[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Nasal passages and nasal sounds



Martin Baeker wrote:

> Although I am guilty of not having read the Science article on the nasal
> passages

For those that might fear I've been overly harsh with Stan on this
subject I'd like to clarify a couple of points.  Messages such as
Martin's which ask questions about unfamiliar work seem fine to me.
Messages criticizing unfamiliar work will rankle me.  I've been harsh
with Stan because I'm trying to send a meta-message.  The list is
about to become unmoderated again (details to follow).  If you look
over the moderation rules, you'll hopefully see that one of my major
goals in setting them up was to force people to think prior to
submitting messages.  Personally I think that deciding to become
familiar with a paper before trashing it is a no-brainer.  IMHO Stan's
infraction got worse because after he was caught with his proverbial
pants down he chose to act as though his exposure was unimportant
rather than taking the prudent course of pulling his pants back up.
Since I (and my replacement) will not be able to proactively force
people to consider their words prior to their words' dissemination,
the method I've been using with Stan will become one of the only tools
at our disposal.  If I've angered and/or caused people to feel concern
I apologize.  My motives as listowner were to promote the health of
the list -- where health is defined as the list being a forum for
*considered* discussion.

Now on to Martin:

> Why is it clear that the width of nasal passages (I hope this is the
> correct term) is strongly correlated with the metabolic rate?

Because (as Guy Leahy seemed to fail to appreciate with respect to the
implications of the following on concomitant rates of respiratory
water loss) endotherms almost by definition have to pull in oxygen at
about ten times the rate of similarly sized ectotherms.

> I always thought that birds (most of them, perhaps this is not
> true for ratites) have a higher body temperature than mammals

It's generally true that birds have higher core temperatures than
mammals, but this difference is apparently not large enough to make a
huge difference in the relative sizes of the two types of animals'
energy budgets (of course, what I really mean is that relative to the
energy budgets of ectotherms this is a "higher order term".  It's not
significant in the context of this discussion).

> The fact that all these data points fall on the same line also tells us,
> that there is a factor limiting the size of nasal passages FROM ABOVE.

My impression (as above and as clearly shown in the data I have
available to me) is that the biggest differences here are between the
two groups (ectotherm and endotherm), and that differences in size
within the groups are smaller.  That doesn't mean that within group
differences aren't important -- by analogy to relative brain sizes,
the within group differences are what is captured by the
"encephalization quotient", and many people think these differences
are very important.  However, with all due respect to complaints about
the small sample sizes in the study, if the within group variances
were large then you probably wouldn't have seen the plotted points
fall so close to the regression lines.  That's not to say that data
from all birds (or all endotherms) would fall close to the regression
line created for the paper in question.  However, thinking (without
evidence) that they *won't* all fall close to the regression line and
accusing the authors of not practicing good science as a result of
that suspicion is not kosher.  Clearly more measurements are necessary
-- no conclusions in science (or even in _Science_) are final.
However, claims that the authors weren't practicing good science seem
rather unwarranted to me (sorry; it's clear I'm still bothered by some
of what's gone through the list the past two months).

> Finally, it was stated that the correlation is clear because of the
> laws of physics; especially the hagen-Poiseulle Law.  (It states
> that the flow through a long narrow pipe is proportional to the
> fourth power of the radius).  Unfortunately, as a physicists I have
> to tell you that the laws of physics seldomly are as straightforward
> as that - usually they apply only in idealized situations.

I would agree that Terry may have overstated his case with his
reference to physical laws.  However, as a physicist, can you tell us
of any biologically relevant situation in which resistance to fluid
flow increases with increasing tube size (all other things being
equal)?

> I would be interested in the scaling of the nasal width with the
> body size.

The regression lines from the paper are:

ectotherms:   A = 0.11 M^^0.76

endotherms:   A = 0.57 M^^0.68

where A is nasal cross-sectional area in square centimeters and M is
mass in kilograms.  For those without easy access to the paper, the
most significant outliers are the horse (Equs), the giant anteater
(Myrmecophaga) and Ornithomimus.  Nasal passages of the horse look to
be about twice as large as they "should" be, those of the anteater and
Ornithomimus are about half as large as they "should" be.  (I've
probably overestimated how far off all of those points are... I'm
trying to be generous.)

Now for Della's project:

> To comment briefly on the estimation of acoustic frequencies of
> complicated air systems: The state-of-the-art method to find these
> out would be to perform a finite-element analysis, which is able to
> solve all the differential equations Dr. Rowe mentioned in his
> mail.

That's one way to go.  You might also use a transmission line matrix
approach, or (I suspect) you might use the technique of invariant
embedding.  I'm sure there are other suitable methods as well, but I
suspect you'll agree that it's not likely to be something a high
school student could do on their own.

> I would guess that students in engeneering could do this within a
> few weeks - for a school project it would probably be a bit
> ambitious.

I think even this is overly optimistic.  It seems to me like it would
be *at least* a Master's thesis.  I'm mainly curious to know what the
physicists and engineers here would have to say about whether or not
it's worth the effort.  Would the increase in accuracy -- especially
given our tenuous grasp on the physical parameters relevant to an
extinct animal -- be worth the effort of acquiring said accuracy?

Something just occurred to me that should have occurred to me
before...  There is a person at IU that might be helpful here (he
studies the mechanisms of song production in birds with some pretty
sophisticated techniques).  I'll see about contacting him and putting
him and Della in touch with each other.

--
Mickey Rowe     (mrowe@indiana.edu)