Smaller Twin Research Articles

Comparison of Dynamic Characteristics between Small and Super-Large Diameter Cross-River Twin Tunnels under Train Vibration

Train vibration from closely aligned adjacent tunnels could cause safety concerns, especially given the soaring size of the tunnel diameter. This paper established a two-dimensional discrete element model (DEM) of small (d = 6.2 m) and super-large (D = 15.2 m) diameter cross-river twin tunnels and discussed the dynamic characteristics of adjacent tunnels during the vibration of a train that runs through the tunnel at a speed of 120 km/h. Results in the D tunnel showed that the horizontal walls have the same horizontal displacement (DH) and the vertical walls have the same vertical displacement (DV). The stress state of the surroundings of the D tunnel is the decisive factor for DH, and the distance from the vibration point to the measurement point is the decisive factor for DV. Results in the comparison of the d and D tunnels showed that the D tunnel is more stable than the d tunnel with respect to two aspects: the time the tunnel reaches the equilibrium state and the vibration amplitude of the structure’s dynamic and static responses. The dynamic characteristic of the d and D tunnel is significantly different. This research is expected to guide the design and construction of large diameter twin tunnels.

Главное о судах с малой площадью ватерлинии

Object and purpose of research. The object of study is small waterplane area twin hull (SWATH) ships whose main advantage is their excellent seaworthiness. The purpose of this work is to demonstrate the broad capabilities of such vessels. Materials and methods. The knowledge from foreign literature along with the author’s data are employed. Comparison methods focus on the main specific features of the technology for different fields of application. Main results. Brief review of the SWATH background is given highlighting the main trends of development. Common features and differences of each SWATH type is identified. The revealed merits and disadvantages, design details point to a broad range of possible applications. Conclusion. SWATH architecture may provide a considerable improvement in seaworthiness of small and medium displacement vessels. SWATH is an economically viable option for all types of marine vessels with a relatively large deck area, so-called capacity carriers, like passenger, research, ro-ro, naval ships, etc. For more efficient application it is recommended that alternative SWATH projects should be developed at an early design of vessels for the above missions.

Far Wake and Its Relation to Aerodynamic Efficiency

Correlations were found between the aerodynamic efficiency and the mean and fluctuating quantities in the far wake of a wall-to-wall SD7003 model and an AR 4 flat plate. This correlation was described algebraically by modeling the wake signature as a function of wing geometry and initial conditions. The model was benchmarked against experimental results to elicit the wing performance as a function of angle of attack by interrogating the wake. In these algebraic models, the drag coefficient along with other initial conditions of the turbulent generator (either airfoil or wing) were used to reconstruct the Reynolds Stress distribution and the momentum deficit distribution in the turbulent wake. Experiments were undertaken at the United States Air Force Research Labs Horizontal Free Surface Water Tunnel (AFRL/HFWT). These experiments build on previous results obtained at the University of Dayton Low Speed Wind Tunnel (UD-LSWT) on a cylinder, an AR 7 SD7062 wing, and a small remote control twin motor aircraft. The Reynolds stress and the momentum deficit of the turbulent generators were experimentally determined using Particle Image Velocimetry (PIV) with a minimum of 1000 image pairs averaged at each condition. The variation of an empirical factor (γ) used to match the Reynolds stress and momentum deficit distributions showed striking correlation to the variation of drag and aerodynamic efficiency of the turbulent generator. This correlation suggests that the wing performance information is preserved in the free shear layer 10 chord lengths downstream of the trailing edge (TE) of the wing irrespective of the dimensionality of the flow.

