Vol. 1 (2017) Central Department of Physics Tribhuvan University, Kirtipur

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3 CDPAbstract Series Vol. 1 (2017) Central Department of Physics Tribhuvan University, Kirtipur

4 CDP, TU, Kirtipur (2017) 2

5 Content Student s Name Supervisor Page Arjun Subedi Prof. Dr. Narayan Pd Adhikari Ashok Shrestha Prof. Dr. Binil Aryal Balendra Bhatt Prof. Dr. Binil Aryal Bhakta Raj Niraula Prof. Dr. Narayan Pd Adhikari Bimal Chemjong Prof. Dr. Jeevan Jyoti Nakarmi Chhabindra Gautam Assoc. Prof. Dr. Hari Pd Lamichhane Deepak Ghimire Asst. Prof. Mr. Rajendra P. Koirala & Mr. B. Jha Ek Narayan Paudel Prof. Dr. Binil Aryal Gokul Acharya Prof. Dr. Narayan Pd Adhikari Hari Prasad Panthi Prof. Dr. Binil Aryal Jiwan Sejwal Prof. Dr. Binil Aryal Kumar Khadka Prof. Dr. Raju Khanal Kunal Tamang Asst. Prof. Dr. Gopi Chandra Kaphle Laxman S. Paudel Prof. Dr. Binil Aryal Mohan Gaire Prof. Dr. Binil Aryal Mukund Pd Joshi Asst. Prof. Dr. Balram Ghimire Narayan Aryal Prof. Dr. Narayan Pd Adhikari NarayanSapkota Prof. Dr. Jeeven Jyoti Nakarmi Naresh Adhikari Prof. Dr. Uday Raj Khanal Nawaraj Paudel Prof. Dr. Narayan Pd Adhikari Necklace Devkota Prof. Dr. Uday Raj Khanal Netra Pd Chapagain Prof. Dr. Ram Prasad Regmi Pradip Sharma Prof. Dr. Uday Raj Khanal Prakash Sharma Prof. Dr. Narayan Pd Adhikari Pramod Baral Prof. Prof. Dr. Raju Khanal Pramod Kharel Prof. Dr. Ram Prasad Regmi Pushpa Raj Paudel Prof. Dr. Narayan Pd Adhikari Puspa Raj Sharma Asst. Prof. Dr. Hari Pd Lamichanne Rajendra Thapa Asst. Prof. Dr. Gopi Chandra Kaphle Romakanta Bhattarai Prof. Dr. Narayan Pd Adhikari Santosh Parajuli Prof. Dr. Bobby Acharya (UK) Saraswati Shrestha Prof. Dr. Ram Prasad Regmi Saroj Danuwar Prof. Dr. Ram Prasad Regmi Shyam Bd Chauhan Prof. Dr. Raju Khanal Sita Kandel Asst. Prof. Dr. Gopi Chandra Kaphle Sudesh Tiwari Prof. Dr. Binil Aryal Sujan Ojha Prof. Dr. Ram Prasad Regmi Sumit Kushwaha Prof. Dr. Jeevan Jyoti Nakarmi Vivekanand K. Deo Prof. Dr. Jeevan Jyoti Nakarmi Yadav Pd Kandel Prof. Dr. Narayan Pd Adhikari Yajan Thapa Prof. Dr. Ram Prasad Regmi Format of Masters Dissertation

6 MOLECULAR DYNAMICS STUDY OF DIFFUSION OF BUTANE IN WATER AT DIFFERENT TEMPERATURES Arjun Subedi (May 2017) Molecular Dynamics (MD) simulation of dilute system of n-butane in water (3 n-butane in 971 water) is performed at six different temperatures ( K, K, K, K, K and K) under the pressure of 1 bar using GROMACS-Groningen Machine for Chemical Simulations. Force field parameters are used according to OPLS-AA-Optimized Potentials for Liquid Simulations-All Atom. The structural property of the system is studied through different pairs of the atoms in the system which shows more than one peaks suggesting that there exists noticeable interactions between the atoms in the system. Self-diffusion coefficients of butane and water are estimated by means of Mean Square Displacement (MSD) plot exploiting Einstein's relation. Mutual or binary diffusion coefficient of the system is calculated by using Darken's relation. Values of self-diffusion coefficient of water estimated in this present work are in excellent agreement with the experimental data available in the literature. Though the diffusion coefficients of binary mixture at low temperatures are close to experimental values, the values at higher temperatures are deviated noticeably from the experimental values with the maximum deviation of 39.53% at K. The obtained diffusion coefficients are found to follow the Arrhenius behavior. Activation energies are estimated using Arrhenius diagrams and these values are found to be in good agreement with the experimental values. Supervisor: Prof. Dr. Narayan Pd. Adhikari 4

7 SUB STRUCTURE IDENTIFICATION IN THE SUPERCLUSTER S[ ] AND THEIR PREFERRED ALIGNMENTS Ashok Shrestha (Feb 2017) We present the sub structure classification and the spatial orientations of angular momentum vectors of galaxies in the supercluster S [ ]. The number density contour map is plotted by varying the distance from one galaxy to other in order to study density enhancement in the supercluster region. The number density enhancement is used to identify the substructures within the superclusters. Three subcluster-like sub structures are found. The positions, position angles and inclination angles are used to convert two-dimensional observed parameters into three-dimensional angular momentum vectors of the galaxy using the `position angle-inclination' method. The expected isotropic distribution curves are determined by running numerical simulation by generating 107 virtual galaxies. Three standard statistical tools namely Chi-square test, auto-correlation test and Fourier test are carried out in order to determine the non-random effects in the expected isotropic distributions. We observed, except in the subcluster S2, random orientation of spin vector of galaxies in the supercluster and other subclusters. However, in all other samples the spin vector projections show isotropic distribution advocating the Hierarchy model of galaxy evolution in the supercluster S[ ]. The radial velocity distribution of galaxies in these subclusters are found to be random, supports Hierarchy model. Supervisor: Prof. Dr. Binil Aryal 5

8 A STUDY OF FORMATION AND EVOLUTION OF GALAXIES IN THE SUPERCLUSTER S[ ] Balendra Prasad Bhatt (Aug 2017) We present an analysis of the spatial orientations of 1,331 SDSS (Soloan Digital Sky Survey) galaxies in supercluster S[ ] using the 7th data release (2008 October). Our main goal is to find out the sub-structures within the large scale structure using the contour map of number densities of galaxies within the appropriate radius values to find out how the spin vector of galaxies in both large scale structure and sub-structure are oriented and their effect in the formation and evolution of galaxies in the boundary of three different evolutionary scenarios(the `primordial vorticity theory', the `pancake model' and the `hierarchy model') and to examine the non-random effect.we used the 'position angle-inclination' method to convert two dimensional observed data of the galaxies into three dimensional rotational axes (polar and azimuthal angles). We assumed a spatially isotropic distribution to examine non-random effects. Random simulation method is used to remove selection effects from the database. To test for anisotropy or isotropy we used three statistical tests namely, Chi-square test, Auto-correlation test and the Fourier test. We used two values of radius; 0:3 degree and 1:0 degree to find substructures in supercluster. From this we found three sub-structures for radius value 0:3 degree and two sub-structurs for radius value 1:0 degree from counter map of number density of galaxies. As a whole, the spatial orientation of spin vectors of galaxies in the superclusters are found to be random supporting hierarchy model of galaxy evolution. In the sub-structures, similar trend was noticed besides some fluctuations. Supervisor: Prof. Dr. Binil Aryal 6

9 MOLECULAR DYNAMICS STUDY OF DIFFUSION OF PROPANE GAS IN WATER AT DIFFERENT TEMPERATURES Bhakta Raj Niraula (May 2017) Molecular dynamics study of binary mixture of propane and SPC/E water, with propane as solute and water as solvent, with propane mole fraction has been carried out using GROMACS-Groningen Machine for Chemical Simulation at temperatures K, K, K, K, K, and K. The solute and solvent are modeled using bonded as well as non - bonded interactions in OPLSAA force field in GROMACS. The structure of system is analysed using radial distribution function of different atom pairs. The self - diffusion coefficient of propane and water are calculated from mean square displacement (MSD) plot using Einstein's relation. Binary diffusion coefficient of system is obtained from self - diffusion coefficient of individual species using Darken's relation. The binary diffusion coefficients at different temperatures obtained from simulation are found to be in agreement with the experimental results within certain error. The temperature dependency of diffusion coefficient is also studied and found to follow Arrhenius formula. Supervisor: Prof. Dr. Narayan Pd Adhikari 7

