Impact of waveguide sidewall roughness on the output uniformity and phase of MMI splitters

In this paper, we develop a model for the effects of waveguide sidewall roughness on the output uniformity and phase of a 3-dB MMI splitter. We achieve this by investigating analytically the effect of sidewall roughness on mode coupling in the MMI section of the splitter using the coupled mode and coupled power equations. Using these equations, the subsequent impact of mode coupling losses on the splitter output uniformity and phase is calculated and results for 1 × 2 and 2 × 2 splitters are presented and compared. Finally, to illustrate the impact of sidewall roughness on the operation of a waveguide device, the response of a Mach Zehnder interferometer comprising 2 × 2 splitters is investigated.     

增益和相位一致性对功率合成效率的影响

发射机在功率合成的时候,由于各固态功率源模块间存在着增益和相位的差异,会导致功率合成效率的下降。针对这一问题,本文通过建立增益和相位的一致性对功率合成效率影响的模型,并结合MATLAB软件进行计算模拟,得到不同增益和相位分布下的最低合成效率分布,为发射机功率合成系统设计提供了具体的相位和增益指标,并为发射机的评估和验收提供了有力的理论依据。     

Trade-off between diffraction efficiency and uniformity for design of binary diffractive laser beam shaper

The trade-off between diffraction efficiency and uniformity is studied when a binary phase-only diffractive optical element (DOE) is designed for transforming a Gaussian beam to an expanded squared uniform intensity distribution. The simulated annealing (SA) algorithm and Fresnel diffraction theory are applied in our design. Two types of cost functions are utilized in the SA algorithm, and the cases of different incident Gaussian diameters and bright-area sizes of the target patterns are studied. The mechanisms of reducing nonuniformity by the two cost functions are essentially different, and the mechanism combining nonuniformity and the intensity difference between the reconstructed and target patterns has better results. Satisfactory performance can be obtained under the trade-off between them.     

Impact ionization and quantum efficiency in semiconductors

This paper presents a general theory of quantum efficiency in semiconductors. A system of equations is derived describing multiple impact ionization (cascade process) due to electrons, or holes, generated by the primary absorption process. Two secondary relaxations processes are considered: interband Auger transitions and emission of phonons. The spectral dependence of quantum efficiency is derived for three special types of the band structure of semiconductors.On leave from the Institute of Solid State Physics, Czechosl. Acad. Sci., Cukrovarnická 10, Praha 6, Czechoslovakia.The writer is greatly indebted to prof. J. Linhard for enabling him to spend a very stimulating time in the Institute of Physics of the University of Aarhus.     

On the efficiency of water soluble antioxidants

The wide use of high intensity ultrasound (HIU) in modern medicine raises the question of bio-safety. It has been shown that the effect of HIU in biological media may have similarity to the effects of ionizing radiation. Exposure of biological media to HIU field may lead to cavitation phenomenon followed by formation of free radicals such as hydroxyl radical (OH) and the super-oxide ion (O₂-). These are highly reactive species that may cause harmful effects and induce oxidative stress. In the present study we employed electron spin resonance (ESR) spectroscopy together with spin traps to quantify the dynamics of hydroxyl radical formation during exposure to HIU field in the presence of different amounts of six antioxidants. Thus, the efficiency of water-soluble antioxidants, namely Allicin, Melatonin, Deoxyribose, Trolox, Nuphlutine and Hermidin, to suppress accumulation of OH radicals was examined. The results show that among the six, Trolox and Allicin reduce hydroxyl concentration with the highest efficiency.     

EAST中加热功率对弹丸注入加料效率的影响

介绍了 EAST 装置气动加速氘弹丸注入加料系统和不同加热功率条件下弹丸加料效率的实验结果。 当等离子体加热功率从 1MW 逐渐增加到 10MW 时,弹丸加料效率从 60%降低到 10%。加热功率的升高导致弹 丸粒子的沉积深度 λp/a 降低达 50%左右,从而导致大量的弹丸粒子沉积在等离子体边界。     

High efficiency dye laser with low fluorescence yield pyrromethene dyes: experimental and theoretical studies

A combined experimental and theoretical study of the photo-physical, laser properties and molecular structures of three relatively recent Pyrromethene (PM) class dyes, PM597, PM580 and PM567, have been carried out. Laser characteristics of these three PM dyes were compared with three other widely used Rhodamine (RH) class dyes, RH6G, RHB and KRS, using a narrow-band dye laser setup, transversely pumped by the second harmonic (532 nm) of a Q-switched Nd-YAG laser. In addition to generating comparative data of these dyes for optimal use in dye lasers, we observed that unlike the RH dyes, the PM dyes show high efficiencies and wide tunability, despite the low fluorescence yield and high rate of non-radiative decay. Particularly, PM597 dye, in spite of a very low quantum yield of fluorescence (Φ=0.42), high non-radiative decay rate, and a large distortion from planarity in its excited state, when used in a laser cavity it exhibited similar laser efficiency and a beneficially wider tuning curve in comparison to other two PM dyes. Theoretical studies were carried out applying density functional theory and time-dependent density functional theory (DFT/TDDFT) to obtain new information on ground and the first excited state geometrical parameters of the PM dyes. Good correlation between calculated molecular properties and experimental results was observed for the evolution of the longest wavelength absorption maximum.     

