Efficient Purging Research Articles

Room Temperature Synthesis of Tellurium by Solution Atomic Layer Deposition.

This study demonstrates the deposition of tellurium (Te) on silicon/silicon nitride substrates using solution atomic layer deposition (sALD) at ambient temperature. The process employs tellurium tetrachloride (TeCl4) and bis(triethylsilyl)-telluride ((TES)2Te) as precursors, with toluene as the solvent. Growth parameters were optimized through systematic variation of the pulse and purge times. Morphological characterization via scanning and transmission electron microscopy revealed needle-like crystallites, while X-ray diffractometry confirmed the crystalline nature of the deposited Te. Increasing the number of deposition cycles resulted in larger Te crystallites and enhanced substrate surface coverage. A thin amorphous carbon shell surrounding the crystallites and carbon inclusions was observed, likely originating from the organic solvent. X-ray photoemission spectroscopy analysis indicated high-purity Te films with minimal surface oxidation. The small chlorine signal suggested a near-complete precursor reaction and the efficient purging of byproducts. This novel sALD approach presents a promising method for depositing Te on various surfaces under mild conditions.

Pervasive relaxed selection in termite genomes.

Genetic changes that enabled the evolution of eusociality have long captivated biologists. More recently, attention has focussed on the consequences of eusociality on genome evolution. Studies have reported higher molecular evolutionary rates in eusocial hymenopteran insects compared with their solitary relatives. To investigate the genomic consequences of eusociality in termites, we analysed nine genomes, including newly sequenced genomes from three non-eusocial cockroaches. Using a phylogenomic approach, we found that termite genomes have experienced lower rates of synonymous substitutions than those of cockroaches, possibly as a result of longer generation times. We identified higher rates of non-synonymous substitutions in termite genomes than in cockroach genomes, and identified pervasive relaxed selection in the former (24-31% of the genes analysed) compared with the latter (2-4%). We infer that this is due to reductions in effective population size, rather than gene-specific effects (e.g. indirect selection of caste-biased genes). We found no obvious signature of increased genetic load in termites, and postulate efficient purging of deleterious alleles at the colony level. Additionally, we identified genomic adaptations that may underpin caste differentiation, such as genes involved in post-translational modifications. Our results provide insights into the evolution of termites and the genomic consequences of eusociality more broadly.

Efficient purging of deleterious mutations contributes to the survival of a rare conifer.

Cupressaceae is a conifer family rich in plants of horticultural importance, including Cupressus, Chamaecyparis, Juniperus, and Thuja, yet genomic surveys are lacking for this family. Cupressus gigantea, one of the many rare conifers that are threatened by climate change and anthropogenic habitat fragmentation, plays an ever-increasing role in ecotourism in Tibet. To infer how past climate change has shaped the population evolution of this species, we generated a de novo chromosome-scale genome (10.92Gb) and compared the species' population history and genetic load with that of a widespread close relative, C. duclouxiana. Our demographic analyses, based on 83 re-sequenced individuals from multiple populations of the two species, revealed a sharp decline of population sizes during the first part of the Quaternary. However, populations of C. duclouxiana then started to recover, while C. gigantea populations continued to decrease until recently. The total genomic diversity of C. gigantea is smaller than that of C. duclouxiana, but contrary to expectations, C. gigantea has fewer highly and mildly deleterious mutations than C. duclouxiana, and simulations and statistical tests support purifying selection during prolonged inbreeding as the explanation. Our results highlight the evolutionary consequences of decreased population size on the genetic burden of a long-lived endangered conifer with large genome size and suggest that genetic purging deserves more attention in conservation management.

Phased genome assemblies reveal haplotype-specific genetic load in the critically endangered Chinese Bahaba (Teleostei, Sciaenidae).

While haplotype-specific genetic load shapes the evolutionary trajectory of natural and captive populations, mixed-haplotype assembly and genotyping hindered its characterization in diploids. Herein, we produced two phased genome assemblies of the critically endangered fish Chinese Bahaba (Bahaba taipingensis, Sciaenidae, Teleostei) and resequenced 20 whole genomes to quantify population genetic load at a haplotype level. We identified frame-shifting variants as the most deleterious type, followed by mutations in the 5'-UTR, 3'-UTR and missense mutations at conserved amino acids. Phased haplotypes revealed gene deletions and high-impact deleterious variants. We estimated ~1.12% of genes missing or interrupted per haplotype, with a significant overlap of disrupted genes (30.35%) between haplotype sets. Relative proportions of deleterious variant categories differed significantly between haplotypes. Simulations suggested that purifying selection struggled to purge slightly deleterious genetic load in captive breeding compared to genotyping interventions, and that higher inter-haplotypic variance of genetic load predicted more efficient purging by artificial selection. Combining the knowledge of haplotype-resolved genetic load with predictive modelling will be immensely useful for understanding the evolution of deleterious variants and guiding conservation planning.