10 AN INTRODUCTION TO MULTIPHOTON IONIZATION AND STUDY OF TRANSITION RATE AND IONIZATION CROSSSECTION OF HYDROGEN ATOM Bimal Chemjong (April 2017) When intense laser pulses incident on atom, they can display various nonlinear optical phenomena. At these field strengths, electrons can be extracted directly out of bound states. If atoms are allowed to intense laser pulses, they can exhibit different non-linear optical process. About these field strengths, electrons can be withdraw directly out of binding states. Multi-photon phenomena process and are most significant for different aspects of matterradiation interaction which include the affluent ionization of different atoms and molecules, and mostly atomic transition mechanism, along with system environment couplings, and dissipative quantum dynamics, laser physics, optical parametric processes and interferometry. Here, we mainly focused our study on atomic transition with the help of presence of different multiple beams in nonlinear medium. The calculation of the matrix element plays an important role to calculate the transition rate which finally useful for the calculation of ionization cross-section. We have discussed the problems of non linear interaction between electromagnetic radiation with atoms from semi-classical point of view. Time dependent Schrodinger equation for single electron system is solved by using perturbative technique to obtain transition probability. The theory is based on the assumption that the perturbation is small. From this transition probability ionization rate and absorption cross-section of hydrogen atom is calculated. Its variation with photon energy and field strength is analyzed which agrees very well with experimental observation. Time dependent Schrodinger equation for single electron system is solved by using perturbative technique to obtain transition probability. In my task the time dependent perturbation have a wide application. First of all, the explanation of probability of transition of system from unperturbed stationary state to another state is described. Then, the Fermi Golden rule is derived which nicely described the transition probability, which becomes our main foundation for calculation ionization cross-section. At the last different graphical relation between cross-section and frequency energy, field strength can be observed. Supervisor: Prof. Dr. Jeevan Jyoti Nakarmi 8

11 ULTRASONOGRAPHIC AND BIOCHEMICAL STUDY OF THYROID GLAND Chhabindra Gautam (July 2017) Ultrasonography is one of the widely used harmless method to visualize the internal structures of the body parts. A group of 172 patients were studied at TU, Teaching Hospital, Institute of Medicine, Radiology Department. Some of the individuals have infection on thyroid and some have normal thyroid gland. The objective of my study was to obtain the average volume of both the lobes of thyroid gland, average concentration of T3, T4 and TSH and their various correlations to eachother in case of Nepalese peoples. The concentration fo hormones are calculated by means of a chemical method called Enhance Chemi-luminescence Immunoassy (ECI) at the Biochemistry Lab of TUTH. The average T3, T4 and TSH concentration on normal Nepalese people is found to be 5:760:92, 16:12:83, 2:170:98 respectively. To calculate the volume,\ three dimensions of both lobes of thyroid gland are noted manually from the Radiology Department of TUTH. High frequency ultrasound wave is used to obtained the highly resolved image of both lobes of thyroid gland. The average volume of left lobe of thyroid and right lobe of thyroid are 2:441:30, 2:951:59 respectively. There is strong correlation, 0:97 between T3 and T4 concentration. Also there is significantly high correlation coefficient, 0:71 between volume of left lobe and volume of right lobe. There is positive correlation between the T3 and T4 concentration while both of them are negatively correlate with the TSH concentration. During my study time we observed few patients having normal thyroid function test and abnormal ultrasonographic result and vice versa. Therefore, for the conformation of the disease one should have both tests. Supervisor: Associate Prof. Dr. Hari Prasad Lamichanne 9

12 STUDY OF DOSIMETRIC PARAMETERS IN COBALT-60 RATDIOTHERAPY Deepak Ghimire (December 2017) This work is carried out in Bhaktapur Cancer Hospital, mainly deals with the absorbed dose and percent depth dose measurement of Cobalt-60, based on NDW based formalism of TRS-398 protocol of IAEA. Furthermore, the tray factor, for using shielding blocks, whose role is to protect high radiosensitive organs in human body; the wedge factor, by using the wedges of di erent angles, in order to maintain uniform doses, mainly in sloppy areas and irregular surfaces, regarding central axis depth dose distribution have also been carried out. The study has been carried out with the help of NE2581 (SN:1182), NE, UK ionization chamber, NE2570/1B Farmer Dosimeter (SN:1299), NE,UK, and water and solid polystyrene phantom following IAEA protocols. Supervisor: Mr. Rajendra Pd Koirala & Bidyapati Jha 10

13 STUDY OF SUB-STRUCTURE EVOLUTION IN SDSS SUPERCLUSTER S[ ] Ek Narayan Paudel (March 2017) We present sub-structure analysis of a supercluster S[ ], the largest supercluster located in Sloan Great Wall region, using two dimensional galaxy congregation analysis. We identified four sub-structures with considerably high concentration of galaxies. We also carried out spin-vector analysis of 3038 galaxies belonging to the supercluster as well as for those four sub-structures using position angle-inclination method". We removed the selection effect present in our data by assuming Cosmological principle and using random simulation method. We used the simulated distribution as expected isotropic distribution. We then used chi-square, auto-correlation and Fourier statistics to test the isotropy of observed distribution taken from SDSS survey with reference to the expected isotropic distribution obtained through simulation. By analyzing the resulting spin-vector orientation of galaxies in supercluster and its four sub-structures, we are able to conform hierarchy model" of galaxy evolution in these structures. We also studied several properties of the identified sub-structures of the supercluster using all-sky maps and velocity distribution contours. We determined their galaxy contents, size, mean redshift, etc. In addition to this, the radial velocity contour map of some sub-structures showed systematic groupings leading into inhomogeneous distribution of matter. However, radial velocity is found to be independent of both spin vectors and its projections. We also compared the location of these sub-structures with Abell catalog of clusters to see if these sub-structures are Abell clusters. Supervisor: Prof. Dr. Binil Aryal 11

14 FIRST-PRINCIPLES STUDY OF ADSORPTION OF IRON ON PHOSPHORENE Gokul Acharya (June 2017) First-Principles calculations to study geometrical structure, stability, electronic properties, and magnetic properties of pristine and iron adsorbed phosphorene monolayer are carried out. Calculations are based on Density Functional Theory (DFT) with van der Waals (vdw) interactions in the DFT-D2 approach within Generalized Gradient Approximation (GGA). These calculations were performed using Quantum ESPRESSO (QE) software package. Our study is based on supercell calculation. We have used unit cell with four phosphorous atoms per unitcell as a basic building block and have taken 33 supercell of phosphorene monolayer for our calculation. Optimized lattice parame- ters of phosphorene mono-layer are found to be a = 4.54, b = 3.31 along X and Y directions where interlayer spacing is taken to be 20 for study of monolayer. These values agree well with previously reported data. In our study, phosphorene monolayer is found to be semiconductor with direct band gap, Eg, of 0.88 ev at point. This band gap agrees to previous DFT calculations wherease experimental results show larger band gap 1.5 ev. Similarly, we found that binding energy per phosphorous atom is 3.60 ev. Also there is symmetric distribution of DOS for spin-up and spin-down electrons near Fermi level indicating the non-magnetic nature of phosphorene. The band structure of the adsorbed system ia studied. Due to the adsorption of iron atom, the bandgap is found to decrease but the bandgap is different for spin up electron and spin down electron: 0.85 ev and 0.56 ev respectively. Therefore, the system shows the characteristics of half metal which results the application in spintronics The DOS of the spin up and spin down states are asymmetrical, which shows that the system is magnetic. The magnetization was found to be 2 B per cell. Supervisor: Prof. Dr. Narayan Pd Adhikari 12

