On Non-Negative Quadratic Programming in Geometric Optimization

We present experimental and theoretical results on a method that applies a numerical solver iteratively to solve several non-negative quadratic programming problems in geometric optimization. The method gains efficiency by exploiting the potential sparsity of the intermediate solutions. We implemented the method to call quadprog of MATLAB iteratively. In comparison with a single call of quadprog, we obtain a 10-fold speedup on two proximity graph problems in $\mathbb{R}^d$ on some public data sets, a 10-fold speedup on the minimum enclosing ball problem on random points in a unit cube in $\mathbb{R}^d$, and a 5-fold speedup on the polytope distance problem on random points from a cube in $\mathbb{R}^d$ when the input size is significantly larger than the dimension; we also obtain a 2-fold or more speedup on deblurring some gray-scale space and thermal images via non-negative least square. We compare with two minimum enclosing ball software by G\"{a}rtner and Fischer et al.; for 1000 nearly cospherical points or random points in a unit cube, the iterative method overtakes the software by G\"{a}rtner at 20 dimensions and the software by Fischer et al. at 170 dimensions. In the image deblurring experiments, the iterative method compares favorably with other software that can solve non-negative least square, including FISTA with backtracking, SBB, FNNLS, and lsqnonneg of MATLAB. We analyze theoretically the number of iterations taken by the iterative scheme to reduce the gap between the current solution value and the optimum by a factor $e$. Under certain assumptions, we prove a bound proportional to the square root of the number of variables

Self-Improving Voronoi Construction for a Hidden Mixture of Product Distributions

We propose a self-improving algorithm for computing Voronoi diagrams under a given convex distance function with constant description complexity. The n input points are drawn from a hidden mixture of product distributions; we are only given an upper bound m = o(?n) on the number of distributions in the mixture, and the property that for each distribution, an input instance is drawn from it with a probability of ?(1/n). For any ? ? (0,1), after spending O(mn log^O(1)(mn) + m^? n^(1+?) log(mn)) time in a training phase, our algorithm achieves an O(1/? n log m + 1/? n 2^O(log^* n) + 1/? H) expected running time with probability at least 1 - O(1/n), where H is the entropy of the distribution of the Voronoi diagram output. The expectation is taken over the input distribution and the randomized decisions of the algorithm. For the Euclidean metric, the expected running time improves to O(1/? n log m + 1/? H)

A Generalization of Self-Improving Algorithms

Ailon et al. [SICOMP'11] proposed self-improving algorithms for sorting and Delaunay triangulation (DT) when the input instances $x_1,\cdots,x_n$ follow some unknown \emph{product distribution}. That is, $x_i$ comes from a fixed unknown distribution $\mathsf{D}_i$, and the $x_i$'s are drawn independently. After spending $O(n^{1+\varepsilon})$ time in a learning phase, the subsequent expected running time is $O((n+ H)/\varepsilon)$, where $H \in \{H_\mathrm{S},H_\mathrm{DT}\}$, and $H_\mathrm{S}$ and $H_\mathrm{DT}$ are the entropies of the distributions of the sorting and DT output, respectively. In this paper, we allow dependence among the $x_i$'s under the \emph{group product distribution}. There is a hidden partition of $[1,n]$ into groups; the $x_i$'s in the $k$-th group are fixed unknown functions of the same hidden variable $u_k$; and the $u_k$'s are drawn from an unknown product distribution. We describe self-improving algorithms for sorting and DT under this model when the functions that map $u_k$ to $x_i$'s are well-behaved. After an $O(\mathrm{poly}(n))$-time training phase, we achieve $O(n + H_\mathrm{S})$ and $O(n\alpha(n) + H_\mathrm{DT})$ expected running times for sorting and DT, respectively, where $\alpha(\cdot)$ is the inverse Ackermann function

Innovation brick cutting machine 創新切磚機械

...The ‘innovative brick cutting machine’ operates automatically, provides bricks that are accurately cut to specified sizes, and gives with additional protection for machine operators. The machine reduces the manual labour involved and yields a more accurate product in terms of brick size. 「創新切磚機械」屬全自動運作，能把磚塊準確切割成指定大小，並為操作人員提供額外保護。這部機械能夠減少作業所需人力，並製成大小規格更統一、更準確的磚塊。 Award: Silver奬項: 銀

