Browsing by Author "Aminul Islam, Md."

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‘A knowledge Base Data Mining Based on Parkinson's Disease
(Daffodil International University, 2019-04-25) Hassan, Md. Redone; Aminul Islam, Md.; Obidul Kadir, S.K.
The approaches of detecting Parkinson’s disease (PD) in human body from voice data using Classification techniques apply three different algorithms for finding the growth rate of Parkinson’s disease. Support vector machine (SVM), K-nearest neighbor (K-NN) and Decision tree (DT) are applied to detect the progression rate of Parkinson’s disease (PD) by using Unified Parkinson’s disease rating scale (UPDRS) and Hoehn &Yahr scale (HYS) . Unified Parkinson’s disease rating scale (UPDRS) deals with motor fluctuations and change over voice after certain period and that can measure the people affected by Parkinson’s disease and healthy people. Hoehn & Yahr scale (HYS) are measures the symptoms which are related to progression of Parkinson’s disease (PD) in human body. Classifier algorithms used to detect the factors and symptoms which are related to progression of Parkinson’s disease (PD) in human body using voice data. The algorithms can detect Parkinson’s disease (PD) by several approaches which criteria are related to progression of Parkinson’s disease (PD) in human body. From the distinctions of all algorithms measures which algorithm give the best accuracy for several approaches to diagnosis Parkinson’s disease (PD) and risk factors of had Parkinson’s disease (PD) in human body.
Assessment of rural transport accessibility in Bangladesh
(Department of Civil Engineering, 2017-04-19) Aminul Islam, Md.; Shamsul Hoque, Dr. Md.
ABSTRACT This research paper has been prepared to estimate rural transport accessibility index to help decision makers integrate transport interventions into poverty reduction programs and to develop the relationships between rural accessibility improvement and socio-economic parameters of Bangladesh. In order to achieve the objectives of this research, at first road transport network of Bangladesh was collected from Roads and Highways Department (RHD) and Local Government Engineering Department (LGED). The district administrative area boundary was collected from LGED. Then the demographic and socio-economic data of sixty-four (64) districts of Bangladesh was collected from Bangladesh Bureau of Statistics (BBS). The road network and administrative boundary data are in the form of GIS environment. The districts demographic statistics are in the form of tabular data. After collecting the data, the analyses were done using GIS software and Microsoft Excel Analysis Toolpack (e.g. Data Analysis Tool, Data Solver Tool). Rural Transport Accessibility was estimated by ArcGIS-ArcMap. From the analysis, rural transport accessibility index of sixty-four (64) districts of Bangladesh has been estimated considering only the paved road transport (motorable all the year round) network across the country. Then the estimated accessibility value has been compared with the poverty incidence and with other socio-economic parameters to establish a relation among them. At the bottom line, a district ranking was prepared to prioritize the budget allocation in physical infrastructure that will seek help the policy maker to foster poverty free and equitable development vision of Bangladesh. Moreover, Data Envelopment Analysis (DEA) and Correlation Analysis were carried out to establish the priority ranking setting the target to minimize the objective function (in this case poverty incidence) and to investigate the correlation (if exists any) among the accessibility to the poverty incidence and socio-economic parameters.
Characterization of anomalous Fe-Ni alloy coating by electrodeposition and its properties
(Department of Materials and Metallurgical Engineering, BUET, 2008-06) Aminul Islam, Md.; Moniruzzaman, Dr. Md.
