Building three-dimensional images using a time-reversal chaotic cavity

The design of two-dimensional (2-D) arrays for three-dimensional (3-D) ultrasonic imaging is a major challenge in medical and nondestructive applications. Thousands of transducers are typically needed for focusing and steering in a 3-D volume. In this article, we propose a different concept allowing us to obtain electronic 3-D focusing with a small number of transducers. The basic idea is to couple a small number of transducers to a chaotic reverberating cavity with one face in contact with the body of the patient. The reverberations of the ultrasonic waves inside the cavity create at each reflection virtual transducers. The cavity acts as an ultrasonic kaleidoscope multiplying the small number of transducers and creating a much larger virtual transducer array. By exploiting time-reversal processing, it is possible to use collectively all the virtual transducers to focus a pulse everywhere in a 3-D volume. The reception process is based on a nonlinear pulse-inversion technique in order to ensure a good contrast. The feasibility of this concept for the building of 3-D images was demonstrated using a prototype relying only on 31 emission transducers and a single reception transducer.     

Spatial distribution and speciation of lead around corroding bullets in a shooting range soil studied by micro-X-ray fluorescence and absorption spectroscopy

We investigated the spatial distribution and speciation of Pb in the weathering crust and soil surrounding corroding metallic Pb bullets in a shooting range soil. The soil had a neutral pH, loamy texture, and was highly contaminated with Pb, with total Pb concentrations in the surface soil up to 68 000 mg kg(-1). Undisturbed soil samples containing corroding bullets were collected and embedded in resin, and polished sections were prepared for micro-X-ray fluorescence (micro-XRF) elemental mapping and micro-X-ray absorption near edge structure (micro-XANES) spectroscopy. Bullet weathering crust material was separated from the metallic Pb cores and analyzed by powder X-ray diffraction analysis. Our results show a steep decrease in total Pb concentrations from the bullet weathering crust into the surrounding soil matrix. The weathering crust consisted of a mixture of litharge [alpha-PbO], hydrocerussite [Pb3(CO3)2-(OH)2], and cerussite [PbCO3], with litharge dominating near the metallic Pb core and cerussite dominating in the outer crust, which is in contact with the soil matrix. On the basis of these results and thermodynamic considerations, we propose that the transition of Pb species after oxidation of Pb(O) to Pb(II) follows the sequence litharge --> hydrocerussite --> cerussite. Consequently, the solubility of cerussite limits the activity of Pb2+ in the soil solution in contact with weathering bullets to < or =1.28 x 10(-6) at pH 7, assuming that the CO2 partial pressure (PCO2) in the soil is equal or larger than in the atmosphere (PCO2 > or = 0.000 35 atm).     

Molecular and submolecular scale effects of comb‐copolymers on tri‐calcium silicate reactivity: Toward molecular design

The impact of organic compounds on the processing and reactivity of inorganic materials has been a source of inspiration for materials scientists for decades and continues to trigger novel and innovative applications in a broad range of disciplines. However, molecular design of such compounds to reach targeted properties remains challenging, particularly for reactive and multicomponent systems. This outstanding challenge is met here by combining a model cement, hosting different coupled reactions of dissolution, nucleation and growth, together with comb‐copolymers that offer large and well‐controlled variations of their molecular architecture. We show that silicate reactivity is affected by a combination of molecular and submolecular scale effects of these polymers. The first can be described by scaling laws from polymer physics, whereas the second involves specific chemical interactions. In particular, the ability of these polymers to hinder dissolution appears to be crucial, something for which strong experimental evidence is provided.     

Production of colloidally stable latices from low molecular weight ethylene–propylene–diene copolymers

The best impact modifiers for coatings and engineering plastics include fixed morphology core-shell particles. For the present work, ethylene–propylene copolymers (EPM) and ethylene–propylene–diene copolymers (EPDM) were chosen, for their good resistance to stringent conditions, like UV-irradiation or high temperatures, to prepare the core of the desired particles.

The solution-emulsification technique was used to produce artificial latices based on low molecular weight EPM and EPDM materials. Conventional emulsification techniques as well as ‘miniemulsification’ methods have been investigated. In both cases, a larger volume of polymer is reduced into smaller sub-units using the mechanical energy of comminution techniques, i.e. an Ultra-Turrax^® and a homogenizer operating at a pressure of 300 bar and with a shear rate of approximately 3.2×10⁷ s⁻¹. The difference between conventional emulsification and miniemulsification resides in the stabilizing system. For the conventional emulsification method, an equimolar mixture of anionic (sodium dodecyl benzene sulfonate, SDBS) and nonionic (polyoxyethylene (100) stearyl ether, Brij 700) surfactants was found to be the optimal surfactant system. For the miniemulsification method, a combination of SDBS as surfactant and hexadecane or cetyl alcohol as costabilizer was the most suitable system. Both conventional emulsification and miniemulsification lead to latices with monomodal particle size distributions and volume-average diameters ranging from 300 to 400 nm, determined with light scattering techniques. The low molecular weight elastomers, exhibiting viscosities lower than 1 Pa s at 20 °C, were easily emulsified without addition of organic solvent.     

