适用于风力发电机的可靠电力电子器件

单个IGBT摸块难以满足风力发电所需的大功率器件要求。本文阐述了采用串并联的方法提高耐压和扩大容量以满足风力发电机驱动器和大功率逆变器的要求，并对用于中压风力发电机驱动器和逆变器的IGBT摸块进行了分析，利用串并联IGBT摸块可得到更高的输出功率和效率。     

Alternative DNA amplification methods to PCR and their application in GMO detection: a review

Nucleic acids, especially DNA, are targets of qualitative and quantitative diagnostics for genetically modified organisms (GMO) in seeds, food- and feedstuff. The amplification of the nucleic acid is an essential step for further analyses of the target sequence. The PCR has been the method of choice for DNA amplification in most laboratories, and its real-time version (qPCR) also enables quantitative analysis of target contents. Despite its numerous advantages, PCR technology has some limitations such as the lack of true multiplexing properties. To alleviate the drawbacks linked to PCR technology, alternative nucleic acid amplification methods with promising characteristics are being developed fast. These methods, their advantages, and the inconveniences, which are not yet resolved are summarized in the paper. Special focus is given to the possibilities of using these alternative methods for GMO detection in future, when expansion of GMOs both in diversity and frequencies will make current GMO detection systems difficult to operate.     

Application of a Standard Power Meter for Detection Source of Harmonic Pollution and Reducing Economic Losses at Power Grid

Abstract—

The modern utility system is faced with two main problems: how to minimize losses in a power system and how to locate the source of harmonic pollution. Namely, the utility has losses whenever the power it delivers is greater than the power it registers at the point of common coupling (PCC). In this paper we will show that these losses occur because the measurement equipment and billing policy are not adequate, and we will stress the reasons why this happens. The main reason is the distortion power generated by nonlinear loads. The number of these loads at power grid is greater every day, thus enlarging the problem. Ordinary power meters are not able to measure distortion power, so in this paper we will also show which small modifications to existing ordinary meters needed, which could lead to the successful detection of sources of harmonic pollution, thus further reducing power losses. The suggested idea will be verified by numerous simulations and measurements on different household/office and industry loads that are commonly used. The proposed method is suitable either for software or hardware upgrade of existing smart meters, or it can be implemented on ordinary measurement systems.     

Numerical computation of impedances of a human tooth for estimation of the root canal length

Alternative current (ac) current conduction through a human tooth has been investigated through numerical simulation. Numerical calculation of impedance between the file (electrode) inserted in the root canal of the tooth and the outer electrode enables investigation of the impedance method used in dentistry for evaluation of the root canal length. Simulations confirm the improved sensitivity of the impedance method using the results of multiple frequency measurements.     

Packet error rate analysis of decode-and-forward free-space optical cooperative networks in the presence of random link blockage

This paper analyses end-to-end packet error rate (PER) of a free-space optical decode-and-forward cooperative network over a gamma–gamma atmospheric turbulence channel in the presence of temporary random link blockage. Closed-form analytical expressions for PER are derived for the cases with and without transmission links being prone to blockage. Two cooperation protocols (denoted as ‘selfish’ and ‘pilot-adaptive’) are presented and compared, where the latter accounts for the presence of blockage and adapts transmission power. The influence of scintillation, link distance, average transmitted signal power, network topology and probability of an uplink and/or internode link being blocked are discussed when the destination applies equal gain combining. The results show that link blockage caused by obstacles can degrade system performance, causing an unavoidable PER floor. The implementation of the pilot-adaptive protocol improves performance when compared to the selfish protocol, diminishing internode link blockage and lowering the PER floor, especially for larger networks.     

Cutting to the Chase

We describe a new algorithm for solving linear integer programming problems. The algorithm performs a DPLL style search for a feasible assignment, while using a novel cut procedure to guide the search away from the conflicting states.     

Automated building extraction from IKONOS images in suburban areas

The article addresses automatic building extraction from IKONOS images in suburban areas. In the proposed approach, we used a stereo pair of IKONOS images. Automatic photogrammetric methods of image matching were used to generate a digital surface model (DSM) and a digital elevation model. In further processing, single-image methods were used. The orthophotos of individual bands were created. The initial building mask was generated from the calculated normalized DSM (nDSM). The calculated normalized difference vegetation index and the road data extracted from the existing topographical database were used to remove vegetation and traffic surfaces. The mask was further improved with our own combination of methods based on non-linear diffusion filtering, unsupervised classification, colour segmentation and region growing. The final mask was vectorized using the Hough transform. Compared with a reference building database, 83.2% of the buildings in the test area were detected using the proposed approach with a quality percentage (how likely a building pixel produced by an automatic approach is correct) of 49.46.     

Single‐layer and bilayer four‐arm mode 1 spiral antennas and their feed structures

Single‐layer and bilayer four‐arm spiral antennas and their feeding methods for Mode 1 operation are discussed in this article. Important design parameters such as metal‐to‐slot ratio and growth rate for better impedance matching and reduced far‐field contamination are studied. Three feeding methods for Mode 1 operation are compared: a bundle of four coaxial cables for a single‐layer spiral and vertical and horizontal feeds by two coaxial cables for bilayer spirals. It is shown that the single‐layer spiral maintains beam symmetry with Wobble on Wave better than 1 dB at θ = 30° over 10:1 bandwidth. However, the required beamformer is complex and expensive. Proposed, horizontally and vertically fed bilayer spirals need simpler beamformer while maintaining similar far‐field performance over narrower 6:1 and 2:1 bandwidths, respectively, thus making them useful for many wideband applications. Modeling is conducted by a method of moments and validated with a finite element method and measurements. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22: 652–662, 2012.     

PM6 and DFT study of free radical scavenging activity of morin

Flavonoids have long been recognised for their general health-promoting properties, of which their antioxidant activity may play an important role. In this work, we have studied the properties of flavonoid morin using semiempirical and density functional theory (DFT) methods in order to validate the application of the recently developed parametric method 6 (PM6). Reaction enthalpies related to mechanisms of free radical scavenging by flavonoid morin were calculated by DFT and PM6 methods in gas-phase, water, DMSO and benzene. It has been shown that fast semiempirical PM6 method can mimic results obtained by means of more accurate time consuming DFT calculations. Thermodynamically favoured mechanism depends on reaction medium: SPLET (sequential proton loss electron transfer) is preferred in water and DMSO, and HAT (hydrogen atom transfer) is predominant in gas-phase. In benzene these two mechanisms are competitive.