Methods based on single-molecule localization and photophysics have brought nanoscale imaging with visible light into reach. This has enabled single-particle tracking applications for studying the dynamics of molecules and nanoparticles and contributed to the recent revolution in super-resolution localization microscopy techniques. Crucial to the optimization of such methods are the precision and accuracy with which single fluorophores and nanoparticles can be localized. We present a lucid synthesis of the developments on this localization precision and accuracy and their practical implications in order to guide the increasing number of researchers using single-particle tracking and super-resolution localization microscopy.

Precisely and accurately localizing single emitters in fluorescence microscopy

Optical microscopy has for centuries been a key tool to study living cells with minimum invasiveness The advent of single molecule techniques over the past two decades has revolutionized the field of cell biology by providing a more quantitative picture of the complex and highly dynamic organization of living systems Amongst these techniques, single particle tracking (SPT) has emerged as a powerful approach to study a variety of dynamic processes in life sciences SPT provides access to single molecule behavior in the natural context of living cells, thereby allowing a complete statistical characterization of the system under study In this review we describe the foundations of SPT together with novel optical implementations that nowadays allow the investigation of single molecule dynamic events with increasingly high spatiotemporal resolution using molecular densities closer to physiological expression levels We outline some of the algorithms for the faithful reconstruction of SPT trajectories as well as data analysis, and highlight biological examples where the technique has provided novel insights into the role of diffusion regulating cellular function The last part of the review concentrates on different theoretical models that describe anomalous transport behavior and ergodicity breaking observed from SPT studies in living cells

https://iopscience.iop.org/article/10.1088/0034-4885/78/12/124601/pdf

A review of progress in single particle tracking: from methods to biophysical insights.

Localization is one of the key technologies in wireless sensor networks (WSNs), since it provides fundamental support for many location-aware protocols and applications. Constraints on cost and power consumption make it infeasible to equip each sensor node in the network with a global position system (GPS) unit, especially for large-scale WSNs. A promising method to localize unknown nodes is to use mobile anchor nodes (MANs), which are equipped with GPS units moving among unknown nodes and periodically broadcasting their current locations to help nearby unknown nodes with localization. A considerable body of research has addressed the mobile anchor node assisted localization (MANAL) problem. However, to the best of our knowledge, no updated surveys on MAAL reflecting recent advances in the field have been presented in the past few years. This survey presents a review of the most successful MANAL algorithms, focusing on the achievements made in the past decade, and aims to become a starting point for researchers who are initiating their endeavors in MANAL research field. In addition, we seek to present a comprehensive review of the recent breakthroughs in the field, providing links to the most interesting and successful advances in this research field.

/pdf/a-survey-on-mobile-anchor-node-assisted-localization-in-cye1ebv78f.pdf

A Survey on Mobile Anchor Node Assisted Localization in Wireless Sensor Networks

A stochastic non-line-of-sight (NLOS) ultraviolet (UV) communication channel model is developed using a Monte Carlo simulation method based on photon tracing. The expected channel impulse response is obtained by computing photon arrival probabilities and associated propagation delay at the receiver. This method captures the multiple scattering effects of UV signal propagation in the atmosphere, and relaxes the assumptions of single scattering theory. The proposed model has a clear advantage in reliable prediction of NLOS path loss, as validated by outdoor experiments at small to medium elevation angles. A Gamma function is shown to agree well with the predicted impulse response, and this provides a simple means to determine the channel bandwidth. The developed model is employed to study the characteristics of NLOS UV scattering channels, including path loss and channel bandwidth, for a variety of scattering conditions, source wavelength, transmitter and receiver optical pointing geometries, and range.

Modeling of non-line-of-sight ultraviolet scattering channels for communication

Liquid crystals are nowadays widely used in all types of display applications. However their unique electro-optic properties also make them a suitable material for nondisplay applications. We will focus on the use of liquid crystals in different photonic components: optical filters and switches, beam-steering devices, spatial light modulators, integrated devices based on optical waveguiding, lasers, and optical nonlinear components. Both the basic operating principles as well as the recent state-of-the art are discussed.

