Zebrafish embryos have been of particular interest in developmental biology research in recent years. Among the properties of zebrafish eggs that need to be characterized, stiffness is a key feature. It is a good indicator of the developmental stage of the egg and embryo. A highly localized stiffness measurement and/or the related Young's modulus requires a force sensor with a tip radius as small as that of an atomic force microscope (AFM). However, the length of an AFM probe tip is often less than a hundred micrometers, whereas zebrafish eggs are about 0.7 mm in diameter. This makes it impossible to penetrate deep into the egg to mechanically characterise the outer membrane, the inner medium and the embryo. This paper presents the proof of concept of the efficiency of quartz tuning forks with tungsten probes of several millimeters long and tip radius of a few tens of nanometers to mechanically characterize zebrafish eggs. The work includes robotics, modelling and control developments as well as experiments on zebrafish eggs. It demonstrates that tungsten probes with tuning fork technology offer sufficient resolution to mechanically differentiate zebrafish eggs at different stages of development, as well as sufficient rigidity and strength to penetrate a zebrafish egg, which was not previously known or evaluated in the state of the art.

In this study, we present a semi-automated microrobotic platform based on a tuning fork for the characterization of the stiffness of soft polydimethylsiloxane (PDMS) samples involving very low-amplitude and highly localized interaction forces. Stiffness characterization is based on the measurement of the shift Delta(f) in the resonance frequency of the tuning fork. A control strategy is proposed and implemented to ensure safe landing and indentation of the tuning fork probe on the sample. A model describing Delta(f) as a function of PDMS stiffness and indentation depth is proposed. The results demonstrate the relevance of tungsten-tipped tuning forks controlled in permanent contact mode to distinguish PDMS samples of different rigidities through frequency shift and indentation depth measurements. Copyright (c) 2025 The Authors. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)

The classification of solar prominences has proven to be challenging, due to their diverse morphologies and dynamical behavior. Complexity is heightened when considering eruptive prominences, where the dynamics demand methods capable of capturing detailed structural information. While there exist a range of line-of-sight and plane-of-sky (POS) techniques that have advanced our understanding of prominence motions, they are subject to limitations, emphasizing the need for effective methods of extracting structural information from prominence dynamics. We present a proof of concept for the spatial Rolling Hough Transform (RHT) algorithm, which identifies fine-scale structural orientation in the POS, applied to prominence structure and dynamics. We demonstrate the RHT approach using two contrasting prominence dynamics events using Solar Dynamics Observatory/Atmospheric Imaging Assembly 304 Å observations: (1) a quiet-Sun eruption, and (2) activation (swirl) of a polar crown prominence. By analyzing the light curves and movies from each event, we divide the events into distinct dynamical phases: from slow rise to drainage. The spatial RHT method enables us to extract structural information and localized dynamics for both events and the different evolution phases. We develop a classification to label the prominences as either radially or tangentially oriented structures. The quiet-Sun eruption has a predominately tangential structure in the slow-rise phase but displays greater radial features during/after the eruption. The polar swirl activation initially shows a strong radial contribution, which diminishes as more tangential structures appear during/after the activation. Our results demonstrate the successful application of the spatial RHT to prominences, leading to the classification of individual prominences and an insight into their dynamics.

The solar minima between solar cycles 22–23, 23–24, and 24–25 are the best observed minima on record. In situ solar wind and interplanetary magnetic field measurements by the Wind and ACE spacecraft at L1 with 1 hr cadence are explored using wavelet analyses for the most quiescent year during each minimum. Times of local peaks in periodicities are identified in the solar wind velocity, magnetic field components, and proton number densities. The measured radial velocities at these times are used to trace magnetic field lines to the photosphere using two models. The first is the Fisk heliospheric magnetic field that traces field lines from L1 to the photosphere. They connect exclusively to solar poles and in 88% of instances to locations of polar coronal holes (PCHs). The second model uses the Parker spiral to trace from L1 to the solar source surface and potential-field extrapolations from the source surface to the photosphere. These field lines terminate at equatorial and midlatitude coordinates, of which some are located close to coronal holes (CHs). This study connects for the first time CH signatures in the ecliptic plane at L1 with PCHs using the Fisk field. It shows how sources from both the solar equator and poles influence the solar wind at L1 and how the two models complement each other to identify these sources.

