Re:Maybe Joe Schmoe shouldn't be using a computer.
on
AOL 9.0 Called Badware
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· Score: 1
How about the number of people who destroy thousand-dollar engines for want of two bucks of motor oil?
Not with today's oil prices. You'd be lucky to coat the end of the dipstick for $2...
As to the rest:
First of all, people *do* operate cars without a thought to safety.
Absolutely true. +1 insightful.
If Joe Schmoe decides he wants to click "Yes" when AnnoyingAdBar, LLC tells him to, than doesn't he pretty much get what he deserves?
No. Sure, it would be nice if the average person was smarter than simply clicking "yes" to any dialog box which appears, but I'm not going to hold my breath waiting for people to become smarter. In the meantime, developers can help by never using modal dialog boxes unless they absolutely need to.
Ask the user when something bad can happen and the program has good reason to believe that the user might not want this to happen. (Good usage: hitting delete in Mozilla when you've got a mailbox selected rather than a specific email message; bad usage: asking the user to confirm that you really want to save the game, or whether you want to quit, etc.)
And, more importantly, when he pays me to fix it, don't I get what *I* deserve?
Sure, if you do your job reasonably well. Being a sysadmin and cleaning up someone else's computer unfortunately resembles being a plumber fixing a broken toilet.
A more cynical person might think that kind of thing, indeed.
I'm not interested in the government writing more laws when they can't be bothered to prosecute the ones we've already got. A cynic might wonder why the government hasn't done a damned thing to fight spam until the spammers started selling presciption drugs from off-shore pharmacies. Regular phishing scams, Nigerian extortion variants, virus-driven keyloggers, and other forms of cracking machines aren't sufficiently interesting to the local cops or to the FBI unless you can demonstrate something like $2000 worth of damages.
Oh yeah, that and Internet gambling. It used to be the case that what you did with your money was between you and your bank, and it stayed that way until and unless a judge signed a warrant; nowadays, financial transactions of some unknown size (it used to be 10K, now it's a secret) will be reported to the feds, credit card agencies & reporting bureaus like Equifax or TRW, etc.
*Astroturfing: In American politics and advertising, the term astroturfing describes formal public relations projects which deliberately seek to engineer the impression of spontaneous, grassroots behavior. The goal is the appearance of independent public reaction to a politician, political group, product, service, event, or similar entities by centrally orchestrating the behavior of many diverse and geographically distributed individuals.
It's also against the law to conceal the existance of relationship between an endoser and the product, see:
People who violate these rules by a lot can get sued/fined for up to 11K per instance.
Re:Maybe Joe Schmoe shouldn't be using a computer.
on
AOL 9.0 Called Badware
·
· Score: 1
Joe something that is simple, easy to use, secure, not very complicated, and that actually works?
That's doable for reasonably simple problem domains, like dedicated appliances (think about a broadband router, some firewalls, dedicated GPS-to-NTP boxes, and perhaps of some game consoles or maybe even the iPod).
When you get a general purpose system that is capable of running a wide range of programs and is often used without proper configuration, you get exposed to the whole range of quality levels, rather than the typically mature, well-tested [1] software that good appliances run.
[1]: In part because it's targetting a very specific deployment/hardware environment, which is easier to handle.
Seconded. Lian-li makes very nice aluminum cases which can be entirely disassembled by hand using the thumbscrews (also used for the PCI/AGP/PCIe/etc slots), they've got a solid ventilation pattern (usually two intake fans in the lower front blowing across a removable bay which'll hold 1-4 hard drives, and a rear exhauster fan), and as a bonus, their black models have a look which reminds me of NeXT hardware (which also used anodized black paint on aluminum).
Having more intakes than outtakes tends to give the case positive pressurization compared to the ambient room, which means that they don't tend to accumulate dust inside. The front intake fans have a removable, washable dust filter.
I would point out that when you drop a much more dense object (generally considered "heavy") compared to a substantially less dense object like a feather in an atmosphere, the heavier and more dense object usually drops much faster. Visibly so.
Of course-- that is so intuitively true that nobody [1] questioned it for the 2000-odd years between Aristotle & Gallileo.
On the other hand, you can take two pieces of paper, which weigh the same, and have the same density, and crumple one into a tight ball, and discover that they also fall at different speeds-- which means your experiment isn't measuring just one thing, but is being strongly influenced by the friction from air resistance.
