Optimizing rabbit production under heat stress: cage density and cage size during fattening, and breeding system and water quality on rabbit does

The aim of this work was to evaluate different management strategies to optimize rabbit production under chronic heat stress. To achieve it, three trials were conducted. In the first trial, to find the optimal cage density in tropical very dry forest condition, were measured growth performance, mortality rate, injured animals and carcass performance over an initial population of 300 cross-breed rabbits of New Zealand, California, Butterfly, Dutch and Satin, weaned at 30 days (535 ± 8 g, standard error). Treatments evaluated were: 6, 12, 18 and 24 rabbits/m2 (3, 6, 9 and 12 rabbits/cage, respectively, each cage of 0.5 m2). The maximal temperature-humidity index indicated a severe heat stress from weaning to 2.2 kg body weight (experimental time). At the end of experimental period 10, 20, 30 and 30 rabbits from the treatments of 6, 12, 18 and 24 rabbits/m2, respectively, were slaughtered and carcass performance recorded. Average daily gain and feed intake decreased by 0.31 ± 0.070 and 1.20 ± 0.25 g, respectively, per each unit that the density increased at the beginning of the experiment (P = 0.001). It increased the length of the fattening period by 0.91 ± 0.16 d (P = 0.001) per each unit of increment of density. However, rabbit production (kg/m2) increased linear and quadratically with the density (P < 0.008). Animals housed at the highest density compared to the lower one tended to show a higher incidence of ringworm (68.9 vs 39.4%; P = 0.075), injured animals (16.8 vs 3.03%; P = 0.12) and mortality (20.5 vs 9.63%; P = 0.043). The proportion of scapular fat (P = 0.042) increased linearly with increasing levels of density. Increasing density reduced linearly dorsal length (P = 0.001), and reduced linear and quadratically drip loss percentage (P = 0.097 and 0.018, respectively). In the second trial, 46 nulliparous rabbit does (23 clipped and 23 unclipped) with a BW of 3.67 ± 0.05 kg (s.e.) were used to evaluate heat stress and circadian rhythms comparing unclipped and clipped rabbit does, and to study if a more extensive breeding system increase litters performance at weaning without impairing rabbit doe performance,. Rectal temperature, feed and water 4 intake were recorded for 24 h. Rabbit does were mated 7 d after circadian measurements, and randomly assigned to two breeding systems. Control (C): mated at 14 d after parturition + litter weaned at 35 d of age. Extensive (E): mate at 21 after parturition + litter weaned at 42 d of age. The first three cycles were evaluated concerning to rabbit doe and litter performance. Two hundred twenty eight weaned rabbits, were divided into two cage sizes: 0.5 and 0.25 m2 with same density (16 rabbit/m2) and growing performance was recorded. Farm and rectal temperatures were minimal and feed and water intake maximal during the night (P < 0.001). Unclipped rabbit does showed higher rectal temperature (P = 0.045) and lower feed intake respect to clipped does (P = 0.019) which suggest a lower heat stress in the latter. Kits weaned per litter was reduced by 33% (P=0.038) in C group. This reduction was more important in the 2nd and 3rd cycles compared to the first (P ≤ 0.054). Rabbit doe feed efficiency tended to decrease in E respect C group (P = 0.093), whereas it was impaired from the first to the third cycle by 48% (P = 0.014). Growing rabbits from the E group were heavier at weaning (by 38%. P < 0.001), showed a higher feed intake (+7.4%) and lower feed efficiency (-8.4%) throughout the fattening period (P ≤ 0.056) respect to C group. Cage size had minor influence in growing performance. In the third trial, forty five non pregnant and non lactating rabbit does (21 nulliparous and 24 multiparous) were assigned randomly to farm water and to potable water to study if a water quality improvement can affect positively rabbit doe response to heat stress during pregnancy and lactation. A transponder was implanted in each animal to record subcutaneous temperature at 07:30 and 14:30 h. Experimental period extended from pregnancy (with no lactation) to the next lactation (until day 28). Body temperature and milk production were recorded daily, and body condition, feed and water intake weekly. Water quality did not affect any trait (P ≥ 0.15). Pregnant rabbit does were classified as does that weaned (W: 47%), not weaned (NW: 44%) or those pregnant that did not deliver (NB: 9%). Body temperature and feed intake decreased during pregnancy (P ≤ 0.031), but water intake remained constant. In this period body temperature decreased with metabolic weight (P ≤ 0.009). In W and NW does, 5 from mating to birth energy and protein balance impaired (P≤0.011). Body temperature of W does tended to be the lowest (P ≤ 0.090). Pregnancy length and total number of kits born tended to be longer and higher in NW than in W does (P = 0.10 and 0.053, respectively). Kit mortality at birth and from birth to 14 d of lactation was high, being worse for NW than for W does (97 vs. 40%; P<0.001). Body temperature during lactation was maximal at day 12, and milk production increased it (P ≤ 0.025). . In conclusion, in our heat stress conditions densities higher than 18 rabbits/m2 (34 kg/m2) at the end of fattening, are not recommended despite cage size, gestation and lactation productivity impaired not only when lactation is extended and along successive reproductive cycles but also due to a reduced embryo/kit survival and finally water quality improvement did not attenuate negative effect of heat stress. RESUMEN El propósito de éste trabajo fue evaluar diferentes estrategias de manejo para optimizar la producción de conejos bajo estrés térmico. Para lo cual se desarrollaron tres experimentos. En el primer experimento, para encontrar el número óptimo de gazapos por m2 de jaula durante el cebo en condiciones de bosque muy seco tropical, se estudiaron los rendimientos durante el cebo, mortalidad, animales