Vibration, Control and Stability of Dynamical Systems

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”

LAGEOS geodetic analysis-SL7.1

Laser ranging measurements to the LAGEOS satellite from 1976 through 1989 are related via geodetic and orbital theories to a variety of geodetic and geodynamic parameters. The SL7.1 analyses are explained of this data set including the estimation process for geodetic parameters such as Earth's gravitational constant (GM), those describing the Earth's elasticity properties (Love numbers), and the temporally varying geodetic parameters such as Earth's orientation (polar motion and Delta UT1) and tracking site horizontal tectonic motions. Descriptions of the reference systems, tectonic models, and adopted geodetic constants are provided; these are the framework within which the SL7.1 solution takes place. Estimates of temporal variations in non-conservative force parameters are included in these SL7.1 analyses as well as parameters describing the orbital states at monthly epochs. This information is useful in further refining models used to describe close-Earth satellite behavior. Estimates of intersite motions and individual tracking site motions computed through the network adjustment scheme are given. Tabulations of tracking site eccentricities, data summaries, estimated monthly orbital and force model parameters, polar motion, Earth rotation, and tracking station coordinate results are also provided

Bacteria in shear flow

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 68-74).Bacteria are ubiquitous and play a critical role in many contexts. Their environment is nearly always dynamic due to the prevalence of fluid flow: creeping flow in soil, highly sheared flow in bodily conduits, and turbulent flow in rivers, streams, lakes, and oceans, as well as anthropogenic habitats such as bioreactors, heat exchangers and water supply systems. The presence of flow not only affects how bacteria are transported and dispersed at the macroscale, but also their ability to interact with their local habitat through motility and chemotaxis (the ability to sense and follow chemical gradients), in particular their foraging. Despite the ubiquitous interaction between motility, foraging and flow, almost all studies of bacterial motility have been confined to still fluids. At the small scales of a bacterium, any natural flow field (e.g. turbulence) is experienced as a linear velocity profile, or 'simple shear'. Therefore, understanding the interaction between a simple shear flow and motility is a critical step towards gaining insight on how the ambient flow favors or hinders microorganisms in their quest for food. In this thesis, I address this important gap by studying the effect of shear on bacteria, using a combination of microfluidic experiments and mathematical modeling. In chapter 2, a method is presented to create microscale vortices using a microfluidic setup specifically designed to investigate the response of swimming microorganisms. Stable, small-scale vortices were generated in the side-cavity of a microchannel by the shear stress in the main flow. The generation of a vortex was found to depend on the cavity's geometry, in particular its depth, aspect ratio, and opening width. Using video-microscopy, the position and orientation of individual microorganisms swimming in vortices of various intensities were tracked. We applied this setup to the marine bacterium Pseudoalteromonas haloplanktis. Under weak flows (shear rates < 0.1 s 1), P. haloplanktis exhibited a random swimming pattern. As the shear rate increased, P. haloplanktis became more aligned with the flow. In order to study the detailed hydrodynamic interaction between shear and bacteria, we developed a mathematical model employing resistive force theory. In general, the modeling of a bacterium requires consideration of two factors: the rotating flagellar bundle and the cell body to which the flagella are attached. To make the problem analytically tractable, we study the hydrodynamics around the head and the flagellum separately. In chapter 3, we present a combined theoretical and experimental investigation of the fluid mechanics of a helix exposed to a shear flow. In addition to classic Jeffery orbits, resistive force theory predicts a drift of the helix across streamlines, perpendicular to the shear plane. The direction of the drift is determined by the direction of the shear and the chirality of the helix. We verify this prediction experimentally using microfluidics, by exposing Leptospira biflexa flaB mutant, a non-motile strain of helix-shaped bacteria, to a plane parabolic flow. As the shear in the top and bottom halves of the microchannel has opposite sign, we predict and observe the bacteria in these two regions to drift in opposite directions. The magnitude of the drift is in good quantitative agreement with theory. We show that this setup can be used to separate microscale chiral objects. In chapter 4, a theoretical and experimental investigation of a swimming bacterium in a shear flow is presented. The presence of the cell body results in a novel phenomenon: chiral forces induce not only a lateral drift, but also a reorienting torque on swimming bacteria. For typical flagellated bacteria, the magnitude of this drift velocity is much smaller (-0.7 gm s-1) than typical swimming speeds of bacteria (-50 [mu]m s-1). However, with the addition of a head, the chirality-dependent forces that lead to a lateral drift also lead to a reorienting torque. The model based on resistive force theory predicts that the drift velocity of swimming bacteria is in the same order of magnitude as the swimming speed. Experimental observations of the motile bacteria Bacillus subtilis exposed to shear flows show good agreement with the theoretical prediction. This process is a purely passive hydrodynamic effect, as demonstrated by further experiments showing that bacteria do not behaviorally (i.e. actively) respond to shear. This newly discovered hydrodynamic reorientation can significantly affect any process that involves changes of swimming direction, so that bacterial 'steering' in a flow cannot be understood unless the effects of chiral reorientation are quantified. Because swimming and reorientation are central to the chemotaxis used by many bacteria for foraging, we expect this coupling of motility and flow to play an important role in the ecology of many bacterial species.by Marcos.Ph.D

Stellar Systems at Low Radio Frequencies:The Discovery of Radio Exoplanets

For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf — the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star, and our follow-up radial-velocity (RV) observations with Harps-N to confirm the exoplanet's presence. Our study highlights the powerful new and developing synergy between low-frequency radio astronomy and RV observations, with radio emission providing a strong prior on the presence of a short-period planet. I will conclude the talk detailing how the radio detection of an star-exoplanet interaction provides unique information for exoplanet climate and habitability studies, and the extension of our survey to other stellar systems

On the hunt for Trappist-1 siblings

The TRAPPIST-South 60cm telescope at La Silla (ESO) is famously known for its detection of the extraordinary TRAPPIST-1 planetary system. A discovery made during the prototype phase of our ultra-cool dwarf transit survey SPECULOOS (Search for Planets EClipsing ULtra-cOOl Stars). This talk will first report on the self-consistence transit occurrence analysis of all observations of 42 bright ultra-cool dwarfs made with TRAPPIST-South during a period ranging from 2011 to 2017. On the basis that, with the exception of the discovery of TRAPPIST-1 planets, we didn't detect any other significant transiting event, we concluded on a 10% lower limit for the occurrence of planets similar to TRAPPIST-1b in this sample. The outcome is very sensitive to the size and period of the planet considered. A comprehensive statistic will be presented. Finally, performance obtained with our recently commissioned SPECULOOS Southern facility installed at Paranal will be presented. The lower occurrence limit measured with TRAPPIST survey will be compared with early results from 6 months of continue SPECULOOS core survey operations <P /