Displaying publications 61 - 80 of 2561 in total

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  1. Nor Hasliza Mat Desa, Maznah Mat Kasim, Abdul Aziz Jemain
    Sains Malaysiana, 2015;44:239-247.
    The issue of age difference in hospital admission should be given special attention since it affects the structure of hospital care and treatments. Patients of different age groups should be given different priority in service provision. Due to crucial time and limited resources, healthcare managers need to make wise decisions in identifying priorities in age of admission. This paper aimed to propose a construction of a daily composite hospital admission index (CHAI) as an indicator that captures relevant information about the overall performance of hospital admission over time. It involves five different age groups of total patients admitted to seven major public hospitals in the Klang Valley, Malaysia for respiratory and cardiovascular diseases for a period of three years, 2008 - 2010. The criteria weights were predetermined by aggregating the subjective weight based on rank ordered centroid (ROC) method and objective weight based on entropy - kernel method. The highest and lowest scores of CHAI were marked, while the groups of patients were prioritized according to the criteria weight ranking orders.
  2. Kamarulzaman Bin Ibrahim, Abdul Aziz Jermain
    Dengue is one of the main factors of mortality of inhabitants in the region of South East Asia. Malaysia is one of the countries which is facing a high incidence of dengue, particularly in the 70's and early 80's. The Ministry of Health has taken various measures in order to reduce the dengue epidemic. These include educating people about dengue and conducting research such as investigation of factors that influence the epidemic of dengue. In this study, a sequential Bayesian approach is applied to data of the proportion of death due to dengue over the period from 1982 to 1992. In the sequential Bayesian approach, the data for the year 1982 becomes the prior information for the 1983 data and so on. The data for the different periods are combined in a chronological manner until the final posterior distribution of the proportion of death due to dengue is obtained. It is found that the overall proportion is 0.59% and its standard deviation is 0.00002%.
    Denggi adalah satu daripada faktor utama kematian bagi penduduk di rantau Asia Tenggara. Malaysia pula merupakan satu daripada negara yang sedang mengalami kadar insiden denggi yang tinggi, khususnya dalam tahun 70-an dan pada awal 80-an. Kementerian Kesihatan telah mengambil pelbagai langkah untuk mengurangkan wabak denggi. Ini termasuk memberikan pendidikan tentang denggi dan membuat kajian tentang faktor-faktor yang mempengaruhinya. Dalam kajian ini kaedah Bayesan jujukan digunakan terhadap data perkadaran yang mati akibat denggi dalam tempoh 1982 hingga 1992. Dalam kaedah ini, data tahun 1982 digunakan sebagai maklumat prior untuk data tahun 1983 dan seterusnya. Data dari tahun yang berlainan digabungkan secara kronologi sehingga diperoleh taburan posterior yang terakhir bagi perkadaran yang mati akibat denggi. Didapati bahawa perkadaran keseluruhan ialah 0.59% dan sisihan piawainya 0.00002%.
  3. Ajmal Iqbal, Shahen Shah, Mohammad Nisar, Abdul Ghafoor
    Sains Malaysiana, 2017;46:1727-1734.
    Twenty lines of Pisum sativum particularly developed for high yield and resistant to powdery mildew were evaluated along with two parents (Falloner and 11760-3ER) and two checks (Climex and a local cultivar) with the objectives to determine morphological characterization, yield potential and resistance to powdery mildew. On the basis of one way cluster, the 24 lines were mainly grouped into four clusters, especially on the vegetative and yield contributing traits. It was observed that the tall and high yielding lines were grouped in cluster-III while the dwarf and high yielding lines were grouped in cluster-IV. Analysis of variance (ANOVA) showed significant difference (p<0.05) in the yield of 24 pea lines. The average grain yield of the 24 pea lines ranged from 22.87 to 102.54 g. The highest grain yield was produced by PL-4 (102.54 g plant-1) followed by PL-5 (82.14 g plant-1). Of the 24 pea lines, two lines (PL-4 and PL-5) were highly resistant to powdery mildew disease. Therefore, the newly developed PL-4 and PL-5 lines were high yielding and highly resistant. Among the 19 morphological traits, six (Eigenvalue >1.0) contributed more than 80% variability among the materials.