Iron-nickel (Fe-Nil alloys are of great commercial interest as thcy possess low thennal cxpansion, soft mab'llctic and widc spectrum of physical properties. Attcmpts have been made to explain the anomalous mechanism of Fe-Ni alloy codeposition and researchers have proposed several models. Main focus of this work is to invcstil':ate the enect and the inlefaction of complexinl': agenl~ on the propertics of electrodeposited Fe-Ni alloy coating as well as the special characteristic of anomalous natlll"e. The Fe-Ni films were deposited from eight different baths; two of them were simple, coutaming NIS04, Fe504, Na1SO., H,BO.l as main ingredients and another six were complex, containiug ascorbic acid, saccharin and citric acid as complexing agent along with the main ingradicllls in varying compositiou. Fe-Ni alloy coatings were etectrodepositcd on Cu substrate at room tcmperature in the cum:nt density raub'e of20- 140 mNcml. Th", effects of current density, pH and bath composition on the coating appearance, composition, hardness, corroSIon resistance, morphologies and magnetization were studied. Chemical analysts, Mil..-TOhardness,Corrosion resistance, M0'Phologics and Magnetization of the coatings were studied by means of Conventional Wet Method, Mierohardness Tester, Salt Immersion Test, Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM) respectively. It was observed that coating obtaliled al higher cllrrent denSity with higher bath pH was blackish (examined with naked eye) while lower current density with higher pH or h'gher current density with lower pH resulted In uniform and bright coatings. The Ni percentage of the coating as well as its VHN increased with increasing current density for SImple baths but the reverse situations occurred for complex baths. Addition of complexing agents suppresscd the anomalous characteristics of the Fe-Ni alloy eJectrodeposition. The corrosion rate decreased with increasing Ni content of the films. Formation of protective NiO layer is supposed to inerease the corrosion resistance of high Ni content thin film Thus, the properlle~ of electrodeposited Fe-Ni alloy are strongly influenced by the electrolytic composition and deposition parameters. Tile filtn 7 obtained from simple baths did 1I0t exhibit smooth surface and the coating developed sharp line microcracks due to the internal stress developed during depositlOn in it. No cracks were observed and the coating gram size became finer for the coatings from complex baths compared to the simple baths. A clear morphological modification was observed due to the addition of eompJexing agent. The saturation magneti£ation of the electrodeposited Fe-Ni coating was fOlmd to decrease with increasing Ni content which is in good agreement with suppression of ferromagnetic character of the films. The highest saturation magneti7<1tionwas seen 131.13 cmwg among the coatings studied which is very close to the acceptable limit (135 emu/g). Charactenzatioll of Fe-Ni alloy plating parameters with its properties was attempted.
Customers’ Attitude Towards Online Shopping: A Descriptive Study
(Daffodil International University, 2019-09-12) Aminul Islam, Md.
During the past two decades, internet was growing its roles in affecting both the local and international organization to achieve its business success. Internet was appeared as an important tool for many purpose uses in this technology era. Business companies using internet for internal communication among the colleagues to link each department to optimize the efficiency and effectiveness for more quality works and also connect their business partners around the globe. Government use internet to provide information and services to the general public and internal communication between the government departments. School or university use internet to search more teaching materials to improve the studies among students while for general public, internet was used to search information, social networking, education and now they can even use internet to purchase goods. The main objective of this study is to know the attitudes of the students towards online shopping behavior. The population of this research consists of people who have the experience of online shopping. Responses have been gathered through a structured questionnaire survey with five point likert scale. The findings reveal that people prefer shopping online for convenience, time consciousness, trust, offers and variety of products. Based on the findings of the empirical data and the comments of the respondents, some recommendations have been given for the online stores.
Dynamic behaviour of unreinforced masonry building
(Department of Civil Engineering, CE , BUET, 2018-12-17) Aminul Islam, Md.; Ahsan, Dr. Raquib
Unreinforced masonry (URM) buildings represent a large portion of the buildings stock around the world and in Bangladesh. During the construction of those buildings very little or no seismic design requirements are considered. Recent earthquakes e.g. Gorkha earthquake in 2015 have shown that many such buildings are seismically vulnerable; therefore, the demand for dynamic analysis and upgrading strategies of these buildings has become increasingly stronger in the last few years. Moreover, no dynamic test on unreinforced masonry building made by Bangladeshi indigenous material is done yet. Therefore, the objective of this study is to understand the dynamic behavior of a typical unreinforced masonry (URM) building of Bangladesh. For this purpose, a half-scale URM room having dimension of 6' x 5' (length x width) with 5' height and 2.5'' wall thickness, were built using M2 type mortar (c:s=1:4) and half-scale brick units. Time history of Imperial Valley Earthquake was chosen as an input motion because pre-dominant frequency (5Hz) of Scaled Imperial Valley earthquake is close to the model's pre-dominent frequency (6Hz). The URM model was tested as reference specimen. Then, the reference specimen was retrofitted on all faces using 18 gauge wire mesh (12mm x 12mm (1/2'' x 1/2'') opening), which is locally available and retested again. The tests were conducted on a uni-directional earthquake simulator. The tests show that wire mesh may be used as a retrofitting material for URM buildings. The retrofitting measure decreased the specimens’ lateral deflection by a factor of 4.3 to 4.8 times compared to the reference (URM) specimen for different intensities of earthquake. In addition, the upgrading enhanced the cracking resistance and the energy dissipation of the upgraded specimen. The upgraded specimen is able to undergo 1.42 times more acceleration than reference specimen. Lateral load of the reference model is compared with the prescribed shear force (capacity) as per Bangladesh National Building Code (BNBC 1993). The reference model failed after reaching the capacity. Therefore, the code is conservative in terms of lateral load resistance capacity.
