A six degree-of-freedom (six-DOF) parallel positioning system with high resolution, high repeatability and low parasitic motions was proposed. It mainly consists of three identical limbs. Each limb consists of two symmetrical six prismatic-universal-spherical (6-PUS) branches. Firstly, the design process for a novel six-DOF limb with input displacement reduction was introduced. By applying bipods and linear displacement output mechanisms, these novel limbs with symmetric configurations were designed. Moreover, a numerical compliance/stiffness model of the proposed mechanism was built based on the matrix method. This numerical model was verified by ANSYS finite element analysis (FEA) software package. Hence, the input stiffness, the output compliance and the stroke of the mechanism can be theoretically estimated. Furthermore, a prototype made of stainless steel 431 was successfully manufactured by wire electrical discharge machining (WEDM) process. It is actuated and sensed by piezo actuators and capacitive displacement sensors respectively. Finally, the working performances of this proposed mechanism were experimentally investigated. It shows that the spatial resolution can be achieved in 10nm × 10nm × 5nm × 100nrad × 100nrad × 200nrad in open-loop control. The closed-loop positioning accuracy in 3σ (σ, standard error) can reach 30nm × 30nm × 15nm × 150nrad × 150nrad × 300nrad. The experimental results not only validate the effectiveness of the proposed positioning system but also verify the nanometer-scale spatial positioning accuracy within several tens of micrometers stroke range. The proposed micro-/nanopositioning system maybe expand the actual application of alignment optical elements in projection lenses of 193nm immersion lithography.

To improve the phase-shifting accuracy, this paper presents a novel integrated framework for design, control and experimental validation of the piezoelectric actuated phase shifter with a trade-off between accuracy and cost. The piezoelectric actuators with built-in sensors are adopted to drive the double parallel four-bar linkage flexure hinge-based mechanisms. Three mechanisms form the tripod structure of the assembled phase shifter. Then, a semi-closed loop controller with inner feedback and outer feedforward loops via the external laser interferometer is developed for accurate positioning of the phase shifter. Finally, experiments related with travel range, step response, linearity and repeatability are carried out. The linearity error is 0.21% and the repeatability error of 10 μm displacement is 3 nm. The results clearly demonstrate the good performance of the developed phase shifter and the feasibility of the proposed integrated framework.

Preoperative left ventricular dysfunction is a risk factor for postoperative mortality and morbidity in cardiovascular surgeries with cardiopulmonary bypass, including thoracic aortic surgery. Using a retrospective study design, this study aimed to clarify the short- and mid-term outcomes of patients who underwent acute type A aortic dissection (ATAAD) repair with reduced left ventricular function.Between July 2007 and February 2018, a total of 510 adult patients underwent surgical repair of ATAAD in a single institution. The patients were classified as having left ventricular ejection fraction (LVEF) <50% (low EF group, n = 86, 16.9%) and LVEF ≥50% (normal group, n = 424, 83.1%) according to transesophageal echocardiographic assessment at the operating room. Preoperative demographics, surgical information, and postoperative complication were compared between the two groups. Three-year survival was analyzed using the Kaplan-Meier actuarial method. Serial echocardiographic evaluations were performed at 1, 2, and 3 years postoperation.Demographics, comorbidities, and surgical procedures were generally homogenous between the 2 groups, except for a lower rate of aortic arch replacement in the low EF group. The averaged LVEFs were 44.3 ± 2.5% and 65.8 ± 6.6% among the low EF and normal groups, respectively. The patients with low EF had higher in-hospital mortality (23.3% versus 13.9%, P = .025) compared with the normal group. Multivariate analysis revealed that intraoperative myocardial failure requiring extracorporeal membrane oxygenation support was an in-hospital mortality predictor (odds ratio, 16.99; 95% confidence interval, 1.23-234.32; P = .034), as was preoperative serum creatinine >1.5 mg/dL. For patients who survived to discharge, the 3-year cumulative survival rates were 77.8% and 82.1% in the low EF and normal groups, respectively (P = .522). The serial echocardiograms revealed no postoperative deterioration of LVEF during the 3-year follow-up.Even with a more conservative aortic repair procedure, the patients with preoperative left ventricular dysfunction are at higher surgical risk for in-hospital mortality. However, once such patients are able to survive to discharge, the midterm outcome can still be promising.