“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small.” -Neil Armstrong
This past week saw a whole lot of interesting things happen, including tonight’s second full moon of the month: a rare blue moon. In my life, I saw the International Space Station for the first time, but here at Starts With A Bang, there was so much to learn about and share, including:
There was also a fun piece about our Solar System’s two-toned moon over at Forbes:
In addition, we reached our second milestone goal on our Patreon, so if you want to vote on which book chapter everyone gets for free in advance of my first book’s release, join and donate today. Other than that, it’s on to our Comments of the Week!
Image credit: White Dwarf, Earth, and Black Dwarf, via BBC / GCSE (L) and SunflowerCosmos (R).
From Omega Centauri on neutron stars going dark: “Sounds like the low temperature neutrino emissions rate is not well known. How else could there be such a large variation in estimated cooling time?
Can neutrinos really pass through neutron stars, even with a tinyl cross-section the column density of a NS is phenomenally high.”
There are two question here, both worthy of an answer and both contrary to what Omega Centauri expects. You see, when you first form a neutron star, you’re taking the core of a massive star that’s so big that the core itself — the part that becomes the neutron star — is more massive than our entire Sun. It collapses down and fuses into a ball of neutrons just a few kilometers wide, heating up to tremendous temperatures of about 10^12 K at the core and 10^6 K at the surface.
Image credit: ESO/L. Calçada, via http://ift.tt/1qChWAE.
It’s actually not the low-temperature cooling that’s a problem; we understand how neutrons behave at low temperatures. It’s not even the high-temperature cooling, although that’s less well understood. (We spend a lot less time with neutrons at 10^12 K than we do at lower temperatures.) It’s the high-density decay time and its gradient, since even though the binding energy is great enough that neutrons shouldn’t decay, they will on long enough timescales thanks to quantum tunneling. Without a perfect model of neutron star interiors, we recognize that the uncertainties in computation leave an uncertainty there. Additionally, your neutrons are more likely to decay close to the neutron-star crust, where the binding energies are lower. Even though the uncertainty is small overall, the decay times are so long that this leads to a few order of magnitude uncertainty in the cooling time of a neutron star.
But don’t worry about your neutrinos interacting. Sure, neutron stars are incredibly dense: about 10 times denser than a Uranium nucleus on average. But they’re also small, at just a few kilometers in radius. So the overall “chances-to-interact-with-a-particle” are only a few times as great your chances for an interaction if you emit a neutrino from the center of the Sun, and most of them are close to the surface anyway. If you randomly pass that neutrino through the core, you’ve got a few percent chance of an interaction (which is high!), but that’s a relatively unlikely path. Most neutrinos escape just fine.
Image credit: © 2015 Brian Kane, via http://ift.tt/1LAKh2l.
From PJ on advertising vs. art: “Then the thought of safety struck home. All these distractions along the highways & byways. Imagine, not knowing the signage was there, in the evening (night) there is an apparition of a phase of the moon before the driver – the moment of panic – WTF – simply because it should not be there.
Once the driver gets used to the sight, however, the brain tends to block such things; unless there is a constant change – a slide show, or something of that nature.
Don’t get me wrong, progress has its place; I would rather see a tree, though, than a picture of one.”
I don’t know, honestly, how well it works, but I always feel like the biggest weirdo when I’m driving down a dark road at night. If the Moon is out, or the stars, or bright planets, I’ll try and sneak a peak every chance I get at the sights of the natural beauty out beyond our Earthly skies.
Image credit: Alan Dyer, via http://ift.tt/1SRnYpD.
Yes, I know it’s dangerous, driving at some 70 mph (110-120 kph) or so, looking at anything other than what’s directly in front of (and around) you. But that’s the whole point of advertising: to distract you from what you’re doing and occupy that mental space with the craving to get you thinking about the product, service or cause in question. For me, if my options are between:
- actual nature,
- simulated nature,
- nothing at all, or
- an advertisement,
those are my choices, in my order of preference. Only actually restoring the natural setting would be a superior choice, to me, from what this art project accomplished.
Image credit: Multiwavelength images of M31, via the Planck mission team; ESA / NASA.
