Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO

We present optically-pumped emission data for ZnO, showing that high excitation effects and stimulated emission / lasing are observed in nanocrystalline ZnO thin films at room temperature, although such effects are not seen in bulk material of better optical quality. A simple model of exciton density profiles is developed which explains our results and those of other authors. Inhibition of exciton diffusion in nanocrystalline samples compared to bulk significantly increases exciton densities in the former, leading, via the nonlinear dependence of emission in the exciton bands on the pump intensity, to large increases in emission and to stimulated emission

Intelligent copolymers based on poly (N-isopropylacrylamide) PNIPAm with potential use in biomedical applications. Part i: PNIPAm functionalization with 3-butenoic acid and piperazine

The synthesis and characterization of the thermosensitive copolymers based on Poly (N-Isopropylacrylamide) (PNIPAm) and 3-butenoic acid and functionalized with piperazine was carried out. The free radical polymerization of the PNIPA copolymer with 3-butenoic acid was performed under microwave radiation. After obtaining this copolymer, the carboxyl groups present in the copolymer chain were activated with 1-ethyl- (3-3-dimethylaminopropyl) carbodiimide in the presence of N-hydroxysuccinimide, improving its reactivity to incorporate the piperazine through its amino group. The characterization consisted: differential scanning calorimetric and ultraviolet-visible spectrophotometry to determine the LCST phase transition temperature, ranging from (30-35)°C. Structurally it was analyzed by infrared spectroscopy. A morphological analysis was performed using scanning electron microscopy, after simulating an injectable process, with the objective to observe internally the porosity and interconnectivity. The biocompatibility was evaluated through hemocompatibility tests and it was observed that the copolymers obtained were not cytotoxic. In base of the results, the chemical structure of these new copolymers confers a functionality that allows them to serve as nuclei to graft other molecules, such as polysaccharides. Then, the results obtained on the LCST temperature, porosity, interconnected pore network morphology, the ability to be injectable and the biocompatible nature of these copolymers are indicative that these new synthetic biomaterials have the potential to be used in biomedical, pharmacological and for tissue engineering. Also, once their biocompatibility was demonstrate, they may serve to generate interesting compounds having chemical anchor points for the possible addition of polysaccharides using insertion reactions, thereby generating graft copolymers with potential use in biomedical applications

Generation of novel activities for English learning and teaching: A learning styles approach

En vista de que el estilo de aprendizaje de cada estudiante es diferente, las actividades que se utilizan en el aula de lengua extranjera (en adelante LE) deben adaptarse a las diversas maneras en que aprenden. Asimismo, los estándares básicos de competencias en inglés deben ser la base de estos de forma tal que la instrucción ofrecida en el sistema educativo nacional se unifique de manera coherente, lo cual es también uno de los objetivos del Ministerio de Educación Nacional. Dado lo anterior, se plantea la generación de actividades para la básica secundaria y media en Colombia que suplan esta necesidad, fundamentados en los estilos de aprendizaje de los aprendientes con base en el Índice de Estilos de Aprendizaje de Richard M. Felder y Barbara A. Soloman. Para este fin, el enfoque es tanto cualitativo como cuantitativo (basado en los resultados de los formularios de juicio y validación por expertos) y el tipo de estudio es interpretativo (fundamentado en los resultados de tales formularios para mejorar las actividades de aprendizaje). Las actividades de aprendizaje, objeto de esta tesis, se apoyan en la plataforma Google Classroom y en recursos tecno-pedagógicos como Hot Potatoes y Padlet. Estas, además de girar en torno a los estándares básicos de competencias en inglés del grado sexto al undécimo, van de la mano con las rutas evaluativas planteadas en el libro Esquema curricular sugerido. De este modo, se dio lugar a la generación de dos actividades por grado, es decir, un paquete de seis actividades en total, indicando el tiempo estimado que toma completar cada una y el nivel de LE sugerido según la Guía 22 y el Marco Común Europeo de Referencia para las lenguas. Al propiciar escenarios interactivos en los que la tecnología es el eje principal de la formación en LE, dichas actividades pretenden que el alumno sea más receptivo al percibir que estas responden a sus necesidades y expectativas personales.Given that each student’s learning style is different, the activities used in the foreign language (hereinafter FL) classroom must be adapted to the various ways in which they learn. Likewise, the basic standards of competences in English must be the basis of these, in such a way that the instruction offered in the national education system is coherently unified, as reflected by the objectives of the Ministry of National Education. For this reason, the learning activities generated within this research attempt to meet these criteria for the basic secondary and middle school in Colombia, taking into account the students’ learning styles as expressed in Richard M. Felder and Barbara A. Soloman’s Index of Learning Styles. To this end, the approach is qualitative and quantitative (based on the expert judgment and validation forms results), and the study is interpretive in nature (based on the results of the aforementioned forms to improve the learning activities). The learning activities, at the core of this thesis, are supported by the Google Classroom platform with the help of techno-pedagogical resources such as Hot Potatoes and Padlet. They aim to meet the basic standards of competences in English from the sixth to 11th grade. Likewise, they mesh with the assessment paths proposed in the book Suggested Curriculum Structure, conditions which resulted in the generation of two activities per grade—that is, one package totaling six activities. The estimated time necessary to complete each activity and the suggested level of proficiency in the FL as per Guide 22 and the Common European Framework of Reference for Languages are indicated. Furthermore, they provide interactive scenarios where technology is the main axis of FL education and, as such, stand a greater chance of being perceived by the students as responding to their personal needs and expectations

