A Prototype X-ray Framing Camera With Variable Exposure Time Based on Double-Gated Micro-Channel Plates

We present a novel X-ray frame camera with variable exposure time that is based on double-gated micro-channel plates (MCP). Two MCPs are connected so that their channels form a Chevron-MCP structure, and four parallel micro-strip lines (MSLs) are deposited on each surface of the Chevron-MCP. The MSLs on opposing surfaces of the Chevron-MCP are oriented normal to each other and subjected to high voltage. The MSLs on the input and output surfaces are fed high voltage pulses to form a gating action. In forming two-dimensional images, modifying the width of the gating pulse serves to set exposure times (ranging from ps to ms) and modifying the delay between each gating pulse serves to set capture times. This prototype provides a new tool for high-speed X-ray imaging, and this paper presents both simulations and experimental results obtained with the camera.

桃树茎直径变化及其与气象因子关系

用线性差分径向变化仪连续监测充分灌溉条件下的仕女红桃树茎直径变化,结合同步观测的气象因子数据,分析2007年3月中旬～10月下旬的仕女红桃树茎直径变化规律,为基于果树直径变化的灌溉管理提供基础依据。结果表明:仕女红桃树茎直径具有很好的时间变化规律,日变化曲线呈均匀"U"型,日最大值出现在黎明前后,日最小值出现在下午4时左右;季节变化方面,MDS呈低—高—低变化规律,从萌芽—开花期到果实成熟期的不同生长阶段,MDS平均值依次为87μm、200.84μm、253.75μm、171.67μm、138.67μm和94.34μm,坐果—展叶期和第一次果实膨大期MDS值居全生育期最高,需水量最大。桃树直径生长呈慢—快—慢变化规律,3月中下旬,开始生长,平均日生长量从12.68μm逐渐增加大36.84μm,7月24日～8月23日之间生长最快,平均日生长量达73.67μm,然后迅速下降,到生长末期平均日生长量仅为7.36μm。3～5月和7～9月可分别采用DI和MDS作为灌溉控制指标。茎直径变化与气象因子响应强烈,但不同生长阶段对茎直径变化产生主要影响的气象因子不同,对MDS产生主要影响的气象因子依次为:Rn、Tmax、Tma...

CONTINUOUSLY CHIRPED DFB GRATINGS BY SPECIALLY BENT WAVE-GUIDES FOR TUNABLE LASERS

We have implemented and studied a new type of tunable multiple-section semiconductor distributed feedback (DFB) laser using tailored chirped DFB gratings. Arbitrarily and continuously chirped DFB gratings are defined by bent waveguides on homogeneous grating fields with ultrahigh spatial precision, The mathematical bending functions are optimized in this case to provide enlarged wavelength tuning ranges. We present the results of model calculations, the technological device realization and experimental results of the DFB laser characterization e.g. a tuning range of 5.5 mm without wavelength gaps and high side mode suppression ratio.

5.2 GHz variable-gain amplifier and power amplifier driver for WLAN IEEE 802.11a transmitter front-end

A 5.2 GHz variable-gain amplifier (VGA) and a power amplifier (PA) driver are designed for WLAN IEEE 802.11a monolithic RFIC. The VGA and the PA driver are implemented in a 50 GHz 0.35 μm SiGe BiCMOS technology and occupy 1.12×1.25 mm~2 die area. The VGA with effective temperature compensation is controlled by 5 bits and has a gain range of 34 dB. The PA driver with tuned loads utilizes a differential input, single-ended output topology, and the tuned loads resonate at 5.2 GHz. The maximum overall gain of the VGA and the PA driver is 29 dB with the output third-order intercept point (OIP3) of 11 dBm. The gain drift over the temperature varying from -30 to 85℃ converges within±3 dB. The total current consumption is 45 mA under a 2.85 V power supply.

Simulation and fabrication of thermo-optic variable optical attenuators based on multimode interference coupler

A type of thermo-optic variable optical attenuator based on multimode interference coupler is proposed. The optical field propagation properties of the devices are simulated using finite difference beam propagation method. The propagation loss of the fabricated device is 2-4.2 dB at the wavelength range 1510-1610 nm. The total power consumption is 370 mW and the maximum attenuation is more than 25 dB, which almost can meet the requirements of optical fiber communication systems.