Dear Mark,

	It is not possible to simulate accurately both nano- and cm- range objects in the same model (the maximal ratio is 1 to 1e5). So I decoupled problems. 
	First in a cm-range problem the coil was simulated (you already have seen these results). I studied small 20-microns region and found that we can consider the field to be distributed linearly (please see coil_to_particle.gif attached). 

	Second the separate model of a 10-micrometer enclosure with the particle inside was simulated. The magnetic field was generated using boundary conditions. As you can see on the picture the flux density distribution closely repeats the one we get in the cm-range model (particle_enclosure.gif).


	Here we meet another difficulty. At the coil left boundary the flux density is 5 T, flux density gradient is 370 T/m 	
	 Near the particle the field changes only by 370[T/m]*100e-9[m] = 37 uT, while the flux density value is 5 T.  Again we meet the accuracy limit 5 : 37e-6 > 1e5


	So I studied the effects of flux density on the force. The field gradient value was kept the same while the flux density was changed.
Gradient: 361 T/m, flux density: 0.5 mT force: 2.2e-16 N
Gradient: 361 T/m, flux density: 5 mT force: 2.2e-15 N
Gradient: 36 T/m, flux density: 0.5 mT force: 2.0e-17 N	



Conclusions: Force depends linearly on the product of flux density and flux density gradient. There is no need to simulate nano-range models anymore (if we keep particle properties unchanged). The force can be calculated as
F = 1.2e-15* FluxDensity * Gradient [N]


At the coil boundary the force is 2e-12 N [43'000 times the particle weight]

At 1.5 cm away from the coil the flux density is 1.57 T, flux gradient is 110 T/m. The force is 2e-13 N [4'300 times the particle weight]

At 10 cm away from the coil the flux density is 0.053 T, flux gradient is 1.3 T/m. The force is 8.3e-17 N [1.8 times the particle weight]