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But there are some drawbacks as well : due to friction between the braid and the inner rubber tube , the relation between pressure , contraction and force exhibits hysteresis and other nonlinear behavior which complicates the control ( see control concept for details ) . Isolated in the test tube , these antibodies were able to block replication of a wide variety of HIV strains collected from around the world . a. Smoke tubes One of the most useful devices for qualitative measurements of airflow and direction is the smoke tube , which can help track contaminant movement and identify pressure differentials . However , since we have no idea whether this much echinacea can actually come in contact with sperm and ova when they are in the body rather than a test tube , these results may not be meaningful in real life . Light for this scan was generated by the linescan tube , which provided an 800-hertz horizontal sweep of an electron beam across a revolving phosphor drum anode . In the picture tube , a beam of electrons strikes the screen making it glow in different colors , according to the type of chemicals ( phosphors ) that coat the glass . However , two studies found no interaction between ginkgo and warfarin ( Coumadin ) ,100,141 -142 and another found no interaction with clopidogrel ( though it did find a slight interaction with the related drug cilostazol ) .150 While these findings are reassuring , prudence nonetheless indicates physician supervision before combining ginkgo with blood-thinning drugs.One study found that when high concentrations of ginkgo were placed in a test tube with hamster sperm and ova , the sperm were less able to penetrate the ova.87 However , since we have no idea whether this much ginkgo can actually come into contact with sperm and ova when they are in the body rather than a test tube , these results may not be meaningful in real life .