I find it hard to believe that you studied botany.
The fact that you disagree with me isn't a very good basis on which to doubt my statement that I studied botany. I may, for example, have had rotten teachers, or it may have been a long time ago, or I may have been an awful student. Or, for that matter you might be wrong. As it turns out, I was a botany major for three years, it was a long time ago, and I'm probably not an impartial judge on the other questions.
If CO2 were a limiting factor, it would be in short demand, but it's in great excess...is very readily available at the elevations in the atmosphere where it's required.
I suspect you mean "great demand" or "short supply" (instead of "short demand"). CO2 is not abundant. It makes up less than 0.04 percent of the atmosphere (Argon, for comparison, is 25 times as common, but you don't hear people talking about Argon as particularly abundant).
N and P on the other hand, are in demand, and usually not in great surplus.
IIRC, this is quite true in areas with exceptionally high water flow (e.g. rain forests, the open sea), since fixed Nitrogen & Phosphorous are generally very soluble, and thus wash away. But most plant growth occurs outside these areas (this is why people are so concerned about the rain forests; they grow very slowly and will take a long time to recover).
Plant matter (dried) is about 45-50% carbon & 40% oxygen by mass. Less than 0.5% is nitrogen & phosphorous (combined). Plants are mostly starch / sugar / cellulose--in short, carbohydrates--and very little protein (which is where the N & P go). So the C/(N+P)ratio in plants is on the order of 100 to 1.
If you look at the volume of space surrounding a plant (say, half air, half soil) you will see fixed nitrogen in the soil between 10 & 50 ppm. Given dirt's specific gravity is around 2.5, and air's is around 0.00127, and therefore dirt is pretty close to 2000 times as dense as air, and carbon is just a little lighter than oxygen, we find an environmental ratio of about: (0.03%/3) to (2000*50/1000000) or 10^-5 to 1.
Thus, from a plants point of view (comparing abundance inside the plant to outside the plant) nitrogen and phosphorous are about 10^7 times as abundant as carbon.
The idea that CO2 is a limiting factor for most ecosystems is laughable.
*smile* You say that, but I'll bet you wouldn't cough up a "+1 Funny" if you had mod points, would you?
Rather than typing in material from my old text books, I did a quick search for similar text on the web (risky, I know, since some of the sites I cite might turn out to be funded by Republicans (*smile*)):
Most of our conventional crops, including rice and wheat, assimilate atmospheric CO2 by the C3 pathway of photosynthesis, which takes place in the mesophyll cells of leaves. Photosynthetically, these plants are underachievers because, on the one hand, they assimilate atmospheric CO2 into sugars but, on the other hand, part of the potential for sugar production is lost by respiration in daylight, releasing CO2 into the atmosphere, a wasteful process termed photorespiration. This is due to the dual function of the key photosynthetic enzyme, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). High CO2 favors the carboxylase reaction and thus net photosynthesis; whereas high O2 promotes the oxygenase reaction leading to photorespiration. When plants first evolved, photorespiration was not a problem because the atmosphere then was high in CO2 and low in O2. As a byproduct of photosynthesis, O2 accumulated in the atmosphere and reached the present level a million years ago. Current atmospheric CO2 levels limit photosynthesis in C3 plants. Furthermore, photorespiration reduces net carbon gain and productivity of C3 plants by as much as 40%. This renders C3 plants less competitive in certain environments. In contrast, with some modifications in leaf anatomy, some tropical species (e.g., maize and sugarcane) have evolved a biochemical "CO2 pump," the C4 pathway of photosynthesis, to concentrate atmospheric CO2 in the leaf and thus overcome photorespiration. Therefore, C4 plants exhibit many desirable agronomic traits: high rate of photosynthesis, fast growth, and high efficiency in water and mineral use.
CO2 enrichment can also affect plant communities directly. For many plant species, increased CO2 concentrations lead to increased rates of net photosynthesis and improved water-use efficiency, resulting in larger plants. This effect is greatest in C3 plants and is typically small or negligible in C4 plants. Where plant communities consist of both C3 and C4 species, the different responses of these two groups can lead to changes in plant community composition over time.
Dude you got hoaxed. That petition was a total hoax. Geri Halliwell of the spice girls is one of the signators as a (biologist).
I'm not disputing that I may have been hoaxed (see my reply to the post above yours) but I don't see her name or any breakdown by field (no one is labled "biologist" etc. that I can see.). How did you determine that she was listed as a signator?
Please do some research before posting bogus links as science.
I never claimed it was science; I claimed that it was the pettition that the poster I was replying to had mentioned.
-- MarkusQ
P.S. And here's an interesting thing to try: go to the list of names, choose one at random (pref. an odd one, e.g. "Ismail B Haggag") and do a web search on them. Most of them seem to be real people at least. When the ones I tested should up in lists (e.g. faculty rosters) I tried picking a random name off the roster and searching for it on the pettition (to see if they had "harvested" the names off of university web sites. None of them were there.
