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Showing papers by "Cornell University published in 2001"


Journal ArticleDOI
16 Nov 2001-Science
TL;DR: This review describes a new paradigm of electronics based on the spin degree of freedom of the electron, which has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices.
Abstract: This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.

9,917 citations


Journal ArticleDOI
08 Mar 2001-Nature
TL;DR: This work aims to understand how an enormous network of interacting dynamical systems — be they neurons, power stations or lasers — will behave collectively, given their individual dynamics and coupling architecture.
Abstract: The study of networks pervades all of science, from neurobiology to statistical physics. The most basic issues are structural: how does one characterize the wiring diagram of a food web or the Internet or the metabolic network of the bacterium Escherichia coli? Are there any unifying principles underlying their topology? From the perspective of nonlinear dynamics, we would also like to understand how an enormous network of interacting dynamical systems-be they neurons, power stations or lasers-will behave collectively, given their individual dynamics and coupling architecture. Researchers are only now beginning to unravel the structure and dynamics of complex networks.

7,665 citations


Journal ArticleDOI
TL;DR: This paper has designed a stand-alone, flexible C++ implementation that enables the evaluation of individual components and that can easily be extended to include new algorithms.
Abstract: Stereo matching is one of the most active research areas in computer vision. While a large number of algorithms for stereo correspondence have been developed, relatively little work has been done on characterizing their performance. In this paper, we present a taxonomy of dense, two-frame stereo methods designed to assess the different components and design decisions made in individual stereo algorithms. Using this taxonomy, we compare existing stereo methods and present experiments evaluating the performance of many different variants. In order to establish a common software platform and a collection of data sets for easy evaluation, we have designed a stand-alone, flexible C++ implementation that enables the evaluation of individual components and that can be easily extended to include new algorithms. We have also produced several new multiframe stereo data sets with ground truth, and are making both the code and data sets available on the Web.

7,458 citations


Journal ArticleDOI
TL;DR: This work presents two algorithms based on graph cuts that efficiently find a local minimum with respect to two types of large moves, namely expansion moves and swap moves that allow important cases of discontinuity preserving energies.
Abstract: Many tasks in computer vision involve assigning a label (such as disparity) to every pixel. A common constraint is that the labels should vary smoothly almost everywhere while preserving sharp discontinuities that may exist, e.g., at object boundaries. These tasks are naturally stated in terms of energy minimization. The authors consider a wide class of energies with various smoothness constraints. Global minimization of these energy functions is NP-hard even in the simplest discontinuity-preserving case. Therefore, our focus is on efficient approximation algorithms. We present two algorithms based on graph cuts that efficiently find a local minimum with respect to two types of large moves, namely expansion moves and swap moves. These moves can simultaneously change the labels of arbitrarily large sets of pixels. In contrast, many standard algorithms (including simulated annealing) use small moves where only one pixel changes its label at a time. Our expansion algorithm finds a labeling within a known factor of the global minimum, while our swap algorithm handles more general energy functions. Both of these algorithms allow important cases of discontinuity preserving energies. We experimentally demonstrate the effectiveness of our approach for image restoration, stereo and motion. On real data with ground truth, we achieve 98 percent accuracy.

7,413 citations


Journal ArticleDOI
TL;DR: It is demonstrated that in some cases random graphs with appropriate distributions of vertex degree predict with surprising accuracy the behavior of the real world, while in others there is a measurable discrepancy between theory and reality, perhaps indicating the presence of additional social structure in the network that is not captured by the random graph.
Abstract: Recent work on the structure of social networks and the internet has focused attention on graphs with distributions of vertex degree that are significantly different from the Poisson degree distributions that have been widely studied in the past. In this paper we develop in detail the theory of random graphs with arbitrary degree distributions. In addition to simple undirected, unipartite graphs, we examine the properties of directed and bipartite graphs. Among other results, we derive exact expressions for the position of the phase transition at which a giant component first forms, the mean component size, the size of the giant component if there is one, the mean number of vertices a certain distance away from a randomly chosen vertex, and the average vertex-vertex distance within a graph. We apply our theory to some real-world graphs, including the worldwide web and collaboration graphs of scientists and Fortune 1000 company directors. We demonstrate that in some cases random graphs with appropriate distributions of vertex degree predict with surprising accuracy the behavior of the real world, while in others there is a measurable discrepancy between theory and reality, perhaps indicating the presence of additional social structure in the network that is not captured by the random graph.

