A general approach to synthesis and analysis of quasi-resonant converters

A method for systematic synthesis of quasi-resonant (QR) topologies by addition of resonant elements to a parent pulse-width modulation (PWM) converter network is proposed. It is found that there are six QR classes with two resonant elements, including two novel classes. More complex QR converters can be generated by a recursive application of the synthesis method. Topological definitions of all known and novel QR classes follow directly from the synthesis method and topological properties of PWM parents. The synthesis of QR converters is augmented by a study of possible switch realizations and operating modes. In particular, it is demonstrated that a controllable rectifier can be used to accomplish the constant-frequency control in all QR classes. Links between the QR converters and the underlying PWM networks are extended to general DC and small-signal AC models in which the model of the PWM parent is explicitly exposed. Results of steady-state analyses of selected QR classes and operating modes include boundaries of operating regions, DC characteristics, a comparison of switching transitions and switch stresses, and a discussion of relevant design trade-offs

QR code awareness in Stockholm, Sweden

This tech report describes the findings of a street survey on awareness of QR codes (2D barcodes) of the general public in Stockholm, Sweden. 108 passers-by were surveyed. Of these participants, a large majority (77%) did not recognize a QR code, and 8% reported seeing such a code before, but did not know it could be scanned using a mobile phone app. Only 15% knew what the shown QR code was, and that it could be read using a QR code reader on a mobile phone. The awareness of QR codes by the general public could be considered rather low, and their utility in Swedish public settings is currently debatable

Congestion avoidance for recharging electric vehicles using smoothed particle hydrodynamics

In this paper, a novel approach for recharging electric vehicles (EVs) is proposed based on managing multiple discrete units of electric power flow, named energy demand particles (EDPs). Key similarities between EDPs and fluid particles (FPs) are established that allow the use of a smoothed particle hydrodynamics (SPH) method for scheduling the recharging times of EVs. It is shown, via simulation, that the scheduling procedure not only minimizes the variance of voltage drops in the secondary circuits, but it also can be used to implement a dynamic demand response and frequency control mechanism. The performance of the proposed scheduling procedure is also compared with alternative approaches recently published in the literature

Student’s attendance system using QR code

The purpose of this project is to develop a system that can record the presence of students using QR code. Previously, teachers needed to use paper to record student attendance. There are many problems that arise when teachers use paper as a record of student attendance such as a loss of attendance record and have been taken a long time. The objective of the study is to design a prototype interface of student attendance system using QR code and casing of QR code scanner, to build up the design the prototype interface of student attendance system using QR code and casing of QR code scanner and test the functionality the prototype of interface student attendance system using QR code and casing of QR code scanner. The interface for this system will be integrated with the LabVIEW Software to develop a database. This system can record the attendance of the student to school and a warning letter will be automatically generated when the student does not come to school in 2 days repeatedly. The development process of the Student Attendance System Using QR Code is based on the Prototype Development Model that consists of a five-phase model, that is planning, analysis, design, Prototype development, and testing. The design of casing for QR code scanner was developed using Sketchup software. LabVIEW Software is used to generate interface displays and built-in databases using Microsoft Excel. Overall, the system that has been developed can work well and achieves the objectives set

Direct QR factorizations for tall-and-skinny matrices in MapReduce architectures

The QR factorization and the SVD are two fundamental matrix decompositions with applications throughout scientific computing and data analysis. For matrices with many more rows than columns, so-called "tall-and-skinny matrices," there is a numerically stable, efficient, communication-avoiding algorithm for computing the QR factorization. It has been used in traditional high performance computing and grid computing environments. For MapReduce environments, existing methods to compute the QR decomposition use a numerically unstable approach that relies on indirectly computing the Q factor. In the best case, these methods require only two passes over the data. In this paper, we describe how to compute a stable tall-and-skinny QR factorization on a MapReduce architecture in only slightly more than 2 passes over the data. We can compute the SVD with only a small change and no difference in performance. We present a performance comparison between our new direct TSQR method, a standard unstable implementation for MapReduce (Cholesky QR), and the classic stable algorithm implemented for MapReduce (Householder QR). We find that our new stable method has a large performance advantage over the Householder QR method. This holds both in a theoretical performance model as well as in an actual implementation

Spin filter using a semiconductor quantum ring side-coupled to a quantum wire

We introduce a new spin filter based on spin-resolved Fano resonances due to spin-split levels in a quantum ring (QR) side-coupled to a quantum wire (QW). Spin-orbit coupling inside the QR, together with external magnetic fields, induces spin splitting, and the Fano resonances due to the spin-split levels result in perfect or considerable suppression of the transport of either spin direction. Using the numerical renormalization group method, we find that the Coulomb interaction in the QR enhances the spin filter operation by widening the separation between dips in conductances for different spins and by allowing perfect blocking for one spin direction and perfect transmission for the other. The spin-filter effect persists as long as the temperature is less than the broadening of QR levels due to the QW-QR coupling. We discuss realistic conditions for the QR-based spin filter and its advantages to other similar devices.Comment: 5 pages, 4 figure

Automotive three-microphone voice activity detector and noise-canceller

This paper addresses issues in improving hands-free speech recognition performance in car environments. A three-microphone array has been used to form a beamformer with leastmean squares (LMS) to improve Signal to Noise Ratio (SNR). A three-microphone array has been paralleled to a Voice Activity Detection (VAD). The VAD uses time-delay estimation together with magnitude-squared coherence (MSC)