A5021425785- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Planetary Science and Exploration
- Space Exploration and Technology
- Spacecraft and Cryogenic Technologies
- Particle Dynamics in Fluid Flows
- Stellar, planetary, and galactic studies
- Magnetic and Electromagnetic Effects
- Granular flow and fluidized beds
- Material Dynamics and Properties
- Advanced Thermodynamic Systems and Engines
- Adhesion, Friction, and Surface Interactions
- Force Microscopy Techniques and Applications
- Aeolian processes and effects
- Advanced Combustion Engine Technologies
- Methane Hydrates and Related Phenomena
- Scientific Research and Discoveries
- Clay minerals and soil interactions
- Combustion and Detonation Processes
- Advanced Algorithms and Applications
- High-pressure geophysics and materials
- Cyclone Separators and Fluid Dynamics
- Pickering emulsions and particle stabilization
- Field-Flow Fractionation Techniques
- Radioactive Decay and Measurement Techniques
Technische Universität Braunschweig
2008-2024
Friedrich Schiller University Jena
2000
The outcome of the first stage planetary formation, which is characterized by ballistic agglomeration preplanetary dust grains due to Brownian motion in free molecular flow regime solar nebula, still somewhat speculative. We performed a microgravity experiment flown onboard space shuttle we simulated, for time, onset accumulation and revealed structures growth rates agglomerates young system. find that thermally aggregating swarm particles evolves very rapidly forms unexpected...
We present experimental results on the mechanical properties of macroscopic agglomerates formed by ballistic hit-and-stick deposition. The agglomerates, produced with a new method, consist monodisperse SiO2 spheres 1.5 microm diameter and have volume filling factor phi=0.15, matching very closely theoretical value for random They are mechanically stable against unidirectional compression up to 500 Pa. For pressures above that value, increases maximum phi=0.33 10(5) tensile strength slightly...
We present laboratory experiments on the formation of macroscopic dust aggregates. The centimeter-sized highly porous bodies are produced by random ballistic deposition from individual micrometer-sized particles. find packing densities between 0.07 and 0.15 for uncompressed samples, dependent shape size distribution constituent grains. Impacts into these simulated uniaxial compression experiments. that maximum compression, equivalent to highest protoplanetary impact velocities ~50 m s-1,...
We derive the diffusion coefficient D of dust under conditions a protostellar disk. A reliable estimate this quantity is essential for transport, especially sedimentation, particles in disk environment. In contrast to earlier treatments, derived on basis mean field theory that allows determination D. course derivation, we used two different turbulence models. applied order calculate how grains sediment and subdisk develops. Starting from physical subdisk, discuss gravitational instabilities...
Observed protoplanetary disks consist of a large amount micrometer-sized particles. Dullemond & Dominik pointed out for the first time difficulty in explaining strong mid-infrared excess classical T Tauri stars without any dust-retention mechanisms. Because high relative velocities between and macroscopic particles exist disks, we present experimental results on erosion agglomerates consisting spherical via impact We find that after an initial phase, which impacting particle erodes up to 10...
We performed micro-gravity collision experiments in our laboratory drop-tower using 5-cm-sized dust agglomerates with volume filling factors of 0.3 and 0.4, respectively. This work is an extension previous reported Beitz et al. (2011) to aggregates more than one order magnitude higher masses. The consisted micrometer-sized silica particles were macroscopically homogeneous. measured the coefficient restitution for velocities ranging from 1 cm/s 0.5 m/s, determined fragmentation velocity. For...
We present laboratory experiments of a vertically vibrated granular medium consisting 1 mm diameter glass beads with embedded 8 intruder beads. The were performed in the as well parabolic flight under reduced-gravity conditions (on Martian and Lunar gravity levels). measured mean rise velocity large its dependence on fill height sample containers, excitation acceleration, ambient level. find that scales same manner for all three regimes roughly linearly gravity.
In a protoplanetary disk, dust aggregates in the $μ$m to mm size range possess mean collision velocities of 10 60 ms$^{-1}$ with respect dm- m-size bodies. We performed laboratory experiments explore this parameter regime and found size- velocity-dependent threshold between erosion growth. By using local Monte Carlo coagulation calculation complementary simple semi-analytical timescale approach, we show that considerably limits particle growth disks leads steady-state dust-size distribution...
