Evaluating DHT-Based Service Placement for Stream Based Overlays

Stream-based overlay networks (SBONs) are one approach to implementing large-scale stream processing systems. A fundamental consideration in an SBON is that of service placement, which determines the physical location of in-network processing services or operators, in such a way that network resources are used efficiently. Service placement consists of two components: node discovery, which selects a candidate set of nodes on which services might be placed, and node selection, which chooses the particular node to host a service. By viewing the placement problem as the composition of these two processes we can trade-off quality and efficiency between them. A bad discovery scheme can yield a good placement, but at the cost of an expensive selection mechanism. Recent work on operator placement [3, 9] proposes to leverage routing paths in a distributed hash table (DHT) to obtain a set of candidate nodes for service placement. We evaluate the appropriateness of using DHT routing paths for service placement in an SBON, when aiming to minimize network usage. For this, we consider two DHT-based algorithms for node discovery, which use either the union or intersection of DHT routing paths in the SBON, and compare their performance to other techniques. We show that current DHT-based schemes are actually rather poor node discovery algorithms, when minimizing network utilization. An efficient DHT may not traverse enough hops to obtain a sufficiently large candidate set for placement. The union of DHT routes may result in a low-quality set of discovered nodes that requires an expensive node selection algorithm. Finally, the intersection of DHT routes relies on route convergence, which prevents the placement of services with a large fan-in.Engineering and Applied Science

Polls and the political process: the use of opinion polls by political parties and mass media organizations in European post‐communist societies (1990–95)

Opinion polling occupies a significant role within the political process of most liberal-capitalist societies, where it is used by governments, parties and the mass media alike. This paper examines the extent to which polls are used for the same purposes in the post-communist countries of Central and Eastern Europe, and in particular, for bringing political elites and citizens together. It argues that these political elites are more concerned with using opinion polls for gaining competitive advantage over their rivals and for reaffirming their political power, than for devolving political power to citizens and improving the general processes of democratization

Integrated Urban Sensing: A Geo-sensor Network for Public Health Monitoring and Beyond

Pervasive environmental monitoring implies a wide range of technical, but also socio-political challenges, and this applies especially to the sensitive context of the city. In this paper, we elucidate issues for bringing out pervasive urban sensor networks and associated concerns relating to fine-grained information provision. We present the Common Scents project, which is based on the Live Geography approach, and show how it can overcome these challenges. As opposed to hitherto sensing networks, which are mostly built up in monolithic and closed systems, the Common Scents approach aims to establish an open, standards based and modular infrastructure. This ensures interoperability, portability and flexibility, which are crucial prerequisites for pervasive urban sensing. The implementation – a real-time data integration and analysis system for air quality assessment – has been realised on top of the CitySense sensor network in the City of Cambridge, MA US together with the city’s Public Health Department responding to concrete needs of the city and its inhabitants. The second pilot using mobile sensors mounted on bicycles has been deployed in Copenhagen, Denmark. Preliminary results show highly fine-grained variability of pollutant dispersion in urban environments.Singapore-MIT Alliance. Center for Environmental Sensing and MonitoringSingapore-MIT Alliance for Research and Technology CenterEuropean Commission (FP7 GENESIS project)Bundesministerium für Wissenschaft und ForschungResearch Studio iSPAC

X-ray confirmation of the intermediate polar HTCam

We report on the first pointed X-ray observations with XMM-Newton and RXTE satellites of the X-ray source RXJ0757.0+6306 = HT Cam. We detect a strong 515 s X-ray modulation confirming the optical photometric period found in 1998, which definitively assigns this source to the intermediate polar class of magnetic cataclysmic variables. The lack of orbital sidebands in the X-rays indicates that the X-ray period is the spin period of the accreting white dwarf. Simultaneous ultraviolet and optical B-band photometry acquired with the XMM-Newton Optical Monitor and coordinated optical UBVRI photometric data acquired at the Nordic Optical Telescope (La Palma) show that the optical pulse is in phase with the X-rays and hence originates in the magnetically-confined accretion flow. The lack of ultraviolet spin modulation suggests that accretion-induced heating on the white dwarf surface is not important in this source. Spectral analyses of XMM-Newton EPIC and RGS data show that HTCam has a multi-temperature spectrum and, contrary to most intermediate polars, it does not suffer from strong absorption. With its 86 min orbital period, HTCam is the third confirmed system of this class below the 2–3 h period gap accreting at a low rate

Mobile network performance from user devices: A longitudinal, multidimensional analysis

