1,881 research outputs found
Temperature-dependent Raman scattering of DyScO3 and GdScO3 single crystals
We report a temperature-dependent Raman scattering investigation of DyScO3
and GdScO3 single crystals from room temperature up to 1200 {\deg}C. With
increasing temperature, all modes decrease monotonously in wavenumber without
anomaly, which attests the absence of a structural phase transition. The high
temperature spectral signature and extrapolation of band positions to higher
temperatures suggest a decreasing orthorhombic distortion towards the ideal
cubic structure. Our study indicates that this orthorhombic-to-cubic phase
transition is close to or higher than the melting point of both rare-earth
scandates (\approx 2100 {\deg}C), which might exclude the possibility of the
experimental observation of such a phase transition before melting. The
temperature-dependent shift of Raman phonons is also discussed in the context
of thermal expansion
Comparing hierarchies of total functionals
In this paper we consider two hierarchies of hereditarily total and
continuous functionals over the reals based on one extensional and one
intensional representation of real numbers, and we discuss under which
asumptions these hierarchies coincide. This coincidense problem is equivalent
to a statement about the topology of the Kleene-Kreisel continuous functionals.
As a tool of independent interest, we show that the Kleene-Kreisel functionals
may be embedded into both these hierarchies.Comment: 28 page
Random local strain effects in homovalent-substituted relaxor ferroelectrics: a first-principles study of BaTi0.74Zr0.26O3
We present first-principles supercell calculations on BaTi0.74Zr0.26O3, a
prototype material for relaxors with a homovalent substitution. From a
statistical analysis of relaxed structures, we give evidence for four types of
Ti-atom polar displacements: along the , , or
directions of the cubic unit cell, or almost cancelled. The type of a Ti
displacement is entirely determined by the Ti/Zr distribution in the adjacent
unit cells. The underlying mechanism involves local strain effects that ensue
from the difference in size between the Ti4+ and Zr4+ cations. These results
shed light on the structural mechanisms that lead to disordered Ti
displacements in BaTi(1-x)Zr(x)O3 relaxors, and probably in other BaTiO3-based
relaxors with homovalent substitution.Comment: 5 pages, 4 figure
Bifurcated polarization rotation in bismuth-based piezoelectrics
ABO3 perovskite-type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, or magnetic fields. Some solid solutions show remarkably enhanced physical properties including colossal magnetoresistance or giant piezoelectricity. It has been recognized that structural distortions, competing on the local level, are key to understanding and tuning these remarkable properties, yet, it remains a challenge to experimentally observe such local structural details. Here, from neutron pair-distribution analysis, a temperature-dependent 3D atomic-level model of the lead-free piezoelectric perovskite Na0.5Bi0.5TiO3 (NBT) is reported. The statistical analysis of this model shows how local distortions compete, how this competition develops with temperature, and, in particular, how different polar displacements of Bi3+ cations coexist as a bifurcated polarization, highlighting the interest of Bi-based materials in the search for new lead-free piezoelectrics
Hard exclusive production of a vector meson
The processes of a light neutral vector meson, V=\rho^0, \omega, \phi,
electroproduction and a heavy quarkonium, V=J/\Psi, \Upsilon, photoproduction
are studied in the framework of QCD factorization. We derive a complete set of
hard-scattering amplitudes which describe these processes at next-to-leading
order (NLO).Comment: 3 pages, prepared for Diffraction 2004, International Workshop on
Diffraction in High-Energy Physics, Cala Gonone, Sardinia, Italy, September
18 - 23, 200
An algorithmic approach to the existence of ideal objects in commutative algebra
The existence of ideal objects, such as maximal ideals in nonzero rings,
plays a crucial role in commutative algebra. These are typically justified
using Zorn's lemma, and thus pose a challenge from a computational point of
view. Giving a constructive meaning to ideal objects is a problem which dates
back to Hilbert's program, and today is still a central theme in the area of
dynamical algebra, which focuses on the elimination of ideal objects via
syntactic methods. In this paper, we take an alternative approach based on
Kreisel's no counterexample interpretation and sequential algorithms. We first
give a computational interpretation to an abstract maximality principle in the
countable setting via an intuitive, state based algorithm. We then carry out a
concrete case study, in which we give an algorithmic account of the result that
in any commutative ring, the intersection of all prime ideals is contained in
its nilradical
Existential witness extraction in classical realizability and via a negative translation
We show how to extract existential witnesses from classical proofs using
Krivine's classical realizability---where classical proofs are interpreted as
lambda-terms with the call/cc control operator. We first recall the basic
framework of classical realizability (in classical second-order arithmetic) and
show how to extend it with primitive numerals for faster computations. Then we
show how to perform witness extraction in this framework, by discussing several
techniques depending on the shape of the existential formula. In particular, we
show that in the Sigma01-case, Krivine's witness extraction method reduces to
Friedman's through a well-suited negative translation to intuitionistic
second-order arithmetic. Finally we discuss the advantages of using call/cc
rather than a negative translation, especially from the point of view of an
implementation.Comment: 52 pages. Accepted in Logical Methods for Computer Science (LMCS),
201
Helmut Brandt and Manfred Beyer, eds.: Ansichten der deutschen Klassik
Berlin and Weimar: Aufbau, 1981. 456 p., 12,- M
Quantitative Models and Implicit Complexity
We give new proofs of soundness (all representable functions on base types
lies in certain complexity classes) for Elementary Affine Logic, LFPL (a
language for polytime computation close to realistic functional programming
introduced by one of us), Light Affine Logic and Soft Affine Logic. The proofs
are based on a common semantical framework which is merely instantiated in four
different ways. The framework consists of an innovative modification of
realizability which allows us to use resource-bounded computations as realisers
as opposed to including all Turing computable functions as is usually the case
in realizability constructions. For example, all realisers in the model for
LFPL are polynomially bounded computations whence soundness holds by
construction of the model. The work then lies in being able to interpret all
the required constructs in the model. While being the first entirely semantical
proof of polytime soundness for light logi cs, our proof also provides a
notable simplification of the original already semantical proof of polytime
soundness for LFPL. A new result made possible by the semantic framework is the
addition of polymorphism and a modality to LFPL thus allowing for an internal
definition of inductive datatypes.Comment: 29 page
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