Large eddy simulation and laboratory experiments on the decay of grid wakes in strongly stratified flows

A detailed analysis of the flow structure resulting from the combination of turbulence and internal waves is carried out and visualized by means of the Schlieren method on waves in a strongly stratified fluid at the Laboratory of the IPM in Moscow. The joint appearance of the more regular internal wave oscillations and the small-scale turbulence that is confined vertically to the Ozmidov length scale favours the use of a simple geometrical analysis to investigate their time-space span and evolution. This provides useful information on the collapse of internal wave breaking processes in the ocean and the atmosphere. The measurements were performed under a variety of linear stratifications and different grid forcing scales, combining the grid wake and velocity shear. A numerical simulation using LES on the passage of a single bar in a linearly stratified fluid medium has been compared with the experiments identifying the different influences of the environmental agents on the actual effective vertical diffusion of the wakes. The equation of state, which connects the density and salinity, is assumed to be linear, with the coefficient of the salt contraction being included into the definition of salinity or heat. The characteristic internal waves as well as the entire beam width are related to the diameter of the bar, the Richardson number and the peak-to-peak value of oscillations. The ultimate frequency of the infinitesimal periodic internal waves is limited by the maximum buoyancy frequency relating the decrease in the vertical scale with the anisotropy of the velocity turbulent r.m.s. velocity.Peer ReviewedPreprin

3D Compartmentalised Human Pluripotent Stem Cell-derived Neuromuscular Co-cultures.

Human neuromuscular diseases represent a diverse group of disorders with unmet clinical need, ranging from muscular dystrophies, such as Duchenne muscular dystrophy (DMD), to neurodegenerative disorders, such as amyotrophic lateral sclerosis (ALS). In many of these conditions, axonal and neuromuscular synapse dysfunction have been implicated as crucial pathological events, highlighting the need for in vitro disease models that accurately recapitulate these aspects of human neuromuscular physiology. The protocol reported here describes the co-culture of neural spheroids composed of human pluripotent stem cell (PSC)-derived motor neurons and astrocytes, and human PSC-derived myofibers in 3D compartmentalised microdevices to generate functional human neuromuscular circuits in vitro. In this microphysiological model, motor axons project from a central nervous system (CNS)-like compartment along microchannels to innervate skeletal myofibers plated in a separate muscle compartment. This mimics the spatial organization of neuromuscular circuits in vivo. Optogenetics, particle image velocimetry (PIV) analysis, and immunocytochemistry are used to control, record, and quantify functional neuromuscular transmission, axonal outgrowth, and neuromuscular synapse number and morphology. This approach has been applied to study disease-specific phenotypes for DMD and ALS by incorporating patient-derived and CRISPR-corrected human PSC-derived motor neurons and skeletal myogenic progenitors into the model, as well as testing candidate drugs for rescuing pathological phenotypes. The main advantages of this approach are: i) its simple design; ii) the in vivo-like anatomical separation between CNS and peripheral muscle; and iii) the amenability of the approach to high power imaging. This opens up the possibility for carrying out live axonal transport and synaptic imaging assays in future studies, in addition to the applications reported in this study. Graphical abstract Graphical abstract abbreviations: Channelrhodopsin-2 (CHR2+), pluripotent stem cell (PSC), motor neurons (MNs), myofibers (MFs), neuromuscular junction (NMJ)

Excitability in a nonlinear magnetoacoustic resonator

We report a nonlinear acoustic system displaying excitability. The considered system is a magnetostrictive material where acoustic waves are parametrically generated. For a set of parameters, the system presents homoclinic and heteroclinic dynamics, whose boundaries define a excitability domain. The excitable behaviour is characterized by analyzing the response of the system to different external stimuli. Single spiking and bursting regimes have been identified.Comment: 4 pages, 5 figure

Osteitis condensante de clavícula

La osteítis condensante de clavícula es una lesión ósea infrecuente, benigna y de etiología desconocida. Se caracteriza por esclerosis densa y homogénea de la porción infero-medial clavicular con obliteración de la cavidad medular sin afectación de la articulación esternoclavicular. Hasta ahora sólo se había descrito en mujeres, en el presente trabajo presentamos un caso en un paciente varón. Se discute el diagnóstico diferencial con otras entidades que producen afectación similar y proponemos la TC como método diagnóstico de elección, defendiendo el tratamiento conservador.Condensing osteitis of the clavicle is a benign and uncommon bone lesion of unknown cause, characterized by homogeneously dense sclerotic patch with obliteration of the marrow cavity at the medial end of the clavicle without involvement of the sternoclavicular joint. To date it had been described only in women. In this work we report a case in a male patient. The differential diagnosis with other disorders of similar findings is discussed. We propose CT-scan as the elective diagnostic test and we defend the conservative treatment

Strain-assisted optomechanical coupling of polariton condensate spin to a micromechanical resonator

We report spin and intensity coupling of an exciton-polariton condensate to the mechanical vibrations of a circular membrane microcavity. We optically drive the microcavity resonator at the lowest mechanical resonance frequency while creating an optically-trapped spin-polarized polariton condensate in different locations on the microcavity, and observe spin and intensity oscillations of the condensate at the vibration frequency of the resonator. Spin oscillations are induced by vibrational strain driving, whilst the modulation of the optical trap due to the displacement of the membrane causes intensity oscillations in the condensate emission. Our results demonstrate spin-phonon coupling in a macroscopically coherent condensate

Metadiffusers : deep-subwavelength sound diffusers

We present deep-subwavelength diffusing surfaces based on acoustic metamaterials, namely metadiffusers. These sound diffusers are rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators. Strong dispersion is produced in the slits and slow sound conditions are induced. Thus, the effective thickness of the panel is lengthened introducing its quarter wavelength resonance in the deep-subwavelength regime. By tuning the geometry of the metamaterial, the reflection coefficient of the panel can be tailored to obtain either a custom reflection phase, moderate or even perfect absorption. Using these concepts, we present ultra-thin diffusers where the geometry of the metadiffuser has been tuned to obtain surfaces with spatially dependent reflection coefficients having uniform magnitude Fourier transforms. Various designs are presented where, quadratic residue, primitive root and ternary sequence diffusers are mimicked by metadiffusers whose thickness are 1/46 to 1/20 times the design wavelength, i.e., between about a twentieth and a tenth of the thickness of traditional designs. Finally, a broadband metadiffuser panel of 3 cm thick was designed using optimization methods for frequencies ranging from 250 Hz to 2 kHz

Oxidation resistance of graphene-coated Cu and Cu/Ni alloy

The ability to protect refined metals from reactive environments is vital to many industrial and academic applications. Current solutions, however, typically introduce several negative effects, including increased thickness and changes in the metal physical properties. In this paper, we demonstrate for the first time the ability of graphene films grown by chemical vapor deposition to protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy from air oxidation. SEM, Raman spectroscopy, and XPS studies show that the metal surface is well protected from oxidation even after heating at 200 \degree C in air for up to 4 hours. Our work further shows that graphene provides effective resistance against hydrogen peroxide. This protection method offers significant advantages and can be used on any metal that catalyzes graphene growth

Asymmetric Dark Matter and Dark Radiation

Asymmetric Dark Matter (ADM) models invoke a particle-antiparticle asymmetry, similar to the one observed in the Baryon sector, to account for the Dark Matter (DM) abundance. Both asymmetries are usually generated by the same mechanism and generally related, thus predicting DM masses around 5 GeV in order to obtain the correct density. The main challenge for successful models is to ensure efficient annihilation of the thermally produced symmetric component of such a light DM candidate without violating constraints from collider or direct searches. A common way to overcome this involves a light mediator, into which DM can efficiently annihilate and which subsequently decays into Standard Model particles. Here we explore the scenario where the light mediator decays instead into lighter degrees of freedom in the dark sector that act as radiation in the early Universe. While this assumption makes indirect DM searches challenging, it leads to signals of extra radiation at BBN and CMB. Under certain conditions, precise measurements of the number of relativistic species, such as those expected from the Planck satellite, can provide information on the structure of the dark sector. We also discuss the constraints of the interactions between DM and Dark Radiation from their imprint in the matter power spectrum.Comment: 22 pages, 5 figures, to be published in JCAP, minor changes to match version to be publishe

On the Interplay between Data Overlay and Real-World Context using See-through Displays

The recent availability of affordable see-through wearable displays has fostered the development of several new interfaces and applications. Some of them take the augmented reality path, by seeking the blending of physical objects with overlaid 3D models or textual information. Some, on the other hand, are much simpler and follow a rather basic paradigm where the spatial integration between real world and data overlay is dropped. This is the case, for instance, with most applications based on Google Glass hardware, where textual data and images partially share the field of view of the user, but are not pinpointed to physical features. This is a rather important difference, since it marks the shift from a cooperative see-through mode, that characterizes proper augmented reality, to a competitive overlay, where the user attention is actually contended between real objects and displayed data. To this end, the user focus must continuously shift from one context to the other, possibly leading to both reduced productivity and usage strain. With this paper we are addressing exactly this issue. Specifically, we are assessing the role of different properties of the overlay, including the level of occlusion, the depth of the data layer, the position of the view frustum and the impact of stereo vision. Such study has been implemented by mean of a real-world evaluation which has been performed using a general purpose see-through device in a practical application scenario.The recent availability of affordable see-through wearable displays has fostered the development of several new interfaces and applications. Some of them take the augmented reality path, by seeking the blending of physical objects with overlaid 3D models or textual information. Some, on the other hand, are much simpler and follow a rather basic paradigm where the spatial integration between real world and data overlay is dropped. This is the case, for instance, with most applications based on Google Glass hardware, where textual data and images partially share the field of view of the user, but are not pinpointed to physical features. This is a rather important difference, since it marks the shift from a cooperative see-through mode, that characterizes proper augmented reality, to a competitive overlay, where the user attention is actually contended between real objects and displayed data. To this end, the user focus must continuously shift from one context to the other, possibly leading to both reduced productivity and usage strain. With this paper we are addressing exactly this issue. Specifically, we are assessing the role of different properties of the overlay, including the level of occlusion, the depth of the data layer, the position of the view frustum and the impact of stereo vision. Such study has been implemented by mean of a real-world evaluation which has been performed using a general purpose see-through device in a practical application scenario