Generalized Quasilinear Approximation: Application to Zonal Jets.

Quasilinear theory is often utilized to approximate the dynamics of fluids exhibiting significant interactions between mean flows and eddies. We present a generalization of quasilinear theory to include dynamic mode interactions on the large scales. This generalized quasilinear (GQL) approximation is achieved by separating the state variables into large and small zonal scales via a spectral filter rather than by a decomposition into a formal mean and fluctuations. Nonlinear interactions involving only small zonal scales are then removed. The approximation is conservative and allows for scattering of energy between small-scale modes via the large scale (through nonlocal spectral interactions). We evaluate GQL for the paradigmatic problems of the driving of large-scale jets on a spherical surface and on the beta plane and show that it is accurate even for a small number of large-scale modes. As GQL is formally linear in the small zonal scales, it allows for the closure of the system and can be utilized in direct statistical simulation schemes that have proved an attractive alternative to direct numerical simulation for many geophysical and astrophysical problems.

Trunk stability in fatiguing frequency-dependent lifting activities.

BACKGROUND: Work-related low-back disorders (WLBDs) are one of the most frequent and costly musculoskeletal conditions. It has been showed that WLBDs may occur when intervertebral or torso equilibrium is altered by a biomechanical perturbations or neuromuscular control error. The capacity to react to such disturbances is heavily determined by the spinal stability, provided by active and passive tissues and controlled by the central nervous system. RESEARCH QUESTION: This study aims to investigate trunk stability through the Lyapunov's maximum exponent during repetitive liftings in relation to risk level, as well as to evaluate its ability to discriminate these risk levels. METHODS: Fifteen healthy volunteers performed fatiguing lifting tasks at three different frequencies corresponding to low, medium, and high risk levels according to the National Institute for Occupational Safety and Health (NIOSH) equation. We investigated changes in spinal stability during fatiguing lifting tasks at different risk levels using the maximum Lyapunov's index (λMax) computed from trunk accelerations recorded by placing three IMUs at pelvis, lower and upper spine levels. A two-way repeated-measures ANOVA was performed to determine if there was any significant effect on λMax among the three risk levels and the time (start, mid, and end of the task). Additionally, we examined the Pearson's correlation of λMax with the trunk muscle co-activation, computed from trunk sEMG. RESULTS: Our findings show an increase in trunk stability with increasing risk level and as the lifting task progressed over time. A negative correlation between λMax and trunk co-activation was observed which illustrates that the increase in spinal stability could be partially attributed to increased trunk muscle co-activation. SIGNIFICANCE: This study highlights the possibility of generating stability measures from kinematic data as risk assessment features in fatiguing tasks which may prove useful to detect the risk of developing work-related low back pain disorders and allow the implementation of early ergonomic interventions.

Multiple scales analysis of slow-fast quasi-linear systems.

This article illustrates the application of multiple scales analysis to two archetypal quasi-linear systems; i.e. to systems involving fast dynamical modes, called fluctuations, that are not directly influenced by fluctuation-fluctuation nonlinearities but nevertheless are strongly coupled to a slow variable whose evolution may be fully nonlinear. In the first case, fast waves drive a slow, spatially inhomogeneous evolution of their celerity field. Multiple scales analysis confirms that, although the energy E, the angular frequency ω and the modal structure of the waves evolve, the wave action E/ω is conserved in the absence of forcing and dissipation. In the second system, the fast modes undergo an instability that is saturated through a feedback on the slow variable. A new multi-scale analysis is developed to treat this case. The key technical point, confirmed by the analysis, is that the fluctuation energy and mode structure evolve slowly to ensure that the slow field remains in a state of near marginal stability. These two model systems appear to be generic, being representative of many if not all quasi-linear systems. In each case, numerical simulations of both the full and reduced dynamical systems are performed to highlight the accuracy and efficiency of the multiple scales approach. Python codes are provided as electronic supplementary material.

Prospectus: towards the development of high-fidelity models of wall turbulence at large Reynolds number.

Recent and on-going advances in mathematical methods and analysis techniques, coupled with the experimental and computational capacity to capture detailed flow structure at increasingly large Reynolds numbers, afford an unprecedented opportunity to develop realistic models of high Reynolds number turbulent wall-flow dynamics. A distinctive attribute of this new generation of models is their grounding in the Navier-Stokes equations. By adhering to this challenging constraint, high-fidelity models ultimately can be developed that not only predict flow properties at high Reynolds numbers, but that possess a mathematical structure that faithfully captures the underlying flow physics. These first-principles models are needed, for example, to reliably manipulate flow behaviours at extreme Reynolds numbers. This theme issue of Philosophical Transactions of the Royal Society A provides a selection of contributions from the community of researchers who are working towards the development of such models. Broadly speaking, the research topics represented herein report on dynamical structure, mechanisms and transport; scale interactions and self-similarity; model reductions that restrict nonlinear interactions; and modern asymptotic theories. In this prospectus, the challenges associated with modelling turbulent wall-flows at large Reynolds numbers are briefly outlined, and the connections between the contributing papers are highlighted.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.

