35,741 research outputs found
Does Time-Symmetry Imply Retrocausality? How the Quantum World Says "Maybe"
It has often been suggested that retrocausality offers a solution to some of
the puzzles of quantum mechanics: e.g., that it allows a Lorentz-invariant
explanation of Bell correlations, and other manifestations of quantum
nonlocality, without action-at-a-distance. Some writers have argued that
time-symmetry counts in favour of such a view, in the sense that retrocausality
would be a natural consequence of a truly time-symmetric theory of the quantum
world. Critics object that there is complete time-symmetry in classical
physics, and yet no apparent retrocausality. Why should the quantum world be
any different? This note throws some new light on these matters. I call
attention to a respect in which quantum mechanics is different, under some
assumptions about quantum ontology. Under these assumptions, the combination of
time-symmetry without retrocausality is unavailable in quantum mechanics, for
reasons intimately connected with the differences between classical and quantum
physics (especially the role of discreteness in the latter). Not all
interpretations of quantum mechanics share these assumptions, however, and in
those that do not, time-symmetry does not entail retrocausality.Comment: 22 pages, 6 figures; significant revision
Toy Models for Retrocausality
A number of writers have been attracted to the idea that some of the
peculiarities of quantum theory might be manifestations of 'backward' or
'retro' causality, underlying the quantum description. This idea has been
explored in the literature in two main ways: firstly in a variety of explicit
models of quantum systems, and secondly at a conceptual level. This note
introduces a third approach, intended to complement the other two. It describes
a simple toy model, which, under a natural interpretation, shows how
retrocausality can emerge from simple global constraints. The model is also
useful in permitting a clear distinction between the kind of retrocausality
likely to be of interest in QM, and a different kind of reverse causality, with
which it is liable to be confused. The model is proposed in the hope that
future elaborations might throw light on the potential of retrocausality to
account for quantum phenomena.Comment: 12 pages, 14 figure
Neural overlap of L1 and L2 semantic representations across visual and auditory modalities : a decoding approach/
This study investigated whether brain activity in Dutch-French bilinguals during semantic access to concepts from one language could be used to predict neural activation during access to the same concepts from another language, in different language modalities/tasks. This was tested using multi-voxel pattern analysis (MVPA), within and across language comprehension (word listening and word reading) and production (picture naming). It was possible to identify the picture or word named, read or heard in one language (e.g. maan, meaning moon) based on the brain activity in a distributed bilateral brain network while, respectively, naming, reading or listening to the picture or word in the other language (e.g. lune). The brain regions identified differed across tasks. During picture naming, brain activation in the occipital and temporal regions allowed concepts to be predicted across languages. During word listening and word reading, across-language predictions were observed in the rolandic operculum and several motor-related areas (pre- and postcentral, the cerebellum). In addition, across-language predictions during reading were identified in regions typically associated with semantic processing (left inferior frontal, middle temporal cortex, right cerebellum and precuneus) and visual processing (inferior and middle occipital regions and calcarine sulcus). Furthermore, across modalities and languages, the left lingual gyrus showed semantic overlap across production and word reading. These findings support the idea of at least partially language- and modality-independent semantic neural representations
Formal vs self-organised knowledge systems: a network approach
In this work we consider the topological analysis of symbolic formal systems
in the framework of network theory. In particular we analyse the network
extracted by Principia Mathematica of B. Russell and A.N. Whitehead, where the
vertices are the statements and two statements are connected with a directed
link if one statement is used to demonstrate the other one. We compare the
obtained network with other directed acyclic graphs, such as a scientific
citation network and a stochastic model. We also introduce a novel topological
ordering for directed acyclic graphs and we discuss its properties in respect
to the classical one. The main result is the observation that formal systems of
knowledge topologically behave similarly to self-organised systems.Comment: research pape
Life, Death and Preferential Attachment
Scientific communities are characterized by strong stratification. The highly
skewed frequency distribution of citations of published scientific papers
suggests a relatively small number of active, cited papers embedded in a sea of
inactive and uncited papers. We propose an analytically soluble model which
allows for the death of nodes. This model provides an excellent description of
the citation distributions for live and dead papers in the SPIRES database.
