535 research outputs found
Two-axis-twisting spin squeezing by multi-pass quantum erasure
Many-body entangled states are key elements in quantum information science
and quantum metrology. One important problem in establishing a high degree of
many-body entanglement using optical techniques is the leakage of the system
information via the light that creates such entanglement. We propose an
all-optical interference-based approach to erase this information. Unwanted
atom-light entanglement can be removed by destructive interference of three or
more successive atom-light interactions, with only the desired effective
atom-atom interaction left. This quantum erasure protocol allows implementation
of Heisenberg-limited spin squeezing using coherent light and a cold or warm
atomic ensemble. Calculations show that significant improvement in the
squeezing exceeding 10 dB is obtained compared to previous methods, and
substantial spin squeezing is attainable even under moderate experimental
conditions. Our method enables the efficient creation of many-body entangled
states with simple setups, and thus is promising for advancing technologies in
quantum metrology and quantum information processing.Comment: 10 pages, 4 figures. We have improved the presentation and added a
new section, in which we have generalized the scheme from a three-pass scheme
to multi-pass schem
Melt Pond Retrieval Based on the LinearPolar Algorithm Using Landsat Data
The formation and distribution of melt ponds have an important influence on the Arctic climate. Therefore, it is necessary to obtain more accurate information on melt ponds on Arctic sea ice by remote sensing. The present large-scale melt pond products, especially the melt pond fraction (MPF), still require verification, and using very high resolution optical satellite remote sensing data is a good way to verify the large-scale retrieval of MPF products. Unlike most MPF algorithms using very high resolution data, the LinearPolar algorithm using Sentinel-2 data considers the albedo of melt ponds unfixed. In this paper, by selecting the best band combination, we applied this algorithm to Landsat 8 (L8) data. Moreover, Sentinel-2 data, as well as support vector machine (SVM) and iterative self-organizing data analysis technique (ISODATA) algorithms, are used as the comparison and verification data. The results show that the recognition accuracy of the LinearPolar algorithm for melt ponds is higher than that of previous algorithms. The overall accuracy and kappa coefficient results achieved by using the LinearPolar algorithm with L8 and Sentinel-2A (S2), the SVM algorithm, and the ISODATA algorithm are 95.38% and 0.88, 94.73% and 0.86, and 92.40%and 0.80, respectively, which are much higher than those of principal component analysis (PCA) and Markus algorithms. The mean MPF (10.0%) obtained from 80 cases from L8 data based on the LinearPolar algorithm is much closer to Sentinel-2 (10.9%) than the Markus (5.0%) and PCA algorithms (4.2%), with a mean MPF difference of only 0.9%, and the correlation coefficients of the two MPFs are as high as 0.95. The overall relative error of the LinearPolar algorithm is 53.5% and 46.4% lower than that of the Markus and PCA algorithms, respectively, and the root mean square error (RMSE) is 30.9% and 27.4% lower than that of the Markus and PCA algorithms, respectively
Detecting stealthy cyberattacks on adaptive cruise control vehicles: A machine learning approach
With the advent of vehicles equipped with advanced driver-assistance systems,
such as adaptive cruise control (ACC) and other automated driving features, the
potential for cyberattacks on these automated vehicles (AVs) has emerged. While
overt attacks that force vehicles to collide may be easily identified, more
insidious attacks, which only slightly alter driving behavior, can result in
network-wide increases in congestion, fuel consumption, and even crash risk
without being easily detected. To address the detection of such attacks, we
first present a traffic model framework for three types of potential
cyberattacks: malicious manipulation of vehicle control commands, false data
injection attacks on sensor measurements, and denial-of-service (DoS) attacks.
We then investigate the impacts of these attacks at both the individual vehicle
(micro) and traffic flow (macro) levels. A novel generative adversarial network
(GAN)-based anomaly detection model is proposed for real-time identification of
such attacks using vehicle trajectory data. We provide numerical evidence {to
demonstrate} the efficacy of our machine learning approach in detecting
cyberattacks on ACC-equipped vehicles. The proposed method is compared against
some recently proposed neural network models and observed to have higher
accuracy in identifying anomalous driving behaviors of ACC vehicles
IS BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) VAL66MET POLYMORPHISM ASSOCIATED WITH OBSESSIVE-COMPULSIVE DISORDER? A META-ANALYSIS
Background: Brain-derived neurotrophic factor (BDNF) polymorphism plays an important role in neural survival and was proposed to be related to obsessive-compulsive disorder (OCD). Genetic association studies of the BDNF Val66Met polymorphism (rs6265) in OCD have produced inconsistent results. A meta-analysis of studies was conducted to compare the frequency of the BDNF Val66Met variant between cases with OCD and age-matched controls.
