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Search Results: 1 - 10 of 722 matches for " Fredrik Allenmark "
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Spatial Stereoresolution for Depth Corrugations May Be Set in Primary Visual Cortex
Fredrik Allenmark ,Jenny C. A. Read
PLOS Computational Biology , 2011, DOI: 10.1371/journal.pcbi.1002142
Abstract: Stereo “3D” depth perception requires the visual system to extract binocular disparities between the two eyes' images. Several current models of this process, based on the known physiology of primary visual cortex (V1), do this by computing a piecewise-frontoparallel local cross-correlation between the left and right eye's images. The size of the “window” within which detectors examine the local cross-correlation corresponds to the receptive field size of V1 neurons. This basic model has successfully captured many aspects of human depth perception. In particular, it accounts for the low human stereoresolution for sinusoidal depth corrugations, suggesting that the limit on stereoresolution may be set in primary visual cortex. An important feature of the model, reflecting a key property of V1 neurons, is that the initial disparity encoding is performed by detectors tuned to locally uniform patches of disparity. Such detectors respond better to square-wave depth corrugations, since these are locally flat, than to sinusoidal corrugations which are slanted almost everywhere. Consequently, for any given window size, current models predict better performance for square-wave disparity corrugations than for sine-wave corrugations at high amplitudes. We have recently shown that this prediction is not borne out: humans perform no better with square-wave than with sine-wave corrugations, even at high amplitudes. The failure of this prediction raised the question of whether stereoresolution may actually be set at later stages of cortical processing, perhaps involving neurons tuned to disparity slant or curvature. Here we extend the local cross-correlation model to include existing physiological and psychophysical evidence indicating that larger disparities are detected by neurons with larger receptive fields (a size/disparity correlation). We show that this simple modification succeeds in reconciling the model with human results, confirming that stereoresolution for disparity gratings may indeed be limited by the size of receptive fields in primary visual cortex.
The Economics of Power Generation Technology Choice and Investment Timing in the Presence of Policy Uncertainty  [PDF]
Robert Lundmark, Fredrik Pettersson
Low Carbon Economy (LCE) , 2012, DOI: 10.4236/lce.2012.31001
Abstract: The purpose of this study is to analyze how market and policy uncertainties affect the general profitability of new investments in the power sector, and investigate the associated investment timing and technology choices. We develop an economic model for new investments in three competing energy technologies in the Swedish electric power sector. The model takes into account the policy impacts of the EU ETS and the Swedish green certificate scheme. By simulating and modeling policy effects through stochastic prices the results suggest that bio-fuelled power is the most profitable technology choice in the presence of existing policy instruments and under our assumptions. The likelihood of choosing gas power increases over time at the expense of wind power due to the relative capital requirement per unit of output for these technologies. Overall the results indicate that the economic incentives to postpone investments into the future are significant.
Teaching Anatomy in the Multimedia World—Using Digital Tools for Progressive Learning over Time  [PDF]
Marcus Granmo, Fredrik Bengtsson
Creative Education (CE) , 2015, DOI: 10.4236/ce.2015.611117
Abstract: In a cross-faculty project journalism students filmed anatomy briefings on a medical program. The material gave medical students free access to rehearse and repeat over time. The journalism students on their part practiced camera technique, directing and editing: It was an opportunity for students to help students. Following a quality evaluation of undergraduate studies at the Lund University medical faculty in 2011, we explored, developed, and implemented novel educational tools to meet students’ need in the multimedia world in which they operate. Incorporating complementary digital learning resources, in particular integration with mobile applications enabled us to meet students in their own world, thereby enhancing the learning process. We produced short video clips on specific anatomic themes, following the curriculum of the well-established anatomy course, and posted them online, allowing continuous rehearsal and repetition over time at a pace that suits individual students. Also, available to all semesters it provides free opportunities for repetition, reducing the risk of knowledge-loss between basic and clinical parts of the program. Besides the obvious benefits for students, the material gave teachers a clear view of the students’ curriculum. Thus, the material can be used for alternative, more interactive forms of examination. The paper describes the project, and the results from evaluations and integration with mobile technology.
