4,831 research outputs found
Solar Neutrinos: Spin Flavour Precession and LMA
The time dependence that appears to be hinted by the data from the first 13
years of the solar neutrino Gallium experiments is viewed as resulting from a
partial conversion of active neutrinos to light sterile ones through the
resonant interaction between the magnetic moment of the neutrino and a varying
solar field. A summary of the model and its predictions are presented for the
forthcoming experiments Borexino and LENS.Comment: 6 pages, 3 figures, contribution to 12th Lomonosov Conference in
Elementary Particle Physics, Moscow, Aug 24-31 (2005
The spectrum of gravitational waves in an f(R) model with a bounce
We present an inflationary model preceded by a bounce in a metric
theory. In this model, modified gravity affects only the early stages of the
universe. We analyse the predicted spectrum of the gravitational waves in this
scenario using the method of the Bogoliubov coefficients. We show that there
are distinctive (oscillatory) signals on the spectrum for very low frequencies;
i.e., corresponding to modes that are currently entering the horizon.Comment: 4 pages, 2 figures. Contribution to the Spanish Relativity Meeting in
Portugal 2012 (ERE2012), Guimaraes, Portuga
Automatic Estimation of the Seafloor Geomorphology of the Santos Basin, Brazil
The bathymetry and acoustic backscatter of Santos Basin, Brazil were mapped using a SeaBeam 2112 (12 kHz, 151 beam) Multibeam Echosounder (MBES) aboard the R/V Falcon Explorer. This MBES data was acquired from January-November, 2000, during a high-resolution multi-channel 3D seismic survey, resulting in 380 parallel lines of 90 km length, spaced 250 m apart. The final survey mapped an area of 5,000 km in water depths of 900--2000 m. These closely spaced multibeam tracks resulted in an average overlap between swaths of 1000%, thereby ensonifying most areas of the seafloor at least ten times. Traditional (hand) processing of a dataset this dense is time-consuming and tedious, and is prone to subjective decisions and operator fatigue. However, the density of the survey makes it ideal for automatic processing methods. Recently, we have developed an algorithm called CUBE that addresses the twin concerns of robustness and reliability that are often raised about automatic processing methods. Based on a very robust multiple hypothesis Bayesian estimator, CUBE processes MBES bathymetry directly into a set of gridded products representing the best estimate of probable depth, and a measure of the uncertainty associated with this estimate. We apply CUBE to the Santos Basin data, illustrating in terms of processing time and human effort the advantages of processing such data automatically. We compare the automatically generated data with a hand-processed set, showing that the results agree to within the estimated experimental uncertainty. We next illustrate the use of CUBE as a data quality measure, indicating areas of concern in the data. Finally, we utilize the bathymetric grid resulting from CUBE to investigate the seafloor morphology, which includes a set of linear depressions parallel and perpendicular to the Shelf break. These linear depressions are the surface expression of fault planes related to subsurface salt walls. In the shallowest part, the detailed bathymetry also shows various pockmarks (350 m wide) possibly associated with fluid expulsion, while in the deeper portion we observe a small number of larger ones (2500 m wide), which are clearly inactive as they are partially filled with recent sediments. Some pockmarks are aligned with fault planes, suggesting a preferential pathway for fluid expulsion. The acquisition geometry for this survey allowed us to analyze the behavior of the backscatter response as a function of grazing angle for any given piece of seafloor, thus eliminating the need to assume a homogeneous seafloor across the swath. Although the backscatter is not calibrated, the variation in response can be used to investigate the effects of gas in shallow sediments of the survey area
A simple rule for the evolution of fast dispersal at the edge of expanding populations
Evolution by natural selection is commonly perceived as a process that favors those that replicate faster to leave more offspring; nature, however, seem to abound with examples where organisms forgo some replicative potential to disperse faster. When does selection favor invasion of the fastest? Motivated by evolution experiments with swarming bacteria we searched for a simple rule. In experiments, a fast hyperswarmer mutant that pays a reproductive cost to make many copies of its flagellum invades a population of mono-flagellated bacteria by reaching the expanding population edge; a two-species mathematical model explains that invasion of the edge occurs only if the invasive species' expansion rate, vâ, which results from the combination of the species growth rate and its dispersal speed (but not its carrying capacity), exceeds the established species', vâ. The simple rule that we derive, vâ > vâ, appears to be general: less favorable initial conditions, such as smaller initial sizes and longer distances to the population edge, delay but do not entirely prevent invasion. Despite intricacies of the swarming system, experimental tests agree well with model predictions suggesting that the general theory should apply to other expanding populations with trade-offs between growth and dispersal, including non-native invasive species and cancer metastases.First author draf
Evolution at the edge of expanding populations
Predicting evolution of expanding populations is critical to control
biological threats such as invasive species and cancer metastasis. Expansion is
primarily driven by reproduction and dispersal, but nature abounds with
examples of evolution where organisms pay a reproductive cost to disperse
faster. When does selection favor this 'survival of the fastest?' We searched
for a simple rule, motivated by evolution experiments where swarming bacteria
evolved into an hyperswarmer mutant which disperses faster but
pays a growth cost of to make many copies of its flagellum. We
analyzed a two-species model based on the Fisher equation to explain this
observation: the population expansion rate () results from an interplay of
growth () and dispersal () and is independent of the carrying capacity:
. A mutant can take over the edge only if its expansion rate
() exceeds the expansion rate of the established species (); this
simple condition () determines the maximum cost in slower growth
that a faster mutant can pay and still be able to take over. Numerical
simulations and time-course experiments where we tracked evolution by imaging
bacteria suggest that our findings are general: less favorable conditions delay
but do not entirely prevent the success of the fastest. Thus, the expansion
rate defines a traveling wave fitness, which could be combined with trade-offs
to predict evolution of expanding populations
Welfare Implications of Selected Supply and Demand Shocks on Producers and Marketers of U.S. Meats
An equilibrium displacement model is developed and used to estimate the welfare impacts of government and industry-funded promotion programs, country of origin labeling (COOL), and the disease-driven, international bans on U.S. beef. The model goes beyond past studies by including the U.S. domestic market and both U.S. meat imports and exports, with meats differentiated by source of origin. The results indicate that while the benefits from beef and pork promotions are higher, the negative impacts of COOL are lower in a model with international trade than in a model without trade. International bans on U.S. beef decrease the welfare of producers and marketers of U.S. beef.beef ban, country of origin, equilibrium displacement model, pork, poultry, promotion, Demand and Price Analysis,
- âŠ