2,103 research outputs found

    Electrophysiological Mechanisms of Atrial Flutter

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    Atrial flutter (AFL) is a common arrhythmia in clinical practice. Several experimental models such as tricuspid regurgitation model, tricuspid ring model, sterile pericarditis model and atrial crush injury model have provided important information about reentrant circuit and can test the effect of antiarrhythmic drugs. Human atrial flutter has typical and atypical forms. Typical atrial flutter rotates around tricuspid annulus and uses the crista terminalis and sometimes sinus venosa as the boundary. The IVC-tricuspid isthmus is a slow conduction zone and the target of radiofrequency ablation. Atypical atrial flutter may arise from the right or left atrium. Right atrial flutter includes upper loop reentry, free wall reentry and figure of eight reentry. Left atrial flutter includes mitral annular atrial flutter, pulmonary vein-related atrial flutter and left septal atrial flutter. Radiofrequency ablation of the isthmus between the boundaries can eliminate these arrhythmias

    The effect of violin, keyboard, and singing instruction on the spatial ability and music aptitude of young children

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    The purpose of this study was to examine the effects of violin, keyboard, and singing instruction on spatial ability and music aptitude of children ages four to seven years. Specifically, this research attempted to determine: (a) whether formal music learning in the violin, keyboard and singing conditions enhanced children's spatial ability and music aptitude, and (b) whether children's spatial ability and music aptitude differed among these learning conditions. In addition, this study sought to examine the relationships among children's age, their development of spatial ability, and music aptitude in the given music instruction. A pretest-posttest two by three factorial design was employed in the study. Children (N=88) ages four to seven years were randomly assigned to one of three instructional groups (violin, keyboard, or singing) and received 45 minutes of music instruction four times a week for 16 days. Spatial reasoning skills were measured using two subtests, the Object Assembly and the Block Design of the Wechsler Preschool and Primary Scale of Intelligence-III, while music aptitude was measured using the Primary Measures of Music Audiation or the Intermediate Measures of Music Audiation. An ANOVA with repeated measures was used to analyze children's mean scores on spatial abilities and music aptitude. Using an alpha level of .05, results indicated that the violin and keyboard groups significantly improved on spatial-temporal reasoning over four weeks of instruction. The spatial-temporal reasoning scores of 4-5 year olds significantly increased from the pretest to posttest while the scores of 6-7 year olds remained statistically constant. Regarding music aptitude, the tonal aptitude scores of 4-5 year olds singing group significantly increased over four weeks of music instruction. No statistically significant differences were found on the spatial recognition and rhythm aptitude scores among the three instructional groups for either age level. The study concluded that (a) violin and keyboard instruction might influence the spatial-temporal reasoning of young children, (b) younger children's spatial-temporal reasoning ability might be more enhanced by music instruction than those of older children, and (c) singing instruction appears to help young children develop their tonal aptitude. Pedagogical implications for music education were discussed

    Relocation and high-rise living : a study of Singapore's public housing

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    Public housing in Singapore is one of the most significant development programmes in the state. It has been centrally planned and implemented by the Government not only to tackle housing problems and rebuild the decaying inner city areas, but also to restructure Singapore society in terms of the visions of the power elite.This study attempts to examine the social and political implications of relocation and public housing in Singapore, and to analyse the difficulties faced by and the impact of relocation on individuals and families from the various constrasting groups of relocatees, with an emphasis on problems of economic hardship, adaptation to high-rise living, and neighbourliness in the public housing estates.To achieve this task, three types of material have been used, viz. official data, empirical material from previous studies, and empirical data and information collected during fieldwork. The fieldwork comprises a sample survey of 1,200 households and an in-depth study of 27 relocated families.The thesis consists of three parts. The first part reviews the literature on relocation and public housing and the conceptual framework employed in their study. The second part examines the policies underlying and the salient social and political aspects of relocation and public housing in Singapore. The final part analyses the data and information obtained from the sample survey and the in-depth study.The findings of the present study show that while the Singapore Government has made some impressive quantitative achievements of its public housing programme, some of its original objectives may never be fully achieved. Two of the eight hypotheses deduced from the assumptions and observations of the previous studies are refuted by data obtained from the present study. Five of them are however supported, and one is inconclusive. Some sensitive issues relating to public housing in Singapore, which have significant social and political effects and yet are usually avoided by most researchers, are also analysed and discussed in the light of their policy implications

