Reliable polarization control of VCSELs through monolithically integrated surface gratings: a comparative theoretical and experimental study

Vertical cavity surface-emitting lasers (VCSELs) with a well-defined and predictable polarization of the emitted light are sought for a number of applications. In this paper, we show that one can define and stabilize the polarization of single- and multimode oxide-confined VCSELs with a monolithically integrated dielectric surface grating. In recent years, we have developed a three-dimensional, fully vectorial model for VCSELs, which proved to nicely reproduce the experimental results of quite complex structures, such as noncircular devices and phase-coupled VCSEL arrays. This software allows for the first time to analyze the effects of a dielectric grating in the output facet cap layer and its capability to fix the polarization of the emitted light. It is here employed as a design tool, yielding excellent agreement with the experimental data. Since the simulations predict the polarization behavior to be sensitively dependent on the grating parameters, hundreds of VCSELs with 99 different parameter sets, two grating orientations and active diameters of 4 and 7 /spl mu/m have been analyzed. Even VCSELs with eight or more coexisting modes turned out to be linearly polarized with an orthogonal polarization suppression ratio in excess of 15 dB. Theoretical and experimental emission far-fields are compared, and it is shown that diffraction side lobes can be prevented with properly chosen grating parameters which simultaneously ensure full polarization stability.     

Springrobot: a prototype autonomous vehicle and its algorithms for lane detection

This work presents the current status of the Springrobot autonomous vehicle project, whose main objective is to develop a safety-warning and driver-assistance system and an automatic pilot for rural and urban traffic environments. This system uses a high precise digital map and a combination of various sensors. The architecture and strategy for the system are briefly described and the details of lane-marking detection algorithms are presented. The R and G channels of the color image are used to form graylevel images. The size of the resulting gray image is reduced and the Sobel operator with a very low threshold is used to get a grayscale edge image. In the adaptive randomized Hough transform, pixels of the gray-edge image are sampled randomly according to their weights corresponding to their gradient magnitudes. The three-dimensional (3-D) parametric space of the curve is reduced to the two-dimensional (2-D) and the one-dimensional (1-D) space. The paired parameters in two dimensions are estimated by gradient directions and the last parameter in one dimension is used to verify the estimated parameters by histogram. The parameters are determined coarsely and quantization accuracy is increased relatively by a multiresolution strategy. Experimental results in different road scene and a comparison with other methods have proven the validity of the proposed method.     

500 kV大胜关长江大跨越输电线路导地线换线施工

介绍了大胜关长江大跨越二期工程导地线的换线施工方法,即采用旧地线"一牵一"张力牵引光缆过江,采用旧导线"一牵一"张力牵引D26牵引绳过江、D26牵引绳"一牵二"张力牵引新导线过江。针对大跨越不封航换线施工时所涉及到的主要施工难点,提出了相对应的解决方法,对今后类似的大跨越改造工程有积极的指导作用。     

SCR 脱硝催化剂再生技术试验研究

对选择性催化还原法(SCR)脱硝催化剂再生工艺进行研究。用X射线晶体衍射(XRD),X射线荧光光谱(XRF),X射线光电子能谱(XPS)和比表面积分析等方法对再生前、后的催化剂进行了表征;采用模拟烟气在自制脱硝反应装置上对催化剂再生效果进行了评价。研究发现:通过鼓泡或超声波辅助的稀H2SO4清洗可有效去除催化剂中的有毒物质并恢复比表面积,且鼓泡的综合效果更好;以乙醇胺为助溶剂,可根据所需钒的补充量配制不同浓度的偏钒酸铵水溶液,采用浸渍-干燥-煅烧工艺,可实现活性物质钒氧化物的补充,使催化剂的脱硝效率恢复至92%;用溶解性较好的硝酸铈代替偏钒酸铵,向失活催化剂中添加活性物质氧化铈,可拓宽脱硝反应的温度区间,并将催化剂的脱硝效率最高值提至90%。     

Towards long-term economic welfare in deregulated electricity markets: Testing capacity mechanisms in an experimental setting

A number of mechanisms have been suggested for capacity adequacy. A study using laboratory experiments both of procurement of long-term strategic reserve contracting and of centralized auctioning for capacity contracts suggests that the centralized auctioning process stabilizes laboratory markets and provides economic welfare comparable to a free market. The strategic reserve contracting process does not seem to improve either of the two aspects compared to a non-regulated market.     

Relay setting considerations and operational experience of a long500 kV transmission line

The large capacitive susceptance, large load magnitude, and substantial phase unbalance before and after a single-pole trip operation have a substantial effect on the performance of the protective relaying systems of the Minneapolis-Duluth 500 kV line. Computer simulation studies show that correct operation of the relays can be assured if these effects are taken into consideration in determining relay settings. The selection, performance, and operation of the primary and secondary relay system are discussed, indicating that the relaying protection used achieved substantial security and dependability     

An experimental and theoretical framework for manufacturing prosthetic sockets for transtibial amputees.

