Search This Blog

Follow adrianbowyer on Twitter

My home page

Monday, 27 August 2018

The Support Shift of Sam McGee


There are strange things done 'neath the midnight sun
     By the bods who moil with code;
An embedded trace gives an endless chase
     When you compile in debug mode.
The panel lights have shown odd bytes,
     But the oddest they displayed
Was that night I thought, in User Support,
     That I'd do a sys upgrade.

From Seattle ground on Puget Sound,
     Where the Duwamish meets the sea,
The system spread like a wound that bled,
     But should not've passed the quay.
I was always told, by coders old,
     That it drained you like a spell;
But I had no choice; the boss's voice:
     "Linux? Rot in Hell!"

As I sipped my brew the screen went blue,
     And then the helpline rang:
"My Word doc's gone! It's almost dawn.
     “You're the one that I'll harangue.
"I've a meeting at ten. Must I use a pen?
     “You're supposed to make it work."
I could tell from his tone at the end of the phone
     That this one was a jerk.

But he had a point: in this hardware joint,
     The server's meant to serve,
With an uptime that, quite unlike FAT,
     Would every bit preserve.
I set down my cup, took the backup,
     Then mounted it in the drive,
And thought to myself, "If the link were ELF,
     “I'd have it up in five."

The drive-LED flashed. The head then crashed.
     My tea soaked round the keys.
So I cursed an oath at the undergrowth
     Of the open-plan tubbed trees.
Then I recalled the machine installed
     To test a new release.
Maybe that would run better than none
     And finally give me peace.

I plugged in a mouse, and keys unsoused,
     And a postcard-sized green screen,
Then I hit reset, with my brows knit,
     Hoping that release was clean.
My luck was in. Beta for the win.
     It booted to a prompt.
I ran the scripts and checked the MIPS;
     It wouldn't end up swamped.

The Post-it note that I wrote
     Had brief words of advice.
"Admins", it said, "The machine is dead.
     "The disk has failed us twice.
"But the spare server is a life preserver
     "That'll run till half-past three.
"When the next shift, if you catch my drift,
     "Takes over" - Sam McGee.

Wednesday, 4 July 2018

ScreenTime


It is pretty easy to add a rectangular fly screen to a sash window.  But the problem with sash windows is that the maximum they can open is half, and the sash mechanism is less reliable than a simple (or complicated; see the picture...) hinge.

So how about an elastic concertina fly screen for a hinged window that folds away into the surround?  It has a magnetic strip like a fridge door that attaches it to the three opening sides of the window frame, and, as the window is opened, it un-concertinas (if that's a verb) to fill the gap.

When the window reaches a certain point (say open about 20 cm) the concertina is fully extended.  Then the magnetic strip pulls off the frame and folds itself away again into the surround using its stored elastic energy.

The magnet eventually re-attaches when the window is re-closed.

It should be simple to make, and could probably come as a retro-fit kit for existing windows, as well as being an option on new ones.

Thursday, 14 June 2018

VerticallyChallenged


This is a couple of Augusta Westland AW609s.  They are vertical take off and landing aircraft that rotate their engines and propellers when up in the air to fly horizontally.  There are quite a few other VTOL aircraft that use this principle.

If you look, you can see that the propeller blades twist like a helix (all propeller blades do this; it compensates for the fact that the tip is moving faster than the middle).  The blades can also be twisted as a whole, which is called variable pitch.  

In a helicopter with just one rotor, variable pitch is essential for forward flight because the blade that is moving forward with the direction of flight is going fast into the air, and so generates more lift, whereas the one on the other side of the rotor that is going backwards relative to the air generates less lift.  Without the blades twisting every half-rotation using their variable pitch to give more lift on the back stroke, the helicopter would simply tip over and fall out of the sky.

But this effect is neutralised with two rotors like the AW609, one on the left and one on the right of the forward direction, as long as one rotates clockwise and the other rotates anticlockwise.  Then the forces balance, and the blades don't need to flap with each half-revolution.

The problem with planes like the AW609 is that the propellers need to be big to act like helicopters, but that makes them very inefficient in horizontal flight, limiting both the plane's speed and range.  What would be ideal for VTOL planes like this would be a propeller that could also shrink to a small radius in horizontal flight, and expand to a big radius when helicopter-style vertical flight was needed.

