Given any stream of random data, one can easily find a stream that, when XORed with the random data, gives whatever message you want. We all know that claiming that this message is a hidden message in the 'random' stream is absurd, but consider who we're talking about here. Now I don't really know, but it seems plausible to me that the same thing could be done, perhaps to a lesser extent, with other encryption schemes. Anyone know anything more on this topic?
Re:Encryption ain't it all tapped out to be...
on
Feds Want to Tap VoIP
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· Score: 1
At least in that case they need (for now) a warrant, and need to actually send people physically. It's not as convenient for them as being able to tap a conversation without ever leaving the office.
Perhaps it's ok if they physically break in to install monitoring devices and such. There are valid reasons for law enforcement to perform survalence. The problem is that it is too easy for them to monitor whoever they want whenever they want, and so they do it without even thinking about whether or not they have any reason to do so. Gaining physical access and installing monitoring devices, while it entirely circumvents any sort of crypto, is more costly than pulling data off the wires, and thus less likely to happen without a good reason. It will still happen without a good reason sometimes, but this will occur less frequently if the costs are greater.
Yes, some theorems can be proved by exhaustion with the help of a computer, but they are something of an exception, and such proofs are not considered terribly satisfactory, as the MathWorld article you refered to points out with regard to Hales' proof of Kepler's Conjecture. It's like 'proving' that 7*6=42 by having a computer compute 7*6 (admittedly I'm exagerating here, but it shows my point). Also, I would consider the code for the program he ran to be the real proof, and that was produced by a person, not a computer. Of course, strong AI would make all this a moot point.
Ok, I know I'm asking for an Offtopic or Redundant here but as a pure math major I have to reply to this:)
Diffeq is not pure math. At least, not the way it is usually presented (there are some more 'pure' aspects to it, but usually the focus is on applications). If you want pure math, try taking an abstract algebra course, or some upper division analysis or geometry.
The question of what 'pure math' means can be rather controversial, and there are those who insist that there is no such thing as pure math, that all mathematics has practical applications as its ultimate goal (I dissagree with this). If you are interested in what pure math is, you might take a look at What Is Pure Mathematics or A Gentle Introduction to the Mathematics Subject Classification Scheme. I'm sure there are many more pages discussing this topic, but I don't recall where they are off the top of my head.
As for calculators, in pure mathematics a calculator generally won't do you much good. Pure mathematics is usually more concerned with proving theorems than with performing computations. Calculators are great at performing computations, but they can't prove theorems for you. That said, a calculator can be a useful tool, and which calculator is best to use depends on personal preference and on the application. Personally I prefer HP over TI (it's a shame HP isn't making calculators anymore), but I understand that TIs can be easier to learn to use. However, it should be noted that HPs can do symbolic manipulations, matrix algebra, regressions and such, and yes, the HP can evaluate expressions in the traditional 'algebraic' format, and you can revise them, etc.
Do we really want to encourage this sort of behavior? It may be cool and pretty, but not cool and pretty enough for the resources it consumes (both in electricity and also manufacturing, etc). Not to mention less explicit costs like the impact on traffic, wildlife, neighbors, and stargazers.
Here are a few links supporting the idea that usable DNA evidence can be obtained from hair: http://biology.usgs.gov/pr/newsrelease/2000 /3-16.h tml http://www.nctimes.net/news/2002/20020627/111 11.ht ml http://expertpages.com/news/dna2.htm http://w ww.forensic.gov.uk/forensic/conference/pap ers/hair_samples.pdf
Oh yes and here's a rather amusing one;) http://www.rense.com/general9/ydna.htm
Anyway, I'm sure you get the idea. It appears that DNA (well, mtDNA actually) from human hairs is difficult to use for conclusive identification, but it can still be useful. IANAL, but it seems to me that it should be possible to use such evidence in support of other evidence or to get a warrant to gather more reliable DNA samples. The same should apply to DNA gathered from fingerprints, which I would expect to be similarly decayed.
That site is for a play by email RPG and describes the modified Start Trek universe used in that RPG. It is based on Star Trek but is by no means an authoritative source on Star Trek technology. Note, I'm not saying you're wrong, just that the link you provided does not answer the question "How do impulse engines in Star Trek work?"
