169 results on '"I. Guedes"'
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2. 20086. DIAGNÓSTICO Y MANEJO DE LA PAPILOPATÍA DIABÉTICA
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I. Guedes Guedes, A. González Hernández, and P. López Méndez
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Neurology. Diseases of the nervous system ,RC346-429 - Published
- 2024
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3. Prospective Study of Prolonged Grief Disorder in Relatives of COVID-19 Deceased
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S. N. Martins, R. Salgado, Â. Nogueira, I. Guedes, N. Carvalho, Â. Ribeiro, B. Ribeiro, and D. Mendes
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Psychiatry ,RC435-571 - Abstract
Introduction COVID-19 pandemic along with its social restrictions changed our burial practices and the way we bury our dead. In consequence, it affected people’s experiences and traditions which could lead to severe, persistent, or disabling grief. Thereby, it is relevant to understand how someone may be more susceptible to developing pathological grief and what can we do to prevent it. Objectives To assess the risk of Prolonged Grief Disorder (PGD) in family members of patients who died from COVID-19 infection and identify possible risk factors. Methods Prospectively, we performed follow-up interviews conducted with family members of all patients who died from COVID-19 infection in 2020 at our hospital. The sample was characterized, and clinical follow-up was performed for at least 6 months after the date of death. By that time, the PG-13 scale was applied. Results A total of 269 individuals who had some type of relationship with patients who died from COVID-19 were included, with 68% being female with a mean age of 53.7 years. After clinical follow-up, 10.8% of the patients met the diagnostic criteria for PGD. Regarding the degree of kinship, the only predictor of PGD was “spouse” (OR 11,236, [4,762; 26,316]; p < 0,001). A closer and more regular interaction with the deceased was also associated with an increase in PDG (OR 5.682, [1.314; 24.390] p = 0.009). Feelings of denial and guilt by the time of death notification were also risk predictors for PGD (OR 2,412, [1,091; 5,332] p = 0,026) and OR 2,888, [1,244; 6,703] p = 0,011, respectively). The impossibility of being present at the funeral was associated with a risk of about 3 times higher of developing PGD (OR 3,817 [1,727; 8,403] p < 0,001). Older age (p
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- 2023
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4. Entropia de emaranhamento de duas partículas carregadas e sem spin em uma armadilha de Penning
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J. P. G. Nascimento, V. Aguiar, and I. Guedes
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Emaranhamento ,Entropia Linear ,Armadilha de Penning ,Physics ,QC1-999 - Abstract
Investigamos o emaranhamento para o estado fundamental de duas partículas sem spin, carregadas e harmonicamente acopladas em uma armadilha de Penning. Encontramos uma expressão analítica para a entropia linear, L, e analisamos o grau de emaranhamento em função da variação da constante de acoplamento e dos parâmetros da armadilha de Penning. Os resultados mostram uma competição entre o acoplamento das partículas e os parâmetros da armadilha. Relacionamos os resultados com a incerteza na posição das partículas.
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- 2021
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5. Dissipative Dynamics and Uncertainty Measures of a Charged Oscillator in the Presence of the Aharonov-Bohm Effect
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J. P. G. Nascimento, V. Aguiar, D. S. Cortez, and I. Guedes
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Aharanov-Bohm effect ,Caldirola-Kanai oscillators ,Lane-Endem oscillators ,uncertainty ,mean energy ,2D parabolic quantum dot ,Physics ,QC1-999 - Abstract
We analyze the effects of dissipation in a charged oscillator in the presence of the Aharonov-Bohm effect by using time-dependent mass (m(t)) Hamiltonians. We consider two different models for the dissipative Hamiltonian and analyze the uncertainties (Δr and Δp) and the quantum mechanical expectation value of energy (⟨E⟩) in terms of time (t), damping parameters and flux parameter (v). For the Caldirola-Kanai model, we observe that the flux parameter v decreases the energy dissipation in a quantum dot for a certain range of t.
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- 2021
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6. Substratos, concentrações de ácido indolbutírico e tipos de miniestacas no enraizamento de melaleuca (Melaleuca alternifolia Cheel) Substrates, indolebutyric acid levels and types of minicuttings on the rooting of tea tree (Melaleuca alternifolia Cheel)
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Y. Oliveira, G.B. Alcantara, I. Guedes, F. Pinto, M. Quoirin, and L.A. Biasi
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Myrtaceae ,auxina ,óleo essencial ,plantas medicinais ,propagação vegetativa ,auxin ,essential oil ,medicinal plants ,vegetative propagation ,Pharmacy and materia medica ,RS1-441 ,Botany ,QK1-989 - Abstract
Melaleuca alternifolia tem como produto principal o óleo essencial extraído das folhas devido às propriedades antifúngicas e antibacterianas. Pouco se tem relatado sobre a propagação desta espécie, sendo a miniestaquia uma alternativa para a propagação vegetativa de clones superiores visando à implantação de campo de produção. Este trabalho teve como objetivo avaliar o efeito de diferentes substratos, concentrações de AIB, e tipo de miniestaca, no enraizamento de Melaleuca alternifolia. No primeiro experimento foram testados os substratos, areia de granulometria média, Plantmax HT®, Golden-Mix® e vermiculita. No segundo experimento foram avaliadas diferentes concentrações de AIB (0, 500, 1000 e 2000 mg L-1), em dois tipos de miniestacas (apical e mediana). As miniestacas foram confeccionadas com 5 cm de comprimento, mantidas em casa de vegetação com nebulização intermitente, e, após 45 dias do plantio, foram avaliadas as porcentagens de miniestacas enraizadas, com calos e não responsivas, o número de raízes formadas por miniestaca e o comprimento das três maiores raízes (cm). O substrato Golden-Mix® e as miniestacas coletadas da porção apical do ramo submetidas ao tratamento com 500 mg L-1 de AIB apresentaram maior porcentagem de enraizamento e melhor qualidade do sistema radicial.Melaleuca alternifolia has as major product the essential oil extracted from its leaves due to its antifungal and antibacterial properties. There are scarce reports about the propagation of this species, and minicutting is an alternative for vegetative propagation of superior clones in order to establish a production field. This study aimed to evaluate the effect of different substrates, IBA levels and types of minicuttings on the rooting of Melaleuca alternifolia. In the first experiment, the following substrates were tested: medium sand, Plantmax HT®, Golden-Mix® and vermiculite. In the second experiment, different IBA levels (0, 500, 1000 and 2000 mg L-1) were tested for two minicutting types (apical and medium). Minicuttings were prepared with 5 cm length and were kept in a greenhouse with intermittent mist; then, at 45 days after planting, we evaluated: the percentages of rooted minicuttings, with callus and non-responsive, the number of roots per minicutting and the length of the three longest roots. The substrate Golden-Mix® and the minicuttings collected from the apical part of the branch and treated with 500 mg L-1 IBA presented the largest rooting percentage and the best root system quality.
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- 2012
7. Osciladores clássicos com massa dependente da posição
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J.P.G. Nascimento and I. Guedes
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oscilador harmônico ,massa dependente da posição ,espaço de fase ,Physics ,QC1-999 - Abstract
Neste trabalho estudamos osciladores clássicos com massa dependente da posição (OMDP). A correspondência entre as soluções do OMDP e do oscilador com massa constante (OMC) é obtida através do método de fatoração do hamiltoniano. Os resultados são ilustrados para o sistema com m(x) = m0(x² + a²), onde analisamos as trajetórias no espaço de fase.
