1,485 research outputs found

    Collisions in shape memory alloys

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    We present here a model for instantaneous collisions in a solid made of shape memory alloys (SMA) by means of a predictive theory which is based on the introduction not only of macroscopic velocities and temperature, but also of microscopic velocities responsible of the austenite-martensites phase changes. Assuming time discontinuities for velocities, volume fractions and temperature, and applying the principles of thermodynamics for non-smooth evolutions together with constitutive laws typical of SMA, we end up with a system of nonlinearly coupled elliptic equations for which we prove an existence and uniqueness result in the 2 and 3 D cases. Finally, we also present numerical results for a SMA 2D solid subject to an external percussion by an hammer stroke

    Ecological factors affecting Alpine chamois population recruitment: remote sensing can support adaptive management

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    The analysis of ecological factors able to affect the life history traits of ungulates is important to reveal key information on population dynamics of wild herbivores. As regard to bovids, it is often crucial for juveniles and yearlings to gain quickly body size and mass, as such growths primarily increase chance to reach re- productive maturity (i.e., an increase in the survival probability). Accordingly, we modeled a set of ecological factors accounting for the variation of Alpine chamois (Rupicapra rupicapra) population recruitment through three indexes: i) the ratio kids/adult females (NK/NF), ii) the ratio yearlings/adult females (NY/NF), and iii) the yearlings eviscerated body mass (YBM). These indexes were derived respectively from block count census and from hunting records in the last 45 years in different ecological contexts in the South-West Trento province. These indexes were associated to forage quality/quantity, winter harshness, and local chamois density. In detail, we considered NDVI (Normalized Difference Vegetation Index) as a proxy for the quality of Alpine meadows used by chamois in spring and summer and snow cover data belonging to the National Aeronautics and Space Ad- ministration (NASA) remote sensing dataset (TERRA-MODIS). The reproductive success of these populations was strongly influenced both by the quality of meadows during births period (May) and by the space-time pattern of growth and maturation of Alpine pastures in spring and summer periods. Even winter harshness played an important role in this process. In particular, i) the NK/NF was positively influenced by the average quality of the grazing season previous to the births period and by the maximum NDVI value recorded in May (i.e., births period); ii) the NY/NF was negatively affected by the extent of snow cover in the first winter of kids and positively related to the average quality of the pasture in the subsequent spring and summer (i.e., the feed intake period in which individuals had to recover weight loss derived from previous winter); and iii) the YBM revealed a negative trend during the study period suggesting a difficult adaptation to climate and environmental changes taking place. Contrary to our expectations, local density was not able to influence these variables. This result may suggest that local density are not exceedingly high in the study area and therefore are not able to promote density dependent phenomena. In conclusion, these results contribute to increase the knowledge of the mechanisms underlying Alpine chamois population dynamics and give insights to plan adaptive management and conservation of this species

    An Extensive Collection of Evaluation Indicators to Assess Occupants' Health and Comfort in Indoor Environment

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    Today, the effects of the indoor environment on occupants' health and comfort represent a very important topic and requires a holistic approach in which the four main environmental factors (thermal comfort, air quality, acoustics, and lighting) should be simultaneously assessed. The present paper shows the results of a literature survey that aimed to collect the indicators for the evaluation of occupants' health and comfort in indoor environmental quality evaluations. A broad number of papers that propose the indicators of a specific environmental factor is available in the scientific literature, but a review that collects the indicators of all four factors is lacking. In this review paper, the difference between indicators for the evaluation of risk for human health and for comfort evaluation is clarified. For each environmental factor, the risk for human health indicators are proposed with the relative threshold values, and the human comfort indicators are grouped into categories according to the number of parameters included, or the specific field of application for which they are proposed. Furthermore, the differences between human health and comfort indicators are highlighted

    Weak binding between two aromatic rings: Feeling the van der Waals attraction by quantum Monte Carlo methods

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    We report a systematic study of the weak chemical bond between two benzene molecules. We first show that it is possible to obtain a very good description of the C_2 dimer and the benzene molecule, by using pseudopotentials for the chemically inert 1s electrons, and a resonating valence bond wave function as a variational ansatz, expanded on a relatively small Gaussian basis set. We employ an improved version of the stochastic reconfiguration technique to optimize the many-body wave function, which is the starting point for highly accurate simulations based on the lattice regularized diffusion Monte Carlo (LRDMC) method. This projection technique provides a rigorous variational upper bound for the total energy, even in the presence of pseudopotentials, and allows to improve systematically the accuracy of the trial wave function, which already yields a large fraction of the dynamical and non-dynamical electron correlation. We show that the energy dispersion of two benzene molecules in the parallel displaced geometry is significantly deeper than the face-to-face configuration. However, contrary to previous studies based on post Hartree-Fock methods, the binding energy remains weak (~ 2 kcal/mol) also in this geometry, and its value is in agreement with the most accurate and recent experimental findings