Forest cover change detection and spatial modelling for identifiction of errosion prone areas in Kaptai reservoir watershed of Bangladesh
(Department of Urban and Regional Planning, 2006-04) Aminul Islam, Md.; Moniruzzaman, Dr. K. M.
Erosion has become an important issue for Kaptai watershed, the largest man made freshwater body in Bangladesh which generales a significant share of Bangladesh's power supply by usiog hydro-power. It contributes significantly to the production of freshwater fish, flood oonlrol, tourism and agriculture. Over lhe past few decades forest depletion has become a main problem here because of human intervention, replacing the forest cover with shllUng cultivation which eventually increasing soil erosion and thus contributing large amounlS ofscdirncll1lltion to the reservoir posing 3 serious threat to the power plant as well as navigability. Studies have been done \0 assess the sedimentation in Kaptai Lake have found that the expected tife time ofthc lake has considemhly reduced. This study is an effort to look into this met and II)' to understand the spatial variation of erosion that leads to siltation. The study has two major goals - first to nwnitor the change ofvcgctation and other major land coven; OYl:rlast two decades (1980-2000) and ~econd to develop a simple spatial model to identify potential erosiOll prone areas in Kaptai watershed. Land cover maps have been produced from satellite image~ of Landsat program. NOVI and bi-spectra! plot techniques were u~ed to identify land covers. Appropriate NOVI has been set chosen based on ground tnllt! data, high resolution satellite image (IRS LlSS 111) and sccondlll'Y land cover maps. Two land cover map~ have been prepared for two nominal years (1980 and 2000). Finally map~ have been compared with each other. It has been found lIlat non-furest land has increased by 10.6% \\'hile low density forest area has decreased by 18.4% but high density fOrest has increased by around 7.9%. However overall forest coverage (Iow+high density) has decreased by 10.6% which is highly significant for20 years time period (1980-2000). A simple potential erosion model has been developed to assess the distribution of potential erosion prone areas in the watershed. This model cmphasize~ potential erosion because it does not estimate the actual erosion; rather it indicates areas that are potentially i, erodabte based on ~npe, soil, land cover and rainfall in the watershed. Modelling result shows that 45% of the area has low erosion risk while 17% has high erosion risk. The rest 36% falls into llVerage erosion category. This is an indication of how much area is to bc conserved for erosion management in Kaptai Watershed. This study is a small preliminary effort to look into the erosion problem spatially. But this might be useful as a starting point for further in depth spatial study of this problem to figure out possible remedies.
