Time-Like Conformal Homogeneous Hypersurfaces with Three Distinct Principal Curvatures

A hypersurface x(M) in Lorentzian space R_1~4 is called conformal homogeneous,if for any two points p, q on M, there exists σ, a conformal transformation of R_1~4, such thatσ(x(M)) = x(M), σ(x(p)) = x(q). In this paper, the authors give a complete classification for regular time-like conformal homogeneous hypersurfaces in R_1~4 with three distinct principal curvatures.     

Extremely fast ambipolar diffusion in n-i-p-i doping superlattices investigated by an all-optical pump-and-probe technique

We report on investigations of the ambipolar diffusion process in n-i-p diodes and n-i-p-i doping superlattices performed by a new all-optical pump-and-probe technique. This new technique allows not only the determination of the ambipolar diffusion coefficient but also the spatially resolved investigation of the stationary distribution of the optically-induced excess carriers. The n-i-p-i doping superlattice exhibited an extremely large ambipolar diffusion coefficient in the range of 10⁴cm²s⁻¹. The ambipolar diffusion coefficient of the n-i-p and n-i-p-i structure was demonstrated not to be a constant but a function of the charge carrier density. This strongly affects the spatial distribution of the excess carriers especially in the large signal regime (density of photo-generated carriers much larger than dark carrier concentration). The spatial distribution of the carriers in the small as well as in the large signal case can be understood theoretically if the real dependence of the ambipolar diffusion coefficient on the carrier density is taken into account.     

Enhanced UVB emission and analysis of chemical states of Ca5(PO4)3OH:Gd3+,Pr3+ phosphor prepared by co-precipitation

Hydroxyapatite (Ca₅(PO₄)₃OH) is a well-known bioceramic material used in medical applications because of its ability to form direct chemical bonds with living tissues. This mineral is currently used as a host for rare-earth ions (e.g. Gd³⁺, Pr³⁺, Tb³⁺, etc.) to prepare phosphors that can be used in light emitting devices of different types. In this study Ca₅(PO₄)₃OH:Gd³⁺,Pr³⁺ phosphors were prepared by the co-precipitation method and were characterised by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive x-ray spectroscopy and photoluminescence spectroscopy. The x-ray diffraction pattern was consistent with the hexagonal phase of Ca₅(PO₄)₃OH referenced in JCPDS card number 73-0293. The x-ray photoelectron spectroscopy data indicated that Ca²⁺ occupied two different lattice sites, referred to as Ca1 and Ca2. The photoluminescence data exhibited a narrowband emission located at 313 nm, which is associated with the ⁶P_7/2→⁸S_7/2 transition of the Gd³⁺ ion. This emission is classified as ultraviolet B and it is suitable for use in phototherapy lamps to treat various skin diseases. The photoluminescence intensity of the 313 nm emission was enhanced considerably by Pr³⁺ co-doping.     

Phonon-assisted energy up-conversion process of Er3+ ions doped in KY F4 crystal

Er³⁺ ions doped in KY F₄ crystal emit blue photoluminescence around 406 nm by energy up-conversion process when excited by 532 or 488 nm laser. By measuring the temperature dependence of up-converted luminescence, we found that the up-conversion process is enhanced with increasing temperature, which is an indication that phonons are assisting the process. This observation is supported by the fact that the energy transfer responsible for the up-conversion involves two transitions that have an energy mismatch.     

ZnO纳米花的制备及其性能

利用化学气相沉积法, 在铜箔上成功制备出形似自然界中刺球花的ZnO纳米花结构. 实验进一步研究了氧气和氩气流量比例分别为1:150, 1:200, 1:250和1:400时对ZnO纳米花结构和性能的影响. 结果表明, ZnO纳米花上的ZnO纳米棒的长径比随氧气氛的减少而减小; 在氧气和氩气流量比例为1:250时制备出的ZnO纳米花尺寸均匀、形貌均一、花型结构最完美. ZnO 纳米花的室温光致发光谱表明, 随着氧气氛的减少, 可见区域的发光从一个波包变成一个宽峰, 且与锌空位相关的缺陷发光峰在减弱, 与氧空位相关的缺陷发光峰在增强. 基于实验结果, 提出了一种在铜箔上制备ZnO纳米花结构的生长模型.     

