Strongly correlated electron systems are at the borderline of competing phases and can be tuned through different ground states by slight modifications. Therefore, they are good examples to study a quantum phase trans...
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Strongly correlated electron systems are at the borderline of competing phases and can be tuned through different ground states by slight modifications. Therefore, they are good examples to study a quantum phase transition (QPT), to reveal how a quantum critical point (QCP) at zero temperature is responsible for the unconventional properties observed at finite temperatures. QPTs are zero-temperature phase transitions, they are more complex and less understood than common phase transitions at finite temperatures. Examples are lacking, especially in the case where disorder is involved. Recent theories predict the possibility of an exotic quantum critical point in itinerant magnets with induced disorder that is accompanied by a quantum Griffiths phase. To explore such unconventional properties in close neighborhood to a magnetic phase, we aim to reveal the relevant quantum critical fluctuations with neutron scattering. We select systems with different magnetic order and choose as tuning parameter chemical substitution to study the effect of disorder. Such experimental study aims to find key elements of a QCP with disorder. The two systems are the ferromagnetic (FM) alloy, Ni-V, tuned by the V-concentration into a paramagnetic phase, and the non-magnetic Kondo semimetal, Ce(Cu,Ni)Sn, tuned by Cu concentration into an antiferromagnetic state. We apply different neutron scattering techniques and simple models to get essential characteristics of the magnetic correlations and fluctuations close to the QCP. Ni-V is a simple FM-alloy with a random atomic distribution that undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state with sufficient substitution of Ni by V. First indication of a quantum Griffiths phase came from magnetization and µSR data, but the scale of the magnetic clusters remained elusive. Optimized small angle neutron scattering (SANS) data on different polycrystalline NiV samples close to the QCP finally show a small magnetic scatte
The electron transfer occurs, for instance, in photosynthetic systems. Among these systems, the bacterial photosynthesis stands for being a cyclical process. The objective of this work is to propose a model of quantum...
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The electron transfer occurs, for instance, in photosynthetic systems. Among these systems, the bacterial photosynthesis stands for being a cyclical process. The objective of this work is to propose a model of quantum wells to study the electrons transfer. The values used to deep of the potential and the size of each well are inspired by the photosynthetic purple bacterium Rhodobacter sphaeroides. From the suggested model it is possible to reproduce and to follow electron transfer in the reaction center of the bacterium. The proposed model consists in four asymmetric potential wells and the suggested method of calculation is to solve the problem two by two using the solution of the asymmetric double well. The eigenvalues of energy is obtained from a transcendental equation. The characteristic time of tunneling from each step of the process is determined from the Rabi formula. In this work, we obtain the analytical solution from independent of time Schrödinger equation for the bistable square symmetric and asymmetric one dimensional potential. For validation of the proposed method the triple square symmetric and asymmetric potentials are resolvedA transferência de elétrons ocorre, por exemplo, em sistemas fotossintéticos. Dentre esses sistemas, a fotossíntese bacteriana destaca-se por ser um processo cíclico. O objetivo deste trabalho é propor um modelo de poços quânticos para estudar a transferência de elétrons em que seus valores de potenciais e o tamanho de cada poço seja inspirado na fotossíntese da bactéria púrpura Rhodobacter sphaeroides, e que através deste modelo seja possível reproduzir e acompanhar a transferência de elétrons no centro de reação. O modelo proposto é formado por quatro poços de potenciais assimétricos e o método de cálculo sugerido é que seja resolvido dois a dois através da solução para o poço duplo assimétrico. Através de uma equação transcendental é possível obter graficamente os autovalores de energia que compõe o modelo. O tempo caracte
The spatial-temporal analysis of transmission is a base resource on approaching of population diseases. The objective of this study is to describe and analyze the spatial-temporal transmission of dengue in the municip...
