Eigenstate versus Zeeman-based approaches to the solid-effect

The solid effect is one of the simplest and most effective mechanisms for Dynamic Nuclear Polarization. It involves the exchange of polarization between one electron and one nuclear spin coupled via the hyperfine interaction. Even for such a small spin system, the theoretical understanding is complicated by the contact with the lattice and the microwave irradiation. Both being weak, they can be treated within perturbation theory. In this work, we analyze the two most popular perturbation schemes: the Zeeman and the eigenstate-based approaches which differ in the way the hyperfine interaction is treated. For both schemes, we derive from first principles an effective Liouville equation which describes the density matrix of the spin system; we then study numerically the behavior of the nuclear polarization for several values of the hyperfine coupling. In general, we obtain that the Zeeman-based approach underestimates the value of the nuclear polarization. By performing a projection onto the diagonal part of the spin-system density matrix, we are able to understand the origin of the discrepancy, which is due to the presence of parasite leakage transitions appearing whenever the Zeeman basis is employed.Comment: 9 pages, 4 figures, 7 pages of supplementary materia

Grit attitudes demonstrated by school superintendents in California urban school settings

This study’s purpose is to explore grit attributes California urban school superintendents demonstrated. The literature review revealed 5 grit attributes: courage, conscientiousness, endurance toward long-term goals, optimism and resilience, and excellence over perfection. There is scant scholarly research connecting urban school superintendents to the 5 grit attributes and understanding grit’s 5 attributes school district leaders reflected is valuable to the industry and the profession. This research implemented a qualitative methodology. Following an extensive review of the literature, a panel of experts developed and reviewed research questions to establish validity. The data collected were gathered from publicly available and accessible published texts regarding superintendents from 7 California urban school districts. Corresponding text from the data sources were reviewed and compared with the grit attributes in the theoretical framework in order to code for themes. The themes were reviewed for alignment to the 5 attributes of grit theory that formed this study’s conceptual framework. Limitations included that there was no interaction with superintendents in this study as only publicly available information served as data, and urban school districts in only 1 state were represented in this study. Findings based on publicly accessed information revealed 15 practices of demonstrating grit in 5 categories: 2 practices demonstrating the attribute of courage; 3 practices demonstrating the attribute of conscientiousness; 5 practices demonstrating the attribute of endurance toward long-term goals; 3 practices demonstrating the attribute of optimism and resilience; and 2 practices demonstrating the attribute of excellence over perfection. In addition to correlating practices with the 5 attributes of grit theory, more than 70 authors supported the 4 theoretical components. The results of the study provide information that can assist leaders, persons providing professional development, and policymakers in education. The data in this study support the relationship of the grit attributes as school superintendents in California urban settings demonstrated. This research adds to the literature regarding the disciplines of educational leadership, organizational leadership, and positive psychology in organizations, including topics related to persistence and resiliency studies. Additionally, the results of this study add to the existing body of literature specifically related to grit theories

Thermalization and many-body localization in systems under dynamic nuclear polarization

We study the role of dipolar interactions in the standard protocol used to achieve dynamic nuclear polarization (DNP). In the so-called spin-temperature regime, where the interactions establish an effective thermodynamic behavior in the out-of-equilibrium stationary state, we provide numerical predictions for the level of hyperpolarization. We show that nuclear spins equilibrate to the effective spin-temperature established among the electron spins of radicals, as expected from the quantum theory of thermalization. Moreover, we present an analytical technique to estimate the spin temperature, and thus, the nuclear hyperpolarization in the steady state, as a function of interaction strength and quenched disorder. This reproduces both our numerical data and experimental results. Our central finding is that the nuclear hyperpolarization increases steadily upon reducing the interaction strength (by diluting the radical density). Interestingly, the highest polarization is reached at a point where the establishment of a spin temperature is just about to break down due to the incipient many-body localization transition in the electron spin system.Comment: 12 pages (+ 3 pages of appendix), 8 figure

Unravelling environmental and economic criteria for resource recovery in centralised and decentralised wastewater treatment

