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Search Results: 1 - 10 of 29270 matches for " Eng Wen Ong "
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Influence of Chemisorbed Oxygen on the Growth of Graphene on Cu(100) by Chemical Vapor Deposition
Zachary R. Robinson,Eng Wen Ong,Tyler R. Mowll,Parul Tyagi,D. Kurt Gaskill,Heike Geisler,Carl A. Ventrice Jr
Physics , 2014, DOI: 10.1021/jp410142r
Abstract: Understanding the influence that copper substrate surface symmetry and oxygen impurities have on the growth of graphene by chemical vapor deposition is important for developing techniques for producing high quality graphene. Therefore, we have studied the growth of graphene by catalytic decomposition of ethylene in an ultra-high vacuum chamber on both a clean Cu(100) surface and a Cu(100) surface pre-dosed with a layer of chemisorbed oxygen. The crystal structure of the graphene films was characterized with \emph{in-situ} low energy electron diffraction. By heating the clean Cu(100) substrate from room temperature to the growth temperature in ethylene, epitaxial graphene films were formed. The crystal quality was found to depend strongly on the growth temperature. At 900 $^\circ$C, well-ordered two-domain graphene films were formed. Pre-dosing the Cu(100) surface with a chemisorbed layer of oxygen before graphene growth was found to adversely affect the crystal quality of the graphene overlayer by inducing a much higher degree of rotational disorder of the graphene grains with respect to the Cu(100) substrate. The growth morphology of the graphene islands during the initial stages of nucleation was monitored with \emph{ex-situ} scanning electron microscopy. The nucleation rate of the graphene islands was observed to drop by an order of magnitude by pre-dosing the Cu(100) surface with a chemisorbed oxygen layer before growth. This reduction in nucleation rate results in the formation of much larger graphene islands. Therefore, the presence of oxygen during graphene growth affects both the relative orientation and average size of grains within the films grown on Cu(100) substrates.
A novel role of sesamol in inhibiting NF-κB-mediated signaling in platelet activation
Chao-Chien Chang, Wan-Jung Lu, Eng-Thiam Ong, Cheng-Wen Chiang, Song-Chow Lin, Shih-Yi Huang, Joen-Rong Sheu
Journal of Biomedical Science , 2011, DOI: 10.1186/1423-0127-18-93
Abstract: Platelet aggregation, Fura 2-AM fluorescence, and immunoblotting analysis were used in this study.NF-κB signaling events, including IKKβ phosphorylation, IκBα degradation, and p65 phosphorylation, were markedly activated by collagen (1 μg/ml) in washed human platelets, and these signaling events were attenuated by sesamol (2.5~25 μM). Furthermore, SQ22536 and ODQ, inhibitors of adenylate cyclase and guanylate cyclase, respectively, strongly reversed the sesamol (25 μM)-mediated inhibitory effects of IKKβ phosphorylation, IκBα degradation, and p65 phosphorylation stimulated by collagen. The protein kinase A (PKA) inhibitor, H89, also reversed sesamol-mediated inhibition of IκBα degradation. Moreover, BAY11-7082, an NF-κB inhibitor, abolished IκBα degradation, phospholipase C (PLC)γ2 phosphorylation, protein kinase C (PKC) activation, [Ca2+]i mobilization, and platelet aggregation stimulated by collagen. Preincubation of platelets with the inhibitors, SQ22536 and H89, both strongly reversed sesamol-mediated inhibition of platelet aggregation and [Ca2+]i mobilization.Sesamol activates cAMP-PKA signaling, followed by inhibition of the NF-κB-PLC-PKC cascade, thereby leading to inhibition of [Ca2+]i mobilization and platelet aggregation. Because platelet activation is not only linked to hemostasis, but also has a relevant role in inflammation and metastasis, our data demonstrating that inhibition of NF-κB interferes with platelet function may have a great impact when these types of drugs are considered for the treatment of cancer and various inflammatory diseases.Sesamol (3,4-methylenedioxyphenol) is a constituent of roasted sesame seeds, Sesamum indicum L., an important oilseed crop [1]. Sesamol is a potent phenolic antioxidant contained only in processed sesame oil. Several beneficial effects of sesamol were reported including antioxidation, chemoprevention, antimutagenic, and antihepatotoxic properties [2-5]. Traditionally, sesame seed oil was used to remove wrinkles a
Integral operators and univalent functions
Kiah Wah Ong,Sin Leng Tan,Yong Eng Tu
Tamkang Journal of Mathematics , 2012, DOI: 10.5556/j.tkjm.43.2012.215-221
Abstract: In this paper, we define two new integral operators $L^k$ and $L_k$ which are iterative in nature. We show that for $f(z)=z+a_2z^2+ cdots +a_nz^n +cdots$ with radius of convergence larger than one, $L^kf(z)$ and $L_kf(z)$ when restricted on $E={z:|z|<1}$ will eventually be univalent for large enough $k$. We then show that these are the best possible results by demonstrating that there exists a holomorphic function $T(z)$ in normalized form and with radius of convergence equal to one such that $L^kT(z)$ and $L_kT(z)$ fail to be univalent when restricted to $E$ for every $kin mathbb{N}$.
