Beta
×

Announcing: Slashdot Deals - Explore geek apps, games, gadgets and more. (what is this?)

### Thank you!

We are sorry to see you leave - Beta is different and we value the time you took to try it out. Before you decide to go, please take a look at some value-adds for Beta and learn more about it. Thank you for reading Slashdot, and for making the site better!

top

### Siphons Work Due To Gravity, Not Atmospheric Pressure: Now With Peer Review

Re:Somebody thought it was atmospheric pressure? (360 comments)

Water siphons have been demonstrated to 24 meters. Water can resist -280 atmospheres pressure without vaporizing. Corresponding to possible siphon heights of more than 2800 meters. Siphons can operate in a vacuum. Siphoning of mercury has been demonstrated to more than 30cm above the barometric height, even in glass which mercury adheres poorly to.

24 meter siphon:

Siphon of ionic liquid in vacuum:

Siphon of mercury to 30cm above barometric height:
http://commons.wikimedia.org/w...

Negative pressures of -280 atmospheres in water have been demonstrated in the ingenious Z-tube:
https://en.wikipedia.org/wiki/...
The Z-tube is a z-shaped tube nearly filled with liquid and set on a spinning table. If the liquid starts to shift away from the center, the "height" of the liquid in the bent inward ends "rises" toward the center, increasing pressure in that end and returning the liquid to the center. By measuring the spinning speed and the distance from the center to the liquid level in the ends, the pressure can be calculated. It helps if the tube is of a material the liquid will adhere well to. And the tube must be very clean and the liquid degassed to prevent cavitation.

Another example of negative pressures in water are in the xylem of very tall trees. The water does not rise by capilary action very far. The water is pulled up by action in the leaves at top. Negative pressures of several atmospheres are achieved in tall trees.

So, many people are correct that liquid cohesion DOES pull the liquid over the top of a siphon in SOME siphons. And everyone agrees that all siphons rely on gravity (or similar acceleration) for their effect. But most practical siphons don't rely on liquid cohesion. And some siphons CAN'T use liquid cohesion to pull the liquid over. It is not the case that only one of the theories: atmospheric pressure, gravity, or liquid cohesion, is the answer to how a siphon works. All three of those explanations are involved. We don't have to choose just one.

One example is the siphoning of CO2 gas, which has been demonstrated. And a demonstration you can easily do with a garden hose is like figure 4 of the Wikipedia siphon article, fill the tall down side of a siphon with water, but leave the top and short up side with only air. When the water in the tall down leg is released, gravity will reduce the pressure at the top of the siphon and atmospheric pressure will push the water from the upper reservoir up and over the siphon. Since the water on each side of the siphon is not touching at the start of this experiment, liquid cohesion cannot explain what force raises the water. The air at the top of the siphon, though reduced in pressure, is still at positive pressure relative to complete vacuum, and therefore it is trying to expand, and pushing DOWN on BOTH sides of the siphon. Since gravity is also pulling down, only atmospheric pressure can supply the force to push the liquid up into the low pressure zone created at the top of the siphon by gravity pulling down the liquid in the taller down tube.

Another observation of the difference between vacuum siphons and practical siphons is that in practical siphons, small and even fairly large air bubbles can flow over the siphon without much change in its working. Whereas in a vacuum siphon, a bubble or void will immediately expand to break the siphon.

In practical siphons near sea level, liquid cohesion is not only unnecessary, it cant even contribute, because all the fluids in the siphon are at positive pressure relative to complete vacuum and therefore all the molecules are being squished together and are repelling each other. There can be no pulling in siphons near sea level pressure. Atmospheric pressure pushes the liquid up despite that the pressurized fluid at top is trying to push the fluid DOWN on both sides.

Atmospheric pressure pushes the liquid up in a typicall siphon the same way atmospheric pressure pushes the liquid up in a barometer or drinking straw. But of course the energy to lower the pressure at the top is provided by gravity.

Some people think that the atmospheric pressure at the entrance and exit cancel. But actually the atmospheric pressure at the exit doesn't completely cancel that at the entrance because the weight of the liquid in the taller down tube partially cancels some of the atmospheric pressure at the exit. The weight of the liquid in the up tube also cancels some of the atmospheric pressure from the entrance, but not as much because the up tube is shorter, and therefore there is a failure to cancel and a remaining imbalance of atmospheric pressure between the entrance and exit.

