Precision Synthesis of Functional Materials via RAFT Polymerization and Click-Type Chemical Reactions

The need to tailor polymeric architectures with specific physico-chemical properties via the simplest, cleanest, and most efficient synthetic route possible has become the ultimate goal in polymer synthesis. Recent progress in macromolecular science, such as the discoveries of controlled/“living” free radical polymerization (CRP) methods, has brought about synthetic capabilities to prepare (co)polymers with advanced topologies, predetermined molecular weights, narrow molecular weight distributions, and precisely located functional groups. In addition, the establishment of click chemistry has redefined the selected few highly efficient chemical reactions that become highly useful in post-polymerization modification strategies. Hence, the ability to make well-defined topologies afforded by controlled polymerization techniques and the facile incorporation of functionalities along the chain via click-type reactions have yielded complex architectures, allowing the investigation of physical phenomena which otherwise could not be studied with systems prepared via conventional methods. The overarching theme of the research work described in this dissertation is the fusion of the excellent attributes of reversible addition-fragmentation chain transfer (RAFT) polymerization method, which is one of the CRP techniques, and click-type chemical reactions in the precision of synthesis of advanced functional materials. Chapter IV is divided into three sections. In Section I, the direct RAFT homopolymerization of 2-(acryloyloxy)ethyl isocyanate (AOI) and subsequent post-polymerization modifications are described. The polymerization conditions were optimized in terms of the choice of RAFT chain transfer agent (CTA), polymerization temperature and the reaction medium. Direct RAFT polymerization of AOI requires a neutral CTA, and relatively low reaction temperature to yield AOI homopolymers with low polydispersities. Efficient side-chain functionalization of PAOI homopolymers was achieved via reaction with model amine, thiol and alcohol compounds yielding urea, thiourethane and urethane derivatives, respectively. Reactions with amines and thiols (in the presence of base) were rapid, quantitative and efficient. However, the reaction with alcohols catalyzed by dibutyltin dilaurate (DBTDL) was relatively slow but proceeded to completion. Selective reaction pathways for the addition of difunctional ethanolamine and mercaptoethanol were also investigated. A related strategy is described in Section II wherein a hydroxyl-containing diblock copolymer precursor was transformed into a library of functional copolymers via two sequential post-polymerization modification reactions. A diblock copolymer scaffold, poly[(N,N-dimethylacrylamide)-b-( N-(2-hydroxyethyl)acrylamide] (PDMA-b-PHEA) was first prepared. The hydroxyl groups of the HEA block were then reacted with 2-(acryloyloxy)ethylisocyanate (AOI) and allylisocyanate (AI) resulting in acrylate- and allyl-functionalized copolymer precursors, respectively. The efficiencies of Michael-type and free radical thiol addition reactions were investigated using selected thiols having alkyl, aryl, hydroxyl, carboxylic acid, amine and amino acid functionalities. The steps of RAFT polymerization, isocyanate-hydroxyl coupling and thiol-ene addition are accomplished under mild conditions, thus offering facile and modular routes to synthesize functional copolymers. The synthesis and solution studies of pH- and salt-responsive triblock copolymer are described in Section III. This system is capable of forming self-locked micellar structures which may be controlled by changing solution pH as well as ionic strength. A triblock copolymer containing a permanently hydrophilic poly(N,N-dimethylacrylamide) (PDMA) outer block, a salt-sensitive zwitterionic poly(3[2-(N-methylacrylamido)ethyl dimethylammonio]propanesulfonate) (PMAEDAPS) middle block and a pH-responsive 3-acrylamido-3-methylbutanoic acid (PAMBA) core block was synthesized using aqueous RAFT polymerization. A facile formation of “self-locking” shell cross-linked micelles is achieved by changing solution pH and salt concentration. The reversible “self-locking” is attained from the interactions of zwitterionic groups in the middle block that constitutes the shell of the micelles. The structure slowly dissociates into unimers in 2-3 days at pH above the pKa of the PAMBA block

