148 research outputs found
Mechanical Properties of Steel Fiber-Reinforced Magnesium Phosphate Cement Mortar
A new cement-based mortar with high early strength and toughness was developed by adding micro steel fibers (MSF) in magnesium phosphate cement (MPC) mortar. The compressive and flexural tests were carried out to investigate the effect of curing time, MSF volume fraction, sand-cement mass ratio, and water-cement mass ratio on the strength and flexural toughness of MSF-reinforced MPC mortar (MSFRMM). Also, the flexural toughness and ductility of MSFRMM were evaluated according to ASTM C1609. The results of this study showed that the addition of MSF from 0% to 1.6% by volume significantly improved the compressive strength of MSFRMM. The MSFRMM showed high early strength, especially during the first 3 days. The addition of MSFs changed the flexural failure mode of MPC-based mortar from brittleness to ductility, and the flexural toughness of MSFRMM remarkably increased with the increase of MSF volume fraction from 0% to 1.6%. The toughness and ductility of MSFRMM slightly increased with the increase of the dosage of cement. The toughness and ductility of MSFRMM increased with the decrease of the water-cement mass ratio due to the improved density of the mortar caused by the reduction of water
Topological holographic quench dynamics in a synthetic dimension
The notion of topological phases extended to dynamical systems stimulates
extensive studies, of which the characterization of non-equilibrium topological
invariants is a central issue and usually necessitates the information of
quantum dynamics in both the time and spatial dimensions. Here we combine the
recently developed concepts of the dynamical classification of topological
phases and synthetic dimension, and propose to efficiently characterize
photonic topological phases via holographic quench dynamics. A pseudo spin
model is constructed with ring resonators in a synthetic lattice formed by
frequencies of light, and the quench dynamics is induced by initializing a
trivial state which evolves under a topological Hamiltonian. Our key prediction
is that the complete topological information of the Hamiltonian is extracted
from quench dynamics solely in the time domain, manifesting holographic
features of the dynamics. In particular, two fundamental time scales emerge in
the quench dynamics, with one mimicking the Bloch momenta of the topological
band and the other characterizing the residue time evolution of the state after
quench. For this a dynamical bulk-surface correspondence is obtained in time
dimension and characterizes the topology of the spin model. This work also
shows that the photonic synthetic frequency dimension provides an efficient and
powerful way to explore the topological non-equilibrium dynamics.Comment: Compared to the previous submission, we made changes to figures and
revised some discussion
Optical neural network architecture for deep learning with the temporal synthetic dimension
The physical concept of synthetic dimensions has recently been introduced
into optics. The fundamental physics and applications are not yet fully
understood, and this report explores an approach to optical neural networks
using synthetic dimension in time domain, by theoretically proposing to utilize
a single resonator network, where the arrival times of optical pulses are
interconnected to construct a temporal synthetic dimension. The set of pulses
in each roundtrip therefore provides the sites in each layer in the optical
neural network, and can be linearly transformed with splitters and delay lines,
including the phase modulators, when pulses circulate inside the network. Such
linear transformation can be arbitrarily controlled by applied modulation
phases, which serve as the building block of the neural network together with a
nonlinear component for pulses. We validate the functionality of the proposed
optical neural network for the deep learning purpose with examples handwritten
digit recognition and optical pulse train distribution classification problems.
