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Tim Wescott
Guest

Thu Jan 05, 2017 3:10 am   



It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M



--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

George Herold
Guest

Thu Jan 05, 2017 3:10 am   



On Wednesday, January 4, 2017 at 3:10:20 PM UTC-5, Tim Wescott wrote:
Quote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M


Fun!
You might like Pippard's "the physics of vibration" vol I.
https://www.abebooks.com/servlet/SearchResults?an=Pippard&cm_sp=SearchF-_-NullResults-_-Results&tn=The+physics+of+vibration

He talks about parametric oscillators (PO).
One thing I'd like to see is that there is a minimum level of
oscillation amplitude that you need before the PO can grow.
Did you see that with your pendulum?
This does lead to the curious fact that you can make a swing that is too high
to pump up. (I accidentally made such a swing in my back yard.)

Did you ever try standing on a swing and flexing your legs up and
down to pump it? (Careful, I almost broke my ass that way. It
was the only way I could get my "too tall" swing to work, without dad
pushing you.)

Finally someone needs to make a PO using the voltage coefficient
of a crappy ceramic cap. (There again there will be some threshold
level to get it started.)

Quote:



--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!


George Herold
Guest

Thu Jan 05, 2017 3:10 am   



On Wednesday, January 4, 2017 at 4:20:36 PM UTC-5, George Herold wrote:
Quote:
On Wednesday, January 4, 2017 at 3:10:20 PM UTC-5, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M

Fun!
You might like Pippard's "the physics of vibration" vol I.
https://www.abebooks.com/servlet/SearchResults?an=Pippard&cm_sp=SearchF-_-NullResults-_-Results&tn=The+physics+of+vibration

He talks about parametric oscillators (PO).
One thing I'd like to see is that there is a minimum level of
oscillation amplitude that you need before the PO can grow.
Did you see that with your pendulum?
This does lead to the curious fact that you can make a swing that is too high
to pump up. (I accidentally made such a swing in my back yard.)

Did you ever try standing on a swing and flexing your legs up and
down to pump it? (Careful, I almost broke my ass that way. It
was the only way I could get my "too tall" swing to work, without dad
pushing you.)

Finally someone needs to make a PO using the voltage coefficient
of a crappy ceramic cap. (There again there will be some threshold
level to get it started.)




--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!


Oh as far as uses of parametric oscillators, There are optical PO's
using non-linear xtals to make different colors of laser light.
(Extremely complicated beasts, I used one as a post doc, but was
not allowed to tweak it.)

George H.


Guest

Thu Jan 05, 2017 3:10 am   



George, I was (and am) allowed to tweek laser OPOs and OPAs. You missed early grey hairs, that's it.

Steve

George Herold
Guest

Thu Jan 05, 2017 4:07 am   



On Wednesday, January 4, 2017 at 5:54:39 PM UTC-5, Tim Wescott wrote:
Quote:
On Wed, 04 Jan 2017 13:20:32 -0800, George Herold wrote:

On Wednesday, January 4, 2017 at 3:10:20 PM UTC-5, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M

Fun!
You might like Pippard's "the physics of vibration" vol I.
https://www.abebooks.com/servlet/SearchResults?an=Pippard&cm_sp=SearchF-
_-NullResults-_-Results&tn=The+physics+of+vibration

He talks about parametric oscillators (PO).
One thing I'd like to see is that there is a minimum level of
oscillation amplitude that you need before the PO can grow.
Did you see that with your pendulum?

Not experimentally, but it did fall out of the math. I didn't manage to
beat the math into the ground (it, OTOH, did a number on me), but I did
get as far as proving to my own satisfaction that bouncing the pivot up
and down subtracts from the damping factor of the system in a way that's
related in some complicated way with the pendulum's effective length,
resonant frequency, period of the bouncing. The damping factor does go
down in a way that's proportional to the absolute value of the bouncing,
or the absolute value squared.

My copy of Pippard is at home.
I wanted to quote a bit out of parametric excitation. It's
got my pencil scribble of "excellent!!" at the end, so I obviously
have read it before, but forgot.
(top of page 287, I'll scan and post the whole thing,
tomorrow at work... He works out in a page that,
a_c = 2/3 *l/Q
where a_c is critcial amplitude modulation,
l is the total length, and Q the Q.)

"There is a certain critical excitation which allow the
oscillation to persist at constant amplitude. It is virtually
impossible to exhibit this in practice, but the reader is
encouraged to try, since more can be learned about the
physical processes by being frustrated than by accepting
defeat at the bidding of the printed page."

George H.

Quote:

This does lead to the curious fact that you can make a swing that is too
high to pump up. (I accidentally made such a swing in my back yard.)

Makes sense.