The Oregon Institute's "petition" is a hoax. The names are largely made-up. I recall Captain Kangeroo being among their number. The OISM is run from a small warehouse in rural Oregon. Their scientific credibility is on a par with the Flat Earth Society.
*laugh*
That will teach me to do a quick link search! (Although to be fair, I haven't really researched your claims either). I don't doubt that there are are people in the "global-warming-is-bunk" camp that have political agendas; for that matter many people in the "humans cause-global warming camp" have a pretty clear political agenda too. In my defense, please note the times on my varrious posts over the past few weeks (and frequent refferences to coffee); we've got a new son, & I've been hopping on while rocking him between diaper changes,, etc. at pretty much random times (read: not enough sleep).
So I will back down to a few statements I know first hand to be correct, and not try to back anything with potentially tainted links:
I don't recall hearing about the pettition until the first poster mentioned it; based on that, I just did a quick google & posted what I found. My bad.
I have seen the long term (>1000 year) climate data, and it is noisy. I worked briefly with someone (him in the field, me on the computer) who was trying to correlate data from varrious locations, and the correlations they found (to distinguish global from local) was about as good as it is at present. The noisy climate record isn't a consequence of our ignorance. Against this background, the size of the signal claimed for global warming is absurdly small (cf the day length change posited in the article here, vs, the change due to tidal forces, etc.).
I'm not an industry flack, fundumentallist, etc. of any stripe, and I am also not a climate expert. I was a botany major for a while, (w. a 4.0 GPA), but then I was also a math major, a physics major, and several others.
The main limiting factor for most plants is CO2 supply. The only reason we have the atmosphere we do (almost no carbon, lots of oxygen) even though we started out with a carbon-heavy atmosphere is that the plants sucked down every scrap they could get their grubby little leaves on. As one on my professors put it, "dumping CO2 into the attmosphere is like throwing money off a building in New York City: you might change the local environment some, but if you expect it to accumulate and block up the street, you're dreaming."
In the 1960s, the more vocal global warming advocates were asserting that, by 2000, the earth would be uninhabitalbly hot. They keep shifting the claims, but it always amounts to "dire things will happen ~40 years from now unless you do what we say now, without wasting time on study or debate." This has biased me against them.
The people I have personally met who have felt most strongly about global warming seem to 1) fear and resent "technology", and 2) have a burning desire to believe that what they do makes a difference in the big picture. This is pretty easy to test if you bait them with "I heard about an article that may have claimed..." and see which silly statements they will accept & which ones they reject. It's my conclusion that the reason the "people are changing the Earth's climate" story sells so well (along with nonsense like "cut the plastic tabs on your six packs to save the dolphins") has much more to do with a fear of insignificance and a need for "redemtion" than with anything rational. And yes, I do see the analogy with my quick acceptence of the pettition, despite the fact that I don't trust "Discovery" and I don't trust "Science-by-pettition"--I suspect I am swayed by my pro-technology/on-the-galactic-scale-humans-are-in significant bias.
1010011010 wrote: when the poles shift in 15,000 -20,000 years, killing most life, shifting the Earth's plates, and plunging the planet into an ice age, it won't matter much to us.
...and somebody (I suppose you know who you are) modded it "Offtopic". Given that the topic was the interaction between the earth's temp. and rotation, and that the effect 1010011010 pointed out is
much more pronounced than the one mentioned in the article (though of course not as dramatic as 1010011010 makes it sound)
much more likely than the one mentioned in the article
much more interesting than the one mentioned in the article
much more established than the one mentioned in the article
...it is hard to see how you could consider it "Offtopic". For that matter, the strength of the data for pole reversals causing major climate shifts is about as strong (or I should say, as weak) as the data for global warming (whether caused by humans or an unrelated trend in the global climate).
-- MarkusQ
P.S. There was a very interesting comparison floating around a few years back (it was cited against me in an argument about my shorting idiodic dot com stocks) between the global warming data and the exponential growth of the internet economy. I replied that I agreed, and that I thought both "trends" were drawing conclussions far in excess of the data.
Boy, did I get flamed.
If anybody has the article I'd love to have a link/copy.
I should state up front that my first post on this topic was off the cuff & contemporanious with my first cup of coffee this morning, and I've haven't sat down and put anything on paper. So some or all of this may fall flat on more detailed analysis. But with that caveat:
If you're trying to minimize Hamming distance, wouldn't it be better to establish the first connection without an ID then ask the peer for its ID and the IDs around it? Then we pick a non-occupied one and use it.
I suppose I'm assuming that there are a relatively few "doors" into the network, and worried about clustering; also, my gut feeling is that starting at a random point lets you disregard a number of potential problems on statistical grounds.
Then we can just start making connections, getting their IDs, and dropping the furthest out, yes?
