S-matrix network models for coherent waves in random media: construction and renormalization

Networks of random quantum scatterers (S-matrices) form paradigmatic models for the propagation of coherent waves in random S-matrix network models cover universal localization-delocalization properties and have some advantages over more traditional Hamiltonian models. In particular, a straightforward implementation of real space renormalization techniques is possible. Starting from a finite elementary cell of the S-matrix network, hierarchical network models can be constructed by recursion. The localization-delocalization properties are contained in the flow of the forward scattering strength ('conductance') under increasing system size. With the aid of 'small scale' numerics qualitative aspects of the localization-delocalization properties of S-matrix network models can be worked out.Comment: 10 pages, LaTeX, 8 eps figures included, proceedings PILS98, to be published in Annalen der Physi

Boosting capacitive blue-energy and desalination devices with waste heat

We show that sustainably harvesting 'blue' energy from the spontaneous mixing process of fresh and salty water can be boosted by varying the water temperature during a capacitive mixing process. Our modified Poisson-Boltzmann calculations predict a strong temperature dependence of the electrostatic potential of a charged electrode in contact with an adjacent aqueous 1:1 electrolyte. We propose to exploit this dependence to boost the efficiency of capacitive blue engines, which are based on cyclically charging and discharging nanoporous supercapacitors immersed in salty and fresh water, respectively [D. Brogioli, Phys. Rev. Lett. 103, 058501 (2009)]. We show that the energy output of blue engines can be increased by a factor of order two if warm (waste-heated) fresh water is mixed with cold sea water. Moreover, the underlying physics can also be used to optimize the reverse process of capacitive desalination of water

Reversible heat production during electric double layer buildup depends sensitively on the electrolyte and its reservoir

Several modern technologies for energy storage and conversion are based on the screening of electric charge on the surface of porous electrodes by ions in an adjacent electrolyte. This so-called electric double layer (EDL) exhibits an intricate interplay with the electrolyte's temperature that was the focus of several recent studies. In one of them, Janssen et al. [Phys. Rev. Lett. 119, 166002 (2017)] experimentally determined the ratio $\mathcal{Q}_\text{rev}/W_\text{el}$ of reversible eat flowing into a supercapacitor during an isothermal charging process and the electric work applied therein. To rationalize that data, here, we determine $\mathcal{Q}_\text{rev}/W_\text{el}$ within different models of the EDL using theoretical approaches like density functional theory (DFT) as well as molecular dynamics simulations. Applying mainly the restricted primitive model, we find quantitative support for a speculation of Janssen et al. that steric ion interactions are key to the ratio $\mathcal{Q}_\text{rev}/W_\text{el}$. Here, we identified the entropic contribution of certain DFT functionals, which grants direct access to the reversible heat. We further demonstrate how $\mathcal{Q}_\text{rev}/W_\text{el}$ changes when calculated in different thermodynamic ensembles and processes. We show that the experiments of Janssen et al. are explained best by a charging process at fixed bulk density, or in a "semi-canonical" system. Finally, we find that $\mathcal{Q}_\text{rev}/W_\text{el}$ significantly depends on parameters as pore and ion size, salt concentration, and valencies of the cat- and anions of the electrolyte. Our findings can guide further heat production measurements and can be applied in studies on, for instance, nervous conduction, where reversible heat is a key element.Comment: 15 pages, 8 figures. This article appeared in J. Chem. Phys. 154, 064901 (2021) and may be found at https://doi.org/10.1063/5.003721

Fundamental measure theory for the electric double layer: implications for blue-energy harvesting and water desalination

Capacitive mixing (CAPMIX) and capacitive deionization (CDI) are promising candidates for harvesting clean, renewable energy and for the energy efficient production of potable water, respectively. Both CAPMIX and CDI involve water-immersed porous carbon (supercapacitors) electrodes at voltages of the order of hundreds of millivolts, such that counter-ionic packing is important for the electric double layer (EDL) which forms near the surface of these porous materials. Thus, we propose a density functional theory (DFT) to model the EDL, where the White-Bear mark II fundamental measure theory functional is combined with a mean-field Coulombic and a mean spherical approximation-type correction to describe the interplay between dense packing and electrostatics, in good agreement with molecular dynamics simulations. We discuss the concentration-dependent potential rise due to changes in the chemical potential in capacitors in the context of an over-ideal theoretical description and its impact on energy harvesting and water desalination. Compared to less elaborate mean-field models our DFT calculations reveal a higher work output for blue-energy cycles and a higher energy demand for desalination cycles

Aircraft-based observations of air-sea fluxes over Denmark Strait and the Irminger sea during high wind speed conditions

