Displaying publications 1 - 20 of 93 in total

Abstract:
Sort:
  1. Ng WC, Lim TL, Yoon TL
    J Chem Inf Model, 2017 03 27;57(3):517-528.
    PMID: 28178783 DOI: 10.1021/acs.jcim.6b00553
    Melting dynamics of hafnium clusters are investigated using a novel approach based on the idea of the chemical similarity index. Ground state configurations of small hafnium clusters are first derived using Basin-Hopping and Genetic Algorithm in the parallel tempering mode, employing the COMB potential in the energy calculator. These assumed ground state structures are verified by using the Low Lying Structures (LLS) method. The melting process is carried out either by using the direct heating method or prolonged simulated annealing. The melting point is identified by a caloric curve. However, it is found that the global similarity index is much more superior in locating premelting and total melting points of hafnium clusters.
    Matched MeSH terms: Phase Transition*
  2. Fun HK, Chantrapromma S, Ong LH
    Molecules, 2014 Jul 11;19(7):10137-49.
    PMID: 25019557 DOI: 10.3390/molecules190710137
    Crystals of 1,6-hexanedioic acid (I) undergo a temperature-dependent reversible phase transition from monoclinic P21/c at a temperature higher than the critical temperature (Tc) 130 K to another monoclinic P21/c at temperature lower than Tc. The phase transition is of first order, involving a discontinuity and a tripling of the b-axis at Tc whereas the other unit cell parameters vary continuously. The transition is described by the phenomenological Landau theory. The crystal structure analyses for data collected at 297(2) K and 120.0(1) K show that there is half of a molecule of (I) in the asymmetric unit at 297(2) K whereas there are one and a half molecules of (I) in the asymmetric unit at 120.0(1) K. At both temperatures, 297(2) and 120.0(1) K, intermolecular O-H···O hydrogen bonds link the molecules of I into infinite 1D chains along [101] direction. However there are significantly more O-H···O hydrogen bonds presented in the 120.0(1) K polymorph, thereby indicating this phase transition is negotiated via hydrogen bonds. The relationship of the conformational changes and hydrogen bonding for these two polymorphs are explained in detail.
    Matched MeSH terms: Phase Transition*
  3. Mardziah CM, Sopyan I, Hamdi M, Ramesh S
    Med J Malaysia, 2008 Jul;63 Suppl A:79-80.
    PMID: 19024993
    Improvement of the mechanical properties of hydroxyapatite (HA) can be achieved by the incorporation of metal. In addition, incorporation of strontium ion into HA crystal structures has been proved effective to enhance biochemical properties of bone implant. In this research, strontium-doped HA powder was developed via a sol-gel method to produce extraordinarily fine strontium-doped HA (Sr-doped HA) powder. XRD measurement had shown that the powder contained hydroxyapatite phase only for all doping concentration except for 2%, showing that Sr atoms have suppressed the appearance of beta-TCP as the secondary phase. Morphological evaluation by FESEM measurement shows that the particles of the Sr-doped HA agglomerates are globular in shape with an average size of 1-2 microm in diameter while the primary particles have a diameter of 30-150 nm in average.
    Matched MeSH terms: Phase Transition*
  4. Rahman AA, Usman A, Chantrapromma S, Fun HK
    Acta Crystallogr C, 2003 Sep;59(Pt 9):i92-4.
    PMID: 12944636
    A sample of hydronium perchlorate, H(3)O(+) x ClO(4)(-), crystallized from ethanol at ambient temperature, was found to be orthorhombic (space group Pnma) at both 193 and 293 K, with no phase transition observed in this temperature range. This contrasts with the earlier observation [Nordman (1962). Acta Cryst. 15, 18-23] of a monoclinic phase (space group P2(1)/n) at 193 K for crystals grown at that temperature from perchloric acid. The hydronium and perchlorate ions lie across a mirror plane but it is not possible to define at either temperature a simple description of the H-atom positions due to the three-dimensional tumbling of the hydronium cation.
    Matched MeSH terms: Phase Transition
  5. Mahmud MN, Siri Z, Vélez JA, Pérez LM, Laroze D
    Chaos, 2020 Jul;30(7):073109.
    PMID: 32752617 DOI: 10.1063/5.0002846
    The control effects on the convection dynamics in a viscoelastic fluid-saturated porous medium heated from below and cooled from above are studied. A truncated Galerkin expansion was applied to balance equations to obtain a four-dimensional generalized Lorenz system. The dynamical behavior is mainly characterized by the Lyapunov exponents, bifurcation, and isospike diagrams. The results show that within a range of moderate and high Rayleigh numbers, proportional controller gain is found to enhance the stabilization and destabilization effects on the thermal convection. Furthermore, due to the effect of viscoelasticity, the system exhibits remarkable topological structures of regular regions embedded in chaotic domains.