Did you ever try standing on a swing and flexing your legs up and down
to pump it? (Careful, I almost broke my ass that way. It was the only
way I could get my "too tall" swing to work, without dad pushing you.)

Nope. But I could see it.

Finally someone needs to make a PO using the voltage coefficient of a
crappy ceramic cap. (There again there will be some threshold level to
get it started.)

Get to it!!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!


George Herold
Guest

Thu Jan 05, 2017 4:53 am   



On Wednesday, January 4, 2017 at 4:49:42 PM UTC-5, srober...@gmail.com wrote:
Quote:
George, I was (and am) allowed to tweek laser OPOs and OPAs. You missed early grey hairs, that's it.

Steve


This was in the late 90's when I was at Vanderbilt.
expensive stuff. (maybe $1M in 1999.)
I was walked through the optics chain.
(most is now a blur..)
What sticks out in my mind where these big
tilted curved gratings, where they expanded (in time)
a pretty fast pulse, compressed it,
(with something I've forgotten)
and then put it back together with the
other grating but much shorter.
non-linear optics is close to magic,
from my point of view. :^)

George H.

Tim Wescott
Guest

Thu Jan 05, 2017 5:54 am   



On Wed, 04 Jan 2017 13:20:32 -0800, George Herold wrote:

Quote:
On Wednesday, January 4, 2017 at 3:10:20 PM UTC-5, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M

Fun!
You might like Pippard's "the physics of vibration" vol I.
https://www.abebooks.com/servlet/SearchResults?an=Pippard&cm_sp=SearchF-
_-NullResults-_-Results&tn=The+physics+of+vibration

He talks about parametric oscillators (PO).
One thing I'd like to see is that there is a minimum level of
oscillation amplitude that you need before the PO can grow.
Did you see that with your pendulum?


Not experimentally, but it did fall out of the math. I didn't manage to
beat the math into the ground (it, OTOH, did a number on me), but I did
get as far as proving to my own satisfaction that bouncing the pivot up
and down subtracts from the damping factor of the system in a way that's
related in some complicated way with the pendulum's effective length,
resonant frequency, period of the bouncing. The damping factor does go
down in a way that's proportional to the absolute value of the bouncing,
or the absolute value squared.

Quote:
This does lead to the curious fact that you can make a swing that is too
high to pump up. (I accidentally made such a swing in my back yard.)


Makes sense.

Quote:
Did you ever try standing on a swing and flexing your legs up and down
to pump it? (Careful, I almost broke my ass that way. It was the only
way I could get my "too tall" swing to work, without dad pushing you.)


Nope. But I could see it.

Quote:
Finally someone needs to make a PO using the voltage coefficient of a
crappy ceramic cap. (There again there will be some threshold level to
get it started.)


Get to it!!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

Tim Wescott
Guest

Thu Jan 05, 2017 8:30 am   



On Wed, 04 Jan 2017 18:07:12 -0800, George Herold wrote:

Quote:
On Wednesday, January 4, 2017 at 5:54:39 PM UTC-5, Tim Wescott wrote:
On Wed, 04 Jan 2017 13:20:32 -0800, George Herold wrote:

On Wednesday, January 4, 2017 at 3:10:20 PM UTC-5, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M

Fun!
You might like Pippard's "the physics of vibration" vol I.
https://www.abebooks.com/servlet/SearchResults?
an=Pippard&cm_sp=SearchF-
_-NullResults-_-Results&tn=The+physics+of+vibration

He talks about parametric oscillators (PO).
One thing I'd like to see is that there is a minimum level of
oscillation amplitude that you need before the PO can grow.
Did you see that with your pendulum?

Not experimentally, but it did fall out of the math. I didn't manage
to beat the math into the ground (it, OTOH, did a number on me), but I
did get as far as proving to my own satisfaction that bouncing the
pivot up and down subtracts from the damping factor of the system in a
way that's related in some complicated way with the pendulum's
effective length, resonant frequency, period of the bouncing. The
damping factor does go down in a way that's proportional to the
absolute value of the bouncing,
or the absolute value squared.
My copy of Pippard is at home.
I wanted to quote a bit out of parametric excitation. It's got my pencil
scribble of "excellent!!" at the end, so I obviously have read it
before, but forgot.
(top of page 287, I'll scan and post the whole thing,
tomorrow at work... He works out in a page that,
a_c = 2/3 *l/Q where a_c is critcial amplitude modulation,
l is the total length, and Q the Q.)

"There is a certain critical excitation which allow the oscillation to
persist at constant amplitude. It is virtually impossible to exhibit
this in practice, but the reader is encouraged to try, since more can be
learned about the physical processes by being frustrated than by
accepting defeat at the bidding of the printed page."


