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Search Results: 1 - 10 of 10747 matches for " Jonathan Yap "
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Transcranial Doppler Ultrasound: A Review of the Physical Principles and Major Applications in Critical Care
Jawad Naqvi,Kok Hooi Yap,Gulraiz Ahmad,Jonathan Ghosh
International Journal of Vascular Medicine , 2013, DOI: 10.1155/2013/629378
Abstract: Transcranial Doppler (TCD) is a noninvasive ultrasound (US) study used to measure cerebral blood flow velocity (CBF-V) in the major intracranial arteries. It involves use of low-frequency (≤2?MHz) US waves to insonate the basal cerebral arteries through relatively thin bone windows. TCD allows dynamic monitoring of CBF-V and vessel pulsatility, with a high temporal resolution. It is relatively inexpensive, repeatable, and portable. However, the performance of TCD is highly operator dependent and can be difficult, with approximately 10–20% of patients having inadequate transtemporal acoustic windows. Current applications of TCD include vasospasm in sickle cell disease, subarachnoid haemorrhage (SAH), and intra- and extracranial arterial stenosis and occlusion. TCD is also used in brain stem death, head injury, raised intracranial pressure (ICP), intraoperative monitoring, cerebral microembolism, and autoregulatory testing. 1. Introduction Transcranial Doppler (TCD), first described in 1982 [1], is a noninvasive ultrasound (US) study that involves the use of a low-frequency (≤2?MHz) transducer probe to insonate the basal cerebral arteries through relatively thin bone windows. TCD allows dynamic monitoring of cerebral blood flow velocity (CBF-V) and vessel pulsatility over extended time periods with a high temporal resolution. It is relatively inexpensive, repeatable, and its portability offers increased convenience over other imaging methods, allowing continuous bedside monitoring of CBF-V, which is particularly useful in the intensive care setting [2]. The technique is however highly operator dependent, which can significantly limit its utility [3–6]. It also has a long learning curve to acquire the three-dimensional understanding of cerebrovascular anatomy necessary for competency [3]. Furthermore, approximately 10–20% of patients have inadequate transtemporal acoustic windows [2, 4, 7]. Current applications of TCD in adults and children include vasospasm in sickle cell disease [8], subarachnoid haemorrhage (SAH) [9], intra- and extracranial arterial stenosis and occlusion [10, 11], brain stem death [12], head injury, raised intracranial pressure (ICP) [13], intraoperative monitoring [14], impaired vasomotor function [15], and cerebral microembolism in right to left cardiac shunts [16]. TCD has also been widely used to investigate cerebral pressure autoregulation [17]. Combined with waveform morphology, indices derived from flow velocity readings such as Gosling’s pulsatility index (PI) and the Lindegaard ratio (LR) allow identification of increased
Knowledge, attitudes and practices towards pandemic influenza among cases, close contacts, and healthcare workers in tropical Singapore: a cross-sectional survey
Jonathan Yap, Vernon J Lee, Teng Yau, Tze Ng, Phern-Chern Tor
BMC Public Health , 2010, DOI: 10.1186/1471-2458-10-442
Abstract: We performed a cross-sectional knowledge, attitudes and practices survey in the Singapore military from mid-August to early-October 2009, among 3054 personnel in four exposure groups - laboratory-confirmed H1N1-2009 cases, close contacts of cases, healthcare workers, and general personnel.1063 (34.8%) participants responded. The mean age was 21.4 (SE 0.2) years old. Close contacts had the highest knowledge score (71.7%, p = 0.004) while cases had the highest practice scores (58.8%, p < 0.001). There was a strong correlation between knowledge and practice scores (r = 0.27, p < 0.01) and knowledge and attitudes scores (r = 0.21, p < 0.01). The significant predictors of higher practice scores were higher knowledge scores (p < 0.001), Malay ethnicity (p < 0.001), exposure group (p < 0.05) and lower education level (p < 0.05). The significant predictors for higher attitudes scores were Malay ethnicity (p = 0.014) and higher knowledge scores (p < 0.001). The