944 resultados para Temperature range
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Physiognomic traits of plant leaves such as size, shape or margin are decisively affected by the prevailing environmental conditions of the plant habitat. On the other hand, if a relationship between environment and leaf physiognomy can be shown to exist, vegetation represents a proxy for environmental conditions. This study investigates the relationship between physiognomic traits of leaves from European hardwood vegetation and environmental parameters in order to create a calibration dataset based on high resolution grid cell data. The leaf data are obtained from synthetic chorologic floras, the environmental data comprise climatic and ecologic data. The high resolution of the data allows for a detailed analysis of the spatial dependencies between the investigated parameters. The comparison of environmental parameters and leaf physiognomic characters reveals a clear correlation between temperature related parameters (e.g. mean annual temperature or ground frost frequency) and the expression of leaf characters (e.g. the type of leaf margin or the base of the lamina). Precipitation related parameters (e.g. mean annual precipitation), however, show no correlation with the leaf physiognomic composition of the vegetation. On the basis of these results, transfer functions for several environmental parameters are calculated from the leaf physiognomic composition of the extant vegetation. In a next step, a cluster analysis is applied to the dataset in order to identify "leaf physiognomic communities". Several of these are distinguished, characterised and subsequently used for vegetation classification. Concerning the leaf physiognomic diversity there are precise differences between each of these "leaf physiognomic classes". There is a clear increase of leaf physiognomic diversity with increasing variability of the environmental parameters: Northern vegetation types are characterised by a more or less homogeneous leaf physiognomic composition whereas southern vegetation types like the Mediterranean vegetation show a considerable higher leaf physiognomic diversity. Finally, the transfer functions are used to estimate palaeo-environmental parameters of three fossil European leaf assemblages from Late Oligocene and Middle Miocene. The results are compared with results obtained from other palaeo-environmental reconstructing methods. The estimates based on a direct linear ordination seem to be the most realistic ones, as they are highly consistent with the Coexistence Approach.
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[1] Previous studies have demonstrated the potential for the Li content of coral aragonite to record information about environmental conditions, but no detailed study of tropical corals exists. Here we present the Li and Mg to Ca ratios at a bimonthly to monthly resolution over 25 years in two modern Porites corals, the genus most often used for paleoclimate reconstructions in the tropical Indo-Pacific. A strong relationship exists between coral Li/Ca and locally measured SST, indicating that coral Li/Ca can be used to reconstruct tropical SST variations. However, Li/Ca ratios of the skeleton deposited during 1979-1980 do not track local SST well and are anomalously high in places. The Mg/Ca ratios of this interval are also anomalously high, and we suggest Li/Ca can be used to reconstruct tropical SST only when Mg/Ca data are used to carefully screen for relatively rare biological effects. Mg/Li or Li/Mg ratios provide little advantage over Li/Ca ratios, except that the slope of the Li/Mg temperature relationship is more similar between the two corals. The Mg/Li temperature relationship for the coral that experienced a large temperature range is similar to that found for cold water corals and aragonitic benthic foraminifera in previous studies. The comparison with data from other biogenic aragonites suggests the relationship between Li/Mg and water temperature can be described by a single exponential relationship. Despite this hint at an overarching control, it is clear that biological processes strongly influence coral Li/Ca, and more calibration work is required before widely applying the proxy.
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This study examines the seed dispersal spectrum of the tropical dry forests of Southern Ecuador, in an effort to contribute to the knowledge of the complex dynamics of tropical dry forests. Seed dispersal spectrum was described for a total number of 160 species. Relationships of dispersal syndromes with plant growth form and climatic seasonality were explored. For a subset of 97 species, we determined whether dispersal spectrum changes when species abundance, in addition to species number, is taken into account. The same subset was used to relate dispersal syndromes with the environmental conditions. Zoochorous species dominated in the studied community. When considering the individual abundance of each species, however, anemochory was the prevalent dispersal syndrome. We found a significant difference in the frequency of dispersal syndromes among plant growth forms, with epizoochory only occurring in shrub species. The dispersal spectrum was dependent on climatic seasonality. The largest proportion of anemochorous species fructified during the dry season, while zoochorous diaspores dominated during the rainy season. A fourth-corner analysis indicated that the seed dispersal spectrum of Southern Ecuador dry forests is controlled by environmental conditions such as annual precipitation, annual temperature range or topography. Our results suggest that spatio-temporal changes in the environmental conditions may affect important ecological processes for dispersal. Thus, the predominance of one syndrome or another may depend on the spatial variation of environmental conditions.