On Updating Preconditioners for the Iterative Solution of Linear Systems

El tema principal de esta tesis es el desarrollo de técnicas de actualización de precondicionadores para resolver sistemas lineales de gran tamaño y dispersos Ax=b mediante el uso de métodos iterativos de Krylov. Se consideran dos tipos interesantes de problemas. En el primero se estudia la solución iterativa de sistemas lineales no singulares y antisimétricos, donde la matriz de coeficientes A tiene parte antisimétrica de rango bajo o puede aproximarse bien con una matriz antisimétrica de rango bajo. Sistemas como este surgen de la discretización de PDEs con ciertas condiciones de frontera de Neumann, la discretización de ecuaciones integrales y métodos de puntos interiores, por ejemplo, el problema de Bratu y la ecuación integral de Love. El segundo tipo de sistemas lineales considerados son problemas de mínimos cuadrados (LS) que se resuelven considerando la solución del sistema equivalente de ecuaciones normales. Concretamente, consideramos la solución de problemas LS modificados y de rango incompleto. Por problema LS modificado se entiende que el conjunto de ecuaciones lineales se actualiza con alguna información nueva, se agrega una nueva variable o, por el contrario, se elimina alguna información o variable del conjunto. En los problemas LS de rango deficiente, la matriz de coeficientes no tiene rango completo, lo que dificulta el cálculo de una factorización incompleta de las ecuaciones normales. Los problemas LS surgen en muchas aplicaciones a gran escala de la ciencia y la ingeniería como, por ejemplo, redes neuronales, programación lineal, sismología de exploración o procesamiento de imágenes. Los precondicionadores directos para métodos iterativos usados habitualmente son las factorizaciones incompletas LU, o de Cholesky cuando la matriz es simétrica definida positiva. La principal contribución de esta tesis es el desarrollo de técnicas de actualización de precondicionadores. Básicamente, el método consiste en el cálculo de una descomposición incompleta para un sistema lineal aumentado equivalente, que se utiliza como precondicionador para el problema original. El estudio teórico y los resultados numéricos presentados en esta tesis muestran el rendimiento de la técnica de precondicionamiento propuesta y su competitividad en comparación con otros métodos disponibles en la literatura para calcular precondicionadores para los problemas estudiados.The main topic of this thesis is updating preconditioners for solving large sparse linear systems Ax=b by using Krylov iterative methods. Two interesting types of problems are considered. In the first one is studied the iterative solution of non-singular, non-symmetric linear systems where the coefficient matrix A has a skew-symmetric part of low-rank or can be well approximated with a skew-symmetric low-rank matrix. Systems like this arise from the discretization of PDEs with certain Neumann boundary conditions, the discretization of integral equations as well as path following methods, for example, the Bratu problem and the Love's integral equation. The second type of linear systems considered are least squares (LS) problems that are solved by considering the solution of the equivalent normal equations system. More precisely, we consider the solution of modified and rank deficient LS problems. By modified LS problem, it is understood that the set of linear relations is updated with some new information, a new variable is added or, contrarily, some information or variable is removed from the set. Rank deficient LS problems are characterized by a coefficient matrix that has not full rank, which makes difficult the computation of an incomplete factorization of the normal equations. LS problems arise in many large-scale applications of the science and engineering as for instance neural networks, linear programming, exploration seismology or image processing. Usually, incomplete LU or incomplete Cholesky factorization are used as preconditioners for iterative methods. The main contribution of this thesis is the development of a technique for updating preconditioners by bordering. It consists in the computation of an approximate decomposition for an equivalent augmented linear system, that is used as preconditioner for the original problem. The theoretical study and the results of the numerical experiments presented in this thesis show the performance of the preconditioner technique proposed and its competitiveness compared with other methods available in the literature for computing preconditioners for the problems studied.El tema principal d'esta tesi és actualitzar precondicionadors per a resoldre sistemes lineals grans i buits Ax=b per mitjà de l'ús de mètodes iteratius de Krylov. Es consideren dos tipus interessants de problemes. En el primer s'estudia la solució iterativa de sistemes lineals no singulars i antisimètrics, on la matriu de coeficients A té una part antisimètrica de baix rang, o bé pot aproximar-se amb una matriu antisimètrica de baix rang. Sistemes com este sorgixen de la discretització de PDEs amb certes condicions de frontera de Neumann, la discretització d'equacions integrals i mètodes de punts interiors, per exemple, el problema de Bratu i l'equació integral de Love. El segon tipus de sistemes lineals considerats, són problemes de mínims quadrats (LS) que es resolen considerant la solució del sistema equivalent d'equacions normals. Concretament, considerem la solució de problemes de LS modificats i de rang incomplet. Per problema LS modificat, s'entén que el conjunt d'equacions lineals s'actualitza amb alguna informació nova, s'agrega una nova variable o, al contrari, s'elimina alguna informació o variable del conjunt. En els problemes LS de rang deficient, la matriu de coeficients no té rang complet, la qual cosa dificultata el calcul d'una factorització incompleta de les equacions normals. Els problemes LS sorgixen en moltes aplicacions a gran escala de la ciència i l'enginyeria com, per exemple, xarxes neuronals, programació lineal, sismologia d'exploració o processament d'imatges. Els precondicionadors directes per a mètodes iteratius utilitzats més a sovint són les factoritzacions incompletes tipus ILU, o la factorització incompleta de Cholesky quan la matriu és simètrica definida positiva. La principal contribució d'esta tesi és el desenvolupament de tècniques d'actualització de precondicionadors. Bàsicament, el mètode consistix en el càlcul d'una descomposició incompleta per a un sistema lineal augmentat equivalent, que s'utilitza com a precondicionador pel problema original. L'estudi teòric i els resultats numèrics presentats en esta tesi mostren el rendiment de la tècnica de precondicionament proposta i la seua competitivitat en comparació amb altres mètodes disponibles en la literatura per a calcular precondicionadors per als problemes considerats.Guerrero Flores, DJ. (2018). On Updating Preconditioners for the Iterative Solution of Linear Systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/10492

