Please remind me.....

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Profile Raistmer
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Message 1448885 - Posted: 1 Dec 2013, 11:39:50 UTC - in response to Message 1448884.  

sign in dechirping

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Message 1448887 - Posted: 1 Dec 2013, 11:48:38 UTC - in response to Message 1448886.  
Last modified: 1 Dec 2013, 11:51:52 UTC

sign in dechirping


Hmm, is that a significant (scientifically speaking) difference?


Well I do vaguely recall musing over the meaning at the time. At some point it was mentioned that something like Crab nebula M1 was examined as some sortof check/calibration. I'd imagine (without having tried to visualise/look at that aspect myself) that the formulae surrounding Astropulse with a wrong sign in there might show the crab Nebula as being some negative parsecs, i.e. in the wrong direction.

Just the way I mused over the small code change at the time, rather than any solid analytical viewpoint.
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Message 1448890 - Posted: 1 Dec 2013, 12:19:08 UTC - in response to Message 1448889.  

...
I will now start banging my head against a wall, trying to beat the confusion out of my brain...


That would be a broadband repeating pulse, and probably detectable.

"Living by the wisdom of computer science doesn't sound so bad after all. And unlike most advice, it's backed up by proofs." -- Algorithms to live by: The computer science of human decisions.
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Message 1448894 - Posted: 1 Dec 2013, 12:31:15 UTC - in response to Message 1448891.  
Last modified: 1 Dec 2013, 12:33:31 UTC

...
I will now start banging my head against a wall, trying to beat the confusion out of my brain...


That would be a broadband repeating pulse, and probably detectable.


LOL



More seriously addressing your query, detections at a given dechirp (de-dispersion) are (I believe) somewhat representative of distance through interstellar space, signals being dispersed more as they travel further. So these dispersed signals, apparently, were chirping 'the other way' before... so that probably means the numbers came out [more or less right], but with a minus sign where there shouldn't have been. That's probably the kind of 'oops' you can only really spot checking some known reference, finding it unexpectedly some hundreds of lightyears behind the telescope.
"Living by the wisdom of computer science doesn't sound so bad after all. And unlike most advice, it's backed up by proofs." -- Algorithms to live by: The computer science of human decisions.
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Message 1448907 - Posted: 1 Dec 2013, 12:57:42 UTC - in response to Message 1448899.  

...
I will now start banging my head against a wall, trying to beat the confusion out of my brain...


That would be a broadband repeating pulse, and probably detectable.


LOL



More seriously addressing your query, detections at a given dechirp (de-dispersion) are (I believe) somewhat representative of distance through interstellar space, signals being dispersed more as they travel further. So these dispersed signals, apparently, were chirping 'the other way' before... so that probably means the numbers came out [more or less right], but with a minus sign where there shouldn't have been. That's probably the kind of 'oops' you can only really spot checking some known reference, finding it unexpectedly some hundreds of lightyears behind the telescope.


I hope that doesn't mean, that all the millions of AP v5.x that we've been crunching over the years, has been a total waste of time, and that they all have to be crunched again with AP v6.

Edit: And further on, does this not also apply to MB, and if so, was this issue fixed in MB v7?


Nope, remembering it's only my guesses, just means that 5.05 AP would have some numbers with minus signs where you'd expect positive numbers. Thresholds and numerics etc would be the same.

MB ? nope, only Autocorrelation's been added, and some initial attempts to aid future cross-platform and cpu-gpu match. Over the time I've been here MB has seen some search sensitivity increases, and the later autocorrelation addition... So if we did happen to run short of data I would imagine reprocessing some data might be reasonable, even if only to refine or confirm existing science database entries with improvement.

"Living by the wisdom of computer science doesn't sound so bad after all. And unlike most advice, it's backed up by proofs." -- Algorithms to live by: The computer science of human decisions.
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Message 1448999 - Posted: 1 Dec 2013, 19:27:27 UTC - in response to Message 1448899.  


More seriously addressing your query, detections at a given dechirp (de-dispersion) are (I believe) somewhat representative of distance through interstellar space, signals being dispersed more as they travel further. So these dispersed signals, apparently, were chirping 'the other way' before... so that probably means the numbers came out [more or less right], but with a minus sign where there shouldn't have been. That's probably the kind of 'oops' you can only really spot checking some known reference, finding it unexpectedly some hundreds of lightyears behind the telescope.


I hope that doesn't mean, that all the millions of AP v5.x that we've been crunching over the years, has been a total waste of time, and that they all have to be crunched again with AP v6.

As it's just the sign of the reported dm (dispersion measure), it would be easy to correct without recrunching. The point is that when an AP WU came from an observation of a known pulsar, the dm ought to be positive since that's the conventional way of expressing dispersion caused by the interstallar medium.

Astropulse v5 was probably reporting the wrong sign, but in March 2009 Josh Von Korff changed the interpretation. So Astropulse v5.05 was reporting the correct sign. The need for Astropulse v6 was because Jeff Cobb had gone through the full set of transformations from how the data is recorded at Arecibo and they had decided to flip the interpretation at the splitter. So the release of v6 was coordinated with a matching splitter change.

Edit: And further on, does this not also apply to MB, and if so, was this issue fixed in MB v7?

Because MB has less than 10 KHz of bandwidth, dispersion is neglibly small so there really isn't an issue. OTOH, there's a recent change in the database code which indicates that for NTPCker there's going to be a flip implemented under some conditions.
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Message 1449047 - Posted: 1 Dec 2013, 21:12:16 UTC

Locked as Sten has had his memory refreshed
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Message boards : Number crunching : Please remind me.....


 
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