810 research outputs found
Avalanche criticality in the martensitic transition of Cu67.64Zn16.71Al15.65 shape-memory alloy: a calorimetric and acoustic emission study
The first-order diffusionless structural transition in Cu67.64Zn16.71Al15.65 is characterized by jerky propagation of phase fronts related to the appearance of avalanches. In this paper, we describe a full analysis of this avalanche behavior using calorimetric heat-flux measurements and acoustic emission measurements. Two different propagation modes, namely, smooth front propagation and jerky avalanches, were observed in extremely slow measurements with heating and cooling rates as low as a few 10−3 K/h. Avalanches show criticality where each avalanche leads to a spike in the heat flux. Their statistical analysis leads to a power law [P(E)∼E−ε, where P(E)dE is the probability to observe an avalanche with energy E in an interval between E and E+dE] with an energy exponent of ε=2.15±0.15 in excellent agreement with the results of acoustic emission measurements. Avalanches appear to be more common for heating rates faster than 5×10−3 K/h whereas smooth front propagation occurs in all calorimetric measurements and (almost) exclusively for slower heating rates. Repeated cooling runs were taken after a waiting time of 1 month (and an intermediate heating run). Correlations between the avalanche sequences of the two cooling runs were found for the strongest avalanche peaks but not for the full sequence of avalanches. The memory effect is hence limited to strong avalanches
Correlations between Elastic, Calorimetric, and Polar Properties of Ferroelectric PbSc0.5Ta0.5O3 (PST)
Calorimetric, elastic, and polar properties of ferrolectric lead scandium tantalate PbSc0.5Ta0.5O3 (PST) with 65% cation
order have been investigated in the vicinity of the paraelectric-ferroelectric transition at Ttrans = 295K. Comparison of
temperature dependencies of the excess specific heat and elastic properties indicate that both anomalies stem from ther-
mal fluctuations of order parameters in three dimensions. These fluctuations are consistent with tweed microstructure.
This transition is driven by several coupled thermodynamic order parameters, as evidenced by a strongly non-linear
scaling of the excess entropy with the squared ferroelectric polarization.National Natural Science Foundation of China (51850410520, 51320105014 and 51621063
Anisotropy and universality: Critical Binder cumulant of the two-dimensional Ising model
We reanalyze transfer matrix and Monte Carlo results for the critical Binder
cumulant U* of an anisotropic two-dimensional Ising model on a square lattice
in a square geometry with periodic boundary conditions. Spins are coupled
between nearest neighboring sites and between next-nearest neighboring sites
along one of the lattice diagonals. We find that U* depends only on the
asymptotic critical long-distance features of the anisotropy, irrespective of
its realization through ferromagnetic or antiferromagnetic next-nearest
neighbor couplings. We modify an earlier renormalization-group calculation to
obtain a quantitative description of the anisotropy dependence of U*. Our
results support our recent claim towards the validity of universality for
critical phenomena in the presence of a weak anisotropy.Comment: 4 pages, 2 figures; one reference and some clarifications adde
Tin telluride: a weakly co-elastic metal
We report resonant ultrasound spectroscopy (RUS),
dilatometry/magnetostriction, magnetotransport, magnetization, specific heat,
and Sn M\"ossbauer spectroscopy measurements on SnTe and
SnCrTe. Hall measurements at K indicate that our
Bridgman-grown single crystals have a -type carrier concentration of cm and that our Cr-doped crystals have an -type
concentration of cm. Although our SnTe crystals are
diamagnetic over the temperature range , the Cr-doped crystals are room temperature ferromagnets with a Curie
temperature of 294 K. For each sample type, three-terminal capacitive
dilatometry measurements detect a subtle 0.5 micron distortion at K. Whereas our RUS measurements on SnTe show elastic hardening near the
structural transition, pointing to co-elastic behavior, similar measurements on
SnCrTe show a pronounced softening, pointing to
ferroelastic behavior. Effective Debye temperature, , values of SnTe
obtained from Sn M\"ossbauer studies show a hardening of phonons in the
range 60--115K ( = 162K) as compared with the 100--300K range
( = 150K). In addition, a precursor softening extending over
approximately 100 K anticipates this collapse at the critical temperature, and
quantitative analysis over three decades of its reduced modulus finds with , a value
indicating a three-dimensional softening of phonon branches at a temperature
K, considerably below . We suggest that the differences in
these two types of elastic behaviors lie in the absence of elastic domain wall
motion in the one case and their nucleation in the other
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Opportunities for improved surveillance and control of dengue from age-specific case data.