Genome sequences and population genomics provide insights into the demographic history, inbreeding, and mutation load of two 'living fossil' tree species of Dipteronia.

'Living fossils', that is, ancient lineages of low taxonomic diversity, represent an exceptional evolutionary heritage, yet we know little about how demographic history and deleterious mutation load have affected their long-term survival and extinction risk. We performed whole-genome sequencing and population genomic analyses on Dipteronia sinensis and D. dyeriana, two East Asian Tertiary relict trees. We found large-scale genome reorganizations and identified species-specific genes under positive selection that are likely involved in adaptation. Our demographic analyses suggest that the wider-ranged D. sinensis repeatedly recovered from population bottlenecks over late Tertiary/Quaternary periods of adverse climate conditions, while the population size of the narrow-ranged D. dyeriana steadily decreased since the late Miocene, especially after the Last Glacial Maximum (LGM). We conclude that the efficient purging of deleterious mutations in D. sinensis facilitated its survival and repeated demographic recovery. By contrast, in D. dyeriana, increased genetic drift and reduced selection efficacy, due to recent severe population bottlenecks and a likely preponderance of vegetative propagation, resulted in fixation of strongly deleterious mutations, reduced fitness, and continuous population decline, with likely detrimental consequences for the species' future viability and adaptive potential. Overall, our findings highlight the significant impact of demographic history on levels of accumulation and purging of putatively deleterious mutations that likely determine the long-term survival and extinction risk of Tertiary relict trees.

Sex differences in deleterious genetic variants in a haplodiploid social insect.

Deleterious variants are selected against but can linger in populations at low frequencies for long periods of time, decreasing fitness and contributing to disease burden in humans and other species. Deleterious variants occur at low frequency but distinguishing deleterious variants from low-frequency neutral variation is challenging based on population genomics data alone. As a result, we have little sense of the number and identity of deleterious variants in wild populations. For haplodiploid species, it has been hypothesised that deleterious alleles will be directly exposed to selection in haploid males, but selection can be masked in diploid females when deleterious variants are recessive, resulting in more efficient purging of deleterious mutations in males. Therefore, comparisons of the differences between haploid and diploid genomes from the same population may be a useful method for inferring rare deleterious variants. This study provides the first formal test of this hypothesis. Using wild populations of Northern paper wasps (Polistes fuscatus), we find that males have fewer missense and nonsense variants per generation than females from the same population. Allele frequency differences are especially pronounced for rare missense and nonsense variants and these differences lead to a lower mutational load in males than females. Based on these data we infer that many highly deleterious mutations are segregating in the paper wasp population. Stronger selection against deleterious alleles in haploid males may have implications for adaptation in other haplodiploid insects and provides evidence that wild populations harbour abundant deleterious variants.

Epistasis, inbreeding depression, and the evolution of self-fertilization.

Inbreeding depression resulting from partially recessive deleterious alleles is thought to be the main genetic factor preventing self-fertilizing mutants from spreading in outcrossing hermaphroditic populations. However, deleterious alleles may also generate an advantage to selfers in terms of more efficient purging, while the effects of epistasis among those alleles on inbreeding depression and mating system evolution remain little explored. In this article, we use a general model of selection to disentangle the effects of different forms of epistasis (additive-by-additive, additive-by-dominance, and dominance-by-dominance) on inbreeding depression and on the strength of selection for selfing. Models with fixed epistasis across loci, and models of stabilizing selection acting on quantitative traits (generating distributions of epistasis) are considered as special cases. Besides its effects on inbreeding depression, epistasis may increase the purging advantage associated with selfing (when it is negative on average), while the variance in epistasis favors selfing through the generation of linkage disequilibria that increase mean fitness. Approximations for the strengths of these effects are derived, and compared with individual-based simulationresults.

The C- and G-value paradox with polyploidy, repeatomes, introns, phenomes and cell economy.

