Nanomedicine, Volume I: Basic Capabilities
© 1999 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999
126.96.36.199 Accelerative Onset
Aside from pure acceleration, the rate of accelerative onset -- sometimes called jolt, surge, or jerk -- can produce additional damaging effects on macroscale mechanical and biological structures. For example, the effects of accelerative onset ('a) on the human body were studied by Col. John Paul Stapp1714 in a series of aggressive rocket sled experiments conducted during the 1950s.1714-1716 For human subjects, cardiovascular shock was entirely absent for 'a >~ 500-600 g/sec but began to appear at 'a >~ 1100-1400 g/sec, at 1-40 g accelerations. Human tolerance to linear decelerative force is determined both by rate of onset and peak acceleration; the endurance limit for well-restrained healthy young males has been given as <~500 g/sec and <~50 g for >~0.2 sec durations.1717
By 1998, the effects of accelerative onset on nanomechanical structures had not been extensively studied, but similar limits might apply to nanomachines. For example, a diamond rod of length Lrod = 1 micron, cross-sectional area Srod = 0.01 micron2, mass mrod = 3.5 x 10-17 kg, and working strength Wrod ~ 5 x 1010 N/m2 (Table 9.3) fails when subjected to a static acceleration afail >~ Wrod Srod / mrod ~ 1012 g. But accelerative shocks can produce dynamic amplification in the response spectrum of elastic systems. Dynamic stress rises to a peak of roughly twice the corresponding static value when 'apeak >~ 4 nres amax for a trapezoidal pulse shape, where nres is the frequency of natural vibration of the system,363 because the stresses from the free oscillations of the system, induced by the changes in the acceleration of the system, can add to the static stresses from the acceleration, with damage done by the total stress. Taking ks ~ 1 N/m for the rod described above, then nres ~ 30 MHz (Section 188.8.131.52) and 'apeak ~ 1020 g/sec at amax ~ 1012 g. For comparison, the teragravity nanocentrifuge (Section 3.2.5) has mass m ~ 10-17 kg and is spun up to amax = 5 x 1011 g's in >~10-6 sec, giving 'a <~ 5 x 1017 g/sec << 'apeak.
Last updated on 17 February 2003