Shuangbao Li

Background: The frequency of long-haul, cross-time zone, and nighttime flights is increasing among multiple airlines. Fatigue from long-distance cross-time zone flights may contribute to hypertension onset in civil aviation pilots. Methods: Subjects were stratified into exposure (cross-time zone flights) and non-exposure groups. Pilots with occupational and general risk factors were prospectively followed up, and data were statistically analyzed. Results: Hypertension prevalence differed significantly between groups χ²=302,P<0.05. Overall cohort prevalence was 3.90% (3.97% in exposure, 3.88% in non-exposure), with risk ratio 1.023 and attributable risk 0.09%. Logistic regression showed cross-time zone flights (OR=1.098, 95% CI=1.000–1.205) and family history of hypertension (OR=5.712, 95% CI=2.563–12.729) were independent risk factors, with family history being the most prominent. Conclusion: Our findings guide hypertension management and flight scheduling optimization for long-term cross-time zone pilots.

In this paper, a new vibro-impact oscillator incorporating negative stiffness and dual rigidly constrained narrow gaps is proposed. An analytical approach for determining periodic orbits in such a non-smooth dynamical system is developed, enabling systematic investigation of bifurcation phenomena in mapping dynamics through parametric variations of external harmonic excitation and vibro-impact. Firstly, a linear approximation of the irrational restoring force due to geometric nonlinearity is carried out, and the original nonlinear non-smooth dynamical model can be closely approximated by a linear non-smooth dynamical system. The theoretical framework of mapping dynamics is proposed by defining switching planes, basic mappings and their composite mapping structures for unilateral, bilateral and mixed subharmonic vibro-impact motions. Secondly, the definitions and geometric interpretations of all types of periodic orbits for such a non-smooth system are given in combination with the mapping dynamics, and the existence theorem of the unilateral impacting three times periodic orbits is provided. Then the initial conditions of periodic motions can be obtained analytically. In addition, the effects of the collision coefficient and excitation amplitude on stability and bifurcation are studied, and the critical parameter values for period-doubling and saddle-node bifurcations are analytically determined. Finally, numerical results show good agreement with theoretical analysis, confirming the validity of the stability and bifurcation analysis and revealing the system's complex bifurcation characteristics.

Background: The frequency of long-haul, cross-time zone, and nighttime flights is increasing among multiple airlines. Fatigue from long-distance cross-time zone flights may contribute to hypertension onset in civil aviation pilots. Methods: Subjects were stratified into exposure (cross-time zone flights) and non-exposure groups. Pilots with occupational and general risk factors were prospectively followed up, and data were statistically analyzed. Results: Hypertension prevalence differed significantly between groups χ²=302,P<0.05. Overall cohort prevalence was 3.90% (3.97% in exposure, 3.88% in non-exposure), with risk ratio 1.023 and attributable risk 0.09%. Logistic regression showed cross-time zone flights (OR=1.098, 95% CI=1.000–1.205) and family history of hypertension (OR=5.712, 95% CI=2.563–12.729) were independent risk factors, with family history being the most prominent. Conclusion: Our findings guide hypertension management and flight scheduling optimization for long-term cross-time zone pilots.

In this paper, a novel two-degree-of-freedom mechanical system under sinusoidal excitation is established by coupling the archetypal Smooth and Discontinuous (SD) oscillator with a harmonic oscillator to analytically study the global perturbation dynamics of homoclinic motions. First, a piecewise-linear approximation of the irrational restoring force induced by the SD oscillator is carried out to reconstruct a four-dimensional piecewise-smooth nonautonomous system with a saddle-center geometrical structure. Second, the Melnikov method for piecewise-defined homoclinic orbits under periodic perturbation in the four-dimensional phase space is generalized to obtain the parameter threshold of chaos. Third, the effectiveness of this global perturbation technique is verified by numerical simulations, through which the regulation of the coupled system’s dynamic response from both damping and periodic external excitation is revealed, along with the observation of rich nonlinear dynamic phenomena induced by their combined effects. Finally, a novel strategy is proposed to control the chaotic motion of the SD oscillator through a linear spring-coupled harmonic oscillator. The dynamic response analysis demonstrates that this coupled system enables passive vibration control of the SD oscillator, establishing a foundation for optimizing vibration absorber designs.

In this paper, a new vibro-impact bistable oscillator by installing an adjustable rigid wall to one side of the smooth–discontinuous (SD) oscillator, is constructed to analytically and numerically reveal its unique global dynamic characteristics. In the unperturbed case, there exist complex unilateral homoclinic structures transversal intersecting, grazing and nonintersecting with the impact boundary due to the adjustability of the rigid constraint. When weak vicious damping, weak periodic excitation and impact energy dissipation are considered, the influences of the adjustable rigid constraint and the evolutions from coexisting periodic orbits to chaos are analyzed through bifurcation diagrams, phase diagrams and Poincaré map and basins of attraction. As the position of the impact boundary moves, the orbits graze multiple times with the boundary, causing period-doubling bifurcations and presenting some new impacting periodic orbits and disconnected chaotic attractors. The vibro-impact SD oscillator also gradually loses stability due to the rapid migration of attractors among coexistence orbits.

This paper studies the effect of Gaussian white noise on homoclinic bifurcations and chaotic dynamics of a bistable, vibro-impact Smooth-and-Discontinuous (SD) oscillator. First, the SD oscillator is reproduced and generalized by installing a slider on a fixed rod, so the slider is connected by a pair of linear springs initially pre-compressed in the vertical direction to achieve bistable vibration characteristics, and two screw nuts are installed on the rod as two adjustable bilateral rigid constraints to generate the vibro-impact. A discontinuous dynamical equation with a map defined on switching boundaries to represent velocity loss during each collision is derived to describe the vibration pattern of the bistable, vibro-impact SD oscillator through studying the persistence of the unique, unperturbed, nonsmooth, homoclinic structure. Second, the general framework of random Melnikov process for a class of bistable, vibro-impact systems contaminated with Gaussian white noise is derived and employed through the corresponding Melnikov function to obtain the necessary parameter thresholds for homoclinic tangency and possible chaos of the bistable, vibro-impact SD oscillator. Third, the effectiveness of a semi-analytical prediction by the Melnikov function is verified using the largest Lyapunov exponent, bifurcation series, and 0–1 test. Finally, the sensitivity to the initial values of chaos is verified by the fractal attractor basins, and the influence of the Gaussian white noise on periodic and chaotic structures is studied through Poincaré mapping to show the rich dynamical geometric structures.