15 SUPERCLUSTER S[ ]: STUDY OF SUBSTRUCTURE AND SPATIAL ORIENTATION Hari Prasad Panthi (May 2017) We present an analysis of the spatial orientations of 1465 galaxies of SDSS (Soloan Digital Sky Survey) supercluster S[ ] that have redshift in the range to Our main goal is to examine the non-random effect and to find out the substructure within the large scale structure using the contour map of number densities of galaxies within the radius of 0:5 degree to find out how the spin vector of galaxies in both large and sub structure to be oriented and their effect in the formation and evolution of galaxies in the boundary of three different evolutionary scenarios. These three evolution scenarios are the `primordial vorticity theory', the `pancake model' and the `hierarchy model'. Two dimensional observed data of the galaxies using is converted into three dimensional rotational axes (polar and azimuthal angles). We assumed a spatially isotropic distribution to examine non-random effects. Random simulation method is used to remove selection effects from the database to obtained the expected isotropic curves. The observed and expected distribution curves are compared by using the three statistical tests namely, Chi-square, Auto-correlation and the Fourier to check for anisotropic or isotropic. Total database has been studied to find the sub-structure in order to check distribution curve of galaxy in it using the three dimensional contour plot of number density maps within the radius of 0.5 degree. Results: Four sub-structures are identified in the number density map of galaxies. The red shift distribution in supercluster and in it s sub-structures are found to be Gaussian. As a whole, the spatial orientation of spin vectors of galaxies in the supercluster is found to be random supporting hierarchy model of galaxy evolution. In the sub-structures, similar trend is noticed. Local effect, however, is found in the sub-structure SS[ ] suggesting gravitational shearing effect. Supervisor: Prof. Dr. Binil Aryal 13

16 STUDY OF SUBSTRUCTURES AND SPATIAL ORIENTATION OF SPIN VECTORS OF GALAXIES IN THE SUPERCLUSTER S[ ] Jiwan Sejwal (Feb 2017) We present the spin vector orientations of SDSS (Sloan Digital Sky Survey) galaxies in the Supercluster S[ ] using seventh data release (2008 october). Using the spectroscopic database of galaxies, we studied number density map in the region of Substructure. Several density enhancement are observed, suggesting the possibility of substructure in the Supercluster. We have identified three subclusters like substructures in the region. Two dimensional observed parameters that we received from the database are used to compute three dimensional galaxy rotation axes by applying `position angle-inclination' method. We aim to examine the non random effects in the spatial orientation of galaxies assuming cosmological principle in the large scale structure. We generate 107 virtual galaxies to minimize the selection e ffects by performing the random simulation method. The expected distribution curves are obtained from the simulation. Chi-square, auto-correlation and Fourier tests are used to examine non-random effects in the polar and azimuthal angle distributions of the galaxy rotation axes. We intend to analyze our results in the frame work of the different galaxy evolution models namely Hierarchy, Primordial and Pancake model. Finally, we observed isotropic distributions in the Supercluster as well as in all three subclusters supporting Hierarchy model, which suggests a random orientation of the spin vector of galaxies with respect to the equatorial co-ordinate system. Supervisor: Prof. Dr. Binil Aryal 14

17 EFFECTS OF IONIZATION RATIO OF TWO SPECIES OF POSITIVE IONS IN MAGNETIZED PLASMA SEATH Kumar Khadka (Jan 2017) Study of multi-component magnetized plasma sheath at different ionization ratio has importance in fusion devices, material surface treatment, etching, thin film deposition, secondary electron emission guns, ion implantation and so on. The effect of ionization ratio on multi component magnetized plasma sheath has been studied using fluid model. The normalized fluid equations are solved numerically to analyze the density, velocity and potential profiles of ions. The plasma considered has two species of non-isothermal positive ions (Helium and Argon) with different ionization ratio. The results show that the density decreases with increase of ionization ratio and it is interesting to note that the charge of lighter ion species has the dominating effect on density profiles of both ions. Also the density peak becomes sharper and shifts towards the sheath edge as the charge number is increased. Unequal temperature of ions results in prominent ripples on bump and depression of density and velocity profiles of lighter ion. Furthermore, sheath potential increases with increasing value of the ionization ratio. Supervisor: Prof. Dr. Raju Khanal 15

18 STUDY OF ELECTRONIC AND MAGNETIC PROPERTIES OF HEUSLER ALLOYS: CoCrAl AND Co2CrAl Kunal Tamang (May 2017) The possible applications of half-metallic magnets in spintronics/ magnetoelectronics have gained a lot of attention in last two decades. Heusler alloys are found to be promising half-metallic materials as predicted by their band structure calculations. They have potential application in magnetoelectronic (spintronic) devices, fundamental and engineering science because of their new possible applications and phenomena. Density functional theory (DFT) based on Tight Binding Linear Muffin-Tin Orbital within Atomic Sphere Approximation (TB-LMTO-ASA) method is used to investigate the structural, electronic and magnetic properties of Al and Heusler alloys Co3-x CrAl (x=1, 2). For the electronic properties, we performed energy minimization process to calculate the optimized lattice parameter. From the present study, optimized lattice parameter of Al, CoCrAl and Co2CrAl are found to be 4.10 A, 5.56 A and 5.69 A respectively, which agree well with experimental value within 1.23 %, 3.17 % and 0.65 % deviation. From the band structure calculations, Al is found to be metallic while the Heusler alloys CoCrAl is semi-metallic and Co2CrAl is found to be half-metallic in nature with 100 % spin polarization. To know the contribution of the different orbitals in the bands, the system is analysed via fat band which reveals that most of the contributions on energy bands for Al is from p orbital. In case of CoCrAl and Co2CrAl main contribution comes from d orbitals of Co and Cr and p orbital of Al. The density of states for majority and minority spin electrons are also calculated to study the magnetic properties of the systems, which shows magnetic nature of Co2CrAl while non-magnetic nature of Al and CoCrAl. The magnetic moment of Co2CrAl is found to be 3.00B while CoCrAl has zero magnetic moment, which coincide with available experimental value and is in accordance with SlaterPauling rule. We also analysed the charge density of Heusler alloys Co 3-x CrAl (x=1, 2) from charge density plot and found that mixed nature of bonds exist between Co, Cr and Al. Supervisor: Associate Prof. Dr. Gopi Chandra Kaphle 16

19 STUDY OF SUBCLUSTER EVOLUTION IN THE SUPERCLUSTER S[ ] Laxman Sharma Paudel (April 2017) We present an analysis of spatial orientations of 1217 galaxies in the supercluster S[ ], named as SC11. The main goal of this work is to search for a new subcluster candidate, examine the orientation of angular momentum in the framework of three different scenarios (hierarchy, pancake, and primordial vorticity models) using position angle-inclination method", and to test the dependence on magnitude with the spin-vector orientations and their projections. We identified two subcluster using number density contour map with considerably high concentration of galaxies. Using random simulation method to remove the selection effect on database, we carried out expected isotropic distribution using cosmological principle. We then used three statistical tests: Chi-square, Auto-correlation, and Fourier to identify isotropy between observed and expected isotropic distributions. By analyzing the result obtained through statistical tests, we are able to conform that evolution of galaxy in the supercluster and subclusters supports Hierarchy model" giving the angular momentum of galaxies in the large scale structure tends to be oriented random with respect to the reference coordinate system. In addition to this, magnitude of galaxies found to be independent of both spin vectors and its projections. Supervisor: Prof. Dr. Binil Aryal 17

20 SUPERCLUSTER S[ ]: SUBSTRUCTURES IDENTIFICATION AND THEIR PREFERRED ALIGNMENT Mohan Gaire (September 2017) We present an analysis of the spatial orientations of 1172 galaxies in the Supercluter S[ ] that have redshift in the range 0:107 to 0:123. The database of supercluster are taken from SDSS 7th data release. The main goal of this work is to find out new substructure candidates in the given large scale structure using contour map of number densities of galaxies. After the identification of substructures, we examine the orientation of angular momentum of galaxies in the framework of three different galaxy evolution scenarios (`Hierarchy model', `Pancake model' and the `Primordial vorticity model'). In addition, we have tested the dependence of magnitude with the spin-vector orientations and their projections. We identified two substructures with considerably high concentration of galaxies. Random simulation method is used to remove the selection effects in our database and obtained the expected isotropic curves using numerical simulation. Then the observed and expected distribution curves are compared using the three statistical tests namely: Chi-square, Auto-correlation and the Fourier test. By analyzing the result obtained through statistical tests, we are able to confirm that evolution of galaxies in the supercluster and its substructures support `Hierarchy model' suggesting the spin vector orientation of galaxies tends to be oriented randomly with respect to the reference co-ordinate system. In addition to this, the magnitude of galaxies found to be independent of spin vectors and its projections in both supercluster and its substructures. Supervisor: Prof. Dr. Binil Aryal 18

