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[en] In this paper, three different widely-used measurement techniques for environmental gamma dose rate were studied and compared, i.e., the thermoluminescent dosimeter, the portable survey meter and the spectrometric analysis. Thirteen investigation sites were selected, and the TLDs were arranged to accumulate the radiation signals during an interval of about one quarter, the instant dose rates by using a portable survey meter were collected around the site, and top surface soils were sampled in the surroundings for radionuclides analyzing in laboratory. The results from these methods were compared, which revealed high correlations. The differences and possible uncertainties for the three methods were analyzed, inspired a further study should be conducted to have more successful estimation of dose rate in surface air. - Highlights: • Gamma dose rate was measured around a proposed nuclear power plant in siting stage. • Three measurement methods for dose rate were used by TLDs, portable survey meter and spectrometric analysis. • Correlations between the values from different methods were analyzed. • The differences and the uncertainties of the dose rate from the different methods were analyzed.
[en] _T_b__0__.__3_D_y__0__.__7_F_e_1_._9_5 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the (Tb,Dy)Fe_2 phase changed from 〈113〉 to 〈111〉 direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb_0_._3Dy_0_._7Fe_1_._9_5 alloys is remarkably improved. The change in magnetostriction of Tb_0_._3Dy_0_._7Fe_1_._9_5 alloys is linked to the amount and the crystal orientation behavior of the (Tb,Dy)Fe_2 phase. (paper)
[en] This paper proposes a novel adaptive control criterion for a class of single-input-single-output (SISO) uncertain nonlinear systems by using extended neural networks (ENNs). Distinguished from the traditional neural networks, our ENNs are composed of radial basis function neural networks (RBFNNs), scalers and saturators. And these ENNs are used to approximate the uncertainties in the nonlinear systems. Based on the Lyapunov stability theory and our ENNs, an adaptive control scheme is designed to guarantee that all the signals in the closed-loop system are uniformly ultimately bounded (UUB). It is also worth pointing out that our control method makes the construction of RBFNNs and the design of adaptive laws separated, which means only the outputs of ENNs and one update law of the parameter in the scaler are to be adjusted. Thus, our control scheme can effectively reduce the online computation burden of the adaptive parameters. Finally, simulation examples are given to verify the effectiveness of our theoretical result.
[en] Highlights: • Periodic inverted pyramid (IP) structures employed for Si heterojunction (SHJ). • Improved carrier collection efficiency by the superior passivation of IP structures. • SHJ cells with the optimized IP structure achieving the efficiency of 14.6. The Si heterojunction (SHJ) solar cell is presently the most popular design in the crystalline Si (c-Si) photovoltaics due to the high open-circuit voltages (VOC). Photon management by surface structuring techniques to control the light entering the devices is critical for boosting cell efficiency although it usually comes with the VOC loss caused by severe surface recombination. For the first time, the periodic inverted pyramid (IP) structure fabricated by photolithography and anisotropic etching processes was employed for SHJ solar cells, demonstrating concurrent improvement in optical and electrical characteristics (i.e., short-circuit current density (JSC) and VOC). Periodic IP structures show superior light-harvesting properties as most of the incident rays bounce three times on the walls of the IPs but only twice between conventional random upright pyramids (UPs). The high minority carrier lifetime of the IP structures after a-Si:H passivation results in an enhanced VOC by 28 mV, showing improved carrier collection efficiency due to the superior passivation of the IP structure over the random UP structures. The superior antireflective (AR) ability and passivation results demonstrate that the IP structure has the potential to replace conventional UP structures to further boost the efficiency in solar cell applications.
[en] In this paper, we present a very important and quite controversial observational property of penumbral filaments that may exhibit twisting motions and change their chirality. Using high-resolution observations from the Solar Optical Telescope on board Hinode, we study the unwinding and twisting motions in the penumbral filaments of active region NOAA 10930. Penumbral filaments, including those to the northwest of the magnetic polarity inversion line (PIL) and those inside the PIL region, are found to make unwinding motions associated with the decrease of their right-handed twists. After unwinding, the filaments inside the PIL region are found to twist continuously to develop left-handed twists in them. Moreover, we find the filament elongating, expanding, splitting, and the screw pitch decreasing in the unwinding process and, getting shorter, shrinking, merging, and the screw pitch increasing in the twisting process. These observational results indicate that penumbral filaments are more inclined to be twisted magnetic flux tubes in nature.