The apparent disconnection between biological complexity and both genome size (C-value) and gene number (G-value) is one of the long-standing biological puzzles. Gene-dense genomic sequences in prokaryotes or simple eukaryotes are highly constrained during selection, whereas gene-sparse genomic sequences in higher eukaryotes have low selection constraints. This review discusses the correlations of the C-value and G-value with genome architecture, polyploidy, repeatomes, introns, cell economy and phenomes. Eukaryotic chromosomes carry an assortment of various repeated DNA sequences (repeatomes). Expansion of copies of repeatomes together with polyploidization or whole-genome duplication (WGD) are major players in genome size (C-value) bloating, but genomes are equipped with counterbalancing systems such as diploidization, illegitimate recombination, and nonhomologous end joining (NHEJ) after double-strand breaks (DSBs). The lack of these efficient purging systems allowed the accumulation of repeat DNA, which resulted in extremely large genomes in several species. However, the correlation between chromosome number and genome size is not clear due to inconsistent results with different sets of species. Positive correlations between genome size and intron size and density were reported in early studies, but these proposals were refuted by the results with increased numbers of species, in which genome-wide features of introns (size, density, gene contents, repeats) were weakly associated with genome size. The assumption of the correlations between C-value and gene number (G-value) and organismal complexity is acceptable in general, but this assumption is often violated in specific lineages or species, suggesting C- and G-value paradoxes. The C-value paradox is partly explained by noncoding repeatomes. The G-value paradox can also be explained by several genomic features: (1) one gene can produce many mature mRNAs by alternative splicing, and eukaryotic gene expression is highly regulated at both the transcriptional and translational levels; (2) many proteins exert multiple functions during development; (3) gene expansion/contraction are frequent events in the gene family among evolutionarily close species; and (4) sets of homeotic genes regulate development such that organismal complexity is sometimes not clear among organisms. A large genome must be burdensome in terms of cell economy, such that a large genome constraint results in the distribution of genome sizes skewed to small genomes. Moreover, the C-value can affect the phenome. A strong positive correlation has been recognized between genome size and cell size, but the relationship is weak or null with higher-level traits. Additional analyses of the relationship between the C-value and phenome should be carried out, because natural selection acts on the phenotype rather than the genotype. Dramatic advancement in genomics has given some answers to the C-value and G-value paradoxes. We know the mechanisms by which the current genomes have been constructed. However, basic questions have not yet been fully resolved. Why have some species retained small genomes yet some closely related species have large genomes? Random genetic drift and mutational pressure might have affected for genome size in the limited population size during evolution; thus, genome size may be quasiadaptable rather than the best adaptive trait.

Comparison of the Full Distribution of Fitness Effects of New Amino Acid Mutations Across Great Apes.

The distribution of fitness effects (DFE) is central to many questions in evolutionary biology. However, little is known about the differences in DFE between closely related species. We use >9000 coding genes orthologous one-to-one across great apes, gibbons, and macaques to assess the stability of the DFE across great apes. We use the unfolded site frequency spectrum of polymorphic mutations (n = 8 haploid chromosomes per population) to estimate the DFE. We find that the shape of the deleterious DFE is strikingly similar across great apes. We confirm that effective population size (Ne ) is a strong predictor of the strength of negative selection, consistent with the nearly neutral theory. However, we also find that the strength of negative selection varies more than expected given the differences in Ne between species. Across species, mean fitness effects of new deleterious mutations covaries with Ne , consistent with positive epistasis among deleterious mutations. We find that the strength of negative selection for the smallest populations, bonobos and western chimpanzees, is higher than expected given their Ne This may result from a more efficient purging of strongly deleterious recessive variants in these populations. Forward simulations confirm that these findings are not artifacts of the way we are inferring Ne and DFE parameters. All findings are replicated using only GC-conservative mutations, thereby confirming that GC-biased gene conversion is not affecting our conclusions.

ЭФФЕКТИВНОСТЬ РЕГЕНЕРАЦИИ ЩЕЛЕВОГО ФИЛЬТРА

This aim of this research was to study the mechanism and efficiency of the regeneration of filtering walls by means of reverse jet blasting with a rotating nozzle during dusty gas treatment by a slotted filter. Within a series of experiments, the rotational speed of the blowing nozzle and its distance to the filtering wall, the number of wire layers and the gaps between them were varied. Air consumption for filtration and purging was measured along with the hydraulic resistance of a clean filtering wall, a wall with dust sedimentation and one following regeneration. The balance of the forces acting on the dust sediment during regeneration and the conditions for the separation of the sediment from the filtering wall were analysed, allowing the minimum velocity of the blowing jet to be mathematically defined. A dependency relation is proposed for calculating the effective working speed of the jet, which ensures efficient regeneration and minimum purging costs. The efficiency of regeneration is found to be exponentially related to the residual creep resistance index determined by the conditions of filtration and regeneration. A dependency relation is derived to calculate the regeneration coefficient, which can be recommended for determining the total hydraulic resistance of the slotted filter, taking into account the resistance of the clean filtering wall, the resistance of the dust sediment and the residual resistance of the filtering wall after regeneration.