21 COMPARISON OF GROUP VELOCITY AND ATTENUATION COEFFICIENT OF EQUALLY SPACED ALTERNATED NANOSPHERES CHAIN OF Pt AND Cu WITH Ag AND Al Mukund Prashad Joshi (June 2017) Here we made the study on the enhancement of electromagnetic energy along the plasmonic wire with in diffraction limit D<<, consists of equal sized metal nanospheres of same type and two types in alternative way which are closely arranged in free space. Because of close separation these oscillating dipoles interact via coupled plasmon mode (dipole), which is strongly depends on distance, frequency of incident field and polarization direction. Using the point dipole approximation, calculations were done for dispersion relation, group velocity and attenuation for each nano-wires consisting of Cu, Pt, Ag and Al separately as well for alternative array of Cu-Pt and Ag-Al. Interaction between two dissimilar metal nanoparticles is less than between same types results decrease in group velocity as well as bandwidth but, increase in attenuation coefficient. Among these two system Cu-Pt system there is more decrease in group velocity and increase in attenuation coefficient but make more selective in nature (less band width) than Ag-Al system. Less band width can be used in that propose where we require selected signal having small band width from large band of frequency. Supervisor: Associate Prof. Dr. Bal Ram Ghimire 19

22 MOLECULAR DYNAMICS STUDY OF DIFFUSION OF ETHANE IN WATER AT DIFFERENT TEMPERATURES Narayan Aryal (April 2017) In the present work, molecular dynamics simulations of a mixture of ethane (C2H6) gas in Extended Simple Point Charge (SPC/E) water model with ethane as a solute and water as a solvent have been performed to understand the diffusion phenomena at different temperatures K, K, K, K, K and K. The work has been carried out by using GROMACS-Groningen Machine for Chemical Simulations. The mole fraction of ethane in the system is and that of water is The equilibrium density and energy profile has been studied to confirm the stability of the system. To study the structural properties of the system, we have determined radial distribution function (RDF) of different atom/molecule. The self diffusion coefficients of ethane and water at different temperatures have been estimated by using mean square displacement (MSD) plot exploiting Einsteins relation. Binary diffusion coefficients are estimated by using Darkens relation. Binary diffusion coefficient thus estimates are found to be in good agreement with the experimental data reported in references. The temperature dependence of self-diffusion coefficients of ethane and water and their binary diffusion coefficient follow the Arrhenius behavior. The activation energy of diffusion processes have estimated from the Arrhenius plot. Supervisor: Prof. Dr. Narayan Pd Adhikari 20

23 FIRST PRINCIPLES STUDY OF STRUCTURAL AND ELECTRONIC PROPERTIES OF BN-nr, BN-ns AND BN-nd STRUCTURES Narayan Sapkota (June 2017) In this work, we investigate the stability, geometrical structures and electronic properties of Boron-Nitride ( nano sheet, nano ribbon and nano disc).the first principles calculations are performed in the Density Functional Theory (DFT) level of approximation with the van der Waals (vdw) interactions in DFT-D2 approach using Generalized Gradient Approximation (GGA), implemented with SIESTA code. The state of art method was used to design the novel structures of BN-nr, BN-ns and BN-nd structures. These structures are optimized using sufficient conjugate gradient steps followed by individual convergence test of Mesh-cut-off, K- points and lattice constants. In order to explore details of electronic properties, the simulation has been performed at ambient conditions. The Cohesive energy per Boron-Nitride pair is found to be ev/atom, ev/atom and ev for BN-nd,BN-nr and BN-ns respectively. The band gap is of the order of 0.45eV, 0.80eV and 1.65 ev for BN-nr,BN-nd and BN-ns respectively. These studies shows that BN-nd, BN-nr and BN-ns all are the semiconductor with differing conductance. The valenceband charge density contours of BN mono layer consists of a pattern of curved triangle around Nitrogen, reflecting the different electro-negativity of Boron and Nitrogen in all three structures. Supervisor: Prof. Dr. Jeevan Jyoti Nakarmi 21

24 A STUDY OF LINEAR PERTURBATIONS OF THE SCHWARZSCHILD BLACK HOLE Naresh Adhikari (June 2017) The gravitational perturbation to the Schwarzschild metric is studied. The perturbations using linear approximation are investigated under tensorial spherical harmonics. Under the parity transformations, the perturbations can be decomposed into two modes, i.e. axial and polar. The axial perturbations of the Schwarzschild metric in the linear approximation reduce to a wave equation called Regge-Wheeler equation. Using Regge-Wheeler equation, one dimensional Schrodinger wave equation is derived consisting of effective potential. This potential behaving like one dimensional potential barrier in elementary quantum mechanics is used to compute reflection and transmission coefficients in the vicinity of Schwarzschild space-time using method of confluent Heun equation and its properties. Supervisor: Prof. Dr. Uday Raj Khanal 22

25 MOLECULAR DYNAMICS STUDY OF DIFFUSION OF HEAVY WATER INTO NORMAL WATER WITH DIFFERENT CONCENTRATIONS AT DIFFERENT TEMPERATURES Nawaraj Paudel (Feb 2017) Molecular Dynamics simulations of D2O, H2O and their binary mixtures with two different mole compositions by mole fraction (D2O = 0:024; D2O = 0:03) is performed at different temperatures 295K, 300K, 305K, 310K, 318K and constant pressure (P= 1.0 bar) for mole fraction D2O = 0:024 and at 273K, 278K, 283K, 288K, 293K, 301K and constant pressure (P = 1.0 bar) for mole fraction D2O = 0:03 using GROMACS { Groningen Machine for Chemical Simulations. The structural property of the system is estimated by the study of O-O, OW-O and OW-OW radial distribution functions (RDFs). The radial distribution functions (RDFs) have three peaks, in general, which indicate the equilibrium structural properties of the system. The self-diffusion coefficient of D2O and H2O is determined by means of mean-square displacement (MSD) curves using Einstein's relation. The mutual diffusion coefficients of the binary mixtures are then determined using Darken's relation. The values of simulated diffusion coefficients are then compared with their corresponding theoretical values (based on and ), numerical estimation and experimental data. A good agreement between these sets of data is found. The values of simulated diffusion coefficient can be used to estimate the corresponding viscosity and thermal conductivity. The values of diffusion coefficient of H20 are found to agree with theoretical values, numerical estimation and experimental data within 5.6 % and for D2O within 5.39 % for mole fraction D2O = 0:024 and within 5.45% for D2O for mole fraction D2O = 0:03. The analysis of temperature dependence of the diffusion coefficients showed. Supervisor: Prof. Dr. Narayan Pd Adhikari 23

26 CASE STUDY OF MASSLESS SCALAR WAVE IN SCHWARZSCHILD SPACE TIME AS BACKGROUND Necklace Devkota (December 2017) The Massless Scalar wave to the Schwarzschild Black hole is studied. For this, Klein-Gordan equation for Schwarzschild Black hole is solved. The radial wave equation is obtained from the solution that consists of e ective potential covering the range from minus infinity to plus infinity. This potential behaving like one dimensional potential barrier in elementary quantum mechanics is used to compute reflection and transmission coefficient for the Schwarzschild Black hole using the method of Confiuent Heun equation and its properties. Comparative work is done for understanding the nature of potential of massless Scalar, gravitational and electromagnetic wave. Furthermore, the potential for the massless Scalar wave is analyzed by varying angular momentum index. Supervisor: Prof. Dr. Uday Raj Khanal 24

27 STUDY ON AIR POLLUTION EMISSION ESTIMATION AND DISPERSION MODELING OVER THE MID-WESTERN REGION OF NEPAL Netra Prasad Chapagain (August 2017) The gridded emission inventory of potential pollutants over the southern part of the Mid Western Nepal Himalayas has been carried out at the horizontal grid resolution of 1km x 1km covering 70 km x 70 km area centered at Kanchanpur of Banke District. The study reveals that , , , , , , and kg/day of SO2, NOX, TSP CO, PM2.5, PM10, NMVOC and PM are emitted into the atmosphere daily from the Kanchanapur and surrounding area. Transport sector has about 85 % contribution in SO2 and 83% contribution in the emission of NOX. Likewise the transportation and residential sector have almost same share in the production of CO. The regional scale atmospheric transport processes over the area have been numerically simulated using the state-of-the-art-of-the Weather Research and Forecasting (WRF) model initialized with the 1 x 1 NCEP reanalysis meteorological and 25-catagories USGS land-use and 1km x 1km terrain elevation data to understand implications for air pollution transport/chemistry/deposition over the area of study. Over the mountainous areas, strong diurnal periodicity on the characteristic local flows has been predicted. During the night and morning times, gentle downslope/downvalley winds prevails over the elevated land area such as Nigalchuli, Hiwalcha and the range that extends from Bardia National park to the east area that may penetrate deep into the southern plain areas whereas during the daytime pronounced upslope/upvalley winds blow towards the north crossing those ranges. The Babai River valley appears to be one of the main wind corridor that may effectively transport lowland pollutants, moisture and heat as well as pollutants towards the high mountainous areas and vice versa. The dispersion of SO2 emitted in the mid-western region is well described as revealed by the CTM simulation. The CTM simulated pollutant fields suggest that the local meteorological flows over the area generally organize lowland pollutants transport towards north through the mountain gap near the southern plains. Similarly, Bardia National Park is prone to the significant proportion of pollutants being transported from the lower plains. Supervisor: Prof. Dr. Ram Prasad Regmi 25

