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Has files: YesSubject: search.filters.subject.0306 Physical Chemistry (incl. Structural)

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    Infinite dilution activity coefficients and thermodynamic properties of selected organic solutes and water dissolved in 1, 6-hexanediol
    (Elsevier BV, 2020-12) Nkosi, Nkululeko; Tumba, Kaniki; Ngema, Peterson; Ramsuroop, Suresh
    The experimental activity coefficients (γ13∞) and gas-to-liquid partition coefficients (KL) at infinite dilution for 34 organic solutes and water were determined in 1.6-hexanediol (HDO) by the gas–liquid chromatography technique (GLC) in the temperature range from (323.15 to 353.15) K. Fundamental thermodynamic functions such as excess partial molar enthalpy (ΔHiE,(∞)), excess partial molar Gibbs energy, (ΔGiE,∞) and entropy, (TrefΔSiE,∞) at infinite dilution were calculated from experimental values of γ13∞. Reported data were discussed in terms of solvent-solute interactions, heat effects and mixing spontaneity. Selectivity (Sij∞) and capacity (kj∞) related to different separation problems were calculated from γ13∞ data and compared to the literature values for selected ionic liquids (ILs), deep eutectic solvents (DESs) and industrial solvents. New data reported in this study suggest that HDO may be proposed as an alternative solvent for the separation of alkanes-pyridine and alkanes-thiophene systems. Furthermore, it was found that adding a hydrogen bond acceptor to HDO enhances its performance as a separation solvent.
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    Thermodynamic stability conditions of clathrate hydrates for refrigerant (R134a or R410a or R507) with MgCl2 aqueous solution
    (Elsevier BV, 2016-04-15) Ngema, Peterson Thokozani; Naidoo, Paramespri; Mohammadi, Amir H.; Richon, Dominique; Ramjugernath, Deresh
    Clathrate hydrate dissociation data were measured for systems comprising of refrigerants (R134a, R410a and R507) + water + MgCl2 at varying salt concentrations. The ternary system for R134a + water + MgCl2 was measured at salt concentrations of (0.259, 0.546, and 0.868) mol.kg-1 in the temperature range of (277.1-283) K and a pressure range of (0.114-0.428) MPa. Hydrate measurements for the {R410a or R507} + water + MgCl2 systems were measured at salt concentrations of (0.259 and 0.546) mol.kg-1 in the temperature range of (274.3-293) K and a pressure range of (0.154-1.421) MPa. The isochoric pressure-search method was used to measure the hydrate dissociation data. This study is a continuation of previous investigations which focused on obtaining hydrate dissociation data for R134a, R410a and R507 refrigerants in NaCl and CaCl2 aqueous solutions. The measured hydrate dissociation data can be used to design industrial wastewater treatment and desalination processes. The results show that the effect of salt concentration on hydrate formation is smaller for MgCl2 aqueous solutions compared to CaCl2 and NaCl as salt concentration increases. Modelling of the measured data is performed using a combination of the solid solution theory of van der Waals and Platteeuw, the Aasberg-Petersen et al. model, and the Peng-Robinson equation of state with classical mixing rules. The model is in good agreement with the measured hydrate dissociation data.
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    Phase stability conditions for clathrate hydrate formation in (fluorinated refrigerant plus water plus single and mixed electrolytes plus cyclopentane) systems : experimental measurements and thermodynamic modelling
    (Elsevier BV, 2019-09) Ngema, Peterson Thokozani; Naidoo, Paramespri; Mohammadi, Amir H.; Ramjugernath, Deresh
    Phase equilibrium conditions (dissociation data) for clathrate hydrates (gas hydrates) were studied for systems involving fluorinated refrigerants + water + single and mixed electrolytes (NaCl, CaCl2, MgCl2 and Na2SO4) at varying salt concentrations in the absence and presence of cyclopentane (CP). The ternary systems for (R410a or R507) + water + CP were performed in the temperature and pressures ranges of (279.8–294.4) K and (0.158–1.385) MPa, respectively. Measurements for {R410a + water + (NaCl or CaCl2) + CP} were undertaken at salt concentrations of (0.10, 0.15 and 0.20) mass fractions in the temperature and pressure ranges of (278.4–293.7) K and (0.214–1.179) MPa, respectively. The temperature and pressure conditions for the (R410a + water + Na2SO4) system were investigated at salt concentration of 0.10 mass fraction in range of (283.3–291.6) K and (0.483–1.373) MPa respectively. Measurements for {(R410a or R507) + water + mixed electrolytes NaCl, CaCl2, MgCl2} were undertaken at various salt concentrations of (0.002–0.15) mass fractions in the temperature and pressure ranges of (274.5–292.9) K and (0.149–1.119) MPa in the absence and presence of CP, for which there are no published data related to mixed salt and a promoter. The phase equilibrium measurements were performed using a non-visual isochoric equilibrium cell and the pressure-search technique. This study was focused on obtaining equilibrium data that can be utilized to design and optimize for water desalination process and the development of a Hydrate Electrolyte–Cubic Plus Association (HE–CPA) Equation of State based model. The results indicate hydrate dissociation pressure reduction/hydrate dissociation temperature increase up to ambient conditions in the presence of promoter (CP). The experimental results were then modelled. The modelling results are in good agreement with the measured hydrate dissociation data.
