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Search Results: 1 - 10 of 883 matches for " Olivia MARTIUS "
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Dynamical Tropopause Variability and Potential Vorticity Streamers in the Northern Hemisphere ---A Climatological Analysis
Dynamical Tropopause Variability and Potential Vorticity Streamers in the Northern Hemisphere —— A Climatological Analysis


大气科学进展 , 2008,
Abstract: This study presents a 44-year climatology of potential vorticity (PV) streamers in the Northern Hemi sphere based upon analyses of the ERA-40 reanalysis data set. A comparison to an existing 15-year clima tology yields very good agreement in the locations of PV streamer frequency maxima, but some differences are found in the amplitude of frequencies. The climatology is assessed with the focus on links between PV streamer frequencies and the synoptic- and planetary-scale variability of the dynamical tropopause. A comprehensive overview is provided on where (zonally) and when (seasonally) short-term variability throughout the extra-tropical and sub-tropical tropopause is enhanced or reduced. Several key processes that influence this variability are discussed. Baroclinic processes, for example, determine the variability in the storm-track areas in winter, whereas the Asian summer monsoon significantly influences the variability over Asia. The paper also describes links between the frequency of PV streamers in the extra-tropical and sub tropical tropopause and three major northern hemisphere teleconnection patterns. The observed changes in the PV streamer frequencies are closely related to concomitant variations of PV and its gradient within the tropopause region. During opposite phases of the North Atlantic Oscillation the location of the streamer frequency maxima shifts significantly in the Atlantic and European region in both the extra-tropics and subtropics. The influence of ENSO on the streamer frequencies is most pronounced in the subtropical Pacific.
Quantifying Emergent Behavior of Autonomous Robots
Georg Martius,Eckehard Olbrich
Computer Science , 2015,
Abstract: Quantifying behaviors of robots which were generated autonomously from task-independent objective functions is an important prerequisite for objective comparisons of algorithms and movements of animals. The temporal sequence of such a behavior can be considered as a time series and hence complexity measures developed for time series are natural candidates for its quantification. The predictive information and the excess entropy are such complexity measures. They measure the amount of information the past contains about the future and thus quantify the nonrandom structure in the temporal sequence. However, when using these measures for systems with continuous states one has to deal with the fact that their values will depend on the resolution with which the systems states are observed. For deterministic systems both measures will diverge with increasing resolution. We therefore propose a new decomposition of the excess entropy in resolution dependent and resolution independent parts and discuss how they depend on the dimensionality of the dynamics, correlations and the noise level. For the practical estimation we propose to use estimates based on the correlation integral instead of the direct estimation of the mutual information using the algorithm by Kraskov et al. (2004) which is based on next neighbor statistics because the latter allows less control of the scale dependencies. Using our algorithm we are able to show how autonomous learning generates behavior of increasing complexity with increasing learning duration.
A novel plasticity rule can explain the development of sensorimotor intelligence
Ralf Der,Georg Martius
Computer Science , 2015,
Abstract: Grounding autonomous behavior in the nervous system is a fundamental challenge for neuroscience. In particular, the self-organized behavioral development provides more questions than answers. Are there special functional units for curiosity, motivation, and creativity? This paper argues that these features can be grounded in synaptic plasticity itself, without requiring any higher level constructs. We propose differential extrinsic plasticity (DEP) as a new synaptic rule for self-learning systems and apply it to a number of complex robotic systems as a test case. Without specifying any purpose or goal, seemingly purposeful and adaptive behavior is developed, displaying a certain level of sensorimotor intelligence. These surprising results require no system specific modifications of the DEP rule but arise rather from the underlying mechanism of spontaneous symmetry breaking due to the tight brain-body-environment coupling. The new synaptic rule is biologically plausible and it would be an interesting target for a neurobiolocal investigation. We also argue that this neuronal mechanism may have been a catalyst in natural evolution.
Information Driven Self-Organization of Complex Robotic Behaviors
Georg Martius, Ralf Der, Nihat Ay
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0063400
Abstract: Information theory is a powerful tool to express principles to drive autonomous systems because it is domain invariant and allows for an intuitive interpretation. This paper studies the use of the predictive information (PI), also called excess entropy or effective measure complexity, of the sensorimotor process as a driving force to generate behavior. We study nonlinear and nonstationary systems and introduce the time-local predicting information (TiPI) which allows us to derive exact results together with explicit update rules for the parameters of the controller in the dynamical systems framework. In this way the information principle, formulated at the level of behavior, is translated to the dynamics of the synapses. We underpin our results with a number of case studies with high-dimensional robotic systems. We show the spontaneous cooperativity in a complex physical system with decentralized control. Moreover, a jointly controlled humanoid robot develops a high behavioral variety depending on its physics and the environment it is dynamically embedded into. The behavior can be decomposed into a succession of low-dimensional modes that increasingly explore the behavior space. This is a promising way to avoid the curse of dimensionality which hinders learning systems to scale well.