Microstructures and mechanical properties of (CoCrFeMnNi)100-xMox high entropy alloy films

The effects of Mo addition on the microstructures and mechanical properties of CoCrFeMnNi high entropy alloy films (HEAFs) were studied in this work. To achieve this, a series of (CoCrFeMnNi)100-xMox HEAFs was prepared by magnetron co-sputtering. The films were FCC without Mo addition and composed of FCC and HCP structures with minor Mo addition. With the further increase in Mo content, the films transformed to an amorphous structure. Nanoindentation revealed an initial decrease in hardness and then increase with the increasing Mo content. While the initial decrease in hardness could be attributed to the detwinning-induced softening for films with small twin spacing as observed by TEM after micropillar compression, the subsequent increase could be attributed to solid solution strengthening and formation of nanotwins with larger twin spacing and no detwinning observed after compression. Using scratch tests, the Mo-doped HEAFs exhibited a high hardness, good wear resistance and low coefficient of friction. The results of micropillar compression tests showed the increasing compressive yield strength and the decreasing fracture strain with the increasing Mo content. When x = 4.9, the film revealed the optimum mechanical properties with fracture strength of 6.51 GPa and little reduction in ductility.

Perinatal outcomes and factors affecting the survival rate of fetuses with twin-to-twin transfusion syndrome treated with fetoscopic laser coagulation: a single-center seven-year experience

Objectives This single-center study aimed to assess the perinatal outcomes and its associated factors in fetuses with twin-to-twin transfusion syndrome (TTTS) treated by fetoscopic laser coagulation (FLC). Methods In this retrospective study, we included fetuses prenatally diagnosed with TTTS at Asan Medical Center, Seoul, Korea, between October 2011 and December 2018. All patients with TTTS stage II or higher and those with stage I TTTS coupled with symptomatic polyhydramnios or cardiac dysfunction were eligible for FLC. Results A total of 172 cases of monochorionic diamniotic twins and one case of dichorionic triamniotic triplets were prenatally diagnosed with TTTS and treated with FLC. The median gestational ages (GAs) at diagnosis and FLC were 20.3 and 20.5 weeks, respectively. The median GA of survivors at delivery was 32.5 weeks. The overall at least one twin- and double-survival rates within 28 days after birth were 82.1% and 55.5%, respectively. The GAs at diagnosis and FLC, Quintero stage, inter-twin weight discordance, associated selective intrauterine growth restriction (sIUGR), procedure time, volume of amnioreduction, preterm prelabor rupture of membranes (PPROM) within one week after FLC, intraoperative intrauterine bleeding, and chorioamnionitis were significant predictive factors of perinatal death. Associated sIUGR, absent end-diastolic flow of umbilical artery, and abnormal cord insertion were significantly associated with donor demise in utero, whereas lower GA at diagnosis and FLC, smaller twins at FLC, pulsatile umbilical vein, and presence of mitral regurgitation were significantly associated with recipient demise in utero. Since the application of the Solomon technique, the survival rate has improved from 75.4% to 88.8%. The FLC before 17 weeks was associated with PPROM within one week after FLC and lower survival rate, whereas that after 24 weeks was associated with twin anemia-polycythemia sequence and higher survival rate. We reached a survival rate of 82% for at least one survival with only 12 procedures. Conclusions FLC is an effective treatment for TTTS. The learning curve reached the acceptable target faster than in previous studies. Several prenatal parameters are identified as predictive factors of fetal survival in TTTS treated with FLC.

Association between intrauterine growth restriction and patent ductus arteriosus: Use of a dichorionic twin pregnancy model

