Has not happened to me in the last 35 years of cycling.
Currently I'm riding about 9500 km/a and of course I hit the ground every now and then, especially during winter.
Either for psychological or physical reasons so called "helmets" must increase the risk of serious accidents.
No, the real problem is cyclists are small and drivers aren't given enough experience when learning to drive to identify small targets; They learn that pedestrian-sized obstacles are on pavements.
Cyclists should wear helmets because it can save their life if hit by a car, not to stop a bruise when they fall over at traffic lights because their fancy shoes didn't unclip.
Drivers in countries like the Netherlands apparently know how to detect cyclists. It is just a matter of training with a reasonable number of cyclists on the road.
For the other question: Bicycle "helmets" can not prevent anything, if you are hit by a car. In fact they are designed for impacts in the order of falling off the bike (Design test: An object in the helmet with the weight of a head (alone) hits the surface at 20km/h).
For impacts with car speed (30..50 km/h) the effect is neglectable, especially if you consider that the impact energy (to be absorbed by the head protection) raises with the square of velocity.
No, it's totally unfair. Have you ever shopped for a graphic card recently, with the goal to put that in your Linux box? There's currently only 2 choices: Nvidia or ATI. Both have totally horrible drivers in Linux, because the chip makers aren't being COOPERATIVE. That is, just not giving enough so that someone can make a decent driver. The problem isn't that Nvidia isn't helping, the problem is that they aren't helping AND we have no other choice.
Well if you hate all powerful graphics cards, use Intel onboard something. Especially if you hate gaming shit.
If you want graphics performance (3D) you will need either ATI or NVIDIA.
NVIDIA works well under Linux for more than a decade now. The provide drivers for all their hardware,
which are definitely superior to any free driver I have tested so far.
They also incorporate most of the interesting recent features of the Linux Kernel, like power saving, suspend etc.
And in contrast to ATI they support pretty much the same features on Linux as on Windows, within a reasonable time frame.
(AFAIR build from similar sources)
They wouldn't need to do this, >90% of the PC-Gamers market still runs Windows. But they do and I don't see much point of complaining.
It is totally their decision, whether they want to release their IP about how to program the graphics pipeline.
Southern germany: last year I counted 1day, the year before 2 days, where I swapped my bicycle for the local train,
because the snow was hindering. (I have to ride 17km)
But cars had an average speed of about 7km/h these days. Perhaps it is easier to telecommute.
This thing, with 16 motors introduces many more points of failure. Very cool, but practical? No. And definitely not useful for real world applications. Not yet, anyway.
Hmm: think again: A normal current helicopter with some hundred moving parts around the head- and the tail rotors under heavy load and wear should be better
than 16 moving parts running smoothly on ball bearings? The only critical part here is the flight control software, everything else is damn simple technology, compared to any existing heli design.
It also already contains redundancy, 4 out of 16 motors are allowed to fail...
First, let me say that I agree that the pilot should probably be under the blades, although I'm more concerned about stability. Lots of people have commented on the possibility of broken propellers, and yes, that is something to consider. However, I'd say it's less of a factor than most people on/. seem to think. I've got somewhere between 900 and 1000 hours of pilot in command time* in about 20 years and guess how many in-flight propeller failures I've seen in that time?...
*admittedly, in airplanes, not helicopters and most definitely not multicopters. I'd be surprised if that made any difference, however.
As far as I understood, the pilot position is wanted above, because it allows to use a typical parachute safety, as in many ultralights.
This is impossible with normal helicopter setups, due to the rotor on top.
As for stability: without the electronic controller this beast will be inherently instable (doesn't matter where the COG is).
With the controller the neutral state is, that the thing balances itself, hovering on the spot. With some reasonable controller (GPS etc.) it
would even stabilize it's absolute position.
Therefore it is relatively easy to fly, especially in contrast to classic Helicopters.
No, it's not. On a helicopter, there's only two rotors, and they're mechanically linked together because there's no reason to spin them at different speeds (you control them by altering the pitch of the blades).
