For neutron shielding, you want low-Z material, not low density material. Neutron shields are pretty much always made of concrete, water, or high density polyethylene (HDPE). All of those are relatively high density (compared to a metal foam anyway). What all those have in common is a high density of hydrogen (concrete less so, but it's cheap so you can put more of it). Metal foam is low density, low hydrogen content, so pretty much the worst thing you could think of for neutron shielding.
And of course gamma and x-rays only differ in the frequency, but that means the energy, and more importantly the radiation length / penetration depth. The mm-thick layer of lead in the aprons they give you at the dentist will block x-rays, and low energy gamma rays, just fine, but they won't do anything to >MeV gammas that are the real problem with radioactive sources.
Also just in case you want to be pedantic, x-rays and gamma rays are labeled as such not just by energy, but by emission source. X-rays are generated by atomic de-excitation, while gammas are generated by nuclear processes, so there are actually some gamma rays with lower energy than some x-ray lines.
I do radiation shielding for a living, and there is no way 1 inch of low density _anything_ is going to give you any kind of useful radiation shielding. Maybe x-rays will be attenuated enough to talk about, but you may as well paper for all the neutron and high energy gamma shielding that will give you.
Get a decent router with QoS capabilities, and you can limit the rate for individual devices all you want, with as much control as you could possibly ask for. We even limited our Roku since it ate through AT&T's ridiculous 200GB cap every month.
It's a pretty slippery slope, though. Maybe now they are treating different end-networks differently for "good" reasons, but what's to stop them from striking a deal with t-mobile to deliver lower-quality streams to all its competitors' networks? Net neutrality, that's what.
Yes. The idea is that Dark Matter particles interact via the same force (the Weak Force) as neutrinos.
Everything else you wrote is spot on, but WIMPs have been ruled out as truly Weakly interacting (where Weak with a capital W means "by the exchange of W or Z bosons) for almost a decade now. The original Weak Miracle posited WIMPs to be truly Weakly interacting, but now they are held to be sub-Weak, interacting most likely through Higgs exchange, but we kept the name. Really we should rename them wIMPs at this point.
Also I hate whoever decided to use Weak and Strong as formal names for those respective interactions.
Sometimes three is just an inherent smarty-pants style to writing academic papers. I lose track of how many times I instinctively try to write something like "utilize" or "make use of" when a simple "use" will work.
But, at least in scientific writing, you use complicated language in order to be absolutely precise about your method and findings (as opposed in particular to scientific journalism...). As an example, I work in the field of direct experimental searches for evidence of interactions between particle dark matter and nuclei. That's a huge mouthful, but every single word in that phrase carries distinct meaning, and if you take any of them out, it is not a correct description of what I do, and may refer to another field entirely.
Now take that kind of precision and discuss an experimental result. "We find that, at 90% confidence level, there is no statistically significant evidence for X". Again, it sounds like buzzwords and jargon, but there is simply no way to turn that statement into "common" English.
Silly me, making the mistake of reading TFA on/. ( aside: what's the proper way to punctuate a sentence ending in/.?) You want to know how we 'know' all of those things with such great precision? It's all about the scale of temperature fluctuations in the cosmic microwave background. The CMB is a snapshot of the universe some 30k years after the big bang, during the time of first neutralization, when the pathlength of photons quickly (on cosmic scales) went form very short in the hot plasma (think neon light tube) to mostly neutral hydrogen. The spectrum of density fluctuations there tells an incredible amount about how the small perturbations left over from inflation evolved during that early time, and is the main stick by which all of our cosmological models are tested. The incredible agreement with the standard cosmological model and the CMB using only 7 free parameters is probably the most successful accomplishment in scientific history.
Nowhere on the article's page of drivel is the CMB mentioned, nor the WMAP or Planck satellites which were responsible for bringing us that data. I didn't read much of the article, but there is simply no way to speak intelligently about early universe models without the CMB. If you actually want to learn about this stuff, take a look at some of the public stuff NASA has put together for WMAP at http://map.gsfc.nasa.gov/missi... ; some of the animations are really quite revealing, and I use them in seminars on the subject all the time. Then if you're still hungry for more and can handle the math, take a look at Dodelson's Modern Cosmology.