Linear combination of one-step predictive information with an external reward in an episodic policy gradient setting: a critical analysis
Keyan Zahedi,Georg Martius,Nihat Ay
Computer Science , 2013,
Abstract: One of the main challenges in the field of embodied artificial intelligence is the open-ended autonomous learning of complex behaviours. Our approach is to use task-independent, information-driven intrinsic motivation(s) to support task-dependent learning. The work presented here is a preliminary step in which we investigate the predictive information (the mutual information of the past and future of the sensor stream) as an intrinsic drive, ideally supporting any kind of task acquisition. Previous experiments have shown that the predictive information (PI) is a good candidate to support autonomous, open-ended learning of complex behaviours, because a maximisation of the PI corresponds to an exploration of morphology- and environment-dependent behavioural regularities. The idea is that these regularities can then be exploited in order to solve any given task. Three different experiments are presented and their results lead to the conclusion that the linear combination of the one-step PI with an external reward function is not generally recommended in an episodic policy gradient setting. Only for hard tasks a great speed-up can be achieved at the cost of an asymptotic performance lost.
Antimicrobial Resistance and β-Lactamase Production among Hospital Dumpsite Isolates  [PDF]
Olivia Sochi Egbule
Journal of Environmental Protection (JEP) , 2016, DOI: 10.4236/jep.2016.77094

Metallo-β-Lactamases (MBLs) and Extended Spectrum β-Lactamses (ESBLs) have emerged world-wide as a significant source of β-lactam resistance. The emergence of MBLs and ESBLs encoded on plasmids among Gram-negative pathogens in hospital dumpsites was investigated. Soils of different government and private hospitals were collected and processed following standard bacteriological techniques. Antimicrobial susceptibility testing was carried out by the disk-diffusion technique using Ceftazidime (30 μg), Cefuroxime (30 μg), Cefotaxime (30 μg), Cefixime (5 μg), Trimethprim-sulfamethoxazole (25 μg), Gentamycin (100 μg) Amoxicillin-Clavunalate (30 μg), Ciprofloxacin (5 μg), Ofloxacin (5 μg), Nitrofurantoin (300 μg) and Imipenem (10 μg). The role of plasmids in resistance was evaluated by subjecting isolates to curing using Sodium Dodecyl Sulfate (SDS). ESBLs production by Double-Disk Synergy Test (DDST) was carried out. Isolates resistant to Imipenem were subjected to a confirmatory test using Modified Hodge’s test and to MBLs production by DDST. Eighty-two Gram-negative isolates comprising of 32 (39.02%) Escherichia coli, 20 (24.39%) Serratia marcescens, 14 (17.07%) Klebsiella pneumonia, 10 (12.28%) Proteus mirabilis and 6 (7.32%) Enterobacter aerogenes were obtained. Susceptibility results revealed a 100% resistance of all isolates to Ceftazidime, Cefuroxime, Cefixime, Amoxycillin-clavulanate and Cefotaxime. A total of 66 (80.48%) isolates harboured plasmids out of which 26 (31.71%) isolates were ESBL producers. MBLs production was observed in 8 (25.00%) E. coli, 2 (2.41%) Klebsiella pneumonia and 2 (2.41%) Proteus mirabilis isolates. All MBLs producing isolates were ESBLs producers. The finding of highly resistant isolates producing ESBLs and MBLs in a hospital environment is quite disturbing and should be addressed urgently.

