Explosions are funny things. An explosion INSIDE a structure does huge damage to it, but an explosion outside a strong structure, especially one that has high pressure inside, does very little. The important structures here are the ones you can't see, the steel and concrete pressure vessels that contain the nuclear reaction. The hydrogen explosions mostly seem not to have damaged those.
The basic design is supposed to have a steam powered feed pump with a source of makeup water. Whether it broke, was never there, or the source of makeup water was a condenser that was mudded out by the tsunami, I don't know. And I would like to know. I used to serve on an SSN, so I have a certain professional curiosity.
Ny understanding is that the pumps were there but the battery power for the controls of the pumps ran out.
The deaths due to coal mining annually exceed all deaths in over fifty years of nuclear power generation.
This might be true, but to be fair you do need to include deaths in an around Uranium mines, especially in Africa, which don't have an especially impressive record.
Background radiation is typically (depends where you live amongst other things) 2.4 miliSieverts per year. So even if the dose was 1 microSievert, and you flew through that particular machine 250 times per year, that's still 10% of background.
No. Your publication of the specs makes their patent invalid, since it is not novel.
If you keep your invention secret, but they somehow discover it then you are vulnerable, but that's exactly what the patent system is designed to prevent,.
The electrons (in the magnetic field they are in) are in effect the lasing medium. They are being accelerated by the magnets so they emit EM radiation. They are relativistic, so that radiation is focused forwards. Finally there is a weird feedback effect whereby the light beam bunches the electrons into bunches one wavelength apart, so that the radiation is coherent.
1. pure ballistic weapons aren't that big a threat. They are in flight, and unsteered for so long that you can dodge them (or shoot them down with some sort of quick reacting machine gun).
2. If you melt the front or side of the shell it will likely tumble and miss, and surely fail to penetrate armour
3. You may be able to detonate and will certainly be able to disable the explosive warhead. Now you just have a cannonball coming at you, which is a lot better than a shell.
We have seen ligth (actually microwaves) from events longer ago and so more distant in space than the early galaxies Webb is targetting -- namely the cosmic microwave background. However there is a gap between that, and the most distant objects we can see in detail with Hubble. Webb is to look into that gap.
Actually not. Suppose we can observe object A, which is influenced by object B. Then the light from B must have been able to reach A before the light that reached us left A. In which case that light could have got all the way to us.
Saying that a universal cure for cancer can be found because cancer cells typically behave in a more primitive way is like saying a crime-free society can be achieved because criminals tend to be less educated.
Ignoring the fact that that isn't what the article says, the analogy is an interesting one. Criminals form mobs and gangs, more primitive structures than a complex society, based, perhaps on behviours we evolved when we lived in tribes. Understanding enough about tribe, mob and gang dynamics might give you ways to disrupt all common, or even all possible, mob or gang structures.
The article gives some reasons to consider that this might not be so. The point is that tumours are not simply a mass of identical cells -- they develop some structure and some organised ways of attacking their surroundings, getting nutrients and so on. This structure is not the same as the structure of normal tissue, so EITHER it evolves from nothing as the tumour develops, OR it is somehow latent in normal tissue. This paper suggests the second option, and furthermore that the latent genes (and mechanisms more complex than single genes) date back to the earliest multi-cellular lifeforms. It's certainly an interesting idea.
If you read further down the web page you cite you see that the specific impulse for a rocket (and an ion engine is a rocket for these purposes) really does only depend on the exhaust velocity. The mass of the propellant cancels out (the more massive it is, the more momentum it carries for given velocity, but the more mass you are throwing away to do it). For an aircraft (or a car for that matter) it's more complex because you are using outside air/road as reaction mass. Some calculation like that would also be appropriate for a Bussard ramjet.
(1) As counterintuitive as it may seem, a rocket's velocity is not limited to its exhaust velocity.
(2) Specific impulse is not directly related to exhaust velocity. It is a measure of how much momentum is imparted to the craft per amount of mass of the propellent. Ion engines actually have a very favorable specific impulse. In fact that is their main advantage over conventional chemical engines.
(3) "Billions of years" have nothing at all to do with hydrogen fusing. They don't just get old and decide to fuse. If it is going to be accomplished at all, it is energy, not years, that will do it.
