Trapping forces

The first tenn is tire dipole force, sometimes called tire trapping force, Fj, because it is a conservative force and can be integrated to define a trapping potential for tire atom ... 

Fig. 7. Schematic diagram of forces exerted on a cell when using an inverted microscope with (A) epi-illumination (i.e., laser focused through the objective) or (B) transillumination (i.e., laser focused through the condenser). is the axial force, and Fl is the lateral trapping force. Curved arrows represent the laser beam waist and point in the direction of light propagation.

S. B. Smith, Y. Cui, and C. Bustamante, An optical-trap force transducer that operates by direct measurement of light momentum. Methods Enzymol. 361, 134-162 (2003). 

The mobilization of a trapped phase during displacement has been the subject of extensive research (ll>24-26,28-32). These papers all dealt with the concept of viscous forces overcoming capillary trapping forces. Their results can be applied to understand the behavior seen in displacement experiments performed over a range of Ca by several researchers to study residual oil structure and saturation. As Ca increased, the maximum trapped blob size decreased, until eventually singlets were mobile. 

Fig. 12.2. Forward and backward step movement of kinesin. (a) A single kinesin molecule moving on microtubules. A kinesin molecule is attached to a bead trapped by a focused laser as a cargo for measurements, (b) Time trajectory of displacement and force of kinesin. In the laser trap measurement, when kinesin moves the trapping force or external load increases indicted, (c) Energy landscape for the forward and backward step of kinesin. The thermodynamic parameters obtained for the forward and backward step movement of kinesin are included in the figure. The rates for the forward and backward steps, fc , are related to the activation energy U and external load F,...

The isomorphism between the radiative trapping force [Eq. (109)] and the electrostatic force [Eq. (Ill)] allows to characterize the coefficient AT [Eq. (110)] in terms of an effective charge for the specification of the radiative trapping force... 

Figure 8. Comparison between traditional and nanophotonic optical trapping. Nanophotonics allows concentration of the optical energy to smaller cross sectional areas and sharper trapping forces due to the sharp gradients in the evanescent field.

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