One problem is the transitional period, the time between establishing a "no shitty add networks" policy and lining up enough "legitimate" advertisers to balance the books. Also even if ads on facebook were legit they would still be dragged down by the poor reputation of web advertising in general.
BTW you do see some pretty seedy adverts on TV too, you just have to watch at the right time (e.g. when most people are asleep). Ever heard of the "london mint office" (a deliberately misleading name) the "microforce" shaver (if it's really so great why is the only time I ever hear about it on adverts run in the early hours of the morning) or "wonga.com" (loans at insanely high rates).
Well pop-up windows are pretty much out because all the major browsers now block them by default. I've seen a few in-page pop-ups but those are probablly pretty easy for an ad-blocker to detect.
The other end of it is that marketers in general are confident that they can overcome adblock if it ever becomes popular to the point where it's a problem. Adblock only works by recognizing the domain hosting the image/scripts or common path names.
That is CURRENTLY how they work. but if the advertisers change their tactics then the ad-blockers likely will as well.
I guess that depends on how you define the "incident". Some would say it's still ongoing.
Which brings us to one of the biggest issues with nuclear incidents. There is no such thing as a gamma ray proof suit. So as the incident progresses it is very difficult to deal with secondary issues and sometimes the people managing the disaster have the agonising descision between sacrificing their workers lives/health and leaving things unfixed (which may make the disaster worse later).
Robots and remote control vehicles work well in well defined envionments but humans in general are much better at dealing with things when the shit hits the fan. At chernobyl the powers that be sacrificed the firefighters lives (afaict it's not clear whether the firefighters knew of the risks or not) to get the fire under control.
Not that I think nuclear power is bad but I think we are fooling ourselves if we think it can ever be completely safe. It's just less bad than the alternatives.
When these fail they fail in place. When they fail and need to be moved you can crank a handwheel.
You can't really crank a handwheel if things are too radioactive to allow you near the valve or the valve itself jams. Still you can mostly mitigate that by having a group of four valves such that with any one valve failed you can still control the flow.
A "no flow" scenario would be a big one for cooling systems.
An even bigger one would be the cooling system breaking open either as the result of an earthquake or as a result of another failure.
You can try to mitigate that with valves that can shut off parts of the system and open bypass routes and a system for emergency refil of the cooling system (one of the big advantages of water is it's easy to replace it) or by having multiple independent loops but ultimately you still need to pass the cooling medium past the stuff that needs to be cooled.
So IMO a reactor can only be considered "passively safe" if the system can remove decay heat without the assistance of coolant flow.
The classic is that all major process plants usually have bypass valves around emergency shutdown valves. These valves are normally shut, hand operated, and locked with a key. Yet there have been plenty of scenarios in the past where operator error (or in some case errors of several operators at once) has led to the wrong valve being unlocked and bypassed or something of the sort.
And of course you can't really get rid of the bypass valves because sometimes you need them:(
Yes there is on online store for the 3DS like there is on the Wii, PS3, PSP and XBOX360. However the online stores on consoles are optional. You can still walk into a game shop, buy any of the aforementioned consoles and one or more games, give the console and games to a kid (either your own kid or a friend/relative's kid) and they can start playing without ever having to connect the console to either the internet or a computer.
Afaict the only way to buy games for a (non-jailbroken) idevice (and at least acording to wikipedia there are no offline games at all included by default) is through the appstore which involves connecting the device to either the internet or to a computer with an internet connection, setting up an account and applying funds either using a credit card or a voucher. It's certainly possible to do this in a child-safe manner but it's more complex and easier to screw-up (witness the horror stories in the news) than just buying games on physical media.
Some android devices allow sideloading by default but I haven't seen any andriod game developers attempt to sell physical copies of thier games and if they did I would expect widespread piracy since afaict there are no provisions for copyprotecting andriod games distributed on physical media.
MMM, it sounds similar to when David Attenborough stepped down as "director of programmes" at the BBC. Being a high level boss allows people to have a bigger impact but it's also highly stressful and takes them away from what they really want to be doing with their life.
Even if the fission reactions require external input to proceed there will still be decay heat after it stops. How do these reactors propose to deal with said decay heat?
Yeah that opens massive cans of worms of it's own though such as compatibility, lift difficulty, storage space for all the batteries that are "on-charge" ownership of batteries and so on. It's been talked about loads but i'm not aware of anyone actually trying to do it.