I'm afraid (2) is just wrong. Specific impule is exhaust velocity divided by g (hence the units of seconds). Ion engines have a very favourable specific impulse (compared to any kind of thermal rocket with a material nozzle) because they have a high exhaust velocity. I know about (1) but mass ratio grows as e^(delta-V/exhaust velocity) so exhaust velocity is extremely relevant.
Re (3) you're right I was being sloppy. In the conditions in the centre of the sun, the average proton takes about 15 billion years to fuse (ie about 1 in 3 have done so so far). If you could achieve greater temperatures and densities they'd fuse faster. Nevertheless, this does make a Bussard ramjet look a bit tricky to engineer.
I heard a lovely lecture almost 30 years ago in which someone took a really fundamental look at this starting with relativity and a model that covers all kinds of rockets, no matter how fueled and powered. Essentially there are just two numbers that matter:
1. The proportion of your fuel which you turn into energy. This ranges from 0.1% for a perfectly efficient U235 fission reactor up to about 0.5% for fusing protons to helium and up to 100% for matter-antimatter.
2. The ratio of reaction mass to that energy which you use for propulsion, which ranges from 0 for a photon rocket to something enormous if you're exhaust velocity is less than relativistic.
Given 1, you can optimise 2 for a given length of journey.
Anyway, the conclusion of this is pretty stark: with any mass ratio you can imagine building, even if your spaceship is a capsule strapped to an asteroid of pur hydrogen ice, fusion will, at best, get you up to 0.2c or so and then stop you again. Fission is much worse.
Ion engines don't have a high enough specific impulse (equivalently exhaust velocity). They would need far too much fuel.
Even a perfectly efficient fusion rocket (which we have no idea how to build) would need a pretty huge mass ratio to achieve a total delta-V of.25c (ie speed up to Daedalus' proposed top speed and then stop again).
Antimatter rockets could work, if we could find a way to (a) build them (b) make enough antimatter and (c) store it.
Ramjets woudl be lovely but (a) we have no idea how to get hydrogen (as opposed to deuterium or helium 3) to fuse in less than billions of years, and a ramjet would have to do it in a few microseconds and (b) the solat system is in the middle of a big bubble in which the interstellar gas is exceptionally thin.
Photon or magnetic sails powered by "ambient" power -- ie starlight, solar wind, etc. do not get nearly enough boost before they have escaped from the star and are too far away from it.
The remaining option is beam riders. We send a beam of momentum, carried by photons (laser beam) or matter in some form (a stream of small very rugged missiles launched by a magnetic cannon at say 0.5c might work). This lets you leave your engine at home, which means it can be very nig and solar powered. The probe needs some way of catching the momentum, probably a light-sail or magnetic trap of some kind (blast the missiles to plasma and bounce them off a magnetic field). Stopping is harder -- Forward proposed detaching part of sail and sending it on ahead as a mirror and then using the reflected laser beam to brake.
It seems the rate is accelerating, from 1.8mm/yr over the last century to about 3mm/yr over the last 10-20 years. Errors in these figures are computed as up to 0.7. so the change is significant. The wikipedia article also gices some information about the techniques of measurement and data analysis and the other sources of change which have been considered and eliminated. And, of course it gives sources.
I'd worry more about the thermal expansion of ocean water; once the ice all melts it's gone, but the oceans will keep expanding so long as the global temperature increases.
Also valid. There is a LOT of ice though -- if all the ice in Antarcitca melted (unlikely) we'd be looking at a global sea level rise of something like 60m.
The ice in question isn't floating. The sea ice (of which there has been rather a lot less in recent years, generally speaking, than the historical norms) is floating and does not affect sea level. The ice on Greenland and Antarctica is sitting on rock.
There is no acceleration in sea-level rise over the medium and long term.... even if you could measure it to an accuracy of mm, which you can't. If sea-level rise is an indicator of AGW, then AGW is false.
Did someone say it was? I've heard no claim of trends in past sea levels as evidence for anything. You can however measure sea level to an accuracy of quite a lot less than 1mm if you average enough measurements over enough places and times and use modern instruments.