  4. Uhammad Fahmi Abdul Ghani, Simon N, Goh TL, Tuan Rosli Tuan Mohamed, Abdul Ghani Rafek
    Sains Malaysiana, 2016;45:1509-1516.
    Perbukitan batu kapur di Lembah Kinta membentuk landskap muka bumi yang unik dan indah hasil daripada proses pelarutan batuan karbonat. Namun begitu, bergantung kepada kawasan perbukitan batu kapur tersebut, kehadiran pelbagai struktur geologi seperti struktur retakan dan kekar yang ekstensif mampu memberi ancaman kepada manusia dan harta benda. Kajian ini bertujuan melihat hubungan antara ketumpatan lineamen dan tahap kestabilan tujuh cerun gunung batu kapur di Lembah Kinta, Malaysia. Kajian ini terbahagi kepada dua peringkat, iaitu pemetaan ketumpatan lineamen dan penilaian kestabilan cerun dengan menggunakan kaedah Kekuatan Jasad Batuan (RMS). Sebanyak 599 lineamen rantau dikenal pasti dengan panjang keseluruhan lineamen mencapai 317 km. Seterusnya, peta ketumpatan lineamen yang dihasilkan dikelaskan kepada tiga kelas: Rendah (137.0-84.23) m, sederhana (84.22-46.83) m dan tinggi (46.82-0.0) m. Kaedah RMS yang dijalankan di lapangan pula adalah bertujuan bagi mengesahkan peta ketumpatan lineamen yang dihasilkan. Sebanyak dua belas stesen dinilai dengan tujuh parameter RMS iaitu kekuatan bahan batuan, tahap luluhawa, bukaan kekar, orientasi kekar, kelebaran kekar, ketakselanjaran dan aliran air bawah tanah. Setiap cerun yang dinilai dikelaskan kepada lima kumpulan daripada sangat lemah hingga sangat kuat. Skor RMS berdasarkan jumlah akhir setiap parameter yang dinilai. Hampir kesemua stesen yang dicerap berada pada kelas sederhana (Gunung Rapat, Datok, Kandu, Panjang, A, Tempurung) manakala hanya satu stesen (Gunung Lang) berada pada kelas lemah. Korelasi antara peta ketumpatan lineamen dan skor RMS menunjukkan korelasi yang baik dengan 73% ketepatan. Ini menunjukkan bahawa kestabilan cerun di Lembah Kinta dipengaruhi secara langsung oleh ketumpatan lineamen rantau.
  5. Goh T, Abdul Rahim Samsudin, Abdul Ghani Rafek
    A geotechnical study needs to be carried out to determine the engineering parameters of the rock mass at the project site in executing construction projects such as tunnels, dams, highways and buildings. Design and safety factor of the construction are highly dependent on soil and rock engineering parameters which are usually determined by in-situ test such as Standard Penetration Test (SPT) and seismic tests. The SPT test which normally involves drilling and laboratory works always incur high operating cost, while seismic tests on the other hand are fast, cheap, non-destructive and an easy to operate method for rock mass characterization. The spectral analysis of surface waves (SASW) method is an in situ and non-destructive measurement that is rapid and cost effective. The aims of this study were to determine Rock Quality Designation (RQD) value, excavation classification analysis as well as site characterization by using the SASW method. WinSASW 3.1.3 was used for inversion processing of the SASW data to produce shear wave velocity (Vs) versus depth profiles. The profiles were then analyzed and correlated with rock mass engineering geological parameters such as RQD and site characterization as well as excavation classification of rock mass. Twenty (20) SASW tests were conducted on the granitic rock mass and four (4) SASW tests were conducted on a cut hill slope of metasedimentary rocks. RQD values were computed based on shear wave velocities and ultrasonic velocities of intact (fresh) rock. The differences between RQD obtained from SASW method and those from discontinuity survey were found to be less than 10%. Excavation classification for granitic rock mass at JKR Quarry was empirically determined using both SASW and ultrasonic velocities as well as RQD value of the rock mass. Site characterization for metasedimentary rocks mass at Bukit Tampoi was determined based on shear wave velocities from SASW method.
  6. Simon N, de Roiste M, Crozier M, Abdul Ghani Rafek
    Sains Malaysiana, 2017;46:27-34.
