A Methodology to Account for the Finger Non-Uniformity in Photovoltaic Solar Cell

Abstract In this work we investigate the impact of a non-uniform finger in the front-side metallization on the performance of c-Si solar cells. For this purpose, we propose a methodology based on a mixed-mode simulation approach, which allows evaluating the solar cell properties by performing both numerical device simulations and circuit simulations. The finger roughness profile is modeled by means of Gaussian function. The impact of roughness on the solar cell efficiency is studied as a function of mean finger height, mean finger width and finger resistivity. The proposed methodology has been applied to typical roughness profiles realized with two different metallization techniques, the conventional single screen-printing (SP) and the double screen-printing (DP)

Optimization of Rear Point Contact Geometry by Means of 3-D Numerical Simulation

Abstract In this work three-dimensional (3-D) numerical simulations, validated by the experimental measurements of a reference cell, have been performed to optimize the rear contact geometry of a PERC-type solar cell, featuring a high sheet resistance (140 Ω/sq) phosphorus-doped emitter and a front-side metallization with narrow and highly-conductive electro-plated copper lines (40 μm wide) on lowly resistive Ti contacts. The simulation results show that an optimization of the rear point contact design potentially leads to an efficiency improvement of 0.68%abs compared to the reference cell

Selection and assembly of indigenous bacteria and methanogens from spent metalworking fluids and their potential as a starting culture in a fluidized bed reactor

Waste metalworking fluids (MWFs) are highly biocidal resulting in real difficulties in the, otherwise favoured, bioremediation of these high chemical oxygen deman (COD) wastes anaerobically in bioreactors. We have shown, as a proof of concept, that it is possible to establish an anaerobic starter culture using strains isolated from spent MWFs which are capable of reducing COD or, most significantly, methanogenesis in this biocidal waste stream. Bacterial strains (n=99) and archaeal methanogens (n=28) were isolated from spent MWFs. The most common bacterial strains were Clostridium species (n=45). All methanogens were identified as Methanosarcina mazei. Using a random partitions design(RPD) mesocosm experiment, we found that bacterial diversity and species–species interactions had significant effects on COD reduction but that bacterial composition did not. The RPD study showed similar effects on methanogenesis, except that composition was also significant. We identified bacterial species with positive and negative effects on methane production. A consortium of 16 bacterial species and three methanogens was used to initiate a fluidized bed bioreactor (FBR), in batch mode. COD reduction and methane production were variable, and the reactor was oscillated between continuous and batch feeds. In both microcosm and FBR experiments,periodic inconsistencies in bacterial reduction in fermentative products to formic and acetic acids were identified as a key issue

Cheating on the Edge

We present the results of an individual agent-based model of antibiotic resistance in bacteria. Our model examines antibiotic resistance when two strategies exist: “producers”–who secrete a substance that breaks down antibiotics–and nonproducers (“cheats”) who do not secrete, or carry the machinery associated with secretion. The model allows for populations of up to 10,000, in which bacteria are affected by their nearest neighbors, and we assume cheaters die when there are no producers in their neighborhood. Each of 10,000 slots on our grid (a torus) could be occupied by a producer or a nonproducer, or could (temporarily) be unoccupied. The most surprising and dramatic result we uncovered is that when producers and nonproducers coexist at equilibrium, nonproducers are almost always found on the edges of clusters of producers

Cheaters allow cooperators to prosper

Cooperation based on the production of costly common goods is observed throughout nature. This is puzzling, as cooperation is vulnerable to exploitation by defectors which enjoy a fitness advantage by consuming the common good without contributing fairly. Depletion of the common good can lead to population collapse and the destruction of cooperation. However, population collapse implies small population size, which, in a structured population, is known to favor cooperation. This happens because small population size increases variability in cooperator frequency across different locations. Since individuals in cooperator-dominated locations (which are most likely cooperators) will grow more than those in defector-dominated locations (which are most likely defectors), cooperators can outgrow defectors globally despite defectors outgrowing cooperators in each location. This raises the possibility that defectors can lead to conditions that sometimes rescue cooperation from defector-induced destruction. We demonstrate multiple mechanisms through which this can occur, using an individual-based approach to model stochastic birth, death, migration, and mutation events. First, during defector-induced population collapse, defectors occasionally go extinct before cooperators by chance, which allows cooperators to grow. Second, empty locations, either preexisting or created by defector-induced population extinction, can favor cooperation because they allow cooperator but not defector migrants to grow. These factors lead to the counterintuitive result that the initial presence of defectors sometimes allows better survival of cooperation compared to when defectors are initially absent. Finally, we find that resource limitation, inducible by defectors, can select for mutations adaptive to resource limitation. When these mutations are initially present at low levels or continuously generated at a moderate rate, they can favor cooperation by further reducing local population size. We predict that in a structured population, small population sizes precipitated by defectors provide a "built-in" mechanism for the persistence of cooperation