From Jan on the topic of where I publish: “But have you considered publishing on anything else but medium? It really is not good. Those images are 90 degrees rotated. Logical top and bottom of the “composite” image are one bellow another. They are split into many pieces, one can’t even save them and view them properly. RSS does not work there and more.”
At the very least, I know that RSS does work on Medium: my blog’s feed is here.
Writing about the Universe — actually, teaching about it and sharing its wonders and joys in general — is what I’m passionate about. Where and how I do it isn’t of the most paramount importance, but enjoying it, giving my audience a good experience and making (as close to) a living as I can doing it are what I value. That latter reason is something I can’t do on my own (but I’m trying with the Patreon), but right now, Medium is the best of all those worlds for me.
Perhaps down the road, though, it won’t be. Have any input on what might be next?
Image credit: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF.
From G, on the “big” question about “small” things like us: “In 1/2 billion years, the Sun will boil Earth’s oceans, so by that time our distant descendants will need to have spread into an interstellar civilization, or Earth-originated life will be another tragic footnote in a distant civilization’s galactic history logs. As we spread across the galaxy, we will discover numerous forms of life in other star systems, and reached some viable conclusions about the types of life that are possible in our galaxy.
But that will not answer the question of whether biology is convergent across galaxies. The only way to get that answer is to go to another galaxy.”
And then there’s the next logical question, if you want to go down that rabbit hole: even though, as far as we can tell, the physical processes of our own galaxy are at play in all galaxies, does that mean the way “life” is realized is the same in our galaxy or local group is the same everywhere? Do giant ellipticals in the heart of Virgo have the same life processes, or are there others unique to its environment?
Image credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.
Do isolated, field galaxies have different types of life that arise? How about more processed material, like that found at the heart of the Perseus cluster (above)?
What we’ve already learned about the Universe is amazing; what we continue to learn is amazing as well. But there will always be more to learn and check out there, and right now, the only thing limiting our knowledge is the resources we’re willing to invest.
Image Credit: NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA).
From Scott on dark matter halos: “I thought the rationale behind dark matter halo theory was that the inner and outer portions of a rotating galaxy have the same red shift, or velocity relative to the observer.”
That’s only one piece of evidence for dark matter halos. If you add a non-collisional component of matter to the Universe, you get large, fluffy, diffuse halos around all massive structures, which actually act as seeds for the massive structures in the first place.
But observationally, there was a piece of evidence that came first (like, 40 years before the rotation curves of galaxies were measured): galaxy clusters and the speeds of the individual galaxies in them. In fact, when we reconstruct what the mass profile of a galaxy cluster looks like, we find that sure, individual galaxies have large masses, but there’s an even greater amount of mass distributed in a diffuse, cluster-scale halo!
Image credit: Greg Kochanski, Ian Dell’Antonio, and Tony Tyson (Bell Labs), of the reconstructed mass in a large galaxy cluster.
This is to say there’s a lot more evidence for dark matter halo theory than just the rotation curves of galaxies. They play a part, but that’s actually the least strong evidence out there.
Image credit: NASA/ESA/Richard Massey (California Institute of Technology).
From Boris Borcic on a possibility for dark matter: “Long shot, but on dark matter not possibly being formed of neutrinos, I’d like to be shown that a Fermi gas of (slightly massive) neutrinos can’t achieve dark matter density.”
The problem with neutrinos isn’t that they couldn’t achieve the necessary density of dark matter: if each type of neutrino had a mass of about 4 eV, we’d be golden. (They’re constrained, experimentally, to be less than about 2 eV apiece, by the way.) The problem is that if neutrinos made up this dark matter, that dark matter would be hot, which means it would be moving relatively quickly when neutral atoms were formed. It would suppress the formation of structure on large scales, something that vehemently disagrees with observations.
Image credit: Maroto A.L., Ramirez J., astro-ph/0409280.
It’s the clustering data that rules this scenario out. Based on the measured mass of neutrinos and the constraints we have, neutrinos appear to be about 0.4% of the dark matter, a number that could increase to a maximum of about 2%, but not more.
It’s a good idea, but one that was explored in incredible detail… and ruled out.
