Año 2009http://hdl.handle.net/20.500.12010/22962024-03-29T12:32:35Z2024-03-29T12:32:35ZInvestigation of AgInSe2 thin films grown by co-evaporationhttp://hdl.handle.net/20.500.12010/281212022-09-16T17:19:11ZInvestigation of AgInSe2 thin films grown by co-evaporation
In this work, special emphasis was dedicated to find conditions to grow AgInSe 2 thin films with chalcopyrite type tetragonal structure using a procedure based on the co-evaporation of the precursors in a two stage process. Through a parameter study a set of synthesis parameters was found, which allowed us to grow thin films in the AgInSe 2 phase in a reproducible way. It was also found that the AgInSe 2 films present p-type conductivity, a high absorption coefficient (greater than 10 4 cm -1 ) and an energy band gap Eg of about 1.37 eV, indicating that this compound has good properties to perform as absorbent layer in single junction thin film and tandem solar cells. The effect of the deposition conditions on the optical, structural and morphological properties was also investigated through spectral transmittance and XRD (X-ray diffraction) measurements.
Multi-Model Smith Predictor Based Control of Multivariable Systems with Uncertain Bounded External Delayshttp://hdl.handle.net/20.500.12010/281202022-09-16T17:05:50ZMulti-Model Smith Predictor Based Control of Multivariable Systems with Uncertain Bounded External Delays
One of the drawbacks of the Smith Predictor (SP) to control systems with external point delays is that its performance is strongly influenced by the knowledge of the time delay of the plant. Hence, as the mismatch between the actual delay of the plant and the nominal one used in the control structure increases, the closed-loop performance degrades accordingly, even potentially causing instability. This effect is particularly important when dealing with multivariable systems, where there is a coupling between input and output variables. In this paper, an intelligent frame to reduce the dasiaa priori' knowledge of the plant delays required in the design of SP controllers for multivariable systems is proposed. The intelligent frame is composed of a set of different plant delay models running in parallel along with a high level supervision algorithm which selects the one that best describes the actual delay of the plant at each time interval to be used for control purposes. In this way, the designer can design the control of the system based on its delay-free part while the appropriate tuning of the delay of the Smith Predictor is performed by the intelligent supervisor. As a consequence, like simulation examples show, the closed-loop performance of the system is improved without the dasiaa priori' requirement of an accurate knowledge of the value for the time delay.
Por qué razones distintas a la filiación política nos matábamos los colombianos en los años 50?http://hdl.handle.net/20.500.12010/281192022-09-16T16:57:57ZPor qué razones distintas a la filiación política nos matábamos los colombianos en los años 50?
Durante la Violencia en Colombia la gran prensa fue vocera de los partidos liberal y conservador. Sucesos, un semanario que no declaró filiación política alguna, registró a través de las crónicas de crímenes pasionales razones de género para asesinar, legitimadas por la cultura y legisladas por el código penal de 1936. Las creencias y los valores relacionados con lo que la sociedad esperaba que hicieran los hombres y las mujeres se descubren como la principal respuesta a la pregunta de investigación. Acaso, estas razones ¿están vigentes?
Population Size-Structure of the Reef-Coral Montastraea Annularis in Two Contrasting Reefs of a Marine Protected Area in the Southern Caribbean Seahttp://hdl.handle.net/20.500.12010/281182022-09-16T16:49:47ZPopulation Size-Structure of the Reef-Coral Montastraea Annularis in Two Contrasting Reefs of a Marine Protected Area in the Southern Caribbean Sea
The decline of Montastraea annularis (Ellis and Solander, 1786) in Caribbean coral communities has been documented, however, studies of its population structure are scarce. Colony size provides information about longevity of the sexual individual in the habitat and the effect of the environment on its survival, while ramet size reflects the effect of accumulated partial mortality in recent years and the contribution of gametes from each asexual individual. We studied the size-structure of two contrasting populations of M. annularis (degraded and less-degraded reef) in a Marine Protected Area in Cartagena, Colombia, to evaluate its current state and infer its persistence in the future. Colony size frequency distribution of 102 colonies and 9646 ramets on a logarithmic scale was negatively skewed in both populations, but larger colonies were found in the less-degraded reef. Ramet size frequency distribution was positively skewed and dominated by individuals smaller than 50 cm2 (∼76% in the degraded vs 57% in the less-degraded reef). Partial and total mortality differed between the populations (27% vs 16%; 10% vs 16%, respectively). Colony and ramet size in the degraded reef were smaller due to greater partial mortality and fission. In conclusion, large, old colonies are present in both populations, but experience high partial mortality that causes high fission rates and therefore a dominance of small, non-reproductive ramets. This condition, coupled with the lack of recruitment of sexual individuals, is evidence of decline in both populations, especially in the degraded reef where mortality was higher and ramets were smaller.