Thymoma in Myasthenia Gravis: From Diagnosis to Treatment
Fredrik Romi
Autoimmune Diseases , 2011, DOI: 10.4061/2011/474512
Abstract: One half of cortical thymoma patients develop myasthenia gravis (MG), while 15% of MG patients have thymomas. MG is a neuromuscular junction disease caused in 85% of the cases by acetylcholine receptor (AChR) antibodies. Titin and ryanodine receptor (RyR) antibodies are found in 95% of thymoma MG and 50% of late-onset MG (MG onset ≥50 years), are associated with severe disease, and may predict thymoma MG outcome. Nonlimb symptom profile at MG onset with bulbar, ocular, neck, and respiratory symptoms should raise the suspicion about the presence of thymoma in MG. The presence of titin and RyR antibodies in an MG patient younger than 60 years strongly suggests a thymoma, while their absence at any age strongly excludes thymoma. Thymoma should be removed surgically. Prethymectomy plasmapheresis/iv-IgG should be considered before thymectomy. The pharmacological treatment does not differ from nonthymoma MG, except for tacrolimus which is an option in difficult thymoma and nonthymoma MG cases with RyR antibodies. 1. Thymoma in Myasthenia Gravis Thymomas in myasthenia gravis (MG) are neoplasms derived from thymic epithelial cells, and are usually of the cortical subtype (WHO type B) [1]. 50% of thymoma patients develop MG (hereafter referred to as thymoma MG in this paper) [2, 3]. Cortical thymomas usually have some morphological similarities with thymic cortex; they share the capacity to propagate the maturation of immature naive CD4 T cells and export mature naive T cells into the periphery. Thymomas lacking this ability do not induce MG [4]. Thymomas with histological similarities to medullary thymic tissue or thymomas lacking developing T cells are seldom associated with MG [4]. Other thymoma characteristics that can cause reduced self-tolerance include defective epithelial expression of the autoimmune regulator (AIRE) gene and/or of major histocompatibility complex class II molecules, absence of myoid cells, failure to generate FOXP3(+) regulatory T cells, and genetic polymorphisms affecting T-cell signalling [5]. Histologically, thymomas are epithelial neoplastic cells surrounded by maturing T cells. The epithelial cells are capable of expressing epitopes cross-reactive with skeletal muscle proteins, such as acetylcholine receptor (AChR), titin, and ryanodine receptor (RyR) [6, 7]. The muscle-like epitopes are presented to T cells together with costimulatory molecules [7]. Autoreactive T cells specific for AChR and titin are found both in thymomas and in thymoma MG patients’ sera [8]. Thymoma epithelial cells present AChR peptides to T-cell lines in
Semiochemical Diversity in Practice: Antiattractant Semiochemicals Reduce Bark Beetle Attacks on Standing Trees—A First Meta-Analysis
Fredrik Schlyter
Psyche , 2012, DOI: 10.1155/2012/268621
Abstract: Reduction of tree mortality caused by bark beetle attacks is not only important for forestry, but also essential for the preservation of biodiversity and forest carbon sinks in the face of climate change. While bark beetle mass trapping (a “pull” approach) is implemented in practice, few studies exist to estimate its effect. The more complex “push-pull” tactic has, in contrast, been repeatedly tested during the last decade. I analysed published data from 32 experiments in 9 papers published during 2000–2011 on Ips typographus and Dendroctonus ponderosae, to test if there was an overall effect of antiattractant semiochemicals, that is, if treatments reduced the number of attacks on standing trees at the habitat or stand scale. This meta-analysis showed a substantial overall effect size (treatment-control means divided by their SD) of ?0.96, with some heterogeneity but little evidence of publication bias. There was no effect of beetle species or publication year. Heterogeneity resulted from different designs and beetle population levels (as year of study). The conventional “% Reduction” measure correlated well with effect size ( ). Recommendations include more precise reporting of responses (avoiding dichotomous data), more unified experimental designs, and further meta-analyses that include “grey literature” and more beetle species. 1. Introduction Strategies to reduce tree mortality caused by bark beetle attacks [1–5] are becoming urgent, not only for forest industry, but also for preservation of forest cover and forest carbon sinks in the face of climate change [6–9]. There is a need for quantitative reviews of management alternatives such as mass-trapping and push-pull [10]. While bark beetle mass trapping (a “pull” tactic) is partly implemented in practise, few replicated studies exist to estimate the efficacy of this approach [1–4]. The more complex “push-pull” (as defined by Cook et al. [11]) and “push” (as defined by Gillette and Munson [12]) tactics have, in contrast, been experimentally tested and reported in >10 papers in the last decade, so a review effort on the subject seems to be timely. I chose the quantitative method of meta-analysis that uses the descriptive data obtained (means, standard deviations, sample sizes), rather than relying on the P values and other analytical statistics which are heavily dependent on sample size when declaring an experiment “significant” or not. Meta-analysis is the method of choice for estimating interventions in complex systems such a clinical medicine, social work, and education [13–16], but also in
Improved Inhibitor Screening Experiments by Comparative Analysis of Simulated Enzyme Progress Curves
Fredrik Tholander
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0046764
Abstract: A difficulty associated with high throughput screening for enzyme inhibitors is to establish reaction conditions that maximize the sensitivity and resolution of the assay. Deduction of information from end-point assays at single concentrations requires a detailed understanding of the time progress of the enzymatic reaction, an essential but often difficult process to model. A tool to simulate the time progress of enzyme catalyzed reactions and allows adjustment of reactant concentrations and parameters (initial concentrations, Km, kcat, Ki values, enzyme half-life, product?enzyme dissociation constant, and the rate constant for the reversed reaction) has been developed. This tool provides comparison of the progress of uninhibited versus inhibited reactions for common inhibitory mechanisms, and guides the tuning of reaction conditions. Possible applications include: analysis of substrate turnover, identification of the point of maximum difference in product concentration (Δmax[P]) between inhibited and uninhibited reactions, determination of an optimal observation window unbiased for inhibitor mechanisms or potency, and interpretation of observed inhibition in terms of true inhibition. An important observation that can be utilized to improve assay signal strength and resolution is that Δmax[P] occurs at a high degree of substrate consumption (commonly >75%) and that observation close to this point does not adversely affect observed inhibition or IC50 values.