Exactly this is not necessary with these Brushless E-Engines.
The control is done by some gyros and electronics. No complex pitch control as in helicopters. No horrible mechanics, required to be maintained every day.
No redundant hydraulic systems, no prove that the system remains halfway stable and controllable by a (extremely experienced) pilot, if the
single (turbine) engine breaks and you have to autogyro.
This prototype is already able to fly up to 20mins with the current LIPO batteries. It stabilizes itself, it weight is about the same as
the human on top. Engines Props and Batteries are nothing special, taken from the shop. Even if some of them break, the beast will be able
to be landed.
... then send thousands of workers right into the heart of it to put a big concrete casket over it. without protective gear.
What was a viable alternative?:
Wait for more things to evaporate out of the reactor?
Run away far enough
Develop some automated and radiation-proof machines to repair the ruins and then come back after 5 years of development to do the work
Delegate only 100 workers to build the whole thing, being sure that they won't survive the next month or so.
The did what was necessary and useful at that point (*after* the reactor went fireworks).
Protective gear for gamma rays did not exist and does not exist today.
The PBR is supposed to be self regulating -- higher temperatures reduce the rate of the reaction, so even a total loss of coolant means that the fuel heats up to some steady state temperature and will stay there forever. What happens to a TWR if the coolant flow stops for any reason?
The heat is self-regulating the chain-reaction only,
But the reactor will still heat up to some state above 2000 Degrees and you reactor structure needs to dissipate the generated decay heat at that point. It should not melt, crack (and let any air or water in) for possibly a loong time.
"the two biggest advantages of the fast reactor design is that it requires no spent fuel pools and uses cooling systems that require no power to function"
A cooling system without power for magnitudes like 10MW does not exist.
You may have a primary sodium circle, but you still need to remove the heat from it by pumping water through a heat exchanger and removing the heat from the water. If you don't do this, the sodium will start to boil at 900 Degrees and then the pressure will break out and be very reactive.
The chain reaction was off in Fukushima, but there was still x*10MW of decay heat that needed to be dissipated.
The process is declining in an exponential curve that starts at 5-10% of the reactors nominal thermal power and
this is the same for *all fission* reactors (including CANDU)
I don't think the melting point of beryllium would be a problem. The moderator is inside the sphere, not on the surface. The outer shell is ceramic.
No, you misunderstood the nature of the pebbles:
In the current designs only the Thorium/Uranium mixed with some small amount of carbon is embedded into a ceramic shield with 0.5mm size
(TRISO-Particle).
15000 of these tiny spheres are then embedded into graphite balls of about tennis ball size for mechanical handling.
The graphite in the outer ball is moderating the reactor and transfers the heat to the He-N Gas flow.
Graphite is also meant to 'lubricate' the movement of balls inside the reactor, but apparently this does not work in the hot and dry atmosphere.
Therefore replacing graphite with a metal would leave you with a molten mess.
Do we really have to keep watching reactors fail in unexpected ways
That's the way progress works. Bridges, for example, used to collapse often enough that it was obvious we didn't yet know enough about building bridges. Engineers learned from their mistakes, and now bridges are reasonably safe.
Well, as usual for architectural and medical failures you can grow Ivy on the remains and forget about it.
You should still not grow anything useful in certain regions of Ukraina and Belorussia for a reason and this will be the case for a couple of generations.
Ukraina is still spending 5% of their gross national product on the remains of the accident 25years ago.
IMHO this should be a difference for anybody who is not extremely short-sighted.
Beryllium is melting at about 1500 and will burn as all other metals in that group.
And of course burning moderator that blows radioactive dust and aerosoles into
the air is causing a problem. The most prominent example is 25 years old, in the
Ukraine and still warm.
These are reactors that (again) are called safe by their inventors, as the light water reactors before.
Of course these had some advantages over graphite moderated types, but are they safe in the sense that
you press the red button an all problems stop?
For breeders, well you woudn't have the water-steam pressure problem, but without active cooling you get
a temperature problem probably even quicker (high concentrations, high power densities).
