7,714 research outputs found
The direct numerical simulations of the turbulent wakes of axisymmetric bodies
Results of direct numerical simulations of turbulence are compared with both laboratory data and self-similarity theory for the case of the turbulent wakes of towed, axisymmetric bodies. In general, the agreement of the simulation results with both the laboratory data and the self-similarity theory is good, although the comparisons are hampered by inadequate procedures for initializing the numerical simulations
Reducing Crop Nutrient Applications: The Yield Reserve Program
A proposed Yield Reserve Program designed to compensate farmers for any reduced yields resulting from reduced nitrogen (N) application rates below recommended rates is evaluated. Assuming that farmers currently follow extension recommendations for applying N, Yield Reserve Program participation reduces expected net revenue by 13/ha. The Yield Reserve Program reduces expected net revenue by 20/ha for farmers who apply N to maximize expected net revenue. Farmers costs of participation increase with lower probabilities of inadequate rainfall and higher corn prices and decline with higher N prices. The Yield Reserve Program can significantly reduce N applications to cropland, which may reduce N content of surface waters, but the costs to taxpayers and farmers will depend on how the program is implemented.compliance cost, nitrogen fertilizer, nonpoint source pollution, policy, yield response function, Crop Production/Industries,
Who Am I Interviewing?
The last twenty years have seen an increasing emphasis on the role of the subject both in sociological theory and in methodological guides on the unstructured qualitative research interview. I will argue that this emphasis on subjects is misplaced and cannot lead to a clear understanding of social relations or sociological interviewing. To make this argument I will look at what could be taken as the basic social relation in social research: the qualitative interview between sociologist and research participant. I will argue that major methodological problems arise when interviewees are addressed as identified subjects and when interviews are understood as exchanges between subjects. I will also argue that sociologists who presume subjectivity in this way are not clear about the methodology of interviews because they are not clear about the basic logic of social relation. As well as trying to clarify this logic, I will also try to draw out some of the practical implications of a genuinely social understanding of the interview
Optimization of resource allocation can explain the temporal dynamics and honesty of sexual signals
In species in which males are free to dynamically alter their allocation to sexual signaling over the breeding season, the optimal investment in signaling should depend on both a maleās state and the level of competition he faces at any given time. We developed a dynamic optimization model within a gameātheoretical framework to explore the resulting signaling dynamics at both individual and population levels and tested two key model predictions with empirical data on threeāspined stickleback (Gasterosteus aculeatus) males subjected to dietary manipulation (carotenoid availability): (1) fish in better nutritional condition should be able to maintain their signal for longer over the breeding season, resulting in an increasingly positive correlation between nutritional status and signal (i.e., increasing signal honesty), and (2) female preference for more ornamented males should thus increase over the breeding season. Both predictions were supported by the experimental data. Our model shows how such patterns can emerge from the optimization of resource allocation to signaling in a competitive situation. The key determinants of the honesty and dynamics of sexual signaling are the condition dependency of male survival, the initial frequency distribution of nutritional condition in the male population, and the cost of signaling
Sun-Like Magnetic Cycles in the Rapidly-Rotating Young Solar Analog HD 30495
A growing body of evidence suggests that multiple dynamo mechanisms can drive
magnetic variability on different timescales, not only in the Sun but also in
other stars. Many solar activity proxies exhibit a quasi-biennial (2
year) variation, which is superimposed upon the dominant 11 year cycle. A
well-characterized stellar sample suggests at least two different relationships
between rotation period and cycle period, with some stars exhibiting long and
short cycles simultaneously. Within this sample, the solar cycle periods are
typical of a more rapidly rotating star, implying that the Sun might be in a
transitional state or that it has an unusual evolutionary history. In this
work, we present new and archival observations of dual magnetic cycles in the
young solar analog HD 30495, an 1 Gyr-old G1.5V star with a rotation
period near 11 days. This star falls squarely on the relationships established
by the broader stellar sample, with short-period variations at 1.7 years
and a long cycle of 12 years. We measure three individual long-period
cycles and find durations ranging from 9.6-15.5 years. We find the short-term
variability to be intermittent, but present throughout the majority of the time
series, though its occurrence and amplitude are uncorrelated with the longer
cycle. These essentially solar-like variations occur in a Sun-like star with
more rapid rotation, though surface differential rotation measurements leave
open the possibility of a solar equivalence.Comment: 12 pages, 6 figures. Submitted to Ap
Asteroseismic Signatures of Stellar Magnetic Activity Cycles
Observations of stellar activity cycles provide an opportunity to study
magnetic dynamos under many different physical conditions. Space-based
asteroseismology missions will soon yield useful constraints on the interior
conditions that nurture such magnetic cycles, and will be sensitive enough to
detect shifts in the oscillation frequencies due to the magnetic variations. We
derive a method for predicting these shifts from changes in the Mg II activity
index by scaling from solar data. We demonstrate this technique on the
solar-type subgiant beta Hyi, using archival International Ultraviolet Explorer
spectra and two epochs of ground-based asteroseismic observations. We find
qualitative evidence of the expected frequency shifts and predict the optimal
timing for future asteroseismic observations of this star.Comment: 5 pages including 3 figures and 1 table, MNRAS Letters accepte
Structural and mechanical effects of interstitial sinks
Changes in structure and mechanical properties due to loss of interstitials to reactive metal coatings studied in dispersion strengthened niobium alloy
Interactions between parental traits, environmental harshness and growth rate in determining telomere length in wild juvenile salmon
A larger body size confers many benefits, such as increased reproductive success, ability to evade predators and increased competitive ability and social status. However, individuals rarely maximise their growth rates, suggesting that this carries costs. One such cost could be faster attrition of the telomeres that cap the ends of eukaryotic chromosomes and play an important role in chromosome protection. A relatively short telomere length is indicative of poor biological state, including poorer tissue and organ performance, reduced potential longevity and increased disease susceptibility. Telomere loss during growth may also be accelerated by environmental factors, but these have rarely been subjected to experimental manipulation in the natural environment. Using a wild system involving experimental manipulations of juvenile Atlantic salmon Salmo salar in Scottish streams, we found that telomere length in juvenile fish was influenced by parental traits and by direct environmental effects. We found that faster-growing fish had shorter telomeres and there was a greater cost (in terms of reduced telomere length) if the growth occurred in a harsher environment. We also found a positive association between offspring telomere length and the growth history of their fathers (but not mothers), represented by the number of years fathers had spent at sea. This suggests that there may be long term consequences of growth conditions and parental life history for individual longevity
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