Tunable integrated radio frequency active resonators.

Los avances en las comunicaciones celulares y su difundido uso han impulsado a los fabricantes de transceptores de radiofrecuencia a integrar sus productos y a disminuir el número de componentes fuera del chip. Además, la proliferación de diferentes estándares para sistemas de radiofrecuencia motiva la realización de diseños flexibles en los que un mismo circuito puede ser utilizado para diferentes esquemas de comunicación. En este contexto, los inductores activos constituyen una herramienta atractiva para la configuración del hardware en tiempo real. Un inductor activo es un circuito sin inductores cuya impedancia vista de pequeña señal, en uno de sus puertos, es inductiva. Generalmente ocupa mucho menos área que su equivalente pasivo y ofrece posibilidad de sintonización. Las principales desventajas son el rango lineal limitado, el consumo de energía adicional y el ruido generado por el circuito. En esta tesis los resonadores activos –construidos con inductores activos– son presentados en varios niveles. Partiendo de la motivación, la necesidad del girador como núcleo del resonador activo se convierte en algo natural. A partir de una definición generalizada del girador, pasando por el concepto de resonador activo ideal, este trabajo desarrolla el modelo de resonador activo perfecto como un primer paso, que incorpora la conductancia de salida de los transconductores, y un modelo de resonador activo completo como una aproximación más precisa que también tiene en cuenta los efectos capacitivos de entrada-salida de los dispositivos. En el desarrollo del modelo se introdujeron definiciones clave y se obtuvieron algunos resultados novedosos. Este trabajo propone un factor de calidad del girador y muestra su relevancia en los diseños de resonadores activos (AR); limita, bajo ciertos supuestos, el máximo factor de calidad que el resonador activo puede alcanzar. También se analizan las relaciones de compromiso entre el ruido, la linealidad y el consumo de energía, y se contrastan con simulaciones. El modelo de resonador activo perfecto ha demostrado ser muy potente para diseñar, analizar y comparar cualitativamente arquitecturas de resonadores activos, mientras que el modelo más completo brinda resultados precisos para realizar análisis computacional. Por último, una de las arquitecturas estándar se probó en un diseño global de un amplificador de bajo ruido (LNA), colocándolo como etapa de entrada, proporcionando una red de adaptación sintonizable. Se demostró que los resultados del modelo siguen siendo válidos en este diseño completo que incorpora el transistor del LNA y las fuentes de corriente reales.The progress in cellular communications and its spread applications have propelledmanufacturers of transceivers to integrate their products and decrease the number ofoff-chip components. Also, the proliferation of different standards of radio frequencysystems motivates flexible designs in which the same circuit could be suitable for dif-ferent communication schemes. In this context, active inductors become an attractivetool for real-time hardware customization.An active inductor is an inductorless circuit whose small signal impedance, atone of its ports, is inductive. Generally, it occupies much less area than its passivecounterpart, and offers tunability. The principal disadvantages are the limited linearrange, the additional power consumption and the noise generated by the circuit.In this thesis, active resonators—built with active inductors—were presented inseveral levels. Starting from the motivation, the need of the gyrator as the activeresonator core becomes natural. From a generalized gyrator definition, passing throughtheideal active resonatorconcept, this work develops theperfect active resonator modelas a first step model which incorporates the output conductance of transconductors,and acomplete active resonator modelas a more accurate approach which also takesinto account the input-output capacitive effects of the devices.In the model development, key definitions were introduced, and some novel resultswere achieved. This work proposes agyrator quality factorand proves its relevance inthe active resonator (AR) designs; it limits, under certain assumptions, the maximumactive resonator quality factor that can be achieved. The trade-offs between noise,linearity and power consumption are also analysed and contrasted with simulations.Theperfect active resonator modelproved to be very powerful to design, analyseand compare qualitatively active resonator architectures, while the more completemodel gives accurately results when performing computational analysis.Finally, one of the standard architectures was proven in an overall design of a lownoise amplifier (LNA) as its input stage, providing a tunable matching network. It isshown that the model results are still valid in this complete design that incorporatesthe LNA core transistor and real current sources.Beca de Maestría ANI

