The Experts below are selected from a list of 32256 Experts worldwide ranked by ideXlab platform
Ian Von Hegner - One of the best experts on this subject based on the ideXlab platform.
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extremophiles a special or general case in the Search for extra terrestrial life
Extremophiles, 2020Co-Authors: Ian Von HegnerAbstract:Since time immemorial life has been viewed as fragile, yet over the past few decades it has been found that many extreme environments are inhabited by organisms known as extremophiles. Knowledge of their emergence, adaptability, and limitations seems to provide a guideline for the Search of extra-terrestrial life, since some extremophiles presumably can survive in extreme environments such as Mars, Europa, and Enceladus. Due to physico-chemical constraints, the first life necessarily came into existence at the lower limit of its conceivable complexity. Thus, the first life could not have been an extremophile; furthermore, since biological evolution occurs over time, then the dual knowledge regarding what specific extremophiles are capable of, and to the analogue environment on extreme worlds, will not be sufficient as a Search Criterion. This is because, even though an extremophile can live in an extreme environment here-and-now, its ancestor however could not live in that very same environment in the past, which means that no contemporary extremophiles exist in that environment. Furthermore, a theoretical framework should be able to predict whether extremophiles can be considered a special or general case in the galaxy. Thus, a question is raised: does Earth's continuous habitability represent an extreme or average value for planets? Thus, dependent on whether it is difficult or easy for worlds to maintain the habitability, the Search for extra-terrestrial life with a focus on extremophiles will either represent a Search for dying worlds, or a Search for special life on living worlds, focusing too narrowly on extreme values.
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extremophiles a special or general case in the Search for extra terrestrial life
viXra, 2019Co-Authors: Ian Von HegnerAbstract:Since time immemorial, life has been viewed as being fragile, yet over the past few decades it has been found that many extreme environments are inhabited by organisms known as extremophiles. Knowledge of their emergence, adaptability, and limitations seems to provide a guideline for the Search of extra-terrestrial life, since some extremophiles presumably can survive in extreme environments such as Mars, Europa, and Enceladus. Due to physico-chemical constraints, the first life necessarily came into existence at the lower limit of life’s conceivable complexity. Thus, the first life could not have been an extremophile, furthermore, since biological evolution occurs over time, then the dual knowledge regarding what specific extremophiles are capable of, and to the analogue environment on extreme worlds, will not be sufficient as a Search Criterion. This is because, even though an extremophile can live in an extreme environment here-and-now, its ancestor however could not live in that very same environment in the past, which means that no contemporary extremophiles exist in that environment. Furthermore, extremophiles are in many ways still special life in comparison to general life. A theoretical framework should be able to predict whether extremophiles can be considered a special or general case in the galaxy. Thus, a question is raised: does Earth’s continuous inhabitability represent an extreme or average value for planets? Thus, dependent on whether it is difficult or easy for worlds to maintain this inhabitability, the Search for extra-terrestrial life with a focus on extremophiles will either represent a Search after dying worlds, or a Search after special life on living worlds, where one focus too narrowly on extreme values.
Pramod K Varshney - One of the best experts on this subject based on the ideXlab platform.
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performance analysis and code design for minimum hamming distance fusion in wireless sensor networks
IEEE Transactions on Information Theory, 2007Co-Authors: Poning Chen, Tsangyi Wang, Pramod K VarshneyAbstract:Distributed classification fusion using error-correcting codes (DCFECC) has recently been proposed for wireless sensor networks operating in a harsh environment. It has been shown to have a considerably better capability against unexpected sensor faults than the optimal likelihood fusion. In this paper, we analyze the performance of a DCFECC code with minimum Hamming distance fusion. No assumption on identical distribution for local observations, as well as common marginal distribution for the additive noises of the wireless links, is made. In addition, sensors are allowed to employ their own local classification rules. Upper bounds on the probability of error that are valid for any finite number of sensors are derived based on large deviations technique. A necessary and sufficient condition under which the minimum Hamming distance fusion error vanishes as the number of sensors tends to infinity is also established. With the necessary and sufficient condition and the upper error bounds, the relation between the fault-tolerance capability of a DCFECC code and its pair-wise Hamming distances is characterized, and can be used together with any code Search Criterion in finding the code with the desired fault-tolerance capability. Based on the above results, we further propose a code Search Criterion of much less complexity than the minimum Hamming distance fusion error Criterion adopted earlier by the authors. This makes the code construction with acceptable fault-tolerance capability for a network with over a hundred of sensors practical. Simulation results show that the code determined based on the new Criterion of much less complexity performs almost identically to the best code that minimizes the minimum Hamming distance fusion error. Also simulated and discussed are the performance trends of the codes Searched based on the new simpler Criterion with respect to the network size and the number of hypotheses
Poning Chen - One of the best experts on this subject based on the ideXlab platform.
