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Item First-principles study of structural, electronic and magnetic properties of defected (monovacant) hexagonal boron nitride sheet(Department of Physics, 2021) Khatri, KisanThe first-principles calculations based GGA functionals was implemented to study the structural, electronic and magnetic properties of pure and defected hexagonal boron nitride (h-BN) monolayer sheet using Quantum ESPRESSO (QE) package, 6.5 version. The pure h-BN is found to be non-magnetic insulator with band gap of 4.64 eV. The calculated values of formation energy reveals the structural stability of defected system. The formation energies for B and N vacant system are found to be 16.45 eV and 12.84 eV respectively which predicts that N vacant system is more preferable with lower formation energy. The defect on a system abruptly changes the electronic and magnetic properties of h-BN system. The 6.25 % B-vacancy and 6.25 % N-Vacancy defects are found to be half metallic ferromagnet with total magnetization of 2.74 /cell and magnetic semiconductor with total magnetization 1.00 B /cell respectively. BItem Investigation of Transport Properties of Sitesubstituted Superstructures of Complex Transition Metal Oxides: (La,Sr)TiO3/(Ca,Y)VO3(Institute of Science & Technology, 2023-11) Rai, Raj KumarTo unravel the structural, chemical and mechanical stabilities, electronic, thermoelectric, and optically driven transport properties of pristine and site-substituted complex transition metal oxides (titanates and vanadates), we have employed the density functional theory (DFT) and the dynamical mean field theory (DMFT) approach. The continuous time quantum Monte-Carlo (CT-QMC) with hybridization expansion technique is used as impurity solver of DMFT and the maximum entropy model (MEM) is employed for analytic continuation (AC). The study also investigates the metal insulator phase transition (MIT) of the strongly correlated electronic materials by analyzing the variation of spectral density with onsite Coulomb interaction (U) and thermodynamic parameter (β). Here, the structural, chemical, and mechanical properties of vanadates: (La1−x SrxVO 3 )n,(Ca1−xSrxVO3) n and (La1−xCaxVO3)n , and titanates: (La1−x CaxTiO3)n, (La1−x SrxTiO 3)n and (Ca1−xYx TiO 3)n systems studied using the first-principles based calculations. The energy minimization curves, and negative values of cohesive energy (CE) and formation energy (FE) reveal their higher structural and chemical stabilities, indicating that these pristines and the site-substituted vanadates and titanates are chemically stable and viable for laboratory synthesis. The modulus of elasticities, Poisson’s and Pugh’s ratios, anisotropy factor, and Cauchy pressure of the systems indicate their mechanical stabilities and the results suggest that superstructures are elastically weaker than pristine systems. The DFT calculation shows the pristine CaVO3, SrVO3, LaVO3, LaTiO3,YTiO 3 , YVO 3and all the superstructures are metallic/semiconducting in nature which contradicts the experimental information, whereas resembles with other theoretical calculations. The pristine SrTiO3 and CaTiO3 found to be band insulators with band gaps 3.42 eV and 2.76 eV respectively, which resembles closely to other available information. For the realistic picture of electronic structures, DMFT approach (CT-QMC data) along with MEM are employed and found that MIT parameters for pristines and superstructures of vanadate systems are mentioned in the parentheses, CaVO3 (U = 5.0 eV, β = 6.0 (eV)−1), LaVO3 (U = 4.5 eV, β = 8.0 (eV)−1), SrVO3 (U = 2.5 eV, β = 6.0 (eV)−1 ), LaSrV2O6 (U = 4.0 eV, β = 10.0 (eV)−1 ) and La0.40Ca0.60VO3 (U = 5.0 eV, β = 10.0 viii(eV)−1), respectively. Similarly, the DMFT results of pristines and superstructures of titanate systems are also computed (mentioned in the parentheses) as, LaTiO3 (U = 4.0 eV, β = 8.0 (eV)−1), YTiO3 (U = 5.0 eV, β = 10.0 (eV)−1), LaSrTi2O6 (U = 4.7 eV, β = 6.0 (eV)−1 ), La 0.8 Sr 0.2TiO 3 (U = 3.2 eV, β = 10.0 (eV)−1 ) and Ca x Y1−xTiO 3 (U = 5.0 eV, β = 7.0 (eV)−1), respectively, and found to be consistent with other results. The analysis of characteristic sharp quasi-particle peaks reveal that vanadate, La0.40 Sr0.60VO3and titanate, La0.80Sr0.20TiO3 superstructures show metallic phases in same set of MIT parameters, (U = 3.0 eV, β = 6.0 (eV)−1 ). The set of Mott quantum critical point (QCP) for La 0.40 Ca 0.60 VO 3 system is observed for an elevated temperatures at (UC = 2.95 eV, βC = 23.58 (eV)−1). The clear Mott gaps for La0.40 Ca0.60VO 3 , and La 0.80 Sr 0.20 TiO 3 are computed as 0.73 eV (U = 5.0 eV, β =10.0 (eV)−1) and 0.74 eV (U = 3.2 eV, β =10.0 (eV)−1), respectively. The BoltzTraP calculations show that La0.40 Ca0.60VO3 and La0.80Sr0.20TiO3 systems have peak values of electrical conductivities (2.11 × 1020 (Ω.m.s)−1 , 3.75 × 1020 (Ω.m.s)−1 ), and thermal conductivities (1.54 × 1015 W/(m.K.s) and 2.68 × 1015 W/(m.K.s) ), respectively, at room temperature (300 K) for a given chemical potential (μ = −0.14eV ) . Both have the larger Seebeck coefficient (S), and thermoelectric power factor (TPF) indicating that these superstructures are better candidate for thermoelectric applications. The study of Seebeck coefficient and Hall coefficient reveal that the thermoelectric phase transition occur due to the site-substitutions of the superstructures. The photo-induced behaviors of materials in IR-to-UV regions, including visible region are investigated using the dielectric function, index of refraction, ELOSS function, absorptivity, reflectivity, optical conductivity and sumrule. The Drude peaks result support the model parameters (U and β) of DMFT calculation for the optically driven MIT in La0.40Sr0.60VO3 and La0.80Sr0.20 TiO3 superstructure systems. Finally, the study of the MIT model parameters and diverse phase diagrams help us to fabricate these materials to design Mottronic devices (neuromorphic computing, quantum computing, resistive memory devices and artificial neurons), and energy harvesting devices (photovoltaics, solar and radioisotope thermoelectric generators and freezers). यस अनुसन्धान कार्यमा जटिल प्रकृतिका ट्रान्जिसन धातुहरुको अक्साईड र तिनीहरुको सुपर संरचनाहरुको संरचनात्मक, रसायनिक र यान्त्रीक स्थायीत्व तथा ईलेक्ट्रोनिक, तापजन्यविद्युतीय र प्रकाश-प्रेरित परिवहन (ट्रान्सपोर्ट) को प्रकृति एवं चालक-अचालकताको अवस्था-संक्रमण (MIT) सम्बन्धित मोडेल प्यारामिटरहरुको विषयमा डेन्सिटी फङ्सनल सिद्धान्त (DFT) र डाईनामिकल मीन फिल्ड सिद्धान्त (DMFT) अन्तर्गतको कन्टिन्युअस टाईम क्वान्टम मोंटे कार्लो (CT- QMC) मध्ये हाईब्रिडाईजेशन विस्तार एल्गोरिदम उपयोग गरी विभिन्न भ्यानेडेट्स: [(Ca1-xSrxVO3)n, (La1-xSrxVO3)n र (La1-xCaxVO3)n] तथा टाइटानेट्स: [(Ca1-xYxTiO3)n, (La1-xSrxTiO3)n र (La1-xCaxTiO3)n] पदार्थहरुको विस्तृत अध्ययन तथा अन्वेशण गरिएको छ । उर्जा न्यूनिकरण कर्भहरु, कोहेसिभ र फर्मेसन उर्जाहरुको ऋणात्मक मानको आधारमा ति भ्यानेडेट र टाइटानेटहरुको आधारभुत संरचना र सुपर–संरचनाहरुको संरचनात्मक र रसायनिक स्थायीत्व रहेको साथै तिनीहरुलाई प्रयोगशालामा संस्लेषण र निर्माण गरी जीवनोपयोगी प्रयोगमा ल्याउन समेत सकिने निस्कर्ष निकालिएको छ । यसै गरी विभिन्न मेकानिकल प्यारामिटर जस्तै ईलास्टिक कन्सट्यान्ट, ईलास्टिक मोड्युलस, पोइसन तथा पगका अनुपातहरु, काउची दबाब र एनाइसोट्रपिक फ्याक्टरहरुका मानहरुको आधारमा, सम्पूर्ण अध्ययन गरिएका संरचनाहरुले यान्त्रिक