3,655 citations


Book ChapterDOI
03 Sep 2001
TL;DR: The goal of this paper is to provide an experimental comparison of the efficiency of min-cut/max flow algorithms for applications in vision, comparing the running times of several standard algorithms, as well as a new algorithm that is recently developed.
Abstract: After [10, 15, 12, 2, 4] minimum cut/maximum flow algorithms on graphs emerged as an increasingly useful tool for exact or approximate energy minimization in low-level vision. The combinatorial optimization literature provides many min-cut/max-flow algorithms with different polynomial time complexity. Their practical efficiency, however, has to date been studied mainly outside the scope of computer vision. The goal of this paper is to provide an experimental comparison of the efficiency of min-cut/max flow algorithms for energy minimization in vision. We compare the running times of several standard algorithms, as well as a new algorithm that we have recently developed. The algorithms we study include both Goldberg-style "push-relabel" methods and algorithms based on Ford-Fulkerson style augmenting paths. We benchmark these algorithms on a number of typical graphs in the contexts of image restoration, stereo, and interactive segmentation. In many cases our new algorithm works several times faster than any of the other methods making near real-time performance possible.

3,099 citations


Book
01 Jan 2001
TL;DR: In recent decades the study of social movements, revolution, democratization and other non-routine politics has flourished as mentioned in this paper, and yet research on the topic remains highly fragmented, reflecting the influence of at least three traditional divisions.
Abstract: In recent decades the study of social movements, revolution, democratization and other non-routine politics has flourished. And yet research on the topic remains highly fragmented, reflecting the influence of at least three traditional divisions. The first of these reflects the view that various forms of contention are distinct and should be studied independent of others. Separate literatures have developed around the study of social movements, revolutions and industrial conflict. A second approach to the study of political contention denies the possibility of general theory in deference to a grounding in the temporal and spatial particulars of any given episode of contention. The study of contentious politics are left to 'area specialists' and/or historians with a thorough knowledge of the time and place in question. Finally, overlaid on these two divisions are stylized theoretical traditions - structuralist, culturalist, and rationalist - that have developed largely in isolation from one another. This book was first published in 2001.

2,809 citations


Journal ArticleDOI
14 Dec 2001-Science
TL;DR: Bayesian inference of phylogeny brings a new perspective to a number of outstanding issues in evolutionary biology, including the analysis of large phylogenetic trees and complex evolutionary models and the detection of the footprint of natural selection in DNA sequences.
Abstract: As a discipline, phylogenetics is becoming transformed by a flood of molecular data. These data allow broad questions to be asked about the history of life, but also present difficult statistical and computational problems. Bayesian inference of phylogeny brings a new perspective to a number of outstanding issues in evolutionary biology, including the analysis of large phylogenetic trees and complex evolutionary models and the detection of the footprint of natural selection in DNA sequences.

2,639 citations


Journal ArticleDOI
TL;DR: In this article, the authors constructed networks of collaboration between scientists in each of these disciplines and proposed a measure of collaboration strength based on the number of papers coauthored by pairs of scientists, and the number other scientists with whom they coauthored those papers.
Abstract: Using computer databases of scientific papers in physics, biomedical research, and computer science, we have constructed networks of collaboration between scientists in each of these disciplines. In these networks two scientists are considered connected if they have coauthored one or more papers together. Here we study a variety of nonlocal statistics for these networks, such as typical distances between scientists through the network, and measures of centrality such as closeness and betweenness. We further argue that simple networks such as these cannot capture variation in the strength of collaborative ties and propose a measure of collaboration strength based on the number of papers coauthored by pairs of scientists, and the number of other scientists with whom they coauthored those papers.

