985 resultados para Graft Survival


Relevância:

20.00% 20.00%

Publicador:

Relevância:

20.00% 20.00%

Publicador:

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The assumption that ‘states' primary goal is survival’ lies at the heart of the neorealist paradigm. A careful examination of the assumption, however, reveals that neorealists draw upon a number of distinct interpretations of the ‘survival assumption’ that are then treated as if they are the same, pointing towards conceptual problems that surround the treatment of state preferences. This article offers a specification that focuses on two questions that highlight the role and function of the survival assumption in the neorealist logic: (i) what do states have to lose if they fail to adopt self-help strategies?; and (ii) how does concern for relevant losses motivate state behaviour and affect international outcomes? Answering these questions through the exploration of governing elites' sensitivity towards regime stability and territorial integrity of the state, in turn, addresses the aforementioned conceptual problems. This specification has further implications for the debates among defensive and offensive realists, potential extensions of the neorealist logic beyond the Westphalian states, and the relationship between neorealist theory and policy analysis.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

This essay aims to make a contribution to the conversation between IR and nationalism literatures by considering a particular question: What is the relationship between interstate military competition and the emergence of nationalism as a potent force in world politics? The conventional wisdom among international security scholars, especially neorealists, holds that nationalism can be more or less treated like a “technology” that allowed states to extract significant resources as well as manpower from their respective populations. This paper underlines some of the problems involved with this perspective and pushes forward an interpretation that is based on the logic of political survival. I argue that nationalism’s emergence as a powerful force in world politics followed from the “mutation” and absorption of the universalistic/cosmopolitan republican ideas that gained temporary primacy in Europe during the eighteenth century into particularistic nationalist ideologies. This transformation, in turn, can be best explained by the French Revolution’s dramatic impacts on rulers’ political survival calculi vis-à-vis both interstate and domestic political challenges. The analysis offered in this essay contributes to our understanding of the relationship between IR and nationalism while also highlighting the potential value of the political survival framework for exploring macrohistorical puzzles.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Soil-dwelling insect herbivores are significant pests in many managed ecosystems. Because eggs and larvae are difficult to observe, mathematical models have been developed to predict life-cycle events occurring in the soil. To date, these models have incorporated very little empirical information about how soil and drought conditions interact to shape these processes. This study investigated how soil temperature (10, 15, 20 and 25 °C), water content (0.02 (air dried), 0.10 and 0.25 g g−1) and pH (5, 7 and 9) interactively affected egg hatching and early larval lifespan of the clover root weevil (Sitona lepidus Gyllenhal, Coleoptera: Curculionidae). Eggs developed over 3.5 times faster at 25 °C compared with 10 °C (hatching after 40.1 and 11.5 days, respectively). The effect of drought on S. lepidus eggs was investigated by exposing eggs to drought conditions before wetting the soil (2–12 days later) at four temperatures. No eggs hatched in dry soil, suggesting that S. lepidus eggs require water to remain viable. Eggs hatched significantly sooner in slightly acidic soil (pH 5) compared with soils with higher pH values. There was also a significant interaction between soil temperature, pH and soil water content. Egg viability was significantly reduced by exposure to drought. When exposed to 2–6 days of drought, egg viability was 80–100% at all temperatures but fell to 50% after 12 days exposure at 10 °C and did not hatch at all at 20 °C and above. Drought exposure also increased hatching time of viable eggs. The effects of soil conditions on unfed larvae were less influential, except for soil temperature which significantly reduced larval longevity by 57% when reared at 25 °C compared with 10 °C (4.1 and 9.7 days, respectively). The effects of soil conditions on S. lepidus eggs and larvae are discussed in the context of global climate change and how such empirically based information could be useful for refining existing mathematical models of these processes.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The aim of this work was to compare alginate and pectin beads for improving the survival of Lactobacillus plantarum and Bifidobacterium longum during storage in pomegranate and cranberry juice, and to evaluate the influence of various coating materials, including chitosan, gelatin and glucomannan on cell survival and on the size and hardness of the beads. In pomegranate juice, free cells of L. plantarum died within 4 weeks of storage and those of B. longum within 1 week; in cranberry juice both types of cells died within one week. Encapsulation within either alginate or pectin beads improved cell survival considerably, but coating of the beads with chitosan or gelatin improved it even further; coating with glucomannan did not have any positive effect. The double gelatin coated pectin beads gave the highest protection among all types of beads, as a final concentration of approximately 108 CFU/mL and 106 CFU/mL for both L. plantarum and B. longum was obtained after 6 weeks of storage in pomegranate and cranberry juice, respectively. The good protection could be attributed to the very strong interaction between the two polymers, as measured by turbidity experiments, leading to the formation of a polyelectrolyte complex. It was also shown that the coating was able to inhibit the penetration of gallic acid within the beads, which was used in this study as a model phenolic compound with antimicrobial activity; this is a likely mechanism through which the beads were able to protect the cells from the antimicrobial activity of phenolic compounds present in both types of juices. Despite their good protective effect, the pectin beads were considerably softer than the alginate beads, an issue that should be addressed in order to increase their mechanical stability.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