स्थायीत्वको प्रत्याभूति गर्दछन् । यि अध्ययनहरुले साइट-प्रतिस्थापित सुपर संरचनाका ईलास्टिक गुणहरु तुलनात्मक रुपले आधारभूत संरचनाहरु भन्दा न्युन देखिएका छन् तथापी तिनीहरुको उपयोग विभिन्न स्मार्ट अनुप्रयोगहरुमा हुन सक्दछन्, जस्तै मोट्रोनिक अनुप्रयोगहरु (न्युरोमोर्फिक कम्प्युटिङ्ग, क्वान्टम कम्प्युटिङ्ग, रजिस्टीभ मेमोरी, कृत्रिम न्यूरोन) तथा उर्जा संकलन अनुप्रयोगहरु (फोटो भोल्टाइक, सौर्य तथा रेडियो आइसोटोपीक तापजन्यविद्युतीय जेनेरेटरहरु, फ्रिजर)को प्रयोजनका लागि सदुपयोग गर्न सकिने निस्कर्ष निकालिएको छ। यहाँ DFT को अध्ययनको आधारमा, केही आधारभूत संरचनाहरु (CaVO3, LaVO3, SrVO3, YVO3, CaTiO3, LaTiO3, SrTiO3, YTiO3)का प्राप्त तथ्याङ्कहरु प्रयोगात्मक अध्ययनको तथ्याङ्कहरुसँग भन्दा सैद्धान्तिक अध्ययनसँग हाम्रो निस्कर्षहरु सहमत देखिन्छन् । हाम्रो गणनाले CaTiO3 र SrTiO3 हरुको व्याण्ड ग्याप क्रमशः 2.76 eV र 3.42 eV सहित व्याण्ड अचालकका गुण देखाउछन् । यसरी नै CaVO3, SrVO3 र YVO3 हरु चाहीं सह-सम्बन्धित चालक गुण देखाउँछन् भने LaVO3, LaTiO3, र YTiO3 चाहीं मोट-अचालकहरु देखिन्छन् । विशेषत: साइट-प्रतिस्थापित सुपर-संरचनाहरु चाहीं सह-सम्बन्धित चालक वा अर्ध-चालक गुण देखाउँछन् । i यसै गरी हामीले DFT तथ्याङ्कहरुको प्रयोगगरी DMFT सहित म्याक्सिमम इन्ट्रोपी मोडल (MEM) को उपयोग गर्दै मोट ग्याप प्यारामिटरहरु विभिन्न आधारभूत संरचनाहरु र तिनीहरुको साइट-प्रतिस्थापित सुपर-संरचनाहरु मध्ये भ्यानेडेट प्रणाली, CaVO3 (U =5.0 eV, β=6.0(eV)^(-1)), LaVO3 (U = 4.5 eV, β=8.0(eV)^(-1)), SrVO3 (U=2.5eV, β=6.0(eV)^(-1)), La0.50Sr0.50VO3 (U = 4.0 eV, β=10.0(eV)^(-1)) / La0.40Ca0.60VO3 (U = 5.0 eV, β=10.0(eV)^(-1)) साथै टाइटानेट प्रणाली, LaTiO3 (U =4.0 eV, β=8.0(eV)^(-1)), YTiO3 (U = 5.0 eV, β=10.0(eV)^(-1)), Ca0.33SrY0.67TiO3 (U = 5.0 eV, β=7.0(eV)^(-1)) / La0.80Sr0.20TiO3 (U = 3.2 eV, β=10.0(eV)^(-1))हरुका MIT मोडेल प्यारामिटरहरु कोष्ठमा उल्लेखीत भए बमोजिम गणना गरिएका छन् । हाम्रा साइट-प्रतिस्थापित सुपर-संरचना मध्ये La040Ca0.60VO3 र La0.80Sr0.20TiO3 प्रणालीहरुको मोट ग्यापहरु क्रमशः 0.73 eV (U = 5.0 eV, β=10.0(eV)^(-1)) र 0.74 eV (U = 3.2 eV, β=10.0(eV)^(-1)) प्राप्त भएका छन् । त्यसरी नै ति दुवै प्रणालीहरुको क्वाजाई पार्टीकल सूचालकता चाहीं एकै मोडेल प्यारामिटरको सेट (U = 3.0 eV, β=6.0(eV)^(-1)) मा देखिएको छ । अर्कोतर्फ La0.40Ca0.60VO3 प्रणाली संवद्ध एक उच्च तापमानको क्वान्टम क्रिटिकल बिन्दु (QCP) को मोडेल प्यारामिटर (UC = 2.95 eV, β_C=23.58(eV)^(-1)) देखिएकोछ । यसरी नै बोल्ट्ज ट्रयाप एल्गोरिद्मको उपयोगगरी गणना गरिएको विद्युतीय चालकता, तापजन्य चालकता, सि-वेक गुणाङ्क तथा तापजन्यविद्युतीय पावर फ्याक्टर (TPF) को आधारमा उल्लेखित सुपर-संरचनाहरु तापजन्यविद्युतीय अनुप्रयोगका लागि उपयोग गर्न सकिने प्रबल संभावना देखिएको छ । यस खोजकार्यमा प्रकाश-प्रेरित परिवहन सम्बन्धी अध्ययनको लागि IR - UV (0 – 20.0eV) रेन्जको फोटोन उर्जा प्रयोग गरी डाईलेक्ट्रिक फङ्सन, अपवर्तक सूचकांक, ELOSS फङ्सन, अवशोषण, परावर्तन, समरुल तथा प्रकाशजन्य चालकताहरुको अध्ययनबाट उपरोक्त पदार्थहरु प्रकाश-प्रेरित उपकरण तथा परिवहन कार्यमा उपयोग हुन सक्ने निस्कर्ष प्रस्तुत गरिएको छ ।Item ADSORPTIONOFHCNANDH2S OVERZnOANDAl-DOPEDZnO MONOLAYER:FIRSTPRINCIPLES STUDY(Amrit Campus, 2024-02-25) Oli, DipakThe adsorption of 𝐻𝐶𝑁 and 𝐻2𝑆 molecules in 3× 3× 1 monolayer and 𝐴𝑙- doped 𝑍𝑛𝑂, replacing one 𝑍𝑛-atom by 𝐴𝑙-atom was studied in spin-polarized DFT by applying the Vienna Abinitio Simulation Package (VASP). Various exchange-correlation functionals like GGA-PBE,metaGGA-SCAN,andDFT+UusingabasissetnamelyPAW(Projected Augmented Wave) pseudopotential were employed in order to determine the structural, electronic, and magnetic properties of the pristine and 𝐴𝑙- doped ZnO before and after the adsorption of 𝐻𝐶𝑁 and 𝐻2𝑆. ZnO monolayer and the ZnO adsorbed with 𝐻𝐶𝑁 and 𝐻2𝑆 were found to be non-magnetic whereas Al-doped ZnO upon the adsorption of 𝐻𝐶𝑁 and 𝐻2𝑆 was found to be magnetic in nature. Similarly, the lattice parameters of ZnO were found to be increasing with the presence of foreign elements. The outcome thus achieved is nearly identical and in good agreement with the earlier theoretical investigations.Item COMPARATIVEANALYSISOFAEROSOL ÅNGSTRÖMEXPONENTVARIATIONIN POKHARA:ACASESTUDYCOMPARINGKANPUR ANDBEIJINGFORTHEYEARS2019AND2020(Amrit Campus, 2024-02-25) Pokhrel, SunilThis thesis presents a collection of AOD data from AERONET followed by calculation and comparative analysis of the Ångström Exponent (𝛼) variation in Pokhara (28.21°N, 83.96°E), Nepal, with Kanpur(26.45°N and 80.33°E), India, and Beijing (39.90°N, 116.41°E), China, for the years 2019 and 2020. The study utilizes mathematical analysis to examine the fluctuations in 𝛼 values observed in these cities and investigates their implications for air pollution dynamics. The maximum and minimum 𝛼 values are calculated to be Pokhara (1.73 & 0.60); Kanpur (1.76 & 0.15) and Beijing (1.65 & 0.13) in the year 2019 and similarly, Pokhara (1.67 & 0.17); Kanpur(1.73 & 0.21) and Beijing(1.65 & 0.16) in the year 2020, providing insights into the seasonal and temporal variations of aerosols. The study explains the trimester-wise analysis of the variation of 𝛼 in Pokhara with the comparison of two calendar years 2019 and 2020. This further delves into the seasonal patterns of 𝛼, shedding light on the influence of specific factors during different periods. The research also explores that 𝛼 does not only depend upon the seasons and weather but also on meteorological parameters, pollutant emissions, atmospheric conditions, and other multidimensional particles dissolved in the atmosphere, however, the trend can be analyzed and compared. The analysis finally can be inferred that in Pokhara, the aerosol loading and water deposition in the atmosphere , is barely affected by anthropogenic sources. The findings underscore the significance of understanding and addressing air pollution challenges in these regions. This study contributes to the scientific understanding of 𝛼 variations and offers valuable insights for policymakers and researchers working towards sustainable air quality management.Item Study on the characteristic emission loading from the public transport and its contribution for air quality degradation over the Kathmandu valley : Grided emission estimation and dispersion modeling(Department of physics, 2021) Shrestha, ChiranjibiThe Kathmandu valley is witnessing an extremely poor air quality from years. The degradation of air quality over Kathmandu is often found to be associated with the spontaneous urbanization, haphazard industrial expansions and vehicular fleet. Present study was conceived to understand the contribution of transport sector in degrading the air quality of Kathmandu valley. We developed a comprehensive gridded emission inventories of potential pollutants and performed particulate pollutant dispersion modelling using a comprehensive Chemical Transport Modelling (CTM) at the horizontal grid resolution of 1 km 2 over an area of 70 km x 70 km that covers the Kathmandu valley and its immediate surroundings, initialized with the Weather Research and Forecasting (WRF) simulated meteorological fields. The gridded emission inventory showed about 1918.17 kg km −2 of TSP, 12872.74 kg km −2 of CO, 6925.82 kg km −2 of NOx and 708.41 kg km −2 of SO2 are currently loaded into the atmosphere of the valley per day from the public transport over the Kathmandu valley. CTM simulation shows the ambient concentration of PM2.5 due to public transport fleets appears a minimum during the day time and remains maximum during the night and morning times. The pollutants