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Search Results: 1 - 10 of 53682 matches for " David Halpern "
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Unsupervised Learning of Noisy-Or Bayesian Networks
Yonatan Halpern,David Sontag
Computer Science , 2013,
Abstract: This paper considers the problem of learning the parameters in Bayesian networks of discrete variables with known structure and hidden variables. Previous approaches in these settings typically use expectation maximization; when the network has high treewidth, the required expectations might be approximated using Monte Carlo or variational methods. We show how to avoid inference altogether during learning by giving a polynomial-time algorithm based on the method-of-moments, building upon recent work on learning discrete-valued mixture models. In particular, we show how to learn the parameters for a family of bipartite noisy-or Bayesian networks. In our experimental results, we demonstrate an application of our algorithm to learning QMR-DT, a large Bayesian network used for medical diagnosis. We show that it is possible to fully learn the parameters of QMR-DT even when only the findings are observed in the training data (ground truth diseases unknown).
Strongly nonlinear nature of interfacial-surfactant instability of Couette flow
Alexander L. Frenkel,David Halpern
Physics , 2006,
Abstract: Nonlinear stages of the recently uncovered instability due to insoluble surfactant at the interface between two fluids are investigated for the case of a creeping plane Couette flow with one of the fluids a thin film and the other one a much thicker layer. Numerical simulation of strongly nonlinear longwave evolution equations which couple the film thickness and the surfactant concentration reveals that in contrast to all similar instabilities of surfactant-free flows, no amount of the interfacial shear rate can lead to a small-amplitude saturation of the instability. Thus, the flow is stable when the shear is zero, but with non-zero shear rates, no matter how small or large (while remaining below an upper limit set by the assumption of creeping flow), it will reach large deviations from the base values-- of the order of the latter or larger. It is conjectured that the time this evolution takes grows to infinity as the interfacial shear approaches zero. It is verified that the absence of small-amplitude saturation is not a singularity of the zero surface diffusivity of the interfacial surfactant.
Diversions: Obstacles for Undergraduate Students when Applying for Internship Positions Online  [PDF]
Clarisse Halpern, Bruno Halpern
Open Journal of Business and Management (OJBM) , 2018, DOI: 10.4236/ojbm.2018.61011
The objective of this research was to investigate how the decision of Brazilian university students to enroll (or not) in internships’ selection processes would be affected by the form and content of the ads published in social media. Thus, a qualitative research was carried out through a multiple-case study. Data were collected in semi-structured interviews via Skype, as well as direct observations of eight individuals. The category?Diversions presented the most relevant results shedding light as to how the interviewees’ focus was shifted while searching for internship positions during their interviews. The title refers to how distractions make students stray from their intended search for internship positions. Instead, social media exerts a sort of magnetism that is more powerful than recruiting posts and ads, attracting their attention away from internship openings search, making them secondary. In conclusion, diversions were found to become obstacles for undergraduate students when applying for internship positions online.
Viewpoint: Journals for Certification, Conferences for Rapid Dissemination
Joseph Y. Halpern,David C. Parkes
Computer Science , 2011,
Abstract: The publication culture in Computer Science is different from that of all other disciplines. Whereas other disciplines focus on journal publication, the standard practice in CS has been to publish in a conference and then (sometimes) publish a journal version of the conference paper. We discuss the role of journal publication in CS. Indeed, it is through publication in selective, leading conferences that the quality of CS research is typically assessed.
Constructive Decision Theory
Lawrence Blume,David Easley,Joseph Y. Halpern
Computer Science , 2009,
Abstract: In most contemporary approaches to decision making, a decision problem is described by a sets of states and set of outcomes, and a rich set of acts, which are functions from states to outcomes over which the decision maker (DM) has preferences. Most interesting decision problems, however, do not come with a state space and an outcome space. Indeed, in complex problems it is often far from clear what the state and outcome spaces would be. We present an alternative foundation for decision making, in which the primitive objects of choice are syntactic programs. A representation theorem is proved in the spirit of standard representation theorems, showing that if the DM's preference relation on objects of choice satisfies appropriate axioms, then there exist a set S of states, a set O of outcomes, a way of interpreting the objects of choice as functions from S to O, a probability on S, and a utility function on O, such that the DM prefers choice a to choice b if and only if the expected utility of a is higher than that of b. Thus, the state space and outcome space are subjective, just like the probability and utility; they are not part of the description of the problem. In principle, a modeler can test for SEU behavior without having access to states or outcomes. We illustrate the power of our approach by showing that it can capture decision makers who are subject to framing effects.