1. Bees are one of the most important groups of pollinators in the temperate zone. Although heavy metal pollution is recognised to be a problem affecting large parts of the European Union, we currently lack insights into the effects of heavy metals on wild bee survival and reproduction. 2. We investigated the impact of heavy metal pollution on the wild bee Osmia rufa (Hymenoptera: Megachilidae) by comparing their survival, reproduction and population dynamics along two independent gradients of heavy metal pollution, one in Poland and the other in the United Kingdom. We used trap nests to evaluate the response of fitness and survival parameters of O. rufa. To quantify the levels of pollution, we directly measured the heavy metal concentration in provisions collected by O. rufa. 3. We found that with increasing heavy metal concentration, there was a steady decrease in number of brood cells constructed by females and an increase in the proportion of dead offspring. In the most polluted site, there were typically 3–4 cells per female with 50–60% dead offspring, whereas in unpolluted sites there were 8 to 10 cells per female and only 10–30% dead offspring. Moreover, the bee population growth rate (R0) decreased along the heavy metal pollution gradients. In unpolluted sites, R0 was above 1, whereas in contaminated sites, the values tended to be below 1. 4. Our findings reveal a negative relationship between heavy metal pollution and several fitness parameters of the wild bee O. rufa, and highlight a mechanism whereby the detrimental effects of heavy metal pollution may severely impact wild bee communities.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We report evidence that helps resolve two competing explanations for stability in the mutualism between Ficus racemosa fig trees and the Ceratosolen fusciceps wasps that pollinate them. The wasps lay eggs in the tree's ovules, with each wasp larva developing at the expense of a fig seed. Upon maturity, the female wasps collect pollen and disperse to a new tree, continuing the cycle. Fig fitness is increased by producing both seeds and female wasps, whereas short-term wasp fitness increases only with more wasps, thereby resulting in a conflict of interests. We show experimentally that wasps exploit the inner layers of ovules first (the biased oviposition explanation), which is consistent with optimal-foraging theory. As oviposition increases, seeds in the middle layer are replaced on a one-to-one basis by pollinator offspring, which is also consistent with biased oviposition. Finally, in the outer layer of ovules, seeds disappear but are only partially replaced by pollinator offspring, which suggests high wasp mortality (the biased survival or ‘unbeatable seeds’ explanation). Our results therefore suggest that both biased oviposition and biased survival ensure seed production, thereby stabilizing the mutualism. We further argue that biased oviposition can maintain biased survival by selecting against wasp traits to overcome fig defenses. Finally, we report evidence suggesting that F. racemosa balances seed and wasp production at the level of the tree. Because figs are probably selected to allocate equally to male and female function, a 1:1 seed:wasp ratio suggests that fig trees are in control of the mutualism.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Between the eleventh and thirteenth centuries AD, the Lower Vistula valley represented a permeable and shifting frontier between Pomerelia (eastern Pomerania), which had been incorporated into the Polish Christian state by the end of the tenth century, and the territories of western Prussian tribes, who had resisted attempts at Christianization. Pomeranian colonization eventually began to falter in the latter decades of the twelfth and early thirteenth centuries, most likely as a result of Prussian incursions, which saw the abandonment of sites across the borderland. Subsequently, the Teutonic Order and its allies led a protracted holy war against the Prussian tribes, which resulted in the conquest of the region and its incorporation into a theocratic state by the end of the thirteenth century. This was accompanied by a second wave of colonization, which resulted in the settlement pattern that is still visible in the landscape of north-central Poland today. However, not all colonies were destroyed or abandoned in between the two phases of colonization. The recently excavated site of Biała Góra, situated on the western side of the Forest of Sztum overlooking the River Nogat, represents a unique example of a transitional settlement that included both Pomeranian and Teutonic Order phases. The aim of this paper is to situate the site within its broader landscape context which can be characterized as a militarized frontier, where, from the later twelfth century and throughout much of the thirteenth century, political and economic expansion was combined with the ideology of Christian holy war and missionary activity. This paper considers how the colonists provisioned and sustained themselves in comparison to other sites within the region, and how Biała Góra may be tentatively linked to a documented but otherwise lost outpost in this volatile borderland.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Sensory thresholds are often collected through ascending forced-choice methods. Group thresholds are important for comparing stimuli or populations; yet, the method has two problems. An individual may correctly guess the correct answer at any concentration step and might detect correctly at low concentrations but become adapted or fatigued at higher concentrations. The survival analysis method deals with both issues. Individual sequences of incorrect and correct answers are adjusted, taking into account the group performance at each concentration. The technique reduces the chance probability where there are consecutive correct answers. Adjusted sequences are submitted to survival analysis to determine group thresholds. The technique was applied to an aroma threshold and a taste threshold study. It resulted in group thresholds similar to ASTM or logarithmic regression procedures. Significant differences in taste thresholds between younger and older adults were determined. The approach provides a more robust technique over previous estimation methods.