Stéphane Régnier

3D Coronal magnetic field from vector magnetograms: non-constant-

The Active Region 8151 (AR 8151) observed in February 1998 is the site of an eruptive event associated with a fila- ment and a S-shaped structure, and producing a slow Coronal Mass Ejection (CME). In order to determine how the CME occurs, we compute the 3D coronal magnetic field and we derive some relevant parameters such as the free magnetic energy and the relative magnetic helicity. The 3D magnetic configuration is reconstructed from photospheric magnetic magnetograms (IVM, Mees Solar Observatory) in the case of a non-constant- force-free (nl) field model. The reconstruction method is divided into three main steps: the analysis of vector magnetograms (transverse fields, vertical density of electric current, ambiguity of 180), the numerical scheme for the nl magnetic field, the interpretation of the computed magnetic field with respect to the observations. For AR 8151, the nl field matches the coronal observations from EIT/SOHO and from SXT/Yohkoh. In particu- lar, three characteristic flux tubes are shown: a highly twisted flux tube, a long twisted flux tube and a quasi-potential flux tube. The maximum energy budget is estimated to 2:6 10 31 erg and the relative magnetic helicity to 4:7 10 34 G 2 cm 4 .F rom the simple photospheric magnetic distribution and the evidence of highly twisted flux tubes, we argue that the flux rope model is the most likely to describe the initiation mechanism of the eruptive event associated with AR 8151.

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During microscale object manipulation, contact (pull-off) forces and non-contact (capillary, van der Waals and electrostatic) forces determine the behaviour of the micro-objects rather than the inertial forces. The aim of this article is to give an experimental analysis of the physical phenomena at a microscopic scale in dry and liquid media. This article introduces a review of the major differences between dry and submerged micromanipulations. The theoretical influences of the medium on van der Waals forces, electrostatic forces, pull-off forces and hydrodynamic forces are presented. Experimental force measurements based on an AFM system are carried out. These experiments exhibit a correlation better than 40% between the theoretical forces and the measured forces (except for pull-off in water). Finally, some comparative experimental micromanipulation results are described and show the advantages of the liquid medium.

force-free configuration of the active region NOAA 8151

Describes a dynamical strategy for releasing micro objects picked-up by means of adhesion forces. While sticking effects are used in order to capture an object by adequately choosing a high surface energy constitutive material for the end-effector, these same effects handicap considerably the release. We propose to take advantage of the inertial effects of both the end-effector and the manipulated object to overbalance adhesion forces and to achieve the release. Simulations show that for this purpose, accelerations as high as 10/sup 5/ m/s/sup 2/ are needed. Successful manipulation of a 40 /spl mu/m radius glass sphere is experimented.

Analysis of forces for micromanipulations in dry and liquid media

Micromanipulation systems have recently been receiving increased attention. Teleoperated or automated micromanipulation is a challenging task due to the need for high-frequency position or force feedback to guarantee stability. In addition, the integration of sensors within micromanipulation platforms is complex. Vision is a commonly used solution for sensing; unfortunately, the update rate of the frame-based acquisition process of current available cameras cannot ensure-at reasonable costs-stable automated or teleoperated control at the microscale level, where low inertia produces highly unreachable dynamic phenomena. This paper presents a novel vision-based microrobotic system combining both an asynchronous address event representation silicon retina and a conventional frame-based camera. Unlike frame-based cameras, recent artificial retinas transmit their outputs as a continuous stream of asynchronous temporal events in a manner similar to the output cells of a biological retina, enabling high update rates. This paper introduces an event-based iterative closest point algorithm to track a microgrippers position at a frequency of 4 kHz. The temporal precision of the asynchronous silicon retina is used to provide a haptic feedback to assist users during manipulation tasks, whereas the frame-based camera is used to retrieve the position of the object that must be manipulated. This paper presents the results of an experiment on teleoperating a sphere of diameter around 50 μm using a piezoelectric gripper in a pick-and-place task.

Manipulation of micro-objects using adhesion forces and dynamical effects

In this paper, teleoperated 3-D microassembly of spherical objects with haptic feedback is presented. A dual-tip gripper controlled through a haptic interface is used to pick-and-place microspheres (diameter: 4-6 μm). The proposed approach to align the gripper with the spheres is based on a user-driven exploration of the object to be manipulated. The haptic feedback is based on amplitude measurements from cantilevers in dynamic mode. That is, the operator perceives the contact while freely exploring the manipulation area. The data recorded during this exploration are processed online and generate a virtual guide to pull the user to the optimum contact point, allowing correct positioning of the dual tips. A preliminary scan is not necessary to compute the haptic feedback, which increases the intuitiveness of our system. For the pick-and-place operation, two haptic feedback schemes are proposed to either provide users with information about microscale interactions occurring during the operation, or to assist them while performing the task. As experimental validation, a two-layer pyramid composed of four microspheres is built in ambient conditions.

