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IEEE International Frequency Control symposium

作者： B. Jaduszliwer Chemistry and Physics Laboratory Aerospace Corporation Los Angeles CA USA

Accurate calculations are performed of atomic trajectories in conventional cesium beam tubes (CBTs) using dispersive, two-wire field magnets and also in a novel configuration using two orthogonal one-dimensional focusing dipoles of the type described by P. Kartaschoff (1969). In the first configuration, it was possible to explain observed differences in atomic velocity distribution in terms of small variations in oven and/or detector offsets. The second configuration yields beam intensities that are significantly higher than the ones obtained with dispersive magnets and/or substantially lower atomic velocities, and thus could improve the frequency stability of compact cesium clocks in the white-noise regime. Present design differs from P. Kartaschoff's prescription in that a one-dimensional focussing dipole, rather than a hexapole or quadrupole magnet, is used as the A magnet in the CBT, making the tube manufacturing simpler.< >

关键词： Atomic beams Clocks Magnets Stability Magnetic fields Detectors Magnetic analysis Microwave ovens distributed computing Signal detection

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On-line confidence machines are well-calibrated

On-line confidence machines are well-calibrated

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Annual IEEE symposium on Foundations of Computer Science

作者： V. Vovk Computer Learning Research Centre Department of Computer Science Royal Holloway University of London Egham Surrey UK

Transductive Confidence Machine (TCM) and its computationally efficient modification, inductive confidence machine (ICM), are ways of complementing machine-learning algorithms with practically useful measures of confidence. We show that when TCM and ICM are used in the on-line mode, their confidence measures are well-calibrated, in the sense that predictive regions at confidence level 1-/spl delta/ will be wrong with relative frequency at most /spl delta/ (approaching /spl delta/ in the case of randomised TCM and ICM) in the long run. This is not just an asymptotic phenomenon: actually the error probability of randomised TCM and ICM is d at every trial and errors happen independently at different trials.

关键词： Prediction algorithms Error probability Computer science Machine learning Frequency measurement distributed computing Reliability theory Testing Packaging Computer errors

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Chapar: Certified Causally Consistent distributed Key-Value Stores

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acm SIGPLAN NOTICES 2016年第1期51卷 357-370页

作者： Lesani, Mohsen Bell, Christian J. Chlipala, Adam MIT Cambridge MA 02139 USA

Today's Internet services are often expected to stay available and render high responsiveness even in the face of site crashes and network partitions. Theoretical results state that causal consistency is one of the strongest consistency guarantees that is possible under these requirements, and many practical systems provide causally consistent key-value stores. In this paper, we present a framework called Chapar for modular verification of causal consistency for replicated key-value store implementations and their client programs. Specifically, we formulate separate correctness conditions for key-value store implementations and for their clients. The interface between the two is a novel operational semantics for causal consistency. We have verified the causal consistency of two key-value store implementations from the literature using a novel proof technique. We have also implemented a simple automatic model checker for the correctness of client programs. The two independently verified results for the implementations and clients can be composed to conclude the correctness of any of the programs when executed with any of the implementations. We have developed and checked our framework in Coq, extracted it to OCaml, and built executable stores.

关键词： Algorithms Reliability Verification causal consistency theorem proving verification

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AP CS principles and the beauty and joy of computing curriculum (abstract only) 12

AP CS principles and the beauty and joy of computing curricu...

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proceedings of the 43rd acm technical symposium on Computer Science Education

作者： Daniel D. Garcia Brian Harvey Tiffany Barnes Luke Segars Eugene Lemon Sean Morris Josh Paley UC Berkeley Berkeley CA USA University of North Carolina Charlotte Charlotte NC USA Ralph J Bunche High School Oakland CA USA Albany High School Albany CA USA Henry M. Gunn High School Palo Alto CA USA

ISBN: (纸本)9781450310987

The Beauty and Joy of computing (BJC) is an introductory computer science curriculum developed at the University of California, Berkeley (and adapted at the University of North Carolina, Charlotte), intended for high school juniors through university non-majors. It was used in two of the five initial pilot programs for the AP CS principles course being developed by the College Board and the National Science Foundation. Our overall goal is to support the CS10K project by preparing instructors to teach the AP CS principles course through the BJC curriculum. In this workshop, we will share our experiences as instructors of the course at the university and high school level, provide a glimpse into a typical week of the course, and share details of NSF-funded summer professional development opportunities.

