DSpace Coleção:
http://www.repositorio.ufc.br/handle/riufc/218
2019-04-20T08:14:20ZPropriedades vibracionais dos aminoácidos DL-isoleucina e Ácido DL-glutâmico monohidratado e do complexo L-leucina oxalato submetidos a altas pressões
http://www.repositorio.ufc.br/handle/riufc/40871
Título: Propriedades vibracionais dos aminoácidos DL-isoleucina e Ácido DL-glutâmico monohidratado e do complexo L-leucina oxalato submetidos a altas pressões
Autor(es): Rêgo, Fellipe dos Santos Campêlo
Abstract: Amino acids in L-form are the constituents of all living beings. In crystalline state their structure is stabilized mainly by hydrogen bonds and they can present two enantiomers (L and D) and a racemic (DL) form. The amount of papers dealing on DL form of amino acid has increased in the last years, but it is still fewer than that on L-form. Although L and DL for being formed essentially by the same molecule the way they are linked can provide very different properties. In this way high pressure Raman spectroscopy is an useful tool that can be used to study the role of hydrogen bonds in the structure that compose amino acids as well as compare the behavior of its counterparts. In this report we present a detailed analysis of the vibrational properties of crystals of DL-isoleucine, DL-glutamic acid monohidrate and L-Leucine oxalate. These compounds were grown by slow evaporation of the solvent at room temperature. Its vibrational properties were studied at room temperature and at high hydrostatic pressure through Raman spectroscopy. For the sample of DL-isoleucine at ambient conditions, the mode assignment was done in terms of the potential energy distribution (PED) through density functional theory calculations. Both nitrogen and neon were used as pressure transmitting media. The pressure-dependent investigation shows modifications in the Raman spectra recorded between 30 cm-1 and 3200 cm-1 that were interpreted as phase transitions undergone by the crystal between 1.3 GPa and 1.9 GPa and between 3.6 GPa and 5.1 GPa. Finally, the stress was simulated on the unit cell of the crystal from ambient pressure to 5.0 GPa. The sample of DL-glutamic acid monohydrate, the modes assignment were made by comparison with works made in L-forms ( and ) glutamic acid and other amino acids. Neon gas was used as pressure transmitting media. In the investigation under high pressures were found three structural phase transitions. The first one at about 0,9 GPa, the second one at about 4.8 GPa showed conformations involving , and the water molecules, while the third one involved various parts of glutamic acid, as well as the water molecules. The crystal of DL-glutamic acid monohydrate demonstrate similar stability compared with its polymorphs -L-glutamic acid and -L-glutamic acid (for the first phase transition). However, phase II of DL-glutamic acid monohydrate demonstrated highest structural stability. Water molecules seem to play important role in this structural stability. In addition, all transitions were reversible. The sample of L-Leucine oxalate, the assignment of the modes has also been made by comparison with literature. Neon gas was used as pressure transmitting media. The results of the experiments under high pressures showed that this sample undergoes two phase transitions at high pressure, the first one between 0.9 GPa and 1.0 GPa and the second one between 2.6 GPa and 3.1 GPa both characterized by the appearance and disappearance of bands related to lattice modes with regard to internal modes. The crystal of L-Leucine oxalate was more stable than your constituent L-Leucine and less stable than oxalic acid. Decompression experiments revealed that the phase transitions observed in the three samples are reversible.2019-01-01T00:00:00ZSpin-phonon coupling in multiferroic compounds obtained by high-pressure/high-temperature synthesis
http://www.repositorio.ufc.br/handle/riufc/40319
Título: Spin-phonon coupling in multiferroic compounds obtained by high-pressure/high-temperature synthesis
Autor(es): Araújo, Bruno Sousa
Abstract: The conventional solid-state reaction and under High-Pressure and High-Temperature methods were applied to synthesis of materials with interesting multiferroic properties. The melanothallite Cu2OCl2 was synthesized through conventional solid-state reaction in air atmosphere. We probed the spin-phonon coupling in Cu2OCl2 by Raman spectroscopy, showing that its incommensurate magnetic structure induces a spin-phonon coupling in accord with the mean field theory and it is similar to those observed in several stretching modes of perovskite compounds. In case of, the orthorhombic TmMnO3 perovskite, the samples were obtained through High-Pressure and High-Temperature treatment of the hexagonal phase of TmMnO3. The temperature-dependent Raman spectrum of orthorhombic TmMnO3 is reported showing the spin-phonon coupling at low temperatures. We also verified that the incommensurate antiferromagnetic ordering induces this spin-phonon coupling in according to the mean field theory and contrasting the assumptions in literature. In addition, we show that the coupling becomes null at the E-type antiferromagnetically ordered phase. The perovskite PbMn7O12 also was synthesized through high-pressure and high-temperatures technique presenting three magnetic transitions