released over the valley are transported to the east and are flushed out into the eastern neighbouring valley. The contribution of the public transport fleet to the deterioration of ambient air quality of the valley appears significant compared to total emission from transport sector.Item Structural and Spectroscopic Studies on Cefalexin ond Methyldopa Using Quantum Mechanical Methods(Institute of Science & Technology, 2024-01) Chaudhary, TarunThe spectroscopic characteristics, conformational stability, electronic and biological activity of cefalexin and methyldopa have been investigated using quantum mechanical techniques. The density functional theory (DFT) at the B3LYP/ 6-311++G(d,p) level was utilized to optimize the molecules and explore their vibrational properties. The intramolecular and intermolecular hydrogen bonding in cephalexin has been discussed in terms of IR and Raman spectra. Additionally, the quantum theory of atoms in molecules (QTAIM) was used to predict the nature of hydrogen bonds. Similarly, determining vibrational properties, the presence of hydrogen bond interactions in methyldopa has been scrutinized more precisely, using QTAIM and the reduced density gradient (RDG) in monomer and dimer form. On the basis of electron localization function (ELF), the electron localized region and the delocalized region have been depicted. The Molecular electrostatic potential (MEP) has been used to describe the charge distribution around the molecules. From the MEP map, the electrophilic and nucleophilic sites were anticipated. The energy of the lowest unoccupied molecular orbital (ELUMO), the highest occupied molecular orbital energy, (EHOMO), and their energy gap (∆E) have been used to examine the chemical stability of the molecules. Furthermore, the nature of chemical reactivity, the energy gap, global, and local reactivity characteristics were established. Natural bond orbital (NBO) analysis was carried out to determine the stabilization energy due to charge delocalization between the bonding and antibonding. The relation of standard thermodynamic parameters like heat capacity, enthalpy and entropy with temperature has been studied. Ultimately, a molecular docking simulation has been performed to study the biological activities of the molecules. The binding activity of cefalexin with the protein matrix carbonic anhydrase II and leukotriene A-4 hydro lase was predicted from molecular docking approach. Similarly, the binding activity of ligand methyldopa with protein Lysine-specific demethylase 4D-like was performed. सेफेलेक्सिन र मेथाइलडोपाका स्पेक्ट्रोस्कोपिक स्वरुपहरु, संरचनात्मक स्थिरता, इलेक्ट्रोनिक र जैविक गतिविधि, क्वान्टम मेकानिकल विधि प्रयोग गरेर अनुसन्धान गरिएको छ। अणुहरूलाई अप्टिमाइज गर्न र तिनीहरूको भाइब्रेशनल गुणहरु अन्वेषण गर्न B3LYP/6-311++G(d,p)/Density Functional Theory (DFT) प्रयोग गरिएको थियो। सेफेलेक्सिनको IR र Raman स्पेक्ट्राका आधारमा इन्ट्रामोलिक्युलर र इन्टरमोलिक्युलर हाइड्रोजन बन्डको व्याख्या गरिएकोछ। । साथै, क्वान्टम थ्योरि अफ एटम्स इन मोलिकुल्स (QTAIM) विधि प्रयोग गरि हाइड्रोजन बन्डको प्रकृतिको बारे प्रस्तुत गरिएकोछ। त्यसै गरी, मेथाइलडोपाको मोनोमर र डाइमर संरचनाका भाइब्रेशनल गुणहरु निर्धारण गरि, हाइड्रोजन बन्डलाई QTAIM र रिडिउस्ड डेनसिटी ग्राफ (RDG) को प्रयोग गरेर थप सटीक रूपमा अध्ययन गरिएको थियो। इलेक्ट्रोन लोकलाइजेसन फंक्सन (ELF) को आधारमा, इलेक्ट्रोन लोकलाइज्ड क्षेत्र र डीलोकलाइज्ड क्षेत्रलाई चित्रण गरिएको छ। मोलिकुलर इलेक्ट्रोस्टेटिक पोटेन्सिअल (MEP) मार्फत अणुहरू वरपर रहेको चार्ज वितरणको अवस्थालाई ब्याख्या गरिएको छ । MEP को सहयोगले, इलेक्ट्रोफिलिक र न्यूक्लियोफिलिक साइटहरू पत्ता लगाइएको छ। लोयस्ट अनअकुपाइड मोलिकुलर अर्बिटल इनर्जी (ELUMO), हाइयस्ट अकुपाइड मोलिकुलर अर्बिटल इनर्जी (EHOMO) र तिनीहरूको इनर्जी ग्याप प्रयोग गरि अणुहरूको रासायनिक स्थिरता जाँच गरिएको छ। यसबाहेक, रासायनिक प्रतिक्रियाशीलताको प्रकृति, इनर्जी ग्याप (ΔE), ग्लोबल र लोकल रियाक्तिभिटीका विशेषताहरू स्थापित गरियो। बन्डिङ र एन्टिबन्डिङ बीचको चार्ज डीलोकलाइजेशनको कारणले हुने इस्ट्याविलाइजेसन इनर्जी को निर्धारण गर्न नेचुरल बन्ड अर्बिटल (NBO) को विश्लेषण गरिएको थियो। ताप क्षमता, एन्थाल्पी र एन्ट्रोपी जस्ता मानक थर्मोडायनामिक प्यारामिटरहरूको तापक्रमसँगको सम्बन्धको अध्ययन गरिएको छ । अन्ततः अणुहरूको जैविक गतिविधिहरु अध्ययन गर्न मोलिकुलर डकिङ्ग सिमुलेशनको प्रयोग गरिएको थियो। सेफेलेक्सिनको प्रोटिन म्याट्रिक्स कार्बोनिक एनहाइड्रेस-II र ल्युकोट्रिन A-4 हाइड्रोलेजसँगको बाइन्डिंग गतिविधि, मोलिकुलर डकिङ्ग विधि बाट अनुसन्धान गरिएको थियो। त्यस्तै, मेथाइलडोपाको जैविक गतिविधिहरु प्रोटीन लाइसिन-स्पेशिफिक डेमेथाइलेज 4D- लाइकसँग प्रस्तुत गरिएको छ ।Item Study of the Mixing Behavior of Some Compound Forming Binary Liquid Alloys (Bi-Pb, Cu-In etc)(Institute of Science & Technology, 2023-04) Bhadari, Indra BahadurAlloys are produced by combining two or more metals, and they often develop from their liquid states. Only a small number of metals are used in their pure form; the majority of applications use alloys instead because they have distinctive qualities above and beyond those of the component metals. In the study of liquid science, it is essential to comprehend the properties of liquid alloys because most solid alloys are produced by cooling them from the corresponding liquid states. Liquid alloys are regarded as disordered materials because they lack long-range atomic or magnetic organization. Because disordered materials show a wide range of atomic configurations, this topic is of significant interest to both theoretical and experimental researchers. They have long sought to comprehend the anomalies in the mixing properties of liquid alloys in order to fully comprehend alloying behavior. Theoretical methods can reduce the amount of time and effort necessary and are quite useful in forecasting the mixing properties. So, we have created focused on a theoretical model to study how alloys behave when they are molten. Commonly, the effectiveness of binary alloy production is assessed based on observed thermo-physical characteristics that depart from the ideal mixing state. Departures from ideality manifest as asymmetries in thermodynamic and structural characteristics away from equiatomic composition and are typically attributed to one or more of the following: the size effect, different electronegativity, interactions between solute and solvent atoms, complex formation, or a combination of these factors. The binary liquid alloys can be divided into two categories symmetric and asymmetric, based on the symmetry of the curves reflecting the thermodynamic and microscopic functions. Numerous theoretical approaches have been devised and implemented to examine the thermodynamic and structural properties of binary systems. The Complex Formation Model (CFM) is founded on a fundamental theoretical model. This model makes it possible to express the energetics of a system in terms of the interaction parameters that reproduce the system's thermodynamic properties, as well as the ordering and phase separation processes that are observed in liquid binary alloys. The CFM makes the assumption that, if compounds are formed in the solid state at one or more stoichiometric compositions, then it follows that they are very likely to exist in the liquid state at those same compositions. The alloying behavior of binary solutions can be investigated by making the assumption that complexes are present near to melting points. The molten alloy is