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Search Results: 1 - 10 of 909 matches for " Timo Smieszek "
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A mechanistic model of infection: why duration and intensity of contacts should be included in models of disease spread
Timo Smieszek
Theoretical Biology and Medical Modelling , 2009, DOI: 10.1186/1742-4682-6-25
Abstract: We present an exposure-based, mechanistic model of disease transmission that reflects heterogeneities in contact duration and intensity. Based on empirical contact data, we calculate the expected number of secondary cases induced by an infector (i) for the mechanistic model and (ii) under the classical assumption of a constant per-contact transmission probability. The results of both approaches are compared for different basic reproduction numbers R0.The outcomes of the mechanistic model differ significantly from those of the assumption of a constant per-contact transmission probability. In particular, cases with many different contacts have much lower expected numbers of secondary cases when using the mechanistic model instead of the common assumption. This is due to the fact that the proportion of long, intensive contacts decreases in the contact dataset with an increasing total number of contacts.The importance of highly connected individuals, so-called super-spreaders, for disease spread seems to be overestimated when a constant per-contact transmission probability is assumed. This holds particularly for diseases with low basic reproduction numbers. Simulations of disease spread should weight contacts by duration and intensity.Research has shown that the arrangement of potentially contagious contacts among the individuals of a society is a determining factor of disease spread: Both the repetition and the clustering of contacts diminish the size of an outbreak compared to a random mixing model [1-3]. Further, the epidemic threshold is low if the degree distribution shows a high dispersion [4,5]. In contrast to the vast body of literature that exists on the importance of network structure, only little emphasis has been put on the quality of such potentially contagious contacts, i.e. how long they last and how intensive they are. In fact, mathematical models and computer simulations of disease propagation often assume a constant per-contact transmission probability
Models of epidemics: when contact repetition and clustering should be included
Timo Smieszek, Lena Fiebig, Roland W Scholz
Theoretical Biology and Medical Modelling , 2009, DOI: 10.1186/1742-4682-6-11
Abstract: We compare two different types of individual-based models: One assumes random mixing without repetition of contacts, whereas the other assumes that the same contacts repeat day-by-day. The latter exists in two variants, with and without clustering. We systematically test and compare how the total size of an outbreak differs between these model types depending on the key parameters transmission probability, number of contacts per day, duration of the infectious period, different levels of clustering and varying proportions of repetitive contacts.The simulation runs under different parameter constellations provide the following results: The difference between both model types is highest for low numbers of contacts per day and low transmission probabilities. The number of contacts and the transmission probability have a higher influence on this difference than the duration of the infectious period. Even when only minor parts of the daily contacts are repetitive and clustered can there be relevant differences compared to a purely random mixing model.We show that random mixing models provide acceptable estimates of the total outbreak size if the number of contacts per day is high or if the per-contact transmission probability is high, as seen in typical childhood diseases such as measles. In the case of very short infectious periods, for instance, as in Norovirus, models assuming repeating contacts will also behave similarly as random mixing models. If the number of daily contacts or the transmission probability is low, as assumed for MRSA or Ebola, particular consideration should be given to the actual structure of potentially contagious contacts when designing the model.The spread of infectious disease is determined by an interplay of biological and social factors [1]. Biological factors are, among others, the virulence of an infectious agent, pre-existing immunity and the pathways of transmission. A major social factor influencing disease spread is the arrangement of
Modelling workplace contact networks: the effects of organizational structure, architecture, and reporting errors on epidemic predictions
Gail E. Potter,Timo Smieszek,Kerstin Sailer
Statistics , 2013,
Abstract: Face-to-face social contacts are potentially important transmission routes for acute respiratory infections, and understanding the contact network can improve our ability to predict, contain, and control epidemics. Although workplaces are important settings for infectious disease transmission, few studies have collected workplace contact data and estimated workplace contact networks. We use contact diaries, architectural distance measures, and institutional structures to estimate social contact networks within a Swiss research institute. Some contact reports were inconsistent, indicating reporting errors. We adjust for this with a latent variable model, jointly estimating the true (unobserved) network of contacts and duration-specific reporting probabilities. We find that contact probability decreases with distance, and research group membership, role, and shared projects are strongly predictive of contact patterns. Estimated reporting probabilities were low only for 0-5 minute contacts. Adjusting for reporting error changed the estimate of the duration distribution, but did not change the estimates of covariate effects and had little effect on epidemic predictions. Our epidemic simulation study indicates that inclusion of network structure based on architectural and organizational structure data can improve the accuracy of epidemic forecasting models.
