196,482 research outputs found
A focus on dynamic modulus: Effects of external and internal morphological features
No full textThe present work examines the effects of external and internal morphological features on the dynamic elastic modulus and its measure. It consists of two parts. The first part considers the effect of geometrical features of probes and shows the key role of roughness as source of a systematic error leading to the underestimation of the Young’s modulus. The second one is focused on the effect of porosity. Several models which consider the porosity as an ideal regular microstructure and the relative equations describing the Young’s modulus vs. porosity have been reviewed and critically discussed. The values of the relative modulus Er predicted by different models are similar for materials with low porosity (p < 0.2) and isolated pores whereas they strongly diverge if p > 0.2 and interconnected pores are present. Moreover, such models fail to describe the elastic behavior of materials correctly also with low porosity (p ≈ 0.1) such as sintered steels in the case of pores with a preferred orientation and an irregular shape
The influence of the dispersed phase on the convective heat transfer in dispersed flow film boiling
No full textThesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1990.Includes bibliographical references (leaves 209-214).by Anthony F. Varone Jr.Sc.D
Tackling local ecological homogeneity. Finding intraspecific trait variability in local populations of Mediterranean plants
Get PDFLocal homogeneity, in ecology, is the often undisclosed assumption that variability within populations is negligible or mostly distributed evenly. In large areas, this can lead to the aggregation of different populations without regard for their unique needs and characteristics, such as drought sensitivity and functional trait distributions. Here, we discuss whether this assumption can be justified, and we hypothesize that discerning the source of variation between plasticity and adaptation could be a feasible approach to formulate an informed decision. We test this hypothesis on plants, resorting to a common garden experiment to determine the source of variation of several plant functional traits at a local scale (~60 km) of three wild species: Quercus ilex, Pistacia lentiscus, and Cistus salviifolius. Individuals of each species were sourced from three key sites chosen along a local aridity gradient. Our approach led to the rejection of the local homogeneity assumption for Q. ilex and C. salviifolius at this scale due to the adaptive divergence observed among neighboring populations. This case study provides evidence that addressing local homogeneity can highlight diverging populations in a relatively simple way. We conclude that gathering empirical evidence on intraspecific variability is a feasible approach that can provide researchers with solid bases to decide whether to adopt the local homogeneity assumption or not
Adaptive photosynthetic strategies of the Mediterranean maquis species according to their origin
No full textIn consideration of their origin the adaptive strategies of the evergreen species of the Mediterranean maquis were analysed. Rosmarinus officinalis L., Erica arborea L., and Erica multiflora L. had the lowest net photosynthetic rate (PN) in the favourable period [7.8±0.6 μmol(CO2) m-2 s-1, mean value], the highest PN decrease (on an average 86 % of the maximum) but the highest recovery capacity (>70 % of the maximum) at the first rainfall in September. Cistus incanus L. and Arbutus unedo L. had the highest PN during the favourable period [15.5±5.2 μmol(CO2) m-2 s-1, mean value], 79 % decrease during drought, and a lower recovery capacity (on an average 54 %). Quercus ilex L., Phillyrea latifolia L., and Pistacia lentiscus L. had an intermediate PN in the favourable period [9.2±1.3 μmol(CO2) m-2 s-1, mean value], a lower reduction during drought (on an average 63 %), and a range from 62 % (Q. ilex and P. latifolia) to 39 % (P. lentiscus) of recovery capacity. The Mediterranean species had higher decrease in PN and stomatal conductance during drought and a higher recovery capacity than the pre-Mediterranean species. Among the pre-Mediterranean species, P. latifolia had the best adaptation to long drought periods also by its higher leaf mass per area (LMA) which lowered leaf temperature thus decreasing transpiration rate during drought. Moreover, its leaf longevity determined a more stable leaf biomass during the year. Among the Mediteranean species, R. officinalis was the best adapted species to short drought periods by its ability to rapidly recover. Nevertheless, R. officinalis had the lowest tolerance to high temperatures by its PN dropping below half its maximum value when leaf temperature was over 33.6 °C. R. officinalis may be used as a bioindicator species of global change
Long-time variations in leaf mass and area of Mediterranean evergreen broad-leaf and narrow-leaf maquis species
No full textMorphological (dry mass, DM; surface area, LA; leaf mass per area, LMA), anatomical (leaf thickness, L), phenological (leaf life span, LL), and physiological (net photosynthetic rate, PN) leaf traits of the evergreen species co-occurring in the Mediterranean maquis developing at Castelporziano (Rome) were tested. The correlation analysis indicated that LMA variation was tightly associated with LL variations: Cistus incanus and Arbutus unedo had a short LL (4±1, summer leaves, and 11±1 months, respectively) and low LMA (153±19 g m–2) values, Quercus ilex, Phillyrea latifolia, and Pistacia lentiscus high LMA (204±7 g m–2) and long LL (22±3 months), Erica arborea, Erica multiflora, and Rosmarinus officinalis a short LL (9±2 months) and an either high (213±29 g m–2, R. officinalis and E. multiflora) or low (115±17 g m–2, E. arborea) LMA. LMA values were significantly (p≤0.05) correlated with PN (r≥0.68). In the tested species, LMA increased in response to the decrease of the total rainfall during the leaf expansion period. LMA variation was due to the unequal variation of DM and LA in the considered species. LMA is thus a good indicator of evergreen maquis species capability to respond to climate change, in particular to total rainfall decrease in the Mediterranean basin
W-1% La2O3 Submitted to a Single Laser Pulse: Effect of Particles on Heat Transfer and Surface Morphology