lesionados y rendimiento de la canal sobre una población inicial de 300 conejos mestizos de Nueva Zelanda, California, Mariposa, Holandés y Satin, destetados a los 30 días de edad (535 ± 8g, error estándar). Los tratamientos evaluados fueron: 6, 12, 18 y 24 conejos/m2 (3, 6, 9 y 12 conejos/jaula, respectivamente, en jaulas de 0.5 m2). Durante el período experimental (destete a 2.2 kg de peso vivo), se observaron valores de THI correspondientes con un estrés térmico severo (THI max. De 31 a 35). Al final del período experimental, 10, 20, 30, y 30 conejos de los tratamientos con densidades de 6, 12, 18 y 24 conejos/m2, respectivamente, fueron sacrificados y su canal fue valorada. El promedio de la ganancia diaria y el consumo de alimento disminuyeron en 0.31 ± 0.070 y 1.20 ± 0.25 g, respectivamente, por cada unidad de incremento en la densidad al inicio del experimento (P=0.001). Esto alargó el período de engorde en 0.91 ± 0.16 d (P=0.001) por cada unidad de incremento de la densidad. Sin embargo, la producción de conejos (kg/m2) aumentó lineal y cuadráticamente con la densidad (P<0.008). Los animales alojados en las mayores densidades en comparación con el resto tendieron a mostrar una mayore incidencia de tiña (68.9 vs 39.4%; P=0.075), de cantidad de animales heridos (16.8 vs 3.03%; P=0.12), así como de mortalidad (20.5 vs 9.63%; P=0.043). El aumento en la densidad aumentó linealmente la proporción de grasa escapular (P=0.042) y redujo linealmente la longitud dorsal (P=0.001), y lineal y cuadráticamente el porcentaje de pérdida por goteo (P=0.018). En el segundo experimento, 46 conejas nulliparas (23 rasuradas y 23 no rasuradas) con un peso vivo de 3.67 ± 0.05 kg (e.e.) fueron usadas para evaluar el estrés 8 térmico y los ritmos circadianos comparando conejas rasuradas o no, y estudiar si un sistema de crianza más extensivo mejora el desempeño de la camada al destete sin perjudicar la productividad de la coneja. Durante 24 h se midió la temperatura rectal, consumo de alimento y de agua. Las conejas fueron montadas 7 días después, y distribuidas en dos sistemas de crianza. El control (C): monta a 14 días posparto y destete a 35 d de edad. El extensivo (E): monta a 21 días posparto y destete a 42 d de edad. Se controló la productividad de la coneja y la camada durante los tres primeros ciclos. Doscientos veintiocho gazapos fueron distribuidos en dos tamaños de jaulas (0.5 y 0.25 m2) con la misma densidad (16 conejos/m2) y se controlaron sus rendimientos productivos. Durante la noche se observaron los valores mínimos para la temperatura ambiental y rectal, y los máximos para consumo de alimento y agua (P< 0.001). Las conejas no rasuradas mostraron mayor temperatura rectal (P=0.045) y menores valores de consumo de alimento con respecto a las conejas rasuradas (P=0.019), lo que sugiere un menor estrés térmico en las últimas. El número de gazapos destetados por camada se redujo en 33% (P=0.038) en el grupo C. Este comportamiento se acentuó en el 2do y 3er ciclo en comparación con el primero (P≤0.054). La eficiencia alimenticia de las conejas tendió a disminuir en el grupo E con respecto al grupo C (P=0.093), dicha tendencia se acentúa del primer al tercer ciclo en un 48% (P=0.014). Los gazapos en fase de crecimiento provenientes del grupo E fueron más pesados al momento del destete (en 38% P<0.001), mostrando un mayor consumo de alimento (+7.4%) y menor eficiencia alimenticia (-8.4%) a lo largo del engorde (P≤0.056) con respecto al grupo C. El tamaño de la jaula tuvo una mínima influencia en el comportamiento durante el crecimiento de éstos gazapos. En el tercer experimento, cuarenta y cinco conejas no gestantes ni lactantes (21 nulíparas y 24 multíparas) se les asignó al azar agua dos tipos de agua: común de la granja y agua potable, con el fin de estudiar si una mejora en la calidad del agua puede afectar positivamente la respuesta de la coneja al estrés térmico durante la gestación y la lactancia. Se les implantó un transponder para registrar la temperatura subcutánea a las 7:30 y a las 14:30 h. El período experimental se extendió desde la gestación (sin 9 lactancia) hasta la lactanción consecutiva (hasta los 28 días). La temperatura corporal y la producción de leche se controlaron diariamente, y la condición corporal, consumo de agua y alimento, semanalmente. La calidad del agua no afectó a ninguna variable (P≥0.15). Las conejas preñadas fueron clasificadas como conejas que destetaron (W: 47%), que no destetaron (NW:44%) o aquellas que no parieron (NB: 9%). La temperatura corporal y consumo de alimento disminuyeron durante la gestación (P≤0.031), mientras que el consumo de agua se mantuvo constante. La temperatura corporal descendió con el peso metabólico durante la gestación (P≤0.009). El balance de energía y proteína disminuyó desde la monta al parto para las conejas W y NW (P≤0.011). Durante la gestación la temperatura corporal tendió a ser menor en las conejas W (P≤0.090). La longitud de la gestación y el número total de gazapos nacidos tendieron a ser mayores en conejas NW que en conejas W (P=0.10 y 0.053, respectivamente). La mortalidad de los gazapos al parto y del parto a los 14 días de lactancia fue alta, siendo peor para las conejas NW que para las W (97 vs 40%; P<0.001). Durante la lactancia la temperatura corporal alcanzó su valor máximo para el día 12, y la producción de leche indujo un incremento en la misma (P≤0.025). En conclusión, en nuestras condiciones de estrés térmico y sin importar el tamaño de la jaula, no se recomiendan densidades mayores a 18 conejos/m2 (34 kg/m2) al final del engorde. La productividad de la gestación y la lactancia disminuyen cuando la lactancia es mayor y se suceden varios ciclos reproductivos seguidos. Esto se debe al efecto negativo del estrés térmico sobre la vitalidad y supervivencia del embrión/gazapo. La mejora de la calidad del agua atenuó el efecto negativo del estrés térmico. Las conejas más productoras parece que son aquéllas que consiguen manejar mejor el estrés térmico.