ObjectiveTo evaluate the association between intrauterine growth restriction (IUGR) and the incidence of fetuses with patent ductus arteriosus (PDA) and Hemodynamically significant PDA (Hs-PDA) in dichorionic twins (DC) with selective IUGR. Materials and methodsThis is an observational cohort study and retrospective case assessment, involved twins born at Linkou Chang Gung Memorial Hospital, Taoyuan, Taiwan between 2013 and 2018. DC twins with selective IUGR (sIUGR) were defined as the presence of a birth weight discordance of >25% and a smaller twin with a birth weight below the tenth percentile. PDA was diagnosed using echocardiography between postnatal day 3 and 7. Hs-PDA was defined as PDA plus increased pulmonary circulation, poor systemic perfusion, cardiomegaly, pulmonary edema, or hypotension requiring pharmacotherapeutic intervention. ResultA total of 1187 twins were delivered during the study period, and 53 DC twins with selective IUGR were included in this study. DC twins with PDA have higher rate of preterm birth, lower gestational age of delivery, and lower mean birth weight of both twins compared with DC twins without PDA. In a comparison of the sIUGR twin with the appropriate for gestational age co-twin, both the incidences of PDA (28.30% vs. 7.55%, respectively; P = 0.003) and Hs-PDA (24.53% vs. 5.66%, respectively; P = 0.002) were higher in sIUGR fetuses than in the appropriate for gestational age co-twins. Small gestational age of delivery was the only variable to predict PDA and Hs-PDA [p = 0.002, Odds ratio = 0.57 (0.39–0.82), p = 0.009, Odds ratio = 0.71 (0.55–0.92), respectively]. ConclusionAn analysis of dichorionic twins with sIUGR indicated that IUGR increased the risk of PDA and hemodynamically significant PDA.

EXPERIMENTAL AND NUMERICAL INVESTIGATION ON MANEUVERING PERFORMANCE OF SMALL WATERPLANE AREA TWIN HULL

Free running model tests and a system-based method are employed to evaluate maneuvering performance for a Small Waterplane Area Twin Hull (SWATH) ship in this paper. A 3 degrees of freedom Maneuvering Modeling Group (MMG) model is implemented to numerically simulate the maneuvering motions in calm water. Virtual captive model tests are performed by using a Reynolds-averaged Navier-Stokes (RANS) method to acquire hydrodynamic derivatives, after a convergence study to check the numerical accuracy. The turning and zigzag maneuvers are simulated by solving the maneuvering motion model and the predicted results agree well with the experimental data. Moreover, free running model tests are carried out for three lateral separations and the influence of the lateral separations on maneuvering performance is investigated. The research results of this paper will be helpful for the maneuvering prediction of the small waterplane area twin hull ship.

Placental glucose transporter 1 and 3 gene expression in Monochorionic twin pregnancies with selective fetal growth restriction

BackgroundIn monochorionic twin (MC) gestations with selective fetal growth restriction (FGR), the discordant fetal growth usually is due to unequal placental sharing. Glucose, which is essential for oxidative metabolism in the growing placenta and fetus, is transferred from maternal blood by facilitated carrier-mediated diffusion via glucose transporters (GLUTs). How the GLUTs expression varies in the two placenta territories manifests discordant perfusion in MC twin pregnancy with selective FGR is unknown. This study evaluates the human placental GLUT1 and GLUT3 gene expression in MC twin gestations with selective FGR.MethodsMC twin pregnancy with selective FGR was defined as the presence of inter-twin birth weight discordance of > 25% and the smaller twin with a birth weight less than the 10th percentile in third trimester. Fetal umbilical artery Doppler was checked within 1 week before delivery in the two fetuses. An abnormal umbilical artery Doppler was defined as persistently absent or reverse end-diastolic flow (UA-AREDF). GLUT1, GLUT3 and HIF-1α gene expression were assayed in each twin’s placental territories. The inter-twin placental gene expression ratio was calculated as the placenta GLUTs or HIF-1α expression level of the selective FGR twin divided by expression level of the appropriate-for-gestational-age (AGA) cotwin. Higher gene expression ratio means elevated gene expression in the selective FGR twin’s placenta territory compared to AGA twin’s placenta territory.Results15 MC twin gestations with selective FGR including nine with normal (group 1) and six with abnormal selective FGR twin UA Doppler (group 2) were included into this study. The GLUT3 and HIF-1α gene expression are significantly elevated in selective FGR twin’s placenta territory in group 2 twin pregnancies (mean gene expression ratio as 2.23 and 1.65, p values as 0.015 and 0.045, respectively), but not in in group 1 twin pregnancies.ConclusionThe upregulation of placental GLUT3 gene expression in selective FGR fetus with abnormal UA Doppler may be due to hypo-perfusion which is mediated by up -regulation of HIF-1α gene expression.