Realistic graphics? Yes. Realism? No. Otherwise military shooters would consist of hours, possibly days, of doing absolutely nothing. Then there might be a 5 minute conflict where you kill a couple guys. Then a few hours later you might end up with a standoff where it takes you 30 minutes just to take out 1 guy. And through it all, if you get shot once in the right place...game over, no continues.
Imagine a situation where the cost to buy something from Amazon was dependent on your distance from an Amazon distribution centre; Amazon's business would quickly fall apart as they would be undercut by a hundred local competitors.
I doubt it, in europe the cost of sending stuff has always depended on which countries* the stuff is being sent between. Further amazon don't have anything like the tax advantages over local retailers that they have in the USA**. Neverthless amazon doesn't seem to be having any problems running their buisness in europe
*countries in europe are comparable in size to US states **there is a dodge for low value items involving the channel islands but at least in the UK books are VAT exempt anyway so that dodge is only really useful for DVDs and music (games are usually too high value to qualify)
Go ahead and do the math to figure out the power that can be transferred in a common filling station fuel pump
According to wikipedia a standard pump does about 10 gallons per minuite and a gallon of gasoline contains about 132 megajoules per gallon. So we are taking a transfer rate of about 1320 megajoules per minuite wihch works out to 22 megawatts. EEK
For a hunting preserve to be sustainable the reproduction rate of the animals has to be high enough to maintain the population of animals in the face of the hunting. Elephants are slow to reproduce (both in terms of how long it takes them to reach sexual maturity and in terms of rate of births) and need a lot of land so your sustainable hunting quota would be very low mammoths would be even worse.
Afaict we don't have elephant hunting preserves and I think it's highly unlikely we will ever have mammoth hunting preserves.
There are different failure modes to consider for an "DSL internet connection"
1: The DSL link itself is fine but something further along in the "ADSL backend network" fails (usually this manifests as the router achiving sync but failing to establish a PPPoA session). 2: The DSL link itself is fine and succesfull link is established through the "DSL backend network" to an IP network but the packets don't actually get through to the internet 3: the phone line has a fault that is a killer for DSL but doesn't kill off voiceband operation (the reverse can happen too of course) 4: the phone line is completely dead and doesn't pass either voice or DSL
Which failure modes are most common will depend a lot on where you live relative to the exchange and how the providers network it set up. In my experiance (admittedly in the UK and in a fairly built-up area) sucessfull sync followed by failure to establish the PPPoA connection is the most common failure mode. Still you should certainly consider the common failure mode in your planning.
instead of a transformer feeding wires that supply your house it would be an inverter.
does an inverter with 10KV DC input and 240V/415V 100A three phase "true sinewave" AC output (or whatever your local standard is) even exist? how much does/would it cost? how reliable would it be? how bulky would it be? how would it handle sitting on a pole for years exposed to wide temperature swings? would it be able to handle power flow in both directions?
If the atomic number is greater than 92, you'll only find it in a lab for a fraction of a second at a time.
BULLSHIT
Elements 93 through 97 all have at least one isotope with a half life of over a thousand years. beyond that calafornium having a maximum half life of 898 years, Einstenium having a maximum half life of 471.7 days, fermium having a maximum half life of 100.5 days, mendelevium having a maximum half life of 51.5 days, with nobelium it's down to 58 minuites, lawrencium is back up to 3.6 hours and so on, it's not until Ununtrium (atomic number 113) that the half life of the most stable isotope drops below a second.
384VDC just seems to be asking for trouble. It would require yet another separate connector that can't be plugged into 120VAC or 240VAC,
True there would be some cost involved in choosing appropriate connectors and certifying power supplies for it.
generators would have to have an adapter for it. It would require a complete retooling to get to that standard.
Afaict in a datacenter the typical structure is you have grid and generator power coming in, those go to an automatic transfer switch and then to a UPS. The UPS (assuming a high quality online unit) converts the AC to DC, takes it past the battery bank and then converts it back to AC. American datacenters also often have transformer based PDUs that step down the voltage between the UPS and the computers. Since generators are placed before the UPS system they do not need to change.
The advantage of going DC distribution inside the datacenter include 1: it takes out the conversion step from DC at the battery bank to AC for distribution. 2: It takes out all the issues of power factor management, 3: It's much easier to paralell up DC busses than AC busses (AC busses have to be brought into phase before they can be paralelled).
