Impedance-based stability and transient-performance assessment applying maximum peak criteria

The impedance-based stability-assessment method has turned out to be a very effective tool and its usage is rapidly growing in different applications ranging from the conventional interconnected dc/dc systems to the grid-connected renewable energy systems. The results are sometime given as a certain forbidden region in the complex plane out of which the impedance ratio--known as minor-loop gain--shall stay for ensuring robust stability. This letter discusses the circle-like forbidden region occupying minimum area in the complex plane, defined by applying maximum peak criteria, which is well-known theory in control engineering. The investigation shows that the circle-like forbidden region will ensure robust stability only if the impedance-based minor-loop gain is determined at the very input or output of each subsystem within the interconnected system. Experimental evidence is provided based on a small-scale dc/dc distributed system.

Modelization of an experimental solar test box equipped with a water-flow based window

A study on a water- ow window installed in a test box is presented. This window is composed of two glass panes separated by a chamber through water ows. The ow of water comes from an isolated tank which contains heat water. In order to fully evaluate the water- ow window performance for different room and window sizes, locations and weather conditions, a mathematical model of the whole box is needed. The proposed model, in which conduction heat transfer mechanism is the only considered, is one dimensional and unsteady based upon test box energy balance. The effect of the heat water tank, which feeds the water- ow window, is included in the model by means of a time delay in the source term. Although some previous work about moving uid chamber has been developed, air was used as heat transfer uid and no uid storage was considered. Finally a comparison between the numerical solution and the obtained experimental data is done.

Experimental and numerical analysis of concrete Slabs subjected to Blast

This paper summarizes the research activities focused on the behaviour of concrete and concrete structures subjected to blast loading carried out by the Department of Materials Science of the Technical University of Madrid (PUM). These activities comprise the design and construction of a test bench that allows for testing up to four planar concrete specimens with one single explosion, the study of the performance of different protection concepts for concrete structures and, finally, the development of a numerical model for the simulation of concrete structural elements subjected to blast. Up to date 6 different types of concrete have been studied, from plain normal strength concrete, to high strength concrete, including also fibre reinforced concretes with different types of fibres. The numerical model is based on the Cohesive Crack Model approach, and has been developed for the LSDYNA finite element code through a user programmed subroutine. Despite its simplicity, the model is able to predict the failure patterns of the concrete slabs tested with a high level of accuracy

Experimental analysis of a photovoltaic concentrator based on a single reflective stage immersed in an optical fluid

This article reviews all the experimental tests carried out to analyze the performance of a FluidReflex photovoltaic concentrator. This novel concentrator concept consists of a single reflective stage immersed in an optical fluid. The presence of the fluid entails significant advantages. It not only allows a high system optical efficiency and increases the attainable concentration but also enhances the heat dissipation from the cell. In addition, the electrical insulation is improved, and the problem of water vapor condensation inside the module is avoided. A complete characterization is addressed in this paper. Among the experimental results, a measured optical efficiency of 83.5% for a concentration of 1035× stands out

Estudio experimental del desgaste del flanco y de la rugosidad superficial en el torneado en seco de alta velocidad del acero AISI 316L