Asynchronous Event-Based Visual Shape Tracking for Stable Haptic Feedback in Microrobotics

A micro manipulation platform consisting of two cubic centimeter sized micro robots each with four degrees of freedom has been developed. This paper discusses four different strategies of manipulation by adhesion for grasping, transferring and releasing a micro object. For each strategy, the interacting forces have been modeled and the results are compared with the real behavior of o 40 µm pollen micro spheres that are manipulated with the developed micro robots. Both theoretical model and experimental results show that the developed micro robots and the proposed strategies are well suited for the manipulation of the proposed micro objects.

Haptic Teleoperation for 3-D Microassembly of Spherical Objects

In this paper, three-dimensional (3D) automated micromanipulation at the scale of several micrometers using a nanotip gripper with multi-feedback is presented. The gripper is constructed from protrudent tips of two individually actuated atomic force microscope cantilevers; each cantilever is equipped with an optical lever. A manipulation protocol allows these two cantilevers to form a gripper to pick and place micro-objects without adhesive-force obstacles in air. For grasping, amplitude feedback from the dithering cantilever with its normal resonant frequency is used to search a grasping point by laterally scanning the side of the microspheres. Real-time force sensing is available for monitoring the whole pick-and-place process with pick-up, transport and release steps. For trajectory planning, an algorithm based on the shortest path solution is used to obtained 3D micropatterns with high levels of efficiency. In experiments, 20 microspheres with diameters from 3 µm to 4 µm were manipulated and 5 3D micropyramids with two layers were built. Three-dimensional micromanipulation and microassembly at the scale of several microns to the submicron scale could become feasible through the newly developed 3D micromanipulation system with a nanotip gripper.

Micro manipulation by adhesion with two collaborating mobile micro robots

Surface tension effects are dominant in miniaturization. Therefore, a lot of capillary forces models have been recently discussed in the literature. The work reported in this paper intends to prove the equivalence between two methods which are very widespread in capillary forces computation at equilibrium: the energetic method based on the derivation of the total interfacial energy and a second method summing both pressure and tension terms obtained from the meniscus profile (based on the Laplace equation). The results are supported by different qualitative arguments, an analytical proof in the case of a prism-plate configuration, numerical simulation, and experiments in the case of two millimetric spheres.

Three-dimensional automated micromanipulation using a nanotip gripper with multi-feedback

A conventional atomic force microscope (AFM) has been successfully applied to manipulating nanoparticles (zero-dimensional), nanowires (one-dimensional) or nanotubes (one- or two-dimensional) by widely used pushing or pulling operations on a single surface. However, pick-and-place nanomanipulation in air is still a challenge. In this research, a modified AFM, called a three-dimensional (3D) manipulation force microscope (3DMFM), was developed to realize 3D nanomanipulation in air. This system consists of two individually actuated cantilevers with protruding tips that are facing each other, constructing a nanotweezer for the pick-and-place nanomanipulation. Before manipulation, one of the cantilevers is employed to position nano-objects and locate the tip of the other cantilever by image scanning. During the manipulation, these two cantilevers work collaboratively as a nanotweezer to grasp, transport and place the nano-objects with real-time force sensing. The manipulation capabilities of the nanotweezer were demonstrated by grabbing and manipulating silicon nanowires to build 3D nanowire crosses. 3D nanomanipulation and nanoassembly performed in air could become feasible through this newly developed 3DMFM.

Comparison between Two Capillary Forces Models

A flexible robotic system (FRS) developed for multiscale manipulation and assembly from nanoscale to microscale is presented. This system is based on the principle of atomic force microscopy and comprises two individually functionalized cantilevers. After reconfiguration, the robotic system could be used for pick-and-place manipulation from nanoscale to the scale of several micrometers, as well as parallel imaging/nanomanipulation. Flexibilities and manipulation capabilities of the developed system were validated by pick-and-place manipulation of microspheres and silicon nanowires to build 3-D micro/nanoscale structures in ambient conditions. Moreover, the capability of parallel nanomanipulation is certified by high-efficiency fabrication of a 2-D pattern with nanoparticles. Complicated micro/nanoscale manipulation and assembly can be reliably and efficiently performed using the proposed FRS.