Time evolution of the extremely diluted Blume-Emery-Griffiths neural network

The time evolution of the extremely diluted Blume-Emery-Griffiths neural network model is studied, and a detailed equilibrium phase diagram is obtained exhibiting pattern retrieval, fluctuation retrieval and self-sustained activity phases. It is shown that saddle-point solutions associated with fluctuation overlaps slow down considerably the flow of the network states towards the retrieval fixed points. A comparison of the performance with other three-state networks is also presented.Comment: 8 pages, 5 figure

The School as a learning organization : A study of how principals and teachers understand suppositions for organizational learning in schools

Masteroppgaven ble presentert 24. januar 2008Norsk : Mål: Vårt mål med studien har vært å få en større forståelse av hva som skal til for å gjøre skolen til en lærende organisasjon. I vårt daglige arbeid har vi behov for kompetanse om og forståelse av hva dette innebærer for praksis. Det har derfor vært viktig for oss å få konkretisert forutsetningene for hva som skaper læring i organisasjoner generelt og i skolen spesielt. Forskningsspørsmål: 1. Hva oppfatter utvalgte rektorer og lærere som forutsetninger for organisasjonslæring i skolen? 2. Hvilke konsekvenser mener vi dette kan antas å ha for tilrettelegging for organisasjonslæring i skolen? Metodisk framgangsmåte: Med utgangspunkt i teorier om læring i organisasjoner generelt og skoler spesielt, utarbeidet vi en idealmodell bestående av utvalgte forutsetninger for organisasjonslæring. Skolen som lærende organisasjon En studie av utvalgte rektorer og læreres oppfatninger av forutsetninger for organisasjonslæring i skolen Forutsetningene var strukturert i to dimensjoner, en kulturell med forutsetningene: Felles forpliktelse for å nå mål, motivasjon, samhandling og en strukturell med forutsetningene: aktører, arenaer, vurdering. Gjennom et casedesign med et kvalitativt opplegg for datainnsamling har vi undersøkt hva et utvalg av rektorer og lærere oppfatter som forutsetninger for organisasjonslæring i skolen. Konklusjoner Studien viser at informantenes oppfatninger av hva som er viktige forutsetninger for organisasjonslæring i skolen samsvarer godt med vår idealmodell. Våre funn viser i tillegg at ledelse er avgjørende for å styre læringsprosessene og sikre at forutsetningene for læring er til stede og utnyttes. Vår oppfatning er at tilrettelegging for organisasjonslæring i skolen først og fremst handler om å skape grunnlag for en overordnet systemtenkning. Denne tenkningen må skape sammenheng mellom de ulike forutsetningene i vår modell og sikre retningen i læringsprosessene. Avslutningsvis reflekterer vi over om det ligger til rette for organisasjonslæring i skolen.English : Research aims Our main purpose with this study is to achieve a better understanding of how to transform the school into a learning organization. As principal and supervisor we have a need for knowledge and understanding of what this means in practice. We want to establish the suppositions for learning in organizations in general and schools in particular. Following questions were asked: 1. What do the chosen principals and teachers find are suppositions for learning organisations in schools? 2. What consequences can we assume this will have for establishing organizational learning in schools? Design and method This analysis is based on case studies. The data is established on interviews with a selection of eight informants: Four principals and four teachers. We have based our study on the theory of learning in organizations in general and schools in particular. Based on this theory we have developed our ideal model. The model has two dimentions; one cultural and one structural. These dimentions have been guidelines for the collection of data, presentation and discussion of empirical research and our conclusions. The model is illustrated in figure 4. Results and conclusions Our study shows us that the suppositions of the principals and teachers cohere with the ones in our model. However, leadership and management are crucial for organisational learning in schools

A canonical ensemble approach to graded-response perceptrons

Perceptrons with graded input-output relations and a limited output precision are studied within the Gardner-Derrida canonical ensemble approach. Soft non- negative error measures are introduced allowing for extended retrieval properties. In particular, the performance of these systems for a linear and quadratic error measure, corresponding to the perceptron respectively the adaline learning algorithm, is compared with the performance for a rigid error measure, simply counting the number of errors. Replica-symmetry-breaking effects are evaluated.Comment: 26 pages, 10 ps figure

Existing data sources for clinical epidemiology: The clinical laboratory information system (LABKA) research database at Aarhus University, Denmark

This paper provides an introduction to the clinical laboratory information system (LABKA) research database in Northern and Central Denmark. The database contains millions of stored laboratory test results for patients living in the two Danish regions, encompassing 1.8 million residents, or one-third of the country’s population. More than 1700 different types of blood test analyses are available. Therefore, the LABKA research database represents an incredible source for studies involving blood test analyses. By record linkage of different Danish registries with the LABKA research database, it is possible to examine a large number of biomarkers as predictors of disease risk and prognosis and as markers of disease severity, and to evaluate medical treatments regarding effectiveness and possible side effects. Large epidemiological studies using routinely stored blood test results for individual patients can be performed because it is possible to link the laboratory data to high-quality individual clinical patient data in Denmark

