However, the speed of sound varies proportionally to the density of the medium,
in this case, air. So at higher temperatures, and higher altitudes, the speed of
sound increases.
Nope, you're wrong too. Speed of sound decreases with increasing altitude (less dense air).
http://www.grc.nasa.gov/WWW/K-12/airplane/sound. ht ml
for the basic information and a cool little demonstrator app. However, even at high altitude, the SOS doesn't change much (-14% is "not much" to me). Now, speed of sound through solid rock, THAT'S fast!
One source of confusion is that SOS is about 1100 feet per sec or about 750 miles per hour. People often get the numbers and units swapped.
- Chris
P.S. Wow, I actually used my Aerospace Engineering degree today!
P.P.S. SR-71 has gone to Mach 3 according to public knowledge, but it's widely expected that it went MUCH faster. Hell, most fighter jets can push Mach 2.0, and the SR-71's design point is Speed At All Costs.
I would have much rather had to wait a few months and had a product that worked nearly flawlessly, so that I could recommend it to my friends, rather than be forced to recommend a winCE powered, or palmOS powered device. It's really a shame that market pressure ruins so many good ideas.
<RANT>
Oh what a steaming pile of self-righteous crap!
I'm sorry to have to inform you that in the private sector these days, virtually everything is always shoved out the door before the engineers say it's done. The fact is we all love to perfect our creations, but time (or VC funding) waits for no man, and the suits do indeed have a job -- get the product out there and start pulling in revenue before all the cash is gone.
</RANT>
Take a look at Mozilla at any time over the past two years -- it always seems like they just need a couple more months and it'll be perfect. Netscape bit the bullet last fall and shoved NS6 out the door -- now it's four months later and Mozilla just issued a
new roadmap that delays '1.0' until Q3. Should Netscape have waited "a few months"?
Things get done in this world by people who design, execute, tweak it up a bit, shove it out the door, evaluate, re-prioritize and do it all again. "Works flawlessly"? Ha! Product design is asymptotic -- you'll get closer and closer, but you're never really THERE, and so someone has to stick their neck out and say "enough already". Companies run by engineers do NOT necessarily succeed -- you need a balance of technical and fiscal considerations in any decision.
Sounds like Agenda's got problems, but as has been stated elsewhere, it's too early to make a judgement on that.
Would one not expect a deluge of men screaming how they can be leet hackers too? Apparently
not. Now why do you think that is?
Perhaps it's because women have had the heel of man on their neck for 10,000 years of human culture and are a bit more sensitive to gender issues than men are. Not the other way around.
Perhaps we need a certifying organization like many other industries out there? Not Microsoft-certified, not
being called a Realtor (tm), and certainly nothing like TRUSTe, but maybe some kind of board that would
allow people to be certified members in good standing, and then based on complaints about them and
recommendations and positive comments made, they could keep or lose their membership
In other words, that certification should be handled by a group that is not beholden to a particular company's technologies or "vision".
Groups like the IEEE and NCEES have long had these professional standards and certifications in place for real engineers, but unfortunately most IT professional fall in a gray area between vo-tech and engineering. I'm not saying that IT jobs are "easier" or less intellectually demanding than jobs that required old-school degreed engineers -- rather, the extreme market forces of the last five years have force many, many smart people to bail out of their college degree track and go for the gold.
Because of that, these organizations are finding that lots of IT professionals are not being educated on the responsibilities of the technical professional, include in particular ethical responsibilities. A whole raft of talent is set adrift...
For a professional engineer, this topic is a no-brainer: as a consultant, you must act in the best interest of your paying customer.
We came up with two fundamental theories. The first was that the hot gasses from the plume had perforated the External Tank and ignited the LOX or Hydrogen. After looking at the tape several more times, there was a frame where the SRB looked a bit askew. This gave rise to the second theory -- that the lower SRB mount had burned through or broken and the SRB swiveled with the top of the SRB striking the top of the ET and causing the breakup. Damn that NASA video was good.