    Matched MeSH terms: Phase Transition
  6. Lim AW, Löbmann K, Grohganz H, Rades T, Chieng N
    J Pharm Pharmacol, 2016 Jan;68(1):36-45.
    PMID: 26663364 DOI: 10.1111/jphp.12494
    The objective was to characterize the structural behaviour of indomethacin-cimetidine and naproxen-cimetidine co-amorphous systems (1 : 1 molar ratio) prepared by quench cooling, co-evaporation and ball milling.
    Matched MeSH terms: Phase Transition
  7. Shi Q, Wang Y, Xu J, Liu Z, Chin CY
    PMID: 35129118 DOI: 10.1107/S2052520621012749
    Understanding crystallization behaviors is of utmost importance for developing robust amorphous pharmaceutical solids. Herein, the crystal growth behaviors of amorphous anti-inflammatory drug nimesulide (NIME) are systemically investigated in the glassy and supercooled liquid state as a function of temperature. A sudden over-tenfold increase is observed in the bulk crystal growth of NIME on cooling below its glass transition temperature (Tg). This fast growth behavior is known as a glass-to-crystal (GC) mode and has been reported in some molecular glasses. Fast surface crystal growth of NIME can persist up to Tg + 57°C with a weak jump in its growth rates at 30-40°C. In addition, surface crystal growth and GC growth of NIME exhibit an almost identical temperature dependence, supporting the view that GC growth is indeed a surface-facilitated process. Moreover, the bubble-induced fast crystal growth of NIME is observed in the interior of its supercooled liquid with approximately the same growth kinetics as surface crystal growth. These findings are relevant for a full understanding of the surface-related crystallization behaviors and physical stability of amorphous pharmaceutical formulations.
    Matched MeSH terms: Phase Transition
  8. Shi Y, Huang L, Soh AK, Weng GJ, Liu S, Redfern SAT
    Sci Rep, 2017 09 11;7(1):11111.
    PMID: 28894256 DOI: 10.1038/s41598-017-11633-y
    Electrocaloric (EC) materials show promise in eco-friendly solid-state refrigeration and integrable on-chip thermal management. While direct measurement of EC thin-films still remains challenging, a generic theoretical framework for quantifying the cooling properties of rich EC materials including normal-, relaxor-, organic- and anti-ferroelectrics is imperative for exploiting new flexible and room-temperature cooling alternatives. Here, we present a versatile theory that combines Master equation with Maxwell relations and analytically relates the macroscopic cooling responses in EC materials with the intrinsic diffuseness of phase transitions and correlation characteristics. Under increased electric fields, both EC entropy and adiabatic temperature changes increase quadratically initially, followed by further linear growth and eventual gradual saturation. The upper bound of entropy change (∆Smax) is limited by distinct correlation volumes (V cr ) and transition diffuseness. The linearity between V cr and the transition diffuseness is emphasized, while ∆Smax = 300 kJ/(K.m3) is obtained for Pb0.8Ba0.2ZrO3. The ∆Smax in antiferroelectric Pb0.95Zr0.05TiO3, Pb0.8Ba0.2ZrO3 and polymeric ferroelectrics scales proportionally with V cr-2.2, owing to the one-dimensional structural constraint on lattice-scale depolarization dynamics; whereas ∆Smax in relaxor and normal ferroelectrics scales as ∆Smax ~ V cr-0.37, which tallies with a dipolar interaction exponent of 2/3 in EC materials and the well-proven fractional dimensionality of 2.5 for ferroelectric domain walls.
    Matched MeSH terms: Phase Transition
  9. Rosli NS, Ibrahim R, Ismail I, Omar M
    PLoS One, 2022;17(11):e0276142.
