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Energy Band Gap Modulation in Nd-Doped BiFeO3/SrRuO3 Heteroepitaxy for Visible Light Photoelectrochemical Activity

Tan KH, Chen YW, Van CN, Wang H, Chen JW, Lim FS, et al.

ACS Appl Mater Interfaces, 2019 Jan 09;11(1):1655-1664.
PMID: 30561192 DOI: 10.1021/acsami.8b17758

The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer and thus altering the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principle calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron-hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.
Fulltext An intelligent payment card fraud detection system

Seera M, Lim CP, Kumar A, Dhamotharan L, Tan KH

Ann Oper Res, 2021 Jun 08.
PMID: 34121790 DOI: 10.1007/s10479-021-04149-2

Payment cards offer a simple and convenient method for making purchases. Owing to the increase in the usage of payment cards, especially in online purchases, fraud cases are on the rise. The rise creates financial risk and uncertainty, as in the commercial sector, it incurs billions of losses each year. However, real transaction records that can facilitate the development of effective predictive models for fraud detection are difficult to obtain, mainly because of issues related to confidentially of customer information. In this paper, we apply a total of 13 statistical and machine learning models for payment card fraud detection using both publicly available and real transaction records. The results from both original features and aggregated features are analyzed and compared. A statistical hypothesis test is conducted to evaluate whether the aggregated features identified by a genetic algorithm can offer a better discriminative power, as compared with the original features, in fraud detection. The outcomes positively ascertain the effectiveness of using aggregated features for undertaking real-world payment card fraud detection problems.
Brain Tumor: A Review of Its Demographic in a Rural Hospital of Sibu in Sarawak, Malaysia

Heng YW, Tan KH, Yap NKB

Asian J Neurosurg, 2023 Mar;18(1):1-4.
PMID: 37056909 DOI: 10.1055/s-0043-1760855

According to World Health Organization's GLOBOCAN 2012 database, brain tumors account for about 2% of all cancers in Malaysia. It was ranked 11th and 13th most common cancer among males and females, respectively. This debilitating disease can cause a tremendous burden to patients and their families and healthcare services. The main objective of this study is to provide demographic data on the type of brain tumors and their distribution of age and gender from the cases presented to the neurosurgical department of a rural hospital in Sibu from 2018 to 2021. This is a retrospective study of the incidence and pattern of brain tumors admitted to the Neurosurgery Department in Sibu Hospital. Data were emanated from the brain tumor registry census from 2018 to 2021. Of all cases, only cases with confirmed histopathological results were included. Inoperable brain tumors that were diagnosed through radiological investigations were excluded. There were 230 patients with brain tumors included in this study. Males constituted 42.6% ( n = 98) of the cases, whereas 57.4% ( n = 132) of them were female. The brain tumor was the least common in the pediatric group (0 to 10 years old) with only 3.5% ( n = 8). The incidence of brain tumors increased with age and reached its peak in the age group of 51 to 60 years (34.8%). The commonest type of brain tumor was meningioma (38.7%), followed by a metastatic brain tumor (25.2%) and glioma (15.6%). Meningothelial WHO grade I was the most common variant that accounted for 67% ( n = 46) of all meningioma. Lung carcinoma was found to be the most common primary, accounting for more than half (69.0%) of the metastatic brain tumors, followed by breast cancer (10.3%), thyroid cancer (8.6%), female genital tract (8.6%), and malignant melanoma (3.5%). The crude incidence of the brain tumor in Sibu was 4.98 per 100,000 population/year. This study showed that the commonest brain tumor in central rural of Sarawak was meningioma, followed by metastatic brain tumor and glioma. Meningothelial is the most frequent subtype of meningioma, whereas lung carcinoma was the commonest primary in brain metastases. The peak age group was 51 to 60 years old, and females showed a higher incidence than males. This study provides a baseline profile of the brain tumor spectrum in rural Sarawak. More data should be collected to aid in future research and healthcare planning.
Fulltext Ethnic differences translate to inadequacy of high-risk screening for gestational diabetes mellitus in an Asian population: a cohort study

Chong YS, Cai S, Lin H, Soh SE, Lee YS, Leow MK, et al.