关键词： AP CS principles beauty and joy of computing advanced placement computer science principles BYOB build your own blocks

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A simple algorithmic characterization of uniform solvability

A simple algorithmic characterization of uniform solvability

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Annual IEEE symposium on Foundations of Computer Science

作者： E. Gafni UCLA-Academic Senate Grant USA

The Herlihy-Shavit (HS) conditions characterizing the solvability of asynchronous tasks over n processors have been a milestone in the development of the theory of distributed computing. Yet, they were of no help when researcher sought algorithms that do not depend on n. To help in this pursuit we investigate the uniform solvability of an infinite uniform sequence of tasks T/sub 0/, T/sub 1/, T/sub 2/,..., where T/sub i/ is a task over processors p/sub 0/, p/sub 1/,...,p/sub i/, and T/sub i/ extends T/sub i-1/. We say that such a sequence is uniformly solvable if there exit protocols to solve each T/sub i/ and the protocol for T/sub i/ extends the protocol for T/sub i-1/. This paper establishes that although each T/sub i/ may be solvable, the uniform sequence is not necessarily uniformly solvable. We show this by proposing a novel uniform sequence of solvable tasks and proving that the sequence is not amenable to a uniform solution. We then extend the HS conditions for a task over n processors, to uniform solvability in a natural way. The technique we use to accomplish this is to generalize the alternative algorithmic proof, by Borowsky and Gafni, of the HS conditions, by showing that the infinite uniform sequence of task of Immediate Snapshots is uniformly solvable. A side benefit of the technique is a widely applicable methodology for the development of uniform protocols.

关键词： Protocols distributed computing Pursuit algorithms Computer science

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Keynote: Time is not a Healer: Before and After 24

Keynote: Time is not a Healer: Before and After

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proceedings of the 43rd acm symposium on principles of distributed computing

作者： Nicola Santoro School of Computer Science Carleton University Ottawa Canada

ISBN: (纸本)9798400706684

distributed computing has been concerned with the topics of faults and failures from its very beginning (before PODC was born). The consensus problem was at the forefront of the research efforts, and an extensive body of literature on the subject was developed very quickly (e.g., [5, 6, 11, 20]). The beautiful proof of the impossibility of consensus under asynchrony [7] put to rest the unsuccessful attempts to prove otherwise, and gave an even stronger impetus to the focus on synchronous *** paper Time is not a Healer [16], which we shall denote by {T¬H}, was concerned with the problem of agreement in synchronous systems where failures have mostly a transient and ubiquitous nature; that is, faults can occur anywhere in the system and, following a failure, normal functioning can resume after a finite (although unpredictable) time. These type of dynamic failures, however, could not be handled by the traditional failure models developed for the consensus and related *** the significance and novelty of the scientific and technical contributions of {T¬H}, including the model, the proof technique, and the unexpected results. Incidentally, while known for its results on omissions, {T¬H} contains also tight bounds on corruptions, additions, and the Byzantine combination of all. While known for its impossibility results, it has tight possibility results, which hold in situations for which the traditional models indicate impossibility. Over the decades, triggered by these results, an extensive literature has been developed (e.g., [3, 4, 8, 9, 13, 15, 19, 21]).The relatively recent developments in communication technology and advent of new virtual systems (e.g., wireless mobile networks, social networks) have driven the research in distributed computing to investigate problems (including consensus) in dynamic networks (e.g., [2, 10, 12]); this has inevitably brought to light the immediate connection between such networks and the ones subject to dynamic omiss

关键词： theory of distributed computation synchronous systems dynamic faults agreement dynamic networks

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PAC=PAExact and other equivalent models in learning

PAC=PAExact and other equivalent models in learning

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Annual IEEE symposium on Foundations of Computer Science

作者： N.H. Bshouty D. Gavinsky Department of Computer Science Technion-Israel Institute of Technology Haifa Israel

The probably almost exact model (PAExact) can be viewed as the exact model relaxed so that: 1. The counterexamples to equivalence queries are distributionally drawn rather than adversarially chosen. 2. The output hypothesis is equal to the target with negligible error (1//spl omega/(poly) for any poly). This model allows studying (almost) exact learnability of infinite classes and is in some sense analogous to the Exact-learning model for finite classes. It is known that PAExact-learnable/spl rArr/PAC-learnable [BJT02]. In this paper we show that if a class is PAC-learnable (in polynomial time) then it is PAExact-learnable (in polynomial time). Therefore, PAExact-learnable=PAC-learnable. It follows from this result that if a class is PAC-learnable then it is learnable in the probabilistic prediction model from examples with an algorithm that runs in polynomial time for each prediction (polynomial in log(the number of trials)) and that after polynomial number of mistakes achieves a hypothesis that predicts the target with probability 1-1/2/sup poly/. We also show that if a class is PAC-learnable in parallel then it is PAExact-learnable in parallel.

