On my tour of the Livermore fusion inducing laser building, it was explained to me that when they first powered up the small scale version, they forgot that the YAG amplifiers they used were not fully depleted when amplifying the forward laser pulse, and that they were happy to amplify the laser pulse resulting from the reflection off of the pellet. Unfortunately, the laser optics were sized to handle the power as it increased in the forward direction, but in the reverse direction, the beam width was reduced, not expanded. After the bounce in the first few stages (what they thought were the “final” stages) the beam power was such as to smash all of the earlier optics. The solution was polarizing the beam (I think it was already polarized) and using Faraday rotators to stop the reverse pulse. As a side note, I asked how they aligned the pinholes used to clean up the beam. I was told there was automatic alignment — they just put in solid 1/8” aluminum plates, and the laser figured it out.
On Jun 12, 2015, at 4:22 PM, Warren D Smith <warren.wds@gmail.com> wrote:
"One way mirrors" seen in police interview rooms on TV, aren't really. Light goes both ways through them, it is just that there is a lot less light coming from one side, since it is a dark place. The other side is brightly lit; and then if you partially-silver the window the scattering and partial reflection tends to overwhelm the transmission from the dark side, making it *appear* to be a mirror from the bright side.
But our recent discussion re the "Faraday effect" being a "loophole" in the time-reversibility claims for Maxwell equations, made it occur to me: we really can make a one-way window for light. ---------------------xxx----------------------- ----light->>----A---F----B----light->>---- ---------------------xxx----------------------- let A be a polarizer, F is a faraday rotatory cell containing magnetic field (generated by cylindrical solenoid xxx surrounding F) pointed rightward, and B is another polarizer whose angle is 45 degrees to A, selected to transmit the 45-rotated linearly-polarized light from A as rotated by F (length of F and magnetic field strength selected to make the rotation angle 45).
Result: light transmits thru left-to-right, albeit halved in power since only one polarization is transmitted.
But if you try to go backward, then the Faraday F will rotate 45 degrees causing the plane-polarized light from B now to be orthogonal to A, and transmission is blocked.
Note this does not work with sugar solution doing the rotating instead of Faraday. Then the backward rotation would undo the forward rotation and transmits equally both ways. Nor would any set of dielectric, partially silvered, polarizing, rotating, etc slabs work -- by time reversibility of Maxwell equations. Faraday effect based on EXTERNALLY applied magnetic field, is crucial to make it work.
On 6/12/15, math-fun-request@mailman.xmission.com <math-fun-request@mailman.xmission.com> wrote:
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Today's Topics:
1. Re: Definition of mathematics (Adam P. Goucher) 2. Re: DIY penrose shower floor (Joerg Arndt) 3. Zimbabweans will get $5 for 175 quadrillion ? (Henry Baker) 4. Re: Zimbabweans will get $5 for 175 quadrillion ? (Charles Greathouse) 5. Re: Zimbabweans will get $5 for 175 quadrillion ? (Andy Latto)
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Message: 1 Date: Fri, 12 Jun 2015 04:37:16 +0200 From: "Adam P. Goucher" <apgoucher@gmx.com> To: math-fun@mailman.xmission.com Subject: Re: [math-fun] Definition of mathematics Message-ID: <trinity-4c2799e5-0665-4dc3-9ed1-6e896eca9c48-1434076635968@3capp-mailcom-bs07>
Content-Type: text/plain; charset=UTF-8
Gauss once said:
"Mathematics is the Queen of the Sciences"
Assuming we've defined `queen' and `science', and established uniqueness, we have a concrete definition of mathematics.
Sincerely,
Adam P. Goucher
Sent: Friday, June 12, 2015 at 2:34 AM From: "Dan Asimov" <asimov@msri.org> To: math-fun <math-fun@mailman.xmission.com> Subject: Re: [math-fun] Definition of mathematics
As a grad student, ca. 1971, I came up with
"Mathematics is the science of patterns."
?Dan
On Jun 11, 2015, at 5:13 PM, Allan Wechsler <acwacw@gmail.com> wrote:
Mathematics is the study of the formal consequences of formal rules. Even more succinctly, mathematics is the study of form.
On Thu, Jun 11, 2015 at 6:23 PM, James Propp <jamespropp@gmail.com> wrote:
A couple of weeks ago, in a gathering of mathematicians throwing out candidate definitions of mathematics, I half-seriously ventured the opinion that mathematics is the subset of philosophy consisting of those philosophical questions that actually have answers, along with the answers to those questions.
