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Method Rapidly Reconstructs Animal's Development Cell By Cell

Doug Merritt Fly neurons? (39 comments)

Very interesting; is there a technical book (or chapter) or paper with a good overview of this comparative aspect of fly neurons?

I was just starting to look around to see what's available on comparative neuroscience in general, based on an interest in the most salient functional differences from human neurons, so anything related to that more general topic would also be welcome.

about 4 months ago
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Study: Earthlings Not Ready For Alien Encounters, Yet

Doug Merritt Re:What SETI can pick up (453 comments)

In theory, if we can capture coherent pictures in the visible spectrum from many billions of light years away, we should be able to do the same with RF.

It's actually very easy to see why the opposite is true: stars famously broadcast a truly vast amount of power in the visible spectrum, which is what makes solar energy and photosynthesis effective.

Humans clearly do not have the power resources of the entire sun to use to power RF broadcasts. The total amount of power we have at our disposal from all sources is a tiny, tiny fraction of what the sun broadcasts.

And most of our power does not go into RF in the first place, it goes into transportation, manufacturing, etc.

So it's quite straightforward that there is no comparison between the brightness of stars in the visible spectrum versus the Earth in RF. Stars win hands down.

It isn't the technology, it's just the hardware.

Unfortunately, it is very much both. It's true that we can do better by building better listening arrays, and SETI has been continually doing that for many years, but there is also a problem of signal to noise ratio that gives a hard limit on sensitivity due to noise from terrestrial sources and from thermal and quantum noise in the receiving electronics.

Part of that could be improved by putting radio telescopes e.g. on the far side of the moon. The electronics issue simply needs better technology.

about 7 months ago
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Study: Earthlings Not Ready For Alien Encounters, Yet

Doug Merritt What SETI can pick up (453 comments)

Yet the sky is not saturated with their communications. So therefor those civilizations must be using some other technology.

That seems logical, but that turns out not to be the case. A SETI scientist said in a talk (and I've seen this in articles since) that our deployed SETI listening technology is still nowhere near sensitive enough to pick up signals even from as close as the nearest star (Proxima Centauri, 4 light years away), if a planet there was broadcasting RF at current Earth levels.

(That doesn't mean SETI to date is pointless, because there's always a chance of a highly directional signal beamed our way, or of just something unexpected, like signals far far brighter than Earth's.)

So no, we have no idea whether the sky is saturated with radio waves or not.

about 7 months ago
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Book Review: Designing With the Mind In Mind

Doug Merritt Re:emphasis of GUI efforts (52 comments)

"a bit much" is an idiomatic way in English of saying "possibly you shouldn't have been modded down so much for that statement" (because the first part of what you said is arguable, not an obvious troll, not obviously flamebait, not an obviously incorrect statement of fact).

about 7 months ago
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Book Review: Designing With the Mind In Mind

Doug Merritt emphasis of GUI efforts (52 comments)

I think that you being modded down to -1 is a bit much, but there is a problem here. What you said is potentially well and good for contexts that are purely utilitarian to the degree that anything but pure pragmatic functionality is to be viewed as an active negative, such as industrial control, power plants, etc.

But for most people's desktops, people expect both functionality *and* some degree of modern aesthetics, and there is an extremely common rejection of interfaces that look 15 years old, even if they were considered close to ideally functional and aesthetic 15 years ago.

Since that is demonstrably what the market generally wants, that is therefore the general trend over time: "flashy graphics" are sometimes overdone, but the word "flashy" is in the eye of the beholder, and most improvements to GUIs over the decades have been about modernization to meet the moving target of whatever "modern" means in each era, with actual breakthroughs in usability being far less common.

Furthermore, the people who design and implement GUIs are (with the exception of 1-person development teams) rarely the same team members who would address software vulnerabilities, so maybe that's where your -1 came from.

about 7 months ago
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Portal 2 Incompatible With SELinux

Doug Merritt Re:why does a decoder need execheap? (212 comments)

There *is* such a thing as (write, execute), and this is what it is currently using, and people are complaining quite bitterly about it doing that, because it's a security weakness that is exploitable via buffer overflows etc.

Basically the fact that it allows for dynamic JIT compilation is exactly what people don't want the bad guys to be doing; potentially that turns a small bug into a complete take-over-the-machine exploit.

I'm afraid I was taking all that for granted in my original comment, which instead was about potential reasons why they might not have done something different as people are suggesting in hindsight.

about 8 months ago
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Portal 2 Incompatible With SELinux

Doug Merritt Re:why does a decoder need execheap? (212 comments)

I did mean that about time pressure, but I don't understand what you are suggesting.

The scenario is to suppose that they have some audio algorithm that is based on creating and executing a block of code a bunch of times, but for a very small fraction of a second, and then, critical assumption, it needs to create and execute a slightly different block of code, and so on, over and over.

Long ago I saw a demo of an Amiga video capture program that had precisely that sort of thing going on, where they could only get the throughput they needed by using self-modifying code, changing one instruction in an inner loop on a regular basis, and their approach held up under scrutiny of 100 developers critiquing them; it really was needed.

So I am sure that such things do arise in the real world; whether the current codebase truly has such a need, I don't know.

So *if* they have this need, then every time they create or modify a code block, they need it to be writable, but when they execute what they wrote, security issues insist that it it should go from (write,no-execute) to (no-write,execute), every single time.

Making that permissions change requires a system call every time, unavoidably.