随机相位误差对空间功率合成效率的影响

采用数理统计方法分析了任意分布的随机相位误差对多台不等功率辐射源组成的天线阵空间功率合成效率的影响,得到了由多台不等幅馈电的阵元组成的天线阵空间功率合成效率期望值的解析表达式。通过该解析式可利用快速傅里叶变换(FFT)快速分析任意数目阵元组成的天线阵在目标点的期望合成效率,为空间功率合成系统的总体合成效率预估并合理分解各分系统随机相位抖动指标提供了一种高效的解析分析方法。作为算例,用得到的解析公式分析相位误差分布呈均匀分布、正态分布和三角形分布三种典型情况对合成效率的影响。     

Impact of PV module configuration on energy yield under realistic conditions

Photovoltaic cell and module manufactures optimise their products according to power measurements performed at a set of standard-test conditions. A key parameter for the financing of a solar project is yield under field or realistic conditions. Field testing modules is time consuming and costly. Hence, we develop a methodology for simulating PV module yield based on the optical, thermal and electrical properties of the components, and the module configuration regarding the cell spacing, interconnection and module layers. With our procedure, we model the performance of standard, half cell and encapsulant free modules in different locations. We present results using our cell to module yield framework for 16 different locations in Australia based on one-minute ground measured solar irradiance and ambient temperature values. We find low-light irradiance losses are directly correlated to the number of cloudy days at a given site. The majority of fielded losses are due to temperature effects, which can be predicted by the average temperature at 3 p.m. We note that wind speed is not accounted for and it will be incorporated in future studies.     

Estimation of relative water content in rice panicle based on hyperspectral vegetation indexes under water saving irrigation

Determining grain water content is a traditional method to quantify maturity, but this method is laborious. Ground-based remote sensing with rapidness and flexibility has been widely used in evaluating rice growth, but less attention has been paid to predicting physiological maturity. A field experiment with rice was conducted to investigate the effects of water saving irrigation on physiological maturity based on hyperspectral data. The results indicated that, with higher coefficients of determination (R² = 0.93 and 0.87, respectively), higher residual prediction deviation (RPD = 3.54 and 2.58, respectively) and lower root mean square error (RMSE = 2.88 and 4.43, respectively) among the tested models, R₁₆₅₄/R₆₆₂ and R₅₄₆/R₅₆₂ were suggested as the optimal indexes for monitoring relative water content in rice panicle under flooding and wetting conditions, respectively. This finding is helpful in providing reference for monitoring rice physiological maturity.     

Effect of soap on the fluorescent lifetime and quantum yield of rhodamine 6G in water

Addition of the soap ammonyx LO to a solution of 2 × 10^-4Mrhodamine 6G in water lengthens the fluorescent lifetime from 3.8 to 5 nsec, and increases the relative quantum yield by ≈ 1.5. Concentrations of soap and solute are those commonly used in cw rhodamine dye lasers. Comparisons are made with rhodamine 6G in ethanol solutions.     

农业节水灌溉远程监控系统的设计与实现

为了提高农业灌溉的效率,节省灌溉成本,进行农业节水灌溉智能监控系统设计,提出一种基于ZigBee多传感器分布式数据采集的监控系统设计方法,系统设计分为硬件和软件两部分,首先进行农业节水灌溉远程监控系统的总体设计构架,灌溉远程监控系统的硬件模块化设计包括农业节水灌溉传感信息采集模块、AD模块、集成控制模块和接口电路。基于FPGA嵌入式设计方法,构建ZigBee多传感器分布式阵列,进行远程多点灌溉控制和监控。软件开发建立在LabWindows/CVI工程开发环境中,通过程序加载控制,实现远程监控系统改进设计。测试结果表明,该系统进行农业节水灌溉远程监控具有较好的人机友好性,监控的覆盖度较高,性能较好。     

The use of stable isotopes to evaluate water mixing and water use by flood plain trees along the Garonne valley

