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Search Results: 1 - 10 of 32691 matches for " Daniel Sabel "
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Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR)
Wolfgang Wagner,Carsten Pathe,Marcela Doubkova,Daniel Sabel
Sensors , 2008,
Abstract: The high spatio-temporal variability of soil moisture is the result of atmosphericforcing and redistribution processes related to terrain, soil, and vegetation characteristics.Despite this high variability, many field studies have shown that in the temporal domainsoil moisture measured at specific locations is correlated to the mean soil moisture contentover an area. Since the measurements taken by Synthetic Aperture Radar (SAR)instruments are very sensitive to soil moisture it is hypothesized that the temporally stablesoil moisture patterns are reflected in the radar backscatter measurements. To verify this hypothesis 73 Wide Swath (WS) images have been acquired by the ENVISAT AdvancedSynthetic Aperture Radar (ASAR) over the REMEDHUS soil moisture network located inthe Duero basin, Spain. It is found that a time-invariant linear relationship is well suited forrelating local scale (pixel) and regional scale (50 km) backscatter. The observed linearmodel coefficients can be estimated by considering the scattering properties of the terrainand vegetation and the soil moisture scaling properties. For both linear model coefficients,the relative error between observed and modelled values is less than 5 % and thecoefficient of determination (R2) is 86 %. The results are of relevance for interpreting anddownscaling coarse resolution soil moisture data retrieved from active (METOP ASCAT)and passive (SMOS, AMSR-E) instruments.
Evaluation of Soil Moisture Retrieval from the ERS and Metop Scatterometers in the Lower Mekong Basin
Vahid Naeimi,Patrick Leinenkugel,Daniel Sabel,Wolfgang Wagner,Heiko Apel,Claudia Kuenzer
Remote Sensing , 2013, DOI: 10.3390/rs5041603
Abstract: The natural environment and livelihoods in the Lower Mekong Basin (LMB) are significantly affected by the annual hydrological cycle. Monitoring of soil moisture as a key variable in the hydrological cycle is of great interest in a number of Hydrological and agricultural applications. In this study we evaluated the quality and spatiotemporal variability of the soil moisture product retrieved from C-band scatterometers data across the LMB sub-catchments. The soil moisture retrieval algorithm showed reasonable performance in most areas of the LMB with the exception of a few sub-catchments in the eastern parts of Laos, where the land cover is characterized by dense vegetation. The best performance of the retrieval algorithm was obtained in agricultural regions. Comparison of the available in situ evaporation data in the LMB and the Basin Water Index (BWI), an indicator of the basin soil moisture condition, showed significant negative correlations up to R = ?0.85. The inter-annual variation of the calculated BWI was also found corresponding to the reported extreme hydro-meteorological events in the Mekong region. The retrieved soil moisture data show high correlation (up to R = 0.92) with monthly anomalies of precipitation in non-irrigated regions. In general, the seasonal variability of soil moisture in the LMB was well captured by the retrieval method. The results of analysis also showed significant correlation between El Ni?o events and the monthly BWI anomaly measurements particularly for the month May with the maximum correlation of R = 0.88.
Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR)
Wolfgang Wagner,Carsten Pathe,Marcela Doubkova,Daniel Sabel,Annett Bartsch,Stefan Hasenauer,Günter Bl?schl,Klaus Scipal,José Martínez-Fernández,Alexander L?w
Sensors , 2008, DOI: 10.3390/s8021174
Abstract: The high spatio-temporal variability of soil moisture is the result of atmosphericforcing and redistribution processes related to terrain, soil, and vegetation characteristics.Despite this high variability, many field studies have shown that in the temporal domainsoil moisture measured at specific locations is correlated to the mean soil moisture contentover an area. Since the measurements taken by Synthetic Aperture Radar (SAR)instruments are very sensitive to soil moisture it is hypothesized that the temporally stablesoil moisture patterns are reflected in the radar backscatter measurements. To verify this hypothesis 73 Wide Swath (WS) images have been acquired by the ENVISAT AdvancedSynthetic Aperture Radar (ASAR) over the REMEDHUS soil moisture network located inthe Duero basin, Spain. It is found that a time-invariant linear relationship is well suited forrelating local scale (pixel) and regional scale (50 km) backscatter. The observed linearmodel coefficients can be estimated by considering the scattering properties of the terrainand vegetation and the soil moisture scaling properties. For both linear model coefficients,the relative error between observed and modelled values is less than 5 % and thecoefficient of determination (R2) is 86 %. The results are of relevance for interpreting anddownscaling coarse resolution soil moisture data retrieved from active (METOP ASCAT)and passive (SMOS, AMSR-E) instruments.
