The basic operation principle of elastic support/dry friction damper in rotor system was introduced and the unbalance response of the rotor with elastic support/dry friction damper was analyzed theoretically. Based on the previous structure using an electromagnet as actuator, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified. The experimental results show that the active elastic support/dry friction damper with piezoelectric ceramic actuator can significantly reduce vibration in rotor system; the vibration amplitude of the rotor in critical speed region decreased more than 2 times, and the active damper can protect the rotor when a blade-out event happened, so the rotor can traverse the critical speed and shut down smoothly. In addition, the structure is much simpler than the previous, the weight was reduced by half and the power consumption was only 5 W.
In partial load torque control for variable speed wind turbine generators(VSWTG) rotational speed, which will be feedback signal, is very important parameter. The mathematical model of wind turbine and control regulation for maximizing energy conversion yield has been introduced in this paper. The control system stability and dynamic response are analyzed when using the wind turbine rotor side rotational speed (RSRS) and the generator side rotational speed(GSRS) as feedback signal in torque control respectively ,and the effect the drive train damping and wind speed on system stability are investigated simultaneously. Analysis-and simulation results show that, when using RSRS the stability of wind turbine control system depends on the damping of drive train and the coming wind speed strongly, while the system will be always stable in partial load torque control when using GSRS although wind speed and damping have some effect on the wind turbine system stability. Two real wind turbines of 1.5MW double fed asynchronous generator(DFIAG) are simultaneouly tested with different feedback rotational speed respectively. Test results show that, when using RSRS the generator rotational speed will fluctuate strongly with severe torsion vibrations in higher wind speed, while the wind turbine operate normally for GSRS feedback, which make a very good agreement with analysis-and simulation results.
BackgroundThe changes in the platelet-to-lymphocyte ratio (PLR) before and after recombinant tissue plasminogen activator (rtPA) treatment and the time point at which the PLR is a potentially valuable prognostic predictor in patients wit ischemic stroke remain largely unknown. Therefore, the purpose of this study was to explore the characteristics of the PLR and evaluate their effects on clinical outcomes before and 24 h after rtPA treatment.MethodsThis study included 741 consecutive patients with acute ischemic stroke who underwent intravenous thrombolysis with rtPA. We collected data on demographics, vascular risk factors, medication history, and other clinical information pertaining to all patients. Specifically, blood samples for PLR measurement were collected on admission and 24 h after stroke. The outcome was assessed by using the Modified Rankin Scale (mRS) at 3 months and whether death occurred within 3 months or not. Univariate and multivariate logistic regression analysis was used to assess the association of the PLR with the risks of poor outcome (mRS>2) and death. An individualized prediction model was established to predict poor outcome.ResultsOf the 741 patients, 255 (34.4%) had poor outcome, and 43 (5.8%) died. The PLR significantly increased 24 h after rtPA in patients with poor outcome and death. Logistic analysis revealed that higher PLR 24 h after rtPA was independently associated with increased risks of poor outcome and death. However, the PLR on admission was not associated with the risks of poor outcome and death. The individualized prediction model for poor outcome based on the 24-h PLR exhibited favorable discrimination (areas under the curves of the training and validation groups: 0.743 and 0.729, respectively), calibration (P > 0.05), and clinical usefulness.ConclusionsWe found the PLR to be a variable that potentially predicts the risks of poor outcome and death in patients with acute ischemic stroke 24 h after rtPA; however, it cannot make the same prediction on admission.
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