629,897 research outputs found
Differential Privacy for Relational Algebra: Improving the Sensitivity Bounds via Constraint Systems
Differential privacy is a modern approach in privacy-preserving data analysis
to control the amount of information that can be inferred about an individual
by querying a database. The most common techniques are based on the
introduction of probabilistic noise, often defined as a Laplacian parametric on
the sensitivity of the query. In order to maximize the utility of the query, it
is crucial to estimate the sensitivity as precisely as possible.
In this paper we consider relational algebra, the classical language for
queries in relational databases, and we propose a method for computing a bound
on the sensitivity of queries in an intuitive and compositional way. We use
constraint-based techniques to accumulate the information on the possible
values for attributes provided by the various components of the query, thus
making it possible to compute tight bounds on the sensitivity.Comment: In Proceedings QAPL 2012, arXiv:1207.055
Prospects for Measuring Cosmic Microwave Background Spectral Distortions in the Presence of Foregrounds
Measurements of cosmic microwave background spectral distortions have
profound implications for our understanding of physical processes taking place
over a vast window in cosmological history. Foreground contamination is
unavoidable in such measurements and detailed signal-foreground separation will
be necessary to extract cosmological science. We present MCMC-based spectral
distortion detection forecasts in the presence of Galactic and extragalactic
foregrounds for a range of possible experimental configurations, focusing on
the Primordial Inflation Explorer (PIXIE) as a fiducial concept. We consider
modifications to the baseline PIXIE mission (operating 12 months in distortion
mode), searching for optimal configurations using a Fisher approach. Using only
spectral information, we forecast an extended PIXIE mission to detect the
expected average non-relativistic and relativistic thermal Sunyaev-Zeldovich
distortions at high significance (194 and 11, respectively),
even in the presence of foregrounds. The CDM Silk damping -type
distortion is not detected without additional modifications of the instrument
or external data. Galactic synchrotron radiation is the most problematic source
of contamination in this respect, an issue that could be mitigated by combining
PIXIE data with future ground-based observations at low frequencies (GHz). Assuming moderate external information on the synchrotron spectrum,
we project an upper limit of (95\% c.l.), slightly
more than one order of magnitude above the fiducial CDM signal from
the damping of small-scale primordial fluctuations, but a factor of improvement over the current upper limit from COBE/FIRAS. This limit could
be further reduced to (95\% c.l.) with more
optimistic assumptions about low-frequency information. (Abridged)Comment: (16 pages, 11 figures, submitted to MNRAS. Fisher code available at
https://github.com/mabitbol/sd_foregrounds. Updated with published version.
Network meta-analysis of diagnostic test accuracy studies identifies and ranks the optimal diagnostic tests and thresholds for healthcare policy and decision making
Objective:
Network meta-analyses have extensively been used to compare the effectiveness of multiple interventions for healthcare policy and decision-making. However, methods for evaluating the performance of multiple diagnostic tests are less established. In a decision-making context, we are often interested in comparing and ranking the performance of multiple diagnostic tests, at varying levels of test thresholds, in one simultaneous analysis.
Study design and setting:
Motivated by an example of cognitive impairment diagnosis following stroke, we synthesized data from 13 studies assessing the efficiency of two diagnostic tests: Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA), at two test thresholds: MMSE <25/30 and <27/30, and MoCA <22/30 and <26/30. Using Markov Chain Monte Carlo (MCMC) methods, we fitted a bivariate network meta-analysis model incorporating constraints on increasing test threshold, and accounting for the correlations between multiple test accuracy measures from the same study.
Results:
We developed and successfully fitted a model comparing multiple tests/threshold combinations while imposing threshold constraints. Using this model, we found that MoCA at threshold <26/30 appeared to have the best true positive rate, whilst MMSE at threshold <25/30 appeared to have the best true negative rate.
