...we also know that there are massive periodic dust storms.
Don't you think the storms would have eroded away the water gullies, or at least filled them with dust by now ? So I would say the formations are a lot more recent than "in the ancient past when Mars had a bigger atmosphere".
The cross-section weighted average particle size of the dust particles is about 5 microns. Think of the particles as being ten times finer than the particles that make up talcum powder. It's more like cigarette smoke than it's like sand; it's not very abrasive, and doesn't do much in the way of erosion.
Sandstorms, like we have on Earth, do much more erosion.
However, yes, burial and deflation of features is a well-known effect on Mars. In some places the ancient surface is exposed, but in other places it is well buried. There are a lot of places on Mars where all you can see is the overlayer of dusty soil.
No, that's quite unlikely. Planets are hard to move.
Not so fast.:-) We have to look at the orbital decay to figure that one out. If Mars has to much velocity for its orbit, it'll work farther out. If it has too little velocity, it'll fall in.
Well, sort of. It won't "work its way out": if a planet has too much velocity for a circular orbit it will be in an elliptical orbit (it won't "work its way" into an elliptical orbit-- it will be in an elliptical orbit). However, if you work out how much energy that takes to move the planet, the number is, uh, extremely large. Planets are hard to move.
Combine that with tidal forces of the planets and the asteroid belt, and you might have a measurable affect.
Indeed, you "might." Turns out, however, that the perturbations do add up, but they don't add up enough to a large enough effect to significantly affect the semimajor axis.
The key to moving mountains (and the planets they are on) is a very small force, over millions or billions of years.
---
*Footnote: The greenhouse effect is well documented in the lab under ideal conditions (in sealed environments). The controversy lies with how much it affects Earth's unsealed atmosphere, its many layers and natural processes of climatic and seasonal variability. And more specifically, how much of that is the fault of human activity. That much is left to science to work out. Where it gets emotional and personal is when we start to engineer human policy. Do we prevent pre-industrialized nations from using fossil fuel, when every nation has needed it to become industrial? Do we make people live in poverty because our energy policy power remains expensive? Whatever we do, I ask that we keep science as science, and not let emotions cloud the science (no pun or global warming intended)
Precisely. In terms of the science, there is no controversy. Anthropogenic greenhouse warming may have been controversial fifteen years ago, but it no longer is.
In terms of the policy, indeed, there is quite reasonable grounds for disagreement. There are a wide number of possible policy choices-- one of which is "do nothing"-- and there is no question that the debate is, as of the moment, inconclusive. The problem, though, is that a small group of people who disagree with (possible future) policy decisions decided to attack the policy by trying to pretend that the science is inconclusive, and make an entirely imaginary case that greenhouse science is unclear, unsettled, and consists of nothing more than opinions put forth for political purposes. This is incorrect.
Is it possible that mars was warmer at a time? Either with a high level of CO2 or some other greenhouse gas that would have warmed the surface enough for running water?
Yes, that's a good summary of the current scientific thinking. The Viking orbital images show a lot of the surface is sculpted by water-carved features, and the belief is that Mars originally has a much thicker carbon dioxide atmosphere, which provided a significant amount of greenhouse warming (*). With the loss of Mars' magnetic field, this thick atmosphere was slowly eroded away by the solar wind to the very thin atmosphere we see today.
Maybe a little more dramatic but maybe even a slightly closer orbit?
No, that's quite unlikely. Planets are hard to move.
-----
*Footnote: The media likes to pretend that there is some controversy about the fact that carbon dioxide produces greenhouse effect warming (because controversy sells newspapers), but in the science community studying planetary atmosphere, there is no controversy whatsoever. It is just physics.
If you search hard enough, you can find somebody who disagrees, and quote them, and say, "look, not all scientists agree!" And since this is/. I'm sure somebody's about to do that: the miracle of the internet is that these fringe thinkers have just as loud a voice as people who have actually stufied the subject. But nevertheless, the greenhouse effect is just physics. And relatively simple physics.