Hmmm. What you are describing (if you drop my assumption of random starting location) results in what is called flocking. Basically, everyone winds up trying to move to the center of the cloud as they see it. Nice dense connectivity, but (since we aren't charged for hamming-distance) there's no real advantage to it, and it increases the risk of fragmentation.
I like the idea of "introduction" via peers - watch addresses that come by, if one is a certain Hamming distance or shorter away from one of our connections, tell that connection. 's that basically how it works?
Yep.
Finding Hamming distance sounds like a parity-class problem (XOR and sum, right?) so it shouldn't be bad at all. Though is there an easier way for the sum part of it than "if the last bit is one, increment counter, rotate right, repeat"? This might not be a problem, and that's an O(n) loop (right?) - not bad, but is there an O(1) solution?
It's O(n) where n is the number of bits in the address, which scales log(n) with the max size of the network; not bad at all. You could reduce it further by doing a lookup table (array [0..255] of 0..8 = (0..255).collect{ |i| i.bits_set } or some such), but there isn't really any need; the amount of work is << the amount required just to receive a packet.
Maybe we'll just want to check addresses at random rather than every one - save cycles for more useful things. Also, saturated hosts will probably not even bother with comparisons - if all n of our local peers are right, then why bother?
Cynical answer: there's no harm (all of this should be very cheap) and we can avoid having the behaviour change after the beast has been running for hours, which would complicate the code and might open the door for mysterious & hard to find bugs. ("It ran fine for about a week, then it just went cross-eyed and dumped grape jelly onto the hard drive!") If I'm going to leave something running for a long time I like (where possible) to have hitting the same code paths at the end as it was in the begining.
How do we handle address space conflicts? If, say, the network were to partition itself in two, somehow (links just happened to be dropped in the right way), and then a host comes up that bridges the two segments, what do we do? Worse, what happens if two perfect hypercubes overlap [all n connections in each are only one bitflip away, and all have the same numbers]?
This is one of the "you can ignore it on statistical grounds" points. With random starting IDs the odds of this scale towards the odds of all the air being on the other side of the room the next time you inhale. It could happen, but I wouldn't hold my breath.
Why not ask the kids? Make it a game of some sort (details depending on age) where they have to find and click on some target word or image. Track how often (or how quickly) each combination is picked, and you'll have all the data you need to answer your question. To keep from wasting time in the parts of colour space where you know the answers (yes, navy blue text shows up well on a pale pink background) have the game advance through levels (each level having less distinction than the one before) until they have three wrong clicks/timeouts. Then start over with another base colour pair.
You still have a problem, though. You are imposing a routing algorithm based on ping times in a dynamic environment. You will get new nodes, others will disappear, while your routing metric will change wildly over time.
No, we have a considerable advantage over the military networks; they are responsible for everything (down to making sure there is power, EMP hardening, etc., etc.) while we just have to worry very top. Specifically, the ping times here are at the IP level, not at the p2p level. Since someone else is kind enough to maintain that level for us (and with much greater stability than we could hope for at the p2p layer) the (IP) ping times won't change when (p2p) nodes come & go.
I don't think your algorithm is dynamic enough to cope without having the nodes broadcast their presence in some way.
Announce, yes. Broadcast, no. In a world with no cheaters, all you need to do (once connected to the network) is talk to your peers (& nodes they refer you to). No broadcasts needed.
If there are cheaters, you need to do a bit more (e.g. buffer & broadcast proportionate to the depth of the expected cheating). It might seem like this would be an open ended arms race, but in order to pass as good nodes the cheaters would have to act like good nodes and if things go far enough the only way to cheat would be to be a good node for a significant fraction of the time. So you wind you winning after all, at least as far as the network topology goes.
As for dealing with cheaters, it just moves the problem to a new level (I won't go into more details since I don't want to give any ideas to the bad guys), but as far as I can see it wouldn't be any worse than what those gnutty lime guys face now. Ultimately, the bad guys could get themselves spiffy uniforms and go door to door with guns, matches & branding irons.
I don't know of a topology that could handle that.
Only detailed simulation or even real-life deployment can truly provide the answers to these sorts of questions. I'm just saying that this particular problem domain tends to be "swampy"; things that appear promising at first run into pitfalls much further down the road, much to everyone's frustration and indignation.
*smile* That's why in real life I tent to bid such jobs by the hour rather than by the project.
You want to have "short" edges in your hypercube in order do reduce the network load and latency. You are in effect organizing a virtual hypercube network on top of a mix of graph- and tree-oriented physical networks. You need to have the hypercube topology make sure that a limited number of physical nodes are in the path between each virtual node.
Not really. If the present system is tree-on-(uncorrelated)tree, you are still better off going to hypercube-on-(uncorrelated)tree. I agree that you'd be much better off going to a hypercube-on-tree where the hypercube is "rotated" to align with short hops, but that doesn't mean you have to do it that way.