La mejora continua de los procesos de fabricación es fundamental para alcanzar niveles óptimos de productividad, calidad y coste en la producción de componentes y productos. Para ello es necesario disponer de modelos que relacionen de forma precisa las variables que intervienen en el proceso de corte. Esta investigación tiene como objetivo determinar la influencia de la velocidad de corte y el avance en el desgaste del flanco de los insertos de carburos recubiertos GC1115 y GC2015 y en la rugosidad superficial de la pieza mecanizada de la pieza en el torneado de alta velocidad en seco del acero AISI 316L. Se utilizaron entre otros los métodos de observación científica, experimental, medición, inteligencia artificial y estadísticos. El inserto GC1115 consigue el mejor resultado de acuerdo al gráfico de medias y de las ecuaciones de regresión múltiple de desgaste del flanco para v= 350 m/min, mientras que para las restantes velocidades el inserto GC2015 consigue el mejor desempeño. El mejor comportamiento en cuanto a la rugosidad superficial de la pieza mecanizada se obtuvo con el inserto GC1115 en las velocidades de 350 m/min y 400 m/min, en la velocidad de 450 m/min el mejor resultado correspondió al inserto GC2015. Se analizaron dos criterios nuevos, el coeficiente de vida útil de la herramienta de corte en relación al volumen de metal cortado y el coeficiente de rugosidad superficial de la pieza mecanizada en relación al volumen de metal cortado. Fueron determinados los modelos de regresión múltiple que permitieron calcular el tiempo de mecanizado de los insertos sin que alcanzaran el límite del criterio de desgaste del flanco. Los modelos desarrollados fueron evaluados por sus capacidades de predicción con los valores medidos experimentalmente. ABSTRACT The continuous improvement of manufacturing processes is critical to achieving optimal levels of productivity, quality and cost in the production of components and products. This is necessary to have models that accurately relate the variables involved in the cutting process. This research aims to determine the influence of the cutting speed and feed on the flank wear of carbide inserts coated by GC1115 and GC2015 and the surface roughness of the workpiece for turning dry high speed steel AISI 316L. Among various scientific methods this study were used of observation, experiment, measurement, statistical and artificial intelligence. The GC1115 insert gets the best result according to the graph of means and multiple regression equations of flank wear for v = 350 m / min, while for the other speeds the GC2015 insert gets the best performance. Two approaches are discussed, the life ratio of the cutting tool relative to the cut volume and surface roughness coefficient in relation to the cut volume. Multiple regression models were determined to calculate the machining time of the inserts without reaching the limit of the criterion flank wear. The developed models were evaluated for their predictive capabilities with the experimentally measured values.

Long Term Performance Study of a Direct Methanol Fuel Cell Fed with Alcohol Blends

The use of alcohol blends in direct alcohol fuel cells may be a more environmentally friendly and less toxic alternative to the use of methanol alone in direct methanol fuel cells. This paper assesses the behaviour of a direct methanol fuel cell fed with aqueous methanol, aqueous ethanol and aqueous methanol/ethanol blends in a long term experimental study followed by modelling of polarization curves. Fuel cell performance is seen to decrease as the ethanol content rises, and subsequent operation with aqueous methanol only partly reverts this loss of performance. It seems that the difference in the oxidation rate of these alcohols may not be the only factor affecting fuel cell performance.

Uncertainty Estimation for Performance Evaluation of a Confocal Microscope as Metrology Equipment

Both in industry and research, the quality control of micrometric manufactured parts is based on the measurement of parameters whose traceability is sometimes difficult to guarantee. In some of these parts, the confocal microscopy shows great aptitudes to characterize a measurand qualitatively and quantitatively. The confocal microscopy allows the acquisition of 2D and 3D images that are easily manipulated. Nowadays, this equipment is manufactured by many different brands, each of them claiming a resolution probably not in accord to their real performance. The Laser Center (Technical University of Madrid) has a confocal microscope to verify the dimensions of the micro mechanizing in their own research projects. The present study pretends to confirm that the magnitudes obtained are true and reliable. To achieve this, a methodology for confocal microscope calibration is proposed, as well as an experimental phase for dimensionally valuing the equipment by 4 different standard positions, with its seven magnifications and the six objective lenses that the equipment currently has, in the x–y and z axis. From the results the uncertainty will be estimated along with an effect analysis of the different magnifications in each of the objective lenses.

