[en] By swapping the entanglement of genuine four-particle entangled states, we propose a bidirectional quantum secure communication protocol. The biggest merit of this protocol is that the information leakage does not exist. In addition, the ideas of the 'two-step' transmission and the block transmission are employed in this protocol. In order to analyze the security of the second sequence transmission, decoy states are used. (general)

[en] This work numerically investigates the radiative properties of film-coupled metamaterials made of a two-dimensional metallic concave grating on a continuous metal film separated by an ultrathin dielectric spacer. Spectrally-selective absorption is demonstrated in the visible and near-infrared regime, and underlying mechanisms are elucidated to be either localized magnetic polaritons (MPs) or surface plasmon polaritons (SPPs). The unique behaviors of MPs and SPPs are explained with the help of electromagnetic field distributions at respective resonance frequencies. An inductor–capacitor model is utilized to further confirm the excitation of MP, while dispersion relation is used to understand the behaviors of different SPP modes. Geometric effects of ridge width and grating period on the resonance absorption peaks are discussed. Moreover, directional responses at oblique incidences for different polarization states are studied. Fundamental understanding gained here will facilitate the design of novel metamaterials in energy harvesting and sensing applications. - Highlights: • Selective absorption was numerically realized with film-coupled concave gratings. • Underlying mechanisms were elucidated as magnetic and surface plasmon polaritons. • An inductor–capacitor model was employed to confirm the magnetic polaritons. • Dispersion relation was used to explain the behavior of surface plasmon polariton. • Effects of geometric factors, oblique angle and polarization were also discussed

[en] In this work, we propose a hybrid near-field radiative thermal modulator made of two graphene-covered silicon carbide (SiC) plates separated by a nanometer vacuum gap. The near-field photon tunneling between the emitter and receiver is modulated by changing graphene chemical potentials with symmetrically or asymmetrically applied voltage biases. The radiative heat flux calculated from fluctuational electrodynamics significantly varies with graphene chemical potentials due to tunable near-field coupling strength between graphene plasmons across the vacuum gap. Thermal modulation and switching, which are the key functionalities required for a thermal modulator, are theoretically realized and analyzed. Newly introduced quantities of the modulation factor, the sensitivity factor and switching factor are studied quite extensively in a large parameter range for both graphene chemical potential and vacuum gap distance. This opto-electronic device with faster operating mode, which is in principle only limited by electronics and not by the thermal inertia, will facilitate the practical application of active thermal management, thermal circuits, and thermal computing with photon-based near-field thermal transport. - Highlights: • A radiation-based thermal modulator was achieved between graphene covered SiC plates. • Strong SPP/SPhP coupling between emitter and receiver was identified. • Near-field radiative heat transfer was modified by tuning graphene chemical potential. • Asymmetric case with different chemical potentials of graphene was investigated.

[en] This paper deals with the counterweight optimization of an asymmetrical hybrid machine tool based on dynamic isotropy. The dynamic model is derived and the dynamic manipulability ellipsoid is studied. Based on dynamic manipulability ellipsoid, the dynamic isotropy is defined. Counterweight block and fluid counterweight are presented to balance the weight of moving parts. The mass of the counterweight block is optimized to obtain the maximum dynamic isotropy in the workspace. The dynamic isotropy of the machine tool after counterweight optimization is compared with that before counterweight optimization. Furthermore, the dynamic isotropy of the machine tool with fluid counterweight is investigated and compared with that of the machine tool with counterweight block.

[en] In the present study, we theoretically demonstrate a vacuum thermal switch based on near-field thermal radiation between phase transition materials, i.e., vanadium dioxide (VO_2), whose phase changes from insulator to metal at 341 K. Strong coupling of surface phonon polaritons between two insulating VO_2 plates significantly enhances the near-field heat flux, which on the other hand is greatly reduced when the VO_2 emitter becomes metallic, resulting in strong thermal switching effect. Fluctuational electrodynamics incorporated with anisotropic wave propagation predicts more than 80% heat transfer reduction at sub-30-nm vacuum gaps and 50% at vacuum gap of 1 μm. Furthermore, the penetration depth inside the uniaxial VO_2 insulator is studied at the vacuum gap of 50 nm, suggesting the possible impact of reduced VO_2 thickness on the near-field thermal radiation with thin-film structures. By replacing the bulk VO_2 receiver with a thin film of several tens of nanometers, the switching effect is further improved over a broad range of vacuum gaps from 10 nm to 1 μm. Finally, the effect of SiO_2 substrate for the thin-film emitter or receiver is also considered to provide insights for future experimental demonstrations. By controlling heat flow with near-field radiative transport, the proposed vacuum thermal switch would find practical applications for energy dissipation in microelectronic devices and for the realization of thermal circuits. - Highlights: • Near-field thermal switching was theoretically demonstrated with phase change VO_2. • Radiative heat flux was reduced by 80% at sub-30-nm vacuum gaps or 50% at 1 μm. • Strong phonon coupling between insulating VO_2 emitter and receiver was elucidated. • Thin-film structures were studied for achieving stronger thermal switching effect. • Effect of SiO_2 substrate was investigated for thin-film vacuum thermal switches

