Vortex dynamics and sound emission in excited high-speed jets

This work aims to study the dynamics of and noise generated by large-scale structures in a Mach 0.9 turbulent jet of Reynolds number using plasma-based excitation of shear layer instabilities. The excitation frequency is varied to produce individual or periodic coherent ring vortices in the shear layer. First, two-point cross-correlations are used between the acoustic near field and far field in order to identify the dominant noise source region. The large-scale structure interactions are then investigated by stochastically estimating time-resolved velocity fields using time-resolved near-field pressure traces and non-time-resolved planar velocity snapshots (obtained by particle image velocimetry) by means of an artificial neural network. The estimated time-resolved velocity fields show multiple mergings of large-scale structures in the shear layer, and indicate that disintegration of coherent ring vortices is the dominant aeroacoustic source mechanism for the jet studied here. However, the merging of vortices in the initial shear layer is also identified as a non-trivial noise source mechanism

Broadband Shock-cell Noise Signature Identification Using a Wavelet-based Method

Civil and military aircraft manufacturers need to respond to increasingly more restrictive standards about noise emission. In order to fulfil those requirements the mechanisms underlying the noise production need to be understood. The supersonic jets at the exit of aircraft engines are known to contain several sources of noise, namely: screech (military air-crafts), Broadband Shock–cell Associated Noise (BBSAN) and large–scale structures. The current work is focused on the study of BBSAN by means of a wavelet–based technique. The technique was applied to a pressure nearfield line array for the sake of extracting the signatures’ related to noise production mechanisms. Each ’signature’ characterized by its shape and time–scale. The signature found up to approximatively x/D = 6D has a ’wave–packet’ like shape. The same shape is obtained at farfield locations for forward angles. The Sound Pressure Level (SPL) was computed using the nearfield signatures and it is in good agreement with the SPL computed using the pressure signals. The ’wave–packet’ like shape ’signature’ is associated to BBSAN as it has the same characteristics: same SPL and forward angles directivity

Cardiologic Manifestations in Omicron‐Type Versus Wild‐Type COVID‐19: A Systematic Echocardiographic Study

Background Information about the cardiac manifestations of the Omicron variant of COVID‐19 is limited. We performed a systematic prospective echocardiographic evaluation of consecutive patients hospitalized with the Omicron variant of COVID‐19 infection and compared them with similarly recruited patients were propensity matched with the wild‐type variant. Methods and Results A total of 162 consecutive patients hospitalized with Omicron COVID‐19 underwent complete echocardiographic evaluation within 24 hours of admission and were compared with propensity‐matched patients with the wild‐type variant (148 pairs). Echocardiography included left ventricular (LV) systolic and diastolic, right ventricular (RV), strain, and hemodynamic assessment. Echocardiographic parameters during acute infection were compared with historic exams in 62 patients with the Omicron variant and 19 patients with the wild‐type variant who had a previous exam within 1 year. Of the patients, 85 (53%) had a normal echocardiogram. The most common cardiac pathology was RV dilatation and dysfunction (33%), followed by elevated LV filling pressure (E/e′ ≥14, 29%) and LV systolic dysfunction (ejection fraction <50%, 10%). Compared with the matched wild‐type cohort, patients with Omicron had smaller RV end‐systolic areas (9.3±4 versus 12.3±4 cm2; P=0.0003), improved RV function (RV fractional‐area change, 53.2%±10% versus 39.7%±13% [P<0.0001]; RV S′, 12.0±3 versus 10.7±3 cm/s [P=0.001]), and higher stroke volume index (35.6 versus 32.5 mL/m2; P=0.004), all possibly related to lower mean pulmonary pressure (34.6±12 versus 41.1±14 mm Hg; P=0.0001) and the pulmonary vascular resistance index (P=0.0003). LV systolic or diastolic parameters were mostly similar to the wild‐type variant‐matched cohort apart from larger LV size. However, in patients who had a previous echocardiographic exam, these LV abnormalities were recorded before acute Omicron infection, but not in the wild‐type cohort. Numerous echocardiographic parameters were associated with higher in‐hospital mortality (LV ejection fraction, stroke volume index, E/e′, RV S′). Conclusions In patients with Omicron, RV function is impaired to a lower extent compared with the wild‐type variant, possibly related to the attenuated pulmonary parenchymal and/or vascular disease. LV systolic and diastolic abnormalities are as common as in the wild‐type variant but were usually recorded before acute infection and probably reflect background cardiac morbidity. Numerous LV and RV abnormalities are associated with adverse outcome in patients with Omicron

Ex post adaptations and hybrid contracts in software development services

We follow the recent literature on ex post adaptations in procurement and argue that highly volatile specifications result in multiple variations of fixed price (FP) and time and materials (T&M) contracts. Specifically, placing a cap on specification change in FP contracts prevents specification volatility, similar to the way that placing a cap on the price in T&M contracts prevents price escalation. We argue that these hybrid mechanisms are particularly important in software development contracting, a new critical business capability involving frequent and costly ex post adaptations to specification change. The level of completeness in these contractual archetypes is hypothesized to be determined by contracting costs and benefits, where costs are related to project uncertainty and benefits are related to the likelihood of vendor opportunism. We test this hypothesis with a unique data set of 270 software development contracts entered into by a leading international bank. The analysis confirms the existence of multiple hybrid contracts that mitigate both price escalation and specification volatility. It also shows that contracting costs and benefits explain more variance in contract choice when these hybrids are included, uncovering the detailed mechanisms used to curb opportunism when the vendor is less familiar to the client