Toxoplasmosis congénita

ResumenIntroducciónLa toxoplasmosis causada por el Toxoplasma gondii se transmite a los humanos de manera transplacentaria, entre otras. Se estima que infecta a un tercio de la población mundial y está asociado con infección congénita y abortos. Solo son sintomáticos del 10 al 20% de los casos.Caso clínicoSe presenta el caso de un recién nacido pretérmino referido a un hospital de mayor complejidad. Durante la hospitalización se realiza el diagnóstico de toxoplasmosis congénita con diversas manifestaciones sistémicas.ConclusionesLa mayor parte de los casos de toxoplasmosis congénita suelen ser asintomáticos. Es necesario realizar pruebas diagnósticas y un examen físico completo ante la sospecha de la infección para detectar tempranamente todas las manifestaciones posibles.AbstractBackgroundToxoplasmosis, caused by Toxoplasma gondii, is transmitted to humans in several ways, such as transplacental spread. It is estimated that this parasite infects a third of the world population and it is associated with congenital infection and fetal loss. Only 10 to 20% of the cases are symptomatic.Case reportWe present the case of a pre-term newborn that had been referred to a tertiary care center. During the in-hospital period, diagnosis of congenital toxoplasmosis with many systemic manifestations was performed.ConclusionsMost cases of congenital toxoplasmosis are asymptomatic. Diagnosis tests and a complete physical examination should be performed on all newborns with suspicion of infection to detect all possible manifestations as in the case reported

Observational and Theoretical Constraints on Singular Dark Matter Halos

The distribution of dark matter around galactic or cluster halos has usually been assumed to be approximately isothermal with a non-zero core radius, which is expected to be of the order of the size of the visible matter distribution. Recently, the possibility has been raised that dark matter halos might be singular in the sense that the dark matter density $\rho$ could increase monotonically with radius $r$ down to a very small distance from the center of galaxies or clusters. Such central cusps in the dark matter density could lead to a high flux of gamma rays from WIMP dark matter annihilation. Here we analyze two possibilities that have been discussed in the literature, $\rho \propto r^{-n}$ with $n \approx 1\ {\rm or}\ 2$, and point out that such density profiles are excluded by gravitional lensing analyses on cluster scales and by the rotation curves of gas-rich, halo-dominated dwarf spirals on small scales. We also point out that if spiral galaxies form by gas infall inside dark matter halos, as they are expected to do in any hierarchical clustering model, such profiles almost always lead to falling rotation curves after infall, contrary to observations.Comment: 15 pages incl 4 figs, submitted to Astrophys J Lett, uuencoded compressed postscript, preprint SCIPP 93/01-re