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The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO3) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<1012 cm−2) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3×1011 cm−2 and 1012 cm−2. The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphous-crystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ∼1014 cm−2. Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystalline-amorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed.
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This work studies the effect of the growth temperature on the morphology and emission characteristics of self-assembled InGaN nanocolumns grown by plasma assisted molecular beam epitaxy. Morphology changes are assessed by scanning electron microscopy, while emission is measured by photoluminescence. Within the growth temperature range of 750 to 650 °C, an increase in In incorporation for decreasing temperature is observed. This effect allows tailoring the InGaN nanocolumns emission line shape by using temperature gradients during growth. Depending on the gradient rate, span, and sign, broad emission line shapes are obtained, covering the yellow to green range, even yielding white emission
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The analysis of the viability of Hydrogen production without CO2 emissions is one of the most challenging activities that have been initiated for a sustainable energy supply. As one of the tracks to fulfil such objective, direct methane cracking has been analysed experimentally to assess the scientific viability and reaction characterization in a broad temperature range, from 875 to 1700 ?C. The effect of temperature, sweeping/carrier gas fraction proposed in some concepts, methane flow rate, residence time, and tube material and porosity has been analysed. The aggregation of carbon black particles to the reaction tube is the main technological show-stopper that has been identified.
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In this work, a fiber-based optical powering (or power-by-light) system capable of providing more than 1 W is developed. The prototype was used in order to power a shunt regulator for controlling the activation and deactivation of solar panels in satellites. The work involves the manufacture of a light receiver (a GaAs multiple photovoltaic converter (MPC)), a power conditioning block, and a regulator and the implementation and characterization of the whole system. The MPC, with an active area of just 3.1 mm2, was able to supply 1 W at 5 V with an efficiency of 30%. The maximum measured device efficiency was over 40% at an input power (Pin) of 0.5 W. Open circuit voltage over 7 V was measured for Pin over 0.5 W. A system optoelectronic efficiency (including the optical fiber, connectors, and MPC) of 27% was measured at an output power (Pout) of 1 W. At Pout = 0.2 W, the efficiency was as high as 36%. The power conditioning block and the regulator were successfully powered with the system. The maximum supplied power in steady state was 0.2 W, whereas in transient state, it reached 0.44 W. The paper also describes the characterization of the system within the temperature range going from -70 to +100?°C.
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We report on the electrical transport properties of all-oxide La0.7Ca0.3MnO3/SrTiO3:Nb heterojunctions with lateral size of just a few micrometers. The use of lithography techniques to pattern manganite pillars ensures perpendicular transport and allows exploration of the microscopic conduction mechanism through the interface. From the analysis of the current-voltage characteristics in the temperature range 20-280 K we find a Schottky-like behavior that can be described by a mechanism of thermally assisted tunneling if a temperature-dependent value of the dielectric permittivity of SrTiO3:Nb (NSTO) is considered.We determine the Schottky energy barrier at the interface, qVB = 1.10 ± 0.02 eV, which is found to be temperature independent, and a value of ? = 17 ± 2 meV for the energy of the Fermi level in NSTO with respect to the bottom of its conduction band.