The Early Clinical Features of Dengue in Adults: Challenges for Early Clinical Diagnosis
Jenny G. H. Low,Adrian Ong,Li Kiang Tan,Shera Chaterji,Angelia Chow,Wen Yan Lim,Koon Wui Lee,Robert Chua,Choon Rong Chua,Sharon W. S. Tan,Yin Bun Cheung,Martin L. Hibberd,Subhash G. Vasudevan,Lee-Ching Ng,Yee Sin Leo,Eng Eong Ooi
PLOS Neglected Tropical Diseases , 2011, DOI: 10.1371/journal.pntd.0001191
Abstract: Background The emergence of dengue throughout the tropical world is affecting an increasing proportion of adult cases. The clinical features of dengue in different age groups have not been well examined, especially in the context of early clinical diagnosis. Methodology/Principal Findings We structured a prospective study of adults (≥18 years of age) presenting with acute febrile illness within 72 hours from illness onset upon informed consent. Patients were followed up over a 3–4 week period to determine the clinical outcome. A total of 2,129 adults were enrolled in the study, of which 250 (11.7%) had dengue. Differences in the rates of dengue-associated symptoms resulted in high sensitivities when the WHO 1997 or 2009 classification schemes for probable dengue fever were applied to the cohort. However, when the cases were stratified into age groups, fewer older adults reported symptoms such as myalgia, arthralgia, retro-orbital pain and mucosal bleeding, resulting in reduced sensitivity of the WHO classification schemes. On the other hand, the risks of severe dengue and hospitalization were not diminshed in older adults, indicating that this group of patients can benefit from early diagnosis, especially when an antiviral drug becomes available. Our data also suggests that older adults who present with fever and leukopenia should be tested for dengue, even in the absence of other symptoms. Conclusion Early clinical diagnosis based on previously defined symptoms that are associated with dengue, even when used in the schematics of both the WHO 1997 and 2009 classifications, is difficult in older adults.
Aldosteronoma causing Conn’s syndrome: a case report and literature review  [PDF]
Hsin-Hui Shao, Hock-Liew Eng, Wen-Sheng Huang, Joseph Nybo Lin
Health (Health) , 2009, DOI: 10.4236/health.2009.14043
Abstract: We report a case of primary aldosteronism caused by bilateral solitary aldosteronomas occurring 6 months apart, the diagnosis being confirmed by clinical features. Multiple aldos-terone-producing adenomas can be unilateral or bilateral. If bilateral, most of them are found simultaneously. Bilateral solitary aldosterono-mas occurring at separate times are rarely re-ported and the pathogenesis is still elusive. We believe, from this case, the postoperative fol-low-up in patients with primary aldosteronism is mandatory.