    In the literatures, discussions on the accuracy of different models for landslide analysis have been discussed widely.
    However, to date, arguments on the type of input data (landslides in the form of point or polygon) and how they affect
    the accuracy of these models can hardly be found. This study assesses how different types of data (point or polygon)
    applied to the same model influence the accuracy of the model in determining areas susceptible to landsliding. A total
    of 137 landslides was digitised as polygon (areal) units and then transformed into points; forming two separate datasets
    both representing the same landslides within the study area. These datasets were later separated into training and
    validation datasets. The polygon unit dataset uses the area density technique reported as percentage, while the point
    data uses the landslide density technique, as means of assigning weighting to landslide factor maps to generate the
    landslide susceptibility map that is based on the analytical hierarchy process (AHP) model. Both data groups show striking
    differences in terms of mapping accuracy for both training and validation datasets. The final landslide susceptibility
    map using area density (polygon) as input only has 48% (training) and 35% (validation) accuracy. The accuracy for
    the susceptibility map using the landslide density as input data achieved 89% and 82% for both training and validation
    datasets, respectively. This result showed that the selection of the type of data for landslide analysis can be critical in
    producing an acceptable level of accuracy for the landslide susceptibility map. The authors hope that the finding of this
    research will assist landslide investigators to determine the appropriateness of the type of landslide data because it will
    influence the accuracy of the final landslide potential map.
  7. Adzhar Rambli, Rossita Mohamad Yunus, Ibrahim Mohamed, Abdul Ghapor Hussin
    Sains Malaysiana, 2015;44:1027-1032.
    Recently, there is strong interest on the subject of outlier problem in circular data. In this paper, we focus on detecting outliers in a circular regression model proposed by Down and Mardia. The basic properties of the model are available including the exact form of covariance matrix of the parameters. Hence, we intend to identify outliers in the model by looking at the effect of the outliers on the covariance matrix. The method resembles closely the COVRATIO statistic for the case of linear regression problem. The corresponding critical values and the performance of the outlier detection procedure are studied via simulations. For illustration, we apply the procedure on the wind data set.
  8. Nurkhairany Amyra Mokhtar, Yong Zulina Zubairi, Abdul Ghapor Hussin
    Sains Malaysiana, 2017;46:1347-1453.
    In this study, we propose the estimation of the concentration parameter for simultaneous circular functional relationship model. In this case, the variances of the error term are not necessarily equal and the ratio of the concentration parameter λ = is not necessarily 1. The modified Bessel function was expended by using the asymptotic power series and it became a cubic equation of κ. From the cubic equation of κ, the roots were obtained by using the polyroot function in SPlus software. Simulation study was done to study the mean, estimated bias, absolute relative estimated bias, estimated standard error and estimated root mean square error of the estimation of the concentration parameter. From the simulation study, large concentration parameter and sample size show that the estimated concentration parameter has smaller bias. Also, an illustration to a real wind and wave data set is given to show its practical applicability.
  9. Meor Hakif Amir Hassan, Yeow Boon Sim, Lee Chai Peng, Abdul Hadi Abdul Rahman
    Sains Malaysiana, 2013;42:1091-1100.
    A detailed sedimentological study and facies analysis of the Permian age, uppermost succession of the Kubang Pasu Formation in Perlis was conducted in order to reconstruct the palaeo-depositional environment. Four stratigraphic sections of the uppermost Kubang Pasu Formation were logged at Bukit Chondong and Bukit Tungku Lembu, Perlis. The sections were divided into facies based on lithology and sedimentary structures. Large scale patterns in the form of facies associations and facies successions were also identified. The uppermost Kubang Pasu Formation can be divided into several coarsening upward facies successions. Each facies succession grades upward from an offshore facies association (FA1) composed of bioturbated mudstone and minor thin sandstone, into a distal lower shoreface facies association (FA 2) composed primarily of mudstone interbedded with hummocky cross-stratified sandstone (HCS) and finally a proximal lower shoreface facies association (FA 3) composed of amalgamated hummocky cross-stratified sandstone beds. The facies succession is interpreted as representing a wave- and storm-influenced coastal depositional environment. The gradual transition from siliciclastics to carbonates is probably related to post rift thermal subsidence and tectonic quiescence due to separation of Sibumasu from Gondwana during the Permian.