Image credit: Aurore Simonnet, Sonoma State University.
From Jim Salsman on primordial black holes as dark matter: “[I]f inflation resulted in sufficient intermediate mass black holes (around 100,000 solar masses each) to explain the formation of relatively recently [discovered] quasars at z>6, those would require that all dark matter be comprised of such black holes, and they would not be detectable through gravitational lensing.”
This statement is phrased as a “this is true,” but in reality it should be asked as, “is this true?” If you allow for the fluctuations inflation produces normally (Gaussian), this is impossible. Producing a fluctuation of more than about 10^-4 solar masses would be ruled out convincingly by power spectrum and CMB data; that can’t happen. So you need an exotic scenario — something involving topological defects — to produce fluctuations at specifically one scale preferential to all others, and that won’t mess up any of our other observations. It is very, very difficult to do this.
Image credit: Sebastian F. Bramberger, Robert H. Brandenberger, Paul Jreidini, and Jerome Quintin, via http://ift.tt/1SRo0xU.
But the kicker is this: you don’t need to! Gaussian fluctuations — the kind inflation normally predicts — can give you the supermassive black holes needed all the way up to a redshift of 15-20 or so through the process of hierarchical mergers. At the redshift of z=6 that you referred to, in fact, in the graph from the only one of the three papers that mentions the scenario you put forth, they show how Gaussian fluctuations lead to SMBHs of ~10^9 solar masses with no problem, beginning from that tiny 10^-4 seed. So what you contend is a plausible (but fringe) explanation, but one that’s not required to explain what we observe. The standard picture does just fine.
But if we start seeing these objects at, say, a redshift of 30, then we’ve got a reason to listen.
Image credit: X-ray: NASA/CXC/U.Birmingham/M.Burke et al.
From Denier on the pieces of evidence for dark matter: “There are implications on all of the above listed phenomena currently attributed to Dark Matter if it is confirmed that antimatter falls up.”
If antimatter falls up, we would be tremendously surprised. A lot of things would be wrong. E=mc^2 would be wrong, for one, or gravitational and inertial mass would not be identical. We’re doing the experiment because we have to check all our theories and expectations against the evidence, but we have been attempting to measure this for maybe 50+ years now, and haven’t been able to create and track neutral antimatter precisely enough to check it out. We will keep trying, and hopefully we’ll verify that it falls in a gravitational field just like we expect.
We see antimatter ejecting out of galactic “jets” with the same velocity profiles as we see for normal matter, so we do expect it to behave gravitationally just like matter does. But we don’t know for certain until we check. Still, if it turned out that antimatter falls up, I would say it’d be the biggest surprise and discovery of the 21st century. I’ll keep watching.
Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration; Acknowledgment: H. Bond (STScI and Penn State University).
And finally, from Wow on the different types of variable stars: “Well, as far as I’m aware, there are three types of variable.
Inherently variable. Stars that change their luminosity.
Multistar variables. Objects that change their luminosity because they appear to be a singe object when they are not.
Occulted variables. Stars that have their brightness changed by having something dark move in front of them.”
This is one way to categorize them, but I was only referring to the inherently variable ones. Even within the inherent variable category, there are a whole slew of different types:
Image credit: NASA, ESA, H.E. Bond (STScI) and The Hubble Heritage Team (STScI/AURA).
- Pulsating variable stars, including Cepheids, RR Lyrae, long-period variables, Mira variables, slow irregular variables and more. This was the major type that I wrote about, but there are others.
- Eruptive variable stars, which shed large amount of mass over long timescales. These include Proto-stars, Herbig Ae/Be (pre-main-sequence) stars, giants, supergiants and hypergiants, luminous blue variables, Wolf-Rayet stars and others.
- And explosive/cataclysmic variable stars, including novae, recurrent novae, dwarf novae and supernovae, among others.
The most important thing I wanted people to take away is that the stars are not fixed, even inherently, but evolve both inside and at the surface, and that every star will have a period in its life where it inherently varies in its brightness, often in the extreme.