What irony that months later, the report showed that our second scenario was exactly correct. As just a bunch of low paid wanna-be techies sitting around looking at the event frame by frame, we had gotten the gist of what had happened within an hour after the explosion.
I understand your pride at rapidly determining "the cause" of the breakup, but really all you identified was the endgame sequence -- it's like witnessing a car crash and saying "the damage was caused by the two cars steering towards each other and colliding".
What took NASA months to determine was the root cause of the explosion. The cold weather that day was out of the specified operational range of the huge O-rings used to seal the gaps in the booster segments, and thus some gases were able to escape out through the gaps. Over time (say, 60 seconds) those gaps got burned out enough to allow visible flames to escape and trigger the endgame sequence you observed.
The cognizant Morton Thiokol engineer had protested the launch that day and had been overridden by management higher up. Everyone had "Go Fever" and safety was ignored.
Yes, the business has to pay a fee to start, but they also get charged postage on the items that actually get used. As to weight limits, a few minutes browsing gets you that info:
This is a pretty unique dish: assymetrical, side-mounted feed arm, movable surface panels...
It appears to me that Green Bank is just a standard offset feed design. This is the same design used in your dinky DBS TV dish and virtually every small satellite antenna in the world. That said, there certainly are other things that distinguish Green Bank, including the colossal size (and [oink] price) and the dynamically adjustable surface.
One of my work colleagues once provided me with the following explanation to help understand how these offsets works.
Visualize a standard "prime focus" antenna. This is the kind that has the struts from the edge of the big reflector to a point in the air above the exact center of the dish. Energy from space hits the metal reflector and is bounced towards the focus point, where the struts meet and your receivers are.
Here's a PDF of a prime focus antenna.
Now imagine that the antenna is pointed straight up, so it's like a bowl catching rain. If you sliced vertically through it, you'd see a perfect parabola, which would go further out and up if you extended the curves of the reflector. The receiver is sitting at the focus point of that parabola.
Imagine that perfect, mathematical parabola sitting there, with the sides extending out and up. The reflector just happen to be a metal realization of the very bottom of that parabola. We could make antennas where the reflector extends furhter up the sides of that mathematical parabola, but eventually it's just lots of expensive metal structure for not much gain (pun intended:)).
Here's the cool part: Now imagine that instead of the metal reflector occupying the bottom of the parabola, you slide the metal "skin" UP THE SIDE of the mathematical parabola that you're envisioning. The parabola doesn't move, and thus neither does the focus point. Just slide the metal "realization" of that paraboloid curve up one side.
The antenna is still "looking" straight up into space, but now the reflector is off to the side a bit. The reflector on your DBS dish is actually a mathematically very complex section of a 3D paraboloid surface. But it's usually hard to tell because the reflector is relatively flat, and thus it's hard ot detect the complex curves involved.
Here's a bunch of pictures of offset-feed dishes.
Green Bank has the feed overhead, unlike your DBS dish. It's still the same idea; they just spun the whole thing around on the line-of-sight axis.
What's the big advantage? As the article hinted, you don't have those struts in the way of the incoming energy, and thus the antenna is more efficient. Also, on a big system like GB, it's possible for them to lower the feed/receiver assembly closer to the ground where it's easier to service.
In my job, we usually have the antennas oriented like your DBS dish, with the feed close to the ground. But when you get to real high latitudes (like in Alaska or Siberia), the satellite you're trying to hit is real close to the horizon, and when we try to aim that low, the feed hits the ground. In those rare cases, we have to spin it around to put the feed high up in the air, like GB, only WAY smaller.
By the way, there's a kind of antenna (called a Cassegrain) that looks sort of like a prime focus, but has a second refector at the feed which bounces the energy back down to the receiver at the center of the main reflector.
Here's a PDF of a Cassegrain antenna.
Sharing workspaces is indeed useful if you are all working on exactly the same project/application/whatever, but even then some leeway should be made for those who absolutely can not tolerate noise pollution. I am one of those people.
