Browsing by Subject "Geometrical optics"

Now showing 1 - 12 of 12

Open Access
3-D motion estimation and wireframe adaptation including photometric effects for model-based coding of facial image sequences
(IEEE, 1994-06) Bozdağı, G.; Tekalp, A. M.; Onural, L.
We propose a novel formulation where 3-D global and local motion estimation and the adaptation of a generic wireframe model to a particular speaker are considered simultaneously within an optical flow based framework including the photometric effects of the motion. We use a flexible wireframe model whose local structure is characterized by the normal vectors of the patches which are related to the coordinates of the nodes. Geometrical constraints that describe the propagation of the movement of the nodes are introduced, which are then efficiently utilized to reduce the number of independent structure parameters. A stochastic relaxation algorithm has been used to determine optimum global motion estimates and the parameters describing the structure of the wireframe model. Results with both simulated and real facial image sequences are provided.
Open Access
CO2 laser polishing of microfluidic channels fabricated by femtosecond laser assisted carving
(Institute of Physics Publishing, 2016-10) Serhatlioglu, M.; Ortaç, B.; Elbuken, C.; Bıyıklı, Necmi; Solmaz, M. E.
In this study, we investigate the effects of CO2 laser polishing on microscopic structures fabricated by femtosecond laser assisted carving (FLAC). FLAC is the peripheral laser irradiation of 2.5D structures suitable for low repetition rate lasers and is first used to define the microwell structures in fused silica followed by chemical etching. Subsequently, the bottom surface of patterned microwells is irradiated with a pulsed CO2 laser. The surfaces were characterized using an atomic force microscope (AFM) and scanning electron microscope (SEM) in terms of roughness and high quality optical imaging before and after the CO2 laser treatment. The AFM measurements show that the surface roughness improves more than threefold after CO2 laser polishing, which promises good channel quality for applications that require optical imaging. In order to demonstrate the ability of this method to produce low surface roughness systems, we have fabricated a microfluidic channel. The channel is filled with polystyrene bead-laden fluid and imaged with transmission mode microscopy. The high quality optical images prove CO2 laser processing as a practical method to reduce the surface roughness of microfluidic channels fabricated by femtosecond laser irradiation. We further compared the traditional and laser-based glass micromachining approaches, which includes FLAC followed by the CO2 polishing technique.
Open Access
A color-based face tracking algorithm for enhancing interaction with mobile devices
(Springer, 2010-05) Bulbul, A.; Cipiloglu, Z.; Capin, T.
A color-based face tracking algorithm is proposed to be used as a human-computer interaction tool on mobile devices. The solution provides a natural means of interaction enabling a motion parallax effect in applications. The algorithm considers the characteristics of mobile useconstrained computational resources and varying environmental conditions. The solution is based on color comparisons and works on images gathered from the front camera of a device. In addition to color comparisons, the coherency of the facial pixels is considered in the algorithm. Several applications are also demonstrated in this work, which use the face position to determine the viewpoint in a virtual scene, or for browsing large images. The accuracy of the system is tested under different environmental conditions such as lighting and background, and the performance of the system is measured in different types of mobile devices. According to these measurements the system allows for accurate (7% RMS error) face tracking in real time (20-100 fps). © Springer-Verlag 2010.
Open Access
Effect of solvent refractive index on the surface plasmon resonance nanoparticle optical absorption
(2007) Ertas, G.; Süzer, Şefik
Optical properties of plasmon coupled silver and gold nanoparticles were studied as a function of the refractive index of the surrounding medium. Our studies confirmed that the effect of changes in the refractive index of the surrounding medium was more difficult to demonstrate from an experimental point of view, because of the very high susceptibility of nanoparticles to aggregate in aqueous and organic solvents. Whereas the position of the absorption bands of triiodide in these solvents shows a clear dependence on medium's refractive index, the surface plasmon band position of silver and gold nanoparticles do not exhibit the same dependence. This is attributed to a non-negligible interaction of these solvents with nanoparticle surfaces. Copyright © 2007 American Scientific Publishers All rights reserved.