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- 2014
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8. Osciladores harmônicos amortecidos dependentes do tempo
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V. Aguiar and I. Guedes
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osciladores amortecidos ,método de Frobenius ,equação de movimento ,Physics ,QC1-999 - Abstract
Neste trabalho analisamos as soluções para a equação de movimento para os osciladores de Lane-Emden, onde a massa é dada por m(t) = m0 tα , com α > 0. Os osciladores de Lane-Emden são osciladores harmônicos amortecidos, onde o fator de amortecimento depende do tempo, γ(t) = = . Obtivemos as expressões analíticas de x(t), (t) = v(t), e p(t) = m(t) para α = 2 e α = 4. Discutimos as diferenças entre as expressões da hamiltoniana e da energia para sistemas dependentes do tempo. Também, comparamos nossos resultados com aqueles do oscilador de Caldirola-Kanai.
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9. Osciladores quânticos com massa dependente da posição
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J. P. G. Nascimento and I. Guedes
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Fisher information ,Shannon entropy ,position-dependent mass ,point canonical transformation ,Physics ,QC1-999 - Abstract
Neste trabalho investigamos as soluções da equação de Schrödinger de osciladores com massa dependente da posição utilizando o método algébrico de operadores escada e uma transformação canônica de ponto. Os resultados são ilustrados para um sistema onde m(x) ∝ x2. De posse das funções de onda, calculamos a informação de Fisher e a entropia de Shannon para a posição e momentum de uma partícula no estado fundamental deste sistema.
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10. Anaesthetic management of tetraplegic pregnant patients during child delivery: A systematic review
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I. Vieira, P. Cunha, M. Pinto, S. Ribeiro, S. Sacramento, A. Silva, C. Almeida, and I. Guedes
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General Medicine - Published
- 2023
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11. Manejo anestésico de las pacientes embarazadas tetrapléjicas durante el parto: una revisión sistemática
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I. Vieira, P. Cunha, M. Pinto, S. Ribeiro, S. Sacramento, A. Silva, C. Almeida, and I. Guedes
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Anesthesiology and Pain Medicine ,Critical Care and Intensive Care Medicine - Published
- 2023
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12. Milk Fraud: Investigative Experiment for Chemistry Teaching
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I. Guedes, Francisco Jonas Nogueira Maia, Nayane Maria de Amorim Lima, Thayllan Teixeira Bezerra, Selma Elaine Mazzetto, Lucas Renan Rocha da Silva, Mayara Oliveira de Almeida, Viviane Gomes Pereira Ribeiro, Bruno Ventura, Kássia Teixeira da Silva, and Samuel Gondim Sampaio
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General Chemistry - Abstract
Na Educacao Basica, os conteudos de Quimica sao considerados pouco atrativos pelos estudantes, que nem compreendem efetivamente os fenomenos quimicos e nem sao capazes de associa-los ao cotidiano. Nesse aspecto, o presente trabalho tem como objetivo a elaboracao de um experimento, investigativo e contextualizado, como recurso didatico para a aprendizagem de conceitos quimicos envolvendo densidade, catalisadores, numero de oxidacao, funcoes orgânicas e reacoes quimicas na abordagem da tematica de fraudes no leite. A pesquisa foi realizada no Laboratorio de Quimica da Seara da Ciencia da Universidade Federal do Ceara (Fortaleza-CE), envolvendo alunos do Ensino Medio. Observamos que todos os alunos conseguiram identificar as adulteracoes nas amostras de leite recebidas, alcancando resultados muito satisfatorios. Os experimentos, alem de motivar, auxiliaram na compreensao dos conceitos quimicos, relacionando-os com a realidade dos alunos no seu entorno, a partir da visualizacao macroscopica do conhecimento quimico.
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- 2019
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13. Dissipative Dynamics and Uncertainty Measures of a Charged Oscillator in the Presence of the Aharonov-Bohm Effect
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D. S. Cortez, V. Aguiar, J. P. G. Nascimento, and I. Guedes
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Physics ,Range (particle radiation) ,QC1-999 ,mean energy ,General Physics and Astronomy ,Expectation value ,Dissipation ,Education ,symbols.namesake ,Aharanov-Bohm effect ,Quantum dot ,Quantum mechanics ,symbols ,Dissipative system ,Hamiltonian (quantum mechanics) ,Aharonov–Bohm effect ,Caldirola-Kanai oscillators ,uncertainty ,Quantum ,Lane-Endem oscillators ,2D parabolic quantum dot - Abstract
We analyze the effects of dissipation in a charged oscillator in the presence of the Aharonov-Bohm effect by using time-dependent mass (m(t)) Hamiltonians. We consider two different models for the dissipative Hamiltonian and analyze the uncertainties (Δr and Δp) and the quantum mechanical expectation value of energy (⟨E⟩) in terms of time (t), damping parameters and flux parameter (v). For the Caldirola-Kanai model, we observe that the flux parameter v decreases the energy dissipation in a quantum dot for a certain range of t.
- Published
- 2021
14. Entanglement entropy of two spinless charged particles in a Penning trap
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V. Aguiar, J. P. G. Nascimento, and I. Guedes
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Entanglement ,Entropia Linear ,Emaranhamento ,Penning Trap ,Physics ,QC1-999 ,Armadilha de Penning ,General Physics and Astronomy ,Linear Entropy ,Education - Abstract
Investigamos o emaranhamento para o estado fundamental de duas partículas sem spin, carregadas e harmonicamente acopladas em uma armadilha de Penning. Encontramos uma expressão analítica para a entropia linear, L, e analisamos o grau de emaranhamento em função da variação da constante de acoplamento e dos parâmetros da armadilha de Penning. Os resultados mostram uma competição entre o acoplamento das partículas e os parâmetros da armadilha. Relacionamos os resultados com a incerteza na posição das partículas. We investigate the entanglement-related features of the ground state of two spinless charged particles harmonically coupled in a Penning trap. We find an analytical expression for the linear entropy, L, and analyze the entanglement properties of the ground state as the trap parameters and coupling constant changes. The results show a competition between the coupling constant and trap parameters and can also be related to the uncertainty in the position of the particles.
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- 2021
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15. Information measures of a deformed harmonic oscillator in a static electric field
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J.P.G. Nascimento, I. Guedes, F.A.P. Ferreira, Raimundo N. Costa Filho, and V. Aguiar
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Statistics and Probability ,Physics ,Euclidean space ,Condensed Matter Physics ,01 natural sciences ,010305 fluids & plasmas ,Electric field ,Quantum mechanics ,0103 physical sciences ,Entropy (information theory) ,010306 general physics ,Ground state ,Harmonic oscillator ,Morse potential - Abstract
The Shannon entropy and the Fischer information are calculated for an harmonic oscillator in the presence of an applied electric field ( e ) in a space with metrics given by g x x − 1 ∕ 2 = 1 + γ x . For that metric the harmonic oscillator can be mapped into a Morse potential in an Euclidean space. For e = 0 , the ground state energy decreases when γ increases. However, for certain values of e the energy decrease can be canceled out. The dependence of the uncertainties, the entropy, and the information on the parameters γ and e are shown.
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- 2018
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16. RECENT DEVELOPMENTS AND CURRENT TRENDS ON BRAZILIAN PRIVATE INTERNATIONAL LAW CONCERNING INTERNATIONAL CONTRACTS
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Fabiola I. Guedes de C. Saldanha and Nadia de Araujo
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Public law ,Conflict of laws ,Political science ,Law ,Private law ,Commercial law ,Comparative law ,Municipal law ,International law ,Public international law - Abstract
This work aims to present the recent changes and the current trends of Brazilian Private International Law in the area of international contracts with especial focus on the enforcement of Convention on the International Sale of Goods (CISG) in Brazilian legal order. Historically, the recognition of party autonomy in Private International Law has not been uniformily recognized. While since 1996, with the enforcement of the new Arbitration Law, party autonomy has been increasingly accepted in terms of international arbitration, jurisprudence on the choice of law and the choice of court clauses does not show the same progress. In fact, despite of important documents which have already been signed by the government, Brazilian Private International Law of Contracts still dates from 1942. Such contrast with internal material law represents a challenge for the full recognition of Party Autonmy in Brazilian Private International Law.
