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Search Results: 1 - 10 of 7542 matches for " Claudio Ebel "
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Strong electric fields induced on a sharp stellar boundary
Igor N. Mishustin,Claudio Ebel,Walter Greiner
Physics , 2010, DOI: 10.1088/0954-3899/37/7/075201
Abstract: Due to a first order phase transition, a compact star may have a discontinuous distribution of baryon as well as electric charge densities, as e.g. at the surface of a strange quark star. The induced separation of positive and negative charges may lead to generation of supercritical electric fields in the vicinity of such a discontinuity. We study this effect within a relativistic Thomas-Fermi approximation and demonstrate that the strength of the electric field depends strongly on the degree of sharpness of the surface. The influence of strong electric fields on the stability of compact stars is discussed. It is demonstrated that stable configurations appear only when the counter-pressure of degenerate fermions is taken into consideration.
Terpenes from Marine-Derived Fungi
Rainer Ebel
Marine Drugs , 2010, DOI: 10.3390/md8082340
Abstract: Terpenes from marine-derived fungi show a pronounced degree of structural diversity, and due to their interesting biological and pharmacological properties many of them have aroused interest from synthetic chemists and the pharmaceutical industry alike. The aim of this paper is to give an overview of the structural diversity of terpenes from marine-derived fungi, highlighting individual examples of chemical structures and placing them in a context of other terpenes of fungal origin. Wherever possible, information regarding the biological activity is presented.
The Greenhouse Effect Does Exist!
Jochen Ebel
Physics , 2009,
Abstract: In particular, without the greenhouse effect, essential features of the atmospheric temperature profile as a function of height cannot be described, i.e., the existence of the tropopause above which we see an almost isothermal temperature curve, whereas beneath it the temperature curve is nearly adiabatic. The relationship between the greenhouse effect and observed temperature curve is explained and the paper by Gerlich and Tscheuschner [arXiv:0707.1161] critically analyzed. Gerlich and Tscheuschner called for this discussion in their paper.
Constructed Ponds and Small Stream Habitats: Hypothesized Interactions and Methods to Minimize Impacts  [PDF]
Jonathan D. Ebel, Winsor H. Lowe
Journal of Water Resource and Protection (JWARP) , 2013, DOI: 10.4236/jwarp.2013.57073
Abstract:

Extensive research has been conducted on how large impoundments and reservoirs affect hydrologic, geomorphologic and ecological processes in downstream ecosystems. Surprisingly, few studies have addressed the effects of smaller impoundments and constructed ponds. Pond construction has been considered an important tool for managers seeking to reduce sediment, nutrient and pollutant loads, and increase habitat heterogeneity in streams in an effort to conserve or enhance aquatic species diversity. However, we lack information on the interaction between ponds and stream habitats, which may compromise the efficacy of conservation efforts. The objective of this review is to outline possible physical and biological changes to stream ecosystems resulting from pond construction. Greater understanding of how ponds influence watershed processes at various spatial scales is crucial to evaluating the effects of constructed ponds on stream ecosystems.

SUSTAINABLE DEVELOPMENT: RESEARCH IN AN INTERCULTURAL CONTEXT
Roland Ebel,Susanne Kissmann
Ra Ximhai , 2011,
Abstract: Although there are various well argued definitions about what sustainable development means, there is a lack ofinformation about its meaning in the particular context of anintercultural university. Generally, sustainability is a goal which could never be obtained completely; sustainability is an ideal while sustainable development means all concrete humans attempts to obtain such goal. There is a direct link between human needs and sustainable development. Therefore, the popular concept of describing sustainable development as an absolutely valid objective for everybody is an illusion. It is based on the failed idea that humanity counts with universal needs. However, this is only correct for the most basic human needs. Except of these basic requirements, there is huge amplitude of very diverse human needs, especially in socio-economic and socio-cultural belongings. The more populated the community to be evaluated is, the more difficult becomes to determine common interests and therefore the more representative evaluation becomes. In other words, sustainable development must be seen as a subjective process – always depending on the persons defining their own needs. This is a factor which definitely complicates measuring; on the other hand it forces researches to take position: they have to declare which subjects have the privilege to determine such needs. In the case of the intercultural universities, the selection of the determinants of sustainable development requires a profound knowledge of the rural communities which usually - in an occidental point of view - do not show huge social-economic variety, but well count with a diverse spectrum of nuances within their habitants, especially valid for political and socio-cultural aspects. This is why it is necessary to establish well developed links between researchers and the population of these small rural communities – a process which requires an ambient of reliance resulting from deep interaction between researchers and local people. Therefore, in this context the only way to realize investigation is participatory research. The academic individual involved in this process has all the right to be exigent selecting the adequate community. Anyhow, this requires a well argued choice neglecting the researcher′s own interests. The academic should be becoming a tool of the rural population′s interests.
