5,393 research outputs found
Recommended from our members
Zeno’s paradox in decision making
Classical probability theory has been influential in modeling decision processes, despite empirical findings that have been persistently paradoxical from classical perspectives. For such findings, some researchers have been successfully pursuing decision models based on quantum theory. One unique feature of quantum theory is the collapse postulate, which entails that measurements (or in decision making, judgments) reset the state to be consistent with the measured outcome. If there is quantum structure in cognition, then there has to be evidence for the collapse postulate. A striking, a priori prediction, is that opinion change will be slowed down (under idealized conditions frozen) by continuous judgments. In physics, this is the quantum Zeno effect. We demonstrate a quantum Zeno effect in decision making in humans and so provide evidence that advocates the use of quantum principles in decision theory, at least in some cases
The Drinfel'd twisted XYZ model
We construct a factorizing Drinfel'd twist for a face type model equivalent
to the XYZ model. Completely symmetric expressions for the operators of the
monodromy matrix are obtained.Comment: 15 pages, 4 figures, second preprint no. added, reference [14] added,
typos correcte
Lake eutrophication and its implications for organic carbon sequestration in Europe
The eutrophication of lowland lakes in Europe by excess nitrogen (N) and phosphorus (P) is severe because of the long history of land-cover change and agricultural intensification. The ecological and socio-economic effects of eutrophication are well understood but its effect on organic carbon (OC) sequestration by lakes and its change overtime has not been determined. Here, we compile data from ~90 culturally impacted European lakes [~60% are eutrophic, Total P (TP) >30 μg P l] and determine the extent to which OC burial rates have increased over the past 100-150 years. The average focussing corrected, OC accumulation rate (C AR) for the period 1950-1990 was ~60 g C m yr, and for lakes with >100 μg TP l the average was ~100 g C m yr. The ratio of post-1950 to 1900-1950 C AR is low (~1.5) indicating that C accumulation rates have been high throughout the 20th century. Compared to background estimates of OC burial (~5-10 g C m yr), contemporary rates have increased by at least four to fivefold. The statistical relationship between C AR and TP derived from this study (r = 0.5) can be used to estimate OC burial at sites lacking estimates of sediment C-burial. The implications of eutrophication, diagenesis, lake morphometry and sediment focussing as controls of OC burial rates are considered. A conservative interpretation of the results of the this study suggests that lowland European meso- to eutrophic lakes with >30 μg TP l had OC burial rates in excess of 50 g C m yr over the past century, indicating that previous estimates of regional lake OC burial have seriously underestimated their contribution to European carbon sequestration. Enhanced OC burial by lakes is one positive side-effect of the otherwise negative impact of the anthropogenic disruption of nutrient cycles. © 2014 John Wiley & Sons Ltd
Like trainer, like bot? Inheritance of bias in algorithmic content moderation
The internet has become a central medium through which `networked publics'
express their opinions and engage in debate. Offensive comments and personal
attacks can inhibit participation in these spaces. Automated content moderation
aims to overcome this problem using machine learning classifiers trained on
large corpora of texts manually annotated for offence. While such systems could
help encourage more civil debate, they must navigate inherently normatively
contestable boundaries, and are subject to the idiosyncratic norms of the human
raters who provide the training data. An important objective for platforms
implementing such measures might be to ensure that they are not unduly biased
towards or against particular norms of offence. This paper provides some
exploratory methods by which the normative biases of algorithmic content
moderation systems can be measured, by way of a case study using an existing
dataset of comments labelled for offence. We train classifiers on comments
labelled by different demographic subsets (men and women) to understand how
differences in conceptions of offence between these groups might affect the
performance of the resulting models on various test sets. We conclude by
discussing some of the ethical choices facing the implementers of algorithmic
moderation systems, given various desired levels of diversity of viewpoints
amongst discussion participants.Comment: 12 pages, 3 figures, 9th International Conference on Social
Informatics (SocInfo 2017), Oxford, UK, 13--15 September 2017 (forthcoming in
Springer Lecture Notes in Computer Science
Dissecting Representations
Choosing effective representations for a problem and for the person solving it has benefits, including the ability or inability to solve it. We previously devised a novel framework consisting of a language to describe representations and computational methods to analyse them in terms of their formal and cognitive properties. In this paper we demonstrate the application of this framework to a variety of notations including natural languages, formal languages, and diagrams. We show how our framework, and the analysis of representations that it enables, gives us insight into how and why we can select representations which are appropriate for both the task and the user
The HST large programme on NGC 6752 – III. Detection of the peak of the white dwarf luminosity function
We report on the white dwarf (WD) cooling sequence of the old globular cluster NGC 6752, which is chemically complex and hosts a blue horizontal branch. This is one of the last globular cluster WD cooling sequences accessible to imaging by the Hubble Space Telescope. Our photometry and completeness tests show that we have reached the peak of the luminosity function of the WD cooling sequence, at a magnitude mF606W = 29.4 ± 0.1, which is consistent with a formal age of ∼14 Gyr. This age is also consistent with the age from fits to the main-sequence turn-off (13–14 Gyr), reinforcing our conclusion that we observe the expected accumulation of WDs along the cooling sequence. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Societ
Statistical Signatures of Photon Localization
The realization that electron localization in disordered systems (Anderson
localization) is ultimately a wave phenomenon has led to the suggestion that
photons could be similarly localized by disorder. This conjecture attracted
wide interest because the differences between photons and electrons - in their
interactions, spin statistics, and methods of injection and detection - may
open a new realm of optical and microwave phenomena, and allow a detailed study
of the Anderson localization transition undisturbed by the Coulomb interaction.
