What most people forget, however, is that while the visible straight-line rays of color are blocked by the moon, most of the diffracting patterns of raycasting shadows and harmful radiation, such as UV [suv.com], infrared [usbirda.com] and gamma [pcpros.net], are not blocked by a line-of-sight blockade by the moon. This is why you often see cancerous lumps on the exposed skin of viewers of eclipses mere days after the event has passed.
<g> (Moderators, in case your physics isn't too fresh, this is "funny", not "informative".)
Didn't you forget all those dangerous, sneaky neutrinos?
Don't those crazy foreigners know that it's almost WINTER?
Well, during the eclipse, the corona will be visible. As it is much hotter than the surface of the Sun itself (millions of K vs. 6000K), it should keep you warm.
Not on the surface of Venus, 50 km up in the atmosphere, where the temperature is not too extreme. Their being lifeforms is inferred from the presence of gases that should recombine over time (like oxygen on Earth, which wouldn't stay in the air if life wasn't there to produce it).
NASA spends $1,000,000 plus to built a space-pen, the Russians use a pencil.
Oh, that urban legend again? Pencils are hazardous in weightlessness; both NASA and the Soviets used them at first, then both switched to the SpacePen when it became available.
The "slingshot effect" is only useful for trajectory changes. It allows one to save fuel when changing directions. Due to conservation of energy, when you approach a planet and slingshot away from it, you end up with the same velocity on the way out as the way in. You will accelerate as you approach a planet, but you will decelerate the same amount on the way out.
All true, but you missed two points:
in a slingshot maneuver you cannot, indeed, gain velocity relative the planet you approach; you can (and space probes do) gain velocity relative to the Sun, since said planet is moving with respect to the latter;
the original poster, I think, did not have a gravitational slingshot in mind, but the effect you would get if the top of the elevator were above GEO, you could launch objects that way.
what about deep space? if we accelerate the payload up the space elevator wont we also get the slingshot effect of the earth's rotation adding to the energy we are putting into the payload to get it flung toward the outer planets at a much higher starting velocity and while using less fuel?
Yes, if the top of the cable is higher than geostationary orbit (which will probably be the case, since the thing's center of mass has to be in GEO itself...)
People learn by doing, as you pointed out. The open source community is a great example of this. There are thousands of self trained people who learned by reading material online, talking to the more skillful through email or through IRC, and just experimenting on their own.
... and not knowing the difference between a hash table and a binary tree, and thinking that self-modifying code is cool. I've been there myself.
I indeed pointed out that people learned by doing, but I didn't mean that it was sufficient, merely necessary. You also have to work out the basics, both are critical if you are to master a subject.
Which is not to say that you can't have both outside of the classroom; if you know you can pull an A at the exam without attending, then by all means do so (I've been there too...)
What is the difference if someone learns something by reading online documents or by going to hear some windbag talk about it for 50 minutes? There isn't.
Well, as a teacher myself (lecturer or assistant professor depending on your equivalences, on optical telecommunications), I see a few issues with this:
You can't really ask questions, especially on adjacent topics: it is not the same to send an email to someone you don't know, as to walk up to the teacher at the end of a lecture.
In the maze of information a Google search yields, it is difficult to get the fundamentals as well as to separate the wheat from the chaff; in fact, you have to already know enough about the topic to get to and understand relevant information. Or ask further references to someone who knows.
When learning on-line, do you really do the exercises? Yet often you don't really understand what is going on until you practice, programming being a prime example of this. More generally, it is easy to think you understand something - see all the self-taught webmasters who think HTML tag soup is a text formatting tool and is correct as long as IE interprets it...
Funny, BTW, we had a small debate a few months ago on whether to put our course material on-line. The consensus seemed to be that we should, except for some marketing types who wanted to make people pay for the service or something like that, and those who wanted a control process for letting out only the good. The comments above were pointed out in the process - some by the students themselves IIRC.
Actually you can define your content-type and encoding via META tags. In fact, that's exactly what the w3 recommends you do!
