Displaying publications 441 - 460 of 2919 in total

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  1. A finite element model to predict wellbore fracture pressure with acid damage
    Fanhui-Zeng, Jianchun-Guo, Yuxuan-Liu
    Sains Malaysiana, 2015;44:1377-1388.
    Hydraulic fracturing becomes more difficult when confronted with a formation of high fracturing pressure. In such formations, acidizing before the main fracturing treatment provide a method to reduce fracture pressure. The aim of this paper was to investigate the evolution of fracture pressure in a wellbore with acidizing. Five experiments were conducted to study the mechanisms of acid damage on reservoir minerals and cementing materials properties. Consequently, a mathematical model to predict fracture pressure with acidizing has been established and verified by field data. The analysis results showed that it is possible to reduce fracture pressure with decreased rock strength and fracture critical stress intensity factor by means of acid damage. Acid damage destroys the crystal structure of mineral particles, breaks the crystalline layers in cementing materials, increases rock porosity and reduces the rock strength. In addition, as the acid concentration, formation temperature and acid treatment time increased, it was useful to reduce fracture pressure in the wellbore. Using the proposed model, we were able to select the optimal acid damage construction parameters to reduce fracture pressure.
    Matched MeSH terms: Temperature
  2. Prediction of lead seven day minimum and maximum surface air temperature using neural network and genetic programming
    K. Ramesh, P. Ramalakshmi, R. Anitha
    Sains Malaysiana, 2015;44:1389-1396.
    The determination of variance of surface air temperature is very essential since it has a direct impact on vegetation, environment and human livelihood. Forecast of surface air temperature is difficult because of the complex physical phenomenon and the random-like behavior of atmospheric system which influences the temperature event on the earth surface. In this study, forecast models based on artificial neural network (ANN) and genetic programming (GP) approaches were proposed to predict lead seven days minimum and maximum surface air temperature using the weather parameters observed at the station Chennai, India. The outcome of this study stated that models formulated using ANN approach are more accurate than genetic programming for all seven days with the highest coefficient of determination (R2), least mean absolute error (MAE), root mean square error (RMSE) and mean absolute percentage error (MAPE) on deployment with independent test dataset. ANN models give statistically acceptable mean absolute error of 0.59oC for lead day one in minimum temperature forecast and 0.86oC variance for lead day one in maximum temperature forecast. The study also clarified that the level of accuracy of the proposed prediction models were found to be better for smaller lead days when compared with higher lead days with both approaches.
    Matched MeSH terms: Temperature
  3. Spatial and temporal variations of water quality and trophic status in Bukit Merah Reservoir, Perak
    Mohd Shafiq Zakeyuddin, Amir Shah Ruddin Md Sah, Mohd Syaiful Mohammad, Nurul Fazlinda Mohd Fadzil, Zarul Hazrin Hashim, Wan Maznah Wan Omar
    Sains Malaysiana, 2016;45:853-863.
    A study of spatial and temporal variations on water quality and trophic status was conducted twice a month from December
    2012 to January 2014 in four sampling stations at Bukit Merah Reservoir (BMR). The concentration of dissolved oxygen
    (DO), water temperature, conductivity, total dissolved solids (TDS), total phosphorous (TP), PO4
    -
    , NO2
    -
    , NO3
    -
    , NH4
    + and
    net primary productivity had significant differences temporally (p<0.05) except for pH, total suspended solids (TSS)
    and chlorophyll-a. Based on correlation analysis, the amount of rainfall and rain days has negatively correlated with
    secchi depth and chlorophyll-a (p<0.01). The water level has significantly decreased the value of the temperature, pH,
    conductivity, TP and NO2
    -
    but it has positive correlation with NO3
    -
    and NH4
    +. Discharged from Sungai Kurau increased
    the value of conductivity, TSS, TP and NO2
    -
    as a result from runoff and erosion, thus decreasing the secchi depth values,
    NO3
    -
    and NH4
    +. The water quality of BMR is classified in Class II and TSI indicates that the BMR has an intermediate level
    of productivity (mesotrophic) and meets the objective of this reservoir which was to provide water for paddy irrigation.