Downsides 1: you need special power supplies (in theory a cheap and nasty SMPSU can actually run off DC but in reality i'd want vendor certification before actually doing it) 2: arcing is far more of an issue with DC than AC because the zero crossings of AC tend to break arcs. This means that switches, circuit breakers, connectors etc need to be explicitly designed for DC. 3: there is little standardisation of connectors ETC for DC (afaict the telco guys tend to just bolt stuff to bussbars which is tolerable at 48V but not really appropriate at higher voltages) 4: normal electricians aren't used to working with DC
Making another voltage level is throwing the baby out with the bathwater. Why not just go with an established DC voltage level?
Because the "established DC voltage levels" are too low to be distributed efficiently and economically arround a datacenter. 12V is way too low, even telco 48V is rather low for the power use in a modern datacenter. Remember for a given acceptable loss the copper requirements go as the inverse square of the voltage.
Also the new voltage is not an accident, it's set at a level to make reuse of existing PC PSU designs easier.
Take 12VDC. Most generators, from the expensive inverters by Honda or Yamaha can generate that, as well as the construction grade open-framed ones.
Yes small generators often have a 12V outlet for running car accessories but afaict it can't supply much power.
The PSU is still a point of failure, a heat source, and is costing 6% efficiency per server at the start.
The thing is even with DC systems you still end up needing a PSU. The voltages needed to efficiently move power round a datacenter are higher than you would reasonablly want to put on a computer motherboard and since computer equipment isn't generally designed to be isolated from the chassis it's bolted to you really want your PSU to be isolating (large return currents running through signal cabling would be BAD).
The trick with 380V DC is that you can run it directly into most 240V AC power supplies and it works fine. (most AC power supplies start off with a bridge rectifier to convert the 240V AC into 380V DC).
Be that as it may I think you would still want a DC certified PSU for a few reasons
1: Some power factor correction systems may respond badly to DC supply 2: Some bridge rectifiers may not be specified to handle having the current running through the same pair of diodes all the time 3: IEC connectors are only designed for AC, not for the (far more arc prone) DC, you would probably want some form of locking connector instead
Afaict the main issue is not the actual splitting of the wiring it's what you do with the connection afterwards. Dealing with high voltage DC requires far more equipment than dealing with high voltage AC. So DC works well for systems with long lines connecting a small number of points, but would be prohibitively expensive for the regular grid (which connects many points through a series of transformers that gradually increase/reduce the voltage).
You just have to be careful WHICH voltage you are talking about;).
In particular when talking about a source supplying power via a cable to a load there are three (interrelated) voltages being considered. Vsupply, Vload and Vdrop (Vload=Vsupply-Vdrop) but only one current (assuming leakage is negliable) is being considered. Further in any reasonable system it is likely that Vsupply >> Vdrop. As a result of all this it's generally best to think of losses as a function of current..
The total power lost in a cable is a function of the current through the cable and the resistance of the cable. It is only indirectly (once you introduce the characteristics of the load) a function of the supply voltage of the system.
You can't easily get a solid 5V supply out of a USB port. Some cheap and nasty devices do run parts of their electronics directly off the USB 5V line (indeed i've done it myself) but doing so is not how you make a solid reliable device unless you are sure all your parts can work down to 4V or so.
USB itself is a 3.3V interface (not 5V as vlm asserts) so pretty much any device needs a 3.3V regulator even if it's just to power the USB physical interface.
Afaict there are a few issues with 48V DC for a dataceventer.
1: it's nonstandard (in the computer industry) so you pay a premium for equipment that runs off it and reduce your choice of equipment. 2: It's lower voltage so for a given level of tolerable loss your cables have to be much bigger 3: It's DC so it's more prone to arcing making all your switches and protective devices more expensive and basically ruling out the use of plug and socket connections for anything other than final connection of individual devices
The combination of these factors make a 48V DC system expensive.
Also at least according to APC you can get a lot of the advantages of a DC system without the hassle by going for a european style AC system (240/415 three phase without transformer based PDUs) rather than an american style AC system (transformer based PDUs). And the vast majority of server and network hardware is perfectly happy on a European style system (after all the vendors want to sell it in europe too).
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One problem is the transitional period, the time between establishing a "no shitty add networks" policy and lining up enough "legitimate" advertisers to balance the books. Also even if ads on facebook were legit they would still be dragged down by the poor reputation of web advertising in general.