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Durante los últimos años el flujo de datos en la transmisión que tiene lugar en los sistemas de comunicación ha aumentado considerablemente de forma que día a día se requieren más aplicaciones trabajando en un rango de frecuencias muy alto (3-30 GHz). Muchos de estos sistemas de comunicación incluyen dispositivos de onda acústica superficial (SAW) y por tanto se hace necesario el aumento de frecuencia a la que éstos trabajan. Pero este incremento de frecuencia de los dispositivos SAW no sólo es utilizado en los sistemas de comunicación, varios tipos de sensores, por ejemplo, aumentan su sensibilidad cuando la frecuencia a la que trabajan también lo hace. Tradicionalmente los dispositivos SAW se han fabricado sobre cuarzo, LiNbO3 y LiTaO3 principalmente. Sin embargo la principal limitación de estos materiales es su velocidad SAW. Además, debido a la alta temperatura a la que se depositan no pueden ser integrados en la tecnología de fabricación CMOS. El uso de la tecnología de capa delgada, en la que un material piezoeléctrico es depositado sobre un substrato, se está utilizando en las últimas décadas para incrementar la velocidad SAW de la estructura y poder obtener dispositivos trabajando en el rango de frecuencias requerido en la actualidad. Por otra parte, esta tecnología podría ser integrada en el proceso de fabricación CMOS. Durante esta tesis nos hemos centrado en la fabricación de dispositivos SAW trabajando a muy alta frecuencia. Para ello, utilizando la tecnología de capa delgada, hemos utilizado la estructura nitruro de aluminio (AlN) sobre diamante que permite conseguir velocidades SAW del sustrato que no se pueden alcanzar con otros materiales. El depósito de AlN se realizó mediante sputtering reactivo. Durante esta tesis se han realizado diferentes experimentos para optimizar dicho depósito de forma que se han obtenido los parámetros óptimos para los cuales se pueden obtener capas de AlN de alta calidad sobre cualquier tipo de sustrato. Además todo el proceso se realizó a baja temperatura para que el procesado de estos dispositivos pueda ser compatible con la tecnología CMOS. Una vez optimizada la estructura AlN/diamante, mediante litografía por haz de electrones se fabricaron resonadores SAW de tamaño nanométrico que sumado a la alta velocidad resultante de la combinación AlN/diamante nos ha permitido obtener dispositivos trabajando en el rango de 10-28 GHz con un alto factor de calidad y rechazo fuera de la banda. Estás frecuencias y prestaciones no han sido alcanzadas por el momento en resonadores de este tipo. Por otra parte, se han utilizado estos dispositivos para fabricar sensores de presión de alta sensibilidad. Estos dispositivos son afectados altamente por los cambios de temperatura. Se realizó también un exhaustivo estudio de cómo se comportan en temperatura estos resonadores, entre -250ºC y 250ºC (rango de temperaturas no estudiado hasta el momento) diferenciándose dos regiones una a muy baja temperatura en la que el dispositivo muestra un coeficiente de retraso en frecuencia (TCF) relativamente bajo y otra a partir de los -100ºC en la que el TCF es similar al observado en la bibliografía. Por tanto, durante esta tesis se ha optimizado el depósito de AlN sobre diamante para que sea compatible con la tecnología CMOS y permita el procesado de dispositivos trabajando a muy alta frecuencia con altas prestaciones para comunicaciones y sensores. ABSTRACT The increasing volume of information in data transmission systems results in a growing demand of applications working in the super-high-frequency band (3–30 GHz). Most of these systems work with surface acoustic wave (SAW) devices and thus there is a necessity of increasing their resonance frequency. Moreover, sensor application includes this kind of devices. The sensitivity of them is proportional with its frequency. Traditionally, quartz, LiNbO3 and LiTaO3 have been used in the fabrication of SAW devices. These materials suffer from a variety of limitations and in particular they have low SAW velocity as well as being incompatible with the CMOS technology. In order to overcome these problems, thin film technology, where a piezoelectric material is deposited on top of a substrate, has been used during the last decades. The piezoelectric/substrate structure allows to reach the frequencies required nowadays and could be compatible with the mass electronic production CMOS technology. This thesis work focuses on the fabrication of SAW devices working in the super-high-frequency range. Thin film technology has been used in order to get it, especially aluminum nitride (AlN) deposited by reactive sputtering on diamond has been used to increase the SAW velocity. Different experiments were carried out to optimize the parameters for the deposit of high quality AlN on any kind of substrates. In addition, the system was optimized under low temperature and thus this process is CMOS compatible. Once the AlN/diamond was optimized, thanks to the used e-beam lithography, nanometric SAW resonators were fabricated. The combination of the structure and the size of the devices allow the fabrication of devices working in the range of 10-28 GHz with a high quality factor and out of band rejection. These high performances and frequencies have not been reached so far for this kind of devices. Moreover, these devices have been used as high sensitivity pressure sensors. They are affected by temperature changes and thus a wide temperature range (-250ºC to 250ºC) study was done. From this study two regions were observed. At very low temperature, the temperature coefficient of frequency (TCF) is low. From -100ºC upwards the TCF is similar to the one appearing in the literature. Therefore, during this thesis work, the sputtering of AlN on diamond substrates was optimized for the CMOS compatible fabrication of high frequency and high performance SAW devices for communication and sensor application.