    Matched MeSH terms: Temperature
  4. Current and conductance modulation at elevated temperature in siliconand InAs-based spin field-effect transistors
    Osintsev D, Sverdlov V, Makarov A, Selberherr S
    Sains Malaysiana, 2013;42:205-211.
    Spin field-effect transistors (SpinFETs) are promising candidates for future integrated microelectronic circuits. A SpinFET is composed of two ferromagnetic contacts (source and drain), which sandwich a semiconductor channel. Current modulation is achieved by electrically tuning the gate voltage dependent strength of the spin-orbit interaction in the semiconductor region. We investigated the properties of SpinFETs for various parameters - the band mismatch, the barrier height between the contacts and the channel and the strength of the spin-orbit coupling, for various temperatures. We demonstrated that the creation of Schottky barriers between the channel and the contacts guarantees a pronounced modulation of the magnetoresistance sufficient to open a possibility to operate SpinFETs at room temperature. We also demonstrated that silicon fins with [100] orientation exhibit a stronger dependence on the value of the spin-orbit interaction and are thus preferable for practical realization of silicon-based SpinFETs.
    Matched MeSH terms: Temperature
  5. New hybridization approach of titanium organometallic: PANi thin films as room temperature gas sensors
    Izura Izzuddin, Mohammad Hafizuddin Jumali, Muhammad Yahaya, Muhamad Mat Salleh
    Sains Malaysiana, 2012;41:1017-1021.
    The aim of this research was to investigate the ability of organometallic titanium-PANi hybrid materials as gas sensor at room temperature. To form the hybrid materials, commercially available polyaniline (PANi) powder were directly added into organometallic titanium sols which was synthesized using the sol gel method. The composite films were prepared via spin coating technique followed by electrode deposition for sensors fabrication. Five different organometallic titanium:PANi ratios namely 1 wt% to 5 wt% of PANi were prepared for this experiment. For gas sensing test, all samples were exposed to ethanol vapour. The sensing mode is based on the variation in the electrical conductivity due to the
    interaction between the gas molecules and the film. It was observed that the composite sensors required appropriate ratio to exhibit optimum sensing properties. This finding proved that the hybridization process is successful and offered much cheaper and easier method for fabrication of room temperature gas sensor.
    Matched MeSH terms: Temperature
  6. Unsteady Mixed Convection near the Forward Stagnation Point of a Two-Dimensional Symmetric Body Prescribed with a Constant Wall Heat Flux
    Roslinda Nazar, Pop I
    Sains Malaysiana, 2004;33.
    The unsteady mixed convection boundary layer flow near the forward stagnation point of a two-dimensional symmetric body prescribed by a uniform heat flux rate is studied in this paper. The main aim of the investigation is to identify situations in which dual solutions for the steady-state flow can be determined when the flow is opposing. It is also shown that there is a smooth transition from the unsteady initial flow (short time) to the final steady state flow (large time).
    Matched MeSH terms: Hot Temperature
  7. One-step anodization of aluminum at room temperature
    Araoyinbo AO, Ahmad Fauzi M, Sreekantan S, Azizan Aziz
    Sains Malaysiana, 2009;38.
    The formation of nano pores on aluminum at 30oC- 38oC, employing a one step anodization technique which does not require removing the oxide layer formed is presented. A 20% phosphoric acid electrolyte (concentration higher than the normal anodization concentration of 5 to 10%) at a cell potential of 60 volts was used. A platinum electrode was used as the cathode electrode while the aluminum substrate as the anode electrode. A dc powered electrochemical cell to provide the required amount of current density (without the use of temperature controlled water bath) suitable or necessary for pore formation at room temperature was employed. The results obtained show that pore formation at room temperature is achievable and the pore diameter ranged between 80-120 nm.
    Matched MeSH terms: Temperature
  8. Effects of fine-scale pattern of dwarf bamboo on understory species diversity in Abies faxoniana forest, Southwest, China
    Wang YJ, Shi XP, Peng Y, Tao JP, Zhong ZC
    Sains Malaysiana, 2012;41:649-657.
