Simplified modeling of the evolution of skills in a spatially resolved environment

We present a model for the spread, transmission and competition of skills with an emphasis on the role of spatial mobility of individuals. From a methodological point of view, we seek mathematical and computational simplicity in the sense of a minimal model. This minimalism lets us use a infinite dimensional simplex space and not a Euclidean space as underlying structure. Such a simplex captures the essentials of spatial heterogeneity without the mathematical difficulties of neighborhood structures. In the presented model, individuals may have no skill or either skill A or B. Individuals are born unskilled and may acquire skills by learning from a skilled individual. Skill A results in a small reproductive advantage and is easy to transmit (teaching happens at high rate), whereas skill B is harder to teach but results in a high benefit. The model exhibits a rich behavior; after an initial transient, the system settles to a fix point (constant distribution of skills), whereby the distribution of skills depends on a mobility parameter m. We observe different regimes, and as the main result, we conclude that for some settings of the system parameters, the spread of the (harder to learn but more beneficial) skill B is only possible within a specific range of the mobility parameter. From a technical point of view, this paper presents the application of the PRESS–method (probability reduced evolution of spatially resolved species) that enables the study of spatial effects in a very efficient manner. We analyze the consequences of spatial organization and argue that we can study aspects of social dynamics in an infinite dimensional simplex space. In spite of this maybe daunting name, the dynamics on such a structure is comparably easy to implement. The model we present is far from reflecting all the details of human interaction. On the contrary, we deliberately tailored the model to be as simple as possible from a mathematical point of view (but still reflecting central properties of spatial organization). This approach is guided by physics, where seemingly simple models which obviously don’t reflect the true physical behavior of a system (such as the Ising model) are nevertheless suited to reveal fundamental aspects and limiting cases of the real world

fMRI BOLD Correlates of EEG Independent Components: Spatial Correspondence With the Default Mode Network

Goal: We aimed to identify electroencephalographic (EEG) signal fluctuations within independent components (ICs) that correlate to spontaneous blood oxygenation level dependent (BOLD) activity in regions of the default mode network (DMN) during eyes-closed resting state.Methods: We analyzed simultaneously acquired EEG and functional magnetic resonance imaging (fMRI) eyes-closed resting state data in a convenience sample of 30 participants. IC analysis (ICA) was used to decompose the EEG time-series and common ICs were identified using data-driven IC clustering across subjects. The IC time courses were filtered into seven frequency bands, convolved with a hemeodynamic response function (HRF) and used to model spontaneous fMRI signal fluctuations across the brain. In parallel, group ICA analysis was used to decompose the fMRI signal into ICs from which the DMN was identified. Frequency and IC cluster associated hemeodynamic correlation maps obtained from the regression analysis were spatially correlated with the DMN. To investigate the reliability of our findings, the analyses were repeated with data collected from the same subjects 1 year later.Results: Our results indicate a relationship between power fluctuations in the delta, theta, beta and gamma frequency range and the DMN in different EEG ICs in our sample as shown by small to moderate spatial correlations at the first measurement (0.234 < |r| < 0.346, p < 0.0001). Furthermore, activity within an EEG component commonly identified as eye movements correlates with BOLD activity within regions of the DMN. In addition, we demonstrate that correlations between EEG ICs and the BOLD signal during rest are in part stable across time.Discussion: We show that ICA source separated EEG signals can be used to investigate electrophysiological correlates of the DMN. The relationship between the eye movement component and the DMN points to a behavioral association between DMN activity and the level of eye movement or the presence of neuronal activity in this component. Previous findings of an association between frontal midline theta activity and the DMN were replicated

A model of ideological struggle

A general model for opinion formation and competition, like in ideological struggles is formulated. The underlying set is a closed one, like a country but in which the population size is variable in time. Several ideologies compete to increase their number of adepts. Such followers can be either converted from one ideology to another or become followers of an ideology though being previously ideologically-free. A reverse process is also allowed. We consider two kinds of conversion: unitary conversion, e.g. by means of mass communication tools, or binary conversion, e.g. by means of interactions between people. It is found that the steady state,when it exists, depends on the number of ideologies. Moreover when the number of ideologies increases some tension arises between them. This tension can change in the course of time. We propose to measure the ideology tensions through an appropriately defined scale index.Comment: 10 pages, 3 figures, 46 references, working pape

Kajian Awal Prospek Bahan Galian Monasit Mengandung U Dan Elemen Asosiasinya Di Semelangan Ketapang, Kalimantan Barat

