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Register a new userSecond Order Operators in the NASA Astrophysics Data System
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Second Order Operators (SOOs) are database functions which form secondary queries based on attributes of the objects returned in an initial query; they can provide powerful methods to investigate complex, multipartite information graphs. The NASA Astrophysics Data System (ADS) has implemented four SOOs, reviews, useful, trending, and similar which use the citations, references, downloads, and abstract text. This tutorial describes these operators in detail, both alone and in conjunction with other functions. It is intended for scientists and others who wish to make fuller use of the ADS database. Basic knowledge of the ADS is assumed.
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By combining data from the text, citation, and reference databases with data from the ADS readership logs we have been able to create Second Order Bibliometric Operators, a customizable class of collaborative filters which permits substantially improved accuracy in literature queries. Using the ADS usage logs along with membership statistics from the International Astronomical Union and data on the population and gross domestic product (GDP) we develop an accurate model for world-wide basic research where the number of scientists in a country is proportional to the GDP of that country, and the amount of basic research done by a country is proportional to the number of scientists in that country times that countrys per capita GDP. We introduce the concept of utility time to measure the impact of the ADS/URANIA and the electronic astronomical library on astronomical research. We find that in 2002 it amounted to the equivalent of 736 FTE researchers, or $250 Million, or the astronomical research done in France. Subject headings: digital libraries; bibliometrics; sociology of science; information retrieval
Astrophysics spans an enormous range of questions on scales from individual planets to the entire cosmos. To address the richness of 21st century astrophysics requires a corresponding richness of telescopes spanning all bands and all messengers. Much scientific benefit comes from having the multi-wavelength capability available at the same time. Most of these bands,or measurement sensitivities, require space-based missions. Historically, NASA has addressed this need for breadth with a small number of flagship-class missions and a larger number of Explorer missions. While the Explorer program continues to flourish, there is a large gap between Explorers and strategic missions. A fortunate combination of new astrophysics technologies with new, high capacity, low dollar-per-kg to orbit launchers, and new satellite buses allow for cheaper missions with capabilities approaching strategic mission levels. NASA has recognized these developments by calling for Probe-class mission ideas for mission studies, spanning most of the electromagnetic spectrum from GeV gamma-rays to the far infrared, and the new messengers of neutrinos and ultra-high energy cosmic rays. The key insight from the Probes exercise is that order-of-magnitude advances in science performance metrics are possible across the board for initial total cost estimates in the range 500M-1B dollars.
The past three decades have seen prodigious advances in astronomy and astrophysics. Beginning with the exploration of our solar system and continuing through the pioneering Explorers and Great Observatories of today, NASA missions have made essential contributions to these advances. This roadmap presents a science-driven 30-year vision for the future of NASA Astrophysics that builds on these achievements to address some of our most ancient and fundamental questions: Are we alone? How did we get here? How does the universe work? The search for the answers constitutes the Enduring Quests of this roadmap. Building on the priorities identified in New Worlds, New Horizons, we envision future science investigations laid out in three Eras, with each representing roughly ten years of mission development in a given field. The immediate Near-Term Era covers ongoing NASA-led activities and planned missions. This will be followed by the missions of the Formative Era, which will build on the preceding technological developments and scientific discoveries, with remarkable capabilities that will enable breakthroughs across the landscape of astrophysics. These will then lay the foundations for the Daring Visions of the Visionary Era: missions and explorations that will take us deep into unchartered scientific and technological terrain. The roadmap outlined herein will require the vision and wherewithal to undertake highly ambitious programs over the next 30 years. The discoveries that emerge will inspire generations of citizen scientists young and old, and inspire all of humanity for decades to come.
We consider properties of second-order operators $H = -sum^d_{i,j=1} partial_i , c_{ij} , partial_j$ on $Ri^d$ with bounded real symmetric measurable coefficients. We assume that $C = (c_{ij}) geq 0$ almost everywhere, but allow for the possibility that $C$ is singular. We associate with $H$ a canonical self-adjoint viscosity operator $H_0$ and examine properties of the viscosity semigroup $S^{(0)}$ generated by $H_0$. The semigroup extends to a positive contraction semigroup on the $L_p$-spaces with $p in [1,infty]$. We establish that it conserves probability, satisfies $L_2$~off-diagonal bounds and that the wave equation associated with $H_0$ has finite speed of propagation. Nevertheless $S^{(0)}$ is not always strictly positive because separation of the system can occur even for subelliptic operators. This demonstrates that subelliptic semigroups are not ergodic in general and their kernels are neither strictly positive nor Holder continuous. In particular one can construct examples for which both upper and lower Gaussian bounds fail even with coefficients in $C^{2-varepsilon}(Ri^d)$ with $varepsilon > 0$.
This study analyzes the differences between the category structure of the Universal Decimal Classification (UDC) system (which is one of the widely used library classification systems in Europe) and Wikipedia. In particular, we compare the emerging structure of category-links to the structure of classes in the UDC. With this comparison we would like to scrutinize the question of how do knowledge maps of the same domain differ when they are created socially (i.e. Wikipedia) as opposed to when they are created formally (UDC) using classificatio theory. As a case study, we focus on the category of Arts.
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