28 STUDY OF SOME BOUND STATES OF MASSIVE KLEIN GORDON FIELD IN SCHWARZSCHILD SPACE TIME Pradip Sharma (July 2017) The bound states properties, potential energy, of scalar particle around the schwarzschild black hole are estimated. By using polynomial conditions of Heun function, the wave functions and its probability density have been obtained. This probability density together with stability time of scalar particle around the schwarzschild black hole has been used to explain the true nature of scalar particle around the schwarzschild blackhole. Furthermore, these results have been used to explain the relation between mass, distance from the black hole, energy, angular momentum, and polynomial order of scalar particle. Supervisor: Prof. Dr. Uday Raj Khanal 26

29 STUDY OF ELECTRONIC AND MAGNETIC PROPERTIES OF PHOSPHORENE MONOLAYER DUE TO THE INTERPLAY BETWEEN VACANCY AND STRAIN Prakash Sharma (August 2017) First-Principles calculations to study geometrical structure, stability, electronic properties, and magnetic properties of pristine, vacancy created and strain applied phospherene monolayer are carried out. Calculations are based on Density Functional Theory (DFT) with van der Waals (vdw) interactions in the DFT-D2 approach within Generalized Gradient Approximation (GGA) in Perdue, Burke, and Ernzerhof (PBE) form, implemented by Quantum ESPRESSO (QE) software package (version 5.0.1). Our study is based on supercell calculation. We have used orthogonal unit cell with four phosphorous atoms per unit cell as a basic building block and have taken 4x4x1 supercell of phosphorene monolayer for our calculations. Phosphorene is highly exible. So, we tried to study the stability, electronic and magnetic properties as well by applying little strain to both the pristine and vacancy created phosphorene monolayer. We noticed there are two distinct optimization path for monovacancy system which gives two different relaxed MV-structures, in which MV (5/9) is ground state of MV-system. It is also found that vacancy and/or strain change(s) the band gap of phosphorene monolayer significantly. Our DFT-D2 calculation shows a band gap of 0.88 ev for a pristine phosphorene monolayer increases to 1:1 ev for biaxial strain of 5% while system shows metallic charecter for 1.56% vacancy without strain. In pristine and strained phosphorene with or without vacancy, band gaps are found to be direct at points. Strains and vacancies can be, therefore, alternative ways to tune the band gaps in thin semiconductors beside the reliance on number of layers. Talking about its magnetic properties, vacancy and external strain alone does not provoke any magnetism in phosphorene; however, interplay between the vacancy and strain result effective magnetism in it. We also found that when a biaxial or uniaxial strain of 5% is applied on a phosphorene monolayer containing monovacancy, the system favors a spin-polarised state with magnetic moment of ~1 B. This provocation of magnetism in defected monolayer is due to the spin-polarised p-states of undercoordinated P atoms nearest to the vacancy site. Supervisor: Prof. Dr. Narayan Pd Adhikari 27

30 COMPARATIVE STUDY OF NEUTRON YIELD FROM A 2.5kJ PLASMA FOCUS (SBUPF1) AT DIFFERENT PRESSURE Pramod Baral (July 2017) Dense Plasma Focus (DPF) is a machine which produces a short-lived plasma: hot and dense enough to cause nuclear fusion and emission of X-ray and neutron. It has wide application in the field of microelectronics, lithography, and also as a neutron source for medical applications. Lee Model Code, which is a computer simulation package, has been successfully used in studying various Plasma Focus (PF) devices across the world. In the Lee Model Code, the PF device is first standardized by obtaining the best match of current waveform by varying various fit parameters. In the present work, we have used the Lee Code to study neutron yield from Shahid Beheshti University Plasma Focus (SBUPF1), a 2.5kJ deuterium based plasma focus device designed for neutron yield. Numerical experiments are carried out under the various operating pressure of the gas to study the neutron yield with other parameter adjusted to the values considered in experiments conducted in the device. Numerical results obtained using Lee Model Code are compared with reported experimental data and the discrepancies are analyzed and 7 discussed. The neutron yield obtained experimentally (0:70x10 ) matches 7 exactly with our numerically predicted value (0:69 x10 ) for the case of 3 Torr. For other values of pressure, neutron yield is not as same as experimental value but the nature of yield is similar and range of pressure is same. The 7 peak neutron yield of 4 x10 is observed at 6 Torr in real experiments for 190 nh inductance and 9 F capacitance. In our numerical experiments the same peak value of neutron yield at 6 Torr is obtained for 190 nh inductance and 24.3 F capacitance while varying capacitance value. Also we get the same experimental peak neutron yield at 54 nh inductance and 9 F while varying inductance value. The differences of neutron yield could be due to the fact that in real experiments the value of inductance (L) and capacitance (C) differs from their starting value for other pressures which is not taken into account while doing the real experiments. Supervisor: Prof. Dr. Raju Khanal 28

31 STUDY ON THE WINTER TIME METEOROLOGICAL FLOWS AND AIR POLLUTION TRANSPORT OVER THE SOUTHERN PLAIN AREA OF CENTRAL NEPAL HIMALAYA Prabin Kharel (July 2017) Air pollution is emerging as one of the major environmental problems in Nepal. The world heritage conservation site the Chitwan National Park located in the Southern plain of Central Himalaya is facing an increased emissions from domestic, transport and residential sectors. This newly emerged is likely to affect the bio- diversity and sustainable development of the area. Air pollution dynamic and their characteristics over the Chitwan valley in winter time was numerically examined by using a comprehensive-chemistry-transport transformation-deposition model (CTM) together with Weather Research and Forecasting Modeling (WRF) System. The spatial and temporal distribution of potential climatic parameters such as temperature, wind, and humidity examined with Weather Research and Forecasting Modeling System over Chitwan valley concluded that hot, humid and windy atmosphere during winter time. The outskirt of valley remain rather warm than central floor of valley. The central area experiences high humidity of around 50% during morning and evening time. Present study has prepared air pollution emission inventories of potential pollutants (BC, CH4, CO2, N2O, NH3, NMVOC, OC, PM, PM2.5, PM10, SO2, NOX, CO and TSP) at 1km x 1km horizontal grid resolution, clarified the wintertime meteorological flow fields and their implications of air pollution dynamics, and dispersion of pollutants in and around the Chitwan National Park. The gridded emission inventory was prepared considering the land use pattern, population density as well as industrial area, and vehicular exhaust, commercial and domestic sectors. Of the total NOx, 749 tonne loading estimated at over the study area, transport sector contributes 51 % whereas domestic and industrial sectors share 51% and 30%, respectively. The estimated 1324 tonnes emission loading of SO2 comprised of 77%, 16% and 1% respectively, from industrial, transport and domestic sectors. Likewise, domestic, transport and the industrial sectors contributed 38%, 5% and 56%, respectively, for TSP emission over the area. The total emission of carbon monoxide turned out to be tonnes annually for which residential sector contributed 87%. Supervisor: Prof. Dr. Ram Prasad Regmi 29

