$ irradiation. The values of grain size, calculated using the TEM, were found to be in good agreement with the crystallite size calculated using the XRD analysis. The yield stress (YS) was increased by increasing the irradiation dose up to 0.0162 dpa, however, the YS exhibited a decreasing trend with a further increase of the dose. The changes in YS were elucidated by grain size reduction and localized heating at higher doses.

In this paper, two kinds of finite-dimensional integrable reduction are studied for the Harry–Dym (HD) hierarchy. From the nonlinearization of Lax pair, the HD hierarchy is reduced to a class of finite-dimensional Hamiltonian systems (FDHSs) in view of a Bargmann map and a set of Neumann type systems by a Neumann map, which separate temporal and spatial variables on the symplectic space $({ℝ}^{2N},{\omega }^2)$ and the tangent bundle of ellipsoid $(T{S}^{N-1},{\omega }^2)$, respectively. It turns out that involutive solutions of the resulted finite-dimensional integrable systems (FDISs) directly give rise to finite parametric solutions of HD hierarchy through the Bargmann and Neumann maps. The finite-gap potential to the high-order stationary HD equation is obtained that cuts out a finite-dimensional invariant subspace for the HD flows. Finally, some comparisons of two kinds of integrable reductions are then discussed.

In this paper, we propose a pair of symmetric three-terminal refrigerator models with a hot cavity connected to two colder reservoirs via ideal tunneling quantum dots. The cooling of the refrigerators is achieved by investing thermal power from a hot reservoir and electric power from an applied voltage. Based on the model proposed, we numerically analyze the performance of the refrigerators with different half width of energy levels, and particularly discuss the coefficient of performance for zero applied voltage in the limit of a small half level width. Finally, we optimize with half width of energy levels and get the optimal region of the refrigerators.

Zn${}_{1-x}$Mn${}_x$O ($x$ = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) nanocrystalline diluted magnetic semiconductors (DMSs) were synthesized using sol–gel-based auto-combustion technique. X-ray diffraction (XRD) analysis of all the synthesized samples indicated pure wurtzite hexagonal structure without any secondary phase with perfect solubility of Mn contents in ZnO matrix. The increase in Mn concentration reduced the average crystallite size as evaluated by the Scherrer’s formula. Morphological analysis performed using a field emission scanning electron microscope (FESEM) indicated nearly an ordered surface morphology with some porosity and few cracks. Energy dispersive X-ray (EDX) spectroscopy confirmed the stoichiometric contents of Zn, Mn and O in each sample. Micrographs of all the samples exhibited a decrease in grain size with increase of Mn contents. Magnetic measurements performed using vibrating sample magnetometer (VSM) confirmed room temperature ferromagnetism exhibiting an increase in saturation magnetization and coercivity with increasing Mn contents in all the prepared samples.

Based on the recent progress on both the temperature dependence of surface tension [H. L. Yi, J. X. Tian, A. Mulero and I. Cachading, J. Therm. Anal. Calorim. 126 (2016) 1603, and the correlation between surface tension and viscosity of liquids [J. X. Tian and A. Mulero, Ind. Eng. Chem. Res. 53 (2014) 9499], we derived a new multiple parameter correlation to describe the temperature-dependent viscosity of liquids. This correlation is verified by comparing with data from NIST Webbook for 35 saturated liquids including refrigerants, hydrocarbons and others, in a wide temperature range from the triple point temperature to the one very near to the critical temperature. Results show that this correlation predicts the NIST data with high accuracy with absolute average deviation (AAD) less than 1% for 21 liquids and more than 3% for only four liquids, and is clearly better than the popularly used Vogel–Fulcher–Tamman (VFT) correlation.

Scheelite (CaWO₄)-type microphosphors were synthesized by the precipitation method assisted with cetyltrimethyl ammonium bromide (CTAB). All compounds crystallized in the tetragonal structure with space group $I41/a$ (No. 88). FE-SEM micrographs illustrate the spherical-like morphologies and rough surface. PL spectra indicate the broad emission peak maximum at 613 nm under UV excitation. Luminescence decay curves monitored by ${}^5{D}_6{-}^7{F}_0$ transition (${\lambda }_{\mathrm{\text{ex}}}=394$ nm) of Eu${}^{3+}$ in doped CaWO₄ are presented, the curves exhibit a single-exponential feature and the lifetime for doped CaWO₄ is 0.61 ms.