Standard practice for DC substations in urban areas was to wire the M-G sets or rotary converters in parallel with a battery. The AC power could drop out for an hour or more, but the DC customers would still have power.
Fixed speed AC motors are lighter, cheaper and more efficient than an equivalet DC motor. Even in 1900, transmission was still an issue, so AC had lots of advantages for power distribution - especially for hydroelectric generation (that's where Tesla convinced Westinghouse to use AC instead of compressed air).
While it was possible to use M-G sets or rotary converters to convert AC to DC, it was a lot cheaper just to put up transformers and use AC for residential use (exceptions being downtown areas of major cities). The power for most streetcars and subways was originally AC and converted to DC at substations - many cases the AC was at 25Hz as the rotary converters ran more efficiently off of 25 Hz than 60 Hz.
Now for an odd bit of trivia - the last 50 Hz utility in the US was Southern California Edison, which completed conversion to 60 Hz in 1948.
The reason the subways use DC was that at the time the subways were developed, DC motors were smaller, lighter, cheaper and more efficient than variable speed AC motors. AC series motors were developed for railway service (e.g. the New Haven electrification between NYC and New Haven), but those required lower frequency (typically 25 Hz in the US, one exception was the Visalia Electric at 15 Hz and 16 2/3Hz in Europe). Commercial frequency electrification didn't become practical until the 1950's with the development of ignitron and silicon rectifiers.
AC's advantage of high voltage transmission doesn't apply to subways as 1200V seems to be the limit for third rail. 2400VDC was tried in 1915 on the Michigan Railways (an electric interurban in central Michigan) with abysmal results - the voltage was changed to 1200V within a year of the initial installation.
US case law does support the right to anonymity in political writings. One example was a City of LA law overturned as unconstitutional because it required contact information for any leaflets distributed within city limits.
Actually, even more to the point is the secret ballot - while the fact you voted is recorded, how you voted should not be traceable to you (unfortunately not always the case).
3) Dismantle companies that violate privacy laws, retain identifiable customer data, or insist on data that is not a necessity to do business.
Better yet, remove the civil and criminal liability protection for the shareholders. There's nothing that would improve corporate behavior faster than if fund managers would be facing prison time and huge fines or lawsuits for the misdeeds of the companies that they bough stock in.
Umm, I would rather say that the US (actually DARPA) founded the Net, and back then it wasn't anything like it was now, they didn't even have IP, let alone TCP/IP.
If I'm not mistaken, TCP was invented in the US and tested ca 1977 (see a recent CNet article on the 'Internet Van'. The focus outside the US was drawing up the specifications for the OSI networking stack. The first widely available OS to support TCP/IP was BSD 4.2 - though it may be argued that Berzerkeley isn't really in the US...
The system from TFA may not be of much help to you. For one, the system still uses a fairly power pre-polarization field which could interact with your plate. Another problem is that the plate could interfere with the excitation and readout fields (this could be minimized by changing orientation).
Your doctors were doing you good service about the warnings with respect to MRI.
It's easier to make a gradiometer work well at low frequencies where the electric field pick-up can be ignored. The interference from the 50/60 Hz power lines is fairly stable and it is possible to get pretty significant attenuation of that interference source.
The one advantage of using the earth's field is that it is reasonably uniform in a clean environment, and the pre-polarizing field doesn't need to be anywhere near as uniform as the readout field. In a not so clean environment, it is possible to use the gradient coils to clean up the earth's field a bit.
This may be the first image of a human head with an ultra low field MRI, but ULF MRI images have been made for at least a decade and a half. Magritek, a New Zealand company, makes a low cost unit ULF MRI system, though the image volume is limited to about one liter.
Another company, Vista Clara, is using a novel form of ULF MRI to map groundwater.
Phones should be required to accept a signal that switches them from ringing to vibrating.
Not sure how easy that would be to implement, but I agree with your sentiment. I would allow 'ringing' if it was confined to the earpiece of a headset.
if you go into a restaurant or theatre where there is a prominent sign stating "Cell Phone Use is Prohibited in this Establishment", with the proprietor either operating a jammer or having made a Faraday cage to isolate the interior,
N.B. My reply is based on laws and regulations in the U.S., other nations may be different.