How oxygen gave rise to eukaryotic sex.

How did full meiotic eukaryotic sex evolve and what was the immediate advantage allowing it to develop? We propose that the crucial determinant can be found in internal reactive oxygen species (ROS) formation at the start of eukaryotic evolution approximately 2 × 109 years ago. The large amount of ROS coming from a bacterial endosymbiont gave rise to DNA damage and vast increases in host genome mutation rates. Eukaryogenesis and chromosome evolution represent adaptations to oxidative stress. The host, an archaeon, most probably already had repair mechanisms based on DNA pairing and recombination, and possibly some kind of primitive cell fusion mechanism. The detrimental effects of internal ROS formation on host genome integrity set the stage allowing evolution of meiotic sex from these humble beginnings. Basic meiotic mechanisms thus probably evolved in response to endogenous ROS production by the ‘pre-mitochondrion’. This alternative to mitosis is crucial under novel, ROS-producing stress situations, like extensive motility or phagotrophy in heterotrophs and endosymbiontic photosynthesis in autotrophs. In multicellular eukaryotes with a germline–soma differentiation, meiotic sex with diploid–haploid cycles improved efficient purging of deleterious mutations. Constant pressure of endogenous ROS explains the ubiquitous maintenance of meiotic sex in practically all eukaryotic kingdoms. Here, we discuss the relevant observations underpinning this model.

No Substantial Evidence for Sexual Transmission of Minority HIV Drug Resistance Mutations in Men Who Have Sex with Men.

During primary HIV infection, the presence of minority drug resistance mutations (DRM) may be a consequence of sexual transmission, de novo mutations, or technical errors in identification. Baseline blood samples were collected from 24 HIV-infected antiretroviral-naive, genetically and epidemiologically linked source and recipient partners shortly after the recipient's estimated date of infection. An additional 32 longitudinal samples were available from 11 recipients. Deep sequencing of HIV reverse transcriptase (RT) was performed (Roche/454), and the sequences were screened for nucleoside and nonnucleoside RT inhibitor DRM. The likelihood of sexual transmission and persistence of DRM was assessed using Bayesian-based statistical modeling. While the majority of DRM (>20%) were consistently transmitted from source to recipient, the probability of detecting a minority DRM in the recipient was not increased when the same minority DRM was detected in the source (Bayes factor [BF] = 6.37). Longitudinal analyses revealed an exponential decay of DRM (BF = 0.05) while genetic diversity increased. Our analysis revealed no substantial evidence for sexual transmission of minority DRM (BF = 0.02). The presence of minority DRM during early infection, followed by a rapid decay, is consistent with the "mutation-selection balance" hypothesis, in which deleterious mutations are more efficiently purged later during HIV infection when the larger effective population size allows more efficient selection. Future studies using more recent sequencing technologies that are less prone to single-base errors should confirm these results by applying a similar Bayesian framework in other clinical settings.IMPORTANCE The advent of sensitive sequencing platforms has led to an increased identification of minority drug resistance mutations (DRM), including among antiretroviral therapy-naive HIV-infected individuals. While transmission of DRM may impact future therapy options for newly infected individuals, the clinical significance of the detection of minority DRM remains controversial. In the present study, we applied deep-sequencing techniques within a Bayesian hierarchical framework to a cohort of 24 transmission pairs to investigate whether minority DRM detected shortly after transmission were the consequence of (i) sexual transmission from the source, (ii) de novo emergence shortly after infection followed by viral selection and evolution, or (iii) technical errors/limitations of deep-sequencing methods. We found no clear evidence to support the sexual transmission of minority resistant variants, and our results suggested that minor resistant variants may emerge de novo shortly after transmission, when the small effective population size limits efficient purge by natural selection.