Bah, still too angry about this kind of crap. Not a good way to start the week.
I got about 1 paragraph into the article before it became obvious that the author had no clue what the hell he was talking about. Maybe the old paper was better, but I don't have the patience to try to find out. From TFA:
They would interact only through the feeble weak nuclear force—one of two forces of nature that ordinarily flex their muscle only within the atomic nucleus—and could disappear only by colliding and annihilating one another
So many things wrong just in that sentence 1) Weakly Interacting Massive Particles (WIMPs) do have very low interaction cross sections (read: rates). There's sometimes an unfortunate ambiguity in the fact that phycisists have no imagination and gave two of the fundamental forces the names Strong and Weak. To say something interacts Weakly means that it interacts by exchange of W or Z bosons, not just that it has a low rate. However the WIMP interaction cross section has been known to be sub-Weak by several orders of magnitude for decades.
2) The Weak force's most obvious manifestation is in the production or absorption of neutrinos (beta decay or inverse beta decay) in a nucleus, but that's certainly not the only place it shows up; it's the mechanism for neutrino-electron scattering, muon decay, and a whole bunch of other stuff up to driving supernova explosions
3) Self-annihilation is the vanilla model for WIMP transformation, but there are plenty of sundaes-with-cherries-on-top models like self-interacting dark matter, which is discussed about 2 sentences later. Also, the chi is the symbol for the supersymmetric neutralino, often equated to a vanilla WIMP, and is not at all specific to the self-interacting dark matter model.
In short, cbtfaij;dr (can't bother to find an intelligent journalist; don't read)
I'm probably a bit biased here, but also an expert, since I am a physicist who studies dark matter for a living.
The title's question doesn't even make sense! Big bang theory, and in particular studying the exact power spectrum of the cosmic microwave background, is by far the strongest evidence we have for the existence of dark matter and dark energy. All those pie charts you've seen showing the divisions of baryonic matter, dark matter, and dark energy? If they're properly cited, I guarantee every single one of them comes from data from WMAP or PLANCK: CMB experiments! You can't say that dark matter gives you room to invalidate the big bang, because without that we don't have really any strong evidence for non-baryonic dark matter in the first place...
You completely missed the point of the book if that's what you got. What made Ender the supreme commander wasn't his intelligence; he was brilliant, but not significantly more so than many of the other kids. Ender's gift was his empathy: what allowed him to overcome his foes was exactly that he DIDN'T see them as less than human, but that he respected, maybe even loved his adversaries, even as he set up to destroy them.
As a good example, you should take a look at trello , which is basically an organization/design/progress list tool, where each atomic activity is represented by a card. I've been using it extensively for about a year now, and the card+board metaphor really seems to make intuitive sense to everyone I've introduced to it.
at least in the particle physics community, practically all anyone uses is open-source code. The most common are GEANT4 for simulating particles interacting with matter, and ROOT which handles data analysis. Both are maintained by dedicated people at CERN.
As to more specialized code, any time I've ever asked someone about their analysis, no matter what institution or relation (or lack of) to me, they've always been happy to share their code source with me. Usually with many caveats about quality, but it's there. The problem for us has always been knowing who to ask, so a dedicated central repository could be interesting.
Maybe a model like the arxiv.org could work. Almost everyone these days puts preprints of upcoming papers on the arxiv. Since there's no review system, you also get lots of garbage from crazies, but it's generally not hard to weed out if you know at least a little about the subject matter of your search, and trivial if you know the relevant big names in your field. In the same vein, a huge code repository where anyone could upload their junky scripts, tagged by name and subject/function/whatever, might work better than it would seem at first glance.
I'm actually only about half-joking here. When you have a newborn, you get practically no sleep for months at a time, and yet people still have multiple kids. Why? Because nobody clearly remembers those early terrible sleepless months!
Not by any means. For probably the best example, look at the Einstein-Rosen-Podalsky paradox , a simple thought experiment used an attempt to disprove the so-called Copenhagen interpretation of quantum mechanics because it would require the instantaneous transmission of quantum states in such a way that would violate special relativity. People did try to think their way out of it, until Bell's theorem "thought" everyone back into the paradoxical corner - leading to the modern sciences of quantum entanglement.
