868 posts • joined Thursday 8th November 2007 17:09 GMT
nice hat, Ms Bee
would you like a stupid car analogy instead?
Oh, and what do they call that? A bonnet, you say? What a quaint country you English have!
I thought reg readers were smarter than this!
> gravity merely causes a vacuum to form at the top.
No. Gravity would cause a *partial* vacuum to form. Or, more concretely, it reduces the pressure at the top of the siphon. If the pressure is low enough, the liquid will evaporate--it'll be more *like* a vacuum, since water vapour is less dense than liquid water, but still not a vacuum. Nature abhors those, apparently, and the effect is that water is pulled up from both legs to prevent this. Of course, if the water at the top *does* evaporate, then a new equilibrium is reached. This time, the vapour can expand (either by losing pressure, which a gas can do more easily than a liquid, or by causing more liquid to evaporate) much more than the pull of gravity down the long leg of the siphon can compensate for, and so no more liquid can flow past the hump.
> If the pressure is completely removed, then there will be a total vacuum both inside and outside the siphon.
No. There's no total vacuum in the tube for a start (it's why we call it a "vapo(u)r lock". And you've failed to account for the weight of water above the tube in the higher container.
> I'm baffled as to why more people didn't learn this in high school physics
It's probably something to do with the "state of education" nowadays. As it always was, probably.
You just demonstrated that the liquid flows uphill in a siphon
Of course it does. I figure you're not entirely serious, what with talk of free energy and such. But of course, this is only a local inversion of entropy. If you take the entire system into account, the overall entropy is increasing. Just like in any thermodynamic system (or hydrodynamic, since it applies to us ugly bags of mostly water too).
Terminal 5 ... a bland Eno track on constant play.
I think Eno was probably being ironic there. Come to think of it, you probably were too. Hmmm.. Will this make up for my ignorant comment?
> A chain can bear tensile force, ie. you can pull on it. In order to pull on water, you must first put it in a sealed pipe and subject both ends to (atmospheric) pressure. Only under those kinds of conditions will it be chain-like, not in a vacuum.
I'd love to have read a post that could have taken what I'd written and shown, clearly, what was wrong with my reasoning. This was not it. I've explained that water in its liquid state can act like a chain, and also that this falls apart when the density falls low enough to form vapour bubbles. I've also described how water pressure plays a big part in the whole system, and this is completely independent of atmospheric pressure.
I'll suggest an alternative experiment. This time connect two reservoirs, one higher than the other, with a piece of tube going from the bottom of the higher into the bottom of the lower one (the tube will just hang between them and will have a 'j' shape). Will water flow from the top to the bottom? Obviously it will. Will it work in a vacuum? Yes it will, because gravity is the only operational force. Now what's the difference between this experiment with an upright J tube and a siphon, with an inverted J? The difference is that at the top of the inverted J tube (aka, a siphon), the pressure is less than that in the upright J tube.
I've already agreed with everyone that in a siphon, if the pressure at the top of the tube isn't enough to prevent the water from evaporating, then an air lock forms and it can't "pull" the water down the long leg (because it loses its chain-like nature, to put it back in metaphorical terms). But as you (and the other down-thumbing commenters) still seem to be missing is that the pressure at the top of the siphon depends not only on atmospheric pressure but on the weight of water above the tube's ingress/egress. The greater the weight of this water on the ingress tube, the higher the pressure on the water in the short leg of the siphon, and thus, the higher the top arc of the siphon can be relative the the ingress of the tube.
I'll suggest one further thought experiment... between the upright J case (which I'm sure everyone can agree will work, even in a vacuum) and the inverted J case (a siphon, which is in dispute), we've got the case of two reservoirs, both initially of unequal height of water, connected with a horizontal tube. It seems fairly clear that water will indeed "find its level" in this system too, even in a vacuum, so we'll end up with water levels oscillating in both vessels, first with one higher, then the other, until both have boiled off. What the "no siphoning in a vacuum" argument is saying is that even if the tube has the slightest kink so that the highest point in the tube is above the highest point on the ingress/egress tubes, then no flow is possible. I submit that that idea is ridiculous.
And the reason? Again, it all comes back to *water pressure* and simple hydrostatic equilibrium calculations. So long as there's a sufficient head of water above the ingress/egress points, there will be sufficient pressure within the tube to prevent an airlock forming.
What say all you naysayers to that?
> surely the liquid above the tube's end point could be considered to be providing atmospheric pressure anyway?
Well, someone seems to have got this point. Except it's not "atmospheric" pressure. It's "water" pressure, but both are translatable into abstract "forces" so it doesn't really matter if the fluid is air or (liquid) water. See my posts above.
prof. from Colorado is wrong
> Air "weighs" about 14.7 pounds per square inch of area on which it rests, including the surface of a liquid; this pressurizes the liquid to this amount.