Looking forward, a rise in global average temperatures of 2 K or more as the vast majority of relevant experts predict for the rest of this century would almost surely cause a largish rise is sea level due to melting of ice which is currently supported by land in Greenland and some parts of Antarctica. Exactly how large a rise is not yet clear and is rather an important question. Understanding in more detail how rates of ice melt relate to local and global temperatures is important, and is the point of these observations.
Okay, so we establish that tablets have a subset of functionality as PCs. I agree with this, I don't do software development, word processing or gaming on a tablet. But then the article notes that tablets herald the end of PCs. So are we expecting the software makers to bridge that gap that prevents me from playing World of Warcraft, writing a book in Word or LibreOffice, coding in Radrails, etc? I just don't see that happening. I think there's a fundamental hardware issue with capacitive touch. I am not certain it will ever get to the point where I feel comfortable doing serious work or serious gaming using a glassy surface as my input device. Maybe I'm getting old but I just have never been impressed with even the latest cellphone displays and their response.
I think you miss the point. Your tablet or phone will have a bunch of peripherals, just like your PC has. Unlike the PC they'll mostly be wireless, although some might be dock-style instead. Those peripherals might well include a mouse & keyboard, a bigger screen, a bunch of storage and maybe some extra CPU power. So if you want to play WoW you drop your phone/tablet somewhere near your comfy chair, big screen and joysticks/mice/keyboard and off you go. In fact, all your phone is probably doing is identifying you to the rest of the system, which is, in fact, not unlike a desktop PC. However, it doesn't look that way to a naive user, nor is it marketed that way. The phone/tablet is in charge and you think of, and buy, your information & media setup as an extension to your phone, rather than a centre in its own right.
From a technical standpoint you're right -- but from a marketing and mindspace standpoint you're wrong. People may actually be using a desktop PC, or something like one, but they won't think that's what they're doing, nor will it be sold to them that way.
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I offer sporks to anyone who wants them, so the government should give me $500 billion in order to provide for the general welfare.
"should" no. "could" yes.
Explosions are funny things. An explosion INSIDE a structure does huge damage to it, but an explosion outside a strong structure, especially one that has high pressure inside, does very little. The important structures here are the ones you can't see, the steel and concrete pressure vessels that contain the nuclear reaction. The hydrogen explosions mostly seem not to have damaged those.
The basic design is supposed to have a steam powered feed pump with a source of makeup water. Whether it broke, was never there, or the source of makeup water was a condenser that was mudded out by the tsunami, I don't know. And I would like to know. I used to serve on an SSN, so I have a certain professional curiosity.
Ny understanding is that the pumps were there but the battery power for the controls of the pumps ran out.
The deaths due to coal mining annually exceed all deaths in over fifty years of nuclear power generation.
This might be true, but to be fair you do need to include deaths in an around Uranium mines, especially in Africa, which don't have an especially
impressive record.
Background radiation is typically (depends where you live amongst other things) 2.4 miliSieverts per year. So even if the dose was 1 microSievert, and you flew through that particular machine 250 times per year, that's still 10% of background.
No. Your publication of the specs makes their patent invalid, since it is not novel.
If you keep your invention secret, but they somehow discover it then you are vulnerable, but that's exactly what the patent system is designed to prevent,.
The electrons (in the magnetic field they are in) are in effect the lasing medium. They are being accelerated by the magnets so they emit EM radiation. They are relativistic, so that radiation is focused forwards. Finally there is a weird feedback effect whereby the light beam bunches the electrons into bunches one wavelength apart, so that the radiation is coherent.
1. pure ballistic weapons aren't that big a threat. They are in flight, and unsteered for so long that you can dodge them (or shoot them down with some sort of quick reacting machine gun).
2. If you melt the front or side of the shell it will likely tumble and miss, and surely fail to penetrate armour
3. You may be able to detonate and will certainly be able to disable the explosive warhead. Now you just have a cannonball coming at you, which is a lot better than a shell.
We have seen ligth (actually microwaves) from events longer ago and so more distant in space than the early galaxies Webb is targetting -- namely the cosmic microwave background. However there is a gap between that, and the most distant objects we can see in detail with Hubble. Webb is to look into that gap.
Actually not. Suppose we can observe object A, which is influenced by object B. Then the light from B must have been able to reach A before the light that reached us left A. In which case that light could have got all the way to us.
Saying that a universal cure for cancer can be found because cancer cells typically behave in a more primitive way is like saying a crime-free society can be achieved because criminals tend to be less educated.