Actually I found it pretty easy to get an excitation value which allows
the oscillation to persist at constant amplitude -- but the greatest
source of damping in my system is wind resistance, which goes by the
square of velocity, so the system as I implement it essentially has a
varying damping ratio.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

George Herold
Guest

Thu Jan 05, 2017 4:17 pm   



On Wednesday, January 4, 2017 at 9:58:51 PM UTC-5, Tim Wescott wrote:
Quote:
On Wed, 04 Jan 2017 18:07:12 -0800, George Herold wrote:

On Wednesday, January 4, 2017 at 5:54:39 PM UTC-5, Tim Wescott wrote:
On Wed, 04 Jan 2017 13:20:32 -0800, George Herold wrote:

On Wednesday, January 4, 2017 at 3:10:20 PM UTC-5, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M

Fun!
You might like Pippard's "the physics of vibration" vol I.
https://www.abebooks.com/servlet/SearchResults?
an=Pippard&cm_sp=SearchF-
_-NullResults-_-Results&tn=The+physics+of+vibration

He talks about parametric oscillators (PO).
One thing I'd like to see is that there is a minimum level of
oscillation amplitude that you need before the PO can grow.
Did you see that with your pendulum?

Not experimentally, but it did fall out of the math. I didn't manage
to beat the math into the ground (it, OTOH, did a number on me), but I
did get as far as proving to my own satisfaction that bouncing the
pivot up and down subtracts from the damping factor of the system in a
way that's related in some complicated way with the pendulum's
effective length, resonant frequency, period of the bouncing. The
damping factor does go down in a way that's proportional to the
absolute value of the bouncing,
or the absolute value squared.
My copy of Pippard is at home.
I wanted to quote a bit out of parametric excitation. It's got my pencil
scribble of "excellent!!" at the end, so I obviously have read it
before, but forgot.
(top of page 287, I'll scan and post the whole thing,
tomorrow at work... He works out in a page that,
a_c = 2/3 *l/Q where a_c is critcial amplitude modulation,
l is the total length, and Q the Q.)

"There is a certain critical excitation which allow the oscillation to
persist at constant amplitude. It is virtually impossible to exhibit
this in practice, but the reader is encouraged to try, since more can be
learned about the physical processes by being frustrated than by
accepting defeat at the bidding of the printed page."

Actually I found it pretty easy to get an excitation value which allows
the oscillation to persist at constant amplitude -- but the greatest
source of damping in my system is wind resistance, which goes by the
square of velocity, so the system as I implement it essentially has a
varying damping ratio.


I think what he meant was to find the excitation amplitude that just makes it
grow. Here's a scan of the first 4 pages of chapter 10.

https://www.dropbox.com/sh/wg7xje3gcemwkie/AAAkvovzOHmERgPNughVgZHja?dl=0
(Sorry I don't know how to flip the pdf's over.)

George H.
Quote:

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!



Guest

Thu Jan 05, 2017 6:10 pm   



Quote:
This was in the late 90's when I was at Vanderbilt.
expensive stuff. (maybe $1M in 1999.)

 I was walked through the optics chain.
(most is now a blur..)


Quote:
 What sticks out in my mind where these big
tilted curved gratings,
where they expanded (in time) a pretty fast pulse, compressed it,
(with something I've forgotten)
and then put it back
together with the other grating but much shorter.  
non-linear optics is close to magic,
from my point of view. :^)


A fibre-grating pulse compressor. The self-phase modulation in a holey fibre broadens the spectrum and dispersion applies a linear chirp to the output pulse, with longer wavelengths arriving first. A zigzag path between two parallelled gratings fixes the relative delays, because longer wavelengths get diffracted through larger angles, resulting in longer path delays. If you get it right, you can make transform-limited pulses.

Steve used to work for the outfit where I got my fancy tunable OPG system (Altos Photonics). Continuously tunable from 420 nm to 10 microns with a small gap near 710 nm where the OPG became degenerate. (It was pumped with a tripled YAG laser at 355 nm.)

The pump laser was much harder to keep working than the OPG! It was pretty cool, but I don't miss it.

Cheers

Phil Hobbs

George Herold
Guest

Fri Jan 06, 2017 2:53 am   



On Thursday, January 5, 2017 at 11:10:07 AM UTC-5, pcdh...@gmail.com wrote:
Quote:
This was in the late 90's when I was at Vanderbilt.
expensive stuff. (maybe $1M in 1999.)

 I was walked through the optics chain.
(most is now a blur..)

 What sticks out in my mind where these big
tilted curved gratings,
where they expanded (in time) a pretty fast pulse, compressed it,
(with something I've forgotten)
and then put it back
together with the other grating but much shorter.  
non-linear optics is close to magic,
from my point of view. :^)

A fibre-grating pulse compressor. The self-phase modulation in a holey fibre broadens the spectrum and dispersion applies a linear chirp to the output pulse, with longer wavelengths arriving first. A zigzag path between two parallelled gratings fixes the relative delays, because longer wavelengths get diffracted through larger angles, resulting in longer path delays. If you get it right, you can make transform-limited pulses.
Right, I don't remember any fiber.