Development of a low-debris laser driven tape drive soft x-ray source

This paper focuses on debris mitigation in a laser driven tape drive x-ray source. A smart design is being used to minimise the effect of shockwave reflection from the target's back and a continuous rough pumping is utilised to obtain an efficient purging of big lumpy debris particles out of the interaction chamber. The effect of low pressure (3–6 mbar) nitrogen buffer gas is studied together with a moderate magnetic field (0.14 Tesla) on both debris spall and hot ions trajectory. The target material for this work is a 15 μm VHS video tape composed of Mylar as carrier film with Fe2O3 and CrO2 powder. The experiments were conducted using a long pulsed 800ps, 50 Hz Nd: YAG laser. The results obtained appeared to be promising in reducing the damaging effect of large debris particles (between 50 and 140 microns) as well as small particles (∼ 5 microns) that deteriorates the efficiency of delicate optics.

Mistranslation can enhance fitness through purging of deleterious mutations

Phenotypic mutations are amino acid changes caused by mistranslation. How phenotypic mutations affect the adaptive evolution of new protein functions is unknown. Here we evolve the antibiotic resistance protein TEM-1 towards resistance on the antibiotic cefotaxime in an Escherichia coli strain with a high mistranslation rate. TEM-1 populations evolved in such strains endow host cells with a general growth advantage, not only on cefotaxime but also on several other antibiotics that ancestral TEM-1 had been unable to deactivate. High-throughput sequencing of TEM-1 populations shows that this advantage is associated with a lower incidence of weakly deleterious genotypic mutations. Our observations show that mistranslation is not just a source of noise that delays adaptive evolution. It could even facilitate adaptive evolution by exacerbating the effects of deleterious mutations and leading to their more efficient purging. The ubiquity of mistranslation and its effects render mistranslation an important factor in adaptive protein evolution.

Sex-specific selection under environmental stress in seed beetles.

Sexual selection can increase rates of adaptation by imposing strong selection in males, thereby allowing efficient purging of the mutation load on population fitness at a low demographic cost. Indeed, sexual selection tends to be male-biased throughout the animal kingdom, but little empirical work has explored the ecological sensitivity of this sex difference. In this study, we generated theoretical predictions of sex-specific strengths of selection, environmental sensitivities and genotype-by-environment interactions and tested them in seed beetles by manipulating either larval host plant or rearing temperature. Using fourteen isofemale lines, we measured sex-specific reductions in fitness components, genotype-by-environment interactions and the strength of selection (variance in fitness) in the juvenile and adult stage. As predicted, variance in fitness increased with stress, was consistently greater in males than females for adult reproductive success (implying strong sexual selection), but was similar in the sexes in terms of juvenile survival across all levels of stress. Although genetic variance in fitness increased in magnitude under severe stress, heritability decreased and particularly so in males. Moreover, genotype-by-environment interactions for fitness were common but specific to the type of stress, sex and life stage, suggesting that new environments may change the relative alignment and strength of selection in males and females. Our study thus exemplifies how environmental stress can influence the relative forces of natural and sexual selection, as well as concomitant changes in genetic variance in fitness, which are predicted to have consequences for rates of adaptation in sexual populations.

Inbreeding depression under mixed outcrossing, self-fertilization and sib-mating.

BackgroundBiparental inbreeding, mating between two relatives, occurs at a low frequency in many natural plant populations, which also often have substantial rates of self-fertilization. Although biparental inbreeding is likely to influence the dynamics of inbreeding depression and the evolution of selfing rates, it has received limited theoretical attention in comparison to selfing. The only previous model suggested that biparental inbreeding can favour the maintenance of stable intermediate selfing rates, but made unrealistic assumptions about the genetic basis of inbreeding depression. Here we extend a genetic model of inbreeding depression, describing nearly recessive lethal mutations at a very large number of loci, to incorporate sib-mating. We also include a constant component of inbreeding depression modelling the effects of mildly deleterious, nearly additive alleles. We analyze how observed rates of sib-mating influence the mean number of heterozygous lethals alleles and inbreeding depression in a population reproducing by a mixture of self-fertilization, sib-mating and outcrossing. We finally use the ensuing relationship between equilibrium inbreeding depression and population selfing rate to infer the evolutionarily stable selfing rates expected under such a mixed mating system.ResultsWe show that for a given rate of inbreeding, sib-mating is more efficient at purging inbreeding depression than selfing, because homozygosity of lethals increases more gradually through sib-mating than through selfing. Because sib-mating promotes the purging of inbreeding depression and the evolution of selfing, our genetic model of inbreeding depression also predicts that sib-mating is unlikely to maintain stable intermediate selfing rates.ConclusionsOur results imply that even low rates of sib-mating affect plant mating system evolution, by facilitating the evolution of selfing via more efficient purging of inbreeding depression. Alternative mechanisms, such as pollination ecology, are necessary to explain stable mixed selfing and outcrossing.