This proof of principle computational work explores the new concept of
developing a photonics-based machine learning in a single ring network using
synthetic dimensions, which allows flexibility and easiness of reconfiguration
with complex functionality in achieving desired optical tasks
Multilayer multifunctional advanced coatings for receivers of concentrated solar power plants
International audienceThe extending market of concentrated solar power plants requires high-temperature materials for solar surface receivers that would ideally heat an air coolant beyond 1300 K. This work presents investigation on high-temperature alloys with ceramic coatings (AlN or SiC/AlN stacking) to combine the properties of the substrate (creep resistance, machinability) and of the coating (slow oxidation kinetics, high solar absorptivity). The first results showed that high temperature oxidation resistance and optical properties of metallic alloys were improved by the different coatings. However, the fast thermal shocks led to high stress levels not compatible due to the differences in thermal expansion coefficients
Single-trial phase entrainment of theta oscillations in sensory regions predicts human associative memory performance
Episodic memories are rich in sensory information and often contain integrated information from different sensory modalities. For instance, we can store memories of a recent concert with visual and auditory impressions being integrated in one episode. Theta oscillations have recently been implicated in playing a causal role synchronizing and effectively binding the different modalities together in memory. However, an open question is whether momentary fluctuations in theta synchronization predict the likelihood of associative memory formation for multisensory events. To address this question we entrained the visual and auditory cortex at theta frequency (4 Hz) and in a synchronous or asynchronous manner by modulating the luminance and volume of movies and sounds at 4 Hz, with a phase offset at 0° or 180°. EEG activity from human subjects (both sexes) was recorded while they memorized the association between a movie and a sound. Associative memory performance was significantly enhanced in the 0° compared with the 180° condition. Source-level analysis demonstrated that the physical stimuli effectively entrained their respective cortical areas with a corresponding phase offset. The findings suggested a successful replication of a previous study (Clouter et al., 2017). Importantly, the strength of entrainment during encoding correlated with the efficacy of associative memory such that small phase differences between visual and auditory cortex predicted a high likelihood of correct retrieval in a later recall test. These findings suggest that theta oscillations serve a specific function in the episodic memory system: binding the contents of different modalities into coherent memory episodes
Elevated Foxp3+ double-negative T cells are associated with disease progression during HIV infection
Persistent immune activation, which occurs during the whole course of HIV infection, plays a pivotal role in CD4+ T cells depletion and AIDS progression. Furthermore, immune activation is a key factor that leads to impaired immune reconstitution after long-term effective antiretroviral therapy (ART), and is even responsible for the increased risk of developing non-AIDS co-morbidities. Therefore, itâs imperative to identify an effective intervention targeting HIV-associated immune activation to improve disease management. Double negative T cells (DNT) were reported to provide immunosuppression during HIV infection, but the related mechanisms remained puzzled. Foxp3 endows Tregs with potent suppressive function to maintain immune homeostasis. However, whether DNT cells expressed Foxp3 and the accurate function of these cells urgently needed to be investigated. Here, we found that Foxp3+ DNT cells accumulated in untreated people living with HIV (PLWH) with CD4+ T cell count less than 200 cells/”l. Moreover, the frequency of Foxp3+ DNT cells was negatively correlated with CD4+ T cell count and CD4/CD8 ratio, and positively correlated with immune activation and systemic inflammation in PLWH. Of note, Foxp3+ DNT cells might exert suppressive regulation by increased expression of CD39, CD25, or vigorous proliferation (high levels of GITR and ki67) in ART-naive PLWH. Our study underlined the importance of Foxp3+ DNT cells in the HIV disease progression, and suggest that Foxp3+ DNT may be a potential target for clinical intervention for the control of immune activation during HIV infection
