663 research outputs found
Adaptive modulations of martensites
Modulated phases occur in numerous functional materials like giant
ferroelectrics and magnetic shape memory alloys. To understand the origin of
these phases, we review and generalize the concept of adaptive martensite. As a
starting point, we investigate the coexistence of austenite, adaptive 14M phase
and tetragonal martensite in Ni-Mn-Ga magnetic shape memory alloy epitaxial
films. The modulated martensite can be constructed from nanotwinned variants of
a tetragonal martensite phase. By combining the concept of adaptive martensite
with branching of twin variants, we can explain key features of modulated
phases from a microscopic view. This includes phase stability, the sequence of
6M-10M-NM intermartensitic transitions, and magnetocrystalline anisotropy.Comment: 4 pages manuscript, 8 pages supplemen
Comparing Transmission- and Epi-BCARS: A Transnational Round Robin on Solid State Materials
Broadband coherent anti-Stokes Raman scattering (BCARS) is an advanced Raman
spectroscopy method that combines the spectral sensitivity of spontaneous Raman
scattering (SR) with the increased signal intensity of single-frequency
coherent Raman techniques. These two features make BCARS particularly suitable
for ultra-fast imaging of heterogeneous samples, as already shown in
biomedicine. Recent studies demonstrated that BCARS also shows exceptional
spectroscopic capabilities when inspecting crystalline materials like lithium
niobate and lithium tantalate, and can be used for fast imaging of
ferroelectric domain walls. These results strongly suggest the extension of
BCARS towards new imaging applications like mapping defects, strain, or dopant
levels, similar to standard SR imaging. Despite these advantages, BCARS suffers
from a spurious and chemically unspecific non-resonant background (NRB) that
distorts and shifts the Raman peaks. Post-processing numerical algorithms are
then used to remove the NRB and to obtain spectra comparable to SR results.
Here, we show the reproducibility of BCARS by conducting an internal Round
Robin with two different BCARS experimental setups, comparing the results on
different crystalline materials of increasing structural complexity: diamond,
6H-SiC, KDP, and KTP. First, we compare the detected and phase-retrieved
signals, the setup-specific NRB-removal steps, and the mode assignment.
Subsequently, we demonstrate the versatility of BCARS by showcasing how the
selection of pump wavelength, pulse width, and detection geometry can be
tailored to suit the specific objectives of the experiment. Finally, we compare
and optimize measurement parameters for the high-speed, hyperspectral imaging
of ferroelectric domain walls in lithium niobate.Comment: 12 pages, 8 figure
Sixteenth Annual Bibliography, 2000 (Contemporary German Literature Collection)
Bibliography of contemporary German literature volumes added the previous year to Washington University Libraries\u27 Contemporary German Literature Collection. These acquisitions generally include novels, poetry, short story collections, essays, autobiographical works, and literary and cultural periodicals from publishers in Germany, Austria, and Switzerland. This Collection serves as the research arm for the Department of Germanic Languages and Literature\u27s Max Kade Center for Contemporary German Literature. This bibliography is compiled by Washington University\u27s Department of Germanic Languages and Literatures in cooperation with the University Libraries. See also Contemporary German Literature Collection and Max Kade Center for Contemporary German Literature
Universal features of fluctuations
Universal scaling laws of fluctuations (the -scaling laws) can be
derived for equilibrium and off-equilibrium systems when combined with the
finite-size scaling analysis. In any system in which the second-order critical
behavior can be identified, the relation between order parameter, criticality
and scaling law of fluctuations has been established and the relation between
the scaling function and the critical exponents has been found.Comment: 10 pages; TORINO 2000, New Frontiers in Soft Physics and Correlations
on the Threshold of the Third Milleniu
Enhanced Event-by-Event Fluctuations in Pion Multiplicity as a Signal of Disoriented Chiral Condensates at RHIC
The factorial moments of the pion multiplicity distributions are calculated
with HIJING and UrQMD and found to be independent of the pT range included, in
contrast to recent simulations with the linear sigma model which leads to large
enhancements for pions with transverse kinetic energies below 200 MeV. This
supports the use of the ratio of the factorial moments of low and high pT pions
