148 research outputs found
Pulsed laser deposition growth of heteroepitaxial YBa2Cu3O7/La0.67Ca0.33MnO3 superlattices on NdGaO3 and Sr0.7La0.3Al0.65Ta0.35O3 substrates
Heteroepitaxial superlattices of [YBa2Cu3O7(n)/ La0.67Ca0.33MnO3(m)]x, where
n and m are the number of YBCO and LCMO monolayers and x the number of bilayer
repetitions, have been grown with pulsed laser deposition on NdGaO3 (110) and
Sr0.7La0.3Al0.65Ta0.35O3 (LSAT) (001). These substrates are well lattice
matched with YBCO and LCMO and, unlike the commonly used SrTiO3, they do not
give rise to complex and uncontrolled strain effects due to structural
transitions at low temperature. The growth dynamics and the structure have been
studied in-situ with reflection high energy electron diffraction (RHEED) and
ex-situ with scanning transmission electron microscopy (STEM), x-ray
diffraction, and neutron reflectometry. The individual layers are found to be
flat and continuous over long lateral distances with sharp and coherent
interfaces and with a well-defined thickness of the individual layer. The only
visible defects are antiphase boundaries in the YBCO layers that originate from
perovskite unit cell height steps at the interfaces with the LCMO layers. We
also find that the first YBCO monolayer at the interface with LCMO has an
unusual growth dynamics and is lacking the CuO chain layer while the subsequent
YBCO layers have the regular Y-123 structure. Accordingly, the CuO2 bilayers at
both the LCMO/YBCO and the YBCO/LCMO interfaces are lacking one of their
neighboring CuO chain layers and thus half of their hole doping reservoir.
Nevertheless, from electric transport measurements on asuperlattice with n=2 we
obtain evidence that the interfacial CuO2 bilayers remain conducting and even
exhibit the onset of a superconducting transition at very low temperature.
Finally, we show from dc magnetization and neutron reflectometry measurements
that the LCMO layers are strongly ferromagnetic
Test-Anchored Vibration Response Predictions for an Acoustically Energized Curved Orthogrid Panel with Mounted Components
A rich body of vibroacoustic test data was recently generated at Marshall Space Flight Center for a curved orthogrid panel typical of launch vehicle skin structures. Several test article configurations were produced by adding component equipment of differing weights to the flight-like vehicle panel. The test data were used to anchor computational predictions of a variety of spatially distributed responses including acceleration, strain and component interface force. Transfer functions relating the responses to the input pressure field were generated from finite element based modal solutions and test-derived damping estimates. A diffuse acoustic field model was employed to describe the assumed correlation of phased input sound pressures across the energized panel. This application demonstrates the ability to quickly and accurately predict a variety of responses to acoustically energized skin panels with mounted components. Favorable comparisons between the measured and predicted responses were established. The validated models were used to examine vibration response sensitivities to relevant modeling parameters such as pressure patch density, mesh density, weight of the mounted component and model form. Convergence metrics include spectral densities and cumulative root-mean squared (RMS) functions for acceleration, velocity, displacement, strain and interface force. Minimum frequencies for response convergence were established as well as recommendations for modeling techniques, particularly in the early stages of a component design when accurate structural vibration requirements are needed relatively quickly. The results were compared with long-established guidelines for modeling accuracy of component-loaded panels. A theoretical basis for the Response/Pressure Transfer Function (RPTF) approach provides insight into trends observed in the response predictions and confirmed in the test data. The software modules developed for the RPTF method can be easily adapted for quick replacement of the diffuse acoustic field with other pressure field models; for example a turbulent boundary layer (TBL) model suitable for vehicle ascent. Wind tunnel tests have been proposed to anchor the predictions and provide new insight into modeling approaches for this type of environment. Finally, component vibration environments for design were developed from the measured and predicted responses and compared with those derived from traditional techniques such as Barrett scaling methods for unloaded and component-loaded panels
Evidence for spin-triplet superconducting correlations in metal-oxide heterostructures with non-collinear magnetization
Heterostructures composed of ferromagnetic La0.7Sr0.3MnO3, ferromagnetic
SrRuO3, and superconducting YBa2Cu3Ox were studied experimentally. Structures
of composition Au/La0.7Sr0.3MnO3/SrRuO3/YBa2Cu3Ox were prepared by pulsed laser
deposition, and their high quality was confirmed by X-ray diffraction and
reflectometry. A non-collinear magnetic state of the heterostructures was
revealed by means of SQUID magnetometry and polarized neutron reflectometry. We
have further observed superconducting currents in mesa-structures fabricated by
deposition of a second superconducting Nb layer on top of the heterostructure,
followed by patterning with photolithography and ion-beam etching. Josephson
effects observed in these mesa-structures can be explained by the penetration
of a triplet component of the superconducting order parameter into the magnetic
layers.Comment: 10 pages, 6 figure
Depth profile of the ferromagnetic order in a YBaCuO / LaCaMnO superlattice on a LSAT substrate: a polarized neutron reflectometry study
Using polarized neutron reflectometry (PNR) we have investigated a
YBa2Cu3O7(10nm)/La2/3Ca1/3MnO3(9nm)]10 (YBCO/LCMO) superlattice grown by pulsed
laser deposition on a La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrate. Due to the
high structural quality of the superlattice and the substrate, the specular
reflectivity signal extends with a high signal-to-background ratio beyond the
fourth order superlattice Bragg peak. This allows us to obtain more detailed
and reliable information about the magnetic depth profile than in previous PNR
studies on similar superlattices that were partially impeded by problems
related to the low temperature structural transitions of the SrTiO3 substrates.