Nonrecirculating flow of a yield stress fluid around a circular cylinder in a poiseuille flow

Although yield stress fluids are very present today in everyday life and in industry, their flow behavior is still poorly understood and the databases are incomplete at this time. The present experimental and numerical study focuses on laminar nonrecirculating flows of an elastoviscoplastic model fluid in a rectangular duct. An original experimental set‐up has been developed. The Particle Image Velocimetry method is used for analyzing the kinematical fields. Results provided concern the morphology of the flow and the evolution of the velocity field around a cylindrical obstacle. Information is provided on the size of the rigid zones where the fluid behaves as a solid. The experimental data are compared with numerical results involving a regularized Herschel–Bulkley viscoplastic model. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4554–4563, 2016     

阳极溶解对面心及体心立方材料循环塑性的影响

本文研究了阳极溶解对316L,Fe-26Cr-1Mo,In600及In690合金循环塑性的影响.试样表面局部的阳极溶解使材料表面软化,其软化程度与试样表面积(S)与体积(V)的比值有关.S/V愈大,其软化程度愈高.     

Evaluation of atrial septal defects with 4D flow MRI—multilevel and inter-reader reproducibility for quantification of shunt severity

Purpose

With the hypothesis that 4D flow can be used in evaluation of cardiac shunts, we seek to evaluate the multilevel and interreader reproducibility of measurements of the blood flow, shunt fraction and shunt volume in patients with atrial septum defect (ASD) in practice at multiple clinical sites.

Materials and methods

Four-dimensional flow MRI examinations were performed at four institutions across Europe and the US. Twenty-nine patients (mean age, 43 years; 11 male) were included in the study. Flow measurements were performed at three levels (valve, main artery and periphery) in both the pulmonary and systemic circulation by two independent readers and compared against stroke volumes from 4D flow anatomic data. Further, the shunt ratio (Q_p/Q_s) was calculated. Additionally, shunt volume was quantified at the atrial level by tracking the atrial septum.

Results

Measurements of the pulmonary blood flow at multiple levels correlate well whether measuring at the valve, main pulmonary artery or branch pulmonary arteries (r = 0.885–0.886). Measurements of the systemic blood flow show excellent correlation, whether measuring at the valve, ascending aorta or sum of flow from the superior vena cava (SVC) and descending aorta (r = 0.974–0.991). Intraclass agreement between the two observers for the flow measurements varies between 0.96 and 0.99. Compared with stroke volume, pulmonic flow is underestimated with 0.26 l/min at the main pulmonary artery level, and systemic flow is overestimated with 0.16 l/min at the ascending aorta level. Direct measurements of ASD flow are feasible in 20 of 29 (69%) patients.

Conclusion

Blood flow and shunt quantification measured at multiple levels and performed by different readers are reproducible and consistent with 4D flow MRI.

     

Packaging of yield stress fluids: Flow patterns

The packaging or filling of a container with a non‐Newtonian fluid without quality failures is a current issue encountered at the final step of industrial product processes. In this work, the container filling of viscoplastic fluids is studied using an experimental laboratory plant able to reproduce the industrial transitory packaging conditions. First, a Newtonian validation was conducted to compare and to confirm our setup results with available literature data. Second five flow patterns including dripping, jet buckling, mounding, planar filling, and air entrainment were observed and characterized for the viscoplastic container filling. Most of them present different types of instabilities during the filling, except the planar filling, which seems to be ideal according to industrial specifications. A flow pattern distribution depending on relevant dimensionless numbers was developed. Finally, flow pattern transition criteria are determined highlighting the influence of rheological and process parameters on container filling. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1117–1126, 2018     

Imprinting of founders' entrepreneurial motivations on enterprises' practices and processes: The context of creative industries

This paper explores the imprinting of entrepreneurs' motivations on the practices and processes of enterprises. We investigate the question in the context of creative industries (CIs) as an extreme case of entrepreneurial motivations (EMs) prevalence. We analyse the EM of 14 founders of design consultancies. Three EMs emerge: self‐fulfilment, freedom and financial motivation. The qualitative analysis reveals that the founders' EMs at the time of a venture's founding has a lasting impact on the characteristics of the venture (name, processes formalization, decision‐making processes, performance measures and growth strategies). Specifically, founders driven by self‐fulfilment tend to build ventures named after them. In these ventures, processes are informal, decision‐making is centralized, performance measures are based on personal satisfaction and recognition and enterprise growth is restrained. Founders who seek freedom tend to run enterprises with semiformal processes, semicentralized decision‐making, a client satisfaction focus, and slow growth strategies. In contrast, founders with financial motivations tend to create enterprises with formal processes, decentralized decision‐making, financial performance metrics and growth ambitions. By focusing on EM and adopting a holistic approach beyond some characteristics of the venture, we complement the imprinting literature.     

Enhanced Collective Magnetic Properties Induced by the Controlled Assembly of Iron Oxide Nanoparticles in Chains

1D assemblies of magnetic nanoparticles are of great potential for designing novel nanostructured materials with enhanced collective magnetic properties. In that challenging context, a new assembly strategy is presented to prepare chains of magnetic nanoparticles that are well‐defined in structure and in spatial arrangement. The 1D assembly of iron oxide nanoparticles onto a substrate is controlled using “click” chemistry under an external magnetic field. Co‐aligned single nanoparticle chains separated by regular distances can be obtained by this strategy. The intrinsic high uniaxial anisotropy results in a strong enhancement of magnetic collective properties in comparison to 2D monolayers or isolated nanoparticles. In contrast to the intensively studied bundle chains of nanoparticles, the finely tuned chain structure reported here allows evidencing a first order intrachain dipolar interaction and a second order interchain magnetic coupling. This study offers new insights into the collective magnetic properties of highly anisotropic particulate assemblies which have been investigated by combining superconducting quantum interference device magnetometry, magnetic force microscopy, and ferromagnetic resonance.