The factors that influence the formation of helium blisters in copper were studied, including crystallographic grain orientation and thermomechanical conditions. Helium implantation experiments were ...conducted at 40 KeV with a dose of 5 × 1017 ions/cm2, and the samples were then subjected to post-implantation heat treatments at 450 °C for different holding times. A scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) detector was used to analyze the samples, revealing that the degree of blistering erosion and its evolution with time varied with the crystallographic plane of the free surface in different ways in annealed and cold rolled copper. Out of the investigated states, rolled copper with a (111) free surface had superior helium blistering durability. This is explained by the consideration of the multivariable situation, including the role of dislocations and vacancies. For future plasma-facing component (PFC) candidate material, similar research should be conducted in order to find the optimal combination of material properties for helium blistering durability. In the case of Cu selection as a PFC, the two practical approaches to obtain the preferred (111) orientation are cold rolling and thin layer technologies.
This study explores the delaying of the formation of helium bubbles and blisters in pure titanium by hydrogen pre-implantation. Titanium, implanted with helium (40 KeV, 5 × 1017 ions/cm²), exhibited ...large bubbles that cause exfoliation after heat treatment, whereas hydrogen pre-implantation inhibited bubble growth at room temperature and reduced the exfoliation after heat treatment.
In the samples pre-implanted with hydrogen, we found evidence of helium diffusion delay by: (a) a fourfold reduction in bubble pressure (b) faceted cavities in the samples (c) a smaller increase in titanium lattice parameters (d) a 16-fold reduction in average bubble size and a sixfold reduction in bubble area fraction (e) a more than twofold decrease in exfoliation (f) a tendency toward the formation of larger bubbles as a result of heat treatment. We believe that it is reasonable to assume that the inhibition of helium diffusion between tetrahedral interstitial lattice sites takes place because of the occupation of the intermediate octahedral sites by hydrogen atoms.
Evidence for the opposite effect, that is inhibition of the diffusion of hydrogen in the presence of helium, is found in the retention of hydrogen in the specimens at elevated temperatures. This retention allowed the existence of titanium hydride after heat treatment at 680 °C. The present study sheds light on the intricate interplay between hydrogen and helium in titanium, providing insights into mechanisms that can potentially mitigate helium-induced damage in materials.
The ultrasonic phase velocity was measured on a high purity nickel single crystal with a bias magnetic field in cooling and heating runs over the interval of temperatures from approximately 100 to ...325 K. An evident anomaly of the phase velocity was observed in both branches of the temperature cycle. The temperature of the anomaly in the heating run was always greater than that in the cooling run, indicating the presence of a hysteretic mechanism. The observed changes are attributed to dimensional alignment of the nickel single crystal twins which are able to distort the crystalline network. The temperature of the anomalies and its hysteretic behavior depend on the synergy between the direction and strength of the magnetic field, the direction of the ultrasonic wave propagation, the internal friction between the domains and the crystallographic orientation. The frictions between magnetic domains that do not contribute to the velocity anomaly produce a hysteretic loop. The process can be easily inhibited by disorientation of the magnetic field.
In this paper we present experimental data of ultrasonic velocity and attenuation of a hydrogenated high-purity crystalline copper sample. Two evident peaks are observed at temperatures higher than ...those corresponding to the Niblett–Wilks and Bordoni peaks, which are characteristic of an uncharged similar sample. The peaks we observed are interpreted in terms of the hydrogen Snoek–Köster relaxation (HSK) proposed by Seeger. This is the first ultrasonic observation of the two HSK relaxations predicted for face-centered cubic samples.
Accurate prediction of vaginal birth after cesarean is crucial for selecting women suitable for a trial of labor after cesarean (TOLAC). We sought to develop a machine learning (ML) model for ...prediction of TOLAC success and to compare its accuracy with that of the MFMU model.
All consecutive singleton TOLAC deliveries from a tertiary academic medical center between February 2017 and December 2018 were included. We developed models using the following ML algorithms: random forest (RF), regularized regression (GLM), and eXtreme gradient-boosted decision trees (XGBoost). For developing the ML models, we disaggregated BMI into height and weight. Similarly, we disaggregated prior arrest of progression into prior arrest of dilatation and prior arrest of descent. We applied a nested cross-validation approach, using 100 random splits of the data to training (80%, 792 samples) and testing sets (20%, 197 samples). We used the area under the precision-recall curve (AUC-PR) as a measure of accuracy.