In agreement with the previous reports, our PNR data reveal a strong magnetic
proximity effect showing that the depth profile of the magnetic potential
differs significantly from the one of the nuclear potential that is given by
the YBCO and LCMO layer thickness. We present fits of the PNR data using
different simple block-like models for which either a ferromagnetic moment is
induced on the YBCO side of the interfaces or the ferromagnetic order is
suppressed on the LCMO side. We show that a good agreement with the PNR data
and with the average magnetization as obtained from dc magnetization data can
only be obtained with the latter model where a so-called depleted layer with a
strongly suppressed ferromagnetic moment develops on the LCMO side of the
interfaces. The models with an induced ferromagnetic moment on the YBCO side
fail to reproduce the details of the higher order superlattice Bragg peaks and
yield a wrong magnitude of the average magnetization. We also show that the PNR
data are still consistent with the small, ferromagnetic Cu moment of 0.25muB
that was previously identified with x-ray magnetic circular dichroism and x-ray
resonant magnetic reflectometry measurements on the same superlattice.Comment: 11 pages, 7 figure
Optimal Control of One-Qubit Gates
We consider the problem of carrying an initial Bloch vector to a final Bloch
vector in a specified amount of time under the action of three control fields
(a vector control field). We show that this control problem is solvable and
therefore it is possible to optimize the control. We choose the physically
motivated criteria of minimum energy spent in the control, minimum magnitude of
the rate of change of the control and a combination of both. We find exact
analytical solutions.Comment: 5 page
ESTUDIO ELECTROQUÍMICO DE LA ADSORCIÓN SUPERFICIAL DE FOSFATOS SOBRE MEZCLAS DE ÁCIDO POLILÁCTICO CON VIDRIO BIOACTIVO Y ÁCIDO POLILÁCTICO CON HIDROXIAPATITA
RESUMEN Se evaluó la interacción entre hidroxiapatita, vidrio bioactivo y ácido poliláctico, los cuales fueron sintetizados por métodos de precipitación acuosa, sol – gel y policondensación, respectivamente; y caracterizados mediante FTIR, DRX, DSC. Se obtuvieron probetas con diferentes porcentajes de polímero - cerámico para estudiar su capacidad de adsorber fosfatos, y de esta manera reconocer cuál de estas mezclas presenta una mejor respuesta a la oseointegración en presencia de fluido corporal simulado. Las probetas fueron sumergidas en el medio con diferentes relaciones de Ca/P y su capacidad de adsorción fue evaluada mediante EIS. Los parámetros electroquímicos obtenidos permitieron estimar los elementos resistivos y capacitivos de un circuito equivalente que relacionan los parámetros termodinámicos asociados al fenómeno de adsorción experimentado. Finalmente se determinó la cantidad de iones adsorbidos mediante AAS. Palabras clave: Biomateriales, recubrimientos, oseointegración ABSTRACT The interaction between hydroxyapatite, bioactive glass and polylactic acid was evaluated, which were synthesized by aqueous precipitation methods, sol - gel and polycondensation respectively, and they were characterized by FTIR, XRD, DSC. Samples with different percentages of polymer and ceramic were obtained to study their ability to absorb phosphate, and later to identify which of these samples of materials present a better response to osseointegration in the presence of simulated body fluid. Samples were immersed in that fluid with different relations of Ca/P and their adsorption capacity was evaluated by EIS. The electrochemical parameters obtained allowed to estimate the resistive and capacitive elements of an equivalent circuit linking the thermodynamic parameters associated with adsorption phenomena experienced. Finally, the amount of adsorbed ions was determined by AAS. Keywords: Biomaterials, coatings, osseointegration
ESTUDIO ELECTROQUÍMICO DE LA ADSORCIÓN SUPERFICIAL DE FOSFATOS SOBRE MEZCLAS DE ÁCIDO POLILÁCTICO CON VIDRIO BIOACTIVO Y ÁCIDO POLILÁCTICO CON HIDROXIAPATITA
RESUMEN Se evaluó la interacción entre hidroxiapatita, vidrio bioactivo y ácido poliláctico, los cuales fueron sintetizados por métodos de precipitación acuosa, sol – gel y policondensación, respectivamente; y caracterizados mediante FTIR, DRX, DSC. Se obtuvieron probetas con diferentes porcentajes de polímero - cerámico para estudiar su capacidad de adsorber fosfatos, y de esta manera reconocer cuál de estas mezclas presenta una mejor respuesta a la oseointegración en presencia de fluido corporal simulado. Las probetas fueron sumergidas en el medio con diferentes relaciones de Ca/P y su capacidad de adsorción fue evaluada mediante EIS. Los parámetros electroquímicos obtenidos permitieron estimar los elementos resistivos y capacitivos de un circuito equivalente que relacionan los parámetros termodinámicos asociados al fenómeno de adsorción experimentado. Finalmente se determinó la cantidad de iones adsorbidos mediante AAS. Palabras clave: Biomateriales, recubrimientos, oseointegración ABSTRACT The interaction between hydroxyapatite, bioactive glass and polylactic acid was evaluated, which were synthesized by aqueous precipitation methods, sol - gel and polycondensation respectively, and they were characterized by FTIR, XRD, DSC. Samples with different percentages of polymer and ceramic were obtained to study their ability to absorb phosphate, and later to identify which of these samples of materials present a better response to osseointegration in the presence of simulated body fluid. Samples were immersed in that fluid with different relations of Ca/P and their adsorption capacity was evaluated by EIS. The electrochemical parameters obtained allowed to estimate the resistive and capacitive elements of an equivalent circuit linking the thermodynamic parameters associated with adsorption phenomena experienced. Finally, the amount of adsorbed ions was determined by AAS. Keywords: Biomaterials, coatings, osseointegration
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