Forming microbial anodes under delayed polarisation modifies the electron transfer network and decreases the polarisation time required.

Microbial anodes were formed from compost leachate on carbon cloth electrodes. The biofilms formed at the surface of electrodes kept at open circuit contained microorganisms that switched their metabolism towards electrode respiration in response to a few minutes of polarisation. When polarisation at -0.2 V/SCE (+0.04 V/SHE) was applied to a pre-established biofilm formed at open circuit (delayed polarisation), the bacteria developed an extracellular electron transport network that showed multiple redox systems, reaching 9.4 A/m(2) after only 3-9 days of polarisation. In contrast, when polarisation was applied from the beginning, bacteria developed a well-tuned extracellular electron transfer network concomitantly with their growth, but 36 days of polarisation were required to get current of the same order (6-8 A/m(2)). The difference in performance was attributed to the thinner, more heterogeneous structure of the biofilms obtained by delayed polarisation compared to the thick uniform structure obtained by full polarisation

Holographic Duals of Flavored N=1 Super Yang-Mills: Beyond the Probe Approximation

We construct backreacted D3/D7 supergravity backgrounds which are dual to four-dimensional N=1 and N=2 supersymmetric Yang-Mills at large N_c with flavor quarks in the fundamental representation of SU(N_c). We take into account the backreaction of D7-branes on either AdS(5) x S(5) or AdS(5) x T^{1,1}, or more generically on backgrounds where the space transverse to the D3-branes is Kaehler. The construction of the backreacted geometry splits into two stages. First we determine the modification of the six-dimensional space transverse to the D3 due to the D7, and then we compute the warp factor due to the D3. The N=2 background corresponds to placing a single stack of N_f D7-branes in AdS(5) x S(5). Here the Kaehler potential is known exactly, while the warp factor is obtained in certain limits as a perturbative expansion. By placing another D7'probe in the backreacted D3/D7 background, we derive the effect of the D7-branes on the spectrum of the scalar fluctuations to first order in N_f. The two systems with N=1 supersymmetry that we discuss are D3/D7/D7' and D3/D7 on the conifold. In both cases, the Kaehler potential is obtained perturbatively in the number of D7-branes. We provide all the ingredients necessary for the computation of each term in the expansion, and in each case give the first few terms explicitly. Finally, we comment on some aspects of the dual gauge theories.Comment: 39 pp, no figures; v.2 section 2.2 modified, singularities clarifie

On the fluid dynamical effects of synchronization in side-by-side swimmers

In-phase and anti-phase synchronization of neighboring swimmers is examined experimentally using two self-propelled independent flexible foils swimming side-by-side in a water tank. The foils are actuated by pitching oscillations at one extremity-the head of the swimmers-and the flow engendered by their undulations is analyzed using two-dimensional particle image velocimetry in their frontal symmetry plane. Following recent observations on the behavior of real fish, we focus on the comparison between in-phase and anti-phase actuation by fixing all other geometric and kinematic parameters. We show that swimming with a neighbor is beneficial for both synchronizations tested, as compared to swimming alone, with an advantage for the anti-phase synchronization. We show that the advantage of anti-phase synchronization in terms of swimming performance for the two-foil "school" results from the emergence of a periodic coherent jet between the two swimmers.Fil: Godoy Diana, Ramiro. Sorbonne University; Francia. Centre National de la Recherche Scientifique; Francia. PSL Research University; FranciaFil: Vacher, Jérôme. Sorbonne University; Francia. Centre National de la Recherche Scientifique; Francia. PSL Research University; FranciaFil: Raspa, Veronica Diana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Thiria, Benjamin. Sorbonne University; Francia. Centre National de la Recherche Scientifique; Francia. PSL Research University; Franci

Propagating waves in bounded elastic media: a transition from standing wave motion to anguilliform kinematics

Waves propagating in confined geometries usually evolve into spatially stationary patterns, built from the interference between the waves that have been reflected upon hitting the boundaries. However, a recent study on bio-locomotion [1] has reported that traveling wave kinematics can naturally emerge in a forced elastic rod, even with boundary conditions involving significant reflections. It has been shown that this particular behavior is observed only in the presence of strong damping. Based on those observations, we aim at giving a quantitative description of the mechanism involved to prevent the built-up of standing waves and establish traveling fish-like kinematics (that optimizes the global swimming efficiency). The question is discussed here in the framework of hand-made artificial swimmers as an example of practical application. REFERENCE [1] Ramananarivo, S., Godoy-Diana, R., Thiria, B. Passive elastic mechanism to mimic fish-muscle action in anguilliform swimming. Journal of the Royal Society Interface. 2013, 10(88), 20130667

TESS Delivers Its First Earth-sized Planet and a Warm Sub-Neptune

The future of exoplanet science is bright, as Transiting Exoplanet Survey Satellite (TESS) once again demonstrates with the discovery of its longest-period confirmed planet to date. We hereby present HD 21749b (TOI 186.01), a sub-Neptune in a 36 day orbit around a bright (V = 8.1) nearby (16 pc) K4.5 dwarf. TESS measures HD 21749b to be 2.61^(+0.17)_(-0.16) R⊕, and combined archival and follow-up precision radial velocity data put the mass of the planet at 22.7^(+2.2)_(-1.9) M⊕. HD 21749b contributes to the TESS Level 1 Science Requirement of providing 50 transiting planets smaller than 4 R⊕ with measured masses. Furthermore, we report the discovery of HD 21749c (TOI 186.02), the first Earth-sized (R_p = 0.892^(+0.064)_(-0.058)R⊕) planet from TESS. The HD 21749 system is a prime target for comparative studies of planetary composition and architecture in multi-planet systems

Electroanalysis of microbial anodes for bioelectrochemical systems: basics, progress and perspectives

Over about the last ten years, microbial anodes have been the subject of a huge number of fundamental studies dealing with an increasing variety of possible application domains. Out of several thousands of studies, only a minority have used 3-electrode set-ups to ensure well-controlled electroanalysis conditions. The present article reviews these electroanalytical studies with the admitted objective of promoting this type of investigation. A first recall of basics emphasises the advantages of the 3-electrode set-up compared to microbial fuel cell devices if analytical objectives are pursued. Experimental precautions specifically relating to microbial anodes are then noted and the existing experimental set-ups and procedures are reviewed. The state-of-the-art is described through three aspects: the effect of the polarisation potential on the characteristics of microbial anodes, the electroanalytical techniques, and the electrode. We hope that the final outlook will encourage researchers working with microbial anodes to strengthen their engagement along the multiple exciting paths of electroanalysis