PubMed · 11753351
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Ritsert C Jansen, Jan-Peter Nap, Ludmila Mlynárová. 2002. Errors in genomics and proteomics.. https://doi.org/10.1038/nbt0102-19b
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Here we analyze the topology of the network formed by the minima and transition states on the potential energy landscape of small clusters. We find that this network has both a small-world and scale-free character. In contrast to other scale-free networks, where the topology results from the dynamics of the network growth, the potential energy landscape is a static entity. Therefore, a fundamentally different organizing principle underlies this behavior: The potential energy landscape is highly heterogeneous with the low-energy minima having large basins of attraction and acting as the highly connected hubs in the network.
We present and verify a theoretical model that predicts trapping forces (escape forces), force constants (trap stiffnesses), and trapping potential depths for dielectric spheres with diameters smaller than or equal to the wavelength of the trapping light. Optical forces can be calculated for arbitrary incident light distributions with a two-component approach that determines the gradient and the scattering force separately. We investigate the influence of spherical aberrations that are due to refractive-index mismatch on the maximum trapping force, the force constant, and the potential depth of a trap, which are important for optical tweezer applications. The relationships between the three parameters are explained and studied for different degrees of spherical aberration and various spheres (refractive indices n(s) = 1.39-1.57, radii a = 0.1-0.5 microm, lambda(0) = 1.064 microm). We find that all three parameters decrease when the distance to the coverslip increases. Effects that could make the interpretation of experimental results ambiguous are simulated and explained. Computational results are compared with the experimental data found in the literature. A good coincidence can be established.
Expressions for radiation-induced forces are presented for the case of a Rayleigh particle near the focus of a Gaussian laser beam at near-resonant conditions. Classical electromagnetic theory was used to obtain the dependence of the scattering and gradient forces on the incident laser frequency, the beam convergence angle, and the spatial position of the particle with respect to the focus. Approximative numerical analysis performed for particles with a single resonant absorption peak demonstrates the occurrence of up to 50-fold enhanced trapping forces at near-resonant frequencies. The use of this technique of gradient force enhancement may provide optical tweezers with enhanced trapping strengths and a degree of specificity.