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Probably not, as new Helium is being made all the time in the long alpha decay chains from heavy elements in rocks. It might become expensive, but that's not the same as running out. It's possible that high temperature superconductors might allow Nitrogen cooling in application currently using Helium, which will have a strongly adverse effect on your position, should you be thinking of investing in Helium futures :-)

Listen here from 21 minutes in: http://downloads.bbc.co.uk/podcasts/radio4/material/material_20120531-1800b.mp3

It's being made deep in the earth all the time, but it's only where it gets trapped by impermeable layers that it accumulates into more exploitable quantities, it's taken geological time to build up those quantities, and it's only when it shares those formations with natural gas that it's been economically feasible to collect it.

The current situation is the result of US government decisions. Around WW1 the US decided to accumulate a strategic reserve of helium, then in 1996 they decided to sell it off until they'd covered the cost of accumulating it. That started in 2003 and was about to stop, but they've decided to taper off the sale instead. http://news.sciencemag.org/2013/04/u.s.-house-passes-bill-would-head-massive-helium-shortage

Long term, once we run out of fossil hydrocarbons, we're out of cheap helium too. In the mean time we're probably wasting loads because it comes up with the natural gas, but people only bother to accumulate it in the few places where it's particularly concentrated. The helium market is pretty dysfunctional because it's piggybacked on the oil and gas industry. No idea if fracking can yeild helium.

err, yeah, that too.

Ahh, so its not a case of how cold you can get things, rather how consistent your cooling is around its environment?

It's both. A cryogenic liquid at atmospheric pressure provides very convenient and even cooling to its boiling point.

So while Nitrogen can be used used as a primary coolant, it's boiling point occurs with any body that's warmer than itself, while helium in liquid form doesn't? or rather, evaporates at a slower rate? Am I getting this or completely off the ball?

A bit off. At atmospheric pressure, liquid nitrogen in contact with any body hotter than 77K will boil, and its latent heat of vaporisation will carry heat away from the body until it is at 77K or all the liquid nitrogen is gone. Liquid helium will do the same, except at 4K, and it's latent heat is much smaller so you have to boil a lot more helium to carry away the same amount of heat. Re-liquefying such refrigerants isn't trivial, but it's still a very convenient way of cooling things. Even below 4K, helium is useful for carrying heat around because it's the only substance not solid at those temperatures.

As for Magnetic Refrigeration. FUCK YOU! My head already hurts. Actually had to dig a little further back and realised how Vapor-Compression refrigeration works. It's not so much as cooling as un-heating! Urgh...my brain...

Thermodynamic cycles are fun. There are also dilution refrigerators which use a varying mixture of helium 3 and 4 to reach temperatures below 4K.

edit: oops got distracted with thermodynamic cycles, so neu was faster.

To the extent that i could see that the expanded polystyrene hadn't adsorbed any collision energy*, i can say that.

If you crash while wearing a helmet, you're right that you can't say for certain what would have happened had you not been wearing one, but you can examine the helmet to see if it adsorbed significant amounts of energy. If it did the polystyrene will be crushed or crumbled. If it isn't, it didn't.

(* It might have adsorbed a little bit without it being visually obvious.)

This is trousers, great flapping loon-pants. Taking a sample of one, when I've crashed I generally hit my head, resulting in three bust helmets and no bust head.

Continue to do what you will, but I reckon most who have had a head injury in an incident haven't been wearing a lid. Incidentally, I have a red, a white and a black helmet with gold bits, like a JPS Lotus but really uncool, choose them by colour, it's is as good as anything.

Tester's point makes sense. Helmets spread the impact force and adsorb energy. Spreading the force helps avoid cracking your skull open, but doesn't help with concussion,. Energy adsorption can protect against both concussion and fracture. Polystyrene adsorbs energy as it crushes and crumbles. You can increase the energy it adsorbs by making it thicker and stronger. But if you make it stronger, lesser impacts won't generate enough force to crush it and all the energy will be transmitted directly to the skull, potentially still causing nasty concussions.

As we're playing the anecdotes game: a couple of friends have had crashes that led to worrying concussion (noticeable effect on thinking that took weeks to months to fade). Both were wearing helmets, and i got a look at one of them. The plastic outer skin was slightly scuffed and cracked, but the expanded polystyrene wasn't crushed - it hadn't softened his concussion.