    Dwarf bamboo is recognized as a significant determinant of the structure and dynamics in temperate forests. Quantitative relationships between the abundance (density and coverage) of dwarf bamboo, Fargesia nitida, and micro-environments, species diversity on the floor were estimated in an Abies faxoniana pure forest in southwest China. Understory microenvironmental conditions (daily differences temperature and moisture, RPPFD under bamboo layer and ground cover) changed dramatically with the bamboo density. Stepwise multiple regression analyses indicated that abundance of F. nitida was mainly correlated with canopy characteristics and disturbance factors in the A. faxoniana pure forest. All richness indices decreased significantly with the bamboo density and RPPFD under bamboo layer. Importance values (IV) of understory species in different bamboo densities and Detrended canonical correspondence analysis (DCCA) indicated three understory plant groups, resistant to high bamboo abundance (Group A), resistant to intermediate bamboo abundance (Group B) and sensitive to bamboo abundance (Group C). These groups mainly responded to abundance of bamboo and RPPFD under bamboo layer, resulted from the integration of characteristics of bamboo, canopy and topography factors. Different bamboo abundance had different influences on understory species diversity and groups. Dense F. nitida condition (> 10 culms/m2) had significant negative effect and 0-5 bamboo condition had not significant negative effect on understory species diversity in A. faxoniana forest. We suggest the fine-scale analysis on effects of bamboo abundance should be taken account into considering in heterogeneous patches in process of the succession and regeneration of natural forests.
    Matched MeSH terms: Temperature
  9. Spectroscopic studies of Er3+-Yb3+ codoped multicomposition tellurite oxide glass
    Baki S, Tan L, Kan C, Kamari H, Noor A, Mardi M
    Sains Malaysiana, 2014;43:843-850.
    Multicomposition of Er3+ -Y11-3+ codoped tellurite oxide, Te02-ZnO-PbO-Ti02-Na20 glass has been investigated. A detailed spectroscopic study of the Judd-Ofelt analysis has been performed from the measured absorption spectrum in order to obtain the intensity parameters S2, (t=2, 4, 6). The calculated S2, values were then utilized in the determination of transition probabilities, radiative lifetimes and branching ratios of the Er3+ transitions between the J(upper)-J'(lower) manifolds. Both visible upconversion and near-infrared spectra were characterized under the 980 nm laser diode excitation at room temperature.
    Matched MeSH terms: Temperature
  10. Modeling of the dissolution kinetics of arbutus wild berries-based tablets as evaluated by electric conductivity
    Tounsia Abbas-Aksil, Salem Benamara
    Sains Malaysiana, 2015;44:301-308.
    Lyophilized powder (LP) from Algerian arbutus wild berries (Arbutus unedo L.) was obtained. This present paper reports about the dissolution (releasing) properties of LP-based tablets, evaluated through the electric conductivity (EC) of distilled water which is employed as surrounding medium, at three different temperatures (291, 298 and 309 K). In addition to this, secondary physicochemical characteristics such as elementary analysis, color and compressibility were evaluated. Regarding the modeling of ionic transfer, among the three tested models, namely Peleg, Singh et al. and Singh and Kulshestha, the latter seems to be the most appropriate (R2 = 0.99), particularly in the case of compacted tablets under 2000 Pa. The temperature dependence of the dissolution process was also studied applying Arrhenius equation (R2>0.8) which allowed to deduce the activation energy, ranging from 18.7 to 21.4 kJ.mol-1 according to the model and compression force employed.
    Matched MeSH terms: Temperature
  11. Self-healing of poly(2-hydroxyethyl methacrylate) hydrogel through molecular diffusion
    Sirajuddin N, Md Jamil M
    Sains Malaysiana, 2015;44:811-818.
    Synthetic materials that are capable of healing upon damage are being developed at a rapid pace because of their
    many potential applications. Here, new healing chemically cross-linked hydrogel of poly(2-hydroxyethyl methacrylate)
    (pHEMA) was prepared. The healing hydrogel was achieved by heating above its glass transition (Tg
    ). The intermolecular
    diffusion of dangling chain and the chain slippage led to healing of the gel. The peaks in attenuated total reflectance
    (ATR) confirmed that hydrogel was formed while rheological studies had determined the minimum for healing temperature
    is 48.5o
    C. The results showed that ratio stress of the healable hydrogel can reach until 92 and 91% of first and second
    healing cycle, respectively. The morphology of the sample was carried out to evaluate the self-property of hydrogel.
