All posts by johncohn

Monday night – questions ?

November 15, 2010 johncohn

One of the weird/fun things about having been a visible face of science on TV is that I sometimes get science and math questions from people I never met.. some are simple .. others are pretty sophisticated.. some are jsut plain wierd..

Last night I got a note from a guy I; ve never met who needed help choosing between two laptops.. Ha !

My favorite came today.. I was busy ‘working’ during a conference call.. when the following window popped up in facebook .. It was from a guy named Charlie in Sydney Australia. whom I’ve never met. He has a differential equations test tomorrow.. and he needed help on a problem They were studying the Laplace transform .. and all is friends were already asleep..

Here’s the problem..

My friend wayne and I stared at it a it. got out the Laplace tables and came up with an answer .. (i think..)

I transformed

y” + 16y = f(t)
into

s^2y(s) – sy'(0) + y(0) + 16 y(s) = 0

which simplified to (when using boundry conditions of y'(0) =0 and y(0) = 1 , for the case t> pi

y(s) (s2+16) = 1

y(s) = 1/(s^2+16)

which un-transforms (i think) to

1/4 sin(4t)

for the case 0< t < pi, I inverse transformed cos(4t)

i got s^2y(s) -1 + 16y(s) = 1/(s^2 + 16)

which I think simplifies to 4sin(4t) (t/2+1)

i think we need to add constants to make the boundary conditions work out..

so maybe

1/4 sin(4t) + 1 : t> pi
4sin(4t) (t/2+1) +1 : 0 < t < pi

But that doesn’t look right..
What did I do wrong ?

I’ll go sleep on it

good luck on your test Charlie.. !

nite all , nite sam
-me

Sunday night – different corner

November 14, 2010 johncohn

Peaceful day working around the house.. not much to relate.. Last night was nice.. Friend Homer had a very nice 60th birthday party. It was a really interesting mix of 5-=60 year old proto-hippies, artists and every manor of craftsperson. .. There were actually two parties.. one upstairs with food..

and one downstairs with tools. Here’s Homer sweeping the bed of his 5 axis router… which we later used as a dance floor.

He’s a looking good at 60.. no ?

ere are many of the party goers moving the router gantry out of the way.. It took us all to move the thing.. but it saved us starting up the generator to have the computer do it. Good bonding ..

Wudn’t cha’ know my camera ran out of juice just before we sang Happy Birthday.. but I did get a picture of homers fish-shaped cake.

This morning we all took it easy.. I found myself sitting in a corner of our house that I don’t recall ever having sat in… (in 30 years.. seems unlikely).. But I looked around and saw my house from a differnt vantage.. and a different eye..

I’ll spare you pictures of cleaning the old lab.. , cleaning the new lab, cleaning the front hall, cleaning the garage, bringin in wood..

This afternoon, new friend Cole came over.. he’s doing a school project. for SBHS. a very cool computer controlled water droplet, time stopping thing …. I met Cole when his dad came out to see the Timecycle.

I liek the fact that local kids call me up to help on things like this.. .. Turns out it’s an interesting project. I helped Cole program his microcontroler and helped him get started soldering.. He’s still out there wiring.. doing a really good job, too !

Oh.. I did make some very good progress on my new tesla coil.. I finished the enclosure, cutouts and mechanical assembly. I’m now working on the internal comonent placement. With any luck, I can get it done the week after next..

So.. that’s it for the day.. and the weekend…

I do want to tell folks that a week from today we will be markign the 4th anniversary of Sam’s death. It’s a hard time of the year… yet.. everyday is still hard.. I want to let folks know that as the week goes on I may … I may what… ? .. I don’t know what to expect of myself or of the day.. It never pays to expect..

Please keep us in your hearts this week.

night all.. nite sam..
-me

Staurday eveining – to e or not to e

November 13, 2010 johncohn

I don’t know if any of you have noticed ut my keyoard has not enn making the letter
” very well for the last several days.. Oh… hmm.. that’s ” as in log, all, at , ox, oat, luster, rick , lack, rain, an, ark
as the list shows .. not having the letter ” soes NOT mean that the spell checker will flag my error… anyone reading this log regularly will recognize that spelling is not one of my strengths.. In fact.. I’m a it dyslexic. all words look funny to me.. I’m guessing the spellchecker flags aout one out of ten words i type.. .. usually I can figure out which word I mean.. ut.. sometimes.. even the list of suggestions is confusing.

Sometimes it’s fun .. I often get costumers instead of customers.. peruse for pursue,
lead before led… and I’m never sure if laid or layed will get you raised eye rows….. and if I sing my letters.. don’t e surprised.

I wonder what would happen if we all started deleting letters from our keyoard every so often.. Think of the laor we’d save.. maybe someone could write an iphone app to tell us how much our caron footprint would e reduced if we started shaving letters from the alphaet.

oh well.. est e going…
ye for now

nite all , nite sam
-me

Thursday night – Vetrans Day

November 11, 2010 johncohn

Thoughtful Veteran’s Day folks. I was listening to Pres Obama speaking from South Korea this morning. He was talking to the troops there about the sacrifices and achievements of the US Military around the world. He was specifically addressing his comments to the service men and women who were stationed on the Korean peninsula. He said that often Veterans never get to see the good that they bring about.. He told the crowd there that they were free because of the work and sacrifices of the folks who , like my dad, served in the Korean war..

That got me thinking about my dad’s service.. He was inthe Navy twoce. He signed up first time when he was 17 .. and the second when he was 19 or 20. He spent his time in a tiny rocket ship (not the space going kind 🙂 ) off the coast of japan. He used to tell us stories aout how cold and crazy it was in that little oat on that big ocean. He told us about explosions and fire fights.. and crazy partying… He still likes to tlak aout it..

I foudn these pictures I’d scanned for him for his 80th birthday.. it’s cool seeing him here. I can’t imagine what life was like for him then..