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Transparent Tm3+/Er3+/Yb3+ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals are prepared. Under excitation of a 980-nm laser diode (LD), compared with the glass before heat treatment, the Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics can emit intense blue, green and red up-conversion luminescence and Stark-split peaks; X-ray diffraction (XRD) and transmission electron microscope (TEM) results show that BaF2 nanocrystals with an average diameter of 20 nm are precipitated from the glass matrix. Stark splitting of the up-conversion luminescence peaks in the glass ceramics indicates that Tm3+, Er3+ and (or) Yb3+ ions are incorporated into the BaF2 nanocrystals. The up-conversion luminescence intensities of Tm3+, Er3+ and the splitting degree of luminescence peaks in the glass ceramics increase significantly with the increase of heat treat temperature and heat treat time extension. In addition, the possible energy transfer process between rare earth ions and the up-conversion luminescence mechanism are also proposed. [ABSTRACT FROM AUTHOR]

We report a theoretical investigation on the accumulation capacitance in MoS2 thin flake transistors using a two-valley band structure. To obtain the relevant two-valley band structure parameters, first-principles calculations are performed. Then, the capacitance-voltage characteristic in the accumulation layer is simulated by a self-consistent Poisson–Schrödinger solution. It is found that the occupation of the K valley in the conduction band has a significant contribution to the accumulation capacitance, especially in the strong accumulation layer. More importantly, the calculated results using a two-valley band structure is in good agreement with the published experimental data without any fitting parameters, highlighting that the inclusion of both the Q and K conduction band valley is necessary to understand the accumulation capacitance in the strong accumulation region. [ABSTRACT FROM AUTHOR]

We propose an underwater asymmetric acoustic transmission structure comprised of two media each with a gradient change of acoustic impedance. By gradually increasing the acoustic impedances of the media, the propagating direction of the acoustic wave can be continuously bent, resulting in allowing the acoustic wave to pass through along the positive direction and blocking acoustic waves from the negative one. The main advantages of this structure are that the asymmetric transmission effect of this structure can be realized and enhanced more easily in water. We investigate both numerically and experimentally the asymmetric transmission effect. The experimental results show that a highly efficient asymmetric acoustic transmission can be yielded within a remarkable broadband frequency range, which agrees well with the numerical prediction. It is of potential practical significance for various underwater applications such as reducing vibration and noise. [ABSTRACT FROM AUTHOR]

A novel bactericidal material, Ag@rGO-Fe3O4-PEI composite is prepared by in situ growth of silver nanoparticles onto the polyethylenimine (PEI)-mediated magnetic reduced graphene oxide (GO). The antibacterial performances of the composite are investigated by using the gram-negative bacteria Escherichia coli O157:H7 (E. coli O157:H7) as a model. The results indicate that the Ag@rGO-Fe3O4-PEI composite exhibits excellent antibacterial performance against E. coli O157:H7, with an antibacterial performance superior to those for the ever-reported photothermal materials. The bactericidal capability or the inhibition capability for bacteria growth is found to depend on the dosage of the Ag@rGO-Fe3O4-PEI and Ag/rGO-Fe3O4-PEI mass ratio within a certain range. By using a dosage of 0.1 μg mL−1, a killing rate of 99.9% is achieved for the E. coli O157:H7 (1 × 107 cfu mL−1) under a 0.5 min NIR laser irradiation (785 nm/50 mW cm−2). In addition, a minimum bactericidal concentration (MBC) of 0.100 μg mL−1 is achieved under near infrared (NIR) laser irradiation for 10 min, for which case there is absolutely no colony of E. coli O157:H7 found in the broth agar plate. [ABSTRACT FROM AUTHOR]

We report a theoretical investigation on the accumulation capacitance in MoS2 thin flake transistors using a two-valley band structure. To obtain the relevant two-valley band structure parameters, first-principles calculations are performed. Then, the capacitance-voltage characteristic in the accumulation layer is simulated by a self-consistent Poisson–Schrödinger solution. It is found that the occupation of the K valley in the conduction band has a significant contribution to the accumulation capacitance, especially in the strong accumulation layer. More importantly, the calculated results using a two-valley band structure is in good agreement with the published experimental data without any fitting parameters, highlighting that the inclusion of both the Q and K conduction band valley is necessary to understand the accumulation capacitance in the strong accumulation region. [ABSTRACT FROM AUTHOR]

