18 research outputs found
Fluid pumped by magnetic stress
A magnetic field rotating on the free surface of a ferrofluid layer is shown
to induce considerable fluid motion toward the direction the field is rolling.
The measured flow velocity i) increases with the square of the magnetic field
amplitude, ii) is proportional to the thickness of the fluid layer, and iii)
has a maximum at a driving frequency of about 3 kHz. The pumping speed can be
estimated with a two-dimensional flow model.Comment: 3 pages, 4 figure
Hexagons become second if symmetry is broken
Pattern formation on the free surface of a magnetic fluid subjected to a
magnetic field is investigated experimentally. By tilting the magnetic field
the symmetry can be broken in a controllable manner. When increasing the
amplitude of the tilted field, the flat surface gives way to liquid ridges. A
further increase results in a hysteretic transition to a pattern of stretched
hexagons. The instabilities are detected by means of a linear array of magnetic
hall sensors and compared with theoretical predictions.Comment: accepted for publication by Physical Review E/Rapid Communicatio
Wave Number of Maximal Growth in Viscous Magnetic Fluids of Arbitrary Depth
An analytical method within the frame of linear stability theory is presented
for the normal field instability in magnetic fluids. It allows to calculate the
maximal growth rate and the corresponding wave number for any combination of
thickness and viscosity of the fluid. Applying this method to magnetic fluids
of finite depth, these results are quantitatively compared to the wave number
of the transient pattern observed experimentally after a jump--like increase of
the field. The wave number grows linearly with increasing induction where the
theoretical and the experimental data agree well. Thereby a long-standing
controversy about the behaviour of the wave number above the critical magnetic
field is tackled.Comment: 19 pages, 15 figures, RevTex; revised version with a new figure and
references added. submitted to Phys Rev
Friction behavior and other material properties of nickel-titanium and titanium-molybdenum archwires following electrochemical surface refinement
The aim of this work was to investigate whether electrochemical surface treatment of nickel-titanium (NiTi) and titanium-molybdenum (TiMo) archwires (OptoTherm (TM) and BetaTitan (TM); Ortho-Dent Specials, Kisdorf, Germany) reduces friction inside the bracket-archwire complex. We also evaluated further material properties and compared these to untreated wires. The material properties of the surface-treated wires (Optotherm/LoFrix (TM) and BetaTitan/LoFrix (TM)) were compared to untreated wires made by the same manufacturer (see above) and by another manufacturer (Neo SentalloyA (R); GAC, Bohemia, NY, USA). We carried out a three-point bending test, leveling test, and friction test using an orthodontic measurement and simulation system (OMSS). In addition, a pure bending test was conducted at a special test station, and scanning electron micrographs were obtained to analyze the various wire types for surface characteristics. Finally, edge beveling and cross-sectional dimensions were assessed. Force losses due to friction were reduced by 10 percentage points (from 36 to 26%) in the NiTi and by 12 percentage points (from 59 to 47%) in the TiMo wire specimens. Most of the other material properties exhibited no significant changes after surface treatment. While the three-point bending tests revealed mildly reduced force levels in the TiMo specimens due to diameter losses of roughly 2%, these force levels remained almost unchanged in the NiTi specimens. Compared to untreated NiTi and TiMo archwire specimens, the surface-treated specimens demonstrated reductions in friction loss by 10 and 12 percentage points, respectively
Bionic tactile sensor for near-range search, localisation and material classification
DĂŒrr V, Krause AF, Neitzel M, Lange O, Reimann B. Bionic tactile sensor for near-range search, localisation and material classification. In: Berns K, Luksch T, eds. Autonome Mobile Systeme 2007, 20. FachgesprĂ€ch Kaiserslautern, 18./19. Oktober 2007. Heidelberg: Springer; 2007: 240-246