But if there was salt in the water, there was probably also life in that water. Life living in the salty water making it saltier by pissing in it every single day.
And, of course, the fact that the Opportunity rover found the Meridiani Planum site to be covered with evaporite deposits (mostly sulfate salts) contributes a lot...
All the source documents for Christian theology are publicly available, and well out of copyright. What are copyrighted is modern translations of documents... which I sort of hate, but then again theology professors have to eat too. If you're willing to take the time and effort to learn Greek and Latin, you can read them more-or-less for free.
And the source documents for Islam are out of copyright, available for free, and written in a language that's isn't dead.
I disagree on the air intakes - generating downforce and brake cooling are also the reasons the air intakes are there. I'm sure those motors do produce heat - but I will bet it's still much less than an equivalent combustion engine.
Well, downforce would be produced much better from aero surfaces. And, with regenerative braking, brake cooling is the same thing as cooling the motors/batteries, but just with the current flowing the opposite direction.
How much is "a bit longer"? Several pre-production cars have already demonstrated 10 minute charging, while BYD claims it on the production F3DM. If you have a really crazy cooling system and, say, a 250kW Aerovironment PosiCharge charger or 300kW Norvik MinitCharge charger, you should be able to do ~5 minutes per ~120 miles.
This car has two hundred-kilowatt motors in it. If you use a 250 kW charger to charge batteries that you're then discharging at 200 kW, you need to spend 45% of the time charging.
Take a look at the air intakes on that car. It doesn't need air to burn, so those intakes have to be entirely for cooling airflow. Yow.
Re:Brazilian Ethanol [Re:Don't blame me]
on
The Great Ethanol Scam
·
· Score: 2, Informative
I agree with the first point you made. However, although it does take energy to produce fertilizer, note that plants do not get their energy from fertilizer, they get it from sunlight.
IF you RTFA you'd see that it's not engines being ruined by ethanol, it's fuel pumps and pickup lines.
Direct quote from the slashdot article: "there is increasing evidence that it is destroying engines in large numbers"
So, basically, you're saying that the slashdot summary is wrong. Well, well.
Stop the subsidies, tax carbon to account for externalities, and then let the market decide.
Ah, that's the trick. If you try to tax carbon to account for externalities, you'll hear such screaming about "tax and spend liberals" that you'll never be able to get to first base.
Add a new tax, in political jargon, is known as "suicide".
Alcohol-fueled racers [Re:Sounds like a crock ...]
on
The Great Ethanol Scam
·
· Score: 1
E100 fuel isn't being chosen by racing because it's a "better fuel". In fact, they don't really care; what matters to them is that everybody is using the same fuel. It's being chosen in an attempt to make a decidedly non-green sport look greener. No other reason.
Actually, Indy cars have been alcohol fueled since the mid-60s, and in fact it is for a good technical reason; it burns cooler. The switch they're currently making is from methanol to ethanol, not from gasoline to ethanol-- they haven't used gasoline for years.
Brazilian Ethanol [Re:Don't blame me]
on
The Great Ethanol Scam
·
· Score: 3, Interesting
It's not clear to me that sugar cane is a sustainable crop.
And, in any case, the Brazilian experience does show that the "ethanol ruins engines" canard is not to believed- 95% ethanol apparently doesn't ruin engines in Brazil.
It's not an irrelevant factor. Without any password changes, you are guaranteed to get the password eventually. If you do change passwords, you are trying to hit a moving target. You might get it, you might not
Good metaphor. Guessing a password by brute force is like a blindfolded man trying to shoot a car on the highway by the technique of shooting a bullet, moving the gun two meters, shooting another bullet, and repeating.
Now, if the cars are not moving (and he knows that there is a car on the road somewhere), this technique guarantees he hits one eventually; while if the cars are moving, there's no such guarantee... but, statistically, he hits the same number of cars, on the average, whether the cars are moving or not. It doesn't make any difference if the cars are moving or not to the average.
