Independent sets in graphs with given minimum degree

We consider numbers and sizes of independent sets in graphs with minimum degree at least $d$, when the number $n$ of vertices is large. In particular we investigate which of these graphs yield the maximum numbers of independent sets of different sizes, and which yield the largest random independent sets. We establish a strengthened form of a conjecture of Galvin concerning the first of these topics

Mechanical Behavior Associated with Metallurgical Aspects of Friction Stir Welded Al-Li Alloy Exposed to Exfoliation Corrosion Test

Open Access articleThis research aims to investigate the effect of the exfoliation corrosion exposure time on the mechanical properties, the strength and elongation, of friction stir welded Al-Li alloy type 2195-T8. The exfoliation corrosion test was performed using the exfoliation corrosion (EXCO) solution, based on ASTM G34. The samples were exposed to different exposure times 24, 48, 96, 192 and 384 hours. The results showed that both the strength and elongation of the welded specimens - exposed to the exfoliation corrosion tests - were reduced. For example, the samples that were exposed to 384 hrs, their initial tensile strength and elongation were reduced by 13% and 17% respectively. The degradation process due to the exfoliation corrosion on the tensile strength was divided into three stages: fast (0-96 hrs: 443.7 MPa-416.3 MPa, the degraded rate was 0.29 MPa/h), steady (96-192 hrs: 416.3 MPa-413.4 MPa, the degraded rate was 0.03 MPa/h) and medium rate (192-384 hrs: 413.4 MPa-386.7 MPa, the degraded rate was 0.14 MPa/h). For the elongation, in general, the reduction was similar to the style of strength, but with different rates. The TEM images showed that this degradation was due to the dissolution of T1 (Al2CuLi) and S´ (Al2CuMg) phase. Also, the corrosion products and their role of adherence on the surface of the tested specimens were investigated. An empirical equation p-t (mechanical properties-exposure time) was established to calculate the effect of exposure corrosion time on the performance of welded specimens

A Time-spectral Approach to Numerical Weather Prediction

Finite difference methods are traditionally used for modelling the time domain in numerical weather prediction (NWP). Time-spectral solution is an attractive alternative for reasons of accuracy and efficiency and because time step limitations associated with causal, CFL-like critera are avoided. In this work, the Lorenz 1984 chaotic equations are solved using the time-spectral algorithm GWRM. Comparisons of accuracy and efficiency are carried out for both explicit and implicit time-stepping algorithms. It is found that the efficiency of the GWRM compares well with these methods, in particular at high accuracy. For perturbative scenarios, the GWRM was found to be as much as four times faster than the finite difference methods. A primary reason is that the GWRM time intervals typically are two orders of magnitude larger than those of the finite difference methods. The GWRM has the additional advantage to produce analytical solutions in the form of Chebyshev series expansions. The results are encouraging for pursuing further studies, including spatial dependence, of the relevance of time-spectral methods for NWP modelling

尋覓於荒誕之中

羅貴祥是八十年代香港文學界繼西西、也斯等人而起的現代派作家。由於他喜歡運用創新、複雜的技巧，並常在文字、結構上玩遊戲，故其作品一般較難讀懂。所以本文嘗試在神話和心理分析的理論基礎上細讀文本，為他的作品〈欲望肚擠眼〉提供一種解讀。本文先以「荒誕」理論分析「荒誕」元素在小說擔任的角色――整篇小說的基調和風格及故事的背景和展開的關鍵；再從兩線人物隱藏的關係及故事情節的發展分析整篇小說的主題 (聖與俗的矛盾) 和結構 (一組反方向的追尋結構)；並在結語部分略評小說未盡完善的地方

Solar System Constraints on Disformal Gravity Theories

Disformal theories of gravity are scalar-tensor theories where the scalar couples derivatively to matter via the Jordan frame metric. These models have recently attracted interest in the cosmological context since they admit accelerating solutions. We derive the solution for a static isolated mass in generic disformal gravity theories and transform it into the parameterised post-Newtonian form. This allows us to investigate constraints placed on such theories by local tests of gravity. The tightest constraints come from preferred-frame effects due to the motion of the Solar System with respect to the evolving cosmological background field. The constraints we obtain improve upon the previous solar system constraints by two orders of magnitude, and constrain the scale of the disformal coupling for generic models to $\mathcal{M} \gtrsim 100$ eV. These constraints render all disformal effects irrelevant for cosmology.Comment: 17 pages, 2 figures v2: Added discussion of implications for cosmology in Sec. 5.2. Version accepted by JCAP. v3: Corrected minor typo

The effect of neighborhood size and regularity on reading Chinese in Hong Kong children