32 FIRST-PRINCIPLES STUDY OF ELECTRONIC AND MAGNETIC PROPERTIES OF B, N, B-N AND Si-S DOPED PHOSPHORENE Pushpa Raj Paudel (Feb 2017) First-Principles calculations to study geometrical structure, stability, electronic properties, and magnetic properties of pristine and impurity (B, N, B-N, Si-S) doped phosphorene monolayer are carried out. Calculations are based on Density Functional Theory (DFT) with van der Waals (vdw) interactions in the DFT-D2 approach within Generalized Gradient Approximation (GGA). These calculations were performed using Quantum ESPRESSO (QE) software package. Our study is based on supercell calculation. We have used orthogonal unit cell with four phosphorous atoms per unit cell as a basic building block and have taken 3x3 supercell of phosphorene monolayer for our calculation. Optimized orthogonal lattice parameters of phosphorene monolayer are found to be a = 4.54 A, b = 3.31 A along X and Y directions where interlayer spacing is taken to be 20 A for study of monolayer. These values match fairly well with previous data. Our study showed phosphorene monolayer is semiconductor with band gap, Eg, of 0.88 ev, band gap being direct at point. Similarly, we found that binding energy per phosphorous atom is 3.60 ev. We have found that there is symmetric distribution of DOS for spin-up and spin-down electrons near Fermi level indicating the non-magnetic nature of phosphorene. Results showed that nitrogen doping alone increases band gap whereas doping of other impurities studied (B, B-N, Si-S) decreases it % nitrogen doping increases band gap from 0.88 ev to 0.92 ev while 2.78% boron doping decreases band gap to 0.64 ev. Simultaneous doping of 2.78% boron and 2.78% nitrogen doping decreases it to 0.74eV. Similarly band gap for simultaneous doping of 2.78% silicon and 2.78% sulphur band gap decreases slightly to 0.82 ev. It is found that doping of N alone and simultaneous doping of Si and S preserves the direct nature of band gap while other types of doping (B, B-N) modifies band gap to indirect: top of conduction band (Ec) lies at k-point X and bottom of valence band (Ev) lies at k-point Y. Like pure state, all doped systems under study are found to be non-magnetic due to the saturation or pairing of valence electrons of dopant and its neighboring P atoms. Supervisor: Prof. Dr. Narayan Prasad Adhikari 30

33 QUANTUM MECHANICAL WAY OF EXPANSION OF WAVE FUNCTION IN TERMS OF STANDARD ORTHONORMAL BASES Puspa Raj Sharma (March 2017) The present work was carried out to develop a technique for expanding a regular function in terms of the orthonormal bases function. The orthonormal bases are the solution of Hermitian operator. Since it is not feasible to calculate all the terms in the expansion of the function in terms of orthonormal bases, a series was truncated after few terms and the result was compared with actual plot of the function. In this research a function f(x) = xexp[- x] was chosen, solution of the time independent Schrodinger wave equation, with one dimensional semi-linear potential well, in terms of bases sets-eigenstates of infinite well potential, shifted Legendre polynomials, and shifted Gegenbauer polynomials within finite range [0; 1]. Among three bases the series expansion of the chosen function was very quickly converged in shifted Legendre polynomials bases function. Supervisor: Associate Prof. Dr. Hari Prasad Lamichanne 31

34 STUDY OF STRUCTURAL AND ELECTRONIC PROPERTIES OF Sr, Ti AND PEROVSKITE SrTiO3 Rajendra Thapa (May 2017) The use of titanates as ferroelectric, electro-conductive, photo-refractive and photovoltaic materials makes them an interesting material in material-science. Calculations involving energy minimization curve, band structure and density of states (DOS) using the density functional theory (DFT) level of approximation implemented in Tight Binding Linear Muffin-Tin Orbital within Atomic Sphere Approximation (TB-LMTOASA) has been carried out. The optimized lattice parameters of face centered cubic Sr and hexagonal Ti are found to be 5.71 A and 2.83 A (a = 2.41 A and c = 4.47 A respectively which are in close agreement with experimental values 6.08 A and (a = 2.95 A and c = 4.68 A) with nearly 6% and 4% deviation. Similarly the estimated lattice parameters of SrTiO3 is found be 4.01 A deviated about 3% from the experimental values A. These are the results of TB-LMTO-ASA method using the local density approximation. From study of band structure, we found that Sr and Ti are metallic in nature while SrTiO3 is semi-conducting in nature. The band gap of SrTiO3 from LDA calculation is found to be direct and the value is 1.86 ev which is lower than the FP-LMTO reported value of 2.68 ev. The origin of this discrepancy may be attributed to the fact that LDA underestimates the band gaps even for insulators because of the discontinuity in the exchange-correlation potential which is not taken into account here. To solve this discrepancy we have used calculation using local density approximation with coulomb parameter (LDA+U). Using U = 7.0eV and J = 0.5eV, the band gap was found to be 2.65eV in close agreement to the above FP-LMTO study reported value. Finally, the existence of mixed ionic-covalent bonding in strontium titanate is pronounced with the charge distribution plot. Supervisor: Associate Prof. Dr. Gopi Chandra Kaphle 32

35 FIRST-PRINCIPLES STUDY OF POSSIBILITY OF HYDROGEN STORAGE ON PHOSPHORENE Romakanta Bhattarai (May 2017) We have performed the first-principles calculations to study the stability, geometrical structures, electronic and magnetic properties of pure phosphorene, H2 adsorbed phosphorene, nickel atom adsorbed phosphorene and H2 adsorbed nickel decorated phosphorene system. We have also studied the adsorption of hydrogen molecules on pure phosphorene as well as nickel decorated phosphorene. The calculations are performed in the Density Functional Theory with van derwaals interactions in the DFT-D2 approach under Generalized Gradient Approximation implemented by the Quantum ESPRESSO version Our findings show that the phosphorene is stable and non-zero direct band gap semiconductor having value 0.87 ev. The estimated value of binding energy per phosphorus atom of pure phosphorene sheets having 4, 16, 36 and 64 phosphorus atoms are 3.32, 3.60, 3.60 and 3.60 ev/atom respectively. From the adsorption energies of nickel atom on the different sites of phosphorene (hollow, bridge and top), hollow site found most favorable with adsorption energy of 4.27 ev for 3 x 3 super cell of phosphorene which agrees with previously reported value 4.33 within 1.4 %. The study of electronic properties of nickel decorated phosphorene shows that the value of direct band gap decreases to 0.79 ev. The study of adsorption H2 on the optimized structures of pure phosphorene and nickel decorated phosphorene system shows that hollow site is most suitable site of adsorption in both cases but the orientation of H2 molecules are perpendicular and parallel for pristine and Ni decorated system respectively. Band gap of pristine phosphorene is slightly increased to 0.88 ev after H2 adsorption but is highly increased to 0.97 ev for adsorption on Ni decorated system. Direct band gap and non magnetic properties unchanged due to adsorption which also agrees with previous result. We have also found from adsorption of H on these two systems that hydrogen is loosely bounded in case of pure phosphorene ( ev for 1-8 number of molecules) whereas tightly bounded (0.86 ev) for Ni decorated system. According to US DOE target and taking the result of graphene as reference, it is concluded that hydrogen storage on nickel decorated phosphorene system is practically infeasible. Supervisor: Prof. Dr. Narayan Pd ADhikari 33

36 SEARCH FOR HIGGS BOSON PAIR PRODUCTION IN PROTON-PROTON COLLISION DATA AT ps = 13 TeV USING THE ATLAS DETECTOR AT THE LARGE HADRON COLLIDER Santosh Parajuli (June 2017) A search is presented for Higgs boson pair production in the bbww* final state in which one W boson decays leptonically (to an electron or a muon plus a neutrino) and the other W boson decays hadronically. The analysis is 1 1/2 performed using an integrated luminosity of 13.2 fb of pp collision at [s] = 13 TeV collected by ATLAS detector at the LHC. No evidence of events beyond the background expectation is found. Limit on the production cross section of hh having invariant mass 400 GeV is obtained at 95% confidence level. Note: Prof. Dr. Binil Aryal, CDP, TU and Dr. Suyog Shrestha, Ohio State Universit, USA remained co-supervisors.) Supervisor: Prof. Bobby Acharya (Kings College, UK) 34