Conclusion:
The combined analysis of multiple tests at multiple thresholds allowed for more rigorous comparisons between competing diagnostics tests for decision making
Introducing the sequential linear programming level-set method for topology optimization
The authors would like to thank Numerical Analysis Group at the Rutherford Appleton Laboratory for their FORTRAN HSL packages (HSL, a collection of Fortran codes for large-scale scientific computation. See http://www.hsl.rl.ac.uk/). Dr H Alicia Kim acknowledges the support from Engineering and Physical Sciences Research Council, grant number EP/M002322/1Peer reviewedPublisher PD
Effects of foreign acquisitions on financial constraints, productivity and investment in R&D of target firms in China
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.This paper examines whether foreign acquisitions lessen financial constraints, improve investment in research & development (R&D) and productivity of the target firms in China based on a sample of 914 cross-border mergers and acquisitions (CBM&A) over the period of 1994-2011. Using investment to cash-flow sensitivity to measure financial constraints, we find that foreign acquisitions in China are associated with a reduction of target firms’ financial constraints, irrespective of the ownership type of the target firm. However, the extent of financial constraint reduction is pronounced for non-SOEs compared to state-owned enterprises (SOEs). This study also provides evidence that foreign acquisitions improve Chinese target firms’ productivity and investment in R&D
The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions
We present the results of the largest (m) direct
imaging survey for exoplanets to date, the Large Binocular Telescope
Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98
stars with spectral types from B to M. Cool planets emit a larger share of
their flux in compared to shorter wavelengths, affording LEECH an
advantage in detecting low-mass, old, and cold-start giant planets. We
emphasize proximity over youth in our target selection, probing physical
separations smaller than other direct imaging surveys. For FGK stars, LEECH
outperforms many previous studies, placing tighter constraints on the hot-start
planet occurrence frequency interior to au. For less luminous,
cold-start planets, LEECH provides the best constraints on giant-planet
frequency interior to au around FGK stars. Direct imaging survey
results depend sensitively on both the choice of evolutionary model (e.g., hot-
or cold-start) and assumptions (explicit or implicit) about the shape of the
underlying planet distribution, in particular its radial extent. Artificially
low limits on the planet occurrence frequency can be derived when the shape of
the planet distribution is assumed to extend to very large separations, well
beyond typical protoplanetary dust-disk radii ( au), and when
hot-start models are used exclusively. We place a conservative upper limit on
the planet occurrence frequency using cold-start models and planetary
population distributions that do not extend beyond typical protoplanetary
dust-disk radii. We find that of FGK systems can host a 7 to 10
planet from 5 to 50 au. This limit leaves open the
possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A
Really Natural Linear Indexed Type Checking
Recent works have shown the power of linear indexed type systems for
enforcing complex program properties. These systems combine linear types with a
language of type-level indices, allowing more fine-grained analyses. Such
systems have been fruitfully applied in diverse domains, including implicit
complexity and differential privacy. A natural way to enhance the
expressiveness of this approach is by allowing the indices to depend on runtime
information, in the spirit of dependent types. This approach is used in DFuzz,
a language for differential privacy. The DFuzz type system relies on an index
language supporting real and natural number arithmetic over constants and
variables. Moreover, DFuzz uses a subtyping mechanism to make types more
flexible. By themselves, linearity, dependency, and subtyping each require
delicate handling when performing type checking or type inference; their
combination increases this challenge substantially, as the features can
interact in non-trivial ways. In this paper, we study the type-checking problem
for DFuzz. We show how we can reduce type checking for (a simple extension of)
DFuzz to constraint solving over a first-order theory of naturals and real
numbers which, although undecidable, can often be handled in practice by
standard numeric solvers
Human-Machine Collaborative Optimization via Apprenticeship Scheduling
Coordinating agents to complete a set of tasks with intercoupled temporal and
resource constraints is computationally challenging, yet human domain experts
can solve these difficult scheduling problems using paradigms learned through
years of apprenticeship. A process for manually codifying this domain knowledge
within a computational framework is necessary to scale beyond the
``single-expert, single-trainee" apprenticeship model. However, human domain
experts often have difficulty describing their decision-making processes,
causing the codification of this knowledge to become laborious. We propose a
new approach for capturing domain-expert heuristics through a pairwise ranking
formulation. Our approach is model-free and does not require enumerating or
iterating through a large state space. We empirically demonstrate that this
approach accurately learns multifaceted heuristics on a synthetic data set
incorporating job-shop scheduling and vehicle routing problems, as well as on
two real-world data sets consisting of demonstrations of experts solving a
weapon-to-target assignment problem and a hospital resource allocation problem.
We also demonstrate that policies learned from human scheduling demonstration
via apprenticeship learning can substantially improve the efficiency of a
branch-and-bound search for an optimal schedule. We employ this human-machine
collaborative optimization technique on a variant of the weapon-to-target
assignment problem. We demonstrate that this technique generates solutions
substantially superior to those produced by human domain experts at a rate up
to 9.5 times faster than an optimization approach and can be applied to
optimally solve problems twice as complex as those solved by a human
demonstrator.Comment: Portions of this paper were published in the Proceedings of the
International Joint Conference on Artificial Intelligence (IJCAI) in 2016 and
in the Proceedings of Robotics: Science and Systems (RSS) in 2016. The paper
consists of 50 pages with 11 figures and 4 table
- …