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- 2018
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17. Theater in Chemistry Teaching: Experience Report
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I. Guedes, Bruno Ventura Ventura de Quieroz, Selma Elaine Mazzetto, Viviane Gomes Pereira Ribeiro, Rebeka Lúcio Neves, and Marcus Raimundo Vale
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General Chemistry - Abstract
O Ensino de Quimica no contexto atual exige que educadores busquem cada vez mais novas ferramentas de ensino. A forma tradicional defronta-se com a resistencia e apatia dos alunos. A fim de modificar essa tendencia, muitas metodologias interessantes vem sendo propostas. Dentre elas, uma que vem ganhando bastante destaque, e o teatro cientifico, que une arte e ciencia no palco. Nesta perspectiva, o presente trabalho tem como objetivo relatar experiencias envolvendo teatro cientifico no Ensino de Quimica, atraves de 6 montagens cenicas, decorrentes de tres anos de pesquisas e divulgacao cientifica teatral em parceria com a Seara da Ciencia da Universidade Federal do Ceara (UFC) e outras Instituicoes de Ensino Superior do pais. As pecas produzidas foram: “ A Liga da Ciencia”, “O Alquimista”, “Somos o que Comemos?”, “Lampiao e Maria Bonita em Busca da Quimica do Amor”, “Os Vingadores Quimicos” e “Doutorado em Quimica do Amor”. Para analisar as contribuicoes pedagogicas advindas dessa experiencia utilizou-se questionarios, debates e comentarios com a plateia. Os resultados apontam que atraves deste meio de divulgacao cientifica foi possivel estimular o aprendizado da Quimica e a motivacao dos alunos.
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- 2018
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18. London superconductivity approach in a time-dependent background
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J. P. G. Nascimento, R. N. Costa Filho, I. Guedes, and V. Aguiar
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Superconductivity ,Physics ,Quantum Physics ,Condensed Matter - Superconductivity ,FOS: Physical sciences ,Energy Engineering and Power Technology ,Condensed Matter Physics ,Nonlinear differential equations ,Electronic, Optical and Magnetic Materials ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Other Condensed Matter ,Quantization (physics) ,Invariant operator ,Statistical physics ,Electrical and Electronic Engineering ,Quantum Physics (quant-ph) ,Quantum ,Other Condensed Matter (cond-mat.other) - Abstract
The main goal of this paper is to obtain the exact quantum solutions for charge space in a superconductor with time-dependent parameters using the London approach. We introduce a new quantization scheme for the charge inside a superconductor based on the Lewis and Riesenfeld invariant operator method. From the wave-functions obtained, we calculated the time-dependent uncertainties and the mean energy of the system. Information measures were also obtained, such as Shannon entropy and complexity. The later is always time-independent and also does not depend on conductivity. The other quantities are written in terms of a time-dependent function, ρ ( t ) , c-number quantity satisfying a nonlinear differential equation.
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- 2021
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19. Exact wave functions and uncertainties for a spinless charged particle in a time-dependent Penning trap
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J.P.G. Nascimento, I. Guedes, and V. Aguiar
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Physics ,Analytical expressions ,010308 nuclear & particles physics ,Invariant (physics) ,Condensed Matter Physics ,Penning trap ,01 natural sciences ,Upper and lower bounds ,Charged particle ,Classical mechanics ,0103 physical sciences ,Physical and Theoretical Chemistry ,010306 general physics ,Wave function ,Instrumentation ,Spectroscopy ,Mathematical physics - Abstract
We use the dynamical invariant method and two unitary transformations to obtain the exact Schrodinger wave functions, ψ n m k ( r , t ) , for a spinless charged particle in a time-dependent Penning trap. For the special case n = m = k = 0 , 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 B ( t ) = B 0 k and V ( t ) = V 0 , we observe that the Heisenberg and Robertson-Schrodinger uncertainty relations are fulfilled and the behavior of the uncertainties Δ x , y and Δ p x , p y when B 0 changes indicates the occurrence of a squeezing phenomenon. For the later, where B ( t ) = ( B 0 2 + B ' c o s 2 ( ν t ) ) 1 / 2 k and V ( t ) = V 0 + V ' C o s 2 ( ν t ) , we observe that Δ 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, S r , and in momentum, S p , satisfy the relation S r + S p ≥ 3 ( 1 + l n π ) , while the Fisher lengths δ r and δ p exhibit a lower bound than the uncertainties Δ r , p .
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- 2016
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20. Spectroscopic properties of highly Nd-doped lead phosphate glass
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M.V.D. Vermelho, A.L.F. Novais, I. Guedes, and Noelio O. Dantas
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Lead phosphate ,Materials science ,Mechanical Engineering ,Doping ,Metals and Alloys ,Analytical chemistry ,Spectral line ,Ion ,Mechanics of Materials ,Covalent bond ,Materials Chemistry ,Radiative transfer ,Spectroscopy ,Luminescence - Abstract
The spectroscopic characteristics of highly Nd3+-doped lead phosphate glasses (xNd:Pb3(PO4)2) have been investigated. The X-ray spectra show that the matrices are glassy up to 25 wt% of Nd3+ doping. From the Judd–Ofelt analysis we observe that while the Ω(2) parameter remains constant indicating that the 4fN and 4fN−15 d1 configurations are not affected by the Nd3+ doping, the behavior of both Ω(4) and Ω(6) changes for 15 wt% of Nd3+ doping. The reduction of the Ω(6) parameter is related to the increase of the covalence bonding between the ligands and the Nd3+ ions. At this particular concentration, the radiative lifetime has a four-fold enhancement. Such behaviors are likely to be related to a modification in the glass structure for high Nd3+ concentrations.
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- 2015
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21. Fisher information and Shannon entropy of position-dependent mass oscillators
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I. Guedes and D.X. Macedo
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Statistics and Probability ,Rényi entropy ,Entropy power inequality ,Shannon's source coding theorem ,Quantum mechanics ,Maximum entropy thermodynamics ,Min entropy ,Entropy in thermodynamics and information theory ,Condensed Matter Physics ,Joint quantum entropy ,Limiting density of discrete points ,Mathematics - Abstract
We calculate the Fisher information and the Shannon entropy for three position-dependent mass oscillators. These systems can be seen as deformed harmonic oscillators in the sense that when the deformation parameter ( λ ) goes to zero, they are identical to the constant mass harmonic oscillator. For two out of the three oscillators we observe that as λ increases the position Fisher information ( F x ) increases while the momentum Fisher information ( F p ) decreases. On the other hand, the Shannon entropy always increases for the three systems with increasing λ . Discussion about squeezing effect in either position or momentum due to the λ variation and a relation between the product of Fisher information and the Shannon entropy are also presented.
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- 2015
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22. Shannon entropy, Fisher information and uncertainty relations for log-periodic oscillators
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V. Aguiar and I. Guedes
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Statistics and Probability ,symbols.namesake ,Mathematical analysis ,symbols ,Entropy (information theory) ,Condensed Matter Physics ,General expression ,Fisher information ,Nonlinear differential equations ,Harmonic oscillator ,Mathematical physics ,Mathematics - Abstract
We calculate the time-dependent Shannon ( S x and S p ) entropy and Fisher ( F x and F p ) information of three log-periodic oscillators. We obtain a general expression for S x , p and F x , p in the state n = 0 in terms of ρ , a c-number quantity satisfying a nonlinear differential equation. For two out of three oscillators S x , p and F x , p depend on time, but S x + S p and F x F p do not. The other oscillator behaves as the time-independent harmonic oscillator where S x , p and F x , p are all constants. Relations among the Fisher information and the Stam and Cramer–Rao inequalities are also discussed.
