YAG：Ce Phosphors for WLED via Nano-Pesudoboehmite Sol-Gel Route

The sub-micron sized YAG ： Ce phosphors were synthesized via a modified sol-gel method by peptizing nano-pesudoboehmite particulate. It is found that YAG phase from the dried gel powders appears at 1000 ℃ then the pure YAG phase exists at a relatively lower sintering temperature of 1400 ℃. The smaller sizes of phosphors in the ranges of 1 - 3 μm are obtained due to the contribution of seeding effects of nano-sized alumina particles to strengthen each step of the processes. Both the excitation and emission spectra of photoluminescence of the phosphor obtained at 1400 ℃ meet well with the spectroscopic requirements of the WLED phosphors.     

NUMERICAL SIMULATION OF TIP-CLEARANCE FLOW IN CASCADE

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｉｐ ｃｌｅａｒａｎｃｅｆｌｏｗｓｏｃｃｕｒｉｎｖａｒｉｏｕｓｅｎｇｉｎｅｅｒ ｉｎｇａｐｐｌｉｃａｔｉｏｎｓｓｕｃｈａｓａｘｉａｌ ｆｌｏｗ ｐｕｍｐｓａｎｄｄｕｃｔ ｅｄｐｒｏｐｅｌｌｅｒｓ .Ｔｈｅｉｎｅｒｔｉａｌｆｏｒｃｅｓａｃｔｉｎｇｕｐｏｎｔｈｅｆｌｕｉｄｉｎｔｈｅｎａｒｒｏｗ ｇａｐｂｅｔｗｅｅｎｂｌａｄｅｔｉｐａｎｄｔｈｅｓｕｒｒｏｕｎｄｉｎｇｗａｌｌａｒｅｓｕｆｆｉｃｉｅｎｔｔｏ ｇｅｎｅｒａｔｅａｔｉｐｌｅａｋａｇｅｖｏｒｔｅｘｏｎｔｈｅｓｕｃｔｉｏｎｓ…     

Photo-bleaching induced electro-optic polymer modulators with dual driving electrodes operating at 1.55 /spl mu/m wavelength

Electro-optic (EO) polymeric Mach-Zehnder (MZ) modulators with photo-bleaching (PB) induced waveguides and dual driving electrodes operating at 1.55 /spl mu/m wavelength have been demonstrated. The half-wave voltage of the integrated polymeric modulator was 4.5 V in a push-pull configuration with a 1.5 cm interaction length. The extinction ratio was greater than 20 dB, and the fibre-to-fibre insertion loss was 8 dB for the TM polarisation. The achieved fibre-to-fibre insertion loss and driving voltage are the best, to the authors knowledge, in the reported PB induced MZ EO polymeric modulators.     

Flammability and thermal stability studies of ABS/Montmorillonite nanocomposite

Acrylonitrile–butadiene–styrene (ABS)/montmorillonite nanocomposites have been prepared using a direct melt intercalation technique by blending ABS and organophilic clay of two different particle sizes: OMTa (5 µm) and OMTb (38 µm). Their structure and flammability properties were characterized by X‐ray diffraction, high resolution electronic microscopy (HREM), thermogravimetric analysis (TGA) and cone calorimeter experiments. The results of HREM showed that ABS/5 wt% OMTa nanocomposite was a kind of intercalated–delaminated structure, while ABS/5 wt% OMTb nanocomposite was mainly an intercalated structure. The nanocomposites showed a lower heat release rate peak and higher thermal stability than the original ABS by TGA and cone calorimeter experiments. Also, the intercalated nanocomposite was more effective than an exfoliated–intercalated nanocomposite in fire retardancy. Copyright © 2003 Society of Chemical Industry     

宣汉——达县地区飞仙关组储层预测方法研究

在宣汉-达县地区,以往仅依据地震属性来预测飞仙关组储层分布,钻探结果与实际情况不符,为此本文提出量化分析预测结合主参数分析的新方法和新思路。在量化分析中首先对飞仙关组储层进行高分辨率反演,获得储能系数图;然后结合主振幅剖面和主频率剖面分析,对储层进行预测。在研究区,本方法的预测结果与实钻情况相吻合。     

Packet acquisition in upstream transmission of the DOCSIS standard

In upstream transmission of the DOCSIS (data over cable service interface specification) 1.0/1.1 and the TDMA mode of DOCSIS 2.0 standard, a packet begins with a preamble, the length and value of which are programmable by the headend. The acquisition process includes packet detection, symbol timing estimation, carrier frequency offset estimation and carrier phase estimation by means of the preamble so that the following information packet can be correctly demodulated. Methods to solve these tasks are not subject to standardization and are left to the system designer. However, they have a great impact on the system performance and thus are key elements for implementation. We present dedicated algorithms. A specific preamble is created and the corresponding scheme for packet acquisition is described in some detail. The packet detecting algorithm is independent of the carrier and symbol timing. The symbol timing estimate is obtained by using the minimum mean square algorithm regardless of the carrier frequency deviation and carrier phase. Algorithms for estimating the carrier frequency offset and carrier phase are proposed. Computer simulation results are given for all algorithms presented.     

Breakdown probabilities for thin heterostructure avalanche photodiodes

The recurrence theory for the breakdown probability in avalanche photodiodes (APDs) is generalized to heterostructure APDs that may have multiple multiplication layers. The generalization addresses layer-boundary effects such as the initial energy of injected carriers as well as the layer-dependent profile of the dead space in the multiplication region. Reducing the width of the multiplication layer serves to both downshift and sharpen the breakdown probability curve as a function of the applied reverse-bias voltage. In structures where the injected carriers have an initial energy that is comparable to the ionization threshold energy, the transition from linear mode to Geiger-mode is more abrupt than in structures in which such initial energy is negligible. The theory is applied to two recently fabricated Al/sub 0.6/Ga/sub 0.4/As-GaAs heterostructure APDs and to other homostructure thin GaAs APDs and the predictions of the breakdown-voltage thresholds are verified.     

An extended cyclic MUSIC algorithm

Many modulated communication signals exhibit a cyclostationarity (or periodic correlation) property, corresponding to the underlying periodicity arising from carrier frequencies or baud rates. In this paper, we propose a new MUSIC-like direction-finding algorithm that exploits cyclostationarity in order to improve the direction-of-arrival (DOA) estimation. Both cyclic and conjugate cyclic correlation matrices are used in the proposed method so that it can be considered as an extension of the cyclic MUSIC algorithm . The proposed cyclic method allows an increase in resolution power and noise robustness. Depending on the modulation type of incoming signals, the proposed method is also able to handle more sources than the number of sensors.