You are refering to the XHTML standard, appendix C. "This appendix is informative", which means that a contradiction with other standards should be resolved in favor of said standards.
The META tags are (supposed to be) read by the HTTP server so as to send the right encoding in HTTP headers; and my point was that, contrarily to what the XHTML standard implies, they cannot replace the ?xml declaration if the actual encoding is not UTF-8/UTF-16.
Therefore, if one is to stick with XHTML and try not to break older browsers, the document must be UTF-8 or UTF-16 (or ASCII, of course, since it is a subset of UTF-8). This is not my encoding of choice, so I call it bugware.
Furthermore, some of the links posted elsewhere in the thread (e.g. "Sending XHTML as text/html Considered Harmful") are quite interesting in that they point out that valid XHTML sent as text/html will be parsed as tag soup (since it is not HTML), negating any advantage such as using an XML parser. But backwards compatibility imposes that the content-type be text/html. HTML4, at least, doesn't have this problem.
Your analysis of the XML standard doesn't seem to contradict the XHTML standard. Both of them say pretty much the same things:
1. If the encoding is not specified, then for the document to be valid it must be UTF-8. Therefore, no ?xml tag is necessary, because both standards say that it's optional when the encoding is UTF-8.
Yes, this isn't the contradiction I wanted to point out; the XHTML standard says that the declaration can be omitted for a document in any encoding if said encoding is specified through external means, such as HTTP headers.
The XML standard seems to concur in one place, but closes that door at the paragraph I quoted.
Therefore, if you need to omit the XML declaration, then use UTF-8 or UTF-16 encoding.
Which isn't the most convenient encoding to me, even though the point of being able to choose an encoding is mostly a matter of convenience. Unless I convert the files to Unicode after editing them, but that's - among others - what I call bugware...
I want to do a nice little page, and do it in XHTML because it's The Way Of The Future (or I want to display a little math, which only XHTML+MathML allows without resorting to ugly inline images). The tag soup itself isn't a problem, I just close all my tags and make sure the doctype declaration says XHTML instead of HTML, as prescribed by the standard.
However, is this enough? The document is now XML, and therefore should have a <?xml declaration, if only to specify its encoding. Except that said XHTML standard says it is optional if the encoding is UTF-8 or UTF-16, or has been otherwise determined (think HTTP headers), which contradicts the XML standard, sec. 4.3.3, the last two paragraphs, one which says that no declaration and no other information means mandatory UTF-8, and the next one "It is also a fatal error if an XML entity contains no encoding declaration and its content is not legal UTF-8 or UTF-16."
So I need a declaration no matter what. But according to this page about the different layout modes in current browsers, MSIE will react to an XML declaration by switching to "quirks" mode, which is precisely what I wants to avoid by sticking to the standards... And I wouldn't want to lock out 85% of WWW users, wouldn't I?
But wait, this is only if the page was served with a text/html content-type. The right answer would then be to use the standard content-type for XML/XHTML... which should beapplication/xhtml+xml! Yes, "application"! Now if I use that content-type, all browsers I have at my disposal except Mozilla (MSIE5, Konqueror, Links, Lynx...) either consider the page an application and offer to save it to disk, or display it as-is! Same with the second-best, text/xml.
Okay, am I the only one experiencing this? Any point in not using good-ol' HTML4 and avoid doing (yet another kind of) horrible bugware?
According to/usr/share/doc/msttcorefonts/READ_ME!.gz on Debian Woody machines:
1. GRANT OF LICENSE. This EULA grants you the following rights: Installation and Use. You may install and use an unlimited number of copies of the SOFTWARE PRODUCT. Reproduction and Distribution. You may reproduce and distribute an unlimited number of copies of the SOFTWARE PRODUCT; provided that each copy shall be a true and complete copy, including all copyright and trademark notices, and shall be accompanied by a copy of this EULA. Copies of the SOFTWARE PRODUCT may not be distributed for profit either on a standalone basis or included as part of your own product. 2. DESCRIPTION OF OTHER RIGHTS AND LIMITATIONS. [...] Software Transfer. You may permanently transfer all of your rights under this EULA, provided the recipient agrees to the terms of this EULA.
