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Synthesis and new properties of nanostructured zinc oxide, carbon and other layered materials.
No full textTesis (Doctorado en Nanociencias y Materiales)"Existe una gran expectativa de que la Nanotecnologia impacte de manera positiva la calidad de vida a través de las nuevas aplicaciones que se deriven de esta.Dichas aplicaciones estarán basadas en fenómenos y características de los materiales que sólo es posible encontrar a escalas nanométricas. Quizas las más importantes aplicaciones sean en 1) medicina, desde mejores herramientas de diagnóstico, hasta mejores medicinas con blancos específicos y hechas a la medida; 2) en problemas de alto impacto social,como remediación de agua, aire y suelo; 3) en materiales para fuentes alternas de energía; y 4) en la industria de semiconductores para sostener la llamada Ley de Moore del escalamiento del tamaño y la capacidad de los elementos de procesamiento.en este trabajo de tesis se han atendido problemas específicos que de alguna u otra manera contribuyen al desarrollo de las aplicaciones esperadas de la Nanotecnologia. En particular,se ha contribuido al desarrollo de dos áreas principalmente: 1) la ciencia del óxido de zinc a nanoescala, y 2) la ciencia del carbono a nanoescala. El carbono, sin lugar a dudas, es el material que más ha sido estudiado en el área de Nanociencias y Nanotecnología, debido, en parte, a la flexibilidad de su química. Tal vez, el segundo material más estudiado es el óxido de zinc (ZnO). Esto es debido a la combinación de sus propiedades: es un semiconductor de brecha prohibida ancha con propiedades ópticas interesantes; presenta propiedades mecánicas interesantes; y es, en principio, un material inofensivo para la salud humana y para el medio ambiente. En este trabajo se optimizó la síntesis de nanoestructuras de ZnO en una dimensión utiliznado un método limpio de baja temperatura y de bajo costo. Esta técnica de síntesis y este material se utilizó para hacer un compósito de ZnO con celulosa, de cual se investigaron sus propiedades piezoeléctricas y piroeléctricas. Los dispositivos construidos a partir de este material compósito son capaces de generar energía eléctrica cuando se someten a excitación mecánica por medio de ondas ultrasónicas, o a gradientes de temperatura.""Nanotechnology is espected to impact the quality of life through many of the novel applications that it will enable. These applications will take advantage of features that are only feasible at the nanoscale. The most important applications are in medicine from better tools for diagnosis, to improved, customΙmade, and specifically targeted drugs; in problems of high social impact such as water, air and soil remediation, and alternative sources of renewable energy; and in the semiconductor industry to try to keep up with the soΙcalled Moore´s Law of the scaling of the size and power of processing units. In this Thesis work we have addressed punctual problems that in some way or another try to contribute to the development of the expected applications of nanotechnology. In particular, we have contributed to the development of mainly two areas: 1) nanoscale !inc oxide science, and Β) nanoscale carbon science. Carbon is, without a doubt, the material which has the most intense research activity in nanoscience and nanotechnology, because of its flexible chemistry. The second most studied material in nanoscience and nanotechnology is probably zinc oxide (ZnO). This is due to the combination of mainly three facts: it is a wide band gap semiconductor with interesting optical properties; it has interesting mechanical properties; and it is, in principle, innocuous to human health and to the environment. We optimi!ed a method for the synthesis of ZnO nanorods using a low temperature, low cost and clean approach. We used this material to make a composite with cellulose and probed its pie!oelectric and pyroelectric response. The constructed devices are capable of generating electricitt when excited with ultrasonic waves or temperature gradients. Through first principles calculations, we have contributed to the understanding of ferromagnetism in non-doped ZnO and in ZnO doped with nonΙmagnetic atoms; Our results suggest that the observed properties are very sensitive to the environment of the atoms at the surface.
Bounded positive control for double-pipe heat exchangers
Get PDF"In this work, an outlet temperature control scheme for double-pipe heat exchangers is proposed. Compared to previously proposed approaches, the algorithm developed here takes into account and actually exploits the analytical and stability properties inherent to the open-loop dynamics. As a result, outlet temperature regulation is achieved through a simple controller which does not need to feed back the whole state vector and does not depend on the exact value of the process parameters. Moreover, the proposed approach guarantees positivity and boundedness of the input flow rate without entailing a complex control algorithm. The analytical developments are corroborated through simulation and experimental results.
