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Fulltext Non-adherence to recommended Pap smear screening guidelines and its associated factors among women attending health clinic in Malaysia

Yunus NA, Mohamed Yusoff H, Draman N

Malays Fam Physician, 2018;13(1):10-17.
PMID: 29796205 MyJurnal

Introduction: Cervical cancer ranks as the second most frequent cancer among women in Malaysia. Although a cervical screening program has been introduced since 1960s and is provided free of charge in all government health facilities, the coverage and adherence rate to recommendation among Malaysian women remains low.

Objectives: To determine the proportion of non-adherence to Pap smear screening guidelines and its associated factors among women attending a health clinic in Malaysia.

Method: A cross sectional study involving 316 women aged 20 to 65 years who had undergone a Pap smear. Universal sampling method was applied to select participants among women who attended the selected health clinic from January 2013 to May 2013. A self-administered questionnaire was used to obtain the socio-demographic characteristics, socio-health data and perceptions about cervical cancer and Pap smear screening. The data was analysed using descriptive statistics and multiple logistic regression.

Result: The proportion of non-adherence to Pap smear screening was 90.5%. Age, marital status, duration of marriage, education level, employment, household income and number of children were not significantly associated with non-adherence. Perceived severity, perceived susceptibility, perceived benefit, perceived barrier and cues to action did not show significant association with non-adherence to Pap smear screening.

Conclusion: Non-adherence to Pap smear screening was high among Malaysian women. Measures should be taken to increase Pap smear screening coverage in our country. Other factors beyond Health Belief Model that influence Pap smear screening practice among Malaysian women should be explored.
Continuous separation of colloidal particles using dielectrophoresis

Yunus NA, Nili H, Green NG

Electrophoresis, 2013 Apr;34(7):969-78.
PMID: 23436439 DOI: 10.1002/elps.201200466

Dielectrophoresis is the movement of particles in nonuniform electric fields and has been of interest for application to manipulation and separation at and below the microscale. This technique has the advantages of being noninvasive, nondestructive, and noncontact, with the movement of particle achieved by means of electric fields generated by miniaturized electrodes and microfluidic systems. Although the majority of applications have been above the microscale, there is increasing interest in application to colloidal particles around a micron and smaller. This paper begins with a review of colloidal and nanoscale dielectrophoresis with specific attention paid to separation applications. An innovative design of integrated microelectrode array and its application to flow-through, continuous separation of colloidal particles is then presented. The details of the angled chevron microelectrode array and the test microfluidic system are then discussed. The variation in device operation with applied signal voltage is presented and discussed in terms of separation efficiency, demonstrating 99.9% separation of a mixture of colloidal latex spheres.
Validation of the Universal Measure of Bias-Fat (UMB Fat) among Malaysian health practitioners using Rasch analysis

Yunus NA, Sturgiss E, Soh SE

Obes Res Clin Pract, 2023 Dec 01.
PMID: 38042691 DOI: 10.1016/j.orcp.2023.11.004

OBJECTIVE: This study aimed to evaluate the structural validity of the Universal Measures of Bias - Fat (UMB Fat) among Malaysian healthcare practitioners using Rasch analysis.
METHODS: Data from a cross-sectional survey of 268 public and private doctors and allied health practitioners in Peninsular Malaysia were used for this analysis. Using Rasch analysis, overall model fit and item fit of the summary UMB Fat and domain scores were examined, together with unidimensionality, response threshold ordering, internal consistency, measurement invariance, and item targeting.
RESULTS: Data showed overall misfit to the Rasch model for both the summary UMB Fat score and domain scores. Whilst unidimensionality was observed for the domain scores, this was not evident for the summary score where multiple local dependencies were present. Disordered thresholds were observed for the response format, in which the majority improved with modification. Suboptimal targeting was also detected with an uneven distribution of items at the upper and lower end of the logit scale for the summary and domain scores. Despite this, excellent internal consistency reliability was observed (person separation index: 0.76-0.89), and no measurement invariance was detected.
CONCLUSION: The Rasch model supports reporting of the UMB Fat domain scores but not the summary score. Several issues related to local dependencies and response format were identified that could benefit from refining the UMB Fat to improve measurement accuracy, particularly when used by healthcare practitioners in Asian countries.
Fulltext Hemiballismus in Uncontrolled Diabetes Mellitus

Jaafar J, Rahman RA, Draman N, Yunus NA

Korean J Fam Med, 2018 May;39(3):200-203.
PMID: 29788710 DOI: 10.4082/kjfm.2018.39.3.200

