Microwave heating-induced DC magnetic flux penetration in YBa2_{2}Cu3_{3}O7−δ_{7-\delta} superconducting thin films

The magneto-optical imaging technique is used to visualize the penetration of the magnetic induction in YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ thin films during surface resistance measurements. The in-situ surface resistance measurements were performed at 7 GHz using the dielectric resonator method. When only the microwave magnetic field $H_{rf}$ is applied to the superconductor, no $H_{rf}$-induced vortex penetration is observed, even at high rf power. In contrast, in the presence of a constant magnetic field superimposed on $H_{rf}$ we observe a progression of the flux front as $H_{rf}$ is increased. A local thermometry method based on the measurement of the resonant frequency of the dielectric resonator placed on the YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ thin film shows that the $H_{rf}$--induced flux penetration is due to the increase of the film temperature.Comment: 6 pages, Journal of Applied Physic

Heating and high frequency nonlinearities in the surface impedance of high Tc superconductors

Using the dielectric resonator method, we have investigated nonlinearities in surface impedance Zs = Rs + jXs of YBa2Cu3O7-delta thin films at 10 GHz as a function of the incident microwave power level and temperature. The use of a rutile dielectric resonator allows us to measure the precise temperature of the films. We conclusively show that the usually observed increase of the surface resistance of YBa2Cu3O7-delta thin film as function of microwave power is due to local heating

Frequency converter based on nanoscale MgO magnetic tunnel junctions

We observe both dc voltage rectification and frequency conversion that occur when a reference microwave current is injected to a MgO based magnetic tunnel junction (MTJ). The rectification that is spin-transfer torque dependent is observed when the frequency of the input microwave current coincides with the resonance frequency of the magnetization of the active layer. In addition, we demonstrate that frequency conversion is the result of amplitude modulation between the reference signal and the resistance of the MTJ that is fluctuating at the resonance frequency of the magnetization of the active layer.Comment: 9 pages, 2 figure

Joule heating and high frequency nonlinear effects in the surface impedance of high Tc superconductors

Using the dielectric resonator method, we have investigated nonlinearities in the surface impedance Zs = Rs + jXs of YBa2Cu3O7 thin films at 10 GHz as function of the incident microwave power level and temperature. The use of a rutile dielectric resonator allows us to measure the precise temperature of the films. We conclusively show that the usually observed increase of the surface resistance of YBa2Cu3O7 thin film as function of microwave power is due to local heating

Digestate color and light intensity affect nutrient removal and competition phenomena in a microalgal-bacterial ecosystem

International audienceDuring anaerobic digestion, nutrients are mineralized and may require post-treatment for optimum valorization. The cultivation of autotrophic microalgae using the digestate supernatant is a promising solution; however the dark color of the influent poses a serious problem. First, the color of the digestates was studied and the results obtained using three different digestates demonstrated a strong heterogeneity although their color remained rather constant over time. The digestates absorbed light over the whole visible spectrum and remained colored even after a ten-fold dilution. Secondly, the impact of light and of substrate color on the growth of Scenedesmus sp. and on nitrogen removal were assessed. These experiments led to the construction of a model for predicting the impact of influent color and light intensity on N removal. Maximum N removal (8.5mgN-NH4+L-1d-1) was observed with an initial optical density of 0.221 and 244?molEm-?s-1 light and the model allows to determine N removal between 15.9 and 22.7mgN-NH4+L-1d-1 in real conditions according to the dilution level of the influent and related color. Changes in the microalgae community were monitored and revealed the advantage of Chlorella over Scenedesmus under light-limitation. Additionally microalgae outcompeted nitrifying bacteria and experiments showed how microalgae become better competitors for nutrients when phosphorus is limiting. Furthermore, nitrification was limited by microalgae growth, even when P was not limiting. © 2014

Development of a microalgae process to recycle nutrients (N and P) from digestate: effect of the influent color

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Design of microalgae process for nutrient extraction from digestate through laboratory tests and modelling

International audienceMicroalgae culture for extraction of nutrient from digestate was studied at laboratory scale to determine the influence of turbidity of influent, light provided, N:P of the influent, CO2 supplementation and solid retention time on microalgae productivity and associated N removal processes. The experimental results obtained in batch and semi-continuous mode showed the importance of turbidity of influent combined with light intensity on the microalgae roductivity compared to the impact of the level of CO2 supplementation and N:P ratio. Additionally to N assimilation by microalgae, nitrification-denitrification was identified as a major N pathway with N removal at least equal to N assimilation. However, limitation of nitrification process appears possible through the N:P ratio of the influent. The evolution of microalgae communities observed during these trials highlighted the interest of using mix culture allowing a better adaption to the conditions evolutions. Finally, all experimental results were used to build and calibrate a model simulating microalgae growth using nutrients from digestate and such a model was used to design a raceway pond treating digestate from a commercial farm producing 4000 pigs per year

Microalgae process design for nutrient extraction from digestate through laboratory tests and model

International audienceEvery year the knowledge about the microbial ecology of anaerobic digestion increases but despite that, the inoculation step of anaerobic digesters still remains empirical. Anaerobic digestion remains a microbial process without any microbial engineering. In this review we try to understand why putting in practice this knowledge remains difficult by identifying bottlenecks of this unsuccessful story