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On Wed, 27 Sep 1995, Christopher M. Parrett wrote: > > The only problem becomes one of emergency gas switches. > If you deviate from the anticipated gas regiment, your Screwed Big-Time, as > the previous deco stops have now become dependant on the subsequent ones. > With the Buhlman system, previous stops are independant of each other. seeing into the future can be a curse, however, i'm all for causality. i'd say future stops depend on subsequent ones. we have one of those map/territory deals here....the computer's recommended stops aren't necessarily stops you actually did. true, iterative bubble code updates the present on an anticipated future, however, the diver still has control of when they get out of the water. in yount/hofmann's scheme for limiting ascents (dynamic critical volume hypothesis), the product of the number of growth-activated nuclei and the elimination gradients are integrated in time. deco is conducted so that the bubbles formed never exceed a critical volume. if bubble code knows you are going to make future gas switches (say O2 shallow) it relaxes your deep stops, allowing a greater number of nuclei to grow into bubbles during the first part of the ascent. because the algorithm is counting on the O2 window to help eliminate bubbles formed in aggressive early stages, you can get in trouble if you "loose" your ascent gases and only have a single *best case* table with you. the gradient for large bubbles tends to be positive on the surface--causing further growth for hours after the dive. this is the crux. the surface is one of the riskiest deco stops....just get rid of the bubbles while you are still under water where you can control bubble growth with time and pressure. i see a few solutions to the problem: -if you are doing a real-time computation (that you believe....), then you can leverage the decompression by staying deep (30ft, or so) and keeping enough bubbles at zero or negative supersaturation so that they shrink. also, for any excess population of growing nuclei and elimination gradients, you can lengthen time at stops to make the future contributions (say on the surface) of the critical-volume integral smaller. as no-one (who i know of...) has real-time capability, this is moot for now. so,...bring a set of worst-case back-up tables.... -if that doesn't work, surface, get on channel 16, yell: se-cure-itay-se-cure-itay-se-cure-itay:we have a diving emergency (details). then grab aquaCOMIX #11 and read rich pyle's article on iwr while you wait for air-evac :0, ;>. regards, em _____________________________________________________________.sig Eric Maiken email: eapg243@ea*.oa*.uc*.ed* Dept. of Physics o: 714 824-6621 U of California fax: 714 824 2175 Irvine, CA 92715-4575
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