/pdf/liquid-crystal-photonic-applications-z0egwi4kfz.pdf

Liquid-crystal photonic applications

A propagation model that describes the characteristics of multiscatter radiation in atmosphere is presented. The model is based on the Monte Carlo method; each scattering process is set as an event of probability. LOWTRAN7 is used to calculate the atmospheric coefficients, and Mie theory is used to calculate the scattering characteristics of the particles. It is shown that the multiscatter model matches the single-scatter model perfectly when the scattering count is 1, and the formula for the single-scatter approximation is modified for the non-line-of-sight (NLOS) problem. It is also shown that the duration of the impulse response is about 8 μs, the proportion of single-scatter irradiance is very small, and the average scattering count is 3.85 instead of 1 when the range is close to 1 km (weather conditions, field of view, and elevation angle are given). All these characteristics are presented for what is, to our knowledge, the first time. This model is wavelength-independent; 0.254 μm is chosen as the wavelength of simulation.

Non-line-of-sight multiscatter propagation model

We have developed a calibration approach for a star tracker camera. A modified version of the least-squares iteration algorithm com- bining Kalman filter is put forward, which allows for autonomous on-orbit calibration of the star tracker camera even with nonlinear camera distor- tions. In the calibration approach, the optimal principal point and focal length are achieved at first via the modified algorithm, and then the high- order focal-plane distortions are estimated using the solution of the first step. To validate this proposed calibration approach, the real star catalog and synthetic attitude data are adopted to test its performance. The test results have demonstrated the proposed approach performs well in terms of accuracy, robustness, and performance. It can satisfy the autonomous on-orbit calibration of the star tracker camera. C 2011 Society of Photo-Optical

Autonomous on-orbit calibration of a star tracker camera

Based on the refractive beam shaping system, the transformation of a quasi-Gaussian beam into a dark hollow Gaussian beam by a phase-only liquid crystal spatial light modulator (LC-SLM) is proposed. According to the energy conservation and constant optical path principle, the phase distribution of the aspheric lens and the phase-only LC-SLM can modulate the wave-front properly to generate the hollow beam. The numerical simulation results indicate that, the dark hollow intensity distribution of the output shaped beam can be maintained well for a certain propagation distance during which the dark region will not decrease whereas the ideal hollow Gaussian beam will do. By designing the phase modulation profile, which loaded into the LC-SLM carefully, the experimental results indicate that the dark hollow intensity distribution of the output shaped beam can be maintained well even at a distance much more than 550 mm from the LC-SLM, which agree with the numerical simulation results.

Hollow Gaussian beam generated by beam shaping with phase-only liquid crystal spatial light modulator

Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the consideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of centroid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid location and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel- and 5-pixel-windows’ centroid estimation are less than 2×10−3 pixels and 2×10−4 pixels respectively.

Systematic error analysis and compensation for high accuracy star centroid estimation of star tracker

An autonomous star tracker is an opto-electronic instrument used to provide the absolute three-axis attitude of a spacecraft utilizing star observations. The precise calibration of the measurement model is crucial, as the performance of the star tracker is highly dependent on the star camera parameters. We focus on proposing a simple and available calibration approach for a star tracker with wide field of view. The star tracker measurement model is described, and a novel approach for laboratory calibration is put forward. This approach is based on a collimator, a two-dimensional adjustable plane mirror, and other ordinary instruments. The calibration procedure consists of two steps: (1) the principal point is estimated using autocollimation adjustment; and (2) the other camera parameters, mainly the principal distance and distortions, are estimated via least-squares iteration, taking into account the extrinsic parameters. To validate this proposed calibration method, simulations with synthetic data are used to quantify its performance considering the errors of the distortion model and calibration data. The theoretical analysis and simulation results indicate that the uncertainties of the measured star direction vectors are less than 4.0×10−5 rad after calibration, and this can be further improved.

Jiankun Yang

Papers

Non-line-of-sight multiscatter propagation model

Autonomous on-orbit calibration of a star tracker camera

Hollow Gaussian beam generated by beam shaping with phase-only liquid crystal spatial light modulator

Systematic error analysis and compensation for high accuracy star centroid estimation of star tracker

Novel approach for laboratory calibration of star tracker