Antirust as a Public-Private Partnership: A Case Study of the NASDAQ Litigation

TesisBackground The Bethesda system is used to classify Pap smear results. Some of the results are ASC-US (atypical squamous cells of undetermined significance) and ASC- H cells (atypical squamous cells cannot exclude intraepithelial lesion). It has been found an association between these results with cervical neoplasia; however they have not been well studied in Peru. Objectives To calculate the probability of severe dysplasia in situ or squamous cell cancer in women with cytology results of ASC-H and ASC-US. Methods An observational, cross-sectional study was carried out in a reference higher complexity health establishment in Lima, Peru (4th level), from 2012 to 2013, in which 1060 data of patients was analyzed. Bivariate and multiple binomial logistic regression analysis were performed. Chi square test was used and p-value < 0.05 was considered as significant. Results 1060 Pap smears were evaluated. Mean age was 46,4 (SD: 13,2) years and 64,9% were under 50 years old. ASC-US prevalence was 3,45% and ASC-H 0,32%. Out of 175 biopsies, 22,9% had moderate to severe dysplasia, carcinoma in situ or squamous carcinoma. There was an association between ASC-H finding and the presence of moderate/severe dysplasia (CIN 2/3), carcinoma in situ and squamous cell carcinoma (PR=2,39; CI(95%):1,49-3,81). Conclusion Given the association found, women with ASC-H findings should be further and thoroughly studied in order to look for moderate/severe dysplasia (CIN2/3) or squamous cell carcinoma

Strobilus and seed production of Dioon edule (Zamiaceae) in a population with low seedling density in San Luis Potosí, Mexico

"We describe strobilus and seed development in a Dioon edule (chamal, palma, dameu') population characterized by low seedling and high adult tree density, in order to improve conservation decisions for this endangered cycad species. Female strobili required 16-17 months and male 4-5 months to develop. During this period 80% female and 100% male strobili were not damaged by herbivores. The method of cone analysis used to evaluate seed production of pines was modified for D. edule, providing actual yield of individual strobili compared to potential seed yield, explaining productivity in terms of seed efficiency, and identifying and quantifying the types of seed failures. Larger strobili have higher seed potential calculated as the number of seeds potentially produced in the fertile megasporophylls of each strobilus, total seeds actually produced, and seeds with an embryo (filled). Calculated average seed potential per strobilus was of 230.4 seeds. Using the X-ray technique, average seed traits were 100.2 full, 1.8 insect damaged, and 0.6 malformed. Seed efficiency (number of filled seeds as a percentage of the seed potential of each strobilus) of 42.5% indicated that major seed loss was attributable to abortive ovules and seeds, possibly due to ineffective pollination. Seedling survival in greenhouse conditions was 100% after one year. Low seed production affects the population structure and hinders its conservation.

Beetle diversity in fragmented thornscrub and isolated trees

Abstract Due to land use change mainly for induced agriculture, Tamaulipan thornscrubin northeast Mexico has been cleared and transformed into small patches of vegetation as small as isolated trees surrounded by agricultural fields. In this study, we explored how tree isolation or growing inside a fragment of remnant vegetation influence diversity of coleopterans in two plant species (Prosopis laevigata (Humb. &Bonpl.exWilld.) M.C. Johnst. (mesquite) and Ebenopsis ebano (Berl.) Barneby (Texas ebony). We found 72 coleopteran morphospecies; fifteen occurred mainly in remnant fragments and ten mainly in isolated trees. There were more insects under isolated mesquites than under those immersed in remnant fragments, while in Texas ebony the highest beetle density for isolated trees coincided with periods of bean and maize in surrounding agriculture. Keywords: coleopterans, vegetation-patches, landscape Resumo Devido a mudança de uso da terra para induzir principalmente a agricultura, o bioma thornscrub no nordeste México tem sido transformado em fragmentos pequenos como árvores isoladas rodeadas por campos agrícolas. Neste estudo exploramos como o isolamento das árvores influi na diversidade de coleópteros em duas espécies de plantas (Prosopis laevigata (Humb. & Bonpl.ex Willd) M.C. Johnst. (mesquite) e Ebenopsis ebano (Berl.) Barneby (Texas ebony). Encontramos 72 morfospecies do coleópteros; quinze ocorreram principalmente em fragmentos remanescentes e dez em árvores isoladas. No estudo houve mais insetos nas “mesquite” isoladas do que nos fragmentos remanescentes do bioma thornscrub, enquanto que em “Texas ebony” a densidade alta de coleópteros para árvores isoladas coincidiu com períodos de produção de feijão e milho na agricultura ao redor. Palavras-chave: coleoptera, paisagem fragmentada, vegetação fragmentad