Thanks for a great week, and I’ll see you back next week for even more!
from ScienceBlogs http://ift.tt/1SRnYG9
“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small.” -Neil Armstrong
This past week saw a whole lot of interesting things happen, including tonight’s second full moon of the month: a rare blue moon. In my life, I saw the International Space Station for the first time, but here at Starts With A Bang, there was so much to learn about and share, including:
There was also a fun piece about our Solar System’s two-toned moon over at Forbes:
In addition, we reached our second milestone goal on our Patreon, so if you want to vote on which book chapter everyone gets for free in advance of my first book’s release, join and donate today. Other than that, it’s on to our Comments of the Week!
Image credit: White Dwarf, Earth, and Black Dwarf, via BBC / GCSE (L) and SunflowerCosmos (R).
From Omega Centauri on neutron stars going dark: “Sounds like the low temperature neutrino emissions rate is not well known. How else could there be such a large variation in estimated cooling time?
Can neutrinos really pass through neutron stars, even with a tinyl cross-section the column density of a NS is phenomenally high.”
There are two question here, both worthy of an answer and both contrary to what Omega Centauri expects. You see, when you first form a neutron star, you’re taking the core of a massive star that’s so big that the core itself — the part that becomes the neutron star — is more massive than our entire Sun. It collapses down and fuses into a ball of neutrons just a few kilometers wide, heating up to tremendous temperatures of about 10^12 K at the core and 10^6 K at the surface.
Image credit: ESO/L. Calçada, via http://ift.tt/1qChWAE.
It’s actually not the low-temperature cooling that’s a problem; we understand how neutrons behave at low temperatures. It’s not even the high-temperature cooling, although that’s less well understood. (We spend a lot less time with neutrons at 10^12 K than we do at lower temperatures.) It’s the high-density decay time and its gradient, since even though the binding energy is great enough that neutrons shouldn’t decay, they will on long enough timescales thanks to quantum tunneling. Without a perfect model of neutron star interiors, we recognize that the uncertainties in computation leave an uncertainty there. Additionally, your neutrons are more likely to decay close to the neutron-star crust, where the binding energies are lower. Even though the uncertainty is small overall, the decay times are so long that this leads to a few order of magnitude uncertainty in the cooling time of a neutron star.
But don’t worry about your neutrinos interacting. Sure, neutron stars are incredibly dense: about 10 times denser than a Uranium nucleus on average. But they’re also small, at just a few kilometers in radius. So the overall “chances-to-interact-with-a-particle” are only a few times as great your chances for an interaction if you emit a neutrino from the center of the Sun, and most of them are close to the surface anyway. If you randomly pass that neutrino through the core, you’ve got a few percent chance of an interaction (which is high!), but that’s a relatively unlikely path. Most neutrinos escape just fine.
Image credit: © 2015 Brian Kane, via http://ift.tt/1LAKh2l.
From PJ on advertising vs. art: “Then the thought of safety struck home. All these distractions along the highways & byways. Imagine, not knowing the signage was there, in the evening (night) there is an apparition of a phase of the moon before the driver – the moment of panic – WTF – simply because it should not be there.
Once the driver gets used to the sight, however, the brain tends to block such things; unless there is a constant change – a slide show, or something of that nature.
Don’t get me wrong, progress has its place; I would rather see a tree, though, than a picture of one.”
I don’t know, honestly, how well it works, but I always feel like the biggest weirdo when I’m driving down a dark road at night. If the Moon is out, or the stars, or bright planets, I’ll try and sneak a peak every chance I get at the sights of the natural beauty out beyond our Earthly skies.
Image credit: Alan Dyer, via http://ift.tt/1SRnYpD.
Yes, I know it’s dangerous, driving at some 70 mph (110-120 kph) or so, looking at anything other than what’s directly in front of (and around) you. But that’s the whole point of advertising: to distract you from what you’re doing and occupy that mental space with the craving to get you thinking about the product, service or cause in question. For me, if my options are between:
- actual nature,
- simulated nature,
- nothing at all, or
- an advertisement,
those are my choices, in my order of preference. Only actually restoring the natural setting would be a superior choice, to me, from what this art project accomplished.
Image credit: Multiwavelength images of M31, via the Planck mission team; ESA / NASA.