Co-evolutionary games on networks
Holger Ebel,Stefan Bornholdt
Physics , 2002, DOI: 10.1103/PhysRevE.66.056118
Abstract: We study agents on a network playing an iterated Prisoner's dilemma against their neighbors. The resulting spatially extended co-evolutionary game exhibits stationary states which are Nash equilibria. After perturbation of these equilibria, avalanches of mutations reestablish a stationary state. Scale-free avalanche distributions are observed that are in accordance with calculations from the Nash equilibria and a confined branching process. The transition from subcritical to critical avalanche dynamics can be traced to a change in the degeneracy of the cooperative macrostate and is observed for many variants of this game.
Evolutionary games and the emergence of complex networks
Holger Ebel,Stefan Bornholdt
Physics , 2002,
Abstract: The emergence of complex networks from evolutionary games is studied occurring when agents are allowed to switch interaction partners. For this purpose a coevolutionary iterated Prisoner's Dilemma game is defined on a random network with agents as nodes and games along the links. The agents change their neighborhoods to improve their payoff. The system relaxes to stationary states corresponding to cooperative Nash equilibria with the additional property that no agent can improve its payoff by changing its neighborhood. Small perturbations of the system lead to avalanches of strategy readjustments reestablishing equilibrium. As a result of the dynamics, the network of interactions develops non-trivial topological properties as a broad degree distribution suggesting scale-free behavior, small-world characteristics, and assortative mixing.
World-Wide Web scaling exponent from Simon's 1955 model
Stefan Bornholdt,Holger Ebel
Physics , 2000, DOI: 10.1103/PhysRevE.64.035104
Abstract: Recently, statistical properties of the World-Wide Web have attracted considerable attention when self-similar regimes have been observed in the scaling of its link structure. Here we recall a classical model for general scaling phenomena and argue that it offers an explanation for the World-Wide Web's scaling exponent when combined with a recent measurement of internet growth.
Drugs from the Sea - Opportunities and Obstacles
Peter Proksch,RuAngelie Edrada-Ebel,Rainer Ebel
Marine Drugs , 2003, DOI: 10.3390/md101005
Abstract: The supply problem with regard to drug development and sustainable production lies in the limited amounts of biomass of most marine invertebrates available from wild stocks. Thus, most pharmacologically active marine natural products can only be isolated in minute yields. Total synthesis of pharmacologically active natural products has been successfully established but is in many cases economically not feasible due to the complexity of the molecular structures and the low yields. To solve the pressing supply issue in marine drug discovery, other strategies appear to be more promising. One of these is mariculture which has successfully been established with the bryozoan Bugula neritina (the source of the bryostatins) and the tunicate Ecteinascidia turbinata (the source of ET-743). Another strategy involves partial synthesis from precursors which are biotechnologically available. An example is ET-743 that can be partially synthesized from safracin B which is a metabolite of Pseudomonas fluorescens. There have been many examples of striking structural similarities between natural products obtained from marine invertebrates and those of microbial origin which suggests that microorganisms living in their invertebrate hosts could be the actual producers of these secondary metabolites. With regard to sustainable biotechnological production of pharmacologically important metabolites from marine invertebrates and their “endosymbionts”, a more advanced strategy is to focus on cloning and expression of the respective key biosynthetic gene clusters. This molecular biological approach will open up new avenues for biotechnological production of drugs or drug candidates from the sea.
Semarkona: Lessons for chondrule and chondrite formation
Alexander Hubbard,Denton S. Ebel
Physics , 2014, DOI: 10.1016/j.icarus.2014.09.025
Abstract: We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.
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