In the context of a world population that is growing every year, environmental problems such as global warming and water scarcity are becoming increasingly critical. For this reason, it is crucial to seek new alternatives in reducing energy demand, waste disposal as well as ensuring water quality. In this last aspect, wastewater treatment plants (WWTPs) play an important role. The main goal of this doctoral thesis was to analyse and compare different wastewater treatment configurations from an environmental and economic point of view to provide insights on the sustainability of existing and innovative schemes of wastewater treatment

Estudio de necesidades más relevantes de la región para ofrecer pasantías y consultorías en el sector de la confección

En el presente proyecto se desarrolló un estudio sobre las necesidades más relevantes de la región metropolitana del departamento de Risaralda para ofrecer pasantías y consultorías en el sector de la confección por parte de la Universidad Tecnológica de Pereira. Durante el desarrollo de la investigación se tomó una muestra de las empresas dedicadas a la confección en la región y se les realizó una encuesta para ver la situación actual, posteriormente realizamos todos los estudios estadísticos pertinentes para llegar a unas conclusiones y así realizar una propuesta que le permita a la universidad Tecnológica de Pereira mejorar el servicio de pasantías y consultorías. El trabajo de grado se realizó por medio de tres fases las cuales se desarrollaron de la siguiente manera: Fase 1 Se recopiló toda la información primaria y secundaria por medio de búsquedas bibliográficas como trabajos de grado, libros, revistas, folletos, artículos, bases de datos, etc., relacionados con el tema para obtener toda la información y documentación necesaria para el desarrollo del trabajo de grado; se realizó un análisis a toda la información recolectada para la toma de decisiones y así dar un aprovechamiento óptimo de la información para continuar con la segunda fase del proyecto. Fase 2 La fases 2 se realizó a través de un muestreo estadístico estratificado y trabajo de campo en donde se recogió información de primera mano por medio de la aplicación de encuestas a las empresas de confección registradas en las cámaras de comercio de Pereira y Dosquebradas. Para realizar el estudio requerido y así cumplir con los objetivos de la investigación, se aplicó la técnica de muestreo estratificado, con un margen de confiabilidad del 95 % y una cota de error de 5 puntos, con lo cual, se obtuvo una muestra poblacional de 141 empresas. Fase 3 En la fase 3 se realizó el análisis a los datos obtenidos, creando así una propuesta para que la Universidad Tecnológica mejore su servicio de pasantías y consultorías al área de la confección en el sector textil del área metropolitana del departamento de Risaralda

El teletrabajo, como modalidad formal de trabajo, mejora la productividad laboral y calidad de vida para los trabajadores en Colombia

Cuando se piensa en la palabra trabajo, vienen a la mente definiciones como: horario, superiores, jefes, puesto de trabajo, órdenes, cumplimiento, etc. Pero en la última década se ha venido escuchando en los ámbitos empresariales, organizacionales y corporativos el término del teletrabajo. Dado lo anterior y a la importancia que como empleado o colaborador se le da al bienestar, calidad de vida y a la familia; la pregunta que guía esta investigación es ¿el teletrabajo, como modalidad de trabajo formal, mejora la productividad y calidad de vida de los trabajadores en Colombia?Cuando se piensa en la palabra trabajo, vienen a la mente definiciones como: horario, superiores, jefes, puesto de trabajo, órdenes, cumplimiento, etc. Pero en la última década se ha venido escuchando en los ámbitos empresariales, organizacionales y corporativos el término del teletrabajo. Dado lo anterior y a la importancia que como empleado o colaborador se le da al bienestar, calidad de vida y a la familia; la pregunta que guía esta investigación es ¿el teletrabajo, como modalidad de trabajo formal, mejora la productividad y calidad de vida de los trabajadores en Colombia

