Displaying publications 21 - 40 of 2561 in total

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  1. Moslem Sharifinia, Mohammadreza Mohammadpour Penchah, Abolhasan Gheibi, Rohallah Zare, Abbas Mahmoudifard
    Sains Malaysiana, 2015;44:387-397.
    During the last two decades, large-scale high biomass algal blooms of the dinoflagellate Cochlodinium have occurred
    frequently. Prior to 1990, blooms had been primarily reported in Southeast Asia. Since then, time blooms have expanded
    across Asia, Europe and North American. A multi-spectral classification and quantification technique is developed for
    estimating chlorophyll-α concentrations. In this study, we explored the use of Sea-viewing Wide Field of-view Sensor
    (SeaWiFS) satellite data in studying the spatio-temporal changes in chlorophyll-α concentration in Persian Gulf. In
    addition, the present study focuses on the temperature, dissolved oxygen, salinity, pH and nutrient concentrations during
    the red tide phenomenon. The resultant chlorophyll-α concentration images derived from SeaWiFS satellite data give an
    indication of the monthly spatial variation in chlorophyll-α concentration from 2008 to 2009. Variability of chlorophyll-α
    plot from September 2008 to May 2009 in Persian Gulf showed that September 2008 had the lowest value (1.57±0.14
    mg m-3) than other years except May 2009, then tended to increase up to January 2009 (Highest value: 7.47±1.67mg
    m-3), then a slow decrease up to May 2009. The result showed all water physicochemical parameters measurement insitu
    (DO and pH) and ex-situ (NO3
    and PO4
    ), were varied among the different months. The highest and lowest values
    of these parameters were recorded in September 2008 and May 2009, respectively. After occurrence of the red tide,
    nutrient concentration (NO3
    and PO4
    ), dissolved oxygen and pH were reduce compared to before this phenomenon.
    Compare mean between various months’ showed significant differences for temperature records among the months of
    study (p≤0.05). Lowest and highest temperature recorded were in February 2009 and September 2008, respectively, but
    no significant differences were found in salinity (p≥0.05). This study showed that SeaWiFS satellite data provide useful
    information on the spatio-temporal variations in Persian Gulf, which is useful in establishing general trends that are
    more difficult to determine through routine ground measurements.
  2. Aziz R, Hashim I, Abbasbandy S
    Sains Malaysiana, 2018;47:1599-1605.
    This study analyzes the heat transfer of a thin film flow on an unsteady stretching sheet in nanofluids. Three different types of nanoparticles are considered; copper Cu, alumina Al2O3 and titania TiO2 with water as the base fluid. The governing equations are simplified using similarity transformations. The resulting coupled nonlinear differential equations are solved by the Homotopy Analysis Method (HAM). The analytical series solutions are presented and the numerical results obtained are tabulated. In particular, it shows that the heat transfer rate decreases when nanoparticles volume fraction increases.
  3. Parvin S, Hossain MY, Rahma MM, Rahman MS, Ahmed ZF, Ohtomi J, et al.
    Sains Malaysiana, 2016;45:899-907.
    The threatened indigenous small fish, Mystus vittatus (Bloch 1794) is a commercially important fish of Bangladesh.
    The present study describes the fecundity and its relationships with some of the morphometrics and condition factors
    (Fulton’s, KF; Relative weight, WR) of M. vittatus. A total of 50 matured female M. vittatus were collected using the cast
    net from the Padma River during May-July, 2012. Total fecundity (FT
    ) of each female was calculated as the number
    of oocytes found in each ovary, whereas relative fecundity (FR) was the number of oocytes per gram of fish weight.
