Modelling and parametric investigation of a large marine two-stroke dual fuel engine

This work deals with the modelling of a large marine two-stroke dual duel engine of the low gas pressure concept by using the GT-PowerTM software. Appropriate models were used to represent the engine processes including combustion, scavenging, heat transfer and friction whereas a knocking model was employed to characterise the engine unstable operation. The model was first validated against the manufacturer data and subsequently, the entire engine envelope in both operating modes was simulated. The derived results were used for analysing and discussing the engine performance and emissions as well as for comparing the two operating modes in terms of the turbocharger matching. In addition, parametric runs were performed and the results were used for identifying the settings that can further optimize the engine operation in the dual fuel mode in terms of CO2 and NOx emissions trade-off

Variation in antral follicle counts at different times in the menstrual cycle: does it matter?

Antral follicle count (AFC) variation was examined across the menstural cycle and its effect on clinical management assessed. In 79 women, AFC was documented in early (iAFC) and late follicular phase (sAFC). Absolute agreement between iAFC and sAFC and agreement for classification into categories of risk of extremes of ovarian response were examined. Ovarian stimulation protocols designed with iAFC and sAFC, and the predictive value of iAFC and sAFC for extremes of ovarian response, were compared in women undergoing ovarian stimulation. Significant differences were found between iAFC and sAFC (16 [IQR 9-24] versus 13 [IQR 7- 21]; P = 0.001), with moderate agreement for the classification into at risk of extremes of response (k = 0.525). Agreement for protocol selection based on either AFC (k = 0.750) and starting gonadotrophin dose was good (concordance correlation coefficient 0.970 [95% CI 0.951 to 0.982]). Predictive value for iAFC and sAFC was maintained for poor ovarian response and risk of ovarian hyperstimulation syndrome (OR 0.634 [0.427 to 0.920], 0.467 [0.233 to 0.935]) and (OR 1.049 [0.974 to 1.131], 1.140 [1.011 to 1.285]). Across the cycle, AFC varies but does not significantly affect ovarian stimulation protocol design and prediction of extreme ovarian response

Ultrasound mapping of pelvic endometriosis: does the location and number of lesions affect the diagnostic accuracy? a multicentre diagnostic accuracy study

BACKGROUND: Endometriosis is a common condition which causes pain and reduced fertility. Treatment can be difficult, especially for severe disease, and an accurate preoperative assessment would greatly help in the managment of these patients. The objective of this study is to assess the accuracy of pre-operative transvaginal ultrasound scanning (TVS) in identifying the specific features of pelvic endometriosis and pelvic adhesions in comparison with laparoscopy. METHODS: Consecutive women with clinically suspected or proven pelvic endometriosis, who were booked for laparoscopy, were invited to join the study. They all underwent a systematic transvaginal ultrasound examination in order to identify discrete endometriotic lesions and pelvic adhesions. The accuracy of ultrasound diagnosis was determined by comparing pre-operative ultrasound to laparoscopy findings. RESULTS: 198 women who underwent preoperative TVS and laparoscopy were included in the final analysis. At laparoscopy 126/198 (63.6%) women had evidence of pelvic endometriosis. 28/126 (22.8%) of them had endometriosis in a single location whilst the remaining 98/126 (77.2%) had endometriosis in two or more locations. Positive likelihood ratios (LR+) for the ultrasound diagnosis of ovarian endometriomas, moderate or severe ovarian adhesions, pouch of Douglas adhesions, and bladder deeply infiltrating endometriosis (DIE), recto-sigmoid colon DIE, rectovaginal DIE, uterovesical fold DIE and uterosacral ligament DIE were >10, whilst for pelvic side wall DIE and any ovarian adhesions the + LH was 8.421 and 9.81 respectively. The negative likelihood ratio (LR-) was: <0.1 for bladder DIE; 0.1-0.2 for ovarian endometriomas, moderate or severe ovarian adhesions, and pouch of Douglas adhesions; 0.5-1 for rectovaginal, uterovesical fold, pelvic side wall and uterosacral ligament DIE. The accuracy of TVS for the diagnosis of both total number of endometriotic lesions and DIE lesions significantly improved with increasing total number of lesions. CONCLUSIONS: Our study has shown that the TVS diagnosis of endometriotic lesion is very specific and false positive results are rare. Negative findings are less reliable and women with significant symptoms may still benefit from further investigation even if TVS findings are normal. The accuracy of ultrasound diagnosis is significantly affected by the location and number of endometriotic lesions

Does ovarian cystectomy pose a risk to ovarian reserve and fertility?

Key content The impact of benign ovarian cysts on a woman’s fertility is dependent on the nature, size, number, bilaterality and risk of recurrence of the cyst(s). Children and adolescents presenting with pathological ovarian cysts require a multidisciplinary team approach and, where possible, fertility sparing treatment should be offered. Laparoscopic detorsion has the potential to preserve ovarian reserve and should remain the optimal treatment for ovarian torsion in girls and premenopausal women. Surgery for bilateral endometriomas has been shown to increase the risk of developing premature ovarian insufficiency. It is important to consider performing ovarian reserve assessments before any ovarian surgery in women who have not completed their family. Learning objectives To understand what factors need to be considered before making a decision to perform an ovarian cystectomy. To be aware of different surgical techniques and their impact on fertility outcomes. To take anatomical considerations into account to minimise damage to healthy ovarian tissue. Ethical issues The UK’s National Health Service does not routinely fund oocyte freezing for benign conditions

Towards marine dual fuel engines digital twins - integrated modelling of thermodynamic processes and control system functions