Before the confluence of the Tarn, the Garonne valley was the driest area in the entire south-west of France, due to the relatively low rainfall and low summer discharge of the Garonne River and its tributaries. The natural abundance of the stable isotope of oxygen (¹⁸O) and ionic charge of surface and ground water were used to estimate the water source for the Garonne River and phreatic subsurface water. We also measured these constituents in the sap of trees at several flood plain sites to better understand the source of water used by these trees. ¹⁸O signatures and conductivity in the Garonne River indicated that the predominance of water was from high altitude surface runoff from the Pyrenees Mountains. Tributary inputs had little effect on isotopic identity, but had a small effect on the conductivity. The isotopic signature and ionic conductivity of river water (δ¹⁸O: ?9.1‰ to ?9.0‰, conductivity: 217–410?µS/cm) was distinctly different from groundwater (δ¹⁸O: ?7.1‰ to ?6.6‰, conductivity: 600–900?µS/cm). Isotopic signatures from the sap of trees on the flood plain showed that the water source was shallow subsurface water (<30?cm), whereas trees further from the river relied on deeper ground water (>1?m). Trees at both locations maintained sap with ionic charges much greater (2.3–3.7×) than that of source water. The combined use of ¹⁸O signatures and ionic conductivity appears to be a potent tool to determine water sources on geographic scales, and source and use patterns by trees at the local forest scale. These analyses also show promise for better understanding of the effects of anthropogenic land-use and water-use changes on flood plain forest dynamics.     

The use of stable isotopes to evaluate water mixing and water use by flood plain trees along the Garonne valley

Before the confluence of the Tarn, the Garonne valley was the driest area in the entire south-west of France, due to the relatively low rainfall and low summer discharge of the Garonne River and its tributaries. The natural abundance of the stable isotope of oxygen (18O) and ionic charge of surface and ground water were used to estimate the water source for the Garonne River and phreatic subsurface water. We also measured these constituents in the sap of trees at several flood plain sites to better understand the source of water used by these trees. 18O signatures and conductivity in the Garonne River indicated that the predominance of water was from high altitude surface runoff from the Pyrenees Mountains. Tributary inputs had little effect on isotopic identity, but had a small effect on the conductivity. The isotopic signature and ionic conductivity of river water (delta18O: -9.1 per thousand to -9.0 per thousand, conductivity: 217-410 microS/cm) was distinctly different from groundwater (delta18O: -7.1 per thousand to -6.6 per thousand, conductivity: 600-900 microS/cm). Isotopic signatures from the sap of trees on the flood plain showed that the water source was shallow subsurface water (<30 cm), whereas trees further from the river relied on deeper ground water (>1 m). Trees at both locations maintained sap with ionic charges much greater (2.3-3.7x) than that of source water. The combined use of 18O signatures and ionic conductivity appears to be a potent tool to determine water sources on geographic scales, and source and use patterns by trees at the local forest scale. These analyses also show promise for better understanding of the effects of anthropogenic land-use and water-use changes on flood plain forest dynamics.     

Pyramidal quantum dots: High uniformity and narrow excitonic emission

We report on the optical properties of site-controlled InGaAs dots in GaAs barriers grown in pre-patterned, large pitch, pyramidal recesses by metalorganic vapour phase epitaxy. The inhomogeneous broadening of excitonic emission from an ensemble of quantum dots is found to be extremely narrow, with a standard deviation of 1.19 meV. A dramatic improvement in the spectral purity of emission lines from individual dots is also reported (18–30 μeV ) when compared to the state-of-the-art for site controlled quantum dots.     

Improving the efficiency of single and multiple teleportation protocols based on the direct use of partially entangled states

We push the limits of the direct use of partially pure entangled states to perform quantum teleportation by presenting several protocols in many different scenarios that achieve the optimal efficiency possible. We review and put in a single formalism the three major strategies known to date that allow one to use partially entangled states for direct quantum teleportation (no distillation strategies permitted) and compare their efficiencies in real world implementations. We show how one can improve the efficiency of many direct teleportation protocols by combining these techniques. We then develop new teleportation protocols employing multipartite partially entangled states. The three techniques are also used here in order to achieve the highest efficiency possible. Finally, we prove the upper bound for the optimal success rate for protocols based on partially entangled Bell states and show that some of the protocols here developed achieve such a bound.     

中子产额活化测量法中γ γ符合探测效率的模拟计算

 为了估计聚变中子产额Cu活化测量法中加速器中子源刻度与实际测量中几何条件不一致对测量结果的影响，通过对MCNP进行二次开发，用蒙特卡罗方法计算了这两种情况下有角关联的γ γ符合探测效率，通过与刻度实验结果比较，验证了计算结果的正确性，得出了几何条件的差别引起探测效率的增加小于3%的结论。     

Enhancing the yield in surface sum-frequency generation by the use of surface polaritons

Received: 23 December 1998