    PMID: 36445921 DOI: 10.1371/journal.pone.0276142
    Achieving reliable power efficiency from a high voltage induction motor (HVIM) is a great challenge, as the rigorous control strategy is susceptible to unexpected failure. External cooling is commonly used in an HVIM cooling system, and it is a vital part of the motor that is responsible for keeping the motor at the proper operating temperature. A malfunctioning cooling system component can cause motor overheating, which can destroy the motor and cause the entire plant to shut down. As a result, creating a dynamic model of the motor cooling system for quality performance, failure diagnosis, and prediction is critical. However, the external motor cooling system design in HVIM is limited and separately done in the past. With this issue in mind, this paper proposes a combined modeling approach to the HVIM cooling system which consists of integrating the electrical, thermal, and cooler model using the mathematical model for thermal performance improvement. Firstly, the development of an electrical model using an established mathematical model. Subsequently, the development of a thermal model using combined mathematical and linear regression models to produce motor temperature. Then, a modified cooler model is developed to provide cold air temperature for cooling monitoring. All validated models are integrated into a single model called the HVIM cooling system as the actual setup of the HVIM. Ultimately, the core of this modeling approach is integrating all models to accurately represent the actual signals of the motor cooler temperature. Then, the actual signals are used to validate the whole structure of the model using Mean Absolute Percentage Error (MAPE) and Root Mean Square Error (RMSE) analysis. The results demonstrate the high accuracy of the HVIM cooling system representation with less than 1% error tolerance based on the industrial plant experts. Thus, it will be helpful for future utilization in quality maintenance, fault identification and prediction study.
    Matched MeSH terms: Phase Transition
  10. Al-Waeli AHA, Sopian K, Kazem HA, Chaichan MT
    Environ Sci Pollut Res Int, 2023 Jul;30(34):81474-81492.
    PMID: 36689112 DOI: 10.1007/s11356-023-25321-0
    The bi-fluid photovoltaic thermal (PVT) collector was introduced to provide more heating options along with improved cooling capabilities for the PV module. Since its introduction, this type of PVT system has been investigated thoroughly in various original works. In this review paper, we intend to put the concept and applications of this technology into question and revise the main achievements and discoveries through research and development with a focus on climatic and operational parameters. The paper encompasses a critical review of the discussed research and future directions for PVT collectors. The main utilized operational modes are discussed in detail, which are (i) water used in both channels, (ii) water in one channel and air in the other, and (iii) air in both channels. The modes were found to lead to different enhancement and performance effects for the utilized photovoltaic modules. The impact of mass flow rate was also taken by keeping one working fluid constant while varying the other to obtain its impact on the energy and exergy efficiency of the collector. In some cases, the fluids were run simultaneously and, in other cases, independently.
    Matched MeSH terms: Phase Transition
  11. Tao J, Chen J, Li J, Mathurin L, Zheng JC, Li Y, et al.
    Proc Natl Acad Sci U S A, 2017 09 12;114(37):9832-9837.
    PMID: 28855335 DOI: 10.1073/pnas.1709163114
    The optimal functionalities of materials often appear at phase transitions involving simultaneous changes in the electronic structure and the symmetry of the underlying lattice. It is experimentally challenging to disentangle which of the two effects--electronic or structural--is the driving force for the phase transition and to use the mechanism to control material properties. Here we report the concurrent pumping and probing of Cu2S nanoplates using an electron beam to directly manipulate the transition between two phases with distinctly different crystal symmetries and charge-carrier concentrations, and show that the transition is the result of charge generation for one phase and charge depletion for the other. We demonstrate that this manipulation is fully reversible and nonthermal in nature. Our observations reveal a phase-transition pathway in materials, where electron-induced changes in the electronic structure can lead to a macroscopic reconstruction of the crystal structure.
    Matched MeSH terms: Phase Transition
  12. Velayutham TS, Ng BK, Gan WC, Abd Majid WH, Hashim R, Zahid NI, et al.
    J Chem Phys, 2014 Aug 28;141(8):085101.
    PMID: 25173043 DOI: 10.1063/1.4893873
    Glycolipid, found commonly in membranes, is also a liquid crystal material which can self-assemble without the presence of a solvent. Here, the dielectric and conductivity properties of three synthetic glycolipid thin films in different thermotropic liquid crystal phases were investigated over a frequency and temperature range of (10(-2)-10(6) Hz) and (303-463 K), respectively. The observed relaxation processes distinguish between the different phases (smectic A, columnar/hexagonal, and bicontinuous cubic Q) and the glycolipid molecular structures. Large dielectric responses were observed in the columnar and bicontinuous cubic phases of the longer branched alkyl chain glycolipids. Glycolipids with the shortest branched alkyl chain experience the most restricted self-assembly dynamic process over the broad temperature range studied compared to the longer ones. A high frequency dielectric absorption (Process I) was observed in all samples. This is related to the dynamics of the hydrogen bond network from the sugar group. An additional low-frequency mechanism (Process II) with a large dielectric strength was observed due to the internal dynamics of the self-assembly organization. Phase sensitive domain heterogeneity in the bicontinuous cubic phase was related to the diffusion of charge carriers. The microscopic features of charge hopping were modelled using the random walk scheme, and two charge carrier hopping lengths were estimated for two glycolipid systems. For Process I, the hopping length is comparable to the hydrogen bond and is related to the dynamics of the hydrogen bond network. Additionally, that for Process II is comparable to the bilayer spacing, hence confirming that this low-frequency mechanism is associated with the internal dynamics within the phase.