    The total length (TL) ranged from 8.21 to 12.36 cm (10.60±1.08 cm) and the body weight (BW) varied between 6.0 and
    21.65 g (14.08±4.15 g). The FT
    ranged from 3256 to 22549 with a mean value of 13064.50±4920 while the FR ranged
    from 472 to 1648 oocytes per gram of female, with a mean of 929±245. Significant and strong relationships were found
    between FT vs. TL (r
    2 = 0.63; p<0.001), FT vs. BW (r2 = 0.61; p<0.001), FT vs. OW (r
    2 = 0.89; p<0.001) and FT vs. GSI (rs =
    0.67; p<0.001), but insignificant relationships were recorded for FT vs. KF (rs = 0.11; p = 0.452), FT vs.WR (rs
    = 0.001;
    p = 0.997). The information provided in this study will help initiating sustainable management and conservation of the
    threatened M. vittatus in the region.
  4. Norshahida Shaadan, Sayang Mohd Deni, Abd Aziz Jemain
    Sains Malaysiana, 2012;41:1335-1344.
    This study highlights the advantage of functional data approach in assessing and comparing the PM10 pollutant behaviour as an alternative statistical approach during and between the two extreme haze years (1997 and 2005) that have been reported in Selangor, state of Malaysia. The aim of the study was to improvise the current conventional methods used in air quality assessment so that any unforeseen implicit information can be revealed and the previous research findings can be justified. An analysis based on the daily diurnal curves in place of discrete point values was performed. The
    analysis results provided evidences of the influence of the change in the climate (due to the El-Nino event), the different levels of different emission sources and meteorological conditions on the severity of the PM10 problem. By means of the cummulative exceedence index and the functional depth method, most of the monitoring stations for the year 2005 experienced the worst day of critical exceedences on the 10th of August, while for the year 1997 it occurred between 13th and 26th September inclusively at different dates among the stations.
  5. Rozaimi Zakaria, Abd Fatah Wahab
    Sains Malaysiana, 2014;43:799-805.
    Di dalam kertas ini, pendekatan dalam mentakrifkan ketakpastian titik data melalui pendekatan konsep nombor kabur yang sedia ada dapat diitlakkan. Pengitlakan ini termasuk pentakrifan ketakpastian data yang akan menjadi titik data kabur (titik kawalan kabur) selepas ditakrifkan oleh konsep nombor kabur. Kemudian, kajian ini juga membincangkan tentang proses pengkaburan (operasi potongan-alfa) terhadap titik data kabur tersebut dalam bentuk segitiga nombor kabur diiringi dengan beberapa teorem dan juga pembuktiannya. Selain itu, kami juga turut memodelkan titik data kabur tersebut melalui fungsi lengkung yang sedia ada iaitu fungsi lengkung Bezier. Selepas itu, turut dicadangkan juga ialah proses penyahkaburan terhadap titik data kabur selepas operasi potongan-alfa diimplementasikan bagi memperoleh penyelesaian titik data kabur rangup sebagai keputusan akhir yang turut dimodelkan melalui fungsi lengkung Bezier dengan disertai beberapa teorem bagi memahami bentuk data tersebut.
  6. Gheisari Y, Abd Ghafur Ahmad
    Sains Malaysiana, 2012;41:129-131.
    Given any semigroup presentation, we may obtain the diagram group. The purpose of this paper is to determine the graphs Γn(P), (n ∈ N), which are obtained from diagram group for the union of two semigroup presentations of integers with s and t different initial generators. The number of vertices and edges in these graphs will be computed.
