Exponential increase in mortality with age is a generic property of a simple model system of damage accumulation and death

The risk of dying increases exponentially with age, in humans as well as in many other species. This increase is often attributed to the "accumulation of damage" known to occur in many biological structures and systems. The aim of this paper is to describe a generic model of damage accumulation and death in which mortality increases exponentially with age. The damage-accumulation process is modeled by a stochastic process know as a queue, and risk of dying is a function of the accumulated damage, i.e. length of the queue. The model has four parameters and the main characteristics of the model are: (i) damage occurs at random times with a constant high rate; (ii) the damage is repaired at a limited rate, and consequently damage can accumulate; (iii) the efficiency of the repair mechanism decays linearly with age; (iv) the risk of dying is a function of the accumulated damage. Using standard results from the mathematical theory of queues it is shown that there is an exponential dependence between risk of dying and age in these models, and that this dependency holds irrespective of how the damage-accumulation process is modeled. Furthermore, the ways in which this exponential dependence is shaped by the model parameters are also independent of the details of the damage accumulation process. These generic features suggest that the model could be useful when interpreting changes in the relation between age and mortality in real data. To examplify, historical mortality data from Sweden are interpreted in the light of the model. The decrease in mortality seen between cohorts born in 1905, compared to those born in 1885, can be accounted for by higher threshold to damage. This fits well with the many advances made in public health during the 20th century

Locomotion-Related Oscillatory Body Movements at 6–12 Hz Modulate the Hippocampal Theta Rhythm

The hippocampal theta rhythm is required for accurate navigation and spatial memory but its relation to the dynamics of locomotion is poorly understood. We used miniature accelerometers to quantify with high temporal and spatial resolution the oscillatory movements associated with running in rats. Simultaneously, we recorded local field potentials in the CA1 area of the hippocampus. We report that when rats run their heads display prominent vertical oscillations with frequencies in the same range as the hippocampal theta rhythm (i.e., 6–12 Hz). In our behavioral set-up, rats run mainly with speeds between 50 and 100 cm/s. In this range of speeds, both the amplitude and frequency of the “theta” head oscillations were increasing functions of running speed, demonstrating that the head oscillations are part of the locomotion dynamics. We found evidence that these rhythmical locomotor dynamics interact with the neuronal activity in the hippocampus. The amplitude of the hippocampal theta rhythm depended on the relative phase shift with the head oscillations, being maximal when the two signals were in phase. Despite similarity in frequency, the head movements and LFP oscillations only displayed weak phase and frequency locking. Our results are consistent with that neurons in the CA1 region receive inputs that are phase locked to the head acceleration signal and that these inputs are integrated with the ongoing theta rhythm

Play values and greenery in an urban schoolyard context : an examination of the schoolyard of Tiundaskolan

Kvaliteten på skolgårdar som utemiljö är mycket viktig för barn i deras vardag. En väl utformad utemiljö uppmuntrar till och möjliggör lek, vilket i sin tur är behövligt för barnens utveckling, hälsa och välmående. Detta arbete syftar till att undersöka hur lekvärden inkluderas på en nyanlagd skolgård i Uppsala kommun, vilket relateras till forskningsstudier och riktlinjer. Med hjälp av dokumentstudier undersöks kvaliteter för barns utemiljöer med relevans för skolgårdar där fokus läggs på lekvärden och grönska. En analys av Tiundaskolans skolgård görs sedan med utgångspunkt i dokumentstudierna samt en platsanalys där lekvärden och grönska inventeras. Även plan- och bygglagen samt riktlinjer för barns utemiljöer ligger till grund för analys och diskussion. Vid analysen framgick att skolgården innehåller många lekvärden men att den också är bristfällig i många avseenden, framförallt gällande tillgången till växtlighet samt skolgårdens storlek på friyta. Hårdgjorda ytor och bollplaner utgör stora delar av skolgårdens yta på bekostnad av vad som kan ge eller utgöra andra potentiella lekvärden. Slutsatsen av arbetet är att Tiundaskolans skolgård innehåller flertalet värden men att omfattande brister i utformning och kvaliteter, vad gäller framförallt ytstorlek och grönska, begränsar dess möjlighet att möta barns behov och att utgöra en god miljö för skolbarnen.The quality of school yards as outdoor spaces is of great importance for children in their everyday lives. A well designed outdoor space encourages and makes play possible, which in turn is needful to children's development, health and wellbeing. This work intends to examine how play values are included in a newly built school yard in Uppsala in Sweden. This in turn, gets related to academic studies and official guidelines. Document studies are used to survey values for children's spaces, with relevance to school yards, where focus is placed on play values and greenery. An analysis of the school yard belonging to Tiundaskolan is then carried out with the document studies as basis along with a place analysis in which play values and greenery are examined. The Swedish Planning and Building Act and official guidelines are also addressed in relation to the school yard in the analysis and discussion. The analysis showed that many play values are present while the school yard also is lacking in many ways, primarily in regards to greenery and the size of the schoolyard. Impervious surfaces and playing surfaces for ball sports cover large parts of the schoolyards area at the expense of what could otherwise contribute to other potential play values. The conclusion is that the school yard belonging to Tiundaskolan has a number of play values, but that the design and qualities are substantially lacking in regards to above all the areas size and greenery, and that this limits the possibilities to meet children's needs and compose a good environment for schoolchildren