Hausdorff Dimension for Range and Graph of Multi-Parameter Operator Stable L\'{e}vy Processes

The lower Hausdorff dimension results for the range and the graph of multi-parameter operator stable L\'{e}vy processes are established. The consequences are completely determined by the eigenvalues of its exponent matrix.     

具有时滞的帕金森模型的振荡动力学分析

研究大脑基底神经节中产生异常β振荡的起源有助于分析帕金森病的致病机理. 本文系统地研究了改进的皮质?基底神经节(E-I-STN-GPe-GPi)共振模型的振荡动力学. 首先, 通过Routh-Hurwitz准则和稳定性理论获得了该模型局部平衡点处的稳定性与Hopf分岔发生的条件, 并且推导出该共振模型存在Hopf分岔的时滞参数范围. 研究发现, 增加突触传输时滞能够使模型产生Hopf分岔, 并且诱导β振荡的产生, 使系统在健康和帕金森病这两个状态之间相互转换. 其次, 揭示了β振荡的产生与丘脑底核相关的突触连接强度有关. 数值模拟发现, 当丘脑底核同时受到兴奋性神经元集群和苍白球外侧较强的促进作用时, 丘脑底核产生振荡. 最后, 分析了与苍白球内侧有关的参数对其产生振荡的影响, 研究结果发现, 当较小的苍白球外侧突触连接强度和较大的突触传输时滞共同作用时, 苍白球内侧更容易发生振荡, 且振幅越来越大. 希望本文对E-I-STN-GPe-GPi共振模型的动力学特征的研究有助于人们理解帕金森病的致病机理和揭示帕金森病异常β振荡的来源.      

Halide/sulfide composite solid-state electrolyte for Li-anode based all-solid-state batteries

Li₂ZrCl₆ (LZC) solid-state electrolytes (SSEs) have been recognized as a candidate halide SSEs for all-solid-state Li batteries (ASSLBs) with high energy density and safety due to its great compatibility with 4 V-class cathodes and low bill-of-material (BOM) cost. However, despite the benefits, the poor chemical/electrochemical stability of LZC against Li metal causes the deterioration of Li/LZC interface, which has a detrimental inhibition on Li⁺ transport in ASSLBs. Herein, we report a composite SSE combining by LZC and argyrodite buffer layer (Li₆PS₅Cl, LPSC) that prevent the unfavorable interaction between LZC and Li metal. The Li/LPSC-LZC-LPSC/Li symmetric cell stably cycles for over 1000 h at 0.3 mA/cm² (0.15 mAh/cm²) and has a high critical current density (CCD) value of 2.1 mA/cm² at 25 °C. Under high temperature (60 °C) which promotes the reaction between Li and LZC, symmetric cell fabricated with composite SSE also display stable cycling performance over 1200 h at 0.3 mAh/cm². Especially, the Li/NCM ASSLBs fabricated with composite SSE exhibit a high initial coulombic efficiency, as well as superior cycling and rate performance. This simple and efficient strategy will be instrumental in the development of halide-based high-performance ASSLBs.     

Composite Eu-MOF@CQDs “off & on” ratiometric luminescent probe for highly sensitive chiral detection of l-lysine and 2-methoxybenzaldehyde

The high amount of l-lysine can increase the potential risk of cardiovascular disease. Additionally, 2-methoxy benzaldehyde (2-MB) has high toxicity and can easily pollute the environment. In this work, carbon quantum dots (CQDs) can be encapsulated into Eu-BTB (H₃BTB = 1,3,5-tri(4-carboxyphenyl)benzene), forming the multi-emission composite material Eu-BTB@CQDs. It has two emissions peaks (617 nm for Eu and 470 nm for CQDs). Eu-BTB@CQDs can be applied as bi-functional ratiometric “off & on” luminescent sensor for l-lysine and 2-MB with high sensitivity and selectivity, the low limit of detection (LOD) for l-lysine is 3.68 µmol/L and for 2-MB is 0.54 µmol/L, respectively. Additionally, Eu-BTB@CQDs can quantitatively discriminate l-lysine in the mixed d- and l-lysine water solutions (five different concentrations ratio of l/d-lysine has been set) makes the chiral detection of l-lysine are more meaningful. On the other hand, Eu-BTB@CQDs also can detect 2-MB over 4-methoxybenzaldehyde (4-MB) with high selectivity. Further the detection of 2-MB and l-lysine in the lake water real samples with the reasonable recovery rate. Finally, the detection mechanisms for l-lysine and 2-MB were also investigated and discussed in detail.