  10. Amir Hamzah A, Abu Bakar Z, Abdul Sani N, Tan JK, Ahmad Damanhuri M, Makpol S, et al.
    Sains Malaysiana, 2016;45:1371-1380.
    Higher level of education is associated with better cognitive performance and lower risk of developing dementia. However, the effect of education on cognitive performance varies across different cognitive domains and in different populations. The aim of this study was to determine the relationship between education and performance of different cognitive domains among healthy Malay adults. A total of 53 individuals aged 29 to 77 years participated in a battery of neurophysiological tests consisting of Mini-Mental State Examination, Montreal Cognitive Assessment, digit span, visual reproduction and digit symbol speed test (DSST). Blood test was performed for each participant to obtain their biochemical profile. Educational level was divided into level 1 (PMR), level 2 (SPM), level 3 (STPM), level 4 (Diploma) and level 5 (Degree). Simple linear regression indicated that years of education was positively associated with scores of delayed visual reproduction (b=1.348, p=0.002) and DSST (b=3.257, p=0.012). However, scores of all the tests were not significantly different among different levels of education after controlling for age, gender and blood test profile by ANCOVA. Multiple linear regression analysis showed that MMSE score was associated with red cell distribution width (b=-0.628, p=0.005), age (b=-0.119, p<0.001) and there was interaction between high density lipoprotein (HDL) with age (b=0.047, p<001). MoCA score was associated with age (b=-0.121, p<0.001), gender (male compared to female, b=1.870, p=0.020) and HDL (b=1.681, p=0.047). Age was associated with backward digit span (b=-0098, p<0.001) and immediate visual reproduction (b=-0.348, p<0.001), resp. Delayed visual reproduction was associated with age (b=-0.323, p<0.001) and potassium level (b=-4.471, p=0.016). DSST was associated with age (b=-0.911, p<0.001) and alanine aminotransferase (b=-0.754, p=0.002). The lack of association between educational level and cognitive performance after adjusting for confounders in this study maybe due to multiple factors influencing cognitive performance and further studies with a larger sample size are needed to further identify the factors involved.
    Keywords: Cognitive performance; education; healthy Malay adults
    ABSTRAK
    Tahap pendidikan yang tinggi telah dikaitkan dengan prestasi kognitif yang lebih baik dan risiko perkembangan dementia yang lebih rendah. Namun, kesan pendidikan terhadap prestasi kognitif berbeza antara domain kognitif dan populasi yang berlainan. Kajian ini bertujuan untuk menentukan hubungan antara pendidikan dengan prestasi pada domain kognitif yang berlainan pada individu dewasa Melayu yang sihat. Seramai 53 individu yang berumur antara 29 hingga 77 tahun telah menyertai ujian neuropsikologi yang terdiri daripada Pemeriksaan Keadaan Mental Mini, Penilaian Kognitif Montreal, digit span, penghasilan semula visual dan ujian kelajuan simbol digit (DSST). Tahap pendidikan dibahagikan kepada tahap 1 (PMR), tahap 2 (SPM), tahap 3 (STPM), tahap 4 (Diploma) dan tahap 5 (Ijazah Sarjana Muda). Regresi linear mudah menunjukkan bahawa tahap pendidikan berhubung kait secara positif dengan penghasilan semula visual tertunda (b=1.348, p=0.002) dan DSST (b=3.257, p=0.012). Namun, semua skor ujian menjadi tidak berbeza antara tahap pendidikan yang berbeza selepas mengambil kira kesan konpengasas dengan menggunakan ANCOVA. Regresi linear berganda menunjukkan bahawa skor MMSE berhubung kait dengan lebar taburan sel merah (b=-0.628, p=0.005), umur (b=-0.119, p<0.001) dan interaksi antara lipoprotein ketumpatan tinggi (HDL) dan umur (b=0.047, p<001). MoCA didapati berhubung kait dengan umur (b=-0.121, p<0.001), jantina (lelaki berbanding perempuan, b=1.870, p=0.020) dan HDL (b=1.681, p=0.047). Umur juga berhubung kait dengan digit span ke belakang (b=-0098, P<0.001) dan penghasilan semula visual segera (b=-0.348, p<0.001). Penghasilan semula visual tertunda berhubung kait dengan umur (b=-0.323, p<0.001) dan tahap kalium (b=-4.471, p=0.016). DSST berhubung kait dengan umur (b=-0.911, p<0.001) dan alanin aminotransferase (b=-0.754, p=0.002). Hubungan antara tahap pendidikan dan prestasi kognitif tidak dikesan selepas mengambil kira kesan konpengasas yang mencadangkan bahawa prestasi kognitif mungkin dipengaruhi oleh pelbagai faktor dan kajian lanjut dengan bilangan sampel yang lebih besar diperlukan untuk mengenal pasti faktor ini.
