15,736 research outputs found
Preparation and field-induced electrical properties of perovskite relaxor ferroelectrics
(111)-oriented and random oriented Pb0.8Ba0.2ZrO3 (PBZ) perovskite relaxor ferroelectric thin films were fabricated on Pt(111)/TiOx/SiO2/Si substrate by sol-gel method. Nano-scaled antiferroelectric and ferroelectric two-phase coexisted in both (111)-oriented and random oriented PBZ thin film. High dielectric tunability (i = 75%, E = 560 kV/ cm ) and figure-of-merit (FOM ~ 236) at room temperature was obtained in (111)-oriented thin film. Meanwhile, giant electrocaloric effect (ECE) (AT = 45.3 K and AS = 46.9 JK-1kg-1 at 598 kVcm-1) at room temperature (290 K), rather than at its Curie temperature (408 K), was observed in random oriented Pb0.8Ba0.2ZrO3 (PBZ) thin film, which makes it a promising material for the application to cooling systems near room temperature. The giant ECE as well as high dielectric tunability are attributed to the coexistence of AFE and FE phases and field-induced nano-scaled AFE to FE phase transition
Apparent horizon and gravitational thermodynamics of Universe in the Eddington-Born-Infeld theory
The thermodynamics of Universe in the Eddington-Born-Infeld (EBI) theory was
restudied by utilizing the holographic-style gravitational equations that
dominate the dynamics of the cosmical apparent horizon and the
evolution of Universe. We started in rewriting the EBI action of the Palatini
approach into the Bigravity-type action with an extra metric . With
the help of the holographic-style dynamical equations, we discussed the
property of the cosmical apparent horizon including timelike,
spacelike and null characters, which depends on the value of the parameter of
state in EBI Universe. The unified first law for the gravitational
thermodynamics and the total energy differential for the open system enveloped
by in EBI Universe were obtained. Finally, applying the
positive-heat-out sign convention, we derived the generalized second law of
gravitational thermodynamics in EBI universe.Comment: 23 pages, 0 figure
Are Discoveries Spurious? Distributions of Maximum Spurious Correlations and Their Applications
Over the last two decades, many exciting variable selection methods have been
developed for finding a small group of covariates that are associated with the
response from a large pool. Can the discoveries from these data mining
approaches be spurious due to high dimensionality and limited sample size? Can
our fundamental assumptions about the exogeneity of the covariates needed for
such variable selection be validated with the data? To answer these questions,
we need to derive the distributions of the maximum spurious correlations given
a certain number of predictors, namely, the distribution of the correlation of
a response variable with the best linear combinations of covariates
, even when and are independent. When the
covariance matrix of possesses the restricted eigenvalue property,
we derive such distributions for both a finite and a diverging , using
Gaussian approximation and empirical process techniques. However, such a
distribution depends on the unknown covariance matrix of . Hence,
we use the multiplier bootstrap procedure to approximate the unknown
distributions and establish the consistency of such a simple bootstrap
approach. The results are further extended to the situation where the residuals
are from regularized fits. Our approach is then used to construct the upper
confidence limit for the maximum spurious correlation and to test the
exogeneity of the covariates. The former provides a baseline for guarding
against false discoveries and the latter tests whether our fundamental
assumptions for high-dimensional model selection are statistically valid. Our
techniques and results are illustrated with both numerical examples and real
data analysis
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