Retrieval behavior and thermodynamic properties of symmetrically diluted Q-Ising neural networks

The retrieval behavior and thermodynamic properties of symmetrically diluted Q-Ising neural networks are derived and studied in replica-symmetric mean-field theory generalizing earlier works on either the fully connected or the symmetrical extremely diluted network. Capacity-gain parameter phase diagrams are obtained for the Q=3, Q=4 and $Q=\infty$ state networks with uniformly distributed patterns of low activity in order to search for the effects of a gradual dilution of the synapses. It is shown that enlarged regions of continuous changeover into a region of optimal performance are obtained for finite stochastic noise and small but finite connectivity. The de Almeida-Thouless lines of stability are obtained for arbitrary connectivity, and the resulting phase diagrams are used to draw conclusions on the behavior of symmetrically diluted networks with other pattern distributions of either high or low activity.Comment: 21 pages, revte

NADPH-diaphorase reactivity in ciliary ganglion neurons: A comparison of distributions in the pigeon, cat, and monkey

Ciliary ganglia from the pigeon, cat, and monkey were investigated for the presence of NADPH-diaphorase reactivity by use of a standard histochemical method. In the pigeon, where the ganglion is known to control lens and pupil function, and the choroidal vasculature, about one-third of the ganglion cells were densely stained and most other somata were lightly stained. In some cases, preganglionic terminals with a cap-like morphology were also darkly stained. The pattern of NADPH-diaphorase staining in mammals was very different from that seen in pigeons. In both mammalian species, where the ganglion is known to control lens and pupil function, a small number (less than 2%) of the ganglion cells were shown to be densely NADPH-diaphorase positive, revealing their neuronal processes. The presence of NADPH-diaphorase positive cells in pigeon, cat, and monkey ciliary ganglia suggests that nitric oxide may be used for intercellular communication in this ganglion, or in light of the known importance of nitric oxide in vascular control, some of these positive neurons may participate in the control of choroidal vasodilation

Using Fos imaging in the rat to reveal the anatomical extent of the disruptive effects of fornix lesions

Activity of the immediate early gene c-fos was compared across hemispheres in rats with unilateral fornix lesions. To engage Fos production, rats first performed a radial arm maze task that is severely disrupted by bilateral fornix lesions. Using immunohistochemical techniques, Fos-positive cells were visualized and counted in 39 sites in both hemispheres. Fornix lesions led to a significant reduction in Fos in all ipsilateral hippocampal subfields, as well as the entorhinal cortex and most of the subicular complex. Other sites that showed reduced activity included the ipsilateral retrosplenial, anterior cingulate, and postrhinal cortices. Subcortical regions showing significant Fos decreases included the anterior thalamic nuclei, supramammillary nucleus, diagonal band of Broca, and lateral septum. Thus, the effects of fornix lesions extended beyond the hippocampal formation and included sites not directly innervated by the tract. These changes were nevertheless selective, as shown by the lack of hemispheric difference in any of the preselected control sites, the perirhinal cortex, or nucleus accumbens. Furthermore, there were no hemispheric differences in an additional group of animals with unilateral fornix lesions that were killed directly from the home cage. The location of Fos changes closely corresponded to those brain regions that when lesioned disrupt spatial working memory. Moreover, there was a correspondence between those brain regions that show increased Fos production in normal animals performing the radial arm maze task and those affected by fornix lesions. These results show that fornix transection has widespread, but selective, effects on a network of structures normally activated by spatial memory processes, with these effects extending beyond the hippocampal formation

Parisi Phase in a Neuron

Pattern storage by a single neuron is revisited. Generalizing Parisi's framework for spin glasses we obtain a variational free energy functional for the neuron. The solution is demonstrated at high temperature and large relative number of examples, where several phases are identified by thermodynamical stability analysis, two of them exhibiting spontaneous full replica symmetry breaking. We give analytically the curved segments of the order parameter function and in representative cases compute the free energy, the storage error, and the entropy.Comment: 4 pages in prl twocolumn format + 3 Postscript figures. Submitted to Physical Review Letter

Towards an Efficient Finite Element Method for the Integral Fractional Laplacian on Polygonal Domains

We explore the connection between fractional order partial differential equations in two or more spatial dimensions with boundary integral operators to develop techniques that enable one to efficiently tackle the integral fractional Laplacian. In particular, we develop techniques for the treatment of the dense stiffness matrix including the computation of the entries, the efficient assembly and storage of a sparse approximation and the efficient solution of the resulting equations. The main idea consists of generalising proven techniques for the treatment of boundary integral equations to general fractional orders. Importantly, the approximation does not make any strong assumptions on the shape of the underlying domain and does not rely on any special structure of the matrix that could be exploited by fast transforms. We demonstrate the flexibility and performance of this approach in a couple of two-dimensional numerical examples