995 research outputs found
The hurdle-race problem.
We consider the problem of how to determine the required level of the current provision in order to be able to meet a series of future deterministic payment obligations, in case the provision is invested according to a given random return process. Approximate solutions are derived, taking into account imposed minimum levels of the future random values of the reserve. The paper ends with numerical examples illustrating the presented approximations.Processes; Value;
On post-Lie algebras, Lie--Butcher series and moving frames
Pre-Lie (or Vinberg) algebras arise from flat and torsion-free connections on
differential manifolds. They have been studied extensively in recent years,
both from algebraic operadic points of view and through numerous applications
in numerical analysis, control theory, stochastic differential equations and
renormalization. Butcher series are formal power series founded on pre-Lie
algebras, used in numerical analysis to study geometric properties of flows on
euclidean spaces. Motivated by the analysis of flows on manifolds and
homogeneous spaces, we investigate algebras arising from flat connections with
constant torsion, leading to the definition of post-Lie algebras, a
generalization of pre-Lie algebras. Whereas pre-Lie algebras are intimately
associated with euclidean geometry, post-Lie algebras occur naturally in the
differential geometry of homogeneous spaces, and are also closely related to
Cartan's method of moving frames. Lie--Butcher series combine Butcher series
with Lie series and are used to analyze flows on manifolds. In this paper we
show that Lie--Butcher series are founded on post-Lie algebras. The functorial
relations between post-Lie algebras and their enveloping algebras, called
D-algebras, are explored. Furthermore, we develop new formulas for computations
in free post-Lie algebras and D-algebras, based on recursions in a magma, and
we show that Lie--Butcher series are related to invariants of curves described
by moving frames.Comment: added discussion of post-Lie algebroid
Genome-wide high-throughput screening to investigate essential genes involved in methicillin-resistant Staphylococcus aureus Sequence Type 398 survival.
Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) Sequence Type 398 (ST398) is an opportunistic pathogen that is able to colonize and cause disease in several animal species including humans. To better understand the adaptation, evolution, transmission and pathogenic capacity, further investigations into the importance of the different genes harboured by LA-MRSA ST398 are required. In this study we generated a genome-wide transposon mutant library in an LA-MRSA ST398 isolate to evaluate genes important for bacterial survival in laboratory and host-specific environments. The transposon mutant library consisted of approximately 1 million mutants with around 140,000 unique insertion sites and an average number of unique inserts per gene of 44.8. We identified LA-MRSA ST398 essential genes comparable to other high-throughput S. aureus essential gene studies. As ST398 is the most common MRSA isolated from pigs, the transposon mutant library was screened in whole porcine blood. Twenty-four genes were specifically identified as important for bacterial survival in porcine blood. Mutations in 23 of these genes resulted in attenuated bacterial fitness. Seven of the 23 genes were of unknown function, whereas 16 genes were annotated with functions predominantly related to carbon metabolism, pH shock and a variety of regulations and only indirectly to virulence factors. Mutations in one gene of unknown function resulted in a hypercompetitive mutant. Further evaluation of these genes is required to determine their specific relevance in blood survival.This work was funded in part by the Danish Ministry of Food, Agriculture and Fisheries (Grant no. 3304-FVFP-09-F-002-1) and The Technical University of DenmarkThis is the final published version distributed under a Creative Commons Attribution License, which can also be found on the publisher's website at: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.008901
Fingerprint-enhanced capacitive-piezoelectric flexible sensing skin to discriminate static and dynamic tactile stimuli
nspired by the structure and functions of the human skin, a highly sensitive capacitiveâpiezoelectric flexible sensing skin with fingerprintâlike patterns to detect and discriminate between spatiotemporal tactile stimuli including static and dynamic pressures and textures is presented. The capacitiveâpiezoelectric tandem sensing structure is embedded in the phalange of a 3Dâprinted robotic hand, and a tempotron classifier system is used for tactile exploration. The dynamic tactile sensor, interfaced with an extended gate configuration to a common source metal oxide semiconductor field effect transistor (MOSFET), exhibits a sensitivity of 2.28âkPaâ1. The capacitive sensing structure has nonlinear characteristics with sensitivity varying from 0.25âkPaâ1 in the lowâpressure range (<100âPa) to 0.002âkPaâ1 in high pressure (â2.5âkPa). The output from the presented sensor under a closedâloop tactile scan, carried out with an industrial robotic arm, is used as latencyâcoded spike trains in a spiking neural network (SNN) tempotron classifier system. With the capability of performing a realâtime binary naturalistic texture classification with a maximum accuracy of 99.45%, the presented bioinspired skin finds applications in robotics, prosthesis, wearable sensors, and medical devices