  11. Yip FW, Yang Farina, Ibrahim Baba, Abdul Hamid Othman
    Organostannum(IV) complexes derived from dicarboxylic acids have been successfully synthesised from triphenylstannum(IV) hydroxide (Ph3SnOH). The complexes were obtained by refluxing Ph3SnOH and the respective dicarboxylic acids (malonic, succinic, glutaric and adipic acids) using a Dean and Stark apparatus in the appropriate solvent. The free ligands and complexes were characterised by C, Hand Sn elemental analysis and spectroscopic methods such as infrared and nuclear magnetic resonance (1H, 13C NMR). Structure determination of triphenylstannum(IV) succinate, 2, showed that each dicarboxylate anion was bonded monodentatically to two triphenylstannum(IV) moieties. The geometry surrounding each stannum atom is close to a tetrahedron. Spectroscopic data obtained for all complexes were found to be similar and thus it may be concluded that all complexes have the same structure as 2.
  12. Farhila Muhid, Wan Mokhtar Wan Yusof, Othman Omar, Aidil Abdul Hamid, Abdul Jalil Abdul Kader
    The effects of ammonium tartrate and glucose concentration on biomass, lipid and GLA accumulation in Cunninghamella sp. 2A1 were investigated using Response Surface Methodology (RSM). Cultivation was carried out in 250 mL shake flask containing 100 mL of nitrogen limiting medium (with various combinations of concentration of ammonium tartrate (1-3 g/L) and glucose (30-60 g/L) at 30°C and 250 rpm agitation for 120 h. The concentration of both compounds significantly affected the biomass, lipid and GLA yield (p<0.05), with the production of each of them being represented by quadratic models. Higher concentration of ammonium tartrate and glucose (2.99 and 59.33 g/L, respectively) was required for enhanced biomass production whereas low nitrogen content with excess glucose was otherwise favoured for lipid and GLA production. Ammonium tartrate and glucose concentration at 1 and 43 g/L, respectively were estimated by the model and proven to give the highest lipid production and GLA yield of 31.06 % (g/g biomass) and 4.15 ×10-2 (g/g lipid less biomass), respectively
  13. Zal U’yun Wan Mahmood, Che Abd Rahim Mohamed, Zaharudin Ahmad, Abdul Kadir Ishak
    Kajian ini dijalankan untuk melihat variasi taburan 210Po dan 210Pb melalui profil menegak aktivitinya, serta nisbah aktiviti 210Po/210Pb di dalam teras sedimen yang diambil di beberapa stesen persampelan pesisir pantai perairan Sarawak. Didapati profil taburan radionuklid tersebut dalam teras sedimen adalah berubah-ubah mengikut lokasi persampelan dan telah dibuktikan melalui analisis ANOVA yang menunjukkan bahawa terdapat perbezaan bererti pada 95% aras keyakinan bagi aktiviti 210Po (p = 0.000), 210Pb (p = 0.035) dan 210Po/210Pb (p = 0.000) di semua lokasi kajian. Secara umumnya, aktiviti 210Po dan 210Pb yang diukur masing-masing dalam julat 337 ke 2460 Bq/kg, 11 ke 84 Bq/kg di SR 01; 224 ke 2008 Bq/kg, 6 ke 80 Bq/kg di SR 02; 119 ke 1595 Bq/kg, 6 ke 84 Bq/kg di SR 03; 241 ke 2294 Bq/kg, 5 ke 82 Bq/kg di SR 04 dan 175 ke 1340 Bq/kg, 4 ke 44 Bq/kg di SR 05. Merujuk kepada julat tersebut, didapati aktiviti 210Po adalah lebih tinggi daripada aktiviti 210Pb dengan purata nisbah 210Po/210Pb di semua stesen adalah melebihi satu, iaitu dalam julat 20 ke 35. Variasi profil taburan radionuklid tersebut dipercayai dipengaruhi oleh beberapa faktor sekitaran dan telah dibuktikan terdapat korelasi yang kuat di antara taburan radionuklid dengan komposisi sedimen jenis kelodak (210Po:r = 0.701 dan 210Pb: r = 0.648), kedalaman air (210Po: r = -0.647) dan jarak stesen dari daratan (210Po: r = 0.746 dan 210Pb: r = 0.975). Oleh itu, dapat disimpulkan bahawa faktor-faktor tersebut merupakan penyumbang utama ke atas perubahan yang berlaku kepada taburan 210Po dan 210Pb.