Matrix-variate, vector-variate and univariate risk measures and related aspects

Généralement, les mesures de risque sont considérées comme des mappings d'un ensemble de variables aléatoires réelles vers des nombres réels. Cependant, il est souvent insuffisant de considérer une seule mesure réelle pour quantifier les risques découlant des activités financières. Au cours de la dernière décennie, de nombreuses extensions de la Valeur à risque multivariée ont été étudiées et certains articles proposent des méthodes alternatives de mesure du risque pour les portefeuilles multivariés. Toutefois, comme le mentionne Li et al. [2012], certaines des traductions univariées sont devenues irréalistes et reposent sur des hypothèses inappropriées qui, dans le contexte des mesures de risque, sont difficiles à élucider. Les mesures de risque les plus utilisées en économie, en assurance et en finance sont probablement la valeur à risque (VaR) et la valeur à risque conditionnelle (CVaR). L'objectif de cette thèse est de proposer de nouvelles méthodologies pour quantifier la VaR et la CVaR à partir d'une approche vecteur-variable et matrice-variable. Dans le premier chapitre de la thèse, une nouvelle approche pour modéliser les mesures de risque vecteur-variable sous le barycentre de Wasserstein des mesures de probabilité est proposée. Un aspect crucial sous-jacent ici pour la nouvelle méthode est que le barycentre de Wasserstein des mesures reste invariant sous les distributions de localisation et d'échelle, il est donc possible de proposer des formules exactes pour le barycentre de Wasserstein de la VaR et de la CVaR. Explicitement, un concept de la théorie des probabilités est incorporé aux modèles financiers en proposant des mesures de Fréchet, qui sont calibrées par une certaine métaréalisation de l'espace des mesures de probabilité. Dans ce cas, la métrique de Wasserstein soutient la méthode et fournit des connexions fondamentales avec le concept émergent de barycentre au sens d'Agueh et Carlier dans Agueh and Carlier [2011]. Le modèle proposé est comparé à d'autres modèles simples et avancés, et ses performances sont vérifiées sur les principaux indices boursiers américains, pendant la pandémie de COVID-19. Le modèle introduit fonctionne de manière satisfaisante dans les périodes de prix d'actifs communs et volatils, fournissant une prévision réaliste de la VaR dans cette ère de distanciation sociale. Maintenant, lorsque nous cherchons une extension matrice-variable de la VaR, la littérature financière ne fournit aucune approche. Cependant, d'un point de vue mathématique, la VaR ne requiert des percentiles significatifs que dans le contexte des fonctions de densité cumulative matricielle. La théorie des distributions matrice-variable est étudiée en profondeur dans Muirhead [2005]. En particulier, des formules sont fournies pour calculer P(X = V) lorsque X suit une distribution de Wishart et V est une matrice définie positive et il a été démontré que la fonction de distribution cumulative peut être exprimée en termes de fonction hypergéométrique gaussienne. Sur la base de cette théorie, nous développons au chapitre 2 une méthode d'estimation de la valeur à risque et de la valeur à risque conditionnelle lorsque les facteurs de risque suivent une distribution bêta dans un environnement univarié et matriciel-varié. Dans ce but, nous connectons la théorie des fonctions hypergéométriques à argument matriciel et l'intégration sur les matrices définies positives. Nous définissons la matrice supérieure VaR et la matrice inferieure VaR, qui sont obtenues comme les zéros de la fonction hypergéométrique gaussienne. On montre que les deux extensions satisfont aux propriétés de monotonicité, d'homogénéité positive et d'invariance par translation. Des expressions analytiques sont développées pour certains paramètres de forme, et une solution numérique est présentée pour toute valeur de ces paramètres. Les mesures de risque proposées sont finalement utilisées pour quantifier la perte économique dans le risque de crédit. Le chapitre 3 propose des intégrales généralisées liées aux distributions classiques de Wishart, bêta et F. Ensuite, l'article définit les distributions matrice-variable bêta et F généralisées et la matrice-variable VaR. Comme corollaires, un certain nombre de résultats publiés sur les fonctions de densité cumulative (FDC) des matrices de Wishart et bêta sont également examinés et unifiés. Un nouveau c.d.f. pour une matrice aléatoire de Wishart et la solution à un problème ouvert proposé par A. C. Constantine en 1963. Les distributions extrêmes des racines latentes pour Wishart, beta et F sont obtenues par simple dérivation. Les relations avec le nombre de conditions de Davis, la théorie des formes et la VaR sont également établies ; certains cas particuliers sont dérivés et une perspective pour les travaux futurs dans cette nouvelle direction est établie. Nous fournissons la VaR pour les distributions gamma, exponentielle, Erlang, chi-carré, bêta et uniforme pour le cas univarié et la VaR pour les distributions Wishart, gamma, bêta et F pour le cas matriciel. En outre, nous établissons des résultats utiles