Energy Analysis of Bare Electrodynamic Tethers

The design of an electrodynamic tether is a complex task that involves the control of dynamic instabilities, optimization of the generated power (or the descent time in deorbiting missions), and minimization of the tether mass. The electrodynamic forces on an electrodynamic tether are responsible for variations in the mechanical energy of the tethered system and can also drive the system to dynamic instability. Energy sources and sinks in this system include the following: 1) ionospheric impedance, 2) the potential drop at the cathodic contactor, 3) ohmic losses in the tether, 4) the corotational plasma electric field, and 5) generated power and/or 6) input power. The analysis of each of these energy components, or bricks, establishes parameters that are useful tools for tether design. In this study, the nondimensional parameters that govern the orbital energy variation, dynamic instability, and power generation were characterized, and their mutual interdependence was established. A space-debris mitigation mission was taken as an example of this approach for the assessment of tether performance. Numerical simulations using a dumbbell model for tether dynamics, the International Geomagnetic Reference Field for the geomagnetic field, and the International Reference Ionosphere for the ionosphere were performed to test the analytical approach. The results obtained herein stress the close relationships that exist among the velocity of descent, dynamic stability, and generated power. An optimal tether design requires a detailed tradeoff among these performances in a real-world scenario.

Leakage and temperature aware server control for improving energy efficiency in data centers

Reducing the energy consumption for computation and cooling in servers is a major challenge considering the data center energy costs today. To ensure energy-efficient operation of servers in data centers, the relationship among computa- tional power, temperature, leakage, and cooling power needs to be analyzed. By means of an innovative setup that enables monitoring and controlling the computing and cooling power consumption separately on a commercial enterprise server, this paper studies temperature-leakage-energy tradeoffs, obtaining an empirical model for the leakage component. Using this model, we design a controller that continuously seeks and settles at the optimal fan speed to minimize the energy consumption for a given workload. We run a customized dynamic load-synthesis tool to stress the system. Our proposed cooling controller achieves up to 9% energy savings and 30W reduction in peak power in comparison to the default cooling control scheme.

Representing microstates of static granular matter in a stress phase space

A stress phase space is proposed to compare the static packings of a granular system (microstates) that are compatible to a macrostate described by external stresses. The equivalent stress of each particle of a static packing can be obtained from the mechanical interaction forces, and the associated volume is given by the respective Voronoi cell. Therefore, particles can be located at different stress levels and grouped into categories or configurations, which are defined in base of the geometrical features of the local arrangement (in particular, of the number of forces that keep them force-balanced). They can be represented as points in a stress phase space. The nature of this space is analyzed in detail. The integration limits of the stress variables that avoid or limit tensile states and the capability of each configuration to represent specific stress states establish its main features. Furthermore, if some stress variables are used, instead of the usual components of the Cauchy stress tensor, then some symmetries can be found. Results obtained from molecular dynamics simulations are used to check this nature. Finally, some statistical ensembles are written in terms of the coordinates of this phase space. These require some assumptions that are made in base on continuum mechanics principles.

Discontinuous solutions and boundary value problems for non-linearly elastic fibre-reinforced materials

En este trabajo se han analizado varios problemas en el contexto de la elasticidad no lineal basándose en modelos constitutivos representativos. En particular, se han analizado problemas relacionados con el fenómeno de perdida de estabilidad asociada con condiciones de contorno en el caso de material reforzados con fibras. Cada problema se ha formulado y se ha analizado por separado en diferentes capítulos. En primer lugar se ha mostrado el análisis del gradiente de deformación discontinuo para un material transversalmente isótropo, en particular, el modelo del material considerado consiste de una base neo-Hookeana isótropa incrustada con fibras de refuerzo direccional caracterizadas con un solo parámetro. La solución de este problema se vincula con instabilidades que dan lugar al mecanismo de fallo conocido como banda de cortante. La perdida de elipticidad de las ecuaciones diferenciales de equilibrio es una condición necesaria para que aparezca este tipo de soluciones y por tanto las inestabilidades asociadas. En segundo lugar se ha analizado una deformación combinada de extensión, inación y torsión de un tubo cilíndrico grueso donde se ha encontrado que la deformación citada anteriormente puede ser controlada solo para determinadas direcciones de las fibras refuerzo. Para entender el comportamiento elástico del tubo considerado se ha ilustrado numéricamente los resultados obtenidos para las direcciones admisibles de las fibras de refuerzo bajo la deformación considerada. En tercer lugar se ha estudiado el caso de un tubo cilíndrico grueso reforzado con dos familias de fibras sometido a cortante en la dirección azimutal para un modelo de refuerzo especial. En este problema se ha encontrado que las inestabilidades que aparecen en el material considerado están asociadas con lo que se llama soluciones múltiples de la ecuación diferencial de equilibrio. Se ha encontrado que el fenómeno de instabilidad ocurre en un estado de deformación previo al estado de deformación donde se pierde la elipticidad de la ecuación diferencial de equilibrio. También se ha demostrado que la condición de perdida de elipticidad y ^W=2 = 0 (la segunda derivada de la función de energía con respecto a la deformación) son dos condiciones necesarias para la existencia de soluciones múltiples. Finalmente, se ha analizado detalladamente en el contexto de elipticidad un problema de un tubo cilíndrico grueso sometido a una deformación combinada en las direcciones helicoidal, axial y radial para distintas geotermias de las fibras de refuerzo . In the present work four main problems have been addressed within the framework of non-linear elasticity based on representative constitutive models. Namely, problems related to the loss of stability phenomena associated with boundary value problems for fibre-reinforced materials. Each of the considered problems is formulated and analysed separately in different chapters. We first start with the analysis of discontinuous deformation gradients for a transversely isotropic material under plane deformation. In particular, the material model is an augmented neo-Hookean base with a simple unidirectional reinforcement characterised by a single parameter. The solution of this problem is related to material instabilities and it is associated with a shear band-type failure mode. The loss of ellipticity of the governing differential equations is a necessary condition for the existence of these material instabilities. The second problem involves a detailed analysis of the combined non-linear extension, inflation and torsion of a thick-walled circular cylindrical tube where it has been found that the aforementioned deformation is controllable only for certain preferred directions of transverse isotropy. Numerical results have been illustrated to understand the elastic behaviour of the tube for the admissible preferred directions under the considered deformation. The third problem deals with the analysis of a doubly fibre-reinforced thickwalled circular cylindrical tube undergoing pure azimuthal shear for a special class of the reinforcing model where multiple non-smooth solutions emerge. The associated instability phenomena are found to occur prior to the point where the nominal stress tensor changes monotonicity in a particular direction. It has been also shown that the loss of ellipticity condition that arises from the equilibrium equation and ^W=2 = 0 (the second derivative of the strain-energy function with respect to the deformation) are equivalent necessary conditions for the emergence of multiple solutions for the considered material. Finally, a detailed analysis in the basis of the loss of ellipticity of the governing differential equations for a combined helical, axial and radial elastic deformations of a fibre-reinforced circular cylindrical tube is carried out.