  7. Diana Sirmayunie Mohd Nasir, Abd Rahni Mt Piah
    Dalam Reka Bentuk Geometri Dibantu Komputer (CAGD), pembinaan permukaan secara asasnya dibentuk daripada koleksi tampalan permukaan, dengan syarat keselanjaran tertentu diletakkan di antara tampalan bersebelahan. Sungguhpun pada masa ini tampalan Bézier hasil darab tensor digunakan secara meluas dalam kebanyakan sistem CAGD untuk memodel permukaan bentuk bebas, kaedah ini hanya boleh digunakan untuk memodel permukaan tertutup bergenus satu, iaitu permukaan yang setara dengan suatu torus. Permukaan dengan keselanjaran satah tangen dikenali sebagai permukaan licin secara geometri peringkat satu atau permukaan G1. Makalah ini mengemukakan satu kaedah pembinaan permukaan G1 yang mudah, iaitu permukaan bergenus sifar, dengan menakrif fungsi bikubik Ball pada muka kubus. Fungsi asas yang dibina mempunyai sokongan yang kecil dan hasil tambah fungsi asas adalah satu. Fungsi ini berguna untuk mereka bentuk, mencari hampiran dan menginterpolasi permukaan tertutup mudah yang genusnya adalah sifar. Kaedah pembinaan sebegini mula diperkenal oleh Goodman pada tahun 1991 yang telah menakrif fungsi splin-B teritlak bikuadratik pada mesy sisi empat mudah. Beberapa contoh permukaan/objek yang dihasilkan melalui kaedah pembinaan yang dikemukakan dipapar dalam makalah ini.
  8. Nordin Fatin-Majdina, Haji Abd Rahim Zubaidah, Mohd Bakri Marina, Abd Razak Monica@Munirah
    Sains Malaysiana, 2014;43:1889-1893.
    The effect of S. persica extract on the population of bacteria in single-species biofilm was investigated. An artificial mouth (NAM) system was used for the development of biofilm. In one experiment, aqueous extract of S. persica at sub-MIC concentration (5 mg/mL) was first pumped into the NAM system to treat the experimental pellicle on glass beads before inoculating it with the bacteria (Strep. mitis, Strep. mutans and Strep. sanguinis). This would resemble using the aqueous extract of S. persica before meals. In another experiment, the aqueous extract of S. persica was pumped into the NAM system after the bacterial inoculation and this would resemble using it after meals. In both experiments, 24 h biofilms were allowed to form. The bacterial population of the biofilms was determined and expressed as colony forming unit per mL (cfu mL-1). For negative control, sterilized distilled water was used whereas for positive control, commercial Listerine. It was found that the population of Strep. mitis, Strep. mutans and Strep. sanguinis in the respective biofilms for both experiments involving treatment with S. persica extract or Listerine was significantly reduced by more than 70% (p<0.05) when compared with the negative control. Comparing the effect of S. persica with Listerine on the bacterial population of the biofilms when used either before or after meal showed that S. persica is slightly less effective towards S. sanguinis before meal and towards S. mutans after meal (p<0.05). This study suggests that the efficiency of the antibacterial effect of S. persica is species-related and by its way of usage.
  9. Mohidin N, Abd Wahab N
    Sains Malaysiana, 2010;39(2):333-336.
    A retrospective study was carried out to determine the distribution of intraocular pressure in normal patients who came for vision problems at the Optometry Clinic, Universiti Kebangsaan Malaysia (UKM) Kuala Lumpur Campus, and to determine the differences in intraocular pressure with respect to age, gender and race. The cohort consisted of 148 subjects divided into five groups with age ranged from 10 to 59 years. The inclusion criteria were, subjects had no sistemic or ocular disease, subjects were not taking any medication, visual acuity was 6/6 or better, refractive errors < ±6.00D, astigmatism < 2.00D, anisometropia <2.00D, and mean intraocular pressure measured using the X-PERT tonometer and taken between 9 am to 2 pm. Statistical analysis (ANOVA) showed the mean intraocular pressure without consideration for age, race or gender was 12.6 mmHg (SD ±2.5). There was no significant differences in intraocular pressure between right and left eyes, between different age groups and between different genders. However, the intraocular pressuse for the Chinese was found to be significantly higher than the Malays. It was found that the intraocular pressure of patients who came for vision problems at the Optometry Clinic UKM follows a normal distribution and there was no significant diference found between right and left eyes, between different age groups and genders. Race seemed to contribute to the differences in intraocular pressure. Keywords: Age; clinic population; genders; pressure; intraocular pressure; race
    Study site: Optometry clinic, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
  10. Muhammad aizat K, Abd shukor R
    Sains Malaysiana, 2018;47:1579-1583.
