Enhanced photovoltaic properties of polymer-fullerene bulk heterojunction solar cells by thermal annealing

The effect of a thermal annealing treatment on the performance of bulk heterojunction photovoltaic cells based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and fullerene (C₆₀) composites is investigated. Upon thermal annealing at 120 ^°C, short-circuit current and power conversion efficiency (η) are more than tripled, while a sharp rise by eight times in and η is found for the device annealed at 200 ^°C. It is concluded that the improved phase separation between MEH-PPV and C₆₀ leads to the enhancement of and η at 120 ^°C, while thermodynamic molecule arrangement at the higher temperature of ∼200 ^°C induces a significant increase in all photovoltaic parameters of composite devices except the open-circuit voltage .     

光学多普勒层析三维矢量测速方法研究

光学多普勒层析术(ODT)是一种高分辨、非侵入的生物医学成像手段,能同时得到组织的结构信息和组织内血管的流速信息.提出了一种新型的基于相位分辨技术的ODT三维矢量测速方法.在ODT系统样品臂的准直镜和聚焦透镜之间加入窄带相位片,形成三个不同的相位延迟,通过计算多普勒频移和不同相位延迟下的多普勒展宽,可得到毛细管内的三维矢量流场分布.对已知浓度的聚苯乙烯溶液进行了一系列不同角度和不同流速的实验,结果证明这种新型的ODT矢量测速方法可以较精确的实现三维矢量流速的测量.     

Long period grating cascaded to photonic crystal fiber modal interferometer for simultaneous measurement of temperature and refractive index

We propose and demonstrate a novel and simple dual-parameter measurement scheme based on a cascaded optical fiber device of long-period grating (LPG) and photonic crystal fiber (PCF) modal interferometer. The temperature and refractive index (RI) can be measured simultaneously by monitoring the spectral characteristics of the device. The implemented sensor shows distinctive spectral sensitivities of -30.82 nm/RIU (refractive index unit) and 47.4 pm/°C by the LPG, and 171.96 nm/RIU and 10.4 pm/°C by the PCF modal interferometer. The simultaneous measurement of the temperature and external RI is experimentally demonstrated by the sensor. The temperature shift and RI shift calculated by the sensor matrix agree well with the actual temperature and RI change in the experiment.     

Traversable braneworld wormholes supported by astrophysical observations

In this study, we investigate the characteristics and properties of a traversable wormhole constrained by the current astrophysical observations in the framework of modified theories of gravity (MOG). As a concrete case, we study traversable wormhole space–time configurations in the Dvali–Gabadadze–Porrati (DGP) braneworld scenario, which are supported by the effects of the gravity leakage of extra dimensions. We find that the wormhole space–time structure will open in terms of the 2σ confidence level when we utilize the joint constraints supernovae (SNe) Ia + observational Hubble parameter data (OHD) + Planck + gravitational wave (GW) and z < 0:2874. Furthermore, we obtain several model-independent conclusions, such as (i) the exotic matter threading the wormholes can be divided into four classes during the evolutionary processes of the universe based on various energy conditions; (ii) we can offer a strict restriction to the local wormhole space–time structure by using the current astrophysical observations; and (iii) we can clearly identify a physical gravitational resource for the wormholes supported by astrophysical observations, namely the dark energy components of the universe or equivalent space–time curvature effects from MOG. Moreover, we find that the strong energy condition is always violated at low redshifts.     

High Efficiency Bridge Double PhaseConjugation in PhotorefractiveTb: Cu: KNSBN Crystal

1.IntroductionMutuallypumPedphaseconjugatemirrorsarenonlineardevicesthatsimultaneouslyproducephaseconjugatereplicasoftwomutuallyincoherentbeams.TheyattractedgreatattentionbecauseoftheirnumerousPotentialapplicationsinadaptiveoptics,opticalinfor-mationprocessing,laserlocking,optica1communication,opticalneuralnetwork,andsoon[l~s1.Variousschemesleadingtomutualphaseconjugationhavebeendemonstrated,includingdoub1ephaseconjugatemirror(DPCM)['J,mutua1lyincoherentbeamcou-pler[:J,birdwingphaseconjugat…     