    Matched MeSH terms: Phase Transition*
  13. Yuvaraj AR, Yam WS, Chan TN, Goh YP, Hegde G
    Spectrochim Acta A Mol Biomol Spectrosc, 2015 Jan 25;135:1115-22.
    PMID: 25173529 DOI: 10.1016/j.saa.2014.08.009
    The first example of non-symmetric isoflavone-based fast photo-switchable liquid crystals with different functional groups at the terminal position were synthesized and characterized. Polarizing optical microscopy study revealed that the compounds showed least ordered nematic phase. Optical photo switching study exhibited very fast photoisomerization effect in solution. The E-Z and Z-E conversion occurred around 3-5s and 40-700 s respectively. This is also the first example of para-substituted non-symmetric isoflavone liquid crystals exhibiting very fast photo switching property in solution. Argument based on non-symmetrical behaviour might be the reason for the observed behaviour.
    Matched MeSH terms: Phase Transition/radiation effects
  14. Muraoka M, Susuki N, Yamaguchi H, Tsuji T, Yamamoto Y
    J Vis Exp, 2016 Mar 21.
    PMID: 27023374 DOI: 10.3791/53956
    Methane hydrates (MHs) are present in large amounts in the ocean floor and permafrost regions. Methane and hydrogen hydrates are being studied as future energy resources and energy storage media. To develop a method for gas production from natural MH-bearing sediments and hydrate-based technologies, it is imperative to understand the thermal properties of gas hydrates. The thermal properties' measurements of samples comprising sand, water, methane, and MH are difficult because the melting heat of MH may affect the measurements. To solve this problem, we performed thermal properties' measurements at supercooled conditions during MH formation. The measurement protocol, calculation method of the saturation change, and tips for thermal constants' analysis of the sample using transient plane source techniques are described here. The effect of the formation heat of MH on measurement is very small because the gas hydrate formation rate is very slow. This measurement method can be applied to the thermal properties of the gas hydrate-water-guest gas system, which contains hydrogen, CO2, and ozone hydrates, because the characteristic low formation rate of gas hydrate is not unique to MH. The key point of this method is the low rate of phase transition of the target material. Hence, this method may be applied to other materials having low phase-transition rates.
    Matched MeSH terms: Phase Transition*
  15. Siti Khuzaimah Soid, Anuar Ishak, Ioan Pop
    Sains Malaysiana, 2018;47:2907-2916.
    The problem of stagnation point flow over a stretching/shrinking sheet immersed in a micropolar fluid is analyzed
    numerically. The governing partial differential equations are transformed into a system of ordinary (similarity) differential
    equation and are then solved numerically using the boundary value problem solver (bvp4c) in Matlab software. The
    effects of various parameters on the velocity and the angular velocity as well as the skin friction coefficient and the couple
    stress are shown in tables and graphs. The noticeable results are found that the micropolar and the slip parameters
    decrease the skin friction coefficient and the couple stress in the existence of magnetic field. Dual solutions appear for
    certain range of the shrinking strength. A stability analysis is performed to determine which one of the solutions is stable.
    Practical applications include polymer extrusion, where one deals with stretching of plastic sheets and in metallurgy
    that involves the cooling of continuous strips.
    Matched MeSH terms: Phase Transition
  16. Anuar MAM, Amran NA, Ruslan MSH
    ACS Omega, 2021 Feb 02;6(4):2707-2716.
    PMID: 33553888 DOI: 10.1021/acsomega.0c04897
    Oil and grease remain the dominant contaminants in the palm oil mill effluent (POME) despite the conventional treatment of POME. The removal of residual oil from palm oil-water mixture (POME model) using the progressive freezing process was investigated. An optimization technique called response surface methodology (RSM) with the design of rotatable central composite design was applied to figure out the optimum experimental variables generated by Design-Expert software (version 6.0.4. Stat-Ease, trial version). Besides, RSM also helps to investigate the interactive effects among the independent variables compared to one factor at a time. The variables involved are coolant temperature, XA (4-12 °C), freezing time, XB (20-60 min), and circulation flow, XC (200-600 rpm). The statistical analysis showed that a two-factor interaction model was developed using the obtained experimental data with a coefficient of determination (R2) value of 0.9582. From the RSM-generated model, the optimum conditions for extraction of oil from the POME model were a coolant temperature of 6 °C in 50 min freezing time with a circulation flowrate of 500 rpm. The validation of the model showed that the predicted oil yield and experimental oil yield were 92.56 and 93.20%, respectively.