BMC Pregnancy Childbirth, 2014 Oct 02;14:345.
PMID: 25273851 DOI: 10.1186/1471-2393-14-345

BACKGROUND: Universal and high-risk screening for gestational diabetes mellitus (GDM) has been widely studied and debated. Few studies have assessed GDM screening in Asian populations and even fewer have compared Asian ethnic groups in a single multi-ethnic population.
METHODS: 1136 pregnant women (56.7% Chinese, 25.5% Malay and 17.8% Indian) from the Growing Up in Singapore Towards healthy Outcomes (GUSTO) birth cohort study were screened for GDM by 75-g oral glucose tolerance test (OGTT) at 26-28 weeks of gestation. GDM was defined using the World Health Organization (WHO) criteria. High-risk screening is based on the guidelines of the UK National Institute for Health and Clinical Excellence.
RESULTS: Universal screening detected significantly more cases than high-risk screening [crude OR 2.2 (95% CI 1.7-2.8)], particularly for Chinese women [crude OR = 3.5 (95% CI 2.5-5.0)]. Pre-pregnancy BMI > 30 kg/m2 (adjusted OR = 3.4, 95% CI 1.5-7.9) and previous GDM history (adjusted OR = 6.6, 95% CI 1.2-37.3) were associated with increased risk of GDM in Malay women while GDM history was the only significant risk factor for GDM in Chinese women (adjusted OR = 4.7, 95% CI 2.0-11.0).
CONCLUSION: Risk factors used in high-risk screening do not sufficiently predict GDM risk and failed to detect half the GDM cases in Asian women. Asian women, particularly Chinese, should be screened to avoid under-diagnosis of GDM and thereby optimize maternal and fetal outcomes.
Fulltext Impact of adopting the 2013 World Health Organization criteria for diagnosis of gestational diabetes in a multi-ethnic Asian cohort: a prospective study

Chi C, Loy SL, Chan SY, Choong C, Cai S, Soh SE, et al.

BMC Pregnancy Childbirth, 2018 03 21;18(1):69.
PMID: 29562895 DOI: 10.1186/s12884-018-1707-3

BACKGROUND: We assessed the impact of adopting the 2013 World Health Organization (WHO) diagnostic criteria on the rates of gestational diabetes (GDM), pregnancy outcomes and identification of women at future risk of type 2 diabetes.
METHODS: During a period when the 1999 WHO GDM criteria were in effect, pregnant women were universally screened using a one-step 75 g 2-h oral glucose tolerance test at 26-28 weeks' gestation. Women were retrospectively reclassified according to the 2013 criteria, but without the 1-h glycaemia measurement. Pregnancy outcomes and glucose tolerance at 4-5 years post-delivery were compared for women with GDM classified by the 1999 criteria alone, GDM by the 2013 criteria alone, GDM by both criteria and without GDM by both sets of criteria.
RESULTS: Of 1092 women, 204 (18.7%) and 142 (13.0%) were diagnosed with GDM by the 1999 and 2013 WHO criteria, respectively, with 27 (2.5%) reclassified to GDM and 89 (8.2%) reclassified to non-GDM when shifting from the 1999 to 2013 criteria. Compared to women without GDM by both criteria, cases reclassified to GDM by the 2013 criteria had an increased risk of neonatal jaundice requiring phototherapy (relative risk (RR) = 2.78, 95% confidence interval (CI) 1.32, 5.86); despite receiving treatment for GDM, cases reclassified to non-GDM by the 2013 criteria had higher risks of prematurity (RR = 2.17, 95% CI 1.12, 4.24), neonatal hypoglycaemia (RR = 3.42, 95% CI 1.04, 11.29), jaundice requiring phototherapy (RR = 1.71, 95% CI 1.04, 2.82), and a higher rate of abnormal glucose tolerance at 4-5 years post-delivery (RR = 3.39, 95% CI 2.30, 5.00).
CONCLUSIONS: Adoption of the 2013 WHO criteria, without the 1-h glycaemia measurement, reduced the GDM rate. Lowering the fasting glucose threshold identified women who might benefit from treatment, but raising the 2-h threshold may fail to identify women at increased risk of adverse pregnancy and future metabolic outcomes.
TRIAL REGISTRATION: NCT01174875 . Registered 1 July 2010 (retrospectively registered).
Fulltext birgHPC: creating instant computing clusters for bioinformatics and molecular dynamics