at 83, 72 and 38 K. Initial temperature dependent Raman spectrum analysis revealed renormalization effects on phonons frequency below 80 K, probably related to spin-phonon coupling. The pressure dependent behavior of PbMn7O12 perovskite also revealed possible phase transitions at 8.5 and 19.03 GPa. Finally, the High-Pressure and High-Temperature prepared monoclinic BiCrO3 perovskite present interesting properties with three anomalies of magnetic ordering founded around 40, 80 and 110 K. In this study, we report a strong spin-phonon coupling observed by Raman spectroscopy, showing that the G-type antiferromagnetic ordering induces the coupling in accord with the mean field theory similar to those observed in the several stretching modes of other perovskite compounds. In addition to the spin-phonon coupling, it was showed that all coupled phonons are also sensitive to the spin reorientation at 80 K and the magnetic anomaly around 40 K.2019-01-01T00:00:00ZEscoamento viscoso em fraturas auto-afins
http://www.repositorio.ufc.br/handle/riufc/40261
Título: Escoamento viscoso em fraturas auto-afins
Autor(es): Leandro Filho, Francisco de Assis
Abstract: This work aims to study the process of flow of a fluid through uneven surfaces. Initially will address the dynamics of flow through rough surfaces with self-affine geometry. Essentially, the relevant aspects in understanding the flow of irregular structural systems are closely associated with topological and morphological formation of the half. The topology and morphology of the irregular system will be described. It will be appreciated that the geometry of the interfaces that constitute the rough channel feature invariant under transformations statistical properties of anisotropic scale, i.e., can be characterized as self-affine fractal surfaces. The irregular nature of this geometry adds a degree of complexity to the flow problem, reflecting on the properties of velocity and pressure fields. This study aims to investigate the fluid flow in self-affines surfaces through direct numerical simulations of the Navier-Stokes equations. We investigate the influence of the surface roughness to the viscous and non-viscous flow of Newtonian fluids in self-affine joints and fractured surfaces. We denote that the effective permeability of the decays exponentially with the Hurst exponent, used as a quantitative measure of the surface roughness. Nonlinear contributions to the fluid hydraulic resistance become important for sufficiently high Reynolds numbers, due inertial forces contributions, which is typical of experiments. To cubic order, we fi nd that it is possible to nd a universal behavior of the hydraulic resistance of the system, with the onset of the nonlinear corrections to Darcy's law being proportional to the Hurst exponent. This implies that the system can be described macroscopically only by the permeability even for very rough surfaces (H ~ 0.3). We also nd the spontaneous occurrence quasi-one-dimensional channeling in the flow, even with no relative shear displacement between the upper and lower surfaces of the self-a ne fracture joints. This unexpected behavior is quanti ed here using the participation index.2019-01-01T00:00:00ZRelações de incerteza entrópicas de sistemas hamiltonianos dependentes do tempo
http://www.repositorio.ufc.br/handle/riufc/40004
Título: Relações de incerteza entrópicas de sistemas hamiltonianos dependentes do tempo
Autor(es): Lima Júnior, Vanderley Aguiar de
Abstract: In this work by using the Lewis and Riesenfeld invariant method we obtain the exact wave functions for two time-dependent systems: (i) a spinless charged particle in the presence of a time-dependent magnetic field , and (ii) a spinless charged particle in a time-dependent Penning trap. By considering the quantum solutions in the lowest-lying states, we were able to obtain the expressions of Fisher infrmation (Fᵣ and Fp), Shannon entropies (Sᵣ and Sp) and uncertainties in terms of a c-number quantity, ρ (and ρz in the system (ii)), which must be a real solution of the Milne–Pinney equation. In the system (i) we analyze three different configurations of time-varying magnetic fields. We observe that the inequality FᵣFᵣ ≤ 16 holds for the systems considered. We also observed squeezing phenomenon in momentum or/and coordinate spaces with increasing time. In the system (ii) we obtain the analytical expressions for the uncertainties in terms of two c-number functions satisfying a Milne-Pinney-like equation. We analyze the static and the time-dependent cases. For the former, where 𝜝(t) = 𝐵₀𝜥 and 𝚅(t) = 𝚅₀, we observe that the Heisenberg and Robertson-Schrödinger uncertainty relations are fulfilled and the behavior of the uncertainties ∆x, y e ∆pₓ, py and when 𝐵₀ changes indicates the occurrence of a squeezing phenomenon. For the later, where 𝜝(t) = (𝜝₀² + B' cos² ( vt ) )¹′² 𝜥 and 𝚅(t) = 𝚅₀ + 𝚅' cos² (vt), we observe that ∆x,y oscillate in time exhibiting a squeezing phenomenon. Relations among the uncertainties, Shannon entropies and Fisher lengths were stablished. We observe for both cases that the Shannon entropy in position, Sr, and in momentum,Sp, satisfy the relation Sr + Sp ≥ 3 (1 + 𝒍nπ), while the product of Fisher lengths 𝜹𝒓𝜹𝒑 exhibits a lower bound than the product of uncertainties ∆𝒓∆p.2018-01-01T00:00:00Z