So the gravity and air pressure explanation are BOTH CORRECT most of the time and the liquid tensile strength with gravity explanation is ALSO CORRECT in the rare case of siphons at very low pressure, though ONLY at low pressures.

top

### Michael E. Mann Sues For Defamation Over Comparison To Jerry Sandusky

If an oil company had did this "hide the decline" then the climate science community would have said it was obviously unscientific behavior. But climate scientists are so biased they cant even admit the rules of good science. If your oppinents say the data is not irrelevant, then you are not supposed to leave it out of the graph to make it cleaner. If the trees are giving falsely low temperatures then that is important information about their credibility. If his opponents say contray data is not fully explained then a scientist is not supposed to decide for himself that contrary data is fully explained. He is supposed to include it and explain it. If the trees weren't giving falsely low temperatures then there would have been nothing for Phil Jones to hide in his own words. The decline wasn't in plain sight or he wouldn't have used the word hide. He left it out of the graph for a reason. He hid it because people would realize his tree rings were unreliable. He hid it because he knew many people wouldn't dig in far enough to realize what he had hidden.

more than 2 years ago
top

### Michael E. Mann Sues For Defamation Over Comparison To Jerry Sandusky

Re:You don't know what "Hide the Decline" means (371 comments)

"wondering whether you agree with the fact that I was modded down to -1 for providing evidence contrary to your post."

Although you shouldn't have advocated breaking the moderation rules, you still shouldn't have been moded down. My partial rebuttal is above.

more than 2 years ago
top

### Michael E. Mann Sues For Defamation Over Comparison To Jerry Sandusky

Re:You don't know what "Hide the Decline" means (371 comments)

There is no -1 incorrect mod choice because it is against the rules to mod down for that.

more than 2 years ago
top

### Michael E. Mann Sues For Defamation Over Comparison To Jerry Sandusky

Re:You don't know what "Hide the Decline" means (371 comments)

"I'd say "Overrated" works well for someone who really is wrong."

No. If I admitted a simple mistake of fact or something then you could go back and mod me down, but the moderation rules prohibit moding somebody overrated on a controversial topic just because you think you have solid reason to say somebody really is wrong. Large majoriies of scientists have been convinced of wrong things before. They're not infallible. On a controversial subject you are only supposed to post a rebuttal not bury with downmods. You will lose your moderator privileges for that.

more than 2 years ago
top

### Michael E. Mann Sues For Defamation Over Comparison To Jerry Sandusky

Re:You don't know what "Hide the Decline" means (371 comments)

"Tree-ring growth has been found to match well with temperature ... However, tree-rings in some high-latitude locations diverge from modern instrumental temperature records after 1960."

If the tree rings are showing falsely low temperatures after 1960 then it is questionabe at best if they were not giving falsely low temperatures back during the medieval warm period. It is a rule of science that you are not supposed to hide such evidence especially if your opponents say it is significant.

To say it was not hiding is rediculous since the alarmist Phil Jones himself described what he was doing as hiding. Burying data deep in an academic paper the public won't see is still hiding. Sure the experts were debating it, but it was hiden from the public who wouldn't look deeper than the graph.

I would have replied earlier but my battery died and i lost my post. I'll have more.

more than 2 years ago
top

### Michael E. Mann Sues For Defamation Over Comparison To Jerry Sandusky

Re:You don't know what "Hide the Decline" means (371 comments)

It is against the moderation rules to mod somebody down even if they REALLY ARE wrong. Especially if it is a controversial issue. I'll address the argument in a minute.

more than 2 years ago
top

### Michael E. Mann Sues For Defamation Over Comparison To Jerry Sandusky

The whitewashes explicity decided not to invetigate Mann's "hide the decline" because he did it and it couldn't be denied. Hiding contrary evidence is a no no in science, Especially after your opponents have made it clear that they think that contrary evidence is significant. You have to include it in your graph and explain it, not leave it out. Worse, nearly the entire climate science community has defended this unscientific conduct, destroying the credibility of the entire community. And they continue to put forth the deception that he was exonerated from this misconduct. One of their leaders was quoted by Discover magazine as saying that they had to choose between honesty and effectiveness. We now know what they chose. It was not defamation because it was an opinion based on at least arguable, if not obviously true evidence. Remember it is against the moderation rules to mod somebody down just because you think they are wrong. It is also not flamebait if it is a sincerely held belief put forward for honest discussion.

more than 2 years ago
top

### FBI Compromises Another Remailer

US law now allows the military to imprison you for life without trial. See the NDAA. or http://www.youtube.com/watch?v=AKaTxjxnYfE This was signed into law by Obama. There is an exemption for American citizens from the requirement that the military take them to Guantanamo Bay, but the exemption is only to the requirement, the military still has the OPTION to imprison you forever without trial. The law says it is only for suspected terrorists, but the law only requires suspicion, not proof, and anyone can be suspected of being a terrorist. It has been claimed that there is a requirement for one hearing before a judge but I haven't seen that in the law. It boggles my mind that Congress and Obama think it is a good idea to make it legal for the military to secretly snatch you in the middle of the night and imprison you for life without trial on mere suspicion.

more than 2 years ago
top

### Kernel.org Attackers Didn't Know What They Had

Kernel.org may not bother with clean wipe (183 comments)

Disturbingly they seem to have considered not wiping and reinstalling.

