8,430 research outputs found
Scaling Behaviour and Complexity of the Portevin-Le Chatelier Effect
The plastic deformation of dilute alloys is often accompanied by plastic
instabilities due to dynamic strain aging and dislocation interaction. The
repeated breakaway of dislocations from and their recapture by solute atoms
leads to stress serrations and localized strain in the strain controlled
tensile tests, known as the Portevin-Le Chatelier (PLC) effect. In this present
work, we analyse the stress time series data of the observed PLC effect in the
constant strain rate tensile tests on Al-2.5%Mg alloy for a wide range of
strain rates at room temperature. The scaling behaviour of the PLC effect was
studied using two complementary scaling analysis methods: the finite variance
scaling method and the diffusion entropy analysis. From these analyses we could
establish that in the entire span of strain rates, PLC effect showed Levy walk
property. Moreover, the multiscale entropy analysis is carried out on the
stress time series data observed during the PLC effect to quantify the
complexity of the distinct spatiotemporal dynamical regimes. It is shown that
for the static type C band, the entropy is very low for all the scales compared
to the hopping type B and the propagating type A bands. The results are
interpreted considering the time and length scales relevant to the effect.Comment: 35 pages, 6 figure
Electronic behavior of the Zn- and O-polar ZnO surfaces studied using conductive atomic force microscopy
We have used conducting atomic force microscopy (CAFM) to study the morphology and electronic behavior of as-received and air-annealed (0001) Zn- and (0001ĀÆ) O-polar surfaces of bulk ZnO. Both polar surfaces exhibit relatively flat morphologies prior to annealing, which rearrange to form well-defined steps upon annealing in air at 1050āĀ°C for 1 h. Long-term exposure to air results in surface layer pitting and the destruction of steps for both the as-received and air-annealed (0001ĀÆ)surfaces, indicating its enhanced reactivity relative to the (0001) surface. CAFM I-V spectra for polar surfaces are similar and indicate Ohmic to rectifying behavior that depends on the maximum applied ramp voltage, where higher voltages result in more conducting behavior. These data and force-displacement curves suggest the presence of a physisorbed H2O layer, which is removed at higher voltages and results in higher conduction
A characterization of Dirac morphisms
Relating the Dirac operators on the total space and on the base manifold of a
horizontally conformal submersion, we characterize Dirac morphisms, i.e. maps
which pull back (local) harmonic spinor fields onto (local) harmonic spinor
fields.Comment: 18 pages; restricted to the even-dimensional cas
An opportunistic sighting of a flock of Black Petrels (Procellaria parkinsoni) at the Galapagos Islands, Ecuador
Compact Autonomous Explosive-Driven Pulsed Power System Based on a Capacitive Energy Storage Charged by a High-Voltage Shock-Wave Ferromagnetic Generator
A new concept for constructing compact autonomous pulsed power systems is presented. This concept utilizes a high-voltage explosive-driven shock-wave ferromagnetic generator (FMG) as a charging source for capacitive energy storage. It has been experimentally demonstrated that miniature FMGs (22-25 cmĀ³ in size and 84-95 g in mass) developed for these experiments can be successfully used to charge capacitor banks. The FMGs, containing NdāFeāāB energy-carrying elements, provided pulsed powers of 35-45 kW in times ranging from 10 to 15 Āµs. A methodology was developed for digital simulation of the operation of the transverse FMG. Experimental results that were obtained are in a good agreement with the results of digital simulations
- ā¦