Given the lack of need for variable pitch, this could be made to work with four-bladed propellers (rather that the three you see in the picture), or, indeed, propellers with any even number of blades.  The blades would be hollow, with one very slightly smaller that the other.  To reduce the propeller diameter the blades would be drawn through the hub and the smaller one would slide inside the slightly larger one opposite.  They would also have to twist as they did this, to accommodate the helical blade shape.

There are a few problems with this idea, but I don't think they are insurmountable:

  1. All current blades are not a constant-pitch helix.  This would be needed for them to fit inside each other.
  2. Careful thought would need to be applied to balancing the propellers given the slight difference in the sizes of the pairs of opposite blades.  The masses need to match, obviously, but so too would the moment of inertia, lift and probably drag.
  3. The blades could not be variable pitch, except when fully extended.
  4. The blades would have to have a constant cross-section.
  5. Your [it-won't-work-because] goes here...
I don't know if the aerodynamic compromises needed to accommodate the above list (plus the things I haven't thought of) would nullify the increased speed and range that would come from having a more-or-less conventional sized propeller for horizontal flight.

But it would be interesting to do some experiments and calculations...

Wednesday, 11 April 2018

OutOfControl





This is an edited version of a letter that was published in the London Review of Books Vol. 39, No. 11, 1 June 2017.


Driving speed is easily controlled by self-funding radar cameras and fines; in contrast, MP3 music sharing is unstoppable.

Every technology sits somewhere on a continuum of controllability that can be adumbrated by another two of its extremes: nuclear energy and genetic engineering. If I want to build a nuclear power station then I will need a big field to put it in, copious supplies of cooling water and a few billion quid. Such requirements mean that others can exert control over my project. Nuclear energy is highly controllable. If, by contrast, I want to genetically engineer night-scented stock to make it glow in the dark so it attracts more pollinators, I could do so in my kitchen with equipment that I could build myself. Genetic engineering is uncontrollable.

We may debate controllable technologies before they are introduced with some hope that the debate will lead to more-or-less sensible regulation (if it is needed).

But it is pointless, or worse damaging, to debate an uncontrollable technology before its introduction.  Every technology starts as an idea in one person’s mind, and the responsibility for uncontrollable technologies lies entirely with their inventors. They alone decide whether or not to release a given technology because - if they put the idea up for debate - its uncontrollability means that people can implement it anyway, regardless of the debate's conclusions. (Note in passing that - all other things being equal - an uncontrollable technology will have greater Darwinian fitness than a controllable one when it comes to its being reproduced.)

In my own case I classify technologies I invent as broadly beneficial or damaging. The former I release online, open-source. The latter I don’t even write down (these include a couple of weapons systems at the uncontrollable end of the continuum); they will die with me.

I may be mistaken in my classification, with consequences we may regret. Other inventors may act differently: we may regret that too. But we shouldn’t make the mistake of indulging in (necessarily) endless discussion of what to do about a technology if it is uncontrollable. The amount of debate that we devote to a technology should, inter alia, be proportional to how controllable it is.

Technological changes have unforeseen and occasionally negative social and political consequences.  This is inevitable when something powerful impinges on things that are relatively weak like regulation; the same applies to the benefits. Fortunately the vast majority of people are well intentioned, and technology amplifies the majority along with its complementary minority. Much happens faster and more spectacularly, but the ratio of more good to less bad stays about the same.

Monday, 12 March 2018

FisherFolk



Castaway, the first British reality TV show nearly two decades ago, dropped a group of about thirty people on the remote Scottish island of Taransay and filmed them as they argued with each other and fell out brutally and in a psychologically damaging way over the following weeks.

I watched the opening episode, which had the whole group in a room in London before they set out discussing what they would do and how they thought things would work, and I predicted to anyone who would listen (i.e. my family and the cat) that the whole thing would be a social and emotional disaster for most of them.  And so it was.

The problem was that - in that London room - they were all talking with each other excitedly and at length in a friendly, convivial, and engaging way.

---o---

Think of two island fishermen in their fifties who have known each other since childhood.  On a Monday their total day's conversation as they pass each other on the quayside might be:

  "Morning,"

  "Morning."

And similarly every day of the week, with - perhaps - on the Friday:

  "Morning,"

  "Morning.  Storm's coming."

  "Aye."

They, and the rest of their island community, have evolved a peaceful system of friendship and cooperation an essential component of which is not annoying each other with their personal views, history, random thoughts, and chatter.