Given that we can't do it perfectly, we can still try to do "reasonably well". As a first stab:
Impose a finer grained (say, 16 bits for each bit of the ID) latice on the space.
Have every node keep 3+ IDs active (using the rules in my prior post).
Track average ping times (using the latice) and periodically introduce new IDs chosen to move you hamming-closer to nodes which are ping-closer, and at the same time gracefully retire IDs that aren't so aligned.
This should drift towards shorter edges without breaking the pseudo-hypercube. Even though you have more IDs active, it shouldn't affect the amount of traffic at each node if the routing/broadcast rules are set up right. Note also that there is no additional routing trafic required to do this.
Keep in mind that some problems are very hard to solve but easy to aproximate; often RightAnswer=NP, 99%Answer=O(N).
Neat idea, only not a very feasible one. You want to have "short" edges in your hypercube in order do reduce the network load and latency. You are in effect organizing a virtual hypercube network on top of a mix of graph- and tree-oriented physical networks. You need to have the hypercube topology make sure that a limited number of physical nodes are in the path between each virtual node.
Excelent point.
Even a quite large hammer won't change this.
But a clever wrench might. Hmmm. Let me think on it...
If you're an exempt employee (which you probably are), you get paid a salary, not by the hour. Wal-Mart workers are non-exempt, and are entitled to overtime pay.
Was, not are.
And joking, not serious.
And at one of the startups, entitled to, not paid.
MarkusQ:we just want to bias the network towards the desired form. For example...New nodes pick a random twenty+ bit ID...New nodes connect up to whoever then can find.
Salamander: Except that you describe routing based on Hamming distance (which won't work because of looping issues) rather than shared prefix/suffix, this sounds a lot like Tapestry.
Actually, I was just using the Hamming distance as a rough gauge for "how far is this node from where it should be in a perfect binary hyper-cube" (since in a perfect binary hyper-cube, each node is connected to all the nodes (and only the nodes) at hamming-distance 1 from its ID. So what I described was a way to 1) pick a corner at random, 2) wander towards it, and 3) go to another nearby location if the one you picked turns out to be occupied.
I'm not familiar with the looping issues you refer to. Can you elucidate? (Note also that this would not be so much a way to "route" as a way to "partially broadcast" (e.g., maybe decrement TTL by two when sending "in the wrong direction" or propogate ox-bow removal info when something is broadcast to you via a sub-optimal path). We wouldn't count on nodes being where they should be, just hamming-close.)
Walmart forces people to work off the clock. It has been on the news and I have had employees confirm this to me. They set a 'goal' and if they don't reach it they are expected to punch out and return to thier job off the clock. Some efficiancy!
Having worked at (note: "at"/= "for") Intel, Microsoft, and two dot coms, I've started thinking of this as normal. In fact, if the trend of the last few decades continues, I expect to wind up at a company that doesn't specify any hours, but just has a little real-time LCD display outside every cube, labled "Your score/GP/Lives remaining."
Now implementing a dynamic network in a hypercude or hypertoroid topology brings on a new set of problems such as dynamically re-allocating the hypercude node addresses as users fall off and climb back on to the network. This can be more of a bear than people realize.
This shouldn't be too hard (at least it doesn't look too hard sitting here on a Sunday morning, half way through my first cup of liquid brains). The key is to note that we can't (and therefore needn't bother trying to) enforce the topology at all times. Instead, we just want to bias the network towards the desired form. For example:
New nodes pick a random twenty+ bit ID. This would probably not be enough to prevent collisions, (cf the Birthday Paradox) but that can be dealt with presently.
New nodes connect up to whoever then can find. This would be pretty much what happens on most p2p now.
Once the node has the desired number of connections, it can rank them by comparing the number of bits its ID has in common with the IDs of each peer (the Hamming Distance between the IDs). As further peers are discovered, it can establish connections to any that are Hamming-closer than its worst ranked peer and drop the worst ranked peers from its connections.
Likewise, if a node detects a pair of peers that are Hamming-closer to each other than either is to it, it can "introduce" them to each other.
If two peers meet and discover they have the same randomly chosen ID, the younger can flip one bit (for each ID bit, count the number of ctive connections that differ on that bit; flip one with the max count) and continue.
Fat pipe peers can run more than one ID if they wish (cf UltraPeers)
This should at least be functional; no doubt there are a number of clever hacks that could be made...
...modern Gnutella servents have reduced traffic and improved network scalability by means of...use of UltraPeer/leaf relationship
A hypernet is an interesting idea, although I can think of a number of reasons why current p2p sharing networks would not implement them. Namely, because authoritarian networks like Napster were shut down by trade associations like the MPAA/RIAA, while more anarchic networks like Gnutella are more immune from such actions - we must consider not only the survival of the scaling network due to technical constraints like Dr. Gunther does, but also it's survival due to legal constraints orchestrated by large corporations.