Selective laser sintering (SLS) is a powerful manufacturing technology that does not require part-specific tooling or significant human intervention and provides the ability to easily generate parts with complex geometric designs. The present work focuses on developing a manufacturing framework using this technology to produce subject-specific transtibial amputee prosthetic sockets made of Duraform PA, which is a nylon-based material. The framework includes establishing an overall socket design (using the patellar-tendon bearing approach), performing a structural analysis using the finite element method (FEM) to ensure structural reliability during patient use, and validating the results by comparing the model output with experimental data. The validation included quantifying the failure conditions for the socket through a series of bending moment and compression tests. In the case study performed, the FEM results were within 3% of the experimental failure loads for the socket and were considered satisfactory.     

一种仿生机器鼠的跟踪与避障策略

针对一种新型仿生机器鼠平台的运动规划问题主要包括跟踪、避障等问题,依据仿生机器鼠的双目视觉系统以及多自由度的机械结构,根据驱动电机的特性,建立仿生机器鼠的扭腰、抬身、攀爬等动力学模型,采用"记忆"目标鼠的特征、"学习"最优避障路径、"推断"目标鼠的运动方向等方法,实现了仿生机器鼠的跟踪与避障行为,提出了一种基于仿生学原理的仿生机器鼠的跟踪与避障策略。在一种新型仿生机器鼠平台上的实验结果表明,相比与基于虚拟阻抗模型的控制方法,该跟踪与避障策略能够更好地实现仿生机器鼠的跟踪与避障行为,从而验证了策略的可行性与有效性。     

An experimental study of the effectiveness of an additive for fuel oil

An available multifunctional additive for low-grade fuel oil is proposed. Its effect on the service properties of fuel oil is experimentally studied, and results from this study are presented.     

贵阳电网110kV线路优化保护配置及整定计算的探讨

对贵阳地区电网运行现状的分析,针对其110kV线路保护的配置情况和整定计算,提出了优化方案。方案中,通过对110kV线路配置光纤电流差动保护,强化主保护,简化后备保护的整定原则,能够进一步提高110kV线路保护可靠性,有效地减轻维护工作难度,提高继电保护整定计算的工作效率,对运行方式的安排也提高了灵活性。     

Conceiving an easy-to-understand and automated polarimeter: application to a study of collagen

In this paper, the authors describe the design and the experimentation of a polarimeter aimed at characterizing the properties of some scattering materials (e.g., a scattering liquid containing a foreign body, or skin components, such as collagen). The polarimeter presents the advantage of offering an easy understanding of Stokes and Mueller formalism. Thus, it is typically suited for university students in physics (Master's level), giving them a clear understanding of polarization and birefringence. Another application is possible in schools of engineering, where students may use their design abilities to improve the apparatus performance. Apparatus automation was performed as well, providing easier use for experiment (commodity of use, reproducibility, and possible multiplication of measurements). The apparatus was tested in transillumination and backscattering modes. More generally, measurements can be performed with angles varying from 0/spl deg/ to 150/spl deg/ between the propagation direction and the line from the sensor to the sample material. In addition, the sensor can be either a photodiode (results presented here) or a two-dimensional (2-D) sensor charge-coupled device (CCD) camera. As an application, the apparatus was used to differentiate irradiated and nonirradiated collagen.     

Locating faults in a transformer winding: An experimental study

Based on terminal measurements on a single, continuous-disc winding of a transformer, it is demonstrated how faults introduced at different positions along the winding could be localized with reasonable accuracy. Fault in the present context represents a discrete change, e.g. short-circuiting a few turns within a disc (i.e. predominantly an inductive change) and/or addition of some tens of pico-Farad capacitance between a disc and ground (i.e. predominantly a capacitive change). Open-circuit and short-circuit natural frequencies are determined by sweep frequency measurements, in addition to measuring effective resistance, shunt capacitance and inductance, at the terminals. The proposed method aims at utilizing the measured data to iteratively synthesize a lumped-parameter ladder network, corresponding to each set of measurement. Comparison of such synthesized circuits with a reference (or fault-free) circuit reveals the location, quantum, and nature of fault. Results presented demonstrate the potential of this method.     

Fast reactor: an experimental study of thermohydraulic processes in different operating regimes

Results of integrated water model studies of temperature fields and a flow pattern of a nonisothermal primary coolant in the elements of the fast neutron reactor (hereinafter, fast reactor) primary circuit with primary sodium in different regimes, such as forced circulation (FC), transition to the reactor cooldown and emergency cooldown with natural coolant convection, are presented. It is shown that, under the influence of lift forces on the nonisothermal coolant flow in the upper chamber at the periphery of its bottom region over the side shields, a stable cold coolant isothermal zone is formed, whose dimensions increase with increase of total water flowrate. An essential and stable coolant temperature stratification is detected in the peripheral area of the upper (hot) chamber over the side shields, in the pressure and cold side chambers, in the elevator baffle, in the cooling system of the reactor vessel, and in the outlet of intermediate and autonomous heat exchangers in different operating regimes. Large gradients and temperature fluctuations are registered at the interface of stratified and recycling formations. In all of the studied cooldown versions, the coolant outlet temperature at the core fuel assembly is decreased and the coolant temperature in the peripheral zone of the upper chamber is increased compared to the FC. High performance of a passive emergency cooldown system of a fast reactor (BN-1200) with submersible autonomous heat exchangers (AHE) is confirmed. Thus, in a normal operation regime, even in case of malfunction of three submersible AHEs, the temperature of the equipment inside the reactor remains within acceptable limits and decay heat removal from the reactor does not exceed safe operation limits. The obtained results can be used both for computer code verification and for approximate estimate of the reactor plant parameters on the similarity criteria basis.     

