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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 Heat transfer analysis of MHD thin film flow of an unsteady second grade fluid past a vertical oscillating belt

Gul T, Islam S, Shah RA, Khan I, Khalid A, Shafie S

PLoS One, 2014;9(11):e103843.
PMID: 25383797 DOI: 10.1371/journal.pone.0103843

This article aims to study the thin film layer flowing on a vertical oscillating belt. The flow is considered to satisfy the constitutive equation of unsteady second grade fluid. The governing equation for velocity and temperature fields with subjected initial and boundary conditions are solved by two analytical techniques namely Adomian Decomposition Method (ADM) and Optimal Homotopy Asymptotic Method (OHAM). The comparisons of ADM and OHAM solutions for velocity and temperature fields are shown numerically and graphically for both the lift and drainage problems. It is found that both these solutions are identical. In order to understand the physical behavior of the embedded parameters such as Stock number, frequency parameter, magnetic parameter, Brinkman number and Prandtl number, the analytical results are plotted graphically and discussed.
Fulltext A review on high-resolution CMOS delay lines: towards sub-picosecond jitter performance

Abdulrazzaq BI, Abdul Halin I, Kawahito S, Sidek RM, Shafie S, Yunus NA

Springerplus, 2016;5:434.
PMID: 27104122 DOI: 10.1186/s40064-016-2090-z

A review on CMOS delay lines with a focus on the most frequently used techniques for high-resolution delay step is presented. The primary types, specifications, delay circuits, and operating principles are presented. The delay circuits reported in this paper are used for delaying digital inputs and clock signals. The most common analog and digitally-controlled delay elements topologies are presented, focusing on the main delay-tuning strategies. IC variables, namely, process, supply voltage, temperature, and noise sources that affect delay resolution through timing jitter are discussed. The design specifications of these delay elements are also discussed and compared for the common delay line circuits. As a result, the main findings of this paper are highlighting and discussing the followings: the most efficient high-resolution delay line techniques, the trade-off challenge found between CMOS delay lines designed using either analog or digitally-controlled delay elements, the trade-off challenge between delay resolution and delay range and the proposed solutions for this challenge, and how CMOS technology scaling can affect the performance of CMOS delay lines. Moreover, the current trends and efforts used in order to generate output delayed signal with low jitter in the sub-picosecond range are presented.
Fulltext Unsteady MHD Thin Film Flow of an Oldroyd-B Fluid over an Oscillating Inclined Belt

Gul T, Islam S, Shah RA, Khalid A, Khan I, Shafie S

PLoS One, 2015;10(7):e0126698.
PMID: 26147287 DOI: 10.1371/journal.pone.0126698

This paper studies the unsteady magnetohydrodynamics (MHD) thin film flow of an incompressible Oldroyd-B fluid over an oscillating inclined belt making a certain angle with the horizontal. The problem is modeled in terms of non-linear partial differential equations with some physical initial and boundary conditions. This problem is solved for the exact analytic solutions using two efficient techniques namely the Optimal Homotopy Asymptotic Method (OHAM) and Homotopy Perturbation Method (HPM). Both of these solutions are presented graphically and compared. This comparison is also shown in tabular form. An excellent agreement is observed. The effects of various physical parameters on velocity have also been studied graphically.
Design of a Sub-Picosecond Jitter with Adjustable-Range CMOS Delay-Locked Loop for High-Speed and Low-Power Applications

Abdulrazzaq BI, Ibrahim OJ, Kawahito S, Sidek RM, Shafie S, Yunus NA, et al.

Sensors (Basel), 2016 Sep 28;16(10).
PMID: 27690040

A Delay-Locked Loop (DLL) with a modified charge pump circuit is proposed for generating high-resolution linear delay steps with sub-picosecond jitter performance and adjustable delay range. The small-signal model of the modified charge pump circuit is analyzed to bring forth the relationship between the DLL's internal control voltage and output time delay. Circuit post-layout simulation shows that a 0.97 ps delay step within a 69 ps delay range with 0.26 ps Root-Mean Square (RMS) jitter performance is achievable using a standard 0.13 µm Complementary Metal-Oxide Semiconductor (CMOS) process. The post-layout simulation results show that the power consumption of the proposed DLL architecture's circuit is 0.1 mW when the DLL is operated at 2 GHz.
Fulltext Accuracy of self-reported height, weight and BMI in a multiethnic Asian population

Roystonn K, Abdin E, Sambasivam R, Zhang Y, Chang S, Shafie S, et al.

