Linear Size Optimal q-ary Constant-Weight Codes and Constant-Composition Codes

An optimal constant-composition or constant-weight code of weight $w$ has linear size if and only if its distance $d$ is at least $2w-1$. When $d\geq 2w$, the determination of the exact size of such a constant-composition or constant-weight code is trivial, but the case of $d=2w-1$ has been solved previously only for binary and ternary constant-composition and constant-weight codes, and for some sporadic instances. This paper provides a construction for quasicyclic optimal constant-composition and constant-weight codes of weight $w$ and distance $2w-1$ based on a new generalization of difference triangle sets. As a result, the sizes of optimal constant-composition codes and optimal constant-weight codes of weight $w$ and distance $2w-1$ are determined for all such codes of sufficiently large lengths. This solves an open problem of Etzion. The sizes of optimal constant-composition codes of weight $w$ and distance $2w-1$ are also determined for all $w\leq 6$, except in two cases.Comment: 12 page

Properties of a hand-printed Chinese character recognizer based on contexted vector quantization

A hand-printed Chinese character recognizer based on Contextual Vector Quantization (CVQ) has been built previously. In this paper, several properties of the recognizer will be discussed and the recognizer of 4516 Chinese characters has a successful rate of 91.0%. Then the output of the recognizer is passed to a language model which when applied to recognize a passage of about 1200 characters raises the rate from 91.5% to 97.5%.published_or_final_versio

"Lose at the Starting Line, Win at the Finishing Line": beating academic adversity

Panel 1 - Beating Academic Adversity in Hong Kong, Singapore, and IndiaThis paper examines public perception and discourse of academic adversity and resilience to understand what are considered to be deterrents of academic success and what are believed to effectively counteract the deterrents and contribute to educational resilience. Data are drawn on discourse analysis of media coverage in Hong Kong of the success stories of students at risk after the release of university entrance exam results. In Hong Kong, educational desires are fuelled by the high value placed on education, and an extremely competitive examination system whereby less than 20 percent of secondary ...postprin

A fast parallelized eigen-based clutter filter framework for ultrasound color flow imaging

Oral presentation - IUS1-D3: Novel imaging systems: abstract no. IUS1-D3-6The Conference program & abstracts' website is located at http://www.ewh.ieee.org/conf/uffc/2013/BACKGROUND, MOTIVATION AND OBJECTIVE: Eigen-filters with attenuation response adapted to clutter statistics have emerged as a new class of clutter suppression techniques in color flow imaging (CFI) to achieve high flow detection sensitivity in the presence of tissue motion. There is growing interest to extend this technique beyond laboratory investigations by incorporating it into the CFI processing routine on ultrasound scanners. Nevertheless, bridging such a gap from theory to practice is known to be challenging from a real-time computing perspective because the singular value decomposition (SVD) operation in eigen-filtering is known to pose heavy computational burden. Here we seek to overcome this issue by formulating a new technical framework that enables fast execution of eigen-filtering so as to foster their practical adoption in …postprin

An overview on interproximal enamel reduction

Ever since its first introduction seven decades ago, there has been continuous advancement of the concept and technique of Interproximal enamel reduction (IPR). It’s demonstrated that with correct case selection and clinical performance, IPR is safe and effective for alleviating crowding, improving dental and gingival aesthetics as well as facilitating post-treatment stability. The fulfilment of treatment outcomes depends on careful pre-treatment examination and planning, appropriate clinical procedures and effective post-treatment protection. This review aims to provide a general introduction to IPR in terms of its history background, risks and benefits and clinical performance.published_or_final_versio

PHASE ERRORS AND DOPPLER EFFECT IN DIGITAL COMMUNICATIONS

The rollout of IEEE 802.16e for high speed mobile communications poses challenges to the design of equalizers for a time-varying multipath fading channel. This thesis investigates the effects of Doppler shift induced phase error in a wireless environment. It presents the performance of QPSK and MQAM waveforms with Doppler in a Rayleigh channel condition. It investigates the performance of ideal coherent modulation and pilot symbol-aided modulation in a Rayleigh channel with Doppler phase errors. The degradation in performance of pilot symbol-aided demodulation as compared to ideal coherent demodulation is presented. The study concludes with results of simulations of QPSK and MQAM waveforms in a Rayleigh Channel with Doppler phase errors.Civilian, Singapore Defence Science & Technology AgencyApproved for public release; distribution is unlimited