And that's the point of scientific reasoning and experimentation-- to recognize that measurements are imprecise and can be biased due to a number of factors [2], sometimes so much that they prevent you from making truthful conclusions about what is actually going on. And that's why clever ways of conducting an experiment so that you can eliminate these biases, or by making a relative comparison where the bias cancels itself out leaving a more meaningful result, are so important and valuable to understand.
Dropping Jupiter onto the surface of the Earth falls just as fast as dropping a proton.
Surely that should be the other way 'round?:-) The Earth is about the size of Jupiter's Red Spot, and would disappear inside Jupiter's atmosphere without making much difference as far as Jupiter was concerned...
[1]: Well, almost nobody. The all-knowing Oracle of Wikipedia mentions John Philoponus and Giambattista Benedetti.
[2]: Not the least of which is human nature. See the.sig below.
You seem to have forgotten we are talking about how fast objects fall, not comparing them.
How do you measure velocity, eh? Measure the distance, divide by the elapsed time?
Well, in the specific example I gave, and in the historic example involving a leaning tower in Italy, the distance and the time are exactly the same for the two objects...so the the velocity ("how fast"), is also the same.
Go back and read the post that started this.
The post by ZorbaTHut, hmm? Modded +5 because it had a good point, which you followed up by a needlessly pedantic correction which isn't actually even true for these specific circumstances? All this guff about "truthiness" is just an attempt to change the subject from matters of fact (which can be, and have been tested in real-world circumstances), to avoid admitting your mistake.
Don't blame me for being wrong...you've managed that all by yourself.
If the object isn't heavy enough to undergo fusion by itself, it's not considered to be a true star...but objects which were heavy enough to be a star, and then went into the red supergiant phase or go nova, the left-over stellar core (a "white dwarf" or "neutron star", respectively) will still be considered a star until they cool below 1000K or so.
IIRC, Jupiter puts out more energy than it gets from the Sun.
This is possibly true, although the difference in energy being received and the observed temperatures are within a reasonable tolerance (~ 10%?); whether this is because Jupiter has some extra energy due to radioactive decay, or continued gravitational compression, or whether it's just a measurement error is not clear.
Is it not smaller than their lower limit?
Yes. It's not expected that Jupiter is fusing any significant amount of deuterium or normal hydrogen. To a good first approximation, the thermal radiation from Jupiter (about 200K IIRC) corresponds with the amount of energy from solar radiation it is receiving.
What's the difference between an object like Jupiter and a brown dwarf or star? As I said earlier, what makes a brown dwarf "brown"? What spectrum range defines a star?
Mass. A brown dwarf emits enough radiation that it is visible in IR or red light, which requires a surface temperature of anywhere from around 800K to about 2000K.
You can figure these things out just by doing a naked-eye judgement of the color of the objects, or you can look at something called Wein's law, which relates temperature to the colors (or wavelength) of the radiation being emitted by that object:
You have an error in your equation: you forgot about the acceleration of the EARTH toward the test object!
No, actually, I haven't.
Notice that both objects are being released at the same time; the motion of the Earth towards them is not different for one object versus the other, presuming it was significant at all (which it is not; the Earth weighs about 10^26 times what a 5kg lead pellet weighs). When you drop two objects from the same height, at the same time, in a vaccuum, they will hit the ground at exactly the same time.
See you need to distinguish between stuff that is emperically 100% correct, and stuff that is USEFULLY correct.
And for your next trick, will you acknowledge the difference between being correct, being wrong, and being an obnoxious pedantic git?
Bit of a problem in your argument there - heavy thing DO fall faster then light things!
Actually, if you go to a decent science museum, they should have an exhibit where they show something like a feather and lead shot being dropped in a vaccuum...really and truely, they fall at exactly the same speed and hit the ground at the same time.
If you plug in F=M1a and F = gM1M2/r^2, you discover that the gravitational attaction of a heavier object to the earth exactly counterbalances the weight of the heavier object, so all objects experience the same acceleration due to the earth's gravity (M1a = gM1M2/r^2 => a = gM2/r^2, or a ~= 9.8m/s, where M1 is the mass of the test object, M2 is the earth's mass, r is the radius of the earth).
