Detector Watch S6 V2

ML1
ML1
Joined: 20 Feb 05
Posts: 347
Credit: 86,292,162
RAC: 797

RE: ... Remember if you

Message 95215 in response to message 95213

Quote:
... Remember if you stir a cup of coffee, it gets slightly warmer due to that - so the 'directed' energy of the spoon's movement dissipates as heat.


Ahhh... But for that example do you not also get an enhanced cooling effect from the increased airflow and increased evaporation over the cup due to the disturbance from stirring?... I would expect that to be more significant than the heat due to the added mechanical energy.

:-p

Regards,
Martin

See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,525
Credit: 281,531,356
RAC: 40,969

RE: RE: ... Remember if

Message 95216 in response to message 95215

Quote:
Quote:
... Remember if you stir a cup of coffee, it gets slightly warmer due to that - so the 'directed' energy of the spoon's movement dissipates as heat.

Ahhh... But for that example do you not also get an enhanced cooling effect from the increased airflow and increased evaporation over the cup due to the disturbance from stirring?... I would expect that to be more significant than the heat due to the added mechanical energy.

:-p


I reckon you're right! My bad .... :-)

It's a tremendous example that has so much physics in it. Since it would take aeons for me to boil a cold cuppa by stirring alone, them you'd deduce the thermal energies ( random molecular kinetic ) far outstrip any directed bulk motion. Suppose everyday room temperatures would give at least, say, 50+ degrees of temperature gradient b/w the coffee and surrounds ( say 350 - 300 Kelvin ). And compared to the probably ceramic cup body which has lower heat conductivity ( I can hold it comfortably by the handle and also usually around the cup body ), then the coffee/air interface is the main conduit of loss. So the stirring would be exposing warmer fluid from within the bulk to reach the top - replacing the hotter ones that left by evaporating.

Or take a windy day. The internal pressure energy of a given mass of air far exceeds it's non-random bulk movement. One can separate the motion of any particular air molecule into two components - a vector to the centre of mass of the parcel of air, and another vector from that point to the molecule. The wind is derived from centre of mass motion, the internal pressure from motion about the centre of mass. By definition/construction, motion about the centre of mass doesn't move the bulk in any specific direction. But the individual molecular speeds are much, much faster than typical wind speeds. So most of a molecule's motion doesn't translate the centre of mass very fast anywhere, as there is always another molecule going the other way of about the same speed. Even if there is no centre of mass drift the molecules are still pushing either amongst themselves or outwards at whatever contains the given mass.

[ But this depends now on what one has defined to be the 'given mass' - you'll get different answers by a different choice. In our coffee case we are actually losing any original mass from what is a volume visible to the naked eye. The most energetic ones are leaving and thus cooling - here temperature is a measure of the average kinetic energy of the molecules - and the average goes down if you trim off the high side outliers. Mind you some molecules above the surface will be entering the fluid too. It's an overall/nett thingy. ]

It's remarkably similiar to heat transport within a star. Huge convective cells drag hotter stuff up from the depths to be exposed to the 'cold' vacuum surrounds. The internal pressure energy resists what would be collapse via gravity ( for a long while anyway ) and the solar wind is the Sun evaporating!

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

ML1
ML1
Joined: 20 Feb 05
Posts: 347
Credit: 86,292,162
RAC: 797

Douglas Adams has a lot to

Message 95217 in response to message 95216

Douglas Adams has a lot to say about a really good hot cup of tea!

And Terry Pratchett likes cats... Probably because of a few ideas from Schrödinger...

And I like a really good beer.

Physics can be amazing :-)

Shame the present UK bureaucracy appears to be hell bent on destroying a lot of the current new physics :-( The UK is to withdraw from the LHC and a lot else besides?!...!...

More beer needed before further sane response...

