495 research outputs found
Differentially Private Data Releasing for Smooth Queries with Synthetic Database Output
We consider accurately answering smooth queries while preserving differential
privacy. A query is said to be -smooth if it is specified by a function
defined on whose partial derivatives up to order are all
bounded. We develop an -differentially private mechanism for the
class of -smooth queries. The major advantage of the algorithm is that it
outputs a synthetic database. In real applications, a synthetic database output
is appealing. Our mechanism achieves an accuracy of , and runs in polynomial time. We also
generalize the mechanism to preserve -differential privacy
with slightly improved accuracy. Extensive experiments on benchmark datasets
demonstrate that the mechanisms have good accuracy and are efficient
Empirical Comparison of Skewed t-copula Models for Insurance and Financial Data
Skewed t-copulas recently became popular as a modeling tool of non-linear dependence in statistics. In this paper we consider three different versions of skewed t-copulas introduced by Demarta and McNeill; Smith, Gan and Kohn; and Azzalini and Capitanio. Each of these versions represents a generalization of the symmetric t-copula model, allowing for a different treatment of lower and upper tails. Each of them has certain advantages in mathematical construction, inferential tools and interpretability. Our objective is to apply models based on different types of skewed t-copulas to the same financial and insurance applications. We consider comovements of stock index returns and times-to-failure of related vehicle parts under the warranty period. In both cases the treatment of both lower and upper tails of the joint distributions is of a special importance. Skewed t-copula model performance is compared to the benchmark cases of Gaussian and symmetric Student t-copulas. Instruments of comparison include information criteria, goodness-of-fit and tail dependence. A special attention is paid to methods of estimation of copula parameters. Some technical problems with the implementation of maximum likelihood method and the method of moments suggest the use of Bayesian estimation. We discuss the accuracy and computational efficiency of Bayesian estimation versus MLE. Metropolis-Hastings algorithm with block updates was suggested to deal with the problem of intractability of conditionals
Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers
We report that the refractive index of transition metal dichacolgenide (TMDC)
monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in
the imaginary part and > 20% in the real part around exciton resonances using
CMOS-compatible electrical gating. This giant tunablility is rooted in the
dominance of excitonic effects in the refractive index of the monolayers and
the strong susceptibility of the excitons to the influence of injected charge
carriers. The tunability mainly results from the effects of injected charge
carriers to broaden the spectral width of excitonic interband transitions and
to facilitate the interconversion of neutral and charged excitons. The other
effects of the injected charge carriers, such as renormalizing bandgap and
changing exciton binding energy, only play negligible roles. We also
demonstrate that the atomically thin monolayers, when combined with photonic
structures, can enable the efficiencies of optical absorption (reflection)
tuned from 40% (60%) to 80% (20%) due to the giant tunability of refractive
index. This work may pave the way towards the development of field-effect
photonics in which the optical functionality can be controlled with CMOS
circuits
Career Experience and Executive Performance: Evidence from Former Equity Research Analysts
This study examines CEOs and CFOs who have prior work experience as equity research analysts. Consistent with backgrounds in forecasting and valuation, we find these executives provide earnings guidance that is more accurate than that of other executives, and their M&A transactions generate significantly higher announcement returns. For available CEOs and CFOs, we examine their track records as research analysts with respect to forecasting accuracy and stock recommendation profitability. We find a positive association between a record of past forecasting accuracy and more accurate earnings guidance, as well as a positive association between past stock recommendation profitability and M&A announcement returns. Beyond these traits, we find these executives provide greater certainty in their answers to analysts during conference calls, especially when answering forward-looking questions. Finally, these executives’ firms exhibit superior accounting and stock return performance. Overall, our evidence suggests early career skill sets can shape top executive performance outcomes
Deep recurrent spiking neural networks capture both static and dynamic representations of the visual cortex under movie stimuli
In the real world, visual stimuli received by the biological visual system
are predominantly dynamic rather than static. A better understanding of how the
visual cortex represents movie stimuli could provide deeper insight into the
information processing mechanisms of the visual system. Although some progress
has been made in modeling neural responses to natural movies with deep neural
networks, the visual representations of static and dynamic information under
such time-series visual stimuli remain to be further explored. In this work,
considering abundant recurrent connections in the mouse visual system, we
design a recurrent module based on the hierarchy of the mouse cortex and add it
into Deep Spiking Neural Networks, which have been demonstrated to be a more
compelling computational model for the visual cortex. Using Time-Series
Representational Similarity Analysis, we measure the representational
similarity between networks and mouse cortical regions under natural movie
stimuli. Subsequently, we conduct a comparison of the representational
similarity across recurrent/feedforward networks and image/video training
tasks. Trained on the video action recognition task, recurrent SNN achieves the
highest representational similarity and significantly outperforms feedforward
SNN trained on the same task by 15% and the recurrent SNN trained on the image
classification task by 8%. We investigate how static and dynamic
representations of SNNs influence the similarity, as a way to explain the
importance of these two forms of representations in biological neural coding.
Taken together, our work is the first to apply deep recurrent SNNs to model the
mouse visual cortex under movie stimuli and we establish that these networks
are competent to capture both static and dynamic representations and make
contributions to understanding the movie information processing mechanisms of
the visual cortex
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