Video-based lane estimation and tracking for driver assistance: survey, system, and evaluation

Driver-assistance systems that monitor driver intent, warn drivers of lane departures, or assist in vehicle guidance are all being actively considered. It is therefore important to take a critical look at key aspects of these systems, one of which is lane-position tracking. It is for these driver-assistance objectives that motivate the development of the novel "video-based lane estimation and tracking" (VioLET) system. The system is designed using steerable filters for robust and accurate lane-marking detection. Steerable filters provide an efficient method for detecting circular-reflector markings, solid-line markings, and segmented-line markings under varying lighting and road conditions. They help in providing robustness to complex shadowing, lighting changes from overpasses and tunnels, and road-surface variations. They are efficient for lane-marking extraction because by computing only three separable convolutions, we can extract a wide variety of lane markings. Curvature detection is made more robust by incorporating both visual cues (lane markings and lane texture) and vehicle-state information. The experiment design and evaluation of the VioLET system is shown using multiple quantitative metrics over a wide variety of test conditions on a large test path using a unique instrumented vehicle. A justification for the choice of metrics based on a previous study with human-factors applications as well as extensive ground-truth testing from different times of day, road conditions, weather, and driving scenarios is also presented. In order to design the VioLET system, an up-to-date and comprehensive analysis of the current state of the art in lane-detection research was first performed. In doing so, a comparison of a wide variety of methods, pointing out the similarities and differences between methods as well as when and where various methods are most useful, is presented.     

Experimental and theoretical study of semiconductor laser dynamics due to filtered optical feedback

We report experimental results on the nonlinear dynamical response of a semiconductor laser subjected to time-delayed (>5 ns), frequency selective, optical feedback from a Fabry-Pe/spl acute/rot interferometer type of filter. Three regimes of interest, based on the relative value of the filter bandwidth with respect to the relevant laser parameters (relaxation oscillation frequency and external cavity mode spacing), are identified, viz. a wide filter case, an intermediate filter width case, and a narrow filter case. The dynamical response of the laser is shown to be quite different in each of these regimes. The principal results are 1) the laser's linewidth enhancement factor, coupled with the nonlinear response of the filter, can be exploited to induce nonlinear dynamics in the instantaneous optical frequency of the laser light on a time scale related to the time-delay of the feedback, 2) a mode mismatch effect which arises from a detuning between the filter center frequency and the nearest external cavity mode and manifests itself in a reduction of the maximum light available for feedback, and 3) a reduction in, or even disappearance of, relaxation oscillations in the laser dynamics when a filter of appropriate width is chosen. More generally, it is observed that certain dynamics that occur due to unfiltered optical feedback may be suppressed when the feedback light is spectrally filtered.     

EMTP modeling of a triggered-lightning strike to the phaseconductor of an overhead distribution line

A triggered-lightning experiment and EMTP modeling of that experiment are used to study the responses of a two-conductor overhead power line to a direct lightning strike. The experiment was conducted at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, FL. The lightning was artificially initiated (triggered) from a natural thundercloud using the rocket-and-wire technique, and its current was directed to the phase conductor. EMTP modeling of the line behavior yields results that are generally consistent with the measurements     

Teaching random signals and noise: an experimental approach

A practical approach for teaching random signals and noise is described, where theoretical aspects are complemented by several laboratory experiments enriching the student's understanding on basic topics, such as histograms and estimation of probability density function, autocorrelation function, and power spectral density. The equipment required is minimum and inexpensive. In fact, the existing equipment of laboratory benches employed for an electronic instrumentation course has been used. No investment from our institution has been necessary due to the full exploitation of the potentials of the existing instruments and their PC connectivity.     

Optimized in-phase and opposed-phase MR imaging for accurate detection of small fat or water fractions: theoretical considerations and experimental application in emulsions

Object  

To optimize strategies and measurement parameters for quantification of small fat and water fractions (<10%) in mixtures of both components by 4-point in-phase and opposed-phase gradient-echo imaging and to compare theoretical results with in-vitro experiments using emulsions.     

地方小电厂上网线路的保护配置与整定

地方小电厂单机容量小,机组的运行特性和稳定性较差,影响了其上网线路继电保护装置的配置和整定,如按常规方法对线路进行保护配置和整定,当系统发生故障,容易导致故障线路与电厂之间变电站的失压。损失负荷。为此,通过分析故障实例,提出优化地方小电厂上网线路继电保护的配置和整定方法,以减少事故的发生和由此造成的经济损失,从而提高系统的供电可靠性。