Any scheme that allows avoiding that system call is inherently making different assumptions than I did above. Without knowledge of their algorithms, I don't see how we can be sure that assumptions like that are either right or wrong; I'm just pointing out that *if* they are correct, they explain why the codebase does what it does.

An alternative explanation that I tried to give a nod to is that they may have simply done a premature optimization that was not actually needed, but again, motivated as outlined above.

about 8 months ago
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Portal 2 Incompatible With SELinux

Doug Merritt Re:why does a decoder need execheap? (212 comments)

Whether it is noticeably expensive depends on endless details of their code, but if they did extremely fast JIT code generation on a very frequent basis (possibly just a single instruction change), then the reflagging syscall would be equally frequent, and the context switch overhead could dominate.

The scenario under which it truly hurts is possibly unlikely, I'll grant, but at the time of implementation it probably seemed like the simplest and fastest approach, and clearly they were thinking about speed, not security and Return Oriented Programming and such.

about 9 months ago
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Portal 2 Incompatible With SELinux

Doug Merritt Re:why does a decoder need execheap? (212 comments)

Yes, but the re-flagging costs a system call, which is potentially very non-trivial overhead in anything that is using JIT for speed.

about 9 months ago
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Why Organic Chemistry Is So Difficult For Pre-Med Students

Doug Merritt Re:Wasn't that difficult when I went through it (279 comments)

You have been misinformed. Doctors are *not* "supposed to be the smartest people on the planet", not even close.

The average citizen in the street may think so, but that's not saying anything.

As for physics, it doesn't make people smart to study physics, it just tends to attract some of the smartest students. Having pre-meds major in physics wouldn't make them any smarter.

1 year,23 days
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GUI nostalgia draws me back to ...

Doug Merritt Rogue is from 1980 (or earlier) (654 comments)

...but my first GUI was Rogue.

What, no love for castle.exe?

Rogue is from 1980, so it's at least 4 years old than Castle Adventure and the Tandy 1000, both of which came out in 1984.

Rogue is actually older than the PC; it was ported to the PC from PDP 11 Unix 7th Edition. It's actually a bit older than 1980, but that's the date that wikipedia gives.

more than 2 years ago
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GUI nostalgia draws me back to ...

Doug Merritt Rogue is from 1980 (654 comments)

...but my first GUI was Rogue.

What, no love for castle.exe?

Rogue is from 1980, so it's at least 4 years old than Castle Adventure and the Tandy 1000, both of which came out in 1984.

Rogue is actually older than the PC; it was ported to the PC from PDP 11 Unix 7th Edition.

more than 2 years ago
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Ask Slashdot: Tools For Teaching High School Kids How To Make Games?

Doug Merritt OpenSimulator (237 comments)

"OpenSimulator lacks support for many of the game-specific features of Second Life (on purpose), while pursuing innovative directions towards becoming the bare bones, but extensible, server of the 3D Web."

Sounds cool, but not for the purpose at hand.

more than 2 years ago
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The Strange Birth and Long Life of Unix

Doug Merritt Re:Smaller /. numbers here, please (293 comments)

I must have joined /. at least an hour before you did, so get off *my*...ah hell, you can use my lawn. :-)

(and: PDP-11 FTW -- I was part of one of the efforts mentioned in this Strange Birth article)

more than 2 years ago
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Rob "CmdrTaco" Malda Resigns From Slashdot

Doug Merritt Re:Hemos Says: "So Long, and Thanks For All The Fi (1521 comments)

And to think I waited a few days before registering an account here.

Tell me about it; my thinking was the same "another site to register at?". But you still managed a 3 digit ID; I delayed a couple weeks I think, when IDs were introduced, and ended up at 4 digits.

more than 3 years ago
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Strings Link the Ultra-Cold With the Super-Hot

Doug Merritt string theory vs. standard model (236 comments)

A modified standard model works for me

Of course it does. That's like saying that digital electronics theory works for you, no need to bother with analog electronics theory.

True, yet digital is nonetheless based on analog.

I'm by no means the biggest advocate of string theory, but obviously it is intended (regardless of its current incompleteness) to be a deeper level of description of the universe than is the standard model.

Even if string theory (or loop quantum gravity or spin foams) eventually succeeds at being a good theory of everything, it is quite possible, even likely, that it will continue to be more practical for most purposes to work in terms of a modified standard model.

We still make heavy use of Newtonian physics, after all.

But that doesn't mean that a theory of everything is pointless; its purpose is not identical to that of simplified working models.

more than 5 years ago
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ATI, Nvidia Reveal New $250 Graphics Cards

Doug Merritt $200 sound card? (84 comments)

Years ago I knew why some premium sound cards were worth the money, but I've long since lost track of the marketplace (aside from reading various things in the last year about old versus current versus upcoming Linux sound support).

So I'm curious, what do you get on today's systems that makes it worthwhile to pay $200 for a sound card?

I had the feeling it was no longer for wavetable, nor for number of bits of d-to-a conversion. Is it 7.1 surround, or what?

more than 5 years ago

Submissions

Doug Merritt hasn't submitted any stories.

Journals

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real time ray tracing

Doug Merritt Doug Merritt writes  |  more than 11 years ago

A real time ray tracer from the demo scene:
http://www.realstorm.com/

And comments on it:
http://www.acm.org/tog/resources/RTNews/html/rtnv5n1.html#art3

Stanford research on real time ray tracing with
the next generation of consumer graphics cards:
http://graphics.stanford.edu/papers/rtongfx/

(thanks to PEB for the pointer)

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