And yes of course you have fission products in the system, generating heat.
I don't even want to know what happens if you reach 900 Degrees
and the Natrium evaporates.
Besides the problem that Natrium cooling erodes the steel of every tank and tube around it, which is the
main reason why most breeders are no longer running (outside of Russia, which does not care for safety).
I wouldn't trust the stability of a 40 year old breeder.
For pebble beds: these are a German invention and they did long therm reasearch on that,
the pebbles are called safe because the *should* withstand
2500+ Degrees and this temperature is inhibiting the nuclear chain reaction (negative temp coefficient).
There was also the idea around that you could leave the reactor without active cooling -- this is releasing heat
just by radiation. In practice this would mean, that a larger volume reactor reaches some 3000 Degrees inside, which
melts down pretty much everything.
In practice the pebbles have also problems with high temps above 1500 Degs (breakage) and apparently release fission
products as well (diffusion problem, loads of radioactive dust in the primary gas cooling).
And there is a really dangerous situation, if the hot reactor gets in any
water or normal air. The latter is not uncommon: there is a gas-water heat exchanger (which became dripping in the
Test Reactor in Juelich) as well as they had problems with the air locks (for feeding/withdrawing pebbles).
The Reactors in Japan are apparently no longer intact, which probably means that a breeder or pebble bed would simply be burning now,
due to the contact with water or air.
And in fact there is Clojure http://www.clojure.org/ , giving you parallel lambda execution and macros.
I'm not quite sure that the Lambda will ever make it into the Java standard.
Not even the Generics are fully supported at a JVM level.
Most of the Java designers still love classic for-loops and consider anything functional as 'strange and exotic programming style'.
It may be that roads are paid for by all taxes (I seriously doubt any significant contributions by other taxes), that does not give bike riders the right to break traffic and safety laws then whine about how dangerous riding a bike is.
Yep you say it: Nobody has the right to break
traffic safety laws. There is a law, that for
overtaking a bicycle you have to keep safety distance from a cyclist (where I live this distance is defined to 1.5m min).
And there is no rule that just because the speed limit is maybe 50km/h you are allowed to use this as your minimum speed. Apart from this I don't whine. I leave this to the Tin box inhabitants.
Roads are paid by all taxes, not only gas taxes.
Effects of car traffic are paid by the society as a whole (accident fatalities, fat and sick drivers,
tons of parking lots...)
I'm paying for the road too, but I only use
1/6 of the space you occupy with the
tin box.
The inventors of this projector thingy suggest, that a bike lane protects you in shared trafficspace,
when there is no extra bike lane on the street.
Contrary to public belief and repeated myths there is scientific evidence, that sharing the road with
the cars is definitely safer than cycling at the very right edge or even on a separate lane.
This is especially because there is no absolute separation: at every crossing you "meet" the cars again
and they will hardly recognize you on the bike lane.
Instead of strange devices I would invest in strong LED lights with hub generator that make you seen
in darkness.
Yet, no Lisp flavor has a feature that comes close to CPAN in saving http://www.cliki.net/asdf-install is a package, going that way. But You are insofar right, the community of Lispers is not that large to produce tons of halfbaked code...
[Object casting...] The Problem is, if I use just general containers in Java, I have to use casting to muffle the compiler. But I have no safety at all, the containers (Vector, Map,...) contain Objects, whatever they are.
So with the static typing as in Java you win nothing: You have to write lots of casts to work with the Compiler, but you are very likely to trap ClassCastExceptions.
If running untyped, you write half of the code, and you will get errors, when the Object, handed over to some method, can not be handled there. Which is not as often as you get ClassCasts in arbitrary places in Java.
At least in Germany, general speed limits
apply only for motor powered vehicles. If no traffic sign sets the limit, you may go with your bicycle as fast as you like. Some
low-racer recumbent cyclists already attacked radar traps to get a foto...