A planet is something which does not have enough mass to sustain a fusion reaction.
Unless a star is nearby, planets are effectively invisible at stellar distances since they radiate no light of their own. Even with a star nearby, it's easier to notice the gravitational wobble of the planet shifting the star's orbit and causing doppler changes to the star's spectrum than to observe the planet directly via reflected light.
A "brown dwarf", sometimes referred to as a T-class star is something that emits enough energy to be detected (ie, mainly in the red or infrared spectrum and thus must have a surface temperature of at least 800-1200 K), which means they have to have at least some energy from gravitational collapse or minimal deuterium fusion happening to generate this light, but they are smaller and cooler than the smallest "normal" star class, which is M.
M-class stars have temperatures between 2000 - 3300K, and apparently have a mass between 0.1 and 0.6 solar masses. Note that astronomy is still integrating the information and updating the classification of stars, so they've added both the L and T classes; I gather that an L-class star is one between the T-class brown dwarfs and M-class, having a mass of ~0.01 to 0.1 solar masses, temperatures of 1200 to 2000K, and are getting enough energy from deuterium fusion to perhaps also be burning some normal hydrogren.
Again, anything that is observed to be radiating mainly infrared and little or no higher-energy/higher-temperature bluish light is going to be a "brown dwarf" by observation, and the smaller M-class and all L & T class stars would qualify as being "brown dwarfs". I gather the difference is that the T-class stars are so small that they go out in a few millions of years (once the initial energy gained from gravitational collapse of the protostellar gas cloud the star condensed from has been radiated away and they cool down below even the deuterium fusion threshold); L-class stars will burn deuterium until they run out (hundreds of millions of years?); and the smallest M-class stars, which weigh enough to fuse normal hydrogen, will burn for trillions of years.
If there were dimmer stars present there, the Hubble's main camera would have been sensitive enough to have seen them...they're pretty sure of this because they were able to notice some very dim white dwarfs (a white dwarf is the remenant stellar core of a bigger star which went nova; they are very hot [initally] but also very tiny), which are dimmer than the smallest M-class stars still in the main sequence.
Basicly, this observation is in reasonably close accordance with the theories about stellar fusion; basicly, an potential star needs to have about ten or fifteen times Jupiter's mass before deuterium fusion is possible, and about 70 times Jupiter's mass before normal hydrogen fusion happens (according to the models).
Jupiter weighs 1.899 * 10^29kg; Sol weighs 1.989 * 10^32 kg (or about 1050 times what Jupiter weighs). 8.4% of Sol's mass is 1.65 * 10^30, or 87 times what Jupiter weighs.
This is actually one of the main benefits to being a sysadmin type rather than a developer-- sysadmins generally end up moving around to look at and solve issues on end-user workstations, move servers or monitors around, check or adjust network cabling, etc, etc.
Having to move around on a regular basis rather than spending 4-8 hours in the coding mindset is helpful...
Yeah, that stuck me as wacky, too. "The book isn't well organized because it doesn't mix everything I might want to see all in the same place." is using some definition of 'organized' that's rather different from my own....
1) 480 3 phase can be 3 wire or 4 wire. 3 wire is called Delta (floating ground or one of the legs can be tied to ground). 4 wire is called Y (typically the 4th wire is the "center" of the Y and is grounded.
3-wire is "delta", 4-wire is called "wye", agreed-- the 4th wire is called "neutral" in the US and "common" in UK parlance, I believe, although the two terms are interchangable. However, the neutral/common wire is not the same thing as the ground or "earth" wire, just as the "cold" side and "ground" in a three-prong 120VAC recepticle are not the same-- although commonly neutral and ground will be tied together at the building service entrance as part of the building grounding. Ideally, common and ground are at the same voltage potential ("equipotential"?), but this is not always the case especially when you've got a big UPS or an isolation transformer in place for computer equipment which provides galvanic isolation from the mains. Look up "isolated ground" and "ground loops"....
As for the other point, I agree that you need a transformer to convert 227/480 to 120/208 "wye" (I guess "delta" is possible but doesn't seem to be commonly used except perhaps for three-phase motors and suchlike).