37 STUDY ON ATMOSPHERIC BOUNDARY LAYER CHARACTERISTICS AND AIR POLLUTION POTENTIAL OVER THE KATHMANDU VALLEY, NEPAL: OBSERVATIONS AND NUMERICAL SIMULATION Saraswati Shrestha (May 2017) Spatial and temporal characteristics of atmospheric boundary layer and air pollution potential over the Kathmandu valley have been studied using the Weather Research and Forecasting (WRF) model complemented with field measurements with Sonic Detection and Ranging (SODAR) and Automatic Weather Station (AWS). A complex combination of regional and local-scale meteorological flow fields has been found to be associated with the broad circular Kathmandu valley located atop a rather isolated mountainous region in the middle hills of Central Nepal Himalaya leading to high air pollution potential during the dry winter season over the valley. Numerical simulations were performed for the same period. The model predictions for potential meteorological fields such as wind speed, wind direction, temperature and relative humidity as well as the mixing height were validated with observations. High correlations between observations and simulations have been achieved with correlation coefficients ranging from 0.7 to 0.99 for potential meteorological parameters. The day and nighttime averages of wind speeds over the valley floor may remain at 2.4 m/s and 0.4 m/s, respectively. Late afternoon appears most windy and the speed of may remain around 5 m/s. Near surface atmosphere of the valley up to the height of 400 m AGL gets stratified and decupled with the regional local flows during the night and mornings. However, mixing activities may develop up to the height of 900 m AGL with capping inversion at the height of the surrounding mountains of the valley. The spatial and temporal distribution of air pollution ventilation coefficients over the valley floor and its immediate surroundings have been found to be well below 2000 m2/s and 6000 m2/s, for stratified night and convective daytimes, respectively, and hence the valley possesses high air pollution potential. Close to 5 million people living in the valley are at high risk if current trends of emission activities continue unabated. Recent upsurge in the level of air pollution in the valley may confirm the present findings. Supervisor: Prof. Dr. Ram Prasad Regmi 35

38 AIR POLLUTION EMISSION ESTIMATION AND DISPERSION MODELING OVER EASTERN DEVELOPMENT REGION OF NEPAL Saroj Danuwar (August 2017) The southern plain and Eastern Nepal Himalaya has been witnessing spontaneous urbanization and uncoordinated industrial expansions. Present study, thus, elucidated the prevailing meteorological flow characteristics and their implications for air pollution transport using the Weather Research and Forecasting (WRF) modeling system, developed gridded emission inventory at the resolution of 1km x 1km, simulated the air pollution transport and formation of pollutant fields using a Chemical Transport Model (CTM). It has been found that about , , , , , , , , , , , and tons of NOX, CO, NMVOC, TSP, PM2.5, NH3, BC, OC, CO2, CH4, N2O and SO2 are, respectively, emitted over the southern part of the Eastern Nepal Himalaya. Biratnagar-Dharan industrial corridor represents the air pollution emission hot spot of the region. Meteorological simulation over the region suggests that a gentle westerly/northwesterly wind prevails over the vast flat land during the morning time followed by westerly wind in the afternoon. In the nighttime, southern part of the flat land experience westerly wind whereas the northern part of the flat land is greatly influenced by the rather strong drainage flow along the Koshi River Gorge bends towards the east over the central area of the flat land. The southern flat land develops surface stratification during the night and morning times and the mixing activities may develop up to the height of 1 km above the ground in the afternoon. The southern flat land is warm and more humid than northern part of the region. The temperature over the southern flat land may reach more than 30 C in the afternoon. The dynamics of air pollutants over the region as revealed by CTM simulation suggests that the pollutants released over the region are poorly dispersed leading to the formation of high concentration in the vicinities of the Biratnagar-Dharan industrial corridor. The stagnated pollutants may disperse towards western region initially and then towards the eastern region during the afternoon and nighttime. The highest concentration of SO2 appears over the Dharan area where it may reach to about 7 ppb. Supervisor: Prof. Dr. Ram Prasad Regmi 36

39 EFFECT OF APPLIED WALL POTENTIAL AND MAGNETIC FIELD IN MIXED PLASMA SHEATH USING KINETIC TRAJECTORY SIMULATION Shyam Bahadur Chauhan (May 2017) The changes in behavior of ions and electrons in the magnetized sheath region with the variations of wall potential and magnetic field has been studied. We have considered two ion species plasma, nitrogen and hydrogen, and guided their motions using magnetic field. We have used kinetic trajectory simulation (KTS) model to obtain solution to a non-neutral, time-independent, collisionless plasma sheath. The electron and ion velocity distribution functions are considered to be cut-off. Maxwellian at sheath edge so that the most important requirements of the presheath-sheath transition are satisfied. The characteristic feature of KTS is that we calculate distribution functions of the particle species involved directly by solving kinetic equations along its collisonless particle trajectories. We found that with variations of wall potential, physical parameters like ion density, electron density, potential, total charge density at the wall varied appreciably. Also, with different applied magnetic field these parameters varied significantly. That is, with the increase in wall potential, particles flow towards the wall decreases with the fixed magnetic field. Similarly, with the increase in magnetic field particles flow decreases considerably with the wall potential kept fixed. The study of these phenomena helped us understand plasma-wall interaction. We have compared our work with previously done similar works and found our result are in good agreement with them. Hence, we conclude that our work is balanced with the previous works, and our model gives better insight to the sheath phenomena for two ion plasma using magnetic field. Supervisor: Prof. Dr. Raju Khanal 37

40 STUDY OF ELECTRONIC AND MAGNETIC PROPERTIES OF QUATERNARY HEUSLER ALLOY CoMnVAl Sita Kandel (June 2017) The zero-gap (gapless) semiconductor in Heusler alloy have created a much interest, because of their extraordinary property some gapless material have numerous practical application in electronic devices, as a photodetector, photogenerator, electromagnetic sensor as well as the gapless semiconductor with magnetism could have wide application in novel spintronic devices. The gapless property is observed in Co-Mn based quaternary Heusler alloy CoMnVAl employing rst principle calculation through Tight Binding Linear Muffin-Tin Orbital within Atomic Sphere Approximation (TB-LMTO-ASA) code based on density functional theory (DFT) with exchange correlation through local density approximation (LDA) approach. Different electronic and magnetic properties are observed with the help of band structure and density of states (DOS) calculations. The optimized lattice parameter of face centered cubic CoMnVAl found to be 5.66 A (10.68 a.u.) which fairly agree with experimental value with around 2.5% deviation. Non-spin polarised band structure and DOS are obtained for CoMnVAl. CoMnVAl constitute zero-gap energy bands of indirect type at Fermi level which also hold the previous calculation and experimental result. The highest energy is required when an electron hole pair is created by transferring the electron from valance band (VB) at L point to conduction band (CB) at same point as the highest energy gap is seen between them, while the lowest (zero) value of indirect gap between CB and VB respectively at X and G designate the smallest energy required for electron hole pair at these point. By the analysis of fatband and partial DOS, the major contribution to energy bands and DOS near fermi level is found from d orbital electron of cobalt (Co), manganese (Mn) and vanadium (V) and little from s and p orbital electron of aluminium (Al). The symmetric nature of DOS in majority and minority spin channel reveals that there is no magnetic moment obtain either in parent CoMnVAl or in individual atomic cite. The abscent of magnetic moment in 24 valance electron quaternary Heusler alloy CoMnVAl strongly support the Slater Pauling rule. Finally, the complex type of bonding (i.e mixture of covalent, metallic and somehow ionic) is ascertained between atoms in CoMnVAl. Supervisor: Associate Prof. Dr. Gopi Chandra Kaphle 38

41 STUDY OF SPATIAL ORIENTATION OF SPIN VECTORS OF GALAXIES IN SUPERCLUSTER S( ) Sudesh Tiwari (May 2017) We present an analysis of the spatial orientations of 1828 galaxies in the Supercluter S[ ] named as SCl 94 in SDSS catalogue. These galaxies are neighbourhood of our own galaxy, Milky way. The main goal of this work is to search for a new substructures candidate and to examine the orientation of angular momentum within the given redshift limit - in the framework of three different scenarios (`Hierarchy model', `Pancake model' and the `Primordial vorticity theory') using `position angle-inclination method' and to test the dependence of magnitude with the spin-vector orientations and their projections. We identified three substructures using number density counter map with considerably high concentration of galaxies. We use numerical method to remove the selection effects from the database. The expected isotropic distribution curve is determined by running numerical simulations. To check for isotropy or anisotropy, we mainly carried out three statistical tests: Chi-square, Auto-correlation and the Fourier. By analysing the result obtained through statistical tests, we are able to confirm that evolution of galaxies in the supercluster and its substructures. Total database is classified into three substructures which supports `Hierarchy model'. This model suggests that the spin vector orientation of galaxies in the large scale structure tends to be oriented randomly with respect to the reference co-ordinate system. In addition to this, the magnitude of galaxies found to be independent of both spin vectors and its projections in both supercluster and its substructures. Supervisor: Prof. Dr. Binil Aryal 39