Slashdot Mirror
Has not happened to me in the last 35 years of cycling. Currently I'm riding about 9500 km/a and of course I hit the ground every now and then, especially during winter.
Either for psychological or physical reasons so called "helmets" must increase the risk of serious accidents.
No, the real problem is cyclists are small and drivers aren't given enough experience when learning to drive to identify small targets; They learn that pedestrian-sized obstacles are on pavements. Cyclists should wear helmets because it can save their life if hit by a car, not to stop a bruise when they fall over at traffic lights because their fancy shoes didn't unclip.
Drivers in countries like the Netherlands apparently know how to detect cyclists. It is just a matter of training with a reasonable number of cyclists on the road. For the other question: Bicycle "helmets" can not prevent anything, if you are hit by a car. In fact they are designed for impacts in the order of falling off the bike (Design test: An object in the helmet with the weight of a head (alone) hits the surface at 20km/h). For impacts with car speed (30..50 km/h) the effect is neglectable, especially if you consider that the impact energy (to be absorbed by the head protection) raises with the square of velocity.
No, it's totally unfair. Have you ever shopped for a graphic card recently, with the goal to put that in your Linux box? There's currently only 2 choices: Nvidia or ATI. Both have totally horrible drivers in Linux, because the chip makers aren't being COOPERATIVE. That is, just not giving enough so that someone can make a decent driver. The problem isn't that Nvidia isn't helping, the problem is that they aren't helping AND we have no other choice.
Well if you hate all powerful graphics cards, use Intel onboard something. Especially if you hate gaming shit.
If you want graphics performance (3D) you will need either ATI or NVIDIA. NVIDIA works well under Linux for more than a decade now. The provide drivers for all their hardware, which are definitely superior to any free driver I have tested so far. They also incorporate most of the interesting recent features of the Linux Kernel, like power saving, suspend etc. And in contrast to ATI they support pretty much the same features on Linux as on Windows, within a reasonable time frame. (AFAIR build from similar sources)
They wouldn't need to do this, >90% of the PC-Gamers market still runs Windows. But they do and I don't see much point of complaining.
It is totally their decision, whether they want to release their IP about how to program the graphics pipeline.
Southern germany: last year I counted 1day, the year before 2 days, where I swapped my bicycle for the local train, because the snow was hindering. (I have to ride 17km) But cars had an average speed of about 7km/h these days. Perhaps it is easier to telecommute.
This thing, with 16 motors introduces many more points of failure. Very cool, but practical? No. And definitely not useful for real world applications. Not yet, anyway.
Hmm: think again: A normal current helicopter with some hundred moving parts around the head- and the tail rotors under heavy load and wear should be better than 16 moving parts running smoothly on ball bearings? The only critical part here is the flight control software, everything else is damn simple technology, compared to any existing heli design. It also already contains redundancy, 4 out of 16 motors are allowed to fail...
AFAIK these are a bit smaller: 1kg weight and up to 5kW surge. http://www.hacker-motor-shop.com/e-vendo.php?shop=hacker&a=article&ProdNr=37410007
First, let me say that I agree that the pilot should probably be under the blades, although I'm more concerned about stability. Lots of people have commented on the possibility of broken propellers, and yes, that is something to consider. However, I'd say it's less of a factor than most people on /. seem to think. I've got somewhere between 900 and 1000 hours of pilot in command time* in about 20 years and guess how many in-flight propeller failures I've seen in that time? ...
*admittedly, in airplanes, not helicopters and most definitely not multicopters. I'd be surprised if that made any difference, however.
As far as I understood, the pilot position is wanted above, because it allows to use a typical parachute safety, as in many ultralights. This is impossible with normal helicopter setups, due to the rotor on top. As for stability: without the electronic controller this beast will be inherently instable (doesn't matter where the COG is). With the controller the neutral state is, that the thing balances itself, hovering on the spot. With some reasonable controller (GPS etc.) it would even stabilize it's absolute position. Therefore it is relatively easy to fly, especially in contrast to classic Helicopters.