Research on wide-bandgap intermediate band solar cells and development of experimental techniques for their characterization

El trabajo que ha dado lugar a esta Tesis Doctoral se enmarca en la invesitagación en células solares de banda intermedia (IBSCs, por sus siglas en inglés). Se trata de un nuevo concepto de célula solar que ofrece la posibilidad de alcanzar altas eficiencias de conversión fotovoltaica. Hasta ahora, se han demostrado de manera experimental los fundamentos de operación de las IBSCs; sin embargo, esto tan sólo has sido posible en condicines de baja temperatura. El concepto de banda intermedia (IB, por sus siglas en inglés) exige que haya desacoplamiento térmico entre la IB y las bandas de valencia y conducción (VB and CB, respectivamente, por sus siglas en inglés). Los materiales de IB actuales presentan un acoplamiento térmico demasiado fuerte entre la IB y una de las otras dos bandas, lo cual impide el correcto funcionamiento de las IBSCs a temperatura ambiente. En el caso particular de las IBSCs fabricadas con puntos cuánticos (QDs, por sus siglas en inglés) de InAs/GaAs - a día de hoy, la tecnología de IBSC más estudiada - , se produce un rápido intercambio de portadores entre la IB y la CB, por dos motivos: (1) una banda prohibida estrecha (< 0.2 eV) entre la IB y la CB, E^, y (2) la existencia de niveles electrónicos entre ellas. El motivo (1) implica, a su vez, que la máxima eficiencia alcanzable en estos dispositivos es inferior al límite teórico de la IBSC ideal, en la cual E^ = 0.71 eV. En este contexto, nuestro trabajo se centra en el estudio de IBSCs de alto gap (o banda prohibida) fabricadsas con QDs, o lo que es lo mismo, QD-IBSCs de alto gap. Hemos fabricado e investigado experimentalmente los primeros prototipos de QD-IBSC en los que se utiliza AlGaAs o InGaP para albergar QDs de InAs. En ellos demostramos une distribución de gaps mejorada con respecto al caso de InAs/GaAs. En concreto, hemos medido valores de E^ mayores que 0.4 eV. En los prototipos de InAs/AlGaAs, este incremento de E^ viene acompaado de un incremento, en más de 100 meV, de la energía de activación del escape térmico. Además, nuestros dispositivos de InAs/AlGaAs demuestran conversión a la alza de tensión; es decir, la producción de una tensión de circuito abierto mayor que la energía de los fotones (dividida por la carga del electrón) de un haz monocromático incidente, así como la preservación del voltaje a temperaura ambiente bajo iluminación de luz blanca concentrada. Asimismo, analizamos el potencial para detección infrarroja de los materiales de IB. Presentamos un nuevo concepto de fotodetector de infrarrojos, basado en la IB, que hemos llamado: fotodetector de infrarrojos activado ópticamente (OTIP, por sus siglas en inglés). Nuestro novedoso dispositivo se basa en un nuevo pricipio físico que permite que la detección de luz infrarroja sea conmutable (ON y OFF) mediante iluminación externa. Hemos fabricado un OTIP basado en QDs de InAs/AlGaAs con el que demostramos fotodetección, bajo incidencia normal, en el rango 2-6/xm, activada ópticamente por un diodoe emisor de luz de 590 nm. El estudio teórico del mecanismo de detección asistido por la IB en el OTIP nos lleva a poner en cuestión la asunción de quasi-niveles de Fermi planos en la zona de carga del espacio de una célula solar. Apoyados por simuaciones a nivel de dispositivo, demostramos y explicamos por qué esta asunción no es válida en condiciones de corto-circuito e iluminación. También llevamos a cabo estudios experimentales en QD-IBSCs de InAs/AlGaAs con la finalidad de ampliar el conocimiento sobre algunos aspectos de estos dispositivos que no han sido tratados aun. En particular, analizamos el impacto que tiene el uso de capas de disminución de campo (FDLs, por sus siglas en inglés), demostrando su eficiencia para evitar el escape por túnel de portadores desde el QD al material anfitrión. Analizamos la relación existente entre el escape por túnel y la preservación del voltaje, y proponemos las medidas de eficiencia cuántica en función de la tensión como una herramienta útil para evaluar la limitación del voltaje relacionada con el túnel en QD-IBSCs. Además, realizamos medidas de luminiscencia en función de la temperatura en muestras de InAs/GaAs y verificamos que los resltados obtenidos están en coherencia con la separación de los quasi-niveles de Fermi de la IB y la CB a baja temperatura. Con objeto de contribuir a la capacidad de fabricación y caracterización del Instituto de Energía Solar de