I ride more and further than them, don't wear a helmet, have had a few crashes over the years, but have yet to injure my head.

The problem is when non-helmet-wearing gets equated with irresponsible cycling, like by your neighbour.

I ride a sit up and beg, hardly ever bother to filter, and indicate like Brown Owl demonstrating semaphore. Yet because a helmet is such a visible signal of "I care about my safety", and the limitations of that safety so poorly understood, many would judge me as a less safe, less responsible cyclist than the hordes of lemmings that flow past me every day taking far higher risks but wearing a helmet.

So to me, those helmet wearers, the ones who protect against the low risk of a specific low-speed head injury but not the high risk of undertaking a left turning vehicle, are a problem because they confuse the picture of what a responsible, safe cyclist looks like. And that confusion becomes a real problem when questions of accident liability and contributory negligence have to be considered.

...

I'd agree with brokenbetty that when helmets provide a false sense of security and do not cause riders to consider more real and present danger, then those riders are being at best naive, and at worst dangerously reckless.

But she's saying a bit more than that. That by supporting the false view that helmets significantly improve safety, helmet wearing riders shift society's perception of what a safe cyclist is away from reality. Then genuinely safe cyclists get the blame for others faults if they fail to wear the expected symbol of safety.

I think that's a bit backwards. The false trust in helmets springs up naturally from common ignorance, and although helmet wearing cyclists help perpetuate it, they're more effect than cause.

^^ when and where did you get yours? I bought one direct a couple of years ago, but was quite disappointed by it. It's a genius idea (that your link utterly fails to understand) but mine was let down by poor manufacturing and second rate materials*. I believe early production was better, with a couple of better but more costly details. Maybe production has got better again now?

( * Rough anodising on the aluminium middle cylinder, mould lines on the outside of the pressure gauge that defeated the inner cylinder seal until i polished them off, the valve between the inner cylinder and the pressure gauge leaks so although the pump works the gauge doesn't and the pump is less efficient than it could be. I think that valve is one of the details they cheapened.)

... Lack of flexibility compared with alternatives (Flying Boats and Hovercraft) probably played a part too.

Could you make a free-flying transport aircraft that was capable of flying in ground effect to boost range and evade detection? You'd loose the vast load-carrying, but would it still be worthwhile? Does flying in ground effect save more fuel than going quickly at high altitude?

We all get stuck behind slow inexperienced bike users or mopeds who think they can fit through a small gap as they just saw a cyclist in-front do it.....

But soon the lights will change and once traffic is flowing it will be easy to overtake them on a full-sized road.

And real roads get the smoothest sweetest tarmac, constantly swept clean by the passage of car tyres.

err, no cycle lane, just normal road markings for vehicles?

Part of me feels strongly that with more bikes on the road and drivers more used to them (and maybe more 20 limits), normal road markings will work better than fiddly cycle lane schemes. That it won't take much more of an increase in London cycling before we're seriously breaking the car's monopoly on defining what roads are for.

Mode specific infrastructure fixes each mode's share of space in concrete. Sharing general infrastructure is much more dynamic. Obviously it's worth separating cars from pedestrians in most cases, but we don't need the complexity and the division of capacity that come with further splits. So cyclists, who move much more like cars than pedestrians, belong on the roads. As bike numbers increase we can just take more space.

But i'm in two minds about this. The kerb nerd's 'think of the children' argument is hard to argue against (that we need cycling infrastructure parents will let their kids use). And although personally i prefer roads with generous lane widths but no cycle-specific paint (i prefer the A4 to Kensington high st.), i'm not sure how optimal that is: There are differences between bikes and cars. Cars are slow because they take up lots of space, and they're fast because they go fast. Bikes are slow because they generally are, and they're fast because they're narrow and can jump queues of cars. Force them to use the road identically and you might get a system with the worst properties of both.

Or maybe general vehicle infrastructure can be flexible enough to get the best from both? (And jamming bikes onto narrow lanes where we loose our queue jumping ability stirs up some visceral opposition in me.)

London, a while ago?