    The regulation of the transferrin receptor by inducers of cellular differentiation and by antisense phosphorothioate oligodeoxynucleotides

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    Modulation of surface transferrin receptor (TfR) activity has been associated with leukemia cell differentiation and proliferation. To examine the mechanisms involved in regulating this event, surface receptor protein and mRNA levels were measured in HL-60 promyelocytic leukemia cells induced to differentiate along the myelocytic and monocytic pathways. Surface TfR down-regulation which occurs during granulocytic differentiation by dimethylsulfoxide, retinoic acid, or aclacinomycin A appears to be kinetically compatible with reduced biosynthesis resulting from reductions in the level of steady-state mRNA. In contrast, biosynthetic modulation does not appear to mediate the intial surface receptor down-regulation seen during 12-O-tetradecanoylphorbol-13-acetate-induced macrophagic differentiation. However, a reduction in levels of receptor message appears to contribute to the maintenance of diminished surface TfR activity in these 12-O-tetradecanoylphorbol-13-acetate-treated cells. The down-regulation of surface TfR, in contrast, is not an early event during monocytic differentiation by 1alpha,25-dihydroxyvitamin D3. A common feature of myelocytic and monocytic differentiating cells is the complete inhibition of cellular proliferation observed within 10 to 16 hours following a four-fold reduction in surface TfR. We conclude that the early decline in surface TfR levels precludes its regulation as a consequence of the decrease in proliferation, but rather implicates its role in the programmed cessation of growth which is requisite for the terminal differentiation of these cells.A series of phosphodiester and phosphorothioate antisense oligonucleotides were synthesized against the human TfR. The phosphorothioate analogues exhibited marked biological efficacy in culture, as assessed by inhibition of surface TfR content and HL-60 growth, whereas their unmodified phosphodiester counterparts were ineffective. Phosphorothioate oligonucleotides were more resistant to hydrolysis by serum and cellular nucleases, and were more readily taken up by cells than the phosphodiesters. A length effect was observed, with antisense 30-mers exhibiting greater TfR inhibitory activity than 17-mers. The degree of surface receptor inhibition observed, however, was not strictly sequence dependent. This suggested that the photphorothioate oligonucleotides may be biologically active in eukaryotic cells by processes other than classical antisense complementary binding to mRNA. (Abstract shortened with permission of author.

    Comparison of uncertainty in modal identification under known and unknown input excitations

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    Modal identification is a technique that can assess modal properties of structures based on vibration data. This technique can be categorized into known and unknown input modal identification. Known input modal identification, e.g. forced vibration tests, is more economically demanding because of the need of special devices to generate artificial loading but the data obtained has higher signal-to-noise ratio. Unknown input modal identification, e.g. ambient vibration, could be performed economically with structures under working conditions. This study employs a fast Bayesian FFT method to not only identify the modal parameters, such as natural frequencies and damping ratios, but also quantify the uncertainties associated with the modal identification results. This provides a tool to investigate the uncertainties in the modal identification. In this study two numerical examples are used to generate synthetic data for investigating and comparing the uncertainties in the known and unknown input modal identification

    Investigation of degradation caused by charge trapping at etching-stop layer under AC gate-bias stress for InGaZnO thin film transistors

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    A great amount of literatures has been focusing on bias-induced instability issues including threshold voltage shift (ΔVt ) and subthreshold swing (S.S) degradations [1]. However, in practical TFT operation circuits, very limited knowledge could be applied since operation modes are mostly applied with alternative current (AC). Based on these backgrounds, in this work, Indium-Gallium-Zinc-Oxide Thin Film Transistors (IGZO TFTs) are applied with AC PBS degradations. Compared with previous work, this work observed a structure dependent degradation. An etch-stop structure IGZO TFT observed a serious threshold voltage shift after AC stress but shown great stability after direct current (DC) stress. The device structure and transfer characteristic curves are demonstrated in Figure 1(a) and (b) respectively. From results of DC PBS/NBS, a favorable stability indicating a great quality of gate insulator. Therefore, the positive threshold voltage shift is believed to be origin from electron trapping at the etching stop layer (ESL), since ESL possesses a relatively poor quality compared to the gate insulator. The charge trapping at etching stop layer could be confirmed by results of asymmetric source/drain metal under AC stress, illustrated in Figure 1(c). Please click Additional Files below to see the full abstract
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