Can't this package be redistributed verbatim for free?
Re:Even worse - we live in town-centralized world
on
Man Conquers Space
·
· Score: 2
Re-read Asimov's "The Caves of Steel" to get the
answer why space exploration stopped.
I wasn't aware that Spacers were already hampering us... <g>
What we (I mean the world economy) need from
space technologies - GPS, InMarSat, Satellite TV.
It is almost all. For town-centric civilisation
it is cheaper to build cellular phone base-station
in every town and connect every TVset with broadcast-station via cable, than launch projects
like Iridium, which uses satellite technology.
Sure, if you look at current markets, we don't need space. But if you look back a few years, we didn't need cell phones or the Internet either.
The point is, if costs drop enough, new markets will appear, be it on Earth (joyrides? New materials?) or directly in space (mining asteroids for materials doesn't make much sense - unless, that is, there are space stations and lunar colonies ready to buy them...)
And the point in my previous message is that dropping costs is possible now, without fancy new tech. The latter can and will be useful, but there is no need to wait for it to be finalized, instead of developing a market where it will develop all the faster.
Re:We live in a money-centered world...
on
Man Conquers Space
·
· Score: 3, Interesting
...and unfortunantely we will not be venturing into space until it is commercially viable to do so.
It could be, right now. Some people are already paying millions of dollars for a seat in the ISS, more would shell out a few tens of thousands for a suborbital parabolic flight, which a few companies are working towards.
"Real" access to space is currently viewed as "way too expensive" because it's the way NASA does it, and people use it as a reference. It's not the technology, see Rand Simberg's recent column, We Don't Need No Stinkin' Technology.
As for why NASA (and some other government agencies) does it that way, beyond the near-mythical "why have one when you can have one for the price of two", the previous one, Pork Versus Vision, could be interesting. Or Stephen Baxter's "Voyage", which describes an alternate reality in which the US go all the way up to Mars as early as 1986, but (as opposed to this documentary) with a realistic view about politics. (You want Mars? OK, scrap this Space Shuttle thing, Apollo 15-20, and you have just enough Saturn V rockets for a single mission; what more do you want? A space station? Get real, Vietnam is expensive, we need the money for serious things!)
It's about choice, people, every bit as much as the Open Source camp purports to be. Locking patented technologies out of open standards means that you cannot choose the best technology for a given task because of someone's arbitrary complant about the 'freeness' of a part of it.
You, as an individual, can always choose to use whatever product you want to, with a patented technology (provided you pay the royalties one way or another, of course). You can still interoperate with a free-software government since they use open standards. You can even try to convince your friends to use the same product as you.
But a non-free-software government, using patented technologies for data exchange, does force everybody to use non-free software, and pay for the "better" tech, locking out free software and therefore restricting choices for everybody. Unless they buy the rights and license them for free to the whole public (not just the taxpayers of a given country), which makes that technology free for all intents and purposes anyway.
A contrario, a free-software policy could send a message to companies: if you patent this, you can still sell it, but the government won't use it and nobody will have to. This would effectively block consumer-locking tactics. Of course it does not benefit the big companies...
In an ideal world, one could let the government use any patented technology for internal use, but not for data exchange with the public, unless they at least provide an alternate method of access for free products. Making the distinction would require IP lawyers in every public service, which had better not happen, I guess.
Research and science receive only a very small part of our national budget. Looking at our national (Dutch) budget and the EU one, I can easily point out loads of stupid and/or wasteful things we are spending tax Euro's on, Euro's that would be much better spent on scientific research.