In fact if you look back, many of the advances in modern physics have come about specifically because of paradoxes arising from thought experiments. See also the ultraviolet catastrophe, or even Schrodinger's cat for that matter.
You still shuffle your deck in Dominion, and it's still possible (though less likely than Magic, granted) to get screwed by chance - your money cards can keep getting spread out just enough that you never manage to get enough buying power on a given turn to buy the top-tier cards. Or you repeatedly get all your good combo-building cards in a row and burn through them without encountering anything practical. I've had both happen...
My biggest problem with Dominion is that you don't really interact with the other players much - it's easily possible to set up a game with none of the "Attack" type cards, in which case you're really just racing N games of solitaire. Even with the attack cards, you don't generally get to respond in any meaningful way - e.g., if you have a Moat you can block the Bandits, but otherwise not. There's no choices, or finite resources - should I save my surprise Bandit Blocker(TM) , or save it for a better opportunity?
I agree completely, but luckily there are alternative formats to Constructed decks, in particular Sealed and Draft tournaments. Everyone puts in their entry fee, then builds decks right there from sealed, virgin packs, so there's no "more money = more wins" mechanic. It's the only way I'd ever consider playing in an environment other than casually with friends.
Clearly the ideal place for a modern Mega Man is in Super Smash Brothers. 3D look, but essentially a 2D game, and he would totally kick that damn Jigglypuff's ass...
I think at this point I would vote for any candidate who would just answer the questions that are being asked...or at least address them tengentially.
There also needs to be a buzzer or something to shut them up whenever they want to discuss their opponent's plans, i.e., put words in their opponent's mouth.
Slashdot Mirror
For neutron shielding, you want low-Z material, not low density material. Neutron shields are pretty much always made of concrete, water, or high density polyethylene (HDPE). All of those are relatively high density (compared to a metal foam anyway). What all those have in common is a high density of hydrogen (concrete less so, but it's cheap so you can put more of it). Metal foam is low density, low hydrogen content, so pretty much the worst thing you could think of for neutron shielding.
And of course gamma and x-rays only differ in the frequency, but that means the energy, and more importantly the radiation length / penetration depth. The mm-thick layer of lead in the aprons they give you at the dentist will block x-rays, and low energy gamma rays, just fine, but they won't do anything to >MeV gammas that are the real problem with radioactive sources.
Also just in case you want to be pedantic, x-rays and gamma rays are labeled as such not just by energy, but by emission source. X-rays are generated by atomic de-excitation, while gammas are generated by nuclear processes, so there are actually some gamma rays with lower energy than some x-ray lines.
I do radiation shielding for a living, and there is no way 1 inch of low density _anything_ is going to give you any kind of useful radiation shielding. Maybe x-rays will be attenuated enough to talk about, but you may as well paper for all the neutron and high energy gamma shielding that will give you.
dd-wrt lets you limit by device as well as service
Get a decent router with QoS capabilities, and you can limit the rate for individual devices all you want, with as much control as you could possibly ask for. We even limited our Roku since it ate through AT&T's ridiculous 200GB cap every month.
It's a pretty slippery slope, though. Maybe now they are treating different end-networks differently for "good" reasons, but what's to stop them from striking a deal with t-mobile to deliver lower-quality streams to all its competitors' networks? Net neutrality, that's what.
Yes. The idea is that Dark Matter particles interact via the same force (the Weak Force) as neutrinos.
Everything else you wrote is spot on, but WIMPs have been ruled out as truly Weakly interacting (where Weak with a capital W means "by the exchange of W or Z bosons) for almost a decade now. The original Weak Miracle posited WIMPs to be truly Weakly interacting, but now they are held to be sub-Weak, interacting most likely through Higgs exchange, but we kept the name. Really we should rename them wIMPs at this point.
Also I hate whoever decided to use Weak and Strong as formal names for those respective interactions.
