新型直流侧级联光伏逆变系统的研究与分析

新型直流侧级联的光伏逆变系统拓扑结构由多路单相全桥变换器与其连接的直流侧电容组成,直流侧电容串联能减少逆变桥电压。该拓扑结构使得MOSFET这种开关器件得到更广泛的应用。使用该拓扑结构可减小主电路的电流,同时由于使用了MOSFET,电路中的开关损耗减少了很多,因此降低了线路损耗。更为重要的是,通过对级联逆变器使用载波移相SPWM方式,降低了系统的工作频率,从而直接有效地降低了开关器件的损耗。最终通过仿真验证了该拓扑结构的有效性,研究结果表明多路直流侧级联光伏逆变系统具有较优越的谐波抑制能力,其直流电压控制简单。     

Sampling-based online motion planning for mobile robots: utilization of Tabu search and adaptive neuro-fuzzy inference system

Despite the proven advantages of sampling-based motion planning algorithms, their inability to handle online navigation tasks and providing low-cost solutions make them less efficient in practice. In this paper, a novel sampling-based algorithm is proposed which is able to plan in an unknown environment and provides solutions with lower cost in terms of path length, runtime and stability of the results. First, a fuzzy controller is designed which incorporates the heuristic rules of Tabu search to enable the planner for solving online navigation tasks. Then, an adaptive neuro-fuzzy inference system (ANFIS) is proposed such that it constructs and optimizes the fuzzy controller based on a set of given input/output data. Furthermore, a heuristic dataset generator is implemented to provide enough data for the ANFIS using a randomized procedure. The performance of the proposed algorithm is evaluated through simulation in different motion planning queries. Finally, the proposed planner is compared to some of the similar motion planning algorithms to support the claim of superiority of its performance.

     

Numerical treatment of nonlinear Emden–Fowler equation using stochastic technique

The article is based on the approximate solution of a well known Lane–Emden–Fowler (LEF) equation. A trial solution of the model is formulated as an artificial feed-forward neural network containing unknown weights which are optimized in an unsupervised way. The proposed scheme is tested successfully on various test cases of initial value problems of LEF equations. The reliability and effectiveness is validated through comprehensive statistical analysis.     

Effects of power line voltage variations on different types of400-W high-pressure sodium ballasts

This paper presents the results of laboratory tests to determine the effects of voltage sags, interruptions and fluctuations on high-pressure sodium (HPS) lamps and ballasts. The way these ballasted lamps react to sags and interruptions in the laboratory is then compared to a model of the real-world electrical environment created from data gathered during three recent North American power quality surveys. This work also shows how HPS immunity to voltage variations depends significantly on the ballast type and the lamp age     

Analysis on the surface adsorption of PEO/PPO/PEO triblock copolymers by radiolabelling and fluorescence techniques

We have examined the adsorption of poly(ethylene oxide)/ poly(propylene oxide)/poly(ethylene oxide) (PEO/PPO/PEO) triblock copolymers (Pluronics?) on dimethyldichlorosilane-treated glass (DDS-glass). The surface concentration of ¹²⁵I-labeled Pluronic F-68(76/30/76) reached a maximum of 0.3 μg/cm² when the bulk concentration in the adsorption solution was 3.0 mg/mL. Above 5.0 mg/ml, the surface Pluronic F-68 concentration started to decrease and reached 0.17 μg/cm² when the bulk concentration for adsorption was 10 mg/mL. The surface concentration of Pluronic F-108 (129/56/129), on the other hand, increased to 4.0 μg/cm² at the same bulk concentration. Fluroscence spectroscopic studies using pyrene suggested that the Pluronic F-68 molecules self-associated at the bulk concentration of 5.0 mg/mL and above. Because the aggregates are expected to expose the hydrophilic PEO segments to water, they may have lower affinity to DDS-glass. Aggregation of Pluronic F-68 also decreases the number of individual Pluronic molecules for adsorption. Pyrene fluorescence in Pluronic F-108 solution, however, suggests that Pluronic F-108 molecules do not form aggregates. It appears that the high surface concentrations of Pluronic F-108 may result from the preferential adsorption of individual molecules in multilayers. This explains the high effectiveness of Pluronic F-108 in preventing protein adsorption and platelet adhesion when adsorbed on to be hydrophobic surface. © 1994 John Wiley & Sons, Inc.     