Design of graphene electronic devices using nanoribbons of different widths
Get PDF"We present a simple design of a field effect transistor based on graphene nanoribbons, taking advantage of the metallic and semiconductor nature of nanoribbons with different widths. Such device could be constructed by using lithography techniques. The conductance of the proposed device is obtained by using the Kubo formula, assuming a strong damping due to the substrate and imperfections of the lattice. By removing the control electrodes, the design could also be used as an electrical resistance.
On modeling and control of multilevel converters and PLL algorithms.
Get PDFTesis (Doctorado en Control y Sistemas Dinámicos)"The present thesis is focuses in the study of the multilevel converters and the the phaselocked loop algorithms. In the first five chapters, two of the main topologies of multilevel converters are studied, namely, diode clamped multilevel converter (NPC) and cascaded H-bridge multilevel converter (HB). First, a model is obtained that described the dynamics of the three level NPC converter used in a synchronous rectifier application. The highly nonlinear model, originally in abc-coordinates, is also expressed in its ®¯°-coordinates. Special attention is given to the °-component of the control input, which represents a degree of freedom crucial for the balancing of the capacitors voltages. Then, based on this model, it is presented an adaptive controller that guarantees regulation and balance of the output capacitors voltages, as well as a close to unity power factor. Next, the modeling and the control design processes are presented for a cascade H-bridge single-phase multilevel converter used as a shunt active filter. Crucial for the developments is the transformation of the model in terms of the sum and the difference of the squares of the capacitors voltages. Moreover, it is shown that, while the current tracking problem and the regulation problem depend on the sum of the injected voltages, the balance depends on the difference between them. It is also presented a controller for the cascade H-bridge three-phase multilevel converter used as a shunt active filter. Based on the proposed mathematical model, the controller is designed to compensate harmonic distortion and reactive power due to a nonlinear distorting load. Simultaneously, the controller guarantees regulation and balance of all capacitor voltages. The idea behind the controller is to allow distortion of the current reference during the transients to guarantee regulation and balance of the capacitors voltages. The chapters 6 and 7 of the thesis deals with the design of phase-locked loop (PLL) algorithms. Although PLLs have been widely used in many electronic applications, the PLL presented here is of special interest in the synchronization of power electronic equipment coupled with the electric network. In particular, the presented PLL has been designed to work in fixed reference frame coordinates, and thus the proposed algorithm is referred as fixed reference frame PLL (FRF-PLL).
Effect of seed density on germination of Isolatocereus dumortieri and Myrtillocactus geometrizans, endemic columnar cacti species from Mexico
Get PDF"Se evaluó el efecto de la densidad de semillas en la germinación de 2 cactáceas columnares: Isolatocereus dumortieri y Myrtillocactus geometrizans. Se utilizaron 5 tratamientos de densidad de semillas (1, 5, 10, 20 y 50 semillas). Isolatocereus dumortieri mostró menor porcentaje de germinación con el aumento de la densidad, mientras que la germinación de M. geometrizans no fue afectada por la densidad de semillas. Estos resultados sugieren que las plántulas de I. dumortieri podrían competir por recursos.""The effect of seed density on the germination of 2 columnar cactus species (Isolatocereus dumortieri and Myrtillocactus geometrizans) was evaluated using 5 seed density treatments (1, 5, 10, 20 and 50 seeds). Isolatocereus dumortieri had a lower germination percentage with increasing seed density; germination of M. geometrizans was not affected by seed density. These results suggest that I. dumortieri seedlings might compete for resources with siblings.
An amplitude-phase (Ermako-Lewis) approach for the Jackiw-Pi model of bilayer graphene
Get PDF"In the context of bilayer graphene we use the simple gauge model of Jackiw and Pi to construct its numerical solutions in powers of the bias poten-tial V according to a general scheme due to Kravchenko. Next, using this numerical solutions, we develop the Ermakov-Lewis approach for the same model. This leads us to numerical calculations of the Lewis-Riesenfeld phases that could be of forthcoming experimental interest for bilayer graphene. We also present a generalization of the Iofe-Korsch nonlinear Darboux transformation.