2,528 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigate the role of information in affecting a firm's cost of capital using a multi-asset rational expectations model and show that differences in the composition of information between public and private information affect the cost of investment, with investors demanding a higher return to hold stocks with greater private information.
Abstract: We investigate the role of information in affecting a firm's cost of capital. Using a multi-asset rational expectations model, we show that differences in the composition of information between public and private information affect the cost of capital, with investors demanding a higher return to hold stocks with greater private information. This higher return arises because informed investors are better able to shift their portfolio weights to incorporate new information, and uninformed investors are thus disadvantaged. The model demonstrates how in equilibrium the quantity and quality of information affect asset prices, resulting in cross-sectional differences in firms' required returns. We show how a firm can influence its cost of capital by choosing features like accounting treatments, financial analyst coverage, and market microstructure.

2,415 citations


Journal ArticleDOI
TL;DR: In a longitudinal study, the authors found that higher group performance was associated with a particular pattern of conflict, and that teams performing well were characterized by low but increasing levels of conflict.
Abstract: In a longitudinal study, we found that higher group performance was associated with a particular pattern of conflict. Teams performing well were characterized by low but increasing levels of proces...

Journal ArticleDOI
TL;DR: Using computer databases of scientific papers in physics, biomedical research, and computer science, a network of collaboration between scientists in each of these disciplines is constructed, and a number of measures of centrality and connectedness in the same networks are studied.
Abstract: Using computer databases of scientific papers in physics, biomedical research, and computer science, we have constructed networks of collaboration between scientists in each of these disciplines. In these networks two scientists are considered connected if they have coauthored one or more papers together. We study a variety of statistical properties of our networks, including numbers of papers written by authors, numbers of authors per paper, numbers of collaborators that scientists have, existence and size of a giant component of connected scientists, and degree of clustering in the networks. We also highlight some apparent differences in collaboration patterns between the subjects studied. In the following paper, we study a number of measures of centrality and connectedness in the same networks.

Journal ArticleDOI
TL;DR: The impact of the resource-based view on the theoretical and empirical development of strategic human resource management (SHRM) has been explored in this article, where the fields of strategy and SHRM are beginning to converge around a number of issues.

Journal ArticleDOI
TL;DR: It is demonstrated that recruitment of VEGF-responsive BM-derived precursors is necessary and sufficient for tumor angiogenesis and suggested new clinical strategies to block tumor growth are suggested.
Abstract: The role of bone marrow (BM)-derived precursor cells in tumor angiogenesis is not known. We demonstrate here that tumor angiogenesis is associated with recruitment of hematopoietic and circulating endothelial precursor cells (CEPs). We used the angiogenic defective, tumor resistant Id-mutant mice to show that transplantation of wild-type BM or vascular endothelial growth factor (VEGF)-mobilized stem cells restore tumor angiogenesis and growth. We detected donor-derived CEPs throughout the neovessels of tumors and Matrigel-plugs in an Id1+/-Id3-/- host, which were associated with VEGF-receptor-1-positive (VEGFR1+) myeloid cells. The angiogenic defect in Id-mutant mice was due to impaired VEGF-driven mobilization of VEGFR2+ CEPs and impaired proliferation and incorporation of VEGFR1+ cells. Although targeting of either VEGFR1 or VEGFR2 alone partially blocks the growth of tumors, inhibition of both VEGFR1 and VEGFR2 was necessary to completely ablate tumor growth. These data demonstrate that recruitment of VEGF-responsive BM-derived precursors is necessary and sufficient for tumor angiogenesis and suggest new clinical strategies to block tumor growth.

Journal ArticleDOI
TL;DR: In this paper, the authors introduce a special issue on the topic of income diversification and livelihoods in rural Africa: Cause and Consequence of change, where the authors concentrate on core conceptual issues that bedevil the literature on rural income diversity and the policy implications of the empirical evidence presented in this special issue.

Journal ArticleDOI
30 Nov 2001-Science
TL;DR: It is shown that the proforms of nerve growth factor (NGF) and the pro forms of brain derived neurotrophic factor (BDNF) are secreted and cleaved extracellularly by the serine protease plasmin and by selective matrix metalloproteinases (MMPs).
Abstract: Neurotrophins are growth factors that promote cell survival, differentiation, and cell death. They are synthesized as proforms that can be cleaved intracellularly to release mature, secreted ligands. Although proneurotrophins have been considered inactive precursors, we show here that the proforms of nerve growth factor (NGF) and the proforms of brain derived neurotrophic factor (BDNF) are secreted and cleaved extracellularly by the serine protease plasmin and by selective matrix metalloproteinases (MMPs). ProNGF is a high-affinity ligand for p75 NTR with high affinity and induced p75 NTR -dependent apoptosis in cultured neurons with minimal activation of TrkA-mediated differentiation or survival. The biological action of neurotrophins is thus regulated by proteolytic cleavage, with proforms preferentially activating p75 NTR to mediate apoptosis and mature forms activating Trk receptors to promote survival.