My job requirements, in priority order, are:
Office with walls and a door
Geographic location (bike to work)
Salary
Yes, that means I am willing to forego #3 for getting #1 and #2.
My current job satisfies #1 and #3 very well. But not #2, so I'll soon be back on the market...
Also, regarding flourescent lights, #1 allows you to turn off the overheads and install incandescent floor and table lamps.
Just this week I was shocked to receive a notice in my phone bill that the telco would be allowing reverse lookups (via operator/411) starting August 1st. The notice was advising me that I could elect to have that reverse lookup blocked on my number. I did so immediately.
Elsewhere in this topic are discussions on why reverse lookup is bad and possibly dangerous.
The Olympic Committee does this with brick and mortar businesses in the host city also. When the Games Mafia came through Atlanta in 1996, they similarly pursued actions against legitimate businesses that happened to have Olympi* in their name.
For example, Olympic Pizza, a Greek pizza joint that had been operating for decades.
The whole inane olympic system is woefully overdue for some serious reform.
The key thing to understand about ITU voice codecs is that they are very very carefully designed to 1) have predictable RAM requirements, 2) have predictable CPU requirements and 3) work well when concatenated with other codecs.
#1 and #2 are clear. If you have known max CPU and RAM requirements, then you can design your codec board with a given processor and memory and be assured that at the end, the software will have enough hardware to do the algorithm. Remember that these codec typically exist in the embedded world where margins are thin and resources must be planned.
#3 is different. What if you are on a cell phone (algorithm #1), with a satellite backhaul from the remote city you're in into the telco headend (algorithm #2, perhaps ADPCM), then through a VoIP backhaul (algorithm #3)? Nearly guaranteed to sound like crap -- lots of swirly audio artifacts, even though going through just one of those algorithms sounds just fine. G.728 and G.729 are designed to work well concatenated with themselves and other codecs while using up reasonable CPU and RAM resources.
As chips follow Moore's law, new algorithms will come out that use more resources to squeeze the signal further, perhaps to 4 kbps and lower.
I am routinely amazed that all this cookie crap is still in the press. Cookie filtering via CookiePal has been around for over three years, and yet people still talk of turning off cookies in their browser before going to a particular site. Let CP do the work -- and let the cookies you WANT/trust go through (i.e. SlashDot).
Of course, it's a Windoze-only solution; works with the following browsers according to their web site:
Microsoft Internet Explorer 3.x, 4.x and 5.x
Netscape Navigator 3.x and 4.x
Opera 3.x (Limited support - View and Delete cookies only)
America Online 3.0, 4.0 and 5.0 for Windows 95/98
CompuServe WinCIM 3.0.1 and 4.0 and CompuServe 2000.
Symantec Internet FastFind
Headliner
.. and can be customized by the user to work with most other 32 bit Internet software which uses cookies, including e-mail programs such as Outlook and Eudora.
Costs a couple bucks after a trial period. To paraphrase JWZ, other solutions are free only only if your time is worthless...
You can always use bigger and fancier digital modulation schemes to pack in more bits per symbol (BPSK -> QPSK -> 16QAM -> 36QAM -> etc.). But you need more and more power to do this, AND/OR you need a cleaner and cleaner transmission media
Regular dialup telephones have peaked at 56 kbps because they can only get so much modulation out of the power allowable by the FCC -- in fact you only get 53.3 kbps because of precisely that FCC power limit.
Satellite systems (my biz) use only BPSK (1 bit per symbol) and QPSK (2 bits per symbol) because A) power is an extremely precious resource on a satellite, so you can't use the higher powered modulations, and B) phase noise effectively smears that bit pattern around and makes it harder to discriminate -- and increasing power is the only way to push those blobs apart enough to where you can tell them apart.
Microwave systems, which are land-based and point to point, have virtually limitless power to draw on (the local AC power grid), so they can run the fancier mods, even though they might be at exactly the same frequency range as satellite.