Why isn't this stuff standardized, and power strips can instead contain one single transformer/recitifer package, with DC sockets, or retractable DC wires coming out of them? Even if we ignored PCs and only did the external peripherals for now, we'd still get a big saving in power just by having fewer transformers.
The cynic in me suggests it's because your typical wall-wart costs about 50 cents to make in bulk and are commonly marked up by a factor of 20 to 100 or so, so when the company sells you a replacement they make out like Enron.
But yeah, standards exist-- most of the time, you can buy a generic PS from Radio Shack which delivers 3V, 5V, 7.5V, 9V, & 12V @ 1amp or so for much less than you can buy the product-specific wall-wart. Some vendors (like Sony) have even deliberately disregarded the JEDEC? standard connector sizes in order to prevent you from using a generic replacement PS.
Does that mean the power supplies use... reverse polarity notation?
Absolutely, but not only that, the bigger ones use "sinusoidal phasors" which "rotate in the counterclockwise direction with a {1-2-3} or {3-2-1}
sequence and angles are measured as positive in the counterclockwise direction." [1]
I betcha never thought of all this when someone on Star Trek "set phasors to stun".
Kind words, my thanks. I'm "Network Operations Manager" for a computer software company in Manhattan, NY-- which is probably a good description as far as job titles go, since they wouldn't let me put "Master of Packets" on my business card.
But I grew up learning how to solder and to use a voltmeter/DMM and an oscilloscope; I've built a bunch of Heathkit and Greymark kits including a 19" TV and learned how to calibrate the thing using the crosshatch generator board I soldered together (came with the kit) back in high school, and I've fixed or adjusted dozens of TVs or CRTs since (especially a certain 17" monochrome NeXT monitor which had the habit of dimming over time [1]). I'm not a licensed electrician, nor will I play one on Slashdot, but I've helped string up temporary lighting and so forth to breaker panels and then had someone who was licensed inspect it.
I've spec'ed out server rooms, gotta a 20KVA Powerware 93xx UPS for my companies' server room, for example. I also collect and fix pinball machines.:-)
Given how damnned hot it's been lately, that actually sounds like a good idea.:-)
[ "HVAC" is also used as an abbreviation for "High Voltage AC", but I admit that it is more commonly used to mean "heating, ventilating and air-conditioning"... ]
Depends on the load. 48V isn't just used as the ring voltage on analog POTS lines, it's also commonly used as a power-delivery bus to PBX switches, SmartJacks and other CSU/DSU equipment for T1/T3/E1/etc lines, perhaps with a wall-mounted 48VDC battery backup unit.
Although, you're right that they don't use 22-gauge wire for that purpose; one of the PBXes at a client site has a 15 or 20amp/48VDC power supply, for example, which seemed to be using 14 gauge wiring, for example.
Obviously, you don't work on live circuits if you have a choice of working with them off instead, but good habits mean you treat even dead circuits as if they were live until fully isolated & disconnected, just as you should treat a gun as being loaded until you've confirmed that it is not.
Well-designed power supplies often have a bleeder resistor across the primary filter caps to drain them of juice, but note that the vaccuum tube in a CRT makes an excellent capacitor as well (it's being charged to 20 kilovolts or more), and it's dangerous to try to dead-short it to drain the residual current. 120VAC current shock can be fatal but that is very uncommon; however, the voltages inside a CRT are probably the most dangerous level of current most people have around in their homes or work environments.
Yeah, you're right that you'd need a transformer to go from 277/480 to 120/208.
On a good day, there is minimal voltage difference between neutral (or common) and ground, but if the site has a poor or floating building ground, you can see some pretty severe voltage swings. Also, if the load on the three phases isn't reasonably well-balanced, that'll nudge neutral away from ground and you'll get current leaking to ground which is wasteful and even dangerous at higher amperages.
I've even seen old wiring in metal conduit where abrasion somewhere had tied the conduit and ground wires to hot...I managed to arc-weld about half the end of my screwdriver to the recepticle finding that out, and the worthless breaker at the site didn't even trip.
Nice shower of electrical sparks and molten bits of the other half of the screwdriver tip, though...