Further, this model suggests a novel and general mechanism for the generation
of power law distributions in networks whenever the fraction of active nodes is
small.Comment: 5 pages, 2 figure
Burden of podoconiosis in poor rural communities in Guliso woreda, western Ethiopia
Background. Podoconiosis is an environmental lymphoedema affecting people living and working barefoot on irritant red clay soil. Podoconiosis is relatively well described in southern Ethiopia, but remains neglected in other parts of the Ethiopian highlands. This study aimed to assess the burden of podoconiosis in rural communities in western Ethiopia.
Methodology/Principal Findings. A cross-sectional study was conducted in Gulliso woreda (district), west Ethiopia. A household survey in the 26 rural kebeles (villages) of this district was conducted to identify podoconiosis patients and to measure disease prevalence. A more detailed study was done in six randomly selected kebeles to describe clinical features of the disease, patientsâ experiences of foot hygiene, and shoe wearing practice. 1,935 cases of podoconiosis were registered, giving a prevalence of 2.8%. The prevalence was higher in those aged 15 â 64 years (5.2%) and in females than males (prevalence ratio 2.6:1). 90.3% of patients were in the 15 â 64 year age group. In the detailed study, 335 cases were interviewed and their feet assessed. The majority of patients were farmers, uneducated, and poor. Two-third of patients developed the disease before the age of thirty. Almost all patients (97.0%) had experienced adenolymphangitis (ALA - red, hot legs, swollen and painful groin) at least once during the previous year. Patients experienced an average of 5.5 ALA episodes annually, each of average 4.4 days, thus 24 working days were lost annually. The incidence of ALA in podoconiosis patients was higher than that reported for filariasis in other countries. Shoe wearing was limited mainly due to financial problems.
Conclusions. We have documented high podoconiosis prevalence, frequent adenolymphangitis and high disease-related morbidity in west Ethiopia. Interventions must be developed to prevent, treat and control podoconiosis, one of the core neglected tropical diseases in Ethiopia
3D modelling of geological and anthropogenic deposits at the World Heritage Site of Bryggen in Bergen, Norway
The landscape of many historic cities and the character of their shallow subsurface environments are
defined by a legacy of interaction between anthropogenic and geological processes. Anthropogenic
deposits and excavations result from processes ranging from archaeological activities to modern urban
development. Hence, in heritage cities, any geological investigation should acknowledge the role of past
and ongoing human activities, while any archaeological investigation should be conducted with geological
processes in mind. In this paper it is shown that 3D geological and anthropogenic models at different scales
can provide a holistic system for the management of the subsurface. It provides a framework for the
integration of other spatial and processmodels to help assess the preservationpotential for buried heritage.
Such an integrated framework model is thus contributing to a decision support system for sustainable
urban (re)development and regeneration in cities, while preserving cultural heritage. A collaborative
approach is proposed to enhance research and implementation of combined geological and archaeological
modelling for sustainable land use planning and heritage preservation, using York and Bryggen as prime
examples. This paper presents the status of 3D framework modelling at Bryggen in Norway as an example
Maps of random walks on complex networks reveal community structure
To comprehend the multipartite organization of large-scale biological and
social systems, we introduce a new information theoretic approach that reveals
community structure in weighted and directed networks. The method decomposes a
network into modules by optimally compressing a description of information
flows on the network. The result is a map that both simplifies and highlights
the regularities in the structure and their relationships. We illustrate the
method by making a map of scientific communication as captured in the citation
patterns of more than 6000 journals. We discover a multicentric organization
with fields that vary dramatically in size and degree of integration into the
network of science. Along the backbone of the network -- including physics,
chemistry, molecular biology, and medicine -- information flows
bidirectionally, but the map reveals a directional pattern of citation from the
applied fields to the basic sciences.Comment: 7 pages and 4 figures plus supporting material. For associated source
code, see http://www.tp.umu.se/~rosvall
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