Ann Acad Med Singap, 2021 04;50(4):306-314.
PMID: 33990818 DOI: 10.47102/annals-acadmedsg.2020183

INTRODUCTION: The study assessed whether self-reported height, weight and derived body mass index (BMI) can provide an accurate measure of anthropometric data in a multiethnic adult population in Singapore.
METHODS: Standardised anthropometric measurements were compared against the self-reported values from 5,132 adult residents in a cross-sectional, epidemiological survey. Discrepancies in self-reports from measurements were examined by comparing overall mean differences. Intraclass correlations, Cohen's kappa and Bland-Altman plots with limits of agreement, and sub-analysis by sex and ethnicity were also explored.
RESULTS: Data were obtained from 5,132 respondents. The mean age of respondents was 43.9 years. Overall, the height was overestimated (0.2cm), while there was an underestimation of weight (0.8kg) and derived BMI (0.4kg/m2). Women had a larger discrepancy in height (0.35cm, 95% confidence interval [CI] 0.22 to 0.49), weight (-0.95kg, 95% CI -1.11 to -0.79) and BMI (-0.49kg/m2, 95% CI -0.57 to -0.41) compared with men. Height reporting bias was highest among Indians (0.28cm, 95% CI 0.12 to 0.44) compared with Chinese and Malays, while weight (-1.32kg, 95% CI -1.53 to -1.11) and derived BMI (-0.57kg/m2, 95% CI -0.67 to -0.47) showed higher degrees of underreporting among Malays compared with Chinese and Indians. Substantially high self-reported versus measured values were obtained for intraclass correlations (0.96-0.99, P<0.001) and kappa (0.74). For BMI categories, good to excellent kappa agreement was observed (0.68-0.81, P<0.0001).
CONCLUSION: Self-reported anthropometric estimates can be used, particularly in large epidemiological studies. However, sufficient care is needed when evaluating data from Indians, Malays and women as there is likely an underestimation of obesity prevalence.
A carbon conductive filament-induced robust resistance switching behavior for brain-inspired computing

Yu T, Wang D, Liu M, Lei W, Shafie S, Mohtar MN, et al.

Mater Horiz, 2024 Mar 04;11(5):1334-1343.
PMID: 38175571 DOI: 10.1039/d3mh01762a

Memristors have revolutionized the path forward for brain-inspired computing. However, the instability of the nucleation process of conductive filaments based on active metal electrodes leads to the discrete distribution of switching parameters, which hinders the realization of high-performance and low-power devices for neuromorphic computing. In response, a carbon conductive filament-induced robust memristor is demonstrated with variation coefficients as low as 3.9%/-1.18%, a threshold power as low as 10-9 W, and 3 × 106 s retention and 107 cycle endurance behaviors can be maintained. The recognition accuracy for Modified National Institute of Standards and Technology (MNIST) handwriting is as high as 96.87%, attributed to the high linearity of the iterative updating of synaptic weights. The demodulation and storage functions of the American Standard Code for Information Interchange (ASCII) are demonstrated by programmable pulse modulation. Notably, the transmission electron microscopy (TEM) images allow the observation of carbon conductive filament paths formed in the low resistance state. First-principles calculations analyze the energetics of defects involved in the diffusion of carbon atoms into MoTe2 films. This work presents a novel guideline for studying memristor-based neuromorphic computing.
Development, validity and reliability of the short multidimensional positive mental health instrument

Vaingankar JA, Subramaniam M, Abdin E, Picco L, Chua BY, Eng GK, et al.

