Characterization of shape and dimensional accuracy of incrementally formed titanium sheet parts with intermediate curvatures between two feature types

Single point incremental forming (SPIF) is a relatively new manufacturing process that has been recently used to form medical grade titanium sheets for implant devices. However, one limitation of the SPIF process may be characterized by dimensional inaccuracies of the final part as compared with the original designed part model. Elimination of these inaccuracies is critical to forming medical implants to meet required tolerances. Prior work on accuracy characterization has shown that feature behavior is important in predicting accuracy. In this study, a set of basic geometric shapes consisting of ruled and freeform features were formed using SPIF to characterize the dimensional inaccuracies of grade 1 titanium sheet parts. Response surface functions using multivariate adaptive regression splines (MARS) are then generated to model the deviations at individual vertices of the STL model of the part as a function of geometric shape parameters such as curvature, depth, distance to feature borders, wall angle, etc. The generated response functions are further used to predict dimensional deviations in a specific clinical implant case where the curvatures in the part lie between that of ruled features and freeform features. It is shown that a mixed-MARS response surface model using a weighted average of the ruled and freeform surface models can be used for such a case to improve the mean prediction accuracy within ±0.5 mm. The predicted deviations show a reasonable match with the actual formed shape for the implant case and are used to generate optimized tool paths for minimized shape and dimensional inaccuracy. Further, an implant part is then made using the accuracy characterization functions for improved accuracy. The results show an improvement in shape and dimensional accuracy of incrementally formed titanium medical implants

Evaluation of strain and stress states in the single point incremental forming process

Single point incremental forming (SPIF) is a promising manufacturing process suitable for small batch production. Furthermore, the material formability is enhanced in comparison with the conventional sheet metal forming processes, resulting from the small plastic zone and the incremental nature. Nevertheless, the further development of the SPIF process requires the full understanding of the material deformation mechanism, which is of great importance for the effective process optimization. In this study, a comprehensive finite element model has been developed to analyse the state of strain and stress in the vicinity of the contact area, where the plastic deformation increases by means of the forming tool action. The numerical model is firstly validated with experimental results from a simple truncated cone of AA7075-O aluminium alloy, namely, the forming force evolution, the final thickness and the plastic strain distributions. In order to evaluate accurately the through-thickness gradients, the blank is modelled with solid finite elements. The small contact area between the forming tool and the sheet produces a negative mean stress under the tool, postponing the ductile fracture occurrence. On the other hand, the residual stresses in both circumferential and meridional directions are positive in the inner skin of the cone and negative in the outer skin. They arise predominantly along the circumferential direction due to the geometrical restrictions in this direction.The authors would like to gratefully acknowledge the financial support from the Portuguese Foundation for Science and Technology (FCT) under project PTDC/EMS-TEC/1805/2012. The first author is also grateful to the FCT for the postdoctoral grant SFRH/BPD/101334/2014.info:eu-repo/semantics/publishedVersio

State-of-the-Art Duolingo Features and Applications

Duolingo is a rapidly growing on-line platform for language learning. In this paper learning theories that are embodied in its design are analyzed and certain shortcomings are identified. In the past two years, Duolingo has expanded its platform with the addition of new applications and features. State-of-the-art updates are reviewed in order to uncover whether they address limitations of Duolingo’s original design or provide enhancements to the learning platform

Full-term extrauterine abdominal pregnancy: a case report

<p>Abstract</p> <p>Introduction</p> <p>Extrauterine abdominal pregnancy is extremely rare and is frequently missed during antenatal care. This is a report of a full-term extrauterine abdominal pregnancy in a primigravida who likely had a ruptured ectopic pregnancy with secondary implantation and subsequently delivered a healthy baby.</p> <p>Case presentation</p> <p>A 23-year-old, Middle Eastern, primigravida presented at 14 weeks gestation with intermittent suprapubic pain and dysuria. An abdominal ultrasound examination showed a single viable fetus with free fluid in her abdomen. A follow-up examination at term showed a breech presentation and the possibility of a bicornute uterus with the fetus present in the left horn of her uterus. Our patient underwent Cesarean delivery under general anesthesia and was found to have a small intact uterus with the fetus lying in her abdomen and surrounded by an amniotic fluid-filled sac. The baby was extracted uneventfully, but the placenta was implanted in the left broad ligament and its removal resulted in massive intraoperative bleeding that necessitated blood and blood products transfusion and the administration of Factor VII to control the bleeding. Both the mother and newborn were discharged home in good condition.</p> <p>Conclusions</p> <p>An extrauterine abdominal pregnancy secondary to a ruptured ectopic pregnancy with secondary implantation could be missed during antenatal care and continue to term with good maternal and fetal outcome. An advanced extrauterine pregnancy should not result in the automatic termination of the pregnancy.</p

