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831
Contention in Shared Memory Algorithms
, 1993
"... Most complexitymeasures for concurrent algorithms for asynchronous sharedmemory architectures focus on process steps and memory consumption. In practice, however, performance of multiprocessor algorithms is heavily influenced by contention, the extent to which processes access the same location at t ..."
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Cited by 63 (1 self)
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Most complexitymeasures for concurrent algorithms for asynchronous sharedmemory architectures focus on process steps and memory consumption. In practice, however, performance of multiprocessor algorithms is heavily influenced by contention, the extent to which processes access the same location at the same time. Nevertheless, even though contention is one of the principal considerations affecting the performance of real algorithms on real multiprocessors, there are no formal tools for analyzing the contention of asynchronous shared-memory algorithms. This paper introduces the first formal complexity model for contention in multiprocessors. We focus on the standard multiprocessor architecture in which n asynchronous processes communicate by applying read, write, and read-modify-write operations to a shared memory. We use our model to derive two kinds of results: (1) lower bounds on contention for well known basic problems such as agreement and mutual exclusion, and (2) trade-offs betwe...
Making, probing and understanding Bose-Einstein condensates
- PROCEEDINGS OF THE INTERNATIONAL SCHOOL OF PHYSICS ”ENRICO FERMI”, COURSE CXL, EDITED BY M. INGUSCIO, S. STRINGARI AND C.E. WIEMAN (IOS
, 1999
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Timing and Climatic Consequences of the Opening of Drake Passage
, 2010
"... This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following ..."
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Cited by 34 (1 self)
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This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following the guidelines here. The following resources related to this article are available online at www.sciencemag.org (this information is current as of July 27, 2010): Updated information and services, including high-resolution figures, can be found in the online version of this article at:
Very High Resolution Simulation of Compressible Turbulence on the IBM-SP System
, 1999
"... Understanding turbulence and mix in compressible flows is of fundamental importance to real-world applications such as chemical combustion and supernova evolution. The ability to run in three dimensions and at very high resolution is required for the simulation to accurately represent the interactio ..."
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Cited by 33 (9 self)
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Understanding turbulence and mix in compressible flows is of fundamental importance to real-world applications such as chemical combustion and supernova evolution. The ability to run in three dimensions and at very high resolution is required for the simulation to accurately represent the interaction of the various length scales, and consequently, the reactivity of the intermixing species. Toward this end, we have carried out a very high resolution (over 8 billion zones) 3-D simulation of the Richtmyer-Meshkov instability and turbulent mixing on the IBM Sustained Stewardship TeraOp (SST) system, developed under the auspices of the Department of Energy (DOE) Accelerated Strategic Computing Initiative (ASCI) and located at Lawrence Livermore National Laboratory. We have also undertaken an even higher resolution proof-of-principle calculation (over 24 billion zones) on 5832 processors of the IBM, which executed for over an hour at a sustained rate of 1.05 Top/s, as well as a sh...
Methods for realistic landscape imaging
, 1993
"... There are five fundamental concerns in the synthesis of realistic imagery of fractal landscapes: 1) convincing geometric models of terrain; 2) efficient algorithms for rendering those potentially-large terrain models; 3) atmospheric effects, or aerial perspective, to provide a sense of scale; 4) sur ..."
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Cited by 23 (0 self)
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There are five fundamental concerns in the synthesis of realistic imagery of fractal landscapes: 1) convincing geometric models of terrain; 2) efficient algorithms for rendering those potentially-large terrain models; 3) atmospheric effects, or aerial perspective, to provide a sense of scale; 4) surface textures as models of natural phenomena such as clouds, water, rock strata, and so forth, to enhance visual detail in the image beyond what can be modelled geometrically; and 5) a global context in which to situate the scenes. Results in these five areas are presented, and some aspects of the development of computer graphics as a new process and medium for the fine arts are discussed. Heterogeneous terrain models are introduced, and preliminary experiments in simulating fluvial erosion are presented to provide fractal drainage network features. For imaging detailed terrain models we describe grid tracing, a time- and memory-efficient algorithm for ray tracing height fields. To obtain aerial perspective we develop geometric models of aerosol density distributions with efficient integration schemes for determining scattering and extinction, and an efficient Rayleigh scattering approximation. We also describe physically-based models of the rainbow and mirage. Proceduralism is an underlying theme of this work; this is the practice of abstracting models of complex form and behaviors into relatively terse algorithms, which are evaluated in a lazy fashion. Procedural textures are developed as models of natural phenomena such as mountains and clouds, culminating a procedural model of an Earth-like planet which in the future may be explored interactively in a virtual reality setting.
