2006 Fragmentation of Comet 73P/Schwassmann-Wachmann 3B Observed with Subaru/Suprime-Cam

We analyzed the Subaru/Suprime-Cam images of 73P/Schwassmann-Wachmann 3B and detected no fewer than 154 mini-comets. We applied synchrone-syndyne analysis, modified for rocket effect analysis, to the mini-fragment spatial distribution. We found that most of these mini-comets were ejected from fragment B by an outburst occurring around 1 April 2006. The ratio of the rocket force to solar gravity was 7 to 23 times larger than that exerted on fragment B. No significant color variation was found. We examined the surface brightness profiles of all detected fragments and estimated the sizes of 154 fragments. We found that the radius of these mini-fragments was in the 5- to 108-m range (equivalent size of Tunguska impactor). The power-law index of the differential size distribution was q = -3.34 +/- 0.05. Based on this size distribution, we found that about 1-10% of the mass of fragment B was lost in the April 2006 outbursts. Modeling the cometary fragment dynamics revealed that it is likely that mini-fragments smaller than ~10-20 m could be depleted in water ice and become inactive, implying that decameter-sized comet fragments could survive against melting and remain as near-Earth objects. We attempted to detect the dust trail, which was clearly found in infrared wavelengths by Spitzer. No brightness enhancement brighter than 30.0 mag arcsec^-2 (3sigma) was detected in the orbit of fragment B.Comment: Total pages: 46 Figures: 12 Tables: 1 To appear ICARU

Sand and Dust on Mars

Mars is a planet of high scientific interest. Various studies are currently being made that involve vehicles that have landed on Mars. Because Mars is known to experience frequent wind storms, mission planners and engineers require knowledge of the physical and chemical properties of Martian windblown sand and dust, and the processes involved in the origin and evolution of sand and dust storms

Levitated Spinning Graphene

A method is described for levitating micron-sized few layer graphene flakes in a quadrupole ion trap. Starting from a liquid suspension containing graphene, charged flakes are injected into the trap using the electrospray ionization technique and are probed optically. At micro-torr pressures, torques from circularly polarized light cause the levitated particles to rotate at frequencies >1 MHz, which can be inferred from modulation of light scattering off the rotating flake when an electric field resonant with the rotation rate is applied. Possible applications of these techniques will be presented, both to fundamental measurements of the mechanical and electronic properties of graphene and to new approaches to graphene crystal growth, modification and manipulation.Comment: 23 pages, 11 figure

Size-dependent aggregation of graphene oxide

Graphene oxides (GO) of highly polydisperse size distribution were prepared by the Brodie method and their dispersion stability was characterized. Exfoliation and fractionation led to well-defined particle populations in the Nano, classical Colloidal (submicron) and Micrometer size ranges, as revealed by atomic force microscopy and light scattering measurements. Time-resolved dynamic light scattering experiments revealed that aggregation processes are fully impeded in the intermediate pH regime of 3–13 in the absence of electrolytes. While the resistance against salt-induced aggregation increases with the pH due to the progressive ionization of the surface functional groups of GO sheets, their dispersions are inherently unstable at supramillimolar concentrations of strong acids and submolar concentrations of bases, in line with the DLVO theory. However, the aggregation behavior quantified by the critical coagulation concentrations (CCCs) shows surprisingly substantial platelet size dependence. The CCC of Nano Brodie-GO reaches 360 mm at pH = 12, which is one of the highest values ever reported for GO aqueous dispersions. These results provide useful quantitative information to design processable GO dispersions of pH- and size-tunable stability for future applications

An overview of multiple DoF magnetic actuated micro-robots.

International audienceThis paper reviews the state of the art of untethered, wirelessly actuated and controlled micro-robots. Research for such tools is being increasingly pursued to provide solutions for medical, biological and industrial applications. Indeed, due to their small size they o er both high velocity, and accessibility to tiny and clustered environments. These systems could be used for in vitro tasks on lab-on-chips in order to push and/or sort biological cells, or for in vivo tasks like minimally invasive surgery and could also be used in the micro-assembly of microcomponents. However, there are many constraints to actuating, manufacturing and controlling micro-robots, such as the impracticability of on-board sensors and actuators, common hysteresis phenomena and nonlinear behavior in the environment, and the high susceptibility to slight variations in the atmosphere like tiny dust or humidity. In this work, the major challenges that must be addressed are reviewed and some of the best performing multiple DoF micro-robots sized from tens to hundreds m are presented. The di erent magnetic micro-robot platforms are presented and compared. The actuation method as well as the control strategies are analyzed. The reviewed magnetic micro-robots highlight the ability of wireless actuation and show that high velocities can be reached. However, major issues on actuation and control must be overcome in order to perform complex micro-manipulation tasks

Scaling forces to asteroid surfaces: The role of cohesion

The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together by van der Waals cohesive forces.Comment: 54 pages, 7 figure

First experiments on MagPieR: a planar wireless magnetic and piezoelectric microrobot.