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- 2015
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23. Magnetic and vibrational properties of Gd2(Mo0.9W0.1O4)3 and Gd1.8Er0.2(MoO4)3
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I. Guedes, L. Bufaiçal, L. Holanda, and G. Barros
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Materials science ,Magnetic moment ,Rietveld refinement ,Analytical chemistry ,Condensed Matter Physics ,Magnetic susceptibility ,Electronic, Optical and Magnetic Materials ,Magnetization ,Paramagnetism ,symbols.namesake ,Nuclear magnetic resonance ,symbols ,Orthorhombic crystal system ,Raman spectroscopy ,Saturation (magnetic) - Abstract
In this work, we report on the analysis of both vibrational and magnetic properties of heavy rare-earth molybdates Gd 2 (Mo 0.9 W 0.1 O 4 ) 3 and Gd 1.8 Er 0.2 (MoO 4 ) 3 . The crystal structures, as determined by X-ray powder diffraction and the Rietveld refinement analysis, established that at room temperature both of these materials belong to orthorhombic Pba 2 space group. Magnetization measurements showed that no saturation is present up to 8 T at T =10 K, and the magnetic susceptibility curves show paramagnetic behavior down to T =10 K. The effective magnetic moments and possible short-range magnetic interactions between Gd 3+ ions are treated and discussed. Raman spectra of both of these molybdates are similar to that of the pure compound Gd 2 (MoO 4 ) 3 , indicating that changes in the Raman spectra due to the introduction of either Er or W doping are negligible at the subject dopant concentrations.
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- 2015
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24. Polarized Raman spectra of LiBaB9O15 single crystal
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Xiaobo Hu, Huaijin Zhang, Xiaoru Pan, I. Guedes, Clenilton Costa dos Santos, Jiyang Wang, Mingjun Song, and Nana Zhang
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Materials science ,Phonon ,Mechanical Engineering ,Primitive cell ,02 engineering and technology ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Crystal ,Crystallography ,symbols.namesake ,Mechanics of Materials ,Irreducible representation ,symbols ,General Materials Science ,Symmetry (geometry) ,0210 nano-technology ,Raman spectroscopy ,Single crystal - Abstract
We use polarized Raman spectroscopy to obtain the room temperature phonon modes of LiBaB 9 O 15 single crystal, that crystallizes in a trigonal structure belonging to the space group R 3 ¯ c ( D 3 d 6 ) with two molecules per primitive cell ( Z B =2). The structure of the LiBaB 9 O 15 crystal consists of a three-dimensional borate framework, formed by two BO 3 triangles and one BO 4 tetrahedra. Since BO 3 and BO 4 units share the oxygen atoms, we can not obtain a correlation scheme where their internal modes are distributed in terms of the irreducible representations of the D 3 d factor group. The only modes that can unambiguously be assigned are the ν 3 (BO 4 ) with A 1 g symmetry at 983 cm − 1 and the ν 1 (BO 3 ) with E g symmetry at 932 cm −1 . We observed 7 A 1 g +6 E g out of 11 A 1 g +25 E g vibrations predicted by the Group Theory.
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- 2016
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25. Monolayer phosphorene under time-dependent magnetic field
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J.P.G. Nascimento, I. Guedes, and V. Aguiar
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FOS: Physical sciences ,02 engineering and technology ,Expectation value ,01 natural sciences ,chemistry.chemical_compound ,0103 physical sciences ,Monolayer ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Electrical and Electronic Engineering ,010306 general physics ,Wave function ,Physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Materials Science (cond-mat.mtrl-sci) ,Landau quantization ,Invariant (physics) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Quantum number ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Phosphorene ,chemistry ,0210 nano-technology - Abstract
We obtain the exact wave function of a monolayer phosphorene under a low- intensity time-dependent magnetic field using the dynamical invariant method. We calculate the quantum-mechanical energy expectation value and the transition probability for a constant and an oscillatory magnetic field. For the former we observe that the Landau level energy varies linearly with the quantum numbers n and m and the magnetic field intensity B_0. No transition takes place. For the latter, we observe that the energy oscillates in time, increasing linearly with the Landau level n and m and nonlinearly with the magnetic field. The (k,l) to (n,m) transitions take place only for l=m. We investigate the (0,0) to (n,0) and (1,l) and (2,l) probability transitions., Comment: 19 pages, 3 figures
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- 2017
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26. Impedance spectroscopy study of SiO2–Li2O:Nd2O3 glasses
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I. Guedes, C.B. Gozzo, Ailton José Terezo, R. Pereira, Marcos Mota do Carmo Costa, and Lynn A. Boatner
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Materials science ,Mechanical Engineering ,Metals and Alloys ,Analytical chemistry ,chemistry.chemical_element ,Activation energy ,Dielectric ,Atmospheric temperature range ,Conductivity ,Dielectric spectroscopy ,chemistry ,Mechanics of Materials ,Electrical resistivity and conductivity ,Materials Chemistry ,Dielectric loss ,Lithium - Abstract
In the present study, neodymium-doped lithium silicate glasses have been prepared by the conventional melt-quenching technique. The dielectric properties, electric modulus, and electrical conductivity of SiO 2 –Li 2 O (SiLi–0Nd) and SiO 2 –Li 2 O:Nd 2 O 3 (SiLi-1.35Nd) have been studied from 1 Hz to 1 MHz in the 333–423 K temperature range. At a given temperature and frequency, we observe that the conductivity decreases when neodymium ions are added to the glass matrix. The activation energy of two distinct regions was evaluated from the ln( σ dc ) = f (1/ T ) plot and was found to be E 1 ( T E 2 ( T > 363 K) = 1.26(1.09) eV for SiLi–0Nd (SiLi–1.35Nd). The dielectric constant ( e Re ) decreases while the dielectric loss (tan ( δ )) increases under Nd 2 O 3 doping. We also observe that for both glasses, e Re and tan ( δ ) tend to increase with increasing temperature and decrease with increasing frequency.
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- 2014
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27. Thermal properties of a DNA denaturation with solvent interaction
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Eudenilson L. Albuquerque, I. Guedes, and D.X. Macedo
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Statistics and Probability ,DNA segment ,Quantitative Biology::Biomolecules ,Materials science ,Hydrogen bond ,Thermodynamics ,Condensed Matter Physics ,Solvent ,Nonlinear system ,chemistry.chemical_compound ,chemistry ,Nonlinear dynamics ,Thermal ,A-DNA ,Morse potential ,Thermodynamics properties ,DNA ,Entropy (order and disorder) - Abstract
In this work we study the effects of the solvent interaction on the nonlinear dynamical structure of a DNA segment, by using a time-independent perturbation approach. Considering a well-known set of values for the spring constant ( k ) and the Morse (solvent) potential parameters D n and a n ( f s and λ s ), we investigate the denaturation temperature profiles of some DNA’s thermodynamical functions, such as the stretching of the hydrogen bonds, the specific heat and the entropy. Besides a sharp thermal profile behavior of these functions, we observe also that the DNA’s melting temperature decreases as the solvent potential increases.
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- 2014
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28. Joint entropy of quantum damped harmonic oscillators
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I. Guedes and V. Aguiar
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Statistics and Probability ,Quantum mechanics ,Unitary transformation ,Condensed Matter Physics ,Wave function ,Joint entropy ,Quantum ,Harmonic oscillator ,Joint quantum entropy ,Quantum relative entropy ,Entropy rate ,Mathematics - Abstract
We use the dynamical invariant method and a unitary transformation to obtain the exact Schrodinger wave function, ψ n ( x , t ) , and calculate for n = 0 the time-dependent joint entropy (Leipnik’s entropy) for two classes of quantum damped harmonic oscillators. We observe that the joint entropy does not vary in time for the Caldirola–Kanai oscillator, while it decreases and tends to a constant value ( ln ( e 2 ) ) for asymptotic times for the Lane–Emden ones. This is due to the fact that for the latter, the damping factor decreases as time increases. The results show that the time dependence of the joint entropy is quite complex and does not obey a general trend of monotonously increase with time.
