26,804 research outputs found
Biased random walk on critical Galton-Watson trees conditioned to survive
We consider the biased random walk on a critical Galton-Watson tree
conditioned to survive, and confirm that this model with trapping belongs to
the same universality class as certain one-dimensional trapping models with
slowly-varying tails. Indeed, in each of these two settings, we establish
closely-related functional limit theorems involving an extremal process and
also demonstrate extremal aging occurs
PLANTING DECISIONS AND UNCERTAIN CONSUMER ACCEPTANCE OF GENETICALLY MODIFIED CROP VARIETIES
There exists much uncertainty about consumer attitudes towards genetically modified foods. If it happens that sufficient (insufficient) acres are planted under non-modified seed to meet post-harvest demand, then a price premium will not (will) emerge for the non-modified varieties. A non-linearity originates in the fact that a price premium may be supported. This non-linearity interacts with the extent of demand uncertainty to determine equilibrium varietal plantings and the probability that post-harvest varietal prices will differ. Also, as planting approaches signals will be received by growers about the nature of demand they will be planting into. We show how the non-linearity affects the order on the types of signals that risk-neutral growers will prefer to receive.Consumer/Household Economics, Crop Production/Industries,
LOCATION, LAND QUALITY, AND RENTAL VOLATILITY
It appears to be widely believed that returns on low quality land are more variable than on high quality land. Using Ricardian rent as the measure of returns and sensitivity to output price as the measure of volatility, we investigate this null hypothesis for three different measures of quality. These are proximity to market, output productivity, and cost efficiency. In all cases, we identify precise conditions on the production technology such that rental volatility varies in a monotone manner with land quality. A method of econometric investigation of the relationship between rental volatility and land quality is developed and applied to Iowa cash rents data collected during 1994-2000. Our preliminary findings provide partial empirical support for the null hypothesis of an inverse relationship between quality and rental volatility with respect to commodity prices.Land Economics/Use,
Exploiting evolution to treat drug resistance: Combination therapy and the double bind
Although many anti cancer therapies are successful in killing a large percentage of tumour cells when initially administered, the evolutionary dynamics underpinning tumour progression mean that often resistance is an inevitable outcome, allowing for new tumour phenotypes to emerge that are unhindered by the therapy. Research in the field of ecology suggests that an evolutionary double bind could be an effective way to treat tumours. In an evolutionary double bind two therapies are used in combination such that evolving resistance to one leaves individuals more susceptible to the other. In this paper we present a general evolutionary game theory model of a double bind to study the effect that such approach would have in cancer. Furthermore we use this mathematical framework to understand recent experimental results that suggest a synergistic effect between a p53 cancer vaccine and chemotherapy. Our model recapitulates the experimental data and provides an explanation for its effectiveness based on the commensalistic relationship between the tumour phenotypes
The impact of cellular characteristics on the evolution of shape homeostasis
The importance of individual cells in a developing multicellular organism is
well known but precisely how the individual cellular characteristics of those
cells collectively drive the emergence of robust, homeostatic structures is
less well understood. For example cell communication via a diffusible factor
allows for information to travel across large distances within the population,
and cell polarisation makes it possible to form structures with a particular
orientation, but how do these processes interact to produce a more robust and
regulated structure? In this study we investigate the ability of cells with
different cellular characteristics to grow and maintain homeostatic structures.
We do this in the context of an individual-based model where cell behaviour is
driven by an intra-cellular network that determines the cell phenotype. More
precisely, we investigated evolution with 96 different permutations of our
model, where cell motility, cell death, long-range growth factor (LGF),
short-range growth factor (SGF) and cell polarisation were either present or
absent. The results show that LGF has the largest positive impact on the
fitness of the evolved solutions. SGF and polarisation also contribute, but all
other capabilities essentially increase the search space, effectively making it
more difficult to achieve a solution. By perturbing the evolved solutions, we
found that they are highly robust to both mutations and wounding. In addition,
we observed that by evolving solutions in more unstable environments they
produce structures that were more robust and adaptive. In conclusion, our
results suggest that robust collective behaviour is most likely to evolve when
cells are endowed with long range communication, cell polarisation, and
selection pressure from an unstable environment
Discrimination and synthesis of recursive quantum states in high-dimensional Hilbert spaces
We propose an interferometric method for statistically discriminating between
nonorthogonal states in high dimensional Hilbert spaces for use in quantum
information processing. The method is illustrated for the case of photon
orbital angular momentum (OAM) states. These states belong to pairs of bases
that are mutually unbiased on a sequence of two-dimensional subspaces of the
full Hilbert space, but the vectors within the same basis are not necessarily
orthogonal to each other. Over multiple trials, this method allows
distinguishing OAM eigenstates from superpositions of multiple such
eigenstates. Variations of the same method are then shown to be capable of
preparing and detecting arbitrary linear combinations of states in Hilbert
space. One further variation allows the construction of chains of states
obeying recurrence relations on the Hilbert space itself, opening a new range
of possibilities for more abstract information-coding algorithms to be carried
out experimentally in a simple manner. Among other applications, we show that
this approach provides a simplified means of switching between pairs of
high-dimensional mutually unbiased OAM bases
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