Approche numérique de la plasticité induite par transformation diffusionnelle : investigations dans le cas de l’interaction plasticité classique TRIP

Le phénomène mécanique appelé TRIP (Transformation Induced Plasticity), correspondant à une déformation permanente induite par une transformation de phase, peut apparaître lors d’une transformation sous chargement extérieur comme lorsque la phase parente a été pré-écrouie. Le TRIP peut apparaître en particulier pendant des opérations de soudage d’aciers, lors de la ou des étapes de refroidissement. Le modèle le plus courant qui permet de tenir compte d'un pré-écrouissage de l'austénite pour prédire le développement de TRIP (modèle de Leblond) s'est montré imparfait pour reproduire les résultats expérimentaux dans le cas d’une phase parente pré-écrouie, d’après ce qu’ont montré Taleb et Petit-Grostabussiat. Ceci a donc motivé le développement de méthodes alternatives, à savoir par éléments finis, pour tenter de mieux rendre compte par modélisation de ces effets de pré-écrouissage. Cet article présente les investigations numériques concernant la transformation bainitique d’un macrovolume cubique dans le cas idéalisé où un seul germe est présent au centre du volume d’étude (ceci constitue un cas test), ainsi que dans le cas où des germes apparaissent aléatoirement dans l’espace et dans le temps selon une loi de distribution donnée.Mots clés: Plasticité induite par transformation; modélisation micromécanique; transformation diffusionnelle; éléments finis. The mechanical phenomenon called TRIP (Transformation Induced Plasticity), corresponding to a permanent strain induced by a phase transformation, can be due to an externally applied load or to a pre-hardening of the parent phase. TRIP can appear particularly during a welding operation on steels, during the cooling step(s). The most currently used model which allows to take into account the pre-hardening of austenite for the prediction of TRIP (Leblond model) has shown to be incorrect to reproduce the experimental results in the case of a pre-hardened austenite, according to the work of Taleb and Petit-Grostabussiat. This has motivated the development of alternative methods, with finite elements analysis, to try to improve the prediction of this effect of pre-hardening. This article presents the numerical investigations concerning the bainitic transformation of a cubic macro-volume. Two cases are treated: the ideal case where a single nucleus is present at the center of the volume (test case); the case where nuclei appear randomly in space and in time, according to a given distribution law.Keywords: Transformation induced plasticity; micromechanical modelling; diffusive transformation; finite elements

Will cool roofs improve the thermal performance of our built environment? A study assessing roof systems in Bahrain

A number of international campaigns have recently proposed the use of cool roofs worldwide in order to cope with the summer urban heat island (UHI) effect. This work investigates cool roof strategy and examines the potential of such a strategy for Bahrain. Full-scale measurement, meteorological modelling and thermal simulation of five standard roofs were performed during particular summer days due to the high intensity levels of solar irradiation. This work shows that the light tile roof and metal decking are relatively cooler and more comfortable than others and that the maximum reduction in heat gain occurs for a light tile roof with thermal insulation materials. Nevertheless, without insulation the cooling load is increased by only 1.3%. This percentage seems not to be cost-effective where economics and building construction are concerned. In contrast, the reduction percentage due to the use of thermal insulation in the case of dark tile roof, felt bitumen roof and screed roof increases to 5–7%, which is more cost effective. This work concludes that the cool roof strategy is the most cost-effective for the hot climate of Bahrain, which has a long cooling season. With the current levels of urban development in Bahrain, cool roofs can reduce UHI intensity and building cooling loads, lowering demand for electricity and greenhouse gas emissions from power plants. To avoid any negative consequences from using this strategy, however, trade-offs between urban mitigation and adoptation strategies and complementary technologies should be accounted for in future urban development plans

Potential of Computer-Vision Cellular-Phone Based System to Extract Traffic Parameters

This research work investigates the potential of computer – vision cellular – phone based systems to extract traffic and pedestrian parameters; using handheld smartphones with different camera characteristics; i.e. resolution, sensor size and image depth. Various locations with different geometry and functions were selected. Different traffic parameters were extracted: vehicle spot speed and three state vehicle speed profiles (steady, acceleration and deceleration), vehicle speed and time headway relation, vehicle classifications, roadway level of service and pedestrian walking and crossing speed in light and congested traffic area. The difference between actual and measured parameters defined as error and the relationship between error and camera characteristics were investigated. Also, a linear regression models were developed to express actual measured parameters as function of smartphone measures, error as function of camera characteristics. Analysis of extracted parameters showed there was a high correlation between camera characteristics and the accuracy of measured parameters. In fact, increasing camera resolution and sensor size would give high accuracy results for all studied parameters. The percentage of error was consistently ranged, for vehicle speeds it ranged between (1.4% - 10%), for pedestrian speeds it ranged between (0.5% - 9%) and for vehicles dimensions it ranged between (10% - 25%). The outcomes of this research showed high potential accuracy of smartphone – based vision systems in extracting traffic parameters and opened the door to integrate smartphones in different transportation engineering and civil engineering applications