Journal ArticleDOI
TL;DR: The authors define cultural entrepreneurship as the process of storytelling that mediates between extant stocks of entrepreneurial resources and subsequent capital acquisition and wealth creation, and propose a framework that focuses on how entrepreneurial stories facilitate the crafting of a new venture identity that serves as a touchstone upon which legitimacy may be conferred by investors, competitors, and consumers.
Abstract: We define cultural entrepreneurship as the process of storytelling that mediates between extant stocks of entrepreneurial resources and subsequent capital acquisition and wealth creation. We propose a framework that focuses on how entrepreneurial stories facilitate the crafting of a new venture identity that serves as a touchstone upon which legitimacy may be conferred by investors, competitors, and consumers, opening up access to new capital and market opportunities. Stories help create competitive advantage for entrepreneurs through focal content shaped by two key forms of entrepreneurial capital: firm-specific resource capital and industry-level institutional capital. We illustrate our ideas with anecdotal entrepreneurial stories that range from contemporary high-technology accounts to the evolution of the mutual fund industry. Propositions are offered to guide future empirical research based on our framework. Theoretically, we aim to extend recent efforts to synthesize strategic and institutional perspectives by incorporating insights from contemporary approaches to culture and organizational identity. Copyright © 2001 John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: The results indicate that, in the context of IT basic skills training in undergraduate education, there are no significant differences in performance between students enrolled in the two environments, however, the VLE leads to higher reported computer self-efficacy, while participants report being less satisfied with the learning process.
Abstract: Internet technologies are having a significant impact on the learning industry. For-profit organizations and traditional institutions of higher education have developed and are using web-based courses, but little is known about their effectiveness compared to traditional classroom education. Our work focuses on the effectiveness of a web-based virtual learning environment (VLE) in the context of basic information technology skills training. This article provides three main contributions. First, it introduces and defines the concept of VLE, discussing how a VLE differs from the traditional classroom and differentiating it from the related, but narrower, concept of computer aided instruction (CAI). Second, it presents a framework of VLE effectiveness, grounded in the technology-mediated learning literature, which frames the VLE research domain, and addresses the relationship between the main constructs. Finally, it focuses on one essential VLE design variable, learner control, and compares a web-based VLE to a traditional classroom through a longitudinal experimental design. Our results indicate that, in the context of IT basic skills training in undergraduate education, there are no significant differences in performance between students enrolled in the two environments. However, the VLE leads to higher reported computer self-efficacy, while participants report being less satisfied with the learning process.

Journal ArticleDOI
TL;DR: A set of 200 Class I SSR markers was developed and integrated into the existing microsatellite map of rice, providing immediate links between the genetic, physical, and sequence-based maps.
Abstract: A total of 57.8 Mb of publicly available rice (Oryza sativa L.) DNA sequence was searched to determine the frequency and distribution of different simple sequence repeats (SSRs) in the genome. SSR loci were categorized into two groups based on the length of the repeat motif. Class I, or hypervariable markers, consisted of SSRs > or =20 bp, and Class II, or potentially variable markers, consisted of SSRs > or =12 bp <20 bp. The occurrence of Class I SSRs in end-sequences of EcoRI- and HindIII-digested BAC clones was one SSR per 40 Kb, whereas in continuous genomic sequence (represented by 27 fully sequenced BAC and PAC clones), the frequency was one SSR every 16 kb. Class II SSRs were estimated to occur every 3.7 kb in BAC ends and every 1.9 kb in fully sequenced BAC and PAC clones. GC-rich trinucleotide repeats (TNRs) were most abundant in protein-coding portions of ESTs and in fully sequenced BACs and PACs, whereas AT-rich TNRs showed no such preference, and di- and tetranucleotide repeats were most frequently found in noncoding, intergenic regions of the rice genome. Microsatellites with poly(AT)n repeats represented the most abundant and polymorphic class of SSRs but were frequently associated with the Micropon family of miniature inverted-repeat transposable elements (MITEs) and were difficult to amplify. A set of 200 Class I SSR markers was developed and integrated into the existing microsatellite map of rice, providing immediate links between the genetic, physical, and sequence-based maps. This contribution brings the number of microsatellite markers that have been rigorously evaluated for amplification, map position, and allelic diversity in Oryza spp. to a total of 500.

