8,166 research outputs found
Convex Optimization for Linear Query Processing under Approximate Differential Privacy
Differential privacy enables organizations to collect accurate aggregates
over sensitive data with strong, rigorous guarantees on individuals' privacy.
Previous work has found that under differential privacy, computing multiple
correlated aggregates as a batch, using an appropriate \emph{strategy}, may
yield higher accuracy than computing each of them independently. However,
finding the best strategy that maximizes result accuracy is non-trivial, as it
involves solving a complex constrained optimization program that appears to be
non-linear and non-convex. Hence, in the past much effort has been devoted in
solving this non-convex optimization program. Existing approaches include
various sophisticated heuristics and expensive numerical solutions. None of
them, however, guarantees to find the optimal solution of this optimization
problem.
This paper points out that under (, )-differential privacy,
the optimal solution of the above constrained optimization problem in search of
a suitable strategy can be found, rather surprisingly, by solving a simple and
elegant convex optimization program. Then, we propose an efficient algorithm
based on Newton's method, which we prove to always converge to the optimal
solution with linear global convergence rate and quadratic local convergence
rate. Empirical evaluations demonstrate the accuracy and efficiency of the
proposed solution.Comment: to appear in ACM SIGKDD 201
Molecular Dynamics Simulation of Strong Shock Waves Propagating in Dense Deuterium With the Effect of Excited Electrons
We present a molecular dynamics simulation of shock waves propagating in
dense deuterium with the electron force field method [J. T. Su and W. A.
Goddard, Phys. Rev. Lett. 99, 185003 (2007)], which explicitly takes the
excitation of electrons into consideration. Non-equilibrium features associated
with the excitation of electrons are systematically investigated. We show that
chemical bonds in D molecules lead to a more complicated shock wave
structure near the shock front, compared with the results of classical
molecular dynamics simulation. Charge separation can bring about accumulation
of net charges on the large scale, instead of the formation of a localized
dipole layer, which might cause extra energy for the shock wave to propagate.
In addition, the simulations also display that molecular dissociation at the
shock front is the major factor corresponding to the "bump" structure in the
principal Hugoniot. These results could help to build a more realistic picture
of shock wave propagation in fuel materials commonly used in the inertial
confinement fusion
Ground-Challenge: A Multi-sensor SLAM Dataset Focusing on Corner Cases for Ground Robots
High-quality datasets can speed up breakthroughs and reveal potential
developing directions in SLAM research. To support the research on corner cases
of visual SLAM systems, this paper presents Ground-Challenge: a challenging
dataset comprising 36 trajectories with diverse corner cases such as aggressive
motion, severe occlusion, changing illumination, few textures, pure rotation,
motion blur, wheel suspension, etc. The dataset was collected by a ground robot
with multiple sensors including an RGB-D camera, an inertial measurement unit
(IMU), a wheel odometer and a 3D LiDAR. All of these sensors were
well-calibrated and synchronized, and their data were recorded simultaneously.
To evaluate the performance of cutting-edge SLAM systems, we tested them on our
dataset and demonstrated that these systems are prone to drift and fail on
specific sequences. We will release the full dataset and relevant materials
upon paper publication to benefit the research community. For more information,
visit our project website at https://github.com/sjtuyinjie/Ground-Challenge
Optimizing Batch Linear Queries under Exact and Approximate Differential Privacy
Differential privacy is a promising privacy-preserving paradigm for
statistical query processing over sensitive data. It works by injecting random
noise into each query result, such that it is provably hard for the adversary
to infer the presence or absence of any individual record from the published
noisy results. The main objective in differentially private query processing is
to maximize the accuracy of the query results, while satisfying the privacy
guarantees. Previous work, notably \cite{LHR+10}, has suggested that with an
appropriate strategy, processing a batch of correlated queries as a whole
achieves considerably higher accuracy than answering them individually.
However, to our knowledge there is currently no practical solution to find such
a strategy for an arbitrary query batch; existing methods either return
strategies of poor quality (often worse than naive methods) or require
prohibitively expensive computations for even moderately large domains.
Motivated by this, we propose low-rank mechanism (LRM), the first practical
differentially private technique for answering batch linear queries with high
accuracy. LRM works for both exact (i.e., -) and approximate (i.e.,
(, )-) differential privacy definitions. We derive the
utility guarantees of LRM, and provide guidance on how to set the privacy
parameters given the user's utility expectation. Extensive experiments using
real data demonstrate that our proposed method consistently outperforms
state-of-the-art query processing solutions under differential privacy, by
large margins.Comment: ACM Transactions on Database Systems (ACM TODS). arXiv admin note:
text overlap with arXiv:1212.230
Can digital finance drive urban–rural integration?
Financial services are an essential source of capital and play a crucial
and significant role in urban–rural integration. We analyse empirically
the effect of digital finance on urban–rural integration and its
mechanism using provincial panel data in China for 2011–2020. The
results indicate that digital finance contributes to urban–rural integration.
Moreover, for every 1 standard deviation increase in digital
finance development, the degree of urban–rural integration
increases by 7.7% on average, and it is more evident in China’s eastern
regions, with regional heterogeneity. The level of entrepreneurship
can be a vital channel for digital finance to facilitate urban–
rural integration. The mechanism of action of digital finance to facilitate
urban–rural integration by improving entrepreneurship levels is
primarily revealed in the group with lower levels of human capital,
which exhibits certain inclusive characteristics. This study is conducive
to developing a policy for promoting the free flow of resources
between urban and rural areas and advancing urban–rural
integration
Heat transfer characteristic analysis of negative pressure type EGR valve based on CFD
The negative pressure valve EGR bears thermal load for a long period, thus its heat transfer characteristics have an important impact on the stability of the engine. The fluid solid coupling method was employed to analyze the contact heat transfer between the inner cavity of the valve and the cooling water as well as the high temperature gas based on CFD. As a result, the characteristics of the internal fluid velocity field, pressure field and temperature field were obtained. Besides, the heat transfer capability of the valve was also improved by adding the annular cooling water channel. The test results showed that the calculation method has a high calculation accuracy providing an important basis for the optimization design of valves
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