Open Access
Homogeneous transit timing analyses of 10 exoplanet systems
(Oxford University Press, 2022-03-07) Baştürk, Ö.; Esmer, E. M.; Yalçınkaya, S.; Torun, Ş.; Mancini, L.; Helweh, Fadel El; Karamanlı, Ertuğrul; Southworth, J.; Aliş, S.; Wünsche, A.; Tezcan, F.; Aladağ, Y.; Aksaker, N.; Tunç, Ege; Davoudi, F.; Fişek, S.; Bretton, M.; Evans, D. F.; Yeşilyaprak, C.; Yılmaz, M.; Tezcan, C. T.; Yelkenci, K.
We study the transit timings of 10 exoplanets in order to investigate potential transit timing variations in them. We model their available ground-based light curves, some presented here and others taken from the literature, and homogeneously measure the mid-transit times. We statistically compare our results with published values and find that the measurement errors agree. However, in terms of recovering the possible frequencies, homogeneous sets can be found to be more useful, of which no statistically relevant example has been found for the planets in our study. We corrected the ephemeris information of all 10 planets we studied and provide these most precise light elements as references for future transit observations with space-borne and ground-based instruments. We found no evidence for secular or periodic changes in the orbital periods of the planets in our sample, including the ultra-short period WASP-103 b, whose orbit is expected to decay on an observable time-scale. Therefore, we derive the lower limits for the reduced tidal quality factors (Q) for the host stars based on best-fitting quadratic functions to their timing data. We also present a global model of all available data for WASP-74 b, which has a Gaia parallax-based distance value ∼25 per cent larger than the published value.
Open Access
Integral-equation study of ray effects and natural-mode resonances in a 2-D dielectric prism
(IEEE, 2015) Sukharevsky, İlya O.; Altıntaş, Ayhan
We analyze the interplay of two different types of electromagnetic behavior demonstrated by a 2-D dielectric prism: Geometrical Optics and resonance. As it is shown, the first is responsible, for instance, for enhanced reflection from an isosceles 90-degree prism of arbitrary epsilon and size, if illuminated from the base. The second is responsible for the peaks in the total scattering and absorption cross-sections (RCS) at the natural-mode frequencies. The numerical model is based on Nystrom discretization of Muller-type integral equations that provides guarantied convergence.
Open Access
Lens or resonator? Electromagnetic behavior of an extended hemielliptic lens for a sub-millimeter-wave receiver
(John Wiley & Sons, 2004) Boriskin, A. V.; Nosich, A. I.; Boriskina, S. V.; Benson, T. M.; Sewell, P.; Altintas, A.
The behavior of a 2D model of an extended hemielliptic silicon lens of a size typical for THz applications is accurately studied for the case of a plane E-wave illumination. The full-wave analysis of the scattering problem is based on the Mutter's boundary integral-equations (MB1E) that are uniquely solvable. A Calerkin discretization scheme with a trigonometric basis leads tu a very efficient numerical algorithm. The numerical results related to the focusability of the lens versus its rear-side extension and the angle of the plane-wave incidence, as well as near-field profiles, demonstrate strong resonances. Such effects can change the principles of optimal design of lens-based receivers.