Evolution of the polarization of the optical afterglow of the gamma-ray burst GRB 030329
We report 31 polarimetric observations of the afterglow of GRB 030329 with
high signal-to-noise and high sampling frequency. We establish the polarization
light curve, detect sustained polarization at the percent level, and find
significant variability of polarization degree and angle. The data imply that
the afterglow magnetic field has small coherence length and is mostly random,
probably generated by turbulence.Comment: Nature 426 (13. Nov. 2003), 2 figure
Cortical topography of intracortical inhibition influences the speed of decision making
The neocortex contains orderly topographic maps; however, their functional role remains controversial. Theoretical studies have suggested a role in minimizing computational costs, whereas empirical studies have focused on spatial localization. Using a tactile multiple-choice reaction time (RT) task before and after the induction of perceptual learning through repetitive sensory stimulation, we extend the framework of cortical topographies by demonstrating that the topographic arrangement of intracortical inhibition contributes to the speed of human perceptual decision-making processes. RTs differ among fingers, displaying an inverted U-shaped function. Simulations using neural fields show the inverted U-shaped RT distribution as an emergent consequence of lateral inhibition. Weakening inhibition through learning shortens RTs, which is modeled through topographically reorganized inhibition. Whereas changes in decision making are often regarded as an outcome of higher cortical areas, our data show that the spatial layout of interaction processes within representational maps contributes to selection and decision-making processes
Evolving structures of star-forming clusters
Understanding the formation and evolution of young star clusters requires
quantitative statistical measures of their structure. We investigate the
structures of observed and modelled star-forming clusters. By considering the
different evolutionary classes in the observations and the temporal evolution
in models of gravoturbulent fragmentation, we study the temporal evolution of
the cluster structures. We apply different statistical methods, in particular
the normalised mean correlation length and the minimum spanning tree technique.
We refine the normalisation of the clustering parameters by defining the area
using the normalised convex hull of the objects and investigate the effect of
two-dimensional projection of three-dimensional clusters. We introduce a new
measure for the elongation of a cluster. It is defined as the ratio of
the cluster radius determined by an enclosing circle to the cluster radius
derived from the normalised convex hull. The mean separation of young stars
increases with the evolutionary class, reflecting the expansion of the cluster.
The clustering parameters of the model clusters correspond in many cases well
to those from observed ones, especially when the values are similar. No
correlation of the clustering parameters with the turbulent environment of the
molecular cloud is found, indicating that possible influences of the
environment on the clustering behaviour are quickly smoothed out by the stellar
velocity dispersion. The temporal evolution of the clustering parameters shows
that the star cluster builds up from several subclusters and evolves to a more
centrally concentrated cluster, while the cluster expands slower than new stars
are formed.Comment: 11 pages, 10 figures, accepted by A&A; slightly modified according to
the referee repor
Computational exploration of molecular receptive fields in the olfactory bulb reveals a glomerulus-centric chemical map
Š The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.Progress in olfactory research is currently hampered by incomplete knowledge about chemical receptive ranges of primary receptors. Moreover, the chemical logic underlying the arrangement of computational units in the olfactory bulb has still not been resolved. We undertook a large-scale approach at characterising molecular receptive ranges (MRRs) of glomeruli in the dorsal olfactory bulb (dOB) innervated by the MOR18-2 olfactory receptor, also known as Olfr78, with human ortholog OR51E2. Guided by an iterative approach that combined biological screening and machine learning, we selected 214 odorants to characterise the response of MOR18-2 and its neighbouring glomeruli. We found that a combination of conventional physico-chemical and vibrational molecular descriptors performed best in predicting glomerular responses using nonlinear Support-Vector Regression. We also discovered several previously unknown odorants activating MOR18-2 glomeruli, and obtained detailed MRRs of MOR18-2 glomeruli and their neighbours. Our results confirm earlier findings that demonstrated tunotopy, that is, glomeruli with similar tuning curves tend to be located in spatial proximity in the dOB. In addition, our results indicate chemotopy, that is, a preference for glomeruli with similar physico-chemical MRR descriptions being located in spatial proximity. Together, these findings suggest the existence of a partial chemical map underlying glomerular arrangement in the dOB. Our methodology that combines machine learning and physiological measurements lights the way towards future high-throughput studies to deorphanise and characterise structure-activity relationships in olfaction.Peer reviewe
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