Regards,
Martin

See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,525
Credit: 281,531,356
RAC: 40,969

Try this derivation for a

Try this derivation for a lump of gas, many molecules indexed/numbered/counted individually :

m(i) = mass of the i'th molecule
v(i) = velocity of i'th molecule with respect to co-ordinate origin
V = velocity of centre of mass of all molecules with respect to co-ordinate origin
vc(i) = velocity of i'th molecule with respect to centre of mass

then for each and every molecule :

v(i) = V + vc(i)

so with

. = ordinary number/scalar multiplication

. = dot or scalar product of vectors

| | = modulus or length of vector

Si{} = sum over all molecules using index i

then

v(i).v(i) = [ V + vc(i) ].[ V + vc(i) ]

|v(i)|^2 = |V|^2 + 2 V.vc(i) + |vc(i)|^2

and

m(i) . |v(i)|^2 = m(i) . |V|^2 + 2 . m(i) . V.vc(i) + m(i) . |vc(i)|^2

Si{m(i) . |v(i)|^2} = Si{m(i) . |V|^2} + Si{2 . m(i) . V.vc(i)} + Si{m(i) . |vc(i)|^2}

2 . Total Kinetic Energy = 2 . Kinetic Energy of Centre of Mass + 2 . Kinetic Energy Around Centre of Mass + Si{2 . m(i) . V.vc(i)}

Total Kinetic Energy = Kinetic Energy of Centre of Mass + Kinetic Energy Around Centre of Mass + Si{m(i) . V.vc(i)}

So what is the 'cross term' Si{m(i) . V.vc(i)} ?

Well a vector dot/scalar product effectively gives the ( square of the ) length of one vector's component along the line of another vector - the 'shadow' of one vector on another. Since any vector is parallel to itself then that becomes it's own length ( squared ). Hence I've used in the above :

v(i).v(i) = |v(i)|^2

and

V.V = |V|^2

and

vc(i).vc(i) = |vc(i)|^2

Now ( since the dot product is distributive and V does not depend on i )

Si{m(i) . V.vc(i)} = V . Si{m(i) . vc(i)}

The centre of mass has the property that motion ( momentum actually ) around it always sums to zero. Hence

Si{m(i) . vc(i)}

is a null vector and thus the entire cross term is zero. Thus the 'there is always another molecule going the other way of about the same speed' comment.

Astute punters may recognise this

Total Kinetic Energy = Kinetic Energy of Centre of Mass + Kinetic Energy Around Centre of Mass

as Someone's Law ( Bernoulli ? ), or conservation of energy in disguise, paraphrased as 'the sum of the pressure energies is a constant' - all other things being equal yada, yada ....

The second term on the right is usually way bigger than the first. So it's really easy for me to explode in outer space without a suit to hold my guts in ..... but it takes a fair wind to knock me down! :-)

It explains the Law of Partial Pressures - total pressure of a mix is the sum of the components separately - as I can simply choose to ( linearly ) sum over particular subsets of types of molecules. Bear in mind this derivation assumes that interaction energies, the electromagnetic potential well of one molecule affecting another, is negligible. This holds well for typical everyday situations and is deemed as the Ideal Gas limit - relatively dilute gas where the molecules spend only the briefest fractions of their existence colliding. Compared with say a metallic lattice where the atoms/ions live in each other's backyards all day.

This gives you Venturi tubes for instance - speed up the centre of mass motion and the 'static' pressure drops, thus carburetors and a host of other gadgets. Plus the lift of an aerofoil ( although there is an equivalent explanation using momenta ), hydrofoils, parachutes, spoilers and air dams generally on cars .... :-)

Now that was a nice spot of mucking about with BB code. :-)

Cheers, Mike.

( edit ) Note that choice of co-ordinate origin changes the relative magnitudes of those pressure terms. So if I'm on a space shuttle plowing into the atmosphere on re-entry, the precise air temperature on the day ( indicating motion about the centre of mass ) is not my major interest. I will be hitting a large centre of mass motion of air relative to me, at some 25000 KPH !! :-)

( edit ) I once did a back of the envelope calculation on the space shuttle deceleration from orbit - it does about 20 minutes of ( thousands of miles ) long and broad sweeping/surfing turns high over the Pacific - to yield the rate of kinetic energy dissipation by the underside tile area to get down to, say, the speed of sound. I came up with ~ 10 MegaWatts per square meter of tile! Wow, what a material!! :-) :-)

( edit ) But of course that's also why the slightest defect on the tile area is so catastrophic ... :-(

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,525
Credit: 281,531,356
RAC: 40,969

Whoops, I blotted/over-wrote

Whoops, I blotted/over-wrote the contents of Message 101390 ( hidden at present, I might be able to recover what I wrote that you replied to )!