    Information on semiconductor/superconductor interface is important in fabricating devices of such hybrid systems. In
    this paper the electrical properties and AC susceptibility of Tl2
    Ba2
    CaCu2
    O8
    (Tl-2212) superconductor added with CdTe
    semiconductor are reported. Samples with nominal starting composition Tl2
    Ba2
    CaCu2
    O8
    (CdTe)x with x = 0 to 0.20 weight
    percent (wt. %) have been prepared by the solid-state reaction method. X-ray diffraction patterns showed essentially
    the Tl-2212 phase with presence of impurities (CuO and Tl2
    Ba2
    CuO6
    ) for x ≥ 0.05 wt. % but did not change the Tl-2212
    structure which is tetragonal with lattice parameter a = b ≠ c. The critical onset temperature, Tc-onset for all samples was
    between 104 and 108 K while the critical zero resistance temperature, Tc-zero was from 93 to 95 K. The superconducting
    transition determined by AC susceptibility measurement showed Tcχ’ between 101 and 103 K. The peak temperature, Tp
    of
    the imaginary part of the susceptibility χ” decreased for x = 0.05 and then increased for x > 0.05. This indicated that the
    superconducting grains were strongly coupled for x > 0.05 as a result of CdTe addition. The intergrain critical current
    density, Jc
    at Tp
    for the x = 0.2 sample Jc (Tp
    = 95 K) = 23 A cm-2was the highest among all samples. This sample also
    showed the highest Tp
    indicating CdTe improved the flux pinning of the Tl-2212 phase. This result can be useful in the
    fabrication of semiconductor/superconductor (Tl-2212) hybrid devices.
  11. Al-Sharabi A, Sarah Yasmin Tajuddin, Au Diya Fatihah Wan Saffiey, Syazana Jasman, Alwi H, Jumali M, et al.
    Sains Malaysiana, 2016;45:1959-1968.
    Kesan penambahan PbO dengan saiz 10 hingga 30 nm terhadap kekondukisan lebihan YBa2Cu3O7-δ telah dikaji. Kekonduksian lebihan ialah fluktuasi kekonduksian elektrik disebabkan oleh interaksi pasangan Cooper dengan elektron biasa berhampiran suhu genting, Tc. Sampel dengan komposisi permulaan YBa2Cu3O7-δ(PbO)x untuk x = 0.00- 0.45 peratus berat (% bt.) telah disediakan melalui tindak balas keadaan pepejal. Analisis fluktuasi dan kekonduksian lebihan menggunakan teori Aslamazov-Larkin (AL) untuk menentukan dimensi kekonduksian l telah dijalankan. Teori Lawrence-Donaich (LD) pula digunakan untuk menentukan panjang koheren ξc(0), gandingan Josephson J dan anisotropi γ = (ξab(0)/ξc(0)). Suhu genting mula adalah tertinggi (Tc mula = 94 K) untuk sampel x = 0.35. Analisis kekonduksian menunjukkan PbO menyebabkan peralihan kekonduksian daripada 2 dimensi ke 3 dimensi dengan suhu peralihan, T2D–3D tertinggi bagi sampel x = 0.20 (120 K). Model Lawrence-Donaich menunjukkan panjang koheren ξc(0) adalah terpanjang dan anisotropi terendah bagi sampel x = 0.25. Sampel ini juga menunjukkan gandingan Josephson tertinggi, J = 0.296. Dua kesan yang mungkin berlaku akibat penambahan PbO ialah pembentukan bahan bukan superkonduktor dalam sampel dan peningkatan hubungan antara butiran yang meningkatkan sifat-sifat kesuperkonduksian.
  12. Ewe L, Hamid N, Abd-Shukor R
    Sains Malaysiana, 2006;35:73-77.
