Calibrating bead displacements in optical tweezers using acousto-optic deflectors

Displacements of optically trapped particles are often recorded using back-focal-plane interferometry. In order to calibrate the detector signals to displacements of the trapped object, several approaches are available. One often relies either on scanning a fixed bead across the waist of the laser beam or on analyzing the power spectrum of movements of the trapped bead. Here, we introduce an alternative method to perform this calibration. The method consists of very rapidly scanning the laser beam across the solvent-immersed, trapped bead using acousto-optic deflectors while recording the detector signals. It does not require any knowledge of solvent viscosity and bead diameter, and works in all types of samples, viscous or viscoelastic. Moreover, it is performed with the same bead as that used in the actual experiment. This represents marked advantages over established methods. © 2006 American Institute of Physics

JUMPING MODE ATOMIC FORCE MICROSCOPY ON GRANA MEMBRANES FROM SPINACH

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Feature-Based Textures

This paper introduces feature-based textures, a new image representation that combines features and texture samples for high-quality texture mapping. Features identify boundaries within a texture where samples change discontinuously. They can be extracted from vector graphics representations, or explicity added to raster images to improve sharpness. Texture lookups are then interpolated from samples while respecting these boundaries. We present results from a software implementation of this technique demonstrating quality, efficiency and low memory overhead

Mechanical properties of viruses

If a virus releases its genomic content prematurely, it loses its infective capability. Yet, the viral shell does need to open at a specific place and time to ensure genome delivery into a new host. Hence, the chemical and mechanical properties of capsids are carefully tuned to fulfill these constraints. Knowledge of these properties will help to elucidate the viral infectious pathway, to develop virus based therapies and to facilitate the use of viruses in nanotechnology. Here we focus on the material properties of viruses mainly based on data obtained by mechanical manipulation of single viral particles. The main tool for such experiments is the atomic force microscope (AFM) and the experimental basis of these measurements will be explained. Next, aspects of the capsid shell structure, presence of encapsidated material, capsid failure, maturation and capsid protein mutations will be discussed in relation to the viral material properties. By comparing the data of various viruses, similarities and differences in the mechanical properties will be highlighted.</p