Use of the energy-release rate in a 2 scale damage analysis of a bonded joint

Stress singularities appear at the extremities of an adhesive bond. They can produce a damage mechanism that we assimilate in this Note to a crack. The energy release rate permits to characterize its evolution. But a very refined mesh would be necessary for a real structure. Using an asymptotic method based on the small thickness of the bond a limit model with a different local behaviour is suggested. It leads to an approximation of the energy release rate

Evaluation of the surface free energy of plant surfaces: toward standardizing the procedure

Plant surfaces have been found to have a major chemical and physical heterogeneity and play a key protecting role against multiple stress factors. During the last decade, there is a raising interest in examining plant surface properties for the development of biomimetic materials. Contact angle measurement of different liquids is a common tool for characterizing synthetic materials, which is just beginning to be applied to plant surfaces. However, some studies performed with polymers and other materials showed that for the same surface, different surface free energy values may be obtained depending on the number and nature of the test liquids analyzed, materials' properties, and surface free energy calculation methods employed. For 3 rough and 3 rather smooth plant materials, we calculated their surface free energy using 2 or 3 test liquids and 3 different calculation methods. Regardless of the degree of surface roughness, the methods based on 2 test liquids often led to the under- or over-estimation of surface free energies as compared to the results derived from the 3-Liquids method. Given the major chemical and structural diversity of plant surfaces, it is concluded that 3 different liquids must be considered for characterizing materials of unknown physico-chemical properties, which may significantly differ in terms of polar and dispersive interactions. Since there are just few surface free energy data of plant surfaces with the aim of standardizing the calculation procedure and interpretation of the results among for instance, different species, organs, or phenological states, we suggest the use of 3 liquids and the mean surface tension values provided in this study.

Analysis of thermo-mechanical stress effects on CPV receiver under high intensity light cycles

After construction of the LYSS (Light cYcling Stressing Source) in early 2014, several CPV receivers, with and without secondary optical element (SOE) have been aged under fast transient illumination cycling,. The test plan for Madrid consisted of 50000 cycles. Receivers with poor heat spreaders showed low reliability but those with thicker metal layers passed the test well. The operation of LYSS along 8 months, after more than 250000 cycles, did not show any significant failure, except lamp reposition every 120 hours, in average. The equipment seems valid for unveiling weak receiver designs with respect to intensive illumination, in steady and transient modes.

Output Impedance Correction Circuit (OICC): A New Concept to Improve the Dynamic Response of DC/DC Converters with Additional Energy Path