considered to be composed of a ternary mixture of A and B atoms, as well as a number of chemical complexes A_p B_q in chemical equilibrium with one another. In this case, p and q are both pairs of small integers that stand for stoichiometric indices of the complex. In the present work, we have examined and explained the mixing behavior of two liquid binary alloys based on Bi, such as Bi-Mg at 975 K and Bi-Pb at 700 K, as well as two In-based alloys, such as Cu-In at 1073 K and In-Pb at 673 K, using the CFM framework. For the aforementioned liquid alloys at a given temperature, the thermodynamic properties, such as free energy of mixing (G_M ), enthalpy of mixing (H_M ), and entropy of mixing (S_M ), structural properties, such as concentration fluctuation in long wave length limit (S_cc (0)) and chemical short range order parameter (α_1 ), and transport property, such as ratio of diffusion coefficients (D_M/D_id ), have been examined. We have calculated the interaction energy parameters 〖(Ψ〗_ij,i,j=1,2,3,i≠j), the energy of complex formation (χ), and the number of complexes (n_3 ) for this purpose. These parameters are used to compute the free energy of mixing (G_M/RT) for each system. Enthalpy of mixing (H_M/RT) and entropy of mixing (S_M/R) have been calculated using these parameters and their temperature coefficients ((∂Ψ_ij)⁄(∂T and ∂χ⁄(∂T ))). Comparing the thermodynamic characteristics of the selected systems, it can be seen that they are in very well agreement with the experimental data reported in the literature. The Bi-Mg system is the most interactive, followed by the Cu-In and Bi-Pb systems, according to a comparison of structural properties (S_cc (0) and α_1 ), the ratio of diffusion coefficients (D_M/D_id ) using the same interaction parameters, and thermodynamic properties. The analysis of these mixing characteristics in the In-Pb liquid alloy, however, shows that segregation does occur in this alloy. We have also used the Budai-Benko-Kaptay (BBK) model to study the viscosity of the selected liquid alloys. For the liquid alloys of Bi-Pb and In-Pb, symmetric viscosity isotherms have been reported; however, Bi-Mg and Cu-In exhibits asymmetry. Within the framework of the updated Butler model, the surface properties of the aforementioned binary alloys, such as surface concentration (c_i^s ) and surface tension (σ), have been investigated. Theoretical analyses show that the component in binary liquid alloys whose surface concentration values are higher than the corresponding ideal values segregates across the surface. It is found that the interaction parameters depend on temperature rather than concentration. To optimize the values of interaction parameters at high temperatures, temperature coefficients and their values at a certain temperature are used. The mixing characteristics of Bi-Pb liquid alloys at 900 K, 1100 K, 1300 K, and 1500 K have been investigated using these optimized values of interaction parameters. The compound-forming propensity of binary liquid systems diminishes with increase in temperature, according to the high temperature investigation of Bi-Pb liquid alloy. The properties of binary liquid alloys at the needed temperature can be carried using this expanded CFM, which is expected to be highly helpful in future work.Item MULTIFRACTAL APPROACH TO THE STUDY OF GORKHA EARTHQUAKE OF 25 APRIL, 2015 NEPAL(Institute of Science & Technology, 2023-02) Tiwari, Ram KrishnaThe devastating earthquake that occurred in the Barpak area of the Gorkha district of Nepal on April 25, 2015, known as the Gorkha earthquake, caused widespread damage and the loss of lives. This study focuses on the central Himalaya region, particularly the area directly impacted by the Gorkha earthquake in 2015, as well as the surrounding regions. This study estimates the fractal dimension of the distribution pattern of the Gorkha earthquake aftershock sequence and the b-value of Gutenberg-Richter law for the earthquakes that occurred between 1964 and 2020 in central Himalaya and vicinity. The data set containing 1126 earthquakes with a completeness magnitude of ≥3.8 is created from the revised International Seismological Centre (ISC) catalogue for the rectangular boundary 26.45°N-30.5°N and 80°E-88.2°E for the study of b-value change. The b-value is estimated by the maximum likelihood estimation (MLE) method. The temporal variation of b-value for the fixed event window (100) shows the increment from 0.44 ± 0.02 to 1.02 ± 0.09 for the period of 21 years (1980 to 2001). The U-shaped variation in b-value was noticed from 2005 to 2015, during which earthquakes from Gorkha to Kodari happened in the region. When the variation in b-value is studied on a long-term basis, the lowest b-value of 0.44 ± 0.06 was noticed for the period between 1984 and 1994, and after 1994, the b-value shows a gradual increase and settles around 1.0 after 2020. The spatial variation of the b-value for the fixed width window shows the variation in the range between 0.59 and 1.0, suggesting the region under study is tectonically active. The b-value around 1.0 for 0 to 11 km of depth suggests the heterogeneity and low strength of the rock. The depth-dependent b-value reveals a significant boundary around the depth 32 km. The contour map shows the low b-value patches (areas) ≤ 0.7, one west and the other east of the 2015 earthquakes, and the areas are overlapped with the zones of the major faults. More importantly, a multifractal analysis of the 2015 Gorkha earthquake's aftershock sequence is presented, focusing on the spatio-temporal distribution of earthquakes from April 25, 2015, to May 14, 2016, for the regions 81.77°–90.41°E and 25.22°–30.15°N. The analysis uses 10,500 earthquakes (Mc = 2.0 ML), divided into 101 windows of 500 events with 100 event shifts. During this period, the box counting dimension (D0) ranged from 0.84 ± 0.07 to 2.39 ± 0.03, and the correlation dimension (D2) ranged from 1.11 ± 0.04 to 1.38 ± 0.03. The generalized dimension spectrum (Dq) showed oscillations in positive q values with consistent peaks from q = 0 to q = 22. From the study, the highest values of the capacity dimension, D0, were found to be 2.28 ± 0.02, 2.39 ± 0.03, and 2.15 ± 0.03 for the temporal windows spanning from 2015-08-15 to 2015-08-26, 2015-11-01 to 2015-11-20, and 2015-11-30 to 2016-01-11, respectively. The study found that the fractal spectrum deviated between D2 and D22, with values ranging from 2.0 to 0.7. This deviation suggests a buildup of strain around an asperity and its subsequent release in the tectonic stress field. The knee-shaped structure of the fractal spectrum suggests that the aftershocks of the Gorkha earthquake show a multifractal structure described by a spectrum of generalized dimensions. Additionally, we found that the distribution of epicenters is not random but rather clusters in certain regions. The temporal correlation dimension (Dt) varies between 0.27 and 0.30 across different time windows, and when calculated for the entire study duration spanning from 1964 to 2020, it yields a value of 0.31 ± 0.004. The low temporal correlation dimension value indicates a high temporal clustering of aftershocks. This high temporal clustering of aftershocks may be due to the interplay of different physical processes, such as stress