Air pressure acting on the liquid in the reservoirs on *both sides* is equal. Actually, it's slightly higher on the lower one. You could even submerge both ends of the tube in the liquid and it would still work, though you will get reduced flow since the outflow tube will now be fighting against water pressure in the lower reservoir.
The original pedant/boffin had the right idea in trying to explain water as a chain. They're maybe not his exact words, but it makes sense if you think about it like this... A previous poster here (Mike Bell) suggests an experiment where you have a physical chain dangling out of a drawer. Once you have enough of the chain dangling over the edge, it will pull the rest of the chain with it. Water is pretty much exactly like a chain, except that at lower temperatures it loses its chain-like nature and becomes a gas, so the individual molecules don't form chains. Once the pressure drops again, and the water condenses, at re-attaches to neighbouring molecules and you've got your chain links back again. It's slightly more complicated than that because there's an energy gap that needs to be crossed in changing state from liquid to gas
The prof from Colorado is completely wrong if he thinks (and it would seem that he does) that atmospheric pressure is the operative force. See my example at the start to disprove that (ie, air pressure at the lower reservoir is *greater*, and the siphon works when both ends are submerged). Also, he completely discounts the much greater *water* pressure which operates on the higher reservoir.
I've rambled on a bit more than I wanted. In summary, though, this is simply a case of hydrostatic equilibrium. You have to take into account all the forces:
* gravity affects atmospheric pressure on both reservoirs
* it also affects water pressure at the inlet and outlet (the weight of water above the tube openings)
* it also affects the water in each leg of the tube
* in all cases where gravity is in effect, you have to add the weight of all the air/water above; in each reservoir the "weight" of the water above it is simply proportional to the depth (ignoring any compression), while within the tube the higher up you go, the less pressure there is
* if and only if the pressure at the top of the tube is not so low that a vapour lock forms, then gravity will naturally continue to draw fluid from the higher to the lower reservoir (aka, "water finds its level").
I'll be heretical here and say that is follows from this that a siphon *can* actually work in a vacuum, provided there is gravity. It would need to be set up so that there was some liquid in both reservoirs to begin with. Depending on the rate of boil-off from the surface of the reservoirs, you would still get a siphoning effect, which would work until there wasn't enough *water pressure* (everyone seems to have completely forgotten about water pressure: it's much more important than atmospheric pressure!) in the upper reservoir to prevent an air lock from forming at the top of the tube, or there is no water pressure at all at the tube's ingress or egress (ie, the tube is just at the water level, which allows all the water on that side to flow down back into the reservoir). You could easily verify this by setting up weighing scales on both the reservoirs, and running the experiment once without the siphon being opened, the other with it open. If the weight of water in the lower reservoir increases or simply decreases at a slower rate (balanced by an increased rate of loss at the higher reservoir) then the experiment would prove that you *can* operate a siphon in a vacuum.
I guess people don't study applied maths in schools these days.
will they ever get 'roud to live space cooking programs
I'm quite looking forward to seeing them wokking on the moon.
because first they're coming for the G's
so if nobody speaks up, they'll be on to the next random letter in the alphabet.
Not sure what version of Ubuntu you're running, but the UNR version for netbooks has a hack that maximises most windows when they're opened. So no need for resizing windows there, for the most part.
The other way of resizing, assuming you're not running UNR, is to hold down Alt, then middle click anywhere on the window to drag-resize it to the shape you want. Works a charm with a proper 3-button mouse, but I'll admit it's not so easy to do on a trackpad if you have to hold down both buttons to simulate the third button. At least not on those weird Acer trackpads with mouse buttons on either side of the pad rather than underneath.
There's probably also some keystroke you can use to start resizing, but to be honest the alt-middle-click is just what I want., so I've never had to look up the key binding.
It's actually things like this (as well as select/middle-click to copy and paste alt left-click and drag to move windows around) that I think makes Linux (well, X Windows probably) far superior for actually getting things done.
There's an app for that. Try LyX. It's been quite a while since I used it, but I was quite impressed with it. It's totally usable even for someone who doesn't know anything about the underlying LaTeX language.
I'll grant you that LaTeX itself doesn't suit everyone (your "why not LaTeX? because it's LaTeX" comment), but for producing professional documents there really is no competition. But ultimately, I suppose, this is an apples and oranges comparison because LaTeX is a typesetting system and Word/OpenOffice are merely "word processors".
You could install use fast-user-switch-applet, but it only seems to allow you to have two concurrent logins. Alternatively, just add the "log out" applet to a panel or menu. When you click it, you'll have the option of either logging out entirely or switching to a new user. Switching users keeps any current session open, so you can switch between active logins by going through a pseudo-login screen (actually it's a screensaver lock, but it also manages setting up new virtual screens for each session and flipping between them).
