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Search Results: 1 - 10 of 257584 matches for " C. Y. Tham "
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Wave Propagation in Lossy and Superconducting Circular Waveguides
K. H. Yeap,C. Y. Tham,K. C. Yeong,H. J. Woo
Radioengineering , 2010,
Abstract: We present an accurate approach to compute the attenuation of waves, propagating in circular waveguides with lossy and superconducting walls. A set of transcendental equation is developed by matching the fields at the surface of the wall with the electrical properties of the wall material. The propagation constant kz is found by numerically solving for the root of the equation. The complex conductivity of the superconductor is obtained from the Mattis-Bardeen equations. We have compared the loss of TE11 mode computed using our technique with that using the perturbation and Stratton’s methods. The results from the three methods agree very well at a reasonable range of frequencies above the cutoff. The curves, however, deviate below cutoff and at millimeter wave frequencies. We attribute the discrepancies to the dispersive effect and the presence of the longitudinal fields in a lossy waveguide. At frequencies below the gap, the superconducting waveguide exhibits lossless transmission behavior. Above the gap frequency, Cooper-pair breaking becomes dominant and the loss increases significantly.
Attenuation in Rectangular Waveguides with Finite Conductivity Walls
K. H. Yeap,C. Y. Tham,G. Yassin,K. C. Yeong
Radioengineering , 2011,
Abstract: We present a fundamental and accurate approach to compute the attenuation of electromagnetic waves propagating in rectangular waveguides with finite conductivity walls. The wavenumbers kx and ky in the x and y directions respectively, are obtained as roots of a set of transcendental equations derived by matching the tangential component of the electric field (E) and the magnetic field (H) at the surface of the waveguide walls. The electrical properties of the wall material are determined by the complex permittivity ε, permeability μ, and conductivity σ. We have examined the validity of our model by carrying out measurements on the loss arising from the fundamental TE10 mode near the cutoff frequency. We also found good agreement between our results and those obtained by others including Papadopoulos’ perturbation method across a wide range of frequencies, in particular in the vicinity of cutoff. In the presence of degenerate modes however, our method gives higher losses, which we attribute to the coupling between modes as a result of dispersion.
Effects of Nitrogen on Nodulation and Promiscuity in the Acacia mangium rhizobia Relationship
Irene Tham,F.Y. Tham
Asian Journal of Plant Sciences , 2007,
Abstract: Two strains of rhizobia, Bradyrhizobia sp. Aust 13c and Tel 8, which have dissimilar characteristics (antibiotic sensitivity and PCR-RFLP profiles) were tested for nodulation of Acacia mangium. Nodulation was carried out on in vitro seedlings growing in Broughton-Dilworth medium supplemented with different levels of nitrogen at 7, 18 and 180 ppm. Control seedlings were grown in nitrogen free nutrient solution. A total of 70 nodules were harvested, with DNA extraction from bacteria in nodules carried out and PCR-RFLP generated. A. mangium seedlings inoculated with a mixture of equal volumes of the two nitrogen fixing bacteria strains, Aust 13c and Tel 8 had 35.7% of the nodules infected only with Aust 13c, 14.3% infected singly with Tel 8 and none doubly infected with both Aust 13c and Tel 8 in medium without nitrogen. Higher levels of nitrogen were found to decrease the percentage of single and increase the percentage of double infection. Our results suggest that increasing nitrogen levels altered the promiscuity of the legume-rhizobia relationship.