The elastic scattering properties for collisions between cold and ultracold 39K atoms in a triplet state are investigated. Based on the recent theoretical and experimental results, the improved hybrid potential is presented for a triplet a3∑u+ ground state of K2. Our calculated value of the s-wave scattering length a by using the Numerov method for the triplet state is 79.578a0 and found to be in good agreement with the previous ones. The numbers of bound states are supported by the molecular potential. Pronounced shape resonances appear for the l = 3 partial waves for the a3∑u+ state. Furthermore, the s-wave scattering cross section, the total cross section and energy positions of shape resonances for the a3∑u+ state are calculated. [ABSTRACT FROM AUTHOR]

Conventional cosmic-ray propagation models usually assume an isotropic diffusion coefficient to account for the random deflection of cosmic rays by the turbulent interstellar magnetic field. Such models very successfully explain many observational phenomena related to the propagation of Galactic cosmic rays, such as broken power-law energy spectra, secondary-to-primary ratios, etc. However, the isotropic diffusion presupposition is facing severe challenges from recent observations. In particular, such observations on the large-scale anisotropy of TeV cosmic rays show that the dipole direction differs from the prediction of the conventional model. One possible reason is that the large-scale regular magnetic field, which leads to an anisotropic diffusion of cosmic rays, has not been included in the model provided by the public numerical packages. In this work, we propose two numerical schemes to solve the three-dimensional anisotropic transport equation: the pseudo-source method and Hundsdorfer–Verwer scheme. Both methods are verified by reproducing the measured B/C and proton spectrum and the radial variation of spectral index expected by former 2D simulation. As a demonstration of the prediction capability, dipole anisotropy is also calculated by a toy simulation with a rough magnetic field. [ABSTRACT FROM AUTHOR]

The discrepancy between the theoretical prediction of primordial lithium abundances and astronomical observations is called the Lithium Problem. We assume that during Big Bang Nucleosynthesis (BBN), nucleons can gain energy and deviate from thermal equilibrium, namely BBN cosmic rays (BBNCRs). BBNCR primary spectra are uncertain and the Coulomb energy-loss processes are neglected; however, we suppose a steady state of BBNCR spectra referring to the Galactic cosmic ray spectra observed today, to see constraints on BBNCRs, for example, the amount and energy range, not sticking to the explicit shape of the spectra. Such extra contributions from BBNCRs can explain the discrepancy, for both Li-7 and Li-6, and will change the deuterium abundance by only a little. The allowed parameter space of such an amount of nonthermal particles and the energy range are shown. The hypothesis is stable regardless of the cross-section uncertainty of relevant reactions and the explicit shape of the energy spectrum. [ABSTRACT FROM AUTHOR]

The magneto-optical Kerr effect susceptometry technique is proposed to determine the uniaxial magnetic anisotropy (UMA) constant Ku. The magnetic properties of Cu/Fe/SiO2/Si grown by dc magnetron sputtering were investigated. The in-plane uniaxial magnetic anisotropy was probed by the magneto-optical Kerr effect (MOKE). The value of UMA, Ku = 2.5 ×103 J/m3, was simulated from the field dependence of ac susceptibility along the hard axis according to the Stoner—Wohlfarth (S—W) model, which is consistent with Ku = 2.7 × 103 J/m3 calculated from the magnetic hysteresis loops. Our results show that the magneto-optical Kerr effect susceptometry can be employed to determine the magnetic anisotropy constant owing to its high sensitivity. [ABSTRACT FROM AUTHOR]

