[SETI@Home] hitparade van 14 mei

vrijdag 15 mei 2009 09:01

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APClll

FP ProMod

[DPC] Team Grazzie

Seti@home

Topicstarter

Voor we verder gaan met de beschrijving van het Astropulse gebeuren, kijken we even vlug naar de stats. Het is namelijk onbeleefd om nieuwe leden te laten wachten.

Welkom Sven Decock

Welkom TDDOL

Dan gaan we nu verder met het uitleggen wat het Astropulse-project van Seti precies doet. In de vorige aflevereing hebben we diverse begrippen geintroduceerd. Vandaag gaan we verder in op de verschillende signalen die gevonden kunnen worden.

Sources of pulses
Where would a microsecond transient radio pulse come from? There are several possibilities, including:

ET: Previous searches have looked for extraterrestrial communications in the form of narrow-band signals, analogous to our own radio stations. Since we know nothing about how ET might communicate, this might be a bit closed-minded.
Pulsars and RRATs: Pulsars are rotating neutron stars that can produce signals as short as 100 microseconds, although typically much longer. 0.4 microseconds seems like a stretch. Astropulse is capable of detecting pulsars, but is unlikely to find any new ones. RRATs are a recently discovered pulsar variant. Perhaps Astropulse will discover a new type of rotating neutron star with a very short duty cycle.
Exploding primordial black holes: Martin Rees has theorized that a black hole, exploding via Hawking radiation, might produce a signal that's detectable in the radio. Click here to learn about black holes.
Extragalactic pulses: Some scientists recently saw a single transient radio pulse from far outside the Milky Way galaxy. No one knows what caused it, but perhaps there are more of them for Astropulse to find.
New phenomena: Perhaps the most likely result is that we will discover some unknown astrophysical phenomenon. Any time an astronomer looks at the sky in a new way, he or she may see a new phenomenon, whether it be a type of star, explosion, galaxy, or something else.

Dispersed pulses

As a microsecond transient radio pulse comes to us from a distant source in space, it passes through the interstellar medium (ISM). The ISM is a gas of hydrogen atoms that pervades the whole galaxy. There is one big difference between the ISM and ordinary hydrogen gas. Some of the hydrogen atoms in the ISM are ionized, meaning they have no electron attached to them. For each ionized hydrogen atom in the ISM, a free electron is floating off somewhere nearby. A substance composed of free floating, ionized particles is called a plasma.

The microsecond radio pulse is composed of many different frequencies. As the pulse passes through the ISM plasma, the high frequency radiation goes slightly faster than the lower frequency radiation.When the pulse reaches Earth, we look at the parts of the signal ranging from 1418.75 MHz to 1421.25 MHz. This is a range of 2.5 MHz. The highest frequency radiation arrives about 0.4 milliseconds to 4 milliseconds earlier than the lowest frequency radiation, depending on the distance from which the signal originates. This effect is called dispersion. Click here to see how dispersed and undispersed pulses can be composed of many different frequencies

In order to see the signal's true shape, we have to undo this dispersion. That is, we must dedisperse the signal. Dedispersion is the primary purpose of the Astropulse algorithm.

Not only does dedispersion allow us to see the true shape of the signal, it also reduces the amount of noise that interferes with the signal's visibility. Noise consists of fluctuations that produce a false signal. There could be electrical noise in the telescope, for instance, creating the illusion of a signal where there is none. Because dispersion spreads a signal out to be up to 10,000 times as long, this can cause 10,000 times as much noise to appear with the signal. (There's a square root factor due to the math, so there's really only 100 times as much noise power, but that's still a lot.)
The amount of dispersion depends on the amount of ISM plasma between the Earth and the source of the pulse. The dispersion measure (DM) tells us how much plasma there is. DM is measured in "parsecs per centimeter cubed", which is written pc cm-3. To get the DM, multiply the distance to the source of the signal (in parsecs) by the electron density in electrons per cubic centimeter. A parsec is about 3 light years. So if a source is 2 parsecs away, and the space between the Earth and that source is filled with plasma, with 3 free electrons per cubic centimeter, then that's 6 pc cm-3. The actual density of free electrons in the ISM is about 0.03 per cubic centimeter.

