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    A simulation study on colloid diffusion under time-varying optical potentials
    (Aip Publishing, 2023) Yucel, Harun
    With its momentum transfer, light is a primary tool for manipulating microscale objects in various research fields, including physics, chemistry, and biology. Optical force fields, also known as energy landscapes, play a crucial role in manipulating micro- and nano-sized objects, enabling the sorting of mixed micro-sized particles. This study investigates the effect of time-varying periodic optical fields created by a structured light illumination technique on the diffusion motion of micro-sized colloidal particles suspended in a liquid. A simulation code is developed to calculate the optical force acting on particles due to any time-varying optical force field. Simulations are performed to produce trajectories of particles of different sizes suspended in a liquid for different illumination patterns. The results show that the average velocities of the particles depend on the projected optical pattern parameters and that mixtures of particles of different sizes can be separated using time-varying sequential patterns, thereby improving particle separation resolution.
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    Toolbox for tracking and analyzing crowded mixture of colloidal particles
    (Elsevier, 2021) Yucel, Harun; Velu, Sabareesh K. P.
    We present a MATLAB-based multiple particle tracking (mPosTracker) algorithm to detect and track crowded colloidal particles that are two-dimensionally imaged using digital video microscopy. Our algorithm adopts three optional detection methods using threshold settings namely; centroid method (CM), radial symmetry method (RSM) and partial radial symmetry method (pRSM). In contrast to other reported algorithms, it allows classifying a maximum of three types of particles based on area or intensity. Furthermore, we include a toolbox to perform quantitative particle analysis like number density, trajectories with mean square displacement, and Voronoi cells with six-fold bond parameters to reveal the physics of examined dataset. To demonstrate the abilities of mPosTracker, we show the analysis outcomes on synthetically and experimentally acquired time-lapse microscopy datasets. mPosTracker is suitable for studying the dynamics of crowd behaviour, self-assembly, and manipulation of multi-component colloids under external fields.
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    Tracking Particle Near a Flat Surface in Digital Video Microscopy
    (Amer Inst Physics, 2019) Yucel, Harun
    Digital video microscopy (DVM) is an important tool to obtain quantitative information about underlying physics in colloidal systems. DVM, however, has the overlap problem caused by particle's diffraction pattern when the detected particles are close to contact. This overlapping problem limits the tracking methods in determining accurate particle position that reflects all interactions exerting to particles or objects in colloidal studies. The problem occurs not only between two spherical particles close to each other but also when a spherical particle is close to a rod shaped particle which have a flat surface. In this study, the simulation results on the tracking spherical particle placed near the flat surface of a rod particle in 2D digital video microscopy are reported. This work shows that the overlap problem can be resolved by using a fraction of the intensity distribution of a spherical particle which is close to a flat surface.