From Jan on the topic of where I publish: “But have you considered publishing on anything else but medium? It really is not good. Those images are 90 degrees rotated. Logical top and bottom of the “composite” image are one bellow another. They are split into many pieces, one can’t even save them and view them properly. RSS does not work there and more.”
At the very least, I know that RSS does work on Medium: my blog’s feed is here.
Writing about the Universe — actually, teaching about it and sharing its wonders and joys in general — is what I’m passionate about. Where and how I do it isn’t of the most paramount importance, but enjoying it, giving my audience a good experience and making (as close to) a living as I can doing it are what I value. That latter reason is something I can’t do on my own (but I’m trying with the Patreon), but right now, Medium is the best of all those worlds for me.
Perhaps down the road, though, it won’t be. Have any input on what might be next?
Image credit: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF.
From G, on the “big” question about “small” things like us: “In 1/2 billion years, the Sun will boil Earth’s oceans, so by that time our distant descendants will need to have spread into an interstellar civilization, or Earth-originated life will be another tragic footnote in a distant civilization’s galactic history logs. As we spread across the galaxy, we will discover numerous forms of life in other star systems, and reached some viable conclusions about the types of life that are possible in our galaxy.
But that will not answer the question of whether biology is convergent across galaxies. The only way to get that answer is to go to another galaxy.”
And then there’s the next logical question, if you want to go down that rabbit hole: even though, as far as we can tell, the physical processes of our own galaxy are at play in all galaxies, does that mean the way “life” is realized is the same in our galaxy or local group is the same everywhere? Do giant ellipticals in the heart of Virgo have the same life processes, or are there others unique to its environment?
Image credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.
Do isolated, field galaxies have different types of life that arise? How about more processed material, like that found at the heart of the Perseus cluster (above)?
What we’ve already learned about the Universe is amazing; what we continue to learn is amazing as well. But there will always be more to learn and check out there, and right now, the only thing limiting our knowledge is the resources we’re willing to invest.
Image Credit: NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA).
From Scott on dark matter halos: “I thought the rationale behind dark matter halo theory was that the inner and outer portions of a rotating galaxy have the same red shift, or velocity relative to the observer.”
That’s only one piece of evidence for dark matter halos. If you add a non-collisional component of matter to the Universe, you get large, fluffy, diffuse halos around all massive structures, which actually act as seeds for the massive structures in the first place.
But observationally, there was a piece of evidence that came first (like, 40 years before the rotation curves of galaxies were measured): galaxy clusters and the speeds of the individual galaxies in them. In fact, when we reconstruct what the mass profile of a galaxy cluster looks like, we find that sure, individual galaxies have large masses, but there’s an even greater amount of mass distributed in a diffuse, cluster-scale halo!
Image credit: Greg Kochanski, Ian Dell’Antonio, and Tony Tyson (Bell Labs), of the reconstructed mass in a large galaxy cluster.
This is to say there’s a lot more evidence for dark matter halo theory than just the rotation curves of galaxies. They play a part, but that’s actually the least strong evidence out there.
Image credit: NASA/ESA/Richard Massey (California Institute of Technology).
From Boris Borcic on a possibility for dark matter: “Long shot, but on dark matter not possibly being formed of neutrinos, I’d like to be shown that a Fermi gas of (slightly massive) neutrinos can’t achieve dark matter density.”
The problem with neutrinos isn’t that they couldn’t achieve the necessary density of dark matter: if each type of neutrino had a mass of about 4 eV, we’d be golden. (They’re constrained, experimentally, to be less than about 2 eV apiece, by the way.) The problem is that if neutrinos made up this dark matter, that dark matter would be hot, which means it would be moving relatively quickly when neutral atoms were formed. It would suppress the formation of structure on large scales, something that vehemently disagrees with observations.
Image credit: Maroto A.L., Ramirez J., astro-ph/0409280.
It’s the clustering data that rules this scenario out. Based on the measured mass of neutrinos and the constraints we have, neutrinos appear to be about 0.4% of the dark matter, a number that could increase to a maximum of about 2%, but not more.
It’s a good idea, but one that was explored in incredible detail… and ruled out.
