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    What Can We Learn Privately?

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    Learning problems form an important category of computational tasks that generalizes many of the computations researchers apply to large real-life data sets. We ask: what concept classes can be learned privately, namely, by an algorithm whose output does not depend too heavily on any one input or specific training example? More precisely, we investigate learning algorithms that satisfy differential privacy, a notion that provides strong confidentiality guarantees in contexts where aggregate information is released about a database containing sensitive information about individuals. We demonstrate that, ignoring computational constraints, it is possible to privately agnostically learn any concept class using a sample size approximately logarithmic in the cardinality of the concept class. Therefore, almost anything learnable is learnable privately: specifically, if a concept class is learnable by a (non-private) algorithm with polynomial sample complexity and output size, then it can be learned privately using a polynomial number of samples. We also present a computationally efficient private PAC learner for the class of parity functions. Local (or randomized response) algorithms are a practical class of private algorithms that have received extensive investigation. We provide a precise characterization of local private learning algorithms. We show that a concept class is learnable by a local algorithm if and only if it is learnable in the statistical query (SQ) model. Finally, we present a separation between the power of interactive and noninteractive local learning algorithms.Comment: 35 pages, 2 figure

    What can we learn from three-pion interferometry ?

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    We address the question which additional information on the source shape and dynamics can be extracted from three-particle Bose-Einstein correlations. For chaotic sources the true three-particle correlation term is shown to be sensitive to the momentum dependence of the saddle point of the source and to its asymmetries around that point. For partially coherent sources the three-pion correlator allows to measure the degree of coherence without contamination from resonance decays. We derive the most general Gaussian parametrization of the two- and three-particle correlator for this case and discuss the space-time interpretation of the corresponding parameters.Comment: 16 pages, to be published in Phys. Rev.

    What can we learn by squeezing a liquid

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    Relaxation times for different temperatures, T, and specific volumes, V, collapse to a master curve versus TV^g, with g a material constant. The isochoric fragility, m_V, is also a material constant, inversely correlated with g. From these we obtain a 3-parameter function, which fits accurately relaxation times of several glass-formers over the supercooled regime, without any divergence below Tg. Although the 3 parameters depend on the material, only g significant varies; thus, by normalizing material-specific quantities related to g, a universal power law for the dynamics is obtained.Comment: 12 pages, 4 figure

    What can We Learn from City Marketing Practice?

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    It is evident in contemporary urban studies that the interest in city marketing both as a practice within urban centre management and as an academic sub-discipline has accelerated. There remain, however, several issues that need clarification before an agreement can be reached as to the exact effects and potential of city marketing as a tool of economic and socio-cultural development. A particular gap can be noticed between theoretical suggestions on the ways in which marketing should be understood and used within cities and the practical implementation as this can be observed in contemporary cities. A common view on this issue highlights the need for practitioners to follow theoretical ideas but the practice can also be a source of useful lessons that might enrich the theory. This paper investigates marketing and branding practices of two European cities in order to extract from the practice lessons that will support the theoretical development of city marketing and city branding and might contribute towards bridging this gap. The cities investigated are Amsterdam and Budapest, both of which provide valuable insights into the challenges of an effective city marketing implementation
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