A self-sustaining process model of inertial layer dynamics in high Reynolds number turbulent wall flows.

Field observations and laboratory experiments suggest that at high Reynolds numbers Re the outer region of turbulent boundary layers self-organizes into quasi-uniform momentum zones (UMZs) separated by internal shear layers termed 'vortical fissures' (VFs). Motivated by this emergent structure, a conceptual model is proposed with dynamical components that collectively have the potential to generate a self-sustaining interaction between a single VF and adjacent UMZs. A large-Re asymptotic analysis of the governing incompressible Navier-Stokes equation is performed to derive reduced equation sets for the streamwise-averaged and streamwise-fluctuating flow within the VF and UMZs. The simplified equations reveal the dominant physics within-and isolate possible coupling mechanisms among-these different regions of the flow.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.

[Hemodynamic stability in thoracic-abdominal trauma with multiple intrahepatic abscesses. A clinical case]. / Stabilità emodinamica in trauma toraco-addominale con ascessi multipli intraepatici. Un caso clinico.

A case of multiple injury is reported in a young 35-year-old man affecting three different areas of the body which showed a septic-type development. Complete recovery was largely determined by the accuracy of the preoperative diagnosis and the correct maintenance of hemodynamic parameters.

Bilateral massive adrenal hemorrhage due to sepsis: report of two cases.

Two cases (a 57-year-old man and an 18-year-old girl) of bilateral massive adrenal hemorrhage (BMAH) due to sepsis (Streptococcus pneumoniae and Neisseira meningitidis, respectively) are reported. At admission, the man presented with fever, severe hypotension, hyperazotemia, acidosis, normonatremia and hypocoagulability, while the girl with severe hypotension, fever, hyponatremia, and hypocoagulability. A diagnostic protocol based on a very quick method for cortisol measurement is proposed, in an attempt to reach an earlier diagnosis of BMAH during sepsis.

[99mTc HMPAO (technetium 99m-hexamethylpropyleneamine oxime) angioscintigraphy in the diagnosis of brain death]. / Angioscintigrafia con 99mTc HMPAO (Technetium 99m-Hexametyl propilene amino oxime) nella diagnosi di morte cerebrale.

The diagnosis of brain death has great importance for the social and medical purposes, such as organs transplantation, and is based on clinical examination and EEG records. We report two doubtful cases of brain death in whom the 99mTc HMPAO scintigraphy was used to confirm the complete absence of cerebral perfusion.

[Role of slime in the pathogenesis of pulmonary infections]. / Ruolo dello slime nella patogenesi delle infezioni polmonari.

Microorganisms have proved to produce an amorphous substance that adheres to surfaces of several medical devices like intravenous catheters and endotracheal tubes. We investigated the presence of slime in endotracheal tubes in our Intensive Care Unit (ICU) in 12 patients. We found in this study no correlation between the strain of bacteria on the surface of endotracheal devices and those responsible for pneumonia.

[Total enteral nutrition versus mixed enteral and parenteral nutrition in patients at an intensive care unit]. / La nutrizione enterale totale verso la nutrizione mista enterale e parenterale in pazienti ricoverati in una terapia intensiva polivalente.

OBJECTIVE: To compare metabolic, nutritional and epidemiological data in two groups of patients, one receiving total enteral nutrition, via nasoenteric tube, and one receiving both enteral and parenteral nutrition. DESIGN: A prospective, randomized study. SETTING: A general ICU, with both medical and surgical patients, in a big regional University and National Health Service hospital. PATIENTS: 24 patients requiring Intensive Care after major surgery or because suffering from severe head injury or major neurological impairment. INTERVENTIONS: All patients initially received total parenteral nutrition: after 4 days 12 patients were "weaned" to total enteral nutrition and 12 stayed on mixed parenteral and enteral nutrition. LABORATORY INVESTIGATIONS AND OBSERVATIONAL DATA: Blood levels of albumin, prealbumin, transferrin, ALT, AST, bilirubin, blood urea, blood glucose, total linfocite count, and nutritional and epidemiological data such as nitrogen balance, calorie intake, diarrhea incidence, blood and sputum cultures and radiologic evidence of pneumonia are analysed. RESULTS: At T1, NET patients were able to reduce their nitrogen losses (0.27.1 g/kg +/-0.12 vs 0.35 +/- 0.13 at TO; p < 0.05) and improve nitrogen balance (-9 +/- 7 vs -2 +/- 6 at T0; p < 0.05); they also had a better total linfocite count (2034 +/- 304 vs. 1413 +/- 360 of the MISTA group; p < 0.05), and a lower incidence of pneumonia as documented by sputum cultures and radiograms. CONCLUSIONS: Patients fed with both parenteral and enteral nutrition did no better than those on total enteral nutrition as far as nutritional and metabolic indices were concerned; they also seemed more prone to infections than those on total enteral nutrition, indicating that mixed nutrition may result in more stable feeding, but this does not seem to have any beneficial nutritional, immunological and metabolic effect.