I think your concern here is exactly backwards. Specifically, higher dimensional topology would decrease the need for central "UltraPeer"s (also known as lawyer bait) and thus make the network harder to shut down. If the trend towards depending more on some "peers" than others continues to the natural limit, you wind up right back at Napster (one UberUltraPeer to rule them all, and in the darkness...get eaten by a grue if it's lucky, sued by the RIAA if it's not).
On the other hand, if the topology is made more scalable, the targets won't be as tempting at any given network size, and the whole thing would be harder to take down by force. If all nodes are equal, cutting one will likely create enough publicity to attract seven more to take its place.
*smile* I assume they only care if it's free-as-in-speech, and not if it's free-as-in-format.
-- MarkusQ
P.S. I say this as a Python fan; truth be known, that's pretty much how I've indented my code (in anything but forth/postscript) since the mid-seventies.
Many years ago we used to have a yearly "printer calling contest" (sort of like hog calling contest) at a local pub. Contestents would immitate a printer, and listeners would try to guess the make (& model, & even in one case someone got the serial number, though this was sort of a set-up).
This was back when computer geeks were very rare, so we were just one more group that shoved a few tables together in the corner, ordered beer, made funny noises, laughed, ordered more beer, rinse, lather, repeat.
MQR: How odd. *smile* Given all her talk about VT-xxx terminals, pine/elm, and scads of users on each box, I would never have guessed that my friend's site was running MsDos.
Reziac::ARealMcCoy: You young'uns just ain't old enough to remember BBSing. Terminal apps emulating VT-xxx, textmode mail, and scads of users on every box.
*laugh* Ah, now you'd be talking about my site. But I don't think I ever had more than a half dozen or so users on a PC at once (dial up that is--on site we had about thirty, but each had their own PC & pooled "connections" for file transfer).
BTW, thanks; I haven't been called a "young'un" for...well let's just say it's been quite some time. Our first dial-up box was a NorthStar Advantage that could only support two remote users at a time (plus one sitting at it).
This was known as an "ANSI bomb". It could only happen if the user had ANSI loaded in DOS, and IIRC then only a version of ANSI that allowed itself to be reset by such sequences (such as the default ANSI.SYS that shipped with M$DOS).
How odd. *smile* Given all her talk about VT-xxx terminals, pine/elm, and scads of users on each box, I would never have guessed that my friend's site was running MsDos.
Guido69: Perfect. Now if I can just get this up and running, I can anonymously ask Kathleen to marry me. 'Taco won't have a clue who's stealing his girl! Bwaahahahah.
Perfect? Hardly. In the unlikely event that she decides to accept she won't know who to accept.
Unless of course she saw your post...unless of course he also saw your post...
Then the e-mail reader was not treating the e-mail as plain text. If the only escape sequences it recognizes are end of message and start of attachment, the only thing that can hurt you is the attachment -- if you are dumb enough to run an executable attachment.
That had been roughly my thinking as well. But the point is that the e-mail reader (either pine or elm, IIRC) was just treating the body as plain text, and happily dumping it (escapes and all) to the terminal.
The terminal (VT100 or some such) was seeing the escape sequence and obligingly reprogramming the specified key to do the dastardly deed. Then it would just as obligingly clear the screen, so that all the user saw was the message telling them to hit the booby-trapped key.
Slashdot Mirror
I find it hard to believe that you studied botany.
The fact that you disagree with me isn't a very good basis on which to doubt my statement that I studied botany. I may, for example, have had rotten teachers, or it may have been a long time ago, or I may have been an awful student. Or, for that matter you might be wrong. As it turns out, I was a botany major for three years, it was a long time ago, and I'm probably not an impartial judge on the other questions.
If CO2 were a limiting factor, it would be in short demand, but it's in great excess...is very readily available at the elevations in the atmosphere where it's required.
I suspect you mean "great demand" or "short supply" (instead of "short demand"). CO2 is not abundant. It makes up less than 0.04 percent of the atmosphere (Argon, for comparison, is 25 times as common, but you don't hear people talking about Argon as particularly abundant).
N and P on the other hand, are in demand, and usually not in great surplus.
IIRC, this is quite true in areas with exceptionally high water flow (e.g. rain forests, the open sea), since fixed Nitrogen & Phosphorous are generally very soluble, and thus wash away. But most plant growth occurs outside these areas (this is why people are so concerned about the rain forests; they grow very slowly and will take a long time to recover).
Plant matter (dried) is about 45-50% carbon & 40% oxygen by mass. Less than 0.5% is nitrogen & phosphorous (combined). Plants are mostly starch / sugar / cellulose--in short, carbohydrates--and very little protein (which is where the N & P go). So the C/(N+P)ratio in plants is on the order of 100 to 1.