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    Nanoindentation mechanical properties on spark plasma sintered 48Ti-48Al-2Cr-2Nb alloy
    (Elsevier BV, 2021) Mphahlele, Mahlatse R.; Olevsky, Eugene; Tshephe, Thato; Olubambi, Peter A.; Jen, Tien-Chien; Machaka, Ronald; Olubambi, Peter
    This study aims to investigate the microstructure, plastic (H) properties, elastic (E) properties, reduced elastic (Er) properties the strain-to-break parameter (H/Er), and the resistance to plastic deformation parameter (H3/Er2) of the Ti-48Al-2Cr-2Nb alloy by use of scanning electron microscopy, nanoindentation and micro-indentation techniques. The results show that the sintering parameters had significant effect on the resulting microstructure. Desirable mechanical properties were obtained with the sample sintered at temperature of 1200 °C, pressure of 50 MPa, holding time of 7.5 min and a heating rate of 50 °C/min which had a near lamellar structure, resulting from the grain boundary pinning effect of the fine equiaxed gamma grains and the impartation of ductility due to the coarsened lamellar colonies. The nano-hardness and elastic modulus were observed to be about 4GPa and 31GPa for the near lamellar microstructure, respectively, with the microhardness of about 4.4GPa. While the duplex and the near gamma microstructures possessed the least nano-hardness (3.65–3.78GPa) and elastic modulus (3.6–29.5GPa) with the exception of sample sintered at temperature of 1150 °C, pressure of 50 MPa, holding time of 7.5 min and a heating rate of 100 °C/min., with nano-hardness and elastic modulus of 4.05GPa and 31.25GPa, respectively, however it had the lowest micro-hardness of 2.7GPa. Furthermore, the ratios H/Er and H3/Er2 values were observed to be greater for the same sample suggesting good wear resistance of the alloy.
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    A taxonomy on smart healthcare technologies : security framework, case study, and future directions
    (Hindawi Limited, 2022-07-05) Chaudhary, Sachi; Kakkar, Riya; Jadav, Nilesh Kumar; Nair, Anuja; Gupta, Rajesh; Tanwar, Sudeep; Agrawal, Smita; Alshehri, Mohammad Dahman; Sharma, Ravi; Sharma, Gulshan; Davidson, Innocent E.
    There is a massive transformation in the traditional healthcare system from the specialist-centric approach to the patient-centric approach by adopting modern and intelligent healthcare solutions to build a smart healthcare system. It permits patients to directly share their medical data with the specialist for remote diagnosis without any human intervention. Furthermore, the remote monitoring of patients utilizing wearable sensors, Internet of Things (IoT) technologies, and artificial intelligence (AI) has made the treatment readily accessible and affordable. However, the advancement also brings several security and privacy concerns that poorly maneuvered the effective performance of the smart healthcare system. An attacker can exploit the IoT infrastructure, perform an adversarial attack on AI models, and proliferate resource starvation attacks in smart healthcare system. To overcome the aforementioned issues, in this survey, we extensively reviewed and created a comprehensive taxonomy of various smart healthcare technologies such as wearable devices, digital healthcare, and body area networks (BANs), along with their security aspects and solutions for the smart healthcare system. Moreover, we propose an AI-based architecture with the 6G network interface to secure the data exchange between patients and medical practitioners. We have examined our proposed architecture with the case study based on the COVID-19 pandemic by adopting unmanned aerial vehicles (UAVs) for data exchange. The performance of the proposed architecture is evaluated using various machine learning (ML) classification algorithms such as random forest (RF), naive Bayes (NB), logistic regression (LR), linear discriminant analysis (LDA), and perceptron. The RF classification algorithm outperforms the conventional algorithms in terms of accuracy, i.e., 98%. Finally, we present open issues and research challenges associated with smart healthcare technologies