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- 2014
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29. RECENT DEVELOPMENTS AND CURRENT TRENDS ON BRAZILIAN PRIVATE INTERNATIONAL LAW CONCERNING INTERNATIONAL CONTRACTS
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Araújo, Nádia de, primary and Saldanha, Fabiola I. Guedes de C., additional
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- 2018
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30. In vivo and in vitro effects of RAD001 on bladder cancer
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Aura Colaço, Rita Ferreira, Regina Arantes-Rodrigues, Paulo Brochado, Maria Luís Cardoso, Rosário Pinto-Leite, Carlos Lopes, Paula A. Oliveira, Carmen Vasconcelos-Nóbrega, Lúcio Lara Santos, Luis F. Palomino, Carlos Palmeira, Alexandre Salvador, and Catarina I. Guedes-Teixeira
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Male ,Pathology ,medicine.medical_specialty ,Cell Survival ,Urology ,Immunoblotting ,Proliferation ,Antineoplastic Agents ,Apoptosis ,Resting Phase, Cell Cycle ,Mice ,Cell Line, Tumor ,medicine ,Animals ,Humans ,MTT assay ,Everolimus ,RAD001 ,Protein kinase B ,PI3K/AKT/mTOR pathway ,Cell Proliferation ,Sirolimus ,Mice, Inbred ICR ,TUNEL assay ,Bladder cancer ,Dose-Response Relationship, Drug ,N-butyl-N-(4-hydroxybutyl) nitrosamine ,Cell growth ,business.industry ,TOR Serine-Threonine Kinases ,Cell Cycle ,G1 Phase ,Akt expressivity ,Flow Cytometry ,medicine.disease ,Immunohistochemistry ,Urinary Bladder Neoplasms ,Oncology ,Terminal deoxynucleotidyl transferase ,mTOR ,Cancer research ,Butylhydroxybutylnitrosamine ,Bladder cancer cell lines ,business ,Proto-Oncogene Proteins c-akt - Abstract
Objective: To evaluate the influence of Everolimus (RAD001) on chemically induced urothelial lesions in mice and its influence on in vitro human bladder cancer cell lines. Methods: ICR male mice were given N-butyl-N-(4-hydroxybutyl) nitrosamine in drinking water for a period of 12 weeks. Subsequently, RAD001 was administered via oral gavage, for 6 weeks. At the end of the experiment, all the animals were sacrificed and tumor development was determined by means of histopathologic evaluation; mammalian target of rapamycin (mTOR) expressivity was evaluated by immunohistochemistry. Three human bladder cancer cell lines (T24, HT1376, and 5637) were treated using a range of RAD001 concentrations. MTT assay, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and flow cytometry were used to assess cell proliferation, apoptosis index, and cell cycle analysis, respectively. Immunoblotting analysis of 3 cell line extracts using mTOR and Akt antibodies was performed in order to study the expression of Akt and mTOR proteins and their phosphorylated forms. Results: The incidence of urothelial lesions in animals treated with RAD001 was similar to those animals not treated. RAD001 did not block T24 and HT1376 cell proliferation or induce apoptosis. A reduction in cell proliferation rate and therefore G 0 /G 1 phase arrest, as well as a statistically significant induction of apoptosis (P 0.001), was only observed in the 5637 cell line. Conclusion: RAD001 seems not to have a significant effect on chemically induced murine bladder tumors. The effect of RAD001 on tumor proliferation and apoptosis was achieved only in superficial derived bladder cancer cell line, no effect was observed in invasive cell lines. © 2011 Elsevier Inc. All rights reserved.
- Published
- 2013
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31. Structural and optical properties of 60B2O3–(20−x)Na2O–10PbO–10Al2O3:xTiO2:yNd2O3 glasses
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N.C.A. de Souza, I. Guedes, Noelio O. Dantas, Clenilton Costa dos Santos, and M.V.D. Vermelho
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Nephelauxetic effect ,Materials science ,Infrared ,Coordination number ,Organic Chemistry ,Analytical chemistry ,Infrared spectroscopy ,Mineralogy ,Borate glass ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,symbols.namesake ,Boron oxide ,symbols ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Spectroscopy ,Electronic density - Abstract
In this work we investigate the effect of replacing Na2O by TiO2 on the structural and spectroscopic characteristics of the Nd2O3-doped 60B2O3–(20−x)Na2O–10PbO–10Al2O3:xTiO2:yNd2O3 borate glass matrix. Measurements of X-ray patterns, glass temperatures (Tg), vibrational (Raman and infrared (IR)) and optical (absorption and emission) spectra were carried out. The trend of Tg, the Judd–Ofelt parameters and Nephelauxetic ratio as the TiO2 and Nd2O3 concentration increases was interpreted quantitatively and qualitatively in terms of the network bonds and coordination numbers. Measurements of Tg across the Nd-doped glass series for different levels of Ti suggests changes in the rigidity of the matrix due to change of coordination of boron oxide resulting from the BO4–BO3 back conversion effect. The changes observed in the Raman and IR spectra are related to the BO3 → BO4 conversion effect. The variation of the Judd–Ofelt parameters Ω ( 2 ) and Ω ( 6 ) indicates that the average rare earth-ligand radius decreases establishing an electronic density distribution when Nd3+ concentration increases. This effect is interpreted in terms of Judd–Ofelt parameters and by the bonding parameter b 1 / 2 due to Nephelauxetic effect.
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- 2013
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32. Subtissue Thermal Sensing Based on Neodymium-Doped LaF3 Nanoparticles
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Daniel Jaque, Frank C. J. M. van Veggel, I. Guedes, Enrico Bovero, W. F. Silva, José García Solé, Laura Martínez Maestro, Carlos Jacinto da Silva, Antonio Benayas, Uéslen Rocha, and Mónica Acosta Elias
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Materials science ,Luminescent Measurements ,Infrared ,Doping ,General Engineering ,General Physics and Astronomy ,chemistry.chemical_element ,Nanoparticle ,Nanotechnology ,Neodymium ,chemistry ,Thermal ,General Materials Science ,Nanorod ,Luminescence - Abstract
In this work, we report the multifunctional character of neodymium-doped LaF3 core/shell nanoparticles. Because of the spectral overlap of the neodymium emission bands with the transparency windows of human tissues, these nanoparticles emerge as relevant subtissue optical probes. For neodymium contents optimizing the luminescence brightness of Nd3+:LaF3 nanoparticles, subtissue penetration depths of several millimeters have been demonstrated. At the same time, it has been found that the infrared emission bands of Nd3+:LaF3 nanoparticles show a remarkable thermal sensitivity, so that they can be advantageously used as luminescent nanothermometers for subtissue thermal sensing. This possibility has been demonstrated in this work: Nd3+:LaF3 nanoparticles have been used to provide optical control over subtissue temperature in a single-beam plasmonic-mediated heating experiment. In this experiment, gold nanorods are used as nanoheaters while thermal reading is performed by the Nd3+:LaF3 nanoparticles. The poss...