I fully agree with this. The original poster (excluding a troll) may be mistaking this mission with the whole man-in-space mumbo-jumbo (I'm all for colonizing space, but not the ISS-billion-government-dollar way). However:
do what you are good at, and buy what others are better at. Rather than design their own rocket to get something into space (like the Ariadne), Europe could just use existing and superior Russian Proton rockets or even a Shuttle. The money saved can go towards research in areas that we excel in (don't ask me which those areas are).
We excel in rocket science. Serious. The Ariane 5 can launch 6 tons in GTO, and the next version due this fall can do 8.
Proton cannot do that AFAIK and using the horrendously exepnsive Shuttle to save money would be ludicrous at best. The next Atlas 5 and Delta 4 will match this kind of performance and are possibly easier to scale up, but are not there yet.
pdflatex doesn't always work - try it with prosper slides for instance - and the times package is obsolete.
Either use package txfonts or maybe pxfonts (uses only PostScript fonts), or mathptmx (keeps Computer Modern fonts for math, but this doesn't always work), or install the vectorial T1 version of the ECM fonts and make sure those are used instead of the bitmap ones.
I can't say I disagree with the fact that flying-wings or blended-wings are a Better Way, but I still remember a popularscience-like magazine dating back from late 1980s telling that now that we had the technology, conventional fuselages would soon disappear to the benefit of those better concepts, including the one we are discussing (even the pictures are the same). So...
modern composites permit a pancaked pressure vessel that will tolerate the load at an acceptable weight.
Remember Lockheed's X-33 fiasco? Part of it was that they just couldn't build reliable composite non-cylindrical fuel tanks of reasonable size. You are talking about a whole cabin? In a couple of decades maybe, but not now IMHO...
For those of you who believe computer controlled and stabilized aircraft are not feasible for service in commercial applications due to safety considerations, look no further than the Airbus A-320 & A-319. Both of these aircraft use full authority fly-by-wire.
Indeed (and you can add 321, 330, 340, they more or less share the same flight controls).
Well, my uncle is a retired AirFrance flight engineer; he was on 747s but he has a few stories about the A320, including one when he flew—as a passenger—in the cockpit.
He says it took one pilot (half the flying crew) the full Paris-Geneva flight to repeatedly tell the computer that the left-wing fuel tank couldn't possibly be at freezing temperature while the right one was still at +15C, and no, they weren't going to unbalance the aircraft and feed both engines off the latter.
All right, it was ten years ago, maybe they sorted the bugs out (and maybe Boeing did a better job with the 777), and after all I never had a problem with flying on A32x...
We haven't seen them before because they weren't feasible before, but now that they are, let's hope Boeing pulls up their socks and builds one
Yeah. How's their SonicCruiser project going, after all their hesitations on whether big or fast would make more economic sense?
The theoretical maximum (for silica) I've heard quoted is 40Tbit/s, but I'm sure you could squeeze a bit more out.
Yes and no. Depending on the transmission window you take, you get a (spectral) bandwidth of a few tens ofTHz. However:
If you take Shannon's law, maximum bit rate depends on the bandwidth but also of signal to noise ratio:
C=W*log2(SNR+1). If you keep the SNR high, you can have an efficiency higher than 1bps per Hertz.
To keep the SNR high, you need good amplifiers, and that's where it gets tough: although you can find amplifiers over the whole band, no single amplifier will cover it all; your system gets complicated, with demultiplexers and separate amplifiers every 100km.
Anyway, with current technology, we can't make good use of the window as a whole. Efficiencies are maybe 0.1bps/Hz, over windows a few tens of nm wide (i.e. a few THz).
Semiconductor Optical Amplifiers (think of them as diode lasers, without the mirrors) could have a wider spectrum than the optical fibre!
Not really. You can cover the whole window with them but only 20 or 30nm at a time.
Actually, the article said they used raman amplification, not Erbium Doped Fiber Amplifiers.
I'd be surprised if they didn't use both. Raman is nice for distributed amplification and keeping the noise factor low (as you said, signal-to-noise ratio never goes too low), but you need Erbium and derivatives to get a good boost once in a while.