For those who don't want to read the article, the fresh water production is sort of a side effect of the process used to extract energy from the ocean's thermal gradient.
Actually, there have been OTECs arround a little longer than that, but I believe (I'm not sure about this) that the Hawaii one is the first to produce more energy than it consumes. It uses about half the energy but the general consensus seems to be that an OTEC only needs about 30% of the energy produced (although there is a tradeoff between efficiency and fresh water production). OTECs do not neccesarily only work for steep ocean wall dropoffs, but these are ideal places for them. They can also be operated from ships, but this requires a more sophisticated setup and various other disadvantages. None of these disadvantages, however, are by any means insurmountable. The biggest problem facing OTEC is the lack of investment into the development of more efficient and cost effective systems due to the relatively low price of fossil fuels. There are no substantial technical obstacles to the use of OTEC.
Orthogonal is a technical term in mathematics and is used to describe two elements, the inner product of which is zero. (The dot product is an example of an inner product.) I doubt you'll hear business and marketing people use it in quite that sense;)
Being a technical term in mathematics, it is entirely appropriate in a technical paper on mathematics, and thus in discussion of that paper.
You say that in jest, but it's partially true, and not because of some silly misinterpretation of the way numbers are represented. One structure of interest to mathematicians (algebraists and number theorests in particular) is the cyclic groups of integers under modulo addition. In one of these groups, (Z_3, +), two plus two equals one. For more details see MathWorld's article on the subject.
(Note: I use the underscore to denote subscripts when the subscript tag is unavailable as it is on/., so Z_3 is Z with a subscripted 3)
First of all, the cost of producing a product doesn't have anywhere near the effect on market price that most people think it does. Market price is determined by the intersection of the supply and demand curves: at price x consumers are willing to buy y units and producers are willing to sell z units; the market price is the x such that y == z. Some people, however, would only be willing to buy at a lower price, but would be willing to settle for a lower end product at that lower price. The producers would be willing to sell the product at that lower price, but they also want to sell it at the higher price to the people who would be willing to pay more. So they sell the same product at different prices, and disable a few features on the units sold at the lower price so that they don't simply have everyone buying at that lower price. It's just one way of charging more to the people who are willing to pay more. Really, when a theater sells matinee (sp?) showings of a film, they're doing the exact same thing from an economic point of view.
So far I havn't seen anyone complaining about this. Even though they are not doing a terribly good job of it, it is a semi-clever way of combatting filesharing, AND it only targets filesharing of specific titles, rather than attempting to take out the whole network. I, at least, have a lot more respect for them when they use tactics like this than when they try to simply get filesharing outlawed. At least this way they give us an interesting technical challenge to play with.:)
If the product is equivalent to products produced by conventional means then they can't charge more and expect people to buy. Perhaps it won't be sold for any less than products produced conventionally but it won't be sold for any more either.
As far as I know, it is difficult if not impossible for foreigners to pass security checks. The research I've done on this isn't terribly clear but it does look to me like it's more difficult for foreigners to pass. I'm not sure this in itself is neccesarily wrong, but if a large portion of MIT's research projects require security checks then this would indirectly discriminate against foreign students.
Furthermore, there is the question of whether or not the particular projects in question are actually sensitive enough to warrant security checks. Remember that agencies like the NSA, DOD, etc are notorious for just assuming everything should be kept secret and require clearance.
I used to feel the same way about those "dumb little educational [games]" but I now work at an elementary school and in light of my observations of kids playing these games I have revised my opinion of them. Yes, usually they are a little below the level of what's being taught but they provide an effective and fun way for kids to get practice and review, both of which are crucial to the learning process.
Oh, and how is sleeping in class any better than doing something on a computer that has the potential to be intellectually stimulating?
The use of "toys" in class is the effect, while distraction is the cause. Professors can remove the toys but not the distraction. Note that here I'm using the term distraction in the sense of the state of being distracted, not an item that distracts. This is probably not exactly the sense you had in mind but I think my point is still valid: If a student is distracted, this is a state of mind, not the act of playing with some gadget. If you take away the gadget they'll look like they're paying attention and taking notes but they'll actually be doodling or doing homework from another class.