Acardiac twin pregnancies part VI: Why does acardiac twinning occur only in the first trimester?

BackgroundClinical observation suggests that acardiac twinning occurs only in the first trimester. In part, this contradicts our previous analysis (part IV) of Benirschke's concept that unequal embryonic splitting causes unequal embryo/fetal blood volumes and pressures. Our aim is to explain why acardiac onset is restricted to the first trimester.MethodsWe applied the vascular resistance scheme of two fetuses connected by arterio‐arterial (AA) and veno‐venous (VV) anastomoses, the small VV resistance approximated as zero. The smaller twin has volume fraction α < 1 of the assumed normal larger twin, and has only access to fraction X < 1 of its placenta; the larger twin's larger mean arterial pressure accesses the remaining fraction. Before 13 weeks, embryos have a much smaller vascular resistance than placentas. After 13 weeks, when maternal blood provides oxygen, smaller twins can increase their vascular volume by hypoxemia‐mediated neovascularization. Estimated AA radii at 40 weeks, , are 0.5–1.3 mm.ResultsEmbryos with α < 0.33 unlikely survive 13 weeks and acardiac twinning occurs under appropriate conditions (AA‐VV, small placenta). Acardiac body perfusion occurs because of a much smaller vascular resistance than the placenta. When α > 0.33 and =1.3 mm, modeled survival is >32 weeks.ConclusionBefore 13 weeks, embryos with α < 0.33 cannot survive and may result in the onset of acardia. Beyond 13 weeks, fetuses with α ≥ 0.33 survive because is too small for acardiac onset. Following fetal demise, exsanguination from the live twin increases its blood volume and, we assumed also, its vascular resistance. Perfusion then occurs through the lower resistance placenta.

Birthweight Differences in Adolescent Monozygotic Twins Influence Androgens, Psychological Morbidity, and Health-Related Quality of Life

Background: Adverse prenatal conditions can exert a long-lasting impact in later life. Patients and Methods: Thirty-eight post-pubertal monozygotic twin pairs (16 female pairs) with divergent birthweight (bw) due to twin-to-twin transfusion syndrome were examined at a median of 15.1 years. Auxological and endocrine parameters were measured. To evaluate effects of intra-twin bw and hormone differences on mental health, adolescents and their parents completed the Strengths and Difficulties Questionnaire (SDQ), identifying psychological problems. Twins answered the questionnaire on health-related quality of life (HrQoL, KIDSCREEN-52). Results: Parents attributed a higher number of psychological challenges to the formerly smaller twins, for example, total difficulties (8.8 vs. 6.5, p = 0.009). Differences in bw were associated with differences in parental evaluation of problems, for example, peer relationship problems (r = −0.57 and p = 0.0001). In contrast, bw differences did not affect subjects’ self-assessment of psychological factors but on physical well-being (r = 0.42, p = 0.017). The formerly smaller discordant twins showed significantly lower HrQoL regarding psychological well-being (24.9 vs. 26.6, T_1,15 = −2.2, and p = 0.043) and moods and emotions (29.8 vs. 32.0, T_1,15 = −2.3, p = 0.039). Higher concentrations of androstenedione were linked to greater psychological well-being (r = 0.39 and p = 0.036) in all twin pairs. Conclusion: Our results show that the prenatal environment leading to bw differences exerts a long-lasting impact on diverging parental evaluation of mental health. Formerly smaller discordant twins showed significantly lower HrQoL regarding psychological well-being and moods and emotions. Higher androstenedione concentrations were linked to greater psychological well-being.

Respiratory distress syndrome and bronchopulmonary dysplasia after fetal growth restriction: Lessons from a natural experiment in identical twins.