    The insulator-metal transition temperature, Tim of La1-xSrxMnO3(x = 0.0, 0.05, 0.15 and 0.3) was studied during warming and cooling between 50 K to 300 K. The results showed that Tim of La1-xSrxMnO3 shifted to a higher temperature as Sr was substituted for La. Scanning electron micrographs showed that the average grain size is in the range of 0.6 µm - 1.4 µm. Grain boundaries are almost completely revealed for x = 0.3. X-Ray powder diffraction patterns showed cubic structure (space group Pm-3m) and contain no secondary phases.
  13. Ewe L, Ramli R, Lim K, Abd-Shukor R
    Sains Malaysiana, 2012;41:761-768.
    The effects of strontium doping on the electrical and magneto-transport properties of magneto resistive La0.7Ca0.28Sr0.02MnO3 at different sintering temperatures have been studied. The samples were prepared by the co-precipitation technique (COP) and sintered at 1120, 1220 and 1320 oC. XRD patterns revealed that the samples have an orthorhombic structure and the diffraction patterns can be indexed with the Pbnm space group. The insulator metal transition, TIM increased linearly from 261 K to 272 K with the increase in sintering temperature. The magnetoresistance (MR) measurements were made in magnetic fields from 0.1 to 1 T at room temperature. The percentage of MR increased with increasing of magnetic field and sintering temperature for all samples. The electrical resistivity data were fitted with several equations in the metallic (ferromagnetic) and insulator (paramagnetic) regime. The density of states at the Fermi level N(EF) and the activation energy (Ea) of electron hopping were estimated by using variable range hopping and small polaron hopping model.
  14. Kong W, Koh A, Abd-Shukor R
    Superkonduktor suhu tinggi berasaskan sistem (Tl0.85Cr0.15)Sr2CaCu2O7-Agx (Tl1212) dengan komposisi x = 0.0, 0.01, 0.02, 0.03 dan 0.05 telah disediakan dengan kaedah tindak balas keadaan pepejal. Rintangan elektrik terhadap suhu telah diukur dengan kaedah penduga empat titik. Suhu genting mula, Tc-mula bagi sistem Tl1212 tanpa penambahan nano Ag adalah 113 K. Penambahan nano Ag menurunkan suhu genting sampel. Corak pembelauan sinar-X menunjukkan bahawa semua sampel mempunyai fasa dominan 1212. Sampel x = 0.02 mempunyai peratusan fasa 1212 yang tertinggi iaitu 87%.
  15. Ilhamsyah Putra Abu Bakar, Nurul Raihan Mohd Suib, Aizat K, Nur-Akasyah J, Radiman S, Abd-Shukor R
    Sains Malaysiana, 2017;46:1971-1977.
    Kesan penambahan In2
    O3
    terhadap superkonduktor (Bi1
    .
    6
    Pb0.4)Sr2
    Ca2
    Cu3
    O10 (In2
    O3
    )x
    (x = 0- 0.1 peratus berat) telah
    dikaji. Pencirian yang dijalankan ialah pembelauan sinar-X, mikrostrukur, rintangan elektrik, kerentanan arus ulang
    alik dan ketumpatan arus genting antara butiran. Suhu genting mula, Tc mula dan suhu genting sifar, Tc sifar adalah
    tertinggi bagi sampel x = 0 iaitu Tc mula = 112 K dan Tc sifar = 90 K. Corak pembelauan sinar-X menunjukkan peratus isi
    padu fasa (Bi1
    .
    6
    Pb0.4)Sr2
    Ca2
    Cu3
    O10 (Bi-2223) dan (Bi1
    .
    6
    Pb0.4)Sr2
    CaCu2
    O8
    (Bi-2212) adalah hampir sama untuk semua
    sampel. Pengukuran kerentanan ulang alik telah dijalankan pada frekuensi 295 Hz dan medan magnet H = 5 Oe.