Reconstructing the 2003/2004 H3N2 influenza epidemic in Switzerland with a spatially explicit, individual-based model
Timo Smieszek, Michael Balmer, Jan Hattendorf, Kay W Axhausen, Jakob Zinsstag, Roland W Scholz
BMC Infectious Diseases , 2011, DOI: 10.1186/1471-2334-11-115
Abstract: We present a spatially explicit, individual-based simulation model of influenza spread. The simulation model bases upon (i) simulated human travel data, (ii) data on human contact patterns and (iii) empirical knowledge on the epidemiology of influenza. For model validation we compare the simulation outcomes with empirical knowledge regarding (i) the shape of the epidemic curve, overall infection rate and reproduction number, (ii) age-dependent infection rates and time of infection, (iii) spatial patterns.The simulation model is capable of reproducing the shape of the 2003/2004 H3N2 epidemic curve of Switzerland and generates an overall infection rate (14.9 percent) and reproduction numbers (between 1.2 and 1.3), which are realistic for seasonal influenza epidemics. Age and spatial patterns observed in empirical data are also reflected by the model: Highest infection rates are in children between 5 and 14 and the disease spreads along the main transport axes from west to east.We show that finding evidence for the validity of simulation models of influenza spread by challenging them with seasonal influenza outbreak data is possible and promising. Simulation models for pandemic spread gain more credibility if they are able to reproduce seasonal influenza outbreaks. For more robust modelling of seasonal influenza, serological data complementing sentinel information would be beneficial.Mathematical models and computer simulations of influenza spread have become increasingly important for pandemic preparedness within the last few years and have influenced the decisions of public health authorities [1,2]. A non-systematic search in the common publication databases identified plenty of studies modelling the spread of (mostly pandemic) influenza outbreaks [3-13]. However, models of pandemic spread are in most cases hypothetical because they focus on future pandemics [e.g. [6,7,10-13]] and, thus, are not validated with empirical data. In contrast, some models of historical ca
Positive Network Assortativity of Influenza Vaccination at a High School: Implications for Outbreak Risk and Herd Immunity
Victoria C. Barclay, Timo Smieszek, Jianping He, Guohong Cao, Jeanette J. Rainey, Hongjiang Gao, Amra Uzicanin, Marcel Salathé
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0087042
Abstract: Schools are known to play a significant role in the spread of influenza. High vaccination coverage can reduce infectious disease spread within schools and the wider community through vaccine-induced immunity in vaccinated individuals and through the indirect effects afforded by herd immunity. In general, herd immunity is greatest when vaccination coverage is highest, but clusters of unvaccinated individuals can reduce herd immunity. Here, we empirically assess the extent of such clustering by measuring whether vaccinated individuals are randomly distributed or demonstrate positive assortativity across a United States high school contact network. Using computational models based on these empirical measurements, we further assess the impact of assortativity on influenza disease dynamics. We found that the contact network was positively assortative with respect to influenza vaccination: unvaccinated individuals tended to be in contact more often with other unvaccinated individuals than with vaccinated individuals, and these effects were most pronounced when we analyzed contact data collected over multiple days. Of note, unvaccinated males contributed substantially more than unvaccinated females towards the measured positive vaccination assortativity. Influenza simulation models using a positively assortative network resulted in larger average outbreak size, and outbreaks were more likely, compared to an otherwise identical network where vaccinated individuals were not clustered. These findings highlight the importance of understanding and addressing heterogeneities in seasonal influenza vaccine uptake for prevention of large, protracted school-based outbreaks of influenza, in addition to continued efforts to increase overall vaccine coverage.