Ignoring the fact that that isn't what the article says, the analogy is an interesting one. Criminals form mobs and gangs, more primitive structures than a complex society, based, perhaps on behviours we evolved when we lived in tribes. Understanding enough about tribe, mob and gang dynamics might give you ways to disrupt all common, or even all possible, mob or gang structures.
The article gives some reasons to consider that this might not be so. The point is that tumours are not simply a mass of identical cells -- they develop some structure and some organised ways of attacking their surroundings, getting nutrients and so on. This structure is not the same as the structure of normal tissue, so EITHER it evolves from nothing as the tumour develops, OR it is somehow latent in normal tissue. This paper suggests the second option, and furthermore that the latent genes (and mechanisms more complex than single genes) date back to the earliest multi-cellular lifeforms. It's certainly an interesting idea.
If you read further down the web page you cite you see that the specific impulse for a rocket (and an ion engine is a rocket for these purposes) really does only depend on the exhaust velocity. The mass of the propellant cancels out (the more massive it is, the more momentum it carries for given velocity, but the more mass you are throwing away to do it). For an aircraft (or a car for that matter) it's more complex because you are using outside air/road as reaction mass. Some calculation like that would also be appropriate for a Bussard ramjet.
(1) As counterintuitive as it may seem, a rocket's velocity is not limited to its exhaust velocity.
(2) Specific impulse is not directly related to exhaust velocity. It is a measure of how much momentum is imparted to the craft per amount of mass of the propellent. Ion engines actually have a very favorable specific impulse. In fact that is their main advantage over conventional chemical engines.
(3) "Billions of years" have nothing at all to do with hydrogen fusing. They don't just get old and decide to fuse. If it is going to be accomplished at all, it is energy, not years, that will do it.
I'm afraid (2) is just wrong. Specific impule is exhaust velocity divided by g (hence the units of seconds). Ion engines have a very favourable specific impulse (compared to any kind of thermal rocket with a material nozzle) because they have a high exhaust velocity. I know about (1) but mass ratio grows as e^(delta-V/exhaust velocity) so exhaust velocity is extremely relevant.
Re (3) you're right I was being sloppy. In the conditions in the centre of the sun, the average proton takes about 15 billion years to fuse (ie about 1 in 3 have done so so far). If you could achieve greater temperatures and densities they'd fuse faster. Nevertheless, this does make a Bussard ramjet look a bit tricky to engineer.
I heard a lovely lecture almost 30 years ago in which someone took a really fundamental look at this starting with relativity and a model that covers all kinds of rockets, no matter how fueled and powered. Essentially there are just two numbers that matter:
1. The proportion of your fuel which you turn into energy. This ranges from 0.1% for a perfectly efficient U235 fission reactor up to about 0.5% for fusing protons to helium and up to 100% for matter-antimatter.
2. The ratio of reaction mass to that energy which you use for propulsion, which ranges from 0 for a photon rocket to something enormous if you're exhaust velocity is less than relativistic.
Given 1, you can optimise 2 for a given length of journey.
Anyway, the conclusion of this is pretty stark: with any mass ratio you can imagine building, even if your spaceship is a capsule strapped to an asteroid of pur hydrogen ice, fusion will, at best, get you up to 0.2c or so and then stop you again. Fission is much worse.
For a laser, or a particle beam, I agree. A beam of guided missiles might be slightly less insanely difficult.
Ion engines don't have a high enough specific impulse (equivalently exhaust velocity). They would need far too much fuel.
Even a perfectly efficient fusion rocket (which we have no idea how to build) would need a pretty huge mass ratio to achieve a total delta-V of .25c (ie speed up to Daedalus' proposed top speed and then stop again).
Antimatter rockets could work, if we could find a way to (a) build them (b) make enough antimatter and (c) store it.
Ramjets woudl be lovely but (a) we have no idea how to get hydrogen (as opposed to deuterium or helium 3) to fuse in less than billions of years, and a ramjet would have to do it in a few microseconds and (b) the solat system is in the middle of a big bubble in which the interstellar gas is exceptionally thin.
Photon or magnetic sails powered by "ambient" power -- ie starlight, solar wind, etc. do not get nearly enough boost before they have escaped from the star and are too far away from it.