Ibuprofen Release from Beads Coated with an Experimental Latex: Effect of Certain Variables

The objective of this study was to evaluate the effect of factors such as drug loading, particle size, plasticizer type, antiadherent type, and annealing method on the release of ibuprofen from controlled-release beads coated with an experimental latex. Further, the in vitro release kinetics and mechanism of drug transport across the polymeric membrane have been investigated. Ibuprofen-loaded beads were coated with the experimental latex using a fluidized-bed coating machine (Uniglatt). The drug release from these spherical membrane reservoir systems appeared to be diffusion controlled. Evaluation of the effect of osmotic pressure by using dissolution media of various osmolal concentrations indicated that it has no significant effect on the drug release. To further elucidate the mechanism of release from these polymeric membranes, the permeation of drug through free films was studied.     

Alumina coated with oxazolone derivative for extraction of trace amounts of cadmium and copper from water and plant samples

A solid phase extraction procedure is proposed for simultaneous separation and preconcentration trace amounts of Cu(II) and Cd(II) using alumina coated with N'-{4-[4-{1-[4-(dimethylamino)phenyl]methylidene}-5-(4-H)oxazolone]phenyle}acetamide and determination by flame atomic absorption spectrometry. Using 0.1g of the sorbent, the metal ions were sorbed at pH 7 and recovered with 5.0 mL of 0.5 mol L(-1) HNO(3). It was found that extraction can be performed from the sample volumes of 2000 and 800 mL for Cu and Cd, respectively (preconcentration factors of 400 for Cu and 160 for Cd). Obtained sorption capacities for 1g sorbent were 8 mg Cu and 14 mg Cd. The linearity was maintained in the concentration range of 0.1 ng mL(-1) to 7.0 μg mL(-1) for Cu and 0.13 ng mL(-1) to 2.0 μg mL(-1) for Cd in the original solution. Eight replicate determinations of a mixture containing 1.0 μg mL(-1) each of the elements in the final solution gave relative standard deviation ±1.6 and ±1.3% for Cu and Cd, respectively. The detection limit was calculated as 0.06 and 0.05 ng mL(-1) for Cu and Cd, respectively. The proposed method was successfully applied to the determination trace amounts of Cu and Cd in the water and plant samples.     

Risk analysis: Casing-while-Drilling (CwD) and modeling approach

In today's volatile economy and uncertain drilling environment, managers are encouraged to reduce well cost and time and have implemented Casing-while-Drilling (CwD) to improve operational excellence. Risk analysis is another valid tool that can be used to improve drilling operations. This paper discusses CwD as a new technology and how its benefits can be strengthened by including risk analysis as a complementary technique. A modeling approach is presented to demonstrate how risk analysis can be applied to CwD programs and to discuss the main concerns a well planner must address to achieve a successful drilling program. The integration of both CwD and risk analysis will add value to the overall excellence of the well operation. Very little work has been done on this integration, and the hope is that this approach will be a standard practice in the future.     

Personal identification using feature and score level fusion of palm- and fingerprints

The ever increasing demand of security has resulted in wide use of Biometric systems. Despite overcoming the traditional verification problems, the unimodal systems suffer from various challenges like intra class variation, noise in the sensor data etc, affecting the system performance. These problems are effectively handled by multimodal systems. In this paper, we present multimodal approach for palm- and fingerprints by feature level and score level fusions (sum and product rules). The proposed multi-modal systems are tested on a developed database consisting of 440 palm- and fingerprints each of 55 individuals. In feature level fusion, directional energy-based feature vectors of palm- and fingerprint identifiers are combined to form joint feature vector that is subsequently used to identify the individual using a distance classifier. In score level fusion, the matching scores of individual classifiers are fused by sum and product rules. Receiver operating characteristics curves are formed for unimodal and multimodal systems. Equal Error Rate (EER) of 0.538% for feature level fusion shows best performance compared to score level fusion of 0.6141 and 0.5482% of sum and product rules, respectively. Multimodal systems, however, significantly outperform unimodal palm- and fingerprints identifiers with EER of 2.822 and 2.553%, respectively.