Chew TH, Joyce-Tan KH, Akma F, Shamsir MS

Bioinformatics, 2011 May 1;27(9):1320-1.
PMID: 21398666 DOI: 10.1093/bioinformatics/btr109

birgHPC, a bootable Linux Live CD has been developed to create high-performance clusters for bioinformatics and molecular dynamics studies using any Local Area Network (LAN)-networked computers. birgHPC features automated hardware and slots detection as well as provides a simple job submission interface. The latest versions of GROMACS, NAMD, mpiBLAST and ClustalW-MPI can be run in parallel by simply booting the birgHPC CD or flash drive from the head node, which immediately positions the rest of the PCs on the network as computing nodes. Thus, a temporary, affordable, scalable and high-performance computing environment can be built by non-computing-based researchers using low-cost commodity hardware.
Bioactive fractions containing methyl eugenol-derived sex pheromonal components in haemolymph of the male fruit fly Bactrocera dorsalis (Diptera: Tephritidae)

Hee AK, Tan KH

Bull. Entomol. Res., 2005 Dec;95(6):615-20.
PMID: 16336709 DOI: 10.1079/BER2005392

Sex pheromonal components of the tephritid fruit fly Bactrocera dorsalis (Hendel), 2-allyl-4,5-dimethoxyphenol and (E)-coniferyl alcohol, are biosynthesized from a highly potent male attractant, methyl eugenol, then sequestered and stored in the rectal gland prior to their release during courtship at dusk. These sex pheromonal components have been detected in the haemolymph and crop organ. Hence, attempts were made to separate and identify the haemolymph fractions which contained the sex pheromonal components. Identification of these bioactive fractions in methyl eugenol-fed male flies using gel filtration column chromatography and biodetection using live male flies showed two fractions as highly attractive to conspecific males. These fractions show a significant increase in protein absorbance in the elution profile of haemolymph from methyl eugenol-fed males compared with that from methyl eugenol-deprived males. The molecular mass of these bioactive fractions as determined by using gel filtration was in the peptide range of 3.3 to 5.5 kDa. Subsequent gas chromatography-mass spectrometry analyses further confirmed the presence of the pheromonal components in the bioactive fractions. The presence of these methyl eugenol-derived sex pheromonal components in specific haemolymph fractions suggests the involvement of a sex pheromone binding complex.
Recaptures of feral Bactrocera dorsalis and B. umbrosa (Diptera: Tephritidae) males after feeding on methyl eugenol

Tan KH

Bull. Entomol. Res., 2019 Jun 13.
PMID: 31190651 DOI: 10.1017/S0007485319000208

Two major fruit fly pest species, Bactrocera dorsalis and B. umbrosa, are strongly attracted to methyl eugenol (ME) found in >450 plant species. They are, however, exclusive pollinators of certain daciniphilous (attracting Dacini fruit flies) Bulbophyllum orchids. A comparison between the recaptures of feral males after feeding ad libitum on 0.6 mg ME (simulating an average floral quantity of an orchid flower - Trial 1) and 480 mg in Trial 2 was investigated using the non-invasive capture-mark-release-recapture (CMRR) technique. Based on daily CMRR over a 16-day period, using a different colour enamel paint each day, percentages of B. dorsalis males recaptured in Trial 1 were significantly higher than those in Trial 2. However, for B. umbrosa, percentages of recaptures for different day-specific colours were highly variable due to low fly numbers captured/day. In Trial 1, of 756 B. dorsalis males released, 36.4% were recaptured once, 7.7 twice, 2.4 three times and 0.4 four times. While in Trial 2 of 1157 released males, 6% were recaptured once and 0.3% twice. Of 67 B. umbrosa males released, 28.4% were recaptured once and none more than once in Trial 1. Nevertheless, of 119 flies released in Trial 2, 25.2% were recaptured once and 3.3% twice. Overall, many marked males did return to a single ME-source to 'refuel' ME (a sex pheromone precursor). The results also show that a relatively high number of flies paid multi-visitations to a single 0.6 mg ME-source and indicate that the presence of natural ME-sources may impact area-wide IPM programmes.
Evolution of Vanadium Redox Flow Battery in Electrode