277/480VAC power distribution involves 3-phases of current which are 120 degrees out of sync with each other and a forth wire for neutral. In order to get 120VAC, you just need to connect between one of the phases and neutral; you don't need a step-down transformer. The wikipedia article here has a decent discussion:
220VAC can be fatal if you manage to ground yourself in a fashion that causes the current to pass through your chest, but it's uncommon and good practice working with live circuits means you try to avoid the situation. In particular, people working on the innards of CRT tubes are advised to keep one hand in their pocket when near the flyback transformer and HVAC power circuitry driving the vacuum tube to avoid a short from one hand -> chest -> other hand.
Getting one hand shocked at 220VAC is not pleasant, but it's not especially painful either...
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Not with today's oil prices. You'd be lucky to coat the end of the dipstick for $2...
As to the rest:
First of all, people *do* operate cars without a thought to safety.
Absolutely true. +1 insightful.
If Joe Schmoe decides he wants to click "Yes" when AnnoyingAdBar, LLC tells him to, than doesn't he pretty much get what he deserves?
No. Sure, it would be nice if the average person was smarter than simply clicking "yes" to any dialog box which appears, but I'm not going to hold my breath waiting for people to become smarter. In the meantime, developers can help by never using modal dialog boxes unless they absolutely need to.
Ask the user when something bad can happen and the program has good reason to believe that the user might not want this to happen. (Good usage: hitting delete in Mozilla when you've got a mailbox selected rather than a specific email message; bad usage: asking the user to confirm that you really want to save the game, or whether you want to quit, etc.)
And, more importantly, when he pays me to fix it, don't I get what *I* deserve?
Sure, if you do your job reasonably well. Being a sysadmin and cleaning up someone else's computer unfortunately resembles being a plumber fixing a broken toilet.
Damn those Internet pipes, always breaking.
I'm not interested in the government writing more laws when they can't be bothered to prosecute the ones we've already got. A cynic might wonder why the government hasn't done a damned thing to fight spam until the spammers started selling presciption drugs from off-shore pharmacies. Regular phishing scams, Nigerian extortion variants, virus-driven keyloggers, and other forms of cracking machines aren't sufficiently interesting to the local cops or to the FBI unless you can demonstrate something like $2000 worth of damages.
Oh yeah, that and Internet gambling. It used to be the case that what you did with your money was between you and your bank, and it stayed that way until and unless a judge signed a warrant; nowadays, financial transactions of some unknown size (it used to be 10K, now it's a secret) will be reported to the feds, credit card agencies & reporting bureaus like Equifax or TRW, etc.
*Astroturfing: In American politics and advertising, the term astroturfing describes formal public relations projects which deliberately seek to engineer the impression of spontaneous, grassroots behavior. The goal is the appearance of independent public reaction to a politician, political group, product, service, event, or similar entities by centrally orchestrating the behavior of many diverse and geographically distributed individuals.
It's also against the law to conceal the existance of relationship between an endoser and the product, see:
FTC section 255.5
People who violate these rules by a lot can get sued/fined for up to 11K per instance.
That's doable for reasonably simple problem domains, like dedicated appliances (think about a broadband router, some firewalls, dedicated GPS-to-NTP boxes, and perhaps of some game consoles or maybe even the iPod).
When you get a general purpose system that is capable of running a wide range of programs and is often used without proper configuration, you get exposed to the whole range of quality levels, rather than the typically mature, well-tested [1] software that good appliances run.
[1]: In part because it's targetting a very specific deployment/hardware environment, which is easier to handle.
Seconded. Lian-li makes very nice aluminum cases which can be entirely disassembled by hand using the thumbscrews (also used for the PCI/AGP/PCIe/etc slots), they've got a solid ventilation pattern (usually two intake fans in the lower front blowing across a removable bay which'll hold 1-4 hard drives, and a rear exhauster fan), and as a bonus, their black models have a look which reminds me of NeXT hardware (which also used anodized black paint on aluminum).
Having more intakes than outtakes tends to give the case positive pressurization compared to the ambient room, which means that they don't tend to accumulate dust inside. The front intake fans have a removable, washable dust filter.
David Weber-- a fine author and a fine series. I'd give props to R.A. Heinlein and "The Moon is a Harsh Mistress" first, though....
Of course-- that is so intuitively true that nobody [1] questioned it for the 2000-odd years between Aristotle & Gallileo.