Journal ArticleDOI
TL;DR: As expected, lovastatin was effective in preventing coronary events in participants whose base-line ratio of total cholesterol to high-de...
Abstract: Background Elevated levels of C-reactive protein, even in the absence of hyperlipidemia, are associated with an increased risk of coronary events. Statin therapy reduces the level of C-reactive protein independently of its effect on lipid levels. We hypothesized that statins might prevent coronary events in persons with elevated C-reactive protein levels who did not have overt hyperlipidemia. Methods The level of C-reactive protein was measured at base line and after one year in 5742 participants in a five-year randomized trial of lovastatin for the primary prevention of acute coronary events. Results The rates of coronary events increased significantly with increases in the base-line levels of C-reactive protein. Lovastatin therapy reduced the C-reactive protein level by 14.8 percent (P<0.001), an effect not explained by lovastatin-induced changes in the lipid profile. As expected, lovastatin was effective in preventing coronary events in participants whose base-line ratio of total cholesterol to high-de...

Proceedings ArticleDOI
07 Mar 2001
TL;DR: This paper presents a new method which properly addresses occlusions, while preserving the advantages of graph cut algorithms, and gives experimental results for stereo as well as motion, which demonstrate that the method performs well both at detecting occlusion and computing disparities.
Abstract: Several new algorithms for visual correspondence based on graph cuts have recently been developed. While these methods give very strong results in practice, they do not handle occlusions properly. Specifically, they treat the two input images asymmetrically, and they do not ensure that a pixel corresponds to at most one pixel in the other image. In this paper, we present a new method which properly addresses occlusions, while preserving the advantages of graph cut algorithms. We give experimental results for stereo as well as motion, which demonstrate that our method performs well both at detecting occlusions and computing disparities.

Journal ArticleDOI
TL;DR: The estimate is that non-native species invasions in the six nations are causing more than US$ 314 billion per year in damages.

Journal ArticleDOI
TL;DR: In this article, the authors present a set of performance criteria for single-use biosensors, i.e., a device that is both disposable after one measurement, and unable to monitor the analyte concentration continuously or after rapid and reproducible regeneration.

Journal ArticleDOI
TL;DR: The results indicate that visual function was restored in this large animal model of childhood blindness, and gene therapy directed at photoreceptors and RPE in a large-animal model of human disease has not been reported.
Abstract: The relationship between the neurosensory photoreceptors and the adjacent retinal pigment epithelium (RPE) controls not only normal retinal function, but also the pathogenesis of hereditary retinal degenerations. The molecular bases for both primary photoreceptor1 and RPE diseases2,3,4 that cause blindness have been identified. Gene therapy has been used successfully to slow degeneration in rodent models of primary photoreceptor diseases5,6, but efficacy of gene therapy directed at photoreceptors and RPE in a large-animal model of human disease has not been reported. Here we study one of the most clinically severe retinal degenerations, Leber congenital amaurosis (LCA). LCA causes near total blindness in infancy and can result from mutations in RPE65 (LCA, type II; MIM 180069 and 204100). A naturally occurring animal model, the RPE65−/− dog, suffers from early and severe visual impairment similar to that seen in human LCA. We used a recombinant adeno-associated virus (AAV) carrying wild-type RPE65 (AAV-RPE65) to test the efficacy of gene therapy in this model. Our results indicate that visual function was restored in this large animal model of childhood blindness.

Journal ArticleDOI
TL;DR: The comparative data indicate that humans are neurally advanced at birth relative to the other species studied, and this 'translation' table will assist in attempts to equate the neurodevelopmental literature across species with either large or small differences in gestation and maturation.

