1,596 research outputs found
Contribution Ă l'Ă©tude de la valeur nutritive de quelques plantes naturellement abondantes en Corse
Assessing fragility of a reinforced concrete element to snow avalanches using a non-linear dynamic mass-spring model
This paper presents an assessment of the fragility of a reinforced concrete
(RC) element subjected to avalanche loads, and more generally to dynamic
pressure fields applied orthogonally to a wall, within a reliability
framework. In order to obtain accurate numerical results with supportable
computation times, a light and efficient Single-Degree-of-Freedom (SDOF)
model describing the mechanical response of the RC element is proposed. The
model represents its dynamic mechanical response up to failure. Material
non-linearity is taken into account by a moment–curvature approach, which
describes the overall bending response. The SDOF model is validated under
quasi-static and dynamic loading conditions by comparing its results
to alternative approaches based on finite element analysis and the yield line
theory. Following this, the deterministic SDOF model is embedded within a reliability
framework to evaluate the failure probability as a function of the maximal
avalanche pressure reached during the loading. Several reliability methods
are implemented and compared, suggesting that non-parametric methods provide
significant results at a moderate level of computational burden. The
sensitivity to material properties, such as tensile and compressive
strengths, steel reinforcement ratio, and wall geometry is investigated. The
effect of the avalanche loading rate is also underlined and discussed.
Finally, the obtained fragility curves are compared with respect to the few
proposals available in the snow avalanche engineering field. This approach is
systematic and will prove useful in refining formal and practical risk
assessments. It could be applied to other similar natural hazards, which
induce dynamic pressure fields onto the element at risk (e.g., mudflows,
floods) and where potential inertial effects are expected and for which
fragility curves are also lacking.</p
Development of hot drawing process for nitinol tube
In recent years, Nitinol, near-equiatomic nickel-titanium alloys, have found growing applications in medical technology and joining technology, due to their special characteristics such as shape memory, superplasticity and biocompatibility. The production of Nitinol tube cost-effectively remains a technical challenge. In this paper, we describe a hot drawing process for Nitinol tube production. A Nitinol tube blank and a metal core are assembled together. The assembly is hot drawn for several passes to a final diameter. The metal core is then plastically stretched to reduce its diameter and removed from the tube. Hot drawing process has been applied to Ni50.7Ti and Ni47Ti44Nb9 alloys. Nitinol tubes of 13.6 mm outer diameter and 1 mm wall thickness have been successfully produced from a tube blank of 20 mm outer diameter and 3.5 mm thickness
A reliability assessment of physical vulnerability of reinforced concrete walls loaded by snow avalanches
Snow avalanches are a threat to many kinds of elements (human beings,
communication axes, structures, etc.) in mountain regions. For risk
evaluation, the vulnerability assessment of civil engineering structures such
as buildings and dwellings exposed to avalanches still needs to be improved.
This paper presents an approach to determine the fragility curves associated
with reinforced concrete (RC) structures loaded by typical avalanche
pressures and provides quantitative results for different geometrical
configurations. First, several mechanical limit states of the RC wall are
defined using classical engineering approaches (Eurocode 2), and the
pressure of structure collapse is calculated from the usual yield line
theory. Next, the fragility curve is evaluated as a function of avalanche
loading using a Monte Carlo approach, and sensitivity studies (Sobol indices)
are conducted to estimate the respective weight of the RC wall model inputs.