ABSTRACT In dead zones of protoplanetary discs, it is assumed that micrometre-sized particles grow Brownian, sediment to the mid-plane and drift radially inward. When collisional compaction sets in, aggregates collect slower therefore dynamically smaller particles. This sedimentation growth phase highly porous ice dust simulated with laboratory experiments in which we obtained mm- cm-sized a porosity 90 per cent as well agglomerates 85 cent. We modelled process during an analytical...
We experimentally investigated tribocharging in bouncing dust grain collisions under conditions which are relevant for the early solar nebula. used silica, diamond, graphite, and silicon carbide grains cm-sized targets of aluminum, iron, graphite. varied particle size around 1 , collision velocity between 38 to 106 target temperature 240 K 360 K. Generally, acquire something order hundreds or thousands negative elementary charges, is at upper end range previously discussed astrophysical...
Abstract In an experiment onboard a microgravity sounding rocket, we observed the growth of agglomerates consisting <?CDATA $\mu \mathrm {m}\text{-sized}$ ?> silica spheres under well-defined conditions. After initial short charge-induced phase, charge-neutralized grew due to Brownian-motion–induced collisions, first in orderly fashion and thereafter, temporal increase particle concentration, runaway process. The latter is characterized by detachment large oligarch agglomerates. We modeled...
For the purpose of investigating evolution dust aggregates in early Solar System, we developed two vacuum drop towers which fragile with sizes up to ~10 cm and porosities 70% can be collided. One is primarily used for very low impact speeds down below 0.01 m/sec makes use a double release mechanism. Collisions are recorded stereo-view by high-speed cameras, fall along glass tube center-of-mass frame aggregates. The other free-fall tower an electromagnetic accelerator that capable gently...
Highly porous agglomerates of silica microspheres (1.5 µm diameter) with a porosity 0.85, formed by random ballistic hit-and-stick deposition, were deformed inside scanning electron microscope using the cantilever an atomic force microscope. The applied and structural deformations single particle resolution could be obtained simultaneously. First results indicate that whole blocks many particles move collectively upon compression. Within these relative positions remain fixed. This in...
Mechanical properties of high-porous microscopic agglomerates have been investigated. For this purpose we installed an atomic force microscope (AFM) cantilever in a scanning electron (SEM) using nanomanipulator. The nanomanipulator is piezoelectric controlled with increments 5 nm the rotational and 0.5 translational direction. Thus, tool allows precise positioning movement AFM under SEM observation. Depending on spring constant step size motion—both quantities determining sensitivity...
The field of planetary system formation relies extensively on our understanding the aerodynamic interaction between gas and dust in protoplanetary disks. Of particular importance are mechanisms triggering fluid instabilities clumping particles into aggregates, their subsequent inclusion planetesimals. We introduce timed Epstein multi-pressure vessel at low accelerations, which is an experimental apparatus for study particle dynamics rarefied under micro-gravity conditions. This facility...
The predecessor of Laplace, ICAPS, was flown in 2019 and 2023 on the Texus-56 Texus-58 sounding rockets. Laplace facility is planned for a usage ISS with launch 2025. Both experiments allow to investigate very first stages planet formation. relevant growth processes require observation many-particle consisting millions &#181;m-sized particles low-density gas environment (typically few 10s Pa, such that Knudsen numbers >>1 are achieved) prolonged time. latter requirement makes it...
In a micro-gravity experiment onboard sounding rocket, we observed the rapid formation of mm-sized fractal dust agglomerates, consisting micrometer-sized spherical silica monomers, due to an unforeseen (but very favorable) spatial concentration cloud&#160; (Schubert.2024). A convergent gas flow was caused by interaction between dust-cloud control mechanism, which generates homogeneous using thermal-creep method, and thermophoresis-driven directed towards cold spot. This rarefied-gas led...
Protoplanetary disks (PPDs), the cradles of planetary systems around young stars, are composed dust and ice particles immersed in a rarefied gas. These grains possess initial sizes less than up to about 1 &#181;m collide due Brownian motion, drift motions relative gas, gas turbulence. Provided that collision velocity remains below threshold value, stick upon first contact form fractal agglomerates with typical dimensions just 2. This is case for collisions caused by which occur at...
For the purpose of investigating evolution dust aggregates in early Solar System, we developed two vacuum drop towers which fragile with sizes up to ~10 cm and porosities 70% can be collided. One is primarily used for very low impact speeds down below 0.01 m/sec makes use a double release mechanism. Collisions are recorded stereo-view by high-speed cameras, fall along glass tube center-of-mass frame aggregates. The other free-fall tower an electromagnetic accelerator that capable gently...