This also addresses your first point, reguarding "these days." It seems to me that it's not a sign of the times, it's a time of the signs. The ways students reacted to distraction in the past weren't as obvious (doodling rather than taking notes, etc) as they are now. Perhaps this makes distraction more contagious but it also provides the professor with valuable feedback. I'm also skeptical that it makes distraction very much more contagious. The more traditional ways of responding to distraction are quite visible to other students, just not the professor.
Sometimes research professors can be great. Just this past term I took a linguistics survey class from a prof who had spent a good part of his carreer developing an alternative theory of syntax. He taught his alternative theory and left it to the book and TA's to teach the traditional theory. He conveyed his own interest and excitement in syntax to me and many others in the class (although there were those who showed no real interest) and I'm now considerating getting a second major in linguistics.
Now there are research profs who seem to only teach because they have to and emit a sense of contempt and disinterest, but this also occurs frequently among profs who aren't doing research. In college the particular professor you take a class from is very important.
Also, some professors will be great for some students and horrible for others. This is especially true of research professors, who are likely to take alternative views, as opposed to the non-research profs who just teach from a book that contains only the well-established traditional views. My linguistics professor's theory of syntax was actually a nonabelian algebra, which I loved (I'm a math major). Other students, on the other hand, expressed alarm.
In general, it's a good idea to do a little research on a professor (especially research professors) before taking a class from him/her. Even if the professor is a good teacher, his or her teaching style or approach to the material may not be entirely compatible with your learning style or background. On the other hand, a particular professor may be an excelent match for a given student.
One way to get more out of a class is to find at least one concept that you can really take an interest in. Then study that concept in depth, ask the professor for more information. If the professor is doing research then go chat with the professor about it and, if you're lucky, how it applies to your field. You aren't likely to get that from a book or a video.
Re:undefined energy is sad?
on
E ~ mc^2
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· Score: 1
Actually it's kinda a fun thought: What if energy IS undefined in some circumstances?
Slashdot Mirror
Given any stream of random data, one can easily find a stream that, when XORed with the random data, gives whatever message you want. We all know that claiming that this message is a hidden message in the 'random' stream is absurd, but consider who we're talking about here. Now I don't really know, but it seems plausible to me that the same thing could be done, perhaps to a lesser extent, with other encryption schemes. Anyone know anything more on this topic?
At least in that case they need (for now) a warrant, and need to actually send people physically. It's not as convenient for them as being able to tap a conversation without ever leaving the office.
Recent events have made it clear that once they gain some ability with judicial oversight the oversight requirement will later be dropped.
Perhaps it's ok if they physically break in to install monitoring devices and such. There are valid reasons for law enforcement to perform survalence. The problem is that it is too easy for them to monitor whoever they want whenever they want, and so they do it without even thinking about whether or not they have any reason to do so. Gaining physical access and installing monitoring devices, while it entirely circumvents any sort of crypto, is more costly than pulling data off the wires, and thus less likely to happen without a good reason. It will still happen without a good reason sometimes, but this will occur less frequently if the costs are greater.
Yes, some theorems can be proved by exhaustion with the help of a computer, but they are something of an exception, and such proofs are not considered terribly satisfactory, as the MathWorld article you refered to points out with regard to Hales' proof of Kepler's Conjecture. It's like 'proving' that 7*6=42 by having a computer compute 7*6 (admittedly I'm exagerating here, but it shows my point). Also, I would consider the code for the program he ran to be the real proof, and that was produced by a person, not a computer. Of course, strong AI would make all this a moot point.
;)
BTW, kudos on the MathWorld reference
Ok, I know I'm asking for an Offtopic or Redundant here but as a pure math major I have to reply to this :)
Diffeq is not pure math. At least, not the way it is usually presented (there are some more 'pure' aspects to it, but usually the focus is on applications). If you want pure math, try taking an abstract algebra course, or some upper division analysis or geometry.
The question of what 'pure math' means can be rather controversial, and there are those who insist that there is no such thing as pure math, that all mathematics has practical applications as its ultimate goal (I dissagree with this). If you are interested in what pure math is, you might take a look at What Is Pure Mathematics or A Gentle Introduction to the Mathematics Subject Classification Scheme. I'm sure there are many more pages discussing this topic, but I don't recall where they are off the top of my head.