If you look at the volume of space surrounding a plant (say, half air, half soil) you will see fixed nitrogen in the soil between 10 & 50 ppm. Given dirt's specific gravity is around 2.5, and air's is around 0.00127, and therefore dirt is pretty close to 2000 times as dense as air, and carbon is just a little lighter than oxygen, we find an environmental ratio of about: (0.03%/3) to (2000*50/1000000) or 10^-5 to 1.
Thus, from a plants point of view (comparing abundance inside the plant to outside the plant) nitrogen and phosphorous are about 10^7 times as abundant as carbon.
The idea that CO2 is a limiting factor for most ecosystems is laughable.
*smile* You say that, but I'll bet you wouldn't cough up a "+1 Funny" if you had mod points, would you?
-- MarkusQ
Most of our conventional crops, including rice and wheat, assimilate atmospheric CO2 by the C3 pathway of photosynthesis, which takes place in the mesophyll cells of leaves. Photosynthetically, these plants are underachievers because, on the one hand, they assimilate atmospheric CO2 into sugars but, on the other hand, part of the potential for sugar production is lost by respiration in daylight, releasing CO2 into the atmosphere, a wasteful process termed photorespiration. This is due to the dual function of the key photosynthetic enzyme, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). High CO2 favors the carboxylase reaction and thus net photosynthesis; whereas high O2 promotes the oxygenase reaction leading to photorespiration. When plants first evolved, photorespiration was not a problem because the atmosphere then was high in CO2 and low in O2. As a byproduct of photosynthesis, O2 accumulated in the atmosphere and reached the present level a million years ago. Current atmospheric CO2 levels limit photosynthesis in C3 plants. Furthermore, photorespiration reduces net carbon gain and productivity of C3 plants by as much as 40%. This renders C3 plants less competitive in certain environments. In contrast, with some modifications in leaf anatomy, some tropical species (e.g., maize and sugarcane) have evolved a biochemical "CO2 pump," the C4 pathway of photosynthesis, to concentrate atmospheric CO2 in the leaf and thus overcome photorespiration. Therefore, C4 plants exhibit many desirable agronomic traits: high rate of photosynthesis, fast growth, and high efficiency in water and mineral use.
CO2 enrichment can also affect plant communities directly. For many plant species, increased CO2 concentrations lead to increased rates of net photosynthesis and improved water-use efficiency, resulting in larger plants. This effect is greatest in C3 plants and is typically small or negligible in C4 plants. Where plant communities consist of both C3 and C4 species, the different responses of these two groups can lead to changes in plant community composition over time.
Finally, IIRC, most of the biomass is C3 plants.
-- MarkusQ
I'm not disputing that I may have been hoaxed (see my reply to the post above yours) but I don't see her name or any breakdown by field (no one is labled "biologist" etc. that I can see.). How did you determine that she was listed as a signator?
Please do some research before posting bogus links as science.
I never claimed it was science; I claimed that it was the pettition that the poster I was replying to had mentioned.
-- MarkusQ
P.S. And here's an interesting thing to try: go to the list of names, choose one at random (pref. an odd one, e.g. "Ismail B Haggag") and do a web search on them. Most of them seem to be real people at least. When the ones I tested should up in lists (e.g. faculty rosters) I tried picking a random name off the roster and searching for it on the pettition (to see if they had "harvested" the names off of university web sites. None of them were there.
*laugh*
That will teach me to do a quick link search! (Although to be fair, I haven't really researched your claims either). I don't doubt that there are are people in the "global-warming-is-bunk" camp that have political agendas; for that matter many people in the "humans cause-global warming camp" have a pretty clear political agenda too. In my defense, please note the times on my varrious posts over the past few weeks (and frequent refferences to coffee); we've got a new son, & I've been hopping on while rocking him between diaper changes,, etc. at pretty much random times (read: not enough sleep).
So I will back down to a few statements I know first hand to be correct, and not try to back anything with potentially tainted links:
Better?-- MarkusQ
Sounds good...I'm reluctant to give up the random address selection but this seems reasonable...hmmm...
-- MarkusQ
I also applaud you for posting this. The pettition you refer to has not received enough attention (see also). But even more important is to look at the data.
-- MarkusQ
much more pronounced than the one mentioned in the article (though of course not as dramatic as 1010011010 makes it sound)
much more likely than the one mentioned in the article
much more interesting than the one mentioned in the article
much more established than the one mentioned in the article
-- MarkusQ
P.S. There was a very interesting comparison floating around a few years back (it was cited against me in an argument about my shorting idiodic dot com stocks) between the global warming data and the exponential growth of the internet economy. I replied that I agreed, and that I thought both "trends" were drawing conclussions far in excess of the data.
Boy, did I get flamed.
If anybody has the article I'd love to have a link/copy.
If you're trying to minimize Hamming distance, wouldn't it be better to establish the first connection without an ID then ask the peer for its ID and the IDs around it? Then we pick a non-occupied one and use it.