Hossain MH, Abdullah N, Tan KH, Saidur R, Mohd Radzi MA, Shafie S

Chem Rec, 2024 Jan;24(1):e202300092.
PMID: 37144668 DOI: 10.1002/tcr.202300092

The vanadium redox flow battery (VRFB) is a highly regarded technology for large-scale energy storage due to its outstanding features, such as scalability, efficiency, long lifespan, and site independence. This paper provides a comprehensive analysis of its performance in carbon-based electrodes, along with a comprehensive review of the system's principles and mechanisms. It discusses potential applications, recent industrial involvement, and economic factors associated with VRFB technology. The study also covers the latest advancements in VRFB electrodes, including electrode surface modification and electrocatalyst materials, and highlights their effects on the VRFB system's performance. Additionally, the potential of two-dimensional material MXene to enhance electrode performance is evaluated, and the author concludes that MXenes offer significant advantages for use in high-power VRFB at a low cost. Finally, the paper reviews the challenges and future development of VRFB technology.
Fulltext High folate and low vitamin B12 status during pregnancy is associated with gestational diabetes mellitus

Lai JS, Pang WW, Cai S, Lee YS, Chan JKY, Shek LPC, et al.

Clin Nutr, 2018 06;37(3):940-947.
PMID: 28381340 DOI: 10.1016/j.clnu.2017.03.022

BACKGROUND & AIMS: B-vitamins and homocysteine may contribute to the development of gestational diabetes mellitus (GDM), but existing studies are inconsistent. We examined the cross-sectional associations of plasma folate, vitamins B6, B12, and homocysteine concentrations with GDM and glycemia in a sample of multi-ethnic Asian pregnant women.
METHODS: Plasma concentrations of folate, vitamins B6, B12, homocysteine and glucose were measured at 26-weeks' gestation in 913 pregnant women. GDM was diagnosed using the 1999 World Health Organization criteria. Associations were examined with linear or logistic regression, adjusted for confounders and stratified by ethnicity.
RESULTS: Higher plasma folate was associated with higher 2-h glucose and higher odds of GDM [0.15 (0.02, 0.23) per 1-SD increment in folate, OR 1.29 (1.00, 1.60)], mainly among Indian mothers. Higher plasma vitamin B12 and homocysteine were associated with lower fasting and 2-h glucose, and lower odds of GDM [-0.04 (-0.07, -0.01) per 1-SD increment in B12 and -0.09 (-0.18, -0.003) respectively, OR: 0.81 (0.68, 0.97); -0.05 (-0.08, -0.02) per 1-SD increment in homocysteine and -0.12 (-0.21, -0.02) respectively, OR: 0.76 (0.62, 0.92)]. The highest odds of GDM were observed among women with combined vitamin B12 insufficiency and high folate concentration [OR: 1.97 (1.05, 3.68)]. An association between higher vitamin B6 and higher 2-h glucose shifted towards null adjusting for other B-vitamins.
CONCLUSIONS: Higher maternal folate coupled with vitamin B12 insufficiency was associated with higher GDM risk. This finding has potential implications for antenatal supplement recommendations but will require confirmation in future studies.
Transport of methyl eugenol-derived sex pheromonal components in the male fruit fly, Bactrocera dorsalis

Kah-Wei Hee A, Tan KH

Comp Biochem Physiol C Toxicol Pharmacol, 2006 Aug;143(4):422-8.
PMID: 16750428 DOI: 10.1016/j.cbpc.2006.04.009

Males of Bactrocera dorsalis (Diptera: Tephritidae) are attracted strongly to and feed compulsively on methyl eugenol (1,2-dimethoxy- 4 -(2-propenyl)benzene), a highly potent male attractant. Pharmacophagy of methyl eugenol results in the production of phenylpropanoids 2-allyl-4,5-dimethoxyphenol and (E)-coniferyl alcohol that are sequestered and stored in the rectal gland prior to release as sex pheromonal components during mating at dusk. While these pheromonal components have also been detected in the hemolymph and crop of methyl eugenol-fed males, there is currently little information on the transport of these compounds from the crop to rectal gland in male B. dorsalis. Therefore, using physiological techniques such as parabiosis, rectal gland transplantation and hemolymph transfusion coupled with gas chromatography-mass spectrometry (GC-MS) analyses, we were able to ascertain and confirm the role of the hemolymph in the transport of these sex pheromonal components from the crop to the rectal gland. Further, the temporal profile of these methyl eugenol-derived bioactive compounds in the hemolymph also shows an increase with time post-methyl eugenol-feeding, i.e., 2-allyl-4,5-dimethoxyphenol attaining maximum amounts 15 min after ME consumption and decreasing thereafter, while for (E)-coniferyl alcohol-the increase and decrease are more gradual. These results further demonstrate the ability of insect hemolymph to transport many diverse forms of bioactive molecules including attractant-derived sex pheromonal components.
Comparative Trap Catches of Male Bactrocera, Dacus, and Zeugodacus Fruit Flies (Diptera: Tephritidae) With Four Floral Phenylbutanoid Lures (Anisyl Acetone, Cue-Lure, Raspberry Ketone, and Zingerone) in Queensland, Australia