Optical properties of nanocrystalline ZnO thin films grown using pulsed laser deposition

Raman spectroscopy, x-ray diffractometry, atomic force microscopy, photoluminescence spectroscopy and reflectance spectroscopy have been used to characterize ZnO thin films grown by pulsed laser deposition as a function of the post-growth annealing temperature. Raman results show enhancement and broadening of certain Raman features which correlate with changes in the widths of the x-ray diffraction peaks for samples with varying grain size in the 50-100 nm range. These data suggest that electric fields, arising from charge trapping at grain boundaries, in conjunction with localised and surface phonon modes, are the cause of the intensity enhancement and asymmetry of the Raman features. Band-edge photoluminescence and reflectance spectra also altered considerably with increases in grain size, showing clearly observable excitonic structure in the reflectance spectra. An analysis using a deformation potential Hamiltonian demonstrates that the experimental exciton energies are not explicable solely in terms of sample strain and give additional evidence for electric fields in the samples due to charge trapping at grain boundaries. This is supported by theoretical estimates of the exciton energy perturbation due to electric fields and also by the behaviour of the green band in the samples. Detailed studies show that reflectance spectra in nanocrystalline ZnO differ substantially from bulk material. Interaction of excitons, damped by strong electric field effects, with photons leads to exciton-polaritons with substantial damping, eliminating the normal Fabry-Perot structure seen in thin films. Good qualitative agreement is achieved between the model and data and the conclusions are also in good agreement with the photoluminescence and Raman data. Finally, high intensity optical pumping data of these samples again shows a dependence on grain size. All samples show evidence of high excitation effects and the sample with the largest grain size displays random lasing at room temperature. All our results indicate the very strong influence of electric fields due to charge trapping at grain boundaries on the optical properties of nanocrystalline ZnO

Cardiac abnormalities in the toxic oil syndrome, with comparative observations on the eosinophilia-myalgia syndrome

