( This ( simply ( ( means ( that ( ( ( ( no matter ) what ) ( ( a particle ) ( 's ( size ( , ( ( shape or ) density ) ) ) ) ) ) ( , ( it ( is ( considered ( to ( have ( properties ( equivalent ( to ( ( the ( sedimentation velocity ) ) ( of ( a ( unit ( density sphere ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (DT This)) (ADVP (RB simply)) (VP (VBZ means) (SBAR (IN that) (S (SBAR (WHNP (ADVP (DT no) (NN matter)) (WP what)) (S (NP (DT a) (NN particle)) (VP (VBZ 's) (NP (NN size) (, ,) (NN shape) (CC or) (NN density))))) (, ,) (NP (PRP it)) (VP (VBZ is) (VP (VBN considered) (S (VP (TO to) (VP (VB have) (NP (NP (NNS properties)) (ADJP (JJ equivalent) (PP (TO to) (NP (NP (DT the) (NN sedimentation) (NN velocity)) (PP (IN of) (NP (DT a) (NN unit) (NN density) (NN sphere))))))))))))))) (. .)))
This simply means that no matter what a particle's size, shape or density, it is  considered to have properties equivalent to the sedimentation velocity of a unit density sphere.
(ROOT (S (NP (NP (NNP Density)) (PP (IN of) (NP (NN matter)))) (VP (VBZ reflects) (SBAR (WHADVP (WRB how) (RB closely)) (S (VP (VBD packed) (SBAR (S (NP (NP (DT the) (NNS particles)) (PP (IN of) (NP (NN matter)))) (VP (VBP are)))))))) (. .)))