564 research outputs found
Microfluidic Continuous Approaches to Produce Magnetic Nanoparticles with Homogeneous Size Distribution
We present a gas-liquid microfluidic system as a reactor to obtain magnetite nanoparticles with an excellent degree of control regarding their crystalline phase, shape and size. Several types of microflow approaches were selected to prevent nanomaterial aggregation and to promote homogenous size distribution. The selected reactor consists of a mixer stage aided by ultrasound waves and a reaction stage using a N2-liquid segmented flow to prevent magnetite oxidation to non-magnetic phases. A milli-fluidic reactor was developed to increase the production rate where a magnetite throughput close to 450 mg/h in a continuous fashion was obtained
Efficient production of hybrid bio-nanomaterials by continuous microchannel emulsification: Dye-doped SiO2 and Au-PLGA nanoparticles
A novel microfluidic system was designed to produce in a continuous manner hybrid nanomaterials using the microchannel double w/o/w emulsification technique. Double w/o/w nanoemulsions were produced combining two inter-digital micromixers that afford working in continuous flow and with a high reproducibility and control on the reaction conditions. High throughput production of two hybrid nanomaterials, dye-doped SiO2 (4 mg/min) and Au-loaded poly(lactic-co-glycolic) acid (PLGA) (168 mg/min) nanoparticles, were achieved, showing the resulting nanomaterials excellent and reproducible optical properties and tunable loading. These hybrid nanomaterials could be potentially used in different biomedical applications. In addition, the microfluidic system designed for carrying out double emulsification enabled to decrease the particle size distribution of dye-doped SiO2 nanoparticles (NPs) up to 20 nm and to improve the Au NPs loading efficiency in Au-loaded PLGA hybrid nanoparticles. The excellent control achieved in the Au NPs loading allowed tuning the payload on demand. Finally, the microfluidic system designed in this work overpasses the productivity described in previously published batch-type reactors, while assuring the same properties of the resulting hybrid nanomaterials
Gas Slug Microfluidics: A Unique Tool for Ultrafast, Highly Controlled Growth of Iron Oxide Nanostructures
The use of nanomaterials in real life applications is often hampered by our inability to produce them in large quantities while preserving their desired properties in terms of size, shape, and crystalline phase. Here we present a novel continuous method to synthesize nanostructures with an unprecedented degree of control regarding their properties. In particular, the excellent properties of microreactors for chemical synthesis are enhanced by the introduction of gas slugs of tailored composition. Slug dynamics accelerate mixing, reduce processing times (from hours in batch processes to minutes or even seconds), and, depending on the gas atmosphere used, allows one to accurately control the crystalline phase and shape of the resulting nanostructures. Inert (N2), oxidizing (O2), or reducing (CO, H2) gases were used, leading to different morphologies and crystalline structures in a high yield, highly reproducible fabrication process
Implementing the weakest failure detector for solving consensus
The concept of unreliable failure detector was introduced by Chandra and Toueg as a mechanism that provides information about process failures. This mechanism has been used to solve several agreement problems, such as the consensus problem. In this paper, algorithms that implement failure detectors in partially synchronous systems are presented. First two simple algorithms of the weakest class to solve the consensus problem, namely the Eventually Strong class (⋄S), are presented. While the first algorithm is wait-free, the second algorithm is f-resilient, where f is a known upper bound on the number of faulty processes. Both algorithms guarantee that, eventually, all the correct processes agree permanently on a common correct process, i.e. they also implement a failure detector of the class Omega (Ω). They are also shown to be optimal in terms of the number of communication links used forever. Additionally, a wait-free algorithm that implements a failure detector of the Eventually Perfect class (⋄P) is presented. This algorithm is shown to be optimal in terms of the number of bidirectional links used forever
Continuous synthesis of drug-loaded nanoparticles using microchannel emulsification and numerical modeling: Effect of passive mixing
