PET/SiO_(2)复合材料的发泡温度窗口研究

为研究纳米二氧化硅(SiO_(2))对聚对苯二甲酸乙二酯(PET)复合材料发泡温度窗口的影响规律,制备了不同SiO_(2)含量的PET复合材料,并以二氧化碳为发泡剂,利用釜压发泡制备了PET/SiO_(2)复合发泡材料。然后,利用扫描电子显微镜研究了在不同温度下制备的PET/SiO_(2)复合发泡材料的泡孔结构,并统计和计算出泡孔尺寸、泡孔密度和膨胀倍率,再结合泡孔结构和膨胀倍率,界定出不同SiO_(2)含量的PET复合材料发泡温度的上下限,并得出发泡温度窗口,还研究了PET/SiO_(2)复合发泡材料的光反射率。结果发现,SiO_(2)对PET复合材料具有显著的气泡异相成核作用,随着SiO_(2)添加量的增加,泡孔尺寸减小、泡孔密度增大、膨胀倍率先增大后减小;发泡温度上限先升高后降低、下限升高,使得发泡温度窗口先变宽后变窄,这与SiO_(2)的气泡异相成核作用、对膨胀倍率的调节作用及对基体黏弹性的影响密切相关。随着SiO_(2)添加量的增加,PET复合发泡材料的光反射率逐渐增大,这归因于泡孔尺寸逐渐减小、泡孔密度逐渐增大更有利于光的反射。

Estimating Fraction of Photosynthetically Active Radiation of Corn with Vegetation Indices and Neural Network from Hyperspectral Data

The fraction of photosynthetically active radiation （FPAR） is a key variable in the assessment of vegetation productivity and land ecosystem carbon cycles. Based on ground-measured corn hyperspectral reflectance and FPAR data over Northeast China, the correlations between corn-canopy FPAR and hyperspectral reflectance were analyzed, and the FPAR estimation performances using vegetation index （VI） and neural network （NN） methods with different two-band-combination hyperspectral reflectance were investigated. The results indicated that the corn-canopy FPAR retained almost a constant value in an entire day. The negative correlations between FPAR and visible and shortwave infrared reflectance （SWIR） bands are stronger than the positive correlations between FPAR and near-infrared band re- flectance （NIR）. For the six VIs, the normalized difference vegetation index （NDVI） and simple ratio （SR） performed best for estimating corn FPAR （the maximum R2 of 0.8849 and 0.8852, respectively）. However, the NN method esti- mated results （the maximum Rz is 0.9417） were obviously better than all of the VIs. For NN method, the two-band combinations showing the best corn FPAR estimation performances were from the NIR and visible bands; for VIs, however, they were from the SWIR and NIR bands. As for both the methods, the SWIR band performed exceptionally well for corn FPAR estimation. This may be attributable to the fact that the reflectance of the SWIR band were strongly controlled by leaf water content, which is a key component of corn photosynthesis and greatly affects the absorption of photosynthetically active radiation （APAR）, and makes further impact on corn-canopy FPAR.

Hyper-spectrum models for monitoring water quality in Dianshan Lake,China

The correlation between water quality parameters and hyper-spectral reflectance is studied with models established for each parameter and applied in Dianshan Lake, in the upstream of the Huangpu River running through Shanghai, China. Models are for dissolved oxygen (DO in mg/L): R720/R680 = 20.362×(R720/R680)2?31.438×(R720/R680)+19.156; for turbidity (NTU): R*714.5 = 206.07× (R*714.5)2?582.5×R*714.5 + 423.24; and for total phosphorus (TP in mg/L): R*509.5 = 16.661× (R*509.5)2?32.646×R*509.5+16.116. The R2 values are 0.770 8, 0.660 4 and 0.738 7, respectively, showing strong positive relationships. The models were then applied to assess water quality of different times. Results are quite satisfactory for some samples.

Differences of silicon photodiode spectral reflectance among the same batch

Photodiode＇s reflectance plays an important role regarding the relation between responsivity and the incident flux. In this work we analyze how the spectral reflectance changes among photodiodes from the same manufacturer and batch and how the reflectance of three standard photodiodes has drifted during six years. The results show that the reflectance changes from diode to diode within the same batch and also show that the reflectance ofphotodiodes changes on time. This ageing is spectraUy dependent.

Dynamics of Light-induced Reflectivity Change in Bulk GaAs by Femtosecond Laser Pulse

The pump-probe technique is an effective method to investigate ultrafast dynamics. And it is widely used in fundamental and application fields of Physics, Chemistry and Biology. The dynamics of bulk GaAs was investigated by femtosecond laser. By changing the area of pump spot, different laser fluences were obtained to excite electron from valence states to conduction states. And it was found that the amplitude of reflectivity change is different. When the carrier density N is 1.44×10^18/cm^3, the change of refraction index is about Dnc=-3.33×10^-5. And when N is0. 36×10^10/cm^3, the change is -2.0×10^-5.

Efficiency Improvement of 590 nm AIGalnP Light Emitting Diode with a Reflective Top Electrode

In this work, enhancement of the light extraction efficiency of a 590 nm AIGaInP light-emitting diodes （LED） with a reflective top electrode （RTE） was investigated. A distributed Bragg reflector （DBR）, consisting of AIAs/AIGaAs pairs, grown on an AlGaInP structure was used as a reflector for a reflective top electrode. It was found that a higher output power was observed from the AIGalnP LED with a RTE than from a conventional one. In addition, it was noted that the improvement in the output power depends strongly on the reflectivity of the reflector and that it exhibits a more effective performance with low injection currents. The increase in the optical output power was attributed to the enhanced extraction efficiency caused by a reduction of light absorbed from the emission region to top electrode through the RTE.

Land cover classification of remote sensing imagery based on interval-valued data fuzzy c-means algorithm

There is a certain degree of ambiguity associated with remote sensing as a means of performing earth observations.Using interval-valued data to describe clustering prototype features may be more suitable for handling the fuzzy nature of remote sensing data,which is caused by the uncertainty and heterogeneity in the surface spectral reflectance of ground objects.After constructing a multi-spectral interval-valued model of source data and defining a distance measure to achieve the maximum dissimilarity between intervals,an interval-valued fuzzy c-means(FCM)clustering algorithm that considers both the functional characteristics of fuzzy clustering algorithms and the interregional features of ground object spectral reflectance was applied in this study.Such a process can significantly improve the clustering effect;specifically,the process can reduce the synonym spectrum phenomenon and the misclassification caused by the overlap of spectral features between classes of clustering results.Clustering analysis experiments aimed at land cover classification using remote sensing imagery from the SPOT-5 satellite sensor for the Pearl River Delta region,China,and the TM sensor for Yushu,Qinghai,China,were conducted,as well as experiments involving the conventional FCM algorithm,the results of which were used for comparative analysis.Next,a supervised classification method was used to validate the clustering results.The final results indicate that the proposed interval-valued FCM clustering is more effective than the conventional FCM clustering method for land cover classification using multi-spectral remote sensing imagery.

An Interrogation System Based on Two Semiconductor Optical Amplifiers for Weak Fiber Bragg Gratings

An interrogation system based on two semiconductor optical amplifiers for weak fiber Bragg gratings （FBGs） was proposed. The first semiconductor optical amplifier （SOA） was used to modulate the light, and the second SOA separated the reflected signal from the different FBGs through delayed switching. The proposed system has lower insertion loss and higher spatial resolution, and can interrogate the time- and wavelength-division multiplexed FBG array. Up to 50 FBGs, with a reflectivity of 0.2% and a spatial resolution of 5 m along the optical fiber, were distinguished to demonstrate the interrogation system.