significant predictor for higher knowledge score was being a contact (p = 0.007).Knowledge is a significant influence on attitudes and practices in a pandemic, and personal experience influences practice behaviors. Efforts should be targeted at educating the general population to improve practices in the current pandemic, as well as for future epidemics.In April 2009, a novel strain of Influenza A (H1N1) surfaced and has since spread widely across the globe with substantial clinical impact [1]. Effective pandemic management requires support from the population at risk for measures undertaken to mitigate the pandemic's spread. Previous studies during the Severe Acute Respiratory Syndrome (SARS) outbreak in 2003 have shown that individual beliefs and perceptions play an important role in subsequent desired behavior change [2,3]. Higher perceived effectiveness of measures undertaken [3,4] and higher perceived threat of the disease led to higher rates of positive behavioral change, and better knowledge also increased the
Evolution of the Retroviral Restriction Gene Fv1: Inhibition of Non-MLV Retroviruses
Melvyn W. Yap,Emily Colbeck,Scott A. Ellis,Jonathan P. Stoye
PLOS Pathogens , 2014, DOI: doi/10.1371/journal.ppat.1003968
Abstract: Fv1 is the prototypic restriction factor that protects against infection by the murine leukemia virus (MLV). It was first identified in cells that were derived from laboratory mice and was found to be homologous to the gag gene of an endogenous retrovirus (ERV). To understand the evolution of the host restriction gene from its retroviral origins, Fv1s from wild mice were isolated and characterized. Most of these possess intact open reading frames but not all restricted N-, B-, NR-or NB-tropic MLVs, suggesting that other viruses could have played a role in the selection of the gene. The Fv1s from Mus spretus and Mus caroli were found to restrict equine infectious anemia virus (EIAV) and feline foamy virus (FFV) respectively, indicating that Fv1 could have a broader target range than previously thought, including activity against lentiviruses and spumaviruses. Analyses of the Fv1 sequences revealed a number of residues in the C-terminal region that had evolved under positive selection. Four of these selected residues were found to be involved in the novel restriction by mapping studies. These results strengthen the similarities between the two capsid binding restriction factors, Fv1 and TRIM5α, which support the hypothesis that Fv1 defended mice against waves of retroviral infection possibly including non-MLVs as well as MLVs.
Novel Escape Mutants Suggest an Extensive TRIM5α Binding Site Spanning the Entire Outer Surface of the Murine Leukemia Virus Capsid Protein
Sadayuki Ohkura,David C. Goldstone,Melvyn W. Yap,Kate Holden-Dye,Ian A. Taylor,Jonathan P. Stoye
PLOS Pathogens , 2011, DOI: 10.1371/journal.ppat.1002011
Abstract: After entry into target cells, retroviruses encounter the host restriction factors such as Fv1 and TRIM5α. While it is clear that these factors target retrovirus capsid proteins (CA), recognition remains poorly defined in the absence of structural information. To better understand the binding interaction between TRIM5α and CA, we selected a panel of novel N-tropic murine leukaemia virus (N-MLV) escape mutants by a serial passage of replication competent N-MLV in rhesus macaque TRIM5α (rhTRIM5α)-positive cells using a small percentage of unrestricted cells to allow multiple rounds of virus replication. The newly identified mutations, many of which involve changes in charge, are distributed over the outer ‘top’ surface of N-MLV CA, including the N-terminal β-hairpin, and map up to 29 Ao apart. Biological characterisation with a number of restriction factors revealed that only one of the new mutations affects restriction by human TRIM5α, indicating significant differences in the binding interaction between N-MLV and the two TRIM5αs, whereas three of the mutations result in dual sensitivity to Fv1n and Fv1b. Structural studies of two mutants show that no major changes in the overall CA conformation are associated with escape from restriction. We conclude that interactions involving much, if not all, of the surface of CA are vital for TRIM5α binding.
