A Novel Approach for Powder Bed Fusion of Ceramics Using Two Laser Systems.

The one-step AM process is considered the goal many researchers seek in the field of Additive Manufacturing (AM) of high-technology ceramics. Among the several AM techniques, only Powder Bed Fusion (PBF) can directly print high-technology ceramics using one step. However, the PBF technique faces numerous challenges to efficiently be employed in the PBF of ceramics. These challenges include the formation of cracks, generated thermal stress, effective laser-powder interaction, and low acquired relative density. This study developed a new preheating mechanism for ceramic materials using two laser systems to surpass beyond these challenges and successfully print ceramics with a single-step AM method. One laser is used to preheat the powder particles before the second laser is utilised to complete the melting/sintering process. Both lasers travel along the same scanning path. There is a slight delay (0.0001 s) between the preheating laser and the melting/sintering laser to guarantee that the melting/sintering laser scans a properly preheated powder. To further facilitate testing of the preheating system, a numerical model has been developed to simulate the preheating and melting process and to acquire proper process parameters. The developed numerical model was shown to determine the correct process parameters without needing costly and time-consuming experiments. Alumina samples (10 × 10 × 6 mm3) were successfully printed using alumina powder as feedstock. The surface of the samples was nearly defect-free. The samples' relative densities exceeded 80%, the highest reported relative density for alumina produced by a single-step AM method. This discovery can significantly accelerate the transition to a one-step AM process of ceramics.

The effects of spinal anesthesia on QT interval in preeclamptic patients.

In this study, we measured the effects of spinal anesthesia on the corrected QT (QTc) interval in women with severe preeclampsia. Twenty-five preeclamptic (preeclamptic group) and 25 healthy pregnant women with normal arterial blood pressure and QTc interval (control group) were enrolled in this prospective, case-controlled study. Arterial blood pressure, heart rate, and QTc interval values were obtained before (baseline value) and at 5, 10, 20, 30, 60, and 120 min after initiation of spinal anesthesia. Total ephedrine dose, time elapsed until sensory block, and Apgar scores were recorded. Prior to spinal anesthesia, QTc interval values were significantly higher in the preeclamptic group (452 +/- 17.5 ms) when compared with that in controls (376 +/- 21.4 ms). Although the QTc interval shortened during spinal anesthesia when compared with baseline value in the preeclamptic group (P < 0.05), it showed no significant change in the control group. In conclusion, the QTc interval may be prolonged in severe preeclamptic patients who have hypertension and hypocalcemia. Spinal anesthesia for cesarean delivery may normalize that prolonged QTc interval due to sympathetic blockade.

Cardiac dysfunction in cirrhosis.

In cirrhosis, cardiac symptoms and physical signs occur as the liver functions worsen. Cirrhosis is associated with hyperdynamic circulation and beta-adrenergic system activation responsible for the cardiovascular changes. The purpose of the present study was to explore the cardiovascular response to exercise in cirrhotic patients. A total of 20 patients (16 men, four women) with cirrhosis of hepatitis B or C without any cardiac dysfunction were included in the study. Ten people (eight men, two women) were enrolled in the control group. Plasma noradrenaline and adrenaline concentrations, blood pressures in supine and standing positions, exercise echocardiography and exercise radionuclide ventriculography were carried out. In cirrhotics, the exercise capacity was lower and also there was an impaired cardiovascular response to exercise with lower than expected peak heart rate without any cardiac dysfunction, which may have important clinical implications for the ability of these patients to withstand cardiovascular stress.