Automatic correction of background phase offset in 4D-flow of great vessels and of the heart in MRI using a third-order surface model

Magnetic Resonance Materials in Physics, Biology and Medicine - To evaluate an automatic correction method for velocity offset errors in cardiac 4D-flow acquisitions. Velocity offset correction was...     

Multi-objective exploration of architectural designs by composition of model transformations

Software and Systems Modeling - Designing software architectures and optimizing them based on extra-functional properties (EFPs) require to identify appropriate design decisions and to apply them...     

Evaluation of the Hall parameter of electrolyte solutions in thermosyphonic MHD flow

The objective of this work is to determine experimentally the Hall parameter of electrolyte solutions using a closed loop thermosyphonic magnetohydrodynamic flow. The upper and lower parts of the loop, which represent the heat sink and heat source of the system respectively, are constructed from copper pipe coated with varnish on the inside surface. The middle region, connecting the upper and lower parts of the loop, is made from plastic vertical pipes, with segmented copper electrodes placed vertically opposite to each other on each side of the loop plastic walls and connected as a Hall generator to measure the open circuit voltage. A transverse magnetic field is imposed in the middle non-conducting plastic-wall region by a set of permanent magnets. The magnets provide a magnetic field strength of up to 0.225 T, whereas the driving temperature difference between the hot and cold portion of the loop ranges from 10 to 80 °C. Measurements of the induced flow rate and induced open circuit voltage are reported as a function of driving temperature difference and magnetic field strength.The analytical one-dimensional model of Ghaddar [Int. J. Heat Mass Transfer 41 (8-9) (1998) 1075] is extended to account for the electrode design and the Hall effect pertinent to electrolyte solutions. The open circuit voltage is related to the driving temperature difference, flow characteristic, magnetic field strength, electrolyte electric properties and electrode design. The developed 1-D model and the measured open circuit voltage are used to evaluate the Hall parameter (ωτ), which is a property of the fluid of the electrolyte liquid. It is found that ωτ can be as large as 100 for electrolytes and causes a significant loss in power output at the electrodes due to electron drift in the fluid leading to generation of current in an axial direction at the expense of the current flowing in the transverse direction between the electrodes.     

Pyroelectric energy conversion: optimization principles

In the framework of microgenerators, we present in this paper the key points for energy harvesting from temperature using ferroelectric materials. Thermoelectric devices profit from temperature spatial gradients, whereas ferroelectric materials require temporal fluctuation of temperature, thus leading to different applications targets. Ferroelectric materials may harvest perfectly the available thermal energy whatever the materials properties (limited by Carnot conversion efficiency) whereas thermoelectric material's efficiency is limited by materials properties (ZT figure of merit). However, it is shown that the necessary electric fields for Carnot cycles are far beyond the breakdown limit of bulk ferroelectric materials. Thin films may be an excellent solution for rising up to ultra-high electric fields and outstanding efficiency. Different thermodynamic cycles are presented in the paper: principles, advantages, and drawbacks. Using the Carnot cycle, the harvested energy would be independent of materials properties. However, using more realistic cycles, the energy conversion effectiveness remains dependent on the materials properties as discussed in the paper. A particular coupling factor is defined to quantify and check the effectiveness of pyroelectric energy harvesting. It is defined similarly to an electromechanical coupling factor as k2=p2theta0/(epsilontheta33cE), where p, theta0, epsilontheta33, cE are pyroelectric coefficient, maximum working temperature, dielectric permittivity, and specific heat, respectively. The importance of the electrothermal coupling factor is shown and discussed as an energy harvesting figure of merit. It gives the effectiveness of all techniques of energy harvesting (except the Carnot cycle). It is finally shown that we could reach very high efficiency using 1110.75Pb(Mg1/3Nb2/3)-0.25PbTiO3 single crystals and synchronized switch harvesting on inductor (almost 50% of Carnot efficiency). Finally, practical implementation key points of pyroelectric energy harvesting are presented showing that the different thermodynamic cycles are feasible and potentially effective, even compared to thermoelectric devices.     

