Active axial vibration control of a shaft-bearing system excited by the dynamic thrust force

The axial vibration of a shaft-bearing system induced by the thrust excitation is usually composed of multiple tones. To suppress the axial vibration of the shaft-bearing system, two inertial electro-magnetic actuators are mounted symmetrically at the thrust bearing and work in parallel to exert control forces. The control signal is generated by an adaptive algorithm with subband filtering, which aims to attenuate over a broadband the vibration of the thrust bearing and its foundation induced by the dynamic thrust force. To reduce computational complexity, the recursive computation is partly realized with the auto-regressive moving average (ARMA) model. The proposed active control approach is evaluated numerically at first with the dynamic model of the shaft-bearing system and then verified with an experimental system. It is demonstrated by the numerical and experimental results that the active control approach is able to suppress the multi-tone vibration of the thrust bearing and the foundation. Moreover, in comparison to the single-band adaptive feedback algorithm, the adaptive algorithm with subband filtering is more effective when the disturbance contains multiple tones.

DETECTION OF A HARMONIC SIGNAL AGAINST THE BACKGROUND OF A NONSTATIONARY GAUSSIANINTERFERENCE WITH COMPLEX SPECTRUM

Background. Modern radar stations for various purposes operate in the conditions of interference created by the imprints of the radar signal from the background surface, from metrological formations (precipitation, clouds, etc.) and artificial radiation sources. Ensuring the operation of the radar in such difficult conditions requires the construction of adaptive signal processing algorithms that have high efficiency and maintain them when changing signal-to-noise situations. Objective. The purpose of the paper is creation of an adaptive algorithm for detecting a harmonic signal against the background of spatially correlated interference and estimating its parameters. Methods. Construction of a two-dimensional autoregressive model of a mixture of correlated spatial noise and harmonic signal and application of the empirical Bayesian approach to the synthesis of an adaptive algorithm for detecting and evaluating signal and noise parameters. Results. A two-dimensional adaptive space-time algorithm for detecting a radar signal reflected from a moving target against the background of a space-correlated interference is synthesized. The analysis of the efficiency of the algorithm by the Monte Carlo method is carried out. Conclusions. It is shown that the empirical Bayesian approach is an effective working methodology in solving the problem of detecting a harmonic signal and estimating its parameters under conditions of interference with a complex frequency spectrum under different conditions of a priori uncertainty of their parameters.

An Adaptive, Algorithm-based Text Message Intervention to Promote Health Behavior Adherence in Type 2 Diabetes: Treatment Development and Proof-of-Concept Trial

Background: Most individuals with type 2 diabetes (T2D) struggle to adhere to one or more health behaviors. Text message interventions (TMIs) have the potential to improve adherence but have had mixed effects on diet and activity in T2D. We developed an eight-week, adaptive, algorithm-driven TMI to promote physical activity, diet, self-care, and well-being. Then, in a single-arm trial, we assessed its feasibility, acceptability, and preliminary efficacy in 15 individuals with T2D and suboptimal adherence. Methods: Participants received daily text messages and were asked to rate the utility of each message (0=not helpful, 10=very helpful). These ratings were used by an algorithm to select subsequent messages based on each participant’s prior ratings. We assessed intervention feasibility by rates of message transmission/response and acceptability through ratings of message utility and burden. Finally, we examined pre-post changes in diabetes self-care, diet, physical activity, and psychological outcomes and calculated effect sizes (Cohen’s d). Results: All text messages were delivered, and participants provided ratings for 79% of messages, above our a priori thresholds for feasibility. Participants rated the individual messages and overall TMI as subjectively useful (utility: 8.1 [SD=2.1] and 7.8 [SD=2.0], respectively) and not burdensome (burden: 0.8 [SD=1.8]). The intervention led to significant, medium- to large-sized improvements in self-care ( d=0.77), diet ( d=0.99), and activity ( d=0.61) but minimal change in psychological outcomes. Conclusions: The TMI was feasible and well-accepted, and it led to promising improvements in adherence-related outcomes. These findings should be confirmed in a larger randomized controlled trial.

Daily monitoring of scattered light noise due to microseismic variability at the Virgo interferometer

Data acquired by the Virgo interferometer during the second part of the O3 scientific run, referred to as O3b, were analysed with the aim of characterising the onset and time evolution of scattered light noise in connection with the variability of microseismic noise in the environment surrounding the detector. The adaptive algorithm used, called pytvfemd, is suitable for the analysis of time series which are both nonlinear and nonstationary. It allowed to obtain the first oscillatory mode of the differential arm motion degree of freedom of the detector during days affected by scattered light noise. The mode’s envelope i.e., its instantaneous amplitude, is then correlated with the motion of the West end bench, a known source of scattered light during O3. The relative velocity between the West end test mass and the West end optical bench is used as a predictor of scattered light noise. Higher values of correlation are obtained in periods of higher seismic noise in the microseismic frequency band. This is also confirmed by the signal-to-noise ratio (SNR) of scattered light glitches from GravitySpy for the January-March 2020 period. Obtained results suggest that the adopted methodology is suited for scattered light noise characterisation and monitoring in gravitational wave interferometers.