42 AIR POLUTION EMISSION ESTIMATION AND DISPERSION MODELING OVER FAR WESTERN REGION OF NEPAL Sujan Ojha (June 2017) Present study was conceived to understand the status air pollution emission, the meteorology and its implication and the air pollution dynamics over the southern part of the Far Western Development Region of Nepal. The emission inventories of criteria pollutants such as SO2, CO, NOx, TSP have been prepared, spatial and temporal distribution of meteorological fields and the dynamics and formation of pollutant fields have been studied by numerical simulations using Weather Research and Forecasting (WRF) and the Chemical Transport Model (CTM) modeling systems. The study reveals that about , , and tons of SO2, NOx, TSP and CO, respectively, are annually loaded into the atmosphere from the southern part of Far Western part of Nepal. The southern flat land areas where major urban and industrial areas of the region are situated largely experience westerly/southwesterly. The Karnali River valley appears to act as one of the major valley wind corridor through which reasonably strong wind of speed 7.3 m/s flow towards the northern mountainous areas. The Siwalik mountainous range may modify the afternoon time westerly wind over the southern flat land into northwesterly wind that may help reduced transport of low land pollutant up into the mountainous areas. The flat land of FWDR appears to have been suffering from surface level inversion during night and morning times but daytime mixing height may reach up to 2.5 km above the ground. The relative humidity over the southern flat land mostly remains around 60-70% except over the northern narrow belt of the flat land close to the mountain ranges where it may remain less than 40%. The central area of the southern flat land appears to be the warmest where the ambient temperature may vary in between 23 to about 31 C. The simulated spatial and temporal distribution of SO2 pollutant suggests that the problem of air pollution over the regions is yet to become serious. The Mahendranagar and Dhangadi are the relatively most polluted areas of the region where the concentration may go up about 4.5 ppb during the morning time. The prevailing local winds transport the pollutants release over the southern flat land towards the northeast and east areas. Supervisor: Prof. Dr. Ram Prasad Regmi 40

43 FIRST PRINCIPLES STUDY OF STRUCTURAL AND ELECTRONIC PROPERTIES OF InO AND InSnO : ab initio approach Sumit Kushwaha (May 2017) The first principles density functional theory calculation is used to study the structural and electronic properties of Indium Oxide and Indium Tin Oxide. The state of art method was used to design the novel structures of InO and InSnO. These structures are optimized using sufficient conjugate gradient steps followed by individual convergence test of Mesh-cut-off, K- points and lattice constants. After structural optimization our ab-initio calculation calculating cohesive energy per pair of atoms to verify the stability of structures in generalized gradient approximation (GGA) within the SIESTA package. In order to explore details of electronic properties of these structures, the density of states, partial/projected density of states, band structure and distribution of charge densities are performed at ambient conditions. These studies show that all are the conductor with different conductivity. From the study we found that InO structure are comparatively more stable and exhibits conducting nature with Zero energy gap, whereas InSnO depicting metallic behaviour with finite density of states at Fermi energy level. It is found that on adding Tin layer in Indium-Oxide it decreases the conductance. Therefore the systems under study may serve as metal. Supervisor: Prof. Dr. Jeevan Jyoti Nakarmi 41

44 FIRST PRINCIPLES STUDY OF STRUCTURAL AND ELECTRONIC PROPERTIES OF TiO2, TiO AND Si DOPED TiO Vivekanand Kumar Deo (June 2017) The first principles density functional theory calculation is used to study the structural and electronic properties of Titanium Dioxide, Titanium Oxide and Si doped Titanium Oxide. The state of art method was used to design the novel structures of TiO2, TiO and Si doped TiO. These structures are optimized using sufficient conjugate gradient steps followed by individual convergence test of Mesh-cut-off, K- points and lattice constants. After structural optimization our ab-initio calculation calculates cohesive energy per pair of atoms to verify the stability of structures in generalized gradient approximation (GGA) within the SIESTA package. In order to explore details of electronic properties of these structures, the density of states, partial/projected density of states, band structure and distribution of charge densities are performed at ambient conditions. These studies shows that TiO2 and Si doped TiO are conductive in nature where as TiO is found to be semiconductor in nature. From the study we found that TiO2 structure are comparatively more stable and exhibits conducting nature with Zero energy gap, whereas TiO shows semiconductor in nature with certain band gap, ion doping Si on TiO depicting metallic behaviour with finite density of states at Fermi energy level. Supervisor: Prof. Dr. Jeevan Jyoti Nakarmi 42

45 MOLECULAR DYNAMICS STUDY OF DIFFUSION OF GLYCINE IN WATER AT DIFFERENT TEMPERATURES AND EFFECT OF POLYMERIZATION ON IT Yadav Prasad Kandel (Feb 2017) Molecular dynamics is promising way of analyzing dynamical and structural properties of matter. Diffusion, transport of mass in response to concentration and thermal energy gradient, is an important transport property, vital in material science and life science. We have done molecular dynamics study of diffusion of zwittterion glycine, zwitterion diglycine and zwitterion triglycine in water. Diffusion of zwitterion glycine has been studied at different temperatures (293.2 K, K, K, K) using GROMACSGroningen Machine for Chemical Simulations. The solute and solvent is modeled using both bonded and non-bonded interactions in GROMOS96A5 platform. The equilibrium density and energy profile has been studied to confirm the stability of syste. The self diffusion coefficiient of different species has been estimated from mean square displacement (MSD) plot exploiting Einstein's relation. Binary diffusion coefficient is obtained from self diffusion coefficient using Darken's relation. Binary or mutual diffusion coefficients are found to be in good agreement with the experimental data reported in references. The temperature dependency of diffusion coefficient zwitterion glycine in water is checked and found to follow Arrhenius formula. Effect of peptide formation in diffusion is studied using peptide chain composed of up to three monomers of glycine and found to decrease with increase in size of peptide chain. The structure of the system is analyzed using RDF of different atom/molecule pairs. In all the cases, at least two or more peaks where obtained which suggests appreciable amount of interaction between atoms and molecules. Further, the co-ordination number of water molecule around the COO-terminal of zwit glycine is calculated which gives us the number of water molecules near that terminal in first co-ordination shell. Supervisor: Prof. Dr. Narayan Pd Adhikari 43

46 AIR POLLUTION EMISSION ESTIMATION AND DISPERSION MODELING OVER WESTERN DEVELOPMENT REGION OF NEPAL Yajan Thapa (July 2017) The gridded emission inventory of potential pollutants has been carried out over the southern part of the Western Nepal Himalayas at the horizontal grid resolution of 1km x 1km covering 70 km x 70 km area centered at Butwal Municipality. The study reveals that , , and tons of SO2, NOX, TSP and CO are, respectively, annually loaded into the atmosphere of the area. Transport sectors have major contribution in the emission of NOX and CO emissions whereas the industrial sector is the main contributor of SO2 and Particulate pollutants. Regional scale atmospheric transport processes over the area have been numerically simulated using the state-of-the-art-of-the Weather Research and Forecasting (WRF) model initialized with the 1 x 1 NCEP reanalysis meteorological and 25-catagories USGS land-use and 1km x 1km terrain elevation data to understand implications for air pollution transport/chemistry/deposition over the area of study. The Tinau River valley appears to be one of the main wind corridor that may effectively transport lowland pollutants, moisture and heat as well as pollutants towards the high mountainous areas and vice versa. Present study further explored the typical regional scale transport and formation of pollutant fields over the southern part of the Western Nepal Himalaya considering three criteria pollutants, namely, the SO2, NO2, and the CO using a comprehensive Eulerian Chemical Transport Model (CTM) initialized with meteorological fields prepared from WRF simulation and the first had gridded emission fields. The CTM simulated pollutant fields suggest that the local meteorological flows over the area generally organize pollutants transport towards northeast and northeastern mountainous areas blanketing the areas such as Bhairahawa, Lumbini, Butwal, Ramgram, Sunwal, and Bardaghat. Significant proportion of pollutants is also transported towards the northern mountainous region affecting Tansen Municipality as well. The concentrations of the three criteria pollutants over the region are yet to cross the National Air Quality Standard except over the areas in the immediate vicinities of sources. Supervisor: Prof. Dr. Ram Prasad Regmi 44

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