Bacterial adaptation is constrained in complex communities

© 2020, The Author(s). A major unresolved question is how bacteria living in complex communities respond to environmental changes. In communities, biotic interactions may either facilitate or constrain evolution depending on whether the interactions expand or contract the range of ecological opportunities. A fundamental challenge is to understand how the surrounding biotic community modifies evolutionary trajectories as species adapt to novel environmental conditions. Here we show that community context can dramatically alter evolutionary dynamics using a novel approach that ‘cages’ individual focal strains within complex communities. We find that evolution of focal bacterial strains depends on properties both of the focal strain and of the surrounding community. In particular, there is a stronger evolutionary response in low-diversity communities, and when the focal species have a larger genome and are initially poorly adapted. We see how community context affects resource usage and detect genetic changes involved in carbon metabolism and inter-specific interaction. The findings demonstrate that adaptation to new environmental conditions should be investigated in the context of interspecific interactions

A barrier to homologous recombination between sympatric strains of the cooperative soil bacterium Myxococcus xanthus

The bacterium Myxococcus xanthus glides through soil in search of prey microbes, but when food sources run out, cells cooperatively construct and sporulate within multicellular fruiting bodies. M. xanthus strains isolated from a 16 × 16-cm-scale patch of soil were previously shown to have diversified into many distinct compatibility types that are distinguished by the failure of swarming colonies to merge upon encounter. We sequenced the genomes of 22 isolates from this population belonging to the two most frequently occurring multilocus sequence type (MLST) clades to trace patterns of incipient genomic divergence, specifically related to social divergence. Although homologous recombination occurs frequently within the two MLST clades, we find an almost complete absence of recombination events between them. As the two clades are very closely related and live in sympatry, either ecological or genetic barriers must reduce genetic exchange between them. We find that the rate of change in the accessory genome is greater than the rate of amino-acid substitution in the core genome. We identify a large genomic tract that consistently differs between isolates that do not freely merge and therefore is a candidate region for harbouring gene(s) responsible for self/non-self discrimination

Emergence and Modular Evolution of a Novel Motility Machinery in Bacteria

Bacteria glide across solid surfaces by mechanisms that have remained largely mysterious despite decades of research. In the deltaproteobacterium Myxococcus xanthus, this locomotion allows the formation stress-resistant fruiting bodies where sporulation takes place. However, despite the large number of genes identified as important for gliding, no specific machinery has been identified so far, hampering in-depth investigations. Based on the premise that components of the gliding machinery must have co-evolved and encode both envelope-spanning proteins and a molecular motor, we re-annotated known gliding motility genes and examined their taxonomic distribution, genomic localization, and phylogeny. We successfully delineated three functionally related genetic clusters, which we proved experimentally carry genes encoding the basal gliding machinery in M. xanthus, using genetic and localization techniques. For the first time, this study identifies structural gliding motility genes in the Myxobacteria and opens new perspectives to study the motility mechanism. Furthermore, phylogenomics provide insight into how this machinery emerged from an ancestral conserved core of genes of unknown function that evolved to gliding by the recruitment of functional modules in Myxococcales. Surprisingly, this motility machinery appears to be highly related to a sporulation system, underscoring unsuspected common mechanisms in these apparently distinct morphogenic phenomena

Analysis of genetic systems using experimental evolution and whole-genome sequencing

The application of whole-genome sequencing to the study of microbial evolution promises to reveal the complex functional networks of mutations that underlie adaptation. A recent study of parallel evolution in populations of Escherichia coli shows how adaptation involves both functional changes to specific proteins as well as global changes in regulation