Open-Source web-based geographical information system for health exposure assessment
Barry Evans, Clive E Sabel
International Journal of Health Geographics , 2012, DOI: 10.1186/1476-072x-11-2
Abstract: Using maps to visualise data can enable quicker interpretation of complex geographical phenomena [1], identify patterns, and aid in planning, resource allocations for policy and decision making [2]. Mapping, in the context of the Environment and Health sub-discipline, provides a visual assessment for investigating the spatial distribution of a disease and potential associations and underlying causes [3]. Developments in Geographical Information Systems (GIS) have now made the mapping of this information commonplace and are used in a large range of applications. Within the environment and health fields, recent applications using GIS have been used in projects such as identifying regions at risk to malaria [4], monitoring effects of air pollution on asthmatics [5] and defining an "Index of Relative Wellbeing" for an area from census data [6].The research presented here, reports on results from the European Union (EU) FP6 funded Health and Environment Integrated Methodology and Toolbox for Scenario Assessment (HEIMTSA) project. The project's overall goal was to support the European Union's (EU's) Environment and Health Action Plan (EHAP) by extending health impact assessment (HIA) coupled with cost benefit analysis (CBA) methods and tools to evaluate the impacts policy scenarios have (at a European level) on the environment and human health. HEIMTSA was structured around loosely coupled modules that deal with pollutants and their media using the full chain (impact pathway) approach. The modelling tools and framework that were developed within this project was focussed on exploring:? Emissions to environmental media ('stressor identification'), derived from sector scenarios in transport, energy, agriculture, industry, households and waste treatment and disposal, that are combined and harmonized to result in consistent scenarios for all relevant stressors for the whole of Europe;? Human exposures (e.g. outdoor and indoor air pollution, water, noise, odour, metals, dioxin
Determination of the Burning Velocity Domain of a Statistically Stationary Turbulent Premixed Flame in Presence of Counter-Gradient Transport
V. A. Sabel'nikov,P. Bruel
Journal of Combustion , 2011, DOI: 10.1155/2011/821358
Abstract: The present study aims at providing a complete picture of the various propagation scenarios that a statistically stationary turbulent premixed flame may possibly undergo. By explicitly splitting the scalar turbulent flux between its gradient and counter-gradient contributions, the scalar governing equation is rewritten as an ordinary differential equation in the phase space. Then, an analysis of the characteristic equations in the vicinity of the reactants and products side is carried out. The domain of existence of the propagation velocity is then determined and positioned over the relevant Bray number range. It is shown in particular that when a counter-gradient transport at the cold leading edge of the flame is dominant, there still exists a possibility of observing a steady regime of propagation. This conclusion is compatible with recent experimental data and observations based on the analysis of direct numerical simulations. 1. Introduction The determination of the burning velocity of turbulent premixed flames has been the subject of many experimental studies. As far as a given modelling of such reacting flows is concerned, the a priori value of for statistically stationary one-dimensional turbulent flame is often estimated through the direct application of the results of the Kolmogorov-Petrovskii-Piskounov (KPP) theory [1] which showed that, for a one-dimensional reaction zone without heat release described through the evolution of a single progress variable and with a constant diffusion coefficient , the steady propagation of the reaction zone is controlled by the behavior of the reaction rate at the reactants side and by the value of the diffusion coefficient. In many situations, experiments (Moss [2], Cheng and Shepherd [3], Troiani et al. [4], Zimmer et al. [5]) as well as direct numerical simulations (DNS) (Veynante et al. [6], Nishiki [7], Hauguel [8], Lee and Huh [9]) show that an expression of the turbulent transports via a gradient expression is not appropriate as some mechanisms may promote a transport with a sign identical to that of the mean scalar gradient. An extensive review of relevant experimental and DNS data can be found in the paper of Lipatnikov and Chomiak [10]. In such situations, the introduction of the Bray number proposed by Veynante et al. [6] proved to be helpful to discriminate between flow configurations featuring gradient turbulent flux (GTF) only ( or counter-gradient turbulent flux (CGTF) ( .The Bray number was defined as where designates the heat release parameter and some order unity efficiency function which
