We propose an expression for a local planetesimal formation rate proportional to the instantaneous radial pebble flux. The result-a radial planetesimal distribution-can be used as an initial ...condition to study the formation of planetary embryos. We follow the idea that one needs particle traps to locally enhance the dust-to-gas ratios sufficiently, such that particle gas interactions can no longer prevent planetesimal formation on small scales. The locations of these traps can emerge everywhere in the disk. Their occurrence and lifetime is subject to ongoing research; thus, here they are implemented via free parameters. This enables us to study the influence of the disk properties on the formation of planetesimals, predicting their time-dependent formation rates and the location of primary pebble accretion. We show that large -values of 0.01 (strong turbulence) prevent the formation of planetesimals in the inner part of the disk, arguing for lower values of around 0.001 (moderate turbulence), at which planetesimals form quickly at all places where they are needed for proto-planets. Planetesimals form as soon as dust has grown to pebbles (mm to dm) and the pebble flux reaches a critical value, which is after a few thousand years at 2-3 au and after a few hundred thousand years at 20-30 au. Planetesimal formation lasts until the pebble supply has decreased below a critical value. The final spatial planetesimal distribution is steeper compared to the initial dust and gas distribution, which helps explain the discrepancy between the minimum mass solar nebula and viscous accretion disks.
Parasitism is a common form of life and represents a strong selective pressure for host organisms. In response to this evolutionary pressure, vertebrates have developed genetically coded defences ...such as the major histocompatibility complex (MHC). Mechanisms of parasite‐mediated selection not only maintain outstanding polymorphism in these genes but have also been proposed to further promote host population divergence and ultimately speciation because it can drive evolution of local adaptation in which MHC genes play a crucial role. This review first highlights the dynamics and complexity of parasite‐mediated selection in natural systems, which not only depends on dominating parasite strategies and on the taxonomic diversity of the parasite community but also includes the differences in parasite communities between habitats and niches, creating divergent selection on locally adapted populations. Then the different ways in which MHC genes potentially allow vertebrates to respond to these dynamics and to adapt locally are outlined. Finally, it is proposed that varying selection strength in time and space may lead to variation in the strength of precopulatory reproductive isolation which has evolved to maintain local adaptation.
Polymorphic genes of the major histocompatibility complex (MHC) are regarded as essential genes for individual fitness under conditions of natural and sexual selection. To test this hypothesis, we ...investigated the ultimate individual fitness trait -- that of reproductive success. We used three-spined sticklebacks (Gasterosteus aculeatus) in seminatural enclosures, located in natural breeding areas where the experimental fish had been caught. During their reproductive period, fish were exposed continuously to their natural sympatric parasites. By genotyping almost 4000 eggs with nine microsatellites, we determined parenthood and inferred female mating decision. We found that with reference to their own MHC profile, female sticklebacks preferred to mate with males sharing an intermediate MHC diversity. In addition, males with a specific MHC haplotype were bigger and better at fighting a common parasite (Gyrodactylus sp.). This translated directly into Darwinian fitness since fish harbouring this specific MHC haplotype were more likely to be chosen and had a higher reproductive output. We conclude that females also based their mating decision on a specific MHC haplotype conferring resistance against a common parasite. This identifies and supports 'good genes'. We argue that such an interaction between host and parasite driving assortative mating is not only a prerequisite for negative frequency-dependent selection -- a potential mechanism to explain the maintenance of MHC polymorphism, but also potentially speciation.
Background
Dual antiplatelet therapy is a pre-requisite for flow diverter (FD) implantation. The purpose of this study was to assess the thrombogenicity of the p48 FD, coated with the newly developed ...phenox Hydrophilic Polymer Coating (p48_HPC, phenox GmbH, Germany) in comparison with uncoated p48 FDs in an in vitro flow model (Chandler Loop).
Methods
p48 and p48_HPC FDs were implanted into silicon tubes filled with whole human blood and incubated at 37 °C under pulsating flow. After 120 min, platelet count was determined in the blood. Platelet activation markers (PAR1) and formation of microparticles were analyzed in a flow cytometer. Fluorescence microscopy of CD42a positive cells and scanning electron microscopy was used to detect adherent platelets on the wire surface.
