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Search Results: 1 - 10 of 223086 matches for " Tim C. Kietzmann "
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Measures and Limits of Models of Fixation Selection
Niklas Wilming, Torsten Betz, Tim C. Kietzmann, Peter K?nig
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0024038
Abstract: Models of fixation selection are a central tool in the quest to understand how the human mind selects relevant information. Using this tool in the evaluation of competing claims often requires comparing different models' relative performance in predicting eye movements. However, studies use a wide variety of performance measures with markedly different properties, which makes a comparison difficult. We make three main contributions to this line of research: First we argue for a set of desirable properties, review commonly used measures, and conclude that no single measure unites all desirable properties. However the area under the ROC curve (a classification measure) and the KL-divergence (a distance measure of probability distributions) combine many desirable properties and allow a meaningful comparison of critical model performance. We give an analytical proof of the linearity of the ROC measure with respect to averaging over subjects and demonstrate an appropriate correction of entropy-based measures like KL-divergence for small sample sizes in the context of eye-tracking data. Second, we provide a lower bound and an upper bound of these measures, based on image-independent properties of fixation data and between subject consistency respectively. Based on these bounds it is possible to give a reference frame to judge the predictive power of a model of fixation selection . We provide open-source python code to compute the reference frame. Third, we show that the upper, between subject consistency bound holds only for models that predict averages of subject populations. Departing from this we show that incorporating subject-specific viewing behavior can generate predictions which surpass that upper bound. Taken together, these findings lay out the required information that allow a well-founded judgment of the quality of any model of fixation selection and should therefore be reported when a new model is introduced.
Overt Visual Attention as a Causal Factor of Perceptual Awareness
Tim C. Kietzmann,Stephan Geuter,Peter K?nig
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0022614
Abstract: Our everyday conscious experience of the visual world is fundamentally shaped by the interaction of overt visual attention and object awareness. Although the principal impact of both components is undisputed, it is still unclear how they interact. Here we recorded eye-movements preceding and following conscious object recognition, collected during the free inspection of ambiguous and corresponding unambiguous stimuli. Using this paradigm, we demonstrate that fixations recorded prior to object awareness predict the later recognized object identity, and that subjects accumulate more evidence that is consistent with their later percept than for the alternative. The timing of reached awareness was verified by a reaction-time based correction method and also based on changes in pupil dilation. Control experiments, in which we manipulated the initial locus of visual attention, confirm a causal influence of overt attention on the subsequent result of object perception. The current study thus demonstrates that distinct patterns of overt attentional selection precede object awareness and thereby directly builds on recent electrophysiological findings suggesting two distinct neuronal mechanisms underlying the two phenomena. Our results emphasize the crucial importance of overt visual attention in the formation of our conscious experience of the visual world.
X-Ray Computed Tomography: Semiautomated Volumetric Analysis of Late-Stage Lung Tumors as a Basis for Response Assessments
C. Bendtsen,M. Kietzmann,R. Korn,P. D. Mozley,G. Schmidt,G. Binnig
International Journal of Biomedical Imaging , 2011, DOI: 10.1155/2011/361589
Abstract: Background. This study presents a semiautomated approach for volumetric analysis of lung tumors and evaluates the feasibility of using volumes as an alternative to line lengths as a basis for response evaluation criteria in solid tumors (RECIST). The overall goal for the implementation was to accurately, precisely, and efficiently enable the analyses of lesions in the lung under the guidance of an operator. Methods. An anthropomorphic phantom with embedded model masses and 71 time points in 10 clinical cases with advanced lung cancer was analyzed using a semi-automated workflow. The implementation was done using the Cognition Network Technology. Results. Analysis of the phantom showed an average accuracy of 97%. The analyses of the clinical cases showed both intra- and interreader variabilities of approximately 5% on average with an upper 95% confidence interval of 14% and 19%, respectively. Compared to line lengths, the use of volumes clearly shows enhanced sensitivity with respect to determining response to therapy. Conclusions. It is feasible to perform volumetric analysis efficiently with high accuracy and low variability, even in patients with late-stage cancer who have complex lesions. 