Open Access
Magnetic resonance imaging assisted by wireless passive implantable fiducial e-markers
(Institute of Electrical and Electronics Engineers, 2017) Gokyar, S.; Alipour, A.; Unal, E.; Atalar, Ergin; Demir, Hilmi Volkan
This paper reports a wireless passive resonator architecture that is used as a fiducial electronic marker (e-marker) intended for internal marking purposes in magnetic resonance imaging (MRI). As a proof-of-concept demonstration, a class of double-layer, sub-cm helical resonators were microfabricated and tuned to the operating frequency of 123 MHz for a three T MRI system. Effects of various geometrical parameters on the resonance frequency of the e-marker were studied, and the resulting specific absorption rate (SAR) increase was analyzed using a full-wave microwave solver. The B1 + field distribution was calculated, and experimental results were compared. As an exemplary application to locate subdural electrodes, these markers were paired with subdural electrodes. It was shown that such sub-cm self-resonant e-markers with biocompatible constituents can be designed and used for implant marking, with sub-mm positioning accuracy, in MRI. In this application, a free-space quality factor ( Q -factor) of approximately 50 was achieved for the proposed resonator architecture. However, this structure caused an SAR increase in certain cases, which limits its usage for in vivo imaging practices. The findings indicate that these implantable resonators hold great promise for wireless fiducial e-marking in MRI as an alternative to multimodal imaging.
Open Access
Manipulation of backscattering from a dielectric cylinder of triangular cross-section using the interplay of go-like ray effects and resonances
(Institute of Electrical and Electronics Engineers, 2015) Sukharevsky, Ilya O.; Nosich, A. I.; Altıtaş, Ayhan
A triangular dielectric cylinder (dielectric prism) of the size, in cross-section, comparable to or moderately larger than the wavelength is a scatterer, which blends together two different types of electromagnetic behavior: geometrical optics (GO) and resonance. As shown in this paper, the first is responsible, for instance, for enhanced reflection from an isosceles 90° prism, if illuminated from the base. The second is responsible for the peaks in the total scattering and absorption cross-sections (ACSs) at the natural-mode frequencies. The numerical analysis is performed by solving the well-conditioned Muller-type boundary integral equation (IE) discretized using an algorithm with controlled accuracy.
Open Access
Modelling a janus particle activated by an optical potential
(2023-09) Rauf, Umar
The flow around a Janus particle under an optical potential is investigated. The thermal effects are majorly overlooked while studying the Janus particle although fluid heating caused by optical potential might negligible but the fluid heating caused due to Janus particle acting as a heating source is not negligible. The stream function approach is used to model the behavior of an activated Janus particle. The explicit finite difference method (FDM) is used to numerically obtain the solution. BIL-FLOW, an in-house FDM code is developed and validated for flow around a Janus particle under an optical potential. Additionally, The BIL-OP, an in-house optical module based on geometric ray approximation is developed and validated. BIL-OP utilizes linear algebra to calculate three dimensional (3D) optical force.
Open Access
Multi-SLM holographic display system with planar configuration
(IEEE, 2010) Yaraş, Fahri; Kang, Hoonjong; Onural, Levent
Holographic display system that uses six phase-only spatial light modulators (SLMs) performs holographic reconstructions from the phase-hologram of a point cloud that is extracted from 3D object. The SLMs are tiled as a three by two matrix on a virtual planar surface. The alignment is successful and the display system generates large holographic reconstructions. The proposed system can be used either to obtain reconstructions of large objects with a narrow field of view or reconstructions of smaller objects with a broader field of view. Therefore, since field of view is broader for smaller objects, observer has the flexibility to move around the reconstruction within a larger angle. This flexibility increases the motion parallax and as a consequence it increases the quality of 3D perception. Results show that even with three SLMs in horizontal direction the 3D perception is significantly increased. Experimental results are satisfactory.
Open Access
Spectrally accelerated biconjugate gradient stabilized method for scattering from and propagation over electrically large inhomogeneous geometries
(John Wiley & Sons, 2005) Babaoglu, B.; Altintas, A.; Ertürk, V. B.
Scattering from and propagation over rough-terrain profiles, as well as reentrant surfaces are investigated using an integral equation (IE)-based spectrally accelerated biconjugate gradient stabilized (SA-BiCGSTAB) method, with a storage requirement and a computational cost of O(N) per iteration, where N is the surface unknowns in the discretized IE. Numerical results in the form of current and path loss are presented and compared with previously published as well as measured results in order to assess the accuracy and efficiency of this method.