The impact of targeted sonde observations on the 1-3 day forecasts for northern Europe is evaluated using the Met Office four-dimensional variational data assimilation scheme and a 24 km gridlength limited-area version of the Unified Model (MetUM). The targeted observations were carried out during February and March 2007 as part of the Greenland Flow Distortion Experiment, using a research aircraft based in Iceland. Sensitive area predictions using either total energy singular vectors or an ensemble transform Kalman filter were used to predict where additional observations should be made to reduce errors in the initial conditions of forecasts for northern Europe. Targeted sonde data was assimilated operationally into the MetUM. Hindcasts show that the impact of the sondes was mixed. Only two out of the five cases showed clear forecast improvement; the maximum forecast improvement seen over the verifying region was approximately 5% of the forecast error 24 hours into the forecast. These two cases are presented in more detail: in the first the improvement propagates into the verification region with a developing polar low; and in the second the improvement is associated with an upper-level trough. The impact of cycling targeted data in the background of the forecast (including the memory of previous targeted observations) is investigated. This is shown to cause a greater forecast impact, but does not necessarily lead to a greater forecast improvement. Finally, the robustness of the results is assessed using a small ensemble of forecasts

Proximity-induced spin ordering at the interface between a ferromagnetic metal and a magnetic semiconductor

14 páginas, 5 figuras.-- PACS number8s): 73.40.Sx, 75.70.-iWe carry on a theoretical investigation of the conditions for the appearance and/or modification of spin ordering in a dilute magnetic semiconductor that is in contact with a ferromagnetic metal. We show that the magnetic proximity effect has a rather complex physical nature in this system. Allowing for the hybridization between the ferromagnetic metal and semiconductor electron states, we calculate the spin polarization and spin susceptibility of carriers in the semiconductor layer near the contact. The peculiar mechanism of indirect exchange coupling that occurs between local spins dissolved in the semiconductor host when a dilute magnetic semiconductor is in contact with a ferromagnetic metal is analyzed. The structure of the proximity-induced ordering of local moments in a dilute magnetic semiconductor is qualitatively described within a mean-field approach. On the basis of our results, we interpret the experimental data on Fe/(Ga,Mn)As and Py/(Ga,Mn)As layered structures.The work was partially supported by the University of the Basque Country [Proyecto GV-UPV/EHU under Grant No. IT-366-07), Spanish Ministerio de Ciencia y Tecnología (Grant No. FIS2007-66711-C02-01)] , and by RFBR (Grant No. 10-02-00118). S.C. also acknowledges financial support by PRIN 2007 under Project No. 2007FW3MJX003. V.V.T. acknowledges financial support by Ikerbasque (Basque Foundation for Science).Peer reviewe

Assessing taxonomic metagenome profilers with OPAL

Meyer F, Bremges A, Belmann P, Janssen S, McHardy AC, Koslicki D. Assessing taxonomic metagenome profilers with OPAL. Genome biology. 2019;20(1): 51.The explosive growth in taxonomic metagenome profiling methods over the past years has created a need for systematic comparisons using relevant performance criteria. The Open-community Profiling Assessment tooL (OPAL) implements commonly used performance metrics, including those of the first challenge of the initiative for the Critical Assessment of Metagenome Interpretation (CAMI), together with convenient visualizations. In addition, we perform in-depth performance comparisons with seven profilers on datasets of CAMI and the Human Microbiome Project. OPAL is freely available at https://github.com/CAMI-challenge/OPAL

Molecular evidence for a single origin of ultrafiltration-based excretory organs

Under embargo until: 2021-06-23Excretion is an essential physiological process, carried out by all living organisms, regardless of their size or complexity.1, 2, 3 Both protostomes (e.g., flies and flatworms) and deuterostomes (e.g., humans and sea urchins) possess specialized excretory organs serving that purpose. Those organs exhibit an astonishing diversity, ranging from units composed of just few distinct cells (e.g., protonephridia) to complex structures, built by millions of cells of multiple types with divergent morphology and function (e.g., vertebrate kidneys).4,5 Although some molecular similarities between the development of kidneys of vertebrates and the regeneration of the protonephridia of flatworms have been reported,6,7 the molecular underpinnings of the development of excretory organs have never been systematically studied in a comparative context.4 Here, we show that a set of transcription factors (eya, six1/2, pou3, sall, lhx1/5, and osr) and structural proteins (nephrin, kirre, and zo1) is expressed in the excretory organs of a phoronid, brachiopod, annelid, onychophoran, priapulid, and hemichordate that represent major protostome lineages and non-vertebrate deuterostomes. We demonstrate that the molecular similarity observed in the vertebrate kidney and flatworm protonephridia6,7 is also seen in the developing excretory organs of those animals. Our results show that all types of ultrafiltration-based excretory organs are patterned by a conserved set of developmental genes, an observation that supports their homology. We propose that the last common ancestor of protostomes and deuterostomes already possessed an ultrafiltration-based organ that later gave rise to the vast diversity of extant excretory organs, including both proto- and metanephridia.acceptedVersio