Browsing by Subject "Single particle tracking"
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Item Characterizing the states of yeast cytoplasm using single particle tracking(2007-08) Ibeneche, Chieze Chinenye; Florin, Ernst-LudwigThe cytoplasmic states of yeast cytoplasm have been characterized using differential interference contrast microscopy and high resolution single particle tracking. Lipid granules naturally occurring in the yeast cytoplasm have been found to diffuse anomalously in the cytoplasm. Two distinct physiological states of yeast cytoplasm were identified with corresponding [Greek small letter alpha] values of [Greek small letter alpha] = 0.66 [plus or minus] 0.1 for the fast moving state and [Greek small letter alpha] = 0.43 [plus or minus] 0.04 for the slow moving state. The generalized diffusion constant D, was identified as a new indicator for cytoplasmic state classification, while a critical value of [Greek small letter alpha] = 0.485 [plus or minus] 0.005 was determined for state transition. Fast moving granules were established as a marker for optimally grown cells, while the origin of the slow moving state was linked to cells constrained to grow under sub-optimal cold conditions.Item High-sensitivity tracking of optically trapped particles in gases and liquids : observation of Brownian motion in velocity space(2014-08) Kheifets, Simon; Raizen, Mark G.The thermal velocity fluctuations of microscopic particles mediate the transition from microscopic statistical mechanics to macroscopic long-time diffusion. Prior to this work, detection methods lacked the sensitivity necessary to resolve motion at the length and time scales at which thermal velocity fluctuations occur. This dissertation details two experiments which resulted in velocity measurement of the thermal motion of dielectric microspheres suspended by an optical trap in gases and liquids. First, optical tweezers were used to trap glass microspheres in air over a wide range of pressures and a detection system was developed to track the trapped microspheres' trajectories with MHz bandwidth and <100 fm/rt(Hz) position sensitivity. Low-noise trajectory measurements allowed for observation of fluctuations in the instantaneous velocity of a trapped particle with a signal to noise ratio (SNR) of 26 dB, and provided direct verification of the equipartition theorem and of the Maxwell-Boltzmann velocity distribution for a single Brownian particle. Next, the detection technology was further optimized and used to track optically trapped silica and barium titanate glass microspheres in water and acetone with >50 MHz bandwidth and <3 fm/rt(Hz) sensitivity. Brownian motion in a liquid is influenced by hydrodynamic, time-retarded coupling between the particle and the fluid flow its motion generates. Our measurements allowed for instantaneous velocity measurement with an SNR of up to 16 dB and confirmed the Maxwell Boltzmann distribution for Brownian motion in a liquid. The measurements also revealed several unusual features predicted for Brownian motion in the regime of hydrodynamic coupling, including faster-than-exponential decay of the velocity autocorrelation function, correlation of the thermal force and non-zero cross-correlation between the particle's velocity and the thermal force preceding it.