To date, claims of three-dimensional photon localization have been based on
observations of the exponential decay of the electromagnetic wave as it
propagates through the disordered medium. But these reports have come under
close scrutiny because of the possibility that the decay observed may be due to
residual absorption, and because absorption itself may suppress localization.
Here we show that the extent of photon localization can be determined by a
different approach - measurement of the relative size of fluctuations of
certain transmission quantities. The variance of relative fluctuations
accurately reflects the extent of localization, even in the presence of
absorption. Using this approach, we demonstrate photon localization in both
weakly and strongly scattering quasi-one-dimensional dielectric samples and in
periodic metallic wire meshes containing metallic scatterers, while ruling it
out in three-dimensional mixtures of aluminum spheres.Comment: 5 pages, including 4 figure
Sperm design and variation in the New World blackbirds (Icteridae)
Post-copulatory sexual selection (PCSS) is thought to be one of the evolutionary forces responsible for the rapid and divergent evolution of sperm design. However, whereas in some taxa particular sperm traits are positively associated with PCSS, in other taxa, these relationships are negative, and the causes of these different patterns across taxa are poorly understood. In a comparative study using New World blackbirds (Icteridae), we tested whether sperm design was influenced by the level of PCSS and found significant positive associations with the level of PCSS for all sperm components but head length. Additionally, whereas the absolute length of sperm components increased, their variation declined with the intensity of PCSS, indicating stabilizing selection around an optimal sperm design. Given the diversity of, and strong selection on, sperm design, it seems likely that sperm phenotype may influence sperm velocity within species. However, in contrast to other recent studies of passerine birds, but consistent with several other studies, we found no significant link between sperm design and velocity, using four different species that vary both in sperm design and PCSS. Potential reasons for this discrepancy between studies are discussed
Single and two-particle energy gaps across the disorder-driven superconductor-insulator transition
The competition between superconductivity and localization raises profound
questions in condensed matter physics. In spite of decades of research, the
mechanism of the superconductor-insulator transition (SIT) and the nature of
the insulator are not understood. We use quantum Monte Carlo simulations that
treat, on an equal footing, inhomogeneous amplitude variations and phase
fluctuations, a major advance over previous theories. We gain new microscopic
insights and make testable predictions for local spectroscopic probes. The
energy gap in the density of states survives across the transition, but
coherence peaks exist only in the superconductor. A characteristic pseudogap
persists above the critical disorder and critical temperature, in contrast to
conventional theories. Surprisingly, the insulator has a two-particle gap scale
that vanishes at the SIT, despite a robust single-particle gap.Comment: 7 pages, 5 figures (plus supplement with 4 pages, 5 figures
Powerlaw optical conductivity with a constant phase angle in high Tc superconductors
In certain materials with strong electron correlations a quantum phase
transition (QPT) at zero temperature can occur, in the proximity of which a
quantum critical state of matter has been anticipated. This possibility has
recently attracted much attention because the response of such a state of
matter is expected to follow universal patterns defined by the quantum
mechanical nature of the fluctuations. Forementioned universality manifests
itself through power-law behaviours of the response functions. Candidates are
found both in heavy fermion systems and in the cuprate high Tc superconductors.
Although there are indications for quantum criticality in the cuprate
superconductors, the reality and the physical nature of such a QPT are still
under debate. Here we identify a universal behaviour of the phase angle of the
frequency dependent conductivity that is characteristic of the quantum critical
region. We demonstrate that the experimentally measured phase angle agrees
precisely with the exponent of the optical conductivity. This points towards a
QPT in the cuprates close to optimal doping, although of an unconventional
kind.Comment: pdf format, 9 pages, 4 color figures include
- …