AbstractEarly in the course of studies of the Spanish toxic oil syndrome it was recognized that vascular lesions were a major problem, most logically attributable to endothelial damage by the toxic oil. However, most clinical attention has been directed to the pulmonary complications and the evolution into a scleroderma-like illness later. p]In this study of 11 victims of the toxic oil syndrome careful postmortem studies of the coronary arteries and conduction system and neural structures of the heart demonstrated major injury to all those components of the heart. Obliterative fibrosis of the sinus node in four cases resembled findings in fatal scleroderma heart disease, and in eight the cardiac lesions resembled those of lupus erythematosus.The more impressive pathologic features involved the coronary arteries and neural structures, which were abnormal in every heart. The arterial disease included widespread focal fibromuscular dysplasia, but there was also an unusual myointimal proliferative degeneration of both small and large coronary arteries in five patients, four of whom were young women. In two hearts, portions of the inner wall of the sinus node artery had actually detached and embolized downstream. Coronary arteritis was rarely found. Inflammatory and noninflammatory degeneration of cardiac nerves was widespread. Fatty infiltration, fibrosis and degeneration were present in the coronary chemoreceptor.In most respects these cardiac abnormalities resemble those described in the eosinophilia-myalgia syndrome caused by an altered form of l-tryptophan. In both diseases there is good reason to anticipate more clinical cardiac difficulties than have so far been reported, and even more basis for future concern, especially relative to coronary disease and cardiac electrical instability

Essays on river mechanics

CER92-93-PYJ-5.Presented by the Graduate Students in CE 717 - River Mechanics (Spring 1993).Includes bibliographical references.April 1993

Correlation of Raman and X-Ray Diffraction Measurements of Annealed Pulsed Laser Deposited ZnO Thin Films.

Raman spectroscopy, X-ray diffractometry and atomic force microscopy have been used to characterise ZnO thin films grown by pulsed laser deposition as a function of the post-growth annealing temperature. The results show substantial enhancement and broadening of certain Raman features which correlate excellently with the change in width of the X-ray diffraction peaks. The 570 cm[-1] Raman feature showed pronounced asymmetry and enhanced intensity in the unannealed sample. An increase in grain size observed after subsequent annealing produced a substantial reduction in both the asymmetry and intensity of this peak. Our experimental data suggest that electric fields, due to charge trapping at grain boundaries, in conjunction with localised and surface phonon modes are the cause of the intensity enhancement and asymmetry of this feature

The impact of fire on habitat use by the short-snouted elephant shrew ('Elephantulus brachyrhynchus') in North West Province, South Africa

Several studies have investigated the response of small mammal populations to fire, but few have investigated behavioural responses to habitat modification. In this study we investigated the impact of fire on home range, habitat use and activity patterns of the short-snouted elephant shrew (Elephantulus brachyrhynchus) by radio-tracking individuals before and after a fire event. All animals survived the passage of fire in termite mound refugia. Before the fire, grassland was used more than thickets, but habitat utilization shifted to thickets after fire had removed the grass cover. Thickets were an important refuge both pre- and post-fire, but the proportion of thicket within the home range was greater post-fire. We conclude that fire-induced habitat modification resulted in a restriction of E. brachyrhynchus movements to patches of unburned vegetation. This may be a behavioural response to an increase in predation pressure associated with a reduction in cover, rather than a lack of food. This study highlights the importance of considering the landscape mosaic in fire management and allowing sufficient island patches to remain post-fire ensures the persistence of the small mammal fauna

Genetic relatedness of infecting and reinfecting respiratory syncytial virus strains identified in a birth cohort from rural Kenya

Background: Respiratory syncytial virus (RSV) reinfects individuals repeatedly. The extent to which this is a consequence of RSV antigenic diversity is unclear. Methods: Six-hundred thirty-five children from rural Kenya were closely monitored for RSV infection from birth through 3 consecutive RSV epidemics. RSV infections were identified by immunofluorescence testing of nasal washing samples collected during acute respiratory illnesses, typed into group A and B, and sequenced in the attachment (G) protein. A positive sample separated from a previous positive by ≥14 days was defined as a reinfection a priori. Results: Phylogenetic analysis was undertaken for 325 (80%) of 409 identified infections, including 53 (64%) of 83 reinfections. Heterologous group reinfections were observed in 28 episodes, and homologous group reinfections were observed in 25 episodes; 10 involved homologous genotypes, 5 showed no amino acid changes, and 3 were separated by 21–24 days and were potentially persistent infections. The temporal distribution of genotypes among reinfections did not differ from that of single infections. Conclusions: The vast majority of infection and reinfection pairs differed by group, genotype, or G amino acid sequence (ie, comprised distinct viruses). The extent to which this is a consequence of immune memory of infection history or prevalent diversity remains unclear