LIkewise, on the average, it makes no difference whether the passwords being probed for by a brute-force search are changing or not. This should be obvious if the cracker is trying to crack, say, a thousand systems, right? So, you should agree that a system administrator who's administrating a thousand accounts, ought to realize that the system is no safer against getting cracked if he makes his thousand users change their passwords every day or every year.
and even if you do, you don't have long before you have to run the attack again.
Now, that is a different story. If the cracker doesn't install his malware on the cracked system once he gets the password, but instead saves the password for later use, then yes, if you change the password before he uses it, that will help.
It isn't irrelevant if you change your password during the attack to something the attacker has already tried.
Nope. Think about it as a statistical thing. There's an equal probability that you'll change your password to something that the cracker is just about to try, as there is to change it to something the cracker hasn't tried yet
Lets say you change the password after the attacker has made it through half of the keyspace...there is a 50% chance that this new password will never be guessed
It's easier to think about statistics if you think about large numbers. Suppose the cracker is trying to crack 1 thousand user accounts, and the password change comes when he is one ten thousandth of the way through. Yes, on the average there's some chance that a users will change their password into one that he's already checked (and if they never changed their password again, they'd be immune from getting cracked.) However, to balance that, an equal chance exists that they happen to change their password to one that he's about to try. There's no net change in the statistics of cracking.
The same statistics work, on the average, whether the cracker is trying to break into one account.
As an example, Grimes assumes... 90 days between password change
How long you go between password changes is an irrelevant parameter, since a password change does not change the probability of success of a brute-force attack (i.e., any change is just as likely to change the password into the window of attack as it is to move it out of the window.)
Requiring frequent password change doesn't change the success statistics at all if the attacker is attacking multiple accounts. Even if the attacker is focussed on a single account, however, requiring a password change at intervals doesn't change the mean time it takes to break an account; it merely means that success is guaranteed, rather than probable, after twice the mean time (since that the mean time to break in is after exactly half the passwords have been tried.)
Re:Why is this review on /. ?
on
Space Vulture
·
· Score: 1
Is there a legitimate reason this is here, or is this just a slashvertisement?
I'm rather curious about that, too.
Actually, I liked the review, thought it was interesting, liked the fact that it wasn't merely an advertisement... but I'm not sure why this particular book was reviewed on Slashdot, and not two or three dozen other SF books that are, frankly, more noteworthy.
Wouldn't it be better just to take the page down and worry about hurt feelings later?
I would think that even if there was the possibility that a page was not right, that either someone could comment on it or it just be taken down.
Because if it were their policy to just remove pages and worry about hurt feelings later (or not at all), and it became widely known that this was their policy, they would get about a hundred thousand demands for pages to be removed every day.
Even if only one tenth of one percent of internet readers are jerks who would abuse the system by spamming out phony requests to delete pages from people they don't like, there are a lot of jerks out there who take offense to pages that they disagree with.
I'm a little unclear on the requirements of the train, it says it needs 110 megawatts but not for how long, how many trains, etc. At its most conservative, I'll specify that the trains will each require 110 megawatts per run, and 11 runs are made per day. (Because that means I get to work with the magic 1.21 gigawatts number, which is just funny.) Ok, so, we need 1.21 GWH/day.
You just switched from power units (MW) to energy units (MW-hours) and then back to different power units (MW-hours per day).
If one train requires 110 MW, it requires 110 MW regardless of how many times that train runs per day.
And MW hours per day is simply equal to power in MW times hours of operation per day.
Given ALL the problems we see with corporations that carry debt, why on earth Microsoft would want to piss away a giant cash reserve AND borrow money...
Slashdot Mirror
...we also know that there are massive periodic dust storms. Don't you think the storms would have eroded away the water gullies, or at least filled them with dust by now ? So I would say the formations are a lot more recent than "in the ancient past when Mars had a bigger atmosphere".