Anchored Discrete Factor Analysis
Yoni Halpern,Steven Horng,David Sontag
Computer Science , 2015,
Abstract: We present a semi-supervised learning algorithm for learning discrete factor analysis models with arbitrary structure on the latent variables. Our algorithm assumes that every latent variable has an "anchor", an observed variable with only that latent variable as its parent. Given such anchors, we show that it is possible to consistently recover moments of the latent variables and use these moments to learn complete models. We also introduce a new technique for improving the robustness of method-of-moment algorithms by optimizing over the marginal polytope or its relaxations. We evaluate our algorithm using two real-world tasks, tag prediction on questions from the Stack Overflow website and medical diagnosis in an emergency department.
Toward Expressive and Scalable Sponsored Search Auctions
David J. Martin,Johannes Gehrke,Joseph Y. Halpern
Computer Science , 2008,
Abstract: Internet search results are a growing and highly profitable advertising platform. Search providers auction advertising slots to advertisers on their search result pages. Due to the high volume of searches and the users' low tolerance for search result latency, it is imperative to resolve these auctions fast. Current approaches restrict the expressiveness of bids in order to achieve fast winner determination, which is the problem of allocating slots to advertisers so as to maximize the expected revenue given the advertisers' bids. The goal of our work is to permit more expressive bidding, thus allowing advertisers to achieve complex advertising goals, while still providing fast and scalable techniques for winner determination.
A Practical Algorithm for Topic Modeling with Provable Guarantees
Sanjeev Arora,Rong Ge,Yoni Halpern,David Mimno,Ankur Moitra,David Sontag,Yichen Wu,Michael Zhu
Computer Science , 2012,
Abstract: Topic models provide a useful method for dimensionality reduction and exploratory data analysis in large text corpora. Most approaches to topic model inference have been based on a maximum likelihood objective. Efficient algorithms exist that approximate this objective, but they have no provable guarantees. Recently, algorithms have been introduced that provide provable bounds, but these algorithms are not practical because they are inefficient and not robust to violations of model assumptions. In this paper we present an algorithm for topic model inference that is both provable and practical. The algorithm produces results comparable to the best MCMC implementations while running orders of magnitude faster.
Worst-Case Background Knowledge for Privacy-Preserving Data Publishing
David J. Martin,Daniel Kifer,Ashwin Machanavajjhala,Johannes Gehrke,Joseph Y. Halpern
Computer Science , 2007,
Abstract: Recent work has shown the necessity of considering an attacker's background knowledge when reasoning about privacy in data publishing. However, in practice, the data publisher does not know what background knowledge the attacker possesses. Thus, it is important to consider the worst-case. In this paper, we initiate a formal study of worst-case background knowledge. We propose a language that can express any background knowledge about the data. We provide a polynomial time algorithm to measure the amount of disclosure of sensitive information in the worst case, given that the attacker has at most a specified number of pieces of information in this language. We also provide a method to efficiently sanitize the data so that the amount of disclosure in the worst case is less than a specified threshold.
The Role of the Researcher When Using the Socio-Anthropological Method to Understand the Phenomenon of Alcoholism  [PDF]
Elizabeth Halpern, Ligia Costa Leite
Open Journal of Social Sciences (JSS) , 2015, DOI: 10.4236/jss.2015.35011
Abstract: The consumption of alcoholic beverages during the Brazilian Armed Forces working hours was studied for the first time only recently, by investigating the patients of the Center for Chemical Dependency (CEDEQ) of the Brazilian Navy. This was possible mainly because one of the researchers was the chief of this clinic and one of the psychologists of the therapeutic groups. This article discussed methodological aspects related to the role of the researcher when conducting a qualitative research through a dense ethnography in CEDEQ over four years, with participant observation in two treatment groups for 24 sessions. Additionally, a multiple case and explanatory study was carried on, through individual and 13 open-ended interviews. The following findings will be discussed: 1) the social construction of truth and accuracy of the oral statements; 2) reflexivity, transparency, and familiarity of the researcher with the field; 3) impression management, standardized behavior, and resistance to perform the research. The use of the qualitative method requires the assessment of the researcher’s role. The anthropological eye helped to deal with a delicate theme that was hard to access: drinking during the military working journey. We found out that the organization had an ambivalent position: though the Brazilian Navy created this specialized clinic and allowed this research, at the same time this organization was not open to discuss inebriation on board, strictly authorizing the investigation of the patients. This was possible mainly because of the researcher’s social and hierarchical position as an officer, as the chief of the CEDEQ, and for being one of the therapists of the groups. We concluded that this position created an obstacle to apply effective measures to protect the military contingency.
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