Path following control of micrometer-sized tools is the key to improve automation capabilities at the small scales. This paper addresses the issue of path following control for piezoelectric inertia actuated nano-robotic systems operating inside electron microscopes. The aim is to control the trajectory of an end effector driven by a stick and slip principle using both electron microscope images and velocity measurements from optical encoders. The path following control is divided into two layers. The high level layer considers a Frenet frame kinematic model to compute velocity references along two orthogonal axes. The low level layer is based on an average closed loop velocity control of the nano-robotic system along the two orthogonal axes. The path following performances are evaluated and analyzed experimentally using an inertia nano-robotic system operating inside a Scanning Electron Microscope and holding an Atomic Force Microscope (AFM) cantilever. Experimental results show the effectiveness of the AFM cantilever for various paths following with a mean tracking error less than 2 mu m in the worst case. These tracking capabilities are of importance toward automated manipulation and assembly sequences inside electron microscopes.

This letter presents a method to determine and control the center of rotation of a parallel micro-robotic platform used as a sample holder for an Atomic Force Microscope (AFM). The AFM is operating inside a Scanning Electron Microscope (SEM) for correlative AFM in SEM imaging. The objective is to spatially co-localize the Pivot Point (PP) and the AFM tip at any region of interest of a sample within the reachable workspace of the AFM. To do so, SEM images are used to land the AFM tip on a desired Point Of Interest (POI). Topographic data obtained with the AFM are used to calculate the Tool Center Point (TCP) of the robot and to identify the coordinates of the POI in the AFM sample holder reference frame. The position of the PP is then controlled relying on the TCP and SEM vision to finally been able to perform, in a controlled way, in-plane rotations of the sample holder around the AFM tip with a micrometer precision. This work shows for the first time how SEM and AFM data can be used in tandem to calibrate the rotational degrees of freedom of an AFM system.

Since the launch of the Solar Dynamics Observatory (SDO) in 2010 and throughout the solar cycle 24, the Sun has produced few tens of X-class flares, which are the most energetic solar events. Those flares are produced in regions where the magnetic flux/energy is large and the magnetic configurations are complex. To provide more insights into the flaring process, we investigate the properties of magnetic null points (MNPs) and their correlation with the energy release sites. During solar cycle 24, we identify 17 X-class flares satisfying selection criteria. From SDO/HMI magnetograms, we perform potential extrapolations around the peak time of the flare to access the 3D coronal magnetic field and thus investigate the existence of coronal MNPs. We then correlate the flaring sites with the existing MNPs using SDO/AIA 171 Å EUV observations, and deduce their properties (sign, spine, fan). Six active regions out of 10 possess at least one MNP which is stable and with large magnetic field gradients: this implies that 35% of X-class flares are associated with a MNP; of which 87.5% of MNPs are of positive type. The MNPs associated with the flare sites are predominantly located at a height between 0.5 and 2 Mm, and with a vertical/radial spine field line. We also find a slight correlation between the MNPs not associated with a flare and negative-type MNPs (55%) within the active region. Regarding the physics of flares, the association between the enhanced intensity at the flaring site and a MNP represents about a third of the possible scenarios for triggering X-class flares.

This paper presents a functionality that has been developed for the home-made AFM-in-SEM robotic system at the ISIR laboratory. The method allows extending the range of an Atomic Force Microscope (AFM) and dealing with drift issues by fusing multiple individually AFM topography patches. The merging of the patches into a single image is done through a Generalized Procrustes Analysis Iterative Closest Point (GPA-ICP) algorithm. To validate the effectiveness of the approach, an AFM image of a TGX1 calibration grid and a 3.4- billion-year-old organic-walled microfossil are reconstructed by automatically merging 50 AFM elementary topography patches of dimension 0.9 μm × 1.2 μm based on feature matching. The overlap between two adjacent patches is 50 % and 33 % in the X and Y axes respectively. The result is a coherent 3.2 μm × 3.0 μm drift-free long range AFM topography without significant artifacts. The method is tested using an AFM-in- SEM system based on a 3-DOF cartesian robot equipped with inertial piezoelectric actuators. This method can be used to extend the range of any type of AFM with a dual XY stage setup. Thus, it opens the door for high-resolution long-range AFM by adding a long-range coarse resolution stage to a preexisting AFM system all without needing to actuate both stages simultaneously.

Oscillatory reconnection is a relaxation process in magnetized plasma, with an inherent periodicity that is exclusively dependent on the properties of the background plasma. This study focuses on the seismological prospects of oscillatory reconnection in the solar corona. We perform three sets of parameter studies (for characteristic coronal values of the background magnetic field, density, and temperature) using the PLUTO code to solve the fully compressive, resistive MHD equations for a 2D magnetic X-point. From each parameter study, we derive the period of the oscillatory reconnection. We find that this period is inversely proportional to the characteristic strength of the background magnetic field and the square root of the initial plasma temperature, while following a square root dependency upon the equilibrium plasma density. These results reveal an inverse proportionality between the magnitude of the Alfvén speed and the period, as well as the background speed of sound and the period. Furthermore, we note that the addition of anisotropic thermal conduction only leads to a small increase in the mean value for the period. Finally, we establish an empirical formula that gives the value for the period in relation to the background magnetic field, density, and temperature. This gives us a quantified relation for oscillatory reconnection, to be used as a plasma diagnostic in the solar corona, opening up the possibility of using oscillatory reconnection for coronal seismology.