It makes up 95% of the universe actually
Sometimes three is just an inherent smarty-pants style to writing academic papers. I lose track of how many times I instinctively try to write something like "utilize" or "make use of" when a simple "use" will work.
But, at least in scientific writing, you use complicated language in order to be absolutely precise about your method and findings (as opposed in particular to scientific journalism...). As an example, I work in the field of direct experimental searches for evidence of interactions between particle dark matter and nuclei. That's a huge mouthful, but every single word in that phrase carries distinct meaning, and if you take any of them out, it is not a correct description of what I do, and may refer to another field entirely.
Now take that kind of precision and discuss an experimental result. "We find that, at 90% confidence level, there is no statistically significant evidence for X". Again, it sounds like buzzwords and jargon, but there is simply no way to turn that statement into "common" English.
Go to smbc-comics.com and keep hitting "random" until it comes up. I guarantee it will be a productive use of your time
Silly me, making the mistake of reading TFA on /. ( aside: what's the proper way to punctuate a sentence ending in /.?)
You want to know how we 'know' all of those things with such great precision? It's all about the scale of temperature fluctuations in the cosmic microwave background. The CMB is a snapshot of the universe some 30k years after the big bang, during the time of first neutralization, when the pathlength of photons quickly (on cosmic scales) went form very short in the hot plasma (think neon light tube) to mostly neutral hydrogen. The spectrum of density fluctuations there tells an incredible amount about how the small perturbations left over from inflation evolved during that early time, and is the main stick by which all of our cosmological models are tested. The incredible agreement with the standard cosmological model and the CMB using only 7 free parameters is probably the most successful accomplishment in scientific history.
Nowhere on the article's page of drivel is the CMB mentioned, nor the WMAP or Planck satellites which were responsible for bringing us that data. I didn't read much of the article, but there is simply no way to speak intelligently about early universe models without the CMB. If you actually want to learn about this stuff, take a look at some of the public stuff NASA has put together for WMAP at http://map.gsfc.nasa.gov/missi... ; some of the animations are really quite revealing, and I use them in seminars on the subject all the time. Then if you're still hungry for more and can handle the math, take a look at Dodelson's Modern Cosmology.
Bah, still too angry about this kind of crap. Not a good way to start the week.
Obligatory xkcd
I got about 1 paragraph into the article before it became obvious that the author had no clue what the hell he was talking about. Maybe the old paper was better, but I don't have the patience to try to find out. From TFA:
They would interact only through the feeble weak nuclear force—one of two forces of nature that ordinarily flex their muscle only within the atomic nucleus—and could disappear only by colliding and annihilating one another
So many things wrong just in that sentence
1) Weakly Interacting Massive Particles (WIMPs) do have very low interaction cross sections (read: rates). There's sometimes an unfortunate ambiguity in the fact that phycisists have no imagination and gave two of the fundamental forces the names Strong and Weak. To say something interacts Weakly means that it interacts by exchange of W or Z bosons, not just that it has a low rate. However the WIMP interaction cross section has been known to be sub-Weak by several orders of magnitude for decades.
2) The Weak force's most obvious manifestation is in the production or absorption of neutrinos (beta decay or inverse beta decay) in a nucleus, but that's certainly not the only place it shows up; it's the mechanism for neutrino-electron scattering, muon decay, and a whole bunch of other stuff up to driving supernova explosions
3) Self-annihilation is the vanilla model for WIMP transformation, but there are plenty of sundaes-with-cherries-on-top models like self-interacting dark matter, which is discussed about 2 sentences later. Also, the chi is the symbol for the supersymmetric neutralino, often equated to a vanilla WIMP, and is not at all specific to the self-interacting dark matter model.
In short, cbtfaij;dr (can't bother to find an intelligent journalist; don't read)
you've been able to make voip calls using your google voice number from android phones for forever using grooveip (and it's free cousin grooveiplite).
I'm probably a bit biased here, but also an expert, since I am a physicist who studies dark matter for a living.