    A new freeware raycasting tool combined with fluorescent coating to allow for object visibility

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    Abstract Time resolved PIV encompassing moving and/or deformable objects interfering with the light source requires the employment of dynamic masking (DM). A few DM techniques have been recently developed, mainly in microfluidics and multiphase flows fields. Most of them require ad-hoc design of the experimental setup, and may spoil the accuracy of the resulting PIV analysis. A new DM technique is here presented which envisages, along with a dedicated masking algorithm, the employment of fluorescent coating to allow for accurate tracking of the object. We show results from measurements obtained through a validated PIV setup demonstrating the need to include a DM step even for objects featuring limited displacements. We compare the proposed algorithm with both a no-masking and a static masking solution. In the framework of developing low cost, flexible and accurate PIV setups, the proposed algorithm is made available through a freeware application able to generate masks to be used by an existing, freeware PIV analysis package. Graphic abstrac

    Regularized lattice Boltzmann Multicomponent models for low Capillary and Reynolds microfluidics flows

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    We present a regularized version of the color gradient lattice Boltzmann (LB) scheme for the simulation of droplet formation in microfluidic devices of experimental relevance. The regularized version is shown to provide computationally efficient access to Capillary number regimes relevant to droplet generation via microfluidic devices, such as flow-focusers and the more recent microfluidic step emulsifier devices.Comment: 9 pages, 5 figure

    Criticalities in the NZEB retrofit of scholastic buildings: analysis of a secondary school in Centre Italy

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    Abstract In Italy, the recast of the European Directive on Energy Performance of Buildings (2010/31/EU) is implemented with specific definitions and deadlines for Nearly Zero Energy Buildings. We focus our attention on schools, not only for their social importance and high visibility, but also because in the next future a significant share of these buildings is likely to undergo refurbishment for different purposes than the energetic one. We start to analyze the criticalities associated with the current Italian legislation on NZEBs by means of a bottom-up approach: we choose a benchmark secondary school (located in Pisa, hosting about 750 students) and perform an accurate energy audit of the building system, together with an energy and economic simulation of an NZEB retrofit. More in detail, we present the case study and explain its choice as an appropriate representative of the existing scholastic buildings in Centre Italy; besides, we build two concurrent energy models, based on tailored and asset rating methods, we propose technically-feasible actions for deep renovation, and simulate, for both models, the associated energy and economic savings after 20 years of use. We observe long payback periods of the retrofit measures, due to low yearly energy uses in the existing configuration. Based on these results, we attempt to extend to a more general level the considerations on strengths and weaknesses encountered in the present application of the Italian regulation on NZEBs

    Towards a holistic approach to indoor environmental quality assessment: Weighting schemes to combine effects of multiple environmental factors

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    Abstract In the recent past, great attention has been posed on the assessment of the energy performance and of the operating and maintenance costs of the building stock. Currently, new approaches of analysis are considered by the scientific community, which put the occupant's well–being at the centre of the evaluation process. In this context, the IEQ assessment acquires an ever increasing importance, especially if the combined effects of multiple environmental factors are considered. With this purpose, to date, different weighting schemes can be found in the literature, obtained through subjective investigations and mathematical methods. In this paper, the weighting schemes proposed in the literature in the period 2002–2018 were examined, considering the survey methodologies used. The more relevant studies found in the literature were compared and the related weighting schemes were discussed, based on the intended use of the buildings. In particular, 122,000 questionnaires in 18 different countries all over the world were examined and the most relevant environmental factors were selected: Thermal Environment (TH), Air Quality (AQ), Acoustics (AC), and Lighting (LT). Three different average weighting schemes were obtained for each of the following uses: offices, schools, dwellings; a final additional weighting scheme was obtained considering the average values of the normalized weights for all the building uses, a possible solution for buildings with an unspecified or not unique intended use. Moreover, an original weighting scheme was obtained and proposed on the basis of the results of three different subjective surveys, involving about 1400 participants, carried out in some university classrooms at the School of Engineering of the University of Pisa: it was compared with the one obtained by the literature for school buildings. It was observed an overestimation of the importance of TH (0.42 instead of 0.33) and an underestimation of AC (0.19 instead of 0.26), whereas AQ and LT are in accordance (0.17 instead of 0.19 and 0.22, respectively). The results of the present study can be useful to those who intend to deal with holistic approaches to building design, for which accurate assessments of occupants' well-being are taken into consideration as well as aspects related to energy performance and building management costs
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