But I don't think this is original. Whom am I quoting (or paraphrasing) here?
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Message: 2 Date: Fri, 12 Jun 2015 15:46:51 +0200 From: Joerg Arndt <arndt@jjj.de> To: math-fun <math-fun@mailman.xmission.com> Subject: Re: [math-fun] DIY penrose shower floor Message-ID: <20150612134651.GA2990@jjj.de> Content-Type: text/plain; charset=us-ascii
Fantastic work!
* Dirk Lattermann <dlatt@alqualonde.de> [Jun 12. 2015 14:42]:
[...]
Yes, I already considered this. Maybe sometime, it'd be nice!
It was a major effort finding a round drain. Only square ones seem to be readily available (and affordable). When my plumber finally came around with this circular drain, it reminded me at once of the metal samples a water jet cutting company had shown me when I inquired them about cutting the tiles (very expensive, but would have saved much time and grief glueing).
For this round drain, I paid about 10 times the price of a square drain. A custom designed penrose drain plate will be expensive, and I have not figured out how it will look like when the rhombs are rather small to leave big enough bridges for stability.
We should have (laser-)cutters powerful enough for metal at our school. I'd need to know the dimensions, mostly the thickness, to be able to ask around.
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Message: 3 Date: Fri, 12 Jun 2015 08:05:48 -0700 From: Henry Baker <hbaker1@pipeline.com> To: math-fun@mailman.xmission.com Subject: [math-fun] Zimbabweans will get $5 for 175 quadrillion ? Message-ID: <E1Z3QXM-0004M0-5z@elasmtp-banded.atl.sa.earthlink.net> Content-Type: text/plain; charset="us-ascii"
FYI -- I can't tell whether "quadrillion" means 10^15 or 10^24, or whether "trillion" means 10^12 or 10^18.
Also, I couldn't tell whether the exchange was forced by an exponent overflow problem or a precision problem.
175 quadrillion requires at least 58 bits ("short scale"), so it is already beyond IEEE754 double. However, the Intel 80-bit x86 extended precision can handle up to 63 bits of precision, so the govt computers are probably running Windoze.
Now we know why there is such interest in Bitcoins.
https://en.wikipedia.org/wiki/Quadrillion
https://en.wikipedia.org/wiki/Trillion
https://news.yahoo.com/currency-dies-zimbabweans-5-175-quadrillion-local-dol...
As currency dies, Zimbabweans will get $5 for 175 quadrillion local dollars
Reuters
By MacDonald Dzirutwe 23 hours ago
A man holds up newly issued 200 million and 500 million Zimbabwe dollar notes in the capital Harare
By MacDonald Dzirutwe
HARARE (Reuters) - Zimbabweans will start exchanging 'quadrillions' of local dollars for a few U.S. dollars next week, as President Robert Mugabe's government discards its virtually worthless national currency, the central bank said on Thursday.
The southern African country started using foreign currencies like the U.S. dollar and South African rand in 2009 after the Zimbabwean dollar was ruined by hyper-inflation, which hit 500 billion percent in 2008.
At the height of Zimbabwe's economic crisis in 2008, Zimbabweans had to carry plastic bags bulging with bank notes to buy basic goods like bread and milk. Prices were rising at least twice a day.
From Monday, customers who held Zimbabwean dollar accounts before March 2009 can approach their banks to convert their Zimbabwean dollar balance into dollars, Reserve Bank of Zimbabwe (RBZ) Governor John Mangudya said in a statement.
The process will legally end the local currency. Zimbabweans have until September to turn in their old bank notes, which some people sell as souvenirs to tourists.
Bank accounts with balances of up to 175 quadrillion Zimbabwean dollars will be paid $5. Those with balances above 175 quadrillion dollars will be paid at an exchange rate of $1 to 35 quadrillion Zimbabwean dollars.
The highest - and last - bank note to be printed by the RBZ in 2008 was 100 trillion Zimbabwean dollars. It was not enough to ride a public bus to work for a week.
The RBZ said customers who still have stashes of old Zimbabwean dollar notes can walk into any bank and get $1 for every 250 trillion they hold.
That means a holder of a 100 trillion bank note will on Monday get 40 cents. The RBZ has set aside $20 million to pay Zimbabwean dollar currency holders.
