45,376 research outputs found
A universal solution
The phenomenon of an implicit function which solves a large set of second
order partial differential equations obtainable from a variational principle is
explicated by the introduction of a class of universal solutions to the
equations derivable from an arbitrary Lagrangian which is homogeneous of weight
one in the field derivatives. This result is extended to many fields. The
imposition of Lorentz invariance makes such Lagrangians unique, and equivalent
to the Companion Lagrangians introduced in [baker].Comment: arxiv version is already officia
Putting it All Together: Agreement, Incorporation, Coordination and External Possession in Wubuy (Australia)
In this paper we examine the interaction of a number of grammatical phenomena in Wubuy, a polysynthetic language from northern Australia, and show how they can be given a comprehensive analysis within the framework of LFG. While each of these phenomena ? noun incorporation, verbal agreement, coordination and external possession ? has received various treatments within the LFG literature, no one study has addressed the compatibility of these analyses under interaction, despite the fact that they frequently co-occur in the world?s languages. We use data from Wubuy to showcase the effects of this interaction, and investigate the implications for LFG and for LFG analyses of polysynthetic languages more generally
Modeling Human Understanding of Complex Intentional Action with a Bayesian Nonparametric Subgoal Model
Most human behaviors consist of multiple parts, steps, or subtasks. These
structures guide our action planning and execution, but when we observe others,
the latent structure of their actions is typically unobservable, and must be
inferred in order to learn new skills by demonstration, or to assist others in
completing their tasks. For example, an assistant who has learned the subgoal
structure of a colleague's task can more rapidly recognize and support their
actions as they unfold. Here we model how humans infer subgoals from
observations of complex action sequences using a nonparametric Bayesian model,
which assumes that observed actions are generated by approximately rational
planning over unknown subgoal sequences. We test this model with a behavioral
experiment in which humans observed different series of goal-directed actions,
and inferred both the number and composition of the subgoal sequences
associated with each goal. The Bayesian model predicts human subgoal inferences
with high accuracy, and significantly better than several alternative models
and straightforward heuristics. Motivated by this result, we simulate how
learning and inference of subgoals can improve performance in an artificial
user assistance task. The Bayesian model learns the correct subgoals from fewer
observations, and better assists users by more rapidly and accurately inferring
the goal of their actions than alternative approaches.Comment: Accepted at AAAI 1
Simultaneous chromatic dispersion, polarization-mode-dispersion and OSNR monitoring at 40Gbit/s
A novel method for independent and simultaneous monitoring of chromatic dispersion ( CD), first-order PMD and OSNR in 40Gbit/s systems is proposed and demonstrated. This is performed using in-band tone monitoring of 5GHz, optically down-converted to a low intermediate-frequency (IF) of 10kHz. The measurement provides a large monitoring range with good accuracies for CD (4742 +/- 100ps/nm), differential group delay (DGD) (200 +/- 4ps) and OSNR (23 +/- 1dB), independently of the bit-rate. In addition, the use of electro-absorption modulators (EAM) for the simultaneous down-conversion of all channels and the use of low-speed detectors makes it cost effective for multi-channel operation. (C) 2008 Optical Society of Americ
Cabling, contact structures and mapping class monoids
In this paper we discuss the change in contact structures as their supporting
open book decompositions have their binding components cabled. To facilitate
this and applications we define the notion of a rational open book
decomposition that generalizes the standard notion of open book decomposition
and allows one to more easily study surgeries on transverse knots. As a
corollary to our investigation we are able to show there are Stein fillable
contact structures supported by open books whose monodromies cannot be written
as a product of positive Dehn twists. We also exhibit several monoids in the
mapping class group of a surface that have contact geometric significance.Comment: 62 pages, 32 figures. Significant expansion of exposition and more
details on some argument
Cephem Potentiation by Inactivation of Nonessential Genes Involved in Cell Wall Biogenesis of ß-Lactamase-Producing Escherichia coli
Reversal of antimicrobial resistance is an appealing and largely unexplored strategy in drug discovery. The objective of this study was to identify potential targets for “helper” drugs reversing cephem resistance in Escherichia coli strains producing β-lactamases. A CMY-2-encoding plasmid was transferred by conjugation to seven isogenic deletion mutants exhibiting cephem hypersusceptibility. The effect of each mutation was evaluated by comparing the MICs in the wild type and the mutant harboring the same plasmid. Mutation of two genes encoding proteins involved in cell wall biosynthesis, dapF and mrcB, restored susceptibility to cefoxitin (FOX) and reduced the MICs of cefotaxime and ceftazidime, respectively, from the resistant to the intermediate category according to clinical breakpoints. The same mutants harboring a CTX-M-1-encoding plasmid fell into the intermediate or susceptible category for all three drugs. Individual deletion of dapF and mrcB in a clinical isolate of CTX-M-15-producing E. coli sequence type 131 (ST131) resulted in partial reversal of ceftazidime and cefepime resistance but did not reduce MICs below susceptibility breakpoints. Growth curve analysis indicated no fitness cost in a ΔmrcB mutant, whereas a ΔdapF mutant had a 3-fold longer lag phase than the wild type, suggesting that drugs targeting DapF may display antimicrobial activity, in addition to synergizing with selected cephems. DapF appeared to be a potential FOX helper drug target candidate, since dapF inactivation resulted in synergistic potentiation of FOX in the genetic backgrounds tested. The study showed that individual inactivation of two nonessential genes involved in cell wall biogenesis potentiates cephem activity according to drug- and strain-specific patterns
Modeling Human Ad Hoc Coordination
Whether in groups of humans or groups of computer agents, collaboration is
most effective between individuals who have the ability to coordinate on a
joint strategy for collective action. However, in general a rational actor will
only intend to coordinate if that actor believes the other group members have
the same intention. This circular dependence makes rational coordination
difficult in uncertain environments if communication between actors is
unreliable and no prior agreements have been made. An important normative
question with regard to coordination in these ad hoc settings is therefore how
one can come to believe that other actors will coordinate, and with regard to
systems involving humans, an important empirical question is how humans arrive
at these expectations. We introduce an exact algorithm for computing the
infinitely recursive hierarchy of graded beliefs required for rational
coordination in uncertain environments, and we introduce a novel mechanism for
multiagent coordination that uses it. Our algorithm is valid in any environment
with a finite state space, and extensions to certain countably infinite state
spaces are likely possible. We test our mechanism for multiagent coordination
as a model for human decisions in a simple coordination game using existing
experimental data. We then explore via simulations whether modeling humans in
this way may improve human-agent collaboration.Comment: AAAI 201
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