Intermittency and non-Gaussian fluctuations of the global energy transfer in fully developed turbulence

We address the experimentally observed non-Gaussian fluctuations for the energy injected into a closed turbulent flow at fixed Reynolds number. We propose that the power fluctuations mirror the internal kinetic energy fluctuations. Using a stochastic cascade model, we construct the excess kinetic energy as the sum over the energy transfers at different levels of the cascade. We find an asymmetric distribution that strongly resembles the experimental data. The asymmetry is an explicit consequence of intermittency and the global measure is dominated by small scale events correlated over the entire system. Our calculation is consistent with the statistical analogy recently made between a confined turbulent flow and a critical system of finite size.Comment: To appear in Physical Review Letter

Flying in 3D with an Insect based Visual Autopilot

International audienceFlying insects rely on Optic Flow (OF) cues to avoid collisions, control their speed, control their height, and land. Recent studies have shown that the principle of “OF regulation” may account for various behaviors observed in freely flying insects. The aim of the present study was to suggest a visually guided autopilot enabling an insect to navigate in 3D, and to test its robustness to natural images. Using computer-simulation experiments, we simulated a bee that flies through a tunnel wallpapered with natural images, by controlling both its ground speed and clearance all four sides: the lateral walls, the ground, and the ceiling. The simulated bee can translate along three directions (the surge, sway, and heave axes): it is therefore fully actuated. The new visuo-motor control system, called ALIS (AutopiLot using an Insect based vision System), is a dual OF regulator consisting of two interdependent feedback loops: the speed control loop (along the surge axis) and the positioning control loop (along both the sway and heave axes), each of which has its own OF set-point. The experiments show that the simulated bee navigates safely along a straight tunnel, while compensating for the major OF perturbations caused by, e.g., a tapering of the tunnel or the lack of texture on one wall. The minimalistic visual system used here (only eight pixels) is robust to naturally contrasted stimuli and tunnels, and is sufficient to control both the clearance from the four sides and the forward speed jointly, without requiring to measure any speeds or distances. Besides, the ALIS autopilot accounts remarkably for the quantitative results of ethological experiments performed on honeybees flying freely in straight or tapered corridors

Renormalisation of the scalar energy-momentum tensor with the Wilson flow

Talk presented at the 34th International Symposium on Lattice Field Theory (Lattice 2016) by Susanne EhretThe non-perturbative computation of the energy-momentum tensor can be used to study the scaling behaviour of strongly coupled quantum field theories. The Wilson flow is an essential tool to find a meaningful formulation of the energy-momentum tensor on the lattice. We extend recent studies of the renormalisation of the energy-momentum tensor in four-dimensional gauge theory to the case of a three-dimensional scalar theory to investigate its intrinsic structure and numerical feasibility on a more basic level. In this paper, we discuss translation Ward identities, introduce the Wilson flow for scalar theory, and present our results for the renormalisation constants of the scalar energy-momentum tensor

Lichen planus mimicking atypical melanocytic lesion in a man with dark skin

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New Antenna Deployment, Pointing and Supporting Mechanism

On ITALSAT Flight 2, the Italian telecommunications satellite, the two L-Ka antennas (Tx and Rx) use two large deployable reflectors (2000-mm diameter), whose deployment and fine pointing functions are accomplished by means of an innovative mechanism concept. The Antenna Deployment & Pointing Mechanism and Supporting Structure (ADPMSS) is based on a new configuration solution, where the reflector and mechanisms are conceived as an integrated, self-contained assembly. This approach is different from the traditional configuration solution. Typically, a rigid arm is used to deploy and then support the reflector in the operating position, and an Antenna Pointing Mechanism (APM) is normally interposed between the reflector and the arm for steering operation. The main characteristics of the ADPMSS are: combined implementation of deployment, pointing, and reflector support; optimum integration of active components and interface matching with the satellite platform; structural link distribution to avoid hyperstatic connections; very light weight and; high performance in terms of deployment torque margin and pointing range/accuracy. After having successfully been subjected to all component-level qualification and system-level acceptance tests, two flight ADPMSS mechanisms (one for each antenna) are now integrated on ITALSAT F2 and are ready for launch. This paper deals with the design concept, development, and testing program performed to qualify the ADPMSS mechanism

Death of a 23-year-old man from cardiac conduction system injury through a blunt chest impact after a car accident.

Cardiac contusion, usually caused by blunt chest trauma, has been recognized with increased frequency over the past decades. Traffic accidents are the most frequent causes of cardiac contusion resulting from a direct blow to the chest. Myocardial contusion is difficult to diagnose; the clinical presentation varies greatly, ranging from a lack of symptoms to cardiogenic shock and arrhythmia. Although death is rare, cardiac contusion can be fatal. The Authors report a case of death due to a cardiac conduction system injury from a blunt chest impact following a car accident. The autopsy showed no external signs of thoracic trauma, no evident rib or sternum fractures. A small subendocardial hemorrhage was found in the region of the atrioventricular node. Histological examination revealed an injury of the atrioventricular node and His' bundle. The cause of the death was attributed to the arrhythmia induced by contusion of the cardiac conduction system

Immune-Mediated Dermatoses in Patients with Haematological Malignancies: A Comprehensive Review

Haematological malignancies induce important alterations of the immune system, which account for the high frequency of autoimmune complications observed in patients. Cutaneous immune-mediated diseases associated with haematological malignancies encompass a heterogeneous group of dermatoses, including, among others, neutrophilic and eosinophilic dermatoses, autoantibody-mediated skin diseases, vasculitis and granulomatous dermatoses. Some of these diseases, such as paraneoplastic pemphigus, are associated with an increased risk of death; others, such as eosinophilic dermatoses of haematological malignancies, run a benign clinical course but portend a significant negative impairment on a patient's quality of life. In rare cases, the skin eruption reflects immunological alterations associated with an unfavourable prognosis of the associated haematological disorder. Therapeutic management of immune-mediated skin diseases in patients with haematological malignancies is often challenging. Systemic corticosteroids and immunosuppressive drugs are considered frontline therapies but may considerably augment the risk of serious infections. Indeed, developing a specific targeted therapeutic approach is of crucial importance for this particularly fragile patient population. This review provides an up-to-date overview on the immune-mediated skin diseases most frequently encountered by patients with onco-haematological disorders, discussing new pathogenic advances and therapeutic options on the horizon

Experimental test of the Gallavotti-Cohen fluctuation theorem in turbulent flows

We test the fluctuation theorem from measurements in turbulent flows. We study the time fluctuations of the force acting on an obstacle, and we consider two experimental situations: the case of a von K\'arm\'an swirling flow between counter-rotating disks (VK) and the case of a wind tunnel jet. We first study the symmetries implied by the Gallavotti-Cohen fluctuation theorem (FT) on the probability density distributions of the force fluctuations; we then test the Sinai scaling. We observe that in both experiments the symmetries implied by the FT are well verified, whereas the Sinai scaling is established, as expected, only for long times

Relevance of soft modes for order parameter fluctuations in the Two-Dimensional XY model

We analyse the spin wave approximation for the 2D-XY model, directly in reciprocal space. In this limit the model is diagonal and the normal modes are statistically independent. Despite this simplicity non-trivial critical properties are observed and exploited. We confirm that the observed asymmetry for the probability density function for order parameter fluctuations comes from the divergence of the mode amplitudes across the Brillouin zone. We show that the asymmetry is a many body effect despite the importance played by the zone centre. The precise form of the function is dependent on the details of the Gibbs measure, giving weight to the idea that an effective Gibbs measure should exist in non-equilibrium systems, if a similar distribution is observed.Comment: 12 pages, 9 figure