Prostate cancer genomics: can we distinguish between indolent and fatal disease using genetic markers?
Fredrik Wiklund
Genome Medicine , 2010, DOI: 10.1186/gm166
Abstract: Prostate cancer constitutes a major health burden, being the most common non-cutaneous malignancy among men in developed countries. In 2007, almost 800,000 new cases of prostate cancer and 250,000 deaths from this disease were estimated to have occurred worldwide [1]. The highest incidence of prostate cancer is observed in the USA, with 192,280 new cases and 27,360 deaths expected in 2009, thereby being the second most common cause of cancer-related death [2]. Prostate cancer is a heterogeneous disease and its natural history is not completely understood. Early autopsy studies have shown a high prevalence of clinically undetected prostate cancer at time of death. In the USA, more than one in three men over 50 years of age had histologic evidence of prostate cancer at autopsy and this prevalence was observed to increase with age, with more than 67% of men aged over 80 years having prostate cancer at time of death [3]. These findings indicate that a high proportion of prostate tumors are clinically insignificant and will never lead to a lethal outcome. Furthermore, the introduction and widespread application of prostate-specific antigen (PSA) testing has led to increased detection of early-stage, low-volume, non-palpable tumors. This has in turn raised concerns of increased overdiagnosis and unnecessary treatment of indolent disease [4,5]. To this end, new strategies to help clinicians distinguish between lethal and indolent prostate cancer are urgently needed. Prostate cancer is one of the most heritable cancers in men and recent studies have revealed numerous genetic variants associated with this disease. This review will give an overview of the current knowledge of prostate cancer genetics, with a special focus on the ability of genetic variants to predict more aggressive forms.A family history of prostate cancer is one of the strongest risk factors, and twin studies suggest that as much as 42% of the disease risk is explained by heritable factors [6]. Attempts to
Bolivia: Un A?o de Vivir Peligrosamente
Revista de ciencia política (Santiago) , 2009, DOI: 10.4067/S0718-090X2009000200002
Abstract: during 2008 bolivia was shaken by political conflicts occurring in an increasingly deinstitutkmalised context. both government and opposition made frequent use of extra-institutional actions and in september, the massacre of a march of government supporters in the department of pando showed the capacity for violence present in the system. still, the year also saw the political system exhibit its capacity for finding solutions at the last moment. already in october, government and opposition negotiated an agreement on the one issue which had been at the centre of the year's conflicts; the proposal for a new constitution. eventually, the year 2008 ended with more calm, although a number of themes and conflicts loomed on the horizon.
Bolivia: Un A o de Vivir Peligrosamente Bolivia: A Year of Living Dangerously
Revista de Ciencia Política , 2009,
Abstract: Durante 2008 Bolivia fue sacudida por conflictos políticos en el contexto de una institucionalidad cada vez más debilitada. Tanto el gobierno como la oposición hacían uso frecuente de acciones extrainstitucionales y en septiembre la masacre de una marcha de simpatizantes oficialistas en el departamento de Pando demostró la capacidad de violencia presente en la política del país. Sin embargo, durante el a o el sistema político también mostró su capacidad para encontrar soluciones en el último momento. Ya en octubre, gobierno y oposición lograron un acuerdo sobre el tema que había estado en el fondo de los conflictos durante el a o; la propuesta para una nueva constitución política. Eso permitió que Bolivia cerrara el a o 2008 con más tranquilidad, aunque con una multitud de temas y conflictos todavía sin solucionar. During 2008 Bolivia was shaken by political conflicts occurring in an increasingly deinstitutkmalised context. Both government and opposition made frequent use of extra-institutional actions and in September, the massacre of a march of government supporters in the department of Pando showed the capacity for violence present in the system. Still, the year also saw the political system exhibit its capacity for finding solutions at the last moment. Already in October, government and opposition negotiated an agreement on the one issue which had been at the centre of the year's conflicts; the proposal for a new constitution. Eventually, the year 2008 ended with more calm, although a number of themes and conflicts loomed on the horizon.
Formaliserade m ten, tidigarelagda val. Reflektioner kring gymnasieutredningens syn p verg ng fr n skola till arbetsmarknad
Fredrik Hertzberg
Utbildning & Demokrati : Tidsskrift f?r Didaktik och Utbildningspolitik , 2008,
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