BackgroundFetal growth restriction (FGR) is thought to negatively affect lung development resulting in increased respiratory morbidity. However, research performed in singletons is often limited by a certain level of bias caused by individual differences in genetic constitution, obstetrical and maternal factors.MethodsRespiratory morbidity was compared between the smaller and the larger twin in monochorionic twins with selective fetal growth restriction (sFGR), defined as a birth weight discordance ≥ 20%, born in our center between 2010 and 2019 in this retrospective study. Respiratory distress syndrome (RDS) was diagnosed based on the clinical picture of a neonate with respiratory failure requiring mechanical ventilation and/or surfactant, confirmed by a chest X-ray. Bronchopulmonary dysplasia (BPD) was diagnosed when the neonate required treatment with >21% oxygen for at least 28 days.FindingsMedian gestational age at birth for the 94 included pregnancies was 32.4 (IQR 30.4–34.3) weeks. Within-pair analyses showed that the prevalence of RDS was lower in the smaller twin compared to the larger twin, 19.1% (18/94) vs 34.0% (32/94), respectively (p = 0.004). The odds of RDS for the larger twin was doubled (OR 2.1 (CI95% 1.3–3.5). In contrast, the rate of BPD in the smaller twin was higher as opposed to the larger twin, 16.7% (15/90) vs 6.7% (6/89), respectively (p = 0.008), with a more than doubled odds (OR 2.5 (CI95% 1.3–4.9)).InterpretationDespite being genetically identical, sFGR twins have different respiratory outcomes. Adverse growth condition in utero in the smaller twin is associated with a reduced odds of RDS at birth but a more than doubled odds of BPD, reflecting the pathophysiologic adverse effect of growth restriction on lung development.FundingThe Dutch Heart Foundation (2017T075).

Ultrasound in the prediction of birthweight discordance in dichorionic twins.

Large birthweight discrepancy has been identified as a risk factor for perinatal morbidity and mortality in twin pregnancies. However, it remains unclear whether such discordance can be predicted by various biological indices with specific cut-off values, and how these depend on the gestational age. We aimed to determine the most effective way to predict large birthweight discordance at various gestational ages. A retrospective cohort study of dichorionic twins, live-born between 2008 and 2018, was conducted. Discordances in biparietal diameter, head circumference, humerus and femur length, abdominal circumference, and estimated fetal weight were calculated-([larger twin-smaller twin]/larger twin)×100%-and compared between those with and without a large birthweight discordance (≥20%). Receiver operating characteristic curves were constructed to analyze the predictive characteristics of each parameter. Of 598 dichorionic twin pregnancies included, 83 (13.9%) had a birthweight discordance ≥20%. Group differences in biparietal diameter and head circumference discordance were the earliest to emerge (before 20weeks of gestation), but became insignificant after 36weeks, followed by humerus and femur length, estimated fetal weight discordance (after 20weeks), and abdominal circumference discordance (after 28weeks). The best predictors (with cut-off values) were discordance in biparietal diameter ≥7.8% at <20weeks, head circumference ≥4.5% at 20-23+6 weeks, humerus length ≥4.5% at 24-27+6 weeks, and estimated fetal weight discordance (≥11.6% at 28-31+6 weeks, ≥10.5% at 32-35+6 weeks, and ≥15.0% ≥36weeks), with sensitivity and specificity of 52%-77% and 69%-82%, respectively. Different predictors and cut-off values may be useful for predicting large inter-twin birthweight discordance in dichorionic twins at different gestational ages. It is more accurate to use biparietal diameter and head circumference discordance in the early second trimester, humerus length discordance in the late second trimester, and estimated fetal weight discordance in the third trimester.

Establishing the Most Accurate Due Date in Dichorionic Twin Gestations by First and Second Trimester Ultrasound.