Funktionserholung und Plastizit t nach Sch digung der zentralen Sehbahn
Gall C,Prilloff S,Sabel BA
Journal für Neurologie, Neurochirurgie und Psychiatrie , 2010,
Abstract: Das visuelle System ist auch jenseits der kritischen Entwicklungsperiode nicht fest verschaltet und unver nderlich. Auf allen Stufen der visuellen Informationsverarbeitung (Retina, Nucleus geniculatum laterale und prim rer visueller Kortex) zeigt das Gehirn selbst bis ins hohe Alter eine gewisse Ver nderlichkeit (Plastizit t). Dies ist besonders deutlich nach L sionen zu beobachten. So wurden Reorganisationsprozesse rezeptiver Felder und Ver nderungen der kortikalen Aktivierungsmuster nach retinalen sowie pr - und postchiasmatischen L sionen der zentralen Sehbahn gefunden. Hinweise auf neuronale Plastizit t sind sowohl in Tiermodellen als auch bei Patienten mit Sch digungen der Retina (Makuladegeneration, Glaukom), des Nervus opticus (z. B. nach Trauma) und postchiasmatischen Arealen, insbesondere des prim ren visuellen Kortex (Hemianopsien) gefunden worden. An die durch die Sch digungen hervorgerufenen Gesichtsfelddefekte versucht sich das Gehirn in gewissen Grenzen anzupassen. Zeichen der Postl sions-Plastizit t sind (1) Ausbildung exzentrischer Fixation bei fovealen L sionen, (2) funktionelle Erholung in den ersten Wochen nach dem Schaden (Spontanremissionen), (3) pseudo-halluzinative Wahrnehmungen von Phosphenen und komplexeren Gebilden als Zeichen der kortikalen Hyperaktivierung sowie (4) Blindsight und Residualsehen in gesch digten Gesichtsfeldarealen. Selbst wenn der Prozess der spontanen Plastizit t abgeschlossen ist, kann die Plastizit t durch repetitive Stimulation von residualen Gesichtsfeldarealen mittels Sehtraining oder, wie erst kürzlich gezeigt, durch transorbitale Elektrostimulation wieder angeregt werden. Das Sehsystem hat somit ein Plastizit tspotenzial, das hinsichtlich seiner spontanen und induzierten Anpassungsf higkeit nicht weniger ausgepr gt ist als in anderen funktionellen Systemen. Es gilt nun, dieses Plastizit tsund Reparaturpotenzial besser in der klinischen Anwendung zu nutzen.
The Second Face of Blindness: Processing Speed Deficits in the Intact Visual Field after Pre- and Post-Chiasmatic Lesions
Micha? Bola, Carolin Gall, Bernhard A. Sabel
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0063700
Abstract: Purpose Damage along the visual pathway results in a visual field defect (scotoma), which retinotopically corresponds to the damaged neural tissue. Other parts of the visual field, processed by the uninjured tissue, are considered to be intact. However, perceptual deficits have been observed in the “intact” visual field, but these functional impairments are poorly understood. We now studied temporal processing deficits in the intact visual field of patients with either pre- or post-chiasmatic lesions to better understand the functional consequences of partial blindness. Methods Patients with pre- (n = 53) or post- chiasmatic lesions (n = 98) were tested with high resolution perimetry – a method used to map visual fields with supra-threshold light stimuli. Reaction time of detections in the intact visual field was then analyzed as an indicator of processing speed and correlated with features of the visual field defect. Results Patients from both groups exhibited processing speed deficits in their presumably “intact” field as indicated by comparison to a normative sample. Further, in both groups processing speed was found to be a function of two factors. Firstly, a spatially restricted (retinotopic) influence of the scotoma was seen in longer reaction times when stimuli were presented in intact field sectors close to the defect. Secondly, patients with larger scotomata had on average longer reaction times in their intact field indicating a more general (non-retinotopic) influence of the scotoma. Conclusions Processing speed deficits in the “intact” visual field of patients with visual system damage demonstrate that visual system lesions have more widespread consequences on perception than previously thought. Because dysfunctions of the seeing field are expected to contribute to subjective vision, including visual tests of the presumed “intact” field may help to better understand vision loss and to improve methods of vision restoration and rehabilitation.