The title's question doesn't even make sense! Big bang theory, and in particular studying the exact power spectrum of the cosmic microwave background, is by far the strongest evidence we have for the existence of dark matter and dark energy. All those pie charts you've seen showing the divisions of baryonic matter, dark matter, and dark energy? If they're properly cited, I guarantee every single one of them comes from data from WMAP or PLANCK: CMB experiments! You can't say that dark matter gives you room to invalidate the big bang, because without that we don't have really any strong evidence for non-baryonic dark matter in the first place...
You completely missed the point of the book if that's what you got. What made Ender the supreme commander wasn't his intelligence; he was brilliant, but not significantly more so than many of the other kids. Ender's gift was his empathy: what allowed him to overcome his foes was exactly that he DIDN'T see them as less than human, but that he respected, maybe even loved his adversaries, even as he set up to destroy them.
I won't argue about the rest of the series though
As a good example, you should take a look at trello , which is basically an organization/design/progress list tool, where each atomic activity is represented by a card. I've been using it extensively for about a year now, and the card+board metaphor really seems to make intuitive sense to everyone I've introduced to it.
Windows 3.1 was DOS based...
98 was the first version of windows that was an actual OS, not a graphical DOS shell
at least in the particle physics community, practically all anyone uses is open-source code. The most common are GEANT4 for simulating particles interacting with matter, and ROOT which handles data analysis. Both are maintained by dedicated people at CERN.
As to more specialized code, any time I've ever asked someone about their analysis, no matter what institution or relation (or lack of) to me, they've always been happy to share their code source with me. Usually with many caveats about quality, but it's there. The problem for us has always been knowing who to ask, so a dedicated central repository could be interesting.
Maybe a model like the arxiv.org could work. Almost everyone these days puts preprints of upcoming papers on the arxiv. Since there's no review system, you also get lots of garbage from crazies, but it's generally not hard to weed out if you know at least a little about the subject matter of your search, and trivial if you know the relevant big names in your field. In the same vein, a huge code repository where anyone could upload their junky scripts, tagged by name and subject/function/whatever, might work better than it would seem at first glance.
I'm actually only about half-joking here. When you have a newborn, you get practically no sleep for months at a time, and yet people still have multiple kids. Why? Because nobody clearly remembers those early terrible sleepless months!
Not by any means. For probably the best example, look at the Einstein-Rosen-Podalsky paradox , a simple thought experiment used an attempt to disprove the so-called Copenhagen interpretation of quantum mechanics because it would require the instantaneous transmission of quantum states in such a way that would violate special relativity. People did try to think their way out of it, until Bell's theorem "thought" everyone back into the paradoxical corner - leading to the modern sciences of quantum entanglement.
In fact if you look back, many of the advances in modern physics have come about specifically because of paradoxes arising from thought experiments. See also the ultraviolet catastrophe, or even Schrodinger's cat for that matter.
You still shuffle your deck in Dominion, and it's still possible (though less likely than Magic, granted) to get screwed by chance - your money cards can keep getting spread out just enough that you never manage to get enough buying power on a given turn to buy the top-tier cards. Or you repeatedly get all your good combo-building cards in a row and burn through them without encountering anything practical. I've had both happen...
My biggest problem with Dominion is that you don't really interact with the other players much - it's easily possible to set up a game with none of the "Attack" type cards, in which case you're really just racing N games of solitaire. Even with the attack cards, you don't generally get to respond in any meaningful way - e.g., if you have a Moat you can block the Bandits, but otherwise not. There's no choices, or finite resources - should I save my surprise Bandit Blocker(TM) , or save it for a better opportunity?
I agree completely, but luckily there are alternative formats to Constructed decks, in particular Sealed and Draft tournaments. Everyone puts in their entry fee, then builds decks right there from sealed, virgin packs, so there's no "more money = more wins" mechanic. It's the only way I'd ever consider playing in an environment other than casually with friends.
Clearly the ideal place for a modern Mega Man is in Super Smash Brothers. 3D look, but essentially a 2D game, and he would totally kick that damn Jigglypuff's ass...
Maybe, but only once I can actually buy a device with a damn PixelQi screen!
I think at this point I would vote for any candidate who would just answer the questions that are being asked...or at least address them tengentially.
There also needs to be a buzzer or something to shut them up whenever they want to discuss their opponent's plans, i.e., put words in their opponent's mouth.