The cross-section weighted average particle size of the dust particles is about 5 microns. Think of the particles as being ten times finer than the particles that make up talcum powder. It's more like cigarette smoke than it's like sand; it's not very abrasive, and doesn't do much in the way of erosion.
Sandstorms, like we have on Earth, do much more erosion.
However, yes, burial and deflation of features is a well-known effect on Mars. In some places the ancient surface is exposed, but in other places it is well buried. There are a lot of places on Mars where all you can see is the overlayer of dusty soil.
No, that's quite unlikely. Planets are hard to move.
Not so fast. :-) We have to look at the orbital decay to figure that one out. If Mars has to much velocity for its orbit, it'll work farther out. If it has too little velocity, it'll fall in.
Well, sort of. It won't "work its way out": if a planet has too much velocity for a circular orbit it will be in an elliptical orbit (it won't "work its way" into an elliptical orbit-- it will be in an elliptical orbit). However, if you work out how much energy that takes to move the planet, the number is, uh, extremely large. Planets are hard to move.
Combine that with tidal forces of the planets and the asteroid belt, and you might have a measurable affect.
Indeed, you "might." Turns out, however, that the perturbations do add up, but they don't add up enough to a large enough effect to significantly affect the semimajor axis.
The key to moving mountains (and the planets they are on) is a very small force, over millions or billions of years.
--- *Footnote: The greenhouse effect is well documented in the lab under ideal conditions (in sealed environments). The controversy lies with how much it affects Earth's unsealed atmosphere, its many layers and natural processes of climatic and seasonal variability. And more specifically, how much of that is the fault of human activity. That much is left to science to work out. Where it gets emotional and personal is when we start to engineer human policy. Do we prevent pre-industrialized nations from using fossil fuel, when every nation has needed it to become industrial? Do we make people live in poverty because our energy policy power remains expensive? Whatever we do, I ask that we keep science as science, and not let emotions cloud the science (no pun or global warming intended)
Precisely. In terms of the science, there is no controversy. Anthropogenic greenhouse warming may have been controversial fifteen years ago, but it no longer is.
In terms of the policy, indeed, there is quite reasonable grounds for disagreement. There are a wide number of possible policy choices-- one of which is "do nothing"-- and there is no question that the debate is, as of the moment, inconclusive. The problem, though, is that a small group of people who disagree with (possible future) policy decisions decided to attack the policy by trying to pretend that the science is inconclusive, and make an entirely imaginary case that greenhouse science is unclear, unsettled, and consists of nothing more than opinions put forth for political purposes. This is incorrect.
Is it possible that mars was warmer at a time? Either with a high level of CO2 or some other greenhouse gas that would have warmed the surface enough for running water?
Yes, that's a good summary of the current scientific thinking. The Viking orbital images show a lot of the surface is sculpted by water-carved features, and the belief is that Mars originally has a much thicker carbon dioxide atmosphere, which provided a significant amount of greenhouse warming (*). With the loss of Mars' magnetic field, this thick atmosphere was slowly eroded away by the solar wind to the very thin atmosphere we see today.
Maybe a little more dramatic but maybe even a slightly closer orbit?
No, that's quite unlikely. Planets are hard to move.
-----
*Footnote: The media likes to pretend that there is some controversy about the fact that carbon dioxide produces greenhouse effect warming (because controversy sells newspapers), but in the science community studying planetary atmosphere, there is no controversy whatsoever. It is just physics.
If you search hard enough, you can find somebody who disagrees, and quote them, and say, "look, not all scientists agree!" And since this is /. I'm sure somebody's about to do that: the miracle of the internet is that these fringe thinkers have just as loud a voice as people who have actually stufied the subject. But nevertheless, the greenhouse effect is just physics. And relatively simple physics.
But if there was salt in the water, there was probably also life in that water. Life living in the salty water making it saltier by pissing in it every single day.
The thinking that brines may keep the water on Mars from freezing is not a new conclusion-- here ( http://www.liebertonline.com/doi/abs/10.1089/153110701753198927?cookieSet=1&journalCode=ast ) is a discussion of the concept from a few years back.