To determine the optimal sonographic dating of dichorionic gestations. We reviewed dichorionic pregnancies conceived with assisted reproductive technologies (ART) at 2 institutions between 2006-2016, excluding fetuses with major anomalies. Gestational age was calculated with smaller, larger, and mean of the crown-rump lengths (CRL) and biometry midgestation and compared to the ART age. The mean and mean absolute deviation of the observed gestational age from the ART age was calculated to assess accuracy, precision, and presence of bias. The incidence of small for gestational age using the smaller and larger CRLs was compared to the ART age via McNemar's test. Based on 140 ultrasounds, the CRL from the smaller twin best approximates the true gestational age with least bias compared to the larger twin or average (mean absolute deviation: 2.8, mean deviation: -0.1 [95% CI: -0.4, 0.2] versus 2.7, -0.9 [-1.1, -0.6] and 2.9, -1.5 [-1.8, -1.3], in days, respectively). Based on 165 ultrasounds, biometry from the smaller fetus is least accurate compared to the larger or mean (11.8, 2.5 [1.5, 3.6] versus 11.7, 0.8 [-0.3, 1.8] and 11.9, -1.0 [-2.0, 0.04], respectively). The incidence of small for gestational age neonates did not differ from the true rate using either the CRL from the larger or smaller twin (p > .05). In ART dichorionic gestations, ultrasound of the smaller fetus is most accurate in establishing gestational age in the first trimester but least accurate in the second, though all methods performed well with little clinical difference.

Quasi-Static Tensile Behaviors, Mechanisms, and Constitutive Descriptions of Commercially Pure Titanium at Diverse Strain Rates in Ambient Air and Liquid Nitrogen

The quasi-static tensile behaviors, mechanisms and the constitutive descriptions of commercially pure titanium over a strain rate range of 10−4–10−1 s−1 at 77 and 293 K have been investigated and compared by means of OM, SEM, EBSD, and TEM. The results show that the strain hardening rate at all strain rates generally shows a falling-increasing-falling changing tendency at 77 K. Due to the small twin’s density at 293 K, strain hardening rate shows monotone decreasing tendency and generally has much lower values at all strain levels than that at 77 K. Serration behavior can be found in the strain hardening rate curves at low strain rates. The repeated pinning and depinning of dislocations with interstitial atoms could be responsible for this. The elongation at 293 K is proportional to the twin volume fraction in microstructure, which is attributed to the twinning-induced plasticity effect. However, it shows the reverse changing tendency at 77 K. This means that excessive twins may exert detrimental effect on the plasticity of CP Ti. Based on the EBSD and TEM results at the uniformly deformed part of the tensile specimens, it is proved that excessive twins in microstructure could act as obstacles to the movement of dislocations. Won model has been used to describe the constitutive curves under different conditions. It shows good prediction accuracy at 293 K. By contrast, due to the lack of specific consideration of the twinning effect in Won model, its prediction performance at 77 K is ordinary.

The Marmoset: The Next Frontier in Understanding the Development of the Human Brain.

Rodent models, particularly mice, have dominated the field of developmental neuroscience for decades, like they have in most fields of biomedicine research. However, with 80 million years since rodents and primates last shared a common ancestor, the use of mice to model the development of the human brain is not without many shortcomings. The human brain diverges from the mouse brain in many aspects and is comprised of novel structures as well as diversified cellular subtypes. While these newly evolved features have no equivalent in rodents, they are observed in nonhuman primates. Therefore, elucidating the cellular mechanisms underlying the development and maturation of the healthy and diseased human brain can be achieved using less complex nonhuman primates. Historically, macaques were the preferred nonhuman primate model. However, over the past decade, the New World marmoset monkey (Callithrix jacchus) has gained more importance, particularly in the field of neurodevelopment. With its small size, twin or triplet birth, and prosocial behavior, the marmoset is an ideal model to study normal brain development as well as neurodevelopmental disorders, which are often associated with abnormal social behaviors. The growing interest in the marmoset has prompted many comparative studies, all demonstrating that the marmoset brain closely resembles that of the human and is perfectly suited to model human brain development. The marmoset is thus poised to extend its influence in the field of neurodevelopment and will hopefully fill the gaps that the mouse has left in our understanding of how our brain forms and how neurodevelopmental disorders originate.