    Matched MeSH terms: Phase Transition
  17. Teh, Chiew Peng, Tan, Aileen Shau Hwai, Vengatesen, Thiyagarajan
    Trop Life Sci Res, 2016;27(11):111-116.
    MyJurnal
    The influence of the cool and warm temperatures on early life development and
    survival of tropical oyster, Crassostrea iredalei was studied. D-hinged larvae (day 1 larvae)
    were reared to three different temperatures (20°C, 27°C, and 34°C) for nine days. Oyster
    larvae reared in temperature 27°C, acted as control (ambient temperature). The highest
    survival rate occurred when the larvae were reared in 20°C and 27°C. Larvae reared at
    34°C exhibited reduced survival but increase in the growth rate. The growth rate in larvae
    reared in high temperature (34°C) was significantly higher compared to larvae reared in
    20°C and 27°C (p
    Matched MeSH terms: Phase Transition
  18. Najiy Rizal Suriani Rizal, Azuddin Mamat, Aidah Jumahat
    MyJurnal
    In recent years, injection moulding process is one of the most advanced and efficient manufacturing processes for mass production of plastic bottles. However, a good quality of parison is difficult to achieve due to uncontrollable humidity, pressure inlet and water inlet velocity. This paper investigates the effect of using multiple mould cavities to improve the process fill time and injection pressure in the production of PET plastic bottles using MoldFlow software. The modelling of parison was developed using CATIA with the consideration of every part of the parison. MoldFlow software was used to analyse the flow of 20 g parison with different cavity numbers (1, 8, 16, 24 cavity), as well as its corresponding runner size towards its fill time and injection pressure. Other important parameters that affect the production of parison, such as melting temperature, mould temperature, atmospheric temperature and cooling time, were remained constant. The fill time required to produce 24 moulds was improved by 60% compared to using 8 mould cavity only, and this enable the production of more plastic bottles in a day. Therefore, fill time and injection pressure are two important parameters to be considered in the injection moulding process, especially to reduce parison defect and increase its production rate.
    Matched MeSH terms: Phase Transition
  19. Bangbai C, Techitdheera W, Chongsri K, Pecharapa W
    Sains Malaysiana, 2013;42:239-246.
    In this work, the preparation of ZnO, N-doped ZnO (NZO), Al-doped ZnO (AZO) and Al, N-doped ZnO (ANZO) thin films by the sol-gel spin-coating method is reported. The structural properties and surface morphologies of films were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The optical properties of the films were interpreted from their transmission spectra using UV-VIS spectrophotometer. The XRD and SEM results disclosed that the crystallization quality and grain size of as-prepared films were highly influenced by N and Al doping. UV-VIS spectrophotometer results indicated that Al and N additives could significantly enhance the optical transparency and induce the blue-shift in optical bandgap of ZnO films.
    Matched MeSH terms: Phase Transition
  20. Syazwani Mohd Zokri, Nur Syamilah Arifin, Muhammad Khairul Anuar Mohamed, Abdul Rahman Mohd Kasim, Mohd Zuki Salleh, Nurul Farahain Mohammad
    Sains Malaysiana, 2018;47:1607-1615.
    This paper delves into the problem of mixed convection boundary layer flow from a horizontal circular cylinder filled in
    a Jeffrey fluid with viscous dissipation effect. Both cases of cooled and heated cylinders are discussed. The governing
    equations which have been converted into a dimensionless form using the appropriate non-dimensional variables are solved
    numerically through the Keller-box method. A comparative study is performed and authentication of the present results
    with documented outcomes from formerly published works is excellently achieved. Tabular and graphical representations
    of the numerical results are executed for the specified distributions, considering the mixed convection parameter, Jeffrey
    fluid parameters and the Prandtl and Eckert numbers. Interestingly, boundary layer separation for mixed convection
    parameter happens for some positive (assisting flow) and negative (opposing flow) values. Strong assisting flow means
    the cylinder is heated, which causes the delay in boundary layer separation, whereas strong opposing flow means the
    cylinder is cooled, which conveys the separation point close to the lower stagnation point. Contradictory behaviours
    of both Jeffrey fluid parameters are observed over the velocity and temperature profiles together with the skin friction
    coefficient and Nusselt number. The increase of the Prandtl number leads to the decrement of the temperature profile,
    while the increase of the Eckert number results in the slight increment of the skin friction coefficient and decrement of
    the Nusselt number. Both velocity and temperature profiles of Eckert number show no effects at the lower stagnation
    point of the cylinder.
    Matched MeSH terms: Phase Transition
Filters
Contact Us

Please provide feedback to Administrator (afdal@afpm.org.my)

External Links