Results
Platelets in contact with the uncoated p48 FDs are significantly more activated than those incubated with p48_HPC (73 ± 9% vs. 65 ± 6%,
p
< 0.05) and release more microparticles (1.8 ± 0.5 vs. 1.4 ± 0.4,
p
< 0.05). The platelet count after 120-min circulation in the Chandler Loop was significantly lower for the uncoated p48 compared to the p48_HPC indicating significantly greater adherence of the platelets to the p48 (71 ± 8% vs. 87 ± 5%,
p
< 0.05). SEM and fluorescent antibody imaging revealed minimal platelet adherence to the surface of the p48_HPC compared to the uncoated p48.
Conclusion
The pHPC coating significantly reduces thrombogenicity of the p48 FD. This may help to reduce the risk of thromboembolic complications when using these devices. A reduction in antiplatelet therapy may be possible.
Various procedures are used for testing the durability of wood and wood based materials for decades. Generally they can be divided in field and laboratory tests, whereby lab tests allow more defined ...and reproducible conditions and benefit from shorter test durations. However, while laboratory test results are hardly transferable to real life situations, field tests ensure more realistic conditions. For instance natural weathering and detoxification of biocidal compounds through so called “non-target-organisms” is assured only under outdoor field exposure. Due to these dissimilarities a diverse and in some cases also unrealistic classification of wood durability can be obtained when testing a material exclusively under laboratory conditions.
This study will exemplarily focus on English oak (Quercus robur L.), which is classified as ‘durable’ according to the European Standard EN 350-2 (1994). Results from several laboratory and field test studies showed an enormously high variation of its durability between ‘very durable’ (Durability class (DC) 1, EN 350-1 (1994)) to ‘not durable’ (DC 5). Therefore this study aimed on a comparative evaluation of the durability of English oak in laboratory and field tests using standard specimens, but also full-size components under in-service conditions.
The test results showed only little variation in durability of different oak origins. However it was indicated that a transferability of results determined in laboratory decay tests with pure cultures to the performance of a certain material in outdoor exposure is possible only to a limited extend.
•Durability of 3 oak assortments tested in laboratory, semi-laboratory, field tests.•Only little variation in durability of the different oak origins was found.•Differences were superposed by the effect of different test methods.•Transferability of lab results to outdoor performance limited.
Abstract Estuaries are important ecosystems due to the ecological services they provide, acting as nurseries for many species of fish and invertebrates, and are also used as environments for the ...extraction and cultivation of mollusks. Oysters are animals that filter water to obtain oxygen and nutrients. In this process, they can bioaccumulate microorganisms and chemical substances in their tissues. The growth of mollusk culture in Northeastern Brazil requires the health identification of cultivated oysters through the quantification of the potentially harmful microbiota accumulated in the animals. Therefore, the present work aims to quantify and identify bacteria and possible pathogens found in the tissues of cultivated oysters and their culture waters. The Most Probable Number of Coliforms (MPN) in oysters and water were considered suitable according to the Brazilian current legislation, Vibrio sp. obtained low colonization and Salmonella sp. was not observed. The prevalence of microorganisms potentially pathogenic to oysters was 33.7%, highlighting metazoans and Nematopsis sp., however, the intensity of the infestation of these organisms was moderate. The low contamination of oysters demonstrates that this culture environment is promising for this activity. However, continuous environmental and sanitary monitoring is fundamental to guarantee the safety of the culture waters and the sustainability of aquaculture activities.
Resumo Os estuários são ecossistemas importantes devido a serviços ecológicos que fornecem, os quais conferem a função de berçário para muitas espécies de peixes e invertebrados, e também são utilizados como ambientes de extração e cultivo de moluscos. As ostras são animais que filtram a água para obtenção de oxigênio e nutrientes. Nesse processo podem bioacumular microorganismos e substâncias químicas em seus tecidos. O crescimento da malacocultura no Nordeste do Brasil fomenta a necessidade de identificar a sanidade das ostras cultivadas através da quantificação da microbiota potencialmente nociva acumulada nos animais. Portanto o presente trabalho visa quantificar e identificar bactérias e possíveis patógenos encontrados nos tecidos dos moluscos cultivados e nas suas águas de cultivo. O Número mais Provável de Coliformes (NMP) nas ostras e na água foram considerados próprios segundo as legislações vigentes, Vibrio sp. obteve baixa colonização e Salmonella sp. não foi observada. A prevalência de microorganismos potencialmente patógenos para as ostras foi de 33,7%, destacando como mais prevalentes os metazoários e Nematopsis sp., porém a intensidade da infestação desses organismos foi moderada. A baixa contaminação das ostras demonstra que este ambiente de cultivo é promissor para esta atividade. No entanto, o contínuo monitoramento ambiental e sanitário é fundamental para garantir a inocuidade das águas de cultivo e a sustentabilidade das atividades aquícolas.