Effects of Al addition on microstructure and mechanical properties of extruded Mg–3Bi alloy

Effects of Al addition to a Mg–Bi binary alloy on its microstructural characteristics and tensile properties after extrusion are investigated via extrusion of Mg–3Bi–xAl (x = 0, 1, and 2 wt%) billets and analysis of the extruded materials. The Al addition negligibly affects the second-phase particles of the extruded alloy; however, an increase in the Al content causes significant decreases in the average grain size and maximum texture intensity of the extruded material owing to an increase in the area fraction of dynamically recrystallized (DRXed) grains. The Al addition improves the strength of the extruded alloy; this improvement is attributed to the enhanced grain-boundary hardening and solid-solution hardening effects induced by grain refinement and Al solute atoms, respectively. As the Al content increases from 0 wt% to 1 wt% and 2 wt%, the tensile elongation increases substantially from 2.8% to 9.4% and 16.9%, respectively. The reduction in the number and size of unDRXed grains with increasing Al content suppresses the formation and coalescence of cracks in the unDRXed grains during tension, which results in a significant improvement in the tensile ductility of the extruded material. During tensile deformation, large undesirable twins that act as crack initiation sites are locally formed in the unDRXed grains of the Mg–3Bi alloy, whereas relatively smaller twins are uniformly formed in both the DRXed and the unDRXed grains of the Mg–3Bi–2Al alloy. Consequently, the extruded Mg–3Bi–2Al alloy has a substantially higher tensile yield strength–elongation product (2924 MPa%) than the extruded Al-free B3 alloy (381 MPa%).

Outcomes of Monochorionic, Diamniotic Twin Pregnancies with Prenatally Diagnosed Intertwin Weight Discordance.

Monochorionic, diamniotic (MCDA) twin pairs are predisposed to various pregnancy complications due to the unique placental angioarchitecture of monochorionicity. Few studies have evaluated the outcomes of weight-discordant MCDA pairs without selective fetal growth restriction (SFGR) or the risk factors for development of SFGR. This study aims to describe the natural history of expectant, noninvasive management of weight-discordant MCDA twins and to evaluate risk factors associated with progression to SFGR. This was a retrospective cohort study at a single, tertiary care center in the United States. All MCDA twins with isolated intertwin weight discordance (ITWD) ≥ 20% diagnosed before 26 weeks' gestational age (GA) were included. The primary outcome of descriptive analyses was overall pregnancy outcome, incorporating both survival to delivery and GA at delivery, as defined by the North American Fetal Therapy Network. The secondary outcome was SFGR in one twin (defined as estimated fetal weight < 10% for GA) and factors associated with this progression. Only those with fetal ultrasound (US) within 4 weeks of delivery were included in this secondary analysis. Among 73 MCDA pairs with ITWD, 73% had a good pregnancy outcome, with dual live delivery at a median GA of 33 weeks. Among the 34 pairs with adequate US follow-up, 56% developed SFGR. There were no differences in GA at delivery or discordance at birth between those who did and those who did not develop SFGR. There was a nonsignificant association between increasing ITWD at diagnosis and subsequent development of SFGR. Expectant, noninvasive management can be considered in MCDA twin pregnancies with ITWD ≥ 20% diagnosed before 26 weeks. This approach is associated with a good pregnancy outcome in the majority of cases, even after the development of SFGR in the smaller twin. · Nearly 75% of weight-discordant mo/di twins have a good pregnancy outcome.. · Weight-discordant mo/di twins deliver at a mean gestational age of 33 weeks without invasive therapy.. · Noninvasive management should be considered for weight-discordant mo/di twins..