No, it's not. On a helicopter, there's only two rotors, and they're mechanically linked together because there's no reason to spin them at different speeds (you control them by altering the pitch of the blades).
Exactly this is not necessary with these Brushless E-Engines. The control is done by some gyros and electronics. No complex pitch control as in helicopters. No horrible mechanics, required to be maintained every day. No redundant hydraulic systems, no prove that the system remains halfway stable and controllable by a (extremely experienced) pilot, if the single (turbine) engine breaks and you have to autogyro. This prototype is already able to fly up to 20mins with the current LIPO batteries. It stabilizes itself, it weight is about the same as the human on top. Engines Props and Batteries are nothing special, taken from the shop. Even if some of them break, the beast will be able to be landed.
... then send thousands of workers right into the heart of it to put a big concrete casket over it. without protective gear.
What was a viable alternative?:
The did what was necessary and useful at that point (*after* the reactor went fireworks). Protective gear for gamma rays did not exist and does not exist today.
The PBR is supposed to be self regulating -- higher temperatures reduce the rate of the reaction, so even a total loss of coolant means that the fuel heats up to some steady state temperature and will stay there forever. What happens to a TWR if the coolant flow stops for any reason?
The heat is self-regulating the chain-reaction only,
But the reactor will still heat up to some state above 2000 Degrees and you reactor structure needs to dissipate the generated decay heat at that point. It should not melt, crack (and let any air or water in) for possibly a loong time.
"the two biggest advantages of the fast reactor design is that it requires no spent fuel pools and uses cooling systems that require no power to function"
A cooling system without power for magnitudes like 10MW does not exist.
You may have a primary sodium circle, but you still need to remove the heat from it by pumping water through a heat exchanger and removing the heat from the water. If you don't do this, the sodium will start to boil at 900 Degrees and then the pressure will break out and be very reactive.
The chain reaction was off in Fukushima, but there was still x*10MW of decay heat that needed to be dissipated. The process is declining in an exponential curve that starts at 5-10% of the reactors nominal thermal power and this is the same for *all fission* reactors (including CANDU)
I don't think the melting point of beryllium would be a problem. The moderator is inside the sphere, not on the surface. The outer shell is ceramic.
No, you misunderstood the nature of the pebbles:
In the current designs only the Thorium/Uranium mixed with some small amount of carbon is embedded into a ceramic shield with 0.5mm size (TRISO-Particle). 15000 of these tiny spheres are then embedded into graphite balls of about tennis ball size for mechanical handling.
The graphite in the outer ball is moderating the reactor and transfers the heat to the He-N Gas flow. Graphite is also meant to 'lubricate' the movement of balls inside the reactor, but apparently this does not work in the hot and dry atmosphere.
Therefore replacing graphite with a metal would leave you with a molten mess.
That's the way progress works. Bridges, for example, used to collapse often enough that it was obvious we didn't yet know enough about building bridges. Engineers learned from their mistakes, and now bridges are reasonably safe.
Well, as usual for architectural and medical failures you can grow Ivy on the remains and forget about it.
You should still not grow anything useful in certain regions of Ukraina and Belorussia for a reason and this will be the case for a couple of generations. Ukraina is still spending 5% of their gross national product on the remains of the accident 25years ago. IMHO this should be a difference for anybody who is not extremely short-sighted.
Beryllium is melting at about 1500 and will burn as all other metals in that group. And of course burning moderator that blows radioactive dust and aerosoles into the air is causing a problem. The most prominent example is 25 years old, in the Ukraine and still warm.
These are reactors that (again) are called safe by their inventors, as the light water reactors before.
Of course these had some advantages over graphite moderated types, but are they safe in the sense that you press the red button an all problems stop?
For breeders, well you woudn't have the water-steam pressure problem, but without active cooling you get a temperature problem probably even quicker (high concentrations, high power densities). And yes of course you have fission products in the system, generating heat. I don't even want to know what happens if you reach 900 Degrees and the Natrium evaporates.
