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A fundamental problem that confronts peer-to-peer applications is to efficiently locate the node that stores a particular data item. This paper presents Chord, a distributed lookup protocol that addresses this problem. Chord provides support for just one operation: given a key, it maps the key onto a node. Data location can be easily implemented on top of Chord by associating a key with each data item, and storing the key/data item pair at the node to which the key maps. Chord adapts efficiently as nodes join and leave the system, and can answer queries even if the system is continuously changing. Results from theoretical analysis, simulations, and experiments show that Chord is scalable, with communication cost and the state maintained by each node scaling logarithmically with the number of Chord nodes.
We analyze the dynamics of part motion for a novel type of planar parts feeder consisting of a longitudinally vibrating flat plate and a part placed on its surface. For each vibration cycle, the plate's velocity is held positive (forward motion) for a longer time than it is held negative (backward motion). This type of asymmetric vibration combined with the nonlinear nature of Coulomb friction causes the part to accelerate along a straight line to a terminal velocity called the "feed rate". The average force exerted by the plate on the part is shown to be proportional to the latter's deviation from the feed rate. In other words, the part behaves as if it were immersed in a forward moving viscous fluid. Expressions for the feed rate and viscosity constants are derived with respect to various physical and control parameters. Rigid-body dynamic simulation results are shown to be in good agreement with the analysis.
Abstract A new expression system containing the Salmonella enterica prpBCDE promoter (P prpB ) responsible for expression of the propionate catabolic genes ( prp BCDE ) and prpR encoding the positive regulator of this promoter has been developed and tested. The main features of the expression system compared to those based on the bacteriophage T7 promoter are low background expression and high induced expression in Escherichia coli strains BL21, BL21(DE3), MG1655, and W3110. In addition, propionate is an inexpensive, simple‐to‐use, nontoxic inducer that is attractive for large‐scale protein production. Hence, this new system is highly complementary to the widely used T7 promoter‐driven expression systems. © 2005 Wiley Periodicals, Inc.
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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTemperature, a Simple and Efficient Tool for the Control of Pore Size Distribution in Macroporous PolymersFrantisek Svec and Jean M. J. FrechetCite this: Macromolecules 1995, 28, 22, 7580–7582Publication Date (Print):October 1, 1995Publication History Published online1 May 2002Published inissue 1 October 1995https://pubs.acs.org/doi/10.1021/ma00126a044https://doi.org/10.1021/ma00126a044research-articleACS PublicationsRequest reuse permissionsArticle Views1280Altmetric-Citations205LEARN 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 InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
view Abstract Citations (186) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of an Extremely Low Luminosity Seyfert 1 Nucleus in the Dwarf Galaxy NGC 4395 Filippenko, Alexei V. ; Sargent, Wallace L. W. Abstract We have discovered a Seyfert 1 nucleus in the center of the nearby (d ~ 2.6 Mpc), late-type (Sd III-IV), dwarf galaxy NGC 4395. Such nuclei have never been seen in galaxies of this kind. The optical spectrum reveals very strong, narrow emission lines covering a wide range of ionization from [O I] to [Fe X]. Weak wings having FWZI ~ 4000-8000 km s^-1^ are visible in the permitted-line profiles, including He II λ4686. H II regions in the rest of the galaxy have normal spectra. The luminosity of the broad Hα emission is ~ 1.2 x 10^38^ ergs s^-1^, a factor of 10 fainter than in the nucleus of M81; thus, NGC 4395 contains the least luminous known Seyfert 1 nucleus. The equivalent width of broad Hα (270 A) is similar to that in normal, luminous Seyfert 1 galaxies. The optical continuum is featureless, and has M_B_ ~ 9.8 mag--less luminous than the brightest known supergiant stars. It is possible that the nuclear properties of NGC 4395 can be explained in terms of stellar phenomena, rather than by accretion onto a black hole. Publication: The Astrophysical Journal Pub Date: July 1989 DOI: 10.1086/185472 Bibcode: 1989ApJ...342L..11F Keywords: Dwarf Galaxies; Galactic Nuclei; Light (Visible Radiation); Seyfert Galaxies; Stellar Luminosity; Emission Spectra; H Alpha Line; H Ii Regions; Line Spectra; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4395; GALAXIES: NUCLEI; GALAXIES: SEYFERT; LINE PROFILES; SPECTROPHOTOMETRY full text sources ADS | data products SIMBAD (2) NED (2)
This paper provides a review on the optimal design of photonic bandgap structures by inverse problem techniques. An overview of inverse problems techniques is given, with a special focus on topology design methods. A review of first applications of inverse problems techniques to photonic bandgap structures and waveguides is given, as well as some model problems, which provide a deeper insight into the structure of the optimal design problems.
The location and bonding of atoms and molecules on surfaces is of great interest to surface chemists and to those interested in the application of surfaces through exploitation of their unique properties. These properties include chemical properties that give rise to selective adsorption and heterogeneous catalysis; mechanical properties that control adhesion, fric tion, slide, or fracture; electrical properties utilized in microelectronic circuitry and xerography; magnetic properties used in information storage on tape or disk drives; and optical properties that give rise to nonlinear effects such as second harmonic and sum frequency generation. During the past 25 years, over 50 new techniques have been developed that permit the investigation of surfaces on the molecular level (l). The ability to study surfaces with increased time and spatial resolution (and energy resolution, when applicable) controls the development of many surface technologies. The contributions of science push and surface technology pull have resulted in an exponential growth in the field of surface science and pro pelled it among the frontier fields of physical chemistry. Several new surface science techniques permit quantitative deter-
Nanoporous, hypercrosslinked polypyrroles with surface areas of up to 720 m2 g(-1) have been prepared; their pore sizes and gas adsorption selectivities were controlled by varying the size of the crosslinking units.