Hemiballismus, a subtype of chorea, is a rare movement disorder, and is most commonly found secondary to stroke. Movements are involuntary, violent, coarse, and have a wide amplitude. There is increasing report of hemiballismus occurring in non-ketotic hyperglycemia. Spontaneous improvements or remissions were observed in many patients, and treatment should be directed towards the cause of hemiballismus. There is no randomized control trial to guide clinicians in deciding the best treatment option when managing hemiballismus. Symptomatic treatment includes the use of drugs such as dopamine receptor blocker and tetrabenazine. Surgical treatment is reserved for severe, persistent, and disabling hemiballismus. This case is of an elderly woman with long standing uncontrolled diabetes who presented with abnormal movement in her left upper limb for 2 months, which resolved slowly with good control of her glucose levels. Treating physicians need to have a high index of suspicion to prevent mismanagement of the condition.
Spatial-economic optimisation of biomethane injection into natural gas grid: The case at southern Malaysia

Hoo PY, Hashim H, Ho WS, Yunus NA

J Environ Manage, 2019 Jul 01;241:603-611.
PMID: 30616893 DOI: 10.1016/j.jenvman.2018.11.092

Energy is widely used in industry for heating and cooling, with natural gas (NG) being the largest primary energy source in Malaysia, closely followed by coal. Renewable energy, such as biogas upgrading to biomethane, could cut the use of fossil fuels by supplementing NG usage due to their similar physicochemical and thermochemical characteristics. Biogas production plants in Malaysia are more commonly seen in waste-to-energy scenarios, with the technology anaerobic digestion, and their deployment is supported via feed-in tariffs (FiT) for power generation. Other potential applications such as the conversion of biogas into biomethane, injection into the natural gas grid or transportation through a virtual pipeline may still need further technical development. This paper presents spatial techno economic optimisation modelling using BeWhere to determine decentralised biomethane production plants using feedstock from multiple sources of biogas, including palm oil mill effluent (POME), food waste, cattle manure and chicken manure. This model considered potential configurations and sizes of the biomethane plants, the transportation of biomethane using a virtual pipeline (at 250 psig) and demand in one of the states in Malaysia, namely Johor. It was found that two to four biomethane plants with capacities ranging between 125 and 700 m3/h were located in densely populated areas or heavier industrial consumers when the carbon tax was implemented at 167.71 EUR/tCO2 (800 MYR/tCO2). Sensitivity analysis suggested that biomethane production increases with the increasing country renewable energy share target to beyond 2080 MW. It is recommended that specific policy regulations and Feed-in Tariff (FiT) mechanisms are used to expand the biomethane market share in the country.
Fulltext A Brief Psychotic Episode with Depressive Symptoms in Silent Right Frontal Lobe Infarct

Badrin S, Mohamad N, Yunus NA, Zulkifli MM

Korean J Fam Med, 2017 Nov;38(6):380-382.
PMID: 29209479 DOI: 10.4082/kjfm.2017.38.6.380

Psychiatric symptoms may be related to a silent cerebral infarct, a phenomenon that has been described previously in literature. Acute psychosis or other neuropsychiatric symptoms including depression may present in stroke patients and patients with lesions either within the prefrontal or occipital cortices, or in subcortical areas such as the basal ganglia, thalamus, mid-brain, and brainstem. Psychosis in clinical stroke or in silent cerebral infarction is uncommon and not well documented in the literature. Neurological deficits are the most common presentation in stroke, and nearly a third of patients that suffer a stroke may experience psychological disorders such as depression and anxiety, related to physical disability. The present case report describes an elderly female patient who presented with hallucinations and depressive symptoms, and was discovered to have a recent right frontal brain infarction, without other significant neurological deficits.
The perceptions of healthcare practitioners on obesity management in Peninsular Malaysia: a cross-sectional survey

Yunus NA, Russell G, Muhamad R, Soh SE, Sturgiss E

BMC Health Serv Res, 2023 Jul 10;23(1):744.
PMID: 37430243 DOI: 10.1186/s12913-023-09759-z

