959 research outputs found
AutonoVi: Autonomous Vehicle Planning with Dynamic Maneuvers and Traffic Constraints
We present AutonoVi:, a novel algorithm for autonomous vehicle navigation
that supports dynamic maneuvers and satisfies traffic constraints and norms.
Our approach is based on optimization-based maneuver planning that supports
dynamic lane-changes, swerving, and braking in all traffic scenarios and guides
the vehicle to its goal position. We take into account various traffic
constraints, including collision avoidance with other vehicles, pedestrians,
and cyclists using control velocity obstacles. We use a data-driven approach to
model the vehicle dynamics for control and collision avoidance. Furthermore,
our trajectory computation algorithm takes into account traffic rules and
behaviors, such as stopping at intersections and stoplights, based on an
arc-spline representation. We have evaluated our algorithm in a simulated
environment and tested its interactive performance in urban and highway driving
scenarios with tens of vehicles, pedestrians, and cyclists. These scenarios
include jaywalking pedestrians, sudden stops from high speeds, safely passing
cyclists, a vehicle suddenly swerving into the roadway, and high-density
traffic where the vehicle must change lanes to progress more effectively.Comment: 9 pages, 6 figure
The evolution of costly acquired immune memory
A key feature of the vertebrate adaptive immune system is acquired immune memory, whereby hosts launch a faster and heightened response when challenged by previously encountered pathogens, preventing full infection. Here, we use a mathematical model to explore the role of ecological and epidemiological processes in shaping selection for costly acquired immune memory. Applying the framework of adaptive dynamics to the classic SIR (Susceptible-Infected-Recovered) epidemiological model, we focus on the conditions that may lead hosts to evolve high levels of immunity. Linking our work to previous theory, we show how investment in immune memory may be greatest at long or intermediate host lifespans depending on whether immunity is long lasting. High initial costs to gain immunity are also found to be essential for a highly effective immune memory. We also find that high disease infectivity and sterility, but intermediate virulence and immune period, increase selection for immunity. Diversity in host populations through evolutionary branching is found to be possible but only for a limited range of parameter space. Our model suggests that specific ecological and epidemiological conditions have to be met for acquired immune memory to evolve
On the Polynomial Szemer\'edi Theorem in Finite Commutative Rings
The polynomial Szemer\'{e}di theorem implies that, for any , any family of nonconstant
polynomials with constant term zero, and any sufficiently large , every
subset of of cardinality at least contains a
nontrivial configuration of the form . When
the polynomials are assumed independent, one can expect a sharper result to
hold over finite fields, special cases of which were proven recently,
culminating with arXiv:1802.02200, which deals with the general case of
independent polynomials. One goal of this article is to explain these theorems
as the result of joint ergodicity in the presence of asymptotic total
ergodicity. Guided by this concept, we establish, over general finite
commutative rings, a version of the polynomial Szemer\'{e}di theorem for
independent polynomials , deriving new combinatorial consequences, such as the following. Let
be a collection of finite commutative rings subject to a mild
condition on their torsion. There exists such that, for
every , every subset of cardinality at least
contains a nontrivial configuration for some , and, moreover, for any subsets
such that , there is a nontrivial configuration . The fact that general rings
have zero divisors is the source of many obstacles, which we overcome; for
example, by studying character sums, we develop a bound on the number of roots
of an integer polynomial over a general finite commutative ring, a result which
is of independent interest.Comment: 110 page
The emergence of 4-cycles in polynomial maps over the extended integers
Let ; for each integer it is interesting to
consider the number of iterates , if possible, needed to satisfy
. The sets generated by the iterates of are
called cycles. For it is known that cycles of length 1 and 2
occur, and no others. While much is known for extensions to number fields, we
concentrate on extending by adjoining reciprocals of primes. Let
denote extended by adding in
the reciprocals of the primes and all their products and
powers with each other and the elements of .
Interestingly, cycles of length 4, called 4-cycles, emerge for polynomials in
under the appropriate
conditions. The problem of finding criteria under which 4-cycles emerge is
equivalent to determining how often a sum of four terms is zero, where the
terms are times a product of elements from the list of primes. We
investigate conditions on sets of primes under which 4-cycles emerge. We
characterize when 4-cycles emerge if the set has one or two primes, and
(assuming a generalization of the ABC conjecture) find conditions on sets of
primes guaranteed not to cause 4-cycles to emerge.Comment: 14 pages, 1 figur
Study protocol for a randomised controlled trial evaluating the effect of prenatal omega-3 LCPUFA supplementation to reduce the incidence of preterm birth: The ORIP trial
Introduction: Preterm birth accounts for more than 85% of all perinatal complications and deaths. Seventy-five per cent of early preterm births (EPTBs) occur spontaneously and without identifiable risk factors. The need for a broadly applicable, effective strategy for primary prevention is paramount. Secondary outcomes from the docosahexaenoic acid (DHA) to Optimise Mother Infant Outcome trial showed that maternal supplementation until delivery with omega-3 (ω-3) long chain polyunsaturated fatty acid (LCPUFA), predominantly as DHA, resulted in a 50% reduction in the incidence of EPTB and an increase in the incidence of post-term induction or post-term prelabour caesarean section due to extended gestation. We aim to determine the effectiveness of supplementing the maternal diet with ω-3 LCPUFA until 34 weeks’ gestation on the incidence of EPTB.
