Chinese Physics B

Zhu, Yong; Xu, Mingquan; Zhou, Wu

doi: 10.1088/1674-1056/27/5/056804pmid: N/A

Heterogeneous catalysts are the most important catalysts in industrial reactions. Nanocatalysts, with size ranging from hundreds of nanometers to the atomic scale, possess activities that are closely connected to their structural characteristics such as particle size, surface morphology, and three-dimensional topography. Recently, the development of advanced analytical transmission electron microscopy (TEM) techniques, especially quantitative high-angle annular dark-field (HAADF) imaging and high-energy resolution spectroscopy analysis in scanning transmission electron microscopy (STEM) at the atomic scale, strengthens the power of (S)TEM in analyzing the structural/chemical information of heterogeneous catalysts. Three-dimensional reconstruction from two-dimensional projected images and the real-time recording of structural evolution during catalytic reactions using in-situ (S)TEM methods further broaden the scope of (S)TEM observation. The atomic-scale structural information obtained from high-resolution (S)TEM has proven to be of significance for better understanding and designing of new catalysts with enhanced performance.

Cocemasov, Alexandr I.; Isacova, Calina I.; Nika, Denis L.

doi: 10.1088/1674-1056/27/5/056301pmid: N/A

We review experimental and theoretical results on thermal transport in semiconductor nanostructures (multilayer thin films, core/shell and segmented nanowires), single- and few-layer graphene, hexagonal boron nitride, molybdenum disulfide, and black phosphorus. Different possibilities of phonon engineering for optimization of electrical and heat conductions are discussed. The role of the phonon energy spectra modification on the thermal conductivity in semiconductor nanostructures is revealed. The dependence of thermal conductivity in graphene and related two-dimensional (2D) materials on temperature, flake size, defect concentration, edge roughness, and strain is analyzed.

Pan, Hui; Jia, Feng; Liu, Zhen-Yu; Zaitsev, Maxim; Hennig, Juergen; G Korvink, Jan

doi: 10.1088/1674-1056/27/5/050201pmid: N/A

A topology optimization method based on the solid isotropic material with penalization interpolation scheme is utilized for designing gradient coils for use in magnetic resonance microscopy. Unlike the popular stream function method, the proposed method has design variables that are the distribution of conductive material. A voltage-driven transverse gradient coil is proposed to be used as micro-scale magnetic resonance imaging (MRI) gradient coils, thus avoiding introducing a coil-winding pattern and simplifying the coil configuration. The proposed method avoids post-processing errors that occur when the continuous current density is approximated by discrete wires in the stream function approach. The feasibility and accuracy of the method are verified through designing the z-gradient and y-gradient coils on a cylindrical surface. Numerical design results show that the proposed method can provide a new coil layout in a compact design space.

Zhou, Yingming; Jiang, Xue-Qin; Liu, Weiqi; Wang, Tao; Huang, Peng; Zeng, Guihua

doi: 10.1088/1674-1056/27/5/050301pmid: N/A

The well-known multi-dimensional reconciliation is an effective method used in the continuous-variable quantum key distribution in the long-distance and the low signal-to-noise-ratio scenarios. The virtual channel employed to exchange data is generally established by using a finite-dimensional rotation in the reconciliation procedure. In this paper, we found that the finite dimension of the multi-dimensional reconciliation inevitably leads to the mismatch of the signal-to-noise-ratio between the quantum channel and the virtual channel, which may be called the finite-dimension effect. Such an effect results in an overestimation on the secret key rate, and subsequently induces vital practical security loopholes.

Zhou, Wen-yan; Wu, Ya-jie; Kou, Su-Peng

doi: 10.1088/1674-1056/27/5/050302pmid: N/A

We study the topological properties of Bogoliubov excitation modes in a Bose–Hubbard model of three-dimensional (3D) hyperhoneycomb lattices. For the non-interacting case, there exist nodal loop excitations in the Bloch bands. As the on-site repulsive interaction increases, the system is first driven into the superfluid phase and then into the Mott-insulator phase. In both phases, the excitation bands exhibit robust nodal-loop structures and bosonic surface states. From a topology point of view, these nodal-loop excitation modes may be viewed as a permanent fingerprint left in the Bloch bands.