    Matched MeSH terms: Temperature
  12. Kesan Medan Magnet Menegak ke atas Lengkung Sut Olakan Benard-Marangoni Mantap dalam Lapisan Mengufuk Bendalir (The Effect of a Vertical Magnetic Field on the Onset of Study Bernard-Marangoni Convection in a Horizontal Layer of Electrically Conducting Fluid)
    Ruwaidiah Idris, Ishak Hashim
    Sains Malaysiana, 2005;34.
    In this work we use an analytical technique to analyse the effect of a vertical uniform magnetic field on the onset of steady Benard-Marangoni convection in a horizontal layer of electrically conducting fluid subject to a uniform vertical temperature gradient in the asymptotic limit short waves. We found that in the limit of short waves, the leading order expression for the marginal curve is not affected by the magnetic field.
    Dalam makalah ini kesan medan magnet menegak seragam ke atas lengkung sut permulaan olakan mantap Benard-Marangoni dalam lapisan bendalir mengufuk berpengalir elektrik dikaji tertakluk kepada kecerunan suhu yang seragam dalam had asimptot gelombang pendek. Kami dapati medan magnet tidak memberi kesan kepada sebutan utama lengkung sut dalam had gelombang pendek.
    Matched MeSH terms: Temperature
  13. An evaluation of thermal characteristics of bacterium Actinobacillus succinogenes for energy use and circular bioeconomy
    Lin BJ, Chen WH, Lin YY, Chang JS, Farooq A, Singh Y, et al.
    Bioresour Technol, 2020 Apr;301:122774.
    PMID: 31954973 DOI: 10.1016/j.biortech.2020.122774
    The thermal characteristics of Actinobacillus succinogenes (AS) from pyrolysis, torrefaction, and combustion are analyzed to evaluate the potential of this biomass as a renewable fuel. AS pyrolysis can be classified into four stages, and its main decomposition zone is at 200-500 °C. The solid yield of AS after 60 min torrefaction is over 60 wt%, and the torrefaction severity index map indicates that a high torrefaction temperature with a short duration has a more profound influence on its decomposition. The Py-GC/MS analysis of AS suggests that the volatile products from 500 °C pyrolysis are similar to microalgae-derived pyrolysis bio-oils. The combustibility index (S) of AS is 4.07 × 10-7 which is much higher than that of lignite coal (0.39 × 10-7) and bituminous coal (0.18 × 10-7), and close to those of biochar and bio-oil. The obtained results are conducive to the development of microorganisms as fuel to achieve a circular bioeconomy.
    Matched MeSH terms: Hot Temperature
  14. Fulltext Data on sea surface biophysical parameters during different monsoon seasons
    Idris MS, Lee Siang H, Amin RM
    Data Brief, 2020 Feb;28:104982.
    PMID: 31890817 DOI: 10.1016/j.dib.2019.104982
    The biophysical data presented in this article were collected in the east coast of Peninsular Malaysia from May to November 2009. These monthly surface data were obtained from 32 stations along the coastal-offshore transect and were analyzed to understand the spatial and temporal distributions of biophysical parameters during different monsoon seasons. The data presented here include sea surface temperature (SST), sea surface salinity (SSS), Secchi disk depth (SDD), Chlorophyll-a (Chl-a), suspended particulate matter (SPM), mineral suspended solid (MSS) and chromophoric dissolved organic matter (CDOM).
    Matched MeSH terms: Temperature
  15. Differences in dry-bulb temperature do not influence moderate-duration exercise performance in warm environments when vapor pressure is equivalent
    Lei TH, Schlader ZJ, Che Muhamed AM, Zheng H, Stannard SR, Kondo N, et al.
    Eur J Appl Physiol, 2020 Apr;120(4):841-852.
    PMID: 32072226 DOI: 10.1007/s00421-020-04322-8
    PURPOSE: Recent studies have determined that ambient humidity plays a more important role in aerobic performance than dry-bulb temperature does in warm environments; however, no studies have kept humidity constant and independently manipulated temperature. Therefore, the purpose of this study was to determine the contribution of dry-bulb temperature, when vapor pressure was matched, on the thermoregulatory, perceptual and performance responses to a 30-min cycling work trial.