Our two friends sit together all evening in the pub in silence, their pints of beer in front of them on the table, taking a sip every minute or two and thinking their own thoughts.  If something needs to be communicated (like a storm) they mention it, then shut up.  Occasionally the whole community all gets very drunk and sing and play the pub piano and talk nonsense for hours then, the following morning, their hangovers enforce a return to their normal reservation.

A lot of folk anthropology consists of just-so stories about how we are adapted to life in a hunter-gatherer village and how we carry that inheritance over to modern global civilised life.  Sometimes, it is claimed, conflict results; one obvious example is xenophobia.  But one thing we have certainly not carried over is the circumspect reservation that we can observe today in isolated small communities.  Every communications technology we have created - printing, the telephone, radio, television, the internet, social media - works against that reservation, and we embrace them all with delight.

And we wonder why we don't get on as well as the two fishermen.



Saturday, 16 September 2017

ProbablePrejudice




Think about this game:  suppose you have an urn filled with equal numbers of red and green marbles.  You reach in and take out a marble in your clenched hand so you can't see it.  What colour do you guess the marble is if you want to be right as often as possible?  The answer is it doesn't matter.  If you guess red or green at the toss of a coin you will score 50%.  If you always guess green you will also score 50%.  The same goes for any proportion of guesses in between.

But this cannot be true if there are more red marbles than green.  In the extreme, if there are only red marbles in the urn, you would clearly be crazy ever to guess green.  So what is the general rule if the proportion of red marbles is p and you know the value of p?

Suppose the proportion of red guesses you make is r.  Should r = p?  That seems to be true from the argument above if p = 1, and maybe if p = 0.5.  But it may not be true if p = 0.8, say.  Let's look at the sums:

A red marble comes out of the urn a fraction p of the time.  If you guess red r of the time you will be right pr of the total time for those red marbles.

A green marble comes out of the urn (1 - p) of the time.  If you guess green (1 - r) of the time you will be right (1 - p)(1 - r) of the total time for those green marbles.

So the total proportion of correct guesses you make, c, is

               c = pr + (1 - p)(1 - r)

                 = r(2p - 1) - p +1

If we plot a graph of correct guesses, c, for different values of r when p = 0.5 we get:


Which tells us what we said when we started - for equal numbers of reds and greens it doesn't matter what proportion of red guesses, r, you make, you will always score c = 50%.

But now suppose p = 0.8 (that is, 80% of the marbles in the urn are red).  Then the graph does this:


Now what is the best guessing strategy, r, to give the biggest value of correct guesses, c? It is not r = p as we conjectured.  It is to guess red all the time.  This gives a highest possible score of 80%.

This happens even for the tiniest majority of red or green marbles.  If you know red is in the majority, no matter how small that majority is, you always guess red.  If you know green is in the majority you always guess green.

This is a really easy rule for evolution to encode: if there are two types of things, A and B, and you know that A are in the majority, then - when encountering a thing with no other knowledge - assume the thing is A.  You will be right as often as it is possible to be.

A and B might be bears and tigers growling out of sight.  If you know there are more bears than tigers, then your best bet is to assume you have to deal with a bear.

This argument affects the best way for you to allocate resources.  Suppose that it costs you the same to prepare to encounter an A in the future as it costs to prepare to encounter a B.  Further suppose that the reward (or loss) you get if you meet an A is the same as the reward (or loss) you get if you meet a B.  Then, if there are even just a few more As than Bs, it is optimal to spend ALL your resources on preparing to meet As and to spend NONE on preparing to meet Bs.

Of course, A and B might not be bears and tigers; they might be people of unknown sexuality, nationality, or (if - like the bears and tigers - they are also out of sight) gender or ethnicity...





Monday, 4 September 2017

FishFerris


I was in Seattle a few days ago, where they have a Ferris wheel on the waterfront (above).

It would not be too difficult to make Ferris pods watertight, whereupon part of the ride in any ocean or river city could go underwater.  At the top you'd get a view across the city, and at the bottom you'd get a view of the fishes.  Plus there would be a small frisson for the wheel riders as each pod submerged.


It would work particularly well next to a reef dropoff, where the pods on the wheel could go down next to the coral wall.

Go build one, World!

Saturday, 12 August 2017

AluminiumFuel


This is what happens when you put aluminium in hydrochloric acid.  It makes aluminium chloride and hydrogen gas, which you can see bubbling off.  If you put aluminium in water it does something similar, giving aluminium oxide and hydrogen.

But the problem with aluminium in water is that aluminium oxide (unlike aluminium chloride) is not soluble.  The aluminium oxide forms a protective film over the aluminium and the reaction stops after a fraction of a second.  So you get hardly any hydrogen.