transfer, and the temporal evolution of the fault system, which can lead to a temporal clustering of aftershocks. The seismic moment release curves for the Gorkha and Kodari (Dolakha) earthquakes in 2015 showed that the majority of the seismic moment was released during the Kodari earthquake. This suggests that the strongest aftershocks tend to carry the most seismic moment in an earthquake sequence. Additionally, it is possible that the high seismic moment release during the Dolakha earthquake was caused by an increase in the rate of plate subduction. A very weak negative correlation between b-value and fractal dimensions of aftershocks distribution means that as the b-value increases (indicating a greater number of small earthquakes relative to larger ones), the fractal dimension decreases (indicating a less complex distribution of aftershocks). This may indicate that as the number of small earthquakes increases, the distribution of aftershocks becomes more homogeneous and less complex. The decline in the number of aftershocks is observed following the Gorkha earthquake within the first 45 days. It is observed that the rate of decline is steep in the first 10 days after the main shock and then gradually slows down. The modified Omori parameter (p) is calculated to be 0.86 ± 0.04, indicating a relatively low temporal decay rate. Additionally, the parameters c and K are calculated to be 0.051 ± 0.019, and 57.9 ± 3.7, respectively. The low value of p compared to the typical value of 1.0 for this study period suggests that the rate of decline in aftershocks has not yet reached equilibrium, and the possibility of additional aftershocks cannot be ruled out. This study provides valuable understandings regarding the spatial distribution of seismic activity in the central Himalayan region, thereby contributing to potential applications in risk evaluation endeavors in the times to come. वि.सं. २०७२ साल बैशाख १२ गते (२५ अप्रिल २०१५) मा मध्य नेपालको गोरखा जिल्लास्थित बारपाक केन्द्रविन्दु बनाएर गएको गोरखा भूकम्पले धेरै जनधनको क्षति गरेको थियो । यस शोधमा सो भूकम्पको प्रभावमा परेको आयाताकार क्षेत्र (२६.४५० उत्तर -३०.५०० उत्तर र ८०.००० पूर्व - ८८.२० पूर्व) मा पर्ने विगतका भूकम्पहरूको अध्ययन गरी बी–मान (बी–भ्यालु) को मापन र गोरखा भूकम्पको पराकम्पनहरूको अध्ययन गरी भग्न आयाम (फ्रेक्टल डाइमेन्सन) को मापन गरिएको छ। यस अध्ययनमा बी–मानको मापन अधिकतम सम्भावनाको अनुमान (म्याक्सिमम लाइक्लिहुड मेथड) बाट गरिएको छ। प्रत्येकमा १०० वटा भूकम्पहरू समेटेर बनाइएको निश्चित विन्डोको आधारमा बी –मानको समयअनुसार (टेम्पोरल) परिवर्तन हेर्दा सन १९८० देखि २००१ सम्मको २१ वर्षको समयमा बी–मान ०.४४±०.०२ देखि १.०२±०.०९ सम्म बढेको पाइएको छ भने अङ्ग्रेजीको यु आकारको परिवर्तन २००५ देखि २०१५ सम्ममा देखिएको छ। दशक अवधिको आधारमा बी–मानको परिवर्तन हेर्दा सबैभन्दा कम (०.४४±०.०६) १९८४ देखि १९९४ को दशकमा देखिन्छ भने १९९४ पछि क्रमिक वृद्धि भई वैशिक औसत (ग्लोबल एभरेज) मान १.० को वरिपरि स्थिर भएको देखिन्छ। निश्चित चौडाइ (फिक्स्ड बीइड्थ) विन्डो बनाएर स्थान अनुसार भिन्नता (स्पेटियल भ्यारिएसन) को आधारमा बी–मानमा गरिएको अध्ययनले ०.५९ देखि १.० सम्म परिवर्तन भएको देखाउँछ। यस परिणामले अध्ययनमा समेटिएको क्षेत्र विवर्तनिक (टेक्टोनिक) रुपले सक्रिय रहेको सङ्केत गर्दछ। हिमालयको सतहभन्दा मुनि गरिएको बी–मानको अध्ययनमा ०–११ कि.मी. गहिराइमा बी–मान १.० को वरिपरि पाइएको छ भने ३२ कि.मि. गहिराइमा बी–मानमा सार्थक परिवर्तन देखिएको छ। बी–मान १.० को वरिपरि रहनुले सक्रिय विवर्तनिक, भूपर्पटी (क्रस्ट) मा रहेको विजायीयता (हेटेरोजिनीटी) र भूपर्पटीमा रहेको चट्टानको तनाब (स्ट्रेस) धान्न सक्ने क्षमताको न्युनतालाई दर्साउँछ। बी–मानका रूपरेखा नक्शा (कन्टुर म्याप) को अध्ययन गर्दा गोरखा भूकम्पको पूर्वतिर र पश्चिमतिर न्यून बी–मान सूचित गर्ने क्षेत्रहरू पाइएको छ र यी क्षेत्रहरू हिमालयमा बिध्यमान मुख्य भ्रंश (थ्रष्ट) सँग अतिव्याप्ति (ओभरलेप) भएको पाइएको छ। यस शोधमा ८१.७७० पूर्व - ९०.४१० पूर्व र २५.२२० उत्तर - ३०.१५० उत्तरमा २५ अप्रिल २०१५ देखि १४ मे २०१६ सम्मका गोरखा भूकम्पको पराकम्पनहरूको भग्न आयाम अध्ययनलाई विशेष जोड दिइएको छ। तीव्रता (म्याग्निचुड) २.० वा सो भन्दा बढी (रिक्टर स्केल) का १०,५०० पराकम्पनहरूलाई प्रत्येकमा ५०० वटा पराकम्पनहरू समाबेश गरी १०१ वटा विन्डो बनाईएको छ। प्रत्येक विन्डोमा पराकम्पनहरू १०० को सङ्ख्यामा सर्दै गएका छन् वा ४०० वटा पराकम्पनहरू अतिव्याप्ति भएका छन्। बाक्शा गणना आयाम (बक्स काउन्टीङ्ग डाइमेन्सन) वा क्षमता आयाम (क्यापासिटी डाइमेन्सन) को मान ०.८४±०.०७ देखि २.३९±०.०३ सम्म र सहसम्बन्ध आयम (कोरिलेसन डाइमेन्सन) को मान १.११±०.००४ देखि १.३८±०.०३ सम्म परिवर्तन भएको देखिन्छ। सामान्यीकृत आयाम (जेनेरलाईज्ड डाइमेन्सन) वर्णक्रम (स्पेक्ट्रम) मानहरू दोलन (ओस्किलेसन) भएको देखिन्छ। सामान्यीकृत आयाम वर्णक्रमको विस्तृत अध्ययन गर्दा बाक्शा गणना आयामको उच्चतम मानहरू २.२८±०.०२, २.३९± ०.०३ र २.१५±०.०३ क्रमशः २०१५–०८–१५ देखि २०१५–०८–२६, २०१५–११–०१ देखि २०१५–११–२० र २०१५–११–३० देखि २०१६–१–११ को समयकालिक विन्डोको लागि पाइएको छ। आयाम वर्णक्रम (डाइमेन्सन स्पेक्ट्रम) मा क्यु (अङ्ग्रेजी अक्षर) को मान २ देखि २२ सम्म परिवर्तन गरी हेर्दा भग्न आयाम २.०–०.७ सम्म घटेको पाइयो। यो विचलनले रूक्षता (एस्पेरिटि) को वरिपरि तनाव (स्ट्रेस) निर्माण र तनावबाट छुटकारा को सङ्केत गर्दछ। भग्न वर्णक्रम (फ्रेक्टल स्पेक्ट्रम) को घुँडा जस्तो वा अवग्रह (सिगमोईड) आकारले गोरखा भूकम्पको पराकम्पनको बाँडफाँड बहुभग्न संरचनामा भएको देखिन्छ। यसको साथै भूकम्पको केन्द्रविन्दु (एपिसेन्टर) हरू निश्चित क्षेत्रहरूमा झुण्ड (क्लष्टर) को रुपमा पाइएको छ। समयकालिक सहसम्बन्ध आयाम (टेम्पोरल कोरिलेसन डाइमेन्स) को मान फरक फरक समय विन्डो को लागि ०.२७ देखि ०.३० बिच रहेको पाइएको छ भने १९६४ देखि २०२० सम्म यसको मान ०.३१±०.००४ रहेको पाइएको छ। यी न्यून मानहरूले पराकम्पनहरूको उच्च अस्थायी झुण्डको सङ्केत गर्दछ। यो उच्च झुण्डको कारण तनावको अन्र्तरक्रिया, नयाँ भ्रंशहरूको निर्माण हुन सक्छ। भूकम्पजनिक मोमेन्ट प्रसारण वक्र (साइजमिक मोमेन्ट रिलिज कर्व) हेर्दा कोदारी (दोलखा) भूकम्प पछि भूकम्पजनिक शक्तिको रिलिज बढी भएको पाइएको छ। जसले शक्तिशाली पराकम्पनले बढी असर गर्छ भन्ने कुरालाई प्रष्टयाउँछ। भूकम्पजनिक शक्ति बढी रिलिज हुनुको कारण भू-पाता सबडक्सन दर बढेको पनि हुन सक्छ। यस अध्ययनमा बी–मान र भग्न आयामको बिचमा कमजोर नकरात्मक सहसम्बन्ध देखिएको छ जसले बी–मान बढ्दै जाँदा भग्न आयमको मान घट्दै जाने सकेत गर्दछ। यसको साथसाथै स–साना पराकम्पनहरूले भूकम्पीय क्षेत्रमा कम जटिल स्थिति बन्दै गएको पनि सङ्केत गर्दछ। गोरखा भूकम्पको पहिलो ४५ दिन सम्मको पराकम्पनहरूको ओमरी नियम अनुसार अध्ययन गर्दा पराकम्पनहरूको सङ्ख्या पहिलो १० दिनमा तीब्र रुपमा घटेको देखिन्छ र त्यसपछि क्रमिक रुपमा घटेको पाईएको छ। परिमार्जित ओमरी मापदण्ड (प्यारामिटर) पि (अङ्ग्रेजी अक्षर) को मान ०.८६±०.०४ मापन गरिएको छ जसले अपेक्षाकृत कम अस्थायी क्षयदर सङ्केत गर्दछ। अन्य मापदण्डहरू सी (अङ्ग्रेजी अक्षर) र के (अङ्ग्रेजी अक्षर) को मान क्रमशः ०.०५१±०.०१९ र ५७.९±३.७ मापन गरिएको छ। यस अध्ययनबाट प्राप्त पी को मान सामान्य मानिने पी को मान (१.०) भन्दा कम छ जसले पराकम्पनमा आएको गिरावट दर अझै सन्तुलनमा पुग्न नसकेको सङ्केत गर्दछ र अतिरिक्त पराकम्पनहरूको सम्भावनालाई नर्कान नसकिने बताउँछ। अन्तमा यस अध्ययनले मध्य हिमाली क्षेत्रमा भूकम्पीय गतिविधिको जानकारी गराई समयमा जोखिम मुल्याङ्कनका प्रयासहरूमा लाग्न जोड दिन्छ। यसले गर्दा भविष्यमा हुने धनजनको क्षतिमा कमी ल्याउन सकिने छ।