17,135 research outputs found
Inductive Reasoning Games as Influenza Vaccination Models: Mean Field Analysis
We define and analyze an inductive reasoning game of voluntary yearly
vaccination in order to establish whether or not a population of individuals
acting in their own self-interest would be able to prevent influenza epidemics.
We find that epidemics are rarely prevented. We also find that severe epidemics
may occur without the introduction of pandemic strains. We further address the
situation where market incentives are introduced to help ameliorating
epidemics. Surprisingly, we find that vaccinating families exacerbates
epidemics. However, a public health program requesting prepayment of
vaccinations may significantly ameliorate influenza epidemics.Comment: 20 pages, 7 figure
The influence of clearance on friction, lubrication and squeaking in large diameter metal-on-metal hip replacements
Large diameter metal-on-metal bearings (MOM) are becoming increasingly popular, addressing the needs of young and more active patients. Clinical data has shown excellent short-to-mid-term results, though incidences of transient squeaking have been noted between implantation and up to 2 years post-operative. Geometric design features, such as clearance, have been significant in influencing the performance of the bearings. Sets of MOM bearings with different clearances were investigated in this study using a hip friction simulator to examine the influence of clearance on friction, lubrication and squeaking. The friction factor was found to be highest in the largest clearance bearings under all test conditions. The incidence of squeaking was also highest in the large clearance bearings, with all bearings in this group squeaking throughout the study. A very low incidence of squeaking was observed in the other two clearance groups. The measured lubricating film was found to be lowest in the large clearance bearings. This study suggests that increasing the bearing clearance results in reduced lubricant film thickness, increased friction and an increased incidence of squeaking
Exponential localization in one-dimensional quasiperiodic optical lattices
We investigate the localization properties of a one-dimensional bichromatic
optical lattice in the tight binding regime, by discussing how exponentially
localized states emerge upon changing the degree of commensurability. We also
review the mapping onto the discrete Aubry-Andre' model, and provide evidences
on how the momentum distribution gets modified in the crossover from extended
to exponentially localized states. This analysis is relevant to the recent
experiment on Anderson localization of a noninteracting Bose-Einstein
condensate in a quasiperiodic optical lattice [G. Roati et al., Nature 453, 895
(2008)].Comment: 13 pages, 6 figure
Local dissipation effects in two-dimensional quantum Josephson junction arrays with magnetic field
We study the quantum phase transitions in two-dimensional arrays of
Josephson-couples junctions with short range Josephson couplings (given by the
Josephson energy) and the charging energy. We map the problem onto the solvable
quantum generalization of the spherical model that improves over the mean-field
theory method. The arrays are placed on the top of a two-dimensional electron
gas separated by an insulator. We include effects of the local dissipation in
the presence of an external magnetic flux f in square lattice for several
rational fluxes f=0,1/2,1/3,1/4 and 1/6. We also have examined the T=0
superconducting-insulator phase boundary as function of a dissipation alpha for
two different geometry of the lattice: square and triangular. We have found
critical value of the dissipation parameter independent on geometry of the
lattice and presence magnetic field.Comment: accepted to PR
Effects of Electron Correlations on Hofstadter Spectrum
By allowing interactions between electrons, a new Harper's equation is
derived to examine the effects of electron correlations on the Hofstadter
energy spectra. It is shown that the structure of the Hofstadter butterfly ofr
the system of correlated electrons is modified only in the band gaps and the
band widths, but not in the characteristics of self-similarity and the Cantor
set.Comment: 13 pages, 5 Postscript figure
Dealing with mobility: Understanding access anytime, anywhere
The rapid and accelerating move towards the adoption and use of mobile technologies has increasingly provided people and organisations with the ability to work away from the office and on the move. The new ways of working afforded by these technologies are often characterised in terms of access to information and people ‘anytime, anywhere’. This paper presents a study of mobile workers that highlights different facets of access to remote people and information, and different facets of anytime, anywhere. Four key factors in mobile work are identified from the study: the role of planning, working in ‘dead time’, accessing remote technological and informational resources, and monitoring the activities of remote colleagues. By reflecting on these issues, we can better understand the role of technology and artefact use in mobile work and identify the opportunities for the development of appropriate technological solutions to support mobile workers
Decrement Operators in Belief Change
While research on iterated revision is predominant in the field of iterated
belief change, the class of iterated contraction operators received more
attention in recent years. In this article, we examine a non-prioritized
generalisation of iterated contraction. In particular, the class of weak
decrement operators is introduced, which are operators that by multiple steps
achieve the same as a contraction. Inspired by Darwiche and Pearl's work on
iterated revision the subclass of decrement operators is defined. For both,
decrement and weak decrement operators, postulates are presented and for each
of them a representation theorem in the framework of total preorders is given.
Furthermore, we present two sub-types of decrement operators
Ground-simulation investigations of VTOL airworthiness criteria for terminal-area operations
Several ground-based simulation experiments undertaken to investigate concerns related to tilt-rotor aircraft airworthiness were conducted. The experiments were conducted on the National Aeronautics and Space Administration (NASA) Ames Research Center's Vertical Motion Simulator, which permits simulation of a wide variety of aircraft with a high degree of fidelity of motion cueing. Variations in conversion/deceleration profile, type of augmentation or automation, level of display assistance, and meteorological conditions were considered in the course of the experiments. Certification pilots from the Federal Aviation Administration (FAA) and the Civil Aviation Authority (CAA) participated, in addition to NASA research pilots. The setup of these experiments on the simulator is summarized, and some of the results highlighted
Organic carbon compounds associated with deep soil carbon stores
Aims
Organic carbon has been reported in deep regolithic profiles to depths of tens of metres, but the composition of the carbon compounds is unknown.
Methods
Residual carbon in the form of non-volatile low molecular weight compounds (LMWC) was characterised in three deep soil profiles to a depth of 19 m under farmland in south-western Australia following extraction with ethyl acetate and analysis by GC/MS. Pyrolysis and off-line thermochemolysis were used to characterise macromolecular organic carbon (MOC) to a depth of 29 m at a fourth site.
Results
Three compound classes occurred across the three different field locations: (1) terpenes, (2) fatty acids, amides and alcohols, and (3) plant steroids; indicating the influence of input of the past and present vegetation. Compounds related to fatty acids were the predominant residual carbon species in deep soils, and may be derived from plants and microorganisms. Biomarkers such as lignin, polysaccharides, proteins and terpenes at 0–0.1 m implied influences of vegetation, fire events and microorganisms. Pyrolysis found that polysaccharides were distributed mainly from 0 to 0.1 m, while aromatic compounds were consistently detected down to 29 m.
Conclusions
Carbon was stabilised in the form of aromatic compounds in deep soil, whereas other carbon sources such as cellulose, chitin, and N-containing compounds were confined to the surface soil. LMWC (Z)-docos-13-enamide and bis(6-methylheptyl) phthalate, were the main components throughout the soil profiles representing 53–81% of the LMWC, and were a greater proportion of the organic matter at depths of 18–19 m
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