Every few years the International Telecommunications Union (ITU) holds a meeting of the World Radiocommunication Conference (WRC). The last one just finished, and was held in Istanbul.
Virtually all countries send representatives to finalize plans for global RF allocation. This allows manufacturers worldwide to be able to design equipment that is more likely to work worldwide. For example, FM radio generally occupies the 88-108 MHz band, although there is some variation as to channel centers. This allows mfgs to design and build RF tuner ciruits optimized for just that band.
As an example of when happens when you DON'T adhere to the ITU WRC plans: Satellite C-band is set at 5.9-6.4 GHz up, 3.7-4.2 GHz down. India decided they didn't like that and went with their own C-band frequency plan -- 6.7-7.0 up and 4.5-4.8 down. Guess what? It's a real pain in the ass to find RF gear that works in India -- any vendor who want to do business in India has to re-engineer their RF cirucits to work at the the India bands.
Of course, India decided they were a big enough market that they could get away with it, and to some extent they have -- INSAT gear exists. But it's more expensive.
WHICH defeats the whole point -- global standards so manufacturers can design one set of RF circuits. Resulting in larger economies of scale and lower prices.
Slashdot Mirror
Nope, you're wrong too. Speed of sound decreases with increasing altitude (less dense air).
See:
- http://www.grc.nasa.gov/WWW/K-12/airplane/atmos
i .h tml
- http://www.grc.nasa.gov/WWW/K-12/airplane/sound
. ht ml
for the basic information and a cool little demonstrator app. However, even at high altitude, the SOS doesn't change much (-14% is "not much" to me). Now, speed of sound through solid rock, THAT'S fast!One source of confusion is that SOS is about 1100 feet per sec or about 750 miles per hour. People often get the numbers and units swapped.
- Chris
P.S. Wow, I actually used my Aerospace Engineering degree today!
P.P.S. SR-71 has gone to Mach 3 according to public knowledge, but it's widely expected that it went MUCH faster. Hell, most fighter jets can push Mach 2.0, and the SR-71's design point is Speed At All Costs.
<RANT> Oh what a steaming pile of self-righteous crap! I'm sorry to have to inform you that in the private sector these days, virtually everything is always shoved out the door before the engineers say it's done. The fact is we all love to perfect our creations, but time (or VC funding) waits for no man, and the suits do indeed have a job -- get the product out there and start pulling in revenue before all the cash is gone. </RANT>
Take a look at Mozilla at any time over the past two years -- it always seems like they just need a couple more months and it'll be perfect. Netscape bit the bullet last fall and shoved NS6 out the door -- now it's four months later and Mozilla just issued a new roadmap that delays '1.0' until Q3. Should Netscape have waited "a few months"?
Things get done in this world by people who design, execute, tweak it up a bit, shove it out the door, evaluate, re-prioritize and do it all again. "Works flawlessly"? Ha! Product design is asymptotic -- you'll get closer and closer, but you're never really THERE, and so someone has to stick their neck out and say "enough already". Companies run by engineers do NOT necessarily succeed -- you need a balance of technical and fiscal considerations in any decision.
Sounds like Agenda's got problems, but as has been stated elsewhere, it's too early to make a judgement on that.
- Master Of The Obvious
Perhaps it's because women have had the heel of man on their neck for 10,000 years of human culture and are a bit more sensitive to gender issues than men are. Not the other way around.
Plus, the Taliban are actively pulling women back into the stone age. You have to admit that women have a slightly different perspective on these issues.
Yeah, we'll use SCPS.
In other words, that certification should be handled by a group that is not beholden to a particular company's technologies or "vision".
Groups like the IEEE and NCEES have long had these professional standards and certifications in place for real engineers, but unfortunately most IT professional fall in a gray area between vo-tech and engineering. I'm not saying that IT jobs are "easier" or less intellectually demanding than jobs that required old-school degreed engineers -- rather, the extreme market forces of the last five years have force many, many smart people to bail out of their college degree track and go for the gold.