Narrative and the cultural psychology of identity
- Personality and Social Psychology Review
, 2008
"... In 1948, a peaceful people underwent a prolific tragedy with the rupture of their homeland. Having wel-comed with open arms the victims of a terrible tragedy in a distant land to a place where people of multiple faiths lived in social harmony, they shared their land, their food, their customs, only ..."
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Cited by 22 (1 self)
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In 1948, a peaceful people underwent a prolific tragedy with the rupture of their homeland. Having wel-comed with open arms the victims of a terrible tragedy in a distant land to a place where people of multiple faiths lived in social harmony, they shared their land, their food, their customs, only to be assaulted in a violent attack on the principles of a pluralistic society. These newcomers, it seemed, were determined to create a nation all for themselves, unwilling to share political authority over a diverse group of individuals and a unique assem-blage of cultural identities. Resisting foreign attempts to split their homeland in two, this inherently peaceful people did what they could only think to do: They turned to their neighbors, whose cultures shared a similar lan-guage, heritage, and way of life. They, with the help of these neighbors, met the aggressive act of such a political demand with a decidedly aggressive response: the decla-ration of war. For them, there was no other way to pre-serve and protect their homeland, united in its historical importance to three religious faiths. These are the stories of the Israelis and the Palestinians—historical narratives of collective struggle characterized by formidable polarization (Hammack, Author’s Note: This article was completed in part while the author was supported by fellowships from the U.S. Institute of Peace, the Spencer Foundation, and the Alfred P. Sloan Foundation. The valu-able comments of three anonymous reviewers and of colleagues on earlier drafts of this article are greatly acknowledged: Bertram J.
Mutual Shaping of Users and Technologies in a National Virtual Community
- Journal of Communication
, 1999
"... In this essay I analyze how technologies and users relate to each other in a national virtual community. I argue that a mutual shaping perspective is best suited to capture the complexity, unpredictability, and recursivity of the interactions among technological features and users ’ discourses and p ..."
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Cited by 22 (1 self)
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In this essay I analyze how technologies and users relate to each other in a national virtual community. I argue that a mutual shaping perspective is best suited to capture the complexity, unpredictability, and recursivity of the interactions among technological features and users ’ discourses and practices. Drawing from recent developments in the study of computer-mediated communication, multidisciplinary technology scholarship, and social psychology of nationhood, I show the mutual shaping of hardware capabilities, national identities, collective remembering, software configurations, and coordination practices that took place during my investigation of the Argentine Mailing List. People have migrated for centuries. Those who have desired to remain in contact with their places of origin have relied heavily upon communication technologies. In this sense, migrants have used material objects such as letters, newspapers, telephones, and television sets to reconstruct what it means to be a member of a territorially, historically, and culturally located community in situations of geographical displacement. More recently, émigrés have increasingly used various
Transidiomatic practices: Language and power in the age of globalization
- Language & Communication
, 2005
"... Abstract This article seeks to assess the communicative mutations resulting from the intersection between mobile people and mobile texts. Sophisticated technologies for rapid human mobility and global communication are transforming the communicative environment of late modernity. Until recently the ..."
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Cited by 20 (0 self)
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Abstract This article seeks to assess the communicative mutations resulting from the intersection between mobile people and mobile texts. Sophisticated technologies for rapid human mobility and global communication are transforming the communicative environment of late modernity. Until recently the majority of linguistic studies which concerned themselves with global phenomena tended to depict the worst possible scenarios: linguistic imperialism, endangered languages, language death. In this paper, I argue that the experience of cultural globalization, and the sociolinguistic disorder it entails, cannot be understood solely through a dystopic vision of linguistic catastrophe, but demand that we also take into account the recombinant qualities of language mixing, hybridization, and creolization. Using communicative data from the Adriatic region, this paper calls for a reconceptualization of what we consider the communicative environment, which must be no longer restricted to its default parameters (focused, monolingual, and face-to-face), but should also account for communicative practices based on multilingual talk (most of the times exercised by de/reterritorialized speakers) channeled through both local and electronic media.