Actually, I think Raman can be used at any point in the spectrum, but don't quote me on that because I am not a physicist!
Well, I am, and a telecommunications engineer as well as Ph.D. student, and you're right; as long as you have a good laser with a wavelength about 100nm lower than that of your signal and the medium responds, you can amplify. This is good for the whole fiber window (1200-1700nm or so).
I don't know much about SOAs, but I've heard they are not good for multichannel systems. Something about the fact that they are noisy?
They're nonlinear, so your signal not only gets distorted, but you get four-wave mixing: two signals at different wavelengths beat together and create harmonics at the same wavelength difference. (Optical frequency actually, but for practical purposes wavelength works too.)
So, with SOAs, there is a lot of crosstalk between different wavelength. Add to this that their output power isn't very high, and you see that they aren't good amplifiers for the moment.
Which is not to say that they don't have other uses, such as signal processing, wavelength conversion, etc. And they are easier to integrate into components.
Slashdot Mirror
<g> (Moderators, in case your physics isn't too fresh, this is "funny", not "informative".)
Didn't you forget all those dangerous, sneaky neutrinos?
Well, during the eclipse, the corona will be visible. As it is much hotter than the surface of the Sun itself (millions of K vs. 6000K), it should keep you warm.
Especially as a solar eclipse must happen during the day...
Not on the surface of Venus, 50 km up in the atmosphere, where the temperature is not too extreme. Their being lifeforms is inferred from the presence of gases that should recombine over time (like oxygen on Earth, which wouldn't stay in the air if life wasn't there to produce it).
Oh, that urban legend again? Pencils are hazardous in weightlessness; both NASA and the Soviets used them at first, then both switched to the SpacePen when it became available.
All true, but you missed two points:
Yes, if the top of the cable is higher than geostationary orbit (which will probably be the case, since the thing's center of mass has to be in GEO itself...)
I indeed pointed out that people learned by doing, but I didn't mean that it was sufficient, merely necessary. You also have to work out the basics, both are critical if you are to master a subject.
Which is not to say that you can't have both outside of the classroom; if you know you can pull an A at the exam without attending, then by all means do so (I've been there too...)
Well, as a teacher myself (lecturer or assistant professor depending on your equivalences, on optical telecommunications), I see a few issues with this:
- You can't really ask questions, especially on adjacent topics: it is not the same to send an email to someone you don't know, as to walk up to the teacher at the end of a lecture.
- In the maze of information a Google search yields, it is difficult to get the fundamentals as well as to separate the wheat from the chaff; in fact, you have to already know enough about the topic to get to and understand relevant information. Or ask further references to someone who knows.
- When learning on-line, do you really do the exercises? Yet often you don't really understand what is going on until you practice, programming being a prime example of this. More generally, it is easy to think you understand something - see all the self-taught webmasters who think HTML tag soup is a text formatting tool and is correct as long as IE interprets it...
Funny, BTW, we had a small debate a few months ago on whether to put our course material on-line. The consensus seemed to be that we should, except for some marketing types who wanted to make people pay for the service or something like that, and those who wanted a control process for letting out only the good. The comments above were pointed out in the process - some by the students themselves IIRC.You are refering to the XHTML standard, appendix C. "This appendix is informative", which means that a contradiction with other standards should be resolved in favor of said standards.
The META tags are (supposed to be) read by the HTTP server so as to send the right encoding in HTTP headers; and my point was that, contrarily to what the XHTML standard implies, they cannot replace the ?xml declaration if the actual encoding is not UTF-8/UTF-16.
Therefore, if one is to stick with XHTML and try not to break older browsers, the document must be UTF-8 or UTF-16 (or ASCII, of course, since it is a subset of UTF-8). This is not my encoding of choice, so I call it bugware.