Genetic insights into the connection between pulmonary TB and non-communicable diseases: An integrated analysis of shared genes and potential treatment targets
(2024-10-21) Mahjabeen, Amira; Hasan, Md. Zahid; Rahman, Md. Tanvir; Aminul Islam, Md.; Khan, Risala Tasin; Kaiser, M. Shamim
Pulmonary Tuberculosis (PTB) is a significant global health issue due to its high incidence, drug resistance, contagious nature, and impact on people with compromised immune systems. As mentioned by the World Health Organization (WHO), TB is responsible for more global fatalities than any other infectious illness. On the other side, WHO also claims that noncommunicable diseases (NCDs) kill 41 million people yearly worldwide. In this regard, several studies suggest that PTB and NCDs are linked in various ways and that people with PTB are more likely to acquire NCDs. At the same time, NCDs can increase susceptibility to active TB infection. Furthermore, because of potential drug interactions and therapeutic challenges, treating individuals with both PTB and NCDs can be difficult. This study focuses on seven NCDs (lung cancer (LC), diabetes mellitus (DM), Parkinson’s disease (PD), silicosis (SI), chronic kidney disease (CKD), cardiovascular disease (CVD), and rheumatoid arthritis (RA)) and rigorously presents the genetic relationship with PTB regarding shared genes and outlines possible treatment plans. BlueThis study aims to identify the drug components that can regulate abnormal gene expression in NCDs. The study will reveal hub genes, potential biomarkers, and drug components associated with hub genes through statistical measures. This will contribute to targeted therapeutic interventions. Numerous investigations, including protein-protein interaction (PPI), gene regulatory network (GRN), enrichment analysis, physical interaction, and protein-chemical interaction, have been carried out to demonstrate the genetic correlation between PTB and NCDs. During the study, nine shared genes such as TNF, IL10, NLRP3, IL18, IFNG, HMGB1, CXCL8, IL17A, and NFKB1 were discovered between TB and the above-mentioned NCDs, and five hub genes (NFKB1, TNF, CXCL8, NLRP3, and IL10) were selected based on degree values. In this study, we found that all of the hub genes are linked with the 10 drug components, and it was observed that aspirin CTD 00005447 was mostly associated with all the other hub genes. This bio-informatics study may help researchers better understand the cause of PTB and its relationship with NCDs, and eventually, this can lead to exploring effective treatment plans.
Influence of span to depth ratio on the shear strength of reinforced concrete deep beam
(Department of Civil Engineering, 1997-12) Aminul Islam, Md.; Bosunia, Dr. M. Shamim Z.
A total of twenty five brick aggregate reinforced concrete deep beams have been tested in this study in order to investigate the influence of span to depth ratio on the shear strength of reinforced concrete deep beam. The test beams were single span and simply supported type. The beams were divided into five series according to their span to depth ratio (LID = 1 to 5). The first beam of each series was designed and detailed as per the recommendations of ACI Building Code (ACI 318-89). In the other four beams of each series, the amount of either flexural or horizontal web reinforcement or both were changed in relation to those of first beam of the corresponding series. All the beams were tested under single concentrated loading at mid span. The effects of different web steel arrangement and span/depth ratio on cracking load, ultimate load, crack patterns and modes of failure were investigated. It was observed in the study that the amount of both flexural and horizontal web reinforcements influenced the diagonal cracking load and the ultimate load capacity of test beams to some extent. It was also found that the change in the amount of either the vertical or the horizontal web reinforcement alone could not bring a significant change in the load carrying capacity of test beams. After comparing the observed initial cracking stress with that of by de Cossio(9), Kabir(7) and Rashid(10) , it was found that the observed initial cracking stress was very close to the stress calculated by de Cossio(9). It was also observed that the shear strength capacity of the deep beam having LID ratio five was very close to the shear capacity of ordinary rectangular beam of similar size. In general the ACI 318-89 recommendations regarding the ultimate strength of deep beams were observed to be conservative. Some available formulae (e.g. ACI 318-89, Ray & Reddy and Ramkrishnan & Ananthanarayana) were used to estimate the ultimate load in shear of deep reinforced concrete beams. It was shown that all the three formulae can be used efficiently to determine the ultimate shear strength of deep beams but these formulae need some modifications as proposed by Kabir(7) and Rashid(10).
Influence of teachers’ emotional intelligence on students’ motivation for academic learning: an empirical study on university students of Bangladesh
(2024-03-18) Hafizur Rahman, Md.; Bin Amin, Mohammad; Yusof, Mohd Faizal; Aminul Islam, Md.; Afrin, Sadia
Excellent teachers produce quality students who resembles their teachers. Teaching is a very challenging and stressful job that create emotional distress for teachers and have a significant impact on students. Bandura’s Social Cognitive Theory of Motivation inspired this study, which focused on Emotional Intelligence. This study attempts to measure the influences of Bangladeshi teachers’ emotional intelligence (EI) on students’ motivation for academic learning. This research incorporates Daniel Goleman’s five EI dimensions: self-awareness (SA), self-regulation (SR), self-motivation (SM), empathy (EM) and social skills (SS). The survey includes students of 14 private and 14 public universities from Bangladesh. A 31-item structured questionnaire survey was designed to collect data from (N = 415) respondents using a five-point Likert scale, and structural equation modeling (PLS-SEM) was employed to measure the reliability, validity, and test of hypotheses. Results revealed that students’ motivation for academic learning is directly influenced by teachers’ emotional self-awareness (SA), self-regulation (SR), self-motivation (SM), empathy (EM) and social skills (SS). The study’s findings indicate that students’ motivation for academic learning is positively influenced by teachers’ emotional intelligence. Consequently, this study contributes to the body of knowledge on emotional intelligence by offering implications for teachers in higher education.