Item First-principles and classical atomistic study of interactions between methane and other substances(Institute of Science and Technology, Physics, 2017) Pantha, NurapatiAvailable with full textItem Study of morphology and star-formation activity of merging dwarf galaxies in the field environment(Institute of Science and Technology, Physics, 2023) Chhatkuli, Daya NidhiAvailable with full textItem Thermodynamic artifacts in liquid alloys(Institute of Science and Technology, Physics, 2023) Gohivar, Ramesh KumarThe experimental and literature values of the excess free energy of mixing of Al–Fe, Al–Mn, Al–Ti, and Li–Mg binary and Al–Li–Zn ternary liquid alloys were modeled in terms of self-consistent interaction energy parameters within the framework of RedlichKister (R-K) polynomials. Initially, these parameters were assumed to be linearly dependent on temperature (T-dependent). The linear T-dependent interaction parameters were used to study various thermodynamic properties, such as free energy of mixing, enthalpy of mixing, activity, and concentration fluctuation in long wavelength limit of the aforementioned liquid alloys at various temperatures. At temperatures close to the melting point, it was found that the thermodynamic properties of the liquid alloys agree well with the corresponding experimental values. However, at higher temperatures, thermodynamic properties of the liquid alloys showed unusual phase equilibrium conditions. These conditions were referred to be artifacts or artificial inverted miscibility gaps because they were only observed in theoretical calculations and not in experimental measurements. The linear T-dependent optimised parameters of R-K polynomials were, therefore, considered inadequate at higher temperatures to account for the presence of such artifacts in the thermodynamic properties of liquid alloys. Consequently, it became clear that the interaction energy parameters must be re-optimized in order to produce parameters appropriate throughout a broad range of T-dependence. The interaction parameters for the respective excess free energy of mixing of the aforementioned liquid alloys were then re-optimized within the R-K polynomial framework, considering the exponential T-dependence of the parameters. Again, the optimized exponential T-dependent interaction parameters were utilized to assess the thermodynamic properties of the liquid alloys. As in the prior case, the thermodynamic properties of the alloys were found to agree well with the corresponding experimental values at temperatures close to the melting point. In addition, the thermodynamic properties of the liquid alloys computed at higher temperatures with T-dependent exponential parameters were free of artifacts. This study, thus, shows clearly that the poor modelling of interaction energy parameters is responsible for the appearance of artifacts in the properties of liquid alloys. It was also found that the exponential T-dependent parameters can be used over a wide temperature range for the evaluation of the thermodynamic properties of liquid alloys without producing artifacts. In addition, the ternary Al–Li–Zn liquid alloy showed the critical mixing behaviour at a Li concentration of 0.3 and a temperature of 973 K at the x Al : x = 1 : 1 cross section from the Li corner. This interesting behaviour in the ternary Al–Li–Zn liquid alloy is recommended for further investigation.Item Radiological mapping by in-situ gamma ray spectrometry in Kathmandu and Makwanpur district(Institute of Science and Technology, Physics, 2023) Mishra, AnitaAvailable with full textItem Theoretical modeling to access the surface phenomenon of liquid ternary alloys(Institute of Science and Technology, Physics, 2023) Mehta, UpendraThe Redlich-Kister (R-K) polynomial was used to optimise the linear temperature dependent interaction energy parameters for excess Gibbs free energy of mixing of binary subsystems of Fe–Si–Ti, Al–Sn–Zn and Al–Cu–Fe ternary liquid alloys using experimental data for excess entropy of mixing and enthalpy of mixing. The optimised parameters of binary subsystems were then used in the Chou equation (General Solution Model) for the excess Gibbs free energy of mixing of ternary liquid alloys to evaluate the partial excess free energy of mixing of components. These partial excess free energies of components of ternary liquid alloys were then used in the Butler equation to compute the surface concentrations of components and surface tensions of these ternary systems from the corner of each element at cross-sections of 3 : 1, 1 : 1 and 1 : 3. In addition, the excess surface tension of the binary subsystems at four different temperatures was used to compute the temperature dependent coefficients of the R-K polynomial for the binary subsystems of the previously mentioned ternary alloy. These coefficients were then used in the Kohler, Toop, and Chou equation to obtain the surface tension of the ternary alloys at different temperatures and concentrations. The obtained values of surface tension using these geometrical models were then compared with those obtained using the Butler equation. It was found that the component with the lowest surface tension leads to the highest surface concentration and the surface concentration of components increases as their bulk concentration increases and vice versa. Furthermore, it was observed that the the interaction between the binary pairings affected the surface concentration of a component in these ternary alloys. All three binary subsystems of Fe–Si–Ti ternary system were found to be ordering in nature and the surface concentration of the components was also affected by the interaction between these binary pairs. The surface concentration of Ti was found to increase with the decrease of its bulk concentration at the low content of Ti in the alloys. This unusual behaviour was observed due to the higher interaction energy between Fe and Si than between Fe and Ti in Fe–Si–Ti ternary liquid alloys. It was observed that the surface concentration of each component in Al–Sn–Zn ternary liquid alloy increased with increasing the respective bulk concentration at all crosssections. In this case, surface concentration was determined by the surface tension of the individual components, as all the binary sub-systems of this ternary alloys were of segregating nature. In case of Al–Cu–Fe liquid ternary alloys, binary sub-systems Al–Cu and Al–Fe are of ordering in nature while Cu–Fe is strongly segregating. When observed from the Fe corner, the surface concentration of Cu increased from 0.060 to 0.081 while the bulk vii concentration decreased from 0.225 to 0.088 at the cross-section x Al : x = 3 : 1. This unusual trend of increasing surface concentration of Cu with the decrease of its bulk concentration may be due to the ordering tendency of Fe with Al and the segregating nature of Fe with Cu. The surface concentration of components changes towards the ideal value (bulk concentration) at elevated temperatures. The surface concentration of Fe and Ti was found to increase while that of Si was found to decrease when the temperature of the alloy was increased from 1873 K to 2173 K. The surface concentration of Fe and Ti were found less than their respective bulk concentration and mole fraction concentration of Si in the surface was found to be much higher than the bulk phase. Similar results were noticed for the variation of surface concentration with temperature in the case of Al–Sn–Zn and Al–Cu–Fe ternary liquid alloys. The surface tension of liquid ternary alloys was found to decrease rapidly with the rise in bulk concentration of the component having the least surface tension in pure state. The value of temperature coefficient of surface tension was found to