BACKGROUND: Practitioners' perceptions of patients with obesity and obesity management shape their engagement in obesity care delivery. This study aims to describe practitioners' perceptions, experiences and needs in managing patients with obesity, determine the extent of weight stigma among health practitioners, and identify the factors associated with negative judgment towards patients with obesity.
METHODS: A cross-sectional online survey was conducted from May to August 2022 with health practitioners commonly involved in obesity management in Peninsular Malaysia, including doctors in primary care, internal medicine and bariatric surgery, and allied health practitioners. The survey explored practitioners' perceptions, barriers and needs in managing obesity, and evaluated weight stigma using the Universal Measures of Bias - Fat (UMB Fat) questionnaire. Multiple linear regression analysis was used to identify demographic and clinical-related factors associated with higher negative judgment towards patients with obesity.
RESULTS: A total of 209 participants completed the survey (completion rate of 55.4%). The majority (n = 196, 94.3%) agreed that obesity is a chronic disease, perceived a responsibility to provide care (n = 176, 84.2%) and were motivated to help patients to lose weight (n = 160, 76.6%). However, only 22% (n = 46) thought their patients were motivated to lose weight. The most frequently reported barriers to obesity discussions were short consultation time, patients' lack of motivation, and having other, more important, concerns to discuss. Practitioners needed support with access to multi-disciplinary care, advanced obesity training, financing, comprehensive obesity management guidelines and access to obesity medications. The mean (SD) of the UMB Fat summary score was 2.99 (0.87), with the mean (SD) domain scores ranging between 2.21 and 4.36 (1.06 to 1.45). No demographic and clinical-related factors were significantly associated with negative judgment from the multiple linear regression analyses.
CONCLUSION: Practitioners in this study considered obesity a chronic disease. While they had the motivation and capacity to engage in obesity management, physical and social opportunities were the reasons for not discussing obesity with their patients. Practitioners needed more support to enhance their capability and opportunity to engage with obesity management. Weight stigma in healthcare settings in Malaysia should be addressed, given the possibility of hindering weight discussions with patients.
Fulltext Patients' experience of accessing healthcare for obesity in Peninsular Malaysia: a qualitative descriptive study

Yunus NA, Russell G, Muhamad R, Sturgiss EA

BMJ Open, 2023 Nov 21;13(11):e071087.
PMID: 37989390 DOI: 10.1136/bmjopen-2022-071087

OBJECTIVE: To explore patients' experiences accessing healthcare for obesity and their perceived behaviour changes following the care.
DESIGN: Using a descriptive qualitative research approach informed by Levesque's framework of access to healthcare, we conducted phone interviews in the Malaysian language, which were audio-recorded and transcribed verbatim. Data were analysed inductively using a reflexive thematic analysis approach.
SETTING: Primary care clinics in five states in Peninsular Malaysia.
PARTICIPANTS: Adult patients with obesity receiving face-to-face care for obesity from healthcare providers in Peninsular Malaysia.
RESULTS: We interviewed 22 participants aged 24-62, with the majority being female (77%), Malay (95%), married (73%) and with tertiary education (82%). Most participants attended obesity management services at public primary care clinics. We identified five themes: (1) moving from perceiving the need to seeking obesity care is a non-linear process for patients, (2) providers' words can inspire patients to change, (3) patients' needs and preferences are not adequately addressed in current obesity care, (4) over-focusing on weight by patients and healthcare providers can lead to self-blame and loss of hope for patients and (5) obesity healthcare can have consequences beyond weight loss.
CONCLUSION: Patients lack the self-regulatory skills to continue their lifestyle changes and struggle with self-blame and hopelessness. Over-focusing on weight by patients and obesity healthcare increase patients' self-stigmatisation. While provider-initiated weight discussions and engaging and personalised consultation provide the initial step towards weight management, obesity healthcare could be enhanced by behavioural support and patient education on the complexity of obesity. Further considerations could be given to shifting from a weight-centric to a more holistic health-centred approach in obesity healthcare.
Fulltext 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

Tiong KH, Mohammed Yunus NA, Yiap BC, Tan EL, Ismail R, Ong CE

PLoS One, 2014;9(1):e86230.
PMID: 24475091 DOI: 10.1371/journal.pone.0086230

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.
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.
Polymerase chain reaction cycle threshold value as prerequisite for reporting of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection

Awang H, Hamzah FH, Ahmad MH, Mahmood MF, Wahab A, Embong K, et al.

