DSpace Coleção:https://repositorio.uema.br/jspui/handle/123456789/22032026-04-02T02:48:29Z2026-04-02T02:48:29ZProblema da difusão em meio poroso via cálculo fracionáriohttps://repositorio.uema.br/jspui/handle/123456789/54422025-10-07T18:28:52Z2024-11-06T00:00:00ZTítulo: Problema da difusão em meio poroso via cálculo fracionário
Abstact: Throughout history, renowned researchers have dedicated themselves and their studies
to investigate, understand and describe nonlinear diffusion processes, using analytical,
numerical and computational tools. In this work, we present a problem of nonlinear
anomalous diffusion in porous media and aim to present Lie symmetry transformation
groups as an alternative to solving the diffusion problem. Initially, a study was carried out
on fractional calculus and its main operators, where we point out definitions, theorems,
properties and applications. Fractional calculus allows us to describe natural characteristics
more precisely, thus obtaining a greater amount of information linked to nonlocal operators,
then called the memory effect. An analysis of anomalous fractional diffusion in porous
media was carried out, where the problem of nonlinear fractional diffusion in time-space
was addressed. Another important point presented here is the Lie point transformation
groups, which we use as an alternative to the diffusion problem, since Lie symmetries
prove to be a very important tool as it allows the transformation of a PDE into an ODE.
We apply Lie symmetries to the discovery of diffusion in fractional porous media in terms
of Riesz derivatives, including the Weyl derivative. And we demonstrate that the results
can be understood for the fractional derivative in terms of the function È. We emphasize
that the study of anomalous diffusion has been increasingly deepened and its concept
applied in several fields such as diffusion in plasmas, diffusion in turbulent fluids, fluid
transport in porous media, diffusion in fractals, anomalous diffusion on liquid surfaces and
analysis of heartbeat histograms in healthy individuals, among other physical systems.
Keywords: Anomalous Diffusion, Fractional Calculus, Fractional Diffusion in Porous Media,
Lie Points2024-11-06T00:00:00ZEstudo teórico das propriedades termodinâmicas e cinéticas nas reações de combustão do diborano como combustível de foguetehttps://repositorio.uema.br/jspui/handle/123456789/53882025-09-12T18:56:12Z2023-12-18T00:00:00ZTítulo: Estudo teórico das propriedades termodinâmicas e cinéticas nas reações de combustão do diborano como combustível de foguete
Abstact: A study was carried out on the thermodynamic and kinetic properties of the combustion
reactions of diborane as rocket fuel. To this end, it aims to understand the characteristics and
thermodynamic and kinetic properties of the thermal decomposition of high energy materials
in order to develop a mechanism of chemical combustion reactions. From the methodological
point of view, the geometrization of the molecules was modeled using the Gaussian9 software,
considering the bonds of each molecule of interest B-B, B-H, B-О, О-О, Н-H, O-H, mentioned
in the isodesmic reactions. It is evident that the optimizations of the equilibrium molecules in
the ground state were performed using the functional B3LYP model of DFT for the geometries
of the molecules. It is stated that the calculations of the reactions were computed at different
temperatures of 100K, 298K, 500K, and 1000K, thus it was possible to extract from the
Gaussian output file, the thermodynamic properties such as enthalpy variation, Gibbs free
energy, and equilibrium constant. The equilibrium constants Keq were computed from the
thermodynamic properties of the reactants and products as a function of temperature, and the
enthalpy variation (AH) was calculated based on the difference between the enthalpies of the
products and reactants. It reinforces that in the Density Functional Theory (B3LYP) the base
set cc-pVTZ (Triple Zeta) was used to determine the enthalpy of formation of neutral and
critical species in thermal decomposition. The presentation of the computational data of the
molecular geometries was presented in the form of tables and graphs. It was concluded that the
isodesmic reaction technique is very successful in determining the types of combustion
reactions, and helped us to clarify which of the reactions are involved in the absorption of the
heat produced during the process. It was observed that reactions I, II and III are reactions with
a high value of the Gibbs energy variation (negative) and that release a high value of energy to
the medium2023-12-18T00:00:00ZEfeitos termo-elétricos e magnéticos das monocamadas TMDs 1T’ – RuWTe2 e 1T’ – WTe2 via simulação computacionalhttps://repositorio.uema.br/jspui/handle/123456789/53642025-09-04T17:12:14Z2024-01-01T00:00:00ZTítulo: Efeitos termo-elétricos e magnéticos das monocamadas TMDs 1T’ – RuWTe2 e 1T’ – WTe2 via simulação computacional
Abstact: Transition metal dichalcogenides (TMDs) are chemical compounds consisting of two chalcogen
atoms (Te, Se or S) connected by covalent bonds to a transition metal atom, having
the structural form MX2. In this research, modeling and computer simulation were carried
out, followed by an analysis of the physical properties of monoclinic monolayers (1T’)
of tungsten ditelluride (WTe2) and tungsten-ruthenium ditelluride (RuWTe2) TMDs, the
latter replacing aWatom with a Ru atom in the primitive cell, from density functional theory
(DFT) formalism, mainly considering the generalized gradient approximation (GGA)
and the HSE06 hybrid functional for bandgap estimation, from nanostructures in their
minimum energy state. The lattice parameters of the proposed 1T’−RuWTe2 TMD are
compatible with the 1T’−WTe2 TMD already known in literature. The estimated bandgap
for 1T’−RuWTe2 was 0.50 and 0.35 eV, for the spin up and down bands, respectively,
characterizing it as a semiconductor, while 1T’−WTe2 showed conductor characteristics.
As for their magnetic nature, these TMDs showed ferromagnetism, with 1T’ − RuWTe2
showing an apparent tendency towards ferrimagnetism. The density of partial states, thermodynamic
potentials and thermal capacity were also analyzed, highlighting the potential
for synthesis and estimation of new Technologies such as thermo-electric and magnetic
nanodevices of the 1T’ − RuWTe2 TMD2024-01-01T00:00:00ZPropriedades físicas das nanoestruturas 2D dos dicalcogenetos do tipo XY2 (X= Mo, W; Y= S,Se) via teoria do funcional da densidadehttps://repositorio.uema.br/jspui/handle/123456789/48262025-05-19T15:36:09Z2022-12-16T00:00:00ZTítulo: Propriedades físicas das nanoestruturas 2D dos dicalcogenetos do tipo XY2 (X= Mo, W; Y= S,Se) via teoria do funcional da densidade
Abstact: The Transition Metal Dichalcogenide nanomaterials or TMDs are a class of materials with a stoichiometric ratio of the type XY2, where X is a transition metal and Y is a chalcogen, characterized by covalent bonding between X and Y elements exhibiting a polarization caused by the transfer between atoms. These materials exhibit a variety of morphologies, from three-dimensional materials to one-dimensional materials, but in the form of two-dimensional layers, they exhibit a variety of behaviors, making them suitable for various industrial applications. In this study, we model and analyze computationally the structural, electronic, optical and thermodynamic properties through DFT theory (Density Functional Theory) for MoS2, WS2, MoSe2 and WSe2 nanostructures, taking into the approximations: the local density approximation (LDA) and the generalized gradient approximation (GGA) of the optimized structure with energy in the fundamental state. The calculated structural parameters approximate the existing experimental and theoretical data in the literature, and even the energy
bandgap characterizes them as semiconductors. The total (DOS) and partial (PDOS) state densities were estimated, indicating the contributions of the atomic orbitals, the light absorptions along polarization planes demonstrate possible applications as sensors in the ultraviolet and visible range. Finally, thermodynamic potentials and specific heat as a function of temperature are analyzed2022-12-16T00:00:00Z