Flow and fracture behaviour of FV535 steel at different triaxialities, strain rates and temperatures
Resumo:
The new generation jet engines operate at highly demanding working conditions. Such conditions need very precise design which implies an exhaustive study of the engine materials and behaviour in their extreme working conditions. With this purpose, this work intends to describe a numerically-based calibration of the widely-used Johnson–Cook fracture model, as well as its validation through high temperature ballistic impact tests. To do so, a widely-used turbine casing material is studied. This material is the Firth Vickers 535 martensitic stainless steel. Quasi-static tensile tests at various temperatures in a universal testing machine, as well as dynamic tests in a Split Hopkinson Pressure Bar, are carried out at different triaxialities. Using ABAQUS/Standard and LS-DYNA numerical codes, experimental data are matched. This method allows the researcher to obtain critical data of equivalent plastic strain and triaxility, which allows for more precise calibration of the Johnson–Cook fracture model. Such enhancement allows study of the fracture behaviour of the material across its usage temperature range.
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Conductive submicronic coatings of carbon black (CB)/silica composites have been prepared by a sol-gel process and deposited by spray-coating on glazed porcelain tiles. Stable CB dispersions with surfactant were rheologically characterized to determine the optimum CB-surfactant ratio. The composites were analyzed by Differential Thermal and Thermogravimetric Analysis and Hg-Porosimetry. Thin coatings were thermally treated in the temperature range of 300-500degC in air atmosphere. The microstructure of the coatings was determined by scanning electron microscopy and the structure evaluated by confocal Raman spectroscopy. The electrical characterization of the samples was carried out using dc intensity-voltage curves. The coatings exhibit good adhesion, high density and homogeneous distribution of the conductive filler (CB) in the insulate matrix (silica) that protects against the thermal degradation of the CB nanoparticles during the sintering process. As consequence, the composite coatings show the lowest resistivity values for CB-based films reported in the literature, with values of ~7times10 -5Omegam.
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Pure and quinine doped silica coatings have been prepared over sodalime glasses. The coatings were consolidated at low temperature (range 60-180 A degrees C) preserving optical activity of quinine molecule. We designed a device to test the guiding properties of the coatings. We confirmed with this device that light injected in pure silica coatings is guided over distances of meters while quinine presence induces isotropic photoluminescence. With the combined use of both type of coatings, it is possible to design light guiding devices and illuminate regions in glass elements without electronic circuits.