The remaining option is beam riders. We send a beam of momentum, carried by photons (laser beam) or matter in some form (a stream of small very rugged missiles launched by a magnetic cannon at say 0.5c might work). This lets you leave your engine at home, which means it can be very nig and solar powered. The probe needs some way of catching the momentum, probably a light-sail or magnetic trap of some kind (blast the missiles to plasma and bounce them off a magnetic field). Stopping is harder -- Forward proposed detaching part of sail and sending it on ahead as a mirror and then using the reflected laser beam to brake.
It can't be measured to that accuracy
Can you justify this claim. The peer-reviewed sources seem to reach the conclusion that it can.
There's a remarkable good wikipedia page on this.
http://en.wikipedia.org/wiki/Current_sea_level_rise
It seems the rate is accelerating, from 1.8mm/yr over the last century to about 3mm/yr over the last 10-20 years. Errors in these figures are computed as up to 0.7. so the change is significant. The wikipedia article also gices some information about the techniques of measurement and data analysis and the other sources of change which have been considered and eliminated. And, of course it gives sources.
I'd worry more about the thermal expansion of ocean water; once the ice all melts it's gone, but the oceans will keep expanding so long as the global temperature increases.
Also valid. There is a LOT of ice though -- if all the ice in Antarcitca melted (unlikely) we'd be looking at a global sea level rise of something like 60m.
The ice in question isn't floating. The sea ice (of which there has been rather a lot less in recent years, generally speaking, than the historical norms) is floating and does not affect sea level. The ice on Greenland and Antarctica is sitting on rock.
There is no acceleration in sea-level rise over the medium and long term.... even if you could measure it to an accuracy of mm, which you can't. If sea-level rise is an indicator of AGW, then AGW is false.
Did someone say it was? I've heard no claim of trends in past sea levels as evidence for anything. You can however measure sea level to an accuracy of quite a lot less than 1mm if you average enough measurements over enough places and times and use modern instruments.
Looking forward, a rise in global average temperatures of 2 K or more as the vast majority of relevant experts predict for the rest of this century would almost surely cause a largish rise is sea level due to melting of ice which is currently supported by land in Greenland and some parts of Antarctica. Exactly how large a rise is not yet clear and is rather an important question. Understanding in more detail how rates of ice melt relate to local and global temperatures is important, and is the point of these observations.
Read the article more carefully:
Melting ice in Greenland is contributing to sea level rise.
Sea level has risen 1.8mm over the last century.
If all the ice on Greenland melted sea level would rise 7m.
Nothing is stated about how long all the ice on Greenland would take to melt if it continued at the present rate.
Okay, so we establish that tablets have a subset of functionality as PCs. I agree with this, I don't do software development, word processing or gaming on a tablet. But then the article notes that tablets herald the end of PCs. So are we expecting the software makers to bridge that gap that prevents me from playing World of Warcraft, writing a book in Word or LibreOffice, coding in Radrails, etc? I just don't see that happening. I think there's a fundamental hardware issue with capacitive touch. I am not certain it will ever get to the point where I feel comfortable doing serious work or serious gaming using a glassy surface as my input device. Maybe I'm getting old but I just have never been impressed with even the latest cellphone displays and their response.
I think you miss the point. Your tablet or phone will have a bunch of peripherals, just like your PC has. Unlike the PC they'll mostly be wireless, although some might be dock-style instead. Those peripherals might well include a mouse & keyboard, a bigger screen, a bunch of storage and maybe some extra CPU power. So if you want to play WoW you drop your phone/tablet somewhere near your comfy chair, big screen and joysticks/mice/keyboard and off you go. In fact, all your phone is probably doing is identifying you to the rest of the system, which is, in fact, not unlike a desktop PC. However, it doesn't look that way to a naive user, nor is it marketed that way. The phone/tablet is in charge and you think of, and buy, your information & media setup as an extension to your phone, rather than a centre in its own right.
From a technical standpoint you're right -- but from a marketing and mindspace standpoint you're wrong. People may actually be using a desktop PC, or something like one, but they won't think that's what they're doing, nor will it be sold to them that way.
Like the Intergovernmental Panel on Climate Change report and the tens of thousands of pages of careful painstaking science behind it?