International audienceThe paper documents the principle and experiments of the "2mm dash" winner at NIST IEEE Mobile Microrobotics Challenge held at ICRA2010 in Alaska [1]. Submission is made for the special session "ICRA Robot Challenge: Advancing Research Through Competitions". The new MagPieR microrobot was specially designed for breaking the speed record, providing a planar magnetic actuation with an optimised coils setup and a subsequent piezoelectric actuation for improved sliding condition. The paper describes the principle of actuation, the microrobot manufacturing flowchart and the assembly setup. Some simulations are provided with a first series of experimental data and conclusions

Interference-based Investigation of Microscopic Objects Near Surfaces: a View From Below

Phenomena occurring when microscopic objects approach planar surfaces are challenging to probe directly because their dynamics cannot be resolved with a sufficiently high spatial/temporal resolution in a non-invasive way, and suitable techniques/methods involve complex instrumentation/computations of limited accessibility/applicability. Interference-based techniques can overcome these barriers. However, because most set-ups and analysis methods are ideal for planar-like geometries, their accurate application for studying microscopic objects has been difficult. Reflection interference contrast microscopy (RICM) has shown particular promise allowing objects in close proximity to a surface to be observed from below, producing interferograms that inherently embed detailed information about the objects’ topography near the substrate. Because precise extraction of this information has been challenging, this study seeks to develop analysis methods applicable to RICM to facilitate its practical implementation for accurate investigation of interfacial phenomena between microscopic objects and surfaces. The most sophisticated theory of RICM was significantly improved and coupled with a general method to simulate the interference pattern from arbitrary convex geometries. Experimental results revealed that accurate reconstruction of an object’s contour is possible by fitting its interferogram; however, this is computationally intensive and of limited applicability, motivating the formulation of a simplified and accurate RICM model. This facilitated a major breakthrough: an innovative analysis of RICM interferograms provides the inclination angles of the geometry under study and a mathematical procedure allows near-instantaneous reconstruction of the contour with nanometer-scale resolution, applicable to arbitrarily shaped convex objects under different experimental conditions. A method for extracting nanometer-scale topographic information from RICM interferograms has been proposed; in particular, microspheres can be conveniently analyzed to measure surface roughness based on fringe visibility. Also, precise and accurate measurements of microspheres’ size were performed by means of optimized and robust fringe spacing analysis. Finally, RICM’s distinctive “view-from-below” perspective was applied in simple experiments involving the deposition of microspheres on surfaces, directly revealing the existence of different scenarios depending on deposition media and unique femtoliter-scale capillary condensation dynamics underneath micron-sized glass beads. Results show that RICM has a clear potential for near real-time analysis of ensembles of objects near surfaces so that statistical/probabilistic behavior can be realistically captured

Mechanisms of adhesive mixing for drug particle inhalation (Numerical investigation of the interplay between formulation variables)

Formulation of therapeutic dry powders for lung drug delivery via inhalation is done via adhesive mixing. In this process, micron-sized active pharmaceutical ingredient particles are blended with relatively coarse carrier particles until stable adhesive units of carrier and drug particles are formed. Inside the inhaler and upon its actuation, the turbulent kinetic energy of air stream is transferred to the bulk powder of adhesive units and consequently drug particles are dispersed into primary respirable particles. The formulation process-besides the inhaler design and the patient’s respiratory manoeuvre- is one of the three pillars that determine the overall performance of drug administration, and therefore, it needs to be genuinely understood. Despite all the recent advancements in the formulation of carrier-based dry powder inhaler, the in vitro efficiency of currently marketed inhalers is at best less than 50% of their nominal values(2017).The goal of this research is to devise a methodology to comprehend the complex nature of the adhesive mixing process for inhalation, and to optimize this process. The small temporal and spatial scales of the adhesive mixing, on one hand, and the omnipresent interplay of process variables, on the other hand, require a modeling framework and several quality-assessment tools. The underlying principle of this framework is to treat the adhesive mixture as a particulate system, whose dynamic behaviour can be modelled by applying the Newton’s laws of motion to individual particles. Several formulation variables are selected, in accordance with their significance in the process and with the capacity of the developed model, for parameter studying. These variables include the (i) adhesive properties of particles, (ii) the mixing intensity, (iii) the shape of carriers, (iv) the surface asperity of particles, and (v) the added fine particles (ternary blend). The process quality is inferred from mixing homogeneity indices, micro-scale structure of adhesive units, and the fragmentation analyses of drug agglomerates. In addition to the formulation process, simulated dispersion tests are performed in order to understand the role of the carrier surface roughness on the drug particle detachment during aerosolization. The combination of mixing energy and particle surface energies is used to map the mixing state. It is found that any imbalance between these two process variables results in poor adhesive mixtures. The non-sphericity of carrier particles is also shown to impose a noticeable difference in the breakage and adhesion pattern of drug agglomerates. In the context of formulation, the carrier surface roughness reduces the drug deposition, and in the context of dispersion, the drug detachment is found proportional to the roughness length scale. Lastly, different cases of ternary formulations are simulated and the relevance of the active site and the buffer theories are examined