Detection and Transfer of Extended Spectrum Beta Lactamase Enzymes from Untreated Hospital Waste Water  [PDF]
Olivia Sochi Egbule
Advances in Microbiology (AiM) , 2016, DOI: 10.4236/aim.2016.67051
Abstract: Untreated Hospital wastewater piped into septic tanks contributes to the spread of antibiotic resistance in developing countries. This study was conducted to determine the resistant profile, and Extended Spectrum Beta-Lactamases (ESBLs) production in isolates from hospital waste water, of 2 hospitals in Delta State, Nigeria. A total of 147 organisms were isolated from 32 waste water samples. One hundred and twenty three isolates were Gram negative and 24 were Gram positive. Escherichia coli was the most prevalent in the two locations. Antimicrobial susceptibility by standard disk diffusion method was performed. All isolates were resistant to 4 or more antimicrobial agents. Out of the 123 Gram negative Bacteria, 33 were pan drug resistant and were selected for plasmid curing, DNA extraction and phenotypic detection of ESBL. Transfer of resistant by broth mating technique was performed. Plasmid curing and extraction result indicated that isolates carried resistance on the plasmid and harboured similar multiple high molecular weight plasmids of 23.13 kb and 9.4 kb. ESBL production was detected in 15.15%. Transfer of resistant genes between ESBL producing and non-ESBL producing isolates was observed. Incidence of ESBL in untreated hospital waste water has public health implications. Therefore establishment of treatment plants in our hospital is paramount in achieving sustainable health.
Effects of Tillage and Crop Residue Application on Soybean Nitrogen Fixation in a Tropical Ferralsol
Job Kihara,Christopher Martius,Andre Bationo,Paul L. G. Vlek
Agriculture , 2011, DOI: 10.3390/agriculture1010022
Abstract: This study was aimed at quantifying soybean ( Glycine max) nitrogen fixation under reduced tillage (RT) and conventional tillage (CT) in a tropical Ferralsol of the sub-humid zone of western Kenya, using the isotope 15N dilution method. Crop residue (CR) management was a superimposed treatment in soybean-maize rotation and intercropping systems. This study quantified N in abscised soybean leaves. Soybean-N derived from the atmosphere (%NDfA) ranged between 41–65%; it was higher ( P < 0.05) in RT (55.6%) than in CT (46.6%). Total fixed-N under ‘RT + CR’ was more than in the other treatments by at least 55% in intercropping and 34% in rotation system. Nitrogen fixed in soybean aboveground parts was 26–48 kg N ha ?1 with intercropping and 53–82 kg N ha ?1 with rotation. Seasonal litter fall contained about 15 kg N ha ?1, with 54% NDfA. Annual nitrogen balances with soybean and maize grain removed were better in RT (?9 to ?32 kg N ha ?1) than in CT (?40 to ?60 kg N ha ?1). Application of P increased nodule weight ( P < 0.05) by 3 to 16 times over the control. Soybean residues should be returned to the field after harvest to reduce soil N mining. We conclude that ‘RT + CR’ increases biological nitrogen fixation in soybean, over CT, and that phosphorus application is needed for better soybean nodulation in western Kenya.
A Sensor-Based Learning Algorithm for the Self-Organization of Robot Behavior
Frank Hesse,Georg Martius,Ralf Der,J. Michael Herrmann
Algorithms , 2009, DOI: 10.3390/a2010398
Abstract: Ideally, sensory information forms the only source of information to a robot. We consider an algorithm for the self-organization of a controller. At short time scales the controller is merely reactive but the parameter dynamics and the acquisition of knowledge by an internal model lead to seemingly purposeful behavior on longer time scales. As a paradigmatic example, we study the simulation of an underactuated snake-like robot. By interacting with the real physical system formed by the robotic hardware and the environment, the controller achieves a sensitive and body-specific actuation of the robot.
Pros and Cons of Adopting Water-Wise Approaches in the Lower Reaches of the Amu Darya: A Socio-Economic View
Maksud Bekchanov,John P.A. Lamers,Christopher Martius
Water , 2010, DOI: 10.3390/w2020200
Abstract: The increased frequency of water shortages parallel to growing demands for agricultural commodities in the lower reaches of the Amu Darya River, Central Asia, calls for improving the system-level water use efficiency, by using interventions at the field level. Despite the existence of various best practices of effective water use (defined here as “water-wise options”), they are not widely adopted by farmers owing to high initial costs of investment and lack of the necessary knowledge and skills of a new generation of farmers after the Soviet era. For assessing the potential of several water-wise techniques, key indicators such as water use reduction rate (WURR), economic efficiency (EE), and financial viability (FV) were combined with expert surveys. A SWOT procedure was used to analyze the (dis)advantages, opportunities and constraints of adopting the selected water-wise methods. Results show that the examined options have substantial potential for increasing water use efficiency under promising EE. The various recommendations aim at improving the sustainability of irrigation water use.
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