as a signal of ``new'' physics at low momentum scales, such as the formation of
disoriented chiral condensates.Comment: 4 pages total, incl 4 eps figures ([email protected]
Tuning of crystal structure and magnetic properties by exceptionally large epitaxial strains
Huge deformations of the crystal lattice can be achieved in materials with
inherent structural instability by epitaxial straining. By coherent growth on
seven different substrates the in-plane lattice constants of 50 nm thick
Fe70Pd30 films are continuously varied. The maximum epitaxial strain reaches
8,3 % relative to the fcc lattice. The in-plane lattice strain results in a
remarkable tetragonal distortion ranging from c/abct = 1.09 to 1.39, covering
most of the Bain transformation path from fcc to bcc crystal structure. This
has dramatic consequences for the magnetic key properties. Magnetometry and
X-ray circular dichroism (XMCD) measurements show that Curie temperature,
orbital magnetic moment, and magnetocrystalline anisotropy are tuned over broad
ranges.Comment: manuscript, 3 figures, auxiliary materia
Integral correlation measures for multiparticle physics
We report on a considerable improvement in the technique of measuring
multiparticle correlations via integrals over correlation functions. A
modification of measures used in the characterization of chaotic dynamical
sytems permits fast and flexible calculation of factorial moments and cumulants
as well as their differential versions. Higher order correlation integral
measurements even of large multiplicity events such as encountered in heavy ion
collisons are now feasible. The change from ``ordinary'' to ``factorial''
powers may have important consequences in other fields such as the study of
galaxy correlations and Bose-Einstein interferometry.Comment: 23 pages, 6 tar-compressed uuencoded PostScript figures appended,
preprint TPR-92-4
Why I tense up when you watch me: inferior parietal cortex mediates an audience’s influence on motor performance
The presence of an evaluative audience can alter skilled motor performance through changes in force output. To investigate how this is mediated within the brain, we emulated real-time social monitoring of participants’ performance of a fine grip task during functional magnetic resonance neuroimaging. We observed an increase in force output during social evaluation that was accompanied by focal reductions in activity within bilateral inferior parietal cortex. Moreover, deactivation of the left inferior parietal cortex predicted both inter- and intra-individual differences in socially-induced change in grip force. Social evaluation also enhanced activation within the posterior superior temporal sulcus, which conveys visual information about others’ actions to the inferior parietal cortex. Interestingly, functional connectivity between these two regions was attenuated by social evaluation. Our data suggest that social evaluation can vary force output through the altered engagement of inferior parietal cortex; a region implicated in sensorimotor integration necessary for object manipulation, and a component of the action-observation network which integrates and facilitates performance of observed actions. Social-evaluative situations may induce high-level representational incoherence between one’s own intentioned action and the perceived intention of others which, by uncoupling the dynamics of sensorimotor facilitation, could ultimately perturbe motor output
Intermittency in Branching Processes
We study the intermittency properties of two branching processes, one with a
uniform and another with a singular splitting kernel. The asymptotic
intermittency indices, as well as the leading corrections to the asymptotic
linear regime are explicitly computed in an analytic framework. Both models are
found to possess a monofractal spectrum with . Relations with
previous results are discussed.Comment: 20 pages, UCLA93/TEP/2
A sensitive test for models of Bose-Einstein correlations
Accurate and sensitive measurements of higher order cumulants open up new
approaches to pion interferometry. It is now possible to test whether a given
theoretical prediction can consistently match cumulants of both second and
third order. Our consistency test utilizes a new technique combining
theoretically predicted functions with experimentally determined weights in a
quasi-Monte Carlo approach. Testing a general quantum statistics-based
framework of Bose-Einstein correlations with this technique, we find that
predictions for third order cumulants differ significantly from UA1 data. This
discrepancy may point the way to more detailed dynamical information.Comment: 5 pages, 2 figures, revte
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