Royer JE, Tan KH, Mayer DG

Environ Entomol, 2020 08 20;49(4):815-822.
PMID: 32514581 DOI: 10.1093/ee/nvaa056

The male fruit fly attractants, cue-lure (CL) and raspberry ketone (RK), are important in pest management. These volatile phenylbutanoids occur in daciniphilous Bulbophyllum Thouar (Orchidaceae: Asparagales) orchids, along with zingerone (ZN) and anisyl acetone (AA). While these four compounds attract a similar range of species, their relative attractiveness to multiple species is unknown. We field tested these compounds in two fruit fly speciose locations in north Queensland, Australia (Lockhart and Cairns) for 8 wk. Of 16 species trapped in significant numbers, 14 were trapped with CL and RK, all in significantly greater numbers with CL traps than RK traps (at least in higher population locations). This included the pest species Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (CL catches ca. 5× > RK), Bactrocera neohumeralis (Hardy) (Diptera: Tephritidae) and Bactrocera bryoniae (Tryon) (Diptera: Tephritidae) (CL catches ca. 3× > RK), and Bactrocera frauenfeldi (Schiner) (Diptera: Tephritidae) (in Cairns-CL catches ca. 1.6× > RK). Seven species were trapped with AA, and all were also caught in CL and RK traps in significantly greater numbers, with the exception of B. frauenfeldi. For this species, catches were not statistically different with CL, RK, and AA in Lockhart, and RK and AA in Cairns. Seven species were trapped with ZN, two at this lure only, and the remainder also with CL or RK but in significantly greater numbers. This is the first quantitative comparison of the relative attractiveness of CL, RK, AA, and ZN against multiple species, and supports the long-held but untested assumption that CL is broadly more attractive lure than RK.
Fulltext Cloning and Characterization of the Autoinducer Synthase Gene from Lipid-Degrading Bacterium Cedecea neteri

Tan KH, How KY, Tan JY, Yin WF, Chan KG

Front Microbiol, 2017;8:72.
PMID: 28197135 DOI: 10.3389/fmicb.2017.00072

The process of intercellular communication among bacteria, termed quorum sensing (QS), is mediated by small diffusible molecules known as the autoinducers. QS allows the population to react to the change of cell density in unison, in processes such as biofilm formation, plasmid conjugation, virulence, motility and root nodulation. In Gram-negative proteobacteria, N-acyl homoserine lactone (AHL) is the common "language" to coordinate gene expression. This signaling molecule is usually synthesized by LuxI-type proteins. We have previously discovered that a rare bacterium, Cedecea neteri, exhibits AHL-type QS activity. With information generated from genome sequencing, we have identified the luxIR gene pair responsible for AHL-type QS and named it cneIR. In this study, we have cloned and expressed the 636 bp luxI homolog in an Escherichia coli host for further characterization. Our findings show that E. coli harboring cneI produced the same AHL profile as the wild type C. neteri, with the synthesis of AHL known as N-butyryl-homoserine lactone. This 25 kDa LuxI homolog shares high similarity with other AHL synthases from closely related species. This work is the first documentation of molecular cloning and characterization of luxI homolog from C. neteri.
Fulltext Draft Genome Sequence of a Quorum-Sensing Bacterium, Dickeya sp. Strain 2B12, Isolated from a Freshwater Lake

