Measurement of the Effective Diffusivity in Porous Media by the Diffusion Cell Method

There has been a vast amount of investigation in the field of experimental and theoretical treatments of the effective diffusivity in porous media for more than half of a century [1-4]. The effective diffusivity is required for several reasons [5]; for example, during catalyst formulation, active species can be laid down precisely or with specified concentration profiles on a porous matrix or support. In experimental work on heterogeneous reactions an effective diffusivity is needed to obtain the value of the Thiele modulus and hence to determine the intrinsic reaction kinetics. In reactor design the diffusivity is needed to evaluate the Thiele modulus, which can then be an aid in predicting reaction rates for heterogeneous systems. In addition, a simple and quick testing method could be used as a screening or quality control procedure during catalyst manufacture.

     

Comparison of model numerical predictions of heat and moisture transfer in porous media with experimental observations at material and wall scales: An analysis of recent trends

Models for the prediction of heat and mass transfers in building porous materials have been developed since the 90’s with simulation programs such as MATCH, UMIDUS, DELPHIN and Wufi. These models are used to analyze the physical phenomena occurring and particularly the impact of moisture on buildings’ energy performance and durability. With this goal in mind, it is important to validate the representation of the physical phenomena made by the numerical models. This article reviews recent studies comparing the results obtained with numerical models and experimental data. An overall trend can be observed for most of these studies, highlighting that the experimental front always rushes faster than the simulation results. Therefore, this study analyses theses comparisons to explain these discrepancies based on the effects of (i) the type of materials, (ii) the boundary conditions, (iii) the scale of the design facility, (iv) the model used to describe the physical phenomena and (v) the influence of the model input parameter. The general trend shows that discrepancies are observed most particularly for highly hygroscopic or bio-based materials. These discrepancies are also greater for time dynamic boundary conditions, particularly at the scale of the wall. Moreover, some of the assumptions on the properties of the materials used as input in the models are questioned. Indeed, the models considering the hysteresis effects and temperature dependency of the moisture storage capacity show better agreement with experimental data. Finally, the physical phenomena used in the models only consider diffusive transport while it appears that the advective of moisture through the porous material may play an important role.     

Improvements in the Ammonium Carbonate Leaching Process During the Treatment of Oxidized Nickel Ores

Based on the experimental data obtained in a volume of solution of 25 dm in a periodic installation for the carbonate-ammonia leaching of Nicaro factory reduced minerals, it was established that the reaction of the oxidation of the Fe (II) up to the moment of maximum cobalt extractions is of zero order. The existing correlation between the constant of speed of oxidation of Ni and Co and the specific mass of speed of air in the different leaching zones according to the behaviour of the iron during its oxidation has been demonstrated. Some alternatives arc suggested to improve the leaching operation with the objective of reaching extraction of cobalt higher than 60% while Ni is at 80%.     

Determination of the surface band bending in InxGa1−xN films by hard x-ray photoemission spectroscopy

Core-level and valence band spectra of In_xGa_1−xN films were measured using hard x-ray photoemission spectroscopy (HX-PES). Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (∼20 nm), the spectra contain both surface and bulk information due to the surface band bending. The In_xGa_1−xN films (x = 0–0.21) exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (E_F) near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that E_F in the bulk of the film must be located in the band gap below the conduction band minimum.     

Hybrid Touch/Tangible Spatial 3D Data Selection

We discuss spatial selection techniques for three‐dimensional datasets. Such 3D spatial selection is fundamental to exploratory data analysis. While 2D selection is efficient for datasets with explicit shapes and structures, it is less efficient for data without such properties. We first propose a new taxonomy of 3D selection techniques, focusing on the amount of control the user has to define the selection volume. We then describe the 3D spatial selection technique Tangible Brush, which gives manual control over the final selection volume. It combines 2D touch with 6‐DOF 3D tangible input to allow users to perform 3D selections in volumetric data. We use touch input to draw a 2D lasso, extruding it to a 3D selection volume based on the motion of a tangible, spatially‐aware tablet. We describe our approach and present its quantitative and qualitative comparison to state‐of‐the‐art structure‐dependent selection. Our results show that, in addition to being dataset‐independent, Tangible Brush is more accurate than existing dataset‐dependent techniques, thus providing a trade‐off between precision and effort.     

Decomposition of sparse graphs into two forests, one having bounded maximum degree

Let G be a graph. The maximum average degree of G, written Mad(G), is the largest average degree among the subgraphs of G. It was proved in Montassier et al. (2010) [11] that, for any integer k?0, every simple graph with maximum average degree less than admits an edge-partition into a forest and a subgraph with maximum degree at most k; furthermore, when k?3 both subgraphs can be required to be forests. In this note, we extend this result proving that, for k=4,5, every simple graph with maximum average degree less than mk admits an edge-partition into two forests, one having maximum degree at most k (i.e. every graph with maximum average degree less than (resp. ) admits an edge-partition into two forests, one having maximum degree at most 4 (resp. 5)).     