Daerah Semelangan termasuk dalam cakupan area geologi regional Ketapang. Analisis kadar geokimia contoh sedimen yang menunjukkan bahwa daerah Semelangan, Kecamatan Nanga Tayap, Kabupaten Ketapang teridentifikasi mengandung endapan mineral radioaktif berupa monasit yang mengandung uranium (U) dan unsur tanah jarang (rare earth elements, REE) yang cukup potensial. Keberadaan elemen radioaktif telah teridentifikasi dari hasil analisis granulometri beberapa sampel mineral berat yang mengandung mineral monasit mencapai 63% dan beberapa sampel mengandung butiran zirkon mencapai 40% (dari jumlah butiran), hasil analisis butiran dari contoh batuan terdapat contoh yang mengandung monasit 0,11%. Studi di daerah ini dilakukan dengan melakukan kajian data sekunder dan evaluasi data laboratorium. Kajian mencakup aspek geologi, batuan sumber, perangkap dan interpretasi sebaran plaser monasit mengandung U, Th dan zirkon beserta REE. Tujuan yang ingin diperoleh adalah informasi tentang karakter geologi dan sebaran sumberdaya bahan galian monasit mengandung Th dan U serta REE dalam monasit dan zircon. Batuan sumber bahan galian monasit, berupa granit berumur 77–115 juta (Yura – Kapur Akhir), termasuk tipe S dari kelompok granit alkali yang terbentuk pada fasa pegmatitik (pegmatitic stage) yang terdefrensiasi tingkat lanjut pada suhu 550 – 600°C. Nilai radioaktivitas anomali batuan granit biotit (400 c/s - 9200 c/s) dicirikan kandungan oleh mineral berupa K-felspar, kuarsa dan plagioklas (rasio K-felspar terhadap plagioklas bervariasi dari 80 – 100 berbanding 10) mengandung mineral penyerta berupa thorit, monasit, zirkon dan alanit. Kadar U batuan granit berkisar dari 2,5 ppm- 64,8 ppm. Sebaran lateral sedimen plaser aluvium mengandung monasit menempati dataran dari lembah banjir antar perbukitan, terletak terpisah dari dataran pantai mengikuti pola sebaran batuan granit (sumber monasit). Daerah propek monasit terletak pada dataran lembah banjir dari DAS S. Pawan, DAS S. Tulah dan DAS S. Laur dengan luas total 2.113.500 Ha. Semelangan study area included in the regional geology Ketapang. Geochemical analysis of sediment samples that represented showed that the region Semelangan Ketapang, District Nanga Tayap, Ketapang identified monazite deposite containing radioactive mineral. The monazite minerals containing rare earth element are potential. The presence of radioactive elements have been identified by the analysis granulometry of some pan consentrate samples. They containt of monazite grain mineral to reach 63% and some sample content of zircon grain mineral up to 40% (from total grains), grain analysis of rock samples are samples containing monazite 0.11 %. Activities study in this area is done by studying ecxisting data and laboratory data evaluation, which covering studies geological aspects, source rock, trap and plaser monazite deposits containing U, Th and REE and zircon. The objective is to obtain information about the character of geological and mineral resource distribution of monazite containing Th and U and rare earth elements in monazite and zircon. Source rock of the monazite minerals is a granite with aged 77-15 million (Yura - Late Cretaceous), including the S type granite group that formed in the alkali granite pegmatitic stage, which highly differentiated advanced at a temperature 550-6000°C. The radioactivity anomalous values is 400 c/s – 9200 c/s (biotite granite) with a mineral character of the form K-feldspar, quartz and plagioclase (K-feldspar to plagioclase ratio varies from 80-100 versus 10), containing minerals association such as thorit, monazite, zircon and alanit. The U content in granite rock ranging from 2.5 ppm - 64.8 ppm U. Lateral distribution plaser alluvial sediments contain monazite occupy flood plains of the valley between the hills, is located separately from the coastal plain and following the granite distribution pattern (source monazite). Monazite prospect region lies at the flood plains of the valley catcment area S. Pawan, S. Tulah and S Laur with a total area of 2.1135 million hectares

Minimal models for spatially resolved population dynamics : applications to coexistence in multi – trait models

Spatial resolution is relevant for many processes in population dynamics because it may give rise to heterogeneity. Simulating the effect of space in two or three dimensions is computationally costly. Furthermore, in Euclidean space, the notion of heterogeneity is complemented by neighbourhood correlations. In this paper, we use an infinite-dimensional simplex as a minimal model of space in which heterogeneity is realized, but neighbourhood is trivial and study the coexistence of viral traits in a SIRS - model. As a function of the migration parameter, multiple regimes are observed. We further discuss the relevance of minimal models for decision support

A High-resolution Mosaic of the Neutral Hydrogen in the M81 Triplet

We present a 3° × 3°, 105-pointing, high-resolution neutral hydrogen (H I) mosaic of the M81 galaxy triplet, (including the main galaxies M81, M82, and NGC 3077, as well as dwarf galaxy NGC 2976) obtained with the Very Large Array C and D arrays. This H I synthesis mosaic uniformly covers the entire area and velocity range of the triplet. The observations have a resolution of ̃20″ or ̃420 pc. The data reveal many small-scale anomalous velocity features highlighting the complexity of the interacting M81 triplet. We compare our data with Green Bank Telescope observations of the same area. This comparison provides evidence for the presence of a substantial reservoir of low-column density gas in the northern part of the triplet, probably associated with M82. Such a reservoir is not found in the southern part. We report a number of newly discovered kpc-sized low-mass H I clouds with H I masses of a few times 106 M ☉. A detailed analysis of their velocity widths show that their dynamical masses are much larger than their baryonic masses, which could indicate the presence of dark matter if the clouds are rotationally supported. However, due to their spatial and kinematical association with H I tidal features, it is more likely that the velocity widths indicate tidal effects or streaming motions. We do not find any clouds that are not associated with tidal features down to an H I mass limit of a few times 104 M ☉. We compare the H I column densities with resolved stellar density maps and find a star formation threshold around 3-6 × 1020 cm-2. We investigate the widths of the H I velocity profiles in the triplet and find that extreme velocity dispersions can be explained by a superposition of multiple components along the line of sight near M81 as well as winds or outflows around M82. The velocity dispersions found are high enough that these processes could explain the linewidths of damped-Lyα absorbers observed at high redshift.</p

