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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
STEPS TOWARDS CRYPTANALYSIS OF CHAOTIC ACTIVE/PASSIVE DECOMPOSITION ENCRYPTION SCHEMES USING AVERAGE DYNAMICS ESTIMATION
No full textWe analyze the security of encryption schemes based on chaos synchronization and active/passive decomposition. The security is quantified by the number of transmitted samples that has to be acquired in order to reconstruct the transmitted message with an accuracy that may compromise the transmitted information. The dynamics is estimated as the average of dynamics of the observed data within a small neighborhood of the time delay embedding phase space. We examine the factors that affect the choice of embedding dimension and neighborhood size by the unauthorized receiver. We show that the security can be enhanced by mixing a large randomly modulated message component with a smaller chaotic component while keeping the message modulation fine grained. This result is in contrast to the common approach to ensure security by adding a small message component to a larger chaotic component. Further, we show that even when a low dimensional chaotic map is used, then the unauthorized receiver is required to use a reconstruction embedding dimension that can be made large by using chaotic dynamics with large conditional negative Lyapunov exponent. This result allows one to avoid the common restriction to use only high dimensional chaotic dynamics to maintain security. We also suggest guidelines for the design of efficient active passive/passive decomposition schemes in order to maintain low transmission power, fast synchronization, and yet preserve security. We demonstrate our analysis using a relatively simple encryption scheme based on a one-dimensional chaotic tent map
Gene Conversion Facilitates Adaptive Evolution on Rugged Fitness Landscapes
No full textAbstract
An important question in evolutionary theory is how adaptation might be hindered on a rugged fitness landscape in the presence of strong selection that..
Gene conversion is a ubiquitous phenomenon that leads to the exchange of genetic information between homologous DNA regions and maintains coevolving multi-gene families in most prokaryotic and eukaryotic organisms. In this paper, we study its implications for the evolution of a single functional gene with a silenced duplicate, using two different models of evolution on rugged fitness landscapes. Our analytical and numerical results show that, by helping to circumvent valleys of low fitness, gene conversion with a passive duplicate gene can cause a significant speedup of adaptation, which depends nontrivially on the frequency of gene conversion and the structure of the landscape. We find that stochastic effects due to finite population sizes further increase the likelihood of exploiting this evolutionary pathway. A universal feature appearing in both deterministic and stochastic analysis of our models is the existence of an optimal gene conversion rate, which maximizes the speed of adaptation. Our results reveal the potential for duplicate genes to act as a “scratch paper” that frees evolution from being limited to strictly beneficial mutations in strongly selective environments.</jats:p
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