The main method of evaluation is Bessel formula.

重复性评定方法，主要是贝塞尔公式。

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Making convenience of computation, the calculation method of the spherical Bessel functions for complex arguments is presented.

为便于计算，给出了复宗量的球贝塞尔函数的计算方法。

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The losses Bessel-Gaussian beams, a kind of non-diffracting beam, propagating through a hard aperture are studied, and a general formula is derived.

对无衍射光束———贝塞尔高斯光束通过硬边光阑时的功率损耗作了研究，给出了普适的损耗公式。

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If you're looking for more technical details you'll find a link to the recently published paper titled, Dexterous manipulation of microparticles using Bessel-function acoustic pressure fields at the source.

ENGADGET

The other two methods rely on specially shaped laser beams - instead of a beam whose intensity peaks at its centre and tails off gradually, the team is investigating two alternatives: solenoid beams and Bessel beams.

BBC: Nasa examines 'tractor beams' for sample gathering

The intensity peaks within a solenoid beam are found in a spiral around the line of the beam itself, while a Bessel beam's intensity rises and falls in peaks and troughs at higher distances from the beam's line.

BBC: Nasa examines 'tractor beams' for sample gathering