Furthermore, some of the links posted elsewhere in the thread (e.g. "Sending XHTML as text/html Considered Harmful") are quite interesting in that they point out that valid XHTML sent as text/html will be parsed as tag soup (since it is not HTML), negating any advantage such as using an XML parser. But backwards compatibility imposes that the content-type be text/html. HTML4, at least, doesn't have this problem.
Yes, this isn't the contradiction I wanted to point out; the XHTML standard says that the declaration can be omitted for a document in any encoding if said encoding is specified through external means, such as HTTP headers. The XML standard seems to concur in one place, but closes that door at the paragraph I quoted.
Which isn't the most convenient encoding to me, even though the point of being able to choose an encoding is mostly a matter of convenience. Unless I convert the files to Unicode after editing them, but that's - among others - what I call bugware...
I want to do a nice little page, and do it in XHTML because it's The Way Of The Future (or I want to display a little math, which only XHTML+MathML allows without resorting to ugly inline images). The tag soup itself isn't a problem, I just close all my tags and make sure the doctype declaration says XHTML instead of HTML, as prescribed by the standard.
However, is this enough? The document is now XML, and therefore should have a <?xml declaration, if only to specify its encoding. Except that said XHTML standard says it is optional if the encoding is UTF-8 or UTF-16, or has been otherwise determined (think HTTP headers), which contradicts the XML standard, sec. 4.3.3, the last two paragraphs, one which says that no declaration and no other information means mandatory UTF-8, and the next one "It is also a fatal error if an XML entity contains no encoding declaration and its content is not legal UTF-8 or UTF-16."
So I need a declaration no matter what. But according to this page about the different layout modes in current browsers, MSIE will react to an XML declaration by switching to "quirks" mode, which is precisely what I wants to avoid by sticking to the standards... And I wouldn't want to lock out 85% of WWW users, wouldn't I?
But wait, this is only if the page was served with a text/html content-type. The right answer would then be to use the standard content-type for XML/XHTML... which should be application/xhtml+xml! Yes, "application"! Now if I use that content-type, all browsers I have at my disposal except Mozilla (MSIE5, Konqueror, Links, Lynx...) either consider the page an application and offer to save it to disk, or display it as-is! Same with the second-best, text/xml.
Okay, am I the only one experiencing this? Any point in not using good-ol' HTML4 and avoid doing (yet another kind of) horrible bugware?
According to this debian-devel message, you may not place the files into a tarball. They must be the original .exe's, with the same file names.
But another poster replied to you to point to SourceForge.
I wasn't aware that Spacers were already hampering us... <g>
Sure, if you look at current markets, we don't need space. But if you look back a few years, we didn't need cell phones or the Internet either.
The point is, if costs drop enough, new markets will appear, be it on Earth (joyrides? New materials?) or directly in space (mining asteroids for materials doesn't make much sense - unless, that is, there are space stations and lunar colonies ready to buy them...)
And the point in my previous message is that dropping costs is possible now, without fancy new tech. The latter can and will be useful, but there is no need to wait for it to be finalized, instead of developing a market where it will develop all the faster.
It could be, right now. Some people are already paying millions of dollars for a seat in the ISS, more would shell out a few tens of thousands for a suborbital parabolic flight, which a few companies are working towards. "Real" access to space is currently viewed as "way too expensive" because it's the way NASA does it, and people use it as a reference. It's not the technology, see Rand Simberg's recent column, We Don't Need No Stinkin' Technology.
As for why NASA (and some other government agencies) does it that way, beyond the near-mythical "why have one when you can have one for the price of two", the previous one, Pork Versus Vision, could be interesting. Or Stephen Baxter's "Voyage", which describes an alternate reality in which the US go all the way up to Mars as early as 1986, but (as opposed to this documentary) with a realistic view about politics. (You want Mars? OK, scrap this Space Shuttle thing, Apollo 15-20, and you have just enough Saturn V rockets for a single mission; what more do you want? A space station? Get real, Vietnam is expensive, we need the money for serious things!)
... they're still doing those encryption-breaking projects!