    Dua peralihan pada kerentanan ulang alik bagi x = 0 menandakan kewujudan fasa Bi-2223 dan Bi-2212. Suhu pada
    puncak kehilangan tenaga, Tp
    untuk kerentanan khayal, χ”adalah tertinggi (74 K dan 104 K) untuk x = 0. Penambahan
    In2
    O3
    telah menyebabkan Tp
    beranjak kepada suhu lebih rendah dan ini menunjukkan fluks magnet menembusi antara
    butiran pada suhu yang semakin menurun apabila In2
    O3
    ditambah. Lengkung puncak Tp
    juga melebar apabila In2
    O3
    ditambah. Ini menunjukkan gandingan antara butiran yang semakin lemah dan tenaga pengepinan fluks yang menurun.
    Ketumpatan arus genting antara butiran Jc
    (Tp
    ) telah diukur menggunakan model Bean dan nilainya adalah antara 16
    hingga 20 A cm-2 bagi semua sampel. Satu model skematik arus aruhan bagi bahan polihablur yang mengandungi dua
    fasa superkonduktor dengan pecahan isi padu yang sama tetapi suhu genting yang berlainan dibincangkan.
  16. Nor Azah Nik-Jaafar, Abd-Shukor R
    Sains Malaysiana, 2018;47:1907-1911.
    The effects of mixed-valence Mn substitution at the Cu site on the superconducting and elastic properties of
    La1.85-1.5xSr0.15+1.5xCu1-xMnx
    O4
    (x = 0, 0.02 and 0.04) were studied. The samples were characterized by X-ray diffraction
    (XRD) method, temperature-dependent resistance measurements, scanning electron microscopy (SEM) and sound velocity
    measurements at room temperature. An elastic softening and a decrease in the critical temperature Tc
    was observed as
    Mn was substituted for Cu. The Debye temperature θD for x = 0 and 0.02 void free samples were calculated to be 459 K
    and 430 K, respectively. Internal lattice strain which is related to lattice parameter ratio a/c did not correlate with Tc
    . The
    electron-phonon coupling estimated using the conventional Bardeen-Cooper-Schrieffer (BCS) theory was λ = 0.367 (x =
    0) and 0.368 (x = 0.02). The electron-phonon coupling in two-dimensional van Hove scenario was calculated to be λvH
    = 0.0148 (x = 0) and 0.0149 (x = 0.02). These results were compared with other cuprates and related superconductors.
    The comparison showed that other than electron-phonon coupling, the elastic moduli might play an important role in
    the mechanism of superconductivity in these materials.
  17. Ahmad A, Shuhaimi Othman M, Lim E, Abd. Aziz Z
    Sains Malaysiana, 2013;42:587-596.
    Satu analisis penentuan parameter kualiti air yang penting untuk penilaian ekosistem cetek telah dilakukan menggunakan kaedah multivariat. Sebanyak 14 parameter kualiti air yang melibatkan komponen biologi, fizik dan kimia telah dikumpulkan setiap bulan selama satu tahun. Data dianalisis menggunakan ujian faktor yang melibatkan tiga proses iaitu mengenal pasti korelasi antara faktor, mengekstrak faktor dan seterusnya melihat kesan gabungan faktor-faktor tersebut. Proses pertama melibatkan pengelompokkan parameter yang berkorelasi kuat ke dalam faktor tersendiri dan mengeluarkan parameter yang mempunyai lebih daripada satu faktor. Analisis pengelasan agglomeratif hierarki (HACA) dan analisis diskriminan (DA) juga dilakukan untuk memperlihatkan kelompokan dan pengaruh faktor terhadap kualiti air tasik. Hasil analisis menunjukkan kualiti air Tasik Chini dipengaruhi oleh lebih daripada satu faktor. Hasil kajian menunjukkan komponen biologi dan kimia (nutrien) mempunyai pengaruh kuat dalam penentuan kualiti air tasik. Parameter berasaskan biologi iaitu BOD5, COD, klorofil a dan kimia (nitrat dan ortofosfat) adalah parameter yang
    penting di Tasik Chini. Ketiga-tiga analisis yang dijalankan menunjukkan kepentingan penentuan komponen biologi dan kimia bagi menentukan kualiti air Tasik Chini.
