Gravity and Weightlessness

The International Space Station is in low earth orbit, approximately 360km above the surface of the Earth. They experience microgravity. I always assumed this is because they are far enough from the earth that the Earth's gravity no longer had a significant impact at this altitude.

It turns out I'm wrong. Gravity only reduces by about 3% for each 100km altitude. So they're still experiencing 91% of the gravity that we

What we experience as weight is known as "Apparent Weight". It is perceived because of force gradients across our body, where each horizontal cross-section of our body is supporting the weight of the parts of our body above the cross section.

When we're standing on the ground, we experience weight due to the reaction force of the ground. When in an aircraft, gravity acts on all mass within the aircraft (including our bodies), but the lift is generated by the aircraft shell, which also causes a reaction force that triggers apparent weight. The fact that gravity acts on all objects in the aircraft, but lift is only generated by the aircraft shell creates this force differential. If you were in a box that was in free-fall (ignoring friction for the moment), you would experience weightlessness because there is no reaction force provided by the box.

So back to the astronauts... They still experience gravity, but it is balanced by the centripedal force created by their orbit around earth. They experience weightlessness because the space station is moving at the same rate and with no friction does not provide a reaction force.

This has got to be my most confusing post yet! As always, for more information, see this Wikipedia article

Anti-matter

From the "I-wish-batteries-were-smaller" department. I've previously blogged about tritrium as an energy source.

Here's another alternative: Antimatter. This article on HowStuffWorks discusses the use of antimatter drives for space exploration.

A quote from the article:
"The amount of antimatter needed to supply the engine for a one-year trip to Mars could be as little as a millionth of a gram"

Now that's energy density!

Wind Turbines

I've always liked the idea of wind power generation. One day I'd like to have a turbine on the roof of my house contributing to my household energy requirements.

There are a couple of major issues with current, propeller type wind turbines. Most turbines put the blades in front (upwind) of the support pole. This requires that the blades are very stiff, so they don't flex and hit the pole. This adds to weight and therefore cost, while also reducing efficiency as there is more mass for the wind to move.

Well, why not put the blades behind (downwind from) the pole, you ask? Seems obvious, because you can have lighter and more flexible blades. Unfortunately there are issues due to the turbulence created by the pole. There is a kind of "dead spot" behind the pole which causes the blades to lose pressure and flex towards the pole. This can set up a rhythmic flexing and can destroy the blades depending on wind speed/strength and rotation frequency.

Here is an alternate design that uses a vertical axis and doesn't have any of these issues. I'm not sure how feasible it is, but hopefully it can result in more efficient wind power generation.

As always, more information is available from Wikipedia here.

Sleep Study

I had a sleep study last night. I slept at a hospital attached to various sensors to help diagnose why I'm not getting much value from my sleep.

The sensors attached to me included:
- 3 ECG sensors to monitor heart activity
- 4 EEG sensors to monitor brain activity. Maybe these weren't connected properly, because they said they weren't getting a signal. What? Did you think I was going to let this cheap shot get through to the comments??
- 2 sensors to monitor leg movement and check for Restless Leg Syndrome
- 3 sensors to monitor breathing. A plug for each nostril and a little plate that hangs over my mouth
- 2 straps around my chest and stomach to measure expansion/contraction
- 1 position sensoron my chest to measure whether I'm lying on my side, back or stomach
- 1 Blood O2 level monitor on my finger
- 3 Sensors on my forehead to measure eye movement (I guess to detect REM sleep)
- 1 Microphone strapped to my neck
- 1 Sensor on my chin that I suspect was monitoring teeth grinding??

For a grand total of 21 sensors and wires hanging off me.

So as you can imagine it wasn't easy to sleep with all this paraphernalia on digging into my head and body. Trying to roll over was a major engineering exercise to avoid tangling or detaching any wires. The only ones that were really uncomfortable were the finger one which caused my finger to throb after a while, and the tubes from the nose/mouth sensors that went behind my ears. When I tried to lie on my side they made my ears ache.

So anyway I've come out unscathed, if a little tired. I get the results in about 4 weeks so hopefully they've got some good information to work with. Kudos go to the nursing staff who have to stay there and actually be awake all night. I couldn't do that job.

Space Elevator

Here's a (kind of) follow up to my earlier entry about Space Fountains.

Here's an article that contains a proposal to build a space elevator. It goes into quite a bit of depth about the construction of the cable and the elevator cars and even addresses failure scenarios. A great read.

Stirling Engines

Stirling Engines are a wonderful technology to convert any heat (including waste heat from other processes) to power. They are completely sealed so there is no harmful exhaust and they're very efficient.