Subjects and methods: Electronic databases were searched for eligible articles in English and ten studies on the association of the BDNF Val66Met polymorphism with OCD were analysed.
Results: A total of ten studies involving 2306 cases with OCD and 4968 healthy controls were included. Findings indicated that the BDNF Val66Met polymorphism was not associated with OCD. But there was a marginally significant effect of the BDNF Val66Met variant on OCD in different ethnicity.
Conclusion: Findings from this meta-analytic investigation of published literature provide little support for the Val66Met variant of BDNF as a predictor of OCD. Future well-powered agnostic genome-wide association studies with more refined phenotype are needed to clarify genetic influences on OCD
A new algorithm for sea ice melt pond fraction estimation from high-resolution optical satellite imagery
doi: 10.1029/2019JC015716Abstract Melt ponds occupy a large fraction of the Arctic sea ice surface during spring and summer. The fraction and distribution of melt ponds have considerable impacts on Arctic climate and ecosystem by reducing the albedo. There is an urgency to obtain improved accuracy and a wider coverage of melt pond fraction (MPF) data for studying these processes. MPF information has generally been acquired from optical imagery. Conventional MPF algorithms based on high-resolution optical sensors have treated melt ponds as features with constant reflectance; however, the spectral reflectance of ponds can vary greatly, even at a local scale. Here we use Sentinel-2 imagery to demonstrate those previous algorithms assuming fixed melt pond-reflectance greatly underestimate MPF. We propose a new algorithm (?LinearPolar?) based on the polar coordinate transformation that treats melt ponds as variable-reflectance features and calculates MPF across the vector between melt pond and bare ice axes. The angular coordinate ? of the polar coordinate system, which is only associated with pond fraction rather than reflectance, is used to determinate MPF. By comparing the new algorithm and previous methods with IceBridge optical imagery data, across a variety of Sentinel-2 images with melt ponds at various stages of development, we show that the RMSE value of the LinearPolar algorithm is about 30% lower than for the previous algorithms. Moreover, based on a sensitivity test, the new algorithm is also less sensitive to the subjective threshold for melt pond reflectance than previous algorithms.Peer reviewe
A detection of the layered structure of nearby open clusters
We applied the newly developed rose diagram overlay method to detect the
layered structure of 88 nearby open clusters (500~pc) on the three
projections after the distance correction of their member stars, based on the
catalog in literature. The results show that with the rose diagram overlay
method, a total of 74 clusters in our sample have a layered structure, while
the remaining clusters are without a clear layered structure. We for the first
time defined the layered structure parameters for the sample clusters.
Meanwhile, we found that the layered circle core area () has a strong
positive correlation with the number of cluster members, while the kernel
instability index () has a strong negative correlation with the number of
cluster members. Our study provides a novel perspective for the detection of
the layered structure of open clusters.Comment: 11 pages, 9 figures, 6 tables, accepted for publication in A&
Improved l1-SPIRiT using 3D walsh transform-based sparsity basis
l1-SPIRiT is a fast magnetic resonance imaging (MRI) method which combines parallel imaging (PI) with compressed sensing (CS) by performing a joint l1-norm and l2-norm optimization procedure. The original l1-SPIRiT method uses two-dimensional (2D) Wavelet transform to exploit the intra-coil data redundancies and a joint sparsity model to exploit the inter-coil data redundancies. In this work, we propose to stack all the coil images into a three-dimensional (3D) matrix, and then a novel 3D Walsh transform-based sparsity basis is applied to simultaneously reduce the intra-coil and inter-coil data redundancies. Both the 2D Wavelet transform-based and the proposed 3D Walsh transform-based sparsity bases were investigated in the l1-SPIRiT method. The experimental results show that the proposed 3D Walsh transform-based l1-SPIRiT method outperformed the original l1-SPIRiT in terms of image quality and computational efficiency
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