Performance evaluation of supply chain network in apparel industry: a case study
(Department of Industrial and Production Engineering(IPE), BUET, 2018-03-31) Aminul Islam, Md.; Ferdous Sarwar, Dr.
Supply chain management has become one of the most discussed topics in business literature and is by many organizations considered a key strategic element. Today, markets have become more dynamic with rapid changes in customer requirements. These rapid changes have increased the importance for companies to ensure that materials and information flow smoothly between the actors in a supply chain. Being able to measure supply chain performance is important since it leads to a greater understanding of the supply chain and provides important feedback on the improvement progress. In spite of companies’ and managers’ recognition of the importance of supply chain management, they often lack the ability to develop effective performance measures and metrics. In addition, relatively little literature covering PMSs and the selection of performance measures in the context of supply chain management exists. Here evaluated performance of supply chain in East west Industrial Park Ltd. A performance measure, or a set of performance measures, is used to determine the efficiency and/ or effectiveness of an existing system, or to compare competing alternative systems. Performance measures are also used to design proposed systems, by determining the values of the decision variables that yield the most desirable levels of performance. Due to complexity of supply chain nature, it is very difficult to measure its performance. In this study Supply Chain Operation Reference (SCOR) model has been used to measure supply chain performance. Four Key Performance Indicators (KPI) have been measured following the measurement of overall KPI which indicates the ultimate supply chain efficiency. The four KPI values are; Quantity and Timely Delivery 55.00%, Adherence to Production Target 69.30%, Quality Capability 14.18% and On-Time Shipment 82.83%. Overall efficiency of the supply chain is only 64.24% which is not well enough. Only On-Time-Shipment has higher KPI value. Other individual KPI values can be enriched by improving backward linkage, labor, management and production line efficiency and also improving the quality level. However, PPC and TQM will play a vital role to improve overall KPI.
Preparation of mixed manganese oxide nano-matrix and studies on its oxidative and pathogenic activities
(Department of Chemistry (Chy), 2015-02) Aminul Islam, Md.; Manwarul Islam, Dr. Md.
Nanotechnology is an emerging interdisciplinary subject that has been booming in many areas during the recent decade. Looking into this aspect, black MnO2 nanoparticles (nps) have been synthesized, via a facile one stop solution phase approach, by co-precipitation method by the reduction from a system containing KMnO4 and MnSO4 solutions. Pure phase, spherical, uniformly dispersed brown Mn3O4 nps powder was synthesized successfully by forced hydrolysis of Mn(II) acetate by heating its aqueous solution at 800C. Blackish brown γ−MnOOH nps was synthesized by a simple route using Mn(II) acetate as precursor by hydrothermal treatment. The evidence of MnO2, Mn3O4 and γ−MnOOH nps formation under the synthesis conditions were confirmed by UV–vis spectra, FT-IR, XRD, SEM, EDX, DLS, TG-DTA, pHpzc and Specific Surface Area (SSA) analysis. FT-IR spectra of MnO2 nps showed the occurrence of O–Mn–O vibrational mode at around 571 and 535 cm-1. The selected area electron diffraction patterns revealed that the MnO2 was crystalline and rod like in nature. Elemental analysis exhibited the presence of Mn and oxygen elements in the MnO2, Mn3O4 and γ−MnOOH and no foreign elements in them. The average crystallite size was calculated from the XRD data for MnO2, Mn3O4 and γ−MnOOH nps were approximately 7.0 nm, 10.0 nm and 11.0 nm respectively. The specific surface area of γ−MnOOH nps was found to be 142.962 and 195.747 (m2 g- 1) respectively. Oxidative decolorization of MB and OG were studied at different pH, concentration, adsorbent dose and contact time by UV-Vis spectroscopy. From kinetic analysis, it was found that decolorization is dependent on parameters such as dye concentration, Mn-oxide doses, pH and other parameters. The observed results were in good agreement with experimental data. The decolorization data showed that both MB and OG could be decolorized by Mnoxide surface. But the extent of MB decolorization was much higher than OG, suggesting the present γ−MnOOH nps can be used as a highly efficient material for oxidative decolorization of MB. MB decolorization was through a surface mechanism, that is, formation of surface precursor complex between MB and surface bound MnOOH center, followed by electron transfer within the surface complex. Kinetic study demonstrated that both MB and OG decolorization followed pseudo-secondorder kinetic. The experimental isotherm results were fitted using Langmuir, Freundlich, Temkin and Sips isotherm. The Freundlich model agreed very well with experimental data. The pathogenic experiment was performed following the standard conventional method by treating the Mn-oxides nps in 7.5% (v/v) DMSO suspension to various pathogenic organisms. The experiments were performed duplicate and triplicate. From the experimental evidence it was clear that Mn-oxides did not have potential antibacterial activity.