  14. Asniza M, Issam A, Abdul Khalil H
    Sains Malaysiana, 2011;40:1123-1127.
    A new heterocyclic coupling agent has been produced from the reaction of maleic anhydride and p-aminophenol, namely N-(4-hydroxylpheneyl)maleimide. The coupling agent underwent azo coupling reaction with aromatic amine, which is p-aminophenol to produce a new heterocyclic azo pigment. The pigment was then subjected to solubility, hiding power and light fastness test. Fourier Transform Infrared Spectroscopy (FTIR), Ultraviolet/Visible (UV/Vis) Spectroscopy, and Nuclear Magnetic Resonance Spectroscopy (1H-NMR, 13C-NMR) were used to obtain the characteristics and structural features of the pigment.
  15. Nashriyah Mat, Nurrul Akmar Rosni, Nor Zaimah Ab Rashid, Norhaslinda Haron, Zanariah Mohd Nor, Nur Fatihah Hasan Nudin, et al.
    Sains Malaysiana, 2012;41:527-538.
    Six varieties of Ficus deltoidea Jack (Moraceae) showed leaf morphological variations through quantitative measurement on different plant parts. There were significant differences among six varieties studied by plant parts. The varieties studied include var. deltoidea Corner, var. angustifolia (Miq.) Corner, var. trengganuensis Corner, var. bilobata Corner, var. intermedia Corner, and var. kunstleri (King) Corner. The upper, middle and lower plant parts showed morphological variations in terms of leaf length, leaf width, leaf area and petiole length. Qualitative parameters also showed trends in morphological variations in terms of leaf shape, leaf base, leaf apex and leaf attachment. However, some qualitative parameters were not the recommended parameters to differentiate among varieties. On the other hand, leaf heterophylly has occurred in F. deltoidea because foliage of the young plant was different from the mature plant. Leaf heterophylly was observed in leaf shape and leaf apex parameters, whereby leaves from the lower plant parts were different from the upper and middle parts. The heterophylly in leaf shape was detected in varieties angustifolia, bilobata, intermedia and trengganuensis, whilst six varieties of F. deltoidea showed leaf apex heterophylly
  16. Nur Suhaili Abd Aziz, Muhammad Khairullah Nor Azmi, Abdul Manaf Hashim
    Sains Malaysiana, 2017;46:1083-1088.
    A one-pot green sonochemical process assisted by ascorbic acid as the reducing agent to produce highly reduced graphene oxide (rGO) decorated with silver nanoparticles (AgNPs) is demonstrated. A complete removal of oxygen-containing group in the GO sheets was confirmed by no observation of the peak corresponds to C-O, C=O and -OH bond. The unexpected decrease of peak intensity corresponds to sp2 hybridized C=C group is explained by a so-called bond polarity effect. The peak observed at ~400 nm seems to show the presence of AgNPs and the red shifting of C=C peak to ~270 nm after the introduction of ascorbic acid indicates the formation of highly reduced GO. The increase of AgNPs size and the crumpled silk-like morphology after the introduction of ascorbic acid also indicate the aggressive reduction of both AgNPs and GO. The increase of ID/IG ratio after the introduction of ascorbic acid seems to indicate the increase of the number of small sp2 domains, the presence of unrepaired defects and the restoration of the sp2 network. This work provides the promising green sonochemical approach by utilizing non-toxic and environmental-friendly reducing agent to produce highly reduced GO decorated with AgNPs for various applications.