Image credit: Aurore Simonnet, Sonoma State University.
From Jim Salsman on primordial black holes as dark matter: “[I]f inflation resulted in sufficient intermediate mass black holes (around 100,000 solar masses each) to explain the formation of relatively recently [discovered] quasars at z>6, those would require that all dark matter be comprised of such black holes, and they would not be detectable through gravitational lensing.”
This statement is phrased as a “this is true,” but in reality it should be asked as, “is this true?” If you allow for the fluctuations inflation produces normally (Gaussian), this is impossible. Producing a fluctuation of more than about 10^-4 solar masses would be ruled out convincingly by power spectrum and CMB data; that can’t happen. So you need an exotic scenario — something involving topological defects — to produce fluctuations at specifically one scale preferential to all others, and that won’t mess up any of our other observations. It is very, very difficult to do this.
Image credit: Sebastian F. Bramberger, Robert H. Brandenberger, Paul Jreidini, and Jerome Quintin, via http://ift.tt/1SRo0xU.
But the kicker is this: you don’t need to! Gaussian fluctuations — the kind inflation normally predicts — can give you the supermassive black holes needed all the way up to a redshift of 15-20 or so through the process of hierarchical mergers. At the redshift of z=6 that you referred to, in fact, in the graph from the only one of the three papers that mentions the scenario you put forth, they show how Gaussian fluctuations lead to SMBHs of ~10^9 solar masses with no problem, beginning from that tiny 10^-4 seed. So what you contend is a plausible (but fringe) explanation, but one that’s not required to explain what we observe. The standard picture does just fine.
But if we start seeing these objects at, say, a redshift of 30, then we’ve got a reason to listen.
Image credit: X-ray: NASA/CXC/U.Birmingham/M.Burke et al.
From Denier on the pieces of evidence for dark matter: “There are implications on all of the above listed phenomena currently attributed to Dark Matter if it is confirmed that antimatter falls up.”
If antimatter falls up, we would be tremendously surprised. A lot of things would be wrong. E=mc^2 would be wrong, for one, or gravitational and inertial mass would not be identical. We’re doing the experiment because we have to check all our theories and expectations against the evidence, but we have been attempting to measure this for maybe 50+ years now, and haven’t been able to create and track neutral antimatter precisely enough to check it out. We will keep trying, and hopefully we’ll verify that it falls in a gravitational field just like we expect.
We see antimatter ejecting out of galactic “jets” with the same velocity profiles as we see for normal matter, so we do expect it to behave gravitationally just like matter does. But we don’t know for certain until we check. Still, if it turned out that antimatter falls up, I would say it’d be the biggest surprise and discovery of the 21st century. I’ll keep watching.
Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration; Acknowledgment: H. Bond (STScI and Penn State University).
And finally, from Wow on the different types of variable stars: “Well, as far as I’m aware, there are three types of variable.
Inherently variable. Stars that change their luminosity.
Multistar variables. Objects that change their luminosity because they appear to be a singe object when they are not.
Occulted variables. Stars that have their brightness changed by having something dark move in front of them.”
This is one way to categorize them, but I was only referring to the inherently variable ones. Even within the inherent variable category, there are a whole slew of different types:
Image credit: NASA, ESA, H.E. Bond (STScI) and The Hubble Heritage Team (STScI/AURA).
- Pulsating variable stars, including Cepheids, RR Lyrae, long-period variables, Mira variables, slow irregular variables and more. This was the major type that I wrote about, but there are others.
- Eruptive variable stars, which shed large amount of mass over long timescales. These include Proto-stars, Herbig Ae/Be (pre-main-sequence) stars, giants, supergiants and hypergiants, luminous blue variables, Wolf-Rayet stars and others.
- And explosive/cataclysmic variable stars, including novae, recurrent novae, dwarf novae and supernovae, among others.
The most important thing I wanted people to take away is that the stars are not fixed, even inherently, but evolve both inside and at the surface, and that every star will have a period in its life where it inherently varies in its brightness, often in the extreme.
Thanks for a great week, and I’ll see you back next week for even more!
from ScienceBlogs http://ift.tt/1SRnYG9
