10,951 research outputs found
Deep Neural Networks Evolve Human-like Attention Distribution during Reading Comprehension
Attention is a key mechanism for information selection in both biological
brains and many state-of-the-art deep neural networks (DNNs). Here, we
investigate whether humans and DNNs allocate attention in comparable ways when
reading a text passage to subsequently answer a specific question. We analyze 3
transformer-based DNNs that reach human-level performance when trained to
perform the reading comprehension task. We find that the DNN attention
distribution quantitatively resembles human attention distribution measured by
fixation times. Human readers fixate longer on words that are more relevant to
the question-answering task, demonstrating that attention is modulated by
top-down reading goals, on top of lower-level visual and text features of the
stimulus. Further analyses reveal that the attention weights in DNNs are also
influenced by both top-down reading goals and lower-level stimulus features,
with the shallow layers more strongly influenced by lower-level text features
and the deep layers attending more to task-relevant words. Additionally, deep
layers' attention to task-relevant words gradually emerges when pre-trained DNN
models are fine-tuned to perform the reading comprehension task, which
coincides with the improvement in task performance. These results demonstrate
that DNNs can evolve human-like attention distribution through task
optimization, which suggests that human attention during goal-directed reading
comprehension is a consequence of task optimization
Byzantine Attack and Defense in Cognitive Radio Networks: A Survey
The Byzantine attack in cooperative spectrum sensing (CSS), also known as the
spectrum sensing data falsification (SSDF) attack in the literature, is one of
the key adversaries to the success of cognitive radio networks (CRNs). In the
past couple of years, the research on the Byzantine attack and defense
strategies has gained worldwide increasing attention. In this paper, we provide
a comprehensive survey and tutorial on the recent advances in the Byzantine
attack and defense for CSS in CRNs. Specifically, we first briefly present the
preliminaries of CSS for general readers, including signal detection
techniques, hypothesis testing, and data fusion. Second, we analyze the spear
and shield relation between Byzantine attack and defense from three aspects:
the vulnerability of CSS to attack, the obstacles in CSS to defense, and the
games between attack and defense. Then, we propose a taxonomy of the existing
Byzantine attack behaviors and elaborate on the corresponding attack
parameters, which determine where, who, how, and when to launch attacks. Next,
from the perspectives of homogeneous or heterogeneous scenarios, we classify
the existing defense algorithms, and provide an in-depth tutorial on the
state-of-the-art Byzantine defense schemes, commonly known as robust or secure
CSS in the literature. Furthermore, we highlight the unsolved research
challenges and depict the future research directions.Comment: Accepted by IEEE Communications Surveys and Tutoiral
Effect of Na doping on flux pinning of YBa1.9Na0.1Cu3O7-d
We have prepared Na-doped YBa2Cu3Oy (YBa1.9Na0.1Cu3Oy +40mol%Y211) (YBNCO)
and Na-free YBa2Cu3Oy (YBCO) samples by the Melt-Textured Growth (MTG) method
to study the effect of doped Na ion on flux pinning. The ac susceptibility
curves (acs) as well as the hysteresis loops were measured for the samples.
Then the effective pinning energy (U(T,Hdc,J)), irreversibility line (Hirr(T))
and critical current density (jc(Hdc)) were determined, where T, Hdc and J are
temperature, dc magnetic field and current density, respectively. We found
that, with Na doping, the Hirr(T) line shifted to lower temperature while the
Jc(Hdc) and U(T,Hdc,J) became smaller. It indicates that the Na ions play a
negative role in the flux pinning of YBCO. The appearance of the second peak in
the Jc(Hdc) curves and the enhancement of anisotropy in YBNCO further support
this finding.Comment: 7 pages, 7figures. Submited to Physica.
Poly[bis[μ-1,4-bis(1,2,4-triazol-1-ylmethyl)benzene-κ2 N 4:N 4′]dichloridomanganese(II)]
The MnII atom in the title coordination polymer, [MnCl2(C12H12N6)2]n, lies on a center of inversion in a six-coordinate octahedral environment comprising four N-atom donors from four N-heterocyclic ligands and two chloride atoms. Bridging by the ligands results in a layer structure of a 14.79 (5) × 14.79 (5) Å (4,4) rhombic net topology, with the MnII atoms all lying on a plane. The parallel layers stack in an ABCABC… manner through interlayer C—H⋯N and C—H⋯Cl hydrogen bonds
Efficient infrared upconversion via a ladder-type atomic configuration
We have demonstrated experimentally that infrared light at 1529.4nm can be
converted into the visible at 780nm with 54% efficiency through a ladder-type
atomic configuration in 85Rb. Specifically we theoretically analyze that high
efficiency is due to the large nonlinear dispersion of the index of refraction
from the off-resonant enhancement in a four-wave mixing (FWM) process. By using
two perpendicular polarized pump fields, the coherence of two FWM processes in
this configuration is verified.Comment: The new version is published in Journal of Modern Optic
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