Measured and Perceived Physical Fitness, Intention, and Self-Reported Physical Activity in Adolescence  [PDF]
Timo Jaakkola, Tracy Washington
Advances in Physical Education (APE) , 2011, DOI: 10.4236/ape.2011.12004
Abstract: Objective: The aim of this study was to investigate the associations among measured physical fitness, perceived fitness, intention towards future physical activity and self-reported physical activity through junior high school years. Methods: Study participants included 122 Finnish students who were 13 years old during Grade 7. The sample was comprised of 80 girls and 42 boys from 3 junior high schools (Grades 7-9). During the autumn semester of Grade 7, students completed fitness tests and a questionnaire analyzing self-perception of their physical fitness. The questionnaire delivered at Grade 8 included intention towards future physical activity. At Grade 9 students’ self-reported physical activity levels. Results: Structural Equation Modelling revealed an indirect path from physical fitness to self-reported physical activity via perceived physical fitness and intention towards future physical activity. The model also demonstrated a correlation between perceived physical fitness and physical activity. Squared multiple correlations revealed that perceived physical fitness explained 33 % of the actual physical fitness. Conclusions: The results of this study highlight the role of physical and cognitive variables in the process of adoption of physical activity in adolescence.
Use of Augmented Reality Methods to Support Legal Conflicts in the Planning Process for Wind Turbines Using the Example of the Landscape Conservation Area “Eulenkopf and Surroundings”  [PDF]
Timo Wundsam, Sascha M. Henninger
Energy and Power Engineering (EPE) , 2014, DOI: 10.4236/epe.2014.611030
Abstract: The world’s growing energy demand poses a serious problem. At the same time fossil fuels are finite, which we must work against. Therefore, the Federal Government of Germany has set itself the goal to push forward the use of renewable energy in order to completely do without the generation of nuclear energy by 2023. There are, however, no specific guidelines from the European Directive on the promotion of electricity from renewable energy sources for the internal electricity market regarding how high each share of the different production method should be and, above all, which specific aim should be achieved by the share of wind energy. Nevertheless, it presents a crucial step toward a nuclear phaseout and a concomitant change of course of the Federal Government of Germany in the spring of 2011 regarding the expansion of renewable energy, taking the nuclear catastrophe in Fukushima into account. Using new legal planning approaches, also including the area of Rhineland-Palatinate, opportunities should be provided to make previously protected land available for setting up facilities for the generation of renewable energy. However, it is important to examine the legal situation regarding the installation of these kinds of constructions more detailed, as no general statements can be made. This will be illustrated using the example of the landscape conservation area “Eulenkopf and surrounding area” in the district of Kaiserslautern. The stated goal of the Social Democrat/Green coalition of the federal state government of Rhineland-Palatinate is to considerably expand the generation of electricity from renewable energy sources so that by 2030 at least the entire electricity demand can be covered by those. Due to the enormous potential of wind power, it is therefore necessary to quintuple its share of electricity generation by 2020, compared to 2011 numbers. In order to achieve the desired political objectives, by 2030 the number of turbines has to be increased to around 2650, representing a capacity of 7500 MW. This increase gives reason for boundary conditions to manage the generation of wind energy to be adjusted. This is intended to facilitate management and simultaneously minimise negative effects, such as the “sprawling” of wind turbines.