la Universidad Politécnica de Madrid (IES-UPM), hemos participado en la instalación y puesta en marcha de un reactor de epitaxia de haz molecular (MBE, por sus siglas en inglés) y el desarrollo de un equipo de caracterización de foto y electroluminiscencia. Utilizando dicho reactor MBE, hemos crecido, y posteriormente caracterizado, la primera QD-IBSC enteramente fabricada en el IES-UPM. ABSTRACT The constituent work of this Thesis is framed in the research on intermediate band solar cells (IBSCs). This concept offers the possibility of achieving devices with high photovoltaic-conversion efficiency. Up to now, the fundamentals of operation of IBSCs have been demonstrated experimentally; however, this has only been possible at low temperatures. The intermediate band (IB) concept demands thermal decoupling between the IB and the valence and conduction bands. Stateof- the-art IB materials exhibit a too strong thermal coupling between the IB and one of the other two bands, which prevents the proper operation of IBSCs at room temperature. In the particular case of InAs/GaAs quantum-dot (QD) IBSCs - as of today, the most widely studied IBSC technology - , there exist fast thermal carrier exchange between the IB and the conduction band (CB), for two reasons: (1) a narrow (< 0.2 eV) energy gap between the IB and the CB, EL, and (2) the existence of multiple electronic levels between them. Reason (1) also implies that maximum achievable efficiency is below the theoretical limit for the ideal IBSC, in which EL = 0.71 eV. In this context, our work focuses on the study of wide-bandgap QD-IBSCs. We have fabricated and experimentally investigated the first QD-IBSC prototypes in which AlGaAs or InGaP is the host material for the InAs QDs. We demonstrate an improved bandgap distribution, compared to the InAs/GaAs case, in our wide-bandgap devices. In particular, we have measured values of EL higher than 0.4 eV. In the case of the AlGaAs prototypes, the increase in EL comes with an increase of more than 100 meV of the activation energy of the thermal carrier escape. In addition, in our InAs/AlGaAs devices, we demonstrate voltage up-conversion; i. e., the production of an open-circuit voltage larger than the photon energy (divided by the electron charge) of the incident monochromatic beam, and the achievement of voltage preservation at room temperature under concentrated white-light illumination. We also analyze the potential of an IB material for infrared detection. We present a IB-based new concept of infrared photodetector that we have called the optically triggered infrared photodetector (OTIP). Our novel device is based on a new physical principle that allows the detection of infrared light to be switched ON and OFF by means of an external light. We have fabricated an OTIP based on InAs/AlGaAs QDs with which we demonstrate normal incidence photodetection in the 2-6 /xm range optically triggered by a 590 nm light-emitting diode. The theoretical study of the IB-assisted detection mechanism in the OTIP leads us to questioning the assumption of flat quasi-Fermi levels in the space-charge region of a solar cell. Based on device simulations, we prove and explain why this assumption is not valid under short-circuit and illumination conditions. We perform new experimental studies on InAs/GaAs QD-IBSC prototypes in order to gain knowledge on yet unexplored aspects of the performance of these devices. Specifically, we analyze the impact of the use of field-damping layers, and demonstrate this technique to be efficient for avoiding tunnel carrier escape from the QDs to the host material. We analyze the relationship between tunnel escape and voltage preservation, and propose voltage-dependent quantum efficiency measurements as an useful technique for assessing the tunneling-related limitation to the voltage preservation of QD-IBSC prototypes. Moreover, we perform temperature-dependent luminescence studies on InAs/GaAs samples and verify that the results are consistent with a split of the quasi-Fermi levels for the CB and the IB at low temperature. In order to contribute to the fabrication and characterization capabilities of the Solar Energy Institute of the Universidad Polite´cnica de Madrid (IES-UPM), we have participated in the installation and start-up of an molecular beam epitaxy (MBE) reactor and the development of a photo and electroluminescence characterization set-up. Using the MBE reactor, we have manufactured and characterized the first QD-IBSC fully fabricated at the IES-UPM.