Steve used to work for the outfit where I got my fancy tunable OPG system (Altos Photonics). Continuously tunable from 420 nm to 10 microns with a small gap near 710 nm where the OPG became degenerate. (It was pumped with a tripled YAG laser at 355 nm.)

Ahh, a fine skill, it's not a field I've at all kept up with.
I assume they are doing more and more with fiber these days.
Quote:

The pump laser was much harder to keep working than the OPG! It was pretty cool, but I don't miss it.

Grin, It was another staff guy at the FEL who was tasked with the
OPA/OPO.. We would hang out after work/ weekends some,
so I did hear some tales of woe. (I wasn't much of an
optics guy then... not that I'm much of an optics guy now. :^)

George H.
Quote:

Cheers

Phil Hobbs


ehsjr
Guest

Fri Jan 06, 2017 8:30 am   



On 1/4/2017 3:10 PM, Tim Wescott wrote:
Quote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M




Wonderful!
Ed

Tim Wescott
Guest

Sat Jan 07, 2017 4:38 am   



On Fri, 06 Jan 2017 00:22:28 -0500, ehsjr wrote:

Quote:
On 1/4/2017 3:10 PM, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M




Wonderful!
Ed


Thanks! I thought it was shitty.

That's not a comment on your opinion -- I often finish a talk or a book
or whatever thinking "gawd, why am I not covered in rotten vegetables?",
only to be accosted by people wanting to _thank_ me for my work.

OTOH, I can finish something up, think "hey, this is pretty good!",
inflict it on an unsuspecting world, and find out that no, in fact, it
was a steaming pile of crap (very powerful! Makes things grow!).

I've decided that I'm not a very good critic of my own work.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

Robert Baer
Guest

Sat Jan 07, 2017 3:14 pm   



Tim Wescott wrote:
Quote:
On Fri, 06 Jan 2017 00:22:28 -0500, ehsjr wrote:

On 1/4/2017 3:10 PM, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M




Wonderful!
Ed

Thanks! I thought it was shitty.

That's not a comment on your opinion -- I often finish a talk or a book
or whatever thinking "gawd, why am I not covered in rotten vegetables?",
only to be accosted by people wanting to _thank_ me for my work.

OTOH, I can finish something up, think "hey, this is pretty good!",
inflict it on an unsuspecting world, and find out that no, in fact, it
was a steaming pile of crap (very powerful! Makes things grow!).

I've decided that I'm not a very good critic of my own work.

Well, i thought that the editing done was implemented very nicely.
The resulting "jumps" or "gas" were rather smooth and only a very
professional system could improve it, along with multiple time-consuming
re-enactments for more accurate body placement and hand-motion merging.
In a word, this ain't Hollywood and we are not seasoned or
professional actors.
WELL DONE!

Tim Wescott
Guest

Sun Jan 08, 2017 2:39 am   



On Sat, 07 Jan 2017 00:14:42 -0800, Robert Baer wrote:

Quote:
Tim Wescott wrote:
On Fri, 06 Jan 2017 00:22:28 -0500, ehsjr wrote:

On 1/4/2017 3:10 PM, Tim Wescott wrote:
It's a bit off-topic from the channel, but hopefully fun.

https://www.youtube.com/watch?v=gY3ymZC6t9M




Wonderful!
Ed

Thanks! I thought it was shitty.

That's not a comment on your opinion -- I often finish a talk or a book
or whatever thinking "gawd, why am I not covered in rotten
vegetables?",
only to be accosted by people wanting to _thank_ me for my work.

OTOH, I can finish something up, think "hey, this is pretty good!",
inflict it on an unsuspecting world, and find out that no, in fact, it
was a steaming pile of crap (very powerful! Makes things grow!).

I've decided that I'm not a very good critic of my own work.

Well, i thought that the editing done was implemented very nicely.
The resulting "jumps" or "gas" were rather smooth and only a very
professional system could improve it, along with multiple time-consuming
re-enactments for more accurate body placement and hand-motion merging.
In a word, this ain't Hollywood and we are not seasoned or
professional actors.
WELL DONE!


I read somewhere, on the blog of some YouTube biggie, that if you're
doing a "talking head" video then the quality of the sound is far more
important than getting the video perfect. I also noticed that quite a
few of the "talking head" video channels that I watch will have even more
sudden visual jumps than I use, and I just don't notice them unless I
concentrate.

Everything is recorded on a Samsung Galaxy S5 cell phone, and edited
using kdenlive open-source video software. I'm pretty amazing that I can
do so well on stuff that I could get for free, or had lying around.

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

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