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.     

Effect of composite electrode thickness on the electrochemical performances of all-solid-state li-ion batteries

Several ceramic half-cells with differing electrode composite thicknesses but identical formulations were assembled using the spark plasma sintering (SPS) technique, in order to conduct comparable investigations of their kinetic limitations. The SPS technique was used to assemble the composite electrode and the electrolyte together within a few minutes. NASICON-type Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) ceramic was used as solid electrolyte, as it offers high ionic conductivity (3 × 10^?4 S.cm^?1 at 25 °C) with a Li⁺ transport number of 1. LiFePO₄ active material was used as a model material; it offers an average flat potential of 3.45 V vs Li⁺/Li and a reasonably high theoretical capacity of 170 mAh.g^?1. Surface capacity values (from 0.8 to 3.5 mAh.cm^?2), which are proportional to electrode thickness, remained quite close to the initial values after more than 20 cycles, even for a 325 μm thick electrode (3.5 mAh.cm^?2). The overpotential in the flat plateau region was proportional to the current density used, which means that it was dependent only on the cell’s ohmic drop. Performances were not limited by the ion transport into the solid electrolyte and composite electrode volume - as in classical Li-ion batteries - since the transport number of LAGP is one. Therefore, very thick electrode-enabling batteries with high-surface capacity can be considered.     

Highly organised and dense vertical silicon nanowire arrays grown in porous alumina template on <100> silicon wafers

In this work, nanoimprint lithography combined with standard anodization etching is used to make perfectly organised triangular arrays of vertical cylindrical alumina nanopores onto standard <100>−oriented silicon wafers. Both the pore diameter and the period of alumina porous array are well controlled and can be tuned: the periods vary from 80 to 460 nm, and the diameters vary from 15 nm to any required diameter. These porous thin layers are then successfully used as templates for the guided epitaxial growth of organised mono-crystalline silicon nanowire arrays in a chemical vapour deposition chamber. We report the densities of silicon nanowires up to 9 × 10⁹ cm⁻² organised in highly regular arrays with excellent diameter distribution. All process steps are demonstrated on surfaces up to 2 × 2 cm². Specific emphasis was made to select techniques compatible with microelectronic fabrication standards, adaptable to large surface samples and with a reasonable cost. Achievements made in the quality of the porous alumina array, therefore on the silicon nanowire array, widen the number of potential applications for this technology, such as optical detectors or biological sensors.     

The Stone Age Revisited: Building a Monolithic Inorganic Lithium‐Ion Battery

A new path for the design of safe and efficient, all‐solid‐state Li‐ion batteries by spark plasma sintering (SPS) is considered. To reach a good electrochemical performance from such batteries, several parameters are investigated, such as the composite‐electrode formulation (active material/electrolyte/carbon ratio) and the influence of the sintering parameters on their compactness. The formulation is optimized to ensure good ionic and electronic percolation through the composite electrode's volume. The compactness has to be sufficient to guarantee a good mechanical aspect, while the residual porosity in the composite electrode allows electrode‐volume changes upon insertion and deinsertion, preserving the electrode/electrolyte interfaces, which are crucial in such technology. Based on these investigations, an all‐solid‐state battery with a surface capacity of 2.2 mA h cm^?2 is assembled by SPS, displaying a promising electrochemical performance at 80 °C.     

Compression dewatering of municipal activated sludge: effects of salt and pH

Even after mechanical dewatering, activated sludge contains a large amount of water. Due to its composition and biological nature this material is usually highly compressible and known to be difficult to dewater. In the present work, two treatments (salt addition and pH modification) are proposed to highlight some aspects which could explain the poor dewaterability of activated sludge. Dewatering tests are carried out in a pressure-driven device in order to well examine both, filtration and compression stages. Physico-chemical parameters, such as surface charge, hydrophobicity, extracellular polymeric substances (EPS) content and filtrate turbidity are measured on the tested sludge, for a better analysis of dewatering results.The dewatering ability of the sludge is widely linked to the cohesion of the flocculated matrix and the presence of fine particles. Both treatments alter the flocculated matrix and release fine particles. The release of fine particles tends to clog both, the filter cake and the filter medium. Consequently, the filtration rate decreases due to higher resistances to the flow. On another hand, the polymeric matrix breakdown enables to release some water trapped within the floc to the bulk liquid phase and thus facilitates its removal, which tends to decrease the moisture content of the filter-cake. It also impacts the compression dewatering step. The more destroyed structures lead to less elastic cakes and thus a slower primary consolidation stage. At the opposite, the mobility of the broken aggregates within the filter-cake does not seem to be improved by size reduction (the kinetics of the secondary consolidation stage are not significantly modified).     

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.     

High‐throughput measurement of recombination rates and genetic interference in Saccharomyces cerevisiae

Allelic recombination owing to meiotic crossovers is a major driver of genome evolution, as well as a key player for the selection of high‐performing genotypes in economically important species. Therefore, we developed a high‐throughput and low‐cost method to measure recombination rates and crossover patterning (including interference) in large populations of the budding yeast Saccharomyces cerevisiae. Recombination and interference were analysed by flow cytometry, which allows time‐consuming steps such as tetrad microdissection or spore growth to be avoided. Moreover, our method can also be used to compare recombination in wild‐type vs. mutant individuals or in different environmental conditions, even if the changes in recombination rates are small. Furthermore, meiotic mutants often present recombination and/or pairing defects affecting spore viability but our method does not involve growth steps and thus avoids filtering out non‐viable spores.     

Evidence of two mobile amorphous phases in semicrystalline polylactide observed from calorimetric investigations

Amorphous phase dynamics in Poly(lactic acid) (PLA) with different crystallinity degrees have been investigated from the vitreous state to the glass transition by means of two calorimetric methods. Temperature Modulated Differential Scanning Calorimetry was used to characterize the heat capacity signals and the average cooperativity length at the glass transition in non‐aged materials. Standard DSC was used to study the physical aging. It is shown that amorphous and fully crystallized PLA exhibit different relaxation parameters. For semicrystalline PLA with an intermediate degree of crystallinity, the peaks of the enthalpy of recovery and the out‐of‐phase heat capacity component are bimodal. The bimodality of the peaks is attributed to the relaxations of the inter‐spherulitic and intra‐spherulitic amorphous phases, respectively. Thus, in partially crystallized PLA, the non‐crystalline fraction of the material could be divided in three fractions, namely the Rigid Amorphous Fraction, the inter‐spherulitic Mobile Amorphous Phase (MAP), and the intra‐spherulitic MAP. Each of them exhibits a distinct molecular mobility. POLYM. ENG. SCI., 54:1144–1150, 2014. © 2013 Society of Plastics Engineers     

Tracking the dynamics of translation and absolute orientation of a sphere in a turbulent flow

We study the six-dimensional dynamics--position and orientation--of a large sphere advected by a turbulent flow. The movement of the sphere is recorded with two high-speed cameras. Its orientation is tracked using a novel, efficient algorithm; it is based on the identification of possible orientation "candidates" at each time step, with the dynamics later obtained from maximization of a likelihood function. Analysis of the resulting linear and angular velocities and accelerations reveal a surprising intermittency for an object whose size lies in the inertial range, close to the integral scale of the underlying turbulent flow.