On the other hand, you can take two pieces of paper, which weigh the same, and have the same density, and crumple one into a tight ball, and discover that they also fall at different speeds-- which means your experiment isn't measuring just one thing, but is being strongly influenced by the friction from air resistance.
And that's the point of scientific reasoning and experimentation-- to recognize that measurements are imprecise and can be biased due to a number of factors [2], sometimes so much that they prevent you from making truthful conclusions about what is actually going on. And that's why clever ways of conducting an experiment so that you can eliminate these biases, or by making a relative comparison where the bias cancels itself out leaving a more meaningful result, are so important and valuable to understand.
Dropping Jupiter onto the surface of the Earth falls just as fast as dropping a proton.
Surely that should be the other way 'round? :-) The Earth is about the size of Jupiter's Red Spot, and would disappear inside Jupiter's atmosphere without making much difference as far as Jupiter was concerned...
[1]: Well, almost nobody. The all-knowing Oracle of Wikipedia mentions John Philoponus and Giambattista Benedetti. .sig below.
[2]: Not the least of which is human nature. See the
How do you measure velocity, eh? Measure the distance, divide by the elapsed time?
Well, in the specific example I gave, and in the historic example involving a leaning tower in Italy, the distance and the time are exactly the same for the two objects...so the the velocity ("how fast"), is also the same.
Go back and read the post that started this.
The post by ZorbaTHut, hmm? Modded +5 because it had a good point, which you followed up by a needlessly pedantic correction which isn't actually even true for these specific circumstances? All this guff about "truthiness" is just an attempt to change the subject from matters of fact (which can be, and have been tested in real-world circumstances), to avoid admitting your mistake.
Don't blame me for being wrong...you've managed that all by yourself.
Yeah, that's about it.
If the object isn't heavy enough to undergo fusion by itself, it's not considered to be a true star...but objects which were heavy enough to be a star, and then went into the red supergiant phase or go nova, the left-over stellar core (a "white dwarf" or "neutron star", respectively) will still be considered a star until they cool below 1000K or so.
This is possibly true, although the difference in energy being received and the observed temperatures are within a reasonable tolerance (~ 10%?); whether this is because Jupiter has some extra energy due to radioactive decay, or continued gravitational compression, or whether it's just a measurement error is not clear.
Is it not smaller than their lower limit?
Yes. It's not expected that Jupiter is fusing any significant amount of deuterium or normal hydrogen. To a good first approximation, the thermal radiation from Jupiter (about 200K IIRC) corresponds with the amount of energy from solar radiation it is receiving.
What's the difference between an object like Jupiter and a brown dwarf or star? As I said earlier, what makes a brown dwarf "brown"? What spectrum range defines a star?
Mass. A brown dwarf emits enough radiation that it is visible in IR or red light, which requires a surface temperature of anywhere from around 800K to about 2000K.
You can figure these things out just by doing a naked-eye judgement of the color of the objects, or you can look at something called Wein's law, which relates temperature to the colors (or wavelength) of the radiation being emitted by that object:
Wikipedia on Wein's law
No, actually, I haven't.
Notice that both objects are being released at the same time; the motion of the Earth towards them is not different for one object versus the other, presuming it was significant at all (which it is not; the Earth weighs about 10^26 times what a 5kg lead pellet weighs). When you drop two objects from the same height, at the same time, in a vaccuum, they will hit the ground at exactly the same time.
See you need to distinguish between stuff that is emperically 100% correct, and stuff that is USEFULLY correct.
And for your next trick, will you acknowledge the difference between being correct, being wrong, and being an obnoxious pedantic git?
Actually, if you go to a decent science museum, they should have an exhibit where they show something like a feather and lead shot being dropped in a vaccuum...really and truely, they fall at exactly the same speed and hit the ground at the same time.
If you plug in F=M1a and F = gM1M2/r^2, you discover that the gravitational attaction of a heavier object to the earth exactly counterbalances the weight of the heavier object, so all objects experience the same acceleration due to the earth's gravity (M1a = gM1M2/r^2 => a = gM2/r^2, or a ~= 9.8m/s, where M1 is the mass of the test object, M2 is the earth's mass, r is the radius of the earth).
A planet is something which does not have enough mass to sustain a fusion reaction.
