15 research outputs found
Implementation of digital detection scheme for fiber optic gyroscope
Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Science of Bilkent Univ., 2013.Thesis (Master's) -- Bilkent University, 2013.Includes bibliographical references leaves 64-67.Fiber optic gyroscope (FOG) is a kind of inertial sensor that can be used for
navigation, control and guidance of air, naval, land and space vehicles. A
FOG measures rotation rate dependent on phase difference between two counterpropagating
light waves through a rotating fiber loop. In this thesis, the main
principles of FOG such as Sagnac effect and reciprocity are described. The optical
scheme consists of a broadband light source, a coupler, a polarizer, an integrated
optic chip and a fiber coil, is developed and established.
The modulation and demodulation techniques used in FOG are also investigated
in detail. The digital detection system is built with a photodetector, a
transimpedance amplifier, a voltage amplifier and a data acquisition (DAQ) system.
A transceiver module and an FPGA processor are the components of DAQ
system. The modulation and demodulation processes are implemented by using
LabVIEW FPGA module. The program created in LabVIEW environment allows
to characterize scale factor and phase modulator parameters. Rotation rate
measurements are performed and analyzed by Allan variance method.
The impacts of different noise types to the performance of FOG are analyzed.
Angle random walk (ARW), noise component to determine short-term accuracy of
FOG, is reduced by integration of spike-free signal. We also show that we obtain
similar noise parameters even if the output power of the system is very low. It is
proven and tested that ARW is reduced by the optimization of modulation depth.
Theoretical and experimental results are quite consistent at every stages of the
work.Öğüt, SerdarM.S
Adsorption and Diffusion of Pt and Au on the Stoichiometric and Reduced TiO2 Rutile (110) Surfaces
A comparative first principles pseudopotential study of the adsorption and
migration profiles of single Pt and Au atoms on the stoichiometric and reduced
TiO2 rutile (110) surfaces is presented. Pt and Au behave similarly with
respect to (i) most favorable adsorption sites, which are found to be the
hollow and substitutional sites on the stoichiometric and reduced surfaces,
respectively, (ii) the large increase in their binding energy (by ~1.7 eV) when
the surface is reduced, and (iii) their low migration barrier near 0.15 eV on
the stoichiometric surface. Pt, on the other hand, binds more strongly (by ~2
eV) to both surfaces. On the stoichiometric surface, Pt migration pattern is
expected to be one-dimensional, which is primarily influenced by interactions
with O atoms. Au migration is expected to be two-dimensional, with Au-Ti
interactions playing a more important role. On the reduced surface, the
migration barrier for Pt diffusion is significantly larger compared to Au.Comment: 3 figures, 1 table, submitted to PR
The Electronic and Superconducting Properties of Oxygen-Ordered MgB2 compounds of the form Mg2B3Ox
Possible candidates for the Mg2B3Ox nanostructures observed in bulk of
polycrystalline MgB2 (Ref.1) have been studied using a combination of
Z-contrast imaging, electron energy loss spectroscopy (EELS) and
first-principles calculations. The electronic structures, phonon modes, and
electron phonon coupling parameters are calculated for two oxygen-ordered MgB2
compounds of composition Mg2B3O and Mg2B3O2, and compared with those of MgB2.
We find that the density of states for both Mg2B3Ox structures show very good
agreement with EELS, indicating that they are excellent candidates to explain
the observed coherent oxygen precipitates. Incorporation of oxygen reduces the
transition temperature and gives calculated TC values of 18.3 K and 1.6 K for
Mg2B3O and Mg2B3O2, respectively.Comment: Submitted to PR
Density-relaxation part of the self energy
A comment is made on the large-cluster limit of the self-energy correction for the quasiparticle energy gap in silicon clusters presented by Serdar Ogut, James R. Chelikowsky and Steven G. Louie in Phys. Rev. Lett. 79, 1770 (1997)
Ab Initio Structural Energetics of Beta-Si3N4 Surfaces
Motivated by recent electron microscopy studies on the Si3N4/rare-earth oxide
interfaces, the atomic and electronic structures of bare beta-Si3N4 surfaces
are investigated from first principles. The equilibrium shape of a Si3N4
crystal is found to have a hexagonal cross section and a faceted dome-like base
in agreement with experimental observations. The large atomic relaxations on
the prismatic planes are driven by the tendency of Si to saturate its dangling
bonds, which gives rise to resonant-bond configurations or planar sp^2-type
bonding. We predict three bare surfaces with lower energies than the open-ring
(10-10) surface observed at the interface, which indicate that
non-stoichiometry and the presence of the rare-earth oxide play crucial roles
in determining the termination of the Si3N4 matrix grains.Comment: 4 Pages, 4 Figures, 1 tabl