RevĂȘtements multicouches Ă base de nitrure d'aluminium pour les rĂ©cepteurs des systĂšmes solaires Ă concentration
There is an increasing interest for concentrated solar power (CSP) systems which can work at temperatures higher than 1000 °C to optimize efficiency. One of the challenges is to design the receiver that will be heated at high temperature in air. Compared to coatings in gas turbine engine, the coating(s)/substrate system must have a high thermal conductivity to ensure a good heat transfer to the fluid. Aluminum nitride (AlN) coating, deposited by chemical vapor deposition at 1100-1200 °C at a growth rate of 10-50 ”m·h-1, is selected for its high thermal conductivity, low thermal expansion coefficient, high temperature stability and its ability to develop stable alumina scales above 1000 °C. Molybdenum-based alloys are selected as substrate materials for their excellent thermal and mechanical properties. The alumina-forming iron-based alloys are also chosen as model substrates to reduce the influencing parameters in real-life receivers and to study the potential of these coatings. Accelerated cyclic oxidation tests and emissivity measurements allow the evaluation of AlN coatings as materials for high temperature CSP receivers. The multilayered systems exhibit low degradation after hundreds of thermal cycles at 800 °C in air and can support higher temperatures (1100 °C) for 100 to 500 h depending on the coating thickness. Nevertheless, the fast cyclic oxidation in solar furnace leads to cracks through the coatings. An analytical model is developed to study the stress evolution within the coating(s)/substrate system. Calculated results are in good agreement with experimental data. The measurements of the optical properties reveal a decrease of absorptivity after oxidation for AlN coatings, but a significant increase of absorptivity when SiC coating is added as a top layer.Il y a un intĂ©rĂȘt croissant pour les systĂšmes d'Ă©nergie solaire concentrĂ©e (CSP) qui peuvent fonctionner Ă des tempĂ©ratures supĂ©rieures Ă 1000 °C afin d'optimiser leur efficacitĂ©. L'un des dĂ©fis consiste Ă dĂ©finir un matĂ©riau rĂ©cepteur qui sera soumis Ă un chauffage Ă haute tempĂ©rature dans l'air. Contrairement aux revĂȘtements utilisĂ©s dans les turbines Ă gaz, le ou les systĂšmes revĂȘtement(s)/substrat doivent avoir une conductivitĂ© thermique Ă©levĂ©e pour assurer un transfert thermique optimal vers le fluide. Les revĂȘtements de nitrure d'aluminium (AlN), dĂ©posĂ©s par dĂ©pĂŽt chimique en phase vapeur Ă 1100-1200 °C Ă une vitesse de croissance de 10-50 ”m·h-1, sont choisis pour leur conductivitĂ© thermique Ă©levĂ©e, leur faible coefficient de dilatation thermique, leur stabilitĂ© thermique Ă©levĂ©e et leur capacitĂ© Ă dĂ©velopper des couches stables d'alumine au-dessus de 1000 °C. Les alliages Ă base de molybdĂšne sont choisis comme substrat pour leurs excellentes propriĂ©tĂ©s thermiques et mĂ©caniques. Les alliages Ă base de fer formant des couches d'alumine sont Ă©galement choisis comme substrats modĂšles pour Ă©tudier le potentiel de ces revĂȘtements et rĂ©duire le nombre de paramĂštres lors de l'oxydation. Des tests accĂ©lĂ©rĂ©s d'oxydation cyclique et des mesures d'Ă©missivitĂ© permettent d'Ă©valuer les revĂȘtements AlN comme matĂ©riaux pour les rĂ©cepteurs CSP haute tempĂ©rature. Les systĂšmes multicouches prĂ©sentent une faible dĂ©gradation aprĂšs des centaines de cycles thermiques Ă 800 °C dans l'air et peuvent supporter des tempĂ©ratures plus Ă©levĂ©es (1100 °C) pendant 100 Ă 500 h selon l'Ă©paisseur du revĂȘtement. NĂ©anmoins, l'oxydation cyclique rapide dans les fours solaires conduit Ă des fissures dans les revĂȘtements. Un modĂšle analytique est dĂ©veloppĂ© pour Ă©tudier l'Ă©volution des contraintes dans le(s) systĂšme(s) revĂȘtement(s)/substrat. Les rĂ©sultats calculĂ©s sont en bon accord avec les donnĂ©es expĂ©rimentales. Les mesures des propriĂ©tĂ©s optiques rĂ©vĂšlent une diminution de l'absorptivitĂ© aprĂšs oxydation pour les revĂȘtements AlN, mais une augmentation significative de l'absorptivitĂ© lorsque un revĂȘtement de SiC est ajoutĂ© comme couche de finition