Infect Dis (Lond), 2021 05;53(5):390-392.
PMID: 33512265 DOI: 10.1080/23744235.2021.1876913
Fulltext Thermal Stability and Rheological Properties of Epoxidized Natural Rubber-Based Magnetorheological Elastomer

Yunus NA, Mazlan SA, Ubaidillah, Abdul Aziz SA, Tan Shilan S, Abdul Wahab NA

Int J Mol Sci, 2019 Feb 10;20(3).
PMID: 30744210 DOI: 10.3390/ijms20030746

Determination of the thermal characteristics and temperature-dependent rheological properties of the magnetorheological elastomers (MREs) is of paramount importance particularly with regards to MRE applications. Hitherto, a paucity of temperature dependent analysis has been conducted by MRE researchers. In this study, an investigation on the thermal and rheological properties of epoxidized natural rubber (ENR)-based MREs was performed. Various percentages of carbonyl iron particles (CIPs) were blended with the ENR compound using a two roll-mill for the preparation of the ENR-based MRE samples. The morphological, elemental, and thermal analyses were performed before the rheological test. Several characterizations, as well as the effects of the strain amplitude, temperature, and magnetic field on the rheological properties of ENR-based MRE samples, were evaluated. The micrographs and elemental results were well-correlated regarding the CIP and Fe contents, and a uniform distribution of CIPs was achieved. The results of the thermal test indicated that the incorporation of CIPs enhanced the thermal stability of the ENR-based MREs. Based on the rheological analysis, the storage modulus and loss factor were dependent on the CIP content and strain amplitude. The effect of temperature on the rheological properties revealed that the stiffness of the ENR-based MREs was considered stable, and they were appropriate to be employed in the MRE devices exposed to high temperatures above 45 °C.
Fulltext Effects of Petroleum-Based Oils as Dispersing Aids on Physicochemical Characteristics of Magnetorheological Elastomers

Muhammad Zaki N, Yunus NA, Yusoff MS, Mazlan SA, Abdul Aziz SA, Izni NA, et al.

Materials (Basel), 2021 Nov 19;14(22).
PMID: 34832425 DOI: 10.3390/ma14227026

This paper investigated the effects of petroleum-based oils (PBOs) as a dispersing aid on the physicochemical characteristics of natural rubber (NR)-based magnetorheological elastomers (MREs). The addition of PBOs was expected to overcome the low performance of magnetorheological (MR) elastomers due to their inhomogeneous dispersion and the mobility of magnetic particles within the elastomer matrix. The NR-based MREs were firstly fabricated by mixing the NR compounds homogeneously with different ratios of naphthenic oil (NO), light mineral oil (LMO), and paraffin oil (PO) to aromatic oil (AO), with weight percentage ratios of 100:0, 70:30, 50:50, and 30:70, respectively. From the obtained results, the ratios of NO mixed with low amounts of AO improved the material physicochemical characteristics, such as thermal properties. Meanwhile, LMO mixed the AO led to the best results for curing characteristics, microstructure observation, and magnetic properties of the MREs. We found that the LMO mixed with a high content of AO could provide good compatibility between the rubber molecular and magnetic particles due to similar chemical structures, which apparently enhance the physicochemical characteristics of MREs. In conclusion, the 30:70 ratio of LMO:AO is considered the preferable dispersing aid for MREs due to structural compounds present in the oil that enhance the physicochemical characteristics of the NR-based MREs.
The experience of living with obesity for adults in Asian countries: A scoping review of qualitative studies

Yunus NA, Russell G, Muhamad R, Chai TL, Ahmad Zawawi MAF, Sturgiss E

Obes Rev, 2023 Nov;24(11):e13619.
PMID: 37558504 DOI: 10.1111/obr.13619

Sociocultural and biological backgrounds significantly influence people's experience of obesity. Yet the experience within the Asian sociocultural context is underexplored. This scoping review aims to summarize the qualitative evidence that explores the lived experience of adults with obesity in Asian countries. Guided by the Joanna Briggs Institute (JBI) approach, we systematically searched five databases (MEDLINE, EMBASE, PsychINFO, CINAHL, and Scopus) for studies exploring the lived experience of adults with obesity in Asian countries. Eligible studies with English full text were screened by two reviewers and analyzed using a descriptive qualitative content analysis. Of the 16,764 articles retrieved, 11 were included. The qualitative data can be summarized into three categories: (1) cultural norms shaped the lived experience with obesity, (2) the influence of obesity on social relationships, and (3) coping with life challenges. Despite the small number of studies, a strong influence of the sociocultural environment on the lived experience of obesity was evident, particularly on social roles and expectations, social relationships, the stigma of obesity, and life challenges. The extent and significance of this sociocultural influence on the Asian population warrant further exploration. Future research should fully report the qualitative methods to provide contextual information about the study.
Fulltext Separation and Detection of Escherichia coli and Saccharomyces cerevisiae Using a Microfluidic Device Integrated with an Optical Fibre