BTW you do see some pretty seedy adverts on TV too, you just have to watch at the right time (e.g. when most people are asleep). Ever heard of the "london mint office" (a deliberately misleading name) the "microforce" shaver (if it's really so great why is the only time I ever hear about it on adverts run in the early hours of the morning) or "wonga.com" (loans at insanely high rates).
pop-ups, etc
Well pop-up windows are pretty much out because all the major browsers now block them by default. I've seen a few in-page pop-ups but those are probablly pretty easy for an ad-blocker to detect.
The other end of it is that marketers in general are confident that they can overcome adblock if it ever becomes popular to the point where it's a problem. Adblock only works by recognizing the domain hosting the image/scripts or common path names.
That is CURRENTLY how they work. but if the advertisers change their tactics then the ad-blockers likely will as well.
Post incident yes.
I guess that depends on how you define the "incident". Some would say it's still ongoing.
Which brings us to one of the biggest issues with nuclear incidents. There is no such thing as a gamma ray proof suit. So as the incident progresses it is very difficult to deal with secondary issues and sometimes the people managing the disaster have the agonising descision between sacrificing their workers lives/health and leaving things unfixed (which may make the disaster worse later).
Robots and remote control vehicles work well in well defined envionments but humans in general are much better at dealing with things when the shit hits the fan. At chernobyl the powers that be sacrificed the firefighters lives (afaict it's not clear whether the firefighters knew of the risks or not) to get the fire under control.
Not that I think nuclear power is bad but I think we are fooling ourselves if we think it can ever be completely safe. It's just less bad than the alternatives.
When these fail they fail in place. When they fail and need to be moved you can crank a handwheel.
You can't really crank a handwheel if things are too radioactive to allow you near the valve or the valve itself jams. Still you can mostly mitigate that by having a group of four valves such that with any one valve failed you can still control the flow.
A "no flow" scenario would be a big one for cooling systems.
An even bigger one would be the cooling system breaking open either as the result of an earthquake or as a result of another failure.
You can try to mitigate that with valves that can shut off parts of the system and open bypass routes and a system for emergency refil of the cooling system (one of the big advantages of water is it's easy to replace it) or by having multiple independent loops but ultimately you still need to pass the cooling medium past the stuff that needs to be cooled.
So IMO a reactor can only be considered "passively safe" if the system can remove decay heat without the assistance of coolant flow.
The classic is that all major process plants usually have bypass valves around emergency shutdown valves. These valves are normally shut, hand operated, and locked with a key. Yet there have been plenty of scenarios in the past where operator error (or in some case errors of several operators at once) has led to the wrong valve being unlocked and bypassed or something of the sort.
And of course you can't really get rid of the bypass valves because sometimes you need them :(
Still I think the GPs point holds.
Yes there is on online store for the 3DS like there is on the Wii, PS3, PSP and XBOX360. However the online stores on consoles are optional. You can still walk into a game shop, buy any of the aforementioned consoles and one or more games, give the console and games to a kid (either your own kid or a friend/relative's kid) and they can start playing without ever having to connect the console to either the internet or a computer.
Afaict the only way to buy games for a (non-jailbroken) idevice (and at least acording to wikipedia there are no offline games at all included by default) is through the appstore which involves connecting the device to either the internet or to a computer with an internet connection, setting up an account and applying funds either using a credit card or a voucher. It's certainly possible to do this in a child-safe manner but it's more complex and easier to screw-up (witness the horror stories in the news) than just buying games on physical media.
Some android devices allow sideloading by default but I haven't seen any andriod game developers attempt to sell physical copies of thier games and if they did I would expect widespread piracy since afaict there are no provisions for copyprotecting andriod games distributed on physical media.
MMM, it sounds similar to when David Attenborough stepped down as "director of programmes" at the BBC. Being a high level boss allows people to have a bigger impact but it's also highly stressful and takes them away from what they really want to be doing with their life.
Even if the fission reactions require external input to proceed there will still be decay heat after it stops. How do these reactors propose to deal with said decay heat?
Yeah that opens massive cans of worms of it's own though such as compatibility, lift difficulty, storage space for all the batteries that are "on-charge" ownership of batteries and so on. It's been talked about loads but i'm not aware of anyone actually trying to do it.
