8,193 research outputs found
Characterizing Intermittency of 4-Hz Quasi-periodic Oscillation in XTE J1550-564 using Hilbert-Huang Transform
We present the time-frequency analysis results based on the Hilbert-Huang
transform (HHT) for the evolution of a 4-Hz low-frequency quasi-periodic
oscillation (LFQPO) around the black hole X-ray binary XTE J1550-564. The
origin of LFQPOs is still debated. To understand the cause of the peak
broadening, we utilized a recently developed time-frequency analysis, HHT, for
tracking the evolution of the 4-Hz LFQPO from XTE J1550 564. By adaptively
decomposing the ~4-Hz oscillatory component from the light curve and acquiring
its instantaneous frequency, the Hilbert spectrum illustrates that the LFQPO is
composed of a series of intermittent oscillations appearing occasionally
between 3 Hz and 5 Hz. We further characterized this intermittency by computing
the confidence limits of the instantaneous amplitudes of the intermittent
oscillations, and constructed both the distributions of the QPO's high and low
amplitude durations, which are the time intervals with and without significant
~4-Hz oscillations, respectively. The mean high amplitude duration is 1.45 s
and 90% of the oscillation segments have lifetimes below 3.1 s. The mean low
amplitude duration is 0.42 s and 90% of these segments are shorter than 0.73 s.
In addition, these intermittent oscillations exhibit a correlation between the
oscillation's rms amplitude and mean count rate. This correlation could be
analogous to the linear rms-flux relation found in the 4-Hz LFQPO through
Fourier analysis. We conclude that the LFQPO peak in the power spectrum is
broadened owing to intermittent oscillations with varying frequencies, which
could be explained by using the Lense-Thirring precession model.Comment: 27 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Diagrammatic approach to excitonic effects on nonlinear optical response
Optical responses of atomically thin 2D materials are greatly influenced by
electron-hole interactions. It is by far established that exciton signatures
can be well-identified in the optical absorption spectrum of quasi-2D
materials. However, the same level of understanding of excitonic effects on
nonlinear optical responses and the ability to compute them accurately is still
much desired. Based on the functional integral formalisms and working in the
velocity gauge, we introduce a convenient Feynman diagram approach for
calculating nonlinear responses including excitonic effects. By dressing
electron-photon interactions with electron-hole ladder diagrams, we derive an
expression for second-order optical responses and provide a comprehensive
description of excitonic effects. We apply our approach to a monolayer h-BN
model and show qualitative changes in the second harmonic generation spectrum
when comparing with results assuming independent particles. Our approach can be
readily extended to higher order optical responses and is feasible for
first-principles calculations
THE ELECTROMYOGRAPHY CHARACTERISTICS BETWEEN DIFFERENT LEVELS OF SOCCER PLAYER ON INSTEP KICKING
This study improves kicking performance by comparing muscle activity between different levels of players. Twelve soccer players in the college cup in division I and division II volunteered to participate in this study. A VlCON motion capture system (200 Hz) was used to capture the kicking motion including back-swing and forward-swing. The Noraxon electromyography system was used to collect and analyze the percentage of maximum voluntary contraction on rectus femoris, bicepsfemoris, tibialis anterior, and gastrocnemius. The Mann-Whilney U (a = -05) test was applied to assess significant differences in this study. The results indicated that division II players had a greater percentage maximum voluntary contraction in tibialis anterior in the back-swing. To avoid stiff movements in soccer kicks, division II players should decrease muscle contraction in the tiblalis anterior In the back-swing
Prompt Tuning for Generative Multimodal Pretrained Models
Prompt tuning has become a new paradigm for model tuning and it has
demonstrated success in natural language pretraining and even vision
pretraining. In this work, we explore the transfer of prompt tuning to
multimodal pretraining, with a focus on generative multimodal pretrained
models, instead of contrastive ones. Specifically, we implement prompt tuning
on the unified sequence-to-sequence pretrained model adaptive to both
understanding and generation tasks. Experimental results demonstrate that the
light-weight prompt tuning can achieve comparable performance with finetuning
and surpass other light-weight tuning methods. Besides, in comparison with
finetuned models, the prompt-tuned models demonstrate improved robustness
against adversarial attacks. We further figure out that experimental factors,
including the prompt length, prompt depth, and reparameteratization, have great
impacts on the model performance, and thus we empirically provide a
recommendation for the setups of prompt tuning. Despite the observed
advantages, we still find some limitations in prompt tuning, and we
correspondingly point out the directions for future studies. Codes are
available at \url{https://github.com/OFA-Sys/OFA}Comment: Work in progres
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