Darn. Maybe I need a good beer.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,525
Credit: 281,531,356
RAC: 40,969

Now here's an interesting

Now here's an interesting comment from Livingston ( 21/ 12 ):

Quote:
A call from MIT regarding the trigger alert for the new radio telescope. They will be calling over the next few days to test this new system.


News to me!! If anyone knows what this refers to, please speak up. Sounds like another trigger/alert system similiar to the GRB's, but in the radio band! Another level of integration in place with 'traditional' astronomy. :-)

Also ( 22/12 ) :

Quote:
Now all frame builder computers and Infiniband switches are on UPS.


That is, the frame builders ( that construct the data segments ) and the network switches are UPS'ed. I don't know which Infiniband product/level they are using - but they are basically hotshot ( point-to-point, bi-directional, high-speed & serial ) 10 - 40 Gigabit links generally used b/w processors and storage.

On 23/12 thru 25/12 was storm/tornado time with little science mode, but probable lightning strike surge requiring replacement of an HEPI sensor ( replacement seen here being clamped externally thus bypassing the damaged module ) :

if the HEPI don't work then one can't isolate the IFO from seismic disturbances. The big blue column is one of the HEPI cradle/mounts. Rugged looking, eh? Here's a diagram on which ( I believe ) I've painted blue the corresponding blue bits in the photo. Though I don't think it refers, as a Horizontal Access Module, to precisely the same component in the above snapshot ( the Y arm ETM station ), but you get the gist :

Think of the HEPI as a most sophisticated suspension system - it's both holding up tons of weight and damping the floor movements from upsetting the beam tube and in vacuo equipment. Anyhows, after this repair and the storm subsidence the science data rate was excellent, generally over 90% apart from earthquakes and high Atlantic wave activity, and 100% for some shifts. The 'H' is for hydraulic, and is the outer of several shells of seismic/vibration protection - sort of like those Russian dolls, one inside another.

OK, here's a good laugh. Why does a directory get called '20010' for time related data? I think this is Perl, but it speaks for itself even if you don't know the language :

Quote:
[pre]hall of shame
Here's the offending code:
@timestamp = localtime(time);
$thisday = (Sun,Mon,Tue,Wed,Thu,Fri,Sat)[$timestamp[6]];
$thismonth = (Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec)[$timestamp[4]];
# Y2k stuff
# Year 2000 defined as $timestamp[5] = 100
if($timestamp[5]> 99) {
$timestamp[5] = $timestamp[5] - 100;
$thisyear = "200".$timestamp[5];
} else {
$thisyear = "19".$timestamp[5];
[/pre]


Which line(s) to correct, why hasn't it mattered 'til now, and what is/are the proper correction(s)? Answers on one foolscap side please ......

Seems someone shot at Y2K and missed ... :-) :-)

I'll be back to do Hanford.

Cheers, Mike.

( edit ) And Marty Ryba is UOTD!! :-)

( edit ) Yes, I'm pretty sure it's Perl. In which case the '$' variable name prefix indicates scalar data ( eg. a string ), '@' indicates an array of values, '()' specifies a list which is pretty much an array in this context, '.' is string concatenation, '[]' is array de-reference, and '#' is comment. [ Beware as Perl has this arcane context dependent interpretation of syntax which tends to obliterate the usual strict typing expectation/protection you get with other languages. You have to know the defaults quite well to avoid error. ]

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

AMD_is_logical
AMD_is_logical
Joined: 30 Jun 09
Posts: 4
Credit: 12,570,301
RAC: 0

OK, I'll give it a try. It

OK, I'll give it a try.

It looks like $thisyear should be set to "20", not "200". And whatever code was generating the directory name was neglecting to include a leading zero for the numbers 0 through 9. Thus, the errors canceled through 2009 (200 9) but not in 2010 (200 10).