Methods and analysis: This is a multicentre, parallel group, randomised, blinded and controlled trial. Women less than 20 weeks’ gestation with a singleton or multiple pregnancy and able to give informed consent are eligible to participate. Women will be randomised to receive high DHA fish oil capsules or control capsules without DHA. Capsules will be taken from enrolment until 34 weeks’ gestation. The primary outcome is the incidence of EPTB, defined as delivery before 34 completed weeks’ gestation. Key secondary outcomes include length of gestation, incidence of post-term induction or prelabour caesarean section and spontaneous EPTB. The target sample size is 5540 women (2770 per group), which will provide 85% power to detect an absolute reduction in the incidence of preterm birth of 1.16% (from 2.45% to 1.29%) between the DHA and control group (two sided α=0.05). The primary analysis will be based on the intention-to-treat principle.
Trial registration number: Australia and New Zealand Clinical Trial Registry Number: 2613001142729; Pre-results
Ramsey Theory Problems over the Integers: Avoiding Generalized Progressions
Two well studied Ramsey-theoretic problems consider subsets of the natural
numbers which either contain no three elements in arithmetic progression, or in
geometric progression. We study generalizations of this problem, by varying the
kinds of progressions to be avoided and the metrics used to evaluate the
density of the resulting subsets. One can view a 3-term arithmetic progression
as a sequence , where , a nonzero
integer. Thus avoiding three-term arithmetic progressions is equivalent to
containing no three elements of the form with , the set of integer translations. One can similarly
construct related progressions using different families of functions. We
investigate several such families, including geometric progressions ( with a natural number) and exponential progressions ().
Progression-free sets are often constructed "greedily," including every
number so long as it is not in progression with any of the previous elements.
Rankin characterized the greedy geometric-progression-free set in terms of the
greedy arithmetic set. We characterize the greedy exponential set and prove
that it has asymptotic density 1, and then discuss how the optimality of the
greedy set depends on the family of functions used to define progressions.
Traditionally, the size of a progression-free set is measured using the (upper)
asymptotic density, however we consider several different notions of density,
including the uniform and exponential densities.Comment: Version 1.0, 13 page
SPA: Verbal Interactions between Agents and Avatars in Shared Virtual Environments using Propositional Planning
We present a novel approach for generating plausible verbal interactions
between virtual human-like agents and user avatars in shared virtual
environments. Sense-Plan-Ask, or SPA, extends prior work in propositional
planning and natural language processing to enable agents to plan with
uncertain information, and leverage question and answer dialogue with other
agents and avatars to obtain the needed information and complete their goals.
The agents are additionally able to respond to questions from the avatars and
other agents using natural-language enabling real-time multi-agent multi-avatar
communication environments.
Our algorithm can simulate tens of virtual agents at interactive rates
interacting, moving, communicating, planning, and replanning. We find that our
algorithm creates a small runtime cost and enables agents to complete their
goals more effectively than agents without the ability to leverage
natural-language communication. We demonstrate quantitative results on a set of
simulated benchmarks and detail the results of a preliminary user-study
conducted to evaluate the plausibility of the virtual interactions generated by
SPA. Overall, we find that participants prefer SPA to prior techniques in 84\%
of responses including significant benefits in terms of the plausibility of
natural-language interactions and the positive impact of those interactions
Evolution of host resistance towards pathogen exclusion: the role of predators
Question: Can increased host resistance drive a pathogen to extinction? Do more complex ecosystems lead to significantly different evolutionary behaviour and new potential extinctions? Mathematical method: Merging host-parasite models with predator-prey models. Analytically studying evolution using adaptive dynamics and trade-off and invasion plots, and carrying out numerical simulations. Key assumptions: Mass action (general mixing). All individuals of a given phenotype are identical. Only prey vulnerable to infection. Mutations are small and rare (however, the assumption on the size of mutation is relaxed later). In simulations, very small (negligible) populations are at risk of extinction. Conclusions: The presence of the predator can significantly change evolutionary outcomes for host resistance to a pathogen and can create branching points where none occurred previously. The pathogen (and sometimes the predator) is protected from exclusion if we take mutations to be arbitrarily small; however, relaxing the assumption on mutation size can lead to its exclusion. Increased resistance can drive the predator and/or pathogen to extinction depending on inter-species dynamics, such as the predator's preference for infected prey. Predator co-evolution can move exclusion boundaries and prevent the predator's own extinction if its rate of mutation is high enough (with respect to that of the prey)
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