The operation of a jammer is illegal and blocking what turns out to be an emergency call is a violation of several FCC regs and possibly state laws (e.g. the California PUC has regulations regarding emergency calls as well) in addition to simply operating the jammer. Things would be even worse for the propietor if the jammer blocked a call on a public area (e.g. street or sidewalk) or on someone else's property - that's why the RF shielding approach is safer (but NOT completely safe). It would be very difficult to design a jamming system to completely cover an establishment without the jamming signal spilling outside the intended coverage area.
The legality of RF shielding is not cut and dry. The rights of the propietor are also not absolute - how long do you think a 'No Colored" sign would last... It is within the right of state and local governments to require businesses open to the public to maintain accessibility to cell phone communications. In addition the shielding of your property may block the reception to an adjacent property or a public street. Finally, most businesses lease rather than own the land and building, which brings up issues of who pays for the shielding.
One other aspect of blocking cell phone use is that the propietor now becomes responsible for emergency communication which may not sit well with the propietor's insurance company - especially if the blocked call atttempt was from off the immediate premises.
The management of those establishments are fully aware that the patrons do not want to be subjected to blabbering idiots on cell phones. They chose to do nothing about it, apart from an announcement at the movies or a sign in a theater.
It's still your choice to patronize that theater and your proposed action may end up with the theater management telling you to never come back. You do have the choice of staying home and watching a DVD.
One other option is to take the theater to small claims court to recover the cost of your ticket.
Then don't plan on needing any emergency services. Ever.
An establishment using passive blocking would still probably need to alert patrons to the blocking and provide an emergency contact number to be completely free of liability. Your point is correct in that passive blocking is on much firmer legal ground than jamming.
Another thing to consider, with the reverse 911 programs now being set-up to call registered cell-phones, the blocked call may be one to you warning of your residence is in danger.
But still, if I ever find you in the seat next to me (or more generally, within arms reach) in a movie theater and your phone rings you are out of a phone.
While I can understand your frustration in those situations, the person who you grabbed the phone from has all sorts of rights to press criminal and civil charges against you. The legally correct way is to complain to the management of the establishment you are patronizing and telling them they will lose your business if nothing is done about it. Remember, you chose to be there as well.
Fair-Rite (and I presume other companies) make ferrite tiles intended for use in anechoic chambers. The upside is that they don't need to be bonded to work at the frequencies used by cell phones (working by absorbing rather than reflecting), the downside is that they are expensive (many $$$/sqft). A somewhat cheaper alternative is radar absorbent material (carbon impregnated foam) or possibly carbon fiber composite (this might have to be bonded to work).
A couple of approached with construction materials might be carbon fibers embedded in concrete for both strength and RF attenuation, or drywall with carbon fibers embedded in the gypsum (though that may impact the fire-proofing ability of drywall).
Anyway, the passive approach is much less likely to lead to legal problems than the active jammer approach, though businesses employing the passive approach would be welll advised to make sure patrons know about the RF blocking.
For the entirety of the space race, we have been using digital photography.
As alexq pointed out, the original electronic cameras (e.g. Tiros weather satellites) were analog in nature. I seem to recall that some of the early Mariner photos were actually film developed on board the spacecraft and scanned for transmission back to earth. The Voyagers used mid-1970's technology (CCD's?) and were examples of digital photography (including data compression). However, the camera on the Voyager was not a stand-alone system as it used the spacecrafts main computer for storage and processing.
Kodak is not being lame for claiming to invent the digital camera.
...but I've never heard of a Smith-Corona printer.
They were making a daisywheel printer in the mid-1980's - pretty much the printer portion of their short-lived daisywheel typewriter. They also made 'Kleinschmidt' teleprinters, which were similar to the Teletype's.
My former boss's nephew married Wayne's daughter - his nephew made a comment that Wayne was a bit of a weird bird.
IIRC, one of Wayne's contributions to the microcomputer scene was getting the 'Kansas City' standard established for recording data on cassette tap. This allowed for ease of swapping data on tapes for the 2 to 4 year period when a large number of hobbyists were using cassette tape for storage and interchange (e.g. Tarbell had an S-100 card with four cassette interfaces in mid-1979).
FWIW, the first computer that I got to run a program on was a CDC-1700 (Jan 1971) - finally got hold of some documentation on the beast a few days ago...