Rapid purging of genetic load in a metapopulation and consequences for range expansion in an invasive plant

Invasive species often display high fitness despite bottlenecks and inbreeding during establishment. We address this paradox through simulations and experiments that assess the potential for purging of genetic load during range expansion. Success of invaders often depends on the production of vigorous inbred offspring allowing for rapid population growth after colonization. Substantial genetic load of outbreeding species reduces the fitness of offspring as inbreeding ensues during the establishment of populations. In our simulations, sustained selfing or outcrossing within isolated populations did little to remove deleterious mutations. Conversely, inbreeding combined with periodic gene flow resulted in efficient purging and accelerated rates of range expansion. Purging efficiency was dependent on initial genetic diversity levels, in line with predictions that multiple introductions facilitate invasion and the evolution of more aggressive invaders. Simulation predictions were tested using the invasive species Brachypodium sylvaticum. Homozygous populations on B. sylvaticum’s range periphery displayed lower inbreeding depression compared to heterozygous populations near introduction sites. Empirical tests with B. sylvaticum demonstrate that purging of genetic load is a plausible scenario promoting range expansion during invasion.

Pre-particle filtration and moisture control by efficient purging in various inlet and outlet of a 450 mm wafer front-opening unified pod

The trend toward narrower line width in semiconductor manufacturing has made contamination control more and more important. The presence of moisture in wafer containers, such as front opening unified pods (FOUP), can lead to the native oxide residues growth, metal corrosion, and thin film cracking on wafer surfaces. Accordingly, decreasing contamination methods and improving factory efficiency are continuously researched. Single or multi-layer particulate shields on top of wafers in FOUPs may be used to prevent pollutant accumulation. In addition, point-of-use (POU) filtration may also been used to control particle contamination in FOUPs during wafer transformation and storage. The demand for stricter filtration led to the usage of 0.10 and 0.20 µm membranes to control the contamination. However, with the introduction of finer membranes end users may have concerns about deleterious remainders on wafers from undergoing filtration. There are a total of 25 pieces of wafers in the FOUP and the arrangement is from the bottom (wafer No. 1) to the top (wafer No. 25) with arising manner. Purging FOUPs to expel moisture vapors with Clean Dry Air (CDA) is one of the most popular methods.There was no previous research for investigating the purge performance on new-generation 450mm FOUPs. This research aims to study main factors influencing the performance of the purge system on 450mm FOUPs, including moisture concentration, CDA flow rate, and filter pressure.

Efficient purging of deleterious mutations in plants with haploid selfing.

In diploid organisms, selfing reduces the efficiency of selection in removing deleterious mutations from a population. This need not be the case for all organisms. Some plants, for example, undergo an extreme form of selfing known as intragametophytic selfing, which immediately exposes all recessive deleterious mutations in a parental genome to selective purging. Here, we ask how effectively deleterious mutations are removed from such plants. Specifically, we study the extent to which deleterious mutations accumulate in a predominantly selfing and a predominantly outcrossing pair of moss species, using genome-wide transcriptome data. We find that the selfing species purge significantly more nonsynonymous mutations, as well as a greater proportion of radical amino acid changes which alter physicochemical properties of amino acids. Moreover, their purging of deleterious mutation is especially strong in conserved regions of protein-coding genes. Our observations show that selfing need not impede but can even accelerate the removal of deleterious mutations, and do so on a genome-wide scale.

The Load Dependent Purge Strategy

In fuel cell systems with an anode recirculation cycle that runs overstoichiometrically, an undesired enrichment of nitrogen and water vapor occurs due to their diffusion through the membrane-electrode-assembly (MEA). This causes an impairment of the power density. So far, this phenomenon was avoided by a time dependent purge strategy. During this process a lot of unconsumed hydrogen gets wasted. A more efficient purge strategy that reduces the waste and improves the system efficiency, which operates load dependently by means of the mass transfer coefficient, is introduced. A comparison of the system efficiency with and without the load-dependent-purge-strategy (LPS) is made and discussed in order to demonstrate the effectiveness of the new method. Static as well as dynamic system simulations were performed for this purpose. A notable improvement of the system efficiency of up to 10% with LPS was achieved. With LPS the purge power losses could be markedly reduced. This reformation also induces an improvement of the system efficiency, which brings us a considerable step forward towards a longer reach. Moreover, LPS is not restricted to a certain fuel cell system and thus affords a more flexible and versatile employment than its predecessor.