Inhibitory Potency of 8-Methoxypsoralen on Cytochrome P450 2A6 (CYP2A6) Allelic Variants CYP2A6*15, CYP2A6*16, CYP2A6*21 and CYP2A6*22: Differential Susceptibility Due to Different Sequence Locations of the Mutations
Kai Hung Tiong, Nafees Ahemad Mohammed Yunus, Beow Chin Yiap, Eng Lai Tan, Rusli Ismail, Chin Eng Ong
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086230
Abstract: Human cytochrome P450 2A6 (CYP2A6) is a highly polymorphic isoform of CYP2A subfamily. Our previous kinetic study on four CYP2A6 allelic variants (CYP2A6*15, CYP2A6*16, CYP2A6*21 and CYP2A6*22) have unveiled the functional significance of sequence mutations in these variants on coumarin 7-hydroxylation activity. In the present study, we further explored the ability of a typical CYP2A6 inhibitor, 8-methoxypsoralen (8-MOP), in inhibition of these alleles and we hypothesized that translational mutations in these variants are likely to give impact on 8-MOP inhibitory potency. The CYP2A6 variant and the wild type proteins were subjected to 8-MOP inhibition to yield IC50 values. In general, a similar trend of change in the IC50 and Km values was noted among the four mutants towards coumarin oxidation. With the exception of CYP2A6*16, differences in IC50 values were highly significant which implied compromised interaction of the mutants with 8-MOP. Molecular models of CYP2A6 were subsequently constructed and ligand-docking experiments were performed to rationalize experimental data. Our docking study has shown that mutations have induced enlargement of the active site volume in all mutants with the exception of CYP2A6*16. Furthermore, loss of hydrogen bond between 8-MOP and active site residue Asn297 was evidenced in all mutants. Our data indicate that the structural changes elicited by the sequence mutations could affect 8-MOP binding to yield differential enzymatic activities in the mutant CYP2A6 proteins.
Pharmacogenomics In Drug Therapy And Interaction: The Role Of Cytochrome P450
Chin-Eng Ong,Yan Pan,Kai-Hung Tiong,Beow-Chin Yiap
International e-Journal of Science, Medicine & Education , 2008,
Abstract: Pharmacogenomics (or pharmacogenetics),the study of the effects of genetic differences on aperson’s response to drugs, can help in optimizing drugefficacy and minimizing adverse drug reactions.Interperson difference in drug metabolism is one of theimportant consequences of such genetic variation. Thisvariation is determined in part by mutations incytochrome P450 enzymes (CYPs). IMU is part of amajor collaborative research project in the area ofphamacogenetics and drug metabolism. Workingtogether with USM and UiTM, our group has, since2000, generated useful population database on geneticpolymorphism of various CYP isoforms. We havesuccessfully genotyped three major ethnic groups,Malay, Indian and Chinese for their allelic frequency ofimportant isoforms. These include CYP2D6, CYP2C9,CYP2C8 and CYP2A6. Data generated so farcollectively have contributed to our effort in mappingand constructing genomic database for Malaysianpopulation.Since early 2002, our research has been focusing ondeveloping in vitro methods in studying the functionalconsequences of genetic polymorphism of CYP enzymes.Using site-directed mutagenesis, CYP mutants, carryingnucleotide changes as reported in known alleles inhuman populations, were generated and expressed inE. coli system, and the expressed recombinant proteinswere characterized using enzyme assays to determinethe functional consequences of mutations. We haveestablished a series of HPLC (high performance liquidchromatography)-based and fluorescence-based assaysto investigate CYP activities. Assays that have beendeveloped include tolbutamide methylhydroxylase,paclitaxel 6α-hydroxylase, dextromethorphanO-demethylation, testosterone 6β-hydroxylation andcoumarin 7-hydroxylase assays. These assays serve asactivity markers allowing comparison of catalyticactivities of mutant proteins generated. Another focusof our work is to use the developed assays as a screeningtool to investigate drug-herb interactions. This wasachieved by co-incubation of herbal extracts and activeconstituents with the probe substrates in the assays ollowed by characterization of the kinetic behaviors ofthe enzymes involved using various pharmacokineticparameters such as Km, Vmax, IC50 and Ki. This work iscurrently carried out with collaboration from theInstitute for Medical Research (IMR) and is supportedby MOSTI’s eScienceFund under RM9. It is envisagedthat this screening work will give us insights on thepotential of the commonly used herbs to causepharmacokinetic interactions with other drugsubstrates, and allow us to elucidate the mechanismsinvolved in the
Aging Effect to Accumulation of Lettucenin A in Lettuce after Elicitation with Various Abiotic Elicitors
Wen Dee Ong,Khim Phin Chong
Modern Applied Science , 2009, DOI: 10.5539/mas.v3n2p66