And here's a couple of videos i think are relevant to the discussion, though i'm sure both sides will find confirmation in them:
In a hurry - YouTube

Meanwhile in The Netherlands... Cycling traffic jam! | Cyclecam - YouTube

Surprised 'Top of the Lake' on bbc 2 hasn't had a mention here. All six episodes are still up on iplayer until Saturday, and worth catching if moody rural New Zealand crime drama is your kind of thing.

As much as it pains me admit, I think you're right :-( My regular road bike for a while now has been a Canyon 62cm, which suits me quite well (I'm 6.4). That frame is 58 c-c and the top tube is 58,5. The Look is 57.5 c-c and top tube 57.5, so I was thinking: saddle a bit higher and a slightly longer stem. I feel really good on the Look, but after while my knee starts to hurt ... next day I ride the Canyon - no problems with the knees :-(

My knees are quite sensitive to q-factor. Is that different for your two bikes?

consider three cases:

The wheel un-built. A rim, a hub, a heap of spokes and nipples. Its components un-stressed.

The wheel built, its spokes tensioned, but the whole under no external load.

The wheel in use, supporting weight at its axle, transferring it to ground via hub, spokes, rim and pnumatic tyre.

You wish to understand the wheel in use. If you do so by comparison with the un-built wheel, you're likely to conclude that the hub hangs from the rim by the spokes above it, while the rim is kept from collapsing by the spokes to either side, and the spokes nearest the ground do nothing to help.

But if you consider that the work of a wheel is in the difference between the built wheel and the wheel in use, you'll see that all the action happens at the bottom, the spokes nearest the ground becoming compressed (less stressed) as the load is applied, and most significantly, barely any increase in tension of the spokes above the hub.

(If the rim was infinitely stiff, then weight applied to the hub would be split, half increasing the tension of the spokes above and half decreasing the tension of the spokes below. Infinitely stiff rims are not commercially available, but very deep section carbon rims might be a close enough approximation to make the idea relevant.)

Is this chap correct when he says that the hub "stands" on the spokes below it, rather than "hanging" from the spokes above?

http://www.astounding.org.uk/ian/wheel/

Yes. Or maybe no, depending on exactly what you think those words mean. Personally i find 'yes' more helpful.

Just that postage isn't cheap these days and a couple of inner tubes would cost me about £3 and I am wondering what are the chances of them giving me anything in return?

If all the punctures are around the valve, you could just send them that section to save on postage weight. Maybe send one full tube, valve sections of the rest you have, a neutral-tone note explaining how many you threw away, and cross fingers.

If it's a real, recurrent defect that's new to them, they should be keen to learn about it and make good all your losses as thanks. If they already know all about it they might only replace proven defects. If they don't even do that they're being arseholes.

?

...

:(

slightly OT here:
why would anyone in the UK use open bored concrete piles rather than continuous flight augered ones? is there any benefit - how common is it to require reinforcement in piles?

Ground conditions?

With CFA you have to screw the whole auger all the way in in one go. Then pull the whole column of earth out in one go. With open bored piles you can auger a bit, lift the spoil out, auger a bit more, drill the casing in a bit further.

Think it would be quite hard to construct secant plied walls with CFA too.

Does the lack of updates on this thread mean you've stealthily sold it via pm?

Interested, but would like to see a photo.

see here from 7:40 for how tubes are made: Schwalbe Manufacturing Process - YouTube

Sorry are you taking to me? If so, no, I wouldn't know what to look for... Should I?

sorry, yes, and i don't know either, but you might spot something obviously wrong that would lay the blame with the tube manufacturer.

(From cutting open and prodding at an old tube here, it looks like the valve is mounted onto a rubber oval with tapered edges that is stuck onto the rest of the tube. Examining the valve hole from the inside, it seems the rubber oval isn't perfectly bonded to the rest of the tube - there's a small area round the hole where they haven't stuck. Maybe in your case the region of poor bonding extends so close to the edge of the oval that full inflation is able to burst through the tapered edge of the oval?)

Have you cut open any of the failed tubes to look for defects on the inside?

It is also undergoing strong mass loss with the outer layers of the star no longer gravitationally bound.

it is being split...

move the twists past each other and they should cancel out