Realistic graphics? Yes. Realism? No. Otherwise military shooters would consist of hours, possibly days, of doing absolutely nothing. Then there might be a 5 minute conflict where you kill a couple guys. Then a few hours later you might end up with a standoff where it takes you 30 minutes just to take out 1 guy. And through it all, if you get shot once in the right place...game over, no continues.
http://www.youtube.com/watch?v=A5tRNs2X5Q4
Imagine a situation where the cost to buy something from Amazon was dependent on your distance from an Amazon distribution centre; Amazon's business would quickly fall apart as they would be undercut by a hundred local competitors.
I doubt it, in europe the cost of sending stuff has always depended on which countries* the stuff is being sent between. Further amazon don't have anything like the tax advantages over local retailers that they have in the USA**. Neverthless amazon doesn't seem to be having any problems running their buisness in europe
*countries in europe are comparable in size to US states
**there is a dodge for low value items involving the channel islands but at least in the UK books are VAT exempt anyway so that dodge is only really useful for DVDs and music (games are usually too high value to qualify)
Go ahead and do the math to figure out the power that can be transferred in a common filling station fuel pump
According to wikipedia a standard pump does about 10 gallons per minuite and a gallon of gasoline contains about 132 megajoules per gallon. So we are taking a transfer rate of about 1320 megajoules per minuite wihch works out to 22 megawatts. EEK
For a hunting preserve to be sustainable the reproduction rate of the animals has to be high enough to maintain the population of animals in the face of the hunting. Elephants are slow to reproduce (both in terms of how long it takes them to reach sexual maturity and in terms of rate of births) and need a lot of land so your sustainable hunting quota would be very low mammoths would be even worse.
Afaict we don't have elephant hunting preserves and I think it's highly unlikely we will ever have mammoth hunting preserves.
There are different failure modes to consider for an "DSL internet connection"
1: The DSL link itself is fine but something further along in the "ADSL backend network" fails (usually this manifests as the router achiving sync but failing to establish a PPPoA session).
2: The DSL link itself is fine and succesfull link is established through the "DSL backend network" to an IP network but the packets don't actually get through to the internet
3: the phone line has a fault that is a killer for DSL but doesn't kill off voiceband operation (the reverse can happen too of course)
4: the phone line is completely dead and doesn't pass either voice or DSL
Which failure modes are most common will depend a lot on where you live relative to the exchange and how the providers network it set up. In my experiance (admittedly in the UK and in a fairly built-up area) sucessfull sync followed by failure to establish the PPPoA connection is the most common failure mode. Still you should certainly consider the common failure mode in your planning.
instead of a transformer feeding wires that supply your house it would be an inverter.
does an inverter with 10KV DC input and 240V/415V 100A three phase "true sinewave" AC output (or whatever your local standard is) even exist?
how much does/would it cost?
how reliable would it be?
how bulky would it be?
how would it handle sitting on a pole for years exposed to wide temperature swings?
would it be able to handle power flow in both directions?
If the atomic number is greater than 92, you'll only find it in a lab for a fraction of a second at a time.
BULLSHIT
Elements 93 through 97 all have at least one isotope with a half life of over a thousand years. beyond that calafornium having a maximum half life of 898 years, Einstenium having a maximum half life of 471.7 days, fermium having a maximum half life of 100.5 days, mendelevium having a maximum half life of 51.5 days, with nobelium it's down to 58 minuites, lawrencium is back up to 3.6 hours and so on, it's not until Ununtrium (atomic number 113) that the half life of the most stable isotope drops below a second.
My understanding is that is is much harder to sustain an arc with AC because the current drops to zero twice per cycle.
384VDC just seems to be asking for trouble. It would require yet another separate connector that can't be plugged into 120VAC or 240VAC,
True there would be some cost involved in choosing appropriate connectors and certifying power supplies for it.
generators would have to have an adapter for it. It would require a complete retooling to get to that standard.
Afaict in a datacenter the typical structure is you have grid and generator power coming in, those go to an automatic transfer switch and then to a UPS. The UPS (assuming a high quality online unit) converts the AC to DC, takes it past the battery bank and then converts it back to AC. American datacenters also often have transformer based PDUs that step down the voltage between the UPS and the computers. Since generators are placed before the UPS system they do not need to change.
The advantage of going DC distribution inside the datacenter include
1: it takes out the conversion step from DC at the battery bank to AC for distribution.
