10,000 publications from this institution
We present results of optical follow-up observations of ultraluminous X-ray source (ULX) candidates. A published ROSAT catalog of 87 ULX candidates named 19 of these as having optical counterparts in Digitized Sky Survey (DSS) images. Using Keck optical spectroscopy, we classify 16 ULX candidates in this subset as well as one other ULX candidate from the catalog with a counterpart in the DSS. This is one of the largest sets of optical identifications of such objects thus far. Fifteen are background active galactic nuclei (AGNs); two are foreground stars in our Galaxy. These findings are consistent with background and foreground object expectations, as derived from log N - log S relations. The logarithmic X-ray to optical flux ratios of these objects are also typical of background and foreground objects. Finally, we discuss the nature of ULX candidates outside the optical extent of their apparent host galaxies.
In 1974, Hawking showed 1 that Black Holes can evaporate by the emission of low temperature thermal radiation, now named Hawking Radiation. Shortly thereafter, a closely related effect called Unruh Radiation became apparent. According to Unruh 2 and Davies 2 , observers of the electromagnetic field in an accelerating reference frame should see thermal radiation at a temperature T: where a is the acceleration relative to an inertial frame, c is the speed of light and ħ and K are Planck's and Boltzmann's constant respectively. In a frame accelerating at g= 980 cm/sec 2 , equivalent to the acceleration experienced at the earth's surface 3 , this thermal radiation is at a temperature of only 4× 10 −20 °K. Therefore, physicists hoping to observe this radiation, have sought out systems being subjected to extreme acceleration. For example, J. S. Bell has suggested 4 that the spin depolarization of electrons accelerating around a synchrotron storage ring may be interpreted as being due to such radiation.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation of the first stable formylsilane, (Me3Si)3SiCHO, from a zirconium .eta.2-silaacyl complexFrederick H. Elsner, Hee Gweon. Woo, and T. Don. TilleyCite this: J. Am. Chem. Soc. 1988, 110, 1, 313–314Publication Date (Print):January 1, 1988Publication History Published online1 May 2002Published inissue 1 January 1988https://doi.org/10.1021/ja00209a063RIGHTS & PERMISSIONSArticle Views337Altmetric-Citations49LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (305 KB) Get e-Alerts Get e-Alerts
A set of catalytic, intermolecular hydroaminations of strained bicyclic olefins and dienes are reported that occur in both high yield and high enantioselectivity. These reactions occur with a catalyst generated from [Ir(cyclooctene)Cl]2, sterically hindered and electron-rich derivatives of the Segphos and BIPHEP family of ligands, and a soluble base. This system catalyzes the addition of various anilines to norbornene, norbornadiene, and other bicyclic olefins. The products from addition of p-anisidine can be transformed to BOC-protected norbornylamine and to substituted cyclopentanes in nearly enantiopure form. Mechanistic studies show that addition of aniline-d2 occurs in a syn fashion and suggest that the catalytic cycle comprises oxidative addition of aniline to form a bis-anilide hydride complex, followed by migratory insertion of olefin and reductive elimination of product in a series of steps involving iridium complexes containing ancillary bisphosphine and arylamide ligands.
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The completion of the Arabidopsis sequence will be followed by a new ten-year project that will determine the function of all angiosperm genes. Funding for the U.S. component of this multinational project will originate from a new initiative from the U.S. National Science Foundation called the 2010 Project. Progress toward completion of this ambitious project will necessitate significant changes in how the plant biology community selects and approaches research objectives. The plan envisions that the project will facilitate the development of a computational model of a virtual plant that will allow predictive queries about basic mechanisms underlying plant growth and development.
Most work, to date, on analysis of earthquake effects on dams treats a dam and a reservoir as two uncoupled systems. The importance of interaction between the two systems is investigated. The analysis is restricted to dams with a vertical upstream face. This idealization is considered to be appropriate for concrete gravity dams. It is assumed that the response of the dam can be satisfactorily represented by the fundamental mode effects. Expressions are derived for the complex frequency responses of the coupled system. For the coupled system, the complex frequency responses, the fundamental period of vibration, and responses to stationary white noise excitation are numerically evaluated for a wide range of the basic parameters: (1) normalized excitation frequency; and (2) the ratio of the fundamental natural frequencies of reservoir and dam separately. The results demonstrate that the interaction effects have considerable influence on the behavior of the system. The analysis of the coupled system is greatly simplified if compressibility of water is neglected. The earthquake response can then be determined as the response of a modified one-degree of freedom system. It is demonstrated that the compressibility of water can be ignored if the dam is flexible enough compared to the reservoir.
Since the invention of packet switching networks, routing is an important, if not the most fundamental, component of networking. Over decades, both academia and industry put huge efforts to improve routing in various scenarios. However, with the explosive growth of Internet, wide adoption for critical business and services, and new environments like data center networks, routing has more difficulties to meet the increasingly stringent requirements. We examine current routing schemes and discover that the problem is more fundamental, because they rely on many assumptions and trade-offs that are no longer applicable for today's networks. Believing that more radical changes are necessary to effectively address the challenge, we start the design process from scratch, with assumptions, trade-offs and design philosophies which better reflect the networks of today and tomorrow. The outcome of the design process is a unified routing framework which utilizes directed acyclic graph (DAG) as routing topology. And we name it Routing Along DAGs (RAD). RAD separates route optimization and connectivity maintenance, handles both failures and congestions, and recovers fast and locally. We explain the details of RAD design and test its performance on various real world topologies. Then we improve RAD to achieve even better performance and cover more use cases. With these extensions, RAD becomes both complete and practical.