1. Introduction The standard tool for assessing the response of solid tumors to therapy is X-ray computed tomography (CT). Based on typically axial CT images, the radiologist is faced with the challenge of assessing the tumor burden prior to treatment (baseline) and then following this over the course of therapy. Most clinicians visually compare the scans that were acquired immediately prior to the start of treatment to each new image set obtained during the course of treatment. Their nonquantitative impressions can be sufficient when changes are conspicuous. However, quantification is useful in many patients with cancer, because most solid tumors do not remit or progress rapidly. Response Evaluation Criteria in Solid Tumors (RECIST) [1] is currently the standard method for performing quantitative assessments. Currently, RECIST uses the sum of the diameters of the lesions that can be measured before treatment begins as a benchmark. These (target lesions) are then remeasured periodically during a course of treatment. A 30% decrease in the sum of the diameters over baseline is categorized as partial response (PR), while a 20% increase in the sum of the diameters over the previously smallest encountered sum of the diameters for the patient (the nadir) is considered progressive disease (PD). Responses which do not meet criteria for either PR or PD are classified as
An Analysis of Regional Income Variation among the Five Regions of Oklahoma  [PDF]
Orley M. Amos Jr., Tim C. Ireland
Modern Economy (ME) , 2015, DOI: 10.4236/me.2015.62011
Abstract: This paper investigates recent trends of per capita personal income in the state of Oklahoma to ascertain what if any long-run trends are exhibited. Standard theoretical analysis suggests that per capita incomes are expected to converge, especially across regions. However, recent research indicates that the national trend is one of the regional income divergences. The question posed by this paper is whether or not the per capita income in Oklahoma supports evidence of divergence. The data for 1969 to 2012 obtained from Department of Commerce, Bureau of Economic Analysis (BEA) are analyzed. These data are used to regionalize the state into five distinct county-based areas. Results suggest that Oklahoma exhibits a transitional pattern from convergence to divergence during the period of study. The three objectives of this study are: 1) a test of the growth pole cycle theory; 2) an extension of previous analysis of Oklahoma regional income variation; and 3) a preliminary test of the impact of the 2008 recession on regional income variation. After identification and analysis of the five substate regions, an overview of the growth pole cycle theory explaining the hypothesized pattern is provided, followed by an exposition of the analytical methodology. The analytical results are twofold, first, a baseline analysis regressing variation on per capita income and second, the inclusion of the unemployment rate.
An Analysis of Regional Income Variation in the United States: 1969-2013  [PDF]
Orley M. Amos, Tim C. Ireland
Modern Economy (ME) , 2017, DOI: 10.4236/me.2017.82016
Abstract: This paper investigates the variation of per capita personal income among counties within each state from 1969-2013. Department of Commerce BEA data and Department of Labor BLS data for 1969 to 2013 are analyzed. This study follows up on previous analysis of U.S. regional income variation by adjusting time series estimates for serial correction and using random effects models for panel data analysis. In addition, potential short-run disruption of a longer run trend is investigated by including an unemployment rate variable into the model. Results suggest that a general pattern of per capita income divergence has transpired in recent decades, contrary to conventional expectations of convergence.
Background Soil Mercury: An Unrecognized Source of Blood Mercury in Infants?  [PDF]
Pamela F. Heckel, Tim C. Keener, Grace K. LeMasters
Open Journal of Soil Science (OJSS) , 2013, DOI: 10.4236/ojss.2013.31004
Abstract: Introduction: During the past four decades, mercury (Hg) research focused on fish consumption has explained less than 22% of Hg in human blood. One overlooked exposure pathway for infants and young children is the concentration of Hg in soils. Although 75% of the U.S. population lives in urban areas near industrial facilities, minimal data exist regarding the concentration and speciation of Hg in residential soils. Chronic exposure through ingestion of low concentrations of Hg in soils may explain a portion of the blood Hg levels noted in infants. Methods: Three relatively unexposed residential sites in a suburban community were selected. The primary route of contamination was atmospheric deposition. Soils were digested in a nitric acid-hydrofluoric acid solution and analyzed by cold vapor atomic absorption spectrophotometry. Measured concentrations of total Hg in local suburban soil samples were compared to levels measured in a national study of 27 remote and rural sites. The Al-Shahristani pharmacokinetic model, developed after the 1971 Iraqi Methyl Hg poisoning incident, was used to calculate the blood Hg concentration in a hypothetical year-old infant. Results: Soil samples contained Hg concentrations ranging from 0.01 to 0.24 ppmw. The distribution of Hg in the soil samples was non-linear and non-normal. The mean soil Hg concentrations at the three locations were 0.08, 0.05 and 0.08 ppm. Calculated blood Hg concentrations for a 10 kg, year-old infant due to ingestion of soil (200 mg/day) containing 0.2, 0.4 and 0.8 ppm Hg were 0.08, 0.17 and 0.26 μg/L, respectively. Conclusions: The pilot study data appear to support the hypothesis that chronic, low-level soil ingestion may be a significant source of Hg for infants. Further study is warranted.


