Reversible photoinduced bi-state polymer solar cells based on fullerene derivatives with azobenzene groups

[6,6]-Phenyl-C61-butyric acid-4′-hydroxyl-azobenzene ester (PCBAb) was synthesized and used as the acceptor in the fabrication of reversible UV–VIS response bi-state polymer solar cells (PSCs) based on the photoinduced cis–trans isomerization of PCBAb. The device can be switched between “active” and “sleep” by the irradiation of UV and visible light, respectively. The active device has a PCE of 2.0%. With UV irradiation, the device goes to “sleep” with a lowered PCE (0.4%), and simultaneously decreased J_sc, V_oc and FF, while after visible light treatment, the device is made “active” again. The mechanism of the bi-state process involves the different electron mobilities of the isomers.     

内置Yb3+…YAG的环形腔输出脉冲激光理论分析

分析了Yb3+…YAG的发射光谱,按照均匀展宽的机理,对发射截面按照波长进行了划分,使之对应于Stark子能级对之间的跃迁。在此基础上,提出了内置Yb3+…YAG的环形腔将连续注入种子激光转换为超短脉冲激光的理论模型。基于速率方程方法,推导得到了描述脉冲激光性能的方程。在此过程中,考虑了Yb3+激光的抽运饱和吸收和自吸收效应。最后利用该模型分析了不同情况下的超短脉冲激光性能。结果表明,要实现性能优良的脉冲激光输出,必须选择合适的种子激光频率、光强和晶体长度等。     

Video coding for OFDM systems with imperfect CSI: A hybrid digital–analog approach

Performance of an orthogonal frequency division multiplexing (OFDM) system is greatest when the exact channel state information (CSI) is used for transmitter rate control and power allocation. However, in real systems CSI can only be approximately known. Moreover, in video communication, it can be difficult to use any CSI for rate control of a video codec if the channel changes significantly during a group of pictures coded jointly, such as when the receiver is moving. We address this issue through a hybrid digital–analog (HDA) coding system where a standard video codec is used to generate a fixed-rate base layer upon which the analog quantization error is superimposed as a refinement layer. The system adapts to channel variations by proper transmit-power allocation between digital and analog components and across OFDM subcarriers, based on CSI. We present a power allocation scheme for this system which explicitly takes into account the imprecise nature of the available CSI. Experimental results obtained with simulated OFDM channel traces show that proposed scheme is able to achieve a much better quality-vs-reliability trade-off in video transmission, compared to the best known digital-only and analog-only alternatives.     

Tristable switching of the electrical conductivity through graphene quantum dots sandwiched in multi-stacked poly(methyl methacrylate) layers

Tristable switching nonvolatile memory (NVM) devices based on graphene quantum dots (GQDs) sandwiched between multi-stacked poly (methyl methacrylate) (PMMA) layers were fabricated on indium-tin-oxide (ITO)-coated glass substrates by using a solution-processed method. Current-voltage (I-V) curves at 300 K for the silver nanowire/PMMA/GQD/PMMA/GQD/PMMA/ITO/glass devices showed tristable switching currents with high-resistance, intermediate-resistance, and low-resistance states. The device's cycling endurance of the three resistance states remained stable with a distinguishable value for each resistance state over 1000 cycles, and the obtained retention results showed well-distinguished resistance states without degradation for up to 1 × 10⁴ s. Schottky emission, Poole-Frenkel emission, trapped-charge limited-current, and ohmic conduction were proposed as the dominant conduction mechanisms for the fabricated NVM devices based on the obtained I-V characteristics. The described energy-band diagrams confirm the proposed conduction band mechanisms.     

Exploring a Stable and Dense 3D Lead Chloride Hybrid with Emission of Self-Trapped Excitons toward X-Ray Scintillation

The exceptional photophysical properties of 3D organic–inorganic lead halide hybrids (OILHs) endow their significant potential for usage in optoelectronics, which has sparked intense research on novel 3D OILHs and associated applications. However, constructing new 3D OILHs based on large organic cations suffers from tough challenges due to the limitation of the Goldschmidt tolerance factor rule, let alone further explorations of their practical applications. Herein, a brand-new 3D lead chloride hybrid, (1MPZ)Pb₄Cl₁₀·H₂O ( 1 , 1MPZ = 1-methylpiperazine) is reported, featuring a dense 3D lead chloride framework made of the corner-, edge-, and face-shared lead chloride polyhedra. 1 presents a broadband white light emission with a large Stokes shift and a nanosecond photoluminescence lifetime, which originates from radiative recombination of self-trapped excitons (STEs) induced by the highly distorted structure. Such a reabsorption-free and fast-decayed STEs emission coupling with the dense 3D architecture further enables 1 with effective X-ray scintillation with good sensitivity. Impressively, 1 also shows superior environmental and radiation stability. This study provides a new 3D OILH with appealing luminescence, not only expanding the 3D OILH family but also inspiring the exploitation of their optoelectronic applications.     

ASIC后端设计中的时钟树综合

时钟树综合是当今集成电路设计中的重要环节,因此在FFT处理器芯片的版图设计过程中,为了达到良好的布局效果,采用时序驱动布局,同时限制了布局密度;为了使时钟偏移尽可能少,采用了时钟树自动综合和手动修改相结合的优化方法,并提出了关于时钟树约束文件的设置、buffer的选型及手动修改时钟树的策略,最终完成了FFT处理器芯片的时钟树综合并满足了设计要求。     

电力线通信中扩频捕获跟踪技术

文中针对电力通信中,载波频率不高,传输信息量较少的特点提出一套数字化扩频通信捕捉,跟踪方案,结合现代通信技术与数字信号处理技术,对传统的扩频通信进行改进,有效提高其传输准确率。     

The novel communication algorithm and the throughput analysis for wireless sensor networks

Aiming at the significance of the energy controls of wireless sensor networks, an economical energy consumption algorithm for wireless communicating in Wireless Sensor Networks (WSN) is presented. Based on the algorithm, the maximal system throughput of WSN is analyzed, and the upper bound of throughput of WSN is proposed and proved. Some numerical simulations are conducted and analyzed. The conclusions include that the transmitting radius of sensor node and the parameters of the energy cost function have significant influence upon the throughput, but the monitoring region radius has little influence. For the same transmitting distance, the more the hopping of information trans- mitting, the better the throughput of WSN. On the other hand, for the energy optimization of the whole WSN, the trade-off problem between the throughput capacity and the relay nodes is proposed, and the specific expression of relay hops that minimized the energy consumptions and the maximal throughput of WSN under the specific situation is derived.     

N∶ZnO薄膜的受主性质研究

使用溶胶-凝胶法制备N∶ZnO薄膜,用X射线衍射仪(XRD)对晶体结构进行表征,用扫描电子显微镜(SEM)观察薄膜表面形貌,用荧光光谱仪测量低温(8K)及变温条件(8～200K)下的光致发光(PL)光谱。分析了各个发射峰的形成机理,通过薄膜缺陷态发光和受主能级的关联性,计算出了N作为受主所需电离能的大小在0.255～0.31eV范围内。研究结果为以后P型ZnO薄膜的制备和研究提供了依据。