[en] This paper presents a 3-RPaS (R and S denote the revolute and spherical joint, pa denotes the parallelogram) parallel manipulator with two-rotational-degrees-of-freedom (2R1T) and one-translational-degree-of-freedom motion. By introducing parallelograms and an innovative driving module, the 3-RPaS manipulator can change the transmission path of the driving and reaction forces, and achieves 27 actuation modes. The kinematic performance of the manipulator under different actuation modes is analyzed with the indices that are defined based on matrix orthogonal degree. Comparative analysis indicates that the kinematic performance of the manipulator varies significantly in different actuation modes. A reasonable selection of actuation modes can effectively improve the kinematic performance and eliminate singularities. The concept of optimal actuation mode and the implementation approach of actuation mode conversion are discussed and analyzed for kinematics promotion. The kinematic performance of the manipulator is greatly improved with optimal actuation modes, without changing the topology structure and dimensional parameters.

[en] Graphical abstract: - Highlights: • Low-friction mechanism of CN_x films in inert gas is explored by first-principles. • The mechanism highlights the positive role of the lone-pairs on nitrogen atoms. • Diamond surface can be passivated by nitrogen atoms due to their lone-pairs. • An ‘electron transfer passivation mechanism’ is identified. • The lone-pairs contribute to the formation of low-friction interface in CN_x. - Abstract: Amorphous CN_x films show low friction coefficients in inert atmospheres, but the mechanism is still not well understood. Here we find that, by first-principles calculations, the dangling bonds on a diamond (1 1 1) surface are replaced with lone-pairs when nitrogen atoms are doped in the 1st or the 2nd top layer, and an ‘electron transfer passivation mechanism’ is identified. Then, two feasible ways for nitrogen atoms to present in the surface layer during the process of wear are suggested. On the basis of the insights gained, we propose a mechanism that highlights the positive role of the nitrogen lone-pairs in the formation of a weak-interacting interface between the friction-induced ‘graphitized’ layer and the intact below part, which is believed to be the reason for the low-frictions of CN_x films in inert atmospheres.

[en] Shanxi radioactive waste repository, intended for storage of solid radioactive waste and disused radioactive sources, must meet the national relevant standards with respect radiation safety. The monitoring results of gamma radiation dose rate in the surrounding area of the repository are consistent with the technical requirements for siting, design and construction of radioactive waste repository. (author)

[en] An asymmetric Fabry-Perot emitter is proposed with a lossless dielectric spacer inserted between a vanadium dioxide (VO₂) thin film and an opaque aluminum substrate. Switchable mid-infrared emittance has been achieved due to the insulator-to-metal transition of VO₂. When VO₂ is dielectric below 341 K, the structure is highly reflective, thereby minimizing thermal radiation loss. Above 345 K, the VO₂ becomes metallic and forms a Fabry-Perot resonance cavity with high broadband emissivity around 10 µm wavelength, providing a radiative cooling effect due to enhanced thermal emission. The radiative properties are calculated via a uniaxial transfer matrix method and Bruggeman effective medium theory. The physical mechanisms that provide the observed absorption enhancements are elucidated by examining the total phase shift in the multilayer structure and the phonon modes of VO_2. When experiencing the VO₂ phase transition, the radiative power of the proposed coating achieves a 6.5 fold enhancement for extraterrestrial spacecraft systems, and 7.3 fold enhancement for terrestrial systems such as buildings, making it a promising choice for dynamic radiative cooling applications in a variable environment. The findings here will facilitate research and development of novel coating materials for radiative cooling applications. - Highlights: • Dynamic radiative cooling was achieved with a VO₂-based Fabry-Perot emitter. • Strong Fabry-Perot resonance was identified when VO₂ is in its metallic phase. • The performance was determined to be insensitive to incidence angle. • The cooling power for building and spacecraft applications was investigated.

[en] To strengthen the safety management of radioactive waste repository, and to ensure the environmental radiation safety, this article analyzed the monitoring results of environmental gamma radiation dose rate in radioactive waste repository from 2013-2018 in Shanxi province radioactive waste repository. Results showed that the environmental gamma radiation levels at the repository meet the 'Technical requirements for siting, design and construction of radioactive waste repository for nuclear technology application (Trial)'. The gamma radiation dose rate at 0.5 m above the top of sources pit cover within the repository building is less than 20 μGy/h. The gamma radiation dose rate at 0.2 m from the outer surface of the repository building wall is less than 2.5 μGy/h. The annual environmental radiation level within the fluctuation range of background, which did not produce radiation effects of on the surrounding environment. Radiation environmental quality is generally good. In addition, a robust security level in the repository area will provide a strong guarantee for promoting the use of nuclear technology and the safety, health and sustainable development of the province. (author)