A SYSTEMS ANALYSIS OF ENERGY USAGE AND EFFECTIVENESS OF A COUNTER-UNMANNED AERIAL SYSTEM USING A CYBER-ATTACK APPROACH

Existing counter-unmanned aerial systems (C-UAS) rely heavily on radio frequency (RF) jamming techniques that require a large amount of energy. RF jamming results in undesirable consequences such as jamming nearby friendly devices as well as increasing RF footprint of local operators. Current cybersecurity analysis of commercial-off-the shelf (COTS) UASs have revealed vulnerabilities that can be used to conduct C-UAS operations in the cyber domain via cyber-attacks that hijack device-specific communication links on narrow RF bands. This thesis validates the cyber-attack C-UAS (CyC-UAS) concept through reviewing recent C-UAS operational experimental scenarios and conducting analysis on the collected data. Then, a model of a defense facility is constructed to analyze and validate specific mission scenarios and several proposed concepts of operation. A comparison of the energy requirements between CyC-UAS and existing C-UAS techniques is performed to assess energy efficiency and trade-offs of different C-UAS approaches. The comparison of energy requirements between the CyC-UAS prototype and existing C-UAS RF jamming products shows CyC-UAS has significant energy savings while not affecting other telecommunication devices operating at the same frequencies. CyC-UAS is able to achieve the same mission by consuming much less energy and shows promise as a new, lower energy, and lower collateral damage approach to defending against UASs.Outstanding ThesisMajor, Republic of Singapore Air ForceApproved for public release. Distribution is unlimited

A study on Discrete Event Simulation (DES) in a High-Level Architecture (HLA) networked simulation

This thesis investigates implementing Discrete Event Simulation (DES) concepts using Simkit packages into a High- Level Architecture (HLA)-networked simulation, thus addressing sustainability of the HLA methodology into the future. Through the DES concept of predicting and anticipating the time of when events will occur, redundant and excessive exchange of common data, like position and sensory status, can be removed. This DES implementation considerably reduces the network load and removes data processing incompatibility between simulations. A design involving several concepts of DES and HLA simulation led to the creation of a Simkit based application library. Interfacing this application library with two DES models demonstrated and proved the feasibility of DES concepts in HLA-networked simulations. A generic combat scenario modeled using this methodology, successfully showed the intended advantages of the thesis. The ease of linking non-DES and non-HLA simulations to an HLA environment was enhanced using a common set of interfaces built based on the resulting application library. Through a simple comparison with traditional time-stepped real-time simulation of the same scenario configuration, it was shown that data exchange between simulations was reduced by several orders of magnitude. This freed a substantial amount of network resources to perform other tasks, hence, improving network performance.http://archive.org/details/astudyondiscrete109454958(Simulation Systems) author (civilian)Approved for public release; distribution is unlimited

Modeling of the ring-hybrid dipole antenna and mutual coupling in a small antenna array

This thesis project modeled a microstrip ring-hybrid dipole that is capable of simultaneously producing a sum pattern and difference pattern using the method of moments (MoM) based on the Rao-Wilton-Glisson (RWG) edge elements. The ringhybrid dipole is simply a ring-hybrid coupler driving a dipole antenna. A two-feed point dipole model was developed and its antenna parameters were found to be a good representation of the ring-hybrid dipole actual values. In the feed network modeling, the matrix solution combined the MoM equations on the antenna surfaces and a magic-tee scattering matrix by applying Kirchhoff's voltage and current laws at the terminals of the antenna. Once the excitation is specified, the complete system of equations was solved to yield the MoM current expansion coefficients and the signals in the feed network. The effect of mutual coupling in an array of three ring-hybrid dipoles was examined by extending the model. In the receive mode, the direction and polarization of the incidence plane wave were varied. The phases for both the sum port and difference port outputs were observed to change smoothly, except during situations of cross polarization and zero phase difference. The array model will form the foundation for the design and analysis of a mutual coupling compensation network.http://archive.org/details/modelingofringhy109456153MAJ, Republic of Singapore NavyApproved for public release; distribution is unlimited