1,720,982 research outputs found
Propagation of electromagnetic waves in left-handed media
Full text linkIn this thesis, we discussed briefly about the artificial material properties which exhibited simultaneously negative values of electric permittivity, magnetic permeability
and refractive index across a common frequency band. Here, we used methods, like
analytical and computational methods to achieve the targeted objectives. The proposed left-handed media are used mainly in optical and electronic devises in better
way as compared to that of the conventional media. Left-handed media are applicable
in electromagnetic absorbers such as, radar microwave absorbers, electrically small
resonators, wave guides that can go beyond the diffraction limit, phase compensators,
advancement in focussing devices(example microwave lens), and improved electrically
small antennas. In this work, we have calculated about the real and imaginary parts
of electric permittivity and magnetic permeability by using Drude model. Currently,
left-handed media are being developed to manipulate electromagnetic radiation.First of all, I would like to thanks my Almighty God for his presence in my work. In
particular, I would like to express my deepest gratitude to my advisor Dr. Menberu
Mengesha for his valuable and constructive suggestions, directive comments, giving
and installing different important softwares and computational supports starting from
the topic selection up to the completion of of this thesis work. I thank him really a lot
for his contractive advice and guidance to the right research direction, enforcing me
in order to developing skills on my work, encouraging and giving supportive guidance
in developing computer skill (including Latex software, and Matlab).
Next, I would like to thank my co-advisor Dr. Nebiyu Gemechu for his insightful
comment to the accuracy of this thesis, continuous encouragement during my proposal delivery up to the final of this thesis.
My sincere thank also goes to Dr.Solomon Negash for his nice approach, directive
comments and giving important softwares.
Finally, I would like to thanks my wife Hawa Ali for her love, moral and
financial support and all my classmates and friends for their supports and constructive
comments for the success of my thesis work
Structural and Electronics Properties of Iron (Ii) Oxide Using Density Function Theory
No full textThe Structural and electronic Properties of Iron(ii)Oxides (F eO) is investigated with
density functional theory (DFT) using Quantum Espresso package. Our study is
based on Density Functional Theory (DFT) with the Perdew-Burke-Ernzerhof (PBE)
exchange-correlation functional, Vanderbilt (ultra soft) pseudo potentials and the
plane wave basis set implemented in the Quantum-ESPRESSO package. The calcu lation of the total minimum energy and the total minimum force of F eO is calculated
as a function of cutoff energy and K-points sampling. The total minimum energy
per cell is monotonically decreasing with increasing cutoff energy due to variational
principle. However, this trend can not be predicted from increasing the k-points sam pling. Moreover, the equilibrium lattice constant is calculated using results obtained
from energy convergence test (i.e., 70 Ry and 6 × 6 × 6 ). The computational value
of the equilibrium lattice constant is 7.5˚A. This result is underestimated by 8% from
the experimental value is 8.19˚A. In addition to this the band structure and total
density of state are calculated. From the band structure it is observed that the band
gap value is under estimated as compared to the experimental band gap value. This
descripancey is due to the inability of GGA to approximate the exchange correlation
potential of d and f block elements. The discontinuety of density of state at Fermi
level show that FeO is a semiconductor
electronic and structural properties of nickel using density functional theory
Full text linkNickel is a metal which is widely distributed in nature; and it is found in animals,
plants, and soil. The density functional theory (DFT) simulation tools were employed
to investigate energies, magnetization and geometrical structure of nickel (Ni) using
quantum ESPRESSO package. A number of convergence test were performed, to establish the optimal value of various parameters in the numerical calculations. Firstly,
the total minimum energy of nickel per atom is calculated as a function of cut-off energy, and k-points. Secondly, the optimal lattice constant and the magnetic ordering
were calculated for bulk nickel. Here to find the equilibrium lattice constant of nickel,
the total energy calculation with a series possible parameters of lattice constant have
been performed. Moreover, the total magnetization of an atom is computed as a
function of smearing(Marzari-Vanderbilt). In addition to these, Fermi-Dirac function was employed to describe the probability of electronic state occupations. Also
the calculations were repeated with Gaussian, Marzari-Vanderbilt and MethfesselPaxton functions. The total minimum energy per atom is monotonically decreasing
with increasing cutoff energy due to variational principle. However, this trend can not
be predicted from increasing the k-point sampling. The computational value of the
equilibrium lattice constant is 6.47 Bohr. This result is in good agreement with experimental value. Furthermore, the negative magnetization observed in low fields has
been ascribed to two oppositely ordered ferromagnetic super exchange interactions.
Moreover, the convergence in cold smearing is very fast than Fermi-Dirac smearin
Structural and electronic properties of feo using density functional theory with hubbard correction
Full text linkIn this thesis, the rst principle calculation based on density functional theory (DFT) with
Hubbard correction was employed to investigate the electronic and structural properties of
FeO using quantum ESPRESSO package. A number of convergence test were performed to
establish the optimal value of various parameters in the numerical calculations. Firstly, the
total minimum energy of FeO per atom was calculated as a function of cuto energy and kpoints sampling. Secondly, the optimal lattice constants of bulk FeO was calculated for a series
possible parameters using the results obtained from energy convergence test (i.e 80 Ry and 10 Ö
10 Ö 10 k-points). Moreover the band structure and density of states with Hubbard correction
of FeO have been calculated based on the frame work of density functional theory. The results of
calculations show that the total minimum energy of FeO per atom is monotonically decreasing
with increasing cuto energy due to variational principle. However, this trend can not be
predicted from increasing the k-point sampling. The computational value of the equilibrium
lattice constant was 8.2 Bohr or 4.338 Angstrom. The band structure and the density of states
of FeO is determine
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Structural, Electronic, Lattice Dynamic, and Elastic Properties of SnTiO3 and PbTiO3 Using Density Functional Theory
No full textThe structural, electronic, and elastic properties of tetragonal phase of SnTiO3 and PbTiO3 are investigated using first principle calculations. The unknown exchange-correlation functional is approximated with generalized gradient approximation (GGA) as implemented in pseudopotential plane wave approach. The convergence test of total energy with respect to energy cutoff and k-point sampling is preformed to ensure the accuracy of the calculations. The structural properties such as equilibrium lattice constant, equilibrium unit cell volume, bulk modulus, and its derivative are in reasonable agreement with the previous experimental and theoretical works. From elastic constants, mechanical parameters such as anisotropy factor A, shear modulus G, bulk modulus B, Young’s modulus E, and Poison’s ratio n are determined by using Voigt–Reuss–Hill average approximation. In addition, Debye temperature and longitudinal and transversal sound velocities are predicted from elastic constants. The electronic band structure and density of states of both compounds are obtained and compared with the available experimental as well as theoretical data. Born effective charge (BEC), phonon dispersion curve, and density of states are computed from functional perturbation theory (DFPT). Lastly, the spontaneous polarization is determined from the modern theory of polarization, and they are in agreement with the previous findings
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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