pour la VaR supérieure et la VaR inferieure de la matrice et obtenons des expressions fermées lorsque X ~ Beta_m(a, m+1/2) y cuando X ~ W_2(n, I).Usually, risk measures are functions of a set of real random variables to the real numbers. However, it is often insufficient to consider a single real-varied measure to quantify the risks derived from different economic and financial activities. In the last decade, many extensions of vector-valued risk measures have been investigated In the last decade, many extensions of vector-valued risk measures have been investigated, see Embrechts and Puccetti [2006], Cousin and Di Bernardino [2013], Torres et al. [2015]. However, as mentioned in Li et al. [2012] some of the univariate transcripts are unrealistic and are based on assumptions that are difficult to elucidate. Probably the most widely used risk measures in economics, insurance, and finance are the Value-at-Risk (VaR) and the Conditional Value-at-Risk (CVaR). The objective of this thesis is to propose new methodologies to quantify VaR and CVaR from an uni-variate, vector-variate and matrix-variate approaches. In the first chapter of this thesis, a new approach is proposed to model vector-varied risk measures under the Wasserstein barycenter of probability measures. A crucial aspect that underlies here for the new method is that the Wasserstein measure-barycenter remains invariant under the location and scale families, so it is possible to propose exact formulas for the Wasserstein Barycenter VaR and the Wasserstein Barycenter Conditional CVaR. The new method considers a reliable risk measure based on distances among probabilistic models. The underlying suitable probability laws obey, for example, opinions, beliefs, and estimates of data sources, in the context of the financial risk. Explicitly, a concept in probability theory is brought into the financial models by proposing the named Fréchet measures; which are calibrated by certain metrization of the probability measure space. In this case, the well-studied metric of Wasserstein supports the method and provides fundamental connections for the rising concept of barycenter in the sense of Agueh and Carlier in Agueh and Carlier [2011]. Simple and advanced multivariate VaR models are compared with the proposed model. The performance of the model is also checked in the major U.S. stock indices during the COVID-19 pandemic. The introduced model behaves satisfactorily in both common and volatile periods of asset prices, providing a realistic VaR forecast in this era of social distancing. If we search for a matrix-variate extension for risk measures, the finance literature does not provide us with any approaches. However, from a mathematical point of view, risk measures just requires meaningful percentiles in the context of matrix cumulative density functions. The theory behind the random matrix setting has been deep studied by Muirhead [2005]. In particular, that paper provided a formulation for calculating P(X = V) when X follows a Wishart distribution and V is a positive definite matrix. They also demonstrated that its cumulative distribution function can be expressed in terms of a Gaussian hypergeometric function of matrix argument. Based on this theory, in chapter 2 a method is developed to estimate the VaR and the CVaR when the risk factors follow a beta distribution in an univariate and a matrix-variate approach. For this purpose, we connect matrix argument theory of hypergeometric functions and integration over positive definite matrices. The upper matrix VaR and the lower matrix VaR are defined, which are obtained as the zeros of the Gaussian hypergeometric function. Both extensions are shown to satisfy the properties of monotonicity, positive homogeneity, and translational invariance. Analytical expressions are developed for certain shape parameters, in addition, a numerical solution is presented for any value of said parameters. The proposed risk measures are finally used to quantify the economic loss in credit risk. Chapter 3, proposes generalized integrals related to the classical Wishart, beta, and F distributions. Then the work defines the termed generalized matrix variate beta and F distributions and the VaR in the matrix setting. As corollaries, a number of published results about cumulative density functions (c.d.f) of Wishart and beta matrices are also revisited and unified. A new c.d.f for a Wishart random matrix and a solution to an open problem proposed by A. C. Constantine in 1963 are also provided. The extreme latent root distributions for Wishart, Beta, and F are obtained by simple derivation. Relations with the Davis' condition number, theory of shape, and VaR are also established; some particular cases are derived and a perspective for future work is set in that novel direction. VaR is provided for gamma, exponential, Erlang, chi-square, beta and uniform distributions for the univariate case and VaR for Wishart, gamma, beta and F distributions for the matrix case. Furthermore, we establish useful results for the upper VaR and the lower matrix VaR and obtain closed expressions when X ~ Beta_m(a, m+1/2) and when X ~ W_2(n, I)