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Message: 4 Date: Fri, 12 Jun 2015 11:18:22 -0400 From: Charles Greathouse <charles.greathouse@case.edu> To: math-fun <math-fun@mailman.xmission.com> Subject: Re: [math-fun] Zimbabweans will get $5 for 175 quadrillion ? Message-ID: <CAAkfSGJH-+u7nWr_2C+BYX3Ka_G+fUiQaUXFNj3zMdzoj8FoPw@mail.gmail.com> Content-Type: text/plain; charset=UTF-8
Here "quadrillion" is 10^15 (the "short scale"). I don't think the change was driven by computer issues at all, rather the need for currency stability. (It's easy enough to use "trillions of dollars" as your unit to avoid precision/overflow issues.)
Charles Greathouse Analyst/Programmer Case Western Reserve University
On Fri, Jun 12, 2015 at 11:05 AM, Henry Baker <hbaker1@pipeline.com> wrote:
FYI -- I can't tell whether "quadrillion" means 10^15 or 10^24, or whether "trillion" means 10^12 or 10^18.
Also, I couldn't tell whether the exchange was forced by an exponent overflow problem or a precision problem.
175 quadrillion requires at least 58 bits ("short scale"), so it is already beyond IEEE754 double. However, the Intel 80-bit x86 extended precision can handle up to 63 bits of precision, so the govt computers are probably running Windoze.
Now we know why there is such interest in Bitcoins.
https://en.wikipedia.org/wiki/Quadrillion
https://en.wikipedia.org/wiki/Trillion
https://news.yahoo.com/currency-dies-zimbabweans-5-175-quadrillion-local-dol...
As currency dies, Zimbabweans will get $5 for 175 quadrillion local dollars
Reuters
By MacDonald Dzirutwe 23 hours ago
A man holds up newly issued 200 million and 500 million Zimbabwe dollar notes in the capital Harare
By MacDonald Dzirutwe
HARARE (Reuters) - Zimbabweans will start exchanging 'quadrillions' of local dollars for a few U.S. dollars next week, as President Robert Mugabe's government discards its virtually worthless national currency, the central bank said on Thursday.
The southern African country started using foreign currencies like the U.S. dollar and South African rand in 2009 after the Zimbabwean dollar was ruined by hyper-inflation, which hit 500 billion percent in 2008.
At the height of Zimbabwe's economic crisis in 2008, Zimbabweans had to carry plastic bags bulging with bank notes to buy basic goods like bread and milk. Prices were rising at least twice a day.
From Monday, customers who held Zimbabwean dollar accounts before March 2009 can approach their banks to convert their Zimbabwean dollar balance into dollars, Reserve Bank of Zimbabwe (RBZ) Governor John Mangudya said in a statement.
The process will legally end the local currency. Zimbabweans have until September to turn in their old bank notes, which some people sell as souvenirs to tourists.
Bank accounts with balances of up to 175 quadrillion Zimbabwean dollars will be paid $5. Those with balances above 175 quadrillion dollars will be paid at an exchange rate of $1 to 35 quadrillion Zimbabwean dollars.
The highest - and last - bank note to be printed by the RBZ in 2008 was 100 trillion Zimbabwean dollars. It was not enough to ride a public bus to work for a week.
The RBZ said customers who still have stashes of old Zimbabwean dollar notes can walk into any bank and get $1 for every 250 trillion they hold.
That means a holder of a 100 trillion bank note will on Monday get 40 cents. The RBZ has set aside $20 million to pay Zimbabwean dollar currency holders.
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------------------------------
Message: 5 Date: Fri, 12 Jun 2015 12:11:23 -0400 From: Andy Latto <andy.latto@pobox.com> To: math-fun <math-fun@mailman.xmission.com> Subject: Re: [math-fun] Zimbabweans will get $5 for 175 quadrillion ? Message-ID: <CAKqg3U0ChRRbvnPiHZv8N-qXBHi0CQK6o47vy_ShQi_d1zL_+g@mail.gmail.com> Content-Type: text/plain; charset=UTF-8
On Fri, Jun 12, 2015 at 11:05 AM, Henry Baker <hbaker1@pipeline.com> wrote:
Bank accounts with balances of up to 175 quadrillion Zimbabwean dollars will be paid $5. Those with balances above 175 quadrillion dollars will be paid at an exchange rate of $1 to 35 quadrillion Zimbabwean dollars.
The RBZ said customers who still have stashes of old Zimbabwean dollar notes can walk into any bank and get $1 for every 250 trillion they hold.
Wonder why the physical currency is so much more valuable (less worthless?) than the bank accounts. These two exchange rates differ by a factor of 140. If you had substantial amounts of money in a Zimbabwean bank account, withdrawing it as currency (which I assume is no longer possible) would make a big difference in how many dollars you ended up with.
Andy
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