Microbial mitigation of greenhouse gas emissions from boreal lakes

The climate change crisis has drawn the attention of both the public and scientific community to the carbon cycle and particularly to the importance of greenhouse gases (GHG) carbon dioxide (CO2) and methane (CH4). CO2 has been a key component of Earth´s climate regulation throughout its geological history and is now the main driver of the current change in climate. CH4 has been responsible for a quarter of the cumulative radiative forcing observed so far. Recent studies suggest that lakes could be a major source of both CO2 and CH4. Boreal lakes are of special interest as they represent 27% of the global lake area, and their production of CO2 and CH4 are expected to increase in the future. This project aimed to investigate microbial processes with the potential to limit the emissions of GHGs from boreal lakes. For that purpose, the impact of an increase in phosphorus (P) concentration in the water on CH4 oxidation under the ice was investigated as well as the community composition of the methanotrophic guild. We also looked at the potential importance of chemolithoautotrophic microorganisms in fixing CO2 in the water column. Using a combination of geochemical analysis, genomic studies, and in vivo assays, we showed that P amendment has the potential to increase methane oxidation, possibly limiting the expected increase in CH4 emissions due to anthropogenic fertilization of boreal lakes. We also showed that methanotrophic community structure in boreal lakes is driven by CH4 concentration and that alphaproteobacterial methanotrophs might play an important role in removing CH4 from surface waters. Finally, we showed that dark carbon fixation is a common trait in boreal lakes and that it seems related to the iron cycle

Narrow-band multiresonant plasmon nanostructure for the coherent control of light: An optical analog of the xylophone

We demonstrate that it is possible to combine several small metallic particles in a very compact geometry without loss of their individual modal properties by adding a gold metallic film underneath. This film essentially acts as a "ground plane" which channels the optical field of each particle and decreases the interparticle coupling. The localization of the electric field can then be controlled temporally by illuminating the chain with a chirped pulse. The sign of the chirp controls the excitation sequence of the particles with great flexibility

Experimental Characterization of Superharmonic Resonances Using Phase-Lock Loop and Control-Based Continuation

Experimental characterization of nonlinear structures usually focuses on fundamental resonances. However, there is useful information about the structure to be gained at frequencies far away from those resonances. For instance, non-fundamental harmonics in the system's response can trigger secondary resonances, including superharmonic resonances. Using the recently-introduced definition of phase resonance nonlinear modes, a phase-locked loop feedback control is used to identify the backbones of even and odd superharmonic resonances, as well as the nonlinear frequency response curve in the vicinity of such resonances. When the backbones of two resonances (either fundamental or superharmonic) cross, modal interactions make the phase-locked loop unable to stabilize some orbits. Control-based continuation can thus be used in conjunction with phase-locked loop testing to stabilize the orbits of interest. The proposed experimental method is demonstrated on a beam with artificial cubic stiffness exhibiting complex resonant behavior. For instance, the frequency response around the third superharmonic resonance of the third mode exhibits a loop, the fifth superharmonic resonance of the fourth mode interacts with the fundamental resonance of the second mode, and the second superharmonic resonance of the third mode exhibits a branch-point bifurcation and interacts with the fourth superharmonic resonance of the fourth mode

Analytical study of the amplitude and phase resonances of a Duffing oscillator

peer reviewedThis paper revisits the resonant behavior of a harmonically-forced Duffing oscillator with a specific attention to phase resonance and to its relation with amplitude resonance. To this end, the different families of resonances, namely primary (1:1), superharmonic (k:1) and subharmonic (1:ν) resonances are carefully studied using first and higher-order averaging. When the phase lag is calculated between the k-th harmonic of the displacement and the harmonic forcing, this study evidences that phase resonance occurs when the phase lag is equal to either π/2 (phase quadrature) or 3π/4ν

Characterizing fundamental, superharmonic and subharmonic resonances using phase resonance nonlinear modes

peer reviewedNonlinear normal modes (NNMs) are often used for the prediction of the backbone of resonance peaks in nonlinear frequency response functions. However, in principle, NNMs require multi-point, multi-harmonic external forcing for their practical realization. The present study proposes a new NNM definition termed phase resonance nonlinear modes. The definition is based on virtual, mono-point, mono-harmonic external forcing proportional to a specific harmonic of the velocity of the forced degree of freedom. Depending on the chosen harmonic, fundamental, superharmonic and subharmonic resonances can be characterized

Phase resonance of an oscillator with polynomial stiffness

peer reviewedThis paper extends the linear concept of phase resonance, which occurs when the damping forces counterbalance exactly the external forces, to oscillators with polynomial stiffness. To this end, a first-order averaging technique is applied to a one degree-of-freedom oscillator with arbitrary polynomial stiffness. We show that phase resonance exists in the vicinity of amplitude resonance and is associated with a phase resonance of π/2