Enhanced mass removal due to phase explosion during high irradiance nanosecond laser ablation of silicon

The morphology of craters resulting from high irradiance laser ablation of silicon was measured using a white light interferometry microscope. The craters show a dramatic increase in their depth and volume at a certain irradiance, indicating a change in the primary mechanism for mass removal. Laser shadowgraph imaging was used to characterize and differentiate the mass ejection processes for laser irradiances above and below the threshold value. Time-resolved images show distinct features of the mass ejected at irradiances above the threshold value including the presence of micron-sized particulates; this begins at approximately 300 {approx} 400 ns after the start of laser heating. The analysis of the phenomena was carried out by using two models: a thermal evaporation model and a phase explosion model. Estimation of the crater depth due to the thermally evaporated mass led to a large underestimation of the crater depth for irradiances above the threshold. Above the threshold irradiance, the possibility of phase explosion was analyzed. Two important results are the thickness of the superheated liquid layer that is close to the critical temperature and the time for vapor bubbles that are generated in the superheated liquid to achieve a critical size. After reaching the critical size, vapor bubbles can grow spontaneously resulting in a violent ejection of liquid droplets from the superheated volume. The effects of an induced transparency, i.e. of liquid silicon turning into an optically transparent liquid dielectric medium, are also introduced. The estimated time for a bubble to reach the critical size is in agreement with the delay time measured for the initiation of large mass ejection. Also, the thickness of the superheated liquid layer that is close to the critical temperature at the time of the beginning of the large mass ejection is representative of the crater depth at the threshold irradiance. These results suggest that phase explosion is a plausible thermal mechanism for high irradiance laser ablation. Laser processing parameters were also investigated for nanosecond laser ablation of silicon. Longer incident wavelengths and larger laser beam sizes were associated with higher values of a threshold irradiance

Sleep state classification using power spectral density and residual neural network with multichannel EEG signals.

This paper proposes a classification framework for automatic sleep stage detection in both male and female human subjects by analyzing the electroencephalogram (EEG) data of polysomnography (PSG) recorded for three regions of the human brain, i.e., the pre-frontal, central, and occipital lobes. Without considering any artifact removal approach, the residual neural network (ResNet) architecture is used to automatically learn the distinctive features of different sleep stages from the power spectral density (PSD) of the raw EEG data. The residual block of the ResNet learns the intrinsic features of different sleep stages from the EEG data while avoiding the vanishing gradient problem. The proposed approach is validated using the sleep dataset of the Dreams database, which comprises of EEG signals for 20 healthy human subjects, 16 female and 4 male. Our experimental results demonstrate the effectiveness of the ResNet based approach in identifying different sleep stages in both female and male subjects compared to state-of-the-art methods with classification accuracies of 87.8% and 83.7%, respectively

Surgical management of pilon fractures with large segmental bone defects using fibular strut allografts: a report of two cases

We present two patients with open pilon fractures with large bone defects treated successfully with fibular strut allografts. The patients were initially treated by massive irrigation, wound debridement, and temporary external fixation. After complete wound healing, the bone defects were managed. Because autologous iliac crest or fibular bone grafts were impossible to be harvested due to multiple fractures, the bone defects were reconstructed with fibular strut allografts. Fixation was performed with a periarticular distal tibia locking plate. At 2 months postoperatively, the patients ambulated with partial weight-bearing; at 6 months, they had full range of motion of the ankle joint and full weight-bearing

Association between maternal coronavirus disease 2019 and transient tachypnea of the newborn: a single-center study

Background Limited clinical reports have investigated the effects of maternal coronavirus disease 2019 (COVID-19) on fetuses and neonates. Purpose This retrospective study aimed to assess the impact of maternal COVID-19 on neonates during the perinatal period, including neonatal clinical outcomes, versus the outcomes of neonates of mothers without COVID-19. Methods Neonates born to COVID-19-infected mothers at the National Health Insurance Service Ilsan Hospital between February 2021 and March 2022 were included. Those with gestational age (GA) ≥35+0 weeks who were born within 2 weeks of the maternal infection were matched 1:2 with a control group based on GA. The main outcomes were respiratory diseases, including transient tachypnea of the newborn (TTN), respiratory distress syndrome, meconium aspiration syndrome, the need for respiratory support, and length of hospital stay. Uni- and multivariate logistic regression analyses were performed and adjusted for relevant covariates, including maternal age, obstetric complications (hypertension and gestational diabetes), delivery mode, birth weight, sex, and small-for-gestational-age status. Results The case group comprised 103 neonates (mean GA, 38.5±1.3 weeks; mean birth weight, 3,121±397 g), while the control group included 206 neonates (mean GA, 38.4±1.2 weeks; mean birth weight, 3088±428 g). In the case and control groups, the proportion of cesarean sections was 91% and 40%, respectively, while the proportion of male infants was 56% and 47%, respectively. After adjusting for covariates, the case group had a higher risk of TTN (adjusted odd ratio [AOR], 3.69; 95% confidence interval [CI], 1.69–8.07), noninvasive respiratory ventilator use (AOR, 2.28; 95% CI, 1.05–4.97), and oxygen support (AOR, 4.83; 95% CI, 1.46–15.95). Conclusion Newborns born to COVID-19-infected mothers are at increased risk of TTN and may require respiratory support. Close monitoring of respiratory symptoms is crucial in neonates

SUCCESSFUL FACTORS OF 540° DWIHURYEOCHAGI IN TAEKWONDO

The purpose of our study was to provide fundamental information about success factors of 540° Dwihuryeochagi in Taekwondo. Twenty Taekwondo athletes who participated in the 2012 Taekwondo Kyukpa Wang (breaking king) championship: ten successful athletes (S, age: 23.1±1.6 yrs, height: 171.0±3.5 cm, body mass: 66.4±7.1 kg) and ten failed athletes (F, age: 22.3±1.8 yrs, height: 172.1±5.4 cm, body mass: 64.4±4.2 kg) were selected. Three-dimensional motion analysis using a system of 3 video cameras with a sampling of 60 fields/s was performed during the competition of 540 ° Dwihuryeochagi. Based on the findings, it is concluded that success factors of 540° Dwihuryeochagi were horizontal velocity of COM during P1, vertical velocity of COM during P2, and the time, kick distance, velocity and angle of lower extremities of P3-P4