Finally, fragility curves and relevant indicators such a their mean and
fragility range are proposed for the different structure boundary conditions
analyzed. The influence of the input distributions on the fragility curves is
investigated. This shows the wider fragility range and/or the slight shift in
the median that has to be considered when a possible slight change in
mean/standard deviation/inter-variable correlation and/or the non-Gaussian
nature of the input distributions is accounted for
Avalanche risk evaluation and protective dam optimal design using extreme value statistics
International audienceIn snow avalanche long-term forecasting, existing risk-based methods remain difficult to use in a real engineering context. In this work, we expand a quasi analytical decisional model to obtain simple formulae to quantify risk and to perform the optimal design of an avalanche dam in a quick and efficient way. Specifically, the exponential runout model is replaced by the Generalized Pareto distribution (GPD), which has theoretical justifications that promote its use for modelling the different possible runout tail behaviours. Regarding the defence structure/flow interaction, a simple law based on kinetic energy dissipation is compared with a law based on the volume stored upstream of the dam, whose flexibility allows us to cope with various types of snow. We show how a detailed sensitivity study can be conducted, leading to intervals and bounds for risk estimates and optimal design values. Application to a typical case study from the French Alps, highlights potential operational difficulties and how they can be tackled. For instance, the highest sensitivity to the runout tail type and interaction law is found at abscissas of legal importance for hazard zoning (return periods of 10-1000 a), a crucial result for practical purposes
Is Using Ornaments Still a Crime? Package Design Complexity and Brand Perception with Application to Champagne Labels
This article investigates the impact of the package design complexity on brand perception. This variable is particularly interesting because it is a choice which must be done by each brand manager no matter the product category. The packaging has been studied in many ways, and we already know its importance. A lot of existing researches are focused on the importance of its shape, its colours or its letter type. But only few studies have been done about the impact of the stylistic choice between simple and complex design on the brand perception. Furthermore, the consumer behaviour and design research both agree that the degree of simplicity of the packaging design has a significant impact on consumer’s attitudes towards a brand. In the case of this study, we defined two overall stylistic trends which come from the art literature: simple design versus overloaded design. In order to study the impact of the complexity degree, we created three labels: two representing the previously exposed styles and another one to study the relevance of a medium-loaded design. These labels were created in partnership with a printing company, present in Champagne since 1910. The three labels have the same text but different graphic designs in order to vary the degree of simplicity/complexity of the packaging observed on the market. Then, they were tested among 305 consumers according to a between-subjects experiment. The results allow the verification of different proposals from the literature: previous researches show that a simple design communicates an authentic and honest value which is also demonstrated in our study as the bottle with the simplest design is perceived as the most successful. Also, the bottle with an overloaded design is perceived as cheerful, imaginative and feminine as demonstrated by previous researches. This study demonstrates a significant impact of the package design’s level of simplicity on the brand perception as well as on consumer’s buying choices
Study of Interesting Solidification Phenomena on the Ground and in Space (MEPHISTO)
Real-time Seebeck voltage variations in a Sn-Bi melt during directional solidification in the MEPHISTO spaceflight experiment flown on the USMP-3 mission, have been correlated with well-characterized thruster firings and an Orbiter Main System (OMS) burn. The Seebeck voltage measurement is related to the response of the instantaneous average melt composition at the melt-crystal interface. This allowed us to make a direct comparison of numerical simulations with the experimentally obtained Seebeck signals. Based on the results of preflight and real-time computations, several well-defined thruster firing events were programmed to occur at specific times during the experiment. In particular, we simulated the effects of the thruster firings on melt and crystal composition in a directionally solidifying Sn-Bi alloy. The relative accelerations produced by the firings were simulated by impulsive accelerations of the same magnitude, duration and orientation as the requested firings. A comparison of the simulation results with the Seebeck signal indicates that there is a good agreement between the two. This unique opportunity allows us to make the first quantitative characterization of actual g-jitter effects on an actual crystal growth experiment and to calibrate our models of g-jitter effects on crystal growth
Mass transport phenomena in microgravity: Preliminary results of the first MEPHISTO flight experiment
The MEPHISTO space program is the result of a cooperative effort that involves the French nuclear and space agencies (Commissariat a l'energie atomique, CEA - Centre National d'Etudes Spatiales, CNES) and the American National Aeronautics and Space Administration (NASA). The scientific studies and apparatus development were funded in the frame of the GRAMME agreement between CEA and CNES, the flight costs being taken in charge by NASA. Six flight opportunities are scheduled, with alternating French and American principal investigators. It is the purpose of this paper to briefly present MEPHISTO along with the preliminary results obtained during its first flight on USMP-1 in October 1992
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