Flush Endplate Connections in Fire: Time-Dependent Behavior of Tension Bolts

Steel connections play a crucial role in maintaining the integrity and stability of steel building frames especially when exposed to fire temperatures. The behavior of flush endplate connections in fire is shown to be governed by tension bolt failure as bolts lose their strength and stiffness more rapidly at higher temperatures. As a result, the ability to predict the development of stresses in tension bolts of flush endplate connections at different stages of fire is of special importance. One of the factors influencing bolt stresses in fire is the thermal creep or time-dependent inelastic response of steel to elevated temperatures. Therefore, time- and temperature-dependent behavior of tension bolts of flush endplate connections in fire is the focus of this study. Stress-time histories in tension bolts are obtained by explicit consideration of thermal creep of steel in FE models of flush endplate connections at elevated temperatures. To better understand the effect of thermal creep on tension bolt behavior, the correlation between time-dependent rotational deformation of flush endplate connections and bolt stresses is also investigated. Further, the isochronous representation is utilized to study the rotational deformation and the tension bolt stresses under various applied moments ranging from 50% to 95% of the moment capacity and fire temperatures ranging from 450°C to 600°C with 25°C increment. Through such representation, it is indicated that the connection behavior is not only dependent on bolt strength degradation and applied moment, but also affected by the time duration of applied moments and temperatures. Also, with the inclusion of thermal creep of steel, the connection experiences higher rotation and excessive endplate deformation with stress relaxation leading to top tension bolt failure at earlier stages of fire. More specifically, for time exposure greater than or equal to 60 min, the failure temperature of the connection decreases from 600°C to around 550°C. Therefore, neglecting thermal creep of structural steel may result in an unsafe prediction of the overall response of flush endplate connections in fire.     

Risk assessment after internal exposure to black sand from Camargue: uptake and prospective dose calculation

Some beaches in the south of France present high levels of natural radioactivity mainly due to thorium (Th) and uranium (U) present in the sand. Risk assessment after internal exposure of members of the public by either inhalation or ingestion of black sand of Camargue was performed. This evaluation required some information on the human bioavailability of U and Th from this sand. In vitro assays to determine the solubility of U, Th and their progeny were performed either in simulated lung fluid, with the inhalable fraction of sand, or in both simulated gastric and intestinal fluids with a sample of the whole sand. The experimental data show that the bioavailability of these radionuclides from Camargue sand is low in the conditions of the study. Prospective dose assessment for both routes of intake show low risk after internal exposure to this sand.     

Materials, structures and power interfaces for efficient piezoelectric energy harvesting

The possibility of recycling ambient energies with miniature electrical generators instead of using batteries with limited lifespan has stimulated important research efforts over the past years. Integration of such miniature generators is mainly envisioned into low power autonomous systems, for various industrial or domestic applications. This paper focuses on the use of piezoelectric materials for generating electrical energy from ambient mechanical vibrations. A review of the piezoelectric materials and the electromechanical structures which have been proposed in this field is first presented. Electrical circuits with one-stage, two-stage and three-stage interfaces which have been developed for optimizing the electrical power flow from piezoelectric devices to energy storage elements are then compared to a novel technique for controlling the energy converted by piezoelectric materials. This novel approach is derived from Ericsson thermodynamic cycle. A solution for practical implementation is proposed, theoretical predictions and experimental results are compared and discussed.     

Investigation of Slow-Propagation Tungsten Delay Mixtures

The burning characteristics and reliability of slow-propagation tungsten delay mixtures (characteristic time 38–42 s/in) were studied experimentally by using various mixture compositions and tungsten particle sizes. Thermal analysis showed that potassium perchlorate is vital to initiate the reaction. Gravimetric analysis indicated that during the reaction overall mass loss of the delay mixtures did not exceed 5% compared to their initial mass. A mixture containing a tungsten powder of 6–8 μm was found to have the lowest effective activation energy, facilitating good ignition and burning zone propagation. The results of this study were successfully used to design a tiny delay which exhibited reliable ignition, burning and propagation characteristics under extreme conditions.     

Etude et réalisation de diviseurs de fréquence analogiques à diode à avalanche

In this paper the potential interest of analog avalanche diode frequency dividers is demonstrated. Their fundamental operation principle relies on the use of an idler signal. Experiments performed on avalanche diode frequency dividers with division ratios of 2, 3 and 4 in the centimeter wave range have pointed out the possibility of wide instantaneous bandwidth and interestingrf conversion efficiencies.