The spatial-temporal analysis of transmission is a base resource on approaching of population diseases. The objective of this study is to describe and analyze the spatial-temporal transmission of dengue in the municipality of São Sebastião - SP, between 2001 and 2015 aiming to elucidate aspects of dengue transmission. The data of cases of Dengue and variables characteristic of population were obtained from the center of epidemiological vigilance "Prof. Alexandre Vranjac", the notification database (SINAN) of health secretary from São Sebastião, the database of vector Aedes aegypti infestation in information system SISAEDES and SISAWEB and previous projects developed by laboratory of culicid biology and ecology from Superintendência de Controle de Endemias (SUCEN). It was observed the vector positivity in 1998 on central region with a growing expansion to near neighborhoods. The occurrence of dengue cases has shown a possible higher level on female gender. The years with low annual precipitation levels had a possible increasing on number of dengue cases and houses with vector. The years with annual temperature ranging from 20 to 31°C have shown a possible increasing on number of cases and infestation of Aedes aegypti.
This thesis is devoted to a study of time-dependent impurity scattering in a one-dimensional system of interacting electrons—a quantum wire. The scattering potential can be characterized by a complex valued parameter...
This thesis is devoted to a study of time-dependent impurity scattering in a one-dimensional system of interacting electrons—a quantum wire. The scattering potential can be characterized by a complex valued parameter, whose periodic variation in time is shown to lead to a time-independent (DC) current in the wire. Using this method of parametric pumping, an experimentally realizable scattering potential is proposed for generating a DC spin current in a wire. The effect of electron-electron interactions on spin and charge current is analyzed; it is shown that repulsive interactions lead to the transport of integer charge 2ne and spin nħ in a single slow pumping cycle. In Chapters I and II, the notion of parametric pumping is developed by studying the quantum wire with a time-dependent impurity potential. The quantum wire is treated within the Luttinger model which treats interactions between electrons by an effective short-ranged potential. Several calculations are described that derive the dependence of pumped charge and spin on the frequency of pumping. For a special value of interaction strength in the Luttinger model, the time-dependent impurity problem is solved exactly, and shown to give the aforementioned quantized charge transport. Based on these calculations, it is argued that this universal behavior of pumped charge distinguishes a quantum wire from a non-interacting gas of electrons for which the average pumped charge is non-universal. In Chapters III and IV, a general approach that applies to a class of one-dimensional systems whose elementary excitations have a continuous spectrum (Luttinger liquid) is developed. The pumped spin or charge is related to a generalized non-equilibrium spin or charge conductance. It is shown that, because of interactions in the wire, this quantity is independent of the impurity couplings in the limit of slow pumping. As a consequence, the pumped charge or spin per cycle is a universal number. Specifically, for a particular p
The Adverse Childhood Experiences (ACEs) researchers report that childhood adversity is relatively common, often co-occurs with multiple types of exposures, and has a dose-response relationship to many leading causes ...
The Adverse Childhood Experiences (ACEs) researchers report that childhood adversity is relatively common, often co-occurs with multiple types of exposures, and has a dose-response relationship to many leading causes of morbidity and mortality in the U.S. Prolonged exposure to stress during early brain development can lead to inflammation and oxidative stress that disrupts brain functioning associated with depressive symptoms. Flavonoids may protect the brain through anti-inflammatory, antioxidant, and additional mechanisms to assist in the survival, maintenance, and growth of neurons. Thus, flavonoids may buffer depressive symptoms after ACEs exposure. In the current longitudinal study, we will examine the relationship between ACEs, perceived stress, depression, and flavonoid intake while controlling for demographic characteristics (e.g., age, gender, ethnicity, education, difficulty meeting expenses, energy). The study sample consisted of 6404 (67.4% female, 67.9% white, Mage = 61.9, SD = 12.7) participants who completed the Adventist Health Study-2 (AHS-2), and both waves of the Biopsychosocial Religion and Health Study (BRHS). The study aim was to examine whether early chronic stress exposure leads to stress sensitivity and depressive symptoms that can be ameliorated with dietary flavonoids. No studies to date have examined the relationship between dietary flavonoids and mental health after stress risk exposures. Study findings indicate that perceived stress significantly mediated the relationship between ACEs and depressive symptoms; and flavonoids significantly moderated the relationship between perceived stress and depressive symptoms; higher consumption of flavonoids was associated with less depressive symptoms after ACE exposure. More human studies are needed to understand the relationship between flavonoids and mental health and whether diet is sufficient to produce the positive effects found in clinical studies.
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