Effects of shade on germination traits of the endangered cycad Dioon edule (Zamiaceae)

"The endangered cycad Dioon edule requires shade provided by filtered sunlight under the canopy of trees or maternal plants during initial growth stages. It is known that germination improves under shade, but there is no report of radiation conditions. In order to understand how photosynthetic photon flux density (PPFD) affect germination traits, we evaluated some germination indexes. A sample of three mature strobili and 200 viable seeds per strobilus were selected to evaluate seed size (length, width, and fresh weight). Two experimental treatments were established simulating shade under the oak forest canopy with PPFD 81 µmol m−2 s−1 (PPFD81), and under maternal plant canopy with PPFD 17 µmol m−2 s−1 (PPFD17), as measured previously in the study site. Means of response variables (germinability, velocity of germination, synchronization, mean germination time and relative frequency of germination) for the two treatments were compared using a t-test and a correlation analysis. No significant correlation between seed size and germination traits was detected. Germinability was higher at PPFD17 (89 %) than PPFD81 (39 %), but mean germination time was similar across treatments. The velocity of germination was greater under PPFD17 but synchronization was the opposite. The low PPFD stimulated D. edule germination, but also the spectral composition must be evaluated.""La cícada en peligro de extinción Dioon edule requiere la sombra que le proporciona el dosel o las plantas maternas al fltrar la luz del sol durante su etapa inicial de crecimiento. Se sabe que la germinación es mejor con sombra, pero no existen reportes sobre las condiciones de la radiación. Evaluamos diferentes indicadores de germinación con el propósito de entender cómo es afectada por la densidad de fujo de fotones fotosintéticos (PPFD). Una muestra de tres estróbilos maduros y 200 semillas viables por estróbilo fueron seleccionadas para evaluar el tamaño de la semilla (largo, ancho y peso fresco). Dos tratamientos experimentales se establecieron simulando la sombra bajo el dosel del encinar con densidad de fujo de fotones fotosintéticos de 81 µmol m-2 s-1 (PPFD81) y bajo las plantas maternas con densidad de fujo de fotones fotosintéticos de17 µmol m-2 s-1 (PPFD17), como se midió previamente en el sitio de estudio. La media de las variables (capacidad germinativa, velocidad de germinación, sincronización, tiempo medio de germinación y frecuencia relativa de germinación) para los dos tratamientos se compararon usando una prueba de t. Se aplicó un análisis de correlación a los datos de germinación y tamaño de semilla. Se aplicó una regresión a los predictores ambientales (temperatura, humedad relativa, densidad de fujo de fotones fotosintéticos) de la capacidad germinativa. No se detectó correlación signifcativa entre el tamaño de la semilla y las variables de germinación. La capacidad germinativa fue mayor en PPFD17 (89 %) que PPFD81 (39 %), pero el tiempo medio de germinación fue similar. La velocidad de germinación fue mayor en PPFD17 pero menor en la sincronización. El bajo PPFD estimuló la germinación de D. edule, pero también la composición espectral debe ser evaluada

Effects of burial depth on seed germination and seedling emergence of Mexican oaks: a glasshouse experiment

"Despite the interest in restoring oak forests in Mexico, very little is known about their regeneration ecology. We assessed the influence of acorn burial depth on seed germination and seedling emergence for eight Mexican oak species (Q. affinis, Q. castanea, Q. coccolobiolia, Q. laeta, Q. mexicana, Q. polymorpha, Q. tinkhamii and Q. viminea). We performed a glasshouse experiment in which acorns were buried at five soil depths (0, 2, 4, 6 and 8 cm). After four months, acorn germination and seedling emergence were recorded. Buried acorns showed higher germination and seedling emergence than unburied ones, but burial depth also influenced these responses. The optimum burial depth for seedling emergence of each species was 2, 4, 6 and 8 cm depth for four species (Q. castanea, Q. mexicana, Q. tinkhamii, and Q. viminea); 2 and 4 cm for Q. laeta; as well as 2, 4 and 8 cm for Q. coccolobifolia.