System is being verified from backups, signatures, etc. As of right
now things look correct, however we MAY take the system down soon to do
a full reinstall and for more invasive checking.

It appears that the chief kernel.org system administrator is so naive about security that he doesn't even realize the absolute necessity of a full wipe and reinstall after compromise of such an important site. It also appears that there was no routine booting from read only media to check system files and startup scripts for changes. And no daily rootkit scan. If it was me, I would trash the motherboard for fear of BIOS or other firmware contamination. Exploits living on the firmware of network cards and other places have been demonstrated.

more than 3 years ago
top

### Russian Lie Detector ATM

>voice rec dont work if you are drunk up on vodka

Voice recognition of lies doesn't work at all. So it seems these bankers have fallen prey to a kind of ATM ripoff before they even deployed these ATMs.

more than 3 years ago
top

### The Fight To End Aging Gains Legitimacy, Funding

>500 years from now, just think how out of touch the elderly will be!

People will learn to keep themselves updated better.

What is this strange thing that makes people want to deny the likelihood of curing aging within the next few decades? I saw a survey of doctors that reported that the doctors thought that the average life expectancy a hundred years from now would be only about a hundred years. That means those doctors thought aging wouldn't be cured for more than 200 years! What on earth possesses people to think that progress will be so slow?

more than 6 years ago

# Submissions

top

### ISPs Consider World IPv6 Day Giant DOS Attack

mindbuilder (960119) writes "Geoff Huston, chief scientist of APNIC, is saying that part of the reason for World IPv6 day is that internet content providers are worried that carriage providers are going to take advantage of the transition to widespread NAT to somehow control access to their customers and make content providers pay extra to carriage providers.

Carriage providers on the other hand see World IPv6 day as almost like a huge denial of service attack against their networks. Among other things they’re worried that they will be swamped by expensive tech support calls as customers can’t get to their favorite web sites. Some carriage providers are planning to block IPv6 traffic on World IPv6 day to protect their networks.

Meanwhile, the fact that many ISPs pay extra for equipment to put millions of internet users behind NAT and TAKE AWAY IPv4 addresses, even though they could get IPv4 addresses practically for free, makes it look to me unlikely that a lot of ISPs will pay extra to do the opposite and give out IPv6 addresses any time soon."

top

### Proof IPv6 Will Never Take Over

mindbuilder (960119) writes "Internet Service Providers can today get IPv4 addresses for all their customers practically for free (except recently in the APNIC region). Yet the ISPs still put hundreds of thousands of users behind NAT. They do this to spite the extra equipment costs of NAT. If they're willing to pay extra to NOT give customers IP addresses, Why would they want to pay extra to upgrade their systems and give away IPv6 addresses, any time soon?"
top

### Will IPv6 never be adopted?

mindbuilder (960119) writes "It is said there are ISPs with hundreds of thousands of users behind NAT. I used to assume this was because they had to pay a small but non-negligible fee for IPv4 addresses. But someone pointed out to me that you get all the addresses you want for a low yearly fee. The difference between the fee for small ISPs and the biggest ISPs is only about 3000 Euros. That seems negligible for a large ISP, even one in a poor country with fierce competition, especially when you factor in the cost of NAT equipment and management.

So the question is: If they can get IP addresses now for nearly free, why don’t they? If they don’t want the IP addresses, are they even going to care when IPv4 addresses run out? Is the incentive to give customers IPv6 addresses ever going to overcome whatever disincentive there is now to give customers IPv4 addresses? Will we have to wait multiple decades before they decide to enable IPv6?"

top

### Asia Has Officially Run Out of IPv4 Addresses

mindbuilder (960119) writes "The Asia Pacific and Australia region has officially run out of Internet protocol version 4 addresses today. Actually they have a few left but they've begun their "final eight policy", so addresses will only be dolled out in tiny quantities over the next several years. Even regions with addresses still available will be effected by this because making contact to computers in the APNIC region will get harder as more APNIC users have to start sharing addresses from behind NAT. If you or your family are in the market for a wireless router or other network gear, be sure to look for IPv6 compatibility."
top

### Asia runs out of internet addresses next month

mindbuilder (960119) writes "At the rate the Asia pacific region has been consuming IPv4 internet address this year, it is expected that they will run out before the end of April, and perhaps closer to the beginning of April. Even if your region will still have addresses available, the sharing of addresses using NAT that will be necessary in the APNIC region will cause communications problems for users in every other region trying to contact APNIC users. Therefore it would be best if users in every region start moving to IPv6 as soon as possible."

# Slashdot: News for Nerds

It's not so hard to lift yourself by your bootstraps once you're off the ground. -- Daniel B. Luten