Comprehensive in vivo Mapping of the Human Basal Ganglia and Thalamic Connectome in Individuals Using 7T MRI

Basal ganglia circuits are affected in neurological disorders such as Parkinson's disease (PD), essential tremor, dystonia and Tourette syndrome. Understanding the structural and functional connectivity of these circuits is critical for elucidating the mechanisms of the movement and neuropsychiatric disorders, and is vital for developing new therapeutic strategies such as deep brain stimulation (DBS). Knowledge about the connectivity of the human basal ganglia and thalamus has rapidly evolved over recent years through non-invasive imaging techniques, but has remained incomplete because of insufficient resolution and sensitivity of these techniques. Here, we present an imaging and computational protocol designed to generate a comprehensive in vivo and subject-specific, three-dimensional model of the structure and connections of the human basal ganglia. High-resolution structural and functional magnetic resonance images were acquired with a 7-Tesla magnet. Capitalizing on the enhanced signal-to-noise ratio (SNR) and enriched contrast obtained at high-field MRI, detailed structural and connectivity representations of the human basal ganglia and thalamus were achieved. This unique combination of multiple imaging modalities enabled the in-vivo visualization of the individual human basal ganglia and thalamic nuclei, the reconstruction of seven white-matter pathways and their connectivity probability that, to date, have only been reported in animal studies, histologically, or group-averaged MRI population studies. Also described are subject-specific parcellations of the basal ganglia and thalamus into sub-territories based on their distinct connectivity patterns. These anatomical connectivity findings are supported by functional connectivity data derived from resting-state functional MRI (R-fMRI). This work demonstrates new capabilities for studying basal ganglia circuitry, and opens new avenues of investigation into the movement and neuropsychiatric disorders, in individual human subjects

Formation mechanism and control of flaring in forward tube spinning

Forward tube spinning (or flow forming) is usually employed to produce cylindrically tubular components to meet the increasing requirements for manufacturing high-performance and light-weight products at low cost and short lead-time. In forward tube spinning, flaring defect may easily occur at the opening end of tubes, which would deteriorate the quality of the spun tubular parts and reduce the material utilization. In addition, an additional operation is needed to trim away the flared end of the spun tabular parts. Efficient control of flaring formation is thus a non-trivial issue in forward tube spinning process and thus become one of the critical bottleneck issues to be addressed in this unique forming process. In this study, the formation mechanism of flaring was systematically studied via finite element (FE) simulation and an in-depth understanding was thus established, which forms basis for control of flaring forming in forward tube spinning. Based on the simulated material flow behaviour, it is found that flaring is formed by the material in non-spun zone flowing away from the mandrel. This material flow behaviour is caused by the pile up and the decreasing stiffness of the non-spun zone. In addition, the effects of process parameters on flaring were investigated to reduce flaring. The results show that the smaller feed rate and thickness reduction per pass can reduce the maximum flaring to a certain extent, but is very limited. To increase productivity and shorten forming lead-time, an efficient method to control flaring was proposed using a pressing ring in front of the roller based on the formation mechanism of flaring. FE simulation was further used to study the feasibility and demonstrates the validity of the method in terms of reducing and even eliminating the flaring with a short production lead-time. Finally, the forward tube spinning experiments were carried out to validate the formation mechanism of flaring and the method to avoid or eliminate the flaring formation in forward tube spinning

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Background: Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. // Methods: We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung's disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. // Findings: We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung's disease) from 264 hospitals (89 in high-income countries, 166 in middle-income countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in low-income countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. // Interpretation: Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between low-income, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030