Unless a star is nearby, planets are effectively invisible at stellar distances since they radiate no light of their own. Even with a star nearby, it's easier to notice the gravitational wobble of the planet shifting the star's orbit and causing doppler changes to the star's spectrum than to observe the planet directly via reflected light.
A "brown dwarf", sometimes referred to as a T-class star is something that emits enough energy to be detected (ie, mainly in the red or infrared spectrum and thus must have a surface temperature of at least 800-1200 K), which means they have to have at least some energy from gravitational collapse or minimal deuterium fusion happening to generate this light, but they are smaller and cooler than the smallest "normal" star class, which is M.
M-class stars have temperatures between 2000 - 3300K, and apparently have a mass between 0.1 and 0.6 solar masses. Note that astronomy is still integrating the information and updating the classification of stars, so they've added both the L and T classes; I gather that an L-class star is one between the T-class brown dwarfs and M-class, having a mass of ~0.01 to 0.1 solar masses, temperatures of 1200 to 2000K, and are getting enough energy from deuterium fusion to perhaps also be burning some normal hydrogren.
Again, anything that is observed to be radiating mainly infrared and little or no higher-energy/higher-temperature bluish light is going to be a "brown dwarf" by observation, and the smaller M-class and all L & T class stars would qualify as being "brown dwarfs". I gather the difference is that the T-class stars are so small that they go out in a few millions of years (once the initial energy gained from gravitational collapse of the protostellar gas cloud the star condensed from has been radiated away and they cool down below even the deuterium fusion threshold); L-class stars will burn deuterium until they run out (hundreds of millions of years?); and the smallest M-class stars, which weigh enough to fuse normal hydrogen, will burn for trillions of years.
If there were dimmer stars present there, the Hubble's main camera would have been sensitive enough to have seen them...they're pretty sure of this because they were able to notice some very dim white dwarfs (a white dwarf is the remenant stellar core of a bigger star which went nova; they are very hot [initally] but also very tiny), which are dimmer than the smallest M-class stars still in the main sequence.
Basicly, this observation is in reasonably close accordance with the theories about stellar fusion; basicly, an potential star needs to have about ten or fifteen times Jupiter's mass before deuterium fusion is possible, and about 70 times Jupiter's mass before normal hydrogen fusion happens (according to the models).
Jupiter weighs 1.899 * 10^29kg; Sol weighs 1.989 * 10^32 kg (or about 1050 times what Jupiter weighs).
8.4% of Sol's mass is 1.65 * 10^30, or 87 times what Jupiter weighs.
This is actually one of the main benefits to being a sysadmin type rather than a developer-- sysadmins generally end up moving around to look at and solve issues on end-user workstations, move servers or monitors around, check or adjust network cabling, etc, etc.
Having to move around on a regular basis rather than spending 4-8 hours in the coding mindset is helpful...
Yeah, that stuck me as wacky, too. "The book isn't well organized because it doesn't mix everything I might want to see all in the same place." is using some definition of 'organized' that's rather different from my own....
3-wire is "delta", 4-wire is called "wye", agreed-- the 4th wire is called "neutral" in the US and "common" in UK parlance, I believe, although the two terms are interchangable. However, the neutral/common wire is not the same thing as the ground or "earth" wire, just as the "cold" side and "ground" in a three-prong 120VAC recepticle are not the same-- although commonly neutral and ground will be tied together at the building service entrance as part of the building grounding. Ideally, common and ground are at the same voltage potential ("equipotential"?), but this is not always the case especially when you've got a big UPS or an isolation transformer in place for computer equipment which provides galvanic isolation from the mains. Look up "isolated ground" and "ground loops"....
As for the other point, I agree that you need a transformer to convert 227/480 to 120/208 "wye" (I guess "delta" is possible but doesn't seem to be commonly used except perhaps for three-phase motors and suchlike).
The cynic in me suggests it's because your typical wall-wart costs about 50 cents to make in bulk and are commonly marked up by a factor of 20 to 100 or so, so when the company sells you a replacement they make out like Enron.
But yeah, standards exist-- most of the time, you can buy a generic PS from Radio Shack which delivers 3V, 5V, 7.5V, 9V, & 12V @ 1amp or so for much less than you can buy the product-specific wall-wart. Some vendors (like Sony) have even deliberately disregarded the JEDEC? standard connector sizes in order to prevent you from using a generic replacement PS.