Nine hundred and eighty-nine TOLAC deliveries were included in the analysis with an observed TOLAC success rate of 85.6%. The AUC-PR in the RF, XGBoost and GLM models were 0.351
0.028, 0.350
0.028 and 0.336
0.024, respectively, compared to 0.325
0.067 for the MFMU-C. The algorithms performed significantly better than the MFMU-C (p-values = .0002, .0004, .0393 for RF, XGBoost, GLM respectively). In the XGBoost model, eight variables were sufficient for accurate prediction. In all ML models, previous vaginal delivery and height were among the three most important predictors of TOLAC success. Prior arrest of descent contributed to prediction more than prior arrest of dilatation, maternal height contributed more than weight.
All ML models performed significantly better than the MFMU-C. In the XGBoost model, eight variables were sufficient for accurate prediction. Prior arrest of descent and maternal height contribute to prediction more than prior arrest of dilation and maternal weight.
Objective
To characterize the length of the second stage of labor among women completing a first vaginal birth after a cesarean (VBAC), according to the stage of labor during primary cesarean ...delivery (CD).
Methods
A retrospective cohort study of VBACs between 2011 and 2020. Study groups were divided as follows: CD not in labor, CD in the first stage of labor, and CD in the second stage of labor. The primary outcome was the length of the second stage.
Results
A total of 1310 VBACs were included. The timing of the primary CD was not associated with the duration of the second stage. The median second stage of duration of VBACs with previous first stage CD versus previous CD not in labor was 81 versus 106 min, respectively (P = 0.050). In multivariable linear regression, maternal age, birth weight, and epidural were independently associated with second‐stage length. Maternal and neonatal outcomes did not differ between study groups and were not affected by the second‐stage length.
Conclusion
When stratified according to the labor stage of the primary CD, second‐stage duration among women completing VBACs was not associated with labor stage at the primary CD. Extremes of the second‐stage duration were not associated with increased morbidity.
Synopsis
The length of the second stage of labor among women completing vaginal birth after a cesarean is not associated with labor stage of the primary cesarean delivery.
Background
We aimed to evaluate the association of the duration of the second stage with labor after cesarean (LAC) success and other outcomes among women with one prior cesarean delivery (CD) and no ...prior vaginal births.
Methods
All women undergoing LAC that reached the second stage of labor from March 2011 to March 2020 were included in this retrospective cohort study. The primary outcome was the mode of delivery by second stage duration. The secondary outcomes included adverse maternal and neonatal outcomes. We allocated the study cohort into five groups of second stage duration. Further analysis compared <3 to ≥3 h of second stage based on prior studies. LAC success rates were compared. Composite maternal outcome was defined as the presence of uterine rupture/dehiscence, postpartum hemorrhage, or intrapartum/postpartum fever.
Results
One thousand three hundred ninety seven deliveries were included. Vaginal birth after cesarean (VBAC) rates decreased as the second stage length time interval increased: 96.4% at <1 h, 94.9% at 1 to <2 h, 94.6% at 2 to <3 h, 92.1% at 3 to <4 h and 79.5% at ≥4 h (p < 0.001). Operative vaginal and CDs were significantly more likely as second stage duration time interval increased (p < 0.001). The composite maternal outcome was comparable among groups (p = 0.226). When comparing the outcomes of deliveries at <3 h versus ≥3 h, the composite maternal outcome and neonatal seizure rates were lower in the <3 h group (p = 0.041 and p = 0.047, respectively).
Conclusion
Vaginal birth after cesarean rates decreased as second stage time interval length increased. Even with prolonged second stage, VBAC rates remained relatively high. Increased risk of composite adverse maternal outcomes and neonatal seizures were observed when the second stage lasted 3 h or more.
Introduction
High birth weight is strongly associated with OASIS; nevertheless, it has not been determined which biometric characteristics most affect OASIS occurrence. We aimed to evaluate the ...association of estimated fetal head circumference with OASIS occurrence among primiparous women delivering by unassisted vaginal delivery.