As an added bonus, even if you're running a dozen different instances of the browser, IM apps, etc., the invariant parts don't take up any more space than running one instance. Of course browsers (in particular) use a lot of working memory, which can't be shared, so you'll still need a good bit of RAM to make this run smoothly for you. If not, it's Languid Lemur time.
There ain't no winds in space.
Er, solar wind perhaps?
donc, qui haute, eh?
This post requires a tilting, with letters and/or numbers.
<- with upside-down windmills, natch.
questionable magnanimity // mergesort prior art
On the one hand, I can't say this is exactly good news for Open Source (OS) projects since all it really means for Google to have given a "free pass" to one high-profile OS project is that they've evaluated the pros and cons of either suing or automatically granting a license and decided that granting a license garners better monetary returns via PR than suing does. It does nothing to help any other OS project with a lesser profile. Also, the Apache license contains no "patent non-compete" clauses, so this announcement is of questionable value to downstream projects.
Which brings me to the second point... basically the ridiculousness of software patents in general. It's quite clear that the "map-reduce" principle has been well known in computer science since, well, pretty much forever. I enter in as evidence here the well-known "mergesort" algorithm. Map-reduce is nothing more than a generalisation of the basic idea of mergesort: ie, partition the problem space, have each partition operated on individually, and have a (usually O(n)) "reduction" step when all partitions have been processed.
It's a sad day when a generalisation of a well-known technique can get patent protection. This both from the point of view of mathematical abstractions (which shouldn't be patentable in general, and generalisations doubly so) and basic computer science (where algorithms in general shouldn't be patentable, and even if a case could be made for them, they'd have to be *more* specific, not less). Both are obviously flip sides of the same coin.
And one more point. All the previous commenters are idiots. Or possibly shills, but I'd prefer to apply Hanlon's Razor, obviously.
survival of the fittest?
What the hell does that mean? Fittest for what, exaclty? To survive?
damn these killjoy scientists
where is it?
The suddenoutbreakofcommonsense icon, that is?
The funny thing is that a helicopter can actually still land safely in the case of engine failure.
No volcano icon on el Reg? Black heli icon is too obvious, so ...
it's "free rein"
Only the Moderatrix reigns supreme here.
between the 5.4 and 5.5 versions? This seems a smidgeon unbelievable to me. Everyone knows that means 10x faster, right? Someone is definitely telling pork pies here.
-1 internets for you!
I don't see anything wrong with the term "private internet". An internet is simply a network of networks connected using the various "internet protocols" such as TCP/IP, UDP/IP or whatever other form of higher-level protocol you want to implement over the IP layer. If you've got a home/office router and you've got different subnets running off it, then you've got "an internet" right there. If this internet is being firewalled behind the same router box, then by definition, it's a "private" internet.
This is the very simplest form of "private internet", but others are common. A corporate internet will very often have VPN (Virtual Private Network) access points so that a person (employee) can connect to the company's internal (private) internet by connecting to and authenticating themselves with a VPN server somewhere out on the (capital "I") Internet. In this case, a higher-level protocol again (ie, VPN) is built on top of the existing TCP/IP infrastructure and provides the illusion that all the company's computer are all on the same physical "internet" or subnet. In other words, VPN provides an "internet over internet" abstraction/encapsulation layer.
There's nothing very difficult to understand about this (you might even call it "simples"), but unfortunately a lot of people can't even distinguish between "the Internet" and "internet" (as a set of protocols). It kind of ticks me off when I hear people who should know better obviously failing to understand even this simple distinction. At least when politicians and media spokesmen display the same kind of non-understanding it can be somewhat funny at times. But Reg readers? Tcshh!
Maybe they could borrow some from the Dutch...
That's the "wisdom of crowds" for you...
"blessed as infallibible" (sic)
Could be a lucrative sector for the Vatican to get involved in... "our certs are infalllibible!"
needs a high-tech approach
I think the enrollment machines should be roughly robot-shaped, with at least a swiveling head and glowing red eyes. It should have one of those low-powered sweeping lasers they use with fog machines to spice up music videos. Give it some motion detection capabilities so they can track and sweep punters as they pass by and (obviously) a metallic-sounding voice circuit and a limited repertoire of phrases like "lifeform detected", "halt! please submit to scanning!", "anomaly detected", "uploading scan", "please remember to report suspicious individuals", "be pure, be vigilant, behave!" and the like.
The great thing about going about it like this is that the original machines could be no more than toys, just randomly going through their repertoires. Then, once the public has gotten used to the idiocy of the machines, TPTB could begin to gradually and covertly upgrade their capabilities so that they actually do the biometric scanning that the earlier models were only pretending to do. By that stage, anyone who had any clue about what was really going on and tried to warn anybody would be treated with derision, because obviously everyone would "know" that the machines were nothing more than electronic scarecrows only designed to scare away terrorists, paedos and illegal immigrants and instill a false, but reassuring, sense of security in the general populace.