Journal ArticleDOI
TL;DR: The biology of CD36 can be broadly divided in terms of functions that it mediates with or without TSP-1, but it is probable that it acts in concert with other proteins, such as fatty acid–binding proteins, caveola-associated proteins, integrins, cytoskeletal proteins, and signaling molecules, to effect its diverse functions.
Abstract: CD36, identified more than a quarter of a century ago as a platelet integral membrane glycoprotein (glycoprotein IV), was until recently best known as a receptor for thrombospondin-1 (TSP-1). TSP-1 is found in ECMs and platelet α granules, and it participates in cell attachment, motility, and proliferation, as well as in modulation of protease activity, TGF-β activation, neurite outgrowth, and angiogenesis (1). Initially, this receptor-ligand pair was shown to mediate interactions between platelets and monocytes, tumor cells, and matrix. Since then, CD36 has been implicated in multiple biological processes that define it as a multiligand scavenger receptor (see ref. 2 for review). These ligands appear remarkably diverse: In addition to TSP-1, they include long-chain fatty acids, modified LDL, retinal photoreceptor outer segments, Plasmodium falciparum malaria-parasitized erythrocytes, sickle erythrocytes, anionic phospholipids, apoptotic cells, and collagens I and IV. The biology of CD36 can be broadly divided in terms of functions that it mediates with or without TSP-1, but it is probable that it acts in concert with other proteins, such as fatty acid–binding proteins, caveola-associated proteins, integrins, cytoskeletal proteins, and signaling molecules, to effect its diverse functions.

Journal ArticleDOI
TL;DR: The substituents on the beta-diiminate ligand exert a significant influence upon the course of the polymerizations, affecting both the degree of stereoselectivity and the rate of polymerization.
Abstract: A series of zinc(II) and magnesium(II) alkoxides based upon a β-diiminate ligand framework has been prepared. [(BDI-1)ZnOiPr]2 [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)...

Journal ArticleDOI
TL;DR: In this paper, statistical methods to account for population structure were extended for use with quantitative variation and applied to their evaluation of maize flowering time, which indicated that a suite of polymorphisms associated with differences in flowering time.
Abstract: Historically, association tests have been used extensively in medical genetics, but have had virtually no application in plant genetics. One obstacle to their application is the structured populations often found in crop plants, which may lead to nonfunctional, spurious associations. In this study, statistical methods to account for population structure were extended for use with quantitative variation and applied to our evaluation of maize flowering time. Mutagenesis and quantitative trait locus (QTL) studies suggested that the maize gene Dwarf8 might affect the quantitative variation of maize flowering time and plant height. The wheat orthologs of this gene contributed to the increased yields seen in the 'Green Revolution' varieties. We used association approaches to evaluate Dwarf8 sequence polymorphisms from 92 maize inbred lines. Population structure was estimated using a Bayesian analysis of 141 simple sequence repeat (SSR) loci. Our results indicate that a suite of polymorphisms associate with differences in flowering time, which include a deletion that may alter a key domain in the coding region. The distribution of nonsynonymous polymorphisms suggests that Dwarf8 has been a target of selection.

Journal ArticleDOI
TL;DR: NMR spectroscopy results suggest that one function of alphaS may be to tether as of yet unidentified partners to lipid surfaces via interactions with its C-terminal tail.

Journal ArticleDOI
TL;DR: This paper developed a theory that explains how and when emotions, produced by social exchange, generate stronger or weaker ties to relations, groups, or networks, which are internally rewarding or punishing.
Abstract: This article develops a theory that explains how and when emotions, produced by social exchange, generate stronger or weaker ties to relations, groups, or networks. It is argued that social exchange produces positive or negative global feelings, which are internally rewarding or punishing. The theory indicates that social units (relations, groups, networks) are perceived as a source of these feelings, contingent on the degree of jointness in the exchange task. The jointness of the task is greatest if (1) actors find it difficult to distinguish their individual effects on or contributions to solving the exchange task (nonseparability) and (2) actors perceive a shared responsibility for success or failure at the exchange task. The theory explicates the effects of different exchange structures on these conditions and, in turn, on cohesion and solidarity. Implications are developed for network‐to‐group transformations.