Kamuri MF, Zainal Abidin Z, Yaacob MH, Hamidon MN, Md Yunus NA, Kamarudin S

Biosensors (Basel), 2019 Mar 14;9(1).
PMID: 30875829 DOI: 10.3390/bios9010040

This paper describes the development of an integrated system using a dry film resistant (DFR) microfluidic channel consisting of pulsed field dielectrophoretic field-flow-fractionation (DEP-FFF) separation and optical detection. The prototype chip employs the pulse DEP-FFF concept to separate the cells (Escherichia coli and Saccharomyces cerevisiae) from a continuous flow, and the rate of release of the cells was measured. The separation experiments were conducted by changing the pulsing time over a pulsing time range of 2⁻24 s and a flow rate range of 1.2⁻9.6 μ L min - 1 . The frequency and voltage were set to a constant value of 1 M Hz and 14 V pk-pk, respectively. After cell sorting, the particles pass the optical fibre, and the incident light is scattered (or absorbed), thus, reducing the intensity of the transmitted light. The change in light level is measured by a spectrophotometer and recorded as an absorbance spectrum. The results revealed that, generally, the flow rate and pulsing time influenced the separation of E. coli and S. cerevisiae. It was found that E. coli had the highest rate of release, followed by S. cerevisiae. In this investigation, the developed integrated chip-in-a lab has enabled two microorganisms of different cell dielectric properties and particle size to be separated and subsequently detected using unique optical properties. Optimum separation between these two microorganisms could be obtained using a longer pulsing time of 12 s and a faster flow rate of 9.6 μ L min - 1 at a constant frequency, voltage, and a low conductivity.
Fulltext A Malaysian Medical Non-Governmental Organization's (NGO) Experience in the Emergency Response for COVID-19, Using the Whole-of-Society Collaborative Concept

Abd Samat AH, Abdul Rashid A, Mohd Yunus NA, Salim AMH, Musa H

Disaster Med Public Health Prep, 2021 Apr 06.
PMID: 33820586 DOI: 10.1017/dmp.2021.106

Non-governmental organizations (NGOs) are one of the important players during a pandemic, including the Islamic Medical Association of Malaysia (IMAM) Response and Relief Team (IMARET). During the coronavirus disease (COVID-19) pandemic, IMARET played a key role in assisting health relief efforts in Malaysia. We are sharing this experience as a medical NGO's response to the pandemic. This report presents data from the March 18 to June 10, 2020, retrieved from IMARET's database with approval from the Executive Committee and the IMARET COVID-19 Task Force. We report that IMARET's task force consists of 30 people, mostly medical doctors. Supplies distributed included personal protective equipment with other medical equipment, such as portable ultrasounds and ventilators. IMARET engaged with 33 collaborators and 92 partners and funders. There were 135 volunteers with the majority being medical volunteers. IMARET raised more than RM $3 million (US $740 000) garnering support from over 40 000 donors in 85 days. In conclusion, NGOs play a significant role that effectively enhance and complement the consolidated works by the authorities and public in the effort to overcome COVID-19 challenges.
Fulltext Rheological Performance of Magnetorheological Grease with Embedded Graphite Additives

Mohd Nasir NA, Nazmi N, Mohamad N, Ubaidillah U, Nordin NA, Mazlan SA, et al.

Materials (Basel), 2021 Sep 06;14(17).
PMID: 34501180 DOI: 10.3390/ma14175091

The use of highly viscous grease as a medium in magnetorheological grease (MRG) provides the benefit of avoiding sedimentation from occurring. However, it limits the expansion of yield stress in the on-state condition, thus reducing the application performance during operation. Therefore, in this study, the improvement in the rheological properties of MRG was investigated through the introduction of graphite as an additive. MRG with 10 wt % graphite (GMRG) was fabricated, and its properties were compared to a reference MRG sample. The microstructure of GMRG was characterized using an environmental scanning electron microscope (ESEM). The rheological properties of both samples, including apparent viscosity, yield stress, and viscoelasticity, were examined using a shear rheometer in rotational and oscillatory modes. The results demonstrated a slight increase in the apparent viscosity in GMRG and a significant improvement in yield stress by 38.8% at 3 A with growth about 32.7% higher compared to MRG from 0 to 3 A. An expansion of the linear viscoelastic region (LVE) from 0.01% to 0.1% was observed for the GMRG, credited to the domination of the elastic properties on the sample. These obtained results were confirmed based on ESEM, which described the contribution of graphite to constructing a more stable chain structure in the GMRG. In conclusion, the findings highlight the influence of the addition of graphite on improving the rheological properties of MRG. Hence, the addition of graphite in MRG shows the potential to be applied in many applications in the near future.
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 Enhancement of Viscoelastic and Electrical Properties of Magnetorheological Elastomers with Nanosized Ni-Mg Cobalt-Ferrites as Fillers