By using interdigital microfluidic reactors, monodisperse poly(d, l lactic-co-glycolic acid) nanoparticles (NPs) can be produced in a continuous manner and at a large scale (~10 g/h). An optimized synthesis protocol was obtained by selecting the appropriated passive mixer and fluid flow conditions to produce monodisperse NPs. A reduced NP polydispersity was obtained when using the microfluidic platform compared with the one obtained with NPs produced in a conventional discontinuous batch reactor. Cyclosporin, an immunosuppressant drug, was used as a model to validate the efficiency of the microfluidic platform to produce drug-loaded monodisperse poly(d, l lactic-co-glycolic acid) NPs. The influence of the mixer geometries and temperatures were analyzed, and the experimental results were corroborated by using computational fluid dynamic three-dimensional simulations. Flow patterns, mixing times, and mixing efficiencies were calculated, and the model supported with experimental results. The progress of mixing in the interdigital mixer was quantified by using the volume fractions of the organic and aqueous phases used during the emulsification–evaporation process. The developed model and methods were applied to determine the required time for achieving a complete mixing in each microreactor at different fluid flow conditions, temperatures, and mixing rates
Laser-assisted surface melting of Al2O3-YSZ eutectic ceramics
[ES] Se presenta un procedimiento para la densificación y/o texturado superficial de cerámicas de Al2O3-YSZ (circona
estabilizada con itria) con composición eutéctica mediante fusión zonal asistida por láser. Haciendo un barrido con la
radiación proveniente de un láser de potencia sobre piezas cerámicas conseguimos modificar la microestructura y densificar
completatmente la capa superficial, con un espesor que va de 30 a 1000 μm. Por ejemplo, con lÃnea estrecha de láser de
diodo, fluencia de 1.23 kW/cm2 y velocidades de barrido de 0.14 mm/s, solidificamos capas de 560 μm. El resultado es una
superficie de baja rugosidad y no porosa. La microestructura de la muestra es fina debido a su composición eutéctica. La
interfase sólido-lÃquido en el proceso de crecimiento determina la orientación de la microestructura. Se estudia la forma de
esta interfase tanto en cortes transversales como longitudinales, lo que permite analizar el efecto que sobre la microestructura
tiene la superposición de barridos, que es una alternativa para tratar superficies extensas. Macroscópicamente la frontera
entre barridos contiguos es suave. Sin embargo, su microestructura presenta discontinuidad en el espaciado entre las fases
debido a la evolución microestructural en la región no fundida sometida a altas temperaturas y a la nucleación preferencial
de Al2O3 al comenzar el crecimiento cristalino. Se analizan distintas posibilidades para disminuir el choque térmico inherente
al proceso y que conduce a la formación de grietas paralelas a la dirección de procesado y de delaminación. Se observa una
mejora importante cuando se precalienta la pieza a tratar, de modo que es posible procesar superficies de cerámicas eutécticas
99% densas.[EN] A procedure for surface densification and/or texturing of Al2O3-YSZ (yttria stabilised zirconia) ceramics with eutectic
composition by means of laser surface melting is presented. By scanning a high-power laser beam on a ceramic surface, we
achieve a textured and fully dense surface layer from 30 to 1000 microns thick. For example, using a thin diode laser line
with fluence 1.23 kW/cm2 and 0.14 mm/s scan rate, the solidified layer has 560 μm depth. We get a low roughness and
dense surface. The microstructure is fine (micron size) due to the eutectic composition. The orientation of the microstructure
is determined by the shape of the solid-liquid interface in the solidification process. We study the shape of this interface
in transverse and longitudinal cross-sections in single as well as overlapping scans, which are required to process large
surfaces. From the macroscopic point of view, the transition between adjacent scans is smooth. However, the microstructure
presents discontinuity in the interphase spacing due to microstructural evolution in the heat affected region as well as the
nucleation of an Al2O3 layer at the beginning of the crystal growth. The thermal shock inherent to the procedure generates
cracks longitudinal and transverse to the scanning direction, as well as delaminating cracks. We analyse different possibilities
to reduce this thermal shock. The best results are obtained by preheating the substrate, allowing us to process surfaces of
Al2O3-YSZ eutectic ceramics 99% dense.Financiación del Ministerio de Ciencia y TecnologÃa a través de los proyectos MAT2000-1495 y MAT2000-1533-C03-02.Peer reviewe
Sequential localization of a complex electron fluid
Complex and correlated quantum systems with promise for new functionality
often involve entwined electronic degrees of freedom. In such materials, highly
unusual properties emerge and could be the result of electron localization.
Here, a cubic heavy fermion metal governed by spins and orbitals is chosen as a
model system for this physics. Its properties are found to originate from
surprisingly simple low-energy behavior, with two distinct localization
transitions driven by a single degree of freedom at a time. This result is
unexpected, but we are able to understand it by advancing the notion of
sequential destruction of an SU(4) spin-orbital-coupled Kondo entanglement. Our
results implicate electron localization as a unified framework for strongly
correlated materials and suggest ways to exploit multiple degrees of freedom
for quantum engineering.Comment: 21 pages, 4 figures (preprint format
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