[en] To accelerate the renewal of working fluid in machining gaps, this paper proposed using a dentate disc foil electrode (DDFE) for rotary micro electrical discharge machining (micro-EDM) to fabricate deep-narrow microgrooves. The DDFEs were machined from 30 µm thick Fe78Si9B13 amorphous alloy foils through wire electrical discharge machining. Under different process parameters, a series of experiments for fabricating microgrooves were performed by micro-EDM using the DDFE in emulsion. The effects of applied voltage, machining modes, clockwise rotation speed of the DDFE, and machining depth on the microgroove width were investigated in detail. Furthermore, the morphologies and dimensions of the microgrooves were characterized using a laser scanning confocal microscope and scanning electron microscope. The experimental results indicate that when the applied voltage U was 60 V, the DDFE clockwise rotation speed n was 3000 r min−1, the machining depth H was equal to the tooth height of 500 µm, the supply direction of the working fluid was right yet opposite to the the workpiece feed direction, a stable and fast micro-EDM process was achieved and a deep-narrow microgroove of width approximately 78 µm and aspect ratio 6.4 was obtained. With the optimized process parameters, array microgroove structures and column microstructures were fabricated successfully on #304 stainless steel workpieces. (paper)
[en] We have investigated the performance of GaN-based blue light-emitting diodes (LEDs) with a p-InGaN/GaN short-period superlattice (SPS) contact layer, which were grown by metal organic chemical vapor deposition. It was found that dot-like features appeared on the surface when a p-InGaN/GaN SPS structure was grown. The LED operating voltage decreased from 3.52 V to 3.15 V and the electrostatic discharge properties of LEDs were improved by using such a SPS structure. The output powers of LEDs were also increased by adjusting the In mole fraction in the SPS. However, the lifetime of LEDs became shorter when such a SPS structure was used
[en] We report a facile method of synthesizing graphene quantum dots (GQDs) with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photoluminescence mechanism is further investigated based on the surfacestructure and the photoluminescence behaviors. Based on our discussion, the green fluorescence emission can be attributed to the oxygen functional groups, which could possess broad emission bands within the π–π* gap. This work is helpful to explain the vague fluorescent mechanism of GQDs, and the reported synthetic method is useful to prepare GQDs with controllable fluorescent colors. (interdisciplinary physics and related areas of science and technology)
[en] In this paper, the principle of discharge-based pulsed I – V technique is introduced. By using it, the energy and spatial distributions of electron traps within the 4-nm HfO2 layer have been extracted. Two peaks are observed, which are located at Δ E ∼ −1.0 eV and −1.43 eV, respectively. It is found that the former one is close to the SiO2/HfO2 interface and the latter one is close to the gate electrode. It is also observed that the maximum discharge time has little effect on the energy distribution. Finally, the impact of electrical stress on the HfO2 layer is also studied. During stress, no new electron traps and interface states are generated. Meanwhile, the electrical stress also has no impact on the energy and spatial distribution of as-grown traps. The results provide valuable information for theoretical modeling establishment, material assessment, and reliability improvement for advanced semiconductor devices. (paper)
[en] In this work, we study the possibility to find Ncc-bar∗ and Λcc-bar∗ resonances with hidden charm with mass above 4 GeV in the photon-induced production. The cross sections for the photoproductions of hidden charmed baryons are predicted in the effective Lagrangian approach with the vector meson dominance mechanism. N∗(4412) can be produced directly by photon excitation with total cross section about 1 nb. N∗(4412) provides an obvious peak near the threshold for J/ψ photoproduction, which is expected to be checked by the future high precision experiment at JLab 12 GeV. The results will be helpful in the experimental search for the hidden-charmed baryon resonances in the forthcoming experiments at JLab 12 GeV, such as SoLID, and the proposed electron–ion colliders at FAIR and HIAF. (paper)