I've noticed that CNN does a dirty little trick to trip up the 'back' button - they typically put three instances of the current page on the history buffer. Found that out after using the down-arrow next to the 'back' button, and that allows me to go back to the previous page.
At least that crazy wacko in Kilobaud was fun to read. It was like a print version of Art Bell.
Sounds like Wayne Green, who has had a reputation as a crazy wacko in print since the early 1960's. Funny you should bring that up, Byte started as an adjunct to Wayne's 73 magazine, but went to his wife as part of their divorce settlement. Wayne then started Kilobyte, which got renamed Kilobaud after McGraw Hill complained about trademarks.
The camera used a DRAM chip from Micron - exposure to light would bleed off the charge on each of the bits - not a very linear sensor.
FWIW, Jerry Pournelle's column had started at least a couple of years before that article - Jerry and Steve were Byte's two leading columnists in the first half of the 1980's - they were in separate enough niches that there wasn't much in the way of competition between them. What caused Byte to go downhill was McGraw-Hill wanting it to be more like PC Magazine and less like the pioneering microcomputer magazine it was from 1975 to ca 1986. This is when Steve Ciarcia decided it was time to leave Byte and start his own rag, which is still doing well - and Byte ceased publication with the July 1998 issue.
I do miss the theme issues from the early years of Byte.
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Standard practice for DC substations in urban areas was to wire the M-G sets or rotary converters in parallel with a battery. The AC power could drop out for an hour or more, but the DC customers would still have power.
While it was possible to use M-G sets or rotary converters to convert AC to DC, it was a lot cheaper just to put up transformers and use AC for residential use (exceptions being downtown areas of major cities). The power for most streetcars and subways was originally AC and converted to DC at substations - many cases the AC was at 25Hz as the rotary converters ran more efficiently off of 25 Hz than 60 Hz.
Now for an odd bit of trivia - the last 50 Hz utility in the US was Southern California Edison, which completed conversion to 60 Hz in 1948.
AC's advantage of high voltage transmission doesn't apply to subways as 1200V seems to be the limit for third rail. 2400VDC was tried in 1915 on the Michigan Railways (an electric interurban in central Michigan) with abysmal results - the voltage was changed to 1200V within a year of the initial installation.
Why not use the power of the expanding nitrogen gas to provide power as well - and yet another use is to put out fires as well.
Actually, even more to the point is the secret ballot - while the fact you voted is recorded, how you voted should not be traceable to you (unfortunately not always the case).
Better yet, remove the civil and criminal liability protection for the shareholders. There's nothing that would improve corporate behavior faster than if fund managers would be facing prison time and huge fines or lawsuits for the misdeeds of the companies that they bough stock in.
If I'm not mistaken, TCP was invented in the US and tested ca 1977 (see a recent CNet article on the 'Internet Van'. The focus outside the US was drawing up the specifications for the OSI networking stack. The first widely available OS to support TCP/IP was BSD 4.2 - though it may be argued that Berzerkeley isn't really in the US...Your doctors were doing you good service about the warnings with respect to MRI.
The one advantage of using the earth's field is that it is reasonably uniform in a clean environment, and the pre-polarizing field doesn't need to be anywhere near as uniform as the readout field. In a not so clean environment, it is possible to use the gradient coils to clean up the earth's field a bit.
The Larmour frequency for 30 mT is about 1.28 MHz, which is in the AM broadcast band. Interference is likely to be a significant problem.
Another company, Vista Clara, is using a novel form of ULF MRI to map groundwater.
You are right on the money is saying it is OLD technology.
Not sure how easy that would be to implement, but I agree with your sentiment. I would allow 'ringing' if it was confined to the earpiece of a headset.
N.B. My reply is based on laws and regulations in the U.S., other nations may be different.The operation of a jammer is illegal and blocking what turns out to be an emergency call is a violation of several FCC regs and possibly state laws (e.g. the California PUC has regulations regarding emergency calls as well) in addition to simply operating the jammer. Things would be even worse for the propietor if the jammer blocked a call on a public area (e.g. street or sidewalk) or on someone else's property - that's why the RF shielding approach is safer (but NOT completely safe). It would be very difficult to design a jamming system to completely cover an establishment without the jamming signal spilling outside the intended coverage area.