Towards historical document indexing: extraction of drop cap letters

This paper deals with the difficult problem of indexing ancient graphic images. It tackles the particular case of indexing drop caps (also called Lettrines) and specifically, considers the problem of letter extraction from this complex graphic images. Based on an analysis of the features of the images to be indexed, an original strategy is proposed. This approach relies on filtering the relevant information, on the basis of Meyer decomposition. Then, in order to accommodate the variability of representation of the information, a Zipf’s law modeling enables detection of the regions belonging to the letter, what allows it to be segmented. The overall process is evaluated using a relevant set of images, which shows the relevance of the approach.     

Bioinspired Electro‐Thermo‐Hygro Reversible Shape‐Changing Materials by 4D Printing

Hygromorph composites are moisture‐induced shape‐changing materials that are increasingly studied to develop autonomously actuated deployable structures. The morphing mechanism is based on the high affinity for moisture and the hygroexpansive nature of at least one component, combined with a bilayer microstructure. Among available hygromorphs, those consisting of cellulosic or hydrogel material‐based actuators trigger fast responses to moisture. Their stiffness however decreases significantly with the moisture content and that restricts their potential application as soft actuators. This work proposes a novel 4D printed multistimuli‐responsive structural material based on conductive carbon reinforcements and combined with a moisture sensitive polymer. These 4D printed materials possess a microstructure that provides the capability of natural actuators like pine cones. The actuation of these functional materials could be either triggered passively by the variation of the ambient moisture, or by electroheating, with the latter leading to the control of the moisture content in initially wet samples via Joule effects. This new class of functional materials shows an increase of the actuation speed by a factor 10 compared to other existing hygromorphs with the same responsiveness. When the electrical heating is turned off, passive cooling and moisture driven actuation is triggered in a full reversible mode.     

Performance evaluation of direct and cooperative transmissions in body area networks

Body area networks (BAN) offer amazing perspectives to instrument and support humans in many aspects of their life. Among all possible applications, this paper focuses on body monitoring applications having a body equipped with a set of sensors transmitting in real time their measures to a common sink. In this context, at the application level, the network fits with a star topology, which is quite usual in the broad scope of wireless networks. Unfortunately, the structure of the network at the physical layer is totally different. Indeed, due to the specificity of BAN radio channel features, all radio links are not stationary and all sensors suffer from link losses during independent time frames. In wireless networks, link losses are often coped with multi-hop transmission schemes to ensure a good connectivity. However, since the radio links are not stationary, the multi-hop routes should adapt quickly to BAN changes. We instead propose in this work a different approach based on opportunistic relaying. The concept relies on electing some sensors to support the transmission of other ones having a worst connection. Instead of changing the relay time to time, we rather select a relay node from a statistical perspective. We evaluate this approach from a theoretical point of view and on realistic simulations using the packet error rate outage probability as a performance criterion.     

Ultrafast compound Doppler imaging: providing full blood flow characterization

Doppler-based flow analysis methods require acquisition of ultrasound data at high spatio-temporal sampling rates. These rates represent a major technical challenge for ultrasound systems because a compromise between spatial and temporal resolution must be made in conventional approaches. Consequently, ultrasound scanners can either provide full quantitative Doppler information on a limited sample volume (spectral Doppler), or averaged Doppler velocity and/or power estimation on a large region of interest (Doppler flow imaging). In this work, we investigate a different strategy for acquiring Doppler information that can overcome the limitations of the existing Doppler modes by significantly reducing the required acquisition time. This technique is called ultrafast compound Doppler imaging and is based on the following concept: instead of successively insonifying the medium with focused beams, several tilted plane waves are sent into the medium and the backscattered signals are coherently summed to produce high-resolution ultrasound images. We demonstrate that this strategy allows reduction of the acquisition time by a factor of up to of 16 while keeping the same Doppler performance. Depending on the application, different directions to increase performance of Doppler analysis are proposed and the improvement is quantified: the ultrafast compound Doppler method allows faster acquisition frame rates for high-velocity flow imaging, or very high sensitivity for low-flow applications. Full quantitative Doppler flow analysis can be performed on a large region of interest, leading to much more information and improved functionality for the physician. By leveraging the recent emergence of ultrafast parallel beamforming systems, this paper demonstrates that breakthrough performances in flow analysis can be reached using this concept of ultrafast compound Doppler.