1,721,379 research outputs found
Geologic constraints on the chaotic diffusion of the Solar System
No full textThe correlation of Earth's orbital parameters with climatic variations has been used to generate astronomically calibrated geologic time scales of high accuracy. However, because of the chaotic behavior of the solar system, two initially close calculations of Earth's orbit diverge exponentially and have a large uncertainty beyond several million years in the past. This chaotic behavior is related to a combination of angles in the precession motion of the orbits of Earth and Mars, θ, which currently is in resonance. How long θ stays in libration critically depends on the dynamical model and initial conditions for the solar system. Here we show that geologic data can differentiate between astronomical solutions that do and do not exhibit a transition in θ since 40 Ma and that sediments can thus provide a history for the evolution of θ. We find that the chaotic transition of θ from libration to circulation did not occur after ca. 30 Ma. We can thus constrain the chaotic diffusion of the solar system in the past, and our results provide new and challenging constraints for astronomical models
Efficiency enhanced and harmonic suppressed differential VCO with novel buffer scheme using transformers for IEEE 802.11a
No full textThe measure of chaos by the numerical analysis of the fundamental frequencies. Application to the standard mapping
No full textA 60-GHz push-push InGaPHBT VCO with dynamic frequency divider
No full textWe present a 60-GHz push-push voltage-controlled oscillator (VCO) with dynamic frequency divider, which is implemented in an InGaP/GaAs heterojunction bipolar transistor technology. A common-base inductive feedback topology is used in the push-push VCO, which generates a pair of 30 GHz differential outputs and a single-ended 60 GHz push-push output. The 30 GHz differential outputs are followed by the proposed dynamic frequency divider. The proposed dynamic frequency divider incorporates active loads with inductive peaking to achieve the higher bandwidth. The maximum operating frequency of the divider was found to be much higher than f(T)/ 2 of transistor. To the best of our knowledge, this is the first report demonstrating the extended bandwidth performance of the dynamic frequency divider with active loads and inductive peaking.This work
was supported by the Agency for Defense Development, Korea, through the
Radio Detection Research Center, Korea Advanced Institute of Science and
Technology
Orbital tuning and re-tuning: art and science (abstract of paper presented at AGU Fall Meeting, San Francisco, 6-10 Dec 2002)
No full textIt is difficult to imagine a situation wherein (a) a geological record built up at a constant rate or (b) a geological deposit built up at a rate that was independent of climate. In addition all geological proxies for climate parameters are subject to both observational noise, and variability in their relationship with climate. Hence considerable judgement is needed in first selecting geological records that will be amenable to "tuning" to a record of changing distribution of solar insolation as calculated by an astronomer, and then in carrying out the operation. Tuning a geological record to an incorrect insolation record, or to the wrong time interval in a correct insolation record, or to a simplified "caricature" of the true insolation record can all provide considerable insights in some circumstances. Nevertheless from the point of view of the geological time scale it is important to carry out the procedure correctly, with the best available astronomical data. It is also important that one can utilize the tuning in order to verify the astronomical calculations. We have recently re-tuned a number of records on the basis of the new calculations discussed by Laskar (2001). Astronomical Solutions for Paleoclimates Studies. Eos Trans. AGU, 82(47), Fall Meet. Suppl. Abstract U11A-01. In the Pliocene re-tuning is generally straightforward and uninformative because the astronomical changes are small and the tuning is so unambiguous that little judgement is required. In the Early Miocene and Oligocene the situation is more interesting. During this time available data suggests that the climatic variability is dominated by 41-ky obliquity cycles but attaining a correct tuning requires identification of the weaker precession signal and making use of the longer-term (100-ky and 400-ky) eccentricity modulation. A surprising aspect of the tuning published by us in 1999 was that between 20Ma and 24Ma there was long-term (about 1.1My) modulation of the obliquity signal that matched that predicted; this match broke down in the earlier part of the record.Re-tuning the records for this interval required a slight "stretching" to take account of the fact that 400-ky eccentricity maxima in the Oligocene are around 100ky older than in the previous astronomical solution. This obviously required the addition of a very small number of additional obliquity cycles; thus it was necessary to make a judgement anew regarding the interpretation of each cycle. This in turn enables us to assess the degree of robustness of the tuning. The fact that in the new tuning the amplitude modulation of the obliquity signal in the 20Ma to 24Ma time window still matches the calculated modulation is not surprising since in this time-window the amplitude envelope of obliquity moved back in age to the same extent as the eccentricity signal, as a result of the new calculations. However, the fact that the re-tuned data now demonstrates an amplitude modulation of the obliquity signal that remains in phase with the calculated signal back to 30Ma, despite the fact that the re-tuning did not entail significant re-interpretation of the record, strongly suggests both that the new solution represents an "improvement" and that the coherence with this long-term modulation constitutes a very strong independent validation of this approach to geological time scale development
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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