Abstract: A series of experiments were conducted to study the effect of age to accumulation of lettucenin A in lettuce (Lactuca sativa) after various elicitations. Lettuces were challenged with four different types of elicitation method; spray with silver nitrate (AgNO3) or copper sulfate (CuSO4), ultraviolet irradiation and freeze-thawed. Lettucenin A, a type of phytoalexin in lettuce accumulated with a higher concentration after challenged with chemical elicitors, silver nitrate (AgNO3) and copper sulfate (CuSO4). Physical elicitation with irradiation of short wavelength (254nm) ultraviolet radiation and freeze-thawed were also effective in eliciting the production of lettucenin A. However, the amounts were considerably lower compared to those elicited by chemical elicitors. Ultraviolet radiation and freeze-thawed stimulated lettuce to produce lettucenin A at a concentration of 1.52 μg/ml and 0.49 μg/ml respectively while AgNO3 and CuSO4 contributing to accumulation of 4.27 μg/ml and 4.26 μg/ml respectively. The elicitations of lettucenin A were both dependent on types of elicitor and the age of the plant. Treatments with AgNO3 and ultraviolet radiation both showed the same pattern production of lettucenin A. Lettucenin A accumulation increased significantly from week nine to the maximum at week twelve before it decreased to minimum at week eighteen. There is a week relation (R2= 0.69) between the accumulation of lettucenin A with the age of the lettuce with elicitation of silver nitrate. However, there is no relation with induction with ultraviolet radiation. Our results suggest lettuce produces the highest amount of lettucenin A after elicitation with chemical elicitors at twelve weeks old throughout the series of trial.
Distributed Phased Arrays and Wireless Beamforming Networks
David Jenn,Yong Loke,Tong Chin Hong Matthew,Yeo Eng Choon,Ong Chin Siang,Yeo Siew Yam
International Journal of Distributed Sensor Networks , 2009, DOI: 10.1080/15501320701863635
Abstract: Distributed phased arrays have advantages over conventional arrays in many radar and communication applications. Additional advantages are realized by replacing the microwave beamforming circuit by a wireless network, thus forming a wirelessly networked distributed sensor array. This article examines various aspects of a distributed phased array that incorporates wireless beamforming. First, the fundamental array theory and digital signal processing are reviewed. Basic equations are presented and compared to simulations for a ship-based radar application. Next the basic array architecture is described and the critical techniques and components that are required to realize the design are discussed. Methods are introduced for time and phase synchronization, transmit-receive isolation, sensor location issues, and bandwidth and frequency dispersion.
Image-guided versus blind corticosteroid injections in adults with shoulder pain: A systematic review
Edmund Soh, Wenyun Li, Keh Ong, Wen Chen, Dianne Bautista
BMC Musculoskeletal Disorders , 2011, DOI: 10.1186/1471-2474-12-137
Abstract: MEDLINE, the Cochrane Controlled Trials Register and EMBASE were searched to May 2010. Additional studies were identified by searching bibliographies of shortlisted articles. Search items included blind, landmark, anatomical, clinical exam, image-guided, ultrasound, fluoroscopy, steroid injection, frozen shoulder, random allocation, randomized controlled trial (RCT) and clinical trial.Randomized controlled studies comparing image-guided versus blind (landmark-guided) corticosteroid shoulder injections that examined pain, function and/or adverse events were included. Independent extraction was done by two authors using a form with pre-specified data fields, including risk of bias appraisal. Conflicts were resolved by discussion. The decision to pool data was based on assessment of clinical design homogeneity. When warranted, studies were pooled under a random-effects model.Two RCTs for pain, function and adverse events (n = 101) met eligibility criteria. No serious threats to validity were found. Both trials compared ultrasound-guided versus landmark-guided injections and were judged similar in clinical design. Low to moderate heterogeneity was observed: shoulder pain I2 = 60%, function I2 = 22%. A meta-analysis demonstrated greater improvement with ultrasound-guided injections at 6 weeks after injection in both pain (mean difference = 2.23 [95% CI: 1.27, 3.18]), as assessed with a 0 to 10 visual analogue scale, and shoulder function (standardised mean difference = 1.09 [95% CI: 0.61, 1.57]) as assessed with shoulder function scores. Although more adverse events (all mild) were reported with landmark-guided injections, the difference was not statistically significant (risk ratio = 0.20 [95% CI: 0.04, 1.13]).This review was only based on two moderate-sized trials. Blinding of patients was not performed in both trials, causing some risk of bias in outcome assessment since primary endpoints were wholly or partially patient-reported.There is a paucity of RCTs on image-gu
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