Electron-Polarization Coupling in Superconductor-Ferroelectric Superlattices

We present a phenomenological model of periodic ferroelectric-superconductor (FE-S) heterostructures containing two alternating ferroelectric and superconducting layers. The interaction at the FE-S contacts is described as a coupling of the local carrier density of the superconductor with the spontaneous ferroelectric polarization near the FE-S interface. We obtain a stable symmetric domain-type phase exhibiting a contact-induced polarization and the ferroelectric domain structure at temperatures above the bulk ferroelectric transition temperature. With an increasing coupling energy, we find the appearance of the ferroelectric phase coexisting with the suppressed superconductivity in the S-film. The system is analyzed for different thicknesses of the FE- and S-films demonstrating the dramatic change of the topology of the phase diagrams with a variation of the layers thickness. The results are expected to shed light on the processes occurring in high-temperature superconducting films grown on perovskite alloy-substrates exhibiting ferroelectric properties at lower temperatures.Comment: 12 pages, 8 figure

Sda full-wave analysis of boxed multistrip lines of finite thickness embedded in a layered lossy medium

Spectral-domain approach (SDA) is applied to modeling propagation characteristics of multiconductor structure on superconducting strip lines with signal strips and ground planes of finite thickness in lossy layered media. Equivalent surface impedance is used to transform the superconducting strip of finite thickness into an infinitely thin strip. A novel procedure of a calculation of the equivalent surface impedance is proposed. Two sets of basis functions (Chebyshev and Legendre polynomials) are compared by their ability to accurate modeling of microwave losses in the structure. The model applicability is illustrated by numerical results compared with experimental and simulated data

Figure of Merit and Limiting Characteristics of Tunable Ferroelectric Microwave Devices

Abstract Microwave application of ferroelectrics is very promising for electrically tunable microwave devices based on the electric field dependence of the dielectric permittivity. Tunable filters and controllable phase shifters are successfully designed as integrated circuits based on multilayer structures containing thin epitaxial ferroelectric (FE) film. As a rule lumped ferroelectric capacitors are used as the tunable components. Quality of the capacitor can be evaluated using Commutation Quality Factor (CQF). There is a unique connection between th

III kooliastme õpilaste sisemine ja väline õpimotivatsioon matemaatikas õpilaste hinnangul Raplamaa koolide näitel

http://www.ester.ee/record=b4499234*es

Paraelectric in a Strong High-Frequency Field

A change in the effective permittivity of a ferroelectric film in the paraelectric phase under the action of a strong high-frequency field (nonequilibrium soft mode heating) is considered. It is shown that this effect must be most clearly pronounced far from the resonance (\omega_0 << \omega_sm), rather than for the external field frequency \omega_0 close to the soft mode frequency \omega_sm. The effective permittivity as a function of the high-frequency field amplitude is calculated using the phenomenological approach and within the microscopic theory based on the simple model of a displacement-type ferroelectric.Comment: 3 two-column page

Game development for Android platform

Antud bakalaureusetöö eesmärgiks oli arendada mäng Android platvormile, mis võimaldaks mängijal mängimiseks kasutada tema enda muusikakollektsiooni. Mängu žanri valimisel oli kõige olulisemaks parameetriks väike konkurents, mis võimaldab mängul potentsiaalsetele ostjatele rohkem silma paista. Töös analüüsiti ning põhjendati erinevaid antud projektiga seotud tehnoloogilisi valikuid ning kirjeldati suuremaid töö käigus tekkinud probleeme ning nende lahendusi. Töö piiratud mahu tõttu oli tähelepanu keskpunktiks valitud ainult Android platvormi ning muusikamängu spetsiifilised teemad. Valminud mäng sisaldab kõiki töö käigus kirjeldatud elemente, kuid kommerts-kõlbliku tooteni jõudmiseks on vaja mängu veel viimistleda. Enne toote turule laskmist on plaanis mängust teha ka iOS versioon, mis on valitud tehnoloogiate ja disainiotsuste tõttu saavutatav suhteliselt väikese vaevaga.The purpose of this thesis was to document the development process of a game on the Android platform. The genre was deliberately chosen to service the relatively undiscovered niche of music games and to avoid competing on the overly saturated mainstream market. The thesis focuses on explaining the numerous technological choices made regarding the development platform, environment and libraries as well as describing multiple encountered problems and their solutions. Due to the limited size of the thesis most of the attention is concentrated on Android platform and music game specific issues, like thread management and onset detection. The game that was developed in the duration of this project includes all the described elements, but requires additional polish to achieve the level of quality commonly found in successful commercial mobile games

High frequency polarization switching of a thin ferroelectric film

We consider both experimentally and analytically the transient oscillatory process that arises when a rapid change in voltage is applied to a $Ba_xSr_{1-x}TiO_3$ ferroelectric thin film deposited on an $Mg0$ substrate. High frequency ($\approx 10^{8} rad/s$) polarization oscillations are observed in the ferroelectric sample. These can be understood using a simple field-polarization model. In particular we obtain analytic expressions for the oscillation frequency and the decay time of the polarization fluctuation in terms of the material parameters. These estimations agree well with the experimental results

Microwave Current Imaging in Passive HTS Components by Low-Temperature Laser Scanning Microscopy (LTLSM)

We have used the LTLSM technique for a spatially resolved investigation of the microwave transport properties, nonlinearities and material inhomogeneities in an operating coplanar waveguide YBa_2Cu_3O_{7-\delta} (YBCO) microwave resonator on an LaAlO_3 (LAO) substrate. The influence of twin-domain blocks, in-plane rotated grains, and micro-cracks in the YBCO film on the nonuniform rf current distribution were measured with a micrometer-scale spatial resolution. The impact of the peaked edge currents and rf field penetration into weak links on the linear device performance were studied as well. The LTLSM capabilities and its future potential for non-destructive characterization of the microwave properties of superconducting circuits are discussed.Comment: 8 pages, 9 figures, 2-column format, presented at High Temperature Superconductors in High Frequency Fields 2004, Journal of Superconductivity (in press