Besides the problem that Natrium cooling erodes the steel of every tank and tube around it, which is the main reason why most breeders are no longer running (outside of Russia, which does not care for safety). I wouldn't trust the stability of a 40 year old breeder.
For pebble beds: these are a German invention and they did long therm reasearch on that, the pebbles are called safe because the *should* withstand 2500+ Degrees and this temperature is inhibiting the nuclear chain reaction (negative temp coefficient). There was also the idea around that you could leave the reactor without active cooling -- this is releasing heat just by radiation. In practice this would mean, that a larger volume reactor reaches some 3000 Degrees inside, which melts down pretty much everything.
In practice the pebbles have also problems with high temps above 1500 Degs (breakage) and apparently release fission products as well (diffusion problem, loads of radioactive dust in the primary gas cooling). And there is a really dangerous situation, if the hot reactor gets in any water or normal air. The latter is not uncommon: there is a gas-water heat exchanger (which became dripping in the Test Reactor in Juelich) as well as they had problems with the air locks (for feeding/withdrawing pebbles).
The Reactors in Japan are apparently no longer intact, which probably means that a breeder or pebble bed would simply be burning now, due to the contact with water or air.
And in fact there is Clojure http://www.clojure.org/ , giving you parallel lambda execution and macros. I'm not quite sure that the Lambda will ever make it into the Java standard. Not even the Generics are fully supported at a JVM level. Most of the Java designers still love classic for-loops and consider anything functional as 'strange and exotic programming style'.
It may be that roads are paid for by all taxes (I seriously doubt any significant contributions by other taxes), that does not give bike riders the right to break traffic and safety laws then whine about how dangerous riding a bike is.
Yep you say it: Nobody has the right to break traffic safety laws. There is a law, that for overtaking a bicycle you have to keep safety distance from a cyclist (where I live this distance is defined to 1.5m min).
And there is no rule that just because the speed limit is maybe 50km/h you are allowed to use this as your minimum speed. Apart from this I don't whine. I leave this to the Tin box inhabitants.
Roads are paid by all taxes, not only gas taxes. Effects of car traffic are paid by the society as a whole (accident fatalities, fat and sick drivers, tons of parking lots ...)
I'm paying for the road too, but I only use
1/6 of the space you occupy with the
tin box.
The inventors of this projector thingy suggest, that a bike lane protects you in shared trafficspace, when there is no extra bike lane on the street.
Contrary to public belief and repeated myths there is scientific evidence, that sharing the road with the cars is definitely safer than cycling at the very right edge or even on a separate lane. This is especially because there is no absolute separation: at every crossing you "meet" the cars again and they will hardly recognize you on the bike lane.
Instead of strange devices I would invest in strong LED lights with hub generator that make you seen in darkness.
Refs: English overview
German quick risk picture
Yet, no Lisp flavor has a feature that comes close to CPAN in saving
http://www.cliki.net/asdf-install
is a package, going that way. But You are insofar right, the community of Lispers is not that large to
produce tons of halfbaked code...
Martin
[Object casting...] ...) contain
The Problem is, if I use just general containers
in Java, I have to use casting to muffle the
compiler. But I have no safety at all,
the containers (Vector, Map,
Objects, whatever they are.
So with the static typing as in Java you win
nothing:
You have to write lots of casts to work
with the Compiler, but you are very likely to
trap ClassCastExceptions.
If running untyped, you write half of the
code, and you will get errors,
when the Object, handed over to some method,
can not be handled there.
Which is not as often as you get ClassCasts in
arbitrary places in Java.
Martin
At least in Germany, general speed limits
apply only for motor powered vehicles. If no traffic sign sets the limit, you may go with your bicycle as fast as you like. Some
low-racer recumbent cyclists already attacked radar traps to get a foto...
What does he do, just keep peddling until he crashes into something and dies?
This bikes *do* have brakes. The virtual edge
(matt waever) had also landing gears.
Already there:
...
leitra,
Quest ,
Aleweder, Go-one, Cab-Bike
But they don't have enougth sales now to be cheap.