250 research outputs found
Avoiding the polarization catastrophe in LaAlO3 overlayers on SrTiO3(001) through a polar distortion
A pronounced uniform polar distortion extending over several unit cells
enables thin LaAlO3 overlayers on SrTiO3(001) to counteract the charge dipole
and thereby neutralize the "polarization catastrophe" that is suggested by
simple ion-counting. This unanticipated mechanism, obtained from density
functional theory calculations, allows several unit cells of the LaAlO3
overlayer to remain insulating (hence, fully ionic). The band gap of the
system, defined by occupied O states at the surface and unoccupied Ti 3d
states at the interface in some cases 20 \AA distant, decreases with
increasing thickness of the LaAlO3-film before an insulator-to-metal transition
and a crossover to an electronic reconstruction occurs at around five
monolayers of LaAlO3.Comment: 5 pages, 4 figures, submitted for publicatio
Ferroelectric Dead Layer Driven by a Polar Interface
Based on first-principles and model calculations we investigate the effect of
polar interfaces on the ferroelectric stability of thin-film ferroelectrics. As
a representative model, we consider a TiO2-terminated BaTiO3 film with LaO
monolayers at the two interfaces that serve as doping layers. We find that the
polar interfaces create an intrinsic electric field that is screened by the
electron charge leaking into the BaTiO3 layer. The amount of the leaking charge
is controlled by the boundary conditions which are different for three
heterostructures considered, namely Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and
SrRuO3/LaO/BaTiO3/LaO. The intrinsic electric field forces ionic displacements
in BaTiO3 to produce the electric polarization directed into the interior of
the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces
that is non-switchable and thus detrimental to ferroelectricity. Our
first-principles and model calculations demonstrate that the effect is stronger
for a larger effective ionic charge at the interface and longer screening
length due to a stronger intrinsic electric field that penetrates deeper into
the ferroelectric. The predicted mechanism for a ferroelectric dead layer at
the interface controls the critical thickness for ferroelectricity in systems
with polar interfaces.Comment: 33 Pages, 5 figure
Treatment Considerations for Mandibulectomy Patients
Prosthetic rehabilitation of patients after resection of the mandible due to operation of malignant tumors usually poses a great problem. Loss of tissues and damage caused by radiotherapy cause various functional deficiencies and dysfunction in the stomatognathic system. The study concerned treatment of a group of mandibulectomy patients with problems related mainly to restoration of jaw relationship, lack of occlusion and dysfunctions. In the escamined cases immediate or delayed reconstructive surgery had been completed before prosthetics to treat mandibular discontinuity defects. Unfortunately, many of the patients exibit lack of occlusion, mandibular deviations and torque due to incorrect muscle activity.
Prosthetic management was part of a multidisciplinary approach to the problem. Treatment included myotherapy, gradual occlusal rearrangement with the use of therapeutic and corrective splints, special appliances and prostheses with leading inclined planes and guiding surfaces. The degree of success was related to the location and extent of the mandibular resection, the shape of the bone
transplants and presence or absence of natural teeth. The aims of treatment realised were the restoration of acceptable occlusion and improved functional efficiency of the masticatory system
Coexistence of Magnetic Order and Two-dimensional Superconductivity at LaAlO/SrTiO Interfaces
A two dimensional electronic system with novel electronic properties forms at
the interface between the insulators LaAlO and SrTiO. Samples
fabricated until now have been found to be either magnetic or superconducting,
depending on growth conditions. We combine transport measurements with
high-resolution magnetic torque magnetometry and report here evidence of
magnetic ordering of the two-dimensional electron liquid at the interface. The
magnetic ordering exists from well below the superconducting transition to up
to 200 K, and is characterized by an in-plane magnetic moment. Our results
suggest that there is either phase separation or coexistence between magnetic
and superconducting states. The coexistence scenario would point to an
unconventional superconducting phase in the ground state.Comment: 10 pages, 4 figure
Effects of magnetostatic coupling on stripe domain structures in magnetic multilayers with perpendicular anisotropy
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Stochastic multiple mapping conditioning for a piloted, turbulent jet diffusion flame
A stochastic implementation of the multiple mapping conditioning (MMC) approach has been applied to a turbulent jet diffusion flame (Sandia Flame D). This implementation combines the advantages of the basic concepts of a mapping closure methodology with a probability density approach. A single reference variable has been chosen. Its evolution is described by a Markov process and then mapped to the mixture fraction space. Scalar micro-mixing is modelled by a modified âinteraction by exchange with the meanâ (IEM) mixing model where the particles mix with their -in reference space- conditionally averaged means. The formulation of the closure leads to localness of mixing in mixture fraction space and consequently improved localness in composition space. Results for mixture fraction and reactive species are in good agreement with the experimental data. The MMC methodology allows for the introduction of an additional âminor dissipation time scaleâ that controls the fluctuations around the conditional mean. A sensitivity analysis based on the conditional temperature fluctuations as a function of this time scale does not endorse earlier estimates for its modelling, but only relatively large dissipation time scales of the order of the integral turbulence time scale yield acceptable levels of conditional fluctuations that agree with experiments. With the choice of a suitable dissipation time scale, MMC-IEM thus provides a simple mixing model that is capable of capturing extinction phenomena, and it gives improved predictions over conventional PDF predictions using simple IEM mixing models
Domain overlap in antiferromagnetically coupled [CoâPt]âNiOâ[CoâPt] multilayers
Metallic and Insulating Oxide Interfaces Controlled by Electronic Correlations
The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO3) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO3 matrix. Such correlation effects can lead to new functionalities in designed heterostructures
The Equilibria of DiosgeninâPhosphatidylcholine and DiosgeninâCholesterol in Monolayers at the Air/Water Interface
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