2: It takes out all the issues of power factor management,
3: It's much easier to paralell up DC busses than AC busses (AC busses have to be brought into phase before they can be paralelled).
Downsides
1: you need special power supplies (in theory a cheap and nasty SMPSU can actually run off DC but in reality i'd want vendor certification before actually doing it)
2: arcing is far more of an issue with DC than AC because the zero crossings of AC tend to break arcs. This means that switches, circuit breakers, connectors etc need to be explicitly designed for DC.
3: there is little standardisation of connectors ETC for DC (afaict the telco guys tend to just bolt stuff to bussbars which is tolerable at 48V but not really appropriate at higher voltages)
4: normal electricians aren't used to working with DC
Making another voltage level is throwing the baby out with the bathwater. Why not just go with an established DC voltage level?
Because the "established DC voltage levels" are too low to be distributed efficiently and economically arround a datacenter. 12V is way too low, even telco 48V is rather low for the power use in a modern datacenter. Remember for a given acceptable loss the copper requirements go as the inverse square of the voltage.
Also the new voltage is not an accident, it's set at a level to make reuse of existing PC PSU designs easier.
Take 12VDC. Most generators, from the expensive inverters by Honda or Yamaha can generate that, as well as the construction grade open-framed ones.
Yes small generators often have a 12V outlet for running car accessories but afaict it can't supply much power.
The PSU is still a point of failure, a heat source, and is costing 6% efficiency per server at the start.
The thing is even with DC systems you still end up needing a PSU. The voltages needed to efficiently move power round a datacenter are higher than you would reasonablly want to put on a computer motherboard and since computer equipment isn't generally designed to be isolated from the chassis it's bolted to you really want your PSU to be isolating (large return currents running through signal cabling would be BAD).
The trick with 380V DC is that you can run it directly into most 240V AC power supplies and it works fine. (most AC power supplies start off with a bridge rectifier to convert the 240V AC into 380V DC).
Be that as it may I think you would still want a DC certified PSU for a few reasons
1: Some power factor correction systems may respond badly to DC supply
2: Some bridge rectifiers may not be specified to handle having the current running through the same pair of diodes all the time
3: IEC connectors are only designed for AC, not for the (far more arc prone) DC, you would probably want some form of locking connector instead
Afaict the main issue is not the actual splitting of the wiring it's what you do with the connection afterwards. Dealing with high voltage DC requires far more equipment than dealing with high voltage AC. So DC works well for systems with long lines connecting a small number of points, but would be prohibitively expensive for the regular grid (which connects many points through a series of transformers that gradually increase/reduce the voltage).
Current and voltage are related to each other,
You just have to be careful WHICH voltage you are talking about ;).
In particular when talking about a source supplying power via a cable to a load there are three (interrelated) voltages being considered. Vsupply, Vload and Vdrop (Vload=Vsupply-Vdrop) but only one current (assuming leakage is negliable) is being considered. Further in any reasonable system it is likely that Vsupply >> Vdrop. As a result of all this it's generally best to think of losses as a function of current..
The total power lost in a cable is a function of the current through the cable and the resistance of the cable. It is only indirectly (once you introduce the characteristics of the load) a function of the supply voltage of the system.
You can't easily get a solid 5V supply out of a USB port. Some cheap and nasty devices do run parts of their electronics directly off the USB 5V line (indeed i've done it myself) but doing so is not how you make a solid reliable device unless you are sure all your parts can work down to 4V or so.
USB itself is a 3.3V interface (not 5V as vlm asserts) so pretty much any device needs a 3.3V regulator even if it's just to power the USB physical interface.
Safe to touch? yes.
Safe to drop metal objects on? HELL NO
Afaict there are a few issues with 48V DC for a dataceventer.
1: it's nonstandard (in the computer industry) so you pay a premium for equipment that runs off it and reduce your choice of equipment.
2: It's lower voltage so for a given level of tolerable loss your cables have to be much bigger
3: It's DC so it's more prone to arcing making all your switches and protective devices more expensive and basically ruling out the use of plug and socket connections for anything other than final connection of individual devices
The combination of these factors make a 48V DC system expensive.
Also at least according to APC you can get a lot of the advantages of a DC system without the hassle by going for a european style AC system (240/415 three phase without transformer based PDUs) rather than an american style AC system (transformer based PDUs). And the vast majority of server and network hardware is perfectly happy on a European style system (after all the vendors want to sell it in europe too).