El desarrollo da las nuevas tecnologías permite a los ingenieros llevar al límite el funcionamiento de los circuitos integrados (Integrated Circuits, IC). Las nuevas generaciones de procesadores, DSPs o FPGAs son capaces de procesar la información a una alta velocidad, con un alto consumo de energía, o esperar en modo de baja potencia con el mínimo consumo posible. Esta gran variación en el consumo de potencia y el corto tiempo necesario para cambiar de un nivel al otro, afecta a las especificaciones del Módulo de Regulador de Tensión (Voltage Regulated Module, VRM) que alimenta al IC. Además, las características adicionales obligatorias, tales como adaptación del nivel de tensión (Adaptive Voltage Positioning, AVP) y escalado dinámico de la tensión (Dynamic Voltage Scaling, DVS), imponen requisitos opuestas en el diseño de la etapa de potencia del VRM. Para poder soportar las altas variaciones de los escalones de carga, el condensador de filtro de salida del VRM se ha de sobredimensionar, penalizando la densidad de energía y el rendimiento durante la operación de DVS. Por tanto, las actuales tendencias de investigación se centran en mejorar la respuesta dinámica del VRM, mientras se reduce el tamaño del condensador de salida. La reducción del condensador de salida lleva a menor coste y una prolongación de la vida del sistema ya que se podría evitar el uso de condensadores voluminosos, normalmente implementados con condensadores OSCON. Una ventaja adicional es que reduciendo el condensador de salida, el DVS se puede realizar más rápido y con menor estrés de la etapa de potencia, ya que la cantidad de carga necesaria para cambiar la tensión de salida es menor. El comportamiento dinámico del sistema con un control lineal (Control Modo Tensión, VMC, o Control Corriente de Pico, Peak Current Mode Control, PCMC,…) está limitado por la frecuencia de conmutación del convertidor y por el tamaño del filtro de salida. La reducción del condensador de salida se puede lograr incrementando la frecuencia de conmutación, así como incrementando el ancho de banda del sistema, y/o aplicando controles avanzados no-lineales. Usando esos controles, las variables del estado se saturan para conseguir el nuevo régimen permanente en un tiempo mínimo, así como el filtro de salida, más específicamente la pendiente de la corriente de la bobina, define la respuesta de la tensión de salida. Por tanto, reduciendo la inductancia de la bobina de salida, la corriente de bobina llega más rápido al nuevo régimen permanente, por lo que una menor cantidad de carga es tomada del condensador de salida durante el tránsito. El inconveniente de esa propuesta es que el rendimiento del sistema es penalizado debido al incremento de pérdidas de conmutación y las corrientes RMS. Para conseguir tanto la reducción del condensador de salida como el alto rendimiento del sistema, mientras se satisfacen las estrictas especificaciones dinámicas, un convertidor multifase es adoptado como estándar para aplicaciones VRM. Para asegurar el reparto de las corrientes entre fases, el convertidor multifase se suele implementar con control de modo de corriente. Para superar la limitación impuesta por el filtro de salida, la segunda posibilidad para reducir el condensador de salida es aplicar alguna modificación topológica (Topologic modifications) de la etapa básica de potencia para incrementar la pendiente de la corriente de bobina y así reducir la duración de tránsito. Como el transitorio se ha reducido, una menor cantidad de carga es tomada del condensador de salida bajo el mismo escalón de la corriente de salida, con lo cual, el condensador de salida se puede reducir para lograr la misma desviación de la tensión de salida. La tercera posibilidad para reducir el condensador de salida del convertidor es introducir un camino auxiliar de energía (additional energy path, AEP) para compensar el desequilibrio de la carga del condensador de salida reduciendo consecuentemente la duración del transitorio y la desviación de la tensión de salida. De esta manera, durante el régimen permanente, el sistema tiene un alto rendimiento debido a que el convertidor principal con bajo ancho de banda es diseñado para trabajar con una frecuencia de conmutación moderada para conseguir requisitos estáticos. Por otro lado, el comportamiento dinámico durante los transitorios es determinado por el AEP con un alto ancho de banda. El AEP puede ser implementado como un camino resistivo, como regulador lineal (Linear regulator, LR) o como un convertidor conmutado. Las dos primeras implementaciones proveen un mayor ancho de banda, acosta del incremento de pérdidas durante el transitorio. Por otro lado, la implementación del convertidor computado presenta menor ancho de banda, limitado por la frecuencia de conmutación, aunque produce menores pérdidas comparado con las dos anteriores implementaciones. Dependiendo de la aplicación, la implementación y la estrategia de control del sistema, hay una variedad de soluciones propuestas en el Estado del Arte (State-of-the-Art, SoA), teniendo diferentes propiedades donde una solución ofrece más ventajas que las otras, pero también unas desventajas. En general, un sistema con AEP ideal debería tener las siguientes propiedades: 1. El impacto del AEP a las pérdidas del sistema debería ser mínimo. A lo largo de la operación, el AEP genera pérdidas adicionales, con lo cual, en el caso ideal, el AEP debería trabajar por un pequeño intervalo de tiempo, solo durante los tránsitos; la otra opción es tener el AEP constantemente activo pero, por la compensación del rizado de la corriente de bobina, se generan pérdidas innecesarias. 2. El AEP debería ser activado inmediatamente para minimizar la desviación de la tensión de salida. Para conseguir una activación casi instantánea, el sistema puede ser informado por la carga antes del escalón o el sistema puede observar la corriente del condensador de salida, debido a que es la primera variable del estado que actúa a la perturbación de la corriente de salida. De esa manera, el AEP es activado con casi cero error de la tensión de salida, logrando una menor desviación de la tensión de salida. 3. El AEP debería ser desactivado una vez que el nuevo régimen permanente es detectado para evitar los transitorios adicionales de establecimiento. La mayoría de las soluciones de SoA estiman la duración del transitorio, que puede provocar un transitorio adicional si la estimación no se ha hecho correctamente (por ejemplo, si la corriente de bobina del convertidor principal tiene un nivel superior o inferior al necesitado, el regulador lento del convertidor principal tiene que compensar esa diferencia una vez que el AEP es desactivado). Otras soluciones de SoA observan las variables de estado, asegurando que el sistema llegue al nuevo régimen permanente, o pueden ser informadas por la carga. 4. Durante el transitorio, como mínimo un subsistema, o bien el convertidor principal o el AEP, debería operar en el lazo cerrado. Implementando un sistema en el lazo cerrado, preferiblemente el subsistema AEP por su ancho de banda elevado, se incrementa la robustez del sistema a los parásitos. Además, el AEP puede operar con cualquier tipo de corriente de carga. Las soluciones que funcionan en el lazo abierto suelen preformar el control de balance de carga con mínimo tiempo, así reducen la duración del transitorio y tienen un impacto menor a las pérdidas del sistema. Por otro lado, esas soluciones demuestran una alta sensibilidad a las tolerancias y parásitos de los componentes. 5. El AEP debería inyectar la corriente a la salida en una manera controlada, así se reduce el riesgo de unas corrientes elevadas y potencialmente peligrosas y se incrementa la robustez del sistema bajo las perturbaciones de la tensión de entrada. Ese problema suele ser relacionado con los sistemas donde el AEP es implementado como un convertidor auxiliar. El convertidor auxiliar es diseñado para una potencia baja, con lo cual, los dispositivos elegidos son de baja corriente/potencia. Si la corriente no es controlada, bajo un pico de tensión de entrada provocada por otro parte del sistema (por ejemplo, otro convertidor conectado al mismo bus), se puede llegar a un pico en la corriente auxiliar que puede causar la perturbación de tensión de salida e incluso el fallo de los dispositivos del convertidor auxiliar. Sin embargo, cuando la corriente es controlada, usando control del pico de corriente o control con histéresis, la corriente auxiliar tiene el control con prealimentación (feed-forward) de tensión de entrada y la corriente es definida y limitada. Por otro lado, si la solución utiliza el control de balance de carga, el sistema puede actuar de forma deficiente si la tensión de entrada tiene un valor diferente del nominal, provocando que el AEP inyecta/toma más/menos carga que necesitada. 