  18. Umar Hamzah, Lee CR, Abd. Ghani Rafek
    Sains Malaysiana, 2007;36:1-8.
    Empat puluh sampel batuan granit berbutir kasar daripada Kuala Kubu Bharu telah dikumpulkan daripada 14 lokaliti di sepanjang singkapan jalan daripada Taman Bukit Bunga hingga ke kampung Pertak. Sampel-sampel teras selinder dan blok empatsegi telah disediakan daripada sampel lapangan tersebut untuk menjalani ujian halaju sonik dan mekanik setelah pengukuran beberapa sifat fizik. Nilai purata porositi berkesan sampel-sampel tersebut ialah 1.33 % manakala purata ketumpatan kering dan tepu adalah 2542 dan 2555 kg/m3. Graviti spesifik yang dihitung berjulat 2.1-2.9. Halaju denyut ultrasonik min gelombang P dan S yang melalui bahan batuan yang diuji ialah 5359 m/s dan 2890 m/s. Ujian-ujian mampatan sepaksi menunjukkan purata kekuatan mampatan sepaksi sampel yang bernilai 138.6 MPa. Nilai purata bagi indeks kekuatan beban titik Is(50) pula ialah 5.63. Oleh itu perkaitan kekuatan mampatan sepaksi dengan kekuatan beban titik ialah dengan faktor multiplikasi 25.
  19. Khor Wei Chung, Chow Weng Sum, Abd. Hadi A. Rahman
    Sains Malaysiana, 2015;44:931-940.
    The Sandakan Formation of the Segama Group is exposed across the Sandakan Peninsular in eastern Sabah. This Upper Miocene part of the Segama Group unconformably overlies the Garinono Formation and is conformably overlain by the Bongaya Formation. This formation was investigated with detailed logging of outcrops and microfossils analysis in order to map the depositional facies and sedimentary environment. This study showed the presence of seven lithofacies: Thick amalgamated sandstone; thin, lenticular interbedded HCS sandstones and mudstone; laminated mudstone with Rhizophora; trough cross-bedded sandstone; laminated mudstone; strip mudstone with thin sandstone and siltstone; and interbedded HCS sandstone and mudstone. Based on the presence of Rhizophora, Brownlowia, Florchuetia sp., Polypodium, Stenochleana palustris, Ascidian spicule low angle cross bedding, very fine grained sandstone, thin alternations of very fine sandstone, silt and clay layers showing cyclicity (muddy rhythemites), rocks in the Sandakan Formation are interpreted as mangal estuary and open marine facies. Three facies associations could be deduced from the seven lithofacies: Gradual coarsening upwards shoreface; abrupt change facies and prograding estuary facies association.
  20. Suppiah D, Hamid F, Kutty M, Abd. Hamid S
    Sains Malaysiana, 2012;41:1245-1251.
    Molybdenum oxides catalysts are extensively used in various selective oxidation reactions. In this work, controlled precipitation method was used to synthesise molybdenum oxides. The effects of various titration parameters on the precipitate growth rate and structure throughout catalyst synthesis were investigated. The titration parameters varied for this study were molybdates (ammonium heptamolybdate) concentration, precipitation agent (HNO3) concentration, precipitating agent rate of addition and temperature of synthesis. X-Ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) were used to characterize the catalysts. This study highlights the significant effects of the titration parameters varied on the supersaturation of the solution therefore yielding precipitate with different morphology. It was observed that the temperature played the major role followed by molybdate concentration in the formation of the bulk catalyst. Supramolecular structure (Mo36O112) was observed at lower temperature (30ºC) and lower molybdate concentration (0.07 M, 0.10 M) while at higher temperature (50ºC) and higher molybdate concentration(0.14 M) hexagonal (h-MoO3) phase structure was formed. Fast rate of addition and high concentration of precipitating agent affected the solution equilibrium leading to unclear inflection point (supersaturation point) at the titration curve.
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