Functional constituency members in Hong Kong's Legislative Council : a study of governance, legitimacy and accountability in action / y Cheung Hin Kei, Hankie, Ho Sing Yan, Simon, Li Man Pong, Charles, Tse Tsz Ying, Amy, Wong Man Ting, Mandy

published_or_final_versionPolitics and Public AdministrationMasterMaster of Public Administratio

Low-cost global MPPT scheme for photovoltaic systems under partially shaded conditions

Maximum Power Point Tracking (MPPT) is a technique applied to improve the efficiency of power conversion in Photovoltaic (PV) systems. Under partially shadowed conditions, the Power-Voltage (P-V) characteristic exhibits multiple peaks and the existing MPPT methods such as the Perturb and Observe (P&O) are incapable of searching for the Global Maximum Power Point (GMPP). This paper proposes a low-cost on-line MPPT scheme to overcome this drawback. By using hybrid numerical searching process, the operating point approaches Local Maximum Power Points (LMPPs) gradually and the GMPP is caught by comparing all the LMPPs. Simulation results prove the effectiveness and correctness of the proposed method. © 2013 IEEE.published_or_final_versio

Parenting approaches, family functionality, and internet addiction among Hong Kong adolescents

© 2016 Wu et al. Background: Internet addiction (IA) among adolescents has become a global health problem, and public awareness of it is increasing. Many IA risk factors relate to parents and the family environment. This study examined the relationship between IA and parenting approaches and family functionality. Methods: A cross-sectional study was conducted with 2021 secondary students to identify the prevalence of IA and to explore the association between adolescent IA and familial variables, including parents' marital status, family income, family conflict, family functionality, and parenting approaches. Results: The results revealed that 25.3 % of the adolescent respondents exhibited IA, and logistic regression positively predicted the IA of adolescents from divorced families, low-income families, families in which family conflict existed, and severely dysfunctional families. Interestingly, adolescents with restricted Internet use were almost 1.9 times more likely to have IA than those whose use was not restricted. Conclusions: Internet addiction is common among Chinese adolescents in Hong Kong, and family-based prevention strategies should be aligned with the risk factors of IA.Link_to_subscribed_fulltex

Multiple Block-Size Search Algorithm for Fast Block Motion Estimation

Abstract-Although variable block-size motion estimation provides significant video quality and coding efficiency improvement, it requires much higher computational complexity compared with fixed block size motion estimation. The reason is that the current motion estimation algorithms are mainly designed for fixed block size. Current variable block-size motion estimation implementation simply applies these existing motion estimation algorithms independently for different block sizes to find the best block size and the corresponding motion vector. Substantial computation is wasted because distortion data reuse among motion searches of different block sizes is not considered. In this paper, a motion estimation algorithm intrinsically designed for variable block-size video coding is presented. The proposed multiple block-size search (MBSS) algorithm unifies the motion searches for different block sizes into a single searching process instead of independently performing the search for each block size. In this unified search, the suboptimal motion vectors for different block sizes are used to determine the next search steps. Its prediction quality is comparable with that obtained by performing motion search for different block sizes independently while the computational load is substantially reduced. Experimental results show that the prediction quality of MBSS is similar to full search. Block matching, motion estimation, video coding, search pattern, directional search

Service learning and school community partnership

Background Service learning offered university students the opportunity to apply knowledge and skills in social care context while strengthening community health. This paper aimed at highlighting the essential features of the program in achieving sustainable outcomes. Project design and methods Students from different faculty, worked as a team to address the health issues of a less resourceful school. The students were required to plan and develop the related resources and products for matching the learning needs. Through the implementation, students shifted from following an instructive guide to acting on a more self-directed learning process at different stages of service. The health promotion programs could include nutritious breakfast, adequate exercises, healthy beverages and interpersonal communication. Efficacy of the service learning was assessed by the pre and post service survey on the attainment of generic skills of interpersonal effectiveness, problem solving, social responsibility and teamwork. Impact of the service was evaluated by the pre and post program testing. Individual learning experience was collected by the reflective journal writing. Significance and implication School community plays a major role in providing a healthy learning environment for children and adolescents. With the input of subject knowledge and field practice, faculty students attained improvement in generic skills. The school participants increased health knowledge and the importance of healthier lifestyle was reinforced. Both parties owned the program materials for the continuity of practice. The partnership creates initiatives of applying health-promoting school concepts. This project work also built up the ground work for a feasible framework of school health service and practice