LReBaCuO (LRe = Nd, Sm, Gd) single domains possess a superior superconducting performance and have exhibited potential applications in the fields of superconducting bearings and permanent magnets. Therefore, the requirement of a large size for LReBaCuO single domains with high values of TC and JC is desirable. However, it has been found that some unexpected spontaneous nucleation actions always take place, which interrupt the growing process of the single domains. In this paper, the behavior of spontaneous nucleation in SmBaCuO-Ag solution has been investigated systematically. Experimental results reveal that the spontaneous nucleation that frequently takes place during the growing process could be eliminated greatly by reducing the cooling rate to a proper level. Based on the framework of the constitutional super-cooling theory, combined with the results obtained in experiments, we discuss the possible explanations for the spontaneous nucleation behavior in SmBaCuO-Ag solution. An assumption that the distribution of solute concentration CL, as well as the solid-liquid phase transition temperature TL, in SmBaCuO-Ag solution might be of a time-dependent nature is put forward. A graph of temperature versus time has been worked out based on the assumption, which matches the growth process behavior satisfactorily with the experimental results. [ABSTRACT FROM AUTHOR]

The acoustical scattering cross section is usually employed to evaluate the scattering ability of the bubbles when they are excited by the incident acoustic waves. This parameter is strongly related to many important applications of performance prediction for search sonar or underwater telemetry, acoustical oceanography, acoustic cavitation, volcanology, and medical and industrial ultrasound. In the present paper, both the analytical and numerical analysis results of the acoustical scattering cross section of a single bubble under multi-frequency excitation are obtained. The nonlinear characteristics (e.g., harmonics, subharmonics, and ultraharmonics) of the scattering cross section curve under multi-frequency excitation are investigated compared with single-frequency excitation. The influence of several paramount parameters (e.g., bubble equilibrium radius, acoustic pressure amplitude, and acoustic frequencies) in the multi-frequency system on the predictions of scattering cross section is discussed. It is shown that the combination resonances become significant in the multi-frequency system when the acoustic power is big enough, and the acoustical scattering cross section is promoted significantly within a much broader range of bubble sizes and acoustic frequencies due to the generation of more resonances. [ABSTRACT FROM AUTHOR]

We present a systematic investigation of magnetic anisotropy induced by oblique deposition of Co thin films on MgO (001) substrates by molecular beam epitaxy at different deposition angles, i.e., 0°, 30°, 45°, 60°, and 75° with respect to the surface normal. Low energy electron diffraction (LEED), surface magneto–optical Kerr effect (SMOKE), and anisotropic magnetoresistance (AMR) setups were employed to investigate the magnetic properties of cobalt films. The values of in-plane uniaxial magnetic anisotropy (UMA) constant Ku and four-fold magnetocrystalline anisotropy constant K1 were derived from magnetic torque curves on the base of AMR results. It was found that the value of Ku increases with increasing deposition angle with respect to the surface normal, while the value of K1 remains almost constant for all the samples. Furthermore, by using MOKE results, the Ku values of the films deposited obliquely were also derived from the magnetization curves along hard axis. The results of AMR method were then compared with that of hard axis fitting method (coherent rotation) and found that both methods have almost identical values of UMA constant for each sample. [ABSTRACT FROM AUTHOR]

A complete understanding of the bubble dynamics is deemed necessary in order to achieve their full potential applications in industry and medicine. For this purpose it is first needed to expand our knowledge of a single bubble behavior under different possible conditions including the frequency and pressure variations of the sound field. In addition, stimulated scattering of sound on a bubble is a special effect in sound field, and its characteristics are associated with bubble oscillation mode. A bubble in liquid can be considered as a representative example of nonlinear dynamical system theory with its resonance, and its dynamics characteristics can be described by the Keller–Miksis equation. The nonlinear dynamics of an acoustically excited gas bubble in water is investigated by using theoretical and numerical analysis methods. Our results show its strongly nonlinear behavior with respect to the pressure amplitude and excitation frequency as the control parameters, and give an intuitive insight into stimulated sound scattering on a bubble. It is seen that the stimulated sound scattering is different from common dynamical behaviors, such as bifurcation and chaos, which is the result of the nonlinear resonance of a bubble under the excitation of a high amplitude acoustic sound wave essentially. The numerical analysis results show that the threshold of stimulated sound scattering is smaller than those of bifurcation and chaos in the common condition. [ABSTRACT FROM AUTHOR]