6. Escalabilidad del sistema a convertidores multifase. Como ya ha sido comentado anteriormente, para las aplicaciones VRM por la corriente de carga elevada, el convertidor principal suele ser implementado como multifase para distribuir las perdidas entre las fases y bajar el estrés térmico de los dispositivos. Para asegurar el reparto de las corrientes, normalmente un control de modo corriente es usado. Las soluciones de SoA que usan VMC son limitadas a la implementación con solo una fase. Esta tesis propone un nuevo método de control del flujo de energía por el AEP y el convertidor principal. El concepto propuesto se basa en la inyección controlada de la corriente auxiliar al nodo de salida donde la amplitud de la corriente es n-1 veces mayor que la corriente del condensador de salida con las direcciones apropiadas. De esta manera, el AEP genera un condensador virtual cuya capacidad es n veces mayor que el condensador físico y reduce la impedancia de salida. Como el concepto propuesto reduce la impedancia de salida usando el AEP, el concepto es llamado Output Impedance Correction Circuit (OICC) concept. El concepto se desarrolla para un convertidor tipo reductor síncrono multifase con control modo de corriente CMC (incluyendo e implementación con una fase) y puede operar con la tensión de salida constante o con AVP. Además, el concepto es extendido a un convertidor de una fase con control modo de tensión VMC. Durante la operación, el control de tensión de salida de convertidor principal y control de corriente del subsistema OICC están siempre cerrados, incrementando la robustez a las tolerancias de componentes y a los parásitos del cirquito y permitiendo que el sistema se pueda enfrentar a cualquier tipo de la corriente de carga. Según el método de control propuesto, el sistema se puede encontrar en dos estados: durante el régimen permanente, el sistema se encuentra en el estado Idle y el subsistema OICC esta desactivado. Por otro lado, durante el transitorio, el sistema se encuentra en estado Activo y el subsistema OICC está activado para reducir la impedancia de salida. El cambio entre los estados se hace de forma autónoma: el sistema entra en el estado Activo observando la corriente de condensador de salida y vuelve al estado Idle cunado el nuevo régimen permanente es detectado, observando las variables del estado. La validación del concepto OICC es hecha aplicándolo a un convertidor tipo reductor síncrono con dos fases y de 30W cuyo condensador de salida tiene capacidad de 140μF, mientras el factor de multiplicación n es 15, generando en el estado Activo el condensador virtual de 2.1mF. El subsistema OICC es implementado como un convertidor tipo reductor síncrono con PCMC. Comparando el funcionamiento del convertidor con y sin el OICC, los resultados demuestran que se ha logrado una reducción de la desviación de tensión de salida con factor 12, tanto con funcionamiento básico como con funcionamiento AVP. Además, los resultados son comparados con un prototipo de referencia que tiene la misma etapa de potencia y un condensador de salida físico de 2.1mF. Los resultados demuestran que los dos sistemas tienen el mismo comportamiento dinámico. Más aun, se ha cuantificado el impacto en las pérdidas del sistema operando bajo una corriente de carga pulsante y bajo DVS. Se demuestra que el sistema con OICC mejora el rendimiento del sistema, considerando las pérdidas cuando el sistema trabaja con la carga pulsante y con DVS. Por lo último, el condensador de salida de sistema con OICC es mucho más pequeño que el condensador de salida del convertidor de referencia, con lo cual, por usar el concepto OICC, la densidad de energía se incrementa. En resumen, las contribuciones principales de la tesis son: • El concepto propuesto de Output Impedance Correction Circuit (OICC), • El control a nivel de sistema basado en el método usado para cambiar los estados de operación, • La implementación del subsistema OICC en lazo cerrado conjunto con la implementación del convertidor principal, • La cuantificación de las perdidas dinámicas bajo la carga pulsante y bajo la operación DVS, y • La robustez del sistema bajo la variación del condensador de salida y bajo los escalones de carga consecutiva. ABSTRACT Development of new technologies allows engineers to push the performance of the integrated circuits to its limits. New generations of processors, DSPs or FPGAs are able to process information with high speed and high consumption or to wait in low power mode with minimum possible consumption. This huge variation in power consumption and the short time needed to change from one level to another, affect the specifications of the Voltage Regulated Module (VRM) that supplies the IC. Furthermore, additional mandatory features, such as Adaptive Voltage Positioning (AVP) and Dynamic Voltage Scaling (DVS), impose opposite trends on the design of the VRM power stage. In order to cope with high load-step amplitudes, the output capacitor of the VRM power stage output filter is drastically oversized, penalizing power density and the efficiency during the DVS operation. Therefore, the ongoing research trend is directed to improve the dynamic response of the VRM while reducing the size of the output capacitor. The output capacitor reduction leads to a smaller cost and longer life-time of the system since the big bulk capacitors, usually implemented with OSCON capacitors, may not be needed to achieve the desired dynamic behavior. An additional advantage is that, by reducing the output capacitance, dynamic voltage scaling (DVS) can be performed faster and with smaller stress on the power stage, since the needed amount of charge to change the output voltage is smaller. The dynamic behavior of the system with a linear control (Voltage mode control, VMC, Peak Current Mode Control, PCMC,…) is limited by the converter switching frequency and filter size. The reduction of the output capacitor can be achieved by increasing the switching frequency of the converter, thus increasing the bandwidth of the system, and/or by applying advanced non-linear controls. Applying nonlinear control, the system variables get saturated in order to reach the new steady-state in a minimum time, thus the output filter, more specifically the output inductor current slew-rate, determines the output voltage response. Therefore, by reducing the output inductor value, the inductor current reaches faster the new steady state, so a smaller amount of charge is taken from the output capacitor during the transient. The drawback of this approach is that the system efficiency is penalized due to increased switching losses and RMS currents. In order to achieve both the output capacitor reduction and high system efficiency, while satisfying strict dynamic specifications, a Multiphase converter system is adopted as a standard for VRM applications. In order to ensure the current sharing among the phases, the multiphase converter is usually implemented with current mode control. In order to overcome the limitation imposed by the output filter, the second possibility to reduce the output capacitor is to apply Topologic modifications of the basic power stage topology in order to increase the slew-rate of the inductor current and, therefore, reduce the transient duration. Since the transient is reduced, smaller amount of charge is taken from the output capacitor under the same load current, thus, the output capacitor can be reduced to achieve the same output voltage deviation. The third possibility to reduce the output capacitor of the converter is to introduce an additional energy path (AEP) to