Theory of local adaptation predicts that nonadapted migrants will suffer increased costs compared to local residents. Ultimately this process can result in the reduction of gene flow and culminate in ...speciation. Here, we experimentally investigated the relative fitness of migrants in foreign habitats, focusing on diverging lake and river ecotypes of three‐spined sticklebacks. A reciprocal transplant experiment performed in the field revealed asymmetric costs of migration: whereas mortality of river fish was increased under lake conditions, lake migrants suffered from reduced growth relative to river residents. Selection against migrants thus involved different traits in each habitat but generally contributed to bidirectional reduction in gene flow. Focusing particularly on the parasitic environments, migrant fish differed from resident fish in the parasite community they harboured. This pattern correlated with both cellular phenotypes of innate immunity as well as with allelic variation at the genes of the major histocompatibility complex. In addition to showing the costs of migration in three‐spined sticklebacks, this study highlights the role of asymmetric selection particularly from parasitism in genotype sorting and in the emergence of local adaptation.
Context. If planetesimal formation is an efficient process, as suggested by several models involving gravitational collapse of pebble clouds, then, not before long, a significant part of the ...primordial dust mass should be absorbed in many km-sized objects. A good understanding of the total amount of solids in the disk around a young star is crucial for planet formation theory. However, as the mass of particles above the mm size cannot be assessed observationally, one must ask how much mass is hidden in bigger objects. Aims. We performed 0-d local simulations to study how the planetesimal to dust and pebble ratio evolves in time and to develop an understanding of the potentially existing mass in planetesimals for a certain amount of dust and pebbles at a given disk age. Methods. We performed a parameter study based on a model considering dust growth, planetesimal formation, and collisional fragmentation of planetesimals, while neglecting radial transport processes. Results. While at early times, dust is the dominant solid particle species, there is a phase during which planetesimals make up a significant portion of the total mass starting at approximately 104–106 yr. The time of this phase and the maximal total planetesimal mass strongly depend on the distance to the star R, the initial disk mass, and the efficiency of planetesimal formation ɛ. Planetesimal collisions are more significant in more massive disks, leading to lower relative planetesimal fractions compared to less massive disks. After approximately 106 yr, our model predicts planetesimal collisions to dominate, which resupplies small particles. Conclusions. In our model, planetesimals form fast and everywhere in the disk. For a given ɛ, we are able to relate the dust content and mass of a given disk to its planetesimal content, providing us with some helpful basic intuition about mass distribution of solids and its dependence on underlying physical processes.
Freshman-15 is a phenomenon of first-year university students resulting in weight gain partly due to new cafeteria eating patterns and stress. This study determined if a premeal walnut snack alters ...planned eating behavior and mealtime nutrient intake during a subsequent buffet-model meal. Healthy university students (
= 36; 18.1 ± 0.5 years; body mass index: 23.6 ± 3.9) received three treatments (90 min premeal) in randomized order on 3 consecutive days: (1) snack of 190 Cal (1 oz) of walnuts (WS), (2) snack of 190 Cal of gummy candy (GS), or (3) no snack (NS; control) before a standard cafeteria dinner (1760 Cal). Visual analog scale (VAS) surveys were administered before and after dinner, and caloric intake was determined. Premeal VAS desire to eat was lower after WS and GS than NS, whereas the sense of hunger and sense of fullness were higher after WS and GS compared with NS. Postmeal VAS was not different between treatments. Mealtime calories, total fat, saturated fat, cholesterol, protein, sodium, fiber, and sugar consumed after WS were significantly less than NS. Total fat and sodium consumed after GS did not significantly differ from NS. Mealtime total fat, sodium, and fiber for WS were significantly less than GC, and a trend was observed for total calories. Differences in calorie intake were not observed between treatments when snack calories were included as part of the mealtime caloric intake. These findings could be helpful for promoting WS and to a lesser degree GS for increased satiety before meals possibly leading to reduced food intake during dinner by university students.
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