Structural, electrical and magnetic properties of (Fe1-xMnx)75P15C10 amorphous alloys
(Department of Physics (PHY), 2017-01) Aminul Islam, Md.; Khan, Dr. Md. Feroz Alam
(Fe1-xMnx)75P15C10 amorphous alloys ribbons have been prepared by conventional melt-spinning technique (rapid cooling) with different wheel speeds in an argon atmosphere. The microstructural analysis were done by X-ray diffraction technique, Scanning electron microscopy (SEM). Both the XRD and SEM confirm the samples the amorphous (glassy) structure of the as made samples. The elemental analysis of the samples was carried out using energy dispersive X-ray spectroscopy (EDS) which reveals the presence of Fe, Mn, P and C elements in the sample. The glass transition temperature (Tg ) , the crystallization temperatures (Tx) and the mass loss and/or gain of all the samples were investigated by differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA). The electrical resistivity (𝜌) of amorphous (Fe1-xMnx)75P15C10 alloy ribbons have been studied as a function of temperature between 77K to 600K. It has been observed that the resistivity increases slightly with increasing temperature upto room temperature then it is increasing rapidly for x=0 and 0.05. At larger x, 𝜌(𝑇)develops a minimum at room temperature which can have different slopes, 𝑑𝜌𝑑𝑇 which has been ascribed to a superposition of scattering from the structural topological disorder and the spin topological disorder. The magnetic field dependence of magneto-resistanceΔ𝜌(𝐻) normalized to the resistivity of the sample in zero magnetic field 𝜌0 have been studied. It is observed that an anomalous change of MR% around 0.3 tesla occurs. Both positive and negative magnetoresistance have been observed as a function of applied magnetic field. The magnetic hysteresis (M–H) loop of the as-made samples show high saturation magnetization (Ms). The value of saturation magnetization is found to decrease with increasing Mn. This is attributed to the magneto-elastic scattering. The coercivity increases gradually with increasing Mn content up to 30 at. % Mn content. The increase in coercivity seems to be related to the decrease in glass-forming ability with increasing Mn content. The variation of complex permeability (real and imaginary part respectively) as a function of frequency from 100Hz-120MHz show high effective permeability of 2.2×104 . The value of effective permeability is found to have decreased with increasing Mn contents .These anomalous magnetic properties lead to the suggestion that the antiferromagnetic interactions introduced by Mn atoms cause deviations from a pure ferromagnetic structure at low Mn concentrations. However at higher Mn contents a competing ferro and antiferromagnetic interaction might result in a frustrating system resulting in magnetic relaxation.
Structural, magnetocaloric and magnetodielectric properties of chromium substituted cobalt ferrites
(Department of Physics, BUET, 2023-12-09) Aminul Islam, Md.; A.K.M. Akther Hossain, Dr.