I suppose I'm assuming that there are a relatively few "doors" into the network, and worried about clustering; also, my gut feeling is that starting at a random point lets you disregard a number of potential problems on statistical grounds.
Then we can just start making connections, getting their IDs, and dropping the furthest out, yes?
Hmmm. What you are describing (if you drop my assumption of random starting location) results in what is called flocking. Basically, everyone winds up trying to move to the center of the cloud as they see it. Nice dense connectivity, but (since we aren't charged for hamming-distance) there's no real advantage to it, and it increases the risk of fragmentation.
I like the idea of "introduction" via peers - watch addresses that come by, if one is a certain Hamming distance or shorter away from one of our connections, tell that connection. 's that basically how it works?
Yep.
Finding Hamming distance sounds like a parity-class problem (XOR and sum, right?) so it shouldn't be bad at all. Though is there an easier way for the sum part of it than "if the last bit is one, increment counter, rotate right, repeat"? This might not be a problem, and that's an O(n) loop (right?) - not bad, but is there an O(1) solution?
It's O(n) where n is the number of bits in the address, which scales log(n) with the max size of the network; not bad at all. You could reduce it further by doing a lookup table (array [0..255] of 0..8 = (0..255).collect{ |i| i.bits_set } or some such), but there isn't really any need; the amount of work is << the amount required just to receive a packet.
Maybe we'll just want to check addresses at random rather than every one - save cycles for more useful things. Also, saturated hosts will probably not even bother with comparisons - if all n of our local peers are right, then why bother?
Cynical answer: there's no harm (all of this should be very cheap) and we can avoid having the behaviour change after the beast has been running for hours, which would complicate the code and might open the door for mysterious & hard to find bugs. ("It ran fine for about a week, then it just went cross-eyed and dumped grape jelly onto the hard drive!") If I'm going to leave something running for a long time I like (where possible) to have hitting the same code paths at the end as it was in the begining.
How do we handle address space conflicts? If, say, the network were to partition itself in two, somehow (links just happened to be dropped in the right way), and then a host comes up that bridges the two segments, what do we do? Worse, what happens if two perfect hypercubes overlap [all n connections in each are only one bitflip away, and all have the same numbers]?
This is one of the "you can ignore it on statistical grounds" points. With random starting IDs the odds of this scale towards the odds of all the air being on the other side of the room the next time you inhale. It could happen, but I wouldn't hold my breath.
-- MarkusQ
-- MarkusQ
No, we have a considerable advantage over the military networks; they are responsible for everything (down to making sure there is power, EMP hardening, etc., etc.) while we just have to worry very top. Specifically, the ping times here are at the IP level, not at the p2p level. Since someone else is kind enough to maintain that level for us (and with much greater stability than we could hope for at the p2p layer) the (IP) ping times won't change when (p2p) nodes come & go.
I don't think your algorithm is dynamic enough to cope without having the nodes broadcast their presence in some way.
Announce, yes. Broadcast, no. In a world with no cheaters, all you need to do (once connected to the network) is talk to your peers (& nodes they refer you to). No broadcasts needed.
If there are cheaters, you need to do a bit more (e.g. buffer & broadcast proportionate to the depth of the expected cheating). It might seem like this would be an open ended arms race, but in order to pass as good nodes the cheaters would have to act like good nodes and if things go far enough the only way to cheat would be to be a good node for a significant fraction of the time. So you wind you winning after all, at least as far as the network topology goes.
As for dealing with cheaters, it just moves the problem to a new level (I won't go into more details since I don't want to give any ideas to the bad guys), but as far as I can see it wouldn't be any worse than what those gnutty lime guys face now. Ultimately, the bad guys could get themselves spiffy uniforms and go door to door with guns, matches & branding irons.
I don't know of a topology that could handle that.
-- MarkusQ
*smile* That's why in real life I tent to bid such jobs by the hour rather than by the project.
-- MarkusQ
Not really. If the present system is tree-on-(uncorrelated)tree, you are still better off going to hypercube-on-(uncorrelated)tree. I agree that you'd be much better off going to a hypercube-on-tree where the hypercube is "rotated" to align with short hops, but that doesn't mean you have to do it that way.
Given that we can't do it perfectly, we can still try to do "reasonably well". As a first stab:
This should drift towards shorter edges without breaking the pseudo-hypercube. Even though you have more IDs active, it shouldn't affect the amount of traffic at each node if the routing/broadcast rules are set up right. Note also that there is no additional routing trafic required to do this.Keep in mind that some problems are very hard to solve but easy to aproximate; often RightAnswer=NP, 99%Answer=O(N).
-- MarkusQ
Excelent point.
Even a quite large hammer won't change this.
But a clever wrench might. Hmmm. Let me think on it...
-- MarkusQ
Was, not are.
And joking, not serious.
And at one of the startups, entitled to, not paid.
But other than that I agree with you.
