Static and Dynamic Coefficient Measurements for a Thrust Collar Used in an Integrally Geared Compressor

Test rigs that replicate the conditions for thrust collars (TCs) used in an integrally geared compressor (IGC) are scarce. The test rig described here is based on a typical IGC and is the first rig specifically designed to measure the dynamic reaction force coefficients of the lubricated area of the TC. The test rig uses low-speed and high-speed shafts with independently controlled speed and a pneumatically pressurized thrust disk to apply an axial load ???v?? to create the hydrodynamic wedge that balances the imposed axial load. The speed ratio between the low-speed shaft (LSS) and the pinion shaft is 11.67. The geometry of the shafts matches that of a typical IGC. Tests were conducted at pinion speeds of 5, 7.5, and 10 krpm and ???v?? = 200, 300, and 400 N. The resulting range of applied pressures is smaller than those arising in practice. The author conducts static tests by applying an incrementally-increasing ??v?? on the pinion shaft and measuring the relative displacement between the BG and the TC (??v??). One test is conducted at each predetermined spin speed. Run-out on the TC as well as the BW obscures the data. Averaging works well to eliminate the effects of run-out. The author uses the averaged ???v?? and ??v?? values to create a static, load/ relative displacement curve and the slope is the measured static stiffness coefficient (???v?? ). The axial stiffness coefficient results are compared to predictions from a code based on a 2016 model due to Cable et. al. Their dynamic reaction-force model is ??v???? = ???v???v?? – ??v???v?? where ?????? is the reaction force of the TC, and ???? is the axial damping coefficient. The trends and the magnitudes of the measured ???v?? values and the predicted values from San Andres code for ??v?? agree very well, especially for the 5 krpm test case. The author then conducts dynamic tests involving an applied impulse load to the TC shaft. One hundred impulses are conducted at each spin speed (??), ???v?? test condition for averaging purposes. A one degree of freedom damped motion model uses ?v??(??) measurements to determine the damped natural frequency (????) and damping factor (??) for each test point. The thrust collar mass ??v???? and the measured ?? were then used to calculate ??v?? and ??v?? . The ???? values obtained in this fashion were consistently (and markedly) smaller than the static ???v?? values. Based on the results, the author uses the following model ??v???? = ???v???v?? ? ??v???v?? ? ? ??v????v?? that includes the virtual-mass coefficient (??v??). The Cable et al. model was based on the Reynolds equation and accordingly did not produce a virtual-mass term. The ??v?? term is calculated for each test point using ???v?? , ??v??, and ??. ??v?? increases as a function ?? and ???v?? . It ranges from 0 to 19.5 kg; the mass of the pinion shaft is 12.8 kg. Both predictions and measurements show an increase in ??v?? with increasing ???v?? . The test rig produced damping coefficients that increased for increasing ??, while the predicted values decreased. The magnitude of ??v?? was lower than the predicted damping by a factor of 2 - 10

Investigating the Relationships Between Three Important Functional Tasks Early After Stroke: Movement Characteristics of Sit-To-Stand, Sit-To-Walk, and Walking.

Background: Walking, sit-to-stand (STS) and sit-to-walk (STW) are all considered important functional tasks in achieving independence after stroke. Despite knowledge that sensitive measurement of movement patterns is crucial to understanding neuromuscular restitution, there is surprisingly little information available about the detailed biomechanical characteristics of, and relationships between, walking, sit-to-stand and sit-to-walk, particularly in the important time window early after stroke. Hence, here, the study aimed to: Identify the biomechanical characteristics of and determine any differences in both movement fluidity (hesitation, coordination and smoothness) and duration of movement phases, between sit-to-stand (STS) and sit-to-walk (STW) in people early after stroke.Determine whether measures of movement fluidity (hesitation, coordination, and smoothness) and movement phases during sit-to-stand (STS) and/or sit-to-walk (STW) are correlated strongly to commonly used measures of walking speed and/or step length ratio in people early after stroke. Methods: This study consisted of secondary data analysis from the SWIFT Cast Trial. Specifically, we investigated movement fluidity using established assessments of smoothness, hesitation and coordination and the time duration for specific movement phases in a group of 48 people after stroke. Comparisons were made between STS and STW and relationships to walking measures were explored. Results: Participants spent significantly more time in the initial movement phase, flexion momentum, during STS [mean time (SD) 1.74 ±1.45 s] than they did during STW [mean time (SD) 1.13 ± 1.03 s]. STS was also completed more smoothly but with more hesitation and greater coordination than the task of STW. No strong relationships were found between movement fluidity or duration with walking speed or step length symmetry. Conclusions: Assessment of movement after stroke requires a range of functional tasks and no one task should predominate over another. Seemingly similar or overlapping tasks such as STS and STW create distinct biomechanical characteristics which can be identified using sensitive, objective measures of fluidity and movement phases but there are no strong relationships between the functional tasks of STS and STW with walking speed or with step-length symmetry

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2–4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease