Phase variance reduction of high order Stokes lines in Brillouin fiber lasers

International audienceSummary form only given. Brillouin fiber ring lasers have already been extensively studied and results have shown that the generated first order Stokes wave has less intensity and phase noise than the seeded pump. This increase in coherence is attractive for many sensing applications, whether in the field of fiber sensors or remote sensing systems such as LIDAR. Brillouin fiber lasers with several Stokes components can further increase the coherence through a cascading effect, the 1st Stokes component being the pump for the 2nd Stokes order and so on. In this communication, we investigate the noise properties of a multi-Stokes Brillouin fiber laser. We present numerical simulations from a model that is an extension of the usual three-waves model of stimulated Brillouin scattering in agreement with experimental results

Spatial Updating Depends on Gravity

As we move through an environment the positions of surrounding objects relative to our body constantly change. Maintaining orientation requires spatial updating, the continuous monitoring of self-motion cues to update external locations. This ability critically depends on the integration of visual, proprioceptive, kinesthetic, and vestibular information. During weightlessness gravity no longer acts as an essential reference, creating a discrepancy between vestibular, visual and sensorimotor signals. Here, we explore the effects of repeated bouts of microgravity and hypergravity on spatial updating performance during parabolic flight. Ten healthy participants (four women, six men) took part in a parabolic flight campaign that comprised a total of 31 parabolas. Each parabola created about 20-25 s of 0 g, preceded and followed by about 20 s of hypergravity (1.8 g). Participants performed a visual-spatial updating task in seated position during 15 parabolas. The task included two updating conditions simulating virtual forward movements of different lengths (short and long), and a static condition with no movement that served as a control condition. Two trials were performed during each phase of the parabola, i.e., at 1 g before the start of the parabola, at 1.8 g during the acceleration phase of the parabola, and during 0 g. Our data demonstrate that 0 g and 1.8 g impaired pointing performance for long updating trials as indicated by increased variability of pointing errors compared to 1 g. In contrast, we found no support for any changes for short updating and static conditions, suggesting that a certain degree of task complexity is required to affect pointing errors. These findings are important for operational requirements during spaceflight because spatial updating is pivotal for navigation when vision is poor or unreliable and objects go out of sight, for example during extravehicular activities in space or the exploration of unfamiliar environments. Future studies should compare the effects on spatial updating during seated and free-floating conditions, and determine at which g-threshold decrements in spatial updating performance emerge

Ultrasound assessments of organs and blood vessels before and after 40 days isolation in a cavern (deep time experiment 2021)

Introduction: Spaceflight simulation studies like confinement in small volume habitat with limited physical activity have reported even after 60 days an abnormal arterial wall adaptation with increase thickness or stiffness. The purpose of the current study was to determine the effects on blood vessel and organ structure of 40 days of isolation in a huge habitat with intensive physical activity.Method: Data were collected from 14 individuals (7 male) who isolated in a cavern for 40-days while performing normal daily activities without time references. Ultrasound assessments were performed pre- and post-isolation using a teleoperated system with eight different acoustic windows to obtain 19 measurements on 12 different organ/vascular structures which included the common carotid artery, femoral artery, tibial artery, jugular vein, portal vein, bile duct, kidney, pancreas, abdominal aorta, cervical and lumbar vertebral distance, and Achilles tendon.Results: Common carotid artery measures, including the intima media thickness, stiffness index, and the index of reflectivity measured from the radiofrequency signal, were not changed with isolation. Similarly, no differences were found for femoral artery measurements or measurements of any of the other organs/vessels assessed. There were no sex differences for any of the assessments.Discussion: Results from this study indicate a lack of physiological effects of 40-days of isolation in a cavern, contrary to what observed in previous 60 days confinement. This suggests a potential protective effect of sustained physical activity, or reduced environmental stress inside the huge volume of the confined facility

Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients

Although somatic mutations in Histone 3.3 (H3.3) are well-studied drivers of oncogenesis, the role of germline mutations remains unreported. We analyze 46 patients bearing de novo germline mutations in histone 3 family 3A (H3F3A) or H3F3B with progressive neurologic dysfunction and congenital anomalies without malignancies. Molecular modeling of all 37 variants demonstrated clear disruptions in interactions with DNA, other histones, and histone chaperone proteins. Patient histone posttranslational modifications (PTMs) analysis revealed notably aberrant local PTM patterns distinct from the somatic lysine mutations that cause global PTM dysregulation. RNA sequencing on patient cells demonstrated up-regulated gene expression related to mitosis and cell division, and cellular assays confirmed an increased proliferative capacity. A zebrafish model showed craniofacial anomalies and a defect in Foxd3-derived glia. These data suggest that the mechanism of germline mutations are distinct from cancer-associated somatic histone mutations but may converge on control of cell proliferation

Performance and application of the Modular Acoustic Velocity Sensor (M.A.V.S.) current meter for laboratory measurements

Every type of current meter is different and has its proper characteristics. Knowing the performance of a current meter is essential in order to use it properly either for field or laboratory measurements (such as in the Offshore Technology Research Center wave basin). A study of the MAVS (Modular Acoustic Velocity Sensor) in a wave basin is a first step essential for later deployment in real studies. This thesis is based on data obtained from different series of laboratory measurements conducted in the OTRC wave basin. The objective of the first part of the study was to characterize the MAVS frequency response using benchmarks such as tow tests or wave tests. These benchmarks allowed us not only to characterize the sensor but also to eventually correct some of the measurement distortions due to flow blockage, vortex shedding, or vibrations of the mounting structure, for example. After the preliminary study was done, we focused on the potential use of the MAVS in the OTRC wave basin. Indeed, in the case of a study of a scale model in the wave basin, the stresses applied to the model have to be accurately known. In the case of current-induced loads, this includes contributions from both the mean flow and the turbulence. Thus, after correcting the values measured by the MAVS, a mapping of the current jet was executed to determine its three-dimensional structure in the wave basin. Knowing the structure of the current in the OTRC wave basin, it was then possible to define a domain in which the current can be considered uniform with a certain tolerable error. This domain of uniformity will allow us to validate the use of the OTRC wave basin to study large models such as FPSOs (Floating Production, Storage and Offloading Units)

Caractérisation du gain Brillouin par spectroscopie en cavité résonante sondée par un signal à dérive de fréquence

National audienceNous montrons qu'un simple sondage d'une cavité résonante par un signal optique à dérive de fréquence (« Cavity Ring-Down Method ») permet d'extraire, à la fois, ses paramètres de couplage et de pertes, et de gain Brillouin du matériau la constituant. Ces mesures de gain sont en accord avec celles référencées dans la littérature

Intracavity Brillouin gain characterization based on cavity ringdown spectroscopy

International audienceWe report a technique based upon the cavity ringdown method that enables to characterize the Brillouin gain coefficient directly in a laser cavity. Material gain, optical cavity parameters and lasing properties can be extracted from measurements whithin a single experiment

Study of the influence of the pressure and rotational motion of 3D substrates processed by magnetron sputtering:A comparative study between Monte Carlo modelling and experiments

Over the last ten years, low pressure plasma solutions for materials surface treatment have been remarkable. Nevertheless, the deposition of films with a uniform thickness on 3D complex shapes is still a challenge for various deposition systems. In several cases, concavities and different substrate orientations and motions lead to macroscopic shadowing and affect the thickness uniformity. The objective of this work is to describe a modelling method able to predict the layer thickness on any surface of 3D substrates in motion and subject to vapour transported in a low pressure vessel. The meshing of objects with Delaunay-triangulation enables the modelling of complex shapes. The deposition process consists of several Monte Carlo simulations involving first the computing of the angular and energy particles distribution from the source, second their transport through the chamber and last the deposition on a meshed substrate. The algorithm is optimised with a “cell-list-linked-like” method and differs from existing models by the computation speed. The benchmarking between simulation and experimental results for Cr, Ag and Ta deposition at various pressures and on moving complex substrates with several shadowed faces is presented. Moreover, particle energy distribution will be discussed for each sample surface, mode and pressure.The authors M. Evrard and S. Lucas gratefully acknowledge the financial support of the Walloon region under the FEDER and 3DCOATER-5: Convention N° 1610258, project 3215. The author A. Besnard also thanks the “Région Bourgogne Franche-Comté” for the concession of the grant (Rech-Mobi-000026)

On the use of imaging and kinematic field measurements for the study of the dynamic behavior of materials

International audienc