One of the challenges faced by global disease surveillance efforts is the lack of comparability across systems. Reporting commonly focuses on overall incidence, despite differences in surveillance quality between and within countries. For most immunizing infections, the age distribution of incident cases provides a more robust picture of trends in transmission. We present a framework to estimate transmission intensity for dengue virus from age-specific incidence data, and apply it to 359 administrative units in Thailand, Colombia, Brazil and Mexico. Our estimates correlate well with those derived from seroprevalence data (the gold standard), capture the expected spatial heterogeneity in risk, and correlate with known environmental drivers of transmission. We show how this approach could be used to guide the implementation of control strategies such as vaccination. Since age-specific counts are routinely collected by masany surveillance systems, they represent a unique opportunity to further our understanding of disease burden and risk for many diseases
Effect of internal friction on transformation twin dynamics in SrxBa1-xSnO3 perovskite
The dynamics of transformation twins in SrxBa1-xSnO3 (x=0.6,0.8) perovskite
has been studied by dynamical mechanical analysis in three-point bend geometry.
This material undergoes phase transitions from orthorhombic to tetragonal and
cubic structures on heating. The mechanical loss signatures of the
transformation twins include relaxation and frequency-independent peaks in the
orthorhombic and tetragonal phases, with no observed energy dissipation in the
cubic phase. The macroscopic shape, orientation and relative displacements of
twin walls have been calculated from bending and anisotropy energies. The
mechanical loss angle and distribution of relaxation time are discussed in term
of bending modes of domain walls.Comment: 20 pages, 4 figure
Low-temperature phase transformations of PZT in the morphotropic phase-boundary region
We present anelastic and dielectric spectroscopy measurements of
PbZr(1-x)Ti(x)O(3) with 0.455 < x < 0.53, which provide new information on the
low temperature phase transitions. The tetragonal-to-monoclinic transformation
is first-order for x < 0.48 and causes a softening of the polycrystal Young's
modulus whose amplitude may exceed the one at the cubic-to-tetragonal
transformation; this is explainable in terms of linear coupling between shear
strain components and tilting angle of polarization in the monoclinic phase.
The transition involving rotations of the octahedra below 200 K is visible both
in the dielectric and anelastic losses, and it extends within the tetragonal
phase, as predicted by recent first-principle calculations.Comment: 4 pages, 4 figure
Experimental evidence of accelerated seismic release without critical failure in acoustic emissions of compressed nanoporous materials
The total energy of acoustic emission (AE) events in externally stressed
materials diverges when approaching macroscopic failure. Numerical and
conceptual models explain this accelerated seismic release (ASR) as the
approach to a critical point that coincides with ultimate failure. Here, we
report ASR during soft uniaxial compression of three silica-based (SiO)
nanoporous materials. Instead of a singular critical point, the distribution of
AE energies is stationary and variations in the activity rate are sufficient to
explain the presence of multiple periods of ASR leading to distinct brittle
failure events. We propose that critical failure is suppressed in the AE
statistics by dissipation and transient hardening. Some of the critical
exponents estimated from the experiments are compatible with mean field models,
while others are still open to interpretation in terms of the solution of
frictional and fracture avalanche models.Comment: preprint, Main article: 7 pages, 3 figures. Supplementary material
included in \anc folder: 6 pages, 3 figure
Critical free energy and Casimir forces in rectangular geometries
We study the critical behavior of the free energy and the thermodynamic
Casimir force in a block geometry in
dimensions with aspect ratio above, at, and below on
the basis of the O symmetric lattice model with periodic boundary
conditions (b.c.). We consider a simple-cubic lattice with isotropic
short-range interactions. Exact results are derived in the large - limit
describing the geometric crossover from film () over cubic to
cylindrical () geometries. For , three perturbation
approaches are presented that cover both the central finite-size regime near
for and the region outside the central
finite-size regime well above and below for arbitrary . At bulk
of isotropic systems with periodic b.c., we predict the critical Casimir
force in the vertical direction to be negative (attractive) for a slab
(), and zero for a cube
. We also present extrapolations to the cylinder limit
() and to the film limit () for and . Our
analytic results for finite-size scaling functions in the minimal
renormalization scheme at fixed dimension agree well with Monte Carlo
data for the three-dimensional Ising model by Hasenbusch for and by
Vasilyev et al. for above, at, and below .Comment: 23 pages, 14 figure
Elastic softening of leucite and the lack of polar domain boundaries
Elastic properties of leucite have been investigated using resonant ultrasound spectroscopy over a temperature range from 300 to 1400 K. According to these measurements, elastic moduli soften by ~50% at the Ia3d-I41/acd ferroelastic transition temperature Tc1 = 940 K relative to the value at 1400 K. A second softening is observed at Tc2 = 920 K, corresponding to the structural change from the space group I41/acd to I41/a. These elastic anomalies are analyzed in a simple model under the assumption that the transitions observed at Tc1 and Tc2 can be approximated by a single pseudoproper ferroelastic transition. The two phase transitions are accompanied by a single peak in mechanical damping attributed to the high mobility of twin walls in the intermediate phase followed by pinning in the low-temperature phase. To determine whether twin walls in tetragonal leucite are polar, resonant piezoelectric spectroscopy and second harmonic generation measurements were performed, but no evidence of polarity was found
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