关键词： Polynomials Predictive models Computer science Computer simulation Computational modeling Computer errors distributed computing Error correction Boosting

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Sharing incremental approaches for adding parallelism to CS curricula (abstract only) 12

Sharing incremental approaches for adding parallelism to CS ...

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proceedings of the 43rd acm technical symposium on Computer Science Education

作者： Richard A. Brown Elizabeth Shoop Joel C. Adams David P. Bunde Jens Mache Paul F. Steinberg Matthew Wolf Michael Wrinn St. Olaf College Northfield MN USA Macalester College St. Paul MN USA Calvin College Grand Rapids MI USA Knox College Galesburg IL USA Lewis & Clark College Portland OR USA Intel Corporation Portland OR USA Georgia Tech Atlanta GA USA

ISBN: (纸本)9781450310987

Recent industry changes, including multi-core processors, cloud computing, and GPU programming, increase the need to teach parallelism to CS undergraduates. But few CS programs can afford to add new courses or greatly alter syllabi, and the large parallelism body of knowledge relates to many courses. Participants in this BOF will share incremental approaches for adding parallelism to undergraduate CS curricula, where students study parallel computing in brief units. This networking event/ brainstorming session/ swap meet will bring together: " people with sharable parallelism expository readings, hands-on exercises, tech support ideas, etc.; "people wishing to include such materials in their courses; and" people curious about incremental approaches to teaching parallel computing.

关键词： map-reduce CS education accelerators education GPGPU distributed computing scalability curriculum. parallel programming distributed programming multicore data-intensive parallelism cloud computing beowulf clusters parallel computing

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Deterministic broadcasting time in radio networks of unknown topology

Deterministic broadcasting time in radio networks of unknown...

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Annual IEEE symposium on Foundations of Computer Science

作者： D.R. Kowalski A. Pelc Instytut Informatyki University of Warszawski Warszawa Poland Département d'Informatique Université du Quàbec à Hull Hull QUE Canada

In a seminal paper, Bar-Yehuda et al. (1992) considered broadcasting in radio networks whose nodes know only their own label and labels of their neighbors. They claimed a linear lower bound on the time of deterministic broadcasting in such radio networks, by constructing a class of graphs of diameter 3, with the property that every broadcasting algorithm requires linear time on one of these graphs. Due to a subtle error in the argument, this result is incorrect. We construct an algorithm that broadcasts in logarithmic time on all graphs from the work of Bar-Yehuda et al. Moreover, we show how to broadcast in sublinear time on all n-node graphs of diameter o(log log n). On the other hand, we construct a class of graphs of diameter 4, such that every broadcasting algorithm requires time /spl Omega/(4/spl radic/n) on one of these graphs. In view of the randomized algorithm, running in expected time O(D log n + log/sup 2/ n) on all n-node graphs of diameter D, our lower bound gives the first correct proof of an exponential gap between determinism and randomization in the time of radio broadcasting.

关键词： Radio broadcasting Intelligent networks Radio networks Network topology Radio network Radio transmitters distributed computing Current measurement Time measurement Clocks

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On the (non)universality of the one-time pad

On the (non)universality of the one-time pad

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Annual IEEE symposium on Foundations of Computer Science

作者： Y. Dodis J. Spencer Department of Computer Science New York University USA

Randomization is vital in cryptography: secret keys should be randomly generated and most cryptographic primitives (e.g., encryption) must be probabilistic. We initiate the quantitative study concerning feasibility of building secure cryptographic primitives using imperfect random sources. Specifically, we concentrate on symmetric-key encryption and message authentication, where the shared secret key comes from an imperfect random source instead of being assumed truly random. In each case, we compare the class of "cryptographic" sources for the task at hand with the classes of "extractable" and "simulatable" sources, where: (1) "cryptographic" refers to sources for which the corresponding symmetric-key primitive can be built; (2) "extractable" refers to a very narrow class of sources from which one can extract nearly perfect randomness; and (3) "simulatable" refers to a very general class of weak random sources which are known to suffice for BPP simulation. For both encryption and authentication, we show that the corresponding cryptographic sources lie strictly in between extractable and simulatable sources, which implies that "cryptographic usage" of randomness is more demanding than the corresponding "algorithmic usage", but still does not require perfect randomness. Interestingly, cryptographic sources for encryption and authentication are also quite different from each other, which suggests that there might not be an elegant way to describe imperfect sources sufficient for "general cryptographic use". We believe that our initial investigation in this new area will inspire a lot of further research.

关键词： Atherosclerosis Cryptography Computer science Cryptographic protocols Computational modeling History Message authentication Approximation algorithms distributed computing Testing

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