Defining Chlorophyll-a Reference Conditions in European Lakes

The concept of “reference conditions” describes the benchmark against which current conditions are compared when assessing the status of water bodies. In this paper we focus on the establishment of reference conditions for European lakes according to a phytoplankton biomass indicator—the concentration of chlorophyll-a. A mostly spatial approach (selection of existing lakes with no or minor human impact) was used to set the reference conditions for chlorophyll-a values, supplemented by historical data, paleolimnological investigations and modelling. The work resulted in definition of reference conditions and the boundary between “high” and “good” status for 15 main lake types and five ecoregions of Europe: Alpine, Atlantic, Central/Baltic, Mediterranean, and Northern. Additionally, empirical models were developed for estimating site-specific reference chlorophyll-a concentrations from a set of potential predictor variables. The results were recently formulated into the EU legislation, marking the first attempt in international water policy to move from chemical quality standards to ecological quality targets

Risk factors and prognosis of young stroke. The FUTURE study: A prospective cohort study. Study rationale and protocol

Contains fulltext : 98322.pdf (postprint version ) (Open Access)BACKGROUND: Young stroke can have devastating consequences with respect to quality of life, the ability to work, plan or run a family, and participate in social life. Better insight into risk factors and the long-term prognosis is extremely important, especially in young stroke patients with a life expectancy of decades. To date, detailed information on risk factors and the long-term prognosis in young stroke patients, and more specific risk of mortality or recurrent vascular events, remains scarce. METHODS/DESIGN: The FUTURE study is a prospective cohort study on risk factors and prognosis of young ischemic and hemorrhagic stroke among 1006 patients, aged 18-50 years, included in our study database between 1-1-1980 and 1-11-2010. Follow-up visits at our research centre take place from the end of 2009 until the end of 2011. Control subjects will be recruited among the patients' spouses, relatives or social environment. Information on mortality and incident vascular events will be retrieved via structured questionnaires. In addition, participants are invited to the research centre to undergo an extensive sub study including MRI. DISCUSSION: The FUTURE study has the potential to make an important contribution to increase the knowledge on risk factors and long-term prognosis in young stroke patients. Our study differs from previous studies by having a maximal follow-up of more than 30 years, including not only TIA and ischemic stroke but also hemorrhagic stroke, the addition of healthy controls and prospectively collect data during an extensive follow-up visit. Completion of the FUTURE study may provide better information for treating physicians and patients with respect to the prognosis of young stroke.8 p

Causes and consequences of cerebral small vessel disease. The RUN DMC study: a prospective cohort study. Study rationale and protocol

Contains fulltext : 96704.pdf (publisher's version ) (Open Access)BACKGROUND: Cerebral small vessel disease (SVD) is a frequent finding on CT and MRI scans of elderly people and is related to vascular risk factors and cognitive and motor impairment, ultimately leading to dementia or parkinsonism in some. In general, the relations are weak, and not all subjects with SVD become demented or get parkinsonism. This might be explained by the diversity of underlying pathology of both white matter lesions (WML) and the normal appearing white matter (NAWM). Both cannot be properly appreciated with conventional MRI. Diffusion tensor imaging (DTI) provides alternative information on microstructural white matter integrity. The association between SVD, its microstructural integrity, and incident dementia and parkinsonism has never been investigated. METHODS/DESIGN: The RUN DMC study is a prospective cohort study on the risk factors and cognitive and motor consequences of brain changes among 503 non-demented elderly, aged between 50-85 years, with cerebral SVD. First follow up is being prepared for July 2011. Participants alive will be included and invited to the research centre to undergo a structured questionnaire on demographics and vascular risk factors, and a cognitive, and motor, assessment, followed by a MRI protocol including conventional MRI, DTI and resting state fMRI. DISCUSSION: The follow up of the RUN DMC study has the potential to further unravel the causes and possibly better predict the consequences of changes in white matter integrity in elderly with SVD by using relatively new imaging techniques. When proven, these changes might function as a surrogate endpoint for cognitive and motor function in future therapeutic trials. Our data could furthermore provide a better understanding of the pathophysiology of cognitive and motor disturbances in elderly with SVD. The execution and completion of the follow up of our study might ultimately unravel the role of SVD on the microstructural integrity of the white matter in the transition from "normal" aging to cognitive and motor decline and impairment and eventually to incident dementia and parkinsonism