And, of course, the fact that the Opportunity rover found the Meridiani Planum site to be covered with evaporite deposits (mostly sulfate salts) contributes a lot...
and, the original source: Powerpoint presentation from LBL: "Global Cooling: Increasing World-wideUrban Albedos to Offset CO2," Hashem Akbari PDF file
All the source documents for Christian theology are publicly available, and well out of copyright. What are copyrighted is modern translations of documents... which I sort of hate, but then again theology professors have to eat too. If you're willing to take the time and effort to learn Greek and Latin, you can read them more-or-less for free.
And the source documents for Islam are out of copyright, available for free, and written in a language that's isn't dead.
So, I'd say Islam has you beat.
I disagree on the air intakes - generating downforce and brake cooling are also the reasons the air intakes are there. I'm sure those motors do produce heat - but I will bet it's still much less than an equivalent combustion engine.
Well, downforce would be produced much better from aero surfaces. And, with regenerative braking, brake cooling is the same thing as cooling the motors/batteries, but just with the current flowing the opposite direction.
How much is "a bit longer"? Several pre-production cars have already demonstrated 10 minute charging, while BYD claims it on the production F3DM. If you have a really crazy cooling system and, say, a 250kW Aerovironment PosiCharge charger or 300kW Norvik MinitCharge charger, you should be able to do ~5 minutes per ~120 miles.
This car has two hundred-kilowatt motors in it. If you use a 250 kW charger to charge batteries that you're then discharging at 200 kW, you need to spend 45% of the time charging.
Take a look at the air intakes on that car. It doesn't need air to burn, so those intakes have to be entirely for cooling airflow. Yow.
IF you RTFA you'd see that it's not engines being ruined by ethanol, it's fuel pumps and pickup lines.
Direct quote from the slashdot article: "there is increasing evidence that it is destroying engines in large numbers"
So, basically, you're saying that the slashdot summary is wrong. Well, well.
Stop the subsidies, tax carbon to account for externalities, and then let the market decide.
Ah, that's the trick. If you try to tax carbon to account for externalities, you'll hear such screaming about "tax and spend liberals" that you'll never be able to get to first base.
Add a new tax, in political jargon, is known as "suicide".
E100 fuel isn't being chosen by racing because it's a "better fuel". In fact, they don't really care; what matters to them is that everybody is using the same fuel. It's being chosen in an attempt to make a decidedly non-green sport look greener. No other reason.
Actually, Indy cars have been alcohol fueled since the mid-60s, and in fact it is for a good technical reason; it burns cooler. The switch they're currently making is from methanol to ethanol, not from gasoline to ethanol-- they haven't used gasoline for years.
It's not clear to me that sugar cane is a sustainable crop.
Still, the wikipedia article about Brazilian ethanol from sugar cane is enlightening, although we might not be able to replicate this in the US.
And, in any case, the Brazilian experience does show that the "ethanol ruins engines" canard is not to believed- 95% ethanol apparently doesn't ruin engines in Brazil.
Of course, it will take somewhat longer than the age of the universe to go through all of the 1x10^111 possible combinations you mention.
It's not an irrelevant factor. Without any password changes, you are guaranteed to get the password eventually. If you do change passwords, you are trying to hit a moving target. You might get it, you might not
Good metaphor. Guessing a password by brute force is like a blindfolded man trying to shoot a car on the highway by the technique of shooting a bullet, moving the gun two meters, shooting another bullet, and repeating.
Now, if the cars are not moving (and he knows that there is a car on the road somewhere), this technique guarantees he hits one eventually; while if the cars are moving, there's no such guarantee... but, statistically, he hits the same number of cars, on the average, whether the cars are moving or not. It doesn't make any difference if the cars are moving or not to the average.