Structural, mechanical, magnetic, magnetocaloric, dielectric, and magnetodielectric properties of Cr3+ substituted stoichiometric and non-stoichiometric cobalt ferrite with a general formula of Co1-xCrxFe2O4 and Co1+xCrxFe2-xO4 have been studied. The samples were synthesized using a standard solid-state reaction technique, with sintering temperatures of 1200, 1250, and 1300 °C. X-ray diffraction studies confirm the formation of a single-phase cubic spinel structure with a space group of Fd-3m for both series. The ferrite formation has also been confirmed by FTIR spectra and Raman spectra. Rietveld refined result shows that Cr occupies both the tetrahedral and octahedral sites. The lattice parameters show increasing trends wherein crystallite size shows a decreasing value with increasing Cr3+ content for both series. The cation-anion vacancies, chemical bonding, and oxygen displacement have been evaluated to understand the effect of Cr3+ substitution on the physical and chemical properties. As estimated from scanning electron microscopic images, the average grain size shows a decreasing trend with an increase of Cr3+ for both series. The elastic properties analysis reveals that the synthesized samples for both series are ductile. The tunability of Cr3+ on the magnetic moment, exchange interaction, magnetocrystalline anisotropy constant, and microwave frequency has been found. The nature of magnetic phase transitions for all the Cr3+ concentrations exhibit second order, confirmed by the analysis of critical scaling, universal curve scaling, and scaling analysis of the magnetocaloric effect. The Cr3+ led to tuning the magnetic moment, exchange interaction, magnetocrystalline anisotropy constant, and microwave frequency. The second-order magnetic phase transition has been confirmed from the Arrot and Arrot-Noakes plots for all the samples. The Cr3+ tuned the magnetocaloric (MCE) properties, showing the maximum relative cooling power of 156 Jkg-1 for 50% of Cr3+ for non-stoichiometric series by decreasing the Curie temperature toward room temperature. The reliability of MCE and the nature of the magnetic phase transition of the investigated samples are confirmed by analyzing the critical exponent analysis, universal curve scaling, and scaling analysis of MCE. A significant impact of grain size on dielectric nature has been observed. The temperature-dependent dielectric constant confirms the ferroelectric nature of the samples. At around relaxation frequency, remarkable magnetodielectric responses have been found for all samples.
Thermophysical and phase change characteristics of R152a/R1234ze(E) refrigerant blends through molecular dynamics simulation
(Department of Mechanical Engineering (ME), BUET, 2025-03-11) Aminul Islam, Md.; Nasim Hasan, Dr. Mohammad
The study of refrigerants and their blends has always been important due to their wide use and environmental impact. In this study, the thermophysical properties and nanoscale phase change characteristics of R152a/R1234ze(E) blends with varying molar fractions have been investigated using non-equilibrium molecular dynamics simulation (NEMD) under non-equilibrium heating conditions. In total, five different compositions of the refrigerant blend have been considered with the blends containing 100%, 67%, 50%, 33% and 0% molar fraction of R152a. Thermophysical properties such as density, liquid thermal conductivity and isobaric specific heat have been computed for the refrigerant blends considered. To study phase characteristics a three-phase domain is considered where liquid and vapor refrigerant molecules are placed over the solid platinum (Pt) surface. Two different heating conditions for the wall have been applied to induce various phase change modes. The first condition involved a linear increase in wall temperature, where temperature rise rates of 80, 160, and 240 K/ns are employed. The second condition maintained constant wall temperatures of 300 K and 320 K respectively. The phase change characteristics of different refrigerant blends under various heating conditions have been reported utilizing various parameters such as net evaporation number, time averaged heat flux, bubble growth, mean square displacement, and energy contours. Three distinct boiling modes are observed, depending on the heating rate and the mixture composition of the refrigerant blend. Moreover, under isothermal heating conditions, diffusive evaporation of the refrigerant blends took place. The results indicate that the increase in percentage of R152a in the refrigerant blend enhances the heat transfer performance. However, considering both environmental impact and thermal performance, refrigerant blend with %R152a of 67% exhibit better overall performance. Furthermore, if environmental considerations are stricter refrigerant blend up to 50% R152a percentage can be considered without significant decline in phase change performance. In addition, in this study the bubble nucleation process and interfacial characteristics of the refrigerant blends have also been examined to elucidate the mechanisms behind the phase change process. The interfacial behavior is analyzed in terms of interfacial thermal resistance, potential energy contours, and spatial density distribution. It is found that R1234ze(E) molecules exhibit a stronger attraction to the solid surface, resulting in lower interfacial thermal resistance.