As for calculators, in pure mathematics a calculator generally won't do you much good. Pure mathematics is usually more concerned with proving theorems than with performing computations. Calculators are great at performing computations, but they can't prove theorems for you. That said, a calculator can be a useful tool, and which calculator is best to use depends on personal preference and on the application. Personally I prefer HP over TI (it's a shame HP isn't making calculators anymore), but I understand that TIs can be easier to learn to use. However, it should be noted that HPs can do symbolic manipulations, matrix algebra, regressions and such, and yes, the HP can evaluate expressions in the traditional 'algebraic' format, and you can revise them, etc.
I don't recall where I saw this, but:
"Invent an idiot-proof system and somebody will invent a better idiot."
Do we really want to encourage this sort of behavior? It may be cool and pretty, but not cool and pretty enough for the resources it consumes (both in electricity and also manufacturing, etc). Not to mention less explicit costs like the impact on traffic, wildlife, neighbors, and stargazers.
Here are a few links supporting the idea that usable DNA evidence can be obtained from hair:0 /3-16.h tml1 11.ht mlw ww.forensic.gov.uk/forensic/conference/pap ers/hair_samples.pdf
;)
http://biology.usgs.gov/pr/newsrelease/200
http://www.nctimes.net/news/2002/20020627/11
http://expertpages.com/news/dna2.htm
http://
Oh yes and here's a rather amusing one
http://www.rense.com/general9/ydna.htm
Anyway, I'm sure you get the idea. It appears that DNA (well, mtDNA actually) from human hairs is difficult to use for conclusive identification, but it can still be useful. IANAL, but it seems to me that it should be possible to use such evidence in support of other evidence or to get a warrant to gather more reliable DNA samples. The same should apply to DNA gathered from fingerprints, which I would expect to be similarly decayed.
That site is for a play by email RPG and describes the modified Start Trek universe used in that RPG. It is based on Star Trek but is by no means an authoritative source on Star Trek technology. Note, I'm not saying you're wrong, just that the link you provided does not answer the question "How do impulse engines in Star Trek work?"
For those who don't want to read the article, the fresh water production is sort of a side effect of the process used to extract energy from the ocean's thermal gradient.
Actually, there have been OTECs arround a little longer than that, but I believe (I'm not sure about this) that the Hawaii one is the first to produce more energy than it consumes. It uses about half the energy but the general consensus seems to be that an OTEC only needs about 30% of the energy produced (although there is a tradeoff between efficiency and fresh water production). OTECs do not neccesarily only work for steep ocean wall dropoffs, but these are ideal places for them. They can also be operated from ships, but this requires a more sophisticated setup and various other disadvantages. None of these disadvantages, however, are by any means insurmountable. The biggest problem facing OTEC is the lack of investment into the development of more efficient and cost effective systems due to the relatively low price of fossil fuels. There are no substantial technical obstacles to the use of OTEC.
Really?? I hadn't heard this. References would be greatly appreciated.
Orthogonal is a technical term in mathematics and is used to describe two elements, the inner product of which is zero. (The dot product is an example of an inner product.) I doubt you'll hear business and marketing people use it in quite that sense ;)
Being a technical term in mathematics, it is entirely appropriate in a technical paper on mathematics, and thus in discussion of that paper.
You say that in jest, but it's partially true, and not because of some silly misinterpretation of the way numbers are represented. One structure of interest to mathematicians (algebraists and number theorests in particular) is the cyclic groups of integers under modulo addition. In one of these groups, (Z_3, +), two plus two equals one. For more details see MathWorld's article on the subject. (Note: I use the underscore to denote subscripts when the subscript tag is unavailable as it is on /., so Z_3 is Z with a subscripted 3)
First of all, the cost of producing a product doesn't have anywhere near the effect on market price that most people think it does. Market price is determined by the intersection of the supply and demand curves: at price x consumers are willing to buy y units and producers are willing to sell z units; the market price is the x such that y == z. Some people, however, would only be willing to buy at a lower price, but would be willing to settle for a lower end product at that lower price. The producers would be willing to sell the product at that lower price, but they also want to sell it at the higher price to the people who would be willing to pay more. So they sell the same product at different prices, and disable a few features on the units sold at the lower price so that they don't simply have everyone buying at that lower price. It's just one way of charging more to the people who are willing to pay more. Really, when a theater sells matinee (sp?) showings of a film, they're doing the exact same thing from an economic point of view.