Silencing of miR-34a Attenuates Cardiac Dysfunction in a Setting of Moderate, but Not Severe, Hypertrophic Cardiomyopathy
Bianca C. Bernardo, Xiao-Ming Gao, Yow Keat Tham, Helen Kiriazis, Catherine E. Winbanks, Jenny Y. Y. Ooi, Esther J. H. Boey, Susanna Obad, Sakari Kauppinen, Paul Gregorevic, Xiao-Jun Du, Ruby C. Y. Lin, Julie R. McMullen
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0090337
Abstract: Therapeutic inhibition of the miR-34 family (miR-34a,-b,-c), or miR-34a alone, have emerged as promising strategies for the treatment of cardiac pathology. However, before advancing these approaches further for potential entry into the clinic, a more comprehensive assessment of the therapeutic potential of inhibiting miR-34a is required for two key reasons. First, miR-34a has ~40% fewer predicted targets than the miR-34 family. Hence, in cardiac stress settings in which inhibition of miR-34a provides adequate protection, this approach is likely to result in less potential off-target effects. Secondly, silencing of miR-34a alone may be insufficient in settings of established cardiac pathology. We recently demonstrated that inhibition of the miR-34 family, but not miR-34a alone, provided benefit in a chronic model of myocardial infarction. Inhibition of miR-34 also attenuated cardiac remodeling and improved heart function following pressure overload, however, silencing of miR-34a alone was not examined. The aim of this study was to assess whether inhibition of miR-34a could attenuate cardiac remodeling in a mouse model with pre-existing pathological hypertrophy. Mice were subjected to pressure overload via constriction of the transverse aorta for four weeks and echocardiography was performed to confirm left ventricular hypertrophy and systolic dysfunction. After four weeks of pressure overload (before treatment), two distinct groups of animals became apparent: (1) mice with moderate pathology (fractional shortening decreased ~20%) and (2) mice with severe pathology (fractional shortening decreased ~37%). Mice were administered locked nucleic acid (LNA)-antimiR-34a or LNA-control with an eight week follow-up. Inhibition of miR-34a in mice with moderate cardiac pathology attenuated atrial enlargement and maintained cardiac function, but had no significant effect on fetal gene expression or cardiac fibrosis. Inhibition of miR-34a in mice with severe pathology provided no therapeutic benefit. Thus, therapies that inhibit miR-34a alone may have limited potential in settings of established cardiac pathology.
Anti-quorum sensing and antimicrobial activities of some traditional Chinese medicinal plants commonly used in South-East Asia
Yeo, S.S.M,Tham, F.Y.
Malaysian Journal of Microbiology , 2012,
Abstract: Aims: Traditional Chinese medicine (TCM) has been used for relief and treatment of ailments dating back thousands of years and continues to the present day, with rapidly increasing interest in evidence-based evaluation of its efficacy. Studies of TCM plants have demonstrated that several have antimicrobial properties but few have explored their anti-quorum sensing potential. Quorum sensing (QS), also known as bacterial cell-to-cell communication, is used by a number of opportunistic pathogenic bacteria in the regulation of virulence expression. Compounds that interfere with QS signals and attenuate bacterial virulence without killing them may offer an alternative therapeutic solution with less pressure of antibiotic resistance developing. This study screened TCM plants for anti-quorum sensing properties and antimicrobial activities.Methodology and Results: Twenty TCM plants commonly used in South-East Asia were screened for QS inhibitors using two biomonitor strains, Chromobacterium violaceum CV026 and Pseudomonas aeruginosa PAO1. Ten of these selected TCM plant (50%) were found to have QS inhibitory properties: Angelica sinensis (Umbelliferae), Cnidium monnieri (Umbelliferae), Astragalus membranaceus (Leguminosae), Crataegus cuneata (Rosaceae), Dioscorea nipponica (Dioscoreaceae), Lilium brownii (Liliaceae), Aloe barbadensis (Liliaceae), Magnolia officinalis (Magnoliaceae), Ephedra sinica (Ephedraceae) and Panax pseudoginseng (Araliaceae). Of these, six (30%) also showed varying antimicrobial activity against C. violaceum and P. aeruginosa.Conclusion, significance and impact of study: The results suggest that traditional Chinese medicinal plants could be a prospective source to explore for useful compounds in the fight against bacterial infections.