Modelización y validación experimental del transporte de tritio en metal líquido y otros materiales para reactores de fusión nuclear magnética e inercial

La presente tesis se centra en el estudio de los fenómenos de transporte de los isótopos de hidrógeno, y más concretamente del tritio, en materiales de interés para los reactores de fusión nuclear. Los futuros reactores de fusión nuclear necesitarán una Planta de Tritio, con una envoltura regeneradora (breeding blanket) y unos sistemas auxiliares claves para su diseño. Por lo tanto su desarrollo y cualificación son cruciales para demostrar que los reactores de fusión son una opción viable como futura fuente de energía. Se han resaltado los diferentes retos de la difusión y retención de estas especies ligeras para cada sistema de la Planta de Tritio, y se han identificado las necesidades experimentales y paramétricas para abordar las simulaciones de difusión, como factores de transporte como la difusividad, absorción/desorción, solubilidad y atrapamiento. Se han estudiado los fenómenos de transporte y parámetros del T en el metal líquido LiPb, componente del breeding blanket tanto para una planta de fusión magnética como inercial. Para ello se han utilizado dos experimentos con características diversas, uno de ellos se ha llevado a cabo en un reactor de alto flujo, y por lo tanto, en condiciones de irradiación, y el otro sin irradiación. Los métodos de simulación numérica aplicados se han adaptado a los experimentos para las mediciones y para estudiar el régimen de transporte. En el estudio de estos experimentos se ha obtenido un valor para algunos de los parámetros claves en el transporte y gestión del tritio en el reactor. Finalmente se realiza un cálculo de la acumulación y difusión de tritio en una primera pared de tungsteno para un reactor de fusión inercial. En concreto para el proyecto de fusión por láser europeo, HiPER (para sus fases 4a y 4b). Se ha estudiado: la implantación de los isótopos de H y He en la pared de W tras una reacción de fusión por iluminación directa con un láser de 48MJ; el efecto en el transporte de T de los picos de temperatura en el W debido a la frecuencia de los eventos de fusión; el régimen de transporte en la primera pared. Se han identificado la naturaleza de las trampas más importantes para el T y se ha propuesto un modelo avanzado para la difusión con trampas. ABSTRACT The present thesis focuses into study the transport phenomenons of hydrogen isotopes, more specifically tritium, in materials of interest for nuclear fusion reactors. The future nuclear reactors will be provided of a Tritium Plant, with its breeding blanket and its auxiliary systems, all of them essential components for the plant. Therefore a reliable development and coalification are key issues to prove the viability of the nuclear fusion reactors as an energy source. The currently challenges for the diffusion and accumulation of these light species for each system of the TP has been studied. Experimental and theoretical needs have been identified and analyzed, specially from the viewpoint of the parameters. To achieve reliable simulations of tritium transport, parameters as diffusivity, absorption/desorption, solubility and trapping must be reliables. Transport phenomenon and parameters of T in liquid metal have been studied. Lead lithium is a key component of the breeding blanket, either in magnetic or inertial fusion confinement. Having this aim in mind, two experiments with different characteristics have been used; one of them has been realized in a high flux reactor, and hence, under irradiation conditions. The other one has been realized without radiation. The mathematical methods for the simulation have been adapted to the experiments, for the measures and also to study the transport behavior. A value for some key parameters for tritium management has been obtained in these studies. Finally, tritium accumulation and diffusion in a W first wall of an inertial nuclear fusion reactor has been assessed. A diffusion model of the implanted H, D, T and He species for the two initial phases of the proposed European laser fusion Project HiPER (namely, phase 4a and phase 4b) has been implemented using Tritium Migration Analysis Program, TMAP7. The effect of the prompt and working temperatures and the operational pulsing modes on the diffusion are studied. The nature of tritium traps in W and their performance has been analyzed and discussed.