Differing clinical characteristics between influenza strains among young healthy adults in the tropics
Jonathan Yap, Chi Tan, Alex R Cook, Jin Loh, Paul A Tambyah, Boon Tan, Vernon J Lee
BMC Infectious Diseases , 2012, DOI: 10.1186/1471-2334-12-12
Abstract: A febrile respiratory illness (FRI) (fever ≥ 37.5°C with cough and/or sore throat) surveillance program was started in 4 large military camps in Singapore on May 2009. Personnel with FRI who visited the camp clinics from 11 May 2009 to 25 June 2010 were recruited. Nasal washes and interviewer-administered questionnaires on demographic information and clinical features were obtained from consenting participants. All personnel who tested positive for influenza were included in the study. Overall symptom load was quantified by counting the symptoms or signs, and differences between strains evaluated using linear models.There were 434 (52.9%) pandemic H1N1-2009, 58 (7.1%) seasonal H3N2, 269 (32.8%) influenza B, and 10 (1.2%) seasonal H1N1 cases. Few seasonal influenza A (H1N1) infections were detected and were therefore excluded from analyses, together with undetermined influenza subtypes (44 (1.5%)), or more than 1 co-infecting subtype (6 (0.2%)). Pandemic H1N1-2009 cases had significantly fewer symptoms or signs (mean 7.2, 95%CI 6.9-7.4, difference 1.6, 95%CI 1.2-2.0, p < 0.001) than the other two subtypes (mean 8.7, 95%CI 8.5-9.0). There were no statistical differences between H3N2 and influenza B (p = 0.58). Those with nasal congestion, rash, eye symptoms, injected pharynx or fever were more likely to have H3N2; and those with sore throat, fever, injected pharynx or rhinorrhoea were more likely to have influenza B than H1N1-2009.Influenza cases have different clinical presentations in the young adult population. Pandemic H1N1 influenza cases had fewer and milder clinical symptoms than seasonal influenza. As we only included febrile cases and had no information on the proportion of afebrile infections, further research is needed to confirm whether the relatively milder presentation of pandemic versus seasonal influenza infections applies to all infections or only febrile illnesses.Influenza infections arising from different influenza strains may result in different c
Potential good reduction of degree 2 rational maps
Diane Yap
Mathematics , 2012,
Abstract: We give a complete characterization of degree two rational maps with potential good reduction over local fields. We show this happens exactly when the map corresponds to an integral point in the moduli space. We detail an algorithm by which to conjugate any degree two rational map corresponding to an integral point in the moduli space into a map with unit resultant. The local fields result is used to solve the same problem for fields over a principal ideal domain. Some additional results are given for degree 2 rational maps over the rationals.
Characterization of the Optical Properties of Heavy Metal Ions Using Surface Plasmon Resonance Technique  [PDF]
Yap Wing Fen, W. Mahmood Mat Yunus
Optics and Photonics Journal (OPJ) , 2011, DOI: 10.4236/opj.2011.13020
Abstract: The aim of this research is to characterize the optical properties of heavy metal ions (Hg2+, Cu2+, Pb2+ and Zn2+) using surface plasmon resonance (SPR) technique. Glass cover slips, used as substrates were coated with a 50 nm gold film using sputter coater. The measurement was carried out at room temperature using Kretchmann SPR technique. When the air medium outside the gold film is changed to heavy metal ions solution, the resonance angle shifted to the higher value for all samples of heavy metal ions solution. By our developed fitting program (using Matlab software), the experimental SPR curves were fitted to obtain the refractive index of Hg2+, Cu2+, Pb2+ and Zn2+ ions solution with different concentrations. Both the real and imaginary part of refractive index of the heavy metal ions solution increased with the concentration. The results give the basic idea such that the SPR technique could be used as an alternative optical sensor for detecting heavy metal ions in solution.