Tan KH, Sheng KY, Chang CY, Yin WF, Chan KG

Genome Announc, 2015;3(1).
PMID: 25657288 DOI: 10.1128/genomeA.01542-14

Dickeya sp. strain 2B12 was isolated from a freshwater lake in Malaysia. Here, we report the draft genome sequence of Dickeya sp. 2B12 sequenced by the Illumina MiSeq platform. With the genome sequence available, this genome sequence will be useful for the study of quorum-sensing activity in this isolate.
Fulltext Complete Genome Sequence of Cedecea neteri Strain SSMD04, a Bacterium Isolated from Pickled Mackerel Sashimi

Chan KG, Tan KH, Yin WF, Tan JY

Genome Announc, 2014;2(6).
PMID: 25523782 DOI: 10.1128/genomeA.01339-14

We report here the complete genome sequence of C. neteri SSMD04, a strain isolated from pickled mackerel sashimi, sequenced by third-generation sequencing technology. To the best of our knowledge, this is the first documentation that reports the complete genome of Cedecea neteri.
Fulltext Analysis of Pectate Lyase Genes in Dickeya chrysanthemi Strain L11, Isolated from a Recreational Lake in Malaysia: a Draft Genome Sequence Perspective

Chan KG, Kher HL, Chang CY, Yin WF, Tan KH

Genome Announc, 2015;3(2).
PMID: 25792063 DOI: 10.1128/genomeA.00145-15

Dickeya chrysanthemi is well known as a plant pathogen that caused major blackleg in the European potato industry in the 1990s. D. chrysanthemi strain L11 was discovered in a recreational lake in Malaysia. Here, we present its draft genome sequence.
Clinical practice of vitamin D screening and supplementation in pregnancy in Asia-pacific countries: A cross-sectional study

Lee RWK, Chng ALB, Tan KH, IPRAMHO International Study Group

Heliyon, 2023 Nov;9(11):e21186.
PMID: 38034721 DOI: 10.1016/j.heliyon.2023.e21186

BACKGROUND: Vitamin D deficiency is common in pregnant women. There is scarce information in the Asia-Pacific region on the understanding of vitamin D screening and supplementation in pregnancy among health care professionals.
METHODS: We performed a cross-sectional study among health care professionals who are part of the Integrated Platform for Research in Advancing Metabolic Health outcomes of Women and Children (IPRMAHO) international study group on their understanding and perception of Vitamin D screening and supplementation in pregnancy. The cross-sectional survey comprised 4 main sections: demographics, existing policies, nutrient supplementation in pregnancy and various practices on screening, treatment and perceptions, with a total of 22 questions. A total of 15 responses were obtained from attendees from distinct health facilities across eleven participating Asia-Pacific countries.
RESULTS: Majority of the surveyed hospitals (11/15, 78.6 %) did not have a national policy or regional guideline regarding Vitamin D screening and supplementation in pregnancy. More than half of respondents were (9/14, 64.3 %) were unsure of the percentage of women seen with Vitamin D deficiencies each year and were unsure of Vitamin D dosage prescribed to pregnant women with (8/15, 53.3 %) or without (6/14, 42.9 %) Vitamin D deficiency. Vitamin D was rarely prescribed in pregnancy when compared to other nutrient supplements such as folic acid and iron. Majority of respondents (9/11, 72.7 %) indicated that their hospital did not screen for Vitamin D deficiencies in pregnancy, even amongst high risk pregnant women. Nevertheless, majority of respondents indicated a need (12/15, 80.0 %) for a guideline or consensus regarding Vitamin D screening and supplementation in pregnancy.
CONCLUSION: While majority of the surveyed hospitals did not have a national policy or regional guideline regarding Vitamin D screening and supplementation in pregnancy, majority of respondents indicated a need for the policy or guideline. There were varying clinical knowledge gaps and different perceptions on Vitamin D screening and supplementation in pregnancy among healthcare professionals.
Expected quality factor of a simple tuned oscillator

Tan KH

IEEE Trans Ultrason Ferroelectr Freq Control, 2011 May;58(5):886-99.
PMID: 21622044 DOI: 10.1109/TUFFC.2011.1889