The legality of RF shielding is not cut and dry. The rights of the propietor are also not absolute - how long do you think a 'No Colored" sign would last... It is within the right of state and local governments to require businesses open to the public to maintain accessibility to cell phone communications. In addition the shielding of your property may block the reception to an adjacent property or a public street. Finally, most businesses lease rather than own the land and building, which brings up issues of who pays for the shielding.
One other aspect of blocking cell phone use is that the propietor now becomes responsible for emergency communication which may not sit well with the propietor's insurance company - especially if the blocked call atttempt was from off the immediate premises.
It's still your choice to patronize that theater and your proposed action may end up with the theater management telling you to never come back. You do have the choice of staying home and watching a DVD.One other option is to take the theater to small claims court to recover the cost of your ticket.
BTW, I almost never carry a cell phone.
An establishment using passive blocking would still probably need to alert patrons to the blocking and provide an emergency contact number to be completely free of liability. Your point is correct in that passive blocking is on much firmer legal ground than jamming.
Another thing to consider, with the reverse 911 programs now being set-up to call registered cell-phones, the blocked call may be one to you warning of your residence is in danger.
While I can understand your frustration in those situations, the person who you grabbed the phone from has all sorts of rights to press criminal and civil charges against you. The legally correct way is to complain to the management of the establishment you are patronizing and telling them they will lose your business if nothing is done about it. Remember, you chose to be there as well.The world doesn't revolve around you either.
A couple of approached with construction materials might be carbon fibers embedded in concrete for both strength and RF attenuation, or drywall with carbon fibers embedded in the gypsum (though that may impact the fire-proofing ability of drywall).
Anyway, the passive approach is much less likely to lead to legal problems than the active jammer approach, though businesses employing the passive approach would be welll advised to make sure patrons know about the RF blocking.
As alexq pointed out, the original electronic cameras (e.g. Tiros weather satellites) were analog in nature. I seem to recall that some of the early Mariner photos were actually film developed on board the spacecraft and scanned for transmission back to earth. The Voyagers used mid-1970's technology (CCD's?) and were examples of digital photography (including data compression). However, the camera on the Voyager was not a stand-alone system as it used the spacecrafts main computer for storage and processing.Kodak is not being lame for claiming to invent the digital camera.
...but I've never heard of a Smith-Corona printer.
They were making a daisywheel printer in the mid-1980's - pretty much the printer portion of their short-lived daisywheel typewriter. They also made 'Kleinschmidt' teleprinters, which were similar to the Teletype's.IIRC, one of Wayne's contributions to the microcomputer scene was getting the 'Kansas City' standard established for recording data on cassette tap. This allowed for ease of swapping data on tapes for the 2 to 4 year period when a large number of hobbyists were using cassette tape for storage and interchange (e.g. Tarbell had an S-100 card with four cassette interfaces in mid-1979).
FWIW, the first computer that I got to run a program on was a CDC-1700 (Jan 1971) - finally got hold of some documentation on the beast a few days ago...
I've noticed that CNN does a dirty little trick to trip up the 'back' button - they typically put three instances of the current page on the history buffer. Found that out after using the down-arrow next to the 'back' button, and that allows me to go back to the previous page.
Sounds like Wayne Green, who has had a reputation as a crazy wacko in print since the early 1960's. Funny you should bring that up, Byte started as an adjunct to Wayne's 73 magazine, but went to his wife as part of their divorce settlement. Wayne then started Kilobyte, which got renamed Kilobaud after McGraw Hill complained about trademarks.FWIW, Jerry Pournelle's column had started at least a couple of years before that article - Jerry and Steve were Byte's two leading columnists in the first half of the 1980's - they were in separate enough niches that there wasn't much in the way of competition between them. What caused Byte to go downhill was McGraw-Hill wanting it to be more like PC Magazine and less like the pioneering microcomputer magazine it was from 1975 to ca 1986. This is when Steve Ciarcia decided it was time to leave Byte and start his own rag, which is still doing well - and Byte ceased publication with the July 1998 issue.
I do miss the theme issues from the early years of Byte.
But just don't store it with the IRFNA (N2O4).
And whatever you do, please don't tell any of the nanny staters about Acetylozone (HOOOCCH).