This study aims at developing an integrated model that combines detailed engine thermodynamic modelling and the control system functional modelling paving the way towards the development of fidel digital twins. To sufficiently represent the combustion process, a multi-Wiebe function approach was employed along with a database for storing the Wiebe functions parameters and the use of quadratic interpolation. The developed model was employed for the systematic investigation of a marine four-stroke dual fuel engine response during demanding transient operation with modes switching and load changes. The derived results are analysed for identifying the engine critical components and their effect on the engine operational limitations. The results demonstrate that the developed model can sufficiently represent the engine and its subsystems/components behaviour and effectively capture the engine control systems functionality. The appropriate turbocharger matching along with the sufficient design of the exhaust gas waste gate valve and fuels control systems are crucial for ensuring the smooth engine operation of dual fuel engines

Numerical investigation of a premixed combustion large marine two-stroke dual fuel engine for optimising engine settings via parametric runs

As the environmental regulations have become more stringent, the shipping industry has been focusing on more efficient and environmentally friendly means of propulsion and electric power generation. In this respect, dual fuel engines, which operate either in diesel mode or dual fuel (DF) mode by burning diesel fuel or natural gas and pilot diesel fuel to initiate ignition respectively, has become one of the most promising solutions as their dual fuel operation leads to reduced nitrogen oxide (NOx), carbon dioxide (CO2), as well as almost elimination of particulate matter (PM) and sulphur oxide (SOx) emissions. The present study focuses on the comprehensive investigation of a large marine two-stroke dual fuel engine of the low gas pressure concept by using the GT-Power™ software. Appropriate combustion, scavenging, heat transfer and friction models were used to fully represent the engine performance and emissions characteristics whereas a knocking model was employed to characterise the engine abnormal combustion. The simulation results were initially validated against the manufacturer data and subsequently, the entire engine envelope in both operating modes was simulated. The derived results were used for analysing and discussing the engine operation, performance and emissions as well as for comparing the two operating modes in terms of the turbocharger matching. In addition, a parametric investigation was performed in the dual fuel mode and the results were used for identifying the settings that can further optimize the engine operation in terms of CO2 and NOx emissions trade-off. The results indicate that the CO2 and NOx emissions can be simultaneously reduced; however, the engine optimisation in the high load region is challenging due to the permissible cylinder pressure constraint

Impact of location on placentation in live tubal and cesarean scar ectopic pregnancies

INTRODUCTION: The objective of this study was to evaluate the impact of implantation outside the normal intra-uterine endometrium on development of the gestational sac. METHODS: We reviewed and compared the ultrasound measurements and vascularity score around the gestational sac in 69 women diagnosed with a live tubal ectopic pregnancy (TEP) and 54 with a cesarean scar ectopic pregnancy (CSP) at 6-11 weeks of gestation who were certain of their last menstrual period. RESULTS: The rate of a fetus with a cardiac activity in the study population was significantly (P < 0.001) higher in CSPs than in TEPs. The median maternal age, gravidity and parity were significantly (P =.005; P < 0.001 and P < 0.001, respectively) lower in the TEP than in the CSP group. The number of gestational sac size <5th centile for gestational age was significantly (P < 0.001) higher in the TEP than in the CSP group. There were no differences between the groups for the other ultrasound measurements. In cases matched for gestational age, the gestational sac size was significantly (P < 0.001) smaller in the TEP compared to the CSP group. There was a significant (P < 0.001) difference in the distribution of blood flow score with CSP presenting with higher incidence of moderate and high vascularity than TEP. DISCUSSION: Both TEP and CSP are associated with a higher rate of miscarriage than intrauterine pregnancies and the slow development of the gestation sac is more pronounced in TEPs probably as a consequence of a limited access to decidual gland secretions

Risk prediction of major haemorrhage with surgical treatment of live cesarean scar pregnancies

Objective: To evaluate the association between demographic and ultrasound variables and major intra-operative blood loss during surgical transcervical evacuation of live caesarean scar pregnancies. Study Design: This was a retrospective cohort study conducted in a tertiary referral center between 2008 and 2019. We included all women diagnosed with a live caesarean scar ectopic pregnancy who chose to have surgical management in the study center. A preoperative ultrasound was performed in each patient. All women underwent transcervical suction curettage under ultrasound guidance. Our primary outcome was the rate of postoperative blood transfusion. The secondary outcomes were estimated intra-operative blood loss (ml), rate of retained products of conception, need for repeat surgery, need for uterine artery embolization and hysterectomy rate. Descriptive statistics were used to describe the variables. Univariate and multivariable logistic regression models were constructed using the relevant covariates to identify the significant predictors for severe blood loss. Results: During the study period, 80 women were diagnosed with a live caesarean scar pregnancy, of whom 62 (78%) opted for surgical management at our center. The median crown-rump length was 9.3 mm (range 1.4–85.7). Median blood loss at the time of surgery was 100 ml (range, 10–2300), and six women (10%; 95%CI 3.6–20) required blood transfusion. Crown-rump length and presence of placental lacunae were significant predictive factors for the need for blood transfusion and blood loss > 500 ml at univariate analysis (p < .01); on multivariate analysis, only crown-rump length was a significant predictor for need for blood transfusion (OR = 1.072; 95% CI 1.02–1.11). Blood transfusion was required in 6/18 (33%) cases with the crown-rump length ≥ 23 mm (≥9+0 weeks of gestation), but in none of 44 women presenting with a crown-rump length < 23 mm (p < .01). Conclusion: The risk of severe intraoperative bleeding and need for blood transfusion during or after surgical evacuation of live caesarean scar pregnancies increases with gestational age and is higher in the presence of placental lacunae. One third of women presenting at ≥ 9 weeks of gestation required blood transfusion and their treatment should be ideally arranged in specialized tertiary centers