Estimating the size of hidden populations from register data

BACKGROUND: Prevalence estimates of drug use, or of its consequences, are considered important in many contexts and may have substantial influence over public policy. However, it is rarely possible to simply count the relevant individuals, in particular when the defining characteristics might be illegal, as in the drug use case. Consequently methods are needed to estimate the size of such partly ‘hidden’ populations, and many such methods have been developed and used within epidemiology including studies of alcohol and drug use. Here we introduce a method appropriate for estimating the size of human populations given a single source of data, for example entries in a health-care registry. METHODS: The setup is the following: during a fixed time-period, e.g. a year, individuals belonging to the target population have a non-zero probability of being “registered”. Each individual might be registered multiple times and the time-points of the registrations are recorded. Assuming that the population is closed and that the probability of being registered at least once is constant, we derive a family of maximum likelihood (ML) estimators of total population size. We study the ML estimator using Monte Carlo simulations and delimit the range of cases where it is useful. In particular we investigate the effect of making the population heterogeneous with respect to probability of being registered. RESULTS: The new estimator is asymptotically unbiased and we show that high precision estimates can be obtained for samples covering as little as 25% of the total population size. However, if the total population size is small (say in the order of 500) a larger fraction needs to be sampled to achieve reliable estimates. Further we show that the estimator give reliable estimates even when individuals differ in the probability of being registered. We also compare the ML estimator to an estimator known as Chao’s estimator and show that the latter can have a substantial bias when applied to epidemiological data. CONCLUSIONS: The population size estimator suggested herein complements existing methods and is less sensitive to certain types of dependencies typical in epidemiological data

A 4D approach to the analysis of functional brain images: Application to FMRI data

This paper presents a new approach to functional magnetic resonance imaging (FMRI) data analysis. The main difference lies in the view of what comprises an observation. Here we treat the data from one scanning session (comprising t volumes, say) as one observation. This is contrary to the conventional way of looking at the data where each session is treated as t different observations. Thus instead of viewing the v voxels comprising the 3D volume of the brain as the variables, we suggest the usage of the vt hypervoxels comprising the 4D volume of the brain-over-session as the variables. A linear model is fitted to the 4D volumes originating from different sessions. Parameter estimation and hypothesis testing in this model can be performed with standard techniques. The hypothesis testing generates 4D statistical images (SIs) to which any relevant test statistic can be applied. In this paper we describe two test statistics, one voxel based and one cluster based, that can be used to test a range of hypotheses. There are several benefits in treating the data from each session as one observation, two of which are: (i) the temporal characteristics of the signal can be investigated without an explicit model for the blood oxygenation level dependent (BOLD) contrast response function, and (ii) the observations (sessions) can be assumed to be independent and hence inference on the 4D SI can be made by nonparametric or Monte Carlo methods. The suggested 4D approach is applied to FMRI data and is shown to accurately detect the expected signa

Spotting the diffusion of New Psychoactive Substances over the Internet

Online availability and diffusion of New Psychoactive Substances (NPS) represent an emerging threat to healthcare systems. In this work, we analyse drugs forums, online shops, and Twitter. By mining the data from these sources, it is possible to understand the dynamics of drugs diffusion and their endorsement, as well as timely detecting new substances. We propose a set of visual analytics tools to support analysts in tackling NPS spreading and provide a better insight about drugs market and analysis

Gearing up for action: attentive tracking dynamically tunes sensory and motor oscillations in the alpha and beta band

Allocation of attention during goal-directed behavior entails simultaneous processing of relevant and attenuation of irrelevant information. How the brain delegates such processes when confronted with dynamic (biological motion) stimuli and harnesses relevant sensory information for sculpting prospective responses remains unclear. We analyzed neuromagnetic signals that were recorded while participants attentively tracked an actor’s pointing movement that ended at the location where subsequently the response-cue indicated the required response. We found the observers’ spatial allocation of attention to be dynamically reflected in lateralized parieto-occipital alpha (8-12Hz) activity and to have a lasting influence on motor preparation. Specifically, beta (16-25Hz) power modulation reflected observers’ tendency to selectively prepare for a spatially compatible response even before knowing the required one. We discuss the observed frequency-specific and temporally evolving neural activity within a framework of integrated visuomotor processing and point towards possible implications about the mechanisms involved in action observation