vary with composition of the alloys. The surface tension of all ternary liquid alloys studied in this work decreased linearly with increase in temperature, regardless of composition.Item Super Substorm Related Signatures at Middle and Low Latitude Ionosphere(Institute of Science and Technology, Physics, 2022) Pandit, DrabindraAvailable with full textItem PERFORMANCE ANALYSIS OF MICROSTRIP ANTENNAS FOR DIFFERENT MATERIALS(Amrit Campus, 2023-08-17) Simkhada, RameshThe Micro-strip antennas are widely used due to its compactness, simple manufacturing process, budget friendly and versatility. Here, carbon, abundant and easily available element is utilized in the process for the design and fabrication of antenna patch. Seeds of lapsi (Choerospondias axillaris), the indigenous plant of Nepal is used to extract carbon. The seeds are powered and activated chemically. The presence of carbon is verified using XRD technique. Resistance of dry powdered activated carbon is in the range Mega-ohm (MΩ) but after the coating of the paste of activated carbon in a polycarbonate substrate and acted by a laser of light-scribe drive various light and dark patterns were. The darker patches were found to be conducting and lighter patches were found to be non-conducting. After the activation by laser in activated carbon in a polycarbonate substrate resistance hugely dropped from Mega ohm (MΩ) to the range of Kilo-ohm (KΩ). For simulation part, High Frequency Structural Simulator (HFSS) software was used. First the basic rectangular antenna is designed and its properties were studied. Fractal swastika shape slot was later introduced in the design. The performance of antenna is optimized using the genetic algorithm. The optimized copper patch antenna with copper as ground in a polycarbonate substrate with no slot resonates at a frequency of 13.80 GHz with VSWR 1.34 and S11 parameter as -22.24 dB. On changing the patch as graphite in firstly mentioned identical conditions, antenna resonates at dual frequency of 15.40 GHz and 17.40 GHz with S11 parameters of -22.04 dB and -20.97 dB resp., VSWR of 1.17 and 1.19 resp. After the introduction of slot in copper patch antenna, multiple resonating frequencies were obtained as 9.0000, 13.8000, 15.0000, 17.4000 and 18.20000 GHz. In Graphite patch antenna also, there were multiple resonating frequencies. In comparison to cooper patch, graphite patch antennas showed better performance. After the introduction of swastika slot also, polycarbonate substrate has shown better performance for copper-copper patch-ground as antenna whereas properties were comparable in polycarbonate and corning glass substrate for graphite-copper as patch-ground antenna.Item STUDY OF DUST PROPERTIES AROUND HELIX NEBULA(NGC–7293) USING IRIS, AKARI, WISE SURVEYS, AND 2-DUST MODEL(Amrit Campus, 2023-08-17) Paudel, RajuThe present study aims to investigate the properties of the dust around Helix Nebula (NGC 7293) using IRIS, AKARI, and WISE surveys and the 2-Dust model. Helix Nebula is one of the well-known planetary nebulae in our Milky Way Galaxy. The study objectives include examining the dust color temperature, dust mass distribution, distribution of flux, and Jean’s criteria of the nebula, producing dust color temperature and dust mass maps of the field, and determining the mass loss rate, luminosity, inner shell radius, outer shell radius, and other dust properties of Helix Nebula using a density distribution function and comparing them to another model. The methodology employed includes using 2-Dust code, Aladin v10.0, and Python 3.7. The FITS image was taken from Sky View Virtual Observatory. The study findings indicate that the relative flux density is maximum around the central region and minimum around the outer region at F100 𝜇m and F22 𝜇m FITS images. The dust particle that emits a flux of 140 𝜇m is minimum in the central region. The dust color temperature of Helix Nebula varies depending on the survey used, with an average dust color temperature of (28.930 ± 0.005) K for the IRIS survey, (24.440 ± 0.078) K for the AKARI survey, and (277.490 ± 0.001) K for the WISE survey. The study also found that the dust color temperature was higher in the WISE survey than in the IRIS and AKARI surveys, suggesting an inverse relationship between the dust color temperature and the wavelength. The dust mass value was found to be higher in the AKARI survey and lower in the WISE survey. The calculated dust mass of Helix nebula using IRIS, AKARI, and WISE survey was found to be 0.10 M⊙, 0.56 M⊙, and 0.034 M⊙ respectively. The estimated dust mass in the circumstellar shell was 0.051 M⊙ and the mass loss rate was found to be 1.04×10−5 M⊙ yr−1 using the axisymmetric model. The study concludes that the results obtained from the 2- Dust code as well as the IRIS, AKARI, and WISE surveys provide a better understanding of the properties of dust around Helix Nebula.Item STUDY ON ELECTRICAL AND OPTICAL PROPERTIES OF ZINC OXIDE SEMICONDUCTOR FOR GAS SENSOR APPLICATION(Amrit Campus, 2023-08-17) CHAUDHARY, DINESH KUMARAmmonia, ethanol, acetone, etc. are commonly found as toxic gases in most places. The real-time monitoring of these gases is essential because their excessive exposure may produce serious health problems. In recent times, several metal oxide semiconductors (MOS) have been exploited for gas detection. In this context, zinc oxide (ZnO) is considered one of the potential materials for its interesting properties such as non-toxicity, high thermal & chemical stability, and easy tunable electrical & optical behavior. High working temperature (>300 °C ), poor selectivity, and low sensitivity are some of its shortcomings. The operation at high temperatures degrades the sensor’s stability and consumes power. This study aims to enhance the sensing characteristics of ZnO-based sensors after utilizing strategies like metal and metal-metal doping into it. Herein, the ZnO and metal-doped films were prepared by using spin coating, spray pyrolysis, and doctor blade methods for an in-depth understanding of gas sensing. Its optical and structural characterizations were done by ultra violet visible (UV-Vis) spectrophotometer and X-ray diffraction (XRD) respectively. Surface morphology and elemental composition were studied using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. The gas sensing performances of ZnO-based sensors were measured using a homemade gas sensor setup. At first, spin-coated ZnO was tested for the detection of traces of ammonia, ethanol, acetone, methanol, and isopropanol at room temperature. Its XRD and SEM micrographs demonstrated the polycrystalline wurtzite phase with a grainy surface. The band gap was found to be 3.202 ± 0.023 eV. The sensitivity measurements revealed the highest response of 38.5 ± 0.6 with an exposure of 400 ppm of ammonia vapour, indicating its selectivity among the tested gases. The results of sensitivity measurements over multiple cycles showed the device’s good stability. The sensing capability here was found to be better than other similar works. Hence, the results obtained here will be helpful in the development of a low-cost, effective room temperature MOS gas sensor with a lower detection limit of 20 ppm which is below the Occupational Safety and Health Administration’s (OSHA) approved