De volgende keer gaan we dieper in op de gebruikte algoritmes. Voor het uitgebreide verhaal is deze startpost wat aan de kleine kant
Wil je nu al het hele verhaal lezen? klik dan hier

quote: http://setiathome.berkeley.edu/tech_news.php
14 May 2009 20:40:07 UTC
We are quite preoccupied with anniversary stuff so we've been doing the bare minimum amount of systems administration to get by until after the event. Still, it should be mentioned we continue to have SATA/driver issues on our data recorder at Arecibo, and haven't collected new data for about a month now. While we have a pile of data yet to crunch readily available on disk, I started pulling up unanalyzed data from our offsite archives.

Before doing so I went through the whole data inventory rigamarole this morning. We have 1787 raw multi-beam data files (mostly all 50GB in size) archived, of which 338 haven't been split at all. However, a portion of these files were recorded before 2008, i.e. before we had a hardware radar blanking signal embedded in the data. So until we get my software radar blanker working (a project postponed until post-anniversary) we can't chew on these files without dealing with major radio frequency interference. This isn't a major problem: 1225 of the 1787 archived data files are from 2008 or later, and of these 249 have yet to be split. So we got plenty of numbers to crunch until we get the data recorder working again.

- Matt

DPC SETI@Home hitparade van 14 mei 2009


Daily Top 30
Flushers: 96 / 997 (9,6 %)
pos		daily	member	total
1.	()	25.522	Searchy! Internet Services V.O.F.	9.548.605	(4)
2.	()	21.182	[DPC]TeamGrazzie	12.792.968	(2)
3.	(1)	19.885	[DPC] hansR	15.331.285	(1)
4.	(1)	15.231	Sp@ceNv@der	11.955.921	(3)
5.	()	11.336	[DPC] Switch	9.351.095	(5)
6.	(5)	10.775	F@stmem	2.438.645	(9)
7.	()	10.564	o25o & Dharkon	4.946.876	(6)
8.	()	9.476	dr bommel	630.508	(32)
9.	()	8.712	Ensign Wildfire	3.435.251	(7)
10.	(4)	7.010	dpc_kluizenaar	682.800	(29)
11.	(10)	6.724	ray	1.387.771	(16)
12.	(37)	5.559	Quark	881.057	(26)
13.	(3)	4.819	Jan Zandvliet & x-RaY99	1.830.383	(13)
14.	(16)	4.229	Override	983.942	(23)
15.	(27)	4.213	apa	248.953	(71)
16.	(24)	3.990	Patty	32.189	(254)
17.	(20)	3.773	Hans vandebos	306.282	(63)
18.	(11)	3.766	Mr Beamer	1.947.109	(11)
19.	(1)	3.748	ZUID-CHEMIE	175.710	(95)
20.	()	3.566	Rydo	826.277	(27)
21.	(9)	2.946	[DPC]NGS	46.271	(208)
22.	(5)	2.596	muppet99	214.016	(81)
23.	(4)	2.556	[DPC] Brainy007	650.302	(31)
24.	(2)	2.541	Jox444	944.765	(24)
25.	(6)	2.496	holy-shit	615.715	(34)
26.	(20)	2.309	Asgoroth	328.567	(62)
27.	(12)	2.187	Wolfje666	71.586	(160)
28.	()	1.975	ERBrouwer	123.085	(115)
29.	(3)	1.803	HellBringer	59.784	(175)
30.	(16)	1.738	seridan	499.381	(39)
	More...