Hybrid breeding in perennial grasses based on self-incompatibility and self-fertility

For a long time, petroleum-based fuels have been used to provide energy, but limited supplies along with environmental effects of fossil fuels created the need of alternative and clean energy sources. Grasses in general have a low lignin content compared to woody species which is desirable for ethanol production. Furthermore, other features such as: low water and nutrient requirements, and a high rate of carbon fixation that make grasses desirable for biomass production. Perennial grasses have also environmental advantages such as reduced soil organic matter and tillage requirements compared with annual species. Perennial ryegrass has been increasingly used in Europe as forage grass. In 2004, it represented 40% of the grass seed production area in the European Union. This species has a two-locus systems SI systems which has been described for other grasses such as rye and switchgrass. For allogamous grasses, selfing rates are considerably low due to SI and the progeny developed by selfing display a strong inbreeding depression (ID). This suggests that grasses are excellent candidates for hybrid breeding. To ensure 100% hybrid seed production, controlled pollinations are required. For ryegrass, male and female organs coexist in the same floral structure and emasculation can be laborious. Conveniently, SI is a built-in pollination control system that can be exploited in hybrid seed production. The objectives of this research are to; i) discuss the perspectives for hybrid breeding in bioenergy grasses; ii) develop a tool to calculate pollen compatibility for self-incompatible allo-and autotetraploid species; iii) map a new source of self-fertility in ryegrass; and iv) determine the inheritance of polymorphic markers close to the Z gene to validate the self-incompatibility model in tetraploid ryegrass and its effectiveness at a higher ploidy leve

Moving forward: The Japanese kelp Undaria pinnatifida (harvey) suringar, 1873 expands in Northern Patagonia, Argentina

Increasingly, global trade and human movement have been transporting species between regions. Undaria pinnatifida (Harvey) Suringar, 1873, a macroalgae native to Korea and Japan, has been transported and became established in several temperate regions of the world. Here we report its presence in a new coastal area of northern Patagonia, Argentina, with a description of the sporophytes.Fil: Pereyra, Patricio Javier. Universidad Nacional del Comahue. Instituto de Biología Marina y Pesquera Almirante Storni; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Arias, Magdalena. Universidad Nacional del Comahue. Instituto de Biología Marina y Pesquera Almirante Storni; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: González, Raul Alberto Candido. Universidad Nacional del Comahue. Instituto de Biología Marina y Pesquera Almirante Storni; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Narvarte, Maite Andrea. Universidad Nacional del Comahue. Instituto de Biología Marina y Pesquera Almirante Storni; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Climate variability over the American monsoon and Amazonian regions during the last decades

textThis dissertation aims to identify the main changes in monsoon activity observed over the American monsoon and Amazonian regions during the last decades and the possible links between such changes. To address this, several observational and reanalysis datasets were used. The results suggest the occurrence of two regime types of the North American monsoon during 1948-2009: two dry regimes during 1948-1959 and 1990-2009 and one wet regime during 1960-1989. The occurrence of such regimes is modulated by the Atlantic Multidecadal Oscillation. However, the two dry regimes have different causes. In particular, the more recent dry regime is mainly due to both an anomalous westward expansion of the North Atlantic Subtropical High and a northward displacement of the subtropical jet stream over the United States. The former enhances the low-level flow from the Gulf of Mexico to the Great Plains and weakens moisture transport to Mexico and the southwestern US. In addition to such a weakening of the North American monsoon during the last two decades, this research shows that the American monsoon systems have shortened after 1978 due to a trend toward earlier retreats of the North American monsoon and delayed onsets of the southern Amazon wet season. These changes produce a longer transition season between both monsoon systems. Whether these changes are caused by a common factor or they are the consequence of independent and unrelated causes was not clear previously. The results discussed here indicate that the observed changes in the American monsoons are partially a consequence of the westward expansion of the North Atlantic surface high observed since 1978. Such a westward expansion enhances the activity of easterly waves over the southern Caribbean Sea and northern South America, producing a dominant easterly flow over the region, which in turn prevents the reversal of the cross-equatorial flow necessary to transport moisture to the southern Amazon and the South American monsoon domain and contributes to its delayed onset. This investigation provides evidence that the shortening and weakening of the American monsoons and the lengthening of the transition season between them are associated with the same large-scale forcing, which may be caused by anthropogenic influence.Geological Science