threshold. For acetone sensing, ZnO deposited on an fluorine doped tin oxide (FTO) substrate prepared by doctor blade was used. XRD and fourier transform infrared (FTIR) spectroscopy were used for phase purity and optical characterization of ZnO nanoparticles (ZnONPs) prepared from the co-precipitation method prior to deposit on the FTO substrate. The sensing measurements demonstrated the maximum value of gas response of 25.697 ± 0.012 at an operating temperature of 285 ± 7 °C for exposure of 800 ppm of acetone along with the rapid response and recovery. This operating temperature was found to be lower than the published values that were prepared by different methods. The response & recovery times were measured to be 39 sec and 79 sec, respectively. Sequentially, in other sets of experiments, the undoped ZnO, Fe-doped ZnO (Fe-ZnO), and Sn-doped ZnO (Sn-ZnO) films were used to detect ethanol vapours in the temperature range of 100-300 °C. The sensitivity measurements for 2% Fe-ZnO film showed the highest response of 40.91 ± 0.23 at the exposure of 400 ppm of ethanol at 260 ± 7 °C. The comparison with similar reported values confirmed its goodness. And 2% Sn-ZnO film showed the highest response of only 17.659 ± 0.011 for 400 ppm exposure at 220 ± 5 °C. This working temperature was found to be slightly lower than the published value. Interestingly, this also reports that 2% Sn-ZnO film was able to detect as small as 0.5 ppm of ethanol. The spin-coated Fe-Al co-doped ZnO sensors were also tested to monitor ethanol in the temperature range of 120 − 360 °C. The 1%Fe-1%Al-ZnO sample showed a very high value of the response, 152.304 ± 0.003 at the exposure of 400 ppm at 290 ± 7 °C. It is due to an increase in specific surface area which occurs due to the reduction of grain size after Fe-Al co-doping. The observed values of response and recovery times were 33 sec and 201 sec respectively at an operating temperature of 290 ± 7 °C. Hence, metal-metal co-doping is found to be a good strategy to improve the sensitivity of ZnO-based gas sensors. Finally, the effect of gate electrode potential on the ammonia sensing ability of ZnO at ambient temperature was also reported here. Required films were prepared by the spray pyrolysis method. The gas response of ZnO for 400 ppm of ammonia was increased from 30.292 ± 0.042 to 54.581 ± 0.062 on increasing the gate electrode potential from 0 to 24V. Hence, this will be a new finding to improve the gas response of future ZnO-based gas sensors.Item ADSORPTION BEHAVIOUR OF NITRIC OXIDE MOLECULES OVER Ni, Pd, AND Pt-EMBEDDED GRAPHITIC CARBON NITRIDE(Amrit Campus, 2023-08-17) Poudel, Guna NidhiNitric Oxide adsorption on Ni, Pt, and Pd-Embedded graphitic carbon nitride has been studied com putationally using density functional theory. PAW pseudopotential with PBE exchange-correlation functional in GGA approximation was used for the relax, SCF, electronics, and magnetic calcula tions. Kinetic energy cutoff 550 eV was set up for plane wave basis set with ‘Gaussian’ type smear ing and width 0.05 eV. After relaxing, we get adsorbed energy of NO-GCN, NO-Ni-GCN, NO Pd-GCN and NO-Pt-GCN are −1.68 eV, −8.63 eV ,−6.61 eV, and −8.74 eV respectively. When functional transitional metals are embedded in GCN by adsorption of NO to its surface the results show that new energy states are introduced near the Fermi surface and modify the electronic prop erties of the system and the structure becomes a wrinkle. It means the conductivity of the system is considerably increased. Fermi energy of the GCN, NO adsorbs on GCN, NO adsorbs on Ni, Pd, Pt Embedded GCN are −1.72 eV, −1.36 eV, −0.65 eV, −0.64 eV, and −0.61 eV respectively. The band gap of the GCN, NO adsorbs on GCN, NO adsorbs on Ni, Pd, Pt-Embedded GCN are 1.3 eV, 1.12 eV, 0.98 eV, 0.45 eV and 0.32 eV respectively. During the adsorption process, electrons are transferred from the TM-Embedded GCN to NO molecules, due to metal the charge transfer from d orbitals to the NO gas. So the bond length of NO in TM-Embedded GCN increases. The magnetic moment of these compounds is 0 µB except NO-Pt-GCN compound which has obtained 0.98 µB due to the dxy and dyz orbital of the Pt atom. The magnetic moment of Ni-GCN and Pd-GCN is found to be 0 µB.Item EFFECT OF GLIDING ARC DISCHARGE PLASMA ON GERMINATION AND PRODUCTION OF OYSTER MUSHROOM (Pleurotus ostreatus)(Amrit Campus, 2023-08-17) Niure, DeepakAn experiment was conducted at plasma lab of the Central Department of Physics, Tribhuvan Univer sity, Kirtipur Kathmandu Nepal to study the effect of cold plasma on the germination and production of oyster mushrooms (Pleurotus ostreatus) by gliding arc discharge. The treatment includes four dif ferent methods for 10 samples on two replicate. Control, spawn treated with plasma, plasma activated water used for spraying and substrates treated with plasma. The main parameters measured during the experiment were the colonization and fruit appearance periods, the length and diameter of the stem and cap (pileus) diameters; the fresh weight of the first and second harvests of mushrooms, and the biological efficiency of various treatment methods. Among the different treatments of plasma, the time for colonization and fruit appearance was found to be faster than control. The length of stem was highest for spawn treated with plasma for three minutes, but the diameter of the stem was found to be the highest for treatment four minutes plasma treated water used and the diameter of cap found most significantly highest for spawn treated with plasma for three minutes. Similarly, the production and biological efficiency were found to be significantly highest in the case of spawn treated with plasma for two minutes, followed by substrates treated for ten minutes with plasma , and eight minutes of plasma activated water used respectively. Plasma treatment on oyster mushroom can play a significant role in the growth and production of mushrooms.Item COMPUTATIONAL STUDY OF HYDROGEN BONDED COMPLEX OF ETHANOL AND WATER USING VARIOUS FUNCTIONALS ON THE BASIS OF DENSITY FUNCTIONAL THEORY(Amrit Campus, 2023-08-17) Pudasaini, AnilComputational study of hydrogen bonded complex of ethanol and water using various functionals on the basis of density functional theory has been carried out using 6- 311++G(d,p), 6-311++G(2d,2p), and aug-cc-pVTZ basis sets. We have calculated binding energy, zero point vibrational energy, distance of the bond formed in the complex, bond angle after complex formation, frequency shift, electron density, and laplacian of electron density for the ethanol and water complex. The binding energy of the complex was found to be in the range of -4.258 kcal/mole to -6.232 kcal/mole . We have calculated the zero-point vibrational energy of the complex and found to be in the range of 1.54 kcal/mole to 1.85 kcal/mole . We have found the distance of bond formation in the complex in the range of 1.907 ˚A to 2.103 ˚A, the bond angle in the range of 172.73◦ to 178.80◦ , and frequency shift in the range of -151.76 cm−1 to -85.99 cm−1 . The electron density(ρ) and laplacian of electron density(∇2ρ) at bond critical points for the C2H5OH...H2O complexes are analyzed in DFT, and different levels of approximation by using AIM All software.
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