    METHODS: Fourteen trained male cyclists (age: 32 ± 12 year; height: 178 ± 6 cm; mass: 76 ± 9 kg; [Formula: see text]: 59 ± 9 mL kg-1 min-1; body surface area: 1.93 ± 0.12 m2; peak power output: 393 ± 53 W) volunteered, and underwent 1 exercise bout in moderate heat (MOD: 34.9 ± 0.2 °C, 50.1 ± 1.1% relative humidity) and 1 in mild heat (MILD: 29.2 ± 0.2 °C, 69.4 ± 0.9% relative humidity) matched for vapor pressure (2.8 ± 0.1 kPa), with trials counterbalanced.

    RESULTS: Despite a higher weighted mean skin temperature during MOD (36.3 ± 0.5 vs. 34.5 ± 0.6 °C, p 

    Matched MeSH terms: Body Temperature Regulation*; Hot Temperature*
  16. Bioflocculant production using palm oil mill and sago mill effluent as a fermentation feedstock: Characterization and mechanism of flocculation
    Hassimi AH, Ezril Hafiz R, Muhamad MH, Sheikh Abdullah SR
    J Environ Manage, 2020 Apr 15;260:110046.
    PMID: 32090804 DOI: 10.1016/j.jenvman.2019.110046
    This study was conducted to examine the production of bioflocculants using agricultural wastewater as a fermentation feedstock under different temperatures and incubation times. The mechanism of flocculation was studied to gain a detailed understanding of the flocculation activity. The highest bioflocculant yield (2.03 g/L) at a temperature of 40 °C was produced in a palm oil mill effluent medium (BioF-POME). Bioflocculant produced from a fermented SME medium (BioF-SME) showed the highest activity. The flocculation tests for colour and turbidity removal from lake water indicated that BioF-SME and BioF-POME performed comparably to commercial alum. Analyses of the bioflocculants using liquid chromatography-mass spectrometry (LC-MS) found that the bioflocculants contained xylose and glucose. The mechanism study showed that flocculation occurred through charge neutralization and interparticle bridging between the bioflocculant polymer and the particles in the lake water. Thus, agricultural wastewater can be used as a fermentation feedstock for high-quality bioflocculants.
    Matched MeSH terms: Temperature
  17. Steam reforming of polystyrene at a low temperature for high H2/CO gas with bimetallic Ni-Fe/ZrO2 catalyst
    Zhou H, Saad JM, Li Q, Xu Y
    Waste Manag, 2020 Mar 01;104:42-50.
    PMID: 31962216 DOI: 10.1016/j.wasman.2020.01.017
    Recovery of chemicals and fuels from unrecyclable waste plastics at high temperatures (>800 °C) has received much research attention. Thermodynamic equilibrium calculation suggests that it is possible to perform the low-temperature steam reforming of polystyrene. In this study, we synthesized a Ni-Fe bimetallic catalyst for the low-temperature (500 °C) steam reforming of polystyrene. XRD characterization showed that Ni-Fe alloy was formed in the catalyst. Compared to conventional Ni catalysts, the Ni-Fe bimetallic catalysts can significantly increase the H2/CO ratio in the produced gas with high gas production yield. The online gas analysis revealed that H2, CO, and CO2 were formed in the same temperature range. H2 and CO were formed simultaneously through steam reforming reactions, and CO2 was formed through water-gas shift reaction. New morphologies of carbon deposition on the catalyst surface were found, suggesting that wax could be condensed on the catalyst surface at a low temperature.
    Matched MeSH terms: Temperature
  18. Fulltext Fabry-Pérot resonances and a crossover to the quantum Hall regime in ballistic graphene quantum point contacts
    Ahmad NF, Komatsu K, Iwasaki T, Watanabe K, Taniguchi T, Mizuta H, et al.
    Sci Rep, 2019 Feb 28;9(1):3031.