Jin, Yan-Fei

doi: 10.1088/1674-1056/27/5/050501pmid: N/A

Stochastic resonance (SR) is studied in an under-damped bistable system driven by the harmonic mixing signal and Gaussian white noise. Using the linear response theory (LRT), the expressions of the spectral amplification at fundamental and higher-order harmonic are obtained. The effects of damping coefficient, noise intensity, signal amplitude, and frequency on spectral amplifications are explored. Meanwhile, the power spectral density (PSD) and signal-to-noise ratio (SNR) are calculated to quantify SR and verify the theoretical results. The SNRs at the first and second harmonics exhibit a minimum first and a maximum later with increasing noise intensity. That is, both of the noise-induced suppression and resonance can be observed by choosing proper system parameters. Especially, when the ratio of the second harmonic amplitude to the fundamental one takes a large value, the SNR at the fundamental harmonic is a monotonic function of noise intensity and the SR phenomenon disappears.

Zhang, Ming-Jiang; Niu, Ya-Nan; Zhao, Tong; Zhang, Jian-Zhong; Liu, Yi; Xu, Yu-Hang; Meng, Jie; Wang, Yun-Cai; Wang, An-Bang

doi: 10.1088/1674-1056/27/5/050502pmid: N/A

We design a hybrid integrated chaotic semiconductor laser with short-cavity optical feedback. It can be assembled in a commercial butterfly shell with just three micro-lenses. One of them is coated by a transflective film to provide the optical feedback for chaos generation while insuring regular laser transmission. We prove the feasibility of the chaos generation in this compact structure and provide critical external parameters for the fabrication by theoretical simulations. Rather than the usual changeless internal parameters used in previous simulation research, we extract the real parameters of the chip by experiment. Moreover, the maps of the largest Lyapunov exponent with varying bias current and feedback intensity Kap demonstrate the dynamic characteristics under different external-cavity conditions. Each laser chip has its own optimal external cavity length (L) and feedback intensity (Kap) to generate chaos because of the different internal parameters. We have acquired two ranges of optimal parameters (L = 4 mm, and L = 5 mm, ) for two different chips.

Qin, Shunda; Ge, Hongxia; Cheng, Rongjun

doi: 10.1088/1674-1056/27/5/050503pmid: N/A

A new feedback control method is derived based on the lattice hydrodynamic model in a single lane. A signal based on the double flux difference is designed in the lattice hydrodynamic model to suppress the traffic jam. The stability of the model is analyzed by using the new control method. The advantage of the new model with and without the effect of double flux difference is explored by the numerical simulation. The numerical simulations demonstrate that the traffic jam can be alleviated by the control signal.

Yang, Kang; Wang, Jialei; Kong, Xiangyan; Yang, Ruihu; Chen, Hua

doi: 10.1088/1674-1056/27/5/050701pmid: N/A

The performance of a superconducting quantum interference device (SQUID) gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupled flux threading a magnetometer obtained by Wikswo, we studied how the gradiometer performance parameters, including the current dipole sensitivity, spatial resolution and signal-to-noise ratio (SNR), are affected by its pick-up coil via MatLab simulation. Depending on the simulation results, the optimal pick-up coil design region for a certain gradiometer can be obtained. To verify the simulation results, we designed and fabricated several first-order gradiometers based on the weakly damped SQUID with different pick-up coils by applying superconducting connection. The experimental measurements were conducted on a simple current dipole in a magnetically shielding room. The measurement results are well in coincidence with the simulation ones, indicating that the simulation model is useful in specific pick-up coil design.

Hasan, Ghasemi; Ali, Mokhtari

doi: 10.1088/1674-1056/27/5/053101pmid: N/A

In the present work, firstly, a first-principles study of the structural, electronic, and electron transport properties of the HgxMg1−xTe (HMT) ternary compound is performed using the ABINIT package and the results are compared with Cd0.9Zn0.1Te (CZT) as a current room-temperature photodetector. Next, the response functions of Hg0.6Mg0.4Te and Cd0.9Zn0.1Te under electromagnetic irradiation with 0.05 MeV, 0.2 MeV, 0.661 MeV and 1.33 MeV energies are simulated by using the MCNP code. According to these simulations, the Hg0.6Mg0.4Te ternary compound is suggested as a good semiconductor photodetector for use at room temperature.