But now the US Army Aberdeen Proving Ground Research Laboratory has made a serendipitous discovery: they have found an aluminium alloy to which the film of oxide does not adhere, and so you can drop it into water and it generates hydrogen gas and aluminium oxide continually.

This is potentially an extremely important discovery.  The big problem with electric power is not generating electricity - we have hundreds of ways to do that, including many renewable techniques. The big problem is storage.  Even the very best and latest batteries are very expensive, very complicated, and store little energy for their weight.  

But aluminium is made from aluminium oxide by electricity, and chunks of aluminium are cheap, and are easy and safe to store and to transport.  And we have fuel-cells that will make electricity from hydrogen.

So. How about an aluminium-fuelled car?  Let's compare it with the most efficient (but very polluting) conventional cars currently on the road - diesels - and also with zero-emission Li-ion battery cars, like the Tesla.  Here's the maths:

First, how much hydrogen do we get from one kilogram of aluminium?

2Al + 3H2→ Al2O3 + 3H2

The atomic mass of aluminium is 27 and the molecular mass of hydrogen gas is 2.  We get three hydrogen molecules for every two aluminium atoms.  With the mass ratio, that means that for every one kilogram of aluminium we get a ninth of a kilogram of hydrogen.

Combining a ninth of a kilogram of hydrogen with oxygen from the air (which is what a fuel cell does) gives 15.5 mega-joules (MJ) of energy.  But fuel cells are about 50% efficient and electric motors are about 80%, so that becomes about 6 MJ of energy going to the car's wheels.

Thus, for our aluminium-powered car, one kilogram of aluminium lays down 6 MJ on the road.  For comparison one kilogram of diesel gives about 15 MJ, or two and a half times as much, and one kilogram of the best Li-ion batteries give around 0.3 MJ - a tiny fraction.

Diesel oil and aluminium pellets are both just simple, tough, cheap stuff; whereas Li-ion batteries are complicated, fragile, and expensive manufactured items.  It's easy to pour diesel into a car, or to drop aluminium powder or pellets into a hopper.  Batteries are time consuming to charge.  And a car carrying aluminium and water is inherently very safe in a crash compared to one with a tank of diesel in the back, and probably better than one with batteries (because of the very high mass of the batteries; lithium fires do happen, but there's actually not a lot of lithium in a lithium battery and it's not in its elemental form).

It looks as if our aluminium-powered car might be a GO.  That assumes, of course, that the US Army's research will scale and work reliably.

The car would be zero-emissions.  Its waste product would be aluminium oxide powder as a sort of ash.  This could be dumped at the refuelling station for re-smelting into aluminium.

And here is a potential problem.  Making one kilogram of aluminium from its bauxite ore (also aluminium oxide) takes about 48 MJ of electricity.  That would probably reduce a bit for recycling the car's ash, because that would be very pure.  Let's say 45 MJ, and assume we're going to be sensible and use renewable electricity like solar.  So the overall thermodynamic efficiency including the power generation (the so called wheel-to-wheel efficiency) of the aluminium-powered car is 6MJ÷45MJ, which is 13%.  The equivalent figure for a diesel car is around 14%, but for a battery electric car it's around 30%.

Note that all this analysis does not take account of the extra energy required to accelerate the considerable mass of the batteries in a battery car, some of which is recovered by regenerative braking.

In conclusion, the aluminium-powered car (if it works) would be a zero-emission vehicle that is as energy efficient as a diesel, but only half as efficient as a battery car.   It would be cheap to make (probably even cheaper in bulk than the diesel, and certainly cheaper than cars with lots of batteries). It would be the safest car on the road, and it would be quick to re-fuel (and ash-dump).

Aluminium as an electricity storage system probably makes sense for vehicles, at least until batteries get a lot better.  But its lower efficiency means it will not make sense for static storage, where mass does not matter.

But the really interesting possibility would be an aluminium-powered aeroplane.  An electric turbine would be more efficient (maybe 80%) than the turbofans that aeroplanes currently use (manufacturers are coy, but I guess around 40%), which would help to compensate for the 2.5:1 ratio of energy per kilogram we saw above between hydrocarbons and aluminium.  So we could have a zero-emission fleet of passenger aircraft, with no fuel fires in crashes.  The only problem is that the plane gets heavier and heavier as it uses up its fuel - aluminium oxide weighs more than aluminium...