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performance analysis and code design for minimum hamming distance fusion in wireless sensor networks
IEEE Transactions on Information Theory, 2007Co-Authors: Poning Chen, Tsangyi Wang, Pramod K VarshneyAbstract:Distributed classification fusion using error-correcting codes (DCFECC) has recently been proposed for wireless sensor networks operating in a harsh environment. It has been shown to have a considerably better capability against unexpected sensor faults than the optimal likelihood fusion. In this paper, we analyze the performance of a DCFECC code with minimum Hamming distance fusion. No assumption on identical distribution for local observations, as well as common marginal distribution for the additive noises of the wireless links, is made. In addition, sensors are allowed to employ their own local classification rules. Upper bounds on the probability of error that are valid for any finite number of sensors are derived based on large deviations technique. A necessary and sufficient condition under which the minimum Hamming distance fusion error vanishes as the number of sensors tends to infinity is also established. With the necessary and sufficient condition and the upper error bounds, the relation between the fault-tolerance capability of a DCFECC code and its pair-wise Hamming distances is characterized, and can be used together with any code Search Criterion in finding the code with the desired fault-tolerance capability. Based on the above results, we further propose a code Search Criterion of much less complexity than the minimum Hamming distance fusion error Criterion adopted earlier by the authors. This makes the code construction with acceptable fault-tolerance capability for a network with over a hundred of sensors practical. Simulation results show that the code determined based on the new Criterion of much less complexity performs almost identically to the best code that minimizes the minimum Hamming distance fusion error. Also simulated and discussed are the performance trends of the codes Searched based on the new simpler Criterion with respect to the network size and the number of hypotheses
Erik W. Grafarend - One of the best experts on this subject based on the ideXlab platform.
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The total optimal Search Criterion in solving the mixed integer linear model with GNSS carrier phase observations
GPS Solutions, 2009Co-Authors: Jianqing Cai, Erik W. GrafarendAbstract:Existing algorithms for GPS ambiguity determination can be classified into three categories, i.e. ambiguity resolution in the measurement domain, the coordinate domain and the ambiguity domain. There are many techniques available for Searching the ambiguity domain, such as FARA (Frei and Beutler in Manuscr Geod 15(4):325–356, 1990), LSAST (Hatch in Proceedings of KIS’90, Banff, Canada, pp 299–308, 1990), the modified Cholesky decomposition method (Euler and Landau in Proceedings of the sixth international geodetic symposium on satellite positioning, Columbus, Ohio, pp 650–659, 1992), LAMBDA (Teunissen in Invited lecture, section IV theory and methodology, IAG general meeting, Beijing, China, 1993), FASF (Chen and Lachapelle in J Inst Navig 42(2):371–390, 1995) and modified LLL Algorithm (Grafarend in GPS Solut 4(2):31–44, 2000; Lou and Grafarend in Zeitschrift fur Vermessungswesen 3:203–210, 2003). The widely applied LAMBDA method is based on the Least Squares Ambiguity Search (LSAS) Criterion and employs an effective decorrelation technique in addition. G. Xu (J Glob Position Syst 1(2):121–131, 2002) proposed also a new general Criterion together with its equivalent objective function for ambiguity Searching that can be carried out in the coordinate domain, the ambiguity domain or both. Xu’s objective function differs from the LSAS function, leading to different numerical results. The cause of this difference is identified in this contribution and corrected. After correction, the Xu’s approach and the one implied in LAMBDA are identical. We have developed a total optimal Search Criterion for the mixed integer linear model resolving integer ambiguities in both coordinate and ambiguity domain, and derived the orthogonal decomposition of the objective function and the related minimum expressions algebraically and geometrically. This Criterion is verified with real GPS phase data. The theoretical and numerical results show that (1) the LSAS objective function can be derived from the total optimal Search Criterion with the constraint on the fixed integer ambiguity parameters, and (2) Xu’s derivation of the equivalent objective function was incorrect, leading to an incorrect Search procedure. The effects of the total optimal Criterion on GPS carrier phase data processing are discussed and its practical implementation is also proposed.
Ester Van Der Voet - One of the best experts on this subject based on the ideXlab platform.
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the rebound effect through industrial ecology s eyes a review of lca based studies
International Journal of Life Cycle Assessment, 2014Co-Authors: David Font Vivanco, Ester Van Der VoetAbstract:Industrial ecology academics have embraced with great interest the rebound effect principle operationalised within energy economics. By pursuing more comprehensive assessments, they applied tools such as life cycle assessment (LCA) to appraise the environmental consequences of the rebound effect. As a result, the mainstream rebound mechanism was broadened and a diversity of (sometimes inconsistent) definitions and approaches unveiled. To depict the state of play, a comprehensive literature review is needed. A literature review has been carried out by targeting scientific documents relevant for the integration of the rebound effect into LCA-based studies. The Search was conducted using two approaches: (1) via online catalogues using a defined Search Criterion and (2) via cross-citation analysis from the documents identified through the first approach. By analysing a total of 42 works yielded during our review, it was possible to bring together the various advantages of the life cycle perspective, as well as to identify the main inconsistencies and uninformed claims present in literature. Concretely, three main advantages have been identified and are discussed: (1) the representation of the rebound effect as a multi-dimensional, life cycle estimate, (2) the improvement of the technology explicitness and (3) the broadening of the consumption and production factors leading to the rebound effect. Also, inconsistencies on the definition and classification of the rebound effect have been found among studies. The review contributes a number of valuable insights to understand how the rebound effect has been treated within the industrial ecology and LCA fields. For instance, the conceptual and methodological refinements introduced by these fields represent a step forward from traditional viewpoints, making the study of the rebound effect more comprehensive and meaningful for environmental assessment and policy making. However, the broadened scope of this new approach unveiled some conceptual inconsistencies, which calls for a common framework. This framework would help the LCA community to consistently integrate the rebound effect as well as to create a common language with other disciplines, favouring learning and co-evolution. We believe that our findings can serve as a starting point in order to delineate such a common framework.