A note on void ratio of fibre-reinforced soils

This technical note extends the concept of void ratio, presented traditionally in soil mechanics, for fibre-reinforced soils. Phase relationships related to the void ratio of fibre-reinforced soils are presented along with their definitions. A simple analytical model verified with experimental data for estimating the void ratio of fibre-reinforced soils is developed which can be used to express the compressibility of fibre-reinforced soils in geotechnical engineering applications. The results indicate that the void ratio of fibre-reinforced soils is dependent on the volume ratio of fibre-soil solid

Quasiparticles dynamics in high-temperature superconductors far from equilibrium: an indication of pairing amplitude without phase coherence

We perform time resolved photoelectron spectroscopy measurements of optimally doped \tn{Bi}_2\tn{Sr}_2\tn{CaCu}_2\tn{O}_{8+\delta} (Bi-2212) and \tn{Bi}_2\tn{Sr}_{2-x}\tn{La}_{x}\tn{Cu}\tn{O}_{6+\delta} (Bi-2201). The electrons dynamics show that inelastic scattering by nodal quasiparticles decreases when the temperature is lowered below the critical value of the superconducting phase transition. This drop of electronic dissipation is astonishingly robust and survives to photoexcitation densities much larger than the value sustained by long-range superconductivity. The unconventional behaviour of quasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to the inelastic path. Our measurements indicate that strongly driven superconductors enter in a regime without phase coherence but finite pairing amplitude. The latter vanishes near to the critical temperature and has no evident link with the pseudogap observed by Angle Resolved Photoelectron Spectroscopy (ARPES).Comment: 7 pages, 5 Figure

Inappropriate prescribing in hospitalized elderly patients

Inappropriate prescribing (IP) is a major healthcare problem in elderly patients. The risk of this problem increases during hospitalization. This is due to increase morbidity and thus increases the use of medications by the inpatients. This study will clarify the problem of IP for elderly people during hospitalization and will identify the different types of it. It also will highlight some tools that are used to assess the different types of IP and the prevalence of it in elderly patients during hospitalization. Finally, the study will address the consequences of IP in the elderly inpatients and the risks associated with the use of some potentially inappropriate medications (PIMs) in the elderly.

Evaluation of inappropriate prescribing to the hospitalized elderly patients in Al Shifa hospital, Gaza, Palestine

Background: The current study aimed to assess the prevalence of inappropriate prescribing (IP) for hospitalized elderly patients at Al Shifa Hospital, Gaza, Palestine.Methods: This study was a retrospective cross-sectional study. A total of 2385 prescribed drugs for 380 elderly inpatients in internal, cardiology, and respiratory departments were screened for IP. Four criteria were used to detect IP using chart review method; Drug-drug interactions (DDIs), drug contra-indications (CI), duplication of therapy and Beers' criteria 2012.Results: The results showed that 44.2% of patients had at least one IP. Around 33.2% of the patients had DDIs, 19.2% had IP according to Beers' criteria and 1.1% had drug CI. There was no duplication of therapy. A total of 323 IP instances were detected. Of them, 74% for DDIs and 24.8% for Beers' criteria. The prevalence of overall IP was significantly influenced by age (p-value=0.024), polypharmacy (p-value<0.001), degree of morbidity (p-value<0.001), and departments (p-value=0.018). The prevalence of DDIs was influenced by polypharmacy (p-value<0.001), degree of morbidity (p-value=0.001), and departments (p-value=0.005). Finally, the prevalence of IP according to Beers' criteria was significantly influenced by departments with the highest in the cardiology department (29.7%) (P-value=0.007).Conclusions: Although the overall IP was common, it was not far higher than that reported worldwide. The majority of IP was DDIs. Age, polypharmacy, degree of morbidity and departments influenced the occurrence of IP

The Effects of Intermittent Solar Radiation in Off-grid Solar Power System A Case Study of Two Cities; Sacramento, CA and Miami, FL 'Worst Month' method

This study illustrates the impact of the solar radiation by comparing the design of two off-grid PV systems installed in two different locations have same annual average solar irradiation (insolation) values at fixed tilt angle. The case study selected the city of Sacramento, CA and Miami, FL. The monthly average Irradiation values in Sacramento are very diverse where the minimum, average and maximum values are spaced compared with the values in Miami which have no significant variation of solar irradiation from month to month. Comparing the Design of the two different systems will reflect the impact of the sporadic solar insolation on the rating values for the components of each system, which is affecting PV system cost. The design assumes the same load based and the worst case scenario of the solar irradiation. Each system will consist of PV modules, charge controller, power inverter and batteries