“Sightblind”: Perceptual Deficits in the “Intact” Visual Field
Micha? Bola,Carolin Gall,Bernhard A. Sabel
Frontiers in Neurology , 2013, DOI: 10.3389/fneur.2013.00080
Abstract: Unilateral visual cortex lesions caused by stroke or trauma lead to blindness in contralateral visual field – a condition called homonymous hemianopia. Although the visual field area processed by the uninjured hemisphere is thought to be “intact,” it also exhibits marked perceptual deficits in contrast sensitivity, processing speed, and contour integration. Such patients are “sightblind” – their blindness reaches far beyond the primary scotoma. Studies showing perceptual deficits in patients’ intact fields are reviewed and implications of these findings are discussed. It is concluded that consequences of partial blindness are greater than previously thought, since perceptual deficits in the “intact” field likely contribute to subjective vision loss in patients with visual field defect. This has important implications for vision diagnosis and rehabilitation.
Asymptotically efficient estimation of a scale parameter in Gaussian time series and closed-form expressions for the Fisher information
Till Sabel,Johannes Schmidt-Hieber
Statistics , 2012, DOI: 10.3150/12-BEJ505
Abstract: Mimicking the maximum likelihood estimator, we construct first order Cramer-Rao efficient and explicitly computable estimators for the scale parameter $\sigma^2$ in the model $Z_{i,n}=\sigma n^{-\beta}X_i+Y_i,i=1,\ldots,n,\beta>0$ with independent, stationary Gaussian processes $(X_i)_{i\in\mathbb{N}}$, $(Y_i)_{i\in\mathbb{N}}$, and $(X_i)_{i\in\mathbb{N}}$ exhibits possibly long-range dependence. In a second part, closed-form expressions for the asymptotic behavior of the corresponding Fisher information are derived. Our main finding is that depending on the behavior of the spectral densities at zero, the Fisher information has asymptotically two different scaling regimes, which are separated by a sharp phase transition. The most prominent example included in our analysis is the Fisher information for the scaling factor of a high-frequency sample of fractional Brownian motion under additive noise.
Proteomics in Melanoma Biomarker Discovery: Great Potential, Many Obstacles
Michael S. Sabel,Yashu Liu,David M. Lubman
International Journal of Proteomics , 2011, DOI: 10.1155/2011/181890
Abstract: The present clinical staging of melanoma stratifies patients into heterogeneous groups, resulting in the application of aggressive therapies to large populations, diluting impact and increasing toxicity. To move to a new era of therapeutic decisions based on highly specific tumor profiling, the discovery and validation of new prognostic and predictive biomarkers in melanoma is critical. Genomic profiling, which is showing promise in other solid tumors, requires fresh tissue from a large number of primary tumors, and thus faces a unique challenge in melanoma. For this and other reasons, proteomics appears to be an ideal choice for the discovery of new melanoma biomarkers. Several approaches to proteomics have been utilized in the search for clinically relevant biomarkers, but to date the results have been relatively limited. This article will review the present work using both tissue and serum proteomics in the search for melanoma biomarkers, highlighting both the relative advantages and disadvantages of each approach. In addition, we review several of the major obstacles that need to be overcome in order to advance the field. 1. Introduction The field of oncology is rapidly attempting to move to a new era of personalized therapy, where individualized therapeutic decisions are based on highly specific tumor profiling. For this to become a reality, the discovery and validation of new prognostic and predictive biomarkers are necessary. This goal seems increasingly realistic thanks to high-throughput screening methods, particularly genomic profiling. The large-scale analysis of gene expression has improved our knowledge of tumorigenesis, invasion, and metastasis. More recently, gene expression assays have helped guide therapeutic decisions, such as the use of multigene assays for decisions regarding systemic therapy in breast cancer [1, 2]. However, despite continued success in the preclinical setting, clinical translation has been slow and several tumor types present unique challenges to the use of genomic profiling. One example is melanoma. The present staging system for melanoma, using Breslow thickness, ulceration, mitotic rate, and the presence of regional and distant metastases, stratifies patients into heterogeneous groups, with wide variability in outcome or response to therapy. Clinically, this results in applying more aggressive surgical and adjuvant therapies to large populations, diluting the impact of therapy while exposing more patients to toxicity. For those treating melanoma, better prognostic and predictive markers in melanoma are sorely
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