Get PDFW-1% La2O3 has been irradiated by a single laser pulse (λ = 1064 nm, pulse duration τ ≈ 15 ns, pulse energy Ep ≈ 4 J, spot size Φ = 200 μm, surface power density I = 8.5 × 1011 W·cm−2) to simulate the effects of transient thermal loads of high energy occurring in a tokamak under operative conditions. The samples have been then examined by scanning electron microscope (SEM) observations to investigate erosion effects and surface morphological features. A surface depression forms in the spot central area surrounded by a ridge due to the movement of molten metal. Owing to the burst of gas bubbles, hemispherical cavities of about 10 μm and deposited droplets are observed in the ridge while the zones surrounding the ridge thermal stresses arising from fast heating and successive cooling produce an extended network of micro-cracks that often follow grain boundaries. The results are discussed and compared to those obtained in a previous work on pure bulk W
Vibrational interaction between urban agglomerates and geological system with heterogeneous composition
Get PDFThis PhD thesis evaluates Site-City Interaction (SCI - Guéguen et al. 2002, Bard et al. 2005, Guéguen and Bard 2005, Kham et al. 2006, Semblat et al. 2008), i.e., the influence of buildings on ground motion and local seismic responses. The free-field conditions of the ground surface, which consider the absence of structures that can generate vibrations, are widely used to analyse the local seismic response for both scientific and technical issues. Nevertheless, this assumption leads to a very strong approximation in urban areas, in which the dynamic interaction between the urban agglomerate and the soil cannot be neglected. Many bibliographic data showed the transmission of vibrations from buildings to the soil, i.e., the amplification of ground shaking during earthquakes and the generated wave field, which can propagate far from the city centre (Wirgin and Bard 1996, Guéguen et al. 2000, Kham et al. 2006, Semblat et al. 2008). Previously published studies mainly focused on engineering, while the geological component was strongly simplified. Thus, complex 1D amplification effects from the soil layering and 2D effects from the lateral heterogeneity, topography and shape of the seismic bedrock have been underestimated. The Fosso di Vallerano valley case study was chosen because this area is characterized by a highly heterogeneous geological setting and has recently experienced a massive expansion of urbanization during the last decade, which completely perturbed the free- field conditions of the original alluvial valley that was created by the tributaries of the Tiber River during the Holocene. In particular, the Fosso di Vallerano valley hosts the “Europarco Business Park”, i.e., the highest buildings (120 m) in Rome. A preliminary phase of this research was dedicated to the reconstruction of the engineering-geological model of the valley, the 1D numerical modelling of the seismo-stratigraphic setting of the alluvial body (Bozzano et al. 2015, 2016) and the calibration of an absorbing layer system to remove spurious wave reflections at the model boundaries (Varone et al. 2014). Several geophysical investigations have also been conducted by considering both seismic events and noise measurements. In recent decades, great effort has been dedicated to numerical approaches to evaluate the local seismic response. Numerical modelling actually represents the main tool to estimate local seismic responses, particularly in urban areas, where geophysical measurements are often not suitable. A proper 2D numerical modelling of the seismic response in free-field conditions that considers the city agglomerate according to an SCI approach is conducted through the CESAR-LCPC FEM code, which considers two geological sections across the Fosso di Vallerano valley. The structural and dynamic features of different building typologies in the selected study area are also considered. The urban agglomerate in this valley mainly consists of residential reinforced
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concrete (RC) buildings, which are characterized by rectangular or square geometry and heights from 6 m to 25 m. The valley also hosts particular type of buildings that are part of the “Europarco Business Park”, including two skyscrapers (named “Europarco Tower” and “Eurosky Tower”) that are 120 m and 155 m high, respectively. These towers are characterized by a rectangular plan geometry and consist of steel that is coupled with a reinforced concrete structure. The eigenmodes are computed through the CESAR-LCPC code to evaluate the dynamic characteristics of the buildings. All the buildings are modelled by considering their super-structure, i.e., columns and beams, and by assuming the concentrated masses and stiffness values in 2D. The main periods of the urban expansion are defined to evaluate the variations in the local response because of the increasing urbanization that was observed over the last decade. Overall, 5 models that assume SCI conditions are simulated. Ricker wavelets (Ricker 1943, 1953) of order 0 with PGD = 1 m (synthetic wavelet) and three real weak motions are applied as seismic input within the seismic bedrock of all the models by assuming visco-elastic conditions. The results are analysed in terms of wave propagation along the models’ surfaces, the spatial variation in the amplification function and the distribution of the kinetic energy along the ground surface. The wave propagation maps show the effectiveness of the absorbing layer system on both sides and at the bottom of the models to dampen spurious waves. Indeed, no spurious contributions enter the valley through the boundaries or the bottom of the model. The presence of the buildings induces major changes in the propagated wave field, inducing a low ground motion at the building’s foundation level and increasing the ground shaking in the area surrounding the structures. The influence of these buildings is also very important in the amplification function: all the modes under free-field surface conditions are nullified in the portions that are occupied by the buildings, and larger amplifications are calculated laterally and near the buildings’ foundations. Additionally, a redistribution of the energy along the ground surface is shown by a strong reduction in the kinetic energy close to the building and an increase in the areas surrounding the buildings. These findings highlight that the presence of buildings significantly changes the seismic response of the alluvial valley at least at the local scale
Decellularization and tissue engineering. Viable therapeutic prospects for transplant patients and infertility?
Get PDFDecellularization and tissue engineering: Viable therapeutic prospects for transplant patients and infertility
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