You, as an individual, can always choose to use whatever product you want to, with a patented technology (provided you pay the royalties one way or another, of course). You can still interoperate with a free-software government since they use open standards. You can even try to convince your friends to use the same product as you.
But a non-free-software government, using patented technologies for data exchange, does force everybody to use non-free software, and pay for the "better" tech, locking out free software and therefore restricting choices for everybody. Unless they buy the rights and license them for free to the whole public (not just the taxpayers of a given country), which makes that technology free for all intents and purposes anyway.
A contrario, a free-software policy could send a message to companies: if you patent this, you can still sell it, but the government won't use it and nobody will have to. This would effectively block consumer-locking tactics. Of course it does not benefit the big companies...
In an ideal world, one could let the government use any patented technology for internal use, but not for data exchange with the public, unless they at least provide an alternate method of access for free products. Making the distinction would require IP lawyers in every public service, which had better not happen, I guess.
I fully agree with this. The original poster (excluding a troll) may be mistaking this mission with the whole man-in-space mumbo-jumbo (I'm all for colonizing space, but not the ISS-billion-government-dollar way). However:
We excel in rocket science. Serious. The Ariane 5 can launch 6 tons in GTO, and the next version due this fall can do 8. Proton cannot do that AFAIK and using the horrendously exepnsive Shuttle to save money would be ludicrous at best. The next Atlas 5 and Delta 4 will match this kind of performance and are possibly easier to scale up, but are not there yet.
Either use package txfonts or maybe pxfonts (uses only PostScript fonts), or mathptmx (keeps Computer Modern fonts for math, but this doesn't always work), or install the vectorial T1 version of the ECM fonts and make sure those are used instead of the bitmap ones.
Remember Lockheed's X-33 fiasco? Part of it was that they just couldn't build reliable composite non-cylindrical fuel tanks of reasonable size. You are talking about a whole cabin? In a couple of decades maybe, but not now IMHO...
Indeed (and you can add 321, 330, 340, they more or less share the same flight controls).
Well, my uncle is a retired AirFrance flight engineer; he was on 747s but he has a few stories about the A320, including one when he flew—as a passenger—in the cockpit. He says it took one pilot (half the flying crew) the full Paris-Geneva flight to repeatedly tell the computer that the left-wing fuel tank couldn't possibly be at freezing temperature while the right one was still at +15C, and no, they weren't going to unbalance the aircraft and feed both engines off the latter.
All right, it was ten years ago, maybe they sorted the bugs out (and maybe Boeing did a better job with the 777), and after all I never had a problem with flying on A32x...
Yeah. How's their SonicCruiser project going, after all their hesitations on whether big or fast would make more economic sense?
The RC5-64 challenge is currently at 73%, moving fast. Can you imagine the project shutting down just now?
Interesting, thanks for the information. Do you get enough gain out of quantum dots? What about nonlinearities?
Yes and no. Depending on the transmission window you take, you get a (spectral) bandwidth of a few tens ofTHz. However:
Not really. You can cover the whole window with them but only 20 or 30nm at a time.
I'd be surprised if they didn't use both. Raman is nice for distributed amplification and keeping the noise factor low (as you said, signal-to-noise ratio never goes too low), but you need Erbium and derivatives to get a good boost once in a while.
Well, I am, and a telecommunications engineer as well as Ph.D. student, and you're right; as long as you have a good laser with a wavelength about 100nm lower than that of your signal and the medium responds, you can amplify. This is good for the whole fiber window (1200-1700nm or so).
They're nonlinear, so your signal not only gets distorted, but you get four-wave mixing: two signals at different wavelengths beat together and create harmonics at the same wavelength difference. (Optical frequency actually, but for practical purposes wavelength works too.)
So, with SOAs, there is a lot of crosstalk between different wavelength. Add to this that their output power isn't very high, and you see that they aren't good amplifiers for the moment.
Which is not to say that they don't have other uses, such as signal processing, wavelength conversion, etc. And they are easier to integrate into components.