A positive feedback system oscillating under self-sustained mode is shown to have an extremely high gain. Modeled as one port, the expected Q is much higher than the loaded Q-factor of the resonator. With just thermal noise present, random phase/frequency deviation is linear. Centered about the oscillator frequency omega/(0), noise frequency on both sides is more amplified with decreasing separation distance. Ultimately, frequency pulling may result in synchronous locking with hysteresis, which occurs because a real oscillator displays a truncated limiting curve. Once locked onto a signal, smaller levels are ignored. A new approach to the design and characterization of a simple tuned oscillator is offered: According to the phenomenon of injection locking, there exists an expected quality factor relating the shape of the truncated limiting curve to an ideal curve. In this paper, synthesis and innovative analytical methods of academic interest are revealed: 1) application of the transducer loss method is revised to establish a new method for oscillator characterization; 2) a transparent method of normalizing a two-port network in the presence of white noise is developed; and 3) in quartz crystal controlled oscillators, characterization of the noise originating from an equivalent noise-resistance determined from parameter of the quartz crystal is proposed. It is shown that the two-port model can also be approximated on a one-port basis. In conclusion, a sample of closed-form estimation of expected Q-factor order of magnitude of piezoelectric resonator oscillators is calculated.
Clinical experience in coronary stenting with the Vivant Z Stent

Chee KH, Siaw FS, Chan CG, Chong WP, Imran ZA, Haizal HK, et al.

Int J Clin Pract, 2005 Jun;59(6):628-31.
PMID: 15924588

This single centre study was designed to demonstrate feasibility, safety and efficacy of the Vivant Z stent (PFM AG, Cologne, Germany). Patients with de novo lesion were recruited. Coronary angioplasty was performed with either direct stenting or after balloon predilatation. Repeated angiogram was performed 6 months later or earlier if clinically indicated. Between January to June 2003, a total of 50 patients were recruited (mean age 55.8 +/- 9 years). A total of 52 lesions were stented successfully. Mean reference diameter was 2.77 mm (+/-0.59 SD, range 2.05-4.39 mm) with mean target lesion stenosis of 65.5% (+/-11.6 SD, range 50.1-93.3%). Forty-six lesions (88.5%) were American College of Cardiologist/American Heart Association class B/C types. Direct stenting was performed in 18 (34.6%) lesions. Mean stent diameter was 3.18 mm (+/-0.41 SD, range 2.5-4 mm), and mean stent length was 14.86 mm (+/-2.72 SD, range 9-18 mm). The procedure was complicated in only one case which involved the loss of side branch with no clinical sequelae. All treated lesions achieved Thrombolysis In Myocardial Infarction 3 flow. Mean residual diameter stenosis was 12.2% (+/-7.55 SD, range 0-22.6%) with acute gain of 1.72 mm (+/-0.50 SD, range 0.5-2.8). At 6 months, there was no major adverse cardiovascular event. Repeated angiography after 6 months showed a restenosis rate of 17% (defined as >50% diameter restenosis). Mean late loss was 0.96 mm (+/-0.48 SD) with loss index of 0.61 (+/-0.38 SD). The restenosis rate of those lesions less than 3.0 mm in diameter was 22.2% compared with 6.25% in those lesions more than 3.0 mm in diameter. The Vivant Z stent was shown to be safe and efficacious with low restenosis rate in de novo coronary artery lesion.
Dissolution of thrombus formed during direct coronary angioplasty with a single 10 mg intracoronary bolus dose of abciximab

Thuraisingham S, Tan KH

Int J Clin Pract, 1999 Dec;53(8):604-7.
PMID: 10692754

Direct coronary angioplasty with stent implantation is an effective treatment for acute myocardial infarction. The use of adjunctive abciximab, a platelet glycoprotein IIb/IIIa receptor antagonist is expensive. We report on three cases of direct coronary angioplasty complicated by extensive thrombus formation that were successfully treated with attenuated dosing of abciximab via the intracoronary route. All patients presented with acute myocardial infarction complicated by cardiogenic shock or eminent cardiogenic shock. Abciximab was administered after balloon dilatation when extensive thrombus formation was noted and persisted despite repeated inflations. In all three patients a single 10 mg vial of intracoronary abciximab was administered, resulting in complete dissolution of thrombus, allowing successful deployment of stents. Thus, a single 10 mg intracoronary bolus dose of abciximab may be sufficient to achieve high local concentrations of antiplatelet activity. This facilitates thrombus dissolution and allows the safe deployment of a stent to normalise intracoronary rheology.

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