Methods
A retrospective study included all primiparous women who delivered at term by spontaneous vaginal delivery from 2011–2019. Women were allocated to two groups: (1) those who experienced OASIS and (2) those who did not experience OASIS. Risk factors for OASIS were analyzed.
Results
Overall, 7646 women were included in the study cohort. Of those, 119/7646 (1.6%; 95% CI, 1.3–1.9%) experienced OASIS. Sonographic head circumference and birth weight did not vary between groups. Prolonged second stage was more common in the OASIS group 23 (19%) vs. 986 (13.3%), 1.58 OR (95% CI 1.003–2.51,
p
= 0.04). Absence of epidural analgesia was more common in the OASIS group 30 (25%) vs. 1197 (15.9%), 1.8 OR (95% CI 1.1–2.7,
p
= 0.006). On multivariate logistic regression analysis, the lack of epidural analgesia and duration of second stage of labor were both independently positively associated with OASIS adjusted OR 2.67 (95% CI 1.55–4.62),
p
< 0.001, adjusted OR 1.23 (95% CI 1.11–1.43),
p
< 0.001, respectively).
Conclusion
Sonographic head circumference and birth weight are not associated with OASIS occurrence among primiparous women delivering by an unassisted vaginal delivery. Prolonged second stage and the use of epidural analgesia are modifiable risk factors among these women.
Objective
To estimate the association of the weight difference between the index trial of labor after cesarean (TOLAC) sonographic estimated fetal weight (sEFW) and prior delivery birth weight with ...TOLAC success rate among women with previous labor dystocia and no prior vaginal delivery.
Methods
A retrospective cohort study including all women with prior cesarean for labor dystocia and no prior vaginal delivery undergoing TOLAC during between March 2011 and June 2020 with a sEFW within 1 week from delivery.
Results
Overall, 168 women were included, of those 107 (63.7%) successfully delivered vaginally. The mean sEFW and mean birth weight were lower in the TOLAC success group (P = 0.010 and P = 0.013, respectively). The rate of higher sEFW in the current delivery compared with the previous delivery did not differ between study groups. The rate of higher TOLAC birth weight was lower in the TOLAC success group (odds ratio 0.30; 95% confidence interval 0.15–0.58). In multivariable regression analysis, maternal age older than 30 years, induction of labor, and higher birth weight were independently negatively associated with TOLAC success (adjusted odds ratio 95% confidence interval: 0.27 0.10–0.70, 0.27 0.08–0.90, and 0.43 0.19–0.94; P = 0.008, P = 0.034, and P = 0.035, respectively).
Conclusions
sEFW characteristics did not predict the success or failure of TOLAC among women with prior labor dystocia and no previous vaginal delivery.
Older maternal age, induction of labor, and higher birth weight are negatively associated with TOLAC success rate among women with prior labor dystocia.
Objective
To study the factors associated with successful trial of labor after cesarean (TOLAC) among women with diabetes and no prior vaginal delivery and compare with TOLAC in nondiabetic women.
...Methods
A retrospective study including all women undergoing TOLAC who had no prior vaginal delivery between March 2011 and June 2020 at Sheba Medical Center. Women with diabetic disorders were compared with those without. Multivariate regression analysis was performed to identify factors independently associated with TOLAC success.
Results
Of 2144 deliveries with TOLAC, 163 (7.6%) were to women with a diabetic disorder. TOLAC success rate was comparable between diabetic and nondiabetic women (124 76.1% vs 1513 76.4%, respectively; P = 0.931). Uterine rupture rate was 1.1% (23 out of 2144). Among women with diabetes the uterine rupture rate was 0.6% (1 out of 163) and did not differ between the success or fail TOLAC groups. Multivariate logistic regression showed that epidural anesthesia and cervical effacement were the only independent factors associated with TOLAC success in women with diabetes (adjusted OR 3.32; 95% CI, 1.31–8.69, P = 0.011 and aOR 1.04; 95% CI, 1.01–1.07, P = 0.007, respectively).
Conclusion
TOLAC in women with diabetes with no prior vaginal delivery has a high success rate. Epidural analgesia is the only modifiable independent predictor of TOLAC success.
Trial of labor after cesarean (TOLAC) among women with diabetic disorders and no prior vaginal delivery has a high success rate. Epidural analgesia is independently associated with TOLAC success.
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