They've hit the press a bit lately and the latest news is that the world's largest solar array will use them to convert the gathered heat to power.

If you want to know more, click here for instructions on how to build your own.

Genetic Modification

I've often heard the theory that my generation is that last generation that will die. I've always thought that was a bit optimistic, but an article I read on The Australian yesterday has made me revise that opinion.

I've also long thought that my generation has missed the Genetic Modification (GM) boat because our genes are already set. Sure, future generations will be modified before they develop much, but I'm pretty much stuck with the genes I've got.

The Article talks about some scientists who have modified a mouse so that it can regenerate damaged legs, tails and even heart tissue. It can't regenerate the brain yet.

But the real kicker is that if they take liver cells from these GM mice and inject them into regular mice, the regular mice gain these regenerative abilities too.

Maybe there's hope for me yet...

CVT

All cars are an exercise in compromise. A major limitation of the internal combustion engine is that it has a fairly narrow rev range where it is efficient in terms of power output for fuel used. Anything outside that band and you start to lose efficiency. This is why electric cars, electric trains and boats are efficient transport. The engine spins at close to it's ideal rev range almost all of the time because they have flexibility built into the drivetrain.

Cars on the other hand, have to vary their speed significantly and often and have a rigid connection between the engine and the tyres on the road. So gears were added. These allow cars to keep their rev range somewhere around their most efficient level but still be able to vary their speed. This applies to both manual and automatic transmissions.

A new kind of transmission has been developed. CVTs (Continuously Variable Transmission) have a theoretically infinite number of gear ratios, allowing the engine to stay in it's most efficient rev range regardless of the road speed. It's a great technology.

You know how lots of automatics now have that 'semi-automatic' mode that allows you to change the gear up or down by moving the transmission selector to the side and moving it forwards or backwards? This always seemed odd to me, because why not get a manual and enjoy the improved efficiency.

So here's the funny part. Yet another example of marketers taking a great engineering idea and weirding it. Nissan has released a car with CVT and they've put in this 'manual' mode. They've taken a masterpiece of engineering that allows an infinite number of transmission ratios and they've deliberately hobbled it by forcing the transmission to stick at certain pre-defined ratios! It's like developing a new, propellent-free rocket, but NASA deciding that the big flames coming out of the space shuttle were more 'dramatic' and putting a rocket engine on the back to produce the flames.

A glimpse into the future

The guys at Pointless waste of time have done it again. There's a hilarious and well written prediction piece about how virtual reality will become the preferred place to live. Click here to read.

He raises some interesting questions. I don't know the answers, but I enjoyed pondering as I read.

Gyroscopes

Check out the gyro car and the gyro train.

They are two wheeled vehicles like motorbikes that use gyroscopes and precession to stay upright, even when they're stationary. They work by having a reasonably sized gyroscope mounted in the vehicle. Tilt sensors detect the vehicle starting to tip over and apply a force to the spin axis of the gyroscope. Precession causes this force to be translated by 90 degrees, righting the vehicle.

More (and probably better) information is provided by HowStuffWorks.

Extra Value Pack!

I went shopping at coles today. I went to grab my normal-sized container of stuff when I noticed a larger "Extra Value Pack". I figured, cool, it has to be cheaper because it's "Extra Value".

But then I decided to check. Of course, the larger pack wasn't any logical multiple larger than the small one (that would have made it easy), so I had to use a calculator.

It turned out that the "Extra Value" pack actually cost more per gram than the regular size! Damn marketing lies!

"Extra Value" my ass.

The best a man can get?

I've got a pretty tough beard and find shaving uncomfortable. However, I just got a new razor, a Gillette M3 Power.

It's got a battery and vibrates as you shave. It's great! It's made shaving a breeze. I can't recommend it highly enough.

Headspins after drinking

You know how the room spins after you've been drinking? Well, have you ever noticed that after a while it stops spinning, then starts spinning the other way?? Ever wondered why?

Balance is handled by a small blob of jelly called the cupola. It is in a small chamber and is attached to the chamber walls by lots of tiny hairs. When you move your head, the ball of jelly moves a bit slower than the chamber which bends the tiny hairs and indicates to the brain that you've moved.

When you drink alcohol, because it's such a terrific solvent, it gets just about everywhere, including in the cupola. The shape of the cupola is distorted by the alcohol, bending the hairs. Your brain interprets this as a rotational force (ie: you're spinning around).

In time the alcohol diffuses out of the cupola. However, by then your brain has gotten used to the the fact that your head is spinning and adjusted it's interpretation of the signals coming from the cupola. So it interprets your normal signals as seeming to spin in the opposite direction!