Integral energy performance characterization of semi-transparent photovoltaic elements for building integration under real operation conditions

In this paper, a methodology for the integral energy performance characterization (thermal, daylighting and electrical behavior) of semi-transparent photovoltaic modules (STPV) under real operation conditions is presented. An outdoor testing facility to analyze simultaneously thermal, luminous and electrical performance of the devices has been designed, constructed and validated. The system, composed of three independent measurement subsystems, has been operated in Madrid with four prototypes of a-Si STPV modules, each one corresponding to a specific degree of transparency. The extensive experimental campaign, continued for a whole year rotating the modules under test, has validated the reliability of the testing facility under varying environmental conditions. The thermal analyses show that both the solar protection and insulating properties of the laminated prototypes are lower than those achieved by a reference glazing whose characteristics are in accordance with the Spanish Technical Building Code. Daylighting analysis shows that STPV elements have an important lighting energy saving potential that could be exploited through their integration with strategies focused to reduce illuminance values in sunny conditions. Finally, the electrical tests show that the degree of transparency is not the most determining factor that affects the conversion efficiency.

Influence of the Fiber Alignment in the Ballistic Performance of Dyneema Non-Woven Fabrics

The aim of this study was the determination of the deforming micromechanisms of needlepunched felts subjected to impact loads. A large experimental campaign has been carried out to analyze the influence of the fiber alignment in the ballistic performance. Ballistic limit curves of predeformed samples were compared. The fiber realignment was experimentally measure by means of 2D X-Ray diffraction. Higher specific absorption was observed for samples with a more isotropic mechanical response. A constitutive physicallybased model was developed within the context of the finite element method, which provided the constitutive response for a mesodomain including micromechanical aspects as fiber alignment, fiber sliding and pull-out. The macroscopic response has been validated with the experimental results, showing a very good agreement. The absorbed energy by the material during the impact was predicted and the fiber realignment evolution was also obtained.

Effect of late weaning and use of alternative cages on performance of does, suckling and fattening rabbits under extensive reproductive management

The effects of the combined use of long lactation periods (46 days) with alternative cages on the reproductive and growth performance of 104 rabbit does and their litters during five consecutive reproductive cycles were studied. Half of does were housed in conventional polyvalent cages (39 cm×100 cm×30 cm) and the other half in alternative polyvalent cages (39 cm×100 cm×60 cm), with a raised platform. Half of the rabbit does in each type of cage were weaned at 32 and the other half at 46 days after parturition. Longer lactation negatively affected the body weight (P<0.001), fat and energy content (P<0.05) of rabbit does at the end of the lactation period, but this effect decreased with the number of parturitions. Fertility, prolificacy and doe mortality were not affected by lactation length. Late weaning led to higher litter size (by 8.9%) and litter weight (by 11.3%) at the end of growing period (P<0.001) and lower feed conversion ratio per cage during the experimental period (13.5%) than weaning at 32 day (P<0.001). These results were paralleled by lower mortality (12.6 vs. 17.6%; P<0.01) of young rabbits weaned later during the overall experimental period. Differences in performance as a result of different weaning ages were only observed during cycles with worst health status (third and fifth cycles) in which late weaning decreased mortality. Type of cage did not affect doe body weight and body condition, mortality, fertility, prolificacy and litter size during the five reproductive cycles. Nevertheless, at day 21 litter weight and feed conversion ratio between 3 and 21 day were 4.2% higher (P<0.01) and 5.0% lower (P<0.05), respectively, in animals housed in alternative rather than in conventional cages. Alternative cages also led to heavier litters at 59 days (P<0.01). It was concluded that the combined use of longer lactations and cages with higher available surface with a raised platform could be alternatives to improve animal welfare in farmed rabbit.