Controlling Chemotherapy-Induced Nausea and Vomiting with Neurokinin-1 Receptor Antagonists in Patients on AC-Based Chemotherapy—Are We There Yet?  [PDF]
Kevin Yap, Cassandra Leong, Alexandre Chan
Journal of Cancer Therapy (JCT) , 2012, DOI: 10.4236/jct.2012.31012
Abstract: Chemotherapy-induced nausea and vomiting (CINV) are distressing side effects of chemotherapy. Neurokinin-1 receptor antagonists (NK1-RAs) have been incorporated in the contemporary management of CINV. However, clinical studies on NK1-RAs have shown mixed results in reducing CINV risk. Most studies focused on the use of aprepitant (APR) and casopitant (CAS) in breast cancer patients receiving AC-type (doxorubicin and cyclophosphamide) chemotherapy. In this study, we compared the study design and clinical efficacies of these NK1-RAs in reducing CINV risk. Among the selected eight studies, 4 APR Randomized Controlled Trials (RCTs), 2 APR Observational Studies (OSs) and 2 CAS RCTs were identified. Patient-related characteristics such as the proportion of females (60.0% - 100.0%), age (46.5 - 59.5 years), histories of motion (5.6% - 47.0% in NK1-RA arms) and morning sicknesses (14.2% - 45.0% in NK1-RA arms) and types of antiemetic regimens; as well as chemotherapy-related characteristics such as the proportion of patients on AC chemotherapy (15.0% - 100.0%) varied greatly. In terms of efficacies, both APR and CAS improved overall CR and vomiting in majority of the studies. None of the studies, however, demonstrated that NK1-RA could provide adequate nausea control. To conclude, NK1-RAs are effective in improving vomiting and overall CR, but not useful in controlling nausea or attaining CC, the ideal CINV endpoint. A shift in paradigm is needed for future CINV research. As healthcare providers continue to strive for optimum CINV control in their patients, we hope this review can help them make better informed clinical decisions.
Face Recognition in the Presence of Expressions  [PDF]
Xia Han, Moi Hoon Yap, Ian Palmer
Journal of Software Engineering and Applications (JSEA) , 2012, DOI: 10.4236/jsea.2012.55038
Abstract: The purpose of this study is to enhance the algorithms towards the development of an efficient three dimensional face recognition system in the presence of expressions. The overall aim is to analyse patterns of expressions based on techniques relating to feature distances compare to the benchmarks. To investigate how the use of distances can help the recognition process, a feature set of diagonal distance patterns, were determined and extracted to distinguish face models. The significant finding is that, to solve the problem arising from data with facial expressions, the feature sets of the expression-invariant and expression-variant regions were determined and described by geodesic distances and Euclidean distances. By using regression models, the correlations between expressions and neutral feature sets were identified. The results of the study have indicated that our proposed analysis methods of facial expressions, was capable of undertaking face recognition using a minimum set of features improving efficiency and computation.
Reducing Fuel Consumption Using Flywheel Battery Technology for Rubber Tyred Gantry Cranes in Container Terminals  [PDF]
Kai Hou Tan, Yap Fook Fah
Journal of Power and Energy Engineering (JPEE) , 2017, DOI: 10.4236/jpee.2017.57002
Abstract: Flywheel Energy Storage System (FESS) is used as an energy regeneration system to help with reducing peak power requirements on RTG cranes that are used to load or unload container ships. Nevertheless, with the use of FESS, Port Operator can deploy undersized generator for new RTG as this will further reduce fuel consumption. This paper presents the investigation of the amount of energy and fuel consumption that can be reduced in Rubber Tyred Gantry (RTG) cranes in container terminals by the use of simulation. In addition, Variable Speed Generator is integrated to the simulation-hybridized RTG. Simulation results reveal that the total energy saving exceeded 30% relatively to conventional RTG. A hardware-in-loop system is introduced for the purpose of validating the simulation results. The hardware components procured include a FESS, a Variable Frequency Drive (VFD) and brake resistors.
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