An emerging actuation technique in piezo driven nanopositioners is differential actuation, where each axis has two opposing actuators that operate differentially and provide bilateral motion. It has simultaneous benefits of improving linearity and range of displacement. However, few methods for displacement sensing employing in-situ transducers have been considered for this kind of nanopositioners. We address a novel application of PZT piezoelectric chips for direct displacement sensing in differentially driven nanopositioners. First, an electromechanical force analysis is performed in order to increase the PZT sensor sensitivity through the structural design of the nanopositioner. Secondly, the sensing performances of the proposed in-situ PZT sensor are compared with those from an alternative built-in piezoresistive (PZR) strain gauge sensor under equal circumstances, in different sensing and actuation configurations. While the PZR sensor has a larger sensing bandwidth than the PZT one and performs better if the actuation frequency is smaller than 30 Hz, the PZT sensors provides better accuracy when the actuation is well within its sensing bandwidth. The accuracy of the differential sensors and the input-displacement linearity are improved when the mechanical preload force magnitudes on the opposing actuators are balanced. The differential PZT sensor can provide accurate measurements even in a non-differential mode after recalibration.

Oscillatory reconnection can manifest through the interaction between the ubiquitous MHD waves and omnipresent null points in the solar atmosphere and is characterized by an inherent periodicity. In the current study, we focus on the relationship between the period of oscillatory reconnection and the strength of the wave pulse initially perturbing the null point, in a hot coronal plasma. We use the PLUTO code to solve the fully compressive, resistive MHD equations for a 2D magnetic X-point. Using wave pulses with a wide range of amplitudes, we perform a parameter study to obtain values for the period, considering the presence and absence of anisotropic thermal conduction separately. In both cases, we find that the resulting period is independent of the strength of the initial perturbation. The addition of anisotropic thermal conduction only leads to an increase in the mean value for the period, in agreement with our previous study. We also consider a different type of initial driver and we obtain an oscillation period matching the independent trend previously mentioned. Thus, we report for the first time on the independence between the type and strength of the initializing wave pulse and the resulting period of oscillatory reconnection in a hot coronal plasma. This makes oscillatory reconnection a promising mechanism to be used within the context of coronal seismology.

Oscillatory reconnection (a relaxation mechanism with periodic changes in connectivity) has been proposed as a potential physical mechanism underpinning several periodic phenomena in the solar atmosphere, including, but not limited to, quasi-periodic pulsations (QPPs). Despite its importance, however, the mechanism has never been studied within a hot, coronal plasma. We investigate oscillatory reconnection in a one million Kelvin plasma by solving the fully-compressive, resistive MHD equations for a 2D magnetic X-point under coronal conditions using the PLUTO code. We report on the resulting oscillatory reconnection including its periodicity and decay rate. We observe a more complicated oscillating profile for the current density compared to that found for a cold plasma, due to mode-conversion at the equipartition layer. We also consider, for the first time, the effect of adding anisotropic thermal conduction to the oscillatory reconnection mechanism, and we find this simplifies the spectrum of the oscillation profile and increases the decay rate. Crucially, the addition of thermal conduction does not prevent the oscillatory reconnection mechanism from manifesting. Finally, we reveal a relationship between the equilibrium magnetic field strength, decay rate, and period of oscillatory reconnection, which opens the tantalising possibility of utilizing oscillatory reconnection as a seismological tool.

This paper presents the first experimental implementation of a XY differential piezo-driven stage in closed loop for tracking reference signals at the kHz with nanometer resolution by an exclusive use of piezoelectric sensors. The sensors are arranged differentially and in series with piezoelectric actuators. The control scheme consists of an internal loop with an analog damping controller and an external digital loop with an Internal Model Control (IMC) tracking controller. The damping controller is designed to attenuate the lightly damped resonances of the system. The tracking controller is especially designed for tracking only single tone sinusoidal reference trajectories. This particularity allows the use of piezoelectric transducers in a narrow frequency band and thus does not require a low frequency correction or the use of additional sensors to compensate for the high pass response of the transducers. The experimental results show that the nano-positioning stage is able to track a sinusoidal trajectory of 1 kHz frequency and 1.25 µm amplitude with a maximum tracking error of 4 nm. These results have never been demonstrated previously with differential piezo-driven stages and open perspectives towards high speed Atomic Force Microscopy (AFM) at the nanoscale using differential actuation and piezoelectric sensing.

