56,909 research outputs found
Tensile strain-induced softening of iron at high temperature
In weakly ferromagnetic materials, already small changes in the atomic
configuration triggered by temperature or chemistry can alter the magnetic
interactions responsible for the non-random atomic-spin orientation. Different
magnetic states, in turn, can give rise to substantially different macroscopic
properties. A classical example is iron, which exhibits a great variety of
properties as one gradually removes the magnetic long-range order by raising
the temperature towards and beyond its Curie point of
\,K. Using first-principles theory, here we demonstrate
that uniaxial tensile strain can also destabilize the magnetic order in iron
and eventually lead to a ferromagnetic to paramagnetic transition at
temperatures far below . In consequence, the intrinsic
strength of the ideal single-crystal body-centered cubic iron dramatically
weakens above a critical temperature of \,K. The discovered
strain-induced magneto-mechanical softening provides a plausible atomic-level
mechanism behind the observed drop of the measured strength of Fe whiskers
around \,K. Alloying additions which have the capability to partially
restore the magnetic order in the strained Fe lattice, push the critical
temperature for the strength-softening scenario towards the magnetic transition
temperature of the undeformed lattice. This can result in a surprisingly large
alloying-driven strengthening effect at high temperature as illustrated here in
the case of Fe-Co alloy.Comment: 3 figure
Measurement of helium-3 and deuterium stopping power ratio for negative muons
The measurement method and results measuring of the stopping power ratio of
helium-3 and deuterium atoms for muons slowed down in the D/He mixture are
presented. Measurements were performed at four values of pure He gas target
densities, (normalized to the
liquid hydrogen density) and at a density 0.0585 of the D/He mixture. The
experiment was carried out at PSI muon beam E4 with the momentum P MeV/c. The measured value of the mean stopping ratio is
. This value can also be interpreted as the value of mean reduced
ratio of probabilities for muon capture by helium-3 and deuterium atoms.Comment: 7 pages, 6 figure
Speeding-up Dynamic Programming with Representative Sets - An Experimental Evaluation of Algorithms for Steiner Tree on Tree Decompositions
Dynamic programming on tree decompositions is a frequently used approach to
solve otherwise intractable problems on instances of small treewidth. In recent
work by Bodlaender et al., it was shown that for many connectivity problems,
there exist algorithms that use time, linear in the number of vertices, and
single exponential in the width of the tree decomposition that is used. The
central idea is that it suffices to compute representative sets, and these can
be computed efficiently with help of Gaussian elimination.
In this paper, we give an experimental evaluation of this technique for the
Steiner Tree problem. A comparison of the classic dynamic programming algorithm
and the improved dynamic programming algorithm that employs the table reduction
shows that the new approach gives significant improvements on the running time
of the algorithm and the size of the tables computed by the dynamic programming
algorithm, and thus that the rank based approach from Bodlaender et al. does
not only give significant theoretical improvements but also is a viable
approach in a practical setting, and showcases the potential of exploiting the
idea of representative sets for speeding up dynamic programming algorithms
Measurement of electron screening in muonic lead
Energies of the transitions between high-lying (n≥6) states of muonic lead were accurately determined. The results are interpreted as a ∼2% test of the electron screening. The agreement between experiment and theory is good if it is assumed that the refilling of the electron K shell is fast. The present results furthermore severely restrict possible ionization of the electron L shell
Modelling and optimisation of a bimorph piezoelectric cantilever beam in an energy harvesting application
Piezoelectric materials are excellent transducers in converting vibrational energy into electrical energy, and vibration-based piezoelectric generators are seen as an enabling technology for wireless sensor networks, especially in selfpowered devices. This paper proposes an alternative method for predicting the power output of a bimorph cantilever beam using a finite element method for both static and dynamic frequency analyses. Experiments are performed to validate the model and the simulation results. In addition, a novel approach is presented for optimising the structure of the bimorph cantilever beam, by which the power output is maximised and the structural volume is minimised simultaneously. Finally, the results of the optimised design are presented and compared with other designs
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