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- 2013
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33. Entropy and Information of a harmonic oscillator in a time-varying electric field in 2D and 3D noncommutative spaces
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I. Guedes, J.P.G. Nascimento, and V. Aguiar
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Statistics and Probability ,Quantum Physics ,Shannon's source coding theorem ,Mathematical analysis ,FOS: Physical sciences ,Min entropy ,Entropy in thermodynamics and information theory ,Condensed Matter Physics ,01 natural sciences ,Joint entropy ,010305 fluids & plasmas ,Entropy power inequality ,Rényi entropy ,0103 physical sciences ,Entropic uncertainty ,Quantum Physics (quant-ph) ,010306 general physics ,Joint quantum entropy ,Mathematics - Abstract
We analyzed the noncommutativity effects on the Fisher information (F_(r,p)) and Shannon entropies (S_(r,p)) of a harmonic oscillator immersed in a time-varying electric field in two and three dimensions. We find the exact solutions of the respective time-dependent Schr\"odinger equation and use them to calculate the Fisher information and the Shannon entropy for the simplest case corresponding the lowest-lying state of each system. While there is no problem in defining the Shannon entropy for noncommutating spaces, the definition of the Fisher information had to be modified to satisfy the Cramer-Rao inequalities. We observe for both systems, how the Fisher information and Shannon entropy in position and momentum change due to the noncommutativity of the space. We verified that the Bialynicki-Birula-Mycielski (BBM) entropic uncertainty relation still holds in the systems considered., Comment: 23 pages, 2 figures
- Published
- 2016
34. Phase transitions investigation by Raman spectroscopy in highly diluted KTN crystals
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R.S. Wei, Huaning Zhang, Clenilton Costa dos Santos, I. Guedes, Jilai Wang, Na Zhang, and Xiaobo Hu
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Phase transition ,symbols.namesake ,Crystallography ,Materials science ,Mechanics of Materials ,Phonon ,Mechanical Engineering ,Materials Chemistry ,Metals and Alloys ,symbols ,Raman spectroscopy ,Raman scattering ,Tantalate - Abstract
Single crystals of potassium tantalate niobate, KTa 1− x Nb x O 3 (KTN x , x = 0.45, 0.50, and 0.55), were synthesized by the top-seeded solution growth method. The Raman scattering technique is used to investigate the sequence of phase transitions undergone by KTN x crystals. We discuss what features in the phonon spectrum are associated to each phase transition.
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- 2012
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35. Phonon spectra of CBN crystals
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Xiaobo Hu, I. Guedes, Clenilton Costa dos Santos, Alejandro Ayala, Nana Zhang, Huaijin Zhang, Jiyang Wang, and Wenlan Gao
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Phase transition ,Materials science ,Condensed matter physics ,Phonon ,Dielectric ,Atmospheric temperature range ,Ferroelectricity ,Condensed Matter::Materials Science ,Tetragonal crystal system ,symbols.namesake ,Crystallography ,symbols ,Raman spectroscopy ,Spectroscopy ,Raman scattering - Abstract
The room temperature phonon modes of both the alkali metal doped and pure CBN (CaxBa1−xNb2O6) crystals were determined using the Raman scattering technique. Owing to the intrinsic disorder of the tetragonal lattice we observe few and broad bands. The wavenumber of the internal modes observed shifts upwards when the volume of the unit cell increases. This blue shift is likely to be related to the closer packing of the NbO6 octahedrons. The Curie temperatures of the ferroelectric to paraelectric phase transition for the CBN-like crystals were obtained from DSC measurements. The Raman spectra of CBN32 in the temperature range from 300 to 568 K were also recorded in order to investigate the phase transformation.
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- 2012
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36. The role of TiO2 in the B2O3–Na2O–PbO–Al2O3 glass system
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Noelio O. Dantas, Clenilton Costa dos Santos, M. T. de Araujo, Carlos Jacinto, M.V.D. Vermelho, N.C.A. de Sousa, and I. Guedes
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Materials science ,Absorption spectroscopy ,Inorganic chemistry ,Analytical chemistry ,Order (ring theory) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Amorphous solid ,Inorganic Chemistry ,symbols.namesake ,Content (measure theory) ,Materials Chemistry ,Ceramics and Composites ,symbols ,Absorption (logic) ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Intensity (heat transfer) ,Energy (signal processing) - Abstract
Optical and vibrational studies have been carried out on 60B{sub 2}O{sub 3}.(20-x)Na{sub 2}O.10PbO.10Al{sub 2}O{sub 3}:xTiO{sub 2} (x=0, 1, 2, 3, 4, and 5 mol%) glasses, in order to understand the role of TiO{sub 2} in the 60B{sub 2}O{sub 3}.20Na{sub 2}O.10PbO.10Al{sub 2}O{sub 3} glass matrix. The X-ray patterns reveal homogeneous glasses over the entire compositional range. The absorption spectra show that the energy of the optical band gap ({Delta}E{sub opt}) and Urbach's energy (E{sub U}) decreases as TiO{sub 2} content increases. The changes observed in the Raman and IR spectra are related to the BO{sub 4}{yields}BO{sub 3} back conversion effect and the appearance of 'loose' BO{sub 4}{sup -} groups. The data indicate that titanium ions act as a network modifier. - Graphical abstract: Behavior of the relative integrated intensity of the IR bands, Ar=A{sub 4}/A{sub 3}, as TiO{sub 2} content increases. A decrease of 45% of Ar indicates that the number of BO{sub 4} groups is decreasing due to the BO{sub 4}{yields}BO{sub 3} back conversion. Highlights: > The XRD data show the amorphous character of all measured glasses. > The optical absorption results evidenced possible change of the glass structure. > The Raman data have revealed some vibrational modifications. > Themore » overall results indicate that titanium acts as a network modifier.« less
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- 2011
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37. Phonons in isostructural (ND,Yb):Y Gd1−(VO4) laser crystals: A Raman scattering study
- Author
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Alejandro Ayala, I. Guedes, Clenilton Costa dos Santos, Jiyang Wang, Huaijin Zhang, Xiaobo Hu, and Nana Zhang
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Phonon ,Doping ,Analytical chemistry ,Mineralogy ,Atmospheric temperature range ,Condensed Matter Physics ,Spectral line ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,symbols.namesake ,Tetragonal crystal system ,Materials Chemistry ,Ceramics and Composites ,symbols ,Physical and Theoretical Chemistry ,Isostructural ,Raman spectroscopy ,Raman scattering - Abstract
The room temperature phonon modes of the isostructural (Nd,Yb):Y{sub x}Gd{sub 1-x}(VO{sub 4}) laser crystals were determined using the Raman scattering technique, and the observed wavenumbers follow the overall mode distribution expected for REVO{sub 4} (RE=rare earth) compounds with the tetragonal zircon structure, D{sub 4h}{sup 19}. They were assigned according to the group theory in terms of the internal modes of the VO{sub 4} tetrahedron and the external modes of the Y{sub x}Gd{sub 1-x}(VO{sub 4}) lattice. No appreciable changes in the phonon wavenumbers were observed for Yb:GdVO{sub 4} (Yb=0.008, 0.015, 0.020, 0.025, and 0.035), indicating that the force fields in the GdVO{sub 4} lattice are not strongly altered by Yb doping at the Gd site. However, most of the phonon wavenumbers in the systems (Nd,Yb):Y{sub x}Gd{sub 1-x}(VO{sub 4}) shifts upwards (one-phonon-like behavior) when Y replaces for Gd. -- Graphical abstract: Plot of the observed wavenumbers of Nd:Y{sub x}Gd{sub 1-x}(VO{sub 4}) versus Y content (x). The linear trend indicates that most of the observed wavenumbers exhibit a one-phonon-like behavior. Display Omitted Research highlights: > Force fields in the GdVO{sub 4} lattice are not strongly altered by Yb doping at the Gd site when the doping content of Yb is below 3.5 at%.more » > Most of the phonon wavenumbers in the systems (Nd,Yb):Y{sub x}Gd{sub 1-x}(VO{sub 4}) shifts upwards with x increasing. > The upward shifting is related to the decrease of the RE-O distance due to the lattice contraction. > Most of the observed wavenumbers exhibits a one-phonon-like behavior.« less
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- 2011
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38. Phase transitions in Pb8O5(XO4)2(X = As and V) compounds
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J. Mendes-Filho, Alejandro Ayala, E. N. Silva, S. M. Dantas, E. A. Oliveira, I. Guedes, Alexandre Rocha Paschoal, and Griselda Polla
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Phase transition ,symbols.namesake ,Structural phase ,Polarized light microscopy ,Chemistry ,symbols ,Analytical chemistry ,General Materials Science ,Raman spectroscopy ,Spectroscopy ,Lead oxide - Abstract
Raman spectroscopy, polarized microscopy and thermal measurements were used to investigate the sequence of phase transition in the lead oxide salts Pb8O5(XO4)2 (where X = As and V). For Pb8O5(AsO4)2, a second-order phase transition is observed at 500 K. For Pb8O5(VO4)2, a second-order and a first-order structural phase transitions are observed at 425 and 525 K, respectively. The ferroelastic character of Pb8O5(VO4)2 is also discussed. Copyright © 2011 John Wiley & Sons, Ltd.