Because of that, these organizations are finding that lots of IT professionals are not being educated on the responsibilities of the technical professional, include in particular ethical responsibilities. A whole raft of talent is set adrift ...
For a professional engineer, this topic is a no-brainer: as a consultant, you must act in the best interest of your paying customer.
To see it in black and white, read the short and simple IEEE Code of Ethics.
What irony that months later, the report showed that our second scenario was exactly correct. As just a bunch of low paid wanna-be techies sitting around looking at the event frame by frame, we had gotten the gist of what had happened within an hour after the explosion.
I understand your pride at rapidly determining "the cause" of the breakup, but really all you identified was the endgame sequence -- it's like witnessing a car crash and saying "the damage was caused by the two cars steering towards each other and colliding".
What took NASA months to determine was the root cause of the explosion. The cold weather that day was out of the specified operational range of the huge O-rings used to seal the gaps in the booster segments, and thus some gases were able to escape out through the gaps. Over time (say, 60 seconds) those gaps got burned out enough to allow visible flames to escape and trigger the endgame sequence you observed.
The cognizant Morton Thiokol engineer had protested the launch that day and had been overridden by management higher up. Everyone had "Go Fever" and safety was ignored.
- HomeRF (Intel)
- HyperLAN II (Ericsson and Nokia)
See also the Wired article dicussing the battle of the standards.Yes, the business has to pay a fee to start, but they also get charged postage on the items that actually get used. As to weight limits, a few minutes browsing gets you that info:
http://pe.usps.gov/text/qsg/q922.htm
http://new.usps.com/cgi-bin/uspsbv/scripts/content .jsp?D=24687#a6
But it's certainly easier to talk about something than shuddup and check your facts.
It appears to me that Green Bank is just a standard offset feed design. This is the same design used in your dinky DBS TV dish and virtually every small satellite antenna in the world. That said, there certainly are other things that distinguish Green Bank, including the colossal size (and [oink] price) and the dynamically adjustable surface.
One of my work colleagues once provided me with the following explanation to help understand how these offsets works.
Visualize a standard "prime focus" antenna. This is the kind that has the struts from the edge of the big reflector to a point in the air above the exact center of the dish. Energy from space hits the metal reflector and is bounced towards the focus point, where the struts meet and your receivers are. Here's a PDF of a prime focus antenna.
Now imagine that the antenna is pointed straight up, so it's like a bowl catching rain. If you sliced vertically through it, you'd see a perfect parabola, which would go further out and up if you extended the curves of the reflector. The receiver is sitting at the focus point of that parabola.
Imagine that perfect, mathematical parabola sitting there, with the sides extending out and up. The reflector just happen to be a metal realization of the very bottom of that parabola. We could make antennas where the reflector extends furhter up the sides of that mathematical parabola, but eventually it's just lots of expensive metal structure for not much gain (pun intended :)).
Here's the cool part: Now imagine that instead of the metal reflector occupying the bottom of the parabola, you slide the metal "skin" UP THE SIDE of the mathematical parabola that you're envisioning. The parabola doesn't move, and thus neither does the focus point. Just slide the metal "realization" of that paraboloid curve up one side.
The antenna is still "looking" straight up into space, but now the reflector is off to the side a bit. The reflector on your DBS dish is actually a mathematically very complex section of a 3D paraboloid surface. But it's usually hard to tell because the reflector is relatively flat, and thus it's hard ot detect the complex curves involved. Here's a bunch of pictures of offset-feed dishes.
Green Bank has the feed overhead, unlike your DBS dish. It's still the same idea; they just spun the whole thing around on the line-of-sight axis.
What's the big advantage? As the article hinted, you don't have those struts in the way of the incoming energy, and thus the antenna is more efficient. Also, on a big system like GB, it's possible for them to lower the feed/receiver assembly closer to the ground where it's easier to service.
In my job, we usually have the antennas oriented like your DBS dish, with the feed close to the ground. But when you get to real high latitudes (like in Alaska or Siberia), the satellite you're trying to hit is real close to the horizon, and when we try to aim that low, the feed hits the ground. In those rare cases, we have to spin it around to put the feed high up in the air, like GB, only WAY smaller.