-- Markus
Salamander: Except that you describe routing based on Hamming distance (which won't work because of looping issues) rather than shared prefix/suffix, this sounds a lot like Tapestry.
Actually, I was just using the Hamming distance as a rough gauge for "how far is this node from where it should be in a perfect binary hyper-cube" (since in a perfect binary hyper-cube, each node is connected to all the nodes (and only the nodes) at hamming-distance 1 from its ID. So what I described was a way to 1) pick a corner at random, 2) wander towards it, and 3) go to another nearby location if the one you picked turns out to be occupied.
I'm not familiar with the looping issues you refer to. Can you elucidate? (Note also that this would not be so much a way to "route" as a way to "partially broadcast" (e.g., maybe decrement TTL by two when sending "in the wrong direction" or propogate ox-bow removal info when something is broadcast to you via a sub-optimal path). We wouldn't count on nodes being where they should be, just hamming-close.)
-- MarkusQ
I can't believe Slashdot just posts this psuedomathematical nonsense without doing even elementary fact-checking
At first, I thought you were refering to your own post, and was tempted to give you a couteracting +1 Insightful.
-- MarkusQ
Having worked at (note: "at" /= "for") Intel, Microsoft, and two dot coms, I've started thinking of this as normal. In fact, if the trend of the last few decades continues, I expect to wind up at a company that doesn't specify any hours, but just has a little real-time LCD display outside every cube, labled "Your score/GP/Lives remaining."
-- MarkusQ
This shouldn't be too hard (at least it doesn't look too hard sitting here on a Sunday morning, half way through my first cup of liquid brains). The key is to note that we can't (and therefore needn't bother trying to) enforce the topology at all times. Instead, we just want to bias the network towards the desired form. For example:
This should at least be functional; no doubt there are a number of clever hacks that could be made...-- MarkusQ
A hypernet is an interesting idea, although I can think of a number of reasons why current p2p sharing networks would not implement them. Namely, because authoritarian networks like Napster were shut down by trade associations like the MPAA/RIAA, while more anarchic networks like Gnutella are more immune from such actions - we must consider not only the survival of the scaling network due to technical constraints like Dr. Gunther does, but also it's survival due to legal constraints orchestrated by large corporations.
I think your concern here is exactly backwards. Specifically, higher dimensional topology would decrease the need for central "UltraPeer"s (also known as lawyer bait) and thus make the network harder to shut down. If the trend towards depending more on some "peers" than others continues to the natural limit, you wind up right back at Napster (one UberUltraPeer to rule them all, and in the darkness...get eaten by a grue if it's lucky, sued by the RIAA if it's not).
On the other hand, if the topology is made more scalable, the targets won't be as tempting at any given network size, and the whole thing would be harder to take down by force. If all nodes are equal, cutting one will likely create enough publicity to attract seven more to take its place.
-- MarkusQ
*smile* I assume they only care if it's free-as-in-speech, and not if it's free-as-in-format.
-- MarkusQ
P.S. I say this as a Python fan; truth be known, that's pretty much how I've indented my code (in anything but forth/postscript) since the mid-seventies.
This was back when computer geeks were very rare, so we were just one more group that shoved a few tables together in the corner, ordered beer, made funny noises, laughed, ordered more beer, rinse, lather, repeat.
-- MarkusQ
Reziac::ARealMcCoy: You young'uns just ain't old enough to remember BBSing. Terminal apps emulating VT-xxx, textmode mail, and scads of users on every box.
*laugh* Ah, now you'd be talking about my site. But I don't think I ever had more than a half dozen or so users on a PC at once (dial up that is--on site we had about thirty, but each had their own PC & pooled "connections" for file transfer).
BTW, thanks; I haven't been called a "young'un" for...well let's just say it's been quite some time. Our first dial-up box was a NorthStar Advantage that could only support two remote users at a time (plus one sitting at it).
-- MarkusQ
How odd. *smile* Given all her talk about VT-xxx terminals, pine/elm, and scads of users on each box, I would never have guessed that my friend's site was running MsDos.
-- MarkusQ
Guido69: Perfect. Now if I can just get this up and running, I can anonymously ask Kathleen to marry me. 'Taco won't have a clue who's stealing his girl! Bwaahahahah.
Perfect? Hardly. In the unlikely event that she decides to accept she won't know who to accept.
Unless of course she saw your post...unless of course he also saw your post...
Anonymity is tricky, yes?
-- MarkusQ
That had been roughly my thinking as well. But the point is that the e-mail reader (either pine or elm, IIRC) was just treating the body as plain text, and happily dumping it (escapes and all) to the terminal.
The terminal (VT100 or some such) was seeing the escape sequence and obligingly reprogramming the specified key to do the dastardly deed. Then it would just as obligingly clear the screen, so that all the user saw was the message telling them to hit the booby-trapped key.
The mail reader was oblivious to all of this.
-- MarkusQ