LIkewise, on the average, it makes no difference whether the passwords being probed for by a brute-force search are changing or not. This should be obvious if the cracker is trying to crack, say, a thousand systems, right? So, you should agree that a system administrator who's administrating a thousand accounts, ought to realize that the system is no safer against getting cracked if he makes his thousand users change their passwords every day or every year.
and even if you do, you don't have long before you have to run the attack again.
Now, that is a different story. If the cracker doesn't install his malware on the cracked system once he gets the password, but instead saves the password for later use, then yes, if you change the password before he uses it, that will help.
It isn't irrelevant if you change your password during the attack to something the attacker has already tried.
Nope. Think about it as a statistical thing. There's an equal probability that you'll change your password to something that the cracker is just about to try, as there is to change it to something the cracker hasn't tried yet
Lets say you change the password after the attacker has made it through half of the keyspace...there is a 50% chance that this new password will never be guessed
It's easier to think about statistics if you think about large numbers. Suppose the cracker is trying to crack 1 thousand user accounts, and the password change comes when he is one ten thousandth of the way through. Yes, on the average there's some chance that a users will change their password into one that he's already checked (and if they never changed their password again, they'd be immune from getting cracked.) However, to balance that, an equal chance exists that they happen to change their password to one that he's about to try. There's no net change in the statistics of cracking.
The same statistics work, on the average, whether the cracker is trying to break into one account.
As an example, Grimes assumes... 90 days between password change
How long you go between password changes is an irrelevant parameter, since a password change does not change the probability of success of a brute-force attack (i.e., any change is just as likely to change the password into the window of attack as it is to move it out of the window.)
Requiring frequent password change doesn't change the success statistics at all if the attacker is attacking multiple accounts. Even if the attacker is focussed on a single account, however, requiring a password change at intervals doesn't change the mean time it takes to break an account; it merely means that success is guaranteed, rather than probable, after twice the mean time (since that the mean time to break in is after exactly half the passwords have been tried.)
You want a backpack with jets?
Who do you think you are, Boba the Fett?
Do you bounty hunt
for Jabba the Hut
to finance your 'Vette?
Say, not bad, but your scansion kinda falls apart on that last line. Maybe, "to get money to finance your 'Vette"?
Also, I'm not sure about rhyming "hunt" with "Hutt".
Not some software thing!
Is there a legitimate reason this is here, or is this just a slashvertisement?
I'm rather curious about that, too.
Actually, I liked the review, thought it was interesting, liked the fact that it wasn't merely an advertisement... but I'm not sure why this particular book was reviewed on Slashdot, and not two or three dozen other SF books that are, frankly, more noteworthy.
That's not the same as having six dimensions.
Wouldn't it be better just to take the page down and worry about hurt feelings later? I would think that even if there was the possibility that a page was not right, that either someone could comment on it or it just be taken down.
Because if it were their policy to just remove pages and worry about hurt feelings later (or not at all), and it became widely known that this was their policy, they would get about a hundred thousand demands for pages to be removed every day.
Even if only one tenth of one percent of internet readers are jerks who would abuse the system by spamming out phony requests to delete pages from people they don't like, there are a lot of jerks out there who take offense to pages that they disagree with.
This is called the "first amendment."
http://photography.about.com/od/copyrightinformation/ss/PhotoRights.htm
I'm a little unclear on the requirements of the train, it says it needs 110 megawatts but not for how long, how many trains, etc. At its most conservative, I'll specify that the trains will each require 110 megawatts per run, and 11 runs are made per day. (Because that means I get to work with the magic 1.21 gigawatts number, which is just funny.) Ok, so, we need 1.21 GWH/day.
You just switched from power units (MW) to energy units (MW-hours) and then back to different power units (MW-hours per day).
If one train requires 110 MW, it requires 110 MW regardless of how many times that train runs per day.
And MW hours per day is simply equal to power in MW times hours of operation per day.
Given ALL the problems we see with corporations that carry debt, why on earth Microsoft would want to piss away a giant cash reserve AND borrow money...
Because debt is really cheap right now.
The name is bonds... Microsoft Bonds.