    PMID: 30816251 DOI: 10.1038/s41598-019-39909-5
    We report on the observation of quantum transport and interference in a graphene device that is attached with a pair of split gates to form an electrostatically-defined quantum point contact (QPC). In the low magnetic field regime, the resistance exhibited Fabry-Pérot (FP) resonances due to np'n(pn'p) cavities formed by the top gate. In the quantum Hall (QH) regime with a high magnetic field, the edge states governed the phenomena, presenting a unique condition where the edge channels of electrons and holes along a p-n junction acted as a solid-state analogue of a monochromatic light beam. We observed a crossover from the FP to QH regimes in ballistic graphene QPC under a magnetic field with varying temperatures. In particular, the collapse of the QH effect was elucidated as the magnetic field was decreased. Our high-mobility graphene device enabled observation of such quantum coherence effects up to several tens of kelvins. The presented device could serve as one of the key elements in future electronic quantum optic devices.
    Matched MeSH terms: Temperature
  19. Fulltext Influence of discrete fibers and mesh elements on the behaviour of lime stabilized soil
    Kaniraj, Shenbaga R., Fung, Y. C.
    Pertanika Journal of Science & Technology, 2018;26(4):1547-1570.
    MyJurnal
    Addition of chemical binders such as lime and cement improves the strength and stiffness
    of fine grained soils. However, the treated soils exhibit brittle stress-strain behaviour.
    Inclusion of randomly oriented discrete fibers in the soil-binder mixture changes its brittle
    behaviour into ductile behaviour. Most synthetic fibers, however, tend to get entangled
    and cannot be easily separated from one another. Therefore, it is difficult to realize soilbinder-
    fiber mixtures in which the fibers are distributed uniformly throughout the mass.
    This issue has been an impediment in the utilization of the positive modification in the
    behaviours of soils and soil-binder mixtures by the fibers. The present study aims to address
    the limitations in using fibers as soil reinforcement. Further, it also aims to investigate
    the use of synthetic mesh or net elements as an alternative type of soil reinforcement.
    The paper presents the experimental study on a fine grained soil. Lime has been chosen
    as the binder due to its low cost and the scarcity of fiber reinforced soil studies in which
    lime has been used as a binder. The main experimental program is a series of unconfined
    compression tests on samples prepared using untreated soil, soil-reinforcement mixture,
    soil-lime mixture, and soil-lime-reinforcement mixture. The lime treated samples were
    cured up to 120 days at laboratory temperature. The results demonstrate the combinational
    effects of lime and discrete reinforcement
    elements on the behaviour and mechanical
    properties of the soil. The performances of
    the fiber and mesh element reinforcements
    have also been compared.
    Matched MeSH terms: Temperature
  20. Fulltext Analysis of Phase-Shift Pulse Brillouin Optical Time-Domain Reflectometry
    Horiguchi T, Masui Y, Zan MSD
    Sensors (Basel), 2019 Mar 27;19(7).
    PMID: 30934806 DOI: 10.3390/s19071497
    Distributed strain and temperature can be measured by using local Brillouin backscatter in optical fibers based on the strain and temperature dependence of the Brillouin frequency shift. The technique of analyzing the local Brillion backscatter in the time domain is called Brillouin optical time domain reflectometry (BOTDR). Although the best spatial resolution of classic BOTDR remains at around 1 m, some recent BOTDR techniques have attained as high as cm-scale spatial resolution. Our laboratory has proposed and demonstrated a high-spatial-resolution BOTDR called phase-shift pulse BOTDR (PSP-BOTDR), using a pair of probe pulses modulated with binary phase-shift keying. PSP-BOTDR is based on the cross-correlation of Brillouin backscatter and on the subtraction of cross-correlations obtained from the Brillouin scatterings evoked by each phase-modulated probe pulse. Although PSP-BOTDR has attained 20-cm spatial resolution, the spectral analysis method of PSP-BOTDR has not been discussed in detail. This article gives in-depth analysis of the Brillouin backscatter and the correlations of the backscatters of the PSP-BOTDR. Based on the analysis, we propose new spectral analysis methods for PSP-BOTDR. The analysis and experiments show that the proposed methods give better frequency resolution than before.
    Matched MeSH terms: Temperature
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