RELATIONSHIPS BETWEEN COGNITIVE ABILITIES AND PATTERNS OF CHILDREN’S CLASSROOM BEHAVIOR AT AGE NINE

Teacher reports are often used to indicate how well children perform in school and help clinicians identify behavioral problems, such as inattentiveness (Charach et al., 2009). However, various factors may have an effect on teacher ratings of children’s behavior, which can have downstream effects on children’s academic achievement (Teisl et al., 2001). Given teachers play a large role in identifying at-risk youth, it is important to understand how their reports of children’s behavior are associated with childhood outcomes such as cognitive development, which is closely tied to academic achievement (Metcalfe et al., 2013). The present study aimed to identify patterns of children’s behavior based on teacher report data, as well as test whether these patterns were associated with five domains of cognitive functioning. We hypothesized that there would be one low-risk pattern of behavior that would include children exhibiting low levels of behavioral issues, and moderate- to high-risk patterns that would include children with varying degrees of behavioral issues. We expected that children with greater performance across the cognitive domains would be more likely to exhibit the low-risk pattern of behavior compared to the moderate- and high-risk patterns of behavioral issues. Analyses were performed with data from wave 5 of the Future of Families and Child Wellbeing study (N=2063). Latent class analysis revealed seven classes, with one low-risk class and six classes of varying risk level. Better performance on reading comprehension and mathematics assessments was associated with a greater likelihood of belonging to the low-risk class, even when controlling for significant demographic constructs. The present study suggests that teachers’ reports of children’s problematic classroom behavior may be useful for identifying children at risk for poor academic outcomes, leading to early intervention

Livestock research for development in a complex, messy world: Reflections on a decade of work for ILRI

On 9 and 10 November 2011, the ILRI Board of Trustees hosted a 2‐day ‘liveSTOCK Exchange’ to discuss and reflect on livestock research for development. During the workshop, Carlos Seré, former Director General of ILRI reflected on his tenure

Agricultural biotechnology for poverty alleviation: one more arrow in the quiver!

Agriculture is the largest contributor to the economies of many African countries, generating more than half of the annual Gross Domestic Product (GDP) for many of these countries. The livelihoods of most rural and low-income communities in these countries are to a large extent based on agriculture. While global availability of food has increased, 35% of the 800 million poor of the world live in Africa, and face food insecurity. And yet agriculture constitutes, for the majority of these poor, the primary means of survival and livelihood sustenance. Agricultural biotechnology, which comprises a wide range of biological disciplines, offers enormous potential to speed up the development of plant varieties with pro-poor traits such as drought tolerance, pest resistance or tolerance, higher yields, increased nutritional value, among others. Similarly in animal production there is substantial opportunity for development of vaccines and diagnostics targeting diseases which constrain livestock production in developing regions of the world. In addition, genetic markers can aid breeding of livestock for important traits such as disease resistance, improved product quality as well as improved productivity. However, to date, the innovation essential to achieve these improvements has largely remained a technology of the North. While biotechnology does not provide the ‘silver bullet’ for poverty alleviation, it does enhance the effectiveness of other disciplines such as plant breeding, integrated pest and nutrient management, and livestock breeding, feeding and disease management. Importantly, because use of these technologies, as any other, is associated with risks, African scientists need to have access to the knowledge and scientific infrastructure to assess these risks and to contribute to better informed public discussions of the opportunities and challenges of these technologies. Should biotechnology be a preserve for the rich? Can developing nations afford to ignore the potential of biotechnology? Rather than debate on whether biotechnology can meet the needs of the poor, this paper argues that being just one aspect of a complex set of inter-related interventions required to enhance the contribution of agricultural development to poverty alleviation, discussions should be had on how best to take advantage of the opportunities and manage the risks associated with these technologies, for the benefit of the poor. There is need to explore new ways to build the capacity of the public sector - notably national governments in developing countries and development partners, as well as to tap into the resources of the private sector - to enable the continent come up with African solutions to the problem of poverty alleviation. This will require closer collaboration and transfer, between the North and the South, of appropriate biotechnology and the management of bio-safety issues. Thus, risk assessment has to be an integral part of biotechnology research and development. Africa missed out on the ‘Green revolution’, and should not miss out on the ‘Gene revolution’ as well

A neural network which computes the square root

AbstractA model for neural network is presented in which the steady state firing frequency of a neuron is related to the amount of feedback in the network. One such network is shown to compute the square root function of the input to the network