compensate the charge unbalance of the output capacitor, consequently reducing the transient time and output voltage deviation. Doing so, during the steady-state operation the system has high efficiency because the main low-bandwidth converter is designed to operate at moderate switching frequency, to meet the static requirements, whereas the dynamic behavior during the transients is determined by the high-bandwidth auxiliary energy path. The auxiliary energy path can be implemented as a resistive path, as a Linear regulator, LR, or as a switching converter. The first two implementations provide higher bandwidth, at the expense of increasing losses during the transient. On the other hand, the switching converter implementation presents lower bandwidth, limited by the auxiliary converter switching frequency, though it produces smaller losses compared to the two previous implementations. Depending on the application, the implementation and the control strategy of the system, there is a variety of proposed solutions in the State-of-the-Art (SoA), having different features where one solution offers some advantages over the others, but also some disadvantages. In general, an ideal additional energy path system should have the following features: 1. The impact on the system losses should be minimal. During its operation, the AEP generates additional losses, thus ideally, the AEP should operate for a short period of time, only when the transient is occurring; the other option is to have the AEP constantly on, but due to the inductor current ripple compensation at the output, unnecessary losses are generated. 2. The AEP should be activated nearly instantaneously to prevent bigger output voltage deviation. To achieve near instantaneous activation, the converter system can be informed by the load prior to the load-step or the system can observe the output capacitor current, which is the first system state variable that reacts on the load current perturbation. In this manner, the AEP is turned on with near zero output voltage error, providing smaller output voltage deviation. 3. The AEP should be deactivated once the new steady state is reached to avoid additional settling transients. Most of the SoA solutions estimate duration of the transient which may cause additional transient if the estimation is not performed correctly (e.g. if the main converter inductor current has higher or lower value than needed, the slow regulator of the main converter needs to compensate the difference after the AEP is deactivated). Other SoA solutions are observing state variables, ensuring that the system reaches the new steady state or they are informed by the load. 4. During the transient, at least one subsystem, either the main converter or the AEP, should be in closed-loop. Implementing a closed loop system, preferably the AEP subsystem, due its higher bandwidth, increases the robustness under system tolerances and circuit parasitic. In addition, the AEP can operate with any type of load. The solutions that operate in open loop usually perform minimum time charge balance control, thus reducing the transient length and minimizing the impact on the losses, however they are very sensitive to tolerances and parasitics. 5. The AEP should inject current at the output in a controlled manner, thus reducing the risk of high and potentially damaging currents and increasing robustness on the input voltage deviation. This issue is mainly related to the systems where AEP is implemented as auxiliary converter. The auxiliary converter is designed for small power and, as such, the MOSFETs are rated for small power/currents. If the current is not controlled, due to the some unpredicted spike in input voltage caused by some other part of the system (e.g. different converter), it may lead to a current spike in auxiliary current which will cause the perturbation of the output voltage and even failure of the switching components of auxiliary converter. In the case when the current is controlled, using peak CMC or Hysteretic Window CMC, the auxiliary converter has inherent feed-forwarding of the input voltage in current control and the current is defined and limited. Furthermore, if the solution employs charge balance control, the system may perform poorly if the input voltage has different value than the nominal, causing that AEP injects/extracts more/less charge than needed. 6. Scalability of the system to multiphase converters. As commented previously, in VRM applications, due to the high load currents, the main converters are implemented as multiphase to redistribute losses among the modules, lowering temperature stress of the components. To ensure the current sharing, usually a Current Mode Control (CMC) is employed. The SoA solutions that are implemented with VMC are limited to a single stage implementation. This thesis proposes a novel control method of the energy flow through the AEP and the main converter system. The proposed concept relays on a controlled injection of the auxiliary current at the output node where the instantaneous current value is n-1 times bigger than the output capacitor current with appropriate directions. Doing so, the AEP creates an equivalent n times bigger virtual capacitor at the output, thus reducing the output impedance. Due to the fact that the proposed concept reduces the output impedance using the AEP, it has been named the Output Impedance Correction Circuit (OICC) concept. The concept is developed for a multiphase CMC synchronous buck converter (including a single phase implementation), operating with a constant output voltage and with AVP feature. Further, it is extended to a single phase VMC synchronous buck converter. During the operation, the main converter voltage loop and the OICC subsystem capacitor current loop is constantly closed, increasing the robustness under system tolerances and circuit parasitic and allowing the system to operate with any load-current shape or pattern. According to the proposed control method, the system operates in two states: during the steady-state the system is in the Idle state and the OICC subsystem is deactivated, while during the load-step transient the system is in the Active state and the OICC subsystem is activated in order to reduce the output impedance. The state changes are performed autonomously: the system enters in the Active state by observing the output capacitor current and it returns back to the Idle state when the steady-state operation is detected by observing the state variables. The validation of the OICC concept has been done by applying it to a 30W two phase synchronous buck converter with 140μF output capacitor and with the multiplication factor n equal to 15, generating during the Active state equivalent output capacitor of 2.1mF. The OICC subsystem is implemented as single phase PCMC synchronous buck converter. Comparing the converter operation with and without the OICC the results demonstrate that the 12 times reduction of the output voltage deviation is achieved, for both basic operation and for the AVP operation. Furthermore, the results have been compared to a reference prototype which has the same power stage and a fiscal output capacitor of 2.1mF. The results show that the two systems have the same dynamic behavior. Moreover, an impact on the system losses under the pulsating load and DVS operation has been quantified and it has been demonstrated that the OICC system has improved the system efficiency, considering the losses when the system operates with the pulsating load and the DVS operation. Lastly, the output capacitor of the OICC system is much smaller than the reference design output capacitor, therefore, by applying the OICC concept the power density can be increased. In summary, the main contributions of the thesis are: • The proposed Output Impedance Correction Circuit (OICC) concept, • The system level control based on the used approach to change the states of operation, • The OICC subsystem closed-loop implementation, together with the main converter implementation, • The dynamic losses under the pulsating load and the DVS operation quantification, and • The system robustness on the capacitor impedance variation and consecutive load-steps.