Transaldolase of Methanocaldococcus jannaschii
Tim Soderberg,Robert C. Alver
Archaea , 2004, DOI: 10.1155/2004/608428
Abstract: The Methanocaldococcus jannaschii genome contains putative genes for all four nonoxidative pentose phosphate pathway enzymes. Open reading frame (ORF) MJ0960 is a member of the mipB/talC family of ‘transaldolase-like’ genes, so named because of their similarity to the well-characterized transaldolase B gene family. However, recently, it has been reported that both the mipB and the talC genes from Escherichia coli encode novel enzymes with fructose-6-phosphate aldolase activity, not transaldolase activity (Schürmann and Sprenger 2001). The same study reports that other members of the mipB/talC family appear to encode transaldolases. To confirm the function of MJ0960 and to clarify the presence of a nonoxidative pentose phosphate pathway in M. jannaschii, we have cloned ORF MJ0960 from M. jannaschii genomic DNA and purified the recombinant protein. MJ0960 encodes a transaldolase and displays no fructose-6-phosphate aldolase activity. It retained full activity for 4 h at 80 °C, and for 3 weeks at 25 °C. Methanocaldococcus jannaschii transaldolase has a maximal velocity (Vmax) of 1.0 ± 0.2 µmol min–1 mg–1 at 25 °C, whereas Vmax = 12.0 ± 0.5 µmol min–1 mg–1 at 50 °C. Apparent Michaelis constants at 50 °C were Km = 0.65 ± 0.09 mM for fructose-6-phosphate and Km = 27.8 ± 4.3 µM for erythrose-4-phosphate. When ribose-5-phosphate replaced erythrose-4-phosphate as an aldose acceptor, Vmax decreased twofold, whereas the Km was 150-fold higher. The molecular mass of the active enzyme is 271 ± 27 kDa as estimated by gel filtration, whereas the predicted monomer size is 23.96 kDa, suggesting that the native form of the protein is probably a decamer. A readily available source of thermophilic pentose phosphate pathway enzymes including transaldolase may have direct application in enzymatic biohydrogen production.
OIL AND DIAMONDS AS CAUSES OF CIVIL WAR IN SUB-SAHARAN AFRICA UNDER WHAT CONDITIONS?
Matthias,Basedau; Wegenast,Tim C;
Colombia Internacional , 2009,
Abstract: recent research has increasingly questioned the link between natural resources and violent conflict while stressing the importance of resource-specific context conditions under which internal conflicts become more likely. this paper engages in a systematic analysis of six of these resource-specific conditions comparing 15 african oil and diamond producing countries. employing a boolean logic, the results of our analysis indicate that, typically, a conflict-ridden diamond or oil producer is highly dependent on resources, its revenues are hardly spent on distributional policies and the security apparatus and, moreover, it suffers from intercommunal problems in the producing regions. little income from resources per capita and substantial production of lootable resources in peripheral regions seem to constitute necessary conditions for civil war. thus, our findings imply that future theoretical models and empirical strategies should integrate the full set of (resource specific) context conditions. efforts to raise a more integrative approach combining quantitative and qualitative research designs seem particularly promising.
Petróleo y diamantes como causas de la guerra civil en áfrica subsahariana.
Matthias Basedau.,Tim C. Wegenast.
Colombia Internacional , 2009,
Abstract: Recent research has increasingly questioned the link between natural resources and violent conflict while stressing the importance of resource-specific context conditions under which internal conflicts become more likely. This paper engages in a systematic analysis of six of these resource-specific conditions comparing 15 African oil and diamond producing countries. Employing a Boolean logic, the results of our analysis indicate that, typically, a conflict-ridden diamond or oil producer is highly dependent on resources, its revenues are hardly spent on distributional policies and the security apparatus and, moreover, it suffers from intercommunal problems in the producing regions. Little income from resources per capita and substantial production of lootable resources in peripheral regions seem to constitute necessary conditions for civil war. Thus, our findings imply that future theoretical models and empirical strategies should integrate the full set of (resource specific) context conditions. Efforts to raise a more integrative approach combining quantitative and qualitative research designs seem particularly promising.
Quorum Sensing in the Squid-Vibrio Symbiosis
Subhash C. Verma,Tim Miyashiro
International Journal of Molecular Sciences , 2013, DOI: 10.3390/ijms140816386
Abstract: Quorum sensing is an intercellular form of communication that bacteria use to coordinate group behaviors such as biofilm formation and the production of antibiotics and virulence factors. The term quorum sensing was originally coined to describe the mechanism underlying the onset of luminescence production in cultures of the marine bacterium Vibrio fischeri. Luminescence and, more generally, quorum sensing are important for V. fischeri to form a mutualistic symbiosis with the Hawaiian bobtail squid, Euprymna scolopes. The symbiosis is established when V. fischeri cells migrate via flagella-based motility from the surrounding seawater into a specialized structure injuvenile squid called the light organ. The cells grow to high cell densities within the light organ where the infection persists over the lifetime of the animal. A hallmark of a successful symbiosis is the luminescence produced by V. fischeri that camouflages the squid at night by eliminating its shadow within the water column. While the regulatory networks governing quorum sensing are critical for properly regulating V. fischeri luminescence within the squid light organ, they also regulate luminescence-independent processes during symbiosis. In this review, we discuss the quorum-sensing network of V. fischeri and highlight its impact at various stages during host colonization.
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