Overall Top 30
pos		total	member	daily
1.	()	15.331.285	[DPC] hansR	19.885	(3)
2.	()	12.792.968	[DPC]TeamGrazzie	21.182	(2)
3.	()	11.955.921	Sp@ceNv@der	15.231	(4)
4.	()	9.548.605	Searchy! Internet Services V.O.F.	25.522	(1)
5.	()	9.351.095	[DPC] Switch	11.336	(5)
6.	()	4.946.876	o25o & Dharkon	10.564	(7)
7.	()	3.435.251	Ensign Wildfire	8.712	(9)
8.	()	2.586.671	[DPC]Spinpoint	422	(64)
9.	()	2.438.645	F@stmem	10.775	(6)
10.	()	2.358.645	[DPC]Trancemaus	1.261	(40)
11.	()	1.947.109	Mr Beamer	3.766	(18)
12.	()	1.890.961	AmeComputers	1.288	(38)
13.	()	1.830.383	Jan Zandvliet & x-RaY99	4.819	(13)
14.	()	1.502.870	MAX3400	0	(-)
15.	()	1.502.235	[DPC]Team Zuid-Holland	715	(56)
16.	()	1.387.771	ray	6.724	(11)
17.	()	1.377.527	Tijntje	962	(54)
18.	()	1.135.713	Speedy67 & Friends	38	(91)
19.	()	1.121.475	visvogel	35	(92)
20.	()	1.069.176	[DPC] Anticimex & Lock Metaaldetectie	0	(-)
21.	()	1.060.791	Berkie	0	(-)
22.	()	1.049.597	[DPC]SjoQing	0	(-)
23.	()	983.942	Override	4.229	(14)
24.	()	944.765	Jox444	2.541	(24)
25.	()	941.775	Dadoke	1.495	(31)
26.	()	881.057	Quark	5.559	(12)
27.	()	826.277	Rydo	3.566	(20)
28.	()	758.376	MaGNeT aka BlueTooth76	1.364	(33)
29.	()	682.800	dpc_kluizenaar	7.010	(10)
30.	()	673.789	Psyed	0	(-)
	More...


Teams Daily Top 15
pos		daily	team	total
1.	()	1.969.307	SETI.USA	1.050.513.196	(1)
22.	(1)	378.734	The Planetary Society	216.486.543	(14)
23.	(2)	365.740	Elite Games	109.186.028	(35)
24.	(2)	364.345	OcUK - Overclockers UK	209.709.098	(15)
25.	()	311.893	BOINC@Poland	130.709.554	(30)
26.	(3)	287.877	U.S.Air Force	150.529.534	(25)
27.	(12)	260.926	Amateur Radio Operators	150.838.386	(24)
28.	(5)	260.682	Brasil [SETIBR]	60.267.840	(57)
29.	(5)	253.541	Dutch Power Cows	136.541.140	(27)
30.	(3)	251.583	BOINC.Italy	151.738.018	(23)
31.	(1)	246.753	Boone Community School District - Iowa	97.284.551	(39)
32.	(1)	243.870	Team Norway	64.704.943	(53)
33.	(1)	238.922	Ars Technica	152.814.615	(22)
34.	(7)	236.661	Team Art Bell	207.093.141	(17)
35.	(2)	231.202	Sweden	45.254.600	(77)
36.	(13)	222.985	SMLUG	25.079.007	(134)
	More...


Teams Overall Top 15
pos		total	team	daily
1.	()	1.050.513.196	SETI.USA	1.969.307	(1)
20.	()	163.789.287	Phoenix Rising	526.580	(16)
21.	()	157.610.159	Canada	379.472	(21)
22.	()	152.814.615	Ars Technica	238.922	(33)
23.	()	151.738.018	BOINC.Italy	251.583	(30)
24.	()	150.838.386	Amateur Radio Operators	260.926	(27)
25.	()	150.529.534	U.S.Air Force	287.877	(26)
26.	()	147.564.180	BOINC@AUSTRALIA	436.633	(18)
27.	()	136.541.140	Dutch Power Cows	253.541	(29)
28.	()	135.043.662	UK BOINC Team	220.852	(37)
29.	()	134.206.697	Universe Examiners	204.973	(43)
30.	()	130.709.554	BOINC@Poland	311.893	(25)
31.	()	126.907.313	AUSTRIA - NATIONAL - TEAM	181.584	(47)
32.	()	121.895.647	BOINC SETI@home RUSSIA	213.873	(39)
33.	()	119.764.900	PC Perspective Killer Frogs	207.986	(42)
34.	()	118.225.696	Team NIPPON	220.347	(38)
	More...


Megaflush Top 5
pos	Team	Flush	Date
1.	[DPC]TeamGrazzie	553.056	04-01-2008
2.	chelloo.com	261.227	09-01-2008
3.	[DPC]Spinpoint	174.423	14-06-2007
4.	hansR	170.409	17-08-2008
5.	REISinformatiegroep	165.307	18-04-2007
More...