Parallel-filter-based observer control for unknown multiple narrow-band disturbance rejection

An observer-based control method with parallel Q-filter is proposed to reject unknown multiple narrow-band disturbances for line of sight stabilization in telescope systems. In general, wide-band or multiple narrow-band disturbances rejection of observer-based control can be transformed into designing Q-filter, which could be too high-order to achieve fully-accuracy digital implementation, resulting in degrading the closed-loop performance or even causing instability. Therefore, a new parallel type of Q-filters is proposed to flexibly adjust the number of Q-filter in the sensitivity function and effectively reduce the computational complexity. A sufficient condition of the effectiveness for the parallel Q-filter and the closed-loop stability is derived and verified through simulations. Furthermore, disturbance frequencies can be on-line identified to adaptively optimize the Q-filter parameters. The effectiveness of the proposed method is validated on the image-based stabilization subsystem of a segmented lightweight large-scaled diffractive telescope.

Measuring sound velocity based on acoustic resonance using multiple narrow band transducers

The sound velocity in a medium is closely related to its material properties, including its composition, structure, density, pressure, and temperature. Various methods have been developed to determine the sound velocity through materials. Among them, a strategy based on ultrasound resonance frequency has been most widely used due to the simplicity. However, it requires a transducer with a wide bandwidth to cover enough resonance frequencies to perform the consequent calculations. In this paper, we develop a resonance method for measuring sound velocity, using multi-frequency narrow-band transducers breaking through the limitation of transducer bandwidth on the utilization of the resonance method. We use different transducers at different center frequencies and with different bandwidth to measure the sound velocity in 100-μm and 400-μm thick steel pieces. The measurement results of different combinations are in good agreement, verifying that the use of multi-frequency narrow-band transducer combinations. Given that most therapeutic transducers have a narrow bandwidth, this method can be used during intracranial ultrasound stimulation to optimize targeting by non-invasively measuring the sound velocity in the skull, especially at thinner locations.

Alterations in regional homogeneity and multiple frequency amplitudes of low-frequency fluctuation in patients with new daily persistent headache: a resting-state functional magnetic resonance imaging study

BACKGROUND

New daily persistent headache (NPDH) is a rare primary headache that is highly disabling. The pathophysiology of NDPH is still unclear, and we aimed to reveal the underlying mechanism of NDPH through functional magnetic resonance imaging (fMRI) analysis.

METHODS

In this cross-sectional study, thirty patients with NDPH and 30 healthy controls (HCs) were recruited. The blood oxygen level-dependent (BOLD) sequences of all participants were obtained using the GE 3.0 T system. We performed ReHo, ALFF (conventional band: 0.01-0.08 Hz, slow-5: 0.01-0.027 Hz, slow-4: 0.027-0.073 Hz) and seed-based to the whole brain functional connectivity (FC) analysis in the NDPH and HC groups. The sex difference analysis of ReHo, ALFF, and FC values was conducted in the NDPH group. We also conducted Pearson's correlation analysis between ReHo, ALFF, FC values and clinical characteristics (pain intensity, disease duration, HIT-6, GAD-7, PHQ-9, and PSQI scores).

RESULTS

Both increased ReHo (P_FWE-corr = 0.012) and ALFF values (0.01-0.08 Hz, P_FWE-corr = 0.009; 0.027-0.073 Hz, P_FWE-corr =0.044) of the left middle occipital gyrus (MOG_L) were found in the NDPH group compared to the HC group. There was no significant difference in FC maps between the two groups. Compared to the HC group, no difference was found in ReHo (p = 0.284), ALFF (p = 0.246), and FC (p = 0.118) z scores of the MOG_L in the NDPH group. There was also no sex difference in ReHo (p = 0.288), ALFF (p = 0.859), or FC z score (p = 0.118) of the MOG_L in patients with NDPH. There was no correlation between ReHo, ALFF, FC z scores and clinical characteristics after Bonferroni correction (p < 0.05/18).

CONCLUSIONS

Patients with NDPH may have abnormal activation of the visual system. Abnormal visual activation may occur mainly in higher frequency band of the classical band. No sex differences in brain activity were found in patients with NDPH.

Brain-computer interface method based on light-flashing and motion hybrid coding

The human best response frequency band for steady-state visual evoked potential stimulus is limited. This results in a reduced number of encoded targets. To circumvent this, we proposed a brain-computer interface (BCI) method based on light-flashing and motion hybrid coding. The hybrid paradigm pattern consisted of a circular light-flashing pattern and a motion pattern located in the inner ring of light-flashing pattern. The motion and light-flashing patterns had different frequencies. This study used five frequencies to encode nine targets. The motion frequency and the light-flashing frequency of the hybrid paradigm consisted of two frequencies in five frequencies. The experimental results showed that the hybrid paradigm could induce stable motion frequency, light-flashing frequency and its harmonic components. Moreover, the modulation between motion and light-flashing was weak. The average accuracy was 92.96% and the information transfer rate was 26.10 bits/min. The experimental results showed that the proposed method could be considered for practical BCI systems.