Absolutely, but not only that, the bigger ones use "sinusoidal phasors" which "rotate in the counterclockwise direction with a {1-2-3} or {3-2-1} sequence and angles are measured as positive in the counterclockwise direction." [1]
I betcha never thought of all this when someone on Star Trek "set phasors to stun".
[1]: Quotes from the first google hit for "3-phase wye"
Kind words, my thanks. I'm "Network Operations Manager" for a computer software company in Manhattan, NY-- which is probably a good description as far as job titles go, since they wouldn't let me put "Master of Packets" on my business card.
:-)
But I grew up learning how to solder and to use a voltmeter/DMM and an oscilloscope; I've built a bunch of Heathkit and Greymark kits including a 19" TV and learned how to calibrate the thing using the crosshatch generator board I soldered together (came with the kit) back in high school, and I've fixed or adjusted dozens of TVs or CRTs since (especially a certain 17" monochrome NeXT monitor which had the habit of dimming over time [1]). I'm not a licensed electrician, nor will I play one on Slashdot, but I've helped string up temporary lighting and so forth to breaker panels and then had someone who was licensed inspect it.
I've spec'ed out server rooms, gotta a 20KVA Powerware 93xx UPS for my companies' server room, for example. I also collect and fix pinball machines.
[1]: Section 5.23 of http://www.faqs.org/faqs/NeXT-FAQ/
Given how damnned hot it's been lately, that actually sounds like a good idea. :-)
[ "HVAC" is also used as an abbreviation for "High Voltage AC", but I admit that it is more commonly used to mean "heating, ventilating and air-conditioning"... ]
Depends on the load. 48V isn't just used as the ring voltage on analog POTS lines, it's also commonly used as a power-delivery bus to PBX switches, SmartJacks and other CSU/DSU equipment for T1/T3/E1/etc lines, perhaps with a wall-mounted 48VDC battery backup unit.
Although, you're right that they don't use 22-gauge wire for that purpose; one of the PBXes at a client site has a 15 or 20amp/48VDC power supply, for example, which seemed to be using 14 gauge wiring, for example.
Obviously, you don't work on live circuits if you have a choice of working with them off instead, but good habits mean you treat even dead circuits as if they were live until fully isolated & disconnected, just as you should treat a gun as being loaded until you've confirmed that it is not.
Well-designed power supplies often have a bleeder resistor across the primary filter caps to drain them of juice, but note that the vaccuum tube in a CRT makes an excellent capacitor as well (it's being charged to 20 kilovolts or more), and it's dangerous to try to dead-short it to drain the residual current. 120VAC current shock can be fatal but that is very uncommon; however, the voltages inside a CRT are probably the most dangerous level of current most people have around in their homes or work environments.
Yeah, you're right that you'd need a transformer to go from 277/480 to 120/208.
On a good day, there is minimal voltage difference between neutral (or common) and ground, but if the site has a poor or floating building ground, you can see some pretty severe voltage swings. Also, if the load on the three phases isn't reasonably well-balanced, that'll nudge neutral away from ground and you'll get current leaking to ground which is wasteful and even dangerous at higher amperages.
I've even seen old wiring in metal conduit where abrasion somewhere had tied the conduit and ground wires to hot...I managed to arc-weld about half the end of my screwdriver to the recepticle finding that out, and the worthless breaker at the site didn't even trip.
Nice shower of electrical sparks and molten bits of the other half of the screwdriver tip, though...
277/480VAC power distribution involves 3-phases of current which are 120 degrees out of sync with each other and a forth wire for neutral. In order to get 120VAC, you just need to connect between one of the phases and neutral; you don't need a step-down transformer. The wikipedia article here has a decent discussion:
http://en.wikipedia.org/wiki/Three-phase_power
220VAC can be fatal if you manage to ground yourself in a fashion that causes the current to pass through your chest, but it's uncommon and good practice working with live circuits means you try to avoid the situation. In particular, people working on the innards of CRT tubes are advised to keep one hand in their pocket when near the flyback transformer and HVAC power circuitry driving the vacuum tube to avoid a short from one hand -> chest -> other hand.
Getting one hand shocked at 220VAC is not pleasant, but it's not especially painful either...