In stage three, the machines could be upgraded to listen in to gossip at the local post office, supermarket, etc., to identify any troublemakers who may have cottoned on to the plan. Then the controllers could use the machines for more direct psyops, suggesting to neighbours that such-and-such a person seems to be behaving strangely this week and wondering if they have something to hide and so on. By then end of stage three, all the tin-foil hat brigade would either be driven insane by the whispering campaign or have fled the country.
Bringing us finally to stage four... a techno-utopian panopticon, where nobody has anything to fear because there is finally nothing left to hide.
liberal pinko "victorian father"
Sir, I draw the line at a table-leg visible underneath a too-short tablecloth.
With all the talk of cyber-this and cyber-that, I often remember the opening story from "Burning Chrome". It says ...
"If they think you're crude, go technical; if they think you're technical, go crude. I'm a very technical boy. So I decided to get as crude as possible."
So battery chargers need software for wtf exactly?
Well, the colours of the Irish flag are green white and orange. Supposed to be symbolic of peace between the two opposing constituents, innit?
My guess is that if you asked those who were complaining what colours made up the Irish flag, they'd probably answer "green, white and gold".
and also ...
The USS Eldridge!
spiderman? green lantern? kids' stuff
In fact for all your wailing to the contrary, if you read Watchmen you'll see that there is an Owl-inspired costumed "superhero" (well, fascist vigilante is probably a more accurate description). Goes by the name "Night Owl".
Who's to say that the idea isn't ripe for a rehash? How about keeping the vigilante angle, and reprising old 3-wood's Equaliser series? Got a problem nobody can help with? Maybe you should call 555-2820 ...
Slay the unbelievers wheresoever ye find them"
Then there's the very Christian messages like "never suffer a witch to live" or "none shall get to heaven except through me [Jesus]". All these cults are pretty much the same: we're the only game in town! Kill/shun/damn the unbelievers!
I much prefer the Buddhist perspective on life and religion, as exemplified (perhaps) by this quote attributed to the Zen master Linji: "If you meet the Buddha on the road, kill him."
Another quote might also be appropriate to show the Buddhist perspective on creating images of the "religion's" central figure.
Monk: What is the Buddha?
Unmon: A dried shit-stick (ie, something to wipe your arse with)
I'm sure some more "moderate" Judeo-Christian cultists will complain that all the talk about killing the infidels/non-believers isn't meant to be taken literally. But really, if you start stripping out those bits, why not all the other literal stuff about heaven/life eternal/etc.? What are you left with then? Just another dog and pony show, IMO.
Oh, and just one more thing I want to mention... all these anit-Jihadist or anti-Al-Queda polemics are just as bad since by negating or opposing something, they end up reifying it too. Thus does the wheel of nonsense go round and round...
(not aon, so you know which one to shun in future)
talking out of my hat here, but ...
Obviously, for a shield of this sort to work, the gaps in the mesh have to have a similar spacing to the wavelength of the incoming radiation. But since we're talking about hydrogen atoms which are accelerated to nearly c, we'll have a hard time creating a crystal lattice that's hard enough and dense enough to stop the radiation. Not to mention the size...
But in one way, Faraday Cages aren't too far from the basic physics principles at play. The solution appears to be to use metamaterials, which are crystals or layered materials with the interesting property that they have a negative refractive index. When placed in front of the ship, incoming particles should be scattered in a cone away from the craft due to Cerenkov Radiation.
I could have just copied and pasted some bits from the wiki page on Cerenkov radiation, but I figured talking about photonic crystals would probably have sounded like pure sci-fi.
on not getting the point of FOSS
> True heroes don't *demand* medals and recognition.
Let me explain it another way. You've crafted a piece of software as a labour of love (or whatever) and you want someone else to download it off the net and claim that they wrote it? A lot of the various open source licenses don't demand recognition, let alone medals. But they are designed specifically to prevent unscrupulous and unethical behaviour, viz outright plagiarism.
Items in the public domain do not have any protections at all. Plus, most things in the public domain are crap anyway, although this is due in no small part to the release of the good stuff increasingly being put on the never-never, due to arbitrary extensions of the copyright charter.
It's all Greek to me (though some would say Latin ... when in Rome and all that mixing of metaphors)
In other words... wtf is this article about, anyway (and no, I didn't click any links... rule 1 of acronyms: first time you mention it, you say what it bloody stands for!)
turtles all the way down
Yeah, but delving into exactly what an executable/interpretive environment *is* opens up a Pandora's box of worms. Elementary application of Godel's Incompleteness Theorem.
And yes, the terminology of coding theory does include such words as "alphabet" and "language", so your point is strictly true. But obviously pointlessly so. Should be fun, indeed.