Traditional Atomic Force Microscopes (AFM) allow a short range displacement of the AFM probe, on the order of several tens of micrometers. When used inside an Electron Microscope (EM), the probe must be able to move on a millimeter scale with nanometer resolution. This is essential for the probe to reach any region of interest on a sample observed by an EM. In this paper, we address a challenging issue related to semi-automated long-range landing of an AFM probe on a sample. The probe is mounted on a piezoelectric inertial actuator. It is initially several millimeters away from the sample and must be safely landed to a distance on the order of hundred of nanometers (intermittent contact region). The control strategy is divided into three steps: (i) long-range velocity control using a stepping control, (ii) short and fine position control using a mixed stepping/scanning control, and (iii) position/force control using a scanning control. While traditional manual landing methods take a tremendous amount of time to complete the procedure, the proposed semi-automated method enables a safe long-range landing in less than 3 minutes. More generally, this is the first experimental demonstration in the literature of such a capability in AFM.

This article proposes a method for the correction of angular deviations caused during the fixing process of samples prepared for Atomic Force Microscopy (AFM). The correction is done using the angular control of a 6-DOF PPPS parallel platform were the sample is placed, while the AFM scan is performed by a 3-DOF serial cartesian robot with a tuning fork probe designed to perform FM-AFM. The method uses the generic x, y, and z data provided by the AFM after performing a scan on a free surface of the sample substrate. This is used to calculate the plane that closest approximates the points by solving a system of linear equations. This plane is then used to estimate the angular corrections that the 6-DOF parallel robot has to do in order to compensate the deviations. The proposed algorithm can be performed iteratively in order to refine the correction. The method also does not require any special preparation of the substrate. It only requires to have a free surface to scan. Experiments are performed using this algorithm to correct the orientation deviation of a substrate of V1 High-grade mica. The results show that the method is able to correct the angular deviation of the sample relatively to the AFM probe with an error of 0.2° after only two iterations of the algorithm.

Actuators with low inertia and high bandwidth are of great interest for haptic devices, as they improve the quality of force rendering and transparency. This paper describes, as a proof of concept, a new design in rotary induction motors, the Axial-DSIM (Axial Double-Sided Induction Motor). This motor has a simple design construction that consists of a thin and lightweight disc-shaped moving secondary (rotor) surrounded by fixed primaries on both sides that generate a rotating magnetic field that induces a force on the disc. The low inertia of this motor and its principle of operation make it possible to render high-fidelity torques with high dynamics.

The Atomic Force Microscope (AFM) is a reliable tool for 3D imaging and manipulation at the micrometer and nanometer scales. When used inside a Scanning Electron Microscope (SEM), AFM probes can be localized and controlled with a nanometer resolution by visual feedback. However, achieving trajectory control and obstacles avoidance is still a major concern for manipulation tasks. We propose a Model Predictive Control (MPC) to address these two issues while AFM probes are actuated by Piezoelectric Inertia type Actuators (PIA). The novelty of this letter is that the model of our MPC-based approach relies on a velocity map of PIAs. It enables path following and obstacle avoidance while preserving safety margins. Control inputs are optimized by Quadratic Programming, referring to their increment and distance constraints. A cost function is defined to navigate the AFM probe with a specified velocity. Simulations and experiments are carried out to demonstrate that the proposed algorithm is suitable to perform path following with obstacle avoidance using map-based velocity references. This is the first time that MPC is implemented in micro/nano-robotic systems for autonomous control inside SEM.

The spherical joint is an effective solution to design parallel micro-robotic systems with rotation capabilities in the three-dimensional space. This type of joint has however some non-linear characteristics, such as the clearance, which affect the positioning accuracy in micro-robotic tasks. The starting point of this study lies in experimental observations of rotation errors from a 3-PPPS 6-DOF parallel micro-robotic systems operating inside a scanning electron microscope. The objective of the paper is to assess the role of the spherical joints in the rotation errors and to evaluate whether the joints non-linearities can cause errors with the same order of magnitude as those observed experimentally. To this end, the first part of the study addresses the modeling of 3-PPPS 6-DOF parallel micro-robotic systems with spherical joints including the clearance. This model allows for analysing the effect of the clearance on position and rotation accuracies of the micro-robotic system. It is found by simulations that the same positioning behavior as in the experiments occurs when the clearance of the spherical joint is included in the model, supporting the hypothesis. Therefore, it is concluded that clearance in spherical joints has a significant effect on the precision of parallel type micro-robotic systems which opens new challenges in the control of poly-articulated micro-robotic systems with clearance compensation.