Blended Learning: Is Game-Based Learning an Effective Instructional Strategy to Engage Students in Higher Education in Singapore? A Pilot Study
Lesley Tham,Raymond Tham
Journal of the Research Center for Educational Technology , 2012,
Abstract: Today’s Internet Generation is accustomed to multi-tasking, graphics, fun, and fantasy. Educators in Asia are finding it increasingly challenging to engage and motivate students with traditional modes of teaching. One tool that may help them in this endeavor is game-based learning, which is beginning to catch on in K-12 schools and higher education. This paper examined whether game-based learning is an effective instructional strategy for engaging and motivating students in higher education in Singapore. Findings indicate that game-based learning can be a useful strategy to motivate students, because the challenge of a game fosters competition between groups and collaboration within groups.
Ambulatory Oxygen in Chronic Obstructive Pulmonary Disease  [PDF]
Kah Yee Tham, Devanand Anantham
Open Journal of Respiratory Diseases (OJRD) , 2011, DOI: 10.4236/ojrd.2011.12002
Abstract: Ambulatory oxygen has been shown to improve pulmonary hemodynamics and reduce dynamic hyperinflation in patients with Chronic Obstructive Pulmonary Disease. Therefore, it is hypothesized to be of benefit in patients with either exertional desaturation or dyspnoea. There is evidence of short-term improvements in exercise distance, exercise time, breathlessness, oxygen saturation and minute ventilation. However, longer term studies only identified improvements in oxygenation and minute ventilation. The benefits were even more limited in patients with no resting hypoxemia. The role in improving exercise training in pulmonary rehabilitation by increasing exercise time and reducing dyspnoea was marginal and no improvements were detected in walking distance or quality of life. Practical considerations make compliance with ambulatory oxygen therapy a major issue with the weight of oxygen and social unacceptability the most often quoted problems. The evidence for any benefit of ambulatory oxygen is therefore limited despite the theoretical benefits.
Interrelation between Climate and Dengue in Malaysia  [PDF]
Bryan Paul, Wai Liang Tham
Health (Health) , 2015, DOI: 10.4236/health.2015.76080
Abstract: Dengue cases in Malaysia are on the rise and have worsened since last decade, and this has generally been attributed to human actions. However, the effects of climate in this situation have been under-mentioned. We argue that climate also plays a role in spreading dengue transmission and multiple studies have shown that climate and transmission of infectious diseases are closely interconnected. Our evaluation examines how local climate influences dengue transmission by studying two parameters, specifically local average surface temperature and average precipitation, and we assume that a changing climate will influence the number of reported dengue cases and mortality rates. We also study the potential impact of climate change on the transmission of dengue and its distribution over a large geographical region, and have found that dengue and infectious diseases in general tend to be widespread in regions with higher or increasing surface temperature.
Controlling Dengue: Effectiveness of Biological Control and Vaccine in Reducing the Prevalence of Dengue Infection in Endemic Areas  [PDF]
Bryan Paul, Wai Liang Tham
Health (Health) , 2016, DOI: 10.4236/health.2016.81008
Abstract: With the increased prevalence of dengue infection in tropical countries, concerned members of the public are now pressing their local health ministries to act immediately and effectively in managing the rising numbers of reported cases. This includes reviews of the methodologies and the effectiveness of current combative systems to find other possible novel approaches that might yield better results. One of those novel approaches is the integration of a parasite into mosquito vector, manipulating the parasite-host interaction to reduce the transmission of dengue in endemic hotspots. Another alternative is by Sanofi-Pasteur’s dengue vaccine that showed over 60.8% success rate in reducing severe dengue infection in children aged 9 - 16 during its final clinical implementation phase. This report will compare and contrast these two novel ideas to determine which of the approaches are more likely to be effective in the long run. The aspects covered will include the application, effectiveness, functionality, and problems with these approaches. The results could then be utilised by governments or organizations to select precise and effective methods in reducing the prevalence of dengue infections in their countries.
H gskolan - en demokratisk kunskapsmilj ?(
Carl Tham
Utbildning & Demokrati : Tidsskrift f?r Didaktik och Utbildningspolitik , 2000,
Abstract:
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