Bikeman (Heinz-Bernd Eggenstein)
Bikeman (Heinz-...
Moderator
Joined: 28 Aug 06
Posts: 3,522
Credit: 669,875,666
RAC: 683,190

I think it's much simpler:

I think it's much simpler: The initial datastructure seems to encode years in the Gregorian calendar as nr of years since 1900 (this is not too anachronistic, JAVA does this for some library functions as well). So you don't need any Y2K handling at all! You just add 1900 to $timestamp[5] and you are set.

CU
Bikeman

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,525
Credit: 281,531,356
RAC: 40,969

As for Hanford ( from 21/12

As for Hanford ( from 21/12 and on ) :

alot of wind @ 40 mph +, but the IFO wouldn't then lock due to gain settings on some optics. These had to be adjusted/fudged to permit lock. 'Gain' refers to those numbers mentioned earlier - in the matrices - that determine how much of a response ( movement of some alignment/pointing device ) should occur with some given input ( some sensor reporting the state of the device ). The culprit, upsetting the balance of things so to speak, was a wave front sensor - number 2B, wherever that one is. From then on through to Boxing Day things were rather better, including good stretches of triple co-incidence.

[ I have this image of a pyramid of acrobats - or sheep on a motor bike as per Wallace and Gromit in A Close Shave - teetering/tottering. You have to achieve one level of stability before one can progress to something more ambitious ]

Here's some numbers that were settled upon ( adjusted numbers in grey ) :

'uRAD' is a micro radian. Radian is an angle measure, just like we have ( nautical ) miles and kilometers as different scales for the same length. We are used to a full circle having 360 degrees, in radians this is 2 * PI ( ~ 6.28 ). So one radian is about 57 degrees. Thus a micro radian is a millionth of that. 'Unit Oplev' refers to a unit of movement of the optical levers ( which I haven't really discussed yet ) in pitch and yaw directions. The smallest numbers are ( generally ) associated with movement of either ends of the 4km arms ( ITM's and ETM's ). Like a spotlight the greatest linear movement of the beam is far way, when you swivel it, as opposed to close in. So we don't want to be swinging too vigorously at one end if we want to stay centered/aligned 4km away ( MMT3, RM, and BS are all optics involved in cavities at the corner station ). Interestingly the ETM numbers are at least twice the ITM numbers, and ETMx is way more than ETMy. Whether this reflects the differences in the sensors ( input ) or the actuators ( output ) or some other factor(s) I couldn't say.

Note that when things aren't ideal, it is noted for any later analysis :

Quote:
After some discussion Corey and I decide to mark up the previous data segment from the last shift (961) with a data quality flag due to continuing non-standard detector configuration (gain setting on WFS set to 0.78).


Nice cake :

To emphasise the importance of seismic isolation here is a traffic plot :

Local time in hours on the horizontal axis, ground movement ( expressed as a speed - millionths of a meter per second ) on the vertical. You can see that it varies ~ tenfold. This plot shows the effect of truck movements to/from the Hanford ( nuclear waste ) site nearby.

[ Astute punters may be asking why we are so worried about seismic noise, in the range of a few Hz and less, when the GW signal band of LIGO interest is way higher @ ~ 50+ Hz. Quite right : we aren't especially looking for GW's in the ( sub ) Hertz band, but what if we don't achieve lock to then listen out at the higher frequencies? It's the low band noise that wobbles the IFO, plus that energy can seep ( up-convert ) into the science area. Best IFO sensitivity is around 200Hz. ]

One thing I have noticed is the level of detail/examination required, by the operators, to tease out causes -> effects within the IFO. Often the reason for a particular 'glitch', say, is not self evident so there has to be a decent amount of 'forensic' activity amongst the logs to hypothecate a mechanism. And thus hopefully a cure follows the diagnosis.

Have a think, in general or heuristic terms, what sort of overall criteria one would seek to, say, lay claim that a signal in channel_A caused or was related to a signal in channel_B? In other words, what is the reasonable 'proof' of cause and effect? Answers on one foolscap side please .....

One might be critical of this in that : why is the IFO not that well understood such that guesswork, trial & error etc is required? If anyone is thinking this then I say - get over it. This is what experimental science is all about, an almost never ending cycle/recursion to refine the physical device ( and understanding of it ) so that no stone is left unturned. This device is seriously approaching quantum limits of precision in measurement. As you can tell I'm quite chuffed to be peeking over the various shoulders in this enterprise.