Multilayer coatings based on aluminum nitride coatings for receivers in concentrated solar power technology
Il y a un intĂ©rĂȘt croissant pour les systĂšmes d'Ă©nergie solaire concentrĂ©e (CSP) qui peuvent fonctionner Ă des tempĂ©ratures supĂ©rieures Ă 1000 °C afin d'optimiser leur efficacitĂ©. L'un des dĂ©fis consiste Ă dĂ©finir un matĂ©riau rĂ©cepteur qui sera soumis Ă un chauffage Ă haute tempĂ©rature dans l'air. Contrairement aux revĂȘtements utilisĂ©s dans les turbines Ă gaz, le ou les systĂšmes revĂȘtement(s)/substrat doivent avoir une conductivitĂ© thermique Ă©levĂ©e pour assurer un transfert thermique optimal vers le fluide. Les revĂȘtements de nitrure d'aluminium (AlN), dĂ©posĂ©s par dĂ©pĂŽt chimique en phase vapeur Ă 1100-1200 °C Ă une vitesse de croissance de 10-50 ”m·h-1, sont choisis pour leur conductivitĂ© thermique Ă©levĂ©e, leur faible coefficient de dilatation thermique, leur stabilitĂ© thermique Ă©levĂ©e et leur capacitĂ© Ă dĂ©velopper des couches stables d'alumine au-dessus de 1000 °C. Les alliages Ă base de molybdĂšne sont choisis comme substrat pour leurs excellentes propriĂ©tĂ©s thermiques et mĂ©caniques. Les alliages Ă base de fer formant des couches d'alumine sont Ă©galement choisis comme substrats modĂšles pour Ă©tudier le potentiel de ces revĂȘtements et rĂ©duire le nombre de paramĂštres lors de l'oxydation. Des tests accĂ©lĂ©rĂ©s d'oxydation cyclique et des mesures d'Ă©missivitĂ© permettent d'Ă©valuer les revĂȘtements AlN comme matĂ©riaux pour les rĂ©cepteurs CSP haute tempĂ©rature. Les systĂšmes multicouches prĂ©sentent une faible dĂ©gradation aprĂšs des centaines de cycles thermiques Ă 800 °C dans l'air et peuvent supporter des tempĂ©ratures plus Ă©levĂ©es (1100 °C) pendant 100 Ă 500 h selon l'Ă©paisseur du revĂȘtement. NĂ©anmoins, l'oxydation cyclique rapide dans les fours solaires conduit Ă des fissures dans les revĂȘtements. Un modĂšle analytique est dĂ©veloppĂ© pour Ă©tudier l'Ă©volution des contraintes dans le(s) systĂšme(s) revĂȘtement(s)/substrat. Les rĂ©sultats calculĂ©s sont en bon accord avec les donnĂ©es expĂ©rimentales. Les mesures des propriĂ©tĂ©s optiques rĂ©vĂšlent une diminution de l'absorptivitĂ© aprĂšs oxydation pour les revĂȘtements AlN, mais une augmentation significative de l'absorptivitĂ© lorsque un revĂȘtement de SiC est ajoutĂ© comme couche de finition.There is an increasing interest for concentrated solar power (CSP) systems which can work at temperatures higher than 1000 °C to optimize efficiency. One of the challenges is to design the receiver that will be heated at high temperature in air. Compared to coatings in gas turbine engine, the coating(s)/substrate system must have a high thermal conductivity to ensure a good heat transfer to the fluid. Aluminum nitride (AlN) coating, deposited by chemical vapor deposition at 1100-1200 °C at a growth rate of 10-50 ”m·h-1, is selected for its high thermal conductivity, low thermal expansion coefficient, high temperature stability and its ability to develop stable alumina scales above 1000 °C. Molybdenum-based alloys are selected as substrate materials for their excellent thermal and mechanical properties. The alumina-forming iron-based alloys are also chosen as model substrates to reduce the influencing parameters in real-life receivers and to study the potential of these coatings. Accelerated cyclic oxidation tests and emissivity measurements allow the evaluation of AlN coatings as materials for high temperature CSP receivers. The multilayered systems exhibit low degradation after hundreds of thermal cycles at 800 °C in air and can support higher temperatures (1100 °C) for 100 to 500 h depending on the coating thickness. Nevertheless, the fast cyclic oxidation in solar furnace leads to cracks through the coatings. An analytical model is developed to study the stress evolution within the coating(s)/substrate system. Calculated results are in good agreement with experimental data. The measurements of the optical properties reveal a decrease of absorptivity after oxidation for AlN coatings, but a significant increase of absorptivity when SiC coating is added as a top layer
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