Shake-table tests of a reinforced concrete frame designed following modern codes: seismic performance and damage evaluation

This paper presents shake-table tests conducted on a two-fifths-scale reinforced concrete frame representing a conventional construction design under current building code provisions in the Mediterranean area. The structure was subjected to a sequence of dynamic tests including free vibrations and four seismic simulations in which a historical ground motion record was scaled to levels of increasing intensity until collapse. Each seismic simulation was associated with a different level of seismic hazard, representing very frequent, frequent, rare and very rare earthquakes. The structure remained basically undamaged and within the inter-story drift limits of the "immediate occupancy" performance level for the very frequent and frequent earthquakes. For the rare earthquake, the specimen sustained significant damage with chord rotations of up to 28% of its ultimate capacity and approached the upper bound limit of inter-story drift associated with "life safety". The specimen collapsed at the beginning of the "very rare" seismic simulation. Besides summarizing the experimental program, this paper evaluates the damage quantitatively at the global and local levels in terms of chord rotation and other damage indexes, together with the energy dissipation demands for each level of seismic hazard. Further, the ratios of column-to-beam moment capacity recommended by Eurocode 8 and ACI-318 to guarantee the formation of a strong column-weak beam mechanism are examined.

Seismic performance and damage evaluation of a reinforced concrete frame with hysteretic dampers through shake-table tests

Passive energy dissipation devices are increasingly implemented in frame structures to improve their performance under seismic loading. Most guidelines for designing this type of system retain the requirements applicable to frames without dampers, and this hinders taking full advantage of the benefits of implementing dampers. Further, assessing the extent of damage suffered by the frame and by the dampers for different levels of seismic hazard is of paramount importance in the framework of performance-based design. This paper presents an experimental investigation whose objectives are to provide empirical data on the response of reinforced concrete (RC) frames equipped with hysteretic dampers (dynamic response and damage) and to evaluate the need for the frame to form a strong column-weak beam mechanism and dissipate large amounts of plastic strain energy. To this end, shake-table tests were conducted on a 2/5-scale RC frame with hysteretic dampers. The frame was designed only for gravitational loads. The dampers provided lateral strength and stiffness, respectively, three and 12 times greater than those of the frame. The test structure was subjected to a sequence of seismic simulations that represented different levels of seismic hazard. The RC frame showed a performance level of "immediate occupancy", with maximum rotation demands below 20% of the ultimate capacity. The dampers dissipated most of the energy input by the earthquake. It is shown that combining hysteretic dampers with flexible reinforced concrete frames leads to structures with improved seismic performance and that requirements of conventional RC frames (without dampers) can be relieved.

Effect of late weaning and use of alternative cages on performance of does, suckling and fattening rabbits under extensive reproductive management

The effects of the combined use of long lactation periods (46 days) with alternative cages on the reproductive and growth performance of 104 rabbit does and their litters during five consecutive reproductive cycles were studied. Half of does were housed in conven- tional polyvalent cages (39 cm x 100 cm x 30 cm) and the other half in alternative polyvalent cages (39 cm x 100 cm x 60 cm), with a raised platform. Half of the rabbit does in each type of cage were weaned at 32 and the other half at 46 days after parturition. Longer lactation negatively affected the body weight ( P o 0.001), fat and energy content ( P o 0.05) of rabbit does at the end of the lactation period, but this effect decreased with the number of parturitions. Fertility, prolificacy and doe mortality were not affected by lactation length. Late weaning led to higher litter size (by 8.9%) and litter weight (by 11.3%) at the end of growing period ( P o 0.001) and lower feed conversion ratio per cage during the experimental period (13.5%) than weaning at 32 day ( P o 0.001). These results were paralleled by lower mortality (12.6 vs. 17.6%; P o 0.01) of young rabbits weaned later during the overall experimental period. Differences in performance as a result of different weaning ages were only observed during cycles with worst health status (third and fifth cycles) in which late weaning decreased mortality. Type of cage did not affect doe body weight and body condition, mortality, fertility, prolificacy and litter size during the five reproductive cycles. Nevertheless, at day 21 litter weight and feed conversion ratio between 3 and 21 day were 4.2% higher ( P o 0.01) and 5.0% lower ( P o 0.05), respectively, in animals housed in alternative rather than in conventional cages. Alternative cages also led to heavier litters at 59 days ( P o 0.01). It was concluded that the combined use of longer lactations and cages with higher available surface with a raised platform could be alternatives to improve animal welfare in farmed rabbit.