Also available in print.Thesis (B.Sc)--University of Hong Kong, 2007.A dissertation submitted in partial fulfilment of the requirements for the Bachelor of Science (Speech and Hearing Sciences), The University of Hong Kong, June 30, 2007.published_or_final_versionSpeech and Hearing SciencesBachelorBachelor of Science in Speech and Hearing Science

Screening for voice problems in school-age children : a comparison between teacher, parent and speech therapist reports

This study investigated untrained parents and teachers’ ability to detect voice disorders in children by comparing their judgments with experienced speech therapists’ judgments. Parents and teachers of 64 Cantonese-speaking primary-one students completed a screening questionnaire for each of their own child or student. The questionnaire comprised three parts: 1) perceptual rating of eight voice quality parameters, 2) overall severity rating, and 3) decision on referral for follow-up. Four experienced speech therapists not knowing the students made judgments using the same questionnaire based on recorded voice samples of passage reading of students. Results revealed poor correlations between parent and speech therapist, as well as between teacher and speech therapist. Percentage of exact agreement was not high between parent and speech therapist, as well as between teacher and speech therapist. The results suggest that parents and teachers may not provide reliable perceptual judgments of children’s voice, compared with that made by speech therapists, and not identify and refer dysphonic cases very accurately.published_or_final_versionSpeech and Hearing SciencesBachelorBachelor of Science in Speech and Hearing Science

Critical comparison of autistic treatment with classic Chinese medicine and western homeopathy

More people seek alternative medicine to treat autism. The effectiveness of Chinese and homeopathic medicine have been reported. This review included 36 studies investigated the treatment efficacy of Chinese and homeopathic medicine for children with autism. This study aimed at (1) summarizing findings about therapeutic effect of Chinese medicine and homeopathy; (2) examining methodological quality of these studies; and (3) recommending further investigation and providing direction for future work. This study evaluated treatment effect of acupuncture, herbal medicine, Qigong, Tuina and homeopathic medicine for children with autism. The study showed that there was a lack of randomized controlled trials with valid statistical evidence. To conclude, neither the therapeutic effect of Chinese medicine nor that of homeopathy could be confirmed.published_or_final_versionSpeech and Hearing SciencesBachelorBachelor of Science in Speech and Hearing Science

Teachers' understanding of the development of students' creativity in liberal studies classrooms

This research aims at studying teachers’ understanding of the development of students' creativity in Liberal Studies classrooms. Education reform and Liberal Studies Curriculum and Assessment Guide emphasize the development of creativity in Liberal Studies classrooms, however, unlike Taiwan and United Kingdom, there is no specialised curriculum in guiding teachers’ development of students’ creativity. It is interested to know how teachers’ perception of creativity in related to Liberal Studies, what pedagogies they use in developing students’ creativity, what students’ behaviors and personalities they regard as creative and their perception of Liberal Studies’s contribution on developing students’ creativity in the education reform. Seven in-service Liberal Studies were participated in semi-structured interviews to express their views on creativity with the relationship of Liberal Studies. To see whether teachers make use of the pedagogies in developing students’ creativity and have a clear understanding of students’ creative behaviors and personalities, the well-known and comprehensive creativity curriculum model, the Williams model is used to match with the pedagogies, behaviors and personalities mentioned by teachers. This study points out that though teachers use various pedagogies in Liberal Studies classrooms to develop students’ creativity, most of the teachers weigh relatively low importance of Liberal Studies in developing students’ creativity. The main constraint for them is the analysis and evaluation need in examination system that critical thinking is much more important than creativity. It is reflected that teachers lack understanding that creativity needs criticality. The study also shows that most teachers do not think Liberal Studies could contribute much in developing students’ creativity in education reform, though education reform and Liberal Studies curriculum emphasize creativity. Teachers have discrepancies in understanding the aim of authority in developing creativity.published_or_final_versionEducationBachelorBachelor of Education in Liberal Studie

The perception of English vowels by native Cantonese English as a foreign language primary school students

This study investigated the perception of English vowels in Cantonese speakers who are beginning learners of English as a foreign language (EFL) in reference to the Perceptual Assimilation Model (PAM). Thirty-one primary school students participated in a perception study that required them to discriminate and identify English minimal vowel pairs. It was founded that Cantonese EFL learner’s vowel perception can be predicted by the similarity of spatial proximity of constriction locations between English vowels and Cantonese vowels. The study also provides support for the PAM. Further research is needed to include EFL learners from different age groups and at different English proficiency levels.published_or_final_versionSpeech and Hearing SciencesBachelorBachelor of Science in Speech and Hearing Science