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En esta tesis doctoral se describe el trabajo de investigación enfocado al estudio y desarrollo de sensores de fibra óptica para la detección de presión, flujo y vibraciones en ductos ascendentes submarinos utilizados en la extracción y transporte de hidrocarburos, con el objetivo de aplicarlos en los campos de explotación de aguas profundas en el Golfo de México pertenecientes a la Industria Petrolera Mexicana. El trabajo se ha enfocado al estudio y desarrollo de sensores ópticos cuasi distribuidos y distribuidos. En especial se ha profundizado en el uso y aplicación de las redes de Bragg (FBG) y de reflectómetros ópticos en el dominio del tiempo sensible a la fase (φ-OTDR). Los sensores de fibra óptica son especialmente interesantes para estas aplicaciones por sus ventajosas características como su inmunidad a interferencias electromagnéticas, capacidad de multiplexado, fiabilidad para trabajar en ambientes hostiles, altas temperaturas, altas presiones, ambientes salino-corrosivos, etc. Además, la fibra óptica no solo es un medio sensor sino que puede usarse como medio de transmisión. Se ha realizado un estudio del estado del arte y las ventajas que presentan los sensores ópticos puntuales, cuasi-distribuidos y distribuidos con respecto a los sensores convencionales. Se han estudiado y descrito los interrogadores de redes de Bragg y se ha desarrollado un método de calibración útil para los interrogadores existentes en el mercado, consiguiendo incertidumbres en la medida de la longitud de onda menores de ± 88 nm e incertidumbres relativas (la mas interesante en el campo de los sensores) menores de ±3 pm. Centrándose en la aplicación de las redes de Bragg en la industria del petróleo, se ha realizado un estudio en detalle del comportamiento que presentan las FBGs en un amplio rango de temperaturas de -40 ºC a 500 oC. Como resultado de este estudio se han evaluado las diferencias en los coeficientes de temperatura en diversos tramos de mas mismas, así como para diferentes recubrimientos protectores. En especial se ha encontrado y evaluado las diferencias de los diferentes recubrimientos en el intervalo de temperaturas entre -40 ºC y 60 ºC. En el caso del intervalo de altas temperaturas, entre 100 ºC y 500 ºC, se ha medido y comprobado el cambio uniforme del coeficiente de temperatura en 1pm/ºC por cada 100 ºC de aumento de temperatura, en redes independientemente del fabricante de las mismas. Se ha aplicado las FBG a la medición de manera no intrusiva de la presión interna en una tubería y a la medición del caudal de un fluido en una tubería, por la medida de diferencia de presión entre dos puntos de la misma. Además se ha realizado un estudio de detección de vibraciones en tuberías con fluidos. Finalmente, se ha implementado un sistema de detección distribuida de vibraciones aplicable a la detección de intrusos en las proximidades de los ductos, mediante un φ-OTDR. En este sistema se ha estudiado el efecto negativo de la inestabilidad de modulación que limita la detección de vibraciones distribuidas, su sensibilidad y su alcance. ABSTRACT This thesis describes the research work focused for the study and development of on optical fiber sensors for detecting pressure, flow and vibration in subsea pipes used in the extraction and transportation of hydrocarbons, in order to apply them in deepwater fields in the Gulf of Mexico belonging to the Mexican oil industry. The work has focused on the study and development of optical sensors distributed and quasi distributed. Especially was done on the use and application of fiber Bragg grating (FBG) and optical reflectometers time domain phase sensitive (φ-OTDR). The optical fiber sensors especially are interesting for these applications for their advantageous characteristics such as immunity to electromagnetic interference, multiplexing capability, reliability to work in harsh environments, high temperatures, high pressures, corrosive saline environments, etc. Furthermore, the optical fiber is not only a sensor means it can be used as transmission medium. We have performed a study of the state of the art and the advantages offered by optical sensors point, quasi-distributed and distributed over conventional sensors. Have studied and described interrogators Bragg grating and has developed a calibration method for interrogators useful for the existing interrogators in the market, resulting uncertainty in the measurement of the wavelength of less than ± 0.17 nm and uncertainties (the more interesting in the field of sensors) less than ± 3 pm. Focusing on the application of the Bragg gratings in the oil industry, has been studied in detail the behavior of the FBGs in a wide range of temperatures from -40 °C to 500 oC. As a result of this study we have evaluated the difference in temperature coefficients over various sections of the same, as well as different protective coatings. In particular evaluated and found the differences coatings in the range of temperatures between -40 º C and 60 º C. For the high temperature range between 20 ° C and 500 ° C, has been measured and verified the uniform change of the temperature coefficient at 1pm / ° C for each 100 ° C increase in temperature, in networks regardless of manufacturer thereof. FBG is applied to the non-intrusive measurement of internal pressure in a pipeline and measuring flow of a fluid in a pipe, by measuring the pressure difference between two points thereof. Therefore, has also made a study of detecting vibrations in pipes with fluids. Finally, we have implemented a distributed sensing system vibration applied to intrusion detection in the vicinity of the pipelines, by φ-OTDR. In this system we have studied the negative effect of modulation instability limits the distributed vibration detection, sensitivity and scope.