By the way, there's a kind of antenna (called a Cassegrain) that looks sort of like a prime focus, but has a second refector at the feed which bounces the energy back down to the receiver at the center of the main reflector. Here's a PDF of a Cassegrain antenna.
PDFs courtesy of my employer :)
My job requirements, in priority order, are:
Yes, that means I am willing to forego #3 for getting #1 and #2.
My current job satisfies #1 and #3 very well. But not #2, so I'll soon be back on the market ...
Also, regarding flourescent lights, #1 allows you to turn off the overheads and install incandescent floor and table lamps.
I believe the laws have changed.
Just this week I was shocked to receive a notice in my phone bill that the telco would be allowing reverse lookups (via operator/411) starting August 1st. The notice was advising me that I could elect to have that reverse lookup blocked on my number. I did so immediately.
Elsewhere in this topic are discussions on why reverse lookup is bad and possibly dangerous.
This page has lots of hacks for lots of players, including detail about other kinds of hacks (e.g. DeCSS) and required firmware versions.
It was actually based on the width of a very special thumb, namely the King's.
Metric will prevail. Lionize Carter, excoriate Reagan.
You'd probably be interested in the new Ford Exhorbitant.
For example, Olympic Pizza, a Greek pizza joint that had been operating for decades.
The whole inane olympic system is woefully overdue for some serious reform.
G.728 = 16 kbps duplex
G.729 = 8 kbps duplex
The key thing to understand about ITU voice codecs is that they are very very carefully designed to 1) have predictable RAM requirements, 2) have predictable CPU requirements and 3) work well when concatenated with other codecs.
#1 and #2 are clear. If you have known max CPU and RAM requirements, then you can design your codec board with a given processor and memory and be assured that at the end, the software will have enough hardware to do the algorithm. Remember that these codec typically exist in the embedded world where margins are thin and resources must be planned.
#3 is different. What if you are on a cell phone (algorithm #1), with a satellite backhaul from the remote city you're in into the telco headend (algorithm #2, perhaps ADPCM), then through a VoIP backhaul (algorithm #3)? Nearly guaranteed to sound like crap -- lots of swirly audio artifacts, even though going through just one of those algorithms sounds just fine. G.728 and G.729 are designed to work well concatenated with themselves and other codecs while using up reasonable CPU and RAM resources.
As chips follow Moore's law, new algorithms will come out that use more resources to squeeze the signal further, perhaps to 4 kbps and lower.
Of course, it's a Windoze-only solution; works with the following browsers according to their web site:
Costs a couple bucks after a trial period. To paraphrase JWZ, other solutions are free only only if your time is worthless ...
You can always use bigger and fancier digital modulation schemes to pack in more bits per symbol (BPSK -> QPSK -> 16QAM -> 36QAM -> etc.). But you need more and more power to do this, AND/OR you need a cleaner and cleaner transmission media
Virtually all countries send representatives to finalize plans for global RF allocation. This allows manufacturers worldwide to be able to design equipment that is more likely to work worldwide. For example, FM radio generally occupies the 88-108 MHz band, although there is some variation as to channel centers. This allows mfgs to design and build RF tuner ciruits optimized for just that band.
As an example of when happens when you DON'T adhere to the ITU WRC plans: Satellite C-band is set at 5.9-6.4 GHz up, 3.7-4.2 GHz down. India decided they didn't like that and went with their own C-band frequency plan -- 6.7-7.0 up and 4.5-4.8 down. Guess what? It's a real pain in the ass to find RF gear that works in India -- any vendor who want to do business in India has to re-engineer their RF cirucits to work at the the India bands.
Of course, India decided they were a big enough market that they could get away with it, and to some extent they have -- INSAT gear exists. But it's more expensive.
WHICH defeats the whole point -- global standards so manufacturers can design one set of RF circuits. Resulting in larger economies of scale and lower prices.