  17. Shaharin Fadzli Abd Rahman, Mohamad Rusop Mahmood, Abdul Manaf Hashim
    Sains Malaysiana, 2014;43:1205-1211.
    We report the growth of few-layer graphene (FLG) on a nickel (Ni) substrate using palm oil as a single carbon source by thermal chemical vapor deposition (T-cvD). Using an ample amount of vaporized palm oil resulted in the formation of a thick, amorphous carbon film on the Ni surface. By decreasing the amount of the carbon source supply, thin films consisting of graphite grains and FLG were obtained at growth temperatures of 900 and 1000°C, confirming the potential of using palm oil as a source for graphene growth. The occasional voids were obtained on the transferred film and these voids were confirmed to be areas where FLGs are formed. These FIEs are likely removed during the transfer process. Further reducing the amount of palm oil suppressed the coverage of graphite grains and increased the void area formation on the transferred films, proving the increase of FLG coverage.
  18. Mastura Shafinaz Zainal Abidin, Shahjahan, Abdul Manaf Hashim
    Sains Malaysiana, 2013;42:197-203.
    Gallium nitride is considered as the most promising material for liquid-phase sensor applications due to its chemical stability and high internal piezoelectric polarization. In this work, the sensing responses of undoped-AlGaN/GaN two terminal devices upon exposure to various pH levels in aqueous solution (a mixture of HCl and NaOH) as well as their possible sensing mechanism have been investigated. No reference voltage or gate voltage is applied. The changes in drain-source current, IDS as a function of pH level were evaluated. In the acidic region, there was an almost linear change in IDS where IDS decreased with the increase in pH level. Hence, the translated channel resistance increases with the pH level. High H+ ion concentration at low pH level which corresponds to the large net positive potential on the surface leads to the enhancement of the flow of electrons in 2DEG channel. As the pH level was increased towards neutral point in the acidic region which corresponds to the increase of OH- ion concentration, the net surface potential on the surface starts to be dominated by negative potential. As a result, the 2DEG channel starts to deplete which resulted in the increase of channel resistance. The estimated current and resistance change for sensing area of 1 mm2 and drain-source voltage, VDS of 1- 6 V are in the range of 2.16-80.1 mA/pH and 154.6-500.5 kΩ/pH, respectively. However, the linear decreases of IDS were not continuously observed in the basic region where OH- ions were dominant. The IDS levels were high, showing that the flows of carriers in 2DEG channel were enhanced again. The resistance was low and almost constant in the basic region. It seems to be resulted by the formation of thin Ga(x)O(y) layer on the AlGaN surface contributed by the interaction of OH- with the Ga-face surface. Hence, the net potential on the AlGaN surface seems to be dominated again by the net positive surface potential.
  19. Shaharin Fadzli Abd Rahman, Kasai S, Abdul Manaf Hashim
    Sains Malaysiana, 2013;42:187-192.
    A graphene-based three-branch nanojunction (TBJ) device having nanowire width of 200 nm was successfully fabricated. The layer number of graphene prepared by mechanical exfoliation was determined using a simple optical contrast method which showed good agreement with theoretical value. n-type doping by Polyethylene imines (PEI) was done to control the position of Dirac point. Baking and PEI doping was found to decrease contact resistance and increase the carrier mobility. The chemically-doped TBJ graphene showed carrier mobility of 20000 cm2/Vs, which gave related mean free path of 175 nm.
  20. Nurul Izni Rusli, Mastura Shafinaz Zainal Abidin, Budi Astuti, Ali NK, Abdul Manaf Hashim
    Sains Malaysiana, 2013;42:643-648.
    We report the formation of macropores in n-Si (100) substrates for different etching times of 20, 40 and 60 min at a constant current density of 25 mA/cm2 under front-side illumination in HF:ethanol (1:4) solution. After etching for 20 min, four-branch-shaped pores of various sizes were observed at discrete locations. Etching time of 40 min led to the formation of highly connected four-branch-shaped pores as the branches of adjacent pores appeared to connect to each other. As the etching time was increased further to 60 min, the density of interconnected branches increased remarkably. The macropore formation process occurred in three consecutive phases. The current burst model was used to discuss this process. Formation of four-branch-shaped pores at random locations were observed because current bursts are more likely to nucleate where other current bursts took place initially.
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