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Se investiga la compleja mineralogía del Yacimiento de Pallancata (6º productor de plata del mundo) y se establecen las condiciones de formación (P.T) basadas en la petrología de las menas comparada con los datos de mineralogía experimental y en la petrografía y microtermometría de inclusiones fluídas en la ganga silicatada, resultando un depósito típicamente caracterizado como epitermal de sulfuración intermedia.ABSTRACT:Pallancata is a world-class intermediate-sulfidation epithermal deposit, hosted by upper Miocene volcanics of the south-central Peruvian Andes in a sinuous N70ºW, ∼75º SW strike-slip structure, with wide (up to 35 m) pull-apart dilation zones related to bends of the vein strike. The structural evolution of the vein from earlier brecciation to later open space infill resembles the Shila Paula district (Chauvet et al. 2006). Fluid inclusion petrography and microthermometry show that ore deposition is related to protracted boiling of very diluted, mainly meteoric fluids, starting at 250–260 ºC, under ∼300 m hydrostatic head. The mineralogical-petrological study reveals a complex sequence of mineralization (eight stages) and mineral reactions consistent with Ag2S enrichment or Sb2S3 depletion, or both, during cooling over the temperature range 250–200 ºC: pyrite, sphalerite, galena, miargyrite, pyrargyrite-proustite, chalcopyrite, polybasite-pearceite, argentite (now acanthite), and Au–Ag alloy (“electrum”). This Ag2S enrichment and Sb2S3depletion during cooling may be explained by decay of a Ag-rich galena precursor at deeper levels (Pb2S2–AgSbS2 solid solution), which rapidly becomes unstable with decreasing temperature, producing residual (stoichiometric) PbS and more mobile Ag and Sb sulfide phases, which migrated upward and laterally away from the thermal core of the system. The core is still undisclosed by mining works, but the available geochemical evidence (logAg/log Pb ratios decreasing at depth) is consistent with this interpretation, implying a deeper potential resource. Data from sulfide geothermometry, based on mineral equilibria, document the thermal evolution of the system below 200 ºC (stephanite, uytenbogaardtite, jalpaite, stromeyerite, mckinstryite, among others). The end of the most productive stages (3, 4, and 5) is marked by the precipitation of stephanite at temperatures below 197 ± 5 ºC, but precipitation of residual silver continues through the waning stages of the hydrothermal system down to <93.3 ºC (stromeyerite) or in a supergene redistribution (stage 8, acanthite II).
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It is known that a green wall brings some advantages to a building. It constitutes a barrier against solar radiation, thus decreasing and delaying the incoming heat flux. The aim of this study is to quantify such advantages through analytical comparison between two facades, a vegetal facade and a conventional facade. Both were highly insulated (U-value = 0.3 W/m2K) and installed facing south on the same building in the central territory of Spain. In order to compare their thermal trend, a series of sensors were used to register superficial and indoor air temperature. The work was carried out between 17th August 2012 and 1st October 2012, with a temperature range of 12°C-36°C and a maximum horizontal radiation of 1020 W/m2. Results show that the indoor temperature of the green wall module was lower than the other. Besides, comparing superficial outdoor and indoor temperatures of the two walls to outdoor air temperatures, it was noticed that, due to the shading plants, the green wall superficial temperature was 5 °C lower on the facade, while the bare wall temperature was 15 °C higher. The living wall module temperature was 1.6 °C lower than the outdoor, while the values of the conventional one were similar to the outdoor air temperature.