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Message 45888 - Posted: 30 Jan 2011, 22:06:18 UTC

We have some new images from Ben Willet's work on the N-Body project. What follows is a technical description; another, less technical explanation will follow later.

Shown in purple is an N-body simulation of the Orphan Stream using the
latest orbit. The Milky Way is shown edge-on, with the disk represented
by a line, the Galactic bulge in the center, and the Sun's position
indicated by the yellow dot.The observed stars in the Orphan Stream were
ripped from a dwarf galaxy by the gravity of the Milky Way galaxy. The
star stream has been labeled "Orphan" because no one has yet yet
positively identified the parent dwarf galaxy from which these stars were
Image Credit: Benjamin A. Willett

This animation shows N-body simulations of tidally stripped mass forming
the Sagittarius (large), Orphan (medium) and GD-1 (small) stellar
streams. The Sagittarius and Orphan streams are formed by tidal
stripping from small dwarf galaxies that have passed too close to the
center of the Milky Way, while the GD-1 stream is formed by tidal
stripping of a globular cluster. The Milky Way Galaxy is shown edge-on,
with the Sun located on the left side of the disk. The line on the top
right shows the +Z direction, out of the Galactic disk. The entire
animated sequence represents four billion years of elapsed time in the
Milky Way, ending at the present day.
Image Credit: Benjamin A. Willett

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Message 45889 - Posted: 30 Jan 2011, 23:03:36 UTC
Last modified: 30 Jan 2011, 23:04:23 UTC

OMG it's a closed timelike curve, lol!
Way cool and good to be part of this work!

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Message 45895 - Posted: 31 Jan 2011, 7:04:28 UTC - in response to Message 45889.

Very impressive simulation and excellent explanation of the galaxy stripping process.


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Message 46898 - Posted: 2 Apr 2011, 1:16:47 UTC
Last modified: 2 Apr 2011, 1:18:13 UTC

Thats fantastic. And to watch that and to think my PC had some small part in helping figure that out. :)

So you are having our CPU's do the N_body work and the GPU's do something else? What is the difference? In retard terms please. :)
32bit Windows XP Home
AMD Opteron 180
ASUS A8N-SLI Motherboard
Nvidia 450GTS GPU
4GB DDR Memory

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Message 57902 - Posted: 12 Apr 2013, 18:41:33 UTC - in response to Message 46898.

What happened with the animation of this thread?
Sunday was working. Today disappeared :''(

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Message 58956 - Posted: 18 Jun 2013, 17:38:00 UTC

Hi, I just signed in and earned 5k credits.

This program uses N*N interactions or some Barnes-Hutt involved to make it N*log(N)?

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Message 59078 - Posted: 24 Jun 2013, 18:36:26 UTC

This uses Barnes Hut for N Log(N) but as the systems are non-linear(chaotic) some parameters will scatter and when a Barnes Hut system is widely scattered it approaches N^2.

So Barnes Hut is optimally N Log (N) but in worse case is N^2. The systems we study vary in case part of what we are learning about the systems.


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Message 63101 - Posted: 4 Feb 2015, 21:42:43 UTC - in response to Message 46898.

The graphics processor unit (GPU) is a specialized processor. It takes an image stream the computer wants to present on the monitor and transforms it into something the monitor can use efficiently. Techies call this "graphic acceleration." It uses its chip real estate to do some (but not all) these things separately because the central processing unit (CPU) has better things to do.

The GPU has its own reduced instruction set. With a little help from the CPU, it can do the work of an additional core of the CPU. A mini-program is the "gatekeeper" that uses the CPU to do what the GPU cannot do, and feed it with stuff the GPU can do. The GPU's result is passed back to its feeder. Meanwhile, the CPU is doing something else while the GPU is doing its thing. The GPU is doing something that it was not designed to do. It does not know or care. It just does what the CPU told it to do.

Modern CPUs contain more than one processor on a single piece of silicon. Using electronic magic, they share work space. That way, we get to process more than one operation at the same time. The central processor unit is a collection of processors called "cores."

MilkyWay@home does not provide the feature that can fool a GPU into doing the work of a processor core. However, MilkyWay@home does have a way to use all of the cores of the CPU for a single task to crunch through a simulation. Other projects offer a GPU feature. SETI@home is an example.

My machine has an Intel i7 processor that can do up to 8 things at once (8 cores). One core plays "musical chairs" with a GPU. That is why my machine shows that it is doing 9 things at once. MilkyWay is doing 8 things in one task. SETI is doing one other thing using the GPU. If MilkyWay is not doing a simulation, SETI and MilkyWay are doing 9 things at the same time.

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Message 63585 - Posted: 15 May 2015, 12:11:41 UTC

Ive had to kill three over 4 hours
Nbody v1.5 looping. 5 min. task Im aborting after 4+ hours running 8 processers. I7, Win 7 Pro-64 bit, 12 GB Ram, 2 TB HD.

Leelan Coin

Name ps_nbody_5_12_15_orphan_sim_1_1431361804_27915_0
Workunit 823277835
Created 14 May 2015, 14:43:11 UTC
Sent 14 May 2015, 15:23:55 UTC
Report deadline 26 May 2015, 15:23:55 UTC
Received ---
Server state In progress
Outcome ---
Client state New
Exit status 0 (0x0)
Computer ID 605363
Run time
CPU time
Validate state Initial
Credit 0.00
Device peak FLOPS 32.39 GFLOPS
Application version MilkyWay@Home N-Body Simulation v1.50 (mt)
Stderr output

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Message 64348 - Posted: 27 Feb 2016, 1:14:36 UTC

I wonder if these stars ever collide with each other :)

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Message 64532 - Posted: 3 May 2016, 21:16:35 UTC

Please advise how stars with different life spans, size - weights, "burning"... effects the calculations? If the plot below represents 4 billion years, I would think there would be some "changes" do to star life, size, and weight spans. Or in the scheme of things are these factors considered too small - insignificant to consider?

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Message 64861 - Posted: 11 Jul 2016, 16:03:27 UTC

Can this data be used to update the overview page written in 2013? It would be good to get an idea of overall progress and future directions

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Message 64862 - Posted: 11 Jul 2016, 16:37:12 UTC

Hey iancantwell,

We will be updating the science page eventually. It is on my list of things to do this summer, but that this is quite long at the moment.


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