Quasiturbine engine

We've all driven piston internal combustion engines, right?

I've driven a Mazda RX-4 with a less common engine type, a wankel rotary engine.

One of the things that prevents a standard piston engine from revving harder is that the pistons have to accelerate and decelerate with every stroke. The momentum of the pistons is a major limiting factor. A rotary engine removes this limit by having all moving parts spinning, no acceleration and deceleration required. I can tell you, those engines rev like mad! The main downside of a rotary is that it doesn't completely burn the fuel, so it's not as clean.

Also, each piston only produces a power stroke once for every 2 revolutions of the driveshaft.

Welcome to the next step in this evolution, the Quasiturbine engine. It is far more efficient (it produces 4 power strokes for every revolution of the driveshaft! 8 times more than piston combustion engines) and burns the fuel more completely.

Can't wait until this is in a car... it will be fun to drive.

Space fountain

A space fountain is a type of active structure. This means that it requires power to retain structural integrity (ie: Not fall down!)

It basically works by having a hollow core through which pellets are shot upwards. A device at the top of the building (most likely a magnetic diverter) will reverse the pellet's direction. Doing this will impart some of the kinetic energy in the pellet to the structure, providing lift.

Therefore some of the weight of the structure is supported by the pellet stream rather than the building, allowing for less bulky building techniques.

Space fountains can be used as a launch pad for spacecraft by reducing the amount of fuel needed to be carried.

A related technique is the space elevator.

Batteries

Everyone hates batteries, right? They're heavy and bulky and they keep going flat at the most inopportune times. Mobile phones these days seem to be not much more than a case around a battery!

Enter Tritium, a radioactive isotope of hydrogen. When Tritium decays, it emits an electron. Sounds pretty darn good for a battery, right? Right? There are plans to make batteries that might last 10-12 years without recharging. See this Wikipedia article for a little more info.

There's an article with a lot of discussion about this on slashdot.

A summary of the posts in favor of these batteries seems to be:

Tritium batteries are already used in pacemakers

They are very easy to shield and give off almost no harmful radiation at all

Even if they're punctured, the results are less harmful than the contents of most chemical batteries

A summary of the posts against seem to be:

Ooohhhh... nukular... bad. Bad nukular!

And a word from the cynics:

Battery makers won't invest in this because they like making us buy lots and lots of disposable, short lived batteries

I say bring it on!

Gaming

Found this great article about gaming.

It's great. It explains very clearly (not to mention verbosely!) my opinions about games in lots of areas.

My favorite part? I hate wandering around lost in FPS's:
<snip>
Did you remember when you were a kid and you got bored on weekends, how you would go to a large building, a hotel or a hospital, then wander around for several hours looking for a certain room? While zombies attacked you? Neither do we. That's because, much to the surprise of FPS game makers everywhere, wandering around lost in hallways isn't fun.
</snip>

Other highlights? Creating 'difficulty' by giving you only 4 bullets in a clip, or making you talk to 10 different NPCs in the right order to be able to accomplish a task.

The Singularity

Slashdot had an article yesterday about downloading your brain.

It reminded me of an essay called Staring into the Singularity.

The essay talks about what happens when we develop an AI that is capable of improving itself, by designing and implementing it's own software and hardware. Once this happens, thanks to ever-increasing hardware speed the work that the AI is capable of doing in a given timeframe rises asymptotically to infinity in a short period of time.

At this point the essay proposes that one by one the neurons in your brain can be replaced by a wireless device that performs the actual processing. The physical neuron will not be shut down until the inputs and outputs are modelled exactly by the computer. This way, your conscious is shifted into a computer seamlessly, and there is never two copies of you running at any point (which is one of the major issues raised in the Slashdot article).

It's a thought-provoking read.

Plane reverse thrusters Part II

I flew to Sydney on the weekend. On the way back, I was sitting just in front of the wing. As we were landing, I checked out the engine on the Boeing 737 and lo and behold, the back part of the engine slid back just as the loud windy noise started. It looked just like this (about half way down the page, under the heading "b) Reverse Thrust Configuration".

So, this just goes to show, not all of the information on the internet is bullshit. Unless this post is also bullshit... hmmmm.

Plane reverse thrusters

I just read about reverse thrusters for jet airplanes. You know when you touch down and then you hear a really loud sound from the engines and the plane slows down quite rapidly?

I always assumed they somehow ran the engine in reverse or something. I knew that didn't make much sense, but I didn't really know how it would work.

Well, it turns out they deploy these big diverters behind the engine that just redirects the jet exhaust!

See this Wikipedia article for more info.