So far I havn't seen anyone complaining about this. Even though they are not doing a terribly good job of it, it is a semi-clever way of combatting filesharing, AND it only targets filesharing of specific titles, rather than attempting to take out the whole network. I, at least, have a lot more respect for them when they use tactics like this than when they try to simply get filesharing outlawed. At least this way they give us an interesting technical challenge to play with. :)
If the product is equivalent to products produced by conventional means then they can't charge more and expect people to buy. Perhaps it won't be sold for any less than products produced conventionally but it won't be sold for any more either.
Don't give them any ideas!
As far as I know, it is difficult if not impossible for foreigners to pass security checks. The research I've done on this isn't terribly clear but it does look to me like it's more difficult for foreigners to pass. I'm not sure this in itself is neccesarily wrong, but if a large portion of MIT's research projects require security checks then this would indirectly discriminate against foreign students.
Furthermore, there is the question of whether or not the particular projects in question are actually sensitive enough to warrant security checks. Remember that agencies like the NSA, DOD, etc are notorious for just assuming everything should be kept secret and require clearance.
I used to feel the same way about those "dumb little educational [games]" but I now work at an elementary school and in light of my observations of kids playing these games I have revised my opinion of them. Yes, usually they are a little below the level of what's being taught but they provide an effective and fun way for kids to get practice and review, both of which are crucial to the learning process.
Oh, and how is sleeping in class any better than doing something on a computer that has the potential to be intellectually stimulating?
The use of "toys" in class is the effect, while distraction is the cause. Professors can remove the toys but not the distraction. Note that here I'm using the term distraction in the sense of the state of being distracted, not an item that distracts. This is probably not exactly the sense you had in mind but I think my point is still valid: If a student is distracted, this is a state of mind, not the act of playing with some gadget. If you take away the gadget they'll look like they're paying attention and taking notes but they'll actually be doodling or doing homework from another class.
This also addresses your first point, reguarding "these days." It seems to me that it's not a sign of the times, it's a time of the signs. The ways students reacted to distraction in the past weren't as obvious (doodling rather than taking notes, etc) as they are now. Perhaps this makes distraction more contagious but it also provides the professor with valuable feedback. I'm also skeptical that it makes distraction very much more contagious. The more traditional ways of responding to distraction are quite visible to other students, just not the professor.
Sometimes research professors can be great. Just this past term I took a linguistics survey class from a prof who had spent a good part of his carreer developing an alternative theory of syntax. He taught his alternative theory and left it to the book and TA's to teach the traditional theory. He conveyed his own interest and excitement in syntax to me and many others in the class (although there were those who showed no real interest) and I'm now considerating getting a second major in linguistics.
Now there are research profs who seem to only teach because they have to and emit a sense of contempt and disinterest, but this also occurs frequently among profs who aren't doing research. In college the particular professor you take a class from is very important.
Also, some professors will be great for some students and horrible for others. This is especially true of research professors, who are likely to take alternative views, as opposed to the non-research profs who just teach from a book that contains only the well-established traditional views. My linguistics professor's theory of syntax was actually a nonabelian algebra, which I loved (I'm a math major). Other students, on the other hand, expressed alarm.
In general, it's a good idea to do a little research on a professor (especially research professors) before taking a class from him/her. Even if the professor is a good teacher, his or her teaching style or approach to the material may not be entirely compatible with your learning style or background. On the other hand, a particular professor may be an excelent match for a given student.
One way to get more out of a class is to find at least one concept that you can really take an interest in. Then study that concept in depth, ask the professor for more information. If the professor is doing research then go chat with the professor about it and, if you're lucky, how it applies to your field. You aren't likely to get that from a book or a video.
Actually it's kinda a fun thought: What if energy IS undefined in some circumstances?
umm.. You don't mean infinitesimal in the strictly mathematical sense, do you?