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- 2011
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39. Third-order nonlinearity of Er3+-doped lead phosphate glass
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Sérgio Carlos Zílio, Clenilton Costa dos Santos, Lino Misoguti, Lynn A. Boatner, I. Guedes, and J. P. Siqueira
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Materials science ,Fabrication ,Physics and Astronomy (miscellaneous) ,business.industry ,Doping ,General Engineering ,Analytical chemistry ,Physics::Optics ,General Physics and Astronomy ,Wavelength ,Optics ,Femtosecond ,LASER ,Photonics ,Dispersion (chemistry) ,business ,Crown glass (optics) ,Refractive index - Abstract
The third-order optical susceptibility and dispersion of the linear refractive index of Er3+-doped lead phosphate glass were measured in the wavelength range between 400 and 1940 nm by using the spectrally resolved femtosecond Maker fringes technique. The nonlinear refractive index obtained from the third-order susceptibility was found to be five times higher than that of silica, indicating that Er3+-doped lead phosphate glass is a potential candidate to be used as the base component for the fabrication of photonic devices. For comparison purposes, the Z-scan technique was also employed to obtain the values of the nonlinear refractive index of Er3+-doped lead phosphate glass at several wavelengths, and the values obtained using the two techniques agree to within 15%.
- Published
- 2010
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40. Raman investigations of rare-earth arsenate single crystals
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Lynn A. Boatner, Chun-Keung Loong, Alejandro Ayala, I. Guedes, Clenilton Costa dos Santos, and G. Barros
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Phonon ,Rare-earth element ,Chemistry ,Inorganic chemistry ,Analytical chemistry ,Arsenate ,symbols.namesake ,Tetragonal crystal system ,chemistry.chemical_compound ,Lattice (order) ,symbols ,Wavenumber ,General Materials Science ,Atomic number ,Raman spectroscopy ,Spectroscopy - Abstract
Polarized Raman Spectroscopy was used to investigate the room-temperature phonon characteristics of a series of rare-earth arsenate (REAsO4, RE = Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu) single crystals. The Raman data were interpreted in a systematic manner based on the known tetragonal zircon structure of these compounds, and assignments and correlations were made for the observed bands. We found that the wavenumber of the internal modes of the AsO4 tetrahedron increased with increasing atomic number, and for three out of four lattice wavenumbers observed, this tendency was not nearly so marked as in the case of the internal mode wavenumber.
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- 2009
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41. Vibrational modes of rare-earth formates
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I. Guedes, D. Tobia, E. N. Silva, Griselda Polla, M. E. Saleta, Daniel Vega, M. R. Moura, and Alejandro Ayala
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Chemistry ,Stereochemistry ,Phonon ,Rare earth ,Lattice expansion ,symbols.namesake ,Molecular vibration ,symbols ,Wavenumber ,General Materials Science ,Atomic physics ,Raman spectroscopy ,Spectroscopy ,Raman scattering - Abstract
In this work we investigate the room-temperature Raman spectra of several rare-earth [RE(HCOO)3; RE = La, Pr, Nd, Gd, Tb and Y] formates. Polarized measurements were carried out for La(HCOO)3 yielding the observation of most of the Raman-active phonons predicted by group theory analysis. The respective assignment is given based on the formate vibrations and correlations with previous results in other RE(HCOO)3 systems. The wavenumber ‘softening’ observed when RE goes from Y to La is accounted for the lattice expansion. Copyright © 2009 John Wiley & Sons, Ltd.
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- 2009
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42. Vibrational study of A3In2B″O9(A = Ba, Sr; B″ = U, W) double perovskites
- Author
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M. del C. Viola, R.M. Pinacca, I. Guedes, E. N. Silva, José C. Pedregosa, Alejandro Ayala, and Sebastián A. Larrégola
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Diffraction ,Phonon ,Chemistry ,Infrared ,Octahedral symmetry ,symbols.namesake ,Crystallography ,Octahedron ,Formula unit ,symbols ,General Materials Science ,Raman spectroscopy ,Spectroscopy ,Raman scattering - Abstract
Raman scattering and infrared transmittance techniques were used to investigate the room-temperature phonon spectra of the polycrystalline Ba3In2UO9, Sr3In2UO9, Ba3In2WO9 and Sr3In2WO9 double perovskites. Although X-ray diffraction has shown that both Ba3In2UO9 and Ba3In2WO9 crystallize in a disordered cubic (Pm3m − Oh1) structure with one formula unit per unit cell (Z = 1), Raman measurements revealed that both Ba3In2UO9 and Ba3In2WO9 compounds should exhibit a 1:1 ordered domains with Fm3m symmetry, embedded in the Pm3m matrix. Observation of a ν1-like vibration of the InO6 octahedron reflects the occurrence of a two-phonon-like behavior due to the intrinsic occupational disorder at octahedral symmetry sites. Assignment of most of the Raman and infrared phonons is also given. Copyright © 2009 John Wiley & Sons, Ltd.
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- 2009
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43. Raman spectroscopic characterization of RECa4O(BO3)3 (RE=La and Gd) crystals
- Author
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Alejandro Ayala, G. Barros, Jun Wang, H. J. Zhang, Xiaobo Hu, I. Guedes, C.-K. Loong, and E. N. Silva
- Subjects
Phonon ,chemistry.chemical_element ,Frequency difference ,Characterization (materials science) ,Ion ,symbols.namesake ,Crystallography ,chemistry ,symbols ,Boron ,Raman spectroscopy ,Spectroscopy ,Raman scattering ,Monoclinic crystal system - Abstract
The phonon modes of the rare-earth calcium oxyborates [RECa 4 O(BO 3 ) 3 , RE = La and Gd] were determined at room-temperature using Raman scattering technique. The observed frequencies were assigned on the basis of the borate (BO 3 ) vibrations and correlations with previous data reported for other similar compounds. The influence of the RE ion substitution on the phonon distribution is discussed. Two main features were observed when La 3+ replaces for Gd 3+ : the frequency of most of the phonons shifts downwards and the frequency difference between the components of the ν 1 (BO 3 ) doublet decreases. All these features result from the monoclinic lattice expansion.
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- 2008
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44. Low-temperature Raman spectra of YbVO4
- Author
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Lynn A. Boatner, Clenilton Costa dos Santos, I. Guedes, and C.-K. Loong
- Subjects
Structural phase ,Range (particle radiation) ,Materials science ,Condensed matter physics ,Phonon ,Atmospheric temperature range ,Coupling (probability) ,Molecular physics ,symbols.namesake ,symbols ,Coherent anti-Stokes Raman spectroscopy ,Raman spectroscopy ,Spectroscopy ,Energy (signal processing) - Abstract
This paper reports on the spectroscopic study of YbVO{sub 4} in the range 10-300 K. All the Raman phonons were properly assigned. Temperature-dependent Raman spectra showed no anomalous changes, which indicate that neither structural phase transition nor strong electron-phonon coupling occur, at least within this temperature range. This result is sharp contrast to those of YbPO{sub 4} where strong mixing of the upper crystal-field states {Gamma}{sub 6} and {Gamma}{sub 7} with an E{sub g}{sup 3} phonon at room-temperature occurs. A possible explanation for the absence of electron-phonon coupling in YbVO{sub 4} is the occurrence of the {Gamma}{sub 6} state at energy higher than the E{sub g}{sup 3} phonon, unlike the coincidence of {Gamma}{sub 6} and E{sub g}{sup 3} energies in YbPO{sub 4}.