Abdul Aziz SA, Mazlan SA, Ubaidillah U, Shabdin MK, Yunus NA, Nordin NA, et al.

Materials (Basel), 2019 Oct 28;12(21).
PMID: 31661837 DOI: 10.3390/ma12213531

Carbon-based particles, such as graphite and graphene, have been widely used as a filler in magnetorheological elastomer (MRE) fabrication in order to obtain electrical properties of the material. However, these kinds of fillers normally require a very high concentration of particles to enhance the conductivity property. Therefore, in this study, the nanosized Ni-Mg cobalt ferrite is introduced as a filler to soften MRE and, at the same time, improve magnetic, rheological, and conductivity properties. Three types of MRE samples without and with different compositions of Mg, namely Co0.5Ni0.2Mg0.3Fe2O4 (A1) and Co0.5Ni0.1Mg0.4Fe2O4 (A2), are fabricated. The characterization related to the micrograph, magnetic, and rheological properties of the MRE samples are analyzed using scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and the rheometer. Meanwhile, the effect of the nanosized Ni-Mg cobalt ferrites on the electrical resistance property is investigated and compared with the different Mg compositions. It is shown that the storage modulus of the MRE sample with the nanosized Ni-Mg cobalt ferrites is 43% higher than that of the MRE sample without the nanomaterials. In addition, it is demonstrated that MREs with the nanosized Ni-Mg cobalt ferrites exhibit relatively low electrical resistance at the on-state as compared to the off-state condition, because MRE with a higher Mg composition shows lower electrical resistance when higher current flow occurs through the materials. This salient property of the proposed MRE can be effectively and potentially used as an actuator to control the viscoelastic property of the magnetic field or sensors to measure the strain of the flexible structures by the electrical resistance signal.
Fulltext Temperature Dependent on Mechanical and Rheological Properties of EPDM-Based Magnetorheological Elastomers Using Silica Nanoparticles

Rashid RZA, Yunus NA, Mazlan SA, Johari N, Aziz SAA, Nordin NA, et al.

Materials (Basel), 2022 Mar 31;15(7).
PMID: 35407889 DOI: 10.3390/ma15072556

Temperature is one of the most influential factors affecting the performance of elastomer matrix in magnetorheological elastomer (MRE). Previous studies have utilized silica as a reinforcing filler in polymer composite and as a coating material in MRE to improve the thermal stability of the base material. However, the usage of silica as an additive in the thermal stability of MRE has not been explored. Thus, in this study, the effect of silica as an additive on the temperature-dependent mechanical and rheological properties of ethylene propylene diene monomer (EPDM)-based MREs was investigated by using 30 wt.% carbonyl iron particles (CIPs) as the main filler, with different contents of silica nanoparticles (0 to 11 wt.%). The microstructure analysis was examined by using field-emission scanning electron microscopy (FESEM), while the thermal characterizations were studied by using a thermogravimetric analyzer and differential scanning calorimetry. The tensile properties were conducted by using Instron Universal Testing Machine in the absence of magnetic field at various temperatures. Meanwhile, the rheological properties were analyzed under oscillatory loadings in the influence of magnetic field, using a rotational rheometer at 25 to 65 °C. The results revealed that the temperature has diminished the interfacial interactions between filler and matrix, thus affecting the properties of MRE, where the tensile properties and MR effect decrease with increasing temperature. However, the presence of silica capable improved the thermal stability of EPDM-based MRE by enhancing the interactions between filler and matrix, thus reducing the interfacial defects when under the influence of temperature. Consequently, the incorporation of silica nanoparticles as an additive in EPDM-based MRE requires more exploration, since it has the potential to sustain the properties of MRE devices in a variety of temperature conditions. Thus, the study on the temperature-dependent mechanical and rheological properties of MRE is necessary, particularly regarding its practical applications.

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