A high-resolution burst-mode laser transmitter with fast and accurate level monitoring for 1.25 Gb/s upstream GPONs

An innovative burst-mode laser transmitter (BM-TX) is presented for gigabit-capable passive optical network (GPON) upstream transmission at 1.25 Gb/s. The laser bias and modulation current each can reach 80 mA with a resolution of 0.1 mA providing a total drive current up to 160 mA. Both currents are generated by 10-bit current steering digital-to-analog converters (DACs), the architecture of which is specially adapted to yield a monotonic current setting at settling times below 12.8 ns. Tests show that fast automatic power control (APC) can stabilize and track the launched optical power with a tolerance of less than 1 dB over a wide temperature range for outdoor operation. The APC only requires a straightforward calibration of the "0" and the "1" level at room temperature. Optical level monitoring on strings of four consecutive "0" bytes and two consecutive "1" bytes at 1.25 Gb/s is demonstrated. APC based on such short strings of data has not been shown before. The circuits have been designed in a 0.35 /spl mu/m SiGe BiCMOS process. Experimental results show that this dc-coupled BM-TX meets the specifications of the recently approved ITU-T Recommendation G.984.2 supporting an intelligent power leveling mechanism (PLM).     

添加VC的TiB2基硬质材料研究

对添加VC的TiB2基硬质材料进行了研究。通过实验测定了硬度、横向断裂强度、高温强度以及耐磨性等性能，通过观察SEM照片研究了VC对TiB2基硬质材料组织结构的影响。综合各种指标，我们确定在TiB2-Fe—Mo硬质材料中VC的最佳添加量为0．5％。     

P–I diagram method for combined failure modes of rigid-plastic beams

Closed-form solutions of pressure-impulse (P–I) diagrams for simply supported and fully clamped rigid-plastic beams subjected to impact load are developed. Two failure categories, i.e., bending failure and shear failure, are considered and the responses of the beams are analyzed based on five transverse velocity profiles. With proper failure criteria, the critical P–I equations for bending and shear failure are derived. After the simplification of the critical P–I equations, the influences of the shear-to-bending strength ratio and the boundary conditions on the P–I diagrams are discussed. The results are compared with those based on a single-degree-of-freedom (SDOF) model. It is shown that the proposed P–I diagram method can be conveniently applied to assess beam damage extents and damage patterns. Especially, the P–I diagrams have good agreement with those based on an elastic, perfectly plastic model when severe damage occurs.     

流体势与油气运聚规律研究——以孤东地区为例

流体势是地下流体所有能的综合表现,不同的流体(如油、气、水)在各自的势场作用下,有各自的势场分布规律运动.通过研究地下流体势空间分布模式,可确定盆地流体系统构成,提高对油气运移规律的认识,明确预测有利油气聚集区,提高钻探成功率.研究表明,孤东地区地下流体势类型分为高势区、低势区,高势区分布与活跃生油洼陷分布一致,是孤东地区油气成藏的主要烃源区和动力源区.低势区与目前的油气田吻合较好.由此可依据流体低势区来预测新的油气聚集部位.      

继续奏响振荡向上主旋律——2002年白银市场回顾及其2003年展望

本文对2002年国际国内白银市场做了全面分析,对2003年白银市场走势进行了分析预测。白银作为一种贵金属,同时又具有工业金属的特性,世界经济形势,世界政治局势的变化,都对白银价格走势产生影响。鉴于该金属的双重特性,本文就从白银的供应、需求、消费及世界经济的发展等方面论述白银市场前进趋势。     

成都市火车南站斜拉桥斜拉索安装工艺

采用倒链葫芦、卷扬机或软牵引装置对斜拉索进行牵引安装 ,使牵引力达到 5 0 0余kN ,解决了斜拉索安装拉力大这一施工难题。     

Facile synthesis of ordered nanocrystalline alumina thin films with tunable mesopore structures

Mesoporous alumina layers have attracted attention for their potential use in ultrafiltration of salts, as a heterogeneous catalyst support, an adsorbent in environmental cleanup, and in petroleum refinement. The ability to control the fast hydrolysis rate of the inorganic precursors using simple and inexpensive routes is important for that potential to be realized. Herein, we introduce a novel and facile route to synthesize mesoporous alumina thin films from the combination of inexpensive and commercially available copolymer with aluminum chloride or nitrate (salts) in an EtOH–surfactant–NH₃ · H₂O–salts (EsNs) system through the evaporation-induced self-assembly (EISA) method. Mesoporous alumina layers obtained utilizing the EsNs system have ordered and tunable pore structures. The ability to easily control the mesophases of the alumina layers within a short time provides distinct advantages over previously reported synthesis procedures. Most importantly, we demonstrate that the binding of surfactant and NH₃ · H₂O for the formation of hydrogen bond between them in the EsNs system controls the fast hydrolysis rate of the inorganic species. This allows for the synthesis of nanocrystalline alumina layers via the aluminum oxo-clusters’ assembly with the surfactant. Such simple route may be applied in the synthesis of other non-silica mesostructured oxides.     

电液比例控制技术在工程船舶中的应用

以长江及沿海航道铺排工程船(长雁1号)液压系统的工程项目为背景,采用电液比例控制技术设计了一种新型的电液比例控制系统,通过对移船马达速度的控制实现了移船的移位和准确定位,同时液压系统的能耗也大大降低.