Qual Life Res, 2014 Jun;23(5):1459-77.
PMID: 24307210 DOI: 10.1007/s11136-013-0589-0

PURPOSE: The 47-item positive mental health (PMH) instrument measures the level of PMH in multiethnic adult Asian populations. This study aimed to (1) develop a short PMH instrument and (2) establish its validity and reliability among the adult Singapore population.
METHODS: Two separate studies were conducted among adult community-dwelling Singapore residents of Chinese, Malay or Indian ethnicity where participants completed self-administered questionnaires. In the first study, secondary data analysis was conducted using confirmatory factor analysis (CFA) to shorten the PMH instrument. In the second study, the newly developed short PMH instrument and other scales were administered to 201 residents to establish its factor structure, validity and reliability.
RESULTS: A 20-item short PMH instrument fulfilling a higher-order six-factor structure was developed following secondary analysis. The mean age of the participants in the second study was 41 years and about 53% were women. One item with poor factor loading was further removed to generate a 19-item version of the PMH instrument. CFA demonstrated a first-order six-factor model of the short PMH instrument. The PMH-19 instrument and its subscales fulfilled criterion validity hypotheses. Internal consistency and test-retest reliability of the PMH-19 instrument were high (Cronbach's α coefficient = 0.87; intraclass correlation coefficient = 0.93, respectively).
CONCLUSIONS: The 19-item PMH instrument is multidimensional, valid and reliable, and most importantly, with its reduced administration time, the short PMH instrument can be used to measure and evaluate PMH in Asian communities.
Development of the Chinese, Malay and Tamil translations of the Positive Mental Health Instrument: Cross-cultural adaptation, validity and internal consistency

Vaingankar JA, Abdin E, Chong SA, Sambasivam R, Shafie S, Ong HL, et al.

Transcult Psychiatry, 2021 02;58(1):76-95.
PMID: 33297859 DOI: 10.1177/1363461520976045

This study describes the development and validation of Chinese, Malay and Tamil translations of the Positive Mental Health Instrument (PMHI) in a general population sample in Singapore. Translations were performed using two independent forward translations followed by expert panel discussions and tested for content, construct and language appropriateness using focus group discussions. The final translated tools were field-tested among 220 residents per language using self-administered questionnaires comprising the translated PMHI and other validity measures. Missing data, floor and ceiling effects, confirmatory factor analysis (CFA), internal consistency, item response theory differential item functioning (IRT-DIF) and criterion validity were assessed. A total of 10 PMHI-Chinese items, 26 PMHI-Malay items and six response categories and six PMHI-Tamil items were modified based on expert panel and focus group discussions. PMHI had low missing data and showed negative but acceptable skewness (<2) and kurtosis (<7) for all translations, except for the PMHI-Malay "spirituality" subscale (skewness: -2.8; kurtosis: 12.5). CFA showed that all three PMHI translations fulfilled the original six-factor-higher-order structure (RMSEA = 0.05, CFI = 0.962, TLI = 0.96). Cronbach's alpha coefficients for total PMHI were 0.958, 0.954, 0.945 and 0.949 in the overall sample and the Chinese, Malay and Tamil translations, respectively. The three translations of the PMHI showed expected and significant positive (r = 0.116 to 0.663) and negative correlations (r = -0.137 to -0.574) with established measures. The findings show that the Chinese, Malay and Tamil translations of the PMHI have high internal consistency and validity in this multi-ethnic population.
Hybridization state transition-driven carbon quantum dot (CQD)-based resistive switches for bionic synapses

Yu T, Fang Y, Chen X, Liu M, Wang D, Liu S, et al.

Mater Horiz, 2023 Jun 06;10(6):2181-2190.
PMID: 36994553 DOI: 10.1039/d3mh00117b

As an emerging carbon-based material, carbon quantum dots (CQDs) have shown unstoppable prospects in the field of bionic electronics with their outstanding optoelectronic properties and unique biocompatible characteristics. In this study, a novel CQD-based memristor is proposed for neuromorphic computing. Unlike the models that rely on the formation and rupturing of conductive filaments, it is speculated that the resistance switching mechanism of CQD-based memristors is due to the conductive path caused by the hybridization state transition of the sp2 carbon domain and sp3 carbon domain induced by the reversible electric field. This avoids the drawback of uncontrollable nucleation sites leading to the random formation of conductive filaments in resistive switching. Importantly, it illustrates that the coefficient of variation (CV) of the threshold voltage can be as low as -1.551% and 0.083%, which confirms the remarkable uniform switching characteristics. Interestingly, the Pavlov's dog reflection as an important biological behavior can be demonstrated by the samples. Finally, the accuracy recognition rate of MNIST handwriting can reach up to 96.7%, which is very close to the ideal number (97.8%). A carbon-based memristor based on a new mechanism presented provides new possibilities for the improvement of brain-like computing.