Synaptic Plasticity and Learning in Animal Models of Tuberous Sclerosis Complex
Timo Kirschstein
Neural Plasticity , 2012, DOI: 10.1155/2012/279834
Abstract: Tuberous sclerosis complex (TSC) is caused by a mutation of either the Tsc1 or Tsc2 gene. As these genes work in concert to negatively regulate the mammalian target of rapamycin (mTOR) kinase which is involved in protein translation, mutations of these genes lead to a disinhibited mTOR activity. Both the clinical appearance of this condition including tumors, cognitive decline, and epileptic seizures and the molecular understanding of the mTOR signaling pathway, not only involved in cell growth, but also in neuronal functioning, have inspired numerous studies on learning behavior as well as on synaptic plasticity which is the key molecular mechanism of information storage in the brain. A couple of interesting animal models have been established, and the data obtained in these animals will be discussed. A special focus will be laid on differences among these models, which may be in part due to different background strains, but also may indicate pathophysiological variation in different mutations. 1. Introduction Tuberous sclerosis complex (TSC) is an inherited disease caused by a heterozygous germ line mutation of either the Tsc1 or Tsc2 gene that is manifested in early childhood. The pathological hallmark of this disorder is the development of hamartomas (benign tumors) arising in a number of organs including the central nervous system [1, 2]. In the brain, TSC lesions typically comprise of cortical tubers, subependymal nodules, and giant cell astrocytomas [3, 4].Hence, common symptoms related to brain lesions are epileptic seizures, mental retardation, multiple neuropsychological impairments, and even autism [5–9]. Consequently, the significant neuropsychiatric morbidity caused by this condition has inspired a number of groups worldwide to study the underlying pathomechanisms aiming to improve our functional understanding of both gene products, named hamartin (Tsc1) and tuberin (Tsc2). These proteins act in concert as a guanosine triphosphate-activating protein (GAP) towards the small G protein Rheb, which is the key regulator of the mammalian target of rapamycin (mTOR) signaling [10, 11]. Since hamartin and tuberin negatively regulate mTOR activity, which in turn phosphorylates and thereby activates important translation factors such as p70 S6 kinase 1 (S6K1) and eukaryote initiation factor 4E-binding protein (eIF4E-BP), a major role of the TSC-mTOR signaling pathway has been suggested for tumorigenesis, and both genes were initially recognized as tumor suppressors [12]. However, increasing evidence has been provided that this pathway is also
Dealing with Ecological Objectives in the Monsu Planning System
Silva Lusitana , 2004,
Abstract: the article describes some approaches to incorporate ecological objectives into numerical forest planning when using the monsu software. monsu first simulates alternative treatment schedules for all stands in the planning area, over a user-specified planning horizon. it then seeks the best combination of stands' treatment schedules using numerical optimisation. management objectives are included in the optimisation model either as objective variables or constraints. the ecological variables that monsu can calculate - and which can therefore be considered in optimisation - include (1) ordinary but ecologically oriented forest characteristics such as deadwood volume and area of old forest, (2) a special biodiversity score calculated for the forest, and (3) a set of landscape metrics. landscape metrics are variables that measure the sizes, shapes, relative arrangement and connectivity of habitat patches as well as their total area. the most recent development of monsu has concentrated on the use of landscape metrics, which measure the forest?s ecological quality at the landscape level. a proper scale of ecological planning depends on the size of the territory of the species considered, and it seems that most of the keynote species have rather large territories and therefore require forest rather than stand level evaluations of ecological quality.
Usage and Impact of Controlled Vocabularies in a Subject Repository for Indexing and Retrieval
Timo Borst
Liber Quarterly : The Journal of European Research Libraries , 2012,
Abstract: Since 2009, the German National Library for Economics (ZBW) supports both indexing and retrieval of Open Access scientific publications like working papers, postprint articles and conference papers by means of a terminology web service. This web service is based on concepts organized as a ‘Standard Thesaurus for Economics’ (STW), which is modelled and regularly published as Linked Open Data. Moreover, it is integrated into the institution’s subject repository for automatically suggesting appropriate key words while indexing and retrieving documents, and for automatically expanding search queries on demand to gain better search results. While this approach looks promising to augment ‘off the shelf’ repository software systems in a lightweight manner with a disciplinary profile, there is still significant uncertainty about the effective usage and impact of controlled terms in the realm of these systems. To cope with this, we analyze the repository’s logfiles to get evidence of search behaviour which is potentially influenced by auto suggestion and expansion of scientific terms derived from a discipline’s literature.
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