Abstract. In the cellular environment, operators, researchers and end users have poor visibility into network performance for devices. Improving visibility is challenging because this performance depends factors that include carrier, access technology, signal strength, geographic location and time. Addressing this requires longitudinal, continuous and large-scale measurements from a diverse set of mobile devices and networks. This paper takes a first look at cellular network performance from this perspective, using 17 months of data collected from devices located throughout the world. We show that (i) there is significant variance in key performance metrics both within and across carriers; (ii) this variance is at best only partially explained by regional and time-of-day patterns; (iii) the stability of network performance varies substantially among carriers. Further, we use the dataset to diagnose the causes behind observed performance problems and identify additional measurements that will improve our ability to reason about mobile network behavior

A Search for Hierarchical Triples using Kepler Eclipse Timing

We present the first results of a Kepler survey of 41 eclipsing binaries that we undertook to search for third star companions. Such tertiaries will periodically alter the eclipse timings through light travel time and dynamical effects. We discuss the prevalence of starspots and pulsation among these binaries and how these phenomena influence the eclipse times. There is no evidence of short period companions (P < 700 d) among this sample, but we do find evidence for long term timing variations in 14 targets (34%). We argue that this finding is consistent with the presence of tertiary companions among a significant fraction of the targets, especially if many have orbits measured in decades. This result supports the idea that the formation of close binaries involves the deposition of angular momentum into the orbital motion of a third star.Comment: AJ, in press, 104 pages, 2 figure sets plus 1 regular figur

Camera Traps Confirm the Presence of the White-naped Mangabey Cercocebus lunulatus in Cape Three Points Forest Reserve, Western Ghana

The white-naped mangabey Cercocebus lunulatus is severely threatened by logging, mining, and hunting. In the last decade, wild populations have been confirmed in just three forested areas in Ghana and a handful of sites in neighboring Côte d’Ivoire and Burkina Faso. Sightings of this species were recently reported in a fourth area in Ghana, the Cape Three Points Forest Reserve, a forest patch in western Ghana, 60 km from the nearest recorded wild population, which is in the Ankasa Conservation Area. We deployed 14 camera traps across 21 different locations throughout the reserve, with the intention of confirming the presence of this species. Images of the white-naped mangabey were captured at four locations, consolidating recent evidence for a fourth sub-population of this species in Ghana and providing only the second-ever photograph of a wild member of this species in the country. We observed evidence of numerous illegal anthropogenic activities in the reserve, which threaten these mangabeys, and we make recommendations for the protection of the reserve, essential for the conservation of this highly endangered species

The white dwarf revealed in the intermediate polar V709 Cassiopeiae

Results are presented from the first detailed spectroscopic observations of the recently identified intermediate polar RXJ0028.8+5917/V709 Cas. The study of the emission line radial velocities allows us to remove the uncertainties on the different aliases of the orbital period and a best value is found at (0.2225 +/- 0.0002) day. It is also found that the system shows significant EW~ (2-4)A, broad absorptions affecting the Balmer lines from Hdelta to Hbeta. These broad absorptions are interpreted as the contribution of an underlying white dwarf atmosphere. The characteristics of the absorptions are found to be consistent with a DA log(g) = 8 white dwarf at a temperature of ~ 23 000 K, contributing ~ 17 % (at 4500 A) to the overall flux. This is the first direct detection of a white dwarf in an intermediate polar system. The absence of significant Zeeman splitting indicates a magnetic field lower than 10 MG, confirming that, at least in some cases, intermediate polars have weaker fields than polars. Different possibilities are discussed to explain the substantial contribution of the white dwarf to the overall flux.Comment: 6 pages, 4 figures, 3 tables. accepted in Astronomy & Astrophysic

The Grizzly, September 21, 1993

Israel and PLO Reach Peace Agreement • The Quilt: To Remember, To Educate, To Celebrate • Russian TV Crew Filming at Ursinus • New Reimert Policies for \u2793-\u2794 • Jurassic Park: It\u27s Only a Movie • Bernie Bernie Headflap Wins the Battle Again! • The Newly Roomie Game • A Unique Affair Awaits Us: Javapalooza \u2793 to Entertain Ursinus • Ursinus Needs AIDS Policy • More Than a Number • The New Wismer? Or a Police State? • Field Hockey Struggles Early • Men\u27s X-Country Starts off 2-0 • Lady Bears Search for Consistencyhttps://digitalcommons.ursinus.edu/grizzlynews/1318/thumbnail.jp