- Published
- 2007
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45. Reverse saturable absorption in 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphyrin with ruthenium outlying complexes
- Author
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Luis R. Dinelli, I. Guedes, Sérgio Carlos Zílio, Lino Misoguti, Samuel L. Oliveira, Alzir A. Batista, Cleber Renato Mendonça, and Newton M. Barbosa Neto
- Subjects
Absorbance ,chemistry.chemical_compound ,Jablonski diagram ,chemistry ,Pyridine ,chemistry.chemical_element ,Free base ,General Chemistry ,Zinc ,Photochemistry ,Fluorescence ,Porphyrin ,Ruthenium - Abstract
Investigations on the excited state absorption signal of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin, modified by either changing the central ion or adding peripheral groups, were performed using 5 ns laser pulses at 532 nm, in association with linear absorbance and fluorescence decay time measurements. The reverse saturable absorption (RSA) increases remarkably when Zn2+ replaces H+ at the central position of the porphyrin ring. However, it decreases when RuCl2(CO)(PPh3)2 and RuCl2(CO)(dppb) groups are attached at outlying positions through the pyridine rings, for both the free base and zinc porphyrins. A theoretical model based on Jablonski diagram was used to verify the main reason for the decrease on the RSA signal caused by ruthenium groups.
- Published
- 2006
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46. Vibrational spectra of monazite-type rare-earth orthophosphates
- Author
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Chun-Keung Loong, Roberto L. Moreira, Carlos William de Araujo Paschoal, E. N. Silva, Alejandro Ayala, Lynn A. Boatner, and I. Guedes
- Subjects
Lanthanide ,Infrared ,Chemistry ,Organic Chemistry ,Analytical chemistry ,Infrared spectroscopy ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Neutron spectroscopy ,Inorganic Chemistry ,symbols.namesake ,Monazite ,symbols ,Density of states ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Spectroscopy ,Raman scattering - Abstract
The room-temperature vibrational spectra of the monazite-type rare-earth orthophosphates (RPO4, R = La, Ce, Pr, Nd, Sm, Eu and Gd) have been investigated using polarized Raman and infrared spectroscopies. As in the case of the previously reported Raman results, we also observe 22 peaks, while only 18 Ag/Bg vibrations are predicted by group theoretical analysis. Through a careful review of the combined Raman–IR modes, in conjunction with the measured generalized phonon density of states of LaPO4 by neutron spectroscopy and a comparison with the corresponding data for the xenotime RPO4 members, we have obtained a self-consistent assignment of the Raman and IR modes. We also discuss on the possible origins of the previously unidentified “extra” peaks.
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- 2006
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47. The Orthorhombic to Tetragonal Phase Transition in Bi2−xTexSrNb2−xHfxO9
- Author
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A. López-García, R. E. Alonso, Alejandro Ayala, E. N. Silva, Alexandre Rocha Paschoal, I. Guedes, and Alicia Castro
- Subjects
Phase transition ,Materials science ,Condensed matter physics ,biology ,Condensed Matter Physics ,biology.organism_classification ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Aurivillius ,Tetragonal crystal system ,symbols.namesake ,Ferroelectric RAM ,symbols ,Orthorhombic crystal system ,Raman spectroscopy ,Raman scattering - Abstract
The necessity of producing materials with better performances than those observed in ferroelectric perovskites has induced the investigation of new oxides, especially those belonging to the Aurivillius family which exhibit better performance than PZT in non-volatile ferroelectric memories (FeRAM). In this contribution a Raman analysis of Bi2-xTexSrNb2-xHfxO9 (x = 0.10) is carried out to investigate the vibrational spectra and the ferro-paraelectric phase transition of these compounds.
- Published
- 2006
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48. Hyperfine characterization of Bi1.9Te0.1SrNb1.9Hf0.1O9
- Author
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A. López-García, I. Guedes, E. N. Silva, Alejandro Ayala, J.A. Martínez, Alexandre Rocha Paschoal, R. E. Alonso, and Alicia Castro
- Subjects
biology ,Condensed matter physics ,Chemistry ,Transition temperature ,General Chemistry ,Condensed Matter Physics ,biology.organism_classification ,Crystallographic defect ,Aurivillius ,Materials Chemistry ,Precession ,Spin (physics) ,Spectroscopy ,Hyperfine structure ,Solid solution - Abstract
The Aurivillius type oxide Bi1.9Te0.1SrNb1.9Hf0.1O9 has been studied by Perturbed Angular Correlations spectroscopy using 181Ta probes. The spin precession curves were measured from room temperature up to 873 K. Two sites are occupied by probes and the temperature dependence of both indicates a continuous phase transition at about 625 K. One site is ordered while the other is disordered. This situation is analyzed in terms of simple models already applied to perovskites. The transition temperature of the solid solution Bi2−xTexSrNb2−xHfxO9 (with 0 ≤ x ≤ 0.5 ) shows a strong dependence on composition.
- Published
- 2006
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- View/download PDF
49. Frequency doubling of phase-modulated chirped ultrashort laser pulses using a deformable mirror
- Author
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Lino Misoguti, I. Guedes, Cleber Renato Mendonça, and Sérgio Carlos Zílio
- Subjects
Physics ,business.industry ,Physics::Optics ,Second-harmonic generation ,Condensed Matter Physics ,Laser ,Industrial and Manufacturing Engineering ,Atomic and Molecular Physics, and Optics ,Deformable mirror ,law.invention ,Condensed Matter::Materials Science ,Optics ,Multiphoton intrapulse interference phase scan ,law ,Chirp ,Physics::Atomic Physics ,business ,Adaptive optics ,Instrumentation ,Phase modulation ,Ultrashort pulse - Abstract
We explore the use of a computer-controlled micro-machined deformable mirror to tailor the spectral phase of an ultrashort laser pulse to control the second-harmonic generation in KDP crystals. The SHG dependence of chirp and phase mask could be observed and adjusted by a simple theory.
- Published
- 2006
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50. Study of the Aurivillius phases Bi4Srn−3TinO3n+3 (n=4, 5) synthesized by mechanochemical activation
- Author
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I. Guedes, Alejandro Ayala, Pilar Ferrer, Alicia Castro, and Juan E. Iglesias
- Subjects
Diffraction ,Materials science ,biology ,Scanning electron microscope ,Analytical chemistry ,Mineralogy ,General Chemistry ,Condensed Matter Physics ,biology.organism_classification ,Aurivillius ,Crystallinity ,symbols.namesake ,Materials Chemistry ,symbols ,Particle size ,Thermal analysis ,Raman spectroscopy ,Stoichiometry - Abstract
The mechanochemical activation method allows one to obtain the Aurivillius phases Bi 4 SrTi 4 O 15 and Bi 4 Sr 2 Ti 5 O 18 with a significant decrease in the temperature of synthesis and reaction time, as compared to the solid-state method, by supplying mechanical energy to the initial reagents. The method leads to homogeneous, activated precursors, whose particle size is reduced to around 250 nm. Further thermal annealing makes crystallinity and particle size to increase. The products are characterized by Raman spectroscopy, X-ray diffraction, thermal analysis and scanning electron microscopy.
- Published
- 2005
- Full Text
- View/download PDF
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