Network Communities: Something Old, Something New, Something Borrowed
- Journal of Collaborative Computing
, 1998
"... Abstract. Collaboration has long been of considerable interest to both designers and researchers in the CHI and CSCW communities. This paper contributes to this discussion by proposing the concept of network communities as a new genre of collaboration for this discussion. Network communities are rob ..."
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Cited by 20 (0 self)
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Abstract. Collaboration has long been of considerable interest to both designers and researchers in the CHI and CSCW communities. This paper contributes to this discussion by proposing the concept of network communities as a new genre of collaboration for this discussion. Network communities are robust and persistent communities based on a sense of locality that spans both the virtual and physical worlds of their users. They are a technosocial construct that requires understanding of both the technology and the sociality embodying them. We consider several familiar systems as well as historical antecedents to describe the affordances these systems offer their community of users. Based on our own experience as designers, users and researchers of a variety of network communities, we extend this initial design space along three dimensions: the boundary negotiations between real and virtual worlds, support for social rhythms and the emergence and development of community. Finally we offer implications for designers, researchers and community members based on our findings.
National elections as institutions for generating social capital.
- In T. Skocpal & M. Fiorina (Eds.), Civic engagement and American democracy
, 1999
"... ABSTRACT Using data from the 1996 National Election Study, we examine the impact of campaignrelated variables on changes in three individual-level orientations that contribute to social capital: generalized trust in others, trust in government, and external political efficacy. We distinguish four t ..."
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Cited by 19 (2 self)
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ABSTRACT Using data from the 1996 National Election Study, we examine the impact of campaignrelated variables on changes in three individual-level orientations that contribute to social capital: generalized trust in others, trust in government, and external political efficacy. We distinguish four types of election-related effects: political mobilization, psychological and behavioral involvement in the campaign, solidarity ritual, and qualities of the campaign and the candidates. We find, first, that there were significant changes in all three orientations in a social-capital enhancing direction in the aftermath of the 1996 election. Second, each of the three orientations was enhanced by different aspects of the campaign. Finally, these three orientations are locked in a causal system, such that changes in one induce changes in the others. We discuss implications of these results for theories of social capital. 3 The concept of social capital has proven to be enormously attractive to scholars in a wide variety of disciplines. Many political scientists have deliberated about how to identify a role for political institutions in the production of social capital. Effective institutions are not just one of the many unintended blessings of a vigorous civil society; rather, political authority that performs well and equitably contributes to the "trust, norms, and networks" (Putnam 1993:167) that enable people to solve collective action problems. Institutions that require more citizen input may also provide an impetus for people to become engaged in something other than their private lives (Schneider, et al. 1997). In this chapter, we examine national elections as political institutions that may contribute to the production of social capital. We begin by describing three attitudinal orientations that we believe to be part of a social capital dynamic. We then hypothesize four ways in which elections may have an impact on these components of social capital. Finally, we examine these mechanisms using the 1996 American National Election Study. ELECTIONS AND SOCIAL CAPITAL Once the ballots have been counted, do elections have any lingering effects on the American polity? One way in which the effects of elections persist is through the policy changes that may be enacted as a result of leadership turnover (e.g., Brady and Stewart 1991). Our focus on elections, however, is not on their direct outcomes, but rather the changes that may be wrought in the larger civic culture as a result of both the practical conduct of elections and their larger symbolic significance. After reviewing the empirical evidence for election-based change in civic attitudes, we present several hypotheses-which are not mutually exclusive-about ways in which elections may improve citizens' orientations toward the larger political community. Our investigation is founded on two earlier empirical treatments of the origins of social capital These papers reflect our belief that some forms of social capital, particularly as manifested in