Ultrafast optical switching in Kerr nonlinear photonic crystals

Nonlinear photonic crystals made from polystyrene materials that have Kerr nonlinearity can exhibit ultrafast optical switching when the samples are pumped by ultrashort optical pulses with high intensity due to the change of the refractive index of polystyrene and subsequent shift of the band gap edge or defect state resonant frequency. Polystyrene has a large Kerr nonlinear susceptibility and almost instantaneous response to pump light, making it suitable for the realization of ultrafast optical switching with a response time as short as a few femtoseconds. In this paper, we review our experimental progress on the continual improvement of all-optical switching speed in two-dimensional and three-dimensional polystyrene nonlinear photonic crystals in the past years. Several relevant issues are discussed and analyzed, including different mechanisms for all-optical switching, preparation of nonlinear photonic crystal samples by means of microfabrication and self-assembly techniques, characterization of optical switching performance by means of femtosecond pump-probe technique, and different ways to lower the pump power of optical switching to facilitate practical applications in optical information processing. Finally, a brief summary and a perspective of future work are provided.     

Enhanced fatigue property of PZT thin films using LaNiO3 thin layer as bottom electrode

A highly (100)-oriented metallic LaNiO₃ film was prepared directly on a Si substrate by a simple metalorganic decomposition (MOD) technique using lanthanum nitrate and nickel acetate as the starting sources. Subsequent Pb(Zr,Ti)O₃ (PZT) thin films deposited on the LaNiO₃-coated Si substrate were obtained by a modified sol–gel method. It was found that the PZT thin films began to form a single perovskite phase at a low annealing temperature of 530 °C, and exhibited highly (100) orientation. A ferroelectric capacitor of Pt/Pb(Zr,Ti)O₃/LaNiO₃/Si annealed at 600 °C displayed a good P-E hysteresis characteristic and was fatigue-free even after 10¹¹ switching cycles. Received: 25 May 2000 / Accepted: 9 August 2000 / Published online: 30 November 2000     

White matter abnormalities in children and adolescents with temporal lobe epilepsy

Background and Purpose

The widespread propagation of synchronized neuronal firing in seizure disorders may affect cortical and subcortical brain regions. Diffusion tensor imaging (DTI) can noninvasively quantify white matter integrity. The purpose of this study was to investigate the abnormal changes of white matter in children and adolescents with focal temporal lobe epilepsy (TLE) using DTI.

Materials and Methods

Eight patients with clinically diagnosed TLE and eight age- and sex-matched healthy controls were studied. DTI images were obtained with a 3-T magnetic resonance imaging scanner. The epileptic foci were localized with magnetoencephalography. Fractional anisotropy (FA), mean diffusivity (MD), parallel (λ_||) and perpendicular (λ_⊥) diffusivities in the genu of the corpus callosum, splenium of the corpus callosum (SCC), external capsule (EC), anterior limbs of the internal capsule (AIC), and the posterior limbs of the internal capsule (PIC) were calculated. The DTI parameters between patients and controls were statistically compared. Correlations of these DTI parameters of each selected structure with age of seizure onset and duration of epilepsy were analysed.

Results

In comparison to controls, both patients' seizure ipsilateral and contralateral had significantly lower FA in the AIC; PIC and SCC and higher MD, λ_|| and λ_⊥ in the EC, AIC, PIC and SCC. The MD, λ_|| and λ_⊥ were significantly correlated with age of seizure onset in the EC and PIC. λ_|| was significantly correlated with the duration of epilepsy in the EC and PIC.

Conclusion

The results of the present study indicate that children and adolescents with TLE had significant abnormalities in the white matter in the hemisphere with seizure foci. Furthermore, these abnormalities may extend to the other brain hemisphere. The age of seizure onset and duration of epilepsy may be important factors in determining the extent of influence of children and adolescents TLE on white matter.     

基于偏振模式转换的声光陀螺研究

提出一种基于偏振模式转换的声光陀螺,分析其原理与结构并对该陀螺进行实验测试.静态测试结果表明,当声光作用长度为15 mm,声表面波输入功率为100 mW,频率为168.201 MHz时,偏振模式转化效率为80.02％.在偏置条件下进行旋转测试,得到输出电压随陀螺转速呈线性变化的曲线,其灵敏度约为1 mY/[(°)/s].偏振型声光陀螺保留声表面波陀螺体积小、成本低等优点,而在灵敏度上有大幅提高.     

相依二值随机变量序列游程的一类强极限定理

本文利用文献[1]与[2]中提出的方法和思想,研究相依二值随机变量序列游程的极限性质,得到游程平均数的一类强极限定理.