Analysis of the Use of Electric and Hybrid Drives on SWATH Ships

The article presents issues related to the possibility of using electric and hybrid systems to drive Small Waterplane Area Twin Hull (SWATH) vessels. Ships of this type have significantly less sway and heave compared to monohull crafts and catamarans. Thanks to the synergistic combination of the hydrodynamic properties of SWATH hull and electric drive systems, they can be an interesting proposition for use in transport of passengers and offshore wind farms service crews. The paper presents comparative test results of an electric drive system powered by Hybrid Energy Storage System, which are a combination of systems consisting of batteries (BAT), hydrogen fuel cells (FC) and diesel generators (D). For the presented configurations of propulsion systems, mathematical models taking into account the hydrodynamic resistance of the hull of the vessel have been developed and implemented in the Modelica simulation environment. The tests carried out for various configurations of the drive system have shown reduced energy consumption by the DIESEL-ELECTRIC drive system (by approx. 62%), as well as the reduction of harmful greenhouse gas emissions to the atmosphere (by approx. 62%) compared to the conventional DIESEL drive.

Strength and Ductility Improvement through Thermomechanical Treatment of Wire-Feed Electron Beam Additive Manufactured Low Stacking Fault Energy (SFE) Aluminum Bronze

An as-cast macrostructure of electron beam additively manufactured metallic materials was represented by coarse columnar grains whose axes were inclined at 25° with respect to the substrate’s plane. One part of the as-grown samples was annealed to form a coarse grain microstructure while the other part was pre-deformed by forging and then annealed what allowed obtaining recrystallized microstructures with small grains and multiple annealing twin boundaries. This sample showed both high strength and plasticity during the tensile tests. These tensile tests demonstrated also two-stage stress-strain curves as depended on their strain hardening rates. High and low strain hardening rates corresponded to a twinning-dominated deformation at stage II and dislocation-base deformation at stage III. A submicron size strain-induced grain-subgrain microstructure was formed in the vicinity of a necked zone as a result of combined twinning/dislocation grain refining.

Abdominal circumference discordance for prediction of small for gestational age at birth in twin pregnancies

Objective To evaluate whether single sonographic abdominal circumference (AC) discordancy estimation can predict small for gestational age (SGA) at birth in twin gestations. Methods A retrospective analysis of prospectively collected data. Cohort included all twin gestations delivered at one university-affiliated medical center between 2010 and 2018, with available sonographic evaluation from 22 gestational weeks to term. Pregnancies complicated by fetal chromosomal abnormalities, major anomalies or twin to twin transfusion syndrome were excluded. One sonographic evaluation per pregnancy was selected randomly. AC discordance was calculated as (large twin AC – small twin AC)/large twin AC*100. Prediction of SGA at birth for at least one newborn (<10% percentile for gestational age by gender-specific local curves for multiples) was evaluated using ROC statistics with calculation of Youden index to establish best AC discordance cutoff. AC discordance prediction performance was compared to estimated fetal weight discordance performance. Results were adjusted for confounders using logistic regression analysis. Results After exclusion, 236 twin gestations entered analysis. Of them, 200/236 (84.7%) were dichorionic-diamniotic twins. Mean gestational age at ultrasound evaluation and at delivery were 30.9 ± 4.4 and 35.9 ± 2.4 weeks, respectively. In 28/236 (11.8%) pregnancies, at least one neonate was born SGA. AC discordance predicted SGA at birth as good as sonographic estimated fetal weight (sEFW) discordance: ROC-AUC 0.76, 95% CI 0.67–0.85 vs. 0.77 95% CI 0.66–0.87, p < .001 for all. Best AC discordance cutoff for prediction of SGA at birth was 7.1% (57% sensitivity, 87% specificity), ROC-AUC 0.72 (95% CI 0.61–0.84, p < .001). Results remained significant after adjustment for maternal age, nulliparity, chorionicity and ultrasound to delivery interval (aOR 1.21 95% CI 1.1–1.32, p < .001). Conclusion According to our results, AC discordance at single sonographic evaluation can predict SGA at birth in twin gestations as good as sEFW discordance. Best cutoff for SGA prediction was 7.1%.