In disperse solution, “osmotic stress” is a restricted case of preferential interactions

In the practice of “osmotic stress,” the effect of excluded cosolvents on a biochemical equilibrium is interpreted as the number of water molecules participating in the reaction. This action is attributed to lowering of solvent water activity by the cosolvent. This concept of osmotic stress in disperse solution is erroneous: (i) A cosolvent cannot be both excluded and inert, i.e., noninteracting, because exclusion requires a positive free energy change; (ii) a decrease in water activity alone by addition of solute cannot affect an equilibrium when the reacting surface is in contact with the solvent; and (iii) osmotic stress in disperse solution is a restricted case of preferential interactions; the reaction is driven by the free energy of cosolvent exclusion, and the derived number of water molecules is solely a measure of the mutual perturbations of the chemical potentials of the cosolvent and the protein.

Chronic stress alters synaptic terminal structure in hippocampus

Repeated psychosocial or restraint stress causes atrophy of apical dendrites in CA3 pyramidal neurons of the hippocampus, accompanied by specific cognitive deficits in spatial learning and memory. Excitatory amino acids mediate this atrophy together with adrenal steroids and the neurotransmitter serotonin. Because the mossy fibers from dentate granule neurons provide a major excitatory input to the CA3 proximal apical dendrites, we measured ultrastructural parameters associated with the mossy fiber–CA3 synapses in control and 21-day restraint-stressed rats in an effort to find additional morphological consequences of stress that could help elucidate the underlying anatomical as well as cellular and molecular mechanisms. Although mossy fiber terminals of control rats were packed with small, clear synaptic vesicles, terminals from stressed animals showed a marked rearrangement of vesicles, with more densely packed clusters localized in the vicinity of active zones. Moreover, compared with controls, restraint stress increased the area of the mossy fiber terminal occupied by mitochondrial profiles and consequently, a larger, localized energy-generating capacity. A single stress session did not produce these changes either immediately after or the next day following the restraint session. These findings provide a morphological marker of the effects of chronic stress on the hippocampus that points to possible underlying neuroanatomical as well as cellular and molecular mechanisms for the ability of repeated stress to cause structural changes within the hippocampus.

Molecular control of vertebrate iron metabolism: mRNA-based regulatory circuits operated by iron, nitric oxide, and oxidative stress.

As an essential nutrient and a potential toxin, iron poses an exquisite regulatory problem in biology and medicine. At the cellular level, the basic molecular framework for the regulation of iron uptake, storage, and utilization has been defined. Two cytoplasmic RNA-binding proteins, iron-regulatory protein-1 (IRP-1) and IRP-2, respond to changes in cellular iron availability and coordinate the expression of mRNAs that harbor IRP-binding sites, iron-responsive elements (IREs). Nitric oxide (NO) and oxidative stress in the form of H2O2 also signal to IRPs and thereby influence cellular iron metabolism. The recent discovery of two IRE-regulated mRNAs encoding enzymes of the mitochondrial citric acid cycle may represent the beginnings of elucidating regulatory coupling between iron and energy metabolism. In addition to providing insights into the regulation of iron metabolism and its connections with other cellular pathways, the IRE/IRP system has emerged as a prime example for the understanding of translational regulation and mRNA stability control. Finally, IRP-1 has highlighted an unexpected role for iron sulfur clusters as post-translational regulatory switches.

Bond orientational order, molecular motion, and free energy of high-density DNA mesophases.

By equilibrating condensed DNA arrays against reservoirs of known osmotic stress and examining them with several structural probes, it has been possible to achieve a detailed thermodynamic and structural characterization of the change between two distinct regions on the liquid-crystalline phase diagram: (i) a higher density hexagonally packed region with long-range bond orientational order in the plane perpendicular to the average molecular direction and (ii) a lower density cholesteric region with fluid-like positional order. X-ray scattering on highly ordered DNA arrays at high density and with the helical axis oriented parallel to the incoming beam showed a sixfold azimuthal modulation of the first-order diffraction peak that reflects the macroscopic bond-orientational order. Transition to the less-dense cholesteric phase through osmotically controlled swelling shows the loss of this bond orientational order, which had been expected from the change in optical birefringence patterns and which is consistent with a rapid onset of molecular positional disorder. This change in order was previously inferred from intermolecular force measurements and is now confirmed by 31P NMR. Controlled reversible swelling and compaction under osmotic stress, spanning a range of densities between approximately 120 mg/ml to approximately 600 mg/ml, allow measurement of the free-energy changes throughout each phase and at the phase transition, essential information for theories of liquid-crystalline states.

Trees as Tools in Environmental Improvement; An Analysis of the Contribution of Vegetation to Energy and Water Conservation in the Front Range of Colorado

The Denver metropolitan area is facing rapid population growth that increases the stress on already limited resources. Research and advanced computer modeling show that trees, especially those in urban areas, have significant environmental benefits. These benefits include air quality improvements, energy savings, greenhouse gas reduction, and possible water conservation. This Capstone Project applies statistical methods to analyze a small data set of residential homes and their energy and water consumption, as a function of their individual landscape. Results indicate that tree shade can influence water conservation, and that irrigation methods can be an influential factor as well. The Capstone is a preliminary analysis for future study to be performed by the Institute for Environmental Solutions in 2007.

Alterations in energy metabolism, neuroprotection and visual signal transduction in the retina of parkinsonian, MPTP-treated monkeys

Parkinson disease is mainly characterized by the degeneration of dopaminergic neurons in the central nervous system, including the retina. Different interrelated molecular mechanisms underlying Parkinson disease-associated neuronal death have been put forward in the brain, including oxidative stress and mitochondrial dysfunction. Systemic injection of the proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to monkeys elicits the appearance of a parkinsonian syndrome, including morphological and functional impairments in the retina. However, the intracellular events leading to derangement of dopaminergic and other retinal neurons in MPTP-treated animal models have not been so far investigated. Here we have used a comparative proteomics approach to identify proteins differentially expressed in the retina of MPTP-treated monkeys. Proteins were solubilized from the neural retinas of control and MPTP-treated animals, labelled separately with two different cyanine fluorophores and run pairwise on 2D DIGE gels. Out of >700 protein spots resolved and quantified, 36 were found to exhibit statistically significant differences in their expression levels, of at least ±1.4-fold, in the parkinsonian monkey retina compared with controls. Most of these spots were excised from preparative 2D gels, trypsinized and subjected to MALDI-TOF MS and LC-MS/MS analyses. Data obtained were used for protein sequence database interrogation, and 15 different proteins were successfully identified, of which 13 were underexpressed and 2 overexpressed. These proteins were involved in key cellular functional pathways such as glycolysis and mitochondrial electron transport, neuronal protection against stress and survival, and phototransduction processes. These functional categories underscore that alterations in energy metabolism, neuroprotective mechanisms and signal transduction are involved in MPTPinduced neuronal degeneration in the retina, in similarity to mechanisms thought to underlie neuronal death in the Parkinson’s diseased brain and neurodegenerative diseases of the retina proper.