41,805 research outputs found
A two-way regularization method for MEG source reconstruction
The MEG inverse problem refers to the reconstruction of the neural activity
of the brain from magnetoencephalography (MEG) measurements. We propose a
two-way regularization (TWR) method to solve the MEG inverse problem under the
assumptions that only a small number of locations in space are responsible for
the measured signals (focality), and each source time course is smooth in time
(smoothness). The focality and smoothness of the reconstructed signals are
ensured respectively by imposing a sparsity-inducing penalty and a roughness
penalty in the data fitting criterion. A two-stage algorithm is developed for
fast computation, where a raw estimate of the source time course is obtained in
the first stage and then refined in the second stage by the two-way
regularization. The proposed method is shown to be effective on both synthetic
and real-world examples.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS531 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Security of a biometric identity-based encryption scheme
Biometric identity-based encryption (Bio-IBE) is a kind of fuzzy
identity-based encryption (fuzzy IBE) where a ciphertext encrypted under an
identity w' can be decrypted using a secret key corresponding to the identity w
which is close to w' as measured by some metric. Recently, Yang et al. proposed
a constant-size Bio-IBE scheme and proved that it is secure against adaptive
chosen-ciphertext attack (CCA2) in the random oracle model. Unfortunately, in
this paper, we will show that their Bio-IBE scheme is even not chosen-plaintext
secure. Specifically, user w using his secret key is able to decrypt any
ciphertext encrypted under an identity w' even though w is not close to w'.Comment: Journal version of the paper will be appearing in International
Journal of Network Securit
Electric Fields and Chiral Magnetic Effect in Cu + Au Collisions
The non-central Cu + Au collisions can create strong out-of-plane magnetic
fields and in-plane electric fields. By using the HIJING model, we study the
general properties of the electromagnetic fields in Cu + Au collisions at 200
GeV and their impacts on the charge-dependent two-particle correlator
(see main text for
definition) which was used for the detection of the chiral magnetic effect
(CME). Compared with Au + Au collisions, we find that the in-plane electric
fields in Cu + Au collisions can strongly suppress the two-particle correlator
or even reverse its sign if the lifetime of the electric fields is long.
Combining with the expectation that if is induced by
elliptic-flow driven effects we would not see such strong suppression or
reversion, our results suggest to use Cu + Au collisions to test CME and
understand the mechanisms that underlie .Comment: V1: 7 pages, 8 figures. V2: Add 2 new figures. Published versio
Contrast Enhancement of Brightness-Distorted Images by Improved Adaptive Gamma Correction
As an efficient image contrast enhancement (CE) tool, adaptive gamma
correction (AGC) was previously proposed by relating gamma parameter with
cumulative distribution function (CDF) of the pixel gray levels within an
image. ACG deals well with most dimmed images, but fails for globally bright
images and the dimmed images with local bright regions. Such two categories of
brightness-distorted images are universal in real scenarios, such as improper
exposure and white object regions. In order to attenuate such deficiencies,
here we propose an improved AGC algorithm. The novel strategy of negative
images is used to realize CE of the bright images, and the gamma correction
modulated by truncated CDF is employed to enhance the dimmed ones. As such,
local over-enhancement and structure distortion can be alleviated. Both
qualitative and quantitative experimental results show that our proposed method
yields consistently good CE results
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