Here's a neat graph :

This shows how much ground movement is predicted to occur over a 24 hour period, on account of changes in the shape of the Earth ( moon, Sun etc ... ). The vertical axis shows 'strain x 10^(+9)' or the small fraction by which lengths change over each of the arms ( in black for X, green for Y ), the total length of the arms ( common in red ), and the difference in length between the arms ( differential in blue ). The peaks are at ~ 25 so over 4km that translates to 25 x 4000 x 10^(-9) = 10^(-4) metre = 1 tenth of a millimeter both longer and shorter than the average amount. As the laser wavelength used is 1064 nm ~ 1 um then this represents ~ 100 wavelengths. Recall an earlier discussion about fringe shifts, so if this effect wasn't corrected for some 200 ( ie. both long & short side ) would be traversed each day.

Some snow fell over New Year ( we don't get much of this strange substance DownUnda so I don't know if 2 inches in a few hours is alot or a little ). If you're curious look at the log entry at '14:32:03 Fri Jan 1 2010' which has links to the 'best of' Hanford ilog entries for 2009. :-) :-)

And ( of course ) :

Quote:
Just fixed a bug whereby autoburt was trying to save to a year directory named 20010, which did not exist.


And there has been some record breaking ( Livingston over Hanford ) :

Quote:

L1 Broke H1's American Record For Longest Science Segment in S6, Twice Last Week
H1's record:
H1-937 68411 s 945308837- 945377248 2009 12/20 01:47:03 - 12/20 20:47:14 utc

L1 breaking H1's record:
L1-1320 69035 s 946040668- 946109703 2009 12/28 13:04:14 - 12/29 08:14:49 utc

L1 breaking its own record yesterday:
L1-1356 76501 s 946474590- 946551091 2010 01/02 13:36:16 - 01/03 10:51:17 utc

It's incredible how well HEPI is working at LLO. Triple coincidence has been regular for the past two weeks.


Cheers, Mike.

( edit ) One might want to think of why is it that the X arm tidal prediction at times closely matches that of the Y arm, but at other times is rather different. Also, is there any useful apparent symmetry to be gleaned from the curves? Hint : construct a vertical line intercepting the time axis at ~ + 6 hours .....

( edit ) I think the common and differential curves have a factor of two divisor. Thus common = (X + Y)/2 and diff = (X - Y)/2

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,525
Credit: 281,531,356
RAC: 40,969

Per the 'Y2K issue' I reckon

Per the 'Y2K issue' I reckon you're both right. Indeed the answer is here. So there were two errors : a bad correction of a non-problem.

As for cause & effect :

- effect(s) should come after the cause(s)

plus depending on how many distinct factors you hypothecate :

- effect is always preceded by the cause and/or

- cause always is followed by effect

but beware of the 'hidden' common factor.

[ Classic example is a child with a fever and a fit : fit -> fever ( muscular activity raising core temperature ), fever -> fit ( simple febrile convulsion, say ), fit & fever co-caused ( central nervous system infection ). So you need extra data to distinguish cases. ]

As for the tidal curves. The common mode ( red ) is symmetric about reflection in the time = 6hrs, the y-arm ( green ) becomes the x-arm ( black ) and vice versa under that same reflection. The differential mode ( blue ) is symmetric about rotation on the point strain = 0 and time = 6 hrs.

To my simple thinking this tells us that for the first part of the period shown - prior to about negative 2.5 hours - the tidal movement is along an axis more or less b/w the x and y arms, so they vary together. So that's along an East-West line at Hanford, the arms being NW and SW.

Later - after about negative 2.5 hours - the x arm changes one way while the y arm changes in the opposite sense, consistent with the 'tidal axis' - for want of a better term - slewing around to being more in line with one arm.

Hence the differential is smaller when they vary together, but is larger when they vary oppositely. In a way this is the same thing that happens upon arrival of a relativistic gravitational wave! Which is why we need to separate this tidal business out of the motions, by adjusting for it. Otherwise it will look like a gravitational wave .... when in fact it is just the slower ( non-relativistic ) motion/movements of the Moon and the Sun. :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.