10 April 2000 
 
Not much to excavate from my brain right now, but I thought I should keep 
track of the talks I go hear.  So I'm going to start with one I went to 
Friday and work backwards.   
 
Andrew Dienstfrey : 
Integral Representations of Lattice Sums 
 
Well, pretty much what it says.  One gets a certain sum on a lattics as 
the solution for particular PDEs with point sources, and one can take 
Taylor (or other) series expansions for certain terms that can be switched 
with certain integrals... It basically involves switching limits.  Big 
thing in applied math.   
 
Remember - everything is integration by parts and the Cauchy-Schwartz 
inequality.  And the regularity of the Lebesgue integral. 
 
 
Stefano Fusi: 
Networks of Integrate & Fire neurons (no leak) - VLSI 
 
Well, there was no leak in his neurons, but there sure was noise.  And the 
neurons weren't allowed to go below a minimum voltage (a hard 
barrier... they bounced).  Since there's inherent randomness one can look 
at the mean field approximation for firing... and the variance, etc.  And 
he hooked up a bunch of these suckers together (and cut out the noise? in 
synaptic transmission) and looked at steady-state firing rates.  Kind of 
interesting what happens when it's in a noisy regime.   
 
I still don't think I understand why all these people want to make a chip 
to simulate "real" neural networks.  Unless one simply wants to understand 
what the brain actually does, I don't think it's necessarily the most 
efficient way to make a learning system. 
 
Dan Tranchina:  
 
I can't remember the title of his talk (I deleted the email announcement), 
but it was about using a simple set of equations (or relatively simple) to 
make an approximation of the calcium currents and membrane potential of 
retinal cells - the rods and the 2nd order cells connected to them. 
 
Brian Wandell: 
Computational Neuroimaging: Color, Motion and Plasticity 
 
I'm not sure I got a bit of the plasticity bit (did he even talk about 
that?) but the main thrust was that color-information (aka the signals 
from the cones in the retina) was used in V1, the primary visual cortex, 
and MT+, a part of the brain associated with motion.  Though there is some 
tuning related to color and motion, dealing with things of different color 
seem to be moving at different speeds even when they're not, one wonders 
if the color signal in these areas is really that significant.  In any 
case, it didn't seem like people were particularly impressed with his 
conclusions. 
 
(Brr I'm freezing) 
 
And, apropos of nothing, I've been rooting around on the web because Brian 
has gotten me hooked to urbanlegends.about.com and I stumbled upon this 
lovely phrase: 
 
 Fresh meat is stored primarily in a self-propelled biounit known as a 
"pig," which is only slaughtered for major occasions. 
 
From Cecil Adams, the Straight Dope Guy, who then goes onto explain that 
this could be a factor in the popularity of Spam among Polynesians. 
 
Oh yeah, it snowed yesterday, and Stu's friend Cindy is here and I met one 
of her sister's in-laws, whose husband used to be a deacon, and I sent a 
couple pics of myself to Salon.com, and I saw a neat exhibit on Walker 
Evans and I really must say I like seeing the quilts at the Metropolitan 
Museum.  There's this really cool crazy quilt made in mourning for a young 
woman named Grace.  I want to learn how to crazy quilt.  I accidentally 
got stuck with a bag of someone else's clothes (who I know will never show 
up again (how do I diagram that?)), and I think it would be perfect to cut 
them up into scraps and make some crazy quilts.  They're colored really 
brightly.  
 
And we had an art exhibit here at Courant last Thursday & Friday.  You 
know I'll always show up for an open bar.  
 
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