2,931 research outputs found
Physics of thin-film ferroelectric oxides
This review covers the important advances in recent years in the physics of
thin film ferroelectric oxides, the strongest emphasis being on those aspects
particular to ferroelectrics in thin film form. We introduce the current state
of development in the application of ferroelectric thin films for electronic
devices and discuss the physics relevant for the performance and failure of
these devices. Following this we cover the enormous progress that has been made
in the first principles computational approach to understanding ferroelectrics.
We then discuss in detail the important role that strain plays in determining
the properties of epitaxial thin ferroelectric films. Finally, we look at the
emerging possibilities for nanoscale ferroelectrics, with particular emphasis
on ferroelectrics in non conventional nanoscale geometries.Comment: This is an invited review for Reviews of Modern Physics. We welcome
feedback and will endeavour to incorporate comments received promptly into
the final versio
Ideal barriers to polarization reversal and domain-wall motion in strained ferroelectric thin films
The ideal intrinsic barriers to domain switching in c-phase PbTiO_3 (PTO),
PbZrO_3 (PZO), and PbZr_{1-x}Ti_xO_3 (PZT) are investigated via
first-principles computational methods. The effects of epitaxial strain on the
atomic structure, ferroelectric response, barrier to coherent domain reversal,
domain-wall energy, and barrier to domain-wall translation are studied. It is
found that PTO has a larger polarization, but smaller energy barrier to domain
reversal, than PZO. Consequentially the idealized coercive field is over two
times smaller in PTO than PZO. The Ti--O bond length is more sensitive to
strain than the other bonds in the crystals. This results in the polarization
and domain-wall energy in PTO having greater sensitivity to strain than in PZO.
Two ordered phases of PZT are considered, the rock-salt structure and a (100)
PTO/PZO superlattice. In these simple structures we find that the ferroelectric
properties do not obey Vergard's law, but instead can be approximated as an
average over individual 5-atom unit cells.Comment: 9 pages, 13 figure
Golden Creditors, Copper Rules: An Analysis of Avoidance Actions Under Section 544(b) of the Bankruptcy Code in Cases Where a Federal Creditor Holds a Claim
Section 544(b) of the Bankruptcy Code endows the trustee with the power to avoid fraudulent transfers that an unsecured creditor could have avoided under applicable law. Most states have adopted versions of the Uniform Fraudulent Conveyances Act (UFCA) or Uniform Fraudulent Transfers Act (UFTA) that impose four- or six-year statutes of limitations on private creditors seeking to unwind fraudulent transfers. Certain government creditors, however, have access to longer statutes of limitation than those available to their private counterparts. Federal creditors acting pursuant to the Federal Debt Collection Procedures Act (FDCPA) or Internal Revenue Code (IRC), for example, can avail themselves of six- or ten-year limitations periods. Courts have disagreed sharply about whether the FDCPA and IRC constitute applicable law under Section 544(b) such that a claim held by a government creditor under the fraudulent transfer provisions of those statutes could be derivatively asserted by a trustee. Particularly, some courts have argued that treating the FDCPA and/or IRC as applicable law under Section 544(b) would impermissibly modify the operation of the Bankruptcy Code, inappropriately delegate inherently sovereign powers to private parties, or produce undesirable policy outcomes. This note argues that all of these arguments are unavailing. The plain text of Section 544(b) suggests that the FDCPA and IRC constitute applicable law under the meaning of the statute; any undesirable policy results should be addressed by Congressional revision rather than by judicial intervention
Comorbidities of patients in tiotropium clinical trials : comparison with observational studies of patients with chronic obstructive pulmonary disease
Acknowledgments The authors are fully responsible for all content and editorial decisions made, were involved at all stages of manuscript development, and have approved the final version for publication. Editorial assistance, supported financially by Boehringer Ingelheim and Pfizer, was provided by Godfrey Lisk of PAREXEL International during the preparation of this manuscript. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution - Non Commercial (unported, v3.0) License. The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. Permissions beyond the scope of the License are administered by Dove Medical Press Limited.Peer reviewedPublisher PD
The MMT API: A Generic MKM System
The MMT language has been developed as a scalable representation and
interchange language for formal mathematical knowledge. It permits natural
representations of the syntax and semantics of virtually all declarative
languages while making MMT-based MKM services easy to implement. It is
foundationally unconstrained and can be instantiated with specific formal
languages.
The MMT API implements the MMT language along with multiple backends for
persistent storage and frontends for machine and user access. Moreover, it
implements a wide variety of MMT-based knowledge management services. The API
and all services are generic and can be applied to any language represented in
MMT. A plugin interface permits injecting syntactic and semantic idiosyncrasies
of individual formal languages.Comment: Conferences on Intelligent Computer Mathematics (CICM) 2013 The final
publication is available at http://link.springer.com
Hexagonal as semiconducting ferroelectrics
We use a first-principles rational-design approach to identify a
previously-unrecognized class of ferroelectric materials in the LiGaGe
structure type. We calculate structural parameters, polarization and
ferroelectric well depths both for reported and as-yet hypothetical
representatives of this class. Our results provide guidance for the
experimental realization and further investigation of high-performance
materials suitable for practical applications.Comment: 5 pages, 2 figures, 3 table
First-principles accurate total-energy surfaces for polar structural distortions of BaTiO3, PbTiO3, and SrTiO3: consequences to structural transition temperatures
Specific forms of the exchange correlation energy functionals in
first-principles density functional theory-based calculations, such as the
local density approximation (LDA) and generalized-gradient approximations
(GGA), give rise to structural lattice parameters with typical errors of -2%
and 2%. Due to a strong coupling between structure and polarization, the order
parameter of ferroelectric transitions, they result in large errors in
estimation of temperature dependent ferroelectric structural transition
properties. Here, we employ a recently developed GGA functional of Wu and Cohen
[Phys. Rev. B 73, 235116 (2006)] and determine total-energy surfaces for
zone-center distortions of BaTiO3, PbTiO3, and SrTiO3, and compare them with
the ones obtained with calculations based on standard LDA and GGA. Confirming
that the Wu and Cohen functional allows better estimation of structural
properties at 0 K, we determine a new set of parameters defining the effective
Hamiltonian for ferroelectric transition in BaTiO3. Using the new set of
parameters, we perform molecular-dynamics (MD) simulations under effective
pressures p=0.0 GPa, p=-2.0 GPa, and p=-0.005T GPa. The simulations under
p=-0.005T GPa, which is for simulating thermal expansion, show a clear
improvement in the cubic to tetragonal transition temperature and c/a parameter
of its ferroelectric tetragonal phase, while the description of transitions at
lower temperatures to orthorhombic and rhombohedral phases is marginally
improved. Our findings augur well for use of Wu-Cohen functional in studies of
ferroelectrics at nano-scale, particularly in the form of epitaxial films where
the properties depend crucially on the lattice mismatch.Comment: 10 pages, 7 figures, 3 tables, resubmitted to PR
- …