A simple electronic circuit realization of the tent map
Get PDF"We present a very simple electronic implementation of the tent map, one of the best-known discrete dynamical systems. This is achieved by using integrated circuits and passive elements only. The experimental behavior of the tent map electronic circuit is compared with its numerical simulation counterpart. We find that the electronic circuit presents fixed points, periodicity, period doubling, chaos and intermittency that match with high accuracy the corresponding theoretical values.
Raman spectroscopy study of heat-treated and boron-doped double wall carbon nanotubes
Get PDF"We performed Raman spectroscopy experiments on undoped and boron-doped double walled carbon nanotubes (DWNTs) that exhibit the "coalescence inducing mode" as these DWNTs are heat treated to temperatures between 1200 C and 2000 C. The fact that boron doping promotes DWNT coalescence at lower temperatures allowed us to study in greater detail the behavior of first- and second-order Raman modes as a function of temperature with regard to the coalescence process. Furthermore, by using various excitation laser energies we probed DWNTs with different metallic (M) and semiconducting (S) inner and outer tubes. We find that regardless of their M and S configurations, the smaller diameter nanotubes disappear at a faster rate than their larger diameter counterparts as the heat treatment temperature is increased. We also observe that the frequency of the G band is mostly determined by the diameter of the semiconducting layer of those DWNTs that are in resonance with the laser excitation energy. Finally, we explain the contributions to the G' band from the inner and outer layers of a DWNT.
Generalizing segregation and chemical ordering in bimetallic nanoclusters through atomistic view points
Get PDF"We predict general trends for surface segregation in binary metal clusters based on the difference between the atomic properties of the constituent elements. The energetically most favorable site for a guest atom on a pure metal cluster is determined considering the attractive and repulsive contributions of the cohesive energy of an atom in the cluster. It is predicted that for adjacent elements in a period of the periodic table, the bimetallic system would be more stable if the component with smallest valence electron density is placed on the surface. On the other hand, in bimetallic clusters built with elements of only one group, the trend to be in the volume (of the atomic component with smaller core density) will be higher for that cluster with atomic components most separated in the group. Such chemical ordering trends in the lowest energy configurations of Pt-Au, Pt-Pd, and Pt-Ni binary alloy clusters are verified for their 561 atom systems through a simulated annealing process. Some of our atomistic predictions are verified through quantum mechanical calculations.
Human papillomavirus type 16 variants in cervical intraepithelial neoplasia and invasive carcinoma in San Luis Potosí City, Mexico
Get PDF"Background In San Luis Potosí City cervical infection by human papillomavirus type 16 (HPV16) associated to dysplastic lesions is more prevalent in younger women. In this work HPV16 subtypes and variants associated to low-grade intraepithelial lesions (LSIL), high-grade intraepithelial lesions (HSIL) and invasive cervical cancer (ICC) of 38 women residing in San Luis Potosí City were identified by comparing their E6 open reading frame sequences. Results Three European (E) variants (E-P, n = 27; E-T350G, n = 7; E-C188G, n = 2) and one AA-a variant (n = 2) were identified among the 38 HPV16 sequences analyzed. E-P variant sequences contained 23 single nucleotide changes, two of which (A334G, A404T) had not been described before and allowed the phylogenetic separation from the other variants. E-P A334G sequences were the most prevalent (22 cases, 57.9%), followed by the E-P Ref prototype (8 cases, 21.1%) and E-P A404T (1 case, 2.6%) sequences. The HSIL + ICC fraction was 0.21 for the E-P A334G variants and 0.00 for the E-P Ref variants. Conclusion We conclude that in the women included in this study the HPV16 E subtype is 19 times more frequent than the AA subtype; that the circulating E variants are E-P (71.1%) > E-T350G (18.4%) > E-C188G (5.3%); that 71.0% of the E-P sequences carry the A334G single nucleotide change and appear to correspond to a HPV16 variant characteristic of San Luis Potosi City more oncogenic than the E-P Ref prototype.